Synthesis of Hafnium-Free Nanostructured Half-Heusler Materials for Thermoelectric Applications

Half-Heusler thermoelectric materials convert heat directly into electricity by means of the Seebeck effect. Improving the conversion efficiency and reducing fabrication costs will reduce the price per watt enabling widespread commercialization for waste heat energy harvesting and self-powered devices. In this work, a rapid low-cost synthesis route utilizing mechanical alloying via high energy planetary ball milling and spark plasma sintering was used to fabricate n-type hafnium-free single phase nano-grained TiZrNiSnSb based half-heusler monoliths with a modest figure of merit performance with significantly reduced thermal conductivity

Evidence for moving breathers in a layered crystal insulator at 300K

We report the ejection of atoms at a crystal surface caused by energetic breathers which have travelled more than 10^7 unit cells in atomic chain directions. The breathers were created by bombardment of a crystal face with heavy ions. This effect was observed at 300K in the layered crystal muscovite, which has linear chains of atoms for which the surrounding lattice has C_2 symmetry. The experimental techniques described could be used to study breathers in other materials and configurations.Comment: 7 pages, 3 figure

Outreach obstetrics training in Western Australia improves neonatal outcome and decreases caesarean sections

The objective of this study was to determine the effect of a multi-professional outreach obstetric training programme on perinatal and neonatal outcomes. This was a retrospective comparison of 5-min low Apgar scores, stillbirth, perinatal death and moderate/severe hypoxic ischaemic encephalopathy rates in 127,753 infants born in Western Australia before and after the introduction of training in rural and remote areas. Following the introduction of the training programme, there was a highly significant (p0.003) decrease in the rate of infants born with low 5-min Apgar scores (from 20.4 to 15.4/1,000 live births). While the changes in the other three outcomes were not significant, all three demonstrated a trend for improvement in the intervention area. This is the second study of an educational intervention in obstetrics to demonstrate improvement in neonatal outcome and the first to be associated with a decrease in caesarean sections

Search for a Point-Source Counterpart of the Unidentified Gamma-Ray Source TeV J2032+4130 in Cygnus

We have made a multiwavelength study of the overlapping error boxes of the unidentified gamma-ray sources TeV J2032+4130 and 3EG J2033+4118 in the direction of the Cygnus OB2 association (d = 1.7 kpc) in order to search for a point-source counterpart of the first unidentified TeV source. Optical identifications and spectroscopic classifications for the brighter X-ray sources in ROSAT PSPC and Chandra ACIS images are obtained, without finding a compelling counterpart. The classified X-ray sources are a mix of early and late-type stars, with one exception. The brightest source in the Chandra observation is a new, hard absorbed source that is both transient and rapidly variable. It lies 7' from the centroid of the TeV emission, which places it outside of the claimed 2 sigma location (r = 4.8'). A possible eclipse or "dip" transition is seen in its light curve. With a peak 1-10 keV luminosity of 7 x 10^(32) (d/1.7 kpc})^2 ergs s^(-1), this source could be a quiescent low-mass X-ray binary that lies beyond the Cyg OB2 association. A coincident, reddened optical object of R = 20.4, J = 15.4, H = 14.2, and K = 13.4 is observed, but not yet classified due to the lack of obvious emission or absorption features in its spectrum. Alternatively, this Chandra} and optical source might be a considered a candidate for a proton blazar, a long hypothesized type of radio-weak gamma-ray source. More detailed observations will be needed to determine the nature of this variable X-ray source, and to assess the possibility of its connection with TeV J2032+4130.Comment: 24 pages, 8 figures, accepted by Ap

INTEGRAL/SPI Limits on Electron-Positron Annihilation Radiation from the Galactic Plane

The center of our Galaxy is a known strong source of electron-positron 511-keV annihilation radiation. Thus far, however, there have been no reliable detections of annihilation radiation outside of the central radian of our Galaxy. One of the primary objectives of the INTEGRAL (INTErnational Gamma-RAy Astrophysics Laboratory) mission, launched in Oct. 2002, is the detailed study of this radiation. The Spectrometer on INTEGRAL (SPI) is a high resolution coded-aperture gamma-ray telescope with an unprecedented combination of sensitivity, angular resolution and energy resolution. We report results from the first 10 months of observation. During this period a significant fraction of the observing time was spent in or near the Galactic Plane. No positive annihilation flux was detected outside of the central region (|l| > 40 deg) of our Galaxy. In this paper we describe the observations and data analysis methods and give limits on the 511-keV flux.Comment: Accepted for publication in the Astrophysical Journal. 13 pages, 3 figure

Dispersion force for materials relevant for micro and nanodevices fabrication

The dispersion (van der Waals and Casimir) force between two semi-spaces are calculated using the Lifshitz theory for different materials relevant for micro and nanodevices fabrication, namely, gold, silicon, gallium arsenide, diamond and two types of diamond-like carbon (DLC), silicon carbide, silicon nitride and silicon dioxide. The calculations were performed using recent experimental optical data available in the literature, usually ranging from the far infrared up to the extreme ultraviolet bands of the electromagnetic spectrum. The results are presented in the form of a correction factor to the Casimir force predicted between perfect conductors, for the separation between the semi-spaces varying from 1 nanometre up to 1 micrometre. The relative importance of the contributions to the dispersion force of the optical properties in different spectral ranges is analyzed. The role of the temperature for semiconductors and insulators is also addressed. The results are meant to be useful for the estimation of the impact of the Casimir and van der Waals forces on the operational parameters of micro and nanodevices

Probing a Complex of Cytochromecand Cardiolipin by Magnetic Circular Dichroism Spectroscopy: Implications for the Initial Events in Apoptosis

Oxidation of cardiolipin (CL) by its complex with cytochrome c (cyt c) plays a crucial role in triggering apoptosis. Through a combination of magnetic circular dichroism spectroscopy and potentiometric titrations, we show that both the ferric and ferrous forms of the heme group of a CL:cyt c complex exist as multiple conformers at a physiologically relevant pH of 7.4. For the ferric state, these conformers are His/Lys- and His/OH–-ligated. The ferrous state is predominantly high-spin and, most likely, His/–. Interconversion of the ferric and ferrous conformers is described by a single midpoint potential of -80 ± 9 mV vs SHE. These results suggest that CL oxidation in mitochondria could occur by the reaction of molecular oxygen with the ferrous CL:cyt c complex in addition to the well-described reaction of peroxides with the ferric form