Much of the earth's remaining natural gas and oil is located in rock shale and rock formations at depths varying from 500-20,000 feet below the surface. Many of the naturally occurring formations suffer from low porosity and permeability, thereby restricting natural gas and/or oil to flow into a well bore where the gas and/or oil can be recovered.
Hydraulic fracturing is a process that creates fractures in low porosity, low permeability rocks of geological formations. A hydraulic fracture may be formed by pumping a fracturing fluid mixture into a well bore at a rate sufficient to increase pressure down-hole to a value in excess of the fracture gradient of the formation rock. The pressure causes the formation to crack or fracture, which allows the fracturing mixture to enter and extend the crack further into the formation.
To keep a fracture open after the pumping process stops, the fracturing fluid mixture contains a solid, called a proppant, that remains in the new fracture and keeps the fracture open. Various types of proppant may be used depending on the permeability or grain strength needed. A completed fracture provides a conductive path connecting a large area of the reservoir to the well, thereby increasing the area from which oil, natural gas and liquids can be recovered from the targeted formation.
Propped hydraulic fracture stimulation is widely used to improve well productivity from tight, otherwise noncommercial reservoirs. Other areas of application include sand control in weakly consolidated reservoirs, gas condensate fields, and high permeability reservoirs that show significant permeability anisotropy.
An important consideration in the practice of hydraulic fracturing is “proppant flow-back”, i.e., the production of proppant back to the surface. Proppant flow-back can lead to damaged equipment and downtime, which necessitates costly and manpower intensive surface handling procedures. Proppant flow-back also presents a problem of proppant disposal. In some cases, a well can be prematurely abandoned if costs to return the well to production are excessive. Proppant flow-back, although not desirable, can be tolerated in certain operational environments. However, proppant flow-back from a fracture during the production phase is problematic. In practice, 20% to 50% of the original proppant pumped into a formation may be produced back.
An integral part of a hydraulic fracturing process is the introduction of proppant particles of various sizes into a fracture to hold the fractures open. Examples of proppants include structural materials such as sand, man-made ceramics, walnut shells and even polymer beads. Additionally, resin coated proppants have been used in an effort to reduce proppant flow-back. The resin coated proppant approach of gluing the sand together at the interface was an excellent starting point to reduce flow-back but mechanical cycling tends to crack the bonds that interconnect the proppant grains, thereby creating failure.
Studies have been undertaken to determine the mechanisms of flow-back. Laboratory work and theoretical simulations of several thousand individual proppant grains have shown that flow-back of plain proppant is critically dependent upon the ratio of mean grain diameter to fracture width. This dependence can be visualized as larger “columns” of proppants that have a greater tendency to buckle under loading. As a result of closure stress and inter-particle friction, a geometrically irregular arch of proppant grains is formed behind the fracture mouth. The buckled columns of proppant in front of the arch carry virtually no load. Therefore, small levels of proppant are initially transported to the well-bore even at low fluid flow rates. The loaded arch is stable until a sufficient fluid drag force is reached that is able to collapse the arch. A collapsing arch results in further proppant flow-back. An arch is a curved structure spanning an opening, serving to support a load by resolving the normal stress into lateral stress. For an arch to form, closure stress is required to generate a reaction force with the face of the fracture. The resolution of the forces in an arch necessarily sets up a pattern of shearing stresses within the material. At high closure stress these shear forces can become excessive and lead to pack failure.
Modes of proppant pack failure leading to proppant flow back are thought to be caused by arch destabilization due to excessive hydraulic and/or gravitational forces. Other modes of proppant pack failure are believed to include a fracture closure stress that is too low, proppant pack shear failure caused by too high fracture closure stress, as well as possible proppant crushing at high closure stress.
Critical parameters determining flow-back of plain proppants include fracture closure stress, both stabilizing and destabilizing. Other critical parameters include hydrodynamic force imposed from fluid production, which is destabilizing as the fluid flow tends to buckle proppant columns at the fracture mouth. Other critical parameters include the fracture width, which affects arch geometry and the transfer of friction and stress forces acting on proppants at a free face. Thus, for the same gradient, larger proppants will experience a greater destabilizing force. Similarly, at the fracture face the larger the proppant the fewer proppants per unit area are available to resist the applied closure stress and the larger the normal stress at the proppant contact.
A typical fracturing fluid mixture is made up of carrier fluid, additives and proppants. Typically, the carrier fluid and proppant comprise 99% of the mixture with less than 1% additives.
There are five types of carrier fluids normally used in the process. The five types are, 1) Water: which is typically un-gelled freshwater or formations of brine; 2) Cross-linked water-based fluids, which are gelled with polymers that employ a cross-linking agent, such as a metallic ion to bond the polymer molecules together for increasing fluid viscosity; 3) Oil-based fluids, which include gelled oils, diesel or lease crude; 4) Oil-in-water emulsions, which are external phase gelled water, internal phase gelled diesel, lease crude or condensates; and 5) Foam, which is a mixture of gas, e.g., nitrogen or carbon dioxide, gelled liquid, such as water or oils, and foaming agents, where mixtures are typically 60% to 80% gas.
Examples of typical additives used in the hydraulic fracturing industry include: acids; alcohols; bases; biocides; buffers; breakers; clay stabilizers and kcl substitutes; cross-linkers such as aluminum, boron, titanium, or zirconium; cross-link accelerators and delay agents; demulsifiers; foamers and defoamers, friction reducers; iron control agents; cellulose and guar polymers including standard, hpg, cmg, cmhpg; polymer slurries, including diesel and “green”; oxygen scavengers; salts; surfactants; and flurosurfactants. This list of additives is only a representative portion of all additives used and is not meant to be a complete list.
Effectively dispersing a well-formulated fracturing fluid with a complex set of additives into a homogeneous emulsion is extremely difficult to accomplish due, primarily, because of chemical affinity mismatches that result from the broad diversity of the additives used. Additionally, because of the toxic nature of some of the chemicals used in hydraulic fracturing, industry is facing stiff and growing environmental regulation. Regulation is anticipated that will establish limits for various materials contained in hydraulic fracturing additives and carrier fluids.
Due to environmental issues associated with hydraulic fracturing, the oil and gas industry has shifted towards using water with mineral additives as the fracturing fluid of choice. The most commonly used additive in water hydraulic fracturing is a friction reducer.
Carrier fluids, additives and proppant must be mixed for use in hydraulic fracturing.
There are three types of commonly used mixing principles:
1. Static mixing, wherein liquids flow around fixed objects, either via force produced flow by pressure through mechanical means or gravity induced flow;
2. Dynamic mixing, wherein liquid induced mixing results from mechanical agitation via impellers, wiping blade and high shear turbines as well as single or double screw extruder designs or screw agitation designs; and
3. Kinetic mixing, wherein liquid is mixed by velocity impacts on a surface or wherein two or more liquids form a velocity impact by impinging on one another.
All three of the above mixing methods have one thing in common that hinders the optimizing of mixing regardless of the fluid being combined and regardless of whether the materials being mixed are polar, nonpolar, organic or inorganic etc. or if it is a filled material with compressible or non-compressible fillers.
The commonality that hinders optimizing of mixing is that all incompressible fluids have a wall effect or a boundary layer effect where the fluid velocity is greatly reduced at the wall or mechanical interface. Static mixing systems use this boundary layer to fold or blend the liquid using this resistive force to promote agitation.
Dynamic mixing, regardless of the geometry of mixing blades or turbine, results in dead zones and incomplete mixing because of the boundary layer. Dynamic mixing uses high shear and a screw blade designed to use the boundary layer to promote friction and compression by centrifugal forces to accomplish agitation while maintaining an incomplete mixed boundary layer on mechanical surfaces.
Kinetic mixing suffers from boundary layer effects on velocity profiles both on the incoming streams and at the injector tip. However, kinetic mixing suffers minimal boundary layer effects except for transport fluid phenomena.
A further explanation of the boundary layer of the flowing fluids follows. Aerodynamic forces depend in a complex way on the viscosity of a fluid. As a fluid moves past an object, the molecules in close proximity to the surface tend to stick to the surface. The molecules just above the surface are slowed down by their collisions with the molecules that are sticking to the surface. These molecules, in turn, slow down the flow just above them. The farther away from the surface, the fewer the collisions that are affected by the object surface. Therefore, a thin layer of fluid is created near the surface in which the velocity of the fluid changes from zero at the surface to the free stream value away from the surface. Engineers call this layer the “boundary layer” because the layer occurs on the boundary of the fluid.
As discussed above, as an object moves through a fluid, or as a fluid moves past an object, molecules of the fluid near the object are disturbed and as the molecules move around the object. Aerodynamic forces are generated between the fluid and the object. The magnitude of the aerodynamic forces depends on the shape of the object, the speed of the object, the mass of the fluid going by the object and on two other important properties of the fluid, i.e., the viscosity, or stickiness, and the compressibility, or springiness, of the fluid. To properly model these effects, aerospace engineers use similarity parameters, which are ratios of these effects to other forces present in the problem. If two experiments have the same values for the similarity parameters, then the relative importance of the forces are being correctly modeled.
Referring now to FIG. 1, a two dimensional representation of the streamwise velocity variation from free stream to the surface is shown. In reality, the effects are three dimensional. From the conservation of mass in three dimensions, a change in velocity in the streamwise direction causes a change in velocity in the other directions as well. A small component of velocity perpendicular to the surface displaces or moves the flow above it. The thickness of the boundary layer can be defined as the amount of this displacement. The displacement thickness depends on the Reynolds number, which is the ratio of inertial (resistant to change or motion) forces to viscous (heavy and gluey) forces and is given by the equation: Reynolds number (Re) equals velocity (V) times density (r) times a characteristic length (l) divided by the viscosity coefficient (mμ), i.e., Re=V*r*l/mμ.
Still referring to FIG. 1, boundary layers may be either laminar (layered), or turbulent (disordered) depending on the value of the Reynolds number. For lower Reynolds numbers, the boundary layer is laminar and the streamwise velocity changes uniformly as a function of distance away from the wall, as may be seen on the left side of FIG. 1. For higher Reynolds numbers, the boundary layer is turbulent and the streamwise velocity is characterized by unsteady, or changing with time, swirling flows inside the boundary layer. The external flow reacts to the edge of the boundary layer just as it would to the physical surface of an object. Therefore, the boundary layer gives any object an effective shape, which is usually slightly different from the physical shape. The boundary layer may lift off or “separate” from the body and create an effective shape that is substantially different from the physical shape. Separation occurs because the flow in the boundary has very low energy relative to the free stream and is, therefore, more easily driven by changes in pressure. Flow separation is the reason for airplane wing stall at high angle of attack.
Boundary-layer Flow
The portion of a fluid flow that occurs near a solid surface is where shear stresses are significant and is where inviscid-flow assumptions may not be used. Solid surfaces interact with a viscous fluid flow because of the no-slip condition discussed above, i.e., because of the physical requirement that fluid and solid have equal velocities at their interface. Therefore, fluid flow is retarded by a fixed solid surface, which results in the formation of a finite, slow-moving boundary layer. For the boundary layer to be thin, the Reynolds number of the body must be large, i.e., 103 or greater. Under these conditions the flow outside the boundary layer is essentially inviscid and plays the role of being a driving mechanism for the layer.
Referring now to FIG. 2, a typical low-speed or laminar boundary layer is shown. Such a display of the streamwise flow vector variation near a wall is called a velocity profile. The no-slip condition requires that u(x,0)=0, as shown, where u is the velocity of flow in the boundary layer. Velocity rises monotonically with distance y from the wall, finally merging smoothly with the outer (inviscid) stream velocity U(x). Assuming a Newtonian fluid, at any point in the boundary layer the fluid shear stress τ is proportional to the local velocity gradient. The value of the shear stress at the wall is most important, since the shear stress value relates not only to the drag of the body but often also to its heat transfer. At the edge of the boundary layer τ approaches zero asymptotically. There is no exact spot where τ=0, therefore the thickness δ of a boundary layer is usually defined arbitrarily as the point where u=0.99 U.
Friction Reducers
As stated above, additives in hydraulic fracturing fluid are typically deployed for use as friction reducers. As shown in FIG. 3, experiments were conducted wherein various friction reducers were added at a concentration of 0.25 gpt in 2% (wt) Kcl tap water flowing through a ½″ OD/0.402″ ID pipe. FIG. 4 shows experimental results comparing of 1.0 gpt of cationic friction reducers in several different fluids through a ½″ OD/0.402″ ID pipe. The graphs are discussed in SPE 119900, “Critical Evaluations of Additives Used in Shale Slickwater Fracs”; (P. Kaufman and G. S. Penny, CESI Chemical a Flotek Co. and J. Paktinat, Universal Well Services Inc.)
Each of FIGS. 3 and 4 show that there are two clear regions where the dispersion of a typical material is greatly influenced, i.e., at 0 to 10 seconds and again at 20 to 30 seconds. During the experiments, the fluid was recycled back into the loop through the circulation pump every 10 seconds. The circulation pump acted like a mixing system, thereby improving the material performance of the additive. The experimental results, represented by the curves of FIGS. 3 and 4, illustrate that dispersion of additives is crucial to the performance of the material. The periods of time from 0 to 10 second and from 20 to 30 seconds correlate to the times when typical friction reduction material passes through the mixing system in the cyclic loop process. The shape of the curves of FIGS. 3 and 4 indicate that, at about 10 seconds, the typical material has not been adequately dispersed and, therefore, is not distributed into the boundary layer of the flowing material. Therefore, the important disbursement of additives is desirable.


