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1

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.

2

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

3

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

4

Snow Avalanches  

NASA Astrophysics Data System (ADS)

Over the last century, mountain ranges in Europe and North America have seen substantial development due to the increase in recreational activities, transportation, construction in high altitude areas, etc. In these mountain ranges, avalanches often threaten man's activities and life. Typical examples include recent disasters, such as the avalanche at Val d'Isère in 1970 (39 people were killed in a hostel) or the series of catastrophic avalanches throughout the Northern Alps in February 1999 (62 residents killed). The rising demand for higher safety measures has given new impetus to the development of mitigation technology and has given rise to a new scientific area entirely devoted to snow and avalanches. This paper summarises the paramount features of avalanches (formation and motion) and outlines the main approaches used for describing their movement. We do not tackle specific problems related to snow mechanics and avalanche forecasting. For more information on the subject, the reader is referred to the main textbooks published in Alpine countries [1-8].

Ancey, C.

5

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

6

Avalanche Town  

NSDL National Science Digital Library

This video segment, adapted ftom 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. The segment is four minutes seventeen seconds in length.

7

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

8

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

9

Avalanche Weather Forecasting  

NSDL National Science Digital Library

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

Linder, Dave

2011-01-01

10

Avalanche modeling in forested terrain  

NASA Astrophysics Data System (ADS)

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

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

2010-12-01

11

Avalanche Hazard Index for Colorado Highways.  

National Technical Information Service (NTIS)

This study conducted an inventory of existing avalanche paths along Colorado Highways. Information was collected on the size and type of each avalanche path, the historical frequency of avalanche occurrences, the number of avalanche tracks, the length of ...

A. I. Mears

1995-01-01

12

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

13

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.

14

Avalanche photodiode statistics in triggered-avalanche detection mode  

NASA Technical Reports Server (NTRS)

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

Tan, H. H.

1984-01-01

15

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.

16

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

17

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

18

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

19

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

20

Avalanches in UGe 2  

NASA Astrophysics Data System (ADS)

In UGe 2 ferromagnetism and superconductivity co-exist for pressures in the range 1.0- 1.6 GPa. The magnetic state, however, has several unusual properties. Here we report measurements of hysteresis loops for fields parallel to the easy-axis at low temperature and ambient pressure, measured for two separate UGe 2 single crystals. Steps in the magnetization as the field is changed at low temperature are observed for both crystals. The general phenomenology associated with the steps strongly suggests that they correspond to avalanches of domain-wall motion.

Lhotel, E.; Paulsen, C.; Huxley, A. D.

2004-05-01

21

Neuronal avalanches and learning  

NASA Astrophysics Data System (ADS)

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

de Arcangelis, Lucilla

2011-05-01

22

Photon Avalanche Laser Improvement Program.  

National Technical Information Service (NTIS)

The main thrust of this program was to increase the output power and efficiency of a photon avalanche laser demonstrated in an earlier and related program. However, material problems plagued the effort from the outset. Identification and solution of these...

M. E. Koch

1984-01-01

23

Culling avalanches in bootstrap percolation  

NASA Astrophysics Data System (ADS)

We study the culling avalanches which occur after the “death” of a single randomly chosen site in a network where sites are unstable, and are culled, if they have coordination less than an integer parameter m . Avalanche distributions are presented for triangular and cubic lattices for values of m where the associated bootstrap transitions are either first or second order. In second order cases, the culling avalanche distribution is found to be exponential, while in first order cases it follows a power law. We present an exact relation between culling avalanches and conventional bootstrap percolation and show that a relation proposed by Manna [Physica A 261, 351 (1998)] can be a good approximation for strongly first order bootstrap transitions but not for continuous bootstrap transitions.

Farrow, C.; Duxbury, P. M.; Moukarzel, Cristian F.

2005-12-01

24

Study of Avalanche Discharge Lasers.  

National Technical Information Service (NTIS)

Basic research carried out at the University of California, San Diego, on the study of avalanche discharge lasers is summarized. This research has resulted in many important scientific discoveries and generated much basic data which are of great value in ...

S. C. Lin

1983-01-01

25

Neuronal avalanches and coherence potentials  

NASA Astrophysics Data System (ADS)

The mammalian cortex consists of a vast network of weakly interacting excitable cells called neurons. Neurons must synchronize their activities in order to trigger activity in neighboring neurons. Moreover, interactions must be carefully regulated to remain weak (but not too weak) such that cascades of active neuronal groups avoid explosive growth yet allow for activity propagation over long-distances. Such a balance is robustly realized for neuronal avalanches, which are defined as cortical activity cascades that follow precise power laws. In experiments, scale-invariant neuronal avalanche dynamics have been observed during spontaneous cortical activity in isolated preparations in vitro as well as in the ongoing cortical activity of awake animals and in humans. Theory, models, and experiments suggest that neuronal avalanches are the signature of brain function near criticality at which the cortex optimally responds to inputs and maximizes its information capacity. Importantly, avalanche dynamics allow for the emergence of a subset of avalanches, the coherence potentials. They emerge when the synchronization of a local neuronal group exceeds a local threshold, at which the system spawns replicas of the local group activity at distant network sites. The functional importance of coherence potentials will be discussed in the context of propagating structures, such as gliders in balanced cellular automata. Gliders constitute local population dynamics that replicate in space after a finite number of generations and are thought to provide cellular automata with universal computation. Avalanches and coherence potentials are proposed to constitute a modern framework of cortical synchronization dynamics that underlies brain function.

Plenz, D.

2012-05-01

26

Single and multiple sensor identification of avalanche-generated infrasound  

Microsoft Academic Search

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

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

2007-01-01

27

Kinetic description of avalanching systems.  

PubMed

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

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

2005-09-01

28

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, Özkan; Tapan, ?lhan; Veenhof, Rob

2013-08-01

29

Emitter Avalanche Stress on Gated Transistors  

Microsoft Academic Search

Emitter avalanche stress is of growing importance for the study of dielectric coatings on semiconductors and for the investigation of the reliability of devices. In particular certain similarities between the behaviour during high temperature reverse bias testing and B-B avalanching indicate that a study of the failure modes occurring during E-B avalanche stress can provide information on the phenomena occurring

C. A. Bosselaar

1970-01-01

30

RESULTS OF RECENT INFRASOUND AVALANCHE MONITORING STUDIES  

Microsoft Academic Search

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

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

31

Sound-Producing Sand Avalanches  

NSDL National Science Digital Library

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

Bretz, Michael; Nori, Franco; Sholtz, Paul

2007-05-18

32

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

33

Statistical properties of directed avalanches  

NASA Astrophysics Data System (ADS)

A two-dimensional directed stochastic sandpile model is studied both numerically and analytically. One of the known analytical approaches is extended by considering general stochastic toppling rules. The probability density distribution for the first-passage time of stochastic process described by a nonlinear Langevin equation with power-law dependence of the diffusion coefficient is obtained. Large-scale Monte Carlo simulations are performed with the aim to analyze statistical properties of the avalanches, such as the asymmetry between the initial and final stages, scaling of voids and the width of the thickest branch. Comparison with random walks description is drawn and different plausible scenarios for the avalanche evolution and the scaling exponents are suggested.

Bunzarova, N. Zh.

2010-09-01

34

Statistical properties of directed avalanches.  

PubMed

A two-dimensional directed stochastic sandpile model is studied both numerically and analytically. One of the known analytical approaches is extended by considering general stochastic toppling rules. The probability density distribution for the first-passage time of stochastic process described by a nonlinear Langevin equation with power-law dependence of the diffusion coefficient is obtained. Large-scale Monte Carlo simulations are performed with the aim to analyze statistical properties of the avalanches, such as the asymmetry between the initial and final stages, scaling of voids and the width of the thickest branch. Comparison with random walks description is drawn and different plausible scenarios for the avalanche evolution and the scaling exponents are suggested. PMID:21230034

Bunzarova, N Zh

2010-09-01

35

Neuronal avalanches and brain plasticity  

NASA Astrophysics Data System (ADS)

Networks of living neurons exhibit an avalanche mode of activity, experimentally found in organotypic cultures. Moreover, experimental studies of morphology indicate that neurons develop a network of small-world-like connections, with the possibility of a very high connectivity degree. Here we discuss a recent model based on self-organized criticality, which consists of an electrical network with threshold firing and activity-dependent synapse strengths. The model is implemented on regular and small world lattices and on a scale-free network, the Apollonian network. The system exhibits an avalanche activity with a power law distribution of sizes and durations. The analysis of the power spectra of the electrical signal reproduces very robustly the power law behaviour with the exponent 0.8, experimentally measured in electroencephalogram (EEG) spectra. The exponents are found to be quite stable with respect to initial configurations and strength of plastic remodelling, indicating that universality holds for a wide class of neural network models.

de Arcangelis, L.; Herrmann, H. J.; Perrone-Capano, C.

2007-12-01

36

Internal avalanches and restructuring in granular media  

NASA Astrophysics Data System (ADS)

We study the phenomenon of internal avalanching within the context of recently proposed “Tetris” lattice models for granular media. We consider a packing of particles subjected to two different dynamics. In the first case, we arrest the system at different instances during an “aging” dynamics during which the packing slowly compactifies under shaking, and study the distribution of internal avalanches at each of these instances. In the second case, we define a recycling dynamics under which the system reaches a steady state under continued avalanching. We study the distribution of avalanches in this steady state. In the former case we investigate numerically the effect of the density of the medium on the avalanche distribution. In the latter case we develop a mean-field theory to help understand the reciprocal effect of the avalanches on the medium.

Krishnamurthy, S.; Loreto, V.; Herrmann, H. J.; Roux, S.

1999-08-01

37

Global landslide and avalanche hotspots  

Microsoft Academic Search

Allocating resources for natural hazard risk management has high priority in development banks and international agencies\\u000a working in developing countries. Global hazard and risk maps for landslides and avalanches were developed to identify the\\u000a most exposed countries. Based on the global datasets of climate, lithology, earthquake activity, and topography, areas with\\u000a the highest hazard, or “hotspots”, were identified. The applied

Farrokh Nadim; Oddvar Kjekstad; Pascal Peduzzi; Christian Herold; Christian Jaedicke

2006-01-01

38

Avalanche Dynamics in Microfracturing Phenomena.  

NASA Astrophysics Data System (ADS)

We study a mesoscopic scalar model for microfracturing processes. The model can reproduce the avalanche behavior observed in acoustic emission experiments (A. Petri, G. Paparo, A. Vespignani, A. Alippi and M. Costantini, Phys. Rev. Lett. 73, 3423 (1994)) on disordered materials. We can as well characterize the geometrical and topological properties of the microfracturing processes that drive the system to a self-organized stationary state.

Zapperi, Stefano; Stanley, H. Eugene; Vespignani, Alessandro

1996-03-01

39

GIS-aided avalanche warning in Norway  

NASA Astrophysics Data System (ADS)

Avalanche warning for large areas requires the processing of an extensive amount of data. Information relating to the three basic requirements for avalanche warning – knowledge of terrain, the snow conditions, and the weather – needs to be available for the forecaster. The information is highly variable in time. The form and visualization of the data is often decisive for the use by the avalanche forecasters and therefore also for the quality of the produced forecasts. Avalanche warnings can be issued at different scales from national to regional and down to object specific. Often the same warning service is working at different scales and for different clients requiring a flexible and scalable approach. The workflow for producing avalanche forecasts must be extremely efficient – all the way from acquiring observation data, evaluating the situation, down to publishing the new forecast. In this study it has been an aim to include the entire workflow in a single web application. A Geographic Information Systems (GIS) solution was chosen to include all data needed by the forecaster for the avalanche danger evaluation. This interactive system of maps features background information for the entire country, such as topographic maps, slope steepness, aspect, hill shades and satellite images. In each avalanche warning area, all active avalanche paths are plotted including information on wind exposure. Each avalanche path is linked to a webpage with more details, such as fall height, release area elevation and pictures. The avalanche path webpage also includes information on the object at risk e.g. buildings, roads, or other objects. Thus, the forecaster can easily get an overview on the overall situation and focus on single avalanche paths to generate detailed avalanche warnings for the client.

Jaedicke, Christian; Syre, Egil; Sverdrup-Thygeson, Kjetil

2014-05-01

40

Snow Supporting Structures for Avalanche Hazard Reduction, 151 Avalanche, Highway US 89/191, Jackson, Wyoming.  

National Technical Information Service (NTIS)

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

J. Hewes P. Wood R. Decker S. Merry

2009-01-01

41

Shocks Generate Crossover Behavior in Lattice Avalanches  

NASA Astrophysics Data System (ADS)

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.

Burridge, James

2013-11-01

42

Avalanche dynamics of elastic interfaces  

NASA Astrophysics Data System (ADS)

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?duc (duc=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=duc. 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? for dimension davalanche-size distribution, and how the instanton relates to the response to an infinitesimal step in the force.

Le Doussal, Pierre; Wiese, Kay Jörg

2013-08-01

43

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

44

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

45

Avalanche!--Teachable Moments in Outdoor Education  

ERIC Educational Resources Information Center

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

Galloway, Shayne

2005-01-01

46

Silicon-indium-gallium-arsenide avalanche photodetectors  

Microsoft Academic Search

Current optical communications systems rely heavily on avalanche photodetectors (APDs) to detect light exiting an optical fiber. APDs have two functions, the absorption and conversion of light to an electrical signal and the amplification of that signal through avalanche multiplication. With the advantage of internal amplification, the speed and sensitivity performance of APDs are unmatched by other types of detectors.

Aaron Roe Hawkins

1998-01-01

47

Field management of avalanche victims.  

PubMed

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 non-buried, persons. Survival probability in completely-buried victims in open areas (n=638) plummets from 91% 18 min after burial to 34% at 35 min, then remains fairly constant until a second drop after 90 min. Likewise, survival probability for completely-buried victims in buildings or on roads (n=97) decreases rapidly following burial initially, but as from 35 min it is significantly higher than that for victims in open areas, with a maximum difference in respective survival probability (31% versus 7%) from 130 to 190 min (P<0.001). Standardised guidelines are introduced for the field management of avalanche victims. Strategy by rescuers confronted with the triad hypoxia, hypercapnia and hypothermia is primarily governed by the length of snow burial and victim's core temperature, in the absence of obviously fatal injuries. With a burial time < or =35 min survival depends on preventing asphyxia by rapid extrication and immediate airway management; cardiopulmonary resuscitation for unconscious victims without spontaneous respiration. With a burial time >35 min combating hypothermia becomes of paramount importance. Thus, gentle extrication, ECG and core temperature monitoring and body insulation are mandatory; unresponsive victims should be intubated and pulseless victims with core temperature <32 degrees C (89.6 degrees F) (prerequisites being an air pocket and free airways) transported with continuous cardiopulmonary resuscitation to a specialist hospital for extracorporeal re-warming. PMID:11719168

Brugger, H; Durrer, B; Adler-Kastner, L; Falk, M; Tschirky, F

2001-10-01

48

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

49

RECENT STUDIES USING INFRASOUND SENSORS TO REMOTELY MONITOR AVALANCHE ACTIVITY  

Microsoft Academic Search

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

Robert H. Comey; Tim Mendenhall

50

Statistical properties of avalanches in networks.  

PubMed

We characterize the distributions of size and duration of avalanches propagating in complex networks. By an avalanche we mean the sequence of events initiated by the externally stimulated excitation of a network node, which may, with some probability, then stimulate subsequent excitations of the nodes to which it is connected, resulting in a cascade of excitations. This type of process is relevant to a wide variety of situations, including neuroscience, cascading failures on electrical power grids, and epidemiology. We find that the statistics of avalanches can be characterized in terms of the largest eigenvalue and corresponding eigenvector of an appropriate adjacency matrix that encodes the structure of the network. By using mean-field analyses, previous studies of avalanches in networks have not considered the effect of network structure on the distribution of size and duration of avalanches. Our results apply to individual networks (rather than network ensembles) and provide expressions for the distributions of size and duration of avalanches starting at particular nodes in the network. These findings might find application in the analysis of branching processes in networks, such as cascading power grid failures and critical brain dynamics. In particular, our results show that some experimental signatures of critical brain dynamics (i.e., power-law distributions of size and duration of neuronal avalanches) are robust to complex underlying network topologies. PMID:23005186

Larremore, Daniel B; Carpenter, Marshall Y; Ott, Edward; Restrepo, Juan G

2012-06-01

51

Statistical properties of avalanches in networks  

NASA Astrophysics Data System (ADS)

We characterize the distributions of size and duration of avalanches propagating in complex networks. By an avalanche we mean the sequence of events initiated by the externally stimulated excitation of a network node, which may, with some probability, then stimulate subsequent excitations of the nodes to which it is connected, resulting in a cascade of excitations. This type of process is relevant to a wide variety of situations, including neuroscience, cascading failures on electrical power grids, and epidemiology. We find that the statistics of avalanches can be characterized in terms of the largest eigenvalue and corresponding eigenvector of an appropriate adjacency matrix that encodes the structure of the network. By using mean-field analyses, previous studies of avalanches in networks have not considered the effect of network structure on the distribution of size and duration of avalanches. Our results apply to individual networks (rather than network ensembles) and provide expressions for the distributions of size and duration of avalanches starting at particular nodes in the network. These findings might find application in the analysis of branching processes in networks, such as cascading power grid failures and critical brain dynamics. In particular, our results show that some experimental signatures of critical brain dynamics (i.e., power-law distributions of size and duration of neuronal avalanches) are robust to complex underlying network topologies.

Larremore, Daniel B.; Carpenter, Marshall Y.; Ott, Edward; Restrepo, Juan G.

2012-06-01

52

SPICE modeling for single photon avalanche diode  

NASA Astrophysics Data System (ADS)

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

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

2013-08-01

53

Avalanche photodiodes for electromagnetic calorimeters  

NASA Astrophysics Data System (ADS)

Hamamatsu S8148 silicon avalanche photodiode (APD) working in proportional mode has been chosen as readout device for the PbWO 4 crystals in the barrel of the CMS electromagnetic calorimeter (ECAL). High hadron fluences strongly affect the main parameters of both the scintillation crystals and the silicon detectors. In this work, we offer a new zinc sulfide-silicon (ZnS-Si) isotype heterojunction APD structure that is able to operate in high-radiation levels. A Monte Carlo simulation code has been performed in order to compare the Hamamatsu S8148 and the ZnS-Si APD structures for the photons emitting from PbWO 4 crystal during 10 years of CMS operation. Based on this work, the performance of these two APD structures has been investigated.

Pilicer, Ercan; Kocak, Fatma; Tapan, Ilhan; Ahmetoglu (Afrailov), Muhitdin

2007-03-01

54

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

55

Silicon Avalanche Photodiode Active-Quenching Circuit.  

National Technical Information Service (NTIS)

Research has shown that actively-quenched silicon avalanche photodiodes (APD) can be successfully operated throughout the visible region. Two patented circuits exist which have been assembled as printed circuit board prototypes. A silicon hybrid of the mo...

M. Johnson R. Jones

1990-01-01

56

Microchannel avalanche photodiode with broad linearity range  

Microsoft Academic Search

Design and operation principles of a new microchannel avalanche photodiode with an avalanche multiplication coefficient of\\u000a up to 105 and a linearity range expanded by an order of magnitude compared to the existing analogs are described. A distinctive feature\\u000a of the new device design is that the forward-biased p_n junctions (playing the role of individual quenching resistors) are situated under

Z. Sadygov; A. Ol’shevskii; N. Anfimov; T. Bokova; A. Dovlatov; V. Zhezher; Z. Krumshtein; R. Mekhtieva; R. Mukhtarov; M. Troitskaya; V. Chalyshev; I. Chirikov-Zorin; V. Shukurova

2010-01-01

57

Controlled avalanche transit-time triode amplifiers  

NASA Astrophysics Data System (ADS)

The purpose of this work is to study the theoretical effects of avalanche multiplication and collector transit time on microwave controlled avalanche transit-time triode (CATT) devices. The objectives of this report are to obtain a better device model, develop a complete one-dimensional large-signal simulation computer program, calculate the large-signal performance of Class C CATT amplifiers and make a comparison between Class C CATT and Class C BJT amplifiers.

Lee, S. W.

1980-11-01

58

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.

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

2012-04-01

59

Mechanisms of large rock avalanche propagation  

NASA Astrophysics Data System (ADS)

Large rock avalanches present a serious mountain hazard to lifelines, infrastructure and lives. They are one of a class of low frequency, high impact events for which there is a still considerable debate over the transport mechanism. The behaviour of large rock avalanches, sometimes referred to as sturzstrom or "stream flow" after Heim, is characterised by a volumetric dependence, so that very large rock avalanches tend to travel with a greater spreading "efficiency" than smaller ones. In this work we propose a mechanism for the volumetric dependence of rock avalanche spread (or runout) in light of the ubiquitous dynamic fragmentation behaviour of brittle solids, Terzaghi's principle of effective stress as used most commonly in soil mechanics, and concepts of momentum transfer. The proposed conceptual model is based on both observations of field scale events, such as made at Elm in Switzerland, Huascaran in Peru and Falling Mountain in New Zealand, and small scale physical model experiments using analogue rock materials which have been conducted at elevated g-level so as to increase stress levels within the experiments. In particular the model aims to explain how momentum transfer between elements within a fragmenting rock avalanche mass may lead to the greater mobility or spreading efficiency that is observed at large scale and may provide insight as to the conditions needed for rock avalanche propagation and arrest.

Bowman, Elisabeth

2014-05-01

60

Modeling temporal fluctuations in avalanching systems  

NASA Astrophysics Data System (ADS)

We demonstrate how to model the toppling activity in avalanching systems by stochastic differential equations (SDEs). The theory is developed as a generalization of the classical mean-field approach to sandpile dynamics by formulating it as a generalization of Itô’s SDE. This equation contains a fractional Gaussian noise term representing the branching of an avalanche into small active clusters and a drift term reflecting the tendency for small avalanches to grow and large avalanches to be constricted by the finite system size. If one defines avalanching to take place when the toppling activity exceeds a certain threshold, the stochastic model allows us to compute the avalanche exponents in the continum limit as functions of the Hurst exponent of the noise. The results are found to agree well with numerical simulations in the Bak-Tang-Wiesenfeld and Zhang sandpile models. The stochastic model also provides a method for computing the probability density functions of the fluctuations in the toppling activity itself. We show that the sandpiles do not belong to the class of phenomena giving rise to universal non-Gaussian probability density functions for the global activity. Moreover, we demonstrate essential differences between the fluctuations of total kinetic energy in a two-dimensional turbulence simulation and the toppling activity in sandpiles.

Rypdal, M.; Rypdal, K.

2008-11-01

61

Avalanche grainflow on a simulated aeolian dune  

NASA Astrophysics Data System (ADS)

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

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

2013-09-01

62

Evolution of the average avalanche shape with the universality class  

NASA Astrophysics Data System (ADS)

A multitude of systems ranging from the Barkhausen effect in ferromagnetic materials to plastic deformation and earthquakes respond to slow external driving by exhibiting intermittent, scale-free avalanche dynamics or crackling noise. The avalanches are power-law distributed in size, and have a typical average shape: these are the two most important signatures of avalanching systems. Here we show how the average avalanche shape evolves with the universality class of the avalanche dynamics by employing a combination of scaling theory, extensive numerical simulations and data from crack propagation experiments. It follows a simple scaling form parameterized by two numbers, the scaling exponent relating the average avalanche size to its duration and a parameter characterizing the temporal asymmetry of the avalanches. The latter reflects a broken time-reversal symmetry in the avalanche dynamics, emerging from the local nature of the interaction kernel mediating the avalanche dynamics.

Laurson, Lasse; Illa, Xavier; Santucci, Stéphane; Tore Tallakstad, Ken; Måløy, Knut Jørgen; Alava, Mikko J.

2013-12-01

63

Evolution of the average avalanche shape with the universality class.  

PubMed

A multitude of systems ranging from the Barkhausen effect in ferromagnetic materials to plastic deformation and earthquakes respond to slow external driving by exhibiting intermittent, scale-free avalanche dynamics or crackling noise. The avalanches are power-law distributed in size, and have a typical average shape: these are the two most important signatures of avalanching systems. Here we show how the average avalanche shape evolves with the universality class of the avalanche dynamics by employing a combination of scaling theory, extensive numerical simulations and data from crack propagation experiments. It follows a simple scaling form parameterized by two numbers, the scaling exponent relating the average avalanche size to its duration and a parameter characterizing the temporal asymmetry of the avalanches. The latter reflects a broken time-reversal symmetry in the avalanche dynamics, emerging from the local nature of the interaction kernel mediating the avalanche dynamics. PMID:24352571

Laurson, Lasse; Illa, Xavier; Santucci, Stéphane; Tore Tallakstad, Ken; Måløy, Knut Jørgen; Alava, Mikko J

2013-01-01

64

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

65

Erosion dynamics of powder snow avalanches - Observations  

NASA Astrophysics Data System (ADS)

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

Sovilla, Betty; Louge, Michel

2013-04-01

66

High Resolution Radar Measurements of Snow Avalanches  

NASA Astrophysics Data System (ADS)

Geophysical mass flows, such as snow avalanches, are a major hazard in mountainous areas and have a significant impact on the infrastructure, economy and tourism of such regions. Obtaining a thorough understanding of the dynamics of snow avalanches is crucial for risk assessment and the design of defensive structures. However, because the underlying physics is poorly understood there are significant uncertainties concerning current models, which are poorly validated due to a lack of high resolution data. Direct observations of the denser core of a large avalanche are particularly difficult, since it is frequently obscured by the dilute powder cloud. We have developed and installed a phased array FMCW radar system that penetrates the powder cloud and directly images the dense core with a resolution of around 1 m at 50 Hz over the entire slope. We present data from recent avalanches at Vallée de la Sionne that show a wealth of internal structure and allow the tracking of individual fronts, roll waves and surges down the slope for the first time. We also show good agreement between the radar results and existing measurement systems that record data at particular points on the avalanche track.

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

2012-12-01

67

High Resolution Radar Measurements of Snow Avalanches  

NASA Astrophysics Data System (ADS)

Geophysical mass flows, such as snow avalanches, are a major hazard in mountainous areas and have a significant impact on the infrastructure, economy and tourism of such regions. Obtaining a thorough understanding of the dynamics of snow avalanches is crucial for risk assessment and the design of defensive structures. However, because the underlying physics is poorly understood there are significant uncertainties concerning current models, which are poorly validated due to a lack of high resolution data. Direct observations of the denser core of a large avalanche are particularly difficult, since it is frequently obscured by the dilute powder cloud. We have developed and installed a phased array FMCW radar system that penetrates the powder cloud and directly images the dense core with a resolution of around 1 m at 50 Hz over the entire slope. We present data from recent avalanches at Vallee de la Sionne that show a wealth of internal structure and allow the tracking of individual fronts, roll waves and surges down the slope for the first time. We also show good agreement between the radar results and existing measurement systems that record data at particular points on the avalanche track.

McElwaine, Jim; Sovilla, Betty; Vriend, Nathalie; Brennan, Paul; Ash, Matt; Keylock, Chris

2013-04-01

68

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

69

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

70

The application of Landsat data to mapping avalanche hazards  

NASA Technical Reports Server (NTRS)

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

Waterman, S.

1979-01-01

71

Snow Avalanches and Their Control on Railways on Sakhalin Island.  

National Technical Information Service (NTIS)

It is indicated that the inception of snow avalanches is intimately bound up with topographic and climatic characteristics of Sakhalin Island. Data are given that characterize levels of damage inflicted by avalanches on railways. Methods and techniques of...

