3,199 research outputs found
"Magnetoscan": A Modified Hall Probe Scanning Technique for the Detection of Inhomogeneities in Bulk High Temperature Superconductors
We present a novel technique for the investigation of local variations of the
critical current density in large bulk superconductors. In contrast to the
usual Hall probe scanning technique, the sample is not magnetized as a whole
before the scan, but locally by a small permanent magnet, which is fixed near
the Hall probe, during the scanning process. The resulting signal can be
interpreted as a qualitative measure of the local shielding currents flowing at
the surface.Comment: 8 pages, 4 figure
Direct observation of substitutional Ga after ion implantation in Ge by means of extended x-ray absorption fine structure
We present an experimental lattice location study of Ga atoms in Ge after ion implantation at elevated temperature (250°C). Using extended x-rayabsorption fine structure (EXAFS) experiments and a dedicated sample preparation method, we have studied the lattice location of Ga atoms in Ge with a concentration ranging from 0.5 at. % down to 0.005 at. %. At Ga concentrations ≤0.05 at.%, all Ga dopants are substitutional directly after ion implantation, without the need for post-implantation thermal annealing. At higher Ga concentrations, a reduction in the EXAFS amplitude is observed, indicating that a fraction of the Ga atoms is located in a defective environment. The local strain induced by the Ga atoms in the Ge matrix is independent of the Ga concentration and extends only to the first nearest neighbor Ge shell, where a 1% contraction in bond length has been measured, in agreement with density functional theory calculations.We acknowledge the support from the Research Foundation
Flanders, the epi-team from imec, the KU Leuven
GOA 09/06 project, the IUAP program P6/42 and the Australian
Research Council. S.C. acknowledges support from
OCAS NV by an OCAS-endowed chair at Ghent University
Inter- and intragrain currents in bulk melt-grown YBaCuO rings
A simple contactless method suitable to discern between the intergrain
(circular) current, which flows in the thin superconducting ring, and the
intragrain current, which does not cross the weakest link, has been proposed.
At first, we show that the intergrain current may directly be estimated from
the magnetic flux density measured by the Hall sensor positioned
in the special points above/below the ring center. The experimental
and the numerical techniques to determine the value are discussed. Being
very promising for characterization of a current flowing across the joints in
welded YBaCuO rings (its dependencies on the temperature and the external
magnetic field as well as the time dissipation), the approach has been applied
to study corresponding properties of the intra- and intergrain currents flowing
across the -twisted grain boundaries which are frequent in bulk
melt-textured YBaCuO samples. We present experimental data related to the flux
penetration inside a bore of MT YBaCuO rings both in the non-magnetized, virgin
state and during the field reversal. The shielding properties and their
dependence on external magnetic fields are also studied. Besides, we consider
the flux creep effects and their influence on the current re-distribution
during a dwell.Comment: 13 pages, 16 figures (EPS), RevTeX4. In the revised version,
corrections to perturbing effects near the weak links are introduced, one
more figure is added. lin
Stimulated perturbation on the neutron flux distribution in the mutually-dependent source-to-absorber geometry
The complexity of the neutron transport phenomenon throws its shadows on
every physical system wherever neutron is produced or absorbed. The Monte Carlo
N-Particle Transport Code (MCNP) was used to investigate the flux perturbations
in the neutron field caused by an absorber. The geometry of the present
experiment was designed to reach a simulation of an isotopic neutron field. The
neutron source was a AmBe with the production physics of neutrons is
dependent only on alpha-beryllium interaction and is independent of what
happened to the neutron after it was generated. The geometries have been
designed to get a volume of uniform neutron densities within a spherical volume
of radius 15 cm in every neutron energy group up to 10 MeV. Absorbers of
different dimensions were placed within the volume to investigate the field
perturbation. Different neutron absorbers were used to correlate the phenomenon
to the integral cross-section of the absorber. Flux density inside and outside
the absorber samples was determined, while the spatial neutron flux
distribution produced by the AmBe source without an absorber was taken as a
reference. This study displayed that absorbers of various dimensions perturb
the neutron field in a way that is dependent on the absorption and scattering
cross-sections, particularly in the neutron resonance region. Unlike the simple
picture of reducing the number density of neutrons, the perturbation was found
to influence the moderation of neutrons in the medium, significantly above 1
MeV.Comment: 10 pages, 13 figures, 26 reference
Perfil lipĂdico, compuestos volátiles y estabilidad oxidativa durante el almacenamiento del aceite de semilla de Opuntia ficus-indica marroquĂ
