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1

Avalanches!  

NSDL National Science Digital Library

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.

Payne, Laura X.

1999-01-01

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

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.

Frank Weisel

4

Avalanche  

NSDL National Science Digital Library

In this geology activity, learners create a model using a mixture of salt and sand inside a CD case. When the case is tilted or inverted, the mixture dramatically sorts into a layered pattern. With this model, learners explore the angle of repose and Brazil Nut Effect to better understand how avalanches occur. Educators have the option of building the model with or without learners present.

Don Rathjen

2005-01-01

5

Avalanche Awareness  

NSDL National Science Digital Library

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.

Laura Cheshire

6

Avalanche Town  

NSDL National Science Digital Library

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.

2005-12-17

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

Avalanche polynomials Robert Cori  

E-print Network

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

Paris-Sud XI, Université de

9

Avalanche precursors R. Delannay,  

E-print Network

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

Gruner, Daniel S.

10

Avalanches in Foam Collapse  

E-print Network

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

Anlage, Steven

11

Dust Avalanches  

NASA Technical Reports Server (NTRS)

[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.

2003-01-01

12

Computing extreme avalanches  

Microsoft Academic Search

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

Christophe Ancey; Christian Gervasoni; Maurice Meunier

2004-01-01

13

Negative feedback avalanche diode  

NASA Technical Reports Server (NTRS)

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.

Itzler, Mark Allen (Inventor)

2010-01-01

14

Snow avalanche formation  

Microsoft Academic Search

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,

Jrg Schweizer; J. Bruce Jamieson; Martin Schneebeli

2003-01-01

15

Avalanche Weather Forecasting  

NSDL National Science Digital Library

Avalanches form through the interaction of snowpack, terrain, and weather, the latter being the focus of this module. The module begins with basic information about avalanches, highlighting weather's role in their development. The rest of the module teaches weather forecasters how to make an avalanche weather forecast, that is, one in which key weather parameters are evaluated for their impact on avalanche potential. The forecasts are used primarily by avalanche forecasters, who integrate them with other information to determine when to issue avalanche hazard warnings. The module contains five cases that let users apply the avalanche weather forecast process to different combinations of snowpack, terrain, and weather conditions. It is a companion to the COMET module "Snowpack and Its Assessment," which describes snowpack development and various assessment techniques.

COMET

2010-09-30

16

AVALANCHES, SANDPILES AND TUTTE DECOMPOSITION  

E-print Network

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

Gabrielov, Andrei

17

Characteristics of human-triggered avalanches  

Microsoft Academic Search

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

Jrg Schweizer; Martina Ltschg

2001-01-01

18

Avalanche statistics of sand heaps  

SciTech Connect

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.

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

1996-09-01

19

Inverse avalanches on Abelian sandpiles  

SciTech Connect

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.

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

20

Granular Avalanches in Fluids  

E-print Network

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.

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

2002-09-03

21

Dune Avalanche Scars  

NASA Technical Reports Server (NTRS)

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.

2004-01-01

22

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.

23

Reuyl Crater Dust Avalanches  

NASA Technical Reports Server (NTRS)

(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!

2002-01-01

24

Avalanche Photodiode Statistics in Triggered-avalanche Detection Mode  

NASA Technical Reports Server (NTRS)

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.

Tan, H. H.

1984-01-01

25

Exclusion processes with avalanches.  

PubMed

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

Bhat, Uttam; Krapivsky, P L

2014-07-01

26

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.

27

Hebes Chasma Dust Avalanches  

NASA Technical Reports Server (NTRS)

[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.

2005-01-01

28

Asymmetric Abelian Avalanches and Sandpiles Andrei Gabrielov  

E-print Network

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

Gabrielov, Andrei

29

Avalanche-Generated Infrasound Signals  

NASA Astrophysics Data System (ADS)

Snow avalanches produce sub-audible acoustic pressure fluctuations in the low frequency infrasound spectrum that can be detected at significant distances. Although such signals have been previously observed and described, information detailing the characteristics of avalanche generated infrasound signals is scanty. During the winters of 2000/2001, 2001/2002, and 2002/2003 infrasonic monitoring systems operated at several locations in the Rocky Mountain West and collected data aimed at characterizing infrasonic signals produced by avalanche activity. Remote DC powered measurement systems providing a 1 - 10 HZ band limited infrasound signal were deployed within 2 kilometers of controlled and observed avalanche slide paths. Infrasonic microphones coupled to porous hose noise reducing filters were placed on the ground and subsequently covered by snowfall. Results obtained from these efforts have shown avalanche-generated infrasound signal amplitude levels approaching a 20 bar dynamic range while occupying a 1 - 8 Hz frequency band. Additional infrasound insights on various avalanche control mechanism signatures, potential interfering event signatures, and ambient noise levels were also obtained. The catalog of data has been utilized to develop avalanche identification signal processing algorithms. Knowledge gained from research results will be applied during the 2003/2004 winter through the operation of a prototype near real-time avalanche alarming system on Teton Pass, Wyoming. Research efforts related to this study will were funded via a Small Business Innovative Research award obtained through the National Oceanic and Atmospheric Administration within the U. S. Department of Commerce.

Scott, E.; Hayward, C.

2003-12-01

30

Triangular avalanches and uphill instabilities  

E-print Network

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.

Jean-Philippe Bouchaud; Michael Cates

1998-01-14

31

Crater Dust Avalanches  

NASA Technical Reports Server (NTRS)

[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.

2005-01-01

32

Lycus Sulci Dust Avalanches  

NASA Technical Reports Server (NTRS)

[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.

2005-01-01

33

Tikhonravov Crater Dust Avalanches  

NASA Technical Reports Server (NTRS)

[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.

2005-01-01

34

Crater Dust Avalanches  

NASA Technical Reports Server (NTRS)

[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.

2005-01-01

35

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

E-print Network

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

Paris-Sud XI, Université de

36

Abelian Avalanches and Tutte Polynomials Andrei Gabrielov  

E-print Network

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

Gabrielov, Andrei

37

Technological advances in avalanche survival.  

PubMed

Over the last decade, a proliferation of interest has emerged in the area of avalanche survival, yielding both an improved understanding of the pathophysiology of death after avalanche burial and technological advances in the development of survival equipment. The dismal survival statistics born out of the modern era of winter recreation unmistakably reveal that elapsed time and depth of burial are the most critical variables of survival and the focus of newer survival devices on the market. Although blunt trauma may kill up to one third of avalanche victims, early asphyxiation is the predominant mechanism of death, and hypothermia is rare. A survival plateau or delay in asphyxiation may be seen in those buried in respiratory communication with an air pocket until a critical accumulation of CO2 or an ice lens develops. The newest survival devices available for adjunctive protection, along with a transceiver and shovel, are the artificial air pocket device (AvaLung), the avalanche air bag system (ABS), and the Avalanche Ball. The artificial air pocket prolongs adequate respiration during snow burial and may improve survival by delaying asphyxiation. The ABS, which forces the wearer to the surface of the avalanche debris by inverse segregation to help prevent burial, has been in use in Europe for the last 10 years with an impressive track record. Finally, the Avalanche Ball is a visual locator device in the form of a spring-loaded ball attached to a tether, which is released from a fanny pack by a rip cord. Despite the excitement surrounding these novel technologies, avalanche avoidance through knowledge and conservative judgment will always be the mainstay of avalanche survival, never to be replaced by any device. PMID:12092969

Radwin, Martin I; Grissom, Colin K

2002-01-01

38

Field management of avalanche victims  

Microsoft Academic Search

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

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

2001-01-01

39

Single and multiple sensor identification of avalanche-generated infrasound  

Microsoft Academic Search

The ability to identify snow avalanches as they occur is essential for aggressive avalanche management in transportation corridors and is a fundamental ingredient of avalanche forecasting. Past studies have shown that moving avalanches emit a detectable sub-audible sound signature in the low frequency infrasonic spectrum. Experimental infrasound avalanche monitoring activities conducted in the United States Rocky Mountain West clarify avalanche

Ernest D. Scott; Christopher T. Hayward; Robert F. Kubichek; Jerry C. Hamann; John W. Pierre; Bob Comey; Tim Mendenhall

2007-01-01

40

Kinetic description of avalanching systems.  

PubMed

Avalanching systems are treated analytically using the renormalization group (in the self-organized-criticality regime) or mean-field approximation, respectively. The latter describes the state in terms of the mean number of active and passive sites, without addressing the inhomogeneity in their distribution. This paper goes one step further by proposing a kinetic description of avalanching systems making use of the distribution function for clusters of active sites. We illustrate an application of the kinetic formalism to a model proposed for the description of the avalanching processes in the reconnecting current sheet of the Earth's magnetosphere. A description of avalanching systems is proposed that makes use of the distribution function for clusters of active sites. A general kinetic equation is derived that describes the temporal evolution of the distribution function, in terms of growth and shrinking probabilities. The distribution of clusters is derived for the stationary regime, for a quite general class of avalanching systems or arbitrary dimensionality. The approach, including the probability calculation, is illustrated by an application of the kinetic description to the recently proposed burning model. PMID:16241616

Gedalin, M; Balikhin, M; Coca, D; Consolini, G; Treumann, R A

2005-09-01

41

Evolution of locally excited avalanches in semiconductors  

E-print Network

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.

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

2010-05-25

42

Advances in Cryogenic Avalanche Detectors  

E-print Network

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.

A. Buzulutskov

2015-03-29

43

Correlations in avalanche critical points.  

PubMed

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

Cerruti, Benedetta; Vives, Eduard

2009-07-01

44

RESULTS OF RECENT INFRASOUND AVALANCHE MONITORING STUDIES  

Microsoft Academic Search

Results of recent infrasound avalanche monitoring studies have advanced technological capabilities and provided further understanding of technological challenges. Avalanche identification performance of single sensor monitoring systems varies according to ambient noise and signal levels. While single sensor signal processing algorithms can identify avalanche activity, uncertainties (missed detections and false alarms) increase with increasing wind noise, and as signal levels decrease

Ernest D. Scott; Christopher T. Hayward; Robert F. Kubichek; Jerry C. Hamann; John W. Pierre

45

Avalanche Collapse of Interdependent Network  

E-print Network

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.

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

2012-12-14

46

Sound-Producing Sand Avalanches  

NSDL National Science Digital Library

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.

Bretz, Michael

47

A branching process model for sand avalanches  

SciTech Connect

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.

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

1993-07-01

48

Lumped transmission line avalanche pulser  

DOEpatents

A lumped linear avalanche transistor pulse generator utilizes stacked transistors in parallel within a stage and couples a plurality of said stages, in series with increasing zener diode limited voltages per stage and decreasing balanced capacitance load per stage to yield a high voltage, high and constant current, very short pulse. 8 figs.

Booth, R.

1995-07-18

49

Lumped transmission line avalanche pulser  

DOEpatents

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

Booth, Rex (Livermore, CA)

1995-01-01

50

Volcano webcam down an avalanche  

USGS Multimedia Gallery

Surpisingly, the Webcam managed to stay on top as it rode the avalanche to the bottom of the crater. When the fume cleared, the broken legs of the tripod (center frame and slightly above and right of center) and the Webcam enclosure (just below the tripod legs at center) were visible on the rubble p...

51

Crossover behavior in failure avalanches  

E-print Network

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.

Srutarshi Pradhan; Alex Hansen; Per C. Hemmer

2006-03-23

52

Neuronal Avalanches in Neocortical Circuits  

Microsoft Academic Search

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

John M. Beggs; Dietmar Plenz

2003-01-01

53

Computational snow avalanche simulation in forested terrain  

NASA Astrophysics Data System (ADS)

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 against avalanches; 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 operationalization of a novel 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 [kg m-1 s-2] accounting for differing forest characteristics. We varied K when simulating 40 well-documented small- to medium-scale avalanches, which were 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 cover, for example, 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 simulations will improve current applications for avalanche simulation tools in mountain forest and natural hazard management.

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

2014-08-01

54

AVAL-1D: AN AVALANCHE DYNAMICS PROGRAM FOR THE PRACTICE  

Microsoft Academic Search

Avalanche hazard maps are prepared by engineers and land use planners. These experts rely both on practical experience and calculation models to predict avalanche runout distances and flow velocities. Both dense flow and powder snow avalanche dynamics models are using sophisticated numerical schemes to track the motion of avalanches from initiation to runout. Since avalanche experts are seldom numerical specialists,

Marc Christen; Perry Bartelt; Urs Gruber

55

The Use of Dendrochronology to Determine Avalanche Frequency Along the Avalanche Path East of Balu Peak, Within  

E-print Network

1 The Use of Dendrochronology to Determine Avalanche Frequency Along the Avalanche Path East for avalanches and the frequency of avalanche events can help to mitigate this risk. Dendrochronology (the study the Balu trail in Glacier National Park using dendrochronological techniques, an avalanche history could

Smith, Dan

56

Highly enhanced avalanche probability using sinusoidally-gated silicon avalanche photodiode  

SciTech Connect

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%.

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

57

A silicon avalanche photodetector fabricated with standard CMOS technology  

E-print Network

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

Choi, Woo-Young

58

Spontaneous cortical activity in awake monkeys composed of neuronal avalanches  

E-print Network

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

Chialvo, Dante R.

59

A probabilistic model for snow avalanche occurrence  

NASA Astrophysics Data System (ADS)

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

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

2009-04-01

60

Time Directed Avalanches in Invasion Models  

SciTech Connect

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.

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

61

Dynamic and instability of submarine avalanches  

E-print Network

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.

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

2005-04-21

62

Shocks Generate Crossover Behaviour In Lattice Avalanches  

E-print Network

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.

James Burridge

2013-10-30

63

Forest damage and snow avalanche flow regime  

NASA Astrophysics Data System (ADS)

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. In the powder regime, the blast of the cloud can produce large bending moments in the tree stem because of the impact area extending over the entire tree crown. We demonstrate that intermittent granular loadings are equivalent to low-density uniform dry snow loadings under the assumption of homogeneous particle distributions. In the wet snow case, avalanche pressure is calculated using a quasi-static model accounting for the motion of plug-like wet snow flows. Wet snow pressure depends both on avalanche volume and terrain features upstream of the tree. Using a numerical model that simulates both powder and wet snow avalanches, we study documented events with forest damage. We find (1) powder clouds with velocities over 20 m s-1 can break tree stems, (2) the intermittent regime seldom controls tree breakage and (3) quasi-static pressures of wet snow avalanches can be much higher than pressures calculated using dynamic pressure formulas.

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

2015-01-01

64

Avalanche dynamics of elastic interfaces.  

PubMed

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

Le Doussal, Pierre; Wiese, Kay Jrg

2013-08-01

65

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

NASA Astrophysics Data System (ADS)

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.

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

2014-05-01

66

On the temporal organization of neuronal avalanches  

PubMed Central

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 12 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

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

2014-01-01

67

On the temporal organization of neuronal avalanches.  

PubMed

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

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

2014-01-01

68

Avalanche dynamics on a rough inclined plane  

E-print Network

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.

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

2008-03-31

69

Avalanche dynamics in a pile of rice  

Microsoft Academic Search

THE idea of self-organized criticality1(SOC) is commonly illustrated conceptually with avalanches in a pile of sand grains. The grains are dropped onto a pile one by one, and the pile ultimately reaches a stationary 'critical' state in which its slope fluctuates about a constant angle of repose, with each new grain being capable of inducing an avalanche on any of

Vidar Frette; Kim Christensen; Anders Malthe-Srenssen; Jens Feder; Torstein Jssang; Paul Meakin

1996-01-01

70

Avalanche!--Teachable Moments in Outdoor Education  

ERIC Educational Resources Information Center

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

Galloway, Shayne

2005-01-01

71

Review of dry snow slab avalanche release  

Microsoft Academic Search

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

Jrg Schweizer

1999-01-01

72

ORIGINAL PAPER Dendrochronological reconstruction of snow avalanche  

E-print Network

ORIGINAL PAPER Dendrochronological reconstruction of snow avalanche activity in the Lahul Himalaya to access. An exploratory dendrochronologic study was undertaken in the Lahul Himalaya of Northern India throughout the western Himalaya. Keywords Dendrochronology Snow avalanche Lahul Himalaya India 1

Smith, Dan

73

On the instability of avalanching glaciers  

Microsoft Academic Search

The instability of hanging glaciers and more generally of avalanching glaciers is discussed on the basis of observations performed on several glaciers located in the European Alps. A classification of avalanching glaciers is proposed, which allows a primary appreciation of the danger inherent in these glaciers. On the basis of field observations and results of numerical simulations of crevassing, the

Antoine Pralong; Martin Funk

2006-01-01

74

Fluctuations in Avalanche Photodiode Structure  

SciTech Connect

The number of primary photo-electrons and the excess noise factor of the Avalanche photodiode (APD) are important parameters for the energy resolution of the crystal-APD system. In the present paper, the mean signal value and its fluctuations have been investigated for the well defined silicon Hamamatsu S8148 APD structure as a function of incident photons wavelength. Calculations were made with a Single Particle Monte Carlo simulation technique. Based on this work, the performance of the Hamamatsu S8148 APD as a photodetector for the PbWO4 scintillation light has been discussed.

Kocak, Fatma; Tapan, Ilhan [Department of Physics, Uludag University, 16059, Bursa (Turkey)

2007-04-23

75

Avalanche in Adhesion at Metal Interfaces  

NASA Technical Reports Server (NTRS)

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.

Banerjea, Amitava; Good, Brian S.

1994-01-01

76

Avalanche prediction in Self-organized systems  

E-print Network

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.

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

2008-08-05

77

Avalanche dynamics of imbibition fronts  

NASA Astrophysics Data System (ADS)

The spatio-temporal dynamics of interfaces driven through random media has become a subject of central importance in non-equilibrium statistical mechanics in last years. A wide variety of slowly driven physical systems - vortex lines in superconductors, dislocation lines in defective crystalline solids, fracture fronts in heterogeneous materials, magnetic domain walls in disordered ferromagnets or wetting contact lines on rough substrates - exhibit a self-affine morphology and burst-like correlated motion, that arise from the interplay between competing interactions. In this context, we address here the problem of forced-flow imbibition in a disordered medium where a fluid (oil) that preferentially wets the medium displaces a resident fluid (air) at a constant flow rate. Using a high resolution fast camera, we follow the propagation of the fluid-air interface invading a disordered Hele-Shaw cell. Measuring the local waiting time fluctuations along the front during its propagation, we show that the imbibition fronts display an intermittent behavior signature of an avalanche-like dynamics. First, we will discuss the Non-Gaussian fluctuations of the global (spatialy averaged) velocity V (t) of the interface. Then, we will focus on the various scaling behavior of the local avalanches defined as spatial clusters of large local velocity. Our experimental results underline the critical behavior of the imbibition dynamics, suggesting the existence of a critical depinning transition for this process at V=0.

Santucci, Stephane

2010-03-01

78

High Arctic avalanche climate in Central Svalbard  

NASA Astrophysics Data System (ADS)

Seven major avalanche cycles were identified during three years of intensive observations (2007-2009), around Svalbard's main settlement Longyearbyen. Most avalanches in these cycles were of a direct-action type, as they were triggered during or directly after a snowstorm. The main avalanche type was the cornice fall avalanche, due to the combination of a prevailing winter wind direction from SE over the study area and plateau mountain topography with cornices accumulating on the west facing crests. Additionally a study of natural dry slab avalanching, the second most occurring avalanche type, was carried out in the study area. We aimed to link the major meteorological variables wind, precipitation, air temperature and the subsequent layering of the snow pack in the snow seasons 2007/2008 and 2008/2009 to the avalanche fracture determining forces in the snow pack. Thus we obtained an insight into the timing/dynamics of natural dry slab avalanches showing that the solar cycle plays an important role as well as the occurrence of persistent weak layers in the snow pack. Meteorological threshold values that determine whether a direct action or a climax slab avalanche releases are suggested for the Svalbard landscape. Nearly 50 % of all slabs can be classified as direct action-snow-wind avalanches that released after snow storms with an average of 12 cm snow precipitation and on average 11 m/s wind velocity per day. Furthermore a first systematic classification of the Arctic snow pack in central Svalbard as a snow climate is presented, based on field observations from the three years (2007-2009). Snow pits were quantitatively analyzed in terms of grain shapes, grain sizes and hand hardness of every snow layer. Special emphasis was given to the occurrence of weak layers inside the snow pack. The parameters were used to define the high Arctic snow pack as a very thin and cold snow pack, with a basa layer of depth hoar and the occurrence of ice layers, which indicate a maritime influence. This data, collected on the 70 km most used snow mobile route around Svalbard's main settlement Longyearbyen, builds the basis for depicting the characteristics of a High Arctic avalanche climate as a new additional avalanche climate to the present classification scheme. This basic knowledge is important for future avalanche forecasting in the Longyearbyen area, since fatal accidents in the last years demand the necessary background data for such a service to be collected allowing for its development to start.

Eckerstorfer, Markus; Christiansen, Hanne H.

2010-05-01

79

Systems/Circuits Neuronal Avalanches in the Resting MEG of  

E-print Network

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

Henson, Rik

80

Huge compact flux avalanches in superconducting Nb thin films  

E-print Network

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

Wijngaarden, Rinke J.

81

Impact energy of an avalanche on a structure  

Microsoft Academic Search

The impact energy of an avalanche on the flat surface of an instrumented structure has been quantified by full-scale experiments performed at the Lautaret avalanche test site, France. The deformation and acceleration of the structure were measured during the avalanche. The impact energy of the avalanche was calculated from an energy balance via the mechanical energy theorem. First the elastic

E. Thibert; D. Baroudi

2010-01-01

82

RECENT STUDIES USING INFRASOUND SENSORS TO REMOTELY MONITOR AVALANCHE ACTIVITY  

Microsoft Academic Search

The ability to detect avalanches as they occur is essential for aggressive avalanche management in transportation corridors and is a fundamental ingredient of avalanche forecasting. Past studies have shown that moving avalanches emit a detectable sub-audible sound signature in the low frequency infrasonic spectrum. Experimental activities conducted in the Rocky Mountain West during the winter of 2002\\/2003 clarified the capabilities

Robert H. Comey; Tim Mendenhall

83

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

E-print Network

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

Moore, John

84

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

E-print Network

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

Jamieson, Bruce

85

SPICE modeling for single photon avalanche diode  

NASA Astrophysics Data System (ADS)

In this paper, a complete SPICE model for single photon avalanche diode (SPAD) is presented, which can be implemented into the Spectre simulation environment in cadence to precisely simulate both static characteristic and the photon detection process. We show how to build the static current model including the forward region, the dynamic junction capacitance model, and the neutral zone resistor model. In addition, an avalanche pulse detection system is established to verify the validity of the SPICE model. The simulated avalanche pulse voltage waveforms show good consistency with the experimented ones.

Huang, Dong; Zhu, Rong-xia; Liu, Si-yang; Sun, Wei-feng; Wu, Jin; Ma, De-jun

2013-08-01

86

Continuum description of avalanches in granular media.  

SciTech Connect

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.

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

2000-12-05

87

Initiation of immersed granular avalanches.  

PubMed

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

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

2014-05-01

88

Avalanches and universality in condensed matter  

NASA Astrophysics Data System (ADS)

An overview is given on recent progress in the study of avalanches in a number of experimental systems and in models having disorder. In particular, we show how recent studies on magnetizing avalanches (``Barkhausen noise'') in magnets (driven by a slowly increasing magnetic field) shed light on modeling damage avalanches in stressed materials, the plastic depinning of charge density waves, the statistics of earthquakes in irregularly shaped fault zones, and other systems characterized by ``crackling noise''. In particular, we focus on the universal, i.e., detail independent, effects of disorder in these cases. Unexpected connections between nonequilibrium and equilibrium ``avalanches'' reveal a surprisingly large universality class of systems that all show the same scaling behavior on long length scales. This universality class includes driven far-from-equilibrium behavior (for various histories), and the equilibrium behavior of some of these systems. The studies draw on methods from the theory of phase transitions, the renormalization group, and numerical simulations.

Dahmen, Karin A.

2010-03-01

89

Shocks generate crossover behavior in lattice avalanches.  

PubMed

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

Burridge, James

2013-11-22

90

Piling and avalanches of magnetized particles  

E-print Network

We performed computer simulations based on a two-dimensional Distinct Element Method to study granular systems of magnetized spherical particles. We measured the angle of repose and the surface roughness of particle piles, and we studied the effect of magnetization on avalanching. We report linear dependence of both angle of repose and surface roughness on the ratio $f$ of the magnetic dipole interaction and the gravitational force (\\emph{interparticle force ratio}). There is a difference in avalanche formation at small and at large interparticle force ratios. The transition is at $f_c \\approx 7$. For $f avalanches leave the system in a quasi-continuous granular flow (\\emph{granular regime}), while for $f > f_c$ the avalanches are formed by long particle clusters (\\emph{correlated regime}). The transition is not sharp. We give plausible estimates for $f_c$ based on stability criteria.

S. Fazekas; J. Kertsz; D. E. Wolf

2004-04-09

91

Laboratory study of avalanches in magnetized plasmas  

NASA Astrophysics Data System (ADS)

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-Alfvn 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.

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

2015-03-01

92

Avalanche injection and second breakdown in transistors  

Microsoft Academic Search

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

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

1970-01-01

93

Avalanche impact pressure on an instrumented structure  

Microsoft Academic Search

Full-scale experiments have been conducted on the Lautaret avalanche test site (France, Hautes-Alpes) to quantify avalanche impact pressure. A structure with a flat surface is used as a large sensor and an inverse analysis procedure is developed to reconstruct the pressure applied on this obstacle. This method is validated by numerical simulations and in-situ impact hammer tests are performed to

Emmanuel Thibert; Djebar Baroudi; Ali Limam; Philippe Berthet-Rambaud

2008-01-01

94

Size Frequency Distributions for Snow Avalanches  

NASA Astrophysics Data System (ADS)

We examine crown size frequencies for two extensive datasets of observations made during operational avalanche control: 10,300 events at Mammoth Mountain, California and 219,000 events from the Westwide Avalanche Network (WAN) which includes ski areas and highway operations. We compare a dozen distributions, and we address observer bias by employing ratio estimates, smoothing functions, and exclusion rules. Knowing that avalanche professionals often do not record small events, we examine both datasets with no exclusions and with a 60 cm exclusion rule. The WAN data are best fit by a power law distribution using the 60 cm exclusion rule. The power law distribution with 60 cm exclusion also fits the Mammoth data, although these data are best fit by a hyperbolic tangent distribution under both the 60 cm exclusion rule and without exclusion. Our findings support past literature showing that power laws provide a good fit for size-frequency relationships across different regions. Power law distributions indicate scale invariance across several orders of magnitude and are consistent with self organized critical systems. Independent of the choice of distribution, we advocate the implementation of probabilistic avalanche forecasts that convey uncertainty to the end-user, unlike deterministic forecasts. We propose the use of cumulative distribution functions (CDFs) as the dependent variables in numerical avalanche forecast models. CDFs allow normalized output for a region or specific path. A user can infer the magnitude of avalanche events for each avalanche path or area of interest from the CDF. We attempt to create a basis for such an implementation in avalanche forecasting.