A. V. Managadze B. A. Anfilofev E. P. Isaenko V. K. Lokhin V. S. Matvienko

1971-01-01

72

Advances in North American Avalanche Technology: 1972 Symposium.  

National Technical Information Service (NTIS)

Seven technical presentations, made in connection with the USDA Forest Service National Avalanche Training Program, discuss acoustic signals emitted by snow under stress, aspects of snow slab mechanics, use of explosives for controlled avalanche release, ...

R. I. Perla

1973-01-01

73

Avalanche Dynamics: Engineering Applications for Land Use Planning.  

National Technical Information Service (NTIS)

Voellmy's (1955) avalanche dynamics equations are reviewed and combined with more recent findings of other workers. Equations are used to estimate flow heights, velocities, specific thrust pressure, maximum specific weight of avalanche debris, and runout ...

C. F. Leaf M. Martinelli

1977-01-01

74

Avalanche Dynamics in a Deposition Model with 'Sliding'.  

National Technical Information Service (NTIS)

In this paper, we investigate the statistical properties of a simple 'avalanche' model in which there is a continuous deposition of mass on a 'tilted substrate, with avalanches occurring whenever the mass at given site reaches a preassigned threshold valu...

Z. Cheng S. Redner P. Meakin F. Family

1989-01-01

75

Predicting extreme avalanches in self-organized critical sandpiles  

NASA Astrophysics Data System (ADS)

In a finite-size Abelian sandpile model, extreme avalanches are repelling each other. Taking a time series of the avalanche size and using a decision variable derived from that, we predict the occurrence of a particularly large avalanche in the next time step. The larger the magnitude of these target avalanches, the better is their predictability. The predictability which is based on a finite-size effect, is discussed as a function of the system size.

Garber, Anja; Hallerberg, Sarah; Kantz, Holger

2009-08-01

76

Identifying single electron avalanches in streamer discharges  

NASA Astrophysics Data System (ADS)

Although some properties of positive streamers in nitrogen-oxygen mixtures, such as velocity and diameter, are remarkably insensitive to the N 2 :O 2 -ratio of the background gas, the visible structure can be quite different. In particular, experiments in high purity nitrogen have demonstrated that streamers can exhibit a feather-like structure, with small hairs connecting to the main streamer channel. Such structures were not observed in mixtures with higher oxygen density, such as air. We hypothesize that these hairs are avalanches started by single electrons that move towards the positively charged streamer head. Using results from numerical simulations, the presence or absence of these hairs can be explained: In air, the electron density outside the streamer channel is high and avalanches overlap, while in high purity nitrogen, the electron density is sufficiently low that avalanches are distinct and visible individually.

Wormeester, Gideon; Nijdam, Sander; Ebert, Ute

2011-11-01

77

Avalanche mode of motion: implications from lunar examples.  

PubMed

A large avalanche (21 square kilometers) at the Apollo 17 landing site moved out several kilometers over flat ground beyond its source slope. If not triggered by impacts, then it was as "efficient" as terrestrial avalanches attributed to air-cushion sliding. Evidently lunar avalanches are able to flow despite the lack of lubricating fluid. PMID:17806579

Howard, K A

1973-06-01

78

Vulnerability assessment in avalanche hazardous areas  

NASA Astrophysics Data System (ADS)

Until a few decades ago, damages and human losses related to the avalanche risk represented only a small part of the destructive effects produced each year by natural events. Nowadays, on the contrary, the situation has considerably changed due to growing of the built-up areas and human presence in the mountain environment: this fact increases the current avalanche risk and puts snow avalanches and hydro-geological risks (floods, landslides, rock falls, etc…) at the same importance level. To mitigate the effects, Authorities provide both specific policies for urban development and mountain land use and simple but reliable methodologies to define the avalanche risk. As is well known, risk can be defined as the product of three factors: the environmental danger P (probability that a given phenomenon with its catastrophic intensity occurs in a specific area and time), the vulnerability V (degree of loss of one or more elements by a natural phenomenon of a known magnitude) and the exposure E (measure of the exposed value for each vulnerable element). A novel approach for the evaluation of the "Vulnerability factor" of a new or existing building under avalanche hazard by considering its structural (materials, strength and robustness, etc…) and architectural (shape, exposure, etc…) peculiarities is presented. A real avalanche event occurred in December, 2008 in Aosta Valley, which caused the total collapse of a building is taken as an example for tesing the effectiveness of the proposed risk assessment. By means of photographical analysis on undamaged parts, local surveys and debris arrangement, the impact pressure and the collapse dynamics are back-analyzed. The results are commented and comparisons between the damages and Vulnerability factor are made.

Frigo, B.; De Biagi, V.; Chiaia, B.

2012-04-01

79

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

80

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

81

Bulk Metallic Glasses Deform via Slip Avalanches  

NASA Astrophysics Data System (ADS)

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.

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

2014-04-01

82

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

83

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

SciTech Connect

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.

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

2007-12-15

84

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

85

High-Efficiency Modes in Avalanche Diodes.  

National Technical Information Service (NTIS)

Some recent experimental results on a high-efficiency mode in avalanche diodes are not explained by the results to date of TRAPATT mode theory despite careful and comprehensive modeling. The note explores one aspect of large-signal theory not previously e...

H. Berger R. J. Sasiela

1970-01-01

86

Using Transistors in the Avalanche Mode.  

National Technical Information Service (NTIS)

A typical feature of the functioning of the transistor in an avalanche mode consists in the marked improvement in the high-frequency and amplifying properties owing to a reduction in the active width of the base, which occurs at high voltages. As a result...

V. D. Dyakonov

1969-01-01

87

Rock avalanches caused by earthquakes: source characteristics.  

PubMed

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 of intensely fractured rock, and exhibited at least one other indicator of low strength or potential instability. PMID:17759365

Keefer, D K

1984-03-23

88

A photomultiplier tube incorporating an avalanche photodiode  

Microsoft Academic Search

A photomultiplier tube incorporating an avalanche photodiode operated in the electron bombardment mode has been developed and tested. It has a large linear dynamic range, can operate with gains up to 106, is unaffected by axial magnetic fields and has been measured to have excellent timing properties. Different versions of the tube were made with bialkali, multi-alkali, and negative electron

P. Cushman; R. Rusack

1993-01-01

89

Fractal avalanche ruptures in biological membranes  

NASA Astrophysics Data System (ADS)

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

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

2010-11-01

90

Measuring acoustic emissions in an avalanche slope  

NASA Astrophysics Data System (ADS)

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

Reiweger, Ingrid; Schweizer, Jürg

2014-05-01

91

Mathematical model of a powder snow avalanche  

NASA Astrophysics Data System (ADS)

A powder snow avalanche of finite length and width is considered as a 3D cloud of dense fluid moving down an incline in an ambient lighter fluid. The shape of the cloud is approximated by a half-ellipsoid with varying dimensions. The model is a generalization of the model proposed by Kulikovskii and Sveshnikova who considered a 2D cloud, i.e. a cloud in the shape of a half-elliptic cylinder. A 3D model takes into account lateral spreading of an avalanche. The equations for calculation of the front and the centre-of-mass velocities of the cloud, mean density, the cloud height, width and length are formulated. The entrainment of ambient air and snow from he slope, as well as sedimentation of the snow particles are taken into account. The forces are gravity, Archimedes force, bed and upper surface friction and the pressure gradient along the avalanche surface arising due to its overflow by air. Motion inside the avalanche is also taken into account. The test calculations are made to describe the possible regimes of motion and to estimate the values of the model coefficients. A comparison with the experimental data and calculations of Beghin and Olagne (1991) is given.

Eglit, Margarita

2013-04-01

92

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

SciTech Connect

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.

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

2007-03-15

93

Nearest neighbour models for local and regional avalanche forecasting  

NASA Astrophysics Data System (ADS)

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

Gassner, M.; Brabec, B.

94

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

95

THE AVALUATOR - A CANADIAN RULE-BASED AVALANCHE DECISION SUPPORT TOOL FOR AMATEUR RECREATIONISTS  

Microsoft Academic Search

5 Parks Canada, Banff AB ABSTRACT: An exceptionally high number of avalanche fatalities during the winter of 2003 forced the Canadian avalanche community to question the effectiveness of existing public ava- lanche safety programs in Canada. In response to the recommendations of several avalanche safety reviews, the Canadian Avalanche Association launched the ADFAR (Avalanche Decision Framework for Amateur Recreationists) Project

Pascal Haegeli; Ian McCammon; Bruce Jamieson; Grant Statham

96

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

97

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

98

Driving pockels cells using avalanche transistor pulsers  

SciTech Connect

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

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

1997-05-28

99

Hierarchical networks, power laws, and neuronal avalanches  

NASA Astrophysics Data System (ADS)

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.

Friedman, Eric J.; Landsberg, Adam S.

2013-03-01

100

Nonuniform thermal conductance in avalanche microwave oscillators  

Microsoft Academic Search

The local dc current densityj(x)in avalanche microwave oscillators is a function of the local breakdown voltageV_{b}(x), which in turn depends on local temperatureT(x)and fieldE(x). Recent progress in junction fabrication has led to very uniform field distributions such that local temperature variations of the order of a few degrees are no longer negligible, calculations ofT(x)for various diode configurations show that the

R. H. Haitz

1968-01-01

101

Avalanches and Damage Clusters in Fracture Processes  

Microsoft Academic Search

By simulating two-dimensional models of electric breakdown and fracture it is possible to characterize the rupture of disordered\\u000a materials subject to an increasing external stress. We provide a review of numerical and analytical results concerning the\\u000a scaling properties of avalanche events prior the macroscopic breakdown of the material. The obtained results suggest a scenario\\u000a that describes fractures as a firstorder

Stefano Zapperi; Purusattam Ray; H. Eugene Stanley; Alessandro Vespignani

2001-01-01

102

Microchannel avalanche photodiode with wide linearity range  

Microsoft Academic Search

Design and physical operation principles of new microchannel avalanche\\u000aphotodiode (MC APD) with gain up to 10^5 and linearity range improved an order\\u000aof magnitude compared to known similar devices. A distinctive feature of the\\u000anew device is a directly biased p-n junction under each pixel which plays role\\u000aof an individual quenching resistor. This allows increasing pixel density up

Z. Sadygov; A. Olshevski; N. Anphimov; T. Bokova; V. Chalyshev; I. Chirikov-Zorin; A. Dovlatov; Z. Krumshtein; R. Mekhtieva; R. Mukhtarov; V. Shukurova; M. Troitskaya; V. Zhezher

2010-01-01

103

Renormalization of one-dimensional avalanche models  

NASA Astrophysics Data System (ADS)

We investigate a renormalization group (RG) scheme for avalanche automata introduced recently by Pietronero et al. to explain universality in self-organized criticality models. Using a modified approach, we construct exact RG equations for a one-dimensional model whose detailed dynamics is exactly solvable. We then investigate in detail the effect of approximations inherent in a practical implementation of the RG transformation where exact dynamical information is unavailable.

Hasty, Jeff; Wiesenfeld, Kurt

1997-03-01

104

Reproducibility of Magnetic Avalanches in a Ferromagnet  

NASA Astrophysics Data System (ADS)

We have been studying the Barkhausen effect (magnetic avalanches produced by the motion of domain walls) in an unsual Fe-Ni-Co ferromagnet that allows us to repeatedly prepare the magnet in a particular disordered domain configuration. We have found that the avalanche sequence produced as the system is forced out of this configuration by an applied magnetic field has features that are almost exactly reproducible (events that occur at the same field on every cycle) intermingled with events that show no apparent reproducibility.(J.S. Urbach, R.C. Madison, J.T. Markert, Phys. Rev. Lett., 12/11/95.) Averaging the avalanche activity over many cycles produces a fingerprint, analogous to effects observed in mesoscopic samples, that reflects the quenched disorder in the material. The fingerprint is not strongly temperature or driving-rate dependent, indicating that the variability is a consequence of dynamical effects. We also have found that the slope of the cycle-averaged magnetization, d/dH, is correlated with the cycle-to-cycle variations in magnetization, <(?M)^2>, suggesting an analogy with the fluctuation-dissipation relationship of equilibrium thermodynamics.

Urbach, J. S.; Madison, R. C.; Markert, J. T.

1996-03-01

105

Simulation of electron avalanches using Geant4  

NASA Astrophysics Data System (ADS)

Self-sustained electron avalanches have been simulated using the toolkit Geant4, developed at CERN for Monte Carlo simulation of the passage of particles through matter. Some 100 keV seed electrons in air are accelerated by means of an electric field about tens of kV/cm. Air is simulated like a compound of 70% Nitrogen and 30% Oxygen. Geant4 calculates the trajectory of each electron and photon using tabulated values of cross section for electron-atom interactions (ionizations and elastic collisions). The main goal of this research is to evaluate the contribution of different physical processes to the avalanche time evolution at the microscopic scale. Also ?- and X- emissions from the avalanche are reported. The kinetic energy of electrons increases to relativistic values ( MeV), which gives rise to the emission of ?-radiation from Bremsstrahlung process. This kind of radiation has a continuous energy spectrum from tens of keV up to MeV. Also a discrete X-ray emission spectrum has been obtained, which is originated from ionization of Nitrogen and Oxygen atomic K-shell.

Abril, C.; Cristancho, L. F.

2012-04-01

106

Avalanche in adhesion. [interfacial separation between two Ni crystals  

NASA Technical Reports Server (NTRS)

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

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

1989-01-01

107

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

PubMed

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

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

2014-05-01

108

From waves to avalanches: Two different mechanisms of sandpile dynamics  

NASA Astrophysics Data System (ADS)

Time series resulting from wave decomposition show the existence of different correlation patterns for avalanche dynamics. For the d=2 Bak-Tang-Wisenfeld model, long range correlations determine a modification of the wave size distribution under coarse graining in time, and multifractal scaling for avalanches. In the Manna model, the distribution of avalanche coincides with that of waves, which are uncorrelated and obey finite size scaling, a result expected also for the d=3 Bak-Tang-Wiesenfeld sandpile.

de Menech, Mario; Stella, Attilio L.

2000-10-01

109

Viscoelastic Effects in Avalanche Dynamics: A Key to Earthquake Statistics  

NASA Astrophysics Data System (ADS)

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

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

2014-05-01

110

Cold Regions Science and Engineering Part 3: Engineering; Section A3; Snow Technology, Avalanches.  

National Technical Information Service (NTIS)

The monograph contains a comprehensive review of the formation and occurrence of avalanches together with a technical treatment of the principles and practice of avalanche defense. Major sections deal with avalanche hazard, snowfall and snow cover, avalan...

M. Mellor

1968-01-01

111

Avalanche exponents and corrections to scaling for a stochastic sandpile  

NASA Astrophysics Data System (ADS)

We study distributions of dissipative and nondissipative avalanches in Manna’s stochastic sandpile, in one and two dimensions. Our results lead to the following conclusions: (1) avalanche distributions, in general, do not follow simple power laws, but rather have the form P(s)˜s-?s(ln s)?f(s/sc), with f a cutoff function; (2) the exponents for sizes of dissipative avalanches in two dimensions differ markedly from the corresponding values for the Bak-Tang-Wiesenfeld (BTW) model, implying that the BTW and Manna models belong to distinct universality classes; (3) dissipative avalanche distributions obey finite-size scaling, unlike in the BTW model.

Dickman, R.; Campelo, J. M.

2003-06-01

112

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

113

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

114

Spectral Matching Properties between Avalanche Photodiodes and Typical Objects  

Microsoft Academic Search

Avalanche photodiode detector has come to more and more attention due to single photon detection sensitivity, low noise in night vision field. However, avalanche photodiodes (APD) made of different materials have different photon detection efficiency characteristics. The spectral matching factors were computed and analyzed based on the spectrums of night sky, Si APD & InGaAs APD and typical object under

Liju Yin; Qian Chen; Canlin Zhang

2009-01-01

115

Climate database for avalanche consulting and warning in Norway  

Microsoft Academic Search

Climate data is an essential tool for the study of weather induced geophysical processes like avalanches. Climate data provides on overview of normal and extreme weather conditions at a given location. This information can be used in risk analysis for the evaluation of past avalanche events and for every day forecasting services. The data can be analyzed for the return

Christian Jaedicke; Steinar Bakkehøi

2007-01-01

116

Avalanches mediate crystallization in a hard-sphere glass  

PubMed Central

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.

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

2014-01-01

117

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.

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

2013-01-01

118

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

119

Photon detection with cooled avalanche photodiodes  

NASA Technical Reports Server (NTRS)

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

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

1987-01-01

120

Cooled avalanche photodiode used for photon detection  

NASA Technical Reports Server (NTRS)

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

Robinson, Deborah L.; Metscher, Brian D.

1987-01-01

121

Lifetime of Bubble Rafts: Cooperativity and Avalanches  

NASA Astrophysics Data System (ADS)

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

Ritacco, Hernán; Kiefer, Flavien; Langevin, Dominique

2007-06-01

122

Lifetime of bubble rafts: cooperativity and avalanches.  

PubMed

We have studied the collapse of pseudo-bi-dimensional foams. These foams are made of uniformly sized soap bubbles packed in an hexagonal lattice sitting at the top of a liquid surface. The collapse process follows the sequence: (1) rupture of a first bubble, driven by thermal fluctuations and (2) a cascade of bursting bubbles. We present a simple numerical model which captures the main characteristics of the dynamics of foam collapse. We show that in a certain range of viscosities of the foaming solutions, the size distribution of the avalanches follows power laws as in self-organized criticality processes. PMID:17677967

Ritacco, Hernán; Kiefer, Flavien; Langevin, Dominique

2007-06-15

123

Temperature characteristics of silicon avalanche photodiodes  

NASA Astrophysics Data System (ADS)

The paper presents the results of studies on temperature dependence of such parameters as a dark current, noise current, gain, noise equivalent power and detectivity of silicon epiplanar avalanche photodiodes at the ITE. The photodiode reach-through structure is of an nPLU-p-(pi) - p+ type with an under-contact ring and a channel stopper. The temperature range was stretching from -40 C to +40 C. Specially developed for this purpose an automatic system for low noise measurements was used. A two- stage micro-cooler with a Peltier's element was applied to control and stabilize the temperature of measured structures.

Wegrzecka, Iwona; Grynglas, Maria; Wegrzecki, Maciej; Bar, Jan; Grodecki, Remigiusz

2001-08-01

124

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

125

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

126

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

127

Avalanche prediction in a self-organized pile of beads.  

PubMed

It is a common belief that power-law distributed avalanches are inherently unpredictable. This idea affects phenomena as diverse as evolution, earthquakes, superconducting vortices, stock markets, etc., from atomic to social scales. It mainly comes from the concept of "self-organized criticality" (SOC), where criticality is interpreted in the way that, at any moment, any small avalanche can eventually cascade into a large event. Nevertheless, this work demonstrates experimentally the possibility of avalanche prediction in the classical paradigm of SOC: a pile of grains. By knowing the position of every grain in a two-dimensional pile, avalanches of moving grains follow a distinct power-law distribution. Large avalanches, although uncorrelated, are on average preceded by continuous, detectable variations in the internal structure of the pile that are monitored in order to achieve prediction. PMID:19257719

Ramos, O; Altshuler, E; Måløy, K J

2009-02-20

128

Avalanches and the distribution of solar flares  

NASA Technical Reports Server (NTRS)

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

Lu, Edward T.; Hamilton, Russell J.

1991-01-01

129

III-nitride photon counting avalanche photodiodes  

NASA Astrophysics Data System (ADS)

In order for solar and visible blind III-nitride based photodetectors to effectively compete with the detective performance of PMT there is a need to develop photodetectors that take advantage of low noise avalanche gain. Furthermore, in certain applications, it is desirable to obtain UV photon counting performance. In this paper, we review the characteristics of III-nitride visible-blind avalanche photodetectors (APDs), and present the state-of-the-art results on photon counting based on the Geiger mode operation of GaN APDs. The devices are fabricated on transparent AlN templates specifically for back-illumination in order to enhance hole-initiated multiplication. The spectral response and Geiger-mode photon counting performance are analyzed under low photon fluxes, with single photon detection capabilities being demonstrated in smaller devices. Other major technical issues associated with the realization of high-quality visible-blind APDs and Geiger mode APDs are also discussed in detail and solutions to the major problems are described where available. Finally, future prospects for improving upon the performance of these devices are outlined.

McClintock, Ryan; Pau, Jose L.; Minder, Kathryn; Bayram, Can; Razeghi, Manijeh

2008-01-01

130

FORECASTING SNOW AVALANCHE DAYS FROM METEOROLOGICAL DATA USING CLASSIFICATION TREES; GRASDALEN, WESTERN NORWAY  

Microsoft Academic Search

Avalanches pose one of the most serious problems to infrastructure and people in the mountains in Norway. Processes leading to avalanche release are deterministic but the time and place of avalanche release is notoriously difficult to predict. Statistical approaches using meteorological parameters to predict the probability of natural avalanche release provide an alternative to deterministic prediction. We used classification trees

Kalle Kronholm; Dagrun Vikhamar-Schuler; Christian Jaedicke; Ketil Isaksen; Asgeir Sorteberg; Krister Kristensen

2006-01-01

131

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 Üzengili (Bayburt province) in 1993 and Yaylaönü (Trabzon province) in 1981. The results demonstrate the value of such an approach for regions with poor avalanche databases, enabling the calculation of different scenarios and the estimation of run-out distances, impact pressure and flow height.

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

2014-05-01

132

Record-Breaking Avalanches in Driven Threshold Systems  

NASA Astrophysics Data System (ADS)

Record-breaking avalanches generated by the dynamics of several driven nonlinear threshold models are analyzed. Such systems are characterized by intermittent behaviour, where 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, Manna model, Olami-Feder-Christensen (OFC) model, and the forest-fire model to investigate the record-breaking statistics of model avalanches which 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 are also compared to that of record-breaking events extracted from the sequences of independent identically distributed (i.i.d.) random variables. It is found that the statistics of record-breaking avalanches for the above cellular automata exhibit behaviour different from that observed for i.i.d. random variables which in turn can be used to characterize complex spatio-temporal 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 spatio-temporal correlations.

Shcherbakov, Robert

2013-04-01

133

Record-breaking avalanches in driven threshold systems  

NASA Astrophysics Data System (ADS)

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

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

2013-05-01

134

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.

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

2003-04-01

135

Statistical Analyses Support Power Law Distributions Found in Neuronal Avalanches  

PubMed Central

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.

Klaus, Andreas; Yu, Shan; Plenz, Dietmar

2011-01-01

136

III-V alloy heterostructure high speed avalanche photodiodes  

NASA Technical Reports Server (NTRS)

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

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

1979-01-01

137

Characterization of avalanche photodiodes for lidar atmospheric return signal detectors  

NASA Technical Reports Server (NTRS)

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

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

1988-01-01

138

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. The mode structure and mode amplitudes are measured with arrays of reflectometers and Mirnov coils. The amplitude of individual modes, and rms amplitude of all TAEs are found to increase by an order of magnitude, coupled with strong downward frequency chirps in the final burst. Fast ion redistribution is seen for the energies > 30 keV with a Neutral Particle Analyzer diagnostic. The plasma equilibrium is reconstructed using Thomson scattering profile and multi-channel Motional Stark Effect data. The NOVA-k code has been used to simulate the eigenmode structures, matched to the measured radial profiles and mode frequencies and are used to simulate the effect of the TAE on fast ion transport with ORBIT.

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

2008-11-01

139

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 world’s largest system of reservoirs, located in the Brazilian semiarid northeast, we reveal that surprisingly it self-organizes into a scale-free network exhibiting also a power-law in the distribution of the lakes and avalanches of discharges. With a new self-organized-criticality-type model we manage to explain the novel critical exponents. Implementing a flow model we are able to reproduce the measured overspill evolution providing a tool for catastrophe mitigation and future planning.

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

2012-01-01

140

High-resolution radar measurements of snow avalanches  

NASA Astrophysics Data System (ADS)

Two snow avalanches that occurred in the winter 2010-2011 at Vallée de la Sionne, Switzerland, are studied using a new phased array FMCW radar system with unprecedented spatial resolution. The 5.3 GHz radar penetrates through the powder cloud and reflects off the underlying denser core. Data are recorded at 50 Hz and have a range resolution better than 1 m over the entire avalanche track. We are able to demonstrate good agreement between the radar results and existing measurement systems that record at particular points on the avalanche track. The radar data reveal a wealth of structure in the avalanche and allow the tracking of individual fronts and surges down the slope for the first time.

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

2013-02-01

141

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

142

Avalanche Multiplication as a Gain Mechanism in Photodiodes.  

National Technical Information Service (NTIS)

The feasibility of a fast, high-gain photodetector based on the phenomenon of avalanche multiplication in semiconductors has been investigated. Such a detector would be a definite requirement for communication systems using light as a carrier, as well as ...

H. W. Ruegg

1966-01-01

143

Avalanche Erosion: Four Years of Measurements from the Guggigraben, Switzerland  

NASA Astrophysics Data System (ADS)

While the geomorphic significance of avalanche erosion has been recognized for some time, relatively few quantitative studies exist that examine their effects in sculpting bedrock landforms and transporting sediment from the upper reaches catchments to adjacent fans and river systems. Large unknowns thus remain as to the efficacy and mechanics of avalanche erosion, and its relative role in mass transfer in alpine mountain belts. Here we present results of field investigations at the Guggigraben catchment (Matter Valley, Switzerland) where we measured transported sediment loads and calculated catchment-wide erosion rates over four years. We further discuss the origin of transported sediment, describe typical features of dirty avalanche deposits, use numerical modeling to predict flow velocities and impact pressures, and comment on mechanisms of bedrock erosion by particle-bed interactions. Combined results highlight the relative importance of avalanche erosion in catchment-scale denudation and mass redistribution, as well as in aiding incision and widening of bedrock gullies.

Moore, J. R.; Egloff, J.; Nagelisen, J.; Hunziker, M.; Aerne, U.; Christen, M.

2013-12-01

144

Narrow-Band Inverted Homo-Heterojunction Avalanche Photodiode.  

National Technical Information Service (NTIS)

The patent application describes a narrow-band, inverted homo-heterojunction avalanche photodiode, configured in the shape of a mesa situated upon a substrate which is transparent to selected light energy wavelengths. The diode is inverted for operation s...

R. C. Eden

1977-01-01

145

Density dependence of the ionization avalanche in ultracold Rydberg gases  

NASA Astrophysics Data System (ADS)

We report on the behavior of the ionization avalanche in an ensemble of ultracold 87Rb atoms coupled to a high-lying Rydberg state and investigate extensions to the current model by including the effects of three-body recombination and plasma expansion. To separate the two effects we study the time dependence of the plasma formation at various densities as well as for different nS and nD states. At medium densities and low n we observe the onset of the avalanche as has been reported in other experiments, as well as a subsequent turn-off of the avalanche for longer excitation times, which we associate with plasma expansion. At higher densities and for higher-lying Rydberg states we observe a disappearance of the avalanche signature, which we attribute to three-body recombination.

Siercke, M.; Oon, F. E.; Mohan, A.; Wang, Z. W.; Lim, M. J.; Dumke, R.

2014-02-01

146

Design Criteria for Avalanche Control Structures in the Runout Zone.  

National Technical Information Service (NTIS)

Guidelines are given for the design and location of deflecting, catching, retarding, and direct protection structures. Terrain, snow conditions, and type and frequency of avalanches are among the most important criteria for planning structural control of ...

