912 research outputs found
Relativistic Cyclotron Radiation Detection of Tritium Decay Electrons as a New Technique for Measuring the Neutrino Mass
The shape of the beta decay energy distribution is sensitive to the mass of
the electron neutrino. Attempts to measure the endpoint shape of tritium decay
have so far seen no distortion from the zero-mass form, thus placing an upper
limit of m_nu_beta < 2.3 eV. Here we show that a new type of electron energy
spectroscopy could improve future measurements of this spectrum and therefore
of the neutrino mass. We propose to detect the coherent cyclotron radiation
emitted by an energetic electron in a magnetic field. For mildly relativistic
electrons, like those in tritium decay, the relativistic shift of the cyclotron
frequency allows us to extract the electron energy from the emitted radiation.
We present calculations for the energy resolution, noise limits, high-rate
measurement capability, and systematic errors expected in such an experiment.Comment: 4 pages, 2 figure
Oscillatory relaxation of zonal flows in a multi-species stellarator plasma
The low frequency oscillatory relaxation of zonal potential perturbations is
studied numerically in the TJ-II stellarator (where it was experimentally
detected for the first time). It is studied in full global gyrokinetic
simulations of multi-species plasmas. The oscillation frequency obtained is
compared with predictions based on single-species simulations using simplified
analytical relations. It is shown that the frequency of this oscillation for a
multi-species plasma can be accurately obtained from single-species
calculations using extrapolation formulas. The damping of the oscillation and
the influence of the different inter-species collisions is studied in detail.
It is concluded that taking into account multiple kinetic ions and electrons
with impurity concentrations realistic for TJ-II plasmas allows to account for
the values of frequency and damping rate in zonal flows relaxations observed
experimentally.Comment: 11 figures, 22 page
Nonradiative Electronic Deexcitation Time Scales in Metal Clusters
The life-times due to Auger-electron emission for a hole on a deep electronic
shell of neutral and charged sodium clusters are studied for different sizes.
We consider spherical clusters and calculate the Auger-transition probabilities
using the energy levels and wave functions calculated in the
Local-Density-Approximation (LDA).
We obtain that Auger emission processes are energetically not allowed for
neutral and positively charged sodium clusters. In general, the Auger
probabilities in small Na clusters are remarkably different from the
atomic ones and exhibit a rich size dependence.
The Auger decay times of most of the cluster sizes studied are orders of
magnitude larger than in atoms and might be comparable with typical
fragmentation times.Comment: 11 pages, 4 figures. Accepted for publication in Phys. Rev.
Simulating the dynamics of soil organic matter in long-term rotation plots of Saskatchewan and Alberta
Non-Peer ReviewedThis study used the Century soil organic matter (SOM) model to simulate the dynamics in soil organic carbon, nitrogen, and phosphorus in long-term crop rotation studies established in Saskatchewan and Alberta. Observed losses of organic C, N, and P in the top 30 cm of a Brown Chernozem under fallow-wheat (FW) were 8.2, 1.7, and 1.0 g m-1 y-1. Soil erosion was responsible for 47% of the organic-N losses. The Century model closely mimicked the direction and magnitude of SOM change, within 10% of measured values. Similar SOM declining trends were observed in a thin Black Chernozem under FW and continuous wheat (CW), although soil erosion losses were higher than in the Brown Chernozem. Soil organic matter increased in the Brown Chernozem under CW and in the Black Chernozem under zero-tillage. Under no-till, the organic C, N, and P accumulated at an average rate of 101.7, 5.3, and 2.0 g m-2 y-1. In comparison, the Century model predicted a depletion of organic-C and N in the Brown Chernozem under CW and of organic-C under no-till. Model sensitivity analyses indicated that the rate of erosion and the fixed rate of organic matter decomposition had greater effects than plant biomass production on soil organic matter levels. Under aggrading SOM conditions, the Century model predicted organic carbon accumulation only
after the respiration rate for the slow organic matter fraction was reduced by 50%
Transcriptional profiling reveals extraordinary diversity among skeletal muscle tissues
