On the relativistic large-angle electron collision operator for runaway avalanches in plasmas

Science.gov (United States)

Embréus, O.; Stahl, A.; Fülöp, T.

2018-02-01

Large-angle Coulomb collisions lead to an avalanching generation of runaway electrons in a plasma. We present the first fully conservative large-angle collision operator, derived from the relativistic Boltzmann operator. The relation to previous models for large-angle collisions is investigated, and their validity assessed. We present a form of the generalized collision operator which is suitable for implementation in a numerical kinetic equation solver, and demonstrate the effect on the runaway-electron growth rate. Finally we consider the reverse avalanche effect, where runaways are slowed down by large-angle collisions, and show that the choice of operator is important if the electric field is close to the avalanche threshold.

Effects of keV electron irradiation on the avalanche-electron generation rates of three donors on oxidized silicon

International Nuclear Information System (INIS)

Sah, C.; Sun, J.Y.; Tzou, J.J.

1983-01-01

After keV electron beam irradiation of oxidized silicon, the avalanche-electron-injection generation rates and densities of the bulk compensating donor, the interface states, and the turnaround trap all increase. Heating at 200 0 C can anneal out these three donor-like traps, however, it cannot restore the generation rates back to their original and lower pre-keV electron irradiation values. The experimental results also indicate that all three traps may be related to the same mobile impurity species whose bonds are loosened by the keV electrons and then broken or released by the avalanche injected electrons

Stability of the discretization of the electron avalanche phenomenon

Energy Technology Data Exchange (ETDEWEB)

Villa, Andrea, E-mail: andrea.villa@rse-web.it [Ricerca Sul Sistema Energetico (RSE), Via Rubattino 50, 20134, Milano (Italy); Barbieri, Luca, E-mail: luca.barbieri@rse-web.it [Ricerca Sul Sistema Energetico (RSE), Via Rubattino 50, 20134, Milano (Italy); Gondola, Marco, E-mail: marco.gondola@rse-web.it [Ricerca Sul Sistema Energetico (RSE), Via Rubattino 50, 20134, Milano (Italy); Leon-Garzon, Andres R., E-mail: andresricardo.leon@polimi.it [CMIC Department “Giulio Natta”, Politecnico di Milano, Piazza Leonardo da Vinci 32, 20133, Milano (Italy); Malgesini, Roberto, E-mail: roberto.malgesini@rse-web.it [Ricerca Sul Sistema Energetico (RSE), Via Rubattino 50, 20134, Milano (Italy)

2015-09-01

The numerical simulation of the discharge inception is an active field of applied physics with many industrial applications. In this work we focus on the drift-reaction equation that describes the electron avalanche. This phenomenon is one of the basic building blocks of the streamer model. The main difficulty of the electron avalanche equation lies in the fact that the reaction term is positive when a high electric field is applied. It leads to exponentially growing solutions and this has a major impact on the behavior of numerical schemes. We analyze the stability of a reference finite volume scheme applied to this latter problem. The stability of the method may impose a strict mesh spacing, therefore a proper stabilized scheme, which is stable whatever spacing is used, has been developed. The convergence of the scheme is treated as well as some numerical experiments.

Kinetic modelling of runaway electron avalanches in tokamak plasmas

International Nuclear Information System (INIS)

Nilsson, E; Peysson, Y; Saint-Laurent, F; Decker, J; Granetz, R S; Vlainic, M

2015-01-01

Runaway electrons can be generated in tokamak plasmas if the accelerating force from the toroidal electric field exceeds the collisional drag force owing to Coulomb collisions with the background plasma. In ITER, disruptions are expected to generate runaway electrons mainly through knock-on collisions (Hender et al 2007 Nucl. Fusion 47 S128–202), where enough momentum can be transferred from existing runaways to slow electrons to transport the latter beyond a critical momentum, setting off an avalanche of runaway electrons. Since knock-on runaways are usually scattered off with a significant perpendicular component of the momentum with respect to the local magnetic field direction, these particles are highly magnetized. Consequently, the momentum dynamics require a full 3D kinetic description, since these electrons are highly sensitive to the magnetic non-uniformity of a toroidal configuration. For this purpose, a bounce-averaged knock-on source term is derived. The generation of runaway electrons from the combined effect of Dreicer mechanism and knock-on collision process is studied with the code LUKE, a solver of the 3D linearized bounce-averaged relativistic electron Fokker–Planck equation (Decker and Peysson 2004 DKE: a fast numerical solver for the 3D drift kinetic equation Report EUR-CEA-FC-1736, Euratom-CEA), through the calculation of the response of the electron distribution function to a constant parallel electric field. The model, which has been successfully benchmarked against the standard Dreicer runaway theory now describes the runaway generation by knock-on collisions as proposed by Rosenbluth (Rosenbluth and Putvinski 1997 Nucl. Fusion 37 1355–62). This paper shows that the avalanche effect can be important even in non-disruptive scenarios. Runaway formation through knock-on collisions is found to be strongly reduced when taking place off the magnetic axis, since trapped electrons can not contribute to the runaway electron population. Finally

Mean secondary electron yield of avalanche electrons in the channels of a microchannel plate detector

International Nuclear Information System (INIS)

Funsten, H.O.; Suszcynsky, D.M.; Harper, R.W.

1996-01-01

By modeling the statistical evolution of an avalanche created by 20 keV protons impacting the input surface of a z-stack microchannel plate (MCP) detector, the mean secondary electron yield γ C of avalanche electrons propagating through a MCP channel is measured to equal 1.37 for 760 V per MCP in the z stack. This value agrees with other studies that used MCP gain measurements to infer γ C . The technique described here to measure γ C is independent of gain saturation effects and simplifying assumptions used in the segmented dynode model, both of which can introduce errors when inferring γ C through gain measurements. copyright 1996 American Institute of Physics

Fast sub-electron detectors review for interferometry

Science.gov (United States)

Feautrier, Philippe; Gach, Jean-Luc; Bério, Philippe

2016-08-01

New disruptive technologies are now emerging for detectors dedicated to interferometry. The detectors needed for this kind of applications need antonymic characteristics: the detector noise must be very low, especially when the signal is dispersed but at the same time must also sample the fast temporal characteristics of the signal. This paper describes the new fast low noise technologies that have been recently developed for interferometry and adaptive optics. The first technology is the Avalanche PhotoDiode (APD) infrared arrays made of HgCdTe. In this paper are presented the two programs that have been developed in that field: the Selex Saphira 320x256 [1] and the 320x255 RAPID detectors developed by Sofradir/CEA LETI in France [2], [3], [4]. Status of these two programs and future developments are presented. Sub-electron noise can now be achieved in the infrared using this technology. The exceptional characteristics of HgCdTe APDs are due to a nearly exclusive impaction ionization of the electrons, and this is why these devices have been called "electrons avalanche photodiodes" or e-APDs. These characteristics have inspired a large effort in developing focal plan arrays using HgCdTe APDs for low photon number applications such as active imaging in gated mode (2D) and/or with direct time of flight detection (3D imaging) and, more recently, passive imaging for infrared wave front correction and fringe tracking in astronomical observations. In addition, a commercial camera solution called C-RED, based on Selex Saphira and commercialized by First Light Imaging [5], is presented here. Some groups are also working with instruments in the visible. In that case, another disruptive technology is showing outstanding performances: the Electron Multiplying CCDs (EMCCD) developed mainly by e2v technologies in UK. The OCAM2 camera, commercialized by First Light Imaging [5], uses the 240x240 EMMCD from e2v and is successfully implemented on the VEGA instrument on the CHARA

Fractal multiplication of electron avalanches and streamers: new mechanism of electrical breakdown?

International Nuclear Information System (INIS)

Ficker, T

2007-01-01

Long-lasting problems concerning peculiar statistical behaviour of high populated electron avalanches have been analysed. These avalanches are precursors of streamer breakdown in gases. The present streamer theory fails in explaining severe systematic deviations from the Furry statistics that is believed to be a governing statistical law. Such a deviated behaviour of high populated avalanches seems to be a consequence of a special pre-breakdown mechanism that is rather different from that known so far in discharge physics. This analysis tends towards formulating a modified theoretical concept supplementing the streamer theory by a new statistical view of pre-streamer states. The correctness of the concept is corroborated by a series of experiments

Performances of a HGCDTE APD Based Detector with Electric Cooling for 2-μm DIAL/IPDA Applications

Directory of Open Access Journals (Sweden)

Dumas A.

2016-01-01

Full Text Available In this work we report on design and testing of an HgCdTe Avalanche Photodiode (APD detector assembly for lidar applications in the Short Wavelength Infrared Region (SWIR : 1,5 - 2 μm. This detector consists in a set of diodes set in parallel -making a 200 μm large sensitive area- and connected to a custom high gain TransImpedance Amplifier (TIA. A commercial four stages Peltier cooler is used to reach an operating temperature of 185K. Crucial performances for lidar use are investigated : linearity, dynamic range, spatial homogeneity, noise and resistance to intense illumination.

Hydrogenated amorphous silicon photoresists for HgCdTe patterning

Energy Technology Data Exchange (ETDEWEB)

Hollingsworth, R.E.; DeHart, C.; Wang, L.; Dinan, J.H.; Johnson, J.N.

1997-07-01

A process to use a hydrogenated amorphous silicon (a-Si:H) film as a dry photoresist mask for plasma etching of HgCdTe has been demonstrated. The a-Si:H films were deposited using standard plasma enhanced chemical vapor deposition with pure silane as the source gas. X-ray photoelectron spectra show that virtually no oxide grows on the surface of an a-Si:H film after 3 hours in air, indicating that it is hydrogen passivated. Ultraviolet light frees hydrogen from the surface and enhances the oxide growth rate. A pattern of 60 micron square pixels was transferred from a contact mask to the surface of an a-Si:H film by ultraviolet enhanced oxidation in air. For the conditions used, the oxide thickness was 0.5--1.0 nm. Hydrogen plasmas were used to develop this pattern by removing the unexposed regions of the film. A hydrogen plasma etch selectivity between oxide and a-Si:H of greater than 500:1 allows patterns as thick as 700 nm to be generated with this very thin oxide. These patterns were transferred into HgCdTe by etching in an electron cyclotron resonance plasma. An etch selectivity between a-Si:H and HgCdTe of greater than 4:1 was observed after etching 2,500 nm into the HgCdTe. All of the steps are compatible with processing in vacuum.

Kinetic modelling of runaway electron avalanches in tokamak plasmas.

Czech Academy of Sciences Publication Activity Database

Nilsson, E.; Decker, J.; Peysson, Y.; Granetz, R.S.; Saint-Laurent, F.; Vlainic, Milos

2015-01-01

Roč. 57, č. 9 (2015), č. článku 095006. ISSN 0741-3335 EU Projects: European Commission(XE) 633053 - EUROfusion Institutional support: RVO:61389021 Keywords : plasma physics * runaway electrons * knock-on collisions * tokamak * Fokker-Planck * runaway avalanches Subject RIV: BL - Plasma and Gas Discharge Physics OBOR OECD: Fluids and plasma physics (including surface physics) Impact factor: 2.404, year: 2015

HgCdTe photovoltaic detectors on Si substrates

International Nuclear Information System (INIS)

Zanio, K.R.; Bean, R.C.

1988-01-01

HgCdTe photovoltaic detectors have been fabricated on Si substrates through intermediate CdTe/GaAs layers. Encapsulation of the GaAs between the CdTe and Si prevents unintentional doping of the HgCdTe by Ga and As. Uniform epitaxial GaAs is grown on three inch diameter Si substrates. Detectors on such large area Si substrates will offer hybrid focal plane arrays whose dimensions are not limited by the difference between the coefficients of thermal expansion of the Si signal processor and the substrate for the HgCdTe detector array. The growth of HgCdTe detectors on the Si signal processors for monolithic focal plane arrays is also considered. 40 references

The electromagnetic radiation fields of a relativistic electron avalanche with special attention to the origin of narrow bipolar pulses

Science.gov (United States)

Cooray, G. V.; Cooray, G. K.

2011-12-01

Gurevich et al. [1] postulated that the source of narrow bipolar pulses, a class of high energy pulses that occur during thunderstorms, could be a runaway electron avalanche driven by the intense electric fields of a thunderstorm. Recently, Watson and Marshall [2] used the modified transmission line model to test the mechanism of the source of narrow bipolar pulses. In a recent paper, Cooray and Cooray [3] demonstrated that the electromagnetic fields of accelerating charges could be used to evaluate the electromagnetic fields from electrical discharges if the temporal and spatial variation of the charges in the discharge is known. In the present study, those equations were utilized to evaluate the electromagnetic fields generated by a relativistic electron avalanche. In the analysis it is assumed that all the electrons in the avalanche are moving with the same speed. In other words, the growth or the decay of the number of electrons takes place only at the head of the avalanche. It is shown that the radiation is emanating only from the head of the avalanche where electrons are being accelerated. It is also shown that an analytical expression for the radiation field of the avalanche at any distance can be written directly in terms of the e-folding length of the avalanche. This makes it possible to extract directly the spatial variation of the e-folding length of the avalanche from the measured radiation fields. In the study this model avalanche was used to investigate whether it can be used to describe the measured electromagnetic fields of narrow bipolar pulses. The results obtained are in reasonable agreement with the two station data of Eack [4] for speeds of propagation around (2 - 2.5) x 10^8 m/s and when the propagation effects on the electric fields measured at the distant station is taken into account. [1] Gurevich et al. (2004), Phys. Lett. A., 329, pp. 348 -361. [2] Watson, S. S. and T. C. Marshall (2007), Geophys. Res. Lett., Vol. 34, L04816, doi: 10

Avalanches in insulating gases

International Nuclear Information System (INIS)

Verhaart, H.F.A.

1982-01-01

Avalanches of charged particles in gases are often studied with the ''electrical method'', the measurement of the waveform of the current in the external circuit. In this thesis a substantial improvement of the time resolution of the measuring setup, to be used for the electrical method, is reported. The avalanche is started by an N 2 -laser with a pulse duration of only 0.6 ns. With this laser it is possible to release a high number of primary electrons (some 10 8 ) which makes it possible to obtain sizeable signals, even at low E/p values. With the setup it is possible to analyze current waveforms with a time resolution down to 1.4 ns, determined by both the laser and the measuring system. Furthermore it is possible to distinguish between the current caused by the electrons and the current caused by the ions in the avalanche and to monitor these currents simultaneously. Avalanche currents are measured in N 2 , CO 2 , O 2 , H 2 O, air of varying humidity, SF 6 and SF 6 /N 2 mixtures. Depending on the nature of the gas and the experimental conditions, processes as diffusion, ionization, attachment, detachment, conversion and secondary emission are observed. Values of parameters with which these processes can be described, are derived from an analysis of the current waveforms. For this analysis already published theories and new theories described in this thesis are used. The drift velocity of both the electrons and the ions could be easily determined from measured avalanche currents. Special attention is paid to avalanches in air becasue of the practical importance of air insulation. (Auth.)

Supershort avalanche electron beam in SF6 and krypton

Science.gov (United States)

Zhang, Cheng; Tarasenko, Victor F.; Gu, Jianwei; Baksht, Evgeni Kh.; Beloplotov, Dmitry V.; Burachenko, Alexander G.; Yan, Ping; Lomaev, Mikhail I.; Shao, Tao

2016-03-01

Runaway electrons play an important role in the avalanche formation in nanosecond- and subnanosecond- pulse discharges. In this paper, characteristics of a supershort avalanche electron beam (SAEB) generated at the subnanosecond and nanosecond breakdown in sulfur hexafluoride (SF6 ) in an inhomogeneous electric field were studied. One pulser operated at negative polarity with voltage pulse amplitude of ˜130 kV and rise time of 0.3 ns. The other pulser operated at negative polarity with voltage pulse amplitude of 70 kV and rise time of ˜1.6 ns . SAEB parameters in SF6 are compared with those obtained in krypton (Kr), nitrogen (N2 ), air, and mixtures of SF6 with krypton or nitrogen. Experimental results showed that SAEB currents appeared during the rise-time of the voltage pulse for both pulsers. Moreover, amplitudes of the SAEB current in SF6 and Kr approximately ranged from several to tens of milliamps at atmospheric pressure, which were smaller than those in N2 and air (ranging from hundreds of milliamps to several amperes). Furthermore, the concentration of SF6 additive could significantly reduce the SAEB current in N2-SF6 mixture, but it slightly affected the SAEB current in Kr -SF6 mixture because of the atomic/molecular ionization cross section of the gas had a much greater impact on the SAEB current rather than the electronegativity.

Supershort avalanche electron beam in SF_{6} and krypton

Directory of Open Access Journals (Sweden)

Cheng Zhang (章程

2016-03-01

Full Text Available Runaway electrons play an important role in the avalanche formation in nanosecond- and subnanosecond- pulse discharges. In this paper, characteristics of a supershort avalanche electron beam (SAEB generated at the subnanosecond and nanosecond breakdown in sulfur hexafluoride (SF_{6} in an inhomogeneous electric field were studied. One pulser operated at negative polarity with voltage pulse amplitude of ∼130  kV and rise time of 0.3 ns. The other pulser operated at negative polarity with voltage pulse amplitude of 70 kV and rise time of ∼1.6  ns. SAEB parameters in SF_{6} are compared with those obtained in krypton (Kr, nitrogen (N_{2}, air, and mixtures of SF_{6} with krypton or nitrogen. Experimental results showed that SAEB currents appeared during the rise-time of the voltage pulse for both pulsers. Moreover, amplitudes of the SAEB current in SF_{6} and Kr approximately ranged from several to tens of milliamps at atmospheric pressure, which were smaller than those in N_{2} and air (ranging from hundreds of milliamps to several amperes. Furthermore, the concentration of SF_{6} additive could significantly reduce the SAEB current in N_{2}-SF_{6} mixture, but it slightly affected the SAEB current in Kr-SF_{6} mixture because of the atomic/molecular ionization cross section of the gas had a much greater impact on the SAEB current rather than the electronegativity.

Relation of the runaway avalanche threshold to momentum space topology

Science.gov (United States)

McDevitt, Christopher J.; Guo, Zehua; Tang, Xian-Zhu

2018-02-01

The underlying physics responsible for the formation of an avalanche instability due to the generation of secondary electrons is studied. A careful examination of the momentum space topology of the runaway electron population is carried out with an eye toward identifying how qualitative changes in the momentum space of the runaway electrons is correlated with the avalanche threshold. It is found that the avalanche threshold is tied to the merger of an O and X point in the momentum space of the primary runaway electron population. Such a change of the momentum space topology is shown to be accurately described by a simple analytic model, thus providing a powerful means of determining the avalanche threshold for a range of model assumptions.

Light from electron avalanches and background rejection in X-ray astronomy

International Nuclear Information System (INIS)

Siegmund, O.H.W.; Sanford, P.W.; Mason, I.M.; Culhane, J.L.; Cockshott, R.

1980-01-01

A modified version of the parallel plate imaging proportional counter, developed to register images of cosmic x-ray sources in the focal planes of x-ray telescopes, has been constructed to investigate the application of risetime discrimination to the scintillation pulses caused by the electron avalanche process. It is shown that efficient background event rejection (> 90%) is achieved and the application of this system for x-ray astronomy is discussed. (U.K.)

Avalanche localization and its effects in proportional counters

International Nuclear Information System (INIS)

Fischer, J.; Okuno, H.; Walenta, A.H.

1977-11-01

Avalanche development around the anode wire in a gas proportional counter is investigated. In the region of proportional gas amplification, the avalanche is found to be well localized on one side of the anode wire, where the electrons arrive along the field lines from the point of primary ionization. Induced signals on electrodes surrounding the anode wire are used to measure the azimuthal position of the avalanche on the anode wire. Practical applications of the phenomena such as left-right assignment in drift chambers and measurement of the angular direction of the primary ionization electrons drifting towards the anode wire are discussed

Supershort avalanche electron beams and x-ray in high-pressure nanosecond discharges

International Nuclear Information System (INIS)

Tarasenko, V F; Baksht, E H; Kostyrya, I D; Lomaev, M I; Rybka, D V

2008-01-01

The properties of a supershort avalanche electron beam (S AEB) and X-ray radiation produced using a nanosecond volume discharge are examined. An electron beam of the runaway electrons with amplitude of ∼ 50 A has been obtained in air atmospheric pressure. It is reported that S AEB is formed in the angle above 2π sr. Three groups of the runaway electrons are formed in a gas diode under atmospheric air pressure, when nanosecond voltage pulses with amplitude of hundreds of kilovolts are applied. The electron beam has been generated behind a 45 μm thick AlBe foil in SF 6 and Xe under the pressure of 2 arm, and in He under the pressure of about 12 atm. The paper gives the analysis of a generation mechanism of SAEB.

Recent progress in MBE grown HgCdTe materials and devices at UWA

Science.gov (United States)

Gu, R.; Lei, W.; Antoszewski, J.; Madni, I.; Umana-Menbreno, G.; Faraone, L.

2016-05-01

HgCdTe has dominated the high performance end of the IR detector market for decades. At present, the fabrication costs of HgCdTe based advanced infrared devices is relatively high, due to the low yield associated with lattice matched CdZnTe substrates and a complicated cooling system. One approach to ease this problem is to use a cost effective alternative substrate, such as Si or GaAs. Recently, GaSb has emerged as a new alternative with better lattice matching. In addition, implementation of MBE-grown unipolar n-type/barrier/n-type detector structures in the HgCdTe material system has been recently proposed and studied intensively to enhance the detector operating temperature. The unipolar nBn photodetector structure can be used to substantially reduce dark current and noise without impeding photocurrent flow. In this paper, recent progress in MBE growth of HgCdTe infrared material at the University of Western Australia (UWA) is reported, including MBE growth of HgCdTe on GaSb alternative substrates and growth of HgCdTe nBn structures.

Parameters of a supershort avalanche electron beam generated in atmospheric-pressure air

International Nuclear Information System (INIS)

Tarasenko, V. F.

2011-01-01

Conditions under which the number of runaway electrons in atmospheric-pressure air reaches ∼5 × 10 10 are determined. Recommendations for creating runaway electron accelerators are given. Methods for measuring the parameters of a supershort avalanche electron beam and X-ray pulses from gas-filled diodes, as well as the discharge current and gap voltage, are described. A technique for determining the instant of runaway electron generation with respect to the voltage pulse is proposed. It is shown that the reduction in the gap voltage and the decrease in the beam current coincide in time. The mechanism of intense electron beam generation in gas-filled diodes is analyzed. It is confirmed experimentally that, in optimal regimes, the number of electrons generated in atmospheric-pressure air with energies T > eU m , where U m is the maximum gap voltage, is relatively small.

Parameters of a supershort avalanche electron beam generated in atmospheric-pressure air

Science.gov (United States)

Tarasenko, V. F.

2011-05-01

Conditions under which the number of runaway electrons in atmospheric-pressure air reaches ˜5 × 1010 are determined. Recommendations for creating runaway electron accelerators are given. Methods for measuring the parameters of a supershort avalanche electron beam and X-ray pulses from gas-filled diodes, as well as the discharge current and gap voltage, are described. A technique for determining the instant of runaway electron generation with respect to the voltage pulse is proposed. It is shown that the reduction in the gap voltage and the decrease in the beam current coincide in time. The mechanism of intense electron beam generation in gas-filled diodes is analyzed. It is confirmed experimentally that, in optimal regimes, the number of electrons generated in atmospheric-pressure air with energies T > eU m , where U m is the maximum gap voltage, is relatively small.

Advances in gas avalanche photomultipliers

CERN Document Server

Breskin, Amos; Buzulutskov, A F; Chechik, R; Garty, E; Shefer, G; Singh, B K

2000-01-01

Gas avalanche detectors, combining solid photocathodes with fast electron multipliers, provide an attractive solution for photon localization over very large sensitive areas and under high illumination flux. They offer single-photon sensitivity and the possibility of operation under very intense magnetic fields. We discuss the principal factors governing the operation of gas avalanche photomultipliers. We summarize the recent progress made in alkali-halide and CVD-diamond UV-photocathodes, capable of operation under gas multiplication, and novel thin-film protected alkali-antimonide photocathodes, providing, for the first time, the possibility of operating gas photomultipliers in the visible range. Electron multipliers, adequate for these photon detectors, are proposed and some applications are briefly discussed.

High pressure pulsed avalanche discharges: Scaling of required preionization rate for homogeneity

International Nuclear Information System (INIS)

Brenning, N.; Axnaes, I.; Nilsson, J.O.; Eninger, J.E.

1994-01-01

Homogeneous high-pressure discharges can be formed by pulsed avalanche breakdown, provided that the individual avalanche heads have diffused to a large enough radius to overlap before streamer breakdown occurs. The overlap condition can be met by using an external mechanism to preionize the neutral gas, e.g., x-rays or uv radiation. There are several scenarios, (1) to preionize the gas, and then trigger the discharge by the sudden application of an electric field, (2) to apply an overvoltage over the discharge and trigger the discharge by external ionization, or (3) to have a continuous rate of external ionization and let the E field rise, with a comparatively long time constant τ, across the breakdown value (E/n) 0 . The authors here study the last of these scenarios, which gives a very efficient use of the preionization source because the avalanche startpoint can accumulate during the pre-avalanche phase. The authors have found that the required avalanche startpoint density N st.p , defined as the density of individual single, or clusters of, electrons at the time when the electric field crosses the breakdown value, scales with pressure and rise time as N st.p ∝ p 21/4 τ -3/4 . This pressure scaling disagrees with the p 3/2 scaling found by Levatter and Lin (J. Appl. Phys. 51(1), 210), while the rise time scaling agrees satisfactorily with their results. For an E field which rises slowly across the breakdown value, the pre-avalanche accumulation of electrons must be taken into account, as well as the fact that the density n e of free electrons becomes larger than the density N st.p of independent avalanche heads: when electron impact ionization closely balances attachment, individual electrons are replaced by clusters of electrons which are too close to form individual avalanche heads

Fluorescence excited in a thunderstorm atmosphere by relativistic runaway electron avalanches

Science.gov (United States)

Babich, L. P.; Bochkov, E. I.

2017-05-01

The spectrum and spatiotemporal evolution of the fluorescence of an atmospheric discharge developing in the regime of relativistic runaway electron avalanche (RREA) generation have been calculated without involving the relativistic feedback. The discharges generating narrow bipolar pulses, along with the discharges responsible for terrestrial gamma-ray flashes, are shown to be relatively dark. Nevertheless, the fluorescence excited by a discharge involving RREAs can be recorded with cameras used to record high-altitude optical phenomena. A possible connection between a certain class of optical phenomena observed at the tops of thunderclouds and RREA emission is pointed out.

Numerical simulation of evolution of electron-hole avalanches and streamers in silicon in a uniform electric field

International Nuclear Information System (INIS)

Kyuregyan, A. S.

2010-01-01

Numerical simulation of origination and evolution of streamers in Si is performed for the first time. It is assumed that an external electric field E 0 is constant and uniform, the avalanche and streamer are axially symmetric, and background electrons and holes are absent. The calculations have been performed in the context of the diffusion-drift approximation with impact and tunneling ionization, Auger recombination, and electron-hole scattering taken into account. The most realistic values of the ionization and recombination rates, diffusion coefficients, and drift mobilities of electrons and holes have been used. It is shown that the features of evolution of avalanches and streamers are generally consistent with the result obtained previously for a hypothetic semiconductor with equal kinetic coefficients for electrons and holes. Asymmetry of these coefficients (mostly, the impact-ionization coefficients) manifests itself only at the initial stage of evolution. However, with time, two exponentially self-similar streamers are formed, differing only in the sign of charge of fronts and directions of their propagation. Empirical dependences of the main parameters of streamers on E 0 in the range of 0.34-0.75 MV/cm have been derived for this most important stage of evolution.

Measurements of electron avalanche formation time in W-band microwave air breakdown

International Nuclear Information System (INIS)

Cook, Alan M.; Hummelt, Jason S.; Shapiro, Michael A.; Temkin, Richard J.

2011-01-01

We present measurements of formation times of electron avalanche ionization discharges induced by a focused 110 GHz millimeter-wave beam in atmospheric air. Discharges take place in a free volume of gas, with no nearby surfaces or objects. When the incident field amplitude is near the breakdown threshold for pulsed conditions, measured formation times are ∼0.1-2 μs over the pressure range 5-700 Torr. Combined with electric field breakdown threshold measurements, the formation time data shows the agreement of 110 GHz air breakdown with the similarity laws of gas discharges.

Measurements of electron avalanche formation time in W-band microwave air breakdown

Science.gov (United States)

Cook, Alan M.; Hummelt, Jason S.; Shapiro, Michael A.; Temkin, Richard J.

2011-08-01

We present measurements of formation times of electron avalanche ionization discharges induced by a focused 110 GHz millimeter-wave beam in atmospheric air. Discharges take place in a free volume of gas, with no nearby surfaces or objects. When the incident field amplitude is near the breakdown threshold for pulsed conditions, measured formation times are ˜0.1-2 μs over the pressure range 5-700 Torr. Combined with electric field breakdown threshold measurements, the formation time data shows the agreement of 110 GHz air breakdown with the similarity laws of gas discharges.

Fokker-Planck simulations of knock-on electron runaway avalanche and bursts in tokamaks

International Nuclear Information System (INIS)

Chiu, S.C.; Rosenbluth, M.N.; Harvey, R.W.; Chan, V.S.

1998-01-01

The avalanche of runaway electrons in an ohmic tokamak plasma triggered by knock-on collisions of traces of energetic electrons with the bulk electrons is simulated by the bounce averaged Fokker-Planck code, CQL3D. It is shown that even when the electric field is small for the production of Dreicer runaways, the knock-on collisions can produce significant runaway electrons in a fraction of a second at typical reactor parameters. The energy spectrum of these knock-on runaways has a characteristic temperature. The growth rate and temperature of the runaway distribution are determined and compared with theory. In simulations of pellet injection into high temperature plasmas, it is shown that a burst of Dreicer runaways may also occur depending on the cooling rate due to the pellet injection. Implications of these phenomena on disruption control in reactor plasmas are discussed. (author)

New method for determining avalanche breakdown voltage of silicon photomultipliers

International Nuclear Information System (INIS)

Chirikov-Zorin, I.

2017-01-01

The avalanche breakdown and Geiger mode of the silicon p-n junction is considered. A precise physically motivated method is proposed for determining the avalanche breakdown voltage of silicon photomultipliers (SiPM). The method is based on measuring the dependence of the relative photon detection efficiency (PDE rel ) on the bias voltage when one type of carriers (electron or hole) is injected into the avalanche multiplication zone of the p-n junction. The injection of electrons or holes from the base region of the SiPM semiconductor structure is performed using short-wave or long-wave light. At a low overvoltage (1-2 V) the detection efficiency is linearly dependent on the bias voltage; therefore, extrapolation to zero PDE rel value determines the SiPM avalanche breakdown voltage with an accuracy within a few millivolts. [ru

Two-dimensional simulation research of secondary electron emission avalanche discharge on vacuum insulator surface

Science.gov (United States)

Cai, Libing; Wang, Jianguo; Zhu, Xiangqin; Wang, Yue; Zhang, Dianhui

2015-01-01

Based on the secondary electron emission avalanche (SEEA) model, the SEEA discharge on the vacuum insulator surface is simulated by using a 2D PIC-MCC code developed by ourselves. The evolutions of the number of discharge electrons, insulator surface charge, current, and 2D particle distribution are obtained. The effects of the strength of the applied electric field, secondary electron yield coefficient, rise time of the pulse, length of the insulator on the discharge are investigated. The results show that the number of the SEEA electrons presents a quadratic dependence upon the applied field strength. The SEEA current, which is on the order of Ampere, is directly proportional to the field strength and secondary electron yield coefficient. Finally, the electron-stimulated outgassing is included in the simulation code, and a three-phase discharge curve is presented by the simulation, which agrees with the experimental data.

Two-dimensional simulation research of secondary electron emission avalanche discharge on vacuum insulator surface

International Nuclear Information System (INIS)

Cai, Libing; Wang, Jianguo; Zhu, Xiangqin; Wang, Yue; Zhang, Dianhui

2015-01-01

Based on the secondary electron emission avalanche (SEEA) model, the SEEA discharge on the vacuum insulator surface is simulated by using a 2D PIC-MCC code developed by ourselves. The evolutions of the number of discharge electrons, insulator surface charge, current, and 2D particle distribution are obtained. The effects of the strength of the applied electric field, secondary electron yield coefficient, rise time of the pulse, length of the insulator on the discharge are investigated. The results show that the number of the SEEA electrons presents a quadratic dependence upon the applied field strength. The SEEA current, which is on the order of Ampere, is directly proportional to the field strength and secondary electron yield coefficient. Finally, the electron-stimulated outgassing is included in the simulation code, and a three-phase discharge curve is presented by the simulation, which agrees with the experimental data

Prediction of picosecond voltage collapse and electromagnetic wave generation in gas avalanche switches

International Nuclear Information System (INIS)

Mayhall, D.J.; Yee, J.H.; Duong-Van, M.; Villa, F.

1988-01-01

A picosecond speed switch, the Gas Avalanche Switch (GAS), has been proposed for GeV linear accelerators. The medium is gas at high pressure (100 - 700 atm). An avalanche discharge is induced between pulse-charged high voltage electrodes by electron deposition from a fast laser pulse. Avalanche electrons move to the positive electrode, causing the applied voltage to collapse in picoseconds. A two-dimensional (2D) electromagnetic electron fluid computer code calculates the avalanche evolution and voltage collapse in air for an infinite parallel plate capacitor with a 0.1 mm spacing. Calculations are done for an accelerator switch geometry consisting of a 0.7 mm wide by 0.8 mm high, rectangular, high voltage center electrode (CE) between the grounded plates of a parallel plate line of 2 mm spacing. Several variations of CE elevation and initial electron deposition are investigated The 2D character of the outgoing TEM waves is shown

Uncooled middle wavelength infrared photoconductors based on (111) and (100) oriented HgCdTe

Science.gov (United States)

Madejczyk, Paweł; Kębłowski, Artur; Gawron, Waldemar; Martyniuk, Piotr; Kopytko, Małgorzata; Stępień, Dawid; Rutkowski, Jarosław; Piotrowski, Józef; Piotrowski, Adam; Rogalski, Antoni

2017-09-01

We present progress in metal organic chemical vapor deposition (MOCVD) growth of (100) HgCdTe epilayers achieved recently at the Institute of Applied Physics, Military University of Technology and Vigo System S.A. It is shown that MOCVD technology is an excellent tool for the fabrication of different HgCdTe detector structures with a wide range of composition, donor/acceptor doping, and without post grown ex-situ annealing. Surface morphology, residual background concentration, and acceptor doping efficiency are compared in (111) and (100) oriented HgCdTe epilayers. At elevated temperatures, the carrier lifetime in measured p-type photoresistors is determined by Auger 7 process with about one order of magnitude difference between theoretical and experimental values. Particular progress has been achieved in the growth of (100) HgCdTe epilayers for medium wavelength infrared photoconductors operated in high-operating temperature conditions.

Highly enhanced avalanche probability using sinusoidally-gated silicon avalanche photodiode

Energy Technology Data Exchange (ETDEWEB)

Suzuki, Shingo; Namekata, Naoto, E-mail: nnao@phys.cst.nihon-u.ac.jp; Inoue, Shuichiro [Institute of Quantum Science, Nihon University, 1-8-14 Kanda-Surugadai, Chiyoda-ku, Tokyo 101-8308 (Japan); Tsujino, Kenji [Tokyo Women' s Medical University, 8-1 Kawada-cho, Shinjuku-ku, Tokyo 162-8666 (Japan)

2014-01-27

We report on visible light single photon detection using a sinusoidally-gated silicon avalanche photodiode. Detection efficiency of 70.6% was achieved at a wavelength of 520 nm when an electrically cooled silicon avalanche photodiode with a quantum efficiency of 72.4% was used, which implies that a photo-excited single charge carrier in a silicon avalanche photodiode can trigger a detectable avalanche (charge) signal with a probability of 97.6%.

Optical study of HgCdTe infrared photodetectors using internal photoemission spectroscopy

International Nuclear Information System (INIS)

Lao, Yan-Feng; Unil Perera, A. G.; Wijewarnasuriya, Priyalal S.

2014-01-01

We report a study of internal photoemission spectroscopy (IPE) applied to a n-type Hg 1−x Cd x Te/Hg 1−y Cd y Te heterojunction. An exponential line-shape of the absorption tail in HgCdTe is identified by IPE fittings of the near-threshold quantum yield spectra. The reduction of quantum yield (at higher photon energy) below the fitting value is explained as a result of carrier-phonon scatterings. In addition, the obtained bias independence of the IPE threshold indicates a negligible electron barrier at the heterojunction interface

STUDY ON SIMULATION METHOD OF AVALANCHE : FLOW ANALYSIS OF AVALANCHE USING PARTICLE METHOD

OpenAIRE

塩澤, 孝哉

2015-01-01

In this paper, modeling for the simulation of the avalanche by a particle method is discussed. There are two kinds of the snow avalanches, one is the surface avalanche which shows a smoke-like flow, and another is the total-layer avalanche which shows a flow like Bingham fluid. In the simulation of the surface avalanche, the particle method in consideration of a rotation resistance model is used. The particle method by Bingham fluid is used in the simulation of the total-layer avalanche. At t...

Pulse-periodic generation of supershort avalanche electron beams and X-ray emission

Science.gov (United States)

Baksht, E. Kh.; Burachenko, A. G.; Erofeev, M. V.; Tarasenko, V. F.

2014-05-01

Pulse-periodic generation of supershort avalanche electron beams (SAEBs) and X-ray emission in nitrogen, as well as the transition from a single-pulse mode to a pulse-periodic mode with a high repetition frequency, was studied experimentally. It is shown that, in the pulse-periodic mode, the full width at halfmaximum of the SAEB is larger and the decrease rate of the gap voltage is lower than those in the single-pulse mode. It is found that, when the front duration of the voltage pulse at a nitrogen pressure of 90 Torr decreases from 2.5 to 0.3 ns, the X-ray exposure dose in the pulse-periodic mode increases by more than one order of magnitude and the number of SAEB electrons also increases. It is shown that, in the pulse-periodic mode of a diffuse discharge, gas heating in the discharge gap results in a severalfold increase in the SAEB amplitude (the number of electrons in the beam). At a generator voltage of 25 kV, nitrogen pressure of 90 Torr, and pulse repetition frequency of 3.5 kHz, a runaway electron beam was detected behind the anode foil.

Crosstalk of HgCdTe LWIR n-on-p diode arrays

International Nuclear Information System (INIS)

Sun Yinghui; Zhang Bo; Yu Meifang; Liao Qingjun; Zhang Yan; Wen Xin; Jiang Peilu; Hu Xiaoning; Dai Ning

2009-01-01

Crosstalk of HgCdTe long-wavelength infrared (LWIR) n-on-p diode arrays was measured using scanning laser microscopy. During the measurement, HgCdTe diode arrays with different diode pitches were frontside illuminated by a He-Ne laser at liquid nitrogen temperature and room temperature. The experimental results show that crosstalk between the nearest neighboring diodes decreases exponentially as the diode pitch increases, and the factors that affect the obtained crosstalk are presented and analyzed. Crosstalk out of the nominal diode area (optically sensitive area) is also measured and discussed.

Development of HgCdTe large format MBE arrays and noise-free high speed MOVPE EAPD arrays for ground based NIR astronomy

Science.gov (United States)

Finger, G.; Baker, I.; Downing, M.; Alvarez, D.; Ives, D.; Mehrgan, L.; Meyer, M.; Stegmeier, J.; Weller, H. J.

2017-11-01

Large format near infrared HgCdTe 2Kx2K and 4Kx4K MBE arrays have reached a level of maturity which meets most of the specifications required for near infrared (NIR) astronomy. The only remaining problem is the persistence effect which is device specific and not yet fully under control. For ground based multi-object spectroscopy on 40 meter class telescopes larger pixels would be advantageous. For high speed near infrared fringe tracking and wavefront sensing the only way to overcome the CMOS noise barrier is the amplification of the photoelectron signal inside the infrared pixel by means of the avalanche gain. A readout chip for a 320x256 pixel HgCdTe eAPD array will be presented which has 32 parallel video outputs being arranged in such a way that the full multiplex advantage is also available for small sub-windows. In combination with the high APD gain this allows reducing the readout noise to the subelectron level by applying nondestructive readout schemes with subpixel sampling. Arrays grown by MOVPE achieve subelectron readout noise and operate with superb cosmetic quality at high APD gain. Efforts are made to reduce the dark current of those arrays to make this technology also available for large format focal planes of NIR instruments offering noise free detectors for deep exposures. The dark current of the latest MOVPE eAPD arrays is already at a level adequate for noiseless broad and narrow band imaging in scientific instruments.

Avalanches near a solid insulator in nitrogen gas at atmospheric pressure

International Nuclear Information System (INIS)

Mahajan, S.M.; Sudarshan, T.S.; Department of Electrical and Computer Engineering, University of South Carolina, Columbia, South Carolina 29208)

1989-01-01

The pulsed Townsend (PT) technique was used to record the growth of avalanches near a solid insulator in nitrogen gas at 0.1 MPa. Several other nonconventional techniques for releasing initiatory electrons at the cathode are discussed. In this paper, experimental results of avalanches initiated by illuminating a fast (0.6-ns) nitrogen laser onto the cathode triple junction are presented. Data were recorded with plexiglas, Teflon, high-density polyethylene, low-density polyethylene, Delrin, etc. Effect of surface condition, variation of the distance between insulator surface and the avalanche initiation region, and the effect of a large number of previous avalanches on the avalanche characteristics at a particular voltage were studied. The Townsend primary ionization coefficient, hereafter referred to as growth coefficient (α), and drift velocity (V/sub e/) were evaluated through the PT technique. Results indicate that the avalanche growth in the vicinity of a solid insulator is less than that in an identical plain gas gap. Existence of a nonuniform field as a result of surface charges on the insulator and/or field modifications due to the avalanche space charge are believed to be responsible for this behavior

Proportional counter with a uniform electric field in the zone of avalanche multiplication of electrons

International Nuclear Information System (INIS)

Marzec, J.; Pawlowski, Z.

1982-01-01

The work describes the construction of a proportional counter with a uniform electric field in the zone of avalanche multiplication of electrons. It has been shown that in this counter filled with Penning's mixtures Ne+Ar+CO 2 , Ne+CH 4 and Ar+C 2 H 2 , much higher resolutions are obtained than in typical cylindrical counters. In the counter described filled with a mixture of Ne+1%CH 4 , a resolution of fwhm=10.5% has been obtained for E=5.9 keV. (orig.)

Characterization of midwave infrared InSb avalanche photodiode

Energy Technology Data Exchange (ETDEWEB)

Abautret, J., E-mail: johan.abautret@ies.univ-montp2.fr; Evirgen, A. [Université Montpellier, IES, UMR 5214, F-34095 Montpellier (France); CNRS, IES, UMR 5214, F-34095 Montpellier (France); SOFRADIR, BP 21, 38113 Veurey-Voroize (France); Perez, J. P.; Christol, P. [Université Montpellier, IES, UMR 5214, F-34095 Montpellier (France); CNRS, IES, UMR 5214, F-34095 Montpellier (France); Rothman, J. [CEA-LETI, 17 rue des Martyrs, 38054 Grenoble Cedex 9 (France); Cordat, A. [SOFRADIR, BP 21, 38113 Veurey-Voroize (France)

2015-06-28

This paper focuses on the InSb material potential for the elaboration of Avalanche Photodiodes (APD) for high performance infrared imaging applications, both in passive or active mode. The first InSb electron-APD structure was grown by molecular beam epitaxy, processed and electrically characterized. The device performances are at the state of the art for the InSb epi-diode technology, with a dark current density J(−50 mV) = 32 nA/cm{sup 2} at 77 K. Then, a pure electron injection was performed, and an avalanche gain, increasing exponentially, was observed with a gain value near 3 at −4 V at 77 K. The Okuto–Crowell model was used to determine the electron ionization coefficient α(E) in InSb, and the InSb gain behavior is compared with the one of InAs and MCT APDs.

Amplitude-temporal characteristics of a supershort avalanche electron beam generated during subnanosecond breakdown in air and nitrogen

Science.gov (United States)

Tarasenko, V. F.; Baksht, E. Kh.; Beloplotov, D. V.; Burachenko, A. G.; Lomaev, M. I.

2016-04-01

The amplitude-temporal characteristics of a supershort avalanche electron beam (SAEB) with an amplitude of up to 100 A, as well as of the breakdown voltage and discharge current, are studied experimentally with a picosecond time resolution. The waveforms of discharge and SAEB currents are synchronized with those of the voltage pulses. It is shown that the amplitude-temporal characteristics of the SAEB depend on the gap length and the designs of the gas diode and cathode. The mechanism for the generation of runaway electron beams in atmospheric-pressure gases is analyzed on the basis of the obtained experimental data.

Amplitude−temporal characteristics of a supershort avalanche electron beam generated during subnanosecond breakdown in air and nitrogen

Energy Technology Data Exchange (ETDEWEB)

Tarasenko, V. F., E-mail: vft@loi.hcei.tsc.ru; Baksht, E. Kh.; Beloplotov, D. V.; Burachenko, A. G.; Lomaev, M. I. [Siberian Branch, Russian Academy of Sciences, Institute of High Current Electronics (Russian Federation)

2016-04-15

The amplitude−temporal characteristics of a supershort avalanche electron beam (SAEB) with an amplitude of up to 100 A, as well as of the breakdown voltage and discharge current, are studied experimentally with a picosecond time resolution. The waveforms of discharge and SAEB currents are synchronized with those of the voltage pulses. It is shown that the amplitude−temporal characteristics of the SAEB depend on the gap length and the designs of the gas diode and cathode. The mechanism for the generation of runaway electron beams in atmospheric-pressure gases is analyzed on the basis of the obtained experimental data.

Proportional counter with a uniform electric field in the zone of avalanche multiplication of electrons

Energy Technology Data Exchange (ETDEWEB)

Marzec, J.; Pawlowski, Z. (Politechnika Warszawska (Poland). Inst. Radioelektroniki)

1982-09-15

The work describes the construction of a proportional counter with a uniform electric field in the zone of avalanche multiplication of electrons. It has been shown that in this counter filled with Penning's mixtures Ne+Ar+CO/sub 2/, Ne+CH/sub 4/ and Ar+C/sub 2/H/sub 2/, much higher resolutions are obtained than in typical cylindrical counters. In the counter described filled with a mixture of Ne+1%CH/sub 4/, a resolution of fwhm=10.5% has been obtained for E=5.9 keV.

Theory of suppressing avalanche process of carrier in short pulse laser irradiated dielectrics

Energy Technology Data Exchange (ETDEWEB)

Deng, H. X., E-mail: hxdeng@uestc.edu.cn, E-mail: xtzu@uestc.edu.cn, E-mail: kaisun@umich.edu; Zu, X. T., E-mail: hxdeng@uestc.edu.cn, E-mail: xtzu@uestc.edu.cn, E-mail: kaisun@umich.edu; Xiang, X. [School of Physical Electronics, University of Electronic Science and Technology of China, Chengdu 610054 (China); Zheng, W. G.; Yuan, X. D. [Research Center of Laser Fusion, China Academy of Engineering Physics, Mianyang 621900 (China); Sun, K., E-mail: hxdeng@uestc.edu.cn, E-mail: xtzu@uestc.edu.cn, E-mail: kaisun@umich.edu [Department of Materials Engineering and Sciences, University of Michigan, 413B Space Research Building, Ann Arbor, Michigan 48109-2143 (United States); Gao, F. [Pacific Northwest National Laboratory, P. O. Box 999, Richland, Washington 99352 (United States)

2014-05-28

A theory for controlling avalanche process of carrier during short pulse laser irradiation is proposed. We show that avalanche process of conduction band electrons (CBEs) is determined by the occupation number of phonons in dielectrics. The theory provides a way to suppress avalanche process and a direct judgment for the contribution of avalanche process and photon ionization process to the generation of CBEs. The obtained temperature dependent rate equation shows that the laser induced damage threshold of dielectrics, e.g., fused silica, increase nonlinearly with the decreases of temperature. Present theory predicts a new approach to improve the laser induced damage threshold of dielectrics.

Status of HgCdTe Barrier Infrared Detectors Grown by MOCVD in Military University of Technology

Science.gov (United States)

Kopytko, M.; Jóźwikowski, K.; Martyniuk, P.; Gawron, W.; Madejczyk, P.; Kowalewski, A.; Markowska, O.; Rogalski, A.; Rutkowski, J.

2016-09-01

In this paper we present the status of HgCdTe barrier detectors with an emphasis on technological progress in metalorganic chemical vapor deposition (MOCVD) growth achieved recently at the Institute of Applied Physics, Military University of Technology. It is shown that MOCVD technology is an excellent tool for HgCdTe barrier architecture growth with a wide range of composition, donor /acceptor doping, and without post-grown annealing. The device concept of a specific barrier bandgap architecture integrated with Auger-suppression is as a good solution for high-operating temperature infrared detectors. Analyzed devices show a high performance comparable with the state-of-the-art of HgCdTe photodiodes. Dark current densities are close to the values given by "Rule 07" and detectivities of non-immersed detectors are close to the value marked for HgCdTe photodiodes. Experimental data of long-wavelength infrared detector structures were confirmed by numerical simulations obtained by a commercially available software APSYS platform. A detailed analysis applied to explain dark current plots was made, taking into account Shockley-Read-Hall, Auger, and tunneling currents.

Monolithic dual-band HgCdTe infrared detector structure

CSIR Research Space (South Africa)

Parish, G

1997-07-01

Full Text Available A monolithic HgCdTe photoconductive device structure is presented that is suitable for dual-band optically registered infrared photodetection in the two atmospheric transmission windows of 3-5 mu m and 8-12 mu m, which correspond to the mid...

Radiation damage of multipixel Geiger-mode avalanche photodiodes irradiated with low-energy γ's and electrons

Energy Technology Data Exchange (ETDEWEB)

Kwon, Y.; Yun, Y. B. [Yonsei University, Seoul (Korea, Republic of); Ha, J. M. [Yonsei University, Seoul (Korea, Republic of); Electronics and Telecommunications Research Institute, Daejeon (Korea, Republic of); Lee, J. S.; Yoon, Y. S. [Electronics and Telecommunications Research Institute, Daejeon (Korea, Republic of); Eun, J. W. [Namseoul University, Cheonan (Korea, Republic of)

2012-05-15

A few types of multipipixel Geiger-mode avalanche photodiodes (also referred to as silicon photomultipliers SiPMs) are irradiated with 1 to 2.5 MeV γ's and electrons. We characterize radiation damage effects appearing in the reverse bias current, the dark current and count rate, the pixel gain, and the photon detection efficiency of the devices. An interesting observation on the dark current and count rate is made and linked to the specific damage caused by the irradiation.

Avalanche hazard and control in Kazakhstan

Directory of Open Access Journals (Sweden)

V. P. Blagoveshchensky

2014-01-01

Full Text Available In Kazakhstan, area of 124 thousand km2 is prone to the avalanche hazard. Avalanches are released down in mountain regions situated along the eastern boundary of Kazakhstan. Systematic studies of avalanches here were started in 1958 by explorer I.S. Sosedov; later on, I.V. Seversky continued these investigations in Institute of Geography of the Kazakh Soviet Republic. Actually, he founded the Kazakh school of the avalanche studies. In 1970–1980s, five snow-avalanche stations operated in Kazakhstan: two in Il’ Alatau, two in Zhetysu Alatau, and one in the Altai. At the present time, only two stations and two snow-avalanche posts operate, and all of them are located in Il’ Alatau.Since 1951 to 2013, 75 avalanches took place in Kazakhstan, releases of them caused significant damages. For this period 172 people happened to be under avalanches, among them 86 perished. Large avalanche catastrophes causing human victims and destructions took place in Altai in 1977 and in Karatau in 1990. In spring of 1966, only in Il’ Alatau avalanches destroyed more 600 ha of mature fir (coniferous forest, and the total area of forest destroyed here by avalanches amounts to 2677 ha or 7% of the total forest area.For 48 years of the avalanche observations, there were 15 winters with increased avalanche activity in the river Almatinka basin when total volume of released snow exceeded annual mean value of 147 thousand m3. During this period, number of days with winter avalanches changed from three (in season of 1973/1974 to 28 (1986/1987, the average for a year is 16 days for a season. Winter with the total volume of snow 1300 thousand m3 occur once in 150 years. Individual avalanches with maximal volume of 350 thousand m3 happen once in 80 years.Preventive avalanche releases aimed at protection of roads and settlements are used in Kazakhstan since 1974. These precautions are taken in Il’ Alatau, Altai, and on Kalbinsky Range. Avalanches are released with the

Review of supershort avalanche electron beam during nanosecond-pulse discharges in some gases

Directory of Open Access Journals (Sweden)

Victor F. Tarasenko

2017-05-01

Full Text Available Supershort avalanche electron beam (SAEB plays an important role in nanosecond-pulse discharges. This paper aims at reviewing experiments results on characteritics of SAEB and its spectra in different gases in nanosecond-pulse discharges. All the joint experiments were carried in the Institute of High Current Electronics of the Russian Academy of Sciences and the Institute of Electrical Engineering of the Chinese Academy of Sciences. In these experiments, the generation of a SAEB in SF6 in an inhomogeneous electric field was studied on three generators with pulse rise times of 0.3, 0.5 and ∼2 ns. Firstly, the comparison of SAEB parameters in SF6 with those obtained in other gases (air, nitrogen, argon, and krypton is introduced. Secondly, the SAEB spectra in SF6 and air at pressures of 10 kPa (75 torr, and 0.1 MPa (750 torr are reviewed and discussed. Finally, 1.5-D theoretical simulation of the supershort pulse of the fast electron beam in a coaxial diode filled with SF6 at atmospheric pressure is described. The simulation was carried out in the framework of hybrid model for discharge and runaway electron kinetics. The above research progress can provide better understanding of the investigation into the mechanism of nanosecond-pulse discharges.

Temperature-sensitive junction transformations for mid-wavelength HgCdTe photovoltaic infrared detector arrays by laser beam induced current microscope

Energy Technology Data Exchange (ETDEWEB)

Qiu, Weicheng [College of Photoelectric Science and Engineering, National University of Defense Technology, Changsha, Hunan 410073 (China); National Laboratory for Infrared Physics, Shanghai Institute of Technical Physics, Chinese Academy of Sciences, Shanghai 200083 (China); Hu, Weida, E-mail: wdhu@mail.sitp.ac.cn; Lin, Tie; Yin, Fei; Zhang, Bo; Chen, Xiaoshuang; Lu, Wei [National Laboratory for Infrared Physics, Shanghai Institute of Technical Physics, Chinese Academy of Sciences, Shanghai 200083 (China); Cheng, Xiang' ai, E-mail: xiang-ai-cheng@126.com; Wang, Rui [College of Photoelectric Science and Engineering, National University of Defense Technology, Changsha, Hunan 410073 (China)

2014-11-10

In this paper, we report on the disappearance of the photosensitive area extension effect and the unusual temperature dependence of junction transformation for mid-wavelength, n-on-p HgCdTe photovoltaic infrared detector arrays. The n-type region is formed by B{sup +} ion implantation on Hg-vacancy-doped p-type HgCdTe. Junction transformations under different temperatures are visually captured by a laser beam induced current microscope. A physical model of temperature dependence on junction transformation is proposed and demonstrated by using numerical simulations. It is shown that Hg-interstitial diffusion and temperature activated defects jointly lead to the p-n junction transformation dependence on temperature, and the weaker mixed conduction compared with long-wavelength HgCdTe photodiode contributes to the disappearance of the photosensitive area extension effect in mid-wavelength HgCdTe infrared detector arrays.

Avalanche risk assessment in Russia

Science.gov (United States)

Komarov, Anton; Seliverstov, Yury; Sokratov, Sergey; Glazovskaya, Tatiana; Turchaniniva, Alla

2017-04-01

The avalanche prone area covers about 3 million square kilometers or 18% of total area of Russia and pose a significant problem in most mountain regions of the country. The constant growth of economic activity, especially in the North Caucasus region and therefore the increased avalanche hazard lead to the demand of the large-scale avalanche risk assessment methods development. Such methods are needed for the determination of appropriate avalanche protection measures as well as for economic assessments during all stages of spatial planning of the territory. The requirement of natural hazard risk assessments is determined by the Federal Law of Russian Federation. However, Russian Guidelines (SP 11-103-97; SP 47.13330.2012) are not clearly presented concerning avalanche risk assessment calculations. A great size of Russia territory, vast diversity of natural conditions and large variations in type and level of economic development of different regions cause significant variations in avalanche risk values. At the first stage of research the small scale avalanche risk assessment was performed in order to identify the most common patterns of risk situations and to calculate full social risk and individual risk. The full social avalanche risk for the territory of country was estimated at 91 victims. The area of territory with individual risk values lesser then 1×10(-6) covers more than 92 % of mountain areas of the country. Within these territories the safety of population can be achieved mainly by organizational activities. Approximately 7% of mountain areas have 1×10(-6) - 1×10(-4) individual risk values and require specific mitigation measures to protect people and infrastructure. Territories with individual risk values 1×10(-4) and above covers about 0,1 % of the territory and include the most severe and hazardous mountain areas. The whole specter of mitigation measures is required in order to minimize risk. The future development of such areas is not recommended

A probabilistic model for snow avalanche occurrence

Science.gov (United States)

Perona, P.; Miescher, A.; Porporato, A.

2009-04-01

Avalanche hazard forecasting is an important issue in relation to the protection of urbanized environments, ski resorts and of ski-touring alpinists. A critical point is to predict the conditions that trigger the snow mass instability determining the onset and the size of avalanches. On steep terrains the risk of avalanches is known to be related to preceding consistent snowfall events and to subsequent changes in the local climatic conditions. Regression analysis has shown that avalanche occurrence indeed correlates to the amount of snow fallen in consecutive three snowing days and to the state of the settled snow at the ground. Moreover, since different type of avalanches may occur as a result of the interactions of different factors, the process of snow avalanche formation is inherently complex and with some degree of unpredictability. For this reason, although several models assess the risk of avalanche by accounting for all the involved processes with a great detail, a high margin of uncertainty invariably remains. In this work, we explicitly describe such an unpredictable behaviour with an intrinsic noise affecting the processes leading snow instability. Eventually, this sets the basis for a minimalist stochastic model, which allows us to investigate the avalanche dynamics and its statistical properties. We employ a continuous time process with stochastic jumps (snowfalls), deterministic decay (snowmelt and compaction) and state dependent avalanche occurrence (renewals) as a minimalist model for the determination of avalanche size and related intertime occurrence. The physics leading to avalanches is simplified to the extent where only meteorological data and terrain data are necessary to estimate avalanche danger. We explore the analytical formulation of the process and the properties of the probability density function of the avalanche process variables. We also discuss what is the probabilistic link between avalanche size and preceding snowfall event and

Spatial shape of avalanches

Science.gov (United States)

Zhu, Zhaoxuan; Wiese, Kay Jörg

2017-12-01

In disordered elastic systems, driven by displacing a parabolic confining potential adiabatically slowly, all advance of the system is in bursts, termed avalanches. Avalanches have a finite extension in time, which is much smaller than the waiting time between them. Avalanches also have a finite extension ℓ in space, i.e., only a part of the interface of size ℓ moves during an avalanche. Here we study their spatial shape 〈S(x ) 〉 ℓ given ℓ , as well as its fluctuations encoded in the second cumulant 〈S2(x ) 〉 ℓ c. We establish scaling relations governing the behavior close to the boundary. We then give analytic results for the Brownian force model, in which the microscopic disorder for each degree of freedom is a random walk. Finally, we confirm these results with numerical simulations. To do this properly we elucidate the influence of discretization effects, which also confirms the assumptions entering into the scaling ansatz. This allows us to reach the scaling limit already for avalanches of moderate size. We find excellent agreement for the universal shape and its fluctuations, including all amplitudes.

Lightning initiation mechanism based on the development of relativistic runaway electron avalanches triggered by background cosmic radiation: Numerical simulation

International Nuclear Information System (INIS)

Babich, L. P.; Bochkov, E. I.; Kutsyk, I. M.

2011-01-01

The mechanism of lightning initiation due to electric field enhancement by the polarization of a conducting channel produced by relativistic runaway electron avalanches triggered by background cosmic radiation has been simulated numerically. It is shown that the fields at which the start of a lightning leader is possible even in the absence of precipitations are locally realized for realistic thundercloud configurations and charges. The computational results agree with the in-situ observations of penetrating radiation enhancement in thunderclouds.

Lightning initiation mechanism based on the development of relativistic runaway electron avalanches triggered by background cosmic radiation: Numerical simulation

Energy Technology Data Exchange (ETDEWEB)

Babich, L. P., E-mail: babich@elph.vniief.ru; Bochkov, E. I.; Kutsyk, I. M. [All-Russian Research Institute of Experimental Physics, Russian Federal Nuclear Center (Russian Federation)

2011-05-15

The mechanism of lightning initiation due to electric field enhancement by the polarization of a conducting channel produced by relativistic runaway electron avalanches triggered by background cosmic radiation has been simulated numerically. It is shown that the fields at which the start of a lightning leader is possible even in the absence of precipitations are locally realized for realistic thundercloud configurations and charges. The computational results agree with the in-situ observations of penetrating radiation enhancement in thunderclouds.

Surface passivation of HgCdTe by CdZnTe and its characteristics

Science.gov (United States)

Lee, T. S.; Choi, K. K.; Jeoung, Y. T.; Kim, H. K.; Kim, J. M.; Kim, Y. H.; Chang, J. M.; Song, W. S.; Kim, S. U.; Park, M. J.; Lee, S. D.

1997-06-01

In this paper, we report the results of capacitance-voltage measurements conducted on several metal-insulator semiconductor (MIS) capacitors in which HgCdTe surfaces are treated with various surface etching and oxidation processes. CdZnTe passivation layers were deposited on HgCdTe surfaces by thermal evaporation after the surfaces were etched with 0.5-2.0% bromine in methanol solution, or thin oxide layers (tox ˜ few ten Å) were grown on the surfaces, in order to investigate effects of the surface treatments on the electrical properties of the surfaces, as determined from capacitance-voltage (C-V) measurements at 80K and 1 MHz. A negative flat band voltage has been observed for MIS capacitors fabricated after etching of HgCdTe surfaces with bromine in methanol solutions, which is reported to make the surface Te-rich. It is inferred that residual Te on the surface is a positive charge, Te4+. C-V characteristics for MIS capacitors fabricated on oxide surfaces grown by air-exposure and electrolytic process have shown large hysteresis effects, from which it is inferred that imperfect and electrically active oxide compounds and HgTe particles near the surface become slow interface states.

Calibration of snow avalanche mathematical models using the data of real avalanches in the Ile (Zailiyskiy Alatau Range

Directory of Open Access Journals (Sweden)

V. P. Blagoveshchensky

2017-01-01

Full Text Available The calibration of the dry friction and turbulent friction coefficients is necessary for computer simulation of avalanches. The method of back calculation based on data on actual avalanches is used for this purpose. The article presents the results of the calibration of the Eglit’s and RAMMS models for Ile Alatau range condi‑ tions. The range is located in Kazakhstan. The data on six avalanches in the same avalanche site were used. Five avalanches were dry, and one avalanche was wet. Avalanches volume varied from 2000 to 12000  m3. Maximum speed avalanches were between 15 and 30  m/s, the flow height  – from 3 to 10  m. Series of back calculations with different values of the friction coefficients was made to obtain the calibrated coeffi‑ cients. The calibrated coefficients were chosen under condition of the best fit with real avalanches. The cal‑ ibrated coefficients were following. For the Eglit’s model for dry avalanches of the volume 2000–5000  m3 μ = 0.46÷0.48, k = 0.005–0.006, and the volume 8000–12000 m3 μ = 0.38÷0.42, k = 0.002÷0.003. For RAMMS model for dry avalanches of the volume of 2000–5000 m3 μ (dry friction coefficient = 0.35÷0.4, ξ (viscous friction coefficient = 1500÷2000 m/s2, and the volume 8,000–12,000 m3 μ = 0.3÷0.35, ξ = 2000÷3000 m/s2. For wet avalanches of the volume 12,000 m3 μ = 0.35, ξ = 1500 m/s2. The work on the calibration will be con‑ tinued to obtain the friction coefficients for the Eglit’s and RAMMS models. The additional data on real ava‑ lanches will be needed for this purpose.

Avalanches and Criticality in Driven Magnetic Skyrmions

Science.gov (United States)

Díaz, S. A.; Reichhardt, C.; Arovas, D. P.; Saxena, A.; Reichhardt, C. J. O.

2018-03-01

We show using numerical simulations that slowly driven Skyrmions interacting with random pinning move via correlated jumps or avalanches. The avalanches exhibit power-law distributions in their duration and size, and the average avalanche shape for different avalanche durations can be scaled to a universal function, in agreement with theoretical predictions for systems in a nonequilibrium critical state. A distinctive feature of Skyrmions is the influence of the nondissipative Magnus term. When we increase the ratio of the Magnus term to the damping term, a change in the universality class of the behavior occurs, the average avalanche shape becomes increasingly asymmetric, and individual avalanches exhibit motion in the direction perpendicular to their own density gradient.

Nano-multiplication region avalanche photodiodes and arrays

Science.gov (United States)

Zheng, Xinyu (Inventor); Pain, Bedabrata (Inventor); Cunningham, Thomas J. (Inventor)

2011-01-01

An avalanche photodiode with a nano-scale reach-through structure comprising n-doped and p-doped regions, formed on a silicon island on an insulator, so that the avalanche photodiode may be electrically isolated from other circuitry on other silicon islands on the same silicon chip as the avalanche photodiode. For some embodiments, multiplied holes generated by an avalanche reduces the electric field in the depletion region of the n-doped and p-doped regions to bring about self-quenching of the avalanche photodiode. Other embodiments are described and claimed.

