657 research outputs found
Scheduling of users with Markovian time-varying transmission rates
We address the problem of developing a well-performing and implementable scheduler of users with wireless connection to the base station. The main feature of such real-life systems is that the quality conditions of the user channels are time-varying, which turn into the time-varying transmission rate due to different modulation and coding schemes. We assume that this phenomenon follows a Markovian law and most of the discussion is dedicated to the case of three quality conditions of each user, for which we characterize an optimal index policy and show that threshold policies (of giving higher priority to users with higher transmission rate) are not necessarily optimal. For the general case of arbitrary number of quality conditions we design a scheduler and propose its two practical approximations, and illustrate the performance of the proposed index-based schedulers and existing alternatives in a variety of simulation scenarios
MesobanK UK: an international mesothelioma bioresource.
Malignant pleural mesothelioma causes the greatest societal burden of all the asbestos-related diseases. Progress in better understanding tumour biology will be facilitated by the availability of quality-assured annotated tissue. MesobanK has been created to establish a bioresource of pleural mesothelioma tissue linked to detailed anonymised clinical data. When complete, the bioresource will comprise a 750-patient tissue microarray and prospectively collected tissue, blood and pleural fluid from 300 patients with mesothelioma. Twenty-six new cell lines have also been developed. MesobanK meets all appropriate ethical and regulatory procedures and has recently opened to requests for tissue and data.RCR and DMR are part funded by the Cambridge Biomedical Research Centre and the Cambridge Cancer Centre. RCR is also funded by the NIHR Clinical Research Network: Eastern.This is the final version of the article. It first appeared from BMJ via http://dx.doi.org/10.1136/thoraxjnl-2015-20749
Prospects for rapid deceleration of small molecules by optical bichromatic forces
We examine the prospects for utilizing the optical bichromatic force (BCF) to
greatly enhance laser deceleration and cooling for near-cycling transitions in
small molecules. We discuss the expected behavior of the BCF in near-cycling
transitions with internal degeneracies, then consider the specific example of
decelerating a beam of calcium monofluoride molecules. We have selected CaF as
a prototype molecule both because it has an easily-accessible near-cycling
transition, and because it is well-suited to studies of ultracold molecular
physics and chemistry. We also report experimental verification of one of the
key requirements, the production of large bichromatic forces in a multi-level
system, by performing tests in an atomic beam of metastable helium.Comment: 11 pages, 6 figures, revised version, to be published in Physical
Review
The Self-Administered Witness Interview Tool (SAW-IT): Enhancing witness recall of workplace incidents
Given the often crucial role of witness evidence in Occupational Health and Safety investigation, statements should be obtained as soon as possible after an incident using best practice methods. The present research systematically tested the efficacy of a novel Self-Administered Witness Interview Tool (SAW-IT); an adapted version of the Self-Administered Interview (SAI©) designed to elicit comprehensive information from witnesses to industrial events. The present study also examined whether completing the SAW-IT mitigated the effect of schematic processing on witness recall. Results indicate that the SAW-IT elicited significantly more correct details, as well as more precise information than a traditional incident report form. Neither the traditional report from, nor the SAW-IT mitigated against biasing effects of contextual information about a worker’s safety history, confirming that witnesses should be shielded from extraneous post-event information prior to reporting. Importantly, these results demonstrate that the SAW-IT can enhance the quality of witness reports
Quantum computing with antiferromagnetic spin clusters
We show that a wide range of spin clusters with antiferromagnetic
intracluster exchange interaction allows one to define a qubit. For these spin
cluster qubits, initialization, quantum gate operation, and readout are
possible using the same techniques as for single spins. Quantum gate operation
for the spin cluster qubit does not require control over the intracluster
exchange interaction. Electric and magnetic fields necessary to effect quantum
gates need only be controlled on the length scale of the spin cluster rather
than the scale for a single spin. Here, we calculate the energy gap separating
the logical qubit states from the next excited state and the matrix elements
which determine quantum gate operation times. We discuss spin cluster qubits
formed by one- and two-dimensional arrays of s=1/2 spins as well as clusters
formed by spins s>1/2. We illustrate the advantages of spin cluster qubits for
various suggested implementations of spin qubits and analyze the scaling of
decoherence time with spin cluster size.Comment: 15 pages, 7 figures; minor change
Bi-stable tunneling current through a molecular quantum dot
An exact solution is presented for tunneling through a negative-U d-fold
degenerate molecular quantum dot weakly coupled to electrical leads. The tunnel
current exhibits hysteresis if the level degeneracy of the negative-U dot is
larger than two (d>2). Switching occurs in the voltage range V1 < V < V2 as a
result of attractive electron correlations in the molecule, which open up a new
conducting channel when the voltage is above the threshold bias voltage V2.
Once this current has been established, the extra channel remains open as the
voltage is reduced down to the lower threshold voltage V1. Possible
realizations of the bi-stable molecular quantum dots are fullerenes, especially
C60, and mixed-valence compounds.Comment: 5 pages, 1 figure. (v2) Figure updated to compare the current
hysteresis for degeneracies d=4 and d>>1 of the level in the dot, minor
corrections in the text. To appear in Phys. Rev.
On the Spiral Structure of the Milky Way Galaxy
We consider the possible pattern of the overall spiral structure of the
Galaxy, using data on the distribution of neutral (atomic), molecular, and
ionized hydrogen, on the base of the hypothesis of the spiral structure being
symmetric, i.e. the assumption that spiral arms are translated into each other
for a rotation around the galactic center by 180{\deg} (a two-arm pattern) or
by 90{\deg} (a four-arm pattern). We demonstrate that, for the inner region,
the observations are best represented with a four-arm scheme of the spiral
pattern, associated with all-Galaxy spiral density waves. The basic position is
that of the Carina arm, reliably determined from distances to HII regions and
from HI and H2 radial velocities. This pattern is continued in the quadrants
III and IV with weak outer HI arms; from their morphology, the Galaxy should be
considered an asymmetric multi-arm spiral. The kneed shape of the outer arms
that consist of straight segments can indicate that these arms are transient
formations that appeared due to a gravitational instability in the gas disk.
The distances between HI superclouds in the two arms that are the brightest in
neutral hydrogen, the Carina arm and the Cygnus (Outer) arm, concentrate to two
values, permitting to assume the presence of a regular magnetic field in these
arms.Comment: 21 pages, 14 fugures; accepted for publication in Astronomichesky
Journal (Astron. Rep.
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