170 research outputs found
Technical Design rules of ETFE membrane structures using the tensile strength measurements in production and development
K X-ray multiplicities for rare earth atoms produced in (H.I., xn) nuclear reactions
K X-ray multiplicities are determined for a number of nuclear reaction products in the rare earth region. It is shown that if certain conditions are fulfilled the values of these multiplicities can be considered as characteristic for the reaction residues independently of the reaction used. They can thus be used for the quantitative determination of cross sections
Trends in Soil Science Education and Employment
During the last several decades, members of the SSSA have discussed several trends related to soil science education, including: (i) declining academic programs and course offerings at land grant universities, (ii) decreased enrollments, and (iii) improved employment opportunities for soil science graduates (SSSA, 2006; Ferris et al., 2010). The SSSA Advocacy/Education Task Force met in 2007 and concluded that quantitative survey information was needed to document trends in soil science academic programs, student enrollment, faculty, and job opportunities for graduates. Suggested survey topics included: Has the recognition of soil science as a distinct discipline increased or decreased? How has the job market changed during the past decade, and how will job opportunities for soil scientists change in the future? How have undergraduate and graduate soils curricula changed during the last decade? Has enrollment in soil science degree programs and courses changed during the past decade? Has there been a change in the degree programs of students enrolling in soils courses in the past decade? Have soil science programs been combined with other programs?
Therefore, the objective of the survey was to quantify trends in student enrollment, faculty positions, pertinent educational issues in soil and related sciences, and career or job opportunities and trends. Expected outcomes included a better understanding of current educational practices and trends, and identification of specific opportunities for SSSA to enhance the practice and profession of soil science
Rapid Suppression of the Spin Gap in Zn-doped CuGeO_3 and SrCu_2O_3
The influence of non-magnetic impurities on the spectrum and dynamical spin
structure factor of a model for CuGeO is studied. A simple extension to
Zn-doped is also discussed. Using Exact Diagonalization
techniques and intuitive arguments we show that Zn-doping introduces states in
the Spin-Peierls gap of CuGeO. This effect can beunderstood easily in the
large dimerization limit where doping by Zn creates ``loose'' S=1/2 spins,
which interact with each other through very weak effective antiferromagnetic
couplings. When the dimerization is small, a similar effect is observed but now
with the free S=1/2 spins being the resulting S=1/2 ground state of severed
chains with an odd number of sites. Experimental consequences of these results
are discussed. It is interesting to observe that the spin correlations along
the chains are enhanced by Zn-doping according to the numerical data presented
here. As recent numerical calculations have shown, similar arguments apply to
ladders with non-magnetic impurities simply replacing the tendency to
dimerization in CuGeO by the tendency to form spin-singlets along the rungs
in SrCuO.Comment: 7 pages, 8 postscript figures, revtex, addition of figure 8 and a
section with experimental predictions, submmited to Phys. Rev. B in May 199
Enhancement of Antiferromagnetic Correlations Induced by Nonmagnetic Impurities: Origin and Predictions for NMR Experiments
Spin models that have been proposed to describe dimerized chains, ladders,
two dimensional antiferromagnets, and other compounds are here studied when
some spins are replaced by spinless vacancies, such as it occurs by
doping. A small percentage of vacancies rapidly destroys the spin gap, and
their presence induces enhanced antiferromagnetic correlations near those
vacancies. The study is performed with computational techniques which includes
Lanczos, world-line Monte Carlo, and the Density Matrix Renormalization Group
methods. Since the phenomenon of enhanced antiferromagnetism is found to occur
in several models and cluster geometries, a common simple explanation for its
presence may exist. It is argued that the resonating-valence-bond character of
the spin correlations at short distances of a large variety of models is
responsible for the presence of robust staggered spin correlations near
