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

NASA Astrophysics Data System (ADS)

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.

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

NASA Astrophysics Data System (ADS)

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: 10.1029/2006GL027426. [3] Cooray, V. and G. Cooray (2010), IEEE Transactions on Electromagnetic Compatibility, 52, No. 4, 944 - 955. [4] Eack, K. B. (2004), Geophys. Res. Lett., Vol. 31, L20102, doi: 10.1029/2005GL023975.

Adjoint method and runaway electron avalanche

DOE PAGES

Liu, Chang; Brennan, Dylan P.; Boozer, Allen H.; ...

2016-12-16

The adjoint method for the study of runaway electron dynamics in momentum space Liu et al (2016 Phys. Plasmas 23 010702) is rederived using the Green's function method, for both the runaway probability function (RPF) and the expected loss time (ELT). The RPF and ELT obtained using the adjoint method are presented, both with and without the synchrotron radiation reaction force. In conclusion, the adjoint method is then applied to study the runaway electron avalanche. Both the critical electric field and the growth rate for the avalanche are calculated using this fast and novel approach.

Breakdown flash at telecom wavelengths in InGaAs avalanche photodiodes

NASA Astrophysics Data System (ADS)

Shi, Yicheng; Lim, Janet Zheng Jie; Poh, Hou Shun; Tan, Peng Kian; Tan, Peiyu Amelia; Ling, Alexander; Kurtsiefer, Christian

2017-11-01

Quantum key distribution (QKD) at telecom wavelengths (1260-1625nm) has the potential for fast deployment due to existing optical fibre infrastructure and mature telecom technologies. At these wavelengths, indium gallium arsenide (InGaAs) avalanche photodiode (APD) based detectors are the preferred choice for photon detection. Similar to their silicon counterparts used at shorter wavelengths, they exhibit fluorescence from recombination of electron-hole pairs generated in the avalanche breakdown process. This fluorescence may open side channels for attacks on QKD systems. Here, we characterize the breakdown fluorescence from two commercial InGaAs single photon counting modules, and find a spectral distribution between 1000nm and 1600nm. We also show that by spectral filtering, this side channel can be efficiently suppressed.

Breakdown flash at telecom wavelengths in InGaAs avalanche photodiodes.

PubMed

Shi, Yicheng; Lim, Janet Zheng Jie; Poh, Hou Shun; Tan, Peng Kian; Tan, Peiyu Amelia; Ling, Alexander; Kurtsiefer, Christian

2017-11-27

Quantum key distribution (QKD) at telecom wavelengths (1260 - 1625 nm) has the potential for fast deployment due to existing optical fibre infrastructure and mature telecom technologies. At these wavelengths, Indium Gallium Arsenide (InGaAs) avalanche photodiode (APD) based detectors are the preferred choice for photon detection. Similar to their Silicon counterparts used at shorter wavelengths, they exhibit fluorescence from recombination of electron-hole pairs generated in the avalanche breakdown process. This fluorescence may open side channels for attacks on QKD systems. Here, we characterize the breakdown fluorescence from two commercial InGaAs single photon counting modules, and find a spectral distribution between 1000 nm and 1600 nm. We also show that by spectral filtering, this side channel can be efficiently suppressed.

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

PubMed

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.

Microgap x-ray detector

DOEpatents

Wuest, Craig R.; Bionta, Richard M.; Ables, Elden

1994-01-01

An x-ray detector which provides for the conversion of x-ray photons into photoelectrons and subsequent amplification of these photoelectrons through the generation of electron avalanches in a thin gas-filled region subject to a high electric potential. The detector comprises a cathode (photocathode) and an anode separated by the thin, gas-filled region. The cathode may comprise a substrate, such a beryllium, coated with a layer of high atomic number material, such as gold, while the anode can be a single conducting plane of material, such as gold, or a plane of resistive material, such as chromium/silicon monoxide, or multiple areas of conductive or resistive material, mounted on a substrate composed of glass, plastic or ceramic. The charge collected from each electron avalanche by the anode is passed through processing electronics to a point of use, such as an oscilloscope.

Microgap x-ray detector

DOEpatents

Wuest, C.R.; Bionta, R.M.; Ables, E.

1994-05-03

An x-ray detector is disclosed which provides for the conversion of x-ray photons into photoelectrons and subsequent amplification of these photoelectrons through the generation of electron avalanches in a thin gas-filled region subject to a high electric potential. The detector comprises a cathode (photocathode) and an anode separated by the thin, gas-filled region. The cathode may comprise a substrate, such a beryllium, coated with a layer of high atomic number material, such as gold, while the anode can be a single conducting plane of material, such as gold, or a plane of resistive material, such as chromium/silicon monoxide, or multiple areas of conductive or resistive material, mounted on a substrate composed of glass, plastic or ceramic. The charge collected from each electron avalanche by the anode is passed through processing electronics to a point of use, such as an oscilloscope. 3 figures.

Breakdown of Zero-Energy Quantum Hall State in Graphene in the Light of Current Fluctuations and Shot Noise

NASA Astrophysics Data System (ADS)

Laitinen, Antti; Kumar, Manohar; Elo, Teemu; Liu, Ying; Abhilash, T. S.; Hakonen, Pertti J.

2018-06-01

We have investigated the cross-over from Zener tunneling of single charge carriers to avalanche type of bunched electron transport in a suspended graphene Corbino disk in the zeroth Landau level. At low bias, we find a tunneling current that follows the gyrotropic Zener tunneling behavior. At larger bias, we find an avalanche type of transport that sets in at a smaller current the larger the magnetic field is. The low-frequency noise indicates strong bunching of the electrons in the avalanches. On the basis of the measured low-frequency switching noise power, we deduce the characteristic switching rates of the avalanche sequence. The simultaneous microwave shot noise measurement also reveals intrinsic correlations within the avalanche pulses and indicate a decrease in correlations with increasing bias.

Electromagnetic interference from electronic devices used in the management of type 1 diabetes can impair the performance of an avalanche transceiver in search mode.

PubMed

Miller, Steven C M

2015-06-01

Portable electronic devices play an important role in the management of type 1 diabetes mellitus. Electromagnetic interference from electronic devices has been shown to impair the function of an avalanche transceiver in search mode (but not in transmitting mode). This study investigates the influence of electromagnetic interference from diabetes devices on a searching avalanche beacon. The greatest distance at which an avalanche transceiver (in search mode) could accurately indicate the location of a transmitting transceiver was assessed when portable electronic devices (including an insulin pump and commonly used real-time continuous subcutaneous glucose monitoring system [rtCGMS]) were held in close proximity to each transceiver. The searching transceiver could accurately locate a transmitted signal at a distance of 30 m when used alone. This distance was unchanged by the Dexcom G4 rtCGMS, but was reduced to 10 m when the Medtronic Guardian rtCGMS was held close (within 30 cm) to the receiving beacon. Interference from the Animas Vibe insulin pump reduced this distance to 5 m, impairing the searching transceiver in a manner identical to the effect of a cell phone. Electromagnetic interference produced by some diabetes devices when held within 30 cm of a searching avalanche transceiver can impair the ability to locate a signal. Such interference could significantly compromise the outcome of a companion rescue scenario. Further investigation using other pumps and rtCGMS devices is required to evaluate all available diabetes electronics. Meantime, all electronic diabetes devices including rtCGMS and insulin pumps should not be used within 30 cm of an avalanche transceiver. Copyright © 2015 Wilderness Medical Society. Published by Elsevier Inc. All rights reserved.

First principles numerical model of avalanche-induced arc discharges in electron-irradiated dielectrics

NASA Technical Reports Server (NTRS)

Beers, B. L.; Pine, V. W.; Hwang, H. C.; Bloomberg, H. W.; Lin, D. L.; Schmidt, M. J.; Strickland, D. J.

1979-01-01

The model consists of four phases: single electron dynamics, single electron avalanche, negative streamer development, and tree formation. Numerical algorithms and computer code implementations are presented for the first three phases. An approach to developing a code description of fourth phase is discussed. Numerical results are presented for a crude material model of Teflon.

Review on Monte-Carlo Tools for Simulating Relativistic Runaway Electron Avalanches and the Propagation of TerretrialTerrestrial-Gamma Ray Flashes in the Atmosphere

NASA Astrophysics Data System (ADS)

Sarria, D.

2016-12-01

The field of High Energy Atmospheric Physics (HEAP) includes the study of energetic events related to thunderstorms, such as Terrestrial Gamma-ray Flashes (TGF), associated electron-positron beams (TEB), gamma-ray glows and Thunderstorm Ground Enhancements (TGE). Understanding these phenomena requires accurate models for the interaction of particles with atmospheric air and electro-magnetic fields in the <100 MeV energy range. This study is the next step of the work presented in [C. Rutjes et al., 2016] that compared the performances of various codes in the absence of electro-magnetic fields. In the first part, we quantify simple but informative test cases of electrons in various electric field profiles. We will compare the avalanche length (of the Relativistic Runaway Electron Avalanche (RREA) process), the photon/electron spectra and spatial scattering. In particular, we test the effect of the low-energy threshold, that was found to be very important [Skeltved et al., 2014]. Note that even without a field, it was found to be important because of the straggling effect [C. Rutjes et al., 2016]. For this first part, we will be comparing GEANT4 (different flavours), FLUKA and the custom made code GRRR. In the second part, we test the propagation of these high energy particles in the atmosphere, from production altitude (around 10 km to 18 km) to satellite altitude (600 km). We use a simple and clearly fixed set-up for the atmospheric density, the geomagnetic field, the initial conditions, and the detection conditions of the particles. For this second part, we will be comparing GEANT4 (different flavours), FLUKA/CORSIKA and the custom made code MC-PEPTITA. References : C. Rutjes et al., 2016. Evaluation of Monte Carlo tools for high energy atmospheric physics. Geosci. Model Dev. Under review. Skeltved, A. B. et al., 2014. Modelling the relativistic runaway electron avalanche and the feedback mechanism with geant4. JGRA, doi :10.1002/2014JA020504.

X-ray imaging using avalanche multiplication in amorphous selenium: investigation of intrinsic avalanche noise.

PubMed

Hunt, D C; Tanioka, Kenkichi; Rowlands, J A

2007-12-01

The flat-panel detector (FPD) is the state-of-the-art detector for digital radiography. The FPD can acquire images in real-time, has superior spatial resolution, and is free of the problems of x-ray image intensifiers-veiling glare, pin-cushion and magnetic distortion. However, FPDs suffer from poor signal to noise ratio performance at typical fluoroscopic exposure rates where the quantum noise is reduced to the point that it becomes comparable to the fixed electronic noise. It has been shown previously that avalanche multiplication gain in amorphous selenium (a-Se) can provide the necessary amplification to overcome the electronic noise of the FPD. Avalanche multiplication, however, comes with its own intrinsic contribution to the noise in the form of gain fluctuation noise. In this article a cascaded systems analysis is used to present a modified metric related to the detective quantum efficiency. The modified metric is used to study a diagnostic x-ray imaging system in the presence of intrinsic avalanche multiplication noise independently from other noise sources, such as electronic noise. An indirect conversion imaging system is considered to make the study independent of other avalanche multiplication related noise sources, such as the fluctuations arising from the depth of x-ray absorption. In this case all the avalanche events are initiated at the surface of the avalanche layer, and there are no fluctuations in the depth of absorption. Experiments on an indirect conversion x-ray imaging system using avalanche multiplication in a layer of a-Se are also presented. The cascaded systems analysis shows that intrinsic noise of avalanche multiplication will not have any deleterious influence on detector performance at zero spatial frequency in x-ray imaging provided the product of conversion gain, coupling efficiency, and optical quantum efficiency are much greater than a factor of 2. The experimental results show that avalanche multiplication in a-Se behaves as an intrinsic noise free avalanche multiplication, in accordance with our theory. Provided good coupling efficiency and high optical quantum efficiency are maintained, avalanche multiplication in a-Se has the potential to increase the gain and make negligible contribution to the noise, thereby improving the performance of indirect FPDs in fluoroscopy.

X-ray imaging using avalanche multiplication in amorphous selenium: Investigation of intrinsic avalanche noise

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hunt, D. C.; Tanioka, Kenkichi; Rowlands, J. A.

2007-12-15

The flat-panel detector (FPD) is the state-of-the-art detector for digital radiography. The FPD can acquire images in real-time, has superior spatial resolution, and is free of the problems of x-ray image intensifiers--veiling glare, pin-cushion and magnetic distortion. However, FPDs suffer from poor signal to noise ratio performance at typical fluoroscopic exposure rates where the quantum noise is reduced to the point that it becomes comparable to the fixed electronic noise. It has been shown previously that avalanche multiplication gain in amorphous selenium (a-Se) can provide the necessary amplification to overcome the electronic noise of the FPD. Avalanche multiplication, however, comesmore » with its own intrinsic contribution to the noise in the form of gain fluctuation noise. In this article a cascaded systems analysis is used to present a modified metric related to the detective quantum efficiency. The modified metric is used to study a diagnostic x-ray imaging system in the presence of intrinsic avalanche multiplication noise independently from other noise sources, such as electronic noise. An indirect conversion imaging system is considered to make the study independent of other avalanche multiplication related noise sources, such as the fluctuations arising from the depth of x-ray absorption. In this case all the avalanche events are initiated at the surface of the avalanche layer, and there are no fluctuations in the depth of absorption. Experiments on an indirect conversion x-ray imaging system using avalanche multiplication in a layer of a-Se are also presented. The cascaded systems analysis shows that intrinsic noise of avalanche multiplication will not have any deleterious influence on detector performance at zero spatial frequency in x-ray imaging provided the product of conversion gain, coupling efficiency, and optical quantum efficiency are much greater than a factor of 2. The experimental results show that avalanche multiplication in a-Se behaves as an intrinsic noise free avalanche multiplication, in accordance with our theory. Provided good coupling efficiency and high optical quantum efficiency are maintained, avalanche multiplication in a-Se has the potential to increase the gain and make negligible contribution to the noise, thereby improving the performance of indirect FPDs in fluoroscopy.« less

SAPHIRE (scintillator avalanche photoconductor with high resolution emitter readout) for low dose x-ray imaging: Spatial resolution

DOE Office of Scientific and Technical Information (OSTI.GOV)

Li Dan; Zhao Wei

2008-07-15

An indirect flat panel imager (FPI) with programmable avalanche gain and field emitter array (FEA) readout is being investigated for low-dose and high resolution x-ray imaging. It is made by optically coupling a structured x-ray scintillator, e.g., thallium (Tl) doped cesium iodide (CsI), to an amorphous selenium (a-Se) avalanche photoconductor called high-gain avalanche rushing amorphous photoconductor (HARP). The charge image created by the scintillator/HARP (SHARP) combination is read out by the electron beams emitted from the FEA. The proposed detector is called scintillator avalanche photoconductor with high resolution emitter readout (SAPHIRE). The programmable avalanche gain of HARP can improve themore » low dose performance of indirect FPI while the FEA can be made with pixel sizes down to 50 {mu}m. Because of the avalanche gain, a high resolution type of CsI (Tl), which has not been widely used in indirect FPI due to its lower light output, can be used to improve the high spatial frequency performance. The purpose of the present article is to investigate the factors affecting the spatial resolution of SAPHIRE. Since the resolution performance of the SHARP combination has been well studied, the focus of the present work is on the inherent resolution of the FEA readout method. The lateral spread of the electron beam emitted from a 50 {mu}mx50 {mu}m pixel FEA was investigated with two different electron-optical designs: mesh-electrode-only and electrostatic focusing. Our results showed that electrostatic focusing can limit the lateral spread of electron beams to within the pixel size of down to 50 {mu}m. Since electrostatic focusing is essentially independent of signal intensity, it will provide excellent spatial uniformity.« less

A demonstration device for cosmic rays telescopes

NASA Astrophysics Data System (ADS)

Esposito, Salvatore

2018-01-01

We describe a hands-on accurate demonstrator for cosmic rays realized by six high school students. The main aim is to show the relevance and the functioning of the principal parts of a cosmic ray telescope (muon detector), with the help of two large sized wooden artefacts. The first one points out how cosmic rays can be tracked in a muon telescope, while the other one shows the key avalanche process of electronic ionization that effectively allows muon detection through a photomultiplier. Incoming cosmic rays are visualized in terms of laser beams, whose 3D trajectory is highlighted by turning on LEDs on two orthogonal matrices. Instead the avalanche ionization process is demonstrated through the avalanche falling off glass marbles on an inclined plane, finally turning on a LED. A pictured poster accompanying the demonstrator is as effective in assisting cosmic ray demonstration and its detection. The success of the demonstrator has been fully proven by the general public during a science festival, in which the corresponding project won the Honorable Mention in a dedicated competition.

Quantitative measurement of electron number in nanosecond and picosecond laser-induced air breakdown

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wu, Yue; Sawyer, Jordan C.; Su, Liu

2016-05-07

Here we present quantitative measurements of total electron numbers in laser-induced air breakdown at pressures ranging from atmospheric to 40 bar{sub g} by 10 ns and 100 ps laser pulses. A quantifiable definition for the laser-induced breakdown threshold is identified by a sharp increase in the measurable total electron numbers via dielectric-calibrated coherent microwave scattering. For the 10 ns laser pulse, the threshold of laser-induced breakdown in atmospheric air is defined as the total electron number of ∼10{sup 6}. This breakdown threshold decreases with an increase of pressure and laser photon energy (shorter wavelength), which is consistent with the theory of initialmore » multiphoton ionization and subsequent avalanche processes. For the 100 ps laser pulse cases, a clear threshold is not present and only marginal pressure effects can be observed, which is due to the short pulse duration leading to stronger multiphoton ionization and minimal collisional avalanche ionization.« less

Development of solid-state avalanche amorphous selenium for medical imaging.

PubMed

Scheuermann, James R; Goldan, Amir H; Tousignant, Olivier; Léveillé, Sébastien; Zhao, Wei

2015-03-01

Active matrix flat panel imagers (AMFPI) have limited performance in low dose applications due to the electronic noise of the thin film transistor (TFT) array. A uniform layer of avalanche amorphous selenium (a-Se) called high gain avalanche rushing photoconductor (HARP) allows for signal amplification prior to readout from the TFT array, largely eliminating the effects of the electronic noise. The authors report preliminary avalanche gain measurements from the first HARP structure developed for direct deposition onto a TFT array. The HARP structure is fabricated on a glass substrate in the form of p-i-n, i.e., the electron blocking layer (p) followed by an intrinsic (i) a-Se layer and finally the hole blocking layer (n). All deposition procedures are scalable to large area detectors. Integrated charge is measured from pulsed optical excitation incident on the top electrode (as would in an indirect AMFPI) under continuous high voltage bias. Avalanche gain measurements were obtained from samples fabricated simultaneously at different locations in the evaporator to evaluate performance uniformity across large area. An avalanche gain of up to 80 was obtained, which showed field dependence consistent with previous measurements from n-i-p HARP structures established for vacuum tubes. Measurements from multiple samples demonstrate the spatial uniformity of performance using large area deposition methods. Finally, the results were highly reproducible during the time course of the entire study. We present promising avalanche gain measurement results from a novel HARP structure that can be deposited onto a TFT array. This is a crucial step toward the practical feasibility of AMFPI with avalanche gain, enabling quantum noise limited performance down to a single x-ray photon per pixel.

The Martian Dust Devil Electron Avalanche: Laboratory Measurements of the E-Field Fortifying Effects of Dust-Electron Absorption

NASA Technical Reports Server (NTRS)

Farrell, W. M.; McLain, J. L.; Collier, M. R.; Keller, J. W.

2017-01-01

Analogous to terrestrial dust devils, charged dust in Mars dust devils should become vertically stratified in the convective features, creating large scale E-fields. This E-field in a Martian-like atmosphere has been shown to stimulate the development of a Townsend discharge (electron avalanche) that acts to dissipate charge in regions where charge build-up occurs. While the stratification of the charged dust is a source of the electrical energy, the uncharged particulates in the dust population may absorb a portion of these avalanching electrons, thereby inhibiting dissipation and leading to the development of anomalously large E-field values. We performed a laboratory study that does indeed show the presence of enhanced E-field strengths between an anode and cathode when dust-absorbing filaments (acting as particulates) are placed in the avalanching electron flow. Further, the E-field threshold condition to create an impulsive spark discharge increases to larger values as more filaments are placed between the anode and cathode. We conclude that the spatially separated charged dust creates the charge centers and E-fields in a dust devil, but the under-charged portion of the population acts to reduce Townsend electron dissipation currents, further fortifying the development of larger-than-expected E-fields.

DIFMOS - A floating-gate electrically erasable nonvolatile semiconductor memory technology. [Dual Injector Floating-gate MOS

NASA Technical Reports Server (NTRS)

Gosney, W. M.

1977-01-01

Electrically alterable read-only memories (EAROM's) or reprogrammable read-only memories (RPROM's) can be fabricated using a single-level metal-gate p-channel MOS technology with all conventional processing steps. Given the acronym DIFMOS for dual-injector floating-gate MOS, this technology utilizes the floating-gate technique for nonvolatile storage of data. Avalanche injection of hot electrons through gate oxide from a special injector diode in each bit is used to charge the floating gates. A second injector structure included in each bit permits discharge of the floating gate by avalanche injection of holes through gate oxide. The overall design of the DIFMOS bit is dictated by the physical considerations required for each of the avalanche injector types. The end result is a circuit technology which can provide fully decoded bit-erasable EAROM-type circuits using conventional manufacturing techniques.

Multi-field plasma sandpile model in tokamaks and applications

NASA Astrophysics Data System (ADS)

Peng, X. D.; Xu, J. Q.

2016-08-01

A multi-field sandpile model of tokamak plasmas is formulated for the first time to simulate the dynamic process with interaction between avalanche events on the fast/micro time-scale and diffusive transports on the slow/macro time-scale. The main characteristics of the model are that both particle and energy avalanches of sand grains are taken into account simultaneously. New redistribution rules of a sand-relaxing process are defined according to the transport properties of special turbulence which allows the uphill particle transport. Applying the model, we first simulate the steady-state plasma profile self-sustained by drift wave turbulences in the Ohmic discharge of a tokamak. A scaling law as f = a q0 b + c for the relation of both center-density n ( 0 ) and electron (ion) temperatures T e ( 0 ) ( T i ( 0 ) ) with the center-safety-factor q 0 is found. Then interesting work about the nonlocal transport phenomenon observed in tokamak experiments proceeds. It is found that the core electron temperature increases rapidly in response to the edge cold pulse and inversely it decreases in response to the edge heat pulse. The results show that the nonlocal response of core electron temperature depending on the amplitudes of background plasma density and temperature is more remarkable in a range of gas injection rate. Analyses indicate that the avalanche transport caused by plasma drift instabilities with thresholds is a possible physical mechanism for the nonlocal transport in tokamaks. It is believed that the model is capable of being applied to more extensive questions occurring in the transport field.

An Avalanche Diode Electron Detector for Observing NEET

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kishimoto, Shunji

2004-05-12

Nuclear excitation by electron transition (NEET) occurs in atomic inner-shell ionization if the nuclear excitation and the electron transition have nearly the same energy and a common multipolarity. We successfully observed the NEET on 197Au and on 193Ir using a silicon avalanche diode electron detector. The detector was used to find internal conversion electrons emitted from excited nuclei in time spectroscopy with a time gate method. Some nuclear resonant levels, including 8.410 keV on 169Tm and 80.577 keV on 166Er, were also observed with the detector.

Solid-state flat panel imager with avalanche amorphous selenium

NASA Astrophysics Data System (ADS)

Scheuermann, James R.; Howansky, Adrian; Goldan, Amir H.; Tousignant, Olivier; Levéille, Sébastien; Tanioka, K.; Zhao, Wei

2016-03-01

Active matrix flat panel imagers (AMFPI) have become the dominant detector technology for digital radiography and fluoroscopy. For low dose imaging, electronic noise from the amorphous silicon thin film transistor (TFT) array degrades imaging performance. We have fabricated the first prototype solid-state AMFPI using a uniform layer of avalanche amorphous selenium (a-Se) photoconductor to amplify the signal to eliminate the effect of electronic noise. We have previously developed a large area solid-state avalanche a-Se sensor structure referred to as High Gain Avalanche Rushing Photoconductor (HARP) capable of achieving gains of 75. In this work we successfully deposited this HARP structure onto a 24 x 30 cm2 TFT array with a pixel pitch of 85 μm. An electric field (ESe) up to 105 Vμm-1 was applied across the a-Se layer without breakdown. Using the HARP layer as a direct detector, an X-ray avalanche gain of 15 +/- 3 was achieved at ESe = 105 Vμm-1. In indirect mode with a 150 μm thick structured CsI scintillator, an optical gain of 76 +/- 5 was measured at ESe = 105 Vμm-1. Image quality at low dose increases with the avalanche gain until the electronic noise is overcome at a constant exposure level of 0.76 mR. We demonstrate the success of a solid-state HARP X-ray imager as well as the largest active area HARP sensor to date.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Scheuermann, James R., E-mail: James.Scheuermann@stonybrook.edu; Goldan, Amir H.; Zhao, Wei

Purpose: Active matrix flat panel imagers (AMFPI) have limited performance in low dose applications due to the electronic noise of the thin film transistor (TFT) array. A uniform layer of avalanche amorphous selenium (a-Se) called high gain avalanche rushing photoconductor (HARP) allows for signal amplification prior to readout from the TFT array, largely eliminating the effects of the electronic noise. The authors report preliminary avalanche gain measurements from the first HARP structure developed for direct deposition onto a TFT array. Methods: The HARP structure is fabricated on a glass substrate in the form of p-i-n, i.e., the electron blocking layermore » (p) followed by an intrinsic (i) a-Se layer and finally the hole blocking layer (n). All deposition procedures are scalable to large area detectors. Integrated charge is measured from pulsed optical excitation incident on the top electrode (as would in an indirect AMFPI) under continuous high voltage bias. Avalanche gain measurements were obtained from samples fabricated simultaneously at different locations in the evaporator to evaluate performance uniformity across large area. Results: An avalanche gain of up to 80 was obtained, which showed field dependence consistent with previous measurements from n-i-p HARP structures established for vacuum tubes. Measurements from multiple samples demonstrate the spatial uniformity of performance using large area deposition methods. Finally, the results were highly reproducible during the time course of the entire study. Conclusions: We present promising avalanche gain measurement results from a novel HARP structure that can be deposited onto a TFT array. This is a crucial step toward the practical feasibility of AMFPI with avalanche gain, enabling quantum noise limited performance down to a single x-ray photon per pixel.« less

Continued development of a detailed model of arc discharge dynamics

NASA Technical Reports Server (NTRS)

Beers, B. L.; Pine, V. W.; Ives, S. T.

1982-01-01

Using a previously developed set of codes (SEMC, CASCAD, ACORN), a parametric study was performed to quantify the parameters which describe the development of a single electron indicated avalanche into a negative tip streamer. The electron distribution function in Teflon is presented for values of the electric field in the range of four-hundred million volts/meter to four billon volts/meter. A formulation of the scattering parameters is developed which shows that the transport can be represented by three independent variables. The distribution of ionization sites is used to indicate an avalanche. The self consistent evolution of the avalanche is computed over the parameter range of scattering set.

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

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wronski, M.; Zhao, W.; Tanioka, K.

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 themore » 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 clinically relevant medical x-ray exposures. Conclusions: This work demonstrates that the HARP-DRL sensor enables the practical implementation of a SHARP solid-state x-ray sensor capable of quantum noise limited operation throughout the entire range of clinically relevant x-ray exposures. This is an important step toward the realization of a SHARP-AMFPI x-ray flat-panel imager.« less

Microgap ultra-violet detector

DOEpatents

Wuest, Craig R.; Bionta, Richard M.

1994-01-01

A microgap ultra-violet detector of photons with wavelengths less than 400 run (4000 Angstroms) which comprises an anode and a cathode separated by a gas-filled gap and having an electric field placed across the gap. Either the anode or the cathode is semi-transparent to UV light. Upon a UV photon striking the cathode an electron is expelled and accelerated across the gap by the electric field causing interactions with other electrons to create an electron avalanche which contacts the anode. The electron avalanche is detected and converted to an output pulse.

Microgap ultra-violet detector

DOEpatents

Wuest, C.R.; Bionta, R.M.

1994-09-20

A microgap ultra-violet detector of photons with wavelengths less than 400 run (4,000 Angstroms) which comprises an anode and a cathode separated by a gas-filled gap and having an electric field placed across the gap is disclosed. Either the anode or the cathode is semi-transparent to UV light. Upon a UV photon striking the cathode an electron is expelled and accelerated across the gap by the electric field causing interactions with other electrons to create an electron avalanche which contacts the anode. The electron avalanche is detected and converted to an output pulse. 2 figs.

Silicon avalanche photodiodes developed at the Institute of Electron Technology

NASA Astrophysics Data System (ADS)

Wegrzecka, Iwona; Wegrzecki, Maciej; Bar, Jan; Grynglas, Maria; Uszynski, Andrzej; Grodecki, Remigiusz; Grabiec, Piotr B.; Krzeminski, Sylwester; Budzynski, Tadeusz

2004-07-01

Silicon avalanche photodiodes (APDs) -- due to the effect of avalanche multiplication of carriers in their structure -- are most sensitive and fastest detectors of visible and near infrared radiation. Also the value of noise equivalent power NEP of these detectors is the smallest. In the paper, the design, technology and properties of the silicon avalanche photodiodes with a n+ - p - π - p+ epiplanar structure developed at the Institute of Electron Technology (ITE) are presented. The diameters of photosensitive area range from 0.3 mm to 5 mm. The ITE photodiodes are optimized for the detection of the 800 nm - 850 nm radiation, but the detailed research on spectral dependencies of the gain and noise parameters has revealed that the spectral operating range of the ITE photodiodes is considerable wider and achieves 550 - 1000 nm. These photodiodes can be used in detection of very weak and very fast optical signals. Presently in the world, the studies are carried out on applying the avalanche photodiodes in detection of X radiation and in the scintillation detection of nuclear radiation.

Calculation of H2-He Flow with Nonequilibrium Ionization and Radiation: an Interim Report

NASA Technical Reports Server (NTRS)

Furudate, Michiko; Chang, Keun-Shik

2005-01-01

The nonequilibrium ionization process in hydrogen-helium mixture behind a strong shock wave is studied numerically using the detailed ionization rate model developed recently by Park which accounts for emission and absorption of Lyman lines. The study finds that, once the avalanche ionization is started, the Lyman line is self-absorbed. The intensity variation of the radiation at 5145 Angstroms found by Leibowitz in a shock tube experiment can be numerically reproduced by assuming that ionization behind the shock wave prior to the onset of avalanche ionization is 1.3%. Because 1.3% initial ionization is highly unlikely, Leibowitz s experimental data is deemed questionable. By varying the initial electron density value in the calculation, the calculated ionization equilibration time is shown to increase approximately as inverse square-root of the initial electron density value. The true ionization equilibration time is most likely much longer than the value found by Leibowitz.

Monte-Carlo simulation of spatial resolution of an image intensifier in a saturation mode

NASA Astrophysics Data System (ADS)

Xie, Yuntao; Wang, Xi; Zhang, Yujun; Sun, Xiaoquan

2018-04-01

In order to investigate the spatial resolution of an image intensifier which is irradiated by high-energy pulsed laser, a three-dimensional electron avalanche model was built and the cascade process of the electrons was numerically simulated. The influence of positive wall charges, due to the failure of replenishing charges extracted from the channel during the avalanche, was considered by calculating its static electric field through particle-in-cell (PIC) method. By tracing the trajectory of electrons throughout the image intensifier, the energy of the electrons at the output of the micro channel plate and the electron distribution at the phosphor screen are numerically calculated. The simulated energy distribution of output electrons are in good agreement with experimental data of previous studies. In addition, the FWHM extensions of the electron spot at phosphor screen as a function of the number of incident electrons are calculated. The results demonstrate that the spot size increases significantly with the increase in the number of incident electrons. Furthermore, we got the MTFs of the image intensifier by Fourier transform of a point spread function at phosphor screen. Comparison between the MTFs in our model and the MTFs by analytic method shows that spatial resolution of the image intensifier decreases significantly as the number of incident electrons increases, and it is particularly obvious when incident electron number greater than 100.

Toward Scintillator High-Gain Avalanche Rushing Photoconductor Active Matrix Flat Panel Imager (SHARP-AMFPI): Initial fabrication and characterization.

PubMed

Scheuermann, James R; Howansky, Adrian; Hansroul, Marc; Léveillé, Sébastien; Tanioka, Kenkichi; Zhao, Wei

2018-02-01

We present the first prototype Scintillator High-Gain Avalanche Rushing Photoconductor Active Matrix Flat Panel Imager (SHARP-AMFPI). This detector includes a layer of avalanche amorphous Selenium (a-Se) (HARP) as the photoconductor in an indirect detector to amplify the signal and reduce the effects of electronic noise to obtain quantum noise-limited images for low-dose applications. It is the first time avalanche a-Se has been used in a solid-state imaging device and poses as a possible solution to eliminate the effects of electronic noise, which is crucial for low-dose imaging performance of AMFPI. We successfully deposited a solid-state HARP structure onto a 24 × 30 cm 2 array of thin-film transistors (TFT array) with a pixel pitch of 85 μm. The HARP layer consists of 16 μm of a-Se with a hole-blocking and electron-blocking layer to prevent charge injection from the high-voltage bias and pixel electrodes, respectively. An electric field (E S e ) up to 105 V μm -1 was applied across the a-Se layer without breakdown. A 150 μm thick-structured CsI:Tl scintillator was used to form SHARP-AMFPI. The x-ray imaging performance is characterized using a 30 kVp Mo/Mo beam. We evaluate the spatial resolution, noise power, and detective quantum efficiency at zero frequency of the system with and without avalanche gain. The results are analyzed using cascaded linear system model (CLSM). An avalanche gain of 76 ± 5 was measured at E S e = 105 V μm -1 . We demonstrate that avalanche gain can amplify the signal to overcome electronic noise. As avalanche gain is increased, image quality improves for a constant (0.76 mR) exposure until electronic noise is overcome. Our system is currently limited by poor optical transparency of our high-voltage electrode and long integrating time which results in dark current noise. These two effects cause high-spatial frequency noise to dominate imaging performance. We demonstrate the feasibility of a solid-state HARP x-ray imager and have fabricated the largest active area HARP sensor to date. Procedures to reduce secondary quantum and dark noise are outlined. Future work will improve optical coupling and charge transport which will allow for frequency DQE and temporal metrics to be obtained. © 2017 American Association of Physicists in Medicine.

Study on avalanche photodiode influence on heterodyne laser interferometer linearity

DOE Office of Scientific and Technical Information (OSTI.GOV)

Budzyn, Grzegorz, E-mail: grzegorz.budzyn@pwr.wroc.pl; Podzorny, Tomasz

2016-06-28

In the paper we analyze factors reducing the possible accuracy of the heterodyne laser interferometers. The analysis is performed for the avalanche-photodiode input stages but is in main points valid also for stages with other type of photodetectors. Instrumental error originating from optical, electronic and digital signal processing factors is taken into consideration. We stress factors which are critical and those which can be neglected at certain accuracy requirements. In the work we prove that it is possible to reduce errors of the laser instrument below 1 nm point for multiaxial APD based interferometers by precise control of incident optical powermore » and the temperature of the photodiode.« less

A Comprehensive Analysis of the Physical Properties of Advanced GaAs/AlGaAs Junctions

NASA Technical Reports Server (NTRS)

Menkara, Hicham M.

1996-01-01

Extensive studies have been performed on MQW junctions and structures because of their potential applications as avalanche photodetectors in optical communications and imaging systems. The role of the avalanche photodiode is to provide for the conversion of an optical signal into charge. Knowledge of junction physics, and the various carrier generation/recombination mechanisms, is crucial for effectively optimizing the conversion process and increasing the structure's quantum efficiency. In addition, the recent interest in the use of APDs in imaging systems has necessitated the development of semiconductor junctions with low dark currents and high gains for low light applications. Because of the high frame rate and high pixel density requirements in new imaging applications, it is necessary to provide some front-end gain in the imager to allow operation under reasonable light conditions. Understanding the electron/hole impact ionization process, as well as diffusion and surface leakage effects, is needed to help maintain low dark currents and high gains for such applications. In addition, the APD must be capable of operating with low power, and low noise. Knowledge of the effects of various doping configurations and electric field profiles, as well as the excess noise resulting from the avalanche process, are needed to help maintain low operating bias and minimize the noise output.

Direct-conversion flat-panel imager with avalanche gain: Feasibility investigation for HARP-AMFPI

PubMed Central

Wronski, M. M.; Rowlands, J. A.

2008-01-01

The authors are investigating the concept of a direct-conversion flat-panel imager with avalanche gain for low-dose x-ray imaging. It consists of an amorphous selenium (a-Se) photoconductor partitioned into a thick drift region for x-ray-to-charge conversion and a relatively thin region called high-gain avalanche rushing photoconductor (HARP) in which the charge undergoes avalanche multiplication. An active matrix of thin film transistors is used to read out the electronic image. The authors call the proposed imager HARP active matrix flat panel imager (HARP-AMFPI). The key advantages of HARP-AMFPI are its high spatial resolution, owing to the direct-conversion a-Se layer, and its programmable avalanche gain, which can be enabled during low dose fluoroscopy to overcome electronic noise and disabled during high dose radiography to prevent saturation of the detector elements. This article investigates key design considerations for HARP-AMFPI. The effects of electronic noise on the imaging performance of HARP-AMFPI were modeled theoretically and system parameters were optimized for radiography and fluoroscopy. The following imager properties were determined as a function of avalanche gain: (1) the spatial frequency dependent detective quantum efficiency; (2) fill factor; (3) dynamic range and linearity; and (4) gain nonuniformities resulting from electric field strength nonuniformities. The authors results showed that avalanche gains of 5 and 20 enable x-ray quantum noise limited performance throughout the entire exposure range in radiography and fluoroscopy, respectively. It was shown that HARP-AMFPI can provide the required gain while maintaining a 100% effective fill factor and a piecewise dynamic range over five orders of magnitude (10−7–10−2 R∕frame). The authors have also shown that imaging performance is not significantly affected by the following: electric field strength nonuniformities, avalanche noise for x-ray energies above 1 keV and direct interaction of x rays in the gain region. Thus, HARP-AMFPI is a promising flat-panel imager structure that enables high-resolution fully quantum noise limited x-ray imaging over a wide exposure range. PMID:19175080

Direct-conversion flat-panel imager with avalanche gain: Feasibility investigation for HARP-AMFPI

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wronski, M. M.; Rowlands, J. A.

2008-12-15

The authors are investigating the concept of a direct-conversion flat-panel imager with avalanche gain for low-dose x-ray imaging. It consists of an amorphous selenium (a-Se) photoconductor partitioned into a thick drift region for x-ray-to-charge conversion and a relatively thin region called high-gain avalanche rushing photoconductor (HARP) in which the charge undergoes avalanche multiplication. An active matrix of thin film transistors is used to read out the electronic image. The authors call the proposed imager HARP active matrix flat panel imager (HARP-AMFPI). The key advantages of HARP-AMFPI are its high spatial resolution, owing to the direct-conversion a-Se layer, and its programmablemore » avalanche gain, which can be enabled during low dose fluoroscopy to overcome electronic noise and disabled during high dose radiography to prevent saturation of the detector elements. This article investigates key design considerations for HARP-AMFPI. The effects of electronic noise on the imaging performance of HARP-AMFPI were modeled theoretically and system parameters were optimized for radiography and fluoroscopy. The following imager properties were determined as a function of avalanche gain: (1) the spatial frequency dependent detective quantum efficiency; (2) fill factor; (3) dynamic range and linearity; and (4) gain nonuniformities resulting from electric field strength nonuniformities. The authors results showed that avalanche gains of 5 and 20 enable x-ray quantum noise limited performance throughout the entire exposure range in radiography and fluoroscopy, respectively. It was shown that HARP-AMFPI can provide the required gain while maintaining a 100% effective fill factor and a piecewise dynamic range over five orders of magnitude (10{sup -7}-10{sup -2} R/frame). The authors have also shown that imaging performance is not significantly affected by the following: electric field strength nonuniformities, avalanche noise for x-ray energies above 1 keV and direct interaction of x rays in the gain region. Thus, HARP-AMFPI is a promising flat-panel imager structure that enables high-resolution fully quantum noise limited x-ray imaging over a wide exposure range.« less

Numerical simulation of compact intracloud discharge and generated electromagnetic pulse

NASA Astrophysics Data System (ADS)

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

2015-06-01

Using the concept of the relativistic runaway electron avalanche, numerical simulation of compact intracloud discharge as a generator of powerful natural electromagnetic pulses (EMPs) in the HF-UHF range was conducted. We evaluated the numbers of electrons initiating the avalanche, with which the calculated EMP characteristics are consistent with measured ones. The discharge capable of generating EMPs produces runaway electrons in numbers close to those in the source of terrestrial γ-flashes (TGF) registered in the nearest space, which may be an argument for a joint EMP and TGF source.

Stability of the discretization of the electron avalanche phenomenon

DOE Office of Scientific and Technical Information (OSTI.GOV)

Villa, Andrea, E-mail: andrea.villa@rse-web.it; Barbieri, Luca, E-mail: luca.barbieri@rse-web.it; Gondola, Marco, E-mail: marco.gondola@rse-web.it

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 tomore » 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.« less

Towards an understanding of flows in avalanche transport phenomena

NASA Astrophysics Data System (ADS)

Jin, Suying; Ramadan, Nikolas; van Compernolle, Bart; Poulos, Matt J.; Morales, George J.

2017-10-01

Recent heat transport experiments conducted in the Large Plasma Device (LAPD) at UCLA, studying avalanche phenomena at steep cross-magnetic field pressure gradients, suggest that flows play a critical role in the evolution of transport phenomena, motivating further characterization. A ring shaped electron beam source injects sub-ionization energy electrons along the strong background magnetic field within a larger quiescent plasma, creating a hollow, high pressure filament. Two distinct regimes are observed as the density decays; the first characterized by multiple small avalanches producing sudden relaxations of the pressure profile which then recovers under continued heating, and the second signaled by a permanent collapse of the density profile after a global avalanche event, then dominated by drift-Alfven waves. The source is modified from previous experiments to gain active control of the flows by controlling the bias between the emitting ring and surrounding carbon masks. The results of flow measurements obtained using a Mach probe and Langmuir/emissive probe are here presented and compared. An analytical model for the behavior of the electron beam source is also in development. Sponsored by NSF Grant 1619505 and by DOE/NSF at BaPSF.

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

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zhao Wei; Li Dan; Reznik, Alla

2005-09-15

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 avoidmore » 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{sub Se} and the applied electric field E{sub Se} of the HARP layer. To determine the optimal design parameter and operational conditions for HARP, we measured the E{sub Se} dependence of both avalanche gain and optical quantum efficiency of an 8 {mu}m 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{sub 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 {mu}m 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.« less

Investigation of spatial resolution and temporal performance of SAPHIRE (scintillator avalanche photoconductor with high resolution emitter readout) with integrated electrostatic focusing

NASA Astrophysics Data System (ADS)

Scaduto, David A.; Lubinsky, Anthony R.; Rowlands, John A.; Kenmotsu, Hidenori; Nishimoto, Norihito; Nishino, Takeshi; Tanioka, Kenkichi; Zhao, Wei

2014-03-01

We have previously proposed SAPHIRE (scintillator avalanche photoconductor with high resolution emitter readout), a novel detector concept with potentially superior spatial resolution and low-dose performance compared with existing flat-panel imagers. The detector comprises a scintillator that is optically coupled to an amorphous selenium photoconductor operated with avalanche gain, known as high-gain avalanche rushing photoconductor (HARP). High resolution electron beam readout is achieved using a field emitter array (FEA). This combination of avalanche gain, allowing for very low-dose imaging, and electron emitter readout, providing high spatial resolution, offers potentially superior image quality compared with existing flat-panel imagers, with specific applications to fluoroscopy and breast imaging. Through the present collaboration, a prototype HARP sensor with integrated electrostatic focusing and nano- Spindt FEA readout technology has been fabricated. The integrated electron-optic focusing approach is more suitable for fabricating large-area detectors. We investigate the dependence of spatial resolution on sensor structure and operating conditions, and compare the performance of electrostatic focusing with previous technologies. Our results show a clear dependence of spatial resolution on electrostatic focusing potential, with performance approaching that of the previous design with external mesh-electrode. Further, temporal performance (lag) of the detector is evaluated and the results show that the integrated electrostatic focusing design exhibits comparable or better performance compared with the mesh-electrode design. This study represents the first technical evaluation and characterization of the SAPHIRE concept with integrated electrostatic focusing.

Note: measurement of extreme-short current pulse duration of runaway electron beam in atmospheric pressure air.

PubMed

Tarasenko, V F; Rybka, D V; Burachenko, A G; Lomaev, M I; Balzovsky, E V

2012-08-01

This note reports the time-amplitude characteristic of the supershort avalanche electron beam with up to 20 ps time resolution. For the first time it is shown that the electron beam downstream of small-diameter diaphragms in atmospheric pressure air has a complex structure which depends on the interelectrode gap width and cathode design. With a spherical cathode and collimator the minimum duration at half maximum of the supershort avalanche electron beam current pulse was shown to be ~25 ps. The minimum duration at half maximum of one peak in the pulses with two peaks can reach ~25 ps too.

On the passive probing of fiber optic quantum communication channels

DOE Office of Scientific and Technical Information (OSTI.GOV)

Korol'kov, A. V., E-mail: sergei.kulik@gmail.co; Katamadze, K. G.; Kulik, S. P.

2010-04-15

Avalanche photodetectors based on InGaAs:P are the most sensitive and only detectors operating in the telecommunication wavelength range 1.30-1.55 {mu}m in the fiber optic quantum cryptography systems that can operate in the single photon count mode. In contrast to the widely used silicon photodetectors for wavelengths up to 1 {mu}m operating in a waiting mode, these detectors always operate in a gated mode. The production of an electron-hole pair in the process of the absorption of a photon and the subsequent appearance of an avalanche of carriers can be accompanied by the inverse processes of the recombination and emission ofmore » photons. Such a backward emission can present a potential serious problem for the stability of fiber optic quantum cryptography systems against passive probing. The results of analyzing the detection of backscattered radiation are reported. The probability of such an emission has been estimated.« less

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

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ivanov, P. A., E-mail: Pavel.Ivanov@mail.ioffe.ru; Potapov, A. S.; Samsonova, T. P.

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}).

Gain properties of doped GaAs/AlGaAs multiple quantum well avalanche photodiode structures

NASA Technical Reports Server (NTRS)

Menkara, H. M.; Wagner, B. K.; Summers, C. J.

1995-01-01

A comprehensive characterization has been made of the static and dynamical response of conventional and multiple quantum well (MQW) avalanche photodiodes (APDs). Comparison of the gain characteristics at low voltages between the MQW and conventional APDs show a direct experimental confirmation of a structure-induced carrier multiplication due to interband impact ionization. Similar studies of the bias dependence of the excess noise characteristics show that the low-voltage gain is primarily due to electron ionization in the MQW-APDS, and to both electron and hole ionization in the conventional APDS. For the doped MQW APDS, the average gain per stage was calculated by comparing gain data with carrier profile measurements, and was found to vary from 1.03 at low bias to 1.09 near avalanche breakdown.

Numerical simulation of narrow bipolar electromagnetic pulses generated by thunderstorm discharges

NASA Astrophysics Data System (ADS)

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

2013-07-01

Using the concept of avalanche relativistic runaway electrons (REs), we perform numerical simulations of compact intracloud discharge (CID) as a generator of powerful natural electromagnetic pulses (EMPs) in the HF-VHF range, called narrow bipolar pulses (NBPs). For several values of the field overvoltage and altitude at which the discharge develops, the numbers of seed electrons initiating the avalanche are evaluated, with which the calculated EMP characteristics are consistent with the measured NBP parameters. We note shortcomings in the hypothesis assuming participation of cosmic ray air showers in avalanche initiation. The discharge capable of generating NBPs produces REs in numbers close to those in the source of terrestrial γ-ray flashes (TGFs), which can be an argument in favor of a unified NBP and TGF source.

Effect of electron irradiation dose on the performance of avalanche photodiode electron detectors

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kawauchi, Taizo; Wilde, Markus; Fukutani, Katsuyuki

2009-01-01

Avalanche photodiodes (APDs) are efficient detectors for electrons with energies below 100 keV. The damaging effects of 8 keV electron beam irradiation on the dark current and the output signal of the APD detector were investigated in this study. The APD dark current increases after electron doses exceeding 1.4x10{sup 13} cm{sup -2}. Preirradiation by high doses of 8 keV electrons further causes a deformation of the pulse height distribution of the APD output in the subsequent detection of low-flux electrons. This effect is particularly prominent when the energy of the detected electrons is lower than that of the damaging electrons.more » By comparing the experimental data with results of a simulation based on an electron trapping model, we conclude that the degradation of the APD performance is attributable to an enhancement of secondary-electron trapping at irradiation induced defects.« less

Predictions of Microstreamer Properties in Dielectric Barrier Discharges

NASA Astrophysics Data System (ADS)

Xu, Xudong; Kushner, Mark J.

1997-10-01

Dielectric Barrier Discharges (DBD) are being investigated for plasma remediation of toxic gases. The microstreamers in DBD's (10s - 100s μm's diameter) are terminated by dielectric charging which removes voltage from the gap. The microstreamers grow by radial diffusion into regions of high electric field and subsequent avalanche. 1-d and 2-d plasma hydrodynamics models have been developed to investigate these processes in DBDs sustained in air, nonattaching gases (Ar, N_2) and highly attaching gas mixtures (10s to 100s ppm of CCl_4). We found that microstreamers continue to radially expand as long as there is sufficient applied voltage in the absence of dielectric charging in advance of the core of the microstreamer. This observation implies that there is a finite surface conductivity which allows radial flow of current and subsequent charging of the dielectric. Predictions for microstreamer radii using this process agree well with experiments.(J. Coogan, Trans. Plasma Sci. 24, 91 (1996)) We also found that in electronegative gases, voltage collapes in the core of the streamer results in cooling and rapid attachment of electrons, creating a core which is largely converted to a negative ion-positive ion plasma, surrounded by an avalanching shell of hot electrons.

Microgap flat panel display

DOEpatents

Wuest, C.R.

1998-12-08

A microgap flat panel display is disclosed which includes a thin gas-filled display tube that utilizes switched X-Y ``pixel`` strips to trigger electron avalanches and activate a phosphor at a given location on a display screen. The panel utilizes the principal of electron multiplication in a gas subjected to a high electric field to provide sufficient electron current to activate standard luminescent phosphors located on an anode. The X-Y conductive strips of a few micron widths may for example, be deposited on opposite sides of a thin insulating substrate, or on one side of the adjacent substrates and function as a cathode. The X-Y strips are separated from the anode by a gap filled with a suitable gas. Electrical bias is selectively switched onto X and Y strips to activate a ``pixel`` in the region where these strips overlap. A small amount of a long-lived radioisotope is used to initiate an electron avalanche in the overlap region when bias is applied. The avalanche travels through the gas filled gap and activates a luminescent phosphor of a selected color. The bias is adjusted to give a proportional electron multiplication to control brightness for given pixel. 6 figs.

HgCdTe avalanche photodiodes: A review

NASA Astrophysics Data System (ADS)

Singh, Anand; Srivastav, Vanya; Pal, Ravinder

2011-10-01

This paper presents a comprehensive review of fundamental issues, device architectures, technology development and applications of HgCdTe based avalanche photodiodes (APD). High gain, above 5×10 3, a low excess noise factor close to unity, THz gain-bandwidth product, and fast response in the range of pico-seconds has been achieved by electron-initiated avalanche multiplication for SWIR, MWIR, and LWIR detector applications involving low optical signals. Detector arrays with good element-to-element uniformity have been fabricated paving the way for fabrication of HgCdTe-APD FPAs.

Ultralow-noise readout circuit with an avalanche photodiode: toward a photon-number-resolving detector.

PubMed

Tsujino, Kenji; Akiba, Makoto; Sasaki, Masahide

2007-03-01

The charge-integration readout circuit was fabricated to achieve an ultralow-noise preamplifier for photoelectrons generated in an avalanche photodiode with linear mode operation at 77 K. To reduce the various kinds of noise, the capacitive transimpedance amplifier was used and consisted of low-capacitance circuit elements that were cooled with liquid nitrogen. As a result, the readout noise is equal to 3.0 electrons averaged for a period of 40 ms. We discuss the requirements for avalanche photodiodes to achieve photon-number-resolving detectors below this noise level.

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

DOE Office of Scientific and Technical Information (OSTI.GOV)

Pokol, G. I.; Kómár, A.; Budai, A.

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 amore » possible experimental detection method for such an interaction.« less

3D PIC-MCC simulations of positive streamers in air gaps

NASA Astrophysics Data System (ADS)

Jiang, M.; Li, Y.; Wang, H.; Liu, C.

2017-10-01

Simulation of positive streamer evolution is important for understanding the microscopic physical process in discharges. Simulations described in this paper are done using a 3D Particle-In-Cell, Monte-Carlo-Collision code with photoionization. Three phases of a positive streamer evolution, identified as initiation, propagation, and branching are studied during simulations. A homogeneous electric field is applied between parallel-flat electrodes forming a millimeter air gap to make simulations and analysis more simple and general. Free electrons created by the photoionization process determine initiation, propagation, and branching of the streamers. Electron avalanches form a positive streamer tip, when the space charge of ions at the positive tip dominates the local electric field. The propagation of the positive tip toward a cathode is the result of combinations of the positive tip and secondary avalanches ahead of it. A curved feather-like channel is formed without obvious branches when the electric field between electrodes is 50 kV/cm. However, a channel is formed with obvious branches when the electric field increases up to 60 kV/cm. In contrast to the branches around a sharp needle electrode, branches near the flat anode are formed at a certain distance away from it. Simulated parameters of the streamer such as diameter, maximum electric field, propagation velocity, and electron density at the streamer tip are in a good agreement with those published earlier.

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

DOE Office of Scientific and Technical Information (OSTI.GOV)

Tarasenko, V. F., E-mail: vft@loi.hcei.tsc.ru; Baksht, E. Kh.; Beloplotov, D. V.

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.

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

NASA Astrophysics Data System (ADS)

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.

Mechanism and computational model for Lyman-α-radiation generation by high-intensity-laser four-wave mixing in Kr-Ar gas

NASA Astrophysics Data System (ADS)

Louchev, Oleg A.; Bakule, Pavel; Saito, Norihito; Wada, Satoshi; Yokoyama, Koji; Ishida, Katsuhiko; Iwasaki, Masahiko

2011-09-01

We present a theoretical model combined with a computational study of a laser four-wave mixing process under optical discharge in which the non-steady-state four-wave amplitude equations are integrated with the kinetic equations of initial optical discharge and electron avalanche ionization in Kr-Ar gas. The model is validated by earlier experimental data showing strong inhibition of the generation of pulsed, tunable Lyman-α (Ly-α) radiation when using sum-difference frequency mixing of 212.6 nm and tunable infrared radiation (820-850 nm). The rigorous computational approach to the problem reveals the possibility and mechanism of strong auto-oscillations in sum-difference resonant Ly-α generation due to the combined effect of (i) 212.6-nm (2+1)-photon ionization producing initial electrons, followed by (ii) the electron avalanche dominated by 843-nm radiation, and (iii) the final breakdown of the phase matching condition. The model shows that the final efficiency of Ly-α radiation generation can achieve a value of ˜5×10-4 which is restricted by the total combined absorption of the fundamental and generated radiation.

Dynamics of avalanche-generated impulse waves: three-dimensional hydrodynamic simulations and sensitivity analysis

NASA Astrophysics Data System (ADS)

Chisolm, Rachel E.; McKinney, Daene C.

2018-05-01

This paper studies the lake dynamics for avalanche-triggered glacial lake outburst floods (GLOFs) in the Cordillera Blanca mountain range in Ancash, Peru. As new glacial lakes emerge and existing lakes continue to grow, they pose an increasing threat of GLOFs that can be catastrophic to the communities living downstream. In this work, the dynamics of displacement waves produced from avalanches are studied through three-dimensional hydrodynamic simulations of Lake Palcacocha, Peru, with an emphasis on the sensitivity of the lake model to input parameters and boundary conditions. This type of avalanche-generated wave is an important link in the GLOF process chain because there is a high potential for overtopping and erosion of the lake-damming moraine. The lake model was evaluated for sensitivity to turbulence model and grid resolution, and the uncertainty due to these model parameters is significantly less than that due to avalanche boundary condition characteristics. Wave generation from avalanche impact was simulated using two different boundary condition methods. Representation of an avalanche as water flowing into the lake generally resulted in higher peak flows and overtopping volumes than simulating the avalanche impact as mass-momentum inflow at the lake boundary. Three different scenarios of avalanche size were simulated for the current lake conditions, and all resulted in significant overtopping of the lake-damming moraine. Although the lake model introduces significant uncertainty, the avalanche portion of the GLOF process chain is likely to be the greatest source of uncertainty. To aid in evaluation of hazard mitigation alternatives, two scenarios of lake lowering were investigated. While large avalanches produced significant overtopping waves for all lake-lowering scenarios, simulations suggest that it may be possible to contain waves generated from smaller avalanches if the surface of the lake is lowered.

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

DOE Office of Scientific and Technical Information (OSTI.GOV)

Babich, L. P., E-mail: babich@elph.vniief.ru; Bochkov, E. I.; Kutsyk, I. M.

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.

Characterizing wet slab and glide slab avalanche occurrence along the Going-to-the-Sun Road, Glacier National Park, Montana, USA

USGS Publications Warehouse

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

2010-01-01

Wet slab and glide slab snow avalanches are dangerous and yet can be particularly difficult to predict. Both wet slab and glide slab avalanches are thought to depend upon free water moving through the snowpack but are driven by different processes. In Glacier National Park, Montana, both types of avalanches can occur in the same year and affect the Going-to-the-Sun Road (GTSR). Both wet slab and glide slab avalanches along the GTSR from 2003-2010 are investigated. Meteorological data from two high-elevation weather stations and one SNOTEL site are used in conjunction with an avalanche database and snowpit profiles. These data were used to characterize years when only glide slab avalanches occurred and those years when both glide slab and wet slab avalanches occurred. Results of 168 glide slab and 57 wet slab avalanches along the GTSR suggest both types of avalanche occurrence depend on sustained warming periods with intense solar radiation (or rain on snow) to produce free water in the snowpack. Differences in temperature and net radiation metrics between wet slab and glide slab avalanches emerge as one moves from one day to seven days prior to avalanche occurrence. On average, a more rapid warming precedes wet slab avalanche occurrence. Glide slab and wet slab avalanches require a similar amount of net radiation. Wet slab avalanches do not occur every year, while glide slab avalanches occur annually. These results aim to enhance understanding of the required meteorological conditions for wet slab and glide slab avalanches and aid in improved wet snow avalanche forecasting.

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

NASA Astrophysics Data System (ADS)

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.

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

NASA Astrophysics Data System (ADS)

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.

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

NASA Astrophysics Data System (ADS)

Bründl, M.; Etter, H.-J.; Steiniger, M.; Klingler, Ch.; Rhyner, J.; Ammann, W. J.

2004-04-01

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.

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

NASA Astrophysics Data System (ADS)

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 was 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 sub eff measurements of the plasma. The signal processing was analyzed using a theoretical model to aid the system design and establish the procedure for data error analysis.

Silicon avalanche photodiode detector circuit for Nd:YAG laser scattering

NASA Astrophysics Data System (ADS)

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

1990-10-01

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 Zeff 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.

Avalanche risk assessment - a multi-temporal approach, results from Galtür, Austria

NASA Astrophysics Data System (ADS)

Keiler, M.; Sailer, R.; Jörg, P.; Weber, C.; Fuchs, S.; Zischg, A.; Sauermoser, S.

2006-07-01

Snow avalanches pose a threat to settlements and infrastructure in alpine environments. Due to the catastrophic events in recent years, the public is more aware of this phenomenon. Alpine settlements have always been confronted with natural hazards, but changes in land use and in dealing with avalanche hazards lead to an altering perception of this threat. In this study, a multi-temporal risk assessment is presented for three avalanche tracks in the municipality of Galtür, Austria. Changes in avalanche risk as well as changes in the risk-influencing factors (process behaviour, values at risk (buildings) and vulnerability) between 1950 and 2000 are quantified. An additional focus is put on the interconnection between these factors and their influence on the resulting risk. The avalanche processes were calculated using different simulation models (SAMOS as well as ELBA+). For each avalanche track, different scenarios were calculated according to the development of mitigation measures. The focus of the study was on a multi-temporal risk assessment; consequently the used models could be replaced with other snow avalanche models providing the same functionalities. The monetary values of buildings were estimated using the volume of the buildings and average prices per cubic meter. The changing size of the buildings over time was inferred from construction plans. The vulnerability of the buildings is understood as a degree of loss to a given element within the area affected by natural hazards. A vulnerability function for different construction types of buildings that depends on avalanche pressure was used to assess the degree of loss. No general risk trend could be determined for the studied avalanche tracks. Due to the high complexity of the variations in risk, small changes of one of several influencing factors can cause considerable differences in the resulting risk. This multi-temporal approach leads to better understanding of the today's risk by identifying the main changes and the underlying processes. Furthermore, this knowledge can be implemented in strategies for sustainable development in Alpine settlements.

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

NASA Astrophysics Data System (ADS)

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, which is consistent with the incremental development of snow-avalanche impact craters through the Holocene.