The invention relates to a method of producing an inspection chip used for a specimen detection device that detects a specimen using localized plasmons and a specimen detecting method of detecting a specimen using localized plasmon.
Among known detection devices for detecting a minute specimen is one using an enhanced electric field created by localized plasmons or an enhanced electric field further intensified by localized plasmon resonance, which is a phenomenon where resonance is produced by coupling between localized plasmons and light.
In a detection device of this type, a specimen is placed on a substrate on a surface of which a number of metallic portions capable of exciting localized plasmons are disposed, with Raman scattered light of the specimen intensified by an enhanced electric field that is generated by localized plasmons. Since Raman scattered light displays a spectrum proper to each specimen under examination, the specimen can be identified or existence of a specific specimen can be determined by detecting Raman scattered light of the specimen.
Substrates that generate an enhanced electric field intensified by localized plasmon resonance include, for example, ones having configurations described in JP 2005-144569 A and JP 2007-240361 A.
JP 2005-144569 A describes a substrate on which particles each coated with a thin metallic film are disposed with a high density. To be more specific, JP 2005-144569 A describes a substrate having a two-dimensional array structure formed by reducing dielectric or semiconductor particles densely arranged on the substrate through anisotropic dry etching process and attaching a metal or a semiconductor onto the particles in a hemispherical form by vapor deposition or sputtering to keep the metallic parts of adjacent particles spaced at a given controlled distance.
JP 2007-240361 A describes a substrate having a number of minute projections formed thereon. The projections have a metallic layer disposed on the surface thereof; the metallic layer has a dielectric layer formed on the surface thereof, and the dielectric layer has secured to the surface thereof specific binding members capable of specifically binding to a substance to be measured that is contained in a test sample to form a specific binding substance.
JP 2005-195440 A describes a specimen detecting method using a microstructure comprising a substrate and first metallic particles. The substrate has micropores formed and distributed on one surface thereof. The first metallic particles each have dimensions permitting excitation of localized plasmon resonance and are disposed in the micropores of the substrate so that the head portions of the first metallic particles project above the surface of the substrate. The microstructure is placed in a solution with a substance capable of specifically binding to the specimen secured to the head portions of the first metallic particles. The solution contains dispersed therein second metallic particles having dimensions permitting excitation of localized plasmon resonance, with a substance capable of specifically binding to the specimen secured to the second metallic particles. The surface of the microstructure from which the head portions of the first metallic particles project is irradiated by light to measure the intensity of light component reflected or transmitted at said surface, thereby detecting the specimen contained in the solution based upon the measured intensity of the light.
According to the method described in JP 2005-195440 A, the specimen binds to the second metallic particles to which a substance capable of specifically binding to the specimen is secured whereas the specimen also binds to the first metallic particles to the head portions of which a substance capable of specifically binding to the specimen is secured, so that the change in plasmon resonance wavelength that varies greatly when the first metallic particles and the second metallic particles approach is detected to achieve detection of the specimen.
In the detection devices using the substrates described in JP 2005-144569 A and JP 2007-240361 A, the metallic particles or metallic projections having dimensions permitting excitation of localized plasmon resonance are allowed to adsorb specimen to detect, for example, the variation in an enhanced electric field, fluorescent light from the specimen excited by the enhanced electric field, and Raman scattered light thereby to achieve detection of the specimen.
According to such a method, however, a great enhancement cannot be achieved because only an enhanced electric field created around metallic particles that lie below the specimen can be used.
Although, according to the method described in JP 2007-240361 A, the efficiency with which the specimen binds to the metallic film may be increased by securing a substance capable of specifically adsorbing the specimen to the surface of the metallic film, a great enhancement cannot be achieved because, also in this case, only an enhanced electric field created around metallic particles that lie below the specimen can be used.
Furthermore, the need to select for each specimen a specific adsorbing substance for attachment to the metallic particles adds to the cumbersome procedure and limits the specimen to which the detection device can be used.
The method proposed in JP 2005-195440 A, which detects the variation of a plasmon resonance wavelength, requires the specific adsorption to be performed twice. Accordingly, two or more molecules of a specific adsorbing substance (referred to as “antibody” below) needs to be bound to the specimen. Thus, where the specimen is a substance having a small molecular mass, two molecules of an antibody cannot be adsorbed onto the specimen, making the detection of the specimen impossible.
Furthermore, because the method described in JP 2005-195440 A achieves detection of the variation in plasmon resonance wavelength caused as the first metallic particles and the second metallic particles come close to each other through the intermediary of the specimen, it is essential that the first metallic particles and the second metallic particles approach each other only through the intermediary of the specimen.


The present invention relates generally to signal spectrum analyzers and more particularly, to such analyzers wherein Chirp-Z forward transforms are utilized.
Conventional Chirp-Z signal analyzers utilize forward transforms to compress the individual continuous wave (hereinafter CW) components of the signal into segregated pulses or time intervals from which such components are then selectively reconstructed or expanded with inverse transforms. Considerable gain is inherent with Chirp-Z forward transforms, however, high attenuation is inherent with Chirp-Z inverse transforms. Consequently, Chirp-Z inverse transforms encumber the overall sensitivity of signal analyzers.


Field of the Invention
The present invention relates to a clock such as an alarm clock, a wall clock, or a watch to be mounted on a knapsack and similar articles. More specifically, the invention relates to interchangeable decorative members which may be mounted on the alarm clock, wall clock or watch to be inserted in the knapsack or similar articles.


