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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.

Weisel, Frank

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.

Rathjen, Don

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

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

2010-08-20

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

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

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

Low noise avalanche photodiodes  

Microsoft Academic Search

The maximum useful gain in avalanche photodiodes (APDs) is limited by the noise associated with the random fluctuations of the avalanche process which increase with multiplication. The conventional McIntyre theory relates this excess noise F, to the value of the mean multiplication, M and the ratio of the hole to electron ionization coefficients (? and ? respectively), k. For electron

J. P. R. David; G. J. Rees

2001-01-01

15

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

16

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

17

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

18

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

19

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

20

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

21

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.

22

Testing predictability criteria in avalanches  

NASA Astrophysics Data System (ADS)

We study a cellular automaton that presents a behavior similar to that of avalanches in sand piles. The size distribution of these events presents a clear separation between small and large avalanches; the former showing a power-law kind of behavior common to these systems. In this article we compare different schemes of possible predictions of the large events. One, using an algorithm proposed by Rosendahl, Veki?, and Rutledge [Phys. Rev. Lett. 73, 537 (1994)], follows the activities of small avalanches between consecutive large avalanches; others analyze the distribution of time intervals between consecutive large events, and the distribution of small events between consecutive large avalanches.

Morales, E.; Peralta-Fabi, R.; Romero-Rochn, V.

1996-10-01

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

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

25

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.

26

Extended wavelength avalanche photodiodes  

Microsoft Academic Search

The ability to detect optical signals beyond 1.65 m is of technological interest for a number of applications. In this work we describe a novel technology that offers considerable promise for high speed, high sensitivity detection in this region utilising avalanche gain. InGaAs\\/GaAsSb type II superlattices as the absorption region and InAlAs as the multiplication region can be combined to

J. P. R. David; J. S. Ng; C. H. Tan; Y. L. Goh

2009-01-01

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

Performance characteristics of avalanche photodiodes  

Microsoft Academic Search

The conventional McIntyre carrier multiplication theory for avalanche photodiodes, APDs, does not adequately describe the experimental results obtained from APDs with thin multiplication regions. Both gain and excess noise factor have reduced values in thin multiplication regions, as confirmed by the reported experimental results, which is not predicted by conventional models. In this paper a new analytical model for avalanche

R. A. AbdelRassoul; M. M. El Zalabani; H. S. Ali

2003-01-01

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

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

34

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

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

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

38

Avalanche crown-depth distributions  

Microsoft Academic Search

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 extreme value distribution provides the most robust fit, followed by a two-parameter variation, the Frchet distribution. The most parsimonious explanation is neither self-organized criticality nor other complex cascades, but the maximum domain

Edward H. Bair; Karl W. Birkeland

2008-01-01

39

Avalanche Crown-Depth Distributions  

Microsoft Academic Search

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 extreme value distribution provides the most robust fit, followed by a two-parameter variation, the Frchet distribution. The most parsimonious explanation is neither self-organized criticality nor other complex cascades, but the maximum domain

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

2008-01-01

40

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

2010-03-03

41

Secondary avalanches in gas mixtures  

NASA Astrophysics Data System (ADS)

Avalanche development in gas-based detectors relies not only on direct ionisation but also on excitation of noble gas atoms. Some quencher molecules can be ionised when they collide with excited atoms, a process on which we reported earlier [1]. Alternatively, excited atoms can decay by photon emission. If these photons are insufficiently absorbed by the quencher, yet capable of ionising, then they may escape from the avalanche region and start secondary avalanches. This process, called photon feedback, leads to an over-exponential increase of the gas gain which limits the working range. In this paper, we derive photon feedback parameters from published gain measurements for several gas mixtures and fit these parameters in a model which describes their dependence on the quencher concentration and the pressure.

?ahin, zkan; Tapan, ?lhan; Veenhof, Rob

2013-08-01

42

Asulkan Valley Avalanche Track, Glacier National Park  

E-print Network

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

Smith, Dan

43

Colloquium: Experiments in vortex avalanches E. Altshuler*  

E-print Network

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

Johansen, Tom Henning

44

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

2012-07-02

45

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

46

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...

47

Material Considerations for Avalanche Photodiodes  

Microsoft Academic Search

Avalanche photodiodes (APDs) are widely used to detect and amplify weak optical signals by utilizing the impact ionization process. The choice of material is critical for the detection of a particular wavelength, and it is often expedient to use a combination of different materials to optimize the overall device performance. The APDs are now capable of covering a wide spectrum

J. P. R. David; C. H. Tan

2008-01-01

48

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

49

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

50

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

51

Buried-mesa avalanche photodiodes  

Microsoft Academic Search

We have developed a low-cost buried-mesa avalanche photodiode (APD) primarily targeted for 2.5-Gb\\/s lightwave applications. These APDs are made by a simple batch process that produces a robust and reliable device with potentially high yield and thus low cost. The entire base structure of our InGaAs-InP APD is grown in one epitaxial step and the remaining process consists of four

Ghulam Hasnain; Wayne G. Bi; S. Song; John T. Anderson; Nick Moll; Chung-Yi Su; James N. Hollenhorst; Nicholas D. Baynes; I. Athroll; Sean Amos; R. M. Ash

1998-01-01

52

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

53

Avalanche Phenomena in Pore Draining  

NASA Astrophysics Data System (ADS)

Hysteresis curves measured for superfluid ^4He capillary condensation in Nuclepore membrane indicate deviations from the independent element model. Nuclepore is an interesting material to study since every pore threads the membrane from top to bottom, but non-trivial in the sense that pore intersections seem to play an important role in the hysteresis phenomena observed. Especially interesting in the hysteresis is the sharp draining which occurs as the pores first begin to empty. This has been seen in other hysteretic capillary systems.footnote J. H. Page, J. Liu, B. Abeles, H. W. Deckman, and D. A. Weitz, Phys. Rev. Letters 71, 1216 (1993), for example. We have observed the existence of steps, or avalanches(M. P. Lilly, P. T. Finley, and R. B. Hallock, Phys. Rev. Letters 71), 4186 (1993). , as large groups of pores (<~10^7 out of a total sample size of ~ 10^9 pores) empty in the steep, initial portion of the draining curve. By use of spatially separated detectors, we show that avalanches involve macroscopic (rather than just local) regions of the Nuclepore. We report measurements of the size distribution, duration, and spatial extent of the avalanche events.

Lilly, M. P.; Hallock, R. B.

1996-03-01

54

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

55

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 .......................................................................................................11 Wet Loose Snow Avalanching in Southwestern Montana ...........................................13 3. RELATING SNOWPACK STRATIGRAPHY TO WET LOOSE SNOW AVALANCHING

Lawrence, Rick L.

56

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.

57

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

58

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

59

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

2013-08-16

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

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

62

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

63

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

64

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

65

Triaging multiple victims in an avalanche setting: the Avalanche Survival Optimizing Rescue Triage algorithmic approach.  

PubMed

As winter backcountry activity increases, so does exposure to avalanche danger. A complicated situation arises when multiple victims are caught in an avalanche and where medical and other rescue demands overwhelm resources in the field. These mass casualty incidents carry a high risk of morbidity and mortality, and there is no recommended approach to patient care specific to this setting other than basic first aid principles. The literature is limited with regard to triaging systems applicable to avalanche incidents. In conjunction with the development of an electronic avalanche rescue training module by the Canadian Avalanche Association, we have designed the Avalanche Survival Optimizing Rescue Triage algorithm to address the triaging of multiple avalanche victims to optimize survival and disposition decisions. PMID:20591351

Bogle, Lee B; Boyd, Jeff J; McLaughlin, Kyle A

2010-03-01

66

Avalanche polynomials of some families of graphs  

Microsoft Academic Search

We study the abelian sandpile model on different families of graphs. We introduced the avalanche polynomial which enumerates the size of the avalanches triggered by the addition of a particle on a recurrent configuration. This polynomial is calculated for several families of graphs. In the case of the complete graph, the result involves some known result on Parking functions (12,

R. Cori; A. Dartois; D. Rossin

67

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

68

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 Á Snow avalanche Á Lahul Á Himalaya Á India 1

Smith, Dan

69

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

70

Spatial determination of magnetic avalanche ignition points  

NASA Astrophysics Data System (ADS)

Using time-resolved measurements of local magnetization in the molecular magnet Mn12-ac, we report studies of magnetic avalanches (fast magnetization reversals) with non-planar propagating fronts, where the curved nature of the magnetic fronts is reflected in the time-of-arrival at micro-Hall sensors placed at the surface of the sample. Assuming that the avalanche interface is a spherical bubble that grows with a radius proportional to time, we are able to locate the approximate ignition point of each avalanche in a two-dimensional cross-section of the crystal. We find that although in most samples the avalanches ignite at the long ends, as found in earlier studies, there are crystals in which ignition points are distributed throughout an entire weak region near the center, with a few avalanches still originating at the ends.

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

71

Thermal energy in dry snow avalanches  

NASA Astrophysics Data System (ADS)

Avalanches can exhibit many different flow regimes from powder clouds to slush flows. Flow regimes are largely controlled by the properties of the snow released and entrained along the path. Recent investigations showed the temperature of the moving snow to be one of the most important factors controlling the mobility of the flow. The temperature of an avalanche is determined by the temperature of the released and entrained snow but also increases by frictional and collisional processes with time. For three artificially released avalanches, we conducted snow profiles along the avalanche track and in the deposition area, which allowed quantifying the temperature of the eroded snow layers. Infrared radiation thermography (IRT) was used to assess the surface temperature before, during and just after the avalanche with high spatial resolution. This data set allowed to calculate the thermal balance, from release to deposition, and to discuss the magnitudes of different sources of thermal energy of the avalanches. We could confirm that, for the investigated dry avalanches, the thermal energy increase due to friction was mainly depending on the elevation drop of the avalanche with a warming of approximately 0.5 C per 100 height meters. Contrary, warming due to entrainment was very specific to the individual avalanche and depended on the temperature of the snow along the path and the erosion depth ranging from nearly no warming to a maximum observed warming of 1 C. Furthermore, we could observe the warmest temperatures are located in the deposits of the dense core. Future research directions, especially for the application of IRT, in the field of thermal investigations in avalanche dynamics are discussed.

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

2014-11-01

72

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

73

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.

74

On estimating avalanche danger from simulated snow profiles Sascha Bellaire  

E-print Network

On estimating avalanche danger from simulated snow profiles Sascha Bellaire 1,2 , Bruce Jamieson 1 and Geophysics, University of Innsbruck, Tyrol, Austria ABSTRACT: Estimating avalanche danger is the primary goal of avalanche warning services. Typically avalanche danger is estimated based on a variety of information

Jamieson, Bruce

75

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

76

Dynamics of Avalanche Activities in Financial Markets  

NASA Astrophysics Data System (ADS)

We study the dynamical properties of avalanche activities in the Korean Treasury Bond (KTB) futures price and the S&P 500 stock index. We apply the detrended fluctuation analysis, multiscale sample entropy and wavelet coefficient correlation to them, which revealed the scale-free dynamics of the bursting time series, avalanche size, and laminar time. We found that the laminar time and the avalanche size are anti-correlated in a short scale but in a large scale strongly correlated in KTB503, and are strongly correlated over all scales in S&P 500.

Kim, Cheol-Hyun; Park, C. H.; Kim, Soo Yong; Kim, Kyungsik; Scalas, Enrico

77

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

78

Initiation of immersed granular avalanches  

NASA Astrophysics Data System (ADS)

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.

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

2014-05-01

79

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

80

Avalanche control: Conservation Guide Series No. 5  

SciTech Connect

This book examines different methods for determining the characteristics of snow cover and for localizing avalanche risk. It describes various techniques for temporary defense; for snow stabilization in the starting zone; and for wind deflection.

Not Available

1985-01-01

81

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

82

MWIR HgCdTe avalanche photodiodes  

Microsoft Academic Search

This paper reports results obtained on mid-wave IR x equals 0.3 Hg1-xCdxTe avalanche photodiodes (APDs) that utilize a cylindrical 'p-around-n' front side illuminated n+\\/n-\\/p geometry. This 'p-around-n' geometry favors electron avalanche gain. These devices are characterized by a uniform, exponential, gain voltage characteristic that is consistent with a hole to electron ionization ratio, k equals (alpha) h\\/(alpha) e, of zero.

Jeffrey D. Beck; Chang-Feng Wan; Michael A. Kinch; James E. Robinson

2001-01-01

83

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

84

Spatial determination of magnetic avalanche ignition points  

Microsoft Academic Search

Using time-resolved measurements of local magnetization in the molecular magnet Mn12-ac, we report studies of magnetic avalanches (fast magnetization reversals) with non-planar propagating fronts, where the curved nature of the magnetic fronts is reflected in the time-of-arrival at micro-Hall sensors placed at the surface of the sample. Assuming that the avalanche interface is a spherical bubble that grows with a

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

2008-01-01

85

Spatial Determination of Magnetic Avalanche Ignition points  

Microsoft Academic Search

Using time-resolved measurements of local magnetization [1], we report studies of the propagation of magnetic avalanches (fast magnetization reversals) in Mn12-ac crystals triggered stochastically in response to a time-varying (swept) magnetic field. The spherical nature of the fronts produced by avalanches originating within the bulk is reflected in the time-of-arrival at an array of micro-Hall sensors placed on the surface

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

2007-01-01

86

Prehistoric rock avalanches at Rinderhorn, Switzerland  

NASA Astrophysics Data System (ADS)

Large prehistoric rock avalanches are frequently associated with the retreat of alpine glaciers following the last glacial maximum. However, due to a lack of accurately dated rock avalanche deposits, precise conclusions regarding the temporal occurrence of these events remain elusive. Here we present two case studies of rock avalanches in the Rinderhorn area of the central Bernese Alps, Switzerland. Preliminary results suggest that the Klein Rinderhorn rock avalanche released approximately 50 million m3 of sedimentary rock with a runout distance of up to 4.7 km. The Daubensee rock avalanche lies slightly upvalley to the south, and first results suggest a released volume of about 10 million m3. The 2.3 km long runout crossed, and apparently breached, a Late glacial moraine. The release and deposit areas of both events are located near the well-known Kandertal rock avalanche, and therefore provide an excellent opportunity to study chronological correlations between deglaciation and the timing of large slope failures in the region. We date the two events using Cl-36 cosmogenic surface exposure dating on deposited boulders. We also model the local pre-failure topographies in order to perform runout simulations. The combined outcomes enable better understanding of the failure scenarios and provide insights into how changes in rock slope boundary conditions associated with glacial retreat helped condition the slope failures.

Grmiger, L.; Moore, J. R.; Ivy-Ochs, S.

2012-04-01

87

Directed avalanche processes with underlying interface dynamics.  

PubMed

We describe a directed avalanche model; a slowly unloading sandbox driven by lowering a retaining wall. The directness of the dynamics allows us to interpret the stable sand surfaces as world sheets of fluctuating interfaces in one lower dimension. In our specific case, the interface growth dynamics belongs to the Kardar-Parisi-Zhang (KPZ) universality class. We formulate relations between the critical exponents of the various avalanche distributions and those of the roughness of the growing interface. The nonlinear nature of the underlying KPZ dynamics provides a nontrivial test of such generic exponent relations. The numerical values of the avalanche exponents are close to the conventional KPZ values, but differ sufficiently to warrant a detailed study of whether avalanche-correlated Monte Carlo sampling changes the scaling exponents of KPZ interfaces. We demonstrate that the exponents remain unchanged, but that the traces left on the surface by previous avalanches give rise to unusually strong finite-size corrections to scaling. This type of slow convergence seems intrinsic to avalanche dynamics. PMID:12241353

Chen, Chun-Chung; den Nijs, Marcel

2002-07-01

88

Directed avalanche processes with underlying interface dynamics  

NASA Astrophysics Data System (ADS)

We describe a directed avalanche model; a slowly unloading sandbox driven by lowering a retaining wall. The directness of the dynamics allows us to interpret the stable sand surfaces as world sheets of fluctuating interfaces in one lower dimension. In our specific case, the interface growth dynamics belongs to the Kardar-Parisi-Zhang (KPZ) universality class. We formulate relations between the critical exponents of the various avalanche distributions and those of the roughness of the growing interface. The nonlinear nature of the underlying KPZ dynamics provides a nontrivial test of such generic exponent relations. The numerical values of the avalanche exponents are close to the conventional KPZ values, but differ sufficiently to warrant a detailed study of whether avalanche-correlated Monte Carlo sampling changes the scaling exponents of KPZ interfaces. We demonstrate that the exponents remain unchanged, but that the traces left on the surface by previous avalanches give rise to unusually strong finite-size corrections to scaling. This type of slow convergence seems intrinsic to avalanche dynamics.

Chen, Chun-Chung; den Nijs, Marcel

2002-07-01

89

On pulsed Doppler radar measurements of avalanches and their implication to avalanche dynamics  

Microsoft Academic Search

Pulsed Doppler radar measurements from several avalanche releases are analyzed to gain an in-depth understanding of avalanche dynamics. A pulsed Doppler radar emits short pulses and samples the echo in distinct time intervals, corresponding to distance intervals (range gates). Frequency analysis of the echo signals, exploiting the Doppler-effect, yields the velocity distribution within the width of a range gate. Thus,

Peter Gauer; Martin Kern; Krister Kristensen; Karstein Lied; Lambert Rammer; Helmut Schreiber

2007-01-01

90

Submarine Avalanche Volume Calculations, A Prerequisite To Tsunami Modeling: The Example of The Ruatoria Debris Avalanche  

Microsoft Academic Search

Initial volumes of material remobilised in submarine avalanches may often be overestimated when calculated from post slope failure deposits, if no provisions are made for the volume expansion resulting from intense material fracturation that inherently occur during collapses. Knowledge of initial volumes is critical if any modelling of tsunami generation is to be meaningful. The massive submarine Ruatoria debris avalanche,

G. Lamarche; J.-Y. Collot; R. Garlick; W. de Langek

2002-01-01

91

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

92

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

93

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

94

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

95

Avalanche frequency and magnitude: using power-law exponents to investigate snow avalanche size proportions through time and space.  

E-print Network

??Power-laws provide a means for investigating snow avalanche frequency/magnitude relationships and their contributing factors. This research uses power-laws to explore variations in avalanche size proportions (more)

Naisbitt, Adam

2008-01-01

96

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

97

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

98

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.

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

2013-01-01

99

Spatial Determination of Magnetic Avalanche Ignition points  

NASA Astrophysics Data System (ADS)

Using time-resolved measurements of local magnetization [1], we report studies of the propagation of magnetic avalanches (fast magnetization reversals) in Mn12-ac crystals triggered stochastically in response to a time-varying (swept) magnetic field. The spherical nature of the fronts produced by avalanches originating within the bulk is reflected in the time-of-arrival at an array of micro-Hall sensors placed on the surface of the sample. By treating the propagating front as a spherical bubble of radius rt, we locate the approximate ignition points in a two-dimensional cross-section of the crystal. The trigger points are stochastically distributed (some in the bulk and some at the edges), with higher density regions that vary from sample to sample. This suggests that avalanches originate preferentially in weak regions of a crystal where the defect density is high. [1] Yoko Suzuki et al. Phys. Rev. Lett. 95, 147201 (2005).

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

2007-03-01

100

Automatic Ionization Measurement in Avalanche Chamber Pictures  

NASA Astrophysics Data System (ADS)

The experiment WA44 at the CERN SPS, "Search for quarks in high-energy neutrino interactions", is equipped with a large volume (2.35 1.25 0.6 m3) streamer chamber for the primary ionization measurement of charged tracks. The streamer chamber, filled with a He-Ne mixture, is operated in the avalanche mode. Image intensifiers are used to record the event on a photographic film. The pictures are automatically scanned by a Flying-Spot-Digitizer and the scanning data are stored on magnetic tape. In this paper the analysis of the FSD data, i.e., the track finding method and the measurement of the avalanche density, are described. The results obtained with this automatic method show that both the efficiency of track finding and the reliability of ionization measurement are good, down to avalanche densities as low as 1/10 of the ionization expected for minimum ionizing charge-one particles.

Basile, M.; Romeo, G. Cara; Castelvetri, A.; Cifarelli, L.; Contin, A.; D'Ali, G.; Di Cesare, P.; Esposito, B.; Favale, L.; Giusti, P.; Laakso, I.; Marrian, C.; Masetti, M.; Massam, T.; Nania, R.; Palmonari, F.; Rohrbach, F.; Rossi, V.; Sartorelli, G.; Spinetti, M.; Susinno, G.; Valenti, G.; Votano, L.; Zichichi, A.

1981-04-01

101

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

102

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.

103

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

104

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

105

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

106

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.

107

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

108

Mathematical modeling of powder-snow avalanche flows  

E-print Network

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

109

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

110

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

111

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

112

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.

113

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

114

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

115

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

116

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

117

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

118

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.

