608 research outputs found
Supersymmetric Many-particle Quantum Systems with Inverse-square Interactions
The development in the study of supersymmetric many-particle quantum systems
with inverse-square interactions is reviewed. The main emphasis is on quantum
systems with dynamical OSp(2|2) supersymmetry. Several results related to
exactly solved supersymmetric rational Calogero model, including shape
invariance, equivalence to a system of free superoscillators and non-uniqueness
in the construction of the Hamiltonian, are presented in some detail. This
review also includes a formulation of pseudo-hermitian supersymmetric quantum
systems with a special emphasis on rational Calogero model. There are quite a
few number of many-particle quantum systems with inverse-square interactions
which are not exactly solved for a complete set of states in spite of the
construction of infinitely many exact eigen functions and eigenvalues. The
Calogero-Marchioro model with dynamical SU(1,1|2) supersymmetry and a quantum
system related to short-range Dyson model belong to this class and certain
aspects of these models are reviewed. Several other related and important
developments are briefly summarized.Comment: LateX, 65 pages, Added Acknowledgment, Discussions and References,
Version to appear in Jouranl of Physics A: Mathematical and Theoretical
(Commissioned Topical Review Article
Supplementary comparison CCRI(I)-S2 of standards for absorbed dose to water in 60Co gamma radiation at radiation processing dose levels
150-250 MeV electron beams in radiation therapy
High-energy electron beams in the range 150-250Â MeV are studied to evaluate the feasibility for radiotherapy. Monte Carlo simulation results from the PENELOPE code are presented and used to determine lateral spread and penetration of these beams. It is shown that the penumbra is comparable to photon beams at depths less than 10 cm and the practical range ( Rp) of these beams is greater than 40 cm. The depth dose distribution of electron beams compares favourably with photon beams. Effects caused by nuclear reactions are evaluated, including increased dose due to neutron production and induced radioactivity resulting in an increased relative biological effectiveness (RBE) factor of <1.03.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/48967/2/m00706.pd
Equivalence of the super Lax and local Dunkl operators for Calogero-like models
Following Shastry and Sutherland I construct the super Lax operators for the
Calogero model in the oscillator potential. These operators can be used for the
derivation of the eigenfunctions and integrals of motion of the Calogero model
and its supersymmetric version. They allow to infer several relations involving
the Lax matrices for this model in a fast way. It is shown that the super Lax
operators for the Calogero and Sutherland models can be expressed in terms of
the supercharges and so called local Dunkl operators constructed in our recent
paper with M. Ioffe. Several important relations involving Lax matrices and
Hamiltonians of the Calogero and Sutherland models are easily derived from the
properties of Dunkl operators.Comment: 25 pages, Latex, no figures. Accepted for publication in: Jounal of
Physics A: Mathematical and Genera
SIV Vpx Is Essential for Macrophage Infection but Not for Development of AIDS
Analysis of rhesus macaques infected with a vpx deletion mutant virus of simian immunodeficiency virus mac239 (SIVΔvpx) demonstrates that Vpx is essential for efficient monocyte/macrophage infection in vivo but is not necessary for development of AIDS. To compare myeloid-lineage cell infection in monkeys infected with SIVΔvpx compared to SIVmac239, we analyzed lymphoid and gastrointestinal tissues from SIVΔvpx-infected rhesus (n = 5), SIVmac239-infected rhesus with SIV encephalitis (7 SIV239E), those without encephalitis (4 SIV239noE), and other SIV mutant viruses with low viral loads (4 SIVΔnef, 2 SIVΔ3). SIV+ macrophages and the percentage of total SIV+ cells that were macrophages in spleen and lymph nodes were significantly lower in rhesus infected with SIVΔvpx (2.2%) compared to those infected with SIV239E (22.7%), SIV239noE (8.2%), and SIV mutant viruses (10.1%). In colon, SIVΔvpx monkeys had fewer SIV+ cells, no SIV+ macrophages, and lower percentage of SIV+ cells that were macrophages than the other 3 groups. Only 2 SIVΔvpx monkeys exhibited detectable virus in the colon. We demonstrate that Vpx is essential for efficient macrophage infection in vivo and that simian AIDS and death can occur in the absence of detectable macrophage infection
Modelling the economic efficiency of using different strategies to control Porcine Reproductive & Respiratory Syndrome at herd level
PRRS is among the diseases with the highest economic impact in pig production worldwide. Different strategies have been developed and applied to combat PRRS at farm level. The broad variety of available intervention strategies makes it difficult to decide on the most cost-efficient strategy for a given farm situation, as it depends on many farm-individual factors like disease severity, prices or farm structure. Aim of this study was to create a simulation tool to estimate the cost-efficiency of different control strategies at individual farm level. Baseline is a model that estimates the costs of PRRS, based on changes in health and productivity, in a specific farm setting (e.g. farm type, herd size, type of batch farrowing).