1. Field of the Invention
The present invention relates to a process for the determination of the amount of irreversibly glycated hemoglobin, or HbA1c, present in a sample of blood, relative to the amount of total hemoglobin. In particular, the invention incorporates in the method an electrochemical, enzyme-catalyzed reaction or reactions.
2. Background Information
HbA1c is a glycated hemoglobin formed by a binding reaction between an amine group of hemoglobin and the glucose aldehyde group, for example between the amine group of the N-terminal valine of the β-chain of hemoglobin and the glucose aldehyde group. The binding reaction first forms a Schiff's base and then a stable ketoamine by Amadori rearrangement. The percentage of HbA1c (i.e. the amount of glycated hemoglobin relative to total hemoglobin in the blood) has come to be taken as a measure of the level of blood glucose control a diabetic patient has maintained for a period of two or three months prior to the measurement. As such, percentage HbA1c has become an important measurement by which health care providers can assist diabetic patients in their care.
There are many known assays that can be used to determine HbA1c percentage. In recent years research efforts have focused on creating assays that are both highly accurate and fast. However, known HbA1c assays typically require a substantial number of time-consuming steps wherein the blood components must be separated and treated.
In the health care context, a diabetic patient is typically guided by a physician to obtain an HbA1c measurement when the physician realizes that there is a need for such information during an office visit. The patient then provides a blood sample to a laboratory and results are returned to the physician hours or days later. Typically, the lab will use a table top analyzer of the type presently available commercially. This time lag between the patient's visit and the result of the test requires that the physician review the result long after the patient has left the office. If the physician believes that further consultation with the patient is required in light of the test result, the patient must be contacted again.
Currently, there is a device sold under the name “A1c NOW” by Metrika, Inc. of Sunnyvale, Calif. This handheld and disposable device (based on technology described in U.S. Pat. No. 5,837,546 entitled “Electronic Assay Device and Method,” incorporated herein by reference) is said to provide an HbA1c test result in eight minutes using a relatively small sample of blood. The A1c NOW device is an example of the market demand for a fast method of providing an HbA1c result for either home or doctor's office use. However, the A1c NOW device is not as accurate as some laboratory assays. Thus, research has continued to focus on finding a highly accurate HbA1c assay that is also fast enough and simple enough to permit a diabetic and his or her doctor to take a blood sample during an office visit and have a trustworthy HbA1c measurement available for discussion in the same visit.


Light emitting diodes (“LEDs”) have been used in various applications including illuminating watches, transmitting information from remote controls, and forming images on jumbo television screens. More recently, LEDs have been used in portable lighting devices, such as flashlights, because, among other things, LEDs can last longer and can be more durable than incandescent lamps commonly used in conventional flashlights.
Notwithstanding the desirable characteristics LEDs may have over incandescent lamps, improvements can be made over existing lighting devices that use an LED as its primary source of light. For example, current LED flashlights typically fail to produce a quality light beam that projects for any appreciable distance. A reason for this is that available LED lamps substantially radiate light in a pattern over an angle less than 180° relative to the position of the LED. FIG. 1 illustrates the brightness or radiation pattern of a typical LED lamp. A typical LED lamp includes an LED and a lens arranged over the LED. The light rays that emanate from the typical LED lamp is generally conical —the brightness (indicated in percentages) is generally concentrated about the center axis 11 and reduces non-linearly as the spherical angle θ increases. Existing LED flashlights have not provided a reflector/lamp combination that effectively captures the brighter light rays that are concentrated about the center axis. Accordingly, although available LED lighting devices may be suitable to illuminate the immediate surrounding area, the distance that the light beam is able to project has been limited.
To try to overcome this deficiency, some devices have used multiple LEDs or a combination of LED lamps and incandescent lamps. However, such devices involve greater complexity, consume more energy, and cost more to manufacture. Accordingly, the present invention provides an energy efficient LED lighting device that has improved optical performance and that projects a quality light beam.
Also, as improvements are made to light sources, such as LEDs, another problem challenging the operation of portable lighting devices is effectively dissipating the increased heat that is generated by the light source. Accordingly, the present invention provides a combination that effectively dissipates heat from the light source of a portable lighting device. The present invention also provides a means to reduce the amount of heat generated by the light source and to use less energy to illuminate the light source.


Field of the Invention
The present invention relates to methods, systems, apparatuses, computer readable media, and other means for reliably using thermophotovoltaic cells to power electronic devices.
Description of Related Art
Electronic devices are known which are powered by rechargeable batteries such as nickel-cadmium, lithium-ion, nickel-metal hydride, and rechargeable alkaline batteries. The batteries of such devices are often recharged using standard recharging means and methods, such as by plugging a charging cable into the device and into a conventional alternating current (AC) outlet. The battery of a device can be conventionally charged by plugging the device into another electronic device using a universal serial bus (USB) connection (such as a USB cable or docking station). However, it can be inconvenient or impossible for the user to charge the batteries when, for example, the user is traveling. In addition, a typical recharge will power the battery for only a limited amount of run time. After the battery has been drained, the user must recharge or replace the battery to continue using the electronic device.
Some electronic devices (e.g., calculators) can further use solar cells to power the device. However, such methods and devices are limited by small size of many electronic devices, which constrains the effective surface area for absorbing sunlight, as well as the inherent characteristics of solar cells, which require the device to track the sun to maintain consistent exposure to sunlight for stable power output. Consequently, while the voltage generated by the solar cells can be enough to power less energy demanding devices, the voltage can be insufficient for electronic devices that demand more power. Furthermore, as electronic devices include an increasing number of advanced features, larger sources of stable and consistent power are required. Thus, there are competing interests between the portability of these devices and the amount of available power.
The effectiveness of using known photovoltaic cells to charge electronic devices is additionally limited by composition and other properties of the cells which frustrate charge separation and transport and permit significant electron-hole pair recombination to occur. Unless rapidly separated and transported from the cell, photogenerated charges recombine and contribute to thermalization and, in low band gap semiconductors, photocorrosion. Increasing the thermal energy of such cells further reduces overall photoconversion efficiency (PCE) by lowering charge mobility and promoting additional recombination.
Thermalization inevitably occurs in such applications notwithstanding the relative speed and degree of separation and transport. In response to AM 1.5 G solar radiation, crystalline silicon cells with a 1.1 eV absorption edge are able to absorb photons representing approximately 77% of the solar spectrum (with wavelengths ranging from about 350 nm to about 1.1 μm); the remainder (with wavelengths ranging from about 1.1 μm to 1 mm) heats the cell and its surrounding structures and environment. Further, almost all of the photons in the flux absorbed by the cell have energies greater than the bandgap energy of silicon, and produce both an electron-hole pair and thermalization losses upon absorption. In total, more than about two thirds of the solar flux striking a conventional solar cell is converted to thermal energy.
Problematically, the performance of electronic devices also degrades in response to elevated temperature. The integration of conventional solar cells into electronic devices is thus further complicated by the implicit expectation that such devices be exposed to solar radiation. However, electronic devices generate heat since such devices are comprised in part of components which only use a portion of the charge they receive. For example, the amount of power discharged from a device's battery that is not used for device function instead increases the thermal energy of the device at rates dependent on the relative efficiency of the device's components. Thus, device manufacturers go to significant lengths to manage heat, in many cases by designing their devices to dissipate heat as a form of waste since it is generally present at low grade temperatures insufficient for known heat recovery technologies to operate cost-effectively, particularly at the scale of a electronic device.
The thermal energy produced by or imparted to known electronic devices, be it from the absorption and inefficient conversion of sunlight or the inefficient use of electrical energy, will eventually dissipate as the system and its surroundings achieve thermal equilibrium. The rate and degree to which that dissipation occurs is in part a function of the ambient temperature in the local environment, which is itself directly and indirectly heated by the vast majority of the incoming solar flux that never comes in contact with the surface of the cell. Most of that energy is absorbed and stored by the environment (e.g., air, water, land, buildings, electronic devices, and so on) in the form of thermal energy which is then released at low grade temperatures by convection, conduction and, importantly, emission of infrared radiation in every direction, day and night, 24 hours a day, and 365 days per year. Humanity then adds to those emissions by engaging in activities that create waste heat, for example, by burning coal and other fossil fuels to provide power to electronic devices. Historical attempts to access and convert such low grade sources of thermal energy into electricity have been limited and unsuccessful.
The increased use of electronic devices in recent years corresponds to increased fossil fuel consumption. For example, the two billion smartphones expected to be in use worldwide by 2014 will consume the equivalent of more than 80 million barrels of fossil fuel per year. Smartphone use alone is growing by more than about 40% per year, with each new generation evolving and selecting for increased performance. It is desirable to provide a method or device for meeting the power needs of such devices that does not rely on the combustion of fossil fuels.
In view of the conventional attempts, needs remain for improved methods, devices and systems for powering and managing thermal energy in electronic devices.


In the past, if solar energy concentrating systems were used on top of buildings or roofed structures to gather radiant solar energy, then one could select from two options. The first option was simply to take a solar energy concentrating system suitable for use on the ground and mount it up on top of a roofed structure. While such an approach did gather radiant solar energy, it also required that the roof support a substantially greater weight. This add-on approach resulted in substantially higher capital costs. Moreover, once the system was atop the roofed structure, inevitably the underlying roof would need repair. The presence of the system atop the roof in a non-integrated fashion increased the ease and cost of making roof repairs.
The second option was to make a substantial portion of the roof into a solar energy concentrating reflector. An example of this unitary reflector approach can be found in U.S. Pat. No. 3,994,435 to Barr. While Barr no longer had the disadvantage of added supporting structure, Barr had to make compromises in gathering the radiant solar energy. The semi-cylindrical reflector and fixed collector did not collect as much solar energy as ground-based units with better geometries. Also, Barr required that the underlying building have a shape similar to the reflector, and thus, the ends of the Barr building had to swoop arcuately upwards, mimicking the reflector arc. Such a requirement had obvious disadvantages in being used on the numerous flat roofed buildings and roofed structures which are used for commercial or industrial purposes.


