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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

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

3

Avalanche Awareness  

NSDL National Science Digital Library

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

Cheshire, Laura

4

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.

5

avalanche.org  

NSDL National Science Digital Library

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

6

Avalanche photodiode  

US Patent & Trademark Office Database

An avalanche photodiode having an absorption zone, a multiplication zone, and a transition zone disposed between the absorption zone and the multiplication zone, the transition zone being doped and being constituted at least in part by a material of composition that is graded such that the energy bands of the structure are substantially continuous when it is biased, wherein said doping is distributed non-uniformly in said graded composition zone so as to compensate, at least in part, the reverse electric field due to the composition grading of the material in the transition zone.

1999-06-15

7

Avalanche: The White Dragon's Wake  

NSDL National Science Digital Library

This site introduces students to the dangers of avalanches. The site explains: the different types of avalanches, such as loose snow and slab avalanches; the mechanism of avalanche release; the forecasting of snow avalanches; avalanche control techniques and hazard ratings; and avalanche training for dogs.

8

Central Avalanche Hazard Forecasting.  

National Technical Information Service (NTIS)

This report summarizes the first year of activity under Washington State Department of Highways project Central Avalanche Hazard Forecasting (Agreement Y-1700) to test the feasibility and effectiveness of central avalanche forecasting for the Cascade Moun...

E. R. LaChapelle R. T. Marriott M. B. Moore F. W. Reanier P. L. Taylor

1976-01-01

9

Computing extreme avalanches  

Microsoft Academic Search

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

Christophe Ancey; Christian Gervasoni; Maurice Meunier

2004-01-01

10

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

11

Controlled-Avalanche Superlattice Transistor.  

National Technical Information Service (NTIS)

A novel bipolar avalanche transistor is proposed. Controlled avalanche and large current output over a significant bias region is achieved by incorporating a staircase multiplication region at the base-collector junction. The III-V materials choice, devic...

P. K. Bhattacharya A. Chin K. S. Seo

1987-01-01

12

Characteristics of avalanche motion from Montserrat volcano  

Microsoft Academic Search

Solid block model is applied to describe avalanche motion under the action of gravity and Coulomb friction. Special attention is paid to characteristics of avalanche flow generated by Soufriere Hills Volcano (Montserrat) in likely directions. Duration of fall and velocity of avalanche are computed in order to estimate potential avalanche and tsunami hazard associated with eruption of Montserrat Volcano.

Irina Nikolkina; Narcisse Zahibo; Tatiana Talipova; Efim Pelinovsky

2010-01-01

13

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

14

Field management of avalanche victims  

Microsoft Academic Search

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

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

2001-01-01

15

The impact of avalanche transceivers on mortality from avalanche accidents.  

PubMed

Rapid extrication is the most important determinant of survival in avalanche victims. To facilitate rapid localization of avalanche victims by uninjured companions, avalanche transceivers are widely used during off-piste and backcountry activities. Despite their widespread use, the influence of transceivers on survival probability in avalanche accidents is controversial. The aim of this retrospective study was to analyze the influence of transceivers on the mortality of avalanche victims. There were 194 accidents in Austria from 1994 to 2003, involving 278 totally buried victims, which were analyzed. Avalanche transceivers were used by 156 (56%) victims and were associated with a significant reduction in median burial time from 102 to 20 min (p < 0.001), as well as a significant reduction in mortality from 68.0% to 53.8% (p = 0.011). This reduction was due to a decrease in mortality during backcountry activities involving ski tourers in free alpine areas (from 78.9% to 50.4%, p < 0.001). Transceivers did not reduce mortality during off-piste activities beside or near organized ski slopes (67.7% with versus 58.5% without transceiver, not significant). Mortality of persons using a transceiver is significantly higher if burial depth exceeds 1.5 m. Despite a significant reduction, mortality still exceeds 50% even with the use of transceivers. Therefore, in addition to the use of emergency equipment like transceivers, avalanche avoidance measures are critically important. The fairly modest influence of the use of transceivers on survival probability may be due to the highly efficient mountain rescue service in the Austrian Alps. In remote areas the reduction in mortality will probably be far more pronounced. PMID:15772502

Hohlrieder, Matthias; Mair, Peter; Wuertl, Walter; Brugger, Hermann

2005-01-01

16

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

17

Alternate Methods of Avalanche Control. Phase IV.  

National Technical Information Service (NTIS)

The Alternate Methods of Avalanche Control project has been funded by the Washington State Highway Commission since August 1974 in order to develop simple, reliable and repeatable methods of triggering avalanche release which are free from the storage, ha...

E. R. LaChapelle D. B. Bell J. B. Johnson R. W. Lindsay E. M. Sackett

1978-01-01

18

Correlations in avalanche critical points.  

PubMed

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

Cerruti, Benedetta; Vives, Eduard

2009-07-06

19

Advances in Cryogenic Avalanche Detectors  

NASA Astrophysics Data System (ADS)

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

Buzulutskov, A.

2012-02-01

20

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

21

Waveguide integrated silicon avalanche photodetectors  

NASA Astrophysics Data System (ADS)

We have fabricated silicon avalanche photodetectors integrated with silicon-on-insulator straight waveguides as well as ring resonator structures. The photodetectors comprise a p-i-n junction, with photogeneration mediated by the presence of deep-levels. For a 400 ?m straight waveguide detector we measure a responsivity of 4.4 A/W at 40 V, and an avalanche multiplication gain of 640. The detectors incorporated with a ring resonator, offer a high sensitivity, wavelength selective detector option suitable for very low power applications, with a responsivity of 20 A/W at 30 V.