119

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

120

On Relationships among Avalanche, Nonlinearity and Correlation Immunity  

E-print Network

On Relationships among Avalanche, Nonlinearity and Correlation Immunity Yuliang Zheng1 and Xian of the degree of avalanche and the order of correlation immunity of a Boolean function of n variables is at most is in harmony with nonlinearity, it goes against correlation immunity. Key Words: Avalanche Criterion, Boolean

Zheng, Yuliang

121

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

2006-09-01

122

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

123

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

124

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

125

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

126

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

127

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

128

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

129

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

PubMed

The flat-panel detector (FPD) is the state-of-the-art detector for digital radiography. The FPD can acquire images in real-time, has superior spatial resolution, and is free of the problems of x-ray image intensifiers-veiling glare, pin-cushion and magnetic distortion. However, FPDs suffer from poor signal to noise ratio performance at typical fluoroscopic exposure rates where the quantum noise is reduced to the point that it becomes comparable to the fixed electronic noise. It has been shown previously that avalanche multiplication gain in amorphous selenium (a-Se) can provide the necessary amplification to overcome the electronic noise of the FPD. Avalanche multiplication, however, comes with its own intrinsic contribution to the noise in the form of gain fluctuation noise. In this article a cascaded systems analysis is used to present a modified metric related to the detective quantum efficiency. The modified metric is used to study a diagnostic x-ray imaging system in the presence of intrinsic avalanche multiplication noise independently from other noise sources, such as electronic noise. An indirect conversion imaging system is considered to make the study independent of other avalanche multiplication related noise sources, such as the fluctuations arising from the depth of x-ray absorption. In this case all the avalanche events are initiated at the surface of the avalanche layer, and there are no fluctuations in the depth of absorption. Experiments on an indirect conversion x-ray imaging system using avalanche multiplication in a layer of a-Se are also presented. The cascaded systems analysis shows that intrinsic noise of avalanche multiplication will not have any deleterious influence on detector performance at zero spatial frequency in x-ray imaging provided the product of conversion gain, coupling efficiency, and optical quantum efficiency are much greater than a factor of 2. The experimental results show that avalanche multiplication in a-Se behaves as an intrinsic noise free avalanche multiplication, in accordance with our theory. Provided good coupling efficiency and high optical quantum efficiency are maintained, avalanche multiplication in a-Se has the potential to increase the gain and make negligible contribution to the noise, thereby improving the performance of indirect FPDs in fluoroscopy. PMID:18196793

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

2007-12-01

130

A new model for avalanche build-up of carriers in a SAGCM avalanche photodiode  

Microsoft Academic Search

A new model for the avalanche build-up of carriers in an avalanche photodiode (APD) including the dead-space effect has been developed and used to study the frequency response of a resonant-cavity-enhanced (RCE) separate absorption, grading, charge, and multiplication (SAGCM) APD. In this model, the carriers are characterized by their energy and position in the region of multiplication. The excess energy

N. R. Das; M. J. Deen

2002-01-01

131

Fractals and multifractals in avalanche models  

Microsoft Academic Search

This note reports work by Kadanoff, Nagel, Wu, and Zhou which has been submitted to Physical Review A. In this paper, we examine extensions of the sandslide (or avalanche) model originally proposed by Bak, Tang, and Wiesenfeld to see the nature of the probability distributions produced by the dynamical processes. In particular, we wish to see (a) whether the distributions

Leo P. Kadanoff

1989-01-01

132

Time Dependence of Avalanche Processes in Silicon  

Microsoft Academic Search

An analysis of the time dependence of avalanche processes encountered in silicon junctions, including the effects of different ionization rates and velocities of the two charge carriers, is presented. An earlier analysis of Read was restricted to equal ionization rates and velocities; that restriction has been removed but the frequency limitation of his analysis has been retained here. Various solutions

C. A. Lee; R. L. Batdorf; W. Wiegmann; G. Kaminsky

1967-01-01

133

Breakdown probabilities for thin heterostructure avalanche photodiodes  

Microsoft Academic Search

The recurrence theory for the breakdown probability in avalanche photodiodes (APDs) is generalized to heterostruc- ture APDs that may have multiple multiplication layers. The generalization addresses layer-boundary effects such as the initial energy of injected carriers as well as the layer-dependent profile of the dead space in the multiplication region. Reducing the width of the multiplication layer serves to both

Majeed M. Hayat; U. Sakoglu; Oh-Hyun Kwon; Shuling Wang; J. C. Campbell; B. E. A. Saleh; M. C. Teich

2003-01-01

134

Excess Noise in Amorphous Selenium Avalanche Photodiodes  

Microsoft Academic Search

Excess noise in amorphous Selenium avalanche photodiodes (a-Se APD) has been measured in a frequency range from 3 kHz to 30 kHz. The deduced excess noise factors, including dependences on photocurrent, frequency, applied electric field and the a-Se layer's thickness, agreed with McIntyre's theoretical values.

Tetsuya Ohshima; Kazutaka Tsuji; Kenji Sameshima; Tadaaki Hirai; Keiichi Shidara; Kazuhisa Taketoshi

1991-01-01

135

Excess Noise in Amorphous Selenium Avalanche Photodiodes  

NASA Astrophysics Data System (ADS)

Excess noise in amorphous Selenium avalanche photodiodes (a-Se APD) has been measured in a frequency range from 3 kHz to 30 kHz. The deduced excess noise factors, including dependences on photocurrent, frequency, applied electric field and the a-Se layers thickness, agreed with McIntyres theoretical values.

Ohshima, Tetsuya; Tsuji, Kazutaka; Sameshima, Kenji; Hirai, Tadaaki; Shidara, Keiichi; Taketoshi, Kazuhisa

1991-06-01

136

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

137

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

138

Avalanche photodiodes for the CMS detector  

Microsoft Academic Search

The CERN LHC experiment CMS has selected for the readout of the barrel crystal calorimeter a 55 mm2 avalanche photodiode (APD) manufactured by Hamamatsu Photonics. In the detector we will equip each crystal with two APDs for a total of 122400 diodes. As the calorimeter will be almost completely inaccessible during the life of the detector, the assurance that they

K. Deiters; A. Dorokhov; Q. Ingram; S. Nicol; I. Musienko; B. Patel; D. Renker; S. Reucroft; R. Rusack; T. Sakhelashvili; A. Singovski; J. Swain; P. Vikas

2000-01-01

139

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

PubMed

The past decade has seen the swift development of the flat-panel detector (FPD), also known as the active matrix flat-panel imager, for digital radiography. This new technology is applicable to other modalities, such as fluoroscopy, which require the acquisition of multiple images, but could benefit from some improvements. In such applications where more than one image is acquired less radiation is available to form each image and amplifier noise becomes a serious problem. Avalanche multiplication in amorphous selenium (a-Se) can provide the necessary amplification prior to read out so as to reduce the effect of electronic noise of the FPD. However, in direct conversion detectors avalanche multiplication can lead to a new source of gain fluctuation noise called depth dependent avalanche noise. A theoretical model was developed to understand depth dependent avalanche noise. Experiments were performed on a direct imaging system implementing avalanche multiplication in a layer of a-Se to validate the theory. For parameters appropriate for a diagnostic imaging FPD for fluoroscopy the detective quantum efficiency (DQE) was found to drop by as much as 50% with increasing electric field, as predicted by the theoretical model. This drop in DQE can be eliminated by separating the collection and avalanche regions. For example by having a region of low electric field where x rays are absorbed and converted into charge that then drifts into a region of high electric field where the x-ray generated charge undergoes avalanche multiplication. This means quantum noise limited direct conversion FPD for low exposure imaging techniques are a possibility. PMID:17441244

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

2007-03-01

140

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

141

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

142

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

143

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

Microsoft Academic Search

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

D. Delparte; B. Jamieson; N. Waters

2008-01-01

144

Modelling the evolution of temperature in avalanche flow  

NASA Astrophysics Data System (ADS)

Because the mechanical properties of snow are temperature dependent, snow temperature has a strong influence on avalanche flow behaviour. In fact, snow avalanche classification schemes implicitly account for the below-zero temperature regime, i.e. wet snow avalanches contain warm moist snow, whereas dry flowing or powder avalanches consist of colder snow. Although thermal effects are an important feature of avalanche flow behaviour, the temperature field is usually not considered in avalanche dynamics calculations. In this presentation we explicitly model the temperature evolution of avalanches by extending the basic set of depth-averaged differential equations of mass, momentum and fluctuation energy to include a depth-averaged internal energy equation. Two dissipative processes contribute to the irreversible rise in internal energy: the shear work and the dissipation of fluctuation energy due to random granular interactions. Snow entrainment is also an important source of thermal energy. As the temperature of the snow can vary between the release area and runout zone, we model the effect of snowcover temperature elevation gradients. Additionally we introduce a physical constraint on the temperature field to account for phase changes: when the temperature of the avalanche flow surpasses the melting point of ice, the surplus rise in internal energy is used to produce meltwater. We do not consider heat losses due to sensible heat exchanges between the atmosphere and the avalanche. Using numerical simulations we demonstrate how the temperature of the snow in the release area in relation to the temperature of the snowcover encountered by the avalanche at lower elevations can modify avalanche velocity and runout behaviour. We show how the production of turbulent fluctuation energy, which separates dense and dilute, fluidized flow regimes, can be controlled by temperature, creating a wide-range of avalanche deposition patterns. Finally, we investigate under what thermal conditions meltwater can be generated during the runout phase of the avalanche.

Vera, Cesar; Christen, Marc; Funk, Martin; Bartelt, Perry

2013-04-01

145

Stochastic simulation of electron avalanches on supercomputers  

NASA Astrophysics Data System (ADS)

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

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

2014-12-01

146

Hierarchical networks, power laws, and neuronal avalanches  

PubMed Central

We show that in networks with a hierarchical architecture, critical dynamical behaviors can emerge even when the underlying dynamical processes are not critical. This finding provides explicit insight into current studies of the brain's neuronal network showing power-law avalanches in neural recordings, and provides a theoretical justification of recent numerical findings. Our analysis shows how the hierarchical organization of a network can itself lead to power-law distributions of avalanche sizes and durations, scaling laws between anomalous exponents, and universal functionseven in the absence of self-organized criticality or critical points. This hierarchy-induced phenomenon is independent of, though can potentially operate in conjunction with, standard dynamical mechanisms for generating power laws. PMID:23556972

Friedman, Eric J.; Landsberg, Adam S.

2013-01-01

147

Fractals and multifractals in avalanche models  

NASA Astrophysics Data System (ADS)

This note reports work by Kadanoff, Nagel, Wu, and Zhou which has been submitted to Physical Review A. In this paper, we examine extensions of the sandslide (or avalanche) model originally proposed by Bak, Tang, and Wiesenfeld to see the nature of the probability distributions produced by the dynamical processes. In particular, we wish to see (a) whether the distributions have a well-defined scaling limit; (b) whether the distributions have a simple (Widom) scaling behavior or are instead multifractal and (c) whether they fail into universality classes. We answer these questions by doing simulational studies of cases in which the models describe one- or two-dimensional arrays of stacks. For the one-dimensional case the answers are:yes, hope that an analogous construction might perhaps provide a renormalization group argument for the determination of the probability distribution in the avalanche examples.

Kadanoff, Leo P.

1989-09-01

148

Hierarchical networks, power laws, and neuronal avalanches.  

PubMed

We show that in networks with a hierarchical architecture, critical dynamical behaviors can emerge even when the underlying dynamical processes are not critical. This finding provides explicit insight into current studies of the brain's neuronal network showing power-law avalanches in neural recordings, and provides a theoretical justification of recent numerical findings. Our analysis shows how the hierarchical organization of a network can itself lead to power-law distributions of avalanche sizes and durations, scaling laws between anomalous exponents, and universal functions-even in the absence of self-organized criticality or critical points. This hierarchy-induced phenomenon is independent of, though can potentially operate in conjunction with, standard dynamical mechanisms for generating power laws. PMID:23556972

Friedman, Eric J; Landsberg, Adam S

2013-03-01

149

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

150

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.

151

Pile density is a control parameter of sand avalanches  

NASA Astrophysics Data System (ADS)

Centrifuge experimentation (10-1000 m/s2) on sand avalanches has shown that (i) grain cohesion and elasticity are negligible; (ii) the avalanche size ?? and the maximum angle of repose ?m depend on the initial pile density d; and (iii) the pile surface evolves spontaneously towards an asymptotic state after a few avalanches, this state being characterized by a mean surface angle equal to the macroscopic friction angle ? and a mean avalanche size equal to 1.7. This demonstrates that the density d is a controlling parameter of the avalanche process. These results are compatible with a unique internal friction angle ? with ?=34 ? corresponds to the value measured with other soil-mechanics devices; however, ? fluctuates within 2 from pile to pile or test to test. These data are also consistent with a dilatancy effect which depends on density, but the existence of at least one other parameter controlling the avalanche size has been also proved.

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

1993-04-01

152

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

153

Noise in avalanche transit-time devices.  

NASA Technical Reports Server (NTRS)

A survey of work performed on noise in avalanche transit-time devices is presented. Both theoretical and experimental results on noise mechanisms and performance of these devices, when they are employed as oscillators, amplifiers, and self-oscillating mixers, are reviewed. Several unexplained experimental results and points of disagreement between the experimental work results of various workers are identified. Suggestions for further studies are offered.

Gupta, M.

1971-01-01

154

Avalanche photodiodes - No longer a laboratory curiosity  

Microsoft Academic Search

Recent advances in avalanche photodiodes (APD) are reviewed. Carrier transit times 1-10 nsec are stressed, and APD noise is compared to photomultiplier noise in the visible and IR. Applications of APD are outlined: laser rangefinders (pulsed or swept-frequency swept-FM CW lasers), detectors in optical communications systems (line-of-sight or fiber optics systems), large-area detectors comprising an array of modules, soft X-ray

R. J. McIntyre; P. P. Webb

1977-01-01

155

Avalanche Photodiode Arrays for Optical Communications Receivers  

Microsoft Academic Search

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 fleld. It is shown that use of an APD array for pulse-position modulation detection can improve performance by up to 4 dB over

M. Srinivasan; V. Vilnrotter

156

FORECASTING RUNOUT OF ROCK AND DEBRIS AVALANCHES  

Microsoft Academic Search

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

R. M. IVERSON

157

Threshold Model for Triggered Avalanches on Networks  

E-print Network

Based on a theoretical model for opinion spreading on a network, through avalanches, the effect of external field is now considered, by using methods from non-equilibrium statistical mechanics. The original part contains the implementation that the avalanche is only triggered when a local variable (a so called awareness) reaches and goes above a threshold. The dynamical rules are constrained to be as simple as possible, in order to sort out the basic features, though more elaborated variants are proposed. Several results are obtained for a Erd\\"os-R\\'enyi network and interpreted through simple analytical laws, scale free or logistic map-like, i.e., (i) the sizes, durations, and number of avalanches, including the respective distributions, (ii) the number of times the external field is applied to one possible node before all nodes are found to be above the threshold, (iii) the number of nodes still below the threshold and the number of hot nodes (close to threshold) at each time step.

Ausloos, Marcel

2014-01-01

158

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

159

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.

160

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

161

Automatic detection of avalanches and debris flows by seismic methods  

NASA Astrophysics Data System (ADS)

The road along the shl hillside in the West Fjords region of Iceland is one of the most hazardous roads in Iceland due to avalanches, rockfalls and debris flows. The road has little traffic, but nevertheless traffic accidents caused by the severe conditions at the site are common. A number of avalanche tracks are found on the hillside. In some of these tracks, avalanches occur more frequently than in others. When there is an avalanche threat, avalanches generally flow over many tracks in a short time. Monitoring vibrations in the tracks with the highest avalanche frequency can indicate when avalanches start flowing down the hillside in a snowstorm, and avalanche hazard can then be declared with the specific site indicated. The same methodology can be used for rockfalls and debris flows, which are strongly affected by weather conditions and typically occur in clusters. Based on this knowledge, a research project was initiated in February 1996 with the objective of developing an automatic system based on seismic measurements to detect and analyze avalanches on the shl hillside and to instantly send a warning to a control station.

Bessason, Bjarni; Eirksson, Gsli; Thrarinsson, inn; Thrarinsson, Andrs; Einarsson, Sigurur

162

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

163

Anterior capsulotomy with a pulsed-electron avalanche knife  

E-print Network

Anterior capsulotomy with a pulsed-electron avalanche knife Daniel Palanker, PhD, Hiroyuki Nomoto-electron avalanche knife design for creating a continuous cur- vilinear capsulotomy (CCC) and compare the CCC- alanche knife produced sharp-edged capsule cutting without radial nicks or tears. CONCLUSIONS: The probe

Palanker, Daniel

164

Measured shear rates in large dry and wet snow avalanches  

Microsoft Academic Search

We present estimates of internal shear rates of real-scale avalanches that are based on velocity measurements. Optical velocity sensors installed on the instrument pylon at the Swiss Valle de la Sionne test site are used to measure flow velocities at different flow heights of three large dry and wet snow avalanches. Possible sources of error in the correlation analysis of

Martin Kern; Perry Bartelt; Betty Sovilla; Othmar Buser

2009-01-01

165

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

166

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

167

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

168

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

169

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

170

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

171

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

172

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

173

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

174

How avalanche pulses evolve in space and time  

NASA Astrophysics Data System (ADS)

Conventional models of the time response of avalanche photodiodes (APDs) assume that carriers travel uniformly at their saturated drift velocity, vsat. To test the validity of this drift velocity assumption (DVA) the model was used to compute the distribution of exit times of electrons generated in an avalanche pulse and the results were compared with those of Monte-Carlo (MC) simulations. The comparison demonstrates that, while the DVA is valid for thick (1um) avalanching regions, it does not take account of non-equilibrium effects which occur in thin avalanching regions, nor of the effects of diffusion. As a consequence, the DVA model may increasingly underestimate the speed of APDs as the width of the avalanche region is reduced.

Plimmer, S. A.; Hambleton, Paul J.; Ng, Beng K.; Dunn, G. M.; Ng, Jo S.; David, John P. R.; Rees, Graham J.

2001-07-01

175

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

176

Avalanches and disorder-induced criticality in artificial spin ices  

NASA Astrophysics Data System (ADS)

We show that both square and kagome artificial spin ice systems exhibit disorder-induced nonequilibrium phase transitions, with power law avalanche distributions at the critical disorder level. The different nature of geometrical frustration in the two lattices produces distinct types of critical avalanche behavior. For the square ice, the avalanches involve the propagation of locally stable domain walls separating the two polarized ground states, and the scaling collapse agrees with an interface depinning mechanism. In contrast, avalanches in the fully frustrated kagome ice exhibit pronounced branching behaviors that resemble those found in directed percolation. The kagome ice also shows an interesting crossover in the power-law scaling of the avalanches at low disorder. Our results show that artificial spin ices are ideal systems in which to study nonequilibrium critical point phenomena.

Chern, Gia-Wei; Reichhardt, C.; Olson Reichhardt, C. J.

2014-06-01

177

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

178

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

179

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

180

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

181

RELATING AVALANCHES TO LARGE-SCALE OCEAN ATMOSPHERIC OSCILLATIONS Scott Thumlert  

E-print Network

avalanche climate which is helpful for planning avalanche hazard mitigation programs. Finally, global climate change is likely to affect these climate oscil- lations; thus, the relationship between avalanche activity and these climate oscillations provides some insight into how avalanche activity could be affected

Jamieson, Bruce

182

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

183

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

184

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

185

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

186

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.

187

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

188

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

189

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

190

IFKIS a basis for organizational measures in avalanche risk management  

NASA Astrophysics Data System (ADS)

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

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

2003-04-01

191

Statistical analyses support power law distributions found in neuronal avalanches.  

PubMed

The size distribution of neuronal avalanches in cortical networks has been reported to follow a power law distribution with exponent close to -1.5, which is a reflection of long-range spatial correlations in spontaneous neuronal activity. However, identifying power law scaling in empirical data can be difficult and sometimes controversial. In the present study, we tested the power law hypothesis for neuronal avalanches by using more stringent statistical analyses. In particular, we performed the following steps: (i) analysis of finite-size scaling to identify scale-free dynamics in neuronal avalanches, (ii) model parameter estimation to determine the specific exponent of the power law, and (iii) comparison of the power law to alternative model distributions. Consistent with critical state dynamics, avalanche size distributions exhibited robust scaling behavior in which the maximum avalanche size was limited only by the spatial extent of sampling ("finite size" effect). This scale-free dynamics suggests the power law as a model for the distribution of avalanche sizes. Using both the Kolmogorov-Smirnov statistic and a maximum likelihood approach, we found the slope to be close to -1.5, which is in line with previous reports. Finally, the power law model for neuronal avalanches was compared to the exponential and to various heavy-tail distributions based on the Kolmogorov-Smirnov distance and by using a log-likelihood ratio test. Both the power law distribution without and with exponential cut-off provided significantly better fits to the cluster size distributions in neuronal avalanches than the exponential, the lognormal and the gamma distribution. In summary, our findings strongly support the power law scaling in neuronal avalanches, providing further evidence for critical state dynamics in superficial layers of cortex. PMID:21720544

Klaus, Andreas; Yu, Shan; Plenz, Dietmar

2011-01-01

192

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

193

Recent advances in avalanche photodiode technology  

NASA Astrophysics Data System (ADS)

Avalanche photodiodes (APDs) are solid state devices having an internal signal gain which gives them a better signal-to-noise ratio than standard photodiodes. Although they have been studied for years, recent advances in the fabrication techniques have allowed the construction of multielement arrays (up to 10 X 10) with high performance capability. This progress has resulted in increased potential for exploiting the advantages of APDs in a variety of important applications including measurements requiring fast response such as nuclear and high energy physics research, industrial nondestructive testing, medical instrumentation, and biomedical research using low energy particles. Recent experimental data characterizing APDs and APD arrays used as x-ray, particle, and low level light detectors are presented.