Infrasound and seismic array analysis of snow avalanches: results from the 2015-2017 experiment in Dischma valley above Davos, Switzerland

NASA Astrophysics Data System (ADS)

Marchetti, Emanuele; van Herwijnen, Alec; Ripepe, Maurizio

2017-04-01

While flowing downhill a snow avalanche radiates seismic and infrasonic waves being coupled both with the ground and the atmosphere. Infrasound waves are mostly generated by the powder cloud of the avalanche, while seismic waves are mostly generated by the dense flowing snow mass on the ground, resulting in different energy partitioning between seismic and infrasound for different kinds of avalanches. This results into a general uncertainty on the efficiency of seismic and infrasound monitoring, in terms of the size and source-to-receiver distance of detectable events. Nevertheless, both seismic and infrasound have been used as monitoring systems for the remote detection of snow avalanches, being the reliable detection of snow avalanches of crucial importance to better understand triggering mechanisms, identify possible precursors, or improve avalanche forecasting. We present infrasonic and seismic array data collected during the winters of 2015- 2016 and 2016-2017 in the Dischma valley above Davos, Switzerland, where a five element infrasound array and a 7 element seismic array had been deployed at short distance from each other and with several avalanche paths nearby. Avalanche observation in the area is performed through automatic cameras providing additional information on the location, type (dry or wet), size and occurrence time of the avalanches released. The use of arrays instead of single sensors allows increasing the signal-to-noise ratio and identifying events in terms of back-azimuth and apparent velocity of the wave-field, thus providing indication on the source position of the recorded signal. For selected snow avalanches captured with automatic cameras, we therefore perform seismic and infrasound array processing to constrain the avalanche path and dynamics and investigate the partitioning of seismic and infrasound energy for the different portions of the avalanche path. Moreover we compare results of seismic and infrasound array processing for the whole 2015-2016 winter season in order to investigate the ability of the two monitoring systems to identify and characterize snow avalanches and the benefit of the combined seismo-acoustic analysis.

Cosmic Rays in Thunderstorms

NASA Astrophysics Data System (ADS)

Buitink, Stijn; Scholten, Olaf; van den Berg, Ad; Ebert, Ute

2013-04-01

Cosmic Rays in Thunderstorms Cosmic rays are protons and heavier nuclei that constantly bombard the Earth's atmosphere with energies spanning a vast range from 109 to 1021 eV. At typical altitudes up to 10-20 km they initiate large particle cascades, called extensive air showers, that contain millions to billions of secondary particles depending on their initial energy. These particles include electrons, positrons, hadrons and muons, and are concentrated in a compact particle front that propagates at relativistic speed. In addition, the shower leaves behind a trail of lower energy electrons from ionization of air molecules. Under thunderstorm conditions these electrons contribute to the electrical and ionization processes in the cloud. When the local electric field is strong enough the secondary electrons can create relativistic electron run-away avalanches [1] or even non-relativistic avalanches. Cosmic rays could even trigger lightning inception. Conversely, strong electric fields also influence the development of the air shower [2]. Extensive air showers emit a short (tens of nanoseconds) radio pulse due to deflection of the shower particles in the Earth's magnetic field [3]. Antenna arrays, such as AERA, LOFAR and LOPES detect these pulses in a frequency window of roughly 10-100 MHz. These systems are also sensitive to the radiation from discharges associated to thunderstorms, and provide a means to study the interaction of cosmic ray air showers and the electrical processes in thunderstorms [4]. In this presentation we discuss the involved radiation mechanisms and present analyses of thunderstorm data from air shower arrays [1] A. Gurevich et al., Phys. Lett. A 165, 463 (1992) [2] S. Buitink et al., Astropart. Phys. 33, 1 (2010) [3] H. Falcke et al., Nature 435, 313 (2005) [4] S. Buitink et al., Astron. & Astrophys. 467, 385 (2007)

Automatic detection of snow avalanches in continuous seismic data using hidden Markov models

NASA Astrophysics Data System (ADS)

Heck, Matthias; Hammer, Conny; van Herwijnen, Alec; Schweizer, Jürg; Fäh, Donat

2018-01-01

Snow avalanches generate seismic signals as many other mass movements. Detection of avalanches by seismic monitoring is highly relevant to assess avalanche danger. In contrast to other seismic events, signals generated by avalanches do not have a characteristic first arrival nor is it possible to detect different wave phases. In addition, the moving source character of avalanches increases the intricacy of the signals. Although it is possible to visually detect seismic signals produced by avalanches, reliable automatic detection methods for all types of avalanches do not exist yet. We therefore evaluate whether hidden Markov models (HMMs) are suitable for the automatic detection of avalanches in continuous seismic data. We analyzed data recorded during the winter season 2010 by a seismic array deployed in an avalanche starting zone above Davos, Switzerland. We re-evaluated a reference catalogue containing 385 events by grouping the events in seven probability classes. Since most of the data consist of noise, we first applied a simple amplitude threshold to reduce the amount of data. As first classification results were unsatisfying, we analyzed the temporal behavior of the seismic signals for the whole data set and found that there is a high variability in the seismic signals. We therefore applied further post-processing steps to reduce the number of false alarms by defining a minimal duration for the detected event, implementing a voting-based approach and analyzing the coherence of the detected events. We obtained the best classification results for events detected by at least five sensors and with a minimal duration of 12 s. These processing steps allowed identifying two periods of high avalanche activity, suggesting that HMMs are suitable for the automatic detection of avalanches in seismic data. However, our results also showed that more sensitive sensors and more appropriate sensor locations are needed to improve the signal-to-noise ratio of the signals and therefore the classification.

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

NASA Astrophysics Data System (ADS)

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

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.

Simulations of electron avalanches in an ultra-low-background proportional counter

DOE Office of Scientific and Technical Information (OSTI.GOV)

Robinson, John W.; Aalseth, Craig; Dion, Michael P.

2016-02-01

New classes have been added to the simulation package Garfield++ to import the potential and electric field solutions generated by ANSYS R MaxwellTM v.16. Using these tools we report results on the simulation of electron avalanches and induced signal waveforms in comparison to experimental data of the ultra-lowbackground gas proportional counters being developed at Pacific Northwest National Laboratory. Furthermore, an improved mesh search algorithm based on Delaunay triangulation was implemented and provided at least a three order of magnitude time savings when compared to the built-in point-location search class of Garfield++.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Diepold, Marc, E-mail: marc.diepold@mpq.mpg.de; Franke, Beatrice; Götzfried, Johannes

Avalanche photodiodes are commonly used as detectors for low energy x-rays. In this work, we report on a fitting technique used to account for different detector responses resulting from photoabsorption in the various avalanche photodiode layers. The use of this technique results in an improvement of the energy resolution at 8.2 keV by up to a factor of 2 and corrects the timing information by up to 25 ns to account for space dependent electron drift time. In addition, this waveform analysis is used for particle identification, e.g., to distinguish between x-rays and MeV electrons in our experiment.

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

NASA Astrophysics Data System (ADS)

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.

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

NASA Astrophysics Data System (ADS)

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.

Modification of the Steel Surface Treated by a Volume Discharge Plasma in Nitrogen at Atmospheric Pressure

NASA Astrophysics Data System (ADS)

Erofeev, M. V.; Shulepov, M. A.; Ivanov, Yu. F.; Oskomov, K. V.; Tarasenko, V. F.

2016-03-01

Effect of volume discharge plasma initiated by an avalanche electron beam on the composition, structure, and properties of the surface steel layer is investigated. Voltage pulses with incident wave amplitude up to 30 kV, full width at half maximum of about 4 ns, and wave front of about 2.5 ns were applied to the gap with an inhomogeneous electric field. Changes indicating the hardening effect of the volume discharge initiated by an avalanche electron beam are revealed in St3-grade steel specimens treated by the discharge of this type.

Fluorescence excited in a thunderstorm atmosphere by relativistic runaway electron avalanches

NASA Astrophysics Data System (ADS)

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.

Low dose digital X-ray imaging with avalanche amorphous selenium

NASA Astrophysics Data System (ADS)

Scheuermann, James R.; Goldan, Amir H.; Tousignant, Olivier; Léveillé, Sébastien; Zhao, Wei

2015-03-01

Active Matrix Flat Panel Imagers (AMFPI) based on an array of thin film transistors (TFT) have become the dominant technology for digital x-ray imaging. In low dose applications, the performance of both direct and indirect conversion detectors are limited by the electronic noise associated with the TFT array. New concepts of direct and indirect detectors have been proposed using avalanche amorphous selenium (a-Se), referred to as high gain avalanche rushing photoconductor (HARP). The indirect detector utilizes a planar layer of HARP to detect light from an x-ray scintillator and amplify the photogenerated charge. The direct detector utilizes separate interaction (non-avalanche) and amplification (avalanche) regions within the a-Se to achieve depth-independent signal gain. Both detectors require the development of large area, solid state HARP. We have previously reported the first avalanche gain in a-Se with deposition techniques scalable to large area detectors. The goal of the present work is to demonstrate the feasibility of large area HARP fabrication in an a-Se deposition facility established for commercial large area AMFPI. We also examine the effect of alternative pixel electrode materials on avalanche gain. The results show that avalanche gain > 50 is achievable in the HARP layers developed in large area coaters, which is sufficient to achieve x-ray quantum noise limited performance down to a single x-ray photon per pixel. Both chromium (Cr) and indium tin oxide (ITO) have been successfully tested as pixel electrodes.

Single photon detection with self-quenching multiplication

NASA Technical Reports Server (NTRS)

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

2011-01-01

A photoelectronic device and an avalanche self-quenching process for a photoelectronic device are described. The photoelectronic device comprises a nanoscale semiconductor multiplication region and a nanoscale doped semiconductor quenching structure including a depletion region and an undepletion region. The photoelectronic device can act as a single photon detector or a single carrier multiplier. The avalanche self-quenching process allows electrical field reduction in the multiplication region by movement of the multiplication carriers, thus quenching the avalanche.

Backcountry snowmobilers' risk perceptions, avalanche related information seeking behaviours, preparedness and decision-making processes

NASA Astrophysics Data System (ADS)

Baker, Jennifer

Although there has been substantial research on the avoidance of risk, much less has been completed on voluntary risk. This study examined backcountry snowmobilers' risk perceptions, avalanche related information seeking behaviours, and decision-making processes when dealing with avalanches and backcountry risk in Canada. To accomplish this, in-depth, semi-structured interviews were conducted with 17 participants who were involved in backcountry snowmobiling. Interviews were done both in person and by telephone. The results of this study show that, unlike previous research on snowmobilers, the participants of this study were well prepared and knowledgeable about backcountry risks. All 17 participants stated that they carried a shovel, probe, and transceiver with them on each backcountry trip, and 10 participants had taken an avalanche safety course. Group dynamics and positive peer pressure were influential in promoting safe backcountry behaviour. KEYWORDS: Backcountry snowmobiling, Avalanches, Voluntary Risk, Preparedness, Decision-Making.

The relativistic feedback discharge model of terrestrial gamma ray flashes

NASA Astrophysics Data System (ADS)

Dwyer, Joseph R.

2012-02-01

As thunderclouds charge, the large-scale fields may approach the relativistic feedback threshold, above which the production of relativistic runaway electron avalanches becomes self-sustaining through the generation of backward propagating runaway positrons and backscattered X-rays. Positive intracloud (IC) lightning may force the large-scale electric fields inside thunderclouds above the relativistic feedback threshold, causing the number of runaway electrons, and the resulting X-ray and gamma ray emission, to grow exponentially, producing very large fluxes of energetic radiation. As the flux of runaway electrons increases, ionization eventually causes the electric field to discharge, bringing the field below the relativistic feedback threshold again and reducing the flux of runaway electrons. These processes are investigated with a new model that includes the production, propagation, diffusion, and avalanche multiplication of runaway electrons; the production and propagation of X-rays and gamma rays; and the production, propagation, and annihilation of runaway positrons. In this model, referred to as the relativistic feedback discharge model, the large-scale electric fields are calculated self-consistently from the charge motion of the drifting low-energy electrons and ions, produced from the ionization of air by the runaway electrons, including two- and three-body attachment and recombination. Simulation results show that when relativistic feedback is considered, bright gamma ray flashes are a natural consequence of upward +IC lightning propagating in large-scale thundercloud fields. Furthermore, these flashes have the same time structures, including both single and multiple pulses, intensities, angular distributions, current moments, and energy spectra as terrestrial gamma ray flashes, and produce large current moments that should be observable in radio waves.

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

NASA Astrophysics Data System (ADS)

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.

Trapping effects in irradiated and avalanche-injected MOS capacitors

NASA Technical Reports Server (NTRS)

Bakowski, M.; Cockrum, R. H.; Zamani, N.; Maserjian, J.; Viswanathan, C. R.

1978-01-01

The trapping parameters for holes, and for electrons in the presence of trapped holes, have been measured from a set of wafers with different oxide thickness processed under controlled conditions. The trap cross-sections and densities indicate at least three trap species, including an interfacial species, a dominant bulk species which is determined to tail off from the silicon interface, and a third, lower density bulk species that is distributed throughout the oxide.

Supression of laser breakdown by pulsed nonequilibrium ns discharge

NASA Astrophysics Data System (ADS)

Starikovskiy, A. Y.; Semenov, I. E.; Shneider, M. N.

2016-10-01

The avalanche ionization induced by infrared laser pulses was investigated in a pre-ionized argon gas. Pre-ionization was created by a high-voltage pulsed nanosecond discharge developed in the form of a fast ionization wave. Then, behind the front of ionization wave additional avalanche ionization was initiated by the focused Nd-YAG laser pulse. It was shown that the gas pre-ionization inhibits the laser spark generation. It was demonstrated that the suppression of laser spark development in the case of strong gas pre-ionization is because of fast electron energy transfer from the laser beam focal region. The main mechanism of this energy transfer is free electrons diffusion.

Catastrophic global-avalanche of a hollow pressure filament

NASA Astrophysics Data System (ADS)

van Compernolle, B.; Poulos, M. J.; Morales, G. J.

2017-10-01

New results are presented of a basic heat transport experiment performed in the Large Plasma Device at UCLA. A ring-shaped electron beam source injects low energy electrons along a strong magnetic field into a preexisting, large and cold plasma. The injected electrons are thermalized by Coulomb collisions within a short distance and provide an off-axis heat source that results in a long, hollow, cylindrical region of elevated plasma pressure. The off-axis source is active for a period long compared to the density decay time, i.e., as time progresses the power per particle increases. Two distinct regimes are observed to take place, an early regime dominated by multiple avalanches, identified as a sudden intermittent rearrangement of the pressure profile that repeats under sustained heating, and a second regime dominated by broadband drift-Alfvén fluctuations. The transition between the two regimes is sudden and global, both radially and axially. The initial regime is characterized by peaked density and temperature profiles, while only the peaked temperature profile survives in the second regime. Recent measurements at multiple axial locations provide new insight into the axial dynamics of the global avalanche. Sponsored by NSF Grant 1619505 and by DOE/NSF at BaPSF.

Progress in low light-level InAs detectors- towards Geiger-mode detection

NASA Astrophysics Data System (ADS)

Tan, Chee Hing; Ng, Jo Shien; Zhou, Xinxin; David, John; Zhang, Shiyong; Krysa, Andrey

2017-05-01

InAs avalanche photodiodes (APDs) can be designed such that only electrons are allowed to initiate impact ionization, leading to the lowest possible excess noise factor. Optimization of wet chemical etching and surface passivation produced mesa APDs with bulk dominated dark current and responsivity that are comparable and higher, respectively, than a commercial InAs detector. Our InAs electron-APDs also show high stability with fluctuation of 0.1% when operated at a gain of 11.2 over 60 s. These InAs APDs can detect very weak signal down to 35 photons per pulse. Fabrication of planar InAs by Be implantation produced planar APDs with bulk dominated dark current. Annealing at 550 °C was necessary to remove implantation damage and to activate Be dopants. Due to minimal diffusion of Be, thick depletion of 8 μm was achieved. Since the avalanche gain increases exponentially with the thickness of avalanche region, our planar APD achieved high gain > 300 at 200 K. Our work suggest that both mesa and planar InAs APDs can exhibit high gain. When combined with a suitable preamplifier, single photon detection using InAs electron-APDs could be achieved.

Dopant-induced ignition of helium nanoplasmas—a mechanistic study

NASA Astrophysics Data System (ADS)

Heidenreich, Andreas; Schomas, Dominik; Mudrich, Marcel

2017-12-01

Helium (He) nanodroplets irradiated by intense near-infrared laser pulses form a nanoplasma by avalanche-like electron impact ionizations (EIIs) even at lower laser intensities where He is not directly field ionized, provided that the droplets contain a few dopant atoms which provide seed electrons for the EII avalanche. In this theoretical paper on calcium and xenon doped He droplets we elucidate the mechanism which induces ionization avalanches, termed ignition. We find that the partial loss of seed electrons from the activated droplets starkly assists ignition, as the Coulomb barrier for ionization of helium is lowered by the electric field of the dopant cations, and this deshielding of the cation charges enhances their electric field. In addition, the dopant ions assist the acceleration of the seed electrons (slingshot effect) by the laser field, supporting EIIs of He and also causing electron loss by catapulting electrons away. The dopants’ ability to lower the Coulomb barriers at He as well as the slingshot effect decrease with the spatial expansion of the dopant, causing a dependence of the dopants’ ignition capability on the dopant mass. Here, we develop criteria (impact count functions) to assess the ignition capability of dopants, based on (i) the spatial overlap of the seed electron cloud with the He atoms and (ii) the overlap of their kinetic energy distribution with the distribution of Coulomb barrier heights at He. The relatively long time delays between the instants of dopant ionization and ignition (incubation times) for calcium doped droplets are determined to a large extent by the time it takes to deshield the dopant ions.

Enhanced low-noise gain from InAs avalanche photodiodes with reduced dark current and background doping

NASA Astrophysics Data System (ADS)

Maddox, S. J.; Sun, W.; Lu, Z.; Nair, H. P.; Campbell, J. C.; Bank, S. R.

2012-10-01

We reduced the room temperature dark current in an InAs avalanche photodiode by increasing the p-type contact doping, resulting in an increased energetic barrier to minority electron injection into the p-region, which is a significant source of dark current at room temperature. In addition, by improving the molecular beam epitaxy growth conditions, we reduced the background doping concentration and realized depletion widths as wide as 5 μm at reverse biases as low as 1.5 V. These improvements culminated in low-noise InAs avalanche photodiodes exhibiting a room temperature multiplication gain of ˜80, at a record low reverse bias of 12 V.

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

NASA Astrophysics Data System (ADS)

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.

Flexible ultrathin-body single-photon avalanche diode sensors and CMOS integration.

PubMed

Sun, Pengfei; Ishihara, Ryoichi; Charbon, Edoardo

2016-02-22

We proposed the world's first flexible ultrathin-body single-photon avalanche diode (SPAD) as photon counting device providing a suitable solution to advanced implantable bio-compatible chronic medical monitoring, diagnostics and other applications. In this paper, we investigate the Geiger-mode performance of this flexible ultrathin-body SPAD comprehensively and we extend this work to the first flexible SPAD image sensor with in-pixel and off-pixel electronics integrated in CMOS. Experimental results show that dark count rate (DCR) by band-to-band tunneling can be reduced by optimizing multiplication doping. DCR by trap-assisted avalanche, which is believed to be originated from the trench etching process, could be further reduced, resulting in a DCR density of tens to hundreds of Hertz per micrometer square at cryogenic temperature. The influence of the trench etching process onto DCR is also proved by comparison with planar ultrathin-body SPAD structures without trench. Photon detection probability (PDP) can be achieved by wider depletion and drift regions and by carefully optimizing body thickness. PDP in frontside- (FSI) and backside-illumination (BSI) are comparable, thus making this technology suitable for both modes of illumination. Afterpulsing and crosstalk are negligible at 2µs dead time, while it has been proved, for the first time, that a CMOS SPAD pixel of this kind could work in a cryogenic environment. By appropriate choice of substrate, this technology is amenable to implantation for biocompatible photon-counting applications and wherever bended imaging sensors are essential.

SPAD electronics for high-speed quantum communications

NASA Astrophysics Data System (ADS)

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.

Crackling to periodic transition in a granular stick-slip experiment

NASA Astrophysics Data System (ADS)

Abed Zadeh, Aghil; BaréS, Jonathan; Behringer, Robert

We perform a stick-slip experiment to characterize avalanches in time and space for granular materials. In our experiment, a constant speed stage pulls a slider which rests on a vertical bed of circular photo-elastic particles in a 2D system. The stage is connected to the slider by a spring. We measure the force on the spring by a force sensor attached to the spring. We study the avalanche size statistics, and other seismicity laws of slip avalanches. Using the power spectrum of the force signal and avalanche statistics, we analyze the effect of the loading speed and of the spring stiffness and we capture a transition from crackling to periodic regime by changing these parameters. From a more local point of view and by using a high speed camera and the photo-elastic properties of our particles, we characterize the local stress change and flow of particles during slip avalanches. By image processing, we detect the local avalanches as connected components in space and time, and we study the avalanche size probability density functions (PDF). The PDF of avalanches obey power laws both at global and local scales, but with different exponents. We try to understand the correlation of local avalanches in space and the way they coarse grain to the global avalanches. NSF Grant DMR-1206351, NASA Grant NNX15AD38G, and the William M. Keck Foundation.

NASA's Potential Contributions to Avalanche Forecasting Using Active and Passive Microwave Measurements

NASA Technical Reports Server (NTRS)

Blonski, Slawomir

2007-01-01

This Candidate Solution is based on using active and passive microwave measurements acquired from NASA satellites to improve USDA (U.S. Department of Agriculture) Forest Service forecasting of avalanche danger. Regional Avalanche Centers prepare avalanche forecasts using ground measurements of snowpack and mountain weather conditions. In this Solution, range of the in situ observations is extended by adding remote sensing measurements of snow depth, snow water equivalent, and snowfall rate acquired by satellite missions that include Aqua, CloudSat, future GPM (Global Precipitation Measurement), and the proposed SCLP (Snow and Cold Land Processes). Measurements of snowpack conditions and time evolution are improved by combining the in situ and satellite observations with a snow model. Recurring snow observations from NASA satellites increase accuracy of avalanche forecasting, which helps the public and the managers of public facilities make better avalanche safety decisions.

Avalanche Statistics Identify Intrinsic Stellar Processes near Criticality in KIC 8462852

NASA Astrophysics Data System (ADS)

Sheikh, Mohammed A.; Weaver, Richard L.; Dahmen, Karin A.

2016-12-01

The star KIC8462852 (Tabby's star) has shown anomalous drops in light flux. We perform a statistical analysis of the more numerous smaller dimming events by using methods found useful for avalanches in ferromagnetism and plastic flow. Scaling exponents for avalanche statistics and temporal profiles of the flux during the dimming events are close to mean field predictions. Scaling collapses suggest that this star may be near a nonequilibrium critical point. The large events are interpreted as avalanches marked by modified dynamics, limited by the system size, and not within the scaling regime.

WE-E-18A-01: Large Area Avalanche Amorphous Selenium Sensors for Low Dose X-Ray Imaging

DOE Office of Scientific and Technical Information (OSTI.GOV)

Scheuermann, J; Goldan, A; Zhao, W

2014-06-15

Purpose: A large area indirect flat panel imager (FPI) with avalanche gain is being developed to achieve x-ray quantum noise limited low dose imaging. It uses a thin optical sensing layer of amorphous selenium (a-Se), known as High-Gain Avalanche Rushing Photoconductor (HARP), to detect optical photons generated from a high resolution x-ray scintillator. We will report initial results in the fabrication of a solid-state HARP structure suitable for a large area FPI. Our objective is to establish the blocking layer structures and defect suppression mechanisms that provide stable and uniform avalanche gain. Methods: Samples were fabricated as follows: (1) ITOmore » signal electrode. (2) Electron blocking layer. (3) A 15 micron layer of intrinsic a-Se. (4) Transparent hole blocking layer. (5) Multiple semitransparent bias electrodes to investigate avalanche gain uniformity over a large area. The sample was exposed to 50ps optical excitation pulses through the bias electrode. Transient time of flight (TOF) and integrated charge was measured. A charge transport simulation was developed to investigate the effects of varying blocking layer charge carrier mobility on defect suppression, avalanche gain and temporal performance. Results: Avalanche gain of ∼200 was achieved experimentally with our multi-layer HARP samples. Simulations using the experimental sensor structure produced the same magnitude of gain as a function of electric field. The simulation predicted that the high dark current at a point defect can be reduced by two orders of magnitude by blocking layer optimization which can prevent irreversible damage while normal operation remained unaffected. Conclusion: We presented the first solid state HARP structure directly scalable to a large area FPI. We have shown reproducible and uniform avalanche gain of 200. By reducing mobility of the blocking layers we can suppress defects and maintain stable avalanche. Future work will optimize the blocking layers to prevent lag and ghosting.« less

Recent progress in high gain InAs avalanche photodiodes (Presentation Recording)

NASA Astrophysics Data System (ADS)

Bank, Seth; Maddox, Scott J.; Sun, Wenlu; Nair, Hari P.; Campbell, Joe C.

2015-08-01

InAs possesses nearly ideal material properties for the fabrication of near- and mid-infrared avalanche photodiodes (APDs), which result in strong electron-initiated impact ionization and negligible hole-initiated impact ionization [1]. Consequently, InAs multiplication regions exhibit several appealing characteristics, including extremely low excess noise factors and bandwidth independent of gain [2], [3]. These properties make InAs APDs attractive for a number of near- and mid-infrared sensing applications including remote gas sensing, light detection and ranging (LIDAR), and both active and passive imaging. Here, we discuss our recent advances in the growth and fabrication of high gain, low noise InAs APDs. Devices yielded room temperature multiplication gains >300, with much reduced (~10x) lower dark current densities. We will also discuss a likely key contributor to our current performance limitations: silicon diffusion into the intrinsic (multiplication) region from the underlying n-type layer during growth. Future work will focus on increasing the intrinsic region thickness, targeting gains >1000. This work was supported by the Army Research Office (W911NF-10-1-0391). [1] A. R. J. Marshall, C. H. Tan, M. J. Steer, and J. P. R. David, "Electron dominated impact ionization and avalanche gain characteristics in InAs photodiodes," Applied Physics Letters, vol. 93, p. 111107, 2008. [2] A. R. J. Marshall, A. Krysa, S. Zhang, A. S. Idris, S. Xie, J. P. R. David, and C. H. Tan, "High gain InAs avalanche photodiodes," in 6th EMRS DTC Technical Conference, Edinburgh, Scotland, UK, 2009. [3] S. J. Maddox, W. Sun, Z. Lu, H. P. Nair, J. C. Campbell, and S. R. Bank, "Enhanced low-noise gain from InAs avalanche photodiodes with reduced dark current and background doping," Applied Physics Letters, vol. 101, no. 15, pp. 151124-151124-3, Oct. 2012.

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

USGS Publications Warehouse

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.

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

NASA Astrophysics Data System (ADS)

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.

Observation and discussion of avalanche electroluminescence in GaN p-n diodes offering a breakdown electric field of 3 MV cm‑1

NASA Astrophysics Data System (ADS)

Mandal, S.; Kanathila, M. B.; Pynn, C. D.; Li, W.; Gao, J.; Margalith, T.; Laurent, M. A.; Chowdhury, S.

2018-06-01

We report on the first observation of avalanche electroluminescence resulting from band-to-band recombination (BTBR) of electron hole pairs at the breakdown limit of Gallium Nitride p-n diodes grown homo-epitaxially on single crystalline GaN substrates. The diodes demonstrated a near ideal breakdown electric field of 3 MV cm‑1 with electroluminescence (EL) demonstrating sharp peaks of emission energies near and at the band gap of GaN. The high critical electric field, near the material limit of GaN, was achieved by generating a smooth curved mesa edge with low plasma damage, using etch engineering without any use of field termination. The superior material quality was critical for such a near-ideal performance. An electric field of 3 MV cm‑1 recorded at the breakdown resulted in impact ionization, confirmed by a positive temperature dependence of the breakdown voltage. The spectral data provided evidence of BTBR of electron hole pairs that were generated by avalanche carrier multiplication in the depletion region.

Infrasonic monitoring of snow avalanches in the Alps

NASA Astrophysics Data System (ADS)

Marchetti, E.; Ulivieri, G.; Ripepe, M.; Chiambretti, I.; Segor, V.

2012-04-01

Risk assessment of snow avalanches is mostly related to weather conditions and snow cover. However a robust risk validation requires to identify all avalanches occurring, in order to compare predictions to real effects. For this purpose on December 2010 we installed a permanent 4-element, small aperture (100 m), infrasound array in the Alps, after a pilot experiment carried out in Gressonay during the 2009-2010 winter season. The array has been deployed in the Ayas Valley, at an elevation of 2000 m a.s.l., where natural avalanches are expected and controlled events are regularly performed. The array consists into 4 Optimic 2180 infrasonic microphones, with a sensitivity of 10-3 Pa in the 0.5-50 Hz frequency band and a 4 channel Guralp CMG-DM24 A/D converter, sampling at 100 Hz. Timing is achieved with a GPS receiver. Data are transmitted to the Department of Earth Sciences of the University of Firenze, where data is recorded and processed in real-time. A multi-channel semblance is carried out on the continuous data set as a function of slowness, back-azimuth and frequency of recorded infrasound in order to detect all avalanches occurring from the back-ground signal, strongly affected by microbarom and mountain induced gravity waves. This permanent installation in Italy will allow to verify the efficiency of the system in short-to-medium range (2-8 km) avalanche detection, and might represent an important validation to model avalanches activity during this winter season. Moreover, the real-time processing of infrasonic array data, might strongly contribute to avalanche risk assessments providing an up-to-description of ongoing events.

Energy mechanics of rock and snow avalanches and the role of fragmentation (invited)

NASA Astrophysics Data System (ADS)

Bartelt, Perry; Buser, Othmar; Glover, James

2014-05-01

The energy mechanics of rock and snow avalanches are traditionally described using a two-step transformation: potential energy is first converted into kinetic energy; kinetic energy is dissipated to heat by frictional processes. If the frictional processes are known, the energy fluxes of avalanches can be calculated completely. The break-up of the released mass, however, introduces several new energy fluxes into the avalanche problem. The first energy is associated with the fragmentation, which generates random particle motions. This is true kinetic energy. Inter-particle interactions (collisions, abrasion, fracture) cause the energy of the random particle motion to dissipate to heat. A constraint on the random motions is the basal boundary. It is at this interface that the dispersive pressure is created by vertical particle motions that are directed upwards into the flow. The integral of the upward particle motions can induce a change in avalanche flow volume and density, depending on the relationship between the weight of the flow and the dispersive pressure. Interestingly, normal pressures will only diverge from hydrostatic when there are changes in flow density. We are therefore confronted with the problem of calculating not only the vertical acceleration of the dispersive pressure, but also the change in vertical acceleration. In this contribution we discuss a method to calculate random particle motions, dispersive pressure and changes in avalanche flow density. These are dependent not only on the absolute mass, but also on the material properties of the disintegrating mass. This becomes particularly interesting when considering the motion of snow and rock avalanches as it allows the prediction of flow regime changes and therefore extreme avalanche run-out potential.

Discrete element modeling of the mass movement and loose material supplying the gully process of a debris avalanche in the Bayi Gully, Southwest China

NASA Astrophysics Data System (ADS)

Zhou, Jia-wen; Huang, Kang-xin; Shi, Chong; Hao, Ming-hui; Guo, Chao-xu

2015-03-01

The dynamic process of a debris avalanche in mountainous areas is influenced by the landslide volume, topographical conditions, mass-material composition, mechanical properties and other factors. A good understanding of the mass movement and loose material supplying the gully process is very important for understanding the dynamic properties of debris avalanches. Three-dimensional particle flow code (PFC3D) was used to simulate a debris avalanche in Quaternary deposits at the Bayi Gully, Southwest China. FORTRAN and AutoCAD were used for the secondary development to display the mass movement process and to quantitatively describe the mass movement and loose material supplying the gully process. The simulated results show that after the landslide is initiated, the gravitational potential energy is converted into kinetic energy with a variation velocity for the sliding masses. Two stages exist for the average-movement velocity: the acceleration stage and the slowdown stage, which are influenced by the topographical conditions. For the loose materials supplying the gully process, the cumulative volume of the sliding masses into the gully gradually increases over the time. When the landslide volume is not large enough, the increasing landslide volume does not obviously influence the movement process of the sliding masses. The travel distance and movement velocity increase with the decreasing numerical parameters, and the mass-movement process is finished more quickly using low-value parameters. The deposition area of the sliding masses decreases with the increasing numerical parameters and the corresponding deposition thickness increases. The mass movement of the debris avalanche is not only influenced by the mechanical parameters but is also controlled by the topographical conditions.

Dielectric Property Enhancement in Polymer Composites with Engineered Interfaces

NASA Astrophysics Data System (ADS)

Krentz, Timothy Michael

This thesis reports studies into the dielectric behavior of polymer composites filled with silica nanoparticles. The permittivity and dielectric breakdown strength (DBS) of these materials are critical to their performance in insulating applications such as high voltage power transmission. Until now, the mechanisms which lead to improvements in DBS in these systems have been poorly understood, in part because the effects of dispersion of the filler and the filler's surface electronic characteristics have been confused. The new surface modifications created in this thesis permit these two parameters to be addressed independently, leading to the hypothesis that nanocomposite dielectric materials exhibit DBS enhancement when electron avalanches are prevented from proceeding to reach a critical size capable of causing failure. The same control of dispersion and surface properties also lead to changes in the permittivity of the composite based upon the polarizability and trapping behavior of the filler. In this work, the dispersion and surface states of silica nanoparticles were independently controlled with two separate populations of surface molecules. Two matrix materials were studied, and in each system, a different, matrix-compatible long chain polymer is required to control dispersion. Conversely, a second population of short molecules is shown to be capable of creating electronic traps associated with the silica nanoparticle surface which lead to DBS enhancements largely independent of the matrix, indicating that the same failure mechanism is operating in both epoxy and polypropylene. Progressive variation in dispersion quality is attained with this surface modification scheme. This creates progressively smaller volumes of matrix polymer unaffected by the filler. This work shows that when these volumes approach and become smaller than the same scale as predicted for electron avalanches, the greatest changes in DBS are seen. Likewise, the plateau behavior of this data implicates that the DBS improvements occur as avalanches are halted in their early phases by the filler, before sufficiently energy can be gathered to damage the matrix. These data indicate that avalanche sizes on the order of 150 nm are sufficient to lead to failure. Furthermore, the depths of the traps induced by small molecules on the silica surface are shown to relate to the DBS enhancement obtained for well dispersed fillers based upon the ability of these localized traps to absorb the energy gathered by growing avalanches.

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

NASA Astrophysics Data System (ADS)

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-based runout indicator in an avalanche path dependent coordinate system. Analyzing and comparing observed and simulated runout distances statistically revealed values for K suitable to simulate the combined influence of four forest characteristics on avalanche runout: forest type, crown coverage, vertical structure and surface roughness, e.g. values for K were higher for dense spruce and mixed spruce-beech forests compared to open larch forests at the upper treeline. Considering forest structural conditions within avalanche simulation will improve current applications for avalanche simulation tools in mountain forest and natural hazard management considerably. Furthermore, we show that an objective and standardized evaluation of two-dimensional simulation results is essential for a successful evaluation and further calibration of avalanche models in general.

Measurement of plasma decay processes in mixture of sodium and argon by coherent microwave scattering

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zhang Zhili; Shneider, Mikhail N.

2010-03-15

This paper presents the experimental measurement and computational model of sodium plasma decay processes in mixture of sodium and argon by using radar resonance-enhanced multiphoton ionization (REMPI), coherent microwave Rayleigh scattering of REMPI. A single laser beam resonantly ionizes the sodium atoms by means of 2+1 REMPI process. The laser beam can only generate the ionization of the sodium atoms and have negligible ionization of argon. Coherent microwave scattering in situ measures the total electron number in the laser-induced plasma. Since the sodium ions decay by recombination with electrons, microwave scattering directly measures the plasma decay processes of the sodiummore » ions. A theoretical plasma dynamic model, including REMPI of the sodium and electron avalanche ionization (EAI) of sodium and argon in the gas mixture, has been developed. It confirms that the EAI of argon is several orders of magnitude lower than the REMPI of sodium. The theoretical prediction made for the plasma decay process of sodium plasma in the mixture matches the experimental measurement.« less

Reliability assessment of multiple quantum well avalanche photodiodes

NASA Technical Reports Server (NTRS)

Yun, Ilgu; Menkara, Hicham M.; Wang, Yang; Oguzman, Isamil H.; Kolnik, Jan; Brennan, Kevin F.; May, Gray S.; Wagner, Brent K.; Summers, Christopher J.

1995-01-01

The reliability of doped-barrier AlGaAs/GsAs multi-quantum well avalanche photodiodes fabricated by molecular beam epitaxy is investigated via accelerated life tests. Dark current and breakdown voltage were the parameters monitored. The activation energy of the degradation mechanism and median device lifetime were determined. Device failure probability as a function of time was computed using the lognormal model. Analysis using the electron beam induced current method revealed the degradation to be caused by ionic impurities or contamination in the passivation layer.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kang, C. S.; Lee, S. G., E-mail: sglee@nfri.re.kr; National Fusion Research Institute, Daejeon 305-806

The behavior of relativistic runaway electrons during Electron Cyclotron Resonance Heating (ECRH) discharges is investigated in the Korea Superconducting Tokamak Advanced Research device. The effect of the ECRH on the runaway electron population is discussed. Observations on the generation of superthermal electrons during ECRH will be reported, which will be shown to be consistent with existing theory for the development of a superthermal electron avalanche during ECRH [A. Lazaros, Phys. Plasmas 8, 1263 (2001)].

High-Accuracy Measurements of the Centre of Gravity of Avalanches in Proportional Chambers

DOE R&D Accomplishments Database

Charpak, G.; Jeavons, A.; Sauli, F.; Stubbs, R.

1973-09-24

In a multiwire proportional chamber the avalanches occur close to the anode wires. The motion of the positive ions in the large electric fields at the vicinity of the wires induces fast-rising positive pulses on the surrounding electrodes. Different methods have been developed in order to determine the position of the centre of the avalanches. In the method we describe, the centre of gravity of the pulse distribution is measured directly. It seems to lead to an accuracy which is limited only by the stability of the spatial distribution of the avalanches generated by the process being measured.

Assessing the interaction between mountain forests and snow avalanches at Nevados de Chillán, Chile and its implications for ecosystem-based disaster risk reduction

NASA Astrophysics Data System (ADS)

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.

Volcanic mixed avalanches: a distinct eruption-triggered mass-flow process at snow-clad volcanoes

USGS Publications Warehouse

Pierson, T.C.; Janda, R.J.

1994-01-01

A generally unrecognized type of pyroclastic deposit was produced by rapid avalanches of intimately mixed snow and hot pyroclastic debris during eruptions at Mount St. Helens, Nevado del Ruiz, and Redoubt Volcano between 1982 and 1989. These "mixed avalanches' traveled as far as 14 km at velocities up to ~27 m/s, involved as much as 107 m3 of rock and ice, and left unmelted deposits of single flow units as thick as 5 m. During flow downslope, heat transfer from hot rocks to snow produced meltwater that partially saturated the mixtures, apparently giving these mixed avalanches mobilities equal to or greater than those of "dry' debris avalanches of similar volume. After melting and desiccation, the deposits are highly susceptible to erosion and unlikely to be well preserved in the stratigraphic record. -Authors

Earth's Most Powerful Natural Particle Accelerator

NASA Technical Reports Server (NTRS)

Rowland, Doug

2012-01-01

Thunderstorms launch antimatter, gamma rays, and highly energetic electrons and neutrons to the edge of space. This witches' brew of radiation is generated at the edge of the stratopause, by the strong electric fields associated with lightning discharges. In less than a quarter millisecond, an explosive feedback process takes an initial seed population of electrons, perhaps produced by cosmic rays from dying stars, and amplifies them a billion billion-fold in the rarefied air over high altitude thunderheads. The electrons generate gamma radiation as they travel through the stratosphere and lower mesosphere, momentarily brighter and of harder spectrum than cosmic gamma ray bursts. These electrons ultimately are absorbed by the atmosphere, but the gamma rays continue on, into the upper reaches of the atmosphere, where they in turn generate a new population of electrons, positrons, and energetic neutrons. These secondary electrons and positrons move along the magnetic field, and can reach near-earth space, streaming through the inner radiation belts, and possibly contributing to the trapped populations there. First postulated by Wilson in 1925, and serendipitously discovered by the Compton Gamma Ray Observatory in 1994 [Fishman et al.], these events, known as "Terrestrial Gamma ray Flashes" (TGFs), represent the most intense episodes of particle acceleration on or near the Earth, resulting in electrons with energies up to 100 MeV. Recent observations by the RHESSI [Smith et al., 2004], Fermi [Briggs et al., 2010], and AGILE [Tavani et al., 2011] satellites, and theoretical and computational modeling, have suggested that the relativistic runaway electron avalanche (RREA) mechanism [Gurevich, 1992], and important modifications, such as the relativistic feedback discharge (RFD) model [Dwyer 2012] can best explain the observations at present. In these models, strong thunderstorm electric fields drive seed electrons, generated from cosmic ray interactions, into a runaway discharge, in which the seed electrons continually gain energy from the electric field, creating a host of secondaries as they interact with the background atmospheric gas. The feedback mechanisms include backwards-propagating positrons and gamma rays, which then can generate new "seed" electrons at the base of the acceleration region, and themselves generate further avalanche chain reactions, greatly amplifying the initial seed population. All these processes happen in the stratosphere, in the altitude range near 15-20 km, where the electric fields and mean free paths are appropriate to allow the discharge to develop.

Evolution from Rydberg gas to ultracold plasma in a supersonic atomic beam of Xe

NASA Astrophysics Data System (ADS)

Hung, J.; Sadeghi, H.; Schulz-Weiling, M.; Grant, E. R.

2014-08-01

A Rydberg gas of xenon, entrained in a supersonic atomic beam, evolves slowly to form an ultracold plasma. In the early stages of this evolution, when the free-electron density is low, Rydberg atoms undergo long-range \\ell -mixing collisions, yielding states of high orbital angular momentum. The development of high-\\ell states promotes dipole-dipole interactions that help to drive Penning ionization. The electron density increases until it reaches the threshold for avalanche. Ninety μs after the production of a Rydberg gas with the initial state, {{n}_{0}}{{\\ell }_{0}}=42d, a 432 V cm-1 electrostatic pulse fails to separate charge in the excited volume, an effect which is ascribed to screening by free electrons. Photoexcitation cross sections, observed rates of \\ell -mixing, and a coupled-rate-equation model simulating the onset of the electron-impact avalanche point consistently to an initial Rydberg gas density of 5\\times {{10}^{8}}\\;c{{m}^{-3}}.

Timing of wet snow avalanche activity: An analysis from Glacier National Park, Montana, USA.

USGS Publications Warehouse

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

2012-01-01

Wet snow avalanches pose a problem for annual spring road opening operations along the Going-to-the-Sun Road (GTSR) in Glacier National Park, Montana, USA. A suite of meteorological metrics and snow observations has been used to forecast for wet slab and glide avalanche activity. However, the timing of spring wet slab and glide avalanches is a difficult process to forecast and requires new capabilities. For the 2011 and 2012 spring seasons we tested a previously developed classification tree model which had been trained on data from 2003-2010. For 2011, this model yielded a 91% predictive rate for avalanche days. For 2012, the model failed to capture any of the avalanche days observed. We then investigated these misclassified avalanche days in the 2012 season by comparing them to the misclassified days from the original dataset from which the model was trained. Results showed no significant difference in air temperature variables between this year and the original training data set for these misclassified days. This indicates that 2012 was characterized by avalanche days most similar to those that the model struggled with in the original training data. The original classification tree model showed air temperature to be a significant variable in wet avalanche activity which implies that subsequent movement of meltwater through the snowpack is also important. To further understand the timing of water flow we installed two lysimeters in fall 2011 before snow accumulation. Water flow showed a moderate correlation with air temperature later in the season and no synchronous pattern associated with wet slab and glide avalanche activity. We also characterized snowpack structure as the snowpack transitioned from a dry to a wet snowpack throughout the spring. This helped to assess potential failure layers of wet snow avalanches and the timing of avalanches compared to water moving through the snowpack. These tools (classification tree model and lysimeter data), combined with standard meteorological and avalanche observations, proved useful to forecasters regarding the timing of wet snow avalanche activity along the GTSR.

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

NASA Astrophysics Data System (ADS)

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 developed countries worldwide, and considering present initiatives conducted to counteract its negative cultural effects by means of grazing and clearing operations, planning is imperative, and this research provides useful information for environmental management policies and risk mitigation in avalanche prone areas.

Acoustic Fluidization and the Extraordinary Mobility of Sturzstroms

NASA Astrophysics Data System (ADS)

Collins, G. S.; Melosh, H. J.

2002-12-01

Sturzstroms are a rare category of rock avalanche that travel vast horizontal distances with only a comparatively small vertical drop in height. Their extraordinary mobility appears to be a consequence of sustained fluid-like behavior during motion that persists even for driving stresses well below those normally associated with large rock avalanches. One mechanism with the potential for explaining this temporary increase in the mobility of rock debris is acoustic fluidization; where transient, high-frequency pressure fluctuations, generated during the initial collapse and subsequent flow of a mass of rock debris, may locally relieve overburden stresses in the rock mass and thus reduce the frictional resistance to slip between fragments. Here we will present the acoustic fluidization model for the mechanics of sturzstroms, and discuss the conditions under which this process may sustain fluid-like flow of large rock avalanches at low driving stresses. Our work has focused on developing equations for describing the temporal and spatial evolution of acoustic energy within a mass of dry rock debris. We apply this model to the specific process of large, dry rock avalanches. To solve the complex system of equations we have: (1) sought steady state solutions to investigate the circumstances under which acoustic fluidization might facilitate fluid-like motion of the debris at low driving stresses; and (2) simulated the flow of dry rock debris in the presence of acoustic vibrations using a hydrocode, to test the stability of the steady state solutions, investigate the effect of initial conditions and study the avalanche termination process. Results from our modeling work are consistent with the characteristic observations of sturzstroms on Earth. They predict that, under realistic conditions, the flow of a mass of dry rock debris can retain and regenerate enough acoustic energy to perpetuate its own motion, even at very low slope angles; thereby explaining the peculiar long-runout of large rock avalanches. Observations of fluid-like behavior of sturzstroms are supported by our modeling work. The predicted velocity profile through the acoustically fluidized rock avalanche is parabolic; the sturzstrom flows with an effective viscosity that is almost independent of depth within the rock avalanche.

Tracking the NOvA Detectors' Performance

NASA Astrophysics Data System (ADS)

Psihas, Fernanda; NOvA Collaboration

2016-03-01

The NOvA experiment measures long baseline νμ -->νe oscillations in Fermilab's NuMI beam. We employ two detectors equipped with over 10 thousand sets of data-taking electronics; avalanche photo diodes and front end boards which collect and process the scintillation signal from particle interactions within the detectors. These sets of electronics -as well as the systems which power and cool them- must be monitored and maintained at precise working conditions to ensure maximal data-taking uptime, good data quality and a lasting life for our detectors. This poster describes the automated systems used on NOvA to simultaneously monitor our data quality, diagnose hardware issues, track our performance and coordinate maintenance for the detectors.

A practitioner's tool for assessing glide crack activity

USGS Publications Warehouse

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

2010-01-01

Glide cracks can result in full-depth glide avalanche release. Avalanches from glide cracks are notoriously difficult to forecast, but are a reoccurring problem in a number of different avalanche forecasting programs across a range of snow climates. Despite this, there is no consensus for how to best manage, mitigate, or even observe glide cracks and the potential resultant avalanche activity. It is thought that an increase in the rate of snow gliding occurs prior to full-depth avalanche activity, so frequent measuring of glide crack movement provides an index of instability. Therefore, a comprehensive avalanche program with glide crack avalanche activity, should at the least, undertake some form of direct monitoring of glide crack movement. In this paper we present a simple, cheap and repeatable method to track glide crack activity using a series of stakes, reflectors and a laser rangefinder (LaserTech TruPulse360B) linked to a GPS (Trimble Geo XH). We tested the methodology in April 2010, on a glide crack above the Going to the Sun Road in Glacier National Park, Montana, USA. This study suggests a new method to better track the development and movement of glide cracks. It is hoped that by introducing a workable method to easily record glide crack movement, avalanche forecasters will improve their understanding of when, or if, avalanche activity will ensue. Our initial results suggest that these new observations, when combined with local micrometeorological data will result in improved process understanding and forecasting of these phenomena.

Fractal avalanche ruptures in biological membranes

NASA Astrophysics Data System (ADS)

Gözen, Irep; Dommersnes, Paul; Czolkos, Ilja; Jesorka, Aldo; Lobovkina, Tatsiana; Orwar, Owe

2010-11-01

Bilayer membranes envelope cells as well as organelles, and constitute the most ubiquitous biological material found in all branches of the phylogenetic tree. Cell membrane rupture is an important biological process, and substantial rupture rates are found in skeletal and cardiac muscle cells under a mechanical load. Rupture can also be induced by processes such as cell death, and active cell membrane repair mechanisms are essential to preserve cell integrity. Pore formation in cell membranes is also at the heart of many biomedical applications such as in drug, gene and short interfering RNA delivery. Membrane rupture dynamics has been studied in bilayer vesicles under tensile stress, which consistently produce circular pores. We observed very different rupture mechanics in bilayer membranes spreading on solid supports: in one instance fingering instabilities were seen resulting in floral-like pores and in another, the rupture proceeded in a series of rapid avalanches causing fractal membrane fragmentation. The intermittent character of rupture evolution and the broad distribution in avalanche sizes is consistent with crackling-noise dynamics. Such noisy dynamics appear in fracture of solid disordered materials, in dislocation avalanches in plastic deformations and domain wall magnetization avalanches. We also observed similar fractal rupture mechanics in spreading cell membranes.

Supershort avalanche electron beam in SF6 and krypton

NASA Astrophysics Data System (ADS)

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.

Stimulated Electronic X-Ray Raman Scattering

NASA Astrophysics Data System (ADS)

Weninger, Clemens; Purvis, Michael; Ryan, Duncan; London, Richard A.; Bozek, John D.; Bostedt, Christoph; Graf, Alexander; Brown, Gregory; Rocca, Jorge J.; Rohringer, Nina

2013-12-01

We demonstrate strong stimulated inelastic x-ray scattering by resonantly exciting a dense gas target of neon with femtosecond, high-intensity x-ray pulses from an x-ray free-electron laser (XFEL). A small number of lower energy XFEL seed photons drive an avalanche of stimulated resonant inelastic x-ray scattering processes that amplify the Raman scattering signal by several orders of magnitude until it reaches saturation. Despite the large overall spectral width, the internal spiky structure of the XFEL spectrum determines the energy resolution of the scattering process in a statistical sense. This is demonstrated by observing a stochastic line shift of the inelastically scattered x-ray radiation. In conjunction with statistical methods, XFELs can be used for stimulated resonant inelastic x-ray scattering, with spectral resolution smaller than the natural width of the core-excited, intermediate state.

Studies with cathode drift chambers for the GlueX experiment at Jefferson Lab

DOE PAGES

Pentchev, L.; Barbosa, F.; Berdnikov, V.; ...

2017-04-22

A drift chamber system consisting of 24 1 m-diameter chambers with both cathode and wire readout (total of 12,672 channels) is operational in Hall D at Jefferson Lab (Virginia). Two cathode strip planes and one wire plane in each chamber register the same avalanche allowing the study of avalanche development, charge induction process, and strip resolution. We demonstrate a method for reconstructing the two-dimensional distribution of the avalanche “center-of-gravity” position around the wire from an 55Fe source with resolutions down to 30 μm. We estimate the azimuthal extent of the avalanche around the wire as a function of the totalmore » charge for an Ar/CO 2 gas mixture. By means of cluster counting using a modified 3 cm-gap chamber, we observe significant space charge effects within the same track, resulting in an extent of the avalanche along the wire.« less

IFKIS a basis for organizational measures in avalanche risk management

NASA Astrophysics Data System (ADS)

Bründl, M.; Etter, H.-J.; Klingler, Ch.; Steiniger, M.; Rhyner, J.; Ammann, W.

2003-04-01

The avalanche winter 1999 in Switzerland showed that the combination of protection measures like avalanche barriers, hazard zone mapping, artificial avalanche release and organisational measures (closure of roads, evacuation etc.) proved to perform well. However, education as well as information and communication between the involved organizations proved to be a weak link in the crisis management. In the first part of the project IFKIS we developed a modular education and training course program for security responsibles of settlements and roads. In the second part an information system was developed which improves on the one hand the information fluxes between the national center for avalanche forecasting, the Swiss Federal Institute for Snow and Avalanche Research SLF, and the local forecasters. On the other hand the communication between the avalanche security services in the communities can be enhanced. During the last two years an information system based on Internet technology has been developed for this purpose. This system allows the transmission of measured data and observations to a central database at SLF and visualization of the data for different users. It also provides the possibility to exchange information on organizational measures like closure of roads, artificial avalanche release etc. on a local and regional scale. This improves the information fluxes and the coordination of safety-measures because all users, although at different places, are on the same information level. Inconsistent safety-measures can be avoided and information and communication concerning avalanche safety becomes much more transparent for all persons involved in hazard management. The training program as well the concept for the information-system are important basics for an efficient avalanche risk management but also for other natural processes and catastrophes.

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

NASA Astrophysics Data System (ADS)

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.

Development of Numerical Models for Performance Predictions of Single-Photon Avalanche Photodetectors (SPAP) for the 2-Micron Regime

NASA Technical Reports Server (NTRS)

Joshi, Ravindra P.; Abedin, M. Nurul (Technical Monitor)

2001-01-01

Field dependent drift velocity results are presented for electron transport in bulk Indium Arsenide (InAs) material based on a Monte Carlo model, which includes an analytical treatment of band-to-band impact ionization. Avalanche multiplication and related excess noise factor (F) are computed as a function of device length and applied voltage. A decrease in F with increases in device length is obtained. The results suggest an inherent utility for InAs-based single-photon avalanche detectors, particularly around the 2 microns region of interest for atmospheric remote sensing applications. The dark current response was also evaluated. The role of the various components has been analyzed. For shorter devices, the tunneling component is shown to dominate at low temperatures. Finally, possible structures for enhanced photodetection are proposed for future research.

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

NASA Astrophysics Data System (ADS)

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

2017-03-01

Not Available Project supported by the State Key Project of Research and Development Plan, China (Grant No. 2016YFB0400903), the National Natural Science Foundation of China (Grant Nos. 61634002, 61274075, and 61474060), the Key Project of Jiangsu Province, China (Grant No. BE2016174), the Anhui University Natural Science Research Project, China (Grant No. KJ2015A153), the Open Fund (KFS) of State Key Lab of Optical Technologieson Nanofabrication and Microengineering, Institute of Optics and Electronics, Chinese Academy of Science.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Scheuermann, J; Howansky, A; Goldan, A

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. Themore » 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.« less

Subelectron readout noise focal plane arrays for space imaging

NASA Astrophysics Data System (ADS)

Atlas, Gene; Wadsworth, Mark

2004-01-01

Readout noise levels of under 1 electron have long been a goal for the FPA community. In the quest to enhance the FPA sensitivity, various approaches have been attempted ranging from the exotic Photo-multiplier tubes, Image Intensifier tubes, Avalanche photo diodes, and now the on-chip avalanche charge amplification technologies from the CCD manufacturers. While these techniques reduce the readout noise, each offers a set of compromises that negatively affect the overall performance of the sensor in parameters such as power dissipation, dynamic range, uniformity or system complexity. In this work, we overview the benefits and tradeoffs of each approach, and introduce a new technique based on ImagerLabs" exclusive HIT technology which promises sub-electron read noise and other benefits without the tradeoffs of the other noise reduction techniques.

Calculations of the Electron Energy Distribution Function in a Uranium Plasma by Analytic and Monte Carlo Techniques. Ph.D. Thesis

NASA Technical Reports Server (NTRS)

Bathke, C. G.

1976-01-01

Electron energy distribution functions were calculated in a U235 plasma at 1 atmosphere for various plasma temperatures and neutron fluxes. The distributions are assumed to be a summation of a high energy tail and a Maxwellian distribution. The sources of energetic electrons considered are the fission-fragment induced ionization of uranium and the electron induced ionization of uranium. The calculation of the high energy tail is reduced to an electron slowing down calculation, from the most energetic source to the energy where the electron is assumed to be incorporated into the Maxwellian distribution. The pertinent collisional processes are electron-electron scattering and electron induced ionization and excitation of uranium. Two distinct methods were employed in the calculation of the distributions. One method is based upon the assumption of continuous slowing and yields a distribution inversely proportional to the stopping power. An iteration scheme is utilized to include the secondary electron avalanche. In the other method, a governing equation is derived without assuming continuous electron slowing. This equation is solved by a Monte Carlo technique.

Simulation of energy spectrum of GEM detector from an x-ray quantum

NASA Astrophysics Data System (ADS)

Malinowski, K.; Chernyshova, M.; Czarski, T.; Kowalska-Strzęciwilk, E.; Linczuk, P.; Wojeński, A.; Krawczyk, R.; Gąska, M.

2018-01-01

This paper presents the results of the energy resolution simulation for the triple GEM-based detector for x-ray quantum of 5.9 keV . Photons of this energy are emitted by 55Fe source, which is a standard calibration marker for this type of detectors. The calculations were made in Garfield++ in two stages. In the first stage, the distribution of the amount of primary electrons generated in the drift volume by the x-ray quantum was simulated using the Heed program. Secondly, the primary electrons of the resulting quantitative distribution were treated as a source of electron avalanches propagated through the whole volume of the triple GEM-based detector. The distribution of the obtained signals created a spectrum corresponding to the peak at 5.9 keV, which allowed us to determine the theoretical energy resolution of the detector. Its knowledge allows observing and improving the eventual experimental deterioration of the energy resolution, inevitably accompanying processes of registration and processing of the signals.

Cycling excitation process: An ultra efficient and quiet signal amplification mechanism in semiconductor

NASA Astrophysics Data System (ADS)

Liu, Yu-Hsin; Yan, Lujiang; Zhang, Alex Ce; Hall, David; Niaz, Iftikhar Ahmad; Zhou, Yuchun; Sham, L. J.; Lo, Yu-Hwa

2015-08-01

Signal amplification, performed by transistor amplifiers with its merit rated by the efficiency and noise characteristics, is ubiquitous in all electronic systems. Because of transistor thermal noise, an intrinsic signal amplification mechanism, impact ionization was sought after to complement the limits of transistor amplifiers. However, due to the high operation voltage (30-200 V typically), low power efficiency, limited scalability, and, above all, rapidly increasing excess noise with amplification factor, impact ionization has been out of favor for most electronic systems except for a few applications such as avalanche photodetectors and single-photon Geiger detectors. Here, we report an internal signal amplification mechanism based on the principle of the phonon-assisted cycling excitation process (CEP). Si devices using this concept show ultrahigh gain, low operation voltage, CMOS compatibility, and, above all, quantum limit noise performance that is 30 times lower than devices using impact ionization. Established on a unique physical effect of attractive properties, CEP-based devices can potentially revolutionize the fields of semiconductor electronics.

Avalanche buildup and propagation effects on photon-timing jitter in Si-SPAD with non-uniform electric field

NASA Astrophysics Data System (ADS)

Ingargiola, Antonino; Assanelli, Mattia; Gallivanoni, Andrea; Rech, Ivan; Ghioni, Massimo; Cova, Sergio

2009-05-01

Improving SPAD performances, such as dark count rate and quantum efficiency, without degrading the photontiming jitter is a challenging task that requires a clear understanding of the physical mechanisms involved. In this paper we investigate the contribution of the avalanche buildup statistics and the lateral avalanche propagation to the photon-timing jitter in silicon SPAD devices. Recent works on the buildup statistics focused on the uniform electric field case, however these results can not be applied to Si SPAD devices in which field profile is far from constant. We developed a 1-D Monte Carlo (MC) simulator using the real non-uniform field profiles derived from Secondary Ion Mass Spectroscopy (SIMS) measurements. Local and non-local models for impact ionization phenomena were considered. The obtained results, in particular the mean multiplication rate and jitter of the buildup filament, allowed us to simulate the statistical spread of the avalanche current on the device active area. We included space charge effects and a detailed lumped model for the external electronics and parasitics. We found that, in agreement with some experimental evidences, the avalanche buildup contribution to the total timing jitter is non-negligible in our devices. Moreover the lateral propagation gives an additional contribution that can explain the increasing trend of the photon-timing jitter with the comparator threshold.

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

NASA Astrophysics Data System (ADS)

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.

Universal avalanche statistics and triggering close to failure in a mean-field model of rheological fracture

NASA Astrophysics Data System (ADS)

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."

Is the Electron Avalanche Process in a Martian Dust Devil Self-Quenching?

NASA Technical Reports Server (NTRS)

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.

Group Dynamics and Decision Making: Backcountry Recreationists in Avalanche Terrain

ERIC Educational Resources Information Center

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,…

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

NASA Astrophysics Data System (ADS)

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.

