3,977 research outputs found
A Magnetic and Moessbauer Spectral Study of Core/Shell Structured Fe/Au Nanoparticles
Fe/Au nanoparticles have been chemically synthesized through a reverse
micelle reaction and investigated by both conventional and synchrotron based
x-ray diffraction and by magnetic and Moessbauer spectral studies. The powder
x-ray diffraction patterns reveal both the presence of crystalline alpha-iron
and gold and the absence of any crystalline iron oxides or other crystalline
products. First-order reversal curves, along with the major hysteresis loops of
the Fe/Au nanoparticles have been measured as a function of time in order to
investigate the evolution of their magnetic properties. The iron-57 Moessbauer
spectra of both uncoated iron nanoparticles and the Fe/Au nanoparticles have
been measured at 78 and 295 K and indicate that two major iron containing
components are present, namely the expected alpha-iron and the unexpected
amorphous Fe1-xBx alloy; several poorly crystallized ordered iron(III) oxide
components as well as paramagnetic iron(II) and iron(III) components are also
observed. These results indicate that the Fe-core/Au-shell nanoparticles
synthesized through reverse micelles are far more complex that had been
believed.Comment: 31 pages, 1 table, 8 figures, to appear in Chemistry of Material
The Approximating Hamiltonian Method for the Imperfect Boson Gas
The pressure for the Imperfect (Mean Field) Boson gas can be derived in
several ways. The aim of the present note is to provide a new method based on
the Approximating Hamiltonian argument which is extremely simple and very
general.Comment: 7 page
Does enforcement deter cartels? A tale of two tails
This paper investigates the deterrent impact of anti-cartel enforcement. It is shown theoretically that if enforcement is effective in deterring and constraining cartels then there will be fewer cartels with low overcharges and fewer with high overcharges. This prediction provides an indirect method for testing whether the enforcement of competition law is effective. Using historical data on legal cartels to generate the counterfactual, we find significantly less mass in the tails of the overcharge distribution, compared to illegal cartels. This result is robust to controlling for confounding factors, and we interpret this as the first tentative confirmation of effective deterrence
Heterotrophy mitigates the response of the temperate coral
Anthropogenic increases in atmospheric carbon dioxide concentration have caused global average sea surface temperature (SST) to increase by approximately 0.11°C per decade between 1971 and 2010 - a trend that is projected to continue through the 21st century. A multitude of research studies have demonstrated that increased SSTs compromise the coral holobiont (cnidarian host and its symbiotic algae) by reducing both host calcification and symbiont density, among other variables. However, we still do not fully understand the role of heterotrophy in the response of the coral holobiont to elevated temperature, particularly for temperate corals. Here, we conducted a pair of independent experiments to investigate the influence of heterotrophy on the response of the temperate scleractinian coral Oculina arbuscula to thermal stress. Colonies of O. arbuscula from Radio Island, North Carolina, were exposed to four feeding treatments (zero, low, moderate, and high concentrations of newly hatched Artemia sp. nauplii) across two independent temperature experiments (average annual SST (20°C) and average summer temperature (28°C) for the interval 2005-2012) to quantify the effects of heterotrophy on coral skeletal growth and symbiont density. Results suggest that heterotrophy mitigated both reduced skeletal growth and decreased symbiont density observed for unfed corals reared at 28°C. This study highlights the importance of heterotrophy in maintaining coral holobiont fitness under thermal stress and has important implications for the interpretation of coral response to climate change
Anisotropy Dependence of Irreversible Switching in Fe/SmCo and FeNi/FePt Exchange Spring Magnet Films
Magnetization reversal in exchange-spring magnet films has been investigated
by a First Order Reversal Curve (FORC) technique and vector magnetometry. In
Fe/epitaxial-SmCo films, the reversal proceeds by a reversible rotation of the
Fe soft layer, followed by an irreversible switching of the SmCo hard layer.
