33,496 research outputs found
The many levels pairing Hamiltonian for two pairs
We address the problem of two pairs of fermions living on an arbitrary number
of single particle levels of a potential well (mean field) and interacting
through a pairing force. The associated solutions of the Richardson's equations
are classified in terms of a number , which reduces to the seniority
in the limit of large values of the pairing strength and yields the number
of pairs not developing a collective behaviour, their energy remaining finite
in the limit. We express analytically, through the moments of the
single particle levels distribution, the collective mode energy and the two
critical values and of the coupling which can
exist on a single particle level with no pair degeneracy. Notably and merge when the number of single particle levels
goes to infinity, where they coincide with the (when it exists) of
a one pair system, not envisioned by the Richardson theory. In correspondence
of the system undergoes a transition from a mean field to a
pairing dominated regime. We finally explore the behaviour of the excitation
energies, wave functions and pair transfer amplitudes finding out that the
former, for , come close to the BCS predictions, whereas the
latter display a divergence at , signaling the onset of a long
range off-diagonal order in the system.Comment: 35 pages, 6 figures, 2 tables, to be published in EPJ
On the analytic solution of the pairing problem: one pair in many levels
We search for approximate, but analytic solutions of the pairing problem for
one pair of nucleons in many levels of a potential well. For the collective
energy a general formula, independent of the details of the single particle
spectrum, is given in both the strong and weak coupling regimes. Next the
displacements of the solutions trapped in between the single particle levels
with respect to the unperturbed energies are explored: their dependence upon a
suitably defined quantum number is found to undergo a transition between two
different regimes.Comment: 30 pages, AMS Latex, 8 figures. Submitted to Phys. Rev.
Reducing inappropriate antibiotics prescribing: The role of online commentary on physical examination findings
Objective: This study investigates the relationship of âonline commentaryâ(contemporaneous physician comments about physical examination [PE] findings) with (i) parent questioning of the treatment recommendation and (ii) inappropriate antibiotic prescribing. Methods: A nested cross-sectional study of 522 encounters motivated by upper respiratory symptoms in 27 California pediatric practices (38 pediatricians). Physicians completed a post-visit survey regarding physical examination findings, diagnosis, treatment, and whether they perceived the parent as expecting an antibiotic. Taped encounters were coded for âproblemâ online commentary (PE findings discussed as significant or clearly abnormal) and âno problemâ online commentary (PE findings discussed reassuringly as normal or insignificant). Results: Online commentary during the PE occurred in 73% of visits with viral diagnoses (n = 261). Compared to similar cases with âno problemâ online commentary, âproblemâ comments were associated with a 13% greater probability of parents uestioning a non-antibiotic treatment plan (95% CI 0-26%, p = .05,) and a 27% (95% CI: 2-52%, p < .05) greater probability of an inappropriate antibiotic prescription. Conclusion: With viral illnesses, problematic online comments are associated with more pediatrician-parent conflict over non-antibiotic treatment recommendations. This may increase inappropriate antibiotic prescribing. Practice implications: In viral cases, physicians should consider avoiding the use of problematic online commentary
Novel atmospheric extinction measurement techniques for aerospace laser system applications
Novel techniques for laser beam atmospheric extinction measurements, suitable for manned and unmanned aerospace vehicle applications, are presented in this paper. Extinction measurements are essential to support the engineering development and the operational employment of a variety of aerospace electro-optical sensor systems, allowing calculation of the range performance attainable with such systems in current and likely future applications. Such applications include ranging, weaponry, Earth remote sensing and possible planetary exploration missions performed by satellites and unmanned flight vehicles. Unlike traditional LIDAR methods, the proposed techniques are based on measurements of the laser energy (intensity and spatial distribution) incident on target surfaces of known geometric and reflective characteristics, by means of infrared detectors and/or infrared cameras calibrated for radiance. Various laser sources can be employed with wavelengths from the visible to the far infrared portions of the spectrum, allowing for data correlation and extended sensitivity. Errors affecting measurements performed using the proposed methods are discussed in the paper and algorithms are proposed that allow a direct determination of the atmospheric transmittance and spatial characteristics of the laser spot
The integration of on-line monitoring and reconfiguration functions using IEEE1149.4 into a safety critical automotive electronic control unit.
This paper presents an innovative application of IEEE 1149.4 and the integrated diagnostic reconfiguration (IDR) as tools for the implementation of an embedded test solution for an automotive electronic control unit, implemented as a fully integrated mixed signal system. The paper describes how the test architecture can be used for fault avoidance with results from a hardware prototype presented. The paper concludes that fault avoidance can be integrated into mixed signal electronic systems to handle key failure modes
New techniques for laser beam atmospheric extinction measurements from manned and unmanned aerospace vehicles
Novel techniques for laser beam atmospheric extinction measurements, suitable for several air and space platform applications, are presented in this paper. Extinction measurements are essential to support the engineering development and the operational employment of a variety of aerospace electro-optical sensor systems, allowing calculation of the range performance attainable with such systems in current and likely future applications. Such applications include ranging, weaponry, Earth remote sensing and possible planetary exploration missions performed by satellites and unmanned flight vehicles. Unlike traditional LIDAR methods, the proposed techniques are based on measurements of the laser energy (intensity and spatial distribution) incident on target surfaces of known geometric and reflective characteristics, by means of infrared detectors and/or infrared cameras calibrated for radiance. Various laser sources can be employed with wavelengths from the visible to the far infrared portions of the spectrum, allowing for data correlation and extended sensitivity. Errors affecting measurements performed using the proposed methods are discussed in the paper and algorithms are proposed that allow a direct determination of the atmospheric transmittance and spatial characteristics of the laser spot. These algorithms take into account a variety of linear and non-linear propagation effects. Finally, results are presented relative to some experimental activities performed to validate the proposed techniques. Particularly, data are presented relative to both ground and flight trials performed with laser systems operating in the near infrared (NIR) at ?= 1064 nm and ?= 1550 nm. This includes ground tests performed with 10 Hz and 20 KHz PRF NIR laser systems in a large variety of atmospheric conditions, and flight trials performed with a 10 Hz airborne NIR laser system installed on a TORNADO aircraft, flying up to altitudes of 22,000 ft
Modular converter system for low-cost off-grid energy storage using second life Li-ion batteries
Lithium ion batteries are promising for small off- grid energy storage
applications in developing countries because of their high energy density and
long life. However, costs are prohibitive. Instead, we consider 'used' Li-ion
batteries for this application, finding experimentally that many discarded
laptop cells, for example, still have good capacity and cycle life. In order to
make safe and optimal use of such cells, we present a modular power management
system using a separate power converter for every cell. This novel approach
allows individual batteries to be used to their full capacity. The power
converters operate in voltage droop control mode to provide easy charge
balancing and implement a battery management system to estimate the capacity of
each cell, as we demonstrate experimentally.Comment: Presented at IEEE GHTC Oct 10-14, 2014, Silicon Valle
Design-for-test structure to facilitate test vector application with low performance loss in non-test mode.
A switching based circuit is described which allows application of voltage test vectors to internal nodes of a chip without the problem of backdriving. The new circuit has low impact on the performance of an analogue circuit in terms of loss of bandwidth and allows simple application of analogue test voltages into internal nodes. The circuit described facilitates implementation of the forthcoming IEEE 1149.4 DfT philosophy [1]
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