4,434 research outputs found
Kerr effect as a tool for the investigation of dynamic heterogeneities
We propose a dynamic Kerr effect experiment for the distinction between
dynamic heterogeneous and homogeneous relaxation in glassy systems. The
possibility of this distinction is due to the inherent nonlinearity of the Kerr
effect signal. We model the slow reorientational molecular motion in
supercooled liquids in terms of non-inertial rotational diffusion. The Kerr
effect response, consisting of two terms, is calculated for heterogeneous and
for homogeneous variants of the stochastic model. It turns out that the
experiment is able to distinguish between the two scenarios. We furthermore
show that exchange between relatively 'slow' and 'fast' environments does not
affect the possibility of frequency-selective modifications. It is demonstrated
how information about changes in the width of the relaxation time distribution
can be obtained from experimental results.Comment: 23 pages incl. 6 figures accepted for publication in The Journal of
Chemical Physic
Correlation potentials for molecular bond dissociation within the self-consistent random phase approximation
Self-consistent correlation potentials for H and LiH for various
inter-atomic separations are obtained within the random phase approximation
(RPA) of density functional theory. The RPA correlation potential shows a peak
at the bond midpoint, which is an exact feature of the true correlation
potential, but lacks another exact feature: the step important to preserve
integer charge on the atomic fragments in the dissociation limit. An analysis
of the RPA energy functional in terms of fractional charge is given which
confirms these observations. We find that the RPA misses the derivative
discontinuity at odd integer particle numbers but explicitly eliminates the
fractional spin error in the exact-exchange functional. The latter finding
explains the accurate total energy in the dissociation limit.Comment: 9 pages, 10 figure
Women Authors in Medicine: A Gender Based Study on Authorship Opportunities and its Implications in Promotions in Medicine
Obtaining first authorship in research and published papers is widely held as grounds for promotions and advancements in the medical field. However, the opportunities to be involved in research and to have the primary authorship position are not equally divided amongst specialties, including primary care. Women physicians are becoming a greater percentage of the workforce in primary care, including Internal Medicine and the potential lack of opportunity for authorship may disproportionately affect their promotion. This poster presents the preliminary research on an investigation into the Indiana University School of Medicineâs Department of Medicine gender authorship profiles in the last five years. By utilizing the search engine scopus, a database of the papers written by physicians was created, and gender identifications of the first, second, and last author was made to find correlations between gender and authorship positions. These results will be used to make a case for reexamining the qualifications for promotions, and ensuring that genders have equal opportunity for job advancement and leadership in the medical field.https://jdc.jefferson.edu/sexandgenderhealth/1014/thumbnail.jp
Exchange-correlation orbital functionals in current-density-functional theory: Application to a quantum dot in magnetic fields
The description of interacting many-electron systems in external magnetic
fields is considered in the framework of the optimized effective potential
method extended to current-spin-density functional theory. As a case study, a
two-dimensional quantum dot in external magnetic fields is investigated.
Excellent agreement with quantum Monte Carlo results is obtained when
self-interaction corrected correlation energies from the standard local
spin-density approximation are added to exact-exchange results. Full
self-consistency within the complete current-spin-density-functional framework
is found to be of minor importance.Comment: 5 pages, 2 figures, submitted to PR
Probing the pairing symmetry in the over-doped Fe-based superconductor Ba_0.35Rb_0.65Fe_2As_2 as a function of hydrostatic pressure
We report muon spin rotation experiments on the magnetic penetration depth
lambda and the temperature dependence of lambda^{-2} in the over-doped Fe-based
high-temperature superconductor (Fe-HTS) Ba_{1-x}Rb_ xFe_2As_2 (x = 0.65)
studied at ambient and under hydrostatic pressures up to p = 2.3 GPa. We find
that in this system lambda^{-2}(T) is best described by d-wave scenario. This
is in contrast to the case of the optimally doped x = 0.35 system which is
known to be a nodeless s^{+-}-wave superconductor. This suggests that the
doping induces the change of the pairing symmetry from s^{+-} to d-wave in
Ba_{1-x}Rb_{x}Fe_{2}As_{2}. In addition, we find that the d-wave order
parameter is robust against pressure, suggesting that d is the common and
dominant pairing symmetry in over-doped Ba_{1-x}Rb_{x}Fe_{2}As_{2}. Application
of pressure of p = 2.3 GPa causes a decrease of lambda(0) by less than 5 %,
while at optimal doping x = 0.35 a significant decrease of lambda(0) was
reported. The superconducting transition temperature T_c as well as the gap to
