52,201 research outputs found
Quasi-static vapor pressure measurements on reactive systems in inert atmosphere box
Apparatus makes vapor pressure measurements on air-sensitive systems in an inert atmosphere glove box. Once the apparatus is loaded with the sample and all connections made, all measuring operations may be performed outside the box. The apparatus is a single-tube adaptation of the double-tube quasi-static technique
Obtaining Stiffness Exponents from Bond-diluted Lattice Spin Glasses
Recently, a method has been proposed to obtain accurate predictions for
low-temperature properties of lattice spin glasses that is practical even above
the upper critical dimension, . This method is based on the observation
that bond-dilution enables the numerical treatment of larger lattices, and that
the subsequent combination of such data at various bond densities into a
finite-size scaling Ansatz produces more robust scaling behavior. In the
present study we test the potential of such a procedure, in particular, to
obtain the stiffness exponent for the hierarchical Migdal-Kadanoff lattice.
Critical exponents for this model are known with great accuracy and any
simulations can be executed to very large lattice sizes at almost any bond
density, effecting a insightful comparison that highlights the advantages -- as
well as the weaknesses -- of this method. These insights are applied to the
Edwards-Anderson model in with Gaussian bonds.Comment: corrected version, 10 pages, RevTex4, 12 ps-figures included; related
papers available a http://www.physics.emory.edu/faculty/boettcher
What the Infrared Behaviour of QCD Vertex Functions in Landau gauge can tell us about Confinement
The infrared behaviour of Landau gauge QCD vertex functions is investigated
employing a skeleton expansion of the Dyson-Schwinger and Renormalization Group
equations. Results for the ghost-gluon, three-gluon, four-gluon and quark-gluon
vertex functions are presented. Positivity violation of the gluon propagator,
and thus gluon confinement, is demonstrated. Results of the Dyson-Schwinger
equations for a finite volume are compared to corresponding lattice data. It is
analytically demonstrated that a linear rising potential between heavy quarks
can be generated by infrared singularities in the dressed quark-gluon vertex.
The selfconsistent mechanism that generates these singularities necessarily
entails the scalar Dirac amplitudes of the full vertex and the quark
propagator. These can only be present when chiral symmetry is broken, either
explicitly or dynamically.Comment: 13 pages, 13 figures; to appear in the Proceedings of ``X Hadron
Physics 2007'', Florianopolis, Brazil, March 26 - 31, 200
A Search for Binary Stars at Low Metallicity
We present initial results measuring the companion fraction of metal-poor
stars ([Fe/H]2.0). We are employing the Lick Observatory planet-finding
system to make high-precision Doppler observations of these objects. The binary
fraction of metal-poor stars provides important constraints on star formation
in the early Galaxy (Carney et al. 2003). Although it has been shown that a
majority of solar metallicity stars are in binaries, it is not clear if this is
the case for metal-poor stars. Is there a metallicity floor below which binary
systems do not form or become rare? To test this we are determining binary
fractions at metallicities below [Fe/H]. Our measurments are not as
precise as the planet finders', but we are still finding errors of only 50 to
300 m/s, depending on the signal-to-noise of a spectrum and stellar atmosphere
of the star. At this precision we can be much more complete than previous
studies in our search for stellar companions.Comment: To appear in conference proceedings,"First Stars III", eds. B.
O'Shea, A. Heger & T. Abel. 3 pages, 5 figure
The re-emission spectrum of digital hardware subjected to EMI
The emission spectrum of digital hardware under the influence of external electromagnetic interference is shown to contain information about the interaction of the incident energy with the digital circuits in the system. The generation mechanism of the re-emission spectrum is reviewed, describing how nonlinear effects may be a precursor to the failure of the equipment under test. Measurements on a simple circuit are used to demonstrate how the characteristics of the re-emission spectrum may be correlated with changes to the digital waveform within the circuit. The technique is also applied to a piece of complex digital hardware where Similar, though more subtle, effects can be measured. It is shown that the re-emission spectrum can be used to detect the interaction of the interference with the digital devices at a level well below that which is able to cause static failures in the circuits. The utility of the technique as a diagnostic tool for immunity testing of digital hardware, by identifying which subsystems are being affected by external interference, is also demonstrated
Equilibrium Configurations of Homogeneous Fluids in General Relativity
By means of a highly accurate, multi-domain, pseudo-spectral method, we
investigate the solution space of uniformly rotating, homogeneous and
axisymmetric relativistic fluid bodies. It turns out that this space can be
divided up into classes of solutions. In this paper, we present two new classes
including relativistic core-ring and two-ring solutions. Combining our
knowledge of the first four classes with post-Newtonian results and the
Newtonian portion of the first ten classes, we present the qualitative
behaviour of the entire relativistic solution space. The Newtonian disc limit
can only be reached by going through infinitely many of the aforementioned
classes. Only once this limiting process has been consummated, can one proceed
again into the relativistic regime and arrive at the analytically known
relativistic disc of dust.Comment: 8 pages, colour figures, v3: minor additions including one reference,
accepted by MNRA
Perturbations of Spatially Closed Bianchi III Spacetimes
Motivated by the recent interest in dynamical properties of topologically
nontrivial spacetimes, we study linear perturbations of spatially closed
Bianchi III vacuum spacetimes, whose spatial topology is the direct product of
a higher genus surface and the circle. We first develop necessary mode
functions, vectors, and tensors, and then perform separations of (perturbation)
variables. The perturbation equations decouple in a way that is similar to but
a generalization of those of the Regge--Wheeler spherically symmetric case. We
further achieve a decoupling of each set of perturbation equations into
gauge-dependent and independent parts, by which we obtain wave equations for
the gauge-invariant variables. We then discuss choices of gauge and stability
properties. Details of the compactification of Bianchi III manifolds and
spacetimes are presented in an appendix. In the other appendices we study
scalar field and electromagnetic equations on the same background to compare
asymptotic properties.Comment: 61 pages, 1 figure, final version with minor corrections, to appear
in Class. Quant. Gravi
Emissivity measurements of reflective surfaces at near-millimeter wavelengths
We have developed an instrument for directly measuring the emissivity of reflective surfaces at near-millimeter wavelengths. The thermal emission of a test sample is compared with that of a reference surface, allowing the emissivity of the sample to be determined without heating. The emissivity of the reference surface is determined by one’s heating the reference surface and measuring the increase in emission. The instrument has an absolute accuracy of Δe = 5 x 10^-4 and can reproducibly measure a difference in emissivity as small as Δe = 10^-4 between flat reflective samples. We have used the instrument to measure the emissivity of metal films evaporated on glass and carbon fiber-reinforced plastic composite surfaces. We measure an emissivity of (2.15 ± 0.4) x 10^-3 for gold evaporated on glass and (2.65 ± 0.5) x 10^-3 for aluminum evaporated on carbon fiber-reinforced plastic composite
Replica symmetry breaking transition of the weakly anisotropic Heisenberg spin glass in magnetic fields
The spin and the chirality orderings of the three-dimensional Heisenberg spin
glass with the weak random anisotropy are studied under applied magnetic fields
by equilibrium Monte Carlo simulations. A replica symmetry breaking transition
occurs in the chiral sector accompanied by the simultaneous spin-glass order.
The ordering behavior differs significantly from that of the Ising SG, despite
the similarity in the global symmetry. Our observation is consistent with the
spin-chirality decoupling-recoupling scenario of a spin-glass transition.Comment: 4 pages, 4 figure
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