Ackert, Jason J.; Huante-Ceron, Edgar; Murray, Kyle J.; Jessop, Paul E.; Knights, Andrew P.

2013-02-01

22

Material Considerations for Avalanche Photodiodes  

Microsoft Academic Search

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

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

2008-01-01

23

Avalanche Diode Sources and Amplifiers.  

National Technical Information Service (NTIS)

The significance of this research and development to the Air Force is the extension of the operational range of high-efficiency silicon avalanche diodes from the original L-band into the S-, C-, X-, and Ku-bands and from the oscillator mode to the amplifi...

K. K. N. Chang A. S. Clorfeine R. V. D'Aiello R. J. Ikola H. Kawamoto

1971-01-01

24

Volcano webcam down an avalanche  

USGS Multimedia Gallery

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

2010-06-18

25

Computational snow avalanche simulation in forested terrain  

NASA Astrophysics Data System (ADS)

Two-dimensional avalanche simulation software operating in three-dimensional terrain is widely used for hazard zoning and engineering to predict runout distances and impact pressures of snow avalanche events. Mountain forests are an effective biological protection measure; however, the protective capacity of forests to decelerate or even to stop avalanches that start within forested areas or directly above the treeline is seldom considered in this context. In particular, runout distances of small- to medium-scale avalanches are strongly influenced by the structural conditions of forests in the avalanche path. We present an evaluation and improvement of a novel forest detrainment function implemented in the avalanche simulation software RAMMS for avalanche simulation in forested terrain. The new approach accounts for the effect of forests in the avalanche path by detraining mass, which leads to a deceleration and runout shortening of avalanches. The relationship is parameterized by the detrainment coefficient K (Pa) accounting for differing forest characteristics. We varied K when simulating 40 well-documented small- to medium-scale avalanches which released in and ran through forests of the Swiss Alps. Analyzing and comparing observed and simulated runout distances statistically revealed values for K suitable to simulate the combined influence of four forest characteristics on avalanche runout: forest type, crown closure, vertical structure and surface roughness, e.g. values for K were higher for dense spruce and mixed spruce-beech forests compared to open larch forests at the upper treeline. Considering forest structural conditions within avalanche simulation will improve current applications for avalanche simulation tools in mountain forest and natural hazard management.

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

2013-10-01

26

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

27

Avalanche dynamics of elastic interfaces.  

PubMed

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

Le Doussal, Pierre; Wiese, Kay Jörg

2013-08-06

28

Gaussian Velocity Distributions in Avalanches  

NASA Astrophysics Data System (ADS)

Imagine a world where gravity is so strong that if an ice cube is tilted the shear forces melt the surface and water avalanches down. Further imagine that the ambient temperature is so low that the water re-freezes almost immediately. This is the world of granular flows. As a granular solid is tilted the surface undergoes a sublimation phase transition and a granular gas avalanches down the surface, but the inelastic collisions rapidly remove energy from the flow lowering the granular temperature (kinetic energy per particle) until the gas solidifies again. It is under these extreme conditions that we attempt to uncover continuum granular flow properties. Typical continuum theories like Navier-Stokes equation for fluids follow the space-time evolution of the first few moments of the velocity distribution. We study continuously avalanching flow in a rotating two-dimensional granular drum using high-speed video imaging and extract the position and velocities of the particles. We find a universal near Gaussian velocity distribution throughout the flowing regions, which are characterized by a liquid-like radial distribution function. In the remaining regions, in which the radial distribution function develops sharp crystalline peaks, the velocity distribution has a Gaussian peak but is much broader in the tails. In a companion experiment on a vibrated two-dimensional granular fluid under constant pressure, we find a clear gas-solid phase transition in which both the temperature and density change discontinuously. This suggests that a low temperature crystal and a high temperature gas can coexist in steady state. This coexistence could result in a narrower, cooler, Gaussian peak and a broader, warmer, Gaussian tail like the non-Gaussian behavior seen in the crystalline portions of the rotating drum.

Shattuck, Mark

2004-03-01

29

Avalanche dynamics in a pile of rice  

Microsoft Academic Search

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

Vidar Frette; Kim Christensen; Anders Malthe-Sørenssen; Jens Feder; Torstein Jøssang; Paul Meakin

1996-01-01

30

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

31

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

2012-06-28

32

Dynamics of Avalanche Activities in Financial Markets  

NASA Astrophysics Data System (ADS)

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

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

33

Electromagnetic radiation field of an electron avalanche  

NASA Astrophysics Data System (ADS)

Electron avalanches are the main constituent of electrical discharges in the atmosphere. However, the electromagnetic radiation field generated by a single electron avalanche growing in different field configurations has not yet been evaluated in the literature. In this paper, the electromagnetic radiation fields created by electron avalanches were evaluated for electric fields in pointed, co-axial and spherical geometries. The results show that the radiation field has a duration of approximately 1-2 ns, with a rise time in the range of 0.25 ns. The wave-shape takes the form of an initial peak followed by an overshoot in the opposite direction. The electromagnetic spectrum generated by the avalanches has a peak around 109 Hz.