Squillante, Michael R.; Gordon, Jeffrey S.; Farrell, Richard; Vasile, Stefan A.; Daley, Kathleen; Oakes, Carlton E.; Vanderpuye, K.

1993-12-01

194

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

195

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

196

Rock-and-soil avalanches: Theory and simulation  

NASA Astrophysics Data System (ADS)

We present a 2-D Contact Dynamics discrete element model for simulating initiation and motion of rock avalanches, integrating hillslope geometry, Mohr-Coulomb rock behavior, pore pressure before avalanche triggering, and avalanche trigger. Avalanche motion is modeled as a dense granular flow of dry frictional and cohesive particles. On the basis of granular physics and shear experiments, we review some of the theories for the unexpectedly long runout of rock avalanches. Different causes are evoked, according to the strength (strong or weak) of the slip surface relative to the bulk. "Mechanical fluidization" and "acoustic fluidization" theories state that agitation of rock particles reduces frictional strength, increasing runout. Conversely, granular mechanics suggests that, as "shear-strain" rate increases, granular material becomes more agitated, more dissipative, and more resistant. Another theory states that dynamic fragmentation of clasts creates an isotropic pressure that drives longer runout. In contrast, granular mechanics suggests that fragmentation may induce fluidization and strengthening of the granular material, while particle size reduction (among others) induces weakening of the granular flow and enhances long runout. Runout is also enhanced for column-like rock masses collapsing from steep hillslopes. Long runout may also be linked to thermal weakening mechanisms at the slip surface (e.g., thermal pressurization, and shear melting), which may lower drastically the shear strength. The model is illustrated with a hypothetical example of a rain-triggered avalanche, mobilizing shallowly dipping layers. Several phases are identified, including slope failure, avalanche triggering resulting from slip weakening, and avalanche motion in which rocks are folded and sheared.

Taboada, Alfredo; Estrada, Nicolas

2009-09-01

197

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

198

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

199

Noise properties and time response of the staircase avalanche photodiode  

Microsoft Academic Search

The staircase avalanche photodiode is a novel graded-gap superlattice device that is expected to detect photons quite noiselessly. It is designed in such a way that only electrons impact-ionize, thereby eliminating the feedback noise associated with conventional two-carrier avalanche devices. Because the electron multiplication can occur only at a small number of discrete locations in the device, the variability of

K. Matsuo; M. C. Teich; B. E. A. Saleh

1985-01-01

200

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

201

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

202

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

203

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

204

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

205

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

206

Fragmentation in the Val Pola rock avalanche, Italian Alps  

Microsoft Academic Search

Grain size data from the deposit of the 1987 Val Pola rock avalanche (central Italian Alps) are compared with data concerning rock avalanching, rock fragmentation, and comminution. The Weibull distribution fits a small part of the entire particle-size distribution of debris samples, with a mean value of the curve shape factor of 0.54 0.28. This is typical of multiple

Giovanni B. Crosta; Paolo Frattini; Nicoletta Fusi

2007-01-01

207

HgCdTe avalanche photodiodes: A review  

Microsoft Academic Search

This paper presents a comprehensive review of fundamental issues, device architectures, technology development and applications of HgCdTe based avalanche photodiodes (APD). High gain, above 5103, a low excess noise factor close to unity, THz gain-bandwidth product, and fast response in the range of pico-seconds has been achieved by electron-initiated avalanche multiplication for SWIR, MWIR, and LWIR detector applications involving low

Anand Singh; Vanya Srivastav; Ravinder Pal

2011-01-01

208

Dense Granular Avalanches: Mathematical Description and Experimental Validation  

NASA Astrophysics Data System (ADS)

Snow avalanches, landslides, rock falls and debris flows are extremely dangerous and destructive natural phenomena. The frequency of occurrence and amplitudes of these disastrous events appear to have increased in recent years perhaps due to recent climate warming. The events endanger the personal property and infra-structure in mountainous regions. For example, from the winters 1940/41 to 1987/88 more than 7000 snow avalanches occurred in Switzerland with damaged property leading to a total of 1269 deaths. In February 1999, 36 people were buried by a single avalanche in Galtr, Austria. In August 1996, a very large debris flow in middle Taiwan resulted in 51 deaths, 22 lost and an approximate property damage of more than 19 billion NT dollars (ca. 600 million US dollars) [18]. In Europe, a suddenly released debris flow in North Italy in August 1998 buried 5 German tourists on the Superhighway "Brenner-Autobahn". The topic has gained so much significance that in 1990 the United Nations declared the International Decade for Natural Disasters Reduction (IDNDR); Germany has its own Deutsches IDNDR-Komitee fr Katastrophenvorbeugung e.V. Special conferences are devoted to the theme, e.g., the CALAR conference on Avalanches, Landslides, Rock Falls and Debris Flows (Vienna, January 2000), INTERPRAEVENT, annual conferences on the protection of habitants from floods, debris flows and avalanches, special conferences on debris flow hazard mi tigation and those exclusively on Avalanches.

Tai, Y.-C.; Hutter, K.; Gray, J. M. N. T.

209

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

210

Fluctuation-dissipation relations for granular snow avalanches  

NASA Astrophysics Data System (ADS)

A fundamental problem in avalanche science is understanding the interaction between frictional processes taking place at the basal running surface and dissipative mechanisms within the avalanche body. In this paper, we address this question by studying how kinetic energy is dissipated into heat in snow avalanches. In doing so we consider the effect of random granular fluctuations and collisions in depth-averaged snow avalanche models. We show that relationships between the size of the granular fluctuations and the energy dissipated by granular collisions can be obtained by studying the energy input required to maintain steady-state flows. The energy input for granular fluctuations comes from mechanisms operating in the basal layer. The kinetic energy of the flow at the basal layer is converted to granular agitation energy, a random kinetic energy, which in turn is dissipated as heat by both viscous shearing and inelastic collisions at higher levels in the avalanche profile. Thus granular fluctuations play a crucial role in understanding the total dissipation process. We apply our theoretical considerations to develop a constitutive model for dense snow avalanches and are able to accurately model steady-state velocity profiles of both snow-chute experiments and field measurements.

Bartelt, Perry; Buser, Othmar; Platzer, Katharina

211

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

212

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

213

Infrasonic monitoring of snow avalanches in the Alps  

NASA Astrophysics Data System (ADS)

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

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

2012-04-01

214

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

215

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

216

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

217

Friction and dynamics of rock avalanches travelling on glaciers  

NASA Astrophysics Data System (ADS)

Rock avalanches travelling on glaciers often exhibit effective friction coefficient lower than those on a rocky terrain. After briefly considering some data of rock avalanches on glaciers, the physics of sliding of solid objects on icy surfaces is reviewed, and a model is put forward for the mechanics of rock avalanche sliding on ice accounting for the formation of a natural lubricating layer. It is suggested that at the beginning of the flow of a rock avalanche, friction results from rocky blocks ploughing on ice. As the erosion continues, a gouge of ice particles results, which clogs the interstices between blocks and may partially melt as a consequence of the production of frictional heat. This conceptual model is numerically investigated for a slab travelling on ice. The results show an increase in mobility as a function of slab thickness, travelled length, and the gravity field, in agreement with case studies. The results are useful to interpret the peculiar features of rock avalanches travelling on icy surfaces such as digitations, out-runner blocks, and longitudinal furrows. The lubrication theory for landslides on ice proposed here may provide a framework for understanding landslides on Earth and for future modelling; in addition, it may help elucidate the presence of similar landslide deposits on the surface of Mars.

De Blasio, Fabio Vittorio

2014-05-01

218

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

219

Precision Blasting Techniques For Avalanche Control  

NASA Astrophysics Data System (ADS)

Experimental firings sponsored by the Center For Snow Science at Alta, Utah have demonstrated the potential of a unique prototype shaped charge device designed to stimulate snow pack and ice. These studies, conducted against stable snow pack, demonstrated a fourfold increase in crater volume yield and introduced a novel application of Shock Tube technology to facilitate position control, detonation and dud recovery of manually deployed charges. The extraordinary penetration capability of the shaped charge mechanism has been exploited in many non-military applications to meet a wide range of rapidpiercing and/or cutting requirements. The broader exploitation of the potential of the shaped charge mechanism has nevertheless remained confined to defence based applications. In the studies reported in this paper, the inimitable ability of the shaped charge mechanism to project shock energy, or a liner material, into a highly focussed energetic stream has been applied uniquely to the stimulation of snow pack. Recent research and development work, conducted within the UK, has resulted in the integration of shaped charge technology into a common Avalauncher and hand charge device. The potential of the common charge configuration and spooled Shock Tube fire and control system to improve the safety and cost effectiveness of explosives used in avalanche control operations was successfully demonstrated at Alta in March 2001. Future programmes of study will include focussed shock/blast mechanisms for suspended wire traverse techniques, application of the shaped charge mechanism to helibombing, and the desig n and development of non-fragmenting shaped charge ammunition formilitary artillery gun systems.

Powell, Kevin M.

220

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

221

Wind may have driven avalanches on Martian dunes  

NASA Astrophysics Data System (ADS)

In the sand dunes in the north polar sand sea of Mars, sand avalanches that appear as wedge-shaped alcoves can be seen above fan-shaped deposits. The avalanches, which are typically several meters across, are currently actively forming, with new alcoves showing up in recent images taken in consecutive Mars years. Some scientists have proposed that these sand avalanches occur when frozen carbon dioxide (CO2) sublimates, triggering the downslope flow (mass wasting) of sand grains and rock that had been lying on top of the CO2 frost. However, Horgan and Bell now suggest that these alcoves may actually have been formed by wind-driven movement of sand, not by CO2 sublimation.

Balcerak, Ernie

2012-07-01

222

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

223

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

224

Mathematical modeling of powder-snow avalanche flows  

E-print Network

Powder-snow avalanches are violent natural disasters which represent a major risk for infrastructures and populations in mountain regions. In this study we present a novel model for the simulation of avalanches in the aerosol regime. The second scope of this study is to get more insight into the interaction process between an avalanche and a rigid obstacle. An incompressible model of two miscible fluids can be successfully employed in this type of problems. We allow for mass diffusion between two phases according to the Fick's law. The governing equations are discretized with a contemporary fully implicit finite volume scheme. The solver is able to deal with arbitrary density ratios. Several numerical results are presented. Volume fraction, velocity and pressure fields are presented and discussed. Finally we point out how this methodology can be used for practical problems.

Denys Dutykh; Cline Acary-Robert; Didier Bresch

2009-01-19

225

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, Université de

226

Geomorphology of snow avalanche impact landforms in the southern Canadian Cordillera  

E-print Network

by excavation on impact. This paper reports on the geomorphology, and surface age and stability of three SAILs passage, tandis que les avalanches en a´erosol emportent les s´ediments en creusant des excavations. Cet excavation. The morphology of the snow avalanche track at Peyto Lake causes large snow avalanches to become

Smith, Dan

227

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

228

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.

229

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

230

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

231

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

232

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

233

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

234

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.

235

Two-fluid barotropic models for powder-snow avalanche flows  

E-print Network

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

Gisclon, Marguerite

236

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

237

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

238

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

239

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

240

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

241

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

242

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

243

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

244

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

245

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.

246

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

247

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

248

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

249

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

250

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

E-print Network

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

251

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

252

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

253

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.

254

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

255

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

256

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

257

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

258

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.

259

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

260

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.

261

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

262

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

263

Practical methods for using vegetation patterns to estimate avalanche frequency and magnitude  

NASA Astrophysics Data System (ADS)

Practitioners working in avalanche terrain may never witness an extreme event, but understanding extreme events is important for categorizing avalanches that occur within a given season. Historical records of avalanche incidents and direct observations are the most reliable evidence of avalanche activity, but patterns in vegetation can be used to further quantify and map the frequency and magnitude of past events. We surveyed published literature to synthesize approaches for using vegetation sampling to characterize avalanche terrain, and developed examples to identify the benefits and caveats of using different practical field methods to estimate avalanche frequency and magnitude. Powerful avalanches can deposit massive piles of snow, rocks, and woody debris in runout zones. Large avalanches (relative to the path) can cut fresh trimlines, widening their tracks by uprooting, stripping, and breaking trees. Discs and cores can be collected from downed trees to detect signals of past avalanche disturbance recorded in woody plant tissue. Signals of disturbance events recorded in tree rings can include direct impact scars from the moving snow and wind blast, development of reaction wood in response to tilting, and abrupt variation in the relative width of annual growth rings. The relative ages of trees in avalanche paths and the surrounding landscape can be an indicator of the area impacted by past avalanches. Repeat photography can also be useful to track changes in vegetation over time. For Colorado, and perhaps elsewhere, several vegetation ecology methods can be used in combination to accurately characterize local avalanche frequency and magnitude.

Simonson, S.; Fassnacht, S. R.

2011-12-01

264

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

Microsoft Academic Search

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

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

2004-01-01

265

Avalanche shape and exponents beyond mean-field theory  

NASA Astrophysics Data System (ADS)

Elastic systems, such as magnetic domain walls, density waves, contact lines, and cracks, are pinned by substrate disorder. When driven, they move via avalanches, with power law distributions of size, duration and velocity. Their exponents, and the shape of an avalanche, defined as its mean velocity as a function of time, were 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 \\varepsilon = d\\text{c}-d expansion around the upper critical dimension, with d\\text{c}=4 for short-ranged elasticity, and d\\text{c}=2 for long-ranged elasticity. Here we calculate analytically the O}(\\varepsilon) , i.e. 1-loop, correction to the avalanche shape at fixed duration T, for both types of elasticity. The exact expression, though different from the phenomenological form presented by Laurson et al. in Nat. Commun., 4 (2013) 2927, is well approximated by ?ft< \\dot u(t=x T)\\right>_T? [ Tx(1-x)]?-1 \\exp?ft( A}?ft[\\frac12-x\\right]\\right) , 0 < x < 1. The asymmetry A}? - 0.336 (1-d/d\\text{c}) is negative for d close to d\\text{c} , skewing the avalanche towards its end, as observed in numerical simulations in d = 2 and 3. The exponent ?=(d+\\zeta)/z is given by the two independent exponents at depinning, the roughness ? and the dynamical exponent z. We propose a general procedure to predict other avalanche exponents in terms of ? and z. We finally introduce and calculate the shape at fixed avalanche size, not yet measured in experiments or simulations.

Dobrinevski, Alexander; Le Doussal, Pierre; Jrg Wiese, Kay

2014-12-01

266

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

267

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

268

Geiger-Mode Avalanche Photodiodes in Particle Detection  

E-print Network

It is well known that avalanche photodiodes operated in the Geiger mode above the breakdown voltage offer a virtually infinite sensitivity and time accuracy in the picosecond range that can be used for single photon detection. However, their performance in particle detection remains still unexplored. In this contribution, we are going to expose the different steps that we have taken in order to prove the efficiency of Geiger mode avalanche photodiodes in the aforementioned field. In particular, we will present an array of pixels of 1mmx1mm fabricated with a standard CMOS technology for characterization in a test beam.

E. Vilella; O. Alonso; J. Trenado; A. Vil; M. Vos; L. Garrido; A. Diguez

2012-01-27

269

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

270

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

271

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

272

Geiger Mode APD performance in a cryogenic two-phase Ar avalanche detector based on THGEMs  

E-print Network

Characteristic properties of a Geiger Mode APD (G-APD) in a THGEM-based cryogenic two-phase Ar avalanche detector were studied in view of potential applications in rare-event experiments. G-APD signal amplitude and noise characteristics at cryogenic temperatures turned out to be superior to those at room temperature. The effective detection of avalanche scintillations from THGEM-multiplier holes in two-phase Ar has been demonstrated using G-APD with no wavelength shifter. At an avalanche gain of 60, the avalanche scintillation yield measured by the G-APD was as high as 1.4 photoelectrons per avalanche electron, over 4pi.

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

2010-01-01

273

1468 IEEE JOURNAL OF QUANTUM ELECTRONICS, VOL. 41, NO. 12, DECEMBER 2005 Theoretical Investigation of Quantum-Dot Avalanche  

E-print Network

of Quantum-Dot Avalanche Photodiodes for Mid-infrared Applications Sanjay Krishna, Student Member, IEEE, Oh-dot avalanche photodiode (QDAP), is proposed which is expected to have improved signal-to-noise ratio (SNR is coupled with a thin, low-noise GaAs avalanche layer through a tunnel barrier. The avalanche layer provides

Hayat, Majeed M.

274

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

275

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

276

Avalanche Photodiode for liquid xenon scintillation: quantum efficiency and gain  

Microsoft Academic Search

We report on measurements with a large area, silicon Avalanche Photodiode (APD) as photodetector for the ultraviolet scintillation light of liquid xenon (LXe) at temperatures between 167 and 188 K. The maximum gain of the APD for the scintillation light from a 210Po alpha-source in LXe was 5.3 103. Based on the geometry of the setup, the quantum efficiency

P. Shagin; R. Gomez; U. Oberlack; P. Cushman; B. Sherwood; M. McClish; R. Farrell

2009-01-01

277

Electron avalanche structure determined by random walk theory  

NASA Technical Reports Server (NTRS)

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

Englert, G. W.

1973-01-01

278

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

279

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

280

Effect of dead space on avalanche speed [APDs  

Microsoft Academic Search

The effects of dead space (the minimum distance travelled by a carrier before acquiring enough energy to impact ionize) on the current impulse response and bandwidth of an avalanche multiplication process are obtained from a numerical model that maintains a constant carrier velocity but allows for a random distribution of impact ionization path lengths. The results show that the main

J. S. Ng; C. H. Tan; B. K. Ng; P. J. Hambleton; J. P. R. David; G. J. Rees; A. H. You; D. S. Ong

2002-01-01

281

Design considerations for high performance avalanche photodiode multiplication layers  

Microsoft Academic Search

We have studied the effect of the thickness of the multiplication region on the noise performance characteristics of avalanche photodiodes (APD's). Our simulation results are based on a full band Monte Carlo model with anisotropic threshold energies for impact ionization. Simulation results suggest that the well known McIntyre expression for the excess noise factor is not directly applicable for devices

V. Chandramouli; Christine M. Maziar; Joe C. Campbell

1994-01-01

282

Photon counting modules using RCA silicon avalanche photodiodes  

Microsoft Academic Search

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

Alexander W. Lightstone; Andrew D. MacGregor; Darlene E. MacSween; Robert J. McIntyre; Claude Trottier; Paul P. Webb

1989-01-01

283

Higher efficiency active quenching circuit for avalanche photodiodes  

SciTech Connect

An improved circuit for actively quenching and recharging avalanche photodiodes (APDs) which allows them to be biased to at least 30V above breakdown is presented. Using this circuit it is possible to achieve the high single photon detection efficiency inherent in Geiger mode APDs while maintaining a modest deadtime. The circuit is described and observed characteristics of the system are shown.

Fenker, H.; Regan, T.; Thomas, J.; Wright, M.

1993-06-01

284

Gain-bandwidth characteristics of thin avalanche photodiodes  

Microsoft Academic Search

The frequency-response characteristics of avalanche photodiodes (APDs) with thin multiplication layers are investigated by means of a recurrence technique that incorporates the history dependence of ionization coefficients. In addition, to characterize the autocorrelation function of the impulse response, new recurrence equations are derived and solved using a parallel computer. The mean frequency response and the gain-bandwidth product are computed and

Majeed M. Hayat; Oh-Hyun Kwon; Yi Pan; Paul Sotirelis; Joe C. Campbell; Bahaa E. A. Saleh; Malvin Carl Teich

2002-01-01

285

Generalized excess noise factor for avalanche photodiodes of arbitrary structure  

Microsoft Academic Search

A generic model for a multilayer avalanche photodiode (APD) that admits arbitrary variation (with position) of the bandgap, dark generation rate, and ionization coefficients within each stage of the device is considered. Expressions for the mean multiplication and excess noise factors for dark carriers alone, injected carriers alone, and for an arbitrary superposition of dark and injected carriers are derived

N. Z. Hakim; B. E. A. Saleh; M. C. Teich

1990-01-01

286

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

287

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

288

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

289

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

290

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

291

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

292

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

293

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

294

Huge compact flux avalanches in superconducting Nb thin films  

NASA Astrophysics Data System (ADS)

Using a magneto-optical technique we perform a quantitative analysis of magnetic flux penetration in superconducting niobium thin films on A-plane (1 1 2bar 0) sapphire substrates as a function of temperature (1.5 K ? T ? Tc = 9.2 K). In these samples we observe huge compact avalanches (HCAs for brevity), very much like some snow-avalanches and unlike the rough dendritic flux penetration observed on R-plane (1 1bar 0 2) sapphire. The behavior observed is consistent with the occurrence of thermo-magnetic avalanches as proposed by Aranson et al. [Phys. Rev. Lett. 87 (2001) 067003]. For increasing temperature, we find: (1) an increased branching of the HCA. (2) An increased applied field necessary for the first HCA to occur. (3) A decrease in the number of HCAs, accompanied by more regular flux penetration (above 6.2 K avalanches are completely absent). (4) An increase of the total amount of flux as well as the area of the HCA.

Welling, M. S.; Westerwaal, R. J.; Lohstroh, W.; Wijngaarden, R. J.

2004-09-01

295

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 The result of a measurement x e.g. of the length of Dutch men or the weight of rice grains is usually-dimensional pile of rice with a 1 ? 1 m2 floor area. Using the more stringent criteria, we discovered [10

Wijngaarden, Rinke J.

