10,145 research outputs found
Field-induced domain interpenetration in tetragonal ferroelectric crystal
Ferroelectric domain structures of a 〈001〉-oriented lead magnesium niobate–lead titanate tetragonal crystal were examined under cyclic bipolar electric fields. Complex patterns of orthogonal domain strips were found to emerge from a simple structure of parallel strips of 90°domains. Near the boundary between the two orthogonal sets of the domain strips, domains were forced to intersect, creating charged domain walls at the intersections. With continued electric cycling, direct impingement of individual domains resulted in domain interpenetration and fine domain cells in the boundary region. Away from the boundary region, initial domain walls were withdrawn and replaced by the walls along a different orientation, resulting in separate areas that each contained a single set of parallel strips of domains. A model based on 180° domain switching is suggested to explain interpenetration of the domains and the withdrawal of the original domain walls
The reinforcing influence of recommendations on global diversification
Recommender systems are promising ways to filter the overabundant information
in modern society. Their algorithms help individuals to explore decent items,
but it is unclear how they allocate popularity among items. In this paper, we
simulate successive recommendations and measure their influence on the
dispersion of item popularity by Gini coefficient. Our result indicates that
local diffusion and collaborative filtering reinforce the popularity of hot
items, widening the popularity dispersion. On the other hand, the heat
conduction algorithm increases the popularity of the niche items and generates
smaller dispersion of item popularity. Simulations are compared to mean-field
predictions. Our results suggest that recommender systems have reinforcing
influence on global diversification.Comment: 6 pages, 6 figure
Forensic Excavation of Rock Masses: A Technique to Investigate Discontinuity Persistence
True persistence of rock discontinuities (areas with insignificant tensile strength) is an important factor controlling the engineering behaviour of fractured rock masses, but is extremely difficult to quantify using current geological survey methodologies, even where there is good rock exposure. Trace length as measured in the field or using remote measurement devices is actually only broadly indicative of persistence for rock engineering practice and numerical modelling. Visible traces of discontinuities are treated as if they were open fractures within rock mass classifications, despite many such traces being non-persistent and actually retaining considerable strength. The common assumption of 100% persistence, based on trace length, is generally extremely conservative in terms of strength and stiffness, but not always so and may lead to a wrong prediction of failure mechanism or of excavatability. Assuming full persistence would give hopelessly incorrect predictions of hydraulic conductivity. A new technique termed forensic excavation of rock masses is introduced, as a procedure for directly investigating discontinuity persistence. This technique involves non-explosive excavation of rock masses by injecting an expansive chemical splitter along incipient discontinuities. On expansion, the splitter causes the incipient traces to open as true joints. Experiments are described in which near-planar rock discontinuities, through siltstone and sandstone, were opened up by injecting the splitter into holes drilled along the lines of visible traces of the discontinuities in the laboratory and in the field. Once exposed the surfaces were examined to investigate the pre-existing persistence characteristics of the incipient discontinuities. One conclusion from this study is that visible trace length of a discontinuity can be a poor indicator of true persistence (defined for a fracture area with negligible tensile strength). An observation from this series of experiments was that freshly failed surfaces through pre-existing rock bridges were relatively rough compared to sections of pre-existing weaker areas of geologically developed (though still incipient) discontinuities. Fractographic features such as hackle and rib marks were typical of the freshly broken rock bridges, whereas opened-up areas of incipient discontinuity were smoother. Schmidt hammer rebound values were generally higher for the rock bridge areas, probably reflecting their lower degree of chemical and physical weathering
Performance of a characteristic-based, 3-D, time-domain Maxwell equations solver on a massively parallel computer
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/77035/1/AIAA-1993-3179-911.pd
Dependence of quantum correlations of twin beams on pump finesse of optical parametric oscillator
The dependence of quantum correlation of twin beams on the pump finesse of an
optical parametric oscillator is studied with a semi-classical analysis. It is
found that the phase-sum correlation of the output signal and idler beams from
an optical parametric oscillator operating above threshold depends on the
finesse of the pump field when the spurious pump phase noise generated inside
the optical cavity and the excess noise of the input pump field are involved in
the Langevin equations. The theoretical calculations can explain the previously
experimental results, quantitatively.Comment: 27 pages, 8 figure
The search for black hole binaries using a genetic algorithm
In this work we use genetic algorithm to search for the gravitational wave
signal from the inspiralling massive Black Hole binaries in the simulated LISA
data. We consider a single signal in the Gaussian instrumental noise. This is a
first step in preparation for analysis of the third round of the mock LISA data
challenge. We have extended a genetic algorithm utilizing the properties of the
signal and the detector response function. The performance of this method is
comparable, if not better, to already existing algorithms.Comment: 11 pages, 4 figures, proceeding for GWDAW13 (Puerto Rico
Nodeless superconductivity in the cage-type superconductor Sc5Ru6Sn18 with preserved time-reversal symmetry
We report the single-crystal synthesis and detailed investigations of the
cage-type superconductor Sc5Ru6Sn18, using powder x-ray diffraction (XRD),
magnetization, specific-heat and muon-spin relaxation (muSR) measurements.
Sc5Ru6Sn18 crystallizes in a tetragonal structure (space group I41/acd) with
the lattice parameters a = 1.387(3) nm and c = 2.641(5) nm. Both DC and AC
magnetization measurements prove the type-II superconductivity in Sc5Ru6Sn18
with Tc = 3.5(1) K, a lower critical field H_c1 (0) = 157(9) Oe and an upper
critical field, H_c2 (0) = 26(1) kOe. The zero-field electronic specific-heat
data are well fitted using a single-gap BCS model, with superconducting gap =
0.64(1) meV. The Sommerfeld constant varies linearly with the applied magnetic
field, indicating s-wave superconductivity in Sc5Ru6Sn18. Specific-heat and
transverse-field (TF) muSR measurements reveal that Sc5Ru6Sn18 is a
superconductor with strong electron-phonon coupling, with TF-muSR also
suggesting the single-gap s-wave character of the superconductivity.
Furthermore, zero-field muSR measurements do not detect spontaneous magnetic
fields below Tc, hence implying that time-reversal symmetry is preserved in
Sc5Ru6Sn18.Comment: 23 pages, 11 figure
Lattice chirality and the decoupling of mirror fermions
We show, using exact lattice chirality, that partition functions of lattice
gauge theories with vectorlike fermion representations can be split into
"light" and "mirror" parts, such that the "light" and "mirror" representations
are chiral. The splitting of the full partition function into "light" and
"mirror" is well defined only if the two sectors are separately anomaly free.
We show that only then is the generating functional, and hence the spectrum, of
the mirror theory a smooth function of the gauge field background. This
explains how ideas to use additional non-gauge, high-scale mirror-sector
dynamics to decouple the mirror fermions without breaking the gauge
symmetry--for example, in symmetric phases at strong mirror Yukawa
coupling--are forced to respect the anomaly-free condition when combined with
the exact lattice chiral symmetry. Our results also explain a paradox posed by
a recent numerical study of the mirror-fermion spectrum in a toy
would-be-anomalous two-dimensional theory. In passing, we prove some general
properties of the partition functions of arbitrary chiral theories on the
lattice that should be of interest for further studies in this field.Comment: 29 pages, 2 figures; published version, new addendu
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