Cooray, Vernon; Cooray, Gerald

2012-11-01

34

Avalanche control: Conservation Guide Series No. 5  

SciTech Connect

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

Not Available

1985-01-01

35

Static Avalanches in a Random Landscape  

NASA Astrophysics Data System (ADS)

We study jumps or avalanches in a model of a d-dimensional elastic interface that is pinned by disorder and tied to a harmonic spring. The interface configuration is the most stable one, given the disorder and spring position: as the spring is moved, this most stable configuration undergoes discrete jumps or shocks. We carry out numerical simulations to study these shocks and find: (1) detailed qualitative and quantitative verification of the validity of the functional renormalization group analysis of such interfaces and (2) that the distribution of avalanche sizes is numerically consistent with our new calculation of the exact shape of the avalanche distribution, computed in an ?=4-d expansion. The results are quite similar to those seen for dynamic avalanches, where the drive pushes interface configurations between metastable (not globally stable) states.

Middleton, A. Alan; Le Doussal, Pierre; Wiese, Kay J.

2009-03-01

36

Computer Simulation of Electron Avalanches and Streamers.  

National Technical Information Service (NTIS)

Computer simulation results are used to calculate velocities for electron avalanches and anode-directed streamers, and a representative volt-ampere characteristic for parallel plane, nitrogen-filled gaps. The simulation includes space-charge effects, elec...

J. G. Siambis L. E. Kline

1970-01-01

37

Modeling of avalanche photodiodes by Crosslight APSYS  

Microsoft Academic Search

Avalanche photodiodes (APDs) are being widely utilized in various application fields where a compact technology computer aided design (TCAD) kit capable for APD modeling is highly demanded. In this work, based on the advanced drift and diffusion model with commercial software, the Crosslight APSYS, avalanche photodiodes, especially the InP\\/InGaAs separate absorption, grading, charge and multiplication (SAGCM) APDs for high bit-rate

Y. G. Xiao; Z. Q. Li; Z. M. Simon Li

2006-01-01

38

Avalanches in anisotropic sheared granular media  

Microsoft Academic Search

We study the influence of particle shape anisotropy on the occurrence of avalanches in sheared granular media. We use molecular\\u000a dynamic simulations to calculate the relative movement of two tectonic plates. Our model considers irregular polygonal particles\\u000a constituting the material within the shear zone. We find that the magnitude of the avalanches is approximately independent\\u000a of particle shape and in

Andrés A. Peña; Sean McNamara; Pedro G. Lind; Hans J. Herrmann

2009-01-01

39

Physical modeling of avalanche-transistor switching  

NASA Astrophysics Data System (ADS)

The phenomenon of avalanche second breakdown in epitaxial planar transistors was studied. It is shown that there are two distinct modes of avalanche second breakdown operation: (1) due to temperature rise the thermal mode; and (2) due to excess injection of current under high voltage bias, the current mode. For a fast switching avalanche transistor, the current mode second breakdown is dominant. A two dimensional analysis is used to model the final destruction of the device. When the duration of the second breakdown in an avalanche transistor is limited however such a device is used as a rather fast and repeatable electrical switch, such as in a pulse generation circuit. To design an avalanche transistor for particular applications or to choose an avalanche transistor for a specific circuit, the fundamental relations between the basic structure of the device and its quasisteady-state operational characteristics, together with its operational limitations, are important. It is suggested that the second breakdown is a result of an expanding plasma wave.

Koo, J. C.; Pocha, M. D.

1982-08-01

40

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

41

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

42

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

43

Career of the Month: Avalanche Researcher  

NSDL National Science Digital Library

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

Sullivan, Megan

2009-01-01

44

Avalanche mode of motion: Implications from lunar examples  

USGS Publications Warehouse

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

Howard, K. A.

1973-01-01

45

Patterns of death among avalanche fatalities: a 21-year review  

Microsoft Academic Search

Background: Avalanches are a significant cause of winter recreational fatalities in mountain regions. The purpose of this study was to determine the relative contributions of trauma and asphyxia to avalanche deaths. Methods: We reviewed all avalanche fatalities between 1984 and 2005 that had been investigated by the offices of the British Columbia Coroners Service and the Chief Medical Examiner of

Jeff Boyd MBBS; Pascal Haegeli; Riyad B. Abu-Laban; Michael Shuster; John C. Butt

2009-01-01

46

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

47

Beyond Critical Exponents in Neuronal Avalanches  

NASA Astrophysics Data System (ADS)

Neurons form a complex network in the brain, where they interact with one another by firing electrical signals. Neurons firing can trigger other neurons to fire, potentially causing avalanches of activity in the network. In many cases these avalanches have been found to be scale independent, similar to critical phenomena in diverse systems such as magnets and earthquakes. We discuss models for neuronal activity that allow for the extraction of testable, statistical predictions. We compare these models to experimental results, and go beyond critical exponents.

Friedman, Nir; Butler, Tom; Deville, Robert; Beggs, John; Dahmen, Karin

2011-03-01

48

High temperature and wavelength dependence of avalanche gain of AlAsSb avalanche photodiodes.  

PubMed

The evolution of the dark currents and breakdown at elevated temperatures of up to 450 ?K are studied using thin AlAsSb avalanche regions. While the dark currents increase rapidly as the temperature is increased, the avalanche gain is shown to only have a weak temperature dependence. Temperature coefficients of breakdown voltage of 0.93 and 1.93 ?mV/K were obtained from the diodes of 80 and 230 ?nm avalanche regions (i-regions), respectively. These values are significantly lower than for other available avalanche materials at these temperatures. The wavelength dependence of multiplication characteristics of AlAsSb p-i-n diodes has also been investigated, and it was found that the ionization coefficients for electrons and holes are comparable within the electric field and wavelength ranges measured. PMID:22048393