296

Advances in gas avalanche radiation detectors for biomedical applications  

Microsoft Academic Search

Gas avalanche detectors are instruments of choice for radiation detection and localization in numerous fields of basic and applied research. Recent advances in detection techniques, involving multiplication and detection of single or a few charges deposited in gas media, or emitted from solid converters into gas, are described. The properties of radiation converters and associated advanced gas multipliers are discussed,

A. Breskin

2000-01-01

297

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

E-print Network

weight is constantly being added to the surface is not often a good idea. In general the windward side as the snow pack becomes lubricated. - Topography and slope angle of the avalanche starting zone, slopes between 28 and 45 are most dangerous, steeper slopes shed snow quickly and are unlikely to produce large

Moore, John

298

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

299

Homeostasis of neuronal avalanches during postnatal cortex development in vitro  

PubMed Central

Cortical networks in vivo and in vitro are spontaneously active in the absence of inputs, generating highly variable bursts of neuronal activity separated by up to seconds of quiescence. Previous measurements in adult rat cortex revealed an intriguing underlying organization of these dynamics, termed neuronal avalanches, which is indicative of a critical network state. Here we demonstrate that neuronal avalanches persist throughout development in cortical slice cultures from newborn rats. More specifically, we find that in spite of large variations of average rate in activity, spontaneous bursts occur with power-law distributed sizes (exponent -1.5) and a critical branching parameter close to 1. Our findings suggest that cortical networks homeostatically regulate a critical state during postnatal maturation. PMID:18082894

Stewart, Craig V.; Plenz, Dietmar

2009-01-01

300

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

301

Photon detection efficiency of Geiger-mode avalanche photodiodes  

E-print Network

The photon detection efficiencies of multi-pixel Geiger-mode avalanche photodiodes manufactured by different produ cers are estimated. A new fit method of the response spectra to low-intensity light, taking into ac count after-pulse and cross-talk effects is proposed to yield the initial number of photons. The value of photon detection efficiency is calculated using a calibrated photodetector as a reference.

Gentile, Simonetta; Meddi, Franco

2010-01-01

302

Pushing technologies: single-photon avalanche diode arrays  

Microsoft Academic Search

We present the development of silicon monolithic arrays of 60 photon-counters (SPADA, Single-Photon Avalanche Diode Array) for the visible. The SPADA system is suitable for state-of-the-art Adaptive Optics operations and Fast Transient image acquisitions, at quite a fraction of the current cost of imaging arrays. The fabricated solid-state photon counters are rugged, easy to be integrated in the optical system.

Franco Zappa; Simone Tisa; Sergio Cova; Piera Maccagnani; Domenico Bonaccini Calia; Giovanni Bonanno; Massimiliano Belluso; Roberto Saletti; Roberto Roncella

2004-01-01

303

Preliminary results on avalanche photodiodes for scintillating fiber readout  

NASA Astrophysics Data System (ADS)

We have measured the properties of two avalanche photodiodes for possible use in conjunction with scintillating fibers as charged particle detectors. The quantities measured so far are the gain of the APD's, the amplitude distribution of pulses from particles through the fibers, and the efficiency of detecting these particles. The preliminary results obtained indicate the importance of the choice of associated electronics and good optical coupling. The results obtained so far have been measured at room temperature and near liquid nitrogen temperatures.

Salomon, M.; Kitching, J.

1991-07-01

304

Recent developments in avalanche photodiodes for scintillating fiber applications  

NASA Astrophysics Data System (ADS)

Research is ongoing to tailor proportional mode avalanche photodiodes (APDs) for use in nuclear radiation environments and for scintillating fiber readout. We report progress on APD design modifications directed toward minimizing signals from ionizing particle interactions and also toward producing APD arrays for scintillating fiber readout. In addition, we present results for very high gain APDs fabricated using a new planar process which shows great promise for lower production costs of both APD arrays and discrete devices.

Farrell, Richard; Vanderpuye, Kofi; Vasile, Stefan; Gordon, Jeffrey S.; Gothoskar, Prakash

1998-11-01

305

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

306

Measurement of proton radiation damage to Si avalanche photodiodes  

Microsoft Academic Search

The effects of proton radiation damage on EG&G C30902S Si avalanche photodiodes (APD's) were measured. The APD bulk leakage current increased at 0.29 fA\\/rad, or about 1800 dark photoelectrons per rad(Si) at -10C under 16.2 MeV protons. There was little change in the breakdown voltage with the radiation doses up to 30 krad(Si). The increase in the total dark currents

Xiaoli Sun; Daniel Reusser; Henri Dautet; James B. Abshire

1997-01-01

307

Characterization of cooled large-area silicon avalanche photodiodes  

Microsoft Academic Search

We characterize the operation of large-area high-gain silicon avalanche photodiodes (APDs) at near liquid-nitrogen temperatures. The APDs that we studied have active areas of 64 mm2 and have gains of up to 20 000 at 85 K. We characterized the devices for both the usual, analog mode of operation and for doing single-photon pulse counting. The experimental results were found

Jeffrey J. Fox; Nathan Woodard; Gregory P. Lafyatis

1999-01-01

308

Single photon counting linear mode avalanche photodiode technologies  

Microsoft Academic Search

The false count rate of a single-photon-sensitive photoreceiver consisting of a high-gain, low-excess-noise linear-mode InGaAs avalanche photodiode (APD) and a high-bandwidth transimpedance amplifier (TIA) is fit to a statistical model. The peak height distribution of the APD's multiplied dark current is approximated by the weighted sum of McIntyre distributions, each characterizing dark current generated at a different location within the

George M. Williams; Andrew S. Huntington

2011-01-01

309

TCAD simulation of avalanche breakdown voltage in GM-APDs  

Microsoft Academic Search

In this paper, the breakdown voltage (VBD) temperature behavior in Geiger-Mode avalanche photodiodes (GM-APDs) is investigated by means of both experimental characterization of silicon photomultiplier (SiPMs) fabricated at FBK-IRST and one-dimensional TCAD simulations of GM-APDs. The analysis aims at relating both the VBD and its temperature coefficient to relevant technological device parameters, such as epitaxial layer thickness and doping concentration,

Nicola Serra; Gabriele Giacomini; Mirko Melchiorri; Alessandro Piazza; Claudio Piemonte; Alessandro Tarolli; Nicola Zorzi

2010-01-01

310

Geiger-mode Avalanche Photodiodes for High Time Resolution Astrophysics  

Microsoft Academic Search

Geiger-mode Avalanche Photodiodes (GM-APDs) are establishing themselves as potential candidates for the broad temporal range\\u000a covered in high time resolution astrophysics (HTRA). These detectors have already been employed in astronomical instrumentation\\u000a and significant results have been obtained to date. Their high time resolution and quantum efficiency make these single photon\\u000a event counting detectors ideal for observations of stochastic phenomena, and

Don Phelan; Alan P. Morrison

2008-01-01

311

Performance of thin separate absorption, charge, and multiplication avalanche photodiodes  

Microsoft Academic Search

Previously, it has been demonstrated that resonant-cavity-enhanced separate-absorption-and-multiplication (SAM) avalanche photodiodes (APDs) can achieve high bandwidths and high gain-bandwidth products while maintaining good quantum efficiency. In this paper, we describe a GaAs-based resonant-cavity-enhanced SAM APD that utilizes a thin charge layer for improved control of the electric field profile. These devices have shown RC-limited bandwidths above 30 GHz at low

K. A. Anselm; H. Nie; C. Hu; C. Lenox; P. Yuan; G. Kinsey; J. C. Campbell; B. G. Streetman

1998-01-01

312

Vortex avalanches and the onset of superfluid turbulence  

Microsoft Academic Search

Quantized circulation, absence of Galilean invariance due to a clamped normal\\u000acomponent, and the vortex mutual friction are the major factors that make\\u000asuperfluid turbulence behave in a way different from that in classical fluids.\\u000aThe model is developed for the onset of superfluid turbulence that describes\\u000athe initial avalanche-like multiplication of vortices into a turbulent vortex\\u000atangle.

N. B. Kopnin; L. D. Landau

2003-01-01

313

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

314

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

315

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

316

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

317

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

318

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

319

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

320

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

321

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

322

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

323

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

NASA Astrophysics Data System (ADS)

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

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

2012-09-01

324

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

325

Avalanches neuronais durante o ciclo sono-viglia de ratos.  

E-print Network

??Neuronal avalanches are spatiotemporal patterns of neuronal activity that occur spontaneously in supercial layers of the mammalian cortex under various experimental conditions. Previous studies in (more)

Tiago Lins Ribeiro

2009-01-01

326

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

327

Development in the design and performance of gas avalanche microdetectors  

NASA Astrophysics Data System (ADS)

There has been continuing development of generic classes of microstrip gas chambers (MSGCs), microgap gas chambers (MGCs) and microdot gas chambers (MDOTs) at Lawrence Berkeley National Laboratory (LBNL) over the past few years, to improve such detectors beyond their present capabilities, to produce detectors suitable for use in current or upcoming experiments, and to allow a basis for new R&D developments which may incorporate these detectors as part of the system. All of these new detectors are collectively referred to as 'gas avalanche microdetectors'. The MSGC, which was motivated by the pioneering work of A. Oed, has many attractive features, especially excellent spatial resolution (~30 ?m rms at normal incidence) and high rate capability (~106 mm -2/cdot s-1). Moreover, the MGC seems to have certain advantages over the MSGC in speed, stability and simplicity, and the MDOT has larger gain (>104) and the intrinsic advantages of two- dimensional readout. Because of these attractive properties, they have received a great deal of attention for nuclear and high energy physics experiments, medical X-ray imaging and many other fields requiring radiation detection and measurement. However, the gas avalanche microdetectors have not yet reached the state-of-the-art in which reliable detectors can be designed and built for the demanding experiments. Therefore, the main concern of this dissertation is to investigate the operating characteristics and design criteria of the gas avalanche microdetectors for a stable and safe operation, focusing on their possible problems. Other interests include the use of a thin (~200 ?m) columnar cesium iodide (CsI) layer coupled to gas avalanche microdetectors, to improve the space and time resolutions, and the detection efficiency by eliminating the sensitivity to the angle of incident particle. This idea also provides the additional advantage that it may be possible to reduce the gain (and operating voltage) of these gas microdetectors, thus reducing the risk of sparking. All of these are important for significant improvement of the operation of the gas avalanche microdetectors.

Cho, Hyo-Sung

1997-12-01

328

Large debris avalanches and associated eruptions in the Holocene eruptive history of Shiveluch Volcano, Kamchatka, Russia  

NASA Astrophysics Data System (ADS)

Shiveluch Volcano, located in the Central Kamchatka Depression, has experienced multiple flank failures during its lifetime, most recently in 1964. The overlapping deposits of at least 13 large Holocene debris avalanches cover an area of approximately 200km2 of the southern sector of the volcano. Deposits of two debris avalanches associated with flank extrusive domes are, in addition, located on its western slope. The maximum travel distance of individual Holocene avalanches exceeds 20km, and their volumes reach 3km3. The deposits of most avalanches typically have a hummocky surface, are poorly sorted and graded, and contain angular heterogeneous rock fragments of various sizes surrounded by coarse to fine matrix. The deposits differ in color, indicating different sources on the edifice. Tephrochronological and radiocarbon dating of the avalanches shows that the first large Holocene avalanches were emplaced approximately 4530-4350 BC. From 2490 BC at least 13 avalanches occurred after intervals of 30-900 years. Six large avalanches were emplaced between 120 and 970 AD, with recurrence intervals of 30-340years. All the debris avalanches were followed by eruptions that produced various types of pyroclastic deposits. Features of some surge deposits suggest that they might have originated as a result of directed blasts triggered by rockslides. Most avalanche deposits are composed of fresh andesitic rocks of extrusive domes, so the avalanches might have resulted from the high magma supply rate and the repetitive formation of the domes. No trace of the 1854 summit failure mentioned in historical records has been found beyond 8km from the crater; perhaps witnesses exaggerated or misinterpreted the events.

Ponomareva, Vera V.; Pevzner, Maria M.; Melekestsev, Ivan V.

329

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

330

Estimating bulk rheological properties of flowing snow avalanches from field data  

Microsoft Academic Search

Knowing the path profile and the avalanche velocity variations with downstream distance makes it possible to deduce the bulk frictional force experienced by an avalanche during its course. This derivation was applied to 15 documented events reported in the literature. Three types of rheological behavior were identified: (1) the inertial regime, where the frictional force drops to zero; (2) the

C. Ancey; M. Meunier

2004-01-01

331

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

332

Possible changes for mudflow and avalanche activity in former Soviet Union due to the global warming  

SciTech Connect

Past research, as well as laboratory evidence have revealed a relationship between climate, mudflow, and avalanche activity. It is possible to predict changes in mudflow and avalanche activity by using climate models. In this study, the GFDL model was used which contained data on mean monthly air temperature, precipitation, and carbon dioxide concentrations.

Glazovskaya, T.G.; Sidorova, T.L.; Seliverstov, Y.G. [Moscow State Univ. (Russian Federation). Research Lab. of Snow Avalanches and Mudflows

1996-12-31

333

A comparison of powder-snow avalanches at Valle de la Sionne, Switzerland, with plume theories  

Microsoft Academic Search

Powder-snow avalanches are natural hazards which affect the way populations live in mountainous areas. Field measurements from avalanches remain one of the most significant and useful sources of information about their dynamics and behaviour. In this paper, we consider all the video data from the Swiss Valle de la Sionne test site from the years 2003-05. General scaling laws are

B. Turnbull; J. N. McElwaine

2007-01-01

334

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

E-print Network

, Banff, AB, Canada ABSTRACT: Climate change is evident and long-term changes of the climate system have we analyzed long-term weather data as well as snow and avalanche data from Glacier National Park to the fact that avalanche cycles are caused by short-term weather systems (days) rather than long-term

Jamieson, Bruce

335

Counting distributions and error probabilities for optical receivers incorporating superlattice avalanche photodiodes  

Microsoft Academic Search

Exact gain distributions and electron counting distribu- tions are presented for superlattice avalanche photodiodes that operate by single-carrier transport perpendicular to the superlattice planes. The characteristic shapes of these distributions are compared with those of the single-carrier conventional avalanche photodiode and the pho- tomultiplier tube. The electron counting distributions, which assume Poisson photocarrier injection, are used to calculate the error

M. C. Teich; B. E. A. Saleh

1986-01-01

336

Frequency response and bandwidth enhancement in Ge/Si avalanche photodiodes  

E-print Network

photodiodes (APDs) References and links 1. R. B. Emmons, "Avalanche photodiode frequency response," J. Appl. Phys. 38(9), 3705­3714 (1967). 2. R. J. McIntyre, "The distribution of gains in uniformly multiplying avalanche photodetectors (APDs), which use internal gain to reduce the noise of the first stage electrical

Bowers, John

337

Avalanche photodiodes operating parameter optimization for the Frascati Tokamak Upgrade Thomson scattering system (abstract)  

Microsoft Academic Search

Measured figures (linearity, avalanche gain, frequency response, and noise) of the avalanche photodiodes (APD) detectors used on the FTU Thomson scattering system (FTU-TS) are reported. This investigation on the APD figures is motivated by the necessity of knowing their values over a wide range of input signals, and also of checking the validity of McIntyre model of APD noise, since

F. Orsitto; A. Brusadin; E. Giovannozzi

1997-01-01

338

A new approach for computing the bandwidth statistics of avalanche photodiodes  

Microsoft Academic Search

A new approach for characterizing the avalanche-buildup-time-limited bandwidth of avalanche photodiodes (APD's) is introduced which relies on the direct knowledge of the statistics of the random response time. The random response time is the actual duration of the APD's finite buildup limited random impulse response function. A theory is developed characterizing the probability distribution function (PDF) of the random response

Majeed M. Hayat; Guoquan Dong

2000-01-01

339

SNR characteristics of 850-nm OEIC receiver with a silicon avalanche photodetector  

E-print Network

receiver is composed of a Si avalanche photodetector (APD) and BiCMOS analog circuits including with 50- loads. We measure APD SNR characteristics dependence on the reverse bias voltage as well as Bi of America OCIS codes: (250.1345) Avalanche photodiodes (APDs); (250.3140) Integrated optoelectronic circuits

Choi, Woo-Young

340

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

E-print Network

for a thin (100nm) GaAs APD. References 1] R. J. McIntyre, \\Multiplication noise in uniform avalanche@bu.edu teich@bu.edu SUMMARY Recent experimental measurements from InP and InAlAs avalanche photodiodes (APDs by the conventional McIntyre theory 1]. The observed dependence of the noise on the multiplication- region width

Hayat, Majeed M.

341

Avalanche photodiodes operating parameter optimization for the Frascati Tokamak Upgrade Thomson scattering system  

Microsoft Academic Search

Measured figures (linearity, avalanche gain, frequency response, and noise) of the avalanche photodiodes (APD) detectors used on the FTU Thomson scattering system (FTU-TS) are reported. This investigation on the APD figures is motivated by the necessity of knowing their values over a wide range of input signals, and also of checking the validity of McIntyre model of APD noise, since

F. Orsitto; A. Brusadin; E. Giovannozzi

1997-01-01

342

Avalanche noise characteristics of thin GaAs structures with distributed carrier generation [APDs  

Microsoft Academic Search

It is known that both pure electron and pure hole injection into thin GaAs multiplication regions gives rise to avalanche multiplication with noise lower than predicted by the local noise model. In this paper, it is shown that the noise from multiplication initiated by carriers generated throughout a 0.1 ?m avalanche region is also lower than predicted by the local

Kim F. Li; Duu S. Ong; John P. R. David; Richard C. Tozer; Graham J. Rees; Stephen A. Plimmer; Keng Y. Chang; John S. Roberts

2000-01-01

343

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

344

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

345

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

346

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

347

Climate Influences on Large-Magnitude Natural Snow Avalanches in John F. Stevens Canyon, Montana  

NASA Astrophysics Data System (ADS)

Snow avalanches are usually characterized as natural hazards. Most literature describes mitigation measures or snow properties and weather processes that contribute to avalanche initiation, with recent research focusing on the spatial variability of snow properties. Some analyses have linked extreme avalanche events (those marked by widespread, large-magnitude, destructive avalanches) with synoptic weather patterns. This study examines the temporal variability of large magnitude natural avalanches in John F. Stevens Canyon in Montana using a long-term (96 winters) historic record and dendrochronology. Results show that shifts in multi-decadal climate patterns such as the Pacific Decadal Oscillation change the frequency and severity of large-magnitude natural avalanches. From their immediate impacts, which include downed trees and dammed streams, such events appear destructive. Cumulatively, however, these events create ecotones and structural diversity in montane forests and dampen reforestation after wildfires. Large magnitude natural avalanches are thus recurring, climate-influenced disturbances that have significant, long-lasting, landscape-level effects. However, potential changes in multi-decadal climate patterns and projected changes in snowpack may lead to changes in natural avalanche frequency and severity, and thus long-term, landscape scale changes in montane forests in the northern Rocky Mountains.

Reardon, B. A.; Fagre, D. B.; Pederson, G. T.; Caruso, C. J.

2005-12-01

348

Journal of Magnetism and Magnetic Materials 320 (2008) 695698 Spatial determination of magnetic avalanche ignition points  

E-print Network

avalanche ignition points Reem Jaafara , S. McHugha , Yoko Suzukia , M.P. Sarachika,?, Y. Myasoedovb , E to locate the approximate ignition point of each avalanche in a two-dimensional cross-section of the crystal studies, there are crystals in which ignition points are distributed throughout an entire weak region near

Zeldov, Eli

349

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

350

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

351

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

352

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

353

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

354

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

355

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

356

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.

357

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.

358

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

359

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.

360

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

361

IEEE ELECTRON DEVICE LETTERS, VOL. 29, NO. 10, OCTOBER 2008 1115 Equivalent Circuit Model for Si Avalanche  

E-print Network

Avalanche Photodetectors Fabricated in Standard CMOS Process Myung-Jae Lee, Student Member, IEEE, Hyo model for CMOS- compatible avalanche photodetectors. The equivalent circuit model includes an inductive component for avalanche delay, a cur- rent source for photogenerated carriers, and several components

Choi, Woo-Young

362

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.

363

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.

364

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

365

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.

366

Morphometric and meteorological controls on recent snow avalanche distribution and activity at hillslopes in steep mountain valleys in western Norway  

NASA Astrophysics Data System (ADS)

Snow avalanches are common phenomena in Norway. Controlling factors of snow avalanche distribution and activity, and the relative importance of snow avalanches regarding contemporary sedimentary mass transfers were explored within two steep, parabolic-shaped and glacier-connected tributary valleys (Erdalen and Bdalen) in western Norway. Mapping of distribution, extent and the entire path lengths of snow avalanches was combined with spatial data analysis (GIS and DEM computing) of morphometric controls. The timing and frequency of snow avalanches were explored by correlating meteorological data with high-resolution monitoring data of snow avalanche events. Sediment masses annually transferred by snow avalanches along hillslopes and from hillslopes into stream channels were estimated. A high inter-annual variability of avalanche activity and a wide spectrum of avalanche sizes and types ranging from small to extreme-sized events were found for the four-year investigation period 2009-2012. Spatial distribution of snow avalanches is governed by the topographical factors valley orientation, slope aspect, relative slope height and rockwall morphometry whereas timing and frequency of snow avalanches are controlled by snowfall intensity, periods with strong winds combined with a prevalent wind direction or sharp air temperature changes within short time periods. Snow avalanches represent one of the dominant denudational processes and have a high relative importance regarding sedimentary mass transfers within the two mountain valleys Erdalen and Bdalen in western Norway.

