13,689 research outputs found
Large Magnetoresistance and Jahn Teller effect in SrFeCoO
Neutron diffraction measurement on the spin glass double perovskite
SrFeCoO reveals site disorder as well as Co intermediate spin
state. In addition, multiple valence states of Fe and Co are confirmed through
M\"{o}ssbauer and X-ray photoelectron spectroscopy. The structural disorder and
multiple valence lead to competing ferromagnetic and antiferromagnetic
interactions and subsequently to a spin glass state, which is reflected in the
form of an additional -linear contribution at low temperatures in specific
heat. A clear evidence of Jahn-Teller distortion at the Co-O complex
is observed and incorporating the physics of Jahn-Teller effect, the presence
of localized magnetic moment is shown. A large, negative and anomalous
magnetoresistance of 63% at 14K in 12T applied field is observed for
SrFeCoO. The observed magnetoresistance could be explained by applying
a semi-empirical fit consisting of a negative and a positive contribution and
show that the negative magnetoresistance is due to spin scattering of carriers
by localized magnetic moments in the spin glass phase
Edible oysters — Present status of product development and domestic market potential in India
The fishery for oyster is worldwide. Extensive
scientific studies on this species have taken
place in our country also and the fishery, though
in a moderate scale, is in existence along the
coasts of Maharashtra and Kerala
Size effect in ion transport through angstrom-scale slits
It has been an ultimate but seemingly distant goal of nanofluidics to
controllably fabricate capillaries with dimensions approaching the size of
small ions and water molecules. We report ion transport through ultimately
narrow slits that are fabricated by effectively removing a single atomic plane
from a bulk crystal. The atomically flat angstrom-scale slits exhibit little
surface charge, allowing elucidation of the role of steric effects. We find
that ions with hydrated diameters larger than the slit size can still permeate
through, albeit with reduced mobility. The confinement also leads to a notable
asymmetry between anions and cations of the same diameter. Our results provide
a platform for studying effects of angstrom-scale confinement, which is
important for development of nanofluidics, molecular separation and other
nanoscale technologies
Mitochondrial Function as a Determinant of Life Span
Average human life expectancy has progressively increased over many decades largely due to improvements in nutrition, vaccination, antimicrobial agents, and effective treatment/prevention of cardiovascular disease, cancer, etc. Maximal life span, in contrast, has changed very little. Caloric restriction (CR) increases maximal life span in many species, in concert with improvements in mitochondrial function. These effects have yet to be demonstrated in humans, and the duration and level of CR required to extend life span in animals is not realistic in humans. Physical activity (voluntary exercise) continues to hold much promise for increasing healthy life expectancy in humans, but remains to show any impact to increase maximal life span. However, longevity in Caenorhabditis elegans is related to activity levels, possibly through maintenance of mitochondrial function throughout the life span. In humans, we reported a progressive decline in muscle mitochondrial DNA abundance and protein synthesis with age. Other investigators also noted age-related declines in muscle mitochondrial function, which are related to peak oxygen uptake. Long-term aerobic exercise largely prevented age-related declines in mitochondrial DNA abundance and function in humans and may increase spontaneous activity levels in mice. Notwithstanding, the impact of aerobic exercise and activity levels on maximal life span is uncertain. It is proposed that age-related declines in mitochondrial content and function not only affect physical function, but also play a major role in regulation of life span. Regular aerobic exercise and prevention of adiposity by healthy diet may increase healthy life expectancy and prolong life span through beneficial effects at the level of the mitochondrion
Quality of multiple choice questions in undergraduate pharmacology assessments in a teaching hospital of Kerala, India: an item analysis
Background: Carefully constructed, high quality multiple choice questions can serve as effective tools to improve standard of teaching. This item analysis was performed to find the difficulty index, discrimination index and number of non functional distractors in single best response type questions.Methods: 40 single best response type questions with four options, each carrying one mark for the correct response, was taken for item analysis. There was no negative marking. The maximum marks was 40. Based on the scores, the evaluated answer scripts were arranged with the highest score on top and the least score at the bottom. Only the upper third and lower third were included. The response to each item was entered in Microsoft excel 2010. Difficulty index, Discrimination index and number of non functional distractors per item were calculated.Results: 40 multiple choice questions and 120 distractors were analysed in this study. 72.5% items were good with a difficulty index between 30%-70%. 25% items were difficult and 2.5% items were easy. 27.5% items showed excellent discrimination between high scoring and low scoring students. One item had a negative discrimination index (-0.1). There were 9 items with non functional distractors.Conclusions: This study emphasises the need for improving the quality of multiple choice questions. Hence repeated evaluation by item analysis and modification of non functional distractors may be performed to enhance standard of teaching in Pharmacology
Biexciton recombination rates in self-assembled quantum dots
The radiative recombination rates of interacting electron-hole pairs in a
quantum dot are strongly affected by quantum correlations among electrons and
holes in the dot. Recent measurements of the biexciton recombination rate in
single self-assembled quantum dots have found values spanning from two times
the single exciton recombination rate to values well below the exciton decay
rate. In this paper, a Feynman path-integral formulation is developed to
calculate recombination rates including thermal and many-body effects. Using
real-space Monte Carlo integration, the path-integral expressions for realistic
three-dimensional models of InGaAs/GaAs, CdSe/ZnSe, and InP/InGaP dots are
evaluated, including anisotropic effective masses. Depending on size, radiative
rates of typical dots lie in the regime between strong and intermediate
confinement. The results compare favorably to recent experiments and
calculations on related dot systems. Configuration interaction calculations
using uncorrelated basis sets are found to be severely limited in calculating
decay rates.Comment: 11 pages, 4 figure
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