1,318 research outputs found
Non-Markovian entanglement dynamics of quantum continuous variable systems in thermal environments
We study two continuous variable systems (or two harmonic oscillators) and
investigate their entanglement evolution under the influence of non-Markovian
thermal environments. The continuous variable systems could be two modes of
electromagnetic fields or two nanomechanical oscillators in the quantum domain.
We use quantum open system method to derive the non-Markovian master equations
of the reduced density matrix for two different but related models of the
continuous variable systems. The two models both consist of two interacting
harmonic oscillators. In model A, each of the two oscillators is coupled to its
own independent thermal reservoir, while in model B the two oscillators are
coupled to a common reservoir. To quantify the degrees of entanglement for the
bipartite continuous variable systems in Gaussian states, logarithmic
negativity is used. We find that the dynamics of the quantum entanglement is
sensitive to the initial states, the oscillator-oscillator interaction, the
oscillator-environment interaction and the coupling to a common bath or to
different, independent baths.Comment: 10 two-column pages, 8 figures, to appear in Phys. Rev.
An assessment of Evans' unified field theory II
Evans developed a classical unified field theory of gravitation and
electromagnetism on the background of a spacetime obeying a Riemann-Cartan
geometry. In an accompanying paper I, we analyzed this theory and summarized it
in nine equations. We now propose a variational principle for Evans' theory and
show that it yields two field equations. The second field equation is algebraic
in the torsion and we can resolve it with respect to the torsion. It turns out
that for all physical cases the torsion vanishes and the first field equation,
together with Evans' unified field theory, collapses to an ordinary Einstein
equation.Comment: 11 pages of late
Effects of Acute Exposures to Carbon Dioxide Upon Cognitive Functions
Large quantities of carbon dioxide (CO2) originate from human metabolism and typically, within spacecraft, remain about 10-fold higher in concentration than at the earth's surface. There have been recurring complaints by crew members of episodes of "mental viscosity" adversely affecting their performance, and there is evidence from the International Space Station (ISS) that associates CO2 levels with reports of headaches by crewmembers. Additionally, there is concern that CO2 may contribute to vision impairment and intracranial pressure that has been observed in some crewmembers. Consequently, flight rules have been employed to control the level of CO2 below 4 mm Hg, which is well below the existing Spacecraft Maximum Allowable Concentration (SMAC) of 10 mm Hg for 24-hour exposures, and 5.3 mm Hg for exposures of 7 to 180 days. However, the flight rule imposed limit, which places additional demands upon resources and current technology, still exceeds the lower bound of the threshold range for reportable headaches (2 - 5 mm Hg). Headaches, while sometime debilitating themselves, are also symptoms that can provide evidence that physiological defense mechanisms have been breached. The causes of the headaches may elicit other subtle adverse effects that occur at CO2 levels well below that for headaches. The concern that CO2 may have effects at levels below the threshold for headaches appears to be substantiated in unexpected findings that CO2 at concentrations below 2 mm Hg substantially reduced some cognitive functions that are associated with the ability to make complex decisions in conditions that are characterized by volatility, uncertainty, complexity, ambiguity, and delayed feedback. These are conditions that could be encountered by crews in off-nominal situations or during the first missions beyond low earth orbit. If findings of the earlier study are confirmed in crew-like subjects, our findings would provide additional evidence that CO2 may need to be controlled at levels that are well below current spacecraft limits. Our study will extend the