Discrete element simulation of the Jiufengershan rock-and-soil avalanche triggered by the 1999 Chi-Chi earthquake, Taiwan

NASA Astrophysics Data System (ADS)

Chang, Kuo-Jen; Taboada, Alfredo

2009-09-01

We present Contact Dynamics discrete element simulations of the earthquake-triggered Jiufengershan avalanche, which mobilized a 60 m thick, 1.5 km long sedimentary layer, dipping ˜22°SE toward a valley. The dynamic behavior of the avalanche is simulated under different assumptions about rock behavior, water table height, and boundary shear strength. Additionally, seismic shaking is introduced using strong motion records from nearby stations. We assume that seismic shaking generates shearing and frictional heating along the surface of rupture, which, in turn, may induce dynamic weakening and avalanche triggering; a simple "slip-weakening" criterion was adopted to simulate shear strength drop along the rupture surface. We investigate the mechanical processes occurring during triggering and propagation of an avalanche mobilizing shallowly dipping layers. Incipient deformation forms a pop-up structure at the toe of the dip slope. As the avalanche propagates, the pop-up deforms into an overturned fold, which overrides the surface of separation along a décollement. Simultaneously, uphill layers slide at high velocity (125 km/h) and are folded and disrupted as they reach the toe of the dip slope. The avalanche foot forms a wedge that is pushed forward as deformed rocks accrete at its rear. We simulated five cross sections across the Jiufengershan avalanche, which differ in the geometry of the surface of separation. Topographic and simulated surface profiles are similar. The friction coefficient at the surface of separation determined from back analysis is abnormally low (μSS = 0.2), possibly due to lubrication by liquefied soils. The granular deposits of simulated earthquake- and rain-triggered avalanches are similar.

Optical ionization detector

DOEpatents

Wuest, C.R.; Lowry, M.E.

1994-03-29

An optical ionization detector wherein a beam of light is split so that one arm passes through a fiber optics and the other arm passes through a gas-filled region, and uses interferometry to detect density changes in a gas when charged particles pass through it. The gas-filled region of the detector is subjected to a high electric field and as a charged particle traverses this gas region electrons are freed from the cathode and accelerated so as to generate an electron avalanche which is collected on the anode. The gas density is effected by the electron avalanche formation and if the index or refraction is proportional to the gas density the index will change accordingly. The detector uses this index change by modulating the one arm of the split light beam passing through the gas, with respect to the other arm that is passed through the fiber optic. Upon recombining of the beams, interference fringe changes as a function of the index change indicates the passage of charged particles through the gaseous medium. 3 figures.

Optical ionization detector

DOEpatents

Wuest, Craig R.; Lowry, Mark E.

1994-01-01

An optical ionization detector wherein a beam of light is split so that one arm passes through a fiber optics and the other arm passes through a gas-filled region, and uses interferometry to detect density changes in a gas when charged particles pass through it. The gas-filled region of the detector is subjected to a high electric field and as a charged particle traverses this gas region electrons are freed from the cathode and accelerated so as to generate an electron avalanche which is collected on the anode. The gas density is effected by the electron avalanche formation and if the index or refraction is proportional to the gas density the index will change accordingly. The detector uses this index change by modulating the one arm of the split light beam passing through the gas, with respect to the other arm that is passed through the fiber optic. Upon recombining of the beams, interference fringe changes as a function of the index change indicates the passage of charged particles through the gaseous medium.

Monitoring and modeling ice-rock avalanches from ice-capped volcanoes: A case study of frequent large avalanches on Iliamna Volcano, Alaska

USGS Publications Warehouse

Huggel, C.; Caplan-Auerbach, J.; Waythomas, C.F.; Wessels, R.L.

2007-01-01

Iliamna is an andesitic stratovolcano of the Aleutian arc with regular gas and steam emissions and mantled by several large glaciers. Iliamna Volcano exhibits an unusual combination of frequent and large ice-rock avalanches in the order of 1 ?? 106??m3 to 3 ?? 107??m3 with recent return periods of 2-4??years. We have reconstructed an avalanche event record for the past 45??years that indicates Iliamna avalanches occur at higher frequency at a given magnitude than other mass failures in volcanic and alpine environments. Iliamna Volcano is thus an ideal site to study such mass failures and its relation to volcanic activity. In this study, we present different methods that fit into a concept of (1) long-term monitoring, (2) early warning, and (3) event documentation and analysis of ice-rock avalanches on ice-capped active volcanoes. Long-term monitoring methods include seismic signal analysis, and space-and airborne observations. Landsat and ASTER satellite data was used to study the extent of hydrothermally altered rocks and surface thermal anomalies at the summit region of Iliamna. Subpixel heat source calculation for the summit regions where avalanches initiate yielded temperatures of 307 to 613??K assuming heat source areas of 1000 to 25??m2, respectively, indicating strong convective heat flux processes. Such heat flow causes ice melting conditions and is thus likely to reduce the strength at the base of the glacier. We furthermore demonstrate typical seismic records of Iliamna avalanches with rarely observed precursory signals up to two hours prior to failure, and show how such signals could be used for a multi-stage avalanche warning system in the future. For event analysis and documentation, space- and airborne observations and seismic records in combination with SRTM and ASTER derived terrain data allowed us to reconstruct avalanche dynamics and to identify remarkably similar failure and propagation mechanisms of Iliamna avalanches for the past 45??years. Simple avalanche flow modeling was able to reasonably replicate Iliamna avalanches and can thus be applied for hazard assessments. Hazards at Iliamna Volcano are low due to its remote location; however, we emphasize the transfer potential of the methods presented here to other ice-capped volcanoes with much higher hazards such as those in the Cascades or the Andes. ?? 2007 Elsevier B.V. All rights reserved.

Loading-rate-independent delay of catastrophic avalanches in a bulk metallic glass

DOE PAGES

Chen, S. H.; Chan, K. C.; Wang, G.; ...

2016-02-25

The plastic flow of bulk metallic glasses (BMGs) is characterized by intermittent bursts of avalanches, and this trend results in disastrous failures of BMGs. In the present work, a double-side-notched BMG specimen is designed, which exhibits chaotic plastic flows consisting of several catastrophic avalanches under the applied loading. The disastrous shear avalanches have, then, been delayed by forming a stable plastic-flow stage in the specimens with tailored distances between the bottoms of the notches, where the distribution of a complex stress field is acquired. Differing from the conventional compressive testing results, such a delaying process is independent of loading rate.more » The statistical analysis shows that in the specimens with delayed catastrophic failures, the plastic flow can evolve to a critical dynamics, making the catastrophic failure more predictable than the ones with chaotic plastic flows. Lastly, the findings are of significance in understanding the plastic-flow mechanisms in BMGs and controlling the avalanches in relating solids.« less

Scaling, clustering and avalanches for steel beads in an external magnetic field

NASA Astrophysics Data System (ADS)

Marquinez, Alyse; Thvedt, Ingrid; Lehman, S. Y.; Jacobs, D. T.

2011-03-01

We investigated avalanches using uniform 3mm steel spheres (``beads'') dropped onto a conical bead pile within a uniform magnetic field. The bead pile is built by pouring beads onto a circular base where the bottom layer of beads had been glued randomly. Beads are then individually dropped from a fixed height after which the pile is massed. This process is repeated for thousands of bead drops. By measuring the number of avalanches of a given size that occurred during the experiment, the resulting avalanche size distribution was compared to a power law description as predicted by self-organized criticality. As the magnetic field intensity increased, the beads clustered to give a larger angle of repose and we measured the change in the avalanche size distribution. The moments of the distribution give a sensitive test of mean-field theory as the universality class for these bead piles. We acknowledge support from Research Corporation and NSF-REU grant DMR 0649112.

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

NASA Astrophysics Data System (ADS)

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.

Bilayer avalanche spin-diode logic

DOE Office of Scientific and Technical Information (OSTI.GOV)

Friedman, Joseph S., E-mail: joseph.friedman@u-psud.fr; Querlioz, Damien; Fadel, Eric R.

2015-11-15

A novel spintronic computing paradigm is proposed and analyzed in which InSb p-n bilayer avalanche spin-diodes are cascaded to efficiently perform complex logic operations. This spin-diode logic family uses control wires to generate magnetic fields that modulate the resistance of the spin-diodes, and currents through these devices control the resistance of cascaded devices. Electromagnetic simulations are performed to demonstrate the cascading mechanism, and guidelines are provided for the development of this innovative computing technology. This cascading scheme permits compact logic circuits with switching speeds determined by electromagnetic wave propagation rather than electron motion, enabling high-performance spintronic computing.

Room temperature single-photon detectors for high bit rate quantum key distribution

DOE Office of Scientific and Technical Information (OSTI.GOV)

Comandar, L. C.; Patel, K. A.; Engineering Department, Cambridge University, 9 J J Thomson Ave., Cambridge CB3 0FA

We report room temperature operation of telecom wavelength single-photon detectors for high bit rate quantum key distribution (QKD). Room temperature operation is achieved using InGaAs avalanche photodiodes integrated with electronics based on the self-differencing technique that increases avalanche discrimination sensitivity. Despite using room temperature detectors, we demonstrate QKD with record secure bit rates over a range of fiber lengths (e.g., 1.26 Mbit/s over 50 km). Furthermore, our results indicate that operating the detectors at room temperature increases the secure bit rate for short distances.

Evaluating terrain based criteria for snow avalanche exposure ratings using GIS

NASA Astrophysics Data System (ADS)

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.

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

NASA Astrophysics Data System (ADS)

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 relation to different drives, neuronal states and microscopic mechanisms of charge storage and release in neuronal networks.

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

NASA Astrophysics Data System (ADS)

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.

Relating rock avalanche morphology to emplacement processes

NASA Astrophysics Data System (ADS)

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/limestone sequences to weaker siliciclastic and evaporitic beds (sand-/siltstones, rauhwacken) can be pinpointed on LiDAR shaded relief images of the rock avalanche deposit. Hence, several morphological signatures are clearly related to differences in mechanical behaviour of the involved lithologies, whereas others reflect particular emplacement modes of the same rock unit: e.g. rockslide motion versus rock avalanche spreading. Reference Patzelt G. 2012. The rock avalanches of Tschirgant and Haiming (Upper Inn Valley, Tyrol, Austria), comment on the map supply. (German language only). Jahrbuch der Geologischen Bundesanstalt 152(1-4): 13-24.

The wiper model: avalanche dynamics in an exclusion process

NASA Astrophysics Data System (ADS)

Politi, Antonio; Romano, M. Carmen

2013-10-01

The exclusion-process model (Ciandrini et al 2010 Phys. Rev. E 81 051904) describing traffic of particles with internal stepping dynamics reveals the presence of strong correlations in realistic regimes. Here we study such a model in the limit of an infinitely fast translocation time, where the evolution can be interpreted as a ‘wiper’ that moves to dry neighbouring sites. We trace back the existence of long-range correlations to the existence of avalanches, where many sites are dried at once. At variance with self-organized criticality, in the wiper model avalanches have a typical size equal to the logarithm of the lattice size. In the thermodynamic limit, we find that the hydrodynamic behaviour is a mixture of stochastic (diffusive) fluctuations and increasingly coherent periodic oscillations that are reminiscent of a collective dynamics.

The blocking probability of Geiger-mode avalanche photo-diodes

NASA Technical Reports Server (NTRS)

Moision, Bruce; Srinivasan, Meera; Hamkins, Jon

2005-01-01

When a photo is detected by a Geiger-mode avalanche photo-diode (GMAPD), the detector is rendered inactive, or blocked, for a certain period of time. In this paper we derive the blocking probability for a GMAPD whose input is either an unmodulated, Benoulli modulated or pulse-position-modulated Poisson process.

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

NASA Technical Reports Server (NTRS)

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 meV valance band offset with InAlAs, which is high enough to hinder the transport of the already cooled holes. Being stopped by the energy barrier, holes are accumulated at the junctions to shield the electric field, resulting in a decrease of the electric field in the multiplication region. Because the impact ionization rate is extremely sensitive to the magnitude of the electric field, the field-screening effect drastically reduces the impact ionization rate and quenches the output signals. After the avalanche pulse signal is self-quenched, the accumulated holes at the InGaAsP/ InAlAs interface escape the energy barrier through thermal excitation and tunneling and finally leave the device. The device is thus reset and ready for subsequent photon detection. This recovery time is controlled by the height of the energy barrier and the hole-cooling rate.

Negative Differential Conductance & Hot-Carrier Avalanching in Monolayer WS2 FETs

DOE Office of Scientific and Technical Information (OSTI.GOV)

He, G.; Nathawat, J.; Kwan, C. -P.

The high field phenomena of inter-valley transfer and avalanching breakdown have long been exploited in devices based on conventional semiconductors. In this Article, we demonstrate the manifestation of these effects in atomically-thin WS 2 field-effect transistors. The negative differential conductance exhibits all of the features familiar from discussions of this phenomenon in bulk semiconductors, including hysteresis in the transistor characteristics and increased noise that is indicative of travelling high-field domains. It is also found to be sensitive to thermal annealing, a result that we attribute to the influence of strain on the energy separation of the different valleys involved inmore » hot-electron transfer. This idea is supported by the results of ensemble Monte Carlo simulations, which highlight the sensitivity of the negative differential conductance to the equilibrium populations of the different valleys. At high drain currents (>10 μA/μm) avalanching breakdown is also observed, and is attributed to trap-assisted inverse Auger scattering. This mechanism is not normally relevant in conventional semiconductors, but is possible in WS 2 due to the narrow width of its energy bands. The various results presented here suggest that WS 2 exhibits strong potential for use in hot-electron devices, including compact high-frequency sources and photonic detectors.« less

Negative Differential Conductance & Hot-Carrier Avalanching in Monolayer WS2 FETs

DOE PAGES

He, G.; Nathawat, J.; Kwan, C. -P.; ...

2017-09-12

The high field phenomena of inter-valley transfer and avalanching breakdown have long been exploited in devices based on conventional semiconductors. In this Article, we demonstrate the manifestation of these effects in atomically-thin WS 2 field-effect transistors. The negative differential conductance exhibits all of the features familiar from discussions of this phenomenon in bulk semiconductors, including hysteresis in the transistor characteristics and increased noise that is indicative of travelling high-field domains. It is also found to be sensitive to thermal annealing, a result that we attribute to the influence of strain on the energy separation of the different valleys involved inmore » hot-electron transfer. This idea is supported by the results of ensemble Monte Carlo simulations, which highlight the sensitivity of the negative differential conductance to the equilibrium populations of the different valleys. At high drain currents (>10 μA/μm) avalanching breakdown is also observed, and is attributed to trap-assisted inverse Auger scattering. This mechanism is not normally relevant in conventional semiconductors, but is possible in WS 2 due to the narrow width of its energy bands. The various results presented here suggest that WS 2 exhibits strong potential for use in hot-electron devices, including compact high-frequency sources and photonic detectors.« less

Preliminary Breakdown: Physical Mechanisms and Potential for Energetic Emissions

NASA Astrophysics Data System (ADS)

Petersen, D.; Beasley, W. H.

2014-12-01

Observations and analysis of the preliminary breakdown phase of virgin negative cloud-to-ground (-CG) lightning strokes will be presented. Of primary interest are the physical processes responsible for the fast electric field "characteristic" pulses that are often observed during this phase. The pulse widths of characteristic pulses are shown to occur as a superposed bimodal distribution, with the short and long modes having characteristic timescales on the order of 1 microsecond and 10 microseconds, respectively. Analysis of these pulses is based on comparison with laboratory observations of long spark discharge processes and with recently acquired high-speed video observations of a single -CG event. It will be argued that the fast electric field bimodal distribution is the result of conventional discharge processes operating in an extensive strong ambient electric field environment. An important related topic will also be discussed, where it will be argued that preliminary breakdown discharges are capable of generating energetic electrons and may therefore seed relativistic electron avalanches that go on to produce pulsed energetic photon emissions.

Modeling a Glacial Lake Outburst Flood Process Chain: The Case of Lake Palcacocha and Huaraz, Peru

NASA Astrophysics Data System (ADS)

Chisolm, Rachel; Somos-Valenzuela, Marcelo; Rivas Gomez, Denny; McKinney, Daene C.; Portocarrero Rodriguez, Cesar

2016-04-01

One of the consequences of recent glacier recession in the Cordillera Blanca, Peru, is the risk of Glacial Lake Outburst Floods (GLOFs) from lakes that have formed at the base of retreating glaciers. GLOFs are often triggered by avalanches falling into glacial lakes, initiating a chain of processes that may culminate in significant inundation and destruction downstream. This paper presents simulations of all of the processes involved in a potential GLOF originating from Lake Palcacocha, the source of a previously catastrophic GLOF on December 13, 1941, 1800 people in the city of Huaraz, Peru. The chain of processes simulated here includes: (1) avalanches above the lake; (2) lake dynamics resulting from the avalanche impact, including wave generation, propagation, and run-up across lakes; (3) terminal moraine overtopping and dynamic moraine erosion simulations to determine the possibility of breaching; (4) flood propagation along downstream valleys; and (5) inundation of populated areas. The results of each process feed into simulations of subsequent processes in the chain, finally resulting in estimates of inundation in the city of Huaraz. The results of the inundation simulations were converted into flood intensity and hazard maps (based on an intensity-likelihood matrix) that may be useful for city planning and regulation. Three avalanche events with volumes ranging from 0.5-3 x 106 m3 were simulated, and two scenarios of 15 m and 30 m lake lowering were simulated to assess the potential of mitigating the hazard level in Huaraz. For all three avalanche events, three-dimensional hydrodynamic models show large waves generated in the lake from the impact resulting in overtopping of the damming-moraine. Despite very high discharge rates (up to 63.4 x 103 m3/s), the erosion from the overtopping wave did not result in failure of the damming-moraine when simulated with a hydro-morphodynamic model using excessively conservative soil characteristics that provide very little erosion resistance. With the current lake level, all three avalanche events result in inundation in Huaraz, and the resulting hazard map shows a total affected area of 2.01 km2, most of which is in the high-hazard category. Lowering the lake has the potential to reduce the affected area by up to 35% resulting in a smaller portion of the inundated area in the high-hazard category.

Electromagnetic cascade in high-energy electron, positron, and photon interactions with intense laser pulses

NASA Astrophysics Data System (ADS)

Bulanov, S. S.; Schroeder, C. B.; Esarey, E.; Leemans, W. P.

2013-06-01

The interaction of high-energy electrons, positrons, and photons with intense laser pulses is studied in head-on collision geometry. It is shown that electrons and/or positrons undergo a cascade-type process involving multiple emissions of photons. These photons can consequently convert into electron-positron pairs. As a result charged particles quickly lose their energy developing an exponentially decaying energy distribution, which suppresses the emission of high-energy photons, thus reducing the number of electron-positron pairs being generated. Therefore, this type of interaction suppresses the development of the electromagnetic avalanche-type discharge, i.e., the exponential growth of the number of electrons, positrons, and photons does not occur in the course of interaction. The suppression will occur when three-dimensional effects can be neglected in the transverse particle orbits, i.e., for sufficiently broad laser pulses with intensities that are not too extreme. The final distributions of electrons, positrons, and photons are calculated for the case of a high-energy e-beam interacting with a counterstreaming, short intense laser pulse. The energy loss of the e-beam, which requires a self-consistent quantum description, plays an important role in this process, as well as provides a clear experimental observable for the transition from the classical to quantum regime of interaction.

Auditory Power-Law Activation Avalanches Exhibit a Fundamental Computational Ground State

NASA Astrophysics Data System (ADS)

Stoop, Ruedi; Gomez, Florian

2016-07-01

The cochlea provides a biological information-processing paradigm that we are only beginning to understand in its full complexity. Our work reveals an interacting network of strongly nonlinear dynamical nodes, on which even a simple sound input triggers subnetworks of activated elements that follow power-law size statistics ("avalanches"). From dynamical systems theory, power-law size distributions relate to a fundamental ground state of biological information processing. Learning destroys these power laws. These results strongly modify the models of mammalian sound processing and provide a novel methodological perspective for understanding how the brain processes information.

Avalanche photodiode for measurement of low-energy electrons

NASA Astrophysics Data System (ADS)

Ogasawara, K.; Asamura, K.; Mukai, T.; Saito, Y.

2005-06-01

We report on the performance of an Avalanche Photodiode (APD) produced by Hamamatsu Photonics Co. Ltd. (Type Z7966-20) for measurements of low energy electrons. We have set up an electron gun, which can generate a 1-20 keV electron beam impinging onto the APD in a vacuum chamber. The result shows that the pulse height distribution (PHD) of the APD signal exhibits a significant peak for electrons with energies above 8 keV, and the variation of the PHD peak shows a good linearity with the energy of incident electrons. The energy resolution is quite good, though it slightly depends on the electron energy. In the case of low-energies (lower than 10 keV), the pulse height distribution has a characteristic tail on the low energy side, and the energy resolution becomes a little worse. The position of the peak appears on a slightly lower channel than is expected from data at higher energies (near 20 keV). Qualitatively, the low-energy tail is caused by the dead-layer on the surface of the device. The nonlinearity and the worse resolution of the peaks for higher energy electrons may have resulted from a space-charge effect due to created e-h pairs. For a quantitative understanding, we have made a Monte Carlo particle simulation of charge transport and collection inside the APD.

Natural hazard fatalities in Switzerland from 1946 to 2015

NASA Astrophysics Data System (ADS)

Badoux, Alexandre; Andres, Norina; Techel, Frank; Hegg, Christoph

2016-12-01

A database of fatalities caused by natural hazard processes in Switzerland was compiled for the period between 1946 and 2015. Using information from the Swiss flood and landslide damage database and the Swiss destructive avalanche database, the data set was extended back in time and more hazard processes were added by conducting an in-depth search of newspaper reports. The new database now covers all natural hazards common in Switzerland, categorised into seven process types: flood, landslide, rockfall, lightning, windstorm, avalanche and other processes (e.g. ice avalanches, earthquakes). Included were all fatal accidents associated with natural hazard processes in which victims did not expose themselves to an important danger on purpose. The database contains information on 635 natural hazard events causing 1023 fatalities, which corresponds to a mean of 14.6 victims per year. The most common causes of death were snow avalanches (37 %), followed by lightning (16 %), floods (12 %), windstorms (10 %), rockfall (8 %), landslides (7 %) and other processes (9 %). About 50 % of all victims died in one of the 507 single-fatality events; the other half were killed in the 128 multi-fatality events. The number of natural hazard fatalities that occurred annually during our 70-year study period ranged from 2 to 112 and exhibited a distinct decrease over time. While the number of victims in the first three decades (until 1975) ranged from 191 to 269 per decade, it ranged from 47 to 109 in the four following decades. This overall decrease was mainly driven by a considerable decline in the number of avalanche and lightning fatalities. About 75 % of victims were males in all natural hazard events considered together, and this ratio was roughly maintained in all individual process categories except landslides (lower) and other processes (higher). The ratio of male to female victims was most likely to be balanced when deaths occurred at home (in or near a building), a situation that mainly occurred in association with landslides and avalanches. The average age of victims of natural hazards was 35.9 years and, accordingly, the age groups with the largest number of victims were the 20-29 and 30-39 year-old groups, which in combination represented 34 % of all fatalities. It appears that the overall natural hazard mortality rate in Switzerland over the past 70 years has been relatively low in comparison to rates in other countries or rates of other types of fatal accidents in Switzerland. However, a large variability in mortality rates was observed within the country with considerably higher rates in Alpine environments.

Robust snow avalanche detection using machine learning on infrasonic array data

NASA Astrophysics Data System (ADS)

Thüring, Thomas; Schoch, Marcel; van Herwijnen, Alec; Schweizer, Jürg

2014-05-01

Snow avalanches may threaten people and infrastructure in mountain areas. Automated detection of avalanche activity would be highly desirable, in particular during times of poor visibility, to improve hazard assessment, but also to monitor the effectiveness of avalanche control by explosives. In the past, a variety of remote sensing techniques and instruments for the automated detection of avalanche activity have been reported, which are based on radio waves (radar), seismic signals (geophone), optical signals (imaging sensor) or infrasonic signals (microphone). Optical imagery enables to assess avalanche activity with very high spatial resolution, however it is strongly weather dependent. Radar and geophone-based detection typically provide robust avalanche detection for all weather conditions, but are very limited in the size of the monitoring area. On the other hand, due to the long propagation distance of infrasound through air, the monitoring area of infrasonic sensors can cover a large territory using a single sensor (or an array). In addition, they are by far more cost effective than radars or optical imaging systems. Unfortunately, the reliability of infrasonic sensor systems has so far been rather low due to the strong variation of ambient noise (e.g. wind) causing a high false alarm rate. We analyzed the data collected by a low-cost infrasonic array system consisting of four sensors for the automated detection of avalanche activity at Lavin in the eastern Swiss Alps. A comparably large array aperture (~350m) allows highly accurate time delay estimations of signals which arrive at different times at the sensors, enabling precise source localization. An array of four sensors is sufficient for the time resolved source localization of signals in full 3D space, which is an excellent method to anticipate true avalanche activity. Robust avalanche detection is then achieved by using machine learning methods such as support vector machines. The system is initially trained by using characteristic data features from known avalanche and non-avalanche events. Data features are obtained from output signals of the source localization algorithm or from Fourier or time domain processing and support the learning phase of the system. A significantly improved detection rate as well as a reduction of the false alarm rate was achieved compared to previous approaches.

The inception of pulsed discharges in air: simulations in background fields above and below breakdown

NASA Astrophysics Data System (ADS)

Sun, Anbang; Teunissen, Jannis; Ebert, Ute

2014-11-01

We investigate discharge inception in air, in uniform background electric fields above and below the breakdown threshold. We perform 3D particle simulations that include a natural level of background ionization in the form of positive and \\text{O}2- ions. In background fields below breakdown, we use a strongly ionized seed of electrons and positive ions to enhance the field locally. In the region of enhanced field, we observe the growth of positive streamers, as in previous simulations with 2D plasma fluid models. The inclusion of background ionization has little effect in this case. When the background field is above the breakdown threshold, the situation is very different. Electrons can then detach from \\text{O}2- and start ionization avalanches in the whole volume. These avalanches together create one extended discharge, in contrast to the ‘double-headed’ streamers found in many fluid simulations.

Triggering Excimer Lasers by Photoionization from Corona Discharges

NASA Astrophysics Data System (ADS)

Xiong, Zhongmin; Duffey, Thomas; Brown, Daniel; Kushner, Mark

2009-10-01

High repetition rate ArF (192 nm) excimer lasers are used for photolithography sources in microelectronics fabrication. In highly attaching gas mixtures, preionization is critical to obtaining stable, reproducible glow discharges. Photoionization from a separate corona discharge is one technique for preionization which triggers the subsequent electron avalanche between the main electrodes. Photoionization triggering of an ArF excimer laser sustained in multi-atmosphere Ne/Ar/F2/Xe gas mixtures has been investigated using a 2-dimensional plasma hydrodynamics model including radiation transport. Continuity equations for charged and neutral species, and Poisson's equation are solved coincident with the electron temperature with transport coefficients obtained from solutions of Boltzmann's equation. Photoionizing radiation is produced by a surface discharge which propagates along a corona-bar located adjacent to the discharge electrodes. The consequences of pulse power waveform, corona bar location, capacitance and gas mixture on uniformity, symmetry and gain of the avalanche discharge will be discussed.

Photo-triggering and secondary electron produced ionization in electric discharge ArF* excimer lasers

NASA Astrophysics Data System (ADS)

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.

Performance optimization of detector electronics for millimeter laser ranging

NASA Technical Reports Server (NTRS)

Cova, Sergio; Lacaita, A.; Ripamonti, Giancarlo

1993-01-01

The front-end electronic circuitry plays a fundamental role in determining the performance actually obtained from ultrafast and highly sensitive photodetectors. We deal here with electronic problems met working with microchannel plate photomultipliers (MCP-PMTs) and single photon avalanche diodes (SPADs) for detecting single optical photons and measuring their arrival time with picosecond resolution. The performance of available fast circuits is critically analyzed. Criteria for selecting the most suitable electronics are derived and solutions for exploiting the detector performance are presented and discussed.

III-V strain layer superlattice based band engineered avalanche photodiodes (Presentation Recording)

NASA Astrophysics Data System (ADS)

Ghosh, Sid

2015-08-01

Laser detection and ranging (LADAR)-based systems operating in the Near Infrared (NIR) and Short Wave Infrared (SWIR) have become popular optical sensors for remote sensing, medical, and environmental applications. Sophisticated laser-based radar and weapon systems used for long-range military and astronomical applications need to detect, recognize, and track a variety of targets under a wide spectrum of atmospheric conditions. Infrared APDs play an important role in LADAR systems by integrating the detection and gain stages in a single device. Robust silicon-APDs are limited to visible and very near infrared region (< 1 um), while InGaAs works well up to wavelengths of about 1.5um. Si APDs have low multiplication or excess noise but are limited to below 1um due very poor quantum efficiency above 0.8um. InGaAs and Ge APDs operate up to wavelengths of 1.5um but have poor multiplication or excess noise due to a low impact ionization coefficient ratio between electrons and holes. For the past several decades HgCdTe has been traditionally used in longer wavelength (> 3um) infrared photon detection applications. Recently, various research groups (including Ghosh et. al.) have reported SWIR and MWIR HgCdTe APDs on CdZnTe and Si substrates. However, HgCdTe APDs suffer from low breakdown fields due to material defects, and excess noise increases significantly at high electric fields. During the past decade, InAs/GaSb Strain Layer Superlattice (SLS) material system has emerged as a potential material for the entire infrared spectrum because of relatively easier growth, comparable absorption coefficients, lower tunneling currents and longer Auger lifetimes resulting in enhanced detectivities (D*). Band engineering in type II SLS allows us to engineer avalanche properties of electrons and holes. This is a great advantage over bulk InGaAs and HgCdTe APDs where engineering avalanche properties is not possible. The talk will discuss the evolution of superlattice based avalanche photodiodes and some of the recent results on the work being done at Raytheon on SWIR avalanche photodiodes.

Hybrid photodetector for single-molecule spectroscopy and microscopy

PubMed Central

Michalet, X.; Cheng, Adrian; Antelman, Joshua; Suyama, Motohiro; Arisaka, Katsushi; Weiss, Shimon

2011-01-01

We report benchmark tests of a new single-photon counting detector based on a GaAsP photocathode and an electron-bombarded avalanche photodiode developed by Hamamatsu Photonics. We compare its performance with those of standard Geiger-mode avalanche photodiodes. We show its advantages for FCS due to the absence of after-pulsing and for fluorescence lifetime measurements due to its excellent time resolution. Its large sensitive area also greatly simplifies setup alignment. Its spectral sensitivity being similar to that of recently introduced CMOS SPADs, this new detector could become a valuable tool for single-molecule fluorescence measurements, as well as for many other applications. PMID:21822361

Runaway electrons in tokamaks

DOE Office of Scientific and Technical Information (OSTI.GOV)

Liu, Chang

The generation of runaway electrons is a complex and important phenomenon that impacts many areas of plasma physics. Due to the decrease of electron collision frequency with increasing velocity, electrons under strong electric field can experience unlimited “runaway” acceleration. In tokamaks, runaway electrons can be produced in disruptions, due to the strong inductive electric field formed as the thermal energy of plasma gets rapidly lost. This population of runaway electrons can undergo an exponential growth, denoted the runaway electron avalanche, due to hard collisions between relativistic runaway electrons and low energy electrons. It is predicted that in a large tokamakmore » device like the International Thermonuclear Experimental Reactor (ITER), a runway electron beam generated in a disruption event can potentially cause severe damage to the device, which poses a significant challenge for ITER to achieve its mission. It is therefore extremely important to seek an effective mitigation mechanism for runaway electrons. Experimental efforts have been made to study the properties of runaway electrons in tokamaks, including their generation, diffusion, and radiation. In order to understand these experimental results, extensive theoretical and simulation studies of runaway electron physics are required. The main topic of this thesis is to study the wave particle interaction associated with runaway electron beams in tokamaks. The runaway electrons can emit and absorb electromagnetic waves through resonances, and can be diffused in momentum space by the waves. Initially, we address the Cherenkov radiation of runaway electrons, which originates from the polarization of the plasma medium. The energy and momentum loss of the Cherenkov radiation can be modeled by adding a correction to the Coulomb logarithm in the collisional drag force. Subsequently, we address pitch angle scattering caused by normal modes in the plasma, which are driven unstable by the anisotropicity of the runaway electron beam. The fluctuating electromagnetic fields are found to act as a seed for the unstable normal modes. Numerical simulations show that the pitch angle scattering effect from the normal modes, mainly whistler waves, can be significantly larger than that from collisional pitch angle scattering. Finally, we present a synthetic diagnostic tool we developed to calculate the electron cyclotron emission (ECE) from the runaway electrons, and successfully reproduce the prompt growth of the ECE signal observed in DIII-D quiescent runaway electron (QRE) experiments. Within the thesis, we also present the application of the adjoint method to runaway electron research, and show the calculations of the runaway probability function (RPF) and the expected loss time (ELT). These calculations not only help depict the dynamics of runaway electrons in momentum space, but also can be used to efficiently calculate experimentally relevant quantities such as the critical electric field for runaway electron avalanche and the avalanche growth rate.« less

Investigating glide snow avalanche release using seismic monitoring in combination with time-lapse photography

NASA Astrophysics Data System (ADS)

van Herwijnen, Alec; Failletaz, Jerome; Berhod, Nicole; Mitterer, Christoph

2013-04-01

Glide avalanches occur when the entire snowpack glides over the ground until an avalanche releases. These avalanches are difficult to forecast since the gliding process can take place over a few hours up to several weeks or months. The presence of liquid water at the interface between the snow cover and the ground surface is of primary importance as it reduces frictional support. Glide avalanches are often preceded by the opening of a tensile crack in the snow cover, called a glide crack. Past research has shown that glide crack opening accelerates prior to avalanche release. During the winter of 2012-2013, we monitored glide crack expansion using time-lapse photography in combination with a seismic sensor and two heat flux sensors on a slope with well documented glide avalanche activity in the Eastern Swiss Alps above Davos, Switzerland. To track changes in glide rates, the number of dark pixels in an area around the glide crack is counted in each image. Using this technique, we observed an increase in glide rates prior to avalanche release. Since the field site is located very close to the town of Davos, the seismic data was very noisy. Nevertheless, the accelerated snow gliding observed in the time-lapse images coincided with increased seismic activity. Overall, these results show that a combination of time-lapse photography with seismic monitoring could provide valuable insight into glide avalanche release. Recordings of the heat flux plates show that the energy input from the soil is fairly small and constant throughout the observed period. The results suggest that ground heat flux is a minor contributor to the water production at the snow-soil interface. Instead, the presence of water at the base of the snowpack is probably due to a strong hydraulic pressure gradient at the snow-soil interface.

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

NASA Astrophysics Data System (ADS)

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 intermediate users under similar avalanche conditions, demonstrating different terrain choice and use as a function of experience rather than hazard level.

Snow avalanche activity in the High Tatras Mountains: new data achieved by means of dendrogeomorphic methods

NASA Astrophysics Data System (ADS)

Tichavsky, R.

2016-12-01

The High Tatras Mountains are permanently affected by the occurrence of hazardous geomorphic processes. Snow avalanches represent a common hazard that threatens the infrastructure and humans living and visiting the mountains. So far, the spatio-temporal reconstruction of snow avalanche histories was based only on existing archival records, orthophoto interpretation and lichenometric dating in the High Tatras Mountains. Dendrogeomorphic methods allow for the intra-seasonal dating of scars on tree stems and branches and have been broadly used for the dating of snow avalanche events all over the world. We extracted the increment cores and cross sections from 189 individuals of Pinus mugo var. mugo growing on four tali in the Great Cold Valley and dated all the past scars that could correspond with the winter to early spring occurrence of snow avalanches. The dating was supported by the visual analysis of three orthophoto images from 2004, 2009 and 2014. In total, nineteen event years of snow avalanches (10 certain events, and 9 probable events) were identified since 1959. Historical archives provided evidence only for nine event years since 1987, and three of them were confirmed dendrogeomorphically. Geomorphic effect of recent snow avalanches identified by the spatial distribution of scarred trees in individual years corresponds with the extent of events visible from the orthophotos. We can confirm higher frequency of snow avalanche events since 1980s (17 out of 19 events) and significant increase during the last ten years. The future expected climatic changes associated with the changes in temperature and precipitation regime could significantly influence on the frequency of snow avalanches. Therefore, our results can become the starting line for more extensive dendrogeomorphic survey in the High Tatras Mountains in order to create a catalogue of all natural hazards for the future prediction and modelling of these phenomena in context of environmental changes.

Cycling excitation process: An ultra efficient and quiet signal amplification mechanism in semiconductor

DOE Office of Scientific and Technical Information (OSTI.GOV)

Liu, Yu-Hsin; Yan, Lujiang; Zhang, Alex Ce

2015-08-03

Signal amplification, performed by transistor amplifiers with its merit rated by the efficiency and noise characteristics, is ubiquitous in all electronic systems. Because of transistor thermal noise, an intrinsic signal amplification mechanism, impact ionization was sought after to complement the limits of transistor amplifiers. However, due to the high operation voltage (30-200 V typically), low power efficiency, limited scalability, and, above all, rapidly increasing excess noise with amplification factor, impact ionization has been out of favor for most electronic systems except for a few applications such as avalanche photodetectors and single-photon Geiger detectors. Here, we report an internal signal amplification mechanismmore » based on the principle of the phonon-assisted cycling excitation process (CEP). Si devices using this concept show ultrahigh gain, low operation voltage, CMOS compatibility, and, above all, quantum limit noise performance that is 30 times lower than devices using impact ionization. Established on a unique physical effect of attractive properties, CEP-based devices can potentially revolutionize the fields of semiconductor electronics.« less

Drainage evolution in the debris avalanche deposits near Mount Saint Helens, Washington

NASA Technical Reports Server (NTRS)

Beach, G. L.; Dzurisin, D.

1984-01-01

The 18 May 1980 eruption of Mount St. Helens was initiated by a massive rockslide-debris avalanche which completely transformed the upper 25 km of the North Fork Toutle River valley. The debris was generated by one of the largest gravitational mass movements ever recorded on Earth. Moving at an average velocity of 35 m/s, the debris avalanche buried approximately 60 sq km of terrain to an average depth of 45 m with unconsolidated, poorly sorted volcaniclastic material, all within a period of 10 minutes. Where exposed and unaltered by subsequent lahars and pyroclastic flows, the new terrain surface was characterized predominantly by hummocks, closed depressions, and the absence of an identifiable channel network. Following emplacement of the debris avalanche, a complex interrelationship of fluvial and mass wasting processes immediately began operating to return the impacted area to an equilibrium status through the removal of material (potential energy) and re-establishment of graded conditions. In an attempt to chronicle the morphologic evolution of this unique environmental setting, a systematic series of interpretative maps of several selected areas was produced. These maps, which document the rate and character of active geomorphic processes, are discussed.

Wavelength dependence of nanosecond infrared laser-induced breakdown in water: Evidence for multiphoton initiation via an intermediate state

NASA Astrophysics Data System (ADS)

Linz, Norbert; Freidank, Sebastian; Liang, Xiao-Xuan; Vogelmann, Hannes; Trickl, Thomas; Vogel, Alfred

2015-04-01

Investigation of the wavelength dependence (725-1025 nm) of the threshold for nanosecond optical breakdown in water revealed steps consistent with breakdown initiation by multiphoton ionization, with an initiation energy of about 6.6 eV. This value is considerably smaller than the autoionization threshold of about 9.5 eV, which can be regarded as band gap relevant for avalanche ionization. Breakdown initiation is likely to occur via excitation of a valence band electron into a solvated state, followed by rapid excitation into the conduction band. Theoretical analysis based on these assumptions suggests that the seed electron density required for initiating avalanche ionization amounts to 2.5 ×1015c m-3 at 725 nm and drops to 1.1 ×1012c m-3 at 1025 nm. These results demand changes of future breakdown modeling for water, including the use of a larger band gap than previously employed, the introduction of an intermediate energy level for initiation, and consideration of the wavelength dependence of seed electron density.

Modeling a glacial lake outburst flood process chain: the case of Lake Palcacocha and Huaraz, Peru

NASA Astrophysics Data System (ADS)

Somos-Valenzuela, Marcelo A.; Chisolm, Rachel E.; Rivas, Denny S.; Portocarrero, Cesar; McKinney, Daene C.

2016-07-01

One of the consequences of recent glacier recession in the Cordillera Blanca, Peru, is the risk of glacial lake outburst floods (GLOFs) from lakes that have formed at the base of retreating glaciers. GLOFs are often triggered by avalanches falling into glacial lakes, initiating a chain of processes that may culminate in significant inundation and destruction downstream. This paper presents simulations of all of the processes involved in a potential GLOF originating from Lake Palcacocha, the source of a previously catastrophic GLOF on 13 December 1941, killing about 1800 people in the city of Huaraz, Peru. The chain of processes simulated here includes (1) avalanches above the lake; (2) lake dynamics resulting from the avalanche impact, including wave generation, propagation, and run-up across lakes; (3) terminal moraine overtopping and dynamic moraine erosion simulations to determine the possibility of breaching; (4) flood propagation along downstream valleys; and (5) inundation of populated areas. The results of each process feed into simulations of subsequent processes in the chain, finally resulting in estimates of inundation in the city of Huaraz. The results of the inundation simulations were converted into flood intensity and preliminary hazard maps (based on an intensity-likelihood matrix) that may be useful for city planning and regulation. Three avalanche events with volumes ranging from 0.5 to 3 × 106 m3 were simulated, and two scenarios of 15 and 30 m lake lowering were simulated to assess the potential of mitigating the hazard level in Huaraz. For all three avalanche events, three-dimensional hydrodynamic models show large waves generated in the lake from the impact resulting in overtopping of the damming moraine. Despite very high discharge rates (up to 63.4 × 103 m3 s-1), the erosion from the overtopping wave did not result in failure of the damming moraine when simulated with a hydro-morphodynamic model using excessively conservative soil characteristics that provide very little erosion resistance. With the current lake level, all three avalanche events result in inundation in Huaraz due to wave overtopping, and the resulting preliminary hazard map shows a total affected area of 2.01 km2, most of which is in the high hazard category. Lowering the lake has the potential to reduce the affected area by up to 35 %, resulting in a smaller portion of the inundated area in the high hazard category.

Development of an integrated four-channel fast avalanche-photodiode detector system with nanosecond time resolution

NASA Astrophysics Data System (ADS)

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.

Energy pumping in electrical circuits under avalanche noise.

PubMed

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.

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

NASA Astrophysics Data System (ADS)

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.

The extreme mobility of debris avalanches: A new model of transport mechanism

NASA Astrophysics Data System (ADS)

Perinotto, Hélène; Schneider, Jean-Luc; Bachèlery, Patrick; Le Bourdonnec, François-Xavier; Famin, Vincent; Michon, Laurent

2015-12-01

Large rockslide-debris avalanches, resulting from flank collapses that shape volcanoes and mountains on Earth and other object of the solar system, are rapid and dangerous gravity-driven granular flows that travel abnormal distances. During the last 50 years, numerous physical models have been put forward to explain their extreme mobility. The principal models are based on fluidization, lubrication, or dynamic disintegration. However, these processes remain poorly constrained. To identify precisely the transport mechanisms during debris avalanches, we examined morphometric (fractal dimension and circularity), grain size, and exoscopic characteristics of the various types of particles (clasts and matrix) from volcanic debris avalanche deposits of La Réunion Island (Indian Ocean). From these data we demonstrate for the first time that syn-transport dynamic disintegration continuously operates with the increasing runout distance from the source down to a grinding limit of 500 µm. Below this limit, the particle size reduction exclusively results from their attrition by frictional interactions. Consequently, the exceptional mobility of debris avalanches may be explained by the combined effect of elastic energy release during the dynamic disintegration of the larger clasts and frictional reduction within the matrix due to interactions between the finer particles.

Research on the discharge characteristics for water tree in crosslinked polyethylene cable based on plasma-chemical model

NASA Astrophysics Data System (ADS)

Fan, Yang; Qi, Yang; Bing, Gao; Rong, Xia; Yanjie, Le; Iroegbu, Paul Ikechukwu

2018-03-01

Water tree is the predominant defect in high-voltage crosslinked polyethylene cables. The microscopic mechanism in the discharge process is not fully understood; hence, a drawback is created towards an effective method to evaluate the insulation status. In order to investigate the growth of water tree, a plasma-chemical model is developed. The dynamic characteristics of the discharge process including voltage waveform, current waveform, electron density, electric potential, and electric field intensity are analyzed. Our results show that the distorted electric field is the predominant contributing factor of electron avalanche formation, which inevitably leads to the formation of pulse current. In addition, it is found that characteristic parameters such as the pulse width and pulse number have a great relevance to the length of water tree. Accordingly, the growth of water tree can be divided into the initial stage, development stage, and pre-breakdown stage, which provides a reference for evaluating the deteriorated stages of crosslinked polyethylene cables.

1/f noise and plastic deformation

NASA Astrophysics Data System (ADS)

Laurson, Lasse

2006-11-01

There is increasing evidence from experiments that plastic deformation in the micro- and meso- scopic scales is an intermittent and heterogeneous process, consisting of avalanches of dislocation activity with a power law distribution of sizes. This has been also discovered in many simulation studies of simplified models. In addition to direct studies of the avalanche statistics, interesting information about the dynamics of the system can be obtained by studying the spectral proper- ties of some associated time series, such as the acoustic emission amplitude in an experiment. We discuss the generic aspects concerning the power spectra of such signals, e.g. the possibility of relating the exponent of the power spectrum to the avalanche exponents of the (dislocation) system.

Avalanche ecology and large magnitude avalanche events: Glacier National Park, Montana, USA

USGS Publications Warehouse

Fagre, Daniel B.; Peitzsch, Erich H.

2010-01-01

Large magnitude snow avalanches play an important role ecologically in terms of wildlife habitat, vegetation diversity, and sediment transport within a watershed. Ecological effects from these infrequent avalanches can last for decades. Understanding the frequency of such large magnitude avalanches is also critical to avalanche forecasting for the Going-to-the-Sun Road (GTSR). In January 2009, a large magnitude avalanche cycle occurred in and around Glacier National Park, Montana. The study site is the Little Granite avalanche path located along the GTSR. The study is designed to quantify change in vegetative cover immediately after a large magnitude event and document ecological response over a multi-year period. GPS field mapping was completed to determine the redefined perimeter of the avalanche path. Vegetation was inventoried using modified U.S. Forest Service Forest Inventory and Analysis plots, cross sections were taken from over 100 dead trees throughout the avalanche path, and an avalanche chronology was developed. Initial results indicate that the perimeter of this path was expanded by 30%. The avalanche travelled approximately 1200 vertical meters and 3 linear kilometers. Stands of large conifers as old as 150 years were decimated by the avalanche, causing a shift in dominant vegetation types in many parts of the avalanche path. Woody debris is a major ground cover up to 3 m in depth on lower portions of the avalanche path and will likely affect tree regrowth. Monitoring and measuring the post-avalanche vegetation recovery of this particular avalanche path provides a unique dataset for determining the ecological role of avalanches in mountain landscapes.

Investigation of field induced trapping on floating gates

NASA Technical Reports Server (NTRS)

Gosney, W. M.

1975-01-01

The development of a technology for building electrically alterable read only memories (EAROMs) or reprogrammable read only memories (RPROMs) using a single level metal gate p channel MOS process with all conventional processing steps is outlined. Nonvolatile storage of data is achieved by the use of charged floating gate electrodes. The floating gates are charged by avalanche injection of hot electrodes through gate oxide, and discharged by avalanche injection of hot holes through gate oxide. Three extra diffusion and patterning steps are all that is required to convert a standard p channel MOS process into a nonvolatile memory process. For identification, this nonvolatile memory technology was given the descriptive acronym DIFMOS which stands for Dual Injector, Floating gate MOS.

Analysis of InP-based single photon avalanche diodes based on a single recess-etching process

NASA Astrophysics Data System (ADS)

Lee, Kiwon

2018-04-01

Effects of the different etching techniques have been investigated by analyzing electrical and optical characteristics of two-types of single-diffused single photon avalanche diodes (SPADs). The fabricated two-types of SPADs have no diffusion depth variation by using a single diffusion process at the same time. The dry-etched SPADs show higher temperature dependence of a breakdown voltage, larger dark-count-rate (DCR), and lower photon-detection-efficiency (PDE) than those of the wet-etched SPADs due to plasma-induced damage of dry-etching process. The results show that the dry etching damages can more significantly affect the performance of the SPADs based on a single recess-etching process.

Response of CMS avalanche photo-diodes to low energy neutrons

NASA Astrophysics Data System (ADS)

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.

Apparatus for time-resolved and energy-resolved measurement of internal conversion electron emission induced by nuclear resonant excitation with synchrotron radiation

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kawauchi, Taizo; Matsumoto, Masuaki; Fukutani, Katsuyuki

2007-01-15

A high-energy and large-object-spot type cylindrical mirror analyzer (CMA) was constructed with the aid of electron trajectory simulations. By adopting a particular shape for the outer cylinder, an energy resolution of 7% was achieved without guide rings as used in conventional CMAs. Combined with an avalanche photodiode as an electron detector, the K-shell internal conversion electrons were successfully measured under irradiation of synchrotron radiation at 14.4 keV in an energy-resolved and time-resolved manner.

Electronic Transport Behaviors due to Charge Density Waves in Ni-Nb-Zr-H Glassy Alloys

NASA Astrophysics Data System (ADS)

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.

Performance of InGaAs short wave infrared avalanche photodetector for low flux imaging

NASA Astrophysics Data System (ADS)

Singh, Anand; Pal, Ravinder

2017-11-01

Opto-electronic performance of the InGaAs/i-InGaAs/InP short wavelength infrared focal plane array suitable for high resolution imaging under low flux conditions and ranging is presented. More than 85% quantum efficiency is achieved in the optimized detector structure. Isotropic nature of the wet etching process poses a challenge in maintaining the required control in the small pitch high density detector array. Etching process is developed to achieve low dark current density of 1 nA/cm2 in the detector array with 25 µm pitch at 298 K. Noise equivalent photon performance less than one is achievable showing single photon detection capability. The reported photodiode with low photon flux is suitable for active cum passive imaging, optical information processing and quantum computing applications.

Test of the HAPD light sensor for the Belle II Aerogel RICH

NASA Astrophysics Data System (ADS)

Yusa, Y.; Adachi, I.; Dolenec, R.; Hayata, K.; Iori, S.; Iwata, S.; Kakuno, H.; Kataura, R.; Kawai, H.; Kindo, H.; Kobayashi, T.; Korpar, S.; Krizan, P.; Kumita, T.; Mrvar, M.; Nishida, S.; Ogawa, K.; Pestotnik, R.; Santelj, L.; Sumiyoshi, T.; Tabata, M.; Yonenaga, M.

2017-12-01

The Aerogel Ring-Imaging Cherenkov detector (ARICH) is being installed in the endcap region of Belle II spectrometer to identify particles from B meson decays by detecting the Cherenkov ring image from aerogel radiators. To detect single photons, high-sensitive photon detector which has wide effective area (∼70 mm × 70 mm), a Hybrid Avalanche Photo Detector (HAPD), has been developed in a collaboration with Hamamatsu K.K. The HAPD consists of hybrid structure of a vacuum tube and an avalanche photodiode (APD). It can be operated in 1.5 T magnetic field of the spectrometer and withstands the radiation levels expected in the Belle II experiment. There are two steps of electric pulse amplification: acceleration of photo-electron in electric field in the vacuum tube part and electron avalanche in the APD part resulting in total gain of order 105. For the ARICH, we use 420 HAPDs in total. Before installing them, we performed quality assessment studies such as measurements of dark current, noise level, signal-to-noise ratio and two-dimensional scan with laser illumination. We also measured quantum efficiency of the photocathode. During the HAPD performance tests in the magnetic field, we observed very large signal pulses which cause long dead time of the readout electronics in some of the HAPDs. We have carried out a number of studies to understand this phenomenon, and have found a way to mitigate it and suppress the degradation of the ARICH performance. In this report, we will show a summary of the HAPD performance and quality assessment measurements including validation in the magnetic field for all of the HAPDs manufactured for the ARICH in the Belle II.

Kinetic and fluid descriptions of charged particle swarms in gases and nonpolar fluids: Theory and applications

NASA Astrophysics Data System (ADS)

Dujko, Sasa

2016-09-01

In this work we review the progress achieved over the last few decades in the fundamental kinetic theory of charged particle swarms with the focus on numerical techniques for the solution of Boltzmann's equation for electrons, as well as on the development of fluid models. We present a time-dependent multi term solution of Boltzmann's equation valid for electrons and positrons in varying configurations of electric and magnetic fields. The capacity of a theory and associated computer code will be illustrated by considering the heating mechanisms for electrons in radio-frequency electric and magnetic fields in a collision-dominated regime under conditions when electron transport is greatly affected by non-conservative collisions. The kinetic theory for solving the Boltzmann equation will be followed by a fluid equation description of charged particle swarms in both the hydrodynamic and non-hydrodynamic regimes, highlighting (i) the utility of momentum transfer theory for evaluating collisional terms in the balance equations and (ii) closure assumptions and approximations. The applications of this theory are split into three sections. First, we will present our 1.5D model of Resistive Plate Chambers (RPCs) which are used for timing and triggering purposes in many high energy physics experiments. The model is employed to study the avalanche to streamer transition in RPCs under the influence of space charge effects and photoionization. Second, we will discuss our high-order fluid model for streamer discharges. Particular emphases will be placed on the correct implementation of transport data in streamer models as well as on the evaluation of the mean-energy-dependent collision rates for electrons required as an input in the high-order fluid model. In the last segment of this work, we will present our model to study the avalanche to streamer transition in non-polar fluids. Using a Monte Carlo simulation technique we have calculated transport coefficients for electrons in liquid argon and liquid xenon. We employ the two model processes in which only momentum and only energy are exchanged to account for structure dependent coherent elastic scattering at low energies. The specific treatment of inelastic collisions in our model will be also discussed using physical arguments.

Growth and decay of runaway electrons above the critical electric field under quiescent conditions

DOE PAGES

Paz-Soldan, Carlos; Eidietis, Nicholas W.; Granetz, Robert S.; ...

2014-02-27

Extremely low density operation free of error eld penetration supports the excitation of trace-level quiescent runaway electron (RE) populations during the at-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 electricmore » eld for avalanche growth and is thus indicative of anomalous RE loss. Lastly, 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.« less

Synaptic plasticity and neuronal refractory time cause scaling behaviour of neuronal avalanches

NASA Astrophysics Data System (ADS)

Michiels van Kessenich, L.; de Arcangelis, L.; Herrmann, H. J.

2016-08-01

Neuronal avalanches measured in vitro and in vivo in different cortical networks consistently exhibit power law behaviour for the size and duration distributions with exponents typical for a mean field self-organized branching process. These exponents are also recovered in neuronal network simulations implementing various neuronal dynamics on different network topologies. They can therefore be considered a very robust feature of spontaneous neuronal activity. Interestingly, this scaling behaviour is also observed on regular lattices in finite dimensions, which raises the question about the origin of the mean field behavior observed experimentally. In this study we provide an answer to this open question by investigating the effect of activity dependent plasticity in combination with the neuronal refractory time in a neuronal network. Results show that the refractory time hinders backward avalanches forcing a directed propagation. Hebbian plastic adaptation plays the role of sculpting these directed avalanche patterns into the topology of the network slowly changing it into a branched structure where loops are marginal.

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

NASA Astrophysics Data System (ADS)

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.

Synaptic plasticity and neuronal refractory time cause scaling behaviour of neuronal avalanches.

PubMed

Michiels van Kessenich, L; de Arcangelis, L; Herrmann, H J

2016-08-18

Neuronal avalanches measured in vitro and in vivo in different cortical networks consistently exhibit power law behaviour for the size and duration distributions with exponents typical for a mean field self-organized branching process. These exponents are also recovered in neuronal network simulations implementing various neuronal dynamics on different network topologies. They can therefore be considered a very robust feature of spontaneous neuronal activity. Interestingly, this scaling behaviour is also observed on regular lattices in finite dimensions, which raises the question about the origin of the mean field behavior observed experimentally. In this study we provide an answer to this open question by investigating the effect of activity dependent plasticity in combination with the neuronal refractory time in a neuronal network. Results show that the refractory time hinders backward avalanches forcing a directed propagation. Hebbian plastic adaptation plays the role of sculpting these directed avalanche patterns into the topology of the network slowly changing it into a branched structure where loops are marginal.

Neuronal avalanches of a self-organized neural network with active-neuron-dominant structure.

PubMed

Li, Xiumin; Small, Michael

2012-06-01

Neuronal avalanche is a spontaneous neuronal activity which obeys a power-law distribution of population event sizes with an exponent of -3/2. It has been observed in the superficial layers of cortex both in vivo and in vitro. In this paper, we analyze the information transmission of a novel self-organized neural network with active-neuron-dominant structure. Neuronal avalanches can be observed in this network with appropriate input intensity. We find that the process of network learning via spike-timing dependent plasticity dramatically increases the complexity of network structure, which is finally self-organized to be active-neuron-dominant connectivity. Both the entropy of activity patterns and the complexity of their resulting post-synaptic inputs are maximized when the network dynamics are propagated as neuronal avalanches. This emergent topology is beneficial for information transmission with high efficiency and also could be responsible for the large information capacity of this network compared with alternative archetypal networks with different neural connectivity.

Single-Photon-Sensitive HgCdTe Avalanche Photodiode Detector

NASA Technical Reports Server (NTRS)

Huntington, Andrew

2013-01-01

The purpose of this program was to develop single-photon-sensitive short-wavelength infrared (SWIR) and mid-wavelength infrared (MWIR) avalanche photodiode (APD) receivers based on linear-mode HgCdTe APDs, for application by NASA in light detection and ranging (lidar) sensors. Linear-mode photon-counting APDs are desired for lidar because they have a shorter pixel dead time than Geiger APDs, and can detect sequential pulse returns from multiple objects that are closely spaced in range. Linear-mode APDs can also measure photon number, which Geiger APDs cannot, adding an extra dimension to lidar scene data for multi-photon returns. High-gain APDs with low multiplication noise are required for efficient linear-mode detection of single photons because of APD gain statistics -- a low-excess-noise APD will generate detectible current pulses from single photon input at a much higher rate of occurrence than will a noisy APD operated at the same average gain. MWIR and LWIR electron-avalanche HgCdTe APDs have been shown to operate in linear mode at high average avalanche gain (M > 1000) without excess multiplication noise (F = 1), and are therefore very good candidates for linear-mode photon counting. However, detectors fashioned from these narrow-bandgap alloys require aggressive cooling to control thermal dark current. Wider-bandgap SWIR HgCdTe APDs were investigated in this program as a strategy to reduce detector cooling requirements.

A comparison between spectra of runaway electron beams in SF6 and air

NASA Astrophysics Data System (ADS)

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.

A debris avalanche at Süphan stratovolcano (Turkey) and implications for hazard evaluation

NASA Astrophysics Data System (ADS)

Özdemir, Yavuz; Akkaya, İsmail; Oyan, Vural; Kelfoun, Karim

2016-02-01

The Quaternary Süphan debris avalanche deposit is located in Eastern Anatolia, Turkey. The avalanche formed by the sector collapse of a major stratovolcano towards the north, possibly during a single catastrophic event. The deposit has an estimated volume of 4 km3 and ran out over 25 km to cover an area of approximately 200 km2. Products of the collapse are overlain by younger eruptive units from the Süphan volcano. We have tested the numerical code VolcFlow to first reproduce the emplacement of the Quaternary Süphan debris avalanche and then to develop a hazard assessment for potential future sector collapses and subsequent emplacement of debris avalanches and associated tsunami. The numerical model captures the main features of the propagation process, including travel distance, lateral spread, and run up. The best fit obtained for the existing flow has a constant retarding stress of 50 kPa and a collapse scar volume of 4 km3. Analysis of potential future collapse scenarios reveals that northern sector debris avalanches (up to 6 km3) could affect several towns. In the case of a sector collapse towards the south, a tsunami will reach the city of Van and several of the biggest towns on the southern shoreline of Lake Van. Cities most affected by the larger amplitude waves would be Van, Edremit, Gevaş, Tatvan, and, to a lesser extent, Erciş, with wave amplitudes (first waves after the onset of the collapse) between 8 and 10 m.

Characterizing the nature and variability of avalanche hazard in western Canada

NASA Astrophysics Data System (ADS)

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.

Electrophysical and optophysical properties of air ionized by a short pulse of fast electrons

NASA Astrophysics Data System (ADS)

Vagin, Iu. P.; Stal', N. L.; Khokhlov, V. D.; Chernoiarskii, A. A.

A method for solving the nonstationary kinetic equation of electron deceleration is developed which is based on the multigroup approximation. The electron distribution function in air ionized by nonstationary sources of primary electrons is determined, and the avalanche formation of secondary electrons is considered. Theoretical and experimental results are presented on the time dependence of the air luminescence intensity in two spectral intervals, one including the 391.4 nm N2(+) band and the other including the 337.1 nm N2 band, for different values of gas pressure under the effect of a short beam of electrons with energies of 100 keV.

Real-space observation of magnetic excitations and avalanche behavior in artificial quasicrystal lattices

DOE PAGES

Brajuskovic, V.; Barrows, F.; Phatak, C.; ...

2016-10-03

Artificial spin ice lattices have emerged as model systems for studying magnetic frustration in recent years. Most work to date has looked at periodic artificial spin ice lattices. In this paper, we observe frustration effects in quasicrystal artificial spin ice lattices that lack translational symmetry and contain vertices with different numbers of interacting elements. We find that as the lattice state changes following demagnetizing and annealing, specific vertex motifs retain low-energy configurations, which excites other motifs into higher energy configurations. In addition, we find that unlike the magnetization reversal process for periodic artificial spin ice lattices, which occurs through 1Dmore » avalanches, quasicrystal lattices undergo reversal through a dendritic 2D avalanche mechanism.« less

Real-space observation of magnetic excitations and avalanche behavior in artificial quasicrystal lattices

DOE Office of Scientific and Technical Information (OSTI.GOV)

Brajuskovic, V.; Barrows, F.; Phatak, C.