The model evaluates different intervention scenarios: depopulation/repopulation (D/R), close & roll-over (C&R), mass vaccination of sows (MS), mass vaccination of sows and vaccination of piglets (MS + piglets), improvements in internal biosecurity (BSM), and combinations of vaccinations with BSM. Data on improvement in health and productivity parameters for each intervention were obtained through literature review and from expert opinions. The economic efficiency of the different strategies was assessed over 5 years through investment appraisals: the resulting expected value (EV) indicated the most cost-effective strategy. Calculations were performed for 5 example scenarios with varying farm type (farrow-to-finish – breeding herd), disease severity (slightly – moderately – severely affected) and PRRSV detection (yes – no). The assumed herd size was 1000 sows with farm and price structure as commonly found in Germany. In a moderately affected (moderate deviations in health and productivity parameters from what could be expected in an average negative herd), unstable farrow-to-finish herd, the most cost-efficient strategies according to their median EV were C&R (€1′126′807) and MS + piglets (€ 1′114′649). In a slightly affected farrow-to-finish herd, no virus detected, the highest median EV was for MS + piglets (€ 721′745) and MS (€ 664′111). Results indicate that the expected benefits of interventions and the most efficient strategy depend on the individual farm situation, e.g. disease severity. The model provides new insights regarding the cost-efficiency of various PRRSV intervention strategies at farm level. It is a valuable tool for farmers and veterinarians to estimate expected economic consequences of an intervention for a specific farm setting and thus enables a better informed decision
Thallium and cadmium in recent snow and firn layers in the Canadian Arctic by atomic fluorescence and absorption spectrometries
Compared to the Antarctic and Greenland, the Canadian Arctic has seen extremely few trace metal studies on snow and ice. Surface, subsurface and depth samples of snow and firns were collected from the Agassiz Ice Cap, Ellesmere Island, Canada using clean room practices. Results for Tl (directly determined by LEAFS) and Cd (determined by GFAAS) are reported. To our knowledge, the thallium depth profile presented here is the first one so far reported for both polar systems, Greenland or other places. Tl concentrations peak in the winter-spring periods, when the Arctic atmosphere is loaded with foreign pollutants and suspended particulates which sometime severely reduce the visibility, creating a phenomenon commonly known as the Arctic haze. These results are in general accordance with the historical Arctic air pollution and acidity/conductivity data on ice cores. Surface concentrations of Tl range from 0.3 to 0.9 pg/g, which is a few times higher than those found in Antarctica. Cadmium shows seasonal characteristics similar to Tl although there is not a definite correlation between the two. However, there could be two predominant origins of metals which were deposited in the snow: Eurasian origin in January–April corresponding to high level metals (main deposition), and a less definite origin in May–December corresponding to low level metals.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/46458/1/216_1996_Article_63550332.pd
Two-dimensional superstrings and the supersymmetric matrix model
We present evidence that the supersymmetric matrix model of Marinari and
Parisi represents the world-line theory of N unstable D-particles in type II
superstring theory in two dimensions. This identification suggests that the
matrix model gives a holographic description of superstrings in a
two-dimensional black hole geometry.Comment: 22 pages, 2 figures; v2: corrected eqn 4.6; v3: corrected appendices
and discussion of vacua, added ref
Non-intersecting squared Bessel paths and multiple orthogonal polynomials for modified Bessel weights
We study a model of non-intersecting squared Bessel processes in the
confluent case: all paths start at time at the same positive value , remain positive, and are conditioned to end at time at . In
the limit , after appropriate rescaling, the paths fill out a
region in the -plane that we describe explicitly. In particular, the paths
initially stay away from the hard edge at , but at a certain critical
time the smallest paths hit the hard edge and from then on are stuck to
it. For we obtain the usual scaling limits from random matrix
theory, namely the sine, Airy, and Bessel kernels. A key fact is that the
positions of the paths at any time constitute a multiple orthogonal
polynomial ensemble, corresponding to a system of two modified Bessel-type
weights. As a consequence, there is a matrix valued
Riemann-Hilbert problem characterizing this model, that we analyze in the large
limit using the Deift-Zhou steepest descent method. There are some novel
ingredients in the Riemann-Hilbert analysis that are of independent interest.Comment: 59 pages, 11 figure
Nitrides as ammonia synthesis catalysts and as potential nitrogen transfer reagents
In this article, an overview of the application of selected metal nitrides as ammonia synthesis catalysts is presented. The potential development of some systems into nitrogen transfer reagents is also described
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