PLASMON EFFECTS IN SOLID-STATE RADIATION DETECTORS

We have examined the role of plasmons on the electron energy response of solid-state (Si and Ge) radiation detectors. We found that at the level of parts per thousand, internal-conversion electron calibration techniques do not suffice to yield an adequate response function. In particular, spectral distortions in the detection of low-energy beta-particles have been found which are not accounted for by the usual calibration methods. Thus, a small but significant error can arise from energy loss to low-energy plasmons in Si and Ge detectors. The proximity of the plasmon energy to the end-point singularity and the quadratic form of the beta-decay spectrum may account for the effect interpreted as a 17 keV neutrino. Similar errors can also arise in other subtle solid-state measurements as, for example, in the X-ray edge absorption and emission spectra of metals and semiconductors

EFFECTIVE-MEDIUM THEORY FOR GRANULAR HIGH-TC SUPERCONDUCTORS ELECTROMAGNETIC PROPERTIES IN THE MICROWAVE REGION

The authors extend to finite frequencies their recently developed effective-medium theory (EMT) for granular high-Tc superconductors (HTS). Here they present results for the electromagnetic properties in the microwave region, which is of potential significance for early commercial applications of HTS materials. Most of their discussions centre on generalisations of classical Mie scattering theory to spherical superconductor grains. However, there are important corrections to previous works on EMT at finite frequencies by Stroud and Pan (1978) and also Mahan (1988), which they discuss. Some illustrative numerical results are presented, deferring lengthy numerical computations and comparisons with experiments, to be published elsewhere

PROPERTIES OF GRANULAR HIGH-TC SUPERCONDUCTORS IN AN EFFECTIVE MEDIUM THEORY

The authors consider the transport, electromagnetic and thermodynamic properties of a granular high-Tc superconductor by constructing a model of weakly coupled (Josephson junctions) superconducting and normal grains. They start by using an effective medium theory (EMT), for the conductivity and susceptibility, which is supplemented by London electrodynamics for the superconducting grains, in the limit of weak magnetic field and zero transport current. Next the authors assume a Gaussian distribution of junction resistances R, with mean Ro and variance sigma , which determines the Josephson coupling energy between grains. The criterion that this energy must be greater than kT for superconducting clusters enables them to determine the superconducting fraction cs as a function of temperature. With this they complete the determination of the conductivity and susceptibility of their model. The authors also discuss the specific heat, neglecting fluctuations, which is directly proportional to cs, in their approximation. Throughout this paper, they adopt the Ginzburg-Landau (GL) expressions for the energy gap Delta (order parameter), which is valid near Tc and for the specific heat CH, but they allow for possible deviations of numerical coefficients in these expressions from the Bardeen, Cooper and Schrieffer (BCS) microscopic theory, by introducing phenomenological parameters. The authors find, in accord with experiments, differences between the temperatures of zero resistivity, of resistivity drop and for maximum Meissner effect

Was Schön ever right?

A few years ago, Jan Hendrik Schön impressed the world of science with exciting ideas and amazing experiments. Those experiments are believed no more. But were we wrong to admire the ideas at the time, or have we been too ready to turn our backs on novel ideas because they are associated with misconduct

AN INVESTIGATION OF THE POROUS SILICON OPTICAL-ABSORPTION POWER-LAW NEAR THE BAND-EDGE

A theoretical investigation of the absorption coefficient of p-type doped porous silicon near the band edge is presented. We assume that the absorption coefficient is constructed by taking an average over a distribution (in terms of band gap) of absorption coefficients of individual crystallites. Exploiting physics fundamental to the crystallite optical absorption process, we derive the relation between the absorption coefficient and the averaged conduction density of states near the band edge for porous silicon. By postulating a specific form for the effective conduction density of states we find excellent agreement with recent optical absorption data for p-type doped porous silicon. We attempt to explain the basis for this postulate phenomenologically by suggesting a certain large-scale behaviour of the particle size distribution. The implication of further experimental verification will be discussed

Field emission theory for an enhanced surface potential: a model for carbon field emitters

We propose a non-JWKB-based theory of electron field emission for carbon field emitters in which, for electrons with energy in the vicinity of the order of v to the Fermi level, the effective (1/x) surface potential is strongly enhanced. The model grossly violates the WKB validity criteria and necessitates an analytic treatment of the one-dimensional Schrodinger equation, which we first obtain. We determine v (which is field-dependent) from the wavefunction matching point close to the surface. For reasonable values of the surface parameters-work function phi approximate to 2-5 eV, electron affinity chi approximate to 2phi and an empirical electron loss factor sigma approximate to 10(-3) (and with no other adjustable parameters)-the theory provides an intriguing agreement with experimental data from carbon epoxy graphite composite (PFE) and certain graphitized carbon nanotube field emitters. We speculate on the surface potential enhancement, which can be interpreted as a massive (field-induced) dielectric effect of dynamic origin. This can be related via time-dependent perturbation theory to second-order non-linear polarizability enhancements at ultraviolet similar to3000 Angstrom wavelengths near the tunnelling region. Finally some exact mathematical results are included in the appendix for future reference