T_c ratio 2Delta/k_BT_c show only a modest decrease with pressure. By combining
the present data with those previously obtained for optimally doped system x =
0.35 and for the end member x = 1 we conclude that the SC gap symmetry as well
as the pressure effects on the SC quantities strongly depend on the Rb doping
level. These results are discussed in the light of the putative Lifshitz
transition, i.e., a disappearance of the electron pockets in the Fermi surface
of Ba_{1-x}Rb_{x}Fe_{2}As_{2} upon hole doping.Comment: Accepted for publication in Physical Review
Focused Fluid Flow along the Nootka Fault Zone and Continental slope, ExplorerâJuan de Fuca Plate Boundary
Key Points:
- Fluid flow is focused along Nootka Fault traces resulting in shallow bright spots
- Two seafloor mounds are the result of basaltic intrusions in the Nootka Fault zone
- Gas hydrates occur at the Nootka Slope and are imaged seismically as bottom-
simulating reflectors suggesting a regional heat-flow of ~80 mW/m2 along the slope
Abstract
Geophysical and geochemical data indicate there is abundant fluid expulsion in the Nootka fault zone (NFZ) between the Juan de Fuca and Explorer plates and the Nootka continental slope. Here we combine observations from > 20 years of investigations to demonstrate the nature of fluidâflow along the NFZ, which is the seismically most active region off Vancouver Island. Seismicity reaching down to the upper mantle is linked to nearâseafloor manifestation of fluid flow through a network of faults. Along the two main fault traces, seismic reflection data imaged bright spots 100 â 300 m below seafloor that lie above changes in basement topography. The bright spots are conformable to sediment layering, show oppositeâtoâseafloor reflection polarity, and are associated with frequencyâreduction and velocity pushâdown indicating the presence of gas in the sediments. Two seafloor mounds ~15 km seaward of the Nootka slope are underlain by deep, nonâconformable high amplitude reflective zones. Measurements in the water column above one mound revealed a plume of warm water, and bottomâvideo observations imaged hydrothermal vent system biota. Pore fluids from a core at this mound contain predominately microbial methane (C1) with a high proportion of ethane (C2) yielding C1/C2 ratios < 500 indicating a possible slight contribution from a deep source. We infer the reflective zones beneath the two mounds are basaltic intrusions that create hydrothermal circulation within the overlying sediments. Across the Nootka continental slope, gas hydrate related bottomâsimulating reflectors are widespread and occur at depths indicating heatâflow values of 80 â 90 mW/m2
Evidence for strong lattice effects as revealed from huge unconventional oxygen isotope effects on the pseudogap temperature in LaSrCuO
The oxygen isotope (O/O) effect (OIE) on the pseudogap
(charge-stripe ordering) temperature is investigated for the cuprate
superconductor LaSrCuO as a function of doping by means
of x-ray absorption near edge structure (XANES) studies. A strong dependent
and sign reversed OIE on is observed. The OIE exponent
systematically decreases from for to for ,
corresponding to increasing and decreasing superconducting
transition temperature . Both and
exhibit a linear doping dependence with different
slopes and critical end points (where and
fall to zero) at and
, indicating a large positive OIE of
with an exponent of . The remarkably large and
strongly doping dependent OIE on signals a substantial involvement
of the lattice in the formation of the pseudogap, consistent with a polaronic
approach to cuprate superconductivity and the vibronic character of its ground
state
Ion and polymer dynamics in polymer electrolytes PPO-LiClO4: II. 2H and 7Li NMR stimulated-echo experiment
We use 2H NMR stimulated-echo spectroscopy to measure two-time correlation
functions characterizing the polymer segmental motion in polymer electrolytes
PPO-LiClO4 near the glass transition temperature Tg. To investigate effects of
the salt on the polymer dynamics, we compare results for different ether oxygen
to lithium ratios, namely, 6:1, 15:1, 30:1 and infinity. For all compositions,
we find nonexponential correlation functions, which can be described by a
Kohlrausch function. The mean correlation times show quantitatively that an
increase of the salt concentration results in a strong slowing down of the
segmental motion. Consistently, for the high 6:1 salt concentration, a high
apparent activation energy E_a=4.1eV characterizes the temperature dependence
of the mean correlation times at Tg < T< 1.1T_g, while smaller values E_a=2.5eV
are observed for moderate salt contents. The correlation functions are most
nonexponential for 15:1 PPO-LiClO4, whereas the stretching is reduced for
higher and lower salt concentrations. A similar dependence of the correlation
functions on the evolution time in the presence and in the absence of ions
indicates that addition of salt hardly affects the reorientational mechanism.
For all compositions, mean jump angles of about 15 degree characterize the
segmental reorientation. In addition, comparison of results from 2H and 7Li NMR
stimulated-echo experiments suggests a coupling of ion and polymer dynamics in
15:1 PPO-LiClO4.Comment: 14 pages, 12 figure
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