3,601 research outputs found
Conditions for free magnetic monopoles in nanoscale square arrays of dipolar spin ice
We study a modified frustrated dipolar array recently proposed by M\"{o}ller
and Moessner [Phys. Rev. Lett. \textbf{96}, 237202 (2006)], which is based on
an array manufactured lithographically by Wang \emph{et al.} [Nature (London)
\textbf{439}, 303 (2006)] and consists of introducing a height offset
between islands (dipoles) pointing along the two different lattice directions.
The ground-states and excitations are studied as a function of . We have
found, in qualitative agreement with the results of M\"{o}ller and Moessner,
that the ground-state changes for , where ( is the
lattice parameter or distance between islands). In addition, the excitations
above the ground-state behave like magnetic poles but confined by a string,
whose tension decreases as increases, in such a way that for
its value is around 20 times smaller than that for . The system exhibits
an anisotropy in the sense that the string tension and magnetic charge depends
significantly on the directions in which the monopoles are separated. In turn,
the intensity of the magnetic charge abruptly changes when the monopoles are
separated along the direction of the longest axis of the islands. Such a gap is
attributed to the transition from the anti to the ferromagnetic ground-state
when .Comment: 6 pages, 7 figures. Published versio
Partnering with Medicaid to Advance and Sustain the Goals of the Child Welfare System
The purpose of this paper is to serve as a practical guide for child welfare directors who are looking to expand or sustain services for the children and families that they serve. This paper focuses on ways to partner with Medicaid to leverage opportunities to provide high quality services for children in child welfare who have behavioral health needs. It also includes information that will provide a foundational understanding of the behavioral health needs of children involved with the child welfare system, with an emphasis on describing child behavior through the lens of child development, adaptive functioning, and trauma; the services that can effectively address those behavioral and trauma related responses that can disrupt a child's skills and abilities; and, examples from states and counties who are providing these services and supports
Proximity effect of vanadium on spin-density-wave magnetism in Cr films
The spin-density wave (SDW) state in thin chromium films is well known to be
strongly affected by proximity effects from neighboring layers. To date the
main attention has been given to effects arising from exchange interactions at
interfaces. In the present work we report on combined neutron and synchrotron
scattering studies of proximity effects in Cr/V films where the boundary
condition is due to the hybridization of Cr with paramagnetic V at the
interface. We find that the V/Cr interface has a strong and long-range effect
on the polarization, period, and the N\'{e}el temperature of the SDW in rather
thick Cr films. This unusually strong effect is unexpected and not predicted by
theory.Comment: 7 figure
Acoustic oceanographic buoy data report Makai Ex 2005
Rep 04/05 - SiPLAB
17/Nov/2005
UniversityIt is now well accepted in the underwater acoustic scientific community that below, say, 1
kHz acoustic propagation models are accurate enough to be able to predict the received
acoustic field up to the point of allowing precise and reliable source tracking in range and
depth with only limited environmental information. This results from a large number of
studies both theoretical and with real data, carried out in the last 20 years. With the
event of underwater communications and the necessity to increase the signal bandwidth for
allowing higher communication rates, the frequency band of interest was raised to above
10 kHz. In this frequency band the detailed knowledge of the environment - acoustic
signal interplay is reduced. The purpose of the MakaiEx sea trial is to acquire data in
a complete range of frequencies from 500 Hz up to 50 kHz, for a variety of applications
ranging from high-frequency tomography, coherent SISO and MIMO applications, vector
- sensor, active and passive sonar, etc...The MakaiEx sea trial, that took place off Kauai I.
from 15 September - 2 October, involved a large number of teams both from government
and international laboratories, universities and private companies, from various countries.
Each team focused on its specific set of objectives in relation with its equipment or
scientific interest. The team from the University of Algarve (UALg) focused on the data
acquired by their receiving Acoustic Oceanographic Buoy - version 2 (AOB2) during six
deployments in the period 15 - 27 September. This report describes the AOB2 data
set as well as all the related environmental and geometrical data relative to the AOB2
deployments. The material described herein represents a valuable data set for supporting
the research objectives of projects NUACE1, namely to fulfill NUACE’s task 3 and 4 and
RADAR2, namely its tasks 2 and 3 devoted to the developement and testing of a field of
sonobuoys.This report presents the testing of the most recent version of the Acoustic Oceanographic
Buoy (AOB) system and the results obtained during the Makai Ex sea trial. The MakaiEx
sea trial took place off the west coast of Kauai I., Hawaii, USA, in the period September
15 - 27, 2005.
The authors of this report would like to thank:
• all the personnel involved, including R/V Kilo Moana crew
• the scientist in charge Michael B. Porter
• the University of Hawaii for its support
• FCT (Portugal) for the funding provided under projects NUACE (POSI/CPS/47824/
2002) and RADAR (POCTI/CTA/47719/2002).
• ONR for the funding under ONR-IFO VSP grant # N00014-04-1-403
Nambu monopoles interacting with lattice defects in two-dimensional artificial square spin ice
The interactions between an excitation (similar to a pair of Nambu monopoles)
and a lattice defect are studied in an artificial two-dimensional square spin
ice. This is done by considering a square array of islands containing only one
island different from all others. This difference is incorporated in the
magnetic moment (spin) of the "imperfect" island and several cases are studied,
including the special situation in which this distinct spin is zero (vacancy).
We have shown that the two extreme points of a malformed island behave like two
opposite magnetic charges. Then, the effective interaction between a pair of
Nambu monopoles with the deformed island is a problem involving four magnetic
charges (two pairs of opposite poles) and a string. We also sketch the
configuration of the field lines of these four charges to confirm this picture.
The influence of the string on this interaction decays rapidly with the string
distance from the defect.Comment: 7 pages, 13 figure
Extended Source Diffraction Effects Near Gravitational Lens Fold Caustics
Calculations are presented detailing the gravitational lens diffraction due
to the steep brightness gradient of the limb of a stellar source. The lensing
case studied is the fold caustic crossing. The limb diffraction signal greatly
exceeds that due to the disk as a whole and should be detectable for white
dwarf sources in our Galaxy and it's satellites with existing telescopes.
Detection of this diffraction signal would provide an additional mathematical
constraint, reducing the degeneracy among models of the lensing geometry. The
diffraction pattern provides pico-arcsecond resolution of the limb profile.Comment: 19 pages including 17 figures, Accepted for publication in ApJ, Minor
conceptual change from previous versio
An environmental equalizer for underwater acoustic communications Tested at Hydralab III
It is known that small changes in source and receiver locations can cause significant changes in underwater acoustic channel impulse responses. At HYDRALAB III an underwater acoustic experiment was conducted to show that a source depth-shift causes a frequency-shift in the channel impulse response and that such behavior can be used to implement an environmental-based equalizer for underwater communications that compensates for the performance loss due to the source depth-shift
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