12,688 research outputs found
Antiferromagnetism in EuCu2As2 and EuCu1.82Sb2 Single Crystals
Single crystals of EuCu2As2 and EuCu2Sb2 were grown from CuAs and CuSb
self-flux, respectively. The crystallographic, magnetic, thermal and electronic
transport properties of the single crystals were investigated by
room-temperature x-ray diffraction (XRD), magnetic susceptibility \chi versus
temperature T, isothermal magnetization M versus magnetic field H, specific
heat Cp(T) and electrical resistivity \rho(T) measurements. EuCu2As2
crystallizes in the body-centered tetragonal ThCr2Si2-type structure (space
group I4/mmm), whereas EuCu2Sb2 crystallizes in the related primitive
tetragonal CaBe2Ge2-type structure (space group P4/nmm). The energy-dispersive
x-ray spectroscopy and XRD data for the EuCu2Sb2 crystals showed the presence
of vacancies on the Cu sites, yielding the actual composition EuCu1.82Sb2. The
\rho(T) and Cp(T) data reveal metallic character for both EuCu2As2 and
EuCu1.82Sb2. Antiferromagnetic (AFM) ordering is indicated from the \chi(T),
Cp(T), and \rho(T) data for both EuCu2As2 (T_N = 17.5 K) and EuCu1.82Sb2 (T_N =
5.1 K). In EuCu1.82Sb2, the ordered-state \chi(T) and M(H) data suggest either
a collinear A-type AFM ordering of Eu+2 spins S=7/2 or a planar noncollinear
AFM structure, with the ordered moments oriented in the tetragonal ab plane in
either case. This ordered-moment orientation for the A-type AFM is consistent
with calculations with magnetic dipole interactions. The anisotropic \chi(T)
and isothermal M(H) data for EuCu2As2, also containing Eu+2 spins S=7/2,
strongly deviate from the predictions of molecular field theory for collinear
AFM ordering and the AFM structure appears to be both noncollinear and
noncoplanar.Comment: 21 pages, 22 figures, 4 Table
Metallic behavior induced by potassium doping of the trigonal antiferromagnetic insulator EuMn2As2
We report magnetic susceptibility \chi, isothermal magnetization M, heat
capacity C_p and electrical resistivity \rho measurements on undoped EuMn2As2
and K-doped Eu0.96K0.04Mn2As2 and Eu0.93K0.07Mn2As2 single crystals with the
trigonal CaAl2Si2-type structure as a function of temperature T and magnetic
field H. EuMn2As2 has an insulating ground state with an activation energy of
52 meV and exhibits antiferromagnetic (AFM) ordering of the Eu+2 spins S=7/2 at
T_N1 = 15 K from C_p(T) and \chi(T) data with a likely spin-reorientation
transition at T_N2 = 5.0 K. The Mn+2 3d5 spins-5/2 exhibit AFM ordering at T_N
= 142 K from all three types of measurements. The M(H) isotherm and \chi(T)
data indicate that the Eu AFM structure is both noncollinear and noncoplanar.
The AFM structure of the Mn spins is also unclear. A 4% substitution of K for
Eu in Eu0.96K0.04Mn2As2 is sufficient to induce a metallic ground state.
Evidence is found for a difference in the AFM structure of the Eu moments in
the metallic crystals from that of undoped EuMn2As2 versus both T and H. For
metallic Eu0.96K0.04Mn2As2 and Eu0.93K0.07Mn2As2, an anomalous S-shape T
dependence of \rho related to the Mn magnetism is found. Upon cooling from 200
K, \rho exhibits a strong negative curvature, reaches maximum positive slope at
the Mn T_N ~ 150 K, and then continues to decrease but more slowly below T_N.
This suggests that dynamic short-range AFM order of the Mn spins above the Mn
T_N strongly suppresses the resistivity, contrary to the conventional decrease
of \rho that is only observed upon cooling below T_N of an antiferromagnet.Comment: 21 pages, 22 figures, 4 Table
Physical properties of EuPd2As2 single crystals
The physical properties of self-flux grown EuPd2As2 single crystals have been
investigated by magnetization M, magnetic susceptibility chi, specific heat Cp,
and electrical resistivity rho measurements versus temperature T and magnetic
field H. The crystal structure was determined by powder x-ray diffraction
measurements, which confirmed the ThCr2Si2-type body-centered tetragonal
structure (space group I4/mmm) reported previously. The rho(T) data indicate
that state of EuPd2As2 is metallic. Long-range antiferromagnetic (AFM) ordering
is apparent from the chi(T), Cp(T), and rho(T) measurements. For H \parallel c
the chi(T) indicates two transitions at TN1 = 11.0 K and TN2 = 5.5 K, whereas
for H \perp c only one transition is observed at TN1 = 11.0 K. Between TN1 and
TN2 the anisotropic chi(T) data suggest a planar noncollinear AFM structure,
whereas at T < TN2 the chi(T) and M(H,T) data suggest a spin reorientation
transition in which equal numbers of spins cant in opposite directions out of
the ab plane. We estimate the critical field at 2 K at which all Eu moments
become aligned with the field to be about 22 T. The magnetic entropy at 25 K
estimated from the Cp(T) measurements is about smaller than expected,
possibly due to an inaccuracy in the lattice heat capacity contribution. An
upturn in rho at T < TN1 suggests superzone energy gap formation below TN1.
This behavior of rho(T < TN1) is not sensitive to applied magnetic fields up to
H = 12 T.Comment: 11 pages, 10 figures, 2 tables and 52 references; To appear in J.
