Orbital Order Effect of Two-Dimensional Spin Gap System for CaV4O9

Effects of possible orbital order in magnetic properties of two-dimensional spin gap system for CaV$_4$O$_9$ are investigated theoretically. After analyzing experimental data, we show that single orbital models assumed in the literature are insufficient to reproduce the data. To understand the origin of the discrepancy, we assume that in $d^1$ state of V, $d_{xz}$ and $d_{yz}$ orbitals have substantial contributions in the lowest-energy atomic level which leads to a double-degeneracy. We study possible configurations of the orbital order. By exact diagonalization and perturbation expansion, we calculate the susceptibility, wavenumber dependence of low-lying excitations and equal-time spin-spin correlations which is related to integrated intensity of the neutron inelastic scattering. These quantities sensitively depend on the configuration of the orbital order. The calculated results for some configurations of the orbital order reproduce many experimental results much better than the previous single-orbital models. However some discrepancy still remains to completely reproduce all of the reported experimental results. To understand the origin of these discrepancies, we point out the possible importance of the partially occupied $d_{xy}$ orbital in addition to orbital order of partially filled $d_{xz}$ and $d_{yz}$ orbitals.Comment: 19 pages LATEX, 15 postscript figures, using jpsj.sty,to be published in J.Phys.Soc.Jpn. Vol.67 No.2 (1998

Biomarkers of environmental tobacco smoke exposure.

Biomarkers are desirable for quantitating human exposure to environmental tobacco smoke (ETS) and for predicting potential health risks for exposed individuals. A number of biomarkers of ETS have been proposed. At present cotinine, measured in blood, saliva, or urine, appears to be the most specific and the most sensitive biomarker. In nonsmokers with significant exposure to ETS, cotinine levels in the body are derived primarily from tobacco smoke, can be measured with extremely high sensitivity, and reflect exposure to a variety of types of cigarettes independent of machine-determined yield. Under conditions of sustained exposure to ETS (i.e., over hours or days), cotinine levels reflect exposure to other components of ETS. Supporting the validity of cotinine as a biomarker, cotinine levels have been positively correlated to the risks of some ETS-related health complications in children who are not cigarette smokers

Various series expansions for a Heisenberg antiferromagnet model for SrCu2_2(BO3_3)2_2

We use a variety of series expansion methods at both zero and finite temperature to study an antiferromagnetic Heisenberg spin model proposed recently by Miyahara and Ueda for the quasi two-dimensional material SrCu$_2$(BO$_3$)$_2$. We confirm that this model exhibits a first-order quantum phase transition at T=0 between a gapped dimer phase and a gapless N\'eel phase when the ratio $x=J'/J$ of nearest and next-nearest neighbour interactions is varied, and locate the transition at $x_c=0.691(6)$. Using longer series we are able to give more accurate estimates of the model parameters by fitting to the high temperature susceptibility data.Comment: RevTeX, 13 figure

Production of Sodium Borohydride by Using Dynamic Behaviors of Protide at the Extreme Surface of Magnesium Particles

Abstract An advanced process for the production of sodium borohydride (NaBH 4 ) as a hydrogen storage material was developed, which applied the dynamic hydriding and dehydriding behaviors of protide (H − ) in Mg-H system under transitional temperature conditions. An abundant natural resource named borax (Na 2 B 4 O 7 ·10H 2 O) and the anhydrous sodium metaborate (NaBO 2 ) recovered from the "spent fuel" as NaBO 2 ·4H 2 O were used as the starting material in the present process. Powder-state Mg played an important role in the transitional hydriding and dehydriding process where the gaseous hydrogen was converted to protide at the extreme surface of Mg to form NaBH 4 in exchange with the simultaneous transition of oxygen in NaBO 2 to form MgO. In the present process, the protide as the most reactive state among the four states of hydrogen is applied for the synthesis of NaBH 4 , which can exist in metal-hydrogen complexes, such as NaAlH 4 and NaBH 4 . The NaBH 4 yield was reached higher than 90% by a single batch process but was found to be largely dependent on the rate of temperature change and the particle size, i.e., the specific surface area of Mg particles

The Association Between Social Networks and Self-rated risk of HIV Infection among Secondary School Students in Moshi Municipality, Tanzania.