A. I. Mears

1981-01-01

147

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

148

Novel Voltage Limiting Concept for Avalanche Breakdown Protection  

Microsoft Academic Search

Destructive over-voltage breakdown of cellular phone power transistors is prevented by using a new voltage-limiting concept. The output voltage is detected by an avalanche-based detector, and limited by decreasing the output power when needed. The voltage detector contains a low voltage bipolar NPN transistor with a well-defined lower breakdown voltage than the high voltage power transistor. Avalanche current in this

L. Ruijs; A. van Bezooijen; R. Mahmoudi; A. H. M. van Roermund

2006-01-01

149

Self-Structuring of Granular Media under Internal Avalanching  

NASA Astrophysics Data System (ADS)

We study the phenomenon of internal avalanching within the context of recently proposed ``Tetris'' lattice models for granular media. We define a recycling dynamics under which the system reaches a steady state which is self-structured, i.e., it shows a complex interplay between textured internal structures and critical avalanche behavior. Furthermore, we develop a general mean-field theory for this class of systems and discuss possible scenarios for the breakdown of universality.

Krishnamurthy, S.; Loreto, V.; Herrmann, H. J.; Manna, S. S.; Roux, S.

1999-07-01

150

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

151

Avalanche behavior of power MOSFETs under different temperature conditions  

Microsoft Academic Search

The ability of high-voltage power MOSFETs to withstand avalanche events under different temperature conditions are studied by experiment and two-dimensional device simulation. The experiment is performed to investigate dynamic avalanche failure behavior of the domestic power MOSFETs which can occur at the rated maximum operation temperature range (-55 to 150 °C). An advanced ISE TCAD two-dimensional mixed mode simulator with

Lu Jiang; Wang Lixin; Lu Shuojin; Wang Xuesheng; Han Zhengsheng

2011-01-01

152

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

153

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

154

Spatio-temporal avalanche forecasting with Support Vector Machines  

NASA Astrophysics Data System (ADS)

This paper explores the use of the Support Vector Machine (SVM) as a data exploration tool and a predictive engine for spatio-temporal forecasting of snow avalanches. Based on the historical observations of avalanche activity, meteorological conditions and snowpack observations in the field, an SVM is used to build a data-driven spatio-temporal forecast for the local mountain region. It incorporates the outputs of simple physics-based and statistical approaches used to interpolate meteorological and snowpack-related data over a digital elevation model of the region. The interpretation of the produced forecast is discussed, and the quality of the model is validated using observations and avalanche bulletins of the recent years. The insight into the model behaviour is presented to highlight the interpretability of the model, its abilities to produce reliable forecasts for individual avalanche paths and sensitivity to input data. Estimates of prediction uncertainty are obtained with ensemble forecasting. The case study was carried out using data from the avalanche forecasting service in the Locaber region of Scotland, where avalanches are forecast on a daily basis during the winter months.

Pozdnoukhov, A.; Matasci, G.; Kanevski, M.; Purves, R. S.

2011-02-01

155

The effect of thresholding on temporal avalanche statistics  

NASA Astrophysics Data System (ADS)

We discuss intermittent time series consisting of discrete bursts or avalanches separated by waiting or silent times. The short time correlations can be understood to follow from the properties of individual avalanches, while longer time correlations often present in such signals reflect correlations between triggerings of different avalanches. As one possible source of the latter kinds of correlations in experimental time series, we consider the effect of a finite detection threshold, due to e.g. experimental noise that needs to be removed. To this end, we study a simple toy model of an avalanche, a random walk returning to the origin or a Brownian bridge, in the presence and absence of superimposed delta-correlated noise. We discuss the properties after thresholding of artificial time series obtained by mixing toy avalanches and waiting times from a Poisson process. Most of the resulting scalings for individual avalanches and the composite time series can be understood via random walk theory, except for the waiting time distributions when strong additional noise is added. Then, to compare with a more complicated case we study the Manna sandpile model of self-organized criticality, where some further complications appear.

Laurson, Lasse; Illa, Xavier; Alava, Mikko J.

2009-01-01

156

On the complementariness of infrasound and seismic sensors for monitoring snow avalanches  

NASA Astrophysics Data System (ADS)

The paper analyses and compares infrasonic and seismic data from snow avalanches monitored at the Vallée de la Sionne test site in Switzerland from 2009 to 2010. Using a combination of seismic and infrasound sensors, it is possible not only to detect a snow avalanche but also to distinguish between the different flow regimes and to analyse duration, average speed (for sections of the avalanche path) and avalanche size. Different sensitiveness of the seismic and infrasound sensors to the avalanche regimes is shown. Furthermore, the high amplitudes observed in the infrasound signal for one avalanche were modelled assuming that the suspension layer of the avalanche acts as a moving turbulent sound source. Our results show reproducibility for similar avalanches on the same avalanche path.

Kogelnig, A.; Suriñach, E.; Vilajosana, I.; Hübl, J.; Sovilla, B.; Hiller, M.; Dufour, F.

2011-08-01

157

The formation and propagation of flux avalanches in tailored MgB2 films  

NASA Astrophysics Data System (ADS)

The applications of superconducting magnesium diboride are substantially limited by the presence of magnetic flux avalanches at low temperatures. Here, quickly moving magnetic vortices create large amounts of heat and magnetic noise. Such avalanches can be suppressed by evaporating metal layers to the surface of the superconductor, which acts both as a heat sink and as an electromagnetic drag by induced eddy currents. We show that it is necessary to distinguish between the mechanisms that are responsible for the formation and the propagation of avalanches. A high critical current favors avalanche formation but avalanche propagation is suppressed. The diverse consequences for creation and propagation explain the preference of avalanches for inhomogeneous superconductors.

Treiber, S.; Albrecht, J.

2010-09-01

158

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, Jörn; Tiampo, Kristy F

2013-05-01

159

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

160

Avalanches in a stochastic model of spiking neurons.  

PubMed

Neuronal avalanches are a form of spontaneous activity widely observed in cortical slices and other types of nervous tissue, both in vivo and in vitro. They are characterized by irregular, isolated population bursts when many neurons fire together, where the number of spikes per burst obeys a power law distribution. We simulate, using the Gillespie algorithm, a model of neuronal avalanches based on stochastic single neurons. The network consists of excitatory and inhibitory neurons, first with all-to-all connectivity and later with random sparse connectivity. Analyzing our model using the system size expansion, we show that the model obeys the standard Wilson-Cowan equations for large network sizes ( neurons). When excitation and inhibition are closely balanced, networks of thousands of neurons exhibit irregular synchronous activity, including the characteristic power law distribution of avalanche size. We show that these avalanches are due to the balanced network having weakly stable functionally feedforward dynamics, which amplifies some small fluctuations into the large population bursts. Balanced networks are thought to underlie a variety of observed network behaviours and have useful computational properties, such as responding quickly to changes in input. Thus, the appearance of avalanches in such functionally feedforward networks indicates that avalanches may be a simple consequence of a widely present network structure, when neuron dynamics are noisy. An important implication is that a network need not be "critical" for the production of avalanches, so experimentally observed power laws in burst size may be a signature of noisy functionally feedforward structure rather than of, for example, self-organized criticality. PMID:20628615

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

2010-01-01

161

Multi-scale modelling of granular avalanches  

NASA Astrophysics Data System (ADS)

Avalanches, debris flows, and landslides are geophysical hazards, which involve rapid mass movement of granular solids, water and air as a single-phase system. The dynamics of a granular flow involve at least three distinct scales: the micro-scale, meso-scale, and the macro-scale. This study aims to understand the ability of continuum models to capture the micro-mechanics of dry granular collapse. Material Point Method (MPM), a hybrid Lagrangian and Eulerian approach, with Mohr-Coulomb failure criterion is used to describe the continuum behaviour of granular column collapse, while the micromechanics is captured using Discrete Element Method (DEM) with tangential contact force model. The run-out profile predicted by the continuum simulations matches with DEM simulations for columns with small aspect ratios (`h/r' < 2), however MPM predicts larger run-out distances for columns with higher aspect ratios (`h/r' > 2). Energy evolution studies in DEM simulations reveal higher collisional dissipation in the initial free-fall regime for tall columns. The lack of a collisional energy dissipation mechanism in MPM simulations results in larger run-out distances. Micro-structural effects, such as shear band formations, were observed both in DEM and MPM simulations. A sliding flow regime is observed above the distinct passive zone at the core of the column. Velocity profiles obtained from both the scales are compared to understand the reason for a slow flow run-out mobilization in MPM simulations.

Kumar, Krishna; Soga, Kenichi; Delenne, Jean-Yves

2013-06-01

162

Solitary granular avalanches: stability, fingering and theoretical modeling  

NASA Astrophysics Data System (ADS)

Avalanching processes do not only occur in the air as we know of snow avalanches, mud flows and land-slides. Such events frequently happen below the see level as they take many forms from turbidity currents to thick sediment waves. In this study we report results on laboratory scale avalanche experiments taking place both in the air and under-water. In both cases a family of stable solitary erosion/deposition waves is observed [1]. 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 diagrams, the wavelengths selection and the avalanche morphology suggest a common erosion/deposition scenario. We also use these erosion/deposition waves to investigate the dynamics of granular flow and jamming in the frame work of the Partial Fluidization Theory (PFT) proposed by Aronson et al. to describe the dynamics of granular matter near jamming [2]. [1] F. Malloggi et al. Europhysics Letters, 2006, Erosion waves: Transverse instabilities and fingering 75, 825-831 [2] I. S. Aranson et al.. Transverse instability of avalanches in granular flows down an incline. Physical Review E, 2006, 73, 050302; I.S.Aronson et al., Non rheological properties of granular flows: exploring the near jamming limit, preprint (2007).

Malloggi, Florent; Andreotti, Bruno; Clément, Eric; Aronson, Igor; Tsimring, Lev

2008-03-01

163

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

164

Infrasound monitoring of snow avalanches in the Italian 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 2009 we installed a temporary 4-element, small aperture (100 m), infrasound array in the Alps. The array has been deployed south of Mt. Rosa, at an elevation of 2000 m a.s.l. in the valley of Gressoney, where natural avalanches are expected and triggered ones are regularly programmed. The array consists into 4 absolute pressure transducers with a sensitivity of 0.01 Pa in the 0.1-50 Hz frequency band and a 7 channel Guralp CMG-DM24 A/D converter, sampling at 100 Hz. Timing is achieved with a GPS receiver. The array is completely buried in snow. Gel cell batteries and 200 W solar panels provide the array power requirements (~3 W) and should allow a continuous operation during the winter season. 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 pilot experiment in Italy will allow to verify the efficiency of the system, and might represent an important validation to modeled avalanches activity during this winter season.

Ripepe, Maurizio; Ulivieri, Giacomo; Marchetti, Emanuele; Chiambretti, Igor; Segor, Valerio; Pitet, Luca

2010-05-01

165

The Snowy Torrents: Avalanche Accidents in the United States, 1967-71.  

National Technical Information Service (NTIS)

The compilation of 76 avalanche accident reports teaches by example, both good and bad. Commentaries will help those who spend time in the mountains in winter to avoid getting caught in an avalanche, or if caught, how to survive.

K. Williams

1975-01-01

166

Implications of geomorphological research for recent and prehistoric avalanches and related hazards at Huascaran, Peru  

Microsoft Academic Search

Detailed research of superficial deposits below the northern peak of Huascaran (Cordillera Blanca) provides new information\\u000a on the limits of a paleo-avalanche originating from this mountain. Geomorphological mapping of the sediments identified glacial\\u000a deposits, deposits from historical rock-debris avalanches and huge boulders from a paleo-avalanche. Schmidt Hammer rock-hardness\\u000a tests were used to distinguish between the several generations of rock-debris avalanches,

Jan Klimeš; Vít Vilímek; Marek Omelka

2009-01-01

167

Effect of avalanche-induced light emission on the multiplication factor in bipolar junction transistors  

NASA Astrophysics Data System (ADS)

In Si bipolar junction transistors, the base and collector currents, including avalanche effects, are often modeled without accounting for the avalanche-induced light emission. The light absorption and light-induced carrier injection into the avalanche region were therefore neglected. In this paper, we formulate the multiplication factor so as to account for the avalanche-induced carrier injection into the breakdown region and we discuss the mechanism neglected earlier.

Sheng-Lyang Jang

1991-11-01

168

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.

169

Activity-Dependent Model for Neuronal Avalanches  

NASA Astrophysics Data System (ADS)

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

de Arcangelis, L.

170

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

171

Inductive braking of thermomagnetic avalanches in superconducting films  

NASA Astrophysics Data System (ADS)

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

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

2014-05-01

172

The diversity of flux avalanche patterns in superconducting films  

NASA Astrophysics Data System (ADS)

The variety of morphologies in flux patterns created by thermomagnetic dendritic avalanches in type-II superconducting films is investigated using numerical simulations. The avalanches are triggered by introducing a hot spot at the edge of a strip-shaped sample, which is initially prepared in a partially penetrated Bean critical state by slowly ramping the transversely applied magnetic field. The simulation scheme is based on a model accounting for the nonlinear and nonlocal electrodynamics of superconductors in the transverse geometry. By systematically varying the parameters representing the Joule heating, heat conduction in the film, and heat transfer to the substrate, a wide variety of avalanche patterns are formed, and quantitative characterizations of the areal extension, branch width etc are made. The results show that branching is suppressed by the lateral heat diffusion, while large Joule heating gives many branches, and heat removal into the substrate limits the areal size. The morphology shows significant dependence also on the initial flux penetration depth.

Vestgården, J. I.; Shantsev, D. V.; Galperin, Y. M.; Johansen, T. H.

2013-05-01

173

Elementary excitations and avalanches in the Coulomb glass  

NASA Astrophysics Data System (ADS)

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

Palassini, Matteo; Goethe, Martin

2012-07-01

174

Solutions to heavy ion induced avalanche burnout in power devices  

SciTech Connect

Silicon power devices fall into two broad categories, bipolar and field effect. Transistors using both of these technologies are often used in satellite applications for power conversion. The present trend is toward integrating power transistors and control electronics on the same chip. In this case, it is the power portion of the chip that is most susceptible to burnout failures, because of it's high voltage operation. Hence, it is important to understand the operational limitations of power transistors when exposed to intense heavy ion and/or dose-rate environments. Reviews of normal breakdown and current induced avalanche breakdown mechanisms in silicon power transistors are presented. We show the applicability of the current induced avalanche model to heavy ion induced burnouts and present solutions to current induced avalanche in silicon power semiconductors. 9 refs., 5 figs.

Wrobel, T.F.; Beutler, D.E.

1991-01-01

175

Flux avalanches in Nb superconducting shifted strip arrays  

NASA Astrophysics Data System (ADS)

Flux penetrations into three-dimensional Nb superconducting strip arrays, where two layers of strip arrays are stacked by shifting a half period, are studied using a magneto-optical imaging method. Flux avalanches are observed when the overlap between the top and bottom layers is large even if the width of each strip is well below the threshold value. In addition, anomalous linear avalanches perpendicular to the strip are observed in the shifted strip array when the overlap is very large and the thickness of the superconductor is greater than the penetration depth. We discuss possible origins for the flux avalanches, including linear ones, by considering flux penetration calculated by the Campbell method assuming the Bean model.

Tsuchiya, Y.; Mawatari, Y.; Ibuka, J.; Tada, S.; Pyon, S.; Nagasawa, S.; Hidaka, M.; Maezawa, M.; Tamegai, T.

2013-09-01

176

Are there "dragon-kings" events (i.e. genuine outliers) among extreme avalanches?  

NASA Astrophysics Data System (ADS)

Predicting the occurrence and spatial extent of extreme avalanches is a longstanding issue. Using field data pooled from various sites within the same mountain range, authors showed that the avalanche size distribution can be described using either an extreme value distribution or a thick-tailed distribution, which implies that although they are much larger than common avalanches, extreme avalanches belong to the same population of events as "small" avalanches. Yet, when looking at historical records of catastrophic avalanches, archives reveal that a few avalanches had features that made them "extra-ordinary." Applying avalanche-dynamics or statistical models to simulate these past events runs into considerable difficulty since the model parameters or the statical properties are very different from the values usually set to model extreme avalanches. Were these events genuine outliers (also called "dragon-kings")? What were their distinctive features? This paper reviews some of the concepts in use to model extreme events, gives examples of processes that were at play in extreme avalanches, and shows that the concept of dragon-king avalanches is of particular relevance to describing some extreme avalanches.

Ancey, C.

2012-05-01

177

Near-surface faceted crystals, avalanches and climate in high-elevation, tropical mountains of Bolivia  

Microsoft Academic Search

The importance of near-surface faceted crystals in forming weak layers associated with snow avalanches has recently received greater attention. However, there is still much to be learned concerning the formation and growth of these crystal types, their geographical extent, and related avalanche activity. Here we report on two avalanches that occurred during late September 1999 at high-elevations in the Bolivian

Douglas Hardy; Mark W. Williams; Carlos Escobar

2001-01-01

178

Investigation of Gate Oscillation of Power MOSFETs Induced by Avalanche Mode Operation  

Microsoft Academic Search

Serious gate oscillation of power MOSFETs under avalanche condition has been observed, degrading an avalanche withstanding capability. Using experiments as well as numerical simulation, it is shown that this gate oscillation in avalanche mode results from the impact ionized hole carrier accumulation on the surface under the gate oxide and the associated reciprocation between the gate of each unit cell

Seung-Chul Lee; Kwang-Hoon Oh; Ho-Cheol Jang; Jae-Gil Lee; Soo-Seong Kim; Chong-Man Yun

2007-01-01

179

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

180

Geophysical investigation of the Sandalp rock avalanche deposits  

NASA Astrophysics Data System (ADS)

In the study of rock avalanche phenomena, numerical modelling makes use of back analyses of the rock avalanche propagation for calibration of the modelling assumptions and parameters. The back analyses require knowledge of the run-out area boundaries and the thickness distribution of the deposit. Geophysical methods can be applied to retrieve the thickness distribution, but, due to strong heterogeneities and logistic problems they are seldom applied. The aim of this work is to assess the potential of integrated geophysical methods to recognise and characterise a deposit created by two rock avalanches which occurred in the Sandalp valley (Switzerland) in 1996. The topography of the site before and after the rock avalanche is known and can be used as a benchmark. Resistivity tomography, seismic P-wave tomography, and active and passive surface wave analysis have been applied on several profiles deployed both on the rock avalanche deposit and in the surrounding area. Innovative approaches for surface wave analysis based on laterally constrained inversion and multimodal inversion have been applied to the data. A comparison of the results of the geophysical investigations with the topographic benchmark has shown the capability of the geophysical methods to locate the bottom of the deposit in the areas where the contrast with the host sediments properties is significant. In these areas, the deposit has higher resistivities and lower seismic velocities than the underlying materials. In the areas where the deposit is thicker and richer in fine-grained materials the geophysical parameters are not able to discriminate between the rock avalanche deposit and the underlying sediments. As a secondary task, the geophysical methods also allowed the bedrock pattern to be outlined.

Socco, Laura Valentina; Jongmans, Denis; Boiero, Daniele; Stocco, Stefano; Maraschini, Margherita; Tokeshi, Ken; Hantz, Didier

181

The geomorphological significance of avalanche sedimentation for landscape evolution  

NASA Astrophysics Data System (ADS)

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

Eckerstorfer, Markus; Christiansen, Hanne

2013-04-01

182

On the formation of glide-snow avalanches  

NASA Astrophysics Data System (ADS)

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

Mitterer, C.; Schweizer, J.

2012-12-01

183

Degradation mechanisms in avalanche transit time diodes (Review)  

NASA Astrophysics Data System (ADS)

The physical mechanisms responsible for the degradation of silicon and GaAs avalanche transit time diodes are reviewed. An analysis is made of the physicochemical processes at the metal-semiconductor interface for an ohmic contact and a Schottky barrier, and the degradation mechanisms in avalanche transit time diodes with p-n homo- and heterojunctions are examined. The characteristics of degradation processes are discussed as a function of the type of the potential barrier, properties of the initial material, and the composition and structure of the contact.

Konakova, R. V.

184

Scale-free avalanches in the multifractal random walk  

Microsoft Academic Search

.   Avalanches, or Avalanche-like, events are often\\u000a observed in the dynamical behaviour of many complex systems which\\u000a span from solar flaring to the Earth's crust dynamics and from\\u000a traffic flows to financial markets. Self-organized criticality\\u000a (SOC) is one of the most popular theories able to explain this\\u000a intermittent charge\\/discharge behaviour. Despite a large amount of\\u000a theoretical work, empirical tests for

M. Bartolozzi

2007-01-01

185

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

NASA Astrophysics Data System (ADS)

Simulations are used to determine the effect of inertia on athermal shear of amorphous two-dimensional solids. 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 disks. Inertia takes the system to a new underdamped universality class rather than driving the system away from criticality as previously thought. 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.

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

2012-09-01

186

A compact gas-filled avalanche counter for DANCE  

NASA Astrophysics Data System (ADS)

A compact gas-filled avalanche counter for the detection of fission fragments was developed for a highly segmented 4? ?-ray calorimeter, namely the Detector for Advanced Neutron Capture Experiments located at the Lujan Center of the Los Alamos Neutron Science Center. It has been used successfully for experiments with 235U, 238Pu, 239Pu, and 241Pu isotopes to provide a unique signature to differentiate the fission from the competing neutron-capture reaction channel. It was also used to study the spontaneous fission in 252Cf. The design and performance of this avalanche counter for targets with extreme ?-decay rate up to ˜2.4×108/s are described.

Wu, C. Y.; Chyzh, A.; Kwan, E.; Henderson, R. A.; Gostic, J. M.; Carter, D.; Bredeweg, T. A.; Couture, A.; Jandel, M.; Ullmann, J. L.

2012-12-01

187

Glacial advance and stagnation caused by rock avalanches  

NASA Astrophysics Data System (ADS)

New model results show that a glacier advance caused by deposition of a rock avalanche on the ice will be followed by stagnation of the advanced ice lobe, producing distributed, hummocky deposits quite different from the single moraine ridges typically dated in paleoclimatic reconstructions. We obtain these results using a numerical flow-line glacier model with superimposed rock debris. In particular, our results imply that the single moraine ridge known as the Waiho Loop of the Franz Josef Glacier, New Zealand, is not the result of an advance triggered by a rock avalanche, else there would be a widespread, hummocky, glacial stagnation deposit associated with it.

Vacco, David A.; Alley, Richard B.; Pollard, David

2010-05-01

188

Electron counting at room temperature in an avalanche bipolar transistor  

NASA Astrophysics Data System (ADS)

We report on real-time detection of single electrons inside a n-p-n bipolar junction transistor at room temperature. Single electrons injected through the base-emitter junction trigger with a high probability the avalanche breakdown of the strongly reverse-biased collector-base junction. The breakdown, rapidly stopped by an avalanche quenching circuit, produces a voltage pulse at the collector which corresponds to the detection of a single electron. Pulse rates corresponding to currents down to the attoampere range are measured with an integration time of about 10 s.

Lany, Marc; Boero, Giovanni; Popovic, Radivoje

2008-01-01

189

Snow avalanche detection and identification for near real-time application  

NASA Astrophysics Data System (ADS)

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

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

2013-12-01

190

Use of radar and automatic weather stations in avalanche forecasting  

Microsoft Academic Search

The following sources of information have been investigated and their data evaluated in order to issue avalanche warnings in case of catastrophic situations such as in February 1984 in the Swiss Alps: -Daily measurement of snow depth -Data of automatic weather stations. They transmit every 10 minutes precipitation, wind, temperature etc. -Images of 2 radars. Every 10 minutes the user

G. KAPPENBERGER; J. JOSS

191

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

192

Catastrophic debris avalanche deposit of Socompa volcano, northern Chile  

NASA Technical Reports Server (NTRS)

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

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

1985-01-01

193

Teaching Avalanche Safety Courses: Instructional Techniques and Field Exercises.  

ERIC Educational Resources Information Center

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

Watters, Ron

194

Solutions to heavy ion induced avalanche burnout in power devices  

Microsoft Academic Search

A review of normal breakdown and current induced avalanche (CIA) breakdown mechanisms in silicon power transistors is presented. The applicability of the CIA model to heavy ion induced burnout is shown, and solutions to CIA in silicon power semiconductors are given. It is noted that solving the problem of CIA burnout in npn bipolar and n-channel DMOS devices is, at

Theodore F. Wrobel; David E. Beutler

1992-01-01

195

Fast readout of plastic and crystal scintillators by avalanche photodiodes  

Microsoft Academic Search

Avalanche photodiodes (APDs) of improved quality and a sensitive area up to cm2 area are becoming commercially available now. In certain applications they can replace photomultipliers for fast readout of scintillation detectors. Expected performances will be discussed and some test measurements presented. Examples of possible applications will be given.

E. Lorenz; S. Natkaniec; D. Renker; B. Schwartz

1994-01-01

196

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

197

Snow drift: acoustic sensors for avalanche warning and research  

Microsoft Academic Search

Based on wind tunnel measurements at the CSTB (Jules Verne) facility in Nantes and based on field observations at the SLF experimental site Versuchsfeld Weissfluhjoch, two acoustic wind drift sensors are evaluated against different mechanical snow traps and one optical snow particle counter. The focus of the work is the suitability of the acoustic sensors for applications such as avalanche

M. Lehning; F. Naaim; M. Naaim; B. Brabec; J. Doorschot; Y. Durand; G. Guyomarc'h; J.-L. Michaux; M. Zimmerli

2002-01-01

198

Monte Carlo calibration of avalanches described as Coulomb fluid flows.  

PubMed

The idea that snow avalanches might behave as granular flows, and thus be described as Coulomb fluid flows, came up very early in the scientific study of avalanches, but it is not until recently that field evidence has been provided that demonstrates the reliability of this idea. This paper aims to specify the bulk frictional behaviour of snow avalanches by seeking a universal friction law. Since the bulk friction coefficient cannot be measured directly in the field, the friction coefficient must be calibrated by adjusting the model outputs to closely match the recorded data. Field data are readily available but are of poor quality and accuracy. We used Bayesian inference techniques to specify the model uncertainty relative to data uncertainty and to robustly and efficiently solve the inverse problem. A sample of 173 events taken from seven paths in the French Alps was used. The first analysis showed that the friction coefficient behaved as a random variable with a smooth and bell-shaped empirical distribution function. Evidence was provided that the friction coefficient varied with the avalanche volume, but any attempt to adjust a one-to-one relationship relating friction to volume produced residual errors that could be as large as three times the maximum uncertainty of field data. A tentative universal friction law is proposed: the friction coefficient is a random variable, the distribution of which can be approximated by a normal distribution with a volume-dependent mean. PMID:16011932

Ancey, Christophe

2005-07-15

199

Debris Avalanche Formation at Kick'em Jenny Submarine Volcano  

Microsoft Academic Search

Kick'em Jenny submarine volcano near Grenada is the most active volcanic center in the Lesser Antilles arc. Multibeam surveys of the volcano by NOAA in 2002 revealed an arcuate fault scarp east of the active cone, suggesting flank collapse. More extensive NOAA surveys in 2003 demonstrated the presence of an associated debris avalanche deposit, judging from their surface morphologic expression

H. Sigurdsson; S. N. Carey; D. Wilson

2005-01-01

200

Recent advances in very large area avalanche photodiodes  

Microsoft Academic Search

The Avalanche Photodiode (APD) is a unique device that combines the advantages of solid state photodetectors with those of high gain devices such as photomultiplier tubes (PMTs). APDs have internal gain that provides a high signal-to-noise ratio. APDs have high quantum efficiency, are fast, compact, and rugged. These properties make them suitable detectors for important applications such as LADAR, detection

Michael R. Squillante; James Christian; Gerald Entine; Richard Farrell; Arieh M. Karger; Mickel McClish; Richard Myers; Kanai S. Shah; David Taylor; Kofi Vanderpuye; Peter Waer; Mitchell Woodring

2003-01-01

201

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.

