186,798 research outputs found
Thermal components for 1.8 K space cryogenics
Work of the summer 1986 is summarized in three areas. First, conceptual design of a laboratory system for heat exchanger evaluation in conjunction with the operation of a thermally activated fountain effect pump (FEP) is presented. Second, Knudsen effect evaluation of fine porous media useful for the pressurization plug which forms the main component of the FEP is described. Third, proof-of-principle test of the lab system selected on the basis of the evaluation is summarized
Crossover from Kramers to phase-diffusion switching in hysteretic DC-SQUIDs
We have measured and propose a model for switching rates in hysteretic
DC-SQUID in the regime where phase diffusion processes start to occur. We show
that the switching rates in this regime are smaller than the rates given by
Kramers' formula due to retrapping of Josephson phase. The retrapping process,
which is affected by the frequency dependent impedance of the environment of
the DC-SQUID, leads to a peaked second moment of the switching distribution as
a function of temperature. The temperature where the peaks occur are
proportional to the critical current of the DC- SQUID.Comment: 4 pages, 4 figure
Inconsistency of Naive Dimensional Regularizations and Quantum Correction to Non-Abelian Chern-Simons-Matter Theory Revisited
We find the inconsistency of dimensional reduction and naive dimensional
regularization in their applications to Chern-Simons type gauge theories.
Further we adopt a consistent dimensional regularization to investigate the
quantum correction to non-Abelian Chern-Simons term coupled with fermionic
matter. Contrary to previous results, we find that not only the Chern-Simons
coefficient receives quantum correction from spinor fields, but the spinor
field also gets a finite quantum correction.Comment: 19 pages, RevTex, Feynman diagrams drawn by FEYNMAN routin
Advanced electrochemical technology Semiannual report, 1 Jul. - 31 Dec. 1967
Gas diffusion advanced fuel cell and related electrochemical system
Spontaneous Scale Symmetry Breaking in 2+1-Dimensional QED at Both Zero and Finite Temperature
A complete analysis of dynamical scale symmetry breaking in 2+1-dimensional
QED at both zero and finite temperature is presented by looking at solutions to
the Schwinger-Dyson equation. In different kinetic energy regimes we use
various numerical and analytic techniques (including an expansion in large
flavour number). It is confirmed that, contrary to the case of 3+1 dimensions,
there is no dynamical scale symmetry breaking at zero temperature, despite the
fact that chiral symmetry breaking can occur dynamically. At finite
temperature, such breaking of scale symmetry may take place.Comment: 12 pages, no figures, uses RevTeX4-bet
Accurate Reaction-Diffusion Operator Splitting on Tetrahedral Meshes for Parallel Stochastic Molecular Simulations
Spatial stochastic molecular simulations in biology are limited by the
intense computation required to track molecules in space either in a discrete
time or discrete space framework, meaning that the serial limit has already
been reached in sub-cellular models. This calls for parallel simulations that
can take advantage of the power of modern supercomputers; however exact methods
are known to be inherently serial. We introduce an operator splitting
implementation for irregular grids with a novel method to improve accuracy, and
demonstrate potential for scalable parallel simulations in an initial MPI
version. We foresee that this groundwork will enable larger scale, whole-cell
stochastic simulations in the near future.Comment: 33 pages, 10 figure
Energetics of Protein-DNA Interactions
Protein-DNA interactions are vital for many processes in living cells,
especially transcriptional regulation and DNA modification. To further our
understanding of these important processes on the microscopic level, it is
necessary that theoretical models describe the macromolecular interaction
energetics accurately. While several methods have been proposed, there has not
been a careful comparison of how well the different methods are able to predict
biologically important quantities such as the correct DNA binding sequence,
total binding free energy, and free energy changes caused by DNA mutation. In
addition to carrying out the comparison, we present two important theoretical
models developed initially in protein folding that have not yet been tried on
protein-DNA interactions. In the process, we find that the results of these
knowledge-based potentials show a strong dependence on the interaction distance
and the derivation method. Finally, we present a knowledge-based potential that
gives comparable or superior results to the best of the other methods,
including the molecular mechanics force field AMBER99
On the Inverse Problem Relative to Dynamics of the w Function
In this paper we shall study the inverse problem relative to dynamics of the
w function which is a special arithmetic function and shall get some results.Comment: 11 page
Causal Relativistic Fluid Dynamics
We derive causal relativistic fluid dynamical equations from the relaxation
model of kinetic theory as in a procedure previously applied in the case of
non-relativistic rarefied gases. By treating space and time on an equal footing
and avoiding the iterative steps of the conventional Chapman-Enskog ---
CE---method, we are able to derive causal equations in the first order of the
expansion in terms of the mean flight time of the particles. This is in
contrast to what is found using the CE approach. We illustrate the general
results with the example of a gas of identical ultrarelativistic particles such
as photons under the assumptions of homogeneity and isotropy. When we couple
the fluid dynamical equations to Einstein's equation we find, in addition to
the geometry-driven expanding solution of the FRW model, a second,
matter-driven nonequilibrium solution to the equations. In only the second
solution, entropy is produced at a significant rate.Comment: 23 pages (CQG, in press
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