High-Gain Avalanche Rushing amorphous Photoconductor (HARP) detector

Energy Technology Data Exchange (ETDEWEB)

Tanioka, K. [NHK Science and Technical Research Laboratories, 1-10-11 Kinuta, Setagaya-ku, Tokyo 157-8510 (Japan)], E-mail: tanioka.k-jg@nhk.or.jp

2009-09-01

We have been studying a very sensitive image sensor since the early 1980s. In 1985, the author found for the first time that an experimental pickup tube with an amorphous selenium photoconductive target exhibits high sensitivity with excellent picture quality because of a continuous and stable avalanche multiplication phenomenon. We named the pickup tube with an amorphous photoconductive layer operating in the avalanche-mode 'HARP': High-gain Avalanche Rushing amorphous Photoconductor. A color camera equipped with the HARP pickup tubes has a maximum sensitivity of 11 lx at F8. This means that the HARP camera is about 100 times as sensitive as that of CCD camera for broadcasting. This ultrahigh-sensitivity HARP pickup tube is a powerful tool for reporting breaking news at night and other low-light conditions, the production of scientific programs, and numerous other applications, including medical diagnoses, biotech research, and nighttime surveillance. In addition, since the HARP target can convert X-rays into electrons directly, it should be possible to exploit this capability to produce X-ray imaging devices with unparalleled levels of resolution and sensitivity.

Arsenic complexes optical signatures in As-doped HgCdTe

Energy Technology Data Exchange (ETDEWEB)

Gemain, F.; Robin, I. C.; Brochen, S.; Ballet, P.; Gravrand, O.; Feuillet, G. [CEA-LETI Minatec Campus, 17 rue des Martyrs, 38000 Grenoble (France)

2013-04-08

In this paper, the optical signatures of arsenic complexes in As-doped HgCdTe samples grown by molecular beam epitaxy are clearly identified using comparison between photoluminescence spectra, Extended X-Ray Absorption Fine Structure, and Hall measurements. The ionization energies of the different complexes are measured both by photoluminescence and Hall measurements.

Arsenic complexes optical signatures in As-doped HgCdTe

International Nuclear Information System (INIS)

Gemain, F.; Robin, I. C.; Brochen, S.; Ballet, P.; Gravrand, O.; Feuillet, G.

2013-01-01

In this paper, the optical signatures of arsenic complexes in As-doped HgCdTe samples grown by molecular beam epitaxy are clearly identified using comparison between photoluminescence spectra, Extended X-Ray Absorption Fine Structure, and Hall measurements. The ionization energies of the different complexes are measured both by photoluminescence and Hall measurements.

Development of an advanced Two-Micron triple-pulse IPDA lidar for carbon dioxide and water vapor measurements

Science.gov (United States)

Petros, Mulugeta; Refaat, Tamer F.; Singh, Upendra N.; Yu, Jirong; Antill, Charles; Remus, Ruben; Taylor, Bryant D.; Wong, Teh-Hwa; Reithmaier, Karl; Lee, Jane; Ismail, Syed; Davis, Kenneth J.

2018-04-01

An advanced airborne triple-pulse 2-μm integrated path differential absorption (IPDA) lidar is under development at NASA Langley Research Center that targets both carbon dioxide (CO2) and water vapor (H2O) measurements simultaneously and independently. This lidar is an upgrade to the successfully demonstrated CO2 2-μm double-pulse IPDA. Upgrades include high-energy, highrepetition rate 2-μm triple-pulse laser transmitter, innovative wavelength control and advanced HgCdTe (MCT) electron-initiated avalanche photodiode detection system. Ground testing and airborne validation plans are presented.

Numerical analysis of three-colour HgCdTe detectors

Science.gov (United States)

Jóźwikowski, K.; Rogalski, A.

2007-12-01

The performance of three-colour HgCdTe photovoltaic heterostructure detector is examined theoretically. In comparison with two-colour detectors with two back-to-back junctions, three-colour structure contains an absorber of intermediate wavelength placed between two junctions and electronic barriers are used to isolate this intermediate region. This structure was first proposed by British workers. Three-detector structures with different localizations of separating barriers are analyzed. The calculation results are presented in the form of spatial distributions of bandgap energy and quantum efficiency. Enhanced original computer programs are applied to solve the system of non-linear continuity equations for carriers and Poisson equations. In addition, the numerical analysis includes the dependence of absorption coefficient on Burstein effect as well as interference effects in heterostructure with metallic electrical contacts. It is shown that the performance of the detector is critically dependent on the barrier’s doping level and position in relation to the junction. This behaviour is serious disadvantage of the considered three-colour detector. A small shift of the barrier location and doping level causes serious changes in spectral responsivity.

Automation and instrument control applied to an experimental study of electron transport dynamics in an avalanche mode resistive plater chamber

International Nuclear Information System (INIS)

Ridenti, Marco A.; Pascholati, Paulo R.

2009-01-01

In this work it is presented a computer based instrumentation system which was developed to perform data acquisition and integrate the control of different devices in an experimental study of electron transport dynamics in an avalanche mode resistive plate chamber detector in the Radiation Technology Center (CTR) at IPEN/CNEN-SP. System control and data acquisition was performed by a computer program called RPCLabOperator written in MatLab environment running on a LeCroy WavePro 7000 digital oscilloscope. (author)

Gallium-based avalanche photodiode optical crosstalk

International Nuclear Information System (INIS)

Blazej, Josef; Prochazka, Ivan; Hamal, Karel; Sopko, Bruno; Chren, Dominik

2006-01-01

Solid-state single photon detectors based on avalanche photodiode are getting more attention in various areas of applied physics: optical sensors, quantum key distribution, optical ranging and Lidar, time-resolved spectroscopy, X-ray laser diagnostics, and turbid media imaging. Avalanche photodiodes specifically designed for single photon counting semiconductor avalanche structures have been developed on the basis of various materials: Si, Ge, GaP, GaAsP, and InGaP/InGaAs at the Czech Technical University in Prague during the last 20 years. They have been tailored for numerous applications. Trends in demand are focused on detection array construction recently. Even extremely small arrays containing a few cells are of great importance for users. Electrical crosstalk between individual gating and quenching circuits and optical crosstalk between individual detecting cells are serious limitation for array design and performance. Optical crosstalk is caused by the parasitic light emission of the avalanche which accompanies the photon detection process. We have studied in detail the optical emission of the avalanche photon counting structure in the silicon- and gallium-based photodiodes. The timing properties and spectral distribution of the emitted light have been measured for different operating conditions to quantify optical crosstalk. We conclude that optical crosstalk is an inherent property of avalanche photodiode operated in Geiger mode. The only way to minimize optical crosstalk in avalanche photodiode array is to build active quenching circuit with minimum response time

Energy and dissipated work in snow avalanches

Science.gov (United States)

Bartelt, P.; Buser, O.

2004-12-01

Using the results of large scale avalanche experiments at the Swiss Vallée de la Sionne test site, the energy balance of several snow avalanches is determined. Avalanches convert approximately one-seventh of their potential energy into kinetic energy. The total potential energy depends strongly on the entrained snowcover, indicating that entrainment processes cannot be ignored when predicting terminal velocities and runout distances. We find energy dissipation rates on the order of 1 GW. Fluidization of the fracture slab can be identified in the experiments as an increase in dissipation rate, thereby explaining the initial and rapid acceleration of avalanches after release. Interestingly, the dissipation rates appear to be constant along the track, although large fluctuations in internal velocity exist. Thus, we can demonstrate within the context of non-equilibrium thermodynamics that -- in space -- granular snow avalanches are irreversible, dissipative systems that minimize entropy production because they appear to reach a steady-state non-equilibrium. A thermodynamic analysis reveals that fluctuations in velocity depend on the roughness of the flow surface and viscosity of the granular system. We speculate that this property explains the transition from flowing avalanches to powder avalanches.

The parallel plate avalanche counter: a simple, rugged, imaging X-ray counter

International Nuclear Information System (INIS)

Joensen, K.D.; Budtz-Joergensen, C.; Bahnsen, A.; Madsen, M.M.; Olesen, C.; Schnopper, H.W.

1995-01-01

A two-dimensional parallel gap proportional counter has been developed at the Danish Space Research Institute. Imaging over the 120 mm diameter active area is obtained using the positive ion component of the avalanche signals as recorded by a system of wedge- and strip-electrodes. An electronically simple, but very effective background rejection is obtained by using the fast electron component of the avalanche signal. Gas gains up to 8x10 5 have been achieved. An energy-resolution of 16% and a sub-millimeter spatial resolution have been measured at 5.9 keV for an operating gas gain of 10 5 . In principle, the position coordinates are linear functions of electronic readouts. The present model, however, exhibits non-linearities, caused by imperfections in the wedge and strip-electrode pattern. These non-linearities are corrected by using a bilinear correction algorithm. We conclude that the rugged construction, the simple electronics, the effectiveness of the background rejection and the actual imaging performance makes this a very attractive laboratory detector for low and intermediate count rate imaging applications. ((orig.))

Passivation Effect of Atomic Layer Deposition of Al2O3 Film on HgCdTe Infrared Detectors

Science.gov (United States)

Zhang, Peng; Ye, Zhen-Hua; Sun, Chang-Hong; Chen, Yi-Yu; Zhang, Tian-Ning; Chen, Xin; Lin, Chun; Ding, Ring-Jun; He, Li

2016-09-01

The passivation effect of atomic layer deposition of (ALD) Al2O3 film on a HgCdTe infrared detector was investigated in this work. The passivation effect of Al2O3 film was evaluated by measuring the minority carrier lifetime, capacitance versus voltage ( C- V) characteristics of metal-insulator-semiconductor devices, and resistance versus voltage ( R- V) characteristics of variable-area photodiodes. The minority carrier lifetime, C- V characteristics, and R- V characteristics of HgCdTe devices passivated by ALD Al2O3 film was comparable to those of HgCdTe devices passivated by e-beam evaporation of ZnS/CdTe film. However, the baking stability of devices passivated by Al2O3 film is inferior to that of devices passivated by ZnS/CdTe film. In future work, by optimizing the ALD Al2O3 film growing process and annealing conditions, it may be feasible to achieve both excellent electrical properties and good baking stability.

Imaging findings of avalanche victims

Energy Technology Data Exchange (ETDEWEB)

Grosse, Alexandra B.; Grosse, Claudia A.; Anderson, Suzanne [University Hospital of Berne, Inselspital, Department of Diagnostic, Pediatric and Interventional Radiology, Berne (Switzerland); Steinbach, Lynne S. [University of California San Francisco, Department of Radiology, San Francisco, CA (United States); Zimmermann, Heinz [University Hospital of Berne, Inselspital, Department of Trauma and Emergency Medicine, Berne (Switzerland)

2007-06-15

Skiing and hiking outside the boundaries remains an attractive wilderness activity despite the danger of avalanches. Avalanches occur on a relatively frequent basis and may be devastating. Musculoskeletal radiologists should be acquainted with these injuries. Fourteen avalanche victims (11 men and 3 women; age range 17-59 years, mean age 37.4 years) were air transported to a high-grade trauma centre over a period of 2 years. Radiographs, CT and MR images were prospectively evaluated by two observers in consensus. Musculoskeletal findings (61%) were more frequent than extraskeletal findings (39%). Fractures were most commonly seen (36.6%), involving the spine (14.6%) more frequently than the extremities (9.8%). Blunt abdominal and thoracic trauma were the most frequent extraskeletal findings. A wide spectrum of injuries can be found in avalanche victims, ranging from extremity fractures to massive polytrauma. Asphyxia remains the main cause of death along with hypoxic brain injury and hypothermia. (orig.)

Thermal stability of atomic layer deposition Al2O3 film on HgCdTe

Science.gov (United States)

Zhang, P.; Sun, C. H.; Zhang, Y.; Chen, X.; He, K.; Chen, Y. Y.; Ye, Z. H.

2015-06-01

Thermal stability of Atomic Layer Deposition Al2O3 film on HgCdTe was investigated by Al2O3 film post-deposition annealing treatment and Metal-Insulator-Semiconductor device low-temperature baking treatment. The effectiveness of Al2O3 film was evaluated by measuring the minority carrier lifetime and capacitance versus voltage characteristics. After annealing treatment, the minority carrier lifetime of the HgCdTe sample presented a slight decrease. Furthermore, the fixed charge density and the slow charge density decreased significantly in the annealed MIS device. After baking treatment, the fixed charge density and the slow charge density of the unannealed and annealed MIS devices decreased and increased, respectively.

Prediction of electromagnetic pulse generation by picosecond avalanches in high-pressure air

International Nuclear Information System (INIS)

Mayhall, D.J.; Yee, J.H.

1993-01-01

The gas avalanche switch is a laser-activated, high-voltage switch, consisting of a set of pulse-charged electrodes in a high-pressure gas. Induced electrons from a picosecond-scale laser pulse initiate an avalanche discharge between high-voltage and grounded electrodes. If the voltage, pressure, and dimensions are correct, the rapid avalanche, fueled by the immense number of electrons available in the gas, collapses the applied voltage in picoseconds and generates electromagnetic pulses with widths as short as 1-10 ps and 3 dB bandwidths of 20-120 GHz. With proper voltage or pressure detuning, wider pulses and lower bandwidths occur. In addition to picosecond electromagnetic pulse generation, application of this switch should result in ultra-fast Marx bank pulsers. A number of versions of the switch are possible. The simplest is a parallel plate capacitor, consisting of a gas between two parallel plate conductors. High voltage is applied across the two plates. A parallel plate, Blumlein geometry features a center electrode between two grounded parallel plates. This geometry emits a single pulse in each direction along the parallel plates. A frozen wave geometry with multiple, oppositely charged center electrodes will emit AC pulses. Series switches consisting of gas gaps between two electrodes are also possible

Computational and experimental progress on laser-activated gas avalanche switches for broadband, high-power electromagnetic pulse generation

International Nuclear Information System (INIS)

Mayhall, D.J.; Yee, J.H.; Villa, F.

1991-01-01

This paper discusses the gas avalanche switch, a high-voltage, picosecond-speed switch, which has been proposed. The basic switch consists of pulse-charged electrodes, immersed in a high-pressure gas. An avalanche discharge is induced in the gas between the electrodes by ionization from a picosecond-scale laser pulse. The avalanching electrons move toward the anode, causing the applied voltage to collapse in picoseconds. This voltage collapse, if rapid enough, generates electromagnetic waves. A two-dimensional (2D), finite difference computer code solves Maxwell's equations for transverse magnetic modes for rectilinear electrodes between parallel plate conductors, along with electron conservation equations for continuity, momentum, and energy. Collision frequencies for ionization and momentum and energy transfer to neutral molecules are assumed to scale linearly with neutral pressure. Electrode charging and laser-driven electron deposition are assumed to be instantaneous. Code calculations are done for a pulse generator geometry, consisting of an 0.7 mm wide by 0.8 mm high, beveled, rectangular center electrode between grounded parallel plates at 2 mm spacing in air

Measuring neuronal avalanches in disordered systems with absorbing states

Science.gov (United States)

Girardi-Schappo, M.; Tragtenberg, M. H. R.

2018-04-01

Power-law-shaped avalanche-size distributions are widely used to probe for critical behavior in many different systems, particularly in neural networks. The definition of avalanche is ambiguous. Usually, theoretical avalanches are defined as the activity between a stimulus and the relaxation to an inactive absorbing state. On the other hand, experimental neuronal avalanches are defined by the activity between consecutive silent states. We claim that the latter definition may be extended to some theoretical models to characterize their power-law avalanches and critical behavior. We study a system in which the separation of driving and relaxation time scales emerges from its structure. We apply both definitions of avalanche to our model. Both yield power-law-distributed avalanches that scale with system size in the critical point as expected. Nevertheless, we find restricted power-law-distributed avalanches outside of the critical region within the experimental procedure, which is not expected by the standard theoretical definition. We remark that these results are dependent on the model details.

A method to eliminate wetting during the homogenization of HgCdTe

Science.gov (United States)

Su, Ching-Hua; Lehoczky, S. L.; Szofran, F. R.

1986-01-01

Adhesion of HgCdTe samples to fused silica ampoule walls, or 'wetting', during the homogenization process was eliminated by adopting a slower heating rate. The idea is to decrease Cd activity in the sample so as to reduce the rate of reaction between Cd and the silica wall.

The development of the room temperature LWIR HgCdTe detectors for free space optics communication systems

Science.gov (United States)

Martyniuk, Piotr; Gawron, Waldemar; Mikołajczyk, Janusz

2017-10-01

There are many room temperature applications to include free space optics (FSO) communication system combining quantum cascade lasers sources where HgCdTe long-wave (8-12 micrometer) infrared radiation (LWIR) detector reaching ultrafast response time 109 cmHz1/2/W. Since commercially available FSO could operate separately in SWIR, MWIR and LWIR range - the dual band detectors should be implemented into FSO. This paper shows theoretical performance of the dual band back-to-back MWIR and LWIR HgCdTe detector operating at 300 K pointing out the MWIR active layer influence on LWIR operating regime.

Spatial determination of magnetic avalanche ignition points

International Nuclear Information System (INIS)

Jaafar, Reem; McHugh, S.; Suzuki, Yoko; Sarachik, M.P.; Myasoedov, Y.; Zeldov, E.; Shtrikman, H.; Bagai, R.; Christou, G.

2008-01-01

Using time-resolved measurements of local magnetization in the molecular magnet Mn 12 -ac, we report studies of magnetic avalanches (fast magnetization reversals) with non-planar propagating fronts, where the curved nature of the magnetic fronts is reflected in the time-of-arrival at micro-Hall sensors placed at the surface of the sample. Assuming that the avalanche interface is a spherical bubble that grows with a radius proportional to time, we are able to locate the approximate ignition point of each avalanche in a two-dimensional cross-section of the crystal. We find that although in most samples the avalanches ignite at the long ends, as found in earlier studies, there are crystals in which ignition points are distributed throughout an entire weak region near the center, with a few avalanches still originating at the ends

Spatial determination of magnetic avalanche ignition points

Energy Technology Data Exchange (ETDEWEB)

Jaafar, Reem; McHugh, S.; Suzuki, Yoko [Physics Department, City College of the City University of New York, New York, NY 10031 (United States); Sarachik, M.P. [Physics Department, City College of the City University of New York, New York, NY 10031 (United States)], E-mail: sarachik@sci.ccny.cuny.edu; Myasoedov, Y.; Zeldov, E.; Shtrikman, H. [Department Condensed Matter Physics, Weizmann Institute of Science, Rehovot 76100 (Israel); Bagai, R.; Christou, G. [Department of Chemistry, University of Florida, Gainesville, FL 32611 (United States)

2008-03-15

Using time-resolved measurements of local magnetization in the molecular magnet Mn{sub 12}-ac, we report studies of magnetic avalanches (fast magnetization reversals) with non-planar propagating fronts, where the curved nature of the magnetic fronts is reflected in the time-of-arrival at micro-Hall sensors placed at the surface of the sample. Assuming that the avalanche interface is a spherical bubble that grows with a radius proportional to time, we are able to locate the approximate ignition point of each avalanche in a two-dimensional cross-section of the crystal. We find that although in most samples the avalanches ignite at the long ends, as found in earlier studies, there are crystals in which ignition points are distributed throughout an entire weak region near the center, with a few avalanches still originating at the ends.

Enhanced numerical analysis of three-color HgCdTe detectors

Science.gov (United States)

Jóźwikowski, K.; Rogalski, A.

2007-04-01

The performance of three-color HgCdTe photovoltaic heterostructure detector is examined theoretically. In comparison with two-color detectors with two back-to-back junctions, three-color structure contain an absorber of intermediate wavelength placed between two junctions, and electronic barriers are used to isolate this intermediate region. This structure was first proposed by British workers. Enhanced original computer programs are applied to solve the system of non-linear continuity equations for carriers and Poisson equations. In addition, the numerical analysis includes the dependence of absorption coefficient on Burstein effect as well as interference effects in heterostructure with metallic electrical contacts. Three detector structures with different localizations of separating barriers are analyzed. The calculations results are presented in the form of spatial distributions of bandgap energy and quantum efficiency. It is shown that the performance of the detector is critically dependent on the barrier's doping level and position in relation to the junction. This behavior is serious disadvantage of the considered three color detector. A small shift of the barrier location and doping level causes serious changes in spectral responsivity.

Real time avalanche detection for high risk areas.

Science.gov (United States)

2014-12-01

Avalanches routinely occur on State Highway 21 (SH21) between Lowman and Stanley, Idaho each winter. The avalanches pose : a threat to the safety of maintenance workers and the traveling public. A real-time avalanche detection system will allow the :...

Assessing the importance of terrain parameters on glide avalanche release

Science.gov (United States)

Peitzsch, E.; Hendrikx, J.; Fagre, D. B.

2013-12-01

Glide snow avalanches are dangerous and difficult to predict. Despite recent research there is still a lack of understanding regarding the controls of glide avalanche release. Glide avalanches often occur in similar terrain or the same locations annually and observations suggest that topography may be critical. Thus, to gain an understanding of the terrain component of these types of avalanches we examined terrain parameters associated with glide avalanche release as well as areas of consistent glide crack formation but no subsequent avalanches. Glide avalanche occurrences visible from the Going-to-the-Sun Road corridor in Glacier National Park, Montana from 2003-2013 were investigated using an avalanche database derived of daily observations each year from April 1 to June 15. This yielded 192 glide avalanches in 53 distinct avalanche paths. Each avalanche occurrence was digitized in a GIS using satellite, oblique, and aerial imagery as reference. Topographical parameters such as area, slope, aspect, elevation and elevation were then derived for the entire dataset utilizing GIS tools and a 10m DEM. Land surface substrate and surface geology were derived from National Park Service Inventory and Monitoring maps and U.S. Geological Survey surface geology maps, respectively. Surface roughness and glide factor were calculated using a four level classification index. . Then, each avalanche occurrence was aggregated to general avalanche release zones and the frequencies were compared. For this study, glide avalanches released in elevations ranging from 1300 to 2700 m with a mean aspect of 98 degrees (east) and a mean slope angle of 38 degrees. The mean profile curvature for all glide avalanches was 0.15 and a plan curvature of -0.01, suggesting a fairly linear surface (i.e. neither convex nor concave). The glide avalanches occurred in mostly bedrock made up of dolomite and limestone slabs and talus deposits with very few occurring in alpine meadows. However, not all glide

Assessing the importance of terrain parameters on glide avalanche release

Science.gov (United States)

Peitzsch, Erich H.; Hendrikx, Jordy; Fagre, Daniel B.

2014-01-01

Glide snow avalanches are dangerous and difficult to predict. Despite recent research there is still a lack of understanding regarding the controls of glide avalanche release. Glide avalanches often occur in similar terrain or the same locations annually and observations suggest that topography may be critical. Thus, to gain an understanding of the terrain component of these types of avalanches we examined terrain parameters associated with glide avalanche release as well as areas of consistent glide crack formation but no subsequent avalanches. Glide avalanche occurrences visible from the Going-to-the-Sun Road corridor in Glacier National Park, Montana from 2003-2013 were investigated using an avalanche database derived of daily observations each year from April 1 to June 15. This yielded 192 glide avalanches in 53 distinct avalanche paths. Each avalanche occurrence was digitized in a GIS using satellite, oblique, and aerial imagery as reference. Topographical parameters such as area, slope, aspect, elevation and elevation were then derived for the entire dataset utilizing GIS tools and a 10m DEM. Land surface substrate and surface geology were derived from National Park Service Inventory and Monitoring maps and U.S. Geological Survey surface geology maps, respectively. Surface roughness and glide factor were calculated using a four level classification index. . Then, each avalanche occurrence was aggregated to general avalanche release zones and the frequencies were compared. For this study, glide avalanches released in elevations ranging from 1300 to 2700 m with a mean aspect of 98 degrees (east) and a mean slope angle of 38 degrees. The mean profile curvature for all glide avalanches was 0.15 and a plan curvature of -0.01, suggesting a fairly linear surface (i.e. neither convex nor concave). The glide avalanches occurred in mostly bedrock made up of dolomite and limestone slabs and talus deposits with very few occurring in alpine meadows. However, not all glide

Development of Buffer Layer Technologies for LWIR and VLWIR HgCdTe Integration on Si

National Research Council Canada - National Science Library

Golding, Terry D

2005-01-01

This program proposed to develop manufacturable, cost-effective buffer layer technologies that would allow either hybrid or monolithic integration of LWIR and VLWIR HgCdTe infrared focal plane arrays...

Effect of gas heating on the generation of an ultrashort avalanche electron beam in the pulse-periodic regime

Science.gov (United States)

Baksht, E. Kh.; Burachenko, A. G.; Lomaev, M. I.; Sorokin, D. A.; Tarasenko, V. F.

2015-07-01

The generation of an ultrashort avalanche electron beam (UAEB) in nitrogen in the pulse-periodic regime is investigated. The gas temperature in the discharge gap of the atmospheric-pressure nitrogen is measured from the intensity distribution of unresolved rotational transitions ( C 3Π u , v' = 0) → ( B 3Π g , v″ = 0) in the nitrogen molecule for an excitation pulse repetition rate of 2 kHz. It is shown that an increase in the UAEB current amplitude in the pulse-periodic regime is due to gas heating by a series of previous pulses, which leads to an increase in the reduced electric field strength as a result of a decrease in the gas density in the zone of the discharge formation. It is found that in the pulse-periodic regime and the formation of the diffuse discharge, the number of electrons in the beam increases by several times for a nitrogen pressure of 9 × 103 Pa. The dependences of the number of electrons in the UAEB on the time of operation of the generator are considered.

Thermal Cycle Annealing and its Application to Arsenic-Ion Implanted HgCdTe

Science.gov (United States)

2014-06-26

Rao Mulpuri Sina Simingalam, Priyalal Wijewarnasuriya, Mulpuri V. Rao 1720BH c. THIS PAGE The public reporting burden for this collection of...Implanted HgCdTe Sina Simingalama,b,c, Priyalal Wijewarnasuriyab, Mulpuri V. Raoc a. School of Physics, Astronomy and Computational Sciences, George

Indirect flat-panel detector with avalanche gain: Fundamental feasibility investigation for SHARP-AMFPI (scintillator HARP active matrix flat panel imager)

International Nuclear Information System (INIS)

Zhao Wei; Li Dan; Reznik, Alla; Lui, B.J.M.; Hunt, D.C.; Rowlands, J.A.; Ohkawa, Yuji; Tanioka, Kenkichi

2005-01-01

An indirect flat-panel imager (FPI) with avalanche gain is being investigated for low-dose x-ray imaging. It is made by optically coupling a structured x-ray scintillator CsI(Tl) to an amorphous selenium (a-Se) avalanche photoconductor called HARP (high-gain avalanche rushing photoconductor). The final electronic image is read out using an active matrix array of thin film transistors (TFT). We call the proposed detector SHARP-AMFPI (scintillator HARP active matrix flat panel imager). The advantage of the SHARP-AMFPI is its programmable gain, which can be turned on during low dose fluoroscopy to overcome electronic noise, and turned off during high dose radiography to avoid pixel saturation. The purpose of this paper is to investigate the important design considerations for SHARP-AMFPI such as avalanche gain, which depends on both the thickness d Se and the applied electric field E Se of the HARP layer. To determine the optimal design parameter and operational conditions for HARP, we measured the E Se dependence of both avalanche gain and optical quantum efficiency of an 8 μm HARP layer. The results were used in a physical model of HARP as well as a linear cascaded model of the FPI to determine the following x-ray imaging properties in both the avalanche and nonavalanche modes as a function of E Se : (1) total gain (which is the product of avalanche gain and optical quantum efficiency); (2) linearity; (3) dynamic range; (4) gain nonuniformity resulting from thickness nonuniformity; and (5) effects of direct x-ray interaction in HARP. Our results showed that a HARP layer thickness of 8 μm can provide adequate avalanche gain and sufficient dynamic range for x-ray imaging applications to permit quantum limited operation over the range of exposures needed for radiography and fluoroscopy

Long wavelength stimulated emission up to 9.5 μm from HgCdTe quantum well heterostructures

Energy Technology Data Exchange (ETDEWEB)

Morozov, S. V.; Rumyantsev, V. V., E-mail: rumyantsev@ipmras.ru; Dubinov, A. A.; Kudryavtsev, K. E.; Antonov, A. V.; Gavrilenko, V. I. [Institute for Physics of Microstructures of Russian Academy of Sciences, 603950 Nizhny Novgorod (Russian Federation); Lobachevsky State University of Nizhny Novgorod, 603950 Nizhny Novgorod (Russian Federation); Kadykov, A. M. [Institute for Physics of Microstructures of Russian Academy of Sciences, 603950 Nizhny Novgorod (Russian Federation); UMR CNRS 5221, GIS-TERALAB, Université Montpellier II, 34095 Montpellier (France); Mikhailov, N. N. [A.V. Rzhanov Institute of Semiconductor Physics, Siberian Branch of Russian Academy of Sciences, 630090 Novosibirsk (Russian Federation); Novosibirsk State University, 630090 Novosibirsk (Russian Federation); Dvoretskii, S. A. [A.V. Rzhanov Institute of Semiconductor Physics, Siberian Branch of Russian Academy of Sciences, 630090 Novosibirsk (Russian Federation)

2016-02-29

Stimulated emission from waveguide HgCdTe structures with several quantum wells inside waveguide core is demonstrated at wavelengths up to 9.5 μm. Photoluminescence line narrowing down to kT energy, as well as superlinear rise in its intensity evidence the onset of the stimulated emission, which takes place under optical pumping with intensity as small as ∼0.1 kW/cm{sup 2} at 18 K and 1 kW/cm{sup 2} at 80 K. One can conclude that HgCdTe structures potential for long-wavelength lasers is not exhausted.

Rock-avalanche dynamics revealed by large-scale field mapping and seismic signals at a highly mobile avalanche in the West Salt Creek valley, western Colorado

Science.gov (United States)

Coe, Jeffrey A.; Baum, Rex L.; Allstadt, Kate E.; Kochevar, Bernard; Schmitt, Robert G.; Morgan, Matthew L.; White, Jonathan L.; Stratton, Benjamin T.; Hayashi, Timothy A.; Kean, Jason W.

2016-01-01

On 25 May 2014, a rain-on-snow–induced rock avalanche occurred in the West Salt Creek valley on the northern flank of Grand Mesa in western Colorado (United States). The avalanche mobilized from a preexisting rock slide in the Green River Formation and traveled 4.6 km down the confined valley, killing three people. The avalanche was rare for the contiguous United States because of its large size (54.5 Mm3) and high mobility (height/length = 0.14). To understand the avalanche failure sequence, mechanisms, and mobility, we conducted a forensic analysis using large-scale (1:1000) structural mapping and seismic data. We used high-resolution, unmanned aircraft system imagery as a base for field mapping, and analyzed seismic data from 22 broadband stations (distances earth and tracked these forces using curves in the avalanche path. Our results revealed that the rock avalanche was a cascade of landslide events, rather than a single massive failure. The sequence began with an early morning landslide/debris flow that started ∼10 h before the main avalanche. The main avalanche lasted ∼3.5 min and traveled at average velocities ranging from 15 to 36 m/s. For at least two hours after the avalanche ceased movement, a central, hummock-rich core continued to move slowly. Since 25 May 2014, numerous shallow landslides, rock slides, and rock falls have created new structures and modified avalanche topography. Mobility of the main avalanche and central core was likely enhanced by valley floor material that liquefied from undrained loading by the overriding avalanche. Although the base was likely at least partially liquefied, our mapping indicates that the overriding avalanche internally deformed predominantly by sliding along discrete shear surfaces in material that was nearly dry and had substantial frictional strength. These results indicate that the West Salt Creek avalanche, and probably other long-traveled avalanches, could be modeled as two layers: a thin, liquefied

Characterizing the nature and variability of avalanche hazard in western Canada

Science.gov (United States)

Shandro, Bret; Haegeli, Pascal

2018-04-01

The snow and avalanche climate types maritime, continental and transitional are well established and have been used extensively to characterize the general nature of avalanche hazard at a location, study inter-seasonal and large-scale spatial variabilities and provide context for the design of avalanche safety operations. While researchers and practitioners have an experience-based understanding of the avalanche hazard associated with the three climate types, no studies have described the hazard character of an avalanche climate in detail. Since the 2009/2010 winter, the consistent use of Statham et al. (2017) conceptual model of avalanche hazard in public avalanche bulletins in Canada has created a new quantitative record of avalanche hazard that offers novel opportunities for addressing this knowledge gap. We identified typical daily avalanche hazard situations using self-organizing maps (SOMs) and then calculated seasonal prevalence values of these situations. This approach produces a concise characterization that is conducive to statistical analyses, but still provides a comprehensive picture that is informative for avalanche risk management due to its link to avalanche problem types. Hazard situation prevalence values for individual seasons, elevations bands and forecast regions provide unprecedented insight into the inter-seasonal and spatial variability of avalanche hazard in western Canada.

Ultralow noise midwave infrared InAs-GaSb strain layer superlattice avalanche photodiode

International Nuclear Information System (INIS)

Mallick, Shubhrangshu; Banerjee, Koushik; Ghosh, Siddhartha; Plis, Elena; Rodriguez, Jean Baptiste; Krishna, Sanjay; Grein, Christoph

2007-01-01

Eye-safe midwavelength infrared InAs-GaSb strain layer superlattice p + -n - -n homojunction avalanche photodiodes (APDs) grown by solid source molecular beam epitaxy were fabricated and characterized. Maximum multiplication gain of 1800 was measured at -20 V at 77 K. Excess noise factors between 0.8 and 1.2 were measured up to gain of 300. Gain of 200 was measured at 120 K. Exponential nature of the gain as a function of reverse bias along with low excess noise factor at higher gain confirms single carrier electron-only impact ionization in the avalanche regime. Decrease in the multiplication gain at higher temperatures correlates with standard APD characteristics

Criticality and avalanches in neural networks

International Nuclear Information System (INIS)

Zare, Marzieh; Grigolini, Paolo

2013-01-01

Highlights: • Temporal criticality is used as criticality indicator. • The Mittag–Leffler function is proposed as a proper form of temporal complexity. • The distribution of avalanche size becomes scale free in the supercritical state. • The scale-free distribution of avalanche sizes is an epileptic manifestation. -- Abstract: Experimental work, both in vitro and in vivo, reveals the occurrence of neural avalanches with an inverse power law distribution in size and time duration. These properties are interpreted as an evident manifestation of criticality, thereby suggesting that the brain is an operating near criticality complex system: an attractive theoretical perspective that according to Gerhard Werner may help to shed light on the origin of consciousness. However, a recent experimental observation shows no clear evidence for power-law scaling in awake and sleeping brain of mammals, casting doubts on the assumption that the brain works at criticality. This article rests on a model proposed by our group in earlier publications to generate neural avalanches with the time duration and size distribution matching the experimental results on neural networks. We now refine the analysis of the time distance between consecutive firing bursts and observe the deviation of the corresponding distribution from the Poisson statistics, as the system moves from the non-cooperative to the cooperative regime. In other words, we make the assumption that the genuine signature of criticality may emerge from temporal complexity rather than from the size and time duration of avalanches. We argue that the Mittag–Leffler (ML) exponential function is a satisfactory indicator of temporal complexity, namely of the occurrence of non-Poisson and renewal events. The assumption that the onset of criticality corresponds to the birth of renewal non-Poisson events establishes a neat distinction between the ML function and the power law avalanches generating regime. We find that

Evaluation of Rockwell HgCdTe arrays for astronomical use

Science.gov (United States)

Lebofsky, M. J.; Montgomery, E. F.; Kailey, W. F.

1986-01-01

The 32 x 32 HgCdTe array manufactured by Rockwell International was proven to be a highly competitive detector type for use at wavelengths shorter than 2.5 microns. The goal of a K=+16 sky survey using this array attached to the Steward Observatory Transit Telescope is clearly within reach. The detector material exhibits high quantum efficiency and low dark currents indicating that its usefulness may extend beyond its use with a CCD readout on groundbased telescopes.

Avalanche breakdown and the probabilistic nature of laser failure

Energy Technology Data Exchange (ETDEWEB)

Mitropol' skii, M M; Khote' enkov, V A; Khodakov, G S

1976-01-01

A study was made of the probabilistic aspects of the development of an electron avalanche arising under the influence of a powerful laser beam in a solid transparent dielectric. The distribution function of time and relative fluctuation of the number of electrons was found. The width of the probability function of failure was determined as a function of intensity. The relative dispersion of time of beginning of breakdown can also be determined. Its numerical value under identical conditions is +-7%. These results are similar to the experimentally defined dispersion from an earlier work. The data produced also show that, in spite of the clearly probabilistic nature of the development of an avalanche, the slight width of the distribution causes the use of the threshold criterion for rupture of transparent dielectrics by laser radiation to be practically correct. The dependence of I/sub 0/ on pulse length agrees with experimental data, whereas I/sub 0/ (V) is significantly weaker than the actually observed value. This disagreement can be explained by various imperfections in the structure of the crystals and by their contamination, the frequency of appearance of which, in the focal volume, is proportional to its size and which were not considered in the theoretical statements developed here.

MO-AB-BRA-07: Low Dose Imaging with Avalanche Amorphous Selenium Flat Panel Imager

Energy Technology Data Exchange (ETDEWEB)

Scheuermann, J; Howansky, A; Goldan, A; Tanioka, K; Zhao, W [Stony Brook University, Stony Brook, New York (United States); Leveille, S; Tousignant, O [2Analogic Canada, Saint-laurent, Quebec (Canada)

2016-06-15

Purpose: We present the first active matrix flat panel imager (AMFPI) capable of producing x-ray quantum noise limited images at low doses by overcoming the electronic noise through signal amplification by photoconductive avalanche gain (gav). The indirect detector fabricated uses an optical sensing layer of amorphous selenium (a-Se) known as High-Gain Avalanche Rushing Photoconductor (HARP). The detector design is called Scintillator HARP (SHARP)-AMFPI. This is the first image sensor to utilize solid-state HARP technology. Methods: The detector’s electronic readout is a 24 × 30 cm{sup 2} array of thin film transistors (TFT) with a pixel pitch of 85 µm. The HARP structure consists of a 15 µm layer of a-Se isolated from the high voltage (HV) and signal electrode by a 2 µm thick hole blocking layer and electron blocking layer, respectively, to reduce dark current. A 150 µm thick structured CsI scintillator with reflective backing and a fiber optic faceplate (FOP) was coupled to the semi-transparent HV bias electrode of the HARP structure. Images were acquired using a 30 kVp Mo/Mo spectrum typically used in mammography. Results: Optical sensitivity measurements demonstrate that gav = 76 ± 5 can be achieved over the entire active area of the detector. At a constant dose to the detector of 6.67 µGy, image quality increases with gav until the effective electronic noise is negligible. Quantum noise limited images can be obtained with doses as low as 0.18 µGy. Conclusion: We demonstrate the feasibility of utilizing avalanche gain to overcome electronic noise. The indirect detector fabricated is the first solid-state imaging sensor to use HARP, and the largest active area HARP sensor to date. Our future work is to improve charge transport within the HARP structure and utilize a transparent HV electrode.

Avalanche photoconductive switching

Science.gov (United States)

Pocha, M. D.; Druce, R. L.; Wilson, M. J.; Hofer, W. W.

This paper describes work being done at Lawrence Livermore National Laboratory on the avalanche mode of operation of laser triggered photoconductive switches. We have been able to generate pulses with amplitudes of 2 kV to 35 kV and rise times of 300 to 500 ps, and with a switching gain (energy of output electrical pulse vs energy of trigger optical pulse) of 10(exp 3) to over 10(exp 5). Switches with two very different physical configurations and with two different illumination wavelengths (1.06 micrometer, 890 nm) exhibit very similar behavior. The avalanche switching behavior, therefore, appears to be related to the material parameters rather than the optical wavelength or switch geometry. Considerable further work needs to be done to fully characterize and understand this mode of operation.

Avalanche photoconductive switching

Energy Technology Data Exchange (ETDEWEB)

Pocha, M.D.; Druce, R.L.; Wilson, M.J.; Hofer, W.W.

1989-01-01

This paper describes work being done at Lawrence Livermore National Laboratory on the avalanche mode of operation of laser triggered photoconductive switches. We have been able to generate pulses with amplitudes of 2 kV--35 kV and rise times of 300--500 ps, and with a switching gain (energy of output electrical pulse vs energy of trigger optical pulse) of 10{sup 3} to over 10{sup 5}. Switches with two very different physical configurations and with two different illumination wavelengths (1.06 {mu}m, 890 nm) exhibit very similar behavior. The avalanche switching behavior, therefore, appears to be related to the material parameters rather than the optical wavelength or switch geometry. Considerable further work needs to be done to fully characterize and understand this mode of operation. 3 refs., 6 figs.

First approximations in avalanche model validations using seismic information

Science.gov (United States)

Roig Lafon, Pere; Suriñach, Emma; Bartelt, Perry; Pérez-Guillén, Cristina; Tapia, Mar; Sovilla, Betty

2017-04-01

Avalanche dynamics modelling is an essential tool for snow hazard management. Scenario based numerical modelling provides quantitative arguments for decision-making. The software tool RAMMS (WSL Institute for Snow and Avalanche Research SLF) is one such tool, often used by government authorities and geotechnical offices. As avalanche models improve, the quality of the numerical results will depend increasingly on user experience on the specification of input (e.g. release and entrainment volumes, secondary releases, snow temperature and quality). New model developments must continue to be validated using real phenomena data, for improving performance and reliability. The avalanches group form University of Barcelona (RISKNAT - UB), has studied the seismic signals generated from avalanches since 1994. Presently, the group manages the seismic installation at SLF's Vallée de la Sionne experimental site (VDLS). At VDLS the recorded seismic signals can be correlated to other avalanche measurement techniques, including both advanced remote sensing methods (radars, videogrammetry) and obstacle based sensors (pressure, capacitance, optical sender-reflector barriers). This comparison between different measurement techniques allows the group to address the question if seismic analysis can be used alone, on more additional avalanche tracks, to gain insight and validate numerical avalanche dynamics models in different terrain conditions. In this study, we aim to add the seismic data as an external record of the phenomena, able to validate RAMMS models. The seismic sensors are considerable easy and cheaper to install than other physical measuring tools, and are able to record data from the phenomena in every atmospheric conditions (e.g. bad weather, low light, freezing make photography, and other kind of sensors not usable). With seismic signals, we record the temporal evolution of the inner and denser parts of the avalanche. We are able to recognize the approximate position

Investigation on properties of ultrafast switching in a bulk gallium arsenide avalanche semiconductor switch

International Nuclear Information System (INIS)

Hu, Long; Su, Jiancang; Ding, Zhenjie; Hao, Qingsong; Yuan, Xuelin

2014-01-01

Properties of ultrafast switching in a bulk gallium arsenide (GaAs) avalanche semiconductor switch based on semi-insulating wafer, triggered by an optical pulse, were analyzed using physics-based numerical simulations. It has been demonstrated that when a voltage with amplitude of 5.2 kV is applied, after an exciting optical pulse with energy of 1 μJ arrival, the structure with thickness of 650 μm reaches a high conductivity state within 110 ps. Carriers are created due to photons absorption, and electrons and holes drift to anode and cathode terminals, respectively. Static ionizing domains appear both at anode and cathode terminals, and create impact-generated carriers which contribute to the formation of electron-hole plasma along entire channel. When the electric field in plasma region increases above the critical value (∼4 kV/cm) at which the electrons drift velocity peaks, a domain comes into being. An increase in carrier concentration due to avalanche multiplication in the domains reduces the domain width and results in the formation of an additional domain as soon as the field outside the domains increases above ∼4 kV/cm. The formation and evolution of multiple powerfully avalanching domains observed in the simulations are the physical reasons of ultrafast switching. The switch exhibits delayed breakdown with the characteristics affected by biased electric field, current density, and optical pulse energy. The dependence of threshold energy of the exciting optical pulse on the biased electric field is discussed

Anthropogenic effect on avalanche and debris flow activity

OpenAIRE

S. A. Sokratov; Yu. G. Seliverstov; A. L. Shnyparkov; K. P. Koltermann

2013-01-01

The paper presents examples of the change in snow avalanches and debris flows activity due to the anthropogenic pressure on vegetation and relief. The changes in dynamical characteristics of selected snow avalanches and debris flows due to the anthropogenic activity are quantified. The conclusion is made that the anthropogenic effects on the snow avalanches and debris flows activity are more pronounced than the possible effects of the climate change. The necessity is expressed on the unavoida...

Dealing with the white death: avalanche risk management for traffic routes.

Science.gov (United States)

Rheinberger, Christoph M; Bründl, Michael; Rhyner, Jakob

2009-01-01

This article discusses mitigation strategies to protect traffic routes from snow avalanches. Up to now, mitigation of snow avalanches on many roads and railways in the Alps has relied on avalanche sheds, which require large initial investments resulting in high opportunity costs. Therefore, avalanche risk managers have increasingly adopted organizational mitigation measures such as warning systems and closure policies instead. The effectiveness of these measures is, however, greatly dependent on human decisions. In this article, we present a method for optimizing avalanche mitigation for traffic routes in terms of both their risk reduction impact and their net benefit to society. First, we introduce a generic framework for assessing avalanche risk and for quantifying the impact of mitigation. This allows for sound cost-benefit comparisons between alternative mitigation strategies. Second, we illustrate the framework with a case study from Switzerland. Our findings suggest that site-specific characteristics of avalanche paths, as well as the economic importance of a traffic route, are decisive for the choice of optimal mitigation strategies. On routes endangered by few avalanche paths with frequent avalanche occurrences, structural measures are most efficient, whereas reliance on organizational mitigation is often the most appropriate strategy on routes endangered by many paths with infrequent or fuzzy avalanche risk. Finally, keeping a traffic route open may be very important for tourism or the transport industry. Hence, local economic value may promote the use of a hybrid strategy that combines organizational and structural measures to optimize the resource allocation of avalanche risk mitigation.

An improved design for AlGaN solar-blind avalanche photodiodes with enhanced avalanche ionization

International Nuclear Information System (INIS)

Tang Yin; Cai Qing; Chen Dun-Jun; Lu Hai; Zhang Rong; Zheng You-Dou; Yang Lian-Hong; Dong Ke-Xiu

2017-01-01

To enhance the avalanche ionization, we designed a new separate absorption and multiplication AlGaN solar-blind avalanche photodiode (APD) by using a high/low-Al-content AlGaN heterostructure as the multiplication region instead of the conventional AlGaN homogeneous layer. The calculated results show that the designed APD with Al 0.3 Ga 0.7 N/Al 0.45 Ga 0.55 N heterostructure multiplication region exhibits a 60% higher gain than the conventional APD and a smaller avalanche breakdown voltage due to the use of the low-Al-content Al 0.3 Ga 0.7 N which has about a six times higher hole ionization coefficient than the high-Al-content Al 0.45 Ga 0.55 N. Meanwhile, the designed APD still remains a good solar-blind characteristic by introducing a quarter-wave AlGaN/AlN distributed Bragg reflectors structure at the bottom of the device. (paper)

On the avalanche generation of runaway electrons during tokamak disruptions

International Nuclear Information System (INIS)

Martín-Solís, J. R.; Loarte, A.; Lehnen, M.

2015-01-01

A simple zero dimensional model for a tokamak disruption is developed to evaluate the avalanche multiplication of a runaway primary seed during the current quench phase of a fast disruptive event. Analytical expressions for the plateau runaway current, the energy of the runaway beam, and the runaway energy distribution function are obtained allowing the identification of the parameters dominating the formation of the runaway current during disruptions. The effect of the electromagnetic coupling to the vessel and the penetration of the external magnetic energy during the disruption current quench as well as of the collisional dissipation of the runaway current at high densities are investigated. Current profile shape effects during the formation of the runaway beam are also addressed by means of an upgraded one-dimensional model

Transient events in bright debris discs: Collisional avalanches revisited

Science.gov (United States)

Thebault, P.; Kral, Q.

2018-01-01

Context. A collisional avalanche is set off by the breakup of a large planetesimal, releasing vast amounts of small unbound grains that enter a debris disc located further away from the star, triggering there a collisional chain reaction that could potentially create detectable transient structures. Aims: We investigate this mechanism, using for the first time a fully self-consistent code coupling dynamical and collisional evolutions. We also quantify for the first time the photometric evolution of the system and investigate whether or not avalanches could explain the short-term luminosity variations recently observed in some extremely bright debris discs. Methods: We use the state-of-the-art LIDT-DD code. We consider an avalanche-favoring A6V star, and two set-ups: a "cold disc" case, with a dust release at 10 au and an outer disc extending from 50 to 120 au, and a "warm disc" case with the release at 1 au and a 5-12 au outer disc. We explore, in addition, two key parameters: the density (parameterized by its optical depth τ) of the main outer disc and the amount of dust released by the initial breakup. Results: We find that avalanches could leave detectable structures on resolved images, for both "cold" and "warm" disc cases, in discs with τ of a few 10-3, provided that large dust masses (≳1020-5 × 1022 g) are initially released. The integrated photometric excess due to an avalanche is relatively limited, less than 10% for these released dust masses, peaking in the λ 10-20 μm domain and becoming insignificant beyond 40-50 μm. Contrary to earlier studies, we do not obtain stronger avalanches when increasing τ to higher values. Likewise, we do not observe a significant luminosity deficit, as compared to the pre-avalanche level, after the passage of the avalanche. These two results concur to make avalanches an unlikely explanation for the sharp luminosity drops observed in some extremely bright debris discs. The ideal configuration for observing an

Snow Avalanche Disturbance Ecology: Examples From the San Juan Mountains, Colorado.

Science.gov (United States)

Simonson, S.; Fassnacht, S. R.

2008-12-01

We evaluated landscape ecology approaches to characterize snow avalanche paths based on patterns of plant species composition and evidence of disturbance. Historical records of avalanche incidents, patterns in the annual growth layers of woody plants, and distributions of plant species can be used to quantify and map the frequency and magnitude of snow slide events. Near Silverton, Colorado, a series of snow storms in January of 2005 resulted in many avalanche paths running full track at 30 and 100 year return frequency. Many avalanches cut fresh trimlines, widening their tracks by uprooting, stripping, and breaking mature trees. Powerful avalanches deposited massive piles of snow, rocks, and woody debris in their runout zones. We used cross-section discs and cores of representative downed trees to detect dendro-ecological signals of past snow avalanche disturbance. Avalanche signals included impact scars from the moving snow and associated wind blast, relative width of annual growth rings, and development of reaction wood in response to tilting. Initial measurements of plant diversity and disturbance along the elevation gradient of an avalanche path near Silverton indicate that avalanche activity influences patterns of forest cover, contributes to the high local plant species diversity, and provides opportunities for new seedling establishment.

SNOW AVALANCHE ACTIVITY IN PARÂNG SKI AREA REVEALED BY TREE-RINGS

Directory of Open Access Journals (Sweden)

F. MESEȘAN

2014-11-01

Full Text Available Snow Avalanche Activity in Parâng Ski Area Revealed by Tree-Rings. Snow avalanches hold favorable conditions to manifest in Parâng Mountains but only one event is historically known, without destructive impact upon infrastructure or fatalities and this region wasn’t yet the object of avalanche research. The existing ski infrastructure of Parâng resort located in the west of Parâng Mountains is proposed to be extended in the steep slopes of subalpine area. Field evidence pinpoints that these steep slopes were affected by snow avalanches in the past. In this study we analyzed 11 stem discs and 31 increment cores extracted from 22 spruces (Picea abies (L. Karst impacted by avalanches, in order to obtain more information about past avalanches activity. Using the dendrogeomorphological approach we found 13 avalanche events that occurred along Scărița avalanche path, since 1935 until 2012, nine of them produced in the last 20 years. The tree-rings data inferred an intense snow avalanche activity along this avalanche path. This study not only calls for more research in the study area but also proves that snow avalanches could constitute an important restrictive factor for the tourism infrastructure and related activities in the area. It must be taken into consideration by the future extension of tourism infrastructure. Keywords: snow avalanche, Parâng Mountains, dendrogeomorphology, ski area.

Relating rock avalanche morphology to emplacement processes

Science.gov (United States)

Dufresne, Anja; Prager, Christoph; Bösmeier, Annette

2015-04-01

The morphology, structure and sedimentological characteristics of rock avalanche deposits reflect both internal emplacement processes and external influences, such as runout path characteristics. The latter is mainly predisposed by topography, substrate types, and hydrogeological conditions. Additionally, the geological setting at the source slope controls, e.g. the spatial distribution of accumulated lithologies and hence material property-related changes in morphology, or the maximum clast size and amount of fines of different lithological units. The Holocene Tschirgant rock avalanche (Tyrol, Austria) resulted from failure of an intensely deformed carbonate rock mass on the southeast face of a 2,370-m-high mountain ridge. The initially sliding rock mass rapidly fragmented as it moved towards the floor of the Inn River valley. Part of the 200-250 x 106 m3 (Patzelt 2012) rock avalanche debris collided with and moved around an opposing bedrock ridge and flowed into the Ötz valley, reaching up to 6.3 km from source. Where the Tschirgant rock avalanche spread freely it formed longitudinal ridges aligned along motion direction as well as smaller hummocks. Encountering high topography, it left runup ridges, fallback patterns (i.e. secondary collapse), and compressional morphology (successively elevated, transverse ridges). Further evidence for the mechanical landslide behaviour is given by large volumes of mobilized valley-fill sediments (polymict gravels and sands). These sediments indicate both shearing and compressional faulting within the rock avalanche mass (forming their own morphological units through, e.g. in situ bulldozing or as distinctly different hummocky terrain), but also indicate extension of the spreading landslide mass (i.e. intercalated/injected gravels encountered mainly in morphological depressions between hummocks). Further influences on its morphology are given by the different lithological units. E.g. the transition from massive dolomite

Studies of light emission by continuously sensitive avalanche chambers

International Nuclear Information System (INIS)

Charpak, G.; Dominik, W.; Fabre, J.P.; Gaudaen, J.; Sauli, F.; Suzuki, M.

1988-01-01

The optimal conditions for the optical recording of images of electron avalanches between parallel meshes have been studied. The emission spectra of gas mixtures have been investigated, where triethylamine (TEA), tetrakis(dimethylamine)ethylene (TMAE), and nitrogen, are used as the photon-emitting agents. For a given charge gain, the photon intensity decreases with electric field. This favours amplification between parallel meshes instead of wires. The use of intensified CCD cameras permits the recording of the local energy loss along the tracks. (orig.)

Setting best practice criteria for self-differencing avalanche photodiodes in quantum key distribution

Science.gov (United States)

Koehler-Sidki, Alexander; Dynes, James F.; Lucamarini, Marco; Roberts, George L.; Sharpe, Andrew W.; Savory, Seb J.; Yuan, Zhiliang; Shields, Andrew J.

2017-10-01

In recent years, the security of avalanche photodiodes as single photon detectors for quantum key distribution has been subjected to much scrutiny. The most prominent example of this surrounds the vulnerability of such devices to blinding under strong illumination. We focus on self-differencing avalanche photodiodes, single photon detectors that have demonstrated count rates exceeding 1 GCounts/s resulting in secure key rates over 1 MBit/s. These detectors use a passive electronic circuit to cancel any periodic signals thereby enhancing detection sensitivity. However this intrinsic feature can be exploited by adversaries to gain control of the devices using illumination of a moderate intensity. Through careful experimental examinations, we define here a set of criteria for these detectors to avoid such attacks.

Terrain Classification of Norwegian Slab Avalanche Accidents

Science.gov (United States)

Hallandvik, Linda; Aadland, Eivind; Vikene, Odd Lennart

2016-01-01

It is difficult to rely on snow conditions, weather, and human factors when making judgments about avalanche risk because these variables are dynamic and complex; terrain, however, is more easily observed and interpreted. Therefore, this study aimed to investigate (1) the type of terrain in which historical fatal snow avalanche accidents in Norway…

Correlation of Etch Pits and Dislocations in As-grown and Thermal Cycle-Annealed HgCdTe(211) Films

Science.gov (United States)

Vaghayenegar, M.; Jacobs, R. N.; Benson, J. D.; Stoltz, A. J.; Almeida, L. A.; Smith, David J.

2017-08-01

This paper reports observations of the different types of etch pits and dislocations present in thick HgCdTe (211) layers grown by molecular beam epitaxy on CdTe/Si (211) composite substrates. Dislocation analysis for as-grown and thermal cycle-annealed samples has been carried out using bright-field transmission electron microscopy. Triangular pits present in as-grown material are associated with a mixture of Frank partials and perfect dislocations, while pits with fish-eye shapes have perfect dislocations with 1/2[0\\bar{1}1] Burgers vector. The dislocations beneath skew pits are more complex as they have two different crystallographic directions, and are associated with a mixture of Shockley partials and perfect dislocations. Dislocation analysis of samples after thermal cycle annealing (TCA) shows that the majority of dislocations under the etch pits are short segments of perfect dislocations with 1/2[0\\bar{1}1] Burgers vector while the remainder are Shockley partials. The absence of fish-eye shape pits in TCA samples suggests that they are associated with mobile dislocations that have reacted during annealing, causing the overall etch pit density to be reduced. Very large pits with a density ˜2×103 cm-2 are observed in as-grown and TCA samples. These defects thread from within the CdTe buffer layer into the upper regions of the HgCdTe layers. Their depth in as-grown material is so large that it is not possible to locate and identify the underlying defects.

Improved HgCdTe detectors with novel antireflection coating

Science.gov (United States)

Babu, Sachi R.; Hu, Kelley; Manthripragada, Sridhar; Martineau, Robert J.; Kotecki, C. A.; Peters, F. A.; Burgess, A. S.; Krebs, Danny J.; Mott, David B.; Ewin, Audrey J.; Miles, A.; Nguyen, Trang L.; Shu, Peter K.

1996-10-01

The composite infrared spctrometer (CIRS) is an important instrument for the upcoming Cassini mission for sensing infrared (IR) radiation from the Saturanian planetary system. We have delivered a linear, ten element, mercury cadmium telluride (HgCdTe) photoconductive detector array for use on focal plane 3 (FP3), which is responsible for detecting radiation from the 9.1 micrometer to 16.6 micrometer wavelength range. Reliable HgCdTe detectors require robust passivation, a low-stress zinc sulfide (ZnS) anti-reflection (AR) coating with good adhesion, and a proper optical cavity design to smooth out the resonance in the detector spectral response. During the development of CIRS flight array, we have demonstrated the potential of using an in-situ interfacial layer, such as SiN(subscript x), between ZnS and the anodic oxide. Such an interfacial layer drastically improves the adhesion between the ZnS and oxide, without degrading the minority carrier lifetime. We have also demonstrated the feasibility of applying a SiN(subscript x) 'rain coat' layer over the ZnS to prevent moisture and other chemicals from attacking the AR coating, thus improving the long term reliability. This also enables device operation in a hazardous environment. The alumina/epoxy/HgCdTe/oxide/ZnS structure is a complicated multi-cavity optical system. We have developed an extensive device simulation, which enables us to make the optimal choice of individual cavity thickness for minimizing the resonance and maximizing the quantum efficiency. We have also used 0.05 micrometer alumina powder loaded epoxy to minimize the reflections at the epoxy/HgCdTe interface, thus minimizing the resonance.

Discrimination capability of avalanche counters detecting different ionizing particles

International Nuclear Information System (INIS)

Prete, G.; Viesti, G.; Padua Univ.

1985-01-01

The discrimination capability of avalanche counters to detect different ionizing particles has been studied using a 252 Cf source. Pulse height, pulse-height resolution and timing properties have been measured as a function of the reduced applied voltage for parallel-plate and parallel-grid avalanche counters. At the highest applied voltages, space charge effects shift the pulse-height signal of the avalanche counter away from being linearly proportional to the stopping power of the detected particles and cause the pulse-height resolution to deteriorate. To optimize the avalanche counter capability, without loss of time resolution, it appears better to operate the detector at voltages well below the breakdown threshold. Measurements with 32 S ions are also reported. (orig.)

Statistical evaluation of waveform collapse reveals scale-free properties of neuronal avalanches

Directory of Open Access Journals (Sweden)

Aleena eShaukat

2016-04-01

Full Text Available Neural avalanches are a prominent form of brain activity characterized by network-wide bursts whose statistics follow a power-law distribution with a slope near 3/2. Recent work suggests that avalanches of different durations can be rescaled and thus collapsed together. This collapse mirrors work in statistical physics where it is proposed to form a signature of systems evolving in a critical state. However, no rigorous statistical test has been proposed to examine the degree to which neuronal avalanches collapse together. Here, we describe a statistical test based on functional data analysis, where raw avalanches are first smoothed with a Fourier basis, then rescaled using a time-warping function. Finally, an F ratio test combined with a bootstrap permutation is employed to determine if avalanches collapse together in a statistically reliable fashion. To illustrate this approach, we recorded avalanches from cortical cultures on multielectrode arrays as in previous work. Analyses show that avalanches of various durations can be collapsed together in a statistically robust fashion. However, a principal components analysis revealed that the offset of avalanches resulted in marked variance in the time-warping function, thus arguing for limitations to the strict fractal nature of avalanche dynamics. We compared these results with those obtained from cultures treated with an AMPA/NMDA receptor antagonist (APV/DNQX, which yield a power-law of avalanche durations with a slope greater than 3/2. When collapsed together, these avalanches showed marked misalignments both at onset and offset time-points. In sum, the proposed statistical evaluation suggests the presence of scale-free avalanche waveforms and constitutes an avenue for examining critical dynamics in neuronal systems.

Avalanche and streamer mode operation of resistive plate chambers

International Nuclear Information System (INIS)

Cardarelli, R.; Makeev, V.; Santonico, R.

1996-01-01

A resistive plate chamber was operated at voltages increasing in steps of 200 V over a 3 kV interval and the transition between the avalanche and streamer modes was studied. The avalanche amplitude was observed to be exponentially dependent on the operating voltage up to a value, characteristic of the gas, where the avalanche saturation occurs and delayed streamer signals start to appear. Signal waveforms, charge and timing distributions are reported. (orig.)

Automated identification of potential snow avalanche release areas based on digital elevation models

Directory of Open Access Journals (Sweden)

Y. Bühler

2013-05-01

Full Text Available The identification of snow avalanche release areas is a very difficult task. The release mechanism of snow avalanches depends on many different terrain, meteorological, snowpack and triggering parameters and their interactions, which are very difficult to assess. In many alpine regions such as the Indian Himalaya, nearly no information on avalanche release areas exists mainly due to the very rough and poorly accessible terrain, the vast size of the region and the lack of avalanche records. However avalanche release information is urgently required for numerical simulation of avalanche events to plan mitigation measures, for hazard mapping and to secure important roads. The Rohtang tunnel access road near Manali, Himachal Pradesh, India, is such an example. By far the most reliable way to identify avalanche release areas is using historic avalanche records and field investigations accomplished by avalanche experts in the formation zones. But both methods are not feasible for this area due to the rough terrain, its vast extent and lack of time. Therefore, we develop an operational, easy-to-use automated potential release area (PRA detection tool in Python/ArcGIS which uses high spatial resolution digital elevation models (DEMs and forest cover information derived from airborne remote sensing instruments as input. Such instruments can acquire spatially continuous data even over inaccessible terrain and cover large areas. We validate our tool using a database of historic avalanches acquired over 56 yr in the neighborhood of Davos, Switzerland, and apply this method for the avalanche tracks along the Rohtang tunnel access road. This tool, used by avalanche experts, delivers valuable input to identify focus areas for more-detailed investigations on avalanche release areas in remote regions such as the Indian Himalaya and is a precondition for large-scale avalanche hazard mapping.

Automated identification of potential snow avalanche release areas based on digital elevation models

Science.gov (United States)

Bühler, Y.; Kumar, S.; Veitinger, J.; Christen, M.; Stoffel, A.; Snehmani

2013-05-01

The identification of snow avalanche release areas is a very difficult task. The release mechanism of snow avalanches depends on many different terrain, meteorological, snowpack and triggering parameters and their interactions, which are very difficult to assess. In many alpine regions such as the Indian Himalaya, nearly no information on avalanche release areas exists mainly due to the very rough and poorly accessible terrain, the vast size of the region and the lack of avalanche records. However avalanche release information is urgently required for numerical simulation of avalanche events to plan mitigation measures, for hazard mapping and to secure important roads. The Rohtang tunnel access road near Manali, Himachal Pradesh, India, is such an example. By far the most reliable way to identify avalanche release areas is using historic avalanche records and field investigations accomplished by avalanche experts in the formation zones. But both methods are not feasible for this area due to the rough terrain, its vast extent and lack of time. Therefore, we develop an operational, easy-to-use automated potential release area (PRA) detection tool in Python/ArcGIS which uses high spatial resolution digital elevation models (DEMs) and forest cover information derived from airborne remote sensing instruments as input. Such instruments can acquire spatially continuous data even over inaccessible terrain and cover large areas. We validate our tool using a database of historic avalanches acquired over 56 yr in the neighborhood of Davos, Switzerland, and apply this method for the avalanche tracks along the Rohtang tunnel access road. This tool, used by avalanche experts, delivers valuable input to identify focus areas for more-detailed investigations on avalanche release areas in remote regions such as the Indian Himalaya and is a precondition for large-scale avalanche hazard mapping.

Velocity distribution in snow avalanches

Science.gov (United States)

Nishimura, K.; Ito, Y.

1997-12-01

In order to investigate the detailed structure of snow avalanches, we have made snow flow experiments at the Miyanomori ski jump in Sapporo and systematic observations in the Shiai-dani, Kurobe Canyon. In the winter of 1995-1996, a new device to measure static pressures was used to estimate velocities in the snow cloud that develops above the flowing layer of avalanches. Measurements during a large avalanche in the Shiai-dani which damaged and destroyed some instruments indicate velocities increased rapidly to more than 50 m/s soon after the front. Velocities decreased gradually in the following 10 s. Velocities of the lower flowing layer were also calculated by differencing measurement of impact pressure. Both recordings in the snow cloud and in the flowing layer changed with a similar trend and suggest a close interaction between the two layers. In addition, the velocity showed a periodic change. Power spectrum analysis of the impact pressure and the static pressure depression showed a strong peak at a frequency between 4 and 6 Hz, which might imply the existence of either ordered structure or a series of surges in the flow.