Sandall, Ian C; Xie, Shiyu; Xie, Jingjing; Tan, Chee Hing

2011-11-01

49

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

50

Silicon avalanche photodiodes for particle detection  

Microsoft Academic Search

The junction termination extension (JTE) avalanche photodiode (APD) with a ring structure around the active area was built with the use of planar technology processing of float zone silicon doped by neutron transmutation. The main junction and JTE structure have been processed simultaneously, by one implantation step followed by annealing. To set a difference in the doping levels of silicon

I. B. Chistokhin; O. P. Pchelyakov; E. G. Tishkovsky; V. I. Obodnikov; V. V. Maksimov; A. A. Ivanov; E. Gramsch

2008-01-01

51

Rare-gas halide avalanche discharge lasers  

Microsoft Academic Search

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

R. Sze

1979-01-01

52

Avalanche prediction in Self-organized systems  

Microsoft Academic Search

It is a common belief that power-law distributed avalanches are inherently\\u000aunpredictable. This idea affects phenomena as diverse as evolution,\\u000aearthquakes, superconducting vortices, stock markets, etc; from atomic to\\u000asocial scales. It mainly comes from the concept of ``Self-organized\\u000acriticality\\

O. Ramos; E. Altshuler; K. J. Mû

2008-01-01

53

The Avalanche Deposits in Lunar Crater Reiner  

NASA Astrophysics Data System (ADS)

Avalanching appears to be a major means of the current erosion on steep lunar slopes. The age of the observed lunar slope degradation is very young. However, the lunar triggering mechanism of the down slope movement of the material remains unclear.

Shevchenko, V. V.; Pinet, P. C.; Chevrel, S.; Daydou, Y.; Skobeleva, T. P.; Kvaratskhelia, O. I.; Rosemberg, C.

2007-03-01

54

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

55

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

56

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

57

Avalanche activity in an extreme maritime climate: The application of classification trees for forecasting  

Microsoft Academic Search

Classification trees were trained to determine periods of significant avalanche activity in terms of an avalanche day, based on meteorological parameters for the Milford Road, Fiordland, New Zealand. Using a 10 year data set of meteorological parameters and over 1800 individual avalanche occurrences from the Transit New Zealand Milford Road Avalanche Programme we have described and statistically explored this avalanche

Jordy Hendrikx; Ian Owens; Wayne Carran; Ann Carran

2005-01-01

58

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

59

Physical models of giant subaqueous rock avalanches  

NASA Astrophysics Data System (ADS)

Large subaqueous rock avalanches are characterized by horizontal run-outs approximately ten times longer than the fall height. It is shown that this mobility is somehow puzzling, as it corresponds to a decrease of the effective friction coefficient by a factor 10-50 compared to bare rock. Two dynamical models are so introduced to explain the observed mobility. In the first model, the fast-moving fragmented rock avalanche is subjected to a lift force that makes it hydroplane, avoiding contact with the sea floor. In a second model the fragmented material ingests water, transforming into a non-Newtonian fluid that progressively reduces its shear strength. Both models give peak velocity of 65-70 m/s, which implies a high potential for tsunami generation.

De Blasio, F. V.

2011-12-01

60

Snow Avalanche Release, Scale Invariance and Criticallity  

NASA Astrophysics Data System (ADS)

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

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

61

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

62

Semiconductor Avalanche Diode Detectors for Quantum Cryptography  

Microsoft Academic Search

Advances in semiconductor single photon avalanche diode detectors have enabled an expansion in photon-counting application areas in the near-infrared. Of particular rele- vance is the application area of quantum key distribution in which secure encryption keys can be shared between users using information derived from streams of encoded single-photons. We report progress towards the objective of a practical, high efficiency

Gerald S Buller; Ryan E. Warburton; Jo Shien Ng; Lionel JJ Tan; Andrey Krysa; John P. R. David; Sergio Cova

63

Avalanche Dynamics of Radio Pulsar Glitches  

Microsoft Academic Search

We test statistically the hypothesis that radio pulsar glitches result from an avalanche process, in which angular momentum is transferred erratically from the flywheel-like superfluid in the star to the slowly decelerating, solid crust via spatially connected chains of local, impulsive, threshold-activated events, so that the system fluctuates around a self-organized critical state. Analysis of the glitch population (currently 285

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

2008-01-01

64

Scaling of Experimental Debris Flows and Avalanches  

NASA Astrophysics Data System (ADS)

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

Iverson, R. M.; Logan, M.

2002-12-01

65

Mechanisms of evolution of avalanches in regular graphs  

NASA Astrophysics Data System (ADS)

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

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

2013-06-01

66

Avalanching silicon drift photodetector (A+SDP)  

NASA Astrophysics Data System (ADS)

The performance of solid-state photodetectors is limited by noise due to their capacitance and leakage current. A new type of photodetector is being investigated, which contains a micro-avalanche multiplication gain stage incorporated into the small anode structure of a silicon drift photodetector (SDP). This technology is expected to result in improved performance over large area avalanche photodiodes (APD's) because of the very small region of multiplication in the new A+SDP versus multiplication over the entire active area for APD's. APD reliability has generally deteriorated as a function of the size of the devices being manufactured. The A+SDP will be markedly better than PIN diodes because of both the low capacitance and the avalanche multiplication. The device also promises to be better than standard large area Silicon Drift Photodetectors (SDP's) by mitigating the remaining noise due to the leakage current that dominates the performance of these devices at room temperature. Large area SDP's require cooling to well below 0 degree(s)C to obtain satisfactory leakage current-related noise. Physical device simulation tools were used to model the dopant concentrations, E-field magnitude and potential distributions. A+SDP's could have practical application in scintillation detectors for gamma ray spectroscopy as well as PMT replacements in nuclear medicine.

