4,809 research outputs found
In-situ Particle Acceleration in Collisionless Shocks
The outflows from gamma ray bursts, active galactic nuclei and relativistic
jets in general interact with the surrounding media through collisionless
shocks. With three dimensional relativistic particle-in-cell simulations we
investigate such shocks. The results from these experiments show that
small--scale magnetic filaments with strengths of up to percents of
equipartition are generated and that electrons are accelerated to power law
distributions N(E)~E^{-p} in the vicinity of the filaments through a new
acceleration mechanism. The acceleration is locally confined, instantaneous and
differs from recursive acceleration processes such as Fermi acceleration. We
find that the proposed acceleration mechanism competes with thermalization and
becomes important at high Lorentz factors.Comment: 4 pages, 2 figures, submitted to Il nuovo cimento (4th Workshop
Gamma-Ray Bursts in the Afterglow Era, Rome, 18-22 October 2004
Non-Fermi Power law Acceleration in Astrophysical Plasma Shocks
Collisionless plasma shock theory, which applies for example to the afterglow
of gamma ray bursts, still contains key issues that are poorly understood. In
this paper we study charged particle dynamics in a highly relativistic
collisionless shock numerically using ~10^9 particles. We find a power law
distribution of accelerated electrons, which upon detailed investigation turns
out to originate from an acceleration mechanism that is decidedly different
from Fermi acceleration.
Electrons are accelerated by strong filamentation instabilities in the
shocked interpenetrating plasmas and coincide spatially with the power law
distributed current filamentary structures. These structures are an inevitable
consequence of the now well established Weibel-like two-stream instability that
operates in relativistic collisionless shocks.
The electrons are accelerated and decelerated instantaneously and locally; a
scenery that differs qualitatively from recursive acceleration mechanisms such
as Fermi acceleration.
The slopes of the electron distribution power laws are in concordance with
the particle power law spectra inferred from observed afterglow synchrotron
radiation in gamma ray bursts, and the mechanism can possibly explain more
generally the origin of non-thermal radiation from shocked inter- and
circum-stellar regions and from relativistic jets.Comment: 4 pages accepted for publication in ApJ Letters. High resolution
figures are available online at http://www.astro.ku.dk/users/hededal/040855
Grain Characteristics, Chemical Composition, and Functional Properties of Rye (Secale cereale L.) As Influenced by Genotype and Harvest Year
Grain characteristic, chemical composition, and functional properties of rye were measured in 19 different cultivars grown in one location in up to 3 years. The cultivars included 8 adapted hybrids, 7 adapted population cultivars, and 4 nonadapted population cultivars. The results showed a significant influence of both harvest year and genotype on grain characteristics, chemical composition, and functional properties of the grain. Multivariate data analysis confirmed that the variations in the data were explained by yearly and genotype differences. Calculations of variance components showed that the variations in plant height, harvest yield, and protein content were mainly due to genotype differences and to a lesser extent to differences among harvest years. The kernel weight, hardness index, and content of dietary fiber components, however, were more strongly influenced by the harvest year than by the genotype. Differences in starch properties measured by falling number (FN), amylograph peak viscosity, and temperature at peak viscosity were more strongly influenced by harvest year. The water absorption was strongly influenced by genotype effects, compared to yearly differences. FN and amylograph peak temperature were positively correlated (r = 0.94). No correlation was found between the water absorption and the relative proportion of water-extractable arabinoxylan (AX) compared to the total AX content. However, the degree of ferulic acid cross-linking showed a negative correlation (r = -0.70) with the water absorption
GeMSE: A new Low-Background Facility for Meteorite and Material Screening
We are currently setting up a facility for low-background gamma-ray
spectrometry based on a HPGe detector. It is dedicated to material screening
for the XENON and DARWIN dark matter projects as well as to the
characterization of meteorites. The detector will be installed in a medium
depth (620 m.w.e.) underground laboratory in Switzerland with several
layers of shielding and an active muon-veto. The GeMSE facility will be
operational by fall 2015 with an expected background rate of 250
counts/day (100-2700 keV).Comment: The following article appeared in AIP Conf. Proc. 1672, 120004 (2015)
and may be found at
http://scitation.aip.org/content/aip/proceeding/aipcp/10.1063/1.4928010. The
muon spectrum in Figure 4 (left) was corrected due to a bug in the code.