Laute, Katja; Beylich, Achim A.

2014-08-01

367

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

368

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

369

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

370

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

371

Barkhausen avalanches in anisotropic ferromagnets with 180 degrees domain walls  

PubMed

We show that Barkhausen noise in two-dimensional disordered ferromagnets with extended domain walls is characterized by the avalanche size exponent tau(s)=1.54 at low disorder. With increasing disorder the characteristic domain size is reduced relative to the system size due to nucleation of new domains and a dynamic phase transition occurs to the scaling behavior with tau(s)=1.30. The exponents decrease at finite driving rate. The results agree with recently observed behavior in amorphous Metglas and Fe-Co-B ribbons when the applied anisotropic stress is varied. PMID:11088264

Tadic; Nowak

2000-04-01

372

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

373

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

2006-04-18

374

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

375

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

376

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

377

The 2002 rock\\/ice avalanche at Kolka\\/Karmadon, Russian Caucasus: assessment of extraordinary avalanche formation and mobility, and application of QuickBird satellite imagery  

Microsoft Academic Search

A massive rock\\/ice avalanche of about 100x106m3 volume took place on the northern slope of the Kazbek massif, North Ossetia, Russian Caucasus, on 20 September 2002. The avalanche started as a slope failure, that almost completely entrained Kolka glacier, traveled down the Genaldon valley for 20km, was stopped at the entrance of the Karmadon gorge, and was finally succeeded by

C. Huggel; S. Zgraggen-Oswald; W. Haeberli; A. Kb; A. Polkvoj; I. Galushkin; S. G. Evans

2005-01-01

378

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

379

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

380

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

381

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

382

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

383

First-principles derivation of static avalanche-size distributions  

NASA Astrophysics Data System (ADS)

We study the energy minimization problem for an elastic interface in a random potential plus a quadratic well. As the position of the well is varied, the ground state undergoes jumps, called shocks or static avalanches. We introduce an efficient and systematic method to compute the statistics of avalanche sizes and manifold displacements. The tree-level calculation, i.e., mean-field limit, is obtained by solving a saddle-point equation. Graphically, it can be interpreted as the sum of all tree graphs. The 1-loop corrections are computed using results from the functional renormalization group. At the upper critical dimension the shock statistics is described by the Brownian force model (BFM), the static version of the so-called Alessandro-Beatrice-Bertotti-Montorsi (ABBM) model in the nonequilibrium context of depinning. This model can itself be treated exactly in any dimension and its shock statistics is that of a Lvy process. Contact is made with classical results in probability theory on the Burgers equation with Brownian initial conditions. In particular we obtain a functional extension of an evolution equation introduced by Carraro and Duchon, which recursively constructs the tree diagrams in the field theory.

Le Doussal, Pierre; Wiese, Kay Jrg

2012-06-01

384

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

385

Silicon Avalanche Pixel Sensor for High Precision Tracking  

E-print Network

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 a large 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 ...

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

2013-01-01

386

Cryogenic CMOS avalanche diodes for nuclear physics research  

NASA Astrophysics Data System (ADS)

Exploration in nuclear physics may require extreme conditions, such as temperatures down to a few Kelvin, high magnetic fields of several Tesla, or the small physical dimensions of a few centimeters. As a standard technique for radiation detection using scintillation materials, it is desirable to develop photodetectors that can operate under these harsh conditions. Though photomultiplier tubes (PMTs) have been used for most applications for readout of scintillation materials, they are bulky, highly susceptible to magnetic fields, and present a large heat load in cryogenic environments. Avalanche photodiodes are a reasonable alternative to PMTs in that they are extremely compact and less susceptible to magnetic fields. Avalanche photodiodes have been developed in a commercial CMOS process for operation at temperatures below 100 Kelvin. Here we present the overall operation of the photodiodes at 5 Kelvin. The diodes show a quantum efficiency of at least 30% at 532 nm at 5 Kelvin. At about 30 Kelvin, the diodes exhibit an internal resistive term, which generates a second breakdown point. The prototype diode shows a proportional response to the intensity of light pulses down to 150 detected photons with a hole to electron ionization ratio, k, of 2.3x10-13 at 5 Kelvin. The properties of the photodiodes and the readout electronics will be discussed for general photon detection below 100 K.

Chen, Xiao Jie; Johnson, Erik B.; Stapels, Christopher J.; Whitney, Chad; Chapman, Eric; Alberghini, Guy; Augustine, Frank; Miskimen, Rory; Christian, James F.

2011-09-01

387

Tuned critical avalanche scaling in bulk metallic glasses.  

PubMed

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

388

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

389

How much of the real avalanche activity can be captured with tree rings? An evaluation of classic dendrogeomorphic approaches and comparison with  

E-print Network

How much of the real avalanche activity can be captured with tree rings? An evaluation of classic Historical archives Snow avalanches Spatio-temporal analysis French Alps In snow-rich areas, snow avalanches endanger settlements and cause heavy damage to infrastructure or transportation routes. In wooded avalanche

Stoffel, Markus

390

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

391

ccsd-00003464,version1-3Dec2004 X-ray observation of micro-failures in granular piles approaching an avalanche  

E-print Network

an avalanche Alexandre Kabla1 , Georges Debr´egeas2 , Jean-Marc di Meglio1,3 , and Tim J. Senden1 1 Department the avalanche angle, we observe intermittent plastic events associated with collective rearrangements as the system approaches the avalanche threshold. By testing various preparation methods, we show that the pre-avalanche

Paris-Sud XI, Université de

392

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

393

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

394

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

395

Is extracorporeal rewarming indicated in avalanche victims with unwitnessed hypothermic cardiorespiratory arrest?  

PubMed

Abstract Mair, Peter, Hermann Brugger, Birgit Mair, Luca Moroder, and Elfriede Ruttmann. Is extracorporeal rewarming indicated in avalanche victims with unwitnessed hypothermic cardiorespiratory arrest? High Alt Med Biol 15:500-503, 2014.-International guidelines recommend using extracorporeal rewarming in all hypothermic avalanche victims with prolonged cardiac arrest if they have patent airways and a plasma potassium level ?12?mmol/L. The aim of this study was to evaluate outcome data to determine if available experience with extracorporeal rewarming of avalanche victims supports this recommendation. At Innsbruck Medical University Hospital, 28 patients with hypothermic cardiac arrest following an avalanche accident were resuscitated using extracorporeal circulation. Of these patients, 25 were extricated from the snow masses with no vital signs and did not survive to hospital discharge. Three patients had witnessed cardiac arrest after extrication and a core temperature of 21.7C, 22C, and 24.0C, two of whom survived long-term with full neurological recovery. A search of the literature revealed only one asystolic avalanche victim with unwitnessed hypothermic cardiac arrest (core temperature 19C) surviving long-term. All other avalanche victims in the medical literature surviving prolonged hypothermic cardiac arrest suffered witnessed arrest after extrication with a core temperature below 24C. Our results suggest that prognosis of hypothermic avalanche victims with unwitnessed asystolic cardiac arrest and a core temperature >24C is extremely poor. Available outcome data do not support the use of extracorporeal rewarming in these patients. PMID:25531463

Mair, Peter; Brugger, Hermann; Mair, Birgit; Moroder, Luca; Ruttmann, Elfriede

2014-12-01

396

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

397

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

PubMed Central

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 metalsemiconductor interface. Results show a semi-Gaussian field distribution inside each well using the field-shaping electrodes, and the electric field at the metalsemiconductor 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. PMID:23298070

Goldan, A. H.; Zhao, W.

2013-01-01

398

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

399

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

400

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

401

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

402

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

403

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

404

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

405

XeCl Avalanche discharge laser employing Ar as a diluent  

DOEpatents

A XeCl avalanche discharge exciplex laser which uses a gaseous lasing starting mixture of: (0.2%-0.4% chlorine donor/2.5%-10% Xe/97.3%-89.6% Ar). The chlorine donor normally comprises HCl but can also comprise CCl.sub.4 BCl.sub.3. Use of Ar as a diluent gas reduces operating pressures over other rare gas halide lasers to near atmospheric pressure, increases output lasing power of the XeCl avalanche discharge laser by 30% to exceed KrF avalanche discharge lasing outputs, and is less expensive to operate.

Sze, Robert C. (Santa Fe, NM)

1981-01-01

406

Avalanche Photodiode for liquid xenon scintillation: quantum efficiency and gain  

NASA Astrophysics Data System (ADS)

We report on measurements with a large area, silicon Avalanche Photodiode (APD) as photodetector for the ultraviolet scintillation light of liquid xenon (LXe) at temperatures between 167 and 188 K. The maximum gain of the APD for the scintillation light from a 210Po ?-source in LXe was 5.3 103. Based on the geometry of the setup, the quantum efficiency of the APD was measured at 34% 5% at the mean scintillation wavelength of 178 nm. The high quantum efficiency and high gain of the APD make it an attractive alternative UV photon sensor to PMTs for LXe detectors, especially for experiments requiring high light yields, such as dark matter searches for Weakly Interacting Massive Particles, or a Compton telescope in MeV ?-ray astronomy.

Shagin, P.; Gomez, R.; Oberlack, U.; Cushman, P.; Sherwood, B.; McClish, M.; Farrell, R.

2009-01-01

407

Comprehensive analysis of new near-infrared avalanche photodiode structure  

NASA Astrophysics Data System (ADS)

The essential steps in simulations of modern separate absorption, grading, charge, and multiplication avalanche photodiode and their results are discussed. All simulations were performed using two commercial technology computer-aided design type software packages, namely Silvaco ATLAS and Crosslight APSYS. Comparison between those two frameworks was made and differences between them were pointed out. Several examples of the influence of changes made in individual layers on overall device characteristics have been shown. Proper selection of models and their parameters as well as its significance on results has been illustrated. Additionally, default values of material parameters were revised and adequate values from the literature were entered. Simulated characteristics of optimized structure were compared with ones obtained from measurements of real devices (e.g., current-voltage curves). Finally, properties of crucial layers in the structure were discussed.

Czuba, Krzysztof; Jurenczyk, Jaroslaw; Kaniewski, Janusz

2014-01-01

408

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

409

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

410

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

411

Studies of avalanche photodiodes for scintillating fibre tracking readout  

SciTech Connect

Avalanche Photodiodes (APDs) operating in ``Geiger Mode`` have been studied in a fibre tracking readout environment. A fast recharge circuit has been developed for high rate data taking, and results obtained from a model fibre tracker in the test beam at Brookhaven National Laboratory are presented. A high rate calibrated light source has been developed using a commercially available laser diode and has been used to measure the efficiency of the devices. The transmission of the light from a 1mm fibre onto a 0.5mm diameter APD surface has been identified as the main problem in the use of these particular devices for scintillating fibre tracking in the Superconducting Supercollider environment. Solutions to this problem are proposed.

Fenker, H; Thomas, J

1993-01-01

412

Simulation of Ion loss during TAE avalanches in NSTX  

NASA Astrophysics Data System (ADS)

Non-linear interactions of multiple Toroidal Alfv'en Eigenmodes (TAE) can result in explosive mode growth and enhanced losses of fast ions in a repetitive cycle of TAE bursts called avalanches. Fast ion losses have been documented with NPA diagnostics and fast neutron measurements during strongly bursting TAE on NSTX. The mode structure and mode amplitudes are measured with arrays of reflectometers and Mirnov coils. These experimental data are used to identify and scale the amplitude and frequency evolution of Toroidal Alfv'en Eigenmodes simulated with the NOVA code. These scaled eigenmodes are then used in the ORBIT code to simulate the fast ion redistribution during a strong, 1ms, TAE burst. Fast ion redistribution is seen for the energies > 30 keV, consistent with experimental observations. The simulated level of fast ion losses are in good agreement with the observed losses.

Fredrickson, E. D.; Darrow, D.; Kramer, G.; Gorelenkov, N. N.; Medley, S. S.; Leblanc, B.; Bell, R. E.; White, R. B.; Podesta, M.; Crocker, N. A.; Kubota, S.; Levinton, F. M.; Yuh, H.

2009-11-01

413

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

414

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

415

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

416

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

417

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

418

Avalanches in the Plastic Deformation of Crystalline Solids  

NASA Astrophysics Data System (ADS)

Plastic avalanches and highly fluctuating stress strain relations have been reported for crystalline materials as diverse as ice or several conventional metals and alloys. The most recent theoretical interpretation of these experimental findings is based upon collective dislocation dynamics and non-equilibrium critical phenomena. Dislocation assemblies in crystalline substrates represent a new example of the broad class of systems that exhibit avalanches and a jamming (or yielding) transition. Rheology experiments carried out on this broad class of systems ranging from granular media to foams show that their dynamics becomes increasingly heterogeneous when approaching the jamming threshold. Likewise, experiments on crystal plasticity at various scales have recently emphasized the heterogeneous character of plastic flow. Here we explore further the analogy between dislocation ensembles and other jamming systems by analyzing the behavior of dynamic response functions, such as the four point dynamic susceptibility, as well as the shear stress distributions in both jammed and moving dislocation arrangements. Our results show the existence of a diverging dynamic correlation length as the jamming threshold is approached. At microscopic scales, where only a limited number of dislocations mediate the deformation process and no dislocation storage phenomena are observed, heterogeneous behavior in the mechanical properties is even more dramatic and technologically relevant. Bursts of plastic activity in microscopic colloidal crystals under compression are broadly distributed, both in strain/stress-controlled tests, but scaling exponents are anomalous, and thus the interpretation of these findings within the framework of collective dislocation phenomena and the yielding transition is no longer appropriate. Moreover, non-trivial size effects on the mechanical properties of micrometer-to nanometer scale crystals can be explained in terms of the interactions of dislocations with the boundaries of the sample.

Miguel, M. Carmen

2010-03-01

419

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

E-print Network

tracks · Bruins Pass = popular backcountry skiing area · Balu Pass Trail is classified as an area · Aim was to create an avalanche reconstruction using dendrochronoligcal techniques · Sub Alpine Fir

Smith, Dan

420

Hybridization process for back-illuminated silicon Geiger-mode avalanche photodiode arrays  

E-print Network

We present a unique hybridization process that permits high-performance back-illuminated silicon Geiger-mode avalanche photodiodes (GM-APDs) to be bonded to custom CMOS readout integrated circuits (ROICs) - a hybridization ...

Schuette, Daniel R.

421

Statistics of electron avalanches and bursts in low pressure gases below the breakdown voltage  

SciTech Connect

Avalanches in different types of dynamical systems have been subject of recent interest. Avalanches building up in gases play an important role in radiation detectors and in the breakdown process of gas discharges. We have used computer simulation to study statistical properties of electron avalanches and bursts (sequences of avalanches) in a gas subjected to a homogeneous electric field. Helium was used as buffer gas, but we believe that our results are more general. The bursts were initiated by injecting low energy electrons into the gas. We applied Monte Carlo procedure to trace the trajectories of electrons. The elementary processes considered in the model were anisotropic elastic scattering of electrons from He atoms, electron impact excitation and ionization of He atoms. The electrons were traced until the are reached the perfectly absorbing anode.

Donko, Z. [Research Inst. for Solid State Physics of the Hungarian Academy of Sciences, Budapest (Hungary)

1995-12-31

422

Statistics of avalanches in the self-organized criticality state of a Josephson junction  

SciTech Connect

Magnetic flux avalanches in Josephson junctions that include superconductor-insulator-superconductor (SIS) tunnel junctions and are magnetized at temperatures lower than approximately 5 K have been studied in detail. Avalanches are of stochastic character and appear when the magnetic field penetration depth {lambda} into a junction becomes equal to the length a of the Josephson junction with a decrease in the temperature. The statistical properties of such avalanches are presented. The size distribution of the avalanches is a power law with a negative noninteger exponent about unity, indicating the self-organized criticality state. The self-organized criticality state is not observed in Josephson junctions with a superconductor-normal metal-superconductor (SNS) junction.

Matizen, E. V.; Martynets, V. G., E-mail: mart@niic.nsc.ru; Bezverkhii, P. P. [Russian Academy of Sciences, Nikolaev Institute of Inorganic Chemistry, Siberian Division (Russian Federation)

2010-08-15

423

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

E-print Network

We probe the dynamics of intermittent avalanches caused by steady addition of grains to a quasi-two dimensional heap. To characterize the time-dependent average avalanche flow speed v(t), we image the top free surface. To characterize the grain fluctuation speed dv(t), we use Speckle-Visibility Spectroscopy. During an avalanche, we find that the fluctuation speed is approximately one-tenth the average flow speed, and that these speeds are largest near the beginning of an event. We also find that the distribution of event durations is peaked, and that event sizes are correlated with the time interval since the end of the previous event. At high rates of grain addition, where successive avalanches merge into smooth continuous flow, the relationship between average and fluctuation speeds changes to dv Sqrt[v].

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

2007-08-08

424

Syn and post- emplacement transformations of the Misti (Peru) volcanic debris avalanches into lahars  

NASA Astrophysics Data System (ADS)

We identify stratigraphic, sedimentological and structural variations in lithofacies of debris-avalanche deposits from El Misti volcano in the Quebrada San Lazaro and Ro Chili Valley, near the city of Arequipa (south Peru), to determine lithofacies transformations. We describe the internal process associated to the external conditions acting on debris-avalanche deposits in order to assess stages of transformations from the proximal to distal debris-avalanche deposits and the associated epiclastic deposits. Syn-emplacement transformations inside the volcanic debris-avalanche deposits in the upper course of the Rio Chili Valley: within a few meters, the proximal block facies of the sheared debris-avalanche deposit is transformed at the contact of the ash-rich alluvial deposits in thick units comprising a strongly sheared base of the deposit, then stratified matrix dominated beds with normally sorted boulders aligned with the beds. This is interpreted as the effect of strong shearing inside the confined and proximal debris avalanche during motion, which generated a localised stretching near the base of the deposit and the bulking of the thin water saturated basal layers: the bearing capacity of the matrix debris- avalanche is modified, the block facies has been transformed in a stratified matrix facies. The transformations by bulking along a strong sheared contact contribute to reduce the run-out distance of the debris avalanches in the Ro Chili valley. Post-deposition evolutions of the debris-avalanche deposits in the Quebrada San Lazaro: in the upper course of the valley, the landslides in the debris- avalanche deposits related to water circulation destabilise the covering scree and volcanic colluvium dipping at 70. The fragmentation and sorting due to gravity and water are the external processes which separate matrix and block elements; This is the first stage of transformation. The remobilisation of these separated fractions into lahars transforms this landslide-colluvium mix. Down valley, the debris-avalanche deposits have been incised and reworked by stream flow, rather than landslides. This causes differential erosion of the block and the matrix facies creating fine (block-derived) and course matrix-derived units, and generally fines dominated lahars. The transformations shown here are either produced in-flow, or long after deposition, leading to different lahar facies. We not that Arequipa lahars material are probably sourced from quite near the city, and important point, as the ravines such as San Lazaro are being altered and developed by human activity. This is likely to change lahar hazards in the future.

Bernard, K.; Van Wyk de Vries, B.; Thouret, J.

2012-12-01

425

Midwavelength Infrared Avalanche Photodiode Using InAsGaSb Strain Layer Superlattice  

Microsoft Academic Search

InAs-GaSb strain layer superlattice p+-n--n avalanche photodiodes (APDs) are fabricated using a newly introduced electron-beam aided zinc sulfide deposition. Temperature-dependent measurements were performed on 300 times 300 mum2 mesa etched APDs. The effect of passivation was also studied on the diode characteristics and APD performances. Temperature-dependent gain strongly correlates with avalanche mechanism.

S. Mallick; K. Banerjee; S. Ghosh; J. B. Rodriguez; S. Krishna

2007-01-01

426

Morphology and emplacement of an unusual debris-avalanche deposit at Jocotitln volcano, Central Mexico  

Microsoft Academic Search

A pre-historic collapse of the northeastern flank of Jocotitln Volcano (3950 m), located in the central part of the Trans Mexican Volcanic Belt, produced a debris-avalanche deposit characterized by surficial hummocks of exceptional size and conical shape. The avalanche covered an area of 80 km2, had an apparent coefficient of friction (H\\/L)_of 0.11, a maximum runout distance of 12 km,

Claus Siebe; Jean-Christophe Komorowski; Michael F Sheridan

1992-01-01

427

Evolution and prospects for single-photon avalanche diodes and quenching circuits  

Microsoft Academic Search

The evolution of solid-state avalanche detectors of single optical photons is outlined and the issues for further progress are discussed. Physical phenomena that underlay the operation of the single-photon avalanche diodes (SPAD) and determine the performance are considered and their role is assessed (detection efficiency; dark-counting rate; afterpulsing; photon timing resolution; etc.). The main technological issues that hamper the development

S. Cova; M. Ghioni; A. Lotito; I. Rech; F. Zappa

2004-01-01

428

Geological history and within-island diversity: a debris avalanche and the Tenerife lizard Gallotia galloti  

Microsoft Academic Search

Several processes have been described that could explain geographical variation and speciation within small islands, including fragmentation of populations through volcanic eruptions. Massive landslides, or debris avalanches, could cause similar effects. Here we analyse the potential impact of the 0.8 million-year-ago (Ma) Gimar valley debris avalanche on the phylogeography of the lizard Gallotia galloti on the Canary Island of Tenerife.

