Sample records for avalanches

  1. Avalanches!

    NSDL National Science Digital Library

    Payne, Laura X.

    1999-01-01

    Over the last two weeks, avalanches have riddled the news from Europe through North America. The deadliest avalanche in decades roared through the Austrian Alps (Galtuer) on February 23, and another struck Valzur the following day. Avalanches in the Austrian, Swiss and French Alps were a result of the heaviest snowfall in more than 50 years. In Washington State on the Pacific coast of North America, Mount Baker was officially closed, as snow depths exceeding 300 inches buried ski lifts and triggered avalanches. The six sites listed provide background information and facts about avalanches.

  2. Avalanche!

    NSDL National Science Digital Library

    This video and companion website explain the mechanics of an avalanche and how scientists are attempting to learning more about the nature of snow pack instability to better predict these oftentimes deadly events.

  3. Avalanche

    NSDL National Science Digital Library

    Frank Weisel

    This lesson plan is part of the DiscoverySchool.com lesson plan library for grades 6-8. It focuses on avalanches and how they occur. Students conduct an experiment, then discuss how lubricants and friction play a role in causing avalanches. Included are objectives, materials, procedures, discussion questions, evaluation ideas, suggested readings, and vocabulary. There are videos available to order which complement this lesson, an audio-enhanced vocabulary list, and links to teaching tools for making custom quizzes, worksheets, puzzles and lesson plans.

  4. Avalanche Awareness

    NSDL National Science Digital Library

    Laura Cheshire

    This guide on avalanche awareness and safety discusses the anatomy of an avalanche (starting zone, track, and runout zone), avalanche factors and conditions, determining if the snowpack is safe (using snowpits and shear tests), when and where avalanches happen, the typical victims, tips for survival, an avalanche danger scale, and a list of avalanche quick checks. Avalanche conditions discussed include weather, snowfall, temperature and wind direction, snowpack, slope angle, slope orientation, terrain, and vegetation.

  5. Avalanche Town

    NSDL National Science Digital Library

    WGBH Educational Foundation

    2005-12-17

    The impact of natural disasters is made vivid in this video segment adapted from NOVA. A small town in Iceland, prepared for recurrent avalanches, is devastated when one takes a new and damaging path.

  6. Avalanche Town

    NSDL National Science Digital Library

    This video segment, adapted from a NOVA broadcast, provides an account of the 1995 avalanche that overran the fishing village of Flateyri, Iceland, killing 20 people. It also points out the unpredictability of such natural disasters and describes some of the Icelandic government's efforts to mitigate the risk. Runtime for the video is 4:17.

  7. avalanche.org

    NSDL National Science Digital Library

    This is the homepage of avalanche.org, a network designed for the professional avalanche community, that also features a wealth of information for anyone interested in avalanches and wintertime mountain weather. Materials include accident reports and statistics, a guide to avalanche observation and terminology, and links to online tutorials and training information for professionals. There are also links to regional avalanche centers, snow and avalanche forecasts, and information on rescue dogs and equipment. A library page features links to papers on avalanche control, forecasting, and rescue, and there is also an image gallery with photos of avalanches and damage, control and rescue operations.

  8. Avalanches in Foam Collapse

    E-print Network

    Anlage, Steven

    Avalanches in Foam Collapse Andrew Rhines (Reed College) Advisor Daniel Lathrop #12;Avalanches Question: What causes foam to collapse in avalanches? Two possibilities Shockwaves Stresses formed Avalanche t (s) MicDiaphragmPosition(AU) Detection threshold tb N2N2 Anechoic chamber `Steady state' foam

  9. Avalanche polynomials Robert Cori

    E-print Network

    Paris-Sud XI, Université de

    Avalanche polynomials Robert Cori , Anne Micheli and Dominique Rossin May 18, 2009 Abstract The avalanche polynomial on a graph, introduced in [5], capture the distribution of avalanches in the abelian. In [5], they show that two different trees could have the same avalanche polynomial. We show here

  10. Avalanche precursors R. Delannay,

    E-print Network

    Gruner, Daniel S.

    Avalanche precursors R. Delannay, Institut de Physique de Rennes, Université de Rennes 1, CNRS UMR at the top of the tray after some avalanches. · 4 or 5 large avalanches then observed during the slow of small "avalanches" which are recorded by a camera.2mm diameter beads #12;N. Nérone et al. Physica A 283

  11. Dust Avalanches

    NASA Technical Reports Server (NTRS)

    2003-01-01

    [figure removed for brevity, see original site]

    Crater wall dust avalanches in southern Arabia Terra.

    Note: this THEMIS visual image has not been radiometrically nor geometrically calibrated for this preliminary release. An empirical correction has been performed to remove instrumental effects. A linear shift has been applied in the cross-track and down-track direction to approximate spacecraft and planetary motion. Fully calibrated and geometrically projected images will be released through the Planetary Data System in accordance with Project policies at a later time.

    NASA's Jet Propulsion Laboratory manages the 2001 Mars Odyssey mission for NASA's Office of Space Science, Washington, D.C. The Thermal Emission Imaging System (THEMIS) was developed by Arizona State University, Tempe, in collaboration with Raytheon Santa Barbara Remote Sensing. The THEMIS investigation is led by Dr. Philip Christensen at Arizona State University. Lockheed Martin Astronautics, Denver, is the prime contractor for the Odyssey project, and developed and built the orbiter. Mission operations are conducted jointly from Lockheed Martin and from JPL, a division of the California Institute of Technology in Pasadena.

    Image information: VIS instrument. Latitude 10.3, Longitude 24.5 East (335.5 West). 19 meter/pixel resolution.

  12. 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.

  13. Snow avalanche formation

    Microsoft Academic Search

    Jürg Schweizer; J. Bruce Jamieson; Martin Schneebeli

    2003-01-01

    Snow avalanches are a major natural hazard, endangering human life and infrastructure in mountainous areas throughout the world. In many countries with seasonally snow-covered mountains, avalanche-forecasting services reliably warn the public by issuing occurrence probabilities for a certain region. However, at present, a single avalanche event cannot be predicted in time and space. Much about the release process remains unknown,

  14. Computing extreme avalanches

    Microsoft Academic Search

    Christophe Ancey; Christian Gervasoni; Maurice Meunier

    2004-01-01

    Increasing the reliability and accuracy of avalanche zoning method is of primary importance in heavily populated areas of the Alps. This usually involves computing the characteristics of large return-period avalanches. Current tools (avalanche-dynamics or statistical models) cannot achieve this objective properly. A new generation of models has emerged, which, by combining statistical and deterministic viewpoints, can reduce a number of

  15. AVALANCHES, SANDPILES AND TUTTE DECOMPOSITION

    E-print Network

    Gabrielov, Andrei

    AVALANCHES, SANDPILES AND TUTTE DECOMPOSITION Andrei GABRIELOV Department of Geology, Cornell and avalanche models of failure were introduced recently (Bak et al., 1987, and an avalanche of publications properties of an important class of these models, Abelian sandpiles (Dhar, 1990) and Abelian avalanches

  16. Avalanche semiconductor radiation detectors

    SciTech Connect

    Sadygov, Z.Y. [Joint Inst. for Nuclear Research, Dubna (Russian Federation)] [Joint Inst. for Nuclear Research, Dubna (Russian Federation); [Azerbaijan Academy of Sciences, Baku (Azerbaijan). Physics Inst.; Zheleznykh, I.M.; Kirillova, T.A. [Russian Academy of Sciences, Moscow (Russian Federation). Inst. for Nuclear Research] [Russian Academy of Sciences, Moscow (Russian Federation). Inst. for Nuclear Research; Malakhov, N.A.; Jejer, V.N. [Joint Inst. for Nuclear Research, Dubna (Russian Federation)] [Joint Inst. for Nuclear Research, Dubna (Russian Federation)

    1996-06-01

    Operation of novel avalanche semiconductor detector, produced on the basis of heterojunctions Si-SiC and Si-Si{sub x}O{sub y} is described. A uniform avalanche process with gain from 10{sup 3} to 10{sup 5} can be reached depending on the conductivity of SiC and Si{sub x}O{sub y} layers. Two types of avalanche photodetectors designed for applications in wavelength range 500--10,00 nm with quantum efficiency 60 {+-} 10% (650 nm) and 200--700 nm with quantum efficiency 60 {+-} 15% (450 nm) are presented.

  17. Avalanche modeling in forested terrain

    NASA Astrophysics Data System (ADS)

    Teich, M.; Bartelt, P. A.; Bebi, P.; Grêt-Regamey, A.

    2010-12-01

    Mountain forests are a valuable defense against snow avalanches. Currently, however, little quantitative information is available to estimate the effect of forest structure on the motion of avalanches. Avalanche flow is strongly influenced by the condition and composition of vegetation in the avalanche path. This potential decelerating effect has, however, not yet been quantified. We apply the numerical avalanche dynamics program RAMMS to simulate several well documented small avalanche events in forests. The two-dimensional model RAMMS predicts avalanche run-out distances, flow velocities and impact pressures in complex three-dimensional terrain by numerically solving a system of partial differential equations governing avalanche flow. Based on detailed data on forest conditions and avalanche characteristics such as release areas, fracture heights and length collected in forested areas, where avalanches were observed, we modify the input parameters of the RAMMS model to match the observations. We compare the model output with observed run-out distances in order to quantify the decelerating effects of different forest structures. Implementing avalanche forest interactions into numerical avalanche simulations will open new fields of application for avalanche models, e.g. for managing mountain forests and by better accounting for mountain forests as an effective biological protection measure against snow avalanches in natural hazard mapping and landscape planning.

  18. Characteristics of human-triggered avalanches

    Microsoft Academic Search

    Jürg Schweizer; Martina Lütschg

    2001-01-01

    In order to find characteristics of human-triggered dry snow slab avalanches, 10 years of avalanche occurrence data from the Swiss Alps have been analysed. Avalanche release and snowpack patterns were studied. Avalanches triggered by recreationists contribute to about 90% of the avalanche fatalities in Switzerland. Nearly exclusively dry snow slab avalanches were triggered. The slab detached of a human-triggered slab

  19. Avalanche photodiode statistics in triggered-avalanche detection mode

    Microsoft Academic Search

    H. H. Tan

    1984-01-01

    The output of a triggered avalanche mode avalanche photodiode is modeled as Poisson distributed primary avalanche events plus conditionally Poisson distributed trapped carrier induced secondary events. The moment generating function as well as the mean and variance of the diode output statistics are derived. The dispersion of the output statistics is shown to always exceed that of the Poisson distribution.

  20. Avalanche statistics of sand heaps

    SciTech Connect

    Buchholtz, V.; Poeschel, T. [Institut fuer Physik, Berlin (Germany)

    1996-09-01

    Large-scale computer simulations are presented to investigate the avalanche statistics of sandpiles using molecular dynamics. We show that different methods of measurement lead to contradictory conclusions, presumably due to avalanches not reaching the end of the experimental table.

  1. Avalanche statistics of sand heaps

    Microsoft Academic Search

    Volkhard Buchholtz; Thorsten Pöschel

    1996-01-01

    Large-scale computer simulations are presented to investigate the avalanche statistics of sandpiles using molecular dynamics. We show that different methods of measurement lead to contradictory conclusions, presumably due to avalanches not reaching the end of the experimental table.

  2. Inverse avalanches on Abelian sandpiles

    SciTech Connect

    Chau, H.F. (School of Natural Sciences, Institute for Advanced Study, Olden Lane, Princeton, New Jersey 08540 (United States) Department of Physics, University of Illinois at Urbana-Champaign, 1110 West Green Street, Urbana, Illinois 61801-3080 (United States))

    1994-11-01

    A simple and computationally efficient way of finding inverse avalanches for Abelian sandpiles, called the inverse particle addition operator, is presented. In addition, the method is shown to be optimal in the sense that it requires the minimum amount of computation among methods of the same kind. The method is also conceptually succinct because avalanche and inverse avalanche are placed in the same footing.

  3. Experiments in superconducting vortex avalanches

    Microsoft Academic Search

    E. Altshuler; T. H. Johansen; Y. Paltiel; P. Jin; K. E. Bassler; O. Ramos; G. F. Reiter; E. Zeldov; C. W. Chu

    2004-01-01

    We detect vortex avalanches in superconducting Nb when an external field is slowly ramped up. Through the combination of micro-Hall probe magnetometry and Magneto-optical imaging, we are able to visualize the magnetic field “landscape” where the “local” vortex avalanches take place. We measure the avalanche size statistics at several locations in the magnetic landscape, comprising a number of events orders

  4. Avalanche!: Slip Sliding Away

    NSDL National Science Digital Library

    This activity will help students in their understanding of the complexities of snowpack formation and using this data to make predictions about how particular slopes might behave. The kind of snow, the incline of the slope, and the terrain all play a role in when and where avalanches will occur. In this activity, students layer foodstuffs to mimic the strong and weak layers within a snowpack and then cause an avalanche to occur. This activity has a stated objective, a list of materials, procedure, activity answer, and links for more information.

  5. Dune Avalanche Scars

    NASA Technical Reports Server (NTRS)

    2004-01-01

    05 August 2004 This Mars Global Surveyor (MGS) Mars Orbiter Camera (MOC) image shows large, low albedo (dark) sand dunes in Kaiser Crater near 47.2oS, 340.4oW. The dunes are--ever so slowly--moving east to west (right to left) as sand avalanches down the steeper, slip face slopes of each. Avalanching sand in the Kaiser dune field has left deep scars on these slopes, suggesting that the sand is not loose but is instead weakly cemented. The image covers an area approximately 3 km (1.9 mi) wide and is illuminated by sunlight from the upper left.

  6. Granular Avalanches in Fluids

    E-print Network

    S. Courrech du Pont; P. Gondret; B. Perrin; M. Rabaud

    2002-09-03

    Three regimes of granular avalanches in fluids are put in light depending on the Stokes number St which prescribes the relative importance of grain inertia and fluid viscous effects, and on the grain/fluid density ratio r. In gas (r >> 1 and St > 1, e.g., the dry case), the amplitude and time duration of avalanches do not depend on any fluid effect. In liquids (r ~ 1), for decreasing St, the amplitude decreases and the time duration increases, exploring an inertial regime and a viscous regime. These regimes are described by the analysis of the elementary motion of one grain.

  7. Avalanches in wood compression

    E-print Network

    Tero Mäkinen; Amandine Miksic; Markus Ovaska; Mikko J. Alava

    2015-06-15

    Wood is a multi-scale material exhibiting a complex viscoplastic response. We study avalanches in small wood samples in compression. "Woodquakes" measured by acoustic emission are surprisingly similar to earthquakes and crackling noise in rocks and laboratory tests on brittle materials. Both the distributions of event energies and of waiting (silent) times follow power-laws. The stress- strain response exhibits clear signatures of localization of deformation to "weak spots" or softwood layers, as identified using Digital Image Correlation. Even though material structure-dependent localization takes place, the avalanche behavior remains scale-free.

  8. 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!

  9. Avalanche Photodiode Statistics in Triggered-avalanche Detection Mode

    NASA Technical Reports Server (NTRS)

    Tan, H. H.

    1984-01-01

    The output of a triggered avalanche mode avalanche photodiode is modeled as Poisson distributed primary avalanche events plus conditionally Poisson distributed trapped carrier induced secondary events. The moment generating function as well as the mean and variance of the diode output statistics are derived. The dispersion of the output statistics is shown to always exceed that of the Poisson distribution. Several examples are considered in detail.

  10. Forest Service National Avalanche Center

    NSDL National Science Digital Library

    The Forest Service's National Avalanche Center teaches users the basics of how to recognize avalanche terrain and how to travel safely in these environments. Users can view images of the four kinds of avalanches: slab, ice fall, point release, and wet. Through a slide presentation, visitors can discover how to safely spend a day in the backcountry. The website also addresses how to survive an avalanche. Afterward, users can take a virtual backcountry tour and test their avalanche skills. Researchers can discover the past and present projects of a variety of scientists to develop avalanche technology for workers including the SnowMicroPen, which is a penetrometer for collecting detailed snow profile information.

  11. Exclusion processes with avalanches.

    PubMed

    Bhat, Uttam; Krapivsky, P L

    2014-07-01

    In an exclusion process with avalanches, when a particle hops to a neighboring empty site which is adjacent to an island the particle on the other end of the island immediately hops, and if it joins another island this triggers another hop. There are no restrictions on the length of the islands and the duration of the avalanche. This process is well defined in the low-density region ? < 1/2. We describe the nature of steady states (on a ring) and determine all correlation functions. For the asymmetric version of the process, we compute the steady state current, and we describe shock and rarefaction waves which arise in the evolution of the step-function initial profile. For the symmetric version, we determine the diffusion coefficient and examine the evolution of a tagged particle. PMID:25122277

  12. Exclusion processes with avalanches

    NASA Astrophysics Data System (ADS)

    Bhat, Uttam; Krapivsky, P. L.

    2014-07-01

    In an exclusion process with avalanches, when a particle hops to a neighboring empty site which is adjacent to an island the particle on the other end of the island immediately hops, and if it joins another island this triggers another hop. There are no restrictions on the length of the islands and the duration of the avalanche. This process is well defined in the low-density region ? <1/2. We describe the nature of steady states (on a ring) and determine all correlation functions. For the asymmetric version of the process, we compute the steady state current, and we describe shock and rarefaction waves which arise in the evolution of the step-function initial profile. For the symmetric version, we determine the diffusion coefficient and examine the evolution of a tagged particle.

  13. Asymmetric Abelian Avalanches and Sandpiles Andrei Gabrielov

    E-print Network

    Gabrielov, Andrei

    Asymmetric Abelian Avalanches and Sandpiles Andrei Gabrielov Mathematical Sciences Institute consider two classes of threshold failure models, Abel- ian avalanches and sandpiles, with the redistribution matrices satisfying nat- ural conditions guaranteeing absence of infinite avalanches. We

  14. Laboratory singing sand avalanches.

    PubMed

    Dagois-Bohy, Simon; Ngo, Sandrine; du Pont, Sylvain Courrech; Douady, Stéphane

    2010-02-01

    Some desert sand dunes have the peculiar ability to emit a loud sound up to 110 dB, with a well-defined frequency: this phenomenon, known since early travelers (Darwin, Marco Polo, etc.), has been called the song of dunes. But only in late 19th century scientific observations were made, showing three important characteristics of singing dunes: first, not all dunes sing, but all the singing dunes are composed of dry and well-sorted sand; second, this sound occurs spontaneously during avalanches on a slip face; third this is not the only way to produce sound with this sand. More recent field observations have shown that during avalanches, the sound frequency does not depend on the dune size or shape, but on the grain diameter only, and scales as the square root of g/d--with g the gravity and d the diameter of the grains--explaining why all the singing dunes in the same vicinity sing at the same frequency. We have been able to reproduce these singing avalanches in laboratory on a hard plate, which made possible to study them more accurately than on the field. Signals of accelerometers at the flowing surface of the avalanche are compared to signals of microphones placed above, and it evidences a very strong vibration of the flowing layer at the same frequency as on the field, responsible for the emission of sound. Moreover, other characteristics of the booming dunes are reproduced and analyzed, such as a threshold under which no sound is produced, or beats in the sound that appears when the flow is too large. Finally, the size of the coherence zones emitting sound has been measured and discussed. PMID:19880153

  15. Hebes Chasma Dust Avalanches

    NASA Technical Reports Server (NTRS)

    2005-01-01

    [figure removed for brevity, see original site]

    Dust avalanches, also called slope streaks, occur on many Martian terrains. The deposition of airborne dust on surfaces causes a bright tone in the THEMIS VIS images. Any movement of the dust downhill, a dust avalanche, will leave behind a streak where the darker, dust-free surface is exposed.

    These dust avalanches are located in Hebes Chasma.

    Image information: VIS instrument. Latitude -1.4, Longitude 286.6 East (73.4 West). 17 meter/pixel resolution.

    Note: this THEMIS visual image has not been radiometrically nor geometrically calibrated for this preliminary release. An empirical correction has been performed to remove instrumental effects. A linear shift has been applied in the cross-track and down-track direction to approximate spacecraft and planetary motion. Fully calibrated and geometrically projected images will be released through the Planetary Data System in accordance with Project policies at a later time.

    NASA's Jet Propulsion Laboratory manages the 2001 Mars Odyssey mission for NASA's Office of Space Science, Washington, D.C. The Thermal Emission Imaging System (THEMIS) was developed by Arizona State University, Tempe, in collaboration with Raytheon Santa Barbara Remote Sensing. The THEMIS investigation is led by Dr. Philip Christensen at Arizona State University. Lockheed Martin Astronautics, Denver, is the prime contractor for the Odyssey project, and developed and built the orbiter. Mission operations are conducted jointly from Lockheed Martin and from JPL, a division of the California Institute of Technology in Pasadena.

  16. Very low noise avalanche detection

    Microsoft Academic Search

    D. C. Herbert; E. T. R. Chidley

    2001-01-01

    Recent theoretical work has shown that the excess noise of an avalanche can be quenched in high-frequency fields. In this brief, we propose a circuit to exploit this result and achieve very low noise avalanche photodiodes. The circuit also has the potential to discriminate against dark counts

  17. Triangular avalanches and uphill instabilities

    E-print Network

    Jean-Philippe Bouchaud; Michael Cates

    1998-01-14

    Recent experiments show that an avalanche initiated from a point source propagates downwards by invading a triangular shaped region. The opening angle of this triangle appears to reach 180$^o$ for a critical inclination of the pile, beyond which avalanches also propage upwards. We propose a simple interpretation of these observations, based on an extension of a phenomenological model for surface flows.

  18. Point release wet snow avalanches

    NASA Astrophysics Data System (ADS)

    Valero, C. Vera; Bühler, Y.; Bartelt, P.

    2015-04-01

    Wet snow avalanches can initiate from large fracture slabs or small point releases. Point release wet snow avalanches can reach dangerous proportions when they (1) initiate on steep and long avalanche paths and (2) entrain warm moist snow. In this paper we investigate the dynamics of point release wet snow avalanches by applying a numerical model to simulate documented case studies on high altitude slopes in the Chilean Andes (33° S). The model predicts avalanche flow temperature as well as meltwater production, given the thermal initial conditions of the release mass and snowcover entrainment. As the release mass is small, avalanche velocity and runout are primarily controlled by snowcover temperature and moisture content. We demonstrate how the interaction between terrain and entrainment processes influence the production of meltwater and therefore lubrication processes leading to longer runout. This information is useful to avalanche forecasters. An understanding of wet snow avalanche dynamics is important to study how climate change scenarios will influence land usage in mountain regions in the near future.

  19. Crater Dust Avalanches

    NASA Technical Reports Server (NTRS)

    2005-01-01

    [figure removed for brevity, see original site]

    Dust avalanches, also called slope streaks, occur on many Martian terrains. The deposition of airborne dust on surfaces causes a bright tone in the THEMIS VIS images. Any movement of the dust downhill, a dust avalanche, will leave behind a streak where the darker, dust-free surface is exposed.

    These dust avalanches are located in a small canyon within a crater rim northeast of Naktong Vallis.

    Image information: VIS instrument. Latitude 7.1, Longitude 34.7 East (325.3 West). 17 meter/pixel resolution.

    Note: this THEMIS visual image has not been radiometrically nor geometrically calibrated for this preliminary release. An empirical correction has been performed to remove instrumental effects. A linear shift has been applied in the cross-track and down-track direction to approximate spacecraft and planetary motion. Fully calibrated and geometrically projected images will be released through the Planetary Data System in accordance with Project policies at a later time.

    NASA's Jet Propulsion Laboratory manages the 2001 Mars Odyssey mission for NASA's Office of Space Science, Washington, D.C. The Thermal Emission Imaging System (THEMIS) was developed by Arizona State University, Tempe, in collaboration with Raytheon Santa Barbara Remote Sensing. The THEMIS investigation is led by Dr. Philip Christensen at Arizona State University. Lockheed Martin Astronautics, Denver, is the prime contractor for the Odyssey project, and developed and built the orbiter. Mission operations are conducted jointly from Lockheed Martin and from JPL, a division of the California Institute of Technology in Pasadena.

  20. Crater Dust Avalanches

    NASA Technical Reports Server (NTRS)

    2005-01-01

    [figure removed for brevity, see original site]

    Dust avalanches, also called slope streaks, occur on many Martian terrains. The deposition of airborne dust on surfaces causes a bright tone in the THEMIS VIS images. Any movement of the dust downhill, a dust avalanche, will leave behind a streak where the darker, dust-free surface is exposed.

    This region of dust avalanches is located in and around a crater to the west of yesterday's image.

    Image information: VIS instrument. Latitude 14.7, Longitude 32.7 East (327.3 West). 18 meter/pixel resolution.

    Note: this THEMIS visual image has not been radiometrically nor geometrically calibrated for this preliminary release. An empirical correction has been performed to remove instrumental effects. A linear shift has been applied in the cross-track and down-track direction to approximate spacecraft and planetary motion. Fully calibrated and geometrically projected images will be released through the Planetary Data System in accordance with Project policies at a later time.

    NASA's Jet Propulsion Laboratory manages the 2001 Mars Odyssey mission for NASA's Office of Space Science, Washington, D.C. The Thermal Emission Imaging System (THEMIS) was developed by Arizona State University, Tempe, in collaboration with Raytheon Santa Barbara Remote Sensing. The THEMIS investigation is led by Dr. Philip Christensen at Arizona State University. Lockheed Martin Astronautics, Denver, is the prime contractor for the Odyssey project, and developed and built the orbiter. Mission operations are conducted jointly from Lockheed Martin and from JPL, a division of the California Institute of Technology in Pasadena.

  1. Tikhonravov Crater Dust Avalanches

    NASA Technical Reports Server (NTRS)

    2005-01-01

    [figure removed for brevity, see original site]

    Dust avalanches, also called slope streaks, occur on many Martian terrains. The deposition of airborne dust on surfaces causes a bright tone in the THEMIS VIS images. Any movement of the dust downhill, a dust avalanche, will leave behind a streak where the darker, dust-free surface is exposed.

    These dust avalanches are located within a small crater inside Tikhonravov Crater.

    Image information: VIS instrument. Latitude 12.6, Longitude 37.1 East (322.9 West). 36 meter/pixel resolution.

    Note: this THEMIS visual image has not been radiometrically nor geometrically calibrated for this preliminary release. An empirical correction has been performed to remove instrumental effects. A linear shift has been applied in the cross-track and down-track direction to approximate spacecraft and planetary motion. Fully calibrated and geometrically projected images will be released through the Planetary Data System in accordance with Project policies at a later time.

    NASA's Jet Propulsion Laboratory manages the 2001 Mars Odyssey mission for NASA's Office of Space Science, Washington, D.C. The Thermal Emission Imaging System (THEMIS) was developed by Arizona State University, Tempe, in collaboration with Raytheon Santa Barbara Remote Sensing. The THEMIS investigation is led by Dr. Philip Christensen at Arizona State University. Lockheed Martin Astronautics, Denver, is the prime contractor for the Odyssey project, and developed and built the orbiter. Mission operations are conducted jointly from Lockheed Martin and from JPL, a division of the California Institute of Technology in Pasadena.

  2. Lycus Sulci Dust Avalanches

    NASA Technical Reports Server (NTRS)

    2005-01-01

    [figure removed for brevity, see original site]

    Dust avalanches, also called slope streaks, occur on many Martian terrains. The deposition of airborne dust on surfaces causes a bright tone in the THEMIS VIS images. Any movement of the dust downhill, a dust avalanche, will leave behind a streak where the darker, dust-free surface is exposed.

    These dust avalanches occur on the slopes of Lycus Sulci near Olympus Mons.

    Image information: VIS instrument. Latitude 28.1, Longitude 220.4 East (139.6 West). 18 meter/pixel resolution.

    Note: this THEMIS visual image has not been radiometrically nor geometrically calibrated for this preliminary release. An empirical correction has been performed to remove instrumental effects. A linear shift has been applied in the cross-track and down-track direction to approximate spacecraft and planetary motion. Fully calibrated and geometrically projected images will be released through the Planetary Data System in accordance with Project policies at a later time.

    NASA's Jet Propulsion Laboratory manages the 2001 Mars Odyssey mission for NASA's Office of Space Science, Washington, D.C. The Thermal Emission Imaging System (THEMIS) was developed by Arizona State University, Tempe, in collaboration with Raytheon Santa Barbara Remote Sensing. The THEMIS investigation is led by Dr. Philip Christensen at Arizona State University. Lockheed Martin Astronautics, Denver, is the prime contractor for the Odyssey project, and developed and built the orbiter. Mission operations are conducted jointly from Lockheed Martin and from JPL, a division of the California Institute of Technology in Pasadena.

  3. Retrieving avalanche basal friction law from high rate positioning of avalanches Pulfer G.1

    E-print Network

    Paris-Sud XI, Université de

    Retrieving avalanche basal friction law from high rate positioning of avalanches Pulfer G.1 : The Voellmy avalanche basal friction parameters are retrieved from high rate positioning of artificially released avalanches. Two dense snow avalanches were triggered at the Lautaret full-scale test site

  4. Abelian Avalanches and Tutte Polynomials Andrei Gabrielov

    E-print Network

    Gabrielov, Andrei

    Abelian Avalanches and Tutte Polynomials Andrei Gabrielov Department of Geology, Cornell University of deterministic lattice models of failure, Abelian avalanche (AA) models, with continuous phase variables, similar and statistical properties of avalanches in these models. We show that the distributions of avalanches in AA

  5. Field management of avalanche victims

    Microsoft Academic Search

    Hermann Brugger; Bruno Durrer; Liselotte Adler-Kastner; Markus Falk; Frank Tschirky

    2001-01-01

    The median annual mortality from snow avalanches registered in Europe and North America 1981-1998 was 146 (range 82-226); trend stable in Alpine countries (r =? 0.29; P= 0.24), increasing in North America (r= 0.68; P= 0.002). Swiss data over the same period document 1886 avalanche victims, with an overall mortality rate of 52.4% in completely-buried, versus 4.2% in partially-, or

  6. Crossover behavior in failure avalanches

    Microsoft Academic Search

    Srutarshi Pradhan; Alex Hansen; Per C. Hemmer

    2006-01-01

    Composite materials, with statistically distributed thresholds for breakdown of individual elements, are considered. During the failure process of such materials under external stress (load or voltage), avalanches consisting of simultaneous rupture of several elements occur, with a distribution D(Delta) of the magnitude Delta of such avalanches. The distribution is typically a power law D(Delta)?Delta-xi . For the systems we study

  7. 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.

  8. Investigations of Avalanche Activity in Rogers Pass, BC

    E-print Network

    Smith, Dan

    Investigations of Avalanche Activity in Rogers Pass, BC using Dendrochronology By: Deborah Bayliss, Mitch Heynen & Stefan Gronsdahl #12;Goals · Document a Chronological record of avalanche events · Determine avalanche magnitude and frequencies · Explore relationships between climate data and avalanche

  9. Evolution of locally excited avalanches in semiconductors

    E-print Network

    Z. L. Yuan; J. F. Dynes; A. W. Sharpe; A. J. Shields

    2010-05-25

    We show that semiconductor avalanche photodiodes can exhibit diminutive amplification noise during the early evolution of avalanches. The noise is so low that the number of locally excited charges that seed each avalanche can be resolved. These findings constitute an important first step towards realization of a solid-state noiseless amplifier. Moreover, we believe that the experimental setup used, \\textit{i.e.}, time-resolving locally excited avalanches, will become a useful tool for optimizing the number resolution.

  10. Colloquium: Experiments in vortex avalanches E. Altshuler*

    E-print Network

    Johansen, Tom Henning

    Colloquium: Experiments in vortex avalanches E. Altshuler* Superconductivity Laboratory and ``Henri) Avalanche dynamics are found in many phenomena, from earthquakes to the evolution of species. They can also magnetic field. Vortex avalanches associated with thermal instabilities can be an undesirable effect

  11. The design of avalanche protection dams

    E-print Network

    Boyer, Edmond

    The design of avalanche protection dams Recent practical & theoretical developments://ec.europa.eu/research/research-eu #12;The design of avalanche protection dams Recent practical and theoretical developments Edited by T 3 CEMAGREF, Research Division on Torrents, Snow and Avalanches, ETNA 4 FLOW-ING s.r.l. 5 Austrian

  12. Asulkan Valley Avalanche Track, Glacier National Park

    E-print Network

    Smith, Dan

    Asulkan Valley Avalanche Track, Glacier National Park Penelope Simpson, Jessica Paramio Maciej with the use of these trails ranges from bear encounters to triggering an avalanche. As in many mountainous regions, a high avalanche risk exists in the park during the winter due to the steep, rugged terrain

  13. Advances in Cryogenic Avalanche Detectors

    E-print Network

    A. Buzulutskov

    2015-03-29

    Cryogenic Avalanche Detectors (CRADs) are referred to as a new class of noble-gas detectors operated at cryogenic temperatures with electron avalanching performed directly in the detection medium, the latter being in gaseous, liquid or two-phase (liquid-gas) state. Electron avalanching is provided by Micro-Pattern Gas Detector (MPGD) multipliers, in particular GEMs and THGEMs, operated at cryogenic temperatures in dense noble gases. The final goal for this kind of detectors is the development of large-volume detectors of ultimate sensitivity for rare-event experiments and medical applications, such as coherent neutrino-nucleus scattering, direct dark matter search, astrophysical (solar and supernova) neutrino detection experiments and Positron Emission Tomography technique. This review is the first attempt to summarize the results on CRAD performances obtained by different groups. A brief overview of the available CRAD concepts is also given and the most remarkable CRAD physics effects are discussed.

  14. Correlations in avalanche critical points.

    PubMed

    Cerruti, Benedetta; Vives, Eduard

    2009-07-01

    Avalanche dynamics and related power-law statistics are ubiquitous in nature, arising in phenomena such as earthquakes, forest fires, and solar flares. Very interestingly, an analogous behavior is associated with many condensed-matter systems, such as ferromagnets and martensites. Bearing it in mind, we study the prototypical random-field Ising model at T=0. We find a finite correlation between waiting intervals and the previous avalanche size. This correlation is not found in other models for avalanches but it is experimentally found in earthquakes and in forest fires. Our study suggests that this effect occurs in critical points that are at the end of a first-order discontinuity separating two regimes: one with high activity from another with low activity. PMID:19658651

  15. Avalanche Collapse of Interdependent Network

    E-print Network

    G. J. Baxter; S. N. Dorogovtsev; A. V. Goltsev; J. F. F. Mendes

    2012-12-14

    We reveal the nature of the avalanche collapse of the giant viable component in multiplex networks under perturbations such as random damage. Specifically, we identify latent critical clusters associated with the avalanches of random damage. Divergence of their mean size signals the approach to the hybrid phase transition from one side, while there are no critical precursors on the other side. We find that this discontinuous transition occurs in scale-free multiplex networks whenever the mean degree of at least one of the interdependent networks does not diverge.

  16. Sound-Producing Sand Avalanches

    NSDL National Science Digital Library

    Bretz, Michael

    This site presents an analysis of the theories and experiments done so far on sound-producing (e.g., roaring, booming) sand avalanches. Several reference articles are cited, and a link to the summary of an article, "Booming Sand", in Scientific American volume 277, number 3, is provided. An on site version of another article, "Sound Producing Sand Avalanches", in Contemporary Physics, volume 38, number 5, is also presented in three different formats: PDF, HTML, and Postscript Preprint.The other main features of this site are sound recordings of booming sand, compressed squeaking sand, and croaking sand, as well as, and images and micrographs of booming dunes.

  17. A branching process model for sand avalanches

    SciTech Connect

    Garcia-Pelayo, R.; Salazar, I.; Schieve, W.C. (Univ. of Texas, Austin (United States))

    1993-07-01

    An analytically solvable model for sand avalanches of noninteracting grains of sand, based on the Chapman-Kolmogorov equations, is presented. For a single avalanche, distributions of lifetimes, sizes of overflows and avalanches, and correlation functions are calculated. Some of these are exponentials, some are power laws. Spatially homogeneous distributions of avalanches are also studied. Computer simulations of avalanches of interacting grains of sand are compared to the solutions to the Chapman-Kolmogorov equations. It is found that within the range of parameters explored in the simulation, the approximation of noninteracting grains of sand is a good one. 20 refs., 4 figs.

  18. Retrieving avalanche basal friction law parameters from high rate positioning of avalanches

    NASA Astrophysics Data System (ADS)

    Pulfer, Gaëtan; Naaim, Mohamed; Thibert, Emmanuel; Soruco, Alvaro

    2015-04-01

    The Voellmy avalanche basal friction parameters are retrieved from high rate positioning of artificially released avalanches. Avalanche fronts were tracked thanks to an accurate photogrammetric system set up at the Lautaret full-scale avalanche test-site (French Alps). Couples of images were acquired at 1 frame per second with 2 APS-C DSLR synchronized cameras set at 800 meters from the avalanche track. The avalanche height and velocity are also measured at a fixed location in the avalanche track. Rheological parameters of the avalanche flow are reconstructed by an inverse optimization method using these in situ data. The direct model is a Saint-Venant type model were basal friction is parameterized according to the Voellmy's friction law. A Sensitivity analysis of the friction parameters is conducted and theirs uncertainty are determined. Finally the results obtained from different avalanches are compared and discussed.

  19. Crossover behavior in failure avalanches

    E-print Network

    Srutarshi Pradhan; Alex Hansen; Per C. Hemmer

    2006-03-23

    Composite materials, with statistically distributed threshold for breakdown of individual elements, are considered. During the failure process of such materials under external stress (load or voltage), avalanches consisting of simultaneous rupture of several elements occur, with a distribution $D(\\Delta)$ of the magnitude $\\Delta$ of such avalanches. The distribution is typically a power law $D(\\Delta)\\propto\\Delta^{-\\xi}$. For the systems we study here, a crossover behavior is seen between two power laws, with a small exponent $\\xi$ in the vicinity of complete breakdown and a larger exponent $\\xi$ for failures away from the breakdown point. We demonstrate this analytically for bundles of many fibers where the load is uniformly distributed among the surviving fibers. In this case $\\xi=3/2$ near the breakdown point and $\\xi=5/2$ away from it. The latter is known to be the generic behavior. This crossover is a signal of imminent catastrophic failure of the material. Near the breakdown point, avalanche statistics show nontrivial finite size scaling. We observe similar crossover behavior in a network of electric fuses, and find $\\xi=2$ near the catastrophic failure and $\\xi=3$ away from it. For this fuse model power dissipation avalanches show a similar crossover near breakdown.

  20. Neuronal Avalanches in Neocortical Circuits

    Microsoft Academic Search

    John M. Beggs; Dietmar Plenz

    2003-01-01

    Networks of living neurons exhibit diverse patterns of activity, including oscillations, synchrony, and waves. Recent work in physics has shown yet another mode of activity in systems composed of many nonlinear units interacting locally. For example, avalanches, earth- quakes, and forest fires all propagate in systems organized into a critical state in which event sizes show no characteristic scale and

  1. Fracture mechanics of snow avalanches.

    PubMed

    Aström, J A; Timonen, J

    2001-07-01

    Dense snow avalanches are analyzed by modeling the snow slab as an elastic and brittle plate, attached by static friction to the underlying ground. The grade of heterogeneity in the local fracture (slip) thresholds, and the ratio of the average substrate slip threshold to the average slab fracture threshold, are the decisive parameters for avalanche dynamics. For a strong pack of snow there appears a stable precursor of local slips when the frictional contacts are weakened (equivalent to rising temperature), which eventually trigger a catastrophic crack growth that suddenly releases the entire slab. In the opposite limit of very high slip thresholds, the slab simply melts when the temperature is increased. In the intermediate regime, and for a homogeneous slab, the model display features typical of real snow avalanches. The model also suggests an explanation to why avalanches are impossible to forecast reliably based on precursor observations. This explanation may as well be applicable to other catastrophic rupture phenomena such as earthquakes. PMID:11461247

  2. Simulations of avalanche breakdown statistics: probability and timing

    Microsoft Academic Search

    Jo Shien Ng; Chee Hing Tan; John P. R. David

    2010-01-01

    Important avalanche breakdown statistics for Single Photon Avalanche Diodes (SPADs), such as avalanche breakdown probability, dark count rate, and the distribution of time taken to reach breakdown (providing mean time to breakdown and jitter), were simulated. These simulations enable unambiguous studies on effects of avalanche region width, ionization coefficient ratio and carrier dead space on the avalanche statistics, which are

  3. Collaboration Surrounding Beacon Use During Companion Avalanche Rescue

    E-print Network

    Greenberg, Saul

    Collaboration Surrounding Beacon Use During Companion Avalanche Rescue Audrey Desjardins 1 , Carman Avalanche companion rescue is a problem of distributed cognition Avalanche beacons hinder rather than of bounds - No avalanche control - No ski patrol Photo: Guillaume Paradis #12;Avalanche A rapid flow of snow

  4. Computational snow avalanche simulation in forested terrain

    NASA Astrophysics Data System (ADS)

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

    2013-10-01

    Two-dimensional avalanche simulation software operating in three-dimensional terrain is 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. We present an evaluation and improvement of a novel forest detrainment function implemented in the avalanche simulation software RAMMS for avalanche simulation in forested terrain. 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 relationship is parameterized by the detrainment coefficient K (Pa) accounting for differing forest characteristics. We varied K when simulating 40 well-documented small- to medium-scale avalanches which released in and ran through forests of the Swiss Alps. 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 closure, 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.