Tewksbury, Barb

202

A Theory of Multiple Modes in Avalanche Diodes.  

National Technical Information Service (NTIS)

The report develops a multidimensional, dynamic analysis of solid state avalanche diodes. Well-established electromagnetic concepts are applied to a widely used model of the diode and reveal a discrete spectrum of new small-signal modes. The approach used...

H. Berger

1970-01-01

203

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

204

A New Trenched Source Power MOSFET Improving Avalanche Energy  

Microsoft Academic Search

A new power metal oxide semiconductor field effect transistor (MOSFET) with a deep body contact, which improves the avalanche energy capability, is proposed and verified by the 2D numerical simulation. The deep body contact employing the trench process alters the direction of the current flow from the edge to the bottom of the p-body under the unclamped inductive switching (UIS)

Soo-Seong Kim; Jae-Keun Oh; Min-Koo Han

2003-01-01

205

Effect of Sonic Booms of Varying Overpressures on Snow Avalanches.  

National Technical Information Service (NTIS)

On 18 - 20 March 1965, a sonic boom program was conducted in the Star Mountain area near Leadville, Colorado, in the San Isabel National Forest. Objective was to determine the effects of sonic boom over-pressures on snow avalanches. A total of 18 combined...

D. C. Lillard T. L. Parrott D. G. Gallagher

1965-01-01

206

Parallel Adaptive Numerical Simulation of Dry Avalanches over Natural Terrain  

Microsoft Academic Search

High fidelity computational simulation can be an invaluable tool in planning strate- gies for hazard risk mitigation. The accuracy and reliability of the predictions are crucial elements of these tools being successful. We present here a new simulation tool for dry granular avalanches using several new techniques to create a highly accurate tool with a combination of good models and

A. K. Patra; A. C. Bauer; C. C. Nichita; E. B. Pitman; M. F. Sheridan; M. Namikawa; S. Renschler

2003-01-01

207

Optical fibers and avalanche photodiodes for scintillator counters  

SciTech Connect

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

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

1980-01-01

208

Avalanche fluctuations within the multigap resistive plate chamber  

Microsoft Academic Search

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

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

1996-01-01

209

High gain multigap avalanche detectors for Cerenkov ring imaging  

Microsoft Academic Search

We report on a continuing study of multigap parallel plate avalanche chambers, primarily as photoelectron detectors for use with Cerenkov ring imaging counters. By suitable control of the fields in successive gaps and by introducing screens to reduce photon feedback to the cathode the gain many be increased considerably. We have obtained gains in excess of 6 x 10 for

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

1980-01-01

210

Silicon avalanche photodiodes developed at the Institute of Electron Technology  

NASA Astrophysics Data System (ADS)

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

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

2004-07-01

211

Single and few photon avalanche photodiode detection process study  

NASA Astrophysics Data System (ADS)

We are presenting the results of the study of the Single Photon Avalanche Diode (SPAD) pulse response risetime and its dependence on several key parameters. We were investigating the unique properties of K14 type SPAD with its high delay uniformity of 200 ?m active area and the correlation between the avalanche buildup time and the photon number involved in the avalanche trigger. The detection chip was operated in a passive quenching circuit with active gating. This setup enabled us to monitor the diode reverse current using an electrometer, a fast digitizing oscilloscope, and using a custom design comparator circuit. The electrometer reading enabled to estimate the photon number per detection event, independently on avalanche process. The avalanche build up was recorded on the oscilloscope and processed by custom designed waveform analysis package. The correlation of avalanche build up to the photon number, bias above break, photon absorption location, optical pulse length and photon energy was investigated in detail. The experimental results are presented. The existing solid state photon counting detectors have been dedicated for picosecond resolution and timing stability of single photon events. However, the high timing stability is maintained for individual single photons detection, only. If more than one photon is absorbed within the detector time resolution, the detection delay will be significantly affected. This fact is restricting the application of the solid state photon counters to cases where single photons may be guaranteed, only. For laser ranging purposes it is highly desirable to have a detector, which detects both single photon and multi photon signals with picoseconds stability. The SPAD based photon counter works in a purely digital mode: a uniform output signal is generated once the photon is detected. If the input signal consists of several photons, the first absorbed one triggers the avalanche. Obviously, for multiple photon signals, the detection delay will be shorter in comparison to the single photon events. The detection delay dependence on the optical input signal strength is called the "detector time walk". To enable the detector operation in both the single and multi photon signal regime with a minimal time walk, a time walk compensation technique has been developed in nineties.

Blazej, Josef; Prochazka, Ivan

2009-07-01

212

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

NASA Astrophysics Data System (ADS)

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

Prokop, Alexander; Wirbel, Anna

2013-04-01

213

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

NASA Astrophysics Data System (ADS)

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

Turchaninova, A.

2012-04-01

214

Soil erosion and organic carbon export by wet snow avalanches  

NASA Astrophysics Data System (ADS)

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

Korup, O.; Rixen, C.

2014-01-01

215

Soil erosion and organic carbon export by wet snow avalanches  

NASA Astrophysics Data System (ADS)

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

Korup, O.; Rixen, C.

2014-04-01

216

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

NASA Astrophysics Data System (ADS)

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

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

2010-05-01

217

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

NASA Technical Reports Server (NTRS)

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

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

1977-01-01

218

Use of Seasonal Meteorological Metrics to Forecast for Deep Slab Avalanches in Southwest Montana  

NASA Astrophysics Data System (ADS)

Deep slab avalanches and avalanches that fail on old persistent weak layers are often more destructive than new snow avalanches, yet are relatively less understood and harder to predict. Newly formed instabilities normally gain strength over time, and the rate of strengthening lessens over time eventually leading to a generally constant strength, independent of meteorological conditions. Determining when a weak layer generally stops gaining strength after it is buried could be a clue to how much stress, resulting from meteorological inputs, is needed later in the season to cause an avalanche on this layer. Previous studies have found correlation between deep slabs and meteorological trends over several days preceding deep slabs, and suggest that deep slabs response to load lags up to 5 days. This study will examine seasonal meteorological metrics on years with deep slab avalanches and years without deep slab avalanches. Seasonal metrics may better reflect the development of weak layers over the course of a season and allow for more precise prediction of ranges of meteorological inputs that precede deep slab avalanches by up to seven days. Avalanche records and meteorological data from Big Sky ski resort and Bridger Bowl ski area will be used. Deep slab avalanches will be identified through specified criteria, and old persistent weak layers will be identified using weather patterns and records of snowpack observations. Seasonal meteorological metrics associated with weak layer development will be derived to test differences in metrics between years with deep slab avalanche activity and years without deep slab avalanche activity. Rank sum tests and classification trees will be used to determine which seasonal meteorological metrics are associated with deep slab avalanche activity, and if the magnitude of seasonal meteorological metrics is associated with the magnitude of meteorological inputs directly preceding days with deep slab activity. The results of this study will help determine seasonal meteorological metrics that can be used to more accurately predict the range of daily meteorological inputs likely to precede a deep slab avalanche.

Marienthal, A.; Hendrikx, J.; Birkeland, K.; Irvine, K.

2012-12-01

219

Structural vulnerability assessment using reliability of slabs in avalanche area  

NASA Astrophysics Data System (ADS)

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

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

2013-04-01

220

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

NASA Astrophysics Data System (ADS)

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

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

2013-12-01

221

Weathering processes implied from analysis of small Martian avalanche chutes  

NASA Technical Reports Server (NTRS)

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

Sullivan, R.

1992-01-01

222

The wiper model: avalanche dynamics in an exclusion process  

NASA Astrophysics Data System (ADS)

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

Politi, Antonio; Romano, M. Carmen

2013-10-01

223

Erosion dynamics of powder snow avalanches - model of frontal entrainment  

NASA Astrophysics Data System (ADS)

We analyze entrainment at the head of powder snow avalanches (PSA) behaving as an eruption current. Instead of invoking an erosion model or other fitted parameters, the analysis assumes that erosion is sustained by a massive blow-out arising as the snow cover is fluidized by the very pore pressure gradients that the avalanche induces within the snow pack. The stability of a mass balance involving snow cover and flow in the PSA's head region then sets frontal speed, height, mixed-mean density, snowpack fluidization depth, frontal impact pressure and static pressure. We show that acceleration of the front is insensitive to local slope, but effectively depends on the rate of change in cloud width. We compare predictions with data collected at the Vallee de la Sionne.

Louge, Michel; Sovilla, Betty

2013-04-01

224

Demonstration of the quantum dot avalanche photodiode (QDAP)  

NASA Astrophysics Data System (ADS)

We report new results on the design, fabrication and characterization of a novel midinfrared sensor called quantum dot avalanche photodiode (QDAP). The QDAP consists of a quantum dots-in-a-well (DWELL) detector coupled with an avalanche photodiode (APD) through a tunnel barrier. In the QDAP, the photons are absorbed in the DWELL active region while the APD section provides photocurrent gain. Spectral response and photocurrent measurements at 77 K were taken to characterize the response of the device. The increase of the spectral response and the nonlinear increase in the photocurrent as the APD voltage increases support theoretical predictions about the QDAP capability to work in Geiger mode. The QDAP photocurrent is similar to the IV characteristic of the APD section, indicating gain in the device.

Ramirez, David A.; Shao, Jiayi; Hayat, Majeed M.; Krishna, Sanjay

2009-05-01

225

Controllable morphology of flux avalanches in microstructured superconductors  

NASA Astrophysics Data System (ADS)

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

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

2014-04-01

226

Modelling and simulation of powder-snow avalanches  

NASA Astrophysics Data System (ADS)

Finite volume release gravity currents of large density contrast on steep slopes, representing powder-snow avalanches, are simulated numerically using a dynamic mesh adaptation technique. This technique allows to treat large Reynolds numbers and large density contrast flows, but it is (presently) restricted to two dimensions. Comparison of numerical results with experiments in the Boussinesq limit shows that 2D simulations capture the essential flow dynamics. The physics of powder-snow avalanches is analysed on hand of the similarity model developed by Rastello and Hopfinger (2004) and briefly reproduced here. The numerical simulations provide the closure parameters required in this model and give access to the flow structure. The non-Boussinesq effect is to decrease substantially the spatial growth in height and to increase the aspect ratio, hence the overall flow structure. To cite this article: J. Étienne et al., C. R. Mecanique 334 (2006).

Étienne, Jocelyn; Rastello, Marie; Hopfinger, Emil J.

2006-08-01

227

Silicon-on-insulator control impact-ionization-avalanche transistor  

NASA Astrophysics Data System (ADS)

In thin silicon-on-insulator structures, the gate effectively controls the longitudinal component of the electric field intensity in the pn+ junction, and thus the impact avalanche ionization of carriers. The present work proposes a device based on this operation principle: the control-impact-ionization-avalanche transistor, which achieves a transconductance of 0.14 (A/V)/mm. According to the developed theoretical model and preliminary experimental data, the device can be optimized to achieve very high transconductance and frequencies such as several (A/V)/mm at frequencies of the order of 100 MHz and lower, and about 1 (A/V)/mm in 0.1-1 THz range.

Dobrovolsky, V.; Pavljuk, S.; Rossokhaty, V.; Cristoloveanu, S.

2006-02-01

228

Elastic collapse and avalanche criticality near a Mott transition  

NASA Astrophysics Data System (ADS)

We study some dynamic aspects of a Mott transition in a rare-earth alloy Ce0.90Th0.10 by resonant-ultrasound spectroscopy (RUS), electrical-transport, and thermal-expansion measurements. In the temperature range spanning the first-order transition, we observe a stiffening of the elastic response that is associated with a continuous front propagation (e.g. solitons). A defining characteristic of a mixed phase regime, slow scanning rates (0.01 K/min) show these solitons to be superimposed with jerks and avalanches in all three data sets: RUS, resistivity, and thermal expansion data. Analysis of the avalanche data give power law distributions with critical exponents P(E)=E^n for energy, in the case of thermal expansion data and length, in the case of electrical transport data.

Smith, J. L.; Safarik, D. J.; Lashley, J. C.; Salje, E. K. H.; Opeil, C. P.; Riseborough, P. S.

2011-03-01

229

Silicon avalanche photodiodes for particle detector:. modelling and fabrication  

NASA Astrophysics Data System (ADS)

Large-area arrays (30×30) of metal/resistive layer/silicon (MRS) avalanche photodiodes as 150×150 ?m sub-pixels were developed and fabricated to detect short-wavelength scintillator signals for high-energy particle detection. Modelling of MRS photodiodes was performed using McIntyre's approach of local electric field to optimize semiconductor doping profiles and resistive layer parameters and to obtain the minimum value of effective k-factor (the holes to electrons ionization coefficients ratio) less than 0.01 under low excess noise factor and high gain. The resistive layer/silicon surface barrier suppresses minority carriers injection to decrease dark current and effective k-factor. Test samples of silicon avalanche photodiodes arrays have been fabricated using low-rate epitaxial growth of silicon layer, impurity doping, and resistive layer deposition processing. The integral gain for experimental specimens was ˜100.

Khodin, Alexandre; Shvarkov, Dmitry; Zalesski, Valery

2001-06-01

230

Mechanisms of avalanche dynamics and forms of scaling in sandpiles  

NASA Astrophysics Data System (ADS)

The probability distributions of several avalanche quantities of the Bak-Tang-Wiesenfeld sandpile in two dimensions display multifractal scaling. This explains why this prototype model remained extremely problematic and controversial for such a long time after its introduction. Other models, like the Manna model, obey instead standard finite size scaling and fall in different universality classes. An analysis of time series for the waves into which avalanches can be decomposed, shows that the different forms of scaling can be ascribed to the respective autocorrelation functions. The intermittency of the Bak-Tang-Wiesenfeld sandpile is due to this autocorrelation being long range in time, unlike in the Manna case. A coarse graining of the wave time series elucidates these differences and the mechanism leading to multifractality.

Stella, Attilio L.; Menech, Mario De

231

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

232

Recent results in scintillation detection with silicon avalanche photodiodes  

SciTech Connect

The authors report on the investigation of silicon avalanche photodiodes in scintillation detection for potential applications in medical imaging and nuclear spectroscopy. Experimental measurements were performed on BGO, CdWO{sub 4}, plastic, NaI(Tl) and CsI(Tl) scintillators, geometrically optimized for light collection. Results show the advantages of a solid state photodetector having an internal gain for the detection of low energy gamma and X-rays.

Carrier, C.; Leconte, R. (Dept. of Nuclear Medicine and Radiobiology, Univ. of Sherbrooke, Sherbrooke, Quebec J1H 5N4 (CA))

1990-04-01

233

Receiver characteristics of laser altimeters with avalanche photodiodes  

NASA Technical Reports Server (NTRS)

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

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

1992-01-01

234

Dense Granular Avalanches: Mathematical Description and Experimental Validation  

Microsoft Academic Search

Snow avalanches, landslides, rock falls and debris flows are extremely dangerous and destructive natural phenomena. The frequency\\u000a of occurrence and amplitudes of these disastrous events appear to have increased in recent years perhaps due to recent climate\\u000a warming. The events endanger the personal property and infra-structure in mountainous regions. For example, from the winters\\u000a 1940\\/41 to 1987\\/88 more than 7000

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

235

Ageing of the avalanche angle in immersed granular matter  

NASA Astrophysics Data System (ADS)

The stability of packings of glass beads immersed in various fluids is studied experimentally in a rotating drum. The avalanche angle depends on the time during which the system remains at rest before measurement only when the grains are immersed in water. The experimental results prove that ageing of immersed granular materials, under low applied stress and in the absence of external sollicitations, only originates from chemical reactions that occur at the surface of the grains.

Gayvallet, H.; Géminard, J.-C.

2002-12-01

236

Application of avalanche photodiodes to confocal and confocal florescence microscopy  

Microsoft Academic Search

We describe the use of avalanche photodiodes as solid state photon counters in scanning confocal microscopy. Photon counters have been of limited use for moderate-to-rapid image acquisition speeds due to comparatively low saturation count rates. Several approaches offer the promise of real-time photon-limited image acquisition using off-the-shelf components and dark count rates which are fully adequate for imaging. We characterize

Thomas G. Brown; Steve T. Kreger

1996-01-01

237

Avalanche localization and crossover scaling in amorphous plasticity  

NASA Astrophysics Data System (ADS)

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.

Budrikis, Zoe; Zapperi, Stefano

2013-12-01

238

Avalanche and spreading exponents in systems with absorbing states  

Microsoft Academic Search

We present generic scaling laws relating spreading critical exponents and avalanche exponents (in the sense of self-organized criticality) in general systems with absorbing states. Using these scaling laws we present a collection of the state-of-the-art exponents for directed percolation, dynamical percolation, and other universality classes. This collection of results should help to elucidate the connections of self-organized criticality and systems

Miguel A. Muñoz; Ronald Dickman; Alessandro Vespignani; Stefano Zapperi

1999-01-01

239

Prediction efficiency in an avalanche model for different target events  

NASA Astrophysics Data System (ADS)

The avalanche formation model has much in common with the formation of earthquakes [Bak and Tang, 1989]. A well-known modification of this model is studied and predictability of the strongest events is demonstrated. The prediction efficiency increases with the size of target events. In particular, 75% of strong events are predicted for a fixed size if an alarm lasts for one-third of the observation time.

Shapoval, A. B.; Shnirman, M. G.

2008-06-01

240

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

241

Recent developments in avalanche photodiodes for scintillating fiber applications  

SciTech Connect

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 [Radiation Monitoring Devices, Inc., 44 Hunt Street, Watertown, Massachusetts 02172 (United States)

1998-11-09

242

Parallel adaptive numerical simulation of dry avalanches over natural terrain  

Microsoft Academic Search

High-fidelity computational simulation can be an invaluable tool in planning strategies for hazard risk mitigation. The accuracy and reliability of the predictions are crucial elements of these tools being successful. We present here a new simulation tool for dry granular avalanches using several new techniques for enhancing numerical solution accuracy.Highlights of our new methodology are the use of a depth-averaged

A. K. Patra; A. C. Bauer; C. C. Nichita; E. B. Pitman; M. F. Sheridan; M. Bursik; B. Rupp; A. Webber; A. J. Stinton; L. M. Namikawa; C. S. Renschler

2005-01-01

243

Avalanche fluctuations within the multigap resistive plate chamber  

NASA Astrophysics Data System (ADS)

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

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

244

Four Applied Methods for Spatial Visualization in Snow Avalanche Forecasting  

NASA Astrophysics Data System (ADS)

This thesis presents four applied methods for seasonal snow observation with respect to avalanches. Previous avalanche-related spatial variation and scale studies have shown a clear need for observation and methods to focus on the scale of interest to human triggering. These methods have the common goal to reveal spatial variation of interest to avalanche formation and human triggering in an efficient, accessible manner. The four methods are: (1) A minimally destructive slope-scale sampling method, (2) A method to relate Google Earth terrain images to surface hoar formation in sparse trees, (3) A method of accessibly presenting complex GIS warming model data over real terrain, and (4) A method of measuring heat in the snowpack using a thermal imager. Despite their common goal of spatial visualization, each new method draws on a different subset of background literature and employs very different methods in development and use. Thus, each method is presented as a self-contained paper with independent results. Of note, these methods have all subsequently received active use, and conclusions from such use are discussed at the end of the thesis.

Shea, Cora

245

Self-organization without conservation: are neuronal avalanches generically critical?  

NASA Astrophysics Data System (ADS)

Recent experiments on cortical neural networks have revealed the existence of well-defined avalanches of electrical activity. Such avalanches have been claimed to be generically scale invariant—i.e. power law distributed—with many exciting implications in neuroscience. Recently, a self-organized model has been proposed by Levina, Herrmann and Geisel to explain this empirical finding. Given that (i) neural dynamics is dissipative and (ii) there is a loading mechanism progressively 'charging' the background synaptic strength, this model/dynamics is very similar in spirit to forest-fire and earthquake models, archetypical examples of non-conserving self-organization, which have recently been shown to lack true criticality. Here we show that cortical neural networks obeying (i) and (ii) are not generically critical; unless parameters are fine-tuned, their dynamics is either subcritical or supercritical, even if the pseudo-critical region is relatively broad. This conclusion seems to be in agreement with the most recent experimental observations. The main implication of our work is that, if future experimental research on cortical networks were to support the observation that truly critical avalanches are the norm and not the exception, then one should look for more elaborate (adaptive/evolutionary) explanations, beyond simple self-organization, to account for this.

Bonachela, Juan A.; de Franciscis, Sebastiano; Torres, Joaquín J.; Muñoz, Miguel A.

2010-02-01

246

Scale-free avalanches in the multifractal random walk  

NASA Astrophysics Data System (ADS)

Avalanches, or Avalanche-like, events are often observed in the dynamical behaviour of many complex systems which span from solar flaring to the Earth's crust dynamics and from traffic flows to financial markets. Self-organized criticality (SOC) is one of the most popular theories able to explain this intermittent charge/discharge behaviour. Despite a large amount of theoretical work, empirical tests for SOC are still in their infancy. In the present paper we address the common problem of revealing SOC from a simple time series without having much information about the underlying system. As a working example we use a modified version of the multifractal random walk originally proposed as a model for the stock market dynamics. The study reveals, despite the lack of the typical ingredients of SOC, an avalanche-like dynamics similar to that of many physical systems. While, on one hand, the results confirm the relevance of cascade models in representing turbulent-like phenomena, on the other, they also raise the question about the current state of reliability of SOC inference from time series analysis.

Bartolozzi, M.

2007-06-01

247

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.; Bühler, Y.

2012-09-01

248

Numerically stable compact strong avalanche model for four-layer device simulation  

Microsoft Academic Search

Since strong avalanche is a central phenomenon in four-layer (PNPN) devices such as thyristors and TOVP's, the usual compact model consisting of two transistors (PNP)- (NPN) must include a numerically stable strong avalanche model. To this end, Miller's empirical expression for avalanche multiplication M(Vcb) in bipolar transistors was modified to eliminate its singularity at the collector-base breakdown voltage (VCBO); by

Rodolfo Quintero Romo

2008-01-01

249

Deposits of large volcanic debris avalanches at Mount St. Helens and Mount Shasta volcanoes  

Microsoft Academic Search

Large volcanic debris avalanches are among the world's largest mass movements. The rockslide-debris avalanche of the May 18, 1980, eruption of Mount St. Helens produced a 2.8 km³ deposit and is the largest historic mass movement. A Pleistocene debris avalanche at Mount Shasta produced a 26 km³ deposit that may be the largest Quaternary mass movement. The hummocky deposits at

Glicken

1985-01-01

250

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

NASA Astrophysics Data System (ADS)

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

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

2014-05-01

251

Transition by Intermittency in Granular Matter: From Discontinuous Avalanches to Continuous Flow  

NASA Astrophysics Data System (ADS)

We investigate, in the rotating drum configuration, the transition from the regime of discontinuous avalanches observed at low angular velocity to the regime of continuous flow observed at higher velocity. Instead of the hysteretic transition reported previously by Rajchenbach [Phys. Rev. Lett. 65, 2221 (1990)], with an apparent bistability of the two flow regimes in a range of drum velocities, we observe intermittency with spontaneous erratic switches from one regime to the other. Both scenarios of transition are recovered by a model dynamic equation for the avalanche flow with two sources of stochasticity: a Langevin noise during the avalanche flow and a distributed maximal stability angle at which avalanches start.

Fischer, Raphaël; Gondret, Philippe; Rabaud, Marc

2009-09-01

252

The Tancitaro Debris Avalanche: Characterization, propagation and modeling  

NASA Astrophysics Data System (ADS)

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

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

2010-06-01

253

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

NASA Astrophysics Data System (ADS)

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.

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

2014-01-01

254

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; Kneževi?, Milan

2014-01-01

255

Avalanches at the Core-Mantle Boundary: Possible Role in Geomagnetic Reversals, Mantle Plumes, and Superchrons  

NASA Astrophysics Data System (ADS)

Avalanches at the core-mantle boundary have not been directly observed, but if they exist they could affect many geophysical phenomena. Avalanches occur in ?sediment? accumulating on the inner surface of the mantle (according to the theory of Buffett et al.). Because the sediment is not evenly deposited, avalanches could provide the primary mechanism to redistribute sedimentary material evenly over the core-mantle boundary. Core-mantle avalanches, like turbidity flows in the ocean, consist of both solid material and entrained liquid. Such flows can occur at shallow angles (less than a few degrees) and could continue for many kilometers or hundreds of kilometers, depending on the topography. However, these avalanches are upside-down: they flow upward, propelled by buoyancy, into inverted valleys on the mantle surface. The avalanches mix relatively cool sediment with hot liquid iron, creating a redistribution of heat near the boundary. If the avalanche is sufficiently thick (100 m) then the cold pulse will create a downward plume in the core which can disrupt the convective cells that maintain the Earth?s dipole field. When the cells reestablish, the result is a geomagnetic reversal or excursion. We predict a reversal pattern different from that of the chaotic reversals seen in simulations by Glatzmeier. Avalanche-triggered reversals begin with a rapid drop in the dipole moment (but with higher order moments increasing), followed by a period with low dipole moment lasting from hundreds to thousands of years, followed by a rapid build-up of the reversed dipole field. Studies of the detailed time structure of reversals can test the model. As with turbidity flows, we expect a spectrum of avalanche sizes. The largest avalanches are the least probable. The sudden removal of a sediment blanket exposes the lower mantle to a pulse of heat, and for sufficiently large avalanches (>> 100 meters thick) this can contribute to the conditions needed for a mantle plume. A large avalanche could trigger sympathetic avalanches at other locations, wiping clean the topography of much of the boundary. No further avalanches could occur until the slopes rebuild, tens of millions of years later. The Cretaceous superchron (no reversals from 120-85 Ma) could have been initiated by such a super avalanche. In this interpretation, the Ontong-Java Plateau is identified as the result of the mantle plume triggered from the same 120 Ma event. A similar quiet period, the Kiaman reversed superchron, occurred from ca. 320-250 Ma. Our interpretation predicts a large mantle plume at the beginning of this superchron. Oblique extraterrestrial impacts impart high shear to the boundary, and could trigger one or more simultaneous avalanches. Such events could account for reported coincidences of reversals with impact craters and tektite fields. Triggered avalanches could also provide a mechanism for the reported coincidences between large flood basalts and extinctions. In our picture, it is the impact that caused both the extinctions and the flood basalts. Small avalanches, occurring every few years, might be detectable by synthetic aperture seismic analysis. Phase lags can be introduced at many seismic detectors that focus on the core-mantle boundary. The resulting map can then be compared to maps just above and below the boundary. It might even be possible to detect the motion of the avalanche. Avalanches could also change the Earth?s dynamic oblateness and be detectable as changes in the Earth?s gravitational field moments, J2 and higher. Such avalanches might contribute to the variations recently reported in J2.

Muller, R. A.; Levine, J.; Rohde, R.

