2,526 research outputs found

    Viscosity in the excluded volume hadron gas model

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    The shear viscosity η\eta in the van der Waals excluded volume hadron-resonance gas model is considered. For the shear viscosity the result of the non-relativistic gas of hard-core particles is extended to the mixture of particles with different masses, but equal values of hard-core radius r. The relativistic corrections to hadron average momenta in thermal equilibrium are also taken into account. The ratio of the viscosity η\eta to the entropy density s is studied. It monotonously decreases along the chemical freeze-out line in nucleus-nucleus collisions with increasing collision energy. As a function of hard-core radius r, a broad minimum of the ratio η/s≈0.3\eta/s\approx 0.3 near r≈0.5r \approx 0.5 fm is found at high collision energies. For the charge-neutral system at T=Tc=180T=T_c=180 MeV, a minimum of the ratio η/s≅0.24\eta/s\cong 0.24 is reached for r≅0.53r\cong 0.53 fm. To justify a hydrodynamic approach to nucleus-nucleus collisions within the hadron phase the restriction from below, r ≥ 0.2r~ \ge ~0.2 fm, on the hard-core hadron radius should be fulfilled in the excluded volume hadron-resonance gas.Comment: 12 pages, 3 figure

    Forward-backward correlations in nucleus-nucleus collisions: baseline contributions from geometrical fluctuations

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    We discuss the effects of initial collision geometry and centrality bin definition on correlation and fluctuation observables in nucleus-nucleus collisions. We focus on the forward-backward correlation coefficient recently measured by the STAR Collaboration in Au+Au collisions at RHIC. Our study is carried out within two models: the Glauber Monte Carlo code with a `toy' wounded nucleon model and the hadron-string dynamics (HSD) transport approach. We show that strong correlations can arise due to averaging over events in one centrality bin. We, furthermore, argue that a study of the dependence of correlations on the centrality bin definition as well as the bin size may distinguish between these `trivial' correlations and correlations arising from `new physics'.Comment: 12 pages, 6 figure

    Reproductive performance of reindeer fed all-grain and hay-grain rations

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    Reproductive performance of grain-fed reindeer {Rangifer tarandus) was evaluated over a 2-year period. Groups of pregnant reindeer were fed one of three rations, (1) 100% whole-grain barley, (2) 98.9% whole-grain barley and 1.2% mineral and trace element supplement, and (3) 70% whole-grain barley and 30% finely-chopped bluegrass hay. Reindeer fed unsupplemented whole-barley failed to produce a single live calf. The addition of mineral and trace element supplement to the ration did not result in any significant improvement in reproductive performance. Eighty-five percent of the reindeer consuming unsupplemented and supplemented all-barley rations became pregnant; however, 76% of the pregnancies resulted in stillborn calves. One-hundred percent of the cows maintained on the grain/hay ration produced live calves. We speculate that reproductive failure in reindeer cows maintained on all-grain rations is most likely a result of a diet induced disfunction in maternal rumen and/or carbohydrate metabolism rather than a micro-nutrient deficiency. More research is neeeded to determine which metabolic pathways are affected

    Progesterone during the breeding season and pregnancy in female muskoxen on different dietary regimens

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    Previously, we documented lowered calving success in captive muskoxen raised for 6 years on a low nutritional plane. In an effort to identify causes of lowered calf production, we looked at serum progesterone during the breeding season in muskoxen raised on either a high (HP) or low (LP) nutritional plane. Complete cessation of estrous cycli-city in 2 parous cows was the only irregularity identified. Abortion and/or embryonic loss occurred in both HP and LP cows. We also compared progesterone during pregnancy between the 2 nutritional planes and lactating and non-lacta-ting cows. The timing of the rise and fall of the mid-pregnant progesterone peak was consistent with stage of gestation and apparently independent of time of breeding, diet or lactational status

    Medical Students’ Use of the Stages of Change Model in Tobacco Cessation Counseling

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    BACKGROUND: Many medical schools have incorporated the Stages of Change Model into their curricula with specific application to tobacco cessation. OBJECTIVE: This study examined the extent to which medical students were prepared to provide stage-based interventions to treat nicotine dependence. DESIGN: Using a quasi-experimental design, medical students’ counseling interactions were evaluated with a standardized patient portraying a smoker in either the precontemplation or preparation stage of change. PARTICIPANTS: Participants were 147 third-year medical students at the University of California, San Francisco. MEASUREMENTS: Checklists completed by standardized patients evaluated students’ clinical performance. Surveys administered before and after the encounters assessed students’ knowledge, attitudes, confidence and previous experience with treating smoking. RESULTS: Most students asked about tobacco use (89%), advised patients of the health benefits of quitting (74%), and assessed the patient’s readiness to quit (76%). The students were more likely to prescribe medications and offer referrals to patients in the preparation than in the precontemplation stage of change (P < 0.001); however, many students had difficulty identifying patients ready to quit, and few encouraged patients to set a quit date or arranged follow-up to assess progress. Students’ tobacco-related knowledge, but not their attitudes, confidence, or previous experience predicted their clinical performance. CONCLUSIONS: The findings indicated evidence of students tailoring their counseling strategies to the patients’ stage of change; however, they still could do more to assist their patients in quitting. Additional training and integration of cessation counseling into clinical rotations are needed

    Population structure and dynamics in captive muskoxen at the Large Animal Research Station, 1988-1994

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    The muskox colony at the Large Animal Research Station, started in 1979, totaled 22 individuals before calving in 1988. Between 1988 -1994 cows of breeding age have been maintained on either a high plane (HP) or low plane (LP) of nutrition, and as far as possible, female offspring are kept with their mother's group. During this time the population has increased from 22 to 43 animals (25 females and 18 males). Fifty-four calves were born with an overall sex ratio of 52:48 (male:female). When partitioned between the 2 nutritional planes the sex ratio was HP 45:55 and LP 62:38. The calf/cow ratio was 0.83 in 1988 and 0.86 in 1994. The LP group accounted for most of the variability in pregnancy rate, primarily through delayed puberty and breeding pauses. Calf mortality was due mainly to abortions, stillbirths and neonatal death (n=12), 7 deaths occurred between 2 weeks and 1 year of age. All stillbirths and abortions (n=4) and 6 of 8 neonatal deaths affected calves of HP cows. Thirteen adults died, 4 males were loaned to other facilities and 2 new calves were added
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