Vilkelis, Gintas; Patt, Bradley E.; Iwanczyk, Jan S.; MacDonald, Lawrence R.; Tull, Carolyn R.

2001-12-01

67

Avalanches, extreme events, and finite size effects  

NASA Astrophysics Data System (ADS)

Bursty transport and energy release are key characteristics of driven, dissipative, out of equilibrium systems, and are ubiquitous in laboratory, space and astrophysical plasmas. This class of phenomenology can be captured, at least in a macroscopic sense, by avalanche models, which algorithmically support a separation of timescales between (slow) driving and (fast) redistribution. A hallmark of avalanche models is the statistical scaling of burst measures in the limit where the system size is large. Importantly, observable physical systems, such as the corona and earth's magnetosphere, are finite sized- they can support at most a few decades in spatial scale. How finite size effects modify the statistical scaling of such natural systems is an open question and in itself is an observable that may inform our understanding. In particular, finite size effects have impact on the statistics and dynamics of the largest (systemwide) events that these systems can support. It is precisely these extreme events which are often of paramount interest from an operational point of view. By referring both to simple models for SOC and to data we will discuss the quantitative statistical properties of bursty energy release (avalanches) for i) events that are small on the scale size of the system - with respect to these events the system is in the large system size limit- and ii) events that are 'systemwide' in scale. We will compare and contrast the quantitative statistical signatures of systems close to SOC with other systems showing bursty dynamics, in particular finite size turbulence.

Chapman, S. C.; Watkins, N. W.

2011-12-01

68

New advances for modelling the debris avalanches  

NASA Astrophysics Data System (ADS)

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

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

2013-04-01

69

towards a continuum theory of avalanches  

NASA Astrophysics Data System (ADS)

Recently there has been increased interest in avalanches and other structures and their role in turbulent transport in confined plasmas. Experimental and computational investigations [1] have provided evidence of avalanche phenomena at work in transport dynamics. Numerical simulations of familiar turbulence models exhibit anisotropic radially extended structures clearly related to mesoscale transport events or bursts [2]. Such structures, also called streamers, may be viewed as radially extended cells of nonlinear nature (as indicated by mounting evidence). Modulational instabilities are explored as a mechanism for avalanche type formation in drift-ITG turbulence. Radially extended streamer cell formation and self-regulation are investigated within both random phase approximation and coherent envelope approaches [3]. The dual roles of the modulated Reynolds stress and nonlinear pressure advection are elucidated. While convection cells are a time-honored topic, a major new theme of this work is the study of the cell saturation mechanisms, which regulate the transport. Both poloidal shearing on the underlying ITG turbulence, Kelvin-Helmholtz type instability and curvature-drift resonant damping are explored as a saturation mechanism. Saturation levels for streamer and underlying turbulence are estimated. Implications for scalings of enhancement factors are discussed. Aspect of streamer structure and dynamics are used to estimate the variance of the drift-wave induced heat flux, which is shown to be proportional to the streamer intensity level. Streamer growth then results in a significant enhancement of the heat flux variance to order unity. [1] B.A. Carreras et al Phys Rev Lett 83 (1999) 3653; P.A. Politzer Phys Rev Lett 84 (2000) 1192 [2] P. Beyer et al Phys Rev Lett 85 (2000) 4892 [3] P.H. Diamond, S. Champeaux et al Nuclear Fusion in press; S. Champeaux & P.H. Diamond Phys Lett A in press

Champeaux, Stephanie

2001-10-01

70

20-ps timing resolution with single-photon avalanche diodes  

Microsoft Academic Search

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

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

1989-01-01

71

Infrasound monitoring of snow avalanches in the Italian Alps  

Microsoft Academic Search

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

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

2010-01-01

72

Avalanche Prediction in a Self-Organized Pile of Beads  

Microsoft Academic Search

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

O. Ramos; E. Altshuler; K. J. Måløy

2009-01-01

73

Research on Avalanche Photodiode Based Photon Imaging System  

Microsoft Academic Search

In order to realize ultra low light level detection and fast response on military, the problems existing in present low light level (LLL) imaging systems are analyzed, a novel imaging system based on avalanche photodiode (APD) detector is proposed. This system is composed of optical system, avalanche photodiode, quench circuit, Peltier cooling setup, signal processing circuit, display element and power

Liju Yin; Qian Chen; Songfeng Kou; Jian Qin

2009-01-01

74

ALife - Increasing Survival Chances in Avalanches by Wearable Sensors  

Microsoft Academic Search

Avalanches are one of the major threats to life in high mountain terrain. Once buried by an avalanche, survival chances dramatically drop from 92% after 15 minutes to only 30% after 35 minutes mostly due to the lack of oxygen. It is therefore extremely important to rescue any victims as fast as possible in order to maximize survival chances. To-

Florian Michahelles; Timo Ahonen; Bernt Schiele

75

Integrated readout electronics for Geiger mode avalanche photodiodes  

Microsoft Academic Search

Geiger mode avalanche photodiodes are devices that count single optical photons. Two disadvantages of these devices, afterpulsing and cross talk in arrays, would be significantly reduced if readout electronics is integrated with the avalanche photodiode. The different methods that exist for biasing the diodes are reviewed with special attention towards their application in integrated circuits. So far, these methods have

W. J. Kindt; K. J. de Langen

1998-01-01

76

Cyclic formation of debris avalanches at Mount St Augustine volcano  

Microsoft Academic Search

VOLCANIC debris avalanches have been seen at many volcanoes since the 1980 eruption of Mount St Helens, but typically only one or two avalanche deposits are identified at each eruptive centre, suggesting that catastrophic slope failures are rare or even unique events in the lifetime of a volcano1-4 Here we present a series of radiocarbon dates from volcanic deposits showing

James E. Begét; Juergen Kienle

1992-01-01

77

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

78

Avalanche Prediction in a Self-Organized Pile of Beads  

NASA Astrophysics Data System (ADS)

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.

