18,947 research outputs found
Exact Nonperturbative Unitary Amplitudes for 1->N Transitions
I present an extension to arbitrary N of a previously proposed field
theoretic model, in which unitary amplitudes for processes were
obtained. The Born amplitude in this extension has the behavior
expected in a bosonic field theory. Unitarity
is violated when , or when Numerical
solutions of the coupled Schr\"odinger equations shows that for weak coupling
and a large range of N>\ncrit, the exact unitary amplitude is reasonably fit
by a factorized expression |A(1->N)| \sim (0.73 /N) \cdot \exp{(-0.025/\g2)}.
The very small size of the coefficient 1/\g2 , indicative of a very weak
exponential suppression, is not in accord with standard discussions based on
saddle point analysis, which give a coefficient The weak dependence
on could have experimental implications in theories where the exponential
suppression is weak (as in this model). Non-perturbative contributions to
few-point correlation functions in this theory would arise at order $K\ \simeq\
\left((0.05/\g2)+ 2\ ln{N}\right)/ \ ln{(1/\g2)}\g2.$Comment: 11 pages, 3 figures (not included
Lunar contour mapping system /lucom/ final report, 5 aug. 1964 - 18 mar. 1965
Radar sensor system for acquisition of lunar surface data - Lunar contour mapping syste
The general relativistic infinite plane
Uniform fields are one of the simplest and most pedagogically useful examples
in introductory courses on electrostatics or Newtonian gravity. In general
relativity there have been several proposals as to what constitutes a uniform
field. In this article we examine two metrics that can be considered the
general relativistic version of the infinite plane with finite mass per unit
area. The first metric is the 4D version of the 5D "brane" world models which
are the starting point for many current research papers. The second case is the
cosmological domain wall metric. We examine to what extent these different
metrics match or deviate from our Newtonian intuition about the gravitational
field of an infinite plane. These solutions provide the beginning student in
general relativity both computational practice and conceptual insight into
Einstein's field equations. In addition they do this by introducing the student
to material that is at the forefront of current research.Comment: Accepted for publication in the American Journal of Physic
Reconstruction of Cluster Masses using Particle Based Lensing I: Application to Weak Lensing
We present Particle-Based Lensing (PBL), a new technique for gravitational
lensing mass reconstructions of galaxy clusters. Traditionally, most methods
have employed either a finite inversion or gridding to turn observational
lensed galaxy ellipticities into an estimate of the surface mass density of a
galaxy cluster. We approach the problem from a different perspective, motivated
by the success of multi-scale analysis in smoothed particle hydrodynamics. In
PBL, we treat each of the lensed galaxies as a particle and then reconstruct
the potential by smoothing over a local kernel with variable smoothing scale.
In this way, we can tune a reconstruction to produce constant signal-noise
throughout, and maximally exploit regions of high information density.
PBL is designed to include all lensing observables, including multiple image
positions and fluxes from strong lensing, as well as weak lensing signals
including shear and flexion. In this paper, however, we describe a shear-only
reconstruction, and apply the method to several test cases, including simulated
lensing clusters, as well as the well-studied ``Bullet Cluster'' (1E0657-56).
In the former cases, we show that PBL is better able to identify cusps and
substructures than are grid-based reconstructions, and in the latter case, we
show that PBL is able to identify substructure in the Bullet Cluster without
even exploiting strong lensing measurements. We also make our codes publicly
available.Comment: Accepted for publication in ApJ; Codes available at
http://www.physics.drexel.edu/~deb/PBL.htm ; 12 pages,9 figures, section 3
shortene
Design of a fault tolerant airborne digital computer. Volume 1: Architecture
This volume is concerned with the architecture of a fault tolerant digital computer for an advanced commercial aircraft. All of the computations of the aircraft, including those presently carried out by analogue techniques, are to be carried out in this digital computer. Among the important qualities of the computer are the following: (1) The capacity is to be matched to the aircraft environment. (2) The reliability is to be selectively matched to the criticality and deadline requirements of each of the computations. (3) The system is to be readily expandable. contractible, and (4) The design is to appropriate to post 1975 technology. Three candidate architectures are discussed and assessed in terms of the above qualities. Of the three candidates, a newly conceived architecture, Software Implemented Fault Tolerance (SIFT), provides the best match to the above qualities. In addition SIFT is particularly simple and believable. The other candidates, Bus Checker System (BUCS), also newly conceived in this project, and the Hopkins multiprocessor are potentially more efficient than SIFT in the use of redundancy, but otherwise are not as attractive
Stakeholder perspectives on the development of a virtual clinic for diabetes care : qualitative study
Background: The development of the Internet has created new opportunities for health care provision, including its use as a
tool to aid the self-management of chronic conditions. We studied stakeholder reactions to an Internet-based “virtual clinic,”
which would allow people with diabetes to communicate with their health care providers, find information about their condition,
and share information and support with other users.
Objective: The aim of the study was to present the results of a detailed consultation with a variety of stakeholder groups in
order to identify what they regard as the desirable, important, and feasible characteristics of an Internet-based intervention to aid
diabetes self-management.
