588 research outputs found
Spin-Correlation Coefficients and Phase-Shift Analysis for p+He Elastic Scattering
Angular Distributions for the target spin-dependent observables A,
A, and A have been measured using polarized proton beams at
several energies between 2 and 6 MeV and a spin-exchange optical pumping
polarized He target. These measurements have been included in a global
phase-shift analysis following that of George and Knutson, who reported two
best-fit phase-shift solutions to the previous global p+He elastic
scattering database below 12 MeV. These new measurements, along with
measurements of cross-section and beam-analyzing power made over a similar
energy range by Fisher \textit{et al.}, allowed a single, unique solution to be
obtained. The new measurements and phase-shifts are compared with theoretical
calculations using realistic nucleon-nucleon potential models.Comment: Submitted to Phys. Rev.
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Non-stoichiometric oxide and metal interfaces and reactions
We have employed a combination of experimental surface science techniques and density functional calculations to study the reduction of TiO2(110) surfaces through the doping with submonolayer transition metals. We concentrate on the role of Ti adatoms in self doping of rutile and contrast the behaviour to that of Cr. DFT+U calculations enable identification of probable adsorption structures and their spectroscopic characteristics. Adsorption of both metals leads to a broken symmetry and an asymmetric charge transfer localised around the defect site of a mixed localised/delocalised character. Charge transfer creates defect states with Ti 3d character in the band gap at similar to 1-eV binding energy. Cr adsorption, however, leads to a very large shift in the valence-band edge to higher binding energy and the creation of Cr 3d states at 2.8-eV binding energy. Low-temperature oxidation lifts the Ti-derived band-gap states and modifies the intensity of the Cr features, indicative of a change of oxidation state from Cr3+ to Cr4+. Higher temperature processing leads to a loss of Cr from the surface region, indicative of its substitution into the bulk
Accelerator Testing of the General Antiparticle Spectrometer, a Novel Approach to Indirect Dark Matter Detection
We report on recent accelerator testing of a prototype general antiparticle
spectrometer (GAPS). GAPS is a novel approach for indirect dark matter searches
that exploits the antideuterons produced in neutralino-neutralino
annihilations. GAPS captures these antideuterons into a target with the
subsequent formation of exotic atoms. These exotic atoms decay with the
emission of X-rays of precisely defined energy and a correlated pion signature
from nuclear annihilation. This signature uniquely characterizes the
antideuterons. Preliminary analysis of data from a prototype GAPS in an
antiproton beam at the KEK accelerator in Japan has confirmed the
multi-X-ray/pion star topology and indicated X-ray yields consistent with prior
expectations. Moreover our success in utilizing solid rather than gas targets
represents a significant simplification over our original approach and offers
potential gains in sensitivity through reduced dead mass in the target area.Comment: 18 pages, 9 figures, submitted to JCA
How metal films de-wet substrates - identifying the kinetic pathways and energetic driving forces
We study how single-crystal chromium films of uniform thickness on W(110)
substrates are converted to arrays of three-dimensional (3D) Cr islands during
annealing. We use low-energy electron microscopy (LEEM) to directly observe a
kinetic pathway that produces trenches that expose the wetting layer. Adjacent
film steps move simultaneously uphill and downhill relative to the staircase of
atomic steps on the substrate. This step motion thickens the film regions where
steps advance. Where film steps retract, the film thins, eventually exposing
the stable wetting layer. Since our analysis shows that thick Cr films have a
lattice constant close to bulk Cr, we propose that surface and interface stress
provide a possible driving force for the observed morphological instability.
Atomistic simulations and analytic elastic models show that surface and
interface stress can cause a dependence of film energy on thickness that leads
to an instability to simultaneous thinning and thickening. We observe that
de-wetting is also initiated at bunches of substrate steps in two other
systems, Ag/W(110) and Ag/Ru(0001). We additionally describe how Cr films are
converted into patterns of unidirectional stripes as the trenches that expose
the wetting layer lengthen along the W[001] direction. Finally, we observe how
3D Cr islands form directly during film growth at elevated temperature. The Cr
mesas (wedges) form as Cr film steps advance down the staircase of substrate
steps, another example of the critical role that substrate steps play in 3D
island formation
Spin-flop transition in uniaxial antiferromagnets: magnetic phases, reorientation effects, multidomain states
The classical spin-flop is the field-driven first-order reorientation
transition in easy-axis antiferromagnets. A comprehensive phenomenological
theory of easy-axis antiferromagnets displaying spin-flops is developed. It is
shown how the hierarchy of magnetic coupling strengths in these
antiferromagnets causes a strongly pronounced two-scale character in their
magnetic phase structure. In contrast to the major part of the magnetic phase
diagram, these antiferromagnets near the spin-flop region are described by an
effective model akin to uniaxial ferromagnets. For a consistent theoretical
description both higher-order anisotropy contributions and dipolar stray-fields
have to be taken into account near the spin-flop. In particular,
thermodynamically stable multidomain states exist in the spin-flop region,
owing to the phase coexistence at this first-order transition. For this region,
equilibrium spin-configurations and parameters of the multidomain states are
derived as functions of the external magnetic field. The components of the
magnetic susceptibility tensor are calculated for homogeneous and multidomain
states in the vicinity of the spin-flop. The remarkable anomalies in these
measurable quantities provide an efficient method to investigate magnetic
states and to determine materials parameters in bulk and confined
antiferromagnets, as well as in nanoscale synthetic antiferromagnets. The
method is demonstrated for experimental data on the magnetic properties near