earlier study to determine if crew-like subjects are similarly effected by CO2. In addition to employing the Strategic Management Simulation tool, we will use the Cognition battery of psychometric measures that are being utilized aboard the ISS. It will be important to learn, by using Cognition, if additional cognitive domains are sensitive to concentrations of CO2 at or below limits currently controlled by flight rules. While spaceflight Cognition data will greatly enhance the knowledge base related to inflight behavioral health and performance, some of the measures may be influenced by fatigue (related to sleep deprivation and or workload) and changes in circadian rhythms. Therefore our use of this battery of tests in a well-controlled, ground-based study that is free of these potential confounding influences will establish a baseline terrestrial data set against which Cognition data collected in flight may be assessed. The findings from this study will be useful to the NASA Toxicology Office and the National Research Council Committee on Toxicology, which assists NASA in setting environmental standards, for revision of the SMAC for CO2, and for designing further studies on effects of CO2 upon cognitive functions
The PT-symmetric brachistochrone problem, Lorentz boosts and non-unitary operator equivalence classes
The PT-symmetric (PTS) quantum brachistochrone problem is reanalyzed as
quantum system consisting of a non-Hermitian PTS component and a purely
Hermitian component simultaneously. Interpreting this specific setup as
subsystem of a larger Hermitian system, we find non-unitary operator
equivalence classes (conjugacy classes) as natural ingredient which contain at
least one Dirac-Hermitian representative. With the help of a geometric analysis
the compatibility of the vanishing passage time solution of a PTS
brachistochrone with the Anandan-Aharonov lower bound for passage times of
Hermitian brachistochrones is demonstrated.Comment: 12 pages, 2 figures, strongly extended versio
Radiation reaction and gravitational waves in the effective field theory approach
We compute the contribution to the Lagrangian from the leading order (2.5
post-Newtonian) radiation reaction and the quadrupolar gravitational waves
emitted from a binary system using the effective field theory (EFT) approach of
Goldberger and Rothstein. We use an initial value formulation of the underlying
(quantum) framework to implement retarded boundary conditions and describe
these real-time dissipative processes. We also demonstrate why the usual
scattering formalism of quantum field theory inadequately accounts for these.
The methods discussed here should be useful for deriving real-time quantities
(including radiation reaction forces and gravitational wave emission) and
hereditary terms in the post-Newtonian approximation (including memory, tail
and other causal, history-dependent integrals) within the EFT approach. We also
provide a consistent formulation of the radiation sector in the equivalent
effective field theory approach of Kol and Smolkin.Comment: 23 pages, 8 figure
Exactly solvable path integral for open cavities in terms of quasinormal modes
We evaluate the finite-temperature Euclidean phase-space path integral for
the generating functional of a scalar field inside a leaky cavity. Provided the
source is confined to the cavity, one can first of all integrate out the fields
on the outside to obtain an effective action for the cavity alone.
Subsequently, one uses an expansion of the cavity field in terms of its
quasinormal modes (QNMs)-the exact, exponentially damped eigenstates of the
classical evolution operator, which previously have been shown to be complete
for a large class of models. Dissipation causes the effective cavity action to
be nondiagonal in the QNM basis. The inversion of this action matrix inherent
in the Gaussian path integral to obtain the generating functional is therefore
nontrivial, but can be accomplished by invoking a novel QNM sum rule. The
results are consistent with those obtained previously using canonical
quantization.Comment: REVTeX, 26 pages, submitted to Phys. Rev.
