A High Efficiency Lateral Light Emitting Device on SOI

The infrared light emission of lateral p/sup +/-p-n/sup +/ diodes realized on SIMOX-SOI (separation by implantation of oxygen - silicon on insulator) substrates has been studied. The confinement of the free carriers in one dimension due to the buried oxide was suggested to be a key point to increase the band-to-band recombination probability in silicon light emitters. We found in our devices an external quantum efficiency comparable to previous results presented in the literature. The wavelength range of the emission was found to be 900-1300 nm which is common for indirect band to band recombination in Si. The SOI technology incorporates an insulating layer between the thin single crystal silicon layer and the much thicker substrate. This electrically insulating layer is also a thermal isolator and so self-heating effects are common in devices fabricated on SOI wafers. Investigation of its influence on the light emission and the light distribution in the device has been carried out in our research. In this paper, the characteristics of the device with different active region lengths were investigated and explained quantitatively based on the recombination rate of carriers inside the active area by using the simulation model in Silvaco

XMM-Newton and INTEGRAL analysis of the Supergiant Fast X-ray Transient IGR J17354-3255

We present the results of combined INTEGRAL and XMM-Newton observations of the supergiant fast X-ray transient (SFXT) IGR J17354$-$3255. Three XMM-Newton observations of lengths 33.4 ks, 32.5 ks and 21.9 ks were undertaken, the first an initial pointing to identify the correct source in the field of view and the latter two performed around periastron. Simultaneous INTEGRAL observations across $\sim66\%$ of the orbital cycle were analysed but the source was neither detected by IBIS/ISGRI nor by JEM-X. The XMM-Newton light curves display a range of moderately bright X-ray activity but there are no particularly strong flares or outbursts in any of the three observations. We show that the spectral shape measured by XMM-Newton can be fitted by a consistent model throughout the observation, suggesting that the observed flux variations are driven by obscuration from a wind of varying density rather than changes in accretion mode. The simultaneous INTEGRAL data rule out simple extrapolation of the simple powerlaw model beyond the XMM-Newton energy range.Comment: 13 pages, 9 figures, This article has been accepted for publication in Monthly Notices of the Royal Astronomical Society Published by Oxford University Pres

Resonantly damped oscillations of longitudinally stratified coronal loops

Soon after coronal loop oscillations were observed by TRACE spacecraft for the first time in 1999, various theoretical models have been put forward to explain the rapid damping of the oscillations of these intriguing objects. Coronal loop oscillations are often interpreted as fast kink modes of a straight cylindrical magnetic flux tube with immovable edges modelling dense photospheric plasma at the ends of the loop. Taking this model as a basis we use cold plasma approximation and consider the tube to be thin to simplify the problem and be able to deal with it analytically. In its equilibrium state the tube is permeated by a homogeneous magnetic field directed along the tube axis. We include the effect of stratification in our model supposing that plasma density varies along the tube. There is also density inhomogeneity in the radial direction confined in a layer with thickness much smaller than the radius of the tube. Considering the system of linearized MHD equations we study the dependence of the spectrum of tube oscillations and its damping due to resonant absorption on the parameters of the unperturbed state. The implication of the obtained results on coronal seismology is discussed

Low-power micro-scale CMOS-compatible silicon sensor on a suspended membrane.

In this paper we describe a new, simple and cheap silicon device operating at high temperature at a very low power of a few mW. The essential part of the device is a nano-size conductive link 10-100 nm in size (the so-called antifuse) formed in between two poly-silicon electrodes separated by a thin SiO2 layer. The device can be utilized in chemical sensors or chemical micro-reactors requiring high temperature and very low power consumption e.g. in portable, battery operated systems. As a direct application, we mention a gas sensor (i.e. Pellistor) for hydrocarbons (butane, methane, propane, etc.) based on temperature changes due to the catalytic combustion of hydrocarbons. The power consumed by our device is at about 2% of the power consumed by conventional Pellistors