  5. Highly enhanced avalanche probability using sinusoidally-gated silicon avalanche photodiode

    SciTech Connect

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

    2014-01-27

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

  6. Spontaneous cortical activity in awake monkeys composed of neuronal avalanches

    E-print Network

    Chialvo, Dante R.

    Spontaneous cortical activity in awake monkeys composed of neuronal avalanches Thomas Petermanna that spontaneous activity forms characteristic clusters in space and time, called neuronal avalanches. Modeling processing, information storage, and transfer, but the relevance of avalanches for fully functional cerebral

  7. A silicon avalanche photodetector fabricated with standard CMOS technology

    E-print Network

    Choi, Woo-Young

    A silicon avalanche photodetector fabricated with standard CMOS technology with over 1 THz gain a silicon avalanche photodetector (APD) fabricated with standard complementary metal-well junction, and its current-voltage characteristics, responsivity, avalanche gain, and photodetection

  8. Snowfall and avalanche synchronization: beyond observational statistics

    NASA Astrophysics Data System (ADS)

    Crouzy, Benoît; Forclaz, Romain; Sovilla, Betty; Corripio, Javier; Perona, Paolo

    2015-04-01

    We present a methodology for quantifying the synchronization between snowfall and avalanches in relation to slope and terrain properties at the detachment zone. Focusing on a particular field situation (SLF study site, Vallée de la Sionne, Valais, Switzerland), we present a dataset consisting of 549 avalanche events and use a stochastic framework (Perona et al., Proceedings of the Royal Society A, 2012) for capturing the avalanche statistics with a minimal number of ingredients. Over the observation period (7 years), meteorological data was collected and pictures of the slope were taken every 30 minutes. For the avalanche events, slope, aspect, coordinates and altitude of the detachment zone are available from georeferenced images, and the timing of the events can be obtained from selecting the images before and after avalanche events. All model parameters can directly be computed from meteorological data (snow depth evolution), except for one parameter: the state-dependent avalanche release rate, which aggregates the influence of slope and terrain properties. From the timing distribution of the precipitation events and of the avalanche events, we calibrate the model and fix the value of the missing parameter by maximizing the likelihood of the field observations, conditional to the value of the model parameter. We carefully discuss confidence intervals for our parameter estimation. The calibrated model allows us to obtain statistical properties of the avalanches in our study site, beyond observational statistics. We compute the synchronization between snowfall and avalanches for low and high slopes, which in turn allows us to derive the return period of avalanche events (dependent and independent on the release depth). We obtain the critical event magnitude above which the return period of avalanche events with release depth h* is shorter than the return period of snowfall with equal deposited snow depth h*. Finally, using the concept of information entropy, we quantify the uncertainty in predicting the occurrence of an avalanche from the observation of snowfall.

  9. Imaging of avalanches in granular materials

    NASA Astrophysics Data System (ADS)

    Bretz, Michael; Cunningham, Jevne B.; Kurczynski, Peter L.; Nori, Franco

    1992-10-01

    Dry, noncohesive granular materials were very slowly driven to the threshold of instability where they produced avalanches. We have used digital image analysis to record avalanches that occurred on the surface of the incline. Results show large slides every 10-13 min which reset the surface from the maximum angle of stability, ?c, back to the angle of repose, ?r. We also find a power-law distribution of sizes for smaller avalanches occurring between the large sliding events. The number of these small avalanches follows a power-law dependence on the reduced angle, (?c-?)/(?c-?r), or time, which demonstrates that ?c behaves like a critical point.

  10. Time Directed Avalanches in Invasion Models

    SciTech Connect

    Maslov, S. (Department of Physics, Brookhaven National Laboratory, Upton, New York 11973 (United States) Department of Physics, SUNY at Stony Brook, Stony Brook, New York 11794 (United States))

    1995-01-23

    We define forward and backward time-directed avalanches for a broad class of self-organized critical models including invasion percolation, interface depinning, and a simple model of evolution. Although the geometrical properties of the avalanches do not change under time reversal, their stationary state statistical distribution does. The overall distribution of forward avalanches [ital P]([ital s])[similar to][ital s][sup [minus]2] is superuniversal in this class of models. The power-law exponent [pi] for the distribution of distances between subsequent active sites is derived from the properties of backward avalanches.

  11. Shocks Generate Crossover Behaviour In Lattice Avalanches

    E-print Network

    James Burridge

    2013-10-30

    A spatial avalanche model is introduced, in which avalanches increase stability in the regions where they occur. Instability is driven globally by a driving process that contains shocks. The system is typically subcritical, but the shocks occasionally lift it into a near or super critical state from which it rapidly retreats due to large avalanches. These shocks leave behind a signature -- a distinct power--law crossover in the avalanche size distribution. The model is inspired by landslide field data, but the principles may be applied to any system that experiences stabilizing failures, possesses a critical point, and is subject to an ongoing process of destabilization which includes occasional dramatic destabilizing events.

  12. Dynamic and instability of submarine avalanches

    E-print Network

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

    2005-04-21

    We perform a laboratory-scale experiment of submarine avalanches on a rough inclined plane. A sediment layer is prepared and thereafter tilted up to an angle lower than the spontaneous avalanche angle. The sediment is scrapped until an avalanche is triggered. Based on the stability diagram of the sediment layer, we investigate different structures for the avalanche front dynamics. First we see a straight front descending the slope, and then a transverse instability occurs. Eventually, a fingering instability shows up similar to rivulets appearing for a viscous fluid flowing down an incline. The mechanisms leading to this new instability and the wavelength selection are discussed.

  13. Avalanche dynamics of elastic interfaces.

    PubMed

    Le Doussal, Pierre; Wiese, Kay Jörg

    2013-08-01

    Slowly driven elastic interfaces, such as domain walls in dirty magnets, contact lines wetting a nonhomogeneous substrate, or cracks in brittle disordered material proceed via intermittent motion, called avalanches. Here we develop a field-theoretic treatment to calculate, from first principles, the space-time statistics of instantaneous velocities within an avalanche. For elastic interfaces at (or above) their (internal) upper critical dimension d?d(uc) (d(uc)=2,4 respectively for long-ranged and short-ranged elasticity) we show that the field theory for the center of mass reduces to the motion of a point particle in a random-force landscape, which is itself a random walk [Alessandro, Beatrice, Bertotti, and Montorsi (ABBM) model]. Furthermore, the full spatial dependence of the velocity correlations is described by the Brownian-force model (BFM) where each point of the interface sees an independent Brownian-force landscape. Both ABBM and BFM can be solved exactly in any dimension d (for monotonous driving) by summing tree graphs, equivalent to solving a (nonlinear) instanton equation. We focus on the limit of slow uniform driving. This tree approximation is the mean-field theory (MFT) for realistic interfaces in short-ranged disorder, up to the renormalization of two parameters at d=d(uc). We calculate a number of observables of direct experimental interest: Both for the center of mass, and for a given Fourier mode q, we obtain various correlations and probability distribution functions (PDF's) of the velocity inside an avalanche, as well as the avalanche shape and its fluctuations (second shape). Within MFT we find that velocity correlations at nonzero q are asymmetric under time reversal. Next we calculate, beyond MFT, i.e., including loop corrections, the one-time PDF of the center-of-mass velocity u[over ·] for dimension davalanche-size distribution, and how the instanton relates to the response to an infinitesimal step in the force. PMID:24032774

  14. Remote detection of artificially triggered avalanches below a fixed avalanche control installation

    NASA Astrophysics Data System (ADS)

    van Herwijnen, Alec; Simioni, Stephan; Schweizer, Juerg

    2014-05-01

    Avalanche control by explosives is widely used as a temporary preventive measure to reduce avalanche hazard. The goal is to artificially trigger smaller less destructive avalanches, by detonating charges either above or on the snow surface. Hand charges are most often used, whereby the explosives are deployed by manually hand tossing or lowering onto the snow slope. Given the inherent dangers and limitations of this type of avalanche control, fixed avalanche control installations are increasingly used. These consist of strategically placed remote controlled installations that generate an explosion above the snow pack in an avalanche starting zone. While fixed installations can be used at any time and minimize the risk to avalanche control personnel, visual confirmation is still required to verify if an avalanche released. In order to remotely detect artificially triggered avalanches, we therefore developed a low-cost seismic monitoring system. We deployed the monitoring system in a ski area above the town of Davos , in the eastern Swiss Alps, below a Gazex installation, a remote controlled installation that generates an air blast by detonating a fuel-air explosive above the snow pack. The monitoring system consists of three vertical component geophones inserted in the ground at approximately 14, 27 and 46 meters from the Gazex installation. Our results show that, despite the relatively low precision of the monitoring equipment, both the detonation and the resulting avalanches can clearly be identified in the seismic data. Specifically, detonations are characterized by short, high amplitude broadband signals, while avalanches generate much longer, low frequency signals. Furthermore, information on the size of the artificially triggered avalanches is also obtained as it directly relates to the duration of the generated seismic signal. The overall goal is to assess the effectiveness of the fixed avalanche control installation with regards to yield (i.e. number of avalanches triggered per explosion) and avalanche size.

  15. Avalanche dynamics on a rough inclined plane

    E-print Network

    Tamas Borzsonyi; Thomas C. Halsey; Robert E. Ecke

    2008-03-31

    Avalanche behavior of gravitationally-forced granular layers on a rough inclined plane are investigated experimentally for different materials and for a variety of grain shapes ranging from spherical beads to highly anisotropic particles with dendritic shape. We measure the front velocity, area and the height of many avalanches and correlate the motion with the area and height. We also measure the avalanche profiles for several example cases. As the shape irregularity of the grains is increased, there is a dramatic qualitative change in avalanche properties. For rough non-spherical grains, avalanches are faster, bigger and overturning in the sense that individual particles have down-slope speeds $u_p$ that exceed the front speed $u_f$ as compared with avalanches of spherical glass beads that are quantitatively slower, smaller and where particles always travel slower than the front speed. There is a linear increase of three quantities i) dimensionless avalanche height ii) ratio of particle to front speed and iii) the growth rate of avalanche speed with increasing avalanche size with increasing $\\tan\\theta_r$ where $\\theta_r$ is the bulk angle of repose, or with increasing $\\beta_P$, the slope of the depth averaged flow rule, where both $\\theta_r$ and $\\beta_P$ reflect the grain shape irregularity. These relations provide a tool for predicting important dynamical properties of avalanches as a function of grain shape irregularity. A relatively simple depth-averaged theoretical description captures some important elements of the avalanche motion, notably the existence of two regimes of this motion.

  16. On the temporal organization of neuronal avalanches.

    PubMed

    Lombardi, Fabrizio; Herrmann, Hans J; Plenz, Dietmar; De Arcangelis, Lucilla

    2014-01-01

    Spontaneous activity of cortex in vitro and in vivo has been shown to organize as neuronal avalanches. Avalanches are cascades of neuronal activity that exhibit a power law in their size and duration distribution, typical features of balanced systems in a critical state. Recently it has been shown that the distribution of quiet times between consecutive avalanches in rat cortex slice cultures displays a non-monotonic behavior with a power law decay at short time scales. This behavior has been attributed to the slow alternation between up and down-states. Here we further characterize the avalanche process and investigate how the functional behavior of the quiet time distribution depends on the fine structure of avalanche sequences. By systematically removing smaller avalanches from the experimental time series we show that size and quiet times are correlated and highlight that avalanche occurrence exhibits the characteristic periodicity of ? and ?/? oscillations, which jointly emerge in most of the analyzed samples. Furthermore, our analysis indicates that smaller avalanches tend to be associated with faster ?/? oscillations, whereas larger ones are associated with slower ? and 1-2 Hz oscillations. In particular, large avalanches corresponding to ? cycles trigger cascades of smaller ones, which occur at ?/? frequency. This temporal structure follows closely the one of nested ? - ?/? oscillations. Finally we demonstrate that, because of the multiple time scales characterizing avalanche dynamics, the distributions of quiet times between avalanches larger than a certain size do not collapse onto a unique function when rescaled by the average occurrence rate. However, when considered separately in the up-state and in the down-state, these distributions are solely controlled by the respective average rate and two different unique function can be identified. PMID:25389393

  17. On the temporal organization of neuronal avalanches

    PubMed Central

    Lombardi, Fabrizio; Herrmann, Hans J.; Plenz, Dietmar; De Arcangelis, Lucilla

    2014-01-01

    Spontaneous activity of cortex in vitro and in vivo has been shown to organize as neuronal avalanches. Avalanches are cascades of neuronal activity that exhibit a power law in their size and duration distribution, typical features of balanced systems in a critical state. Recently it has been shown that the distribution of quiet times between consecutive avalanches in rat cortex slice cultures displays a non-monotonic behavior with a power law decay at short time scales. This behavior has been attributed to the slow alternation between up and down-states. Here we further characterize the avalanche process and investigate how the functional behavior of the quiet time distribution depends on the fine structure of avalanche sequences. By systematically removing smaller avalanches from the experimental time series we show that size and quiet times are correlated and highlight that avalanche occurrence exhibits the characteristic periodicity of ? and ?/? oscillations, which jointly emerge in most of the analyzed samples. Furthermore, our analysis indicates that smaller avalanches tend to be associated with faster ?/? oscillations, whereas larger ones are associated with slower ? and 1–2 Hz oscillations. In particular, large avalanches corresponding to ? cycles trigger cascades of smaller ones, which occur at ?/? frequency. This temporal structure follows closely the one of nested ? ? ?/? oscillations. Finally we demonstrate that, because of the multiple time scales characterizing avalanche dynamics, the distributions of quiet times between avalanches larger than a certain size do not collapse onto a unique function when rescaled by the average occurrence rate. However, when considered separately in the up-state and in the down-state, these distributions are solely controlled by the respective average rate and two different unique function can be identified. PMID:25389393

  18. Review of dry snow slab avalanche release

    Microsoft Academic Search

    Jürg Schweizer

    1999-01-01

    Dry snow slab avalanche release starts with failure in the weak layer underlying the slab. The stress in the weak layer has to locally exceed the strength that strongly depends on the strain rate. Models for dry snow slab avalanche release are reviewed, with emphasis on the role of deficit zones. Most models assume a priori existing deficit or superweak

  19. Avalanche!--Teachable Moments in Outdoor Education

    ERIC Educational Resources Information Center

    Galloway, Shayne

    2005-01-01

    Rarely do outdoor educators get the opportunity to safely incorporate an avalanche while the topic of the day is actually avalanche awareness and forecasting. Many similar possibilities exist in the expeditionary context, but even brief excursions may result in incredible learning experiences. These "teachable moments" occur regularly in the…

  20. SPACE-CHARGE SLOWINGDOWN OF ELECTRON AVALANCHES

    Microsoft Academic Search

    Schmidt-Tiedemann

    1959-01-01

    The electric field generated by the positive and negative space charge ; of single electron avalanche moving in a homogeneous electric field is calculated. ; Treating the interaction of the avalanche with its own space charge field as a ; first order perturbation, a growth formula is obtained which differs markedly ; from the common Townsend formula. The theoretical results

  1. A fiber-optically triggered avalanche transistor

    Microsoft Academic Search

    R. J. Baker; G. T. Perryman; P. W. Watts

    1991-01-01

    A silicon bipolar transistor operating in the avalanche region was optically triggered into secondary breakdown. This transistor has been given the name fiber-optically triggered avalanche transistor (FOTAT). The FOTAT acts as an optical power discriminator. That is, secondary breakdown occurs when the triggering optical power exceeds the triggering threshold of the FOTAT. This secondary breakdown is seen as a negative

  2. Forest damage and snow avalanche flow regime

    NASA Astrophysics Data System (ADS)

    Feistl, T.; Bebi, P.; Christen, M.; Margreth, S.; Diefenbach, L.; Bartelt, P.

    2015-06-01

    Snow avalanches break, uproot and overturn trees causing damage to forests. The extent of forest damage provides useful information on avalanche frequency and intensity. However, impact forces depend on avalanche flow regime. In this paper, we define avalanche loading cases representing four different avalanche flow regimes: powder, intermittent, dry and wet. Using a numerical model that simulates both powder and wet snow avalanches, we study documented events with forest damage. First we show that in the powder regime, although the applied impact pressures can be small, large bending moments in the tree stem can be produced due to the torque action of the blast. The impact area of the blast extends over the entire tree crown. We find that, powder clouds with velocities over 20 m s-1 can break tree stems. Second we demonstrate that intermittent granular loadings are equivalent to low-density uniform dry snow loadings under the assumption of homogeneous particle distributions. The intermittent regime seldom controls tree breakage. Third we calculate quasi-static pressures of wet snow avalanches and show that they can be much higher than pressures calculated using dynamic pressure formulas. Wet snow pressure depends both on avalanche volume and terrain features upstream of the tree.

  3. Driving Pockels cells using avalanche transistor pulsers

    Microsoft Academic Search

    E. S. Fulkerson; D. C. Norman; R. Booth

    1997-01-01

    The purpose of this paper is to describe the current state of avalanche transistor-based Pockels cell driver development at LLNL and to provide the reader with a set of useful design guidelines. A general description of the units is followed by a short section on the circuit design of avalanche transistor pulsers. Techniques for delivering either ¼ or ½ wave

  4. Avalanche prediction in Self-organized systems

    E-print Network

    O. Ramos; E. Altshuler; K. J. Maloy

    2008-08-05

    It is a common belief that power-law distributed avalanches are inherently unpredictable. This idea affects phenomena as diverse as evolution, earthquakes, superconducting vortices, stock markets, etc; from atomic to social scales. It mainly comes from the concept of ``Self-organized criticality" (SOC), where criticality is interpreted in the way that at any moment, any small avalanche can eventually cascade into a large event. Nevertheless, this work demonstrates experimentally the possibility of avalanche prediction in the classical paradigm of SOC: a sandpile. By knowing the position of every grain in a two-dimensional pile, avalanches of moving grains follow a distinct power-law distribution. Large avalanches, although uncorrelated, are preceded by continuous, detectable variations in the internal structure of the pile that are monitored in order to achieve prediction.

  5. Avalanche in Adhesion at Metal Interfaces

    NASA Technical Reports Server (NTRS)

    Banerjea, Amitava; Good, Brian S.

    1994-01-01

    Simulations have shown that as two metal surfaces approach each other, the surface layers can avalanche together when the rigid interfacial spacing falls below a critical distance. This is accompanied by a discontinuous decrease in the adhesive energy. Here we present an examination of this phenomenon for the body centered cubic (BCC) metals Fe and W using the Equivalent Crystal Theory. In order to identify the circumstances under which avalanche might be inhibited, the effect of loss of registry between the two surfaces is investigated in detail. The avalanche is inhibited when the two surfaces are sufficiently far out of registry and when only a few layers near the surface are allowed to relax. As the relaxing slabs get thicker a sharp avalanche reappears. However, as the loss of registry increases the energy released in the avalanche decreases.

  6. Statistical Properties of Avalanches in Networks

    E-print Network

    Larremore, Daniel B; Ott, Edward; Restrepo, Juan G

    2012-01-01

    We characterize the distributions of size and duration of avalanches propagating in complex networks. By an avalanche we mean the sequence of events initiated by the externally stimulated `excitation' of a network node, which may, with some probability, then stimulate subsequent firings of the nodes to which it is connected, resulting in a cascade of firings. This type of process is relevant to a wide variety of situations, including neuroscience, cascading failures on electrical power grids, and epidemology. We find that the statistics of avalanches can be characterized in terms of the largest eigenvalue and corresponding eigenvector of an appropriate adjacency matrix which encodes the structure of the network. By using mean-field analyses, previous studies of avalanches in networks have not considered the effect of network structure on the distribution of size and duration of avalanches. Our results apply to individual networks (rather than network ensembles) and provide expressions for the distributions of...

  7. Huge compact flux avalanches in superconducting Nb thin films

    E-print Network

    Wijngaarden, Rinke J.

    Huge compact flux avalanches in superconducting Nb thin films M.S. Welling *, R.J. Westerwaal, W avalanches (HCAs for brevity), very much like some snow-avalanches and unlike the rough dendritic flux of thermo-magnetic avalanches as proposed by Aranson et al. [Phys. Rev. Lett. 87 (2001) 067003

  8. Systems/Circuits Neuronal Avalanches in the Resting MEG of

    E-print Network

    Henson, Rik

    Systems/Circuits Neuronal Avalanches in the Resting MEG of the Human Brain Oren Shriki,1 Jeff of activity across many spatial scales, termed neuronal avalanches. In experiment and theory, avalanche.Itwasabsentinphase-shuffledcontrolswiththesamepowerspectrumoremptyscannerdata.Ourresultsdemonstratethat normal cortical activity in healthy human subjects at rest organizes as neuronal avalanches and is well

  9. Some recent advances in snow and avalanche science 1. Introduction

    E-print Network

    Marshall, Hans-Peter

    , a statistical analysis of avalanches in the high Arctic, and forecasting of ice avalanches. 2. Snow coverEditorial Some recent advances in snow and avalanche science 1. Introduction The 2010 International meeting of snow avalanche practitioners and scientists was the largest gathering to date, with over 920

  10. Calibration and hypothesis testing for a model of avalanche behaviour

    E-print Network

    . The runout of extreme avalanches is mainly a function of topography = statistical approach basedCalibration and hypothesis testing for a model of avalanche behaviour Jonathan Rougier1 joint work and Avalanche Research, Davos) IHRR, Durham, 31 January 2011 #12;Avalanches: A Statistician's guide (on two

  11. Improving the Strict Avalanche Characteristics of Cryptographic Functions

    E-print Network

    Seberry, Jennifer

    Improving the Strict Avalanche Characteristics of Cryptographic Functions Jennifer Seberry Xian not satisfy the strict avalanche criterion (SAC) into ones that satisfy the criterion. Such a method has in digital systems, strict avalanche criterion (SAC), substitu- tion boxes (S-boxes). 1 The Strict Avalanche

  12. Avalanches: A novice guide Avalanches are very complex phenomena and are certainly one of the major natural hazards

    E-print Network

    Moore, John

    Avalanches: A novice guide J.C. Moore Avalanches are very complex phenomena and are certainly one of the major natural hazards in mountain areas. Thousands of avalanches happen every year without causing any casualties or damage, however in the European Alps about 150 people are killed every year by snow avalanches

  13. Solar Warming Submitted to Avalanche.ca Journal Feb. 2008 Can solar warming contribute to dry slab avalanches?

    E-print Network

    Jamieson, Bruce

    Solar Warming Submitted to Avalanche.ca Journal Feb. 2008 Can solar warming contribute to dry slab avalanches? Thomas Exner1 (texner@ucalgary.ca) and Bruce Jamieson1,2 ASARC ­ Applied Snow and Avalanche temperatures are close to 0°C and the likelihood of wet avalanches increases rapidly as soon as the sun softens

  14. Preliminary Study on Rock Avalanche in Taiwan

    NASA Astrophysics Data System (ADS)

    Shen, Y.; Wen, Y.; Hsieh, M.

    2012-12-01

    Rock avalanche is a kind of rapid (average >100 km/h) granule flow caused by crushing and pulverization of rock materials during catastrophic rock slide. Literature researches show that rock avalanches typically occur on steep, high-relief slopes underlain by hard rocks, and have volumes >10,000,000 m3. Rock avalanches also are characterized by long runout distances, which are 5 to 10 times the total fall heights. Some cases can run up the opposing valley wall. Rock avalanches generally occurred in active mountains (e.g., New Zealand) and were triggered by earthquakes or rainfall (snowmelt), but with exceptions. There were few rock avalanches in historical time in Taiwan. This could reflect: (1) intrinsic instability of hillslopes due to weak rock, frequent earthquakes/heavy rains, which resulted in landslides of high frequency/low magnitude; (2) limited runout space along deeply incised river-valley systems, which increased the likelihood of rock-slope failures to transform to debris flows. However, there are ancient rock-avalanche records, found at Shou-shan coast (SW Taiwan) and Shin-she, Chang-pin, Tu-lan along Hua-tung coast (E Taiwan), which is likely to have undergone coseismic uplift. These places, with steep slopes, underlain by hard rock, and free for materials to run, are most prone to rock avalanches in the future.

  15. Characterization of debris avalanche deposits in Japan

    NASA Astrophysics Data System (ADS)

    Ui, Tadahide; Yamamoto, Hiroshi; Suzuki-Kamata, Keiko

    1986-09-01

    Seventy-one debris avalanche deposits are identified from 52 Japanese Quaternary volcanoes. The structures of these volcanoes are mostly stratovolcanoes and lava domes. No avalanche deposit is found in calderas, pyroclastic cones or maar volcanoes. Debris avalanche deposits are found in 18% of all Quaternary volcanoes or 25% of Quaternary stratovolcanoes and lava domes. The ratio rises to 49% when considering only active stratovolcanoes and lava domes. At least five debris avalanche deposits have formed since 9th century. The maximum height difference of sliding ( H) for each debris avalanche ranges from 200 to 2400 meters and the maximum runout distance of sliding ( L) ranges from 1.6 to 32 km. The ratio H/ L ranges from 0.2 to 0.06, and becomes smaller in larger debris avalanches. They are more mobile than landslides in non-volcanic areas. Volume is within a range of 0.03 and 9 km 3. There is no relation between the direction of sliding and the regional horizontal compressional stress axis at the site of a volcano. Two-dimensional computer simulations of avalanches using a simplified physical model are made. The maximum velocity is mainly controlled by the length of steep slope.

  16. Continuum description of avalanches in granular media.

    SciTech Connect

    Aranson, I. S.; Tsimring, L. S.

    2000-12-05

    A continuum theory of partially fluidized granular flows is proposed. The theory is based on a combination of the mass and momentum conservation equations with the order parameter equation which describes the transition between flowing and static components of the granular system. We apply this model to the dynamics of avalanches in chutes. The theory provides a quantitative description of recent observations of granular flows on rough inclined planes (Daerr and Douady 1999): layer bistability, and the transition from triangular avalanches propagating downhill at small inclination angles to balloon-shaped avalanches also propagating uphill for larger angles.

  17. Initiation of immersed granular avalanches.

    PubMed

    Mutabaruka, Patrick; Delenne, Jean-Yves; Soga, Kenichi; Radjai, Farhang

    2014-05-01

    By means of coupled molecular dynamics-computational fluid dynamics simulations, we analyze the initiation of avalanches in a granular bed of spherical particles immersed in a viscous fluid and inclined above its angle of repose. In quantitative agreement with experiments, we find that the bed is unstable for a packing fraction below 0.59 but is stabilized above this packing fraction by negative excess pore pressure induced by the effect of dilatancy. From detailed numerical data, we explore the time evolution of shear strain, packing fraction, excess pore pressures, and granular microstructure in this creeplike pressure redistribution regime, and we show that they scale excellently with a characteristic time extracted from a model based on the balance of granular stresses in the presence of a negative excess pressure and its interplay with dilatancy. The cumulative shear strain at failure is found to be ? 0.2, in close agreement with the experiments, irrespective of the initial packing fraction and inclination angle. Remarkably, the avalanche is triggered when dilatancy vanishes instantly as a result of fluctuations while the average dilatancy is still positive (expanding bed) with a packing fraction that declines with the initial packing fraction. Another nontrivial feature of this creeplike regime is that, in contrast to dry granular materials, the internal friction angle of the bed at failure is independent of dilatancy but depends on the inclination angle, leading therefore to a nonlinear dependence of the excess pore pressure on the inclination angle. We show that this behavior may be described in terms of the contact network anisotropy, which increases with a nearly constant connectivity and levels off at a value (critical state) that increases with the inclination angle. These features suggest that the behavior of immersed granular materials is controlled not only directly by hydrodynamic forces acting on the particles but also by the influence of the fluid on the granular microstructure. PMID:25353783

  18. Shocks generate crossover behavior in lattice avalanches.

    PubMed

    Burridge, James

    2013-11-22

    A spatial avalanche model is introduced, in which avalanches increase stability in the regions where they occur. Instability is driven globally by a driving process that contains shocks. The system is typically subcritical, but the shocks occasionally lift it into a near- or supercritical state from which it rapidly retreats due to large avalanches. These shocks leave behind a signature-a distinct power-law crossover in the avalanche size distribution. The model is inspired by landslide field data, but the principles may be applied to any system that experiences stabilizing failures, possesses a critical point, and is subject to an ongoing process of destabilization that includes occasional dramatic destabilizing events. PMID:24313528

  19. Gravity and density dependences of sand avalanches

    NASA Astrophysics Data System (ADS)

    Evesque, P.; Fargeix, D.; Habib, P.; Luong, M. P.; Porion, P.

    1992-07-01

    We demonstrate using centrifuge experiment (10 1000 m/s^2) on sand avalanches that: i) grain cohesion is negligible, ii) the avalanche size and the maximum angle of repose depend on the initial pile-density, iii) an internal friction angle may be defined and corresponds to that measured with triaxial cell as assumed in soil mechanics. These data are coherent with a dilatancy effect which depends on density. Nous démontrons en utilisant les résultats d'expériences faites en centrifugeuse (LCPC Nantes) (10 1000 m/s^2) sur les avalanches de sable que la cohésion entre grain est négligeable, que la taile des avalanches et l'angle maximal de repos dépendent de la densité initial du tas, et qu'un angle de frottement interne peut être défini, dont la correspond à celle mesurée par un essai triaxial de mécanique des sols. Ces données sont cohérentes avec un effet de dilatance qui dépend de la densité.

  20. Laboratory study of avalanches in magnetized plasmas.

    PubMed

    Van Compernolle, B; Morales, G J; Maggs, J E; Sydora, R D

    2015-03-01

    It is demonstrated that a novel heating configuration applied to a large and cold magnetized plasma allows the study of avalanche phenomena under controlled conditions. Intermittent collapses of the plasma pressure profile, associated with unstable drift-Alfvén waves, exhibit a two-slope power-law spectrum with exponents near -1 at lower frequencies and in the range of -2 to -4 at higher frequencies. A detailed mapping of the spatiotemporal evolution of a single avalanche event is presented. PMID:25871044

  1. Avalanche injection and second breakdown in transistors

    Microsoft Academic Search

    P. L. Hower; V. G. Krishna Reddi

    1970-01-01

    A rapid type of second breakdown observed in silicon n+-p-n-n+transistors is shown to be due to avalanche injection at the collector n-n+junction. Localized thermal effects, which are usually associated With second breakdown, are shown to play a minor role in the initiation of the transition to the low voltage state. A useful tool in the analysis of avalanche injection is

  2. Gravity and density dependences of sand avalanches

    Microsoft Academic Search

    P. Evesque; D. Fargeix; P. Habib; M. P. Luong; P. Porion

    1992-01-01

    We demonstrate using centrifuge experiment (10 1000 m\\/s^2) on sand avalanches that: i) grain cohesion is negligible, ii) the avalanche size and the maximum angle of repose depend on the initial pile-density, iii) an internal friction angle may be defined and corresponds to that measured with triaxial cell as assumed in soil mechanics. These data are coherent with a dilatancy

  3. Avalanche grainflow on a simulated aeolian dune

    NASA Astrophysics Data System (ADS)

    Sutton, S. L. F.; McKenna Neuman, C.; Nickling, W.

    2013-09-01

    Avalanches maintain the slipface of aeolian dunes, which alters their airflow characteristics and sediment dynamics, and results in the development of grainflow cross-bedding. We report on a series of experiments in which avalanches were observed on a 1:1 replica of a small (1.2 m brink height) transverse dune in the Dune Simulation Wind Tunnel under wind velocities of 8-11 m s-1. Changes in slipface topography were observed photographically and measured utilizing a 3-D laser scanner with 1 mm2 spatial resolution. Avalanches in noncohesive sands were observed to progress through scarp recession from the point of initiation and continue until the slope angle is reduced. Changes in local slope confirm that the steep, pre-avalanche mean slope relaxes to a uniform value equal to the angle of repose of the test sand (32°) over all involved portions of the slipface. Avalanche volumes are measured, and demonstrate that avalanche magnitude is independent of wind speed over the range of velocities observed. This independence provides the potential to significantly simplify the modeling of grainflow as a function of only the total cross brink sediment transport.

  4. Prehistoric rock avalanches in the Olympic Mountains, Washington

    USGS Publications Warehouse

    Schuster, R.L.; Logan, R.L.; Pringle, P.T.

    1992-01-01

    Rock avalanches blocked streams in the Olympic Mountains southwest of Puget Sound during the past few thousand years. Limiting radiocarbon ages indicated that three or four of six avalanches occurred from 1000 to 1300 years ago or shortly thereafter. Most of the dates were from the outer preserved rings of trees drowned behind avalanche dams. These three or four avalanches may be coeval not only with one another but also with abrupt tectonic deformation in western Washington. No rock avalanches in the Olympic Mountains are known to have resulted from storms or earthquakes during the past century. The avalanches strengthen the case that a large prehistoric earthquake occurred in the Puget Sound region.

  5. Electron avalanches in liquid argon mixtures

    SciTech Connect

    Kim, J.G.; Dardin, S.M.; Kadel, R.W.; Kadyk, J.A.; Wenzel, W.B.; Peskov, V.

    2004-03-19

    We have observed stable avalanche gain in liquid argon when mixed with small amounts of xenon in the high electric field (>7 MV/cm) near the point of a chemically etched needle in a point-plane geometry. We identify two gain mechanisms, one pressure dependent, and the other independent of the applied pressure. We conclude that the pressure dependent signals are from avalanche gain in gas bubbles at the tip of the needle, while the pressure independent pulses are from avalanche gain in liquid. We measure the decay time spectra of photons from both types of avalanches. The decay times from the pressure dependent pulses decrease (increase) with the applied pressure (high voltage), while the decay times from the pressure independent pulses are approximately independent of pressure or high voltage. For our operating conditions, the collected charge distribution from avalanches is similar for 60 keV or 122 keV photon sources. With krypton additives, instead of Xe, we measure behavior consistent with only the pressure dependent pulses. Neon and TMS were also investigated as additives, and designs for practical detectors were tested.

  6. Deterministically Driven Avalanche Models of Solar Flares

    NASA Astrophysics Data System (ADS)

    Strugarek, Antoine; Charbonneau, Paul; Joseph, Richard; Pirot, Dorian

    2014-08-01

    We develop and discuss the properties of a new class of lattice-based avalanche models of solar flares. These models are readily amenable to a relatively unambiguous physical interpretation in terms of slow twisting of a coronal loop. They share similarities with other avalanche models, such as the classical stick-slip self-organized critical model of earthquakes, in that they are driven globally by a fully deterministic energy-loading process. The model design leads to a systematic deficit of small-scale avalanches. In some portions of model space, mid-size and large avalanching behavior is scale-free, being characterized by event size distributions that have the form of power-laws with index values, which, in some parameter regimes, compare favorably to those inferred from solar EUV and X-ray flare data. For models using conservative or near-conservative redistribution rules, a population of large, quasiperiodic avalanches can also appear. Although without direct counterparts in the observational global statistics of flare energy release, this latter behavior may be relevant to recurrent flaring in individual coronal loops. This class of models could provide a basis for the prediction of large solar flares.

  7. Unambiguous reconstruction of network structure using avalanche dynamics

    NASA Astrophysics Data System (ADS)

    Leleu, Timothée; Aihara, Kazuyuki

    2015-02-01

    A robust method for inferring the structure of networks is presented based on the one-to-one correspondence between the expected composition of cascades of bursts of activity, called crackling noise or avalanches, and the weight matrix. Using a model of neuronal avalanches as a paradigmatic example, we derive this correspondence exactly by calculating the closed-form expression of the joint probability distribution of avalanche sizes obtained by counting separately the number of elements active in each subnetwork during avalanches.

  8. ENVIRONMENTAL HAZARDS OF AVALANCHES: PRELIMINARY RESEARCH IN GLACIER NATIONAL

    E-print Network

    Smith, Dan

    ENVIRONMENTAL HAZARDS OF AVALANCHES: PRELIMINARY RESEARCH IN GLACIER NATIONAL PARK Site Focus: Balu Pass, Glacier National Park, B.C. Avalanche path near Balu Pass. (Photo Courtesy of: www in avalanche areas? #12;Researchers · Ben Ferrel · Keri Laughlin · Kevin McPhedran · Mark Brown · also thanks

  9. AVALANCHE THREATS AND MITIGATION MEASURES IN CANADA Cam Campbell1,*

    E-print Network

    Jamieson, Bruce

    AVALANCHE THREATS AND MITIGATION MEASURES IN CANADA Cam Campbell1,* , Laura Bakermans2 , Bruce Jamieson2 , Chris Stethem3 1 Canadian Avalanche Centre 2 Department of Civil Engineering, University commissioned report to inventory current and predict future trends in avalanche threats and mitigation programs

  10. Dynamical equilibrium of avalanches on a rough plane Adrian Daerra)

    E-print Network

    Dynamical equilibrium of avalanches on a rough plane Adrian Daerra) Laboratoire de Physique 2001 We present experimental results on avalanches which are triggered in a metastable static layer. Next to the problem of foreseeing an avalanche or a landslide, a major unknown is the actual size

  11. Kadanoff Sand Pile Model Avalanches and Fixed Points

    E-print Network

    Liège, Université de

    Kadanoff Sand Pile Model Avalanches and Fixed Points K´evin Perrot and ´Eric R´emila ´equipe MC2 #12;Aim of this work 1 2 D-1 ... #12;Introduction Definition Representation Known results Avalanches Inductive computation Avalanche as a carry the Snowball Conjecture Statement Approach and issues #12

  12. Avalanche: A Communication and Memory Architecture for Scalable Parallel Computing

    E-print Network

    Carter, John B.

    Avalanche: A Communication and Memory Architecture for Scalable Parallel Computing John B. Carter communication performance and limit effective scalability. In the Avalanche project we are re­ designing­level context sensitive cache that is tightly coupled to the communication fabric. The primary goal of Avalanche

  13. Schmas numriques pour des avalanches viscoplastiques Paul Vigneaux

    E-print Network

    Mancini, Simona

    Schémas numériques pour des avalanches viscoplastiques Paul Vigneaux We talk about the numerical flows like a fluid. In the context of avalanches, it means that after going down a slope, the material­Moreno) to discretize the problem. To be able to accurately simulate the stopping behavior of the avalanche, new schemes

  14. CHARACTERISTICS OF OLD-DEEP-SLAB AVALANCHES David Tracz1,*

    E-print Network

    Jamieson, Bruce

    CHARACTERISTICS OF OLD-DEEP-SLAB AVALANCHES David Tracz1,* , Bruce Jamieson1,2 1 Dept. of Civil, Canada ABSTRACT: Deep and old slab avalanches (ODS) are often hard-to-forecast. The size and destructive potential of ODS avalanches can be disturbing. As a starting point for a study of hard-to- forecast

  15. Anisotropic avalanches and flux penetration in patterned superconductors

    E-print Network

    Wijngaarden, Rinke J.

    Anisotropic avalanches and flux penetration in patterned superconductors Diana G. Gheorghe a current as a rectangular lattice of square anti- dots. In addition we show how thermo-magnetic avalanches rights reserved. PACS: 74.25.Qt Keywords: Vortex dynamics; Periodic pinning; Vortex avalanches 1

  16. Granular Avalanches in Fluids Sylvain Courrech du Pont,1

    E-print Network

    Weeks, Eric R.

    Granular Avalanches in Fluids Sylvain Courrech du Pont,1 Philippe Gondret,1 Bernard Perrin,2 2003) Three regimes of granular avalanches in fluids are put in light depending on the Stokes number St of avalanches do not depend on any fluid effect. In liquids (r 1), for decreasing St, the amplitude decreases

  17. Neuronal avalanches, epileptic quakes and other transient forms of neurodynamics

    E-print Network

    Milton, John G.

    Neuronal avalanches, epileptic quakes and other transient forms of neurodynamics John G. Milton W: avalanches, epilepsy, multistability, power laws, time delays Abstract Power-law behaviors in brain activity in healthy animals, in the form of neuronal avalanches, potentially benefit the computational activities

  18. Nonlinear Dynamics and Fractal Avalanches in a Pile of Rice

    E-print Network

    Wijngaarden, Rinke J.

    Nonlinear Dynamics and Fractal Avalanches in a Pile of Rice Rinke J. Wijngaarden1 , Kinga A dominated by similar punctu- ated behaviour, which we call here generically `avalanches'. Other examples are: snow-avalanches [2], forest fires, rain fall [3], stock-market indices [4] and the extinction

  19. Avalanche dynamics of elastic interfaces LPTENS-13/02

    E-print Network

    Wiese, Kay Jörg

    Avalanche dynamics of elastic interfaces LPTENS-13/02 Pierre Le Doussal and Kay J¨org Wiese CNRS substrate, or cracks in brittle disordered material proceed via intermittent motion, called avalanches. Here- tics of instantaneous velocities within an avalanche. For elastic interfaces at (or above

  20. Avalanche spin-valve transistor K. J. Russell,a)

    E-print Network

    Russell, Kasey

    Avalanche spin-valve transistor K. J. Russell,a) Ian Appelbaum,b) Wei Yi, D. J. Monsma, F. CapassoAs/AlGaAs avalanche-multiplying collector is demonstrated with 1000% magnetocurrent variation and 35 amplification-valve transistor that utilizes an avalanche- multiplying collector, without significant decrease

  1. 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.