Modification of surface layers of copper under the action of the volumetric discharge initiated by an avalanche electron beam in nitrogen and CO2 at atmospheric pressure

Science.gov (United States)

Shulepov, M. A.; Akhmadeev, Yu. Kh.; Tarasenko, V. F.; Kolubaeva, Yu. A.; Krysina, O. V.; Kostyrya, I. D.

2011-05-01

The results of experimental investigations of the action of the volumetric discharge initiated by an avalanche electron beam on the surface of copper specimens are presented. The volumetric (diffuse) discharge in nitrogen and CO2 at atmospheric pressure was initiated by applying high voltage pulses of nanosecond duration to a tubular foil cathode. It has been found that the treatment of a copper surface by this type of discharge increases the hardness of the surface layer due to oxidation.

Current–voltage characteristics of high-voltage 4H-SiC p{sup +}–n{sub 0}–n{sup +} diodes in the avalanche breakdown mode

Energy Technology Data Exchange (ETDEWEB)

Ivanov, P. A., E-mail: Pavel.Ivanov@mail.ioffe.ru; Potapov, A. S.; Samsonova, T. P.; Grekhov, I. V. [Ioffe Physical–Technical Institute (Russian Federation)

2017-03-15

p{sup +}–n{sub 0}–n{sup +} 4H-SiC diodes with homogeneous avalanche breakdown at 1860 V are fabricated. The pulse current–voltage characteristics are measured in the avalanche-breakdown mode up to a current density of 4000 A/cm{sup 2}. It is shown that the avalanche-breakdown voltage increases with increasing temperature. The following diode parameters are determined: the avalanche resistance (8.6 × 10{sup –2} Ω cm{sup 2}), the electron drift velocity in the n{sub 0} base at electric fields higher than 10{sup 6} V/cm (7.8 × 10{sup 6} cm/s), and the relative temperature coefficient of the breakdown voltage (2.1 × 10{sup –4} K{sup –1}).

Anthropogenic effect on avalanche and debris flow activity

Directory of Open Access Journals (Sweden)

S. A. Sokratov

2013-01-01

Full Text Available The paper presents examples of the change in snow avalanches and debris flows activity due to the anthropogenic pressure on vegetation and relief. The changes in dynamical characteristics of selected snow avalanches and debris flows due to the anthropogenic activity are quantified. The conclusion is made that the anthropogenic effects on the snow avalanches and debris flows activity are more pronounced than the possible effects of the climate change. The necessity is expressed on the unavoidable changes of the natural environment as the result of a construction and of use of the constructed infrastructure to be account for in corresponding planning of the protection measures.

Beyond Critical Exponents in Neuronal Avalanches

Science.gov (United States)

Friedman, Nir; Butler, Tom; Deville, Robert; Beggs, John; Dahmen, Karin

2011-03-01

Neurons form a complex network in the brain, where they interact with one another by firing electrical signals. Neurons firing can trigger other neurons to fire, potentially causing avalanches of activity in the network. In many cases these avalanches have been found to be scale independent, similar to critical phenomena in diverse systems such as magnets and earthquakes. We discuss models for neuronal activity that allow for the extraction of testable, statistical predictions. We compare these models to experimental results, and go beyond critical exponents.

A novel approach to evaluate and compare computational snow avalanche simulation

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J.-T. Fischer

2013-06-01

Full Text Available An innovative approach for the analysis and interpretation of snow avalanche simulation in three dimensional terrain is presented. Snow avalanche simulation software is used as a supporting tool in hazard mapping. When performing a high number of simulation runs the user is confronted with a considerable amount of simulation results. The objective of this work is to establish an objective, model independent framework to evaluate and compare results of different simulation approaches with respect to indicators of practical relevance, providing an answer to the important questions: how far and how destructive does an avalanche move down slope. For this purpose the Automated Indicator based Model Evaluation and Comparison (AIMEC method is introduced. It operates on a coordinate system which follows a given avalanche path. A multitude of simulation runs is performed with the snow avalanche simulation software SamosAT (Snow Avalanche MOdelling and Simulation – Advanced Technology. The variability of pressure-based run out and avalanche destructiveness along the path is investigated for multiple simulation runs, varying release volume and model parameters. With this, results of deterministic simulation software are processed and analysed by means of statistical methods. Uncertainties originating from varying input conditions, model parameters or the different model implementations are assessed. The results show that AIMEC contributes to the interpretation of avalanche simulations with a broad applicability in model evaluation, comparison as well as examination of scenario variations.

Experimental method to predict avalanches based on neural networks

Directory of Open Access Journals (Sweden)

V. V. Zhdanov

2016-01-01

Full Text Available The article presents results of experimental use of currently available statistical methods to classify the avalanche‑dangerous precipitations and snowfalls in the Kishi Almaty river basin. The avalanche service of Kazakhstan uses graphical methods for prediction of avalanches developed by I.V. Kondrashov and E.I. Kolesnikov. The main objective of this work was to develop a modern model that could be used directly at the avalanche stations. Classification of winter precipitations into dangerous snowfalls and non‑dangerous ones was performed by two following ways: the linear discriminant function (canonical analysis and artificial neural networks. Observational data on weather and avalanches in the gorge Kishi Almaty in the gorge Kishi Almaty were used as a training sample. Coefficients for the canonical variables were calculated by the software «Statistica» (Russian version 6.0, and then the necessary formula had been constructed. The accuracy of the above classification was 96%. Simulator by the authors L.N. Yasnitsky and F.М. Cherepanov was used to learn the neural networks. The trained neural network demonstrated 98% accuracy of the classification. Prepared statistical models are recommended to be tested at the snow‑avalanche stations. Results of the tests will be used for estimation of the model quality and its readiness for the operational work. In future, we plan to apply these models for classification of the avalanche danger by the five‑point international scale.

Spike avalanches exhibit universal dynamics across the sleep-wake cycle.

Directory of Open Access Journals (Sweden)

Tiago L Ribeiro

2010-11-01

Full Text Available Scale-invariant neuronal avalanches have been observed in cell cultures and slices as well as anesthetized and awake brains, suggesting that the brain operates near criticality, i.e. within a narrow margin between avalanche propagation and extinction. In theory, criticality provides many desirable features for the behaving brain, optimizing computational capabilities, information transmission, sensitivity to sensory stimuli and size of memory repertoires. However, a thorough characterization of neuronal avalanches in freely-behaving (FB animals is still missing, thus raising doubts about their relevance for brain function.To address this issue, we employed chronically implanted multielectrode arrays (MEA to record avalanches of action potentials (spikes from the cerebral cortex and hippocampus of 14 rats, as they spontaneously traversed the wake-sleep cycle, explored novel objects or were subjected to anesthesia (AN. We then modeled spike avalanches to evaluate the impact of sparse MEA sampling on their statistics. We found that the size distribution of spike avalanches are well fit by lognormal distributions in FB animals, and by truncated power laws in the AN group. FB data surrogation markedly decreases the tail of the distribution, i.e. spike shuffling destroys the largest avalanches. The FB data are also characterized by multiple key features compatible with criticality in the temporal domain, such as 1/f spectra and long-term correlations as measured by detrended fluctuation analysis. These signatures are very stable across waking, slow-wave sleep and rapid-eye-movement sleep, but collapse during anesthesia. Likewise, waiting time distributions obey a single scaling function during all natural behavioral states, but not during anesthesia. Results are equivalent for neuronal ensembles recorded from visual and tactile areas of the cerebral cortex, as well as the hippocampus.Altogether, the data provide a comprehensive link between behavior

Are dragon-king neuronal avalanches dungeons for self-organized brain activity?

Science.gov (United States)

de Arcangelis, L.

2012-05-01

Recent experiments have detected a novel form of spontaneous neuronal activity both in vitro and in vivo: neuronal avalanches. The statistical properties of this activity are typical of critical phenomena, with power laws characterizing the distributions of avalanche size and duration. A critical behaviour for the spontaneous brain activity has important consequences on stimulated activity and learning. Very interestingly, these statistical properties can be altered in significant ways in epilepsy and by pharmacological manipulations. In particular, there can be an increase in the number of large events anticipated by the power law, referred to herein as dragon-king avalanches. This behaviour, as verified by numerical models, can originate from a number of different mechanisms. For instance, it is observed experimentally that the emergence of a critical behaviour depends on the subtle balance between excitatory and inhibitory mechanisms acting in the system. Perturbing this balance, by increasing either synaptic excitation or the incidence of depolarized neuronal up-states causes frequent dragon-king avalanches. Conversely, an unbalanced GABAergic inhibition or long periods of low activity in the network give rise to sub-critical behaviour. Moreover, the existence of power laws, common to other stochastic processes, like earthquakes or solar flares, suggests that correlations are relevant in these phenomena. The dragon-king avalanches may then also be the expression of pathological correlations leading to frequent avalanches encompassing all neurons. We will review the statistics of neuronal avalanches in experimental systems. We then present numerical simulations of a neuronal network model introducing within the self-organized criticality framework ingredients from the physiology of real neurons, as the refractory period, synaptic plasticity and inhibitory synapses. The avalanche critical behaviour and the role of dragon-king avalanches will be discussed in

Catastrophic avalanches and methods of their control

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N. A. Volodicheva

2014-01-01

Full Text Available Definition of such phenomenon as “catastrophic avalanche” is presented in this arti-cle. Several situations with releases of catastrophic avalanches in mountains of Caucasus, Alps, and Central Asia are investigated. Materials of snow-avalanche ob-servations performed since 1960s at the Elbrus station of the Lomonosov Moscow State University (Central Caucasus were used for this work. Complex-valued measures of engineering protection demonstrating different efficiencies are consid-ered.

Design and characterization of single photon avalanche diodes arrays

Science.gov (United States)

Neri, L.; Tudisco, S.; Lanzanò, L.; Musumeci, F.; Privitera, S.; Scordino, A.; Condorelli, G.; Fallica, G.; Mazzillo, M.; Sanfilippo, D.; Valvo, G.

2010-05-01

During the last years, in collaboration with ST-Microelectronics, we developed a new avalanche photo sensor, single photon avalanche diode (SPAD) see Ref.[S. Privitera, et al., Sensors 8 (2008) 4636 [1];S. Tudisco et al., IEEE Sensors Journal 8 (2008) 1324 [2

Active Pixel HgCdTe Detectors With Built-in Dark Current Reduction for Near-Room Temperature Operation, Phase II

Data.gov (United States)

National Aeronautics and Space Administration — High sensitivity HgCdTe infrared arrays operating at 77K can now be tailored in a wide range of wavelengths from 1 to 14 microns. However, due to the cooling...

Active Pixel HgCdTe Detectors With Built-in Dark Current Reduction for Near-Room Temperature Operation, Phase I

Data.gov (United States)

National Aeronautics and Space Administration — High sensitivity HgCdTe infrared arrays operating at 77K can now be tailored in a wide range of wavelengths from 1 to14 um. However, the cooling requirements make...

Magnetic avalanches in manganese-acetate, "magnetic deflagration"

Science.gov (United States)

Suzuki, Yoko

Mn12-acetate, first synthesized in 1980 by Lis, is one example of a class of many molecules called single molecule magnets (SMMs) or molecular nanomagnets. These molecules have several atomic spins strongly coupled together within each molecule. They exhibit interesting quantum mechanical phenomena at low temperatures such as quantum tunneling of magnetization, which was first found with Mn12-acetate in 1996 by Friedman, et al. , and Berry phase oscillations which were measured in Fe8 (another SMM) in 1999 by Wernsdorfer, et al. In addition to possible application as memory storage and qubits for quantum computers, these systems provide the means for studies of mesoscopic physics as well as the interactions of the molecules with their environment, such as phonon, photon, nuclear spin, intermolecular dipole, and exchange interactions. Mn12-acetate has twelve Mn ions magnetically coupled in the center of the molecule yielding a giant spin of S = 10 at low temperature. It also has a large uniaxial anisotropy of 65 K. Below 3 K, magnetization curves show strong hysteresis due to the anisotropy barrier. At thesis temperatures, the spin relaxes through the barrier by quantum tunneling of magnetization, which produces regularly-spaced multiple resonant steps in the hysteresis curve. Magnetic avalanches, first detected by Paulsen et al., also occur for some samples only at low temperature, leading to a very fast single-step reversal of the full magnetization, which clearly differs from relaxation by tunneling. In this thesis, I present the results of detailed experimental studies of two aspects of magnetic avalanche phenomenon: "conditions for the triggering of avalanches" and "propagation of the avalanche front". In the first study, we find the magnetic fields at which avalanches occur are stochastically distributed in a particular range of fields. For the second study, we conducted local time-resolved measurements. The results indicate the magnetization avalanches spread

La Carte de Localisation Probable des Avalanches (CPLA

Directory of Open Access Journals (Sweden)

Gilles BORREL

1994-12-01

Full Text Available La Carte de Localisation Probable des Avalanches (CPLA indique l’enveloppe des limites extrêmes connues atteintes par les avalanches, ainsi que les travaux de protection associés. Il s’agit d’un document informatif et non d’une carte de risque. Depuis 1990, les données thématiques sont numérisées.

Phase avalanches in near-adiabatic evolutions

International Nuclear Information System (INIS)

Vertesi, T.; Englman, R.

2006-01-01

In the course of slow, nearly adiabatic motion of a system, relative changes in the slowness can cause abrupt and high magnitude phase changes, ''phase avalanches,'' superimposed on the ordinary geometric phases. The generality of this effect is examined for arbitrary Hamiltonians and multicomponent (>2) wave packets and is found to be connected (through the Blaschke term in the theory of analytic signals) to amplitude zeros in the lower half of the complex time plane. Motion on a nonmaximal circle on the Poincare-sphere suppresses the effect. A spectroscopic transition experiment can independently verify the phase-avalanche magnitudes

Theoretical issues in tokamak confinement: (i) Internal/edge transport barriers and (ii) runaway avalanche confinement

International Nuclear Information System (INIS)

Connor, J.W.; Helander, P.; Thyagaraja, A.; Andersson, F.; Fueloep, T.; Eriksson, L.-G.; Romanelli, M.

2001-01-01

This paper summarises a number of distinct, but related, pieces of work on key confinement issues for tokamaks, in particular the formation of internal and edge transport barriers, both within turbulent and neoclassical models, and radial diffusion of avalanching runaway electrons. First-principle simulations of tokamak turbulence and transport using the two-fluid, electromagnetic, global code CUTIE are described. The code has demonstrated the spontaneous formation of internal transport barriers near mode rational surfaces, in qualitative agreement with observations on JET and RTP. The theory of neoclassical transport in an impure, toroidal plasma has been extended to allow for steeper pressure and temperature gradients than are usually considered, and is then found to become nonlinear under conditions typical of the tokamak edge. For instance, the particle flux is found to be a nonmonotonic function of the gradients, thus allowing for a bifurcation in the ion particle flux. Finally, it is shown that radial diffusion caused by magnetic fluctuations can effectively suppress avalanches of runaway electrons if the fluctuation amplitude exceeds δB/B∼10 -3 . (author)

IFKIS - a basis for managing avalanche risk in settlements and on roads in Switzerland

Directory of Open Access Journals (Sweden)

M. Bründl

2004-01-01

Full Text Available After the avalanche winter of 1999 in Switzerland, which caused 17 deaths and damage of over CHF 600 mill. in buildings and on roads, the project IFKIS, aimed at improving the basics of organizational measures (closure of roads, evacuation etc. in avalanche risk management, was initiated. The three main parts of the project were the development of a compulsory checklist for avalanche safety services, a modular education and training course program and an information system for safety services. The information system was developed in order to improve both the information flux between the national centre for avalanche forecasting, the Swiss Federal Institute for Snow and Avalanche Research SLF, and the local safety services on the one hand and the communication between avalanche safety services in the communities on the other hand. The results of this project make a valuable contribution to strengthening organizational measures in avalanche risk management and to closing the gaps, which became apparent during the avalanche winter of 1999. They are not restricted to snow avalanches but can also be adapted for dealing with other natural hazard processes and catastrophes.

Post-glacial rock avalanches in the Obersee Valley, Glarner Alps, Switzerland

Science.gov (United States)

Nagelisen, Jan; Moore, Jeffrey R.; Vockenhuber, Christoph; Ivy-Ochs, Susan

2015-06-01

The geological record of prehistoric rock avalanches provides invaluable data for assessing the hazard posed by these rare but destructive mass movements. Here we investigate two large rock avalanches in the Obersee valley of the Glarner Alps, Switzerland, providing detailed mapping of landslide and related Quaternary phenomena, revised volume estimates for each event, and surface exposure dating of rock avalanche deposits. The Rautispitz rock avalanche originated from the southern flank of the Obersee valley, releasing approximately 91 million m3 of limestone on steeply-dipping bedding planes. Debris had maximum horizontal travel distance of ~ 5000 m, a fahrboeschung angle (relating fall height to length) of 18°, and was responsible for the creation of Lake Obersee; deposits are more than 130 m thick in places. The Platten rock avalanche encompassed a source volume of 11 million m3 sliding from the northern flank of the Obersee valley on similar steeply-dipping limestone beds (bedrock forms a syncline under the valley). Debris had a maximum horizontal travel distance of 1600 m with a fahrboeschung angle of 21°, and is more than 80 m thick in places. Deposits of the Platten rock avalanche are superposed atop those from the Rautispitz event at the end of the Obersee valley where they dam Lake Haslensee. Runout for both events was simulated using the dynamic analysis code DAN3D; results showed excellent match to mapped deposit extents and thickness and helped confirm the hypothesized single-event failure scenarios. 36Cl cosmogenic nuclide surface exposure dating of 13 deposited boulders revealed a Younger Dryas age of 12.6 ± 1.0 ka for the Rautispitz rock avalanche and a mid-Holocene age of 6.1 ± 0.8 ka for the Platten rock avalanche. A seismological trigger is proposed for the former event due to potentially correlated turbidite deposits in nearby Lake Zurich.

Low-Noise Free-Running High-Rate Photon-Counting for Space Communication and Ranging

Science.gov (United States)

Lu, Wei; Krainak, Michael A.; Yang, Guan; Sun, Xiaoli; Merritt, Scott

2016-01-01

We present performance data for low-noise free-running high-rate photon counting method for space optical communication and ranging. NASA GSFC is testing the performance of two types of novel photon-counting detectors 1) a 2x8 mercury cadmium telluride (HgCdTe) avalanche array made by DRS Inc., and a 2) a commercial 2880-element silicon avalanche photodiode (APD) array. We successfully measured real-time communication performance using both the 2 detected-photon threshold and logic AND-gate coincidence methods. Use of these methods allows mitigation of dark count, after-pulsing and background noise effects without using other method of Time Gating The HgCdTe APD array routinely demonstrated very high photon detection efficiencies (50) at near infrared wavelength. The commercial silicon APD array exhibited a fast output with rise times of 300 ps and pulse widths of 600 ps. On-chip individually filtered signals from the entire array were multiplexed onto a single fast output. NASA GSFC has tested both detectors for their potential application for space communications and ranging. We developed and compare their performances using both the 2 detected photon threshold and coincidence methods.

Forecasting of wet snow avalanche activity: Proof of concept and operational implementation

Science.gov (United States)

Gobiet, Andreas; Jöbstl, Lisa; Rieder, Hannes; Bellaire, Sascha; Mitterer, Christoph

2017-04-01

State-of-the-art tools for the operational assessment of avalanche danger include field observations, recordings from automatic weather stations, meteorological analyses and forecasts, and recently also indices derived from snowpack models. In particular, an index for identifying the onset of wet-snow avalanche cycles (LWCindex), has been demonstrated to be useful. However, its value for operational avalanche forecasting is currently limited, since detailed, physically based snowpack models are usually driven by meteorological data from automatic weather stations only and have therefore no prognostic ability. Since avalanche risk management heavily relies on timely information and early warnings, many avalanche services in Europe nowadays start issuing forecasts for the following days, instead of the traditional assessment of the current avalanche danger. In this context, the prognostic operation of detailed snowpack models has recently been objective of extensive research. In this study a new, observationally constrained setup for forecasting the onset of wet-snow avalanche cycles with the detailed snow cover model SNOWPACK is presented and evaluated. Based on data from weather stations and different numerical weather prediction models, we demonstrate that forecasts of the LWCindex as indicator for wet-snow avalanche cycles can be useful for operational warning services, but is so far not reliable enough to be used as single warning tool without considering other factors. Therefore, further development currently focuses on the improvement of the forecasts by applying ensemble techniques and suitable post processing approaches to the output of numerical weather prediction models. In parallel, the prognostic meteo-snow model chain is operationally used by two regional avalanche warning services in Austria since winter 2016/2017 for the first time. Experiences from the first operational season and first results from current model developments will be reported.

Application of statistical and dynamics models for snow avalanche hazard assessment in mountain regions of Russia

Science.gov (United States)

Turchaninova, A.

2012-04-01

The estimation of extreme avalanche runout distances, flow velocities, impact pressures and volumes is an essential part of snow engineering in mountain regions of Russia. It implies the avalanche hazard assessment and mapping. Russian guidelines accept the application of different avalanche models as well as approaches for the estimation of model input parameters. Consequently different teams of engineers in Russia apply various dynamics and statistical models for engineering practice. However it gives more freedom to avalanche practitioners and experts but causes lots of uncertainties in case of serious limitations of avalanche models. We discuss these problems by presenting the application results of different well known and widely used statistical (developed in Russia) and avalanche dynamics models for several avalanche test sites in the Khibini Mountains (The Kola Peninsula) and the Caucasus. The most accurate and well-documented data from different powder and wet, big rare and small frequent snow avalanche events is collected from 1960th till today in the Khibini Mountains by the Avalanche Safety Center of "Apatit". This data was digitized and is available for use and analysis. Then the detailed digital avalanche database (GIS) was created for the first time. It contains contours of observed avalanches (ESRI shapes, more than 50 years of observations), DEMs, remote sensing data, description of snow pits, photos etc. Thus, the Russian avalanche data is a unique source of information for understanding of an avalanche flow rheology and the future development and calibration of the avalanche dynamics models. GIS database was used to analyze model input parameters and to calibrate and verify avalanche models. Regarding extreme dynamic parameters the outputs using different models can differ significantly. This is unacceptable for the engineering purposes in case of the absence of the well-defined guidelines in Russia. The frequency curves for the runout distance

High voltage short plus generation based on avalanche circuit

International Nuclear Information System (INIS)

Hu Yuanfeng; Yu Xiaoqi

2006-01-01

Simulate the avalanche circuit in series with PSPICE module, design the high voltage short plus generation circuit by avalanche transistor in series for the sweep deflection circuit of streak camera. The output voltage ranges 1.2 KV into 50 ohm load. The rise time of the circuit is less than 3 ns. (authors)

2D Dark-Count-Rate Modeling of PureB Single-Photon Avalanche Diodes in a TCAD Environment

NARCIS (Netherlands)

Knežević, Tihomir; Nanver, Lis K.; Suligoj, Tomislav; Witzigmann, Bernd; Osiński, Marek; Arakawa, Yasuhiko

2018-01-01

PureB silicon photodiodes have nm-shallow p+n junctions with which photons/electrons with penetration-depths of a few nanometer can be detected. PureB Single-Photon Avalanche Diodes (SPADs) were fabricated and analysed by 2D numerical modeling as an extension to TCAD software. The very shallow

Application of avalanche photodiode for soft X-ray pulse-height analyses in the Ht-7 tokamak

CERN Document Server

Shi Yue Jiang; Hu Li Qun; Sun Yan Jun; LiuSheng; Ling Bil

2002-01-01

An avalanche photodiode (APD) has been used as soft X-ray energy pulse-height analysis system for the measurement of the electron temperature on the HT-7 tokamak. The experimental results obtained with the APD with its inferior energy resolution show a little difference compared to the conventional high energy-resolution Si (Li) detector. Both numerical analysis and experimental results prove that the APD is good enough for application of the electron temperature measurement in tokamaks.

Growth features of HgCdTe LPE layers

International Nuclear Information System (INIS)

Huseynov, E.K.; Eminov, Sh.O.; Ibragimov, T.I.; Ismaylov, N.J.; Rajabli, A.A.

2010-01-01

Full text : The results of growth of Hg 1 -xCd x Te (MCT) layers by liquid phase epitaxy (LPE) from Te-rich solutions (molar fraction (Hg 1 -zCd z )(1.y)Te y , z=0.054, y=0.805 for TL=501 degrees Celsium) obtained by the tipping method in closed system is presented. Epitaxial layers with different compositions (x=0.20-0.22) and thicknesses (10-20 μm) suitable for manufacturing the photodiode structures operable at 8-14 μm spectrum range were grown on B oriented Cd 0 .96Zn 0 ,04Te polished and repolished substrates. The growth was carried out in the temperature range 500-480 degrees Celsium with cooling rates 0.05-0.1 degrees Celsium/min in a sealed quartz ampoule using the original apparatus for LPE. The attention was paid mainly to the surface morphological quality, good decantation from the layers, uniformity of composition and thickness of films. One of the limitations of the most LPE growth apparatus (cassettes) with slider or tipping system is their impossibility to wipe the last drop of growth solution from the surface of just-grown epilayer. Some remnant or residual of the growth solution tends to adhere to the surface of the epilayer after growth in such apparatus and strongly affect the surface quality. The novel apparatus for LPE providing the surface without unwanted residual drops of melt solution of Hg, Cd and Te was developed with the aim of solving such a problem. The effect of different steps of LPE growth on morphology and composition of epitaxial layers was studied. By holding the CdZnTe substrate inside the growth ampoule at the melt homogenization temperature during of 15-50 min without contact with the melt resulted in visually (using the Leitzorthoplan microscopes x 500-1000) observed surface roughness. Using the expressions for the Te-angle of Hg-Cd-Te phase diagram the effect of the preliminary synthesis of the source on liquidus temperature and composition of the epilayers was numerically evaluated. HgCdTe layers were characterized using

Electric field distribution and simulation of avalanche formation due ...

Indian Academy of Sciences (India)

Electric field distributions and their role in the formation of avalanche due to the passage of heavy ions in parallel grid avalanche type wire chamber detectors are evaluated using a Monte Carlo simulation. The relative merits and demerits of parallel and crossed wire grid configurations are studied. It is found that the crossed ...

A new web-based system to improve the monitoring of snow avalanche hazard in France

Science.gov (United States)

Bourova, Ekaterina; Maldonado, Eric; Leroy, Jean-Baptiste; Alouani, Rachid; Eckert, Nicolas; Bonnefoy-Demongeot, Mylene; Deschatres, Michael

2016-05-01

Snow avalanche data in the French Alps and Pyrenees have been recorded for more than 100 years in several databases. The increasing amount of observed data required a more integrative and automated service. Here we report the comprehensive web-based Snow Avalanche Information System newly developed to this end for three important data sets: an avalanche chronicle (Enquête Permanente sur les Avalanches, EPA), an avalanche map (Carte de Localisation des Phénomènes d'Avalanche, CLPA) and a compilation of hazard and vulnerability data recorded on selected paths endangering human settlements (Sites Habités Sensibles aux Avalanches, SSA). These data sets are now integrated into a common database, enabling full interoperability between all different types of snow avalanche records: digitized geographic data, avalanche descriptive parameters, eyewitness reports, photographs, hazard and risk levels, etc. The new information system is implemented through modular components using Java-based web technologies with Spring and Hibernate frameworks. It automates the manual data entry and improves the process of information collection and sharing, enhancing user experience and data quality, and offering new outlooks to explore and exploit the huge amount of snow avalanche data available for fundamental research and more applied risk assessment.

Evaluation and operationalization of a novel forest detrainment modeling approach for computational snow avalanche simulation

Science.gov (United States)

Teich, M.; Feistl, T.; Fischer, J.; Bartelt, P.; Bebi, P.; Christen, M.; Grêt-Regamey, A.

2013-12-01

Two-dimensional avalanche simulation software operating in three-dimensional terrain are widely used for hazard zoning and engineering to predict runout distances and impact pressures of snow avalanche events. Mountain forests are an effective biological protection measure; however, the protective capacity of forests to decelerate or even to stop avalanches that start within forested areas or directly above the treeline is seldom considered in this context. In particular, runout distances of small- to medium-scale avalanches are strongly influenced by the structural conditions of forests in the avalanche path. This varying decelerating effect has rarely been addressed or implemented in avalanche simulation. We present an evaluation and operationalization of a novel forest detrainment modeling approach implemented in the avalanche simulation software RAMMS. The new approach accounts for the effect of forests in the avalanche path by detraining mass, which leads to a deceleration and runout shortening of avalanches. The extracted avalanche mass caught behind trees stops immediately and, therefore, is instantly subtracted from the flow and the momentum of the stopped mass is removed from the total momentum of the avalanche flow. This relationship is parameterized by the empirical detrainment coefficient K [Pa] which accounts for the braking power of different forest types per unit area. To define K dependent on specific forest characteristics, we simulated 40 well-documented small- to medium-scale avalanches which released in and ran through forests with varying K-values. Comparing two-dimensional simulation results with one-dimensional field observations for a high number of avalanche events and simulations manually is however time consuming and rather subjective. In order to process simulation results in a comprehensive and standardized way, we used a recently developed automatic evaluation and comparison method defining runout distances based on a pressure

Rock avalanches clusters along the northern Chile coastal scarp

Science.gov (United States)

Crosta, G. B.; Hermanns, R. L.; Dehls, J.; Lari, S.; Sepulveda, S.

2017-07-01

Rock avalanche clusters can be relevant indicators of the evolution of specific regions. They can be used to define: the type and intensity of triggering events, their recurrence and potential probability of occurrence, the progressive damage of the rock mass, the mechanisms of transport and deposition, as well as the environmental conditions at the time of occurrence. This paper tackles these subjects by analyzing two main clusters of rock avalanches (each event between 0.6 and 30 Mm3), separated by few kilometers and located along the coastal scarp of Northern Chile, south of Iquique. It lies, hence, within a seismic area characterized by a long seismic gap that ended on April 1st, 2014 with a Mw 8.2 earthquake. The scar position, high along the coastal cliff, supports seismic triggering for these clusters. The deposits' relative positions are used to obtain the sequence of rock avalanching events for each cluster. The progressive decrease of volume in the sequence of rock avalanches forming each cluster fits well the theoretical models for successive slope failures. These sequences seem to agree with those derived by dating the deposits with ages spanning between 4 kyr and 60 kyr. An average uplift rate of 0.2 mm/yr in the last 40 kyr is estimated for the coastal plain giving a further constraint to the rock avalanche deposition considering the absence of reworking of the deposits. Volume estimates and datings allow the estimation of an erosion rate contribution of about 0.098-0.112 mm km- 2 yr- 1 which is well comparable to values presented in the literature for earthquake induced landslides. We have carried out numerical modeling in order to analyze the mobility of the rock avalanches and examine the environmental conditions that controlled the runout. In doing so, we have considered the sequence of individual rock avalanches within the specific clusters, thus including in the models the confining effect caused by the presence of previous deposits. Bingham

Extended short wavelength infrared HgCdTe detectors on silicon substrates

Science.gov (United States)

Park, J. H.; Hansel, D.; Mukhortova, A.; Chang, Y.; Kodama, R.; Zhao, J.; Velicu, S.; Aqariden, F.

2016-09-01

We report high-quality n-type extended short wavelength infrared (eSWIR) HgCdTe (cutoff wavelength 2.59 μm at 77 K) layers grown on three-inch diameter CdTe/Si substrates by molecular beam epitaxy (MBE). This material is used to fabricate test diodes and arrays with a planar device architecture using arsenic implantation to achieve p-type doping. We use different variations of a test structure with a guarded design to compensate for the lateral leakage current of traditional test diodes. These test diodes with guarded arrays characterize the electrical performance of the active 640 × 512 format, 15 μm pitch detector array.

Using stereo satellite imagery to account for ablation, entrainment, and compaction in volume calculations for rock avalanches on Glaciers: Application to the 2016 Lamplugh Rock Avalanche in Glacier Bay National Park, Alaska

Science.gov (United States)

Bessette-Kirton, Erin; Coe, Jeffrey A.; Zhou, Wendy

2018-01-01

The use of preevent and postevent digital elevation models (DEMs) to estimate the volume of rock avalanches on glaciers is complicated by ablation of ice before and after the rock avalanche, scour of material during rock avalanche emplacement, and postevent ablation and compaction of the rock avalanche deposit. We present a model to account for these processes in volume estimates of rock avalanches on glaciers. We applied our model by calculating the volume of the 28 June 2016 Lamplugh rock avalanche in Glacier Bay National Park, Alaska. We derived preevent and postevent 2‐m resolution DEMs from WorldView satellite stereo imagery. Using data from DEM differencing, we reconstructed the rock avalanche and adjacent surfaces at the time of occurrence by accounting for elevation changes due to ablation and scour of the ice surface, and postevent deposit changes. We accounted for uncertainties in our DEMs through precise coregistration and an assessment of relative elevation accuracy in bedrock control areas. The rock avalanche initially displaced 51.7 ± 1.5 Mm3 of intact rock and then scoured and entrained 13.2 ± 2.2 Mm3 of snow and ice during emplacement. We calculated the total deposit volume to be 69.9 ± 7.9 Mm3. Volume estimates that did not account for topographic changes due to ablation, scour, and compaction underestimated the deposit volume by 31.0–46.8 Mm3. Our model provides an improved framework for estimating uncertainties affecting rock avalanche volume measurements in glacial environments. These improvements can contribute to advances in the understanding of rock avalanche hazards and dynamics.

Intermittent flow under constant forcing: Acoustic emission from creep avalanches

Science.gov (United States)

Salje, Ekhard K. H.; Liu, Hanlong; Jin, Linsen; Jiang, Deyi; Xiao, Yang; Jiang, Xiang

2018-01-01

While avalanches in field driven ferroic systems (e.g., Barkhausen noise), domain switching of martensitic nanostructures, and the collapse of porous materials are well documented, creep avalanches (avalanches under constant forcing) were never observed. Collapse avalanches generate particularly large acoustic emission (AE) signals and were hence chosen to investigate crackling noise under creep conditions. Piezoelectric SiO2 has a strong piezoelectric response even at the nanoscale so that we chose weakly bound SiO2 spheres in natural sandstone as a representative for the study of avalanches under time-independent, constant force. We found highly non-stationary crackling noise with four activity periods, each with power law distributed AE emission. Only the period before the final collapse shows the mean field behavior (ɛ near 1.39), in agreement with previous dynamic measurements at a constant stress rate. All earlier event periods show collapse with larger exponents (ɛ = 1.65). The waiting time exponents are classic with τ near 2.2 and 1.32. Creep data generate power law mixing with "effective" exponents for the full dataset with combinations of mean field and non-mean field regimes. We find close agreement with the predicted time-dependent fiber bound simulations, including events and waiting time distributions. Båth's law holds under creep conditions.

Stellar Winds and Dust Avalanches in the AU Mic Debris Disk

Energy Technology Data Exchange (ETDEWEB)

Chiang, Eugene; Fung, Jeffrey, E-mail: echiang@astro.berkeley.edu, E-mail: jeffrey.fung@berkeley.edu [Department of Astronomy, University of California at Berkeley, Campbell Hall, Berkeley, CA 94720-3411 (United States)

2017-10-10

We explain the fast-moving, ripple-like features in the edge-on debris disk orbiting the young M dwarf AU Mic. The bright features are clouds of submicron dust repelled by the host star’s wind. The clouds are produced by avalanches: radial outflows of dust that gain exponentially more mass as they shatter background disk particles in collisional chain reactions. The avalanches are triggered from a region a few au across—the “avalanche zone”—located on AU Mic’s primary “birth” ring at a true distance of ∼35 au from the star but at a projected distance more than a factor of 10 smaller: the avalanche zone sits directly along the line of sight to the star, on the side of the ring nearest Earth, launching clouds that disk rotation sends wholly to the southeast, as observed. The avalanche zone marks where the primary ring intersects a secondary ring of debris left by the catastrophic disruption of a progenitor up to Varuna in size, less than tens of thousands of years ago. Only where the rings intersect are particle collisions sufficiently violent to spawn the submicron dust needed to seed the avalanches. We show that this picture works quantitatively, reproducing the masses, sizes, and velocities of the observed escaping clouds. The Lorentz force exerted by the wind’s magnetic field, whose polarity reverses periodically according to the stellar magnetic cycle, promises to explain the observed vertical undulations. The timescale between avalanches, about 10 yr, might be set by time variability of the wind mass loss rate or, more speculatively, by some self-regulating limit cycle.

Time lapse photography as an approach to understanding glide avalanche activity

Science.gov (United States)

Hendrikx, Jordy; Peitzsch, Erich H.; Fagre, Daniel B.

2012-01-01

Avalanches resulting from glide cracks are notoriously difficult to forecast, but are a recurring problem for numerous avalanche forecasting programs. In some cases glide cracks are observed to open and then melt away in situ. In other cases, they open and then fail catastrophically as large, full-depth avalanches. Our understanding and management of these phenomena are currently limited. It is thought that an increase in the rate of snow gliding occurs prior to full-depth avalanche activity so frequent observation of glide crack movement can provide an index of instability. During spring 2011 in Glacier National Park, Montana, USA, we began an approach to track glide crack avalanche activity using a time-lapse camera focused on a southwest facing glide crack. This crack melted in-situ without failing as a glide avalanche, while other nearby glide cracks on north through southeast aspects failed. In spring 2012, a camera was aimed at a large and productive glide crack adjacent to the Going to the Sun Road. We captured three unique glide events in the field of view. Unfortunately, all of them either failed very quickly, or during periods of obscured view, so measurements of glide rate could not be obtained. However, we compared the hourly meteorological variables during the period of glide activity to the same variables prior to glide activity. The variables air temperature, relative humidity, air pressure, incoming and reflected long wave radiation, SWE, total precipitation, and snow depth were found to be statistically different for our cases examined. We propose that these are some of the potential precursors for glide avalanche activity, but do urge caution in their use, due to the simple approach and small data set size. It is hoped that by introducing a workable method to easily record glide crack movement, combined with ongoing analysis of the associated meteorological data, we will improve our understanding of when, or if, glide avalanche activity will ensue.

Avalanches and plastic flow in crystal plasticity: an overview

Science.gov (United States)

Papanikolaou, Stefanos; Cui, Yinan; Ghoniem, Nasr

2018-01-01

Crystal plasticity is mediated through dislocations, which form knotted configurations in a complex energy landscape. Once they disentangle and move, they may also be impeded by permanent obstacles with finite energy barriers or frustrating long-range interactions. The outcome of such complexity is the emergence of dislocation avalanches as the basic mechanism of plastic flow in solids at the nanoscale. While the deformation behavior of bulk materials appears smooth, a predictive model should clearly be based upon the character of these dislocation avalanches and their associated strain bursts. We provide here a comprehensive overview of experimental observations, theoretical models and computational approaches that have been developed to unravel the multiple aspects of dislocation avalanche physics and the phenomena leading to strain bursts in crystal plasticity.

La carte de localisation des phénomènes d'avalanche (CLPA : enjeux et perspectives The Localization Map of Avalanche Phenomena (CLPA in French: stakes and prospects

Directory of Open Access Journals (Sweden)

Mylène Bonnefoy, Gilles Borrel, Didier Richard, Laurent Bélanger et Mohamed Naaim

2010-09-01

Full Text Available Après presque quarante ans d’existence, la carte de localisation des phénomènes d'avalanche (CLPA constitue aujourd’hui un outil incontournable pour la prise en compte du risque d’avalanche dans l’aménagement et la gestion des territoires de montagne. Pour optimiser la sécurité des zones urbanisées, ce dispositif a su se rénover par une mise à jour régulière et étendue des données et l'étude de nouvelles zones, mais aussi par une meilleure diffusion auprès des opérationnels et du public concernés. Les auteurs nous rappellent ici l'évolution du fonctionnement de la CLPA et l'intérêt d'élargir la valorisation de ses données dans de nouveaux outils scientifiques.The Localization Map of Avalanche Phenomena (CLPA in French was created in 1971 as a response to the deadly avalanche occurred in Val d’Isère (February 1970, 39 persons killed. The aim is to inventory and to memorize areas where avalanches occurred in the past in order to keep in memory precisely greatest limits of those avalanches. The CLPA was rapidly considered as an essential element for developing plan in mountain areas. After the other catastrophic avalanche, which occurred in the Montroc Village (Chamonix in February 1999, it was recommended “the mutual valuation of the EPA and the CLPA integrated into an information system containing the information on avalanches and the information on the other natural risks in mountain”. The ministry in charge of environment decided therefore to continue and to modernize the CLPA, mission that was assigned to the Cemagref with the ONF collaboration. This modernization was based on the end of maps and testimonies records digitizing, on the compilation of summary notes concerning main avalanches information in reference to a mountain massif, on the institution of a durable updating of the map and on the possibility of having all information on line on the website www.avalanches.fr. Information recorded in the

Comparison of Measured Dark Current Distributions with Calculated Damage Energy Distributions in HgCdTe

Science.gov (United States)

Marshall, C. J.; Marshall, P. W.; Howe, C. L.; Reed, R. A.; Weller, R. A.; Mendenhall, M.; Waczynski, A.; Ladbury, R.; Jordan, T. M.

2007-01-01

This paper presents a combined Monte Carlo and analytic approach to the calculation of the pixel-to-pixel distribution of proton-induced damage in a HgCdTe sensor array and compares the results to measured dark current distributions after damage by 63 MeV protons. The moments of the Coulombic, nuclear elastic and nuclear inelastic damage distributions were extracted from Monte Carlo simulations and combined to form a damage distribution using the analytic techniques first described in [1]. The calculations show that the high energy recoils from the nuclear inelastic reactions (calculated using the Monte Carlo code MCNPX [2]) produce a pronounced skewing of the damage energy distribution. While the nuclear elastic component (also calculated using the MCNPX) contributes only a small fraction of the total nonionizing damage energy, its inclusion in the shape of the damage across the array is significant. The Coulombic contribution was calculated using MRED [3-5], a Geant4 [4,6] application. The comparison with the dark current distribution strongly suggests that mechanisms which are not linearly correlated with nonionizing damage produced according to collision kinematics are responsible for the observed dark current increases. This has important implications for the process of predicting the on-orbit dark current response of the HgCdTe sensor array.

THEORY AND PRACTICE OF INDIVIDUAL SNOW AVALANCHE RISK ASSESSMENT IN THE RUSSIAN ARCTIC

Directory of Open Access Journals (Sweden)

Aleksandr Shnyparkov

2012-01-01

Full Text Available In recent years, the Government of the Russian Federation considerably increased attention to the exploitation of the Russian Arctic territories. Simultaneously, the evaluation of snow avalanches danger was enhanced with the aim to decrease fatalities and reduce economic losses. However, it turned out that solely reporting the degree of avalanche danger is not sufficient. Instead, quantitative information on probabilistic parameters of natural hazards, the characteristics of their effects on the environment and possibly resulting losses is increasingly needed. Such information allows for the estimation of risk, including risk related to snow avalanches. Here, snow avalanche risk is quantified for the Khibiny Mountains, one of the most industrialized parts of the Russian Arctic: Major parts of the territory have an acceptable degree of individual snow avalanche risk (<1×10-6. The territories with an admissible (10-4–10-6 or unacceptable (>1×10-4 degree of individual snow avalanche risk (0.5 and 2% of the total area correspond to the Southeast of the Khibiny Mountains where settlements and mining industries are situated. Moreover, due to an increase in winter tourism, some traffic infrastructure is located in valleys with an admissible or unacceptable degree of individual snow avalanches risk.

Massless Dirac fermions in semimetal HgCdTe

Science.gov (United States)

Marchewka, M.; Grendysa, J.; Żak, D.; Tomaka, G.; Śliż, P.; Sheregii, E. M.

2017-01-01

Magneto-transport results obtained for the strained 100 nm thick Hg1-x CdxTe (x=0.135) layer grown by MBE on the CdTe/GaAs substrate are interpreted by the 8×8 kp model with the in-plane tensile strain. The dispersion relation for the investigated structure proves that the Dirac point is located in the gap caused by the strain. It is also shown that the fan of the Landau Levels (LL's) energy calculated for topological protected surface states for the studied HgCdTe alloy corresponds to the fan of the LL's calculated using the graphen-like Hamiltonian which gives excellent agreement with the experimental data for velocity on the Fermi level equal to vf ≈ 0.85×106 m/s. That characterized strained Hg1-x CdxTe layers (0.13 < x < 0.14) are a perfect Topological Insulator with good perspectives of further applications.

Stretched exponentials and power laws in granular avalanching

Science.gov (United States)

Head, D. A.; Rodgers, G. J.

1999-02-01

We introduce a model for granular surface flow which exhibits both stretched exponential and power law avalanching over its parameter range. Two modes of transport are incorporated, a rolling layer consisting of individual particles and the overdamped, sliding motion of particle clusters. The crossover in behaviour observed in experiments on piles of rice is attributed to a change in the dominant mode of transport. We predict that power law avalanching will be observed whenever surface flow is dominated by clustered motion.

Regional snow-avalanche detection using object-based image analysis of near-infrared aerial imagery

Directory of Open Access Journals (Sweden)

K. Korzeniowska

2017-10-01

Full Text Available Snow avalanches are destructive mass movements in mountain regions that continue to claim lives and cause infrastructural damage and traffic detours. Given that avalanches often occur in remote and poorly accessible steep terrain, their detection and mapping is extensive and time consuming. Nonetheless, systematic avalanche detection over large areas could help to generate more complete and up-to-date inventories (cadastres necessary for validating avalanche forecasting and hazard mapping. In this study, we focused on automatically detecting avalanches and classifying them into release zones, tracks, and run-out zones based on 0.25 m near-infrared (NIR ADS80-SH92 aerial imagery using an object-based image analysis (OBIA approach. Our algorithm takes into account the brightness, the normalised difference vegetation index (NDVI, the normalised difference water index (NDWI, and its standard deviation (SDNDWI to distinguish avalanches from other land-surface elements. Using normalised parameters allows applying this method across large areas. We trained the method by analysing the properties of snow avalanches at three 4 km−2 areas near Davos, Switzerland. We compared the results with manually mapped avalanche polygons and obtained a user's accuracy of > 0.9 and a Cohen's kappa of 0.79–0.85. Testing the method for a larger area of 226.3 km−2, we estimated producer's and user's accuracies of 0.61 and 0.78, respectively, with a Cohen's kappa of 0.67. Detected avalanches that overlapped with reference data by > 80 % occurred randomly throughout the testing area, showing that our method avoids overfitting. Our method has potential for large-scale avalanche mapping, although further investigations into other regions are desirable to verify the robustness of our selected thresholds and the transferability of the method.

Emplacement of rock avalanche material across saturated sediments, Southern Alp, New Zealand

Science.gov (United States)

Dufresne, A.; Davies, T. R.; McSaveney, M. J.

2012-04-01

The spreading of material from slope failure events is not only influenced by the volume and nature of the source material and the local topography, but also by the materials encountered in the runout path. In this study, evidence of complex interactions between rock avalanche and sedimentary runout path material were investigated at the 45 x 106 m3 long-runout (L: 4.8 km) Round Top rock avalanche deposit, New Zealand. It was sourced within myolinitic schists of the active strike-slip Alpine Fault. The narrow and in-failure-direction elongate source scarp is deep-seated, indicating slope failure was triggered by strong seismic activity. The most striking morphological deposit features are longitudinal ridges aligned radially to source. Trenching and geophysical surveys show bulldozed and sheared substrate material at ridge termini and laterally displaced sedimentary strata. The substrate failed at a minimum depth of 3 m indicating a ploughing motion of the ridges into the saturated material below. Internal avalanche compression features suggest deceleration behind the bulldozed substrate obstacle. Contorted fabric in material ahead of the ridge document substrate disruption by the overriding avalanche material deposited as the next down-motion hummock. Comparison with rock avalanches of similar volume but different emplacement environments places Round Top between longer runout avalanches emplaced over e.g. playa lake sediments and those with shorter travel distances, whose runout was apparently retarded by topographic obstacles or that entrained high-friction debris. These empirical observations indicate the importance of runout path materials on tentative trends in rock avalanche emplacement dynamics and runout behaviour.

Nanomechanics of slip avalanches in amorphous plasticity

Science.gov (United States)

Cao, Penghui; Dahmen, Karin A.; Kushima, Akihiro; Wright, Wendelin J.; Park, Harold S.; Short, Michael P.; Yip, Sidney

2018-05-01

Discrete stress relaxations (slip avalanches) in a model metallic glass under uniaxial compression are studied using a metadynamics algorithm for molecular simulation at experimental strain rates. The onset of yielding is observed at the first major stress drop, accompanied, upon analysis, by the formation of a single localized shear band region spanning the entire system. During the elastic response prior to yielding, low concentrations of shear transformation deformation events appear intermittently and spatially uncorrelated. During serrated flow following yielding, small stress drops occur interspersed between large drops. The simulation results point to a threshold value of stress dissipation as a characteristic feature separating major and minor avalanches consistent with mean-field modeling analysis and mechanical testing experiments. We further interpret this behavior to be a consequence of a nonlinear interplay of two prevailing mechanisms of amorphous plasticity, thermally activated atomic diffusion and stress-induced shear transformations, originally proposed by Spaepen and Argon, respectively. Probing the atomistic processes at widely separate strain rates gives insight to different modes of shear band formation: percolation of shear transformations versus crack-like propagation. Additionally a focus on crossover avalanche size has implications for nanomechanical modeling of spatially and temporally heterogeneous dynamics.

Scintillator high-gain avalanche rushing photoconductor active-matrix flat panel imager: zero-spatial frequency x-ray imaging properties of the solid-state SHARP sensor structure.

Science.gov (United States)

Wronski, M; Zhao, W; Tanioka, K; Decrescenzo, G; Rowlands, J A

2012-11-01

The authors are investigating the feasibility of a new type of solid-state x-ray imaging sensor with programmable avalanche gain: scintillator high-gain avalanche rushing photoconductor active matrix flat panel imager (SHARP-AMFPI). The purpose of the present work is to investigate the inherent x-ray detection properties of SHARP and demonstrate its wide dynamic range through programmable gain. A distributed resistive layer (DRL) was developed to maintain stable avalanche gain operation in a solid-state HARP. The signal and noise properties of the HARP-DRL for optical photon detection were investigated as a function of avalanche gain both theoretically and experimentally, and the results were compared with HARP tube (with electron beam readout) used in previous investigations of zero spatial frequency performance of SHARP. For this new investigation, a solid-state SHARP x-ray image sensor was formed by direct optical coupling of the HARP-DRL with a structured cesium iodide (CsI) scintillator. The x-ray sensitivity of this sensor was measured as a function of avalanche gain and the results were compared with the sensitivity of HARP-DRL measured optically. The dynamic range of HARP-DRL with variable avalanche gain was investigated for the entire exposure range encountered in radiography∕fluoroscopy (R∕F) applications. The signal from HARP-DRL as a function of electric field showed stable avalanche gain, and the noise associated with the avalanche process agrees well with theory and previous measurements from a HARP tube. This result indicates that when coupled with CsI for x-ray detection, the additional noise associated with avalanche gain in HARP-DRL is negligible. The x-ray sensitivity measurements using the SHARP sensor produced identical avalanche gain dependence on electric field as the optical measurements with HARP-DRL. Adjusting the avalanche multiplication gain in HARP-DRL enabled a very wide dynamic range which encompassed all clinically relevant

Scintillator high-gain avalanche rushing photoconductor active-matrix flat panel imager: Zero-spatial frequency x-ray imaging properties of the solid-state SHARP sensor structure

International Nuclear Information System (INIS)

Wronski, M.; Zhao, W.; Tanioka, K.; DeCrescenzo, G.; Rowlands, J. A.

2012-01-01

Purpose: The authors are investigating the feasibility of a new type of solid-state x-ray imaging sensor with programmable avalanche gain: scintillator high-gain avalanche rushing photoconductor active matrix flat panel imager (SHARP-AMFPI). The purpose of the present work is to investigate the inherent x-ray detection properties of SHARP and demonstrate its wide dynamic range through programmable gain. Methods: A distributed resistive layer (DRL) was developed to maintain stable avalanche gain operation in a solid-state HARP. The signal and noise properties of the HARP-DRL for optical photon detection were investigated as a function of avalanche gain both theoretically and experimentally, and the results were compared with HARP tube (with electron beam readout) used in previous investigations of zero spatial frequency performance of SHARP. For this new investigation, a solid-state SHARP x-ray image sensor was formed by direct optical coupling of the HARP-DRL with a structured cesium iodide (CsI) scintillator. The x-ray sensitivity of this sensor was measured as a function of avalanche gain and the results were compared with the sensitivity of HARP-DRL measured optically. The dynamic range of HARP-DRL with variable avalanche gain was investigated for the entire exposure range encountered in radiography/fluoroscopy (R/F) applications. Results: The signal from HARP-DRL as a function of electric field showed stable avalanche gain, and the noise associated with the avalanche process agrees well with theory and previous measurements from a HARP tube. This result indicates that when coupled with CsI for x-ray detection, the additional noise associated with avalanche gain in HARP-DRL is negligible. The x-ray sensitivity measurements using the SHARP sensor produced identical avalanche gain dependence on electric field as the optical measurements with HARP-DRL. Adjusting the avalanche multiplication gain in HARP-DRL enabled a very wide dynamic range which encompassed all

Solar-Blind Photodetector with High Avalanche Gains and Bias-Tunable Detecting Functionality Based on Metastable Phase α-Ga2O3/ZnO Isotype Heterostructures.

Science.gov (United States)

Chen, Xuanhu; Xu, Yang; Zhou, Dong; Yang, Sen; Ren, Fang-Fang; Lu, Hai; Tang, Kun; Gu, Shulin; Zhang, Rong; Zheng, Youdou; Ye, Jiandong

2017-10-25

The metastable α-phase Ga 2 O 3 is an emerging material for developing solar-blind photodetectors and power electronic devices toward civil and military applications. Despite its superior physical properties, the high quality epitaxy of metastable phase α-Ga 2 O 3 remains challenging. To this end, single crystalline α-Ga 2 O 3 epilayers are achieved on nonpolar ZnO (112̅0) substrates for the first time and a high performance Au/α-Ga 2 O 3 /ZnO isotype heterostructure-based Schottky barrier avalanche diode is demonstrated. The device exhibits self-powered functions with a dark current lower than 1 pA, a UV/visible rejection ratio of 10 3 and a detectivity of 9.66 × 10 12 cm Hz 1/2 W -1 . Dual responsivity bands with cutoff wavelengths at 255 and 375 nm are observed with their peak responsivities of 0.50 and 0.071 A W -1 at -5 V, respectively. High photoconductive gain at low bias is governed by a barrier lowing effect at the Au/Ga 2 O 3 and Ga 2 O 3 /ZnO heterointerfaces. The device also allows avalanche multiplication processes initiated by pure electron and hole injections under different illumination conditions. High avalanche gains over 10 3 and a low ionization coefficient ratio of electrons and holes are yielded, leading to a total gain over 10 5 and a high responsivity of 1.10 × 10 4 A W -1 . Such avalanche heterostructures with ultrahigh gains and bias-tunable UV detecting functionality hold promise for developing high performance solar-blind photodetectors.

The December 2008 Crammont rock avalanche, Mont Blanc massif area, Italy

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P. Deline

2011-12-01

Full Text Available We describe a 0.5 Mm³ rock avalanche that occurred in 2008 in the western Alps and discuss possible roles of controlling factors in the context of current climate change. The source is located between 2410 m and 2653 m a.s.l. on Mont Crammont and is controlled by a densely fractured rock structure. The main part of the collapsed rock mass deposited at the foot of the rock wall. A smaller part travelled much farther, reaching horizontal and vertical travel distances of 3050 m and 1560 m, respectively. The mobility of the rock mass was enhanced by channelization and snow. The rock-avalanche volume was calculated by comparison of pre- and post-event DTMs, and geomechanical characterization of the detachment zone was extracted from LiDAR point cloud processing. Back analysis of the rock-avalanche runout suggests a two stage event.

There was no previous rock avalanche activity from the Mont Crammont ridge during the Holocene. The 2008 rock avalanche may have resulted from permafrost degradation in the steep rock wall, as suggested by seepage water in the scar after the collapse in spite of negative air temperatures, and modelling of rock temperatures that indicate warm permafrost (T > −2 °C.

Progress on Development of an Airborne Two-Micron IPDA Lidar for Water Vapor and Carbon Dioxide Column Measurements

Science.gov (United States)

Singh, Upendra N.; Petros, Mulugeta; Refaat, Tamer F.; Yu, Jirong; Antill, Charles W.; Taylor, Bryant D.; Bowen, Stephen C.; Welters, Angela M.; Remus, Ruben G.; Wong, Teh-Hwa;

Avalanches in functional materials and geophysics

CERN Document Server

Saxena, Avadh; Planes, Antoni

2017-01-01

This book provides the state-of-the art of the present understanding of avalanche phenomena in both functional materials and geophysics. The main emphasis of the book is analyzing these apparently different problems within the common perspective of out-of-equilibrium phenomena displaying spatial and temporal complexity that occur in a broad range of scales. Many systems, when subjected to an external force, respond intermittently in the form of avalanches that often span over a wide range of sizes, energies and durations. This is often related to a class of critical behavior characterized by the absence of characteristic scales. Typical examples are magnetization processes, plastic deformation and failure occuring in functional materials. These phenomena share many similarities with seismicity arising from the earth crust failure due to stresses that originate from plate tectonics.

Rockslide-debris avalanche of May 18, 1980, Mount St. Helens Volcano, Washington

Science.gov (United States)

Glicken, Harry

1996-01-01

This report provides a detailed picture of the rockslide-debris avalanche of the May 18, 1980, eruption of Mount St. Helens volcano. It provides a characterization of the deposit, a reinterpretation of the details of the first minutes of the eruption of May 18, and insight into the transport mechanism of the mass movement. Details of the rockslide event, as revealed by eyewitness photographs, are correlated with features of the deposit. The photographs show three slide blocks in the rockslide movement. Slide block I was triggered by a magnitude 5.1 earthquake at 8:32 a.m. Pacific Daylight Time (P.D.T.). An exploding cryptodome burst through slide block II to produce the 'blast surge.' Slide block III consisted of many discrete failures that were carried out in continuing pyroclastic currents generated from the exploding cryptodome. The cryptodome continued to depressurize after slide block III, producing a blast deposit that rests on top of the debris-avalanche deposit. The hummocky 2.5 cubic kilometer debris-avalanche deposit consists of block facies (pieces of the pre-eruption Mount St. Helens transported relatively intact) and matrix facies (a mixture of rocks from the old mountain and cryptodome dacite). Block facies is divided into five lithologic units. Matrix facies was derived from the explosively generated current of slide block III as well as from disaggregation and mixing of debris-avalanche blocks. The mean density of the old cone was measured to be abut 20 percent greater than the mean density of the avalanche deposit. Density in the deposit does not decrease with distance which suggests that debris-avalanche blocks were dilated at the mountain, rather than during transport. Various grain-size parameters that show that clast size converges about a mean with distance suggest mixing during transport. The debris-avalanche flow can be considered a grain flow, where particles -- either debris-avalanche blocks or the clasts within the blocks -- collided and

On the high gain operation of low-pressure microdot gas avalanche chambers

International Nuclear Information System (INIS)

Breskin, A.

1997-01-01

Microdot avalanche chambers (MDOT) equipped with thin semitransparent Cr photocathodes, were characterized with UV photons at low gas pressure. Gains superior to 10 4 were reached with gas multiplication at the dots. In a mode where preamplification in the gas volume precedes the additional dot multiplication, gains superior to 10 6 were measured at 30-60 torr of propane. The fast amplification mechanism results in narrow high amplitude pulses with 2-3 ns rise time, visible with no further electronic amplification means. We present here our preliminary results and briefly discuss potential applications. (orig.)

Statistical analysis and trends of wet snow avalanches in the French Alps over the period 1959-2010

Science.gov (United States)

Naaim, Mohamed

2017-04-01

Since an avalanche contains a significant proportion of wet snow, its characteristics and its behavior change significantly (heterogeneous and polydisperse). Even if on a steep given slope, wet snow avalanches are slow. They can flow over gentle slopes and reach the same extensions as dry avalanches. To highlight the link between climate warming and the proliferation of wet snow avlanches, we crossed two well-documented avalanche databases: the permanent avalanche chronicle (EPA) and the meteorological re-analyzes. For each avalanche referenced in EPA, a moisture index I is buit. It represents the ratio of the thickness of the wet snow layer to the total snow thickness, at the date of the avalanche on the concerned massif at 2400 m.a.s.l. The daily and annual proportion of avalanches exceeding a given threshold of I are calculated for each massif of the French alps. The statistical distribution of wet avalanches per massif is calculated over the period 1959-2009. The statistical quantities are also calculated over two successive periods of the same duration 1959-1984 and 1984-2009, and the annual evolution of the proportion of wet avalanches is studied using time-series tools to detect potential rupture or trends. This study showed that about 77% of avalanches on the French alpine massif mobilize dry snow. The probability of having an avalanche of a moisture index greater than 10 % in a given year is 0.2. This value varies from one massif to another. The analysis between the two successive periods showed a significant growth of wet avalanches on 20 massifs and a decrease on 3 massifs. The study of time-series confirmed these trends, which are of the inter-annual variability level.

Lumped transmission line avalanche pulser

Science.gov (United States)

Booth, Rex

1995-01-01

A lumped linear avalanche transistor pulse generator utilizes stacked transistors in parallel within a stage and couples a plurality of said stages, in series with increasing zener diode limited voltages per stage and decreasing balanced capacitance load per stage to yield a high voltage, high and constant current, very short pulse.

Numerical simulations of compact intracloud discharges as the Relativistic Runaway Electron Avalanche-Extensive Air Shower process

Science.gov (United States)

Arabshahi, S.; Dwyer, J. R.; Nag, A.; Rakov, V. A.; Rassoul, H. K.

2014-01-01

Compact intracloud discharges (CIDs) are sources of the powerful, often isolated radio pulses emitted by thunderstorms. The VLF-LF radio pulses are called narrow bipolar pulses (NBPs). It is still not clear how CIDs are produced, but two categories of theoretical models that have previously been considered are the Transmission Line (TL) model and the Relativistic Runaway Electron Avalanche-Extensive Air Showers (RREA-EAS) model. In this paper, we perform numerical calculations of RREA-EASs for various electric field configurations inside thunderstorms. The results of these calculations are compared to results from the other models and to the experimental data. Our analysis shows that different theoretical models predict different fundamental characteristics for CIDs. Therefore, many previously published properties of CIDs are highly model dependent. This is because of the fact that measurements of the radiation field usually provide information about the current moment of the source, and different physical models with different discharge currents could have the same current moment. We have also found that although the RREA-EAS model could explain the current moments of CIDs, the required electric fields in the thundercloud are rather large and may not be realistic. Furthermore, the production of NBPs from RREA-EAS requires very energetic primary cosmic ray particles, not observed in nature. If such ultrahigh-energy particles were responsible for NBPs, then they should be far less frequent than is actually observed.

Information processing occurs via critical avalanches in a model of the primary visual cortex

International Nuclear Information System (INIS)

Bortolotto, G. S.; Girardi-Schappo, M.; Gonsalves, J. J.; Tragtenberg, M. H. R.; Pinto, L. T.

2016-01-01

We study a new biologically motivated model for the Macaque monkey primary visual cortex which presents power-law avalanches after a visual stimulus. The signal propagates through all the layers of the model via avalanches that depend on network structure and synaptic parameter. We identify four different avalanche profiles as a function of the excitatory postsynaptic potential. The avalanches follow a size-duration scaling relation and present critical exponents that match experiments. The structure of the network gives rise to a regime of two characteristic spatial scales, one of which vanishes in the thermodynamic limit. (paper)

Avalanches in the Bean critical-state model

International Nuclear Information System (INIS)

Barford, W.

1997-01-01

A macroscopic equation of motion for the flux density in dirty type-II superconductors is introduced. The flux density is subject to various types of spatially varying pinning force. When there is no stick-slip dynamics, i.e., when the static pinning force equals the dynamic pinning force, it is shown that in both one and two dimensions an increase in the surface magnetic field leads to an overall height change and hence to a change in magnetization equal to the change in the surface magnetic field. More interesting behavior occurs on introducing stick-slip dynamics, i.e., when the static pinning force exceeds the dynamic pinning force. In this limit a distribution of avalanche sizes over four orders of magnitude is found for a 100x100 lattice. Apart from the anomalous behavior at large sizes, this is shown to fit a distribution of the form P(s)∼s -ν exp(-s/α), where s is the avalanche size. The anomalous behavior for large sizes corresponds to avalanches which involve most of the lattice and, hence, cause the flux to open-quotes slide over the edge,close quotes as detected by a change in the edge magnetization. copyright 1997 The American Physical Society

Necessary conditions for the homogeneous formation of a volume avalanche discharge with specific applications to rare gas-halide excimer laser discharges

International Nuclear Information System (INIS)

Levatter, J.I.