Methods: Three focus groups were conducted with 12 people with type 1 diabetes who used insulin pumps. Participants were
recruited through a local diabetes clinic. One-on-one interviews were conducted with 5 health care professionals from the same
clinic (2 doctors, 2 nurses, 1 dietitian) and with 1 representative of an insulin pump company. We gathered patient consensus via
email on the important and useful features of Internet-based systems used for other chronic conditions (asthma, epilepsy, myalgic
encephalopathy, mental health problems). A workshop to gather expert consensus on the use of information technology to improve
the care of young people with diabetes was organized.
Results: Stakeholder groups identified the following important characteristics of an Internet-based virtual clinic: being grounded
on personal needs rather than only providing general information; having the facility to communicate with, and learn from, peers;
providing information on the latest developments and news in diabetes; being quick and easy to use. This paper discusses these
characteristics in light of a review of the relevant literature. The development of a virtual clinic for diabetes that embodies these
principles, and that is based on self-efficacy theory, is described.
Conclusions: Involvement of stakeholders is vital early in the development of a complex intervention. Stakeholders have clear
and relevant views on what a virtual clinic system should provide, and these views can be captured and synthesized with relative
ease. This work has led to the design of a system that is able to meet user needs and is currently being evaluated in a pilot study
Early detection of Haemonchus contortus infection in sheep using three different faecal occult blood tests
Haemonchus contortus is a blood-sucking parasite causing the presence of faecal occult blood (FOB). The objective was to study three different FOB tests in order to have a new indicator of H. contortus infection in sheep that could be included in the genetic evaluation system as an alternative selection criterion to faecal worm egg count (FEC). A total of 29 Corriedale lambs were experimentally infected with 10.000 larvae of H. contortus. Stool samples were recorded for FEC and FOB tests (Hexagon, Hematest® and Multistix®), blood for packed cell volume (PCV), haemoglobin, white and red blood cell count (RBC), and FAMACHA© for scoring anaemia. At the end of the experiment lambs were slaughtered to worm burden count. Field infection was achieved in 309 Merino lambs under natural parasite challenge. FEC data were normalized through logarithmic transformation (LnFEC). Pearson correlation was estimated to examine the relationship between all traits. The three tests were able to detect the presence of FOB at day 11. FEC, PCV and RBC decreased to sub-normal values from day 18. FAMACHA© score 3 was considered to be indicative of anaemia. Most of the correlations were of high magnitude, with the exception of Multistix® test that was moderately correlated with haematological parameters, LnFEC and FEC. In field infection, most samples were negative to FOB tests and the correlations were lower than those calculated under experimental infection. In conclusion, FOB tests were able to detect haemonchosis earlier than FEC under high experimental parasite challenge. However, they were not able to detect FOB under natural mixed parasite challenge. FAMACHA© and PCV demonstrated to be good indicators of Haemonchosis, having moderate to high correlations with FEC.Keywords: Faecal occult blood test, Faecal worm egg count, Haemonchosis, Sheep
Differential Forms and Wave Equations for General Relativity
Recently, Choquet-Bruhat and York and Abrahams, Anderson, Choquet-Bruhat, and
York (AACY) have cast the 3+1 evolution equations of general relativity in
gauge-covariant and causal ``first-order symmetric hyperbolic form,'' thereby
cleanly separating physical from gauge degrees of freedom in the Cauchy problem
for general relativity. A key ingredient in their construction is a certain
wave equation which governs the light-speed propagation of the extrinsic
curvature tensor. Along a similar line, we construct a related wave equation
which, as the key equation in a system, describes vacuum general relativity.
Whereas the approach of AACY is based on tensor-index methods, the present
formulation is written solely in the language of differential forms. Our
approach starts with Sparling's tetrad-dependent differential forms, and our
wave equation governs the propagation of Sparling's 2-form, which in the
``time-gauge'' is built linearly from the ``extrinsic curvature 1-form.'' The
tensor-index version of our wave equation describes the propagation of (what is
essentially) the Arnowitt-Deser-Misner gravitational momentum.Comment: REVTeX, 26 pages, no figures, 1 macr
End of the cosmic neutrino energy spectrum
There may be a high-energy cutoff of neutrino events in IceCube data. In
particular, IceCube does not observe either continuum events above 2 PeV, or
the Standard Model Glashow-resonance events expected at 6.3 PeV. There are also
no higher energy neutrino signatures in the ANITA and Auger experiments. This
absence of high-energy neutrino events motivates a fundamental restriction on
neutrino energies above a few PeV. We postulate a simple scenario to terminate
the neutrino spectrum that is Lorentz-invariance violating, but with a limiting
neutrino velocity that is always smaller than the speed of light. If the
limiting velocity of the neutrino applies also to its associated charged
lepton, then a significant consequence is that the two-body decay modes of the
charged pion are forbidden above two times the maximum neutrino energy, while
the radiative decay modes are suppressed at higher energies. Such stabilized
pions may serve as cosmic ray primaries.Comment: 6 pages. Version to appear in PL
Automated multigravity assist trajectory planning with a modified ant colony algorithm
The paper presents an approach to transcribe a multigravity assist trajectory design problem into an integrated planning and scheduling problem. A modified Ant Colony Optimization (ACO) algorithm is then used to generate optimal plans corresponding to optimal sequences of gravity assists and deep space manoeuvers to reach a given destination. The modified Ant Colony Algorithm is based on a hybridization between standard ACO paradigms and a tabu-based heuristic. The scheduling algorithm is integrated into the trajectory model to provide a fast time-allocation of the events along the trajectory. The approach demonstrated to be very effective on a number of real trajectory design problems
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