  2. Mountain Snowmobilers and Avalanches: An Examination of Precautionary Behaviour

    E-print Network

    Mountain Snowmobilers and Avalanches: An Examination of Precautionary Behaviour by Luke Robbins of Resource Management (Planning) Report No. 586 Title of Thesis: Mountain Snowmobilers and Avalanches avalanche fatalities and the tragic season of 2008-2009, the BC Coroner's Death Review Panel convened

  3. Avalanche Characteristics of Substitution-Permutation Encryption Networks

    E-print Network

    Heys, Howard

    Avalanche Characteristics of Substitution- Permutation Encryption Networks Howard M. Heys and Stafford E. Tavares, member IEEE Abstract -- This paper develops analytical models for the avalanche or SPNs. An SPN is considered to display good avalanche characteristics if a one bit change

  4. Avalanche crown-depth distributions Edward H. Bair,1

    E-print Network

    Dozier, Jeff

    Avalanche crown-depth distributions Edward H. Bair,1 Jeff Dozier,1 and Karl W. Birkeland2 Received] The literature disagrees about the statistical distribution of snow avalanche crown depths. Large datasets from Mammoth Mountain, California and the Westwide Avalanche Network show that the three-parameter generalized

  5. Short Communication Granta Gravel model of sandpile avalanches: towards critical

    E-print Network

    Paris-Sud XI, Université de

    2515 Short Communication Granta Gravel model of sandpile avalanches: towards critical fluctuations inspirant du modèle de "Granta Gravel", nous proposons une approche théo- rique des avalanches de billes ou plastiques et des effets de dilatance. On montre en particulier, que la taille des avalanches est controlée

  6. A simple avalanche model for astroplasma and laboratory confinement systems

    Microsoft Academic Search

    S. C. Chapman; R. O. Dendy; B. Hnat

    2001-01-01

    An avalanche or ``sandpile'' model is discussed that generalizes the original self-organized criticality avalanche model of Bak, Tang, and Wiesenfeld [Phys. Rev. Lett. 59, 381 (1987)] to include spatially extended local redistribution. A single control parameter specifies the spatial extent of local redistribution when the critical gradient is exceeded: this has profound consequences for nonlocal avalanching transport and for the

  7. A simple avalanche model for astroplasma and laboratory confinement systems

    Microsoft Academic Search

    S. C. Chapman; R. O. Dendy; B. Hnat

    2001-01-01

    An avalanche or “sandpile” model is discussed that generalizes the original self-organized criticality avalanche model of Bak, Tang, and Wiesenfeld [Phys. Rev. Lett. 59, 381 (1987)] to include spatially extended local redistribution. A single control parameter specifies the spatial extent of local redistribution when the critical gradient is exceeded: this has profound consequences for nonlocal avalanching transport and for the

  8. Simulated Avalanches in the Draining of Superfluid Helium from Nuclepore

    Microsoft Academic Search

    A. H. Wootters; R. B. Hallock

    2002-01-01

    Superfluid ^4He exhibits hysteretic behavior in the percolated nano-porous material Nuclepore during filling and draining of the pores due to capillary condensation. In this system one observes avalanches in the pore draining within a narrow range of chemical potential. We have previously demonstrated that the avalanches involve pores distributed across the entire sample, and that the avalanches are enabled by

  9. Avalanches in the Lung: A Statistical Mechanical Model

    Microsoft Academic Search

    Albert-László Barabási; Sergey V. Buldyrev; H. Eugene Stanley; Béla Suki

    1996-01-01

    We study a statistical mechanical model for the dynamics of lung inflation which incorporates recent experimental observations on the opening of individual airways by a cascade or avalanche mechanism. Using an exact mapping of the avalanche problem onto percolation on a Cayley tree, we analytically derive the exponents describing the size distribution of the first avalanches and test the analytical

  10. Advances in gas avalanche radiation detectors for biomedical applications

    E-print Network

    primary ionization statistics and #uctuations in the avalanche process, low detection e$ciency for enerAdvances in gas avalanche radiation detectors for biomedical applications A. Breskin* Department of Particle Physics, The Weizmann Institute of Science, 76100 Rehovot, Israel Abstract Gas avalanche detectors

  11. The effect of thresholding on temporal avalanche statistics

    Microsoft Academic Search

    Lasse Laurson; Xavier Illa; Mikko J. Alava

    2009-01-01

    We discuss intermittent time series consisting of discrete bursts or avalanches separated by waiting or silent times. The short time correlations can be understood to follow from the properties of individual avalanches, while longer time correlations often present in such signals reflect correlations between triggerings of different avalanches. As one possible source of the latter kinds of correlations in experimental

  12. Extreme avalanche runout: a comparison of empirical models

    Microsoft Academic Search

    D. M. McClung

    2001-01-01

    The prediction of snow avalanche runout distances and the probability of exceeding the predicted positions is the first and most important step required before making decisions about placement of facilities or control structures in snow avalanche prone terrain. There are two main prediction methods for calculating runout distances: (1) procedures linked to the selection of friction coefficients in avalanche dynamic

  13. Collaboration Surrounding Beacon Use During Companion Avalanche Rescue

    E-print Network

    Greenberg, Saul

    Collaboration Surrounding Beacon Use During Companion Avalanche Rescue Audrey Desjardins1 , Carman facing an avalanche, backcountry skiers need to work effectively both individually and as a group of avalanche rescue and the interactions with beacons while backcountry skiing. We conducted interviews

  14. Dynamic Modeling of Speed Profiles of Extreme Dry Snow Avalanches

    Microsoft Academic Search

    C. P. Borstad; D. McClung

    2006-01-01

    We present an improved method for calculating the speed of long-return-period, or extreme, dry snow avalanches. This is a response to the uncertainty surrounding the dynamics of frontal ploughing, basal erosion, and entrainment of existing snowcover by a flowing avalanche. This uncertainty is implicit when modeling an avalanche beginning from rest in the starting zone, and is often neglected entirely

  15. Scaling of connected spin avalanches in growing networks

    Microsoft Academic Search

    Joanna Tomkowicz; Krzysztof Kulakowski

    2010-01-01

    We use the damage spreading method to investigate the spectra of connected spin avalanches in the exponential networks and the scale-free networks with antiferromagnetically coupled spins. The results suggest that the avalanche spectra are characterized by the same statistics as the degree distribution in their home networks. Further, the obtained mean range Z of an avalanche, i.e., the maximal distance

  16. DYNAMIC MODELLING OF EXTREME SPEED PROFILES OF DRY FLOWING AVALANCHES

    Microsoft Academic Search

    Christopher Paul Borstad

    Abstract A brief review of dierent approaches to avalanche dynamics modelling is considered, drawing on observations and knowledge of avalanche behaviour and analogies with other physical phenomena. The numerical model used for this analysis, DAN, is described with respect to the formulation of the equations of momentum,and continuity. Avalanche path geometry is approximated as a rectangular channel with the possibility

  17. Avalanche mode of motion: implications from lunar examples.

    PubMed

    Howard, K A

    1973-06-01

    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 fluid. PMID:17806579

  18. Mathematical modeling of powder-snow avalanche flows

    E-print Network

    Mathematical modeling of powder-snow avalanche flows Denys Dutykh a, aLAMA, UMR 5127 CNRS´e de Savoie, 73376 Le Bourget-du-Lac Cedex, France Abstract Powder-snow avalanches are violent natural. In this study we present a novel model for the simulation of avalanches in the aerosol regime. The second scope

  19. Career of the Month: Avalanche Researcher

    NSDL National Science Digital Library

    Megan Sullivan

    2009-01-01

    Many of us enjoy snowboarding, snowshoeing, and other winter sports at the season's first sign of snow. But what about when a massive amount of snow crashes down the mountain, gains speed and size with every second, buries everything in its path, and researches the bottom as compact as cement? Getting caught in an avalanche is extremely dangerous--every year, dozens of people die trapped in a snowy landslide. Most of us are able to enjoy the snow safely because of avalanche researchers such as Karl Birkeland, who studies the science behind avalanches to help us avoid and survive these natural disasters. A lifelong outdoor enthusiast, snow lover (he was on skies by age 2), and innate scientist, Birkeland is in his element.

  20. Dynamic scaling for avalanches in disordered systems

    SciTech Connect

    Zheng, Guang-Ping; Li, Mo

    2001-03-01

    Dynamic scaling for fracture or breakdown process in disordered systems is investigated in a two-dimensional random field Ising model (RFIM). We find two evolving stages in the avalanche process in the RFIM. At the short-time regime, a power-law growth of the avalanche size {Delta}s is observed; and at late times, the conventional nucleation and growth process is found. At the critical point of the RFIM, the avalanche size is found to obey the dynamic scaling law {Delta}s{approx}t{sup (d-{beta}/{nu})/z}. From this dynamic scaling relation, the critical strength of the random field D{sub c} and the critical exponents, {beta}, {nu}, and z, are determined. The observed dynamics is explained by a simple nucleation theory of first-order phase transformations.

  1. Bulk Metallic Glasses Deform via Slip Avalanches

    E-print Network

    James Antonaglia; Wendelin J. Wright; Xiaojun Gu; Rachel R. Byer; Todd C. Hufnagel; Michael LeBlanc; Jonathan T. Uhl; Karin A. Dahmen

    2013-12-21

    Inelastic deformation of metallic glasses occurs via slip events with avalanche dynamics similar to those of earthquakes. For the first time in these materials, measurements have been obtained with sufficiently high temporal resolution to extract both the exponents and the scaling functions that describe the nature, statistics and dynamics of the slips according to a simple mean-field model. These slips originate from localized deformation in shear bands. The mean-field model describes the slip process as an avalanche of rearrangements of atoms in shear transformation zones (STZs). Small slips show the predicted power-law scaling and correspond to limited propagation of a shear front, while large slips are associated with uniform shear on unconstrained shear bands. The agreement between the model and data across multiple independent measures of slip statistics and dynamics provides compelling evidence for slip avalanches of STZs as the elementary mechanism of inhomogeneous deformation in metallic glasses.

  2. Advances in Cryogenic Avalanche Detectors (review)

    E-print Network

    Buzulutskov, A

    2011-01-01

    Cryogenic Avalanche Detectors (CRADs) are referred to as a new class of noble-gas detectors operated at cryogenic temperatures with electron avalanching performed directly in the detection medium, the latter being in gaseous, liquid or two-phase (liquid-gas) state. Electron avalanching is provided by Micro-Pattern Gas Detector (MPGD) multipliers, in particular GEMs and THGEMs, operated at cryogenic temperatures in dense noble gases. The final goal for this kind of detectors is the development of large-volume detectors of ultimate sensitivity for rare-event experiments and medical applications, such as coherent neutrino-nucleus scattering, direct dark matter search, astrophysical (solar and supernova) neutrino detection experiments and Positron Emission Tomography technique. This review is the first attempt to summarize the results on CRAD performances obtained by different groups. A brief overview of the available CRAD concepts is also given and the most remarkable CRAD physics effects are discussed.

  3. 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.

  4. Collisional dust avalanches in debris discs

    E-print Network

    Anna Grigorieva; Pawel Artymowicz; Philippe Thébault

    2006-09-26

    We quantitatively investigate how collisional avalanches may developin debris discs as the result of the initial break-up of a planetesimal or comet-like object, triggering a collisional chain reaction due to outward escaping small dust grains. We use a specifically developed numerical code that follows both the spatial distribution of the dust grains and the evolution of their size-frequency distribution due to collisions. We investigate how strongly avalanche propagation depends on different parameters (e.g., amount of dust released in the initial break-up, collisional properties of dust grains and their distribution in the disc). Our simulations show that avalanches evolve on timescales of ~1000 years, propagating outwards following a spiral-like pattern, and that their amplitude exponentially depends on the number density of dust grains in the system. We estimate a probability for witnessing an avalanche event as a function of disc densities, for a gas-free case around an A-type star, and find that features created by avalanche propagation can lead to observable asymmetries for dusty systems with a beta Pictoris-like dust content or higher. Characteristic observable features include: (i) a brightness asymmetry of the two sides for a disc viewed edge-on, and (ii) a one-armed open spiral or a lumpy structure in the case of face-on orientation. A possible system in which avalanche-induced structures might have been observed is the edge-on seen debris disc around HD32297, which displays a strong luminosity difference between its two sides.

  5. Bulk metallic glasses deform via slip avalanches.

    PubMed

    Antonaglia, James; Wright, Wendelin J; Gu, Xiaojun; Byer, Rachel R; Hufnagel, Todd C; LeBlanc, Michael; Uhl, Jonathan T; Dahmen, Karin A

    2014-04-18

    For the first time in metallic glasses, we extract both the exponents and scaling functions that describe the nature, statistics, and dynamics of slip events during slow deformation, according to a simple mean field model. We model the slips as avalanches of rearrangements of atoms in coupled shear transformation zones (STZs). Using high temporal resolution measurements, we find the predicted, different statistics and dynamics for small and large slips thereby excluding self-organized criticality. The agreement between model and data across numerous independent measures provides evidence for slip avalanches of STZs as the elementary mechanism of inhomogeneous deformation in metallic glasses. PMID:24785049

  6. Avalanches, Barkhausen noise, and plain old criticality

    SciTech Connect

    Perkovic, O.; Dahmen, K.; Sethna, J.P. [Laboratory of Atomic and Solid State Physics, Cornell University, Ithaca, New York 14853-2501 (United States)

    1995-12-01

    We explain Barkhausen noise in magnetic systems in terms of avalanches of domains near a plain old critical point in the hysteretic zero-temperature random-field Ising model. The avalanche size distribution has a universal scaling function, making nontrivial predictions of the shape of the distribution up to 50{percent} above the critical point, where two decades of scaling are still observed. We simulate systems with up to 1000{sup 3} domains, extract critical exponents in 2, 3, 4, and 5 dimensions, compare with our 2D and 6{minus}{epsilon} predictions, and compare to a variety of experiments. {copyright} {ital 1995 The American Physical Society.}

  7. Internal Avalanches in a Granular Medium

    E-print Network

    S. S. Manna; D. V. Khakhar

    1998-08-04

    Avalanches of grain displacements can be generated by creating local voids within the interior of a granular material at rest in a bin. Modeling such a two-dimensional granular system by a collection of mono-disperse discs, the system on repeated perturbations, shows all signatures of Self-Organized Criticality. During the propagation of avalanches the competition among grains creates arches and in the critical state a distribution of arches of different sizes is obtained. Using a cellular automata model we demonstrate that the existence of arches determines the universal behaviour of the model system.

  8. Phase avalanches in near-adiabatic evolutions

    SciTech Connect

    Vertesi, T. [Institute of Nuclear Research of the Hungarian Academy of Sciences, H-4001 Debrecen, P.O. Box 51 (Hungary); Englman, R. [Soreq NRC, Yavne 81800 (Israel)

    2006-02-15

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

  9. 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.

  10. Large mobility of dry snow avalanches: insights from1 small-scale laboratory tests on granular avalanches of2

    E-print Network

    Paris-Sud XI, Université de

    Large mobility of dry snow avalanches: insights from1 small-scale laboratory tests on granular avalanches of2 bidisperse materials3 F. Moro1 , T. Faug2 , H. Bellot2 , F. Ousset2 4 1 Universit`a degli on granular avalanches of8 bidisperse materials made of fine particles and larger ones. These experi-9 ments

  11. On The Estimation of Avalanche Encounter Probabilities (or: A New Method For The Estimation of Avalanche Encounter Probabilities)

    Microsoft Academic Search

    M. Barbolini; V. Blagovechshenskiy; M. Eglit; C. J. Keylock; F. Savi

    2002-01-01

    A crucial point in any methodology for avalanche hazard assessment is the evaluation of avalanche encounter probability, i.e. the annual probability that any given locations along a given path is reached or exceeded by an avalanche. This estimate can be obtained following two different approaches: (a) statistical analysis of historical records of runout distance (however there is rarely enough historical

  12. alpha - β model: Can we learn more from the statistical avalanche model with respect to the dynamical behavior of avalanches

    Microsoft Academic Search

    P. Gauer; K. Lied; S. Bakkehoi; K. Kronholm; L. Rammer; P. Hoeller

    2009-01-01

    Hazard and risk assessment in avalanche prone areas involves the estimation of the runout of potential avalanches. Methods for determination of the runout may be grouped into two groups: 1) based on statistical methods such as the well known alpha - β model or 2) based on numerical avalanche models such as the PCM-model or Voellmy-Salm type models (just to

  13. 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. PMID:18196793

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

    SciTech Connect

    Hunt, D. C.; Tanioka, Kenkichi; Rowlands, J. A. [Imaging Research, Sunnybrook Research Institute, Department of Medical Biophysics, University of Toronto, 2075 Bayview Avenue, Toronto, M4N 3M5 (Canada); Advanced Imaging Devices Research Division, NHK Science and Technical Research Laboratories, 1-10-11 Kinuta, Setagaya-Ku, Tokyo, 157-8510 (Japan); Imaging Research, Sunnybrook Research Institute, Department of Medical Biophysics, University of Toronto, 2075 Bayview Avenue, Toronto, M4N 3M5 (Canada)

    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, 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.

  15. Rock avalanches caused by earthquakes: Source characteristics

    USGS Publications Warehouse

    Keefer, D.K.

    1984-01-01

    Study of a worldwide sample of historical earthquakes showed that slopes most susceptible to catastrophic rock avalanches were higher than 150 meters and steeper than 25 degrees. The slopes were undercut by fluvial or glacial erosion, were composed ofintensely fractured rock, and exhibited at least one other indicator of low strength or potential instability.

  16. Vortex avalanches in a type II superconductor

    SciTech Connect

    Behnia, K.; Capan, C.; Mailly, D.; Etienne, B.

    1999-12-01

    The authors report on a study of the spatiotemporal variation of magnetic induction in a superconducting niobium sample during a slow sweep of external magnetic field. A sizable fraction of the increase in the local vortex population occurs in abrupt jumps. They compare the size distribution of these avalanches with the predictions of self-organized-criticality models for vortex dynamics.

  17. Avalanche dynamics on a rough inclined plane

    Microsoft Academic Search

    Tamás Börzsönyi; Robert Ecke

    2003-01-01

    We report experimental studies of granular dynamics on an inclined plane. For a low flow rate of the incoming particles and for a range of the inclination angle, a static thin layer of granular material builds up on the plane. This layer is metastable in the sense that the continuously arriving new particles can trigger avalanches which are stable, traveling

  18. Carrier multiplication and noise in avalanche devices

    Microsoft Academic Search

    K. M. van Vliet

    1978-01-01

    The standard theories of avalanche statistics for two carrier impact ionization by Tager, McIntyre, Personnick, and others, tacidly assume that the number of possible ionizations per primary carrier transit is very large; this assumption is not valid in modern small dimension devices. A new realistic theory is presented based on a finite number of discrete ionization processes. New expressions are

  19. Measuring acoustic emissions in an avalanche slope

    NASA Astrophysics Data System (ADS)

    Reiweger, Ingrid; Schweizer, Jürg

    2014-05-01

    Measurements of acoustic emissions are a common technique for monitoring damage and predicting imminent failure of a material. Within natural hazards it has already been used to successfully predict the break-off of a hanging glacier. To explore the applicability of the acoustic emission (AE) technique for avalanche prediction, we installed two acoustic sensors (with 30 kHz and 60 kHz resonance frequency) in an avalanche prone slope at the Mittelgrat in the Parsenn ski area above Davos, Switzerland. The slope is north-east facing, frequently wind loaded, and approximately 35° steep. The AE signals - in particular the event energy and waiting time distributions - were compared with slope stability. The latter was determined by observing avalanche activity. The results of two winter's measurements yielded that the exponent ? of the inverse cumulative distribution of event energy showed a significant drop (from a value of 3.5 to roughly 2.5) at very unstable conditions, i.e. on the three days during our measurement periods when spontaneous avalanches released on our study slope.

  20. Relief and snow avalanches in the Tatra Mts.

    NASA Astrophysics Data System (ADS)

    R?czkowska, Zofia; D?ugosz, Micha?; Rojan, El?bieta

    2015-04-01

    Snow avalanches are among the main factors influencing the high-mountain environment of the Tatra Mts. and their denudation system in the three uppermost geoecological belts. Dirty avalanches are assumed to be an important morphogenetic factor but also relief affects spatial differentiation of snow avalanche activity. The research aims to recognize the geomorphological conditions for avalanches and assessment of the morphogenetic role of avalanches in the whole Tatra Mts. For recognition of geomorphological conditions of snow avalanches activity was made map of avalanches paths, based on maps of snow avalanches occurred in the recent past, air- photos and digital terrain model. Starting zone and transition zone were specified within each path. For each type of designated zones the morphometric analysis was made, taking in account slope aspect and inclination. The map presents more than 3700 avalanche paths. The number of avalanche paths is more than double in the High Tatras than in the Western Tatras. Morphometric features and altitudinal range of avalanche paths also differ in individual parts of the Tatras what correspond with the relief differences. Length of avalanche paths reach up to 3138 m and in average is the biggest avalanche in the Bielanske Tatra. The paths are located about 200 m higher in the High Tatras than in other parts of the massif. There is no clear relationship between exposure of the slopes and the distribution of the avalanche path, while relationship with slope inclination is distinct. Over 70% of the avalanche paths occur on slopes 26-55o. Similar patterns were found in the distribution of avalanche accumulation zones. Detailed studies of morphogenetic role of avalanches are conducted in four chosen avalanche paths located both in the Western and the High Tatras. Measuring points of erosion, transport and accumulation installed there in the autumn 2012 are checked two times a year. It was found that effects of snow avalanches on the relief is characterised by temporal and spatial variability. The study are supported by the National Science Centre, project no 2011/03/B/ST10/06115

  1. CMOS Avalanche Radio-over-Fiber wchoi@yonsei.ac.kr

    E-print Network

    Choi, Woo-Young

    #12;#12;CMOS Avalanche Radio-over-Fiber , wchoi@yonsei.ac.kr CMOS Avalanche Photo-detector for Radio-over-Fiber Systems Yonsei Univ. 0.13um CMOS avalanche (avalanche photo-detector, APDF) [1-2]. RoF CMOS . CMOS GaAs responsivity . APD avalanche

  2. A field study on failure of storm snow slab avalanches Edward H. Bair a,

    E-print Network

    Dozier, Jeff

    A field study on failure of storm snow slab avalanches Edward H. Bair a, , Ron Simenhois b , Karl Alaska Avalanche Center, Juneau, AK, USA c US Forest Service National Avalanche Center, Bozeman, MT, USA 2012 Keywords: Snow Avalanche Anticrack Storm snow often avalanches before crystals metamorphose

  3. Teaching Natural Hazards: The Use of Snow Avalanches in Demonstrating and Addressing Geographic Topics and Principles.

    ERIC Educational Resources Information Center

    Butler, David R.

    1988-01-01

    Illustrates the importance of studying the snow avalanche as a natural hazard. Describes the various kinds of snow avalanches, the types of triggering mechanisms that produce them, the typical avalanche terrain, and the geomorphic and the vegetative evidence for snow avalanching. Depicts methods of human adjustment to the avalanche hazard.…

  4. Statistical runout modeling of snow avalanches using GIS in Glacier National Park, Canada

    Microsoft Academic Search

    D. Delparte; B. Jamieson; N. Waters

    2008-01-01

    Using models to estimate snow avalanche runout distance is useful for areas where there is a lack of historical avalanche observations and no obvious physical signs of avalanche activity. Along roadways, details of avalanche runout are often recorded; however, in Canada, backcountry areas typically used by recreationists may not have a recorded history of avalanche activity or runout distances. Knowledge

  5. Application of a regional approach for hazard mapping at an avalanche site in northern Italy

    Microsoft Academic Search

    D. Bocchiola; R. Rosso

    2008-01-01

    The currently adopted approach to avalanche hazard mapping in northern Italy includes avalanche dynamic modelling, coupled with statistical analysis of snow depth at avalanche start. The 30-years and 300-years return period avalanches at a given site are modelled and their run out zone and pressure are evaluated. The snow depth in the avalanche release zone is assumed to coincide with

  6. Scaling and complex avalanche dynamics in the Abelian sandpile model

    NASA Astrophysics Data System (ADS)

    Abdolvand, Amir; Montakhab, Afshin

    2010-07-01

    We study the two-dimensional Abelian Sandpile Model on a square lattice of linear size L. We introduce the notion of avalanche’s fine structure and compare the behavior of avalanches and waves of toppling. We show that according to the degree of complexity in the fine structure of avalanches, which is a direct consequence of the intricate superposition of the boundaries of successive waves, avalanches fall into two different categories. We propose scaling ansätz for these avalanche types and verify them numerically. We find that while the first type of avalanches ( ?) has a simple scaling behavior, the second complex type ( ?) is characterized by an avalanche-size dependent scaling exponent. In particular, we define an exponent ? to characterize the conditional probability distribution functions for these types of avalanches and show that ? ? = 0.42, while 0.7 ? ? ? ? 1.0 depending on the avalanche size. This distinction provides a framework within which one can understand the lack of a consistent scaling behavior in this model, and directly addresses the long-standing puzzle of finite-size scaling in the Abelian sandpile model.

  7. The Marocche rock avalanches (Trentino, Italy)

    NASA Astrophysics Data System (ADS)

    Ivy-Ochs, Susan; Martin, Silvana; Campedel, Paolo; Viganò, Alfio; Alberti, Silvio; Rigo, Manuel; Vockenhuber, Christof

    2015-04-01

    The floors of the Adige and Sarca River valleys are punctuated by numerous rock avalanche deposits of undetermined age. With a view to understanding predisposition and triggering factors, thus ultimately paleoseismicity in the region, we are studying the geomorphology and timing of the largest rock avalanches of the River Sarca-Lake Garda area (e.g., Marocche, Monte Spinale, Lago di Tovel, Lago di Molveno, San Giovanni and Torbole). Among the most extensive of these deposits, with an area of 13 km2 and a volume of about 109 m3, are the Marocche. Marocche deposits cover the lower Sarca valley north of Lake Garda for a length of more than 8 km with 200 m of debris. Both collapse and bedding parallel sliding are a consequence of dip slopes and the extreme relief on the right side of the valley of nearly 2000 m from the bedrock below the valley floor to the peaks combined with the zones of structural weakness. The rock avalanches developed within carbonate rocks of Mesozoic age, mainly limestones of the Jurassic Calcari Grigi Group. The main scarps are located on the western side of the lower Sarca Valley, along the steep faces of Mt. Brento and Mt. Casale. The presence of these scarps is strictly related to the Southern Giudicarie and the Ballino fault systems. The former is here constituted by regular NNE-directed ESE-vergent thrust faults. The latter has been reactivated as normal faults. These complicated structural relationships favored complex failure mechanisms, including rock slide and massive collapse. At the Marocche itself, based on field relationships and analysis of lidar imagery, we differentiated two large rock avalanches: the Marocca di Kas in the south which overlies and in part buries the Marocche (s.s.) in the northern sector. Previous mapping had suggested up to five rock avalanches in the area where we differentiate two. In spite of hypotheses suggesting failure of the rock avalanches onto stagnating late Pleistocene glaciers, preliminary 36Cl exposure dating results for boulders of the two deposits suggests middle and late Holocene ages. The latter are well comparable with post-Roman ages proposed by Trener in 1924 based on the presence of artifacts found at the base of the younger deposits during construction of hydroelectric tunnels early in the last century.

  8. Experiments in superconducting vortex avalanches E. Altshuler a,b,*, T.H. Johansen c,b

    E-print Network

    Zeldov, Eli

    '' vortex avalanches take place. We measure the avalanche size statistics at several locations distributions of avalanche sizes, depending on the measuring parameters. The rel- atively poor statistics measurements of vortex avalanches with unprecedent statistics at different, controlled locations

  9. Olokele rock avalanche, island of Kauai, Hawaii.

    USGS Publications Warehouse

    Jones, B.L.; Chinn, S.S.W.; Brice, J.C.

    1984-01-01

    In October 1981 a mass of rock and soil having an estimated volume of 500 000 m3 fell as a rock fall-avalanche from a steep slope 800 m high near the head of Olokele Canyon. Boulders were launched into the air from a bench on the slope for a downstream distance of about 850 m. The velocity of the avalanche was rapidly diminished by impact against the valley sides, and it became a muddy debris flow that traveled 4.6 km downstream, severely eroding the valley sides. The volume of debris deposited on the canyon bottom is estimated to be 2 500 000 m3, or about four times the volume derived from the slope. -from Authors

  10. 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.

  11. Avalanche dynamics of radio pulsar glitches

    E-print Network

    Melatos, A; Wyithe, J S B

    2007-01-01

    We test statistically the hypothesis that radio pulsar glitches result from an avalanche process, in which angular momentum is transferred erratically from the flywheel-like superfluid in the star to the slowly decelerating, solid crust via spatially connected chains of local, impulsive, threshold-activated events, so that the system fluctuates around a self-organised critical state. Analysis of the glitch population (currently 285 events from 101 pulsars) demonstrates that the size distribution in individual pulsars is consistent with being scale invariant, as expected for an avalanche process. The waiting-time distribution is consistent with being exponential in seven out of nine pulsars where it can be measured reliably, after adjusting for observational limits on the minimum waiting time, as for a constant-rate Poisson process. PSR J0537$-$6910 and PSR J0835$-$4510 are the exceptions; their waiting-time distributions show evidence of quasiperiodicity. In each object, stationarity requires that the rate $\\...

  12. Stochastic simulation of electron avalanches on supercomputers

    NASA Astrophysics Data System (ADS)

    Rogasinsky, S. V.; Marchenko, M. A.

    2014-12-01

    In the paper, we present a three-dimensional parallel Monte Carlo algorithm named ELSHOW which is developed for simulation of electron avalanches in gases. Parallel implementation of the ELSHOW was made on supercomputers with different architectures (massive parallel and hybrid ones). Using the ELSHOW, calculations of such integral characteristics as the number of particles in an avalanche, the coefficient of impact ionization, the drift velocity, and the others were made. Also, special precise computations were made to select an appropriate size of the time step using the technique of dependent statistical tests. Particularly, the algorithm consists of special methods of distribution modeling, a lexicographic implementation scheme for "branching" of trajectories, justified estimation of functionals. A comparison of the obtained results for nitrogen with previously published theoretical and experimental data was made.

  13. GEM scintillation readout with avalanche photodiodes

    NASA Astrophysics Data System (ADS)

    Conceição, A. S.; Requicha Ferreira, L. F.; Fernandes, L. M. P.; Monteiro, C. M. B.; Coelho, L. C. C.; Azevedo, C. D. R.; Veloso, J. F. C. A.; Lopes, J. A. M.; dos Santos, J. M. F.

    2007-09-01

    The use of the scintillation produced in the charge avalanches in GEM holes as signal amplification and readout is investigated for xenon. A VUV-sensitive avalanche photodiode has been used as photosensor. Detector gains of about 4 × 104 are achieved in scintillation readout mode, for GEM voltages of 490 V and for a photosensor gain of 150. Those gains are more than one order of magnitude larger than what is obtained using charge readout. In addition, the energy resolutions achieved with the scintillation readout are lower than those achieved with charge readout. The GEM scintillation yield in xenon was measured as a function of GEM voltage, presenting values that are about a half of those achieved for the charge yield, and reach about 730 photons per primary electron at GEM voltages of 490 V.

  14. Driving pockels cells using avalanche transistor pulsers

    SciTech Connect

    Fulkerson, E.S.; Norman, D.C.; Booth, R.

    1997-05-28

    The purpose of this paper is to describe the current state of avalanche transistor based Pockels cell driver development at LLNL and to provide the reader with a set of useful design guidelines. A general description of the units is followed by a short section on the circuit design of avalanche transistor pulsers. A more detailed design guide is given. Techniques for delivering either {1/4} or {1/2} wave voltages to a Pockels cell are covered. Recently these units have been modified for use at repetition rates up to 10kHz. Operating at high repetition rates represents problems for both the driver and the Pockels Cell. Design solutions for the pulser are presented as well as discussion of Pockels cell acoustic resonance.

  15. Analysis of Avalanche's Shared Memory Architecture Ravindra Kuramkote, John Carter, Alan Davis,

    E-print Network

    Carter, John B.

    Analysis of Avalanche's Shared Memory Architecture Ravindra Kuramkote, John Carter, Alan Davis write update, and (soon) write invalidate). We describe the performance implications of Avalanche; Analysis of Avalanche's Shared Memory Architecture Ravindra Kuramkote, John Carter, Alan Davis, Chen

  16. Scaling of Experimental Debris Flows and Avalanches

    NASA Astrophysics Data System (ADS)

    Iverson, R. M.; Logan, M.

    2002-12-01

    Controlled experiments play a critical role in motivating and testing mathematical models of debris flows, rock avalanches, and other rapid mass movements, but scaling poses significant issues for interpretation of experimental mass movements that are much smaller than geophysical prototypes. To illustrate these issues we describe scaling and interpretation of experiments with dry granular avalanches and water-saturated debris flows. Normalization of equations governing unsteady, gravity-driven motion of deforming, finite masses of solid-fluid mixtures shows that important scaling parameters for debris flows and avalanches include a quasi-Reynolds number, R = ? H (g L)1/2 /n?, and a number T = k (L/g)1/2/ ? C H2 that characterizes the timescale for downslope mass movement divided by the timescale for pore-pressure diffusion normal to the slope [Iverson and Denlinger, 2001, JGR, 106(B1), 537-552]. Here H is the typical thickness and L is the typical length of the moving mass, g is gravitational acceleration, ? is pore-fluid viscosity, ? is mixture bulk density, n is mixture porosity, k is mixture intrinsic permeability, and C is mixture compressibility. Miniature experiments can encounter a severe scaling problem because reduction of H decreases R but increases T, and this opposing change in R and T skews the effects of intergranular fluids on mass-movement dynamics. The problem is minimized if R >>1 and the pore-pressure diffusivity k/?C is large enough that T >> 1 (as is true in avalanches of dry rocks through air, for example), in which case the effects of pore fluid are negligible on almost any scale. However, for debris flows in which the pore fluid is muddy water, scaled-down experiments poorly simulate full-scale geophysical events, in which R >> 1 and T << 1 apply almost universally. Similar scaling problems arise if debris-flow mixtures have finite strength due to intermolecular forces, which have exaggerated effects at miniature scales.

  17. Precursors and prediction of catastrophic avalanches

    E-print Network

    Srutarshi Pradhan; Bikas K. Chakrabarti

    2006-03-23

    In this work we review the precursors of catastrophic avalanches (global failures) in several failure models, namely (a) Fiber Bundle Model (FBM), (b) Random Fuse Model (RFM), (c) Sandpile Models and (d) Fractal Overlap Model. The precursor parameters identified here essentially reflect the growing correlations within such systems as they approach their respective failure points. As we show, often they help us to predict the global failure points in advance.

  18. FORECASTING RUNOUT OF ROCK AND DEBRIS AVALANCHES

    Microsoft Academic Search

    R. M. IVERSON

    Physically based mathematical models and statistically based empirical equations each may provide useful means of forecasting\\u000a runout of rock and debris avalanches. This paper compares the foundations, strengths, and limitations of a physically based\\u000a model and a statistically based forecasting method, both of which were developed to predict runout across three-dimensional\\u000a topography. The chief advantage of the physically based model

  19. Scaling of spin avalanches in growing networks

    Microsoft Academic Search

    Joanna Tomkowiczand; Krzysztof Kulakowski

    2009-01-01

    Growing networks decorated with antiferromagnetically coupled spins are\\u000aarchetypal examples of complex systems due to the frustration and the\\u000amultivalley character of their energy landscapes. Here we use the damage\\u000aspreading method (DS) to investigate the cohesion of spin avalanches in the\\u000aexponential networks and the scale-free networks. On the contrary to the\\u000aconventional methods, the results obtained from DS

  20. Viscoelastic effects in avalanche dynamics: a key to earthquake statistics.

    PubMed

    Jagla, E A; Landes, François P; Rosso, Alberto

    2014-05-01

    In many complex systems a continuous input of energy over time can be suddenly relaxed in the form of avalanches. Conventional avalanche models disregard the possibility of internal dynamical effects in the interavalanche periods, and thus miss basic features observed in some real systems. We address this issue by studying a model with viscoelastic relaxation, showing how coherent oscillations of the stress field can emerge spontaneously. Remarkably, these oscillations generate avalanche patterns that are similar to those observed in seismic phenomena. PMID:24836251

  1. Avalanche in adhesion. [interfacial separation between two Ni crystals

    NASA Technical Reports Server (NTRS)

    Smith, John R.; Bozzolo, Guillermo; Banerjea, Amitava; Ferrante, John

    1989-01-01

    Consider surfaces being brought into contact. It is proposed that atomic layers can collapse or avalanche together when the interfacial spacing falls below a critical distance. This causes a discontinuous drop in the adhesive binding energy. Avalanche can occur regardless of the stiffness of external supports. A simple understanding of the origin of this phenomenon is provided. A numerical calculation has been carried out for adhesion in Ni. A new wear mechanism due to avalanche is suggested.

  2. Avalanche statistics of driven granular slides in a miniature mound

    Microsoft Academic Search

    D. E. Juanico; A. Longjas; R. Batac; C. Monterola

    2008-01-01

    We examine avalanche statistics of rain- and vibration-driven granular slides in miniature sand mounds. A crossover from power-law to non power-law avalanche-size statistics is demonstrated as a generic driving rate nu is increased. For slowly-driven mounds, the tail of the avalanche-size distribution is a power-law with exponent -1.97 +\\/- 0.31, reasonably close to a value previously reported for landslide volumes.

  3. Viscoelastic Effects in Avalanche Dynamics: A Key to Earthquake Statistics

    NASA Astrophysics Data System (ADS)

    Jagla, E. A.; Landes, François P.; Rosso, Alberto

    2014-05-01

    In many complex systems a continuous input of energy over time can be suddenly relaxed in the form of avalanches. Conventional avalanche models disregard the possibility of internal dynamical effects in the interavalanche periods, and thus miss basic features observed in some real systems. We address this issue by studying a model with viscoelastic relaxation, showing how coherent oscillations of the stress field can emerge spontaneously. Remarkably, these oscillations generate avalanche patterns that are similar to those observed in seismic phenomena.

  4. Avalanche statistics of driven granular slides in a miniature mound

    Microsoft Academic Search

    D. E. Juanico; A. Longjas; R. Batac; C. Monterola

    2008-01-01

    We examine avalanche statistics of rain- and vibration-driven granular slides in miniature sand mounds. A crossover from power-law to non power-law avalanche-size statistics is demonstrated as a generic driving rate ? is increased. For slowly-driven mounds, the tail of the avalanche-size distribution is a power-law with exponent ?1.97 ± 0.31, reasonably close to a value previously reported for landslide volumes.

  5. A Discontinuous Approach to the Numerical Modelling of Rock Avalanches

    Microsoft Academic Search

    P. Tommasi; P. Campedel; C. Consorti; R. Ribacchi

    2008-01-01

    Summary.  The runout of dry rock avalanches produced by planar rockslides affecting a limestone formation with clayey interbeds is analysed\\u000a by means of distinct element modelling. Potential and past rock avalanche events are described with reference to the geotechnical\\u000a and structural conditions of the slope, typical of several Alpine valleys. Runout prediction analyses of potential rock avalanches\\u000a performed with the PFC2D

  6. Avalanche Risk During Backcountry Skiing – An Analysis of Risk Factors

    Microsoft Academic Search

    Harpa Grímsdóttir; David Mcclung

    2006-01-01

    Skier-triggered avalanches are the main cause of avalanche accidents in backcountry skiing. The risk of accidents during backcountry\\u000a skiing was analysed statistically and related to factors such as elevation level, aspect, stability rating and the time of\\u000a the year. The analysis is based on a database about terrain usage and avalanche accidents from a large heli-skiing operator\\u000a in Canada, which

  7. Unjamming and jamming transitions of granular avalanches

    NASA Astrophysics Data System (ADS)

    Zhang, Jie; Wang, Ziwei

    2014-03-01

    Study of the jamming transitions of granular materials has become an active field of research in recent years. A closely related inverse process is the unjamming transition, where granular systems may suddenly lose rigidity and start to flow freely. Understanding such a process is of crucial implication towards the understanding of natural disasters such as snow avalanches, landslides and earthquakes. Recent work by Banigan and colleagues (Nature Physics 2013) has provided a new perspective in the study of unjamming and jamming transitions by applying nonlinear dynamical methods. To test their proposition experimentally, we have designed a rotating drum filled with bidisperse photo-elastic disks to create particle avalanches. In unjamming transition, Lyapunov vector and velocity fields are indeed strongly correlated in spatial domain, whereas in jamming transition no such a strong correlation is observed. The Lyapunov exponents are positive in unjamming transition and negative in jamming transition. In addition, the total stress variation, kinetic energy, and non-affine motion of particles all show strong correlations in the time domain during avalanches. Their spatial correlations have also been analyzed.

  8. Thermal avalanches near a Mott transition.

    PubMed

    Lashley, J C; Gofryk, K; Mihaila, B; Smith, J L; Salje, E K H

    2014-01-22

    We probe the volume collapse transition (?V/Vo ? 15%) between the isostructural ? and ? phases (T ? 100 K) of Ce0.9Th0.1 using the Hall effect, three-terminal capacitive dilatometry, and electrical resistivity measurements. Hall effect measurements confirm the itinerant ground state as the carrier concentration increases by a factor of 7 in the ? phase, ? phase (nH = 5.28 × 10(26) m(-3)), and the ? phase (nH = 3.76 × 10(27) m(-3)). We were able to detect a noise spectrum consisting of avalanches while slowly varying the temperature through the hysteretic region. We surmise that the avalanches originate from intergranular stresses at the interfaces between partially transformed high-volume and low-volume phases. The statistical distribution of avalanches obey power laws with energy exponent ? ? 1.5. Hall effect measurements, combined with universal critical exponents, point to short electron mean-free percolation pathways and carrier localization at phase interfaces. Carrier localization was predicted many years ago for elemental cerium by Johansson (1974 Phil. Mag. 30 469). PMID:24351548

  9. Avalanche characteristics of silicide Schottky Barrier Diodes

    NASA Astrophysics Data System (ADS)

    Yates, Kenneth L.

