2,171 research outputs found
Automated data acquisition and reduction system for torsional braid analyzer
Automated Data Acquisition and Reduction System (ADAR) evaluates damping coefficient and relative rigidity by storing four successive peaks of waveform and time period between two successive peaks. Damping coefficient and relative rigidity are then calculated and plotted against temperature or time in real time
Coherent manipulation of electron spins up to ambient temperatures in Cr(S=1/2) doped KNbO
We report coherent spin manipulation on Cr (\emph{S} = 1/2, \emph{I} =
0) doped KNbO, which constitutes a dilute two-level model relevant for
use as a spin qubit. Rabi oscillations are observed for the first time in a
spin system based on transition metal oxides up to room temperature. At liquid
helium temperature the phase coherence relaxation time \emph{} reaches
s and, with a Rabi frequency of 20 MHz, yields a single qubit
figure of merit \emph{} of about 500. This shows that a diluted ensemble
of Cr (\emph{S} = 1/2) doped KNbO is a potential candidate for
solid-state quantum information processing.Comment: 4 page
Erosive Burning and its Applications for Performance Prediction
A modified method for prediction of performance of large motors based on erosion constant obtained by partial burning technique is discussed. Erosion constants for two different double base compositions have been determined by partial burning technique. These constraints have been used to predict the performance of the large scale motors developed for Defence applications. The predicted performance compares well with the experimental values
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
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
The MACHO Project HST Follow-Up: The Large Magellanic Cloud Microlensing Source Stars
We present Hubble Space Telescope (HST) WFPC2 photometry of 13 microlensed
source stars from the 5.7 year Large Magellanic Cloud (LMC) survey conducted by
the MACHO Project. The microlensing source stars are identified by deriving
accurate centroids in the ground-based MACHO images using difference image
analysis (DIA) and then transforming the DIA coordinates to the HST frame. None
of these sources is coincident with a background galaxy, which rules out the
possibility that the MACHO LMC microlensing sample is contaminated with
misidentified supernovae or AGN in galaxies behind the LMC. This supports the
conclusion that the MACHO LMC microlensing sample has only a small amount of
contamination due to non-microlensing forms of variability. We compare the
WFPC2 source star magnitudes with the lensed flux predictions derived from
microlensing fits to the light curve data. In most cases the source star
brightness is accurately predicted. Finally, we develop a statistic which
constrains the location of the Large Magellanic Cloud (LMC) microlensing source
stars with respect to the distributions of stars and dust in the LMC and
compare this to the predictions of various models of LMC microlensing. This
test excludes at > 90% confidence level models where more than 80% of the
source stars lie behind the LMC. Exotic models that attempt to explain the
excess LMC microlensing optical depth seen by MACHO with a population of
background sources are disfavored or excluded by this test. Models in which
most of the lenses reside in a halo or spheroid distribution associated with
either the Milky Way or the LMC are consistent which these data, but LMC halo
or spheroid models are favored by the combined MACHO and EROS microlensing
results.Comment: 28 pages with 10 included PDF figures, submitted to Ap
Towards the theory of ferrimagnetism
Two-sublattice ferrimagnet, with spin- operators at the
sublattice site and spin- operators at the sublattice
site, is considered. The magnon of the system, the transversal fluctuation
of the total magnetization, is a complicate mixture of the transversal
fluctuations of the sublattice and spins. As a result, the magnons'
fluctuations suppress in a different way the magnetic orders of the and
sublattices and one obtains two phases. At low temperature the
magnetic orders of the and spins contribute to the magnetization of the
system, while at the high temperature , the magnetic order of the
spins with a weaker intra-sublattice exchange is suppressed by magnon
fluctuations, and only the spins with stronger intra-sublattice exchange has
non-zero spontaneous magnetization. The transition is a transition
between two spin-ordered phases in contrast to the transition from spin-ordered
state to disordered state (-transition). There is no additional symmetry
breaking, and the Goldstone boson has a ferromagnetic dispersion in both
phases. A modified spin-wave theory is developed to describe the two phases.
All known Neel's anomalous curves are reproduced, in particular that
with "compensation point". The theoretical curves are compared with
experimental ones for sulpho-spinel and rare earth iron
garnets.Comment: 9 pages, 8 figure
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