1979-01-01

Self-sustained/avalanche discharges are an efficient method of rare gas-halide excimer laser excitation in small systems. However, with the exceptions of the work reported here, experiments attempting to increase the laser energy output by scaling up the discharge volume and/or pulse duration have not been successful. The major problem encountered in scaling experiments has been the formation of arc channels in the discharge volume. The presence of arcing can totally disrupt proper laser operation. This problem stems from a general lack of understanding of high pressure avalanche discharge phenomena. Therefore, clarifying the basic discharge formation process and establishing a set of criteria under which a homogeneous avalanche discharge can be obtained is of central importance in defining the scaling limits of avalanche discharge lasers. The work presented here reviews the phenomena involved in high E/n (electric field to gas number density ratio) breakdown and its relationship to the formation of spatially homogeneous discharges. This relationship was first explored by A.J. Palmer in 1974. The basic requirement of his model was that the preionization density be large enough to cause an appreciable overlap of the primary electron avalanches and hence smooth out the ensuing space-charge fields to the extent that individual streamer formation would be prevented. This is the same basic model used in the more detailed discharge formation analysis developed here except that the effects of a time varying electric field caused by a finite voltage rise time and the effects due to the various electrochemical properties of the gas mixture are property taken into consideration

Snow-avalanche impact craters in southern Norway: Their morphology and dynamics compared with small terrestrial meteorite craters

Science.gov (United States)

Matthews, John A.; Owen, Geraint; McEwen, Lindsey J.; Shakesby, Richard A.; Hill, Jennifer L.; Vater, Amber E.; Ratcliffe, Anna C.

2017-11-01

This regional inventory and study of a globally uncommon landform type reveals similarities in form and process between craters produced by snow-avalanche and meteorite impacts. Fifty-two snow-avalanche impact craters (mean diameter 85 m, range 10-185 m) were investigated through field research, aerial photographic interpretation and analysis of topographic maps. The craters are sited on valley bottoms or lake margins at the foot of steep avalanche paths (α = 28-59°), generally with an easterly aspect, where the slope of the final 200 m of the avalanche path (β) typically exceeds 15°. Crater diameter correlates with the area of the avalanche start zone, which points to snow-avalanche volume as the main control on crater size. Proximal erosional scars ('blast zones') up to 40 m high indicate up-range ejection of material from the crater, assisted by air-launch of the avalanches and impulse waves generated by their impact into water-filled craters. Formation of distal mounds up to 12 m high of variable shape is favoured by more dispersed down-range deposition of ejecta. Key to the development of snow-avalanche impact craters is the repeated occurrence of topographically-focused snow avalanches that impact with a steep angle on unconsolidated sediment. Secondary craters or pits, a few metres in diameter, are attributed to the impact of individual boulders or smaller bodies of snow ejected from the main avalanche. The process of crater formation by low-density, low-velocity, large-volume snow flows occurring as multiple events is broadly comparable with cratering by single-event, high-density, high-velocity, small-volume projectiles such as small meteorites. Simple comparative modelling of snow-avalanche events associated with a crater of average size (diameter 85 m) indicates that the kinetic energy of a single snow-avalanche impact event is two orders of magnitude less than that of a single meteorite-impact event capable of producing a crater of similar size

Can graphene make better HgCdTe infrared detectors?

Directory of Open Access Journals (Sweden)

Shi Yanli

2011-01-01

Full Text Available Abstract We develop a simple and low-cost technique based on chemical vapor deposition from which large-size graphene films with 5-10 graphene layers can be produced reliably and the graphene films can be transferred easily onto HgCdTe (MCT thin wafers at room temperature. The proposed technique does not cause any thermal and mechanical damages to the MCT wafers. It is found that the averaged light transmittance of the graphene film on MCT thin wafer is about 80% in the mid-infrared bandwidth at room temperature and 77 K. Moreover, we find that the electrical conductance of the graphene film on the MCT substrate is about 25 times larger than that of the MCT substrate at room temperature and 77 K. These experimental findings suggest that, from a physics point of view, graphene can be utilized as transparent electrodes as a replacement for metal electrodes while producing better and cheaper MCT infrared detectors.

Validating numerical simulations of snow avalanches using dendrochronology: the Cerro Ventana event in Northern Patagonia, Argentina

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A. Casteller

2008-05-01

Full Text Available The damage caused by snow avalanches to property and human lives is underestimated in many regions around the world, especially where this natural hazard remains poorly documented. One such region is the Argentinean Andes, where numerous settlements are threatened almost every winter by large snow avalanches. On 1 September 2002, the largest tragedy in the history of Argentinean mountaineering took place at Cerro Ventana, Northern Patagonia: nine persons were killed and seven others injured by a snow avalanche. In this paper, we combine both numerical modeling and dendrochronological investigations to reconstruct this event. Using information released by local governmental authorities and compiled in the field, the avalanche event was numerically simulated using the avalanche dynamics programs AVAL-1D and RAMMS. Avalanche characteristics, such as extent and date were determined using dendrochronological techniques. Model simulation results were compared with documentary and tree-ring evidences for the 2002 event. Our results show a good agreement between the simulated projection of the avalanche and its reconstructed extent using tree-ring records. Differences between the observed and the simulated avalanche, principally related to the snow height deposition in the run-out zone, are mostly attributed to the low resolution of the digital elevation model used to represent the valley topography. The main contributions of this study are (1 to provide the first calibration of numerical avalanche models for the Patagonian Andes and (2 to highlight the potential of Nothofagus pumilio tree-ring records to reconstruct past snow-avalanche events in time and space. Future research should focus on testing this combined approach in other forested regions of the Andes.

Massive Formation of Equiaxed Crystals by Avalanches of Mushy Zone Segments

Science.gov (United States)

Ludwig, A.; Stefan-Kharicha, M.; Kharicha, A.; Wu, M.

2017-06-01

It is well known that the growth and motion of equiaxed crystals govern important microstructural features, especially in larger castings such as heavy ingots. To determine the origin of the equiaxed crystals, heterogeneous nucleation, and/or fragmentation of dendrite arms from columnar regions are often discussed. In the present study, we demonstrate that under certain conditions relatively large areas of mushy regions slide downward and form spectacular crystal avalanches. These avalanches crumble into thousands of dendritic fragments, whereby the larger fragments immediately sediment and the smaller proceed to behave as equiaxed crystals. Traces of such crystal avalanches can be seen by conspicuous equiaxed layers in the lower part of the casting. From the arguments in the discussion, it is believed that such a phenomenon may occur in alloys which reveal an upward solutal buoyancy in the interdendritic mush. This would include certain steels and other alloys such as Cu-Al, Pb-Sn, or Ni-Al-alloys. Moreover, the occurrence of crystal avalanches contribute to the formation of V-segregations.

Response of CMS avalanche photo-diodes to low energy neutrons

Science.gov (United States)

Brown, R. M.; Deiters, K.; Ingram, Q.; Renker, D.

2012-12-01

The response of the Avalanche Photo-diodes (APDs) installed in the CMS detector at the LHC to neutrons from 241AmBe and 252Cf sources is reported. Signals in size equivalent to those of up to 106 photo-electrons with the nominal APD gain are observed. Measurements with an APD with the protective epoxy coating removed and with the source placed behind the APD show that there is an important response due to recoil protons from neutron interactions with the hydrogen in the epoxy, in addition to signals from neutron interactions with the silicon of the diode. The effective gain of these signals is much smaller than the diode's nominal gain.

A concept for optimizing avalanche rescue strategies using a Monte Carlo simulation approach.

Directory of Open Access Journals (Sweden)

Ingrid Reiweger

Full Text Available Recent technical and strategical developments have increased the survival chances for avalanche victims. Still hundreds of people, primarily recreationists, get caught and buried by snow avalanches every year. About 100 die each year in the European Alps-and many more worldwide. Refining concepts for avalanche rescue means to optimize the procedures such that the survival chances are maximized in order to save the greatest possible number of lives. Avalanche rescue includes several parameters related to terrain, natural hazards, the people affected by the event, the rescuers, and the applied search and rescue equipment. The numerous parameters and their complex interaction make it unrealistic for a rescuer to take, in the urgency of the situation, the best possible decisions without clearly structured, easily applicable decision support systems. In order to analyse which measures lead to the best possible survival outcome in the complex environment of an avalanche accident, we present a numerical approach, namely a Monte Carlo simulation. We demonstrate the application of Monte Carlo simulations for two typical, yet tricky questions in avalanche rescue: (1 calculating how deep one should probe in the first passage of a probe line depending on search area, and (2 determining for how long resuscitation should be performed on a specific patient while others are still buried. In both cases, we demonstrate that optimized strategies can be calculated with the Monte Carlo method, provided that the necessary input data are available. Our Monte Carlo simulations also suggest that with a strict focus on the "greatest good for the greatest number", today's rescue strategies can be further optimized in the best interest of patients involved in an avalanche accident.

Investigation of avalanche photodiodes

Energy Technology Data Exchange (ETDEWEB)

Si Mohand, D.; Benhammou, Y.; Depasse, P.; Goyot, M.; Ille, B.; Linard, E.; Martin, F.; Musienko, Y.

1996-06-01

Some characteristics and performances of a set of nine Hamamatsu avalanche photodiodes have been investigated. These APDs have equipped a small 3x3 PbWO{sub 4} crystal matrix in X3 beam during the summer of 1995. This note summarizes the main results of this work. An electromagnetic calorimeter with a high resolution is necessary to search for the Higgs if it has a mass between 80 and 160 GeV. A PbWO{sub 4} crystal option has been chosen by the CMS collaboration to achieve this task. The light is collected and converted into an electric charge by an Avalanche Photodiode (APD) followed by a fast preamplifier. The advantage of the APDs is that they are not sensitive to the strong magnetic field when compared to photomultipliers and they are a small nuclear counter effect when compared to PIN diodes. In this study, we have tested nine low capacitance Hamamatsu APDs (S5345) received in spring, 1995 with an area of 0.2 cm{sup 2}. We have measured the capacitance and dark current for each APD. The gain measurements have also been done with gamma sources, continuous and pulsed light. The gain sensitivity versus bias and temperature have also been investigated succinctly. (author). 8 refs., 16 figs., 1 tab.

Investigation of avalanche photodiodes

International Nuclear Information System (INIS)

Si Mohand, D.; Benhammou, Y.; Depasse, P.; Goyot, M.; Ille, B.; Linard, E.; Martin, F.; Musienko, Y.

1996-06-01

Some characteristics and performances of a set of nine Hamamatsu avalanche photodiodes have been investigated. These APDs have equipped a small 3x3 PbWO 4 crystal matrix in X3 beam during the summer of 1995. This note summarizes the main results of this work. An electromagnetic calorimeter with a high resolution is necessary to search for the Higgs if it has a mass between 80 and 160 GeV. A PbWO 4 crystal option has been chosen by the CMS collaboration to achieve this task. The light is collected and converted into an electric charge by an Avalanche Photodiode (APD) followed by a fast preamplifier. The advantage of the APDs is that they are not sensitive to the strong magnetic field when compared to photomultipliers and they are a small nuclear counter effect when compared to PIN diodes. In this study, we have tested nine low capacitance Hamamatsu APDs (S5345) received in spring, 1995 with an area of 0.2 cm 2 . We have measured the capacitance and dark current for each APD. The gain measurements have also been done with gamma sources, continuous and pulsed light. The gain sensitivity versus bias and temperature have also been investigated succinctly. (author). 8 refs., 16 figs., 1 tab

Modeling the influence of snow cover temperature and water content on wet-snow avalanche runout

Directory of Open Access Journals (Sweden)

C. Vera Valero

2018-03-01

Full Text Available Snow avalanche motion is strongly dependent on the temperature and water content of the snow cover. In this paper we use a snow cover model, driven by measured meteorological data, to set the initial and boundary conditions for wet-snow avalanche calculations. The snow cover model provides estimates of snow height, density, temperature and liquid water content. This information is used to prescribe fracture heights and erosion heights for an avalanche dynamics model. We compare simulated runout distances with observed avalanche deposition fields using a contingency table analysis. Our analysis of the simulations reveals a large variability in predicted runout for tracks with flat terraces and gradual slope transitions to the runout zone. Reliable estimates of avalanche mass (height and density in the release and erosion zones are identified to be more important than an exact specification of temperature and water content. For wet-snow avalanches, this implies that the layers where meltwater accumulates in the release zone must be identified accurately as this defines the height of the fracture slab and therefore the release mass. Advanced thermomechanical models appear to be better suited to simulate wet-snow avalanche inundation areas than existing guideline procedures if and only if accurate snow cover information is available.

Non-Geiger-Mode Single-Photon Avalanche Detector with Low Excess Noise

Science.gov (United States)

Zhao, Kai; Lo, YuHwa; Farr, William

2010-01-01

This design constitutes a self-resetting (gain quenching), room-temperature operational semiconductor single-photon-sensitive detector that is sensitive to telecommunications optical wavelengths and is scalable to large areas (millimeter diameter) with high bandwidth and efficiencies. The device can detect single photons at a 1,550-nm wavelength at a gain of 1 x 10(exp 6). Unlike conventional single photon avalanche detectors (SPADs), where gain is an extremely sensitive function to the bias voltage, the multiplication gain of this device is stable at 1 x 10(exp 6) over a wide range of bias from 30.2 to 30.9 V. Here, the multiplication gain is defined as the total number of charge carriers contained in one output pulse that is triggered by the absorption of a single photon. The statistics of magnitude of output signals also shows that the device has a very narrow pulse height distribution, which demonstrates a greatly suppressed gain fluctuation. From the histograms of both pulse height and pulse charge, the equivalent gain variance (excess noise) is between 1.001 and 1.007 at a gain of 1 x 10(exp 6). With these advantages, the device holds promise to function as a PMT-like photon counter at a 1,550- nm wavelength. The epitaxial layer structure of the device allows photons to be absorbed in the InGaAs layer, generating electron/hole (e-h) pairs. Driven by an electrical field in InGaAs, electrons are collected at the anode while holes reach the multiplication region (InAlAs p-i-n structure) and trigger the avalanche process. As a result, a large number of e-h pairs are created, and the holes move toward the cathode. Holes created by the avalanche process gain large kinetic energy through the electric field, and are considered hot. These hot holes are cooled as they travel across a p -InAlAs low field region, and are eventually blocked by energy barriers formed by the InGaAsP/ InAlAs heterojunctions. The composition of the InGaAsP alloy was chosen to have an 80 me

Avalanche photodiode based time-of-flight mass spectrometry

Energy Technology Data Exchange (ETDEWEB)

Ogasawara, Keiichi, E-mail: kogasawara@swri.edu; Livi, Stefano A.; Desai, Mihir I.; Ebert, Robert W.; McComas, David J.; Walther, Brandon C. [Southwest Research Institute, 6220 Culebra Road, San Antonio, Texas 78238 (United States)

2015-08-15

This study reports on the performance of Avalanche Photodiodes (APDs) as a timing detector for ion Time-of-Flight (TOF) mass spectroscopy. We found that the fast signal carrier speed in a reach-through type APD enables an extremely short timescale response with a mass or energy independent <2 ns rise time for <200 keV ions (1−40 AMU) under proper bias voltage operations. When combined with a microchannel plate to detect start electron signals from an ultra-thin carbon foil, the APD comprises a novel TOF system that successfully operates with a <0.8 ns intrinsic timing resolution even using commercial off-the-shelf constant-fraction discriminators. By replacing conventional total-energy detectors in the TOF-Energy system, APDs offer significant power and mass savings or an anti-coincidence background rejection capability in future space instrumentation.

Hybrid phase transition into an absorbing state: Percolation and avalanches

Science.gov (United States)

Lee, Deokjae; Choi, S.; Stippinger, M.; Kertész, J.; Kahng, B.

2016-04-01

Interdependent networks are more fragile under random attacks than simplex networks, because interlayer dependencies lead to cascading failures and finally to a sudden collapse. This is a hybrid phase transition (HPT), meaning that at the transition point the order parameter has a jump but there are also critical phenomena related to it. Here we study these phenomena on the Erdős-Rényi and the two-dimensional interdependent networks and show that the hybrid percolation transition exhibits two kinds of critical behaviors: divergence of the fluctuations of the order parameter and power-law size distribution of finite avalanches at a transition point. At the transition point global or "infinite" avalanches occur, while the finite ones have a power law size distribution; thus the avalanche statistics also has the nature of a HPT. The exponent βm of the order parameter is 1 /2 under general conditions, while the value of the exponent γm characterizing the fluctuations of the order parameter depends on the system. The critical behavior of the finite avalanches can be described by another set of exponents, βa and γa. These two critical behaviors are coupled by a scaling law: 1 -βm=γa .

High gain multigap avalanche detectors for Cerenkov ring imaging

Energy Technology Data Exchange (ETDEWEB)

Gilmore, R.S.; Lavender, W.M.; Leith, D.W.G.S.; Williams, S.H.

1980-10-01

We report on a continuing study of multigap parallel plate avalanche chambers, primarily as photoelectron detectors for use with Cerenkov ring imaging counters. By suitable control of the fields in successive gaps and by introducing screens to reduce photon feedback to the cathode the gain many be increased considerably. We have obtained gains in excess of 6 x 10/sup 7/ for photoelectrons with a good pulse height spectrum and expect to increase this further. We discuss the use of resistive anodes to give avalanche positions in two dimensions by charge division.

Dynamic avalanche behavior of power MOSFETs and IGBTs under unclamped inductive switching conditions

International Nuclear Information System (INIS)

Lu Jiang; Tian Xiaoli; Lu Shuojin; Zhou Hongyu; Zhu Yangjun; Han Zhengsheng

2013-01-01

The ability of high-voltage power MOSFETs and IGBTs to withstand avalanche events under unclamped inductive switching (UIS) conditions is measured. This measurement is to investigate and compare the dynamic avalanche failure behavior of the power MOSFETs and the IGBT, which occur at different current conditions. The UIS measurement results at different current conditions show that the main failure reason of the power MOSFETs is related to the parasitic bipolar transistor, which leads to the deterioration of the avalanche reliability of power MOSFETs. However, the results of the IGBT show two different failure behaviors. At high current mode, the failure behavior is similar to the power MOSFETs situation. But at low current mode, the main failure mechanism is related to the parasitic thyristor activity during the occurrence of the avalanche process and which is in good agreement with the experiment result. (semiconductor devices)

New advances for modelling the debris avalanches

Science.gov (United States)

Cuomo, Sabatino; Cascini, Leonardo; Pastor, Manuel; Castorino, Giuseppe Claudio

2013-04-01

Flow-like landslides are a major global hazard and they occur worldwide causing a large number of casualties, significant structural damages to property and infrastructures as well as economic losses. When involving open slopes, these landslides often occur in triangular source areas where initial slides turn into avalanches through further failures and/or eventual soil entrainment. This paper deals with the numerical modelling of the propagation stage of debris avalanches which provides information such as the propagation pattern of the mobilized material, its velocity, thickness and run-out distance. In the paper, a "depth integrated" model is used which allows: i) adequately taking into account the irregular topography of real slopes which greatly affect the propagation stage and ii) using a less time consuming model than fully 3D approaches. The used model is named "GeoFlow_SPH" and it was formerly applied to theoretical, experimental and real case histories (Pastor et al., 2009; Cascini et al., 2012). In this work the behavior of debris avalanches is analyzed with special emphasis on the apical angle, one of the main features of this type of landslide, in relation to soil rheology, hillslope geometry and features of triggering area. Furthermore, the role of erosion has been investigated with reference to the uppermost parts of open slopes with a different steepness. These analyses are firstly carried out for simplified benchmark slopes, using both water-like materials (with no shear strength) and debris type materials. Then, three important case studies of Campania region (Cervinara, Nocera Inferiore e Sarno) are analyzed where debris avalanches involved pyroclastic soils originated from the eruptive products of Vesusius volcano. The results achieved for both benchmark slopes and real case histories outline the key role played by the erosion on the whole propagation stage of debris avalanches. The results are particularly satisfactory since they indicate the

The production and confinement of runaway electrons with impurity ''killer'' pellets in DIII-D

International Nuclear Information System (INIS)

Evans, T.E.; Taylor, P.L.; Whyte, D.G.

1998-12-01

Prompt runaway electron bursts, generated by rapidly cooling DIII-D plasmas with argon killer pellets, are used to test a recent knock-on avalanche theory describing the growth of multi-MeV runaway electron currents during disruptions in tokamaks. Runaway current amplitudes, observed during some but not all DIII-D current quenches, are consistent with growth rates predicted by the theory assuming a pre-current quench runaway electron density of approximately 10 15 m -3 . Argon killer pellet modeling yields runaway densities of between 10 15 --10 16 m -3 in these discharges. Although knock-on avalanching appears to agree rather well with the measurements, relatively small avalanche amplification factors combined with uncertainties in the spatial distribution of pellet mass and cooling rates make it difficult to unambiguously confirm the proposed theory with existing data

Scaling behavior of individual barkhausen avalanches in nucleation-mediated magnetization reversal processes

Energy Technology Data Exchange (ETDEWEB)

Im, Mi-Young; Fischer, Peter; Kim, Dong-Hyun; Shin, Sung-Chul

2009-11-09

We report the scaling behavior of Barkhausen avalanches along the hysteresis loop of a CoCrPt alloy film with perpendicular magnetic anisotropy for every field step of 200 Oe. Individual Barkhausen avalanches are directly observed via high-resolution soft X-ray microscopy with a spatial resolution of 15 nm. The Barkhausen avalanches exhibit a power-law scaling behavior, where the scaling exponent of the power-law distribution drastically changes from 1 {+-} 0.04 to 1.47 {+-} 0.03 as the applied magnetic field approaches the coercivity of the CoCrPt film. We infer that this is due to the coupling of adjacent domains.

Angle sensitive single photon avalanche diode

Energy Technology Data Exchange (ETDEWEB)

Lee, Changhyuk, E-mail: cl678@cornell.edu; Johnson, Ben, E-mail: bcj25@cornell.edu; Molnar, Alyosha, E-mail: am699@cornell.edu [Electrical and Computer Engineering, Cornell University, Ithaca, New York 14850 (United States)

2015-06-08

An ideal light sensor would provide exact information on intensity, timing, location, and angle of incoming photons. Single photon avalanche diodes (SPADs) provide such desired high (single photon) sensitivity with precise time information and can be implemented at a pixel-scale to form an array to extract spatial information. Furthermore, recent work has demonstrated photodiode-based structures (combined with micro-lenses or diffraction gratings) that are capable of encoding both spatial and angular information of incident light. In this letter, we describe the implementation of such a grating structure on SPADs to realize a pixel-scale angle-sensitive single photon avalanche diode (A-SPAD) built in a standard CMOS process. While the underlying SPAD structure provides high sensitivity, the time information of the two layers of diffraction gratings above offers angle-sensitivity. Such a unique combination of SPAD and diffraction gratings expands the sensing dimensions to pave a path towards lens-less 3-D imaging and light-field time-of-flight imaging.

First Townsend coefficient of organic vapour in avalanche counters

International Nuclear Information System (INIS)

Sernicki, J.

1990-01-01

A new concept is presented in the paper for implementing the proven method of determining the first Townsend coefficient (α) of gases using an avalanche counter. The A and B gas constants, interrelated by the expression α/p=A exp[-B/(K/p)], are analyzed. Parallel-plate avalanche counters (PPAC) with an electrode spacing d from 0.1 to 0.4 cm have been employed for the investigation, arranged to register low-energy alpha particles at n-heptane vapour pressures of p≥5 Torr. An in-depth discussion is given, covering the veracity and the behaviour vs K/p, of the n-heptane A and B constants determined at reduced electric-field intensity values ranging from 173.5 to 940 V/cm Torr; the constants have been found to depend upon d. The results of the investigation are compared to available data of the α coefficient of organic vapours used in avalanche counters. The PPAC method of determining α reveals some imperfections at very low values of the pd product. (orig.)

AN MHD AVALANCHE IN A MULTI-THREADED CORONAL LOOP

Energy Technology Data Exchange (ETDEWEB)

Hood, A. W.; Cargill, P. J.; Tam, K. V. [School of Mathematics and Statistics, University of St Andrews, St Andrews, Fife, KY16 9SS (United Kingdom); Browning, P. K., E-mail: awh@st-andrews.ac.uk [School of Physics and Astronomy, University of Manchester, Oxford Road, Manchester, M13 9PL (United Kingdom)

2016-01-20

For the first time, we demonstrate how an MHD avalanche might occur in a multithreaded coronal loop. Considering 23 non-potential magnetic threads within a loop, we use 3D MHD simulations to show that only one thread needs to be unstable in order to start an avalanche even when the others are below marginal stability. This has significant implications for coronal heating in that it provides for energy dissipation with a trigger mechanism. The instability of the unstable thread follows the evolution determined in many earlier investigations. However, once one stable thread is disrupted, it coalesces with a neighboring thread and this process disrupts other nearby threads. Coalescence with these disrupted threads then occurs leading to the disruption of yet more threads as the avalanche develops. Magnetic energy is released in discrete bursts as the surrounding stable threads are disrupted. The volume integrated heating, as a function of time, shows short spikes suggesting that the temporal form of the heating is more like that of nanoflares than of constant heating.

High speed quantitative digital beta autoradiography using a multi-step avalanche detector and an Apple-II microcomputer

International Nuclear Information System (INIS)

Bateman, J.E.; Connolly, J.F.; Stephenson, R.

1985-04-01

The development of an electronic, digital beta autoradiography system is described. Using a Multi-Step Avalanche/Multi-Wire Proportional Counter (MSA/MWPC) detector system fitted with delay line readout, high speed digital imaging is demonstrated with sub-millimeter spatial resolution. Good proportionality of observed counting rate relative to the known tritium activity is demonstrated. The application of the system to autoradiography in immunoelectrophoresis, histopathology and DNA sequencing is described. (author)

Evaluating terrain based criteria for snow avalanche exposure ratings using GIS

Science.gov (United States)

Delparte, Donna; Jamieson, Bruce; Waters, Nigel

2010-05-01

Snow avalanche terrain in backcountry regions of Canada is increasingly being assessed based upon the Avalanche Terrain Exposure Scale (ATES). ATES is a terrain based classification introduced in 2004 by Parks Canada to identify "simple", "challenging" and "complex" backcountry areas. The ATES rating system has been applied to well over 200 backcountry routes, has been used in guidebooks, trailhead signs and maps and is part of the trip planning component of the AVALUATOR™, a simple decision-support tool for backcountry users. Geographic Information Systems (GIS) offers a means to model and visualize terrain based criteria through the use of digital elevation model (DEM) and land cover data. Primary topographic variables such as slope, aspect and curvature are easily derived from a DEM and are compatible with the equivalent evaluation criteria in ATES. Other components of the ATES classification are difficult to extract from a DEM as they are not strictly terrain based. An overview is provided of the terrain variables that can be generated from DEM and land cover data; criteria from ATES which are not clearly terrain based are identified for further study or revision. The second component of this investigation was the development of an algorithm for inputting suitable ATES criteria into a GIS, thereby mimicking the process avalanche experts use when applying the ATES classification to snow avalanche terrain. GIS based classifications were compared to existing expert assessments for validity. The advantage of automating the ATES classification process through GIS is to assist avalanche experts with categorizing and mapping remote backcountry terrain.

The Effect of Electron versus Hole Photocurrent on Optoelectric Properties of p+-p-n-n+ Wz-GaN Reach-Through Avalanche Photodiodes

Directory of Open Access Journals (Sweden)

Moumita Ghosh

2013-01-01

Full Text Available The authors have made an attempt to investigate the effect of electron versus hole photocurrent on the optoelectric properties of p+-p-n-n+ structured Wurtzite-GaN (Wz-GaN reach-through avalanche photodiodes (RAPDs. The photo responsivity and optical gain of the devices are obtained within the wavelength range of 300 to 450 nm using a novel modeling and simulation technique developed by the authors. Two optical illumination configurations of the device such as Top Mounted (TM and Flip Chip (FC are considered for the present study to investigate the optoelectric performance of the device separately due to electron dominated and hole dominated photocurrents, respectively, in the visible-blind ultraviolet (UV spectrum. The results show that the peak unity gain responsivity and corresponding optical gain of the device are 555.78 mA W−1 and 9.4144×103, respectively, due to hole dominated photocurrent (i.e., in FC structure; while those are 480.56 mA W−1 and 7.8800×103, respectively, due to electron dominated photocurrent (i.e., in TM structure at the wavelength of 365 nm and for applied reverse bias of 85 V. Thus, better optoelectric performance of Wz-GaN RAPDs can be achieved when the photocurrent is made hole dominated by allowing the UV light to be shined on the n+-layer instead of p+-layer of the device.

MTF measurement and analysis of linear array HgCdTe infrared detectors

Science.gov (United States)

Zhang, Tong; Lin, Chun; Chen, Honglei; Sun, Changhong; Lin, Jiamu; Wang, Xi

2018-01-01

The slanted-edge technique is the main method for measurement detectors MTF, however this method is commonly used on planar array detectors. In this paper the authors present a modified slanted-edge method to measure the MTF of linear array HgCdTe detectors. Crosstalk is one of the major factors that degrade the MTF value of such an infrared detector. This paper presents an ion implantation guard-ring structure which was designed to effectively absorb photo-carriers that may laterally defuse between adjacent pixels thereby suppressing crosstalk. Measurement and analysis of the MTF of the linear array detectors with and without a guard-ring were carried out. The experimental results indicated that the ion implantation guard-ring structure effectively suppresses crosstalk and increases MTF value.

A mineralogical and granulometric study of Cayambe volcano debris avalanche deposit

Science.gov (United States)

Detienne, M.; Delmelle, P.; Guevara, A.; Samaniego, P.; Bustillos, J.; Sonnet, P.; Opfergelt, S.

2013-12-01

Volcano flank/sector collapse represents one of the most catastrophic volcanic hazards. Various volcanic and non-volcanic processes are known to decrease the stability of a volcanic cone, eventually precipitating its gravitational failure. Among them, hydrothermal alteration of volcanic rocks leading to clay mineral formation is recognized as having a large negative impact on rock strength properties. Furthermore, the presence of hydrothermal clays in the collapsing mass influences the behavior of the associated volcanic debris avalanche. In particular, clay-containing debris avalanches seem to travel farther and spread more widely than avalanches of similar volume but which do not incorporate hydrothermally-altered materials. However, the relationship between hydrothermal alteration, flank collapse and debris avalanche behavior is not well understood. The objective of this study is to better determine the volume and composition of hydrothermal clay minerals in the poorly characterized debris avalanche deposit (DAD) of Cayambe composite volcano, located in a densely populated area ~70 km northeast of Quito, Ecuador. Cayambe DAD originated from a sector collapse, which occurred less than 200 ka ago. The DAD is 10-20 m thick and has an estimated total volume of ~0.85 Km3. The H/L ratio (where H is the vertical drop and L is the travel distance of the avalanche) for Cayambe DAD is ~0.095, suggesting a high mobility. In the medial-distal zone, at 9-20 km from its source, the DAD consists of an unstratified and unsorted matrix supporting millimetric to metric clasts. It has a matrix facies (i.e. rich in particles DAD behaved as a cohesive debris flow. Analysis of 13 matrix samples reveals a large variability in particle size distribution. This may reflect poor mixing of the collapsed material during transport. The clay fraction content in the matrix ranges from 15 to 30 wt.%, and does not show a relationship with the sample position in the DAD. Mineralogical

Critical state transformation in hard superconductors resulting from thermomagnetic avalanches

International Nuclear Information System (INIS)

Chabanenko, V.V.; Kuchuk, E.I.; Rusakov, V.F.; Abaloszewa, I.; Nabialek, A.; Perez-Rodriguez, F.

2016-01-01

The results of experimental investigations of magnetic flux dynamics in finite superconductors, obtained using integral and local measurements methods, are presented. Local methods were aimed at clarifying the role of demagnetizing factor in dynamic formation of a complex magnetic structure of the critical state of hard superconductors. To understand the reasons for cardinal restructuring of the induction, we further analyzed the literature data of flux dynamics visualization during avalanches, obtained by magneto-optical methods. New features in the behavior of the magnetic flux during and after the avalanche were discovered. Two stages of the formation of the induction structures in the avalanche area were established, i.e. of homogeneous and heterogeneous filling with the magnetic flux. The mechanism of the inversion of the induction profile was considered. Oscillations in the speed of the front of the magnetic flux were revealed. Transformation of the critical state near the edge of the sample was analyzed. The role of thermal effects and of de-magnetizing factor in the dissipative flux dynamics was shown. Generalized information allowed, in the framework of the Bean concept, to present a model the transformation of the picture of the induction of the critical state and of the superconducting currents of a finite superconductor as a result of flux avalanches for two regimes - of screening and trapping of the magnetic flux.

Avalanches in a Bose-Einstein condensate

NARCIS (Netherlands)

Schuster, J.; Marte, A.; Amtage, S.; Sang, B.; Rempe, G.; Beijerinck, H.C.W.

2001-01-01

Collisional avalanches are identified to be responsible for an 8-fold increase of the initial loss rate of a large 87Rb condensate. We show that the collisional opacity of an ultracold gas exhibits a critical value. When exceeded, losses due to inelastic collisions are substantially enhanced. Under

High performance waveguide-coupled Ge-on-Si linear mode avalanche photodiodes.

Science.gov (United States)

Martinez, Nicholas J D; Derose, Christopher T; Brock, Reinhard W; Starbuck, Andrew L; Pomerene, Andrew T; Lentine, Anthony L; Trotter, Douglas C; Davids, Paul S

2016-08-22

We present experimental results for a selective epitaxially grown Ge-on-Si separate absorption and charge multiplication (SACM) integrated waveguide coupled avalanche photodiode (APD) compatible with our silicon photonics platform. Epitaxially grown Ge-on-Si waveguide-coupled linear mode avalanche photodiodes with varying lateral multiplication regions and different charge implant dimensions are fabricated and their illuminated device characteristics and high-speed performance is measured. We report a record gain-bandwidth product of 432 GHz for our highest performing waveguide-coupled avalanche photodiode operating at 1510nm. Bit error rate measurements show operation with BER-12, in the range from -18.3 dBm to -12 dBm received optical power into a 50 Ω load and open eye diagrams with 13 Gbps pseudo-random data at 1550 nm.

Avalanche effect in the planar array of superheated superconductors

International Nuclear Information System (INIS)

Meagher, G.; Pond, J.; Kotlicki, A.; Turrell, B.G.; Eska, G.; Drukier, A.K.

1996-01-01

An avalanche effect has been observed in a cryogenic detector based on the planar array of superheated superconductors (PASS). The indium PASS, fabricated by photolithography on a mylar substrate, consisted of 40 well-separated lines each containing about 175 spheres of diameter 18 μm and separation 20 μm with those at the end being shielded by superconducting wire. The magnetic field was applied in the PASS plane parallel to the lines. Avalanche events in which several granules changed their state from superconducting to normal were triggered by the nucleation of the transition in a single grain by an alpha particle. (author)

Avalanche size scaling in sheared three-dimensional amorphous solid

DEFF Research Database (Denmark)

Bailey, Nicholas; Schiøtz, Jakob; Lemaître, A.

2007-01-01

We study the statistics of plastic rearrangement events in a simulated amorphous solid at T=0. Events are characterized by the energy release and the "slip volume", the product of plastic strain and system volume. Their distributions for a given system size L appear to be exponential......, but a characteristic event size cannot be inferred, because the mean values of these quantities increase as L-alpha with alpha similar to 3/2. In contrast with results obtained in 2D models, we do not see simply connected avalanches. The exponent suggests a fractal shape of the avalanches, which is also evidenced...

Analysis of avalanche risk factors in backcountry terrain based on usage frequency and accident data in Switzerland

Science.gov (United States)

Techel, F.; Zweifel, B.; Winkler, K.

2015-09-01

Recreational activities in snow-covered mountainous terrain in the backcountry account for the vast majority of avalanche accidents. Studies analyzing avalanche risk mostly rely on accident statistics without considering exposure (or the elements at risk), i.e., how many, when and where people are recreating, as data on recreational activity in the winter mountains are scarce. To fill this gap, we explored volunteered geographic information on two social media mountaineering websites - bergportal.ch and camptocamp.org. Based on these data, we present a spatiotemporal pattern of winter backcountry touring activity in the Swiss Alps and compare this with accident statistics. Geographically, activity was concentrated in Alpine regions relatively close to the main Swiss population centers in the west and north. In contrast, accidents occurred equally often in the less-frequented inner-alpine regions. Weekends, weather and avalanche conditions influenced the number of recreationists, while the odds to be involved in a severe avalanche accident did not depend on weekends or weather conditions. However, the likelihood of being involved in an accident increased with increasing avalanche danger level, but also with a more unfavorable snowpack containing persistent weak layers (also referred to as an old snow problem). In fact, the most critical situation for backcountry recreationists and professionals occurred on days and in regions when both the avalanche danger was critical and when the snowpack contained persistent weak layers. The frequently occurring geographical pattern of a more unfavorable snowpack structure also explains the relatively high proportion of accidents in the less-frequented inner-alpine regions. These results have practical implications: avalanche forecasters should clearly communicate the avalanche danger and the avalanche problem to the backcountry user, particularly if persistent weak layers are of concern. Professionals and recreationists, on the

Alpha- and gamma-detection by the avalanche detectors with metal-resistor-semiconductor structure

International Nuclear Information System (INIS)

Vetokhin, S.S.; Evtushenko, V.P.; Zalesskij, V.B.; Malyshev, S.A.; Chudakov, V.A.; Shunevich, S.A.

1992-01-01

Possibility to use silicon avalanche photodetectors with metal-resistor-semiconductor structure with 0.12 cm 2 photosensitive area as detectors of α-particles, as well as, photodetector of γ-quanta scintillation detector is shown. When detection of α-particles the energy resolution reaches 10%. R energy resolution for avalanche photodetector-CsI(Tl) scintillator system cooled up to - 60 deg C at 59 keV ( 241 Am) and 662 keV ( 137 Cs) energy of γ-quanta constitutes 60% and 80%, respectively. R minimal value in the conducted experiments is determined by the degree of irregularity of avalanche amplification along the photodetector area

Volcanic avalanche fault zone with pseudotachylite and gouge in French Massif Central

Science.gov (United States)

Bernard, Karine; van Wyk de Vries, Benjamin

2017-11-01

Structures and textures with sedimentological variations at different scales of the lithofacies assemblage help us to constrain the basal kinematic transition from non-depositional to depositional conditions during volcanic avalanche emplacement. In the well-exposed impact-sheared contact along volcanic avalanche fault zone in the French Massif Central, we observe how the granular textures of the pseudotachylite and fault gouge have recorded the propagation of shock wave with granular oscillatory stress. Sequential events of basal aggradation along avalanche fault zone have been established related to fractal D-values, temperature pressure regime and oscillatory stress during slow wave velocity. A typical lithofacies assemblage with a reverse grading shows the pseudotachylite and fault gouge. A cataclastic gradient is characterised by the fractal D-values from 2.7 in jigsaw breccias with pseudotachylite partial melt, to 2.6 in the polymodal gouge. Shock, brecciation and comminution produce cataclastic shear bands in the pseudotachylite and quartz microstructures along the basal contact of the volcanic debris-avalanche deposit. Gouge microstructures show granular segregation, cataclasis with antithetic rotational Riedel shear, and an arching effect between the Riedel shear bands. X-ray microtomography provided 3D microfabrics along the clastic vein in the sandy-gouge. From the available statistical dataset, a few equations have been developed implicating the same cataclastic origin with a co-genetic evolution of lithofacies. An impact wave during primary shear propagation may contribute to produce hydroclastic matrix, pseudotachylite partial melt and proximal gouge thixotropy with v 50m/s and a T < 654 °C. The interseismic period with oscillatory stress is related to crushed clasts and basaltic melt around 800 °C, Riedel shear bands with granular segregation along the fault gouge. The secondary shock by matrix-rich avalanche (ΔP = 10GPa, T ≥ 1000-1500 �

Infrasound array criteria for automatic detection and front velocity estimation of snow avalanches: towards a real-time early-warning system

Science.gov (United States)

Marchetti, E.; Ripepe, M.; Ulivieri, G.; Kogelnig, A.

2015-11-01

Avalanche risk management is strongly related to the ability to identify and timely report the occurrence of snow avalanches. Infrasound has been applied to avalanche research and monitoring for the last 20 years but it never turned into an operational tool to identify clear signals related to avalanches. We present here a method based on the analysis of infrasound signals recorded by a small aperture array in Ischgl (Austria), which provides a significant improvement to overcome this limit. The method is based on array-derived wave parameters, such as back azimuth and apparent velocity. The method defines threshold criteria for automatic avalanche identification by considering avalanches as a moving source of infrasound. We validate the efficiency of the automatic infrasound detection with continuous observations with Doppler radar and we show how the velocity of a snow avalanche in any given path around the array can be efficiently derived. Our results indicate that a proper infrasound array analysis allows a robust, real-time, remote detection of snow avalanches that is able to provide the number and the time of occurrence of snow avalanches occurring all around the array, which represent key information for a proper validation of avalanche forecast models and risk management in a given area.

Numerical simulation of crosstalk in reduced pitch HgCdTe photon-trapping structure pixel arrays.

Science.gov (United States)

Schuster, Jonathan; Bellotti, Enrico

2013-06-17

We have investigated crosstalk in HgCdTe photovoltaic pixel arrays employing a photon trapping (PT) structure realized with a periodic array of pillars intended to provide broadband operation. We have found that, compared to non-PT pixel arrays with similar geometry, the array employing the PT structure has a slightly higher optical crosstalk. However, when the total crosstalk is evaluated, the presence of the PT region drastically reduces the total crosstalk; making the use of the PT structure not only useful to obtain broadband operation, but also desirable for reducing crosstalk in small pitch detector arrays.

High-Operating Temperature HgCdTe: A Vision for the Near Future

Science.gov (United States)

Lee, D.; Carmody, M.; Piquette, E.; Dreiske, P.; Chen, A.; Yulius, A.; Edwall, D.; Bhargava, S.; Zandian, M.; Tennant, W. E.

2016-09-01

We review recent advances in the HgCdTe material quality and detector performance achieved at Teledyne using molecular beam epitaxy growth and the double-layer planar hetero-junction (DLPH) detector architecture. By using an un-doped, fully depleted absorber, Teledyne's DLPH architecture can be extended for use in high operating temperatures and other applications. We assess the potential achievable performance for long wavelength infrared (LWIR) hetero-junction p-lightly-doped n or p-intrinsic- n (p-i-n) detectors based on recently reported results for 10.7 μm cutoff 1 K × 1 K focal plane arrays (FPAs) tested at temperatures down to 30 K. Variable temperature dark current measurements show that any Shockley-Read-Hall currents in the depletion region of these devices have lifetimes that are reproducibly greater than 100 ms. Under the assumption of comparable lifetimes at higher temperatures, it is predicted that fully-depleted background radiation-limited performance can be expected for 10- μm cutoff detectors from room temperature to well below liquid nitrogen temperatures, with room-temperature dark current nearly 400 times lower than predicted by Rule 07. The hetero-junction p-i-n diode is shown to have numerous other significant potential advantages including minimal or no passivation requirements for pBn-like processing, low 1/ f noise, compatibility with small pixel pitch while maintaining high modulation transfer function, low crosstalk and good quantum efficiency. By appropriate design of the FPA dewar shielding, analysis shows that dark current can theoretically be further reduced below the thermal equilibrium radiative limit. Modeling shows that background radiation-limited LWIR HgCdTe operating with f/1 optics has the potential to operate within √2 of background-limited performance at 215 K. By reducing the background radiation by 2/3 using novel shielding methods, operation with a single-stage thermo-electric-cooler may be possible. If the

Spatially Extended Avalanches in a Hysteretic Capillary Condensation System: Superfluid 4He in Nuclepore

International Nuclear Information System (INIS)

Lilly, M.P.; Wootters, A.H.; Hallock, R.B.

1996-01-01

Capacitive studies of hysteretic capillary condensation of superfluid 4 He in Nuclepore have shown that the initial draining of the pores occurs over a small range of the chemical potential with avalanches present as groups of pores drain. In the work reported here, the avalanches in this system are shown to be nonlocal events which involve pores distributed at low density across the entire sample. The nonlocal avalanche behavior is shown to be enabled by the presence of a superfluid film connection among the pores. copyright 1996 The American Physical Society

Hole-Initiated-Avalanche, Linear-Mode, Single-Photon-Sensitive Avalanche Photodetector with Reduced Excess Noise and Low Dark Count Rate, Phase I

Data.gov (United States)

National Aeronautics and Space Administration — A radiation hard, single photon sensitive InGaAs avalanche photodiode (APD) receiver technology will be demonstrated useful for long range space based optical...

Reducing financial avalanches by random investments

Science.gov (United States)

Biondo, Alessio Emanuele; Pluchino, Alessandro; Rapisarda, Andrea; Helbing, Dirk

2013-12-01

Building on similarities between earthquakes and extreme financial events, we use a self-organized criticality-generating model to study herding and avalanche dynamics in financial markets. We consider a community of interacting investors, distributed in a small-world network, who bet on the bullish (increasing) or bearish (decreasing) behavior of the market which has been specified according to the S&P 500 historical time series. Remarkably, we find that the size of herding-related avalanches in the community can be strongly reduced by the presence of a relatively small percentage of traders, randomly distributed inside the network, who adopt a random investment strategy. Our findings suggest a promising strategy to limit the size of financial bubbles and crashes. We also obtain that the resulting wealth distribution of all traders corresponds to the well-known Pareto power law, while that of random traders is exponential. In other words, for technical traders, the risk of losses is much greater than the probability of gains compared to those of random traders.

Avalanches in Mn12-Acetate: ``Magnetic Burning"

Science.gov (United States)

McHugh, Sean; Suzuki, Y.; Graybill, D.; Sarachik, M. P.; Avraham, N.; Myasoedov, Y.; Shtrikman, H.; Zeldov, E.; Bagai, R.; Chakov, N. E.; Christou, G.

2006-03-01

From local time-resolved measurements of fast reversal of the magnetization in single crystals of the molecular magnet Mn12-acetate, we have shown[1] that the magnetization avalanche spreads as a narrow interface that propagates through the crystal at a constant velocity roughly two orders of magnitude smaller than the speed of sound. This phenomenon is closely analogous to the propagation of a flame front (deflagration) through a flammable chemical substance. The propagation speed of the avalanche depends on the energy stored in each molecule, which can be controlled and tuned using an external magnetic field. We report studies of propagation speed with different external fields in Mn12-acetate. [1] Yoko Suzuki, M.P. Sarachik, E.M. Chudnovsky, S. McHugh, R. Gonzalez-Rubio, N. Avraham, Y. Myasoedov, H. Shtrikman, E. Zeldov, N.E. Chakov and G. Christou, Phys. Rev. Lett. 95, 147201 (2005).

Using GIS and Google Earth for the creation of the Going-to-the-Sun Road Avalanche Atlas, Glacier National Park, Montana, USA

Science.gov (United States)

Peitzsch, Erich H.; Fagre, Daniel B.; Dundas, Mark

2010-01-01

Snow avalanche paths are key geomorphologic features in Glacier National Park, Montana, and an important component of mountain ecosystems: they are isolated within a larger ecosystem, they are continuously disturbed, and they contain unique physical characteristics (Malanson and Butler, 1984). Avalanches impact subalpine forest structure and function, as well as overall biodiversity (Bebi et al., 2009). Because avalanches are dynamic phenomena, avalanche path geometry and spatial extent depend upon climatic regimes. The USGS/GNP Avalanche Program formally began in 2003 as an avalanche forecasting program for the spring opening of the ever-popular Going-to-the-Sun Road (GTSR), which crosses through 37 identified avalanche paths. Avalanche safety and forecasting is a necessary part of the GTSR spring opening procedures. An avalanche atlas detailing topographic parameters and oblique photographs was completed for the GTSR corridor in response to a request from GNP personnel for planning and resource management. Using ArcMap 9.2 GIS software, polygons were created for every avalanche path affecting the GTSR using aerial imagery, field-based observations, and GPS measurements of sub-meter accuracy. Spatial attributes for each path were derived within the GIS. Resulting products include an avalanche atlas book for operational use, a geoPDF of the atlas, and a Google Earth flyover illustrating each path and associated photographs. The avalanche atlas aids park management in worker safety, infrastructure planning, and natural resource protection by identifying avalanche path patterns and location. The atlas was created for operational and planning purposes and is also used as a foundation for research such as avalanche ecology projects and avalanche path runout modeling.

The development of structures in analogue and natural debris avalanches

Science.gov (United States)

Paguican, Engielle Mae; van Wyk de Vries, Benjamin; Mahar Francisco Lagmay, Alfredo; Grosse, Pablo

2010-05-01

All types of rockslide-debris avalanches present a plethora of internal structures that are also well observed on the surface. Many of these are seen as faults and folds that can be used to determine deformation history and kinematics. We present two sets of simple and well-constrained experiments of reduced basal friction laboratory rockslides, equivalent to a highly deformed simple shear layer, with plug-flow. These follow the original ramp-slide work of Shea and van Wyk de Vries (Geosphere, 2008). The experiments used a curved ramp where materials accelerate until reaching a gently-sloped depositional surface and a constantly inclined ramp with a more regular slope and longer slides. A detailed description of deposit structures, their sequential formation and morphology is then used to investigate the transport type and deformation chronology from slide initiation to runout stopping of avalanches. Results using a curved ramp show accumulation and thickening at where the slope decreases. The thickened mass then further remobilises and advances by secondary collapse of the mass. Such a stop-start process may be important in many mountainous avalanches where there are rapid changes in slope. The constantly inclined ramp shows shearing and extensional structures at the levees and a set of compression and extension structures in the middle. We noted that frontal accumulation during flow occurs as materials at the front move slower relative to those in the medial and proximal zones. This also leads to secondary frontal collapse, and helps to maintain a thicker mass that can flow further. Descriptions and analyses of these structures are then applied to the kinematics and dynamics of natural examples. We study the 2006 Guinsaugon Rockslide event in the Philippines and find that frontal accumulation and secondary avalanching had also occurred and were important in determining the distribution and runout of the mass. Frontal bulking and collapse may also have occurred at

Nanosecond air breakdown parameters for electron and microwave beam propagation

International Nuclear Information System (INIS)

Ali, A.W.

1988-01-01

Air breakdown by avalanche ionization plays an important role in the electron beam and microwave propagations. For high electric fields and short pulse applications one needs avalanche ionization parameters for modeling and scaling of experimental devices. However, the breakdown parameters, i.e., the ionization frequency vs E/p (volt. cm -1 . Torr -1 ) in air is uncertain for very high values of E/P. A review is given of the experimental data for the electron drift velocity, the Townsend ionization coefficient in N 2 and O 2 and the ionization frequency and the collision frequency for momentum transfer in air are developed. (author)

Avalanche photodiodes for ISABELLE detectors

International Nuclear Information System (INIS)

Strand, R.C.

1979-01-01

At ISABELLE some requirements for detecting bursts of photons are not met by standard photomultiplier tubes. The characteristics of immunity to magnetic fields, small size (few mm), low power consumption (approx. 100 mW), insensitivity to optical overloads, and wide dynamic range (approx. 60 dB) are achieved with difficulty, if at all, with PMTs. These are characteristics of the solid state avalanche photodiode (APD), the preferred detector for light-wave communications. Successful field tests with APD detectors stimulated the design of standard optical-fiber communication systems to replace wire carriers by the early 1980's. In other characteristics, i.e., counting rate, pulse-height resolution, effective quantum efficiency, detection efficiency, and reliability, bare APDs are equivalent to standard PMTs. APDs with currently available amplifiers cannot resolve single photoelectrons but they could provide reasonable detection efficiencies and pulse-height resolution for packets of approx. > 100 photons. Commercially available APDs can cost up to 100 times as much as PMTs per active area, but they are potentially much cheaper. Six topics are discussed: (1) detectors for light-wave communication and detectors for particles, (2) avalanche photodiodes, (3) commercially available APDs, (4) dynamic response of PMTs and bare APDs, (5) photon counting with cold APDs, and (6) conclusions and recommendations

Low power wide spectrum optical transmitter using avalanche mode LEDs in SOI CMOS technology

NARCIS (Netherlands)

Agarwal, V.; Dutta, S; Annema, AJ; Hueting, RJE; Steeneken, P.G.; Nauta, B

2017-01-01

This paper presents a low power monolithically integrated optical transmitter with avalanche mode light emitting diodes in a 140 nm silicon-on-insulator CMOS technology. Avalanche mode LEDs in silicon exhibit wide-spectrum electroluminescence (400 nm < λ < 850 nm), which has a significant

Multiwire proportional chamber and multistage avalanche chamber with low concentration photoionization gas

International Nuclear Information System (INIS)

Zhao Pingde; Xu Zhiqing; Tang Xiaowei

1986-01-01

The characteristics of multiwire proportional chamber and multistage avalanche chamber filled with argon and photoionization gas (C 2 H 5 ) 3 N were measured. The spatial resolution curves and output pulse height spectra were measured as well. Low concentration (C 2 H 5 ) 3 N can play an effective part in quenching. At very low concentration, the phenomena of avalanche transverse expansion was observed obviously

The Vaigat Rock Avalanche Laboratory, west-central Greenland

Science.gov (United States)

Dunning, S.; Rosser, N. J.; Szczucinski, W.; Norman, E. C.; Benjamin, J.; Strzelecki, M.; Long, A. J.; Drewniak, M.

2013-12-01

Rock avalanches have unusually high mobility and pose both an immediate hazard, but also produce far-field impacts associated with dam breach, glacier collapse and where they run-out into water, tsunami. Such secondary hazards can often pose higher risks than the original landslide. The prediction of future threats posed by potential rock avalanches is heavily reliant upon understanding of the physics derived from an interpretation of deposits left by previous events, yet drawing comparisons between multiple events is normally challenging as interactions with complex mountainous terrain makes deposits from each event unique. As such numerical models and the interpretation of the underlying physics which govern landslide mobility is commonly case-specific and poorly suited to extrapolation beyond the single events the model is tuned to. Here we present a high-resolution LiDAR and hyperspectral dataset captured across a unique cluster of large rock avalanche source areas and deposits in the Vaigat straight, west central Greenland. Vaigat offers the unprecedented opportunity to model a sample of > 15 rock avalanches of various age sourced from an 80 km coastal escarpment. At Vaigat many of the key variables (topography, geology, post-glacial history) are held constant across all landslides providing the chance to investigate the variations in dynamics and emplacement style related to variable landslide volume, drop-heights, and thinning/spreading over relatively simple, unrestricted run-out zones both onto land and into water. Our data suggest that this region represents excellent preservation of landslide deposits, and hence is well suited to calibrate numerical models of run out dynamics. We use this data to aid the interpretation of deposit morphology, structure lithology and run-out characteristics in more complex settings. Uniquely, we are also able to calibrate our models using a far-field dataset of well-preserved tsunami run-up deposits, resulting from the 21

A method to harness global crowd-sourced data to understand travel behavior in avalanche terrain.

Science.gov (United States)

Hendrikx, J.; Johnson, J.

2015-12-01

To date, most studies of the human dimensions of decision making in avalanche terrain has focused on two areas - post-accident analysis using accident reports/interviews and, the development of tools as decision forcing aids. We present an alternate method using crowd-sourced citizen science, for understanding decision-making in avalanche terrain. Our project combines real-time GPS tracking via a smartphone application, with internet based surveys of winter backcountry users as a method to describe and quantify travel practices in concert with group decision-making dynamics, and demographic data of participants during excursions. Effectively, we use the recorded GPS track taken within the landscape as an expression of the decision making processes and terrain usage by the group. Preliminary data analysis shows that individual experience levels, gender, avalanche hazard, and group composition all influence the ways in which people travel in avalanche terrain. Our results provide the first analysis of coupled real-time GPS tracking of the crowd while moving in avalanche terrain combined with psychographic and demographic correlates. This research will lead to an improved understanding of real-time decision making in avalanche terrain. In this paper we will specifically focus on the presentation of the methods used to solicit, and then harness the crowd to obtain data in a unique and innovative application of citizen science where the movements within the terrain are the desired output data (Figure 1). Figure 1: Example GPS tracks sourced from backcountry winter users in the Teton Pass area (Wyoming), from the 2014-15 winter season, where tracks in red represent those recorded as self-assessed experts (as per our survey), and where tracks in blue represent those recorded as self-assessed intermediates. All tracks shown were obtained under similar avalanche conditions. Statistical analysis of terrain metrics showed that the experts used steeper terrain than the

Gas sampling calorimeter studies in proportional, saturated avalanche, and streamer modes

International Nuclear Information System (INIS)

Atac, M.; Bedeschi, F.; Yoh, J.; Morse, R.; Procario, M.

1982-01-01

Recently, satisfactory new results were obtained at SLAC from gas sampling calorimeters running in the saturated avalanche mode within the energy range of 1.5 to 17.5 GeV. To study the higher energy behavior of this mode, more tests were carried out in the M4 beamline at Fermilab. This paper contains results obtained from the MAC prototype electromagnetic and hadronic calorimeters running in the proportional, saturated avalanche, and the streamer regions for energies between 12 and 150 GeV

Athermal avalanche in bilayer superconducting nanowire single-photon detectors

Energy Technology Data Exchange (ETDEWEB)

Verma, V. B., E-mail: verma@nist.gov; Lita, A. E.; Stevens, M. J.; Mirin, R. P.; Nam, S. W. [National Institute of Standards and Technology, 325 Broadway, Boulder, Colorado 80305 (United States)

2016-03-28

We demonstrate that two superconducting nanowires separated by a thin insulating barrier can undergo an avalanche process. In this process, Joule heating caused by a photodetection event in one nanowire and the associated production of athermal phonons which are transmitted through the barrier cause the transition of the adjacent nanowire from the superconducting to the normal state. We show that this process can be utilized in the fabrication of superconducting nanowire single photon detectors to improve the signal-to-noise ratio, reduce system jitter, maximize device area, and increase the external efficiency over a very broad range of wavelengths. Furthermore, the avalanche mechanism may provide a path towards a superconducting logic element based on athermal gating.

Mechanism of Runaway Electron Generation at Gas Pressures from a Few Atmospheres to Several Tens of Atmospheres

Science.gov (United States)

Zubarev, N. M.; Ivanov, S. N.

2018-04-01

The mechanism of runaway electron generation at gas pressures from a few atmospheres to several tens of atmospheres is proposed. According to this mechanism, the electrons pass into the runaway mode in the enhanced field zone that arises between a cathode micropoint—a source of field-emission electrons—and the region of the positive ion space charge accumulated near the cathode in the tails of the developing electron avalanches. As a result, volume gas ionization by runaway electrons begins with a time delay required for the formation of the enhanced field zone. This process determines the delay time of breakdown. The influence of the gas pressure on the formation dynamics of the space charge region is analyzed. At gas pressures of a few atmospheres, the space charge arises due to the avalanche multiplication of the very first field-emission electron, whereas at pressures of several tens of atmospheres, the space charge forms as a result of superposition of many electron avalanches with a relatively small number of charge carriers in each.

Oscillatory regime of avalanche particle detectors

International Nuclear Information System (INIS)

Lukin, K.A.; Cerdeira, H.A.; Colavita, A.A.

1995-06-01

We describe the model of an avalanche high energy particle detector consisting of two pn-junctions, connected through an intrinsic semiconductor with a reverse biased voltage applied. We show that this detector is able to generate the oscillatory response on the single particle passage through the structure. The possibility of oscillations leading to chaotic behaviour is pointed out. (author). 15 refs, 7 figs

3D Silicon Coincidence Avalanche Detector (3D-SiCAD) for charged particle detection

Science.gov (United States)

Vignetti, M. M.; Calmon, F.; Pittet, P.; Pares, G.; Cellier, R.; Quiquerez, L.; Chaves de Albuquerque, T.; Bechetoille, E.; Testa, E.; Lopez, J.-P.; Dauvergne, D.; Savoy-Navarro, A.

2018-02-01

Single-Photon Avalanche Diodes (SPADs) are p-n junctions operated in Geiger Mode by applying a reverse bias above the breakdown voltage. SPADs have the advantage of featuring single photon sensitivity with timing resolution in the picoseconds range. Nevertheless, their relatively high Dark Count Rate (DCR) is a major issue for charged particle detection, especially when it is much higher than the incoming particle rate. To tackle this issue, we have developed a 3D Silicon Coincidence Avalanche Detector (3D-SiCAD). This novel device implements two vertically aligned SPADs featuring on-chip electronics for the detection of coincident avalanche events occurring on both SPADs. Such a coincidence detection mode allows an efficient discrimination of events related to an incoming charged particle (producing a quasi-simultaneous activation of both SPADs) from dark counts occurring independently on each SPAD. A 3D-SiCAD detector prototype has been fabricated in CMOS technology adopting a 3D flip-chip integration technique, and the main results of its characterization are reported in this work. The particle detection efficiency and noise rejection capability for this novel device have been evaluated by means of a β- strontium-90 radioactive source. Moreover the impact of the main operating parameters (i.e. the hold-off time, the coincidence window duration, the SPAD excess bias voltage) over the particle detection efficiency has been studied. Measurements have been performed with different β- particles rates and show that a 3D-SiCAD device outperforms single SPAD detectors: the former is indeed capable to detect particle rates much lower than the individual DCR observed in a single SPAD-based detectors (i.e. 2 to 3 orders of magnitudes lower).

Smartphone applications for communicating avalanche risk information - a review of existing practices

Science.gov (United States)

Charrière, M. K. M.; Bogaard, T. A.

2015-11-01

Every year, in all mountainous regions, people are victims of avalanches. One way to decrease those losses is believed to be informing about danger levels. The paper presents a study on current practices in the development of smartphones applications that are dedicated to avalanche risk communication. The analysis based on semi-structured interviews with developers of smartphone apps highlights the context of their development, how choices of content and visualization were made as well as how their effectiveness is evaluated. It appears that although the communicators agree on the message to disseminate, its representation triggers debate. Moreover, only simple evaluation processes are conducted but there is a clear awareness that further scientific efforts are needed to analyze the effectiveness of the smartphone apps. Finally, the current or planned possibility for non-experts users to report feedback on the snow and avalanches conditions open the doors to a transition of these apps from one-way communication tools to two-ways communication platforms. This paper also indicates the remaining challenges that avalanche risk communication is facing, although it is disputably the most advanced and standardized practice compared to other natural hazards. Therefore, this research is of interest for the entire field of natural hazards related risk communication.

Performances of a HGCDTE APD based direct detection lidar at 2 μm. Application to dial measurements

Science.gov (United States)

Gibert, Fabien; Dumas, Arnaud; Rothman, Johan; Edouart, Dimitri; Cénac, Claire; Pellegrino, Jessica

2018-04-01

A lidar receiver with a direct detection chain adapted to a HgCdTe APD based detector with electric cooling is associated to a 2.05 μm Ho :YLF pulsed dual wavelength single mode transmitter to provide the first atmospheric lidar measurements using this technology. Experiments confirm the outstanding sensitivity of the detector and hightligth its huge potential for DIAL measurements of trace gas (CO2 and H2O) in this spectral domain. Performances of coherent vs direct detection at 2.05 μm is assessed.

Performances of a HGCDTE APD based direct detection lidar at 2 μm. Application to dial measurements

Directory of Open Access Journals (Sweden)

Gibert Fabien

2018-01-01

Full Text Available A lidar receiver with a direct detection chain adapted to a HgCdTe APD based detector with electric cooling is associated to a 2.05 μm Ho :YLF pulsed dual wavelength single mode transmitter to provide the first atmospheric lidar measurements using this technology. Experiments confirm the outstanding sensitivity of the detector and hightligth its huge potential for DIAL measurements of trace gas (CO2 and H2O in this spectral domain. Performances of coherent vs direct detection at 2.05 μm is assessed.

Study of an avalanche-mode resistive plate chamber

International Nuclear Information System (INIS)

Ying, J.; Ban, Y.; Liu, H.T.; Zhu, Z.M.; Zhu, Z.Y.; Chen, T.; Ma, J.G.; Ye, Y.L.

2000-01-01

Resistive plate chambers (RPCs) are widely used to detect high-energy charged particles, especially muons, due to the high gain, moderate time and spatial resolution, simple design and low cost of these detectors. While the simple streamer mode is adequate for cosmic-ray and low-rate accelerator experiments, the avalanche mode is required for high-rate experiments such as CMS at LHC. In this paper construction of a medium-sized double-gap RPC made of Chinese materials is reported. The experimental set-up of cosmic-ray and muon beam tests are introduced. The avalanche mode was clearly observed. Good efficiency and time resolution were obtained from the beam test at CERN under normal irradiation conditions. At very high radiation background the chamber efficiency decreases, indicating the necessity to change the resistivity value of the Chinese bakelites. (author)

Predamage threshold electron emission from insulator and semiconductor surfaces

International Nuclear Information System (INIS)

Siekhaus, W.J.; Kinney, J.H.; Milam, D.

1985-01-01

Predamage electron emission shows a dependence on fluence, bandgap and wavelength consistent with multiphoton excitation across the bandgap and inconsistent with avalanche ionization and thermionic emission models. The electron emission scales with pulselength as 1/√T. 6 references, 8 figures, 1 table

Single-Photon Avalanche Diodes (SPAD) in CMOS 0.35 µm technology

Energy Technology Data Exchange (ETDEWEB)

Pellion, D.; Jradi, K.; Brochard, N. [Le2i – CNRS/Univ. de Bourgogne, Dijon (France); Prêle, D. [APC – CNRS/Univ. Paris Diderot, Paris (France); Ginhac, D. [Le2i – CNRS/Univ. de Bourgogne, Dijon (France)

2015-07-01

Some decades ago single photon detection used to be the terrain of photomultiplier tube (PMT), thanks to its characteristics of sensitivity and speed. However, PMT has several disadvantages such as low quantum efficiency, overall dimensions, and cost, making them unsuitable for compact design of integrated systems. So, the past decade has seen a dramatic increase in interest in new integrated single-photon detectors called Single-Photon Avalanche Diodes (SPAD) or Geiger-mode APD. SPAD are working in avalanche mode above the breakdown level. When an incident photon is captured, a very fast avalanche is triggered, generating an easily detectable current pulse. This paper discusses SPAD detectors fabricated in a standard CMOS technology featuring both single-photon sensitivity, and excellent timing resolution, while guaranteeing a high integration. In this work, we investigate the design of SPAD detectors using the AMS 0.35 µm CMOS Opto technology. Indeed, such standard CMOS technology allows producing large surface (few mm{sup 2}) of single photon sensitive detectors. Moreover, SPAD in CMOS technologies could be associated to electronic readout such as active quenching, digital to analog converter, memories and any specific processing required to build efficient calorimeters (Silicon PhotoMultiplier – SiPM) or high resolution imagers (SPAD imager). The present work investigates SPAD geometry. MOS transistor has been used instead of resistor to adjust the quenching resistance and find optimum value. From this first set of results, a detailed study of the dark count rate (DCR) has been conducted. Our results show a dark count rate increase with the size of the photodiodes and the temperature (at T=22.5 °C, the DCR of a 10 µm-photodiode is 2020 count s{sup −1} while it is 270 count s{sup −1} at T=−40 °C for a overvoltage of 800 mV). A small pixel size is desirable, because the DCR per unit area decreases with the pixel size. We also found that the adjustment

Improving the performance of the MWPC X-ray imaging detector by means of the Multi-Step Avalanche technique

International Nuclear Information System (INIS)

Bateman, J.E.; Connolly, J.F.; Stephenson, R.

