13,357 research outputs found
Jacobi Crossover Ensembles of Random Matrices and Statistics of Transmission Eigenvalues
We study the transition in conductance properties of chaotic mesoscopic
cavities as time-reversal symmetry is broken. We consider the Brownian motion
model for transmission eigenvalues for both types of transitions, viz.,
orthogonal-unitary and symplectic-unitary crossovers depending on the presence
or absence of spin-rotation symmetry of the electron. In both cases the
crossover is governed by a Brownian motion parameter {\tau}, which measures the
extent of time-reversal symmetry breaking. It is shown that the results
obtained correspond to the Jacobi crossover ensembles of random matrices. We
derive the level density and the correlation functions of higher orders for the
transmission eigenvalues. We also obtain the exact expressions for the average
conductance, average shot-noise power and variance of conductance, as functions
of {\tau}, for arbitrary number of modes (channels) in the two leads connected
to the cavity. Moreover, we give the asymptotic result for the variance of
shot-noise power for both the crossovers, the exact results being too long. In
the {\tau} \rightarrow 0 and {\tau} \rightarrow \infty limits the known results
for the orthogonal (or symplectic) and unitary ensembles are reproduced. In the
weak time-reversal symmetry breaking regime our results are shown to be in
agreement with the semiclassical predictions.Comment: 24 pages, 5 figure
Electronic conduction in a three-terminal molecular transistor
The electronic conduction of a novel, three-terminal molecular architecture,
analogous to a heterojunction bipolar transistor is studied. In this
architecture, two diode arms consisting of donor-acceptor molecular wires fuse
through a ring, while a gate modulating wire is a \pi-conjugated wire. The
calculated results show the enhancement or depletion mode of a transistor by
applying a gate field along the positive or negative direction. A small gate
field is required to switch on the current in the proposed architecture. The
changes in the electronic conduction can be attributed to the intrinsic dipolar
molecular architecture in terms of the evolution of molecular wavefunctions,
specifically the one associated with the terphenyl group of the modulating wire
in the presence of the gate field.Comment: 13 pages, 5 figure
Are We Seeing Magnetic Axis Reorientation in the Crab and Vela Pulsars?
Variation in the angle between a pulsar's rotational and magnetic
axes would change the torque and spin-down rate. We show that sudden increases
in , coincident with glitches, could be responsible for the persistent
increases in spin-down rate that follow glitches in the Crab pulsar. Moreover,
changes in at a rate similar to that inferred for the Crab pulsar
account naturally for the very low braking index of the Vela pulsar. If
increases with time, all pulsar ages obtained from the conventional
braking model are underestimates. Decoupling of the neutron star liquid
interior from the external torque cannot account for Vela's low braking index.
Variations in the Crab's pulse profile due to changes in might be
measurable.Comment: 14 pages and one figure, Latex, uses aasms4.sty. Accepted to ApJ
Letter
Availability and Usage of Information Sources and Services at Select Media Libraries in Delhi Region: A Study
Information is a basic need of today’s fast changing world important for one’s day to day life. People need information to efficiently carry out work in their respective fields. Media professionals working in Media organisations needs current, authoritative and factual information to construct news and programmes. Such information is made available by Media libraries in the shortest time frame to meet the targets of the Media Professionals. The information is collected from the printed as well from the electronic resources available in the Media libraries.
In view of the remarkable contribution made by the media libraries, the present research has been conceive with the broad objective of studying the adequacy and availability of information sources and how optimally the same has been used by the users. The study is confined to two Media Libraries such as The Indian Institute of Mass Communication Media Library and Anwar Jamal Kidwai Mass communication Research Centre Media Library in the NCT of Delhi have been taken for research investigation. The study adopted the survey method and data was gathered through close ended questionnaire and through in-depth personal interviews with the Media Professionals and media library staff. Two separate sets of questionnaire were used to elicit the desired information.
The Research investigation highlighted survey findings in term of availability of sources in two media libraries. Apart from media professionals and media librarians, the library use pattern, e-resources use pattern, library visit pattern and the problems encounter by media professionals in accessing the information sources etc. were highlighted. At the end, the researcher made some suggestions and important recommendations for the overall improvement in providing quality services to the users
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