Ramos, O.; Altshuler, E.; Måløy, K. J.

2009-02-01

79

How long does an avalanche in a fluid last?  

NASA Astrophysics Data System (ADS)

Avalanche duration is important for example in submarine sediment transport, in order to know if under a permanent sand feeding, avalanches will be discontinuous or continuous at the lee-slope of dunes. Our set-up consists in a slowly rotating drum half filled with grains immersed in a fluid. By video means we record the time evolution of the angle of the heap that evolves between two extreme values, the angle of motion and the angle of repose. By changing the diameter of the beads, their density and the viscosity of the fluid we put in light two regimes of avalanches depending upon the value of the Stokes number (ratio of the particle inertia to the viscous dissipation of the fluid). At large Stokes (inertia regime, St > 10) the avalanche duration is independent of the Stokes number and is equal to the duration of avalanches of large beads in air. At small Stokes (viscous regime, St < 10) the duration of avalanches scale as 1/St. Simultaneously the hysteresis angle (difference between the mean angle of motion and the mean angle of repose) decrease when St decreases. Thus for viscous fluids and small particles the avalanches last longer and are smaller.

Gondret, Philippe; Courrech Du Pont, Sylvain; Rabaud, Marc; Perrin, Bernard

2001-11-01

80

Indirect flat-panel detector with avalanche gain  

NASA Astrophysics Data System (ADS)

A new concept - an indirect flat-panel detector with avalanche gain - for low dose x-ray imaging has been proposed. The detector consists of an amorphous selenium (a-Se) photoconductor optically coupled to a structured cesium iodide (CsI) scintillator. Under an electric field ESe, the a-Se is sensitive to light and converts the optical photons emitted from CsI into electronic signal. These signals can be stored and read out in the same fashion as in existing flat-panel detectors. When ESe is increased to > 90 V/?m, avalanche multiplication occurs. The avalanche gain ranges between 1-800 depending on ESe and the thickness of the a-Se layer dSe. The avalanche a-Se photoconductor is referred to as HARP (High-gain Avalanche Rushing amorphous Photoconductor). A cascaded linear system model for the proposed detector was developed in order to determine the optimal CsI properties and avalanche gain for different x-ray imaging applications. Our results showed that x-ray quantum noise limited performance can be achieved at the lowest exposure level necessary for fluoroscopy (0.1 ?R) and mammography (0.1 mR) with a moderate avalanche gain of 20 (d = 1-2 ?m). A laboratory test system using an existing HARP tube optically coupled (through a lens) to a CsI layer was built and the advantage of avalanche gain in overcoming electronic noise was demonstrated experimentally. One of the advantages of the avalanche gain is that it will permit the use of high resolution (HR) CsI (which due to its low light output has not previously been used in flat-panel detectors) to improve DQE at high spatial frequencies.

Zhao, Wei; Hunt, Dylan C.; Tanioka, Kenkichi; Rowlands, John A.

2004-05-01

81

Supraglacial rock avalanches and their effect on glacial deposition  

NASA Astrophysics Data System (ADS)

Although rock avalanches occur commonly in glaciated valleys, it is only recently that their effects on the regime and final deposits of debris-covered glaciers have been recognized. The supraglacially-emplaced rock avalanche deposits are distinct features on glacial surfaces due to their different sedimentology and greater depth than other debris covers. The metre-scale thickness and large areal extent of these deposits significantly impact the glacier mass balance by preventing ice-surface ablation (Reznichenko et al., 2011). These effects are often neglected in estimating the total change of glacial mass balance and its response to the catastrophic event. A supraglacial rock avalanche deposit can cause a glacier to form a moraine that will not reflect any current climate forcing. It is likely that only larger rock avalanche events (with respect to the size of the glacier) will result in a significant glacial response (e.g. advance or cessation of retreat). However, all supraglacially transported rock avalanche sediment will be recycled into moraines. The climatic signals extracted from the moraine chronologies of such glaciers may consequently have significant errors. The specific sedimentary characteristics of rock avalanche sediment such as agglomerates produced under high stress conditions (Reznichenko et al., in press) can be used to identify moraines that may have been formed from rock avalanche effect. Reznichenko, N.V., Davies, T.R.H. and Alexander, D.J., 2011. Effects of rock avalanches on glacier behaviour and moraine formation. Geomorphology, v. 132, is.3-4, p. 327-338 Reznichenko, N.V., Davies, T.R.H., Shulmeister, J. and Larsen S.H. Accepted. A new technique for identifying rock-avalanche-sourced sediment in moraines and some paleoclimatic implications. Geology.

Reznichenko, N.; Davies, T. R. H.; Shulmeister, J.; Winkler, S.

2012-04-01

82

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

83

Statistics of static avalanches in a random pinning landscape  

NASA Astrophysics Data System (ADS)

We study the minimum-energy configuration of a d -dimensional elastic interface in a random potential tied to a harmonic spring. As a function of the spring position, the center of mass of the interface changes in discrete jumps, also called shocks or “static avalanches.” We obtain analytically the distribution of avalanche sizes and its cumulants within an ?=4-d expansion from a tree and one-loop resummation using functional renormalization. This is compared with exact numerical minimizations of interface energies for random-field disorder in d=2,3 . Connections to dynamic avalanches are mentioned.