1984-01-01

X-ray imaging systems based on conventional MWPC technology and artificial delay line readout techniques have been developed at RAL for several applications over a period of some eight years. It is perceived that very limited scope exists for the further improvement of the imaging capability of the standard MWPC design. Attention has therefore been turned to the possibility of exploiting the Multi-Step Avalanche (MSA) system of electron multiplication in this context. Results from a prototype system are presented which show spatial resolution better than that achieved in the MWPC systems. The facility for controlling the effective depth of the detector electronically is also demonstrated. (author)

Universal Critical Dynamics in High Resolution Neuronal Avalanche Data

Science.gov (United States)

Friedman, Nir; Ito, Shinya; Brinkman, Braden A. W.; Shimono, Masanori; DeVille, R. E. Lee; Dahmen, Karin A.; Beggs, John M.; Butler, Thomas C.

2012-05-01

The tasks of neural computation are remarkably diverse. To function optimally, neuronal networks have been hypothesized to operate near a nonequilibrium critical point. However, experimental evidence for critical dynamics has been inconclusive. Here, we show that the dynamics of cultured cortical networks are critical. We analyze neuronal network data collected at the individual neuron level using the framework of nonequilibrium phase transitions. Among the most striking predictions confirmed is that the mean temporal profiles of avalanches of widely varying durations are quantitatively described by a single universal scaling function. We also show that the data have three additional features predicted by critical phenomena: approximate power law distributions of avalanche sizes and durations, samples in subcritical and supercritical phases, and scaling laws between anomalous exponents.

A micropixel avalanche phototransistor for time of flight measurements

Energy Technology Data Exchange (ETDEWEB)

Sadigov, A., E-mail: saazik@yandex.ru [National Nuclear Research Center, Baku (Azerbaijan); Institute of Radiation Problems, Baku (Azerbaijan); Suleymanov, S. [National Nuclear Research Center, Baku (Azerbaijan); Institute of Radiation Problems, Baku (Azerbaijan); Ahmadov, F. [National Nuclear Research Center, Baku (Azerbaijan); Ahmadov, G. [National Nuclear Research Center, Baku (Azerbaijan); Joint Institute for Nuclear Research, Dubna (Russian Federation); Abdullayev, K. [National Aviation Academy, Baku (Azerbaijan); Akberov, R. [National Nuclear Research Center, Baku (Azerbaijan); Institute of Radiation Problems, Baku (Azerbaijan); Heydarov, N. [National Nuclear Research Center, Baku (Azerbaijan); Madatov, R. [Institute of Radiation Problems, Baku (Azerbaijan); Mukhtarov, R. [National Aviation Academy, Baku (Azerbaijan); Nazarov, M.; Valiyev, R. [National Nuclear Research Center, Baku (Azerbaijan)

2017-02-11

This paper presents results of studies of the silicon based new micropixel avalanche phototransistor (MAPT). MAPT is a modification of well-known silicon photomultipliers (SiPMs) and differs since each photosensitive pixel of the MAPT operates in Geiger mode and comprises an individual micro-transistor operating in binary mode. This provides a high amplitude single photoelectron signal with significantly shorter rise time. The obtained results are compared with appropriate parameters of known SiPMs. - Highlights: • A new photo detector – micropixel avalanche phototransistor was developed. • MAPT has a matrix of microtransistors with fast output. • In these modules the duration of the leading edge of the signal from the photodetectors are not worse than 50–100 ps.

SPAD electronics for high-speed quantum communications

Science.gov (United States)

Bienfang, Joshua C.; Restelli, Alessandro; Migdall, Alan

2011-01-01

We discuss high-speed electronics that support the use of single-photon avalanche diodes (SPADs) in gigahertz singlephoton communications systems. For InGaAs/InP SPADs, recent work has demonstrated reduced afterpulsing and count rates approaching 500 MHz can be achieved with gigahertz periodic-gating techniques designed to minimize the total avalanche charge to less than 100 fC. We investigate afterpulsing in this regime and establish a connection to observations using more conventional techniques. For Si SPADs, we report the benefits of improved timing electronics that enhance the temporal resolution of Si SPADs used in a free-space quantum key distribution (QKD) system operating in the GHz regime. We establish that the effects of count-rate fluctuations induced by daytime turbulent scintillation are significantly reduced, benefitting the performance of the QKD system.

Optical fibers and avalanche photodiodes for scintillator counters

International Nuclear Information System (INIS)

Borenstein, S.R.; Palmer, R.B.; Strand, R.C.

1980-01-01

Fine hodoscopes can be made of new scintillating optical fibers and one half inch end-on PMT's. An avalanche photodiode with small size and immunity to magnetic fields remains as a tempting new device to be proven as a photodetector for the fibers

Positron camera with high-density avalanche chambers

International Nuclear Information System (INIS)

Manfrass, D.; Enghardt, W.; Fromm, W.D.; Wohlfarth, D.; Hennig, K.

1988-01-01

The results of an extensive investigation of the properties of high-density avalanche chambers (HIDAC) are presented. This study has been performed in order to optimize the layout of HIDAC detectors, since they are intended to be applied as position sensitive detectors for annihilation radiation in a positron emission tomograph being under construction. (author)

Etching of anode wire deposits with CF4/isobutane (80:20) avalanches

International Nuclear Information System (INIS)

Openshaw, R.; Henderson, R.S.; Faszer, W.; Salomon, M.

1991-01-01

An ionization exposure of 0.5 C per cm of wire in a gas mixture of CF 4 /isobutane (80:20) is shown to reverse anode wire damage in single-wire chambers. Several chambers aged in argon/ethane (50:50) and argon/ethane/ethanol (50:50:0.2) and having pulse height reduction of 25-30% have recovered pulse heights and currents to greater than 98% of their initial values. Inspection of the anode wires indicates that the thick deposits caused by the exposure in argon/ethane have been removed. Auger electron spectroscopy reveals only a thin residual layer containing primarily carbon and oxygen. This etching ability of CF 4 /isobutane (80:20) avalanches may explain the extremely good ageing characteristics previously reported for this mixture. (orig.)

Developing an Experimental Simulation Method for Rock Avalanches: Fragmentation Behavior of Brittle Analogue Material

Science.gov (United States)

Thordén Haug, Øystein; Rosenau, Matthias; Leever, Karen; Oncken, Onno

2013-04-01

Gravitational mass movement on earth and other planets show a scale dependent behavior, of which the physics is not fully understood. In particular, the runout distance for small to medium sized landslides (volume dynamics control small and large landslides/rock avalanches. Several mechanisms have been proposed to explain this scale dependent behavior, but no consensus has been reached. Experimental simulations of rock avalanches usually involve transport of loose granular material down a chute. Though such granular avalanche models provide important insights into avalanche dynamics, they imply that the material fully disintegrate instantaneously. Observations from nature, however, suggests that a transition from solid to "liquid" occurs over some finite distance downhill, critically controlling the mobility and energy budget of the avalanche. Few experimental studies simulated more realistically the material failing during sliding and those were realized in a labscale centrifuge, where the range of volumes/scales is limited. To develop a new modeling technique to study the scale dependent runout behavior of rock avalanches, we designed, tested and verified several brittle materials allowing fragmentation to occur under normal gravity conditions. According to the model similarity theory, the analogue material must behave dynamically similar to the rocks in natural rock avalanches. Ideally, the material should therefore deform in a brittle manner with limited elastic and ductile strains up to a certain critical stress, beyond which the material breaks and deforms irreversibly. According to scaling relations derived from dimensional analysis and for a model-to-prototype length ratio of 1/1000, the appropriate yield strength for an analogue material is in the order of 10 kPa, friction coefficient around 0.8 and stiffness in the order of MPa. We used different sand (garnet, quartz) in combination with different matrix materials (sugar, salt, starch, plaster) to cement

A new solver for granular avalanche simulation: Indoor experiment verification and field scale case study

Science.gov (United States)

Wang, XiaoLiang; Li, JiaChun

2017-12-01

A new solver based on the high-resolution scheme with novel treatments of source terms and interface capture for the Savage-Hutter model is developed to simulate granular avalanche flows. The capability to simulate flow spread and deposit processes is verified through indoor experiments of a two-dimensional granular avalanche. Parameter studies show that reduction in bed friction enhances runout efficiency, and that lower earth pressure restraints enlarge the deposit spread. The April 9, 2000, Yigong avalanche in Tibet, China, is simulated as a case study by this new solver. The predicted results, including evolution process, deposit spread, and hazard impacts, generally agree with site observations. It is concluded that the new solver for the Savage-Hutter equation provides a comprehensive software platform for granular avalanche simulation at both experimental and field scales. In particular, the solver can be a valuable tool for providing necessary information for hazard forecasts, disaster mitigation, and countermeasure decisions in mountainous areas.

Swedish skiers knowledge, experience and attitudes towards off-piste skiing and avalanches

OpenAIRE

Mårtensson, Stefan; Wikberg, Per-Olov; Palmgren, Petter

2013-01-01

The winter of 2012/2013 was the most accident-prone season in the Swedish avalanche history with a total of seven dead Swedes. In April 2013 the Swedish Mountain Safety Council initiated a web-based survey aimed towards Swedish skiers. The aim was to identify the target group's knowledge, experience and attitudes towards off-piste skiing and avalanches. Respondents were asked to answer a total of 28 questions. 1047 Swedish off-piste skiers answered, and we analysed them in more detail. The Sw...

Analysis of the snow-atmosphere energy balance during wet-snow instabilities and implications for avalanche prediction

Directory of Open Access Journals (Sweden)

C. Mitterer

2013-02-01

Full Text Available Wet-snow avalanches are notoriously difficult to predict; their formation mechanism is poorly understood since in situ measurements representing the thermal and mechanical evolution are difficult to perform. Instead, air temperature is commonly used as a predictor variable for days with high wet-snow avalanche danger – often with limited success. As melt water is a major driver of wet-snow instability and snow melt depends on the energy input into the snow cover, we computed the energy balance for predicting periods with high wet-snow avalanche activity. The energy balance was partly measured and partly modelled for virtual slopes at different elevations for the aspects south and north using the 1-D snow cover model SNOWPACK. We used measured meteorological variables and computed energy balance and its components to compare wet-snow avalanche days to non-avalanche days for four consecutive winter seasons in the surroundings of Davos, Switzerland. Air temperature, the net shortwave radiation and the energy input integrated over 3 or 5 days showed best results in discriminating event from non-event days. Multivariate statistics, however, revealed that for better predicting avalanche days, information on the cold content of the snowpack is necessary. Wet-snow avalanche activity was closely related to periods when large parts of the snowpack reached an isothermal state (0 °C and energy input exceeded a maximum value of 200 kJ m⁻² in one day, or the 3-day sum of positive energy input was larger than 1.2 MJ m⁻². Prediction accuracy with measured meteorological variables was as good as with computed energy balance parameters, but simulated energy balance variables accounted better for different aspects, slopes and elevations than meteorological data.

Neuronal avalanches and learning

Energy Technology Data Exchange (ETDEWEB)

Arcangelis, Lucilla de, E-mail: dearcangelis@na.infn.it [Department of Information Engineering and CNISM, Second University of Naples, 81031 Aversa (Italy)

2011-05-01

Networks of living neurons represent one of the most fascinating systems of biology. If the physical and chemical mechanisms at the basis of the functioning of a single neuron are quite well understood, the collective behaviour of a system of many neurons is an extremely intriguing subject. Crucial ingredient of this complex behaviour is the plasticity property of the network, namely the capacity to adapt and evolve depending on the level of activity. This plastic ability is believed, nowadays, to be at the basis of learning and memory in real brains. Spontaneous neuronal activity has recently shown features in common to other complex systems. Experimental data have, in fact, shown that electrical information propagates in a cortex slice via an avalanche mode. These avalanches are characterized by a power law distribution for the size and duration, features found in other problems in the context of the physics of complex systems and successful models have been developed to describe their behaviour. In this contribution we discuss a statistical mechanical model for the complex activity in a neuronal network. The model implements the main physiological properties of living neurons and is able to reproduce recent experimental results. Then, we discuss the learning abilities of this neuronal network. Learning occurs via plastic adaptation of synaptic strengths by a non-uniform negative feedback mechanism. The system is able to learn all the tested rules, in particular the exclusive OR (XOR) and a random rule with three inputs. The learning dynamics exhibits universal features as function of the strength of plastic adaptation. Any rule could be learned provided that the plastic adaptation is sufficiently slow.

Neuronal avalanches and learning

International Nuclear Information System (INIS)

Arcangelis, Lucilla de

2011-01-01

Networks of living neurons represent one of the most fascinating systems of biology. If the physical and chemical mechanisms at the basis of the functioning of a single neuron are quite well understood, the collective behaviour of a system of many neurons is an extremely intriguing subject. Crucial ingredient of this complex behaviour is the plasticity property of the network, namely the capacity to adapt and evolve depending on the level of activity. This plastic ability is believed, nowadays, to be at the basis of learning and memory in real brains. Spontaneous neuronal activity has recently shown features in common to other complex systems. Experimental data have, in fact, shown that electrical information propagates in a cortex slice via an avalanche mode. These avalanches are characterized by a power law distribution for the size and duration, features found in other problems in the context of the physics of complex systems and successful models have been developed to describe their behaviour. In this contribution we discuss a statistical mechanical model for the complex activity in a neuronal network. The model implements the main physiological properties of living neurons and is able to reproduce recent experimental results. Then, we discuss the learning abilities of this neuronal network. Learning occurs via plastic adaptation of synaptic strengths by a non-uniform negative feedback mechanism. The system is able to learn all the tested rules, in particular the exclusive OR (XOR) and a random rule with three inputs. The learning dynamics exhibits universal features as function of the strength of plastic adaptation. Any rule could be learned provided that the plastic adaptation is sufficiently slow.

Recalculation of an artificially released avalanche with SAMOS and validation with measurements from a pulsed Doppler radar

Directory of Open Access Journals (Sweden)

R. Sailer

2002-01-01

Full Text Available A joint experiment was carried out on 10 February 1999 by the Swiss Federal Institute for Snow and Avalanche Research (SFISAR and the Austrian Institute for Avalanche and Torrent Research (AIATR, of the Federal Office and Re-search Centre for Forests, BFW to measure forces and velocities at the full scale experimental site CRÊTA BESSE in VALLÉE DE LA SIONNE, Canton du Valais, Switzerland. A huge avalanche could be released artificially, which permitted extensive investigations (dynamic measurements, im-provement of measurement systems, simulation model verification, design of protective measures, etc.. The results of the velocity measurements from the dual frequency pulsed Doppler avalanche radar of the AIATR and the recalculation with the numerical simulation model SAMOS are explained in this paper.

Very high resolution detection of gamma radiation at room-temperature using P-I-N detectors of CdZnTe and HgCdTe

Science.gov (United States)

Hamilton, W. J.; Rhiger, D. R.; Sen, S.; Kalisher, M. H.; James, K.; Reid, C. P.; Gerrish, V.; Baccash, C. O.

1994-08-01

High-energy photon detectors have been constructed by engineering and fabricating p-i-n diode structures consisting of bulk CdZnTe and epitaxial HgCdTe. The p-i-n structure was obtained by liquid-phase epitaxial growth of p and n doped HgCdTe layers on 'intrinsic' CdZnTe material about 1mm thick and approximately 25mm square. Curve tracing shows I-V curves with diode characteristics having resistivity above 1011 Omega -cm and leakage current of less than 400 pA to about - 60V reverse bias on a typical test piece approximately 5 x 8 x 1 mm. Spectra of similar test pieces have been obtained at room temperature with various nuclear isotopic sources over the range of 22 keV to 662 keV which show exceptionally high energy resolution. Resolution as good as 1.82% FWHM was obtained for the 356 keV line of 133Ba with a P/V = 3.4. The performance of these detectors combined with contemporary infrared technology capable of fabricating 2D arrays of these II-VI materials opens up manifold exciting applications in astrophysics, medical, industrial, environmental, and defense spectroscopy and imaging.

Network dynamics in nociceptive pathways assessed by the neuronal avalanche model

Directory of Open Access Journals (Sweden)

Wu José

2012-04-01

Full Text Available Abstract Background Traditional electroencephalography provides a critical assessment of pain responses. The perception of pain, however, may involve a series of signal transmission pathways in higher cortical function. Recent studies have shown that a mathematical method, the neuronal avalanche model, may be applied to evaluate higher-order network dynamics. The neuronal avalanche is a cascade of neuronal activity, the size distribution of which can be approximated by a power law relationship manifested by the slope of a straight line (i.e., the α value. We investigated whether the neuronal avalanche could be a useful index for nociceptive assessment. Findings Neuronal activity was recorded with a 4 × 8 multichannel electrode array in the primary somatosensory cortex (S1 and anterior cingulate cortex (ACC. Under light anesthesia, peripheral pinch stimulation increased the slope of the α value in both the ACC and S1, whereas brush stimulation increased the α value only in the S1. The increase in α values was blocked in both regions under deep anesthesia. The increase in α values in the ACC induced by peripheral pinch stimulation was blocked by medial thalamic lesion, but the increase in α values in the S1 induced by brush and pinch stimulation was not affected. Conclusions The neuronal avalanche model shows a critical state in the cortical network for noxious-related signal processing. The α value may provide an index of brain network activity that distinguishes the responses to somatic stimuli from the control state. These network dynamics may be valuable for the evaluation of acute nociceptive processes and may be applied to chronic pathological pain conditions.

Low Gain Avalanche Detectors (LGAD) for particle physics and synchrotron applications

Science.gov (United States)

Moffat, N.; Bates, R.; Bullough, M.; Flores, L.; Maneuski, D.; Simon, L.; Tartoni, N.; Doherty, F.; Ashby, J.

2018-03-01

A new avalanche silicon detector concept is introduced with a low gain in the region of ten, known as a Low Gain Avalanche Detector, LGAD. The detector's characteristics are simulated via a full process simulation to obtain the required doping profiles which demonstrate the desired operational characteristics of high breakdown voltage (500 V) and a gain of 10 at 200 V reverse bias for X-ray detection. The first low gain avalanche detectors fabricated by Micron Semiconductor Ltd are presented. The doping profiles of the multiplication junctions were measured with SIMS and reproduced by simulating the full fabrication process which enabled further development of the manufacturing process. The detectors are 300 μm thick p-type silicon with a resistivity of 8.5 kΩcm, which fully depletes at 116 V. The current characteristics are presented and demonstrate breakdown voltages in excess of 500 V and a current density of 40 to 100 nAcm‑2 before breakdown measured at 20oC. The gain of the LGAD has been measured with a red laser (660 nm) and shown to be between 9 and 12 for an external bias voltage range from 150 V to 300 V.

Assessing the value of real-time snow and avalanche information

Science.gov (United States)

Zeidler, Antonia; Adams, Marc; Schuster, Martin; Berner, Martin; Nagy, Wilhelm

2017-04-01

This poster presentation shows first results from a pilot study on exploring the possibilities of using existing and new information and communication technologies (ICT) for snow and avalanche assessments. Today, ICT solutions allow the utilisation of information at a high spatiotemporal resolution, due to the widespread availability of internet access, high computing power and affordable mobile devices. Therefore, there is an increasing request for up to date information on snow and avalanche decision-making. However, there are challenges that need to be addressed from different view points. These include topics in the field of technological feasibility of providing a stable network, exchanging trustworthy information and motivation of experts to participate. This contribution discusses the lessons-learnt, from the establishment of a platform to the user-experience.

Etching of anode wire deposits with CF4/isobutane (80:20) avalanches

International Nuclear Information System (INIS)

Openshaw, R.; Henderson, R.S.; Faszer, W.; Salomon, M.

1990-11-01

An ionization exposure of 0.5 coulombs per cm of wire in a gas mixture of CF 4 /isobutane (80:20) is shown to reverse anode wire damage in single-wire chambers. Several chambers aged in argon/ethane (50:50) and argon/ethane/ethanol (50:50:0.2) and having pulse height reductions of 25-30% have recovered pulse heights and currents to greater than 98% of their initial values. Inspection of the anode wires indicates that the thick deposits caused by the exposure in argon/ethane have been removed. Auger electron spectroscopy reveals only a thin residual layer containing primarily carbon and oxygen. This etching ability of CF 4 /isobutane (80:20) avalanches may explain the extremely good ageing characteristics previously reported for this mixture. (Author) (13 refs., 3 tabs., 11 figs.)

Investigation of the performance of alpha particle counting and alpha-gamma discrimination by pulse shape with micro-pixel avalanche photodiode

International Nuclear Information System (INIS)

Ahmadov, G.; Madatov, R.; Sadigov, A.; Sadygov, Z.; Jafarova, E.; Ahmadov, G.; Sadygov, Z.; Olshevski, A.; Zerrouk, F.; Mukhtarov, R.

2015-01-01

Being capable measuring small lights gives possibility to use micro-pixel avalanche photodiodes with scintillators. It is shown two prototypes to use micro-pixel avalanche photodiodes with and without scintillators as alpha and gamma counters in this paper. First prototype is to use two micro-pixel avalanche photodiodes. One for detecting alpha particles and closer to it, the second one with a thin plastic scintillator for detecting gamma rays. Second prototype is called two-layers configuration in which it is used only one micro-pixel avalanche photodiode, but two scntillators with different decay times. One can distinquish alpha particle and gamma ray events by using pulse shape discrimination techniques in the two-layer configuration. In this work an alpha particle and gamma ray counting performance of micro-pixel avalanche photodiodes without scintillators and its combination of plastic and BGO+ plastic scintillators was investigated. Obtained results showed the detection performance of the micro-pixel avalanche photodiodes in combination with plastic scintillator was about the same as conventional semiconductor detectors

Avalanches of Singing Sand in the Laboratory

Science.gov (United States)

Dagois-Bohy, Simon; Courrech Du Pont, Sylvain; Douady, Stéphane

2011-03-01

The song of dunes is a natural phenomenon that has arisen travellers' curiosity for a long time, from Marco Polo to R.A. Bagnold. Scientific observations in the XXth century have shown that the sound is emitted during a shear flow of these particular grains, the free surface of the flow having coherent vibrations like a loud speaker. The sound emission is also submitted to a threshold effect with many parameters like humidity, flow speed, surface of the grains. The sound has been reproduced in laboratory avalanche experiments close to the natural phenomenon on field, but set in a channel with a hard bottom and a few centimeters of sand flowing, which contradicts explanations of the sound that involve a sand dune under the avalanche flow. Flow rates measurements also show the presence of a plug region in the flow above the sheared band, with the same characteristic length as the coherence zones of the sound. Finally we show experimentally that the Froude number, once modified to take into account the height of this plug band, is the parameter that sets the amplitude of the sound, and produces a threshold that depends on the grain type.

Townsend coefficients of gases in avalanche counters

International Nuclear Information System (INIS)

Brunner, G.

1978-01-01

Though much work has been done by many authors in the last few years in the development and application of avalanche counters for ion radiation, it is based upon values of the Townsend coefficients as the essential gas parameter, which were determined many years ago for much lower reduced field strengths F/p than prevail in such counters. Therefore absolute determinations of α in vapours of methyl alcohol, cyclohexane, acetone, and n-heptene were performed under original conditions of avalanche counters. The values obtained do not differ by more than 30%-50% from the former values indeed, extrapolated over F/p for the first three mentioned substances, but the amounts of A and B in the usual representation α/p=A exp(-B(F/p)) are much greater for the stronger reduced fields. This is of importance for such counter properties as the dependence of pulse heights on pressure, voltage, electrode distance etc., which are governed by other combinations of A and B than α/p itself. A comparison of results for different ionic radiations shows a marked influence of the primary ionization density along the particle tracks which is hard to explain. (Auth.)

X-ray imaging with amorphous selenium: Pulse height measurements of avalanche gain fluctuations

International Nuclear Information System (INIS)

Lui, Brian J. M.; Hunt, D. C.; Reznik, A.; Tanioka, K.; Rowlands, J. A.

2006-01-01

Avalanche multiplication in amorphous selenium (a-Se) can provide a large, adjustable gain for active matrix flat panel imagers (AMFPI), enabling quantum noise limited x-ray imaging during both radiography and fluoroscopy. In the case of direct conversion AMFPI, the multiplication factor for each x ray is a function of its depth of interaction, and the resulting variations in gain can reduce the detective quantum efficiency (DQE) of the system. An experimental method was developed to measure gain fluctuations by analyzing images of individual x rays that were obtained using a video camera with an a-Se target operated in avalanche mode. Pulse height spectra (PHS) of the charge produced per x ray were recorded for monoenergetic 30.9, 49.4, and 73.8 keV x-ray sources. The rapid initial decay and long tail of each PHS can be explained by a model in which positive charge dominates the initiation of avalanche. The Swank information factor quantifies the effect of gain fluctuation on DQE and was calculated from the PHS. The information factor was found to be 0.5 for a 25 μm a-Se layer with a maximum gain of ∼300. Changing the energy of the incident x ray influenced the range of the primary photoelectron and noticeably affected the tail of the experimental PHS, but did not significantly change the avalanche Swank factor

Avalanche weak layer shear fracture parameters from the cohesive crack model

Science.gov (United States)

McClung, David

2014-05-01

Dry slab avalanches release by mode II shear fracture within thin weak layers under cohesive snow slabs. The important fracture parameters include: nominal shear strength, mode II fracture toughness and mode II fracture energy. Alpine snow is not an elastic material unless the rate of deformation is very high. For natural avalanche release, it would not be possible that the fracture parameters can be considered as from classical fracture mechanics from an elastic framework. The strong rate dependence of alpine snow implies that it is a quasi-brittle material (Bažant et al., 2003) with an important size effect on nominal shear strength. Further, the rate of deformation for release of an avalanche is unknown, so it is not possible to calculate the fracture parameters for avalanche release from any model which requires the effective elastic modulus. The cohesive crack model does not require the modulus to be known to estimate the fracture energy. In this paper, the cohesive crack model was used to calculate the mode II fracture energy as a function of a brittleness number and nominal shear strength values calculated from slab avalanche fracture line data (60 with natural triggers; 191 with a mix of triggers). The brittleness number models the ratio of the approximate peak value of shear strength to nominal shear strength. A high brittleness number (> 10) represents large size relative to fracture process zone (FPZ) size and the implications of LEFM (Linear Elastic Fracture Mechanics). A low brittleness number (e.g. 0.1) represents small sample size and primarily plastic response. An intermediate value (e.g. 5) implies non-linear fracture mechanics with intermediate relative size. The calculations also implied effective values for the modulus and the critical shear fracture toughness as functions of the brittleness number. The results showed that the effective mode II fracture energy may vary by two orders of magnitude for alpine snow with median values ranging from 0

Quasi-linear analysis of the extraordinary electron wave destabilized by runaway electrons

Energy Technology Data Exchange (ETDEWEB)

Pokol, G. I.; Kómár, A.; Budai, A. [Department of Nuclear Techniques, Budapest University of Technology and Economics, Budapest (Hungary); Stahl, A.; Fülöp, T. [Department of Applied Physics, Chalmers University of Technology, Göteborg (Sweden)

2014-10-15

Runaway electrons with strongly anisotropic distributions present in post-disruption tokamak plasmas can destabilize the extraordinary electron (EXEL) wave. The present work investigates the dynamics of the quasi-linear evolution of the EXEL instability for a range of different plasma parameters using a model runaway distribution function valid for highly relativistic runaway electron beams produced primarily by the avalanche process. Simulations show a rapid pitch-angle scattering of the runaway electrons in the high energy tail on the 100–1000 μs time scale. Due to the wave-particle interaction, a modification to the synchrotron radiation spectrum emitted by the runaway electron population is foreseen, exposing a possible experimental detection method for such an interaction.

Error diagrams and temporal correlations in a fracture model with characteristic and power-law distributed avalanches

DEFF Research Database (Denmark)

Moreno, Y.; Vázquez-Prada, M.; Pacheco, A.F.

2003-01-01

to the heterogeneity of the system. In one regime, a characteristic event is observed while for the second regime a power-law spectrum of avalanches is obtained reminiscent of self-organized criticality. We find that both regimes are different when predicting large avalanches and that, in the second regime...

Emplacement mechanisms of contrasting debris avalanches at Volcán Mombacho (Nicaragua), provided by structural and facies analysis

Science.gov (United States)

Shea, Thomas; van Wyk de Vries, Benjamin; Pilato, Martín

2008-07-01

We study the lithology, structure, and emplacement of two debris-avalanche deposits (DADs) with contrasting origins and materials from the Quaternary-Holocene Mombacho Volcano, Nicaragua. A clear comparison is possible because both DADs were emplaced onto similar nearly flat (3° slope) topography with no apparent barrier to transport. This lack of confinement allows us to study, in nature, the perfect case scenario of a freely spreading avalanche. In addition, there is good evidence that no substratum was incorporated in the events during flow, so facies changes are related only to internal dynamics. Mombacho shows evidence of at least three large flank collapses, producing the two well-preserved debris avalanches of this study; one on its northern flank, “Las Isletas,” directed northeast, and the other on its southern flank, “El Crater,” directed south. Other south-eastern features indicate that the debris-avalanche corresponding to the third collapse (La Danta) occurred before Las Isletas and El Crater events. The materials involved in each event were similar, except in their alteration state and in the amount of substrata initially included in the collapse. While “El Crater” avalanche shows no signs of substratum involvement and has characteristics of a hydrothermal weakening-related collapse, the “Las Isletas” avalanche involves significant substratum and was generated by gravity spreading-related failure. The latter avalanche may have interacted with Lake Nicaragua during transport, in which case its run-out could have been modified. Through a detailed morphological and structural description of the Mombacho avalanches, we provide two contrasting examples of non-eruptive volcanic flank collapse. We show that, remarkably, even with two distinct collapse mechanisms, the debris avalanches developed the same gross stratigraphy of a coarse layer above a fine layer. This fine layer provided a low friction basal slide layer. Whereas DAD layering and

Meshfree simulation of avalanches with the Finite Pointset Method (FPM)

Science.gov (United States)

Michel, Isabel; Kuhnert, Jörg; Kolymbas, Dimitrios

2017-04-01

Meshfree methods are the numerical method of choice in case of applications which are characterized by strong deformations in conjunction with free surfaces or phase boundaries. In the past the meshfree Finite Pointset Method (FPM) developed by Fraunhofer ITWM (Kaiserslautern, Germany) has been successfully applied to problems in computational fluid dynamics such as water crossing of cars, water turbines, and hydraulic valves. Most recently the simulation of granular flows, e.g. soil interaction with cars (rollover), has also been tackled. This advancement is the basis for the simulation of avalanches. Due to the generalized finite difference formulation in FPM, the implementation of different material models is quite simple. We will demonstrate 3D simulations of avalanches based on the Drucker-Prager yield criterion as well as the nonlinear barodesy model. The barodesy model (Division of Geotechnical and Tunnel Engineering, University of Innsbruck, Austria) describes the mechanical behavior of soil by an evolution equation for the stress tensor. The key feature of successful and realistic simulations of avalanches - apart from the numerical approximation of the occurring differential operators - is the choice of the boundary conditions (slip, no-slip, friction) between the different phases of the flow as well as the geometry. We will discuss their influences for simplified one- and two-phase flow examples. This research is funded by the German Research Foundation (DFG) and the FWF Austrian Science Fund.

Structural properties of layers of HgCdTe, grown by the laser epitaxy method on silicon substrates

International Nuclear Information System (INIS)

Plyatsko, S.V.; Vergush, M.M.; Litvin, P.M.; Kozirjev, Yu.M.; Shevlyakov, S.A.

2001-01-01

Thin films (0.1-1.5 μm) of HgCdTe on substrates Si (100) and Si (111) from monocrystal and pressed sources Hg 1-x Cd x Te (x=0.22) sprayed by laser IR radiation were grown and are investigated. The concentration of macro defects (drops) on the surface of films is determined by the relation of the diameter of a laser beam and depth of the crater, formed by laser irradiation. The size of crystal grains almost does not depend on the temperature of a substrate and power densities of a laser radiation and increases with the thickness of a layer

Silicon avalanche photodiodes on the base of metal-resistor-semiconductor (MRS) structures

CERN Document Server

Saveliev, V

2000-01-01

The development of a high quantum efficiency, fast photodetector, with internal gain amplification for the wavelength range 450-600 nm is one of the critical issues for experimental physics - registration of low-intensity light photons flux. The new structure of Silicon Avalanche Detectors with high internal amplification (10 sup 5 -10 sup 6) has been designed, manufactured and tested for registration of visible light photons and charge particles. The main features of Metal-Resistor-Semiconductor (MRS) structures are the high charge multiplication in nonuniform electric field near the 'needle' pn-junction and negative feedback for stabilization of avalanche process due to resistive layer.

Early Holocene (8.6 ka) rock avalanche deposits, Obernberg valley (Eastern Alps): Landform interpretation and kinematics of rapid mass movement.

Science.gov (United States)

Ostermann, Marc; Sanders, Diethard; Ivy-Ochs, Susan; Alfimov, Vasily; Rockenschaub, Manfred; Römer, Alexander

2012-10-15

In the Obernberg valley, the Eastern Alps, landforms recently interpreted as moraines are re-interpreted as rock avalanche deposits. The catastrophic slope failure involved an initial rock volume of about 45 million m³, with a runout of 7.2 km over a total vertical distance of 1330 m (fahrböschung 10°). 36 Cl surface-exposure dating of boulders of the avalanche mass indicates an event age of 8.6 ± 0.6 ka. A 14 C age of 7785 ± 190 cal yr BP of a palaeosoil within an alluvial fan downlapping the rock avalanche is consistent with the event age. The distal 2 km of the rock-avalanche deposit is characterized by a highly regular array of transverse ridges that were previously interpreted as terminal moraines of Late-Glacial. 'Jigsaw-puzzle structure' of gravel to boulder-size clasts in the ridges and a matrix of cataclastic gouge indicate a rock avalanche origin. For a wide altitude range the avalanche deposit is preserved, and the event age of mass-wasting precludes both runout over glacial ice and subsequent glacial overprint. The regularly arrayed transverse ridges thus were formed during freezing of the rock avalanche deposits.

Avalanches and generalized memory associativity in a network model for conscious and unconscious mental functioning

Science.gov (United States)

Siddiqui, Maheen; Wedemann, Roseli S.; Jensen, Henrik Jeldtoft

2018-01-01

We explore statistical characteristics of avalanches associated with the dynamics of a complex-network model, where two modules corresponding to sensorial and symbolic memories interact, representing unconscious and conscious mental processes. The model illustrates Freud's ideas regarding the neuroses and that consciousness is related with symbolic and linguistic memory activity in the brain. It incorporates the Stariolo-Tsallis generalization of the Boltzmann Machine in order to model memory retrieval and associativity. In the present work, we define and measure avalanche size distributions during memory retrieval, in order to gain insight regarding basic aspects of the functioning of these complex networks. The avalanche sizes defined for our model should be related to the time consumed and also to the size of the neuronal region which is activated, during memory retrieval. This allows the qualitative comparison of the behaviour of the distribution of cluster sizes, obtained during fMRI measurements of the propagation of signals in the brain, with the distribution of avalanche sizes obtained in our simulation experiments. This comparison corroborates the indication that the Nonextensive Statistical Mechanics formalism may indeed be more well suited to model the complex networks which constitute brain and mental structure.

First characterisation of the "Rumi-Pana" rock avalanche deposits (Famatina Range, La Rioja, Argentina)

Science.gov (United States)

Santiago Pullarello, José; Derron, Marc-Henri; Penna, Ivanna; Leiva, Alicia; Jaboyadoff, Michel

2017-04-01

Active mountain fronts are subject to large scale slope collapses which have the capacity to run long distances on piedmont areas. Along time, fluvial activity and other gravitatory processes can intensively erode and mask primary features related to the collapses. Therefore, to reconstruct the history of their occurrence, further analyses are needed, e.g. sedimentologic analyses. This work focuses on the occurrence of large rock avalanches in the Vinchina region, La Rioja (28°43'27.81'' S / 68°00'25.42'' W) on the western side of the Famatina range(Argentina). Here, photointerpretation of high resolution satellite images (Google Earth) allowed us to identify two rock avalanches, main scarps developed at 2575 and 2750 m a.s.l. . There are no absolute ages for these deposits, however, comparing their preservation degree with those dated further north (in similar climatic and landscape dynamics contexts [i]), we can suggest these rock avalanches took place during the Pleistocene. We carried out a fieldwork survey in this remote area, including classical landslide mapping, structural analysis, deposits characterization and sampling. The deposits reach the valley bottom (at around 1700 m a.s.l.) with runouts about 5 and 5.3 km long. In one of the cases, the morphology of the deposit is well preserved, allowing to reconstruct accurately its extension. However, in the second case, the deposits are strongly eroded by courses draining the mountain front, therefore further analyses should be done to reconstruct its extension. In addition to morphologic interpretations, a multiscale grain-size analysis was done to differentiate rock avalanches from other hillslope deposits: (1) 3D surface models of surface plots (5x5m) have been built by SfM photogrammetry; 2) classical sieving and 3) laser grain-size analysis of deposits. Samples were collected on different parts of the slope, but also along cross sections through the avalanche deposit. This deposits characterization will

Trigger mechanisms of debris avalanche. Comparison between Bandai-san 1888 and the other cases

Energy Technology Data Exchange (ETDEWEB)

Ui, Tadahide

1988-08-25

This report describes a trial of classifying the trigger mechanisms of debris avalanche in a volcanic action, on the basis of a geography and the structure of the sedimentation. Reason of disintegration is diversified but the debris avalanche is caused by the destruction of the unstable mountain mass. In the case of the 1888 debris avalanche of Bandai-san, a small steam explosion at the end of the strato-volcanic activity caused the instability of a part of the mountain mass, inducing a landslide. At the active period of the volcano, a viscous magma penetrates into the volcano mass, sometimes deforming the mountain body and eventually reaching disintegration. Furthermore, an eroded valley on the surface of the volcano body develops and disintegrates and, also along the slope of the volcano, a disintegration towards the sea-bottom will occur. (4 figs, 4 tabs, 19 refs)

The Large-Scale Debris Avalanche From The Tancitaro Volcano (Mexico): Characterization And Modeling

Science.gov (United States)

Morelli, S.; Gigli, G.; Falorni, G.; Garduno Monroy, V. H.; Arreygue, E.

2008-12-01

The Tancitaro is an andesitic-dacitic stratovolcano located in the Michoacán Guanajuato volcanic field within the west-central portion of the trans-Mexican Volcanic Belt. The volcanism in this area is characterized by two composite volcanoes, the highest of which is the Tancitaro volcanic edifice (3840 m), some low angle lava cones and more than 1,000 monogenetic cinder cones. The distribution of the cinder cones is controlled by NE-SW active faults, although there are also additional faults with NNW-SSE trends along which some cones are aligned. The Tancitaro stratovolcano is located at the intersection of the tectonical structures that originate these alignments. All this geological activity has contributed to the gravitational instability of the volcano, leading to a huge sector collapse which produced the investigated debris avalanche. The collapse structure is an east-facing horseshoe-shaped crater (4 km wide and 5.3 km long), related with a large fan that was deposited within the Tepalcatepec depression. The deposit starts only 7 km downslope from the failure scar, it is 66 km long and covers an area of approximately 1155 km2. The landslide magnitude is about 20 km3 and it was firstly determined by the reconstruction of the paleo-edifice using a GIS software and then validated by the observation of significant outcrops. The fan was primarily formed by the deposit of this huge debris avalanche and subsequently by debris flow and fluvial deposits. Field investigations on the fan area highlighted the presence of two texturally distinct parts, which are referred to the 'block facies' and the 'matrix facies'. The first sedimentary structure is responsible for the typical hummock morphologies in the proximal area, as seen in many other debris avalanche deposits. Instead in the distal zones, the deposit is made up by the 'mixed block and matrix facies'. Blocks and megablocks, some of which are characterized by a jigsaw puzzle texture, gradually decrease in size

Application of avalanche photodiodes for the measurement of actinides by alpha liquid scintillation counting

International Nuclear Information System (INIS)

Reboli, A.

2005-10-01

Alpha emitters analysis using liquid scintillation spectroscopy is often used when sensitivity and fast samples preparation are the important points. A more extensive use of this technique is until now limited by its poor resolution compared to alpha particle spectroscopy with semiconductor detectors. To improve the resolution and thus promote this method for the measurement of actinides in environment, we have tested silicon avalanche photodiodes (APD) as new detectors for scintillation photons. The set-up consists of a large area avalanche photodiode (16 mm diameter) coupled to a thin vial containing alpha-emitters within a liquid scintillation cocktail. After optimization of several parameters like bias voltage, temperature, counting geometry and composition of the scintillating cocktail, energy resolutions have been found to be better than those obtained with standard photomultiplier tubes (PMT): 5% (200 keV FWHM) for 232 Th and 4.2% (240 keV FWHM) for 236 Pu. Our results show that the improvement is due to less fluctuations associated with light collection since the spatial response of APDs is more uniform than that of PMTs. The expected gain on quantum efficiency (80% for APDs instead of 25% for PMTs) is nullified by a corresponding increase on electronic noise and excess noise factor. Significant better results are foreseen by using green scintillators (450 - 550 nm wavelengths region) with larger Stokes-shift and blue-enhanced APDs which reach their maximum quantum efficiency in this region. (author)

Caldera formation at Volcán Colima, Mexico, by a large large holocene volcanic debris avalanche

Science.gov (United States)

Luhr, James F.; Prestegaard, Karen L.

1988-12-01

About 4,300 years ago, 10 km 3 of the upper cone of ancestral Volcán Colima collapsed to the southwest leaving a horseshoe-shaped caldera 4 km in diameter. The collapse produced a massive volcanic debris avalanche deposit covering over 1550 km 2 on the southern flanks of the volcano and extending at least 70 km from the former summit. The avalanche followed a steep topographic gradient unobstructed by barriers, resulting in an unusually high area/volume ratio for the Colima deposit. The apparent coefficient of friction (fall height/distance traveled) for the Colima avalanche is 0.06, a low value similar to those of other large-volume deposits. The debris avalanche deposit contains 40-75% angular volcanic clasts from the ancestral cone, a small proportion of vesicular blocks that may be juvenile, and in distal exposures, rare carbonate clasts plucked from the underlying surface by the moving avalanche. Clasts range in size to over 20 m in diameter and are brecciated to different degrees, pulverized, and surrounded by a rock-flour matrix. The upper surface of the deposit shows prominent hummocky topography with closed depressions and surface boulders. A thick, coarse-grained, compositionally zoned scoria-fall layer on the upper northeastern slope of the volcano may have erupted at the time of collapse. A fine-grained surge layer is present beneath the avalanche deposit at one locality, apparently representing an initial blast event. Most of the missing volume of the ancestral volcano has since been restored at an average rate of 0.002 km 3/yr through repeated eruptions from the post-caldera cone. As a result, the southern slope of Volcán Colima may again be susceptible to collapse. Over 200,000 people are now living on primary or secondary deposits of the debris avalanche, and a repetition of this event would constitute a volcanic disaster of great magnitude. Ancestral Volcán Colima grew on the southern, trenchward flank of the earlier and larger volcano Nevado de

Characterisation of Geiger-mode avalanche photodiodes for medical imaging applications

Energy Technology Data Exchange (ETDEWEB)

Britvitch, I. [Swiss Federal Institute of Technology, CH-8092 Zurich (Switzerland)]. E-mail: Ilia.britvitch@psi.ch; Johnson, I. [Joint Institute for Nuclear Research, 141980 Dubna (Russian Federation); Renker, D. [Paul Scherrer Institut, CH-5232 Villigen PSI (Switzerland); Stoykov, A. [Paul Scherrer Institut, CH-5232 Villigen PSI (Switzerland); Joint Institute for Nuclear Research, 141980 Dubna (Russian Federation); Lorenz, E. [Swiss Federal Institute of Technology, CH-8092 Zurich (Switzerland); Max Planck Institute for Physics, 80805 Munich (Germany)

2007-02-01

Recently developed multipixel Geiger-mode avalanche photodiodes (G-APDs) are very promising candidates for the detection of light in medical imaging instruments (e.g. positron emission tomography) as well as in high-energy physics experiments and astrophysical applications. G-APDs are especially well suited for morpho-functional imaging (multimodality PET/CT, SPECT/CT, PET/MRI, SPECT/MRI). G-APDs have many advantages compared to conventional photosensors such as photomultiplier tubes because of their compact size, low-power consumption, high quantum efficiency and insensitivity to magnetic fields. Compared to avalanche photodiodes and PIN diodes, they are advantageous because of their high gain, reduced sensitivity to pick up and the so-called nuclear counter effect and lower noise. We present measurements of the basic G-APD characteristics: photon detection efficiency, gain, inter-cell crosstalk, dynamic range, recovery time and dark count rate.

Characterisation of Geiger-mode avalanche photodiodes for medical imaging applications

International Nuclear Information System (INIS)

Britvitch, I.; Johnson, I.; Renker, D.; Stoykov, A.; Lorenz, E.

2007-01-01

Recently developed multipixel Geiger-mode avalanche photodiodes (G-APDs) are very promising candidates for the detection of light in medical imaging instruments (e.g. positron emission tomography) as well as in high-energy physics experiments and astrophysical applications. G-APDs are especially well suited for morpho-functional imaging (multimodality PET/CT, SPECT/CT, PET/MRI, SPECT/MRI). G-APDs have many advantages compared to conventional photosensors such as photomultiplier tubes because of their compact size, low-power consumption, high quantum efficiency and insensitivity to magnetic fields. Compared to avalanche photodiodes and PIN diodes, they are advantageous because of their high gain, reduced sensitivity to pick up and the so-called nuclear counter effect and lower noise. We present measurements of the basic G-APD characteristics: photon detection efficiency, gain, inter-cell crosstalk, dynamic range, recovery time and dark count rate

Collisional avalanche exponentiation of runaway electrons in electrified plasmas

International Nuclear Information System (INIS)

Jayakumar, R.; Fleischmann, H.H.; Zweben, S.J.

1993-01-01

In contrast to earlier expectations, it is estimated that generation of runaway electrons from close collisions of existing runaways with cold plasma electrons can be significant even for small electric fields, whenever runaways can gain energies of about 20 MeV or more. In that case, the runaway population will grow exponentially with the energy spectrum showing an exponential decrease towards higher energies. Energy gains of the required magnitude may occur in large tokamak devices as well as in cosmic-ray generation. (orig.)

Large area avalanche MRS-photodiodes for nuclear spectroscopy

Energy Technology Data Exchange (ETDEWEB)

Ermalitski, F A; Zalesski, V B

1996-12-31

Problems of application of avalanche photodiodes (APD) in readout systems of nuclear spectrometers are considered. APD`s with a large sensitive area of a diameter 1-5 mm and a high multiplication coefficient 200-1000 are created. MPS-photodiodes provide for the energy resolution 80% at temperature 231 K for detecting gamma-quanta with energy 662 keV. 4 refs.

Statistical distributions of avalanche size and waiting times in an inter-sandpile cascade model

Science.gov (United States)

Batac, Rene; Longjas, Anthony; Monterola, Christopher

2012-02-01

Sandpile-based models have successfully shed light on key features of nonlinear relaxational processes in nature, particularly the occurrence of fat-tailed magnitude distributions and exponential return times, from simple local stress redistributions. In this work, we extend the existing sandpile paradigm into an inter-sandpile cascade, wherein the avalanches emanating from a uniformly-driven sandpile (first layer) is used to trigger the next (second layer), and so on, in a successive fashion. Statistical characterizations reveal that avalanche size distributions evolve from a power-law p(S)≈S-1.3 for the first layer to gamma distributions p(S)≈Sαexp(-S/S0) for layers far away from the uniformly driven sandpile. The resulting avalanche size statistics is found to be associated with the corresponding waiting time distribution, as explained in an accompanying analytic formulation. Interestingly, both the numerical and analytic models show good agreement with actual inventories of non-uniformly driven events in nature.

A new avalanche photo diode based readout for the crystal barrel calorimeter

Energy Technology Data Exchange (ETDEWEB)

Urban, Martin [Helmholtz-Institut fuer Strahlen- und Kernphysik, Nussallee 14-16, 53115 Bonn (Germany); Collaboration: CBELSA/TAPS-Collaboration

2015-07-01

The CBELSA/TAPS experiment at ELSA has proven successful in the measurement of double polarization observables in meson photoproduction off protons and neutrons. To be able to measure purely neutral reactions on a polarized neutron target with high efficiency, the main calorimeter consisting of 1320 CsI(Tl) crystals has to be integrated into the first level trigger. Key requirement to achieve this goal is an exchange of the existing PIN photo diode by a new avalanche photo diode (APD) readout. The main advantage of the new readout system is that it will provide timing information which allows a fast trigger signal. The energy resolution will remain compatible to the previous system. Besides the development of automated test routines for the front end electronics, the characterization of all APDs was successfully accomplished in Bonn. After tests with a 3 x 3 CsI(Tl) crystal matrix at the tagged photon beam facilities at ELSA and MAMI the first half of the Crystal Barrel was upgraded in 2014. This talk shows the result of the latest test measurements including the gain stabilization of the new APD readout electronics and presents the progress of the ongoing upgrade.

Electronic equipment and software for device 'FAZA'

International Nuclear Information System (INIS)

Avdeev, S.P.; Karnaukhov, V.A.; Kuznetsov, V.D.; Petrov, L.A.; Oeschler, H.; Lips, F.; Bart, R.

1992-01-01

Electronic equipment and software for the device FAZA are described. The device, designed for studying the nuclear multifragmentation process, consists of 5 time-of-flight telescopes, a position-sensitive avalanche chamber and 58 PM tubes. The time resolution of the time-of-flight telescopes is 0.5 ns, which allows a velocity resolution of 1.5%. The spatial resolution of the large avalanche counter is 4 mm, which allows angular resolution of 1 deg. Analogue signals from each PM tube come to two ADCs, to which strobes are supplied with a 400 ns shift. It allows codes corresponding to Cherenkov radiation and deexcitation of CsJ(Tl) to be distinguished in a two-dimensional plot. 8 refs.; 2 figs

Posttraumatic stress and other health consequences of catastrophic avalanches: A 16-year follow-up of survivors.

Science.gov (United States)

Thordardottir, Edda Bjork; Valdimarsdottir, Unnur Anna; Hansdottir, Ingunn; Resnick, Heidi; Shipherd, Jillian C; Gudmundsdottir, Berglind

2015-05-01

To date, no study has investigated the effects of avalanches on survivor's health beyond the first years. The aim of this study was to examine long-term health status 16 years after exposure to avalanches using a matched cohort design. Mental health, sleep quality and somatic symptoms among avalanche survivors (n=286) and non-exposed controls (n=357) were examined. Results showed that 16% of survivors currently experience avalanche-specific PTSD symptoms (PDS score>14). In addition, survivors presented with increased risk of PTSD hyperarousal symptoms (>85th percentile) (aRR=1.83; 98.3% CI [1.23-2.74]); sleep-related problems (PSQI score>5) (aRR=1.34; 95% CI [1.05-1.70]); PTSD-related sleep disturbances (PSQI-A score≥4) (aRR=1.86; 95% CI [1.30-2.67]); musculoskeletal and nervous system problems (aRR 1.43; 99% CI 1.06-1.93) and gastrointestinal problems (aRR 2.16; 99% CI 1.21-3.86) compared to the unexposed group. Results highlight the need for treatment for long-term PTSD symptoms and sleep disruption in disaster communities. Copyright © 2015 Elsevier Ltd. All rights reserved.

heat flow in a finite isolated pulsed avalanche semiconductor diode

African Journals Online (AJOL)

ES Obe

1981-03-01

Mar 1, 1981 ... high-power high-efficiency avalanche semiconductor devices. The ... computed, and useful practical design curves for a specified operation .... iv. For spherical shells of radius, ρ(x,y,z) = √x2+y2+z2. > R, the heat source.

A position sensitive parallel plate avalanche counter

International Nuclear Information System (INIS)

Lombardi, M.; Tan Jilian; Potenza, R.; D'amico, V.

1986-01-01

A position sensitive parallel plate avalanche counter with a distributed constant delay-line-cathode (PSAC) is described. The strips formed on the printed board were served as the cathode and the delay line for readout of signals. The detector (PSAC) was operated in isobutane gas at the pressure range from 10 to 20 torr. The position resolution is better than 1 mm and the time resolution is about 350 ps, for 252 Cf fission-spectrum source

Current oscillations in avalanche particle detectors with PNIPN-structure

International Nuclear Information System (INIS)

Lukin, K.A.

1995-08-01

The model of an avalanche high energy particle detector consisting of two pn-junctions, connected through an intrinsic semiconductor with a reverse biased voltage applied. This detector is able to generate the oscillatory response on the single particle passage through the structure. The possibility of oscillations leading to chaotic behaviour is pointed out

A simulated avalanche search and rescue mission induces temporary physiological and behavioural changes in military dogs.

Science.gov (United States)

Diverio, Silvana; Barbato, Olimpia; Cavallina, Roberta; Guelfi, Gabriella; Iaboni, Martina; Zasso, Renato; Di Mari, Walter; Santoro, Michele Matteo; Knowles, Toby G

2016-09-01

Saving human lives is of paramount importance in avalanche rescue missions. Avalanche military dogs represent an invaluable resource in these operations. However, their performance can be influenced by several environmental, social and transport challenges. If too severe, these are likely to activate a range of responses to stress, which might put at risk the dogs' welfare. The aim of this study was to assess the physiological and behavioural responses of a group of military dogs to a Simulated Avalanche Search and Rescue mission (SASR). Seventeen avalanche dogs from the Italian Military Force Guardia di Finanza (SAGF dogs) were monitored during a simulated search for a buried operator in an artificial avalanche area (SASR). Heart rate (HR), body temperature (RBT) and blood samples were collected at rest the day before the trial (T0), immediately after helicopter transport at the onset of the SASR (T1), after the discovery of the buried operator (T2) and 2h later (T3). Heart rate (HR), rectal body temperature (RBT), cortisol, aspartate aminotransferase (AST), creatine kinase (CK), non-esterified fatty acids (NEFA) and lactate dehydrogenase (LDH) were measured. During the search mission the behaviour of each SAGF dog was measured by focal animal sampling and qualitatively assessed by its handler and two observers. Inter-rater agreement was evaluated. Snow and environmental variables were also measured. All dogs successfully completed their search for the buried, simulated victim within 10min. The SASR was shown to exert significant increases on RBT, NEFA and cortisol (Pdog's search mission ability was found only for motivation, signalling behaviour, signs of stress and possessive reward playing. More time signalling was related to shorter search time. In conclusion, despite extreme environmental and training conditions only temporary physiological and behavioural changes were recorded in the avalanche dogs. Their excellent performance in successful simulated SASR

Progresses in the simulation of Resistive Plate Chambers in avalanche mode

Energy Technology Data Exchange (ETDEWEB)

Abbrescia, M.; Colaleo, A.; Iaselli, G.; Loddo, F.; Maggi, M.; Marangelli, B.; Natali, S.; Nuzzo, S.; Pugliese, G.; Ranieri, A.; Romano, F.; Altieri, S.; Bruno, G.; Gianini, G.; Ratti, S.P.; Viola, L.; Vitulo, P

1999-08-01

New results about the simulation of Resistive Plate Chambers are reported; particular emphasis is put in the understanding of charge spectra in regions where deviations from the pure avalanche mode of operation can be present.

The Chimborazo sector collapse and debris avalanche : deposit characteristics as evidence of emplacement mechanisms

OpenAIRE

Bernard, B.; Vries de, B. V.; Barba, D.; Leyrit, H.; Robin, Claude; Alcaraz, S.; Samaniego, Pablo

2008-01-01

Chimborazo is a Late Pleistocene to Holocene stratovolcano located at the southwest end of the main Ecuadorian volcanic arc. It experienced a large sector collapse and debris avalanche (DA) of the initial edifice (CH-1). This left a 4 km wide scar, removing 8.0 +/- 0.5 km(3) of the edifice. The debris avalanche deposit (DAD) is abundantly exposed throughout the Riobamba Basin to the Rio Chambo, more than 35 km southeast of the volcano. The DAD averages a thickness of 40 m, covers about 280 km...

Cataclysmic Rock Avalanche from El Capitan, Yosemite Valley, circa 3.6 ka

Science.gov (United States)

Stock, G. M.

2008-12-01

El Capitan in Yosemite Valley is one of the largest and most iconic granite faces in the world. Despite glacially steepened walls exceeding 90 degrees, a historic database shows relatively few rock falls from El Capitan in the past 150 years. However, a massive bouldery deposit beneath the southeast face suggests an earlier rock avalanche of unusually large size. Spatial analysis of airborne LiDAR data indicate that the rock avalanche deposit has a volume of ~2.70 x 106 m3, a maximum thickness of 18 m, and a runout distance of 660 m, roughly twice the horizontal extent of the adjacent talus. The deposit is very coarse on its distal edge, with individual boulder volumes up to 2500 m3. Cosmogenic 10Be exposure dates from boulders distributed across the deposit confirm this interpretation. Four 10Be samples are tightly clustered between 3.5 and 3.8 ka, with a mean age of 3.6 +/- 0.6 ka. A fifth sample gives a much older age of 22.0 ka, but a glacier occupied Yosemite Valley at this time, prohibiting deposition; thus, the older age likely results from exposure on the cliff face prior to failure. The similarity of ages and overall morphology suggest that the entire deposit formed during a single event. The mean exposure age coincides with inferred Holocene rupture of the northern Owens Valley and/or White Mountain fault(s) between 3.3 and 3.8 ka (Lee et al., 2001; Bacon and Pezzopane, 2007). This time coincidence, combined with the fact that historic rupture of the Owens Valley fault in A.D. 1872 generated numerous large rock falls in Yosemite Valley, strongly suggests that the El Capitan rock avalanche was triggered by a seismic event along the eastern margin of the Sierra Nevada circa 3.6 ka. As there is not an obvious "scar" on the expansive southeast face, the exact source area of the rock avalanche is not yet known. Detrital apatite U-Th/(He) thermochronometry can determine the elevation(s) from which rock fall boulders originate, but significant inter-sample age

Data collapse and critical dynamics in neuronal avalanche data

Science.gov (United States)

Butler, Thomas; Friedman, Nir; Dahmen, Karin; Beggs, John; Deville, Lee; Ito, Shinya

2012-02-01

The tasks of information processing, computation, and response to stimuli require neural computation to be remarkably flexible and diverse. To optimally satisfy the demands of neural computation, neuronal networks have been hypothesized to operate near a non-equilibrium critical point. In spite of their importance for neural dynamics, experimental evidence for critical dynamics has been primarily limited to power law statistics that can also emerge from non-critical mechanisms. By tracking the firing of large numbers of synaptically connected cortical neurons and comparing the resulting data to the predictions of critical phenomena, we show that cortical tissues in vitro can function near criticality. Among the most striking predictions of critical dynamics is that the mean temporal profiles of avalanches of widely varying durations are quantitatively described by a single universal scaling function (data collapse). We show for the first time that this prediction is confirmed in neuronal networks. We also show that the data have three additional features predicted by critical phenomena: approximate power law distributions of avalanche sizes and durations, samples in subcritical and supercritical phases, and scaling laws between anomalous exponents.

Discrimination Voltage and Overdrive Bias Dependent Performance Evaluation of Passively Quenched SiC Single-Photon-Counting Avalanche Photodiodes

International Nuclear Information System (INIS)

Liu Fei; Yang Sen; Zhou Dong; Lu Hai; Zhang Rong; Zheng You-Dou

2015-01-01

In many critical civil and emerging military applications, low-level UV detection, sometimes at single photon level, is highly desired. In this work, a mesa-type 4H-SiC UV avalanche photodiode (APD) is designed and fabricated, which exhibits low leakage current and high avalanche gain. When studied by using a passive quenching circuit, the APD exhibits self-quenching characteristics due to its high differential resistance in the avalanche region. The single photon detection efficiency and dark count rate of the APD are evaluated as functions of discrimination voltage and over-drive voltage. The optimized operation conditions of the single photon counting APD are discussed. (paper)

Avalanche diode having reduced dark current and method for its manufacture

Science.gov (United States)

Davids, Paul; Starbuck, Andrew Lee; Pomerene, Andrew T. S.

2017-08-29

An avalanche diode includes an absorption region in a germanium body epitaxially grown on a silicon body including a multiplication region. Aspect-ratio trapping is used to suppress dislocation growth in the vicinity of the absorption region.

Secondary instability in drift wave turbulence as a mechanism for avalanche and zonal flow formation

International Nuclear Information System (INIS)

Diamond, P.H.; Champeaux, S.; Malkov, M.

2001-01-01

We report on recent developments in the theory of secondary instability in drift-ITG turbulence. Specifically, we explore secondary instability as a mechanism for avalanche formation. A theory of radially extended streamer cell formation and self-regulation is presented. Aspects of streamer structure and dynamics are used to estimate the variance of the drift-wave induced flux. The relation between streamer cell structures and the avalanche concept is discussed, as are the implications of our results for transport modeling. (author)

Textural analysis of particles from El Zaguán debris avalanche deposit, Nevado de Toluca volcano, Mexico: Evidence of flow behavior during emplacement

Science.gov (United States)

Caballero, Lizeth; Capra, Lucia

2011-02-01

El Zaguán deposit originated at 28,000 yrs. B.P. from the flank collapse of Nevado de Toluca, a dacitic stratovolcano of the Transmexican Volcanic Belt. Scanning Electron Microprobe analyses (SEM) were performed on some particles from this deposit to observe microtextures produced during transport and emplacement of the debris avalanche flow. Particles from 2ϕ (250 μm), 0ϕ (1 mm) and - 2ϕ (4 mm) granulometric classes were randomly selected at different outcrops, and their surface textures were described. The observed textures are divided in two groups, Basal and Upper textures, each one indicating different clast interactions. Basal textures are observed predominantly in the lower part of the deposit and consist of parallel ridges, parallel grooves, scratches and lips. Upper textures are mainly present in the upper part of the deposit and consisted of fractures, percussion marks, and broken or grinded crystals. These characteristics, coupled with field observations such as the presence of clastic dikes and deformed lacustrine mega-blocks, indicate that the basal part of the debris avalanche was moving in a partially liquefied state. By contrast, the particles in the upper part were able to move freely, interacting by collision. These microscopic textures are in agreement with previously described emplacement behaviors in debris avalanches of volcanic origin, suggesting a stratified flow dominated by different transport and depositional mechanisms depending upon flow depth and possible fluid content at their base.

The Non-Equilibrium Statistical Distribution Function for Electrons and Holes in Semiconductor Heterostructures in Steady-State Conditions

Directory of Open Access Journals (Sweden)

Krzysztof Jόzwikowska

2015-06-01

Full Text Available The main goal of this work is to determine a statistical non-equilibrium distribution function for the electron and holes in semiconductor heterostructures in steady-state conditions. Based on the postulates of local equilibrium, as well as on the integral form of the weighted Gyarmati’s variational principle in the force representation, using an alternative method, we have derived general expressions, which have the form of the Fermi–Dirac distribution function with four additional components. The physical interpretation of these components has been carried out in this paper. Some numerical results of a non-equilibrium distribution function for an electron in HgCdTe structures are also presented.

Runaway electron beam in atmospheric pressure discharges

International Nuclear Information System (INIS)

Oreshkin, E V; Barengolts, S A; Chaikovsky, S A; Oreshkin, V I

2015-01-01

A numerical simulation was performed to study the formation of a runaway electron (RAE) beam from an individual emission zone in atmospheric pressure air discharges with a highly overvolted interelectrode gap. It is shown that the formation of a RAE beam in discharges at high overvoltages is much contributed by avalanche processes. (paper)

The characteristic patterns of neuronal avalanches in mice under anesthesia and at rest: An investigation using constrained artificial neural networks

Science.gov (United States)

Knöpfel, Thomas; Leech, Robert

2018-01-01

Local perturbations within complex dynamical systems can trigger cascade-like events that spread across significant portions of the system. Cascades of this type have been observed across a broad range of scales in the brain. Studies of these cascades, known as neuronal avalanches, usually report the statistics of large numbers of avalanches, without probing the characteristic patterns produced by the avalanches themselves. This is partly due to limitations in the extent or spatiotemporal resolution of commonly used neuroimaging techniques. In this study, we overcome these limitations by using optical voltage (genetically encoded voltage indicators) imaging. This allows us to record cortical activity in vivo across an entire cortical hemisphere, at both high spatial (~30um) and temporal (~20ms) resolution in mice that are either in an anesthetized or awake state. We then use artificial neural networks to identify the characteristic patterns created by neuronal avalanches in our data. The avalanches in the anesthetized cortex are most accurately classified by an artificial neural network architecture that simultaneously connects spatial and temporal information. This is in contrast with the awake cortex, in which avalanches are most accurately classified by an architecture that treats spatial and temporal information separately, due to the increased levels of spatiotemporal complexity. This is in keeping with reports of higher levels of spatiotemporal complexity in the awake brain coinciding with features of a dynamical system operating close to criticality. PMID:29795654

Avalanche analysis from multi-electrode ensemble recordings in cat, monkey and human cerebral cortex during wakefulness and sleep.