The invention relates to a process for the production of xylenes by adsorption-reaction in a simulated moving bed and particularly a simultaneous process for dismutation and separation of a toluene feedstock into benzene and xylenes.
Paraxylene is a raw material that makes it possible to synthesize terephthalic acid and toluene terephthalate that are then transformed into resins and fibers, such as, for example, Tergal. The most effective process for the production and purification of paraxylene in terms of productivity is the adsorption in a simulated moving bed or countercurrent that may or may not be combined with a final purification by crystallization and necessarily coupled to a catalytic isomerization on a zeolite, for example an EUO-structural-type zeolite that is mentioned, for example, in the French patent application of the applicant 99/07 968. The paraxylene is produced mixed with the other isomers into C8-aromatic compounds primarily by the processes of isomerization, reforming and dismutation of toluene.
The dismutation of toluene consists in using two toluene molecules to produce a benzene molecule and a xylene molecule. This dismutation is referred to as paraselective when the paraxylene constitutes the majority of the xylenes that are produced.
The non-selective reaction is catalyzed by MFI-type zeolites (or pentasil) or mordenite or else metals of group VIII; examples will be found in Patents FR 2761904, U.S. Pat. Nos. 4,007,231, 4,011,276, 4,029,716 and 4,052,476. In the case of the selective dismutation, the catalysts that are used are pentasils of type ZSM5, ZSM 11, ZSM22 or ZSM23 or ZSM 35 on which a deposit of outside material such as carbon (coke) or silicon was placed, as described in U.S. Pat. Nos. 4,260,843, 4,274,982, 4,380,685, 4,908,342, 5,173,461 and EP26962. The Mobil Oil Company uses two commercial processes for dismutation of toluene: the MTDP (non-selective) (see Oil and Gas Journal Vol. 69 No. 48, 1971 by Grandio et al.), and the MSTDP (selective) (see Oil and Gas Journal Vol. 90 No. 41, 1992 by Gora et al. or Europ. Chem. News Vol. 54, p. 1418, 1990). For these two processes, the major drawback is that the conversion of toluene is limited to 30% by the thermodynamic equilibrium. At the outlet of the reactor, the typical composition of the mixture is therefore benzene 15%, toluene 70%, and xylenes 15%. A series of two columns to be distilled is therefore necessary to separate these three products and to recycle the largest portion of the toluene to the inlet of the reactor. In the case of the paraselective process, among the isomers of the xylene, it is possible to obtain up to 90% of paraxylene, but if a compromise between the conversion of toluene and the paraselectivity is sought, the proportion of paraxylene is smaller (from 75 to 85%).
Since the 1970""s, it has been known to use adsorption and reaction simultaneously (IandEC Fundam, 17 (1978) 1 D Sweich, J Villermaux). In the 1980""s, it was proposed by Barker and Ganestsos to use the adsorption reaction in a simulated moving bed and in liquid phase, for example, for the inversion of saccharose and its total separation into glucose and fructose. Since the beginning of the 1990""s, the idea of using adsorption and vapor-phase reaction simultaneously by using hydrogen as a vector fluid and as a reagent was first conceived by A. K. Ray and R. W. Carr (Chem Eng. Sci 50 (1995) n14, 2195-2202). It applied to the reaction for hydrogenation of mesitylene. Other authors adopted the idea of the separation reaction in a simulated moving bed and applied it to refining or to petrochemistry. It is thus possible to cite U.S. Pat. No. 5,530,173 that offers the additional original feature that the feedstock (mixture of aliphatic hydrocarbons with 6 to 8 carbon atoms) and the desorbent (normal pentane) are converted and separated simultaneously into isoparaffins with a high octane rating. Even more recently, U.S. Pat. No. 5,877,373 proposed the transalkylation of aromatic hydrocarbons into C9 and C10 by a mixture of toluene and benzene in a vapor phase and in the presence of hydrogen in such a way as to produce xylenes. In the latter document, it is not the implementation in a simulated moving bed but the circulation in opposite directions in the two reactors.
The object of the invention is the simultaneous production of benzene and xylenes by dismutation of toluene substantially without recycling toluene at the inlet of the reactor. To do this, the invention uses separation by adsorption, and the simultaneous reaction used in a simulated moving bed and in vapor phase.
More specifically, the invention relates to a simultaneous process for dismutation and separation of a feedstock that essentially consists of toluene, benzene and xylenes in the presence of a desorbent that is high in hydrogen in an adsorber-reactor that comprises at least three zones, characterized in that
a) the vapor-phase or supercritical feedstock is introduced at the inlet of a reaction and adsorption zone (zone III), and at the outlet of said zone, a raffinate that is high in benzene and desorbent is recovered,
b) the desorbent is introduced at the inlet of a desorption zone (zone I), and an effluent is recovered at the outlet of said zone from which a portion in the form of an extract that is high in xylenes and desorbent is drawn off,
c) the other portion of the effluent of zone I is introduced at the inlet of a reaction and desorption zone (zone II), and an effluent that is sent to the inlet of reaction and adsorption zone III is recovered at the outlet of said zone.
The process is also characterized in that each of the zones comprises at least one bed that contains an adsorbent that is adapted to separate benzene, toluene and xylenes and a catalyst that is adapted to dismutate toluene into benzene and xylenes, whereby the adsorbent and the catalyst are in solid form.
When one of the zones comprises several beds, the latter comprises at least one bed that contains an adsorbent and a catalyst, whereby the remaining beds can contain either only a catalyst or only an adsorbent.
According to a variant of the invention, the catalyst can be a non-selective catalyst for paraxylene, adapted to obtain in the extract a mixture of xylenes that is close to the thermodynamic equilibrium.
It may be selected from the group that is formed by MFI zeolites or pentasils, mordenite in acid form or a precious metal of group VIIIB that is deposited on mordenite, or the Y zeolite that is exchanged with nickel, sodium, lanthanum or in acid form, the X zeolite that is exchanged with sodium, lanthanum or in acid form.
According to another variant of the invention, the catalyst is selective for the paraxylene and adapted to obtain a mixture of xylenes containing at least 80% of paraxylene.
These catalysts have very few active sites on their surface; they can be selected from the group of MFI zeolites, in particular ZSM5, ZSM11, ZSM22, ZSM23 that are made selective by deposition of coke, or silicon, or magnesium, or germanium or a combination of these elements at the surface of the zeolite.
With regard to the adsorbent, it may be selected from the group that is formed by silicalite, MFI zeolites or pentasils, faujasites (X or Y zeolites) that are exchanged by a cation of group IA or a cation of group IIA, or a cation of group IA and a cation of group IIA, the mordenites that are exchanged by a cation of group IA or a cation of group IIA, and the preceding zeolites made selective by deposition at the surface of carbon or magnesium or germanium or silicon or a combination of these elements.
According to a first variant, it is possible to use the same solid both as adsorbent and as catalyst in each bed.
According to a second variant, it is possible to produce an approximately homogenous mixture of adsorbent and catalyst in each of the beds in proportions of 95:5 to 5:95.
According to a third variant, it is possible to use a layer of catalyst and a layer of adsorbent in each bed in proportions of 95:5 to 5:95.
The operating conditions in the adsorber-reactor are generally as follows:
the temperature is between 220 and 520xc2x0 C. and preferably between 275 and 350xc2x0 C.
the H2/feedstock molar ratio is in, for example, proportions of 0.5/1 to 50/1 and preferably between 2/1 and 10/1
the total pressure in the adsorber-reactor is between atmospheric pressure and 400 bar and preferably between 1.5 and 40 bar (1 bar=105 Pa)
the partial pressure of hydrocarbons at the injection point of the feedstock is generally between 0.1 and 40 bar and preferably between 0.2 and 10 bar
the volumetric flow rate is between a pph of 0.025 hxe2x88x921 and 25 hxe2x88x921, and preferably between 0.05 and 5 hxe2x88x921.
According to a first implementation of the process according to the invention that corresponds to a 3-zone adsorber-reactor, the fluid circulation between the last bed of zone III and the first bed of zone 1 can be interrupted with an all-or-nothing valve that is placed downstream from the sampling of the entire raffinate.
According to a second implementation of the process that corresponds to an adsorber-reactor with at least 4 zones, a recycling compressor that is located between the first bed and the last bed is adapted to control the flow of fluid that circulates successively in each of the zones.
According to a third implementation of the process that corresponds to an adsorber-reactor with at least four zones, the circulation of fluid between the last bed of zone IV and the first bed of zone I is interrupted with an all-or-nothing valve, and the fluid that contains the hydrogen that is obtained from zone IV is recovered and sent back to the intake of the hydrogen compressor that delivers this desorbent to the inlet of zone I.