    This thesis investigates the use of an avalanche Platinum Silicide (PtSi) Schottky Barrier Diode as a detector in fiber optic communication systems for the 1.3 to 1.5 micron spectral region. The avalanche process is used to amplify the signal prior to electrical interfacing in order to enhance the signal-to-noise ratio. The proper environment for avalanche use is when the system is pre amplifier noise limited. The amount of multiplication is predicted by the impact ionization coefficients for electrons and holes, alpha and beta, respectively. Detectors should be constructed of materials where alpha and beta differ greatly, and then the multiplication should be initiated by the carrier with the higher ionization coefficient. By using PtSi Schottky diodes, where alpha is greater than beta, pure electron injection can be accomplished by irradiating with photons of energy psi less than Hnu less than Eg (where psi is the Schottky Barrier height and Eg is the bandgap of silicon), thus maximizing multiplication and minimizing noise. Experimental results on the PtSi diodes studied showed high dark currents at room temperature and premature reverse breakdown which prevented multiplication. However, values from previous reported results allow us to predict a multiplication of 68 with an excess-noise factor of 11.1, an NEP of 2.5 x 10 to the minus 8th power watts, and finally a gain-bandwidth product of 242 GHz.

  10. Unambiguous reconstruction of network structure using avalanche dynamics.

    PubMed

    Leleu, Timothée; Aihara, Kazuyuki

    2015-02-01

    A robust method for inferring the structure of networks is presented based on the one-to-one correspondence between the expected composition of cascades of bursts of activity, called crackling noise or avalanches, and the weight matrix. Using a model of neuronal avalanches as a paradigmatic example, we derive this correspondence exactly by calculating the closed-form expression of the joint probability distribution of avalanche sizes obtained by counting separately the number of elements active in each subnetwork during avalanches. PMID:25768549

  11. Integral stochastic avalanche equation and its application to noise analysis of IMPATT diodes with a wide avalanche layer

    SciTech Connect

    Ovchinnikov, K.D.

    1986-05-01

    A stochastic integral avalanche equation describing noise generation in IMPATT diodes and taking account of avalanche layer transit phenomena, which play an important role in millimeter-range instruments, is derived. To solve this equation, a procedure is developed which takes account of transit effects and the real cross section of the diode doping, as well as its avalanche nonlinearity, saturation current, and differences in the magnitudes of ionization coefficients and drift velocities of electrons and holes.

  12. On The Estimation of Avalanche Encounter Probabilities (or: A New Method For The Estimation of Avalanche Encounter Probabilities)

    NASA Astrophysics Data System (ADS)

    Barbolini, M.; Blagovechshenskiy, V.; Eglit, M.; Keylock, C. J.; Savi, F.

    A crucial point in any methodology for avalanche hazard assessment is the evaluation of avalanche encounter probability, i.e. the annual probability that any given locations along a given path is reached or exceeded by an avalanche. This estimate can be obtained following two different approaches: (a) statistical analysis of historical records of runout distance (however there is rarely enough historical evidence on a path to obtain statistically reliable estimates); (b) avalanche dynamics simulation. Within this latter approach, typical of alpine countries, statistical analysis of snowfall record allow to estimate the T = T yrs snow volume in the starting zone, and then this volume is used as input to an appropriately calibrated avalanche dynamics model to determine the runout distances x T = T yrs for this ( ) design. This approach identify the areas that can be affected by an avalanche for each considered value of the return period event (for instance in the Swiss Guidelines T is set to 30 and 300 years), but does not allow to evaluate the actual avalanche encounter probability for a given point in the runout zone, which is indeed the relevant variable in hazard assessment. This probability can be computed as: P = P*(V ) f (V )dV V0 where f is probability density function (PDF) of the avalanche release volume V, and P* is the probability of the point being reached or exceeded by an avalanche if the release volume is V. The proposed method solve the above integral via numerical integration, having estimated the function f; for each value of V the avalanche dynamics is simulated, and the value of the probability P* is evaluated for each point of the runout zone (P*=1 if the point is reached by the avalanche, P*=0 otherwise). The procedure is implemented using a one-dimensional hydraulic- continuum avalanche dynamic model, calibrated on data from the Zailiyskiy Alatau Range, Kazakhstan, and applied to a real world hazard mapping problem.

  13. Modelling rock avalanche propagation onto glaciers

    NASA Astrophysics Data System (ADS)

    Sosio, Rosanna; Crosta, Giovanni B.; Chen, Joanna H.; Hungr, Oldrich

    2012-07-01

    Ice-rock avalanches which occur in glacial environments are controlled by the presence of snow and ice in the moving material and by possible propagation onto icy basal surfaces. All these factors contribute to enhancing the flow mobility. Mixing with ice and snow hampers block collisions and favours dense flow behaviour. Ice melting reduces granular friction by saturation of the basal material and fluidization effects. Propagating onto glaciers offers a smooth surface with low shear resistance. This work is a review of the best documented ice-rock avalanches and focuses on evaluating their mobility for hazard analysis purposes by providing a set of calibrated cases. The rock avalanches have volumes ranging from 5*106 m3 to 25*106 m3. We replicate these events by using SPH and FEM numerical methods, assuming frictional and Voellmy basal rheologies. The Voellmy rheology best performs at replicating the landslide propagation. Among the back analyzed cases, the frictional coefficient ranges in the interval 0.03-0.1, the turbulent coefficient within 1000 m s-2-2000 m s-2. The bulk basal friction angle ranges within 2.75° and 14° with values inversely related to event volumes. Forward selection of the basal friction angle based on event volume, allows the replication of the Mount Cook ice-rock avalanche predicting a maximum runout which is less than 4% larger than observed. In the perspective of forward modelling, large uncertainty is related to the reconstruction of the post-event topographies, particularly for the sliding surface. Mixing with ice and snow reduces basal friction proportionally to ice and snow content. Pure ice has a basal friction which is reduced by about 75% than basal friction of pure rock. Melting of ice during rock avalanche propagation has been evaluated for the Sherman event. The frictional heat generated at the glacier surface results in the melting of 86.2 ± 5.9 kg m-2, which could have contributed to a minimum 20-35% (±10%) reduction of the material friction angle through the sole pore pressure generation within a 40 and 20 cm thick shear layer, respectively. The largest uncertainty is related to the area of contact between rock and ice.

  14. New advances for modelling the debris avalanches

    NASA Astrophysics Data System (ADS)

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

    2013-04-01

    Flow-like landslides are a major global hazard and they occur worldwide causing a large number of casualties, significant structural damages to property and infrastructures as well as economic losses. When involving open slopes, these landslides often occur in triangular source areas where initial slides turn into avalanches through further failures and/or eventual soil entrainment. This paper deals with the numerical modelling of the propagation stage of debris avalanches which provides information such as the propagation pattern of the mobilized material, its velocity, thickness and run-out distance. In the paper, a "depth integrated" model is used which allows: i) adequately taking into account the irregular topography of real slopes which greatly affect the propagation stage and ii) using a less time consuming model than fully 3D approaches. The used model is named "GeoFlow_SPH" and it was formerly applied to theoretical, experimental and real case histories (Pastor et al., 2009; Cascini et al., 2012). In this work the behavior of debris avalanches is analyzed with special emphasis on the apical angle, one of the main features of this type of landslide, in relation to soil rheology, hillslope geometry and features of triggering area. Furthermore, the role of erosion has been investigated with reference to the uppermost parts of open slopes with a different steepness. These analyses are firstly carried out for simplified benchmark slopes, using both water-like materials (with no shear strength) and debris type materials. Then, three important case studies of Campania region (Cervinara, Nocera Inferiore e Sarno) are analyzed where debris avalanches involved pyroclastic soils originated from the eruptive products of Vesusius volcano. The results achieved for both benchmark slopes and real case histories outline the key role played by the erosion on the whole propagation stage of debris avalanches. The results are particularly satisfactory since they indicate the "GeoFlow_SPH" model as a suitable tool for the analysis of these phenomena. References Pastor, M., Haddad, B., Sorbino, G., Cuomo, S., Drempetic V. (2009). A depth-integrated, coupled SPH model for flow-like landslides and related phenomena. International Journal for Numerical and Analytical Methods in Geomechanics, 33, 143-184. Cascini L., Cuomo S., Pastor M., Sorbino G., Piciullo L. (2012). Modeling of propagation and entrainment phenomena for landslides of the flow type: the May 1998 case study. Proc. of 11th Int. Symposium on Landslides: Landslides and Engineered Slopes, Banf, Canada June 3-8, 2012, Ed. E. Eberhardt, C. Froese, K. Turner, S. Leroueil, ISBN 978-0-415-62423-6, 1723-1729.

  15. ? - β model: Can we learn more from the statistical avalanche model with respect to the dynamical behavior of avalanches.

    NASA Astrophysics Data System (ADS)

    Gauer, P.; Lied, K.; Bakkehoi, S.; Kronholm, K.; Rammer, L.; Hoeller, P.

    2009-04-01

    Hazard and risk assessment in avalanche prone areas involves the estimation of the runout of potential avalanches. Methods for determination of the runout may be grouped into two groups: 1) based on statistical methods such as the well known ? - β model or 2) based on numerical avalanche models such as the PCM-model or Voellmy-Salm type models (just to name the more traditional ones). The later method has the advantage that besides the runout also information on velocity and impact pressure distributions along the avalanche track can be obtained. However, the success of the dynamical models depends on the knowledge of suitable rheological models and their parameters. The statistical ?-β model was developed at NGI and governs maximum runout distance solely as a function of topography. The runout distance equations are found by regression analysis, correlating the longest registered runout distance from several hundred avalanche paths to a selection of topographic parameters. Similar regression analysis were also performed for different regions of United States, Canada or Austria. We re-evaluate the Norwegian and Austrian avalanche data on which the ? - β model were based with respect to dynamical measures. As all those avalanche data belong more or less to extreme events (i.e. avalanches with return periods of 100 years to more) the dynamical measures can give hints for suitable rheological model for dynamical models suitable for extreme avalanche events.

  16. Avalanches mediate crystallization in a hard-sphere glass

    PubMed Central

    Sanz, Eduardo; Valeriani, Chantal; Zaccarelli, Emanuela; Poon, Wilson C. K.; Cates, Michael E.; Pusey, Peter N.

    2014-01-01

    By molecular-dynamics simulations, we have studied the devitrification (or crystallization) of aged hard-sphere glasses. First, we find that the dynamics of the particles are intermittent: Quiescent periods, when the particles simply “rattle” in their nearest-neighbor cages, are interrupted by abrupt “avalanches,” where a subset of particles undergo large rearrangements. Second, we find that crystallization is associated with these avalanches but that the connection is not straightforward. The amount of crystal in the system increases during an avalanche, but most of the particles that become crystalline are different from those involved in the avalanche. Third, the occurrence of the avalanches is a largely stochastic process. Randomizing the velocities of the particles at any time during the simulation leads to a different subsequent series of avalanches. The spatial distribution of avalanching particles appears random, although correlations are found among avalanche initiation events. By contrast, we find that crystallization tends to take place in regions that already show incipient local order. PMID:24306932

  17. Avalanches mediate crystallization in a hard-sphere glass

    E-print Network

    Eduardo Sanz; Chantal Valeriani; Emanuela Zaccarelli; Wilson C K Poon; Michael E Cates; Peter N Pusey

    2014-04-02

    By molecular-dynamics simulations, we have studied the devitrification (or crystallization) of aged hard-sphere glasses. First, we find that the dynamics of the particles are intermittent: Quiescent periods, when the particles simply "rattle" in their nearest-neighbor cages, are interrupted by abrupt "avalanches," where a subset of particles undergo large rearrangements. Second, we find that crystallization is associated with these avalanches but that the connection is not straightforward. The amount of crystal in the system increases during an avalanche, but most of the particles that become crystalline are different from those involved in the avalanche. Third, the occurrence of the avalanches is a largely stochastic process. Randomizing the velocities of the particles at any time during the simulation leads to a different subsequent series of avalanches. The spatial distribution of avalanching particles appears random, although correlations are found among avalanche initiation events. By contrast, we find that crystallization tends to take place in regions that already show incipient local order.

  18. The HgCdTe electron avalanche photodiode

    Microsoft Academic Search

    J. D. Beck; C.-F. Wan; M. A. Kinch; J. E. Robinson; F. Ma; J. C. Campbell

    2003-01-01

    In this paper, a theory for avalanche gain has been developed that takes into account the unique band structure of HgCdTe with allowance being made for the relevant scattering mechanisms of both electrons and holes. These theoretical arguments justify proposition, based on experimental results, that the avalanche gain process in 2 ?m to 11 ?m cutoff photodiodes is characterised by

  19. Avalanches mediate crystallization in a hard-sphere glass.

    PubMed

    Sanz, Eduardo; Valeriani, Chantal; Zaccarelli, Emanuela; Poon, Wilson C K; Cates, Michael E; Pusey, Peter N

    2014-01-01

    By molecular-dynamics simulations, we have studied the devitrification (or crystallization) of aged hard-sphere glasses. First, we find that the dynamics of the particles are intermittent: Quiescent periods, when the particles simply "rattle" in their nearest-neighbor cages, are interrupted by abrupt "avalanches," where a subset of particles undergo large rearrangements. Second, we find that crystallization is associated with these avalanches but that the connection is not straightforward. The amount of crystal in the system increases during an avalanche, but most of the particles that become crystalline are different from those involved in the avalanche. Third, the occurrence of the avalanches is a largely stochastic process. Randomizing the velocities of the particles at any time during the simulation leads to a different subsequent series of avalanches. The spatial distribution of avalanching particles appears random, although correlations are found among avalanche initiation events. By contrast, we find that crystallization tends to take place in regions that already show incipient local order. PMID:24306932

  20. A cooled avalanche photodiode with high photon detection probability

    NASA Technical Reports Server (NTRS)

    Robinson, D. L.; Metscher, B. D.

    1986-01-01

    An avalanche photodiode has been operated as a photon-counting detector with 2 to 3 times the sensitivity of currently-available photomultiplier tubes. APD (avalanche photodiodes) detection probabilities that exceed 27% and approach 50% have been measured at an optimum operating temperature which minimizes noise. The sources of noise and their dependence on operating temperature and bias voltage are discussed.

  1. Noise theory for the read type avalanche diode

    Microsoft Academic Search

    M. E. Hines

    1966-01-01

    An analysis is presented for the noise current spectrum of an avalanche diode under assumed conditions of ideal uniform avalanche behavior in a zone which is thin compared with the total high-field depletion zone. The result is applied to the Read diode amplifier. For a typical set of operating parameters, the theory predicts a noise figure on the order of

  2. 20-ps timing resolution with single-photon avalanche diodes

    Microsoft Academic Search

    S. Cova; A. Lacaita; M. Ghioni; G. Ripamonti; T. A. Louis

    1989-01-01

    Single photon avalanche diodes (SPADs) are avalanche photodiodes specifically designed for reverse bias operation above the breakdown voltage and used for detecting single optical photons. A new silicon epitaxial device structure was designed to give improved timing performance with respect to previous SPADs. Extensive tests were carried out in order to establish the timing resolution of the device in time

  3. Avalanche dynamics in evolution, growth, and depinning models

    Microsoft Academic Search

    Maya Paczuski; Sergei Maslov; Per Bak

    1996-01-01

    The dynamics of complex systems in nature often occurs in terms of punctuations, or avalanches, rather than following a smooth, gradual path. A comprehensive theory of avalanche dynamics in models of growth, interface depinning, and evolution is presented. Specifically, we include the Bak-Sneppen evolution model, the Sneppen interface depinning model, the Zaitsev flux creep model, invasion percolation, and several other

  4. Vortex avalanches with robust statistics observed in superconducting niobium

    Microsoft Academic Search

    E. Altshuler; T. H. Johansen; Y. Paltiel; Peng Jin; K. E. Bassler; O. Ramos; Q. Y. Chen; G. F. Reiter; E. Zeldov; C. W. Chu

    2004-01-01

    By combining micro-Hall probe and magneto-optical imaging techniques we have been able to examine vortex avalanches at different locations of the ridgelike magnetic topography of superconducting niobium samples as the external field is slowly increased. The avalanche size distributions are shown to be power laws for two decades with very similar critical exponents at all locations, thus demonstrating a remarkable

  5. LEGAL CONSEQUENCES OF FATAL AVALANCHE ACCIDENTS IN THE EUROPEAN ALPS

    Microsoft Academic Search

    Jürg Schweizer; Stephan Harvey

    If a fatal avalanche occurs in an Alpine country such as France, Italy, Austria, Germany or Switzerland the circumstances need to be investigated by law. This procedure is common in continental European countries where civil law applies (in opposite to Anglo-American common law). Any unusual death is officially investigated. An avalanche death might happen on a ski run, a highway,

  6. Avalanche Statistics of Driven Granular Slides in a Miniature Mound

    E-print Network

    Juanico, D E; Batac, R; Monterola, C

    2008-01-01

    We examine avalanche statistics of rain- and vibration-driven granular slides in miniature soil mounds using experimental and numerical approaches. A crossover from power-law to non power-law avalanche-size statistics is demonstrated as a generic driving rate $\

  7. Martian dust devil electron avalanche process and associated electrochemistry

    E-print Network

    California at Berkeley, University of

    Click Here for Full Article Martian dust devil electron avalanche process and associated' dynamic atmosphere displays localized dust devils and larger, global dust storms. Based on terrestrial/ion recombination. This new model is called the Dust Devil Electron Avalanche Model (DDEAM). This model solves

  8. Measurements of multiplication effects on noise in silicon avalanche diodes

    Microsoft Academic Search

    I. M. Naqvi; C. A. Lee; G. C. Dalman

    1968-01-01

    Fine grain measurements of avalanche multiplication and noise in large area uniform silicon avalanche diodes are discussed. A high resolution apparatus is described which is capable of resolving multiplication noise in regions separated by only 10-4inches (?2.5 microns) and recording this noise as a function of position over the entire diode area.

  9. Avalanche-like behavior in ciliary import

    PubMed Central

    Ludington, William B.; Wemmer, Kimberly A.; Lechtreck, Karl F.; Witman, George B.; Marshall, Wallace F.

    2013-01-01

    Cilia and flagella are microtubule-based organelles that protrude from the cell body. Ciliary assembly requires intraflagellar transport (IFT), a motile system that delivers cargo from the cell body to the flagellar tip for assembly. The process controlling injections of IFT proteins into the flagellar compartment is, therefore, crucial to ciliogenesis. Extensive biochemical and genetic analyses have determined the molecular machinery of IFT, but these studies do not explain what regulates IFT injection rate. Here, we provide evidence that IFT injections result from avalanche-like releases of accumulated IFT material at the flagellar base and that the key regulated feature of length control is the recruitment of IFT material to the flagellar base. We used total internal reflection fluorescence microscopy of IFT proteins in live cells to quantify the size and frequency of injections over time. The injection dynamics reveal a power-law tailed distribution of injection event sizes and a negative correlation between injection size and frequency, as well as rich behaviors such as quasiperiodicity, bursting, and long-memory effects tied to the size of the localized load of IFT material awaiting injection at the flagellar base, collectively indicating that IFT injection dynamics result from avalanche-like behavior. Computational models based on avalanching recapitulate observed IFT dynamics, and we further show that the flagellar Ras-related nuclear protein (Ran) guanosine 5'-triphosphate (GTP) gradient can in theory act as a flagellar length sensor to regulate this localized accumulation of IFT. These results demonstrate that a self-organizing, physical mechanism can control a biochemically complex intracellular transport pathway. PMID:23431147

  10. 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.

  11. Scaling of connected spin avalanches in growing networks.

    PubMed

    Tomkowicz, Joanna; Ku?akowski, Krzysztof

    2010-05-01

    We use the damage spreading method to investigate the spectra of connected spin avalanches in the exponential networks and the scale-free networks with antiferromagnetically coupled spins. The results suggest that the avalanche spectra are characterized by the same statistics as the degree distribution in their home networks. Further, the obtained mean range Z of an avalanche, i.e., the maximal distance reached by an avalanche from the damaged site, scales with the avalanche size s as Z/N ?=f(s/N ?), where ?=0.5 and ?=0.33. These values are true for both kinds of networks for the number M of nodes to which new nodes are attached between 4 and 10; a check for M=25 confirms these values as well. PMID:20866281

  12. Scaling of connected spin avalanches in growing networks

    NASA Astrophysics Data System (ADS)

    Tomkowicz, Joanna; Ku?akowski, Krzysztof

    2010-05-01

    We use the damage spreading method to investigate the spectra of connected spin avalanches in the exponential networks and the scale-free networks with antiferromagnetically coupled spins. The results suggest that the avalanche spectra are characterized by the same statistics as the degree distribution in their home networks. Further, the obtained mean range Z of an avalanche, i.e., the maximal distance reached by an avalanche from the damaged site, scales with the avalanche size s as Z/N?=f(s/N?) , where ?=0.5 and ?=0.33 . These values are true for both kinds of networks for the number M of nodes to which new nodes are attached between 4 and 10; a check for M=25 confirms these values as well.

  13. Cooled avalanche photodiode used for photon detection

    NASA Technical Reports Server (NTRS)

    Robinson, Deborah L.; Metscher, Brian D.

    1987-01-01

    Commercial avalanche photodiodes have been operated as single-photon detectors at an optimum operating temperature and bias voltage. These detectors were found to be 1.5 to 3 times more sensitive than presently-available photomultiplier tubes (PPMTs). Both single-photon detection probability and detector noise increase with bias voltage; detection probabilities greater than 25 percent were obtained with detector noise levels comparable to the noise of a PMT; higher probabilities were measured at higher noise levels. The sources of noise and their dependence on temperature and bias voltage are discussed.

  14. Avalanche Photodiode Arrays for Optical Communications Receivers

    NASA Technical Reports Server (NTRS)

    Srinivasan, M.; Vilnrotter, V.

    2001-01-01

    An avalanche photodiode (APD) array for ground-based optical communications receivers is investigated for the reception of optical signals through the turbulent atmosphere. Kolmogorov phase screen simulations are used to generate realistic spatial distributions of the received optical field. It is shown that use of an APD array for pulse-position modulation detection can improve performance by up to 4 dB over single APD detection in the presence of turbulence, but that photon-counting detector arrays yield even greater gains.

  15. Photon detection with cooled avalanche photodiodes

    NASA Technical Reports Server (NTRS)

    Robinson, D. L.; Metscher, B. D.

    1987-01-01

    Commercial avalanche photodiodes have been operated as single-photon detectors at an optimum operating temperature and bias voltage. These detectors were found to be 1.5-3 times more sensitive than presently available photomultiplier tubes (PMTs). Both single-photon detection probability and detector noise increase with bias voltage; detection probabilities greater than twice that of a PMT were obtained with detector noise levels below 100 counts per second. Higher probabilities were measured at higher noise levels. The sources of noise and their dependence on temperature and bias voltage are discussed.

  16. Avalanches and Dynamical Correlations in supercooled liquids

    E-print Network

    R. Candelier; A. Widmer-Cooper; J. K. Kummerfeld; O. Dauchot; G. Biroli; P. Harrowell; D. R. Reichman

    2009-12-01

    We identify the pattern of microscopic dynamical relaxation for a two dimensional glass forming liquid. On short timescales, bursts of irreversible particle motion, called cage jumps, aggregate into clusters. On larger time scales, clusters aggregate both spatially and temporally into avalanches. This propagation of mobility, or dynamic facilitation, takes place along the soft regions of the systems, which have been identified by computing isoconfigurational Debye-Waller maps. Our results characterize the way in which dynamical heterogeneity evolves in moderately supercooled liquids and reveal that it is astonishingly similar to the one found for dense glassy granular media.

  17. Theoretical characterisation of a superlattice avalanche photodiode

    NASA Astrophysics Data System (ADS)

    Pal, B. B.; Chakrabarti, P.

    1987-03-01

    A superlattice avalanche photodiode using III V materials is expected to be used in long-distance fiberoptic communication systems in the 1.3 to 1.55 ?m wavelength range. Theoretical studies have been made on the effective ionization rates of electrons and holes of the device, I V characteristic and the frequency response characteristic of the Al x Ga1- x As/GaAs superlattice p+-i-n+ structure. It is observed that the ?/? ratio of the device increases with the field and the bandwidth of the response curve increases with decrease in the dc multiplication gain.

  18. Cartographic Analysis of Avalanche Hazard Maps A Comparison of Relevant Cartographic Factors for the Visualization of the Avalanche Bulletin

    Microsoft Academic Search

    Markus Eckerstorfer

    We cartographically analysed the avalanche hazard maps of 26 avalanche warning services. Th e range of the cartographic products reaches from high quality visualizations over simple bitmap-pictures to hazard charts. A survey involving 167 pro- tagonists was conducted. Alpinists indicated that a map with detailed hazard levels for small, well-defi ned areas is indispens- able, while a map with the

  19. Statistics of Avalanches with Relaxation, and Barkhausen Noise: A Solvable Model Alexander Dobrinevski,

    E-print Network

    Wiese, Kay Jörg

    Statistics of Avalanches with Relaxation, and Barkhausen Noise: A Solvable Model Alexander of each avalanche of the standard ABBM model into a cluster of sub-avalanches, sharply delimited for slow at which the particle velocity never vanishes, are modified. We also analyze non-stationary avalanches

  20. PHYSICAL REVIEW E 85, 066131 (2012) Statistical properties of avalanches in networks

    E-print Network

    Restrepo, Juan G.

    2012-01-01

    PHYSICAL REVIEW E 85, 066131 (2012) Statistical properties of avalanches in networks Daniel B the distributions of size and duration of avalanches propagating in complex networks. By an avalanche we mean that the statistics of avalanches can be characterized in terms of the largest eigenvalue and corresponding

  1. Continuum description of avalanches in granular media Igor S. Aranson1

    E-print Network

    Hasty, Jeff

    Continuum description of avalanches in granular media Igor S. Aranson1 and Lev S. Tsimring2 1 avalanches propagating downhill at small inclination angles to balloon-shaped avalanches also propagating- lar flow. The most spectacular manifestation of such a tran- sition occurs during an avalanche

  2. Snow Avalanches in a Nutshell: A Brief Phenomenology for Non-Specialists

    E-print Network

    Tradacete, Pedro

    Snow Avalanches in a Nutshell: A Brief Phenomenology for Non-Specialists Dieter Issler Norwegian Geotechnical Institute, Oslo, Norway #12;Why are snow avalanches interesting? Practical reason: Avalanches by the power and beauty of this natural phenomenon... #12;Content 1. Avalanche classification by flow regime 2

  3. Maximal avalanches in the Bak-Sneppen model Alexis Gillett1

    E-print Network

    Meester, Ronald

    Maximal avalanches in the Bak-Sneppen model Alexis Gillett1 , Ronald Meester1 and Peter van der Wal2 May 18, 2004 Abstract We study the durations of the avalanches in the maximal avalanche decomposition of the Bak-Sneppen evolution model. We show that all the avalanches in this maximal decomposition

  4. SELF-ORGANIZATION AND NEURONAL AVALANCHES IN NETWORKS OF DISSOCIATED CORTICAL NEURONS

    E-print Network

    Arleo, Angelo

    SELF-ORGANIZATION AND NEURONAL AVALANCHES IN NETWORKS OF DISSOCIATED CORTICAL NEURONS V. PASQUALE of neuronal avalanches. Choosing an appropriate time scale of observation to detect such neu- ronal avalanches-critical, critical or su- per-critical distributions of avalanche sizes and durations, depending on both the age

  5. Particle Size Segregation in Granular Avalanches PhD Supervisor: Professor Nico Gray

    E-print Network

    Heil, Matthias

    Particle Size Segregation in Granular Avalanches PhD Supervisor: Professor Nico Gray (a) (b) (c mass flows, such as debris-flows, dense pyroclastic avalanches and snow avalanches. Larger rougher, recirculation and deposition of coarse particles near two-dimensional avalanche fronts. J. Fluid Mech. 629, 387

  6. Estimating extreme snow avalanche runout for the Columbia Mountains, British Columbia, Canada

    E-print Network

    Jamieson, Bruce

    was first developed by McClung et al. (1989) by applying extreme value statistics to avalanche runout dataEstimating extreme snow avalanche runout for the Columbia Mountains, British Columbia, Canada Avalanche Consulting Ltd., Revelstoke, British Columbia, Canada ABSTRACT Extreme avalanche runout

  7. UNIVERSITY OF CALGARY Avalanche Terrain Modeling in Glacier National Park, Canada

    E-print Network

    Jamieson, Bruce

    runout in the Rogers Pass area based upon the detailed avalanche record from the highway corridor. Along roadways or in areas where there is a human presence, details of avalanche runout distance are often history of avalanche activity or runout distances. Patterns from well known avalanche occurrences along

  8. Computer Tools from the SLF to Support Local Swiss Avalanche and Road Officials

    Microsoft Academic Search

    Michael Lehning; Walter Ammann; Perry Bartelt; Marc Christen; Martin Gassner

    This paper presents computer tools and models developed at the Swiss Federal Institute for Snow and Avalanche Research (SLF) and used by authorities in charge of avalanche safety in Switzerland. The tools are a) the statistical model of local avalanche danger NXD- Lawinen which searches a data base for similar situations in the past and presents the associated avalanche activity;

  9. IEEE PHOTONICS TECHNOLOGY LETTERS, VOL. 19, NO. 22, NOVEMBER 15, 2007 1843 Midwavelength Infrared Avalanche Photodiode

    E-print Network

    Krishna, Sanjay

    Avalanche Photodiode Using InAs­GaSb Strain Layer Superlattice S. Mallick, K. Banerjee, S. Ghosh, J. B. Rodriguez, and S. Krishna Abstract--InAs­GaSb strain layer superlattice p+-n0-n avalanche photodiodes (APDs with avalanche mechanism. Index Terms--Avalanche photodiodes (APDs), bias voltage, mid- wavelength infrared (MWIR

  10. Quantum-dot based avalanche photodiodes for mid-infrared Majeed M. Hayat a

    E-print Network

    Hayat, Majeed M.

    Quantum-dot based avalanche photodiodes for mid-infrared sensing Majeed M. Hayat a , Oh-Hyun Kwon b with an avalanche photodiode (APD) through a tunnel barrier. In the proposed three-terminal device, the applied temperatures. Keywords: Quantum dots, avalanche photodiodes, infrared, sensors, mid-wave infrared, avalanche

  11. Snow avalanche disturbances in forest ecosystems—State of research and implications for management

    Microsoft Academic Search

    Peter Bebi; Dominik Kulakowski; Christian Rixen

    2009-01-01

    Avalanche disturbances are important processes in many subalpine forest ecosystems but have received relatively little research attention in comparison to other major types of disturbances. This paper presents a review of interactions between forests and snow avalanches in mountain ecosystems and discusses how avalanche disturbance regimes and associated management may change in the future. Avalanche disturbance regimes are two-way interactions

  12. Avalanches in Multiplex and Interdependent Networks

    NASA Astrophysics Data System (ADS)

    Baxter, G. J.; Dorogovtsev, S. N.; Goltsev, A. V.; Mendes, J. F. F.

    Many real-world complex systems are represented not by single networks but rather by sets of interdependent networks. In these specific networks, vertices in each network mutually depend on vertices in other networks. In the simplest representative case, interdependent networks are equivalent to the so-called multiplex networks containing vertices of one sort but several kinds of edges. Connectivity properties of these networks and their robustness against damage differ sharply from ordinary networks. Connected components in ordinary networks are naturally generalized to viable clusters in multiplex networks whose vertices are connected by paths passing over each individual sort of their edges. We examine the robustness of the giant viable cluster to random damage. We show that random damage to these systems can lead to the avalanche collapse of the viable cluster, and that this collapse is a hybrid phase transition combining a discontinuity and the critical singularity. For this transition we identify latent critical clusters associated with the avalanches triggered by a removal of single vertices. Divergence of their mean size signals the approach to the hybrid phase transition from one side, while there are no critical precursors on the other side. We find that this discontinuous transition occurs in scale-free multiplex networks whenever the mean degree of at least one of the interdependent networks does not diverge.

  13. Avalanche dynamics of radio pulsar glitches

    E-print Network

    A. Melatos; C. Peralta; J. S. B. Wyithe

    2007-10-04

    We test statistically the hypothesis that radio pulsar glitches result from an avalanche process, in which angular momentum is transferred erratically from the flywheel-like superfluid in the star to the slowly decelerating, solid crust via spatially connected chains of local, impulsive, threshold-activated events, so that the system fluctuates around a self-organised critical state. Analysis of the glitch population (currently 285 events from 101 pulsars) demonstrates that the size distribution in individual pulsars is consistent with being scale invariant, as expected for an avalanche process. The waiting-time distribution is consistent with being exponential in seven out of nine pulsars where it can be measured reliably, after adjusting for observational limits on the minimum waiting time, as for a constant-rate Poisson process. PSR J0537$-$6910 and PSR J0835$-$4510 are the exceptions; their waiting-time distributions show evidence of quasiperiodicity. In each object, stationarity requires that the rate $\\lambda$ equals $- \\epsilon \\dot{\

  14. Avalanches and the distribution of solar flares

    NASA Technical Reports Server (NTRS)

    Lu, Edward T.; Hamilton, Russell J.

    1991-01-01

    The solar coronal magnetic field is proposed to be in a self-organized critical state, thus explaining the observed power-law dependence of solar-flare-occurrence rate on flare size which extends over more than five orders of magnitude in peak flux. The physical picture that arises is that solar flares are avalanches of many small reconnection events, analogous to avalanches of sand in the models published by Bak and colleagues in 1987 and 1988. Flares of all sizes are manifestations of the same physical processes, where the size of a given flare is determined by the number of elementary reconnection events. The relation between small-scale processes and the statistics of global-flare properties which follows from the self-organized magnetic-field configuration provides a way to learn about the physics of the unobservable small-scale reconnection processes. A simple lattice-reconnection model is presented which is consistent with the observed flare statistics. The implications for coronal heating are discussed and some observational tests of this picture are given.

  15. Avalanches and scaling in plastic deformation

    SciTech Connect

    Koslowski, M. (Marisol)

    2004-01-01

    Plastic deformation of crystalline materials is a complex non-homogeneous process characterized by avalanches in the motion of dislocations. We study the evolution of dislocations loops using an analytically solvable phase-field model of dislocations for ductile single crystals during monotonic loading. We present simulations of dislocations under slow external loading that generate scale-free avalanches and power-law behavior that are characteristics of self organized criticality. The distribution of dislocation loop sizes is given by P(A) {approx} A{sup -{sigma}}, with {sigma} = 1.8 {+-} 0.1. The power law exponent is in agreement with those found in acoustic emission measurements on stressed ice single crystals. In addition to the jerky character of dislocation motion, this model also predicts a range of macroscopic behaviors in agreement with observation, including hardening and dislocation multiplication with monotonic loading and a maximum in the acoustic emission signal at the onset of yielding. At sufficient large stress, the hardening rate drops and the stress-strain curve saturates. At the same time the acoustic emission as well as the dislocation production decreases in agreement with experimental observation.

  16. Angle sensitive single photon avalanche diode

    NASA Astrophysics Data System (ADS)

    Lee, Changhyuk; Johnson, Ben; Molnar, Alyosha

    2015-06-01

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

  17. Reducing financial avalanches by random investments.

    PubMed

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

    2013-12-01

    Building on similarities between earthquakes and extreme financial events, we use a self-organized criticality-generating model to study herding and avalanche dynamics in financial markets. We consider a community of interacting investors, distributed in a small-world network, who bet on the bullish (increasing) or bearish (decreasing) behavior of the market which has been specified according to the S&P 500 historical time series. Remarkably, we find that the size of herding-related avalanches in the community can be strongly reduced by the presence of a relatively small percentage of traders, randomly distributed inside the network, who adopt a random investment strategy. Our findings suggest a promising strategy to limit the size of financial bubbles and crashes. We also obtain that the resulting wealth distribution of all traders corresponds to the well-known Pareto power law, while that of random traders is exponential. In other words, for technical traders, the risk of losses is much greater than the probability of gains compared to those of random traders. PMID:24483518

  18. Avalanches of Singing Sand in the Laboratory

    NASA Astrophysics Data System (ADS)

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

    2011-03-01

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

  19. Avalanche situation in Turkey and back calculation of selected events

    NASA Astrophysics Data System (ADS)

    Aydin, A.; Bühler, Y.; Christen, M.; Gürer, I.

    2014-05-01

    In Turkey, an average of 24 people die in snow avalanches every year, mainly in the eastern part of Anatolia and in the eastern Black Sea region, where high-mountain ranges are close to the sea. The proportion of people killed in buildings is very high (87%), especially in comparison to other European countries and North America. In this paper we discuss avalanche occurrence, the climatic situation and historical avalanche events in Turkey; in addition, we identify bottlenecks and suggest solutions to tackle avalanche problems. Furthermore, we have applied the numerical avalanche simulation software RAMMS (rapid mass movements simulation) combined with a (digital elevation model) DEM-based potential release zone identification algorithm to analyze the catastrophic avalanche events in the villages of Üzengili (Bayburt province) in 1993 and Yaylaönü (Trabzon province) in 1981. The results demonstrate the value of such an approach for regions with poor avalanche databases, enabling the calculation of different scenarios and the estimation of run-out distances, impact pressure and flow height.

  20. 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. PMID:21720544

  1. ELECTRON AVALANCHE MODEL OF DIELECTRIC-VACUUM SURFACE BREAKDOWN

    SciTech Connect

    Lauer, E J

    2007-02-21

    The model assumes that an 'initiating event' results in positive ions on the surface near the anode and reverses the direction of the normal component of electric field so that electrons in vacuum are attracted to the dielectric locally. A sequence of surface electron avalanches progresses in steps from the anode to the cathode. For 200 kV across 1 cm, the spacing of avalanches is predicted to be about 13 microns. The time for avalanches to step from the anode to the cathode is predicted to be about a ns.

  2. Transverse Instability of Avalanches in Granular Flows down Incline

    E-print Network

    Igor S. Aranson; Florent Malloggi; Eric Clement

    2005-10-04

    Avalanche experiments on an erodible substrate are treated in the framework of ``partial fluidization'' model of dense granular flows. The model identifies a family of propagating soliton-like avalanches with shape and velocity controlled by the inclination angle and the depth of substrate. At high inclination angles the solitons display a transverse instability, followed by coarsening and fingering similar to recent experimental observation. A primary cause for the transverse instability is directly related to the dependence of soliton velocity on the granular mass trapped in the avalanche.

  3. Characterization of avalanche photodiodes for lidar atmospheric return signal detectors

    NASA Technical Reports Server (NTRS)

    Antill, C. W., Jr.; Holloway, R. M.

    1988-01-01

    Results are presented from tests to characterize noise, dark current, overload, and gain versus bias, relationships of ten avalanche photodiodes. The advantages of avalanche photodiodes over photomultiplier tubes for given laser wavelengths and return signal amplitudes are outlined. The relationship between responsivity and temperature and dark current and temperature are examined. Also, measurements of the noise equivalent power, the excess noise factor, and linearity are given. The advantages of using avalanche photodiodes in the Lidar Atmospheric Sensing Experiment and the Lidar In-Space Technology Experiment are discussed.

  4. AlxGa1-xN-based avalanche photodiodes with high reproducible avalanche gain

    E-print Network

    Ozbay, Ekmel

    to be lower than 8 fA for bias voltages up to 20 V. The responsivity of the photodetectors is 0.13 A/W at 272-blind photodetectors with reproducible avalanche gain as high as 1560 under ultraviolet illumination. The solar-blind photodetectors have a sharp cutoff around 276 nm. The dark currents of the 40 m diameter devices are measured

  5. Bayesian optimal design of an avalanche dam using a multivariate numerical avalanche model

    Microsoft Academic Search

    N. Eckert; E. Parent; T. Faug; M. Naaim

    2009-01-01

    For snow avalanches, passive defense structures are generally designed by considering high return period events. However,\\u000a defining a return period turns out to be tricky as soon as different variables are simultaneously considered. This problem\\u000a can be overcome by maximizing the expected economic benefit of the defense structure, but purely stochastic approaches are\\u000a not possible for paths with a complex

  6. Topographic Avalanche Risk: DEM Sensitivity Analysis

    NASA Astrophysics Data System (ADS)

    Nazarkulova, Ainura; Strobl, Josef

    2015-04-01

    GIS-based models are frequently used to assess the risk and trigger probabilities of (snow) avalanche releases, based on parameters and geomorphometric derivatives like elevation, exposure, slope, proximity to ridges and local relief energy. Numerous models, and model-based specific applications and project results have been published based on a variety of approaches and parametrizations as well as calibrations. Digital Elevation Models (DEM) come with many different resolution (scale) and quality (accuracy) properties, some of these resulting from sensor characteristics and DEM generation algorithms, others from different DEM processing workflows and analysis strategies. This paper explores the impact of using different types and characteristics of DEMs for avalanche risk modeling approaches, and aims at establishing a framework for assessing the uncertainty of results. The research question is derived from simply demonstrating the differences in release risk areas and intensities by applying identical models to DEMs with different properties, and then extending this into a broader sensitivity analysis. For the quantification and calibration of uncertainty parameters different metrics are established, based on simple value ranges, probabilities, as well as fuzzy expressions and fractal metrics. As a specific approach the work on DEM resolution-dependent 'slope spectra' is being considered and linked with the specific application of geomorphometry-base risk assessment. For the purpose of this study focusing on DEM characteristics, factors like land cover, meteorological recordings and snowpack structure and transformation are kept constant, i.e. not considered explicitly. Key aims of the research presented here are the development of a multi-resolution and multi-scale framework supporting the consistent combination of large area basic risk assessment with local mitigation-oriented studies, and the transferability of the latter into areas without availability of higher resolution elevation modes. Worked examples are provided from different DEMs for Alpine as well as Central Asian study areas (including an avalanche cadaster of a mountain road in the Kyrgyz Republic), exploring the transfer of uncertainty parameters into regions where only lower resolution DEMs are available.