Directory of Open Access Journals (Sweden)

Nima eDehghani

2012-08-01

Full Text Available Self-organized critical states are found in many natural systems, from earthquakes to forest fires, they have also been observed in neural systems, particularly, in neuronal cultures. However, the presence of critical states in the awake brain remains controversial. Here, we compared avalanche analyses performed on different in vivo preparations during wakefulness, slow-wave sleep and REM sleep, using high-density electrode arrays in cat motor cortex (96 electrodes, monkey motor cortex and premotor cortex and human temporal cortex (96 electrodes in epileptic patients. In neuronal avalanches defined from units (up to 160 single units, the size of avalanches never clearly scaled as power-law, but rather scaled exponentially or displayed intermediate scaling. We also analyzed the dynamics of local field potentials (LFPs and in particular LFP negative peaks (nLFPs among the different electrodes (up to 96 sites in temporal cortex or up to 128 sites in adjacent motor and pre-motor cortices. In this case, the avalanches defined from nLFPs displayed power-law scaling in double logarithmic representations, as reported previously in monkey. However, avalanche defined as positive LFP (pLFP peaks, which are less directly related to neuronal firing, also displayed apparent power-law scaling. Closer examination of this scaling using the more reliable cumulative distribution function (CDF and other rigorous statistical measures, did not confirm power-law scaling. The same pattern was seen for cats, monkey and human, as well as for different brain states of wakefulness and sleep. We also tested other alternative distributions. Multiple exponential fitting yielded optimal fits of the avalanche dynamics with bi-exponential distributions. Collectively, these results show no clear evidence for power-law scaling or self-organized critical states in the awake and sleeping brain of mammals, from cat to man.

Group Dynamics and Decision Making: Backcountry Recreationists in Avalanche Terrain

Science.gov (United States)

Bright, Leslie Shay

2010-01-01

The purpose of this study was to describe and determine the prevalence of decision-making characteristics of recreational backcountry groups when making a decision of where to travel and ride in avalanche terrain from the perspective of individuals. Decision-making characteristics encompassed communication, decision-making processes, leadership,…

Tuning magnetization avalanches in Mn12-acetate

Science.gov (United States)

Wen, Bo; McHugh, S.; Ma, Xiang; Sarachik, M. P.; Myasoedov, Y.; Shtrikman, H.; Zeldov, E.; Bagai, R.; Christou, G.

2009-03-01

We report the results of a systematic study of magnetic avalanches (abrupt magnetization reversals) in the molecular magnet Mn12-acetate using a micron-sized Hall sensor array. Measurements were taken for: (a) fixed magnetic field (constant barrier against spin reversal); and (b) fixed energy release obtained by adjusting the barrier and δM. A detailed comparison with the theory of magnetic deflagration of Garanin and Chudnovsky [1] will be presented and discussed. [1] D. A. Garanin and E. M. Chudnovsky, Phys. Rev. B 76, 054410 (2007)

Readout of scintillator light with avalanche photodiodes for positron emission tomography

International Nuclear Information System (INIS)

Chen, Ruru; Fremout, A.; Tavernier, S.; Bruyndonckx, P.; Clement, D.; Loude, J.-F.; Morel, C.

1999-01-01

The noise properties and other relevant characteristics of avalanche photodiodes have been investigated with the perspective of replacing photomultiplier tubes in positron emission tomography. It is clearly demonstrated that they are a valid alternative to photomultiplier tubes in this application

Characteristics of debris avalanche deposits inferred from source volume estimate and hummock morphology around Mt. Erciyes, central Turkey

Science.gov (United States)

Hayakawa, Yuichi S.; Yoshida, Hidetsugu; Obanawa, Hiroyuki; Naruhashi, Ryutaro; Okumura, Koji; Zaiki, Masumi; Kontani, Ryoichi

2018-02-01

Debris avalanches caused by volcano sector collapse often form characteristic depositional landforms such as hummocks. Sedimentological and geomorphological analyses of debris avalanche deposits (DADs) are crucial to clarify the size, mechanisms, and emplacement of debris avalanches. We describe the morphology of hummocks on the northeastern flank of Mt. Erciyes in Kayseri, central Turkey, likely formed in the late Pleistocene. Using a remotely piloted aircraft system (RPAS) and the structure-from-motion and multi-view stereo (SfM-MVS) photogrammetry, we obtained high-definition digital elevation model (DEM) and orthorectified images of the hummocks to investigate their geometric features. We estimated the source volume of the DAD by reconstructing the topography of the volcano edifice using a satellite-based DEM. We examined the topographic cross sections based on the slopes around the scar regarded as remnant topography. Spatial distribution of hummocks is anomalously concentrated at a certain distance from the source, unlike those that follow the distance-size relationship. The high-definition land surface data by RPAS and SfM revealed that many of the hummocks are aligned toward the flow direction of the debris avalanche, suggesting that the extensional regime of the debris avalanche was dominant. However, some displaced hummocks were also found, indicating that the compressional regime of the flow contributed to the formation of hummocks. These indicate that the flow and emplacement of the avalanche were constrained by the topography. The existing caldera wall forced the initial eastward flow to move northward, and the north-side caldera wall forced the flow into the narrow and steepened outlet valley where the sliding debris underwent a compressional regime, and out into the unconfined terrain where the debris was most likely emplaced on an extensional regime. Also, the estimated volume of 12-15 × 108 m3 gives a mean thickness of 60-75 m, which is much

HgCdTe APD-based linear-mode photon counting components and ladar receivers

Science.gov (United States)

Jack, Michael; Wehner, Justin; Edwards, John; Chapman, George; Hall, Donald N. B.; Jacobson, Shane M.

2011-05-01

Linear mode photon counting (LMPC) provides significant advantages in comparison with Geiger Mode (GM) Photon Counting including absence of after-pulsing, nanosecond pulse to pulse temporal resolution and robust operation in the present of high density obscurants or variable reflectivity objects. For this reason Raytheon has developed and previously reported on unique linear mode photon counting components and modules based on combining advanced APDs and advanced high gain circuits. By using HgCdTe APDs we enable Poisson number preserving photon counting. A metric of photon counting technology is dark count rate and detection probability. In this paper we report on a performance breakthrough resulting from improvement in design, process and readout operation enabling >10x reduction in dark counts rate to ~10,000 cps and >104x reduction in surface dark current enabling long 10 ms integration times. Our analysis of key dark current contributors suggest that substantial further reduction in DCR to ~ 1/sec or less can be achieved by optimizing wavelength, operating voltage and temperature.

A high current, high speed pulser using avalanche transistors

International Nuclear Information System (INIS)

Hosono, Yoneichi; Hasegawa, Ken-ichi

1985-01-01

A high current, high speed pulser for the beam pulsing of a linear accelerator is described. It uses seven avalanche transistors in cascade. Design of a trigger circuit to obtain fast rise time is discussed. The characteristics of the pulser are : (a) Rise time = 0.9 ns (FWHM) and (d) Life time asymptotically equals 2000 -- 3000 hr (at 50 Hz). (author)

2D dark-count-rate modeling of PureB single-photon avalanche diodes in a TCAD environment

Science.gov (United States)

Knežević, Tihomir; Nanver, Lis K.; Suligoj, Tomislav

2018-02-01

PureB silicon photodiodes have nm-shallow p+n junctions with which photons/electrons with penetration-depths of a few nanometer can be detected. PureB Single-Photon Avalanche Diodes (SPADs) were fabricated and analysed by 2D numerical modeling as an extension to TCAD software. The very shallow p+ -anode has high perimeter curvature that enhances the electric field. In SPADs, noise is quantified by the dark count rate (DCR) that is a measure for the number of false counts triggered by unwanted processes in the non-illuminated device. Just like for desired events, the probability a dark count increases with increasing electric field and the perimeter conditions are critical. In this work, the DCR was studied by two 2D methods of analysis: the "quasi-2D" (Q-2D) method where vertical 1D cross-sections were assumed for calculating the electron/hole avalanche-probabilities, and the "ionization-integral 2D" (II-2D) method where crosssections were placed where the maximum ionization-integrals were calculated. The Q-2D method gave satisfactory results in structures where the peripheral regions had a small contribution to the DCR, such as in devices with conventional deepjunction guard rings (GRs). Otherwise, the II-2D method proved to be much more precise. The results show that the DCR simulation methods are useful for optimizing the compromise between fill-factor and p-/n-doping profile design in SPAD devices. For the experimentally investigated PureB SPADs, excellent agreement of the measured and simulated DCR was achieved. This shows that although an implicit GR is attractively compact, the very shallow pn-junction gives a risk of having such a low breakdown voltage at the perimeter that the DCR of the device may be negatively impacted.

Snow avalanche hazard of the Krkonose National Park, Czech Republic

Czech Academy of Sciences Publication Activity Database

Blahůt, Jan; Klimeš, Jan; Balek, Jan; Hájek, P.; Červená, L.; Lysák, J.

2017-01-01

Roč. 13, č. 2 (2017), s. 86-90 ISSN 1744-5647 R&D Projects: GA MV VG20132015115 Institutional support: RVO:67985891 Keywords : snow avalanches * hazard * inventory * hazard mitigation * Krkonoše Subject RIV: DE - Earth Magnetism, Geodesy, Geography OBOR OECD: Physical geography Impact factor: 2.174, year: 2016

Single Photon Sensitive HgCdTe Avalanche Photodiode Detector (APD), Phase II

Data.gov (United States)

National Aeronautics and Space Administration — Leveraging Phase I SBIR successes, in Phase II, a single photon sensitive LIDAR receiver will be fabricated and delivered to NASA. In Phase I, high-gain,...

Cosmogenic Nuclide Exposure Dating of the Tiltill Rock Avalanche, Yosemite National Park

Science.gov (United States)

Ford, K. R.; Pluhar, C. J.; Stone, J. O.; Stock, G. M.; Zimmerman, S. R.

2013-12-01

Yosemite National Park serves as an excellent natural laboratory for studying rock falls and rock avalanches because these are the main processes modifying the nearly vertical slopes of this recently glaciated landscape. Mass wasting represents a significant hazard in the region and the database of previous rock falls and other mass wasting events in Yosemite is extensive, dating back to the mid-1800s. However, this record is too short to capture the recurrence characteristics and triggering mechanisms of the very largest events, necessitating studies of the geologic record of mass wasting. Rock falls and rock avalanches are readily dated by cosmogenic nuclide methods due to their instantaneous formation, and results can be tied to triggering events such as seismic activity (e.g. Stock et al., 2009). Here, we apply exposure dating to the Holocene Tiltill rock avalanche north of Hetch Hetchy Reservoir. The deposit comprises what appear to be two separate lobes of rock and debris, yielding a total volume of ~3.1 x 106 m3. Assuming an erosion rate of 0.0006 cm/yr and neglecting snowpack shielding, preliminary data suggest a mean exposure age of 11,000 + 600 year B.P. for both deposits, indicating that they were emplaced in a single event. The age of the Tiltill 'slide' is similar to earthquakes on the Owens Valley Fault between 10,800 + 600 and 10,200 + 200 cal year B.P. (Bacon, 2007) and the White Mountain Fault, ~10,000 cal year B.P. (Reheis, 1996; DePolo, 1989). Given that movement on the Owens Valley fault in 1872 caused a number of rock falls in Yosemite and the coincidence of ages between the Tiltill 'slide' and paleoseismic events, a large earthquake in Eastern Sierra Nevada may have triggered this event. Other trigger events are also possibilities, but only through compilation of a database of large rock avalanches can statistically significant groupings of events begin to demonstrate whether seismic triggering is a dominant process.

Generation efficiency of single-photon current pulses in the Geiger mode of silicon avalanche photodiodes

International Nuclear Information System (INIS)

Verkhovtseva, A. V.; Gergel, V. A.

2009-01-01

Statistical fluctuations of the avalanche's multiplication efficiency were studied as applied to the single-photon (Geiger) mode of avalanche photodiodes. The distribution function of partial multiplication factors with an anomalously wide (of the order of the average) dispersion was obtained. Expressions for partial feedback factors were derived in terms of the average gain and the corresponding dependences on the diode's overvoltage were calculated. Final expressions for the photon-electric pulse's conversion were derived by averaging corresponding formulas over the coordinate of initiating photoelectron generation using the functions of optical photon absorption in silicon.

Radiation damage effect on avalanche photodiodes

CERN Document Server

Baccaro, S; Cavallari, F; Da Ponte, V; Deiters, K; Denes, P; Diemoz, M; Kirn, Th; Lintern, A L; Longo, E; Montecchi, M; Musienko, Y; Pansart, J P; Renker, D; Reucroft, S; Rosi, G; Rusack, R; Ruuska, D; Stephenson, R; Torbet, M J

1999-01-01

Avalanche Photodiodes have been chosen as photon sensors for the electromagnetic calorimeter of the CMS experiment at the LHC. These sensors should operate in the 4T magnetic field of the experiment. Because of the high neutron radiation in the detector extensive studies have been done by the CMS collaboration on the APD neutron radiation damage. The characteristics of these devices after irradiation have been analized, with particular attention to the quantum efficiency and the dark current. The recovery of the radiation induced dark current has been studied carefully at room temperature and at slightly lower and higher temperatures. The temperature dependence of the defects decay-time has been evaluated.

Practical photon number detection with electric field-modulated silicon avalanche photodiodes.

Science.gov (United States)

Thomas, O; Yuan, Z L; Shields, A J

2012-01-24

Low-noise single-photon detection is a prerequisite for quantum information processing using photonic qubits. In particular, detectors that are able to accurately resolve the number of photons in an incident light pulse will find application in functions such as quantum teleportation and linear optics quantum computing. More generally, such a detector will allow the advantages of quantum light detection to be extended to stronger optical signals, permitting optical measurements limited only by fluctuations in the photon number of the source. Here we demonstrate a practical high-speed device, which allows the signals arising from multiple photon-induced avalanches to be precisely discriminated. We use a type of silicon avalanche photodiode in which the lateral electric field profile is strongly modulated in order to realize a spatially multiplexed detector. Clearly discerned multiphoton signals are obtained by applying sub-nanosecond voltage gates in order to restrict the detector current.

Effect of surface fields on the dynamic resistance of planar HgCdTe mid-wavelength infrared photodiodes

Energy Technology Data Exchange (ETDEWEB)

He, Kai; Wang, Xi; Zhang, Peng; Chen, Yi-Yu [Key Laboratory of Infrared Imaging Materials and Detectors, Shanghai Institute of Technical Physics, Chinese Academy of Sciences, Shanghai 200083 (China); University of Chinese Academy of Sciences, Beijing 100049 (China); Zhou, Song-Min; Xie, Xiao-Hui; Lin, Chun, E-mail: chun-lin@mail.sitp.ac.cn; Ye, Zhen-Hua; Wang, Jian-Xin; Zhang, Qin-Yao, E-mail: qinyao@mail.sitp.ac.cn [Key Laboratory of Infrared Imaging Materials and Detectors, Shanghai Institute of Technical Physics, Chinese Academy of Sciences, Shanghai 200083 (China); Li, Yang [Graduate School of Information Science and Technology, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-8656 (Japan)

2015-05-28

This work investigates the effect of surface fields on the dynamic resistance of a planar HgCdTe mid-wavelength infrared photodiode from both theoretical and experimental aspects, considering a gated n-on-p diode with the surface potential of its p-region modulated. Theoretical models of the surface leakage current are developed, where the surface tunnelling current in the case of accumulation is expressed by modifying the formulation of bulk tunnelling currents, and the surface channel current for strong inversion is simulated with a transmission line method. Experimental data from the fabricated devices show a flat-band voltage of V{sub FB}=−5.7 V by capacitance-voltage measurement, and then the physical parameters for bulk properties are determined from the resistance-voltage characteristics of the diode working at a flat-band gate voltage. With proper values of the modeling parameters such as surface trap density and channel electron mobility, the theoretical R{sub 0}A product and corresponding dark current calculated from the proposed model as functions of the gate voltage V{sub g} demonstrate good consistency with the measured values. The R{sub 0}A product remarkably degenerates when V{sub g} is far below or above V{sub FB} because of the surface tunnelling current or channel current, respectively; and it attains the maximum value of 5.7×10{sup 7} Ω · cm{sup 2} around the transition between surface depletion and weak inversion when V{sub g}≈−4 V, which might result from reduced generation-recombination current.

Burial duration, depth and air pocket explain avalanche survival patterns in Austria and Switzerland.

Science.gov (United States)

Procter, Emily; Strapazzon, Giacomo; Dal Cappello, Tomas; Zweifel, Benjamin; Würtele, Andreas; Renner, Andreas; Falk, Markus; Brugger, Hermann

2016-08-01

To calculate the first Austrian avalanche survival curve and update a Swiss survival curve to explore survival patterns in the Alps. Avalanche accidents occurring between 2005/06 and 2012/13 in Austria and Switzerland were collected. Completely buried victims (i.e. burial of the head and chest) in open terrain with known outcome (survived or not survived) were included in the analysis. Extrication and survival curves were calculated using the Turnbull algorithm, as in previous studies. 633 of the 796 completely buried victims were included (Austria n=333, Switzerland n=300). Overall survival was 56% (Austria 59%; Switzerland 52%; p=0.065). Time to extrication was shorter in Austria for victims buried ≤60min (p15min. The survival curves resembled those previously published and support the idea that underlying survival patterns are reproducible. The results are in accordance with current recommendations for management of avalanche victims and serve as a reminder that expedient companion rescue within a few minutes is critical for survival. An air pocket was shown to be a positive prognostic factor for survival. Copyright © 2016 Elsevier Ireland Ltd. All rights reserved.

A silicon avalanche photodiode detector circuit for Nd:YAG laser scattering

International Nuclear Information System (INIS)

Hsieh, C.L.; Haskovec, J.; Carlstrom, T.N.; DeBoo, J.C.; Greenfield, C.M.; Snider, R.T.; Trost, P.

1990-06-01

A silicon avalanche photodiode with an internal gain of about 50 to 100 is used in a temperature controlled environment to measure the Nd:YAG laser Thomson scattered spectrum in the wavelength range from 700 to 1150 nm. A charge sensitive preamplifier has been developed for minimizing the noise contribution from the detector electronics. Signal levels as low as 20 photoelectrons (S/N = 1) can be detected. Measurements show that both the signal and the variance of the signal vary linearly with the input light level over the range of interest, indicating Poisson statistics. The signal is processed using a 100 ns delay line and a differential amplifier which subtracts the low frequency background light component. The background signal is amplified with a computer controlled variable gain amplifier and is used for an estimate of the measurement error, calibration, and Z eff measurements of the plasma. The signal processing has been analyzed using a theoretical model to aid the system design and establish the procedure for data error analysis. 4 refs., 5 figs

Azimuthal spread of the avalanche in proportional chambers

International Nuclear Information System (INIS)

Okuno, H.; Fischer, J.; Radeka, V.; Walenta, A.H.

1978-10-01

The angular distribution of the avalanche around the anode wire in the gas proportional counter is determined by measuring the distribution of positive ions arriving on cathode strips surrounding the anode wire for each single event. The shape and width of the distribution depend on such factors as the gas gain, the anode diameter, the counting gas and the primary ionization density. Effects of these factors are studied systematically, and their importance for practical counter applications is discussed

Research and development on a sub 100 PICO second time-of-flight system based on silicon avalanche diodes

Energy Technology Data Exchange (ETDEWEB)

Choi, Y.; Hirsch, A.; Hauger, A.; Scharenberg, R.; Tincknell, M. [Purdue Univ., West Lafayette, IN (United States); Rai, G. [Lawrence Berkeley Lab., CA (United States)

1991-12-31

Particle identification requires a momentum measurement and a second independent determination either energy loss (dE/dx) or time of flight (TOF). To cover a momentum range from 0.1 GeV/c to 1.5 GeV/c in the STAR detector requires both the dE/dx and TOF techniques. This research is designed to develop the avalanche diode (AVD) detectors for TOF systems and evaluate their performance. The test of a small prototype system would be carried out at Purdue and at accelerator test beam sites. The Purdue group has developed a complete test setup for evaluating the time resolution of the AVD`s which includes fast-slow electronic channels, CAMAC based electronic modules and a temperature controlled environment. The AVDs also need to be tested in a 0.5 tesla magnetic field. The Purdue group would augment this test set up to include a magnetic field.

Subsampling effects in neuronal avalanche distributions recorded in vivo

Directory of Open Access Journals (Sweden)

Munk Matthias HJ

2009-04-01

Full Text Available Abstract Background Many systems in nature are characterized by complex behaviour where large cascades of events, or avalanches, unpredictably alternate with periods of little activity. Snow avalanches are an example. Often the size distribution f(s of a system's avalanches follows a power law, and the branching parameter sigma, the average number of events triggered by a single preceding event, is unity. A power law for f(s, and sigma = 1, are hallmark features of self-organized critical (SOC systems, and both have been found for neuronal activity in vitro. Therefore, and since SOC systems and neuronal activity both show large variability, long-term stability and memory capabilities, SOC has been proposed to govern neuronal dynamics in vivo. Testing this hypothesis is difficult because neuronal activity is spatially or temporally subsampled, while theories of SOC systems assume full sampling. To close this gap, we investigated how subsampling affects f(s and sigma by imposing subsampling on three different SOC models. We then compared f(s and sigma of the subsampled models with those of multielectrode local field potential (LFP activity recorded in three macaque monkeys performing a short term memory task. Results Neither the LFP nor the subsampled SOC models showed a power law for f(s. Both, f(s and sigma, depended sensitively on the subsampling geometry and the dynamics of the model. Only one of the SOC models, the Abelian Sandpile Model, exhibited f(s and sigma similar to those calculated from LFP activity. Conclusion Since subsampling can prevent the observation of the characteristic power law and sigma in SOC systems, misclassifications of critical systems as sub- or supercritical are possible. Nevertheless, the system specific scaling of f(s and sigma under subsampling conditions may prove useful to select physiologically motivated models of brain function. Models that better reproduce f(s and sigma calculated from the physiological

Collisional avalanche exponentiation of run-away electrons in electrified plasmas

International Nuclear Information System (INIS)

Jayakumar, R.; Fleischmann, H.H.; Zweben, S.J.; Cornell Univ., Ithaca, NY

1992-07-01

In contrast to earlier expectations, it is estimated that generation of runaway electrons from close collisions of existing runaways with cold plasma electrons can be significant even for small electric fields, whenever runaways can gain energies of about 20 MeV or more. In that case, the runaway population will grow exponentially with the energy spectrum showing an exponential decrease towards higher energies.Energy gains of the required magnitude may occur in large Tokamak devices as well as in cosmic-ray generation

CMOS-based avalanche photodiodes for direct particle detection

International Nuclear Information System (INIS)

Stapels, Christopher J.; Squillante, Michael R.; Lawrence, William G.; Augustine, Frank L.; Christian, James F.

2007-01-01

Active Pixel Sensors (APSs) in complementary metal-oxide-semiconductor (CMOS) technology are augmenting Charge-Coupled Devices (CCDs) as imaging devices and cameras in some demanding optical imaging applications. Radiation Monitoring Devices are investigating the APS concept for nuclear detection applications and has successfully migrated avalanche photodiode (APD) pixel fabrication to a CMOS environment, creating pixel detectors that can be operated with internal gain as proportional detectors. Amplification of the signal within the diode allows identification of events previously hidden within the readout noise of the electronics. Such devices can be used to read out a scintillation crystal, as in SPECT or PET, and as direct-conversion particle detectors. The charge produced by an ionizing particle in the epitaxial layer is collected by an electric field within the diode in each pixel. The monolithic integration of the readout circuitry with the pixel sensors represents an improved design compared to the current hybrid-detector technology that requires wire or bump bonding. In this work, we investigate designs for CMOS APD detector elements and compare these to typical values for large area devices. We characterize the achievable detector gain and the gain uniformity over the active area. The excess noise in two different pixel structures is compared. The CMOS APD performance is demonstrated by measuring the energy spectra of X-rays from 55 Fe

Reforestation and land use change as drivers for a decrease of avalanche damage in mid-latitude mountains (NW Spain)

Science.gov (United States)

García-Hernández, Cristina; Ruiz-Fernández, Jesús; Sánchez-Posada, Covadonga; Pereira, Susana; Oliva, Marc; Vieira, Gonçalo

2017-06-01

Natural conditions that explain the triggering of snow avalanches are becoming better-known, but our understanding of how socio-environmental changes can influence the occurrence of damaging avalanches is still limited. This study analyses the evolution of snow avalanche damage in the Asturian Massif (NW Spain) between 1800 and 2015, paying special attention to changes in land-use and land-cover patterns. A damage index has been performed using historical sources, photointerpretation and fieldwork-based data, which were introduced in a GIS and processed by means of statistical analysis. Mapping allowed connecting spatiotemporal variations of damage and changes in human-environment interactions. The total number of victims was 342 (192 dead and 150 injured). Results show stability in the number of avalanches during the study period, but a progressive decrease in the damage per avalanche. Changes in land use explain the evolution of damage and its spatial/temporal behaviour. The role played by vegetation cover is at the root of this process: damage was the highest during the late 19th and early 20th centuries, when a massive deforestation process affected the protective forest. This deforestation was the result of demographic growth and intensive grazing, disentailment laws and emerging coal mining. Since the mid-20th century, the transformation of a traditional land-management system based on overexploitation into a system based on land marginalization and reforestation, together with the decline of deforestation due to industrial and legal causes, resulted in the decrease of avalanches that affected settlements (mostly those released below the potential timberline). The decrease of damage has been sharper in the western sector of the Asturian Massif, where oak deforestation was very intense in the past and where lithology allows for a more successful ecological succession at present. Taking into account that reforestation can be observed in mountain environments of

Characteristics of debris avalanche deposits inferred from source volume estimate and hummock morphology around Mt. Erciyes, central Turkey

Directory of Open Access Journals (Sweden)

Y. S. Hayakawa

2018-02-01

Full Text Available Debris avalanches caused by volcano sector collapse often form characteristic depositional landforms such as hummocks. Sedimentological and geomorphological analyses of debris avalanche deposits (DADs are crucial to clarify the size, mechanisms, and emplacement of debris avalanches. We describe the morphology of hummocks on the northeastern flank of Mt. Erciyes in Kayseri, central Turkey, likely formed in the late Pleistocene. Using a remotely piloted aircraft system (RPAS and the structure-from-motion and multi-view stereo (SfM–MVS photogrammetry, we obtained high-definition digital elevation model (DEM and orthorectified images of the hummocks to investigate their geometric features. We estimated the source volume of the DAD by reconstructing the topography of the volcano edifice using a satellite-based DEM. We examined the topographic cross sections based on the slopes around the scar regarded as remnant topography. Spatial distribution of hummocks is anomalously concentrated at a certain distance from the source, unlike those that follow the distance–size relationship. The high-definition land surface data by RPAS and SfM revealed that many of the hummocks are aligned toward the flow direction of the debris avalanche, suggesting that the extensional regime of the debris avalanche was dominant. However, some displaced hummocks were also found, indicating that the compressional regime of the flow contributed to the formation of hummocks. These indicate that the flow and emplacement of the avalanche were constrained by the topography. The existing caldera wall forced the initial eastward flow to move northward, and the north-side caldera wall forced the flow into the narrow and steepened outlet valley where the sliding debris underwent a compressional regime, and out into the unconfined terrain where the debris was most likely emplaced on an extensional regime. Also, the estimated volume of 12–15 × 108 m3 gives a mean thickness of

Numerical modeling of debris avalanches at Nevado de Toluca (Mexico): implications for hazard evaluation and mapping

Science.gov (United States)

Grieco, F.; Capra, L.; Groppelli, G.; Norini, G.

2007-05-01

The present study concerns the numerical modeling of debris avalanches on the Nevado de Toluca Volcano (Mexico) using TITAN2D simulation software, and its application to create hazard maps. Nevado de Toluca is an andesitic to dacitic stratovolcano of Late Pliocene-Holocene age, located in central México near to the cities of Toluca and México City; its past activity has endangered an area with more than 25 million inhabitants today. The present work is based upon the data collected during extensive field work finalized to the realization of the geological map of Nevado de Toluca at 1:25,000 scale. The activity of the volcano has developed from 2.6 Ma until 10.5 ka with both effusive and explosive events; the Nevado de Toluca has presented long phases of inactivity characterized by erosion and emplacement of debris flow and debris avalanche deposits on its flanks. The largest epiclastic events in the history of the volcano are wide debris flows and debris avalanches, occurred between 1 Ma and 50 ka, during a prolonged hiatus in eruptive activity. Other minor events happened mainly during the most recent volcanic activity (less than 50 ka), characterized by magmatic and tectonic-induced instability of the summit dome complex. According to the most recent tectonic analysis, the active transtensive kinematics of the E-W Tenango Fault System had a strong influence on the preferential directions of the last three documented lateral collapses, which generated the Arroyo Grande and Zaguàn debris avalanche deposits towards E and Nopal debris avalanche deposit towards W. The analysis of the data collected during the field work permitted to create a detailed GIS database of the spatial and temporal distribution of debris avalanche deposits on the volcano. Flow models, that have been performed with the software TITAN2D, developed by GMFG at Buffalo, were entirely based upon the information stored in the geological database. The modeling software is built upon equations

Avalanche fluctuations within the multigap resistive plate chamber

International Nuclear Information System (INIS)

Cerron Zeballos, E.; Crotty, I.; Lamas Valverde, J.; Veenhof, R.J.; Williams, M.C.S.; Zichichi, A.

1996-01-01

The multigap resistive plate chamber (MRPC) was originally designed to have improved time resolution (compared to the wide gap RPC), but also to keep the good high rate behaviour and ease of construction associated with the wide gap RPC. However in addition we observed a very long efficiency plateau, even at high rates. Here we consider fluctuations in avalanche growth, and show that the inherent ''averaging'' of these fluctuations can account for the enhanced performance of the multigap RPC. (orig.)

Propagation of avalanches in Mn12-acetate: magnetic deflagration.

Science.gov (United States)

Suzuki, Yoko; Sarachik, M P; Chudnovsky, E M; McHugh, S; Gonzalez-Rubio, R; Avraham, Nurit; Myasoedov, Y; Zeldov, E; Shtrikman, H; Chakov, N E; Christou, G

2005-09-30

Local time-resolved measurements of fast reversal of the magnetization of single crystals of Mn12-acetate indicate that the magnetization avalanche spreads as a narrow interface that propagates through the crystal at a constant velocity that is roughly 2 orders of magnitude smaller than the speed of sound. We argue that this phenomenon is closely analogous to the propagation of a flame front (deflagration) through a flammable chemical substance.

Projected changes of snow conditions and avalanche activity in a warming climate: the French Alps over the 2020-2050 and 2070-2100 periods

Science.gov (United States)

Castebrunet, H.; Eckert, N.; Giraud, G.; Durand, Y.; Morin, S.

2014-09-01

Projecting changes in snow cover due to climate warming is important for many societal issues, including the adaptation of avalanche risk mitigation strategies. Efficient modelling of future snow cover requires high resolution to properly resolve the topography. Here, we introduce results obtained through statistical downscaling techniques allowing simulations of future snowpack conditions including mechanical stability estimates for the mid and late 21st century in the French Alps under three climate change scenarios. Refined statistical descriptions of snowpack characteristics are provided in comparison to a 1960-1990 reference period, including latitudinal, altitudinal and seasonal gradients. These results are then used to feed a statistical model relating avalanche activity to snow and meteorological conditions, so as to produce the first projection on annual/seasonal timescales of future natural avalanche activity based on past observations. The resulting statistical indicators are fundamental for the mountain economy in terms of anticipation of changes. Whereas precipitation is expected to remain quite stationary, temperature increase interacting with topography will constrain the evolution of snow-related variables on all considered spatio-temporal scales and will, in particular, lead to a reduction of the dry snowpack and an increase of the wet snowpack. Overall, compared to the reference period, changes are strong for the end of the 21st century, but already significant for the mid century. Changes in winter are less important than in spring, but wet-snow conditions are projected to appear at high elevations earlier in the season. At the same altitude, the southern French Alps will not be significantly more affected than the northern French Alps, which means that the snowpack will be preserved for longer in the southern massifs which are higher on average. Regarding avalanche activity, a general decrease in mean (20-30%) and interannual variability is

Effects of the intrinsic layer width on the band-to-band tunneling current in p-i-n GaN-based avalanche photodiodes

International Nuclear Information System (INIS)

Wang, Ling; Bao, Xichang; Zhang, Wenjing; Li, Chao; Yuan, Yonggang; Xu, Jintong; Zhang, Yan; Li, Xiangyang

2009-01-01

Dark current is critical for GaN-based avalanche photodiodes because it significantly increases the noise current and limits the multiplication factor. It has been found that the band-to-band tunneling current is the dominant origin of the dark current for avalanche photodiodes at the onset of breakdown voltage. Experimentally, for GaN-based avalanche photodiodes with a thinner intrinsic layer, the dark current increases nearly exponentially with the applied voltage even at a lower bias voltage. In this paper, the intrinsic layer (i-layer) width of GaN-based avalanche photodiodes has been varied to study its effect on the band-to-band tunneling current. A widely used equation was used to calculate the band-to-band tunneling current of avalanche photodiodes with different i-layer widths (i-layer 0.1 µm, 0.2 µm and 0.4 µm). At −40 V, the band-to-band tunneling current significantly reduces by a magnitude of 10 −15 A with an increase in the i-layer width from 0.1 µm to 0.2 µm, and a magnitude of 10 −29 A with an increase in the i-layer width from 0.2 µm to 0.4 µm. Then, GaN-based avalanche photodiodes (i-layer 0.1 µm, 0.2 µm and 0.4 µm) with different-sized mesa were fabricated. Also, the measurement of dark current of all three different structures was performed, and their multiplication factors were given

A new CMOS SiGeC avalanche photo-diode pixel for IR sensing

Science.gov (United States)

Augusto, Carlos; Forester, Lynn; Diniz, Pedro C.

2009-05-01

Near-infra-red sensing with silicon is limited by the bandgap of silicon, corresponding to a maximum wavelength of absorption of 1.1 μm. A new type of CMOS sensor is presented, which uses a SiGeC epitaxial film in conjunction with novel device architecture to extend absorption into the infra-red. The SiGeC film composition and thickness determine the spectrum of absorption; in particular for SiGeC superlattices, the layer ordering to create pseudo direct bandgaps is the critical parameter. In this new device architecture, the p-type SiGeC film is grown on an active region surrounded by STI, linked to the S/D region of an adjacent NMOS, under the STI by a floating N-Well. On a n-type active, a P-I-N device is formed, and on a p-type active, a P-I-P device is formed, each sensing different regions of the spectrum. The SiGeC films can be biased for avalanche operation, as the required vertical electric field is confined to the region near the heterojunction interface, thereby not affecting the gate oxide of the adjacent NMOS. With suitable heterojunction and doping profiles, the avalanche region can also be bandgap engineered, allowing for avalanche breakdown voltages that are compatible with CMOS devices.

Acceleration of electrons and supplementary ionization during parametrical plasma heating

International Nuclear Information System (INIS)

Grach, S.M.; Mityakov, N.A.; Trakhtengerts, V.Yu.; AN SSSR, Gor'kij. Inst. Prikladnoj Fiziki)

1986-01-01

Acceleration of electrons by plasma waves in partially ionized plasma is considered with provision for the effects of turbulent scattering and formation of secondary electrons, which are produced in the process of electron shock ionization. It is shown that the avalanche density growth of electrons accelerated up to 1-2 ionization potential (instability) takes place beginning from some critical density of plasma waves. Density of fast electrons is found out along with plasma wave energy density at the stage of instability saturation. Additional concentration of a background plasma, which manifests itself due to ionization, is evaluated

Lifetime of Bubble Rafts: Cooperativity and Avalanches

Science.gov (United States)

Ritacco, Hernán; Kiefer, Flavien; Langevin, Dominique

2007-06-01

We have studied the collapse of pseudo-bi-dimensional foams. These foams are made of uniformly sized soap bubbles packed in an hexagonal lattice sitting at the top of a liquid surface. The collapse process follows the sequence: (1) rupture of a first bubble, driven by thermal fluctuations and (2) a cascade of bursting bubbles. We present a simple numerical model which captures the main characteristics of the dynamics of foam collapse. We show that in a certain range of viscosities of the foaming solutions, the size distribution of the avalanches follows power laws as in self-organized criticality processes.

Numerical simulation of quantum efficiency and surface recombination in HgCdTe IR photon-trapping structures

Science.gov (United States)

Schuster, Jonathan; Bellotti, Enrico

2013-06-01

We have investigated the quantum effiency in HgCdTe photovoltaic pixel arrays employing a photon-trapping structure realized with a periodic array of pillars intended to provide broadband operation. We have found that the quantum efficiency depends heavily on the passivation of the pillar surface. Pillars passivated with anodicoxide have a large fixed positive charge on the pillar surface. We use our three-dimensional numerical simulation model to study the effect of surface charge and surface recombination velocity on the exterior of the pillars. We then evaluate the quantum efficiency of this structure subject to different surface conditions. We have found that by themselves, the surface charge and surface recombination are detrimental to the quantum efficiency but the quantum efficiency is recovered when both phenomena are present. We will discuss the effects of these phenomena and the trade offs that exist between the two.

Detection of X-ray fluorescence of light elements by electron counting in a low-pressure gaseous electron multiplier

International Nuclear Information System (INIS)

Pansky, A.; Breskin, A.; Chechik, R.; Malamud, G.

1992-12-01

Ionization electrons deposited by soft X-rays in a low pressure (10 Torr) gas medium are efficiently counted by a multistage electron multiplier, providing an accurate measurement of the X-ray photon energy. Energy resolution of 56-28% FWHM were measured for X-rays of 110-676 eV, recording electrical induced charges or visible photons emitted during the avalanche process. It is demonstrated that a combined analysis of the number of electron trail length of an event, provides a powerful and competitive way of resolving ultra soft X-rays. We present the experimental technique, discuss the advantages and limitations of the Primary Electron Counter, and suggest ways to improve its performances. (authors)

Growth characteristics of (100)HgCdTe layers in low-temperature MOVPE with ditertiarybutyltelluride

Science.gov (United States)

Yasuda, K.; Hatano, H.; Ferid, T.; Minamide, M.; Maejima, T.; Kawamoto, K.

1996-09-01

Low-temperature growth of (100)HgCdTe (MCT) layers in MOVPE has been studied using ditertiarybutyltelluride (DtBTe), dimethylcadmium (DMCd), and elementary mercury as precursors. MCT layers were grown at 275°C on (100)GaAs substrates. Growths were carried out in a vertical growth cell which has a narrow spacing between the substrate and cell ceiling. Using the growth cell, the Cd-composition ( x) of MCT layers was controlled over a wide range from 0 to 0.98 by the DMCd flow. The growth rate of the MCT layers was constant at 5 μm h -1 for the increased DMCd flow. Preferential Cd-incorporation into MCT layers and an increase of the growth rate were observed in the presence of mercury vapor. The growth characteristics were considered to be due to the alkyl-exchange reaction between DMCd and mercury. The electrical properties and crystallinity of grown layers were also evaluated, which showed that layers with high quality can be grown at 275°C.

Study of CdTe and HgCdTe thin films obtained by electrochemical methods

International Nuclear Information System (INIS)

Guillen, C.

1990-01-01

Cadmium telluride polycrystalline thin films were fabricated on SnO 2 -coated glass substrates by potentiostatic electrodeposition and characterized by X-ray diffraction, energy dispersive X-ray analyses (EDAX), optical and electrical measurements. The films dseposited at potentials more positive than -0.65 V vs.SCE were p-type but those deposited at more negative potentials were n-type. All CdTe thin films showed a band-gap energy about 1.45 eV and a large absorption coeffici-ent (a=10 5 cm -1 ) above de band edge. The addition of even small amounts of mercury to the CdTe produces higuer conductivity values and lower band-gap energies. We have prepared HgCdTe thin films where the band-gap energies ranged between 0.93 and 0.88 eV depending on the ratio of mercury to cadmium. Heat treatment at 300 0 C increases the crystalline diameter and alter the composition of the electrodeposited films, a decrease of the resistivity values was also observed. (Author)

A how-to approach for a 3D simulation of charge transfer characteristics in a gas electron multiplier (GEM)

CERN Document Server

Sharma, A

1999-01-01

In this paper a detailed description of how to simulate charge transfer processes in a gaseous device is presented, taking the gas electron multiplier (GEM) as an example. A 3-dimensional simulation of the electric field and avalanche is performed. Results on charge transport are compared to experiment and agree within experimental errors; the avalanche mechanism and positive ion feedback are studied. The procedures used in the simulation are described in detail, and program scripts are appended. (15 refs).

Two-phase Cryogenic Avalanche Detector with electroluminescence gap operated in argon doped with nitrogen

Energy Technology Data Exchange (ETDEWEB)

Bondar, A.; Buzulutskov, A. [Budker Institute of Nuclear Physics SB RAS, Lavrentiev avenue 11, 630090 Novosibirsk (Russian Federation); Novosibirsk State University, Pirogov street 2, 630090 Novosibirsk (Russian Federation); Dolgov, A. [Novosibirsk State University, Pirogov street 2, 630090 Novosibirsk (Russian Federation); Nosov, V.; Shekhtman, L.; Shemyakina, E.; Sokolov, A. [Budker Institute of Nuclear Physics SB RAS, Lavrentiev avenue 11, 630090 Novosibirsk (Russian Federation); Novosibirsk State University, Pirogov street 2, 630090 Novosibirsk (Russian Federation)

2017-02-11

A two-phase Cryogenic Avalanche Detector (CRAD) with electroluminescence (EL) gap, operated in argon doped with a minor (49±7 ppm) admixture of nitrogen, has been studied. The EL gap was optically read out using cryogenic PMTs located on the perimeter of the gap. We present the results of the measurements of the N{sub 2} content, detector sensitivity to X-ray-induced signals, EL gap yield and electron lifetime in the liquid. The detector sensitivity, at a drift field in liquid Ar of 0.6 kV/cm, was measured to be 9 and 16 photoelectrons recorded at the PMTs per keV of deposited energy at 23 and 88 keV respectively. Such two-phase detectors, with enhanced sensitivity to the S2 (ionization-induced) signal, are relevant in the field of argon detectors for dark matter search and low energy neutrino detection.

Geiger-Mode Avalanche Photodiode Arrays Integrated to All-Digital CMOS Circuits.

Science.gov (United States)

Aull, Brian

2016-04-08

This article reviews MIT Lincoln Laboratory's work over the past 20 years to develop photon-sensitive image sensors based on arrays of silicon Geiger-mode avalanche photodiodes. Integration of these detectors to all-digital CMOS readout circuits enable exquisitely sensitive solid-state imagers for lidar, wavefront sensing, and passive imaging.

Development of advanced solid state radiation detectors: mercuric iodide and high gain silicon avalanche structures. Annual progress report, December 1, 1984-November 30, 1985

International Nuclear Information System (INIS)

Huth, G.C.; Dabrowski, A.J.

1986-04-01

This report covers the period from December 1984 through November 1985 for this research project sponsored by the Office of Health and Environmental Research of the Dept. of Energy. This work has two primary research objectives. The first is continuing development of the material mercuric iodide (HgI 2 ) and its applications to energy dispersive x-ray analysis and gamma ray spectrometry. The second task involves investigation of silicon ''avalanche'' (internal electron gain) radiation detector structures fabricated from new neutron transmutation doped (NTD) silicon single crystal

Neural avalanches at the critical point between replay and non-replay of spatiotemporal patterns.

Directory of Open Access Journals (Sweden)

Silvia Scarpetta

Full Text Available We model spontaneous cortical activity with a network of coupled spiking units, in which multiple spatio-temporal patterns are stored as dynamical attractors. We introduce an order parameter, which measures the overlap (similarity between the activity of the network and the stored patterns. We find that, depending on the excitability of the network, different working regimes are possible. For high excitability, the dynamical attractors are stable, and a collective activity that replays one of the stored patterns emerges spontaneously, while for low excitability, no replay is induced. Between these two regimes, there is a critical region in which the dynamical attractors are unstable, and intermittent short replays are induced by noise. At the critical spiking threshold, the order parameter goes from zero to one, and its fluctuations are maximized, as expected for a phase transition (and as observed in recent experimental results in the brain. Notably, in this critical region, the avalanche size and duration distributions follow power laws. Critical exponents are consistent with a scaling relationship observed recently in neural avalanches measurements. In conclusion, our simple model suggests that avalanche power laws in cortical spontaneous activity may be the effect of a network at the critical point between the replay and non-replay of spatio-temporal patterns.

Highly Efficient Spin-to-Charge Current Conversion in Strained HgTe Surface States Protected by a HgCdTe Layer

Science.gov (United States)

Noel, P.; Thomas, C.; Fu, Y.; Vila, L.; Haas, B.; Jouneau, P.-H.; Gambarelli, S.; Meunier, T.; Ballet, P.; Attané, J. P.

2018-04-01

We report the observation of spin-to-charge current conversion in strained mercury telluride at room temperature, using spin pumping experiments. We show that a HgCdTe barrier can be used to protect the HgTe from direct contact with the ferromagnet, leading to very high conversion rates, with inverse Edelstein lengths up to 2.0 ±0.5 nm . The influence of the HgTe layer thickness on the conversion efficiency is found to differ strongly from what is expected in spin Hall effect systems. These measurements, associated with the temperature dependence of the resistivity, suggest that these high conversion rates are due to the spin momentum locking property of HgTe surface states.

Intrinsic Bistability and Critical Slowing in Tm3+/Yb3+ Codoped Laser Crystal with the Photon Avalanche Mechanism

International Nuclear Information System (INIS)

Li, Li; Li-Xue, Chen; Xin-Lu, Zhang

2009-01-01

We present theoretically a novel intrinsic optical bistability (IOB) in the Tm 3+ /Yb 3+ codoped system with a photon avalanche mechanism. Numerical simulations based on the rate equation model demonstrate distinct IOB hysteresis and critical slowing dynamics around the avalanche thresholds. Such an IOB characteristic in Tm 3+ /Yb 3+ codoped crystal has potential applications in solid-state bistable optical displays and luminescence switchers in visible-infrared spectra. (fundamental areas of phenomenology (including applications))

A microstrip gas avalanche chamber with two-dimensional readout

International Nuclear Information System (INIS)

Angelini, F.; Bellazzini, R.; Brez, A.; Massai, M.M.; Spandre, G.; Torquati, M.R.

1989-01-01

A microstrip gas avalanche chamber with a 200 μm anode pitch has been built and successfully tested in our laboratory. A gas gain of 10 4 and an energy resolution of 18% (FWHM) at 6 keV have been measured using a gas mixture of argon-CO 2 at atmospheric pressure. A preliminary measurement of the positional sensitivity indicates that a spatial resolution of 50 μm can be obtained. (orig.)

Charge-transfer properties in the gas electron multiplier

International Nuclear Information System (INIS)

Han, Sanghyo; Kim, Yongkyun; Cho, Hyosung

2004-01-01

The charge transfer properties of a gas electron multiplier (GEM) were systematically investigated over a broad range of electric field configurations. The electron collection efficiency and the charge sharing were found to depend on the external fields, as well as on the GEM voltage. The electron collection efficiency increased with the collection field up to 90%, but was essentially independent of the drift field strength. A double conical GEM has a 10% gain increase with time due to surface charging by avalanche ions whereas this effect was eliminated with the cylindrical GEM. The positive-ion feedback is also estimated. (author)

Transmission line pulse system for avalanche characterization of high power semiconductor devices

Science.gov (United States)

Riccio, Michele; Ascione, Giovanni; De Falco, Giuseppe; Maresca, Luca; De Laurentis, Martina; Irace, Andrea; Breglio, Giovanni

2013-05-01

Because of the increasing in power density of electronic devices for medium and high power application, reliabilty of these devices is of great interest. Understanding the avalanche behaviour of a power device has become very important in these last years because it gives an indication of the maximum energy ratings which can be seen as an index of the device ruggedness. A good description of this behaviour is given by the static IV blocking characteristc. In order to avoid self heating, very relevant in high power devices, very short pulses of current have to be used, whose value can change from few milliamps up to tens of amps. The most used method to generate short pulses is the TLP (Transmission Line Pulse) test, which is based on charging the equivalent capacitance of a transmission line to high value of voltage and subsequently discharging it onto a load. This circuit let to obtain very short square pulses but it is mostly used for evaluate the ESD capability of semiconductor and, in this environment, it generates pulses of low amplitude which are not high enough to characterize the avalanche behaviour of high power devices . Advanced TLP circuit able to generate high current are usually very expensive and often suffer of distorption of the output pulse. In this article is proposed a simple, low cost circuit, based on a boosted-TLP configuration, which is capable to produce very square pulses of about one hundreds of nanosecond with amplitude up to some tens of amps. A prototype is implemented which can produce pulses up to 20A of amplitude with 200 ns of duration which can characterize power devices up to 1600V of breakdown voltage. Usage of microcontroller based logic make the circuit very flexible. Results of SPICE simulation are provided, together with experimental results. To prove the effectiveness of the circuit, the I-V blocking characteristics of two commercial devices, namely a 600V PowerMOS and a 1200V Trench-IGBT, are measured at different

Thermodynamics of the Heat-Flux Avalanches at the First-Order Magnetic Transition in Magnetocaloric Materials

Science.gov (United States)

Piazzi, Marco; Bennati, Cecilia; Basso, Vittorio

2017-10-01

We investigate the kinetics of first-order magnetic phase transitions by measuring and modeling the heat-flux avalanches corresponding to the irreversible motion of the phase-boundary interface separating the coexisting low- and high-temperature stable magnetic phases. By means of out-of-equilibrium thermodynamics, we encompass the damping mechanisms of the boundary motion in a phenomenological parameter αs. By analyzing the time behavior of the heat-flux signals measured on La (Fe -Mn -Si )13-H magnetocaloric compounds through Peltier calorimetry temperature scans performed at low rates, we relate the linear rise of the individual avalanches to the intrinsic-damping parameter αs.

Stratigraphic reconstruction of two debris avalanche deposits at Colima Volcano (Mexico): Insights into pre-failure conditions and climate influence

Science.gov (United States)

Roverato, M.; Capra, L.; Sulpizio, R.; Norini, G.

2011-10-01

Throughout its history, Colima Volcano has experienced numerous partial edifice collapses with associated emplacement of debris avalanche deposits of contrasting volume, morphology and texture. A detailed stratigraphic study in the south-eastern sector of the volcano allowed the recognition of two debris avalanche deposits, named San Marcos (> 28,000 cal yr BP, V = ~ 1.3 km 3) and Tonila (15,000-16,000 cal yr BP, V = ~ 1 km 3 ). This work sheds light on the pre-failure conditions of the volcano based primarily on a detailed textural study of debris avalanche deposits and their associated pyroclastic and volcaniclastic successions. Furthermore, we show how the climate at the time of the Tonila collapse influenced the failure mechanisms. The > 28,000 cal yr BP San Marcos collapse was promoted by edifice steep flanks and ongoing tectonic and volcanotectonic deformation, and was followed by a magmatic eruption that emplaced pyroclastic flow deposits. In contrast, the Tonila failure occurred just after the Last Glacial Maximum (22,000-18,000 cal BP) and, in addition to the typical debris avalanche textural characteristics (angular to sub-angular clasts, coarse matrix, jigsaw fit) it shows a hybrid facies characterized by debris avalanche blocks embedded in a finer, homogenous and partially cemented matrix, a texture more characteristic of debris flow deposits. The Tonila debris avalanche is directly overlain by a 7-m thick hydromagmatic pyroclastic succession. Massive debris flow deposits, often more than 10 m thick and containing large amounts of tree trunk logs, represent the top unit in the succession. Fluvial deposits also occur throughout all successions; these represent periods of highly localized stream reworking. All these lines of evidence point to the presence of water in the edifice prior to the Tonila failure, suggesting it may have been a weakening factor. The Tonila failure appears to represent an anomalous event related to the particular climatic

Self-focusing of a pulsed electron beam in gases and their ionization

International Nuclear Information System (INIS)

Hotta, Hiroshi; Arai, Hidehiko; Tanaka, Ryuichi; Sunaga, Hiromi.

1982-06-01

A relativistic high-intensity pulsed electron beam generated from a Febetron 706 was strongly self-focused in two pressure regions, i.e., below and above 5 Torr. The dependence of the electron energy spectrum on pressure and path length in He was at first studied by measuring depth-dose distributions in an aluminum-blue cellophane stack. Then, maximum doses of the depth-dose curves in the dosimeter placed on the beam axis at 10.4 cm from the cell window were measured as functions of pressure in He, Ne, Ar, Kr, Xe, H 2 , D 2 , N 2 , O 2 , N 2 O, CO 2 , SF 6 , CH 4 , C 2 H 2 , C 2 H 4 , C 2 H 6 , C 3 H 8 , CH 3 F, CHClF 2 , CCl 2 F 2 , He + X, Ar + X, and O 2 + X (X: additive gas). The strong self-focusing at pressure lower than 5 Torr is attributed to space-charge neutralization by positive ions due to escaping of secondary electrons. Therefore, relative total ionization cross sections for beam electrons could be obtained in this region. When the spa ce-charge neutralization time becomes shorter than a rise time of the pulsed beam, secondary electrons are accelerated by a backward electric field E sub(z) induced by the pulsed beam so that the self-focusing declines abruptly due to electron avalanching. The beam is self-focused again gradually with further increasing pressure because of suppression of this avalanching. The avalanching was analyzed self-consistently for He, Ar, H 2 , N 2 , and CH 4 by a computer simulation in the pressure region between 5 and 300 Torr. The present computational results indicate that the larger cose is given by the longer mean ionization time t sub(i) which depends on E sub(z)/p. The value of t sub(i) increases with increasing pressure in the pressure region of gradually-increasing self-focusing. (J.P.N.)

Vortex Avalanches with Periodic Arrays of Pinning Sites

Science.gov (United States)

Abbas, J.; Heckel, T.; Kakalios, J.

2001-03-01

Numerical simulations by Nori and co-workers of dynamical phase transitions for magnetic vortices in type II superconductors when the defects which act as pinning sites are arranged in a periodic array have found a dramatic non-linear relationship between vortex voltage and driving current.2,4 In order to experimentally test the predictions of these simulations, a macroscopic physical analog of an array of flux vortices in the presense of an ordered lattice of pinning sites has been constructed. This simple table-top experimental system consists of conventional household magnets, arranged in an ordered grid (serving as the lattice of fixed pinning centers). A plexiglass sheet is positioned above these fixed magnets, and another collection of magnets (representing the magnetic flux vortices), oriented so that they are attracted to the fixed magnets are placed on top of the sheet. The entire apparatus is then tilted to a given angle (the analog of the driving voltage) and the velocity of the avalanching magnets is recorded using the induced voltage in a pick-up coil. By varying the ratio of movable magnets to fixed pinning magnets, the filling fraction can be adjusted, as can the pinning strength, by adjusting the separation of the plexiglass sheet between the fixed and movable magnets. The velocity of the avalanching magnets as the filling fraction is varied displays a jamming transition, with a non-trivial dependence on the pinning strength of the lattice of fixed magnets below the sheet.

Space charge limited avalanche growth in multigap resistive plate chambers

International Nuclear Information System (INIS)

Akindinov, A.N.; Kaidalov, A.B.; Kisselev, S.M.; Alici, A.; Basile, M.; Cifarelli, L.; Anselmo, F.; Antonioli, P.; Romeo, G. Cara; Cindolo, F.; Baek, Y.; Kim, D.H.; Cosenza, F.; Caro, A. De; Pasquale, S. De; Bartolomeo, A. Di; Girard, M. Fusco; Guida, M.; Hatzifotiadou, D.; Kim, D.W.; Laurenti, G.; Lee, K.; Lee, S.C.; Lioublev, E.; Luvisetto, M.L.; Margotti, A.; Martemiyanov, A.N.; Nania, R.; Noferini, F.; Otiougova, P.; Pierella, F.; Polozov, P.A.; Scapparone, E.; Scioli, G.; Sellitto, S.B.; Smirnitski, A.V.; Tchoumakov, M.M.; Valenti, G.; Vicinanza, D.; Voloshin, K.G.; Williams, M.C.S.; Zagreev, B.V.; Zampolli, C.; Zichichi, A.

2004-01-01

Abstract The ALICE TOF array will be built using the Multigap Resistive Plate Chamber(MRPC) configured as a double stack. Each stack contains 5 gas gaps with width of 250 μm. There has been an intense R and D effort to optimise this new detector to withstand the problems connected with the high level of radiation at the LHC. One clear outcome of the R and D is that the growth of the gas avalanche is strongly affected by space charge. The effect of the space charge is a decrease in the rate of change in gain with electric field; this allows more stable operation of this detector. We have measured the gain as a function of the electric field and also measured the ratio of the fast charge to the total charge produced in the gas gap. It is well established that RPCs built with 250 μm gas gap have a much superior performance than 2 mm gaps; we discuss and compare the performance of 250 μm gap MRPCs with 2 mm gap RPCs to show the importance of space-charge limitation of avalanche growth. (orig.)

The simulation of resistive plate chambers in avalanche mode: charge spectra and efficiency

Energy Technology Data Exchange (ETDEWEB)

Abbrescia, M. E-mail: Marcello.abbrescia@ba.infn.it; Colaleo, A.; Iaselli, G.; Loddo, F.; Maggi, M.; Marangelli, B.; Natali, S.; Nuzzo, S.; Pugliese, G.; Ranieri, A.; Romano, F.; Altieri, S.; Bruno, G.; Gianini, G.; Ratti, S.P.; Viola, L.; Vitulo, P

1999-07-21

A model to simulate the avalanche formation process and the induced signal in a Resistive Plate Chamber is presented. A first investigation of the effects of various parameters on the performance of this detector is reported. (author)

Energy pumping in electrical circuits under avalanche noise.

Science.gov (United States)

Kanazawa, Kiyoshi; Sagawa, Takahiro; Hayakawa, Hisao

2014-07-01

We theoretically study energy pumping processes in an electrical circuit with avalanche diodes, where non-Gaussian athermal noise plays a crucial role. We show that a positive amount of energy (work) can be extracted by an external manipulation of the circuit in a cyclic way, even when the system is spatially symmetric. We discuss the properties of the energy pumping process for both quasistatic and finite-time cases, and analytically obtain formulas for the amounts of the work and the power. Our results demonstrate the significance of the non-Gaussianity in energetics of electrical circuits.

Sixteen-year follow-up of childhood avalanche survivors

DEFF Research Database (Denmark)

Thordardottir, E.B.; Valdimarsdóttir, Unnur A; Hansdottir, Ingunn

2016-01-01

: Childhood survivors (aged 2-19 at the time of exposure) of two avalanches were identified through nationwide registers 16 years later. The PosttraumaticDiagnostic Scale was used to assess current PTSD symptoms. One-way ANOVA was used to explore PTSD symptoms by background and trauma-specific factors......, as well as associations with current SES. Predictors of PTSD symptoms were examined by multivariable regression analysis. Results: Response rate was 66% (108/163). Results from univariate ANOVA analysis revealed that female sex was associated with PTSD symptoms (F =5.96, p...

A new method to improve multiplication factor in micro-pixel avalanche photodiodes with high pixel density

Energy Technology Data Exchange (ETDEWEB)

Sadygov, Z. [National Nuclear Research Center, Baku (Azerbaijan); Joint Institute for Nuclear Research, Dubna (Russian Federation); Ahmadov, F. [National Nuclear Research Center, Baku (Azerbaijan); Khorev, S. [Zecotek Photonics Inc., Vancouver (Canada); Sadigov, A., E-mail: saazik@yandex.ru [National Nuclear Research Center, Baku (Azerbaijan); Suleymanov, S. [National Nuclear Research Center, Baku (Azerbaijan); Madatov, R.; Mehdiyeva, R. [Institute of Radiation Problems, Baku (Azerbaijan); Zerrouk, F. [Zecotek Photonics Inc., Vancouver (Canada)

2016-07-11

Presented is a new model describing development of the avalanche process in time, taking into account the dynamics of electric field within the depleted region of the diode and the effect of parasitic capacitance shunting individual quenching micro-resistors on device parameters. Simulations show that the effective capacitance of a single pixel, which defines the multiplication factor, is the sum of the pixel capacitance and a parasitic capacitance shunting its quenching micro-resistor. Conclusions obtained as a result of modeling open possibilities of improving the pixel gain in micropixel avalanche photodiodes with high pixel density (or low pixel capacitance).

X-ray spectrometry with Peltier-cooled large area avalanche photodiodes

International Nuclear Information System (INIS)

Fernandes, L.M.P.; Lopes, J.A.M.; Santos, J.M.F. dos; Conde, C.A.N.

2004-01-01

Performance characteristics of the response of a Peltier-cooled large-area avalanche photodiode are investigated. Detector gain, energy linearity, energy resolution and minimum detectable energy are studied at different operation temperatures. Detector energy resolution and lowest detectable X-ray energy present a strong improvement as the operation temperature is reduced from 25 to 15 deg. C and slower improvements are achieved for temperatures below 10 deg. C

Avalanche mode of high-voltage overloaded p+–i–n+ diode switching to the conductive state by pulsed illumination

International Nuclear Information System (INIS)

Kyuregyan, A. S.

2015-01-01

A simple analytical theory of the picosecond switching of high-voltage overloaded p + –i–n + photodiodes to the conductive state by pulsed illumination is presented. The relations between the parameters of structure, light pulse, external circuit, and main process characteristics, i.e., the amplitude of the active load current pulse, delay time, and switching duration, are derived and confirmed by numerical simulation. It is shown that the picosecond light pulse energy required for efficient switching can be decreased by 6–7 orders of magnitude due to the intense avalanche multiplication of electrons and holes. This offers the possibility of using pulsed semiconductor lasers as a control element of optron pairs

Effect of avalanche-type barrier discharge on a silver halide photographic material in the case of blocked ionic conductivity

International Nuclear Information System (INIS)

Boychenko, A. P.

2012-01-01

Imaging of avalanche-type barrier gas discharge excited by single videopulses ∼7 μs long is studied via chemical activation of an ion subsystem of microcrystals of silver halide photographic emulsions by 1-phenyl-5-mercaptotetrazole. Using “Retina” commercial X-ray film and specially fabricated photoemulsion microcrystals with effective surface and deep electron traps as an example, the selective gas-discharge sensitivity of photographic layers to applied-voltage polarity is detected. It is shown that their sensitivity to barrier discharge ignited by negative-polarity pulses (on the electrode with a photographic material) is higher than in the case of positive pulses, irrespective of the photographic material’s position in the capacitor system.

ALS-based hummock size-distance relationship assessment of Mt Shasta debris avalanche deposit, Northern California, USA

Science.gov (United States)

Tortini, Riccardo; Carn, Simon; van Wyk de Vries, Benjamin

2015-04-01

The failure of destabilized volcano flanks is a likely occurrence during the lifetime of a stratovolcano, generating large debris avalanches and drastically changing landforms around volcanoes. The significant hazards associated with these events in the Cascade range were demonstrated, for example, by the collapse of Mt St Helens (WA), which triggered its devastating explosive eruption in 1980. The rapid modification of the landforms due to these events makes it difficult to estimate the magnitude of prehistoric avalanches. However, the widespread preservation of hummocks along the course of rockslide-debris avalanches is highly significant for understanding the physical characteristics of these landslides. Mt Shasta is a 4,317 m high, snow-capped, steep-sloped stratovolcano located in Northern California. The current edifice began forming on the remnants of an ancestral Mt Shasta that collapsed ~300-380k years ago producing one of the largest debris avalanches known on Earth. The debris avalanche deposit (DAD) covers a surface of ~450 km2 across the Shasta valley, with an estimated volume of ~26 km3. We analyze ALS data on hummocks from the prehistoric Shasta valley DAD in northern California (USA) to derive the relationship between hummock size and distance from landslide source, and interpret the geomorphic significance of the intercept and slope coefficients of the observed functional relationships. Given the limited extent of the ALS survey (i.e. 40 km2), the high-resolution dataset is used for validation of the morphological parameters extracted from freely available, broader coverage DTMs such as the National Elevation Dataset (NED). The ALS dataset also permits the identification of subtle topographic features not apparent in the field or in coarser resolution datasets, including a previously unmapped fault, of crucial importance for both seismic and volcanic hazard assessment in volcanic areas. We present evidence from the Shasta DAD of neotectonic

Storage and methyl jasmonate in postharvest conservation of roses cv. Avalanche

Directory of Open Access Journals (Sweden)

Elka Fabiana Aparecida Almeida

2017-07-01

Full Text Available The use of methyl jasmonate has demonstrated its efficiency to extend the vase life of cut flowers. The objective of this study was to evaluate the effect of methyl jasmonate associated with storage at low temperatures on the postharvest quality of Rosa cv. Avalanche stems. The treatments consisted of 125, 250, 500 and 1000 μM of methyl jasmonate, besides the control with distilled water. The flower buds were sprayed with 4 mL of the solution, according to the treatments, and then kept in a cold chamber (1 °C for periods of 2 and 6 days. Subsequently, the stems were taken to the postharvest laboratory at a temperature of 16 °C. Better quality, higher fresh weight and water absorption were observed in flower stems stored for 2 days. The application of methyl jasmonate caused less turgescence and greater darkening of roses. It was possible to conclude that two days is the best storage time at 1 °C and the use of methyl jasmonate does not maintain the quality of roses cv. Avalanche after harvest.

TCAD simulation of Low Gain Avalanche Detectors

Science.gov (United States)

Dalal, Ranjeet; Jain, Geetika; Bhardwaj, Ashutosh; Ranjan, Kirti

2016-11-01

In the present work, detailed simulation using Technology Computer Aided Design (TCAD) tool, Silvaco for non-irradiated and irradiated LGAD (Low Gain Avalanche Detector) devices has been carried out. The effects of different design parameters and proton irradiation on LGAD operation are discussed in detail. An already published effective two trap bulk damage model is used to simulate the radiation damage without implementing any acceptor removal term. The TCAD simulation for irradiated LGAD devices produce decreasing gain with increasing fluence, similar to the measurement results. The space charge density and electric field distribution are used to illustrate the possible reasons for the degradation of gain of the irradiated LGAD devices.