vacancies and lattice edges. The phenomenon takes place regardless of the long
distance properties of the ground state, and it is caused by a ``pruning'' of
the available spin singlets in the vicinity of the vacancies. The effect
produces a broadening of the low temperature NMR signal for the compounds
analyzed here. This broadening should be experimentally observable in the
structurally dimerized chain systems
, , , and
, in ladder materials such as , in the
spin-Peierls systems and , and in several others since it
is a universal effect common to a wide variety of models and compounds.Comment: 18 pages revtex with 26 figures include
Methylphenidate Attenuates Limbic Brain Inhibition after Cocaine-Cues Exposure in Cocaine Abusers
Dopamine (phasic release) is implicated in conditioned responses. Imaging studies in cocaine abusers show decreases in striatal dopamine levels, which we hypothesize may enhance conditioned responses since tonic dopamine levels modulate phasic dopamine release. To test this we assessed the effects of increasing tonic dopamine levels (using oral methylphenidate) on brain activation induced by cocaine-cues in cocaine abusers. Brain metabolism (marker of brain function) was measured with PET and 18FDG in 24 active cocaine abusers tested four times; twice watching a Neutral video (nature scenes) and twice watching a Cocaine-cues video; each video was preceded once by placebo and once by methylphenidate (20 mg). The Cocaine-cues video increased craving to the same extent with placebo (68%) and with methylphenidate (64%). In contrast, SPM analysis of metabolic images revealed that differences between Neutral versus Cocaine-cues conditions were greater with placebo than methylphenidate; whereas with placebo the Cocaine-cues decreased metabolism (p<0.005) in left limbic regions (insula, orbitofrontal, accumbens) and right parahippocampus, with methylphenidate it only decreased in auditory and visual regions, which also occurred with placebo. Decreases in metabolism in these regions were not associated with craving; in contrast the voxel-wise SPM analysis identified significant correlations with craving in anterior orbitofrontal cortex (p<0.005), amygdala, striatum and middle insula (p<0.05). This suggests that methylphenidate's attenuation of brain reactivity to Cocaine-cues is distinct from that involved in craving. Cocaine-cues decreased metabolism in limbic regions (reflects activity over 30 minutes), which contrasts with activations reported by fMRI studies (reflects activity over 2–5 minutes) that may reflect long-lasting limbic inhibition following activation. Studies to evaluate the clinical significance of methylphenidate's blunting of cue-induced limbic inhibition may help identify potential benefits of this medication in cocaine addiction
Phono-spectrographic analysis of heart murmur in children
This is an Open Access article distributed under the terms of the Creative Commons Attribution Licens
Fenfluramine and N-ethyl amphetamine: Comparison of the reinforcing and rate-decreasing actions in the rhesus monkey
N-ethyl amphetamine HCl (NEA) and fenfluramine HCl ( meta -trifluoromethyl N-ethyl amphetamine) were evaluated as reinforcers in rhesus monkeys that had been previously trained to press a lever using food presentations and cocaine HCl injections as reinforcers. Each daily session consisted of episodic opportunities to obtain reinforcers under a fixed-ratio schedule of 30. A drug period was interpolated between two periods in which lever-press responding was maintained by food presentations. Compared to saline, none of the drugs altered the rate of responding in the food periods which preceded the drug sessions, indicating the absence of residual response-disrupting drug actions from previous sessions. However, NEA and fenfluramine self-injection resulted in dose-related decreases in response rates during the food periods which immediately followed the drug sessions. Cocaine HCl (30 Îœg/kg/injection) maintained high response rates at over one response/second during the drug periods, as did the same dose of NEA. Doses of 10 and 100 Îœg/kg/injection of NEA as well as all doses of fenfluramine HCl (10 through 300 Îœg/kg/injection) maintained rates that were not different from those associated with saline injections. These results substantiate and extend earlier findings with fenfluramine and indicate that its failure to act as a reinforcer is attributable to its meta -trifluoromethyl group.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/46392/1/213_2004_Article_BF00429257.pd
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