The present invention relates to a method and apparatus for the precision cutting of corrugated paperboard panels into specimens having square, or other rectangular, shapes of predetermined size, e.g., four inches on a side, etc. The precision, cut to size specimens are subsequently used as test specimens for various measurements, e.g., bending tests, column strength tests, edge compression tests, flat crush tests, and adhesion tests.
Apparatus has previously been developed for cutting corrugated paperboard panels into square or rectangular configurations for subsequent use as test specimens in standardized testing of the paperboard material. The conventional cutting apparatus can take various forms. One known cutting apparatus comprises a horizontal table or platform having a flat upper surface adapted to receive the corrugated paperboard panel flatwise thereon, and an elongated knife blade swingably connected to the table for downward motion along one edge of the table. A handle extending from the elongated knife is pulled downwardly so that the knife blade slices through the paperboard panel in a downward arc, to thereby form a straight edge on the panel. The panel is then repositioned on the table, and the cutting process is repeated to form four straight edges on the paperboard panel.
The above table is equipped with an upstanding linear abutment, or backstop, oriented at right angles to the cutting plane of the knife blade, whereby the paperboard panel can be positioned with a cut straight edge engaged against the abutment, while the various cuts are being made in the panel. The abutment, or backstop, permits successive cuts to be made at right angles to one another, so that the final test specimen has a rectangular, usually square, or other rectangular, configuration.
The cutting table, or platform, may have a slidably adjustable T-square, that includes a horizontal upstanding straight edge extending parallel to the cutting plane of the vertically-oriented knife blade. The horizontal spacing between the upstanding straight edge and the blade cutting plane, can be varied or changed to permit variation in the size of the cut specimen, or test specimen panel. As previously noted, the cut test specimen will usually have a square, or other rectangular, shape. Typically, the cut square or rectangular specimen, will vary in size from an upper limit of about six inches along each edge, to a lower limit of about one inch along each edge. The size of the cut test specimen is determined by tests to be performed, and effectuated by the settings of the slidable T-square, or, more properly, an L-square.
The cutting blade can be arranged for vertical motion along an edge of the panel support table, as previously described. However, a vertically moving cutter blade does not achieve an optimum cutting action, since it exerts a downward pressure on the upper surface of the paperboard panel. The cut edge may thus be slightly depressed, or squashed, especially if the cutter blade is slightly worn, in which case, there is a greater cutter blade edge area in contact with the paperboard surface.
As an alternative, and as practiced in the present invention, the cutter blade can be made to move horizontally through the paperboard panel parallel to the panel faces, i.e., the cutting blade can be arranged to move horizontally along the table surface so as to produce essentially no deformation of the panel face. In such a case, the lower end of the cutter blade extends into a slot in the table surface, while the cutting edge of the cutter blade extends generally vertically, so that the cutter blade attacks the edge of the paperboard panel along a horizontal action line.
The cutter mechanism can be operated manually, or with a power actuated mechanism, e.g., a fluid cylinder. In one known apparatus, an air-operated fluid cylinder is supported for horizontal motion across the table surface. A cutter blade is carried by the movable portion of the cylinder, such that pressurization of the cylinder sends the cutter blade across the table to form a cut straight edge on the corrugated paperboard panel. Reverse motion of the cylinder returns the cutter blade to its original position ready for the next cutting cycle, after repositionment of the paperboard panel.
One major and serious disadvantage of all existing prior art cutting apparatus, is the fact that there is no mechanism for precisely determining, and effecting, the precise orientations of the test specimen panel cut edges, relative to the internal flutes in the corrugated paperboard panels, prior to making the cuts. The term, "flutes," is herein used to mean the linear passages, or `tunnels,` formed within the corrugated paperboard panel, by the corrugated internal liner sheet.
Typically, the corrugated paperboard panels have two flat spaced-apart outer sheets, and an internal corrugated liner sheet. The corrugations, or undulations, defining the flutes, space the two outer sheets apart, and determine the overall thickness of the panel. Typically the paperboard panel will have a thickness of about one-eighth of an inch, such that each undulation has a transverse dimension slightly less than about one-eighth of an inch.
The square or rectangular test panels are designed to be subjected to several different tests, including an extremely important edgewise compression test, which should be performed `perfectly`, or precisely, parallel, to the direction of the internal flutes, or, alternately, `perfectly` normal to the flute direction. In order to produce reproducible, or duplicate, test results on similarly constructed paperboard panels, it is necessary that the square or rectangular test specimen panels be uniformly and precisely cut, or formed, so that two of the test specimen panel edges are always precisely parallel to the flutes, and the other two specimen panel edges are always precisely normal to the flutes.
The hollow, internal flutes are located within the corrugated paperboard panels, so that the flute direction is not always readily determined by a visual inspection of the uncut corrugated paperboard panel. However, it is possible to form a panel edge running "approximately" parallel to the flute direction, by a trial-and-error process, wherein the edge of the test specimen, or sample, is inspected after the first cut, to determine the approximate extent of the deviation from parallelism.
However, such visual trial-and-error inspection, involves an inspection of the corrugated panel sheet edges that are in semi-concealed locations between the outer facing sheets of the corrugated paperboard panel. Therefore, the observer is never quite certain, from a visual inspection, whether or not, the first cut is, in fact, exactly, or precisely, parallel to the internal flute direction. In any event, such visual inspections, as flawed as they are, also require a lengthy amount of time, and a certain degree of skill, on the part of the operator.
It is possible to pry apart the edges of the outer facing sheets of the paperboard panel, in order to better see the directions of the flutes. However, such an operation destroys the integrity of the panel edge, and thus renders the panel essentially useless for edge compression strength testing, and other test measuring purposes.
There is a clear and strong need for a corrugated paperboard panel cutting method and apparatus, wherein the first cut of the panel test specimen, is made either precisely parallel, or precisely normal, to the flute direction, such that the final square, or other rectangular, test speimen panel, has two edges running precisely normal to the flute direction and two edges running precisely parallel to the flute direction. If the test specimen's first cut edge can have the desired precise orientation relative to the flute direction, the remaining three test specimen edges can automatically be made to have the necessary orientations, e.g., by using T-square cutting guide surfaces properly oriented to the cutter blade plane. The present invention is directed to a method and apparatus for achieving either the desired parallelism, or normalcy, between the test specimen's first cut edge and the flute direction, as well as subsequent cut edges.
An additional problem inherent in conventional cutter blade constructions, which has been elegantly solved by the present invention, is the premature dulling of the cutter blade. With conventional arrangements, the same zone of the cutter blade's cutting edge is used continually for each cutting cycle. The cutting pressure is repetitively applied to a relatively small localized area of the cutter blade edge, so that the cutter blade becomes dull after only a relatively few cutting cycles, necessitating frequency replacement of the cutter blade.
Cutter blade replacement requires time, and also involves potential danger to the operator, because the cutter blade edge is extremely sharp, especially the new replacement cutter blade. Manual handling of the cutter blade during blade removal or installation can, therefore, cause serious injury to the operator.
The present invention also seeks, in part, to provide a cutter blade construction, wherein, different zones of the cutter blade's cutting edge are used for cutting purposes during successive cutting cycles. Wear on the cutter blade is, therefore, distributed over a longer cutting edge area, such that cutter blade replacement is less frequent, compared to prior art arrangements.


In certain system arrangements duplicated buffer memory units are employed in an active-standby configuration to reduce so-called "down time" in the presence of a failure and, thereby, improve system reliability. In such duplicated memory system arrangements proper system operation requires that the contents of each of the memory units be identical. Prior arrangements are known in which synchronization of such duplicated memory units is realized. (See, for example, U.S. patent application Ser. No. 07/739,928, filed Aug. 2, 1991 now U.S. Pat No. 5,278,969 issued Jan. 11, 1994.) It should be noted that ATM transmission of data is on a cell-by-cell basis wherein each cell comprises a fixed length packet. Thus, in the ATM context, the terms cell and packet are interchangeable. In the noted prior duplicated memory arrangement, a plurality of queues is employed to store cells, with each of the queues being associated on a one-to-one basis with either inputs or outputs of the memory unit. Synchronization of the active and standby memory units is realized in this prior arrangement by employing a queue length counter with each queue and observing when all of the counters have reached zero count at least once. Although this prior arrangement will indicate that the duplicated memories are in synchronization at some particular time after synchronization has been initiated, it does not determine when or how to initiate resynchronization. Once synchronization has been obtained, if the contents of the corresponding queues in the active and standby memories become different during any cell interval, problems can arise.