TCAD simulation of Low Gain Avalanche Detectors

Energy Technology Data Exchange (ETDEWEB)

Dalal, Ranjeet; Jain, Geetika; Bhardwaj, Ashutosh, E-mail: ashutosh.bhardwaj@cern.ch; Ranjan, Kirti

2016-11-11

In the present work, detailed simulation using Technology Computer Aided Design (TCAD) tool, Silvaco for non-irradiated and irradiated LGAD (Low Gain Avalanche Detector) devices has been carried out. The effects of different design parameters and proton irradiation on LGAD operation are discussed in detail. An already published effective two trap bulk damage model is used to simulate the radiation damage without implementing any acceptor removal term. The TCAD simulation for irradiated LGAD devices produce decreasing gain with increasing fluence, similar to the measurement results. The space charge density and electric field distribution are used to illustrate the possible reasons for the degradation of gain of the irradiated LGAD devices.

TCAD simulation of Low Gain Avalanche Detectors

International Nuclear Information System (INIS)

Dalal, Ranjeet; Jain, Geetika; Bhardwaj, Ashutosh; Ranjan, Kirti

2016-01-01

In the present work, detailed simulation using Technology Computer Aided Design (TCAD) tool, Silvaco for non-irradiated and irradiated LGAD (Low Gain Avalanche Detector) devices has been carried out. The effects of different design parameters and proton irradiation on LGAD operation are discussed in detail. An already published effective two trap bulk damage model is used to simulate the radiation damage without implementing any acceptor removal term. The TCAD simulation for irradiated LGAD devices produce decreasing gain with increasing fluence, similar to the measurement results. The space charge density and electric field distribution are used to illustrate the possible reasons for the degradation of gain of the irradiated LGAD devices.

Radiation hardness of thin Low Gain Avalanche Detectors

Science.gov (United States)

Kramberger, G.; Carulla, M.; Cavallaro, E.; Cindro, V.; Flores, D.; Galloway, Z.; Grinstein, S.; Hidalgo, S.; Fadeyev, V.; Lange, J.; Mandić, I.; Medin, G.; Merlos, A.; McKinney-Martinez, F.; Mikuž, M.; Quirion, D.; Pellegrini, G.; Petek, M.; Sadrozinski, H. F.-W.; Seiden, A.; Zavrtanik, M.

2018-05-01

Low Gain Avalanche Detectors (LGAD) are based on a n++-p+-p-p++ structure where an appropriate doping of the multiplication layer (p+) leads to high enough electric fields for impact ionization. Gain factors of few tens in charge significantly improve the resolution of timing measurements, particularly for thin detectors, where the timing performance was shown to be limited by Landau fluctuations. The main obstacle for their operation is the decrease of gain with irradiation, attributed to effective acceptor removal in the gain layer. Sets of thin sensors were produced by two different producers on different substrates, with different gain layer doping profiles and thicknesses (45, 50 and 80 μm). Their performance in terms of gain/collected charge and leakage current was compared before and after irradiation with neutrons and pions up to the equivalent fluences of 5 ṡ 1015 cm-2. Transient Current Technique and charge collection measurements with LHC speed electronics were employed to characterize the detectors. The thin LGAD sensors were shown to perform much better than sensors of standard thickness (∼300 μm) and offer larger charge collection with respect to detectors without gain layer for fluences gain prolongs the beneficial performance of LGADs. Pions were found to be more damaging than neutrons at the same equivalent fluence, while no significant difference was found between different producers. At very high fluences and bias voltages the gain appears due to deep acceptors in the bulk, hence also in thin standard detectors.

The performance of photon counting imaging with a Geiger mode silicon avalanche photodiode

International Nuclear Information System (INIS)

Qu, Hui-Ming; Zhang, Yi-Fan; Ji, Zhong-Jie; Chen, Qian

2013-01-01

In principle, photon counting imaging can detect a photon. With the development of low-level-light image intensifier techniques and low-level-light detection devices, photon counting imaging can now detect photon images under extremely low illumination. Based on a Geiger mode silicon avalanche photodiode single photon counter, an experimental system for photon counting imaging was built through two-dimensional scanning of a SPAD (single photon avalanche diode) detector. The feasibility of the imaging platform was validated experimentally. Two images with different characteristics, namely, the USAF 1951 resolution test panel and the image of Lena, were chosen to evaluate the imaging performance of the experimental system. The results were compared and analysed. The imaging properties under various illumination and scanning steps were studied. The lowest illumination limit of the SPAD photon counting imaging was determined. (letter)

A discrete model of the development and relaxation of a local microbreakdown in silicon avalanche photodiodes operating in the Geiger mode

International Nuclear Information System (INIS)

Vanyushin, I. V.; Gergel, V. A.; Gontar', V. M.; Zimoglyad, V. A.; Tishin, Yu. I.; Kholodnov, V. A.; Shcheleva, I. M.

2007-01-01

A new discrete theoretical model of the development and relaxation of a local microbreakdown in silicon avalanche photodiodes operating in the Geiger mode is developed. It is shown that the spreading resistance in the substrate profoundly affects both the amplitude of a single-photon electrical pulse and the possibility of attaining the steady-state form of the avalanche breakdown excluding the Geiger mode of the photodiode's operation. The model is employed to interpret the experimental data obtained using test single-photon cells of avalanche photodiodes fabricated on the basis of the 0.25-μm silicon technology with the use of deep implantation to form the region of avalanche multiplication for the charge carriers. Excellent functional properties of the studied type of the single-photon (Geiger) cell are noted. A typical amplitude characteristic of the cell for optical radiation with the wavelength λ = 0.56 μm in the irradiance range of 10 -3 -10 2 lx is presented; this characteristic indicates that the quantum efficiency of photoconversion is extremely high

Ground thermal and geomechanical conditions in a permafrost-affected high-latitude rock avalanche site (Polvartinden, northern Norway)

Science.gov (United States)

Frauenfelder, Regula; Isaksen, Ketil; Lato, Matthew J.; Noetzli, Jeannette

2018-04-01

On 26 June 2008, a rock avalanche detached in the northeast facing slope of Polvartinden, a high-alpine mountain in Signaldalen, northern Norway. Here, we report on the observed and modelled past and present near-surface temperature regime close to the failure zone, as well as on a subsequent simulation of the subsurface temperature regime, and on initial geomechanical mapping based on laser scanning. The volume of the rock avalanche was estimated to be approximately 500 000 m3. The depth to the actual failure surface was found to range from 40 m at the back of the failure zone to 0 m at its toe. Visible in situ ice was observed in the failure zone just after the rock avalanche. Between September 2009 and August 2013, ground surface temperatures were measured with miniature temperature data loggers at 14 different localities, close to the original failure zone along the northern ridge of Polvartinden and on the valley floor. The results from these measurements and from a basic three-dimensional heat conduction model suggest that the lower altitudinal limit of permafrost at present is at 600-650 m a.s.l., which corresponds to the upper limit of the failure zone. A coupling of our in situ data with regional climate data since 1958 suggests a general gradual warming and that the period with highest mean near surface temperatures on record ended four months before the Signaldalen rock avalanche detached. A comparison with a transient permafrost model run at 10 m depth, representative for areas where snow accumulates, strengthen these findings, which are also in congruence with measurements in nearby permafrost boreholes. It is likely that permafrost in and near the failure zone is presently subject to degradation. This degradation, in combination with the extreme warm year antecedent to the rock failure, is seen to have played an important role in the detaching of the Signaldalen rock avalanche.

Ground thermal and geomechanical conditions in a permafrost-affected high-latitude rock avalanche site (Polvartinden, northern Norway

Directory of Open Access Journals (Sweden)

R. Frauenfelder

2018-04-01

Full Text Available On 26 June 2008, a rock avalanche detached in the northeast facing slope of Polvartinden, a high-alpine mountain in Signaldalen, northern Norway. Here, we report on the observed and modelled past and present near-surface temperature regime close to the failure zone, as well as on a subsequent simulation of the subsurface temperature regime, and on initial geomechanical mapping based on laser scanning. The volume of the rock avalanche was estimated to be approximately 500 000 m3. The depth to the actual failure surface was found to range from 40 m at the back of the failure zone to 0 m at its toe. Visible in situ ice was observed in the failure zone just after the rock avalanche. Between September 2009 and August 2013, ground surface temperatures were measured with miniature temperature data loggers at 14 different localities, close to the original failure zone along the northern ridge of Polvartinden and on the valley floor. The results from these measurements and from a basic three-dimensional heat conduction model suggest that the lower altitudinal limit of permafrost at present is at 600–650 m a.s.l., which corresponds to the upper limit of the failure zone. A coupling of our in situ data with regional climate data since 1958 suggests a general gradual warming and that the period with highest mean near surface temperatures on record ended four months before the Signaldalen rock avalanche detached. A comparison with a transient permafrost model run at 10 m depth, representative for areas where snow accumulates, strengthen these findings, which are also in congruence with measurements in nearby permafrost boreholes. It is likely that permafrost in and near the failure zone is presently subject to degradation. This degradation, in combination with the extreme warm year antecedent to the rock failure, is seen to have played an important role in the detaching of the Signaldalen rock avalanche.

A parallel plate avalanche chamber for relativistic heavy ions

International Nuclear Information System (INIS)

Burgei, R.

1989-01-01

In order to determine the interaction point of relativistic heavy ions in the Diogene target, we have built and tested an X-Y low pressure parallel plate avalanche chamber. It uses three thin metallized foils and is filled with isobutane. A preliminary study shows that it is the only detector with the required specifications: efficiency, accurate position determination and a small uniform amount of material for the particle beam to go through. The electronics system is designed for reliability, easy adjustments and high stability. The interaction point is given on delay-line read-out. This represents the optimum compromise between low price and good performance. Laboratory measurements of gain, efficiency and position accuracy are done with an alpha-particle source. Two of these detectors are working at the Saturne National Laboratory. They allow the trajectory of several tens of particles (among a million per second) to be reconstructed. With an argon beam at 400 MeV per nucleon, the position uncertainty in the target has been measured to be 0.5 mm (standard deviation). This uncertainty is 0.3 mm for each detector, with an efficiency of 94 per cent. Our set-up, which is now operational, improves the accuracy of the results and speed of analysis of Diogene experiments devoted to the study of central collisions between heavy ions [fr

A low-cost, ultra-fast and ultra-low noise preamplifier for silicon avalanche photodiodes

Science.gov (United States)

Gasmi, Khaled

2018-02-01

An ultra-fast and ultra-low noise preamplifier for amplifying the fast and weak electrical signals generated by silicon avalanche photodiodes has been designed and developed. It is characterized by its simplicity, compactness, reliability and low cost of construction. A very wide bandwidth of 300 MHz, a very good linearity from 1 kHz to 280 MHz, an ultra-low noise level at the input of only 1.7 nV Hz-1/2 and a very good stability are its key features. The compact size (70 mm  ×  90 mm) and light weight (45 g), as well as its excellent characteristics, make this preamplifier very competitive compared to any commercial preamplifier. The preamplifier, which is a main part of the detection system of a homemade laser remote sensing system, has been successfully tested. In addition, it is versatile and can be used in any optical detection system requiring high speed and very low noise electronics.

Studies of a hybrid avalanche photo-detector in magnetic field

Energy Technology Data Exchange (ETDEWEB)

Šantelj, L., E-mail: luka.santelj@kek.jp [High Energy Accelerator Research Organization (KEK) (Japan); Adachi, I. [High Energy Accelerator Research Organization (KEK) (Japan); Sokendai University (Japan); Hataya, K. [Tokyo Metropolitan University (Japan); Iori, S. [Toho University (Japan); Iwata, S.; Kakuno, H. [Tokyo Metropolitan University (Japan); Kataura, R. [Niigata University (Japan); Kawai, H. [Chiba University (Japan); Kindo, H. [Sokendai University (Japan); Korpar, S. [University of Maribor (Slovenia); Jožef Stefan Institute, Ljubljana (Slovenia); Križan, P. [Jožef Stefan Institute, Ljubljana (Slovenia); University of Ljubljana (Slovenia); Mrvar, M. [Jožef Stefan Institute, Ljubljana (Slovenia); Nath, K. [Indian Institute of Technology Guwahati (India); Nishida, S. [High Energy Accelerator Research Organization (KEK) (Japan); Sokendai University (Japan); Ogawa, S. [Niigata University (Japan); Pestotnik, R.; Stanovnik, A.; Seljak, A. [Jožef Stefan Institute, Ljubljana (Slovenia); Sumiyoshi, T. [Tokyo University of Science, Tokyo (Japan); Tabata, M. [Chiba University (Japan); and others

2017-02-11

For the Belle II spectrometer a proximity focusing RICH counter with an aerogel radiator (ARICH) will be employed as a PID system in the forward endcap region of the spectrometer. The main challenge was the development of a reliable multichannel sensor for single photons that operates in the high magnetic field of the spectrometer (1.5 T) and withstands the radiation levels expected at the experiment. A 144-channel Hybrid Avalanche Photo-Detector (HAPD) was developed with Hamamatsu Photonics K.K. and the mass production of ∼480 HAPDs was completed recently. While our first tests of HAPD performance in the magnetic field (before mass production) showed no issues, we lately observed a presence of very large signal pulses (∼5000× single photon signal), generated internally within about 20% of HAPDs, while operating in the magnetic field. The rate of these pulses varies from sample to sample. These pulses impact the HAPD performance in two ways: they introduce periods of dead time and, in some cases, damage to the front-end electronics was observed. Here we present conditions under which such large pulses are generated, their properties and impact on HAPD performance, and discuss possible mechanism of their origin.

The Effect of Metal-Semiconductor Contact on the Transient Photovoltaic Characteristic of HgCdTe PV Detector

Directory of Open Access Journals (Sweden)

Haoyang Cui

2013-01-01

Full Text Available The transient photovoltaic (PV characteristic of HgCdTe PV array is studied using an ultrafast laser. The photoresponse shows an apparent negative valley first, then it evolves into a positive peak. By employing a combined theoretical model of pn junction and Schottky potential, this photo-response polarity changing curves can be interpreted well. An obvious decreasing of ratio of negative valley to positive peak can be realized by limiting the illumination area of the array electrode. This shows that the photoelectric effect of Schottky barrier at metal-semiconductor (M/S interface is suppressed, which will verify the correctness of the model. The characteristic parameters of transient photo-response induced from p-n junction and Schottky potential are extracted by fitting the response curve utilizing this model. It shows that the negative PV response induced by the Schottky barrier decreases the positive photovoltage generated by the pn junction.

EXTREME WINTERS IN XX–XXI CENTURIES AS INDICATORS OF SNOWINESS AND AVALANCHE HAZARD IN THE PAST AND EXPECTED CLIMATE CHANGE CONDITIONS

Directory of Open Access Journals (Sweden)

A. D. Oleynikov

2012-01-01

Full Text Available Currently, due to the global climate change and increasing frequency of weather events focus is on prediction of climate extremes. Large-scale meteorological anomalies can cause long-term paralysis of social and economic infrastructure of the major mountain regions and even individual states. In winter periods, these anomalies are associated with prolonged heavy snowfalls and associated with them catastrophic avalanches which cause significant social and economic damage. The climate system maintains a certain momentum during periods of adjustment and transition to other conditions in the ratio of heat and moisture and contains a climate «signal» of the climates of the past and the future. In our view seasonal and yearly extremes perform the role of these indicators, study of which enables for a deeper understanding and appreciation of the real situation of the climate periods related to the modern ones. The paper provides an overview of the criteria for selection of extreme winters. Identification of extremely cold winters during the period of instrumental observation and assessment of their snowiness and avalanche activity done for the Elbrus region, which is a model site for study of the avalanche regime in the Central Caucasus. The studies aim to identify the extreme winters in the Greater Caucasus, assess their frequency of occurrence, characterize the scale and intensity of the avalanche formation. The data obtained can be used to identify winter-analogues in the reconstruction and long-term forecast of avalanches. 

Universal avalanche statistics and triggering close to failure in a mean-field model of rheological fracture

Science.gov (United States)

Baró, Jordi; Davidsen, Jörn

2018-03-01

The hypothesis of critical failure relates the presence of an ultimate stability point in the structural constitutive equation of materials to a divergence of characteristic scales in the microscopic dynamics responsible for deformation. Avalanche models involving critical failure have determined common universality classes for stick-slip processes and fracture. However, not all empirical failure processes exhibit the trademarks of criticality. The rheological properties of materials introduce dissipation, usually reproduced in conceptual models as a hardening of the coarse grained elements of the system. Here, we investigate the effects of transient hardening on (i) the activity rate and (ii) the statistical properties of avalanches. We find the explicit representation of transient hardening in the presence of generalized viscoelasticity and solve the corresponding mean-field model of fracture. In the quasistatic limit, the accelerated energy release is invariant with respect to rheology and the avalanche propagation can be reinterpreted in terms of a stochastic counting process. A single universality class can be defined from such analogy, and all statistical properties depend only on the distance to criticality. We also prove that interevent correlations emerge due to the hardening—even in the quasistatic limit—that can be interpreted as "aftershocks" and "foreshocks."

Performance and simulation of a double-gap resistive plate chamber in the avalanche mode

CERN Document Server

Ahn Sung Hwan; Hong Byung Sik; Hong Seong Jong; Ito, M; Kang, T I; Kim, B I; Kim, J H; Kim, Y J; Kim, Y U; Koo, D G; Lee Hyup Woo; Lee, K B; Lee Kyong Sei; Lee Seok Jae; Lim, J K; Moon, D H; Nam, S K; Park, S; Park, W J; Rhee June Tak; Ryu, M S; Sim Kwang Souk

2004-01-01

We present a detailed analysis of the time and the charge signals of a prototype double-gap resistive plate chamber for the endcap region of the Compact Muon Solenoid (CMS) detector at the Large Hadron Collider (LHC). The chamber was built with relatively low-resistivity bakelite. The time and the charge results demonstrate that the high- voltage plateau, which satisfies various CMS requirements for the efficiency, the noise cluster rate, the fraction of the large signal, and the streamer probability, can be extended at least up to 400 V with the present design. In addition, a simple avalanche multiplication model is studied in detail. The model can reproduce the experimental charge spectra reasonably well. The charge information enables us to estimate the effective Townsend coefficient in avalanche-mode operation.

Mapping flux avalanches in MgB2 films-equivalence between magneto-optical imaging and magnetic measurements

International Nuclear Information System (INIS)

Colauto, F; Choi, E M; Lee, J Y; Lee, S I; Yurchenko, V V; Johansen, T H; Ortiz, W A

2007-01-01

Vortex avalanches are known to occur in MgB 2 films within a certain range of temperatures and magnetic fields. These events, resulting from a thermomagnetic instability, were first revealed by real-time magneto-optical imaging, which exposed dendritic paths of abrupt flux propagation. This very powerful technique has, however, a practical limitation, since sensors that are currently available cannot be used at high magnetic fields. This letter shows that results obtained using dc magnetometry are in good correspondence with those furnished by magneto-optical imaging, demonstrating that the two techniques can be efficiently used as complementary tools to map vortex avalanches in superconducting films. (rapid communication)

Observation of Spectral Signatures of 1/f Dynamics in Avalanches on Granular Piles

Science.gov (United States)

Kim, Yong W.; Nishino, Thomas K.

1997-03-01

Granular piles of monodisperse glass spheres, 0.46+0.03 mm in diameter, have been studied. The base diameter of the pile has been varied from 3/8" to 2" in 1/8" increments. A single-grain dispenser with greater than 95consisting of a stepping motor-actuated reciprocating arm with a single-grain scoop. Each grain is dropped on the apex of the pile with lowest possible landing velocity at intervals at least 30longer than the duration of largest avalanches for each given pile. Each grain being added and being lost in avalanches from the pile is optically detected and recorded. The power spectrum of the net addition of grains to the pile as a function of time is found to be robustly 1/f for all base sizes. A wide variety of dynamical properties of 1/f systems, as obtained from the high precision data, will be presented.

Effect of thermal stress on the performance of HgCdTe/Si diodes and FPAs

International Nuclear Information System (INIS)

Zhang, Shan; Hu, Xiao-Ning

2012-01-01

As a typical hetero-epitaxial material, the HgCdTe film which directly grows on the Si substrate possesses great residual stress for the large lattice and thermal expansion mismatch. Thermal stress caused by the thermal expansion mismatch dominates the stress mechanism after growth and seriously affects the device performance. In this paper, the performance of the HgCdTe/Si material, diodes and focal plane arrays under different thermal stress condition was studied. The experimental results indicate that the performance regularly changes with the thermal stress and all the results can be duplicated and recoverable. By analyzing the changes of the energy band under different stress conditions, it was found that the stress in the HgCdTe film impacts the film's characteristics. The HgCdTe film with tensile stress exhibits higher electron mobility, while with the compressive stress, the film exhibits higher hole mobility than that of the bulk HgCdTe crystal. Finally, the theoretical analysis can explain the experimental results well. (paper)

Photon-counting monolithic avalanche photodiode arrays for the super collider

International Nuclear Information System (INIS)

Ishaque, A.N.; Castleberry, D.E.; Rougeot, H.M.

1994-01-01

In fiber tracking, calorimetry, and other high energy and nuclear physics experiments, the need arises to detect an optical signal consisting of a few photons (in some cases a single photoelectron) with a detector insensitive to magnetic fields. Previous attempts to detect a single photoelectron have involved avalanche photodiodes (APDs) operated in the Geiger mode, the visible light photon counter, and a photomultiplier tube with an APD as the anode. In this paper it is demonstrated that silicon APDs, biased below the breakdown voltage, can be used to detect a signal of a few photons with conventional pulse counting circuitry at room temperature. Moderate cooling, it is further argued, could make it possible to detect a single photoelectron. Monolithic arrays of silicon avalanche photodiodes fabricated by Radiation Monitoring Devices, Inc. (RMD) were evaluated for possible use in the Super Collider detector systems. Measurements on 3 element x 3 element (2 mm pitch) APD arrays, using pulse counting circuitry with a charge sensitive amplifier (CSA) and a Gaussian filter, are reported and found to conform to a simple noise model. The model is used to obtain the optimal operating point. Experimental results are described in Section II, modeling results in Section III, and the conclusions are summarized in Section IV

Does Avalanche Shovel Shape Affect Excavation Time: A Pilot Study

Directory of Open Access Journals (Sweden)

Kurt Schindelwig

2017-05-01

Full Text Available In Europe and North America, approximately 150 fatalities occur as a result of avalanches every year. However, it is unclear whether certain shovel shapes are more effective than others in snow removal during avalanche victim recovery. The objective was to determine the performance parameters with a developed standardized test using different shovel shapes and to determine sex-specific differences. Hence, several parameters were determined for clearing the snow from a snow filled box (15 men, 14 women. A flat (F and a deep (D shovel blade with the shaft connected straight (S or in clearing mode (C were used for the investigation of the shovel shapes FS, DC and the subsequent use of DC&DS. Mean snow mass shifted per unit time increased significantly from 1.50 kg/s with FS to 1.71 kg/s (14% with DS and further to 1.79 kg/s (4% with DC&DS for all participants. Snow mass shifted per unit time was 44% higher (p < 0.05 for men than for women. In excavation operations, the sex-specific physical performance should be taken into account. The results were limited to barely binding snow, because only with this snow did the tests show a high reliability.

Electron impact ionization of large krypton clusters

Institute of Scientific and Technical Information of China (English)

Li Shao-Hui; Li Ru-Xin; Ni Guo-Quan; Xu Zhi-Zhan

2004-01-01

We show that the detection of ionization of very large van der Waals clusters in a pulsed jet or a beam can be realized by using a fast ion gauge. Rapid positive feedback electron impact ionization and fragmentation processes,which are initially ignited by electron impact ionization of the krypton clusters with the electron current of the ion gauge, result in the appearance of a progressional oscillation-like ion spectrum, or just of a single fast event under critical conditions. Each line in the spectrum represents a correlated explosion or avalanche ionization of the clusters.The phenomena have been analysed qualitatively along with a Rayleigh scattering experiment of the corresponding cluster jet.

Ultra-Low Dark Current HgCdTe Detector in SWIR for Space Applications

Science.gov (United States)

Cervera, C.; Boulade, O.; Gravrand, O.; Lobre, C.; Guellec, F.; Sanson, E.; Ballet, P.; Santailler, J. L.; Moreau, V.; Zanatta, J. P.; Fieque, B.; Castelein, P.

2017-10-01

This paper presents recent developments at Commissariat à l'Energie atomique, Laboratoire d'Electronique et de Technologie de l'Information infrared laboratory on processing and characterization of p-on- n HgCdTe (MCT) planar infrared focal plane arrays (FPAs) in short-wave infrared (SWIR) spectral band for the astrophysics applications. These FPAs have been grown using both liquid phase epitaxy and molecular beam epitaxy on a lattice-matched CdZnTe substrate. This technology exhibits lower dark current and lower series resistance in comparison with n-on- p vacancy-doped architecture and is well adapted for low flux detection or high operating temperature. This architecture has been evaluated for space applications in long-wave infrared and very-long-wave infrared spectral bands with cut-off wavelengths from 10 μm up to 17 μm at 78 K and is now evaluated for the SWIR range. The metallurgical nature of the absorbing layer is also examined and both molecular beam epitaxy and liquid phase epitaxy have been investigated. Electro-optical characterizations have been performed on individual photodiodes from test arrays, whereas dark current investigation has been performed with a fully functional readout integrated circuit dedicated to low flux operations.

Stratigraphy, age, and correlation of voluminous debris-avalanche events from an ancestral Egmont Volcano : implications for coastal plain construction and regional hazard assessment

International Nuclear Information System (INIS)

Alloway, B.V.; McComb, P.; Neall, V.; Vucetich, C.; Gibb, J.; Sherburn, S.; Stirling, M.W.

2005-01-01

Two previously unrecognised debris-avalanche deposits have been identified on the eastern flanks of Egmont Volcano beneath a thick mantle of tephric and andic soil material that has mostly subdued their topographic expression. The Ngaere Formation is a c. 23 14 C ka large volume (>5.85 km 3 ) debris-avalanche deposit that is widely distributed over 320-500 km 2 of the north-east, south-east, and south portions of the Egmont ring plain. The second deposit, Okawa Formation, is a c. 105 ka large volume (>3.62 km 3 ) debris-avalanche deposit that has been mapped over a minimum area of 255 km 2 in northern and north-eastern Taranaki. Both debris-avalanche formations contain axial facies with hummocks composed mainly of block-supported brecciated andesitic debris. A less conspicuous marginal facies, texturally resembling a mudflow, is more extensive. A third debris-avalanche deposit (Motunui Formation) is extensively preserved along the north Taranaki coast where it is truncated by a c. 127 ka wave cut surface (NT2) and closely overlies a c. 210 ka wave cut surface (NT3). The source of this debris-avalanche deposit is unknown. Side-scan sonar and shallow seismic profiling have been useful in accurately delineating the distribution of combined Okawa and Motunui debris-avalanche deposits in the offshore environment but cannot distinguish between the two deposits or enable onshore spatial and volumetric estimates for each unit to be revised. However, the widespread occurrence of debris-avalanche rock material offshore does emphasise the importance of this lag material altering the orientation of the coast influencing both wave climate and rates of coastal erosion. Similarly, the extensive onshore occurrence of debris-avalanche rock material appears to be a significant factor in widening of the north Taranaki coastal plain and preservation of the NT2 and NT3 uplifted marine terrace surfaces. Initiation of collapse by magmatically-induced seismicity is apparently common at

Sem Analysis of particles from the 28, 000 B.P El Zaguan debris avalanche deposit, Nevado de Toluca volcano, Central Mexico: evidences of flow behavior during emplacement

Science.gov (United States)

Caballero, L.; Capra, L.

2008-12-01

The Zaguan deposit originated at 28, 000 yr. B.P from the flank collapse of the Nevado de Toluca volcano, a dacitic stratovolcano of the Transmexican Volcanic Belt. A Scanning Electron Microprobe analysis (SEM) was made to some clasts of this deposit to observe microtextures produced during transport and emplacement of the debris avalanche flow. Particles from 2, 0 and -2 Φ granulometric classes were randomly selected and their surface textures were described. The textures observed were divided in two groups, collision and shear structures indicating different clast interaction. Shear textures were observed predominantly on the basal part of the deposit and consisted of parallel ridges, parallel grooves, scratches and lips. Collision textures were mainly present in the upper part of the deposit and consisted of fractures, percussion marks, and broken or grinded crystals. These characteristics, coupled with field observation, like the presence of clast dikes and deformed lacustrine megaclasts, indicate that the basal part of the debris avalanche was moving in a partially liquefied state, were particles were not able to move freely because of the confinement exerted by the upper part of the flow, so shear stresses dominated. On the contrary, the particles in the upper part were able to move freely so the principal mechanism of interaction between particles was collision. These microscopic textures are in agreement with previously described behavior of emplacement of debris avalanches of volcanic origin, that suggest a stratified flow dominated by different transport and depositional mechanism depending on flow depth and possible fluid content at their base.

Cosmic Ray Measurements by Scintillators with Metal Resistor Semiconductor Avalanche Photo Diodes

Science.gov (United States)

Blanco, Francesco; La Rocca, Paola; Riggi, Francesco; Akindinov, Alexandre; Mal'kevich, Dmitry

2008-01-01

An educational set-up for cosmic ray physics experiments is described. The detector is based on scintillator tiles with a readout through metal resistor semiconductor (MRS) avalanche photo diode (APD) arrays. Typical measurements of the cosmic angular distribution at sea level and a study of the East-West asymmetry obtained by such a device are…

Photo-triggering and secondary electron produced ionization in electric discharge ArF* excimer lasers

Science.gov (United States)

Xiong, Zhongmin; Kushner, Mark J.

2011-10-01

Electric discharge excimer lasers are sustained in multi-atmosphere attaching gas mixtures that are typically preionized to enable a reproducible, uniform glow, which maximizes optical quality and gain. This preionization is often accomplished using UV light produced by a corona discharge within the plasma cavity. To quantify the relationship between corona discharge properties and those of the laser discharge, the triggering of electron avalanche by preionizing UV light in an electric discharge-pumped ArF* excimer laser was numerically investigated using a two-dimensional model. The preionizing UV fluxes were generated by a corona-bar discharge driven by the same voltage pulse as the main discharge sustained in a multi-atmospheric Ne/Ar/Xe/F2 gas mixture. The resulting peak photo-electron density in the inter-electrode spacing is around 108 cm-3, and its distribution is biased toward the UV source. The preionization density increases with increasing dielectric constant and capacitance of the corona bar. The symmetry and uniformity of the discharge are, however, improved significantly once the main avalanche develops. In addition to bulk electron impact ionization, the ionization generated by sheath accelerated secondary electrons was found to be important in sustaining the discharge current at experimentally observed values. At peak current, the magnitude of the ionization by sheath accelerated electrons is comparable to that from bulk electron impact in the vicinity of the cathode.

An accurate behavioral model for single-photon avalanche diode statistical performance simulation

Science.gov (United States)

Xu, Yue; Zhao, Tingchen; Li, Ding

2018-01-01

An accurate behavioral model is presented to simulate important statistical performance of single-photon avalanche diodes (SPADs), such as dark count and after-pulsing noise. The derived simulation model takes into account all important generation mechanisms of the two kinds of noise. For the first time, thermal agitation, trap-assisted tunneling and band-to-band tunneling mechanisms are simultaneously incorporated in the simulation model to evaluate dark count behavior of SPADs fabricated in deep sub-micron CMOS technology. Meanwhile, a complete carrier trapping and de-trapping process is considered in afterpulsing model and a simple analytical expression is derived to estimate after-pulsing probability. In particular, the key model parameters of avalanche triggering probability and electric field dependence of excess bias voltage are extracted from Geiger-mode TCAD simulation and this behavioral simulation model doesn't include any empirical parameters. The developed SPAD model is implemented in Verilog-A behavioral hardware description language and successfully operated on commercial Cadence Spectre simulator, showing good universality and compatibility. The model simulation results are in a good accordance with the test data, validating high simulation accuracy.

Single photon detection in a waveguide-coupled Ge-on-Si lateral avalanche photodiode.

Science.gov (United States)

Martinez, Nicholas J D; Gehl, Michael; Derose, Christopher T; Starbuck, Andrew L; Pomerene, Andrew T; Lentine, Anthony L; Trotter, Douglas C; Davids, Paul S

2017-07-10

We examine gated-Geiger mode operation of an integrated waveguide-coupled Ge-on-Si lateral avalanche photodiode (APD) and demonstrate single photon detection at low dark count for this mode of operation. Our integrated waveguide-coupled APD is fabricated using a selective epitaxial Ge-on-Si growth process resulting in a separate absorption and charge multiplication (SACM) design compatible with our silicon photonics platform. Single photon detection efficiency and dark count rate is measured as a function of temperature in order to understand and optimize performance characteristics in this device. We report single photon detection of 5.27% at 1310 nm and a dark count rate of 534 kHz at 80 K for a Ge-on-Si single photon avalanche diode. Dark count rate is the lowest for a Ge-on-Si single photon detector in this range of temperatures while maintaining competitive detection efficiency. A jitter of 105 ps was measured for this device.

Increasing rock-avalanche size and mobility in Glacier Bay National Park and Preserve, Alaska detected from 1984 to 2016 Landsat imagery

Science.gov (United States)

Coe, Jeffrey A.; Bessette-Kirton, Erin; Geertsema, Marten

2018-01-01

In the USA, climate change is expected to have an adverse impact on slope stability in Alaska. However, to date, there has been limited work done in Alaska to assess if changes in slope stability are occurring. To address this issue, we used 30-m Landsat imagery acquired from 1984 to 2016 to establish an inventory of 24 rock avalanches in a 5000-km2 area of Glacier Bay National Park and Preserve in southeast Alaska. A search of available earthquake catalogs revealed that none of the avalanches were triggered by earthquakes. Analyses of rock-avalanche magnitude, mobility, and frequency reveal a cluster of large (areas ranging from 5.5 to 22.2 km2), highly mobile (height/length slopes for failure during periods of warm temperatures.

Memory effect in gated single-photon avalanche diodes: a limiting noise contribution similar to afterpulsing

Science.gov (United States)

Contini, D.; Dalla Mora, A.; Di Sieno, L.; Cubeddu, R.; Tosi, A.; Boso, G.; Pifferi, A.

2013-03-01

In recent years, emerging applications, such as diffuse optical imaging and spectroscopy (e.g., functional brain imaging and optical mammography), in which a wide dynamic range is crucial, have turned the interest towards Single-Photon Avalanche Diode (SPAD). In these fields, the use of a fast-gated SPAD has proven to be a successful technique to increase the measurement sensitivity of different orders of magnitude. However, an unknown background noise has been observed at high illumination during the gate-OFF time, thus setting a limit to the maximum increase of the dynamic range. In this paper we describe this noise in thin-junction silicon single-photon avalanche diode when a large amount of photons reaches the gated detector during the OFF time preceding the enabling time. This memory effect increases the background noise with respect to primary dark count rate similarly to a classical afterpulsing process, but differently it is not related to a previous avalanche ignition in the detector. We discovered that memory effect increases linearly with the power of light impinging on the detector and it has an exponential trend with time constants far different from those of afterpulsing and independently of the bias voltage applied to the junction. For these reasons, the memory effect is not due to the same trapping states of afterpulsing and must be described as a different process.

Tuning magnetic avalanches in the molecular magnet Mn12 -acetate

Science.gov (United States)

McHugh, S.; Wen, Bo; Ma, Xiang; Sarachik, M. P.; Myasoedov, Y.; Zeldov, E.; Bagai, R.; Christou, G.

2009-05-01

Using micron-sized Hall sensor arrays to obtain time-resolved measurements of the local magnetization, we report a systematic study in the molecular magnet Mn12 acetate of magnetic avalanches controllably triggered in different fixed external magnetic fields and for different values of the initial magnetization. The speeds of propagation of the spin-reversal fronts are in good overall agreement with the theory of magnetic deflagration of Garanin and Chudnovsky [Phys. Rev. B 76, 054410 (2007)].

Electron trapping during irradiation in reoxidized nitrided oxide

International Nuclear Information System (INIS)

Mallik, A.; Vasi, J.; Chandorkar, A.N.

1993-01-01

Isochronal detrapping experiments have been performed following irradiation under different gate biases in reoxidized nitrided oxide (RNO) MOS capacitors. These show electron trapping by the nitridation-induced electron traps at low oxide fields during irradiation. A difference in the detrapping behavior of trapped holes and electrons is observed, with trapped holes being detrapped at relatively lower temperatures compared to trapped electrons. Electron trapping shows a strong dependence on tile magnitude of the applied gate bias during irradiation but is independent of its polarity. Conventional oxide devices, as expected, do not show any electron trapping during irradiation by the native electron traps. Finally, a comparison of the isochronal detrapping behavior following irradiation and following avalanche injection of electrons has been made to estimate the extent of electron trapping. The results show that electron trapping by the nitridation-induced electron traps does not play the dominant role in improving radiation performance of RNO, though its contribution cannot be completely neglected for low oxide field irradiations

Avalanche mode of high-voltage overloaded p{sup +}–i–n{sup +} diode switching to the conductive state by pulsed illumination

Energy Technology Data Exchange (ETDEWEB)

Kyuregyan, A. S., E-mail: ask@vei.ru [Lenin All-Russia Electrical Engineering Institute (Russian Federation)

2015-07-15

A simple analytical theory of the picosecond switching of high-voltage overloaded p{sup +}–i–n{sup +} photodiodes to the conductive state by pulsed illumination is presented. The relations between the parameters of structure, light pulse, external circuit, and main process characteristics, i.e., the amplitude of the active load current pulse, delay time, and switching duration, are derived and confirmed by numerical simulation. It is shown that the picosecond light pulse energy required for efficient switching can be decreased by 6–7 orders of magnitude due to the intense avalanche multiplication of electrons and holes. This offers the possibility of using pulsed semiconductor lasers as a control element of optron pairs.

Avalanche criticality in thermal-driven martensitic transitions: the asymmetry of the forward and reverse transitions in shape-memory materials

Science.gov (United States)

Planes, Antoni; Vives, Eduard

2017-08-01

Martensitic transitions take place intermittently as a sequence of avalanches which are accompanied by the emission of acoustic waves. The study of this acoustic emission (AE) reveals the scale-free nature of the avalanches. In a number of shape memory materials undergoing a martensitic transition it has been found that, in spite of relatively low hysteresis, the dynamics of forward and reverse transitions are different, which may explain the fact that the AE activity is different in both forward and reverse transitions. The asymmetry could be a consequence of the fact that, while nucleation is required for the transition from the parent to martensitic phase to take place, reverse transition occurs by fast shrinkage of martensitic domains. We have analysed in detail the distribution of avalanches in cooling and heating runs in Fe-Pd and Cu-Zn-Al shape-memory alloys. In the former, the martensitic transition is weakly first order while it shows a significant first order character in the latter. We have found that in Fe-Pd the distributions are power law for the forward and reverse transitions characterized by the same critical exponents. For Cu-Zn-Al the distribution of avalanches is critical in forward transitions but exponentially damped in the reverse transition. It is suggested that this different behaviour could originate from the different dynamic mechanisms in forward and reverse transitions. This paper is dedicated to our friend Ekhard Salje in the occasion of his 70th birthday.

LOCAL CONDITIONS AND IMPACTS OF THE AVALANCHES. CASE STUDIES IN REPRESENTATIVE SECTORS WITHIN PIATRA CRAIULUI AND FĂGĂRAȘ MOUNTAINS

Directory of Open Access Journals (Sweden)

ANCA MUNTEANU

2014-05-01

Full Text Available Genesis conditions and effects of avalanches. Case studies in representative sectors within Piatra Craiului and Fagars mountains. The present paper aims at investigating the avalanches and their impact on the environment components. Snow avalanches are natural phenomena, which are controlled by the specific features of the mountain realm. They start suddenly due to the combination of meteorological and non-meteorological factors, which make the loose materials (snow, ice, detritus, vegetation or soil collapse or slide down along the slope. In consequence, erosion is increased or facilitated because of the impact they have on the other components of the environment (thalwegs deepening, forest destruction. The distribution of avalanches is hard to be highlighted, because of the inaccessible lands and the adverse meteorological conditions. From this reason, one needs to know their complex features, namely the morphology, vegetation and spatial dynamics of the areas prone to such phenomena. The effects on the environment can be easily identified in the mountain realm, inasmuch as they create typical corridors along the streams crossing the forests. At the same time, however, they have certain effects on the slope deposits, too. These will be further presented with examples for the eastern slope of the Piatra Craiului Mts. and the Suru – Negoiu section in the Făgăraș Mts. These areas are deemed representative for each of the mentioned mountain massifs.

Stratigraphic reconstruction of the 13 ka BP debris avalanche deposit at Colima volcano (Mexico): effect of climatic conditions on the flow mobility

Science.gov (United States)

Roverato, M.; Capra, L.

2010-12-01

Colima volcano is an andesitic stratovolcano located in the western part of the Trans-Mexican Volcanic Belt (TMVB) and at the southern end of the N-S trending Colima graben, about 70 km from the Pacific Ocean coast. It is probably the most active Mexican volcano in historic time and one of the most active of North America. Colima volcano yielded numerous partial edifice collapses with emplacement of debris avalanche deposits (DADs) of contrasting volume, morphology, texture and origin. This work has the aim to provide the evidences of how the climatic condition during the 13 ka flank collapse of the Colima volcano affected the textural characteristic and the mobility of the debris avalanche and debris flow originated from this event that occurred just after the Last Glacial Maximum in Mexico (18.4-14.5 ka 14C BP with snow line at 3600 m a.s.l. up to 13 ka BP). The 13,000 yrs old debris avalanche deposit, here named Tonila (TDAD) presents the typical debris avalanche textural characteristics (angular to sub-angular clasts, coarse matrix, jigsaw fit) but at approximately 13 km from the source, the deposit transforms to an hybrid phase with debris avalanche fragments imbedded in a finer, homogenous and indurated matrix more similar to a debris flow deposit. The debris avalanche deposit is directly overly by debris flows, often more than 10 m thick that contains large amount of logs from pine tree, mostly accumulated toward the base and imbricated down flow. Fluvial deposits also occur throughout all successions, representing periods of stream and river reworking highly localized and re-establishment. All these evidences point to the presence of water in the mass previous to the failure. The event here described represent an anomalous event between the previously described deposit associated to volcanic complex, and evidence as climatic condition can alter and modifies the depositional sequences incrementing the hazard.

Best-Practice Criteria for Practical Security of Self-Differencing Avalanche Photodiode Detectors in Quantum Key Distribution

Science.gov (United States)

Koehler-Sidki, A.; Dynes, J. F.; Lucamarini, M.; Roberts, G. L.; Sharpe, A. W.; Yuan, Z. L.; Shields, A. J.

2018-04-01

Fast-gated avalanche photodiodes (APDs) are the most commonly used single photon detectors for high-bit-rate quantum key distribution (QKD). Their robustness against external attacks is crucial to the overall security of a QKD system, or even an entire QKD network. We investigate the behavior of a gigahertz-gated, self-differencing (In,Ga)As APD under strong illumination, a tactic Eve often uses to bring detectors under her control. Our experiment and modeling reveal that the negative feedback by the photocurrent safeguards the detector from being blinded through reducing its avalanche probability and/or strengthening the capacitive response. Based on this finding, we propose a set of best-practice criteria for designing and operating fast-gated APD detectors to ensure their practical security in QKD.

Rock avalanche and rock glacier: A compound landform study from Hornsund, Svalbard

Czech Academy of Sciences Publication Activity Database

Hartvich, Filip; Blahůt, Jan; Stemberk, Josef

2017-01-01

Roč. 276, JAN 1 (2017), s. 244-256 ISSN 0169-555X R&D Projects: GA MŠk(CZ) LM2015079; GA MŠk(CZ) LG15007 Institutional support: RVO:67985891 Keywords : ERT * TLS (LiDAR) * lichenometry * morphometry * rock avalanche * rock glacier * Schmidt hammer * Svalbard * Hornsund Subject RIV: DB - Geology ; Mineralogy OBOR OECD: Geology Impact factor: 2.958, year: 2016

Geomorphological analysis, monitoring and modeling of large rock avalanches in northern Chile (Iquique area) for regional hazard assessment.

Science.gov (United States)

Yugsi Molina, F. X.; Hermanns, R. L.; Crosta, G. B.; Dehls, J.; Sosio, R.; Sepúlveda, S. A.

2012-04-01

Iquique is a city of about 215,000 inhabitants (Chilean national census 2002) settled on one of the seismic gaps in the South American subduction zone, where a M >8 earthquake with overdue return periods of ca. 100 yr is expected in the near future. The city has only two access roads coming from the east and south. The road to the east comes down along the escarpment that connects the Coastal Cordillera to the Coastal Plain. The road has been blocked by small magnitude earthquake-triggered landslides at least once in recent years. The second road, coming from the south, crosses along the Coastal Plain and connects the city to the airport where at least ten ancient debris deposits related to rock avalanches are found. These facts show the importance of determining the effects of a future high magnitude earthquake on the stability of the slopes in the area and the impact of possible slope failures on people, infrastructure and emergency management. The present work covers an area of approximately 130 km2 parallel to the coastline to the south of Iquique, divided into the two main morphological units briefly mentioned above. The eastern part corresponds to the Coastal Cordillera, a set of smoothed hills and shallow valleys that reaches up to 1200 m asl. This sector is limited to the west by a steep escarpment followed by the Coastal Plain and a narrow emerged marine plateau (1-3 km wide) locally overlaid by deposits of recent rock avalanches. Rock avalanche events have recurrently occurred at two sites to the north and center of the study area on the Coastal Cordillera escarpment. Another major single event has been mapped to the south. Marls, red and black shales, and shallow marine glauconitic deposits from Jurassic constitute the source rock for the rock avalanches in all sites. Clusters of deposits are found in the first two sites (retrogressive advance) with younger events running shorter distances and partially overlaying the older ones. Multiple lobes have been

InGaAs/InAlAs single photon avalanche diode for 1550 nm photons.

Science.gov (United States)

Meng, Xiao; Xie, Shiyu; Zhou, Xinxin; Calandri, Niccolò; Sanzaro, Mirko; Tosi, Alberto; Tan, Chee Hing; Ng, Jo Shien

2016-03-01

A single photon avalanche diode (SPAD) with an InGaAs absorption region, and an InAlAs avalanche region was designed and demonstrated to detect 1550 nm wavelength photons. The characterization included leakage current, dark count rate and single photon detection efficiency as functions of temperature from 210 to 294 K. The SPAD exhibited good temperature stability, with breakdown voltage dependence of approximately 45 mV K(-1). Operating at 210 K and in a gated mode, the SPAD achieved a photon detection probability of 26% at 1550 nm with a dark count rate of 1 × 10(8) Hz. The time response of the SPAD showed decreasing timing jitter (full width at half maximum) with increasing overbias voltage, with 70 ps being the smallest timing jitter measured.

High speed, wide dynamic range analog signal processing for avalanche photodiode

CERN Document Server

Walder, J P; Pangaud, P

2000-01-01

A wide dynamic range multi-gain analog transimpedance amplifier integrated circuit has been developed for avalanche photodiode signal processing. The 96 dB input dynamic range is divided into four ranges of 12-bits each in order to provide 40 MHz analog sampled data to a 12-bits ADC. This concept which has been integrated in both BiCMOS and full complementary bipolar technology along with fitted design techniques will be presented.

High speed, wide dynamic range analog signal processing for avalanche photodiode

International Nuclear Information System (INIS)

Walder, J.P.; El Mamouni, Houmani; Pangaud, Patrick

2000-01-01

A wide dynamic range multi-gain analog transimpedance amplifier integrated circuit has been developed for avalanche photodiode signal processing. The 96 dB input dynamic range is divided into four ranges of 12-bits each in order to provide 40 MHz analog sampled data to a 12-bits ADC. This concept which has been integrated in both BiCMOS and full complementary bipolar technology along with fitted design techniques will be presented

High speed, wide dynamic range analog signal processing for avalanche photodiode

Energy Technology Data Exchange (ETDEWEB)

Walder, J.P. E-mail: walder@in2p3.fr; El Mamouni, Houmani; Pangaud, Patrick

2000-03-11

A wide dynamic range multi-gain analog transimpedance amplifier integrated circuit has been developed for avalanche photodiode signal processing. The 96 dB input dynamic range is divided into four ranges of 12-bits each in order to provide 40 MHz analog sampled data to a 12-bits ADC. This concept which has been integrated in both BiCMOS and full complementary bipolar technology along with fitted design techniques will be presented.

Efficient numerical schemes for viscoplastic avalanches. Part 1: The 1D case

Energy Technology Data Exchange (ETDEWEB)

Fernández-Nieto, Enrique D., E-mail: edofer@us.es [Departamento de Matemática Aplicada I, Universidad de Sevilla, E.T.S. Arquitectura, Avda, Reina Mercedes, s/n, 41012 Sevilla (Spain); Gallardo, José M., E-mail: jmgallardo@uma.es [Departamento de Análisis Matemático, Universidad de Málaga, F. Ciencias, Campus Teatinos S/N (Spain); Vigneaux, Paul, E-mail: Paul.Vigneaux@math.cnrs.fr [Unitée de Mathématiques Pures et Appliquées, Ecole Normale Supérieure de Lyon, 46 allée d' Italie, 69364 Lyon Cedex 07 (France)

2014-05-01

This paper deals with the numerical resolution of a shallow water viscoplastic flow model. Viscoplastic materials are characterized by the existence of a yield stress: below a certain critical threshold in the imposed stress, there is no deformation and the material behaves like a rigid solid, but when that yield value is exceeded, the material flows like a fluid. In the context of avalanches, it means that after going down a slope, the material can stop and its free surface has a non-trivial shape, as opposed to the case of water (Newtonian fluid). The model involves variational inequalities associated with the yield threshold: finite-volume schemes are used together with duality methods (namely Augmented Lagrangian and Bermúdez–Moreno) to discretize the problem. To be able to accurately simulate the stopping behavior of the avalanche, new schemes need to be designed, involving the classical notion of well-balancing. In the present context, it needs to be extended to take into account the viscoplastic nature of the material as well as general bottoms with wet/dry fronts which are encountered in geophysical geometries. We derived such schemes and numerical experiments are presented to show their performances.

The use dynamic avalanching and fractal analysis to characterise uranium oxide powders

International Nuclear Information System (INIS)

Hobbs, J.W.; Rhodes, D.

2000-01-01

Direct thermal denitration is an attractive method of co-converting mixed-metal nitrate solutions of plutonium and uranium into oxide because of its apparent simplicity. Such benefits are often marred by the relatively poor powder quality and handling characteristics, which can be overcome by modifications to the process chemistry. To ensure that powder synthesis routes under assessment require the minimal further processing it is necessary to be able to characterise the powder fully in term of the key fundamental properties. This paper will demonstrate the use of a dynamic avalanching technique, fractal analysis and morphology to assess processing behaviour. The use of dynamic avalanching to uniquely characterise the chaotic flow properties of urania powders has proved successful and results have shown that this technique is capable of detecting small differences in processing behaviour due changes in morphologies and particle size distribution. This technique has promise for being able to provide nearly instantaneous feedback to the powder generation process being monitored (e.g. calcination, milling, mixing). The use of fractals to describe powders is an interesting characterisation tool when combined with morphological shape factors and the flow index. (authors)

An avalanche counter and encoder system for counting and mapping radioactive specimens

International Nuclear Information System (INIS)

Britten, R.J.

1988-01-01

A parallel plate counter utilizes avalanche event counting over a large area with the ability to locate radioactive sources in two dimensions. One novel embodiment comprises a gas-filled chamber formed by a stretched stainless steel window cathode spaced from a flat semiconductive anode surface between which a high voltage is applied. When a beta ray, for example, enters the chamber, an ionization event occurs and the avalanche effect multiplies the event and results in charge collection on the anode surface for a limited period of time before the charge leaks away. An encoder system, comprising a symmetrical array of planar conductive surfaces separated from the anode by a dielectric material, couples charge currents the amplitude of which define the relative position of the ionization event. A number of preferred encoder system embodiments are disclosed including a novel matrix or grid pattern of electrical paths connected to voltage dividers and charge sensitive integrating amplifiers. The amplitude of coupled current delivered to the amplifiers defines the location of the event, and spatial resolution for a given signal-to-noise ratio can be controlled by changing the number of such amplifiers. (author) 11 figs

The properties of ITE's silicon avalanche photodiodes within the spectral range used in scintillation detection

CERN Document Server

Wegrzecka, I

1999-01-01

The design and properties of 3 mm silicon avalanche photodiodes developed at ITE are presented. Their performance parameters within the spectral range applicable in scintillation detection (400-700 nm) are discussed and compared to those for near infrared radiation.

The properties of ITE's silicon avalanche photodiodes within the spectral range used in scintillation detection

Science.gov (United States)

Wegrzecka, Iwona; Wegrzecki, Maciej

1999-04-01

The design and properties of 3 mm silicon avalanche photodiodes developed at ITE are presented. Their performance parameters within the spectral range applicable in scintillation detection (400-700 nm) are discussed and compared to those for near infrared radiation.

The Acheron rock avalanche deposit, Canterbury, New Zealand : age and implications for dating landslides

International Nuclear Information System (INIS)

Smith, G.M.; Bell, D.H.; Davies, T.R.H.

2012-01-01

New radiocarbon ages for wood samples retrieved from the base of the Acheron rock avalanche near Porters Pass, Canterbury, show a clustering of ages between 1370 and 1101 yr BP. This is significantly dissimilar to the established radiocarbon age of 500 ± 69 yr BP (NZ547), from weathering-rind thickness measurements and from lichen studies. This contradiction impacts on current calibrations of lichenometric and weathering-rind dating methods, which has serious implications for landslide and earthquake dates based on them. A 500-600 yr BP earthquake event along the Porters Pass-Amberley Fault Zone has been dated in an adjacent trench and is consistent with previous dates but does not correspond to the Acheron rock avalanche emplacement as previously proposed. The landslide may have been caused by either a Porters Pass Fault event (1100-800 yr BP) or by the better-constrained Round Top event (1010 ± 50 yr BP) on the Alpine Fault. (author). 30 refs., 13 figs., 2 tabs.

Hybrid AlGaN-SiC Avalanche Photodiode for Deep-UV Photon Detection

Science.gov (United States)

Aslam, Shahid; Herrero, Federico A.; Sigwarth, John; Goldsman, Neil; Akturk, Akin

2010-01-01

The proposed device is capable of counting ultraviolet (UV) photons, is compatible for inclusion into space instruments, and has applications as deep- UV detectors for calibration systems, curing systems, and crack detection. The device is based on a Separate Absorption and Charge Multiplication (SACM) structure. It is based on aluminum gallium nitride (AlGaN) absorber on a silicon carbide APD (avalanche photodiode). The AlGaN layer absorbs incident UV photons and injects photogenerated carriers into an underlying SiC APD that is operated in Geiger mode and provides current multiplication via avalanche breakdown. The solid-state detector is capable of sensing 100-to-365-nanometer wavelength radiation at a flux level as low as 6 photons/pixel/s. Advantages include, visible-light blindness, operation in harsh environments (e.g., high temperatures), deep-UV detection response, high gain, and Geiger mode operation at low voltage. Furthermore, the device can also be designed in array formats, e.g., linear arrays or 2D arrays (micropixels inside a superpixel).

Large-area NbN superconducting nanowire avalanche photon detectors with saturated detection efficiency

Science.gov (United States)

Murphy, Ryan P.; Grein, Matthew E.; Gudmundsen, Theodore J.; McCaughan, Adam; Najafi, Faraz; Berggren, Karl K.; Marsili, Francesco; Dauler, Eric A.

2015-05-01

Superconducting circuits comprising SNSPDs placed in parallel—superconducting nanowire avalanche photodetectors, or SNAPs—have previously been demonstrated to improve the output signal-to-noise ratio (SNR) by increasing the critical current. In this work, we employ a 2-SNAP superconducting circuit with narrow (40 nm) niobium nitride (NbN) nanowires to improve the system detection efficiency to near-IR photons while maintaining high SNR. Additionally, while previous 2-SNAP demonstrations have added external choke inductance to stabilize the avalanching photocurrent, we show that the external inductance can be entirely folded into the active area by cascading 2-SNAP devices in series to produce a greatly increased active area. We fabricated series-2-SNAP (s2-SNAP) circuits with a nanowire length of 20 μm with cascades of 2-SNAPs providing the choke inductance necessary for SNAP operation. We observed that (1) the detection efficiency saturated at high bias currents, and (2) the 40 nm 2-SNAP circuit critical current was approximately twice that for a 40 nm non-SNAP configuration.

Spatial and temporal analysis of fatal off-piste and backcountry avalanche accidents in Austria with a comparison of results in Switzerland, France, Italy and the US

Science.gov (United States)

Pfeifer, Christian; Höller, Peter; Zeileis, Achim

2018-02-01

In this article we analyzed spatial and temporal patterns of fatal Austrian avalanche accidents caused by backcountry and off-piste skiers and snowboarders within the winter periods 1967/1968-2015/2016. The data were based on reports of the Austrian Board for Alpine Safety and reports of the information services of the federal states. Using the date and the location of the recorded avalanche accidents, we were able to carry out spatial and temporal analyses applying generalized additive models and Markov random-field models. As a result of the trend analysis we noticed an increasing trend of backcountry and off-piste avalanche fatalities within the winter periods 1967/1968-2015/2016 (although slightly decreasing in recent years), which is in contradiction to the widespread opinion in Austria that the number of fatalities is constant over time. Additionally, we compared Austrian results with results of Switzerland, France, Italy and the US based on data from the International Commission of Alpine Rescue (ICAR). As a result of the spatial analysis, we noticed two hot spots of avalanche fatalities (Arlberg-Silvretta and Sölden). Because of the increasing trend and the rather narrow regional distribution of the fatalities, initiatives aimed at preventing avalanche accidents were highly recommended.

Implications of geomorphological research for recent and prehistoric avalanches and related hazards at Huascaran, Peru

Czech Academy of Sciences Publication Activity Database

Klimeš, Jan; Vilímek, V.; Omelka, M.

2009-01-01

Roč. 50, č. 1 (2009), s. 193-209 ISSN 0921-030X Institutional research plan: CEZ:AV0Z30460519 Keywords : rock debris avalanches * natural hazards * Huascaran Subject RIV: DE - Earth Magnetism, Geodesy, Geography Impact factor: 1.217, year: 2009

The Morsárjökull rock avalanche in the southern part of the Vatnajökull glacier, south Iceland

Science.gov (United States)

Sæmundsson, Şorsteinn; Sigurősson, Ingvar A.; Pétursson, Halldór G.; Decaulne, Armelle; Jónsson, Helgi P.

2010-05-01

On the 20th of March 2007 a large rock avalanche fell on Morsárjökull, one of the outlet glaciers from the southern part of the Vatnajökull ice cap, in south Iceland. This is considered to be one of the largest rock avalanches which have occurred in Iceland during the last decades. It is believed that it fell in two separate stages, the main part fell on the 20th of March and the second and smaller one, on the 17th of April 2007. The Morsárjökull outlet glacier is about 4 km long and surrounded by up to 1000 m high valley slopes. The outlet glacier is fed by two ice falls which are partly disconnected to the main ice cap of Vatnajökull, which indicates that the glacier is mainly fed by ice avalanches. The rock avalanche fell on the eastern side of the uppermost part of the Morsárjökull outlet glacier and covered about 1/5 of the glacier surface, an area of about 720,000 m2. The scar of the rock avalanche is located on the north face of the headwall above the uppermost part of the glacier. It is around 330 m high, reaching from about 620 m up to 950 m, showing that the main part of the slope collapsed. It is estimated that about 4 million m3 of rock debris fell on the glacier, or about 10 million tons. The accumulation lobe is up to 1.6 km long, reaching from 520 m a.s.l., to about 350 m a.s.l. Its width is from 125 m to 650 m, or on average 480 m. The total area which the lobe covers is around 720.000 m2 and its mean thickness 5.5 m. The surface of the lobe shows longitudinal ridges and grooves and narrow flow-like lobes, indicating that the debris mass evolved down glacier as a mixture of a slide and debris flow. The debris mass is coarse grained and boulder rich. Blocks over 5 to 8 m in diameter are common on the edges of the lobe up to 1.6 km from the source. No indication was observed of any deformation of the glacier surface under the debris mass. The first glaciological measurements of Morsárjökull outlet glacier were carried out in the year 1896

Electronic Transport Behaviors due to Charge Density Waves in Ni-Nb-Zr-H Glassy Alloys

Science.gov (United States)

Fukuhara, Mikio; Umemori, Yoshimasa

2013-11-01

The amorphous Ni-Nb-Zr-H glassy alloy containing subnanometer-sized icosahedral Zr5 Nb5Ni3 clusters exhibited four types of electronic phenomena: a metal/insulator transition, an electric current-induced voltage oscillation (Coulomb oscillation), giant capacitor behavior and an electron avalanche with superior resistivity. These findings could be excluded by charge density waves that the low-dimensional component of clusters, in which the atoms are lined up in chains along the [130] direction, plays important roles in various electron transport phenomena.

Development of a 144-channel Hybrid Avalanche Photo-Detector for Belle II ring-imaging Cherenkov counter with an aerogel radiator

Energy Technology Data Exchange (ETDEWEB)

Nishida, S., E-mail: shohei.nishida@kek.jp [High Energy Accelerator Research Organization (KEK), Tsukuba (Japan); Adachi, I. [High Energy Accelerator Research Organization (KEK), Tsukuba (Japan); Hamada, N. [Toho University, Funabashi (Japan); Hara, K. [High Energy Accelerator Research Organization (KEK), Tsukuba (Japan); Iijima, T. [Nagoya University, Nagoya (Japan); Iwata, S.; Kakuno, H. [Tokyo Metropolitan University, Hachioji (Japan); Kawai, H. [Chiba University, Chiba (Japan); Korpar, S.; Krizan, P. [Jozef Stefan Institute, Ljubljana (Slovenia); Ogawa, S. [Toho University, Funabashi (Japan); Pestotnik, R.; Ŝantelj, L.; Seljak, A. [Jozef Stefan Institute, Ljubljana (Slovenia); Sumiyoshi, T. [Tokyo Metropolitan University, Hachioji (Japan); Tabata, M. [Chiba University, Chiba (Japan); Tahirovic, E. [Jozef Stefan Institute, Ljubljana (Slovenia); Yoshida, K. [Tokyo Metropolitan University, Hachioji (Japan); Yusa, Y. [Niigata University, Niigata (Japan)

2015-07-01

The Belle II detector, a follow up of the very successful Belle experiment, is under construction at the SuperKEKB electron–positron collider at KEK in Japan. For the PID system in the forward region of the spectrometer, a proximity-focusing ring-imaging Cherenkov counter with an aerogel radiator is being developed. For the position sensitive photon sensor, a 144-channel Hybrid Avalanche Photo-Detector has been developed with Hamamatsu Photonics K.K. In this report, we describe the specification of the Hybrid Avalanche Photo-Detector and the status of the mass production.

Novel Photon-Counting Detectors for Free-Space Communication

Science.gov (United States)

Krainak, Michael A.; Yang, Guan; Sun, Xiaoli; Lu, Wei; Merritt, Scott; Beck, Jeff

2016-01-01

We present performance data for novel photon counting detectors for free space optical communication. NASA GSFC is testing the performance of three novel photon counting detectors 1) a 2x8 mercury cadmium telluride avalanche array made by DRS Inc. 2) a commercial 2880 silicon avalanche photodiode array and 3) a prototype resonant cavity silicon avalanche photodiode array. We will present and compare dark count, photon detection efficiency, wavelength response and communication performance data for these detectors. We discuss system wavelength trades and architectures for optimizing overall communication link sensitivity, data rate and cost performance. The HgCdTe APD array has photon detection efficiencies of greater than 50 were routinely demonstrated across 5 arrays, with one array reaching a maximum PDE of 70. High resolution pixel-surface spot scans were performed and the junction diameters of the diodes were measured. The junction diameter was decreased from 31 m to 25 m resulting in a 2x increase in e-APD gain from 470 on the 2010 array to 1100 on the array delivered to NASA GSFC. Mean single photon SNRs of over 12 were demonstrated at excess noise factors of 1.2-1.3.The commercial silicon APD array has a fast output with rise times of 300ps and pulse widths of 600ps. Received and filtered signals from the entire array are multiplexed onto this single fast output. The prototype resonant cavity silicon APD array is being developed for use at 1 micron wavelength.

The Chimborazo sector collapse and debris avalanche: Deposit characteristics as evidence of emplacement mechanisms

Science.gov (United States)

Bernard, Benjamin; van Wyk de Vries, Benjamin; Barba, Diego; Leyrit, Hervé; Robin, Claude; Alcaraz, Samantha; Samaniego, Pablo

2008-09-01

Chimborazo is a Late Pleistocene to Holocene stratovolcano located at the southwest end of the main Ecuadorian volcanic arc. It experienced a large sector collapse and debris avalanche (DA) of the initial edifice (CH-I). This left a 4 km wide scar, removing 8.0 ± 0.5 km 3 of the edifice. The debris avalanche deposit (DAD) is abundantly exposed throughout the Riobamba Basin to the Río Chambo, more than 35 km southeast of the volcano. The DAD averages a thickness of 40 m, covers about 280 km 2, and has a volume of > 11 km 3. Two main DAD facies are recognized: block and mixed facies. The block facies is derived predominantly from edifice lava and forms > 80 vol.% of the DAD, with a probable volume increase of 15-25 vol.%. The mixed facies was essentially created by mixing brecciated edifice rock with substratum and is found mainly in distal and marginal areas. The DAD has clear surface ridges and hummocks, and internal structures such as jigsaw cracks, injections, and shear-zone features are widespread. Structures such as stretched blocks along the base contact indicate high basal shear. Substratum incorporation is directly observed at the base and is inferred from the presence of substratum-derived material in the DAD body. Based on the facies and structural interpretation, we propose an emplacement model of a lava-rich avalanche strongly cataclased before and/or during failure initiation. The flow mobilises and incorporates significant substrata (10-14 vol.%) while developing a fine lubricating basal layer. The substrata-dominated mixed facies is transported to the DAD interior and top in dykes invading previously-formed fractures.