Artificial spin ice lattices have emerged as model systems for studying magnetic frustration in recent years. Most work to date has looked at periodic artificial spin ice lattices. In this paper, we observe frustration effects in quasicrystal artificial spin ice lattices that lack translational symmetry and contain vertices with different numbers of interacting elements. We find that as the lattice state changes following demagnetizing and annealing, specific vertex motifs retain low-energy configurations, which excites other motifs into higher energy configurations. In addition, we find that unlike the magnetization reversal process for periodic artificial spin ice lattices, which occurs through 1Dmore » avalanches, quasicrystal lattices undergo reversal through a dendritic 2D avalanche mechanism.« less

Lifetime of Bubble Rafts: Cooperativity and Avalanches

NASA Astrophysics Data System (ADS)

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.

Lifetime of bubble rafts: cooperativity and avalanches.

PubMed

Ritacco, Hernán; Kiefer, Flavien; Langevin, Dominique

2007-06-15

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.

Estimation of NOx Production from Terrestrial Gamma-ray Flashes

NASA Astrophysics Data System (ADS)

Cramer, E. S.; Briggs, M. S.; Liu, N.; Mailyan, B.; Rassoul, H.; Dwyer, J. R.

2016-12-01

The motivation of this work is to understand the effects of TGFs on the ozone layer. One of the main ozone-destroying mechanisms is the production of NOx in the stratospheric region. We first review the mechanisms for NOx production in this region, specifically looking at the global rate produced by lightning. Terrestrial Gamma-ray Flashes, with runaway electron avalanches and the subsequent bremsstrahlung gamma rays, produce atmospheric ionization at all altitudes of the atmosphere. TGFs might have a greater impact on the ozone concentration in the stratosphere since they directly produce ionization and thus NOx in the ozone layer. In order to study the effect from TGFs, we use the runaway electron avalanche model (REAM) to simulate a typical TGF. The photons are then transported through Earth's atmosphere, where they deposit some of their energy as ionization in the ozone layer. We then calculate the number of NOx molecules produced by considering the average energy required to produce one electron-ion pair (W = 35 eV). The W factor has been experimentally quantified and is constant for various types of radiation and over large energy ranges and electric fields. Finally, the effect of TGF NOx production is estimated using the global annual rate of TGFs.

Quaternary gravitational morpho-genesis of Central Apennines (Italy): Insights from the Mt. Genzana case history

NASA Astrophysics Data System (ADS)

Esposito, C.; Bianchi-Fasani, G.; Martino, S.; Scarascia-Mugnozza, G.

2013-10-01

This paper focuses on a study aimed at defining the role of geological-structural setting and Quaternary morpho-structural evolution on the onset and development of a deep-seated gravitational slope deformation which affects the western slope of Mt. Genzana ridge (Central Apennines, Italy). This case history is particularly significant as it comprises several aspects of such gravitational processes both in general terms and with particular reference to the Apennines. In fact: i) the morpho-structural setting is representative of widespread conditions in Central Apennines; ii) the deforming slope partially evolved in a large rockslide-avalanche; iii) the deformational process provides evidence of an ongoing state of activity; iv) the rockslide-avalanche debris formed a stable natural dam, thus implying significant variations in the morphologic, hydraulic and hydrogeological setting; v) the gravitational deformation as well as the rockslide-avalanche reveal a strong structural control. The main study activities were addressed to define a detailed geological model of the gravity-driven process, by means of geological, structural, geomorphological and geomechanical surveys. As a result, a robust hypothesis about the kinematics of the process was possible, with particular reference to the identification of geological-structural constraints. The process, in fact, involves a specific section of the slope exactly where a dextral transtensional structure is present, thus implying local structural conditions that favor sliding processes: the rock mass is intensively jointed by high angle discontinuity sets and the bedding attitude is quite parallel to the slope angle. Within this frame the gravitational process can be classified as a structurally constrained translational slide, locally evolved into a rockslide-avalanche. The activation of such a deformation can be in its turn related to the Quaternary morphological evolution of the area, which was affected by a significant topographic stress increase, testified by stratigraphic and morphologic evidence.

Determination of the excess noise of avalanche photodiodes integrated in 0.35-μm CMOS technologies

NASA Astrophysics Data System (ADS)

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.

Gaps between avalanches in one-dimensional random-field Ising models

NASA Astrophysics Data System (ADS)

Nampoothiri, Jishnu N.; Ramola, Kabir; Sabhapandit, Sanjib; Chakraborty, Bulbul

2017-09-01

We analyze the statistics of gaps (Δ H ) between successive avalanches in one-dimensional random-field Ising models (RFIMs) in an external field H at zero temperature. In the first part of the paper we study the nearest-neighbor ferromagnetic RFIM. We map the sequence of avalanches in this system to a nonhomogeneous Poisson process with an H -dependent rate ρ (H ) . We use this to analytically compute the distribution of gaps P (Δ H ) between avalanches as the field is increased monotonically from -∞ to +∞ . We show that P (Δ H ) tends to a constant C (R ) as Δ H →0+ , which displays a nontrivial behavior with the strength of disorder R . We verify our predictions with numerical simulations. In the second part of the paper, motivated by avalanche gap distributions in driven disordered amorphous solids, we study a long-range antiferromagnetic RFIM. This model displays a gapped behavior P (Δ H )=0 up to a system size dependent offset value Δ Hoff , and P (Δ H ) ˜(ΔH -Δ Hoff) θ as Δ H →Hoff+ . We perform numerical simulations on this model and determine θ ≈0.95 (5 ) . We also discuss mechanisms which would lead to a nonzero exponent θ for general spin models with quenched random fields.

Criticality in the brain

NASA Astrophysics Data System (ADS)

de Arcangelis, L.; Lombardi, F.; Herrmann, H. J.

2014-03-01

Spontaneous brain activity has been recently characterized by avalanche dynamics with critical features for systems in vitro and in vivo. In this contribution we present a review of experimental results on neuronal avalanches in cortex slices, together with numerical results from a neuronal model implementing several physiological properties of living neurons. Numerical data reproduce experimental results for avalanche statistics. The temporal organization of avalanches can be characterized by the distribution of waiting times between successive avalanches. Experimental measurements exhibit a non-monotonic behaviour, not usually found in other natural processes. Numerical simulations provide evidence that this behaviour is a consequence of the alternation between states of high and low activity, leading to a balance between excitation and inhibition controlled by a single parameter. During these periods both the single neuron state and the network excitability level, keeping memory of past activity, are tuned by homoeostatic mechanisms. Interestingly, the same homoeostatic balance is detected for neuronal activity at the scale of the whole brain. We finally review 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 and the learning dynamics exhibits universal features as a function of the strength of plastic adaptation. Any rule could be learned provided that the plastic adaptation is sufficiently slow.

Assessing the importance of terrain parameters on glide avalanche release

NASA Astrophysics Data System (ADS)

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 avalanches failed as cohesive slabs on this bedrock surface. Consequently, surface roughness proved to be a useful descriptive variable to discriminate between slopes that avalanched and those that did not. Annual 'repeat offender' glide avalanche paths were characterized by smooth outcropping rock plates with stratification planes parallel to the slope. Combined with aspect these repeat offenders were also members of the highest glide category. Using this understanding of the role of topographic parameters on glide avalanche activity, a spatial terrain based model was developed to identify other areas with high glide avalanche potential outside of our immediate observation area.

Assessing the importance of terrain parameters on glide avalanche release

USGS Publications Warehouse

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 avalanches failed as cohesive slabs on this bedrock surface. Consequently, surface roughness proved to be a useful descriptive variable to discriminate between slopes that avalanched and those that did not. Annual 'repeat offender' glide avalanche paths were characterized by smooth outcropping rock plates with stratification planes parallel to the slope. Combined with aspect these repeat offenders were also members of the highest glide category. Using this understanding of the role of topographic parameters on glide avalanche activity, a spatial terrain based model was developed to identify other areas with high glide avalanche potential outside of our immediate observation area.

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

USGS Publications Warehouse

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.

Mechanisms of self-organized criticality in social processes of knowledge creation

NASA Astrophysics Data System (ADS)

Tadić, Bosiljka; Dankulov, Marija Mitrović; Melnik, Roderick

2017-09-01

In online social dynamics, a robust scale invariance appears as a key feature of collaborative efforts that lead to new social value. The underlying empirical data thus offers a unique opportunity to study the origin of self-organized criticality (SOC) in social systems. In contrast to physical systems in the laboratory, various human attributes of the actors play an essential role in the process along with the contents (cognitive, emotional) of the communicated artifacts. As a prototypical example, we consider the social endeavor of knowledge creation via Questions and Answers (Q&A). Using a large empirical data set from one of such Q&A sites and theoretical modeling, we reveal fundamental characteristics of SOC by investigating the temporal correlations at all scales and the role of cognitive contents to the avalanches of the knowledge-creation process. Our analysis shows that the universal social dynamics with power-law inhomogeneities of the actions and delay times provides the primary mechanism for self-tuning towards the critical state; it leads to the long-range correlations and the event clustering in response to the external driving by the arrival of new users. In addition, the involved cognitive contents (systematically annotated in the data and observed in the model) exert important constraints that identify unique classes of the knowledge-creation avalanches. Specifically, besides determining a fine structure of the developing knowledge networks, they affect the values of scaling exponents and the geometry of large avalanches and shape the multifractal spectrum. Furthermore, we find that the level of the activity of the communities that share the knowledge correlates with the fluctuations of the innovation rate, implying that the increase of innovation may serve as the active principle of self-organization. To identify relevant parameters and unravel the role of the network evolution underlying the process in the social system under consideration, we compare the social avalanches to the avalanche sequences occurring in the field-driven physical model of disordered solids, where the factors contributing to the collective dynamics are better understood.

Mechanisms of self-organized criticality in social processes of knowledge creation.

PubMed

Tadić, Bosiljka; Dankulov, Marija Mitrović; Melnik, Roderick

2017-09-01

In online social dynamics, a robust scale invariance appears as a key feature of collaborative efforts that lead to new social value. The underlying empirical data thus offers a unique opportunity to study the origin of self-organized criticality (SOC) in social systems. In contrast to physical systems in the laboratory, various human attributes of the actors play an essential role in the process along with the contents (cognitive, emotional) of the communicated artifacts. As a prototypical example, we consider the social endeavor of knowledge creation via Questions and Answers (Q&A). Using a large empirical data set from one of such Q&A sites and theoretical modeling, we reveal fundamental characteristics of SOC by investigating the temporal correlations at all scales and the role of cognitive contents to the avalanches of the knowledge-creation process. Our analysis shows that the universal social dynamics with power-law inhomogeneities of the actions and delay times provides the primary mechanism for self-tuning towards the critical state; it leads to the long-range correlations and the event clustering in response to the external driving by the arrival of new users. In addition, the involved cognitive contents (systematically annotated in the data and observed in the model) exert important constraints that identify unique classes of the knowledge-creation avalanches. Specifically, besides determining a fine structure of the developing knowledge networks, they affect the values of scaling exponents and the geometry of large avalanches and shape the multifractal spectrum. Furthermore, we find that the level of the activity of the communities that share the knowledge correlates with the fluctuations of the innovation rate, implying that the increase of innovation may serve as the active principle of self-organization. To identify relevant parameters and unravel the role of the network evolution underlying the process in the social system under consideration, we compare the social avalanches to the avalanche sequences occurring in the field-driven physical model of disordered solids, where the factors contributing to the collective dynamics are better understood.

A 1.5k x 1.5k class photon counting HgCdTe linear avalanche photo-diode array for low background space astronomy in the 1-5micron infrared

NASA Astrophysics Data System (ADS)

Hall, Donald

Under a current award, NASA NNX 13AC13G "EXTENDING THE ASTRONOMICAL APPLICATION OF PHOTON COUNTING HgCdTe LINEAR AVALANCHE PHOTODIODE ARRAYS TO LOW BACKGROUND SPACE OBSERVATIONS" UH has used Selex SAPHIRA 320 x 256 MOVPE L-APD HgCdTe arrays developed for Adaptive Optics (AO) wavefront (WF) sensing to investigate the potential of this technology for low background space astronomy applications. After suppressing readout integrated circuit (ROIC) glow, we have placed upper limits on gain normalized dark current of 0.01 e-/sec at up to 8 volts avalanche bias, corresponding to avalanche gain of 5, and have operated with avalanche gains of up to several hundred at higher bias. We have also demonstrated detection of individual photon events. The proposed investigation would scale the format to 1536 x 1536 at 12um (the largest achievable in a standard reticule without requiring stitching) while incorporating reference pixels required at these low dark current levels. The primary objective is to develop, produce and characterize a 1.5k x 1.5k at 12um pitch MOVPE HgCdTe L-APD array, with nearly 30 times the pixel count of the 320 x 256 SAPHIRA, optimized for low background space astronomy. This will involve: 1) Selex design of a 1.5k x 1.5k at 12um pitch ROIC optimized for low background operation, silicon wafer fabrication at the German XFab foundry in 0.35 um 3V3 process and dicing/test at Selex, 2) provision by GL Scientific of a 3-side close-buttable carrier building from the heritage of the HAWAII xRG family, 3) Selex development and fabrication of 1.5k x 1.5k at 12 um pitch MOVPE HgCdTe L-APD detector arrays optimized for low background applications, 4) hybridization, packaging into a sensor chip assembly (SCA) with initial characterization by Selex and, 5) comprehensive characterization of low background performance, both in the laboratory and at ground based telescopes, by UH. The ultimate goal is to produce and eventually market a large format array, the L-APD equivalent of the Teledyne H1RG and H2RG, able to achieve sub-electron read noise and count 1 - 5 um photons with high quantum efficiency and low dark count rate while preserving their Poisson statistics and noise.

Application of LANDSAT data to delimitation of avalanche hazards in Montane Colorado

NASA Technical Reports Server (NTRS)

Knepper, D. H., Jr. (Principal Investigator)

1977-01-01

The author has identified the following significant results. Many avalanche hazard zones can be identified on LANDSAT imagery, but not consistently over a large region. Therefore, regional avalanche hazard mapping, using LANDSAT imagery, must draw on additional sources of information. A method was devised that depicts three levels of avalanche hazards according to three corresponding levels of certainty that active avalanches occur. The lowest level, potential avalanche hazards, was defined by delineating slopes steep enough to support avalanches at elevations where snowfall was likely to be sufficient to produce a thick snowpack. The intermediate level of avalanche hazard was interpreted as avalanche hazard zones. These zones have direct and indirect indicators of active avalanche activity and were interpreted from LANDSAT imagery. The highest level of known or active avalanche hazards was compiled from existing maps. Some landslides in Colorado were identified and, to a degree, delimited on LANDSAT imagery, but the conditions of their identification were highly variable. Because of local topographic, geologic, structural, and vegetational variations, there was no unique landslide spectral appearance.

Meteorological variables associated with deep slab avalanches on persistent weak layers

USGS Publications Warehouse

Marienthal, Alex; Hendrikx, Jordy; Birkeland, Karl; Irvine, Kathryn M.

2014-01-01

Deep slab avalanches are a particularly challenging avalanche forecasting problem. These avalanches are typically difficult to trigger, yet when they are triggered they tend to propagate far and result in large and destructive avalanches. For this work we define deep slab avalanches as those that fail on persistent weak layers deeper than 0.9m (3 feet), and that occur after February 1st. We utilized a 44-year record of avalanche control and meteorological data from Bridger Bowl Ski Area to test the usefulness of meteorological variables for predicting deep slab avalanches. As in previous studies, we used data from the days preceding deep slab cycles, but we also considered meteorological metrics over the early months of the season. We utilized classification trees for our analyses. Our results showed warmer temperatures in the prior twenty-four hours and more loading over the seven days before days with deep slab avalanches on persistent weak layers. In line with previous research, extended periods of above freezing temperatures led to days with deep wet slab avalanches on persistent weak layers. Seasons with either dry or wet avalanches on deep persistent weak layers typically had drier early months, and often had some significant snow depth prior to those dry months. This paper provides insights for ski patrollers, guides, and avalanche forecasters who struggle to forecast deep slab avalanches on persistent weak layers late in the season.

Two dimensional numerical analysis of snow avalanche interaction with structures

NASA Astrophysics Data System (ADS)

Bovet, Eloïse; Chiaia, Bernardino; Preziosi, Luigi

2010-05-01

The purpose of this work, within the Project "DynAval - Dynamique des avalanches: départ et interactions écoulement/obstacles" - European Territorial Cooperation objective Italy - France (Alps), is to analyse the snow avalanche and structure interaction, through a numerical analysis. The avalanche behaviour, considered as an incompressible fluid, is described by a two-dimensional, in the avalanche slope, Navier-Stokes equations to which an advection equation is coupled to take into account the shape variation. The model allows to describe the velocity and the pressure at every point, representing important features for the structural design. The simulations are carried using a FEM Multiphysics software. For a such problem different analysis can be carried. Firstly, changing the obstacle shape (circle, square, triangle) and its dimension in relation to the avalanche size, the drag coefficient Cd can be evaluated. The obtained results are then compared with the values indicated by the procedures, concerning the avalanches, available in the literature. This study is realized for different Froude numbers too. Secondarily the pressure acting on the different parts of the obstacle (up-wind, down-wind, lateral) is studied. The first investigation concerns the evaluation of the Cp coefficient and on its comparison with the wind effects. The second analysis allows to evaluates, by an integration process, the total load exerted by the avalanche on the obstacle. A practical example of a building design is presented, taking into account the results of the simulations. Thirdly the study is focused on the characterization of the two dead zones created up-wind and down-wind the obstacle. The dependence of the dead zone on the obstacle characteristics, such as dimension and shape, and on the avalanche features, such as density and velocity, is analysed. The results obtained are compared with the data available in the literature concerning snow or granular material interaction with obstacle. In addition the dead zone is studied using a two dimensional model in the avalanche section too. In this way, in fact, the jet length created in the impact, for instance with a dam, can be measured and compared with the laws proposed in the literature. Fourthly the evolution in time of the pressure during the impact is investigated, showing a peak in the first times steps of the interaction. The time and the intensity of this maximum value is related with the flow and the obstacle characteristics. In conclusion, the fan of the analysis carried recovers different and very important features that represent the starting point for reliable design of the structures in avalanche-risk zones. In addition it shows the capabilities and the deficiencies of the model proposed and, finally, it introduces some aspects that will should be furtherer experimentally studied and validated.

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

NASA Astrophysics Data System (ADS)

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.

Characterization of Martian near-subsurface materials by determination of cohesion and angle of internal friction

NASA Technical Reports Server (NTRS)

Sullivan, R. J.

1992-01-01

Back-analysis (reconstruction) of the stability of thirty avalanche chutes was performed in the very limited areas where high resolution imaging overlapped with available 1:500 K topographic map coverage. A new technique was developed to incorporate the third dimension (width) of an avalanche chute in stability back-analysis in order to yield unambiguous values of cohesion and angle of internal friction. The procedure is based upon extending the ordinary method of slices to three dimensions, in order to construct avalanche chute cross-sections whose widths and depths vary as a function of gradient, gravity, density of material, and phi and c. Applying the technique to the well documented slide at Lodalen, Norway as a test produces excellent correspondence with reality. Generally, the technique reveals that the width:depth ratio of any avalanche chute decreases with increasing contrast between the average slope angle and the angle of internal friction. Applying this technique to the martian avalanche chute yields results consistent with indications from earlier work, but with greater certainty. Values of cohesion and angle of internal friction identify the materials at the time of failure as moderately cohesive debris. If Sharp's identification of these features as avalanche chutes is correct, then the results here imply that weathering processes have had a significant effect to depths of tens of meters (where failure has occured) below the martian surface. It is also implied that on relatively steep slopes within Valles Marineris, sizable, unaltered, unmantled bedrock exposures for high resolution spectral and spatial scanning by Mars Observer may be scarce.

Avalanches, breathers, and flow reversal in a continuous Lorenz-96 model

NASA Astrophysics Data System (ADS)

Blender, R.; Wouters, J.; Lucarini, V.

2013-07-01

For the discrete model suggested by Lorenz in 1996, a one-dimensional long-wave approximation with nonlinear excitation and diffusion is derived. The model is energy conserving but non-Hamiltonian. In a low-order truncation, weak external forcing of the zonal mean flow induces avalanchelike breather solutions which cause reversal of the mean flow by a wave-mean flow interaction. The mechanism is an outburst-recharge process similar to avalanches in a sandpile model.

New Perspectives on Long Run-out Rock Avalanches: A Dynamic Analysis of 20 Events in the Vaigat Strait, West Greenland

NASA Astrophysics Data System (ADS)

Benjamin, J.; Rosser, N. J.; Dunning, S.; Hardy, R. J.; Karim, K.; Szczucinski, W.; Norman, E. C.; Strzelecki, M.; Drewniak, M.

2014-12-01

Risk assessments of the threat posed by rock avalanches rely upon numerical modelling of potential run-out and spreading, and are contingent upon a thorough understanding of the flow dynamics inferred from deposits left by previous events. Few records exist of multiple rock avalanches with boundary conditions sufficiently consistent to develop a set of more generalised rules for behaviour across events. A unique cluster of 20 large (3 x 106 - 94 x 106 m3) rock avalanche deposits along the Vaigat Strait, West Greenland, offers a unique opportunity to model a large sample of adjacent events sourced from a stretch of coastal mountains of relatively uniform geology and structure. Our simulations of these events were performed using VolcFlow, a geophysical mass flow code developed to simulate volcanic debris avalanches. Rheological calibration of the model was performed using a well-constrained event at Paatuut (AD 2000). The best-fit simulation assumes a constant retarding stress with a collisional stress coefficient (T0 = 250 kPa, ξ = 0.01), and simulates run-out to within ±0.3% of that observed. Despite being widely used to simulate rock avalanche propagation, other models, that assume either a Coulomb frictional or a Voellmy rheology, failed to reproduce the observed event characteristics and deposit distribution at Paatuut. We applied this calibration to 19 other events, simulating rock avalanche motion across 3D terrain of varying levels of complexity. Our findings illustrate the utility and sensitivity of modelling a single rock avalanche satisfactorily as a function of rheology, alongside the validity of applying the same parameters elsewhere, even within similar boundary conditions. VolcFlow can plausibly account for the observed morphology of a series of deposits emplaced by events of different types, although its performance is sensitive to a range of topographic and geometric factors. These exercises show encouraging results in the model's ability to simulate a series of events using a single set of parameters obtained by back-analysis of the Paatuut event alone. The results also hold important implications for our process understanding of rock avalanches in confined fjord settings, where correctly modelling material flux at the point of entry into the water is critical in tsunami generation.

Avalanches and power-law behaviour in lung inflation

NASA Astrophysics Data System (ADS)

Suki, Béla; Barabási, Albert-László; Hantos, Zoltán; Peták, Ferenc; Stanley, H. Eugene

1994-04-01

WHEN lungs are emptied during exhalation, peripheral airways close up1. For people with lung disease, they may not reopen for a significant portion of inhalation, impairing gas exchange2,3. A knowledge of the mechanisms that govern reinflation of collapsed regions of lungs is therefore central to the development of ventilation strategies for combating respiratory problems. Here we report measurements of the terminal airway resistance, Rt , during the opening of isolated dog lungs. When inflated by a constant flow, Rt decreases in discrete jumps. We find that the probability distribution of the sizes of the jumps and of the time intervals between them exhibit power-law behaviour over two decades. We develop a model of the inflation process in which 'avalanches' of airway openings are seen-with power-law distributions of both the size of avalanches and the time intervals between them-which agree quantitatively with those seen experimentally, and are reminiscent of the power-law behaviour observed for self-organized critical systems4. Thus power-law distributions, arising from avalanches associated with threshold phenomena propagating down a branching tree structure, appear to govern the recruitment of terminal airspaces.

Monte Carlo simulations within avalanche rescue

NASA Astrophysics Data System (ADS)

Reiweger, Ingrid; Genswein, Manuel; Schweizer, Jürg

2016-04-01

Refining concepts for avalanche rescue involves calculating suitable settings for rescue strategies such as an adequate probing depth for probe line searches or an optimal time for performing resuscitation for a recovered avalanche victim in case of additional burials. In the latter case, treatment decisions have to be made in the context of triage. However, given the low number of incidents it is rarely possible to derive quantitative criteria based on historical statistics in the context of evidence-based medicine. For these rare, but complex rescue scenarios, most of the associated concepts, theories, and processes involve a number of unknown "random" parameters which have to be estimated in order to calculate anything quantitatively. An obvious approach for incorporating a number of random variables and their distributions into a calculation is to perform a Monte Carlo (MC) simulation. We here present Monte Carlo simulations for calculating the most suitable probing depth for probe line searches depending on search area and an optimal resuscitation time in case of multiple avalanche burials. The MC approach reveals, e.g., new optimized values for the duration of resuscitation that differ from previous, mainly case-based assumptions.

AN MHD AVALANCHE IN A MULTI-THREADED CORONAL LOOP

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hood, A. W.; Cargill, P. J.; Tam, K. V.

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 andmore » 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.« less

The transitional behaviour of avalanches in cohesive granular materials

NASA Astrophysics Data System (ADS)

Quintanilla, M. A. S.; Valverde, J. M.; Castellanos, A.

2006-07-01

We present a statistical analysis of avalanches of granular materials that partially fill a slowly rotated horizontal drum. For large sized noncohesive grains the classical coherent oscillation is reproduced, consisting of a quasi-periodic succession of regularly sized avalanches. As the powder cohesiveness is increased by decreasing the particle size, we observe a gradual crossover to a complex dynamics that resembles the transitional behaviour observed in fusion plasmas. For particle size below ~50 µm, avalanches lose a characteristic size, retain a short term memory and turn gradually decorrelated in the long term as described by a Markov process. In contrast, large grains made cohesive by coating them with adhesive microparticles display a distinct phenomenology, characterized by a quasi-regular succession of well defined small precursors and large relaxation events. The transition from a one-peaked distribution (noncohesive large beads) to a flattened distribution (fine cohesive beads) passing through the two-peaked distribution of cohesive large beads had already been predicted using a coupled-map lattice model, as the relaxation mechanism of grain reorganization becomes dominant to the detriment of inertia.

Prospects and fundamental limitations of room temperature, non-avalanche, semiconductor photon-counting sensors (Conference Presentation)

NASA Astrophysics Data System (ADS)

Ma, Jiaju; Zhang, Yang; Wang, Xiaoxin; Ying, Lei; Masoodian, Saleh; Wang, Zhiyuan; Starkey, Dakota A.; Deng, Wei; Kumar, Rahul; Wu, Yang; Ghetmiri, Seyed Amir; Yu, Zongfu; Yu, Shui-Qing; Salamo, Gregory J.; Fossum, Eric R.; Liu, Jifeng

2017-05-01

This research investigates the fundamental limits and trade-space of quantum semiconductor photodetectors using the Schrödinger equation and the laws of thermodynamics.We envision that, to optimize the metrics of single photon detection, it is critical to maximize the optical absorption in the minimal volume and minimize the carrier transit process simultaneously. Integration of photon management with quantum charge transport/redistribution upon optical excitation can be engineered to maximize the quantum efficiency (QE) and data rate and minimize timing jitter at the same time. Due to the ultra-low capacitance of these quantum devices, even a single photoelectron transfer can induce a notable change in the voltage, enabling non-avalanche single photon detection at room temperature as has been recently demonstrated in Si quanta image sensors (QIS). In this research, uniform III-V quantum dots (QDs) and Si QIS are used as model systems to test the theory experimentally. Based on the fundamental understanding, we also propose proof-of-concept, photon-managed quantum capacitance photodetectors. Built upon the concepts of QIS and single electron transistor (SET), this novel device structure provides a model system to synergistically test the fundamental limits and tradespace predicted by the theory for semiconductor detectors. This project is sponsored under DARPA/ARO's DETECT Program: Fundamental Limits of Quantum Semiconductor Photodetectors.

Avalanche Accidents Causing Fatalities: Are They Any Different in the Summer?

PubMed

Pasquier, Mathieu; Hugli, Olivier; Kottmann, Alexandre; Techel, Frank

2017-03-01

Pasquier, Mathieu, Olivier Hugli, Alexandre Kottmann, and Frank Techel. Avalanche accidents causing fatalities: are they any different in the summer? High Alt Med Biol. 18:67-72, 2017. This retrospective study investigated the epidemiology of summer avalanche accidents that occurred in Switzerland and caused at least one fatality between 1984 and 2014. Summer avalanche accidents were defined as those that occurred between June 1st and October 31st. Summer avalanches caused 21 (4%) of the 482 avalanches with at least one fatality occurring during the study period, and 40 (6%) of the 655 fatalities. The number of completely buried victims per avalanche and the proportion of complete burials among trapped people were lower in summer than in winter. Nevertheless, the mean number of fatalities per avalanche was higher in summer than in winter: 1.9 ± 1.2 (standard deviation; range 1-6) versus 1.3 ± 0.9 (range 1-7; p < 0.001). Trauma was the presumed cause of death in 94% (33 of 35) in summer avalanche accidents. Sixty-five percent of fully buried were found due to visual clues at the snow surface. Fatal summer avalanche accidents caused a higher mean number of fatalities per avalanche than winter avalanches, and those deaths resulted mostly from trauma. Rescue teams should anticipate managing polytrauma for victims in summer avalanche accidents rather than hypothermia or asphyxia; they should be trained in prehospital trauma life support and equipped accordingly to ensure efficient patient care.

Modeling of a sensitive time-of-flight flash LiDAR system

NASA Astrophysics Data System (ADS)

Fathipour, V.; Wheaton, S.; Johnson, W. E.; Mohseni, H.

2016-09-01

used for monitoring and profiling structures, range, velocity, vibration, and air turbulence. Remote sensing in the IR region has several advantages over the visible region, including higher transmitter energy while maintaining eye-safety requirements. Electron-injection detectors are a new class of detectors with high internal avalanche-free amplification together with an excess-noise-factor of unity. They have a cutoff wavelength of 1700 nm. Furthermore, they have an extremely low jitter. The detector operates in linear-mode and requires only bias voltage of a few volts. This together with the feedback stabilized gain mechanism, makes formation of large-format high pixel density electron-injection FPAs less challenging compared to other detector technologies such as avalanche photodetectors. These characteristics make electron-injection detectors an ideal choice for flash LiDAR application with mm scale resolution at longer ranges. Based on our experimentally measured device characteristics, a detailed theoretical LiDAR model was developed. In this model we compare the performance of the electron-injection detector with commercially available linear-mode InGaAs APD from (Hamamatsu G8931-20) as well as a p-i-n diode (Hamamatsu 11193 p-i-n). Flash LiDAR images obtained by our model, show the electron-injection detector array (of 100 x 100 element) achieves better resolution with higher signal-to-noise compared with both the InGaAs APD and the p-i-n array (of 100 x 100 element).

Multipactor experiment on a dielectric surface

NASA Astrophysics Data System (ADS)

Anderson, Rex Beach, III

2001-12-01

Multipactor is an electron multiplication process, or electron avalanche, that occurs on metallic and dielectric surfaces in the presence of rf microwave fields. Just as a rock avalanche only needs one rock to cause a larger slide of destruction, one electron under multipactor conditions can cause a tremendous amount of damage to electrical components. Multipactor is a nuisance that can cause excessive noise in communication satellites and radar, and damage to vacuum windows in particle accelerators. Single-surface multipactor on dielectrics is responsible for poor transmission properties of vacuum windows and can eventually lead to vacuum window failure. The repercussions of multipactor affect a wide range of people. For example, a civilian placing a call on a cell phone, or a captain dependent on radar for his ship's safety could both be affected by multipactor. In order to combat this expensive annoyance, a unique experiment to investigate single-surface multipactor on a dielectric surface was developed and tested. The motivation of this thesis is to introduce a novel experiment for multipactor that is designed to verify theoretical calculations and explore the physics behind the phenomenon. The compact apparatus consists of a small brass microwave cavity in a high vacuum system. Most single-surface multipactor experiments consist of a large resonant ring wave guide with a MW power supply. This experiment is the first to utilize a high Q resonant cavity and kW-level power supply to create multipactor on a dielectric surface. The small brass resonant cavity has an inner length of 9.154 cm with an inner diameter of 9.045 cm. A pulsed, variable frequency microwave source at ˜2.4 GHz, 2 kW peak excites the TE111 mode with a strong electric field parallel to a dielectric plate (˜0.2 cm thickness) that is inserted at the mid-plane of the cavity. The microwave pulses from the power supply are monitored by calibrated microwave diodes. These calibrated diodes along with a bead pull perturbation method are used to calculate the threshold rf fields at the dielectric surface when multipactor occurs. This experiment is the first to measure electron current from the dielectric using an electron probe. The electron probe provides temporal measurements of the multipactor electron current with respect to the microwave pulses. Another unique electron diagnostic utilized in this multipactor experiment is phosphor. Phosphor on the dielectric surface is used to detect multipactor electrons by photoemission. Phosphors with different excitation energies are used as a crude electron energy analyzer. Experimental results from these diagnostics match well with theoretical calculations.

Temporal dependence of transient dark counts in an avalanche photodiode: A solution for power-law behavior of afterpulsing

DOE Office of Scientific and Technical Information (OSTI.GOV)

Akiba, M., E-mail: akiba@nict.go.jp; Tsujino, K.

This paper offers a theoretical explanation of the temperature and temporal dependencies of transient dark count rates (DCRs) measured for a linear-mode silicon avalanche photodiode (APD) and the dependencies of afterpulsing that were measured in Geiger-mode Si and InGaAs/InP APDs. The temporal dependencies exhibit power-law behavior, at least to some extent. For the transient DCR, the value of the DCR for a given time period increases with decreases in temperature, while the power-law behavior remains unchanged. The transient DCR is attributed to electron emissions from traps in the multiplication layer of the APD with a high electric field, and itsmore » temporal dependence is explained by a continuous change in the electron emission rate as a function of the electric field strength. The electron emission rate is calculated using a quantum model for phonon-assisted tunnel emission. We applied the theory to the temporal dependence of afterpulsing that was measured for Si and InGaAs/InP APDs. The power-law temporal dependence is attributed to the power-law function of the electron emission rate from the traps as a function of their position across the p–n junction of the APD. Deviations from the power-law temporal dependence can be derived from the upper and lower limits of the electric field strength.« less

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

USGS Publications Warehouse

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 < 656 km from the rock-slide source area) and one short-period network. We inverted broadband data to derive a time series of forces that the avalanche exerted on the 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 basal layer, and a thicker and stronger overriding layer.

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

NASA Astrophysics Data System (ADS)

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.

Grain Flow at High Stresses

NASA Astrophysics Data System (ADS)

McSaveney, M. J.

2015-12-01

The transport mechanism of rapid long-runout rock avalanches was a hotly debated topic when I came on the scene in 1967. So how come it is still debated today? My explanation is that it is the expected outcome of peer review, poor comprehension, and technological advances outpacing intellectual advances. Why think about the problem when we can model it! So let us think about the problem. Shreve thought that rock avalanches fell upon and trapped a layer of air. What physics was he thinking about? It is how feathers and tissue papers fall. When my rock avalanches fly, they fly like unlubricated bricks using the physics of projectiles and ballistics. But the main transport mechanism is not flight. The dominant impression from watching a rock avalanche in motion is of fluid flow, as Heim described it in 1882. A rock avalanche is a very large grain flow. Bagnold studied dispersive grain flows, but why should one assume that rock avalanches are dispersive grain flows as many do. The more common grain flow type is a dense grain flow and rock avalanches are dense grain flows in which the weight can and does generate very high stresses at grain contacts. Brittle rock deforms elastically up to its compressive strength, whereupon it breaks, releasing elastic strain as transient elastic strain (seismic energy to a seismologist, acoustic energy to a physicist). Melosh and others have shown that acoustic energy can fluidize a grain mass. There is no exotic physics behind grain flow at high stress. When grains break, the released elastic strain has to go somewhere, and it goes somewhere principally by transmission though grain contacts. Depending on the state of stress at the grain contact, the contact will pass the stress or will slip at conventional values of Coulomb friction. Enough thinking! A physical model of the entire process is too big for any laboratory. So whose numerical model will do it?

Particle size segregation in granular avalanches: A brief review of recent progress

NASA Astrophysics Data System (ADS)

Gray, J. M. N. T.

2010-05-01

Hazardous natural flows such as snow avalanches, debris-flows, lahars and pyroclastic flows are part of a much wider class of granular avalanches, that frequently occur in industrial processes and in our kitchens! Granular avalanches are very efficient at sorting particles by size, with the smaller ones percolating down towards the base and squeezing the larger grains up towards the free-surface, to create inversely-graded layers. This paper provides a short introduction and review of recent theoretical advances in describing segregation and remixing with relatively simple hyperbolic and parabolic models. The derivation from two phase mixture theory is briefly summarized and links are drawn to earlier models of Savage & Lun and Dolgunin & Ukolov. The more complex parabolic version of the theory has a diffusive force that competes against segregation and yields S-shaped steady-state concentration profiles through the avalanche depth, that are able to reproduce results obtained from particle dynamics simulations. Time-dependent exact solutions can be constructed by using the Cole-Hopf transformation to linearize the segregation-remixing equation and the nonlinear surface and basal boundary conditions. In the limit of no diffusion, the theory is hyperbolic and the grains tend to separate out into completely segregated inversely graded layers. A series of elementary problems are used to demonstrate how concentration shocks, expansion fans, breaking waves and the large and small particles paths can be computed exactly using the model. The theory is able to capture the key features of the size distribution observed in stratification experiments, and explains how a large particle rich front is connected to an inversely graded avalanche in the interior. The theory is simple enough to couple it to the bulk flow field to investigate segregation-mobility feedback effects that spontaneously generate self-channelizing leveed avalanches, which can significantly enhance the total run-out distance of geophysical mass flows.

Experimental Avalanches in a Rotating Drum

NASA Astrophysics Data System (ADS)

Hubard, Aline; O'Hern, Corey; Shattuck, Mark

We address the question of universality in granular avalanches and the system size effects on it. We set up an experiment made from a quasi-two-dimensional rotating drum half-filled with a monolayer of stainless-steel spheres. We measure the size of the avalanches created by the increased gravitational stress on the pile as we quasi-statically rotate the drum. We find two kinds of avalanches determined by the drum size. The size and duration distributions of the avalanches that do not span the whole system follow a power law and the avalanche shapes are self-similar and nearly parabolic. The distributions of the avalanches that span the whole system are limited by the maximal amount of potential energy stored in the system at the moment of the avalanche. NSF CMMI-1462439, CMMI-1463455.

Forensic Analysis of the May 2014 West Salt Creek Rock Avalanche in Western Colorado

NASA Astrophysics Data System (ADS)

Coe, J. A.; Baum, R. L.; Allstadt, K.; Kochevar, B. F.; Schmitt, R. G.; Morgan, M. L.; White, J. L.; Stratton, B. T.; Hayashi, T. A.; Kean, J. W.

2015-12-01

The rain-on-snow induced West Salt Creek rock avalanche occurred on May 25, 2014 on the northern flank of Grand Mesa. The avalanche was rare for the contiguous U.S. because of its large size (59 M m3) and high mobility (Length/Height=7.2). 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 (UAS) imagery as a base for our field mapping and analyzed seismic data from 22 broadband stations (distances <656 km) and one short-period network. We inverted broadband data to derive a time series of forces that the avalanche exerted on the 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 a landslide/debris flow that started about 10 hours before the main avalanche. The main avalanche lasted just over 3 minutes 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, strike-slip bound core continued to move slowly. Following movement of the core, numerous shallow landslides, rock slides, and rock falls created new structures and modified topography. Mobility of the main avalanche and central core were 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 liquefied basal layer; and a thicker and stronger overriding layer.

QED-driven laser absorption

NASA Astrophysics Data System (ADS)

Levy, Matthew; Blackburn, T.; Ratan, N.; Sadler, J.; Ridgers, C.; Kasim, M.; Ceurvorst, L.; Holloway, J.; Baring, M.; Bell, A.; Glenzer, S.; Gregori, G.; Ilderton, A.; Marklund, M.; Tabak, M.; Wilks, S.; Norreys, P.

2016-10-01

Absorption covers the physical processes which convert intense photon flux into energetic particles when a high-power laser (I >1018 W cm-2 where I is intensity at 1 μm wavelength) illuminates optically-thick matter. It underpins important applications of petawatt laser systems today, e.g., in isochoric heating of materials. Next-generation lasers such as ELI are anticipated to produce quantum electrodynamical (QED) bursts of γ-rays and anti-matter via the multiphoton Breit-Wheeler process which could enable scaled laboratory probes, e.g., of black hole winds. Here, applying strong-field QED to advances in plasma kinematic theory, we present a model elucidating absorption limited only by an avalanche of self-created electron-positron pairs at ultra-high-field. The model, confirmed by multidimensional QED-PIC simulations, works over six orders of magnitude in optical intensity and reveals this cascade is initiated at 1.8 x 1025 W cm-2 using a realistic linearly-polarized laser pulse. Here the laser couples its energy into highly-collimated electrons, ions, γ-rays, and positrons at 12%, 6%, 58% and 13% efficiency, respectively. We remark on attributes of the QED plasma state and possible applications.

High resolution tree-ring based spatial reconstructions of snow avalanche activity in Glacier National Park, Montana, USA

USGS Publications Warehouse

Pederson, Gregory T.; Reardon, Blase; Caruso, C.J.; Fagre, Daniel B.

2006-01-01

Effective design of avalanche hazard mitigation measures requires long-term records of natural avalanche frequency and extent. Such records are also vital for determining whether natural avalanche frequency and extent vary over time due to climatic or biophysical changes. Where historic records are lacking, an accepted substitute is a chronology developed from tree-ring responses to avalanche-induced damage. This study evaluates a method for using tree-ring chronologies to provide spatially explicit differentiations of avalanche frequency and temporally explicit records of avalanche extent that are often lacking. The study area - part of John F. Stevens Canyon on the southern border of Glacier National Park – is within a heavily used railroad and highway corridor with two dozen active avalanche paths. Using a spatially geo-referenced network of avalanche-damaged trees (n=109) from a single path, we reconstructed a 96-year tree-ring based chronology of avalanche extent and frequency. Comparison of the chronology with historic records revealed that trees recorded all known events as well as the same number of previously unidentified events. Kriging methods provided spatially explicit estimates of avalanche return periods. Estimated return periods for the entire avalanche path averaged 3.2 years. Within this path, return intervals ranged from ~2.3 yrs in the lower track, to ~9-11 yrs and ~12 to >25 yrs in the runout zone, where the railroad and highway are located. For avalanche professionals, engineers, and transportation managers this technique proves a powerful tool in landscape risk assessment and decision making.

The role of initial coherence and path materials in the dynamics of three rock avalanche case histories

USGS Publications Warehouse

Aaron, Jordan; McDougall, Scott; Moore, Jeffrey R.; Coe, Jeffrey A.; Hungr, Oldrich

2017-01-01

BackgroundRock avalanches are flow-like landslides that can travel at extremely rapid velocities and impact surprisingly large areas. The mechanisms that lead to the unexpected mobility of these flows are unknown and debated. Mechanisms proposed in the literature can be broadly classified into those that rely on intrinsic characteristics of the rock avalanche material, and those that rely on extrinsic factors such as path material. In this work a calibration-based numerical model is used to back-analyze three rock avalanche case histories. The results of these back-analyses are then used to infer factors that govern rock avalanche motionResultsOur study has revealed two key insights that must be considered when analyzing rock avalanches. Results from two of the case histories demonstrate the importance of accounting for the initially coherent phase of rock avalanche motion. Additionally, the back-analyzed basal resistance parameters, as well as the best-fit rheology, are different for each case history. This suggests that the governing mechanisms controlling rock avalanche motion are unlikely to be intrinsic. The back-analyzed strength parameters correspond well to those that would be expected by considering the path material that the rock avalanches overran.ConclusionOur results show that accurate simulation of rock avalanche motion must account for the initially coherent phase of movement, and that the mechanisms governing rock avalanche motion are unlikely to be intrinsic to the failed material. Interaction of rock avalanche debris with path materials is the likely mechanism that governs the motion of many rock avalanches.

On the avalanche generation of runaway electrons during tokamak disruptions

DOE Office of Scientific and Technical Information (OSTI.GOV)

Martín-Solís, J. R., E-mail: solis@fis.uc3m.es; Loarte, A.; Lehnen, M.

2015-08-15

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 currentmore » 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.« less

On the localization properties of an RPWELL gas-avalanche detector

NASA Astrophysics Data System (ADS)

Moleri, L.; Bhattacharya, P.; Coimbra, A. E. C.; Breskin, A.; Bressler, S.

2017-10-01

A study of the localization properties of a single-element Resistive Plate WELL (RPWELL) detector is presented. The detector comprises of a single-sided THick Gaseous Electron Multiplier (THGEM) coupled to a segmented readout anode through a doped silicate-glass plate of 1010 Ωṡcm bulk resistivity. Operated in ambient \

AlInAsSb/GaSb staircase avalanche photodiode

NASA Astrophysics Data System (ADS)

Ren, Min; Maddox, Scott; Chen, Yaojia; Woodson, Madison; Campbell, Joe C.; Bank, Seth

2016-02-01

Over 30 years ago, Capasso and co-workers [IEEE Trans. Electron Devices 30, 381 (1982)] proposed the staircase avalanche photodetector (APD) as a solid-state analog of the photomultiplier tube. In this structure, electron multiplication occurs deterministically at steps in the conduction band profile, which function as the dynodes of a photomultiplier tube, leading to low excess multiplication noise. Unlike traditional APDs, the origin of staircase gain is band engineering rather than large applied electric fields. Unfortunately, the materials available at the time, principally AlxGa1-xAs/GaAs, did not offer sufficiently large conduction band offsets and energy separations between the direct and indirect valleys to realize the full potential of the staircase gain mechanism. Here, we report a true staircase APD operation using alloys of a rather underexplored material, AlxIn1-xAsySb1-y, lattice-matched to GaSb. Single step "staircase" devices exhibited a constant gain of ˜2×, over a broad range of applied bias, operating temperature, and excitation wavelengths/intensities, consistent with Monte Carlo calculations.

Influence of ion transport on discharge propagation of nanosecond dielectric barrier discharge plasma actuator

NASA Astrophysics Data System (ADS)

Hua, Weizhuo; Koji, Fukagata

2017-11-01

A numerical study has been conducted to understand the streamer formation and propagation of nanosecond pulsed surface dielectric barrier discharge of positive polarity. First we compared the result of different grid configuration to investigate the influence of x and y direction grid spacing on the streamer propagation. The streamer propagation is sensitive to y grid spacing especially at the dielectric surface. The streamer propagation velocity can reach 0.2 cm/ns when the voltage magnitude is 12 kV. A narrow gap was found between the streamer and dielectric barrier, where the plasma density is several orders of magnitude smaller than the streamer region. Analyses on the ion transport in the gap and streamer regions show the different ion transport mechanisms in the two different region. In the gap region, the diffusion of electron toward the dielectric layer decreases the seed electron in the beginning of voltage pulse, resulting that ionization avalanche does not occur. The streamer region is not significantly affected by the diffusion flux toward the dielectric layer, so that ionization avalanche takes place and leads to dramatic increase of plasma density.

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

NASA Astrophysics Data System (ADS)

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.

Empirical prediction for travel distance of channelized rock avalanches in the Wenchuan earthquake area

NASA Astrophysics Data System (ADS)

Zhan, Weiwei; Fan, Xuanmei; Huang, Runqiu; Pei, Xiangjun; Xu, Qiang; Li, Weile

2017-06-01

Rock avalanches are extremely rapid, massive flow-like movements of fragmented rock. The travel path of the rock avalanches may be confined by channels in some cases, which are referred to as channelized rock avalanches. Channelized rock avalanches are potentially dangerous due to their difficult-to-predict travel distance. In this study, we constructed a dataset with detailed characteristic parameters of 38 channelized rock avalanches triggered by the 2008 Wenchuan earthquake using the visual interpretation of remote sensing imagery, field investigation and literature review. Based on this dataset, we assessed the influence of different factors on the runout distance and developed prediction models of the channelized rock avalanches using the multivariate regression method. The results suggested that the movement of channelized rock avalanche was dominated by the landslide volume, total relief and channel gradient. The performance of both models was then tested with an independent validation dataset of eight rock avalanches that were induced by the 2008 Wenchuan earthquake, the Ms 7.0 Lushan earthquake and heavy rainfall in 2013, showing acceptable good prediction results. Therefore, the travel-distance prediction models for channelized rock avalanches constructed in this study are applicable and reliable for predicting the runout of similar rock avalanches in other regions.

Tornado-like transport in a magnetized plasma

NASA Astrophysics Data System (ADS)

Poulos, Matthew; van Compernolle, Bart; Morales, George

2017-10-01

Recent heat transport experiments conducted in the LAPD device at UCLA in which avalanche events have been previously documented have also lead to the identification of a new tornado-like transport phenomenon. These tornados occur much earlier than the avalanches events, essentially in the interval following the application of the bias voltage that causes the injection of an electron beam from a ring-shaped LaB6 cathode into the afterglow of a cold, magnetized plasma. The tornados exhibit a low-frequency (4 kHz) (much lower than drift-waves), spiraling, global eigenmode whose transient behavior is responsible for significant radial transport well outside the heated region. Detailed experimental observations are compared with a Braginskii transport code that includes the effects of ExB convection induced by the spiraling global eigenmode. New insights are gained into the necessary modifications of classical transport to accurately simulate the spiraling effects and the possible interaction with avalanches. This work is supported by the NSF/DOE partnership in basic plasma science and engineering, Grant Number 1619505, and is performed at the Basic Plasma Science Facility, sponsored jointly by DOE and NSF. Sponsored by DOE/NSF at BaPSF and NSF 1619505.

Pixelated Geiger-Mode Avalanche Photo-Diode Characterization Through Dark Current Measurement

NASA Astrophysics Data System (ADS)

Amaudruz, Pierre-Andre; Bishop, Daryl; Gilhully, Colleen; Goertzen, Andrew; James, Lloyd; Kozlowski, Piotr; Retiere, Fabrice; Shams, Ehsan; Sossi, Vesna; Stortz, Greg; Thiessen, Jonathan D.; Thompson, Christopher J.

2014-06-01

PIXELATED geiger-mode avalanche photodiodes (PPDs), often called silicon photomultipliers (SiPMs) are emerging as an excellent replacement for traditional photomultiplier tubes (PMTs) in a variety of detectors, especially those for subatomic physics experiments, which requires extensive test and operation procedures in order to achieve uniform responses from all the devices. In this paper, we show for two PPD brands, Hamamatsu MPPC and SensL SPM, that at room temperature, the dark noise rate, breakdown voltage and rate of correlated avalanches can be inferred from the sole measure of dark current as a function of operating voltage, hence greatly simplifying the characterization procedure. We introduce a custom electronics system that allows measurement for many devices concurrently, hence allowing rapid testing and monitoring of many devices at low cost. Finally, we show that the dark current of Hamamastu Multi-Pixel Photon Counter (MPPC) is rather independent of temperature at constant operating voltage, hence the current measure cannot be used to probe temperature variations. On the other hand, the MPPC current can be used to monitor light source conditions in DC mode without requiring strong temperature stability, as long as the integrated source brightness is comparable to the dark noise rate.

Measuring neuronal avalanches in disordered systems with absorbing states

NASA Astrophysics Data System (ADS)

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.

Numerical run-out modelling used for reassessment of existing permanent avalanche paths in the Krkonose Mts., Czechia

NASA Astrophysics Data System (ADS)

Blahut, Jan; Klimes, Jan; Balek, Jan; Taborik, Petr; Juras, Roman; Pavlasek, Jiri

2015-04-01

Run-out modelling of snow avalanches is being widely applied in high mountain areas worldwide. This study presents application of snow avalanche run-out calculation applied to mid-mountain ranges - the Krkonose, Jeseniky and Kralicky Sneznik Mountains. All mentioned mountain ranges lie in the northern part of Czechia, close to the border with Poland. Its highest peak reaches only 1602 m a.s.l. However, climatic conditions and regular snowpack presence are the reason why these mountain ranges experience considerable snow avalanche activity every year, sometimes resulting in injuries or even fatalities. Within the aim of an applied project dealing with snow avalanche hazard prediction a re-assessment of permanent snow avalanche paths has been performed based on extensive statistics covering period from 1961/62 till present. On each avalanche path different avalanches with different return periods were modelled using the RAMMS code. As a result, an up-to-date snow avalanche hazard map was prepared.

Spike avalanches in vivo suggest a driven, slightly subcritical brain state

PubMed Central

Priesemann, Viola; Wibral, Michael; Valderrama, Mario; Pröpper, Robert; Le Van Quyen, Michel; Geisel, Theo; Triesch, Jochen; Nikolić, Danko; Munk, Matthias H. J.

2014-01-01

In self-organized critical (SOC) systems avalanche size distributions follow power-laws. Power-laws have also been observed for neural activity, and so it has been proposed that SOC underlies brain organization as well. Surprisingly, for spiking activity in vivo, evidence for SOC is still lacking. Therefore, we analyzed highly parallel spike recordings from awake rats and monkeys, anesthetized cats, and also local field potentials from humans. We compared these to spiking activity from two established critical models: the Bak-Tang-Wiesenfeld model, and a stochastic branching model. We found fundamental differences between the neural and the model activity. These differences could be overcome for both models through a combination of three modifications: (1) subsampling, (2) increasing the input to the model (this way eliminating the separation of time scales, which is fundamental to SOC and its avalanche definition), and (3) making the model slightly sub-critical. The match between the neural activity and the modified models held not only for the classical avalanche size distributions and estimated branching parameters, but also for two novel measures (mean avalanche size, and frequency of single spikes), and for the dependence of all these measures on the temporal bin size. Our results suggest that neural activity in vivo shows a mélange of avalanches, and not temporally separated ones, and that their global activity propagation can be approximated by the principle that one spike on average triggers a little less than one spike in the next step. This implies that neural activity does not reflect a SOC state but a slightly sub-critical regime without a separation of time scales. Potential advantages of this regime may be faster information processing, and a safety margin from super-criticality, which has been linked to epilepsy. PMID:25009473

Meteorological variables to aid forecasting deep slab avalanches on persistent weak layers

USGS Publications Warehouse

Marienthal, Alex; Hendrikx, Jordy; Birkeland, Karl; Irvine, Kathryn M.

2015-01-01

Deep slab avalanches are particularly challenging to forecast. These avalanches are difficult to trigger, yet when they release they tend to propagate far and can result in large and destructive avalanches. We utilized a 44-year record of avalanche control and meteorological data from Bridger Bowl ski area in southwest Montana to test the usefulness of meteorological variables for predicting seasons and days with deep slab avalanches. We defined deep slab avalanches as those that failed on persistent weak layers deeper than 0.9 m, and that occurred after February 1st. Previous studies often used meteorological variables from days prior to avalanches, but we also considered meteorological variables over the early months of the season. We used classification trees and random forests for our analyses. Our results showed seasons with either dry or wet deep slabs on persistent weak layers typically had less precipitation from November through January than seasons without deep slabs on persistent weak layers. Days with deep slab avalanches on persistent weak layers often had warmer minimum 24-hour air temperatures, and more precipitation over the prior seven days, than days without deep slabs on persistent weak layers. Days with deep wet slab avalanches on persistent weak layers were typically preceded by three days of above freezing air temperatures. Seasonal and daily meteorological variables were found useful to aid forecasting dry and wet deep slab avalanches on persistent weak layers, and should be used in combination with continuous observation of the snowpack and avalanche activity.

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

PubMed

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.

Medium-energy particle experiments—electron analyzer (MEP-e) for the exploration of energization and radiation in geospace (ERG) mission

NASA Astrophysics Data System (ADS)

Kasahara, Satoshi; Yokota, Shoichiro; Mitani, Takefumi; Asamura, Kazushi; Hirahara, Masafumi; Shibano, Yasuko; Takashima, Takeshi

2018-05-01

The medium-energy particle experiments—electron analyzer onboard the exploration of energization and radiation in geospace spacecraft measures the energy and direction of each incoming electron in the energy range of 7-87 keV. The sensor covers a 2 π-radian disklike field of view with 16 detectors, and the full solid angle coverage is achieved through the spacecraft's spin motion. The electron energy is independently measured by both an electrostatic analyzer and avalanche photodiodes, enabling significant background reduction. We describe the technical approach, data output, and examples of initial observations.[Figure not available: see fulltext.

Avalanches and Criticality in Driven Magnetic Skyrmions

NASA Astrophysics Data System (ADS)

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.

Historic avalanches in the northern front range and the central and northern mountains of Colorado

Treesearch

M. Martinelli; Charles F. Leaf

1999-01-01

Newspaper accounts of avalanche accidents from the 1860s through 1950 have been compiled, summarized, and discussed. Many of the avalanches that caused fatalities came down rather small, innocuous-looking paths. Land use planners can use historical avalanche information as a reminder of the power of snow avalanches and to assure rational development in the future....

[Morphology determination of multi-needle bipolar corona discharge by OES].

PubMed

Chen, Hai-Feng; Su, Peng-Hao; Zhu, Yi-Min

2009-01-01

Using the method of OES (optical emission spectrum) for measuring N2 emission spectrum, the spacial distribution of energetic electrons in multi-needle bipolar corona discharge at atmospheric pressure was investigated. According to the distribution of N2 second positive band's intensity ISPB, the outline of ionisation region was drawn accurately. The relationship between ISPB and discharge current I was obtained through the sum of ISPB. There are two ionisation regions in the multi-needle bipolar corona discharge. One is near the HV electrode and the other is near the grounded electrode. The ionisation region exists around the needlepoint within 2-3 mm. The volume of ionisation region becomes big with the applied voltage U increasing. The ionisation region of negative corona is bigger than that of positive corona. Near the HV discharge electrode, the outline of electron avalanche is similar to the configuration of electric field lines in the ionisation region, so the electron avalanche along the axis direction of needle develops farther than that along the radial direction. The electric field in the migration area is weak, and the distribution of space charges is large along the radial direction. The sum of ISPB in each ionisation region is second order linear with I, but the quadratic coefficient is very small. So the sum of ISPB is nearly linear with I, the distribution of ISPB is corresponding to the density distribution of energetic electrons. So the charged particles forming the discharge current in ionisation region are electrons. No emission spectrum of N2 can be measured in migration area, so there is no energetic electron. The energetic electrons only exist in ionisation region and the charged particles in migration area are ions.

Ponderomotive electron acceleration in a silicon-based nanoplasmonic waveguide.

PubMed

Sederberg, S; Elezzabi, A Y

2014-10-17

Ponderomotive electron acceleration is demonstrated in a semiconductor-loaded nanoplasmonic waveguide. Photogenerated free carriers are accelerated by the tightly confined nanoplasmonic fields and reach energies exceeding the threshold for impact ionization. Broadband (375 nm ≤ λ ≤ 650  nm) white light emission is observed from the nanoplasmonic waveguides. Exponential growth of visible light emission confirms the exponential growth of the electron population, demonstrating the presence of an optical-field-driven electron avalanche. Electron sweeping dynamics are visualized using pump-probe measurements, and a sweeping time of 1.98 ± 0.40 ps is measured. These findings offer a means to harness the potential of the emerging field of ultrafast nonlinear nanoplasmonics.

Automated detection of snow avalanche deposits: segmentation and classification of optical remote sensing imagery

NASA Astrophysics Data System (ADS)

Lato, M. J.; Frauenfelder, R.; Bühler, Y.

2012-09-01

Snow avalanches in mountainous areas pose a significant threat to infrastructure (roads, railways, energy transmission corridors), personal property (homes) and recreational areas as well as for lives of people living and moving in alpine terrain. The impacts of snow avalanches range from delays and financial loss through road and railway closures, destruction of property and infrastructure, to loss of life. Avalanche warnings today are mainly based on meteorological information, snow pack information, field observations, historically recorded avalanche events as well as experience and expert knowledge. The ability to automatically identify snow avalanches using Very High Resolution (VHR) optical remote sensing imagery has the potential to assist in the development of accurate, spatially widespread, detailed maps of zones prone to avalanches as well as to build up data bases of past avalanche events in poorly accessible regions. This would provide decision makers with improved knowledge of the frequency and size distributions of avalanches in such areas. We used an object-oriented image interpretation approach, which employs segmentation and classification methodologies, to detect recent snow avalanche deposits within VHR panchromatic optical remote sensing imagery. This produces avalanche deposit maps, which can be integrated with other spatial mapping and terrain data. The object-oriented approach has been tested and validated against manually generated maps in which avalanches are visually recognized and digitized. The accuracy (both users and producers) are over 0.9 with errors of commission less than 0.05. Future research is directed to widespread testing of the algorithm on data generated by various sensors and improvement of the algorithm in high noise regions as well as the mapping of avalanche paths alongside their deposits.

Nano-multiplication region avalanche photodiodes and arrays

NASA Technical Reports Server (NTRS)

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.

Dynamic magnification factors for tree blow-down by powder snow avalanche air blasts

NASA Astrophysics Data System (ADS)

Bartelt, Perry; Bebi, Peter; Feistl, Thomas; Buser, Othmar; Caviezel, Andrin

2018-03-01

We study how short duration powder avalanche blasts can break and overturn tall trees. Tree blow-down is often used to back-calculate avalanche pressure and therefore constrain avalanche flow velocity and motion. We find that tall trees are susceptible to avalanche air blasts because the duration of the air blast is near to the period of vibration of tall trees, both in bending and root-plate overturning. Dynamic magnification factors for bending and overturning failures should therefore be considered when back-calculating avalanche impact pressures.

