  We observed MS 1054-0321, the highest redshift cluster of galaxies in the
Einstein Medium Sensitivity Survey (EMSS), with the Chandra ACIS-S detector. We
find the X-ray temperature of the cluster to be 10.4^{+1.7}_{-1.5} keV,
slightly lower than that inferred previously and in agreement with the observed
velocity dispersion and that found from weak lensing. We confirm significant
substructure in the form of two distinct clumps in the X-ray distribution. We
find the virial mass of the cluster to be at least 4.5 x 10^{14} h^{-1}
M_{\odot} and the existence of this cluster constrains Omega_m to be less than
one. If Omega_m = 1 and assuming Gaussian initial perturbations, we find the
probability of observing MS 1054 in the EMSS is ~ 7 x 10^{-4}. We also present
the first high-resolution X-ray spectra of two high-redshift quasars, S5
0836+710 and PKS 2149-306, obtained with the Chandra HETGS. The primary goal of
this observation is to use the high spectral resolving power of the HETGS to
detect X-ray absorption produced by a hot intergalactic medium. No significant
emission or absorption feature is detected in either source at +/-3sigma level.
Based on the detection limits we constrain the properties of possible emitters
and absorbers. We propose a method to constrain the cosmological parameters via
the X-ray forest theory, but current data do not give significant constraints.
We also find that combined with the constraints from the distortion of the CMB
spectrum, the X-ray Gunn-Peterson test can marginally constrain a uniform,
enriched IGM.
