519 research outputs found
Natural and projectively equivariant quantizations by means of Cartan Connections
The existence of a natural and projectively equivariant quantization in the
sense of Lecomte [20] was proved recently by M. Bordemann [4], using the
framework of Thomas-Whitehead connections. We give a new proof of existence
using the notion of Cartan projective connections and we obtain an explicit
formula in terms of these connections. Our method yields the existence of a
projectively equivariant quantization if and only if an \sl(m+1,\R)-equivariant
quantization exists in the flat situation in the sense of [18], thus solving
one of the problems left open by M. Bordemann.Comment: 13 page
Nonuniform Self-Organized Dynamical States in Superconductors with Periodic Pinning
We consider magnetic flux moving in superconductors with periodic pinning
arrays. We show that sample heating by moving vortices produces negative
differential resistivity (NDR) of both N and S type (i.e., N- and S-shaped) in
the voltage-current characteristic (VI curve). The uniform flux flow state is
unstable in the NDR region of the VI curve. Domain structures appear during the
NDR part of the VI curve of an N type, while a filamentary instability is
observed for the NDR of an S type. The simultaneous existence of the NDR of
both types gives rise to the appearance of striking self-organized (both
stationary and non-stationary) two-dimensional dynamical structures.Comment: 4 pages, 2 figure
Freeze-out configuration properties in the 197Au + 197Au reaction at 23 AMeV
Data from the experiment on the 197Au + 197Au reaction at 23 AMeV are
analyzed with an aim to find signatures of exotic nuclear configurations such
as toroid-shaped objects. The experimental data are compared with predictions
of the ETNA code dedicated to look for such configurations and with the QMD
model. A novel criterion of selecting events possibly resulting from the
formation of exotic freeze-out configurations, "the efficiency factor", is
tested. Comparison between experimental data and model predictions may indicate
for the formation of flat/toroidal nuclear systems
Two-dimensional turbulence in magnetised plasmas
In an inhomogeneous magnetised plasma the transport of energy and particles
perpendicular to the magnetic field is in general mainly caused by quasi
two-dimensional turbulent fluid mixing. The physics of turbulence and structure
formation is of ubiquitous importance to every magnetically confined laboratory
plasma for experimental or industrial application. Specifically, high
temperature plasmas for fusion energy research are also dominated by the
properties of this turbulent transport. Self-organisation of turbulent vortices
to mesoscopic structures like zonal flows is related to the formation of
transport barriers that can significantly enhance the confinement of a fusion
plasma. This subject of great importance in research is rarely touched on in
introductory plasma physics or continuum dynamics courses. Here a brief
tutorial on 2D fluid and plasma turbulence is presented as an introduction to
the field, appropriate for inclusion in undergraduate and graduate courses.Comment: This is an author-created, un-copyedited version of an article
published in European Journal of Physics. IOP Publishing Ltd is not
responsible for any errors or omissions in this version of the manuscript or
any version derived from it. The definitive publisher authenticated version
is available online at doi: 10.1088/0143-0807/29/5/00
MICROMEGAS chambers for hadronic calorimetry at a future linear collider
Prototypes of MICROMEGAS chambers, using bulk technology and analog readout,
with 1x1cm2 readout segmentation have been built and tested. Measurements in
Ar/iC4H10 (95/5) and Ar/CO2 (80/20) are reported. The dependency of the
prototypes gas gain versus pressure, gas temperature and amplification gap
thickness variations has been measured with an 55Fe source and a method for
temperature and pressure correction of data is presented. A stack of four
chambers has been tested in 200GeV/c and 7GeV/c muon and pion beams
respectively. Measurements of response uniformity, detection efficiency and hit
multiplicity are reported. A bulk MICROMEGAS prototype with embedded digital
readout electronics has been assembled and tested. The chamber layout and first
results are presented
Liquid chromatography/mass spectrometry analysis of exhaled leukotriene B(4 )in asthmatic children
BACKGROUND: The role of leukotriene (LT) B(4), a potent inflammatory mediator, in atopic asthmatic and atopic nonasthmatic children is largely unknown. The lack of a gold standard technique for measuring LTB(4 )in exhaled breath condensate (EBC) has hampered its quantitative assessment in this biological fluid. We sought to measure LTB(4 )in EBC in atopic asthmatic children and atopic nonasthmatic children. Exhaled nitric oxide (NO) was measured as an independent marker of airway inflammation. METHODS: Fifteen healthy children, 20 atopic nonasthmatic children, 25 steroid-naïve atopic asthmatic children, and 22 atopic asthmatic children receiving inhaled corticosteroids were studied. The study design was of cross-sectional type. Exhaled LTB(4 )concentrations were measured using liquid chromatography/mass spectrometry-mass spectrometry (LC/MS/MS) with a triple quadrupole mass spectrometer. Exhaled NO was measured by chemiluminescence with a single breath on-line method. LTB(4 )values were expressed as the total amount (in pg) of eicosanoid expired in the 15-minute breath test. Kruskal-Wallis test was used to compare groups. RESULTS: Compared with healthy children [87.5 (82.5–102.5) pg, median and interquartile range], exhaled LTB(4 )was increased in steroid-naïve atopic asthmatic [255.1 (175.0–314.7) pg, p < 0.001], but not in atopic nonasthmatic children [96.5 (87.3–102.5) pg, p = 0.59)]. Asthmatic children who were receiving inhaled corticosteroids had lower concentrations of exhaled LTB(4 )than steroid-naïve asthmatics [125.0 (25.0–245.0) pg vs 255.1 (175.0–314.7) pg, p < 0.01, respectively]. Exhaled NO was higher in atopic nonasthmatic children [16.2 (13.5–22.4) ppb, p < 0.05] and, to a greater extent, in atopic steroid-naïve asthmatic children [37.0 (31.7–57.6) ppb, p < 0.001] than in healthy children [8.3 (6.1–9.9) ppb]. Compared with steroid-naïve asthmatic children, exhaled NO levels were reduced in asthmatic children who were receiving inhaled corticosteroids [15.9 (11.5–31.7) ppb, p < 0.01]. CONCLUSION: In contrast to exhaled NO concentrations, exhaled LTB(4 )values are selectively elevated in steroid-naïve atopic asthmatic children, but not in atopic nonasthmatic children. Although placebo control studies are warranted, inhaled corticosteroids seem to reduce exhaled LTB(4 )in asthmatic children. LC/MS/MS analysis of exhaled LTB(4 )might provide a non-invasive, sensitive, and quantitative method for airway inflammation assessment in asthmatic children
Projected Quasi-particle Perturbation theory
The BCS and/or HFB theories are extended by treating the effect of four
quasi-particle states perturbatively. The approach is tested on the pairing
hamiltonian, showing that it combines the advantage of standard perturbation
theory valid at low pairing strength and of non-perturbative approaches
breaking particle number valid at higher pairing strength. Including the
restoration of particle number, further improves the description of pairing
correlation. In the presented test, the agreement between the exact solution
and the combined perturbative + projection is almost perfect. The proposed
method scales friendly when the number of particles increases and provides a
simple alternative to other more complicated approaches
Producing valid statistics when legislation, culture, and medical practices differ for births at or before the threshold of survival: Report of a European workshop
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