Bair, E. H.; Birkeland, K.; Dozier, J.

2007-12-01

95

Coherent Phonon Avalanches in an Acoustical Cavity  

Microsoft Academic Search

Avalanches of acoustic phonons arising from stimulated emission by an inverted one-phonon transition are observed in a single crystal of dilute ruby (Al_2O_3:Cr^3+). The phonons are resonant with the Zeeman-split \\\\overlineE(^2E) Kramers doublet, complete initial inversion of which is achieved in a limited volume of the crystal by selective pulsed optical pumping into its upper component. The phonon avalanche appears

P. A. van Walree; A. F. M. Arts; H. W. de Wijn

1997-01-01

96

Prehistoric rock avalanches in the Olympic Mountains, Washington  

USGS Publications Warehouse

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.

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

1992-01-01

97

Erosion dynamics of powder snow avalanches - Observations  

NASA Astrophysics Data System (ADS)

Powder snow avalanches (PSA) entrain massive amounts of material from the underlying snow cover by erosion mechanisms that are not fully understood. Despite their inherent diversity, PSAs have recognizable flow features: they are fast, reaching velocity up to 80 m/s, they develop a tall, low density powder cloud and, at the same time, they can exert impact pressure with similar magnitudes of high density flow. In this talk, we report observations that underscore the interplay between entrainment and flow dynamics qualitatively shared by several PSAs at the Valle de la Sionne test site in Switzerland. Measurements include time-histories of snow pack thickness with buried FMCW radar and time-histories of particle velocity using optical sensors, cloud density and cluster size using capacitance probes, and impact pressure measured at several elevations on a pylon. Measurements show that, at the avalanche front, a layer of light, cold and cohesionless snow is rapidly entrained, creating a turbulent and stratified head region with intermittent snow clusters. Fast and localized entrainment of deeper and warmer snow layers may also occur well behind the front, up to a distance of hundreds of meters, where pronounced stratification appears and snow clusters grow larger. In the avalanche head, impact pressure strongly fluctuates and is larger near the ground. Velocity profiles change throughout the avalanche head, with more abrupt changes localized where rapid entrainment occurs. A basal, continuous dense layer forms as deeper, warmer and denser snow cover is entrained and as suspended material starts to deposit. The thickness of the basal layer progressively increases toward the avalanche tail where, finally, deposition occurs en masse. Toward the avalanche tail, velocity profiles tend to become uniform, impact pressures are lower and nearly constant, while entrainment processes are negligible. These observations underscore the relevance of entrainment location and the nature of the erodible material on avalanche dynamics and contrast the sharply different behaviors observed at the head of PSAs and well behind it.

Sovilla, Betty; Louge, Michel

2013-04-01

98

Rock avalanches: significance and progress (Invited)  

NASA Astrophysics Data System (ADS)

1. The probability distribution of landslide volumes follows a power-law indicating that large rock avalanches dominate the terrestrial sediment supply from mountains, and that their source area morphologies dominate mountain topography. 2. Large rock slope failures (~ 106 m3 or greater) often mobilise into rock avalanches, which can travel extraordinarily long distances with devastating effect. This hypermobility has been the subject of many investigations; we have demonstrated that it can be explained quantitatively and accurately by considering the energetics of the intense rock fragmentation that always occurs during motion of a large rock mass. 3. Study of rock avalanche debris psd shows that the energy used in creating new rock surface area during fragmentation is not lost to surface energy, but is recycled generating a high-frequency elastic energy field that reduces the frictional resistance to motion during runout. 4. Rock avalanches that deposit on glaciers can eventually form large terminal moraines that have no connection with any climatic event; unless these are identified as rock-avalanche-influenced they can confuse palaeoclimatic inferences drawn from moraine ages. Rock-avalanche-derived fines, however, can be identified in moraine debris up to ten thousand years old by the characteristic micron-scale agglomerates that form during intense fragmentation, and which are absent from purely climatically-induced moraines; there is thus a strong case for re-examining existing palaeoclimatic databases to eliminate potentially rock-avalanche-influenced moraine ages. 5. Rock avalanches (especially coseismic ones) are a serious hazard, being very destructive in their own right; they also block river valleys, forming landslide dams and potentially devastating dambreak floods, and subsequent severe decade-scale aggradation of downstream fans and floodplains. Rock avalanches falling into lakes or fiords can cause catastrophic tsunami that pose a serious risk to waterside developments. Lake tsunami risk assessments can be derived from submarine landslide deposits. 6. Delineating hazard zones for these phenomena depends entirely on identifying the sites of future coseismic slope failures; in some cases this appears possible by identifying precursory coseismic displacements accumulated during previous earthquakes.

Davies, T. R.

2013-12-01

99

Collaboration Surrounding Beacon Use During Companion Avalanche Rescue  

E-print Network

and situational awareness are often lost. "Beat the myopia of the device" - P8, Head of Avalanche Safety Center and situational awareness are often lost. "Beat the myopia of the device" - P8, Head of Avalanche Safety Center

Greenberg, Saul

100

The application of Landsat data to mapping avalanche hazards  

NASA Technical Reports Server (NTRS)

Two test areas, representing a variety of avalanche hazards, were selected in the San Juan Mountains of Colorado. Midwinter Landsat digital data were analyzed using a clustering technique, and the results compared to 1:24,000 scale maps of avalanche hazards derived from air photo interpretation and field surveys. Confined avalanches were readily identified because of the high contrast between the snow covered avalanche track and the adjacent forested slopes. Unconfined avalanches could not be identified without supplementary topographic data. Spatial characteristics were of primary importance in delineating avalanche tracks. Spatial resolution was the limiting factor in avalanche detection. Landsat data should prove useful for rapid reconnaissance mapping of avalanche hazards, particularly in the absence of other data sources.

Waterman, S.

1979-01-01

101

Singing-sand avalanches without dunes  

NASA Astrophysics Data System (ADS)

Singing-sand dunes have attracted curiosity for centuries and are now the subject of controversy. We address here two aspects of this controversy: first the possible link between the frequency heard and the shear rate (for a gravity avalanche on a dune slip-face, scaling as 0.4g/d, with d the mean grain diameter), and second, the assumed necessity of a layered dune structure under the avalanche that acts as a resonator. Field recordings of singing dunes over the world reveal that they can present very different spectral characteristics: a dune with polydisperse grains produces a very broad and noisy spectrum, while a dune with sorted grains produces a well-defined frequency. Performing laboratory avalanches on a hard plate with singing-dune sand shows that there is no need for a dune below the sand avalanche to produce the singing sound, and a fortiori neither for the dune's layered structure nor for its particular sound transmission. By sieving the polydisperse grains, the same well-defined frequency is obtained to that of the dune with sorted grains, with the same diameter-frequency relation. The various frequencies heard in the field avalanches match the shear rates not calculated from the average size, but from the various peaks of the grain size distributions.

Dagois-Bohy, S.; Courrech du Pont, S.; Douady, S.

2012-10-01

102

Deterministically Driven Avalanche Models of Solar Flares  

NASA Astrophysics Data System (ADS)

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.

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

2014-08-01

103

Electron avalanches in liquid argon mixtures  

SciTech Connect

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.

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

2004-03-19

104

Deterministically Driven Avalanche Models of Solar Flares  

E-print Network

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 st...

Strugarek, Antoine; Joseph, Richard; Pirot, Dorian

2014-01-01

105

Unambiguous reconstruction of network structure using avalanche dynamics  

NASA Astrophysics Data System (ADS)

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.

Leleu, Timothe; Aihara, Kazuyuki

2015-02-01

106

Career of the Month: Avalanche Researcher  

NSDL National Science Digital Library

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.

Megan Sullivan

2009-01-01

107

Bulk Metallic Glasses Deform via Slip Avalanches  

E-print Network

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.

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

2013-12-21

108

Dynamic scaling for avalanches in disordered systems  

SciTech Connect

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.

Zheng, Guang-Ping; Li, Mo

2001-03-01

109

Avalanche dynamics of elastic interfaces LPTENS-13/02  

E-print Network

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

Wiese, Kay Jörg

110

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

111

Avalanche: A Communication and Memory Architecture for Scalable Parallel Computing  

E-print Network

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

Carter, John B.

112

Anisotropic avalanches and flux penetration in patterned superconductors  

E-print Network

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

Wijngaarden, Rinke J.

113

Short Communication Granta Gravel model of sandpile avalanches: towards critical  

E-print Network

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

Paris-Sud XI, Université de

114

AVALANCHE THREATS AND MITIGATION MEASURES IN CANADA Cam Campbell1,*  

E-print Network

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

Jamieson, Bruce

115

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

116

Granular Avalanches in Fluids Sylvain Courrech du Pont,1  

E-print Network

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

Weeks, Eric R.

117

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

E-print Network

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

Jamieson, Bruce

118

ENVIRONMENTAL HAZARDS OF AVALANCHES: PRELIMINARY RESEARCH IN GLACIER NATIONAL  

E-print Network

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

Smith, Dan

119

Schmas numriques pour des avalanches viscoplastiques Paul Vigneaux  

E-print Network

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

Mancini, Simona

120

Avalanches through windows: Multiscale visualization in magnetic thin films  

E-print Network

Avalanches through windows: Multiscale visualization in magnetic thin films Alessandro Magni, for different field of view. The resulting avalanche distributions give interesting hints on the magnetization detect the size of the single avalanches, and how to understand the finite-size effects of the boundary

Sethna, James P.

121

Nonlinear Dynamics and Fractal Avalanches in a Pile of Rice  

E-print Network

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

Wijngaarden, Rinke J.

122

DENSE AVALANCHE FRICTION COEFFICIENTS INFLUENCE OF NIVOLOGICAL PARAMETERS  

E-print Network

DENSE AVALANCHE FRICTION COEFFICIENTS INFLUENCE OF NIVOLOGICAL PARAMETERS M. NAAIM* 1 AND Y. D RAND (Chamonix, France) one of the most threatened areas by snow avalanches. 115 paths from this area were included in the avalanches national observatory, 26 of them have experienced between 20 and 100 events over

Paris-Sud XI, Université de

123

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

E-print Network

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

Russell, Kasey

124

Kadanoff Sand Pile Model Avalanches and Fixed Points  

E-print Network

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

Liège, Université de

125

Avalanche mode of motion: Implications from lunar examples  

USGS Publications Warehouse

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.

Howard, K.A.

1973-01-01

126

Avalanche Characteristics of Substitution-Permutation Encryption Networks  

E-print Network

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

Heys, Howard

127

Neuronal avalanches, epileptic quakes and other transient forms of neurodynamics  

E-print Network

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

Milton, John G.

128

Avalanche crown-depth distributions Edward H. Bair,1  

E-print Network

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

Dozier, Jeff

129

Monolithic germanium/silicon avalanche photodiodes with 340 GHz gainbandwidth  

E-print Network

Monolithic germanium/silicon avalanche photodiodes with 340 GHz gainbandwidth product Yimin Kang1 a monolithically grown germanium/silicon avalanche photodetector with a gainbandwidth product of 340 GHz, a keff for the future development of low-cost, CMOS-based germanium/silicon avalanche photodetectors operating at data

Bowers, John

130

Collisional dust avalanches in debris discs  

E-print Network

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.

Anna Grigorieva; Pawel Artymowicz; Philippe Thbault

2006-09-26

131

Assessing the importance of terrain parameters on glide avalanche release  

NASA Astrophysics Data System (ADS)

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.

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

2013-12-01

132

Internal Avalanches in a Granular Medium  

E-print Network

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.

S. S. Manna; D. V. Khakhar

1998-08-04

133

Avalanches, Barkhausen noise, and plain old criticality  

SciTech Connect

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.}

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

134

Phase avalanches in near-adiabatic evolutions  

SciTech Connect

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.

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

135

Bulk metallic glasses deform via slip avalanches.  

PubMed

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

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

2014-04-18

136

Stable dynamic avalanche in Si power diodes  

NASA Astrophysics Data System (ADS)

A stable dynamic avalanche at a maximum power density of about 2.4 MW/cm2 was measured in small areas of 3.3 kV Si power diodes, using an optical measurement technique, and very good dynamic ruggedness was verified in a conventional turn-off measurement. Device simulations of a diode with a shallow n+ emitter indicate that impact ionization at the nn+ junction can result in negative differential resistance (NDR) and current filamentation, whereas a deep n+ emitter in the experimentally studied diode suppresses NDR. It is, therefore, proposed that the deep n+ emitter is important for the stable dynamic avalanche.

Domeij, Martin; Breitholtz, Bo; stling, Mikael; Lutz, Josef

1999-05-01

137

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

E-print Network

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

Paris-Sud XI, Université de

138

Nano-multiplication region avalanche photodiodes and arrays  

NASA Technical Reports Server (NTRS)

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

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

2011-01-01

139

Simulations of avalanche breakdown statistics: probability and timing  

NASA Astrophysics Data System (ADS)

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 the fundamental limits of the SPADs. The effects of quenching resistor/circuit have been ignored. Due to competing effects between dead spaces, which are significant in modern SPADs with narrow avalanche regions, and converging ionization coefficients, the breakdown probability versus overbias characteristics from different avalanche region widths are fairly close to each other. Concerning avalanche breakdown timing at given value of breakdown probability, using avalanche material with similar ionization coefficients yields fast avalanche breakdowns with small timing jitter (albeit higher operating field), compared to material with dissimilar ionization coefficients. This is the opposite requirement for abrupt breakdown probability versus overbias characteristics. In addition, by taking band-to-band tunneling current (dark carriers) into account, minimum avalanche region width for practical SPADs was found to be 0.3 and 0.2 ?m, for InP and InAlAs, respectively.

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

2010-04-01

140

Fractal avalanche ruptures in biological membranes  

NASA Astrophysics Data System (ADS)

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

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

2010-11-01

141

Colloquium: Experiments in vortex avalanches E. Altshuler*  

E-print Network

as pinning centers, and the vortex motion becomes impeded. The interplay of pinning with an ex- ternal driveColloquium: Experiments in vortex avalanches E. Altshuler* Superconductivity Laboratory and ``Henri be found in vortex matter when a type-II superconductor is externally driven, for example, by an increasing

Johansen, Tom Henning

142

Measuring acoustic emissions in an avalanche slope  

NASA Astrophysics Data System (ADS)

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.

Reiweger, Ingrid; Schweizer, Jrg

2014-05-01

143

Rare-gas halide avalanche discharge lasers  

Microsoft Academic Search

This paper summarizes a series of studies aimed at understanding rare-gas halide lasers excited by UV preionized avalanche discharges. Discussions include steady-state rate equation calculations of the kinetics, parametric variations and optimizations of discharge characteristics, and gas mixture optimizations for high-energy lasing.

R. Sze

1979-01-01

144

Vortex avalanches in a type II superconductor  

SciTech Connect

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.

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

1999-12-01

145

Rock avalanches caused by earthquakes: Source characteristics  

USGS Publications Warehouse

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.

Keefer, D.K.

1984-01-01

146

Single Photon Avalanche Diodes for space applications  

Microsoft Academic Search

We study the possibility to use Single Photon Avalanche Diodes (SPADs) optically coupled to scintillating fibers as a novel type of gamma-ray detector for space applications. SPADs are silicon devices operating under polarization conditions above the junction breakdown voltage (typical overvoltage of 5V), for which a single photon interacting in the active region is sufficient to trigger a self sustainable

Martino Marisaldi; Piera Maccagnani; Francesco Moscatelli; Claudio Labanti; Fabio Fuschino; Michela Prest; Alessandro Berra; Davide Bolognini; Massimo Ghioni; Ivan Rech; Angelo Gulinatti; Andrea Giudice; Georg Simmerle; Danilo Rubini; Andrea Candelori; Serena Mattiazzo

2011-01-01

147

GPS Tracking Performance under Avalanche Deposited Snow  

E-print Network

With the recent advent of low-cost High Sensitivity Global Positioning System (HSGPS) receivers it may be possible Positioning System (HSGPS) receivers under avalanche deposited snow was investigated. Two field trials were and positioning performance. The PLAN Group at the University of Calgary has developed the miniature Global

Calgary, University of

148

Measuring Avalanche Frequency on the Balu Pass Trail, Glacier National Park, BC  

E-print Network

Measuring Avalanche Frequency on the Balu Pass Trail, Glacier National Park, BC Geog 477 ­ Fall reconstructions of avalanche activity · Use avalanche reconstruction in conjunction with snowpack data to determine avalanche frequency ­ may be used as a predictive measure to aid in mitigating avalanche related

Smith, Dan

149

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

ERIC Educational Resources Information Center

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.

Butler, David R.

1988-01-01

150

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

E-print Network

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

Dozier, Jeff

151

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

E-print Network

#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

Choi, Woo-Young

152

Nearest neighbour models for local and regional avalanche forecasting  

NASA Astrophysics Data System (ADS)

This paper presents two avalanche forecasting applications NXD2000 and NXD-REG which were developed at the Swiss Federal Institute for Snow and Avalanche Re-search (SLF). Even both are based on the nearest neighbour method they are targeted to different scales. NXD2000 is used to forecast avalanches on a local scale. It is operated by avalanche forecasters responsible for snow safety at snow sport areas, villages or cross country roads. The area covered ranges from 10 km2 up to 100 km2 depending on the climatological homogeneity. It provides the forecaster with ten most similar days to a given situation. The observed avalanches of these days are an indication of the actual avalanche danger. NXD-REG is used operationally by the Swiss avalanche warning service for regional avalanche forecasting. The Nearest Neighbour approach is applied to the data sets of 60 observer stations. The results of each station are then compiled into a map of current and future avalanche hazard. Evaluation of the model by cross-validation has shown that the model can reproduce the official SLF avalanche forecasts in about 52% of the days.

Gassner, M.; Brabec, B.

153

Snow Avalanche Release, Scale Invariance and Criticallity  

NASA Astrophysics Data System (ADS)

It is widely recognised that a number of geophysical phenomena as volcanic eruptions, landslides, etc, obey the so-called Gutenberg-Richter relation, first established for the frequency-magnitude statistics of earthquakes, where is the occurence frequency of earthquakes with a magnitude greater than m. This power law behaviour, character- istic of critical phenomena, is usually evidenced in the form of a linear distribution in a double logarithmic plot, in a way similar to the self organised criticality of a sand pile (2). We have shown very recently and for the first time that snow avalanche release exhibited such a behaviour (3). The only reliable parameter we had at that time was the amplitude of the acoustic emission associated with the avalanche release. Since it was not possible to record several events in the same gully, data were taken in sev- eral gullys of the same mountain range. Yet, the data aligned quite well on a unique straight line, with a critical exponent of about 1.6. This observation suggests that the very nature of the release mechanism is independent of the average slope and mor- phology of the gully. In order to understand the origin of this critical behaviour and to further investigate the mechanisms responsible for avalanche release, the avalanche release is studied in the present paper both by discrete elements simulations and cel- lular automata, and compared to further field data. The discrete elements simulations deal with a population of spheres on a slope, experiencing both a gravitational stress, interactions with the substrate, and mutual contact interactions. A gradual increase of the slope or a gradual change in contact forces (accounting for thermal snow mi- crostructure evolution) eventually result in avalanche release. The conditions are ad- justed until the frequency-magnitude of avalanches exhibit a critical behaviour. The cellular automaton is more or less similar to a game of life: a 2-d grid of boxes repre- sents the interface between the substrate and the snow slab, loaded in shear by the slab weight. Each box can be in one of two states labelled 0 and 1, according whether the slab/substrate interface is locally cracked or not. The state of a box can be changed ac- cording whether a given number of neighbours are in a 0 state or in a 1 state. A group of adjacent boxes in the 0 state represents a crack. The automaton is run from vari- ous randomly generated initial populations. Avalanches of various sizes are recorded. The local rules are adjusted until the avalanche frequency- size distribution aligns on a critical line. In both cases, the critical slopes are compared to field data. 1 (1) B. Gutenberg and C.F. Richter, seismicity of the earth and associated phenomenon, 2d edition, Princeton University Press, Princeton (1954) (2) P. Bak, How Nature Works, Springer Verlag (1996) (3) F. Louchet, J. Faillettaz, D. Daudon, N. Bdouin, E. Collet, J. Lhuissier and A-M. Portal XXVI General Assembly of the European Geophysical Society, Nice (F), 25-30 mars 2001 2

Dendievel, R.; Faillettaz, J.; Daudon, D.; Louchet, F.

154

Olokele rock avalanche, island of Kauai, Hawaii.  

USGS Publications Warehouse

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

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

1984-01-01

155

Mechanisms of evolution of avalanches in regular graphs.  

PubMed

A mapping of avalanches occurring in the zero-temperature random-field Ising model to life periods of a population experiencing immigration is established. Such a mapping allows the microscopic criteria for the occurrence of an infinite avalanche in a q-regular graph to be determined. A key factor for an avalanche of spin flips to become infinite is that it interacts in an optimal way with previously flipped spins. Based on these criteria, we explain why an infinite avalanche can occur in q-regular graphs only for q>3 and suggest that this criterion might be relevant for other systems. The generating function techniques developed for branching processes are applied to obtain analytical expressions for the durations, pulse shapes, and power spectra of the avalanches. The results show that only very long avalanches exhibit a significant degree of universality. PMID:23848642

Handford, Thomas P; Prez-Reche, Francisco J; Taraskin, Sergei N

2013-06-01

156

Precursors and prediction of catastrophic avalanches  

E-print Network

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.

Srutarshi Pradhan; Bikas K. Chakrabarti

2006-03-23

157

Shot Noise Suppression in Avalanche Photodiodes  

NASA Astrophysics Data System (ADS)

We identify a new shot noise suppression mechanism in a thin (100nm) heterostructure avalanche photodiode. In the low-gain regime the shot noise is suppressed due to temporal correlations within amplified current pulses. We demonstrate in a Monte Carlo simulation that the effective excess noise factors can be <1, and reconcile the apparent conflict between theory and experiments. This shot noise suppression mechanism is independent of known mechanisms such as Coulomb interaction, or reflection at heterojunction interfaces.

Ma, Feng; Wang, Shuling; Campbell, Joe C.

2005-10-01

158

Thermal avalanches near a Mott transition.  

PubMed

We probe the volume collapse transition (?V/Vo?15%) between the isostructural ? and ? phases (T?100K) 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=5.28נ10(26)m(-3)), and the ? phase (nH=3.76נ10(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.30469). PMID:24351548

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

2014-01-22

159

Predictive Capabilities of Avalanche Models for Solar Flares  

NASA Astrophysics Data System (ADS)

We assess the predictive capabilities of various classes of avalanche models for solar flares. We demonstrate that avalanche models cannot generally be used to predict specific events because of their high sensitivity to the embedded stochastic process. We show that deterministically driven models can nevertheless alleviate this caveat and be efficiently used for predictions of large events. Our results suggest a new approach for predictions of large (typically X-class) solar flares based on simple and computationally inexpensive avalanche models.

Strugarek, A.; Charbonneau, P.

2014-11-01

160

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

PubMed

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

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

2014-05-01

161

Avalanche in adhesion. [interfacial separation between two Ni crystals  

NASA Technical Reports Server (NTRS)

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.

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

1989-01-01

162

Predictive Capabilities of Avalanche Models for Solar Flares  

E-print Network

We assess the predictive capabilities of various classes of avalanche models for solar flares. We demonstrate that avalanche models cannot generally be used to predict specific events due to their high sensitivity to their embedded stochastic process. We show that deterministically driven models can nevertheless alleviate this caveat and be efficiently used for large events predictions. Our results promote a new approach for large (typically X-class) solar flares predictions based on simple and computationally inexpensive avalanche models.

Strugarek, Antoine

2014-01-01

163

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

E-print Network

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

Carter, John B.

164

Investigations using dendrochronology to determine snow avalanche characteristics in Rogers Pass, British Columbia  

E-print Network

Investigations using dendrochronology to determine snow avalanche characteristics in Rogers Pass multiple trees in the run out area of a major avalanche path. Dendrochronology was used to analyze......................................................................................................................................14 3.3.1 Dendrochronology and Avalanche Occurrence

Smith, Dan

165

Quantifying snowfall and avalanche release synchronization: A case study  

NASA Astrophysics Data System (ADS)

We quantify the synchronization between snowfall and natural avalanches in relation to terrain properties at the detachment zone. We analyze field statistics of 549 avalanche events in terms of slope, aspect, timing, coordinate, and release area, identified by a georeferencing procedure applied on terrestrial photography. The information from the digital pictures, together with associated meteorological data, provides us with the input needed for model calibration, namely, the magnitude of snowfall, the snow compaction rate, and the timing of precipitation and of avalanche events. Synchronization between snowfall and avalanches is established for different slope categories. We obtain an average probability of release after a snow event of 30% and 16% for the high- and low-slope categories (average slope 44 and 36, respectively). Using the notion of information entropy, we quantify the uncertainty in predicting avalanche occurrence from a snow event. The steeper slopes correspond to a larger entropy in avalanche prediction. Further, the presented method allows us to establish the return period of avalanches without requiring a long series of data. When considering events regardless of their release depth, the avalanches had a return period of 48 days (higher slopes) and 88 days (lower slopes). Finally, we determine the average daily detachment rate as a function of snow depth and the return period of avalanches as a function of the release depth.

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

2015-02-01

166

WET LOOSE SNOW AVALANCHING IN SOUTHWESTERN MONTANA Simon August Trautman  

E-print Network

WET LOOSE SNOW AVALANCHING IN SOUTHWESTERN MONTANA by Simon August Trautman A thesis submitted ..........................................................................................................1 2. WET SNOW...................................................................................................................3 Metamorphism of Wet Snow

Lawrence, Rick L.

167

New advances for modelling the debris avalanches  

NASA Astrophysics Data System (ADS)

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.

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

2013-04-01

168

Assessment and mapping of snow avalanche risk in Russia  

NASA Astrophysics Data System (ADS)

The term 'risk' can be defined as the probability of unfavourable consequences or negative effects. Risk can be expressed by means of various indices, such as collective or social risk (possible number of dead), individual risk (probability of a person's death within a certain territory during 1 year), probability of losses, etc. This paper is a case study of the small-scale assessment and mapping of individual avalanche risk focused on the two regions of Russia with the highest levels of avalanche activity: the northern Caucasus and the mountainous parts of Sakhalin island. The basic indices applied for individual avalanche risk estimation are: recurrence interval of avalanches (avalanche frequency), percentage of the whole investigated territory that is occupied by avalanche-prone areas, duration of avalanche danger period, probability of a person's stay in an avalanche-prone area during 1 day (24 hours) and during 1 year, total population of the area and its density. The results of individual avalanche risk assessment, undertaken for the territory of Russia as a whole, show that its values generally do not exceed the admissible level (from 1 10-6 to 1 10-4). However, some areas of the northern Caucasus, including famous alpine skiing resorts (Krasnaya Poliana, Dombai, the Mount Elbrus region, etc.), and of Sakhalin, including the environs of towns (Kholmsk, Nevel'sk) and other smaller human settlements, are characterized by an unacceptable level of risk. In the aggregate, areas with an unacceptable (>1 10-4) level of individual avalanche risk comprise about 7% of the whole avalanche-prone territory of the northern Caucasus, those with an admissible level comprise 52% and those with an acceptable level (<1 10-6) 41%. The corresponding values for Sakhalin are 0.1%, 14.8% and 85.1%.