The switching fields are clearly manifested by separate steps in both
longitudinal and transverse hysteresis loops, as well as sharp boundaries in
the FORC distribution. In FeNi/polycrystalline-FePt films, particularly with
thin FeNi, the switching fields are masked by the smooth and step-free major
loop. However, the FORC diagram still displays a distinct onset of irreversible
switching and transverse hysteresis loops exhibit a pair of peaks, whose
amplitude is larger than the maximum possible contribution from the FeNi layer
alone. This suggests that the FeNi and FePt layers reverse in a continuous
process via a vertical spiral. The successive vs. continuous rotation of the
soft/hard layer system is primarily due to the different crystal structure of
the hard layer, which results in different anisotropies.Comment: 13 pages, 2 figures, APL in pres
Technology use by people with intellectual and developmental disabilities to support employment activities: A single-subject design meta analysis
This is the published version. Copyright 2006 IOS PressObjectives: Technology has the potential to improve employment and rehabilitation related outcomes for persons with disabilities. The purpose of this study was to examine the impact of technology use on employment-related outcomes for people with intellectual and developmental disabilities. Study design: A comprehensive search of the literature pertaining to technology use by people with intellectual disabilities was conducted, and a single-subject design meta analysis was conducted for a subset of those studies, which focused on employment and rehabilitation related outcomes. Results: The use of technology to promote outcomes in this area was shown to be generally effective, in particular when universal design features were addressed. Conclusions: Technology has the potential to enable people with intellectual and developmental disabilities to achieve more positive employment and rehabilitation outcomes. It is important to focus on universal design features important to persons with cognitive disabilities, and there is a need for more research in this area
Reconstructing phase-resolved hysteresis loops from first-order reversal curves
The first order reversal curve (FORC) method is a magnetometry based
technique used to capture nanoscale magnetic phase separation and interactions
with macroscopic measurements using minor hysteresis loop analysis. This makes
the FORC technique a powerful tool in the analysis of complex systems which
cannot be effectively probed using localized techniques. However, recovering
quantitative details about the identified phases which can be compared to
traditionally measured metrics remains an enigmatic challenge. We demonstrate a
technique to reconstruct phase-resolved magnetic hysteresis loops by
selectively integrating the measured FORC distribution. From these minor loops,
the traditional metrics - including the coercivity and saturation field, and
the remanent and saturation magnetization - can be determined. In order to
perform this analysis, special consideration must be paid to the accurate
quantitative management of the so-called reversible features. This technique is
demonstrated on three representative materials systems, high anisotropy FeCuPt
thin-films, Fe nanodots, and SmCo/Fe exchange spring magnet films, and shows
excellent agreement with the direct measured major loop, as well as the phase
separated loops
Magnetization Reversal and Nanoscopic Magnetic Phase Separation in Doped La1-xSrxCoO3
The doped perovskite cobaltite La1-xSrxCoO3 (LSCO) has been advanced as a
model system for studying intrinsic magnetic phase separation. We have employed
a first-order reversal curve (FORC) method to probe the amount of irreversible
switching in bulk polycrystalline LSCO as a function of Sr doping, field
cooling procedure, and temperature. The value of the FORC distribution, rho, is
used as a measure of the extent of irreversible switching. For x < 0.18, the
small values of rho and its ridge-like distribution along local coercivity (Hc)
and zero bias (Hb), are characteristic of non-interacting single domain
particles. This is consistent with the formation of an array of isolated
nanoscopic ferromagnetic clusters, as observed in previous work. For x >= 0.18,
the much larger values of rho, the tilting of its distribution towards negative
bias field, and the emergence of regions with negative rho, are consistent with
increased long-range ferromagnetic ordering. The FORC distributions display
little dependence on the cooling procedure. With increasing temperature, the
fraction of irreversible switching determined from the FORC distribution
follows closely the ferromagnetic phase fraction measured by La nuclear
magnetic resonance. Our results furthermore demonstrate that the FORC method is
a valuable first-pass characterization tool for magnetic phase separation.Comment: 30 pages, 8 figures, to appear in PR
Hyperstrong Radio-Wave Scattering in the Galactic Center. II. A Likelihood Analysis of Free Electrons in the Galactic Center
The scattering diameters of Sgr A* and several nearby OH masers (~ 1" at 1
GHz) indicate that a region of enhanced scattering is along the line of sight
to the Galactic center. We combine radio-wave scattering data and free-free
emission and absorption measurements in a likelihood analysis that constrains
the following parameters of the GC scattering region: The GC-scattering region
separation, d; the angular extent of the region, \psi_l; the outer scale on
which density fluctuations occur, l_0; and the gas temperature, T. The maximum
likelihood estimates of these parameters are d = 133_{-80}^{+200} pc, 0.5
degrees <= \psi_l <~ 1 degrees, and (l_0/1 pc)^{2/3}T^{-1/2} = 10^{-7 +/- 0.8}.
As host media for the scattering, we consider the photoionized surface layers
of molecular clouds and the interfaces between molecular clouds and the 10^7 K
ambient gas. We are unable to make an unambiguous determination, but we favor
an interface model in which the scattering medium is hot (T ~ 10^6 K) and dense
(n_e ~ 10 cm^{-3}). The GC scattering region produces a 1 GHz scattering
diameter for an extragalactic source of 90", if the region is a single screen,
or 180", if the region wraps around the GC, as appears probable. We modify the
Taylor-Cordes model for the Galactic distribution of free electrons in order to
include an explicit GC component. Pulsars seen through this region will have a
dispersion measure of approximately 2000 pc cm^{-3}, of which 75% arises from
the GC component. We stress the uniqueness of the GC scattering region,
probably resulting from the high-pressure environment in the GC.Comment: 39 pages with 9 PostScript figures; LaTeX2e with AASTeX macro aaspp4,
to be published in Ap
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