Le Doussal, Pierre; Middleton, A. Alan; Wiese, Kay Jörg

2009-05-01

84

Statistics of static avalanches in a random pinning landscape.  

PubMed

We study the minimum-energy configuration of a d -dimensional elastic interface in a random potential tied to a harmonic spring. As a function of the spring position, the center of mass of the interface changes in discrete jumps, also called shocks or "static avalanches." We obtain analytically the distribution of avalanche sizes and its cumulants within an =4-d expansion from a tree and one-loop resummation using functional renormalization. This is compared with exact numerical minimizations of interface energies for random-field disorder in d=2,3 . Connections to dynamic avalanches are mentioned. PMID:19518396

Le Doussal, Pierre; Middleton, A Alan; Wiese, Kay Jörg

2009-05-07

85

Dynamics of Avalanche Quantum Dot Infrared Photodetectors  

NASA Astrophysics Data System (ADS)

Time and frequency response of an avalanche quantum dot infrared photodetector (A-QDIP) operating at long infrared (IR) wavelengths is calculated and the effect of its structure on the dynamic behavior is studied. For this purpose, the rate equations of different regions are numerically solved considering the boundary conditions. Results show that detector with long multiplication region has a slower time response. Also frequency analysis predicts a 3-dB bandwidth above 100 GHz for a device with multiplication length of 200 nm. Gain bandwidth product (GBP) is calculated and a value of about 1000 GHz is obtained. Effect of charge layer doping on dynamic response of detector is also studied and results show that increase in doping improves the GBP while the bandwidth is reduced. We also study the effect of quantum dots of absorption region on frequency response of device and results show that longer electron relaxation time into quantum dot decreases the bandwidth of detector.

Zavvari, Mahdi; Ahmadi, Vahid

2012-12-01

86

Unpinning triggers for superfluid vortex avalanches  

NASA Astrophysics Data System (ADS)

The pinning and collective unpinning of superfluid vortices in a decelerating container is a key element of the canonical model of neutron star glitches and laboratory spin-down experiments with helium II. Here the dynamics of vortex (un-)pinning is explored using numerical Gross-Pitaevskii calculations, with a view to understanding the triggers for catastrophic unpinning events (vortex avalanches) that lead to rotational glitches. We explicitly identify three triggers: rotational shear between the bulk condensate and the pinned vortices, a vortex proximity effect driven by the repulsive vortex-vortex interaction, and sound waves emitted by moving and repinning vortices. So long as dissipation is low, sound waves emitted by a repinning vortex are found to be sufficiently strong to unpin a nearby vortex. For both ballistic and forced vortex motion, the maximum inter-vortex separation required to unpin scales inversely with pinning strength.

Warszawski, L.; Melatos, A.; Berloff, N. G.

2012-03-01

87

Particle-size segregation in granular avalanches  

NASA Astrophysics Data System (ADS)

Particle size segregation in avalanches occurs through shearing within the granular flow. In such a flow, large particles migrate upwards, their vacated spaces being filled by smaller particles. Gray and Thornton recently proposed a simple model to capture this segregation, based on conservation of mass for two-phase flow, and basic mixture theory. The equation is a scalar conservation law in two space variables and time, but with variable coefficients corresponding to the spatially dependent velocity in shear flow. In this talk, I describe initial boundary value problems for this equation, and show numerical simulations. In simple circumstances, the problem can be solved explicitly, by combining basic multidimensional solutions to understand the overall flow and segregation. Interfaces with large particles below small are physically unstable, and this property can be explained mathematically. Indeed, unstable interfaces provide the richest multidimensional structures, one of which is analyzed in this talk.

Shearer, Michael

2005-11-01

88

Pinning and Avalanches in Hydrophobic Microchannels  

NASA Astrophysics Data System (ADS)

Rare events appear in a wide variety of phenomena such as rainfall, floods, earthquakes, and risk. We demonstrate that the stochastic behavior induced by the natural roughening present in standard microchannels is so important that the dynamics for the advancement of a water front displacing air has plenty of rare events. We observe that for low pressure differences the hydrophobic interactions of the water front with the walls of the microchannel put the front close to the pinning point. This causes a burstlike dynamics, characterized by series of pinning and avalanches, that leads to an extreme-value Gumbel distribution for the velocity fluctuations and a nonclassical time exponent for the advancement of the mean front position as low as 0.38.

Queralt-Martín, M.; Pradas, M.; Rodríguez-Trujillo, R.; Arundell, M.; Corvera Poiré, E.; Hernández-Machado, A.

2011-05-01

89

Avalanche breakdown in microscale VO2 structures  

NASA Astrophysics Data System (ADS)

The mechanism of triggering the metal-insulator transition (MIT) by an external electric field in small scale VO2 structures has been attributed to excess carrier injection, rather than Joule heating. This is in part due to the fact that the delay time for MIT to be induced by Joule heating seems much longer than what is observed. However, modeling the resistivity as a function of temperature, explicitly considering phase coexistence of metallic and insulating states near the MIT, and considering thermal dissipation in realistic structures, we demonstrate that Joule heating can exhibit a self-accelerating, avalanche-like behavior, in which the time scale for thermally driven breakdown can be in the nanosecond regime if the device is small enough. This model matches experimental results of our micrometer scale device quite well. Over-threshold voltages, temperature, and size effects on switching delay time and threshold voltage are discussed.

Zhong, Xing; Zhang, Xueyu; Gupta, Arunava; Leclair, P.