Involvement of Mhc Loci in immune responses that are not Ir-gene-controlled
Twenty-nine randomly chosen, soluble antigens, many of them highly complex, were used to immunize mice of two strains, C3H and B10.RIII. Lymphnode cells from the immunized mice were restimulated in vitro with the priming antigens and the proliferative response of the cells was determined. Both strains were responders to 28 of 29 antigens. Eight antigens were then used to immunize 11 congenic strains carrying different H-2 haplotypes, and the T-cell proliferative responses of these strains were determined. Again, all the strains responded to seven of the eight antigens. These experiments were then repeated, but this time -antibodies specific for the A (AA) or E (EE) molecules were added to the culture to block the in vitro responsiveness. In all but one of the responses, inhibition with both A-specific and E-specific antibodies was observed. The response to one antigen (Blastoinyces) was exceptional in that some strains were nonresponders to this antigen. Furthermore, the response in the responder strains was blocked with A-specific, but not with E-specific, antibodies. The study demonstrates that responses to antigens not controlled by Irr genes nevertheless require participation of class II Mhc molecules. In contrast to Ir gene-controlled responses involving either the A- or the E-molecule controlling loci (but never both), the responses not Ir-controlled involve participation of both A- and E-controlling loci. The lack of Ir-gene control is probably the result of complexity of the responses to multiple determinants. There is thus no principal difference between responses controlled and those not controlled by Ir genes: both types involve the recognition of the antigen, in the context of Mhc molecules
Dependence of radio halo properties on star formation activity and galaxy mass
We investigate the relation between the existence and size of radio halos,
which are believed to be created by star formation (SF) related energy input
into the interstellar medium, and other galaxy properties, most importantly
star formation activity and galaxy mass. Based on radio continuum and H-alpha
observations of a sample of seven late-type spiral galaxies we find a direct,
linear correlation of the radial extent of gaseous halos on the size of the
actively star-forming parts of the galaxy disks. Data of a larger sample of 22
galaxies indicate that the threshold energy input rate into the disk ISM per
unit surface area for the creation of a gaseous halo depends on the mass
surface density of the galaxy, in the sense that a higher threshold must be
surpassed for galaxies with a higher surface density. Because of the good
prediction of the existence of a radio halo from these two parameters, we
conclude that they are important, albeit not the only contributors. The
compactness of the SF-related energy input is also found to be a relevant
factor. Galaxies with relatively compact SF distributions are more likely to
have gaseous halos than others with more widespread SF activity. These results
quantify the so-called "break-out" condition for matter to escape from galaxy
disks, as used in all current models of the interstellar medium and first
defined by Norman and Ikeuchi (1989).Comment: accepted for publication in Astronomy & Astrophysic
Dust in Spiral Galaxies: Comparing Emission and Absorption to Constrain Small-Scale and Very Cold Structures
The detailed distribution of dust in the disks of spiral galaxies is
important to understanding the radiative transfer within disks, and to
measuring overall dust masses if significant quantities of dust are either very
opaque or very cold. We address this issue by comparing measures of dust
absorption, using the galaxy-overlap technique in the optical, with measures of
the dust grains' thermal emission from 50-2000 micron using ISOPHOT on board
ISO and SCUBA at the JCMT. We examine three spiral galaxies projected partially
in front of E/S0 galaxies --- AM1316-241, NGC 5545, and NGC 5091 (for NGC 5091
we have only optical and ISO data). Adopting an empirical exponential model for
the dust distribution, we compare column densities and dust masses derived from
the absorption and emission techniques. This comparison is sensitive to the
amount of dust mass in small, opaque structures, which would not contribute
strongly to area-weighted absorption measures, and to very cold dust, which
would contribute to optical absorption but provide only a small fraction of the
sub-mm emission. In AM1316-241, we find global dust masses of 2-5 x 10^7
M_solar, both techniques agreeing at the 50% level. NGC 5545 has about half
this dust mass. The concordance of dust masses is well within the errors
expected from our knowledge of the radial distribution of dust, and argues
against any dominant part of the dust mass being so cold or opaque. The 50-2000
micron data are well fitted by modified Planck functions with an emissivity law
beta=-2, at 21 +/- 2 K. We also present 12 micron ISOCAM observations of these
pairs.Comparison of H-alpha and 12 micron images of NGC 5545 indicate that
ISOCAM images are reliable tracers of star formation.Comment: 16 pages, 4 tables, 8 figures, in press for October Astronomical
Journa
Self-Dual Bending Theory for Vesicles
We present a self-dual bending theory that may enable a better understanding
of highly nonlinear global behavior observed in biological vesicles. Adopting
this topological approach for spherical vesicles of revolution allows us to
describe them as frustrated sine-Gordon kinks. Finally, to illustrate an
application of our results, we consider a spherical vesicle globally distorted
by two polar latex beads.Comment: 10 pages, 3 figures, LaTeX2e+IOPar
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