2,777 research outputs found
Toxicological safeguards in the manned Mars missions
Safeguards against toxic chemical exposures during manned Mars missions (MMMs) will be important for the maintenance of crew health and the accomplishment of mission objectives. Potential sources include offgassing, thermodegradation or combustion of materials, metabolic products of crew members, and escape of chemical from containment. Spacecraft maximum allowable concentration (SMAC) limits will have to be established for potential contaminants during the MMMs. The following factors will be used in establishing these limits: duration of mission, simultaneous exposure to other contaminants, deconditioning of crew members after long periods of reduced gravity, and simultaneous exposure to ionizing radiation. Atmospheric contaminant levels in all compartments of the transit spacecraft and Manned Mars Station (MMS) will be monitored at frequent intervals with a real time analyzer. This analyzer will be highly automated, requiring minimal crew time and expertise. The atmospheric analyzer will find other usages during the MMMs such as analyzing Martian atmospheres and soils, exhaled breath and body fluids of crew members, and reaction products in chemical processing facilities
Gauge Group TQFT and Improved Perturbative Yang-Mills Theory
We reinterpret the Faddeev-Popov gauge-fixing procedure of Yang-Mills
theories as the definition of a topological quantum field theory for gauge
group elements depending on a background connection. This has the advantage of
relating topological gauge-fixing ambiguities to the global breaking of a
supersymmetry. The global zero modes of the Faddeev-Popov ghosts are handled in
the context of an equivariant cohomology without breaking translational
invariance. The gauge-fixing involves constant fields which play the role of
moduli and modify the behavior of Green functions at subasymptotic scales. At
the one loop level physical implications from these power corrections are gauge
invariant.Comment: 28 pages, uuencoded and compressed tar-file, LATEX+4 PS-figures, uses
psfig.sty. New appendix and some clarifying modifications, references adde
Cosmological Particle Creation in the Presence of Lorentz Violation
In recent years, the effects of Lorentz symmetry breaking in cosmology has
attracted considerable amount of attention. In cosmological context several
topics can be affected by Lorentz violation,e.g., inflationary scenario, CMB,
dark energy problem and barryogenesis. In this paper we consider the
cosmological particle creation due to Lorentz violation (LV). We consider an
exactly solvable model for finding the spectral properties of particle creation
in an expanding space-time exhibiting Lorentz violation. In this model we
calculate the spectrum and its variations with respect to the rate and the
amount of space-time expansion.Comment: 6 pages, 6 figures, To appear in Physics Letters
Co-operative Kondo Effect in the two-channel Kondo Lattice
We discuss the possibility of a co-operative Kondo effect driven by channel
interference in a Kondo lattice where local moments are coupled to a single
Fermi sea via two orthogonal scattering channels. In this situation, the
channel quantum number is not conserved. We argue that the absence of channel
conservation causes the Kondo effect in the two channels to constructively
interfere, giving rise to a superconducting condensate of composite pairs,
formed between the local moments and the conduction electrons. Our arguments
are based on the observation that a heavy Fermi surface gives rise to zero
modes for Kondo singlets to fluctuate between screening channels of different
symmetry, producing a divergent composite pair susceptibility. Secondary
screening channels couple to these divergent fluctuations, promoting an
instability into a state with long-range composite order. We present detailed a
detailed mean-field theory for this superconducting phase, and discuss the
possible implications for heavy fermion physics.Comment: 23 double column pages. 9 fig
The Robustness of Quintessence
Recent observations seem to suggest that our Universe is accelerating
implying that it is dominated by a fluid whose equation of state is negative.
Quintessence is a possible explanation. In particular, the concept of tracking
solutions permits to adress the fine-tuning and coincidence problems. We study
this proposal in the simplest case of an inverse power potential and
investigate its robustness to corrections. We show that quintessence is not
affected by the one-loop quantum corrections. In the supersymmetric case where
the quintessential potential is motivated by non-perturbative effects in gauge
theories, we consider the curvature effects and the K\"ahler corrections. We
find that the curvature effects are negligible while the K\"ahler corrections
modify the early evolution of the quintessence field. Finally we study the
supergravity corrections and show that they must be taken into account as
at small red-shifts. We discuss simple supergravity
models exhibiting the quintessential behaviour. In particular, we propose a
model where the scalar potential is given by . We argue that the fine-tuning problem
can be overcome if . This model leads to
for which is in good agreement with the presently
available data.Comment: 16 pages, 7 figure
Small Fermi surface in the one-dimensional Kondo lattice model
We study the one-dimensional Kondo lattice model through the density matrix
renormalization group (DMRG). Our results for the spin correlation function
indicate the presence of a small Fermi surface in large portions of the phase
diagram, in contrast to some previous studies that used the same technique. We
argue that the discrepancy is due to the open boundary conditions, which
introduce strong charge perturbations that strongly affect the spin Friedel
oscillations.Comment: 5 pages, 7 figure
Post-Newtonian corrections to the motion of spinning bodies in NRGR
In this paper we include spin and multipole moment effects in the formalism
used to describe the motion of extended objects recently introduced in
hep-th/0409156. A suitable description for spinning bodies is developed and
spin-orbit, spin-spin and quadrupole-spin Hamiltonians are found at leading
order. The existence of tidal, as well as self induced finite size effects is
shown, and the contribution to the Hamiltonian is calculated in the latter. It
is shown that tidal deformations start formally at O(v^6) and O(v^10) for
maximally rotating general and compact objects respectively, whereas self
induced effects can show up at leading order. Agreement is found for the cases
where the results are known.Comment: 18 pages, 9 figures. Typos corrected, to appear in Physical Review
Electromagnetic Moments of the Baryon Decuplet
We compute the leading contributions to the magnetic dipole and electric
quadrupole moments of the baryon decuplet in chiral perturbation theory. The
measured value for the magnetic moment of the is used to determine
the local counterterm for the magnetic moments. We compare the chiral
perturbation theory predictions for the magnetic moments of the decuplet with
those of the baryon octet and find reasonable agreement with the predictions of
the large-- limit of QCD. The leading contribution to the quadrupole
moment of the and other members of the decuplet comes from one--loop
graphs. The pionic contribution is shown to be proportional to (and so
will not contribute to the quadrupole moment of nuclei), while the
contribution from kaons has both isovector and isoscalar components. The chiral
logarithmic enhancement of both pion and kaon loops has a coefficient that
vanishes in the limit. The third allowed moment, the magnetic octupole,
is shown to be dominated by a local counterterm with corrections arising at two
loops. We briefly mention the strange counterparts of these moments.Comment: Uses harvmac.tex, 15 pages with 3 PostScript figures packed using
uufiles. UCSD/PTH 93-22, QUSTH-93-05, Duke-TH-93-5
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