329 research outputs found

### Models for the description of uniaxially modulated materials

Models which allow an explicit application to structurally modulated
substances are reviewed within the frame of a symmetry-based approach starting
from discrete lattice theory. Focus is set on models formulated in terms of
local variables assigned to discrete crystallographic units (unit cells or
parts of them). Especially considered are symmetry-based pseudo spin models.
Methods are discussed which permit the handling of the statistical mechanics of
such models, the translation of model calculation results to a form allowing
the prediction of experimental data, and the theoretical determination of point
defect influences.Comment: 25 pages, 10 figures, RevTex, to be published in Ferroelectric

### Derivation of symmetry-based pseudo spin models for modulated materials

A general concept for the derivation of symmetry-based pseudo spin
Hamiltonians is described. It systematically bridges the gap between the
atomistic basis and various pseudo spin models presented in literature. It thus
allows the application of the multitude of analytical and numerical procedures
derived for the statistical mechanics treatment of the latter to the
description of structurally modulated crystals and furnishes a general frame
for reviewing these models from a common point of view.Comment: 4 pages, RevTe

### Transitions between Phases with Equal Wave Numbers in a Double Ising Spin Model. Application to Betaine Calcium Chloride Dihydrate

A Double Ising Spin model for uniaxially structurally modulated materials
exhibits as a special feature phase transitions between phases with equal wave
numbers but different pseudo spin configurations. The character of these
`internal' transitions is investigated in mean field approximation, with the
mean field transfer matrix method, and in Monte Carlo simulations. The
structural changes at the transitions are characterized by different strengths
of harmonics in a Fourier analysis of the spatial modulation. A dielectric
anomaly in the phase diagram of betaine calcium chloride dihydrate (BCCD) and
seemingly contradictory structure analyses are explained.Comment: 14 pages, 9 figures, submitted to J. Phys. Condens. Matte

### Object Detection in 3D Point Clouds via Local Correlation-Aware Point Embedding

We present an improved approach for 3D object detection in point clouds data based on the Frustum PointNet (F-PointNet). Compared to the original F-PointNet, our newly proposed method considers the point neighborhood when computing point features. The newly introduced local neighborhood embedding operation mimics the convolutional operations in 2D neural networks. Thus features of each point are not only computed with the features of its own or of the whole point cloud, but also computed especially with respect to the features of its neighbors. Experiments show that our proposed method achieves better performance than the F-Pointnet baseline on 3D object detection tasks

### An algorithm for the proportional division of indivisible items

An allocation of indivisible items among n ≥ 2 players is proportional if and only if each player receives a proportional subset—one that it thinks is worth at least 1/n of the total value of all the items. We show that a proportional allocation exists if and only if there is an allocation in which each player receives one of its minimal bundles, from which the subtraction of any item would make the bundle worth less than 1/n.
We give a practicable algorithm, based on players’ rankings of minimal bundles, that finds a proportional allocation if one exists; if not, it gives as many players as possible minimal bundles. The resulting allocation is maximin, but it may be neither envy-free nor Pareto-optimal. However, there always exists a Pareto-optimal maximin allocation which, when n = 2, is also envy-free. We compare our algorithm with two other 2-person algorithms, and we discuss its applicability to real-world disputes among two or more players

### On the Determination of $|V_{ub}|$ from Inclusive Semileptonic Decay Spectra

We propose a model independent method to determine $|V_{ub}|$ from the energy
spectrum of the charged lepton in inclusive semileptonic $B$ decays. The method
includes perturbative QCD corrections as well as nonperturbative ones.Comment: LaTeX, 19 pages, 8 figures appended after \end{document} as
uu-encoded and compressed .eps files, uses epsf, Technion-PH-94/9,
CERN-TH.7308/9