Seliverstov, Yuri; Glazovskaya, Tatiana; Shnyparkov, Alexander; Vilchek, Yana; Sergeeva, Ksenia; Martynov, Alexei

169

LEGAL CONSEQUENCES OF FATAL AVALANCHE ACCIDENTS IN THE EUROPEAN ALPS  

Microsoft Academic Search

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,

Jrg Schweizer; Stephan Harvey

170

Advances in gas avalanche radiation detectors for biomedical applications  

E-print Network

Advances in gas avalanche radiation detectors for biomedical applications A. Breskin* Department avalanche radiation detectors have been massively employed over the past decades, mostly in particle physics on Applications of Radiation Detectors in Medicine, Biology and Astrophysics. Siegen, Germany, October 6}8, 1999

171

20-ps timing resolution with single-photon avalanche diodes  

Microsoft Academic Search

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

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

1989-01-01

172

Avalanches mediate crystallization in a hard-sphere glass.  

PubMed

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

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

2014-01-01

173

Avalanches mediate crystallization in a hard-sphere glass  

E-print Network

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.

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

2014-04-02

174

Avalanche dynamics in evolution, growth, and depinning models  

Microsoft Academic Search

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

Maya Paczuski; Sergei Maslov; Per Bak

1996-01-01

175

The HgCdTe electron avalanche photodiode  

Microsoft Academic Search

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

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

2003-01-01

176

A cooled avalanche photodiode with high photon detection probability  

NASA Technical Reports Server (NTRS)

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.

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

1986-01-01

177

Noise theory for the read type avalanche diode  

Microsoft Academic Search

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

M. E. Hines

1966-01-01

178

Avalanche-like behavior in ciliary import.  

PubMed

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

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

2013-03-01

179

Avalanche-like behavior in ciliary import  

PubMed Central

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

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

2013-01-01

180

Photon detection with cooled avalanche photodiodes  

NASA Technical Reports Server (NTRS)

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.

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

1987-01-01

181

Avalanches and Dynamical Correlations in supercooled liquids  

E-print Network

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.

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

2009-12-01

182

Avalanche Photodiode Arrays for Optical Communications Receivers  

NASA Technical Reports Server (NTRS)

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.

Srinivasan, M.; Vilnrotter, V.

2001-01-01

183

Cooled avalanche photodiode used for photon detection  

NASA Technical Reports Server (NTRS)

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.

Robinson, Deborah L.; Metscher, Brian D.

1987-01-01

184

Single photon avalanche diode radiation tests  

NASA Astrophysics Data System (ADS)

The single photon counting diodes are recently planned for applications in deep space missions. That is why the proton radiation and gamma ray radiation tests of silicon based single photon avalanche diodes were measured and compared. The main characteristic that changed after the irradiation was effective dark count rate, which was measured using actively quenching and gating circuit. The radiation reached 6.5 krad at 53 MeV protons energy and 34 krad using gamma ray radiation source 60Co. The annealing rates were monitored at room temperature and at 60 C.

Kodet, Jan; Prochazka, Ivan; Blazej, Josef; Sun, Xiaoli; Cavanaugh, John

2012-12-01

185

Avalanche prediction in a self-organized pile of beads.  

PubMed

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 pile of grains. 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 on average preceded by continuous, detectable variations in the internal structure of the pile that are monitored in order to achieve prediction. PMID:19257719

Ramos, O; Altshuler, E; Mly, K J

2009-02-20

186

Age of Palos Verdes submarine debris avalanche, southern California  

USGS Publications Warehouse

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.

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

2004-01-01

187

Stopping Financial Avalanches By Random Trading  

E-print Network

Building on similarities between earthquakes and extreme financial events, we use a self-organized criticality-generating model to study herding and avalanches dynamics in financial markets. We consider a community of interacting investors, distributed on a small world network, who bet on the bullish (increasing) or bearish (decreasing) behavior of the market compared to the day before, following the S&P500 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 trader s, randomly distributed inside the network, who adopt a random investment strategy. These results suggest a promising strategy to limit the size of financial bubbles and crashes. We also find that the final wealth distribution of all traders corresponds to the well-known Pareto power law, while that one of random traders only is exponential. In other words, for technical traders, the risk of losses is much greater tha...

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

2013-01-01

188

Reducing financial avalanches by random investments  

NASA Astrophysics Data System (ADS)

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.

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

2013-12-01

189

Reducing financial avalanches by random investments.  

PubMed

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

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

2013-12-01

190

Avalanche dynamics of radio pulsar glitches  

E-print Network

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{\

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

2007-10-04

191

Avalanches and the distribution of solar flares  

NASA Technical Reports Server (NTRS)

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.

Lu, Edward T.; Hamilton, Russell J.

1991-01-01

192

Germanium avalanche receiver for low power interconnects.  

PubMed

Recent advances in silicon photonics have aided the development of on-chip communications. Power consumption, however, remains an issue in almost all integrated devices. Here, we report a 10?Gbit per second waveguide avalanche germanium photodiode under low reverse bias. The avalanche photodiode scheme requires only simple technological steps that are fully compatible with complementary metal oxide semiconductor processes and do not need nanometre accuracy and/or complex epitaxial growth schemes. An intrinsic gain higher than 20 was demonstrated under a bias voltage as low as -7?V. The Q-factor relating to the signal-to-noise ratio at 10?Gbit per second was maintained over 20?dB without the use of a trans-impedance amplifier for an input optical power lower than -26?dBm thanks to an aggressive shrinkage of the germanium multiplication region. A maximum gain over 140 was also obtained for optical powers below -35?dBm. These results pave the way for low-power-consumption on-chip communication applications. PMID:25232823

Virot, Lopold; Crozat, Paul; Fdli, Jean-Marc; Hartmann, Jean-Michel; Marris-Morini, Delphine; Cassan, Eric; Boeuf, Frdric; Vivien, Laurent

2014-01-01

193

Germanium avalanche receiver for low power interconnects  

NASA Astrophysics Data System (ADS)

Recent advances in silicon photonics have aided the development of on-chip communications. Power consumption, however, remains an issue in almost all integrated devices. Here, we report a 10?Gbit per second waveguide avalanche germanium photodiode under low reverse bias. The avalanche photodiode scheme requires only simple technological steps that are fully compatible with complementary metal oxide semiconductor processes and do not need nanometre accuracy and/or complex epitaxial growth schemes. An intrinsic gain higher than 20 was demonstrated under a bias voltage as low as ?7?V. The Q-factor relating to the signal-to-noise ratio at 10?Gbit per second was maintained over 20?dB without the use of a trans-impedance amplifier for an input optical power lower than ?26?dBm thanks to an aggressive shrinkage of the germanium multiplication region. A maximum gain over 140 was also obtained for optical powers below ?35?dBm. These results pave the way for low-power-consumption on-chip communication applications.

Virot, Lopold; Crozat, Paul; Fdli, Jean-Marc; Hartmann, Jean-Michel; Marris-Morini, Delphine; Cassan, Eric; Boeuf, Frdric; Vivien, Laurent

2014-09-01

194

AVALANCHE CYCLES IN AUSTRIA - AN ANALYSIS OF THE GREATEST EVENTS IN THE LAST 50 YEARS  

Microsoft Academic Search

This paper deals with an analysis of major avalanche cycles in Austria. In particular the effects of certain weather situations on avalanche cycles are investigated. During the last 50 years an average of 30 persons per year were killed by avalanches in Austria. About one third of all avalanche fatalities occurred as a result of so-called \\

Peter Hller

195

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

E-print Network

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

Restrepo, Juan G.

196

Maximal avalanches in the Bak-Sneppen model Alexis Gillett1  

E-print Network

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

Meester, Ronald

197

Continuum description of avalanches in granular media Igor S. Aranson1  

E-print Network

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

Hasty, Jeff

198

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

E-print Network

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

Arleo, Angelo

199

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

E-print Network

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

Wiese, Kay Jörg

200

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

E-print Network

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

Tradacete, Pedro

201

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

E-print Network

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

Heil, Matthias

202

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

Microsoft Academic Search

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;

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

203

Record-breaking avalanches in driven threshold systems  

NASA Astrophysics Data System (ADS)

Record-breaking avalanches generated by the dynamics of several driven nonlinear threshold models are studied. Such systems are characterized by intermittent behavior, where a slow buildup of energy is punctuated by an abrupt release of energy through avalanche events, which usually follow scale-invariant statistics. From the simulations of these systems it is possible to extract sequences of record-breaking avalanches, where each subsequent record-breaking event is larger in magnitude than all previous events. In the present work, several cellular automata are analyzed, among them the sandpile model, the Manna model, the Olami-Feder-Christensen (OFC) model, and the forest-fire model to investigate the record-breaking statistics of model avalanches that exhibit temporal and spatial correlations. Several statistical measures of record-breaking events are derived analytically and confirmed through numerical simulations. The statistics of record-breaking avalanches for the four models are compared to those of record-breaking events extracted from the sequences of independent and identically distributed (i.i.d.) random variables. It is found that the statistics of record-breaking avalanches for the above cellular automata exhibit behavior different from that observed for i.i.d. random variables, which in turn can be used to characterize complex spatiotemporal dynamics. The most pronounced deviations are observed in the case of the OFC model with a strong dependence on the conservation parameter of the model. This indicates that avalanches in the OFC model are not independent and exhibit spatiotemporal correlations.

Shcherbakov, Robert; Davidsen, Jrn; Tiampo, Kristy F.

2013-05-01

204

Avalanche situation in Turkey and back calculation of selected events  

NASA Astrophysics Data System (ADS)

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 zengili (Bayburt province) in 1993 and Yaylan (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.

Aydin, A.; Bhler, Y.; Christen, M.; Grer, I.

2014-05-01

205

Transverse Instability of Avalanches in Granular Flows down Incline  

E-print Network

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.

Igor S. Aranson; Florent Malloggi; Eric Clement

2005-10-04

206

III-V alloy heterostructure high speed avalanche photodiodes  

NASA Technical Reports Server (NTRS)

Heterostructure avalanche photodiodes have been successfully fabricated in several III-V alloy systems: GaAlAs/GaAs, GaAlSb/GaAlSb, and InGaAsP/InP. These diodes cover optical wavelengths from 0.4 to 1.8 micron. Early stages of development show very encouraging results. High speed response of less than 35 ps and high quantum efficiency more than 95 percent have been obtained. The dark currents and the excess avalanche noise are also dicussed. A direct comparison of GaAlSb, GaAlAsSb, and In GaAsP avalanche photodiodes is given.

Law, H. D.; Nakano, K.; Tomasetta, L. R.

1979-01-01

207

Characterization of avalanche photodiodes for lidar atmospheric return signal detectors  

NASA Technical Reports Server (NTRS)

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.

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

1988-01-01

208

ELECTRON AVALANCHE MODEL OF DIELECTRIC-VACUUM SURFACE BREAKDOWN  

SciTech Connect

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.

Lauer, E J

2007-02-21

209

Overspill avalanching in a dense reservoir network  

PubMed Central

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 worlds 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

Mamede, George L.; Arajo, Nuno A. M.; Schneider, Christian M.; de Arajo, Jos Carlos; Herrmann, Hans J.

2012-01-01

210

Avalanche of particles in evaporating coffee drops  

E-print Network

The pioneering work of Deegan et al. [Nature 389, (1997)] showed how a drying sessile droplet suspension of particles presents a maximum evaporating flux at its contact line which drags liquid and particles creating the well known coffee stain ring. In this Fluid Dynamics Video, measurements using micro Particle Image Velocimetry and Particle Tracking clearly show an avalanche of particles being dragged in the last moments, for vanishing contact angles and droplet height. This explains the different characteristic packing of the particles in the layers of the ring: the outer one resembles a crystalline array, while the inner one looks more like a jammed granular fluid. Using the basic hydrodynamic model used by Deegan et al. [Phys. Rev. E 62, (2000)] it will be shown how the liquid radial velocity diverges as the droplet life comes to an end, yielding a good comparison with the experimental data.

Marin, Alvaro G; Snoeijer, Jacco; Lohse, Detlef

2010-01-01

211

Photon counting techniques with silicon avalanche photodiodes.  

PubMed

The properties of avalanche photodiodes and associated electronics required for photon counting in the Geiger and the sub-Geiger modes are reviewed. When the Geiger mode is used, there are significant improvements reported in overall photon detection efficiencies (approaching 70% at 633 nm), and a timing jitter (under 200 ps) is achieved with passive quenching at high overvoltages (20-30 V). The results obtained by using an active-mode fast quench circuit capable of switching overvoltages as high as 15 V (giving photon detection efficiencies in the 50% range) with a dead time of less than 50 ns are reported. Larger diodes (up to 1 mm in diameter) that are usable in the Geiger mode and that have quantum efficiencies over 80% in the 500-800-nm range are also reported. PMID:20830022

Dautet, H; Deschamps, P; Dion, B; Macgregor, A D; Macsween, D; McIntyre, R J; Trottier, C; Webb, P P

1993-07-20

212

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

E-print Network

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

Wijngaarden, Rinke J.

213

Modeling Advanced Avalanche Effects for Bipolar Transistor Circuit Design  

E-print Network

Modeling Advanced Avalanche Effects for Bipolar Transistor Circuit Design Vladimir Milovanovi operating frequency and high output power of modern bipolar transistor circuits increase, designers are trying to exploit transistor operating regions where they would be able satisfy both conditions, namely

Technische Universiteit Delft

214

Relative degradation of near infrared avalanche photodiodes from proton irradiation  

NASA Technical Reports Server (NTRS)

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.

Becker, Heidi; Johnston, Allan H.

2004-01-01

215

Failure avalanches in fiber bundles for discrete load increase  

E-print Network

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.

Per C. Hemmer; Srutarshi Pradhan

2007-01-11

216

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

E-print Network

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.

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

2010-06-21

217

Topographic reflection of the Socompa debris avalanche, Chile  

NASA Astrophysics Data System (ADS)

One of the most remarkable features of the exceptionally well preserved 26 km3 Socompa debris avalanche deposit is the evidence for topographically driven secondary flow. The avalanche formed by sector collapse of Socompa stratovolcano and spread 40 km across a pre-existing basin, forming a sheet of 50 m average thickness. As the avalanche impinged on the western and northern margins of the basin, it was reflected back, forming a secondary flow that continued to travel 15 km down a gentle slope at an oblique angle to the primary flow, the front of the return wave being preserved frozen on the surface of the deposit as a prominent escarpment. Satellite images, aerial photos, digital elevation models and field observations were used to reconstruct the sequence of events during avalanche emplacement, and in particular during secondary flow. The avalanche sheet was divided into distinct terrane groups, each believed to have experienced a particular strain history during emplacement. Evidence for avalanche reflection includes clearly recognizable secondary slide masses, sub-parallel sets of curvilinear shear zones, headwall scarps separating the (primary) leve from the secondary terranes, extensional jigsaw breakup of surface lithologies during return flow, and cross cutting, or deflection, of primary flow fabrics by secondary terranes. Reflection off the basin margin took place in an essentially continuous manner, most major return motions being simultaneous with, or shortly following, primary flow. The secondary flow occurred as a wave that swept obliquely across the primary avalanche direction, remobilizing the primary material, which was first compressed, then stretched, as it passed over and rearward of the wave front. As return flow occurred, surface lithologies were rifted in a brittle manner, and the slabs were sheared pervasively as they glided and rotated back into the basin; some sank into the more fluidal interior of the avalanche, which drained out into a prominent distal lobe. Extension by factors of up to 1.8 took place during return flow. Secondary flow took place on slopes of only a few degrees, and the distal lobe flowed 8 km on a slope of 1. Overall the avalanche is inferred to have slid into place as a fast-moving sheet of fragmental rock debris, with a leading edge and crust with near-normal friction and an almost frictionless, fluidal interior and base. The avalanche emplacement history deduced from field evidence is consistent with the results of a previously published numerical model of the Socompa avalanche.

Kelfoun, Karim; Druitt, Tim; van Wyk de Vries, Benjamin; Guilbaud, Marie-Nolle

2008-10-01

218

Effect of volume fraction on granular avalanche dynamics  

NASA Astrophysics Data System (ADS)

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=7.71.4? and occurred intermittently prior to the onset of an avalanche. Avalanches occurred at the maximal slope angle ?m=28.51.0?. Granular material at ?0-?c>0 did not experience precursor compaction prior to avalanche flow, and instead experienced a single dilational motion at ?0=32.11.5? prior to the onset of an avalanche at ?m=35.90.7?. 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=222?, 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 conditionsincluding volume fractionare important determinants of granular slope stability and the onset of avalanches.

Gravish, Nick; Goldman, Daniel I.

2014-09-01

219

On the internal flow velocity of snow avalanches  

NASA Astrophysics Data System (ADS)

Large-scale snow avalanches are hazardous and captivating examples of geophysical mass flows. In-situ measurements are challenging to obtain, limiting our understanding of the internal dynamics of these large mass movements. This research presents comprehensive results of an exciting new method based on a multi-chirp, multiple-receiver phased array Doppler radar that resolves the internal flow velocity of snow avalanches in unparalleled detail. Existing observations of dense snow avalanches are limited and generally fall into two categories: point measurements at a single fixed location or video measurements tracking the edge of the flow. Many avalanches, especially larger ones, give rise to a powder cloud that obscures the view of the denser core and renders video observations moot. Radar-based instruments may measure the dense avalanche directly, but up to now these systems have had poor down-slope resolution (> 50 m) and no cross-slope discrimination. We present a unique phased array radar imaging technique, with multiple waveforms and Doppler processing, to visualize internal flow fronts and waves in the denser core of a snow avalanche. The 5.3 GHz radar has been deployed at the avalanche test site of Valle de la Sionne in Switzerland and has captured several naturally occurring snow avalanches last winter. The depth-averaged 2D velocity field is resolved at 50 Hz intervals with a spatial resolution of ~1m in up-slope and ~10m in cross-slope direction. We use a 200 MHz frequency modulated sweep bandwidth of a radar chirp to determine the propagation velocity of each individual front accurately. Existing data on local topography and point measurements of event pressure, velocity and flow depth are combined with our 2D velocity profiles to provide a better understanding of the physics of these large-scale geophysical mass flows. In the future, we hope to apply this system to pyroclastic density currents and other natural mass movement flows.

Vriend, N. M.; Mcelwaine, J. N.; Keylock, C. J.; Ash, M.; Brennan, P. V.; Sovilla, B.

2011-12-01

220

Influence of snow-cover properties on avalanche dynamics  

NASA Astrophysics Data System (ADS)

Snow avalanches with the potential of reaching traffic routes and settlements are a permanent winter threat for many mountain communities. Snow safety officers have to take the decision whether to close a road, a railway line or a ski slope. Those decisions are often very difficult as they demand the ability to interpret weather forecasts, to establish their implication for the stability and the structure of the snow cover and to evaluate the influence of the snow cover on avalanche run-out distances. In the operational programme 'Italy-Switzerland, project STRADA' we focus on the effects of snow cover on avalanche dynamics, and thus run-out distance, with the aim to provide a better understanding of this influence and to ultimately develop tools to support snow safety officers in their decision process. We selected five avalanches, measured at the Valle de la Sionne field site, with similar initial mass and topography but different flow dynamics and run-out distances. Significant differences amongst the individual avalanches could be observed for front and internal velocities, impact pressures, flow regimes, deposition volumes and run-out distances. For each of these avalanches, the prevailing snow conditions at release were reconstructed using field data from local snowpits or were modeled with SNOWPACK. Combining flow dynamical data with snow cover properties shows that erodible snow depth, snow density and snow temperature in the snow pack along the avalanche track are among the decisive variables that appear to explain the observed differences. It is further discussed, how these influencing factors can be quantified and used for improved predictions of site and time specific avalanche hazard.

Steinkogler, W.; Sovilla, B.; Lehning, M.

2012-04-01

221

Avalanche-induced effects in polysilicon thin-film transistors  

Microsoft Academic Search

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

M. Hack; Alan G. Lewis

1991-01-01

222

Optimum Receiver Structure for PPM Signals with Avalanche Photodiode Statistics  

NASA Technical Reports Server (NTRS)

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.

Vilnrotter, V.; Srinivasan, M.

1998-01-01

223

Position-sensitive avalanche photodiodes for gamma-ray imaging  

Microsoft Academic Search

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

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

2002-01-01

224

A physical SNOWPACK model for the Swiss avalanche warning  

Microsoft Academic Search

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

Perry Bartelt; Michael Lehning

2002-01-01

225

Effect of volume fraction on granular avalanche dynamics.  

PubMed

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)=7.71.4 and occurred intermittently prior to the onset of an avalanche. Avalanches occurred at the maximal slope angle ?(m)=28.51.0. Granular material at ?(0)-?(c)>0 did not experience precursor compaction prior to avalanche flow, and instead experienced a single dilational motion at ?(0)=32.11.5 prior to the onset of an avalanche at ?(m)=35.90.7. 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)=222, 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

Gravish, Nick; Goldman, Daniel I

2014-09-01

226

Multigigabit-per-second avalanche photodiode lightwave receivers  

Microsoft Academic Search

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

B. L. Kasper; J. C. Campbell

1987-01-01

227

Avalanche dynamics in evolution, growth, and depinning models  

SciTech Connect

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)

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

228

MOBILITY OF ROCK AVALANCHES TRIGGERED BY UNDERGROUND NUCLEAR EXPLOSIONS  

Microsoft Academic Search

Several large rockslides and rock avalanches ranging in volume from 10 m up to 10 m 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

V. V. ADUSHKIN

229

Avalanche hazards and mitigation in Austria: a review  

Microsoft Academic Search

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

Peter Hller

2007-01-01

230

Why do some ice avalanches give warning prior to failure?  

NASA Astrophysics Data System (ADS)

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.

Caplan-Auerbach, J.

2006-12-01

231

Avalanches and hysteresis in frustrated superconductors and XY spin glasses  

NASA Astrophysics Data System (ADS)

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.

Sharma, Auditya; Andreanov, Alexei; Mller, Markus

2014-10-01

232

Pattern formation of granular avalanches with vortex convection  

E-print Network

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.

Hirofumi Niiya; Akinori Awazu; Hiraku Nishimori

2013-02-06

233

Avalanches and hysteresis in frustrated superconductors and XY spin glasses.  

PubMed

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

Sharma, Auditya; Andreanov, Alexei; Mller, Markus

2014-10-01

234

Avalanches, Plasticity, and Ordering in Colloidal Crystals Under Compression  

E-print Network

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.

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

2015-03-09

235

Prehistoric Rock Avalanches in the Obersee Valley, Glarner Alps, Switzerland  

NASA Astrophysics Data System (ADS)

Prehistoric rock avalanches in Alpine valleys have come under renewed scientific scrutiny as cosmogenic nuclide surface exposure dating allows new measurements of absolute failure timing. Many recently dated landslides reveal failure ages thousands of years younger than deglaciation of inner Alpine valleys, challenging commonly held assumptions regarding triggering by glacial retreat and debuttressing. Here we investigate two large rock avalanches in the Obersee area of the Glarner Alps, Switzerland, providing detailed mapping of all landslide and related Quaternary phenomena, revised volume estimates for each event, and surface exposure dating of rock avalanche deposits. The Rautispitz rock avalanche originated from the southern flank of the Obersee valley, releasing approximately 91 million m3 of material on steeply-dipping limestone beds. Debris had maximum horizontal travel distance of ~5000 m, a fahrboeschung angle (relating fall height to length) of 18, and was responsible for creation of the Lake Obersee. Deposits are more than 130 m thick in places. The Platten rock avalanche released a total of 11 million m3 of material from the northern flank of the Obersee valley on similar steeply-dipping limestone beds (bedrock forms a syncline under the valley). Debris had a maximum horizontal travel distance of 1600 m with a fahrbschung angle of 21, and is more than 80 m thick in places. Deposits of the Platten rock avalanche are superposed atop those from the Rautispitz event at the end of the Obersee valley where they dam the Lake Haslensee. Runout for both events was assessed using the quasi-3D dynamic analysis code DAN3D; results showed excellent match to mapped deposit extents and thickness distributions and helped confirm the hypothesized failure scenarios. 36Cl cosmogenic nuclide surface exposure dating of 13 deposited boulders revealed an early Holocene age for the Rautispitz event and a mid-Holocene age for the Platten rock avalanche; a seismological trigger is suspected for the former due to coincident turbidite deposits in nearby Lake Zurich.

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

2013-12-01

236

Record-breaking avalanches in driven threshold systems.  

PubMed

Record-breaking avalanches generated by the dynamics of several driven nonlinear threshold models are studied. Such systems are characterized by intermittent behavior, where a slow buildup of energy is punctuated by an abrupt release of energy through avalanche events, which usually follow scale-invariant statistics. From the simulations of these systems it is possible to extract sequences of record-breaking avalanches, where each subsequent record-breaking event is larger in magnitude than all previous events. In the present work, several cellular automata are analyzed, among them the sandpile model, the Manna model, the Olami-Feder-Christensen (OFC) model, and the forest-fire model to investigate the record-breaking statistics of model avalanches that exhibit temporal and spatial correlations. Several statistical measures of record-breaking events are derived analytically and confirmed through numerical simulations. The statistics of record-breaking avalanches for the four models are compared to those of record-breaking events extracted from the sequences of independent and identically distributed (i.i.d.) random variables. It is found that the statistics of record-breaking avalanches for the above cellular automata exhibit behavior different from that observed for i.i.d. random variables, which in turn can be used to characterize complex spatiotemporal dynamics. The most pronounced deviations are observed in the case of the OFC model with a strong dependence on the conservation parameter of the model. This indicates that avalanches in the OFC model are not independent and exhibit spatiotemporal correlations. PMID:23767588

Shcherbakov, Robert; Davidsen, Jrn; Tiampo, Kristy F

2013-05-01

237

Dead Time of Single Photon Avalanche Diodes  

NASA Astrophysics Data System (ADS)

Single Photon Avalanche Diode (SPAD) is the new generation of Geiger-Muller counter device developed in semiconductor technology [S. Privitera et al. Sensors Journal, vol 8 Iss. 8 (2008) 4636; S. Tudisco et al. IEEE Sensors Journal vol 8 ISS 7-8 (2008) 1324; S. Cova et al. Applied Optics 35 (1996) 1956]. Physical dead time model and noise production process has been analyzed and their corrections have been performed [S.H. Lee, R.P. Gardner, M. Jae, Nucl. Instr. and Meth. in Phys. Res. B 263 (2007) 46]. We have been able to extract the real amount of incident photon rate up to 10 7cps using a device with 0.97?s total deadtime. We also developed the equation of the noise count rate vs incoming photon rate, supported by Montecarlo simulation and experimental data. We marked the difference between dark rate and noise count rate, and introduced the noise rate inside the hybrid deadtime equation used for SPAD device.