On boundaries of ping-pong modes in multipacting

NASA Astrophysics Data System (ADS)

Shemelin, Valery

2018-05-01

Multipactor is an avalanche multiplication of the number of electrons in radio-frequency devices due to secondary electron emission. One of the possible modes of this kind of discharge was studied in detail and was named "a ping-pong mode" in a publication by R. A. Kishek [Phys. Rev. Lett. 108, 035003 (2012) and Phys. Plasmas 20, 056702 (2013)]. In the present paper, I show that conditions of stability and cutoff limits are quite different from those derived in the cited papers.

Development of novel technologies to enhance performance and reliability of III-Nitride avalanche photodiodes

NASA Astrophysics Data System (ADS)

Suvarna, Puneet Harischandra

Solar-blind ultraviolet avalanche photodiodes are an enabling technology for applications in the fields of astronomy, communication, missile warning systems, biological agent detection and particle physics research. Avalanche photodiodes (APDs) are capable of detecting low-intensity light with high quantum efficiency and signal-to-noise ratio without the need for external amplification. The properties of III-N materials (GaN and AlGaN) are promising for UV photodetectors that are highly efficient, radiation-hard and capable of visible-blind or solar-blind operation without the need for external filters. However, the realization of reliable and high performance III-N APDs and imaging arrays has several technological challenges. The high price and lack of availability of bulk III-N substrates necessitates the growth of III-Ns on lattice mismatched substrates leading to a high density of dislocations in the material that can cause high leakage currents, noise and premature breakdown in APDs. The etched sidewalls of III-N APDs and high electric fields at contact edges are also detrimental to APD performance and reliability. In this work, novel technologies have been developed and implemented that address the issues of performance and reliability in III-Nitride based APDs. To address the issue of extended defects in the bulk of the material, a novel pulsed MOCVD process was developed for the growth of AlGaN. This process enables growth of high crystal quality AlxGa1-xN with excellent control over composition, doping and thickness. The process has also been adapted for the growth of high quality III-N materials on silicon substrate for devices such as high electron mobility transistors (HEMTs). A novel post-growth defect isolation technique is also discussed that can isolate the impact of conductive defects from devices. A new sidewall passivation technique using atomic layer deposition (ALD) of dielectric materials was developed for III-N APDs that is effective in reducing the dark-current and trap states at sidewalls by close to an order of magnitude, leading to improved APD performance. Development and implementation of an ion implantation based contact edge termination technique for III-N APDs that helps prevent premature breakdown from the contact edge of the devices, has further lead to improved reliability. Finally novel improved III-N APD device designs are proposed using preliminary experiments and numerical simulations for future implementations.

Assessing risk based on uncertain avalanche activity patterns

NASA Astrophysics Data System (ADS)

Zeidler, Antonia; Fromm, Reinhard

2015-04-01

Avalanches may affect critical infrastructure and may cause great economic losses. The planning horizon of infrastructures, e.g. hydropower generation facilities, reaches well into the future. Based on the results of previous studies on the effect of changing meteorological parameters (precipitation, temperature) and the effect on avalanche activity we assume that there will be a change of the risk pattern in future. The decision makers need to understand what the future might bring to best formulate their mitigation strategies. Therefore, we explore a commercial risk software to calculate risk for the coming years that might help in decision processes. The software @risk, is known to many larger companies, and therefore we explore its capabilities to include avalanche risk simulations in order to guarantee a comparability of different risks. In a first step, we develop a model for a hydropower generation facility that reflects the problem of changing avalanche activity patterns in future by selecting relevant input parameters and assigning likely probability distributions. The uncertain input variables include the probability of avalanches affecting an object, the vulnerability of an object, the expected costs for repairing the object and the expected cost due to interruption. The crux is to find the distribution that best represents the input variables under changing meteorological conditions. Our focus is on including the uncertain probability of avalanches based on the analysis of past avalanche data and expert knowledge. In order to explore different likely outcomes we base the analysis on three different climate scenarios (likely, worst case, baseline). For some variables, it is possible to fit a distribution to historical data, whereas in cases where the past dataset is insufficient or not available the software allows to select from over 30 different distribution types. The Monte Carlo simulation uses the probability distribution of uncertain variables using all valid combinations of the values of input variables to simulate all possible outcomes. In our case the output is the expected risk (Euro/year) for each object (e.g. water intake) considered and the entire hydropower generation system. The output is again a distribution that is interpreted by the decision makers as the final strategy depends on the needs and requirements of the end-user, which may be driven by personal preferences. In this presentation, we will show a way on how we used the uncertain information on avalanche activity in future to subsequently use it in a commercial risk software and therefore bringing the knowledge of natural hazard experts to decision makers.

The origins of Late Quaternary debris avalanche and debris flow deposits from Cofre de Perote volcano, México

USGS Publications Warehouse

Diaz-Castellon, Rodolfo; Hubbard, Bernard E.; Carrasco-Nunez, Gerardo; Rodríguez-Vargas, José Luis

2012-01-01

Cofre de Perote volcano is a compound, shield-like volcano located in the northeastern Trans-Mexican volcanic belt. Large debris avalanche and lahar deposits are associated with the evolution of Cofre. The two best preserved of these debris-avalanche and debris-flow deposits are the ∼42 ka “Los Pescados debris flow” deposit and the ∼11–13 ka “Xico avalanche” deposit, both of which display contrasting morphological and textural characteristics, source materials, origins and emplacement environments. Laboratory X-ray diffraction and visible-infrared reflectance spectroscopy were used to identify the most abundant clay, sulfate, ferric-iron, and silica minerals in the deposits, which were either related to hydrothermal alteration or chemical weathering processes. Cloud-free Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) remote sensing imagery, supporting EO-1 Hyperion image spectra, and field ground truth samples were used to map the mineralogy and distribution of hydrothermally altered rocks on the modern summit of Cofre de Perote. The results were then compared to minerals identified in the two debris-avalanche and debris-flow deposits in order to assess possible source materials and origins for the two deposits.The older Los Pescados debris-flow deposit contains mostly halloysite and hydrous silica minerals, which match the dominant mineralogy of soils and weathered volcanic deposit in the surrounding flanks of Cofre de Perote. Its source materials were most likely derived from initially noncohesive or clay-poor flows, which subsequently bulked with clay-rich valley soils and alluvium in a manner similar to lahars from Nevado del Ruiz in 1985, but on a larger scale. The younger Xico avalanche deposit contains abundant smectite, jarosite, kaolinite, gypsum, and mixed-layered illite/smectite, which are either definitely or most likely of hydrothermal alteration origin. Smectite in particular appears to be the most abundant and spectrally dominant mineral in summit ground truth samples, ASTER mapping results, Xico avalanche deposit, and an older (pre-Xico avalanche) deposit derived from collapse(s) of ancestral Cofre de Perote edifice. However, both Xico avalanche and Los Pescados debris flow deposits show some evidence of secondary, postemplacement weathering and induration, which is evident by the presence of gibbsite, and hydroxyl interlayered minerals, in addition to recently formed halloysite and hydrous silica (i.e., indurating) cements. Field-based, visible infrared image spectroscopy (VIS/IR) spectral measurements offer the possibility of distinguishing primary minerals of hydrothermal alteration origin in debris-avalanche and debris-flow deposits from those produced either by in situ chemical weathering or bulked from weathered source materials.

Runaway electron dynamics in tokamak plasmas with high impurity content

DOE Office of Scientific and Technical Information (OSTI.GOV)

Martín-Solís, J. R., E-mail: solis@fis.uc3m.es; Loarte, A.; Lehnen, M.

2015-09-15

The dynamics of high energy runaway electrons is analyzed for plasmas with high impurity content. It is shown that modified collision terms are required in order to account for the collisions of the relativistic runaway electrons with partially stripped impurity ions, including the effect of the collisions with free and bound electrons, as well as the scattering by the full nuclear and the electron-shielded ion charge. The effect of the impurities on the avalanche runaway growth rate is discussed. The results are applied, for illustration, to the interpretation of the runaway electron behavior during disruptions, where large amounts of impuritiesmore » are expected, particularly during disruption mitigation by massive gas injection. The consequences for the electron synchrotron radiation losses and the resulting runaway electron dynamics are also analyzed.« less

High-resolution distributed temperature sensing with the multiphoton-timing technique

NASA Astrophysics Data System (ADS)

Höbel, M.; Ricka, J.; Wüthrich, M.; Binkert, Th.

1995-06-01

We report on a multiphoton-timing distributed temperature sensor (DTS) based on the concept of distributed anti-Stokes Raman thermometry. The sensor combines the advantage of very high spatial resolution (40 cm) with moderate measurement times. In 5 min it is possible to determine the temperature of as many as 4000 points along an optical fiber with an accuracy Delta T less than 2 deg C. The new feature of the DTS system is the combination of a fast single-photon avalanche diode with specially designed real-time signal-processing electronics. We discuss various parameters that affect the operation of analog and photon-timing DTS systems. Particular emphasis is put on the consequences of the nonideal behavior of sensor components and the corresponding correction procedures.

Nanomechanics of slip avalanches in amorphous plasticity

NASA Astrophysics Data System (ADS)

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.

Segregating photoelastic particles in free-surface granular flows

NASA Astrophysics Data System (ADS)

Thomas, Amalia; Vriend, Nathalie; Environmental; Industrial Fluid Dynamics Team

2017-11-01

We present results from a novel experimental set-up creating 2D avalanches of photoelastic discs. Two distinct hoppers supply either monodisperse or bidisperse particles at adjustable flow-rates into a 2 meter long, narrow acrylic chute inclined at 20°. For 20-40 seconds the avalanche maintains a steady-state that accelerates and thins downstream. The chute basal roughness is variable, allowing for different flow profiles. Using a set of polarizers and a high-speed camera, we visualize and quantify the forces due to dynamic interactions between the discs using photoelastic theory. Velocity and density profiles are derived from particle tracking at different distances from the discharge point and are coarse-grained to obtain continuous fields. With the access to both force information and dynamical properties via particle-tracking, we can experimentally validate existing mu(I) and non-local rheologies. As an extension, we probe the effect of granular segregation in bimodal mixtures by using the two separate inflow hoppers. We derive the state of segregation along the avalanche channel and measure the segregation velocities of each species. This provides insight in, and a unique validation of, the fundamental physical processes that drive segregation in avalanching geometries.

Real time avalanche detection for high risk areas.

DOT National Transportation Integrated Search

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 :...

The laser lightning rod system: thunderstorm domestication.

PubMed

Ball, L M

1974-10-01

An unusual application of the laser, namely protection of life and property from lightning, is described. The device relies on multiphoton ionization in mode-locked beams, rather than on collisional (avalanche) electron production. Feasibility is demonstrated numerically, and relevant principles explained. A method of mobile deployment is mentioned, by which economic (as opposed to scientific) feasibility might be achieved.

Avalanche boron fusion by laser picosecond block ignition with magnetic trapping for clean and economic reactor

DOE PAGES

Hora, H.; Korn, G.; Eliezer, S.; ...

2016-10-11

Measured highly elevated gains of proton–boron (HB11) fusion (Picciottoet al., Phys. Rev. X4, 031030 (2014)) confirmed the exceptional avalanche reaction process (Lalousiset al., Laser Part. Beams 32, 409 (2014); Horaet al., Laser Part. Beams33, 607 (2015)) for the combination of the non-thermal block ignition using ultrahigh intensity laser pulses of picoseconds duration. The ultrahigh accelerationabovemore » $$10^{20}~\\text{cm}~\\text{s}^{-2}$$ for plasma blocks was theoretically and numerically predicted since 1978 (Hora,Physics of Laser Driven Plasmas(Wiley, 1981), pp. 178 and 179) and measured (Sauerbrey, Phys. Plasmas3, 4712 (1996)) in exact agreement (Horaet al., Phys. Plasmas14, 072701 (2007)) when the dominating force was overcoming thermal processes. This is based on Maxwell’s stress tensor by the dielectric properties of plasma leading to the nonlinear (ponderomotive) force $$f_{\\text{NL}}$$ resulting in ultra-fast expanding plasma blocks by a dielectric explosion. Combining this with measured ultrahigh magnetic fields and the avalanche process opens an option for an environmentally absolute clean and economic boron fusion power reactor. Finally, this is supported also by other experiments with very high HB11 reactions under different conditions (Labauneet al., Nature Commun.4, 2506 (2013)).« less

Possible layout solutions for the improvement of the dark rate of geiger mode avalanche structures in the GLOBALFOUNDRIES BCDLITE 0.18 μm CMOS technology

NASA Astrophysics Data System (ADS)

D'Ascenzo, N.; Xie, Q.

2018-04-01

Modern concepts of single photon or charged particle detection systems are based on geiger mode avalanche devices developed in CMOS technology. The key-problem encountered in the fabrication of these devices in CMOS is the dark rate level. The dark rate and single photon signal are not distinguishable. This sets also the limits of the application of geiger mode avalanche devices to single photon or charged particle detection systems. We report the design and fabrication of four possible layouts of these devices using the 0.18 μm BCDLite GLOBALFOUNDRIES process. The devices have an area of 50×50 μm2. They are characterized by a fast response time and an approximately 60 ns recovery time. The best topology exhibits an average dark rate as low as 3×103 kHz/mm2.

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

PubMed

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.

Communicators' perspective on snow avalanche risk communication

NASA Astrophysics Data System (ADS)

Charriere, M. K. M.; Bogaard, T.; Mostert, E.

2014-12-01

Among all the natural hazards, snow avalanches are the only ones for which a public danger scale is globally used. It consists of 5 levels of danger displayed with a given number and colour and for each of them, behavioural advices are provided. Even though this is standardized in most of the countries affected by this natural hazard, the tools (usually websites or smartphone applications) with which the information is disseminated to the general pubic differs, particularly in terms of target audience and level of details. This study aims at gathering the perspectives of several communicators that are responsible for these communication practices. The survey was created to assess how and why choices were made in the design process of the communication tools and to determine how their effectiveness is evaluated. Along with a review of existing avalanche risk communication tools, this study provides guidelines for communication and the evaluation of its effectiveness.

Nano-indentation used to study pyramidal slip in GaN single crystals

NASA Astrophysics Data System (ADS)

Krimsky, E.; Jones, K. A.; Tompkins, R. P.; Rotella, P.; Ligda, J.; Schuster, B. E.

2018-02-01

The nucleation and structure of dislocations created by the nano-indentation of GaN samples with dislocation densities ≈103, 106 or 109 ⊥/cm2 were studied in the interest of learning how dislocations can be created to relieve the mismatch strain in ternary nitride films grown on (0001) oriented binary nitride substrates. Using transmission electron microscopy and stress analyses to assist in interpreting the nano-indentation data, we determined that the pop-ins in the indenter load vs. penetration depth curves are created by an avalanche process at stresses well above the typical yield stress. The process begins by the homogeneous formation of a basal plane screw dislocation that triggers the formation of pyramidal and other basal plane dislocations that relieve the excess stored elastic energy. It appears that pyramidal slip can occur on either the {1122} or {0111} planes, as there is little resistance to the cross slip of screw dislocations.

Erosion waves: Transverse instabilities and fingering

NASA Astrophysics Data System (ADS)

Malloggi, F.; Lanuza, J.; Andreotti, B.; Clément, E.

2006-09-01

Two laboratory scale experiments of dry and underwater avalanches of non-cohesive granular materials are investigated. We trigger solitary waves and study the conditions under which the front is transversally stable. We show the existence of a linear instability followed by a coarsening dynamics and finally the onset of a fingering pattern. Due to the different operating conditions, both experiments strongly differ by the spatial and time scales involved. Nevertheless, the quantitative agreement between the stability diagram, the wavelengths selected and the avalanche morphology suggest a common scenario for an erosion/deposition process.

An experimental study of subaqueous slipface deposition.

USGS Publications Warehouse

Hunter, R.E.; Kocurek, G.

1986-01-01

A flume study indicates that grainflow on slipfaces accounts for most cross-strata formed in unidirectional, shallow-water flows. The slipfaces studied were on small megaripples and delta-like steps (0.06-0.28 m high). During intermittent avalanching, at relatively low flow velocities, periods between avalanches were marked by grainfall onto the slipface, the intensity of which was greatest near the brink of the slipface and increased with current velocity. The lee eddy proved very significant in slipface processes by redistributing grainfall sediments and both promoting and impeding grainflow. -from Authors

A comparison between spectra of runaway electron beams in SF{sub 6} and air

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zhang, Cheng; Wang, Ruexue; Yan, Ping

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,more » 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.« less

A field-shaping multi-well avalanche detector for direct conversion amorphous selenium

DOE Office of Scientific and Technical Information (OSTI.GOV)

Goldan, A. H.; Zhao, W.

2013-01-15

Purpose: A practical detector structure is proposed to achieve stable avalanche multiplication gain in direct-conversion amorphous selenium radiation detectors. Methods: The detector structure is referred to as a field-shaping multi-well avalanche detector. Stable avalanche multiplication gain is achieved by eliminating field hot spots using high-density avalanche wells with insulated walls and field-shaping inside each well. Results: The authors demonstrate the impact of high-density insulated wells and field-shaping to eliminate the formation of both field hot spots in the avalanche region and high fields at the metal-semiconductor interface. Results show a semi-Gaussian field distribution inside each well using the field-shaping electrodes,more » and the electric field at the metal-semiconductor interface can be one order-of-magnitude lower than the peak value where avalanche occurs. Conclusions: This is the first attempt to design a practical direct-conversion amorphous selenium detector with avalanche gain.« less

Gated IR imaging with 128 × 128 HgCdTe electron avalanche photodiode FPA

NASA Astrophysics Data System (ADS)

Beck, Jeff; Woodall, Milton; Scritchfield, Richard; Ohlson, Martha; Wood, Lewis; Mitra, Pradip; Robinson, Jim

2007-04-01

The next generation of IR sensor systems will include active imaging capabilities. One example of such a system is a gated-active/passive system. The gated-active/passive system promises long-range target detection and identification. A detector that is capable of both active and passive modes of operation opens up the possibility of a self-aligned system that uses a single focal plane. The detector would need to be sensitive in the 3-5 μm band for passive mode operation. In the active mode, the detector would need to be sensitive in eye-safe range, e.g. 1.55 μm, and have internal gain to achieve the required system sensitivity. The MWIR HgCdTe electron injection avalanche photodiode (e-APD) not only provides state-of-the-art 3-5 μm spectral sensitivity, but also high avalanche photodiode gain without minimal excess noise. Gains of greater than 1000 have been measured in MWIR e-APDs with a gain independent excess noise factor of 1.3. This paper reports the application of the mid-wave HgCdTe e-APD for near-IR gated-active/passive imaging. Specifically a 128x128 FPA composed of 40 μm pitch, 4.2 μm to 5 μm cutoff, APD detectors with a custom readout integrated circuit was designed, fabricated, and tested. Median gains as high as 946 at 11 V bias with noise equivalent inputs as low as 0.4 photon were measured at 80 K. A gated imaging demonstration system was designed and built using commercially available parts. High resolution gated imagery out to 9 km was obtained with this system that demonstrated predicted MTF, precision gating, and sub 10 photon sensitivity.

Lag and light-transfer characteristics of amorphous selenium photoconductive film with tellurium-doped layer

NASA Astrophysics Data System (ADS)

Park, Wug-Dong; Tanioka, Kenkichi

2016-07-01

Amorphous selenium (a-Se) high-gain avalanche rushing amorphous photoconductor (HARP) films have been used for highly sensitive imaging devices. To study a-Se HARP films for a solid-state image sensor, current-voltage, lag, spectral response, and light-transfer characteristics of 0.4-µm-thick a-Se HARP films are investigated. Also, to clarify a suitable Te-doped a-Se layer thickness in the a-Se photoconductor, we considered the effects of Te-doped layer thickness on the lag, spectral response, and light-transfer characteristics of 0.4-µm-thick a-Se HARP films. The threshold field, at which avalanche multiplication occurs in the a-Se HARP targets, decreases when the Te-doped layer thickness increases. The lag of 0.4-µm-thick a-Se HARP targets with Te-doped layers is higher than that of the target without Te doping. The lag of the targets with Te-doped layers is caused by the electrons trapped in the Te-doped layers within the 0.4-µm-thick a-Se HARP films. From the results of the spectral response measurement of about 15 min, the 0.4-µm-thick a-Se HARP targets with Te-doped layers of 90 and 120 nm are observed to be unstable owing to the electrons trapped in the Te-doped a-Se layer. From the light-transfer characteristics of 0.4-µm-thick a-Se HARP targets, as the slope at the operating point of signal current-voltage characteristics in the avalanche mode increases, the γ of the a-Se HARP targets decreases. Considering the effects of dark current on the lag and spectral response characteristics, a Te-doped layer of 60 nm is suitable for 0.4-µm-thick a-Se HARP films.

Volcanic hazards from Bezymianny- and Bandai-type eruptions

USGS Publications Warehouse

Siebert, L.; Glicken, H.; Ui, T.

1987-01-01

Major slope failures are a significant degradational process at volcanoes. Slope failures and associated explosive eruptions have resulted in more than 20 000 fatalities in the past 400 years; the historic record provides evidence for at least six of these events in the past century. Several historic debris avalanches exceed 1 km3 in volume. Holocene avalanches an order of magnitude larger have traveled 50-100 km from the source volcano and affected areas of 500-1500 km2. Historic eruptions associated with major slope failures include those with a magmatic component (Bezymianny type) and those solely phreatic (Bandai type). The associated gravitational failures remove major segments of the volcanoes, creating massive horseshoe-shaped depressions commonly of caldera size. The paroxysmal phase of a Bezymianny-type eruption may include powerful lateral explosions and pumiceous pyroclastic flows; it is often followed by construction of lava dome or pyroclastic cone in the new crater. Bandai-type eruptions begin and end with the paroxysmal phase, during which slope failure removes a portion of the edifice. Massive volcanic landslides can also occur without related explosive eruptions, as at the Unzen volcano in 1792. The main potential hazards from these events derive from lateral blasts, the debris avalanche itself, and avalanche-induced tsunamis. Lateral blasts produced by sudden decompression of hydrothermal and/or magmatic systems can devastate areas in excess of 500km2 at velocities exceeding 100 m s-1. The ratio of area covered to distance traveled for the Mount St. Helens and Bezymianny lateral blasts exceeds that of many pyroclastic flows or surges of comparable volume. The potential for large-scale lateral blasts is likely related to the location of magma at the time of slope failure and appears highest when magma has intruded into the upper edifice, as at Mount St. Helens and Bezymianny. Debris avalanches can move faster than 100 ms-1 and travel tens of kilometers. When not confined by valley walls, avalanches can affect wide areas beyond the volcano's flanks. Tsunamis from debris avalanches at coastal volcanoes have caused more fatalities than have the landslides themselves or associated eruptions. The probable travel distance (L) of avalanches can be estimated by considering the potential vertical drop (H). Data from a catalog of around 200 debris avalanches indicates that the H/L rations for avalanches with volumes of 0.1-1 km3 average 0.13 and range 0.09-0.18; for avalanches exceeding 1 km3, H/L ratios average 0.09 and range 0.5-0.13. Large-scale deformation of the volcanic edefice and intense local seismicity precede many slope failures and can indicate the likely failure direction and orientation of potential lateral blasts. The nature and duration of precursory activity vary widely, and the timing of slope faliure greatly affects the type of associated eruption. Bandai-type eruptions are particularly difficult to anticipate because they typically climax suddenly without precursory eruptions and may be preceded by only short periods of seismicity. ?? 1987 Springer-Verlag.

Mountain Search and Rescue with Remotely Piloted Aircraft Systems

NASA Astrophysics Data System (ADS)

Silvagni, Mario; Tonoli, Andrea; Zenerino, Enrico; Chiaberge, Marcello

2016-04-01

Remotely Piloted Aircraft Systems (RPAS) also known as Unmanned Aerial Systems (UAS) are nowadays becoming more and more popular in several applications. Even though a complete regulation is not yet available all over the world, researches, tests and some real case applications are wide spreading. These technologies can bring many benefits also to the mountain operations especially in emergencies and harsh environmental conditions, such as Search and Rescue (SAR) and avalanche rescue missions. In fact, during last decade, the number of people practicing winter sports in backcountry environment is increased and one of the greatest hazards for recreationists and professionals are avalanches. Often these accidents have severe consequences leading, mostly, to asphyxia-related death, which is confirmed by the hard drop of survival probability after ten minutes from the burying. Therefore, it is essential to minimize the time of burial. Modern avalanche beacon (ARTVA) interface guides the rescuer during the search phase reducing its time. Even if modern avalanche beacons are valid and reliable, the seeking range influences the rescue time. Furthermore, the environment and morphologic conditions of avalanches usually complicates the rescues. The recursive methodology of this kind of searching offers the opportunity to use automatic device like drones (RPAS). These systems allow performing all the required tasks autonomously, with high accuracy and without exposing the rescuers to additional risks due to secondary avalanches. The availability of highly integrated electronics and subsystems specifically meant for the applications, better batteries, miniaturized payload and, in general, affordable prices, has led to the availability of small RPAS with very good performances that can give interesting application opportunities in unconventional environments. The present work is one of the outcome from the experience made by the authors in RPAS fields and in Mechatronics devices for Mountain Safety and shows the design, construction and testing of a multipurpose RPAS to be used in mountain operations. The flying, multi-rotors based, platform and its embedded avionics is designed to meet environmental requirements such as temperature, altitude and wind, assuring the capability of carrying different payloads (separately or together) aimed to: • Avalanche Beacon search with automatic signal recognition and path following algorithms for quick buried identification. • Visual (visible and InfraRed) search and rescue for identifying missing persons on snow and woods even during night. • Customizable payload deployment to drop emergency kits or specific explosive cartridge for controlled avalanche detachment. The resulting small (less than 5kg) RPA is capable of full autonomous flight (including take-off and landing) on a pre-programmed, or easily configurable, custom mission. Furthermore, the embedded autopilot manages the sensors measurements (i.e. beacons or cameras) to update the flying mission. Specific features such as laser altimeter for terrain following have been developed and implemented. Remote control of the RPA from a ground station is available and a possible infrastructure, based on cloud/on-line architecture, for the real application is presented.

A mineralogical and granulometric study of Cayambe volcano debris avalanche deposit

NASA Astrophysics Data System (ADS)

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 < 2 mm) enriched in hydrothermally-altered materials. Preliminary results of granulometry measurements indicate that the matrix corresponds to ~55 wt.% of the deposit and suggest that the 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 determinations are in progress and will be presented.

A method for automated snow avalanche debris detection through use of synthetic aperture radar (SAR) imaging

NASA Astrophysics Data System (ADS)

Vickers, H.; Eckerstorfer, M.; Malnes, E.; Larsen, Y.; Hindberg, H.

2016-11-01

Avalanches are a natural hazard that occur in mountainous regions of Troms County in northern Norway during winter and can cause loss of human life and damage to infrastructure. Knowledge of when and where they occur especially in remote, high mountain areas is often lacking due to difficult access. However, complete, spatiotemporal avalanche activity data sets are important for accurate avalanche forecasting, as well as for deeper understanding of the link between avalanche occurrences and the triggering snowpack and meteorological factors. It is therefore desirable to develop a technique that enables active mapping and monitoring of avalanches over an entire winter. Avalanche debris can be observed remotely over large spatial areas, under all weather and light conditions by synthetic aperture radar (SAR) satellites. The recently launched Sentinel-1A satellite acquires SAR images covering the entire Troms County with frequent updates. By focusing on a case study from New Year 2015 we use Sentinel-1A images to develop an automated avalanche debris detection algorithm that utilizes change detection and unsupervised object classification methods. We compare our results with manually identified avalanche debris and field-based images to quantify the algorithm accuracy. Our results indicate that a correct detection rate of over 60% can be achieved, which is sensitive to several algorithm parameters that may need revising. With further development and refinement of the algorithm, we believe that this method could play an effective role in future operational monitoring of avalanches within Troms and has potential application in avalanche forecasting areas worldwide.

On the initiation of lightning in thunderclouds.

PubMed

Chilingarian, Ashot; Chilingaryan, Suren; Karapetyan, Tigran; Kozliner, Lev; Khanikyants, Yeghia; Hovsepyan, Gagik; Pokhsraryan, David; Soghomonyan, Suren

2017-05-02

The relationship of lightning and elementary particle fluxes in the thunderclouds is not fully understood to date. Using the particle beams (the so-called Thunderstorm Ground Enhancements - TGEs) as a probe we investigate the characteristics of the interrelated atmospheric processes. The well-known effect of the TGE dynamics is the abrupt termination of the particle flux by the lightning flash. With new precise electronics, we can see that particle flux decline occurred simultaneously with the rearranging of the charge centers in the cloud. The analysis of the TGE energy spectra before and after the lightning demonstrates that the high-energy part of the TGE energy spectra disappeared just after lightning. The decline of particle flux coincides on millisecond time scale with first atmospheric discharges and we can conclude that Relativistic Runaway Electron Avalanches (RREA) in the thundercloud assist initiation of the negative cloud to ground lightning. Thus, RREA can provide enough ionization to play a significant role in the unleashing of the lightning flash.

NASA Tech Briefs, March 2008

NASA Technical Reports Server (NTRS)

2008-01-01

Topics covered include: WRATS Integrated Data Acquisition System; Breadboard Signal Processor for Arraying DSN Antennas; Digital Receiver Phase Meter; Split-Block Waveguide Polarization Twist for 220 to 325 GHz; Nano-Multiplication-Region Avalanche Photodiodes and Arrays; Tailored Asymmetry for Enhanced Coupling to WGM Resonators; Disabling CNT Electronic Devices by Use of Electron Beams; Conical Bearingless Motor/Generators; Integrated Force Method for Indeterminate Structures; Carbon-Nanotube-Based Electrodes for Biomedical Applications; Compact Directional Microwave Antenna for Localized Heating; Using Hyperspectral Imagery to Identify Turfgrass Stresses; Shaping Diffraction-Grating Grooves to Optimize Efficiency; Low-Light-Shift Cesium Fountain without Mechanical Shutters; Magnetic Compensation for Second-Order Doppler Shift in LITS; Nanostructures Exploit Hybrid-Polariton Resonances; Microfluidics, Chromatography, and Atomic-Force Microscopy; Model of Image Artifacts from Dust Particles; Pattern-Recognition System for Approaching a Known Target; Orchestrator Telemetry Processing Pipeline; Scheme for Quantum Computing Immune to Decoherence; Spin-Stabilized Microsatellites with Solar Concentrators; Phase Calibration of Antenna Arrays Aimed at Spacecraft; Ring Bus Architecture for a Solid-State Recorder; and Image Compression Algorithm Altered to Improve Stereo Ranging.

Development and verification of signal processing system of avalanche photo diode for the active shields onboard ASTRO-H

NASA Astrophysics Data System (ADS)

Ohno, M.; Kawano, T.; Edahiro, I.; Shirakawa, H.; Ohashi, N.; Okada, C.; Habata, S.; Katsuta, J.; Tanaka, Y.; Takahashi, H.; Mizuno, T.; Fukazawa, Y.; Murakami, H.; Kobayashi, S.; Miyake, K.; Ono, K.; Kato, Y.; Furuta, Y.; Murota, Y.; Okuda, K.; Wada, Y.; Nakazawa, K.; Mimura, T.; Kataoka, J.; Ichinohe, Y.; Uchida, Y.; Katsuragawa, M.; Yoneda, H.; Sato, G.; Sato, R.; Kawaharada, M.; Harayama, A.; Odaka, H.; Hayashi, K.; Ohta, M.; Watanabe, S.; Kokubun, M.; Takahashi, T.; Takeda, S.; Kinoshita, M.; Yamaoka, K.; Tajima, H.; Yatsu, Y.; Uchiyama, H.; Saito, S.; Yuasa, T.; Makishima, K.; ASTRO-H HXI/SGD Team

2016-09-01

The hard X-ray Imager and Soft Gamma-ray Detector onboard ASTRO-H demonstrate high sensitivity to hard X-ray (5-80 keV) and soft gamma-rays (60-600 keV), respectively. To reduce the background, both instruments are actively shielded by large, thick Bismuth Germanate scintillators. We have developed the signal processing system of the avalanche photodiode in the BGO active shields and have demonstrated its effectiveness after assembly in the flight model of the HXI/SGD sensor and after integration into the satellite. The energy threshold achieved is about 150 keV and anti-coincidence efficiency for cosmic-ray events is almost 100%. Installed in the BGO active shield, the developed signal processing system successfully reduces the room background level of the main detector.

Impact of network topology on self-organized criticality

NASA Astrophysics Data System (ADS)

Hoffmann, Heiko

2018-02-01

The general mechanisms behind self-organized criticality (SOC) are still unknown. Several microscopic and mean-field theory approaches have been suggested, but they do not explain the dependence of the exponents on the underlying network topology of the SOC system. Here, we first report the phenomena that in the Bak-Tang-Wiesenfeld (BTW) model, sites inside an avalanche area largely return to their original state after the passing of an avalanche, forming, effectively, critically arranged clusters of sites. Then, we hypothesize that SOC relies on the formation process of these clusters, and present a model of such formation. For low-dimensional networks, we show theoretically and in simulation that the exponent of the cluster-size distribution is proportional to the ratio of the fractal dimension of the cluster boundary and the dimensionality of the network. For the BTW model, in our simulations, the exponent of the avalanche-area distribution matched approximately our prediction based on this ratio for two-dimensional networks, but deviated for higher dimensions. We hypothesize a transition from cluster formation to the mean-field theory process with increasing dimensionality. This work sheds light onto the mechanisms behind SOC, particularly, the impact of the network topology.

Tellurium doping effect in avalanche-mode amorphous selenium photoconductive film

NASA Astrophysics Data System (ADS)

Park, Wug-Dong; Tanioka, Kenkichi

2014-11-01

Amorphous selenium (a-Se) high-gain avalanche rushing amorphous photoconductor (HARP) film has been used for highly sensitive imaging devices. To improve the spectral response of a-Se HARP photoconductive film at a long wavelength, the tellurium (Te) doping effect in an 8-μm-thick a-Se HARP film was investigated. The thickness of the Te-doped a-Se layer in the 8-μm-thick a-Se HARP films was varied from 60 to 120 nm. The signal current increases significantly due to the avalanche multiplication when the target voltage is increased over the threshold voltage. In the 8-μm-thick a-Se HARP film with a Te-doped layer, the spectral response at a long wavelength was improved in comparison with the a-Se HARP film without a Te-doped layer. In addition, the increase of the lag in the 8-μm-thick a-Se HARP target with a Te-doped layer of 120 nm is caused by the photoconductive lag due to the electrons trapped in the Te-doped layer. Based on the current-voltage characteristics, spectral response, and lag characteristics of the 8-μm-thick a-Se HARP targets, the Te-doped layer thickness of 90 nm is suitable for the 8-μm-thick a-Se HARP film.

Modeling and Scaling of the Distribution of Trade Avalanches in a STOCK Market

NASA Astrophysics Data System (ADS)

Kim, Hyun-Joo

We study the trading activity in the Korea Stock Exchange by considering trade avalanches. A series of successive trading with small trade time interval is regarded as a trade avalanche of which the size s is defined as the number of trade in a series of successive trades. We measure the distribution of trade avalanches sizes P(s) and find that it follows the power-law behavior P(s) ~ s-α with the exponent α ≈ 2 for two stocks with the largest number of trades. A simple stochastic model which describes the power-law behavior of the distribution of trade avalanche size is introduced. In the model it is assumed that the some trades induce the accompanying trades, which results in the trade avalanches and we find that the distribution of the trade avalanche size also follows power-law behavior with the exponent α ≈ 2.

Negative feedback avalanche diode

NASA Technical Reports Server (NTRS)

Itzler, Mark Allen (Inventor)

2010-01-01

A single-photon avalanche detector is disclosed that is operable at wavelengths greater than 1000 nm and at operating speeds greater than 10 MHz. The single-photon avalanche detector comprises a thin-film resistor and avalanche photodiode that are monolithically integrated such that little or no additional capacitance is associated with the addition of the resistor.

Snow supporting structures for avalanche hazard reduction, 151 Avalanche, US 89/191, Jackson, Wyoming.

DOT National Transportation Integrated Search

2009-04-01

The 151 Avalanche, near Jackson, Wyoming has, historically, avalanched to the road below 1.5 to 2 times a year. The road, US 89/191 is four lanes and carries an estimated 8,000 vehicles per day in the winter months. The starting zone of the 151 Avala...

Short-Wave Infrared HgCdTe Electron Avalanche Photodiodes for Gated Viewing

NASA Astrophysics Data System (ADS)

Sieck, A.; Benecke, M.; Eich, D.; Oelmaier, R.; Wendler, J.; Figgemeier, H.

2018-06-01

Short-wave infrared (SWIR) HgCdTe electron avalanche photodiodes (eAPDs) with different doping profiles have been characterized for use in SWIR gated viewing systems. Gated viewing offers enhanced image contrast in scenes with clutter from the foreground or background. HgCdTe-based eAPDs show exponential gain-voltage characteristics and low excess noise and are, therefore, well suited for active imaging applications. The gain achievable at a fixed reverse voltage varies with the bandgap of the Hg1-xCdxTe detector material. We analyze current-voltage and gain-voltage plots measured on SWIR Hg1-xCdxTe eAPDs with x = 0.45, corresponding to a cutoff wavelength of 2.55 μm at 150 K. The cutoff has been chosen as a trade-off between achievable APD gain and operating temperature for SWIR gated-viewing systems with target distances of about 1000 m. Focal plane arrays with a readout-integrated circuit featuring a fast internal clock have been built and their performance with respect to gated viewing applications has been evaluated on a laboratory demonstrator for short distances. Future plans for a field demonstrator for distances up to 1000 m are described briefly at the end.

[Morphology determination of ionization region in multi-needle-to-plate negative corona discharge].

PubMed

Su, Peng-Hao; Zhu, Yi-Min; Chen, Hai-Feng

2007-11-01

Based on the former work on the current-voltage characteristics of a multi-needle-to-plate negative corona discharge at atmospheric pressure, the present work uses the method of OES (optical emission spectrum) for measuring N2 emission spectrum, and the morphology determination of the ionization region has been investigated. According to the distribution of N2 second positive band's intensity I(SPB), the highest of all bands, the outline of the ionization region was drawn fairly accurately. The relationship between I(SPB) and discharge current I can be obtained through the volume integral of the I(SPB). The experimental results show that the size of the ionization region enhances with the rise of the applied voltage U, and the electron avalanche begins at about 1 mm off the tips of needle electrode and multiplies only in the range of several millimeters, indicating that, the range of the ionization region is at the magnitude of mm. The electron avalanche along the axis of the needle develops farther than that along the radial direction of needle, and the shape of the ionization region looks like a bullet. The integral of I(SPB) is second-order linear to I, with a very second order coefficient, meaning that the main excited substance is N2. Energetic electrons mainly exist in ionization region while ions are the main charged particles to form discharge current in the transfer region.

Forecasting for natural avalanches during spring opening of Going-to-the-Sun Road, Glacier National Park, Montana, USA

USGS Publications Warehouse

Reardon, Blase; Lundy, Chris

2004-01-01

The annual spring opening of the Going-to-the-Sun Road in Glacier National Park presents a unique avalanche forecasting challenge. The highway traverses dozens of avalanche paths mid-track in a 23-kilometer section that crosses the Continental Divide. Workers removing seasonal snow and avalanche debris are exposed to paths that can produce avalanches of destructive class 4. The starting zones for most slide paths are within proposed Wilderness, and explosive testing or control are not currently used. Spring weather along the Divide is highly variable; rain-on-snow events are common, storms can bring several feet of new snow as late as June, and temperature swings can be dramatic. Natural avalanches - dry and wet slab, dry and wet loose, and glide avalanches - present a wide range of hazards and forecasting issues. This paper summarizes the forecasting program instituted in 2002 for the annual snow removal operations. It focuses on tools and techniques for forecasting natural wet snow avalanches by incorporating two case studies, including a widespread climax wet slab cycle in 2003. We examine weather and snowpack conditions conducive to wet snow avalanches, indicators for instability, and suggest a conceptual model for wet snow stability in a northern intermountain snow climate.

Analysis of the dynamic avalanche of carrier stored trench bipolar transistor (CSTBT) during clamped inductive turn-off transient

NASA Astrophysics Data System (ADS)

Xue, Peng; Fu, Guicui

2017-03-01

The dynamic avalanche has a huge impact on the switching robustness of carrier stored trench bipolar transistor (CSTBT). The purpose of this work is to investigate the CSTBT's dynamic avalanche mechanism during clamped inductive turn-off transient. At first, with a Mitsubishi 600 V/150 A CSTBT and a Infineon 600 V/200 A field stop insulated gate bipolar transistor (FS-IGBT) utilized, the clamped inductive turn-off characteristics are obtained by double pulse test. The unclamped inductive switching (UIS) test is also utilized to identify the CSTBT's clamping voltage under dynamic avalanche condition. After the test data analysis, it is found that the CSTBT's dynamic avalanche is abnormal and can be triggered under much looser condition than the conventional buffer layer IGBT. The comparison between the FS-IGBT and CSTBT's experimental results implies that the CSTBT's abnormal dynamic avalanche phenomenon may be induced by the carrier storage (CS) layer. Based on the semiconductor physics, the electric field distribution and dynamic avalanche generation in the depletion region are analyzed. The analysis confirms that the CS layer is the root cause of the CSTBT's abnormal dynamic avalanche mechanism. Moreover, the CSTBT's negative gate capacitance effect is also investigated to clarify the underlying mechanism of the gate voltage bump observed in the test. In the end, the mixed-mode numerical simulation is utilized to reproduce the CSTBT's dynamic avalanche behavior. The simulation results validate the proposed dynamic avalanche mechanisms.

Breakdown voltage reduction by field emission in multi-walled carbon nanotubes based ionization gas sensor

DOE Office of Scientific and Technical Information (OSTI.GOV)

Saheed, M. Shuaib M.; Muti Mohamed, Norani; Arif Burhanudin, Zainal, E-mail: zainabh@petronas.com.my

2014-03-24

Ionization gas sensors using vertically aligned multi-wall carbon nanotubes (MWCNT) are demonstrated. The sharp tips of the nanotubes generate large non-uniform electric fields at relatively low applied voltage. The enhancement of the electric field results in field emission of electrons that dominates the breakdown mechanism in gas sensor with gap spacing below 14 μm. More than 90% reduction in breakdown voltage is observed for sensors with MWCNT and 7 μm gap spacing. Transition of breakdown mechanism, dominated by avalanche electrons to field emission electrons, as decreasing gap spacing is also observed and discussed.

Generation of subnanosecond electron beams in air at atmospheric pressure

NASA Astrophysics Data System (ADS)

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.

Simulating the inception of pulsed discharges near positive electrodes

NASA Astrophysics Data System (ADS)

Teunissen, Jannis; Ebert, Ute

2013-09-01

With 3D particle simulations we study the inception of pulsed discharges near positive electrodes. In different geometries, we first determine the breakdown voltage. Then we study the probability of inception for a fast voltage pulse. This probability mostly depends on the availability of seed electrons to generate the initial electron avalanches. These results are compared with experimental observations. Then we investigate how the shape of a starting discharge affects its further development. In particular, we discuss the formation of so-called ``inception clouds.'' JT was supported by STW-project 10755.

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

NASA Astrophysics Data System (ADS)

Korzeniowska, Karolina; Bühler, Yves; Marty, Mauro; Korup, Oliver

2017-10-01

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.

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

NASA Astrophysics Data System (ADS)

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 other hand, require the expertise to adjust the planning of a tour and their backcountry travel behavior depending on the avalanche danger and the avalanche problem.

Risk analysis for dry snow slab avalanche release by skier triggering

NASA Astrophysics Data System (ADS)

McClung, David

2013-04-01

Risk analysis is of primary importance for skier triggering of avalanches since human triggering is responsible for about 90% of deaths from slab avalanches in Europe and North America. Two key measureable quantities about dry slab avalanche release prior to initiation are the depth to the weak layer and the slope angle. Both are important in risk analysis. As the slope angle increases, the probability of avalanche release increases dramatically. As the slab depth increases, the consequences increase if an avalanche releases. Among the simplest risk definitions is (Vick, 2002): Risk = (Probability of failure) x (Consequences of failure). Here, these two components of risk are the probability or chance of avalanche release and the consequences given avalanche release. In this paper, for the first time, skier triggered avalanches were analyzed from probability theory and its relation to risk for both the D and . The data consisted of two quantities : (,D) taken from avalanche fracture line profiles after an avalanche has taken place. Two data sets from accidentally skier triggered avalanches were considered: (1) 718 for and (2) a set of 1242 values of D which represent average values along the fracture line. The values of D were both estimated (about 2/3) and measured (about 1/3) by ski guides from Canadian Mountain Holidays CMH). I also analyzed 1231 accidentally skier triggered avalanches reported by CMH ski guides for avalanche size (representing destructive potential) on the Canadian scale. The size analysis provided a second analysis of consequences to verify that using D. The results showed that there is an intermediate range of both D and with highest risk. ForD, the risk (product of consequences and probability of occurrence) is highest for D in the approximate range 0.6 m - 1.0 m. The consequences are low for lower values of D and the chance of release is low for higher values of D. Thus, the highest product is in the intermediate range. For slope angles, the risk analysis showed there are two ranges: ˜ 320; × 460for which risk is lowest. In this case, both the range of and the consequences vary by about a factor of two so the probability of release dominates the risk analysis to yield low risk at the tails of the distribution of with highest risk in the middle (330 - 450) of the expected range (250 - 550).

Modeling of snow avalanches for protection measures designing

NASA Astrophysics Data System (ADS)

Turchaninova, Alla; Lazarev, Anton; Loginova, Ekaterina; Seliverstov, Yuri; Glazovskaya, Tatiana; Komarov, Anton

2017-04-01

Avalanche protection structures such as dams have to be designed using well known standard engineering procedures that differ in different countries. Our intent is to conduct a research on structural avalanche protection measures designing and their reliability assessment during the operation using numerical modeling. In the Khibini Mountains, Russia, several avalanche dams have been constructed at different times to protect settlements and mining. Compared with other mitigation structures dams are often less expensive to construct in mining regions. The main goal of our investigation was to test the capabilities of Swiss avalanche dynamics model RAMMS and Russian methods to simulate the interaction of avalanches with mitigation structures such as catching and reflecting dams as well as to reach the observed runout distances after the transition through a dam. We present the RAMMS back-calculation results of an artificially triggered and well-documented catastrophic avalanche occurred in the town of Kirovsk, Khibini Mountains in February 2016 that has unexpectedly passed through a system of two catching dams and took the lives of 3 victims. The estimated volume of an avalanche was approximately 120,000 m3. For the calculation we used a 5 m DEM including catching dams generated from field measurements in summer 2015. We simulated this avalanche (occurred below 1000 m.a.s.l.) in RAMMS having taken the friction parameters (µ and ζ) from the upper altitude limit (above 1500 m.a.s.l.) from the table recommended for Switzerland (implemented into RAMMS) according to the results of our previous research. RAMMS reproduced the observed avalanche behavior and runout distance. No information is available concerning the flow velocity; however, calculated values correspond in general to the values measured in this avalanche track before. We applied RAMMS using an option of adding structures to DEM (including a dam in GIS) in other to test other operating catching dams in Khibini Mountains by different avalanche scenarios and discuss the technical procedure and obtained results. RAMMS results were compared with field observations data and values received with Russian well-known one dimensional avalanche models. In the Caucasus, Russia, new ski resorts are being under the development which is impossible without avalanche protection. The choice of the avalanche mitigation type has to be done by experts depending on many factors. Within the ski resort Arkhyz, Caucasus we implemented RAMMS into the procedure of the structural measures type decision making. RAMMS as well as Russian well-known one-dimensional models were used to calculate the key input parameters for structures designing. The calculation results were coupled with field observations data and historical records. Finally we suggested the avalanche protection plan for the area of interest. The interpretation of RAMMS simulations including mitigation structures has been made in order to assess the reliability of the proposed protection.

Experimental investigation on the effect of plasma jet in the triggered discharge process of a gas switch

DOE Office of Scientific and Technical Information (OSTI.GOV)

Tie, W., E-mail: twh.110.666@163.com, E-mail: 84470220@qq.com; Xi'an Jiaotong University, Xi'an 710049; Liu, S.

The temporal and spatial evolution of a plasma jet generated by a spark discharge was observed. The electron temperature and density were obtained under different time and gas pressures by optical emission spectroscopy. Moreover, the discharge process of the plasma-jet triggered gas switch was recorded and analyzed at the lowest working coefficient. The results showed that the plasma jet moved forward in a bullet mode, and the advancing velocity increased with the decrease of pressure, and decreased with time growing. At initial time, the maximum velocity of a plasma jet could reach 3.68 × 10{sup 6 }cm/s. The electron temperature decreased from 2.0 eVmore » to 1.3 eV, and the electron density increased from 3.1 × 10{sup 15}/cm{sup 3} to 6.3 × 10{sup 15}/cm{sup 3} at the initial moment as the gas pressure increases from 0.1 MPa to 0.32 MPa. For a two-gap gas switch, the discharge performances were more depended on the second discharge spark gap (gap 2). Because plasma jet promoted the discharge in Gap 2, the gas switch operating in mode II had better triggered discharge characteristics. In the discharge process, the plasma-jet triggering had the effect of non-penetrating inducing, which not only provided initial electrons for reducing statistical lag but also enhanced the local electric field. The discharge was initiated and accelerated from electron avalanche to streamer. Therefore, a fast discharge was occurred in the gas switch.« less

Type-II Superlattice Avalanche Photodiodes

NASA Astrophysics Data System (ADS)

Huang, Jun

Type-II superlattice avalanche photodiodes have shown advantages compared to conventional mercury cadmium telluride photodiodes for infrared wavelength detection. However, surface or interface leakage current has been a major issue for superlattice avalanche photodiodes, especially in infrared wavelength region. First, passivation of the superlattice device with ammonium sulfide and thioacetamide was carried out, and its surface quality was studied by X-ray Photoelectron Spectroscopy. The study showed that both ammonium sulfide and thiacetamide passivation can actively remove the native oxide at the surface. Thiacetamide passivation combine more sulfur bonds with III-V elements than that of ammonium sulfide. Another X-ray photoelectron spectra of thiacetamide-treated atomic layer deposited zinc sulfide capped InAs/GaSb superlattice was performed to investigate the interface sulfur bond conditions. Sb--S and As--S bonds disappear while In-S bond gets enhanced, indicating that Indium Sulfide should be the major components at the interface after ZnS deposition. Second, the simulation of electrical characteristics for zinc sulfide, silicon nitride and silicon dioxide passivated superlattice devices was performed by SILVACO software to fit the experimental results and to discover the surface current mechanism. Different surface current mechanism strengths were found. Third, several novel dual-carrier avalanche photodiode structures were designed and simulated. The structures had alternate carrier multiplication regions, placed next to a wider electron multiplication region, creating dual-carrier multiplication feedback systems. Gain and excess noise factor of these structures were simulated and compared based on the dead space multiplication theory under uniform electric field. From the simulation, the applied bias can be greatly lowered or the thickness can be shrunk to achieve the same gain from the conventional device. The width of the thin region was the most critical parameter determining the device performance.

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

NASA Astrophysics Data System (ADS)

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).

Volcanic Processes and Geology of Augustine Volcano, Alaska

USGS Publications Warehouse

Waitt, Richard B.; Beget, James E.

2009-01-01

Augustine Island (volcano) in lower Cook Inlet, Alaska, has erupted repeatedly in late-Holocene and historical times. Eruptions typically beget high-energy volcanic processes. Most notable are bouldery debris avalanches containing immense angular clasts shed from summit domes. Coarse deposits of these avalanches form much of Augustine's lower flanks. A new geologic map at 1:25,000 scale depicts these deposits, these processes. We correlate deposits by tephra layers calibrated by many radiocarbon dates. Augustine Volcano began erupting on the flank of a small island of Jurassic clastic-sedimentary rock before the late Wisconsin glaciation (late Pleistocene). The oldest known effusions ranged from olivine basalt explosively propelled by steam, to highly explosive magmatic eruptions of dacite or rhyodacite shed as pumice flows. Late Wisconsin piedmont glaciers issuing from the mountainous western mainland surrounded the island while dacitic eruptive debris swept down the south volcano flank. Evidence is scant for eruptions between the late Wisconsin and about 2,200 yr B.P. On a few south-flank inliers, thick stratigraphically low pumiceous pyroclastic-flow and fall deposits probably represent this period from which we have no radiocarbon dates on Augustine Island. Eruptions between about 5,350 and 2,200 yr B.P. we know with certainty by distal tephras. On Shuyak Island 100 km southeast of Augustine, two distal fall ashes of Augustinian chemical provenance (microprobe analysis of glass) date respectively between about 5,330 and 5,020 yr B.P. and between about 3,620 and 3,360 yr B.P. An Augustine ash along Kamishak Creek 70 km southwest of Augustine dates between about 3,850 and 3,660 yr B.P. A probably Augustinian ash lying within peat near Homer dates to about 2,275 yr B.P. From before 2,200 yr B.P. to the present, Augustine eruptive products abundantly mantle the island. During this period, numerous coarse debris avalanches swept beyond Augustine's coast, most recently in A.D. 1883. The decapitated summit after the 1883 eruption, replaced by andesite domes of six eruptions since, shows a general process: collapse of steep summit domes, then the summit regrown by later dome eruptions. The island's stratigraphy is based on six or seven coarse-pumice tephra 'marker beds'. In upward succession they are layers G (2,100 yr B.P.), I (1,700 yr B.P.), H (1,400 yr B.P.), C (1,200-1,000 yr B.P.), M (750 yr B.P.), and B (390 yr B.P.). A coarse, hummocky debris-avalanche deposit older than about 2,100 yr B.P. - or perhaps a stack of three of them - lies along the east coast, the oldest exposed such bouldery diamicts on Augustine Island. Two large debris avalanches swept east and southeast into the sea between about 2,100 and 1,800 yr B.P. A large debris avalanche shed east and east-northeast into the sea between 1,700 and 14,00 yr B.P. Between about 1,400 and 1,100 yr B.P. debris avalanches swept into the sea on the volcano's south, southwest, and north-northwest. Pumiceous pyroclastic fans spread to the southeast and southwest, lithic pyroclastic flows and lahars (?) to the south and southeast. Pyroclastic flows, pyroclastic surges, and lahars swept down the west and south flanks between about 1,000 and 750 yr B.P. A debris avalanche swept into the sea on the west, and a small one on the south-southeast, between about 750 and 400 yr B.P. Large lithic pyroclastic flows shed to the southeast; smaller ones descended existing swales on the southwest and south. Between about 400 yr B.P. and historical time (late 1770s), three debris avalanches swept into the sea on the west-northwest, north-northwest, and north flanks. One of them (West Island) was large and fast: most of it rode to sea far beyond a former sea cliff, and its surface includes geomorphic evidence of having initiating a tsunami. Augustine's only conspicuous lava flow erupted on the north flank. During this prehistoric period numerous domes grew at th

The development of structures in analogue and natural debris avalanches

NASA Astrophysics Data System (ADS)

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 the Tacna Avalanche, Peru and the Pajonales-Aracar event in Argentina.

Risk Management and Physical Modelling for Mountainous Natural Hazards

NASA Astrophysics Data System (ADS)

Lehning, Michael; Wilhelm, Christian

Population growth and climate change cause rapid changes in mountainous regions resulting in increased risks of floods, avalanches, debris flows and other natural hazards. Xevents are of particular concern, since attempts to protect against them result in exponentially growing costs. In this contribution, we suggest an integral risk management approach to dealing with natural hazards that occur in mountainous areas. Using the example of a mountain pass road, which can be protected from the danger of an avalanche by engineering (galleries) and/or organisational (road closure) measures, we show the advantage of an optimal combination of both versus the traditional approach, which is to rely solely on engineering structures. Organisational measures become especially important for Xevents because engineering structures cannot be designed for those events. However, organisational measures need a reliable and objective forecast of the hazard. Therefore, we further suggest that such forecasts should be developed using physical numerical modelling. We present the status of current approaches to using physical modelling to predict snow cover stability for avalanche warnings and peak runoff from mountain catchments for flood warnings. While detailed physical models can already predict peak runoff reliably, they are only used to support avalanche warnings. With increased process knowledge and computer power, current developments should lead to a enhanced role for detailed physical models in natural mountain hazard prediction.

On the enhancement of p-11B fusion reaction rate in laser-driven plasma by α → p collisional energy transfer

NASA Astrophysics Data System (ADS)

Belloni, Fabio; Margarone, Daniele; Picciotto, Antonino; Schillaci, Francesco; Giuffrida, Lorenzo

2018-02-01

The possibility of triggering an avalanche reaction in laser-driven p-11B fusion by the effect of collisional energy transfer from α particles to protons has recently been debated, especially in connection to the high yield of α particles (4 × 108 per laser shot) achieved on engineered targets at the Prague Asterix Laser System (PALS), with a pulse of 500 J, 0.3 ns FWHM. We elucidate this controversial subject within the framework of a simple two-population model for protons, based on the binary collision theory in a plasma. We find an avalanche characteristic time of almost 1 μs for the 675 keV fusion cross section resonance in typical PALS plasma, upon idealized confinement conditions. This avalanche time is one order of magnitude higher than previously reported, meaning that no such process can substantially develop in plasma at the PALS on the 675 keV resonance, not even in the most optimistic confinement scenarios. Nevertheless, we put forward for further investigation that more realistic conditions for setting up the avalanche regime could rather be attained by suitably targeting the narrow 163 keV resonance in the fusion cross section, also in connection to recently proposed laser-driven magnetic trapping techniques.

Avalanche mode of motion - Implications from lunar examples.

NASA Technical Reports Server (NTRS)

Howard, K. A.

1973-01-01

A large avalanche (21 square kilometers) at the Apollo 17 landing site moved out several kilometers over flat ground beyond its source slope. If not triggered by impacts, then it was as 'efficient' as terrestrial avalanches attributed to air-cushion sliding. Evidently lunar avalanches are able to flow despite the lack of lubricating or cushioning fluid.

Avalanche mode of motion: Implications from lunar examples

USGS Publications Warehouse

Howard, K.A.

1973-01-01

A large avalanche (21 square kilometers) at the Apollo 17 landing site moved out several kilometers over flat ground beyond its source slope. If not triggered by impacts, then it was as "efficient" as terrestrial avalanches attributed to air-cushion sliding. Evidently lunar avalanches are able to flow despite the lack of lubricating or cushioning fluid.

Avalanches and scaling collapse in the large-N Kuramoto model

NASA Astrophysics Data System (ADS)

Coleman, J. Patrick; Dahmen, Karin A.; Weaver, Richard L.

2018-04-01

We study avalanches in the Kuramoto model, defined as excursions of the order parameter due to ephemeral episodes of synchronization. We present scaling collapses of the avalanche sizes, durations, heights, and temporal profiles, extracting scaling exponents, exponent relations, and scaling functions that are shown to be consistent with the scaling behavior of the power spectrum, a quantity independent of our particular definition of an avalanche. A comprehensive scaling picture of the noise in the subcritical finite-N Kuramoto model is developed, linking this undriven system to a larger class of driven avalanching systems.

Impulse response measurement in the HgCdTe avalanche photodiode

NASA Astrophysics Data System (ADS)

Singh, Anand; Pal, Ravinder

2018-04-01

HgCdTe based mid-wave infrared focal plane arrays (MWIR FPAs) are being developed for high resolution imaging and range determination of distant camouflaged targets. Effect of bandgap grading on the response time in the n+/ν/p+ HgCdTe electron avalanche photodiode (e-APD) is evaluated using impulse response measurement. Gain normalized dark current density of 2 × 10-9 A/cm2 at low reverse bias for passive mode and 2 × 10-4 A/cm2 at -8 V for active mode is measured in the fabricated APD device, yielding high gain bandwidth product of 2.4 THZ at the maximum gain. Diffusion of carriers is minimized to achieve transit time limited impulse response by introducing composition grading in the HgCdTe epilayer. The noise equivalent photon performance less than one is achievable in the FPA that is suitable for active cum passive imaging applications.

Avalanche photodiode based time-of-flight mass spectrometry

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ogasawara, Keiichi, E-mail: kogasawara@swri.edu; Livi, Stefano A.; Desai, Mihir I.

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. Bymore » 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.« less

Linear Mode HgCdTe Avalanche Photodiodes for Photon Counting Applications

NASA Technical Reports Server (NTRS)

Sullivan, William, III; Beck, Jeffrey; Scritchfield, Richard; Skokan, Mark; Mitra, Pradip; Sun, Xiaoli; Abshire, James; Carpenter, Darren; Lane, Barry

2015-01-01

An overview of recent improvements in the understanding and maturity of linear mode photon counting with HgCdTe electron-initiated avalanche photodiodes is presented. The first HgCdTe LMPC 2x8 format array fabricated in 2011 with 64 micron pitch was a remarkable success in terms of demonstrating a high single photon signal to noise ratio of 13.7 with an excess noise factor of 1.3-1.4, a 7 ns minimum time between events, and a broad spectral response extending from 0.4 micron to 4.2 micron. The main limitations were a greater than 10x higher false event rate than expected of greater than 1 MHz, a 5-7x lower than expected APD gain, and a photon detection efficiency of only 50% when greater than 60% was expected. This paper discusses the reasons behind these limitations and the implementation of their mitigations with new results.

Characterization of breakdown behavior of diamond Schottky barrier diodes using impact ionization coefficients

NASA Astrophysics Data System (ADS)

Driche, Khaled; Umezawa, Hitoshi; Rouger, Nicolas; Chicot, Gauthier; Gheeraert, Etienne

2017-04-01

Diamond has the advantage of having an exceptionally high critical electric field owing to its large band gap, which implies its high ability to withstand high voltages. At this maximum electric field, the operation of Schottky barrier diodes (SBDs), as well as FETs, may be limited by impact ionization, leading to avalanche multiplication, and hence the devices may breakdown. In this study, three of the reported impact ionization coefficients for electrons, αn, and holes, αp, in diamond at room temperature (300 K) are analyzed. Experimental data on reverse operation characteristics obtained from two different diamond SBDs are compared with those obtained from their corresponding simulated structures. Owing to the crucial role played by the impact ionization rate in determining the carrier transport, the three reported avalanche parameters implemented affect the behavior not only of the breakdown voltage but also of the leakage current for the same structure.