RICHARD P. B ROWN; PAUL A. H OSKISSON; JOHN-HENRY WELTON; MARCOS BEZ

2006-01-01

429

Sensitivity penalty calculation for burst-mode receivers using avalanche photodiodes  

Microsoft Academic Search

This paper presents the sensitivity penalty for burst-mode receivers using avalanche photodiodes. The analysis takes into account detailed avalanche photodiode statistics, additive Gaussian noise, intersymbol interference and dc offsets in the receiver channel. The penalty has been calculated via comparison of bit-error rates (BERs), obtained using numerical integration, both in continuous- and burst-mode operation. Sensitivity penalties for burst-mode operation as

Peter Ossieur; Xing-Zhi Qiu; Johan Bauwelinck; Jan Vandewege

2003-01-01

430

Avalanche Noise Characteristics of Single Al Ga As GaAs Heterojunction APDs  

Microsoft Academic Search

AbstractAvalanche multiplication and,excess noise have been measured on a series of Al Ga,AsGaAs and GaAsAl Ga As (,, and ) single hetero- junction p -i-n diodes. In some devices excess noise is lower than in equivalent homojunction devices with avalanche regions composed of either of the constituent materials, the heterojunction with,showing the greatest improvement. Excess noise deteriorates with higher values

C. Groves; C. K. Chia; R. C. Tozer; J. P. R. David; G. J. Rees

2005-01-01

431

Effect of dead space on the excess noise factor and time response of avalanche photodiodes  

Microsoft Academic Search

The effect of dead space on the statistics of the gain process in continuous-multiplication avalanche photodiodes (APDs) is determined using the theory of age-dependent branching processes. Analytical expressions are derived for the mean gain, the excess noise factor, and the mean and standard deviation of the impulse response function, for the dead-space-modified avalanche photodiode (DAPD), under conditions of single carrier

Bahaa E. A. Saleh; Majeed M. Hayat; Malvin C. Teich

1990-01-01

432

NUMERICAL ANALYSIS OF HOMOJUNCTION GALLIUM ARSENIDE AVALANCHE PHOTODIODES (GAAS-APDS)  

Microsoft Academic Search

AbstractIn our earlier work we introduce a numerical analysis to investigate the excess noise and performance factor of double carrier multiplication homojunction,avalanche photodiodes (APDs) considering the nonlocal nature of the ionization process. In this paper we investigate the gain,breakdown voltage and carrier injection breakdown probability of homojunction avalanche photodiode in the wide range of multiplication region width. Also in our

Hosein Mokari; Pouya Derakhshan-Barjoei

2008-01-01

433

A small-signal theory of avalanche noise in IMPATT diodes  

Microsoft Academic Search

A general small-signal theory of the avalanche noise in IMPATT diodes is presented. The theory is applicable to structures of arbitrary doping profile and uses realistic (alpha neq betain Si) ionization coefficients. The theory accounts in a self-consistent manner for space-charge feedback effects in the avalanche and drift regions. Two single-diffusedn-pdiodes of identical doping profile, one of germanium and the

HERMANN K. GUMMEL; JAMES L. BLUE

1967-01-01

434

Avalanches in One-Dimensional Piles with Different Types of Bases  

SciTech Connect

We perform a systematic experimental study of the influence of the type of base on the avalanche dynamics of slowly driven 1D ball piles. The control of base details allows us to explore a wide spectrum of pile structures and dynamics. The scaling properties of the observed avalanche distributions suggest that self-organized critical behavior is approached as the {open_quotes}base-induced{close_quotes} disorder at the pile profile increases.

Altshuler, E.; Ramos, O.; Martinez, C.; Flores, L. E.; Noda, C.

2001-06-11

435

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

USGS Publications Warehouse

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

Waythomas, C.F.

2000-01-01

436

Improved sinusoidal gating with balanced InGaAs/InP Single Photon Avalanche Diodes.  

PubMed

We report balanced InGaAs/InP single photon avalanche diodes (SPADs) operated in sinusoidal gating mode with a tunable phase shifter to reduce common mode noise. This technique enables detection of small avalanche pulses, which results in reduced afterpulsing. For laser repletion rate of 20 MHz at 240 K, the dark count rate for photon detection efficiency of 10% is 8.9 kHz. PMID:23938523

Lu, Zhiwen; Sun, Wenlu; Zhou, Qiugui; Campbell, Joe; Jiang, Xudong; Itzler, Mark A

2013-07-15

437

Modeling of InGaAs/InAlAs/InP avalanche photodiodes with undepleted absorber  

NASA Astrophysics Data System (ADS)

For high-bit rate and long-haul receivers in optical telecommunication systems the avalanche photodiodes are preferred since they offer an improvement of the receiver sensitivity by several decibels. Recently critical sensing and imaging applications stimulated development of modified avalanche photodiodes structures operating in 1.55 ?m spectral range. For these devices speed is not further critical. Instead, very low current densities and low multiplication noises are the main requirements. The most advanced structure of avalanche photodiodes is known as Separate Absorption, Grading, Charge and Multiplication (SAGCM). In the present work the performance of uncooled InGaAs/InAlAs/InP avalanche photodiodes operating near 1.55 ?m has been studied theoretically. Device modeling based on advanced drift - diffusion model with commercial Crosslight APSYS software has been performed. Conventional SAGCM avalanche photodiodes as well as devices with a relatively thick undepleted p-type InGaAs absorption region and thin InAlAs multiplication layer have been considered. This type of avalanche photodiodes enables to increase device quantum efficiency, reduce dark current and eliminate impact ionization processes within absorbing layer. Extensive calculations allowed for detailed analysis of individual regions of the device and determination of their influence on diode characteristics.

Kaniewski, Janusz; Jurenczyk, Jaroslaw; Zak, Dariusz; Muszalski, Jan

2012-01-01

438

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

PubMed Central

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

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

2010-01-01

439

Monitoring snow avalanches in the medium range by a network of infrasonic arrays: first results  

NASA Astrophysics Data System (ADS)

Monitoring of small-to-medium sized avalanches activity represents a crucial parameter to compare predictions and real effects. However, at present natural avalanche activity is mainly based on field observations, which have a limited range and are possible only during the daylight. Since 2009, the Department of Earth Sciences of University of Florence in collaboration with the Regione Valle d'Aosta is using the infrasonic array technology for near real-time monitoring of natural and artificial avalanche activity in the Alpine area. The results obtained during the last 3 years indicate that small-to-medium sized snow avalanches can be detected in the short-to-medium range distance (2-6 km). However, despite single array analysis allows to recognise many natural (microbarom, earthquakes, avalanches) and artificial (airplane, explosions) infrasound sources by using apparent velocity criterion, any unique identification and precise location of infrasonic sources is not possible without any additional information. In order to solve this problem, the monitoring system is upgraded by installing two additional arrays. In fact, a network of 3 arrays is operating since December 2012 around the MonteRosa and Cervino international ski resorts on the related massifs. Each infrasonic array consists of 4 infrasonic sensors deployed in triangular geometry and ~150 m of aperture. Data are sampled at 100 Hz and transmitted in real-time to Department of Earth Sciences in Florence for near real-time (<2 minutes) processing. The network has improved the capability in locating avalanches sources in a medium range distance (from 6 km to more than 10 km). In fact, the 3 arrays are covering an area of ~ 250 km2. Efficiency of source location and sensitivity of this infrasonic array network are tested by using artificial triggered avalanches: avalanches can now be located with a precision of ~ 1 km. Information on geographical position, origin time and infrasonic energy will be supplied to Avalanche Warning Service of Aosta Valley in near real-time. The research is supported by the Operational programme Italy - France (Alps - ALCOTRA) - Project "Map3 - Monitoring for the Avalanche Prevision, Prediction and Protection".

ulivieri, giacomo; marchetti, emanuele; ripepe, maurizio; durand, nathalie; frigo, barbara; chiambretti, igor; segor, valerio

2013-04-01

440

The September 1988 intracaldera avalanche and eruption at Fernandina volcano, Galapagos Islands  

USGS Publications Warehouse

During 14-16 September 1988, a large intracaldera avalanche and an eruption of basaltic tephra and lava at Fernandina volcano, Galapagos, produced the most profound changes within the caldera since its collapse in 1968. A swarm of eight earthquakes (mb 4.7-5.5) occurred in a 14 h period on 24 February 1988 at Fernandina, and two more earthquakes of this size followed on 15 April and 20 May, respectively. On 14 September 1988, another earthquake (mb 4.6) preceded a complex series of events. A debris avalanche was generated by the failure of a fault-bounded segment of the east caldera wall, approximately 2 km long and 300 m wide. The avalanche deposit is up to 250 m thick and has an approximate volume of 0.9 km3. The avalanche rapidly displaced a preexisting lake from the southeast end of the caldera floor to the northwest end, where the water washed up against the lower part of the caldera wall, then gradually seeped into the avalanche deposit and was completely gone by mid-January 1989. An eruption began in the caldera within about 1-2 h of the earthquake, producing a vigorous tephra plume for about 12 h, then lava flows during the next two days. The eruption ended late on 16 September. Most of the eruptive activity was from vents on the caldera floor near the base of the new avalanche scar. Unequivocal relative timing of events is difficult to determine, but seismic records suggest that the avalanche may have occurred 1.6 h after the earthquake, and field relations show that lava was clearly erupted after the avalanche was emplaced. The most likely sequence of events seems to be that the 1988 feeder dike intruded upward into the east caldera wall, dislocated the unstable wall block, and triggered the avalanche. The avalanche immediately exposed the newly emplaced dike and initiated the eruption. The exact cause of the earthquakes is unknown. ?? 1991 Springer-Verlag.

Chadwick, W.W., Jr.; De Roy, T.; Carrasco, A.

1991-01-01

441

Characterization of Advanced Avalanche Photodiodes for Water Vapor Lidar Receivers  

NASA Technical Reports Server (NTRS)

Development of advanced differential absorption lidar (DIAL) receivers is very important to increase the accuracy of atmospheric water vapor measurements. A major component of such receivers is the optical detector. In the near-infrared wavelength range avalanche photodiodes (APD's) are the best choice for higher signal-to-noise ratio, where there are many water vapor absorption lines. In this study, characterization experiments were performed to evaluate a group of silicon-based APD's. The APD's have different structures representative of different manufacturers. The experiments include setups to calibrate these devices, as well as characterization of the effects of voltage bias and temperature on the responsivity, surface scans, noise measurements, and frequency response measurements. For each experiment, the setup, procedure, data analysis, and results are given and discussed. This research was done to choose a suitable APD detector for the development of an advanced atmospheric water vapor differential absorption lidar detection system operating either at 720, 820, or 940 nm. The results point out the benefits of using the super low ionization ratio (SLIK) structure APD for its lower noise-equivalent power, which was found to be on the order of 2 to 4 fW/Hz(sup (1/2)), with an appropriate optical system and electronics. The water vapor detection systems signal-to-noise ratio will increase by a factor of 10.

Refaat, Tamer F.; Halama, Gary E.; DeYoung, Russell J.

2000-01-01

442

Avalanche photodiode photon counting receivers for space-borne lidars  

NASA Technical Reports Server (NTRS)

Avalanche photodiodes (APD) are studied for uses as photon counting detectors in spaceborne lidars. Non-breakdown APD photon counters, in which the APD's are biased below the breakdown point, are shown to outperform: (1) conventional APD photon counters biased above the breakdown point; (2) conventional APD photon counters biased above the breakdown point; and (3) APD's in analog mode when the received optical signal is extremely weak. Non-breakdown APD photon counters were shown experimentally to achieve an effective photon counting quantum efficiency of 5.0 percent at lambda = 820 nm with a dead time of 15 ns and a dark count rate of 7000/s which agreed with the theoretically predicted values. The interarrival times of the counts followed an exponential distribution and the counting statistics appeared to follow a Poisson distribution with no after pulsing. It is predicted that the effective photon counting quantum efficiency can be improved to 18.7 percent at lambda = 820 nm and 1.46 percent at lambda = 1060 nm with a dead time of a few nanoseconds by using more advanced commercially available electronic components.

Sun, Xiaoli; Davidson, Frederic M.

1991-01-01

443

Design considerations for high performance avalanche photodiode multiplication layers  

NASA Astrophysics Data System (ADS)

We have studied the effect of the thickness of the multiplication region on the noise performance characteristics of avalanche photodiodes (APD's). Our simulation results are based on a full band Monte Carlo model with anisotropic threshold energies for impact ionization. Simulation results suggest that the well known McIntyre expression for the excess noise factor is not directly applicable for devices with a very thin multiplication region. Since the number of ionization events is drastically reduced when the multiplication layer is very thin, the 'ionization coefficient' is not a good physical parameter to characterize the process. Instead 'effective quantum yield,' which is a measure of the total electron-hole pair generation in the device, is a more appropriate parameter to consider. We also show that for the device structure considered here, modeling the excess noise factor using a 'discrete Bernoulli trial' model as opposed to the conventional 'continuum theory' produces closer agreement to experimental measurements. Our results reinforce the understanding that impact ionization is a strong function of carrier energy and the use of simplified field-dependent models to characterize this high energy process fails to accurately model this phenomenon.

Chandramouli, V.; Maziar, Christine M.; Campbell, Joe C.

1994-05-01

444

Single photon counting linear mode avalanche photodiode technologies  

NASA Astrophysics Data System (ADS)

The false count rate of a single-photon-sensitive photoreceiver consisting of a high-gain, low-excess-noise linear-mode InGaAs avalanche photodiode (APD) and a high-bandwidth transimpedance amplifier (TIA) is fit to a statistical model. The peak height distribution of the APD's multiplied dark current is approximated by the weighted sum of McIntyre distributions, each characterizing dark current generated at a different location within the APD's junction. The peak height distribution approximated in this way is convolved with a Gaussian distribution representing the input-referred noise of the TIA to generate the statistical distribution of the uncorrelated sum. The cumulative distribution function (CDF) representing count probability as a function of detection threshold is computed, and the CDF model fit to empirical false count data. It is found that only k=0 McIntyre distributions fit the empirically measured CDF at high detection threshold, and that false count rate drops faster than photon count rate as detection threshold is raised. Once fit to empirical false count data, the model predicts the improvement of the false count rate to be expected from reductions in TIA noise and APD dark current. Improvement by at least three orders of magnitude is thought feasible with further manufacturing development and a capacitive-feedback TIA (CTIA).

Williams, George M.; Huntington, Andrew S.

2011-10-01

445

Characterization of avalanche photodiode arrays for temporally resolved photon counting  

NASA Astrophysics Data System (ADS)

The Apache Point Observatory Lunar Laser-ranging Operation (APOLLO) is a next-generation campaign aimed at measuring the earth-moon separation with millimeter precision. Doing so requires precision measurements of the time-of-flight of photons between the earth and moon. APOLLO will utilize new technology in the form of avalanche photodiode (APD) arrays to detect and time-tag the lunar return photons. The APD arrays were provided by Massachusetts Institute of Technology, Lincoln Laboratory but with no accompanying electronic circuitry for biasing or reading out the detectors. I describe the design, construction and testing of the electronics to bias the arrays and detect photons. Once a final prototype version of the electronics was developed, I characterized the temporal and spatial response of the detectors at two different wavelengths: 786 nm and 668 nm. A simple model of APD performance was developed and compared reasonably well with the experimental data. This model was used to predict the detector performance at 532 nmthe wavelength used for APOLLO.

Strasburg, Jana Dee

2004-10-01

446

Avalanches in compressed porous SiO(2)-based materials.  

PubMed

The failure dynamics in SiO(2)-based porous materials under compression, namely the synthetic glass Gelsil and three natural sandstones, has been studied for slowly increasing compressive uniaxial stress with rates between 0.2 and 2.8 kPa/s. The measured collapsed dynamics is similar to Vycor, which is another synthetic porous SiO(2) glass similar to Gelsil but with a different porous mesostructure. Compression occurs by jerks of strain release and a major collapse at the failure point. The acoustic emission and shrinking of the samples during jerks are measured and analyzed. The energy of acoustic emission events, its duration, and waiting times between events show that the failure process follows avalanche criticality with power law statistics over ca. 4 decades with a power law exponent ?? 1.4 for the energy distribution. This exponent is consistent with the mean-field value for the collapse of granular media. Besides the absence of length, energy, and time scales, we demonstrate the existence of aftershock correlations during the failure process. PMID:25215740

Nataf, Guillaume F; Castillo-Villa, Pedro O; Bar, Jordi; Illa, Xavier; Vives, Eduard; Planes, Antoni; Salje, Ekhard K H

2014-08-01

447

Transport, hysteresis and avalanches in artificial spin ice systems  

SciTech Connect

We examine the hopping dynamics of an artificial spin ice system constructed from colloids on a kagome optical trap array where each trap has two possible states. By applying an external drive from an electric field which is analogous to a biasing applied magnetic field for real spin systems, we can create polarized states that obey the spin-ice rules of two spins in and one spin out at each vertex. We demonstrate that when we sweep the external drive and measure the fraction of the system that has been polarized, we can generate a hysteresis loop analogous to the hysteretic magnetization versus external magnetic field curves for real spin systems. The disorder in our system can be readily controlled by changing the barrier that must be overcome before a colloid can hop from one side of a trap to the other. For systems with no disorder, the effective spins all flip simultaneously as the biasing field is changed, while for strong disorder the hysteresis curves show a series of discontinuous jumps or avalanches similar to Barkhausen noise.

Reichhardt, Charles [Los Alamos National Laboratory; Reichhardt, Cynthia J [Los Alamos National Laboratory; Libal, A [BABES-BOLYAI UNIV.

2010-01-01

448

Avalanche photodiode based detector for beam emission spectroscopy  

SciTech Connect

An avalanche photodiode based (APD) detector for the visible wavelength range was developed for low light level, high frequency beam emission spectroscopy (BES) experiments in fusion plasmas. This solid state detector has higher quantum efficiency than photomultiplier tubes, and unlike normal photodiodes, it has internal gain. This paper describes the developed detector as well as the noise model of the electronic circuit. By understanding the noise sources and the amplification process, the optimal amplifier and APD reverse voltage setting can be determined, where the signal-to-noise ratio is the highest for a given photon flux. The calculations are compared to the absolute calibration results of the implemented circuit. It was found that for a certain photon flux range, relevant for BES measurements ({approx_equal}10{sup 8}-10{sup 10} photons/s), the new detector is superior to both photomultipliers and photodiodes, although it does not require cryogenic cooling of any component. The position of this photon flux window sensitively depends on the parameters of the actual experimental implementation (desired bandwidth, detector size, etc.) Several detector units based on these developments have been built and installed in various tokamaks. Some illustrative results are presented from the 8-channel trial BES system installed at Mega-Ampere Spherical Tokamak (MAST) and the 16-channel BES system installed at the Torus Experiment for Technology Oriented Research (TEXTOR).

Dunai, D.; Zoletnik, S.; Sarkoezi, J. [KFKI Research Institute for Particle and Nuclear Physics, EURATOM Association, P.O. Box 49, H-1525 Budapest (Hungary); Field, A. R. [EURATOM/CCFE Fusion Association, Culham Science Centre, Abingdon, Oxon OX14 3DB (United Kingdom)

2010-10-15

449

Rock avalanches and glacier dynamics: a case study in the Chugach Mountains, Alaska  

NASA Astrophysics Data System (ADS)

Massive rock slope failures resulting in rock avalanches in glacierized environments can have serious consequences for downstream areas. Furthermore they are important drivers of erosion. The Chugach Mountains in south-central Alaska are a vast remote and strongly glacierized area with evidence of numerous rock avalanches, although a systematic documentation and assessment of their role as geomorphic agents is missing so far. Here we use glaciers as a unique archive of rock avalanches that have deposited extensive debris sheets on glaciers. A number of well preserved rock avalanche deposits from past years and decades furthermore facilitate the quantification of hitherto poorly known historic glacier surface velocities in the region. The principal objective of this work was first to create an inventory of rock avalanches on the basis of Landsat satellite images in the Chugach Mountains, and to analyze their characteristics regarding lithology, climate, runout-distance, area and volume, as well as their spatial distribution. The runout distances of mass movements are generally larger in glacial environments than in non-glacial environments. This characteristic was also shown in the studied cases as they always travelled over glaciers, firn or snow. The distribution of the rock avalanches was compared with the occurrence of earthquakes in the region. It has been shown in this study, that especially big earthquakes trigger rock avalanches. Smaller earthquakes do not appear to have enough energy to trigger rock avalanches. Furthermore, the climate conditions were analyzed of being responsible for the spatial pattern of the rock avalanches. The south-eastern part of the Chugach Mountains is affected by high precipitation and mild temperatures. Concentration of rock avalanches occurs in the same area. To analyze glacier dynamics over more than 20 years, rock avalanche deposits on the glaciers were used to derive simple but robust measures of flow velocities over periods of several years to decades. Such long-term averaged flow velocities are difficult to be achieved by measurement techniques such as satellite based SAR or GPS as they operate over much shorter periods of time. Most of the inferred flow velocities are in the range of 50 to 100 m/a. A few calving or surging glaciers displayed flow velocities of > 300 m/a. In the case of several rock avalanche deposits on the same glacier, differential flow velocities were evaluated, which confirmed the expected patterns of faster velocities in the middle of the glacier and slower velocities at the margins. This study adds important evidence on the spatio-temporal distribution of rock avalanches in glacial environments, their relation to seismic triggers and climate. The successful identification of glacier flow velocities over a larger mountain region and a larger period of time is unique and can provide important insights into glacier dynamics and change in a region that is highly sensitive to climate change, and the contribution to sea level rise from melting glaciers under ongoing debate.

