1,897 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
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
The missing link between thermodynamics and structure in F_1-ATPase
F_1F_o-ATP synthase is the enzyme responsible for most of the ATP synthesis in living systems. The catalytic domain F_1 of the F_1F_o complex, F_1-ATPase, has the ability to hydrolyze ATP. A fundamental problem in the development of a detailed mechanism for this enzyme is that it has not been possible to determine experimentally the relation between the ligand binding affinities measured in solution and the different conformations of the catalytic ÎČ subunits (ÎČ_(TP), ÎČ_(DP), ÎČ_E) observed in the crystal structures of the mitochondrial enzyme, MF_1. Using free energy difference simulations for the hydrolysis reaction ATP+H_2O â ADP+P_i in the ÎČ_(TP) and ÎČ_(DP) sites and unisite hydrolysis data, we are able to identify ÎČ_(TP) as the âtightâ (K_D = 10^(â12) M, MF_1) binding site for ATP and ÎČ_(DP) as the âlooseâ site. An energy decomposition analysis demonstrates how certain residues, some of which have been shown to be important in catalysis, modulate the free energy of the hydrolysis reaction in the ÎČ_(TP) and ÎČ_(DP) sites, even though their structures are very similar. Combined with the recently published simulations of the rotation cycle of F_1-ATPase, the present results make possible a consistent description of the binding change mechanism of F_1-ATPase at an atomic level of detail
Comparison of 3D Classical Trajectory and TransitionâState Theory Reaction Cross Sections
This report addresses the comparison of 3D classical trajectory and transition-state theory reaction cross sections
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.
Introduction to Workshop on Physics Teaching and the Development of Reasoning
Are physics teachers in high schools, colleges, and universities knowledgeable concerning the reasoning patterns their students use? The personal experiences of many instructors and research carried out during the last few years indicate that a substantial fraction of physics students have difficulty applying functional relationships among variables, considering all necessary combinations of experimental and theoretical conditions of a problem, and examining their own reasoning critically to locate possible errors. The theory of intellectual development formulated by the Swiss psychologist and epistemologist Jean Piaget deals with these matters and can therefore be of help to physics teachers. We have prepared these individualized workshop materials to present the two principal concepts of Piagetâs theory, stages of development and self- regulation, with background and illustrations that will make clear their relevance for physics teaching
Introduction to Workshop on Physics Teaching and the Development of Reasoning
Are physics teachers in high schools, colleges, and universities knowledgeable concerning the reasoning patterns their students use? The personal experiences of many instructors and research carried out during the last few years indicate that a substantial fraction of physics students have difficulty applying functional relationships among variables, considering all necessary combinations of experimental and theoretical conditions of a problem, and examining their own reasoning critically to locate possible errors. The theory of intellectual development formulated by the Swiss psychologist and epistemologist Jean Piaget deals with these matters and can therefore be of help to physics teachers. We have prepared these individualized workshop materials to present the two principal concepts of Piagetâs theory, stages of development and self- regulation, with background and illustrations that will make clear their relevance for physics teaching
Ultraviolet and soft X--ray photon--photon elastic scattering in an electron gas
We have considered the processes which lead to elastic scattering between two
far ultraviolet or X--ray photons while they propagate inside a solid, modeled
as a simple electron gas. The new ingredient, with respect to the standard
theory of photon--photon scattering in vacuum, is the presence of low--energy,
nonrelativistic electron--hole excitations. Owing to the existence of
two--photon vertices, the scattering processes in the metal are predominantly
of second order, as opposed to fourth order for the vacuum case. The main
processes in second order are dominated by exchange of virtual plasmons between
the two photons. For two photons of similar energy , this gives
rise to a cross section rising like up to maximum of around
~cm, and then decreasing like . The maximal cross
section is found for the photon wavevector , the Fermi surface
size, which typically means a photon energy in the keV range.
Possible experiments aimed at checking the existence of these rare but
seemingly measurable elastic photon--photon scattering processes are discussed,
using in particular intense synchrotron sources.Comment: 33 pages, TeX, Version 3.1, S.I.S.S.A. preprint 35/93/C
Sequencing of folding events in Go-like proteins
We have studied folding mechanisms of three small globular proteins: crambin
(CRN), chymotrypsin inhibitor 2 (CI2) and the fyn Src Homology 3 domain (SH3)
which are modelled by a Go-like Hamiltonian with the Lennard-Jones
interactions. It is shown that folding is dominated by a well-defined
sequencing of events as determined by establishment of particular contacts. The
order of events depends primarily on the geometry of the native state.
Variations in temperature, coupling strengths and viscosity affect the
sequencing scenarios to a rather small extent. The sequencing is strongly
correlated with the distance of the contacting aminoacids along the sequence.
Thus -helices get established first. Crambin is found to behave like a
single-route folder, whereas in CI2 and SH3 the folding trajectories are more
diversified. The folding scenarios for CI2 and SH3 are consistent with
experimental studies of their transition states.Comment: REVTeX, 12 pages, 11 EPS figures, J. Chem. Phys (in press
- âŠ