The formation of diffuse discharge by short-front nanosecond voltage pulses and the modification of dielectrics in this discharge

NASA Astrophysics Data System (ADS)

Orlovskii, V. M.; Panarin, V. A.; Shulepov, M. A.

2014-07-01

The dynamics of diffuse discharge formation under the action of nanosecond voltage pulses with short fronts (below 1 ns) in the absence of a source of additional preionization and the influence of a dielectric film on this process have been studied. It is established that the diffuse discharge is induced by the avalanche multiplication of charge initiated by high-energy electrons and then maintained due to secondary breakdowns propagating via ionized gas channels. If a dielectric film (polyethylene, Lavsan, etc.) is placed on the anode, then multiply repeated discharge will lead to surface and bulk modification of the film material. Discharge-treated polyethylene film exhibits a change in the optical absorption spectrum in the near-IR range.

Subnanosecond breakdown development in high-voltage pulse discharge: Effect of secondary electron emission

NASA Astrophysics Data System (ADS)

Alexandrov, A. L.; Schweigert, I. V.; Zakrevskiy, Dm. E.; Bokhan, P. A.; Gugin, P.; Lavrukhin, M.

2017-10-01

A subnanosecond breakdown in high-voltage pulse discharge may be a key tool for superfast commutation of high power devices. The breakdown in high-voltage open discharge at mid-high pressure in helium was studied in experiment and in kinetic simulations. The kinetic model of electron avalanche development was constructed, based on PIC-MCC simulations, including dynamics of electrons, ions and fast helium atoms, produced by ions scattering. Special attention was paid to electron emission processes from cathode, such as: photoemission by Doppler-shifted resonant photons, produced in excitation processes involving fast atoms; electron emission by ions and fast atoms bombardment of cathode; the secondary electron emission (SEE) by hot electrons from bulk plasma. The simulations show that the fast atoms accumulation is the main reason of emission growth at the early stage of breakdown, but at the final stage, when the voltage on plasma gap diminishes, namely the SEE is responsible for subnanosecond rate of current growth. It was shown that the characteristic time of the current growth can be controlled by the SEE yield. The influence of SEE yield for three types of cathode material (titanium, SiC, and CuAlMg-alloy) was tested. By changing the pulse voltage amplitude and gas pressure, the area of existence of subnanosecond breakdown is identified. It is shown that in discharge with SiC and CuAlMg-alloy cathodes (which have enhanced SEE) the current can increase with a subnanosecond characteristic time value as small as τs = 0.4 ns, for the pulse voltage amplitude of 5÷12 kV. An increase of gas pressure from 15 Torr to 30 Torr essentially decreases the time of of current front growth, whereas the pulse voltage variation weakly affects the results.

On the Internal Structure of Mobile Barchan Sand Dunes due to Granular Processes

NASA Astrophysics Data System (ADS)

Vriend, N. M.; Arran, M.; Louge, M. Y.; Hay, A. G.; Valance, A.

2017-12-01

In this work, we visualize the internal structure of mobile barchan desert dunes at the avalanche scale. We reveal an intriguing history of dune building using a novel combination of local sand sampling and advanced geophysical techniques resulting in high resolution measurements of individual avalanche events. Due to progressive rebuilding, granular avalanching, erosional and depositional processes, these marching barchan dunes are reworked every few years and a characteristic zebra-pattern (figure 1a), orientated parallel to the slipface at the angle of repose, appears at regular intervals. We present scientific data on the structure obtained from several mobile barchan dunes of different sizes during recent desert field campaigns (2014, 2015, 2017) in a mobile barchan dune field in Qatar (25.01°N, 51.34°E in the AlWakrah municipality). The site has been equipped with a weather station and has been regularly visited by a multidisciplinary research team in recent years (e.g. [1]). By applying high-frequency (1200 MHz) ground penetrating radar (GPR) transects across the midline (figure 1b) we map the continuous evolution of this cross-bedding at high resolution deep within the dune. The GPR reveals a slope reduction of the slipface near the base of the dune; evidence of irregular wind reversals; and the presence of a harder aeolian cap around the crest and extending to the brink. The data is supplemented with granulometry from layers stabilized by dyed water injection and uncovered by excavating vertical walls perpendicular to old buried avalanches. We attribute visible differences in water penetration between adjacent layers to fine particle segregation processes in granular avalanches. This work was made possible by the support of NPRP grant 6-059-2-023 from the Qatar National Research Fund to MYL and AGH, and a Royal Society Dorothy Hodgkin Research Fellowship to NMV. We thank Jean-Luc Métayer for performing detailed particle size distribution measurements. References: [1] Louge, M. Y., A. Valance, A. Ould el-Moctar, J. Xu, A. G. Hay, and R. Richer, Temperature and humidity within a mobile barchan sand dune, implications for microbial survival, J. Geophys. Res. 118, doi:10.1002/2013JF002839 (2013).

Disordered artificial spin ices: Avalanches and criticality (invited)

NASA Astrophysics Data System (ADS)

Reichhardt, Cynthia J. Olson; Chern, Gia-Wei; Libál, Andras; Reichhardt, Charles

2015-05-01

We show that square and kagome artificial spin ices with disconnected islands exhibit disorder-induced nonequilibrium phase transitions. The critical point of the transition is characterized by a diverging length scale and the effective spin reconfiguration avalanche sizes are power-law distributed. For weak disorder, the magnetization reversal is dominated by system-spanning avalanche events characteristic of a supercritical regime, while at strong disorder, the avalanche distributions have subcritical behavior and are cut off above a length scale that decreases with increasing disorder. The different type of geometrical frustration in the two lattices produces distinct forms of critical avalanche behavior. Avalanches in the square ice consist of the propagation of locally stable domain walls separating the two polarized ground states, and we find a scaling collapse consistent with an interface depinning mechanism. In the fully frustrated kagome ice, however, the avalanches branch strongly in a manner reminiscent of directed percolation. We also observe an interesting crossover in the power-law scaling of the kagome ice avalanches at low disorder. Our results show that artificial spin ices are ideal systems in which to study a variety of nonequilibrium critical point phenomena as the microscopic degrees of freedom can be accessed directly in experiments.

Risk assessment in the North Caucasus ski resorts

NASA Astrophysics Data System (ADS)

Komarov, Anton Y.; Seliverstov, Yury G.; Glazovskaya, Tatyana G.; Turchaninova, Alla S.

2016-10-01

Avalanches pose a significant problem in most mountain regions of Russia. The constant growth of economic activity, and therefore the increased avalanche hazard, in the North Caucasus region lead to demand for the development of large-scale avalanche risk assessment methods. Such methods are needed for the determination of appropriate avalanche protection measures as well as for economic assessments.The requirement of natural hazard risk assessments is determined by the Federal Law of the Russian Federation (Federal Law 21.12.1994 N 68-FZ, 2016). However, Russian guidelines (SNIP 11-02-96, 2013; SNIP 22-02-2003, 2012) are not clearly presented concerning avalanche risk assessment calculations. Thus, we discuss these problems by presenting a new avalanche risk assessment approach, with the example of developing but poorly researched ski resort areas. The suggested method includes the formulas to calculate collective and individual avalanche risk. The results of risk analysis are shown in quantitative data that can be used to determine levels of avalanche risk (appropriate, acceptable and inappropriate) and to suggest methods to decrease the individual risk to an acceptable level or better. The analysis makes it possible to compare risk quantitative data obtained from different regions, analyze them and evaluate the economic feasibility of protection measures.

Disordered artificial spin ices: Avalanches and criticality (invited)

DOE Office of Scientific and Technical Information (OSTI.GOV)

Reichhardt, Cynthia J. Olson, E-mail: cjrx@lanl.gov; Chern, Gia-Wei; Reichhardt, Charles

2015-05-07

We show that square and kagome artificial spin ices with disconnected islands exhibit disorder-induced nonequilibrium phase transitions. The critical point of the transition is characterized by a diverging length scale and the effective spin reconfiguration avalanche sizes are power-law distributed. For weak disorder, the magnetization reversal is dominated by system-spanning avalanche events characteristic of a supercritical regime, while at strong disorder, the avalanche distributions have subcritical behavior and are cut off above a length scale that decreases with increasing disorder. The different type of geometrical frustration in the two lattices produces distinct forms of critical avalanche behavior. Avalanches in themore » square ice consist of the propagation of locally stable domain walls separating the two polarized ground states, and we find a scaling collapse consistent with an interface depinning mechanism. In the fully frustrated kagome ice, however, the avalanches branch strongly in a manner reminiscent of directed percolation. We also observe an interesting crossover in the power-law scaling of the kagome ice avalanches at low disorder. Our results show that artificial spin ices are ideal systems in which to study a variety of nonequilibrium critical point phenomena as the microscopic degrees of freedom can be accessed directly in experiments.« less

Wet and full-depth glide snow avalanche onset monitoring and detection with ground based Ku-band radar

NASA Astrophysics Data System (ADS)

Lucas, Célia; Bühler, Yves; Leinss, Silvan; Hajnsek, Irena

2017-04-01

Wet and full-depth glide snow avalanches can be of considerable danger for people and infrastructure in alpine regions. In Switzerland avalanche hazard predictions are performed by the Institute for Snow and Avalanche Research SLF. However these predictions are issued on regional scale and do not yield information about the current status of particular slopes of interest. To investigate the potential of radar technology for avalanche prediction on the slope scale, we performed the following experiment. During the winter seasons 2015/2016 and 2016/2017, a ground-based Ku-band radar was placed in the vicinity of Davos (GR) in order to monitor the Dorfberg slope with 4-minute measurement intervals [1]. With Differential Interferometry [2] line of sight movements on the order of a fraction of the radar wavelength (1.7 cm) can be measured. Applying this technique to the Dorfberg scenario, it was possible to detect snowpack displacement of up to 0.4 m over 3 days in the avalanche release area prior to a snow avalanche event. A proof of concept of this approach was previously made by [3-5]. The analysis of the snowpack displacement history of such release areas shows that an avalanche is generally released after several cycles of acceleration and deceleration of a specific area of the snowpack, followed by an abrupt termination of the movement at the moment of the avalanche release. The acceleration and deceleration trends are related to thawing and refreezing of the snowpack induced by the daily temperature variations. The proposed method for the detection of snowpack displacements as indication for potential wet and full-depth glide snow avalanches is a promising tool to increase avalanche safety on specific slopes putting infrastructure or people at risk. The identification of a singular signature to discriminate the time window immediately prior to the release is still under investigation, but the ability to monitor snowpack displacement allows for mapping of zones prone to wet and full-depth glide snow avalanches in the near future. Therefore in the current winter season, we attempt to automatically detect snowpack displacement and avalanche releases at Dorfberg. Automatic warnings issued by the radar about the presence and amount of displacement and information about location and altitude of creeping regions as well as released avalanches will be combined with simulated LWC (Liquid Water Content) for the observed area. This slope-specific knowledge will be evaluated for inclusion into the more regional avalanche bulletin issued by SLF. Two cameras capture photographs at 1 and 10 minute intervals respectively to reference the opening of optically visible tensile cracks and triggering of avalanches. [1] C. Lucas, Y. Buehler, A. Marino, I. Hajnsek: Investigation of Snow Avalanches wit Ground Based Ku-band Radar, EUSAR 2016; 11th European Conference on Synthetic Aperture Radar; Proceedings of, 2016 [2] R. Bamler, P. Hartl: Synthetic aperture radar interferometry, Inverse Problems, Vol. 14 R1-R54, 1988 [3] Y. Buehler, C. Pielmeier, R. Frauenfelder, C. Jaedicke, G. Bippus, A. Wiesmann and R. Caduff: Improved Alpine Avalanche Forecast Service AAF, Final Report, European Space Agency ESA, 2014 [4] R. Caduff, A. Wiesmann, Y. Buehler, and C. Pielmeier: Continuous monitoring of snowpack displacement at high spatial and temporal resolution with terrestrial radar interferometry, Geophysical Research Letters, vol. 42, no. 3, 2015. [5] R. Caduff, A. Wiesmann, Y. Bühler, C. Bieler, and P. Limpach, "Terrestrial radar interferometry for snow glide activity monitoring and its potential as precursor of wet snow," in Interpraevent, 2016, pp. 239-248.

Relativistic runaway ionization fronts.

PubMed

Luque, A

2014-01-31

We investigate the first example of self-consistent impact ionization fronts propagating at relativistic speeds and involving interacting, high-energy electrons. These fronts, which we name relativistic runaway ionization fronts, show remarkable features such as a bulk speed within less than one percent of the speed of light and the stochastic selection of high-energy electrons for further acceleration, which leads to a power-law distribution of particle energies. A simplified model explains this selection in terms of the overrun of Coulomb-scattered electrons. Appearing as the electromagnetic interaction between electrons saturates the exponential growth of a relativistic runaway electron avalanche, relativistic runaway ionization fronts may occur in conjunction with terrestrial gamma-ray flashes and thus explain recent observations of long, power-law tails in the terrestrial gamma-ray flash energy spectrum.

Modeling the GLOF Hazard Process Chain at Imja Lake in the Nepal Himalaya

NASA Astrophysics Data System (ADS)

Lala, J.; McKinney, D. C.; Rounce, D.

2017-12-01

The Hindu Kush-Himalaya region contains more glacial ice than any other non-polar region on earth. Many glacial lakes in Nepal are held in place by natural moraine dams, which are inherently unstable. Avalanches or landslides entering glacial lakes can cause tsunami-like waves that can overtop the moraines and trigger glacial lake outburst floods (GLOF). Mass loss at the Imja glacier is the highest in the Mount Everest region, and contributes to the expansion of Imja Tsho, a lake with several villages downstream. A GLOF from the lake might destroy both property and human life, making an understanding of flood triggering processes beneficial for both the downstream villages and other GLOF-prone areas globally. The process chain for an avalanche-induced GLOF was modeled numerically. The volume and velocity of debris from avalanches entering various future lake extents were calculated using RAMMS. Resulting waves and downstream flooding were simulated using BASEMENT to evaluate erosion at the terminal moraine. Wave characteristics in BASEMENT were validated with empirical equations to ensure the proper transfer of momentum from the avalanche to the lake. Moraine erosion was determined for two geomorphologic scenarios: a site-specific scenario using field samples, and a worst-case scenario based on past literature. Both cases resulted in no flooding outside the river channel at downstream villages. Worst-case scenario geomorphology resulted in increased channelization of the lake outlet and some moraine erosion but no catastrophic collapse. Site-specific data yielded similar results but with even less erosion and downstream discharge. While the models confirmed that Imja Tsho is unlikely to produce a catastrophic GLOF in the near future, they also highlight the importance of continued monitoring of the lake. Furthermore, the ease and flexibility of these methods allows for their adoption by a wide range of stakeholders for modeling other high-risk lakes.

Photon detector system

DOEpatents

Ekstrom, Philip A.

1981-01-01

A photon detector includes a semiconductor device, such as a Schottky barrier diode, which has an avalanche breakdown characteristic. The diode is cooled to cryogenic temperatures to eliminate thermally generated charge carriers from the device. The diode is then biased to a voltage level exceeding the avalanche breakdown threshold level such that, upon receipt of a photon, avalanche breakdown occurs. This breakdown is detected by appropriate circuitry which thereafter reduces the diode bias potential to a level below the avalanche breakdown threshold level to terminate the avalanche condition. Subsequently, the bias potential is reapplied to the diode in preparation for detection of a subsequently received photon.

Assessment and prevention of the avalanche risk on medium-high mountain from a geo-historical point of view. The Vosges range (France) as a case study.

NASA Astrophysics Data System (ADS)

Giacona, Florie; Martin, Brice; David, Pierre-Marie

2010-05-01

To mention avalanche risks in the Vosges generally causes certain disbelief because of its modest height. Moreover, as far as natural risks are concerned, and especially the avalanche risk, medium-high mountains are not usually studied. The attention is more focused on the spectacular and destructive phenomena that occur in highest mountains such as the Alps or the Pyrenees. However, in January and February 2000, fifteen people were victims of avalanches and three of them died. These accidents have suddenly drawn attention to the fact that avalanche risk is underestimated. In opposition to the Alps and Pyrenees there is no study or systematic inventory of avalanches in the medium-high mountain ranges. Moreover, the many research and methodological articles dedicated to studies on avalanches in the high mountain ranges do not, unfortunately, raise any concerns about medium-high mountain ranges. So, we had to develop a new research method based on handwritten, printed, and oral sources as well as on observations. The results of this historical research exceeded all expectations. About 300 avalanche events have been reported since the end of the 18th century; they happened in about 90 avalanche paths. Spatial and temporal distributions of the avalanche events can be explained by climate, vulnerability and land use evolutions. The vulnerability has evolved since the 18th century: material vulnerability decreased whereas human vulnerability increased due to the expansion of winter sports. Finally we focus our study on the perception of the avalanche risk by the winter sports adepts in the Vosges mountains. Indeed, at the beginning of this research, we were directly confronted to a lack of knowledge, or even to an ignorance, of the avalanche risk. Several factors contribute to this situation among which the topography. Even though some places in the Vosges mountains look like the alpine topography, most of the summits are rounded. Furthermore, this mountain presents an annual and seasonal variability of snowfall and snow height. And the summits and slopes which present an avalanche risk can be easily reached in wintertime thanks to car parks close to the summits and the clearing of snow from the roads. A study is therefore being carried out in order to understand the mechanisms of perception and awareness of the avalanche risk. This is the first step towards the development of a new prevention method adapted to the recreational public in medium-high mountains.

Electrostatic Discharge Training Manual

DTIC Science & Technology

1980-09-01

CAN BE MOLDED INTO FORMED SHAPES. FIBERBOARD, MELAMINE LAMINATES AND OTHER MATERIALS (LAMINATED OR HOMOGENEOUS) CAN BE CONSTRUCTED INTO BOXES AND...COVERED WITH, ESD PROTECTIVE MATERIALS SUCH AS METAL, MIL-B-81705 TYPE II, MIL-P- 82646 (REFERENCES 17, 16), MELAMINE LAMINATES OR OTHER ESD PROTECTIVE...CONDUCTANCE IN AVALANCHE MICROWAVE OSCILLATORS", IEEE TRANSACTIONS ON ELECTRON DEVICES, ED-i5, JUNE 1968. 32. HOLM, R., ELECTRIC CONTACTS HANDBOOK, BERLIN

Single photon detection in a waveguide-coupled Ge-on-Si lateral avalanche photodiode.

PubMed

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.

Modelling of streamer ignition and propagation in the system of two approaching hydrometeors

NASA Astrophysics Data System (ADS)

Jansky, J.; Pasko, V. P.

2017-12-01

The lightning initiation in low thundercloud fields represents an unsolved problem in lightning discharge physics. One of the initial conditions required for formation of a hot leader channel is initiation of non-thermal streamer discharges. Streamers can be initiated from electron avalanches, however, the problem of existence of an electric field strong enough for streamer initiation in thunderclouds is still open. The maximum electric field in thunderstorms measured by balloons is typically 3-4 kV cm-1 atm-1, that is significantly smaller than the breakdown electric field needed for avalanche multiplication of electrons Ek≃28.7 kV cm-1 atm-1. One of the possible explanations for the streamer corona initiation is that hydrometeors greatly intensify the local electric field by at least an order of magnitude to initiate an electron avalanche. It was suggested that a particle pair or chain create more favorable conditions for initiation of lightning discharge than a single precipitation particle in low electric fields. Recently Cai et al. [GRL, 44, 5758-5765, 2017] analyzed the ignition conditions for two hydrometeors of same radii. In the present work we use streamer fluid model to study streamer initiation scenarios in a system of two hydrometeors with different radii. When the hydrometeors are approaching the Townsend discharge may develop first between them. Then the Townsend discharge transforms to streamer and two hydrometeors connect electrically, which leads to increase of the electric field on the outside hemispheres of hydrometeors. This increase of field for two particles of same radii was analyzed by Cooray et al. [Proceedings of 24th International Conference on Lightning Protection, Birmingham, United Kingdom, 1998]. The combination of small and large hydrometeors leads to higher enhancement on the outside of small hydrometeor. Simulation results show that streamer ignites there and propagates away from two hydrometeors. The streamer ignites at fields below Meek criterion due to the effects of photoionization feedback [Naidis, JPD, 38, 2211-2214, 2005; Liu et al., JASTP, 80, 179-186, 2012].

Explosive-residue compounds resulting from snow avalanche control in the Wasatch Mountains of Utah

USGS Publications Warehouse

Naftz, David L.; Kanagy, Leslie K.; Susong, David D.; Wydoski, Duane S.; Kanagy, Christopher J.

2003-01-01

A snow avalanche is a powerful force of nature that can play a significant role in developing mountain landscapes (Perla and Martinelli, 1975). More importantly, loss of life can occur when people are caught in the path of snow avalanches (Grossman, 1999). Increasing winter recreation, including skiing, snowboarding, snowmobiling, snowshoeing, and climbing in mountainous areas, has increased the likelihood of people encountering snow avalanches (fig. 1). Explosives are used by most ski areas and State highway departments throughout the Western United States to control the release of snow avalanches, thus minimizing the loss of human life during winter recreation and highway travel (fig. 2).Common explosives used for snow avalanche control include trinitrotoluene (TNT), pentaerythritoltetranitrate (PETN), cyclotrimethylenetrinitramine (RDX), tetrytol, ammonium nitrate, and nitroglycerin (Perla and Martinelli, 1975). During and after snowfall or wind loading of potential avalanche slopes, ski patrollers and Utah Department of Transportation personnel deliver explosive charges onto predetermined targets to artificially release snow avalanches, thereby rendering the slope safer for winter activities. Explosives can be thrown by hand onto target zones or shot from cannons for more remote delivery of explosive charges. Hand-delivered charges typically contain about 2 pounds of TNT or its equivalent (Perla and Martinelli, 1975).Depending on the size of the ski area, acreage of potential avalanche terrain, and weather conditions, the annual quantity of explosives used during a season of snow avalanche control can be substantial. For example, the three ski areas of Alta, Snowbird, and Brighton, plus the Utah Department of Transportation, may use as many as 11,200 hand charges per year (Wasatch Powderbird Guides, unpub. data, 1999) for snow avalanche control in Big and Little Cottonwood Canyons (fig. 3). If each charge is assumed to weigh 2 pounds, this equates to about 22,400 pounds of explosive hand charges per year. In addition, 2,240 to 3,160 Avalauncher rounds and 626 to 958 military artillery rounds (explosive mass not specified) are used each year by the three ski areas and the Utah Department of Transportation for snow avalanche control in Big and Little Cottonwood Canyons (Wasatch Powderbird Guides, unpub. data, 1999). The other ski area in Big Cottonwood Canyon, Brighton, uses about 2,000 pounds of explosives per year for snow avalanche control (Michele Weidner, Cirrus Ecological Solutions consultant, written commun., 2001).

Multiple remote-sensing assessment of the catastrophic collapse in Langtang Valley induced by the 2015 Gorkha earthquake

NASA Astrophysics Data System (ADS)

Nagai, Hiroto; Watanabe, Manabu; Tomii, Naoya; Tadono, Takeo; Suzuki, Shinichi

2017-11-01

The main shock of the 2015 Gorkha Earthquake in Nepal induced numerous avalanches, rockfalls, and landslides in Himalayan mountain regions. A major village in the Langtang Valley was destroyed and numerous people were victims of a catastrophic avalanche event, which consisted of snow, ice, rock, and blast wind. Understanding the hazard process mainly depends on limited witness accounts, interviews, and an in situ survey after a monsoon season. To record the immediate situation and to understand the deposition process, we performed an assessment by means of satellite-based observations carried out no later than 2 weeks after the event. The avalanche-induced sediment deposition was delineated with the calculation of decreasing coherence and visual interpretation of amplitude images acquired from the Phased Array-type L-band Synthetic Aperture Radar-2 (PALSAR-2). These outline areas are highly consistent with that delineated from a high-resolution optical image of WorldView-3 (WV-3). The delineated sediment areas were estimated as 0.63 km2 (PALSAR-2 coherence calculation), 0.73 km2 (PALSAR-2 visual interpretation), and 0.88 km2 (WV-3). In the WV-3 image, surface features were classified into 10 groups. Our analysis suggests that the avalanche event contained a sequence of (1) a fast splashing body with an air blast, (2) a huge, flowing muddy mass, (3) less mass flowing from another source, (4) a smaller amount of splashing and flowing mass, and (5) splashing mass without flowing on the east and west sides. By means of satellite-derived pre- and post-event digital surface models, differences in the surface altitudes of the collapse events estimated the total volume of the sediments as 5.51 ± 0.09 × 106 m3, the largest mass of which are distributed along the river floor and a tributary water stream. These findings contribute to detailed numerical simulation of the avalanche sequences and source identification; furthermore, altitude measurements after ice and snow melting would reveal a contained volume of melting ice and snow.

Detection and characterization of debris avalanche and pyroclastic flow dynamics from the simulation of the seismic signal they generate: application to Montserrat, Lesser Antilles

NASA Astrophysics Data System (ADS)

Zhao, J.; Mangeney, A.; Moretti, L.; Stutzmann, E.; Calder, E. S.; Smith, P. J.; Capdeville, Y.; Le Friant, A.; Cole, P.; Luckett, R.; Robertson, R.

2011-12-01

Gravitational instabilities such as debris avalanches or pyroclastic flows represent one of the major natural hazards for populations who live in mountainous or volcanic areas. Detection and understanding of the dynamics of these events is crucial for risk assessment. Furthermore, during an eruption, a series of explosions and gravitational flows can occur, making it difficult to retrieve the characteristics of the individual gravitational events such as their volume, velocity, etc. In this context, the seismic signal generated by these events provides a unique tool to extract information on the history of the eruptive process and to validate gravitational flow models. We analyze here a series of events including explosions, debris avalanche and pyroclastic flows occurring in Montserrat in December 1997. This seismic signal is composed of six main pulses. The characteristics of the seismic signals generated by pyroclastic flows (amplitude, emergent onset, frequency spectrum, etc.) are described and linked to the volume of the individual events estimated from past field surveys. As a first step, we simulate the waveform of each event by assuming that the generation process reduces to a simple force applied at the surface of the topography. Going further, we perform detailed numerical simulation of the Boxing Day debris avalanche and of the following pyroclastic flow using a landslide model able to take into account the 3D topography. The stress field generated by the gravitational flows on the topography is then applied as surface boundary condition in a wave propagation model, making it possible to simulate the seismic signal generated by the avalanche and pyroclastic flow. Comparison between the simulated signal and the seismic signal recorded at the Puerto Rico seismic station located 450 km away from the source, show that this method allows us to reproduce the low frequency seismic signal and to constrain the volume and frictional behavior of the individual events. As a result, simulation of seismic signals generated by gravitational flows provides insight into the history of eruptive sequences and into the characteristics of the individual events.

Natural avalanches and transportation: A case study from Glacier National Park, Montana, USA

USGS Publications Warehouse

Reardon, B.A.; Fagre, Daniel B.; Steiner, R.W.

2004-01-01

In January 2004, two natural avalanches (destructive class 3) derailed a freight train in John F. Stevens Canyon, on the southern boundary of Glacier National Park. The railroad tracks were closed for 29 hours due to cleanup and lingering avalanche hazard, backing up 112km of trains and shutting down Amtrak’s passenger service. The incident marked the fourth time in three winters that natural avalanches have disrupted transportation in the canyon, which is also the route of U.S. Highway 2. It was the latest in a 94-year history of accidents that includes three fatalities and the destruction of a major highway bridge. Despite that history and the presence of over 40 avalanche paths in the 16km canyon, mitigation is limited to nine railroad snow sheds and occasional highway closures. This case study examines natural avalanche cycles of the past 28 winters using data from field observations, a Natural Resources Conservation Service (NRCS) SNOTEL station, and data collected since 2001 at a high-elevation weather station. The avalanches occurred when storms with sustained snowfall buried a persistent near-surface faceted layer and/or were followed by rain-on-snow or dramatic warming (as much as 21oC in 30 minutes). Natural avalanche activity peaked when temperatures clustered near freezing (mean of -1.5oC at 1800m elev.). Avalanches initiated through rapid loading, rain falling on new snow, and/ or temperature-related changes in the mechanical properties of slabs. Lastly, the case study describes how recent incidents have prompted a unique partnership of land management agencies, private corporations and non-profit organizations to develop an avalanche mitigation program for the transportation corridor.

Statistical analyses support power law distributions found in neuronal avalanches.

PubMed

Klaus, Andreas; Yu, Shan; Plenz, Dietmar

2011-01-01

The size distribution of neuronal avalanches in cortical networks has been reported to follow a power law distribution with exponent close to -1.5, which is a reflection of long-range spatial correlations in spontaneous neuronal activity. However, identifying power law scaling in empirical data can be difficult and sometimes controversial. In the present study, we tested the power law hypothesis for neuronal avalanches by using more stringent statistical analyses. In particular, we performed the following steps: (i) analysis of finite-size scaling to identify scale-free dynamics in neuronal avalanches, (ii) model parameter estimation to determine the specific exponent of the power law, and (iii) comparison of the power law to alternative model distributions. Consistent with critical state dynamics, avalanche size distributions exhibited robust scaling behavior in which the maximum avalanche size was limited only by the spatial extent of sampling ("finite size" effect). This scale-free dynamics suggests the power law as a model for the distribution of avalanche sizes. Using both the Kolmogorov-Smirnov statistic and a maximum likelihood approach, we found the slope to be close to -1.5, which is in line with previous reports. Finally, the power law model for neuronal avalanches was compared to the exponential and to various heavy-tail distributions based on the Kolmogorov-Smirnov distance and by using a log-likelihood ratio test. Both the power law distribution without and with exponential cut-off provided significantly better fits to the cluster size distributions in neuronal avalanches than the exponential, the lognormal and the gamma distribution. In summary, our findings strongly support the power law scaling in neuronal avalanches, providing further evidence for critical state dynamics in superficial layers of cortex.

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

NASA Astrophysics Data System (ADS)

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 be combined with results from mapping and image analysis in order to provide a first description of the sequence and extension of events related to the evolution of this mountain front. [i] Hermanns et Strecker, Structural and lithological controls on large Quaternary rock avalanches (sturzstroms) in arid northwestern Argentina, Geological Society of America Bulletin 1999.

Substorm onset: Current sheet avalanche and stop layer

NASA Astrophysics Data System (ADS)

Haerendel, Gerhard

2015-03-01

A new scenario is presented for the onset of a substorm and the nature of the breakup arc. There are two main components, current sheet avalanche and stop layer. The first refers to an earthward flow of plasma and magnetic flux from the central current sheet of the tail, triggered spontaneously or by some unknown interaction with an auroral streamer or a suddenly appearing eastward flow at the end of the growth phase. The second offers a mechanism to stop the flow abruptly at the interface between magnetosphere and tail and extract momentum and energy to be partially processed locally and partially transmitted as Poynting flux toward the ionosphere. The stop layer has a width of the order of the ion inertial length. The different dynamics of the ions entering freely and the magnetized electrons create an electric polarization field which stops the ion flow and drives a Hall current by which flow momentum is transferred to the magnetic field. A simple formalism is used to describe the operation of the process and to enable quantitative conclusions. An important conclusion is that by necessity the stop layer is also highly structured in longitude. This offers a natural explanation for the coarse ray structure of the breakup arc as manifestation of elementary paths of energy and momentum transport. The currents aligned with the rays are balanced between upward and downward directions. While the avalanche is invoked for explaining the spontaneous substorm onset at the inner edge of the tail, the expansion of the breakup arc for many minutes is taken as evidence for a continued formation of new stop layers by arrival of flow bursts from the near-Earth neutral line. This is in line with earlier conclusions about the nature of the breakup arc. Small-scale structure, propagation speed, and energy flux are quantitatively consistent with observations. However, the balanced small-scale currents cannot constitute the substorm current wedge. The source of the latter must be located just earthward of the stop layer in the near-dipolar magnetosphere and be powered by the internal energy of the flow bursts. The stop layer mechanism is in some way the inverse of reconnection, as it converts flow into electromagnetic energy, and may have wide applicability in astrophysical plasmas.

Forest management to minimize landslide risk

Treesearch

Raymond M. Rice

1977-01-01

Mass wasting is the dominant erosional process in most steep-sloped catchments. major mechanism in this process is the landslide (2, 6, 8, 19, 24, 25, 29). In this paper, unless explicitly stated to the contrary, the reference to debris avalanches and other forms of shallow failures

Age of Palos Verdes submarine debris avalanche, southern California

USGS Publications Warehouse

Normark, W.R.; McGann, M.; Sliter, R.

2004-01-01

The Palos Verdes debris avalanche is the largest, by volume, late Quaternary mass-wasted deposit recognized from the inner California Borderland basins. Early workers speculated that the sediment failure giving rise to the deposit is young, taking place well after sea level reached its present position. A newly acquired, closely-spaced grid of high-resolution, deep-tow boomer profiles of the debris avalanche shows that the Palos Verdes debris avalanche fills a turbidite leveed channel that extends seaward from San Pedro Sea Valley, with the bulk of the avalanche deposit appearing to result from a single failure on the adjacent slope. Radiocarbon dates from piston-cored sediment samples acquired near the distal edge of the avalanche deposit indicate that the main failure took place about 7500 yr BP. ?? 2003 Elsevier B.V. All rights reserved.

Apparatus and method for recharging a string a avalanche transistors within a pulse generator

DOEpatents

Fulkerson, E. Stephen

2000-01-01

An apparatus and method for recharging a string of avalanche transistors within a pulse generator is disclosed. A plurality of amplification stages are connected in series. Each stage includes an avalanche transistor and a capacitor. A trigger signal, causes the apparatus to generate a very high voltage pulse of a very brief duration which discharges the capacitors. Charge resistors inject current into the string of avalanche transistors at various points, recharging the capacitors. The method of the present invention includes the steps of supplying current to charge resistors from a power supply; using the charge resistors to charge capacitors connected to a set of serially connected avalanche transistors; triggering the avalanche transistors; generating a high-voltage pulse from the charge stored in the capacitors; and recharging the capacitors through the charge resistors.

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

PubMed

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.

Avalanche risk in backcountry terrain based on usage frequency and accident data

NASA Astrophysics Data System (ADS)

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

2014-08-01

In Switzerland, the vast majority of avalanche accidents occurs during recreational activities. Risk analysis studies mostly rely on accident statistics without considering exposure (or the elements at risk), i.e. how many and where people are recreating. We compared the accident data (backcountry touring) with reports from two social media mountaineering networks - bergportal.ch and camptocamp.org. On these websites, users reported more than 15 000 backcountry tours during the five winters 2009/2010 to 2013/2014. We noted similar patterns in avalanche accident data and user data like demographics of recreationists, distribution of the day of the week (weekday vs. weekend) or weather conditions (fine vs. poor weather). However, we also found differences such as the avalanche danger conditions on days with activities and accidents, but also the geographic distribution. While backcountry activities are concentrated in proximity to the main population centres in the West and North of the Swiss Alps, a large proportion of the severe avalanche accidents occurred in the inner-alpine, more continental regions with frequently unfavorably snowpack structure. This suggests that even greater emphasis should be put on the type of avalanche problem in avalanche education and avalanche forecasting to increase the safety of backcountry recreationists.

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

NASA Astrophysics Data System (ADS)

Valero, Cesar Vera; Wever, Nander; Christen, Marc; Bartelt, Perry

2018-03-01

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.

A regional analysis of elements at risk exposed to mountain hazards in the Eastern European Alps

NASA Astrophysics Data System (ADS)

Fuchs, Sven; Zischg, Andreas

2014-05-01

We present a method to quantify the number and value of buildings exposed to torrents and snow avalanches in the Austrian Alps, as well as the number of exposed people. Based on a unique population and building register dataset, a relational SQL database was developed that allows in combination with GIS data a rule-based nation-wide automated analysis. Furthermore, possibilities and challenges are discussed with respect to the use of such data in vulnerability assessment and with respect to resilience measures. We comprehensively address the challenge of data accuracy, scale and uncertainties. From the total of approximately 2.4 million buildings with a clearly attributable geographical location, around 120,000 are exposed to torrent processes (5 %) and snow avalanches (0.4 %); exposition was defined here as located within the digitally available hazard maps of the Austrian Torrent and Avalanche Control Service. Around 5 % of the population (360,000 out of 8.5 million inhabitants), based on those people being compulsory listed in the population register, are located in these areas. The analysis according to the building category resulted in 2.05 million residential buildings in Austria (85 %), 93,000 of which (4.5 %) are exposed to these hazards. In contrast, 37,300 buildings (1.6 %) throughout the country belong to the category of accommodation facilities, 5,600 of which are exposed (15 %). Out of the 140,500 commercial buildings, 8,000 (5 %) are exposed. A considerable spatial variation was detectable within the communities and Federal States. In general, an above-average exposition of buildings to torrent process and snow avalanches was detectable in communities located in the Federal State of Salzburg, Styria and Vorarlberg (torrents), and Tyrol and Vorarlberg (snow avalanches). In the alpine part of Austria, the share of exposed accommodation buildings was two times (Salzburg) and three times (Vorarlberg) higher than the regional average of exposed buildings, and the share of agricultural buildings was around 50 % lower than on the national level. A significantly higher share of people is exposed in Salzburg (torrents) and Tyrol and Vorarlberg (snow avalanches); nevertheless, there is a need for a further in-depth local analysis. The results clearly indicate that an assessment using nation-wide data on buildings and population has advantages in vulnerability assessment compared to traditional approaches. However, the data has some limits if information on the large scale of individual catchments is needed, which restricts the application when an increase in resilience towards mountain hazards is targeted.

Synchrotron radiation from a runaway electron distribution in tokamaks

DOE Office of Scientific and Technical Information (OSTI.GOV)

Stahl, A.; Fülöp, T.; Landreman, M.

2013-09-15

The synchrotron radiation emitted by runaway electrons in a fusion plasma provides information regarding the particle momenta and pitch-angles of the runaway electron population through the strong dependence of the synchrotron spectrum on these parameters. Information about the runaway density and its spatial distribution, as well as the time evolution of the above quantities, can also be deduced. In this paper, we present the synchrotron radiation spectra for typical avalanching runaway electron distributions. Spectra obtained for a distribution of electrons are compared with the emission of mono-energetic electrons with a prescribed pitch-angle. We also examine the effects of magnetic fieldmore » curvature and analyse the sensitivity of the resulting spectrum to perturbations to the runaway distribution. The implications for the deduced runaway electron parameters are discussed. We compare our calculations to experimental data from DIII-D and estimate the maximum observed runaway energy.« less

The Avalanche Catastrophe of El Teniente-chile: August 8 of 1944.

NASA Astrophysics Data System (ADS)

Vergara, J.; Baros, M.

The avalanche of El Teniente-Chile (~34S) August 8 of 1944, was the most serious avalanche accident in Chile of the last 100 years. On the night of August 8, 1944, a major avalanche impacted a The Sewell, a worked village of the Copper Mine of El Teniente, there were 102 fatalities, 8 building, one school and one bridged de- stroyed. Due to a storm over the central part of Chile where intense precipitation fall over the Andes mountains during nine days. Historical precipitation records near to Sewell shows that total rainfall during the storms was 299mm (La Rufina) and 349mm (Bullileo), and the day before of avalanche the 24 hours rain intensity was 93mm. The Weilbull statistical analysis of monthly snowfall (water equivalent) record in Sewell from 1912-2001 show that the total August 1944 snowfall (621mm) was the larger of the all historical records and the return period is close one events in 180 years, and the annual snowfall during 1944 was 1140mm and return periods was 3.8 years. KEYWRODS: Chile, Avalanches, Andes Mountains, Avalanche Disaster, Historical Snow Records.

Avalanches, plasticity, and ordering in colloidal crystals under compression.

PubMed

McDermott, D; Reichhardt, C J Olson; Reichhardt, C

2016-06-01

Using numerical simulations we examine colloids with a long-range Coulomb interaction confined in a two-dimensional trough potential undergoing dynamical compression. As the depth of the confining well is increased, the colloids move via elastic distortions interspersed with intermittent bursts or avalanches of plastic motion. In these avalanches, the colloids rearrange to minimize their colloid-colloid repulsive interaction energy by adopting an average lattice constant that is isotropic despite the anisotropic nature of the compression. The avalanches take the form of shear banding events that decrease or increase the structural order of the system. At larger compression, the avalanches are associated with a reduction of the number of rows of colloids that fit within the confining potential, and between avalanches the colloids can exhibit partially crystalline or anisotropic ordering. The colloid velocity distributions during the avalanches have a non-Gaussian form with power-law tails and exponents that are consistent with those found for the velocity distributions of gliding dislocations. We observe similar behavior when we subsequently decompress the system, and find a partially hysteretic response reflecting the irreversibility of the plastic events.

A solid-state amorphous selenium avalanche technology for low photon flux imaging applications

PubMed Central

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

2010-01-01

Purpose: The feasibility of a practical solid-state technology for low photon flux imaging applications was investigated. The technology is based on an amorphous selenium photoreceptor with a voltage-controlled avalanche multiplication gain. If this photoreceptor can provide sufficient internal gain, it will be useful for an extensive range of diagnostic imaging systems. Methods: The avalanche photoreceptor under investigation is referred to as HARP-DRL. This is a novel concept in which a high-gain avalanche rushing photoconductor (HARP) is integrated with a distributed resistance layer (DRL) and sandwiched between two electrodes. The avalanche gain and leakage current characteristics of this photoreceptor were measured. Results: HARP-DRL has been found to sustain very high electric field strengths without electrical breakdown. It has shown avalanche multiplication gains as high as 104 and a very low leakage current (≤20 pA∕mm2). Conclusions: This is the first experimental demonstration of a solid-state amorphous photoreceptor which provides sufficient internal avalanche gain for photon counting and photon starved imaging applications. PMID:20964217

Leonardo (formerly Selex ES) infrared sensors for astronomy: present and future

NASA Astrophysics Data System (ADS)

Baker, Ian; Maxey, Chris; Hipwood, Les; Barnes, Keith

2016-07-01

Many branches of science require infrared detectors sensitive to individual photons. Applications range from low background astronomy to high speed imaging. Leonardo in Southampton, UK, has been developing HgCdTe avalanche photodiode (APD) sensors for astronomy in collaboration with European Southern Observatory (ESO) since 2008 and more recently the University of Hawaii. The devices utilise Metal Organic Vapour Phase Epitaxy, MOVPE, grown on low-cost GaAs substrates and in combination with a mesa device structure achieve very low dark current and near-ideal MTF. MOVPE provides the ability to grow complex HgCdTe heterostructures and these have proved crucial to suppress breakdown currents and allow high avalanche gain in low background situations. A custom device called Saphira (320x256/24μm) has been developed for wavefront sensors, interferometry and transient event imaging. This device has achieved read noise as low as 0.26 electrons rms and single photon imaging with avalanche gain up to x450. It is used in the ESO Gravity program for adaptive optics and fringe tracking and has been successfully trialled on the 3m NASA IRTF, 8.2m Subaru and 60 inch Mt Palomar for lucky imaging and wavefront sensing. In future the technology offers much shorter observation times for read-noise limited instruments, particularly spectroscopy. The paper will describe the MOVPE APD technology and current performance status.

Measurement of luminescence decays: High performance at low cost

NASA Astrophysics Data System (ADS)

Sulkes, Mark; Sulkes, Zoe

2011-11-01

The availability of inexpensive ultra bright LEDs spanning the visible and near-ultraviolet combined with the availability of inexpensive electronics equipment makes it possible to construct a high performance luminescence lifetime apparatus (˜5 ns instrumental response or better) at low cost. A central need for time domain measurement systems is the ability to obtain short (˜1 ns or less) excitation light pulses from the LEDs. It is possible to build the necessary LED driver using a simple avalanche transistor circuit. We describe first a circuit to test for small signal NPN transistors that can avalanche. We then describe a final optimized avalanche mode circuit that we developed on a prototyping board by measuring driven light pulse duration as a function of the circuit on the board and passive component values. We demonstrate that the combination of the LED pulser and a 1P28 photomultiplier tube used in decay waveform acquisition has a time response that allows for detection and lifetime determination of luminescence decays down to ˜5 ns. The time response and data quality afforded with the same components in time-correlated single photon counting are even better. For time-correlated single photon counting an even simpler NAND-gate based LED driver circuit is also applicable. We also demonstrate the possible utility of a simple frequency domain method for luminescence lifetime determinations.

First approximations in avalanche model validations using seismic information

NASA Astrophysics Data System (ADS)

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 of the flow in the slope, and make observations of the internal flow dynamics, especially flow regimes transitions, which depend on the slope-perpendicular energy fluxes induced by collisions at the basal boundary. The recorded data over several experimental seasons provide a catalogue of seismic data from different types and sizes of avalanches triggered at the VDLS experimental site. These avalanches are recorded also by the SLF instrumentation (FMCW radars, photography, photogrammetry, video, videogrammetry, pressure sensors). We select the best-quality avalanche data to model and establish comparisons. All this information allows us to calibrate parameters governing the internal energy fluxes, especially parameters governing the interaction of the avalanche with the incumbent snow cover. For the comparison between the seismic signal and the RAMMS models, we are focusing at the temporal evolution of the flow, trying to find the same arrival times of the front at the seismic sensor location in the avalanche path. We make direct quantitative comparisons between measurements and model outputs, using modelled flow height, normal stress, velocity, and pressure values, compared with the seismic signal, its envelope and its running spectrogram. In all cases, the first comparisons between the seismic signal and RAMMS outputs are very promising.

The solid state detector technology for picosecond laser ranging

NASA Technical Reports Server (NTRS)

Prochazka, Ivan

1993-01-01

We developed an all solid state laser ranging detector technology, which makes the goal of millimeter accuracy achievable. Our design and construction philosophy is to combine the techniques of single photon ranging, ultrashort laser pulses, and fast fixed threshold discrimination while avoiding any analog signal processing within the laser ranging chain. The all solid state laser ranging detector package consists of the START detector and the STOP solid state photon counting module. Both the detectors are working in an optically triggered avalanche switching regime. The optical signal is triggering an avalanche current buildup which results in the generation of a uniform, fast risetime output pulse.

Practical operational implementation of Teton Pass avalanche monitoring infrasound system.

DOT National Transportation Integrated Search

2008-12-01

Highway snow avalanche forecasting programs typically rely on weather and field observations to make road closure and hazard : evaluations. Recently, infrasonic avalanche monitoring technology has been developed for practical use near Teton Pass, WY ...

Avalanche risk assessment in Russia

NASA Astrophysics Data System (ADS)

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. The case studies of specific territories are performed using large-scale risk assessment methods. Thus, we discuss these problems by presenting an avalanche risk assessment approach on example of the developing but poorly researched ski resort areas in the North Caucasus. The suggested method includes the formulas to calculate collective and individual avalanche risk. The results of risk analysis are shown in quantitative data that can be used to determine levels of avalanche risk (acceptable, admissible and unacceptable) and to suggest methods to decrease the individual risk to acceptable level or better. It makes possible to compare risk quantitative data obtained from different mountain regions, analyze it and evaluate the economic feasibility of protection measures. At present, we are developing methods of avalanche risk assessment in economic performance. It conceder costs of objects located in avalanche prone area, traffic density values and probability of financial loss.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Shlapakovski, A. S.; Beilin, L.; Krasik, Ya. E.

Nanosecond-scale evolution of plasma and RF electromagnetic fields during the release of energy from a microwave pulse compressor with a plasma interference switch was investigated numerically using the code MAGIC. The plasma was simulated in the scope of the gas conductivity model in MAGIC. The compressor embodied an S-band cavity and H-plane waveguide tee with a shorted side arm filled with pressurized gas. In a simplified approach, the gas discharge was initiated by setting an external ionization rate in a layer crossing the side arm waveguide in the location of the electric field antinode. It was found that with increasingmore » ionization rate, the microwave energy absorbed by the plasma in the first few nanoseconds increases, but the absorption for the whole duration of energy release, on the contrary, decreases. In a hybrid approach modeling laser ignition of the discharge, seed electrons were set around the electric field antinode. In this case, the plasma extends along the field forming a filament and the plasma density increases up to the level at which the electric field within the plasma decreases due to the skin effect. Then, the avalanche rate decreases but the density still rises until the microwave energy release begins and the electric field becomes insufficient to support the avalanche process. The extraction of the microwave pulse limits its own power by terminating the rise of the plasma density and filament length. For efficient extraction, a sufficiently long filament of dense plasma must have sufficient time to be formed.« less

Advanced Avalanche Safety Equipment of Backcountry Users: Current Trends and Perceptions.

PubMed

Ng, Pearlly; Smith, William R; Wheeler, Albert; McIntosh, Scott E

2015-09-01

Backcountry travelers should carry a standard set of safety gear (transceiver, shovel, and probe) to improve rescue chances and reduce mortality risk. Many backcountry enthusiasts are using other advanced equipment such as an artificial air pocket (eg, the AvaLung) or an avalanche air bag. Our goal was to determine the numbers of backcountry users carrying advanced equipment and their perceptions of mortality and morbidity benefit while carrying this gear. A convenience sample of backcountry skiers, snowboarders, snowshoers, and snowmobilers was surveyed between February and April 2014. Participants of this study were backcountry mountain users recruited at trailheads in the Wasatch and Teton mountain ranges of Utah and Wyoming, respectively. Questions included prior avalanche education, equipment carried, and perceived safety benefit derived from advanced equipment. In all, 193 surveys were collected. Skiers and snowboarders were likely to have taken an avalanche safety course, whereas snowshoers and snowmobilers were less likely to have taken a course. Most backcountry users (149, 77.2%), predominantly skiers and snowboarders, carried standard safety equipment. The AvaLung was carried more often (47 users) than an avalanche air bag (10 users). The avalanche air bag had a more favorable perceived safety benefit. A majority of participants reported cost as the barrier to obtaining advanced equipment. Standard avalanche safety practices, including taking an avalanche safety course and carrying standard equipment, remain the most common safety practices among backcountry users in the Wasatch and Tetons. Snowshoers remain an ideal target for outreach to increase avalanche awareness and safety. Copyright © 2015 Wilderness Medical Society. Published by Elsevier Inc. All rights reserved.

Natural glide slab avalanches, Glacier National Park, USA: A unique hazard and forecasting challenge

USGS Publications Warehouse

Reardon, Blase; Fagre, Daniel B.; Dundas, Mark; Lundy, Chris

2006-01-01

In a museum of avalanche phenomena, glide cracks and glide avalanches might be housed in the “strange but true” section. These oddities are uncommon in most snow climates and tend to be isolated to specific terrain features such as bedrock slabs. Many glide cracks never result in avalanches, and when they do, the wide range of time between crack formation and slab failure makes them highly unpredictable. Despite their relative rarity, glide cracks and glide avalanches pose a regular threat and complex forecasting challenge during the annual spring opening of the Going-to-the-Sun Road in Glacier National Park, U.S.A. During the 2006 season, a series of unusual glide cracks delayed snow removal operations by over a week and provided a unique opportunity to record detailed observations of glide avalanches and characterize their occurrence and associated weather conditions. Field observations were from snowpits, crown profiles and where possible, measurements of slab thickness, bed surface slope angle, substrate and other physical characteristics. Weather data were recorded at one SNOTEL site and two automated stations located from 0.6-10 km of observed glide slab avalanches. Nearly half (43%) of the 35 glide slab avalanches recorded were Class D2-2.5, with 15% Class D3-D3.5. The time between glide crack opening and failure ranged from 2 days to over six weeks, and the avalanches occurred in cycles associated with loss of snow water equivalent and spikes in temperature and radiation. We conclude with suggest ions for further study.

Seismic spectrograms analysis applying the Hough transform to estimate the front speed of mass movements: Application to snow avalanches

NASA Astrophysics Data System (ADS)

Flores-Marquez, L.; Suriñach-Cornet, E., Sr.

2017-12-01

Seismic signals generated by snow avalanches and other mass movements are analyzed in their spectrogram representation. Spectrogram displays the evolution in time of the frequency content of the signals. The spectrogram of a seismic signal of a station to which a sliding mass, such as a snow avalanche, approaches, exhibits a triangular time / frequency signature. This increase in its higher frequency content over time is a consequence of the attenuation of the waves propagating in a media. Recognition of characteristic footprints in a spectrogram could help to identify and characterize diverse mass movement events such as landslides or snow avalanches. In order to recognize spectrogram features of seismic signals of Alpine snow avalanches, we propose an algorithm based on the Hough transform. The proposed algorithm is applied on an edge representation image of the seismic spectrogram obtained after fixing a threshold filter to the spectrogram, which enhances the most interesting frequencies of the seismogram that appear over time. This enables us to identify parameters (slopes) that correspond to the speeds associated with the type of snow avalanches, such as, powder, dense or transitional snow avalanches. The data analyzed in this work correspond to twenty different seismic signals generated by snow avalanches artificially released in the experimental site of Vallée de la Sionne (VDLS, SLF, Switzerland). The shape of the signal spectrograms are linked to the flow regimes previously identified. Our findings show that some ranges of speeds are inherent to the type of avalanche.

Active quench and reset integrated circuit with novel hold-off time control logic for Geiger-mode avalanche photodiodes.

PubMed

Deng, Shijie; Morrison, Alan P

2012-09-15

This Letter presents an active quench-and-reset circuit for Geiger-mode avalanche photodiodes (GM-APDs). The integrated circuit was fabricated using a conventional 0.35 μm complementary metal oxide semiconductor process. Experimental results show that the circuit is capable of linearly setting the hold-off time from several nanoseconds to microseconds with a resolution of 6.5 ns. This allows the selection of the optimal afterpulse-free hold-off time for the GM-APD via external digital inputs or additional signal processing circuitry. Moreover, this circuit resets the APD automatically following the end of the hold-off period, thus simplifying the control for the end user. Results also show that a minimum dead time of 28.4 ns is achieved, demonstrating a saturated photon-counting rate of 35.2 Mcounts/s.

Study of Z scaling of runaway electron plateau final loss energy deposition into wall of DIII-D

DOE PAGES

Hollmann, Eric M.; Commaux, Nicolas; Eidietis, Nicholas; ...

2017-06-12

Here, controlled runaway electron (RE) plateau-wall strikes with different initial impurity levels are used to study the effect of background plasma ion charge Z (resistivity) on RE-­wall loss dynamics. It is found that Joule heating (magnetic to kinetic energy conversion) during the final loss does not go up monotonically with increasing Z, but peaks at intermediate Z ~ 6. Joule heating and overall time scales of the RE final loss are found to be reasonably well-described by a basic 0D coupled-circuit model, with only the loss time as a free parameter. This loss time is found to be fairly wellmore » correlated with the avalanche time, possibly suggesting that the RE final loss rate is limited by the avalanche rate. First attempts at measuring total energy deposition to the vessel walls by REs during the final loss are made. At higher plasma impurity levels Z > 5, energy deposition to the wall appears be consistent with modeling, at least within the large uncertainties of the measurement. At low impurity levels Z < 5, however, local energy deposition appears around 5-­20× less than expected, suggesting that the RE energy dissipation at low Z is not fully understood.« less

Study of Z scaling of runaway electron plateau final loss energy deposition into wall of DIII-D

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hollmann, Eric M.; Commaux, Nicolas; Eidietis, Nicholas

Here, controlled runaway electron (RE) plateau-wall strikes with different initial impurity levels are used to study the effect of background plasma ion charge Z (resistivity) on RE-­wall loss dynamics. It is found that Joule heating (magnetic to kinetic energy conversion) during the final loss does not go up monotonically with increasing Z, but peaks at intermediate Z ~ 6. Joule heating and overall time scales of the RE final loss are found to be reasonably well-described by a basic 0D coupled-circuit model, with only the loss time as a free parameter. This loss time is found to be fairly wellmore » correlated with the avalanche time, possibly suggesting that the RE final loss rate is limited by the avalanche rate. First attempts at measuring total energy deposition to the vessel walls by REs during the final loss are made. At higher plasma impurity levels Z > 5, energy deposition to the wall appears be consistent with modeling, at least within the large uncertainties of the measurement. At low impurity levels Z < 5, however, local energy deposition appears around 5-­20× less than expected, suggesting that the RE energy dissipation at low Z is not fully understood.« less

Modeling of ablation threshold dependence on pulse duration for dielectrics with ultrashort pulsed laser

NASA Astrophysics Data System (ADS)

Sun, Mingying; Zhu, Jianqiang; Lin, Zunqi

2017-01-01

We present a numerical model of plasma formation in ultrafast laser ablation on the dielectrics surface. Ablation threshold dependence on pulse duration is predicted with the model and the numerical results for water agrees well with the experimental data for pulse duration from 140 fs to 10 ps. Influences of parameters and approximations of photo- and avalanche-ionization on the ablation threshold prediction are analyzed in detail for various pulse lengths. The calculated ablation threshold is strongly dependent on electron collision time for all the pulse durations. The complete photoionization model is preferred for pulses shorter than 1 ps rather than the multiphoton ionization approximations. The transition time of inverse bremsstrahlung absorption needs to be considered when pulses are shorter than 5 ps and it can also ensure the avalanche ionization (AI) coefficient consistent with that in multiple rate equations (MREs) for pulses shorter than 300 fs. The threshold electron density for AI is only crucial for longer pulses. It is reasonable to ignore the recombination loss for pulses shorter than 100 fs. In addition to thermal transport and hydrodynamics, neglecting the threshold density for AI and recombination could also contribute to the disagreements between the numerical and the experimental results for longer pulses.

Transient events in bright debris discs: Collisional avalanches revisited

NASA Astrophysics Data System (ADS)

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 avalanche would be a two-belt structure, with an inner belt (at 1 or 10 au for the "warm" and "cold" disc cases, respectively) of fractional luminosity f ≳ 10-4 where breakups of massive planetesimals occur, and a more massive outer belt, with τ of a few 10-3, into which the avalanche chain reaction develops and propagates.

On the design of experiments for the study of extreme field limits in the ultra-relativistic interaction of electromagnetic waves with plasmas

NASA Astrophysics Data System (ADS)

Bulanov, Sergei V.; Esirkepov, Timur Z.; Hayashi, Yukio; Kando, Masaki; Kiriyama, Hiromitsu; Koga, James K.; Kondo, Kiminori; Kotaki, Hideyuki; Pirozhkov, Alexander S.; Bulanov, Stepan S.; Zhidkov, Alexei G.; Chen, Pisin; Neely, David; Kato, Yoshiaki; Narozhny, Nikolay B.; Korn, Georg

2011-06-01

The critical electric field of quantum electrodynamics, called also the Schwinger field, is so strong that it produces electron-positron pairs from vacuum, converting the energy of light into matter. Since the dawn of quantum electrodynamics, there has been a dream on how to reach it on Earth. With the rise of laser technology this field has become feasible through the construction of extremely high power lasers or/and with the sophisticated use of nonlinear processes in relativistic plasmas. This is one of the most attractive motivations for extremely high power laser development, i.e. producing matter from vacuum by pure light in fundamental process of quantum electrodynamics in the nonperturbative regime. Recently it has been realized that a laser with intensity well below the Schwinger limit can create an avalanche of electron-positron pairs similar to a discharge before attaining the Schwinger field. It has also been realized that the Schwinger limit can be reached using an appropriate configuration of laser beams. In experiments on the collision of laser light and high intensity electromagnetic pulses generated by relativistic flying mirrors, with electron bunches produced by a conventional accelerator and with laser wake field accelerated electrons the studying of extreme field limits in the nonlinear interaction of electromagnetic waves is proposed. The regimes of dominant radiation reaction, which completely changes the electromagnetic wave-matter interaction, will be revealed. This will result in a new powerful source of high brightness gamma-rays. A possibility of the demonstration of the electronpositron pair creation in vacuum via multi-photon processes can be realized. This will allow modeling under terrestrial laboratory conditions neutron star magnetospheres, cosmological gamma ray bursts and the Leptonic Era of the Universe.

Avalanche multiplication in AlGaN-based heterostructures for the ultraviolet spectral range

NASA Astrophysics Data System (ADS)

Hahn, L.; Fuchs, F.; Kirste, L.; Driad, R.; Rutz, F.; Passow, T.; Köhler, K.; Rehm, R.; Ambacher, O.

2018-04-01

AlxGa1-xN based avalanche photodiodes grown on sapphire substrate with Al-contents of x = 0.65 and x = 0.60 have been examined under back- and frontside illumination with respect to their avalanche gain properties. The photodetectors suitable for the solar-blind ultraviolet spectral regime show avalanche gain for voltages in excess of 30 V reverse bias in the linear gain mode. Devices with a mesa diameter of 100 μm exhibit stable avalanche gain below the break through threshold voltage, exceeding a multiplication gain of 5500 at 84 V reverse bias. A dark current below 1 pA can be found for reverse voltages up to 60 V.

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

PubMed Central

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

2012-01-01

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°). 36Cl surface-exposure dating of boulders of the avalanche mass indicates an event age of 8.6 ± 0.6 ka. A 14C 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. PMID:24966447

Information Transparency in Education: Three Sides of a Two-Sided Process

ERIC Educational Resources Information Center

Mertsalova, T. A.

2015-01-01

Information transparency is the result of informational globalization and the avalanche of information and communication technologies: thus, these processes are natural for the whole modern society. Statistics show that during the past several years the transparency situation not just in education but in the entire society has expanded…

On ionizing shock waves

NASA Astrophysics Data System (ADS)

Kaniel, A.; Igra, O.; Ben-Dor, G.; Mond, M.