the spin-flop region in the orthorhombic layered antiferromagnet
(C_2H_5NH_3)_2CuCl_4.Comment: (15 pages, 12 figures; 2nd version: improved notation and figures,
correction of various typos
The relationship between obesity, hyperglycemia symptoms, and health-related quality of life among Hispanic and non-Hispanic white children and adolescents
BACKGROUND: The current study was conducted to evaluate the effects of overweight, hyperglycemia symptoms, Hispanic ethnicity, and language barriers on health-related quality of life (HRQoL) among children and adolescents. METHODS: Parents'/guardians of a population based sample of 5530 children between ages 3 and 18 were administered the parents' version of the KINDL(® )survey instrument to assess HRQoL in children and adolescents. Multiple linear regression analysis was used to assess relationships between HRQoL, body mass index, and hyperglycemia symptoms categories. RESULTS: The mean age of children was 10.6 (SD = 4.3). The mean KINDL(® )total score was 79.7 (SD = 11.6) and the mean physical functioning score was 81.9 (SD = 20.3). Male children exhibited better physical health as compared to the female children (p < 0.001). Overweight children had lower overall HRQoL (p = 0.008). However, the association was not significant for the four of the six subscales including the physical health domain. Children with hyperglycemia symptoms and a family history of diabetes also had significantly lower overall and physical health HRQoL (p < 0.05). Children diagnosed with diabetes and in lower income strata also had significantly lower overall HRQoL (p < 0.05). No significant association between the Hispanic ethnicity and HRQoL was observed. However, those who reported mostly speaking Spanish exhibited significantly lower overall HRQoL (p = 0.001). CONCLUSION: Results suggest that overweight may reduce overall quality of life among children, though it does not directly influence physical functioning. However, hyperglycemia symptoms may affect both overall health and physical functioning. Findings also suggest the need for developing programs directed at overcoming language barriers that may face Spanish-speaking children or their parents. Furthermore, targeting children who have hyperglycemia symptoms with public information campaigns may be more appropriate than targeting overweight children
Apraxia and motor dysfunction in corticobasal syndrome
Background: Corticobasal syndrome (CBS) is characterized by multifaceted motor system dysfunction and cognitive disturbance; distinctive clinical features include limb apraxia and visuospatial dysfunction. Transcranial magnetic stimulation (TMS) has been used to study motor system dysfunction in CBS, but the relationship of TMS parameters to clinical features has not been studied. The present study explored several hypotheses; firstly, that limb apraxia may be partly due to visuospatial impairment in CBS. Secondly, that motor system dysfunction can be demonstrated in CBS, using threshold-tracking TMS, and is linked to limb apraxia. Finally, that atrophy of the primary motor cortex, studied using voxel-based morphometry analysis (VBM), is associated with motor system dysfunction and limb apraxia in CBS. Â Methods: Imitation of meaningful and meaningless hand gestures was graded to assess limb apraxia, while cognitive performance was assessed using the Addenbrooke's Cognitive Examination - Revised (ACE-R), with particular emphasis placed on the visuospatial subtask. Patients underwent TMS, to assess cortical function, and VBM. Â Results: In total, 17 patients with CBS (7 male, 10 female; mean age 64.4+/2 6.6 years) were studied and compared to 17 matched control subjects. Of the CBS patients, 23.5% had a relatively inexcitable motor cortex, with evidence of cortical dysfunction in the remaining 76.5% patients. Reduced resting motor threshold, and visuospatial performance, correlated with limb apraxia. Patients with a resting motor threshold <50% performed significantly worse on the visuospatial sub-task of the ACE-R than other CBS patients. Cortical function correlated with atrophy of the primary and pre-motor cortices, and the thalamus, while apraxia correlated with atrophy of the pre-motor and parietal cortices. Â Conclusions: Cortical dysfunction appears to underlie the core clinical features of CBS, and is associated with atrophy of the primary motor and pre-motor cortices, as well as the thalamus, while apraxia correlates with pre-motor and parietal atrophy
Sialic Acid Glycobiology Unveils Trypanosoma cruzi Trypomastigote Membrane Physiology.
Trypanosoma cruzi, the flagellate protozoan agent of Chagas disease or American trypanosomiasis, is unable to synthesize sialic acids de novo. Mucins and trans-sialidase (TS) are substrate and enzyme, respectively, of the glycobiological system that scavenges sialic acid from the host in a crucial interplay for T. cruzi life cycle. The acquisition of the sialyl residue allows the parasite to avoid lysis by serum factors and to interact with the host cell. A major drawback to studying the sialylation kinetics and turnover of the trypomastigote glycoconjugates is the difficulty to identify and follow the recently acquired sialyl residues. To tackle this issue, we followed an unnatural sugar approach as bioorthogonal chemical reporters, where the use of azidosialyl residues allowed identifying the acquired sugar. Advanced microscopy techniques, together with biochemical methods, were used to study the trypomastigote membrane from its glycobiological perspective. Main sialyl acceptors were identified as mucins by biochemical procedures and protein markers. Together with determining their shedding and turnover rates, we also report that several membrane proteins, including TS and its substrates, both glycosylphosphatidylinositol-anchored proteins, are separately distributed on parasite surface and contained in different and highly stable membrane microdomains. Notably, labeling for α(1,3)Galactosyl residues only partially colocalize with sialylated mucins, indicating that two species of glycosylated mucins do exist, which are segregated at the parasite surface. Moreover, sialylated mucins were included in lipid-raft-domains, whereas TS molecules are not. The location of the surface-anchored TS resulted too far off as to be capable to sialylate mucins, a role played by the shed TS instead. Phosphatidylinositol-phospholipase-C activity is actually not present in trypomastigotes. Therefore, shedding of TS occurs via microvesicles instead of as a fully soluble form
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