Uhlmann, Manuela; Fischer, Luzia; Huggel, Christian; Kargell, Jeffrey; Korup, Oliver

2010-05-01

450

Characterization of the artificially triggered avalanches in the MonterosaSki resort (North-western Italian Alps)  

NASA Astrophysics Data System (ADS)

Artificially triggering methods are nowadays commonly used for avalanche prevention within ski-resorts. The knowledge of possible relations between the characteristics of the avalanche events and the snowpack and weather conditions might help to foresee the avalanche release probability after a favorable weather cycle. The forecast might be helped by models, like for example snowpack evolution models or nearest neighbor models. The latters are based on statistics performed on large databases where the avalanche events, together with the related snow and weather conditions, are well recorded. Within the Operational programme 'Italy - France (Alps - ALCOTRA)', Project "Gestion en scurit des territories de montagne transfrontalire - Risk-Nat", from winter 2009-2010, in the MonterosaSki resort all the artificially triggered avalanches are registered with their characteristics (e.g. outline, type of avalanches, elevation, aspect), the triggering method (e.g. explosive, Daisy-Bell) and the snow and weather conditions. The aim of this project is to create a well documented database in order to perform some simple statistical analysis to find possible relation between the characteristics of the avalanches (e.g. type, size, run-out distance), the topography of the site (e.g. slope angle, aspect), snowpack condition (e.g. snow crystal type, snow temperature, density) and meteorological parameters (e.g. new snow, air temperature, wind). Moreover, the avalanche release method and the result of the triggering are recorded, in order to understand which are the most favorable conditions for avalanche release. This project is at its first operational winter, therefore in this work we present preliminary data concerning the study area, the methodology and the results from the first winter season, which might be useful to improve our knowledge about artificially triggered avalanches and to help the ski-piste security personnel to take decisions about the avalanche situation within ski-resorts. Keywords: artificial release, snowpack characteristics, topography, prevention, forecast.

Maggioni, Margherita; Brulport, A.; Freppaz, M.; Welf, A.; Purves, R.

2010-05-01

451

Large rock avalanches in southern Per: the Cerro Caquilluco - Cerrillos Negros rock slide - avalanche (Tacna, Tomasiri, Per)  

NASA Astrophysics Data System (ADS)

The Andean bent which coincides with the Peruvian-Chilean border region is characterised by one of the largest relief contrasts on earth with depth of the subduction trench ranging from 5000 to 6000 m below sea level and mountain tops ranging from 5500 to 6300 m a.s.l.. The western flank of the Andes is subdivided in 4 major geologic zones (i.e. Coastal Cordillera, longitudinal Basin or depression, the Precordillera or western escarpment and western Cordillera). Local relief contrasts are also pronounced due to the incision of deep canyons into several million old uplifted surfaces, preserved because of the extremely dry climate with precipitation averaging a few mm and less per year. The Lluta collapse (minimum age of 2.5 Ma; volume 26 km3) is one of the largest non-volcanic non-marine landslides on Earth and has been mapped in that area (Wrner et al., 2002). Systematic mapping in northern Chile and Southern Peru has revealed that this is not the only gigantic landslide in the area but that further landslides of similar size occurred in the area, located both along the canyon slopes and along the western escarpment of the Cordillera. This suggests that landsliding has been a major factor in controlling erosion. This contribution describes first results on mapping a giant landslide complex in southern Per called the Cerro Caquilluco - Cerrillos Negros Tomasiri rock slide - avalanche complex. The systematic mapping we have carried out in the area is presented in a further contribution to this conference. The Cerro Caquilluco - Cerrillos Negros Tomasiri rock slide - avalanche complex affected the upper part of a SW dipping paleosurface (8 to 9) cut by a disconnected and regular primitive drainage network organized in a series of SW trending parallel valleys. This network developed within the lower Miocene pinkish tuffaceous deposits of the Huaylillas formation, whereas the main landslide scarp lies within the conglomerates of the Upper Moquegua formation (lower Oligocene). The same type of landscape is found to the southeast of Tacna and Arica (Huaylillas anticline, Oxaya anticline and Sucuna homocline) The Cerro Caquilluco - Cerrillos Negros Tomasiri rock slide - avalanche complex has a total length of about 43 km, a source area width and length of about 4 km and 5.1 km, respectively. The computed fahrbschung is equal to 4.6 with an H/L ratio of about 0.08 and resulting in an extremely large excessive travel distance. The H/L value is well below the expected value computed according to the classical (H/L) vs volume empirical relationships presented in the literature. Deposition occurred along most of the transportation area and is evidenced by a series of wide lobes (10 to 65 m high) and levees (from a few meters to some tens of meters high) with an average extent of 8 km transversally to the flow direction. Flow structures are visible all over the transportation area and several lobes can be mapped out. Presently, we cannot determine if most of these failures belong to a consequent large retrogressive event or to different events separated in time. The longest lobe has only pristine morphology in the most distal part of the accumulation area. Here the deposit is represented by a unique tongue shaped deposit, 11 km long, 3 km wide and 25 to 60 m thick (rough volume estimate 1.15 km3) ), deposited along the piedmont surface (ave. slope: 2). This deposit presents a series of features typical of rock avalanches deposited on regular smooth surfaces, like: lateral levees, longitudinal and transversal ridges and furrows. The extreme runout of this failure could be explained assuming a single failure event or the detachment from a part of the slope located well below the present day upper scarp. In the middle part of the deposition/transportation area few lateral levees are preserved and deep valleys have been eroded into the deposit. Considering the relationship with the piedmont deposits and the faults cutting through the area the deposit could be up to 2-2.3 Ma old. The morphology of this lower lobe is contrasti

Crosta, G.; Hermanns, R. L.; Murillo, P. V.

2012-04-01

452

Optimal design of snow avalanche passive defence structure using reliability approach to quantify buildings vulnerability  

NASA Astrophysics Data System (ADS)

To protect elements at risk (humans, roads, houses, etc.) against snow avalanches, civil engineering structures, such as dams or mounds, are used. The design of such defence structures is done following a deterministic approach which considers European regulation. The minimization of expected total losses is an interesting alternative that generalizes cost-benefit approach to a continuous decision variable. For this purpose, not only the hazard magnitude but also the buildings vulnerability must be evaluated carefully. The aim of this work is therefore to combine state of the art sub-models for the probabilistic description of avalanche flows and the numerical evaluation of damages to buildings. We defined the risk as the expectation of the cost consequences of avalanches activity. Disposal consequences are quantified thanks to reliability methods. In this formulation, the accuracy of both the hazard estimation and the vulnerability calculation has to be consistent according to precision and computational costs. To do so, a numerical approach has been developed to evaluate the physical vulnerability of concrete buildings submitted to avalanche loadings. The ensuing application illustrates our approach. A reinforced concrete slab is considered to model the building with a finite element method. Reliability approach enables to produce a response spectrum of the structure against avalanche impact. Finally, vulnerability curves are built. Outcomes of the risk calculation are examined to find sensitivity on the optimal design of snow defence structures.

Favier, P.; Bertrand, D.; Eckert, N.; Naaim, M.

2012-04-01

453

Rockfalls and Avalanches from Little Tahoma Peak on Mount Rainier, Washington  

USGS Publications Warehouse

In December 1963 rockfalls from Little Tahoma Peak on the east side of Mount Rainier volcano fell onto Emmons Glacier and formed avalanches of rock debris that traveled about 4 miles down the glacier and the White River valley. In this distance, the rock debris descended as much as 6,200 feet in altitude. Minor lithologic differences and crosscutting relations indicate that the rockfalls caused at least seven separate avalanches, having an estimated total volume of 14 million cubic yards. The initial rockfall may have been caused by a small steam explosion near the base of Little Tahoma Peak. During movement, some of the avalanches were deflected from one side of the valley to the other. Calculations based on the height to which the avalanches rose on the valley walls suggest that their velocity reached at least 80 or 90 miles per hour. The unusually long distance some of the avalanches were transported is attributed to a cushion of trapped and compressed air at their base, which buoyed them up amid reduced friction.

Crandell, Dwight Raymond; Fahnestock, Robert K.

1965-01-01

454

Quantification of basal friction for technical and silvicultural glide-snow avalanche mitigation measures  

NASA Astrophysics Data System (ADS)

A long-standing problem in avalanche engineering is to design defense structures and manage forest stands such that they can withstand the forces of the natural snow cover. In this way, glide-snow avalanches can be prevented. Ground friction plays a crucial role in this process. To verify existing guidelines, we collected data on the vegetation cover and terrain characteristics of 101 glide-snow release areas in Davos, Switzerland. We quantified the Coulomb friction parameter ?m by applying a physical model that accounts for the dynamic forces of the moving snow in the stauch zone. We investigated the role of glide length, slope steepness and friction in avalanche release. Our calculations revealed that the slope angle and slab length for smooth slopes correspond to the technical guidelines for defense structure distances in Switzerland. Artificial defense structures, built in accordance with guidelines, prevent glide-snow avalanche releases, even when the terrain is smooth. Slopes over 40 m in length and 45 in steepness require a ground friction of ?m = 0.7 corresponding to stumps or tree regeneration to ensure protection. Forest management guidelines that define maximum forest gap sizes to prevent glide-snow avalanche release neglect the role of surface roughness and therefore underestimate the danger on smooth slopes.

Feistl, T.; Bebi, P.; Dreier, L.; Hanewinkel, M.; Bartelt, P.

2014-11-01

455

Intrinsic Noise Induces Critical Behavior in Leaky Markovian Networks Leading to Avalanching  

PubMed Central

The role intrinsic statistical fluctuations play in creating avalanches patterns of complex bursting activity with scale-free properties is examined in leaky Markovian networks. Using this broad class of models, we develop a probabilistic approach that employs a potential energy landscape perspective coupled with a macroscopic description based on statistical thermodynamics. We identify six important thermodynamic quantities essential for characterizing system behavior as a function of network size: the internal potential energy, entropy, free potential energy, internal pressure, pressure, and bulk modulus. In agreement with classical phase transitions, these quantities evolve smoothly as a function of the network size until a critical value is reached. At that value, a discontinuity in pressure is observed that leads to a spike in the bulk modulus demarcating loss of thermodynamic robustness. We attribute this novel result to a reallocation of the ground states (global minima) of the system's stationary potential energy landscape caused by a noise-induced deformation of its topographic surface. Further analysis demonstrates that appreciable levels of intrinsic noise can cause avalanching, a complex mode of operation that dominates system dynamics at near-critical or subcritical network sizes. Illustrative examples are provided using an epidemiological model of bacterial infection, where avalanching has not been characterized before, and a previously studied model of computational neuroscience, where avalanching was erroneously attributed to specific neural architectures. The general methods developed here can be used to study the emergence of avalanching (and other complex phenomena) in many biological, physical and man-made interaction networks. PMID:24415927

Jenkinson, Garrett; Goutsias, John

2014-01-01

456

Short-Wave Infrared HgCdTe Avalanche Photodiodes  

NASA Astrophysics Data System (ADS)

Short-wave infrared (SWIR) HgCdTe avalanche photodiodes (APDs) have been developed to address low-flux applications at low operating temperature and for laser detection at higher temperatures. Stable multiplication gains in excess of 200 have been observed in homojunction APDs with cutoff wavelengths down to 2.8 ?m and operating temperatures up to 300 K, associated with low excess noise F < 1.3 and low 1/ f noise. The measured dark current density at 200 K of 6.2 ?A/cm2 is low enough to enable high-sensitivity single-element light detection and ranging (lidar) applications and time-of-flight imaging. Corresponding APD arrays have been hybridized on a readout integrated circuit (ROIC) designed for low-flux low-SNR imaging with low noise and frame rates higher than 1500 frames/s. Preliminary focal-plane array characterization has confirmed the nominal ROIC performance and showed pixel operability above 99.5% (pixels within 50% of average gain). The bias dependence of the multiplication gain has been characterized as a function of temperature, cadmium composition, and junction geometry. A qualitative change in the bias dependence of the gain compared with mid-wave infrared (MWIR) HgCdTe has motivated the development of a modified local electric field model for the electron impaction ionization coefficient and multiplication gain. This model gives a close fit to the gain curves in both SWIR and MWIR APDs at temperatures between 80 K and 300 K, using two parameters that scale as a function of the energy gap and temperature. This property opens the path to quantitative predictive device simulations and to estimations of the junction geometry of APDs from the bias dependence of the gain.

Rothman, Johan; Mollard, Laurent; Bosson, Sylvie; Vojetta, Gautier; Foubert, Kevin; Gatti, Sylvain; Bonnouvrier, Gwladys; Salveti, Frederic; Kerlain, Alexandre; Pacaud, Olivier

2012-10-01

457

A few strong connections: optimizing information retention in neuronal avalanches  

PubMed Central

Background How living neural networks retain information is still incompletely understood. Two prominent ideas on this topic have developed in parallel, but have remained somewhat unconnected. The first of these, the "synaptic hypothesis," holds that information can be retained in synaptic connection strengths, or weights, between neurons. Recent work inspired by statistical mechanics has suggested that networks will retain the most information when their weights are distributed in a skewed manner, with many weak weights and only a few strong ones. The second of these ideas is that information can be represented by stable activity patterns. Multineuron recordings have shown that sequences of neural activity distributed over many neurons are repeated above chance levels when animals perform well-learned tasks. Although these two ideas are compelling, no one to our knowledge has yet linked the predicted optimum distribution of weights to stable activity patterns actually observed in living neural networks. Results Here, we explore this link by comparing stable activity patterns from cortical slice networks recorded with multielectrode arrays to stable patterns produced by a model with a tunable weight distribution. This model was previously shown to capture central features of the dynamics in these slice networks, including neuronal avalanche cascades. We find that when the model weight distribution is appropriately skewed, it correctly matches the distribution of repeating patterns observed in the data. In addition, this same distribution of weights maximizes the capacity of the network model to retain stable activity patterns. Thus, the distribution that best fits the data is also the distribution that maximizes the number of stable patterns. Conclusions We conclude that local cortical networks are very likely to use a highly skewed weight distribution to optimize information retention, as predicted by theory. Fixed distributions impose constraints on learning, however. The network must have mechanisms for preserving the overall weight distribution while allowing individual connection strengths to change with learning. PMID:20053290

2010-01-01

458

Signal and Noise Properties of Position-Sensitive Avalanche Photodiodes  

PubMed Central

After many years of development, position-sensitive avalanche photodiodes (PSAPDs) are now being incorporated into a range of scintillation detector systems, including those used in high-resolution small-animal PET and PET/MR scanners. In this work, the signal, noise, signal-to-noise ratio (SNR), flood histogram and timing resolution were measured for lutetium oxyorthosilicate (LSO) scintillator arrays coupled to PSAPDs ranging in size from 1020 mm, and the optimum bias voltage and working temperature determined. Variations in the SNR performance of PSAPDs with the same dimensions were small, but the SNR decreased significantly with increasing PSAPD size and increasing temperature. Smaller PSAPDs (10 mm and 15 mm in width) produced acceptable flood histograms at 24 C, and cooling lower than 16 C produced little improvement. The optimum bias voltage was about 25 V below the break down voltage. The larger 20 mm PSAPDs have lower SNR and require cooling to 07 C for acceptable performance. The optimum bias voltage also is lower (35 V or more below the break down voltage depending on the temperature). Significant changes in the timing resolution were observed as the bias voltage and temperature were varied. Higher bias voltages provided better timing resolution. The best timing resolution obtained for individual crystals was 2.8 ns and 3.3 ns for the 10 mm and 15 mm PSAPDs, respectively. The results of this work provide useful guidance for selecting the bias voltage and working temperature for scintillation detectors that incorporate PSAPDs as the photodetector. PMID:21896961

Yang, Yongfeng; Wu, Yibao; Farrell, Richard; Dokhale, Purushottam A.; Shah, Kanai S.; Cherry, Simon R.

2011-01-01

459

Dating of snow avalanches by means of wound-induced vessel anomalies in sub-arctic Betula pubescens  

E-print Network

Dating of snow avalanches by means of wound-induced vessel anomalies in sub-arctic Betula pubescens): Dating of snow avalanches by means of wound-induced vessel anomalies in sub-arctic Betula pubescens records of past events. We investigated 12 sub-arctic downy birch (Betula pubescens Ehrh.) trees scarred

Stoffel, Markus

460

Snow avalanche release in forest ecosystems: A case study in the Aosta Valley Region (NW-Italy)  

Microsoft Academic Search

Snow avalanches are among the most important disturbances that affect mountain ecosystems, influencing forest dynamics, establishment and mortality processes. At the same time, forests can affect the likelihood of avalanche release and can, in some cases, protect human settlements and infrastructure. Yet, since the ability of a forest to protect settlements is largely a function of its stand structure and

D. Viglietti; S. Letey; R. Motta; M. Maggioni; M. Freppaz

2010-01-01

461

Seasonally active frost-dust avalanches on a north polar scarp of Mars captured by HiRISE  

E-print Network

Seasonally active frost-dust avalanches on a north polar scarp of Mars captured by HiRISE Patrick, P., et al. (2008), Seasonally active frost-dust avalanches on a north polar scarp of Mars captured-rich layers of the north polar layered deposits (NPLD) with varying dust content. Mars Orbiter Laser Altimeter

Byrne, Shane

462

Transient and steady-state dark current mechanisms in amorphous selenium avalanche radiation detectors  

SciTech Connect

A theoretical model for describing bias-dependent transient and steady-state behaviors of dark current in amorphous selenium (a-Se) avalanche detector structures has been developed. The analytical model considers bulk thermal generation current from mid-gap sates, transient carrier depletion, and carrier injection from the electrodes incorporating avalanche multiplication. The proposed physics-based dark current model is compared with the published experimental results on three potential a-Se avalanche detector structures. The steady-state dark current is the minimum for the structures that have effective blocking layers for both holes and electrons. The transient decay time to reach a plateau decreases considerably with increasing electric field.

Kabir, M. Z.; Imam, Safayat-Al [Department of Electrical and Computer Engineering, Concordia University, 1455 Blvd. de Maisonneuve West, Montreal, Quebec H3G 1M8 (Canada)] [Department of Electrical and Computer Engineering, Concordia University, 1455 Blvd. de Maisonneuve West, Montreal, Quebec H3G 1M8 (Canada)

2013-04-15

463

Avalanches in 2D dislocation systems: plastic yielding is not depinning.  

PubMed

We study the properties of strain bursts (dislocation avalanches) occurring in two-dimensional discrete dislocation dynamics models under quasistatic stress-controlled loading. Contrary to previous suggestions, the avalanche statistics differ fundamentally from predictions obtained for the depinning of elastic manifolds in quenched random media. Instead, we find an exponent ?=1 of the power-law distribution of slip or released energy, with a cutoff that increases exponentially with the applied stress and diverges with system size at all stresses. These observations demonstrate that the avalanche dynamics of 2D dislocation systems is scale-free at every applied stress and, therefore, cannot be envisaged in terms of critical behavior associated with a depinning transition. PMID:24972216

Ispnovity, Pter Dusn; Laurson, Lasse; Zaiser, Michael; Groma, Istvn; Zapperi, Stefano; Alava, Mikko J

2014-06-13

464

Signal-to-noise ratio of Geiger-mode avalanche photodiode single-photon counting detectors  

NASA Astrophysics Data System (ADS)

Geiger-mode avalanche photodiodes (GM-APDs) use the avalanche mechanism of semiconductors to amplify signals in individual pixels. With proper thresholding, a pixel will be either "on" (avalanching) or "off." This discrete detection scheme eliminates read noise, which makes these devices capable of counting single photons. Using these detectors for imaging applications requires a well-developed and comprehensive expression for the expected signal-to-noise ratio (SNR). This paper derives the expected SNR of a GM-APD detector in gated operation based on gate length, number of samples, signal flux, dark count rate, photon detection efficiency, and afterpulsing probability. To verify the theoretical results, carrier-level Monte Carlo simulation results are compared to the derived equations and found to be in good agreement.

Kolb, Kimberly

2014-08-01

465

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

NASA Astrophysics Data System (ADS)

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

Ficker, T.

2007-12-01

466

Avalanches and Dimensional Reduction Breakdown in the Critical Behavior of Disordered Systems  

NASA Astrophysics Data System (ADS)

We investigate the connection between a formal property of the critical behavior of several disordered systems, known as dimensional reduction, and the presence in these systems at zero temperature of collective events known as avalanches. Avalanches generically produce nonanalyticities in the functional dependence of the cumulants of the renormalized disorder. We show that this leads to a breakdown of the dimensional reduction predictions if and only if the fractal dimension characterizing the scaling properties of the avalanches is exactly equal to the difference between the dimension of space and the scaling dimension of the primary field. This is proven by combining scaling theory and the functional renormalization group. We therefore clarify the puzzle of why dimensional reduction remains valid in random field systems above a nontrivial dimension (but fails below), always applies to the statistics of branched polymer, and is always wrong in elastic models of interfaces in a random environment.

Tarjus, Gilles; Baczyk, Maxime; Tissier, Matthieu

2013-03-01

467

Avalanches and dimensional reduction breakdown in the critical behavior of disordered systems.  