The flow field in the ionizing relaxation zone developed behind a normal shock wave in an electrically neutral, homogeneous, two temperature mixture of thermally ideal gases (molecules, atoms, ions, electrons) was numerically solved. The heat transfer between the electron gas and the other components was taken into account while all the other transport phenomena (molecular, turbulent and radiative) were neglected in the relaxation zone, since it is dominated by inelastic collisions. The threshold cross sections measured by Specht (1981), for excitation of argon by electron collisions, were used. The calculated results show good agreement with the results of the shock tube experiments presented by Glass and Liu (1978), especially in the electron avalanche region. A critical examination was made of the common assumptions regarding the average energy with which electrons are produced by atom-atom collisions and the relative effectiveness of atom-atom collisions (versus electron-atom collisions) in ionizing excited argon.

Fluid and hybrid models for streamers

NASA Astrophysics Data System (ADS)

Bonaventura, Zdeněk

2016-09-01

Streamers are contracted ionizing waves with self-generated field enhancement that propagate into a low-ionized medium exposed to high electric field leaving filamentary trails of plasma behind. The widely used model to study streamer dynamics is based on drift-diffusion equations for electrons and ions, assuming local field approximation, coupled with Poisson's equation. For problems where presence of energetic electrons become important a fluid approach needs to be extended by a particle model, accompanied also with Monte Carlo Collision technique, that takes care of motion of these electrons. A combined fluid-particle approach is used to study an influence of surface emission processes on a fast-pulsed dielectric barrier discharge in air at atmospheric pressure. It is found that fluid-only model predicts substantially faster reignition dynamics compared to coupled fluid-particle model. Furthermore, a hybrid model can be created in which the population of electrons is divided in the energy space into two distinct groups: (1) low energy `bulk' electrons that are treated with fluid model, and (2) high energy `beam' electrons, followed as particles. The hybrid model is then capable not only to deal with streamer discharges in laboratory conditions, but also allows us to study electron acceleration in streamer zone of lighting leaders. There, the production of fast electrons from streamers is investigated, since these (runaway) electrons act as seeds for the relativistic runaway electron avalanche (RREA) mechanism, important for high-energy atmospheric physics phenomena. Results suggest that high energy electrons effect the streamer propagation, namely the velocity, the peak electric field, and thus also the production rate of runaway electrons. This work has been supported by the Czech Science Foundation research project 15-04023S.

A debris avalanche at Forest Falls, San Bernardino County, California, July 11, 1999

USGS Publications Warehouse

Morton, Douglas M.; Hauser, Rachel M.

2001-01-01

This publication consists of the online version of a CD-ROM publication, U.S. Geological Survey Open-File Report 01-146. The data for this publication total 557 MB on the CD-ROM. For speed of transfer, the main PDF document has been compressed (with a subsequent loss of image quality) from 145 to 18.1 MB. The community of Forest Falls, California, is frequently subject to relatively slow moving debris flows. Some 11 debris flow events that were destructive to property have been recorded between 1955 and 1998. On July 11 and 13, 1999, debris flows again occurred, produced by high-intensity, short-duration monsoon rains. Unlike previous debris flow events, the July 11 rainfall generated a high-velocity debris avalanche in Snow Creek, one of the several creeks crossing the composite, debris flow dominated, alluvial fan on which Forest Falls is located. This debris avalanche overshot the bank of the active debris flow channel of Snow Creek, destroying property in the near vicinity and taking a life. The minimum velocity of this avalanche is calculated to have been in the range of 40 to 55 miles per hour. Impact from high-velocity boulders removed trees where the avalanche overshot the channel bank. Further down the fan, the rapidly moving debris fragmented the outer parts of the upslope side of large pine trees and embedded rock fragments into the tree trunks. Unlike the characteristic deposits formed by debris flows, the avalanche spread out down-slope and left no deposit suggestive of a debris avalanche. This summer monsoon-generated debris avalanche is apparently the first recorded for Forest Falls. The best indications of past debris avalanches may be the degree of permanent scars produced by extensive abrasion and splintering of the outer parts of pine trees that were in the path of an avalanche.

Extracting functionally feedforward networks from a population of spiking neurons

PubMed Central

Vincent, Kathleen; Tauskela, Joseph S.; Thivierge, Jean-Philippe

2012-01-01

Neuronal avalanches are a ubiquitous form of activity characterized by spontaneous bursts whose size distribution follows a power-law. Recent theoretical models have replicated power-law avalanches by assuming the presence of functionally feedforward connections (FFCs) in the underlying dynamics of the system. Accordingly, avalanches are generated by a feedforward chain of activation that persists despite being embedded in a larger, massively recurrent circuit. However, it is unclear to what extent networks of living neurons that exhibit power-law avalanches rely on FFCs. Here, we employed a computational approach to reconstruct the functional connectivity of cultured cortical neurons plated on multielectrode arrays (MEAs) and investigated whether pharmacologically induced alterations in avalanche dynamics are accompanied by changes in FFCs. This approach begins by extracting a functional network of directed links between pairs of neurons, and then evaluates the strength of FFCs using Schur decomposition. In a first step, we examined the ability of this approach to extract FFCs from simulated spiking neurons. The strength of FFCs obtained in strictly feedforward networks diminished monotonically as links were gradually rewired at random. Next, we estimated the FFCs of spontaneously active cortical neuron cultures in the presence of either a control medium, a GABAA receptor antagonist (PTX), or an AMPA receptor antagonist combined with an NMDA receptor antagonist (APV/DNQX). The distribution of avalanche sizes in these cultures was modulated by this pharmacology, with a shallower power-law under PTX (due to the prominence of larger avalanches) and a steeper power-law under APV/DNQX (due to avalanches recruiting fewer neurons) relative to control cultures. The strength of FFCs increased in networks after application of PTX, consistent with an amplification of feedforward activity during avalanches. Conversely, FFCs decreased after application of APV/DNQX, consistent with fading feedforward activation. The observed alterations in FFCs provide experimental support for recent theoretical work linking power-law avalanches to the feedforward organization of functional connections in local neuronal circuits. PMID:23091458

Extracting functionally feedforward networks from a population of spiking neurons.

PubMed

Vincent, Kathleen; Tauskela, Joseph S; Thivierge, Jean-Philippe

2012-01-01

Neuronal avalanches are a ubiquitous form of activity characterized by spontaneous bursts whose size distribution follows a power-law. Recent theoretical models have replicated power-law avalanches by assuming the presence of functionally feedforward connections (FFCs) in the underlying dynamics of the system. Accordingly, avalanches are generated by a feedforward chain of activation that persists despite being embedded in a larger, massively recurrent circuit. However, it is unclear to what extent networks of living neurons that exhibit power-law avalanches rely on FFCs. Here, we employed a computational approach to reconstruct the functional connectivity of cultured cortical neurons plated on multielectrode arrays (MEAs) and investigated whether pharmacologically induced alterations in avalanche dynamics are accompanied by changes in FFCs. This approach begins by extracting a functional network of directed links between pairs of neurons, and then evaluates the strength of FFCs using Schur decomposition. In a first step, we examined the ability of this approach to extract FFCs from simulated spiking neurons. The strength of FFCs obtained in strictly feedforward networks diminished monotonically as links were gradually rewired at random. Next, we estimated the FFCs of spontaneously active cortical neuron cultures in the presence of either a control medium, a GABA(A) receptor antagonist (PTX), or an AMPA receptor antagonist combined with an NMDA receptor antagonist (APV/DNQX). The distribution of avalanche sizes in these cultures was modulated by this pharmacology, with a shallower power-law under PTX (due to the prominence of larger avalanches) and a steeper power-law under APV/DNQX (due to avalanches recruiting fewer neurons) relative to control cultures. The strength of FFCs increased in networks after application of PTX, consistent with an amplification of feedforward activity during avalanches. Conversely, FFCs decreased after application of APV/DNQX, consistent with fading feedforward activation. The observed alterations in FFCs provide experimental support for recent theoretical work linking power-law avalanches to the feedforward organization of functional connections in local neuronal circuits.

Conditions for Triggering Avalanches in Mn12-acetate.

NASA Astrophysics Data System (ADS)

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

2007-03-01

Recent measurements in Mn12-acetate have shown that magnetic avalanches (corresponding to fast magnetization reversal) propagate as a narrow front with a velocity that is roughly two orders of magnitude smaller than the speed of sound. This phenomenon is closely analogous to the propagation of a flame front through a flammable chemical substance (deflagration) [1]. The conditions for nucleation of avalanches triggered in response to a time-varying (swept) magnetic field were studied for different fields and temperatures. In these crystals, avalanches happened only at low temperatures and were found to occur stochastically at fields ranging from 1.0 T to 4.5 T. There is no apparent structure in the distribution of avalanches for fields below 3.5 T; at higher fields we find evidence that the probability is lower at ``nonresonant'' magnetic fields where tunneling across the anisotropy barrier is suppressed. This provides evidence that lowering the barrier by quantum mechanical tunneling facilitates the ignition of avalanches. Based on these and other measurements, we suggest that avalanches are triggered below 3.5 T by defects with lower energy barriers. [1] Y. Suzuki, et al., Phys. Rev. Lett. 95, 147201 (2005).

Comparison of runaway electron generation parameters in small, medium-sized and large tokamaks—A survey of experiments in COMPASS, TCV, ASDEX-Upgrade and JET

NASA Astrophysics Data System (ADS)

Plyusnin, V. V.; Reux, C.; Kiptily, V. G.; Pautasso, G.; Decker, J.; Papp, G.; Kallenbach, A.; Weinzettl, V.; Mlynar, J.; Coda, S.; Riccardo, V.; Lomas, P.; Jachmich, S.; Shevelev, A. E.; Alper, B.; Khilkevitch, E.; Martin, Y.; Dux, R.; Fuchs, C.; Duval, B.; Brix, M.; Tardini, G.; Maraschek, M.; Treutterer, W.; Giannone, L.; Mlynek, A.; Ficker, O.; Martin, P.; Gerasimov, S.; Potzel, S.; Paprok, R.; McCarthy, P. J.; Imrisek, M.; Boboc, A.; Lackner, K.; Fernandes, A.; Havlicek, J.; Giacomelli, L.; Vlainic, M.; Nocente, M.; Kruezi, U.; COMPASS Team; TCV Team; ASDEX-Upgrade Team; EUROFusion MST1 Team; contributors, JET

2018-01-01

This paper presents a survey of the experiments on runaway electrons (RE) carried out recently in frames of EUROFusion Consortium in different tokamaks: COMPASS, ASDEX-Upgrade, TCV and JET. Massive gas injection (MGI) has been used in different scenarios for RE generation in small and medium-sized tokamaks to elaborate the most efficient and reliable ones for future RE experiments. New data on RE generated at disruptions in COMPASS and ASDEX-Upgrade was collected and added to the JET database. Different accessible parameters of disruptions, such as current quench rate, conversion rate of plasma current into runaways, etc have been analysed for each tokamak and compared to JET data. It was shown, that tokamaks with larger geometrical sizes provide the wider limits for spatial and temporal variation of plasma parameters during disruptions, thus extending the parameter space for RE generation. The second part of experiments was dedicated to study of RE generation in stationary discharges in COMPASS, TCV and JET. Injection of Ne/Ar have been used to mock-up the JET MGI runaway suppression experiments. Secondary RE avalanching was identified and quantified for the first time in the TCV tokamak in RE generating discharges after massive Ne injection. Simulations of the primary RE generation and secondary avalanching dynamics in stationary discharges has demonstrated that RE current fraction created via avalanching could achieve up to 70-75% of the total plasma current in TCV. Relaxations which are reminiscent the phenomena associated to the kinetic instability driven by RE have been detected in RE discharges in TCV. Macroscopic parameters of RE dominating discharges in TCV before and after onset of the instability fit well to the empirical instability criterion, which was established in the early tokamaks and examined by results of recent numerical simulations.

Study of the quasi-tragic snow-avalanche event occurred on August 2009 at Aconcagua Provincial Park, Mendoza, Argentina

NASA Astrophysics Data System (ADS)

Leiva, J. C.; Casteller, A.; Martínez, H. H.; Norte, F. A.; Simonelli, S. C.

2010-03-01

Snow avalanches commonly threaten people and infrastructure in mountainous areas worldwide. Winter precipitation events in the Central Andes are caused by the interaction of the atmospheric general circulation and their steep orography. Almost every winter season snow storms and winds cause the blockage of routes and lead to the snowpack conditions that generate avalanche events. The amount of winter snow accumulation is highly variable and is one of the most important factors for assessing the impacts of climate change not only on the water availability, but also to plan future mitigation measures to reduce the avalanche hazard. The authors have conducted studies on snow avalanches that regularly affect the international route linking Mendoza (Argentina) with Santiago de Chile (Chile) but none of them was done at the Aconcagua Provincial Park The park is nearby this route, about 13 km kilometers east from the international border, which in this sector of the Andes coincides with the continental divide. On the night of 17 August 2009, seven people were caught by an avalanche that hit the Aconcagua Park rangers refuge (32° 48' 40'' S, 69° 56' 33'' W; 2950 masl).This paper describes the meteorological and snow precipitation conditions originating the event. On August 14 th. the synoptic surface and upper-air conditions from NCEP reanalysis were those associated with a severe Zonda wind occurrence in the region, that is: a 500 hPa level trough, a deep low-pressure surface system located over the Pacific Ocean close to the Chilean coast, approximately over 48 ° S and 80° W, and a jet stream at middle upper-air levels. The avalanche event occurred during a new and very heavy snowfall a while more than two days later of these extreme episodes. The topographical characteristics of the avalanche path, the snow storm intensity and the snow accumulation on the avalanche starting zone allowed the authors to simulate the avalanche flow. Snow storm intensity and snow accumulation data from Los Penitentes ski resort (about 10 km east of the Park entrance) were used as input data for the avalanche modeling. However, an additional snow mass was considered due to the fact that the starting zone is in a leeward slope. Vertical aerial photographs (1974), topographic profiles, a DEM generated from ASTER images and the snow accumulation data enabled the authors to simulate the avalanche flow using a bi-dimensional and a three-dimensional avalanche dynamics model. Our results indicate that the studied avalanche event was originated by two main factors. Firstly, prior to the studied event, the snowpack had gone through several cycles of high and low temperatures, thus producing a highly metamorphosed snowpack that facilitated the slide of the new snow. Secondly, the high intensity of the new snow precipitation did not allow for its good settlement. This study is the first step towards an avalanche hazard map of Aconcagua Park and will serve as a basis for advising the Park authorities in regards to the definition of the location of a new refuge and the necessary building structure requirements to be fulfilled.

Two-threshold model for scaling laws of noninteracting snow avalanches

USGS Publications Warehouse

Faillettaz, J.; Louchet, F.; Grasso, J.-R.

2004-01-01

A two-threshold model was proposed for scaling laws of noninteracting snow avalanches. It was found that the sizes of the largest avalanches just preceding the lattice system were power-law distributed. The proposed model reproduced the range of power-law exponents observe for land, rock or snow avalanches, by tuning the maximum value of the ratio of the two failure thresholds. A two-threshold 2D cellular automation was introduced to study the scaling for gravity-driven systems.

3D PIC-MCC simulations of discharge inception around a sharp anode in nitrogen/oxygen mixtures

NASA Astrophysics Data System (ADS)

Teunissen, Jannis; Ebert, Ute

2016-08-01

We investigate how photoionization, electron avalanches and space charge affect the inception of nanosecond pulsed discharges. Simulations are performed with a 3D PIC-MCC (particle-in-cell, Monte Carlo collision) model with adaptive mesh refinement for the field solver. This model, whose source code is available online, is described in the first part of the paper. Then we present simulation results in a needle-to-plane geometry, using different nitrogen/oxygen mixtures at atmospheric pressure. In these mixtures non-local photoionization is important for the discharge growth. The typical length scale for this process depends on the oxygen concentration. With 0.2% oxygen the discharges grow quite irregularly, due to the limited supply of free electrons around them. With 2% or more oxygen the development is much smoother. An almost spherical ionized region can form around the electrode tip, which increases in size with the electrode voltage. Eventually this inception cloud destabilizes into streamer channels. In our simulations, discharge velocities are almost independent of the oxygen concentration. We discuss the physical mechanisms behind these phenomena and compare our simulations with experimental observations.

Slope Stability Analysis and Event Reconstruction of the Karrat Fjord (W Greenland) Rock Avalanche from June 2017 using Sentinel-1 and Sentinel-2 data

NASA Astrophysics Data System (ADS)

Langley, K.; Caduff, R.; Wiesmann, A.; Mätzler, E.

2017-12-01

A massive rock slope failure that led to a rock avalanche in the Karrat Fjord, Western Greenland, caused a tsunami on 17 June 2017. The tsunami reached local villages and resulted in loss of life and damage to infrastructure. The length of the rock avalanche detachment zone is on the order of 800 m. It is located at an elevation of 1'000 m above the fjord with a slant distance of 2'000 m to the shore line. Since very little information was available on the state of the originating mountain slope, satellite based information was gathered immediately after the event in order to assess the processes on the slope. Thanks to the quick data distribution through Copernicus, we could process the entire available datasets of the Synthetic Aperture Radar (SAR) sensors Sentinel-1A/B and the optical sensor Sentinel-2. The pre-, syn, and post-event history could be reconstructed using ascending orbit Sentinel-1 data, available from October 2014 in 12 and from early 2017 on in 6d interval. We looked at the differential interferograms to detect coherent surface displacements in line-of-sight (LOS). Coherent interferograms after the snow-melt in May 2017 revealed surface displacements of 10-15 cm/year with accelerating trend in the later detachment zone. The known limitation for interferometry in wet-snow condition hinders the determination of areas undergoing surface deformation. However, a detailed coherence analysis showed that during the previous winter, a large avalanche type process must have happened in the later detachment zone. A radar backscatter analysis showed, that significant changes in the corridor of 500 m of the area affected by the rock avalanche can be dated between 5 and 11 November 2016. The traces of the event could be verified with optical imagery from Sentinel-2 dating from 23 May 2017. An overall analysis on the mountain side revealed the presence of a number of active zones. An inventory of the outlines of the moving areas containing information on the LOS surface velocities was created, helping to assess possible accelerated or new slope instability appearances in the ongoing analysis of Sentinel-1 acquisitions. We present the methodology, the results and conclude with a discussion on the future impact of the analysis and the experience of the Karrat Fjord event for future hazard monitoring using Sentinel-1/2 data.

Simulating TGF and gamma ray emission above and within stormclouds due to the interaction of TeV cosmic ray shower electrons/positrons/photons with plausible electric field geometries generated in stormclouds.

NASA Astrophysics Data System (ADS)

Connell, P. H.

2017-12-01

The University of Valencia has developed a software simulator LEPTRACK to simulate lepton and photon scattering in any kind of media with a variable density, and permeated by electric/magnetic fields of any geometry, and which can handle an exponential runaway avalanche. Here we show results of simulating the interaction of electrons/positrons/photons in an incoming TeV cosmic ray shower with the kind of electric fields expected in a stormcloud after a CG discharge which removes much of the positive charge build up at the centre of the cloud. The point is to show not just a Relativistic Runaway Electron Avalanche (RREA) above the upper negative shielding layer at 12 km but other gamma ray emission due to electron/positron interaction in the remaining positive charge around 9km and the lower negative charge at 6km altitude. We present here images, lightcurves, altitude profiles, spectra and videos showing the different ionization, excitation and photon density fields produced, their time evolution, and how they depend critically on where the cosmic ray shower beam intercepts the electric field geometry. We also show a new effect of incoming positrons, which make up a significant fraction of the shower, where they appear to "orbit" within the high altitude negative shielding layer, and which has been conjectured to produce significant microwave emission, as well as a short range 511 keV annihilation line. The interesting question is if this conjectured emission can be observed and correlated with TGF orbital observations to prove that a TGF originates in the macro-fields of stormclouds or the micro-fields of light leaders and streamers where this "positron orbiting" is not likely to occur.

Electron kinetic effects in atmosphere breakdown by an intense electromagnetic pulse.

PubMed

Solovyev, A A; Terekhin, V A; Tikhonchuk, V T; Altgilbers, L L

1999-12-01

A physical model is proposed for description of electron kinetics driven by a powerful electromagnetic pulse in the Earth's atmosphere. The model is based on a numerical solution to the Boltzmann kinetic equation for two groups of electrons. Slow electrons (with energies below a few keV) are described in a two-term approximation assuming a weak anisotropy of the electron distribution function. Fast electrons (with energies above a few keV) are described by a modified macroparticle method, taking into account the electron acceleration in the electric field, energy losses in the continuous deceleration approximation, and the multiple pitch angle scattering. The model is applied to a problem of the electric discharge in a nitrogen, which is preionized by an external gamma-ray source. It is shown that the runaway electrons have an important effect on the energy distribution of free electrons, and on the avalanche ionization rate. This mechanism might explain the observation of multiple lightning discharges observed in the Ivy-Mike thermonuclear test in the early 1950's.

Influence of snow temperature on avalanche impact pressure

NASA Astrophysics Data System (ADS)

Sovilla, Betty; Koehler, Anselm; Steinkogler, Walter; Fischer, Jan-Thomas

2015-04-01

The properties of the snow entrained by an avalanche during its motion (density, temperature) significantly affect flow dynamics and can determine whether the flowing material forms granules or maintains its original fine-grained structure. In general, a cold and light snow cover typically fluidizes, while warmer and more cohesive snow may form a granular denser layer in a flowing avalanche. This structural difference has a fundamental influence not only in the mobility of the flow but also on the impact pressure of avalanches. Using measurements of impact pressure, velocity, density and snow temperature performed at the Swiss Vallée de la Sionne full-scale test site, we show that, impact pressure fundamentally changes with snow temperature. A transition threshold of about -2°C is determined, the same temperature at which snow granulation starts. On the one hand warm avalanches, characterized by temperatures larger than -2°C, move as a plug and exert impact pressures linearly proportional to the avalanche depth. For Froude numbers larger than 1, an additional square-velocity dependent contribution cannot be neglected. On the other hand cold avalanches, characterized by a temperature smaller than -2°C, move as dense sheared flows, or completely dilute powder clouds and exert impact pressures, which are mainly proportional to the square of the flow velocity. For these avalanches the impact pressures strongly depend on density variations within the flow. We suggest that the proposed temperature threshold can be used as a criterion to define the transition between the impact pressures exerted by warm and cold avalanches, thus offering a new way to elude the notorious difficulties in defining the differences between wet and dry flow, respectively.

Dynamics of the Bingham Canyon rock avalanches (Utah, USA) resolved from topographic, seismic, and infrasound data: Bingham Canyon Rock Avalanches

DOE PAGES

Moore, Jeffrey R.; Pankow, Kristine L.; Ford, Sean R.; ...

2017-03-01

The 2013 Bingham Canyon Mine rock avalanches represent one of the largest cumulative landslide events in recorded U.S. history and provide a unique opportunity to test remote analysis techniques for landslide characterization. We combine aerial photogrammetry surveying, topographic reconstruction, numerical runout modeling, and analysis of broadband seismic and infrasound data to extract salient details of the dynamics and evolution of the multiphase landslide event. Our results reveal a cumulative intact rock source volume of 52 Mm 3, which mobilized in two main rock avalanche phases separated by 1.5 h. We estimate that the first rock avalanche had 1.5–2 times greatermore » volume than the second. Each failure initiated by sliding along a gently dipping (21°), highly persistent basal fault before transitioning to a rock avalanche and spilling into the inner pit. The trajectory and duration of the two rock avalanches were reconstructed using runout modeling and independent force history inversion of intermediate-period (10–50 s) seismic data. Intermediate- and shorter-period (1–50 s) seismic data were sensitive to intervals of mass redirection and constrained finer details of the individual slide dynamics. Back projecting short-period (0.2–1 s) seismic energy, we located the two rock avalanches within 2 and 4 km of the mine. Further analysis of infrasound and seismic data revealed that the cumulative event included an additional 11 smaller landslides (volumes ~10 4–10 5 m 3) and that a trailing signal following the second rock avalanche may result from an air-coupled Rayleigh wave. These results demonstrate new and refined techniques for detailed remote characterization of the dynamics and evolution of large landslides.« less

Reevaluation of tsunami formation by debris avalanche at Augustine Volcano, Alaska

USGS Publications Warehouse

Waythomas, C.F.

2000-01-01

Debris avalanches entering the sea at Augustine Volcano, Alaska have been proposed as a mechanism for generating tsunamis. Historical accounts of the 1883 eruption of the volcano describe 6- to 9-meter-high waves that struck the coastline at English Bay (Nanwalek), Alaska about 80 kilometers east of Augustine Island. These accounts are often cited as proof that volcanigenic tsunamis from Augustine Volcano are significant hazards to the coastal zone of lower Cook Inlet. This claim is disputed because deposits of unequivocal tsunami origin are not evident at more than 50 sites along the lower Cook Inlet coastline where they might be preserved. Shallow water (<25 m) around Augustine Island, in the run-out zone for debris avalanches, limits the size of an avalanche-caused wave. If the two most recent debris avalanches, Burr Point (A.D. 1883) and West Island (<500 yr. B.P.) were traveling at velocities in the range of 50 to 100 meters per second, the kinetic energy of the avalanches at the point of impact with the ocean would have been between 1014 and 1015 joules. Although some of this energy would be dissipated through boundary interactions and momentum transfer between the avalanche and the sea, the initial wave should have possessed sufficient kinetic energy to do geomorphic work (erosion, sediment transport, formation of wave-cut features) on the coastline of lowwer Cook Inlet. Because widespread evidence of the effects of large waves cannot be found, it appears that the debris avalanches could not have been traveling very fast when they entered the sea, or they happened during low tide and displaced only small volumes of water. In light of these results, the hazard from volcanigenic tsunamis from Augustine Volcano appears minor, unless a very large debris avalanche occurs at high tide.

Design and characterization of single photon avalanche diodes arrays

NASA Astrophysics Data System (ADS)

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

Irregular spiking of pyramidal neurons organizes as scale-invariant neuronal avalanches in the awake state

PubMed Central

Bellay, Timothy; Klaus, Andreas; Seshadri, Saurav; Plenz, Dietmar

2015-01-01

Spontaneous fluctuations in neuronal activity emerge at many spatial and temporal scales in cortex. Population measures found these fluctuations to organize as scale-invariant neuronal avalanches, suggesting cortical dynamics to be critical. Macroscopic dynamics, though, depend on physiological states and are ambiguous as to their cellular composition, spatiotemporal origin, and contributions from synaptic input or action potential (AP) output. Here, we study spontaneous firing in pyramidal neurons (PNs) from rat superficial cortical layers in vivo and in vitro using 2-photon imaging. As the animal transitions from the anesthetized to awake state, spontaneous single neuron firing increases in irregularity and assembles into scale-invariant avalanches at the group level. In vitro spike avalanches emerged naturally yet required balanced excitation and inhibition. This demonstrates that neuronal avalanches are linked to the global physiological state of wakefulness and that cortical resting activity organizes as avalanches from firing of local PN groups to global population activity. DOI: http://dx.doi.org/10.7554/eLife.07224.001 PMID:26151674

Thermally Driven Inhibition of Superconducting Vortex Avalanches

NASA Astrophysics Data System (ADS)

Lara, Antonio; Aliev, Farkhad G.; Moshchalkov, Victor V.; Galperin, Yuri M.

2017-09-01

Complex systems close to their critical state can exhibit abrupt transitions—avalanches—between their metastable states. It is a challenging task to understand the mechanism of the avalanches and control their behavior. Here, we investigate microwave stimulation of avalanches in the so-called vortex matter of type-II superconductors—a system of interacting Abrikosov vortices close to the critical (Bean) state. Our main finding is that the avalanche incubation strongly depends on the excitation frequency, a completely unexpected behavior observed close to the so-called depinning frequencies. Namely, the triggered vortex avalanches in Pb superconducting films become effectively inhibited approaching the critical temperature or critical magnetic field when the microwave stimulus is close to the vortex depinning frequency. We suggest a simple model explaining the observed counterintuitive behaviors as a manifestation of the strongly nonlinear dependence of the driven vortex core size on the microwave excitation intensity. This paves the way to controlling avalanches in superconductor-based devices through their nonlinear response.

Single Photon Counting UV Solar-Blind Detectors Using Silicon and III-Nitride Materials

PubMed Central

Nikzad, Shouleh; Hoenk, Michael; Jewell, April D.; Hennessy, John J.; Carver, Alexander G.; Jones, Todd J.; Goodsall, Timothy M.; Hamden, Erika T.; Suvarna, Puneet; Bulmer, J.; Shahedipour-Sandvik, F.; Charbon, Edoardo; Padmanabhan, Preethi; Hancock, Bruce; Bell, L. Douglas

2016-01-01

Ultraviolet (UV) studies in astronomy, cosmology, planetary studies, biological and medical applications often require precision detection of faint objects and in many cases require photon-counting detection. We present an overview of two approaches for achieving photon counting in the UV. The first approach involves UV enhancement of photon-counting silicon detectors, including electron multiplying charge-coupled devices and avalanche photodiodes. The approach used here employs molecular beam epitaxy for delta doping and superlattice doping for surface passivation and high UV quantum efficiency. Additional UV enhancements include antireflection (AR) and solar-blind UV bandpass coatings prepared by atomic layer deposition. Quantum efficiency (QE) measurements show QE > 50% in the 100–300 nm range for detectors with simple AR coatings, and QE ≅ 80% at ~206 nm has been shown when more complex AR coatings are used. The second approach is based on avalanche photodiodes in III-nitride materials with high QE and intrinsic solar blindness. PMID:27338399

Single Photon Counting UV Solar-Blind Detectors Using Silicon and III-Nitride Materials.

PubMed

Nikzad, Shouleh; Hoenk, Michael; Jewell, April D; Hennessy, John J; Carver, Alexander G; Jones, Todd J; Goodsall, Timothy M; Hamden, Erika T; Suvarna, Puneet; Bulmer, J; Shahedipour-Sandvik, F; Charbon, Edoardo; Padmanabhan, Preethi; Hancock, Bruce; Bell, L Douglas

2016-06-21

Ultraviolet (UV) studies in astronomy, cosmology, planetary studies, biological and medical applications often require precision detection of faint objects and in many cases require photon-counting detection. We present an overview of two approaches for achieving photon counting in the UV. The first approach involves UV enhancement of photon-counting silicon detectors, including electron multiplying charge-coupled devices and avalanche photodiodes. The approach used here employs molecular beam epitaxy for delta doping and superlattice doping for surface passivation and high UV quantum efficiency. Additional UV enhancements include antireflection (AR) and solar-blind UV bandpass coatings prepared by atomic layer deposition. Quantum efficiency (QE) measurements show QE > 50% in the 100-300 nm range for detectors with simple AR coatings, and QE ≅ 80% at ~206 nm has been shown when more complex AR coatings are used. The second approach is based on avalanche photodiodes in III-nitride materials with high QE and intrinsic solar blindness.

A low-cost, ultra-fast and ultra-low noise preamplifier for silicon avalanche photodiodes

NASA Astrophysics Data System (ADS)

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.

Design considerations of high-performance InGaAs/InP single-photon avalanche diodes for quantum key distribution.

PubMed

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.

An accurate behavioral model for single-photon avalanche diode statistical performance simulation

NASA Astrophysics Data System (ADS)

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.

Data collapse and critical dynamics in neuronal avalanche data

NASA Astrophysics Data System (ADS)

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.

Unusual gravitational failures on lava domes of Tatun Volcanic Group, Northern Taiwan.

NASA Astrophysics Data System (ADS)

Belousov, Alexander; Belousova, Marina; Chen, Chang-Hwa; Zellmer, Georg

2010-05-01

Tatun Volcanic Group of Northern Taiwan was formed mainly during the Pleistocene - Early Holocene. Most of the volcanoes are represented by andesitic lava domes of moderate sizes: heights up to 400 m (absolute altitudes 800-1100 m a.s.l.), base diameters up to 2 km, and volumes up to 0.3 km³. Many of the domes have broadly opened (0.5-1.0 km across and up to 140° wide), shallow-incised horseshoe-shaped scars formed by gravitational collapses. The failure planes did not intersect the volcanic conduits, and the scars were not filled by younger volcanic edifices: most of the collapses occurred a long time after the eruptions had ceased. The largest collapse, with a volume 0.1 km³, occurred at eastern part of Datun lava dome. Specific feature of the collapse was that the rear slide blocks did not travel far from the source; they stopped high inside the collapse scar, forming multiple narrow toreva blocks descending downslope. The leading slide blocks formed a low mobile debris avalanche (L~5 km; H~1 km; H/L~0.2). The deposit is composed mainly of block facies. The age of the collapse is older than 24,000 yrs, because the related debris avalanche deposit is covered by a younger debris avalanche deposit of Siaoguanyin volcano having calibrated 14C age 22,600-23,780 BP. The Siaoguanyin debris avalanche was formed as a result of collapse of southern part of a small flank dome. Specific feature of the resulted avalanche - it was hot during deposition. The deposit contains carbonized wood; andesite boulders within the deposit frequently have radial cooling joints, and in rare cases "bread-crust" surfaces. The paucity of fine fractions in the deposit can be connected with elutriation of fines into the convective cloud when the hot avalanche travelled downslope. However in several locations the deposit is represented by typical avalanche blocks surrounded by heterolithologic mixed facies containing abundant clasts of Miocene sandstone (picked up from the substrate). Thus the deposit bears features of both debris avalanches and lithic-rich block-and-ash flows. The avalanche was rather mobile (L~6 km; H~1 km; H/L~0.16), despite its small volume (0.02 km³). Its speed reached 40 m/s at a distance of 5 km from the source (based on 80 m high runup of the avalanche). The characteristics of the avalanche deposit indicate that crystallized, degassed, but still hot material of a newly extruded lava dome was involved in the collapse. Unusual low mobile debris avalanche was formed as a result of collapse of western slope of Mt. Cising. A former lava coulee, which was involved in the collapse, underwent only weak disintegration: debris avalanche deposit is represented by big boulders with few fine grained matrix. Leading snout of the landslide traveled only 2 km, while rear slide blocks stopped near the landslide source forming multiple narrow toreva blocks descending downslope. Volume of the collapse 0.05 km³; maximum dropped height 0.5 km, H/L 0.25. Around the distal snout of the avalanche a "bulldozer facies" is well developed. Dating of vegetation entrained into the deposit gave 14C calibrated age 6000-6080 BP. Mobility of the studied debris avalanches was twice smaller than the average mobility of volcanic debris avalanches. Relatively small volume of the collapses, the particular type of material involved (massive lava domes) and the fact that the collapses occurred long after the volcanoes stopped erupting may have played a role in the low mobility of the debris avalanches of the Tatun Group.

Fully Digital Arrays of Silicon Photomultipliers (dSiPM) - a Scalable Alternative to Vacuum Photomultiplier Tubes (PMT)

NASA Astrophysics Data System (ADS)

Haemisch, York; Frach, Thomas; Degenhardt, Carsten; Thon, Andreas

Silicon Photomultipliers (SiPMs) have emerged as promising alternative to fast vacuum photomultiplier tubes (PMT). A fully digital implementation of the Silicon Photomultiplier (dSiPM) has been developed in order to overcome the deficiencies and limitations of the so far only analog SiPMs (aSiPMs). Our sensor is based on arrays of single photon avalanche photodiodes (SPADs) integrated in a standard CMOS process. Photons are detected directly by sensing the voltage at the SPAD anode using a dedicated cell electronics block next to each diode. This block also contains active quenching and recharge circuits as well as a one bit memory for the selective inhibit of detector cells. A balanced trigger network is used to propagate the trigger signal from all cells to the integrated time-to-digital converter. In consequence, photons are detected and counted as digital signals, thus making the sensor less susceptible to temperature variations and electronic noise. The integration with CMOS logic provides the added benefit of low power consumption and possible integration of data post-processing directly in the sensor. In this overview paper, we discuss the sensor architecture together with its characteristics with a focus on scalability and practicability aspects for applications in medical imaging, high energy- and astrophysics.

Effect of electron divergence in air gaps on the measurement of the energy of cascades in emulsion chambers

NASA Technical Reports Server (NTRS)

Apanasenko, A. V.; Baradzey, L. T.; Kanevskaya, Y. A.; Smorodin, Y. A.

1975-01-01

The effect of an increase in electron density in the vicinity of the cascade axis caused by an avalanche passing through the gap between lead filters of the emulsion chamber was investigated experimentally. Optical densities were measured in three X-ray films spaced at 400, 800 and 1200 micrometer from the filter surface having a thickness of 6 cascade units. The optical densities of blackening spots caused by electron photon cascades of 1 to 2, 2 to 7 and greater than 7 BeV energies were measured. The results prove the presence of a gap between the filter and the nuclear emulsion which results in the underestimation of energy by several tenths of a percent.

Generation of runaway electrons beams during the breakdown of high-pressure gases

NASA Astrophysics Data System (ADS)

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

2017-11-01

Generation of run-away electrons in SF6, CO2, argon and nitrogen at high and super high pressures is studied. Super-short avalanches electron beams (SAEB) was obtained and measured with a collector at pressures up to 0.3, 0.7, 1.0 and 1.2 MPa in SF6, CO2, argon and nitrogen, respectively. The SAEB duration was shown to be ∼60 ps (FWHM) and gas composition has only minor effect on the duration. It was found that in a gap of 4 mm in SF6, CO2, argon and nitrogen at pressure up to 0.3, 0.7, 1.0 и 1.2 MPa the voltage pulse duration (FWHM) and amplitude increase with pressure.

Dragon Stream Cipher for Secure Blackbox Cockpit Voice Recorder

NASA Astrophysics Data System (ADS)

Akmal, Fadira; Michrandi Nasution, Surya; Azmi, Fairuz

2017-11-01

Aircraft blackbox is a device used to record all aircraft information, which consists of Flight Data Recorder (FDR) and Cockpit Voice Recorder (CVR). Cockpit Voice Recorder contains conversations in the aircraft during the flight.Investigations on aircraft crashes usually take a long time, because it is difficult to find the aircraft blackbox. Then blackbox should have the ability to send information to other places. Aircraft blackbox must have a data security system, data security is a very important part at the time of information exchange process. The system in this research is to perform the encryption and decryption process on Cockpit Voice Recorder by people who are entitled by using Dragon Stream Cipher algorithm. The tests performed are time of data encryption and decryption, and avalanche effect. Result in this paper show us time encryption and decryption are 0,85 seconds and 1,84 second for 30 seconds Cockpit Voice Recorder data witn an avalanche effect 48,67 %.

Reversibility and criticality in amorphous solids

DOE PAGES

Regev, Ido; Weber, John; Reichhardt, Charles; ...

2015-11-13

The physical processes governing the onset of yield, where a material changes its shape permanently under external deformation, are not yet understood for amorphous solids that are intrinsically disordered. Here, using molecular dynamics simulations and mean-field theory, we show that at a critical strain amplitude the sizes of clusters of atoms undergoing cooperative rearrangements of displacements (avalanches) diverges. We compare this non-equilibrium critical behaviour to the prevailing concept of a ‘front depinning’ transition that has been used to describe steady-state avalanche behaviour in different materials. We explain why a depinning-like process can result in a transition from periodic to chaoticmore » behaviour and why chaotic motion is not possible in pinned systems. As a result, these findings suggest that, at least for highly jammed amorphous systems, the irreversibility transition may be a side effect of depinning that occurs in systems where the disorder is not quenched.« less

XeCl Avalanche discharge laser employing Ar as a diluent

DOEpatents

Sze, Robert C.

1981-01-01

A XeCl avalanche discharge exciplex laser which uses a gaseous lasing starting mixture of: (0.2%-0.4% chlorine donor/2.5%-10% Xe/97.3%-89.6% Ar). The chlorine donor normally comprises HCl but can also comprise CCl.sub.4 BCl.sub.3. Use of Ar as a diluent gas reduces operating pressures over other rare gas halide lasers to near atmospheric pressure, increases output lasing power of the XeCl avalanche discharge laser by 30% to exceed KrF avalanche discharge lasing outputs, and is less expensive to operate.

Application of LANDSAT data to delimitation of avalanche hazards in Montane, Colorado

NASA Technical Reports Server (NTRS)

Knepper, D. H. (Principal Investigator); Ives, J. D.; Summer, R.

1976-01-01

The author has identified the following significant results. Photointerpretation of individual avalanche paths on single band black and white LANDSAT images is greatly hindered by terrain shadows and the low spatial resolution of the LANDSAT system. Maps produced in this way are biased towards the larger avalanche paths that are under the most favorable illumination conditions during imaging; other large avalanche paths, under less favorable illumination, are often not detectable and the smaller paths, even those defined by sharp trimlines, are only rarely identifiable.

Precursory seismicity associated with frequent, large ice avalanches on Iliamna Volcano, Alaska, USA

USGS Publications Warehouse

Caplan-Auerbach, Jacqueline; Huggel, C.

2007-01-01

Since 1994, at least six major (volume>106 m3) ice and rock avalanches have occurred on Iliamna volcano, Alaska, USA. Each of the avalanches was preceded by up to 2 hours of seismicity believed to represent the initial stages of failure. Each seismic sequence begins with a series of repeating earthquakes thought to represent slip on an ice-rock interface, or between layers of ice. This stage is followed by a prolonged period of continuous ground-shaking that reflects constant slip accommodated by deformation at the glacier base. Finally the glacier fails in a large avalanche. Some of the events appear to have entrained large amounts of rock, while others comprise mostly snow and ice. Several avalanches initiated from the same source region, suggesting that this part of the volcano is particularly susceptible to failure, possibly due to the presence of nearby fumaroles. Although thermal conditions at the time of failure are not well constrained, it is likely that geothermal energy causes melting at the glacier base, promoting slip and culminating in failure. The frequent nature and predictable failure sequence of Iliamna avalanches makes the volcano an excellent laboratory for the study of ice avalanches. The prolonged nature of the seismic signal suggests that warning may one day be given for similar events occurring in populated regions.

r.avaflow, the GIS simulation model for avalanche and debris flows: new developments and challenges

NASA Astrophysics Data System (ADS)

Mergili, Martin; Queiroz de Oliveira, Gustavo; Fischer, Jan-Thomas; Krenn, Julia; Kulisch, Helmut; Malcherek, Andreas; Pudasaini, Shiva P.

2016-04-01

We present the latest developments and discuss some of the key challenges with regard to the novel and unified computational tool r.avaflow, representing an advanced, comprehensive, GIS-based open source simulation environment for two-phase geophysical mass flows such as avalanches of snow or rock, flows of debris or mud, and related process chains. r.avaflow is freely available and adoptable as a raster module of the GRASS GIS software (http://www.avaflow.org). We focus on the following issues: (1) We back-calculate a laboratory-scale debris flow experiment with r.avaflow and thereby show that different types of drag may govern the evolving flow dynamics, depending on the initial flow configuratiuon. In particular, it appears necessary to consider viscous ambient drag in order to achieve simulation results in line with experimentally measurements. (2) We employ a set of well-documented rock avalanche events to illustrate the use of a built-in functionality for parameter sensitivity analysis and optimization. To do so, we demonstrate possible strategies going beyond the deficient one-at-a-time simulation approach. They allow us to test three or more parameters at once with a limited number of model runs. Computational times are kept at an acceptable level by multi-core processing strategies and use of the Vienna Scientific Cluster. We further discuss a number of key issues with regard to (i) arbitrary mountain topography; and (ii) entrainment and deposition of material. Most tests indicate a good model performance when the affected areas predicted for a late stage of the flow simulation are compared with observed affected areas. However, we note that such a validation is not fully justified without the implementation of a physically correct model for the deposition process. Acknowledgement: The work was conducted as part of the international cooperation project "A GIS simulation model for avalanche and debris flows (avaflow)" supported by the Austrian Science Fund (FWF, project number I 1600-N30) and the German Research Foundation (DFG, project number PU 386/3-1).

Sedimentary control of volcanic debris-avalanche structures and transformation into lahars

NASA Astrophysics Data System (ADS)

Bernard, Karine; van Wyk de Vries, Benjamin; Thouret, Jean-Claude; Roche, Olivier; Samaniego Eguiguren, Pablo

2017-04-01

Volcanic debris avalanche structures and related transformations into lahars have been extensively analysed in order to establish a sedimentary classification of the deposits. Textural and structural variations of eight debris-avalanche deposits (DADs) have been correlated with Shape Preferred Orientation of 30,000 clasts together with grain-size distributions and statistical parameters from 156 sieved matrix samples. Granular segregation patterns have been observed with structural fault controls: proximal granular-segregation structures of the Tutupaca DAD ridges in Peru, basal sheared bands along overthrust lateral levee (Mt. Dore, France), mixing and cataclasis of fault-controlled deposits in half-graben during lateral spreading of distal thrust lobe (Pichu-Pichu, Peru), neo-cataclasis at the frontal thrust lobe (Meager, Canada and Mt. Dore, France). A logarithmic regression characterises the % matrix vs. matrix/gravels showing proximal and primary cataclasis, hybrid DADs with polymodal matrix and mixed facies up to transformations into lahar (Misti, Mt Dore). The sequential fragmentation helps to distinguish DAD that belong to Andean and Cascade Volcanic arcs (Tutupaca and Misti, Peru; Meager, Canada) to the hybrid DADs, before distal transformation into lahars (Pichu-Pichu); and hydrovolcanic fragmentation characterises the transformed lahar deposits (Misti). The fractal values of 150 sieved samples range between 2.3 and 2.7, implying extensional fractures with granular disaggregation. Skewness vs. kurtosis values help to distinguish the proximal mass wasting deposits and the transformed deposits by dilution. The sorting vs. median values enable us to differentiate the hybrid DADs with the transformed deposits by dilution. The sedimentological statistical parameters with Shape Preferred Orientation analysis that have been correlated with textural and structural observations show textural fabrics resulting from kinematic processes: cataclasis, hybrid matrix facies and transformations. Inherited fractures from tectono-volcanic structures contribute to the particle size distributions of DAD and associated deposits such as pyroclastic and lahar deposits (Misti, Mt Dore, Tutupaca). The statistical results highlight granular structure and kinematic process of DAD transformations into lahars and associated deposits, which would contribute to understand the rheological process behind the excess DAD run-out and to test granular models for DAD transformations. Key words: volcanic debris-avalanche deposits, lahar transformation, structure, sedimentology, hazard

Measurement of runaway electron energy distribution function during high-Z gas injection into runaway electron plateaus in DIII-Da)

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hollmann, E. M.; Parks, P. B.; Commaux, N.

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 appearsmore » 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.« less

Measurement of runaway electron energy distribution function during high-Z gas injection into runaway electron plateaus in DIII-D

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hollmann, E. M.; Parks, P. B.; Commaux, Nicolas J. C.

2015-05-14

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 theta is not uniform, but tends to be large at low energies and small theta similar to 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 onmore » the plasma current appears to be dominated by collisions with impurity ions in most cases. In conclusion, synchrotron emission appears not to be significant for overall RE energy dissipation but may be important for limiting the peak RE energy.« less

Generation of runaway electron beams in high-pressure nitrogen

NASA Astrophysics Data System (ADS)

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.

Neutron detector using sol-gel absorber

DOEpatents

Hiller, John M.; Wallace, Steven A.; Dai, Sheng

1999-01-01

An neutron detector composed of fissionable material having ions of lithium, uranium, thorium, plutonium, or neptunium, contained within a glass film fabricated using a sol-gel method combined with a particle detector is disclosed. When the glass film is bombarded with neutrons, the fissionable material emits fission particles and electrons. Prompt emitting activated elements yielding a high energy electron contained within a sol-gel glass film in combination with a particle detector is also disclosed. The emissions resulting from neutron bombardment can then be detected using standard UV and particle detection methods well known in the art, such as microchannel plates, channeltrons, and silicon avalanche photodiodes.

Development of the Damage Potential resulting from Avalanche Risks, Case Study Galtür (Tyrol, Austria)

NASA Astrophysics Data System (ADS)

Keiler, M.

2003-04-01

Reports on catastrophes with high damage caused by natural hazards seem to have increased in number recently. A new trend in dealing with these natural processes leads to the integration of risk into natural hazards evaluations and approaches of integral risk management. The risk resulting from natural hazards can be derived from the combination of parameters of physical processes (intensity and recurrence probability) and damage potential (probability of presence and expected damage value). Natural hazard research focuses mainly on the examination, modelling and estimation of individual geomorphological processes as well as on future developments caused by climate change. Even though damage potential has been taken into account more frequently, quantifying statements are still missing. Due to the changes of the socio-economic structures in mountain regions (urban sprawl, population growth, increased mobility and tourism) these studies are mandatory. This study presents a conceptual method that records the damage potential (probability of physical presence, evaluation of buildings) and shows the development of the damage potential resulting from avalanches since 1950. The study area is the community of Galtür, Austria. 36 percent of the existing buildings are found in officially declared avalanche hazard zones. The majority of these buildings are either agricultural or accommodation facilities. Additionally, the effects of physical planning and/or technical measures on the spatial development of the potential damage are illustrated. The results serve to improve risk determination and point out an unnoticed increase of damage potential and risk in apparently safe settlement areas.

High voltage threshold for stable operation in a dc electron gun

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yamamoto, Masahiro, E-mail: masahiro@post.kek.jp; Nishimori, Nobuyuki, E-mail: n-nishim@tagen.tohoku.ac.jp

We report clear observation of a high voltage (HV) threshold for stable operation in a dc electron gun. The HV hold-off time without any discharge is longer than many hours for operation below the threshold, while it is roughly 10 min above the threshold. The HV threshold corresponds to the minimum voltage where discharge ceases. The threshold increases with the number of discharges during HV conditioning of the gun. Above the threshold, the amount of gas desorption per discharge increases linearly with the voltage difference from the threshold. The present experimental observations can be explained by an avalanche discharge modelmore » based on the interplay between electron stimulated desorption (ESD) from the anode surface and subsequent secondary electron emission from the cathode by the impact of ionic components of the ESD molecules or atoms.« less

Increasing rock-avalanche size and mobility in Glacier Bay National Park and Preserve, Alaska detected from 1984 to 2016 Landsat imagery

USGS Publications Warehouse

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 < 0.3) rock avalanches that occurred from June 2012 through June 2016 (near the end of the 33-year period of record). These rock avalanches began about 2  years after the long-term trend in mean annual maximum air temperature may have exceeded 0 °C. Possibly more important, most of these rock avalanches occurred during a multiple-year period of record-breaking warm winter and spring air temperatures. These observations suggested to us that rock avalanches in the study area may be becoming larger because of rock-permafrost degradation. However, other factors, such as accumulating elastic strain, glacial thinning, and increased precipitation, may also play an important role in preconditioning slopes for failure during periods of warm temperatures.

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

NASA Astrophysics Data System (ADS)

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.

Charge amplitude distribution of the Gossip gaseous pixel detector

NASA Astrophysics Data System (ADS)

Blanco Carballo, V. M.; Chefdeville, M.; Colas, P.; Giomataris, Y.; van der Graaf, H.; Gromov, V.; Hartjes, F.; Kluit, R.; Koffeman, E.; Salm, C.; Schmitz, J.; Smits, S. M.; Timmermans, J.; Visschers, J. L.

2007-12-01

The Gossip gaseous pixel detector is being developed for the detection of charged particles in extreme high radiation environments as foreseen close to the interaction point of the proposed super LHC. The detecting medium is a thin layer of gas. Because of the low density of this medium, only a few primary electron/ion pairs are created by the traversing particle. To get a detectable signal, the electrons drift towards a perforated metal foil (Micromegas) whereafter they are multiplied in a gas avalanche to provide a detectable signal. The gas avalanche occurs in the high field between the Micromegas and the pixel readout chip (ROC). Compared to a silicon pixel detector, Gossip features a low material budget and a low cooling power. An experiment using X-rays has indicated a possible high radiation tolerance exceeding 10 16 hadrons/cm 2. The amplified charge signal has a broad amplitude distribution due to the limited statistics of the primary ionization and the statistical variation of the gas amplification. Therefore, some degree of inefficiency is inevitable. This study presents experimental results on the charge amplitude distribution for CO 2/DME (dimethyl-ether) and Ar/iC 4H 10 mixtures. The measured curves were fitted with the outcome of a theoretical model. In the model, the physical Landau distribution is approximated by a Poisson distribution that is convoluted with the variation of the gas gain and the electronic noise. The value for the fraction of pedestal events is used for a direct calculation of the cluster density. For some gases, the measured cluster density is considerably lower than given in literature.

Terrain Classification of Norwegian Slab Avalanche Accidents

ERIC Educational Resources Information Center

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…

Snow supporting structures for milepost 151 Avalanche, Highway US 89/191, Jackson, Wyoming : plans.

DOT National Transportation Integrated Search

2009-04-01

The 151 Avalanche, near Jackson, Wyoming has, historically, avalanched to the road below 1.5 to 2 times a year. The road, US 89/191 is four lanes and carries an estimated 8,000 vehicles per day in the winter months. The starting zone of the 151 Avala...

Rockfalls and Avalanches from Little Tahoma Peak on Mount Rainier, Washington

USGS Publications Warehouse

Crandell, Dwight Raymond; Fahnestock, Robert K.

1965-01-01

In December 1963 rockfalls from Little Tahoma Peak on the east side of Mount Rainier volcano fell onto Emmons Glacier and formed avalanches of rock debris that traveled about 4 miles down the glacier and the White River valley. In this distance, the rock debris descended as much as 6,200 feet in altitude. Minor lithologic differences and crosscutting relations indicate that the rockfalls caused at least seven separate avalanches, having an estimated total volume of 14 million cubic yards. The initial rockfall may have been caused by a small steam explosion near the base of Little Tahoma Peak. During movement, some of the avalanches were deflected from one side of the valley to the other. Calculations based on the height to which the avalanches rose on the valley walls suggest that their velocity reached at least 80 or 90 miles per hour. The unusually long distance some of the avalanches were transported is attributed to a cushion of trapped and compressed air at their base, which buoyed them up amid reduced friction.

Spatial shape of avalanches

NASA Astrophysics Data System (ADS)

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.

Geological history and within-island diversity: a debris avalanche and the Tenerife lizard Gallotia galloti.

PubMed

Brown, Richard P; Hoskisson, Paul A; Welton, John-Henry; Báez, Marcos

2006-10-01

Several processes have been described that could explain geographical variation and speciation within small islands, including fragmentation of populations through volcanic eruptions. Massive landslides, or debris avalanches, could cause similar effects. Here we analyse the potential impact of the 0.8 million-year-ago (Ma) Güimar valley debris avalanche on the phylogeography of the lizard Gallotia galloti on the Canary Island of Tenerife. Distributions of mitochondrial DNA lineages (based on cytochrome b sequences) were analysed on a 60-km southeastern coast transect centred on this area. Three main clades were detected, which can be divided into northern (one clade) and southern (two clades) groups that introgress across the valley. Maximum-likelihood estimates of migration rates (scaled for mutation rate) revealed highly asymmetric patterns, indicating that long-term gene flow into this region from both the northern and the southern populations greatly exceeded that in the opposite directions, consistent with recolonization of the area. The ancestral Tenerife node on the G. galloti tree is estimated at 0.80 Ma, matching closely with the geological estimate for the debris avalanche. Morphological variation (body dimensions and scalation) was also analysed and indicated a stepped cline in female scalation across the valley, although the patterns for male scalation and male and female body dimensions were not as clear. Together these findings provide support for the hypothesis that the debris avalanche has shaped the phylogeography of G. galloti and may even have been a primary cause of the within-island cladogenesis through population fragmentation and isolation. Current estimates of timing of island unification mean that the original hypothesis that within-island diversity is explained by the secondary contact of populations from the two ancient precursor islands of Teno and Anaga is less plausible for this and some other Tenerife species. Large-scale landslides have occurred on many volcanic islands, and so may have been instrumental in shaping within-island diversities.

Rock-avalanche and ocean-resurge deposits in the late Eocene Chesapeake Bay impact structure: Evidence from the ICDP-USGS Eyreville cores, Virginia, USA

USGS Publications Warehouse

Gohn, G.S.; Powars, D.S.; Dypvik, H.; Edwards, L.E.

2009-01-01

An unusually thick section of sedimentary breccias dominated by target-sediment clasts is a distinctive feature of the late Eocene Chesapeake Bay impact structure. A cored 1766-m-deep section recovered from the central part of this marine-target structure by the International Continental Scientific Drilling Program (ICDP)-U.S. Geological Survey (USGS) drilling project contains 678 m of these breccias and associated sediments and an intervening 275-m-thick granite slab. Two sedimentary breccia units consist almost entirely of Cretaceous nonmarine sediments derived from the lower part of the target sediment layer. These sediments are present as coherent clasts and as autoclastic matrix between the clasts. Primary (Cretaceous) sedimentary structures are well preserved in some clasts, and liquefaction and fluidization structures produced at the site of deposition occur in the clasts and matrix. These sedimentary breccias are interpreted as one or more rock avalanches from the upper part of the transient-cavity wall. The little-deformed, unshocked granite slab probably was transported as part of an extremely large slide or avalanche. Water-saturated Cretaceous quartz sand below the slab was transported into the seafloor crater prior to, or concurrently with, the granite slab. Two sedimentary breccia units consist of polymict diamictons that contain cobbles, boulders, and blocks of Cretaceous nonmarine target sediments and less common shocked-rock and melt ejecta in an unsorted, unstratified, muddy, fossiliferous, glauconitic quartz matrix. Much of the matrix material was derived from Upper Cretaceous and Paleogene marine target sediments. These units are interpreted as the deposits of debris flows initiated by the resurge of ocean water into the seafloor crater. Interlayering of avalanche and debris-flow units indicates a partial temporal overlap of the earlier avalanche and later resurge processes. A thin unit of stratified turbidite deposits and overlying laminated fine-grained deposits at the top of the section represents the transition to normal shelf sedimentation. ?? 2009 The Geological Society of America.

Damage effect and mechanism of the GaAs high electron mobility transistor induced by high power microwave

NASA Astrophysics Data System (ADS)

Yang, Liu; Chang-Chun, Chai; Yin-Tang, Yang; Jing, Sun; Zhi-Peng, Li

2016-04-01

In this paper, we present the damage effect and mechanism of high power microwave (HPM) on AlGaAs/GaAs pseudomorphic high-electron-mobility transistor (pHEMT) of low-noise amplifier (LNA). A detailed investigation is carried out by simulation and experiment study. A two-dimensional electro-thermal model of the typical GaAs pHEMT induced by HPM is established in this paper. The simulation result reveals that avalanche breakdown, intrinsic excitation, and thermal breakdown all contribute to damage process. Heat accumulation occurs during the positive half cycle and the cylinder under the gate near the source side is most susceptible to burn-out. Experiment is carried out by injecting high power microwave into GaAs pHEMT LNA samples. It is found that the damage to LNA is because of the burn-out at first stage pHEMT. The interiors of the damaged samples are observed by scanning electron microscopy (SEM) and energy dispersive spectrometer (EDS). Experimental results accord well with the simulation of our model. Project supported by the National Basic Research Program of China (Grant No. 2014CB339900) and the Open Fund of Key Laboratory of Complex Electromagnetic Environment Science and Technology, China Academy of Engineering Physics (Grant No. 2015-0214.XY.K).

Single-shot measurements of laser-induced avalanche breakdown demonstrating spatial and temporal control by an external source

NASA Astrophysics Data System (ADS)

Woodbury, Daniel; Wahlstrand, Jared; Goers, Andy; Feder, Linus; Miao, Bo; Hine, George; Salehi, Fatholah; Milchberg, Howard

2016-10-01

We report on the use of single-shot supercontinuum spectral interferometry (SSSI) to make temporally and spatially resolved measurements of laser-induced avalanche breakdown in ambient air by a 200 ps pulse. By seeding the breakdown using an external 100 fs pulse, we demonstrate control over the timing and spatial characteristics of the avalanche. In addition, we calculate the collisional ionization rates at various laser intensities and demonstrate seeding of the avalanche breakdown both by multiphoton ionization and by photodetaching ions produced from a radioactive source. These observations provide proof-of-concept support for recent proposals to remotely measure radioactivity using laser-induced avalanche breakdown. This work supported by a DTRA, C-WMD Basic Research Program, and by the DOE NNSA Stewardship Science Graduate Fellowship, provided under Grant Number DE-NA0002135.

Intermittency between avalanche regimes on grain piles

NASA Astrophysics Data System (ADS)

Arran, M. I.; Vriend, N. M.

2018-06-01

We experimentally investigate discrete avalanches of grains, driven by a low inflow rate, on an erodible pile in a channel. We observe intermittency between one regime, in which avalanches are quasiperiodic and system spanning, and another, in which they pass at irregular intervals and have a power-law size distribution. Observations are robust to changes of inflow rate and grain type and require no tuning of external parameters. We demonstrate that the state of the pile's surface determines whether avalanche fronts propagate to the end of the channel or stop partway down, and we introduce a toy model for the latter case that reproduces the observed power-law size distribution. We suggest direct applications to avalanches of pharmaceutical and geophysical grains, and the possibility of reconciling the "self-organized criticality" predicted by several authors with the hysteretic behavior described by others.

Discovery of a photoresponse amplification mechanism in compensated PN junctions

NASA Astrophysics Data System (ADS)

Zhou, Yuchun; Liu, Yu-Hsin; Rahman, Samia N.; Hall, David; Sham, L. J.; Lo, Yu-Hwa

2015-01-01

We report the experimental evidence of uncovering a photoresponse amplification mechanism in heavily doped, partially compensated silicon p-n junctions under very low bias voltage. We show that the observed photocurrent gain occurs at a bias that is more than an order of magnitude below the threshold voltage for conventional impact ionization. Moreover, contrary to the case of avalanche detectors and p-i-n diodes, the amplified photoresponse is enhanced rather than suppressed with increasing temperature. These distinctive characteristics lead us to hypothesize that the inelastic scattering between energetic electrons (holes) and the ionized impurities in the depletion and charge neutral regions of the p-n junction in a cyclic manner plays a significant role in the amplification process. Such an internal signal amplification mechanism, which occurs at much lower bias than impact ionization and favors room temperature over cryogenic temperature, makes it promising for practical device applications.