Skeletal muscle comprises a family of diverse tissues with highly specialized functions. Many acquired diseases, including HIV and COPD, affect specific muscles while sparing others. Even monogenic muscular dystrophies selectively affect certain muscle groups. These observations suggest that factors intrinsic to muscle tissues influence their resistance to disease. Nevertheless, most studies have not addressed transcriptional diversity among skeletal muscles. Here we use RNAseq to profile mRNA expression in skeletal, smooth, and cardiac muscle tissues from mice and rats. Our data set, MuscleDB, reveals extensive transcriptional diversity, with greater than 50% of transcripts differentially expressed among skeletal muscle tissues. We detect mRNA expression of hundreds of putative myokines that may underlie the endocrine functions of skeletal muscle. We identify candidate genes that may drive tissue specialization, including Smarca4, Vegfa, and Myostatin. By demonstrating the intrinsic diversity of skeletal muscles, these data provide a resource for studying the mechanisms of tissue specialization
Emprendimiento cooperativo de trabajo : resultados, expectativas y desempeño empresarial. Un análisis en cooperativas valencianas de trabajo asociado
El contexto de las cooperativas de trabajadores mantiene importantes diferencias con el de las empresas tradicionales, y el estudio del emprendimiento difiere también de forma sustancial. El análisis de la creación y puesta en marcha de las cooperativas de trabajo asociado requiere enfoques diferenciados, ya que los modelos más convencionales de entrepreneurship no resultan adecuados. Tales modelos, de carácter multidimensional en su mayor parte, recogen factores que resultan determinantes para explicar el proceso emprendedor, aunque no es frecuente encontrar en esos modelos una relación causal de los factores con los resultados del emprendimiento. Desde el enfoque sociocultural y la orientación emprendedora, en este trabajo se analiza la influencia o relación de algunos factores presentes en el proceso de emprendimiento sobre dichos resultados, tanto los referidos al desempeño o la performance de la propia empresa, como a las expectativas o resultados personales esperados por parte de dichos emprendedores. Con una muestra de cooperativas de trabajo asociado creadas en la Comunidad Valenciana (España) en el periodo 2008-2014, y mediante una metodología cuantitativa, se realiza un análisis exploratorio para comprobar la relación o influencia de los factores estudiados sobre los resultados del emprendimiento
Strangelets: Who is Looking, and How?
It has been over 30 years since the first suggestion that the true ground
state of cold hadronic matter might be not nuclear matter but rather strange
quark matter (SQM). Ever since, searches for stable SQM have been proceeding in
various forms and have observed a handful of interesting events but have
neither been able to find compelling evidence for stable strangelets nor to
rule out their existence. I will survey the current status and near future of
such searches with particular emphasis on the idea of SQM from strange star
collisions as part of the cosmic ray flux.Comment: Talk given at International Conference on Strangeness in Quark
Matter, 2006. 8 pages. 1 figur
Sex differences in ochratoxin a toxicity in F344 rats after 7 and 21 days of daily oral administration
Ochratoxin A (OTA) is a potent renal carcinogen in male rats but not in females. The mechanisms underlying these differences are unknown. The sex-dependent response of F344 rats after a repeated OTA oral administration for 7 (0.50 mg/kg bw) or 21 days (0.21 and 0.50 mg/kg bw) was evaluated. General toxicity, sex and thyroid hormones and histopathology were studied. OTA was quantified (HPLC-FLD) in plasma, kidney and liver and the expression of kidney transporters (RT-qPCR) was studied. After 7 days, kidney histopathology showed more pronounced signs of toxicity in males than in females. After 21 days, a higher toxicity was observed but sex differences disappeared. OTA concentration in plasma and tissues was similar in both sexes. Downregulation was the general OTA-induced effect. Oats' downregulation was slow in males and Oat3 did not change in females. Oatp1 was strongly downregulated in males after 21 days. An opposite effect was observed in Bcrp after 21 days: downregulation in males and upregulation in females. Females showed a dose- and time-dependent decrease of progesterone. Despite the sex differences, the final balance in OTA toxicokinetics at renal cell level does not seem to support a higher accumulation of OTA in male kidneys
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