Neri, L.; Tudisco, S.; Musumeci, F.; Scordino, A.; Fallica, G.; Mazzillo, M.; Zimbone, M.

2011-06-01

238

OPTIMIZING THROUGH CO-EVOLUTIONARY AVALANCHES  

SciTech Connect

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.

S. BOETTCHER; A. PERCUS

2000-08-01

239

Arrest of Avalanche Propagation by Discontinuities on Snow Cover  

NASA Astrophysics Data System (ADS)

Considering the spatial variability of the snow cover, the paper analyses, in the framework of Fracture Mechanics, the Mode II fracture propagation on snow cover that leads to large dry slab avalanches. Under the hypothesis of a perfectly brittle phenomenon, avalanche triggering is usually investigated numerically by means of Linear Elastic Fracture Mechanics (McClung, 1979; Chiaia et al., 2008). Since, however, the real phenomenon is intrinsically dynamical, another aspect to investigate is represented by dynamic fracture propagation. In this paper, we model dynamic crack propagation into a dry snow slab, to assess the possibility of crack arrest due to the presence of weak zones distributed along the snow slope. As a consequence of the first triggering mechanism (the Mode II fracture propagation on the weak plane), the secondary Mode I crack propagation in the crown is studied by means of numerical simulations based on Dynamic Elastic Fracture Mechanics and on the theory of crack arresters. By taking into account kinetic energy and using the FEM software FRANC 2D (Wawrzynek and Ingraffea, 1993), several paths of crown fracture propagation and their stability have been investigated. The snowpack is considered as a linear-elastic plate (2D problem), whose physical and mechanical parameters are chosen according to classical literature values. To investigate the possible arrest of crown fracture, we apply the theory of crack arresters, usually adopted for pipelines and perforated steel sheets fracture problems. To study crack arrest, different crack paths are simulated, in discontinuous (equipped with different shapes and geometries of artificial voids) snowpacks. The simulations show the effectiveness of these weak zones, to reduce substantially the crack driving force of the propagating fracture. This means that, increasing spatial variability tends to stabilize the snow slope, eventually splitting a major avalanche event into smaller, independent avalanches. Our results are supported also by other investigations, which suggested that increased spatial variability in the snow cover leads to a lower release probability of snow avalanches. The above studies are based on very different approaches, such as cellular automata (Kronholm and Birkeland, 2005) and statistical renormalization (Chiaia and Frigo, 2009) models, but come to the same conclusion, i.e. that the presence of randomly distributed weak zones increase the global robustness and toughness of the snow slope. From a practical engineering viewpoint, results could be used towards a new idea of active avalanche protection, based on the presence of natural (e.g., trees) or artificial objects throughout the slope, able to create low deposition zones as discontinuities in the snow cover. Key words: snow avalanche, fracture mechanics, crack arrester. References Chiaia, B., Cornetti, P., Frigo, B., 2008. Triggering of dry snow slab avalanches: Stress versus fracture mechanical approach Cold Reg. Sci. Technol. 53 170-178. Chiaia, B., Frigo, B., 2009, A scale-invariant model for snow slab-avalanches, J. Stat. Phys., submitted Fhn, P.M.B., Camponovo, C., Krsi, G., 1998. Mechanical and structural properties of weak snow layers measured in situ. Annals of Glaciology 26, 1-6. Jamieson, J.B., Johnston, C.D., 1992. A fracture-arrest model for unconfined dry slab avalanches. Canadian Geotechnical Journal, 29, 61-66. Jamieson, B., Johnston, C.D., 2001. Evaluation of shear frame test for weak snowpack layers. Annals of Glaciology 32, 59-69. Kirchner, H.O.K., Michot, G., Schweizer, J., 2002. Fracture toughness of snow in shear and tension. Scripta Materialia 46, 425-429. Kronholm, K., Birkeland, K. W., 2005. Integrating spatial patterns into a snow avalanche cellular automata model, Geophysical Research Letters 32, L19504. McClung, D. M. 1979. Shear fracture precipitated by strain softening as a mechanism of dry slab avalanche release, J. Geophys. Res. 84(B7) 3519-3526. Schweizer, J., 1999. Review of dry snow avalanche release Cold Reg. Sci. Technol. 30 43-57. Wawrzynek, P., Ingr

Frigo, B.; Chiaia, B.

2009-04-01

240

Ge on Si and InP/InGaAs single photon avalanche diodes  

NASA Astrophysics Data System (ADS)

This paper describes single photon detection for Ge on Si separate-absorption-charge-multiplication (SACM) avalanche photodiodes and advances in quenching for InP/InGaAs single photon avalanche diodes.

Lu, Zhiwen; Sun, Wenlu; Hu, Chong; Holmes, Archie; Campbell, Joe C.; Kang, Yimin; Liu, Han-Din

2011-10-01

241

Debris avalanche deposits: emplacement dynamics, morphology and hazards (Invited)  

NASA Astrophysics Data System (ADS)

Debris avalanches from volcanoes form some of the largest subaerial and submarine landslide deposits on Earth, covering vast areas (10s to 100s km2) and displaying typically hummocky surface topography. Numerical models have been developed that can identify the area threatened by an event of known volume from a known volcano, if the runout mechanics can be understood. Better understanding the hazards from these enormous events requires realistic parameterization of models, which must be able to explain debris avalanche deposit geometries under water, in air, on Mars and in vacuo on the Moon. We have shown that the complex deposit geometry of the 25 km3 Socompa deposit in Chile can be explained by the effects of basal debris fragmenting during runout. The hummocky surface morphology of many debris avalanche deposits again indicates that the emplacement process involved a very mobile basal layer, above which the travelling mass passively extends, leading to lateral and longitudinal disaggregation of the mass into discrete blocks whose dimension reflects the mass depth. Submarine debris avalanches can also be modelled on this basis, because the presence of ambient water does not fundamentally alter the fragmentation process; to assess the additional hazards of debris avalanches entering into water, models are available to simulate the tsunami generated by such events.

Davies, T. R.; Dufresne, A.

2013-12-01

242

Avalanches in the Weakly Driven Frenkel-Kontorova Model  

E-print Network

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

Franz-Josef Elmer

1994-09-29

243

Avalanches of rearrangements in quasi-2D emulsion hopper flow  

E-print Network

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.

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

2015-03-25

244

Inductive braking of thermomagnetic avalanches in superconducting films  

NASA Astrophysics Data System (ADS)

The stabilizing effect of placing a normal metal layer adjacent to a thermomagnetically unstable superconducting film is investigated. By solving the coupled Maxwell and heat transfer equations numerically it is shown that the metal, via inductive braking of the rapidly propagating flux avalanches, strongly reduces their impact. It is found that with increasing thickness and/or electrical conductivity of the metal layer, the number of avalanche events increases, while the amount of flux involved in each avalanche is strongly reduced, resulting in an overall more stable thermomagnetic system. The numerical results provide detailed insight into the braking process, and explain both previous dc magnetometry measurements and new magneto-optical imaging results obtained for a superconducting NbN film coated with a Cu-layer.

Vestgrden, J. I.; Mikheenko, P.; Galperin, Y. M.; Johansen, T. H.

2014-05-01

245

Crack roughness and avalanche precursors in the random fuse model.  

PubMed

We analyze the scaling of the crack roughness and of avalanche precursors in the two-dimensional random fuse model by numerical simulations, employing large system sizes and extensive sample averaging. We find that the crack roughness exhibits anomalous scaling, as recently observed in experiments. The roughness exponents (zeta, zeta(loc) ) and the global width distributions are found to be universal with respect to the lattice geometry. Failure is preceded by avalanche precursors whose distribution follows a power law up to a cutoff size. While the characteristic avalanche size scales as s(0) approximately L(D) , with a universal fractal dimension D , the distribution exponent tau differs slightly for triangular and diamond lattices and, in both cases, it is larger than the mean-field (fiber bundle) value tau=5/2 . PMID:15783377

Zapperi, Stefano; Nukala, Phani Kumar V V; Simunovi?, Srdan

2005-02-01

246

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

USGS Publications Warehouse

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

McEwen, A.S.

1989-01-01

247

Avalanche Dynamics of Crackle Sound in the Lung  

SciTech Connect

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.

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

2001-08-20

248

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

SciTech Connect

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.

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

2007-01-01

249

Secondary Instability in Drift Wave Turbulence as a Mechanism for Avalanche Formation  

E-print Network

Secondary Instability in Drift Wave Turbulence as a Mechanism for Avalanche Formation P.H. Diamond for avalanche formation. A theory of radially extended streamer cell formation and self-regulation is presented is indicative of the formation of structures akin to avalanches[3], #12;c.) the observation that the pdf

Lin, Zhihong

250

FATAL OCCUPATIONAL INJURIES OF AVALANCHE WORKERS IN NORTH AMERICA Ethan M. Greene1  

E-print Network

FATAL OCCUPATIONAL INJURIES OF AVALANCHE WORKERS IN NORTH AMERICA Ethan M. Greene1 *, Bruce the rate of fatal avalanche injuries of avalanche workers in North America with other occupational makes examining work- place injuries of this group extremely difficult. For the purpose of this study

Jamieson, Bruce

251

An evaluation of rule-based decision tools for travel in avalanche terrain  

Microsoft Academic Search

Avalanche forecasting at the slope scale is an essential skill for traveling safely in avalanche terrain. Recent studies indicate that this skill is difficult for recreationists to master, and is subject to a number of persistent biases that can lead to avalanche accidents and their associated fatalities. In an effort to address this problem, researchers have developed a number of

Ian McCammon; Pascal Hgeli

2007-01-01

252

Size of snow particles in a powder-snow avalanche LIP Research Report 2009-25  

E-print Network

Size of snow particles in a powder-snow avalanche LIP Research Report 2009-25 M. Rastello F. Rastello H. Bellot F. Ousset F. Dufour The size of the snow particles involved in a powder-snow avalanche snow particles within powder-snow avalanches. Snow particles have been captured in the powder-snow part

Paris-Sud XI, Universit de

253

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

E-print Network

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

Weinmüller, Ewa B.

254

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

E-print Network

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

Bowers, John

255

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

E-print Network

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

Saramito, Pierre

256

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

E-print Network

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

Destexhe, Alain

257

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

E-print Network

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

Sethna, James P.

258

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

E-print Network

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

Noelle, Sebastian

259

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

E-print Network

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

McElwaine, Jim

260

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

E-print Network

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

Williams, Mark W.

261

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

E-print Network

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

Jamieson, Bruce

262

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

E-print Network

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

Boyer, Edmond

263

Si avalanche photodetectors fabricated in standard complementary metal-oxide-semiconductor process  

E-print Network

Si avalanche photodetectors fabricated in standard complementary metal-oxide-semiconductor process; accepted 10 March 2007; published online 12 April 2007 The authors report silicon avalanche photodetectors process modification or a special substrate. When the bias is above the avalanche breakdown voltage, CMOS

Choi, Woo-Young

264

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

E-print Network

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

Jamieson, Bruce

265

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

E-print Network

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

Martín-Solís, José Ramón

266

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

E-print Network

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

Jamieson, Bruce

267

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

E-print Network

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

Granada, Universidad de

268

Regional comparison of old-deep slab avalanches David Tracz1  

E-print Network

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

Jamieson, Bruce

269

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

E-print Network

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

Rieh, Jae-Sung

270

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

E-print Network

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

Gray, Nico

271

Large area avalanche photodiode detector array upgrade for a ruby-laser Thomson scattering system  

E-print Network

Large area avalanche photodiode detector array upgrade for a ruby-laser Thomson scattering system T microchannel plate MCP detector was replaced with an array of modular large area avalanche photodiode detectors-laser head, collection optics, a Jarrell-Ash MonoSpec-27 Model 82-499 spectrometer, and avalanche photodiode

Biewer, Theodore

272

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

E-print Network

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

Wiese, Kay Jörg

273

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

E-print Network

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

Hasty, Jeff

274

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

E-print Network

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

Smith, Dan

275

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

E-print Network

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

Johansen, Tom Henning

276

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

E-print Network

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

Paris-Sud XI, Université de

277

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

278

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

E-print Network

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

Sethna, James P.

279

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

ERIC Educational Resources Information Center

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)

Grant, Frank

2003-01-01

280

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

E-print Network

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

Jamieson, Bruce

281

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

E-print Network

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

Johansen, Tom Henning

282

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

E-print Network

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

Saramito, Pierre

283

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

E-print Network

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

Lombardi, John R.

284

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

E-print Network

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

Johansen, Tom Henning

285

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

E-print Network

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

Shearer, Michael

286

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

E-print Network

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

Newton, Ryan R.

287

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

E-print Network

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

Gleeson, James P.

288

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

289

LAUTARET AVALANCHE TEST SITE : OUTCOMES FROM THE 11 APRIL 2012 EVENT  

E-print Network

LAUTARET AVALANCHE TEST SITE : OUTCOMES FROM THE 11 th APRIL 2012 EVENT Xavier Ravanat, Hervé Saint Martin d'Hères France ABSTRACT: The Lautaret full-scale avalanche test site has been used by Cemagref-Irstea since the early 70's. The first studies were dedicated to avalanche released systems. Later

Paris-Sud XI, Université de

290

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

E-print Network

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

Kääb, Andreas

291

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

E-print Network

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

Middleton, Alan

292

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

E-print Network

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

Martín-Solís, José Ramón

293

RELATING AVALANCHES TO LARGE-SCALE OCEAN ATMOSPHERIC OSCILLATIONS Scott Thumlert  

E-print Network

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

Jamieson, Bruce

294

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

E-print Network

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

Hogg, Andrew

295

Using AVAL-1D to simulate avalanches in the eastern Pyrenees  

Microsoft Academic Search

The two friction parameters used in the numerical avalanche dynamics program AVAL-1D, were calibrated empirically with data from observed avalanches in the Swiss Alps. The implementation of the model with these friction parameters in other regions with different characteristics can lead to considerable uncertainty if a previous calibration is not performed. However, direct calibration for a specific avalanche path is

Pere Oller; Marc Janeras; Hctor de Buen; Georgina Arn; Marc Christen; Carles Garca; Pere Martnez

2010-01-01

296

Release of Wet Snow Avalanches: A Grain-scale Approach  

NASA Astrophysics Data System (ADS)

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.

Gan, Yixiang; Faug, Thierry; Einav, Itai

2014-05-01

297

Avalanche shape and exponents beyond mean-field theory  

E-print Network

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 $\\left_T\\simeq [ Tx(1-x)]^{\\gamma-1} \\exp\\left( {\\cal A}\\left[\\frac12-x\\right]\\right)$, $0avalanche towards its end, as observed in numerical simulations in $d=2$ and $3$. The exponent $\\gamma=(d+\\zeta)/z$ is given by the two independent exponents at depinning, the roughness $\\zeta$ and the dynamical exponent $z$. We propose a general procedure to predict other avalanche exponents in terms of $\\zeta$ and $z$. We finally introduce and calculate the shape at fixed avalanche size, not yet measured in experiments or simulations.

Alexander Dobrinevski; Pierre Le Doussal; Kay Jrg Wiese

2014-07-28

298

The geomorphological significance of avalanche sedimentation for landscape evolution  

NASA Astrophysics Data System (ADS)

Snow avalanches, especially dirty snow and slush avalanches, are recognized as important geomorphological agents in periglacial landscapes. Especially where relief, climate and lithology are favourable. Therefore, the study of avalanche sedimentation adds to the understanding of classic concepts in periglacial geomorphology: rock weathering, erosion and transport, associated with periglacial landscape evolution. However, the importance of long-term, large-scale landscape evolution by periglacial processes is questioned. While major glaciations determine landscape evolution on large time and spatial scales, periglacial processes act normally on a much smaller time and spatial scales, bound to the supply of a water and/or snow source. In Svalbard, many rock walls, that underwent large retreat in the Holocene are presently covered in lichens and only undergo slow biogenic flacking. There is thus a discrepancy between small contemporary rockwall retreat and significantly higher Holocene rates. However, there are examples of long-term periglacial landscape evolution, induced for example by nivation processes. Nivation transformed the Saalian glacial landscape in southwestern Denmark, being especially effective in unconsolidated sediments, at perennial snow patches, but also at avalanche sites . The nivation concept therefore applies also for the process of cornice fall avalanche sedimentation in the Longyeardalen valley, central Svalbard. Here we show for the first time, that even after the early Holocene deglaciation of the hill slopes in Longyeardalen, the present-day rockwall retreat rates are higher than the Holocene ones. This contributes not only to the rock slope denudation, but also to the active development of a rock glacier and avalanches sedimentation fans.

Eckerstorfer, Markus; Christiansen, Hanne

2013-04-01

299

On the formation of glide-snow avalanches  

NASA Astrophysics Data System (ADS)

On steep slopes the full snowpack can glide on the ground; tension cracks may open and eventually the slope may fail as a glide-snow avalanche. Due to their large mass they have considerable destructive potential. Glide-snow avalanches typically occur when the snow-soil interface is moist or wet so that basal friction is reduced. The occurrence, however, of glide cracks and their evolution to glide avalanches are still poorly understood. Consequently, glides are difficult to predict as (i) not all cracks develop into an avalanche, and (ii) for those that do, the time between crack opening and avalanche event might vary from hours to weeks - or on the other hand be so short that there is no warning at all by crack opening. To improve our understanding we monitored several slopes and related glide snow activity to meteorological data. In addition, we explored conditions that favor the formation of a thin wet basal snowpack layer with a physical-based model representing water and heat flux at the snow-soil interface. The statistical analyses revealed that glide-snow avalanche activity might be associated to an early season and a spring condition. While early season conditions tend to have warm and dry autumns followed by heavy snowfalls, spring conditions showed good agreement with increasing air temperature. The model indicates that energy (summer heat) stored in the ground might be sufficient to melt snow at the bottom of the snowpack. Due to capillary forces, water will rise for a few centimeters into the snowpack and thereby reduce friction at the interface. Alternatively, we demonstrate that also in the absence of melt water production at the bottom of the snowpack water may accumulate in the bottom layer due to an upward flux into the snowpack if a dry snowpack overlies a wet soil. The particular conditions that are obviously required at the snow-soil interface explain the strong winter-to-winter variations in snow gliding.

Mitterer, C.; Schweizer, J.

2012-12-01

300

Neutron irradiation studies of avalanche photodiodes using californium-252  

NASA Astrophysics Data System (ADS)

Californium-252 is a convenient and copious source of neutrons of energies around 1 MeV, and provides many advantages over reactors for neutron irradiation studies of detector components. We describe here an experimental setup at Oak Ridge National Laboratory which has been constructed to study the performance of avalanche photodiodes in neutron fluences up to 10 13 neutrons/cm 2, similar to what is expected in parts of the CMS detector at the LHC. An irradiation study of some avalanche photodiodes is discussed, followed by a brief summary of results obtained.

Reucroft, S.; Rusack, R.; Ruuska, D.; Swain, J.

1997-02-01

301

Asymmetric Avalanche Behavior in a Zeeman-Limited Superconductor  

NASA Astrophysics Data System (ADS)

We have performed transport and tunneling density of states measurements of ultra-thin Al films through the first-order parallel critical field transition. The transition is intrinsically hysteretic and exhibits avalanche-like jumps in both resistivity and tunneling density states. Tunneling measurements on films with sheet resistances of a few hundred ohms show large avalanche-like collapses of the condensate on the superheating branch of the critical field hysteresis loop. In contrast, the transition back into the superconducting phase (i.e., along the supercooling branch) is always continuous.

Adams, P. W.; Prestigiacomo, J. C.

2014-12-01

302

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

E-print Network

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.

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

2012-04-26

303

Further studies of electron avalanche gain in liquid argon  

SciTech Connect

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.

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

304

Self-Organization in a Granular Medium by Internal Avalanches  

E-print Network

Internal avalanches of grain displacements can be created inside a granular material kept in a bin in two ways: (i) By removing a radomly selected grain at the bottom of the bin (ii) By breaking a stable arch of grains clogging a hole at the bottom of the bin. Repeated generations of such avalanches lead the system to a steady state. The question asked, is this state a critical state as that in Self-Organized Criticality? We review here some of the recent studies on this problem using cellular automata as well as hard disc models.

S. S. Manna

2000-09-12

305

Sub 100ps time resolution using silicon avalanche diodes  

SciTech Connect

We have investigated silicon avalanche diodes (AVDs) as time of flight detectors for nuclear and particle physics applications. The signal is created by the large number of electron-hole pairs ({approx}100 pairs/mm) deposited along the path of a particle passing through the AVD. The electrons drift in a strong electric field to the diode junction, where they multiply in an avalanche region. A single diode time resolution of 65 ps has been obtained using fast leading-edge discriminators. This time resolution is comparable to the best obtained with the conventional alternative of plastic scintillator and photomultiplier tube. Further optimization appears possible.

Hauger, J.A.; Choi, Y.; Hirsch, A.S.; Porile, N.T. [and others

1993-10-01

306

Snow avalanche detection and identification for near real-time application  

NASA Astrophysics Data System (ADS)

A near real-time avalanche detection system will provide highway avalanche forecasters with a tool to remotely monitor major avalanche paths and provide information about regional avalanche activity and timing. For the last three winters, a network of infrasound arrays has been remotely monitoring both avalanche and non-avalanche events along a 10 mile section of Highway 21 in Idaho. To provide the best results to avalanche forecasters, the system must be robust and detect all major avalanche events of interest that affect the highway. Over the last three winters, the infrasound arrays recorded multiple avalanche cycles and we explore different methods of event detection for both large dry avalanches (strong infrasound signal) and small wet avalanches (weak infrasound signal). We compare the F-statistic and cross-correlation techniques (i.e. PMCC) to determine the most robust method and develop computationally efficient algorithms to implement in near-real time using parallel processing and GPU computing. Once an event has been detected, we use the artificial intelligence method of recursive neural networks to classify based on similar characteristics to past known signals.

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

2013-12-01

307

Powder Snow Avalanches - Results From Valle de la Sionne, Winter 2004  

NASA Astrophysics Data System (ADS)

Powder snow avalanche surfaces can be effectively tracked using videogrammetry. 3-dimensional surface maps were generated from two digital video recordings of an artificially released avalanche, captured from different places. From these maps the avalanche volume and front velocity is inferred. Several different types of sensor are mounted on a mast in the avalanche path. These include impact pressure sensors, optical velocity sensors and a pitot air pressure sensor. In this paper the air pressure data and the information it gives about the air flow both outside and inside the avalanche is described in detail. A simple dipole approximation is used to estimate the speed and size of the avalanche and a comparison with the videogrammetric analysis can be made. In addition the internal structure of the avalanche is considered and its implications for modelling discussed.

Turnbull, B.; McElwaine, J.; Bartelt, P.

2004-12-01

308

Reducing the Odds: Backcountry Powder Skiing in Avalanche Terrain.  

ERIC Educational Resources Information Center

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

Daffern, Tony

309

Structural Control of Giant Rock Avalanches in Argentina  

NSDL National Science Digital Library

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.

Barb Tewksbury

310

Group Dynamics and Decision Making: Backcountry Recreationists in Avalanche Terrain  

ERIC Educational Resources Information Center

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,

Bright, Leslie Shay

2010-01-01

311

Improving the Strict Avalanche Characteristics of Cryptographic Functions  

E-print Network

Improving the Strict Avalanche Characteristics of Cryptographic Functions Jennifer Seberry Xian-Mo a wide range of applications in designing cryptographically strong functions, including substitution, or simply, f(x) f(x ) is balanced, for every 2 Vn with W( ) = 1, where x = (x1 ::: xn) and W( ) denotes

Seberry, Jennifer

312

Evolution of avalanche conducting states in electrorheological liquids.  

PubMed

Charge transport in electrorheological fluids is studied experimentally under strongly nonequilibrium conditions. By injecting an electrical current into a suspension of conducting nanoparticles we are able to initiate a process of self-organization which leads, in certain cases, to formation of a stable pattern which consists of continuous conducting chains of particles. The evolution of the dissipative state in such a system is a complex process. It starts as an avalanche process characterized by nucleation, growth, and thermal destruction of such dissipative elements as continuous conducting chains of particles as well as electroconvective vortices. A power-law distribution of avalanche sizes and durations, observed at this stage of the evolution, indicates that the system is in a self-organized critical state. A sharp transition into an avalanche-free state with a stable pattern of conducting chains is observed when the power dissipated in the fluid reaches its maximum. We propose a simple evolution model which obeys the maximum power condition and also shows a power-law distribution of the avalanche sizes. PMID:11969677

Bezryadin, A; Westervelt, R M; Tinkham, M

1999-06-01

313

Anterior capsulotomy with a pulsed-electron avalanche knife  

E-print Network

Anterior capsulotomy with a pulsed-electron avalanche knife Daniel Palanker, PhD, Hiroyuki Nomoto, MD, PhD, Philip Huie, MA, Alexander Vankov, PhD, David F. Chang, MD PURPOSE: To evaluate a new pulsed-electron, and burst duration. Tissue samples were fixed and processed for histology and scanning electron microscopy

Palanker, Daniel

314

Photon-counting techniques with silicon avalanche photodiodes  

Microsoft Academic Search

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).

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

1993-01-01

315

Vortex avalanches and the onset of superfluid turbulence  

E-print Network

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.

N. B. Kopnin

2003-09-30

316

Teaching Avalanche Safety Courses: Instructional Techniques and Field Exercises.  

ERIC Educational Resources Information Center

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,

Watters, Ron

317

Threshold energy effect on avalanche breakdown voltage in semiconductor junctions  

Microsoft Academic Search

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

Y. Okuto; C. R. Crowell

1975-01-01

318

Bipolar transistor modeling of avalanche generation for computer circuit simulation  

Microsoft Academic Search

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.

R. W. Dutton

1975-01-01

319

Initial results from the Sherbrooke avalanche photodiode positron tomograph  

Microsoft Academic Search

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.

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

1996-01-01

320

Catastrophic debris avalanche deposit of Socompa volcano, northern Chile  

NASA Technical Reports Server (NTRS)

Between 10,000 and 500 yr ago the Socompa volcano in northern Chile experienced a catastrophic collapse of a 70 deg sector of the original cone, causing a debris avalanche that descended nearly 3000 m vertically and traveled more than 35 km from the volcano. The deposits cover some 490 sq km and have a minimum volume of 15 cu km. Parts of the original cone slumped in a nearly coherent form and are now preserved as large blocks more than 400 m high. The primary avalanche traveled northwestward over sloping ground before coming to rest transiently, forming a prominent marginal ridge, and then slid away northeastward to form a secondary flow, overriding much of the primary avalanche deposit. Abundant, prismatic, jointed dacite blocks within the debris avalanche deposit and a thin, fine-grained pumiceous deposit beneath it suggest that the collapse was triggered by magmatic activity and may have been accompanied by a violent lateral blast. Collapse was followed by eruption of pumiceous pyroclastic flows and extrusion of voluminous dacite domes.

Francis, P. W.; Gardeweg, M.; Ramirez, C. F.; Rothery, D. A.