2002-12-01

256

HIGH RESOLUTION TREE-RING BASED SPATIAL RECONSTRUCTIONS OF SNOW AVALANCHE ACTIVITY IN GLACIER NATIONAL PARK, MONTANA, USA  

Microsoft Academic Search

Effective design of avalanche hazard mitigation measures requires long-term records of natural avalanche frequency and extent. Such records are also vital for determining whether natural avalanche frequency and extent vary over time due to climatic or biophysical changes. Where historic records are lacking, an accepted substitute is a chronology developed from tree-ring responses to avalanche-induced damage. This study evaluates a

Gregory T. Pederson; Christian J. Caruso

257

Hot carrier reliability of high-speed SiGe HBT’s under accelerated collector-base avalanche bias  

Microsoft Academic Search

As SiGe heterojunction bipolar transistor (HBT) based technologies reach fT performance above 200 GHz the transistors are more likely to be operating in the avalanche region of collector-base junction. This avalanche effect imposes a reliability concern due to the damage induced by high-energy avalanche charges (hot carriers) on the Si-SiO2 interfaces. The impact of accelerated avalanche bias stress on 200

Zhijian Yang; Fernando Guarin; Ed Hostetter; Ping-Chuan Wang

2008-01-01

258

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

Microsoft Academic Search

Many parts of our planet are exposed to natural disasters such as snow avalanches, floods and earthquakes. Detailed knowledge\\u000a on these natural disasters is crucial for human safety. On December 25–26, 1992, two avalanches occurred at Kayaarkas?-Kastamonu\\u000a in northern Turkey. The first avalanche took place at night of 25–26 December and caused no damage. The second avalanche took\\u000a place at

Nesibe Köse; Abdurrahim Ayd?n; Ünal Akkemik; Hüseyin Yurtseven; Tuncay Güner

2010-01-01

259

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

260

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

NASA Technical Reports Server (NTRS)

The author has identified the following significant results. With rare exceptions, avalanche areas cannot be identified on LANDSAT imagery. Avalanche hazard mapping on a regional scale is best conducted using LANDSAT imagery in conjunction with complementary data sources. Level of detail of such maps will be limited by the amount and completeness of the complementary information used.

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

1976-01-01

261

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

262

New perspective on passively quenched single photon avalanche diodes: effect of feedback on impact ionization.  

PubMed

Single-photon avalanche diodes (SPADs) are primary devices in photon counting systems used in quantum cryptography, time resolved spectroscopy and photon counting optical communication. SPADs convert each photo-generated electron hole pair to a measurable current via an avalanche of impact ionizations. In this paper, a stochastically self-regulating avalanche model for passively quenched SPADs is presented. The model predicts, in qualitative agreement with experiments, three important phenomena that traditional models are unable to predict. These are: (1) an oscillatory behavior of the persistent avalanche current; (2) an exponential (memoryless) decay of the probability density function of the stochastic quenching time of the persistent avalanche current; and (3) a fast collapse of the avalanche current, under strong feedback conditions, preventing the development of a persistent avalanche current. The model specifically captures the effect of the load's feedback on the stochastic avalanche multiplication, an effect believed to be key in breaking today's counting rate barrier in the 1.55-?m detection window. PMID:22274495

Ramirez, David A; Hayat, Majeed M; Rees, Graham J; Jiang, Xudong; Itzler, Mark A

2012-01-16

263

Avalanche Detection using Atmospheric Infrasound. Final Report Winter 1994-1995.  

National Technical Information Service (NTIS)

This report describes the phenomena that snow avalanches produce sounds in the 0.5 to 5.0 Hertz range. It also documents testing of an infrasound detection system to detect snow avalanches in the southwest mountains of Colorado. Two infrasound sensors wer...

A. J. Bedard

1997-01-01

264

Fractal dimension of debris-avalanche deposits in the Hawaiian submarine landslide deposits  

Microsoft Academic Search

17 landslide deposits on the flanks of the southern Hawaiian Ridge have been classified into two major types: SLUMPS, which moved slowly as a coherent mass, and DEBRIS AVALANCHES, which moved quickly.The debris-avalanche deposits are predominant on submarine flanks of volcanic ocean islands elsewhere in the world. Such huge landslides are considered to produce giant tsunamis and megaturbidites covering large

H. Yokose; S. Yamato

2005-01-01

265

Measurement results from an avalanche amplifying pnCCD for single photon imaging  

Microsoft Academic Search

The company PNSensor and the MPI Semiconductor Laboratory are developing and have produced first prototypes of pnCCDs with an avalanche readout which aim at single photon sensitivity in the visible wavelength range. This resolution is provided by an avalanche diode integrated in the readout chain of every CCD column. The diode features a new topology and can collect signal electrons

I. Ordavo; R. Hartmann; P. Holl; A. Irlbeck; G. Lutz; R. H. Richter; G. Schaller; H. Soltau; L. Strüder

2010-01-01

266

A novel approach to evaluate and compare computational snow avalanche simulation  

NASA Astrophysics Data System (ADS)

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

Fischer, J.-T.

2013-06-01

267

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

268

Alluvial fan and catchment initiation by rock avalanching, Owens Valley, California  

Microsoft Academic Search

The North Long John alluvial fan of the Inyo Mountains piedmont, Owens Valley, CA, was catastrophically initiated by a prehistoric (early Holocene?) rock avalanche. This avalanche resulted from the collapse and disintegration of the central part of a 1.1×2.0 km range front bedrock facet comprising the divide between the catchments of two large, adjoining alluvial fans. Failure rapidly produced and

Terence C Blair

1999-01-01

269

Integrated avalanche diode for 600 V Trench IGBT over-voltage protection  

Microsoft Academic Search

Avalanche multiplication has been one of the major destructive failure mechanisms in IGBTs; in order to avoid operating an IGBT under abnormal conditions, it is desirable to develop peripheral protecting circuits monolithically integrated without compromising the operation and performance of the IGBT. In this paper, a monolithically integrated avalanche diode (Dav) for 600V Trench IGBT over-voltage protection is proposed. The

Alice Pei-Shan Hsieh; Florin Udrea; Wei-Chieh Lin

2011-01-01

270

RPC simulation in avalanche and streamer modes using transport equations for electrons andions  

Microsoft Academic Search

A simulation of the development of a signal inside an RPC is presented using simultaneous solution of the transport equations for electrons, negative and positive ions. The simulation also includes effects of space-charge and photo-ionization which are important during the development of a streamer signal. In the results, three different modes of RPC operation can be distinguished; avalanche, saturated avalanche,

Ahmad Moshaii; Larousse Khosravi Khorashad; Mehdi Eskandari; Somayeh Hosseini

271

Hybrid optical bistability and optical logic gates with avalanche heterojunction phototransistor and semiconductor laser diodes  

Microsoft Academic Search

A bistable optical device (BOD) which employs an avalanche heterojunction phototransistor (AHPT) and an LD is proposed. Steady state operation of the AHPT-LD-BOD involves the operating modes of linear amplification, avalanche gain, optical bistability, and optoelectronic switching. In the optical bistability mode, a critical triggering optical power of no more than 10 microwatts and an output power at the ON

Jie Dong; Xiao-Kang Huang; Bao-Yin Sun

1987-01-01

272

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

273

Problem of Experimental Study of the Physical-Mechanical Characteristics of Avalanche Flow.  

National Technical Information Service (NTIS)

Many domestic and foreign research papers are devoted to the resolution of the problems of dynamics of snow avalanches. In these papers efforts have been made many times to present methods of quantitative evaluation of the impact of a snow avalanche again...

V. S. Matvienko

1971-01-01

274

Source electrode evolution of a low voltage power MOSFET under avalanche cycling  

Microsoft Academic Search

This paper presents the impact of high current repetitive avalanche pulses on a low voltage vertical power MOSFET at high temperature. Measurements show that RDSon decreases with the number of avalanche cycles whereas other electrical parameters stay constant. A simple model proposed in this paper shows that RDSon measurements are linked to MOSFET source electrode evolution. Also once source electrode

B. Bernoux; R. Escoffier; P. Jalbaud; J. M. Dorkel

2009-01-01

275

Geomorphological Features of Avalanche Furrows in Heavy Snow Region in Japan  

NASA Astrophysics Data System (ADS)

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

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

2005-03-01

276

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

277

Neuronal Avalanches in the Resting MEG of the Human Brain  

PubMed Central

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.

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

2013-01-01

278

Martian dust devil electron avalanche process and associated electrochemistry  

NASA Astrophysics Data System (ADS)

Mars' dynamic atmosphere displays localized dust devils and larger, global dust storms. Based on terrestrial analog studies, electrostatic modeling, and laboratory work, these features will contain large electrostatic fields formed via triboelectric processes. In the low-pressure Martian atmosphere, these fields may create an electron avalanche and collisional plasma due to an increase in electron density driven by the internal electrical forces. To test the hypothesis that an electron avalanche is sustained under these conditions, a self-consistent atmospheric process model is created including electron impact ionization sources and electron losses via dust absorption, electron dissociation attachment, and electron/ion recombination. This new model is called the Dust Devil Electron Avalanche Model (DDEAM). This model solves simultaneously nine continuity equations describing the evolution of the primary gaseous chemical species involved in the electrochemistry. DDEAM monitors the evolution of the electrons and primary gas constituents, including electron/water interactions. We especially focus on electron dynamics and follow the electrons as they evolve in the E field driven collisional gas. When sources and losses are self-consistently included in the electron continuity equation, the electron density grows exponentially with increasing electric field, reaching an equilibrium that forms a sustained time-stable collisional plasma. However, the character of this plasma differs depending upon the assumed growth rate saturation process (chemical saturation versus space charge). DDEAM also shows the possibility of the loss of atmospheric methane as a function of electric field due to electron dissociative attachment of the hydrocarbon. The methane destruction rates are presented and can be included in other larger atmospheric models.

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

2010-05-01

279

Flowers in flour: Avalanches in cohesive granular matter  

NASA Astrophysics Data System (ADS)

We report on the intermittent dynamics of the free surface of a cohesive granular material during a silo discharge. In absence of cohesion, one observes the formation and the growth of a conical crater whose angle is well defined and constant in time. When the cohesion is involved the free surface exhibits a complex dynamics and the crater, resulting from a series of individual avalanches, is no longer axisymmetric. However, in spite of the intermittent behavior of the free surface, the flow rate is observed to remain constant throughout the discharge.

Freyssingeas, E.; Dalbe, M.-J.; Géminard, J.-C.

2011-05-01

280

Some exact solutions for debris and avalanche flows  

NASA Astrophysics Data System (ADS)

Exact analytical solutions to simplified cases of nonlinear debris avalanche model equations are necessary to calibrate numerical simulations of flow depth and velocity profiles on inclined surfaces. These problem-specific solutions provide important insight into the full behavior of the system. In this paper, we present some new analytical solutions for debris and avalanche flows and then compare these solutions with experimental data to measure their performance and determine their relevance. First, by combining the mass and momentum balance equations with a Bagnold rheology, a new and special kinematic wave equation is constructed in which the flux and the wave celerity are complex nonlinear functions of the pressure gradient and the flow depth itself. The new model can explain the mechanisms of wave advection and distortion, and the quasiasymptotic front bore observed in many natural and laboratory debris and granular flows. Exact time-dependent solutions for debris flow fronts and associated velocity profiles are then constructed. We also present a novel semiexact two-dimensional plane velocity field through the flow depth. Second, starting with the force balance between gravity, the pressure gradient, and Bagnold's grain-inertia or macroviscous forces, we construct a simple and very special nonlinear ordinary differential equation to model the steady state debris front profile. An empirical pressure gradient enhancement factor is introduced to adequately stretch the flow front and properly model nonhydrostatic pressure in granular and debris avalanches. An exact solution in explicit form is constructed, and is expressed in terms of the Lambert-Euler omega function. Third, we consider rapid flows of frictional granular materials down a channel. The steady state mass and the momentum balance equations are combined together with the Coulomb friction law. The Chebyshev radicals are employed and the exact solutions are developed for the velocity profile and the debris depth. Similarly, Bagnold's fluids are also used to construct alternative exact solutions. Many interesting and important aspects of all these exact solutions, their applications to real-flow situations, and the influence of model parameters are discussed in detail. These analytical solutions, although simple, compare very well with experimental data of debris flows, granular avalanches, and the wave tips of dam break flows. A new scaling law for Bagnold's fluids is established to relate the settlement time of debris deposition. It is found analytically that the macroviscous fluid settles (comes to a standstill) considerably faster than the grain-inertia fluid, as manifested by dispersive pressure.

Pudasaini, Shiva P.

2011-04-01

281

Application of avalanche photodiodes to confocal and confocal florescence microscopy  

NASA Astrophysics Data System (ADS)

We describe the use of avalanche photodiodes as solid state photon counters in scanning confocal microscopy. Photon counters have been of limited use for moderate-to-rapid image acquisition speeds due to comparatively low saturation count rates. Several approaches offer the promise of real-time photon-limited image acquisition using off-the-shelf components and dark count rates which are fully adequate for imaging. We characterize in some detail a gated NPN switch/pulse-bias circuit which offers excellent, economical performance over a wide wavelength range, and discuss specific imaging applications.

Brown, Thomas G.; Kreger, Steve T.

1996-04-01

282

Numerical simulation of neutron radiation effects in avalanche photodiodes  

SciTech Connect

A new one-dimensional (1-D) device model developed for the simulation of neutron radiation effects in silicon avalanche photodiodes is described. The model uses a finite difference technique to solve the time-independent semiconductor equations across a user specified structure. The model includes impact ionization and illumination allowing accurate simulation with minimal assumptions. The effect of neutron radiation damage is incorporated via the introduction of deep acceptor levels subject to Shockley-Read-Hall statistics. Preliminary analysis of an EG and G reverse APD structure is compared with experimental data from a commercial EG and G C30719F APD.

Osborne, M.D.; Hobson, P.R.; Watts, S.J.

2000-03-01

283

Exact phase diagram for an asymmetric avalanche process.  

PubMed

The Bethe ansatz method and an iterative procedure based on detailed balance are used to obtain exact results for an asymmetric avalanche process on a ring. The average velocity of particle flow, v, is derived as a function of the toppling probabilities and the density of particles, rho. As rho increases, the system shows a transition from intermittent to continuous flow, and v diverges at a critical point rho(c) with exponent alpha. The exact phase diagram of the transition is obtained and alpha is found to depend on the toppling rules. PMID:11497944

Priezzhev, V B; Ivashkevich, E V; Povolotsky, A M; Hu, C K

2001-08-20

284

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

NASA Astrophysics Data System (ADS)

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

Mallick, Shubhrangshu

285

UV photodetectors, focal plane arrays, and avalanche photodiodes  

NASA Astrophysics Data System (ADS)

The study of III-Nitride based optoelectronics devices is a maturing field, but there are still many underdeveloped areas in which to make a contribution of new and original research. This work specifically targets the goals of realizing high-efficiency back-illuminated solar-blind photodetectors, solar-blind focal plane arrays, and visible- and solar-blind Avalanche photodiodes. Achieving these goals has required systematic development of the material growth and characterization, device modeling and design, device fabrication and processing, and the device testing and qualification. This work describes the research conducted and presents relevant devices results. The AlGaN material system has a tunable direct bandgap that is ideally suited to detection of ultraviolet light, however this material system suffers from several key issues, making realization of high-efficiency photodetectors difficult: large dislocation densities, low n-type and p-type doping efficiency, and lattice and thermal expansion mismatches leading to cracking of the material. All of these problems are exacerbated by the increased aluminum compositions necessary in back-illuminated and solar-blind devices. Overcoming these obstacles has required extensive development and optimization of the material growth techniques necessary: this includes everything from the growth of the buffer and template, to the growth of the active region. The broad area devices realized in this work demonstrate a quantum efficiency that is among the highest ever reported for a back-illuminated solar-blind photodetector (responsivity of 157 mA/W at 280nm, external quantum efficiency of 68%). Taking advantage of the back illuminated nature of these detectors, we have successfully developed the technology to hybridize and test a solar-blind focal plane array camera. The initial focal plane array shows good uniformity and reasonable operability, and several images from this first camera are presented. However, in order to improve the performance of these devices to the point where they can effectively compete with photo-multiplier tube technology, it is necessary to develop devices with internal gain. To this end GaN and AlGaN based avalanche photodiodes have been studied, and we report the first realization of a solar-blind back-illuminated avalanche photodiode. The next logical step is to continue this work and realize Geiger mode avalanche photodiodes capable of single photon detection.

McClintock, Ryan

286

Photon detection with high gain avalanche photodiode arrays  

SciTech Connect

The detection of light emitted in fast scintillating fibers and Cerenkov radiators used for fiber calorimetry and tracking applications in high energy colliders, requires fast detector arrays with high sensitivity to short wavelength photons. Photomultiplier tubes, the traditional imaging detectors for short wavelength optical radiation, have limited spatial resolution and require expensive anti-magnetic shielding. The authors report on short wavelength sensitivity improvement and detection efficiency performance for a novel p-n junction planar structure silicon avalanche photodiode (APD) array, operated in Geiger mode. The APD array provides a high sensitivity detector for applications requiring the detection of light spatial distributions with single photon sensitivity.

Vasile, S.; Gothoskar, P.; Farrell, R. [Radiation Monitoring Devices, Inc., Watertown, MA (United States)] [Radiation Monitoring Devices, Inc., Watertown, MA (United States); Sdrulla, D. [Advanced Power Technology, Bend, OR (United States)] [Advanced Power Technology, Bend, OR (United States)

1998-06-01

287

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

288

The Vaigat Rock Avalanche Laboratory, west-central Greenland  

NASA Astrophysics Data System (ADS)

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

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

2013-12-01

289

Debris Avalanches along the South Aegean Volcanic Arc  

NASA Astrophysics Data System (ADS)

Several hummocky deposits have been discovered along the Aegean Volcanic Arc using multibeam bathymetric mapping, airgun seismic profiling, side scan sonar survey and ROV dives. In particular, these hummocks have been discovered on the submarine flanks of Antimilos, Santorini and Nisyros volcanic islands: (i)The seabed morphology of the area northeast of Antimilos exhibits a rather irregular small-scale rough relief and an assembly of three hills in the form of volcanic domes with decreasing size eastwards. The seabed topography and the character of the backscattered intensity of the small scale morpho-bathymetric features, led us to interpret them accordingly as submarine volcanic debris avalanche, flows, domes or dikes, analogous to the on-land outcropping volcanic features. (ii) Analysing of geophysical data shows that hummocky seafloor features on the eastern flank of Santorini volcano cover an area 6 Km wide by 20 Km long and up to 75m in thickness in the central region where the highest concentration of hummocky deposits occur. The hummocks are composed of several individual blocks that are a few meters to hundreds of meters in diameter and protrude up to tens of meters from the surrounding seafloor. The total volume of the deposit is estimated to be approximately 4.4×109 m3 as a result of multi-stage landslide event. (iii) The hummocky topography on the sea bottom in front of the southeastern Nisyros coastline is characterized by numerous hills and longitudinal ridges which cover a tongue-shaped area in plan view (about 16 km2), elongated towards SE. The overall morphology of this area can be viewed as a large deposit from a volcanic debris avalanche with a seaward termination displaying an irregular pattern characterized by elongated lobes. The source of these hummocks may be found in Nikia lava flow in the south-eastern flank of Nisyros volcano. The above described hummocks are the result of debris avalanches that were triggered during Holocene either by large earthquakes or volcanic eruptions. Debris avalanches are one of the most significant causes of dangerous hazards in coastal volcanic environments. Understanding how these events are triggered and the potential dynamics of future events is of utmost importance, particularly in highly populated regions such as the Aegean.

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

2012-04-01

290

A 1.06 micrometer avalanche photodiode receiver  

NASA Technical Reports Server (NTRS)

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

Eden, R. C.

1975-01-01

291

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 Bødalen) 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 Bødalen in western Norway.

Laute, Katja; Beylich, Achim A.

2014-08-01

292

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

NASA Astrophysics Data System (ADS)

The study of snow avalanches and their geomorphological effect in the periglacial parts of the cryosphere is important for enhanced geomorphological process understanding as well as hazard-related studies. Only a few field studies, and particularly few in the High Arctic, have quantified avalanche sedimentation. Snow avalanches are traditionally ranked behind rockfall in terms of their significance for mass-wasting processes of rockslopes. Cornice fall avalanches are at present the most dominant snow avalanche type at two slope systems, called Nybyen and Larsbreen, in the valley Longyeardalen in central Svalbard. Both slope systems are on northwest-facing lee slopes underneath a large summit plateau, with annual cornices forming on the top. High-frequency and magnitude cornice fall avalanching is observed by daily automatic time-lapse photography. In addition, rock debris sedimentation by cornice fall avalanches was measured directly in permanent sediment traps or by snow inventories. The results from a maximum of seven years of measurements in a total of 13 catchments show maximum mean rock debris sedimentation rates ranging from 8.2 to 38.7 kg m-2 at Nybyen, and from 0.8 to 55.4 kg m-2 at Larsbreen. Correspondingly, avalanche fan surfaces accreted from 2.6 to 8.8 mm yr-1 at Nybyen, and from 0.2 to 13.9 mm yr-1 at Larsbreen. This comparably efficient rockslope mass wasting is due to collapsing cornices producing cornice fall avalanches containing large amounts of rock debris throughout the entire winter. The rock debris of different origin stems from the plateau crests, the adjacent free rock face and the transport pathway, accumulating distinct avalanche fans at both slope systems. Cornice fall avalanche sedimentation also contributed to the development of a rock glacier at the Larsbreen site during the Holocene. We have recorded present maximum rockwall retreat rates of 0.9 mm yr-1 at Nybyen, but as much as 6.7 mm yr-1 at Larsbreen, while average Holocene rockwall retreat rates of 1.1 mm yr-1 at Nybyen have been determined earlier. As cornice fall avalanches are the dominant type of avalanche in central Svalbard, the related geomorphological effect is assumed to be of significance at periglacial landscape scale. A climate-induced shift in prevailing winter wind direction could change the rockslope sedimentation effectively by changing the snow avalanche activity.

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

2013-09-01

293

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

294

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

295

The Savage-Hutter model for the avalanche dynamics in inclined channels: analytical solutions  

NASA Astrophysics Data System (ADS)

The Savage-Hutter model is applied to describe gravity driven shallow-water flows in inclined channels of parabolic-like shapes modeling avalanches moving in mountain valleys or landslide motions in underwater canyons. The Coulomb (sliding) friction term is included in the model. Several analytical solutions describing the nonlinear dynamics of avalanche are obtained: the nonlinear deformed (Riemann) wave, the dam-break problem, self-similar solutions and others. Some of them extend the known solution for an inclined plate (1D geometry). The cross section shape of the inclined channels significantly influences the speed of avalanche propagation and characteristic time of dynamical processes. Obtained analytical solutions can be used to test numerical models and to give insights into the structure of avalanche flow and to highlight basic mechanisms of avalanche dynamics.

Talipova, Tatiana; Zahibo, Narcisse; Pelinovsky, Efim; Nikolkina, Irina

2010-05-01

296

Savage-Hutter model for avalanche dynamics in inclined channels: Analytical solutions  

NASA Astrophysics Data System (ADS)

The Savage-Hutter model is applied to describe gravity driven shallow water flows in inclined channels of parabolic-like shapes modeling avalanches moving in mountain valleys or landslide motions in underwater canyons. The Coulomb (sliding) friction term is included in the model. Several analytical solutions describing the nonlinear dynamics of avalanches are obtained: the nonlinear deformed (Riemann) wave, the dam break problem, self-similar solutions and others. Some of them extend the known solution for an inclined plate (one-dimensional geometry). The cross-section shape of the inclined channels significantly influences the speed of avalanche propagation and characteristic time of dynamical processes. Obtained analytical solutions can be used to test numerical models and to give insights into the structure of avalanche flow and to highlight basic mechanisms of avalanche dynamics.

Zahibo, Narcisse; Pelinovsky, Efim; Talipova, Tatiana; Nikolkina, Irina

2010-03-01

297

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

PubMed

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

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

2014-05-01

298

Corrections to scaling and probability distribution of avalanches for the stochastic Zhang sandpile model  

NASA Astrophysics Data System (ADS)

We study the distributions of dissipative and nondissipative avalanches separately in the stochastic Zhang (SP-Z) sandpile in two dimension. We find that dissipative and nondissipative avalanches obey simple power laws and do not have the logarithmic correction, while the avalanche distributions in the Abelian Manna model should include a logarithmic correction. We use the moment analysis to determine the numerical critical exponents of dissipative and nondissipative avalanches, respectively, and find that they are different from the corresponding values in the Abelian Manna model. All these indicate that the stochastic Zhang model and the Abelian Manna model belong to distinct universality classes, which imply that the Abelian symmetry breaking changes the scaling behavior of the avalanches in the case of the stochastic sandpile model.

Zhang, Duan-Ming; Yin, Yan-Ping; Pan, Gui-Jun; Sun, Fan

2006-05-01

299

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. Kääb; A. Polkvoj; I. Galushkin; S. G. Evans

2005-01-01

300

Snow-avalanche hazard forecasting in the Krkonoše Mountains, Czechia  

NASA Astrophysics Data System (ADS)

The Krkonoše 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 Krkonoše 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 Krkonoše 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

301

Morphometric and meteorological controls of 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 due to the interactions between the prevalent climatic factors and local topography. Research on snow avalanches provides insights into possible effects of predicted climate change on avalanche activity and connected sediment transport in mountain areas. This study focuses on (i) controlling factors of avalanche distribution and activity, and (ii) their relative importance regarding mass transfers in two steep, parabolic-shaped and glacier-connected tributary valleys (Erdalen and Bødalen) in western Norway. Mapping of distribution, extension and run-out distances of avalanches is combined with spatial data analysis of morphometric controls. Based on correlation of climate data with monitored avalanche events the timing and frequency of avalanches is explored and debris mass transfer on hillslopes caused by avalanches is estimated. The denudative effect of snow avalanches occurs in two steps: firstly throughout erosion directly on the surface of the rockwall and secondly due to their transport ability which causes significant remobilization and transport of available debris further downslope. The spatial distribution of snow avalanches depends on the valley orientation, slope aspect and rockwall morphometry. Especially distinct laterally convex-shaped leeside upper rockwall areas allow a high accumulation rate of snow during winter which is then released as avalanches during spring. The timing and frequency of avalanches in both valleys depend mainly on snowfall intensity, periods with strong winds combined with a stable wind direction or sudden air temperature changes. Snow avalanche activity leads in some valley areas to significant hillslope-channel coupling because debris is transported far enough by avalanches to reach channels. Snow avalanches represent one of the dominant denudational processes and have a high relative importance regarding mass transfer within the sedimentary budgets of the entire valleys.

Laute, Katja; Beylich, Achim A.

2013-04-01

302

First-principles derivation of static avalanche-size distributions.  

PubMed

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 Lévy 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. PMID:23005046

Le Doussal, Pierre; Wiese, Kay Jörg

2012-06-01

303

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

304

Vortex Avalanches with Periodic Arrays of Pinning Sites  

NASA Astrophysics Data System (ADS)

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

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

2001-03-01

305

Single photon detection using Geiger mode CMOS avalanche photodiodes  

NASA Astrophysics Data System (ADS)

Geiger mode Avalanche Photodiodes fabricated using complementary metal-oxide-semiconductor (CMOS) fabrication technology combine high sensitivity detectors with pixel-level auxiliary circuitry. Radiation Monitoring Devices has successfully implemented CMOS manufacturing techniques to develop prototype detectors with active diameters ranging from 5 to 60 microns and measured detection efficiencies of up to 60%. CMOS active quenching circuits are included in the pixel layout. The actively quenched pixels have a quenching time less than 30 ns and a maximum count rate greater than 10 MHz. The actively quenched Geiger mode avalanche photodiode (GPD) has linear response at room temperature over six orders of magnitude. When operating in Geiger mode, these GPDs act as single photon-counting detectors that produce a digital output pulse for each photon with no associated read noise. Thermoelectrically cooled detectors have less than 1 Hz dark counts. The detection efficiency, dark count rate, and after-pulsing of two different pixel designs are measured and demonstrate the differences in the device operation. Additional applications for these devices include nuclear imaging and replacement of photomultiplier tubes in dosimeters.