  7. Edge effect on the power law distribution of granular avalanches Kinga A. Lrincz and Rinke J. Wijngaarden

    E-print Network

    Wijngaarden, Rinke J.

    Edge effect on the power law distribution of granular avalanches Kinga A. Lrincz and Rinke J-law-distributed avalanche sizes to quasiperiodic system-spanning avalanches. Conversely, by removing ledges the incidence of system- spanning avalanches is significantly reduced. This may offer a perspective on new avalanche

  8. Overspill avalanching in a dense reservoir network.

    PubMed

    Mamede, George L; Araújo, Nuno A M; Schneider, Christian M; de Araújo, José Carlos; Herrmann, Hans J

    2012-05-01

    Sustainability of communities, agriculture, and industry is strongly dependent on an effective storage and supply of water resources. In some regions the economic growth has led to a level of water demand that can only be accomplished through efficient reservoir networks. Such infrastructures are not always planned at larger scale but rather made by farmers according to their local needs of irrigation during droughts. Based on extensive data from the upper Jaguaribe basin, one of the world's largest system of reservoirs, located in the Brazilian semiarid northeast, we reveal that surprisingly it self-organizes into a scale-free network exhibiting also a power-law in the distribution of the lakes and avalanches of discharges. With a new self-organized-criticality-type model we manage to explain the novel critical exponents. Implementing a flow model we are able to reproduce the measured overspill evolution providing a tool for catastrophe mitigation and future planning. PMID:22529343

  9. Subnanosecond Pockels cell switching using avalanche transistors

    NASA Astrophysics Data System (ADS)

    Bishop, A. I.; Barker, P. F.

    2006-04-01

    Achieving subnanosecond optical switching using a Pockels cell requires an electrically optimized cell design and a compatible fast driver. We report on the design and operation of a high voltage, high speed switching circuit which is capable of achieving an optical switching time of 238ps when used in conjunction with a 6mm aperture Pockels cell. The driver uses a Marx-configured avalanche-transistor design to deliver up to 4kV pulses into a 50? load with approximately 12ps jitter and an output pulse length of 7ns. The Pockels cell is a commercially available unit. The observed optical switching time and the jitter in timing of the output pulse are the best currently reported in the literature. We also demonstrate the production of rectangular optical pulses of approximately 3.6ns duration by reflecting the electrical pulse using a mismatched termination.

  10. Computing Granular Avalanches Over Complex Topography

    NASA Astrophysics Data System (ADS)

    Vollmoeller, P.; Dedner, A.; Ancey, C.

    2004-12-01

    Rapid Granular mass movement phenomena such as snow avalanches, rock avalanches and debris flows are natural phenomena that occur in mountainous areas throughout the world. Whereas the physical understanding of their release is quite complex, depend of many very different parameters and hence difficult to understand, the understanding of motion and stopping is less difficult and is investigated in this work using numerical simulations. Savage and Hutter (1989) proposed a one-dimensional continuum model for the numerical simulation of dry granular mixtures. It assumes an incompressible shallow flow behaviour and that the flowing mass behaves as a Mohr-Coulomb plastic material when yielding. This was extended by Gray et al. (1998) and Iverson & Denlinger on multi dimensions and by Iverson & Denlinger (2001) and Savage & Iverson (2003) for rapid two-phase flow phenomena. In this paper we are presenting a new numerical model approach for the solution of the Iverson & Denlinger equations in the case of dry rapid granular flows, with the following characteristics: - it solves the conservation laws for rapid dry granular flows. - it operates on unstructured triangular grids in the finite volume context. - it works with a dynamic adaptive grid strategy. - it operates with a higher order approximate Riemann solver and a new source term balancing technique. - it operates in a parallelized environment. We tested the numerical model against several numerical testproblems and laboratory experiments such as: - the classical lake at rest problem; - a dry granular flow down an inclined chute; - a dry granular flow down an inclined plane with and without a flow diverting obstacle; - a dry granular flow down an unregular laboratory topography .

  11. Relative degradation of near infrared avalanche photodiodes from proton irradiation

    NASA Technical Reports Server (NTRS)

    Becker, Heidi; Johnston, Allan H.

    2004-01-01

    InGaAs and Ge avalanche photodiodes are compared for the effects of 63-MeV protons on dark current. Differences in displacement damage factors are discussed as they relate to structural differences between devices.

  12. Failure avalanches in fiber bundles for discrete load increase

    E-print Network

    Per C. Hemmer; Srutarshi Pradhan

    2007-01-11

    The statistics of burst avalanche sizes $n$ during failure processes in a fiber bundle follows a power law, $D(n)\\sim n^{-\\xi}$, for large avalanches. The exponent $\\xi$ depends upon how the avalanches are provoked. While it is known that when the load on the bundle is increased in a continuous manner, the exponent takes the value $\\xi=5/2$, we show that when the external load is increased in discrete and not too small steps, the exponent value $\\xi=3$ is relevant. Our analytic treatment applies to bundles with a general probability distribution of the breakdown thresholds for the individual fibers. The pre-asymptotic size distribution of avalanches is also considered.

  13. Activity statistics, avalanche kinetics, and velocity correlations in surface growth

    E-print Network

    Juan M. Lopez; Marc Pradas; Aurora Hernandez-Machado

    2010-06-21

    We investigate the complex spatio-temporal dynamics in avalanche driven surface growth by means of scaling theory. We study local activity statistics, avalanche kinetics, and temporal correlations in the global interface velocity, obtaining different scaling relationships among the involved critical exponents depending on how far from or close to a critical point the system is. Our scaling arguments are very general and connect local and global magnitudes through several scaling relationships. We expect our results to be applicable in a wide range of systems exhibiting interface kinetic roughening driven by avalanches of local activity, either critical or not. As an example we apply the scaling theory to analyze avalanches and roughening of forced-flow imbibition fronts in excellent agreement with phase-field numerical simulations.

  14. Photon avalanche upconversion in rare earth laser materials

    Microsoft Academic Search

    Marie-France Joubert

    1999-01-01

    We present an overview of the upconversion mechanisms with special attention to the Photon Avalanche (PA) process and to give the state of the art concerning the upconversion pumped solid state lasers.

  15. Random walk theory applied to electron avalanche formation

    NASA Technical Reports Server (NTRS)

    Englert, G. W.

    1974-01-01

    Use of microscopic detail in random walk theory describing the initial formations of a large number of avalanches shows that concomitant electron transport coefficients quickly relax to equilibrium values. This enables the use of random walks having step sizes and probabilities based only on local electric field strengths and densities. A self-consistent avalanche solution which accounts for collective long range Coulomb interactions as well as short range elastic and inelastic collisions between electrons and background atoms is demonstrated for helium. Avalanche growth retardation followed by an abrupt growth augmentation as time proceeds is shown to be associated with the formation of regions of charge density extrema near the avalanche axis and within the axial distance covered by the electron swarm.

  16. Non-linear behaviour of large-area avalanche photodiodes

    NASA Astrophysics Data System (ADS)

    Fernandes, L. M. P.; Lopes, J. A. M.; Monteiro, C. M. B.; dos Santos, J. M. F.; Morgado, R. E.

    2002-02-01

    The characterisation of photodiodes used as photosensors requires a determination of the number of electron-hole pairs produced by scintillation light. One method involves comparing signals produced by X-ray absorptions occurring directly in the avalanche photodiode with the light signals. When the light is derived from light-emitting diodes in the 400-600 nm range, significant non-linear behaviour is reported. In the present work, we extend the study of the linear behaviour to large-area avalanche photodiodes, of Advanced Photonix, used as photosensors of the vacuum ultraviolet (VUV) scintillation light produced by argon (128 nm) and xenon (173 nm). We observed greater non-linearities in the avalanche photodiodes for the VUV scintillation light than reported previously for visible light, but considerably less than the non-linearities observed in other commercially available avalanche photodiodes.

  17. ORIGINAL PAPER Amateur decision-making in avalanche terrain with

    E-print Network

    . Using a discrete choice experiment (DCE), a stated preference technique, the study first examines-making Á Avalanche safety Á Decision aid Á Discrete choice experiment Á Choice complexity Á Backcountry

  18. A method for modeling water tables at debris avalanche headscarps

    NASA Astrophysics Data System (ADS)

    Buchanan, P.; Savigny, K. W.; De Vries, J.

    1990-02-01

    Heavy rainfall during a January 9 and 10, 1983 storm triggered numerous debris avalanches and associated debris torrents in the Smith Creek basin, western Whatcom County, Washington, U.S.A. Rainfall hyetographs and soil parameters are entered in a one-dimensional, vertical, transient, unsaturated finite-difference model to produce vertical soil discharge rates at selected debris avalanche headscarps. The discharge rates are entered in a kinematic wave equation to model water table profiles above the headscarps. Factors controlling hydrologic response to rainfall are assessed. The discharge rates and water tables modeled for the failure-initiating, January 1983 storm are distinguished from those modeled for other severe storms which did not trigger widespread debris avalanches. The modeling technique is suggested as a method of predicting the risk of debris avalanche recurrence.

  19. Spatio-temporal reconstruction of snow avalanche activity using tree rings: Pierres Jean Jeanne avalanche talus, Massif de l'Oisans, France

    E-print Network

    Stoffel, Markus

    Spatio-temporal reconstruction of snow avalanche activity using tree rings: Pierres Jean Jeanne avalanche talus, Massif de l'Oisans, France Corona Christophe a, , Rovéra Georges b , Lopez Saez Jérôme Grenoble, Unité Erosion Torrentielle Neige et Avalanche, Domaine Universitaire, 2 rue de la papeterie BP 76

  20. Avalanche region width in various structures of IMPATT diodes

    Microsoft Academic Search

    W. E. Schroeder; G. I. Haddad

    1971-01-01

    The avalanche region of one-sided and two-sided abrupt junctions has been studied. These are the structures most commonly utilized for IMPATT diodes. Numerical results are presented which show that n+-p Si diodes have much narrower avalanche regions, due to the unequal ionization rates in Si, than the complementary p+-n type. The implications of these results with respect to IMPATT diode

  1. Effect of volume fraction on granular avalanche dynamics.

    PubMed

    Gravish, Nick; Goldman, Daniel I

    2014-09-01

    We study the evolution and failure of a granular slope as a function of prepared volume fraction, ?(0). We rotated an initially horizontal layer of granular material (0.3-mm-diam glass spheres) to a 45° angle while we monitor the motion of grains from the side and top with high-speed video cameras. The dynamics of grain motion during the tilt process depended sensitively on ?(0)?[0.58-0.63] and differed above or below the granular critical state, ?(c), defined as the onset of dilation as a function of increasing volume fraction. For ?(0)-?(c)<0, slopes experienced short, rapid, precursor compaction events prior to the onset of a sustained avalanche. Precursor compaction events began at an initial angle ?(0)=7.7±1.4° and occurred intermittently prior to the onset of an avalanche. Avalanches occurred at the maximal slope angle ?(m)=28.5±1.0°. Granular material at ?(0)-?(c)>0 did not experience precursor compaction prior to avalanche flow, and instead experienced a single dilational motion at ?(0)=32.1±1.5° prior to the onset of an avalanche at ?(m)=35.9±0.7°. Both ?(0) and ?(m) increased with ?(0) and approached the same value in the limit of random close packing. The angle at which avalanching grains came to rest, ?(R)=22±2°, was independent of ?(0). From side-view high-speed video, we measured the velocity field of intermittent and avalanching flow. We found that flow direction, depth, and duration were affected by ?(0), with ?(0)-?(c)<0 precursor flow extending deeper into the granular bed and occurring more rapidly than precursor flow at ?(0)-?(c)>0. Our study elucidates how initial conditions-including volume fraction-are important determinants of granular slope stability and the onset of avalanches. PMID:25314432

  2. A physical SNOWPACK model for the Swiss avalanche warning

    Microsoft Academic Search

    Perry Bartelt; Michael Lehning

    2002-01-01

    The numerical formulation of a one-dimensional physical snowpack model is presented. The model is operationally employed on a day-to-day basis by avalanche warners to predict snowpack settlement, layering, surface energy exchange and mass balance. Meteorological data obtained from automatic weather stations positioned near avalanche starting zones is used as model input. In this paper, the one-dimensional equations governing the heat

  3. Avalanche-induced effects in polysilicon thin-film transistors

    Microsoft Academic Search

    M. Hack; Alan G. Lewis

    1991-01-01

    A comparison of experimental data and two-dimensional numerical simulations of polysilicon thin-film transistors (TFTs) is presented. It is shown that avalanche multiplication causes both the kink effect in the output characteristics and the reduction of threshold voltage in short-channel device. It is shown that exactly the same physical model for avalanche multiplication gives very good agreement between simulations and experimental

  4. Multigigabit-per-second avalanche photodiode lightwave receivers

    Microsoft Academic Search

    B. L. Kasper; J. C. Campbell

    1987-01-01

    High-speed avalanche photodiodes and high-sensitivity receivers are vital components for future multigigabit-per-second lightwave transmission systems. We review theoretical and experimental performance of high-speed III-V avalanche photodiodes, and also that of multigigabit-per-second lightwave receivers using FET and bi-polar amplifiers. Particular attention is given to APD gain-bandwidth product, and to its effect on high-speed receiver sensitivity. Comparisons between measured receiver sensitivities and

  5. Avalanche dynamics in evolution, growth, and depinning models

    SciTech Connect

    Paczuski, M.; Maslov, S.; Bak, P. [Department of Physics, Brookhaven National Laboratory, Upton, New York 11973 (United States)] [Department of Physics, Brookhaven National Laboratory, Upton, New York 11973 (United States); [Department of Physics, State University of New York at Stony Brook, Stony Brook, New York 11794 (United States)

    1996-01-01

    Dynamics of complex systems in nature often occurs in terms of punctuations, or avalanches, rather than following a smooth, gradual path. Theory of avalanche dynamics in models of growth, interface depinning, and evolution is presented. Specifically, we include the Bak-Sneppen evolution model, Sneppen interface depinning model, Zaitsev flux creep model, invasion percolation, and several other depinning models into a unified treatment encompassing a large class of far from equilibrium processes. The formation of fractal structures, the appearance of 1/{ital f} noise, diffusion with anomalous Hurst exponents, L{acute e}vy flights, and punctuated equilibria can all be related to the same underlying avalanche dynamics. This dynamics can be represented as a fractal in {ital d} spatial plus one temporal dimension. The complex state can be reached either by tuning a parameter, or it can be self-organized. We present two {ital exact} equations for the avalanche behavior in the latter case. (1) The slow approach to the critical attractor, i.e., the process of self-organization, is governed by a ``gap`` equation for divergence of avalanche sizes. (2) The hierarchical structure of avalanches is described by an equation for the average number of sites covered by an avalanche. The exponent {gamma} governing the approach to the critical state appears as a constant rather than as a critical exponent. In addition, the conservation of activity in the stationary state manifests itself through the superuniversal result {eta}=0. The exponent {pi} for the L{acute e}vy flight jumps between subsequent active sites can be related to other critical exponents through a study of {open_quote}{open_quote}backward avalanches.{close_quote}{close_quote} We develop a scaling theory that relates many of the critical exponents in this broad category of extremal models, representing different universality classes, to two basic exponents characterizing the fractal attractor. (Abstract Truncated)

  6. Position-sensitive avalanche photodiodes for gamma-ray imaging

    Microsoft Academic Search

    Kanai S. Shah; Richard Farrell; Ronald Grazioso; Eric S. Harmon; Eric Karplus

    2002-01-01

    In this paper, we report on the investigation of silicon avalanche photodiodes (APDs) for high-energy photon imaging applications. This includes a new APD design that provides X-ray and ?-ray imaging with significant reduction in electronic readout requirements. This new APD design, referred to as position-sensitive avalanche photodiode (PSAPD), involves charge sharing amongst the electrodes that enable determination of position of

  7. Internal Avalanches in a Growing Pile of Superconducting Vortices

    Microsoft Academic Search

    Choong-Seop Lee; Kevin E. Bassler; Maya Paczuski

    2002-01-01

    Avalanches of magnetic vortices produced by systematically increasing an external magnetic field applied to a type-II superconductor are studied using a simple ``sandpile'' type cellular model (K. E. Bassler and M. Paczuski, Phys. Rev. Lett. 81), 3761 (1998).. The cellular model describes the over-damped stick-slip dynamics of the vortices, which results in avalanches of vortex motion as the magnetic field

  8. Breakdown voltage in thin IIIV avalanche photodiodes Mohammad A. Saleh

    E-print Network

    Teich, Malvin C.

    Breakdown voltage in thin III­V avalanche photodiodes Mohammad A. Saleh Electro-Optics Program breakdown voltages for thin avalanche photodiodes of GaAs, InP, In0.52Al0.48As, and Al0.2Ga0.8As, over probability distribution, and statistics of the time response of APDs to be calculated in the presence of dead

  9. Avalanche hazards and mitigation in Austria: a review

    Microsoft Academic Search

    Peter Höller

    2007-01-01

    At all times natural hazards like torrents or avalanches pose a threat to settlements and infrastructures in the Austrian\\u000a Alps. Since 1950 more than 1,600 persons have been killed by avalanches in Austria, which is on average approximately 30 fatalities\\u000a per year. In particular, the winter periods 1950\\/1951 and 1953\\/1954 stand out with more than 100 fatalities. Those events\\u000a led

  10. 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.

  11. Why do some ice avalanches give warning prior to failure?

    NASA Astrophysics Data System (ADS)

    Caplan-Auerbach, J.

    2006-12-01

    Ice avalanches on Iliamna volcano Alaska, Mt. Baker, Washington, and Mt. Steller in the Chugach range of Alaska, exhibit up to several hours of precursory seismicity prior to failure. The precursory sequence includes a series of repeating earthquakes that become progressively more frequent, eventually degrading into continuous ground shaking. The amplitude of ground shaking typically grows until the avalanche suddenly fails. Avalanche propagation is represented by a broadband, spindle-shaped seismic signal. This sequence is interpreted as resulting from slip at the base of a glacier, or within a weak rocky layer beneath the ice. Avalanches with precursory seismicity also share certain physical characteristics, including exposure of the underlying rock surface and evidence of nearby liquid water. In contrast, many other mass-wasting events fail without any kind of seismic warning. These events, however, appear to have initiated in rock or due to glacial calving, rather than at an ice-rock interface. Precursory seismicity may be a characteristic common to glacial ramp failures, in which slip is promoted by a decrease in basal drag. Precursory activity was also not identified in association with avalanches such as the 2002 Kolka or 2005 Monte Rosa events, although this may be due to the large distance between these avalanches and regional seismic stations. The frequent identification of such events on volcanoes may therefore be a consequence of seismic network density, allowing identification of small precursory seismic events. In the case of Iliamna and Mt. Baker volcanoes, avalanches recur in fairly predictable locations at short (1-5 year) intervals. Such frequent failure, as well as the presence of active fumaroles near the failure site, indicates that these events are promoted by geothermal melting. However, the Mt. Steller event confirms that precursory seismicity is not unique to volcanic ice avalanches. Since temperate slab fractures do not fail at predictable intervals (Pralong and Funk, 2006), identification of precursory seismicity could be a critical means by which imminent events could be identified and warning given.

  12. Size of snow particles in a powder-snow avalanche

    Microsoft Academic Search

    M. Rastello; F. Rastello; H. Bellot; F. Ousset; F. Dufour

    2009-01-01

    The size of the snow particles involved in a powder-snow ava- lanche is a key parameter of the local dynamic of the flow. An experimental device has been realized to collect snow particles within powder-snow avalanches. Snow particles have been cap- tured in the powder-snow part of an avalanche triggered artifi- cially on the experimental test site of the vallee

  13. MOBILITY OF ROCK AVALANCHES TRIGGERED BY UNDERGROUND NUCLEAR EXPLOSIONS

    Microsoft Academic Search

    V. V. ADUSHKIN

    Several large rockslides and rock avalanches ranging in volume from 10µ m³ up to 10¸ m³ were triggered by underground nuclear\\u000a explosions at the Novaya Zemlia test site. Rapid filming of rock avalanche formation allowed direct measuring of the velocities\\u000a of debris spreading. Dynamics of two case studies derived from the real time observations and from the analysis of debris

  14. Optimum Receiver Structure for PPM Signals with Avalanche Photodiode Statistics

    NASA Technical Reports Server (NTRS)

    Vilnrotter, V.; Srinivasan, M.

    1998-01-01

    The maximum likelihood decision statistic for detection of pulse-position modulated signals with an avalanche photodiode is derived, using the more accurate Webb density rather than Poisson or Gaussian approximations for the distribution of avalanche photodiode output electrons. It is shown that for Webb-distributed output electtrons, the maximum likelihood rule is to choose the PPM word corresponding to the slot with the maximum electron count.

  15. Avalanche risk assessment for the link Osh - Bishkek, Kyrgyzstan

    NASA Astrophysics Data System (ADS)

    Nazarkulova, Kydyr

    2015-04-01

    The Bishkek-Osh road is main North-South ground transportation connection between the two major cities of Kyrgyzstan. One of the causes for frequent interruptions and closures between November and May is the avalanche risk due to local terrain characteristics and orographically induced precipitation maxima during winter. As a first step towards more effective prediction and implementation of mitigating measures the development of a digital avalanche inventory ('avalanche cadastre') has been initiated. This is aiming at modeling regional risk, and prioritizes the implementation of protective infrastructures in the most avalanche-prone zones. In addition, this helps with continuous monitoring of avalanche behaviour and the assessment of potential influence of climate change. For the parameterisation of models and support of decisions, details about avalanche incidences need to be collected. Historical data collected during Soviet time serve as an important baseline, complemented by more recent data. Overall, developing such a geo database shall be useful and effective for future planning at the Ministry of Emergency Services. This paper demonstrates important parameters to be collected and critical role of historical data as a baseline. Geodatabases are being developed on ArcGIS and used locally for planning preventive measures.

  16. Avalanches and hysteresis in frustrated superconductors and XY spin glasses.

    PubMed

    Sharma, Auditya; Andreanov, Alexei; Müller, Markus

    2014-10-01

    We study avalanches along the hysteresis loop of long-range interacting spin glasses with continuous XY symmetry, which serves as a toy model of granular superconductors with long-range and frustrated Josephson couplings. We identify sudden jumps in the T=0 configurations of the XY phases as an external field is increased. They are initiated by the softest mode of the inverse susceptibility matrix becoming unstable, which induces an avalanche of phase updates (or spin alignments). We analyze the statistics of these events and study the correlation between the nonlinear avalanches and the soft mode that initiates them. We find that the avalanches follow the directions of a small fraction of the softest modes of the inverse susceptibility matrix, similarly as was found in avalanches in jammed systems. In contrast to the similar Ising spin glass (Sherrington-Kirkpatrick) studied previously, we find that avalanches are not distributed with a scale-free power law but rather have a typical size which scales with the system size. We also observe that the Hessians of the spin-glass minima are not part of standard random matrix ensembles as the lowest eigenvector has a fractal support. PMID:25375434

  17. Avalanches, Plasticity, and Ordering in Colloidal Crystals Under Compression

    E-print Network

    D. McDermott; C. J. Olson Reichhardt; C. Reichhardt

    2015-03-09

    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 compressions, 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 even smectic 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.

  18. Pattern formation of granular avalanches with vortex convection

    E-print Network

    Hirofumi Niiya; Akinori Awazu; Hiraku Nishimori

    2013-02-06

    It has been known that the granular flow of polystyrene particles down a slope forms a wavy pattern with many heads at the moving front of the resulting avalanche. In experiments of granular flow using low-density particles, the instability of the moving front and the subsequent head formation are driven by gravity and air drag. To elucidate the instability mechanism of granular avalanches, we propose a particle method considering gravity as the driving force for the avalanche, the contact interaction between granular particles, and the long-range interaction between granular particles through the ambient fluid as a type of air drag. Using this model, we simulate the head formation at the moving front of the avalanche, and we investigate the particle flow caused by the air drag. It is found that the air drag destabilizes the shape of the avalanche that deforms into a wavy pattern, leading to the generation of a pair of granular vortex convection currents inside the head. Further, the relationship between the particle radius and head size is found to satisfy the positive linear scaling law. Moreover, the hydrodynamic interaction between the particles causes their aggregation at the moving front of the avalanche, and this aggregation effect generates the head-tail structure. These numerical results are qualitatively consistent with the results of previous experiments.

  19. Avalanches and hysteresis in frustrated superconductors and XY spin glasses

    NASA Astrophysics Data System (ADS)

    Sharma, Auditya; Andreanov, Alexei; Müller, Markus

    2014-10-01

    We study avalanches along the hysteresis loop of long-range interacting spin glasses with continuous XY symmetry, which serves as a toy model of granular superconductors with long-range and frustrated Josephson couplings. We identify sudden jumps in the T =0 configurations of the XY phases as an external field is increased. They are initiated by the softest mode of the inverse susceptibility matrix becoming unstable, which induces an avalanche of phase updates (or spin alignments). We analyze the statistics of these events and study the correlation between the nonlinear avalanches and the soft mode that initiates them. We find that the avalanches follow the directions of a small fraction of the softest modes of the inverse susceptibility matrix, similarly as was found in avalanches in jammed systems. In contrast to the similar Ising spin glass (Sherrington-Kirkpatrick) studied previously, we find that avalanches are not distributed with a scale-free power law but rather have a typical size which scales with the system size. We also observe that the Hessians of the spin-glass minima are not part of standard random matrix ensembles as the lowest eigenvector has a fractal support.

  20. Insights into rock-ice avalanche dynamics by combined analysis of seismic recordings and a numerical avalanche model

    NASA Astrophysics Data System (ADS)

    Schneider, Demian; Bartelt, Perry; Caplan-Auerbach, Jacqueline; Christen, Marc; Huggel, Christian; McArdell, Brian W.

    2010-12-01

    Rock-ice avalanches larger than 1 × 106 m3 are high-magnitude, low-frequency events that may occur in all ice-covered, high mountain areas around the world and can cause extensive damage if they reach populated regions. The temporal and spatial evolution of the seismic signature from two events was analyzed, and recordings at selected stations were compared to numerical model results of avalanche propagation. The first event is a rock-ice avalanche from Iliamna volcano in Alaska which serves as a “natural laboratory” with simple geometric conditions. The second one originated on Aoraki/Mt. Cook, New Zealand Southern Alps, and is characterized by a much more complex topography. A dynamic numerical model was used to calculate total avalanche momentum, total kinetic energy, and total frictional work rate, among other parameters. These three parameters correlate with characteristics of the seismic signature such as duration and signal envelopes, while other parameters such as flow depths, flow path and deposition geometry are well in agreement with observations. The total frictional work rate shows the best correlation with the absolute seismic amplitude, suggesting that it may be used as an independent model evaluation criterion and in certain cases as model calibration parameter. The good fit is likely because the total frictional work rate represents the avalanche's energy loss rate, part of which is captured by the seismometer. Deviations between corresponding calculated and measured parameters result from site and path effects which affect the recorded seismic signal or indicate deficiencies of the numerical model. The seismic recordings contain additional information about when an avalanche reaches changes in topography along the runout path and enable more accurate velocity calculations. The new concept of direct comparison of seismic and avalanche modeling data helps to constrain the numerical model input parameters and to improve the understanding of (rock-ice) avalanche dynamics.

  1. 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.

  2. Physically-sound scaling laws for snow avalanche impact pressure

    NASA Astrophysics Data System (ADS)

    Faug, T.; Chanut, B.; Caccamo, P.; Naaim, M.

    2012-04-01

    Estimating the force on obstacles stemming from snow avalanches is a non trivial task in avalanche-flow regimes at low velocity for which inertia does not prevail. In addition to the gravity force -proportional to the weight of the undisturbed incoming flow- that takes place at low velocity, extra forces induced by friction for granular snow avalanches, or by some possible viscosity effects for more fluid-like snow avalanches, should be considered. We discuss here the case of a wall-like obstacle overflowed by a granular snow avalanche. Recent small-scale discrete numerical simulations and laboratory tests with granular flows have allowed developing and validating an analytical model to predict the force on the wall. This model shows that the force is the sum of the inertial force, the gravity force of the undisturbed flow and an additional contribution caused by the presence of a stagnant zone formed upstream of the wall and co-existing with an inertial zone above. The model is used to derive a physically-sound scaling law giving the pressure relative to the typical inertial force of the undisturbed flow as a function of the Froude number. Rheological properties of the granular flowing material such as the typical friction angles of the granular material as well as the restitution coefficient of granules are included in the proposed scaling law. With appropriate values of those rheological properties for flowing granular snow, the scaling law can be used to interpret existing pressure data from full-scale snow avalanches and can be cross-compared to classical approaches used in snow avalanche engineering.

  3. OPTIMIZING THROUGH CO-EVOLUTIONARY AVALANCHES

    SciTech Connect

    S. BOETTCHER; A. PERCUS

    2000-08-01

    We explore a new general-purpose heuristic for finding high-quality solutions to hard optimization problems. The method, called extremal optimization, is inspired by ''self-organized critically,'' a concept introduced to describe emergent complexity in many physical systems. In contrast to Genetic Algorithms which operate on an entire ''gene-pool'' of possible solutions, extremal optimization successively replaces extremely undesirable elements of a sub-optimal solution with new, random ones. Large fluctuations, called ''avalanches,'' ensue that efficiently explore many local optima. Drawing upon models used to simulate far-from-equilibrium dynamics, extremal optimization complements approximation methods inspired by equilibrium statistical physics, such as simulated annealing. With only one adjustable parameter, its performance has proved competitive with more elaborate methods, especially near phase transitions. Those phase transitions are found in the parameter space of most optimization problems, and have recently been conjectured to be the origin of some of the hardest instances in computational complexity. We will demonstrate how extremal optimization can be implemented for a variety of combinatorial optimization problems. We believe that extremal optimization will be a useful tool in the investigation of phase transitions in combinatorial optimization problems, hence valuable in elucidating the origin of computational complexity.

  4. High density avalanche chamber (HIDAC) positron camera.

    PubMed

    Townsend, D; Frey, P; Jeavons, A; Reich, G; Tochon-Danguy, H J; Donath, A; Christin, A; Schaller, G

    1987-10-01

    A prototype positron camera has been constructed consisting of two high density avalanche chamber (HIDAC) detectors operated in coincidence with a resolving time (2 tau) of 40 nsec. The detectors are multiwire chambers, with specially constructed lead converters added to improve the photon detection efficiency at 511 keV. The current HIDAC detectors have a singles efficiency of approximately 12%, a sensitive area of 31 X 31 cm and an intrinsic spatial resolution of less than 2 mm full width at half maximum (FWHM). During data acquisition, the detectors are rotated around the patient in order to collect a complete angular data set. A three-dimensional image of the positron distribution is reconstructed from a single scan by weighted backprojection of the data into a matrix of either 64 X 64 X 64 or 128 X 128 X 16 voxels. The camera point response function is deconvolved by frequency-space filtering. Corrections are made during backprojection both for photon attenuation and for spatial variations in point source sensitivity. The reconstructed image is further corrected for contributions from accidental and scattered coincidences and displayed as a sequence of two-dimensional transverse, sagittal, or coronal sections. In addition, three-dimensional display is available using shaded graphics techniques. The prototype camera is currently undergoing clinical evaluation. PMID:3498804

  5. Linking snow avalanche path characteristics and simulation parameters

    NASA Astrophysics Data System (ADS)

    Kofler, Andreas; Fischer, Jan-Thomas; Tollinger, Christian; Granig, Matthias; Fellin, Wolfgang

    2015-04-01

    In this work an objective optimization algorithm is utilized to determine adjusted parameter distributions for avalanche simulation in 3d terrain. Multiple documented extreme avalanche events are investigated to emphasize similarities and differences between adjusted parameter distributions and the corresponding event. A probabilistic simulation setup, using a depth averaged flow model with a simple entrainment and the Voellmy friction law implemented in the SamosAT simulation software, is used to randomly vary the two friction (Coulomb friction, turbulent drag) and one entrainment parameter in their entire physically relevant range. The simulation results (peak pressures and flow depths) are analyzed in 3d terrain, performing a transformation in an avalanche path dependent coordinate system. The model parameters for entrainment and the Voellmy friction relation are systematically optimized, back calculating each documented event by introducing different optimization variables (runout, matched and exceeded affected area, maximum velocity, mass growth, etc.) and maximizing the degree of simulation-observation correspondence. This trial and error approach leads to distributions representing the optimal parameter settings. Different avalanche paths are characterized, distinguishing between avalanche size, total fall height, path shape and others. Statistical dependencies between those path characteristics and the optimal parameters are highlighted. We show that investigating dependencies between optimal parameter distributions and path characteristics is indispensable, when a systematic framework for simulation optimization is applied.

  6. Avalanches in the Weakly Driven Frenkel-Kontorova Model

    E-print Network

    Franz-Josef Elmer

    1994-09-29

    A damped chain of particles with harmonic nearest-neighbor interactions in a spatially periodic, piecewise harmonic potential (Frenkel-Kontorova model) is studied numerically. One end of the chain is pulled slowly which acts as a weak driving mechanism. The numerical study was performed in the limit of infinitely weak driving. The model exhibits avalanches starting at the pulled end of the chain. The dynamics of the avalanches and their size and strength distributions are studied in detail. The behavior depends on the value of the damping constant. For moderate values a erratic sequence of avalanches of all sizes occurs. The avalanche distributions are power-laws which is a key feature of self-organized criticality (SOC). It will be shown that the system selects a state where perturbations are just able to propagate through the whole system. For strong damping a regular behavior occurs where a sequence of states reappears periodically but shifted by an integer multiple of the period of the external potential. There is a broad transition regime between regular and irregular behavior, which is characterized by multistability between regular and irregular behavior. The avalanches are build up by sound waves and shock waves. Shock waves can turn their direction of propagation, or they can split into two pulses propagating in opposite directions leading to transient spatio-temporal chaos. PACS numbers: 05.70.Ln,05.50.+q,46.10.+z

  7. 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 ?E 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 ? 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 ? and the avalanche multiplication factor M in the 0.4-µm-thick a-Se HARP target agree with the theoretical results.

  8. The Sentinel Rock Avalanche of Zion National Park, Utah

    NASA Astrophysics Data System (ADS)

    Castleton, J.; Moore, J. R.; Ivy-Ochs, S.

    2014-12-01

    Blocking the mouth of Zion Canyon over a distance of 2.3 km, the prehistoric Sentinel rock avalanche has had long-lasting impact on the spectacular scenery of Zion National Park, once damming a large lake that filled the rocky canyon with sediment. Today few of Zion's nearly 3 million annual visitors appreciate that the gentle and inviting, flat valley floor amidst great sandstone cliffs owes its origin to a massive landslide. In addition to representing an extreme-magnitude natural hazard with potentially devastating consequences, we also point out the constructive geomorphic and anthropogenic significance of large rock avalanches in this steep desert landscape. We combine new mapping of rock avalanche and related lacustrine deposits to reconstruct topography before and after the landslide, comment on failure kinematics, and determine new, refined volume estimates for the event. Cosmogenic nuclide surface exposure dating of deposited rock avalanche boulders allows us to date the landslide, determine subsequent rates of deposit erosion, and propose potential triggering mechanisms. Evidence suggests that boulders from across the slide surface were deposited simultaneously, yielding similar exposure ages and indicating a single massive and catastrophic rock slope failure. Rich anthropogenic use of the slide-dammed canyon attests to the long-lasting and diverse impacts of large rock avalanches.

  9. The Roles of Heuristics, Avalanche Forecast, and Risk Propensity in the Decision Making of Backcountry Skiers

    Microsoft Academic Search

    Nate Furman; Wynn Shooter; Scott Schumann

    2010-01-01

    Backcountry winter recreation accidents and deaths due to avalanches have grown considerably in recent decades. To better understand how individuals make decisions in avalanche terrain, this study examined the decision-making factors identified by McCammon (2004) that are said to be complicit in avalanche accidents. This study also explored risk-taking propensity and avalanche forecast variables in decision making. Results indicate that

  10. Modeling and monitoring avalanches caused by rain-on-snow events

    NASA Astrophysics Data System (ADS)

    Havens, S.; Marshall, H. P.; Trisca, G. O.; Johnson, J. B.; Nicholson, B.

    2014-12-01

    Direct-action avalanches occur during large storm cycles in mountainous regions, when stresses on the snowpack increase rapidly due to the load of new snow and outpace snow strengthening due to compaction. If temperatures rise above freezing during the storm and snowfall turns to rain, the near-surface snow undergoes rapid densification caused by the introduction of liquid water. This shock to the snowpack, if stability is near critical, can cause widespread immediate avalanching due to the large induced strain rates in the slab, followed by secondary delayed avalanches due to both the increased load as well as water percolation to the depth of a weak layer. We use the semi-empirical SNOow Slope Stability model (SNOSS) to estimate the evolution of stability prior to large avalanches during rain-on-snow events on Highway 21 north of Boise, Idaho. We have continuously monitored avalanche activity using arrays of infrasound sensors in the avalanche-prone section of HW21 near Stanley, in collaboration with the Idaho Transportation Department's avalanche forecasting program. The autonomous infrasound avalanche monitoring system provides accurate timing of avalanche events, in addition to capturing avalanche dynamics during some major releases adjacent to the array. Due to the remote location and low winter traffic volume, the highway is typically closed for multiple days during major avalanche cycles. Many major avalanches typically release naturally and reach the road, but due the complex terrain and poor visibility, manual observations are often not possible until several days later. Since most avalanche programs typically use explosives on a regular basis to control slope stability, the infrasound record of avalanche activity we have recorded on HW21 provides a unique opportunity to study large naturally triggered avalanches. We use a first-order physically based stability model to estimate the importance of precipitation phase, amount, and rate during major rain-on-snow avalanche cycles.

  11. Granular avalanches across irregular three-dimensional terrain: 2. Experimental tests

    Microsoft Academic Search

    Richard M. Iverson; Matthew Logan; Roger P. Denlinger

    2004-01-01

    Scaling considerations indicate that miniature experiments can be used to test models of granular avalanches in which the effects of intergranular fluid and cohesion are negligible. To test predictions of a granular avalanche model described in a companion paper, we performed bench top experiments involving avalanches of dry sand across irregular basal topography that mimicked the complexity of natural terrain.

  12. Numerical simulations of dense clouds on steep slopes: Application to powdersnow avalanches

    E-print Network

    Saramito, Pierre

    Numerical simulations of dense clouds on steep slopes: Application to powder­snow avalanches results. The interest of the results for powder­ snow avalanches is discussed, concluding that two. Introduction A powder­snow avalanche is a dense cloud of suspended snow particles moving down a steep slope

  13. Avalanche Considerations in SiGe HBT Scaling Greg Freeman, Basanth Jagannathan, Jae-Sung Rieh

    E-print Network

    Rieh, Jae-Sung

    Avalanche Considerations in SiGe HBT Scaling Greg Freeman, Basanth Jagannathan, Jae-Sung Rieh IBM-base space-charge region of the device. The higher electric fields result in collector current avalanche multiplication, the effect of which is only now being explored because such trends result in greater avalanche

  14. Flying avalanches Kristin Martha Hakonardottir, Andrew J. Hogg, and Jenny Batey

    E-print Network

    Hogg, Andrew

    Flying avalanches Kristi´n Martha Ha´konardo´ttir, Andrew J. Hogg, and Jenny Batey Centre November 2003; published 4 December 2003. [1] Rapidly flowing avalanches are highly destructive natural important practical consequences for the design of dams used to provide protection from snow avalanches

  15. Hysteresis, Avalanches, and Noise Matthew C. Kuntz, Olga Perkovi'c, Karin A. Dahmen,

    E-print Network

    Sethna, James P.

    Hysteresis, Avalanches, and Noise Matthew C. Kuntz, Olga Perkovi'c, Karin A. Dahmen, Bruce W simulations. In our studies of hysteresis and avalanches in a sim­ ple model of magnetism (the random be triggered when one of its neighbors flips (by participating in an avalanche), or a spin can be triggered

  16. Avalanche mobility induced by the presence of an erodible bed and associated entrainment

    E-print Network

    Hasty, Jeff

    Avalanche mobility induced by the presence of an erodible bed and associated entrainment A mass changes from a decelerating avalanche to a traveling wave. Numerical simulation suggest, and F. Bouchut (2007), Avalanche mobility induced by the presence of an erodible bed and associated

  17. Mean size of avalanches on directed random networks with arbitrary degree distributions James P. Gleeson

    E-print Network

    Gleeson, James P.

