Two pressure-induced structural phase transitions in TiOCl

We studied the crystal structure of TiOCl up to pressures of $p$=25~GPa at room temperature by x-ray powder diffraction measurements. Two pressure-induced structural phase transitions are observed: At $p_{c1}$$\approx$15~GPa emerges an 2$a$$\times$2$b$$\times$$c$ superstructure with $b$-axis unique monoclinic symmetry (space group P2$_1$/$m$). At $p_{c2}$$\approx$22~GPa all lattice parameters of the monoclinic phase show a pronounced anomaly. A fraction of the sample persists in the ambient orthorhombic phase (space group $Pmmn$) over the whole pressure range.Comment: 5 pages, 5 figures; accepted for publication in Phys. Rev.

Pressure-induced metallization and structural phase transition of the Mott-Hubbard insulator TiOBr

We investigated the pressure-dependent optical response of the low-dimensional Mott-Hubbard insulator TiOBr by transmittance and reflectance measurements in the infrared and visible frequency range. A suppression of the transmittance above a critical pressure and a concomitant increase of the reflectance are observed, suggesting a pressure-induced metallization of TiOBr. The metallic phase of TiOBr at high pressure is confirmed by the presence of additional excitations extending down to the far-infrared range. The pressure-induced metallization coincides with a structural phase transition, according to the results of x-ray powder diffraction experiments under pressure.Comment: 4 pages, 3 figure

Psychosis and relapse in bipolar disorder are related to GRM3, DAOA, and GRIN2B genotype

Objective:  Key Words: Manic-Depressive Psychosis; Glutamate; GRIN2B receptor; mGluR3; G72 protein; HumanDysfunction in glutamate signalling is thought to play a role in the pathophysiology of bipolar disorder (BD). There is evidence of associations between single nucleotide polymorphisms (SNPs) in GRM3, GRIN2B, and DAOA genes and the diagnosis of BD. In this pilot study, we investigated the frequency of SNP variants in these 3 genes within South African population groups, and assessed interactions between genes and phenotypes of BD disease severity. Method: Multiplex SNaPshotTM PCR was used to genotype 191 case and 188 control samples. Cases comprised of 191 individuals in a South African cohort of mixed ancestry and Caucasians, with BD Type 1. Phenotypes of BD disease severity were: age of onset, number of illness episodes, number of hospitalisations for depression or mania and history of psychotic symptoms. Results: There were no significant difference in SNP allele frequencies between cases and controls. In the case-only analysis, the GRM3 rs6465084 heterozygote was associated with a 4-fold increased risk of lifetime history of psychotic symptoms, and the specific variants within the gene pair, DAOA and GRIN2B, had a significant interaction with the number of hospitalisations for mania, with lowest admission rates associated with both pairs of ancestral alleles. Conclusion: In BD, variations in glutamatergic genes may influence phenotypes related to the severity of illness. Speculatively, newly derived genes associated with various evolutionary advantages, may also increase the risk for more severe BD. These preliminary findings deserve validation in a larger cohort

Comparison of Astrand VO2 Max Prediction to a Graded Leg Ergometry VO2 Max Test in Endurance Athletes

Please refer to the pdf version of the abstract located adjacent to the title

A Miniaturized Enzymatic Biosensor for Detection of Sensory-Evoked D-serine Release in the Brain

D-serine has been implicated as a brain messenger with central roles in neural signaling and plasticity. Disrupted levels of D-serine in the brain have been associated with neurological disorders, including schizophrenia, depression and Alzheimer's disease. Electrochemical biosensors are attractive tools for measuring real-time in vivo D-serine concentration changes. Current biosensors suffer from relatively large sizes (≥25 μm) making localized cellular measurements challenging, especially for single cell studies. In this work, a robust methodology for the fabrication of a reproducible miniaturized 10 μm D-serine detecting amperometric biosensor was developed. The miniature biosensor incorporated yeast D-amino acid oxidase immobilized on a poly-meta-phenylenediamine modified 10 μm Pt disk microelectrode. The biosensor offered a limit of detection of 0.361 μM (RSD < 10%) with high sensitivity (283 μA cm-2 mM-1, R2 = 0.983). The biosensor was stable for over four hours of continuous use, demonstrated a storage stability of four days and high analyte selectivity. Biosensor selectivity was validated with LC-MS and interferences with yeast D-amino acid oxidase were evaluated using drugs believed to stimulate D-serine release. Ex vivo D-serine measurements were made from Xenopus laevis tadpole brains, demonstrating the utility of the biosensors for measurements on living tissue. We observed that D-serine levels in the brain fluctuate with sensory experience. The biosensors were also used in vivo successfully. Taken together, this study addresses factors for successful and reproducible miniature biosensor fabrication for measuring D-serine in biological samples, for pharmacological evaluation, and for designing point of care devices