1. Field of the Invention
The present invention relates, in general, to a magnetoresistive (MR) read/write head and method for making a MR read/write head, and, more particularly, to a MR read/write head having decreased track width and method for making a MR read/write head with high control over track width definition.
2. Relevant Background
The desktop personal computer market continues to demand higher capacity and faster performance from hard disk and tape drives. With applications such as file downloading, increased file sizes, advanced operating systems, and multimedia applications, demand for hard disk drive capacity, for example, is doubling every year. Technologies for storing and retrieving data from magnetic media must also be cost effective. Because lower cost per megabyte (MB) is also desired, the prior practice of simply adding more disks and "heads" (i.e., structure in which read and write elements are provided) to a hard drive is less and less effective. Disk and tape drive suppliers continue to increase areal densities, or the number of data bits per square inch, to meet the increasing demand for storage at competitive pricing. Read and write head design are key technologies needed to achieve these capacity increases.
The write element that writes data on the disk is typically made up of two poles that are separated by a write gap, and which generate a magnetic field when they are excited by a coil magnetically coupled to the poles. When the write element is in proximity to the disk, a magnetic field generated by the poles sets the magnetic orientation in given locations on the disk. In this manner, data is written on the disk.
The read element that reads data from the disk is sandwiched between two shields. During a read operation the read element flies in proximity to the disk so that the read element senses the magnetic orientation of the given disk locations. To enable the read element to focus on a small disk location during reading at (i.e. the read element must not be affected by the magnetic orientation of adjoining disk locations), it is desirable to shield the read element. The two relatively large shields filter out the magnetic effects of adjoining disk locations, so that a specific disk location can be focused upon for reading.
Hard disk drives with lower areal densities typically use inductive read and write elements. Inductive heads offer low cost and mature processing technology suitable for high volume production. To increase the signal strength from an inductive head, designers have increased the number of turns in the read head as the read signal is directly proportional to the number of turns. Some inductive heads use fifty or more turns in the read/write head. However, increasing the number of turns increases the head's inductance. There is a limit to the amount of inductance a head can tolerate to effectively perform data write operations. Since thin-film inductive heads use the same inductive element for both reading and writing, the head cannot be optimized for either operation. Moreover, the increased inductance decreases the frequency at which data can be written to and read from the magnetic media.
Magnetoresistive (MR) head technology is used to provide higher areal density than possible with inductive heads in both disk and tape drives. MR head structures include an MR element as a magnetic field sensor. A coil is formed above the read head and magnetically coupled to the magnetic yoke that defines the poles of the write element. Although the coil and yoke are magnetically coupled, they are separated by an insulating material to prevent current flow between the coils and the yoke. To provide an area efficient structure, it is desirable to vertically stack the coils in two or more layers.
An MR head generally combines the read and write elements of the head into an integrated unit. It does so by eliminating one of the poles of the write element and substituting in its place one of the shields of the read element. In doing so an integrated pole/shield element is created.
Using an MR structure as a read element provides high signal output and low noise compared to inductive heads. This higher signal output allows the write element to write data in a much narrower track while still being reliably detected by the MR read element. Separate read and write heads allow each head to be optimized for one particular function (i.e., reading or writing data). With an MR head, the number of wire turns in the write element can be greatly reduced, resulting in a low inductance head enabling high frequency write operations.
The track width of an MR head is largely determined by the size of the area of the disk that is affected by the write head. Where the pole/shield structure is physically large, the pole/shield will tend to undesirably affect a larger part of the disk during a write operation, which is a phenomenon referred to as "fringing". Fringing has an adverse effect on the efficient storage of data on the disk given that it is usually desirable to pack data on the disk as densely as possible, thereby increasing the storage capacity of the disk.
The track width can be decreased by making the poles physically small at the write tip (i.e., the portion of the yoke that forms the poles), thereby concentrating the magnetic field into a smaller area. However, in conventional MR head processes, the yoke, including the write tip, are formed as an integrated structure over the coil structure. The coil structure is very thick, especially when vertically stacked coils are used. Hence, the write tip is typically patterned using thick photoresist (on the order of 10-15 microns thick) making it difficult to define the small structures that are required to decrease track width. Critical dimension control is poor when patterning thick layers of photoresist resulting in unacceptable variation in the size of the patterned feature.
What is needed therefore, is an MR head that combines the advantages of a small write tip structure, but that can be manufactured with a high degree of process control.


1. Field of Invention
The invention relates to a cooling device and, in particular, to an air flow channel.
2. Description of the Prior Art
FIG. 1 shows the cooling method for a conventional projector lamp. Normally, a blower 800 directly blows cooling air into the lamp reflector 700, taking away heat generated by the projector lamp 500. The cooling places of the projector lamp 500 are mainly the high-temperature points above and below the filament 510, the soldering point 520, and the end points 530. Each high-temperature point has to be controlled within a certain temperature range. Aside from the projector lamp 500, the lamp reflector 700 has to be cooled below a predetermined temperature in order to prevent the lamp reflector from breaking. Using the conventional cooling method on the projector lamp 500, the cooling air has a directly impact on the projector lamp 500 instead of cooling each of the high-temperature points according to the required temperature ranges. Moreover, the cooling air first flows by the end point 530, the soldering point 520, and the filament 510 and absorbs their heat before reaching the bottom of the lamp reflector 700. However, these high-temperature points have temperatures higher than the bottom of the lamp reflector 700. The cooling air after absorbing heat from them is very difficult to further cool down the bottom of the lamp reflector 700. If one solves the problem by increasing the fan speed, the temperatures are those high-temperature points will be lowered too much out of the required ranges. This method of first cooling down the high-temperature points with higher temperatures before cooling down the lamp reflector has the drawback that when the temperature of the lamp reflector becomes too high, adjusting the fan speed to lower the temperature of the lamp reflector will render the temperature of the filament out of the specific range. This makes the temperature control very difficult.
As described, the prior art results in non-uniform cooling on different parts of the projector lamp 500 and the lamp reflector 700 or cannot cool the system in such a way that the projector lamp 500 and the lamp reflector 700 fall right within the desired temperature ranges. These effects will affect the performance and lifetime of the projector lamp and the lamp reflector. Thus, it is desirable to provide a better cooling system.


1. Field of the Invention
This invention primarily relates to a guiding means for an endless apron provided in the drafting part of a spinning frame, and further, to a guiding means for an endless belt in the feeding mechanism of, for example, a printing machine, duplicator, precision packaging machine, film processor, and the like.
2. Description of the Prior Art
FIG. 1 is an illustration showing a typical apron zone of a long apron type drafting device which comprises such components as a bottom roller BR and a top roller TR, both being disposed on a roller stand RS which supports a roller, a cradle CR, a tensor bar TB, a tension guide TG pressed by a tension lever TL in the direction of the arrow, a top apron TA and a bottom apron BA, in addition to a weighting arm WA.
However, the above said apron guiding device in respect of performance and operability for tightening, balancing and guiding the bottom apron, as well as performance of the tensor bar itself and operability in maintenance thereof, has not proved satisfactory.


1. Field of the Invention
The present invention generally relates to the manufacture of electrical conductor lines and vias that interconnect circuits on substrates such as semiconductors and related packages and, more particularly, to a low cost method of filling seams or holes in substrates using a combination of a low resistivity metal deposited by physical vapor deposition (PVD) and a refractory metal deposited by chemical vapor deposition (CVD). The invention has particular application in submicron circuit manufacture.
2. Description of the Prior Art
Low resistivity metals such as aluminum and copper and their binary and ternary alloys have been widely explored as fine line interconnects in semiconductor manufacturing. Typical examples of fine line interconnect metals include Al.sub.x Cu.sub.y, where the sum of x and y is equal to one and both x and y are greater than or equal to zero and less than or equal to one, ternary alloys such as Al--Pd--Cu and Al--Pd--Nb, Al--Cu--Si, and other similar low resistivity metal based alloys. Today's emphasis on scaling down line width dimensions in very large scale integrated (VLSI) circuitry manufacture has led to reliability problems including inadequate isolation, electromigration, and planarization.
The IBM Technical Disclosure Bulletin to Ahn et al., Vol. 33, No. 5, October 1990, pages 217-218, discloses tungsten wrapped copper conductors and via holes fabricated by selective deposition using a mixture of WF.sub.6 and SiH.sub.4 in the presence of hydrogen. Encapsulated interconnects like those of Ahn et al. have significantly higher resistance to electromigration and the small grain size of a selective tungsten film reduces reflectance and thereby enhances the ability of photolithography tools to focus and resolve photoresist images. However, the tungsten layer formed using the low temperatures described by Ahn et al. would be silicon rich (e.g., 3-4%) and would not be a good diffusion barrier for copper since copper resistivity would be degraded by the formation of copper silicide. Thus, it is difficult to deposit a diffusion barrier by selective means at low temperature. Moreover, the Ahn et al. technique relies on the formation of a donut shape at the bottom of the lines which is normally created by the reaction of outgassing moisture and WF.sub.6. The creation of the donut shape is believed to be not reliable.
Dalton et al., VMIC Conference, Jun. 12-13, 1990, pages 289-292, points out that a hot wall CVD reaction involving SiH.sub.4 and H.sub.2 reduction of WF.sub.6 to form a selective tungsten layer on an aluminum or alloy conductor results in the incorporation of fluorine at the aluminum and tungsten interface. The fluorine incorporation is a byproduct of the reaction of WF.sub.6 with aluminum as shown by Equation 1. EQU WF.sub.6 +2Al.fwdarw.2AlF.sub.3 +W Eq. 1
The thin layer of aluminum fluoride will increase the series contact resistance of Metal 1 to Metal 2 vias. Dalton reported that sputtering TiW film on top of the aluminum prior to tungsten encapsulation using CVD eliminates the problem of fluorine absorption.
Dalton discloses a traditional scheme for interconnect formation wherein aluminum is first deposited on a planar surface, it is overcoated with the sputtered TiW layer (the only difference from traditional processing), the aluminum is then patterned using photoresist imaging and developing followed by reactive ion etching (RIE). The resulting structure is then overcoated with a passivation dielectric such as SiO.sub.2 or polyimide which itself is subsequently patterned, subjected to RIE, and metallized to create a multilayered structure. FIG. 1 is taken from Dalton and shows that multilayer devices produced by traditional processing schemes have seams in the dielectric layers at the location of the metal conductor lines and have a very irregular top surface.
It is difficult to achieve planarity of the dielectric using RIE. Planarity is in part dependent on the pattern density, and non-planar surfaces result in puddling problems during subsequent metalization. If an RIE technique is used on polyimide, an etch stop is needed for removal of photoresist on top of aluminum or copper based lines when the lines are etched down to the polyimide surface because the photoresist removal process would also remove polyimide. RIE of any high copper content, aluminum or copper alloy is extremely difficult. A serious drawback of traditional processes which include metal RIE is that a large number of metal shorts tend to develop with fine geometry due to particle defects.
U.S. Pat. No. 4,824,802 to Brown et al. discloses a method for filling interlevel dielectric vias or contact holes in multilevel VLSI metalization structures. In particular, an intermediary metal such as tungsten or molybdenum is either selectively deposited in openings in an insulator or non-selectively deposited over the entire surface and in the openings of the insulator by CVD, then a planarization resist, such as azoquinonenovolac-type resists, polymethacrylates, polyimides, or other thermoplastic materials, is applied over the top of the intermediary metal. A planarized structure is then obtained by etching to a level where the intermediary metal is even with the resist. The Brown et al. method does not avoid metal corrosion and other problems associated with etching and is not useful for planarizing Al--Cu or other soft alloys because they have different properties from the harder metals such as tungsten and molybdenum. Moreover, using the Brown et al. method, it is difficult to completely fill vias and lines.
U.S. Pat. No. 4,944,836 to Beyer et al. discloses a chemical-mechanical polishing technique which can be used to produce coplanar metal/insulator films on a substrate. In particular, Beyer et al. contemplate patterning an underlying insulating layer, depositing an Al--Cu film, and then using a chemical-mechanical polishing technique wherein an alumina slurry in dilute nitric acid is mechanically rubbed on the surface to remove Al--Cu. The polishing compound tends to have a significantly higher removal rate for Al--Cu than the underlying insulator. The resulting structure includes Al--Cu lines planarized with the insulating layer, and subsequent layers can easily be added in the fabrication of multilayer structures.
U.S. Pat. No. 4,956,313 to Cote et al. discloses a via filling and planarization technique wherein Al--Cu alloy lines are patterned on top of a first passivation layer on a substrate, the lines are overcoated with a second passivation layer which is preferably a doped glass such as phosphosilicate glass (PSG) or borophosphosilicate glass (BPSG) which conforms over the contours of the Al--Cu alloy lines, vias are then formed in the second passivation layer to expose the lines, and tungsten is applied over the surface of the second passivation layer and in the vias by CVD. It is reported in Cote et al. that CVD tungsten is conformal in character and can fill the vias without creating voids. The structure is then planarized by polishing with an abrasive slurry.
Neither Beyer et al. nor Cote et al. recognize that polishing is not practical for low resistivity, soft metals such as Al--Cu alloys. This is because such materials tend to scratch, smear on the surface, and corrode under the influence of the slurry. Moreover, creation of the planarized structures in accordance with Cote et al. takes several processing steps which increases costs and reduces output.
Rossnagel et al. J. Vac. Sci. Technol. 2:261 (Mar/Apr. 1991) discloses a collimated magnetron sputter deposition technique for depositing films that are compatible with lift-off patterning techniques and hole filling. The technique is also presented in U.S. Pat. No. 4,824,544 which is herein incorporated by reference.
Shiozaki et al., Abstracts of the 19th Conference on Solid State Devices and Materials, discloses the use of selective tungsten deposition for hole filling on top of a high resistivity hard metal such as MoSi.sub.x and is unrelated to encapsulation of a soft metal.