After correction the muon flux is reduced by a factor of about
Vaginal yeasts in the era of "over the counter" antifungals
OBJECTIVE: To establish whether there has been any rise in the prevalence of non-albicans
Candida species isolated from vaginal swabs since the introduction of “over the counter” antifungal
treatments.
METHOD: A retrospective review looking at all positive vaginal yeast isolates collected from
women attending one genitourinary medicine clinic during the 6 year period from 1993 to 1998
inclusive. All positive vaginal yeast isolates were included, regardless of whether or not the
patients were symptomatic. Isolates from HIV positive women were excluded from the analysis.
RESULT: No increase in non-albicans vaginal yeast isolates was shown during the period studied.
The proportion of non-albicans yeasts remained constant at approximately 5% of the total yeasts
isolated. The most common non-albicans yeast isolated was C glabrata.
CONCLUSION: There is no evidence from this study to suggest that the increasing use of “over the
counter” antifungal treatment has selected for atypical, possibly inherently azole resistant, strains
of vaginal yeasts in HIV seronegative women
Clostridium difficile cytotoxin B in adults with diarrhea: a comparison of patients treated or not treated with antibiotics prior to infection
AbstractDepartments of Medicine and Immunology Microbiology, Pathology and Infectious Diseases, Karolinska Institute, Huddinge University Hospital, Huddinge, SwedenObjectiveTo study the detection rate of Clostridium difficile cytotoxin B in stool specimens from adults with diarrhea as related to previous antimicrobial treatment.MethodsStool specimens from 802 adult patients with diarrhea and 203 healthy controls were tested for C. dificile cytotoxin B using a cell cytotoxicity assay. Antibiotic susceptibility testing of C. difficile was performed with the E test.ResultsOf 173 patients treated with antimicrobial medication within 5 weeks of onset of diarrhea, 60 (35%) were positive for C. difficile cytotoxin B (group A) compared to only 41 (7%) of 629 untreated patients (group B) and two of the 203 (1%) healthy controls. Compared to patients in group A, patients in group B possessed characteristics not usually connected with C. difficile disease. They were generally younger (median age 40 years vs. 73 years), had been hospitalized less frequently (10% vs. 67%), had more often travelled abroad within the previous 2 weeks (46% vs. 1%), and more often had multiple enteropathogens (41% vs. 3%). Minimal inhibitory concentrations for vancomycin, metronidazole and fucidic acid to C. difficile isolates ranged from 0.5 to 4 mg/L, from 0.125 to 256 mg/L and 0.25 to 4 mg/L, respectively.ConclusionsThe detection rate of C. difficile cytotoxin B in patients with diarrhea, not associated with antibiotic treatment, is comparable to that in healthy control subjects. It probably merely reflects a carrier state without clinical significance
Neutrino masses from discrete gauge symmetries
We investigate a model with an extra gauge symmetry in the Standard
Model. We assume that only the scalars and the leptons carry non-zero charge.
The symmetry gives a structure to the mass matrix for the neutrinos. With two
extra Higgs singlets and two extra singlet right-handed neutrinos we can build
a model that fits the requirements of the MSW-solution of the Solar neutrino
problem. With a third singlet right-handed neutrino it is also possible to have
a 10 eV neutrino, a dark matter candidate.Comment: SNUTP 92-105, Late
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Living with diabetes - development of learning patterns over a 3-year period
Background: Learning involves acquiring new knowledge and skills, and changing our ways of thinking, acting, and feeling. Learning in relation to living with diabetes is a lifelong process where there is limited knowledge of how it is experienced and established over time. It was considered important to explore how learning was developed over time for persons living with diabetes.
Aim: The aim of the study was to identify patterns in learning when living with diabetes, from recently being diagnosed, and over a 3-year period.
Materials and methods: A longitudinal qualitative descriptive design was used. Thirteen participants, with both type I and type II diabetes, were interviewed at three different occasions during a 3-year period. Qualitative content analysis was used in different steps in order to distinguish patterns.
Findings: Five main patterns of learning were identified. Two of the patterns (I and II) were characterized by gradually becoming comfortable living with diabetes, whereas for one pattern (IV) living with diabetes became gradually more difficult. For pattern V living with diabetes was making only a limited impact on life, whereas for Pattern III there was a constant management of obstacles related to illness. The different patterns in the present study showed common and different ways of learning and using different learning strategies at different timespans.
Conclusion: The present study showed that duration of illness is not of importance for how far a person has come in his own learning process. A person-centered care is needed to meet the different and changing needs of persons living with diabetes in relation to learning to live with a lifelong illness
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