4,463 research outputs found
Control of tetrahedral coordination and superconductivity in FeSe0.5Te0.5 thin films
We demonstrate a close relationship between superconductivity and the
dimensions of the Fe-Se(Te) tetrahedron in FeSe0.5Te0.5. This is done by
exploiting thin film epitaxy, which provides controlled biaxial stress, both
compressive and tensile, to distort the tetrahedron. The Se/Te height within
the tetrahedron is found to be of crucial importance to superconductivity, in
agreement with the theoretical proposal that (pi,pi) spin fluctuations promote
superconductivity in Fe superconductors
Accuracy of Electronic Wave Functions in Quantum Monte Carlo: the Effect of High-Order Correlations
Compact and accurate wave functions can be constructed by quantum Monte Carlo
methods. Typically, these wave functions consist of a sum of a small number of
Slater determinants multiplied by a Jastrow factor. In this paper we study the
importance of including high-order, nucleus-three-electron correlations in the
Jastrow factor. An efficient algorithm based on the theory of invariants is
used to compute the high-body correlations. We observe significant improvements
in the variational Monte Carlo energy and in the fluctuations of the local
energies but not in the fixed-node diffusion Monte Carlo energies. Improvements
for the ground states of physical, fermionic atoms are found to be smaller than
those for the ground states of fictitious, bosonic atoms, indicating that
errors in the nodal surfaces of the fermionic wave functions are a limiting
factor.Comment: 9 pages, no figures, Late
Antisymmetric magnetoresistance in magnetic multilayers with perpendicular anisotropy
While magnetoresistance (MR) has generally been found to be symmetric in
applied field in non-magnetic or magnetic metals, we have observed
antisymmetric MR in Co/Pt multilayers. Simultaneous domain imaging and
transport measurements show that the antisymmetric MR is due to the appearance
of domain walls that run perpendicular to both the magnetization and the
current, a geometry existing only in materials with perpendicular magnetic
anisotropy. As a result, the extraordinary Hall effect (EHE) gives rise to
circulating currents in the vicinity of the domain walls that contributes to
the MR. The antisymmetric MR and EHE have been quantitatively accounted for by
a theoretical model.Comment: 17 pages, 4 figure
Translational Invariance and the Anisotropy of the Cosmic Microwave Background
Primordial quantum fluctuations produced by inflation are conventionally
assumed to be statistically homogeneous, a consequence of translational
invariance. In this paper we quantify the potentially observable effects of a
small violation of translational invariance during inflation, as characterized
by the presence of a preferred point, line, or plane. We explore the imprint
such a violation would leave on the cosmic microwave background anisotropy, and
provide explicit formulas for the expected amplitudes of
the spherical-harmonic coefficients.Comment: Notation improve
The Fourier signatures of memristive hysteresis
While resistors with memory, sometimes called memristive elements (such as
ReRAM cells), are often studied under conditions of periodic driving, little
attention has been paid to the Fourier features of their memory response
(hysteresis). Here we demonstrate experimentally that the hysteresis of
memristive systems can be unambiguously distinguished from the linear or
non-linear response of systems without hysteresis by the values of certain
Fourier series coefficients. We also show that the Fourier series convergence
depends on driving conditions, and introduce a measure of hysteresis. These
results may be used to quantify the memory content of resistive memories, and
tune their Fourier spectrum according to the excitation signal
The Kolmogorov-Smirnov test and its use for the identification of fireball fragmentation
We propose an application of the Kolmogorov-Smirnov test for rapidity
distributions of individual events in ultrarelativistic heavy ion collisions.
The test is particularly suitable to recognise non-statistical differences
between the events. Thus when applied to a narrow centrality class it could
indicate differences between events which would not be expected if all events
evolve according to the same scenario. In particular, as an example we assume
here a possible fragmentation of the fireball into smaller pieces at the
quark/hadron phase transition. Quantitative studies are performed with a Monte
Carlo model capable of simulating such a distribution of hadrons. We conclude
that the Kolmogorov-Smirnov test is a very powerful tool for the identification
of the fragmentation process.Comment: 9 pages, 10 figure
Passenger transmission and productiveness of transit lines with high loads
Deterministic transit capacity analysis applies to planning, design and operational management of urban transit systems. The Transit Capacity and Quality of Service Manual (1) and Vuchic (2, 3) enable transit performance to be quantified and assessed using transit capacity and productive capacity. This paper further defines important productive performance measures of an individual transit service and transit line. Transit work (p-km) captures the transit task performed over distance. Passenger transmission (p-km/h) captures the passenger task delivered by service at speed. Transit productiveness (p-km/h) captures transit work performed over time. These measures are useful to operators in understanding their services’ or systems’ capabilities and passenger quality of service. This paper accounts for variability in utilized demand by passengers along a line and high passenger load conditions where passenger pass-up delay occurs. A hypothetical case study of an individual bus service’s operation demonstrates the usefulness of passenger transmission in comparing existing and growth scenarios. A hypothetical case study of a bus line’s operation during a peak hour window demonstrates the theory’s usefulness in examining the contribution of individual services to line productive performance. Scenarios may be assessed using this theory to benchmark or compare lines and segments, conditions, or consider improvements
Augmenting Bragg Reflection with Polymer-sustained Conical Helix
There has been a recent surge of interest in smart materials and devices with stimuli-responsive properties for optical modulations. Cholesteric liquid crystals (CLCs) are a unique class of light-manipulating materials, and strongly interact with light and other electromagnetic (EM) waves. Because of their intricate helical structure, new properties of CLC have emerged revealing unique optical behavior that has resulted in rewriting Braggs’ law for how light interacts with soft materials. The aim of this work is to push the limits of spectral tuning with a new method of augmenting light-cholesteric interactions using a polymer-sustained conical helix (PSCH) structure. We experimentally explore the reversibility of reflective wavelength modulation and validate the mechanism enhanced by a polymer-sustained helicoidal structure via theoretical analyses. The conical helix structure of a CLC, formed by low-field-induced oblique orientation of cholesteric helices, is comprised of a chiral dopant, a conventional nematic, and bimesogenic and trimesogenic nematics. Polymerizing a small amount of a reactive mesogen in the CLC with an applied electric field produces a templated helical polymer network that enables three switched optical states, including light-scattering and transparent states as well as color reflection in response to an applied increasing or decreasing electric field. An electro-activated PSCH optical film covers a wide color space, which is appropriate for tunable color device applications. We envisage that this PSCH material will lead to new avenues for controlling EM waves in imaging and thermal control, smart windows and electronic papers
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