Optical properties of organic materials for optical communication devices

2005 International Symposium on Intelligent Signal Processing and Communication Systems (ISPACS 2005), Hong Kong, 13-16 December 2005Recently, organic materials have been considered as a potential candidate for making optoelectronic devices. In order to optimize the performance of the optoelectronic devices, the absolute refractive index and absorption coefficient of the organic materials have to be determined. In this article, the absolute optical properties of two novel bipolar organic materials will be investigated through ellipsometry and modeling using Lorentz Oscillator model and stimulated annealing algorithm. © 2005 IEEE.published_or_final_versio

The Challenge Non-Typhoidal Salmonella (CHANTS) Consortium: Development of a non-typhoidal Salmonella controlled human infection model: Report from a consultation group workshop, 05 July 2022, London, UK [version 2; peer review: 2 approved]

Invasive non-typhoidal Salmonella disease (iNTS) is a major cause of morbidity and mortality globally, particularly as a cause of bloodstream infection in children and immunocompromised adults in sub-Saharan Africa. Vaccines to prevent non-typhoidal Salmonella (NTS) would represent a valuable public health tool in this setting to avert cases and prevent expansion of antimicrobial resistance. Several NTS and combination typhoidal-NTS vaccine candidates are in early-stage development, although the pathway to licensure is unclear due to challenges in conducting large phase III field trials. Controlled human infection models (CHIM) present an opportunity to accelerate vaccine development for a range of enteric pathogens. Several recent typhoidal Salmonella CHIMs have been conducted safely and have played pivotal roles in progressing vaccine candidates to pre-qualification and licensure. The Challenge Non-Typhoidal Salmonella (CHANTS) consortium has been formed with funding from the Wellcome Trust, to deliver the first NTS CHIM, which can act as a platform for future vaccine evaluation. This paper reports the conclusions of a consultation group workshop convened with key stakeholders. The aims of this meeting were to: (1) define the rationale for an NTS CHIM (2) map the NTS vaccine pipeline (3) refine study design and (4) establish potential future use cases

Natural coagulates for wastewater treatment; a review for application and mechanism

The increase of water demand and wastewater generation is among the global concerns in the world. The less effective management of water sources leads to serious consequences, the direct disposal of untreated wastewater is associated with the environmental pollution, elimination of aquatic life and the spread of deadly epidemics. The flocculation process is one of the most important stages in water and wastewater treatment plants, wherein this phase the plankton, colloidal particles, and pollutants are precipitated and removed. Two major types of coagulants are used in the flocculation process included the chemical and natural coagulants. Many studies have been performed to optimize the flocculation process while most of these studies have confirmed the hazardous effects of chemical coagulants utilization on the ecosystem. This chapter reviews a summary of the coagulation/flocculation processes using natural coagulants as well as reviews one of the most effective natural methods of water and wastewater treatment

Direct Sensing of Endothelial Oxidants by Vascular Endothelial Growth Factor Receptor-2 and c-Src

BACKGROUND: ADPH oxidase-derived reactive oxygen species (ROS) play important roles in redox homeostasis and signal transduction in endothelial cells (ECs). We previously demonstrated that c-Src plays a key role in VEGF-induced, ROS-dependent selective activation of PI3K-Akt but not PLCγ-1-ERK1/2 signaling pathways. The aim of the present study was to understand how VEGFR-2-c-Src signaling axis 'senses' NADPH oxidase-derived ROS levels and couples VEGF activation of c-Src to the redox state of ECs. METHODOLOGY/PRINCIPAL FINDINGS: Using biotinylated probe that detects oxidation of cysteine thiol (cys-OH) in intracellular proteins, we demonstrate that VEGF induced oxidative modification in c-Src and VEGFR-2, and that reduction in ROS levels using siRNA against p47(phox) subunit of Rac1-dependent NADPH oxidase inhibited this phenomenon. Co-immunoprecipitation studies using human coronary artery ECs (HCAEC) showed that VEGF-induced ROS-dependent interaction between VEGFR-2 and c-Src correlated with their thiol oxidation status. Immunofluorescence studies using antibodies against internalized VEGFR-2 and c-Src demonstrated that VEGF-induced subcellular co-localization of these tyrosine kinases were also dependent on NADPH oxidsase-derived ROS. CONCLUSION/SIGNIFICANCE: These results demonstrate that VEGF induces cysteine oxidation in VEGFR-2 and c-Src in an NADPH oxidase-derived ROS-dependent manner, suggesting that VEGFR-2 and c-Src can 'sense' redox levels in ECs. The data also suggest that thiol oxidation status of VEGFR-2 and c-Src correlates with their ability to physically interact with each other and c-Src activation. Taken together, these findings suggest that prior to activating downstream c-Src-PI3K-Akt signaling pathway, VEGFR-2-c-Src axis requires an NADPH oxidase-derived ROS threshold in ECs