Abstract This study describes the social networks of secondary school students in Moshi Municipality, and their association with self-rated risk of human immunodeficiency virus (HIV) infection. A cross-sectional analytical study was conducted among 300 students aged 15-24 years in 5 secondary schools in Moshi, Tanzania. Bonding networks were defined as social groupings of students participating in activities within the school, while bridging networks were groups that included students participating in social groupings from outside of the school environs. A structured questionnaire was used to ask about participation in bonding and bridging social networks and self-rated HIV risk behavior. More participants participated in bonding networks (72%) than in bridging networks (29%). Participation in bridging networks was greater among females (25%) than males (12%, p < .005). Of 300 participants, 88 (29%) were sexually experienced, and of these 62 (70%) considered themselves to be at low risk of HIV infection. Factors associated with self-rated risk of HIV included: type of school (p < .003), family structure (p < .008), being sexually experienced (p < .004), having had sex in the past three months (p < .009), having an extra sexual partner (p < .054) and non-condom use in last sexual intercourse (p < .001), but not the presence or type of social capital. The study found no association between bonding and bridging social networks on self-rated risk of HIV among study participants. However, sexually experienced participants rated themselves at low risk of HIV infection despite practicing unsafe sex. Efforts to raise adolescents' self-awareness of risk of HIV infection through life skills education and HIV/acquired immunodeficiency syndrome risk reduction strategies may be beneficial to students in this at-risk group

Altered ATP release and metabolism in dorsal root ganglia of neuropathic rats

<p>Abstract</p> <p>Background</p> <p>Adenosine 5'-triphosphate (ATP) has a ubiquitous role in metabolism and a major role in pain responses after tissue injury. We investigated the changes in basal and KCl-evoked ATP release from rat dorsal root ganglia (DRG) after peripheral neuropathy induction by unilateral sciatic nerve entrapment (SNE).</p> <p>Results</p> <p>After SNE, rats develop long-lasting decreases in ipsilateral hindpaw withdrawal thresholds to mechanical and thermal stimulation. At 15–21 days after neuropathy induction, excised ipsilateral L4-L5 DRG display significantly elevated basal extracellular ATP levels compared to contralateral or control (naive) DRG. However, KCl-evoked ATP release is no longer observed in ipsilateral DRG. We hypothesized that the differential SNE effects on basal and evoked ATP release could result from the conversion of extracellular ATP to adenosine with subsequent activation of adenosine A1 receptors (A1Rs) on DRG neurons. Adding the selective A1R agonist, 2-chloro-N⁶-cyclopentyladenosine (100 nM) significantly decreased basal and evoked ATP release in DRG from naïve rats, indicating functional A1R activation. In DRG ipsilateral to SNE, adding a selective A1R antagonist, 8-cyclopentyl-1,3-dipropylxanthine (30 nM), further increased basal ATP levels and relieved the blockade of KCl-evoked ATP release suggesting that increased A1R activation attenuates evoked ATP release in neurons ipsilateral to SNE. To determine if altered ATP release was a consequence of altered DRG metabolism we compared O₂consumption between control and neuropathic DRG. DRG ipsilateral to SNE consumed O₂at a higher rate than control or contralateral DRG.</p> <p>Conclusion</p> <p>These data suggest that peripheral nerve entrapment increases DRG metabolism and ATP release, which in turn is modulated by increased A1R activation.</p

Infrared and Raman spectra of LiV2O5 single crystals

The phonon dynamics of LiV2O5 single crystals is studied using infrared and Raman spectroscopy techniques. The infrared-active phonon frequencies and dielectric constants are obtained by oscillator fitting procedure of the reflectivity data measured at room temperature. The Raman scattering spectra are measured at room temperature and at T=10 K in all nonequivalent polarized configurations. The assignment of the phonons is done by comparing the infrared and Raman spectra of LiV2O5 and NaV2O5. The factor-group-analysis of the LiV2O5 crystal symmetry and of its constituent layers is performed to explain the symmetry properties of the observed modes. We concluded that layer symmetry dominates in the vibrational properties of this compound.Comment: 10 pages, 5 figure

Recombination dynamics of a human Y-chromosomal palindrome:rapid GC-biased gene conversion, multi-kilobase conversion tracts, and rare inversions

The male-specific region of the human Y chromosome (MSY) includes eight large inverted repeats (palindromes) in which arm-to-arm similarity exceeds 99.9%, due to gene conversion activity. Here, we studied one of these palindromes, P6, in order to illuminate the dynamics of the gene conversion process. We genotyped ten paralogous sequence variants (PSVs) within the arms of P6 in 378 Y chromosomes whose evolutionary relationships within the SNP-defined Y phylogeny are known. This allowed the identification of 146 historical gene conversion events involving individual PSVs, occurring at a rate of 2.9-8.4×10(-4) events per generation. A consideration of the nature of nucleotide change and the ancestral state of each PSV showed that the conversion process was significantly biased towards the fixation of G or C nucleotides (GC-biased), and also towards the ancestral state. Determination of haplotypes by long-PCR allowed likely co-conversion of PSVs to be identified, and suggested that conversion tract lengths are large, with a mean of 2068 bp, and a maximum in excess of 9 kb. Despite the frequent formation of recombination intermediates implied by the rapid observed gene conversion activity, resolution via crossover is rare: only three inversions within P6 were detected in the sample. An analysis of chimpanzee and gorilla P6 orthologs showed that the ancestral state bias has existed in all three species, and comparison of human and chimpanzee sequences with the gorilla outgroup confirmed that GC bias of the conversion process has apparently been active in both the human and chimpanzee lineages