1985-01-01

321

Submicron chip ESD protection schemes which avoid avalanching junctions  

Microsoft Academic Search

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

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

1995-01-01

322

Trapping phenomena in avalanche photodiodes on nanosecond scale  

Microsoft Academic Search

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

Sergio Cova; A. Lacaita; G. Ripamonti

1991-01-01

323

The distribution of gains in uniformly multiplying avalanche photodiodes: Experimental  

Microsoft Academic Search

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.

J. Conradi

1972-01-01

324

Pulsed Electron Avalanche Knife (PEAK) for Intraocular Surgery  

E-print Network

it promising for many ophthalmic applications, including retinal, cataract, and glaucoma surgery. In additionPulsed Electron Avalanche Knife (PEAK) for Intraocular Surgery Daniel V. Palanker,1,2 Jason M, the instrument may be useful in nonophthalmic procedures such as intravascular surgery and neurosurgery. (Invest

Palanker, Daniel

325

Avalanches in a Stochastic Model of Spiking Neurons  

Microsoft Academic Search

Neuronal avalanches are a form of spontaneous activity widely observed in cortical slices and other types of nervous tissue, both in vivo and in vitro. They are characterized by irregular, isolated population bursts when many neurons fire together, where the number of spikes per burst obeys a power law distribution. We simulate, using the Gillespie algorithm, a model of neuronal

Marc Benayoun; Jack D. Cowan; Wim van Drongelen; Edward Wallace

2010-01-01

326

A model for frictional melt production beneath large rock avalanches  

Microsoft Academic Search

Two puzzling traits of giant rock avalanches (sturzstroms) are the decrease of the effective friction coefficient as a function of the volume (volume effect) and the remarkable preservation of large geological structures during the flow, demonstrating that the upper cap of a sturzstrom travels coherently on top of a basal shear layer. Hence, frictional heat is rapidly produced along the

Fabio Vittorio De Blasio; Anders Elverhi

2008-01-01

327

High quantum efficiency GaP avalanche photodiodes.  

PubMed

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

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

2011-09-26

328

Dry friction avalanches: Experiment and theory Sergey V. Buldyrev,1  

E-print Network

Dry friction avalanches: Experiment and theory Sergey V. Buldyrev,1 John Ferrante,2 and Fredy R and theoretical models are presented supporting the conjecture that dry friction stick-slip is described by self the variation of the friction force as a function of time. We study nominally flat surfaces of matching aluminum

Buldyrev, Sergey

329

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

NASA Astrophysics Data System (ADS)

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

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

2013-05-01

330

A multi path, weather independent avalanche monitoring tool using distributed acoustic fiber optic sensing  

NASA Astrophysics Data System (ADS)

Information on avalanche activity is a paramount parameter in avalanche forecasting. When avalanches are released spontaneously, the risk of avalanches is very high. Triggering avalanches by artificial means, such as explosives launched from helicopter or avalanche towers, can also give information on the stability of the snow pack. Hence, monitoring of avalanches released naturally or artificially, is an important quantity in avalanche forecasting. This information is also needed when deciding whether to close or not endangered ski runs, roads or railway lines. So far monitoring systems lack certain benefits. Either they monitor only large avalanches, can only be used for single avalanche tracks or are weather/sight dependant. Therefore a new tool for avalanche- monitoring, a distributed fiber optic system, is for the first time installed and adapted for the purpose of monitoring snow avalanche activity. The method is based on an optical time domain reflectometer (OTDR) system, which dates back to the 1970`s and detects seismic vibrations and acoustic signals on a fiber optic cable that can have a length of up to 30 km. An appropriate test slope for this configuration has been found in the ski area of "Lech am Arlberg". In this work a detailed description of the theoretical background, the system implementation, the field installation, realization of tests and an investigation of the recorded data is presented. We conducted 100 tests and triggered 41 avalanches so far with a runout distances ranging from a few meters to approximately 250 meters, all of which were detected by the system, as well as the 59 not successful attempts of artificial triggering. Moreover we measured properly if critical infrastructure (in our case a ski run) was reached by the avalanches or not. The spatial distributed sensing approach allowed us to relate the amplitude and spectral content of the signals to avalanche size, avalanche speed and snow properties of the avalanches. In conclusion we summarize that distributed acoustic fiber optic sensing is a precise method to monitor avalanche activity, runout distances and avalanche properties.

Prokop, Alexander; Wirbel, Anna

2013-04-01

331

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

NASA Astrophysics Data System (ADS)

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.

Turchaninova, A.

2012-04-01

332

Soil erosion and organic carbon export by wet snow avalanches  

NASA Astrophysics Data System (ADS)

Many mountain belts sustain prolonged snow cover for parts of the year, although enquiries into rates of erosion in these landscapes have focused almost exclusively on the snow-free periods. This raises the question of whether annual snow cover contributes significantly to modulating rates of erosion in high-relief terrain. In this context, the sudden release of snow avalanches is a frequent and potentially relevant process, judging from the physical damage to subalpine forest ecosystems, and the amount of debris contained in avalanche deposits. To quantitatively constrain this visual impression and to expand the sparse literature, we sampled sediment concentrations of n = 28 river-spanning snow-avalanche deposits (snow bridges) in the area around Davos, eastern Swiss Alps, and inferred an orders-of-magnitude variability in specific fine sediment and organic carbon yields (1.8 to 830 t km-2 yr-1, and 0.04 to 131 t C km-2 yr-1, respectively). A Monte Carlo simulation demonstrates that, with a minimum of free parameters, such variability is inherent to the geometric scaling used for computing specific yields. Moreover, the widely applied method of linearly extrapolating plot scale sample data may be prone to substantial under- or overestimates. A comparison of our inferred yields with previously published work demonstrates the relevance of wet snow avalanches as prominent agents of soil erosion and transporters of biogeochemical constituents to mountain rivers. Given that a number of snow bridges persisted below the insulating debris cover well into the summer months, snow-avalanche deposits also contribute to regulating in-channel sediment and organic debris storage on seasonal timescales. Finally, our results underline the potential shortcomings of neglecting erosional processes in the winter and spring months in mountainous terrain subjected to prominent snow cover.

Korup, O.; Rixen, C.

2014-04-01

333

Soil erosion and organic carbon export by wet snow avalanches  

NASA Astrophysics Data System (ADS)

Many mountain belts sustain prolonged snow cover for parts of the year, although enquiries into rates of erosion in these landscapes have focused almost exclusively on the snow-free periods. This raises the question of whether annual snow cover contributes significantly to modulating rates of erosion in high-relief terrain. In this context, the sudden release of snow avalanches is a frequent and potentially relevant process, judging from the physical damage to subalpine forest ecosystems, and the amount of debris contained in avalanche deposits. To quantitatively constrain this visual impression and to expand the sparse existing literature, we sampled sediment concentrations of n = 28 river-spanning snow-avalanche deposits (snow bridges) in the eastern Swiss Alps, and infer an orders-of-magnitude variability in specific fine sediment and organic carbon yields (1.8 to 830 t km-2 yr-1, and 0.04 to 131 t C km-2 yr-1, respectively). A Monte Carlo simulation demonstrates that, with a minimum of free parameters, such variability is inherent to the geometric scaling used for computing specific yields. Moreover, the widely applied method of linearly extrapolating plot-scale sample data may be prone to substantial under- or over-estimates. A comparison of our inferred yields with previously published work demonstrates the relevance of wet snow avalanches as prominent agents of soil erosion and transporters of biogeochemical constituents to mountain rivers. Given that a number of snow bridges persisted below the insulating debris cover well into the summer months, snow-avalanche deposits also contribute to regulating in-channel sediment and organic debris storage on seasonal timescales. Finally, our results underline the potential shortcomings of neglecting erosional processes in the winter and spring months in mountainous terrain subjected to prominent snow cover.

Korup, O.; Rixen, C.

2014-01-01

334

The development of structures in analogue and natural debris avalanches  

NASA Astrophysics Data System (ADS)

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

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

2010-05-01

335

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

Microsoft Academic Search

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

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

2010-01-01

336

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

NASA Astrophysics Data System (ADS)

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.

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

2013-12-01

337

Calculating the velocity of a fast-moving snow avalanche using an infrasound array  

NASA Astrophysics Data System (ADS)

On 19 January 2012, a large D3 avalanche (approximately 103 t) was recorded with an infrasound array ideally situated for observing the avalanche velocity. The avalanche crossed Highway 21 in Central Idaho during the largest avalanche cycle in the 15 years of recorded history and deposited approximately 8 m of snow on the roadway. Possible source locations along the avalanche path were estimated at 0.5 s intervals and were used to calculate the avalanche velocity during the 64 s event. Approximately 10 s prior to the main avalanche signal, a small infrasound signal originated from the direction of the start zone. We infer this to be the initial snow pack failure, a precursory signal to the impending avalanche. The avalanche accelerated to a maximum velocity of 35.9 7.6m s-1 within 30 s before impacting the highway. We present a new technique to obtain high spatial and temporal resolution velocity estimates not previously demonstrated with infrasound for avalanches and other mass wasting events.

Havens, Scott; Marshall, Hans-Peter; Johnson, Jeffrey B.; Nicholson, Bill

2014-09-01

338

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

NASA Technical Reports Server (NTRS)

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.

Knepper, D. H., Jr. (principal investigator)

1977-01-01

339

Structural vulnerability assessment using reliability of slabs in avalanche area  

NASA Astrophysics Data System (ADS)

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.

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

2013-04-01

340

Hummocks: how they form and evolve in debris avalanches (Invited)  

NASA Astrophysics Data System (ADS)

Hummocks are topographic features of large landslides and rockslide-debris avalanches common in volcanic settings. We use scaled analog models to study hummock formation and explore their importance in understanding landslide kinematics and dynamics. The models are designed to replicate large-scale volcanic collapses but are relevant also to non-volcanic settings. We characterize hummocks in terms of their evolution, spatial distribution, and internal structure from slide initiation to final arrest. Hummocks initially form by extensional faulting as a landslide begins to move. During motion, individual large blocks develop and spread, creating an initial distribution, with small hummocks at the landslide front and larger ones at the back. As the mass spreads, hummocks remain as discrete entities. They can get wider but may decrease in height, break up, or merge to form bigger and long anticlinal hummocks when confined. In areas of transverse movement within a landslide, elongate hummocks develop between strike-slip flower structures. Absence of hummocks and fault-like features in the deposit may imply a more fluidal flow of emplacement or very low cohesion of lithologies. Hummock size depends on their position in the initial mass, modified by subsequent breakup or coalescence. Hummock size, shape and spatial distribution vary between and within deposits. Such a universal structure with clear connection to the deformation process should provide a framework with which to study avalanche emplacement dynamics and conditions. We study well-preserved and well-sectioned hummocks in the Mt Iriga rockslide-debris avalanches (Philippines), to characterise the internal structure and relate hummocks to the landslide-avalanche behaviour. All the model structures are consistent with field observations and suggest a general brittle-slide emplacement for most landslide avalanches. The upper and outer hummock surface is destabilised by minor slumps and scree formation forming a rubbly carapace. The central parts of many hummocks are dissected by high angle normal faults that descend and merge into low angle detachments of listric shear zones and merge at the base. In the upper parts of the hummocks, second-order smaller ones can form when the layers parallel to the thinning boudinage and generate blocks. The type of stretch structure depends on the lithology and layer interface. The study shows that hummock distribution is independent of distance and transport disintegration but could be related to lithology, initial position, and avalanche kinematics. In conclusion, hummocks as intact survivors do not provide clear evidence of fragmentation during transport, but do provide information on the transport conditions, kinematics, and initial composition of the landslide.

Paguican, E. R.; van Wyk de Vries, B.; Lagmay, A.

2013-12-01

341

GaN/InGaN avalanche phototransistors  

NASA Astrophysics Data System (ADS)

We report on IIInitride (IIIN) avalanche phototransistor (APT) action by illuminating ultraviolet (UV) photons onto a GaN/InGaN npn heterojunction bipolar transistor in an open-base configuration. A high responsivity of >1 A/W was measured for the device operating at a collector-to-emitter voltage (VCE) of <15 V in the phototransistor mode. The carrier multiplication in the reversed biased collector leads to a photocurrent avalanche as VCE increases. At ? = 380 nm, the GaN/InGaN APT shows a responsivity of >68 A/W at VCE = 95 V. The InGaN APT demonstrates the feasibility of using IIIN bipolar transistor structures for high-sensitivity UV photodetection applications.

Shen, Shyh-Chiang; Kao, Tsung-Ting; Kim, Hee-Jin; Lee, Yi-Che; Kim, Jeomoh; Ji, Mi-Hee; Ryou, Jae-Hyun; Detchprohm, Theeradetch; Dupuis, Russell D.

2015-03-01

342

Controllable morphology of flux avalanches in microstructured superconductors  

NASA Astrophysics Data System (ADS)

The morphology of abrupt bursts of magnetic flux into superconducting films with engineered periodic pinning centers (antidots) has been investigated. Guided flux avalanches of thermomagnetic origin develop a treelike structure, with the main trunk perpendicular to the borders of the sample, while secondary branches follow well-defined directions determined by the geometrical details of the underlying periodic pinning landscape. Strikingly, we demonstrate that in a superconductor with relatively weak random pinning the morphology of such flux avalanches can be fully controlled by proper combinations of lattice symmetry and antidot geometry. Moreover, the resulting flux patterns can be reproduced, to the finest details, by simulations based on a phenomenological thermomagnetic model. In turn, this model can be used to predict such complex structures and to estimate physical variables of more difficult experimental access, such as the local values of temperature and electric field.

Motta, M.; Colauto, F.; Vestgrden, J. I.; Fritzsche, J.; Timmermans, M.; Cuppens, J.; Attanasio, C.; Cirillo, C.; Moshchalkov, V. V.; Van de Vondel, J.; Johansen, T. H.; Ortiz, W. A.; Silhanek, A. V.

2014-04-01

343

Ray optics behavior of flux avalanche propagation in superconducting films  

NASA Astrophysics Data System (ADS)

Experimental evidence of wave properties of dendritic flux avalanches in superconducting films is reported. Using magneto-optical imaging the propagation of dendrites across boundaries between a bare NbN film and areas coated by a Cu layer was visualized, and it was found that the propagation is refracted in full quantitative agreement with Snell's law. For the studied film of 170 nm thickness and a 0.9 ? m thick metal layer, the refractive index was close to n =1.4 . The origin of the refraction is believed to be caused by the dendrites propagating as an electromagnetic shock wave, similar to damped modes considered previously for normal metals. The analogy is justified by the large dissipation during the avalanches raising the local temperature significantly. Additional time-resolved measurements of voltage pulses generated by segments of the dendrites traversing an electrode confirm the consistency of the adopted physical picture.

Mikheenko, P.; Johansen, T. H.; Chaudhuri, S.; Maasilta, I. J.; Galperin, Y. M.

2015-02-01

344

Weathering processes implied from analysis of small Martian avalanche chutes  

NASA Technical Reports Server (NTRS)

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.

Sullivan, R.

1992-01-01

345

Spatiotemporal Chaotic unjamming and jamming in granular avalanches  

E-print Network

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.

Ziwei Wang; Jie Zhang

2014-10-23

346

Macroscopic control parameter for avalanche models for bursty transport  

SciTech Connect

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.

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

347

Automated characterization of single-photon avalanche photodiode  

E-print Network

We report an automated characterization of a single-photon detector based on commercial silicon avalanche photodiode (PerkinElmer C30902SH). The photodiode is characterized by I-V curves at different illumination levels (darkness, 10 pW and 10 uW), dark count rate and photon detection efficiency at different bias voltages. The automated characterization routine is implemented in C++ running on a Linux computer.

Aina M. M. Ghazali; Audun N. Bugge; Sebastien Sauge; Vadim Makarov

2012-02-08

348

Progress in Silicon Single-Photon Avalanche Diodes  

Microsoft Academic Search

Silicon single-photon avalanche diodes (SPADs) are nowadays a solid-state alternative to photomultiplier tubes (PMTs) in single-photon counting (SPC) and time-correlated single-photon counting (TCSPC) over the visible spectral range up to 1-mum wavelength. SPADs implemented in planar technology compatible with CMOS circuits offer typical advantages of microelectronic devices (small size, ruggedness, low voltage, low power, etc.). Furthermore, they have inherently higher

Massimo Ghioni; Angelo Gulinatti; Ivan Rech; Franco Zappa; Sergio Cova

2007-01-01

349

Electronic tuning effects in the read microwave avalanche diode  

Microsoft Academic Search

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

M. Gilden; M. E. Hines

1966-01-01

350

Avalanche localization and crossover scaling in amorphous plasticity.  

PubMed

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

Budrikis, Zoe; Zapperi, Stefano

2013-12-01

351

Novel type of avalanche photodetector with Geiger mode operation  

Microsoft Academic Search

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 metalresistor semiconductor (MRS) microcells with a density of 1000\\/mm2, operating

V. Golovin; V. Saveliev

2004-01-01

352

A numerical model of avalanche breakdown in MOSFET's  

Microsoft Academic Search

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

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

1978-01-01

353

Theory of electron-avalanche breakdown in solids  

Microsoft Academic Search

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

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

1981-01-01

354

Flux avalanches in superconducting films with periodic arrays of holes.  

SciTech Connect

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.

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

2000-01-01

355

Fracture Mechanical Models of Dry Slab Avalanche Release  

Microsoft Academic Search

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

David M. McClung

1981-01-01

356

Receiver characteristics of laser altimeters with avalanche photodiodes  

NASA Technical Reports Server (NTRS)

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.

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

1992-01-01

357

Recent results in scintillation detection with silicon avalanche photodiodes  

Microsoft Academic Search

An investigation of silicon avalanche photodiodes (APDs) in scintillation detection for potential applications in medical imaging and nuclear spectroscopy is reported. Experimental measurements were performed on bismuth germanate (BGO), CdWO4, plastic, NaI(Tl) and CsI(Tl) scintillators, geometrically optimized for light collection. Results show the advantages of a solid-state photodetector having an internal gain for the detection of low-energy gamma and X-rays.

C. Carrier; R. Lecomte

1990-01-01

358

A thermal neutron beam monitor based on avalanche counter  

NASA Astrophysics Data System (ADS)

A simple neutron beam monitor based on the combination of a low-pressure position-sensitive avalanche counter with a 6Li neutron converter has been developed. The details of the construction of the device, as well as, the results of the test of the device with a thermal neutron beam are described. The main features of the neutron beam monitor are high count-rate capability, low ?-sensitivity, low perturbation on neutron beams and a position sensitivity of 2 mm.

Nakhostin, M.; Baba, M.

2013-05-01

359

Signal and noise response of high speed germanium avalanche photodiodes  

Microsoft Academic Search

Germanium avalanche photodiodes, providing gain at microwave frequencies, have been fabricated and tested. The diodes employ a guard ring structure to achieve a uniform, microplasma-free, multiplying region with an active diameter of 40 microns. Low-frequency chopped light current gains of greater than 200, and small-signal 6 GHz current gains of greater than 10 have been obtained at room temperature for

H. Melchior; W. T. Lynch

1966-01-01

360

High-Gain Avalanche Rushing amorphous Photoconductor (HARP) detector  

NASA Astrophysics Data System (ADS)

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

Tanioka, K.

2009-09-01

361

Avalanches in the Bean critical-state model  

SciTech Connect

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}

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

362

Solar flares and avalanches in driven dissipative systems  

NASA Technical Reports Server (NTRS)

The contention of Lu and Hamilton (1991) that the energy release process in solar flares can be understood as avalanches of many small reconnection events is further developed. The dynamics of the complex magnetized plasma of solar active regions is modeled with a simple driven dissipative system, consisting of a vector field with local instabilities that cause rapid diffusion of the field. It is argued that the avalanches in this model are analogous to solar flares. The distributions of avalanches in this model are compared with the solar flare frequency distributions obtained from ISEE 3/ICE satellite observations. Quantitative agreement is found with the energy, peak luminosity, and duration distributions over four orders of magnitude in flare energy, from the largest flares down to the completeness limit of the observations. It is predicted that the power-law solar flare frequency distributions will be found to continue downward with the same logarithmic slopes to an energy of about 3 x 10 exp 25 ergs and duration of about 0.3 s, with deviations from power-law behavior below these values.

Lu, Edward T.; Hamilton, Russell J.; Mctiernan, J. M.; Bromund, Kenneth R.

1993-01-01

363

Experimental Investigation of Plastic Deformations Before Granular Avalanche  

E-print Network

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.

Axelle Amon; Roman Bertoni; Jrme Crassous

2012-11-23

364

A novel stream encryption scheme with avalanche effect  

NASA Astrophysics Data System (ADS)

This paper proposes a novel stream encryption scheme with avalanche effect (SESAE). Using this scheme and an ideal pseudorandom number generator (PRNG) to generate d-bit segment binary key streams, one can encrypt a plaintext such that by using any key stream generated from a different seed to decrypt the ciphertext, the decrypted plaintext will become an avalanche-like text which has 2 d - 1 consecutive one's with a high probability. As a cost, the required bits of the ciphertext are d times those of the plaintext. A corresponding avalanche-type encryption theorem is established. Two chaotic 12-bit segment PRNGs are designed. A generalized FIPS140 test and SESAE test for the two chaotic PRNGs, RC4 12-bit segment PRNG and 12-bit segment Matlab PRNG are implemented. The SESAE tests for 16-bit segment PRNGs are also compared. The results suggest that those PRNGs are able to generate the SESAEs which are similar to those generated via ideal PRNGs.

Min, Lequan; Chen, Guanrong

2013-11-01

365

Avalanche photodiodes and quenching circuits for single-photon detection.  

PubMed

Avalanche photodiodes, which operate above the breakdown voltage in Geiger mode connected with avalanche-quenching circuits, can be used to detect single photons and are therefore called singlephoton avalanche diodes SPAD's. Circuit configurations suitable for this operation mode are critically analyzed and their relative merits in photon counting and timing applications are assessed. Simple passive-quenching circuits (PQC's), which are useful for SPAD device testing and selection, have fairly limited application. Suitably designed active-quenching circuits (AQC's) make it possible to exploit the best performance of SPAD's. Thick silicon SPAD's that operate at high voltages (250-450 V) have photon detection efficiency higher than 50% from 540- to 850-nm wavelength and still ~3% at 1064 nm. Thin silicon SPAD's that operate at low voltages (10-50 V) have 45% efficiency at 500 nm, declining to 10% at 830 nm and to as little as 0.1% at 1064 nm. The time resolution achieved in photon timing is 20 ps FWHM with thin SPAD's; it ranges from 350 to 150 ps FWHM with thick SPAD's. The achieved minimum counting dead time and maximum counting rate are 40 ns and 10 Mcps with thick silicon SPAD's, 10 ns and 40 Mcps with thin SPAD's. Germanium and III-V compound semiconductor SPAD's extend the range of photon-counting techniques in the near-infrared region to at least 1600-nm wavelength. PMID:21085320

Cova, S; Ghioni, M; Lacaita, A; Samori, C; Zappa, F

1996-04-20

366

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

NASA Astrophysics Data System (ADS)

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.

Deng, H. X.; Zu, X. T.; Zheng, W. G.; Yuan, X. D.; Xiang, X.; Sun, K.; Gao, F.

2014-05-01

367

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

USGS Publications Warehouse

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.

Morton, Douglas M.; Hauser, Rachel M.

2001-01-01

368

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

SciTech Connect

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.

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

2014-05-28

369

Avalanche dynamics of magnetic flux in a two-dimensional discrete superconductor  

SciTech Connect

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.

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

370

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

Microsoft Academic Search

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

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

2010-01-01

371

The Tancitaro Debris Avalanche: Characterization, propagation and modeling  

NASA Astrophysics Data System (ADS)

The Tancitaro volcano (3860 m) is an andesitic-dacitic stratovolcano located in the western portion of the Trans-Mexican Volcanic Belt within the state of Michoacn (Mexico). The tectonic activity of this area has likely contributed to a large sector collapse of the volcano. The first findings of a multidisciplinary investigation into this debris avalanche are presented here. Geomorphological analyses, based on the interpretation of orthophotos, satellite imagery and on GIS elaborations, had the objective of determining the main morphometric features of the landslide. The collapse structure is an east-facing horseshoe-shaped crater (4 km wide and 5.3 km long), while the deposit forms a large fan that is 66 km long, covers an area of approximately 1155 km 2 and has an estimated volume of 18 km 3. Event volume was established by reconstructing the paleo-edifice in a GIS and taking into account volumetric expansion. Cross sections measured in the field were also used for this purpose. Field investigations also highlighted the presence of two texturally distinct units, which are referred to as the "block facies" and the "matrix facies", respectively. The first is responsible for the typical hummock morphologies found in the proximal area. A transitional zone contains a "mixed block and matrix facies" while in the distal portion blocks and megablocks, some of which have a jigsaw puzzle texture, gradually decrease in size until they disappear entirely. A number of matrix samples were collected to conduct direct shear tests, granulometric analyses and classification of the materials. The data and analyses described above were used to discuss the mechanism controlling the long runout of the avalanche. Based on the comparison between the Tancitaro debris avalanche and similar events we propose that mechanical fluidization was the mechanism responsible for the remarkable mobility of the landslide. The predisposing factors leading to the collapse were also considered. Field observations suggest that these are mainly related to weakening processes operating both in volcanoes and in non-volcanic areas. The runout of the Tancitaro debris avalanche was numerically modeled using DAN-W. The geotechnical parameters determined in the field and from the laboratory analyses were used as input. The DAN-W code models longitudinal spreading and the thickness and velocity of the failed mass by opportunely selecting a specific rheological model (Voellmy, Frictional, Bingham). Thus, it was determined that the two-parameter "Voellmy model" provided the best simulation of the Tancitaro debris avalanche movement, and the best fitting rheological parameters have been found through back analysis.

Morelli, Stefano; Monroy, Victor Hugo Garduo; Gigli, Giovanni; Falorni, Giacomo; Rocha, Eleazar Arreygue; Casagli, Nicola

2010-06-01

372

A supplement to nearest-neighbour method of avalanche forecasting  

NASA Astrophysics Data System (ADS)

One of the initially developed avalanche forecasting tools based on the statistical approach, used the nearest-neighbor method, which is still widely used in various versions independently as well as in combination with other models (Buser, 1983; McClung and Tweedy, 1994; Gassner and others, 2000). Though, the nearest-neighbour method has proven fairly helpful under usual circumstances of avalanching, the difficulty that forecasters often face with its output is in determining the number of days that are true neighbour of the current day. To some extent, value of geometrical distance between a neigbour and current day help, but forecasters experience and knowledge are the main decisive factors. Under such a condition, where sufficient true neighbors are not present in database, usual nearest-neighbour method output may lead to unrealistic decisions. The proposed method is offered as a supplement to the existing nearest-neighbor method for avalanche forecasting. The method is applied on the same database and parameter vector space being used for nearest neighbor method. However, instead of using a distance metric for searching the nearest neighbors to the current day, forecaster here defines the ranges of various parameters of vector space around the current day values. A geometrical closed surface is then generated in the parametric vector space according to the given ranges, within which only the search is made. The output provides direct indication of uniqueness (or commonness) of the current day condition within the defined ranges. This result, when analysed in the backdrop of nearest-neigbour method result on the same data, helps forecasters in fine-tuning the decision. The combination of nearest-neighbor method with proposed supplement was applied for avalanche forecasting in Chowkibal-Tangdhar road axis, on a stretch of about 20 km with 17 prominent avalanche sites, in Shamsabari range of Indian Western Himalaya. The results are presented in the paper. The method has proved as a vital tool to corroborate the output of nearest-neighbor method.

