5,505 research outputs found
Low-energy vibrational density of states of plasticized poly(methyl methacrylate)
The low-energy vibrational density of states (VDOS)of hydrogenated or
deuterated poly(methyl methacrylate)(PMMA)plasticized by dibutyl phtalate (DBP)
is determined by inelastic neutron scattering.From experiment, it is equal to
the sum of the ones of the PMMA and DBP components.However, a partition of the
total low-energy VDOS among PMMA and DBP was observed.Contrary to Raman
scattering, neutron scattering does not show enhancement of the boson peak due
to plasticization.Comment: 9 pages, 2 figures (Workshop on Disordered Systems, Andalo
Filling the holes: Evolving excised binary black hole initial data with puncture techniques
We follow the inspiral and merger of equal-mass black holes (BHs) by the
moving puncture technique and demonstrate that both the exterior solution and
the asymptotic gravitational waveforms are unchanged when the initial interior
solution is replaced by constraint-violating ``junk'' initial data. We apply
this result to evolve conformal thin-sandwich (CTS) binary BH initial data by
filling their excised interiors with arbitrary, but smooth, initial data and
evolving with standard puncture gauge choices. The waveforms generated for both
puncture and filled-CTS initial data are remarkably similar, and there are only
minor differences between irrotational and corotational CTS BH binaries. Even
the interior solutions appear to evolve to the same constraint-satisfying
solution at late times, independent of the initial data.Comment: 5 pages, 5 figures, accepted by PRD Rapid Communications, RevTe
Effect of physical aging on the low-frequency vibrational density of states of a glassy polymer
The effects of the physical aging on the vibrational density of states (VDOS)
of a polymeric glass is studied. The VDOS of a poly(methyl methacrylate) glass
at low-energy (<15 meV), was determined from inelastic neutron scattering at
low-temperature for two different physical thermodynamical states. One sample
was annealed during a long time at temperature lower than Tg, and another was
quenched from a temperature higher than Tg. It was found that the VDOS around
the boson peak, relatively to the one at higher energy, decreases with the
annealing at lower temperature than Tg, i.e., with the physical aging.Comment: To be published in Europhys. Let
High order vibration modes of glass embedded AgAu nanoparticles
High resolution low frequency Raman scattering measurements from embedded
AgAu nanoparticles unveil efficient scattering by harmonics of both the
quadrupolar and the spherical modes. Comparing the experimental data with
theoretical calculations that account for both the embedding medium and the
resonant Raman process enables a very complete description of the observed
multiple components in terms of harmonics of both the quadrupolar and spherical
modes, with a dominating Raman response from the former ones. It is found that
only selected harmonics of the quadrupolar mode contribute significantly to the
Raman spectra in agreement with earlier theoretical predictions.Comment: 11 pages, 4 figure
Importance of cooling in triggering the collapse of hypermassive neutron stars
The inspiral and merger of a binary neutron star (NSNS) can lead to the
formation of a hypermassive neutron star (HMNS). As the HMNS loses thermal
pressure due to neutrino cooling and/or centrifugal support due to
gravitational wave (GW) emission, and/or magnetic breaking of differential
rotation it will collapse to a black hole. To assess the importance of
shock-induced thermal pressure and cooling, we adopt an idealized equation of
state and perform NSNS simulations in full GR through late inspiral, merger,
and HMNS formation, accounting for cooling. We show that thermal pressure
contributes significantly to the support of the HMNS against collapse and that
thermal cooling accelerates its "delayed" collapse. Our simulations demonstrate
explicitly that cooling can induce the catastrophic collapse of a hot
hypermassive neutron star formed following the merger of binary neutron stars.
