Analytical Model for the Optical Functions of Indium Gallium Nitride with Application to Thin Film Solar Photovoltaic Cells

This paper presents the preliminary results of optical characterization using spectroscopic ellipsometry of wurtzite indium gallium nitride (InxGa1-xN) thin films with medium indium content (0.38<x<0.68) that were deposited on silicon dioxide using plasma-enhanced evaporation. A Kramers-Kronig consistent parametric analytical model using Gaussian oscillators to describe the absorption spectra has been developed to extract the real and imaginary components of the dielectric function ({\epsilon}1, {\epsilon}2) of InxGa1-xN films. Scanning electron microscope (SEM) images are presented to examine film microstructure and verify film thicknesses determined from ellipsometry modelling. This fitting procedure, model, and parameters can be employed in the future to extract physical parameters from ellipsometric data from other InxGa1-xN films

Examining c-di-GMP and possible quorum sensing regulation in Pseudomonas fluorescens SBW25:links between intra and inter-cellular regulation benefits community cooperative activities such as biofilm formation

Bacterial success in colonizing complex environments requires individual response to micro-scale conditions as well as community-level cooperation to produce large-scale structures such as biofilms. Connecting individual and community responses could be achieved by linking the intracellular sensory and regulatory systems mediated by bis-(3′-5′)-cyclic dimeric guanosine monophosphate (c-di-GMP) and other compounds of individuals with intercellular quorum sensing (QS) regulation controlling populations. There is growing evidence to suggest that biofilm formation by many pseudomonads is regulated by both intra and intercellular systems, though in the case of the model Pseudomonas fluorescens SBW25 Wrinkly Spreader in which mutations increasing c-di-GMP levels result in the production of a robust cellulose-based air-liquid interface biofilm, no evidence for the involvement of QS regulation has been reported. However, our recent review of the P. fluorescens SBW25 genome has identified a potential QS regulatory pathway and other QS–associated genes linked to c-di-GMP homeostasis, and QS signal molecules have also been identified in culture supernatants. These findings suggest a possible link between c-di-GMP and QS regulation in P. fluorescens SBW25 which might allow a more sophisticated and responsive control of cellulose production and biofilm formation when colonising the soil and plant-associated environments P. fluorescens SBW25 normally inhabits.Анализ ц-ди-ГМФ и возможного чувства кворума у Pseudomonas fluorescens SBW 25: связь между внутри и межклеточной регуляцией способствует кооперативному поведению в сообществе и формированию биоплёнкиУспешность бактериальной колонизации сложных экониш требует индивидуального ответа на изменения условий на микроуровне равно как и кооперации на уровне сообщества для продукции таких крупно масштабных структур как биоплёнки. Координация индивидуальных ответ ов и ответов сообщества может быть достигнута путем связывания внутриклеточных сенсорных и регуляторных систем, опосредуемых бис-(3',5')-циклическим димерным гуанозинмонофосфатом (ц-ди-ГМФ) и другими соединениями индивидуумов с межклеточной регуляцией - чувством кворума (ЧК), контролирующем популяци ю. Накапливается всё больше доказательств того, что формирование биопленки многими псевдомонадами регулируется как внутри клеточными, так и меж клеточными регуляторными системами, хотя в случае модельной Pseudomonas fluorescens SBW25 Wrinkly Spreader, у которой мутации, повышающ ие уровни ц-ди-ГМФ, приводят к созданию прочной целлюлозной биоплёнки на границе раздела фаз воздух-жидкость, не было обнаружено ни ка кого свидетельства вовлечения кворум-зависимой регуляции. Однако наш недавний обзор генома P. fluorescens SBW25 выявил потенциальный ЧК-зависимый регуляторный пу ть и другие ЧК-зависимые гены, связанные с гомеостазом ц-ди-ГМФ, а молекулы ЧК-сигналинга были идентифицированы в культуре. Эти данные свидетельствуют о возможной связи между ц-ди-ГМФ-регуляцией и ЧК у P. fluorescens SBW25, что позволяет более сложный и гибкий контроль над продукцией целлюлозы и образовани ем биопленки при колонизации почв и экониш, aссоциированных с растениям и, - естественными средами обитания P. fluorescens SBW25

The Double Pulsar Eclipses I: Phenomenology and Multi-frequency Analysis

The double pulsar PSR J0737-3039A/B displays short, 30 s eclipses that arise around conjunction when the radio waves emitted by pulsar A are absorbed as they propagate through the magnetosphere of its companion pulsar B. These eclipses offer a unique opportunity to probe directly the magnetospheric structure and the plasma properties of pulsar B. We have performed a comprehensive analysis of the eclipse phenomenology using multi-frequency radio observations obtained with the Green Bank Telescope. We have characterized the periodic flux modulations previously discovered at 820 MHz by McLaughlin et al., and investigated the radio frequency dependence of the duration and depth of the eclipses. Based on their weak radio frequency evolution, we conclude that the plasma in pulsar B's magnetosphere requires a large multiplicity factor (~ 10^5). We also found that, as expected, flux modulations are present at all radio frequencies in which eclipses can be detected. Their complex behavior is consistent with the confinement of the absorbing plasma in the dipolar magnetic field of pulsar B as suggested by Lyutikov & Thompson and such a geometric connection explains that the observed periodicity is harmonically related to pulsar B's spin frequency. We observe that the eclipses require a sharp transition region beyond which the plasma density drops off abruptly. Such a region defines a plasmasphere which would be well inside the magnetospheric boundary of an undisturbed pulsar. It is also two times smaller than the expected standoff radius calculated using the balance of the wind pressure from pulsar A and the nominally estimated magnetic pressure of pulsar B.Comment: 9 pages, 7 figures, 3 tables, ApJ in pres