Phys.: Condens. Matte
Wireless Handheld Computers in the Preclinical Undergraduate Curriculum
This report presents the results of a pilot project using wireless PDAs as teaching tools in an undergraduate medical curriculum. This technology was used to foster a transition from a passive to an interactive learning environment in the classroom and provided a solution for the implementation of computer-based exams for a large class. Wayne State Medical School recently provided model e570 Toshiba PocketPCs® (personal digital assistants or PDAs), network interface cards, and application software developed by CampusMobility® to 20 sophomore medical students. The pilot group of preclinical students used the PDAs to access web-based course content, for communication, scheduling, to participate in interactive teaching sessions, and to complete course evaluations. Another part of this pilot has been to utilize the PDAs for computer-based exams in a wireless environment. Server authentication that restricted access during the exams and a proctoring console to monitor and record the PDA screens will be described in this report. Results of a student satisfaction survey will be present
Enhancing Energy Minimization Framework for Scene Text Recognition with Top-Down Cues
Recognizing scene text is a challenging problem, even more so than the
recognition of scanned documents. This problem has gained significant attention
from the computer vision community in recent years, and several methods based
on energy minimization frameworks and deep learning approaches have been
proposed. In this work, we focus on the energy minimization framework and
propose a model that exploits both bottom-up and top-down cues for recognizing
cropped words extracted from street images. The bottom-up cues are derived from
individual character detections from an image. We build a conditional random
field model on these detections to jointly model the strength of the detections
and the interactions between them. These interactions are top-down cues
obtained from a lexicon-based prior, i.e., language statistics. The optimal
word represented by the text image is obtained by minimizing the energy
function corresponding to the random field model. We evaluate our proposed
algorithm extensively on a number of cropped scene text benchmark datasets,
namely Street View Text, ICDAR 2003, 2011 and 2013 datasets, and IIIT 5K-word,
and show better performance than comparable methods. We perform a rigorous
analysis of all the steps in our approach and analyze the results. We also show
that state-of-the-art convolutional neural network features can be integrated
in our framework to further improve the recognition performance
Model-independent Analyses of Dark-Matter Particle Interactions
A model-independent treatment of dark-matter particle elastic scattering has
been developed, yielding the most general interaction for WIMP-nucleon
low-energy scattering, and the resulting amplitude has been embedded in the
nucleus, taking into account the selection rules imposed by parity and
time-reversal. One finds that, in contrast to the usual
spin-independent/spin-dependent (SI/SD) formulation, the resulting cross
section contains six independent nuclear response functions, three of which are
associated with possible velocity-dependent interactions. We find that current
experiments are four orders of magnitude more sensitive to derivative couplings
than is apparent in the standard SI/SD treatment, which necessarily associates
such interactions with cross sections proportional to the square of the WIMP
velocity relative to the nuclear center of mass.Comment: 10 pages, 2 figures; talk presented at TAUP201
Model-independent WIMP Scattering Responses and Event Rates: A Mathematica Package for Experimental Analysis
The community's reliance on simplified descriptions of WIMP-nucleus
interactions reflects the absence of analysis tools that integrate general
theories of dark matter with standard treatments of nuclear response functions.
To bridge this gap, we have constructed a public-domain Mathematica package for
WIMP analyses based on our effective theory formulation. Script inputs are 1)
the coefficients of the effective theory, through which one can characterize
the low-energy consequences of arbitrary ultraviolet theories of WIMP
interactions; and 2) one-body density matrices for commonly used targets, the
most compact description of the relevant nuclear physics. The generality of the
effective theory expansion guarantees that the script will remain relevant as
new ultraviolet theories are explored; the use of density matrices to factor
the nuclear physics from the particle physics will allow nuclear structure
theorists to update the script as new calculations become available,
independent of specific particle-physics contexts. The Mathematica package
outputs the resulting response functions (and associated form factors) and also
the differential event rate, once a galactic WIMP velocity profile is
specified, and thus in its present form provides a complete framework for
experimental analysis. The Mathematica script requires no a priori knowledge of
the details of the non-relativistic effective field theory or nuclear physics,
though the core concepts are reviewed here and in arXiv:1203.3542.Comment: 30+6 page
Recommended from our members
Implant Prophylaxis: The Next Best Practice Toward Asepsis in Spine Surgery.
Study designA literature review.ObjectivesAn evaluation of the contaminants prevalent on implants used for surgery and the aseptic methods being employed against them.MethodsPubMed was searched for articles published between 2000 and 2017 for studies evaluating the contaminants present on spine implants, and associated pre- and intraoperative implant processing and handling methodology suggested to avoid them. Systematic reviews, observational studies, bench-top studies, and expert opinions were included.ResultsEleven studies were identified whose major focus was the asepsis of implants to reduce the incidence of surgical site infection incidences during surgery. These studies measured the colony forming units of bacteria on sterilized implants and/or gloves from the surgeon, scrub nurse, and assistants, as well as reductions of surgical site infection rates in spine surgery due to changes in implant handling techniques. Additionally, the search included assessments of endotoxins and carbohydrates present on reprocessed implants. The suggested changes to surgical practice based on these studies included handling implants with only fresh gloves, keeping implants covered until the immediate time of use, reducing operating room traffic, avoiding reprocessing of implants (ie, providing terminally sterilized implants), and avoiding touching the implants altogether.ConclusionsBoth reprocessing (preoperative) and handling (intraoperative) of implants seem to lead to contamination of sterilized implants. Using a terminally sterilized device may mitigate reprocessing (preoperative implant prophylaxis), whereas the use of fresh gloves for handling each implant and/or a permanent shielding technique (intraoperative implant prophylaxis) could potentially avoid recontamination at the theatre
- …