23,032 research outputs found
Search procedures revisited
Search Procedures reflects on a series of studies carried out over a four year period in the late 1970s. It was published at an interesting time for Information Retrieval. Written before Information Retrieval became synonymous with online information seeking it focuses on Information Retrieval within Public Libraries, then the major location for everyday information seeking. While many of his contemporaries focused on information seeking in academic or special library settings, Peter chose instead to focus a setting that was visited by a more diverse set of people with a broader range of information needs
Polarization dependent photoionization cross-sections and radiative lifetimes of atomic states in Ba
The photoionization cross-sections of two even-parity excited states, and , of atomic Ba at the ionization-laser wavelength of
556.6 nm were measured. We found that the total cross-section depends on the
relative polarization of the atoms and the ionization-laser light. With
density-matrix algebra, we show that, in general, there are at most three
parameters in the photoionization cross-section. Some of these parameters are
determined in this work. We also present the measurement of the radiative
lifetime of five even-parity excited states of barium.Comment: 11 pages, 7 figure
Induced superfluidity of imbalanced Fermi gases near unitarity
The induced intraspecies interactions among the majority species, mediated by
the minority species, is computed for a population-imbalanced two-component
Fermi gas. Although the Feshbach-resonance mediated interspecies interaction is
dominant for equal populations, leading to singlet s-wave pairing, we find that
in the strongly imbalanced regime the induced intraspecies interaction leads to
p-wave pairing and superfluidity of the majority species. Thus, we predict that
the observed spin-polaron Fermi liquid state in this regime is unstable to
p-wave superfluidity, in accordance with the results of Kohn and Luttinger,
below a temperature that, near unitarity, we find to be within current
experimental capabilities. Possible experimental signatures of the p-wave state
using radio-frequency spectroscopy as well as density-density correlations
after free expansion are presented.Comment: 15 pages, 13 figures, submitted to Phys. Rev.
Quenching of Spin Hall Effect in Ballistic nano-junctions
We show that a nanometric four-probe ballistic junction can be used to check
the presence of a transverse spin Hall current in a system with a Spin Orbit
coupling not of the Rashba type, but rather due to the in-plane electric field.
Indeed, the spin Hall effect is due to the presence of an effective small
transverse magnetic field corresponding to the Spin Orbit coupling generated by
the confining potential. The strength of the field and the junction shape
characterize the quenching Hall regime, usually studied by applying
semi-classical approaches. We discuss how a quantum mechanical relativistic
effect, such as the Spin Orbit one, can be observed in a low energy system and
explained by using classical mechanics techniques.Comment: 5 pages, 4 figures, PACS: 72.25.-b, 72.20.My, 73.50.Jt, to appear in
Phys. Rev.
Wide energy-window view on the density of states and hole mobility of poly(p-phenylene vinylene)
Using an electrochemically gated transistor, we achieved controlled and
reversible doping of poly(p-phenylene vinylene) in a large concentration range.
Our data open a wide energy-window view on the density of states (DOS) and
show, for the first time, that the core of the DOS function is Gaussian, while
the low-energy tail has a more complex structure. The hole mobility increases
by more than four orders of magnitude when the electrochemical potential is
scanned through the DOS.Comment: 4 pages, 4 figure
Integer Spin Hall Effect in Ballistic Quantum Wires
We investigate the ballistic electron transport in a two dimensional Quantum
Wire under the action of an electric field (). We demonstrate how the
presence of a Spin Orbit coupling, due to the uniform electric confinement
field gives a non-commutative effect as in the presence of a transverse
magnetic field.
We discuss how the non commutation implies an edge localization of the
currents depending on the electron spins also giving a semi-classical spin
dependent Hall current.
We also discuss how it is possible obtain a quantized Spin Hall conductance
in the ballistic transport regime by developing the Landauer formalism and show
the coupling between the spin magnetic momentum and the orbital one due to the
presence of a circulating current.Comment: 7 pages, 5 figures, accepted for publication in Phys. Rev. B, PACS:
72.25.-b, 72.10.-d, 72.15.Rn, 73.23.-b, 71.10.P
Healthiness from Duality
Healthiness is a good old question in program logics that dates back to
Dijkstra. It asks for an intrinsic characterization of those predicate
transformers which arise as the (backward) interpretation of a certain class of
programs. There are several results known for healthiness conditions: for
deterministic programs, nondeterministic ones, probabilistic ones, etc.
Building upon our previous works on so-called state-and-effect triangles, we
contribute a unified categorical framework for investigating healthiness
conditions. We find the framework to be centered around a dual adjunction
induced by a dualizing object, together with our notion of relative
Eilenberg-Moore algebra playing fundamental roles too. The latter notion seems
interesting in its own right in the context of monads, Lawvere theories and
enriched categories.Comment: 13 pages, Extended version with appendices of a paper accepted to
LICS 201
Tunable far infrared studies of molecular parameters in support of stratospheric measurements
Lab studies were made in support of far infrared spectroscopy of the stratosphere using the Tunable Far InfraRed (TuFIR) method of ultrahigh resolution spectroscopy and, more recently, spectroscopic and retrieval calculations performed in support of satellite-based atmospheric measurement programs: the Global Ozone Monitoring Experiment (GOME), and the SCanning Imaging Absorption spectroMeter for Atmospheric CHartographY (SCIAMACHY)
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