Lawrence, William G.; Stapels, Christopher; Augustine, Frank L.; Christian, James F.

2005-10-01

306

Tuned Critical Avalanche Scaling in Bulk Metallic Glasses  

NASA Astrophysics Data System (ADS)

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.

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

2014-03-01

307

Nucleation and Avalanche of 4He Crystals in Aerogel  

NASA Astrophysics Data System (ADS)

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

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

2010-02-01

308

Data collapse and critical dynamics in neuronal avalanche data  

NASA Astrophysics Data System (ADS)

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

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

2012-02-01

309

Space charge limited avalanche growth in multigap resistive plate chambers  

NASA Astrophysics Data System (ADS)

The ALICE TOF array will be built using the Multigap Resistive Plate Chamber(MRPC) configured as a double stack. Each stack contains 5 gas gaps with width of 250 ?m. There has been an intense R&D effort to optimise this new detector to withstand the problems connected with the high level of radiation at the LHC. One clear outcome of the R&D is that the growth of the gas avalanche is strongly affected by space charge. The effect of the space charge is a decrease in the rate of change in gain with electric field; this allows more stable operation of this detector. We have measured the gain as a function of the electric field and also measured the ratio of the fast charge to the total charge produced in the gas gap. It is well established that RPCs built with 250 ?m gas gap have a much superior performance than 2 mm gaps; we discuss and compare the performance of 250 ?m gap MRPCs with 2 mm gap RPCs to show the importance of space-charge limitation of avalanche growth. PACS: 29.40.Cs - 7.77.-n - 52.80.Dy

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

310

Risk analysis for dry snow slab avalanche release by skier triggering  

NASA Astrophysics Data System (ADS)

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

McClung, David

2013-04-01

311

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 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.

2013-01-01

312

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 Üzengili (Bayburt province) in 1993 and Yaylaönü (Trabzon province) in 1981. The results demonstrate the value of such an approach for regions with poor avalanche databases, enabling the calculation of different scenarios and the estimation of run-out distances, flow velocities, impact pressure and flow height.

Ayd?n, A.; Bühler, Y.; Christen, M.; Gürer, I.

2014-01-01

313

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

NASA Astrophysics Data System (ADS)

In arctic and alpine high relief landscapes snow avalanches are traditionally ranked behind rockfall in terms of their significance for mass wasting processes of rock slopes. Cornice fall avalanches are at present the most dominant snow avalanche type at two slope systems, called Nybyen and Larsbreen, in the valley Longyeardalen in Central Svalbard. Both slope systems are situated on NW-facing lee slopes underneath large summit plateau, where cornices form annually, and high frequency and magnitude cornice fall avalanching is observed by daily automatic time-lapse photography. In addition, rock debris sedimentation by these cornice fall avalanches was measured directly in either permanent sediment traps or by snow inventories. The results from a maximum of 7 yr of measurements in a total of 13 catchments show maximum avalanche sedimentation rates ranging from 8.2 to 38.7 kg m-2 at Nybyen and from 0.8 to 55.4 kg m-2 at Larsbreen. Correspondingly, the avalanche fan-surfaces accreted annually in a~maximum range from 3.7 to 13 mm yr-1 at Nybyen and from 0.3 to 21.4 mm yr-1 at Larsbreen. This comparably efficient rock slope mass wasting is due to collapsing cornices producing cornice fall avalanche with high rock debris content throughout the entire winter. The rock debris of different origin stems from the plateau crests, the adjacent free rock face and the transport pathway, accumulating distinct avalanche fans at both slope systems and contributing to the development of a rock glacier at the Larsbreen slope system.

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

2012-12-01

314

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

NASA Astrophysics Data System (ADS)

In Obernberg valley, Eastern Alps, Austria, an array of landforms previously interpreted as terminal moraines (by other authors) is re-interpreted by us as a rock avalanche. In their distal 2 km, the rock avalanche mass is characterized by an ensemble of 40 hillocks and transversal ridges up to 17 m in vertical relief. The internal fabric of the ridges is incompatible with a glacial origin, but consistent with dynamic disintegration as diagnostic of rock avalanches. Catastrophic slope failure involved a rock volume of 4.5e7 m³, and a runout of 7.2 km over a vertical distance of 1330 m (fahrböschung 10°); the deposits cover an area of ~3 km². Ground electrical tomography with six multielectrode profiles provided information on the depth to substrate, and on the internal structure, of the rock avalanche. The volume of accumulated rock debris is estimated at 5.3e7 m³. A radiocarbon age of 7785 ± 190 cal yr BP of organic remnants in an alluvial fan that downlaps the rock avalanche provides a minimum-age constraint ('older-than' age) on mass-wasting. A mean 36Cl surface-exposure age of 8.6 ± 0.6 ka BP of boulders of the avalanche mass indicates that the event took place during the early Holocene. Palaeoclimatic records indicate that, neither, the detachment scar, nor the runout track of the rock avalanche were glaciated at the time of mass-wasting. A lake basin in the proximal part of the rock-avalanche mass thus did not form as a result of dead ice melting. Marked seasonal fluctuations of lake level, combined with strong changes in shedding of springs downslope of the lake, suggest that the basin had formed by combined eluviation and dissolution of cataclastic rock-avalanche matrix and, perhaps, by karstification of underlying carbonate rocks.

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

2013-04-01

315

Infrasound array observations of snow avalanches: support to controlled activity and implications to risk assessment  

NASA Astrophysics Data System (ADS)

Snow avalanches can radiate infrasound (low frequency <20 Hz sound) as the front moves downhill and accelerates. An highly variable efficiency in the infrasound radiation, related to the coupling of the front with the atmosphere, is documented for different kinds of events, being maximum for powder snow avalanches. Here, once infrasound is radiated from the avalanche front, it can propagate far away (> several km), thus representing a valuable monitoring system. However, snow avalanche infrasound did not develop significantly after the first pioneer studies, and attempts to use infrasound as a monitoring/alert systems are sparse and often abandoned, given the high uncertainty of the results and the large numbers of false alarms. The main source of difficulty is the strong ambiguity in the waveform, with the infrasound radiated from avalanches being emergent, of long duration, and low amplitude (typically < few Pa) making identification from noise or infrasound from additional sources not trivial. Significant advances in the infrasound analysis of snow avalanches result from the use of arrays, rather then single sensors, as they allow to robustly retrieve wave parameters (etc. back-azimuth/slowness) that support the identification of the possible source mechanism. We presents results from observations performed during the last 4 years in Italy (Champoluc, Valtournenche and Gressoney, AO), Austria (Ischgl) and Swiss (Goms) and discuss them in terms of real-time monitoring of avalanche activity, spanning from a qualitative analysis of medium-range (> several km) avalanche observations for a general risk assessment, up to detailed, quantitative, short range (1-2 km) observation to support controlled avalanche release.

Marchetti, Emanuele; Ripepe, Maurizio; Ulivieri, Giacomo

2014-05-01

316

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

NASA Astrophysics Data System (ADS)

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

de Arcangelis, L.

2012-05-01

317

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 levée 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

318

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

NASA Astrophysics Data System (ADS)

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

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

2002-11-01

319

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

320

Back-illuminated separate absorption and multiplication AlGaN solar-blind avalanche photodiodes  

NASA Astrophysics Data System (ADS)

This letter reports the fabrication and performance of back-illuminated separate absorption and multiplication AlGaN solar-blind avalanche photodiodes. Devices with a 60-?m-diameter active area and a double-mesa structure exhibit a low dark current density of 1.06 × 10-8 A/cm2 at the reverse bias of 20 V and a maximum multiplication gain up to 3000 at the reverse bias of 91 V. The temperature dependence of avalanche voltage shows a large positive temperature coefficient of 0.05 V/K, confirming that avalanche multiplication is the dominant gain mechanism in the photodiodes.

Huang, Y.; Chen, D. J.; Lu, H.; Dong, K. X.; Zhang, R.; Zheng, Y. D.; Li, L.; Li, Z. H.

2012-12-01

321

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

322

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

323

Study of avalanche mode operation of resistive plate chambers with different gas gap structures  

NASA Astrophysics Data System (ADS)

The operation of narrow gap, wide gap and multigap resistive plate chambers in an avalanche mode was studied. No advantage in avalanche-streamer separation was found for the wide gap and multigap chambers operating with Ar-based mixture as compared with the narrow gap chamber. For dense tetrafluoroethane-based mixture, proportionality was observed between streamer-free plateau width and total gas thickness, in rough agreement with corresponding shift of the maximum of avalanche charge distributions from zero. The best result was obtained for double-gap chamber with the read-out electrode located between two subgaps.

Ammosov, V. V.; Gapienko, V. A.; Konstantinov, V. F.; Sviridov, Yu. M.; Zaets, V. G.

2000-03-01

324

Avalanches and waves in the Abelian sandpile model  

NASA Astrophysics Data System (ADS)

We numerically study avalanches in the two-dimensional Abelian sandpile model in terms of a sequence of waves of toppling events. Priezzhev et al. [Phys. Rev. Lett. 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, ?s=sk-sk+1, where the size of the previous wave sk was considered to be almost always an upper bound for the size of the next wave sk+1. Here we show that the significant contribution to ?s comes from waves that violate the bound; the average is actually negative and diverges with the system size, contradicting the proposed solution.

Paczuski, Maya; Boettcher, Stefan

1997-10-01

325

High resolution, low energy avalanche photodiode X-ray detectors  

NASA Technical Reports Server (NTRS)

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

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

1991-01-01

326

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

327

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

328

Design and characterization of avalanche photodiodes in submicron CMOS technologies  

NASA Astrophysics Data System (ADS)

The fabrication of Avalanche Photodiodes (APDs) in CMOS processes can be exploited in several application domains, including telecommunications, time-resolved optical detection and scintillation detection. CMOS integration allows the realization of systems with a high degree of parallelization which are competitive with hybrid solutions in terms of cost and complexity. In this work, we present a linear-mode APD fabricated in a 0.15?m process, and report its gain and noise characterization. The experimental observations can be accurately predicted using Hayat dead-space noise model. Device simulations based on dead-space model are then used to discuss the current status and the perspectives for the integration of high-performance low-noise devices in standard CMOS processes.

Pancheri, L.; Bendib, T.; Dalla Betta, G.-F.; Stoppa, D.

2014-03-01

329

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

330

Snow drift: acoustic sensors for avalanche warning and research  

NASA Astrophysics Data System (ADS)

Based on wind tunnel measurements at the CSTB (Jules Verne) facility in Nantes and based on field observations at the SLF experimental site Versuchsfeld Weissfluhjoch, two acoustic wind drift sensors are evaluated against different mechanical snow traps and one optical snow particle counter. The focus of the work is the suitability of the acoustic sensors for applications such as avalanche warning and research. Although the acoustic sensors have not yet reached the accuracy required for typical research applications, they can, however, be useful for snow drift monitoring to help avalanche forecasters. The main problem of the acoustic sensors is a difficult calibration that has to take into account the variable snow properties. Further difficulties arise from snow fall and high wind speeds. However, the sensor is robust and can be operated remotely under harsh conditions. It is emphasized that due to the lack of an accurate reference method for snow drift measurements, all sensors play a role in improving and evaluating snow drift models. Finally, current operational snow drift models and snow drift sensors are compared with respect to their usefulness as an aid for avalanche warning. While drift sensors always make a point measurement, the models are able to give a more representative drift index that is valid for a larger area. Therefore, models have the potential to replace difficult observations such as snow drift in operational applications. Current models on snow drift are either only applicable in flat terrain, are still too complex for an operational application (Lehning et al., 2000b), or offer only limited information on snow drift, such as the SNOWPACK drift index (Lehning et al., 2000a). On the other hand, snow drift is also difficult to measure. While mechanical traps (Mellor 1960; Budd et al., 1966) are probably still the best reference, they require more or less continuous manual operation and are thus not suitable for remote locations or long-term monitoring. Optical sensors (Schmidt, 1977; Brown and Pomeroy, 1989; Sato and Kimura, 1993) have been very successful for research applications, but suffer from the fact that they give a single flux value at one specific height. In addition, they have not been used, to our knowledge, for long-term monitoring applications or at remote sites. New developments of acoustic sensors have taken place recently (Chritin et al., 1999; Font et al., 1998). Jaedicke (2001) gives examples of possible applications of acoustic snow drift sensors. He emphasizes the advantages of acoustic sensors for snow drift monitoring at remote locations, but could not present any evaluation of the accuracy of the measurements. We present a complete evaluation of the new acoustic sensors for snow drift and discuss their applications for research or avalanche warning. We compare the suitability of sensors for operational applications.

Lehning, M.; Naaim, F.; Naaim, M.; Brabec, B.; Doorschot, J.; Durand, Y.; Guyomarc'h, G.; Michaux, J.-L.; Zimmerli, M.

331

High gain avalanche photodiode arrays for DIRC applications  

SciTech Connect

The detection of light emitted in Cherenkov radiators requires fast detector arrays with high sensitivity to short wavelength photons. Photomultiplier tubes, the traditional imaging detectors for short wavelength optical radiation, have limited spatial resolution and require expensive anti-magnetic shielding. The authors report on the performance of a new, Geiger mode operated, silicon micro-avalanche photodiode ({micro}APD) array, designed for Cherenkov light imaging applications. They address issues of optical interfacing, speed, and pulse spectra achievable with these {micro}APDs. The new {micro}APD array provides a high sensitivity detector for applications requiring two dimensional light mapping with single photon sensitivity. These features make it a promising candidate for the detection of Cherenko light in modern high energy physics experiments.

Vasile, S.; Shera, S.; Shamo, D.; Squillante, M.R. [Radiation Monitoring Devices, Inc., Watertown, MA (United States)] [Radiation Monitoring Devices, Inc., Watertown, MA (United States); Wilson, R.J. [Colorado State Univ., Fort Collins, CO (United States)] [Colorado State Univ., Fort Collins, CO (United States)

1999-08-01

332

Some tests of avalanche photodiodes produced by Advanced Photonix, Inc  

NASA Astrophysics Data System (ADS)

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

Foster, G. W.; Ronzhin, A.; Rusack, R.

1995-08-01

333

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

334

Fast Thermal Shutdown of Tokamak Discharges Without Runaway Electron Avalanching  

SciTech Connect

The possibility of using massive quantities of injected deuterium with and without additional admixture of lesser quantities of higher-Z impurities to effect fast thermal shutdown of a tokamak discharge without causing runaway electron avalanching is systematically studied. It is found that various combinations of deuterium alone and deuterium with impurities (helium, nitrogen, argon, and krypton) can provide acceptable runaway-free thermal shutdown. The admixture of impurities cited reduces the quantity of deuterium needed and also reduces the radiative cooling time needed for the plasma to reach final thermal equilibrium, where radiation losses balance ohmic input. In contrast, the addition of neon does not appreciably reduce deuterium quantity or promote faster cooling. This difference relative to the other impurity studies can be understood from the radiation versus plasma temperature characteristics for neon.

Bakhtiari, M.; Yoshino, R.; Nishida, Y

2002-03-15

335

Design, fabrication, and characterization of InSb avalanche photodiode  

NASA Astrophysics Data System (ADS)

In this communication, the potentiality of InSb material as an avalanche photodiode (APD) device is investigated. Current density-voltage (J-V) characteristics at 77K of InSb pin photodiodes were simulated by using ATLAS software from SILVACO, in dark conditions and under illumination. In order to validate parameter values used for the modeling, theoretical J-V results were compared with experimental measurements performed on InSb diodes fabricated by molecular beam epitaxy. Next, assuming a multiplication process only induced by the electrons (e-APD), different designs of separate absorption and multiplication (SAM) APD structure were theoretically investigated and the first InSb SAM APD structure with 1?m thick multiplication layer was then fabricated and characterized.

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

2013-12-01

336

Investigations as to the Noise Characteristics of GaAs Avalanche Transit Time Diode Oscillators.  

National Technical Information Service (NTIS)

Gallium arsenide p-n junction avalanche transit time oscillators were characterized with respect to noise performance. The results of these measurements were compared to other p-n junction oscillators, Read diodes, and Gunn diodes. Measurements include: r...

J. J. Baranowski V. J. Higgins

1970-01-01

337

Landsat Thematic Mapper observations of debris avalanche deposits in the Central Andes  

NASA Technical Reports Server (NTRS)

Remote sensing with the Landsat Thematic Mapper of debris avalanche deposits in the Central Andes between 18 and 27 deg S revealed, for the first time, the presence of 28 breached volcanic cones and 11 major volcanic debris avalanche deposits, several of which cover areas in excess of 100 sq km. It is concluded that such avalanche deposits are normal products of the evolution of large composite volcanoes, comparable with lava and pyroclastic flow deposits. A statistical survey of 578 composite volcanoes in the same area indicated that a majority of cones which achieve edifice heights between 2000 and 3000 m may undergo sector collapse. The paper describes morphological criteria for identifying breached composite cones and volcanic debris avalanches using orbital images.

Francis, P. W.; Wells, G. L.

1988-01-01

338

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

NASA Astrophysics Data System (ADS)

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

Baker, Jennifer

339

Mechanics of Debris Avalanching in Shallow Till Soils of Southeast Alaska.  

National Technical Information Service (NTIS)

Studies indicate a combination of total saturation, slopes with gradients above the natural angle of stability (greater than 34 degrees), and loss of the stabilizing effect of anchoring tree roots are the principal causes of debris avalanching on till soi...

D. N. Swanston

1970-01-01

340

Critical Scaling of Avalanche Dynamics in Sheared Amorphous Solids with Inertia  

NASA Astrophysics Data System (ADS)

We present results from molecular-dynamics simulations of model disordered solids under quasi-static, steady-state shear in two and three dimensions. Plastic deformation occurs through intermittent ``avalanches'' of local rearrangements. As in other slowly-driven systems from magnets to geologic faults, avalanches exhibit critical scaling behavior. Results for the avalanche statistics, duration and power spectrum are analyzed with finite-size scaling. The exponents describing the power law distribution of avalanches and the relation between their size and duration are independent of dimension, suggesting that mean field behavior extends to two dimensions. In contrast, the scaling exponents depend on the degree of inertia or damping, with distinct universality classes in the underdamped and overdamped limits [1]. The same universality classes are observed with Galilean-invariant and non-Galilean-invariant thermostats, but the crossover between these limits will be contrasted. The implications for different experimental systems will be discussed. [1] PRL 109, 105703 (2012).

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

2013-03-01

341

Methods to improve gain and dark current of photon counting avalanche photo-diodes  

Microsoft Academic Search

By controlling the voltage difference between the punch-through and breakdown voltages photon-counting APD leakage current and avalanche I-V characteristics can be improved. We fabricated different devices and demonstrated performance improvement at different temperatures.

S. Wu; Xiucheng Wu; Fow-Sen Choa; M. A. Krainak

2006-01-01

342

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

NASA Astrophysics Data System (ADS)

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

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

2013-03-01

343

The properties of ITE's silicon avalanche photodiodes within the spectral range used in scintillation detection  

NASA Astrophysics Data System (ADS)

The design and properties of 3 mm silicon avalanche photodiodes developed at ITE are presented. Their performance parameters within the spectral range applicable in scintillation detection (400-700 nm) are discussed and compared to those for near infrared radiation.

Wegrzecka, Iwona; Wegrzecki, Maciej

1999-04-01

344

Robust snow avalanche detection using machine learning on infrasonic array data  

NASA Astrophysics Data System (ADS)

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

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

2014-05-01

345

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

Microsoft Academic Search

Shiveluch Volcano, located in the Central Kamchatka Depression, has experienced multiple flank failures during its lifetime,\\u000a most recently in 1964. The overlapping deposits of at least 13 large Holocene debris avalanches cover an area of approximately\\u000a 200?km2 of the southern sector of the volcano. Deposits of two debris avalanches associated with flank extrusive domes are, in addition,\\u000a located on its

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

1998-01-01

346

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

Microsoft Academic Search

We discuss a leading-edge model used in the computation of the run-out length of dry-flowing avalanches. The model has the form of a singular initial value problem for a scalar ordinary dierential equation describing the avalanche dynamics. Exis- tence, uniqueness and smoothness properties of the analytical solution are shown. We also prove the existence of a unique root of the

Othmar Koch; Ewa Weinmuller

2003-01-01

347

A xenon gas proportional scintillation counter with a UV-sensitive large-area avalanche photodiode  

Microsoft Academic Search

The performance characteristics of a xenon gas proportional scintillation counter comprising a large-area avalanche photodiode with enhanced ultraviolet sensitivity were evaluated. By integrating the photodiode within the xenon gas envelope of the scintillator, the intervening quartz window was eliminated. Energy resolutions of 7.8% and 4.4% were measured for 5.9- and 22.1-keV X-rays, respectively. The results demonstrate that large-area avalanche photodiodes

J. A. M. Lopes; J. M. F. dos Santos; R. E. Morgado; C. A. N. Conde

2001-01-01

348

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

Microsoft Academic Search

The authors report silicon avalanche photodetectors (APDs) fabricated with 0.18 mum standard complementary metal-oxide-semiconductor (CMOS) process without any process modification or a special substrate. When the bias is above the avalanche breakdown voltage, CMOS-compatible APD (CMOS-APD) exhibits negative photoconductance in photocurrent-voltage relationship and rf peaking in the photodetection frequency response. The reflection coefficient measurement of CMOS-APD indicates that rf peaking

Hyo-Soon Kang; Myung-Jae Lee; Woo-Young Choi

2007-01-01

349

Electrothermal instability in multi-cellular Trench-IGBTs in avalanche condition: Experiments and simulations  

Microsoft Academic Search

This paper reports on the results of a study on electro-thermal instability induced in multi-cellular Trench- IGBTs in avalanche condition. Experimental measurements, made on T-IGBTs, show possible inhomogeneous current distri- bution under Unclamped Inductive Switching (UIS) confirmed by transient infrared thermography measurements. Together with this, an analytical modeling of avalanche behavior has been included in a compact electro-thermal simulator to

M. Riccio; A. Irace; G. Breglio; P. Spirito; E. Napoli; Y. Mizuno

2011-01-01

350

An early Holocene rock avalanche at Obernberg (Brenner Pass Area, Tyrol)  

NASA Astrophysics Data System (ADS)

In Obernberg valley, Eastern Alps, Austria, the character of a rock avalanche deposit led to diverse interpretations for more than a hundred years. Recently, this landform was interpreted as moraines, but we could verify its origin from a rock avalanche. The most controversial parts of the landform are the distal two kilometers of the rock-avalanche deposit which are characterized by a highly regular array of transverse ridges. These ridges and hills previously were interpreted as terminal moraines of late-Glacial glaciers. 'Jigsaw-puzzle structure' of gravel to boulder-size clasts in the ridges combined with a matrix of cataclastic gouge indicate that they originated from a rock avalanche. Additionally the transversal ridges are arranged into two highly regular, 'higher-order waves' each composed of waxing and shrinking ridges. We suggest that the arrayed ridges reflect an aspect of the mechanics of movement, perhaps propagation of waves towards the snout of the rock avalanche deposit. The catastrophic slope failure involved an initial rock volume of about 45 mio m3, with a runout of 7.2 km over a total vertical distance of 1330 m (fahrböschung 10°). A minimum-age constraint of the mass-wasting event was obtained by radiocarbon dating of organic remnants found in an alluvial fan on top of the rock avalanche deposits. The radiocarbon age is consistent with a 36Cl surface-exposure age of 8.6 ± 0.6 ka BP of boulders of the avalanche mass. To get more detailed information on the depth extent of the rock avalanche body, the internal structure of the mass movement, and the depth to rock basement, six geoelectrical multielectrode profiles were measured. The interpretations of the results have been used to estimate the volume of accumulated rock debris.

Ostermann, M.; Sanders, D.; Ivy-Ochs, S.; Alfimov, V.; Rockenschaub, M.; Römer, A.

2012-04-01

351

Gigahertz quantum key distribution with InGaAs avalanche photodiodes  

Microsoft Academic Search

We report a demonstration of quantum key distribution (QKD) at gigahertz clock rates with InGaAs avalanche photodiodes (APDs) operating in a self-differencing mode. Such a mode of operation allows detection of extremely weak avalanches so that the detector afterpulse noise is sufficiently suppressed. The system is characterized by a secure bit rate of 2.37 Mbit?s at 5.6 km and 27.9

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

2008-01-01

352

Numerical examination of silicon avalanche photodiodes operated in charge storage mode  

Microsoft Academic Search

The behavior of silicon-based avalanche photodiodes (APD's) operated in the charge storage mode is examined. In the charge storage mode, the diodes are periodically biased to a sub-breakdown voltage and then open-circuited. During this integration period, photo-excited and thermally generated carriers are accumulated within the structure. The dynamics of this accumulation and its effects upon the avalanching of the diode

J. W. Parks; K. F. Brennan

1998-01-01

353

Single-photon avalanche diodes for the near-infrared range: detector and circuit issues  

Microsoft Academic Search

Recently developed InGaAs\\/InP devices suitable as single-photon avalanche diodes (SPADs) in the near-infrared range provide good detection efficiency and low time jitter, together with fairly low dark-count rate at moderately low temperature. However, the overall performance is still severely limited by the afterpulsing effect (due to carriers trapped in deep levels during the avalanche and later released). Experimental studies and

Alberto Tosi; Alberto Dalla Mora; Franco Zappa; Sergio Cova

2009-01-01

354

Avalanche multiplication in forward- and reverse-active mode bipolar junction transistors  

Microsoft Academic Search

Impact ionization in the reverse-biased base-collector space-charge layer of the bipolar junction transistor (BJT) can cause an avalanche collector current as well as a reverse (or negative) base current. We develop analytical models to predict and compare avalanche phenomena in the BJT biased under forward-active and under reverse-active operations. The models consider a position-dependent electric field in the space-charge layer,

J. J. LIOU

1993-01-01

355

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

356

Study of avalanche mode operation of resistive plate chambers with different gas gap structures  

Microsoft Academic Search

The operation of narrow gap, wide gap and multigap resistive plate chambers in an avalanche mode was studied. No advantage in avalanche-streamer separation was found for the wide gap and multigap chambers operating with Ar-based mixture as compared with the narrow gap chamber. For dense tetrafluoroethane-based mixture, proportionality was observed between streamer-free plateau width and total gas thickness, in rough

V. V. Ammosov; V. A. Gapienko; V. F. Konstantinov; Y. M. Sviridov; V. G. Zaets

2000-01-01

357

Study of avalanche mode operation of resistive plate chambers with different gas gap structures  

Microsoft Academic Search

The operation of narrow gap, wide gap and multigap resistive plate chambers in an avalanche mode was studied. No advantage in avalanche–streamer separation was found for the wide gap and multigap chambers operating with Ar-based mixture as compared with the narrow gap chamber. For dense tetrafluoroethane-based mixture, proportionality was observed between streamer-free plateau width and total gas thickness, in rough

V. V. Ammosov; V. A. Gapienko; V. F. Konstantinov; Yu. M. Sviridov; V. G. Zaets

2000-01-01

358

Design and Simulation Result of N Substrate Reverse Type Avalanche Photodiode (APD)  

Microsoft Academic Search

We present results of design and simulation of the n-substrate reverse type avalanche photodiode (APD), which internally amplifies the photocurrent by an avalanche process, with the diffusion and the epitaxial methods. We aim to develop the APD which is coupled with scintillating materials for X-ray and delta-ray detections. The purpose of this simulation is to investigate optimal design parameters including

M. H. Mun; S. W. Jung; Heedong Kang; Dosung Kim; H. J. Kim; Sang Hoon Lee

2009-01-01

359

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

360

A first dendrogeomorphologic approach of snow avalanche magnitude-frequency in Northern Iceland  

NASA Astrophysics Data System (ADS)

The paper examines the potential of dendrogeomorphic analyses to deliver a one-year resolution chronology of snow-avalanche winters in Northern Iceland, at the scale of a colluvial cone covered with European White Birch trees and shrubs (Betula pubescens Ehrh.). Reconstruction of the avalanche history is performed using tree-ring analyses. Determination of the most reliable growth disturbance (class 1 of growth eccentricity) and applying a tempering index value with threshold 10% of trees responding in the same year and at least two trees affected, avalanche-activity years are highlighted, resulting in 52 avalanche winters. Amongst those, 5 winters have activity index over 40%, indicating major years. Calculation of frequency of similar growth disturbances at each tree provides a return period ranging from 4.2 to 19 years. Inferred spatial extent of snow-avalanche events induces flow-like snow avalanches with limited extent around the tree-less parts of the cone with a return period under 6 years; the cone is totally covered and the distal tree-limit over-passed with a return period of 15-20 years.

