  We model a coronal loop as a bundle of seven separate strands or filaments.
Each of the loop strands used in this model can independently be heated (near
their left footpoints) by Alfv\'en/ion-cyclotron waves via wave-particle
interactions. The Alfv\'en waves are assumed to penetrate the strands from
their footpoints, at which we consider different wave energy inputs. As a
result, the loop strands can have different heating profiles, and the
differential heating can lead to a varying cross-field temperature in the total
coronal loop. The simulation of TRACE observations by means of this loop model
implies two uniform temperatures along the loop length, one inferred from the
171:195 filter ratio and the other from the 171:284 ratio. The reproduced flat
temperature profiles are consistent with those inferred from the observed EUV
coronal loops. According to our model, the flat temperature profile is a
consequence of the coronal loop consisting of filaments, which have different
temperatures but almost similar emission measures in the cross-field direction.
Furthermore, when we assume certain errors in the simulated loop emissions
(e.g., due to photometric uncertainties in the TRACE filters) and use the
triple-filter analysis, our simulated loop conditions become consistent with
those of an isothermal plasma. This implies that the use of TRACE/EIT triple
filters for observation of a warm coronal loop may not help in determining
whether the cross-field isothermal assumption is satisfied or not.