    Mean size of avalanches on directed random networks with arbitrary degree distributions James P avalanches on infinite directed random networks may be determined using the damage propagation function.057101 PACS number s : 89.75.Da, 02.50.Ey, 02.10.Ox, 05.50. q Unordered binary avalanches UBAs on directed net

  18. Avalanche properties in a transport model based on critical-gradient fluctuation dynamics

    E-print Network

    Martín-Solís, José Ramón

    Avalanche properties in a transport model based on critical-gradient fluctuation dynamics L avalanche-like transport with diffusion. The particle flux is self-regulated by the stability properties. In steady state, the core remains at the subcritical gradient. The avalanches change from quasiperiodic

  19. Safety on the Hills in Winter: Avalanche Risk--Snow Formation.

    ERIC Educational Resources Information Center

    Grant, Frank

    2003-01-01

    This compact training session on avalanche risk reviews snow crystal formations and common generalities about avalanches. Two types of avalanches--loose and slab--are described, and the characteristics of each are given along with danger signs that accompany each one. Three books are highly recommended for further information. (TD)

  20. Avalanches, precursors and finite size fluctuations in a mesoscopic model of amorphous plasticity

    E-print Network

    Avalanches, precursors and finite size fluctuations in a mesoscopic model of amorphous plasticity Cachan cedex, France (Dated: March 28, 2011) We discuss avalanche and finite size fluctuations transition. We show evidence for a scale free distribution of avalanches P(s) S- with a non trivial exponent

  1. Avalanche: A Fine-Grained Flow Graph Model for Irregular Applications on Distributed-Memory Systems

    E-print Network

    Newton, Ryan R.

    Avalanche: A Fine-Grained Flow Graph Model for Irregular Applications on Distributed-Memory Systems this problem, we present Avalanche, a flow graph model for fine-grained applications that automatically generates active-message handlers. Avalanche is built as a C++ library on top of our previously

  2. Onset of Dendritic Flux Avalanches in Superconducting Films D. V. Denisov,1,2

    E-print Network

    Johansen, Tom Henning

    Onset of Dendritic Flux Avalanches in Superconducting Films D. V. Denisov,1,2 D. V. Shantsev,1,2 Y], viscous fluid flow [17], and electric discharge [18]. Abrupt flux avalanches are known to occur in super such avalanches should develop into dendritic patterns is a topic under vivid discussion, and several competing

  3. The avalanche climate of Glacier National Park, B.C., Canada during 1965-2011

    E-print Network

    Jamieson, Bruce

    The avalanche climate of Glacier National Park, B.C., Canada during 1965-2011 Sascha Bellaire 1 and evolution of the seasonal mountain snow cover and therefore determine the avalanche hazard. For this study we analyzed long-term weather data as well as snow and avalanche data from Glacier National Park

  4. Variation of deposition depth with slope angle in snow avalanches: Measurements from Valle de la Sionne

    E-print Network

    McElwaine, Jim

    Click Here for Full Article Variation of deposition depth with slope angle in snow avalanches drymixed avalanches in Vallée de la Sionne during the winter of 2005­2006. The measurements were used to calculate the depth of the deposited snow along each entire avalanche path with a height resolution of 100

  5. Flow of dense avalanches past obstructions J. M. N.T. Gray,2

    E-print Network

    Gray, Nico

    Flow of dense avalanches past obstructions Y. C.Tai,1 J. M. N.T. Gray,2 K. Hutter,1 S. Noelle3 1 being hit by avalanches is to divert the flow by straight or curved walls or tetrahedral or cylindrical-type structures. Thus, there arises the question how a given avalanche flow is changed regarding the diverted

  6. Can Power-Law Scaling and Neuronal Avalanches Arise from Stochastic Dynamics?

    E-print Network

    Destexhe, Alain

    Can Power-Law Scaling and Neuronal Avalanches Arise from Stochastic Dynamics? Jonathan Touboul1 with no ambiguity that the avalanche size is distributed as a power-law. We conclude that logarithmic and Neuronal Avalanches Arise from Stochastic Dynamics? PLoS ONE 5(2): e8982. doi:10.1371/ journal.pone.0008982

  7. Avalanche-driven fractal flux distributions in NbN superconducting films I. A. Rudnev

    E-print Network

    Johansen, Tom Henning

    Avalanche-driven fractal flux distributions in NbN superconducting films I. A. Rudnev Moscow of abrupt avalanches resulting in dendritic structures. Magnetization curves in this regime exhibit instability; that is, avalanche-like penetration of magnetic flux along narrow branching channels. Using

  8. RELATING AVALANCHES TO LARGE-SCALE OCEAN ATMOSPHERIC OSCILLATIONS Scott Thumlert

    E-print Network

    Jamieson, Bruce

    RELATING AVALANCHES TO LARGE-SCALE OCEAN ­ ATMOSPHERIC OSCILLATIONS Scott Thumlert 1 , Sascha, thus they can affect the snow avalanche ac- tivity. Major oscillations of sea-surface temperature and sea-level pressure have been shown to exist on the 2 to 15 year time-scales. In this paper, avalanche

  9. Avalanche Forecasting for Transportation Corridor and Backcountry in Glacier National Park (BC, Canada)

    E-print Network

    Smith, Dan

    Avalanche Forecasting for Transportation Corridor and Backcountry in Glacier National Park (BC, 2500 University Drive NW Calgary AB T2N 1N4, Canada David Skjonsberg Avalanche Control, Mt. Revelstoke and Glacier National Parks, PO Box 350 Revelstoke BC V0E 2S0, Canada ABSTRACT. The Avalanche Control Section

  10. Computational Complexity of Avalanches in the Kadanoff two-dimensional Sandpile Model

    E-print Network

    Boyer, Edmond

    Computational Complexity of Avalanches in the Kadanoff two-dimensional Sandpile Model Eric Goles. In this paper we prove that the avalanche problem for Kadanoff sandpile model (KSPM) is P-complete for two a single grain may cause avalanches of grains to fall down along the sides of the sandpile. Then

  11. Regional comparison of old-deep slab avalanches David Tracz1

    E-print Network

    Jamieson, Bruce

    Regional comparison of old-deep slab avalanches David Tracz1 ,Sascha Bellaire1 , Bruce Jamieson1, University of Calgary, Alberta, Canada ABSTRACT Deep slab avalanches are rare events that are often forecasting and mitigation efforts. We analyzed avalanche data from 17 winters between 1991 and 2010

  12. VALIDATION OF THE PROPAGATION SAW TEST NEAR WHUMPFS AND AVALANCHES Dave Gauthier*1

    E-print Network

    Jamieson, Bruce

    VALIDATION OF THE PROPAGATION SAW TEST NEAR WHUMPFS AND AVALANCHES Dave Gauthier*1 , Cameron Ross2 to an extent that would lead to avalanche release. We review a recent PST validation study in which fracture present new PST results from 17 whumpf and avalanche sites in the Columbia Mountains of British Columbia

  13. MEASUREMENTS AT RECENT DEEP SLAB AVALANCHES Michael J.W. Conlan

    E-print Network

    Jamieson, Bruce

    MEASUREMENTS AT RECENT DEEP SLAB AVALANCHES Michael J.W. Conlan 1* , David Tracz 1 , and Bruce of Geoscience, University of Calgary, Alberta, Canada ABSTRACT: Hard-to-forecast deep slab avalanches can to the snowpack. For the formation of many natural avalanches, a point is reached where the mass loading

  14. cond-mat/9809122v223Apr1999 Hysteresis, Avalanches, and Noise

    E-print Network

    Sethna, James P.

    cond-mat/9809122v223Apr1999 Hysteresis, Avalanches, and Noise Matthew C. Kuntz, Olga Perkovi becomes crucial for larger simulations. In our studies of hysteresis and avalanches in a sim- ple model participating in an avalanche), or a spin can be triggered because of an increase in the external field H

  15. A Single Particle Impact Model for Motion in Avalanches J. J. P. Veerman

    E-print Network

    Granada, Universidad de

    A Single Particle Impact Model for Motion in Avalanches J. J. P. Veerman (1,2), D. Daescu (1), M particles falling down a rough slope as well as measurements in laboratory controlled avalanches. This (and the robustness of the results) suggests that many-particle systems (avalanches) behave in similar ways as our low

  16. Shock-Capturing and Front-Tracking Methods for Granular Avalanches 1

    E-print Network

    Noelle, Sebastian

    Shock-Capturing and Front-Tracking Methods for Granular Avalanches 1 Y.C. Tai 1 , S. Noelle 2 , J formations are observed in granular avalanches when supercritical ow merges into a region of subcritical ow or WENO cell reconstruction for the conservative equations is therefore introduced. For the avalanche free

  17. Soil Erosion Caused by Snow Avalanches: a Case Study in the Aosta Valley Michele Freppaz*{

    E-print Network

    Williams, Mark W.

    Soil Erosion Caused by Snow Avalanches: a Case Study in the Aosta Valley (NW Italy) Michele Freppaz- 0450, U.S.A. #Corresponding author: margherita.maggioni@unito.it Abstract Snow avalanches can exert considerable erosive forces on soils. If a snow avalanche flows directly over bare ground, basal shear forces

  18. Propagation of Avalanches in Mn12-acetate: Magnetic Deflagration Yoko Suzuki,1

    E-print Network

    Lombardi, John R.

    Propagation of Avalanches in Mn12-acetate: Magnetic Deflagration Yoko Suzuki,1 M. P. Sarachik,1 E- acetate indicate that the magnetization avalanche spreads as a narrow interface that propagates through. This phenomenon, also ob- served in other molecular magnets, has been attributed to a thermal runaway (avalanche

  19. Avalanche structure in a running sandpile model B. A. Carreras and V. E. Lynch

    E-print Network

    Martín-Solís, José Ramón

    Avalanche structure in a running sandpile model B. A. Carreras and V. E. Lynch Oak Ridge National of the avalanche size in the sandpile model does not verify strict self-similarity under changes of the sandpile size. Here we show the existence of avalanches with different space-time structure, and each type

  20. Assessment of the hazard potential of ice avalanches using remote sensing and GIS-modelling

    E-print Network

    Kääb, Andreas

    Assessment of the hazard potential of ice avalanches using remote sensing and GIS-modelling NADINE., Huggel, C., Allgo¨wer, B. & Haeberli, W. 2004. Assessment of the hazard potential of ice avalanches using­84. Oslo. ISSN 0029-1951. Ice avalanches typically occur when a large mass of ice breaks off from steep

  1. Numerical simulations of dense clouds on steep slopes: Application to powder-snow avalanches

    E-print Network

    Saramito, Pierre

    Numerical simulations of dense clouds on steep slopes: Application to powder-snow avalanches results. The interest of the results for powder- snow avalanches is discussed, concluding that two. Introduction A powder-snow avalanche is a dense cloud of suspended snow particles moving down a steep slope

  2. Shock Formation and Breaking in Granular Avalanches M. Shearer and N. Giffen

    E-print Network

    Shearer, Michael

    Shock Formation and Breaking in Granular Avalanches M. Shearer and N. Giffen Department of shock wave solutions of the Gray-Thornton model for particle size segregation in granular avalanches conditions under which a shock wave forms in the interior of the avalanche in finite time. Shocks typically

  3. Statistics of static avalanches in a random pinning landscape Pierre Le Doussal,1

    E-print Network

    Middleton, Alan

    Statistics of static avalanches in a random pinning landscape Pierre Le Doussal,1 A. Alan Middleton, the center of mass of the interface changes in discrete jumps, also called shocks or "static avalanches." We obtain analytically the distribution of avalanche sizes and its cumulants within an =4-d expansion from

  4. Dendritic flux avalanches in superconducting Nb3Sn films I.A. Rudnev a

    E-print Network

    Johansen, Tom Henning

    Dendritic flux avalanches in superconducting Nb3Sn films I.A. Rudnev a , S.V. Antonenko a , D was visualized using magneto-optical imaging. Below 8 K an avalanche-like flux penetration in form of big a flux-filled defect and continue growth from its other end. The avalanches manifest themselves

  5. Numerical modelling of avalanches based on Saint-Venant equations using a kinetic scheme

    E-print Network

    Paris-Sud XI, Université de

    1 Numerical modelling of avalanches based on Saint-Venant equations using a kinetic scheme A@cdac.ernet.in Abstract Numerical modelling of debris avalanches is presented here. The model uses the long waves ratio of debris avalanches, as in classical Saint-Venant models for shal- low water. Depth

  6. Avalanche-size distribution at the depinning transition: A numerical test of the theory

    E-print Network

    Wiese, Kay Jörg

    Avalanche-size distribution at the depinning transition: A numerical test of the theory Alberto S of jumps (avalanches) between successively pinned config- urations of an elastic line (d = 1) or interface(S/Sm) where Sm := S2 2 S m-d- is the scale of avalanches, and the roughness exponent at the depinning

  7. International Snow Science Workshop Grenoble Chamonix Mont-Blanc -2013 Weather preceding persistent deep slab avalanches

    E-print Network

    Jamieson, Bruce

    persistent deep slab avalanches Michael Conlan* and Bruce Jamieson Department of Civil Engineering, University of Calgary, Alberta, Canada ABSTRACT: Deep slab avalanches release on persistent weak layers such as skiers, snowmobilers, and explosives. For natural deep slab avalanches, weather preceding the release

  8. Avalanches and finite size fluctuations in a mesoscopic model of amorphous plasticity

    E-print Network

    Avalanches and finite size fluctuations in a mesoscopic model of amorphous plasticity Mehdi Cachan cedex, France (Dated: September 30, 2010) We discuss avalanche and finite size fluctuations show evidence for a scale free distribution of avalanches P(s) S- with a non trivial exponent 1

  9. Vortex avalanches with robust statistics observed in superconducting niobium E. Altshuler,1,2

    E-print Network

    Zeldov, Eli

    Vortex avalanches with robust statistics observed in superconducting niobium E. Altshuler,1,2 T. H at high fields and very low temperatures in YBaCuO crystals. The avalanche statistics, later worked out techniques we have been able to examine vortex avalanches at different locations of the ridgelike magnetic

  10. Avalanche warning on Chowkibal-Tangdhar axis (J&K): A hybrid approach

    Microsoft Academic Search

    J. C. Joshi; A. Ganju

    Conventional as well as numerical techniques are being widely used for the prediction of snow avalanches. The present approach combines both the techniques and delivers avalanche danger warning for 24 h in ad- vance. Initially different levels of avalanche danger have been decided by observing fresh snow of 24 h and standing snow from a snow-meteorological data- base of the

  11. Road closure to mitigate avalanche danger: a case study for Little Cottonwood Canyon

    Microsoft Academic Search

    Gail Blattenberger; Richard Fowles

    1995-01-01

    Avalanche forecasters make decisions to close the Little Cottonwood Canyon Highway to vehicular traffic in the case of avalanche danger. A statistical model improves forecasting performance. Conditions do not vary simply by day as implied in the statistical model, but the development of the snowpack varies substantially among seasons. There are persistent features of a snowpack which affect avalanche danger

  12. Avalanche characteristics of a transitional snow climate—Columbia Mountains, British Columbia, Canada

    Microsoft Academic Search

    Pascal Hagelia; David M. McClung

    The focus of this study lies on the analysis of avalanche characteristics in the Columbia Mountains in relation to the local snow climate. First, the snow climate of the mountain range is examined using a recently developed snow climate classification scheme. Avalanche observations made by a large helicopter operator are used to examine the characteristics of natural avalanche activity. The

  13. PHYSICAL REVIEW E 85, 061102 (2012) First-principles derivation of static avalanche-size distributions

    E-print Network

    Wiese, Kay Jörg

    2012-01-01

    avalanches. We introduce an efficient and systematic method to compute the statistics of avalanche sizesPHYSICAL REVIEW E 85, 061102 (2012) First-principles derivation of static avalanche statistics is described by the Brownian force model (BFM), the static version of the so-called Alessandro

  14. Multiplication theory for dynamically biased avalanche photodiodes: new limits for gain

    E-print Network

    Hayat, Majeed M.

    Multiplication theory for dynamically biased avalanche photodiodes: new limits for gain bandwidth@ece.unm.edu Abstract: Novel theory is developed for the avalanche multiplication process in avalanche photodiodes (APDs the statistics of the multiplication factor and the impulse-response function of APDs, as well as their breakdown

  15. Full counting statistics of avalanche transport: An experiment J. Gabelli and B. Reulet

    E-print Network

    Full counting statistics of avalanche transport: An experiment J. Gabelli and B. Reulet Laboratoire of total charge Me with M 1. This avalanche is a statistical process, since the e-h pair creation occurs the measurement of higher order cumulants of the current fluctuations in an avalanche diode with a stationary dc

  16. Classical noise and nonlinear effects in the ideal avalanche diode A. A. Walma

    E-print Network

    Paris-Sud XI, Université de

    formulation of the avalanche statistics in an ideal diode is presented, in an effort to extend the theory1585 Classical noise and nonlinear effects in the ideal avalanche diode A. A. Walma Centre d. 2014 On présente une formulation générale de la statistique de l'avalanche dans une diode idéale en s

  17. Avalanche characteristics of a transitional snow climate—Columbia Mountains, British Columbia, Canada

    Microsoft Academic Search

    Pascal Hägeli; David M McClung

    2003-01-01

    The focus of this study lies on the analysis of avalanche characteristics in the Columbia Mountains in relation to the local snow climate. First, the snow climate of the mountain range is examined using a recently developed snow climate classification scheme. Avalanche observations made by a large helicopter operator are used to examine the characteristics of natural avalanche activity. The

  18. New perspective on passively quenched single photon avalanche diodes: effect of

    E-print Network

    Hayat, Majeed M.

    the bandwidth statistics of avalanche photodiodes," IEEE Trans. Electron Devices 47, 1273­1279 (2000). 12. M. MNew perspective on passively quenched single photon avalanche diodes: effect of feedback on impact South, Cranbury, NJ 08512, USA davramir@unm.edu Abstract: Single-photon avalanche diodes (SPADs

  19. A new method for avalanche hazard mapping using a combination of statistical and deterministic models

    Microsoft Academic Search

    M. Barbolini

    2002-01-01

    The purpose of the present paper is to pro- pose a new method for avalanche hazard mapping using a combination of statistical and deterministic modelling tools. The methodology is based on frequency-weighted impact pressure, and uses an avalanche dynamics model embedded within a statistical framework. The outlined procedure pro- vides a useful way for avalanche experts to produce haz- ard

  20. A New Method for the Estimation of Avalanche Distance Exceeded Probabilities

    Microsoft Academic Search

    Massimiliano Barbolini; Federica Cappabianca; Fabrizio Savi

    2003-01-01

    A crucial point in any methodology for avalanche hazard assessment is the evaluation of avalanche distance exceeded probability, i.e., the annual probability that any assigned location along a given path is reached or exceeded by an avalanche. Typically this problem is faced by estimating the snow volume in the starting zone that is likely to accumulate an average every T

  1. Geomorphology of snow avalanche impact landforms in the southern Canadian Cordillera

    E-print Network

    Smith, Dan

    Geomorphology of snow avalanche impact landforms in the southern Canadian Cordillera ALEXIS L@uvic.ca) Snow avalanche impact landforms (SAILs) are typically elliptical-shaped depressions bounded by an arcuate ridge located at the base of avalanche paths. The geomorphology of these features is controlled

  2. A methodology to allow avalanche forecasting on an information retrieval system R. S. Purves

    E-print Network

    Sanderson, Mark

    1 A methodology to allow avalanche forecasting on an information retrieval system R. S. Purves an Information Re- trieval (IR) system to forecast the likelihood of avalanches on a particular day. The forecasting process uses historical data of the weather and avalanche conditions for a large number of days

  3. Prediction of Excess Noise Factor and Frequency Response for Thin Avalanche Photodiodes

    E-print Network

    Hayat, Majeed M.

    Prediction of Excess Noise Factor and Frequency Response for Thin Avalanche Photodiodes Majeed M@bu.edu teich@bu.edu SUMMARY Recent experimental measurements from InP and InAlAs avalanche photodiodes (APDs of the avalanching mechanism is reduced. For thin multiplication-region APDs, this e ect is proportionally higher

  4. Ultralow noise midwave infrared InAsGaSb strain layer superlattice avalanche photodiode

    E-print Network

    Krishna, Sanjay

    Ultralow noise midwave infrared InAs­GaSb strain layer superlattice avalanche photodiode InAs­GaSb strain layer superlattice p+ -n- -n homojunction avalanche photodiodes APDs grown by solid in the avalanche regime. Decrease in the multiplication gain at higher temperatures correlates with standard APD

  5. Avalanches and bursts in low-pressure helium gas below the breakdown voltage

    Microsoft Academic Search

    Z. Donkó

    1995-01-01

    External ionizing particles may induce electron avalanches and bursts (sequences of avalanches) in a gas subjected to an electric field. The properties of these avalanches and bursts at a given pressure depend on the strength of the electric field, which in our case is considered to be homogeneous between two plane-parallel metal electrodes. With increasing voltage (V) applied to the

  6. ccsd00003464, X-ray observation of micro-failures in granular piles approaching an avalanche

    E-print Network

    approaching an avalanche Alexandre Kabla 1 , Georges Debr#19;egeas 2 , Jean-Marc di Meglio 1;3 , and Tim J before the surface reaches the avalanche angle, we observe intermittent plastic events associated by these discrete events grows as the system approaches the avalanche threshold. By testing various preparation

  7. Two-fluid barotropic models for powder-snow avalanche flows

    E-print Network

    Gisclon, Marguerite

    Chapter 1 Two-fluid barotropic models for powder-snow avalanche flows Yannick Meyapin, Denys Dutykh and Marguerite Gisclon Abstract In the present study we discuss several modeling issues of powder-snow avalanche, an incompressible limit of this model is derived. 1.1 Introduction Snow avalanches represent a serious problem

  8. Resonant normal-incidence separate-absorption-charge-multiplication Ge/Si avalanche

    E-print Network

    Bowers, John

    Resonant normal-incidence separate-absorption- charge-multiplication Ge/Si avalanche photodiodes the impedance of separate-absorption-charge- multiplication Ge/Si avalanche photodiodes (APD) is characterized in the avalanche region, the frequency response of the APD has a peak enhancement when the bias voltage

  9. Analytical and Numerical Treatment of a Singular Initial Value Problem in Avalanche

    E-print Network

    Weinmüller, Ewa B.

    Analytical and Numerical Treatment of a Singular Initial Value Problem in Avalanche Modeling Othmar of dry-flowing avalanches. The model has the form of a singular initial value problem for a scalar ordinary differential equation describing the avalanche dynamics. Exis- tence, uniqueness and smoothness

  10. Elementary excitations and avalanches in the Coulomb glass

    NASA Astrophysics Data System (ADS)

    Palassini, Matteo; Goethe, Martin

    2012-07-01

    We study numerically the statistics of elementary excitations and charge avalanches in the classical Coulomb glass model of localized charges with unscreened Coulomb interaction and disorder. We compute the single-particle density of states with an energy minimization algorithm for systems of up to 1003 sites. The shape of the Coulomb gap is consistent with a power-law with exponent ? simeq 2.4 and marginally consistent with exponential behavior. The results are also compared with a recently proposed self-consistent approach. We then analyze the size distribution of the charge avalanches produced by a small perturbation of the system. We show that the distribution decays as a power law in the limit of large system size, and explain this behavior in terms of the elementary excitations. Similarities and differences with the scale-free avalanches observed in mean-field spin glasses are discussed.

  11. Mobility of large rock avalanches: evidence from Valles Marineris, Mars

    USGS Publications Warehouse

    McEwen, A.S.

    1989-01-01

    Measurements of H/L (height of drop/length of runout) vs. volume for landslides in Valles Marineris on Mars show a trend of decreasing H/L with increasing volume. This trend, which is linear on a log-log plot, is parallel to but lies above the trend for terrestrial dry rock avalanches. This result and estimates of 104 to 105 Pa yield strength suggest that the landslides were not water saturated, as suggested by previous workers. The offset between the H/L vs. volume trends shows that a typical Martian avalanche must be nearly two orders of magnitude more voluminous than a typical terrestrial avalance in order to achieve the same mobility. This offset might be explained by the effects of gravity on flows with high yield strengths. These results should prove useful to future efforts to resolve the controversy over the mechanics of long-runout avalanches. -Author

  12. Avalanches of rearrangements in quasi-2D emulsion hopper flow

    E-print Network

    Xia Hong; Kenneth W. Desmond; Dandan Chen; Eric R. Weeks

    2015-03-25

    We experimentally study the flow of a quasi-two-dimensional emulsion through a constricting hopper shape. Our area fractions range from 0.83 to 0.99, such that the droplets are always in contact with one another and are in many cases highly deformed. At the lowest flow rates, the droplets exit the hopper via intermittent avalanches. At the highest flow rates, the droplets exit continuously. The transition between these two types of behaviors is a fairly smooth function of the mean strain rate. The avalanches are characterized by a power law distribution of the time interval between droplets exiting the hopper, with long intervals between the avalanches. There is little or no dependence of the flow behavior on the area fraction of the system.

  13. Erosive granular avalanches : a cross confrontation between theory and experiment.

    SciTech Connect

    Clement, E.; Malloggi, F.; Andreotti, B.; Aranson, I. S.; Materials Science Division; ESPCI-Univ. Paris; Univ. of Twente

    2007-01-01

    Results on two laboratory scale avalanches experiments taking place both in the air and under-water, are presented. In both cases a family of solitary erosion/deposition waves are observed. At higher inclination angles, we show the existence of a long wavelength transverse instability followed by a coarsening and the onset of a fingering pattern. While the experiments strongly differ by the spatial and time scales, the agreement between the stability diagram, the wavelengths selection and the avalanche morphology suggest a common erosion/deposition scenario. These experiments are studied theoretically in the framework of the 'partial fluidization' model of dense granular flows. This model identifies a family of propagating solitary waves displaying a behavior similar to the experimental observation. A primary cause for the transverse instability is related to the dependence of avalanche velocity on the granular mass trapped by the flow.

  14. Communicators' perspective on snow avalanche risk communication using smartphone applications

    NASA Astrophysics Data System (ADS)

    Charrière, Marie; Bogaard, Thom; Junier, Sandra; Mostert, Erik

    2015-04-01

    Among all the natural hazards, snow avalanches are the only ones for which a public danger scale is used globally. 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 smartphone applications with which the information is disseminated to the general public differ, particularly in terms of target audience and level of details. This study aims to gather the perspectives of several persons that are responsible for these avalanche risk communication practices. The survey was created to assess how and why choices were made in the design process of the applications and to determine how their effectiveness is evaluated. Along with a review of existing avalanche risk communication smartphone applications, this study provides guidelines for communication and the evaluation of its effectiveness.

  15. Avalanche Dynamics of Crackle Sound in the Lung

    SciTech Connect

    Alencar, Adriano M.; Buldyrev, Sergey V.; Majumdar, Arnab; Stanley, H. Eugene; Suki, Bela

    2001-08-20

    We analyze a sequence of short transient sound waves, called 'crackles,' which are associated with explosive openings of airways during lung inflation. The distribution of time intervals between consecutive crackles {Delta}t shows two regimes of power law behavior. We develop an avalanche model which fits the data over five decades of {Delta}t. We find that the regime for large {Delta}t is related to the dynamics of distinct avalanches in a Cayley tree, and the regime for small {Delta}t is determined by the dynamics of crackle propagation within a single avalanche. We also obtain a mean-field solution of the model which provides information about lung inflation.

  16. Activity-Dependent Model for Neuronal Avalanches

    NASA Astrophysics Data System (ADS)

    de Arcangelis, L.

    Networks of living neurons represent one of the most fascinating systems of modern biology. If the physical and chemical mechanisms at the basis of the functioning of a single neuron are quite well understood, the collective behavior of a system of many neurons is an extremely intriguing subject. Crucial ingredient of this complex behavior is the plasticity property of the network, namely the capacity to adapt and evolve depending on the level of activity. This plastic ability is believed, nowadays, to be at the basis of learning and memory in real brains. This fundamental problem in neurobiology has recently shown a number of features in common to other complex systems. These features mainly concern the morphology of the network, namely the spatial organization of the established connections, and a novel kind of neuronal activity. Experimental data have, in fact, shown that electrical information propagates in a cortex slice via an avalanche mode. Both features have been found in other problems in the context of the physics of complex systems and successful models have been developed to describe their behavior. In this contribution, we apply a statistical mechanical model to describe the complex activity in a neuronal network. The network is chosen to have a number of connections in long range, as found for neurons in vitro. The model implements the main physiological properties of living neurons and is able to reproduce recent experimental results. The numerical power spectra for electrical activity reproduces also the power law behavior measured in an EEG of man resting with the eyes closed.

  17. Release of Wet Snow Avalanches: A Grain-scale Approach

    NASA Astrophysics Data System (ADS)

    Gan, Yixiang; Faug, Thierry; Einav, Itai

    2014-05-01

    This work provides a first grain-scale investigation of wet snow avalanches, considering the role of temperature field, mass transfer, and phase changes of snow grains. Snow avalanche release can be related to the dynamics of snow grains, which have typical sizes of 0.5-1 mm. The basal layer, with a thickness of only a few centimetres, is often the weakest link responsible for the instability of the whole snowpack. Previous investigations of snow avalanche release using discrete element methods have mainly focused on "dry" snow. "Wet" snow avalanches are governed by a variety of grain-scale processes, including melting within the snowpack and water flow in surrounding micro-pores. We separate the triggering mechanisms of wet snow avalanches into two categories: (1) infiltration of melted ice into the weak layer located near the ground surface, and (2) melting of snow grains within the layer. The first mechanism corresponds to cases with ice melting in the snowpack above the basal weak layer, while the second mechanism is due to heating from the ground. The purpose of this paper is to present a discrete element method that describes the generation of fluid due to melting of snow grains, and the transport of fluid along the surrounding pores. By varying the total amount of liquid in terms of these two mechanisms, we will show that as the basal weak layer undergoes a transition from low saturation to high saturation the bulk snowpack could start sliding. We will motivate the idea that the balance between these grain-scale weakening mechanisms is a major factor controlling the onset of wet avalanches. We will further discuss the roles of other possible grain-scale effects on this instability phenomenon, including the effects of adhesive forces and lubrication.

  18. High gain multigap avalanche detectors for Cerenkov ring imaging

    SciTech Connect

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

    1980-10-01

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

  19. 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.

  20. Negative Avalanche Feedback Detectors for Photon-Counting Optical Communications

    NASA Technical Reports Server (NTRS)

    Farr, William H.

    2009-01-01

    Negative Avalanche Feedback photon counting detectors with near-infrared spectral sensitivity offer an alternative to conventional Geiger mode avalanche photodiode or phototube detectors for free space communications links at 1 and 1.55 microns. These devices demonstrate linear mode photon counting without requiring any external reset circuitry and may even be operated at room temperature. We have now characterized the detection efficiency, dark count rate, after-pulsing, and single photon jitter for three variants of this new detector class, as well as operated these uniquely simple to use devices in actual photon starved free space optical communications links.

  1. Avalanches in Strained Amorphous Solids: Does Inertia Destroy Critical Behavior?

    E-print Network

    K. Michael Salerno; Craig E. Maloney; Mark O. Robbins

    2012-04-26

    Simulations are used to determine the effect of inertia on athermal shear of a two-dimensional binary Lennard-Jones glass. In the quasistatic limit, shear occurs through a series of rapid avalanches. The distribution of avalanches is analyzed using finite-size scaling with thousands to millions of particles. Inertia takes the system to a new underdamped universality class rather than driving the system away from criticality. Scaling exponents are determined for the underdamped and overdamped limits and a critical damping that separates the two regimes. Systems are in the overdamped universality class even when most vibrational modes are underdamped.

  2. Further studies of electron avalanche gain in liquid argon

    SciTech Connect

    Kim, J.G.; Dardin, S.M.; Kadel, R.W.; Kadyk, J.A.; Jackson, K.H.; Peskov, V.; Wenzel, W.A.; Joo, K.S.

    2003-03-07

    Previously we showed how small admixtures of xenon (Xe) stabilize electron avalanches in liquid Argon (LAr). In the present work, we have measured the positive charge carrier mobility in LAr with small admixtures of Xe to be 6.4 x 10{sup -3} cm{sup 2}/Vsec, in approximate agreement with the mobility measured in pure LAr, and consistent with holes as charge carriers. We have measured the concentration of Xe actually dissolved in the liquid and compared the results with expectations based on the amount of Xe gas added to the LAr. We also have tested LAr doped with krypton to investigate the mechanism of avalanche stabilization.

  3. Overrun length of avalanches overtopping catching dams: Cross-comparison of small-scale laboratory experiments and observations from full-scale avalanches

    Microsoft Academic Search

    T. Faug; P. Gauer; K. Lied; M. Naaim

    2008-01-01

    Results from small-scale and full-scale experiments on avalanche–dam interactions are presented and compared. These experiments were analyzed with respect to the overrun length (i.e., the distance that the avalanche traveled beyond a catching dam). The differences and similarities in the results are discussed through a cross-comparison of the small-scale experiments and by comparing them with observations from Ryggfonn on avalanche–dam

  4. Use of a magnetic field to modify and detect avalanche behavior on a conical bead pile

    NASA Astrophysics Data System (ADS)

    Johnson, Nathan; Lehman, Susan

    2015-03-01

    A conical bead pile subject to slow driving and an external magnetic field is used to test the effects of drop height and cohesion on avalanche statistics. Magnetically susceptible beads were dropped onto a pile from different heights and into different strengths of magnetic field. Avalanches were recorded by the change in mass as beads fall off the pile. For beads dropped from a low drop height with no cohesion, the avalanche size distribution follows a power law. As cohesion increases, we observe an increase in the probability of very large avalanches and decreases in the mid-size avalanches. The resulting bump in the avalanche distribution moves to larger avalanche size as the cohesion in the system is increased, matching the prediction by an analytic theory from a mean-field model of slip avalanches. The model also makes predictions for avalanche duration, which is not measurable with our current system. Since the steel beads are magnetized while in the applied magnetic field, their motion during an avalanche creates a change in magnetic flux. To detect this motion, we have placed a large-diameter pick-up coil around the pile. Results of the testing and calibration of this coil to measure avalanche duration are presented.

  5. Fracture toughness of dry snow slab avalanches from field measurements

    Microsoft Academic Search

    D. M. McClung; Jürg Schweizer

    2006-01-01

    Dry snow slab avalanches release by propagating fractures. The first fracture occurs in shear within a thin weak layer underneath a planar slab which eventually fails in tension perpendicular to the weak layer at some distance up-slope. Thus fracture properties of both the weak layer (in shear) and the slab (in tension) are important for determining the character of the

  6. Recent progress on cooled avalanche photodiodes for single photon detection

    Microsoft Academic Search

    A. Dorokhov; A. Glauser; Y. Musienko; C. Regenfus; S. Reucroft; J. Swain

    2004-01-01

    Recent results on the properties of cooled avalanche photodiodes for single photon detection are presented. Results from Hamamatsu silicon photodiodes, originally developed as radiation-hard photodetectors for high energy physics experiments, are extremely encouraging. Gains of approximately 10,000 can be achieved with the APD operating in proportional mode. Together with a low noise amplifier they allow photon counting with extremely high

  7. 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,…

  8. Photon-counting techniques with silicon avalanche photodiodes

    Microsoft Academic Search

    Henri Dautet; Pierre Deschamps; Bruno Dion; Andrew D. MacGregor; Darleene MacSween; Robert J. McIntyre; Claude Trottier; Paul P. Webb

    1993-01-01

    Silicon avalanche photodiodes (APD) have been used for photon counting for a number of years. This paper reviews their properties and the associated electronics required for photon counting in the Geiger mode. Significant improvements are reported in overall photon detection efficiencies (approaching 75% at 633 nm), and timing jitter (under 200 ps) achieved at high over-voltages (20 - 30 V).

  9. Teaching Avalanche Safety Courses: Instructional Techniques and Field Exercises.

    ERIC Educational Resources Information Center

    Watters, Ron

    This paper discusses course structure, teaching techniques, and field exercises for enhancing winter travelers' avalanche knowledge and skills. In two class sessions, the course typically consists of a historical perspective; a section on snow physics (clouds, types of snow crystals, effects of riming, identification of precipitated snow crystals,…

  10. Initial results from the Sherbrooke avalanche photodiode positron tomograph

    Microsoft Academic Search

    R. Lecomte; J. Cadorette; S. Rodrigue; D. Lapointe; D. Rouleau; M. Bentourkia; R. Yao; P. Msaki

    1996-01-01

    The design features and engineering constraints of a PET system based on avalanche photodiode (APD) detectors have been described in a previous report. Here, the authors present the initial results obtained with the Sherbrooke APD-PET scanner, a very high spatial resolution device designed for dynamic imaging of small and medium-sized laboratory animals such as rats, cats, rabbits and small monkeys.

  11. Bipolar transistor modeling of avalanche generation for computer circuit simulation

    Microsoft Academic Search

    R. W. Dutton

    1975-01-01

    An avalanche generation model is developed and incorporated into computer circuit analysis programs SLIC and NICAP. A modified form of Miller's empirical expression for generation is found to agree well with measured data for Western Electric and commercial n-p-n transistors. Measurement techniques and parameter determination for the three model coefficients are discussed. Equation constraints appropriate for computer implementation are presented.

  12. Threshold energy effect on avalanche breakdown voltage in semiconductor junctions

    Microsoft Academic Search

    Y. Okuto; C. R. Crowell

    1975-01-01

    The band bending for avalanche breakdown in semiconductor junctions and its temperature dependence are predicted taking account of threshold energy effects on the ionization process in semiconductors. Where experimental results exist, the theoretical predictions and experimental results are in excellent agreement. In the high electric field region inclusion of both bulk and boundary threshold energy effects is essential. The predictions

  13. Trapping phenomena in avalanche photodiodes on nanosecond scale

    Microsoft Academic Search

    Sergio Cova; A. Lacaita; G. Ripamonti

    1991-01-01

    A technique for measuring the release of minority carriers emitted from deep levels in avalanche photodiodes (APDs) at operating conditions is discussed. The method, time-correlated carrier counting (TCCC), is very sensitive and accurate. Densities of filled traps were measured down to 109 cm-3 and lifetimes in the nanosecond range. This technique can be useful in tailoring gettering processes for APDs

  14. Vortex avalanches and the onset of superfluid turbulence

    E-print Network

    N. B. Kopnin

    2003-09-30

    Quantized circulation, absence of Galilean invariance due to a clamped normal component, and the vortex mutual friction are the major factors that make superfluid turbulence behave in a way different from that in classical fluids. The model is developed for the onset of superfluid turbulence that describes the initial avalanche-like multiplication of vortices into a turbulent vortex tangle.

  15. The distribution of gains in uniformly multiplying avalanche photodiodes: Experimental

    Microsoft Academic Search

    J. Conradi

    1972-01-01

    Experimental measurements of the gain distribution and noise spectral density of silicon avalanche photodiodes are presented and compared with McIntyre's theories [7], [8]. Excellent agreement is obtained using keff, the effective ratio of the hole and electron ionization coefficients, as the only adjustable parameter.

  16. Reducing the Odds: Backcountry Powder Skiing in Avalanche Terrain.

    ERIC Educational Resources Information Center

    Daffern, Tony

    This paper provides information and strategies to reduce the risk of encountering an avalanche when skiing or climbing on steep slopes. Skiers must recognize that the risk exists, be aware of their own tolerance for risk, and not allow companions to pressure them into taking more risk than they can tolerate. Ideally, one should ski with a small…

  17. Structural Control of Giant Rock Avalanches in Argentina

    NSDL National Science Digital Library

    Barb Tewksbury

    Jigsaw version: To prepare, students do background reading on landslides and rock avalanches and read the introductory portion of Hermanns and Strecker's 1999 article on rock avalanches in Argentina. In class, students receive data (assembled from figures in the article) on bedrock geology and physiography, as well as stereonets showing orientations of prominent joint sets, bedding, and foliations in the bedrock. Their task is to answer the question of why gigantic rock avalanches occur is some places but not others in this part of Argentina. Each student receives one of four possible data sets and works with a team to analyze the data and solve the problem for the team's area. Each team member must then individually explain his/her analysis to a group of three other students, one from each of the other teams, and the group then compares the four locations for similarities and differences. The activity gives students practice in interpreting geologic maps, using stereonets, and peer teaching. The activity also connects structural geology to another geoscience discipline.Short case example version: This is an abbreviated version of the jigsaw activity described above and focuses on only one of the rock avalanche areas.