Decaulne, Armelle; Eggertsson, Ólafur; Sæmundsson, Þorsteinn

2012-09-01

361

Geometrical Properties of Avalanches in a Pseudo-3D Coronal Loop  

NASA Astrophysics Data System (ADS)

We investigate the geometrical properties of energy release of synthetic coronal loops constructed using a recently published self-organized critical avalanche model of solar flares. The model is based on an idealized representation of a coronal loop as a bundle of closely packed magnetic flux strands wrapping around one another in response to photospheric fluid motions, much as in Parker's nanoflare model. Simulations are performed with a two-dimensional cellular automaton that satisfies the constraint ? · B = 0 by design. We transform the avalanching nodes produced by simulations into synthetic flare images by converting the two-dimensional lattice into a bent cylindrical loop that is projected onto the plane of the sky. We study the statistical properties of avalanches peak snapshots and time-integrated avalanches occurring in these synthetic coronal loops. We find that the frequency distribution of avalanche peak areas A assumes a power-law form f(A) ? A^{-?_{A}} with an index ? A sime 2.37, in excellent agreement with observationally inferred values and reducing error bars from previous works. We also measure the area fractal dimension D of avalanches produced by our simulations using the box counting method, which yields 1.17 <= D <= 1.24, a result falling nicely within the range of observational determinations.

Morales, Laura; Charbonneau, Paul

2009-06-01

362

Abelian deterministic self-organized-criticality model: complex dynamics of avalanche waves.  

PubMed

The aim of this study is to investigate a wave dynamics and a size scaling of avalanches which were created by the mathematical model [J. ?ernák, Phys. Rev. E 65, 046141 (2002)]. Numerical simulations were carried out on a two-dimensional lattice L×L in which two constant thresholds E(c)(I) = 4 and E(c)(II) > E(c)(I) were randomly distributed. The density of sites c of the thresholds E(c)(II) and threshold E(c)(II) are parameters of the model. Autocorrelations of avalanche size waves, Hurst exponents, avalanche structures, and avalanche size moments were determined for several densities c and thresholds E(c)(II). The results show correlated avalanche size waves and multifractal scaling of avalanche sizes not only for specific conditions, densities c = 0.0,1.0 and thresholds 8 ? E(c)(II) ? 32, in which relaxation rules were precisely balanced, but also for more general conditions, densities 0.0 < c < 1.0 and thresholds 8 ? E(c)(II) ? 32, in which relaxation rules were unbalanced. The results suggest that the hypothesis of a precise relaxation balance could be a specific case of a more general rule. PMID:21230653

Cernák, Jozef

2010-12-01

363

Artificial kagome spin ice: dimensional reduction, avalanche control and emergent magnetic monopoles.  

PubMed

Artificial spin-ice systems consisting of nanolithographic arrays of isolated nanomagnets are model systems for the study of frustration-induced phenomena. We have recently demonstrated that monopoles and Dirac strings can be directly observed via synchrotron-based photoemission electron microscopy, where the magnetic state of individual nanoislands can be imaged in real space. These experimental results of Dirac string formation are in excellent agreement with Monte Carlo simulations of the hysteresis of an array of dipoles situated on a kagome lattice with randomized switching fields. This formation of one-dimensional avalanches in a two-dimensional system is in sharp contrast to disordered thin films, where avalanches associated with magnetization reversal are two-dimensional. The self-organized restriction of avalanches to one dimension provides an example of dimensional reduction due to frustration. We give simple explanations for the origin of this dimensional reduction and discuss the disorder dependence of these avalanches. We conclude with the explicit demonstration of how these avalanches can be controlled via locally modified anisotropies. Such a controlled start and stop of avalanches will have potential applications in data storage and information processing. PMID:23166379

Hügli, R V; Duff, G; O'Conchuir, B; Mengotti, E; Rodríguez, A Fraile; Nolting, F; Heyderman, L J; Braun, H B

2012-12-28

364

Erosion and its Effects on Geophysical Granular Avalanches  

NASA Astrophysics Data System (ADS)

Many types of extreme geophysical flows such as debris avalanches and pyroclastic flows can be classified as granular avalanches. While sedimentation from these flows and their resulting deposits have been the subject of intense study for the past half-century, the effects of erosion have been difficult to ascertain. Despite the known relationship between slope angle and thickness of a stable layer of loose debris on a slope, hstop, which requires erosion during flow events, the positive change in volume of geophysical granular flows during transport has not been systematically studied. We present the results of experiments on the propagation of erosive granular flows. We use the experimental results to test a model that simulates granular avalanches in which erosion and deposition cause significant changes in mass and momentum during flow. Granular flow experiments were conducted under a variety of initial conditions to gain a quantitative understanding of erosion and its effects on propagation. Sand flows were released on a masonite plane to which 36 grit sandpaper had been glued. The masonite plane measured 95 cm times 60 cm. The plane was tilted at angles of 29.4 -- 36.5 degrees. Particles of sand grains sieved to 2 and 2.5 phi were used. The 2 phi particles were dyed blue to aid in visualization. The angles of repose for the 2 and 2.5 phi particles were measured in two types of slumping experiments yielding angles of 34 degrees for the 2 phi particles and 35 degrees for the 2.5 phi particles. The 2.5 phi particles were poured onto the plane before each experiment to provide an erodible surface. The thickness of the erodible layer was hstop. 425 +/- 0.9 g of 2 phi particles were then released on this surface from a 10.5-cm diameter cylindrical container. The propagation of the sand was measured by videotaping while a horizontal grid was projected onto the plane to measure flow thickness. Because of geometrical distortions and the difficulty in ascertaining the edge of the flow during periods when the material was thinly spread, the error in the measurements of the flows positions is estimated to range from 1 -- 2.5 cm. The sand was allowed to flow off the end of the inclined plane into a bin. We separated the two fractions by sieving. Using this technique, we were almost always able to ensure that < 1% of the blue, 2 phi particles were lost due to experimental error. It was possible to determine an erosion gradient for the experiments by starting separarate runs at each angle at different positions on the inclined plane. In this way, particles were collected after flowing different distances down the plane. Using the erosion gradient and flow speed data, we estimated erosion rate. It was possible to quantitatively match data on amount of material eroded and flow speed with the numerical model. Because it was not possible to distinguish bed particles in the numerical model, the results were summarized by comparing the mass of particles transported off the end of the slope. The results show that as slope angle increased and distance of the starting mass from the end of the slope decreased, the total mass of particles transported off the slope increased in both data and model. The results suggest that the numerical model is able to reproduce erosion conditions reasonably well over a range of slope angle and slope length conditions. The numerical model could be used to understand the process and effects of erosion in extreme geophysical granular flows.

Webb, A.; Bursik, M.; Patra, A.; Nichita, C.; Pitman, B.

2003-12-01

365

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

366

Simple models for intermittent deformation and slip avalanches: from crystals to granular materials and earthquakes  

NASA Astrophysics Data System (ADS)

Slowly sheared solid or densely packed granular materials often deform in an intermittent way with slip avalanches. The distribution of sizes follows often a power law over a broad range of sizes. In these cases, universal (i.e. detail-independent) scaling behavior governs the statistics of the slip-avalanches. Under some conditions, there are also "characteristic" statistics associated with enhanced occurrence of system-size events, and long-term mode switching between power law and characteristic behavior. These dynamic regimes can be understood with basic micromechanical model for deformation of solids with only two tuning parameter: weakening and dissipation of elastic stress transfer. For granular materials the packing fraction plays the role of the dissipation parameter and it sets the size of the largest slip avalanche. The model can reproduce observed stress-strain curves, power spectra of acoustic emissions, statistics of slip avalanches, and geometrical properties of slip, with a continuous phase transition from brittle to ductile behavior. Exact universal predictions for the power law exponents of the avalanche size distributions, durations, power spectra of acoustic emissions, and scaling functions are extracted using an analytical mean field theory and renormalization group tools. For granular materials a dynamic phase diagram with solid-like behavior and large slip avalanches at large packing fractions, and fluid-like behavior at lower packing fractions is obtained. The results agree with recent experimental observations and simulations of the statistics of dislocation dynamics in sheared crystals such as ice [1], slip avalanches in sheared granular materials [2], and avalanches in magnetic and fault systems [3,4]. [1] K. A. Dahmen, Y. Ben-Zion, and J.T. Uhl, "A micromechanical model for deformation in solids with universal predictions for stress strain curves and slip avalanches", Physical Review Letters 102, 175501/1-4 (2009). [2] K. A. Dahmen, Y. Ben-Zion, and J.T. Uhl, "A simple analytic theory for the statistics of avalanches in sheared granular materials" Nature Physics 7, 554-557 (2011) [3] K.A. Dahmen and Y. Ben-Zion, "The physics of jerky motion in slowly driven magnetic and earthquake fault systems", Encyclopedia of Complexity and Systems Science Springer. (Eds.: M.C. Marchetti and R. Meyers), Vol. 5, 5021-5037 Springer, (2009). [4] Ben-Zion, Y., K. A. Dahmen and J. T. Uhl, A unifying phase diagram for the dynamics of sheared solids and granular materials , Pure Appl. Geophys., DOI: 10.1007/s00024-011-0273-7, 2011.

Dahmen, K.; Ben-Zion, Y.; Uhl, J.

2011-12-01

367

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

NASA Astrophysics Data System (ADS)

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

Bartelt, Perry; Buser, Othmar; Glover, James

2014-05-01

368

Foliage penetration optimization for Geiger-mode avalanche photodiode lidar  

NASA Astrophysics Data System (ADS)

Geiger-mode avalanche photodiode (GMAPD) Lidar systems can be used to image targets that are partially concealed by foliage. This application of GMAPD Lidar is challenging because most APDs operating in Geiger- mode report only one range measurement per transmitted laser pulse. If a GMAPD makes a foliage range measurement, it cannot make a range measurement to a target concealed by the foliage. When too much laser energy is received, the vast majority of range measurements are from the foliage and only a small percentage are from the target. Some GMAPD Lidar systems can report their average detection probability during operation. The average detection probability, which is often called "P-det", is calculated over an array of GMAPDs, over multiple laser pulses, or over both. However, the detection probability does not distinguish between target range measurements, foliage range measurements, and noise events. In this paper, it is shown that when certain collection parameters are known, that the probability of detecting a target obscured by foliage can be maximized by selecting the appropriate "P-det". It is also shown that for a typical foliage penetration scenario where most of the reflected laser energy is from the foliage that operating with a "P-det" between 65% and 80% produces a near-maximum target detection probability.

Johnson, Steven E.

2013-05-01

369

Influence of snow properties on dense avalanche friction parameters  

NASA Astrophysics Data System (ADS)

The values of the Voellmy friction parameters of 735 historical avalanches that occurred along 26 paths in the Chamonix valley since 1958 are back-analysed with a depth-averaged hydraulic model including sub models for erosion, entrainment and deposition. For each path, the longitudinal and crosswise topographic profiles were derived from a high resolution digital elevation model acquired by laser scanning. The initial snow depth and snow cohesion, as well as various physical properties of snow, were computed from numerical simulations of the detailed snowpack model Crocus fed by the SAFRAN meteorological analysis. For each event, the full ranges of the two friction parameters were scanned and the pairs of friction parameters for which the run-out altitude is found close enough to the observed one (with an uncertainty of 5m), were retained. Statistical class analysis was used to investigate the correlation between the obtained friction coefficients and the snow physical properties. Concerning the inertial friction coefficient, no evident trend with the snow parameters was found. For the static friction coefficient, an increasing trend with the temperature and the density was observed, as well as a decreasing trend with the liquid water content and the initial snow depth.

Mohamed, Naaim

2013-04-01

370

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

371

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

372

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

373

Avalanches in the growth of stress-induced martensites  

NASA Astrophysics Data System (ADS)

We present an experimental study of phase-transition avalanches during the stress-induced formation of martensite in a Cu-Zn-Al alloy, with particular attention to the effect of cycling. We have analyzed statistically the amplitudes, durations, and energies of the thermal events accompanying the transition, and found that these magnitudes distribute according to power laws in the first fifty cycles, within experimental error, with exponents ?=2.3+/-0.2, ?=2.9+/-0.7, and ?=1.8+/-0.3, respectively. However, the extent of power-law behavior is reduced by at least one decade after five hundred transition cycles, and the system is seen to become progressively subcritical. We present a method of measuring the distribution of energy barriers encountered along the transition, which in our case is found to spread over more than four orders of magnitude. Finally, we have observed that repeated cycling leads to a statistical reproducibility of transformation trajectories, and to the remarkable correlation between the cycle-to-cycle trajectory fluctuations and the cycle-averaged response function of the system observed recently in magnetic systems [J.S. Urbach, R.C. Madison, and J.T. Markert, Phys. Rev. Lett. 75, 4694 (1995)].

Carrillo, Lluís; Ortín, Jordi

1997-11-01

374

Hot Spots from Dislocation Pile-up Avalanches  

NASA Astrophysics Data System (ADS)

The model of hot spots developed at dislocation pile-up avalanches has been employed to explain both: greater drop- weight heights being required to initiate chemical decomposition of smaller crystals [1]; and, the susceptibility to shear banding of energetic and reference inert materials, for example, adiabatic shear banding in steel [2]. The evidence for RDX (cyclotrimethylenetrinitramine) is that few dislocations are needed in the pile-ups thus providing justification for assessing dynamic pile-up release on a numerical basis for few dislocation numbers [3]. For release from a viscous obstacle, previous and new computations lead to a local temperature plateau occurring at the origin of pile-up release [4], in line with the physical concept of a hot spot. [1] R.W. Armstrong, C.S. Coffey, V.F. DeVost and W.L. Elban, J. Appl. Phys. 68 (1990) 979. [2] R.W. Armstrong and F.J. Zerilli, Mech. Mater. 17 (1994) 319. [3] R.W. Armstrong, Proc. Eighth Intern. Seminar: New Trends in Research of Energetic Materials, April 19- 21, 2005, Pardubice, CZ. [4] W.R. Grise, NRC/AFOSR Summer Faculty Fellowship Program, AFRL/MNME, Eglin Air Force Base, FL, 2003.

Armstrong, Ronald; Grise, William

2005-07-01

375

Radiation tests of single photon avalanche diode for space applications  

NASA Astrophysics Data System (ADS)

Single photon avalanche diodes (SPADs) have been recently studied as photodetectors for applications in space missions. In this presentation we report the results of radiation hardness test on large area SPAD (actual results refer to SPADs having 500 ?m diameter). Dark counts rate as low as few kHz at -10 °C has been obtained for the 500 ?m devices, before irradiation. We performed bulk damage and total dose radiation tests with protons and gamma-rays in order to evaluate their radiation hardness properties and their suitability for application in a Low Earth Orbit (LEO) space mission. With this aim SPAD devices have been irradiated using up to 20 krad total dose with gamma-rays and 5 krad with protons. The test performed show that large area SPADs are very sensitive to proton doses as low as 2×108 (1 MeV eq) n/cm2 with a significant increase in dark counts rate (DCR) as well as in the manifestation of the "random telegraph signal" effect. Annealing studies at room temperature (RT) and at 80 °C have been carried out, showing a high decrease of DCR after 24-48 h at RT. Lower protons doses in the range 1-10×107 (1 MeV eq) n/cm2 result in a lower increase of DCR suggesting that the large-area SPADs tested in this study are well suitable for application in low-inclination LEO, particularly useful for gamma-ray astrophysics.

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

2013-05-01

376

Capacity of avalanche-photodiode-detected pulse position modulation  

NASA Astrophysics Data System (ADS)

The capacity of channel is the highest data rate it can reliably support. Whenever the data rate is less than the capacity of the channel, there exists an error-correcting code for the channel that has an output probability of error as small as desired, and conversely, whenever the data rate is more than the capacity the probability of error is bounded away from zero. The capacity is determined an optical channel employing Pulse Position modulation (PPM) and an Avalanche Photodiode (APD) detector. The channel is different from the usual optical channel in that the detector output is characterized by a webb-plus-gaussian distribution, not a poisson distribution. The capacity is expressed as a function of the PPM order, solt width, laser dead time, average number of incident signal and background photons received, and APD parameters. Based on a system using a laser and detector proposed for x2000 second delivery, numerical results provide upper bounds on the data rate and level of background noise that the channel can support while operating at a given BER. For the particular case studied, the capacity-maximizing PPM order is near 2048 for nighttime reception and 16 for daytime reception. Reed- Solomon codes can handle background levels 2.3 to 7.6 dB below the ultimate level that can be handled by codes operating at the Shannon limit.

Chen, GuiFen; Yin, FuChang

2002-08-01

377

Estimating impact force of granular avalanche on obstacles by DEM  

NASA Astrophysics Data System (ADS)

The paper presents a DEM model which allows the simulation of dry granular avalanche flow down incline. It allows the simulation of the flow pattern and computation of impact forces on rigid obstacles. The model is compared with experimental data in literature. The experiments include granular flow along an inclined channel and three-dimensional free surface flow along an inclined cute merging into a horizontal run-out region. The introduction of the constraint of particle rotation allows realistic description of the flow behavior. The influence of the model parameters on granular flow is studied, e.g. the run-out distance, deposition pattern, flow pattern and impact forces against obstacle. The three-dimensional DEM is an appropriate tool for modeling granular flows and their interactions with obstacles. Due to the fully three-dimensional approach it is possible to calculate the impact forces with these simulation techniques. It is shown that the model performance is strongly dependent on the rotation control. Without any rotation constraint the flow behavior of rough and angular granules cannot be described by DEM correctly. The comparison of impact forces and flow patterns with laboratory experiments shows the potential of DEM for a wide range of laboratory setups.

Teufelsbauer, Harald; Wang, Yongqi; Wawra, Markus; Wu, Wei

2010-05-01

378

Novel micropixel avalanche photodiodes (MAPD) with super high pixel density  

NASA Astrophysics Data System (ADS)

In many detectors based on scintillators the photomultiplier tubes (PMTs) are used as photodetectors. At present photodiodes are finding wide application. Solid state photodetectors allow operation in strong magnetic fields that are often present in applications, e.g. some calorimeters operating near magnets, combined PET and MRT, etc. The photon detection efficiency (PDE) of photodiodes may reach values a few times higher than that of PMTs. Also, they are rigid, compact and have relatively low operating voltage. In the last few years Micropixel Avalanche PhotoDiodes (MAPD) have been developed and started to be used. The MAPD combines a lot of advantages of semiconductor photodetectors and has a high gain, which is close to that of the PMT. Yet, they have some disadvantages, and one of them is a limited dynamic range that corresponds to a total number of pixels. The novel deep microwell MAPD with high pixel density produced by the Zecotek Company partially avoids this disadvantage. In this paper characteristics of these photodetectors are presented in comparison with the PMT characteristics. The results refer to measurements of the gain, PDE, cross-talks, photon counting and applications: beam test results of two different "Shashlyk" EM calorimeters for COMPASS (CERN) and NICA-MPD (JINR) with the MAPD readout and a possibility of using the MAPD in PET.

Anfimov, N.; Chirikov-Zorin, I.; Dovlatov, A.; Gavrishchuk, O.; Guskov, A.; Khovanskiy, N.; Krumshtein, Z.; Leitner, R.; Meshcheryakov, G.; Nagaytsev, A.; Olchevski, A.; Rezinko, T.; Sadovskiy, A.; Sadygov, Z.; Savin, I.; Tchalyshev, V.; Tyapkin, I.; Yarygin, G.; Zerrouk, F.

2011-02-01

379

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

NASA Astrophysics Data System (ADS)

Rock avalanching is a very hazardous process in high mountain area, that generates a high risk in inhabited valleys (e.g. Kolka-Karmadon, 2002). Present glacier shrinkage and permafrost degradation in steep rockwalls could increase the frequency and magnitude of rock avalanching in the context of the current climate change. We describe a small (c. 0.4 M m3) rock avalanche that occurred in December 2008 on Mont Crammont, 10 km from Mont Blanc summit (western Italian Alps), to discuss its control factors, and to consider the potential risk of this type of landslide. The 400-m-high North face of Mont Crammont, composed by the ‘Flysch de Tarentaise' sequence of the Valais Zone, is culminating at 2653 m a.s.l. in the rock avalanche area, with a mean slope angle of 50°. Located between 2400 m and the crest, the tens meters deep scar is controlled by the dense fracturing in the rock assemblage (conglomerate, limestones, schists, and sandstones). The main part of the collapsed rock mass settled on the plateau at the foot of the rockwall, between 2150 and 1950 m a.s.l.. But c. 10 % of the rock mass travelled farther in two torrent beds, and reached the Doire river bed (1090 m a.s.l.), with horizontal and vertical travel distances of 3400 m and 1560 m, respectively. The rock avalanche mobility was enhanced by (i) the channelization in the torrent gullies, and (ii) the dense snow cover, that reduces the friction and fluidises the moving mass: a large amount of snow was incorporated, with e.g. a several m-thick mixed snow/rock deposit into the two gullies. Three elements suggest that the rock avalanche could have been triggered by the current degradation of the permafrost: (i) seepage water was observed in the detachement zone in the days after the collapse, in spite of the negative air temperature; (ii) modelling of the rock temperature for north-aspect rockwalls within the range of elevation of the scar indicates that ‘warm' permafrost (T > -2°C) could be present; (ii) no other rock avalanche deposit detached from the Mont Crammont ridge is present on the Lateglacial morainic complex deposited on the plateau. Rock avalanche volume was computed by comparison of pre- and post-event LiDAR DTMs. We also present geomechanical characterization of the detachement zone from LiDAR point cloud processing, and back analysis calculation of the rock avalanche runout.

Deline, Philip; Broccolato, Massimo; Noetzli, Jeannette; Ravanel, Ludovic; Tamburini, Andrea

2010-05-01

380

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

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 (Wörner 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 Perù 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 fahrböschung 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

381

Deposits of large volcanic debris avalanches at Mount St. Helens and Mount Shasta volcanoes  

SciTech Connect

Large volcanic debris avalanches are among the world's largest mass movements. The rockslide-debris avalanche of the May 18, 1980, eruption of Mount St. Helens produced a 2.8 km/sup 3/ deposit and is the largest historic mass movement. A Pleistocene debris avalanche at Mount Shasta produced a 26 km/sup 3/ deposit that may be the largest Quaternary mass movement. The hummocky deposits at both volcanoes consist of rubble divided into (1) block facies that comprises unconsolidated pieces of the old edifice transported relatively intact, and (2) matrix facies that comprises a mixture of rocks from the old mountain and material picked up from the surrounding terrain. At Mount St. Helens, the juvenile dacite is found in the matrix facies, indicating that matrix facies formed from explosions of the erupting magma as well as from disaggregation and mixing of blocks. The block facies forms both hummocks and interhummock areas in the proximal part of the St. Helens avalanche deposit. At Mount St. Helens, the density of the old cone is 21% greater than the density of the avalanche deposit. Block size decreases with distance. Clast size, measured in the field and by sieving, coverages about a mean with distance, which suggests that blocks disaggregated and mixed together during transport.

Glicken, H.

1985-01-01

382

A statistical analysis of avalanching heat transport in stationary enhanced core confinement regimes  

SciTech Connect

We present a statistical analysis of heat transport in stationary enhanced confinement regimes obtained from flux-driven gyrofluid simulations. The probability density functions of heat flux in improved confinement regimes, characterized by the Nusselt number, show significant deviation from Gaussian, with a markedly fat tail, implying the existence of heat avalanches. Two types of avalanching transport are found to be relevant to stationary states, depending on the degree of turbulence suppression. In the weakly suppressed regime, heat avalanches occur in the form of quasi-periodic (QP) heat pulses. Collisional relaxation of zonal flow is likely to be the origin of these QP heat pulses. This phenomenon is similar to transient limit cycle oscillations observed prior to edge pedestal formation in recent experiments. On the other hand, a spectral analysis of heat flux in the strongly suppressed regime shows the emergence of a 1/f (f is the frequency) band, suggesting the presence of self-organized criticality (SOC)-like episodic heat avalanches. This episodic 1/f heat avalanches have a long temporal correlation and constitute the dominant transport process in this regime.

Tokunaga, S.; Jhang, Hogun; Kim, S. S. [WCI Center for Fusion Theory, National Fusion Research Institute, 52, Yeoeun-dong, Yusung-Gu, Daejon (Korea, Republic of); Diamond, P. H. [WCI Center for Fusion Theory, National Fusion Research Institute, 52, Yeoeun-dong, Yusung-Gu, Daejon (Korea, Republic of); Center for Astrophysics and Space Sciences and Department of Physics, University of California San Diego, La Jolla, California 92093-0429 (United States)

2012-09-15

383

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

384

Potential changes in slab avalanche activity in Colorado in response to climate change  

NASA Astrophysics Data System (ADS)

The development of slab avalanches is a complex interaction between terrain, meteorological forcing, and snowpack microphysical processes. The magnitude, frequency, and seasonal timing of avalanches are likely to be influenced by climate change over the next century. Here we present spatial and seasonal variability in meteorological forcing of slab avalanches in several mountain ranges in Colorado, and changes in avalanche activity simulated using enhanced GHG concentrations. In particular, the study identifies loading factors (new snow, snow density, wind) and the development of weak layers using observed and modeled inputs. For the development of weak layers (especially depth hoar), the study will assess early season periods of cold temperatures and shallow snowpack, and also utilizes the SNOWPACK model, whose inputs are surface temperature and humidity, accumulated snow, wind, and surface radiation terms. Results using observed data are compared to those from model output from NCAR's Colorado Headwaters project, which coupled a high-resolution WRF model with the NOAH surface model. Changes in enhanced GHG simulations of the WRF model reveal potential changes in avalanche hazard, including differences in the seasonal cycle.

Wagner, R.; Barlow, N.; Smith, A.

2013-12-01

385

Evaluating terrain based criteria for snow avalanche exposure ratings using GIS  

NASA Astrophysics Data System (ADS)

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

Delparte, Donna; Jamieson, Bruce; Waters, Nigel

2010-05-01

386

Classification of circulation type sequences applied to snow avalanches over the eastern Pyrenees (Andorra and Catalonia)  

NASA Astrophysics Data System (ADS)

Using data associated with accidents or damages caused by snow avalanches over the eastern Pyrenees (Andorra and Catalonia) several atmospheric circulation type catalogues have been obtained. For this purpose, different circulation type classification methods based on Principal Component Analysis (T-mode and S-mode using the extreme scores) and on optimization procedures (Improved K-means and SANDRA) were applied . Considering the characteristics of the phenomena studied, not only single day circulation patterns were taken into account but also sequences of circulation types of varying length. Thus different classifications with different numbers of types and for different sequence lengths were obtained using the different classification methods. Simple between type variability, within type variability, and outlier detection procedures have been applied for selecting the best result concerning snow avalanches type classifications. Furthermore, days without occurrence of the hazards were also related to the avalanche centroids using pattern-correlations, facilitating the calculation of the anomalies between hazardous and no hazardous days, and also frequencies of occurrence of hazardous events for each circulation type. Finally, the catalogues statistically considered the best results are evaluated using the avalanche forecaster expert knowledge. Consistent explanation of snow avalanches occurrence by means of circulation sequences is obtained, but always considering results from classifications with different sequence length. This work has been developed in the framework of the COST Action 733 (Harmonisation and Applications of Weather Type Classifications for European regions).

