1,522 research outputs found
Effect of Defects on the Line shape of Electron Paramagnetic Resonance Signals from the Single-Molecule Magnet Mn12: A Theoretical Study
We herein estimate the effect of lattice defects on the line shape of
electron paramagnetic resonance (EPR) signals from a single crystal of the S=10
single-molecule magnet Mn with the external magnetic field along the
crystal c axis. A second-order perturbation treatment of an effective
single-spin Hamiltonian indicates that a small, random, static misorientation
of the magnetic symmetry axes in a crystalline lattice can lead to asymmetric
EPR peaks. Full spectra are simulated by calculating probability-distribution
functions for the resonant fields, employing distributions in the tilt angle of
the easy axis from the c axis, in the uniaxial anisotropy parameter, and in the
-factor. We discuss conditions under which the asymmetry in the EPR spectra
becomes prominent. The direction and magnitude of the asymmetry provide
information on the specific energy levels involved with the EPR transition, the
EPR frequency, and the distribution in the tilt angle.Comment: published versio
Analysis of Rank Aggregation Techniques for Rank Based on the Feature Selection Technique
In order to improve classification accuracy and lower future computation and data collecting costs, feature selection is the process of choosing the most crucial features from a group of attributes and removing the less crucial or redundant ones. To narrow down the features that need to be analyzed, a variety of feature selection procedures have been detailed in published publications. Chi-Square (CS), IG, Relief, GR, Symmetrical Uncertainty (SU), and MI are six alternative feature selection methods used in this study. The provided dataset is aggregated using four rank aggregation strategies: "rank aggregation," "Borda Count (BC) methodology," "score and rank combination," and "unified feature scoring" based on the outcomes of the six feature selection method (UFS). These four procedures by themselves were unable to generate a clear selection rank for the characteristic. To produce different ranks of traits, this ensemble of aggregating ranks is carried out. For this, the bagging method of majority voting was applied
Video Object Detection with an Aligned Spatial-Temporal Memory
We introduce Spatial-Temporal Memory Networks for video object detection. At
its core, a novel Spatial-Temporal Memory module (STMM) serves as the recurrent
computation unit to model long-term temporal appearance and motion dynamics.
The STMM's design enables full integration of pretrained backbone CNN weights,
which we find to be critical for accurate detection. Furthermore, in order to
tackle object motion in videos, we propose a novel MatchTrans module to align
the spatial-temporal memory from frame to frame. Our method produces
state-of-the-art results on the benchmark ImageNet VID dataset, and our
ablative studies clearly demonstrate the contribution of our different design
choices. We release our code and models at
http://fanyix.cs.ucdavis.edu/project/stmn/project.html
A New Survey for Giant Arcs
We report on the first results of an imaging survey to detect strong
gravitational lensing targeting the richest clusters selected from the
photometric data of the Sloan Digital Sky Survey (SDSS) with follow-up deep
imaging observations from the Wisconsin Indiana Yale NOAO (WIYN) 3.5m telescope
and the University of Hawaii 88-inch telescope (UH88). The clusters are
selected from an area of 8000 deg^2 using the Red Cluster Sequence technique
and span the redshift range 0.1 < z < 0.6, corresponding to a comoving
cosmological volume of ~ 2 Gpc^3. Our imaging survey thus targets a volume more
than an order of magnitude larger than any previous search. A total of 240
clusters were imaged of which 141 had sub-arcsecond image quality. Our survey
has uncovered16 new lensing clusters with definite giant arcs, an additional 12
systems for which the lensing interpretation is very likely, and 9 possible
lenses which contain shorter arclets or candidate arcs which are less certain
and will require further observations to confirm their lensing origin. The
number of new cluster lenses detected in this survey is likely > 30. Among
these new systems are several of the most dramatic examples of strong
gravitational lensing ever discovered with multiple bright arcs at large
angular separation. These will likely become 'poster-child' gravitational
lenses similar to Abell 1689 and CL0024+1654. The new lenses discovered in this
survey will enable future sysetmatic studies of the statistics of strong
lensing and its implications for cosmology and our structure formation
paradigm.Comment: 19 pages, 7 pages of Figures, submitted to AJ. Fixed Typo
Self-Lensing Models of the LMC
All of the proposed explanations for the microlensing events observed towards
the LMC have difficulties. One of these proposed explanations, LMC
self-lensing, which invokes ordinary LMC stars as the long sought-after lenses,
has recently gained considerable popularity as a possible solution to the
microlensing conundrum. In this paper, we carefully examine the set of LMC
self-lensing models. In particular, we review the pertinent observations made
of the LMC, and show how these observations place limits on such self-lensing
models. We find that, given current observational constraints, no purely LMC
disk models are capable of producing optical depths as large as that reported
in the MACHO collaboration 2-year analysis. Besides pure disk, we also consider
alternate geometries, and present a framework which encompasses the previous
studies of LMC self-lensing. We discuss which model parameters need to be
pushed in order for such models to succeed. For example, like previous workers,
we find that an LMC halo geometry may be able to explain the observed events.
However, since all known LMC tracer stellar populations exhibit disk-like
kinematics, such models will have difficulty being reconciled with
observations. For SMC self-lensing, we find predicted optical depths differing
from previous results, but more than sufficient to explain all observed SMC
microlensing. In contrast, for the LMC we find a self-lensing optical depth
contribution between 0.47e-8 and 7.84e-8, with 2.44e-8 being the value for the
set of LMC parameters most consistent with current observations.Comment: 20 pages, Latex, 14 figures, submitted to Ap
Electron Paramagnetic Resonance Linewidths and Lineshapes for the Molecular Magnets Fe8 and Mn12
We study theoretically Electron Paramagentic Resonance (EPR) linewidths for
single crystals of the molecular magnets Fe and Mn as functions of
energy eigenstates , frequency, and temperature when a magnetic field
along the easy axis is swept at fixed excitation frequency. This work was
motivated by recent EPR experiments. To calculate the linewidths, we use
density-matrix equations, including dipolar interactions and distributions of
the uniaxial anisotropy parameter and the Land\'{e} factor. Our
calculated linewidths agree well with the experimental data. We also examine
the lineshapes of the EPR spectra due to local rotations of the magnetic
anisotropy axes caused by defects in samples. Our preliminary results predict
that this effect leads to asymmetry in the EPR spectra.Comment: 2001 MMM conferenc
AC susceptibility and V NMR study of MnVO
We report V zero-field NMR of manganese vanadate spinel of
MnVO, together with both ac and dc magnetization measurements. The
field and temperature dependence of ac susceptibilities show a
reentrant-spin-glass-like behavior below the ferrimagnetic(FEM) ordering
temperature. The zero-field NMR spectrum consists of multiple lines ranging
from 240 MHz to 320 MHz. Its temperature dependence reveals that the ground
state is given by the simultaneous formation of a long-range FEM order and a
short-range order component. We attribute the spin-glass-like anomalies to
freezing and fluctuations of the short-range ordered state caused by the
competition between spin and orbital ordering of the V site
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