  18. Submicron chip ESD protection schemes which avoid avalanching junctions

    Microsoft Academic Search

    E. R. Worley; R. Gupta; B. Jones; R. Kjar; C. Nguyen; M. Tennyson

    1995-01-01

    Because of leakage problems related to avalanche breakdown of salicided junctions, an array of ESD protection methods has been developed and tested which depend on forward biased diodes and normal MOSFET conduction. These methods include the case of multiple power supplies, the case where the pad voltage can exceed the power supply voltage, and the case where the pad voltage

  19. Sandpiles, avalanches, and the statistical mechanics of nonequilibrium stationary states

    Microsoft Academic Search

    Ashvin B. Chhabra; Mitchell J. Feigenbaum; Leo P. Kadanoff; Amy J. Kolan; Itamar Procaccia

    1993-01-01

    The scaling properties of three nontrivial one-dimensional avalanche models are analyzed. The first two of them are the local limited model with one open, one closed, and with periodic boundary conditions, respectively. A theory for the scaling properties of these models based on the existence of two fundamental length scales, which diverge in the thermodynamic limit, is developed. The third

  20. Avalanche Behavior and Statistical Properties in a Microcrack Coalescence Process

    Microsoft Academic Search

    Chunsheng Lu; David Vere-Jones; Hideki Takayasu

    1999-01-01

    Fracture owing to the coalescence of numerous microcracks can be described by a simple statistical model, where a coalescence event stochastically occurs as the number density of nucleated microcracks increases. Both numerical simulation and statistical analysis reveal that a microcrack coalescence process may display avalanche behavior and that the final failure is catastrophic. The cumulative distribution of coalescence events in

  1. Avalanche photodiode detection statistics for direct detection laser radar

    Microsoft Academic Search

    Douglas G. Youmans

    1992-01-01

    The detection statistics of avalanche photodiode detectors when used in laser radar systems are examined. In the laser radar systems considered here, a diffuse hard target is illuminated by a transmitted laser beam and the photons subtended by the receiving aperture and focused onto the detector obey negative-binomial statistics. The specific negative-binomial distribution is determined by the coherence length of

  2. High quantum efficiency GaP avalanche photodiodes.

    PubMed

    McIntosh, Dion; Zhou, Qiugui; Chen, Yaojia; Campbell, Joe C

    2011-09-26

    Gallium Phosphide (GaP) reach-through avalanche photodiodes (APDs) are reported. The APDs exhibited dark current less than a pico-ampere at unity gain. A quantum efficiency of 70% was achieved with a recessed window structure; this is almost two times higher than previous work. PMID:21996902

  3. Optical fibers and avalanche photodiodes for scintillator counters

    SciTech Connect

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

    1980-01-01

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

  4. Avalanches through windows: Multiscale visualization in magnetic thin films

    E-print Network

    Sethna, James P.

    Avalanches through windows: Multiscale visualization in magnetic thin films Alessandro Magni dynamics, but are strongly dependent on the size of the windows chosen. Here we investigate how to properly sub-window of the entire sample. Usually, windows of varying sizes are used, and the distributions

  5. Electron avalanche structure determined by random walk theory

    NASA Technical Reports Server (NTRS)

    Englert, G. W.

    1973-01-01

    A self-consistent avalanche solution which accounts for collective long range Coulomb interactions as well as short range elastic and inelastic collisions between electrons and background atoms is made possible by a random walk technique. Results show that the electric field patterns in the early formation stages of avalanches in helium are close to those obtained from theory based on constant transport coefficients. Regions of maximum and minimum induced electrostatic potential phi are located on the axis of symmetry and within the volume covered by the electron swarm. As formation time continues, however, the region of minimum phi moves to slightly higher radii and the electric field between the extrema becomes somewhat erratic. In the intermediate formation periods the avalanche growth is slightly retarded by the high concentration of ions in the tail which oppose the external electric field. Eventually the formation of ions and electrons in the localized regions of high field strength more than offset this effect causing a very abrupt increase in avalanche growth.

  6. Controlling microwave driven vortex avalanches by superconductivity stimulation

    NASA Astrophysics Data System (ADS)

    Lara, Antonio; Aliev, Farkhad G.; Silhanek, Alejandro V.; Moshchalkov, Victor V.

    2015-03-01

    The response of superconducting devices to electromagnetic radiation is a core concept implemented in diverse applications, ranging from the currently used voltage standard to single photon detectors in astronomy. Surprisingly, a sufficiently high power subgap radiation may stimulate superconductivity itself. Recently we have demonstrated the possibility of stimulating also type II superconductors, in which the radiation may cause nonlinear response of the vortex core. This effect opens the possibility of effective control over vortex avalanches. Here we report on a detailed study of superconductivity enhancement and avalanche control by GHz radiation in type II superconducting Pb films in the presence of vortices. The magnetic field dependence of the vortex related microwave losses in a film with periodic pinning reveals a reduced dissipation of mobile vortices in the stimulated regime due to a reduction of the core size. Results of numerical simulations support the validity of this conclusion. Moreover, we demonstrate that microwave stimulated superconductivity induces a notable increase of microwave depinning power needed to trigger avalanches in the proximity of vortex depinning frequencies. Our findings open new ways to control the vortex dissipation and depinning induced avalanches by using superconductivity stimulation.

  7. Avalanche shape and exponents beyond mean-field theory

    E-print Network

    Alexander Dobrinevski; Pierre Le Doussal; Kay Jörg Wiese

    2014-07-28

    Elastic systems, such as magnetic domain walls, density waves, contact lines, and cracks, are all pinned by substrate disorder. When driven, they move via successive jumps called avalanches, with power law distributions of size, duration and velocity. Their exponents, and the shape of an avalanche, defined as its mean velocity as function of time, have recently been studied. They are known approximatively from experiments and simulations, and were predicted from mean-field models, such as the Brownian force model (BFM), where each point of the elastic interface sees a force field which itself is a random walk. As we showed in EPL 97 (2012) 46004, the BFM is the starting point for an $\\epsilon = d_{\\rm c}-d$ expansion around the upper critical dimension, with $d_{\\rm c}=4$ for short-ranged elasticity, and $d_{\\rm c}=2$ for long-ranged elasticity. Here we calculate analytically the ${\\cal O}(\\epsilon)$, i.e. 1-loop, correction to the avalanche shape at fixed duration $T$, for both types of elasticity. The exact expression is well approximated by $\\left_T\\simeq [ Tx(1-x)]^{\\gamma-1} \\exp\\left( {\\cal A}\\left[\\frac12-x\\right]\\right)$, $0fixed avalanche size, not yet measured in experiments or simulations.

  8. Fast Thermal Shutdown of Tokamak Discharges Without Runaway Electron Avalanching

    Microsoft Academic Search

    M. Bakhtiari; R. Yoshino; Y Nishida

    2002-01-01

    The possibility of using massive quantities of injected deuterium with and without additional admixture of lesser quantities of higher-Z impurities to effect fast thermal shutdown of a tokamak discharge without causing runaway electron avalanching is systematically studied. It is found that various combinations of deuterium alone and deuterium with impurities (helium, nitrogen, argon, and krypton) can provide acceptable runaway-free thermal

  9. Avalanche Debris Detection Using Satellite- and Drone Based Radar and Optical Remote Sensing

    NASA Astrophysics Data System (ADS)

    Eckerstorfer, M.; Malnes, E.; Vickers, H.; Solbø, S. A.; Tøllefsen, A.

    2014-12-01

    The mountainous fjord landscape in the county of Troms, around its capital Tromsø in Northern Norway is prone to high avalanche activity during the snow season. Large avalanches pose a hazard to infrastructure, such as buildings and roads, located between the steep mountainsides and the fjords. A prolonged cold spell during January and February 2014 was followed by rapid new-snow loading during March 2014, inducing a significant avalanche cycle with many spontaneous, size D4 avalanches that affected major transport veins. During and shortly after the avalanche cycle of March 2014, we obtained 11 Radarsat-2 Ultrafine mode scenes, chosen according to reported avalanche activity. We further collected four Radarsat-2 ScanSAR mode scenes and two Landsat-8 scenes covering the entire county of Troms. For one particular avalanche, we obtained a drone-based orthophoto, from which a DEM of the avalanche debris surface was derived, using structure-from-motion photogrammetry. This enabled us to calculate the debris volume accurately. We detected avalanche debris in the radar images visually, by applying two detection algorithms that make use of the increased backscatter in avalanche debris. This backscatter increase is a product of increased snow water equivalent and surface roughness, roughly of the order of 3 dB. In addition, we applied a multi-temporal approach by repeatedly detecting avalanche debris at different acquisition times, as well as a multi-sensor approach, covering similar areas with different sensors. This multi-temporal and multi-sensor approach enabled us to map the spatial extent and magnitude of the March 2014 avalanche cycle in the county Troms. With ESA's Sentinel-1 satellite, providing high-resolution, large swath radar images with a short repeat cycle, a complete avalanche record for a forecasting region could become feasible. In this first test season, we detected more than 550 avalanches that were released during a one-month period over an area of roughly 3000 km2.

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

    NASA Astrophysics Data System (ADS)

    Turchaninova, A.

    2012-04-01

    The estimation of extreme avalanche runout distances, flow velocities, impact pressures and volumes is an essential part of snow engineering in mountain regions of Russia. It implies the avalanche hazard assessment and mapping. Russian guidelines accept the application of different avalanche models as well as approaches for the estimation of model input parameters. Consequently different teams of engineers in Russia apply various dynamics and statistical models for engineering practice. However it gives more freedom to avalanche practitioners and experts but causes lots of uncertainties in case of serious limitations of avalanche models. We discuss these problems by presenting the application results of different well known and widely used statistical (developed in Russia) and avalanche dynamics models for several avalanche test sites in the Khibini Mountains (The Kola Peninsula) and the Caucasus. The most accurate and well-documented data from different powder and wet, big rare and small frequent snow avalanche events is collected from 1960th till today in the Khibini Mountains by the Avalanche Safety Center of "Apatit". This data was digitized and is available for use and analysis. Then the detailed digital avalanche database (GIS) was created for the first time. It contains contours of observed avalanches (ESRI shapes, more than 50 years of observations), DEMs, remote sensing data, description of snow pits, photos etc. Thus, the Russian avalanche data is a unique source of information for understanding of an avalanche flow rheology and the future development and calibration of the avalanche dynamics models. GIS database was used to analyze model input parameters and to calibrate and verify avalanche models. Regarding extreme dynamic parameters the outputs using different models can differ significantly. This is unacceptable for the engineering purposes in case of the absence of the well-defined guidelines in Russia. The frequency curves for the runout distance in different avalanche sites were constructed using the field data. It allowed us to assess the probability (return period) of the calculated extreme runout distances using obtained frequency curves. Avalanche zoning is not yet used by land planning authorities to prevent construction in avalanche hazard zones in Russia. Our approach can be used for the future development of avalanche zoning in Russia.

  11. Electroded avalanche amorphous selenium (a-Se) photosensor.

    PubMed

    Bubon, Oleksandr; Decrescenzo, Giovanni; Zhao, Wei; Ohkawa, Yuji; Miyakawa, Kazunori; Matsubara, Tomoki; Kikuchi, Kenji; Tanioka, Kenkichi; Kubota, Misao; Rowlands, John A; Reznik, Alla

    2012-05-01

    Although avalanche amorphous selenium (a-Se) is a very promising photoconductor for a variety of imaging applications, it is currently restricted to applications with electron beam readout in vacuum pick-up tube called a High-gain Avalanche Rushing Photoconductor (HARP). The electron beam readout is compatible with high definition television (HDTV) applications, but for use in solid-state medical imaging devices it should be replaced by an electronic readout with a two-dimensional array of metal pixel electrodes. However, due to the high electric field required for avalanche multiplication, it is a technological challenge to avoid possible dielectric breakdown at the edges, where electric field experiences local enhancement. It has been shown recently that this problem can be overcome by the use of a Resistive Interface Layer (RIL) deposited between a-Se and the metal electrode, however, at that time, at a sacrifice in transport properties.Here we show that optimization of RIL deposition technique allows for electroded avalanche a-Se with transport properties and time performance previously not achievable with any other a-Se structures. We have demonstrated this by detailed analysis of transport properties performed by Time-of-Flight (TOF) technique. Our results showed that a stable gain of 200 is reached at 104 V/?m for a 15-?m thick a-Se layer, which is the maximum theoretical gain for this thickness. We conclude that RIL is an enabling technology for practical implementation of solid-state avalanche a-Se image sensors. PMID:23115545

  12. Ice insulation by rock avalanche debris: the Mt. Cook (1991) and Beatrice (2004) rock avalanches, Southern Alps, New Zealand

    NASA Astrophysics Data System (ADS)

    Reznichenko, Natalya V.; Davies, Tim R.; Shulmeister, James; Winkler, Stefan

    2010-05-01

    The formation of terminal moraines mainly results from glacier changes in response to climate variations. But glaciers may also react sensitively to increased debris cover caused by large-scale failure of bedrock slopes. Catastrophic rock avalanches are a major source of sediment in active orogens like e.g. the Southern Alps, New Zealand (Shulmeister et al., 2009). They often occur as a result of earthquakes, and also due to slope failure driven in the longer term by regional uplift. Rock avalanche deposits can drastically alter glacier mass balance through reduced ablation and consequential altered flow rates, and can contribute to glacier moraine formation (see e.g. Hewitt, 2005, 2009; Shulmeister et al., 2009). Consequently, the frequently-assumed linkage between terminal moraine formation and climate forcing may need to be reconsidered. Especially for the investigation of the regional Holocene glacier and climate chronologies it is essential to separate and assess the tectonic/coseismic impact on terminal moraine formation. In order to investigate the role of catastrophic landslide events in moraine formation, Ground Penetrating Radar (GPR) surveys of rock avalanche deposits on the Tasman and Hooker Glaciers, Southern Alps, New Zealand, were compared with laboratory experiments of the debris cover effect on underlying ice ablation. The 1991 Mt. Cook rock avalanche deposit on the Tasman Glacier is up to 10 m thick and has caused a 25 m high ridge to form at the upvalley edge of the deposit. The smaller 2004 Mt. Beatrice rock avalanche onto Hooker Glacier has formed an elevated plateau with similar raised edges because of reduced ice melting under the rock avalanche deposit. The reduction of ice-surface ablation on the glaciers is compared with laboratory data on ice ablation rates under various thickness of debris-cover, under controlled conditions with replication of diurnal temperature, radiation cycles and rainfall conditions. The latest results are presented, accompanied by some remarks on related future research activities. Hewitt, K. (2005): The Karakoram Anomaly? Glacier expansion and the ‘elevation effect', Karakoram Himalaya. Mountain Research and Development 25, 332 - 340. Hewitt, K. (2009): Rock avalanches that travel onto glaciers and related developments, Karakoram Himalaya, Inner Asia. Geomorphology 103, 66 - 79. Shulmeister, J.; Davies, T.R.; Evans, D.J.A.; Hyatt, O.M. & Tovar, D.S. (2009): Catastrophic landslides, glacier behaviour and moraine formation - a view from an active plate margin. Quaternary Science Reviews 28, 1085 - 1096.

  13. 2500 University Drive N.W., Calgary, Alberta, Canada T2N 1N4 www.ucalgary.ca Post-doctoral opportunity in snow avalanche research

    E-print Network

    Jamieson, Bruce

    forecasting of deep slab avalanches 4. Statistical avalanche runout models for land-use planning 5. Coupled-doctoral opportunity in snow avalanche research 25 January 2012 The Applied Snow and Avalanche Research group-based research on risk- based decisions on snow avalanches and related topics. Current topics for the group

  14. 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.

  15. A New Method for the Estimation of Avalanche Distance Exceeded Probabilities

    NASA Astrophysics Data System (ADS)

    Barbolini, Massimiliano; Cappabianca, Federica; Savi, Fabrizio

    2003-11-01

    A crucial point in any methodology for avalanche hazard assessment is the evaluation of avalanche distance exceeded probability, i.e., the annual probability that any assigned location along a given path is reached or exceeded by an avalanche. Typically this problem is faced by estimating the snow volume in the starting zone that is likely to accumulate an average every T years by statistical analysis of snowfall record, and then using this volume as input to an appropriately calibrated avalanche dynamics model to determine the runout distances for this design event. This methodology identifies the areas that can be affected by an avalanche for the considered value of the return period (i.e. the average interval of time for a certain event to repeat itself), T. However, it does not allow us to evaluate the actual avalanche encounter probability for any given point in the runout zone. In the present work this probability is computed by numerical integration of the expression P(x) = ?0? P*(V)f(V) dV, where f is the probability density function (PDF) of the avalanche release volume V, and P* is the probability of the point x being reached or passed by an avalanche if the release volume is V; this latter probability is calculated by avalanche dynamics simulations. The procedure is implemented using a one-dimensional hydraulic-continuum avalanche dynamic model, calibrated on data from different Italian Alpine ranges, and is applied to a real world hazard mapping problem.

  16. 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.

  17. Cross-comparison of meteorological and avalanche data for characterising avalanche cycles: The example of December 2008 in the eastern part of the French Alps

    Microsoft Academic Search

    N. Eckert; C. Coleou; H. Castebrunet; M. Deschatres; G. Giraud; J. Gaume

    2010-01-01

    In December 2008, an intense avalanche cycle occurred in the eastern part of the southern French Alps. Southerly atmospheric fluxes that progressively evolved into an easterly return caused important snowfalls with return periods up to 10years. Cold temperatures and drifting snow had important aggravating effects. The return period for the number of avalanches was above 50years in two massifs and

  18. Direct observation of avalanche scintillations in a THGEM-based two-phase Ar avalanche detector using Geiger-mode APD

    NASA Astrophysics Data System (ADS)

    Bondar, A.; Buzulutskov, A.; Grebenuk, A.; Sokolov, A.; Akimov, D.; Alexandrov, I.; Breskin, A.

    2010-08-01

    A novel concept of optical signal recording in cryogenic two-phase avalanche detectors, with Geiger-mode Avalanche Photodiodes (G-APD) measuring avalanche-scintillation photons in a thick Gas Electron Multiplier (THGEM), has been studied in view of its potential applications in rare-event experiments. The effective detection of avalanche scintillations in THGEM holes has been demonstrated in two-phase Ar with a bare G-APD without wavelength shifter, i.e. insensitive to VUV emission of Ar. At gas-avalanche gain of 400 and under ±70° viewing-angle, the G-APD yielded 640 photoelectrons (pe) per 60 keV X-ray converted in liquid Ar; this corresponds to 0.7 pe per initial (prior to multiplication) electron. The avalanche-scintillation light yield measured by the G-APD was about 0.7 pe per avalanche electron, extrapolated to 4? acceptance. The avalanche scintillations observed occurred presumably in the near infrared (NIR) where G-APDs may have high sensitivity. The measured scintillation yield is similar to that observed by others in the VUV. Other related topics discussed in this work are the G-APD's single-pixel and quenching resistor characteristics at cryogenic temperatures.

  19. Structural vulnerability assessment using reliability of slabs in avalanche area

    NASA Astrophysics Data System (ADS)

    Favier, Philomène; Bertrand, David; Eckert, Nicolas; Naaim, Mohamed

    2013-04-01

    Improvement of risk assessment or hazard zoning requires a better understanding of the physical vulnerability of structures. To consider natural hazard issue such as snow avalanches, once the flow is characterized, highlight on the mechanical behaviour of the structure is a decisive step. A challenging approach is to quantify the physical vulnerability of impacted structures according to various avalanche loadings. The main objective of this presentation is to introduce methodology and outcomes regarding the assessment of vulnerability of reinforced concrete buildings using reliability methods. Reinforced concrete has been chosen as it is one of the usual material used to build structures exposed to potential avalanche loadings. In avalanche blue zones, structures have to resist to a pressure up to 30kPa. Thus, by providing systematic fragility relations linked to the global failure of the structure, this method may serve the avalanche risk assessment. To do so, a slab was numerically designed. It represented the avalanche facing wall of a house. Different configuration cases of the element in stake have been treated to quantify numerical aspects of the problem, such as the boundary conditions or the mechanical behaviour of the structure. The structure is analysed according to four different limit states, semi-local and global failures are considered to describe the slab behaviour. The first state is attained when cracks appear in the tensile zone, then the two next states are described consistent with the Eurocode, the final state is the total collapse of the structure characterized by the yield line theory. Failure probability is estimated in accordance to the reliability framework. Monte Carlo simulations were conducted to quantify the fragility to different loadings. Sensitivity of models in terms of input distributions were defined with statistical tools such as confidence intervals and Sobol's indexes. Conclusion and discussion of this work are established to well determine contributions, limits and future needs or developments of the research. First of all, this study provides spectrum of fragility curves of reinforced concrete structures which could be used to improve risk assessment. Second, the influence of the failure criterion picked up in this survey are discussed. Then, the weight of the statistical distribution choice is analysed. Finally, the limit between vulnerability and fragility relations is set up to establish the boundary use of our approach.

  20. 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.

  1. Characterization of midwave infrared InSb avalanche photodiode

    NASA Astrophysics Data System (ADS)

    Abautret, J.; Perez, J. P.; Evirgen, A.; Rothman, J.; Cordat, A.; Christol, P.

    2015-06-01

    This paper focuses on the InSb material potential for the elaboration of Avalanche Photodiodes (APD) for high performance infrared imaging applications, both in passive or active mode. The first InSb electron-APD structure was grown by molecular beam epitaxy, processed and electrically characterized. The device performances are at the state of the art for the InSb epi-diode technology, with a dark current density J(-50 mV) = 32 nA/cm2 at 77 K. Then, a pure electron injection was performed, and an avalanche gain, increasing exponentially, was observed with a gain value near 3 at -4 V at 77 K. The Okuto-Crowell model was used to determine the electron ionization coefficient ?(E) in InSb, and the InSb gain behavior is compared with the one of InAs and MCT APDs.

  2. Robust quantum random number generator based on avalanche photodiodes

    E-print Network

    Fang-Xiang Wang; Chao Wang; Wei Chen; Shuang Wang; Fu-Sheng Lv; De-Yong He; Zhen-Qiang Yin; Hong-Wei Li; Guang-Can Guo; Zheng-Fu Han

    2015-06-18

    We propose and demonstrate a scheme to realize a high-efficiency truly quantum random number generator (RNG) at room temperature (RT). Using an effective extractor with simple time bin encoding method, the avalanche pulses of avalanche photodiode (APD) are converted into high-quality random numbers (RNs) that are robust to slow varying noise such as fluctuations of pulse intensity and temperature. A light source is compatible but not necessary in this scheme. Therefor the robustness of the system is effective enhanced. The random bits generation rate of this proof-of-principle system is 0.69 Mbps with double APDs and 0.34 Mbps with single APD. The results indicate that a high-speed RNG chip based on the scheme is potentially available with an integrable APD array.

  3. Macroscopic control parameter for avalanche models for bursty transport

    SciTech Connect

    Chapman, S. C.; Rowlands, G. [Centre for Fusion, Space and Astrophysics, University of Warwick, Coventry CV4 7AL (United Kingdom); Watkins, N. W. [Physical Sciences Division, British Antarctic Survey (NERC), Cambridge CB3 0ET (United Kingdom)

    2009-01-15

    Similarity analysis is used to identify the control parameter R{sub A} for the subset of avalanching systems that can exhibit self-organized criticality (SOC). This parameter expresses the ratio of driving to dissipation. The transition to SOC, when the number of excited degrees of freedom is maximal, is found to occur when R{sub A}{yields}0. This is in the opposite sense to (Kolmogorov) turbulence, thus identifying a deep distinction between turbulence and SOC and suggesting an observable property that could distinguish them. A corollary of this similarity analysis is that SOC phenomenology, that is, power law scaling of avalanches, can persist for finite R{sub A} with the same R{sub A}{yields}0 exponent if the system supports a sufficiently large range of lengthscales, necessary for SOC to be a candidate for physical (R{sub A} finite) systems.

  4. Spatiotemporal Chaotic unjamming and jamming in granular avalanches

    E-print Network

    Ziwei Wang; Jie Zhang

    2014-10-23

    We have investigated the spatiotemporal chaotic dynamics of unjamming and jamming of particles in a toy-model system -- a rotating drum partially filled with bidisperse disks to create avalanches. The magnitudes of the first Lyapunov vector $\\delta u(t)$ and velocity $v(t)$ of particles are directly measured for the first time to yield insights into their spatial correlation $C_{\\delta u,v}$, which is stronger near the unjamming but is weaker near the jamming transition, consistent with the recent work of Banigan et al., Nature Phys. $\\bf{9}$, 288, (2013). $v(t)$ shows rich dynamics: it grows exponentially for unstable particles and keeps increasing despite stochastic interactions; after the maximum, it decays with large fluctuations. Hence the spatiotemporal chaotic dynamics of avalanche particles are entangled, causing temporal correlations of macroscopic quantities of the system. We propose a simple model for these observations.

  5. Avalanche size distributions in mean field plastic yielding models

    E-print Network

    E. A. Jagla

    2015-06-02

    I discuss the size distribution ${\\cal N}(S)$ of avalanches occurring at the yielding transition of mean field (i.e., Hebraud-Lequeux) models of amorphous solids. The size distribution follows a power law dependence of the form: ${\\cal N}(S)\\sim S^{-\\tau}$. However (contrary to what is found in its depinning counterpart) the value of $\\tau$ depends on details of the dynamic protocol used. For random triggering of avalanches I recover the $\\tau=3/2$ exponent typical of mean field models, which in particular is valid for the depinning case. However, for the physically relevant case of external loading through a quasistatic increase of applied strain, a smaller exponent (close to 1) is obtained. This result is rationalized by mapping the problem to an effective random walk in the presence of a moving absorbing boundary.

  6. Weathering processes implied from analysis of small Martian avalanche chutes

    NASA Technical Reports Server (NTRS)

    Sullivan, R.

    1992-01-01

    It has been proposed that the smaller features of martian spur and gully slope morphology, located along the upper walls of Valles Marineris, are avalanche chutes. A three-dimensional stability back-analysis technique was developed and applied to these small avalanche chutes, yielding average values of cohesion and angle of internal friction for the mobile layer materials on these slopes at the time of each slope failure. Generally, the analysis showed that at the time of each slope failure material strengths had been reduced to those of moderately cohesive debris down through depths of tens of meters. These results have implications and possible constraints for the nature and rate of martian weathering processes.

  7. Avalanche amplification of a single exciton in a semiconductor nanowire

    NASA Astrophysics Data System (ADS)

    Bulgarini, Gabriele; Reimer, Michael E.; Hocevar, Moïra; Bakkers, Erik P. A. M.; Kouwenhoven, Leo P.; Zwiller, Val

    2012-07-01

    Interfacing single photons and electrons is a crucial element in sharing quantum information between remote solid-state qubits. Semiconductor nanowires offer the unique possibility of combining optical quantum dots with avalanche photodiodes, thus enabling the conversion of an incoming single photon into a macroscopic current for efficient electrical detection. Currently, millions of excitation events are required to perform electrical readout of an exciton qubit state. Here, we demonstrate multiplication of carriers from only a single exciton generated in a quantum dot after tunnelling into a nanowire avalanche photodiode. Owing to the large amplification of both electrons and holes (>104), we reduce by four orders of magnitude the number of excitation events required to electrically detect a single exciton generated in a quantum dot. This work represents a significant step towards achieving single-shot electrical readout and offers a new functionality for on-chip quantum information circuits.

  8. Amorphous silicon/silicon carbide superlattice avalanche photodiodes

    NASA Astrophysics Data System (ADS)

    Jwo, Shin-Cherng; Wu, Meng-Tsang; Fang, Jean-Kuen; Hong, Jyh-Wong; Chen, Yu-Wen

    1988-08-01

    An a-Si/SiC:H superlattice avalanche photodiode (SAPD) has been successfully fabricated on an ITO/glass substrate by plasma-enhanced chemical vapor deposition. The room-temperature electron and hole impact ionization rates, alpha and beta, have been determined for the a-Si/SiC:H superlattice structure by photocurrent multiplication measurements. The ratio alpha/beta is 6.5 at a maximum electric field of 2.08 x 10 to the 5th V/cm. Avalanche multiplications in the superlattice layer yields an optical gain of 184 at a reverse bias VR = 20 V and an incident light power Pin = 5 micro-W. An LED-SAPD photocouple exhibited a switching time of 4.5 micro-s at a load resistance R = 1.8 k-Ohms.

  9. Thin multiplication region InAlAs homojunction avalanche photodiodes

    NASA Astrophysics Data System (ADS)

    Lenox, C.; Yuan, P.; Nie, H.; Baklenov, O.; Hansing, C.; Campbell, J. C.; Holmes, A. L.; Streetman, B. G.

    1998-08-01

    Low excess noise in avalanche photodetectors (APDs) is desired for improved sensitivity and high-frequency performance. Gain and noise characteristics are measured for InAlAs p-i-n homojunction APDs that were grown with varying i-region widths on InP by molecular beam epitaxy. The effective ionization ratio k (?/?) determined by noise measurements shows a dependence on multiplication region width, reducing from 0.31 to 0.18 for multiplication region thicknesses of 1600-200 nm. This trend follows previously shown results in AlGaAs-based APDs, which exhibit reduced excess noise due to nonlocal multiplication effects. These results show that this effect is a characteristic of thin avalanche regions and is not a material-specific phenomenon.

  10. Noise and Multiplication Measurements in InSb Avalanche Photodiodes

    Microsoft Academic Search

    R. D. Baertsch

    1967-01-01

    Multiplication and noise measurements on InSb avalanche photodiodes have been made from 77° to 125°K. For the diodes studied, the electron ionization rate is much larger than the hole ionization rate and depends only weakly on the field for fields between 5×103 and 104 V?cm. The electron ionization rate increases and the breakdown voltage decreases with increasing temperature. The dependence

  11. Large-current radiator with avalanche transistor switch

    Microsoft Academic Search

    K. A. Lukin; G. P. Pochanin; S. A. Masalov

    1997-01-01

    The development and experimental investigation of a large-current radiator (LCR) with a pulse generator using avalanche transistors is reported. The LCR is intend for radiating nonsinusoidal pulse electromagnetic waves with a duration of 2 ns. The radiated field strengths in both the near and the far field are measured. The LCR described produces magnetic field strengths of about 4.2 mA\\/m

  12. Subnanosecond timing with large area avalanche photodiodes and LSO scintillator

    Microsoft Academic Search

    M. Moszynski; T. Ludziejewski; D. Wolski; W. Klamra; M. Szawlowski; M. Kapusta

    1996-01-01

    The detection properties of 10 mm and 16 mm diameter bevelled-edge avalanche photodiodes fitted with LSO crystal were measured using ?-sources. Among the properties measured were the electron-hole pair yield, time resolution and energy resolution. These detectors provide excellent time resolution of 570±17 ps for 60Co ?-rays with the energy threshold set at 1 MeV. The energy resolution of the

  13. LSO\\/photodiode and LSO avalanche photodiode detectors

    Microsoft Academic Search

    C. L. Melcher

    1992-01-01

    The performance of Lu2(1-x)Ce2x(SiO4 )O (LSO) detectors was assessed under laboratory conditions. The PMT (photomultiplier tube) and the APD (avalanche photodiode) gave the same energy resolution when used with LSO, although the APD displayed a thermal noise threshold of 30 keV compared to <5 keV for the PMT. The PD resulted in a power energy resolution of 14% and also

  14. Novel type of avalanche photodetector with Geiger mode operation

    Microsoft Academic Search

    V. Golovin; V. Saveliev

    2004-01-01

    A novel type of avalanche photodetector with Geiger mode operation, known as Silicon Photomultiplier (SiPM) is presented. Development of photodetectors for the detection of low intensity photon flux is one of the critical issues for experimental physics, medical tomography and many others. The structure of the photodetector is based on metal–resistor semiconductor (MRS) microcells with a density of 1000\\/mm2, operating

  15. Electronic tuning effects in the read microwave avalanche diode

    Microsoft Academic Search

    M. Gilden; M. E. Hines

    1966-01-01

    Read's theory of the negative-resistance avalanche diode has been examined in detail for the small-signal case. The space-charge wave approach has been used in the analysis leading directly to a simple equivalent circuit and a general expression for the small-signal impedance which includes the significant design and operating parameters. The theory indicates that strong tuning effects will occur through variation

  16. Fracture Mechanical Models of Dry Slab Avalanche Release

    Microsoft Academic Search

    David M. McClung

    1981-01-01

    Experimental evidence shows that snow is a pressure sensitive, dilatant, strain-softening material in slow, constant rate, shear deformation. When strain softening initiates in a weak layer underneath a snow slab, avalanche release is hypothesized to be possible with or without additional loading. Specifically, two cases are discussed: (1) a shear-crack-like disturbance can initiate after formation of a slip surface in

  17. Receiver characteristics of laser altimeters with avalanche photodiodes

    NASA Technical Reports Server (NTRS)

    Sun, Xiaoli; Davidson, Frederic M.; Boutsikaris, Leo; Abshire, James B.

    1992-01-01

    The receiver characteristics of a laser altimeter system containing an avalanche photodiode photodetector are analyzed using the Gaussian approximation, the saddle-point approximation, and a nearly exact analysis. The last two methods are shown to yield very similar results except when the background noise is extremely low and the probability of false alarm is high. However, the Gaussian approximation method is shown to cause significant errors even under relatively high levels of background noise and received signal energy.

  18. Flux avalanches in superconducting films with periodic arrays of holes.

    SciTech Connect

    Vlasko-Vlasov, V.; Welp, U.; Metlushko, V.; Crabtree, G. W.; Materials Science Division; Inst. of Solid State Physics RAS

    2000-01-01

    The magnetic flux dynamics in Nb films with periodic hole arrays is studied magneto-optically. Flux motion in the shape of microavalanches along {l_brace}100{r_brace} and {l_brace}110{r_brace} directions of the hole lattice is observed. At lower temperatures anisotropic large scale thermo-magnetic avalanches dominate flux entry and exit. At T-T{sub c} critical-state-like field patterns periodically appear at fractions of the matching field.

  19. Investigation of avalanche photodiodes radiation hardness for baryonic matter studies

    E-print Network

    Kushpil, V; Ladygin, V P; Kugler, A; Kushpil, S; Svoboda, O; Tlustý, P

    2015-01-01

    Modern avalanche photodiodes (APDs) with high gain are good device candidates for light readout from detectors applied in relativistic heavy ion collisions experiments. The results of the investigations of the APDs properties from Zecotek, Ketek and Hamamatsu manufacturers after irradiation using secondary neutrons from cyclotron facility U120M at NPI of ASCR in \\v{R}e\\v{z} are presented. The results of the investigations can be used for the design of the detectors for the experiments at NICA and FAIR.

  20. Avalanche localization and crossover scaling in amorphous plasticity.

    PubMed

    Budrikis, Zoe; Zapperi, Stefano

    2013-12-01

    We perform large-scale simulations of a two-dimensional lattice model for amorphous plasticity with random local yield stresses and long-range quadrupolar elastic interactions. We show that as the external stress increases towards the yielding phase transition, the scaling behavior of the avalanches crosses over from mean-field theory to a different universality class. This behavior is associated with strain localization, which significantly depends on the short-range properties of the interaction kernel. PMID:24483457

  1. A numerical model of avalanche breakdown in MOSFET's

    Microsoft Academic Search

    T. Toyabe; K. Yamaguchi; S. Asai; M. S. Mock

    1978-01-01

    An accurate numerical model of avalanche breakdown in MOSFET's is presented. Features of this model are a) use of an accurate electric-field distribution calculated by a two-dimensional numerical analysis, b) introduction of multiplication factors for a high-field path and the channel current path, and c) incorporation of the feedback effect of the excess substrate current induced by impact ionization into

  2. Theory of electron-avalanche breakdown in solids

    Microsoft Academic Search

    M. Sparks; D. L. Mills; R. Warren; T. Holstein; A. A. Maradudin; L. J. Sham; E. Loh Jr.; D. F. King

    1981-01-01

    Electron-avalanche breakdown in solids is explained by a theory that agrees with experimental results for the magnitude of the breakdown field and its temperature dependence, pulse-duration dependence, material-to-material variation, and wavelength dependence for lambda>=1 mu m. The good agreement between experiment and theory with no parameters adjusted is obtained by using improved magnitudes and energy dependences of the electron-phonon relaxation

  3. Probing Avalanche Dynamics using Speckle-Visibility Spectroscopy

    Microsoft Academic Search

    Adam Abate; Hiroaki Katsuragi; Doug Durian

    2007-01-01

    We apply a new light scattering technique called Speckle-Visibility Spectroscopy to the study of avalanches. By directly relating the rate of change of the scattered speckle pattern to the fluctuation dynamics of the flowing sand particles, we attain a precision of 0.1 mm\\/s. Running for 35 hours at 58 kHz, we simultaneously observe the microscopic short-time fluctuations of the sand

  4. Electric and Magnetic Detection of Avalanche Behavior in Chemical Reactions

    Microsoft Academic Search

    James Claycomb; M. Nersesyan; Martin Miller; John Miller; Dan Luss

    2001-01-01

    Intermittent bursts of chemical activity, displaying avalanche like behavior, have been observed in liquid-solid replacement reactions between metals and liquid electrolytes by measuring the time-dependent electric and magnetic fields. Magnetic measurements are conducted using a high-Tc SQUID inside a magnetically shielded enclosure. Electric potential difference measurements exhibit temporal behavior that is qualitatively similar to the recorded magnetic signals. The observed

  5. Thin multiplication region InAlAs homojunction avalanche photodiodes

    Microsoft Academic Search

    C. Lenox; P. Yuan; H. Nie; O. Baklenov; C. Hansing; J. C. Campbell; A. L. Holmes; B. G. Streetman

    1998-01-01

    Low excess noise in avalanche photodetectors (APDs) is desired for improved sensitivity and high-frequency performance. Gain and noise characteristics are measured for InAlAs p-i-n homojunction APDs that were grown with varying i-region widths on InP by molecular beam epitaxy. The effective ionization ratio k (beta\\/alpha) determined by noise measurements shows a dependence on multiplication region width, reducing from 0.31 to

  6. Design Of Reliable High Voltage Avalanche Transistor Pulsers

    Microsoft Academic Search

    E. S. Fulkerson; R. Booth

    1994-01-01

    Avalanche transistor based pulsers were developed for use as pockel cell drivers and for impulse radar work. The output voltages range from 1 to 8kV, with rise times of 100 to 200 picoseconds and repetition rates in excess of 1kHz. Several of these units have been in service for over a year with no failures. The design of these units

  7. Design of reliable high voltage avalanche transistor pulsers

    NASA Astrophysics Data System (ADS)

    Fulkerson, E. S.; Booth, R.

    1994-06-01

    Avalanche transistor based pulsers were developed for use as pockel cell drivers and for impulse radar work. The output voltages range from 1 to 8kV, with rise times of 100 to 200 picoseconds and repetition rates in excess of 1kHz. Several of these units have been in service for over a year with no failures. The design of these units is discussed in detail, including circuit design, component selection, diagnostics, and the all important physical layout.

  8. High voltage fast ramp pulse generation using avalanche transistor

    Microsoft Academic Search

    Liu Jinyuan; Shan Bing; Chang Zenghu

    1998-01-01

    The authors have developed an avalanche transistor based pulser for use as a pockel cells driver and for gating a microchannel plate. The output voltage ranges from 1-4 kV to 50 Omega, with fall times of 200-300 ps. The repetition rate is less than 1 kHz. The trig jitter is less than 100 ps. Trig delay is about 8 ns.

  9. High voltage fast ramp pulse generation using avalanche transistor

    NASA Astrophysics Data System (ADS)

    Jinyuan, Liu; Bing, Shan; Zenghu, Chang

    1998-08-01

    The authors have developed an avalanche transistor based pulser for use as a pockel cells driver and for gating a microchannel plate. The output voltage ranges from 1-4 kV to 50 ?, with fall times of 200-300 ps. The repetition rate is less than 1 kHz. The trig jitter is less than 100 ps. Trig delay is about 8 ns.

  10. Internal cancellation of spikes using two avalanche photodiodes in series for single photon detection

    Microsoft Academic Search

    Yun Liu; Qing-Lin Wu; Zheng-Fu Han; Yi-Min Dai; Guang-Can Guo

    2010-01-01

    We propose a method of improving the performance of InGaAs\\/InP avalanche photodiodes by using two avalanche photodiodes in series as single photon detectors for 1550-nm wavelength. In this method, the raw single photon avalanche signals are not attenuated, thus a high signal-to-noise ratio can be obtained compared with the existing results. The performance of the scheme is investigated and the

  11. Fractures in weak snowpack layers in relation to slab avalanche release

    Microsoft Academic Search

    Alec Francois Guillaume van Herwijnen

    2005-01-01

    The vast majority of recreational avalanche incidents are caused by human-triggering of the slab avalanche. Specific snowpack characteristics, including hardness difference and difference in crystal size across the failure layer, associated with skier-triggered dry slab avalanches were identified. The relation of these snowpack variables with fracture initiation and fracture propagation, both of which are required for skier-triggering, was investigated. The

  12. Avalanche statistics and time-resolved grain dynamics for a driven heap

    Microsoft Academic Search

    A. R. Abate; H. Katsuragi; D. J. Durian

    2007-01-01

    We probe the dynamics of intermittent avalanches caused by steady addition of grains to a quasi-two-dimensional heap. To characterize the time-dependent average avalanche flow speed v(t) , we image the top free surface. To characterize the grain fluctuation speed deltav(t) , we use speckle-visibility spectroscopy. During an avalanche, we find that the fluctuation speed is approximately one-tenth the average flow

  13. The Safran-Crocus-Mepra results and avalanches in Iceland 2001-2002

    NASA Astrophysics Data System (ADS)

    Haraldsdóttir, S.; Ólafsson, H.; Durand, Y.; Giraud, G.; Mérindol, L.