Mechanical cleaning of graphene

Contamination of graphene due to residues from nanofabrication often introduces background doping and reduces charge carrier mobility. For samples of high electronic quality, post-lithography cleaning treatments are therefore needed. We report that mechanical cleaning based on contact mode AFM removes residues and significantly improves the electronic properties. A mechanically cleaned dual-gated bilayer graphene transistor with hBN dielectrics exhibited a mobility of ~36,000 cm2/Vs at low temperature.Comment: 4 pages, 4 figure

ATLAS Commander: an ATLAS production tool

This paper describes the ATLAS production tool AtCom (for ATLAS Commander). The purpose of the tool is to automate as much as possible the task of a production manager: defining and submitting jobs in large quantities, following up upon their execution, scanning log files for known and unknown errors, updating the various ATLAS bookkeeping databases on successful completion of a job whilst cleaning up and resubmitting otherwise. The design of AtCom is modular, separating the generic basic job management functionality from the interactions with the various databases on the one hand, and the computing systems on the other hand. Given the near future reality of different flavors of computing systems (legacy and GRID) deployed concurrently at the various, or even a single ATLAS site, AtCom allows several of them to be used at the same time transparently.Comment: Talk from the 2003 Computing in High Energy and Nuclear Physics Conference (CHEP03), La Jolla, Ca, USA, March 2003, 7 pages, PDF, PSN : MONT00

New insights on accretion in Supergiant Fast X-ray Transients from XMM-Newton and INTEGRAL observations of IGR J17544−-2619

XMM-Newton observations of the supergiant fast X-ray transient IGR$~$J17544$-$2619 are reported and placed in the context of an analysis of archival INTEGRAL/IBIS data that provides a refined estimate of the orbital period at 4.9272$\pm$0.0004 days. A complete outburst history across the INTEGRAL mission is reported. Although the new XMM-Newton observations (each lasting $\sim$15 ks) targeted the peak flux in the phase-folded hard X-ray light curve of IGR$~$J17544$-$2619, no bright outbursts were observed, the source spending the majority of the exposure at intermediate luminosities of the order of several 10$^{33}\,$erg$\,$s$^{-1}$ (0.5$\,-\,$10$\,$keV) and displaying only low level flickering activity. For the final portion of the exposure, the luminosity of IGR$~$J17544$-$2619 dropped to $\sim$4$\times$10$^{32}\,$erg$\,$s$^{-1}$ (0.5 - 10 keV), comparable with the lowest luminosities ever detected from this source, despite the observations being taken near to periastron. We consider the possible orbital geometry of IGR$~$J17544$-$2619 and the implications for the nature of the mass transfer and accretion mechanisms for both IGR$~$J17544$-$2619 and the SFXT population. We conclude that accretion under the `quasi-spherical accretion' model provides a good description of the behaviour of IGR$~$J17544$-$2619, and suggest an additional mechanism for generating outbursts based upon the mass accumulation rate in the hot shell (atmosphere) that forms around the NS under the quasi-spherical formulation. Hence we hope to aid in explaining the varied outburst behaviours observed across the SFXT population with a consistent underlying physical model.Comment: 12 pages, 5 figures, accepted for publication in MNRA

Coronal loop seismology using multiple transverse loop oscillation harmonics

Context. TRACE observations (23/11/1998 06:35:57−06:48:43 UT) in the 171 Å bandpass of an active region are studied. Coronal loop oscillations are observed after a violent disruption of the equilibrium. Aims. The oscillation properties are studied to give seismological estimates of physical quantities, such as the density scale height. Methods. A loop segment is traced during the oscillation, and the resulting time series is analysed for periodicities. Results. In the loop segment displacement, two periods are found: 435.6 ± 4.5 s and 242.7 ± 6.4 s, consistent with the periods of the fundamental and 2nd harmonic fast kink oscillation. The small uncertainties allow us to estimate the density scale height in the loop to be 109 Mm, which is about double the estimated hydrostatical value of 50 Mm. Because a loop segment is traced, the amplitude dependence along the loop is found for each of these oscillations. The obtained spatial information is used as a seismological tool to give details about the geometry of the observed loop