Relative numbers of cortical and brainstem inputs to the lateral geniculate nucleus

ABSTRACT Terminals of a morphological type known as RD (for round vesicles and dense mitochondria, which we define here as the aggregate of types formerly known as RSD and RLD, where ''S'' is small and ''L'' is large) constitute at least half of the synaptic inputs to the feline lateral geniculate nucleus, which represents the thalamic relay of retinal input to cortex. It had been thought that the vast majority of these RD terminals were of cortical origin, making the corticogeniculate pathway by far the largest source of input to geniculate relay cells. However, another source of RD terminals recently identified derives from cholinergic cells of the brainstem parabrachial region. (These cells also contain NO.) We used techniques of electron microscopy to determine quantitatively the relative contribution of cortex and brainstem to the population of RD terminals. We identified corticogeniculate terminals by orthograde transport of biocytin injected into the visual cortex and identified brainstem terminals by immunocytochemical labeling for choline acetyltransferase or brain NO synthase (the synthesizing enzymes for acetylcholine and NO, respectively). We estimated the relative numbers of corticogeniculate and brainstem terminals with a two-step algorithm: First, we determined the relative probability of sampling each terminal type in our material, and then we calculated what mixture of identified corticogeniculate and brainstem terminals was needed to recreate the size distribution of the parent RD terminal population. We conclude that brainstem terminals comprise roughly one-half of the RD population. Thus, the cortical input is perhaps half as large and the brainstem input is an order of magnitude larger than had been thought. This further suggests that the brainstem inputs might play a surprisingly complex and subtle role in the control of the geniculocortical relay. It is often claimed that terminals from visual cortex form the dominant input to the lateral geniculate nucleus, which is the thalamic relay of retinal input to the visual cortex (1-4). This is because corticogeniculate axons end in a characteristic type of synaptic terminal we shall refer to as ''RD'' (for round vesicles and dense mitochondria), and RD terminals are the majority found in the geniculate neuropil (1, 2, 4, 5). The RD terminal type represents an aggregate of what was previously defined as RSD and RLD terminals (1, 6), where the ''S'' and ''L'' refer to small and large, respectively. However, we have shown that, based on size, RSD and RLD terminals form a continuum (6) and that there is thus little justification for separating them, so we prefer to lump them together under the new term ''RD.'' Until recently, few candidate sources for RD terminals other than corticogeniculate axons have been identified, and it has been assumed that nearly all of these emanate in the feedback pathway from visual cortex (refs. 1-4 but also see ref. 7). As a result, many functions have been suggested for the corticothalamic pathway in controlling or modifying the thalamic relay (reviewed in ref. 5), and other extrathalamic sources of input have been relegated a less important role. However, we now know that cholinergic terminals from the parabrachial region of the brainstem also display RD morphology, but we have lacked quantitative data permitting us to determine what proportion of the dominant RD terminal population is cortical vs. brainstem in origin. Using material from the cat's lateral geniculate nucleus, we used an algorithm based on size distributions of RD terminals identified as deriving from cortical neurons or from cholinergic brainstem neurons, and we conclude that the brainstem contribution is much greater than previously thought, providing approximately half of the RD terminals. We suggest that, although the corticothalamic input is large, it is not as dominant as once thought, and inputs from the brainstem are much more important in the geniculate relay than has been appreciated. Our basic methods have been fully described elsewher