This invention was made in part with support from the National Science Foundation Grant Number DMR 9315914.
The present invention relates to a process for forming high quality crystalline refractory materials, particularly gallium (Ill) nitride (GaN), from solid precursors. GaN is a material newly available for use in the optoelectronics industry fur the fabrication of light-emitting diodes (LEDs) and blue lasers. It is also possible that doped GaN crystals may have utility as semiconductors. A particularly suitable application is the replacement of standard light bulbs in large outdoor displays, traffic lights and street lighting by GaN LEDs. GaN crystals, when properly activated, fluoresce producing a bright blue glow which is about 60 times brighter than the best GaP based yellow-green LEDs and many times brighter than a standard light bulb which it would replace. Further, a GaN LED display would have an operating life far in excess of the standard light bulb.
Currently, bulk quantities of high purity, polycrystalline gallium nitride are not available. Current techniques to produce such materials require maintaining reactants at high temperatures and pressures for long periods of time. Prior attempts to manufacture GaN by reacting gallium iodide with lithium nitride, which appears to be a suitable approach, produces elemental Ga, nitrogen and Lil and not GaN. Thus there is a need for a low cost, rapid process to produce large quantities of powdered crystalline materials for use in such applications as lighting, signal displays, and flat screen displays for computers and television screens.


Hyaluronic acid is a naturally occurring linear polysaccharide. It is a polymer of disaccharide units composed of β-1,4-D-glucuronic acid and N-acetyl-D-glucosamine linked together by β-1,3-glycosidic bonds. Hyaluronic acid has a molecular weight ranging from 1,000 to 10,000,000 daltons.
Hyaluronic acid is the only non-sulfated glucosaminoglycan (GAG) found in the extracellular matrix (ECM) of higher animals.
Biomaterials derived from hyaluronic acid are used, for example, in regeneration of cartilage and skin. Also, they play key roles in drug delivery or surgery. Chemically unmodified hyaluronic acid is utilized as the aid for the delivery of ophthalmologic drug to improve the absorption of drugs and proteins at the mucosal tissue.
Further, with regard to the treatment of osteoarthritis, hyaluronic acid improves lubrication at the joint surface and thus reduces pain. Arthritis reduces the production of hyaluronic acid and the increased breakdown by proteases further reduces hyaluronic acid in the joint. As a result, the articular damage can be aggravated because external impact cannot be adequately absorbed or distributed at the joint.
Since approved by the FDA in 1997, the injection of hyaluronic acid is widely used. With compositions similar to those of the joint fluid, hyaluronic acid solution regains viscosity and elasticity when injected into the joint and improves lubrication and absorbs impact, thereby protecting the joint cartilage and preventing further damage.
Also, it is reported to have anti-inflammatory effect and inhibit the breakdown of chondrocytes by several in vitro researches. Based on this, it can be inferred that hyaluronic acid can be utilized as scaffold for cell delivery in the process of cell transplantation therapy of chondrocytes for cartilage tissue regeneration.
The in vivo metabolism of hyaluronic acid is regulated by hyaluronic acid synthase (HA synthase) and hyaluronidase. Hyaluronic acid synthase is an integral membrane enzyme, which synthesizes hyaluronic acid polymers and excretes them out of the cell. In mammals, HAS1, HAS2 and HAS3 isoenzymes are found.
Hyaluronidase is an enzyme that breaks down hyaluronic acid. Depending on the activation pH, it can be classified into neutral hyaluronidase and acidic hyaluronidase. Neutral hyaluronidase (PH-20) is specifically found in the testis (sperm) and shows activity in the physiological pH.
Acidic hyaluronidase (Hyal1-4) is found in body fluids as well as in a variety of human organs, including spleen, cartilage, skin, eyes, liver, kidney, bladder, placenta, etc., and shows activity around at pH 3. Since this enzyme is present in the lysosome, hyaluronic acid is transported into the cytoplasm by endocytosis and degraded.
The endocytosis of hyaluronic acid is mediated by the cell surface receptors. The primary cell surface receptor for HA is CD44. CD44 is a transmembrane glycoprotein and binds primarily to hyaluronic acid. It is expressed in most of human cell membranes. The hyaluronic acid fragments degraded at the lysosome induce different signal transfers depending on their size, affecting cell proliferation and differentiation.
Various porous scaffolds are used in the field of tissue engineering. Chondrocytes cultured in 2D condition such as petridish cannot maintain their chondrocytic phenotype, resulting in synthesis of type I collagen rather than type II.
In contrast, chondrocytes cultured in 3D condition maintain their characters and functions, resulting in spherical cell shape. That is, a 3-dimensional scaffold helps the cell attachment and cartilage formation in vitro and in vivo.
The use of porous scaffolds is very useful in that chondrocytes can be cultured under a restricted condition with significantly reduced necrosis of the tissue.
Thus, as one of new treatments for joint cartilage damage, the technique of culturing stem or progenitor cells derived from the cartilage, bone marrow or periosteum in vitro using biodegradable scaffolds and transplanting them into lesion site is attempted instead of direct injection of autologous chondrocytes.
This technique is advantageous over the method of using cell suspension since necrosis of the cartilage tissue to serve as cell sources is significantly reduced and the cells can be incubated under a restricted condition. Further, it is also adequate considering that cell attachement is improved by a scaffold.
In addition to cell delivery, a scaffold can serve as mold to fill lesion site of tissue. An ideal scaffold is required to be non-immunogenic, non-toxic, biocompatible, biodegradable and easy to manipulate.
The pore size of the scaffold is important. An inadequate pore size may result in the restricted nutrient supply to the cells being cultured in the scaffold or ineffective removal of the wastes from the cells.
If the pore size is too small, the cells may not be completely filled inside the scaffold, which negatively affects the generation of the tissue. In contrast, if the pore size is too large, not all the extracellular matrix proteins synthesized by cells are accumulated. That is, the proteoglycan and collagen accumulated in the scaffold can be found only a part of the total degree of actually synthesized ECM.
Accordingly, even though chondrocytes cultured in a porous scaffold in a metabolically active state, the scaffold may deem as inadequate for the growth of chondrocytes.
Thus, the control of the pore size is important in improving the retention rate of newly synthesized extracellular matrix molecules inside the scaffold.
Also, in case the sponge type scaffold with minimal porosity required for survival, growth and differentiation of cells is in solid state, it comes into problem that the surgical operation is the only way of delivering the entire scaffold including cells to a disease site.