Intermittency, avalanche statistics, and long-term correlations in a turbulent plasma

International Nuclear Information System (INIS)

Castellanos, Omar; Sentíes, José M; Anabitarte, Ernesto; López, Juan M

2013-01-01

We study the turbulent dynamics of a helium plasma in a non-confining cylindrical configuration. Our experimental setup allows us to analyze particle transport in different plasma regions. We find that, whereas the transport is diffusive in the innermost regions of the plasma, distinctive non-diffusive features appear in regions away from the center. Indeed, at the plasma edge we find that particle flux exhibits a power-law distribution of avalanche durations, intermittency, and long-term correlations. (paper)

On the short-circuit and avalanche ruggedness reliability assessment of SiC MOSFET modules

DEFF Research Database (Denmark)

Ionita, Claudiu; Nawaz, Muhammad; Ilves, Kalle

2017-01-01

to failure, a gate-source voltage drop has been recorded, which is associated with a high G-S leakage current. The main failure mechanism, however, is the thermal runaway which leads the devices into avalanche breakdown mode. During the UIS tests, multiple samples from the three vendors of the power modules...

Projected changes of snow conditions and avalanche activity in a warming climate: a case study in the French Alps over the 2020-2050 and 2070-2100 periods

Science.gov (United States)

Castebrunet, H.; Eckert, N.; Giraud, G.; Durand, Y.; Morin, S.

2014-01-01

Projecting changes in snow cover due to climate warming is important for many societal issues, including adaptation of avalanche risk mitigation strategies. Efficient modeling of future snow cover requires high resolution to properly resolve the topography. Here, we detail results obtained through statistical downscaling techniques allowing simulations of future snowpack conditions for the mid- and late 21st century in the French Alps under three climate change scenarios. Refined statistical descriptions of snowpack characteristics are provided with regards to a 1960-1990 reference period, including latitudinal, altitudinal and seasonal gradients. These results are then used to feed a statistical model of avalanche activity-snow conditions-meteorological conditions relationships, so as to produce the first prognoses at annual/seasonal time scales of future natural avalanche activity eventually based on past observations. The resulting statistical indicators are fundamental for the mountain economy in terms of changes anticipation. At all considered spatio-temporal scales, whereas precipitations are expected to remain quite stationary, temperature increase interacting with topography will control snow-related variables, for instance the rate of decrease of total and dry snow depths, and the successive increase/decrease of the wet snow pack. Overall, with regards to the reference period, changes are strong for the end of the 21st century, but already significant for the mid-century. Changes in winter are somewhat less important than in spring, but wet snow conditions will appear at high elevations earlier in the season. For a given altitude, the Southern French Alps will not be significantly more affected than the Northern French Alps, so that the snowpack characteristics will be preserved more lately in the southern massifs of higher mean altitude. Regarding avalanche activity, a general -20-30% decrease and interannual variability is forecasted, relatively strong

A method to quench and recharge avalanche photo diodes for use in high rate situations

International Nuclear Information System (INIS)

Regan, T.O.; Fenker, H.C.; Thomas, J.; Oliver, J.

1992-06-01

We present a new method of using Avalanche Photo Diodes (APDS) for low level light detection in Geiger mode in high rate situations such as those encountered at the Superconducting Super Collider (SSC). The new technique is readily adaptable to implementation in CMOS VLSI

Rock avalanche occurrence in the San Juan province (Argentina): an analysis of their spatial distribution and main forcing factors

Science.gov (United States)

Penna, Ivanna; Tonini, Marj; Vega Orozco, Carmen D.; Longchamp, Céline; Derron, Marc-Henri; Jaboyedoff, Michel

2013-04-01

Rock avalanches are frequent phenomena in the Argentinean Andes and a particular high concentration of these events is observed in the Northwest (~25°S) and in the Central Andes from 30°S until the transition with the Patagonian Andes (~38°S). Tectonic deformation and seismicity are generally proposed as main driving factors, with weather and lithologic conditions playing a subordinate role. From 28°S to 33°S, the subhorizontal subduction of the Nazca plate drives higher shortening rates than in the surrounding areas, and an intense seismicity. Main morphotectonic units in this regions are the Cordillera and Precordillera, separated by the Barreal-Calingasta depression. In the southern central part of the flat subduction area (30°30'°-32°30'S), it is observed high valley incision and maximum local relief of 2900 m, while in the Precordillera main fluvial courses developed in the inter-thrust valleys, where local relief is up to 2400 m. In both mountain ranges, we recognized 34 rock avalanches deposits with volumes up to 0.3 km3. There is no apparent lithologic control on detachments, which involved sedimentary, volcanic and granite rocks, even though ~20% of them were favored by layering orientation. However, about 50% of the inventoried rock avalanches with the greatest volumes, developed along tectonic structures or less than 1 km far from them. The main objective of the present study is to explore the spatial distribution of rock avalanche deposits, and compare it with the instrumental seismicity and landscape conditions by means of statistical tools (e.g. exploratory data analyses, Ripley's K-function). Those analyses allow to highlight the spatial correlation between the geological events. Moreover, to visually display the detected cluster spatial patterns we elaborated kernel density maps. Our findings revealed that most of the rock avalanches show a high spatial aggregation mainly between 31°20'S-31°50'S. Main concentration of bedrock landslides

Influence of roughness bottom on the dynamics of a buoyant cloud : application to a powder avalanche

Science.gov (United States)

Brossard, D.; Naaim-Bouvet, F.; Naaim, M.; Caccamo, P.

2009-04-01

A powder avalanche is referred to as a turbulent flow of snow particles in air. In the past such avalanches have been modelled by buoyant cloud in a watertank: buoyant clouds flow along an inclined plane from a small immersed tank with a release gate (injection is of short duration). The powder avalanches are simulated by a heavy fluid (salt water + colorant or kaolin) which is dispersing in a lighter one. Such experiments allow studies for the influence of roughness bottoms on the dynamics of a buoyant clouds. The authors studied the flows of buoyant clouds on an uniform slope of 20° with different roughness: smooth PVC, abrasive paper, bottom covered with glued particles of PMMA or with glued glass beads of different sizes arranged in a compact way. The released volume varies between 2 to 4 liters and the density of salted water is 1.2. Two cameras are used to obtain the height together with the front velocity. Inside the study area the front velocity is approximately constant and the height of the clouds varies linearly with the distance from the released gate as usually observed in previous experiments. So for each roughness a front velocity and height growth can be defined. It was shown from the experiments that: As the bottom increases in roughness, the front speed increases and the height growth decreases. Nevertheless the height of glued elements does not seem to be the most appropriate parameter to characterize the roughness.

Pressure-Dependent Friction on Granular Slopes Close to Avalanche.

Science.gov (United States)

Crassous, Jérôme; Humeau, Antoine; Boury, Samuel; Casas, Jérôme

2017-08-04

We investigate the sliding of objects on an inclined granular surface close to the avalanche threshold. Our experiments show that the stability is driven by the surface deformations. Heavy objects generate footprintlike deformations which stabilize the objects on the slopes. Light objects do not disturb the sandy surfaces and are also stable. For intermediate weights, the deformations of the surface generate a sliding of the objects. The solid friction coefficient does not follow the Amontons-Coulomb laws, but is found minimal for a characteristic pressure. Applications to the locomotion of devices and animals on sandy slopes as a function of their mass are proposed.

Pressure-Dependent Friction on Granular Slopes Close to Avalanche

Science.gov (United States)

Crassous, Jérôme; Humeau, Antoine; Boury, Samuel; Casas, Jérôme

2017-08-01

We investigate the sliding of objects on an inclined granular surface close to the avalanche threshold. Our experiments show that the stability is driven by the surface deformations. Heavy objects generate footprintlike deformations which stabilize the objects on the slopes. Light objects do not disturb the sandy surfaces and are also stable. For intermediate weights, the deformations of the surface generate a sliding of the objects. The solid friction coefficient does not follow the Amontons-Coulomb laws, but is found minimal for a characteristic pressure. Applications to the locomotion of devices and animals on sandy slopes as a function of their mass are proposed.

Mechanics of debris flows and rock avalanches: Chapter 43

Science.gov (United States)

Iverson, Richard M.; Fernando, Harindra Joseph

2012-01-01

Debris flows are geophysical phenomena intermediate in character between rock avalanches and flash floods. They commonly originate as water-laden landslides on steep slopes and transform into liquefied masses of fragmented rock, muddy water, and entrained organic matter that disgorge from canyons onto valley floors. Typically including 50%–70% solid grains by volume, attaining speeds >10 m/s, and ranging in size up to ∼109 m3, debris flows can denude mountainsides, inundate floodplains, and devastate people and property (Figure 43.1). Notable recent debris-flow disasters resulted in more than 20,000 fatalities in Armero, Colombia, in 1985 and in Vargas state, Venezuela, in 1999.

Assessing the interaction between mountain forests and snow avalanches at Nevados de Chillán, Chile and its implications for ecosystem-based disaster risk reduction

Science.gov (United States)

Casteller, Alejandro; Häfelfinger, Thomas; Cortés Donoso, Erika; Podvin, Karen; Kulakowski, Dominik; Bebi, Peter

2018-04-01

Gravitational natural hazards such as snow avalanches, rockfalls, shallow landslides and volcanic activity represent a risk to mountain communities around the world. In particular, where documentary records about these processes are rare, decisions on risk management and land-use planning have to be based on a variety of other sources including vegetation, tree-ring data and natural hazard process models. We used a combination of these methods in order to evaluate dynamics of natural hazards with a focus on snow avalanches at Valle Las Trancas, in the Biobío region in Chile. Along this valley, natural hazards threaten not only the local human population, but also the numerous tourists attracted by outdoor recreational activities. Given the regional scarcity of documentary records, tree-ring methods were applied in order to reconstruct the local history of snow avalanches and debris flow events, which are the most important weather-related processes at respective tracks. A recent version of the model Rapid Mass MovementS (RAMMS), which includes influences of forest structure, was used to calculate different avalanche parameters such as runout distances and maximum pressures, taking into consideration the presence or absence of forest along the tracks as well as different modeled return periods. Our results show that local Nothofagus broadleaf forests contribute to a reduction of avalanche runout distances as well as impact pressure on present infrastructure, thus constituting a valuable ecosystem disaster risk reduction measure that can substitute or complement other traditional measures such as snow sheds.

Laser-enhanced ionization of mercury atoms in an inert atmosphere with avalanche amplification of the signal.

Science.gov (United States)

Clevenger, W L; Matveev, O I; Cabredo, S; Omenetto, N; Smith, B W; Winefordner, J D

1997-07-01

A new method for laser-enhanced ionization detection of mercury atoms in an inert gas atmosphere is described. The method, which is based on the avalanche amplification of the signal resulting from the ionization from a selected Rydberg level reached by a three-step laser excitation of mercury vapor in a simple quartz cell, can be applied to the determination of this element in various matrices by the use of conventional cold atomization techniques. The overall (collisional + photo) ionization efficiency is investigated at different temperatures, and the avalanche amplification effect is reported for Ar and P-10 gases at atmospheric pressure. It is shown that the amplified signal is related to the number of charges produced in the laser-irradiated volume. Under amplifier noise-limited conditions, a detection limit of ∼15 Hg atoms/laser pulse in the interaction region is estimated.

Indirect optical crosstalk reduction by highly-doped backside layer in single-photon avalanche diode arrays

NARCIS (Netherlands)

Osrečki, Željko; Knežević, Tihomir; Nanver, Lis K.; Suligoj, Tomislav

2018-01-01

A method of reducing indirect optical crosstalk in single-photon avalanche diode arrays is investigated by TCAD simulations. The reduction is accomplished by taking advantage of an enhanced optical absorption in a highly-doped Si layer on the backside of the wafer. A simulation environment was

Is the Electron Avalanche Process in a Martian Dust Devil Self-Quenching?

Science.gov (United States)

Farrell, William M.; McLain, Jason L.; Collier, M. R.; Keller, J. W.; Jackson, T. J.; Delory, G. T.

2015-01-01

Viking era laboratory experiments show that mixing tribocharged grains in a low pressure CO2 gas can form a discharge that glows, indicating the presence of an excited electron population that persists over many seconds. Based on these early experiments, it has been predicted that martian dust devils and storms may also contain a plasma and new plasma chemical species as a result of dust grain tribo-charging. However, recent results from modeling suggest a contrasting result: that a sustained electron discharge may not be easily established since the increase in gas conductivity would act to short-out the local E-fields and quickly dissipate the charged grains driving the process. In essence, the system was thought to be self-quenching (i.e., turn itself off). In this work, we attempt to reconcile the difference between observation and model via new laboratory measurements. We conclude that in a Mars-like low pressure CO2 atmosphere and expected E-fields, the electron current remains (for the most part) below the expected driving tribo-electric dust currents (approx. 10 microA/m(exp. 2)), thereby making quenching unlikely.

Investigation of silicon/silicon germanium multiple quantum well layers in silicon avalanche photodiodes

International Nuclear Information System (INIS)

Loudon, A.Y.

2002-01-01

Silicon single photon avalanche diodes (SPADs) are currently utilised in many single photon counting systems due to their high efficiency, fast response times, low voltage operation and potentially low cost. For fibre based applications however (at wavelengths 1.3 and 1.55μm) and eye-safe wavelength applications (>1.4μm), Si devices are not suitable due to their 1.1μm absorption edge and hence greatly reduced absorption above this wavelength. InGaAs/InP or Ge SPADs absorb at these longer wavelengths, but both require cryogenic cooling for low noise operation and III-V integration with conventional Si circuitry is difficult. Si/SiGe is currently attracting great interest for optoelectronic applications and attempts to combine Si avalanche photodiodes with Si/SiGe multiple quantum well absorbing layers have been successful. Here, an effort to utilise this material system has shown an improvement in photon counting efficiency above 1.1μm of more than 30 times compared to an all-Si control device. In addition to its longer wavelength response, this Si/SiGe device has room temperature operation, low cost fabrication and is compatible with conventional Si circuitry. (author)

Mapping and evaluation of snow avalanche risk using GIS technique in Rodnei National Park

Science.gov (United States)

Covǎsnianu, Adrian; Grigoraş, Ioan-Rǎducu; Covǎsnianu, Liliana-Elena; Iordache, Iulian; Balin, Daniela

2010-05-01

The study consisted in a precise mapping project (GPS field campaign, on-screen digitization of the topographic maps at 1:25.000 scale and updated with ASTER mission) of the Rodnei National Park area (Romanian Carpathians) with a focus on snow avalanche risk survey. Parameters taken into account were slope, aspect, altitude, landforms and roughness resulted from a high resolute numerical terrain model obtained by ASTER (Advanced Spaceborne Thermal Emission and Reflection Radiometer) mission. The resulted digital surface model with a spatial resolution of 10 m covered a total area of 187 square kilometers and was improved by the help of Topo to Raster tool. All these parameters were calibrated after a model applied onto Tatra Massive and also Ceahlău Mountain. The results were adapted and interpreted in accordance with European avalanche hazard scale. This work was made in the context of the elaboration of Risk Map and is directly concerning both the security of tourism activities but also the management of the Rodnei Natural Park. The extension of this method to similar mountain areas is ongoing.

Degradation and Its Control of Ultraviolet Avalanche Photodiodes Using PEDOT:PSS/ZnSSe Organic-Inorganic Hybrid Structure

Science.gov (United States)

Abe, Tomoki; Uchida, Shigeto; Tanaka, Keita; Fujisawa, Takanobu; Kasada, Hirofumi; Ando, Koshi; Akaiwa, Kazuaki; Ichino, Kunio

2018-05-01

We investigated device degradation in PEDOT:PSS/ZnSSe organic-inorganic hybrid ultraviolet avalanche photodiodes (UV-APDs). ZnSSe/n-GaAs wafers were grown by molecular beam epitaxy, and PEDOT:PSS window layers were formed by inkjet technique. We observed rapid degradation with APD-mode stress (˜ 30 V) in the N2 (4 N) atmosphere, while we observed no marked change in forward bias current stress and photocurrent stress. In the case of a vacuum condition, we observed no detectable degradation in the dark avalanche current with APD-mode stress. Therefore, the degradation in the PEDOT:PSS/ZnSSe interface under the APD-mode stress was caused by the residual water vapor or oxygen in the N2 atmosphere and could be controlled by vacuum packaging.

New Very Low Noise Multilayer And Graded-Gap Avalanche Photodiodes For The 0.8 To 1 .8 μm Wavelength Region

Science.gov (United States)

Capasso, F.; Tsang, W. T.; Williams, G. F.

1982-12-01

Recent experimental and theoretical results on a new class of low noise avalanche photo-diodes are reviewed. A large enhancement of the impact ionization rates ratio (a/(3=10) has been demonstrated in AlGaAs/GaAs superlattices and graded band gap detector structures. In addition two novel photodiodes ("staircase" and "channeling" APDs) where only electrons multiply, have been proposed. The staircase APD is the solid state analog of the photo-multiplier with discrete dynodes. It has a low operating voltage (5-20 volts) and a lower excess noise factor, in the ideal case, than that of an ideal conventional APD The channeling APD is instead the solid state analog of a channeltron photomultiplier and has the unique feature of an ultrahigh a/β, ratio (≍∞) compatible with high gain (>100).

Study of influence of gas mixture composition on the multistep avalanche chambers characteristics

International Nuclear Information System (INIS)

Abdushukurov, D.A.; Zanevskij, Yu.V.; Peshekhonov, V.D.

1987-01-01

The influence of the concentration of organic quenchers on the operation of multistep avalanche chambers /MSAC/ has been studied. An empirical dependence of the gas amplification factor of MSAC on the quencher concentration has been derived. Measures are considered to increase the stability of the MSAC operation. To improve the MSAC operation argon + n-heptane, neon + methane and neon + argon + methane mixtures are suggested

Systematic test on fast time resolution parallel plate avalanche counter

International Nuclear Information System (INIS)

Chen Yu; Li Guangwu; Gu Xianbao; Chen Yanchao; Zhang Gang; Zhang Wenhui; Yan Guohong

2011-01-01

Systematic test on each detect unit of parallel plate avalanche counter (PPAC) used in the fission multi-parameter measurement was performed with a 241 Am α source to get the time resolution and position resolution. The detectors work at 600 Pa flowing isobutane and with-600 V on cathode. The time resolution was got by TOF method and the position resolution was got by delay line method. The time resolution of detect units is better than 400 ps, and the position resolution is 6 mm. The results show that the demand of measurement is fully covered. (authors)

Scintillation detector composed by new type of avalanche photodiode and CsI(Tl) crystal

International Nuclear Information System (INIS)

He Jingtang; Chen Duanbao; Li Zuhao; Mao Yufang; Dong Xiaoli

1996-01-01

Using S5345 type of avalanche photodiode produced by Hamamatsu for the CsI(Tl) crystal readout, the spectrum of γ ray were measured. Energy resolution of 6.8% for 1.27 MeV γ ray from 22 Na source was obtained. The relation between energy resolution and coupling area, dimension of crystal, shaping time and bias were measured

Calorimeter detector consisting of a KMgF3 scintillator and parallel-plate avalanche chamber

International Nuclear Information System (INIS)

Buzulutskov, A.F.; Turchanovich, L.K.; Vasil'chenko, V.G.

1989-01-01

Scintillations of a KMgF 3 crystal have been detected in the parallel-plate avalanche chamber with a TEA gaseous photocathode, the scintillation signal is shown to be much higher than the direct ionization one. The characteristic properties of the calorimeters on the basis of such structure with electrical and optical readout are discussed. 10 refs.; 4 figs

Long-wavelength photonic integrated circuits and avalanche photodetectors

Science.gov (United States)

Tsou, Yi-Jen D.; Zaytsev, Sergey; Pauchard, Alexandre; Hummel, Steve; Lo, Yu-Hwa

2001-10-01

Fast-growing internet traffic volume require high data communication bandwidth over longer distances. Access network bottlenecks put pressure on short-range (SR) telecommunication systems. To effectively address these datacom and telecom market needs, low-cost, high-speed laser modules at 1310 to 1550 nm wavelengths and avalanche photodetectors are required. The great success of GaAs 850nm VCSEls for Gb/s Ethernet has motivated efforts to extend VCSEL technology to longer wavelengths in the 1310 and 1550 nm regimes. However, the technological challenges associated with materials for long wavelength VCSELs are tremendous. Even with recent advances in this area, it is believed that significant additional development is necessary before long wavelength VCSELs that meet commercial specifications will be widely available. In addition, the more stringent OC192 and OC768 specifications for single-mode fiber (SMF) datacom may require more than just a long wavelength laser diode, VCSEL or not, to address numerous cost and performance issues. We believe that photonic integrated circuits (PICs), which compactly integrate surface-emitting lasers with additional active and passive optical components with extended functionality, will provide the best solutions to today's problems. Photonic integrated circuits have been investigated for more than a decade. However, they have produced limited commercial impact to date primarily because the highly complicated fabrication processes produce significant yield and device performance issues. In this presentation, we will discuss a new technology platform of InP-based PICs compatible with surface-emitting laser technology, as well as a high data rate externally modulated laser module. Avalanche photodetectors (APDs) are the key component in the receiver to achieve high data rate over long transmission distance because of their high sensitivity and large gain- bandwidth product. We have used wafer fusion technology to achieve In

Measurement of runaway electron energy distribution function during high-Z gas injection into runaway electron plateaus in DIII-Da)

Energy Technology Data Exchange (ETDEWEB)

Hollmann, E. M. [University of California—San Diego, 9500 Gilman Dr., La Jolla, California 92093, USA; Parks, P. B. [General Atomics, PO Box 85608, San Diego, California 92186, USA; Commaux, N. [Oak Ridge National Laboratory, PO Box 2008, Oak Ridge, Tennessee 37831, USA; Eidietis, N. W. [General Atomics, PO Box 85608, San Diego, California 92186, USA; Moyer, R. A. [University of California—San Diego, 9500 Gilman Dr., La Jolla, California 92093, USA; Shiraki, D. [Oak Ridge National Laboratory, PO Box 2008, Oak Ridge, Tennessee 37831, USA; Austin, M. E. [Institute for Fusion Studies, University of Texas—Austin, 2100 San Jacinto Blvd, Austin, Texas 78712, USA; Lasnier, C. J. [Lawrence Livermore National Laboratory, 7000 East Ave, Livermore, California 94550, USA; Paz-Soldan, C. [General Atomics, PO Box 85608, San Diego, California 92186, USA; Rudakov, D. L. [University of California—San Diego, 9500 Gilman Dr., La Jolla, California 92093, USA

2015-05-01

The evolution of the runaway electron (RE) energy distribution function fεfε during massive gas injection into centered post-disruption runaway electron plateaus has been reconstructed. Overall, fεfε is found to be much more skewed toward low energy than predicted by avalanche theory. The reconstructions also indicate that the RE pitch angle θ is not uniform, but tends to be large at low energies and small θ ~0.1–0.2 at high energies. Overall power loss from the RE plateau appears to be dominated by collisions with background free and bound electrons, leading to line radiation. However, the drag on the plasma current appears to be dominated by collisions with impurity ions in most cases. Synchrotron emission appears not to be significant for overall RE energy dissipation but may be important for limiting the peak RE energy.

Measurement of runaway electron energy distribution function during high-Z gas injection into runaway electron plateaus in DIII-D

International Nuclear Information System (INIS)

Hollmann, E. M.; Moyer, R. A.; Rudakov, D. L.; Parks, P. B.; Eidietis, N. W.; Paz-Soldan, C.; Commaux, N.; Shiraki, D.; Austin, M. E.; Lasnier, C. J.

2015-01-01

The evolution of the runaway electron (RE) energy distribution function f ε during massive gas injection into centered post-disruption runaway electron plateaus has been reconstructed. Overall, f ε is found to be much more skewed toward low energy than predicted by avalanche theory. The reconstructions also indicate that the RE pitch angle θ is not uniform, but tends to be large at low energies and small θ ∼ 0.1–0.2 at high energies. Overall power loss from the RE plateau appears to be dominated by collisions with background free and bound electrons, leading to line radiation. However, the drag on the plasma current appears to be dominated by collisions with impurity ions in most cases. Synchrotron emission appears not to be significant for overall RE energy dissipation but may be important for limiting the peak RE energy

Technology developments and first measurements of Low Gain Avalanche Detectors (LGAD) for high energy physics applications

International Nuclear Information System (INIS)

Pellegrini, G.; Fernández-Martínez, P.; Baselga, M.; Fleta, C.; Flores, D.; Greco, V; Hidalgo, S.; Mandić, I.; Kramberger, G.; Quirion, D.; Ullan, M.

2014-01-01

This paper introduces a new concept of silicon radiation detector with intrinsic multiplication of the charge, called Low Gain Avalanche Detector (LGAD). These new devices are based on the standard Avalanche Photo Diodes (APD) normally used for optical and X-ray detection applications. The main differences to standard APD detectors are the low gain requested to detect high energy charged particles, and the possibility to have fine segmentation pitches: this allows fabrication of microstrip or pixel devices which do not suffer from the limitations normally found [1] in avalanche detectors. In addition, a moderate multiplication value will allow the fabrication of thinner devices with the same output signal of standard thick substrates. The investigation of these detectors provides important indications on the ability of such modified electrode geometry to control and optimize the charge multiplication effect, in order to fully recover the collection efficiency of heavily irradiated silicon detectors, at reasonable bias voltage, compatible with the voltage feed limitation of the CERN High Luminosity Large Hadron Collider (HL-LHC) experiments [2]. For instance, the inner most pixel detector layers of the ATLAS tracker will be exposed to fluences up to 2×10 16 1 MeV n eq /cm 2 , while for the inner strip detector region fluences of 1×10 15 n eq /cm 2 are expected. The gain implemented in the non-irradiated devices must retain some effect also after irradiation, with a higher multiplication factor with respect to standard structures, in order to be used in harsh environments such those expected at collider experiments

A simple and accurate method for bidimensional position read-out of parallel plate avalanche counters

International Nuclear Information System (INIS)

Breskin, A.; Zwang, N.

1977-01-01

A simple method for bidimensional position read-out of Parallel Plate Avalanche counters (PPAC) has been developed, using the induced charge technique. An accuracy better than 0.5 mm (FWHM) has been achieved for both coordinates with 5.5. MeV α-particles at gas pressures of 10-40 torr. (author)

TCAD simulations for a novel single-photon avalanche diode

Science.gov (United States)

Jin, Xiangliang; Yang, Jia; Yang, Hongjiao; Tang, Lizhen; Liu, Weihui

2015-03-01

A single-photon avalanche diode (SPAD) device with P+-SEN junction, and a low concentration of N-type doping circular virtual guard-ring was presented in this paper. SEN layer of the proposed SPAD has high concentration of N-type doping, causing the SPAD low breakdown voltage (~14.26 V). What's more, an efficient and narrow (about 2μm) guard-ring of the proposed SPAD not only can withstand considerably higher electric fields for preventing edge breakdown, but also offers a little increment in fill factor compared with existing SPADs due to its small area. In addition, some Silvaco TCAD simulations have been done and verify characteristics and performance of the design in this work.

Studies of avalanche photodiodes for scintillating fibre tracking readout

International Nuclear Information System (INIS)

Fenker, H.; Thomas, J.

1993-01-01

Avalanche Photodiodes (APDs) operating in ''Geiger Mode'' have been studied in a fibre tracking readout environment. A fast recharge circuit has been developed for high rate data taking, and results obtained from a model fibre tracker in the test beam at Brookhaven National Laboratory are presented. A high rate calibrated light source has been developed using a commercially available laser diode and has been used to measure the efficiency of the devices. The transmission of the light from a 1mm fibre onto a 0.5mm diameter APD surface has been identified as the main problem in the use of these particular devices for scintillating fibre tracking in the Superconducting Supercollider environment. Solutions to this problem are proposed

Implementation of the Electron conversion Moessbauer spectroscopy

International Nuclear Information System (INIS)

Hernandez, Torres, D.; Noriega Scull, C.

1996-01-01

In the present work has been exposed the principles of the Conversion Moessbauer Electron Spectroscopy and its possibilities of application. Is also described the operation of the parallel plate avalanche detector made at the CEADEN starting from modifications done to the Gancedo's model and is exposed examples of the use of this detector in the characterization of corroded surfaces, with chemical cleaning and in samples of welded joints. The experiences obtained of this work were extended to the National Polytechnic Institute of Mexico where a similar detector, made in our center, was installed there

Generation of runaway electron beams in high-pressure nitrogen

Science.gov (United States)

Tarasenko, V. F.; Burachenko, A. G.; Baksht, E. Kh

2017-07-01

In this paper the results of experimental studies of the amplitude-temporal characteristics of a runaway electron beam, as well as breakdown voltage in nitrogen are presented. The voltage pulses with the amplitude in incident wave ≈120 kV and the rise time of ≈0.3 ns was used. The supershort avalanche electron beam (SAEB) was detected by a collector behind the flat anode. The amplitude-time characteristics of the voltage and SAEB current were studied with subnanosecond time resolution. The maximum pressure at which a SAEB is detectable by collector was ∼1 MPa. This pressure increases with decreasing the voltage rise time. The waveforms of the discharge and runaway electron beam currents was synchronized with the voltage pulses. The mechanism of the runaway electron generation in atmospheric-pressure gases is analyzed on the basis of the obtained experimental data.

Development of an integrated four-channel fast avalanche-photodiode detector system with nanosecond time resolution

Science.gov (United States)

Li, Zhenjie; Li, Qiuju; Chang, Jinfan; Ma, Yichao; Liu, Peng; Wang, Zheng; Hu, Michael Y.; Zhao, Jiyong; Alp, E. E.; Xu, Wei; Tao, Ye; Wu, Chaoqun; Zhou, Yangfan

2017-10-01

A four-channel nanosecond time-resolved avalanche-photodiode (APD) detector system is developed at Beijing Synchrotron Radiation. It uses a single module for signal processing and readout. This integrated system provides better reliability and flexibility for custom improvement. The detector system consists of three parts: (i) four APD sensors, (ii) four fast preamplifiers and (iii) a time-digital-converter (TDC) readout electronics. The C30703FH silicon APD chips fabricated by Excelitas are used as the sensors of the detectors. It has an effective light-sensitive area of 10 × 10 mm2 and an absorption layer thickness of 110 μm. A fast preamplifier with a gain of 59 dB and bandwidth of 2 GHz is designed to readout of the weak signal from the C30703FH APD. The TDC is realized by a Spartan-6 field-programmable-gate-array (FPGA) with multiphase method in a resolution of 1ns. The arrival time of all scattering events between two start triggers can be recorded by the TDC. The detector has been used for nuclear resonant scattering study at both Advanced Photon Source and also at Beijing Synchrotron Radiation Facility. For the X-ray energy of 14.4 keV, the time resolution, the full width of half maximum (FWHM) of the detector (APD sensor + fast amplifier) is 0.86 ns, and the whole detector system (APD sensors + fast amplifiers + TDC readout electronics) achieves a time resolution of 1.4 ns.

Design considerations of high-performance InGaAs/InP single-photon avalanche diodes for quantum key distribution.

Science.gov (United States)

Ma, Jian; Bai, Bing; Wang, Liu-Jun; Tong, Cun-Zhu; Jin, Ge; Zhang, Jun; Pan, Jian-Wei

2016-09-20

InGaAs/InP single-photon avalanche diodes (SPADs) are widely used in practical applications requiring near-infrared photon counting such as quantum key distribution (QKD). Photon detection efficiency and dark count rate are the intrinsic parameters of InGaAs/InP SPADs, due to the fact that their performances cannot be improved using different quenching electronics given the same operation conditions. After modeling these parameters and developing a simulation platform for InGaAs/InP SPADs, we investigate the semiconductor structure design and optimization. The parameters of photon detection efficiency and dark count rate highly depend on the variables of absorption layer thickness, multiplication layer thickness, excess bias voltage, and temperature. By evaluating the decoy-state QKD performance, the variables for SPAD design and operation can be globally optimized. Such optimization from the perspective of specific applications can provide an effective approach to design high-performance InGaAs/InP SPADs.

Near-Saturation Single-Photon Avalanche Diode Afterpulse and Sensitivity Correction Scheme for the LHC Longitudinal density Monitor

CERN Document Server

Bravin, E; Palm, M

2014-01-01

Single-Photon Avalanche Diodes (SPADs) monitor the longitudinal density of the LHC beams by measuring the temporal distribution of synchrotron radiation. The relative population of nominally empty RF-buckets (satellites or ghosts) with respect to filled bunches is a key figure for the luminosity calibration of the LHC experiments. Since afterpulsing from a main bunch avalanche can be as high as, or higher than, the signal from satellites or ghosts, an accurate correction algorithm is needed. Furthermore, to reduce the integration time, the amount of light sent to the SPAD is enough so that pile-up effects and afterpulsing cannot be neglected. The SPAD sensitivity has also been found to vary at the end of the active quenching phase. We present a method to characterize and correct for SPAD deadtime, afterpulsing and sensitivity variation near saturation, together with laboratory benchmarking.

Spectral dependence of the main parameters of ITE silicon avalanche photodiodes

Science.gov (United States)

Wegrzecka, Iwona; Grynglas, Maria; Wegrzecki, Maciej

2001-08-01

New applications for avalanche photodiodes (APDs) as in systems using visible radiation, have prompted the need for the evaluation of detection properties of ITE APDs in the 400 divided by 700 nm spectral range. The paper presents the method and result of studies on the spectral dependence of the gain, dark and noise currents, sensitivity and excess noise factor of ITE APDs. The studies have shown that ITE APDs optimized for the near IR radiation can be effectively applied in the detection of radiation above the 500 nm wavelength.

A comparison between spectra of runaway electron beams in SF6 and air

International Nuclear Information System (INIS)

Zhang, Cheng; Wang, Ruexue; Yan, Ping; Shao, Tao; Tarasenko, Victor; Gu, Jianwei; Baksht, Evgenii

2015-01-01

Runaway electron (RAE) with extremely high-energy plays important role on the avalanche propagation, streamer formation, and ionization waves in nanosecond-pulse discharges. In this paper, the generation of a supershort avalanche electron beam (SAEB) in SF 6 and air in an inhomogeneous electric field is investigated. A VPG-30-200 generator with a pulse rise time of ∼1.6 ns and a full width at half maximum of 3–5 ns is used to produce RAE beams. The SAEBs in SF 6 and air are measured by using aluminum foils with different thicknesses. Furthermore, the SAEB spectra in SF 6 and air at pressures of 7.5 Torr, 75 Torr, and 750 Torr are compared. The results showed that amplitude of RAE beam current generated at the breakdown in SF 6 was approximately an order of magnitude less than that in air. The energy of SAEB in air was not smaller than that in SF 6 in nanosecond-pulse discharges under otherwise equal conditions. Moreover, the difference between the maximum energy of the electron distributions in air and SF 6 decreased when the rise time of the voltage pulse increased. It was because the difference between the breakdown voltages in air and SF 6 decreased when the rise time of the voltage pulse increased

A comparison between spectra of runaway electron beams in SF6 and air

Science.gov (United States)

Zhang, Cheng; Tarasenko, Victor; Gu, Jianwei; Baksht, Evgenii; Wang, Ruexue; Yan, Ping; Shao, Tao

2015-12-01

Runaway electron (RAE) with extremely high-energy plays important role on the avalanche propagation, streamer formation, and ionization waves in nanosecond-pulse discharges. In this paper, the generation of a supershort avalanche electron beam (SAEB) in SF6 and air in an inhomogeneous electric field is investigated. A VPG-30-200 generator with a pulse rise time of ˜1.6 ns and a full width at half maximum of 3-5 ns is used to produce RAE beams. The SAEBs in SF6 and air are measured by using aluminum foils with different thicknesses. Furthermore, the SAEB spectra in SF6 and air at pressures of 7.5 Torr, 75 Torr, and 750 Torr are compared. The results showed that amplitude of RAE beam current generated at the breakdown in SF6 was approximately an order of magnitude less than that in air. The energy of SAEB in air was not smaller than that in SF6 in nanosecond-pulse discharges under otherwise equal conditions. Moreover, the difference between the maximum energy of the electron distributions in air and SF6 decreased when the rise time of the voltage pulse increased. It was because the difference between the breakdown voltages in air and SF6 decreased when the rise time of the voltage pulse increased.

Overspill avalanching in a dense reservoir network

Science.gov (United States)

Mamede, George L.; Araújo, Nuno A. M.; Schneider, Christian M.; de Araújo, José Carlos; Herrmann, Hans J.

2012-01-01

Sustainability of communities, agriculture, and industry is strongly dependent on an effective storage and supply of water resources. In some regions the economic growth has led to a level of water demand that can only be accomplished through efficient reservoir networks. Such infrastructures are not always planned at larger scale but rather made by farmers according to their local needs of irrigation during droughts. Based on extensive data from the upper Jaguaribe basin, one of the world’s largest system of reservoirs, located in the Brazilian semiarid northeast, we reveal that surprisingly it self-organizes into a scale-free network exhibiting also a power-law in the distribution of the lakes and avalanches of discharges. With a new self-organized-criticality-type model we manage to explain the novel critical exponents. Implementing a flow model we are able to reproduce the measured overspill evolution providing a tool for catastrophe mitigation and future planning. PMID:22529343

Generation of subnanosecond electron beams in air at atmospheric pressure

Science.gov (United States)

Kostyrya, I. D.; Tarasenko, V. F.; Baksht, E. Kh.; Burachenko, A. G.; Lomaev, M. I.; Rybka, D. V.

2009-11-01

Optimum conditions for the generation of runaway electron beams with maximum current amplitudes and densities in nanosecond pulsed discharges in air at atmospheric pressure are determined. A supershort avalanche electron beam (SAEB) with a current amplitude of ˜30 A, a current density of ˜20 A/cm2, and a pulse full width at half maximum (FWHM) of ˜100 ps has been observed behind the output foil of an air-filled diode. It is shown that the position of the SAEB current maximum relative to the voltage pulse front exhibits a time shift that varies when the small-size collector is moved over the foil surface.

Determination of the excess noise of avalanche photodiodes integrated in 0.35-μm CMOS technologies

Science.gov (United States)

Jukić, Tomislav; Brandl, Paul; Zimmermann, Horst

2018-04-01

The excess noise of avalanche photodiodes (APDs) integrated in a high-voltage (HV) CMOS process and in a pin-photodiode CMOS process, both with 0.35-μm structure sizes, is described. A precise excess noise measurement technique is applied using a laser source, a spectrum analyzer, a voltage source, a current meter, a cheap transimpedance amplifier, and a personal computer with a MATLAB program. In addition, usage for on-wafer measurements is demonstrated. The measurement technique is verified with a low excess noise APD as a reference device with known ratio k = 0.01 of the impact ionization coefficients. The k-factor of an APD developed in HV CMOS is determined more accurately than known before. In addition, it is shown that the excess noise of the pin-photodiode CMOS APD depends on the optical power for avalanche gains above 35 and that modulation doping can suppress this power dependence. Modulation doping, however, increases the excess noise.

Readout electronics for low dark count pixel detectors based on Geiger mode avalanche photodiodes fabricated in conventional CMOS technologies for future linear colliders

International Nuclear Information System (INIS)

Vilella, E.; Arbat, A.; Comerma, A.; Trenado, J.; Alonso, O.; Gascon, D.; Vila, A.; Garrido, L.; Dieguez, A.

2011-01-01

High sensitivity and excellent timing accuracy of the Geiger mode avalanche photodiodes make them ideal sensors as pixel detectors for particle tracking in high energy physics experiments to be performed in future linear colliders. Nevertheless, it is well known that these sensors suffer from dark counts and afterpulsing noise, which induce false hits (indistinguishable from event detection) as well as an increase in the necessary area of the readout system. In this work, we present a comparison between APDs fabricated in a high voltage 0.35 μm and a high integration 0.13 μm commercially available CMOS technologies that has been performed to determine which of them best fits the particle collider requirements. In addition, a readout circuit that allows low noise operation is introduced. Experimental characterization of the proposed pixel is also presented in this work.

Automatic scanning of Cerenkov light photograms from a multistep avalanche chamber using a television digitizer

International Nuclear Information System (INIS)

Vascon, M.; Zanella, G.

1980-01-01

A television digitizer and its application to automatic scanning of Cerenkov imaging using the multistep avalanche chamber in front of optical spark chamber are described. The results are of interest in the adoption of the automatic scanning of photographic plates of these events or for the on-line application of the television digitizer itself. (orig.)

Runaway electron generation in tokamak disruptions

International Nuclear Information System (INIS)

Helander, P.; Andersson, F.; Fueloep, T.; Smith, H.; Anderson, D.; Lisak, M.; Eriksson, L.-G.

2005-01-01

The time evolution of the plasma current during a tokamak disruption is calculated by solving the equations for runaway electron production simultaneously with the induction equation for the toroidal electric field. The resistive diffusion time in a post-disruption plasma is typically comparable to the runaway avalanche growth time. Accordingly, the toroidal electric field induced after the thermal quench of a disruption diffuses radially through the plasma at the same time as it accelerates runaway electrons, which in turn back-react on the electric field. When these processes are accounted for in a self-consistent way, it is found that (1) the efficiency and time scale of runaway generation agrees with JET experiments; (2) the runaway current profile typically becomes more peaked than the pre-disruption current profile; and (3) can easily become radially filamented. It is also shown that higher runaway electron generation is expected if the thermal quench is sufficiently fast. (author)

An electron counting mechanism for the open counter operated in air

International Nuclear Information System (INIS)

Noguchi, T.; Nagashima, S.; Uda, M.

1994-01-01

An electron counting mechanism for an open or air filled counter has been explicitly explained for the first time. Electrons emitted from a solid surface or formed in air by radiations are transported to the neighborhood of the anode in the counter in the form of O 2 - ions, and are detached from the ions and multiplied in the proximity to the anode through electronic avalanche process. The estimation of the number of the emitted electrons from observed count rates has successively been performed by expressing the dead time as the sum of time intervals necessary for quenching using an external circuit and for drifting of the O 2 - ions, and also by taking into account the reduction in the number of electrons during transportation, which is due to scattering of the O 2 - ions in air. (orig.)

Imaging Findings of a Survivor of Avalanche without Any Life Support at Very High Altitude and Extreme Low Temperatures

Directory of Open Access Journals (Sweden)

Abhishek Dwivedi

2016-10-01

Full Text Available Survival at high altitude is very challenging and in spite of adequate training and acclimatization, injuries are frequent. The fate of mountaineers and soldiers at such areas largely depends on the mercy of the climate. An avalanche causes physical trauma, cold injury and asphyxia to the victim. The patient in our report had diffuse cerebral edema, bilateral pulmonary consolidation and pneumothorax. In spite of the best efforts the victim succumbed to the injuries. There are many incidents of high altitude accidents in India. This case report is of a soldier deployed at the high altitude, is a lone ever reported survivor above 5000 meters, under 35 feet snow and below - 45°C for greater than 5 days of exposure to an avalanche

Single Photon Avalanche Diodes: Towards the Large Bidimensional Arrays

Directory of Open Access Journals (Sweden)

Emilio Sciacca

2008-08-01

Full Text Available Single photon detection is one of the most challenging goals of photonics. In recent years, the study of ultra-fast and/or low-intensity phenomena has received renewed attention from the academic and industrial communities. Intense research activity has been focused on bio-imaging applications, bio-luminescence, bio-scattering methods, and, more in general, on several applications requiring high speed operation and high timing resolution. In this paper we present design and characterization of bi-dimensional arrays of a next generation of single photon avalanche diodes (SPADs. Single photon sensitivity, dark noise, afterpulsing and timing resolution of the single SPAD have been examined in several experimental conditions. Moreover, the effects arising from their integration and the readout mode have also been deeply investigated.

Study on the property of the avalanche photodiode as the readout component for scintillation crystals

International Nuclear Information System (INIS)

He Jingtang; Chen Duanbao; Zhu Guoyi; Mao Yufang; Dong Xiaoli; Li Zuhao

1996-01-01

The new avalanche photodiode (APD) and a CsI(Tl) crystal formed a scintillation detector. The energy spectrum of γ rays was measured by this detector. The measured results were compared with that measured by photomultiplier. Our plan is to use APD as PbWO 4 readout component for forward luminosity electromagnetic calorimeter at τ-C factory

Characteristics of post-disruption runaway electrons with impurity pellet injection

International Nuclear Information System (INIS)

Kawano, Yasunori; Nakano, Tomohide; Isayama, Akihiko; Asakura, Nobuyuki; Tamai, Hiroshi; Kubo, Hirotaka; Takenaga, Hidenobu; Bakhtiari, Mohammad; Ide, Shunsuke; Kondoh, Takashi; Hatae, Takaki

2005-01-01

Characteristics of post-disruption runaway electrons with impurity pellet injection were investigated for the first time using the JT-60U tokamak device. A clear deposition of impurity neon ice pellets was observed in a post-disruption runaway plasma. The pellet ablation was attributed to the energy deposition of relativistic runaway electrons in the pellet. A high normalized electron density was stably obtained with n e bar /n GW ∼2.2. Effects of prompt exhaust of runaway electrons and reduction of runaway plasma current without large amplitude MHD activities were found. One possible explanation for the basic behavior of runaway plasma current is that it follows the balance of avalanche generation of runaway electrons and slowing down predicted by the Andersson-Helander model, including the combined effect of collisional pitch angle scattering and synchrotron radiation. Our results suggested that the impurity pellet injection reduced the energy of runaway electrons in a stepwise manner. (author)

A comparison between spectra of runaway electron beams in SF{sub 6} and air

Energy Technology Data Exchange (ETDEWEB)

Zhang, Cheng; Wang, Ruexue; Yan, Ping; Shao, Tao, E-mail: st@mail.iee.ac.cn [Institute of Electrical Engineering, Chinese Academy of Sciences, Beijing 100190 (China); Key Laboratory of Power Electronics and Electric Drive, Chinese Academy of Sciences, Beijing 100190 (China); Tarasenko, Victor [Institute of High Current Electronics, 2/3 Akademichesky Ave., Tomsk 634055 (Russian Federation); National Research Tomsk State University, 36 Lenin Ave., Tomsk 634050 (Russian Federation); Gu, Jianwei [Institute of Electrical Engineering, Chinese Academy of Sciences, Beijing 100190 (China); Baksht, Evgenii [Institute of High Current Electronics, 2/3 Akademichesky Ave., Tomsk 634055 (Russian Federation)

2015-12-15

Runaway electron (RAE) with extremely high-energy plays important role on the avalanche propagation, streamer formation, and ionization waves in nanosecond-pulse discharges. In this paper, the generation of a supershort avalanche electron beam (SAEB) in SF{sub 6} and air in an inhomogeneous electric field is investigated. A VPG-30-200 generator with a pulse rise time of ∼1.6 ns and a full width at half maximum of 3–5 ns is used to produce RAE beams. The SAEBs in SF{sub 6} and air are measured by using aluminum foils with different thicknesses. Furthermore, the SAEB spectra in SF{sub 6} and air at pressures of 7.5 Torr, 75 Torr, and 750 Torr are compared. The results showed that amplitude of RAE beam current generated at the breakdown in SF{sub 6} was approximately an order of magnitude less than that in air. The energy of SAEB in air was not smaller than that in SF{sub 6} in nanosecond-pulse discharges under otherwise equal conditions. Moreover, the difference between the maximum energy of the electron distributions in air and SF{sub 6} decreased when the rise time of the voltage pulse increased. It was because the difference between the breakdown voltages in air and SF{sub 6} decreased when the rise time of the voltage pulse increased.

Multi-stage low-pressure avalanche chamber

International Nuclear Information System (INIS)

Zanevskij, Yu.V.; Peshekhonov, V.D.; Smykov, L.P.

1985-01-01

A multi-stage avalanche-chamber filled with isobutane operating at the pressure of 6 torr is described. The chamber comprises an amplifying gap, drift gap and multiwire proportional chamber with interelectrode gaps equal to 4 mm. The anode plane of the proportional chamber is winded of wire 2 μm in diameter with 2 mm pitch. The cathode are winded orthogonally to anode wires of wire 50 μm in diameter with 1 mm pitch. Drift and preamplifier gaps are formed by grid electrodes made of wire 50 μm in diameter with dimension of the cell equal to 1x1 mm. Width of the drift gap is 5 mm, width of the preamplification gap is 3 or 9 mm. Coordinate data are removed from the cathodes of the proportional chamber by means of delay lines. Sensitive square of the chamber equals 240x180 mm. Gas gain coefficient is 3x10 6 at its square nonuniformity equal to approximately 3%. Spatial resolution by both coordinates equals 170 μm; spatial resolution for isotropic α-emitters located close to the preamplifier gap is equal to 500 μm

Ge/graded-SiGe multiplication layers for low-voltage and low-noise Ge avalanche photodiodes on Si

Science.gov (United States)

Miyasaka, Yuji; Hiraki, Tatsurou; Okazaki, Kota; Takeda, Kotaro; Tsuchizawa, Tai; Yamada, Koji; Wada, Kazumi; Ishikawa, Yasuhiko

2016-04-01

A new structure is examined for low-voltage and low-noise Ge-based avalanche photodiodes (APDs) on Si, where a Ge/graded-SiGe heterostructure is used as the multiplication layer of a separate-absorption-carrier-multiplication structure. The Ge/SiGe heterojunction multiplication layer is theoretically shown to be useful for preferentially enhancing impact ionization for photogenerated holes injected from the Ge optical-absorption layer via the graded SiGe, reflecting the valence band discontinuity at the Ge/SiGe interface. This property is effective not only for the reduction of operation voltage/electric field strength in Ge-based APDs but also for the reduction of excess noise resulting from the ratio of the ionization coefficients between electrons and holes being far from unity. Such Ge/graded-SiGe heterostructures are successfully fabricated by ultrahigh-vacuum chemical vapor deposition. Preliminary pin diodes having a Ge/graded-SiGe multiplication layer act reasonably as photodetectors, showing a multiplication gain larger than those for diodes without the Ge/SiGe heterojunction.

Characterization and quality control of avalanche photodiode arrays for the Clear-PEM detector modules

International Nuclear Information System (INIS)

Abreu, Conceicao; Amaral, Pedro; Carrico, Bruno; Ferreira, Miguel; Luyten, Joan; Moura, Rui; Ortigao, Catarina; Rato, Pedro; Varela, Joao

2007-01-01

Clear-PEM is a Positron Emission Mammography (PEM) prototype being developed in the framework of the Crystal Clear Collaboration at CERN. This device is a dedicated PET camera for mammography, based on LYSO:Ce scintillator crystals, Avalanche PhotoDiodes (APD) and a fast, low-noise electronics readout system, designed to examine both the breast and the axillary lymph node areas, and aiming at the detection of tumors down to 2 mm in diameter. The prototype has two planar detector heads, each composed of 96 detector modules. The Clear-PEM detector module is composed of a matrix of 32 identical 2x2x20 mm 3 LYSO:Ce crystals read at both ends by Hamamatsu S8550 APD arrays (4x8) for Depth-of-Interaction (DoI) capability. The APD arrays were characterized by the measurement of gain and dark current as a function of bias voltage, under controlled temperature conditions. Two independent setups were used. The full set of 398 APD arrays followed a well-defined quality control (QC) protocol, aiming at the rejection of arrays not complying within defined specifications. From a total of 398 arrays, only 2 (0.5%) were rejected, reassuring the trust in these detectors for prototype assembly and future developments

A position sensitive parallel plate avalanche fission detector for use in particle induced fission coincidence measurements

NARCIS (Netherlands)

Plicht, J. van der

1980-01-01

A parallel plate avalanche detector developed for the detection of fission fragments in particle induced fission reactions is described. The active area is 6 × 10 cm2; it is position sensitive in one dimension with a resolution of 2.5 mm. The detector can withstand a count rate of 25000 fission

Deactivation of group III acceptors in silicon during keV electron irradiation

International Nuclear Information System (INIS)

Sah, C.; Sun, J.Y.; Tzou, J.J.; Pan, S.C.

1983-01-01

Experimental results on p-Si metal-oxide-semiconductor capacitors (MOSC's) are presented which demonstrate the electrical deactivation of the acceptor dopant impurity during 8-keV electron irradiation not only in boron but also aluminum and indium-doped silicon. The deactivation rates of the acceptors during the 8-keV electron irradiation are nearly independent of the acceptor impurity type. The final density of the remaining active acceptor approaches nonzero values N/sub infinity/, with N/sub infinity/(B) Al--H>In-H. These deactivation results are consistent with our hydrogen bond model. The thermal annealing or regeneration rate of the deactivated acceptors in the MOSC's irradiated by 8-keV electron is much smaller than that in the MOSC's that have undergone avalanche electron injection, indicating that the keV electron irradiation gives rise to stronger hydrogen-acceptor bond

Growth and decay of runaway electrons above the critical electric field under quiescent conditions

International Nuclear Information System (INIS)

Paz-Soldan, C.; Eidietis, N. W.; Wesley, J. C.; Granetz, R.; Hollmann, E. M.; Moyer, R. A.; Zhang, J.; Crocker, N. A.; Austin, M. E.; Wingen, A.; Zhu, Y.

2014-01-01

Extremely low density operation free of error field penetration supports the excitation of trace-level quiescent runaway electron (RE) populations during the flat-top of DIII-D Ohmic discharges. Operation in the quiescent regime allows accurate measurement of all key parameters important to RE excitation, including the internal broadband magnetic fluctuation level. RE onset is characterized and found to be consistent with primary (Dreicer) generation rates. Impurity-free collisional suppression of the RE population is investigated by stepping the late-time main-ion density, until RE decay is observed. The transition from growth to decay is found to occur 3–5 times above the theoretical critical electric field for avalanche growth and is thus indicative of anomalous RE loss. This suggests that suppression of tokamak RE avalanches can be achieved at lower density than previously expected, though extrapolation requires predictive understanding of the RE loss mechanism and magnitude

Correlation Immunity, Avalanche Features, and Other Cryptographic Properties of Generalized Boolean Functions

Science.gov (United States)

2017-09-01

satisfying the strict avalanche criterion,” Discrete Math ., vol. 185, pp. 29–39, 1998. [2] R.C. Bose, “On some connections between the design of... Discrete Appl. Math ., vol. 149, pp. 73–86, 2005. [11] T.W. Cusick and P. Stănică, Cryptographic Boolean Functions and Applications, 2nd ed., San Diego...Stănică, “Bisecting binomial coefficients,” Discrete Appl. Math ., vol. 227, pp. 70–83, 2017. [28] T. Martinsen, W. Meidl, and P. Stănică, “Generalized

Recent results on avalanche phenomena for Al and Zn superconducting granule colloids

International Nuclear Information System (INIS)

Freund, P.; Gebauer, J.; Boniface, J.; Gonzalez-Mestres, L.; Perret-Gallix, D.

1989-11-01

Recent results on Al and Zn superheated superconducting granules (SSG) embedded into varnish GE 7031, and operated at very low temperature (down to 40 mK) are presented. The observed signals exhibit possible evidence for avalanche phenomena that could be due to thermal exchanges inside the detector. Such a result may confirm previous claims based on tests with Cd granules at T < 300 mK. Present observations indeed suggest that the SSG colloid should be dealt with as a composite medium rather than as an assembly of single grains

Optimal design under uncertainty of a passive defense structure against snow avalanches: from a general Bayesian framework to a simple analytical model

Directory of Open Access Journals (Sweden)

N. Eckert

2008-10-01

Full Text Available For snow avalanches, passive defense structures are generally designed by considering high return period events. In this paper, taking inspiration from other natural hazards, an alternative method based on the maximization of the economic benefit of the defense structure is proposed. A general Bayesian framework is described first. Special attention is given to the problem of taking the poor local information into account in the decision-making process. Therefore, simplifying assumptions are made. The avalanche hazard is represented by a Peak Over Threshold (POT model. The influence of the dam is quantified in terms of runout distance reduction with a simple relation derived from small-scale experiments using granular media. The costs corresponding to dam construction and the damage to the element at risk are roughly evaluated for each dam height-hazard value pair, with damage evaluation corresponding to the maximal expected loss. Both the classical and the Bayesian risk functions can then be computed analytically. The results are illustrated with a case study from the French avalanche database. A sensitivity analysis is performed and modelling assumptions are discussed in addition to possible further developments.

Granular avalanches on the Moon: Mass-wasting conditions, processes, and features

Science.gov (United States)

Kokelaar, B. P.; Bahia, R. S.; Joy, K. H.; Viroulet, S.; Gray, J. M. N. T.

2017-09-01

Seven lunar crater sites of granular avalanches are studied utilizing high-resolution images (0.42-1.3 m/pixel) from the Lunar Reconnaissance Orbiter Camera; one, in Kepler crater, is examined in detail. All the sites are slopes of debris extensively aggraded by frictional freezing at their dynamic angle of repose, four in craters formed in basaltic mare and three in the anorthositic highlands. Diverse styles of mass wasting occur, and three types of dry-debris flow deposit are recognized: (1) multiple channel-and-lobe type, with coarse-grained levees and lobate terminations that impound finer debris, (2) single-surge polylobate type, with subparallel arrays of lobes and fingers with segregated coarse-grained margins, and (3) multiple-ribbon type, with tracks reflecting reworked substrate, minor levees, and no coarse terminations. The latter type results from propagation of granular erosion-deposition waves down slopes dominantly of fine regolith, and it is the first recognized natural example. Dimensions, architectures, and granular segregation styles of the two coarse-grained deposit types are like those formed in natural and experimental avalanches on Earth, although the timescale of motion differs due to the reduced gravity. Influences of reduced gravity and fine-grained regolith on dynamics of granular flow and deposition appear slight, but we distinguish, for the first time, extensive remobilization of coarse talus by inundation with finer debris. The (few) sites show no clear difference attributable to the contrasting mare basalt and highland megaregolith host rocks and their fragmentation. This lunar study offers a benchmarking of deposit types that can be attributed to formation without influence of liquid or gas.

Local and global performance of double-gap resistive plate chambers operated in avalanche mode

Energy Technology Data Exchange (ETDEWEB)

Abbrescia, M.; Colaleo, A.; Iaselli, G.; Loddo, F.; Maggi, M.; Marangelli, B.; Natali, S.; Nuzzo, S.; Pugliese, G.; Ranieri, A.; Romano, F.; Altieri, S.; Belli, G.; Bruno, G.; Gianini, G.; Ratti, S.P.; Viola, L.; Vitulo, P.; Sergueev, S

1999-09-21

Two large double-gap resistive plate chambers, with 2 and 3 mm gap widths, were tested to study their response uniformity when operated in avalanche mode. The effects of mechanical tolerances and the presence of the spacers is thoroughly examined. Results on efficiency and time resolution are presented. We find that average performance and response uniformity over the whole chamber surface are fully adequate to the requirements of future collider experiments. (author)

Influence of the angular scattering of electrons on the runaway threshold in air

DEFF Research Database (Denmark)

Chanrion, O.; Bonaventura, Z.; Bourdon, A.

2016-01-01

The runaway electron mechanism is of great importance for the understanding of the generation of x- and gamma rays in atmospheric discharges. In 1991, terrestrial gamma-ray flashes (TGFs) were discovered by the Compton Gamma-Ray Observatory. Those emissions are bremsstrahlung from high energy...... electrons that run away in electric fields associated with thunderstorms. In this paper, we discuss the runaway threshold definition with a particular interest in the influence of the angular scattering for electron energy close to the threshold. In order to understand the mechanism of runaway, we compare...... scattering is not valid below 1 MeV where the runaway threshold usually is defined. These results are important for the thermal runaway and the runaway electron avalanche discharge mechanisms suggested to participate in the TGF generation....

Non-invasive assessment of animal exercise stress: real-time PCR of GLUT4, COX2, SOD1 and HSP70 in avalanche military dog saliva.

Science.gov (United States)

Diverio, S; Guelfi, G; Barbato, O; Di Mari, W; Egidi, M G; Santoro, M M

2015-01-01

Exercise has been shown to increase mRNA expression of a growing number of genes. The aim of this study was to assess if mRNA expression of the metabolism- and oxidative stress-related genes GLUT4 (glucose transporter 4), COX2 (cyclooxygenase 2), SOD1 (superoxide dismutase 1) and HSP70 (heat shock protein 70) in saliva changes following acute exercise stress in dogs. For this purpose, 12 avalanche dogs of the Italian Military Force Guardia di Finanza were monitored during simulation of a search for a buried person in an artificial avalanche area. Rectal temperature (RT) and saliva samples were collected the day before the trial (T0), immediately after the descent from a helicopter at the onset of a simulated avalanche search and rescue operation (T1), after the discovery of the buried person (T2) and 2 h later (T3). Expressions of GLUT4, SOD1, COX2 and HSP70 were measured by real-time PCR. The simulated avalanche search and rescue operation was shown to exert a significant effect on RT, as well as on the expression of all metabolism- and oxidative stress-related genes investigated, which peaked at T2. The observed expression patterns indicate an acute exercise stress-induced upregulation, as confirmed by the reductions in expression at T3. Moreover, our findings indicate that saliva is useful for assessing metabolism- and oxidative stress-related genes without the need for restraint, which could affect working dog performance.

Avalanche dynamics for active matter in heterogeneous media

Science.gov (United States)

Reichhardt, C. J. O.; Reichhardt, C.

2018-02-01

Using numerical simulations, we examine the dynamics of run-and-tumble disks moving in a disordered array of fixed obstacles. As a function of increasing active disk density and activity, we find a transition from a completely clogged state to a continuous flowing phase, and in the large activity limit, we observe an intermittent state where the motion occurs in avalanches that are power law distributed in size with an exponent of β =1.46. In contrast, in the thermal or low activity limit we find bursts of motion that are not broadly distributed in size. We argue that in the highly active regime, the system reaches a self-jamming state due to the activity-induced self-clustering, and that the intermittent dynamics is similar to that found in the yielding of amorphous solids. Our results show that activity is another route by which particulate systems can be tuned to a nonequilibrium critical state.

Annual report 1985

International Nuclear Information System (INIS)

1985-01-01

Aspects regarding ceramics, electronic materials, metals, the specialist task group, services to industry and other organizations and research support activities are discussed in the report. The highlights of the period are given, namely: the effect of high pressure on twophase systems, spinel structures, elastic moduli of stabilized zirconia crystals, alumina ceramics, a fast sodium-ion conducting solid electrolyte (Nasicon), liquid phase epitaxial growth of (HgCd)Te, compositional uniformity of bulk-grown (HgCd)Te, semi-quantitative mass spectrography of Cd and Te, depth profiling of metal semiconductor interdiffusion, low resistance ohmic contacts on GaAs, studies of Fe-Mn-Al alloys, surface mechanical properties of materials, electron diffraction, ceramic mould laboratory for investment casting of metals, grain boundary, sliding in the deformation of polycrystalline copper and a theory of work-hardening in face-centered cubic metals

Avalanche outbreaks emerging in cooperative contagions

Science.gov (United States)

Cai, Weiran; Chen, Li; Ghanbarnejad, Fakhteh; Grassberger, Peter

2015-11-01

The spreading of contagions can exhibit a percolation transition, which separates transitory prevalence from outbreaks that reach a finite fraction of the population. Such transitions are commonly believed to be continuous, but empirical studies have shown more violent spreading modes when the participating agents are not limited to one type. Striking examples include the co-epidemic of the Spanish flu and pneumonia that occurred in 1918 (refs , ), and, more recently, the concurrent prevalence of HIV/AIDS and a host of diseases. It remains unclear to what extent an outbreak in the presence of interacting pathogens differs from that due to an ordinary single-agent process. Here we study a mechanistic model for understanding contagion processes involving inter-agent cooperation. Our stochastic simulations reveal the possible emergence of a massive avalanche-like outbreak right at the threshold, which is manifested as a discontinuous phase transition. Such an abrupt change arises only if the underlying network topology supports a bottleneck for cascaded mutual infections. Surprisingly, all these discontinuous transitions are accompanied by non-trivial critical behaviours, presenting a rare case of hybrid transition. The findings may imply the origin of catastrophic occurrences in many realistic systems, from co-epidemics to financial contagions.

Ignition Features of Plasma-Beam Discharge in Gas-Discharge Electron Gun Operation

Directory of Open Access Journals (Sweden)

Valery A. Tutyk

2013-01-01

Full Text Available The current paper presents the results of experimental researches to determine the mode features of plasma-beam discharge (PBD generation by an electron beam injected by a low-vacuum gasdischarge electron gun (LGEG with the cold cathode and hollow anode on the basis of the high-voltage glow discharge and in the range of helium pressure of P ? 10 ÷ 130 Pa. The PBD boundaries and their dependences on parameters of an electron beam are found. The influence of PBD on parameters of low-vacuum gas-discharge electron gun is revealed. It causes an avalanche increase of electron beam current and burning of plasma-beam discharge in the whole space of the vacuum chamber volume and generation of electromagnetic radiation is revealed. Achieved results will be used for implementation of various vacuum technologies in the medium of reaction gas and generated electromagnetic radiation.

Indirect optical crosstalk reduction by highly-doped backside layer in PureB single-photon avalanche diode arrays

NARCIS (Netherlands)

Osrečki, Željko; Knežević, Tihomir; Nanver, Lis K.; Suligoj, Tomislav

2017-01-01

A method of reducing indirect optical crosstalk in a PureB single-photon avalanche diode (SPAD) array is investigated by TCAD simulations. The reduction is accomplished by taking advantage of the enhanced optical absorption of a highly-doped Si layer (p-type, 3×1020 cm-3) on the backside of the