    2003-04-01

    Numerical models, Safran, Crocus and Mepra (SCM) have been developed by Météo-France to predict the evolution of the snow pack and its stability with respect to avalanches. The Safran-Crocus models have been adapted to Icelandic weather conditions, where most avalanches are caused by heavy snow precipitation in strong winds. The adapted SCM-models were run operationally during the winter 2001-2002 for testing the avalanche danger prediction, knowing that the models did not take into account the transport of snow by wind. The performance of the models was analysed during 19 avalanche cycles, each consisting of 2-21 recorded avalanches. First indicators of avalanche danger in the models are weak snow layers, leading to moderate, or in most of the 19 cases, high danger of avalanches triggered by human activities. In 5 of these 19 avalanche cycles, the models predicted moderate or high natural avalanche danger. Besides the detection of weak layers the models provide an estimation of the amount of snow available for transport by wind. This together with the fact that the recorded mean wind speed exceeded 15 m/s in all cases make it possible to construct natural avalanche prediction criteria, where the key parameters from the models are the stability of the snow pack and an indication of the availability of snow for transport by wind. Used with the wind speed from observations or numerical weather prediction models the effect of blowing snow can be estimated. As a result the models turn out to be a very useful tool for predicting avalanche danger when considering simultaneously the blowing snow and its potential accumulation in the avalanche starting zones.

  14. 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.

  15. Depositional features and transportation mechanism of valley-filling Iwasegawa and Kaida debris avalanches, Japan

    Microsoft Academic Search

    Shinji Takarada; Tadahide Ui; Yuko Yamamoto

    1999-01-01

    The depositional features of two valley-filling debris avalanche deposits were studied to reveal their transportation and\\u000a depositional mechanisms. The valley-filling Iwasegawa debris avalanche deposit (ca. 0.1 km3) is distributed along the valleys at the southeastern foot of Tashirodake Volcano, northern Honshu, Japan. Debris-avalanche\\u000a blocks range in size from <35?m proximally to <10?m in the distal zone and consist dominantly of

  16. A random kinetic energy model for rock avalanches: Eight case studies

    Microsoft Academic Search

    T. Preuth; P. Bartelt; O. Korup; B. W. McArdell

    2010-01-01

    We apply a numerical avalanche dynamics model to predict runout, velocity, and spatial distribution of deposit thickness of eight rock avalanches. The model solves depth-averaged mass and momentum conservation equations for avalanche flow in general three-dimensional terrain using a second-order finite-volume method. In this paper, these standard mass and momentum equations are supplemented with an additional relation describing the production

  17. Antimonide-based Geiger-mode avalanche photodiodes for SWIR and MWIR photon counting

    Microsoft Academic Search

    Erik K. Duerr; Michael J. Manfra; Mohamed A. Diagne; Robert J. Bailey; John J. Zayhowski; Joseph P. Donnelly; Michael K. Connors; Michael J. Grzesik; George W. Turner

    2010-01-01

    At MIT Lincoln Laboratory, avalanche photodiodes (APDs) have been developed for both 2-mum and 3.4-mum detection using the antimonide material system. These bulk, lattice-matched detectors operate in Geiger mode at temperatures up to 160 K. The 2-mum APDs use a separate-absorber-multiplier design with an InGaAsSb absorber and electron-initiated avalanching in the multiplier. These APDs have exhibited normalized avalanche probability (product

  18. Avalanches in the Bean critical-state model

    SciTech Connect

    Barford, W. [Department of Physics, The University of Sheffield, Sheffield, S3 7HR (United Kingdom)] [Department of Physics, The University of Sheffield, Sheffield, S3 7HR (United Kingdom)

    1997-07-01

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

  19. Experimental Investigation of Plastic Deformations Before Granular Avalanche

    E-print Network

    Axelle Amon; Roman Bertoni; Jérôme Crassous

    2012-11-23

    We present an experimental study of the deformation inside a granular material that is progressively tilted. We investigate the deformation before the avalanche with a spatially resolved Diffusive Wave Spectroscopy setup. At the beginning of the inclination process, we first observe localized and isolated events in the bulk, with a density which decreases with the depth. As the angle of inclination increases, series of micro-failures occur periodically in the bulk, and finally a granular avalanche takes place. The micro-failures are observed only when the tilt angles are larger than a threshold angle much smaller than the granular avalanche angle. We have characterized the density of reorganizations and the localization of micro-failures. We have also explored the effect of the nature of the grains, the relative humidity conditions and the packing fraction of the sample. We discuss those observations in the framework of the plasticity of granular matter. Micro-failures may then be viewed as the result of the accumulation of numerous plastic events.

  20. Three-dimensional mapping of dislocation avalanches: clustering and space/time coupling.

    PubMed

    Weiss, Jérôme; Marsan, David

    2003-01-01

    There is growing evidence for the complex, intermittent, and heterogeneous character of plastic flow. Here we report a three-dimensional mapping of dislocation avalanches during creep deformation of an ice crystal, from a multiple-transducers acoustic emission analysis. Correlation analysis shows that dislocation avalanches are spatially clustered according to a fractal pattern and that the closer in time two avalanches are, the larger the probability is that they will be closer in space. Such a space/time coupling may contribute to the self-organization of the avalanches into a clustered pattern. PMID:12511646

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

    SciTech Connect

    Deng, Hongxiang; Zu, Xiaotao; Zheng, WG; Yuan, XD; Xiang, Xia; Sun, Kai; Gao, Fei

    2014-05-28

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

  2. 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

    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.

  3. Avalanche dynamics of magnetic flux in a two-dimensional discrete superconductor

    SciTech Connect

    Ginzburg, S. L.; Nakin, A. V.; Savitskaya, N. E. [Russian Academy of Sciences, Petersburg Nuclear Physics Institute (Russian Federation)], E-mail: savitska@thd.pnpi.spb.ru

    2006-11-15

    The critical state of a two-dimensional discrete superconductor in an external magnetic field is studied. This state is found to be self-organized in the generalized sense, i.e., is a set of metastable states that transform to each other by means of avalanches. An avalanche is characterized by the penetration of a magnetic flux to the system. The sizes of the occurring avalanches, i.e., changes in the magnetic flux, exhibit the power-law distribution. It is also shown that the size of the avalanche occurring in the critical state and the external magnetic field causing its change are statistically independent quantities.

  4. Analysis of spanning avalanches in the two-dimensional nonequilibrium zero-temperature random-field Ising model.

    PubMed

    Spasojevi?, Djordje; Jani?evi?, Sanja; Kneževi?, Milan

    2014-01-01

    We present a numerical analysis of spanning avalanches in a two-dimensional (2D) nonequilibrium zero-temperature random field Ising model. Finite-size scaling analysis, performed for distribution of the average number of spanning avalanches per single run, spanning avalanche size distribution, average size of spanning avalanche, and contribution of spanning avalanches to magnetization jump, is augmented by analysis of spanning field (i.e., field triggering spanning avalanche), which enabled us to collapse averaged magnetization curves below critical disorder. Our study, based on extensive simulations of sufficiently large systems, reveals the dominant role of subcritical 2D-spanning avalanches in model behavior below and at the critical disorder. Other types of avalanches influence finite systems, but their contribution for large systems remains small or vanish. PMID:24580183

  5. 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.

  6. Multiple-pulsed debris avalanche emplacement at Mount St. Helens in 1980: Evidence from numerical continuum flow simulations

    Microsoft Academic Search

    James Sousa; Barry Voight

    1995-01-01

    The complex 1980 Mount St. Helens debris avalanche is modeled numerically as a transient biviscous fluid flow. Several approaches are considered, including two-step rheologically-distinct models for avalanche I and combined avalanches II\\/III, and a composite flow model consisting of retrogressive slides of identical rheology successively accreted to the main avalanche flow. For the two-step situation, flow rheologies are evaluated separately

  7. A Monolithically Integrated Optical Receiver With a Silicon Avalanche Photodetector for

    E-print Network

    Choi, Woo-Young

    W with the supply voltage of 2.5 V [7]. For realization of high-speed and high-responsivity photodetectors#12;#12;A Monolithically Integrated Optical Receiver With a Silicon Avalanche Photodetector. The receiver contains a silicon avalanche photodetector and a transimpedance amplifier and has up to 5.6- GHz

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

    Microsoft Academic Search

    G. L. Beach; D. Dzurisin

    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

  9. An electron-avalanche amplifier based on the electronic Venturi effect D. Taubert,1

    E-print Network

    Ludwig-Maximilians-Universität, München

    An electron-avalanche amplifier based on the electronic Venturi effect D. Taubert,1 G. J. Schinner, this electronic version of the Venturi effect enables us to build an avalanche amplifier based on non leads to the Venturi effect. That is, the pressure in a fluid decreases as it passes through a tube

  10. SEISMIC RECORDINGS OF ICE AND DEBRIS AVALANCHES OF ILIAMNA VOLCANO, ALASKA

    Microsoft Academic Search

    Jacqueline Caplan-Auerbach; Stephanie G. Prejean; John A. Power

    Seismic data recorded on Iliamna Volcano, Alaska, indicate that Iliamna ice avalanches are preceded by up to several hours of p recursory seismicity. This precursory activity is represented by a 1-3 hour period of activity comprising a sequence of discrete repeatin g earthquakes and a period of continuous groundshaking that builds in amplitude. The avalanche itself is represented by a

  11. The Avalanche Drift Diode: A New Detector Concept for Single Photon Detection

    Microsoft Academic Search

    Gerhard Lutz; Nepomuk Otte; Rainer H. Richter; Lothar Strüder

    2005-01-01

    A concept for single optical photon detection promises high quantum efficiency and large area sensitivity while restricting the avalanche region to a very narrow (“point-like”) region of the device. This is accomplished by combining the principle of drift diode with an avalanche structure situated close by the electron collection electrode on the wafer surface opposite to the large area radiation

  12. The dynamics of avalanches of granular materials from initiation to runout. Part I: Analysis

    Microsoft Academic Search

    S. B. Savage; K. Hutter

    1991-01-01

    Summary This paper describes a model to predict the flow of an initially stationary mass of cohesion-less granular material down rough curved beds. This work is of interest in connection with the motion of rock and ice avalanches and dense flow snow avalanches. The constitutive behaviour of the material making up the pile is assumed to be described by a

  13. Effect of dead space on gain and noise in Si and GaAs avalanche photodiodes

    Microsoft Academic Search

    M. M. Hayat; W. L. Sargeant; B. E. A. Saleh

    1992-01-01

    The effect of dead space on the mean gain, the excess noise factor, and the avalanche breakdown voltage for Si and GaAs avalanche photodiodes (APDs) with nonuniform carrier ionization coefficients are examined. The dead space, which is a function of the electric field and position within the multiplication region of the APD, is the minimum distance that a newly generated

  14. A Methodology To Allow Avalanche Forecasting on an Information Retrieval System.

    ERIC Educational Resources Information Center

    Purves, R. S.; Sanderson, M.

    1998-01-01

    Presents adaptations and tests undertaken to allow an information retrieval system to forecast the likelihood of avalanches on a particular day; the forecasting process uses historical data of the weather and avalanche conditions for a large number of days. Describes a method for adapting these data into a form usable by a text-based IR system and…

  15. Teaching Natural Hazards: The Use of Snow Avalanches in Demonstrating and Addressing Geographic Topics and Principles.

    ERIC Educational Resources Information Center

    Barber, David L.

    1988-01-01

    Because of increased recreational use of alpine environments in the western United States, this lesson plan integrates the themes of location, place, and human-environment interaction in order to teach avalanche hazard awareness. Presents classroom activities and research topics to enhance student awareness of snow avalanche hazards. Provides…

  16. Computing bit-error probabilities for avalanche photodiode receivers by large deviations theory

    Microsoft Academic Search

    Khaled Ben Letaief; John S. Sadowsky

    1992-01-01

    A bit error probability analysis of direct detection optical receivers is presented employing avalanche photodiodes. An asymptotic analysis for large signal intensities is presented. This analysis provides some useful insight into the balance between the Poisson statistics, the avalanche gain statistics, and the Gaussian thermal noise. The conjugate distribution is developed. It is obtained by applying the large-deviation exponential twisting

  17. Avalanche Current Measurements in SPADs by Means of Hot-Carrier Luminescence

    Microsoft Academic Search

    Antonino Ingargiola; Mattia Assanelli; Ivan Rech; Angelo Gulinatti; Massimo Ghioni

    2011-01-01

    A growing number of applications require arrays of single-photon avalanche diode (SPAD) detectors with low timing jitter. In order to improve jitter without compromising other performance parameters, a clear understanding of avalanche dynamics and statistics is necessary. In this work, a noninvasive electro-luminescence technique has been employed to investigate the current growing in a SPAD device. The obtained results let

  18. A simple lattice model for the effect of voids on slip avalanches in sheared granular materials

    Microsoft Academic Search

    K. Dahmen; Y. Ben-Zion; J. T. Uhl

    2009-01-01

    It is well known that densely packed granular materials respond to slow shear with slip avalanches. Experiments and simulations show that the avalanche statistics depend strongly on the granular volume fraction v and grain shape related properties [1]. Previous studies have focused on force chain properties [2-6]. Here we use a mean field technique to construct an analytic model of

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

    E-print Network

    Lin, Zhihong

    Secondary instability in drift wave turbulence as a mechanism for zonal flow and avalanche instability as a mechanism for zonal flow generation, transport barrier dynamics and avalanche formation. These in turn are related to the space­time statistics of the drift wave induced flux, the scaling of transport

  20. PHYSICAL REVIEW E 88, 022106 (2013) Avalanche dynamics of elastic interfaces

    E-print Network

    Wiese, Kay Jörg

    2013-01-01

    PHYSICAL REVIEW E 88, 022106 (2013) Avalanche dynamics of elastic interfaces Pierre Le Doussal, or cracks in brittle disordered material proceed via intermittent motion, called avalanches. Here we develop a field-theoretic treatment to calculate, from first principles, the space-time statistics

  1. STATISTICAL AVALANCHE RUNOUT MODELS: HOW WELL CAN COMPUTERS PREDICT BETA? Alexandra Sinickas*1

    E-print Network

    Jamieson, Bruce

    STATISTICAL AVALANCHE RUNOUT MODELS: HOW WELL CAN COMPUTERS PREDICT BETA? Alexandra Sinickas*1 in this study. KEYWORDS: extreme avalanche runout; statistical model; alpha-beta; runout ratio; repeatability Digital Elevation Model (DEM) and Google Earth in predicting beta () points for statistical runout

  2. Definition of Transformation Random Transformation Group Action Skew Product Literature Ergodicity of Avalanche Transfromations

    E-print Network

    Liu, I-Shih

    of Avalanche Transfromations Manfred Denker May 26, 2014 Pennsylvania State University #12;Definition Action Skew Product Literature Motivation: Avalanches in neuronal dynamics (see the talk at the Sao Paulo linear isometry on C = {x : i : x(i) i}, where x(1) x(2) ... x(N) is the order statistics. Fact 2

  3. ICPP: A simple avalanche model for astroplasma and laboratory confinement systems

    Microsoft Academic Search

    Sandra Catherine Chapman

    2000-01-01

    We discuss a new avalanche or `sandpile' model that is a generalization of the original SOC avalanche model of Bak, Tang and Wiesenfeld to include nonlocal transport as well as thresholded diffusion. A single control parameter specifies the spatial extent of nonlocal transport and thus the dynamical behavior of the system, this is insensitive to other details such as the

  4. Secondary Instability in Drift Wave Turbulence as a Mechanism for Zonal Flow and Avalanche Formation

    E-print Network

    Diamond, Patrick H.

    Secondary Instability in Drift Wave Turbulence as a Mechanism for Zonal Flow and Avalanche instability as a mechanism for zonal flow generation, transport barrier dynamics, and avalanche formation. These, in turn, are related to the space-time statistics of the drift wave-induced flux, the scaling

  5. Photon-Timing Jitter Dependence on Injection Position in Single-Photon Avalanche Diodes

    Microsoft Academic Search

    Mattia Assanelli; Antonino Ingargiola; Ivan Rech; Angelo Gulinatti; Massimo Ghioni

    2011-01-01

    In recent years, a growing number of applications demand better timing resolution from single-photon avalanche diodes (SPADs). The challenge is pursuing improved timing resolution without impairing other device characteristics such as quantum efficiency and dark count rate. This task requires a clear understanding of the statistical phenomena involved in the avalanche current growth in order to drive the device engineering

  6. Return period calculation and passive structure design at the Taconnaz avalanche path, France

    Microsoft Academic Search

    Mohamed Naaim; Thierry Faug; Florence Naaim; Nicolas Eckert

    2010-01-01

    This paper aims to show how recent knowledge developed in the field of avalanche research can be used for a real case study, the Taconnaz avalanche path, where passive structures already existed but had to be improved. First a morphological analysis of the site is done and historical data are analysed. Second, each recorded event is back-calculated using a numerical

  7. Application of a regional approach for hazard mapping at an avalanche site in northern Italy

    NASA Astrophysics Data System (ADS)

    Bocchiola, D.; Rosso, R.

    2008-04-01

    The currently adopted approach to avalanche hazard mapping in northern Italy includes avalanche dynamic modelling, coupled with statistical analysis of snow depth at avalanche start. The 30-years and 300-years return period avalanches at a given site are modelled and their run out zone and pressure are evaluated. The snow depth in the avalanche release zone is assumed to coincide with the three days snow fall depth H72 featuring a return period of 30 years and 300 years, respectively. In the Italian alps only short series of observed snow depth are available, covering a period of 20 years or so, thus requiring a regional approach, or index value approach for the purpose of high return period quantile estimation. Based of former studies, here we apply the index value approach developed for the Lombardia region, in northern Italy, for hazard mapping in a particular avalanche site. A dynamic avalanche model is tuned using the runout data for two major observed avalanche events. Then, the 30-years and 300-years runout zone and dynamic pressure are calculated. It is then shown that the obtained hazard maps are more accurate than those obtained using the evaluation of H72 as deduced from distribution fitting in a single site.

  8. Estimation of hazard potentials from ice avalanches using remote sensing and GIS-modelling

    Microsoft Academic Search

    N. Salzmann; A. Kaeaeb; C. Huggel; B. Allgoewer; W. Haeberli

    2003-01-01

    Ice avalanches occur when a large mass of ice breaks off from steep glaciers. Due to the usually low reach of ice avalanches, their hazard potentials are generally restricted to high mountain areas with dense population or under frequent touristic use. But in consequence of climatic changes and intensified land use, the related hazard potentials are presently increasing. Therefore, dealing

  9. Revisiting statistical–topographical methods for avalanche predetermination: Bayesian modelling for runout distance predictive distribution

    Microsoft Academic Search

    N. Eckert; E. Parent; D. Richard

    2007-01-01

    Return period is a classical tool for avalanche hazard mapping but is often poorly defined. To reduce ambiguity, high quantiles of a given quantity should be preferred. Inspired by the statistical–topographical “Norwegian” approaches and concepts developed by Ancey and Meunier, this paper presents a new method for computing the predictive distribution of snow avalanche runout distances. We evaluate the uncertainties

  10. 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.

  11. Climate Influences on Large-Magnitude Natural Snow Avalanches in John F. Stevens Canyon, Montana

    NASA Astrophysics Data System (ADS)

    Reardon, B. A.; Fagre, D. B.; Pederson, G. T.; Caruso, C. J.

    2005-12-01

    Snow avalanches are usually characterized as natural hazards. Most literature describes mitigation measures or snow properties and weather processes that contribute to avalanche initiation, with recent research focusing on the spatial variability of snow properties. Some analyses have linked extreme avalanche events (those marked by widespread, large-magnitude, destructive avalanches) with synoptic weather patterns. This study examines the temporal variability of large magnitude natural avalanches in John F. Stevens Canyon in Montana using a long-term (96 winters) historic record and dendrochronology. Results show that shifts in multi-decadal climate patterns such as the Pacific Decadal Oscillation change the frequency and severity of large-magnitude natural avalanches. From their immediate impacts, which include downed trees and dammed streams, such events appear destructive. Cumulatively, however, these events create ecotones and structural diversity in montane forests and dampen reforestation after wildfires. Large magnitude natural avalanches are thus recurring, climate-influenced disturbances that have significant, long-lasting, landscape-level effects. However, potential changes in multi-decadal climate patterns and projected changes in snowpack may lead to changes in natural avalanche frequency and severity, and thus long-term, landscape scale changes in montane forests in the northern Rocky Mountains.

  12. Microwave diagnostics of laser-induced avalanche ionization Zhili Zhang,a

    E-print Network

    Miles, Richard

    to the initial electron number density. The first part of this paper addresses the microwave scat- tering modelMicrowave diagnostics of laser-induced avalanche ionization in air Zhili Zhang,a Mikhail N presents a simplified model of microwave scattering during the avalanche ionization stage of laser

  13. Investigation of the possibility of creating a multichannel photodetector based on the avalanche MRS-structure

    NASA Astrophysics Data System (ADS)

    Sadyigov, Z. Y.; Gasanov, A. G.; Yusipov, N. Y.; Golovin, V. M.; Gulanian, Emin H.; Vinokurov, Y. S.; Simonov, A. V.

    1991-11-01

    Investigation results of the avalanche process in MRS-structure are given and the possibility of creating the multichannel avalanche photodetector based on such a structure for the one- dimensional hologram disk memory system is considered. The experimental sample of the photodetector has sensitivity approximately 104 A/W with wavelength (lambda) approximately equals 0.63 micrometers and response speed approximately 5 nsec.

  14. Measurements of Snow Avalanche Basal Shear to Normal Stress Ratios (S\\/N)

    Microsoft Academic Search

    P. A. Bartelt; K. Platzer

    2006-01-01

    A long-standing problem in snow science is the value of the basal friction coefficient for dense, flowing avalanches. This parameter is defined by the ratio of shear (S) to normal (N) stress and determines the runout distance of snow avalanches. It is therefore the crucial parameter in hazard mitigation studies. In this paper we present measurements of (S\\/N). The measurements

  15. Analysis of inter-event times for avalanches on a conical bead pile with cohesion

    NASA Astrophysics Data System (ADS)

    Lehman, Susan; Johnson, Nathan; Tieman, Catherine; Wainwright, Elliot

    2015-03-01

    We investigate the critical behavior of a 3D conical bead pile built from uniform 3 mm steel spheres. Beads are added to the pile by dropping them onto the apex one at a time; avalanches are measured through changes in pile mass. We investigate the dynamic response of the pile by recording avalanches from the pile over tens of thousands of bead drops. We have previously shown that the avalanche size distribution follows a power law for beads dropped onto the pile apex from a low drop height. We are now tuning the critical behavior of the system by adding cohesion from a uniform magnetic field and find an increase in both size and number for very large avalanches and decreases in the mid-size avalanches. The resulting bump in the avalanche distribution moves to larger avalanche size as the cohesion in the system is increased. We compare the experimental inter-event time distribution to both the Brownian passage-time and Weibull distributions, and observe a shift from the Weibull to Brownian passage-time as we raise the threshold from measuring time between events of all sizes to time between only the largest system-spanning events. These results are both consistent with those from a mean-field model of slip avalanches in a shear system [Dahmen, Nat Phys 7, 554 (2011)].

  16. Snow-avalanche impact landforms in Breheimen, southern Norway: Origin, age, and paleoclimatic implications

    SciTech Connect

    Matthews, J.A.; McCarroll, D. (Univ. of Wales, Swansea (United Kingdom))

    1994-05-01

    Twelve snow-avalanche ramparts in Jostedalen and Sprongdalen (Breheimen, southern Norway) are investigated to elucidate processes of formation, the history of avalanche activity, and their potential for paleoclimatic reconstruction. Variation in the form of these riverbank boulder ramparts reflects local patterns of avalanche impact. Differences in clast roundness between ramparts, avalanche tracks, and river beds indicate that, on average, 50 to 60% of the clasts in the ramparts originate from river bedload as opposed to avalanche source areas or tracks. Rampart clasts increase in roundness downstream over a distance of 12 km, and the contribution from the river bed varies from 26 to 80% depending on local factors. Conventional lichenometric dating suggests ages for the initiation of rampart formation of 250 to 2000 yr, but they probably have a much longer history. Lichen-size frequency distributions, using the largest lichen from each of n boulders, reflect the age-frequency of surface boulders, providing a record of late Holocene avalanche activity. A simulation model suggests that maximum avalanche activity affected nine of the ramparts during the 19th century, after the peak of the Little Ice Age. The pattern of avalanche activity differs from the pattern of glacier variations but is in close agreement with that of debris-flow activity. The ramparts may yield a valuable proxy record of winter snowfall. 48 refs., 12 figs., 4 tabs.

  17. International Snow Science Workshop Grenoble Chamonix Mont-Blanc -2013 Impulse water waves generated by snow avalanches

    E-print Network

    Paris-Sud XI, Université de

    generated by snow avalanches Mohamed Naaim 1, * 1 Irstea, UR ETGR, Grenoble, France ABSTRACT: Retaining dams and may be threatened by snow avalanche impacts. To assess the risk of over toppings (overflows), the estimation of the consequences of an avalanche impact in terms of wave magnitude is required. Due to the low

  18. Experimental studies on fast-ion transport by Alfvn wave avalanches on the National Spherical Torus Experimenta...

    E-print Network

    Heidbrink, William W.

    Experimental studies on fast-ion transport by Alfvén wave avalanches on the National Spherical , which interact nonlinearly and terminate in avalanches, are characterized. A depletion of the energy a broad spatial range. It is shown that avalanches lead to a relaxation of the fast-ion profile, which

  19. Avalanche dynamics, surface roughening, and self-organized criticality: Experiments on a three-dimensional pile of rice

    E-print Network

    Wijngaarden, Rinke J.

    Avalanche dynamics, surface roughening, and self-organized criticality: Experiments on a three-organized criticality. The avalanches that occur on the surface of a pile of rice are found to exhibit finite size scaling in their probability distribution. The critical exponents are 1.21(2) for the avalanche size

  20. Hysteresis, avalanches, and disorder-induced critical scaling: A renormalization-group approach Karin Dahmen* and James P. Sethna

    E-print Network

    Sethna, James P.

    Hysteresis, avalanches, and disorder-induced critical scaling: A renormalization-group approach is added, one finds a transition where the jump in the magnetization corresponding to an infinite avalanche avalanches , and universal behavior. We expand the critical exponents about mean-field theory in 6 dimensions

  1. Self-organized criticality induced by quenched disorder: Experiments on flux avalanches in NbHx films

    E-print Network

    Wijngaarden, Rinke J.

    Self-organized criticality induced by quenched disorder: Experiments on flux avalanches in Nb, the avalanche sizes are power- law distributed and show finite-size scaling, as expected from self-organized criticality SOC . Furthermore, the shape of the avalanches is observed to be fractal. In the absence

  2. Size distributions of shocks and static avalanches from the functional renormalization group Pierre Le Doussal and Kay Jrg Wiese

    E-print Network

    Wiese, Kay Jörg

    Size distributions of shocks and static avalanches from the functional renormalization group Pierre avalanches, or shocks, defined here as jumps between distinct global minima upon changing an external field fixed-point functions. This allows us to obtain the size distribution P S of static avalanches

  3. Journal of Glaciology, Vol. 00, No. 000, 2007 1 A Comparison of Powder Snow Avalanches at Vallee de la

    E-print Network

    McElwaine, Jim

    Journal of Glaciology, Vol. 00, No. 000, 2007 1 A Comparison of Powder Snow Avalanches at Vall for Snow and Avalanche Research, CH 7260 Davos Dorf, Switzerland 2 Department of Applied Mathematics and Theoretical Physics, University of Cambridge, UK. ABSTRACT. Powder snow avalanches are natural hazards which

  4. Dendritic magnetic avalanches in carbon-free MgB2 thin films with and without a deposited Au layer

    E-print Network

    Johansen, Tom Henning

    Dendritic magnetic avalanches in carbon-free MgB2 thin films with and without a deposited Au layer October 2005 From magneto optic images MOI , the dendritic magnetic avalanche is known to appear that carbon contamination was not the main source of the avalanche. The MOI clearly showed that the deposition

  5. PHYSICAL REVIEW E 88, 032106 (2013) Statistics of avalanches with relaxation and Barkhausen noise: A solvable model

    E-print Network

    Wiese, Kay Jörg

    2013-01-01

    PHYSICAL REVIEW E 88, 032106 (2013) Statistics of avalanches with relaxation and Barkhausen noise shapes. We elucidate another qualitatively new feature: the breakup of each avalanche of the standard velocity never vanishes, are modified. We also analyze nonstationary avalanches following a step

  6. Avalanches and Self-Organized Criticality in Superconductors Rinke J. Wijngaarden, Marco S. Welling, Christof M. Aegerter and Mariela Menghini

    E-print Network

    Wijngaarden, Rinke J.

    Avalanches and Self-Organized Criticality in Superconductors Rinke J. Wijngaarden, Marco S. Welling and avalanches. Using the magneto-optical technique, the spatial distribution of the vortex density in the sample' are determined and compared to the exponents that char- acterize the avalanches in the framework of Self

  7. Experimental studies on fast-ion transport by Alfven wave avalanches on the National Spherical Torus Experiment

    E-print Network

    Princeton Plasma Physics Laboratory

    Experimental studies on fast-ion transport by Alfv´en wave avalanches on the National Spherical-linearly and disrupt in avalanches, are characterized. A depletion of the energy range > 20 keV, leading to sudden that avalanches lead to a relaxation of the fast-ion profile, which in turn reduces the drive

  8. PHYSICAL REVIEW E 83, 061301 (2011) Simulation of a Casimir-like effect in a granular pile with avalanches

    E-print Network

    Wijngaarden, Rinke J.

    2011-01-01

    with avalanches D. V. Denisov, Y. Y. Villanueva, and R. J. Wijngaarden Department of Physics, Faculty of Sciences-Tang-Wiesenfeld model for sand piles, we simulate a Casimir-like effect in a granular pile with avalanches. Results, with the aim of avalanche prevention, the possibility of suppressing self-organized criticality with an array

  9. Correlation Between Gain and Buildup-Time Fluctuations in Ultrafast Avalanche Photodiodes and Its Effect on Receiver Sensitivity

    E-print Network

    Hayat, Majeed M.

    : The joint statistics of the random gain and random buildup time in ultrafast avalanche photodiodes, it is plausible to suspect that the statistical correlation between the random gain and the random avalancheCorrelation Between Gain and Buildup-Time Fluctuations in Ultrafast Avalanche Photodiodes and Its

  10. LARGE-SCALE AVALANCHE BRAKING MOUND AND CATCHING DAM EXPERIMENTS WITH SNOW: A STUDY OF THE AIRBORNE JET

    E-print Network

    Hogg, Andrew

    LARGE-SCALE AVALANCHE BRAKING MOUND AND CATCHING DAM EXPERIMENTS WITH SNOW: A STUDY OF THE AIRBORNE-scale experiments to study the interaction of a snow avalanche with a dam and a row of mounds which to smaller-scale experiments with glass particles, the avalanche detaches from the top of the dam or mound

  11. Summary Rockfall and snow avalanche events often cause injury to European larch (Larix decidua Mill.) trees, giving rise

    E-print Network

    Stoffel, Markus

    Summary Rockfall and snow avalanche events often cause injury to European larch (Larix decidua Mill of the growing season by snow avalanches (15 trees, 324 cross sec- tions) or rockfalls (18 trees, 270 cross.3% of the rockfall samples and 87.3% of the snow avalanche samples. Traumatic resin ducts were formed

  12. Giant debris avalanches from the Colima Volcanic Complex, Mexico: Implications for long-runout landslides (>100 km) and hazard assessment

    Microsoft Academic Search

    Gary R. Stoopes; Michael F. Sheridan

    1992-01-01

    At least two giant volcanic debris-avalanche deposits are associated with the Colima Volcanic Complex located in the western part of the Trans-Mexican volcanic belt. One avalanche originated from Volcán de Colima (3820 m), probably 4300 yr ago. A much larger avalanche originated from Nevado de Colima (4240 m) 18500 yr ago; it traveled more than 120 km from its source

  13. IEEE ELECTRON DEVICE LETTERS, VOL. 29, NO. 10, OCTOBER 2008 1115 Equivalent Circuit Model for Si Avalanche

    E-print Network

    Choi, Woo-Young

    Avalanche Photodetectors Fabricated in Standard CMOS Process Myung-Jae Lee, Student Member, IEEE, Hyo model for CMOS- compatible avalanche photodetectors. The equivalent circuit model includes an inductive component for avalanche delay, a cur- rent source for photogenerated carriers, and several components

  14. The geomorphological effect of cornice fall avalanches in the Longyeardalen valley, Svalbard

    NASA Astrophysics Data System (ADS)

    Eckerstorfer, M.; Christiansen, H. H.; Rubensdotter, L.; Vogel, S.

    2013-09-01

    The study of snow avalanches and their geomorphological effect in the periglacial parts of the cryosphere is important for enhanced geomorphological process understanding as well as hazard-related studies. Only a few field studies, and particularly few in the High Arctic, have quantified avalanche sedimentation. Snow avalanches are traditionally ranked behind rockfall in terms of their significance for mass-wasting processes of rockslopes. Cornice fall avalanches are at present the most dominant snow avalanche type at two slope systems, called Nybyen and Larsbreen, in the valley Longyeardalen in central Svalbard. Both slope systems are on northwest-facing lee slopes underneath a large summit plateau, with annual cornices forming on the top. High-frequency and magnitude cornice fall avalanching is observed by daily automatic time-lapse photography. In addition, rock debris sedimentation by cornice fall avalanches was measured directly in permanent sediment traps or by snow inventories. The results from a maximum of seven years of measurements in a total of 13 catchments show maximum mean rock debris sedimentation rates ranging from 8.2 to 38.7 kg m-2 at Nybyen, and from 0.8 to 55.4 kg m-2 at Larsbreen. Correspondingly, avalanche fan surfaces accreted from 2.6 to 8.8 mm yr-1 at Nybyen, and from 0.2 to 13.9 mm yr-1 at Larsbreen. This comparably efficient rockslope mass wasting is due to collapsing cornices producing cornice fall avalanches containing large amounts of rock debris throughout the entire winter. The rock debris of different origin stems from the plateau crests, the adjacent free rock face and the transport pathway, accumulating distinct avalanche fans at both slope systems. Cornice fall avalanche sedimentation also contributed to the development of a rock glacier at the Larsbreen site during the Holocene. We have recorded present maximum rockwall retreat rates of 0.9 mm yr-1 at Nybyen, but as much as 6.7 mm yr-1 at Larsbreen, while average Holocene rockwall retreat rates of 1.1 mm yr-1 at Nybyen have been determined earlier. As cornice fall avalanches are the dominant type of avalanche in central Svalbard, the related geomorphological effect is assumed to be of significance at periglacial landscape scale. A climate-induced shift in prevailing winter wind direction could change the rockslope sedimentation effectively by changing the snow avalanche activity.

  15. Two examples of expert knowledge based system for avalanche forecasting and protection

    NASA Astrophysics Data System (ADS)

    Buisson, Laurent; Giraud, Gérald

    1995-11-01

    In avalanche modelling and control and in avalanche forecasting, most of the knowledge is based on scientific theory but the experience of specialists (field practitioners, forecasters...) plays a large role. This paper presents two French computer-based systems dedicated to avalanche modelling and control and to avalanche forecasting. They are both based on expert knowledge. ELSA (Etude et Limites de Sites d'Avalanches), is a computer system dedicated to the modelling of the knowledge of avalanche experts and to the integration of new symbolic computer models with classical numerical models. The basic aim of integration is to build a unique computer system incorporating all these models. After a description of the terrain representation, we present the different scenarios that ELSA takes into account. Then, the methods which deal with some phenomena occurring in avalanches are described. The problems involved in the integration of these methods close this first part. MEPRA is an expert system built to create an objective tool in avalanche risk forecasting. This development allowed us to imagine a processing system for 2 of the most important problems in avalanche risk forecasting: representation of the present snow cover characteristics and evaluation of avalanche instability and risk. In this way, mechanics and thermodynamics play a major role in the system. After a punctual validation at the location of a snow weather station and in order to describe the great variability of the snow pack and the avalanche risk in a massif, the MEPRA expert system was connected with a meteorological analysis system, SAFRAN and a numerical model to simulate the snow cover CROCUS. Then, every day, a MEPRA expert analysis is carried out in different locations with different orientations, slopes and altitudes. Its results were used successfully during the Winter Olympic Games of Albertville and by avalanche forecasters during the 92/93 winter season. The daily avalanche risks estimated by MEPRA are also compared with the observed avalanche activity during the 10 last winters. For a better description of local phenomena like wind slab or snow accumulation, a local version of this tool should be developed to integrate field characteristics.

  16. Martian Dust Devil Electron Avalanche Process and Associated Electrochemistry

    NASA Technical Reports Server (NTRS)

    Jackson, Telana L.; Farrell, William M.; Delory, Gregory T.; Nithianandam, Jeyasingh

    2010-01-01

    Mars' dynamic atmosphere displays localized dust devils and larger, global dust storms. Based on terrestrial analog studies, electrostatic modeling, and laboratory work these features will contain large electrostatic fields formed via triboelectric processes. In the low-pressure Martian atmosphere, these fields may create an electron avalanche and collisional plasma due to an increase in electron density driven by the internal electrical forces. To test the hypothesis that an electron avalanche is sustained under these conditions, a self-consistent atmospheric process model is created including electron impact ionization sources and electron losses via dust absorption, electron dissociation attachment, and electron/ion recombination. This new model is called the Dust Devil Electron Avalanche Model (DDEAM). This model solves simultaneously nine continuity equations describing the evolution of the primary gaseous chemical species involved in the electrochemistry. DDEAM monitors the evolution of the electrons and primary gas constituents, including electron/water interactions. We especially focus on electron dynamics and follow the electrons as they evolve in the E field driven collisional gas. When sources and losses are self-consistently included in the electron continuity equation, the electron density grows exponentially with increasing electric field, reaching an equilibrium that forms a sustained time-stable collisional plasma. However, the character of this plasma differs depending upon the assumed growth rate saturation process (chemical saturation versus space charge). DDEAM also shows the possibility of the loss of atmospheric methane as a function of electric field due to electron dissociative attachment of the hydrocarbon. The methane destruction rates are presented and can be included in other larger atmospheric models.

  17. Avalanche-diode oscillator circuit with tuning at multiple frequencies

    NASA Technical Reports Server (NTRS)

    Parker, D.; Ablow, C. M.; Lee, R. E.; Karp, A.; Chambers, D. R.

    1971-01-01

    Detailed theoretical analysis of three different modes or types of high efficiency oscillation in a PIN diode are presented. For the TRAPATT mode in a PIN diode, it is shown that a traveling avalanche zone is not necessary to generate a dense trapped plasma. An economical computer program for TRAPATT oscillations in a PIN diode is described. Typical results of diode power, dc-to-RF conversion efficiency, and required circuit impedances are presented for several different current waveforms. A semianalytical solution for a second type of high efficiency mode in a PIN diode is derived assuming a rectangular current waveform. A quasi-static approximation is employed to derive a semianalytical solution for the voltage across a PIN diode in a third mode, where avalanching occurs during a major portion of a half cycle. Calculations for this mode indicate that the power increases proportionally to the magnitude of the drive current with a small decrease in efficiency relative to the ordinary TRAPATT mode. An analytical solution is also given for a PIN diode, where it is assumed that the ionization coefficient is a step function. It is shown that the step-ionization approximation permits one to draw possible patterns of avalanche region in the depletion layer as a function of time. A rule governing admissible patterns is derived and an example solution given for one admissible pattern. Preliminary experimental results on the high-efficiency oscillations are presented and discussed. Two different experimental circuits, which used channel-dropping filters to provide independent harmonic tuning, are described. Simpler circuits used to produce high-efficiency oscillations are discussed. Results of experiments using inexpensive Fairchild FD300 diodes are given.

  18. 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.

  19. Starving avalanches: Frictional mechanisms at the tails of finite-sized mass movements

    NASA Astrophysics Data System (ADS)

    Bartelt, P.; Buser, O.; Platzer, K.

    2007-10-01

    The tail of an avalanche is characterized by diminishing flow heights. The decreasing flow heights are due to increased friction and therefore tails are ideally suited to investigate frictional mechanisms in avalanches. Using chute experiments with granular material, we observe two properties of avalanche tails: (1) Coulomb friction ? increases in proportion to the decrease in the gravitational work rate ${\\dot{W} g ; (2) flow heights h are proportional to the square of the basal slip velocity u 0; h $\\propto$ u 0 2. Another non-steady region can be observed at the front of the avalanche. Although this region is shorter than the tail, we were able to detect a hysteresis of the friction ? coefficient as a function of the gravitational work rate. This fact indicates a time dependence of the frictional mechanisms. The results explain why avalanches starve when they are not fed by the intake of additional material at the front.

  20. Scaling Behavior of Barkhausen Avalanches along the Hysteresis loop in Nucleation-Mediated Magnetization Reversal Process

    SciTech Connect

    Im, Mi-Young; Fischer, Peter; Kim, D.-H.; Shin, S.-C.

    2008-10-14

    We report the scaling behavior of Barkhausen avalanches for every small field step along the hysteresis loop in CoCrPt alloy film having perpendicular magnetic anisotropy. Individual Barkhausen avalanche is directly observed utilizing a high-resolution soft X-ray microscopy that provides real space images with a spatial resolution of 15 nm. Barkhausen avalanches are found to exhibit power-law scaling behavior at all field steps along the hysteresis loop, despite their different patterns for each field step. Surprisingly, the scaling exponent of the power-law distribution of Barkhausen avalanches is abruptly altered from 1 {+-} 0.04 to 1.47 {+-} 0.03 as the field step is close to the coercive field. The contribution of coupling among adjacent domains to Barkhausen avalanche process affects the sudden change of the scaling behavior observed at the coercivity-field region on the hysteresis loop of CoCrPt alloy film.