The fatty acids, sterol, tocopherol and volatile compositions of Moroccan cold-pressed cactus (Opuntia ficus-indica) seed oil were studied. The most abundant fatty acid, tocopherol and sterol were linoleic acid (60.6%), Îł-tocopherol (533 mg/kg) and β-sitosterol (6075 mg/kg), respectively. In this study, 23 volatile compounds were identified with perceivable odor attributes for 14 compounds. The oxidative quality of cactus seed oil was monitored over 4 weeks at 50 °C. Increases in PV, K232 and FFA were detected during the first two weeks as well as a decrease in the induction time; whereas no change was reported for the K270 values. The amount of total phenolic content increased until it reached 0.3 mg/kg and then decreased by the end of the storage period; while tocopherols started to decrease after the first week. The fat-free residue extracts showed a very strong effect to reduce the oxidation of linoleic acid. Consequently, the extracts were significantly more effective to bleach β-carotene in the β-carotene-linoleic acid assay in comparison with the control.Se estudiaron los ácidos grasos, esteroles, tocoferoles y la composiciĂłn volátil del aceite de semilla de cactus marroquĂ (Opuntia ficus-indica) prensado en frĂo. Los ácidos grasos, tocoferoles y esteroles más abundantes fueron el ácido linoleico (60,6%), Îł-tocoferol (533 mg/kg) y β-sitosterol (6075 mg/kg), respectivamente. En este estudio, se identificaron 23 compuestos volátiles con atributos perceptibles para 14 de ellos. La oxidaciĂłn del aceite de semilla de cactus fue monitoreada durante 4 semanas a 50°C. Se observĂł un aumento en el PV, K232 y FFA durante las dos primeras semanas y una disminuciĂłn en el tiempo de inducciĂłn, mientras que no se apreciaron cambios para los valores de K270. La cantidad de fenoles totales aumentĂł hasta alcanzar 0,3 mg/kg y luego disminuyĂł al final del almacenamiento, mientras que los tocoferoles comenzaron a disminuir despuĂ©s de la primera semana. Los extractos de residuos libres de grasa mostraron un efecto muy fuerte para reducir la oxidaciĂłn del ácido linoleico. En consecuencia, los extractos fueron significativamente más efectivos para blanquear el β-caroteno en el ensayo de β-caroteno-ácido linoleico en comparaciĂłn con el control
Mild Cognitive Impairment among Type II Diabetes Mellitus Patients Attending University Teaching Hospital
BACKGROUND: Type II diabetes mellitus (TIIDM) has been associated with structural and functional changes in the brain. TIIDM is commonly associated with obesity, insulin resistance, hypertension, and dyslipidemia, all of which can have negative impact on brain.
AIM: The aim of the study was to study the risk of mild cognitive impairment (MCI) among both diabetics and non-diabetics and to identify risk factors to MCI among both groups.
METHODS: Two comparative cross-sectional studies were carried out enrolling 100 diabetics and 100 age, sex, and education matching non-diabetics. Cognitive function was assessed using Montreal Cognitive Assessment (MoCA) test and risk factors for MCI were assessed.
RESULTS: The subjective complaint of memory impairment among diabetics was significantly higher (34%) compared to non-diabetics (13.0%), p < 0.05. The mean of objective MoCA score was significantly lower among diabetics (25.9 ± 2.5) compared to non-diabetics (27.4 ± 2.4), p < 0.001. The rate of MCI was significantly higher among TIIDM patients (22%) compared to non-diabetics (9%), p < 0.01 and odds ratio (OR) 2.8 (95% confidence interval 1.2–6.5). Among the two studied groups, the rate of MCI was significantly higher among those aged over 50 years compared to younger age as well as among hypertensive compared to non-hypertensive persons, (p < 0.05). Among diabetics, the MCI was significantly higher among those with secondary education, having heart diseases, longer duration of DM, or repeated hypoglycemia attack, p < 0.05. A healthy diet, brain training, and social activities were found to be significantly associated with normal cognition. Logistic analysis revealed that diabetics aged above 50 was the only significant predicting factor for MCI with an OR 2.9 (95% CI: 3.8–123.3), p < 0.001.
CONCLUSION: TIIDM is significantly associated with 3-times increasing risk of having MCI compared to non-diabetics. The age, hypertension, cardiovascular diseases, duration of diabetes, and frequency of hypoglycemic episodes are risk factors for cognitive impairment. A healthy diet, brain training, and social activities were associated with better cognitive function
The AKARI/IRC Mid-Infrared All-Sky Survey
Context : AKARI is the first Japanese astronomical satellite dedicated to
infrar ed astronomy. One of the main purposes of AKARI is the all-sky survey
performed with six infrared bands between 9 and 200um during the period from
2006 May 6 to
2007 August 28. In this paper, we present the mid-infrared part (9um and 18um
b ands) of the survey carried out with one of the on-board instruments, the
Infrar ed Camera (IRC). Aims : We present unprecedented observational results
of the 9 and 18um AKARI al l-sky survey and detail the operation and data
processing leading to the point s ource detection and measurements. Methods :
The raw data are processed to produce small images for every scan and point
sources candidates, above the 5-sigma noise level per single scan, are der
ived. The celestial coordinates and fluxes of the events are determined
statisti cally and the reliability of their detections is secured through
multiple detect ions of the same source within milli-seconds, hours, and months
from each other. Results : The sky coverage is more than 90% for both bands. A
total of 877,091 s ources (851,189 for 9um, 195,893 for 18um) are confirmed and
included in the cur rent release of the point source catalogue. The detection
limit for point source s is 50mJy and 90mJy for the 9um and 18um bands,
respectively. The position accu racy is estimated to be better than 2".
Uncertainties in the in-flight absolute flux calibration are estimated to be 3%
for the 9um band and 4% for the 18um ban d. The coordinates and fluxes of
detected sources in this survey are also compar ed with those of the IRAS
survey and found to be statistically consistent.Comment: Accepted for publication in AandA AKARI special issu
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