18 research outputs found
Approximate ab initio calculation of vibrational properties of hydrogenated amorphous silicon with inner voids
We have performed an approximate ab initio calculation of vibrational
properties of hydrogenated amorphous silicon (a-Si:H) using a molecular
dynamics method. A 216 atom model for pure amorphous silicon (a-Si) has been
employed as a starting point for our a-Si:H models with voids that were made by
removing a cluster of silicon atoms out of the bulk and terminating the
resulting dangling bonds with hydrogens.
Our calculation shows that the presence of voids leads to localized low
energy (30-50 cm^{-1}) states in the vibrational spectrum of the system. The
nature and localization properties of these states are analyzed by various
visualization techniques.Comment: 15 pages with 6 PS figures, to appear in PRB in December 199
Onset of depature from linearized hydrodynamic behavior in argon gas studied with neutron Brillouin scattering
Whose shoe fits best? Dubious physics and power politics in the TMD footprint controversy
Apparent design breakthroughs in short-range missile defense systems such as Theater High-Altitude Air Defense (THAAD) have prompted questions about the legality of such systems under the 1972 Antiballistic Missile (ABM) Treaty. Prominent physicists have used computer “footprint” methodology to prove that if engineered to specifications, THAAD might exceed ABM Treaty performance limits banning highly effective missile defense systems. In response, missile defense officials commissioned Sparta, Inc. to conduct secret research casting doubt on the validity of such findings. The substantial diplomatic issues at stake and the interesting rhetorical dynamics involved in this dispute warrant close scholarly analysis. Attention to the iterative relationship between the interpenetrating spheres of public argument and scientific practice in this case yields novel insight about the processes in which technical knowledge of defense systems is forged and raises fresh issues for the “closure project” in science and technology controversy studies