2,086 research outputs found
Computers for real time flight simulation: A market survey
An extensive computer market survey was made to determine those available systems suitable for current and future flight simulation studies at Ames Research Center. The primary requirement is for the computation of relatively high frequency content (5 Hz) math models representing powered lift flight vehicles. The Rotor Systems Research Aircraft (RSRA) was used as a benchmark vehicle for computation comparison studies. The general nature of helicopter simulations and a description of the benchmark model are presented, and some of the sources of simulation difficulties are examined. A description of various applicable computer architectures is presented, along with detailed discussions of leading candidate systems and comparisons between them
Spin symmetry and spin current of helicity eigenstates of the Luttinger Hamiltonian
A general spin symmetry argument is proposed for spin currents in
semiconductors. In particular, due to the symmetry with respect to spin
polarization of the helicity eigenstates of the Luttinger Hamiltonian for a
hole-doped semiconductor, the spin polarized flux from a single helicity
eigenstate induced by an external electric field, is canceled exactly when all
such contributions from eigenstates that are degenerate in energy are summed.
Thus, the net spin current predicted by Murakami et al, Science 301, 1348
(2003), cannot be produced by such a Hamiltonian. Possible symmetry breaking
mechanisms which may generate a spin current are discussed
Pair Production at the Photon Linear Collider
scattering at the Photon Linear Collider is
considered. Explicit formulas for helicity amplitudes due to boson loops
are presented. It is shown that the pair production will be easily
observable at PLC and separation of the loop contribution will be possible
at c.m. energy of 300~GeV or higher.Comment: 9 pages of standard LaTeX + 3 PostScript figures (uuencoded and
compressed
Photon-Photon Scattering at the Photon Linear Collider
Photon-photon scattering at the Photon Linear Collider is considered.
Explicit formulas for helicity amplitudes due to boson loops are presented.
It is shown that photon-photon scattering should be easily observable at PLC
and separation of the loop contribution (which dominates at high energies)
will be possible at c.m. energy of 500~GeV or higher.Comment: Standard LaTeX. 8 pages+5 figures (available by regular mail). IHEP
93-8
Nonlinear interaction between electromagnetic fields at high temperature
The electron-positron `box' diagram produces an effective action which is
fourth order in the electromagnetic field. We examine the behaviour of this
effective action at high-temperature (in analytically continued imaginary-time
thermal perturbation theory). We argue that there is a finite, nonzero limit as
(where is the temperature). We calculate this limit
in the nonrelativistic static case, and in the long-wavelength limit. We also
briefly discuss the self-energy in 2-dimensional QED, which is similar in some
respects.Comment: 13 pages, DAMTP 94/3
How does conformational flexibility influence key structural features involved in activation of anaplastic lymphoma kinase?
Anaplastic Lymphoma Kinase (ALK) plays a major role in developing tumor processes and therefore has emerged as a validated therapeutic target. Applying atomistic molecular dynamics simulations on the wild type enzyme and the nine most frequently occurring and clinically important activation mutants we revealed important conformational effects on key interactions responsible for the activation of the enzyme
A Central Partition of Molecular Conformational Space.III. Combinatorial Determination of the Volume Spanned by a Molecular System
In the first work of this series [physics/0204035] it was shown that the
conformational space of a molecule could be described to a fair degree of
accuracy by means of a central hyperplane arrangement. The hyperplanes divide
the espace into a hierarchical set of cells that can be encoded by the face
lattice poset of the arrangement. The model however, lacked explicit rotational
symmetry which made impossible to distinguish rotated structures in
conformational space. This problem was solved in a second work
[physics/0404052] by sorting the elementary 3D components of the molecular
system into a set of morphological classes that can be properly oriented in a
standard 3D reference frame. This also made possible to find a solution to the
problem that is being adressed in the present work: for a molecular system
immersed in a heat bath we want to enumerate the subset of cells in
conformational space that are visited by the molecule in its thermal wandering.
If each visited cell is a vertex on a graph with edges to the adjacent cells,
here it is explained how such graph can be built
One Loop Multiphoton Helicity Amplitudes
We use the solutions to the recursion relations for double-off-shell fermion
currents to compute helicity amplitudes for -photon scattering and
electron-positron annihilation to photons in the massless limit of QED. The
form of these solutions is simple enough to allow {\it all}\ of the
integrations to be performed explicitly. For -photon scattering, we find
that unless , the amplitudes for the helicity configurations (+++...+) and
(-++...+) vanish to one-loop order.Comment: 27 pages + 4 uuencoded figures (included), Fermilab-Pub-93/327-T,
RevTe
QED Corrections to Planck's Radiation Law and Photon Thermodynamics
Leading corrections to Planck's formula and photon thermodynamics arising
from the pair-mediated photon-photon interaction are calculated. This
interaction is attractive and causes an increase in occupation number for all
modes. Possible consequences, including the role of the cosmic photon gas in
structure formation, are considered.Comment: 15 pages, Revtex 3.
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