31,943 research outputs found
The viscoplasticity theory based on overstress applied to the modeling of a nickel base superalloy at 815 C
Short term strain rate change, creep and relaxation tests were performed in an MTS computer controlled servohydraulic testing machine. Aging and recovery were found to be insignificant for test times not exceeding 30 hrs. The material functions and constants of the theory were identified from results of strain rate change tests. Numerical integration of the theory for relaxation and creep tests showed good predictive capabilities of the viscoplasticity theory based on overstress
Halo-to-Halo Similarity and Scatter in the Velocity Distribution of Dark Matter
We examine the Velocity Distribution Function (VDF) in dark matter halos from
Milky Way to cluster mass scales. We identify an empirical model for the VDF
with a wider peak and a steeper tail than a Maxwell--Boltzmann distribution,
and discuss physical explanations. We quantify sources of scatter in the VDF of
cosmological halos and their implication for direct detection of dark matter.
Given modern simulations and observations, we find that the most significant
uncertainty in the VDF of the Milky Way arises from the unknown radial position
of the solar system relative to the dark matter halo scale radius.Comment: Accepted to ApJ. Figure 3 and 5 and Section 4 newly added. 6 pages, 6
figures, typeset using emulateap
The glass transition and crystallization kinetic studies on BaNaB9O15 glasses
Transparent glasses of BaNaB9O15 (BNBO) were fabricated via the conventional
melt-quenching technique. The amorphous and the glassy nature of the
as-quenched samples were respectively, confirmed by X-ray powder diffraction
(XRD) and differential scanning calorimetry (DSC). The glass transition and
crystallization parameters were evaluated under non-isothermal conditions using
DSC. The correlation between the heating rate dependent glass transition and
the crystallization temperatures was discussed and deduced the Kauzmann
temperature for BNBO glass-plates and powdered samples. The values of the
Kauzmann temperature for the plates and powdered samples were 776 K and 768 K,
respectively. Approximation-free method was used to evaluate the
crystallization kinetic parameters for the BNBO glass samples. The effect of
the sample thickness on the crystallization kinetics of BNBO glasses was also
investigated.Comment: 23 pages, 12 figure
Thermal Diffusivities of Functionalized Pentacene Semiconductors
We have measured the interlayer and in-plane (needle axis) thermal
diffusivities of 6,13-bis(triisopropylsilylethynyl) pentacene (TIPS-Pn). The
needle axis value is comparable to the phonon thermal conductivities of
quasi-one dimensional organic metals with excellent pi-orbital overlap, and its
value suggests that a significant fraction of heat is carried by optical
phonons. Furthermore, the interlayer (c-axis) thermal diffusivity is at least
an order of magnitude larger, and this unusual anisotropy implies very strong
dispersion of optical modes in the interlayer direction, presumably due to
interactions between the silyl-containing side groups. Similar values for both
in-plane and interlayer diffusivities have been observed for several other
functionalized pentacene semiconductors with related structures.Comment: 9 pages, including 4 figures; submitted to Applied Physics Letter
Theoretical Evidence for the Berry-Phase Mechanism of Anomalous Hall Transport: First-principles Studies on CuCrSeBr
To justify the origin of anomalous Hall effect (AHE), it is highly desirable
to have the system parameters tuned continuously. By quantitative calculations,
we show that the doping dependent sign reversal in
CuCrSeBr, observed but not understood, is nothing but
direct evidence for the Berry-Phase mechanism of AHE. The systematic
calculations well explain the experiment data for the whole doping range where
the impurity scattering rates is changed by several orders with Br
substitution. Further sign change is also predicted, which may be tested by
future experiments.Comment: 4 page
Phase equilibrium in two orbital model under magnetic field
The phase equilibrium in manganites under magnetic field is studied using a
two orbital model, based on the equivalent chemical potential principle for the
competitive phases. We focus on the magnetic field induced melting process of
CE phase in half-doped manganites. It is predicted that the homogenous CE phase
begins to decompose into coexisting ferromagnetic phase and CE phase once the
magnetic field exceeds the threshold field. In a more quantitative way, the
volume fractions of the two competitive phases in the phase separation regime
are evaluated.Comment: 4 pages, 4 figure
Yield strength measurement of ferromagnetic materials based on the inverse magnetostrictive effect
Ferromagnetic materials are widely used in industry and risking the hazards of aging and degradation of their mechanical properties. This paper proposed a non-destructive method for the measurement of the yield strength of ferromagnetic materials imprinted by the materials’ microstructure as the microstructure influences the pattern of the inverse magnetostrictive effect of ferromagnetic materials. For experimental verification, yield strengths of ferromagnetic specimens were measured on an electromagnetic ultrasonic transducer (EMAT) detection system. The relationship between electromagnetic acoustic transducer signals and the static magnetic field strength was obtained, from which we extracted the pattern parameters related to the yield strength. The regression model of the pattern parameters versus the yield strength was established and then verified with trial on a specimen processed in the same batch with a maximum prediction accuracy of 12.78%
Pion-nucleon scattering in covariant baryon chiral perturbation theory with explicit Delta resonances
We present the results of a third order calculation of the pion-nucleon
scattering amplitude in a chiral effective field theory with pions, nucleons
and delta resonances as explicit degrees of freedom. We work in a manifestly
Lorentz invariant formulation of baryon chiral perturbation theory using
dimensional regularization and the extended on-mass-shell renormalization
scheme. In the delta resonance sector, the on mass-shell renormalization is
realized as a complex-mass scheme. By fitting the low-energy constants of the
effective Lagrangian to the - and -partial waves a satisfactory
description of the phase shifts from the analysis of the Roy-Steiner equations
is obtained. We predict the phase shifts for the and waves and compare
them with the results of the analysis of the George Washington University
group. The threshold parameters are calculated both in the delta-less and
delta-full cases. Based on the determined low-energy constants, we discuss the
pion-nucleon sigma term. Additionally, in order to determine the strangeness
content of the nucleon, we calculate the octet baryon masses in the presence of
decuplet resonances up to next-to-next-to-leading order in SU(3) baryon chiral
perturbation theory. The octet baryon sigma terms are predicted as a byproduct
of this calculation.Comment: 41 pages, 12 figures, 7 table
Benchmark generator for CEC 2009 competition on dynamic optimization
Evolutionary algorithms(EAs) have been widely applied to solve stationary optimization problems. However, many real-world applications are actually dynamic. In order to study the performance of EAs in dynamic environments, one important task is to develop proper dynamic benchmark problems. Over the years, researchers have applied a number of dynamic test problems to compare the performance of EAs in dynamic environments, e.g., the “moving peaks ” benchmark (MPB) proposed by Branke [1], the DF1 generator introduced by Morrison and De Jong [6], the singleand multi-objective dynamic test problem generator by dynamically combining different objective functions of exiting stationary multi-objective benchmark problems suggested by Jin and Sendhoff [2], Yang and Yao’s exclusive-or (XOR) operator [10, 11, 12], Kang’s dynamic traveling salesman problem (DTSP) [3] and dynamic multi knapsack problem (DKP), etc. Though a number of DOP generators exist in the literature, there is no unified approach of constructing dynamic problems across the binary space, real space and combinatorial space so far. This report uses the generalized dynamic benchmark generator (GDBG) proposed in [4], which construct dynamic environments for all the three solution spaces. Especially, in the rea
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