Positronium scattering by atomic hydrogen with inclusion of target excitation channels

Calculations are reported for positronium (Ps) scattering by atomic hydrogen (H) in the energy range 0-6.5 eV in a coupled- pseudostate approximation in which excitation and ionization channels of both the Ps and the H are taken into account. The approximation contains an accurate representation of the van der Waals coefficient. Results are presented for phase shifts, scattering lengths, effective ranges, and various cross sections including partial wave, total, and ortho-para conversion cross sections. An analysis of the possible spin transitions is provided and the energy of the positronium hydride (PsH) bound state is determined. Substantial differences are found from earlier work within the frozen target approximation, now clearly confirming the importance of target excitation channels. Good agreement is obtained with recent calculations of S-wave phase shifts and scattering lengths using the stabilization method. Convergence to the exact binding energy for PsH appears to be slow. Resonances corresponding to unstable states of the positron orbiting H- are seen in the electronic spin singlet partial waves. The importance of the H- formation channel is discussed.

Self-cooling of a micro-mirror by radiation pressure

Cooling of mechanical resonators is currently a popular topic in many fields of physics including ultra-high precision measurements, detection of gravitational waves and the study of the transition between classical and quantum behaviour of a mechanical system. Here we report the observation of self-cooling of a micromirror by radiation pressure inside a high-finesse optical cavity. In essence, changes in intensity in a detuned cavity, as caused by the thermal vibration of the mirror, provide the mechanism for entropy flow from the mirror's oscillatory motion to the low-entropy cavity field. The crucial coupling between radiation and mechanical motion was made possible by producing free-standing micromirrors of low mass (m approximately 400 ng), high reflectance (more than 99.6%) and high mechanical quality (Q approximately 10,000). We observe cooling of the mechanical oscillator by a factor of more than 30; that is, from room temperature to below 10 K. In addition to purely photothermal effects we identify radiation pressure as a relevant mechanism responsible for the cooling. In contrast with earlier experiments, our technique does not need any active feedback. We expect that improvements of our method will permit cooling ratios beyond 1,000 and will thus possibly enable cooling all the way down to the quantum mechanical ground state of the micromirror.

HOS-Based Semi-Blind Spatial Equalization for MIMO Rayleigh Fading Channels

In this paper we concentrate on the direct semi-blind spatial equalizer design for MIMO systems with Rayleigh fading channels. Our aim is to develop an algorithm which can outperform the classical training based method with the same training information used, and avoid the problems of low convergence speed and local minima due to pure blind methods. A general semi-blind cost function is first constructed which incorporates both the training information from the known data and some kind of higher order statistics (HOS) from the unknown sequence. Then, based on the developed cost function, we propose two semi-blind iterative and adaptive algorithms to find the desired spatial equalizer. To further improve the performance and convergence speed of the proposed adaptive method, we propose a technique to find the optimal choice of step size. Simulation results demonstrate the performance of the proposed algorithms and comparable schemes.

Detection of Lead Contamination of Water and VOC Contamination of Air Using SOI Micro-Optical Devices

Micro-photonic SOI Mach-Zehnder interferometers were coated with solid-phase micro-extraction materials derived from polydimethylsiloxane to enable sensing of volatile organic compounds of the BTEX class in air. A different coating based on functionalized mesoporous silicates is used to detect lead Pb(II) with a detection limit of <;; 100 ppb in water.

The human micro-vascular enclothelial cells in vitro interaction with atomic-nitrogen-doped diamond-like carbon thin films

This paper reports the initial response of atomic nitrogen doped diamond like carbon (DLC) to endothelial cells in vitro. The introduction of nitrogen atoms/molecules to the diamond like carbon structures leads to an atomic structural change favorable to the attachment of human micro-vascular enclothelial cells. Whilst the semi-conductivity induced by nitrogen in DLC is thought to play a part, the increase in the inion-bonded N atoms and N-2 molecules in the atomic doped species (with the exclusion of the charged species) seems to contribute to the improved attachment of human microvascular endothelial cells. The increased endothelial attachment is associated with a lower work function and slightly higher water contact angle in the atomic doped films, where the heavy charged particles are excluded. The films used in the study were synthesized by the RF PECVD technique followed by post deposition doping with nitrogen, and afterwards the films were characterized by XPS, Raman spectroscopy, SIMS and Kelvin probe. The water contact angles were measured, and the counts of the adherent endothelial cells on the samples were carried out. This study is relevant and contributory to improving biocompatibility of surgical implants and prostheses.

Optical diagnostics of micro discharge jets

Micro plasmas operated at ambient pressure with dimensions of the confining geometry in the order of a few ten micrometers to a millimeter are actually in the focus of interest due to the broad regime of applicability they offer and due to a similarly broad range of open physical questions. Here we present optical measurements within the discharge core and the effluent region of an especially developed micro discharge jet. To get an understanding of the complex system of this discharge it is important to analyse transport phenomena of energy and particles within both parts of the discharge by various highly sophisticated diagnostics. As a consequence of the limited access and the dimensions of the micro discharge most of these diagnostics are optical. Here we present diagnostics applied to determine spatially resolved absolute atomic oxygen densities as the most reactive constituent of the effluent, density maps of ozone as final reaction product of the gas chemical chain induced by the discharge and phase resolved optical emission spectroscopy yielding insight into the excitation dynamics of the discharge. (C) 2007 WILEY-VCH Verlag GmbH & Co. KGaA. Weinheim.

Higher order statistics for lognormal small-scale fading in mobile radio channels

This letter reports the statistical characterization and modeling of the indoor radio channel for a mobile wireless personal area network operating at 868 MHz. Line of sight (LOS) and non-LOS conditions were considered for three environments: anechoic chamber, open office area and hallway. Overall, the Nakagami-m cdf best described fading for bodyworn operation in 60% of all measured channels in anechoic chamber and open office area environments. The Nakagami distribution was also found to provide a good description of Rician distributed channels which predominated in the hallway. Multipath played an important role in channel statistics with the mean recorded m value being reduced from 7.8 in the anechoic chamber to 1.3 in both the open office area and hallway.