Singh, A.; Ganju, A.

2003-04-01

373

Analysis of spanning avalanches in the two-dimensional nonequilibrium zero-temperature random-field Ising model.  

PubMed

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

Spasojevi?, Djordje; Jani?evi?, Sanja; Kneevi?, Milan

2014-01-01

374

Using tree-ring signals and numerical model to identify the snow avalanche tracks in Kastamonu, Turkey  

Microsoft Academic Search

Many parts of our planet are exposed to natural disasters such as snow avalanches, floods and earthquakes. Detailed knowledge\\u000a on these natural disasters is crucial for human safety. On December 2526, 1992, two avalanches occurred at Kayaarkas?-Kastamonu\\u000a in northern Turkey. The first avalanche took place at night of 2526 December and caused no damage. The second avalanche took\\u000a place at

Nesibe Kse; Abdurrahim Ayd?n; nal Akkemik; Hseyin Yurtseven; Tuncay Gner

2010-01-01

375

The Savage-Hutter avalanche model: how far can it be pushed?  

PubMed

The Savage-Hutter (SH) avalanche model is a depth-averaged dynamical model of a fluid-like continuum implementing the following simplifying assumptions: (i) density preserving, (ii) shallowness of the avalanche piles and small topographic curvatures, (iii) Coulomb-type sliding with bed friction angle delta and (iv) Mohr-Coulomb behaviour in the interior with internal angle of friction phi> or =delta and an ad hoc assumption reducing the number of Mohr's circles in three-dimensional stress states to one. We scrutinize the available literature on information regarding these assumptions and thus delineate the ranges of validity of the proposed model equations. The discussion is limited to relatively large snow avalanches with negligible powder snow component and laboratory sand avalanches starting on steep slopes. The conclusion of the analysis is that the SH model is a valid model for sand avalanches, but its Mohr-Coulomb sliding law may have to be complemented for snow avalanches by a second velocity-dependent contribution. For very small snow avalanches and for laboratory avalanches starting on moderately steep and bumpy slopes it may not be adequate. PMID:16011931

Hutter, Kolumban; Wang, Yongqi; Pudasaini, Shiva P

2005-07-15

376

Quaternary Moraines vs Catastrophic Rock Avalanches in the Karakoram Himalaya, Northern Pakistan  

Microsoft Academic Search

A history and conception of glacial events for the central Karakoram Himalaya, proposed some 80 years ago by Giotto Dainelli, are largely accepted today. However, certain deposits identified as terminal moraine complexes marking glacial episodes were actually emplaced by rock avalanches. In the Skardu and Shigar intermontane basins of Baltistan, at least 15 rock avalanche events were previously mapped as

Kenneth Hewitt

1999-01-01

377

Large-rock avalanche deposits, eastern Basin and Range, Utah: Emplacement, diagenesis, and economic potential  

Microsoft Academic Search

Large-rock avalanche deposits are a common component of the basin fill within the extensional tectonic terrain of the Basin and Range; these deposits recently have been interpreted to host oil and gas within the Railroad Valley area of eastern Nevada. Large blocks of brecciated bedrock are a primary component of these avalanche deposits and are potentially excellent oil and gas

T. H. Morris; G. F. Hebertson

1996-01-01

378

High Speed Heterostructure Avalanche Photodiodes Majeed M. Hayata and Oh-Hyun Kwonb  

E-print Network

factor, increased abruptness in the breakdown probability, as well as an increase in the bandwidth, excess noise factor, heterostructure APDs, initial-energy effect. 1. INTRODUCTION Avalanche photodiodes and inherent avalanche buildup time, which is the time required for all the carrier impact ionizations

Hayat, Majeed M.

379

Geomorphological Features of Avalanche Furrows in Heavy Snow Region in Japan  

NASA Astrophysics Data System (ADS)

The occurence of full-depth snow avalanches (FDSAs) on slopes in Japanese mountain areas is indicated by narrow straight scratch patterns, called "avalanche furrows", on aerial photographs. Avalanche furrows show a semi-circular or U-shaped transverse profile as if they had been scored by a round chisel. They have a width of 2-4m and a depth of 1-3m and occur mainly on slopes with a 35-45 inclination. Avalanche furrows are exposed on a smooth surface of bedrock and show striae produced by FDSAs. Aerial-photo interpretation over Japanese Islands shows that avalanche furrows are mainly distributed from Hokkaido to the Chugoku Mountains along the Japan Sea coast. The distribution of avalanche furrows corresponds to mountains with deep snow cover over 2m and increases with altitude. In other countries, wet snow avalanches occur mainly in polar and alpine areas with much colder climates. In contrast, FDSAs occur in temperate climates and at altitudes as low as 300m in Japan. The major factors controlling the formation of avalanche furrows in Japan are considered to be the temperate climate, heavy snowfall, steep slopes and poor vegetation.

Sekiguchi, Tatsuo; Sato, Hiroshi P.; Akiyama, Kazuya

2005-03-01

380

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

NASA Technical Reports Server (NTRS)

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.

Knepper, D. H. (principal investigator); Summer, R.

1976-01-01

381

Snow-avalanche impact landforms in Breheimen, southern Norway: Origin, age, and paleoclimatic implications  

SciTech Connect

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.

Matthews, J.A.; McCarroll, D. (Univ. of Wales, Swansea (United Kingdom))

1994-05-01

382

Effect of dead space on gain and noise in Si and GaAs avalanche photodiodes  

Microsoft Academic Search

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

M. M. Hayat; W. L. Sargeant; B. E. A. Saleh

1992-01-01

383

The dynamics of avalanches of granular materials from initiation to runout. Part I: Analysis  

Microsoft Academic Search

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

S. B. Savage; K. Hutter

1991-01-01

384

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

ERIC Educational Resources Information Center

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

Barber, David L.

1988-01-01

385

A Methodology To Allow Avalanche Forecasting on an Information Retrieval System.  

ERIC Educational Resources Information Center

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

Purves, R. S.; Sanderson, M.

1998-01-01

386

In situ and photographic measurements of avalanche crown transects Edward H. Bair a,  

E-print Network

In situ and photographic measurements of avalanche crown transects Edward H. Bair a, , Karl W August 2010 Keywords: Avalanche Snow Power law Gaussian process Despite its fundamental importance, crown models. To date, no studies have examined the distribution of depth across crown transects. We present

Dozier, Jeff

387

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

Microsoft Academic Search

The damage caused by snow avalanches to property and human lives is underestimated in many regions around the world, especially where this natural hazard remains poorly documented. One such region is the Argentinean Andes, where numerous settlements are threatened almost every winter by large snow avalanches. On 1 September 2002, the largest tragedy in the history of Argentinean mountaineering took

A. Casteller; M. Christen; R. Villalba; H. Martnez; V. Stckli; J. C. Leiva; P. Bartelt

2008-01-01

388

Geomorphology of snow avalanche impact landforms in the southern Canadian Cordillera  

E-print Network

Geomorphology of snow avalanche impact landforms in the southern Canadian Cordillera ALEXIS L by an arcuate ridge located at the base of avalanche paths. The geomorphology of these features is controlled by excavation on impact. This paper reports on the geomorphology, and surface age and stability of three SAILs

Smith, Dan

389

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

Microsoft Academic Search

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

G. L. Beach; D. Dzurisin

1984-01-01

390

The HgCdTe electron avalanche photodiode  

NASA Astrophysics Data System (ADS)

Electron injection avalanche photodiodes in SWIR to LWIR HgCdTe show gain and excess noise properties indicative of a single ionizing carrier gain process. The result is an electron avalanche photodiode (EAPD) with "ideal" APD characteristics including near noiseless gain. This paper reports results obtained on long-wave, mid-wave, and short wave cutoff infrared HgCdTe EAPDs that utilize a cylindrical "p-around-n", front side illuminated, n+/n-/p geometry that favors electron injection into the gain region. These devices are characterized by a uniform, exponential, gain voltage characteristic that is consistent with a hole-to-electron ionization coefficient ratio, k, of zero. Gains of greater than 1000 have been measured in MWIR EAPDS without any sign of avalanche breakdown. Excess noise measurements on MWIR and SWIR EAPDs show a gain independent excess noise factor at high gains that has a limiting value less than 2. At 77 K, 4.3 ?m cutoff devices show excess noise factors of close to unity out to gains of 1000. The excess noise factor at room temperature on SWIR EAPDs, while still consistent with the k = 0 operation, approaches a gain independent limiting value of just under 2. The k = 0 operation is explained by the band structure of the HgCdTe. Monte Carlo modeling based on the band structure and scattering models for HgCdTe predict the measured gain and excess noise behavior. A noise equivalent input of 7.5 photons at a 10 ns pulsed signal gain of 964, measured on an MWIR APD at 77 K, provides an indication of the capability of the HgCdTe EAPD.

Beck, Jeffrey D.; Wan, Chang-Feng; Kinch, Michael A.; Robinson, James E.; Mitra, Pradip; Scritchfield, Richard E.; Ma, Feng; Campbell, Joe C.

2004-10-01

391

Martian Dust Devil Electron Avalanche Process and Associated Electrochemistry  

NASA Technical Reports Server (NTRS)

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.

Jackson, Telana L.; Farrell, William M.; Delory, Gregory T.; Nithianandam, Jeyasingh

2010-01-01

392

Neuronal avalanches in the resting MEG of the human brain.  

PubMed

What constitutes normal cortical dynamics in healthy human subjects is a major question in systems neuroscience. Numerous in vitro and in vivo animal studies have shown that ongoing or resting cortical dynamics are characterized by cascades of activity across many spatial scales, termed neuronal avalanches. In experiment and theory, avalanche dynamics are identified by two measures: (1) a power law in the size distribution of activity cascades with an exponent of -3/2 and (2) a branching parameter of the critical value of 1, reflecting balanced propagation of activity at the border of premature termination and potential blowup. Here we analyzed resting-state brain activity recorded using noninvasive magnetoencephalography (MEG) from 124 healthy human subjects and two different MEG facilities using different sensor technologies. We identified large deflections at single MEG sensors and combined them into spatiotemporal cascades on the sensor array using multiple timescales. Cascade size distributions obeyed power laws. For the timescale at which the branching parameter was close to 1, the power law exponent was -3/2. This relationship was robust to scaling and coarse graining of the sensor array. It was absent in phase-shuffled controls with the same power spectrum or empty scanner data. Our results demonstrate that normal cortical activity in healthy human subjects at rest organizes as neuronal avalanches and is well described by a critical branching process. Theory and experiment have shown that such critical, scale-free dynamics optimize information processing. Therefore, our findings imply that the human brain attains an optimal dynamical regime for information processing. PMID:23595765

Shriki, Oren; Alstott, Jeff; Carver, Frederick; Holroyd, Tom; Henson, Richard N A; Smith, Marie L; Coppola, Richard; Bullmore, Edward; Plenz, Dietmar

2013-04-17

393

Avalanche-diode oscillator circuit with tuning at multiple frequencies  

NASA Technical Reports Server (NTRS)

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.

Parker, D.; Ablow, C. M.; Lee, R. E.; Karp, A.; Chambers, D. R.

1971-01-01

394

Martian dust devil electron avalanche process and associated electrochemistry  

NASA Astrophysics Data System (ADS)

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.

Jackson, Telana L.; Farrell, William M.; Delory, Gregory T.; Nithianandam, Jeyasingh

2010-05-01

395

Journal of Glaciology, Vol. 00, No. 000, 2007 1 A Comparison of Powder Snow Avalanches at Vallee de la  

E-print Network

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

McElwaine, Jim

396

Avalanche dynamics, surface roughening, and self-organized criticality: Experiments on a three-dimensional pile of rice  

E-print Network

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

Wijngaarden, Rinke J.

397

International Snow Science Workshop Grenoble Chamonix Mont-Blanc -2013 Impulse water waves generated by snow avalanches  

E-print Network

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

Paris-Sud XI, Université de

398

PHYSICAL REVIEW E 83, 061301 (2011) Simulation of a Casimir-like effect in a granular pile with avalanches  

E-print Network

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

Wijngaarden, Rinke J.

399

Self-organized criticality induced by quenched disorder: Experiments on flux avalanches in NbHx films  

E-print Network

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

Wijngaarden, Rinke J.

400

Size distributions of shocks and static avalanches from the functional renormalization group Pierre Le Doussal and Kay Jrg Wiese  

E-print Network

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

Wiese, Kay Jörg

401

LARGE-SCALE AVALANCHE BRAKING MOUND AND CATCHING DAM EXPERIMENTS WITH SNOW: A STUDY OF THE AIRBORNE JET  

E-print Network

LARGE-SCALE AVALANCHE BRAKING MOUND AND CATCHING DAM EXPERIMENTS WITH SNOW: A STUDY OF THE AIRBORNE TIEFENBACHER Swiss Federal Institute of Snow and Avalanche Research, Flüelstrasse 11, CH-7260 Davos Dorf-scale experiments to study the interaction of a snow avalanche with a dam and a row of mounds which

Hogg, Andrew

402

Dendritic magnetic avalanches in carbon-free MgB2 thin films with and without a deposited Au layer  

E-print Network

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

Johansen, Tom Henning

403

Avalanches and Self-Organized Criticality in Superconductors Rinke J. Wijngaarden, Marco S. Welling, Christof M. Aegerter and Mariela Menghini  

E-print Network

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

Wijngaarden, Rinke J.

404

Hysteresis, avalanches, and disorder-induced critical scaling: A renormalization-group approach Karin Dahmen* and James P. Sethna  

E-print Network

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

Sethna, James P.

405

Experimental studies on fast-ion transport by Alfven wave avalanches on the National Spherical Torus Experiment  

E-print Network

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

Princeton Plasma Physics Laboratory

406

PHYSICAL REVIEW E 88, 032106 (2013) Statistics of avalanches with relaxation and Barkhausen noise: A solvable model  

E-print Network

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

Wiese, Kay Jörg

407

Experimental studies on fast-ion transport by Alfvn wave avalanches on the National Spherical Torus Experimenta...  

E-print Network

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

Heidbrink, William W.

408

The geomorphological effect of cornice fall avalanches in the Longyeardalen valley, Svalbard  

NASA Astrophysics Data System (ADS)

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.

Eckerstorfer, M.; Christiansen, H. H.; Rubensdotter, L.; Vogel, S.

2013-09-01

409

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

USGS Publications Warehouse

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.

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

2007-01-01

410

Avalanche contribution to shear modulus of granular materials  

NASA Astrophysics Data System (ADS)

Shear modulus of frictionless granular materials near the jamming transition under oscillatory shear is numerically investigated. It is found that the shear modulus G satisfies a scaling law to interpolate between G (?-?J)1/2 and G ?0-1/2(?-?J) for a linear spring model of the elastic interaction between contacting grains, where ?, ?J, and ?0 are, respectively, the volume fraction of grains, the fraction at the jamming point, and the amplitude of the oscillatory shear. The linear relation between the shear modulus and ? -?J can be understood by slip avalanches.

Otsuki, Michio; Hayakawa, Hisao

2014-10-01

411

CMOS compatible avalanche photodetector and its application in communications  

NASA Astrophysics Data System (ADS)

CMOS compatible avalanche photodiodes (CMOS APDs) can be fabricated with standard CMOS technology, which make CMOS APDs are considered as a key optoelectronic device for optical communication systems and optical wireless communication systems. The guard-ring (GR) structure in CMOS APDs can alleviate the premature edge breakdown (PEB) effects and greatly improve the device performance. In this paper, the influence of various type GR structure on CMOS APDs performance are discussed, and its important applications in radio-over-fibre (RoF) are reviewed.

Tang, Miangang; Wu, Zhigang; Li, Guohui

2014-11-01

412

A 1.06 micrometer avalanche photodiode receiver  

NASA Technical Reports Server (NTRS)

The development of a complete solid state 1.06 micron optical receiver which can be used in optical communications at data rates approaching 1.5 Gb/s, or in other applications requiring sensitive, short pulse detection, is reported. This work entailed both the development of a new type of heterojunction III-V semiconductor alloy avalanche photodiode and an extremely charge-sensitive wideband low noise preamp design making use of GaAs Schottky barrier-gate field effect transistors (GAASFET's) operating in in the negative-feedback transimpedance mode. The electrical characteristics of the device are described.

Eden, R. C.

1975-01-01

413

Operation of silicon single photon avalanche diodes at cryogenic temperature.  

PubMed

This article reports a complete characterization of single photon avalanche diodes (SPADs) at temperatures down to 120 K. We show that deep cooling of the device by means of a compact liquid-nitrogen Dewar brings several advantages, such as extremely low dark counting rates (down to 1 counts/s), better time resolution, and higher quantum efficiency in the visible range. By using a special current pick-off circuit, we achieved a time resolution of 20 ps full width at half maximum at 120 K for a 50 mum diameter SPAD. Afterpulsing effects are avoided by using a sufficiently long hold-off time (microseconds). PMID:17614603

Rech, Ivan; Labanca, Ivan; Armellini, Giacomo; Gulinatti, Angelo; Ghioni, Massimo; Cova, Sergio

2007-06-01

414

Reliability assessment of multiple quantum well avalanche photodiodes  

NASA Technical Reports Server (NTRS)

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

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

1995-01-01

415

Design, fabrication, and characterization of mid wavelength infrared avalanche photodiode  

NASA Astrophysics Data System (ADS)

Photodetectors with high bandwidth and internal gain are required to detect highly attenuated optical signals for defense applications and long distance communication. Modern laser detection and ranging (LADAR) systems as well as weapon systems, used for long range military and astronomical applications, need to detect, recognize and track a variety of targets under a wide spectrum of atmospheric conditions. A continually varying atmospheric conditions and optical absorption by carbon dioxide, carbon monoxide and water vapor pose severe threats for the proper recognition of the target. The choice of an additional amplification stage along with the detection stage becomes obvious to enhance the signal to noise ratio at the receiver. Avalanche Photodiode (APD) plays a unique role by combing the detection and amplification stage and hence reduces the complexity. But due to the probabilistic nature associated with the incident radiation absorption and multiplication of the photo-generated carriers, the noise level (known as excess noise) of an APD increases and might result in the deterioration of the signal to noise ratio at the detector output. Participation of both electrons and holes in the avalanche mechanism increases the probability, hence the excess noise at the detector output. So, the goal of the APD design lies in the fact of the minimization of the excess noise along with a reasonable multiplication gain. In this research, two material systems, II-VI based Hg1-xCd xTe on Si, and III-V based InAs/GaSb strained layer superlattice (SLS) was studied extensively to achieve the noiseless avalanche characteristics in the mid wavelength infrared region. The electronic bandstructure of the multiplication region of these APDs were designed with the help of 14 band k.p model. The doping and thickness of individual layers were designed with the help of Atlas and Sentaurus simulation platform. The devices were fabricated using standard UV Photo-lithography and wet etching. During the fabrication of the III-V SLS APDs, a detailed study was carried out in terms of the surface preparation and passivation to improve the device characteristics. The noiseless avalanche characteristics from these two material systems were found to be comparable to the more expensive and fragile Hg1- xCdxTe on CdZnTe APDs.

Mallick, Shubhrangshu

416

Silicon avalanche photodiode operation and lifetime analysis for small satellites  

E-print Network

Silicon avalanche photodiodes (APDs) are sensitive to operating temperature fluctuations and are also susceptible to radiation flux expected in satellite-based quantum experiments. We introduce a low power voltage adjusting mechanism to overcome the effects of in-orbit temperature fluctuations. We also present data on the performance of Si APDs after irradiation (gamma-ray and proton beam). Combined with an analysis of expected orbital irradiation, we propose that a Si APD in a 400 km equatorial orbit may operate beyond the lifetime of the satellite.

Yue Chuan Tan; Rakhitha Chandrasekara; Cliff Cheng; Alexander Ling

2013-06-28

417

Debris Avalanches along the South Aegean Volcanic Arc  

NASA Astrophysics Data System (ADS)

Several hummocky deposits have been discovered along the Aegean Volcanic Arc using multibeam bathymetric mapping, airgun seismic profiling, side scan sonar survey and ROV dives. In particular, these hummocks have been discovered on the submarine flanks of Antimilos, Santorini and Nisyros volcanic islands: (i)The seabed morphology of the area northeast of Antimilos exhibits a rather irregular small-scale rough relief and an assembly of three hills in the form of volcanic domes with decreasing size eastwards. The seabed topography and the character of the backscattered intensity of the small scale morpho-bathymetric features, led us to interpret them accordingly as submarine volcanic debris avalanche, flows, domes or dikes, analogous to the on-land outcropping volcanic features. (ii) Analysing of geophysical data shows that hummocky seafloor features on the eastern flank of Santorini volcano cover an area 6 Km wide by 20 Km long and up to 75m in thickness in the central region where the highest concentration of hummocky deposits occur. The hummocks are composed of several individual blocks that are a few meters to hundreds of meters in diameter and protrude up to tens of meters from the surrounding seafloor. The total volume of the deposit is estimated to be approximately 4.4109 m3 as a result of multi-stage landslide event. (iii) The hummocky topography on the sea bottom in front of the southeastern Nisyros coastline is characterized by numerous hills and longitudinal ridges which cover a tongue-shaped area in plan view (about 16 km2), elongated towards SE. The overall morphology of this area can be viewed as a large deposit from a volcanic debris avalanche with a seaward termination displaying an irregular pattern characterized by elongated lobes. The source of these hummocks may be found in Nikia lava flow in the south-eastern flank of Nisyros volcano. The above described hummocks are the result of debris avalanches that were triggered during Holocene either by large earthquakes or volcanic eruptions. Debris avalanches are one of the most significant causes of dangerous hazards in coastal volcanic environments. Understanding how these events are triggered and the potential dynamics of future events is of utmost importance, particularly in highly populated regions such as the Aegean.

Nomikou, P.; Papanikolaou, P.; Tibaldi, A.; Carey, S.; Croff Bell, K.; Pasquar, F. A.; Livanos, I.

2012-04-01

418

Photon counting modules using RCA silicon avalanche photodiodes  

NASA Technical Reports Server (NTRS)

Avalanche photodiodes (APD) are excellent small area, solid state detectors for photon counting. Performance possibilities include: photon detection efficiency in excess of 50 percent; wavelength response from 400 to 1000 nm; count rate to 10 (exp 7) counts per sec; afterpulsing at negligible levels; timing resolution better than 1 ns. Unfortunately, these performance levels are not simultaneously available in a single detector amplifier configuration. By considering theoretical performance predictions and previous and new measurements of APD performance, the anticipated performance of a range of proposed APD-based photon counting modules is derived.

Lightstone, Alexander W.; Macgregor, Andrew D.; Macsween, Darlene E.; Mcintyre, Robert J.; Trottier, Claude; Webb, Paul P.

1989-01-01

419

Avalanche contribution to shear modulus of granular materials  

E-print Network

Shear modulus of frictionless granular materials near the jamming transition under oscillatory shear is numerically investigated. It is found that the shear modulus $G$ satisfies a scaling law to interpolate between $G \\sim (\\phi - \\phi_J)^{1/2}$ and $G \\sim \\gamma_0^{-1/2}(\\phi-\\phi_J)$ for a linear spring model of the elastic interaction between contacting grains, where $\\phi$, $\\phi_J$, and $\\gamma_0$ are, respectively, the volume fraction of grains, the fraction at the jamming point, and the amplitude of the oscillatory shear. The linear relation between the shear modulus and $\\phi - \\phi_J$ can be understood by slip avalanches.

Michio Otsuki; Hisao Hayakawa

2014-10-06

420

Ultraviolet avalanche in anisotropic non-Abelian plasmas  

E-print Network

We present solutions of coupled particle-field evolution in classical U(1) and SU(2) gauge theories in real time on three-dimensional lattices. For strongly anisotropic particle momentum distributions, we find qualitatively different behavior for the two theories when the field strength is high enough that non-Abelian self-interactions matter for SU(2). It appears that the energy drained by a Weibel-like plasma instability from the particles does not build up exponentially in transverse magnetic fields but instead returns, isotropically, to the hard scale via a rapid avalanche into the ultraviolet.

Adrian Dumitru; Yasushi Nara; Michael Strickland

2007-01-12

421

Avalanche contribution to shear modulus of granular materials.  

PubMed

Shear modulus of frictionless granular materials near the jamming transition under oscillatory shear is numerically investigated. It is found that the shear modulus G satisfies a scaling law to interpolate between G?(?-?J)(1/2) and G??0(-1/2)(?-?J) for a linear spring model of the elastic interaction between contacting grains, where ?, ?J, and ?0 are, respectively, the volume fraction of grains, the fraction at the jamming point, and the amplitude of the oscillatory shear. The linear relation between the shear modulus and ?-?J can be understood by slip avalanches. PMID:25375484

Otsuki, Michio; Hayakawa, Hisao

2014-10-01

422

Simulation of displacement damage for silicon avalanche photo-diodes  

NASA Astrophysics Data System (ADS)

The silicon avalanche photo-diodes (APDs) in the CMS barrel electromagnetic calorimeter will be exposed to an integrated neutron fluence of about 21013 n/cm2 over 10 years of operation. High neutron fluences change the electrical properties of silicon detectors. The changes are proportional to the non-ionising energy loss in the APDs. Using the Geant4 toolkit, we have calculated the non-ionising energy loss as well as the rate of generation of primary defects in the APDs, for the expected neutron fluence.

K?l?, Adnan; Pilier, Ercan; Tapan, ?lhan; zmutlu, Emin N.

2011-12-01

423

Traceable calibration of Si avalanche photodiodes using synchrotron radiation  

NASA Astrophysics Data System (ADS)

In this paper, we present a new substitution method based on the unique properties of synchrotron radiation and of the Metrology Light Source (MLS), the dedicated electron storage ring of the PTB. The MLS is used as a light source with a dynamic range of its photon flux of 11 orders of magnitude to bridge the gap in optical power measurement between a cryogenic electrical substitution radiometer and a single photon detector. Two single photon avalanche diodes were calibrated at 651 nm with combined relative uncertainties of 0.17% and 0.16% traceable to a primary standard, a cryogenic electrical substitution radiometer.

Mller, I.; Klein, R. M.; Hollandt, J.; Ulm, G.; Werner, L.