Recently, IP-related protocol groups such as not only IP (Internet Protocol) but also SIP (Session Initiation Protocol; RFC3261) to execute call control among radio communication terminals have been used also in a radio communication system such as a mobile communication system.
In a radio communication system using the protocol groups, a group call is provided in which a call within a group consisting of multiple radio communication terminals is established when one of the radio communication terminals (for example, a cellular telephone terminal) calls up the other radio communication terminals. Each of the radio communication terminals participating in the group call can transmit and receive voice data and video data to and from the other radio communication terminals participating in the group call.
Meanwhile, there is proposed a radio communication system which allows a radio communication terminal to participate halfway in a group call (hereinafter such participation being referred to as halfway participation) (see Patent Document 1). Specifically, in this radio communication system, a control station device periodically broadcasts notification information including information on the group call to radio communication terminals through a radio base station.
In this way, a radio communication terminal which has failed to receive a call-up signal can receive the notification information, and participate halfway in the group call by transmitting a request for participation in the group call. Patent Document 1: JP-A 2001-168793 (pages 5 to 7, FIGS. 1 and 3)


The purpose of the invention is to saw particularly hard stones with two parallel blades tensioned in a frame having an almost vertical oscillating motion.
For hard stone sawing like granites, one commonly uses sawing machines with one or more blades, animated by a straight reciprocal or oscillating movement. The blades used are either steel ones, sprinkled with water and abrasive grits (like sand, steel shot or silicon carbide) either ones with diamond segments.
Some of those machines only have one blade animated by a horizontal axis oscillation while the stone blocks are in horizontal traverse movement. The blade is tensioned in a frame to avoid deviations during the sawing. It is better to place the blade laterally in order to accomodate blocks of unlimited width.
The major inconvenience of such machines is that one has to cut one slab at a time, rendering the sawing slow and expensive. Another inconvenience is given by the asymmetrical disposition of the blade in tne frame, introducing a bad equilibrium of the tensions in the machine and this creates deviations during the sawing.
Machines having several blades are also well known. Those blades are tensioned parallely in a frame which is animated by a horizontal axis oscillation or a straight reciprocal vertical movement, with a horizontal traverse movement for the block to be sawn. The distance between the blades is chosen in order to saw the slabs with a desired thickness. The evident advantage of such machine is that series of slabs can be sawn in one operation.
The inconveniences of such machine are unfortunately numerous. The tensioning of the blades in the frame is, indeed, a long and arduous operation and it is not possible to modify the distance between the blades as one would like. The width of the sawn slabs can not be regulated in accordance with clients' demands and one has to be satisfied with standard width.
Another inconvenience of multiblade machines lies in the frame wherein the block to be sawn has to pass through. One can thus see that the frame dimensions are determined for those of the blocks. In particular, the width of the blocks has always to be below the inside width of the frame.
It must also be observed that the construction of such kind of multiblade machine is sophisticated and always expensive.
The object of the hereby invention is to remedy the above mentioned inconveniences, realizing a double blade sawing machine, giving the opportunity of simultaneous sawing of two slabs with arbitrary thickness in two independent blocks placed on both sides of the machine. One realizes like this a symmetrical machine, fast and economical.


There is a need for low bend loss optical fibers, particularly for optical fibers utilized in so-called “access” and fiber to the premises (FTTx) optical networks. Optical fiber can be deployed in such networks in a manner which induces bend losses in optical signals. transmitted through the optical fiber. Some applications that can impose physical demands, such as tight bend radii, compression of optical fiber, etc., that induce bend losses include the deployment of optical fiber in optical drop cable assemblies, distribution cables with Factory Installed Termination Systems (FITS) and slack loops, small bend radius multiports located in cabinets that connect feeder and distribution cables, and jumpers in Network Access Points between distribution and drop cables. It has been difficult in some optical fiber designs to achieve both low bend loss and low cable cutoff wavelength at the same time.


1. Field of the Invention
The present invention pertains to a pressure plate assembly for a friction clutch, which assembly includes a housing; a pressure plate connected to the housing for rotation in common around an axis of rotation which is free to move axially with respect to the housing; a stored-energy device which pretensions the pressure plate in the axial direction with respect to the housing; a wear-compensating device which acts in the path of support between the stored-energy device and at least one of the housing and the pressure plate and comprises at least one wear-compensating element, which is free to move when wear occurs and/or when wear is compensated; an indicator arrangement comprising at least one indicator opening in the housing and at least one indicator element on a wear-compensating element, where information concerning the amount of wear which has occurred can be derived from the position of the indicator element relative to the minimum of one indicator opening.
2. Description of the Related Art
U.S. Pat. No. 5,531,308 discloses a friction clutch in which a wear-compensating device can be used to ensure that the wear which occurs during the operation of the clutch, such as the wear of the friction linings of a clutch disk, for example, is compensated. For this purpose, two adjusting rings are provided, one of which is held nonrotatably with respect to a housing, whereas the other adjusting ring is free to rotate to compensate for wear. The two rings have corresponding ramp surfaces, so that, upon rotation of the second adjusting ring, the total axial length of the wear-compensating device consisting essentially of the two adjusting rings changes. On the adjusting ring which can rotate relative to the housing, an axial projection is provided, which engages in a curved, slot-like opening in the housing, i.e., in a bottom area of the housing. When the adjusting ring turns, this projection moves in the opening through which it passes. From the position which this projection occupies in the opening, it can be determined how far the rotatable adjusting ring has rotated up to that point, which is an indication in turn of the extent to which wear compensation has occurred and thus also of the amount of wear which has occurred.
It is the task of the present invention to improve a pressure plate assembly of the general type in question in such a way that, by the use of a simple design, the amount of wear which has occurred can be detected more easily.
According to the invention, the indicator element at least partially fills at least one indicator opening in at least one state of wear.
With the design of a pressure plate assembly according to the invention, the geometry of the indicator element can be made essentially independent of the geometry of the indicator opening. This facilitates the design and also makes it possible for both the indicator element and the indicator opening to be designed with respect to their shape and/or configuration in such a way that, through the cooperation of these two assemblies, a very precise indication of the actual amount of wear which has occurred or of the degree of wear compensation which has occurred can be obtained.
It is possible, for example, for the width of the indicator element, i.e., the dimension essentially transverse to the direction of its movement with respect to the minimum of one indicator opening, to change over the length of the indicator element in the direction of movement. It is thus achieved that the width of the indicator element visible in the minimum of one indicator opening changes as the element moves past, so that, as the indicator element moves, the area of the indicator opening which it fills also changes, from which information can be derived concerning different states of wear.
For this purpose, it is possible, for example, for the width of the indicator element to change continuously, at least in certain of its areas. Alternatively or in addition, it is possible for the width of the indicator element to change in step-like increments. Although a step-like change in width produces a very clear-cut discontinuity in the indicator characteristic, an indicator element with a continuous change in width provides information of higher resolution concerning the state of wear.
It is also possible to provide a plurality of indicator openings in succession in the direction of the movement of the indicator element. In another, preferred embodiment of the pressure plate assembly according to the invention, it is possible, in conjunction with the provision of a plurality of indicator openings, for the indicator element to have an indicator section which fills essentially all of the indicator openings in one wear state and at least partially fills one indicator opening or essentially no indicator opening in at least one other wear state. It can therefore be provided, for example, that the indicator fills all of the indicator openings when the clutch is new and has not yet been affected by wear, and that, as the amount of wear increases, the indicator element moves successively along the indicator openings and thus opens various indicator openings one after the other.
As an alternative, it is also possible for the indicator element to have an indicator section which does not fill all of the indicator openings in any wear state. It can be provided in this case, for example, that, as a function of the amount of wear which has occurred, the indicator section completely fills one of the indicator openings or partially fills two of the indicator openings.
In a design of the pressure plate assembly which is very simple to realize, it is possible for the wear-compensating device to comprise an adjusting ring, which can rotate around the axis of rotation for the purpose of wear compensation, and for the indicator element to be free to move along with the adjusting ring constituting the wear-compensating element.
An alternative embodiment of the pressure plate assembly according to the invention can be designed in such a way that the wear-compensating device comprises: an arresting element which, upon the occurrence of wear, is able to move with respect to the pressure plate assembly in correspondence with the amount of wear which has occurred; an essentially wedge-shaped slider element, which is installed between the pressure plate assembly and the arresting element and which, upon movement of the arresting element with respect to the pressure plate assembly, is free to move under the pretensioning effect in correspondence with the extent of the movement of the arresting element with respect to the pressure plate assembly in order to keep the arresting element in the position relative to the pressure plate assembly to which it has moved as a result of wear; and an adjusting ring, which is able to rotate around the axis of rotation to perform a wear-compensating movement, where the adjusting rotation of the adjusting ring is limited by the slider element and/or by the arresting element, where the indicator element is able to move along with the slider element forming the wear-compensating element.
In addition, the pressure plate assembly according to the invention can be designed so that the stored-energy device is located in an area between the indicator element and the minimum of one indicator opening and has a see-through opening associated with the minimum of one indicator opening. To avoid the introduction of additional openings in the stored-energy device, it is possible, for example, for the see-through opening to be formed by an area between two of the spring tongues of the stored-energy device.
It is also possible, according to the invention, for the indicator element to be connected to the wear-compensating element by connecting sections provided on the indicator element. It is also possible for the indicator element to have a contact area, by means of which it is supported on a surface of the wear-compensating element facing the axis of rotation. It is possible in this way to prevent the indicator element from shifting position as a result of centrifugal force during rotational operation.
The present invention also pertains to a friction clutch which contains a pressure plate assembly according to the invention.
Other objects and features of the present invention will become apparent from the following detailed description considered in conjunction with the accompanying drawings. It is to be understood, however, that the drawings are designed solely for purposes of illustration and not as a definition of the limits of the invention, for which reference should be made to the appended claims. It should be further understood that the drawings are not necessarily drawn to scale and that, unless otherwise indicated, they are merely intended to conceptually illustrate the structures and procedures described herein.