Thus, cooling physics is important to include in NSNS merger calculations to
accurately determine the lifetime of the HMNS remnant and to extract
information about the NS equation of state, cooling mechanisms, bar
instabilities and B-fields from the GWs emitted during the transient phase
prior to BH formation.Comment: 13 pages, 7 figures, matches published versio
Light Element Abundance Patterns in the Orion Association: I) HST Observations of Boron in G-dwarfs
The boron abundances for two young solar-type members of the Orion
association, BD -6 1250 and HD 294297, are derived from HST STIS spectra of the
B I transition at 2496.771 A. The best-fit boron abundances for the target
stars are 0.13 and 0.44 dex lower than the solar meteoritic value of log
e(B)=2.78. An anticorrelation of boron and oxygen is found for Orion when these
results are added to previous abundances obtained for 4 B-type stars and the
G-type star BD -5 1317. An analysis of the uncertainties in the abundance
calculations indicates that the observed anticorrelation is probably real. The
B versus O relation observed in the Orion association does not follow the
positive correlation of boron versus oxygen which is observed for the field
stars with roughly solar metallicity. The observed anticorrelation can be
accounted for by a simple model in which two poorly mixed components of gas
(supernova ejecta and boron-enriched ambient medium) contribute to the new
stars that form within the lifetime of the association. This model predicts an
anticorrelation for Be as well, at least as strong as for boron.Comment: 16 pages + 1 table + 7 figures, accepted for publication in Ap
Volatility Spillover and Time-Varying Conditional Correlation Between DDGS, Corn, and Soybean Meal Markets
We find distiller\u27s dried grains with solubles (DDGS) prices to be positively correlated with both corn and soybean meal prices in the long run. However, neither corn nor soybean meal prices respond to deviations from this long-run relationship. We also identify strong time-varying dynamic conditional correlations between the markets, with the correlation between DDGS and corn strengthened after the expansion of ethanol production. There also appear to exist significant volatility spillovers from both the corn and soybean meal markets to the DDGS market, with the impact from corn shocks much larger compared to soybean meal shocks
Heat Transport in a Strongly Overdoped Cuprate: Fermi Liquid and Pure d-wave BCS Superconductor
The transport of heat and charge in the overdoped cuprate superconductor
Tl_2Ba_2CuO_(6+delta) was measured down to low temperature. In the normal
state, obtained by applying a magnetic field greater than the upper critical
field, the Wiedemann-Franz law is verified to hold perfectly. In the
superconducting state, a large residual linear term is observed in the thermal
conductivity, in quantitative agreement with BCS theory for a d-wave
superconductor. This is compelling evidence that the electrons in overdoped
cuprates form a Fermi liquid, with no indication of spin-charge separation.Comment: 4 pages, 2 figures, published version, title changed, Phys. Rev.
Lett. 89, 147003 (2002
Hamiltonian of a spinning test-particle in curved spacetime
Using a Legendre transformation, we compute the unconstrained Hamiltonian of
a spinning test-particle in a curved spacetime at linear order in the particle
spin. The equations of motion of this unconstrained Hamiltonian coincide with
the Mathisson-Papapetrou-Pirani equations. We then use the formalism of Dirac
brackets to derive the constrained Hamiltonian and the corresponding
phase-space algebra in the Newton-Wigner spin supplementary condition (SSC),
suitably generalized to curved spacetime, and find that the phase-space algebra
(q,p,S) is canonical at linear order in the particle spin. We provide explicit
expressions for this Hamiltonian in a spherically symmetric spacetime, both in
isotropic and spherical coordinates, and in the Kerr spacetime in
Boyer-Lindquist coordinates. Furthermore, we find that our Hamiltonian, when
expanded in Post-Newtonian (PN) orders, agrees with the Arnowitt-Deser-Misner
(ADM) canonical Hamiltonian computed in PN theory in the test-particle limit.
Notably, we recover the known spin-orbit couplings through 2.5PN order and the
spin-spin couplings of type S_Kerr S (and S_Kerr^2) through 3PN order, S_Kerr
being the spin of the Kerr spacetime. Our method allows one to compute the PN
Hamiltonian at any order, in the test-particle limit and at linear order in the
particle spin. As an application we compute it at 3.5PN order.Comment: Corrected typo in the ADM Hamiltonian at 3.5 PN order (eq. 6.20
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