2012-04-01

424

Energy pumping in electrical circuits under avalanche noise  

NASA Astrophysics Data System (ADS)

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

Kanazawa, Kiyoshi; Sagawa, Takahiro; Hayakawa, Hisao

2014-07-01

425

The Vaigat Rock Avalanche Laboratory, west-central Greenland  

NASA Astrophysics Data System (ADS)

Rock avalanches have unusually high mobility and pose both an immediate hazard, but also produce far-field impacts associated with dam breach, glacier collapse and where they run-out into water, tsunami. Such secondary hazards can often pose higher risks than the original landslide. The prediction of future threats posed by potential rock avalanches is heavily reliant upon understanding of the physics derived from an interpretation of deposits left by previous events, yet drawing comparisons between multiple events is normally challenging as interactions with complex mountainous terrain makes deposits from each event unique. As such numerical models and the interpretation of the underlying physics which govern landslide mobility is commonly case-specific and poorly suited to extrapolation beyond the single events the model is tuned to. Here we present a high-resolution LiDAR and hyperspectral dataset captured across a unique cluster of large rock avalanche source areas and deposits in the Vaigat straight, west central Greenland. Vaigat offers the unprecedented opportunity to model a sample of > 15 rock avalanches of various age sourced from an 80 km coastal escarpment. At Vaigat many of the key variables (topography, geology, post-glacial history) are held constant across all landslides providing the chance to investigate the variations in dynamics and emplacement style related to variable landslide volume, drop-heights, and thinning/spreading over relatively simple, unrestricted run-out zones both onto land and into water. Our data suggest that this region represents excellent preservation of landslide deposits, and hence is well suited to calibrate numerical models of run out dynamics. We use this data to aid the interpretation of deposit morphology, structure lithology and run-out characteristics in more complex settings. Uniquely, we are also able to calibrate our models using a far-field dataset of well-preserved tsunami run-up deposits, resulting from the 21.11.00 Paatuut landslide. The study was funded by Polish National Science Centre grant No. 2011/01/B/ST10/01553, and project UK NERC ARSF IG13-15.

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

2013-12-01

426

Avalanche and bit independence characteristics of double random phase encoding in the Fourier and Fresnel domains.  

PubMed

In this work, we evaluate the avalanche effect and bit independence properties of the double random phase encoding (DRPE) algorithm in the Fourier and Fresnel domains. Experimental results show that DRPE has excellent bit independence characteristics in both the Fourier and Fresnel domains. However, DRPE achieves better avalanche effect results in the Fresnel domain than in the Fourier domain. DRPE gives especially poor avalanche effect results in the Fourier domain when only one bit is changed in the plaintext or in the encryption key. Despite this, DRPE shows satisfactory avalanche effect results in the Fresnel domain when any other number of bits changes in the plaintext or in the encryption key. To the best of our knowledge, this is the first report on the avalanche effect and bit independence behaviors of optical encryption approaches for bit units. PMID:24979643

Moon, Inkyu; Yi, Faliu; Lee, Yeon H; Javidi, Bahram

2014-05-01

427

Scaling Behavior of Barkhausen Avalanches along the Hysteresis loop in Nucleation-Mediated Magnetization Reversal Process  

SciTech Connect

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.

Im, Mi-Young; Fischer, Peter; Kim, D.-H.; Shin, S.-C.

2008-10-14

428

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

DOEpatents

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

Fulkerson, E. Stephen (Livermore, CA)

2000-01-01

429

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

NASA Technical Reports Server (NTRS)

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

Blonski, Slawomir

2007-01-01

430

Geometrical properties of avalanches in self-organized critical models of solar flares.  

PubMed

We investigate the geometrical properties of avalanches in self-organized critical models of solar flares. Traditionally, such models differ from the classical sandpile model in their formulation of stability criteria in terms of the curvature of the nodal field, and belong to a distinct universality class. With a view toward comparing these properties to those inferred from spatially and temporally resolved flare observations, we consider the properties of avalanche peak snapshots, time-integrated avalanches in two and three dimensions, and the two-dimensional projections of the latter. The nature of the relationship between the avalanching volume and its projected area is an issue of particular interest in the solar flare context. Using our simulation results we investigate this relationship, and demonstrate that proper accounting of the fractal nature of avalanches can bring into agreement hitherto discrepant results of observational analyses based on simple, nonfractal geometries for the flaring volume. PMID:12005944

McIntosh, Scott W; Charbonneau, Paul; Bogdan, Thomas J; Liu, Han-Li; Norman, James P

2002-04-01

431

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

NASA Astrophysics Data System (ADS)

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

Casteller, A.; Christen, M.; Villalba, R.; Martnez, H.; Stckli, V.; Leiva, J. C.; Bartelt, P.

2008-05-01

432

Snow-avalanche hazard forecasting in the Krkonoe Mountains, Czechia  

NASA Astrophysics Data System (ADS)

The Krkonoe Mts., with the highest peak at 1602 m, are the highest mountains in the Czech Republic. This middle-mountain range covers an area of 454 km2 and includes 53 permanent avalanche paths. Despite its low altitude Krkonoe experience considerably high avalanche activity, even causing fatalities. Unfortunately, and so far, the local authorities do not have a professional tool for avalanche forecasting available. Within the framework of a project devoted to preparation of a tool for snow avalanche hazard forecasting an analysis of historical datasets was performed including weather and snow condition data covering more than 1100 avalanche events in the last 50 years. HR-DEM from airborne LiDAR was used to get accurate slope and terrain characteristics, which were used for calculation of a release susceptibility map using ANN method. Afterwards and regional runout susceptibility was calculated employing Flow-R code (http://www.flow-r.org) and information from the regression analysis of avalanche runout length. This "static" information about avalanche hazard is then being coupled with snow distribution and stability models in order to assess the snow-avalanche hazard in near-real time. For the snow distribution modelling are being tested two models - Alpine 3D and newly developed spatial distributed HBV-ETH model. It is planned that the forecasting system will be employed as a public avalanche alert system for the Krkonoe Mts. and consequently will be extended for the whole Czechia under the patronage of the Mountain Rescue Service, an organization responsible for the public snow-avalanche hazard forecasting. The system will use forecasted ALADIN weather data.

Blahut, Jan; Pavlasek, Jiri; Juras, Roman; Klimes, Jan; Klose, Zbynek; Balek, Jan; Roubinek, Jiri; Taborik, Petr; Hajek, Petr

2014-05-01

433

Granular avalanches in a two-dimensional rotating drum with imposed vertical vibration.  

PubMed

We present statistics on granular avalanches in a rotating drum with and without imposed vertical vibration. The experiment consists of a quasi-two-dimensional, vertical drum containing pentagonal particles and rotated at a constant angular velocity. The drum rests on an electromagnetic shaker to allow vibration of the assembly as it rotates. We measure time series of the slope of the interface and find that the critical angle for slope failure ?(c) and the resulting angle of repose ?(r) are broadly distributed with an approximate power-law distribution of avalanches ?(c)-?(r) for large avalanches. The faceted pentagonal grains used lead to significant interlocking with critical and repose angles (?(c)?45 and ?(r)?39) larger than experiments using spherical grains, even with vibration, and avalanche magnitudes correlated with the prior build-up and anti-correlated with the prior avalanche. We find that the stability of the assembly increases with small vibrations and is destabilized at vibration amplitudes above a dimensionless acceleration (peak acceleration divided by acceleration due to gravity) of ?=0.2. We also study history dependence of the avalanches by periodically oscillating the drum to compare the initial avalanche upon reversal of shear to steady-state distributions for avalanches during continuous rotation. We observe history dependence as an initial decrease in critical angle upon reversal of the drum rotation direction, indicating that a texture is induced to resist continued shear such that the surface is weaker to reversals in shear direction. Memory of this history is removed by sufficient external vibration (??0.8), which leads to compaction and relaxation of the surface layer grains responsible for avalanching dynamics, as initial and steady-state avalanche distributions become indistinguishable. PMID:23944450

Amon, Daniel L; Niculescu, Tatiana; Utter, Brian C

2013-07-01

434

Silicon avalanche pixel sensor for high precision tracking  

NASA Astrophysics Data System (ADS)

The development of an innovative position sensitive pixelated sensor to detect and measure with high precision the coordinates of the ionizing particles is proposed. The silicon avalanche pixel sensors (APiX) is based on the vertical integration of avalanche pixels connected in pairs and operated in coincidence in fully digital mode and with the processing electronics embedded on the chip. The APiX sensor addresses the need to minimize the material budget and related multiple scattering effects in tracking systems requiring a high spatial resolution in the presence of the large track occupancy. The expected operation of the new sensor features: low noise, low power consumption and suitable radiation tolerance. The APiX device provides on-chip digital information on the position of the coordinate of the impinging charged particle and can be seen as the building block of a modular system of pixelated arrays, implementing a sparsified readout. The technological challenges are the 3D integration of the device under CMOS processes and integration of processing electronics.

D'Ascenzo, N.; Marrocchesi, P. S.; Moon, C. S.; Morsani, F.; Ratti, L.; Saveliev, V.; Savoy Navarro, A.; Xie, Q.

2014-03-01

435

Active microrheology in active matter systems: Mobility, intermittency, and avalanches  

NASA Astrophysics Data System (ADS)

We examine the mobility and velocity fluctuations of a driven particle moving through an active matter bath of self-mobile disks for varied density or area coverage and varied activity. We show that the driven particle mobility can exhibit nonmonotonic behavior that is correlated with distinct changes in the spatiotemporal structures that arise in the active media. We demonstrate that the probe particle velocity distributions exhibit specific features in the different dynamic regimes and identify an activity-induced uniform crystallization that occurs for moderate activity levels and is distinct from the previously observed higher activity cluster phase. The velocity distribution in the cluster phase has telegraph noise characteristics produced when the probe particle moves alternately through high-mobility areas that are in the gas state and low-mobility areas that are in the dense phase. For higher densities and large activities, the system enters what we characterize as an active jamming regime. Here the probe particle moves in intermittent jumps or avalanches that have power-law-distributed sizes that are similar to the avalanche distributions observed for nonactive disk systems near the jamming transition.

Reichhardt, C.; Reichhardt, C. J. Olson

2015-03-01

436

Nucleation and Avalanche of 4He Crystals in Aerogel  

NASA Astrophysics Data System (ADS)

Dynamical transition of 4He crystals in aerogel was reported recently (Nomura et al. Phys. Rev. Lett. 101:175703, 2008). Bare aerogel, which was placed in the bulk 4He crystals, was used in the report. 4He crystals inside the aerogel grew via creep at high temperatures and via avalanche at low temperatures owing to the competition between thermal fluctuation and quenched disorder. Crystal-liquid interface advanced from the edge to inside of the aerogel. Crystal has a greater density than liquid so that the extra mass has to be transported in the crystallization process. It is not known how the mass is transported in the aerogel. To find a clue to this issue, we did an experiment with aerogel in a glass tube so that the aerogel had contact with the bulk on only one surface. In this case, a similar dynamical transition was observed at low temperatures. In the avalanche region, however, 4He crystals did not grow from the outer surface of the aerogel but nucleated at various sites inside the aerogel. This means that crystallization in aerogel does not occur by the forced invasion of 4He crystal but by a process of the bulk crystal once being melted and transported to increase the pressure of the liquid in the aerogel. Thus, a mass transport mechanisms for the crystallization has been revealed by this observation.

Ueno, Ken-Ichi; Masumoto, Ryota; Mimori, Tomohiro; Osawa, Aiko; Nomura, Ryuji; Okuda, Yuichi

2010-02-01

437

Spontaneous avalanche ionization of a strongly blockaded Rydberg gas.  

PubMed

We report the sudden and spontaneous evolution of an initially correlated gas of repulsively interacting Rydberg atoms to an ultracold plasma. Under continuous laser coupling we create a Rydberg ensemble in the strong blockade regime, which at longer times undergoes an ionization avalanche. By combining optical imaging and ion detection, we access the full information on the dynamical evolution of the system, including the rapid increase in the number of ions and a sudden depletion of the Rydberg and ground state densities. Rydberg-Rydberg interactions are observed to strongly affect the dynamics of plasma formation. Using a coupled rate-equation model to describe our data, we extract the average energy of electrons trapped in the plasma, and an effective cross section for ionizing collisions between Rydberg atoms and atoms in low-lying states. Our results suggest that the initial correlations of the Rydberg ensemble should persist through the avalanche. This would provide the means to overcome disorder-induced heating, and offer a route to enter new strongly coupled regimes. PMID:25166173

Robert-de-Saint-Vincent, M; Hofmann, C S; Schempp, H; Gnter, G; Whitlock, S; Weidemller, M

2013-01-25

438

Spatiotemporal chaotic unjamming and jamming in granular avalanches  

PubMed Central

We have investigated the spatiotemporal chaotic dynamics of unjamming and jamming of particles in a model experiment a rotating drum partially filled with bidisperse disks to create avalanches. The magnitudes of the first Lyapunov vector ?u(t) and velocity v(t) of particles are directly measured for the first time to yield insights into their spatial correlation C?u,v, which is on statistical average slightly larger near the unjamming than the value near the jamming transition. These results are consistent with the recent work of Banigan et al (Nature Phys. 2013), and it is for the first time to validate their theoretical models in a real scenario. 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. PMID:25634753

Wang, Ziwei; Zhang, Jie

2015-01-01

439

Avalanche Photo-Detection for High Data Rate Applications  

E-print Network

Avalanche photo detection is commonly used in applications which require single photon sensitivity. We examine the limits of using avalanche photo diodes (APD) for characterising photon statistics at high data rates. To identify the regime of linear APD operation we employ a ps-pulsed diode laser with variable repetition rates between 0.5MHz and 80MHz. We modify the mean optical power of the coherent pulses by applying different levels of well-calibrated attenuation. The linearity at high repetition rates is limited by the APD dead time and a non-linear response arises at higher photon-numbers due to multiphoton events. Assuming Poissonian input light statistics we ascertain the effective mean photon-number of the incident light with high accuracy. Time multiplexed detectors (TMD) allow to accomplish photon- number resolution by photon chopping. This detection setup extends the linear response function to higher photon-numbers and statistical methods may be used to compensate for non-linearity. We investigated this effect, compare it to the single APD case and show the validity of the convolution treatment in the TMD data analysis.

H. B. Coldenstrodt-Ronge; C. Silberhorn

2007-09-19

440

Spatiotemporal chaotic unjamming and jamming in granular avalanches.  

PubMed

We have investigated the spatiotemporal chaotic dynamics of unjamming and jamming of particles in a model experiment - a rotating drum partially filled with bidisperse disks to create avalanches. The magnitudes of the first Lyapunov vector ?u(t) and velocity v(t) of particles are directly measured for the first time to yield insights into their spatial correlation C?u,v, which is on statistical average slightly larger near the unjamming than the value near the jamming transition. These results are consistent with the recent work of Banigan et al (Nature Phys. 2013), and it is for the first time to validate their theoretical models in a real scenario. 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. PMID:25634753

Wang, Ziwei; Zhang, Jie

2015-01-01

441

Spatiotemporal chaotic unjamming and jamming in granular avalanches  

NASA Astrophysics Data System (ADS)

We have investigated the spatiotemporal chaotic dynamics of unjamming and jamming of particles in a model experiment - a rotating drum partially filled with bidisperse disks to create avalanches. The magnitudes of the first Lyapunov vector ?u(t) and velocity v(t) of particles are directly measured for the first time to yield insights into their spatial correlation C?u,v, which is on statistical average slightly larger near the unjamming than the value near the jamming transition. These results are consistent with the recent work of Banigan et al (Nature Phys. 2013), and it is for the first time to validate their theoretical models in a real scenario. 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.

Wang, Ziwei; Zhang, Jie

2015-01-01

442

Active Microrheology in Active Matter Systems: Mobility, Intermittency and Avalanches  

E-print Network

We examine the mobility and velocity fluctuations of a driven particle moving through an active matter bath of self-mobile disks for varied density or area coverage and varied activity. We show that the driven particle mobility can exhibit non-monotonic behavior that is correlated with distinct changes in the spatial-temporal structures that arise in the active media. We demonstrate that the probe particle velocity distributions exhibit specific features in the different dynamic regimes, and identify an activity-induced uniform crystallization that occurs for moderate activity levels and that is distinct from the previously observed higher activity cluster phase. The velocity distribution in the cluster phase has telegraph noise characteristics produced when the probe particle moves alternately through high mobility areas that are in the gas state and low mobility areas that are in the dense phase. For higher densities and large activities, the system enters what we characterize as an active jamming regime. Here the probe particle moves in intermittent jumps or avalanches which how power-law distributed sizes that are similar to the avalanche distributions observed for non-active disk systems near the jamming transition.

C. Reichhardt; C. J. Olson Reichhardt

2015-02-20

443

Tuned Critical Avalanche Scaling in Bulk Metallic Glasses  

PubMed Central

Ingots of the bulk metallic glass (BMG), Zr64.13Cu15.75Ni10.12Al10 in atomic percent (at. %), are compressed at slow strain rates. The deformation behavior is characterized by discrete, jerky stress-drop bursts (serrations). Here we present a quantitative theory for the serration behavior of BMGs, which is a critical issue for the understanding of the deformation characteristics of BMGs. The mean-field interaction model predicts the scaling behavior of the distribution, D(S), of avalanche sizes, S, in the experiments. D(S) follows a power law multiplied by an exponentially-decaying scaling function. The size of the largest observed avalanche depends on experimental tuning-parameters, such as either imposed strain rate or stress. Similar to crystalline materials, the plasticity of BMGs reflects tuned criticality showing remarkable quantitative agreement with the slip statistics of slowly-compressed nanocrystals. The results imply that material-evaluation methods based on slip statistics apply to both crystalline and BMG materials. PMID:24632786

Antonaglia, James; Xie, Xie; Schwarz, Gregory; Wraith, Matthew; Qiao, Junwei; Zhang, Yong; Liaw, Peter K.; Uhl, Jonathan T.; Dahmen, Karin A.

2014-01-01

444

Risk analysis for dry snow slab avalanche release by skier triggering  

NASA Astrophysics Data System (ADS)

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

McClung, David

2013-04-01

445

Avalanche protection dam of Cialancier in Saint Etienne de Tine : From 2D digital modeling to the start of the onsite work  

E-print Network

Avalanche protection dam of Cialancier in Saint Etienne de Tinée : From 2D digital modeling to design and build an avalanche protection dam. KEYWORDS Avalanche protection ­ Modeling ­ Work Adresse de. SEGEL, M. SCHMITT, E. MICHEL VILLAZ, T. EME, S. ROUDNITSKA, M. NAAIM. Avalanche protection dam

Paris-Sud XI, Université de

446

HOW TO EXPLAIN AVALANCHE DYNAMICS TO CHILDREN AND ...THEIR PARENTS Florence Naaim-Bouvet*, Thierry Faug, Frdric Ousset, Xavier Ravanat, Paolo Caccamo  

E-print Network

HOW TO EXPLAIN AVALANCHE DYNAMICS TO CHILDREN AND ...THEIR PARENTS Florence Naaim-Bouvet*, Thierry: Snow avalanches threaten mountain communities worldwide: avalanches affect not only snow sport tourists of 1998/99 in the Alps. It means that we have to increase local population awareness of avalanche hazard

Paris-Sud XI, Université de

447

Measurement of electrical avalanches and optical radiation near solid insulators in high pressure (up to 0. 3 MPa) nitrogen gas  

SciTech Connect

Electron and ion avalanches have been recorded near a variety of insulators (plexiglas, teflon, high-density polyethylene, low-density polyethylene, polypropylene, delrin, polyvinyl chloride, and nylon) in nitrogen gas at pressures of 0.1, 0.2, and 0.3 MPa. With the exception of nylon, suppression of avalanches has been observed in the presence of insulators. In addition to electron and ion avalanches, simultaneous measurement of optical radiation associated with an electron avalanche was successfully carried out. Qualitative explanations have been provided for the suppression of avalanches near most insulators and an anomalous growth of avalanches near nylon insulators. Photoemission from nylon surfaces appears to be responsible for the enhanced growth of avalanches near nylon insulators. More precise measurements of optical radiation are needed to better understand the electron-photon interactions near a solid insulator in a gaseous dielectric medium.

Mahajan, S.M. (Tennessee Technological University, Cookeville, Tennessee (US)); Sudarshan, T.S. (University of South Carolina, Columbia, South Carolina (US))

1991-03-01

448

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

SciTech Connect

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

Goldan, A. H.; Zhao, W. [Department of Radiology, School of Medicine, SUNY at Stony Brook, Stony Brook, New York 11794 (United States)

2013-01-15

449

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

NASA Astrophysics Data System (ADS)

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

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

2014-08-01

450

Cingulate seizure-like activity reveals neuronal avalanche regulated by network excitability and thalamic inputs  

PubMed Central

Background Cortical neurons display network-level dynamics with unique spatiotemporal patterns that construct the backbone of processing information signals and contribute to higher functions. Recent years have seen a wealth of research on the characteristics of neuronal networks that are sufficient conditions to activate or cease network functions. Local field potentials (LFPs) exhibit a scale-free and unique event size distribution (i.e., a neuronal avalanche) that has been proven in the cortex across species, including mice, rats, and humans, and may be used as an index of cortical excitability. In the present study, we induced seizure activity in the anterior cingulate cortex (ACC) with medial thalamic inputs and evaluated the impact of cortical excitability and thalamic inputs on network-level dynamics. We measured LFPs from multi-electrode recordings in mouse cortical slices and isoflurane-anesthetized rats. Results The ACC activity exhibited a neuronal avalanche with regard to avalanche size distribution, and the slope of the power-law distribution of the neuronal avalanche reflected network excitability in vitro and in vivo. We found that the slope of the neuronal avalanche in seizure-like activity significantly correlated with cortical excitability induced by ?-aminobutyric acid system manipulation. The thalamic inputs desynchronized cingulate seizures and affected the level of cortical excitability, the modulation of which could be determined by the slope of the avalanche size. Conclusions We propose that the neuronal avalanche may be a tool for analyzing cortical activity through LFPs to determine alterations in network dynamics. PMID:24387299

2014-01-01

451

Avalanches near a solid insulator in nitrogen gas at atmospheric pressure  

SciTech Connect

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

Mahajan, S. M.; Sudarshan, T. S.

1989-08-01

452

Avalanche situation in Turkey and back-calculation of selected events  

NASA Astrophysics Data System (ADS)

In Turkey, an average of 24 people dies 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 and American countries. 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 combined with a Digital Elevation Model (DEM)-based potential release zone identification algorithm to analyze the catastrophic avalanche events in the villages of zengili (Bayburt province) in 1993 and Yaylan (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, flow velocities, impact pressure and flow height.

Ayd?n, A.; Bhler, Y.; Christen, M.; Grer, I.

2014-01-01

453

A simple Monte Carlo model for prediction of avalanche multiplication process in Silicon  

NASA Astrophysics Data System (ADS)

A Simple Monte Carlo model has been developed to model the avalanche characteristics of Silicon. Good agreement with experimental results from Silicon p+-i-n+ diodes with i-regions ranging from 0.082 to 0.26 ?m, an n+-i-p+ diode with an i-region of 0.82 ?m and a p+n diode was obtained. Therefore our model can be used to model the avalanche process in diodes with varying electric field profiles. We also studied the competing effects of the ratio of electron to hole ionization coefficients and the dead space on excess noise factor, by varying these parameters in our simulations of ideal p+-i-n+ diodes with avalanche regions width of 0.05 to 0.3 ?m to cover the electric field range in the measured devices. As avalanche region width reduces from 0.3 to 0.05 ?m, the electron to hole ionisation coefficient ratio decreases from 3.42 to 1.23 while the dead space to avalanche width ratio increases from 0.19 to 0.49 for electrons. The former increases the excess noise while the latter suppresses the avalanche noise such that on balance, a weak dependence of excess noise on the avalanche width for w < 0.3 ?m was observed in these p+-i-n+ diodes, consistent with the excess noise results reported in thin Silicon p+-i-n+ diodes.

Zhou, X.; Ng, J. S.; Tan, C. H.

2012-08-01

454

Influence of snow cover on location and extension of avalanche release areas  

NASA Astrophysics Data System (ADS)

Location and extent of release areas are a crucial input in avalanche dynamics modelling, as they determine together with fracture depth the initial volume of an avalanche. Presently, avalanche release areas and locations are directly derived from geomorphological parameters but results are not always satisfactory. To improve existing algorithms, in the operational programme 'Italy-Switzerland, project STRADA', we assume that the spatial variability of the snow cover change the terrain morphology, and thus can have an influence on extension and location of avalanche slabs. One aim of this project is to provide a better understanding of this influence and to ultimately improve algorithms for automatic detection of avalanche release areas. In the starting zone of an avalanche, a rather homogeneous snow distribution is required to allow the formation of continuous weak layers and slabs which both favors fracture propagation und thus determines the size of the release area. By calculating the surface roughness, we believe to capture this homogeneity notion. To investigate how different snow cover scenarios may change the surface roughness, we used three different sets of snow depth measurements performed by airborne laser scanning at the Swiss Valle de la Sionne test site. The data sets are characterized by average snow depths ranging from 1m to 3m. For one scenario, 5 avalanches were artificially triggered and an additional laser scan was performed after the releases. We show that surface roughness progressively decreases with increasing snow depth up to an average snow depth of about 1-1.5m. Only little differences in roughness are observed if the mean snow depth exceeds this value. Furthermore, we show that release area extent increases with decreasing roughness. In the same manner, slab homogeneity increases with increasing release area extent and thus decreasing roughness. These findings demonstrate the power of roughness to determine avalanche release area size. The integration of roughness in combination with information about the current snow depth distribution is thus of great potential to improve the avalanche release definition.

Veitinger, J.; Sovilla, B.; Purves, R.

2012-04-01

455

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

NASA Astrophysics Data System (ADS)

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

de Arcangelis, L.

2012-05-01

456

The rock avalanche in Obernberg valley (Tyrol, Austria): Characteristics and age.  

NASA Astrophysics Data System (ADS)

In Obernberg valley, Eastern Alps, Austria, an array of landforms previously interpreted as terminal moraines (by other authors) is re-interpreted by us as a rock avalanche. In their distal 2 km, the rock avalanche mass is characterized by an ensemble of 40 hillocks and transversal ridges up to 17 m in vertical relief. The internal fabric of the ridges is incompatible with a glacial origin, but consistent with dynamic disintegration as diagnostic of rock avalanches. Catastrophic slope failure involved a rock volume of 4.5e7 m, and a runout of 7.2 km over a vertical distance of 1330 m (fahrbschung 10); the deposits cover an area of ~3 km. Ground electrical tomography with six multielectrode profiles provided information on the depth to substrate, and on the internal structure, of the rock avalanche. The volume of accumulated rock debris is estimated at 5.3e7 m. A radiocarbon age of 7785 190 cal yr BP of organic remnants in an alluvial fan that downlaps the rock avalanche provides a minimum-age constraint ('older-than' age) on mass-wasting. A mean 36Cl surface-exposure age of 8.6 0.6 ka BP of boulders of the avalanche mass indicates that the event took place during the early Holocene. Palaeoclimatic records indicate that, neither, the detachment scar, nor the runout track of the rock avalanche were glaciated at the time of mass-wasting. A lake basin in the proximal part of the rock-avalanche mass thus did not form as a result of dead ice melting. Marked seasonal fluctuations of lake level, combined with strong changes in shedding of springs downslope of the lake, suggest that the basin had formed by combined eluviation and dissolution of cataclastic rock-avalanche matrix and, perhaps, by karstification of underlying carbonate rocks.