The HPS electromagnetic calorimeter

NASA Astrophysics Data System (ADS)

Balossino, I.; Baltzell, N.; Battaglieri, M.; Bondì, M.; Buchanan, E.; Calvo, D.; Celentano, A.; Charles, G.; Colaneri, L.; D'Angelo, A.; Napoli, M. De; Vita, R. De; Dupré, R.; Egiyan, H.; Ehrhart, M.; Filippi, A.; Garçon, M.; Gevorgyan, N.; Girod, F.-X.; Guidal, M.; Holtrop, M.; Iurasov, V.; Kubarovsky, V.; Livingston, K.; McCarty, K.; McCormick, J.; McKinnon, B.; Osipenko, M.; Paremuzyan, R.; Randazzo, N.; Rauly, E.; Raydo, B.; Rindel, E.; Rizzo, A.; Rosier, P.; Sipala, V.; Stepanyan, S.; Szumila-Vance, H.; Weinstein, L. B.

2017-05-01

The Heavy Photon Search experiment (HPS) is searching for a new gauge boson, the so-called "heavy photon." Through its kinetic mixing with the Standard Model photon, this particle could decay into an electron-positron pair. It would then be detectable as a narrow peak in the invariant mass spectrum of such pairs, or, depending on its lifetime, by a decay downstream of the production target. The HPS experiment is installed in Hall-B of Jefferson Lab. This article presents the design and performance of one of the two detectors of the experiment, the electromagnetic calorimeter, during the runs performed in 2015-2016. The calorimeter's main purpose is to provide a fast trigger and reduce the copious background from electromagnetic processes through matching with a tracking detector. The detector is a homogeneous calorimeter, made of 442 lead-tungstate (PbWO4) scintillating crystals, each read out by an avalanche photodiode coupled to a custom trans-impedance amplifier.

The HPS electromagnetic calorimeter

DOE PAGES

Balossino, I.; Baltzell, N.; Battaglieri, M.; ...

2017-02-22

The Heavy Photon Search experiment (HPS) is searching for a new gauge boson, the so-called "heavy photon". Through its kinetic mixing with the Standard Model photon, this particle could decay into an electron-positron pair. It would then be detectable as a narrow peak in the invariant mass spectrum of such pairs, or, depending on its lifetime, by a decay downstream of the production target. The HPS experiment is installed in Hall-B of Jefferson Lab. This article presents the design and performance of one of the two detectors of the experiment, the electromagnetic calorimeter, during the runs performed in 2015-2016. The calorimeter's main purpose is to provide a fast trigger and reduce the copious background from electromagnetic processes through matching with a tracking detector. Finally, the detector is a homogeneous calorimeter, made of 442 lead-tungsten (PbWOmore » $$_4$$) scintillating crystals, each read-out by an avalanche photodiode coupled to a custom trans-impedance amplifier.« less

The HPS electromagnetic calorimeter

DOE Office of Scientific and Technical Information (OSTI.GOV)

Balossino, I.; Baltzell, N.; Battaglieri, M.

The Heavy Photon Search experiment (HPS) is searching for a new gauge boson, the so-called "heavy photon". Through its kinetic mixing with the Standard Model photon, this particle could decay into an electron-positron pair. It would then be detectable as a narrow peak in the invariant mass spectrum of such pairs, or, depending on its lifetime, by a decay downstream of the production target. The HPS experiment is installed in Hall-B of Jefferson Lab. This article presents the design and performance of one of the two detectors of the experiment, the electromagnetic calorimeter, during the runs performed in 2015-2016. The calorimeter's main purpose is to provide a fast trigger and reduce the copious background from electromagnetic processes through matching with a tracking detector. Finally, the detector is a homogeneous calorimeter, made of 442 lead-tungsten (PbWOmore » $$_4$$) scintillating crystals, each read-out by an avalanche photodiode coupled to a custom trans-impedance amplifier.« less

Kinetic simulations of gas breakdown in the dense plasma focus

NASA Astrophysics Data System (ADS)

Bennett, N.; Blasco, M.; Breeding, K.; DiPuccio, V.; Gall, B.; Garcia, M.; Gardner, S.; Gatling, J.; Hagen, E. C.; Luttman, A.; Meehan, B. T.; Molnar, S.; O'Brien, R.; Ormond, E.; Robbins, L.; Savage, M.; Sipe, N.; Welch, D. R.

2017-06-01

The first fully kinetic, collisional, and electromagnetic simulations of the breakdown phase of a MA-scale dense plasma focus are described and shown to agree with measured electrical characteristics, including breakdown time. In the model, avalanche ionization is driven by cathode electron emission, and this results in incomplete gas breakdown along the insulator. This reinforces the importance of the conditioning process that creates a metallic layer on the insulator surface. The simulations, nonetheless, help explain the relationship between the gas pressure, the insulator length, and the coaxial gap width. Previously, researchers noted three breakdown patterns related to pressure. Simulation and analytical results show that at low pressures, long ionization path lengths lead to volumetric breakdown, while high pressures lead to breakdown across the relatively small coaxial electrode gap. In an intermediate pressure regime, ionization path lengths are comparable to the insulator length which promotes ideal breakdown along the insulator surface.

Atmospheric-Pressure Cold Plasmas Used to Embed Bioactive Compounds in Matrix Material for Active Packaging of Fruits and Vegetables

NASA Astrophysics Data System (ADS)

Fernandez, Sulmer; Pedrow, Patrick; Powers, Joseph; Pitts, Marvin

2009-10-01

Active thin film packaging is a technology with the potential to provide consumers with new fruit and vegetable products-if the film can be applied without deactivating bioactive compounds.Atmospheric pressure cold plasma (APCP) processing can be used to activate monomer with concomitant deposition of an organic plasma polymerized matrix material and to immobilize a bioactive compound all at or below room temperature.Aims of this work include: 1) immobilize an antimicrobial in the matrix; 2) determine if the antimicrobial retains its functionality and 3) optimize the reactor design.The plasma zone will be obtained by increasing the voltage on an electrode structure until the electric field in the feed material (argon + monomer) yields electron avalanches. Results will be described using Red Delicious apples.Prospective matrix precursors are vanillin and cinnamic acid.A prospective bioactive compound is benzoic acid.

Possible origin and roles of nano-porosity in ZrO2 scales for hydrogen pick-up in Zr alloys

NASA Astrophysics Data System (ADS)

Lindgren, Mikaela; Geers, Christine; Panas, Itai

2017-08-01

A mechanistic understanding of Wagnerian build-up and subsequent non-Wagnerian break-down of barrier oxide upon oxidation of zirconium alloys by water is reiterated. Hydrogen assisted build-up of nano-porosity is addressed. Growth of sub-nanometer wide stalactitic pores owing to increasing aggregation of neutral oxygen vacancies offering a means to permeate hydrogen into the alloy is explored by density functional theory. The Wagnerian channel utilizes charge separation allowing charged oxygen vacancies and electrons to move separately from nominal anode to nominal cathode. This process becomes increasingly controlled by the charging of the barrier oxide resulting in sub-parabolic rate law for oxide growth. The break-down of the barrier oxide is understood to be preceded by avalanching hydrogen pick-up in the alloy. Pore mediated diffusion allows water to effectively short circuit the barrier oxide.

Discovery of a photoresponse amplification mechanism in compensated PN junctions

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zhou, Yuchun; Rahman, Samia N.; Hall, David

2015-01-19

We report the experimental evidence of uncovering a photoresponse amplification mechanism in heavily doped, partially compensated silicon p-n junctions under very low bias voltage. We show that the observed photocurrent gain occurs at a bias that is more than an order of magnitude below the threshold voltage for conventional impact ionization. Moreover, contrary to the case of avalanche detectors and p-i-n diodes, the amplified photoresponse is enhanced rather than suppressed with increasing temperature. These distinctive characteristics lead us to hypothesize that the inelastic scattering between energetic electrons (holes) and the ionized impurities in the depletion and charge neutral regions ofmore » the p-n junction in a cyclic manner plays a significant role in the amplification process. Such an internal signal amplification mechanism, which occurs at much lower bias than impact ionization and favors room temperature over cryogenic temperature, makes it promising for practical device applications.« less

Time lapse photography as an approach to understanding glide avalanche activity

USGS Publications Warehouse

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.

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

NASA Astrophysics Data System (ADS)

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.

Nonlinear X-Ray and Auger Spectroscopy at X-Ray Free-Electron Laser Sources

NASA Astrophysics Data System (ADS)

Rohringer, Nina

2015-05-01

X-ray free-electron lasers (XFELs) open the pathway to transfer non-linear spectroscopic techniques to the x-ray domain. A promising all x-ray pump probe technique is based on coherent stimulated electronic x-ray Raman scattering, which was recently demonstrated in atomic neon. By tuning the XFEL pulse to core-excited resonances, a few seed photons in the spectral tail of the XFEL pulse drive an avalanche of resonant inelastic x-ray scattering events, resulting in exponential amplification of the scattering signal by of 6-7 orders of magnitude. Analysis of the line profile of the emitted radiation permits to demonstrate the cross over from amplified spontaneous emission to coherent stimulated resonance scattering. In combination with statistical covariance mapping, a high-resolution spectrum of the resonant inelastic scattering process can be obtained, opening the path to coherent stimulated x-ray Raman spectroscopy. An extension of these ideas to molecules and a realistic feasibility study of stimulated electronic x-ray Raman scattering in CO will be presented. Challenges to realizing stimulated electronic x-ray Raman scattering at present-day XFEL sources will be discussed, corroborated by results of a recent experiment at the LCLS XFEL. Due to the small gain cross section in molecular targets, other nonlinear spectroscopic techniques such as nonlinear Auger spectroscopy could become a powerful alternative. Theory predictions of a novel pump probe technique based on resonant nonlinear Auger spectroscopic will be discussed and the method will be compared to stimulated x-ray Raman spectroscopy.

XeCl avalanche discharge laser employing Ar as a diluent

DOEpatents

Sze, R.C.

1979-10-10

A XeCl avalanche discharge exciplex laser which uses a gaseous lasing starting mixture of: 0.2 to 0.4% chlorine donor/2.5% to 10% Xe/97.3% to 89.6% Ar) is provided. The chlorine donor normally comprises HCl but can also comprise CCl/sub 4/ BCl/sub 3/. Use of Ar as a diluent gas reduces operating pressures over other rare gas halide lasers to near atmospheric pressure, increases output lasing power of the XeCl avalanche discharge laser by 30% to exceed KrF avalanche discharge lasing outputs, and is less expensive to operate.

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

NASA Astrophysics Data System (ADS)

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 the run-outs are roughly similar, the distribution of structures is different and related to lithology: Las Isletas has clear proximal faults replaced distally by inter-hummock depressions where basal unit zones are exhumed, whereas El Crater has faults throughout, but the basal layer is hidden in the distal zone. Hummocky forms depend on material type, with steep hummocks being formed of coherent lava units, and low hummocks by matrix-rich units. In both avalanches, extensional structures predominate; the upper layers exclusively underwent longitudinal and lateral extension. This is consistent with evidence of only small amounts of block-to-block interactions during bulk horizontal spreading. The base of the moving mass accommodated transport by large amounts of simple shear. We suggest that contractional structures and inter-block collisions seen in many other avalanches are artifacts related to topographic confinement.

Ionizing gas breakdown waves in strong electric fields.

NASA Technical Reports Server (NTRS)

Klingbeil, R.; Tidman, D. A.; Fernsler, R. F.

1972-01-01

A previous analysis by Albright and Tidman (1972) of the structure of an ionizing potential wave driven through a dense gas by a strong electric field is extended to include atomic structure details of the background atoms and radiative effects, especially, photoionization. It is found that photoionization plays an important role in avalanche propagation. Velocities, electron densities, and temperatures are presented as a function of electric field for both negative and positive breakdown waves in nitrogen.

Self-consistent evolution of plasma discharge and electromagnetic fields in a microwave pulse compressor

NASA Astrophysics Data System (ADS)

Shlapakovski, A. S.; Beilin, L.; Hadas, Y.; Schamiloglu, E.; Krasik, Ya. E.

2015-07-01

Nanosecond-scale evolution of plasma and RF electromagnetic fields during the release of energy from a microwave pulse compressor with a plasma interference switch was investigated numerically using the code MAGIC. The plasma was simulated in the scope of the gas conductivity model in MAGIC. The compressor embodied an S-band cavity and H-plane waveguide tee with a shorted side arm filled with pressurized gas. In a simplified approach, the gas discharge was initiated by setting an external ionization rate in a layer crossing the side arm waveguide in the location of the electric field antinode. It was found that with increasing ionization rate, the microwave energy absorbed by the plasma in the first few nanoseconds increases, but the absorption for the whole duration of energy release, on the contrary, decreases. In a hybrid approach modeling laser ignition of the discharge, seed electrons were set around the electric field antinode. In this case, the plasma extends along the field forming a filament and the plasma density increases up to the level at which the electric field within the plasma decreases due to the skin effect. Then, the avalanche rate decreases but the density still rises until the microwave energy release begins and the electric field becomes insufficient to support the avalanche process. The extraction of the microwave pulse limits its own power by terminating the rise of the plasma density and filament length. For efficient extraction, a sufficiently long filament of dense plasma must have sufficient time to be formed.

Dense Granular Avalanches: Mathematical Description and Experimental Validation

NASA Astrophysics Data System (ADS)

Tai, Y.-C.; Hutter, K.; Gray, J. M. N. T.

Snow avalanches, landslides, rock falls and debris flows are extremely dangerous and destructive natural phenomena. The frequency of occurrence and amplitudes of these disastrous events appear to have increased in recent years perhaps due to recent climate warming. The events endanger the personal property and infra-structure in mountainous regions. For example, from the winters 1940/41 to 1987/88 more than 7000 snow avalanches occurred in Switzerland with damaged property leading to a total of 1269 deaths. In February 1999, 36 people were buried by a single avalanche in Galtür, Austria. In August 1996, a very large debris flow in middle Taiwan resulted in 51 deaths, 22 lost and an approximate property damage of more than 19 billion NT dollars (ca. 600 million US dollars) [18]. In Europe, a suddenly released debris flow in North Italy in August 1998 buried 5 German tourists on the Superhighway "Brenner-Autobahn". The topic has gained so much significance that in 1990 the United Nations declared the International Decade for Natural Disasters Reduction (IDNDR); Germany has its own Deutsches IDNDR-Komitee für Katastrophenvorbeugung e.V. Special conferences are devoted to the theme, e.g., the CALAR conference on Avalanches, Landslides, Rock Falls and Debris Flows (Vienna, January 2000), INTERPRAEVENT, annual conferences on the protection of habitants from floods, debris flows and avalanches, special conferences on debris flow hazard mi tigation and those exclusively on Avalanches.

Ultra-violet avalanche photodiode based on AlN/GaN periodically-stacked-structure

NASA Astrophysics Data System (ADS)

Wu, Xingzhao; Zheng, Jiyuan; Wang, Lai; Brault, Julien; Matta, Samuel; Hao, Zhibiao; Sun, Changzheng; Xiong, Bing; Luo, Yi; Han, Yianjun; Wang, Jian; Li, Hongtao; Khalfioui, Mohamed A.; Li, Mo; Kang, Jianbin; Li, Qian

2018-02-01

The high-gain photomultiplier tube (PMT) is the most popular method to detect weak ultra-violet signals which attenuate quickly in atmosphere, although the vacuum tube makes it fragile and difficult to integrate. To overcome the disadvantage of PMT, an AlN/GaN periodically-stacked-structure (PSS) avalanche photodiode (APD) has been proposed, finally achieving good quality of high gain and low excessive noise. As there is a deep g valley only in the conduction band of both GaN and AlN, the electron transfers suffering less scattering and thus becomes easier to obtain the threshold of ionization impact. Because of unipolar ionization in the PSS APD, it works in linear mode. Four prototype devices of 5-period, 10-period, 15-period, and 20-period were fabricated to verify that the gain of APD increases exponentially with period number. And in 20-period device, a recorded high and stable gain of 104 was achieved under constant bias. In addition, it is proved both experimentally and theoretically, that temperature stability on gain is significantly improved in PSS APD. And it is found that the resonant enhancement in interfacial ionization may bring significant enhancement of electron ionization performance. To make further progress in PSS APD, the device structure is investigated by simulation. Both the gain and temperature stability are optimized alternatively by a proper design of periodical thickness and AlN layer occupancy.

Periglacial Geomorphology.

ERIC Educational Resources Information Center

Potter, Noel, Jr.

1984-01-01

Describes preglacial processes, focusing on weathering, rate and timing of movement of material, snow and snow avalanches, rock glaciers, gelifluction, pingos, patterned ground, and the thaw of permafrost. This information is provided for individuals teaching introductory geology/geomorphology and whose specialty is not cold-climate phenomena. (JN)

Reuyl Crater Dust Avalanches

NASA Technical Reports Server (NTRS)

2002-01-01

(Released 13 May 2002) The Science The rugged, arcuate rim of the 90 km crater Reuyl dominates this THEMIS image. Reuyl crater is at the southern edge of a region known to be blanketed in thick dust based on its high albedo (brightness) and low thermal inertia values. This thick mantle of dust creates the appearance of snow covered mountains in the image. Like snow accumulation on Earth, Martian dust can become so thick that it eventually slides down the face of steep slopes, creating runaway avalanches of dust. In the center of this image about 1/3 of the way down is evidence of this phenomenon. A few dozen dark streaks can be seen on the bright, sunlit slopes of the crater rim. The narrow streaks extend downslope following the local topography in a manner very similar to snow avalanches on Earth. But unlike their terrestrial counterparts, no accumulation occurs at the bottom. The dust particles are so small that they are easily launched into the thin atmosphere where they remain suspended and ultimately blow away. The apparent darkness of the avalanche scars is due to the presence of relatively dark underlying material that becomes exposed following the passage of the avalanche. Over time, new dust deposition occurs, brightening the scars until they fade into the background. Although dark slope streaks had been observed in Viking mission images, a clear understanding of this dynamic phenomenon wasn't possible until the much higher resolution images from the Mars Global Surveyor MOC camera revealed the details. MOC images also showed that new avalanches have occurred during the time MGS has been in orbit. THEMIS images will allow additional mapping of their distribution and frequency, contributing new insights about Martian dust avalanches. The Story The stiff peaks in this image might remind you of the Alps here on Earth, but they really outline the choppy edge of a large Martian crater over 50 miles wide (seen in the context image at right). While these aren't the Alps, you will find quite a few avalanches. Avalanches of dust, however, not snow. Martian dust can become so thick in this area that it eventually slides down the steep slopes, creating runaway avalanches of dust. No dedicated, Swiss-like avalanche rescue teams would be needed much on Mars, however. Unlike snow, the dust doesn't pile up and accumulate at the bottom. Instead, dust particles are so small that they get launched into the atmosphere where they remain suspended until . . . poof! They are blown away and distributed lightly elsewhere. For evidence of past avalanches, check out the dark streaks running down the bright, sunlit slopes (western side of the peaks about 1/3 of the way down the image). These avalanche scars are dark because the underlying surface is not as bright as the removed dust. Eventually, new dust will settle over these scars, and the streaks will brighten until they fade into the background. The neat thing is that we'll be able to see all of these changes happening over time. Our current two Mars orbiters (called Mars Global Surveyor and 2001 Mars Odyssey) are showing that avalanche action is happening right now, all of the time on Mars. For example, the camera on Mars Global Surveyor has already taken pictures of the Martian surface in some areas that showed no avalanches - the first time the picture was snapped, that is. The next time around, the camera took a picture of the same area, only voila! New streaks, meaning new avalanches! That's why it can be so exciting to look at the Martian landscape over time to see how it changes. The THEMIS camera on Odyssey will continue to map out the places where the avalanches occur and how often. This information will really help scientists understand how dust is works to shape the terrain and to influence the Martian climate as it constantly swings into the atmosphere, falls down to the ground, and rises back up again. Stay tuned to see if you too can pick out the changes over time!

Stellar Winds and Dust Avalanches in the AU Mic Debris Disk

NASA Astrophysics Data System (ADS)

Chiang, Eugene; Fung, Jeffrey

2017-10-01

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.

Dynamics of the Bingham Canyon rock avalanches (Utah, USA) resolved from topographic, seismic, and infrasound data

NASA Astrophysics Data System (ADS)

Moore, Jeffrey R.; Pankow, Kristine L.; Ford, Sean R.; Koper, Keith D.; Hale, J. Mark; Aaron, Jordan; Larsen, Chris F.

2017-03-01

The 2013 Bingham Canyon Mine rock avalanches represent one of the largest cumulative landslide events in recorded U.S. history and provide a unique opportunity to test remote analysis techniques for landslide characterization. Here we combine aerial photogrammetry surveying, topographic reconstruction, numerical runout modeling, and analysis of broadband seismic and infrasound data to extract salient details of the dynamics and evolution of the multiphase landslide event. Our results reveal a cumulative intact rock source volume of 52 Mm3, which mobilized in two main rock avalanche phases separated by 1.5 h. We estimate that the first rock avalanche had 1.5-2 times greater volume than the second. Each failure initiated by sliding along a gently dipping (21°), highly persistent basal fault before transitioning to a rock avalanche and spilling into the inner pit. The trajectory and duration of the two rock avalanches were reconstructed using runout modeling and independent force history inversion of intermediate-period (10-50 s) seismic data. Intermediate- and shorter-period (1-50 s) seismic data were sensitive to intervals of mass redirection and constrained finer details of the individual slide dynamics. Back projecting short-period (0.2-1 s) seismic energy, we located the two rock avalanches within 2 and 4 km of the mine. Further analysis of infrasound and seismic data revealed that the cumulative event included an additional 11 smaller landslides (volumes 104-105 m3) and that a trailing signal following the second rock avalanche may result from an air-coupled Rayleigh wave. Our results demonstrate new and refined techniques for detailed remote characterization of the dynamics and evolution of large landslides.

Dynamics of glide avalanches and snow gliding

NASA Astrophysics Data System (ADS)

Ancey, Christophe; Bain, Vincent

2015-09-01

In recent years, due to warmer snow cover, there has been a significant increase in the number of cases of damage caused by gliding snowpacks and glide avalanches. On most occasions, these have been full-depth, wet-snow avalanches, and this led some people to express their surprise: how could low-speed masses of wet snow exert sufficiently high levels of pressure to severely damage engineered structures designed to carry heavy loads? This paper reviews the current state of knowledge about the formation of glide avalanches and the forces exerted on simple structures by a gliding mass of snow. One particular difficulty in reviewing the existing literature on gliding snow and on force calculations is that much of the theoretical and phenomenological analyses were presented in technical reports that date back to the earliest developments of avalanche science in the 1930s. Returning to these primary sources and attempting to put them into a contemporary perspective are vital. A detailed, modern analysis of them shows that the order of magnitude of the forces exerted by gliding snow can indeed be estimated correctly. The precise physical mechanisms remain elusive, however. We comment on the existing approaches in light of the most recent findings about related topics, including the physics of granular and plastic flows, and from field surveys of snow and avalanches (as well as glaciers and debris flows). Methods of calculating the forces exerted by glide avalanches are compared quantitatively on the basis of two case studies. This paper shows that if snow depth and density are known, then certain approaches can indeed predict the forces exerted on simple obstacles in the event of glide avalanches or gliding snow cover.

Avalanche statistics from data with low time resolution

DOE Office of Scientific and Technical Information (OSTI.GOV)

LeBlanc, Michael; Nawano, Aya; Wright, Wendelin J.

Extracting avalanche distributions from experimental microplasticity data can be hampered by limited time resolution. We compute the effects of low time resolution on avalanche size distributions and give quantitative criteria for diagnosing and circumventing problems associated with low time resolution. We show that traditional analysis of data obtained at low acquisition rates can lead to avalanche size distributions with incorrect power-law exponents or no power-law scaling at all. Furthermore, we demonstrate that it can lead to apparent data collapses with incorrect power-law and cutoff exponents. We propose new methods to analyze low-resolution stress-time series that can recover the size distributionmore » of the underlying avalanches even when the resolution is so low that naive analysis methods give incorrect results. We test these methods on both downsampled simulation data from a simple model and downsampled bulk metallic glass compression data and find that the methods recover the correct critical exponents.« less

Avalanche statistics from data with low time resolution

DOE PAGES

LeBlanc, Michael; Nawano, Aya; Wright, Wendelin J.; ...

2016-11-22

Extracting avalanche distributions from experimental microplasticity data can be hampered by limited time resolution. We compute the effects of low time resolution on avalanche size distributions and give quantitative criteria for diagnosing and circumventing problems associated with low time resolution. We show that traditional analysis of data obtained at low acquisition rates can lead to avalanche size distributions with incorrect power-law exponents or no power-law scaling at all. Furthermore, we demonstrate that it can lead to apparent data collapses with incorrect power-law and cutoff exponents. We propose new methods to analyze low-resolution stress-time series that can recover the size distributionmore » of the underlying avalanches even when the resolution is so low that naive analysis methods give incorrect results. We test these methods on both downsampled simulation data from a simple model and downsampled bulk metallic glass compression data and find that the methods recover the correct critical exponents.« less

Mount Aragats as a stable electron accelerator for atmospheric high-energy physics research

NASA Astrophysics Data System (ADS)

Chilingarian, Ashot; Hovsepyan, Gagik; Mnatsakanyan, Eduard

2016-03-01

Observation of the numerous thunderstorm ground enhancements (TGEs), i.e., enhanced fluxes of electrons, gamma rays, and neutrons detected by particle detectors located on the Earth's surface and related to the strong thunderstorms above it, helped to establish a new scientific topic—high-energy physics in the atmosphere. Relativistic runaway electron avalanches (RREAs) are believed to be a central engine initiating high-energy processes in thunderstorm atmospheres. RREAs observed on Mount Aragats in Armenia during the strongest thunderstorms and simultaneous measurements of TGE electron and gamma-ray energy spectra proved that RREAs are a robust and realistic mechanism for electron acceleration. TGE research facilitates investigations of the long-standing lightning initiation problem. For the last 5 years we were experimenting with the "beams" of "electron accelerators" operating in the thunderclouds above the Aragats research station. Thunderstorms are very frequent above Aragats, peaking in May-June, and almost all of them are accompanied with enhanced particle fluxes. The station is located on a plateau at an altitude 3200 asl near a large lake. Numerous particle detectors and field meters are located in three experimental halls as well as outdoors; the facilities are operated all year round. All relevant information is being gathered, including data on particle fluxes, fields, lightning occurrences, and meteorological conditions. By the example of the huge thunderstorm that took place at Mount Aragats on August 28, 2015, we show that simultaneous detection of all the relevant data allowed us to reveal the temporal pattern of the storm development and to investigate the atmospheric discharges and particle fluxes.

Radiation and Temperature Hard Multi-Pixel Avalanche Photodiodes

NASA Technical Reports Server (NTRS)

Bensaoula, Abdelhak (Inventor); Starikov, David (Inventor); Pillai, Rajeev (Inventor)

2017-01-01

The structure and method of fabricating a radiation and temperature hard avalanche photodiode with integrated radiation and temperature hard readout circuit, comprising a substrate, an avalanche region, an absorption region, and a plurality of Ohmic contacts are presented. The present disclosure provides for tuning of spectral sensitivity and high device efficiency, resulting in photon counting capability with decreased crosstalk and reduced dark current.

Application of LANDSAT data to delimitation of avalanche hazards in Montane, Colorado

NASA Technical Reports Server (NTRS)

Knepper, D. H. (Principal Investigator); Summer, R.

1976-01-01

The author has identified the following significant results. With rare exceptions, avalanche areas cannot be identified on LANDSAT imagery. Avalanche hazard mapping on a regional scale is best conducted using LANDSAT imagery in conjunction with complementary data sources. Level of detail of such maps will be limited by the amount and completeness of the complementary information used.

Avalanche multiplication and impact ionization in amorphous selenium photoconductive target

NASA Astrophysics Data System (ADS)

Park, Wug-Dong; Tanioka, Kenkichi

2014-03-01

The avalanche multiplication factor and the hole ionization coefficient in the amorphous selenium (a-Se) high-gain avalanche rushing amorphous photoconductor (HARP) target depend on the electric field. The phenomenon of avalanche multiplication and impact ionization in the 0.4-µm-thick a-Se HARP target is investigated. The hot carrier energy in the 0.4-µm-thick a-Se HARP target increases linearly as the target voltage increases. The energy relaxation length of hot carriers in the a-Se photoconductor of the 0.4-µm-thick HARP target saturates as the electric field increases. The average energy Eav of a hot carrier and the energy relaxation length λE in the a-Se photoconductor of the 0.4-µm-thick HARP target at 1 × 108 V/m were 0.25 eV and 2.5 nm, respectively. In addition, the hole ionization coefficient β and the avalanche multiplication factor M are derived as a function of the electric field, the average energy of a hot carrier, and the impact ionization energy. The experimental hole ionization coefficient β and the avalanche multiplication factor M in the 0.4-µm-thick a-Se HARP target agree with the theoretical results.

Magnetically switched power supply system for lasers

NASA Technical Reports Server (NTRS)

Pacala, Thomas J. (Inventor)

1987-01-01

A laser power supply system is described in which separate pulses are utilized to avalanche ionize the gas within the laser and then produce a sustained discharge to cause the gas to emit light energy. A pulsed voltage source is used to charge a storage device such as a distributed capacitance. A transmission line or other suitable electrical conductor connects the storage device to the laser. A saturable inductor switch is coupled in the transmission line for containing the energy within the storage device until the voltage level across the storage device reaches a predetermined level, which level is less than that required to avalanche ionize the gas. An avalanche ionization pulse generating circuit is coupled to the laser for generating a high voltage pulse of sufficient amplitude to avalanche ionize the laser gas. Once the laser gas is avalanche ionized, the energy within the storage device is discharged through the saturable inductor switch into the laser to provide the sustained discharge. The avalanche ionization generating circuit may include a separate voltage source which is connected across the laser or may be in the form of a voltage multiplier circuit connected between the storage device and the laser.

Scale-free avalanche dynamics in the stock market

NASA Astrophysics Data System (ADS)

Bartolozzi, M.; Leinweber, D. B.; Thomas, A. W.

2006-10-01

Self-organized criticality (SOC) has been claimed to play an important role in many natural and social systems. In the present work we empirically investigate the relevance of this theory to stock-market dynamics. Avalanches in stock-market indices are identified using a multi-scale wavelet-filtering analysis designed to remove Gaussian noise from the index. Here, new methods are developed to identify the optimal filtering parameters which maximize the noise removal. The filtered time series is reconstructed and compared with the original time series. A statistical analysis of both high-frequency Nasdaq E-mini Futures and daily Dow Jones data is performed. The results of this new analysis confirm earlier results revealing a robust power-law behaviour in the probability distribution function of the sizes, duration and laminar times between avalanches. This power-law behaviour holds the potential to be established as a stylized fact of stock market indices in general. While the memory process, implied by the power-law distribution of the laminar times, is not consistent with classical models for SOC, we note that a power-law distribution of the laminar times cannot be used to rule out self-organized critical behaviour.

Spontaneous neuronal activity as a self-organized critical phenomenon

NASA Astrophysics Data System (ADS)

de Arcangelis, L.; Herrmann, H. J.

2013-01-01

Neuronal avalanches are a novel mode of activity in neuronal networks, experimentally found in vitro and in vivo, and exhibit a robust critical behaviour. Avalanche activity can be modelled within the self-organized criticality framework, including threshold firing, refractory period and activity-dependent synaptic plasticity. The size and duration distributions confirm that the system acts in a critical state, whose scaling behaviour is very robust. Next, we discuss the temporal organization of neuronal avalanches. This is given by the alternation between states of high and low activity, named up and down states, leading to a balance between excitation and inhibition controlled by a single parameter. During these periods both the single neuron state and the network excitability level, keeping memory of past activity, are tuned by homeostatic mechanisms. Finally, we verify if a system with no characteristic response can ever learn in a controlled and reproducible way. Learning in the model occurs via plastic adaptation of synaptic strengths by a non-uniform negative feedback mechanism. Learning is a truly collective process and the learning dynamics exhibits universal features. Even complex rules can be learned provided that the plastic adaptation is sufficiently slow.

Geological and geotechnical characterization of the debris avalanche and pyroclastic deposits of Cotopaxi Volcano (Ecuador). A contribute to instability-related hazard studies

NASA Astrophysics Data System (ADS)

Vezzoli, L.; Apuani, T.; Corazzato, C.; Uttini, A.

2017-02-01

The huge volcanic debris avalanche occurred at 4.5 ka is a major event in the evolution of the Cotopaxi volcano, Ecuador. The present volcanic hazard in the Cotopaxi region is related to lahars generated by volcanic eruptions and concurrent ice melting. This paper presents the geological and geotechnical field and laboratory characterization of the 4.5 ka Cotopaxi debris avalanche deposit and of the younger unconsolidated pyroclastic deposits, representing the probable source of future shallow landslides. The debris avalanche formed a deposit with a well-developed hummocky topography, and climbed a difference in height of about 260 m along the slopes of the adjacent Sincholagua volcano. The debris avalanche deposit includes four lithofacies (megablock, block, mixed, and sheared facies) that represent different flow regimes and degrees of substratum involvement. The facies distribution suggests that, in the proximal area, the debris avalanche slid predominantly confined to the valleys along the N and NE flank of the volcanic cone, emplacing a stack of megablocks. When the flow reached the break in slope at the base of the edifice, it became unconfined and spread laterally over most of the area of the Rio Pita valley. A dynamic block fragmentation and dilation occurred during the debris avalanche transport, emplacing the block facies. The incorporation of the older Chalupas Ignimbrite is responsible for the mixed facies and the sheared facies. Geotechnical results include a full-range grain size characterization, which enabled to make broader considerations on possible variability among the sampled facies. Consolidated drained triaxial compression tests, carried out on the fine fraction < 4.76 mm, point out that shear strength for cohesionless sandy materials is only due to effective friction angle, and show a quite homogeneous behaviour over the set of tested samples. The investigated post-4.5 pyroclastic deposits constitute a 5-12 m thick sequence of poorly consolidated materials that are interlayered with lava flows. Their geotechnical analyses have evidenced a strong variability in grain size distribution, reflecting the depositional processes, and a generally high porosity. Consolidated drained triaxial compression tests delineated a similar shear stress-strain behaviour among the different units, where shear strength is only due to friction angle. Failure surfaces are always well developed, indicating that the poorly consolidated pyroclastic cover could undergo failure leading to the formation of a gravity driven instability phenomena, like granular or debris flows, which are mainly controlled by the fine fraction. This work underlies the general necessity for a site-specific, and interdisciplinary approach in the characterization of volcanic successions to provide reliable data for gravitational instability studies.

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

PubMed Central

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

Neuronal avalanches and coherence potentials

NASA Astrophysics Data System (ADS)

Plenz, D.

2012-05-01

The mammalian cortex consists of a vast network of weakly interacting excitable cells called neurons. Neurons must synchronize their activities in order to trigger activity in neighboring neurons. Moreover, interactions must be carefully regulated to remain weak (but not too weak) such that cascades of active neuronal groups avoid explosive growth yet allow for activity propagation over long-distances. Such a balance is robustly realized for neuronal avalanches, which are defined as cortical activity cascades that follow precise power laws. In experiments, scale-invariant neuronal avalanche dynamics have been observed during spontaneous cortical activity in isolated preparations in vitro as well as in the ongoing cortical activity of awake animals and in humans. Theory, models, and experiments suggest that neuronal avalanches are the signature of brain function near criticality at which the cortex optimally responds to inputs and maximizes its information capacity. Importantly, avalanche dynamics allow for the emergence of a subset of avalanches, the coherence potentials. They emerge when the synchronization of a local neuronal group exceeds a local threshold, at which the system spawns replicas of the local group activity at distant network sites. The functional importance of coherence potentials will be discussed in the context of propagating structures, such as gliders in balanced cellular automata. Gliders constitute local population dynamics that replicate in space after a finite number of generations and are thought to provide cellular automata with universal computation. Avalanches and coherence potentials are proposed to constitute a modern framework of cortical synchronization dynamics that underlies brain function.

Knowledge of the Avalanche Victim Resuscitation Checklist and Utility of a Standardized Lecture in Italy.

PubMed

Strapazzon, Giacomo; Migliaccio, Daniel; Fontana, Diego; Stawinoga, Agnieszka Elzbieta; Milani, Mario; Brugger, Hermann

2018-03-01

To explore baseline knowledge about avalanche guidelines and the Avalanche Victim Resuscitation Checklist (AVReCh) in Italy and the knowledge acquisition from a standardized lecture. Standardized lecture material discussing AVReCh was presented during 8 mountain medicine courses from November 2014 to April 2016 in different regions of Italy. To determine the knowledge acquisition from the lecture, a pre- and postlecture survey was utilized. A total of 193 surveys were analyzed. More than 50% of the participants had never participated in lectures/courses on avalanche guidelines, and less than 50% of the participants knew about the AVReCh before the lecture. The correct temporal sequence of reportable information in the basic life support section of the AVReCh was selected by 40% of the participants before the lecture and by 75% after the lecture (P<0.001). Within subgroups analysis, most groups saw significant improvement in performance (P<0.05). The selection of the correct burial time increased from 36 to 84% (P<0.05). Health care providers and mountain rescue personnel are not widely aware of avalanche guidelines. The standardized lecture significantly improved knowledge of the principles of avalanche management related to core AVReCh elements. However, the effect that this knowledge acquisition has on avalanche victim survival or adherence to the AVReCh in the field is yet to be determined. Copyright © 2017 Wilderness Medical Society. Published by Elsevier Inc. All rights reserved.

Dynamic Mars

NASA Image and Video Library

2015-09-30

This image from NASA Mars Reconnaissance Orbiter spacecraft shows a channel system flowing to the southwest toward the huge Hellas impact basin. Click on the image for larger version The scarp at the edge of the North Polar layered deposits of Mars is the site of the most frequent frost avalanches seen by HiRISE. At this season, northern spring, frost avalanches are common and HiRISE monitors the scarp to learn more about the timing and frequency of the avalanches, and their relationship to the evolution of frost on the flat ground above and below the scarp. This picture managed to capture a small avalanche in progress, right in the color strip. See if you can spot it in the browse image, and then click on the cutout to see it at full resolution. The small white cloud in front of the brick red cliff is likely carbon dioxide frost dislodged from the layers above, caught in the act of cascading down the cliff. It is larger than it looks, more than 20 meters across, and (based on previous examples) it will likely kick up clouds of dust when it hits the ground. The avalanches tend to take place at a season when the North Polar region is warming, suggesting that the avalanches may be triggered by thermal expansion. The avalanches remind us, along with active sand dunes, dust devils, slope streaks and recurring slope lineae, that Mars is an active and dynamic planet. http://photojournal.jpl.nasa.gov/catalog/PIA19961

Fully Integrated Linear Single Photon Avalanche Diode (SPAD) Array with Parallel Readout Circuit in a Standard 180 nm CMOS Process

NASA Astrophysics Data System (ADS)

Isaak, S.; Bull, S.; Pitter, M. C.; Harrison, Ian.

2011-05-01

This paper reports on the development of a SPAD device and its subsequent use in an actively quenched single photon counting imaging system, and was fabricated in a UMC 0.18 μm CMOS process. A low-doped p- guard ring (t-well layer) encircling the active area to prevent the premature reverse breakdown. The array is a 16×1 parallel output SPAD array, which comprises of an active quenched SPAD circuit in each pixel with the current value being set by an external resistor RRef = 300 kΩ. The SPAD I-V response, ID was found to slowly increase until VBD was reached at excess bias voltage, Ve = 11.03 V, and then rapidly increase due to avalanche multiplication. Digital circuitry to control the SPAD array and perform the necessary data processing was designed in VHDL and implemented on a FPGA chip. At room temperature, the dark count was found to be approximately 13 KHz for most of the 16 SPAD pixels and the dead time was estimated to be 40 ns.

Ultracold neutral plasmas

NASA Astrophysics Data System (ADS)

Lyon, M.; Rolston, S. L.

2017-01-01

By photoionizing samples of laser-cooled atoms with laser light tuned just above the ionization limit, plasmas can be created with electron and ion temperatures below 10 K. These ultracold neutral plasmas have extended the temperature bounds of plasma physics by two orders of magnitude. Table-top experiments, using many of the tools from atomic physics, allow for the study of plasma phenomena in this new regime with independent control over the density and temperature of the plasma through the excitation process. Characteristic of these systems is an inhomogeneous density profile, inherited from the density distribution of the laser-cooled neutral atom sample. Most work has dealt with unconfined plasmas in vacuum, which expand outward at velocities of order 100 m/s, governed by electron pressure, and with lifetimes of order 100 μs, limited by stray electric fields. Using detection of charged particles and optical detection techniques, a wide variety of properties and phenomena have been observed, including expansion dynamics, collective excitations in both the electrons and ions, and collisional properties. Through three-body recombination collisions, the plasmas rapidly form Rydberg atoms, and clouds of cold Rydberg atoms have been observed to spontaneously avalanche ionize to form plasmas. Of particular interest is the possibility of the formation of strongly coupled plasmas, where Coulomb forces dominate thermal motion and correlations become important. The strongest impediment to strong coupling is disorder-induced heating, a process in which Coulomb energy from an initially disordered sample is converted into thermal energy. This restricts electrons to a weakly coupled regime and leaves the ions barely within the strongly coupled regime. This review will give an overview of the field of ultracold neutral plasmas, from its inception in 1999 to current work, including efforts to increase strong coupling and effects on plasma properties due to strong coupling.

Readout ASICs and Electronics for the 144-channel HAPDs for the Aerogel RICH at Belle II

NASA Astrophysics Data System (ADS)

Nishida, S.; Adachi, I.; Ikeda, H.; Hara, K.; Iijima, T.; Iwata, S.; Korpar, S.; Križan, P.; Kuroda, E.; Pestotnik, R.; Seljak, A.; Sumiyoshi, T.; Takagaki, H.

The particle identification (PID) device in the endcap of the Belle detector will be upgraded to a ring imaging Cherenkov counter (RICH) using aerogel as a radiator at the Belle II experiment. We develop the electronics to read out the 70,000 channels of hit information from the 144-channel hybrid avalanche photodetectors (HAPD), of the aerogel RICH detector. A readout ASIC is developed to digitize the HAPD signals, and was used in a beam test with the prototype detector. The performance and plan of the ASIC is reported in this study. We have also designed the readout electronics for the aerogel RICH, which consist of front-end boards with the ASICs merger boards to collect data from the front-end boards. A front-end board that fits in the actual available space for the aerogel RICH electronics was produced.

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

NASA Astrophysics Data System (ADS)

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 projected. These changes are relatively strong compared to changes in snow and meteorological variables. The decrease is amplified in spring and at low altitude. In contrast, an increase in avalanche activity is expected in winter at high altitude because of conditions favourable to wet-snow avalanches earlier in the season. Comparison with the outputs of the deterministic avalanche hazard model MEPRA (Modèle Expert d'aide à la Prévision du Risque d'Avalanche) shows generally consistent results but suggests that, even if the frequency of winters with high avalanche activity is clearly projected to decrease, the decreasing trend may be less strong and smooth than suggested by the statistical analysis based on changes in snowpack characteristics and their links to avalanches observations in the past. This important point for risk assessment pleads for further work focusing on shorter timescales. Finally, the small differences between different climate change scenarios show the robustness of the predicted avalanche activity changes.

Comparison between the effects of positive noncatastrophic HMB ESD stress in n-channel and p-channel power MOSFET's

NASA Astrophysics Data System (ADS)

Zupac, Dragan; Kosier, Steven L.; Schrimpf, Ronald D.; Galloway, Kenneth F.; Baum, Keith W.

1991-10-01

The effect of noncatastrophic positive human body model (HBM) electrostatic discharge (ESD) stress on n-channel power MOSFETs is radically different from that on p-channel MOSFETs. In n-channel transistors, the stress causes negative shifts of the current-voltage characteristics indicative of positive charge trapping in the gate oxide. In p-channel transistors, the stress increases the drain-to-source leakage current, probably due to localized avalanche electron injection from the p-doped drain.

Recent improvements of the JET lithium beam diagnostica)

NASA Astrophysics Data System (ADS)

Brix, M.; Dodt, D.; Dunai, D.; Lupelli, I.; Marsen, S.; Melson, T. F.; Meszaros, B.; Morgan, P.; Petravich, G.; Refy, D. I.; Silva, C.; Stamp, M.; Szabolics, T.; Zastrow, K.-D.; Zoletnik, S.; JET-EFDA Contributors

2012-10-01

A 60 kV neutral lithium diagnostic beam probes the edge plasma of JET for the measurement of electron density profiles. This paper describes recent enhancements of the diagnostic setup, new procedures for calibration and protection measures for the lithium ion gun during massive gas puffs for disruption mitigation. New light splitting optics allow in parallel beam emission measurements with a new double entrance slit CCD spectrometer (spectrally resolved) and a new interference filter avalanche photodiode camera (fast density and fluctuation studies).

Relating Silicon Carbide Avalanche Breakdown Diode Design to Pulsed-Energy Capability

DTIC Science & Technology

2017-03-01

Relating Silicon Carbide Avalanche Breakdown Diode Design to Pulsed- Energy Capability Damian Urciuoli, Miguel Hinojosa, and Ronald Green US...were pulse tested in an inductive load circuit at peak powers of over 110 kW. Total pulsed- energy dissipation was kept nearly the same among the...voltages about which design provides the highest pulsed- energy capability. Keywords: Avalanche; Breakdown; Diode; Silicon Carbide Introduction

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

USGS Publications Warehouse

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 created dispersive stress normal to the movement of material. The dispersive stress preserved the dilation of the material and allowed it to flow.

Stochastic Oscillation in Self-Organized Critical States of Small Systems: Sensitive Resting State in Neural Systems

NASA Astrophysics Data System (ADS)

Wang, Sheng-Jun; Ouyang, Guang; Guang, Jing; Zhang, Mingsha; Wong, K. Y. Michael; Zhou, Changsong

2016-01-01

Self-organized critical states (SOCs) and stochastic oscillations (SOs) are simultaneously observed in neural systems, which appears to be theoretically contradictory since SOCs are characterized by scale-free avalanche sizes but oscillations indicate typical scales. Here, we show that SOs can emerge in SOCs of small size systems due to temporal correlation between large avalanches at the finite-size cutoff, resulting from the accumulation-release process in SOCs. In contrast, the critical branching process without accumulation-release dynamics cannot exhibit oscillations. The reconciliation of SOCs and SOs is demonstrated both in the sandpile model and robustly in biologically plausible neuronal networks. The oscillations can be suppressed if external inputs eliminate the prominent slow accumulation process, providing a potential explanation of the widely studied Berger effect or event-related desynchronization in neural response. The features of neural oscillations and suppression are confirmed during task processing in monkey eye-movement experiments. Our results suggest that finite-size, columnar neural circuits may play an important role in generating neural oscillations around the critical states, potentially enabling functional advantages of both SOCs and oscillations for sensitive response to transient stimuli.

Avalanche photodiode photon counting receivers for space-borne lidars

NASA Technical Reports Server (NTRS)

Sun, Xiaoli; Davidson, Frederic M.

1991-01-01

Avalanche photodiodes (APD) are studied for uses as photon counting detectors in spaceborne lidars. Non-breakdown APD photon counters, in which the APD's are biased below the breakdown point, are shown to outperform: (1) conventional APD photon counters biased above the breakdown point; (2) conventional APD photon counters biased above the breakdown point; and (3) APD's in analog mode when the received optical signal is extremely weak. Non-breakdown APD photon counters were shown experimentally to achieve an effective photon counting quantum efficiency of 5.0 percent at lambda = 820 nm with a dead time of 15 ns and a dark count rate of 7000/s which agreed with the theoretically predicted values. The interarrival times of the counts followed an exponential distribution and the counting statistics appeared to follow a Poisson distribution with no after pulsing. It is predicted that the effective photon counting quantum efficiency can be improved to 18.7 percent at lambda = 820 nm and 1.46 percent at lambda = 1060 nm with a dead time of a few nanoseconds by using more advanced commercially available electronic components.

Ge/graded-SiGe multiplication layers for low-voltage and low-noise Ge avalanche photodiodes on Si

NASA Astrophysics Data System (ADS)

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.

Skier triggering of backcountry avalanches with skilled route selection

NASA Astrophysics Data System (ADS)

Sinickas, Alexandra; Haegeli, Pascal; Jamieson, Bruce

2015-04-01

Jamieson (2009) provided numerical estimates for the baseline probabilities of triggering an avalanche by a backcountry skier making fresh tracks without skilled route selection as a function of the North American avalanche danger scale (i.e., hazard levels Low, Moderate, Considerable, High and Extreme). Using the results of an expert survey, he showed that triggering probabilities while skiing directly up, down or across a trigger zone without skilled route selection increase roughly by a factor of 10 with each step of the North American avalanche danger scale (i.e. hazard level). The objective of the present study is to examine the effect of skilled route selection on the relationship between triggering probability and hazard level. To assess the effect of skilled route selection on triggering probability by hazard level, we analysed avalanche hazard assessments as well as reports of skiing activity and triggering of avalanches from 11 Canadian helicopter and snowcat operations during two winters (2012-13 and 2013-14). These reports were submitted to the daily information exchange among Canadian avalanche safety operations, and reflect professional decision-making and route selection practices of guides leading groups of skiers. We selected all skier-controlled or accidentally triggered avalanches with a destructive size greater than size 1 according to the Canadian avalanche size classification, triggered by any member of a guided group (guide or guest). These operations forecast the avalanche hazard daily for each of three elevation bands: alpine, treeline and below treeline. In contrast to the 2009 study, an exposure was defined as a group skiing within any one of the three elevation bands, and consequently within a hazard rating, for the day (~4,300 ratings over two winters). For example, a group that skied below treeline (rated Moderate) and treeline (rated Considerable) in one day, would receive one count for exposure to Moderate hazard, and one count for exposure to Considerable hazard. While the absolute values for triggering probability cannot be compared to the 2009 study because of different definitions of exposure, our preliminary results suggest that with skilled route selection the triggering probability is similar all hazard levels, except for extreme for which there are few exposures. This means that the guiding teams of backcountry skiing operations effectively control the hazard from triggering avalanches with skilled route selection. Groups were exposed relatively evenly to Low hazard (1275 times or 29% of total exposure), Moderate hazard (1450 times or 33 %) and Considerable hazard (1215 times or 28 %). At higher levels, the exposure reduced to roughly 380 times (9 % of total exposure) to High hazard, and only 13 times (0.3 %) to Extreme hazard. We assess the sensitivity of the results to some of our key assumptions.

Ultrashort pulse laser ablation of dielectrics: Thresholds, mechanisms, role of breakdown

PubMed Central

Mirza, Inam; Bulgakova, Nadezhda M.; Tomáštík, Jan; Michálek, Václav; Haderka, Ondřej; Fekete, Ladislav; Mocek, Tomáš

2016-01-01

In this paper, we establish connections between the thresholds and mechanisms of the damage and white-light generation upon femtosecond laser irradiation of wide-bandgap transparent materials. On the example of Corning Willow glass, evolution of ablation craters, their quality, and white-light emission were studied experimentally for 130-fs, 800-nm laser pulses. The experimental results indicate co-existence of several ablation mechanisms which can be separated in time. Suppression of the phase explosion mechanism of ablation was revealed at the middle of the irradiation spots. At high laser fluences, air ionization was found to strongly influence ablation rate and quality and the main mechanisms of the influence are analysed. To gain insight into the processes triggered by laser radiation in glass, numerical simulations have been performed with accounting for the balance of laser energy absorption and its distribution/redistribution in the sample, including bremsstrahlung emission from excited free-electron plasma. The simulations have shown an insignificant role of avalanche ionization at such short durations of laser pulses while pointing to high average energy of electrons up to several dozens of eV. At multi-pulse ablation regimes, improvement of crater quality was found as compared to single/few pulses. PMID:27991543

Predicting the performance of linear optical detectors in free space laser communication links

NASA Astrophysics Data System (ADS)

Farrell, Thomas C.

2018-05-01

While the fundamental performance limit for optical communications is set by the quantum nature of light, in practical systems background light, dark current, and thermal noise of the electronics also degrade performance. In this paper, we derive a set of equations predicting the performance of PIN diodes and linear mode avalanche photo diodes (APDs) in the presence of such noise sources. Electrons generated by signal, background, and dark current shot noise are well modeled in PIN diodes as Poissonian statistical processes. In APDs, on the other hand, the amplifying effects of the device result in statistics that are distinctly non-Poissonian. Thermal noise is well modeled as Gaussian. In this paper, we appeal to the central limit theorem and treat both the variability of the signal and the sum of noise sources as Gaussian. Comparison against Monte-Carlo simulation of PIN diode performance (where we do model shot noise with draws from a Poissonian distribution) validates the legitimacy of this approximation. On-off keying, M-ary pulse position, and binary differential phase shift keying modulation are modeled. We conclude with examples showing how the equations may be used in a link budget to estimate the performance of optical links using linear receivers.

Ultrashort pulse laser ablation of dielectrics: Thresholds, mechanisms, role of breakdown

NASA Astrophysics Data System (ADS)

Mirza, Inam; Bulgakova, Nadezhda M.; Tomáštík, Jan; Michálek, Václav; Haderka, Ondřej; Fekete, Ladislav; Mocek, Tomáš

2016-12-01

In this paper, we establish connections between the thresholds and mechanisms of the damage and white-light generation upon femtosecond laser irradiation of wide-bandgap transparent materials. On the example of Corning Willow glass, evolution of ablation craters, their quality, and white-light emission were studied experimentally for 130-fs, 800-nm laser pulses. The experimental results indicate co-existence of several ablation mechanisms which can be separated in time. Suppression of the phase explosion mechanism of ablation was revealed at the middle of the irradiation spots. At high laser fluences, air ionization was found to strongly influence ablation rate and quality and the main mechanisms of the influence are analysed. To gain insight into the processes triggered by laser radiation in glass, numerical simulations have been performed with accounting for the balance of laser energy absorption and its distribution/redistribution in the sample, including bremsstrahlung emission from excited free-electron plasma. The simulations have shown an insignificant role of avalanche ionization at such short durations of laser pulses while pointing to high average energy of electrons up to several dozens of eV. At multi-pulse ablation regimes, improvement of crater quality was found as compared to single/few pulses.

Ultrashort pulse laser ablation of dielectrics: Thresholds, mechanisms, role of breakdown.

PubMed

Mirza, Inam; Bulgakova, Nadezhda M; Tomáštík, Jan; Michálek, Václav; Haderka, Ondřej; Fekete, Ladislav; Mocek, Tomáš

2016-12-19

In this paper, we establish connections between the thresholds and mechanisms of the damage and white-light generation upon femtosecond laser irradiation of wide-bandgap transparent materials. On the example of Corning Willow glass, evolution of ablation craters, their quality, and white-light emission were studied experimentally for 130-fs, 800-nm laser pulses. The experimental results indicate co-existence of several ablation mechanisms which can be separated in time. Suppression of the phase explosion mechanism of ablation was revealed at the middle of the irradiation spots. At high laser fluences, air ionization was found to strongly influence ablation rate and quality and the main mechanisms of the influence are analysed. To gain insight into the processes triggered by laser radiation in glass, numerical simulations have been performed with accounting for the balance of laser energy absorption and its distribution/redistribution in the sample, including bremsstrahlung emission from excited free-electron plasma. The simulations have shown an insignificant role of avalanche ionization at such short durations of laser pulses while pointing to high average energy of electrons up to several dozens of eV. At multi-pulse ablation regimes, improvement of crater quality was found as compared to single/few pulses.

Simulation of Silicon Photomultiplier Signals

NASA Astrophysics Data System (ADS)

Seifert, Stefan; van Dam, Herman T.; Huizenga, Jan; Vinke, Ruud; Dendooven, Peter; Lohner, Herbert; Schaart, Dennis R.

2009-12-01

In a silicon photomultiplier (SiPM), also referred to as multi-pixel photon counter (MPPC), many Geiger-mode avalanche photodiodes (GM-APDs) are connected in parallel so as to combine the photon counting capabilities of each of these so-called microcells into a proportional light sensor. The discharge of a single microcell is relatively well understood and electronic models exist to simulate this process. In this paper we introduce an extended model that is able to simulate the simultaneous discharge of multiple cells. This model is used to predict the SiPM signal in response to fast light pulses as a function of the number of fired cells, taking into account the influence of the input impedance of the SiPM preamplifier. The model predicts that the electronic signal is not proportional to the number of fired cells if the preamplifier input impedance is not zero. This effect becomes more important for SiPMs with lower parasitic capacitance (which otherwise is a favorable property). The model is validated by comparing its predictions to experimental data obtained with two different SiPMs (Hamamatsu S10362-11-25u and Hamamatsu S10362-33-25c) illuminated with ps laser pulses. The experimental results are in good agreement with the model predictions.

Damage effect and mechanism of the GaAs pseudomorphic high electron mobility transistor induced by the electromagnetic pulse

NASA Astrophysics Data System (ADS)

Xiao-Wen, Xi; Chang-Chun, Chai; Gang, Zhao; Yin-Tang, Yang; Xin-Hai, Yu; Yang, Liu

2016-04-01

The damage effect and mechanism of the electromagnetic pulse (EMP) on the GaAs pseudomorphic high electron mobility transistor (PHEMT) are investigated in this paper. By using the device simulation software, the distributions and variations of the electric field, the current density and the temperature are analyzed. The simulation results show that there are three physical effects, i.e., the forward-biased effect of the gate Schottky junction, the avalanche breakdown, and the thermal breakdown of the barrier layer, which influence the device current in the damage process. It is found that the damage position of the device changes with the amplitude of the step voltage pulse. The damage appears under the gate near the drain when the amplitude of the pulse is low, and it also occurs under the gate near the source when the amplitude is sufficiently high, which is consistent with the experimental results. Project supported by the National Basic Research Program of China (Grant No. 2014CB339900), and the Open Fund of Key Laboratory of Complex Electromagnetic Environment Science and Technology, China Academy of Engineering Physics (CAEP) (Grant No. 2015-0214.XY.K).

Seasonally active frost-dust avalanches on a north polar scarp of Mars captured by HiRISE

USGS Publications Warehouse

Russell, P.; Thomas, N.; Byrne, S.; Herkenhoff, K.; Fishbaugh, K.; Bridges, N.; Okubo, C.; Milazzo, M.; Daubar, I.; Hansen, C.; McEwen, A.

2008-01-01

North-polar temporal monitoring by the High Resolution Imaging Science Experiment (HiRISE) orbiting Mars has discovered new, dramatic examples that Mars1 CO2-dominated seasonal volatile cycle is not limited to quiet deposition and sublimation of frost. In early northern martian spring, 2008, HiRISE captured several cases of CO2 frost and dust cascading down a steep, polar scarp in discrete clouds. Analysis of morphology and process reveals these events to be similar to terrestrial powder avalanches, sluffs, and falls of loose, dry snow. Potential material sources and initiating mechanisms are discussed in the context of the Martian polar spring environment and of additional, active, aeolian processes observed on the plateau above the scarp. The scarp events are identified as a trigger for mass wasting of bright, fractured layers within the basal unit, and may indirectly influence the retreat rate of steep polar scarps in competing ways. Copyright 2008 by the American Geophysical Union.

Relation between self-organized criticality and grain aspect ratio in granular piles

NASA Astrophysics Data System (ADS)

Denisov, D. V.; Villanueva, Y. Y.; Lőrincz, K. A.; May, S.; Wijngaarden, R. J.

2012-05-01

We investigate experimentally whether self-organized criticality (SOC) occurs in granular piles composed of different grains, namely, rice, lentils, quinoa, and mung beans. These four grains were selected to have different aspect ratios, from oblong to oblate. As a function of aspect ratio, we determined the growth (β) and roughness (α) exponents, the avalanche fractal dimension (D), the avalanche size distribution exponent (τ), the critical angle (γ), and its fluctuation. At superficial inspection, three types of grains seem to have power-law-distributed avalanches with a well-defined τ. However, only rice is truly SOC if we take three criteria into account: a power-law-shaped avalanche size distribution, finite size scaling, and a universal scaling relation relating characteristic exponents. We study SOC as a spatiotemporal fractal; in particular, we study the spatial structure of criticality from local observation of the slope angle. From the fluctuation of the slope angle we conclude that greater fluctuation (and thus bigger avalanches) happen in piles consisting of grains with larger aspect ratio.

Griffiths phase and long-range correlations in a biologically motivated visual cortex model

NASA Astrophysics Data System (ADS)

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

2016-07-01

Activity in the brain propagates as waves of firing neurons, namely avalanches. These waves’ size and duration distributions have been experimentally shown to display a stable power-law profile, long-range correlations and 1/f b power spectrum in vivo and in vitro. We study an avalanching biologically motivated model of mammals visual cortex and find an extended critical-like region - a Griffiths phase - characterized by divergent susceptibility and zero order parameter. This phase lies close to the expected experimental value of the excitatory postsynaptic potential in the cortex suggesting that critical be-havior may be found in the visual system. Avalanches are not perfectly power-law distributed, but it is possible to collapse the distributions and define a cutoff avalanche size that diverges as the network size is increased inside the critical region. The avalanches present long-range correlations and 1/f b power spectrum, matching experiments. The phase transition is analytically determined by a mean-field approximation.