### Electrically Detected Magnetic Resonance on a Chip (EDMRoC) for Analysis of Thin-Film Silicon Photovoltaics

Electrically detected magnetic resonance (EDMR) is a spectroscopic technique that provides information about the physical properties of materials through the detection of variations in conductivity induced by spin-dependent processes. EDMR has been widely applied to investigate thin-film semiconductor materials in which the presence of defects can induce the current limiting processes. Conventional EDMR measurements are performed on samples with a special geometry that allows the use of a typical electron paramagnetic resonance (EPR) resonator. For such measurements, it is of utmost importance that the geometry of the sample under assessment does not influence the results of the experiment. Here, we present a single-board EPR spectrometer using a chip-integrated, voltage-controlled oscillator (VCO) array as a planar microwave source, whose geometry optimally matches that of a standard EDMR sample, and which greatly facilitates electrical interfacing to the device under assessment. The probehead combined an ultrasensitive transimpedance amplifier (TIA) with a twelve-coil array, VCO-based, single-board EPR spectrometer to permit EDMR-on-a-Chip (EDMRoC) investigations. EDMRoC measurements were performed at room temperature on a thin-film hydrogenated amorphous silicon (a-Si:H) pin solar cell under dark and forward bias conditions, and the recombination current driven by the a-Si:H dangling bonds (db) was detected. These experiments serve as a proof of concept for a new generation of small and versatile spectrometers that allow in situ and operando EDMR experiments

### Calculation of 1/m^3 terms in the total semileptonic width of D mesons.

We calculate the 1/$m^3_c$ corrections in the inclusive semileptonic widths
of $D$ mesons. We show that these are due to the novel penguin type operators
that appear at this level in the transition operator. Taking into account the
nonperturbative corrections leads to the predicted value of the semileptonic
width significantly lower than the experimental value. The $1/m^3_c$ worsen the
situation or at the very least, within uncertainty, give small contribution. We
indicate possible ways out. It seems most probable that violations of duality
are noticeable in the energy range characteristic to the inclusive decays in
the charm family. Theoretically these deviations are related to divergence of
the high-order terms in the power expansion in the inverse heavy quark mass.Comment: Final version accepted for publication in Physical Review D (19
pages, 5 figures appended as two PS files at the end of the LATEX file

### Report and preliminary results of SONNE cruise SO175, Miami - Bremerhaven, 12.11 - 30.12.2003 : (GAP, Gibraltar Arc Processes)

Expedition SO175 using FS Sonne aimed for a multidisciplinerary geoscientific approach with an international group of researchers. Methods covered the entire span from geophysical data acquisition (seafloor mapping, echography, seismic reflection), sediment coring at sites of active fluid venting, in situ heat flow measurements across the entire length of the Gibraltar thrust wedge, the deformation front, landslide bodies, and mud volcanoes, and finally the deployment of a long-term pore pressure probe. Video-supported operations helped to identify fluid vent sites, regions with tectonic activity, and other attractive high priority targets. Qualitative and quantitative examinations took place on board and are continued on land with respect to pore pressure variation, geomicrobiology, sediment- and fluid mobilization, geochemical processes, faunal assemblages (e.g. cold water corals), and gas hydrates (flammable methane-ice-crystals). Main focus of the expedition has been a better understanding of interaction between dynamic processes in a seismically active region region with slow plate convergence.
In the context of earthquake nucleation and subduction zone processes, the SO175 research programme had a variety of goals, such as:
• To test the frictional behaviour of the abyssal plain sediments.
• To explore the temperature field of the 1755 thrust earthquake event via heat flow measurements.
• To assess the role of fluid venting and gas hydrate processes control slope stability and mud volcanic activity along the Iberian continental margin.
• To measure isotope geochemistry of pore waters and carbonates of deep fluids.
• To quantify microbial activity in Gibraltar wedge sediments.
• To test whether microseismicity in the area corresponds to in situ pore pressure changes.
• To find out if enhanced heat flow max be indicative of active subduction.
Initial tentative results during the cruise suggest that there is a component of active thrusting at the base of the wedge, as attested by heat flow data. Based on mostly geochemical evidence, mud volcanism was found less active than previously assumed. Highlights from post-cruise research include the successful deployment of the long-term station and high frictional resistance of all incoming sediment on the three abyssal plains

### Annihilation, Rescattering, and CP Asymmetries in B Meson Decays

A number of $B$ meson decays may proceed only through participation of the
spectator quark, whether through amplitudes proportional to $f_B/m_B$ or via
rescattering from other less-suppressed amplitudes. An expected hierarchy of
amplitudes in the absence of rescattering will be violated by rescattering
corrections. Such violations could point the way toward channels in which
final-state interactions could be important. Cases in which final state phases
can lead to large CP asymmetries are pointed out.Comment: 9 page

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