NDT of Composites by Thermography

This paper describes ongoing research efforts to evaluate thermographic techniques for locating flaws or damage in structural fiber composite laminates. An infra-red camera with video isotherm readout is used to identify perturbations in uniform or linear thermal fields which may be caused by presence of flaws or damage such as matrix cracks, delaminations, blind side impact damage, and partial through holes. This procedure has potential for rapid qualitative screening of large surface areas. Potential defective areas may then be analyzed by a more accurate (but more time consuming) method . Two techniques are discussed; externally applied thermal field (EATF) and stress-generated thermal field (SGTF). The EATF technique involves applying heat to a composite structure and observing theresulting transient thermal pattern. The SGTF technique requires stress cycling to create hot spots in regions of high stress concentrations adjacent to flaws or damage sites

Formation of "Lightnings" in a Neutron Star Magnetosphere and the Nature of RRATs

The connection between the radio emission from "lightnings" produced by the absorption of high-energy photons from the cosmic gamma-ray background in a neutron star magnetosphere and radio bursts from rotating radio transients (RRATs) is investigated. The lightning length reaches 1000 km; the lightning radius is 100 m and is comparable to the polar cap radius. If a closed magnetosphere is filled with a dense plasma, then lightnings are efficiently formed only in the region of open magnetic field lines. For the radio emission from a separate lightning to be observed, the polar cap of the neutron star must be directed toward the observer and, at the same time, the lightning must be formed. The maximum burst rate is related to the time of the plasma outflow from the polar cap region. The typical interval between two consecutive bursts is ~100 s. The width of a single radio burst can be determined both by the width of the emission cone formed by the lightning emitting regions at some height above the neutron star surface and by a finite lightning lifetime. The width of the phase distribution for radio bursts from RRATs, along with the integrated pulse width, is determined by the width of the bundle of open magnetic field lines at the formation height of the radio emission. The results obtained are consistent with the currently available data and are indicative of a close connection between RRATs, intermittent pulsars, and extreme nullers.Comment: 24 pages, no figures, references update

The Early Palomar Program (1950-1955) for the Discovery of Classical Novae in M81: Analysis of the Spatial Distribution, Magnitude Distribution, and Distance Suggestion

Data obtained in the 1950-1955 Palomar campaign for the discovery of classical novae in M81 are set out in detail. Positions and apparent B magnitudes are listed for the 23 novae that were found. There is modest evidence that the spatial distribution of the novae does not track the B brightness distribution of either the total light or the light beyond an isophotal radius that is 70\arcsec from the center of M81. The nova distribution is more extended than the aforementioned light, with a significant fraction of the sample appearing in the outer disk/spiral arm region. We suggest that many (perhaps a majority) of the M81 novae that are observed at any given epoch (compared with say $10^{10}$ years ago) are daughters of Population I interacting binaries. The conclusion that the present day novae are drawn from two population groups, one from low mass white dwarf secondaries of close binaries identified with the bulge/thick disk population, and the other from massive white dwarf secondaries identified with the outer thin disk/spiral arm population, is discussed. We conclude that the M81 data are consistent with the two population division as argued previously from (1) the observational studies on other grounds by Della Valle et al. (1992, 1994), Della Valle & Livio (1998), and Shafter et al. (1996) of nearby galaxies, (2) the Hatano et al. (1997a,b) Monte Carlo simulations of novae in M31 and in the Galaxy, and (3) the Yungelson et al. (1997) population synthesis modeling of nova binaries. Two different methods of using M81 novae as distance indicators give a nova distance modulus for M81 as $(m-M)_0 = 27.75$, consistent with the Cepheid modulus that is the same value.Comment: 24 pages, 7 figures, accepted to PAS

Some exact non-vacuum Bianchi VI0 and VII0 instantons

We report some new exact instantons in general relativity. These solutions are K\"ahler and fall into the symmetry classes of Bianchi types VI0 and VII0, with matter content of a stiff fluid. The qualitative behaviour of the solutions is presented, and we compare it to the known results of the corresponding self-dual Bianchi solutions. We also give axisymmetric Bianchi VII0 solutions with an electromagnetic field.Comment: latex, 15 pages with 3 eps figure

CoRoT measures solar-like oscillations and granulation in stars hotter than the Sun

Oscillations of the Sun have been used to understand its interior structure. The extension of similar studies to more distant stars has raised many difficulties despite the strong efforts of the international community over the past decades. The CoRoT (Convection Rotation and Planetary Transits) satellite, launched in December 2006, has now measured oscillations and the stellar granulation signature in three main sequence stars that are noticeably hotter than the sun. The oscillation amplitudes are about 1.5 times as large as those in the Sun; the stellar granulation is up to three times as high. The stellar amplitudes are about 25% below the theoretic values, providing a measurement of the nonadiabaticity of the process ruling the oscillations in the outer layers of the stars.Comment: 7 pages, 4 figure

Experimental investigation of flux motion in exponentially shaped Josephson junctions

We report experimental and numerical analysis of expontentially shaped long Josephson junctions with lateral current injection. Quasi-linear flux flow branches are observed in the current-voltage characteristic of the junctions in the absence of magnetic field. A strongly asymmetric response to an applied magnetic field is also exhibited by the junctions. Experimental data are found in agreement with numerical predictions and demonstrate the existence of a geometry-induced potential experienced by the flux quanta in nonuniform width junctions.Comment: 16 pg, 8 figures, Submitted in PRB March