Ostermann, Marc; Sanders, Diethard; Ivy-Ochs, Susan; Rockenschaub, Manfred

2013-04-01

457

The role of cornice fall avalanche sedimentation in the valley Longyeardalen, Central Svalbard  

NASA Astrophysics Data System (ADS)

In arctic and alpine high relief landscapes snow avalanches are traditionally ranked behind rockfall in terms of their significance for mass wasting processes of rock slopes. 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 situated on NW-facing lee slopes underneath large summit plateau, where cornices form annually, and high frequency and magnitude cornice fall avalanching is observed by daily automatic time-lapse photography. In addition, rock debris sedimentation by these cornice fall avalanches was measured directly in either permanent sediment traps or by snow inventories. The results from a maximum of 7 yr of measurements in a total of 13 catchments show maximum avalanche 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, the avalanche fan-surfaces accreted annually in a~maximum range from 3.7 to 13 mm yr-1 at Nybyen and from 0.3 to 21.4 mm yr-1 at Larsbreen. This comparably efficient rock slope mass wasting is due to collapsing cornices producing cornice fall avalanche with high rock debris content 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 and contributing to the development of a rock glacier at the Larsbreen slope system.

Eckerstorfer, M.; Christiansen, H. H.; Rubensdotter, L.; Vogel, S.

2012-12-01

458

Transport and emplacement mechanisms of channelised long-runout debris avalanches, Ruapehu volcano, New Zealand  

NASA Astrophysics Data System (ADS)

The steep flanks of composite volcanoes are prone to collapse, producing debris avalanches that completely reshape the landscape. This study describes new insights into the runout of large debris avalanches enhanced by topography, using the example of six debris avalanche deposits from Mount Ruapehu, New Zealand. Individual large flank collapses (>1 km3) produced all of these units, with four not previously recognised. Five major valleys within the highly dissected landscape surrounding Mount Ruapehu channelled the debris avalanches into deep gorges (?15 m) and resulted in extremely long debris avalanche runouts of up to 80 km from source. Classical sedimentary features of debris avalanche deposits preserved in these units include the following: very poor sorting with a clay-sand matrix hosting large subrounded boulders up to 5 m in diameter, jigsaw-fractured clasts, deformed clasts and numerous rip-up clasts of late-Pliocene marine sediments. The unusually long runouts led to unique features in distal deposits, including a pervasive and consolidated interclast matrix, and common rip-up clasts of Tertiary mudstone, as well as fluvial gravels and boulders. The great travel distances can be explained by the debris avalanches entering deep confined channels (?15 m), where friction was minimised by a reduced basal contact area along with loading of water-saturated substrates which formed a basal lubrication zone for the overlying flowing mass. Extremely long-runout debris avalanches are most likely to occur in settings where initially partly saturated collapsing masses move down deep valleys and become thoroughly liquified at their base. This happens when pore water is available within the base of the flowing mass or in the sediments immediately below it. Based on their H/L ratio, confined volcanic debris avalanches are two to three times longer than unconfined, spreading flows of similar volume. The hybrid qualities of the deposits, which have some similarities to those of debris flows, are important to recognise when evaluating mass flow hazards at stratovolcanoes.

Tost, M.; Cronin, S. J.; Procter, J. N.

2014-12-01

459

Influence of bed surface changes on snow avalanche simulation  

NASA Astrophysics Data System (ADS)

Gravitational flows, such as snow avalanches, are often modeled employing the shallowness assumption. The driving gravitational force has a first order effect on the dynamics of the flow, especially in complex terrain. Under suitable conditions, erosion and deposition during passage of the flow may change the bed surface by a similar amount as the flow depth itself. The accompanying changes of local slope angle and curvature are particularly significant at the side margins of the flow, where they may induce self-channeling and leve formation. Generally, one ought to expect visible effects wherever the flow depth and velocity are small, e.g., in deposition zones. Most current numerical models in practical use neglect this effect. In order to study the importance of these effects in typical applications, we modified the quasi-3D (depth-averaged) code MoT-Voellmy, which implements the well-known Voellmy friction law that is traditionally used in hazard mapping: The bed shear stress is given by ?iz(h,u) = -ui(?gh cos?+ ku2), ||u|| (1) with ? = O(0.1...0.5) and k = O(10-3...10-2) the dimensionless friction and drag coefficients, respectively. The leading curvature effects, i.e., extra friction due to centrifugal normal forces, are taken into account. The mass and momentum balances are solved by the (simplified) method of transport on a grid whose cells are squares when projected onto the horizontal plane. The direction of depth-averaging is everywhere perpendicular to the topographic surface. A simple erosion model is used. The erosion formula is based on the assumption that the snow cover behaves as a perfectly brittle solid with shear strength ?c, above which it instantaneously fails. The erosion rate is derived from the balance of momentum across the interface between bed and flow, where there is a discontinuity of the shear stress, which is given by equation 1 just above the interface and by ?c just below it according to the assumptions. This immediately leads to the formula 2 qe = ?gh-cos?+-ku- ?c/?f? (?gh cos?+ ku2 - ?c/?f). ||u|| (2) We present numerical simulations with static and dynamic beds in two different cases. First, an avalanche simulation on an inclined plane allows to study the occurring effects in their most immediate form. This allows to study the influence of spatial resolution of the computational grid. Second, we back-calculate a typical mid-size avalanche that was measured and documented in 1993 at the Norwegian test site Ryggfonn. This case study serves to test the relevance of including bed surface changes under conditions typical of real-world applications.

Fischer, Jan-Thomas; Issler, Dieter

2014-05-01

460

Sheet Flows, Avalanches, and Dune Migration on Earth and Mars  

NASA Astrophysics Data System (ADS)

We provide an overview of our research on sheet flows and avalanches of granular materials, primarily in terrestrial conditions. Sheet flows are relatively thin, highly concentrated regions of grains that flow near the ground under the influence of a strong turbulent wind. In them grains are suspended by interparticle collisions and the velocity fluctuations of the turbulent gas. Avalanches are flows of dry, cohesionless granular materials that are driven by gravity down inclines against the frictional and collisional resistance of the grains of the bed. In our study of sheet flows, we have extended existing theories that involve particle-particle and gas-particle interactions to apply to the conditions of a typical terrestrial sand dune during a sandstorm. This has involved the incorporation of both the viscous dissipation of the particle fluctuation energy due to the gas and the turbulent suspension of the grains due to velocity fluctuations of the gas. It has also involved an examination of several different boundary conditions at the bed and a more precise characterization of the conditions that apply at the top of a sheet flow, where the mean-free-path between collisions becomes comparable to the length of a ballistic trajectory. Solutions to the resulting differential equations have been obtained for both steady and unsteady fully-developed flow. The latter solutions provide information on the characteristic time to achieve a steady flow that plays a key role in dune formation. In support of this modeling effort, experiments have been undertaken to provide a better understanding of the interaction of particles colliding with the bed, and the energy of the rebounding particle and additional ejected particles has been measured in two-dimensional situations. The research on avalanches has focused on dense, frictional flows. Experiment and numerical simulations indicate that relatively thin dense flows, on the order of ten particle diameters, occur in layers. In these, momentum transfer occurs by rubbing between contacting particles and bumping between particles falling under gravity, rather than in collisions between freely flying particles. Thicker dense flows, on the other hand, do seem to involve collisional transfer of momentum. Theories based on the appropriated mechanisms of momentum transfer predict velocity profiles that are in agreement with those measured in experiment and numerical simulations, some of which have been carried out in the course of the research.

Jenkins, James; Hanes, D.; Bideau, D.; Berton, G.; Rioual, F.; Valance, A.

2002-11-01

461

Afterpulsing characteristics of InGaAs/InP single photon avalanche diodes  

NASA Astrophysics Data System (ADS)

InGaAs/InP single photon avalanche diodes (SPADs) are more and more available in many research fields. They are affected by afterpulsing which leads to a poor single photon detection probability. We present an InGaAs/InP avalanche photodiode with an active quenching circuit on an application specific integrated circuit (ASIC). It can quench the avalanche rapidly and then reduce the afterpulse rate. Also this quenching circuit can operate in both free-running and gated modes. Furthermore, a new technique is introduced to characterize the influence of the higher order of afterpulses, which uses a program running on a field programmable gate array (FPGA) integrated circuit.

Ma, Hai-Qiang; Yang, Jian-Hui; Wei, Ke-Jin; Li, Rui-Xue; Zhu, Wu

2014-12-01

462

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

NASA Technical Reports Server (NTRS)

The author has identified the following significant results. Photointerpretation of individual avalanche paths on single band black and white LANDSAT images is greatly hindered by terrain shadows and the low spatial resolution of the LANDSAT system. Maps produced in this way are biased towards the larger avalanche paths that are under the most favorable illumination conditions during imaging; other large avalanche paths, under less favorable illumination, are often not detectable and the smaller paths, even those defined by sharp trimlines, are only rarely identifiable.

Knepper, D. H. (principal investigator); Ives, J. D.; Summer, R.

1976-01-01

463

Critical avalanches and subsampling in map-based neural networks coupled with noisy synapses.  

PubMed

Many different kinds of noise are experimentally observed in the brain. Among them, we study a model of noisy chemical synapse and obtain critical avalanches for the spatiotemporal activity of the neural network. Neurons and synapses are modeled by dynamical maps. We discuss the relevant neuronal and synaptic properties to achieve the critical state. We verify that networks of functionally excitable neurons with fast synapses present power-law avalanches, due to rebound spiking dynamics. We also discuss the measuring of neuronal avalanches by subsampling our data, shedding light on the experimental search for self-organized criticality in neural networks. PMID:24032969

Girardi-Schappo, M; Kinouchi, O; Tragtenberg, M H R

2013-08-01

464

Spatially Extended Avalanches in a Hysteretic Capillary Condensation System: Superfluid {sup {bold 4}}He in Nuclepore  

SciTech Connect

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

Lilly, M.P.; Wootters, A.H.; Hallock, R.B. [Laboratory for Low Temperature Physics, Department of Physics and Astronomy, University of Massachusetts, Amherst, Massachusetts 01003 (United States)] [Laboratory for Low Temperature Physics, Department of Physics and Astronomy, University of Massachusetts, Amherst, Massachusetts 01003 (United States)

1996-11-01

465

Two-threshold model for scaling laws of noninteracting snow avalanches  

USGS Publications Warehouse

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

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

2004-01-01

466

Vortex avalanches at one thousandth the superconducting transition temperature  

SciTech Connect

We study the nonequilibrium dynamics of vortex motion at millikelvin temperatures in untwinned single crystals of YBa{sub 2}Cu{sub 3}O{sub 7{minus}{delta}}. Above threshold fields of many tesla, flux jumps appear in the magnetic hysteresis {ital B}({ital H}). These jumps correspond to a change of 750 vortices, on average, under our micrometer-sized Bi Hall probes. Not only are the threshold fields large, but they, and the characteristics of the flux jumps themselves, are essentially independent of magnet ramp rate or sample thickness, militating against a thermally triggered instability. Moreover, the threshold differs significantly on the ascending and descending branches of the hysteresis loop. We argue for a dynamical origin for these vortex avalanches and invoke a sandpile analogy to guide our detailed explorations of the {ital H}-{ital T} plane. {copyright} {ital 1996 The American Physical Society.}

Zieve, R.J.; Rosenbaum, T.F.; Jaeger, H.M. [The James Franck Institute and Department of Physics, The University of Chicago, Chicago, Illinois 60637 (United States)] [The James Franck Institute and Department of Physics, The University of Chicago, Chicago, Illinois 60637 (United States); Seidler, G.T. [NEC Research Institute, 4 Independence Way, Princeton, New Jersey 08540 (United States)] [NEC Research Institute, 4 Independence Way, Princeton, New Jersey 08540 (United States); Crabtree, G.W.; Welp, U. [Materials Science Division, Argonne National Laboratory, Argonne, Illinois 60439 (United States)] [Materials Science Division, Argonne National Laboratory, Argonne, Illinois 60439 (United States)

1996-05-01

467

Ultraviolet avalanche in anisotropic non-Abelian plasmas  

SciTech Connect

We present solutions of coupled particle-field evolution in classical U(1) and SU(2) gauge theories in real time on three-dimensional lattices. Our simulations are performed in a regime of extreme anisotropy of the momentum distribution of hard particles where backreaction is important. We find qualitatively different behavior for the two theories when the field strength is high enough that non-Abelian self-interactions matter for SU(2). It appears that the energy drained by a Weibel-like plasma instability from the particles does not build up exponentially in soft transverse magnetic fields but instead returns, isotropically, to the hard scale via a rapid avalanche into the ultraviolet.

Dumitru, Adrian; Nara, Yasushi [Institut fuer Theoretische Physik, Johann Wolfgang Goethe Universitaet, Max von Laue Strasse 1, D-60438 Frankfurt (Germany); Strickland, Michael [Frankfurt Institute for Advanced Study, Johann Wolfgang Goethe Universitaet, Max von Laue Strasse 1, D-60438 Frankfurt (Germany)

2007-01-15

468

Submicron Plasticity: Yield Stress, Dislocation Avalanches, and Velocity Distribution  

NASA Astrophysics Data System (ADS)

The existence of a well-defined yield stress, where a macroscopic crystal begins to plastically flow, has been a basic observation in materials science. In contrast with macroscopic samples, in microcrystals the strain accumulates in random bursts, which makes controlled plastic formation difficult. Here we study by 2D and 3D simulations the plastic deformation of submicron objects under increasing stress. We show that, while the stress-strain relation of individual samples exhibits jumps, its average and mean deviation still specify a well-defined critical stress. The statistical background of this phenomenon is analyzed through the velocity distribution of dislocations, revealing a universal cubic decay and the appearance of a shoulder due to dislocation avalanches.

Ispnovity, Pter Dusn; Groma, Istvn; Gyrgyi, Gza; Csikor, Ferenc F.; Weygand, Daniel

2010-08-01

469

Single Photon Avalanche Diodes: Towards the Large Bidimensional Arrays  

PubMed Central

Single photon detection is one of the most challenging goals of photonics. In recent years, the study of ultra-fast and/or low-intensity phenomena has received renewed attention from the academic and industrial communities. Intense research activity has been focused on bio-imaging applications, bio-luminescence, bio-scattering methods, and, more in general, on several applications requiring high speed operation and high timing resolution. In this paper we present design and characterization of bi-dimensional arrays of a next generation of single photon avalanche diodes (SPADs). Single photon sensitivity, dark noise, afterpulsing and timing resolution of the single SPAD have been examined in several experimental conditions. Moreover, the effects arising from their integration and the readout mode have also been deeply investigated.

Privitera, Simona; Tudisco, Salvatore; Lanzan, Luca; Musumeci, Francesco; Pluchino, Alessandro; Scordino, Agata; Campisi, Angelo; Cosentino, Luigi; Finocchiaro, Paolo; Condorelli, Giovanni; Mazzillo, Massimo; Lombardo, Salvo; Sciacca, Emilio

2008-01-01

470

Solutions to heavy ion induced avalanche burnout in power devices  

NASA Astrophysics Data System (ADS)

A review of normal breakdown and current induced avalanche (CIA) breakdown mechanisms in silicon power transistors is presented. The applicability of the CIA model to heavy ion induced burnout is shown, and solutions to CIA in silicon power semiconductors are given. It is noted that solving the problem of CIA burnout in npn bipolar and n-channel DMOS devices is, at best, difficult. Several techniques of hardening these devices to the effects of heavy ion, dose-rate induced failure, and any other condition producing CIA are discussed. The most effective techniques are those that minimize the emitter current injection by reducing the emitter injection efficiency or making the parasitic bipolar more difficult to turn on. However, it is believed that the simplest solution to the problem is to use pnp bipolar and p-channel DMOS devices whenever possible.

Wrobel, Theodore F.; Beutler, David E.

1992-12-01

471

Avalanches and waves in the Abelian sandpile model  

SciTech Connect

We numerically study avalanches in the two-dimensional Abelian sandpile model in terms of a sequence of waves of toppling events. Priezzhev {ital et al.} [Phys. Rev. Lett. {bold 76}, 2093 (1996)] have recently proposed exact results for the critical exponents in this model based on the existence of a proposed scaling relation for the difference in sizes of subsequent waves, {Delta}s=s{sub k}{minus}s{sub k+1}, where the size of the previous wave s{sub k} was considered to be almost always an upper bound for the size of the next wave s{sub k+1}. Here we show that the significant contribution to {Delta}s comes from waves that violate the bound; the average {l_angle}{Delta}s(s{sub k}){r_angle} is actually negative and diverges with the system size, contradicting the proposed solution. {copyright} {ital 1997} {ital The American Physical Society}

Paczuski, M. [Department of Physics, University of Houston, Houston, Texas 77204-5506 (United States)] [Department of Physics, University of Houston, Houston, Texas 77204-5506 (United States); Boettcher, S. [Center for Nonlinear Studies, MS-B258, Los Alamos National Laboratory, Los Alamos, New Mexico 87545 (United States)] [Center for Nonlinear Studies, MS-B258, Los Alamos National Laboratory, Los Alamos, New Mexico 87545 (United States)

1997-10-01

472

Avalanches and Continuous Flow in Aging Aqueous Foam  

E-print Network

We used coherent light scattering in a multi-speckle detection scheme to investigate the mesoscale dynamics in aqueous foam. Time-resolved correlation of the scattered speckle intensities reveals the details of foam dynamics during aging. We introduce Temporal Contrast Analysis, a novel statistical tool that can be effective in characterizing structural rearrangements. Using Temporal Contrast Analysis we were able to detect two distinct dynamical components present during foam aging: spontaneous and intermittent, avalanche-like events and continuous, flow-like rearrangements in the foam structure. We were able to measure these contributions separately from the intrinsic statistical noise contribution, and thereby independently analyze the decay of each dynamical component during foam aging process.

Michael M. Folkerts; Sam W. Stanwyck; Oleg G. Shpyrko

2012-02-25

473

High resolution, low energy avalanche photodiode X-ray detectors  

NASA Technical Reports Server (NTRS)

Silicon avalanche photodiodes have been fabricated, and their performance as X-ray detectors has been measured. Photon sensitivity and energy resolution were measured as a function of size and operating parameters. Noise thresholds as low as 212 eV were obtained at room temperature, and backscatter X-ray fluorescence data were obtained for aluminum and other light elements. It is concluded that the results with the X-ray detector are extremely encouraging, and the performance is challenging the best available proportional counters. While not at the performance level of either cryogenic silicon or HgI2, these device operate at room temperature and can be reproduced in large numbers and with much larger areas than typically achieved with HgI2. In addition, they are rugged and appear to be indefinitely stable.

Farrell, R.; Vanderpuye, K.; Entine, G.; Squillante, M. R.

1991-01-01

474

Temperature Control of Avalanche Photodiode Using Thermoelectric Cooler  

NASA Technical Reports Server (NTRS)

Avalanche photodiodes (APDS) are quantum optical detectors that are used for visible and near infrared optical detection applications. Although APDs are compact, rugged, and have an internal gain mechanism that is suitable for low light intensity; their responsivity, and therefore their output, is strongly dependent on the device temperature. Thermoelectric coolers (TEC) offers a suitable solution to this problem. A TEC is a solid state cooling device, which can be controlled by changing its current. TECs are compact and rugged, and they can precisely control the temperature to within 0.1 C with more than a 150 C temperature gradient between its surfaces. In this Memorandum, a proportional integral (PI) temperature controller for APDs using a TEC is discussed. The controller is compact and can successfully cool the APD to almost 0 C in an ambient temperature environment of up to 27 C.

Refaat, Tamer F.; Luck, William S., Jr.; DeYoung, Russell J.

1999-01-01

475

Elastic-plastic-brittle transitions and avalanches in disordered media.  

PubMed

A spring lattice model with the ability to simulate elastic-plastic-brittle transitions in a disordered medium is presented. The model is based on bilinear constitutive law defined at the spring level and power-law-type disorder introduced in the yield and failure limits of the springs. The key parameters of the proposed model effectively control the disorder distribution, significantly affecting the stress-strain response, the damage accumulation process, and the fracture surfaces. The model demonstrates a plastic strain avalanche behavior for perfectly plastic as well as hardening materials with a power-law distribution, in agreement with the experiments and related models. The strength of the model is in its generality and ability to interpolate between elastic-plastic hardening and elastic-brittle transitions. PMID:24580467

Kale, Sohan; Ostoja-Starzewski, Martin

2014-01-31

476

Improving the performance of silicon single-photon avalanche diodes  

NASA Astrophysics Data System (ADS)

Many applications require high performance Single Photon Avalanche Diodes (SPAD) either as single pixels or as small arrays of detectors. Although currently available silicon devices reached remarkable performance, nevertheless further improvements are needed in order to meet the requirements of most demanding time-resolved techniques. In this paper we present a new planar silicon technology for the fabrication of SPAD detectors, aimed at improving the Photon Detection Efficiency (PDE) of classical thin SPAD in the near infrared range while maintaining a good Temporal Resolution (TR). Experimental characterization showed a significant increase in the PDE with a remarkable value of 40% at 800nm; a photon timing jitter as low as 93ps FWHM as been also attained, while other device performances, such as Dark Count Rate (DCR) and Afterpulsing Probability (AP) are essentially unchanged, compared to thin SPAD. Being planar, the new technology is also intrinsically compatible with the fabrication of arrays of detectors.

Gulinatti, Angelo; Rech, Ivan; Maccagnani, Piera; Ghioni, Massimo; Cova, Sergio

2011-05-01

477

Some tests of avalanche photodiodes produced by Advanced Photonix, Inc.  

SciTech Connect

The goal of the measurements presented here is to check some parameters of the high gain avalanche photodiodes (APD`s) produced by Advanced Photonix, Inc. Samples with 16 mm and 5 mm diameter sensitive areas were tested. The tests were performed at FNAL. The new photomultiplier testing facility were used for gain measurements, linearity, and nonuniformity studies. The setup consists of laser with shifted wavelength of 440 nm, 10 Hz repetition rate and a pulse duration of 15 nsec. The laser light was transported to the APD by 1 mm diameter clear fiber. An amount of laser light was adjusted by rotating wheels of fixed light attenuation. The dynamic range of the APD, an amplifier (AMP) and an ADC was about 1000. To get the nonuniformity data the APD was mounted on a moveable stage under management and control of computer. The positioning of the fiber along sensitive surface of the APD was better than 100 microns.

Foster, G.W.; Ronzhin, A. [Fermi National Accelerator Lab., Batavia, IL (United States); Rusack, R. [Minnesota State Univ., Minneapolis, MN (United States)

1995-08-01

478

Photoelectron multipliers based on avalanche pn i pn structures  

NASA Astrophysics Data System (ADS)

We present a new physical principle to design an optoelectronic device, which consists of a multilayered semiconductor structure, where the necessary conditions for generation of photoelectrons are met, such that it will enable sequential avalanche multiplication of electrons and holes inside two depletion slabs created around the p - n junctions of a reverse biased pn - i - pn structure. The mathematical model and computer simulations of this Semiconductor Photo-electron Multiplier (SPEM) for different semiconductor materials are presented. Its performance is evaluated and compared with that of conventional devices. The Geiger operational mode is briefly discussed which may be used in Silicon Photomultiplier (SiPM) as an elementary photo detector to enhance its performance.

Lukin, K. A.; Maksymov, P. P.; Cerdeira, H. A.

2014-12-01

479

Multiscale modeling of multi-component granular avalanches  

NASA Astrophysics Data System (ADS)

Geophysical flows (e.g. snow slab avalanches, debris flows and pyroclastic flows and landslides) often contain particles of different sizes, shapes and materials, which can cause the constituent phases to segregate. Here we will focus of the effects of size and density. Kinetic sieving causes the particles to segregate by size, with small particles sifting downwards, as they have a higher probability than large particles to fit into void spaces [1]. The large particles on the surface are transported sideways to form levees that increase the resistance to lateral motion and thus enhance the run-out. At the same time, particles also segregate by density due to buoyancy, which shifts lighter particles upwards. For bidisperse flows, a mixture-theory continuum model is used that includes the effects of both size and density segregation [2]. We use DEM (DPM) simulations to investigate two key model parameters that are hard to obtain from experiments. A novel coarse-graining expression for the stress tensor of discrete mechanical systems is applied for mixtures to obtain the partial stresses and the interaction drag force [3,4]. The goal is to develop predictive multi-component models of granular avalanches by utilising both continuum and particle simulation approaches. REFERENCES [1] Thornton, A.R., Weinhart, T., Luding, S., Bokhove, O., Modelling of particle size segregation: Calibration using the discrete particle method, Int. J. Mod. Phys. C 23, (2012). [2] Tunuguntla, D., Bokhove, O., Thornton, A.R., Particle segregation in free-surface flows, submitted to JFM rapids (2013) [3] T. Weinhart, A. R. Thornton, S. Luding, O. Bokhove, From discrete particles to continuum fields near a boundary, Granular Matter 14(2), 289-294 (2012). [4] T. Weinhart, S. Luding, A.R. Thornton, From discrete particles to continuum fields in mixtures, AIP Conf. Proc. 1542, 1202-1205 (2013)

Weinhart, Thomas; Tunuguntla, Deepak; Luding, Stefan; Thornton, Anthony

2014-05-01

480

Long-wavelength photonic integrated circuits and avalanche photodetectors  

NASA Astrophysics Data System (ADS)

Fast-growing internet traffic volume require high data communication bandwidth over longer distances. Access network bottlenecks put pressure on short-range (SR) telecommunication systems. To effectively address these datacom and telecom market needs, low-cost, high-speed laser modules at 1310 to 1550 nm wavelengths and avalanche photodetectors are required. The great success of GaAs 850nm VCSEls for Gb/s Ethernet has motivated efforts to extend VCSEL technology to longer wavelengths in the 1310 and 1550 nm regimes. However, the technological challenges associated with materials for long wavelength VCSELs are tremendous. Even with recent advances in this area, it is believed that significant additional development is necessary before long wavelength VCSELs that meet commercial specifications will be widely available. In addition, the more stringent OC192 and OC768 specifications for single-mode fiber (SMF) datacom may require more than just a long wavelength laser diode, VCSEL or not, to address numerous cost and performance issues. We believe that photonic integrated circuits (PICs), which compactly integrate surface-emitting lasers with additional active and passive optical components with extended functionality, will provide the best solutions to today's problems. Photonic integrated circuits have been investigated for more than a decade. However, they have produced limited commercial impact to date primarily because the highly complicated fabrication processes produce significant yield and device performance issues. In this presentation, we will discuss a new technology platform of InP-based PICs compatible with surface-emitting laser technology, as well as a high data rate externally modulated laser module. Avalanche photodetectors (APDs) are the key component in the receiver to achieve high data rate over long transmission distance because of their high sensitivity and large gain- bandwidth product. We have used wafer fusion technology to achieve InGaAs/Si APDs with much greater potential than the traditional InGaAs/InP APDs. Preliminary results on their performance will be presented.

Tsou, Yi-Jen D.; Zaytsev, Sergey; Pauchard, Alexandre; Hummel, Steve; Lo, Yu-Hwa

2001-10-01