9,963 research outputs found
Piezoelectric rotator for studying quantum effects in semiconductor nanostructures at high magnetic fields and low temperatures
We report the design and development of a piezoelectric sample rotation
system, and its integration into an Oxford Instruments Kelvinox 100 dilution
refrigerator, for orientation-dependent studies of quantum transport in
semiconductor nanodevices at millikelvin temperatures in magnetic fields up to
10T. Our apparatus allows for continuous in situ rotation of a device through
>100deg in two possible configurations. The first enables rotation of the field
within the plane of the device, and the second allows the field to be rotated
from in-plane to perpendicular to the device plane. An integrated angle sensor
coupled with a closed-loop feedback system allows the device orientation to be
known to within +/-0.03deg whilst maintaining the sample temperature below
100mK.Comment: 8 pages, 5 figure
Schwinger's Propagator Is Only A Green's Function
Schwinger used an analytic continuation of the effective action to correctly
compute the particle production rate per unit volume for QED in a uniform
electric field. However, if one simply evaluates the one loop expectation value
of the current operator using his propagator, the result is zero! We analyze
this curious fact from the context of a canonical formalism of operators and
states. The explanation turns out to be that Schwinger's propagator is not
actually the expectation value of the time-ordered product of field operators
in the presence of a time-independent state, although it is of course a Green's
function. We compute the true propagator in the presence of a state which is
empty at where is the lightcone
evolution parameter. Our result can be generalized to electric fields which
depend arbitrarily on .Comment: 18 pages, LaTeX 2 epsilo
Bayesian model of HIV/AIDS in India: A spatial analysis
Background: Bayesian models are very aexible enough to incorporate spatial correlation and to
!&$jut overall mean ratio when relatively few cases exist whereas our conventional Disease mapping has
beral limitation and it requires the Standardization Incidence Ratio which is derived from observed
cases to what might be expected from larger population. This study explains the importance and advantage
of Bayesian methods in Disease mapping
Online Corpora for English Language Learning
The use of corpora and corpus- based materials has set a trend in language teaching and learning. This paper discusses how the corpora can be utilised for learning as suggested by various experts. Then it provides a framework about learner corpora and the information that is available to support teachers in understanding the mistakes that are frequently made by students. The paper also presents the list of websites for learner corpora. Finally, the issues involved in using corpora are discussed. Keywords: online corpora, language learning
On long-wavelength magnetic anomalies over Indian region
A data set composed of vector magnetic measurements obtained by MAGSAT and very accurate altitude determinations made using Sun sensors and star cameras was used to obtain data for very quiet days over the Indian region at 10 S to 40 N and 60 E to 110 E in an effort to determine the validity of quantitative estimates made from aeromagnetic data obtained by removing the core field. To further account for the external effects, the ring current contributions estimated using both X and Z variations were subtracted from the observed values. Before this, the core contribution was eliminated through a spherical harmonic expansion with terms up to N=13. Analysis of the residual measurements using Fast Fourier techniques indicates that the anomalies contain substantial power for wavelengths of about 1500 kms. Because the ring current effect has a spatial structure of this dimension over India, efforts are being made to exactly eliminate these two interfering effects from the data
Identification of critical residues in loop E in the 5-HT(3AS)R binding site
BACKGROUND: The serotonin type 3 receptor (5-HT(3)R) is a member of a superfamily of ligand gated ion channels. All members of this family share a large degree of sequence homology and presumably significant structural similarity. A large number of studies have explored the structure-function relationships of members of this family, particularly the nicotinic and GABA receptors. This information can be utilized to gain additional insights into specific structural and functional features of other receptors in this family. RESULTS: Thirteen amino acids in the mouse 5-HT(3AS)R that correspond to the putative E binding loop of the nicotinic α7 receptor were chosen for mutagenesis. Due to the presence of a highly conserved glycine in this region, it has been suggested that this binding loop is comprised of a hairpin turn and may form a portion of the ligand-binding site in this ion channel family. Mutation of the conserved glycine (G147) to alanine eliminated binding of the 5-HT(3)R antagonist [(3)H]granisetron. Three tyrosine residues (Y140, Y142 and Y152) also significantly altered the binding of 5-HT(3)R ligands. Mutations in neighboring residues had little or no effect on binding of these ligands to the 5-HT(3AS)R. CONCLUSION: Our data supports a role for the putative E-loop region of the 5-HT(3)R in the binding of 5-HT, mCPBG, d-tc and lerisetron. 5-HT and mCPBG interact with Y142, d-tc with Y140 and lerisetron with both Y142 and Y152. Our data also provides support for the hypothesis that this region of the receptor is present in a loop structure
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