PubMed

We investigate the connection between a formal property of the critical behavior of several disordered systems, known as "dimensional reduction," and the presence in these systems at zero temperature of collective events known as "avalanches." Avalanches generically produce nonanalyticities in the functional dependence of the cumulants of the renormalized disorder. We show that this leads to a breakdown of the dimensional reduction predictions if and only if the fractal dimension characterizing the scaling properties of the avalanches is exactly equal to the difference between the dimension of space and the scaling dimension of the primary field. This is proven by combining scaling theory and the functional renormalization group. We therefore clarify the puzzle of why dimensional reduction remains valid in random field systems above a nontrivial dimension (but fails below), always applies to the statistics of branched polymer, and is always wrong in elastic models of interfaces in a random environment. PMID:23581342

Tarjus, Gilles; Baczyk, Maxime; Tissier, Matthieu

2013-03-29

468

Bounds for avalanche critical values of the Bak-Sneppen model  

E-print Network

We study the Bak-Sneppen model on locally finite transitive graphs $G$, in particular on Z^d and on T_Delta, the regular tree with common degree Delta. We show that the avalanches of the Bak-Sneppen model dominate independent site percolation, in a sense to be made precise. Since avalanches of the Bak-Sneppen model are dominated by a simple branching process, this yields upper and lower bounds for the so-called avalanche critical value $p_c^{BS}(G)$. Our main results imply that 1/(Delta+1) <= \\leq p_c^{BS}(T_Delta) \\leq 1/(Delta -1)$, and that $1/(2d+1)\\leq p_c^{BS}(Z^d)\\leq 1/(2d)+ 1/(2d)^2+O(d^{-3}), as d\\to\\infty.

Alexis Gillett; Ronald Meester; Misja Nuyens

2005-08-09

469

Mesa-isolated InGaAs avalanche photodiode damage by ionizing radiation  

NASA Astrophysics Data System (ADS)

InGaAs avalanche photodiodes (APDs) fabricated from epitaxial material by etching detector mesas and encapsulating the etched mesas under bisbenzocyclobutene (BCB) resin were irradiated by Co-60 gamma-rays to assess their sensitivity to a total ionizing dose of 200 krad(Si). A low-excess-noise APD design with a multi-stage avalanche gain region was tested. Ninety-six identical 20-?m-diameter APDs were characterized to assess the response of the design to ionizing radiation. The APDs were not under bias during irradiation. Damage to the APDs was characterized by measuring the change in room temperature dark current following irradiation, at a reverse bias for which the average avalanche gain is M=10. No significant increase of dark current was observed following gamma irradiation: the average increase was 5% and the standard deviation for the measurement was 10%.

Huntington, Andrew S.; Sellsted, Leah A.; Compton, Madison A.; Taylor, Edward W.

2011-09-01

470

Cartographic modeling of snow avalanche path location within Glacier National Park, Montana  

NASA Technical Reports Server (NTRS)

Geographic information system (GIS) techniques were applied to the study of snow-avalanche path location within Glacier National Park, Montana. Aerial photointerpretation and field surveys confirmed the location of 121 avalanche paths within the selected study area. Spatial and nonspatial information on each path were integrated using the ARC/INFO GIS. Lithologic, structural, hydrographic, topographic, and land-cover impacts on path location were analyzed. All path frequencies within variable classes were normalized by the area of class occurrence relative to the total area of the study area and were added to the morphometric information contained within INFO tables. The normalized values for each GIS coverage were used to cartographically model, by means of composite factor weightings, avalanche path locations.

Walsh, Stephen J.; Brown, Daniel G.; Bian, Ling; Butler, David R.

1990-01-01

471

1550 nm InGaAs/InAlAs single photon avalanche diode at room temperature.  

PubMed

An InGaAs/InAlAs Single Photon Avalanche Diode was fabricated and characterized. Leakage current, dark count and photon count measurements were carried out on the devices from 260 to 290 K. Due to better temperature stability of avalanche breakdown in InAlAs, the device breakdown voltage varied by < 0.2 V over the 30 K temperature range studied, which corresponds to a temperature coefficient of breakdown voltage less than 7 mV/K. The single photon detection efficiency achieved in gated mode was 21 and 10% at 260 and 290 K, respectively. However the dark count rates were high due to excessive band-to-band tunneling current in the InAlAs avalanche region. PMID:25321730

Meng, Xiao; Tan, Chee Hing; Dimler, Simon; David, John P R; Ng, Jo Shien

2014-09-22

472

Debris-flow activity and snow avalanches in a steep watershed of the Valais Alps (Switzerland): Dendrogeomorphic event reconstruction and identification of triggers  

E-print Network

Debris-flow activity and snow avalanches in a steep watershed of the Valais Alps (Switzerland: Debris flow Snow avalanche Dendrogeomorphology Seasonality Conifers Broad-leaved trees Triggering Debris flows and snow avalanches are common processes in the headwaters of steep watersheds worldwide

Stoffel, Markus

473

Propagation of Magnetic Avalanches in Mn12Ac at High Field Sweep Rates W. Decelle, J. Vanacken, and V. V. Moshchalkov  

E-print Network

Propagation of Magnetic Avalanches in Mn12Ac at High Field Sweep Rates W. Decelle, J. Vanacken of the magnetization, attributed to the occurrence of spin-phonon avalanches, was observed and it was shown that the rever- sal occurred inhomogeneously throughout the crystals [11,12]. These magnetic avalanches are now

Moshchalkov, Victor V.

474

arXiv:1406.6845v1[cond-mat.dis-nn]26Jun2014 Avalanches and hysteresis in frustrated superconductors and XY-spin-glasses  

E-print Network

arXiv:1406.6845v1[cond-mat.dis-nn]26Jun2014 Avalanches and hysteresis in frustrated superconductors. 38, 01187 Dresden, Germany (Dated: June 27, 2014) We study avalanches along the hysteresis loop by the softest mode of the inverse susceptibility matrix becoming unstable, which induces an avalanche of phase

Müller, Markus

475

Paramagnetic reentrance of ac screening: Evidence of vortex avalanches in Pb thin films A. V. Silhanek, S. Raedts, and V. V. Moshchalkov  

E-print Network

Paramagnetic reentrance of ac screening: Evidence of vortex avalanches in Pb thin films A. V the influence of a square array of pinning centers on the dynamics of vortex avalanches in Pb thin films disappear. Further down in temperature, vortex avalanches develop and dominate the magnetic response

Moshchalkov, Victor V.

476

Avalanche-size distribution at the depinning transition: A numerical test of the theory Alberto Rosso,1,2 Pierre Le Doussal,2 and Kay Jrg Wiese2  

E-print Network

Avalanche-size distribution at the depinning transition: A numerical test of the theory Alberto; published 30 October 2009 We calculate numerically the sizes S of jumps avalanches between successively-scale cutoff, takes the form P S = S Sm 2 p S/Sm where Smª S2 2 S m-d- is the scale of avalanches

Wiese, Kay Jörg

477

A NOVEL AVALANCHE-FREE SINGLE PHOTON DETECTOR H. Mohseni (Senior Member), O.G. Memis (Member), and S.C. Kong  

E-print Network

A NOVEL AVALANCHE-FREE SINGLE PHOTON DETECTOR H. Mohseni (Senior Member), O.G. Memis (Member. Unlike avalanche, this method produces no excess noise, and can potentially cover wavelengths from UV of the works on compact solid-state SPDs have been focused on Geiger mode avalanche photodetectors (APD), we

Mohseni, Hooman

478

Dramatic Role of Critical Current Anisotropy on Flux Avalanches in MgB2 Films J. Albrecht and A. T. Matveev*  

E-print Network

Dramatic Role of Critical Current Anisotropy on Flux Avalanches in MgB2 Films J. Albrecht and A. T occurs via abrupt dendritic avalanches that preferentially propagate perpendicular to the surface steps avalanches propagate in the strongest pinning direction. The observed behavior is fully explained using

Johansen, Tom Henning

479

International Snow Science Workshop Grenoble -Chamonix Mont-Blanc -2013 Vulnerability of a reinforced concrete wall loaded by a snow avalanche  

E-print Network

of a reinforced concrete wall loaded by a snow avalanche: experimental testing and FEM analysis Ousset I.1 and stop snow avalanches was partially destroyed. Experimental pushover tests on a 1/6 scale model have under dynamic avalanche loading. Finally, the physical vulnerability of the structure is assessed

Paris-Sud XI, Université de

480

Robustness of the avalanche dynamics in data-packet transport on scale-free networks E. J. Lee, K.-I. Goh, B. Kahng, and D. Kim  

E-print Network

Robustness of the avalanche dynamics in data-packet transport on scale-free networks E. J. Lee, K; published 16 May 2005 We study the avalanche dynamics in the data-packet transport on scale-free networks is redistrib- uted, followed by subsequent failures of overloaded vertices. The avalanche size depends

Kim, Doochul

481

Avalanches injecting flux into the central hole of a superconducting MgB2 ring ge Andreas Falnes Olsen,* Tom Henning Johansen, and Daniel Shantsev  

E-print Network

Avalanches injecting flux into the central hole of a superconducting MgB2 ring ?ge Andreas Falnes dendritic flux avalanches connecting the outer and inner edges of a ring-shaped superconducting MgB2 film. Such avalanches create heated channels across the entire width of the ring, and inject large amounts of flux

Johansen, Tom Henning

482

Size distributions of shocks and static avalanches from the Functional Renormalization Group arXiv:0812.1893, LPTENS 08/63  

E-print Network

Size distributions of shocks and static avalanches from the Functional Renormalization Group ar by quenched disorder are often used to model jerky self-organized critical motion. We study static avalanches. This allows us to obtain the size distribution P(S) of static avalanches in an expansion in the internal

Wiese, Kay Jörg

483

A two-phase mechanical model for rock-ice avalanches  

NASA Astrophysics Data System (ADS)

Rock-ice avalanche events are among the most hazardous natural disasters in the last century. In contrast to rock avalanches, the solid phase (ice) can transform to fluid during the course of the rock-ice avalanche and fundamentally alter mechanical processes. A real two-phase debris flow model could better address the dynamic interaction of solid (rock and ice) and fluid (water, snow, slurry, and fine particles) than presently used single-phase Voellmy- or Coulomb-type models. We present a two-phase model capable of performing dynamic strength weakening due to internal fluidization and basal lubrication and internal mass and momentum exchanges between the phases. Effective basal and internal friction angles are variable and correspond to evolving effective solid volume fraction, friction factors, volume fraction of the ice, true friction coefficients, and lubrication and fluidization factors. Benchmark numerical simulations demonstrate that the two-phase model can explain dynamically changing frictional properties of rock-ice avalanches that occur internally and along the flow path. The interphase mass and momentum exchanges are capable of demonstrating the mechanics of frontal surge head and multiple other surges in the debris body. This is an observed phenomenon in a real two-phase debris flow, but newly simulated here by applying the two-phase mass flow model. Mass and momentum exchanges between the phases and the associated internal and basal strength weakening control the exceptional long runout distances, provide a more realistic simulation especially during the critical initial and propagation stages of avalanche, and explain the exceptionally high and dynamically changing mobility of rock-ice avalanches.

Pudasaini, Shiva P.; Krautblatter, Michael

2014-10-01

484

Circuit model for characterizing the nearly linear behavior of avalanche diodes in amplifier circuits  

NASA Technical Reports Server (NTRS)

A nonlinear circuit model for avalanche diodes is proposed. The model was derived by assuming that the bias dependence of the elements in a known small-signal equivalent-circuit model for existing diodes arises in a manner consistent with the theory of an idealized Read-type device. The model contains a nonlinear R-L branch, a controlled source, and a linear depletion capacitance. The model is used in the nearly linear sense to predict intermodulation distortion and gain compression in avalanche diode amplifiers. Computed results for amplifiers with existing diodes are shown to be in good agreement with experiment.

Penfield, P., Jr.; Peterson, D. F.; Steinbrecher, D. H.

1972-01-01

485

Design and testing of an active quenching circuit for an avalanche photodiode photon detector  

NASA Technical Reports Server (NTRS)

The photon-detection capabilities of avalanche photodiodes (APDs) operating above their theoretical breakdown voltages are described, with particular attention given to the needs and methods of quenching an avalanche once breakdown has occurred. A brief background on the motives of and previous work with this mode of operation is presented. Finally, a description of the design and testing of an active quenching circuit is given. Although the active quenching circuit did not perform as expected, knowledge was gained as to the signal amplitudes necessary for quenching and the need for a better model for the above-breakdown circuit characteristics of the Geiger-mode APD.

Arbel, D.; Schwartz, J. A.

1991-01-01

486

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

PubMed

The charge-integration readout circuit was fabricated to achieve an ultralow-noise preamplifier for photoelectrons generated in an avalanche photodiode with linear mode operation at 77 K. To reduce the various kinds of noise, the capacitive transimpedance amplifier was used and consisted of low-capacitance circuit elements that were cooled with liquid nitrogen. As a result, the readout noise is equal to 3.0 electrons averaged for a period of 40 ms. We discuss the requirements for avalanche photodiodes to achieve photon-number-resolving detectors below this noise level. PMID:17304297

Tsujino, Kenji; Akiba, Makoto; Sasaki, Masahide

2007-03-01

487

Avalanche photodiodes operating parameter optimization for the Frascati Tokamak Upgrade Thomson scattering system (abstract)  

NASA Astrophysics Data System (ADS)

Measured figures (linearity, avalanche gain, frequency response, and noise) of the avalanche photodiodes (APD) detectors used on the FTU Thomson scattering system (FTU-TS) are reported. This investigation on the APD figures is motivated by the necessity of knowing their values over a wide range of input signals, and also of checking the validity of McIntyre model of APD noise, since using this model the experimental signal-to-noise ratio is calculated. From the noise analysis, a method of optimization of the detection system sensitivity is derived, leading to the optimization of the signal-to-noise ratio over the entire FTU-TS system.

Orsitto, F.; Brusadin, A.; Giovannozzi, E.

1997-01-01

488

Avalanche photodiodes operating parameter optimization for the Frascati Tokamak Upgrade Thomson scattering system  

NASA Astrophysics Data System (ADS)

Measured figures (linearity, avalanche gain, frequency response, and noise) of the avalanche photodiodes (APD) detectors used on the FTU Thomson scattering system (FTU-TS) are reported. This investigation on the APD figures is motivated by the necessity of knowing their values over a wide range of input signals, and also of checking the validity of McIntyre model of APD noise, since using this model the experimental signal-to-noise ratio is calculated. From the noise analysis, a method of optimization of the detection system sensitivity is derived, leading to the optimization of the signal-to-noise ratio over the entire FTU-TS system.

Orsitto, F.; Brusadin, A.; Giovannozzi, E.

1997-02-01

489

Reaching the hydrodynamic regime in a Bose-Einstein condensate by suppression of avalanches  

SciTech Connect

We report the realization of a Bose-Einstein condensate (BEC) in the hydrodynamic regime. The hydrodynamic regime is reached by evaporative cooling at a relatively low density suppressing the effect of avalanches. With the suppression of avalanches a BEC containing more than 10{sup 8} atoms is produced. The collisional opacity can be tuned from the collisionless regime to a collisional opacity of more than 2 by compressing the trap after condensation. In the collisional opaque regime a significant heating of the cloud at time scales shorter than half of the radial trap period is measured, which is a direct proof that the BEC is hydrodynamic.

Stam, K. M. R. van der; Meppelink, R.; Vogels, J. M.; Straten, P. van der [Atom Optics and Ultrafast Dynamics, Utrecht University, P.O. Box 80000, 3508 TA Utrecht (Netherlands)

2007-03-15

490

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

SciTech Connect

A simple one-dimensional transport model based on critical-gradient fluctuation dynamics is applied to describe some of the properties of plasma-turbulence-induced transport. This model combines avalanche-like transport with diffusion. The particle flux is self-regulated by the stability properties of the fluctuations. A high-gradient edge region emerges where transport dynamics is close to marginal stability. In steady state, the core remains at the subcritical gradient. The avalanches change from quasiperiodic events triggered mostly near the edge region to intermittent transport events depending on the noise level of the particle source.

Garcia, L.; Carreras, B.A. [Universidad Carlos III, 28911 Leganes, Madrid (Spain); Oak Ridge National Laboratory, Oak Ridge, Tennessee 37830 (United States)

2005-09-15

491

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

USGS Publications Warehouse

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

Glicken, Harry

1996-01-01

492

Nano-Multiplication-Region Avalanche Photodiodes and Arrays  

NASA Technical Reports Server (NTRS)

Nano-multiplication-region avalanche photodiodes (NAPDs), and imaging arrays of NAPDs integrated with complementary metal oxide/semiconductor (CMOS) active-pixel-sensor integrated circuitry, are being developed for applications in which there are requirements for high-sensitivity (including photoncounting) detection and imaging at wavelengths from about 250 to 950 nm. With respect to sensitivity and to such other characteristics as speed, geometric array format, radiation hardness, power demand of associated circuitry, size, weight, and robustness, NAPDs and arrays thereof are expected to be superior to prior photodetectors and arrays including CMOS active-pixel sensors (APSs), charge-coupled devices (CCDs), traditional APDs, and microchannelplate/ CCD combinations. Figure 1 depicts a conceptual NAPD array, integrated with APS circuitry, fabricated on a thick silicon-on-insulator wafer (SOI). Figure 2 presents selected aspects of the structure of a typical single pixel, which would include a metal oxide/semiconductor field-effect transistor (MOSFET) integrated with the NAPD. The NAPDs would reside in silicon islands formed on the buried oxide (BOX) layer of the SOI wafer. The silicon islands would be surrounded by oxide-filled insulation trenches, which, together with the BOX layer, would constitute an oxide embedding structure. There would be two kinds of silicon islands: NAPD islands for the NAPDs and MOSFET islands for in-pixel and global CMOS circuits. Typically, the silicon islands would be made between 5 and 10 m thick, but, if necessary, the thickness could be chosen outside this range. The side walls of the silicon islands would be heavily doped with electron-acceptor impurities (p+-doped) to form anodes for the photodiodes and guard layers for the MOSFETs. A nanoscale reach-through structure at the front (top in the figures) central position of each NAPD island would contain the APD multiplication region. Typically, the reach-through structure would be about 0.1 microns in diameter and between 0.3 and 0.4 nm high. The top layer in the reach-through structure would be heavily doped with electron-donor impurities (n+-doped) to make it act as a cathode. A layer beneath the cathode, between 0.1 and 0.2 nm thick, would be p-doped to a concentration .10(exp 17)cu cm. A thin n+-doped polysilicon pad would be formed on the top of the cathode to protect the cathode against erosion during a metal-silicon alloying step that would be part of the process of fabricating the array.

Zheng, Xinyu; Pain, Bedabrata; Cunningham, Thomas

2008-01-01

493

Telephone Interface for Avalanche Warnings based on Information Server for Adaptable Content Delivery  

Microsoft Academic Search

We present a system that provides an advanced telephone service for the dissemination of both national and regional avalanche forecasts in the Swiss Alps. The service enables members of the public and also mountain guides to access forecast information while travelling in mountain areas and, particularly, to be notified when entering regions of high risk. By telephone access, we include

Beat Signer; Moira C. Norrie; Peter Geissbuehler; Daniel Heiniger

2002-01-01

494

Avalanche transistor selection for long term stability in streak camera sweep and pulser applications  

SciTech Connect

We have identified the Motorola 2N4014 and 2N5551 and the Raytheon RS3944 as three transistor types that exhibit avalanche characteristics and have long term collector breakdown voltage stability superior to other transistors tested. Stability on all types has been improved by power burnin. An automatic avalanche transistor burnin tester has been constructed to allow power burnin of up to 1008 transistors at a time. The tester is controlled by an IBM Personal Computer (PC) and can be programmed to acquire data, unattended, at any desired rate or period. Data are collected from each run and stored on a floppy disk in ASCII format. The data analysis software, RS/1, was used for analysis and display. Data runs were typically 3 to 4 months long, with readings taken weekly. The transistors were biased into the avalanche or Zener region by individual current sources set to about 20% of the self-avalanche current for each type of transistor. Motorola, Zetex and National transistors were operated at 100 microamperes ({mu}A), and the Raytheon units were operated at 20 {mu}A. The electric field causes migration of material in the high field region at the surface near the collector-base junction, creating the voltage instability. 7 refs., 9 figs., 1 tab.

Thomas, S.W.; Griffith, R.L.; Teruya, A.T.

1990-09-05

495

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

PubMed

Avalanche multiplication in amorphous selenium (a-Se) can provide a large, adjustable gain for active matrix flat panel imagers (AMFPI), enabling quantum noise limited x-ray imaging during both radiography and fluoroscopy. In the case of direct conversion AMFPI, the multiplication factor for each x ray is a function of its depth of interaction, and the resulting variations in gain can reduce the detective quantum efficiency (DQE) of the system. An experimental method was developed to measure gain fluctuations by analyzing images of individual x rays that were obtained using a video camera with an a-Se target operated in avalanche mode. Pulse height spectra (PHS) of the charge produced per x ray were recorded for monoenergetic 30.9, 49.4, and 73.8 keV x-ray sources. The rapid initial decay and long tail of each PHS can be explained by a model in which positive charge dominates the initiation of avalanche. The Swank information factor quantifies the effect of gain fluctuation on DQE and was calculated from the PHS. The information factor was found to be 0.5 for a 25 microm a-Se layer with a maximum gain of approximately 300. Changing the energy of the incident x ray influenced the range of the primary photoelectron and noticeably affected the tail of the experimental PHS, but did not significantly change the avalanche Swank factor. PMID:17022211

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

2006-09-01

496