Ultracold Neutral Plasmas

Ultracold neutral plasmas are formed by photoionizing laser-cooled atoms near the ionization threshold. Through the application of atomic physics techniques and diagnostics, these experiments stretch the boundaries of traditional neutral plasma physics. The electron temperature in these plasmas ranges from 1-1000 K and the ion temperature is around 1 K. The density can approach $10^{11}$ cm$^{-3}$. Fundamental interest stems from the possibility of creating strongly-coupled plasmas, but recombination, collective modes, and thermalization in these systems have also been studied. Optical absorption images of a strontium plasma, using the Sr$^+$ ${^2S\_{1/2}} -> {^2P\_{1/2}}$ transition at 422 nm, depict the density profile of the plasma, and probe kinetics on a 50 ns time-scale. The Doppler-broadened ion absorption spectrum measures the ion velocity distribution, which gives an accurate measure of the ion dynamics in the first microsecond after photoionization.Comment: 12th International Congress on Plasma Physics, 25-29 October 2004, Nice (France

Pubertal timing and breast density in young women: a prospective cohort study.

BACKGROUND:Earlier age at onset of pubertal events and longer intervals between them (tempo) have been associated with increased breast cancer risk. It is unknown whether the timing and tempo of puberty are associated with adult breast density, which could mediate the increased risk. METHODS:From 1988 to 1997, girls participating in the Dietary Intervention Study in Children (DISC) were clinically assessed annually between ages 8 and 17 years for Tanner stages of breast development (thelarche) and pubic hair (pubarche), and onset of menses (menarche) was self-reported. In 2006-2008, 182 participants then aged 25-29 years had their percent dense breast volume (%DBV) measured by magnetic resonance imaging. Multivariable, linear mixed-effects regression models adjusted for reproductive factors, demographics, and body size were used to evaluate associations of age and tempo of puberty events with %DBV. RESULTS:The mean (standard deviation) and range of %DBV were 27.6 (20.5) and 0.2-86.1. Age at thelarche was negatively associated with %DBV (p trend = 0.04), while pubertal tempo between thelarche and menarche was positively associated with %DBV (p trend = 0.007). %DBV was 40% higher in women whose thelarche-to-menarche tempo was 2.9 years or longer (geometric mean (95%CI) = 21.8% (18.2-26.2%)) compared to women whose thelarche-to-menarche tempo was less than 1.6 years (geometric mean (95%CI) = 15.6% (13.9-17.5%)). CONCLUSIONS:Our results suggest that a slower pubertal tempo, i.e., greater number of months between thelarche and menarche, is associated with higher percent breast density in young women. Future research should examine whether breast density mediates the association between slower tempo and increased breast cancer risk

The Effect of Neutrino Radiation on Magnetorotational Instability in Proto-Neutron Stars

Neutrino radiation takes a major role in the momentum, heat, and lepton transports in proto-neutron stars (PNSs). These diffusive processes affect the growth of magnetorotational instability (MRI) in PNSs. We perform a local linear analysis for the axisymmetric and nonaxisymmetric MRI including the effects of neutrino transports and ohmic dissipation. We find that the MRI can grow even in the multi-diffusive situations that are realized in neutrino loaded PNSs. When the toroidal magnetic component dominates over the poloidal one, nonaxisymmetric MRI modes grow much faster than axisymmetric modes. These results suggest the importance of the nonaxisymmetric MRI in PNSs. Thus the understandings of three-dimensional nonlinear evolutions of the MRI are necessary to reveal the explosion mechanism of core-collapse supernovae.Comment: Accepted for publication in ApJ, 24 pages,6 figure

Mott-Hubbard gap closure and structural phase transition in the oxyhalides TiOBr and TiOCl under pressure

Pressure-dependent transmittance and reflectance spectra of TiOBr and TiOCl single crystals at room temperature suggest the closure of the Mott-Hubbard gap, i.e., the gap is filled with additional electronic states extending down to the far-infrared range. According to pressure-dependent x-ray powder diffraction data the gap closure coincides with a structural phase transition. The transition in TiOBr occurs at slightly lower pressure ($p$=14 GPa) compared to TiOCl ($p$=16 GPa) under hydrostatic conditions, which is discussed in terms of the chemical pressure effect. The results of pressure-dependent transmittance measurements on TiOBr at low temperatures reveal similar effects at 23 K, where the compound is in the spin-Peierls phase at ambient pressure.Comment: 11 pages, 12 figures; to appear in Phys. Rev.