Esteban, Pere; Beck, Christoph; Philipp, Andreas

2010-05-01

387

Kulikovskiy-Sveshnikova-Beghin model of powder snow avalanches: Development and application  

NASA Astrophysics Data System (ADS)

A simple theoretical model, the Kulikovskiy-Sveshnikova-Beghin (KSB) model, is outlined, describing the motion of a particle cloud moving down an incline. This model includes both the entrainment of surrounding ambient fluid and the entrainment of particles from the slope and is equally valid for Boussinesq and non-Boussinesq flows. However, this model can predict physically impossible densities when there is significant particle entrainment. Modifications to the model are proposed which eliminate this problem by including the entrained snow volume. With the modified model, physically realistic mean densities are predicted which have a significant impact on the Richardson number-dependent ambient entrainment. The improvements are illustrated by comparing analytical solutions to the original and the modified KSB equations for the case of a particle cloud traveling on a slope of constant angle, with constant ambient fluid and particle entrainment. Solving the modified model numerically, predictions are compared with data from several large powder snow avalanches at the Swiss Vallée de la Sionne avalanche test site. The modified KSB model appears to capture the dynamics of the avalanche front well; however, problems remain with relating the theoretical geometry to a real avalanche geometry. The success of this model in capturing the front dynamics shows that with careful assumptions that reflect the physics, it is possible to describe aspects of complex flows such as powder snow avalanches with simple models.

Turnbull, B.; McElwaine, J. N.; Ancey, C.

2007-03-01

388

InGaAs/InP negative feedback avalanche diodes (NFADs)  

NASA Astrophysics Data System (ADS)

In recent years substantial effort has been made in material growth, device design and fabrication, and driving circuitry to improve the performance of InGaAs/InP single photon avalanche diodes (SPADs) operated in Geiger mode. Despite these efforts, InGaAs/InP SPADs are constrained by certain performance limitations due to the inherent positive feedback involved in the avalanche process. With the goal of overcoming some of these performance limitations, we have successfully designed and implemented thin film resistors monolithically integrated with InGaAs/InP SPADs to provide a negative feedback mechanism to regulate the avalanche sizes. The monolithic integration scheme ensures very small parasitic effects, results in fast quenching of avalanches, and allows for wafer-level integration which facilitates the fabrication of array structures. We will discuss the design and operation of NFAD devices and performance characterization of these devices. Basic characteristics of NFADs such as pulse response, quenching and recovery dynamics will be described. We will also present device performance parameters such as photon detection efficiency (PDE), dark count rate (DCR) and afterpulsing probability (Pap). InGaAs/InP negative feedback avalanche diodes with different device sizes and quenching resistances have been designed and fabricated. Devices with ~10% PDE and acceptable Pap has been realized, which provides a simple, practical solution for certain photon-counting applications.

Jiang, Xudong; Itzler, Mark A.; O'Donnell, Kevin; Entwistle, Mark; Slomkowski, Krystyna

2011-05-01

389

Investigation of hot electron emission in MOS structure under avalanche conditions  

NASA Astrophysics Data System (ADS)

There is currently much attention given to charge exchange processes investigation in MIS (metal-insulator-semiconductor) structure under strong field conditions due to the creation of a new generation of optoelectronic and microelectronic devices in silicon technology. The matrix type MIS avalanche pulsed spectro-photometer with spatial resolution (matrix-pulsed-spectro- photometer) and the new type of color video camera are examples of working in a hot electron injection (from Si to SiO2) regime. Many experiments have been performed to study this effect. Ning's experimental setup is the most interesting, allowing measurement of the absolute emission probability of electrons which were optically generated in the silicon depletion layer and accelerated toward the Si-SiO2 interface. But in these experiments the substrate voltage range was restricted by 19 V value that is far below the avalanche process conditions in MISAPs. This paper presents a new experimental technique for emission probability investigation in MIS structure under avalanche conditions based on pulsed avalanche multiplication parameters extraction. This technique is a part of the complex experimental method for charge exchange investigation (hot carriers transport in Si, generation- recombination processes in Si-SiO2 interface, injection of hot carriers from Si into SiO2, trapping and detrapping phenomena in SiO2) in avalanche-MIS-structure (MISAS).

Solonko, Alexander G.

1991-07-01

390

The critical size of macroscopic imperfections in dry snow slab avalanche initiation  

NASA Astrophysics Data System (ADS)

Dry snow slab avalanches initiate after mode II fracture propagation within a thin, weak layer under a planar slab. Dry alpine snow in which avalanches form is a porous material, typically with volume fraction filled by solids of between 10% and 50%. If snow slab avalanches were caused by small scale flaws, there would be continuous avalanches and alpine snow would not survive on steep slopes. Instead, snow slab avalanches initiate from macroscopic imperfections or weak zones within the weak layer. These are called "sweet spots" by practitioners and deficit zones in the pioneering work by Conway and Abrahamson in the 1980s. In this paper, the results of 750 in situ shear fracture tests from 68 slab-weak layer combinations are summarized in relation to the critical sweet spot length and weak layer crystal form. The results show that the critical sweet spot lengths follow a gamma probability density function with a range from 0.14 to 1.3 m and most probable value 0.5 m. The results also imply that critical sweet spot length depends on weak layer grain type with significantly larger values for persistent forms (surface hoar and facets) than for nonpersistent forms (decomposing and fragmented grains).

McClung, D. M.

2011-09-01

391

A statistical analysis of avalanching heat transport in stationary enhanced core confinement regimes  

NASA Astrophysics Data System (ADS)

We present a statistical analysis of heat transport in stationary enhanced confinement regimes obtained from flux-driven gyrofluid simulations. The probability density functions of heat flux in improved confinement regimes, characterized by the Nusselt number, show significant deviation from Gaussian, with a markedly fat tail, implying the existence of heat avalanches. Two types of avalanching transport are found to be relevant to stationary states, depending on the degree of turbulence suppression. In the weakly suppressed regime, heat avalanches occur in the form of quasi-periodic (QP) heat pulses. Collisional relaxation of zonal flow is likely to be the origin of these QP heat pulses. This phenomenon is similar to transient limit cycle oscillations observed prior to edge pedestal formation in recent experiments. On the other hand, a spectral analysis of heat flux in the strongly suppressed regime shows the emergence of a 1/f (f is the frequency) band, suggesting the presence of self-organized criticality (SOC)-like episodic heat avalanches. This episodic 1/f heat avalanches have a long temporal correlation and constitute the dominant transport process in this regime.

Tokunaga, S.; Jhang, Hogun; Kim, S. S.; Diamond, P. H.

2012-09-01

392

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.

Jenkinson, Garrett; Goutsias, John

2014-01-01

393

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

NASA Technical Reports Server (NTRS)

This investigation is a collaboration between researchers at Cornell University, the University of Florida, and the University of Rennes 1, France. Flow modeling at Cornell University focused on mechanisms for the suspension and transport of wind-blown sand that are important in both terrestrial and Martian environments. These mechanisms include the saltation (or jumping) of grains, collisions between grains, and the interaction of grains with the velocity fluctuations of the turbulent wind. Of particular interest are sheet flows; these are relatively thin, highly concentrated regions of grains flowing near the ground under the influence of a strong turbulent wind. In them, the grains are suspended by interparticle collisions. Sheet flows may be relatively rare events, but they have the capacity to move great amounts of sand. In order to describe sheet flows, a turbulent mixture theory was formulated for particles in a fluid in which fluctuations in the volume fiaction of the particles take place on the scale of the turbulent eddies. Ensemble averaged equations for particle and fluid mass, momentum, and energy and fluid rate of dissipation were expressed in terms of Farve (concentration) averaged velocities and the associated velocity fluctuations. Correlations that describe the turbulent suspension of particles and dissipation of turbulent energy of both phases due to fluid particle interactions were modeled and boundary conditions at the bed and at the upper surface of the collisional flow were formulated. The boundary conditions at the upper surface were tested in a numerical simulation developed at the University of Florida. Steady and unsteady solutions for steady and unsteady fully-developed flows were obtained over a range of wind speeds fiom the lowest for which collisional between particles occurred to at which turbulent suspension is found to dominate collisional suspension. Below the value of the wind speed at which collisions between particles were unimportant, numerical solutions were obtained for the velocity distribution function and the resulting fields of concentration, particle and gas mean velocity, and particle shear stress for the steady two-dimensional saltation of spherical sand particles driven by a turbulent wind over a bed characterized by a simple relationship (the splash function) between the properties of incoming particles and those of the rebounding particles and other particles ejected fiom the bed. At the University of Rennes 1, experiments devoted to the characterization of the splash function for beds consisting of either random or ordered arrays of spheres in two- dimensions were completed. These indicated the role played by the packing geometry in the rebound and ejection of grains. Preliminary experiments on response of a three- dimensional collision bed to a collision with a single particle were performed. Data was taken with a single camera focused on the plane of collision. Here, for example, the decrease of the effective coefficient of restitution of the bed with an increase of the angle of incidence of the incoming particle has been measured. Other experiments on avalanches at Rennes studied the properties of the flows of particles that are responsible for the motion of the leeward side of a dune. In these, the dependence of the initiation of avalanches on the packing and depth of the particles was measured. Particle migration was studied in inclined flows of a binary mixture of disks and the mechanisms of diffision and segregation were isolated and characterized. The influence of side wall on dense, rapid inclined flows was measured and shown to be the reason why the angle of the free surface in such flows can exceed the static angle of repose. Future research will be devoted to a better understanding the transition between saltating (collisionless) and collisional flows as the wind speed the increases. This will involve the understanding of the evolution of the splash function as clisions with the bed become more numerous, more frequent, and more violent.

2003-01-01

394

Using Classification Trees to Examine Spring Wet Slab and Glide Avalanche Occurrence Along the Going-To Road Corridor, Glacier National Park, Montana, USA  

NASA Astrophysics Data System (ADS)

Wet slab and glide snow avalanches are dangerous and yet can be particularly difficult to predict. In Glacier National Park, Montana, both types of avalanches can occur in the same year and affect the Going-to-the-Sun Road (GTSR) during spring plowing and road opening activities. We investigated wet slab and glide avalanche occurrence along the GTSR from 2003-2011 using meteorological and snowpack data from two high-elevation weather stations, one SNOTEL site, and an avalanche database to characterize 55 wet slab and 182 glide avalanches. Daily wet slab and glide avalanche occurrence were combined to represent an avalanche day and were compared to non-avalanche days (no avalanche occurrence) for 60 variables (both direct measurements and derived) using a univariate analysis. A classification tree (CART) was then trained to capture the most important variables in characterizing these types of avalanches. The CART was 10-fold cross validated using the data for 2003-2010 seasons and resulted in overall predictive accuracy of 73%. We then used the statistically optimal CART as a predictive model for the spring avalanche season of 2011 which resulted in an overall predictive accuracy of 82% for both avalanche and non-avalanche days, and a predictive accuracy of 91% for avalanche days. The results of this analysis suggest that the role of air temperature, snow pack settlement, and snowpack structure appear to be the most important variables in wet slab and glide avalanche occurrence. When applied to the 2011 season, the results of the CART model are encouraging and they enhance our understanding of the required meteorological and snowpack conditions for wet slab and glide avalanches.

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

2011-12-01

395

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 10–20 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 0–7 °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.

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

2011-01-01

396

Signal and noise properties of position-sensitive avalanche photodiodes.  

PubMed

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 10 to 20 mm, and the optimum bias voltage and working temperature were 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 0-7 °C for acceptable performance. The optimum bias voltage is also 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 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

2011-10-01

397

Measuring snow properties relevant to slab avalanche release  

NASA Astrophysics Data System (ADS)

The release of a slab avalanche is preceded by a sequence of fractures. The main material properties relevant for the fracture processes are the specific fracture energy of the weak layer, as also the elastic modulus and the density of the overlying slab layers. The snow micro-penetrometer (SMP) is the method of choice for snow stratigraphy measurements in the field with high resolution. Recent advances in signal processing allow us to derive the most needed material properties to model the fracture behaviour of snow. On a smaller scale, the three dimensional structure of snow samples is obtained from snow micro-tomography (CT) providing snow density directly. By modelling the mechanical behaviour of the ice matrix the elastic properties of the snow sample can be calculated. At the macro-scale, fracture mechanical field tests with particle tracking velocimetry (PTV) allow observing the in-situ fracture behaviour. Specific fracture energy and slab stiffness are derived from PTV measurement by fitting an analytical beam equation to the observed deformation field. Over the past years we were able to generate two datasets of overlapping SMP and CT as well as SMP and PTV measurements. SMP measurements and micro-tomography of snow samples show that snow density is well reproduced with current SMP signal processing algorithms. Also the specific fracture energy as derived from the SMP signal is in agreement with PTV results. The effective modulus, however, being the most sensitive parameter in fracture covers three orders of magnitude depending on measurement method. The present work discusses observed similarities and differences arising from measurement methods, theoretical assumptions and process scales. Reliable methods to determine the parameters describing the fracture process are key to snow instability modelling based on either snow cover simulations or field measurements. Preliminary modelling results from ongoing spatial variability studies illustrate the practical relevance.

Reuter, Benjamin; Proksch, Martin; Löwe, Henning; van Herwijnen, Alec; Schweizer, Jürg

2014-05-01

398

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

399

Design considerations for high-altitude altimetry and lidar systems incorporating single-photon avalanche diode detectors  

Microsoft Academic Search

Typical commercially available airborne lidar systems utilise analogue avalanche photodiodes to detect the return pulses but can be restricted to operation at low altitudes because of the weak pulse energies associated with returns from Lambertian surfaces. The ultra high sensitivity of single photon avalanche diodes have been demonstrated in many applications such as time-resolved photoluminescence and quantum key distribution and

P. A. Hiskett; R. A. Lamb

2011-01-01

400

A theoretical study of improved front-illuminated avalanche drift detectors  

NASA Astrophysics Data System (ADS)

In this study, two avalanche drift detector (ADD) concepts were theoretically examined. One was an improved detector with an avalanche photodiode (APD) collecting and double pn-junction drift configuration, and the other was a combination of an APD collecting and metal oxide semiconductor (MOS) drift structure. The feasibility of the devices was theoretically investigated by the ISE-TCAD program. ADD can be operated in either Geiger mode or linear mode. In the former case, the detector was found to be appropriate for a single photon avalanche detector with a large collection area. In the latter case, the detector was observed to be well suited to be coupled to a scintillator for gamma-ray detection. The improved ADDs are considered to have good performances in the short wavelength optical detection and in matching common scintillation crystals with more flexibility.

Liang, K.; Yuan, J.; Li, H. R.; Yang, R.; Han, D. J.

2013-06-01

401

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

402

0.35 ?m CMOS avalanche photodiode with high responsivity and responsivity-bandwidth product.  

PubMed

A highly sensitive avalanche photodiode (APD) in 0.35 ?m CMOS technology is presented. Due to a thick intrinsic absorption layer, a high responsivity at a low bias voltage, where the avalanche gain is 1, is combined with an excellent avalanche gain at high voltages to achieve a maximum overall responsivity of the APD of more than 10 kA/W. This responsivity exceeds that of other submicrometer CMOS APDs by a factor of more than 700. As a figure of merit the responsivity-bandwidth product is defined, and the achieved value of 23.46 A/W·GHz is 2.4 times higher than the values found in the literature. PMID:24487872

Gaberl, Wolfgang; Steindl, Bernhard; Schneider-Hornstein, Kerstin; Enne, Reinhard; Zimmermann, Horst

2014-02-01

403

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

Ispánovity, Péter Dusán; Laurson, Lasse; Zaiser, Michael; Groma, István; Zapperi, Stefano; Alava, Mikko J

2014-06-13

404

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

405

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

SciTech Connect

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

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

2009-11-09

406

Radiocarbon ages for the timing of debris avalanches at Mombacho Volcano, Nicaragua  

NASA Astrophysics Data System (ADS)

Radiocarbon-dated lake sediments provide minimum-limiting ages for two major debris avalanches originating from Mombacho Volcano in Nicaragua. A basal age from Lake El Gancho indicates that the northeast debris avalanche (Las Isletas) occurred sometime before ˜140 to 345 A.D. Basal ages from Lakes Blanca and Verde indicate that the southern (El Crater) debris avalanche occurred sometime before ˜270 to 650 A.D. Both events therefore occurred in the space of a few centuries, yet there is strong evidence that the mechanisms varied for destabilization of each flank. Possibly, the influence of a developing hydrothermal system lead first to deeper structural failure in the substrata to produce the Las Isletas sector collapse, progressing to higher level destabilization within the edifice and the El Crater collapse.

Stansell, Nathan D.

2013-01-01

407

Rock avalanches on a glacier and morainic complex in Haut Val Ferret (Mont Blanc Massif, Italy)  

NASA Astrophysics Data System (ADS)

Deposits in upper Val Ferret (Mont Blanc Massif, Italy) have been attributed to glacier advances and to a rock avalanche of 12 September AD 1717. We review evidence for the timing and mode of emplacement of the deposit, and present a new geomorphic interpretation and relative and absolute dating to show that the AD 1717 deposit is less extensive than previously thought. The landslide was deflected along one side of the valley floor, preserving older slope and morainic sediments along the other side. An earlier rock avalanche onto the Triolet Glacier occurred before AD 1000. The deposits of these landslides partly cover older moraine several kilometres downstream from the present glacier front, and have affected the glacier regimen and construction of its moraines. This study highlights the geomorphic impact of rock avalanches in glacierized high mountains.

Deline, Philip; Kirkbride, Martin P.

2009-01-01

408

Avalanches in 2D Dislocation Systems: Plastic Yielding Is Not Depinning  

NASA Astrophysics Data System (ADS)

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.

Ispánovity, Péter Dusán; Laurson, Lasse; Zaiser, Michael; Groma, István; Zapperi, Stefano; Alava, Mikko J.

2014-06-01

409

Runout of the Socompa volcanic debris avalanche, Chile: a mechanical explanation for low basal shear resistance  

NASA Astrophysics Data System (ADS)

We propose a mechanical explanation for the low basal shear resistance (about 50 kPa) previously used to simulate successfully the complex, well-documented deposit morphology and lithological distribution produced by emplacement of the 25 km3 Socompa volcanic debris avalanche deposit, Chile. Stratigraphic evidence for intense basal comminution indicates the occurrence of dynamic rock fragmentation in the basal region of this large granular mass flow, and we show that such fragmentation generates a basal shear stress, retarding motion of the avalanche, that is a function of the flow thickness and intact rock strength. The topography of the Socompa deposit is realistically simulated using this fragmentation-derived resistance function. Basal fragmentation is also compatible with the evidence from the deposit that reflection of the avalanche from topography caused a secondary wave that interacted with the primary flow.

Davies, Tim; McSaveney, Mauri; Kelfoun, Karim

2010-10-01

410

A simple lattice model for the effect of voids on slip avalanches in sheared granular materials  

NASA Astrophysics Data System (ADS)

It is well known that densely packed granular materials respond to slow shear with slip avalanches. Experiments and simulations show that the avalanche statistics depend strongly on the granular volume fraction v and grain shape related properties [1]. Previous studies have focused on force chain properties [2-6]. Here we use a mean field technique to construct an analytic model of the universal (i.e. detail-independent) slip avalanche statistics. For large v, and small frictional weakening ?, the model predicts solid-like behavior, with power-law avalanche size distributions and universal exponents and scaling functions. For large v and large ? it predicts mode switching between stick slip behavior and power law avalanche size distributions. For small v it predicts fluid-like flow. The results are presented in a (v, ?) phase diagram. They agree with published experiments [6-10] and simulations [2-4]. They complement recent studies on static properties, such as the shear modulus as a function of v near the jamming transition [2-4,7-10]. References: [1] V. Frette et al., “Avalanche Dynamics in a Pile of Rice”, Nature 379, 49-52 (1996). [2] E. Aharonov and D. Sparks, “Rigidity phase transition in granular packings”, Phys. Rev E, 60, 6890-6896 (1999). [3] E. Aharonov and D. Sparks, “Stick-slip motion in simulated granular layers”, J. Geophys. Res, 109, B09306 (2004). [4] E. Aharonov and D. Sparks, “Shear profiles and localization in simulations of granular materials”, Phys. Rev. E 65, 051302/1-12 (2002). [5] M.E. Cates, J.P. Wittmer, J.-P. Bouchaud, and P. Claudin, “Jamming, Force Chains, and Fragile Matter”, Phys. Rev. Lett., 81, 1841 (1998) and references therein. [6

Dahmen, K.; Ben-Zion, Y.; Uhl, J. T.

2009-12-01

411

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

412

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

413

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

414

Superfluid Avalanches in Nuclepore: Constrained versus Free-Boundary Experiments and Simulations  

NASA Astrophysics Data System (ADS)

Superfluid 4He exhibits hysteretic behavior in the percolated nanoporous material Nuclepore during the filling and draining of pores due to capillary condensation, and one observes avalanches during the pore draining. We observe that the size and frequency of the avalanches depend upon whether the fluid flow off the substrate during draining is impeded or unimpeded. We simulate the draining of superfluid 4He from Nuclepore with and without a perturbation of the pore menisci and find results similar to the results seen in the experiments in the presence or the absence of flow inhibition.

Wootters, A. H.; Hallock, R. B.

2003-10-01

415

Cheaper by the dozen: The avalanche of rideshares in the 21st century  

NASA Astrophysics Data System (ADS)

In the previous two conferences, we presented a statistics-based history of rideshares, first with the 300 rideshares launched from 1990-2010, then with the 600 rideshares launched in the first 54 years of spaceflight. We showed that there have been several waves of rideshares, each with their own particular characteristics: the avalanche of US military rideshares of the 60s (acting as calibration targets, environmental sensors and performing other space-qualification tasks); the slow-build of commercial rideshares starting with the Ariane ASAP in the early 80s, and now a bifurcation into 100-kg ESPA-class spacecraft and a second, larger avalanche of CubeSats.

Swartwout, M.

416

Balance between Excitation and Inhibition Controls the Temporal Organization of Neuronal Avalanches  

NASA Astrophysics Data System (ADS)

Neuronal avalanches, measured in vitro and in vivo, exhibit a robust critical behavior. Their temporal organization hides the presence of correlations. Here we present experimental measurements of the waiting time distribution between successive avalanches in the rat cortex in vitro. This exhibits a nonmonotonic behavior not usually found in other natural processes. Numerical simulations provide evidence that this behavior is a consequence of the alternation between states of high and low activity, named up and down states, leading to a balance between excitation and inhibition controlled by a single parameter. During these periods, both the single neuron state and the network excitability level, keeping memory of past activity, are tuned by homeostatic mechanisms.

Lombardi, F.; Herrmann, H. J.; Perrone-Capano, C.; Plenz, D.; de Arcangelis, L.

2012-06-01

417

Avalanche-enhanced photocurrents in pin silicon waveguides at 1550 nm wavelength  

NASA Astrophysics Data System (ADS)

The photocurrent effect in pin silicon waveguides at 1550 nm wavelength is experimentally investigated. The photocurrent is mainly attributed to surface-state absorption, defect-state absorption and/or two-photon absorption. Experimental results show that the photocurrent is enhanced by the avalanche effect. A pin silicon waveguide with an intrinsic region width of 3.4 ?m and a length of 2000 ?m achieves a responsivity of 4.6 mA/W and an avalanche multiplication factor of about five.

Yong, Zhao; Chao, Xu; Xiaoqing, Jiang; Huiliang, Ge

2013-06-01

418

Simulation of a Casimir-like effect in a granular pile with avalanches  

NASA Astrophysics Data System (ADS)

Using a modified Bak-Tang-Wiesenfeld model for sand piles, we simulate a Casimir-like effect in a granular pile with avalanches. Results obtained in the simulation are in good agreement with results previously acquired experimentally: two parallel walls are attracted to each other at small separation distances, with a force decreasing with increasing distance. In the simulation only, at medium distances a weak repulsion exists. Additionally, with the aim of avalanche prevention, the possibility of suppressing self-organized criticality with an array of walls placed on the slope of the pile is investigated, but the prevention effect is found to be negligible.

Denisov, D. V.; Villanueva, Y. Y.; Wijngaarden, R. J.

2011-06-01

419

Hybrid optical bistability and optical logic gates with avalanche heterojunction phototransistor and semiconductor laser diodes  

NASA Astrophysics Data System (ADS)

A bistable optical device (BOD) which employs an avalanche heterojunction phototransistor (AHPT) and an LD is proposed. Steady state operation of the AHPT-LD-BOD involves the operating modes of linear amplification, avalanche gain, optical bistability, and optoelectronic switching. In the optical bistability mode, a critical triggering optical power of no more than 10 microwatts and an output power at the ON state of larger than 1 mwatt are found. The ratio of the output optical power at the ON state to the OFF state is greater than 4 dB. The advantage of the present scheme over conventional ones is that neither external optical nor electrical feedback is required.

Dong, Jie; Huang, Xiao-Kang; Sun, Bao-Yin

1987-11-01

420

Simulation of a Casimir-like effect in a granular pile with avalanches.  

PubMed

Using a modified Bak-Tang-Wiesenfeld model for sand piles, we simulate a Casimir-like effect in a granular pile with avalanches. Results obtained in the simulation are in good agreement with results previously acquired experimentally: two parallel walls are attracted to each other at small separation distances, with a force decreasing with increasing distance. In the simulation only, at medium distances a weak repulsion exists. Additionally, with the aim of avalanche prevention, the possibility of suppressing self-organized criticality with an array of walls placed on the slope of the pile is investigated, but the prevention effect is found to be negligible. PMID:21797352

Denisov, D V; Villanueva, Y Y; Wijngaarden, R J

2011-06-01

421

The Average Avalanche Size in the Manna Model and Other Models of Self-Organized Criticality  

NASA Astrophysics Data System (ADS)

The average avalanche size can be calculated exactly in a number of models of self-organized criticality (SOC). While the calculation is straight-forward in one dimension, it is more involved in higher dimensions and further complicated by the presence of different boundary conditions and different forms of external driving. Amplitudes of the leading order are determined analytically and evaluated to obtain analytical references for numerical work. A subtle link exists between the procedure to calculate the average avalanche size and the field theory of SOC.

Pruessner, Gunnar

2013-02-01

422

Laser frequency upshift and self-defocusing under avalanche breakdown of air  

SciTech Connect

A theoretical model of avalanche breakdown of air by a Gaussian laser beam and frequency upshift is developed. The laser beam, below the threshold for tunnel ionization, heats the seed electrons to high energy and initiates avalanche ionization of the air. The ensuing plasma density profile that has maximum on axis and falls off radially causes refraction divergence of the beam. The temporal evolution of plasma density causes self-phase modulation of the laser, causing frequency broadening and spectral emission in the visible.

Verma, Updesh; Sharma, A. K. [Center for Energy Studies, Indian Institute of Technology Delhi, New Delhi 110016 (India)

2010-12-15