2011-10-01

90

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

91

Pinning and avalanches in hydrophobic microchannels.  

PubMed

Rare events appear in a wide variety of phenomena such as rainfall, floods, earthquakes, and risk. We demonstrate that the stochastic behavior induced by the natural roughening present in standard microchannels is so important that the dynamics for the advancement of a water front displacing air has plenty of rare events. We observe that for low pressure differences the hydrophobic interactions of the water front with the walls of the microchannel put the front close to the pinning point. This causes a burstlike dynamics, characterized by series of pinning and avalanches, that leads to an extreme-value Gumbel distribution for the velocity fluctuations and a nonclassical time exponent for the advancement of the mean front position as low as 0.38. PMID:21668164

Queralt-Martín, M; Pradas, M; Rodríguez-Trujillo, R; Arundell, M; Corvera Poiré, E; Hernández-Machado, A

2011-05-10

92

Scaling crossover for the average avalanche shape  

NASA Astrophysics Data System (ADS)

Universality and the renormalization group claim to predict all behavior on long length and time scales asymptotically close to critical points. In practice, large simulations and heroic experiments have been needed to unambiguously test and measure the critical exponents and scaling functions. We announce here the measurement and prediction of universal corrections to scaling, applied to the temporal average shape of Barkhausen noise avalanches. We bypass the confounding factors of time-retarded interactions (eddy currents) by measuring thin permalloy films, and bypass thresholding effects and amplifier distortions by applying Wiener deconvolution. We show experimental shapes that are approximately symmetric, and measure the leading corrections to scaling. We solve a mean-field theory for the magnetization dynamics and calculate the relevant demagnetizing-field correction to scaling, showing qualitative agreement with the experiment. In this way, we move toward a quantitative theory useful at smaller time and length scales and farther from the critical point.

Papanikolaou, Stefanos; Bohn, Felipe; Sommer, Rubem L.; Durin, Gianfranco; Zapperi, Stefano; Sethna, James P.

2010-03-01

93

Overspill avalanching in a dense reservoir network.  

PubMed

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

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

2012-04-23

94

UV-enhanced silicon avalanche photodiodes  

NASA Astrophysics Data System (ADS)

Silicon avalanche photodiodes (APDs) fabricated through a deep diffusion process underwent a modified surface treatment in an attempt to improve their response in the ultraviolet region of the optical spectrum. After adjusting the doping profile in the near-surface region of the detectors, APDs were fabricated and tested at several wavelengths from ultraviolet to the near-infrared. At the target wavelength of 355 nm, the detector bandwidth was increased by a factor of 20 over devices fabricated without the modified surface treatment. Modest improvements in the internal quantum efficiency were also measured. Most importantly, the modified detectors maintained the high gain and low noise performance specifications that are hallmarks of traditional deep diffusion APDs.

Myers, Richard A.; Farrell, Richard; Riccardi, Suzannah L.; McClish, Mickel

2013-03-01

95

Electron Avalanche Structure Determined by Random Walk Theory.  

National Technical Information Service (NTIS)

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 tha...

G. W. Englert

1973-01-01

96

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

97

Avalanche Photodiode Photon Counting Receivers for Space-Borne Lidars.  

National Technical Information Service (NTIS)

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 b...

X. Sun F. M. Davidson

1991-01-01

98

Fragmentation in the Val Pola rock avalanche, Italian Alps  

Microsoft Academic Search

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

Giovanni B. Crosta; Paolo Frattini; Nicoletta Fusi

2007-01-01

99

On the internal flow velocity of snow avalanches  

NASA Astrophysics Data System (ADS)

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

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

2011-12-01

100

Breakdown of avalanche critical behaviour in polycrystalline plasticity  

Microsoft Academic Search

Acoustic emission experiments on creeping ice as well as numerical simulations argue for a self-organization of collective dislocation dynamics during plastic deformation of single crystals into a scale-free pattern of dislocation avalanches characterized by intermittency, power-law distributions of avalanche sizes, complex space-time correlations and aftershock triggering. Here, we address the question of whether such scale-free, close-to-critical dislocation dynamics will still

Thiebaud Richeton; Jérôme Weiss; François Louchet

2005-01-01

101

Capacitive Quenching Measurement Circuit for Geiger-Mode Avalanche Photodiodes  

Microsoft Academic Search

Characterization of Geiger-mode avalanche photodiodes operated in gated mode requires fast rising-edge, well-defined over-bias pulses, and effective avalanche quenching. There has not been a suitable circuit that meets both criteria, thus, making systematic characterization and accurate comparison of these devices difficult. We present a capacitive quenching circuit (CQC) that satisfies both criteria and, thus, offers advantages over existing options such

S. J. Dimler; J. S. Ng; R. C. Tozer; G. J. Rees; J. P. R. David

2007-01-01

102

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

103

Modeling negative feedback in single-photon avalanche diodes  

Microsoft Academic Search

Recently, considerable attention has been placed upon exploiting the negative-feedback effect in accelerating the quenching time of the avalanche current in passively quenched single-photon avalanche-diode (SPAD) circuits. Reducing the quenching time results in a reduction in the total charge generated in the SPAD, thereby reducing the number of trapped carries; this, in turn, can lead to improved after-pulsing characteristics. A

Majeed M. Hayat; David A. Ramirez; Graham J. Rees; Mark A. Itzler

2010-01-01

104

The Runaway Electron Avalanche as a Radio Emitter in Thunderstorms  

NASA Astrophysics Data System (ADS)

Previous simulations of runaway electron avalanches in the atmosphere, which solve the modified relativistic Boltzmann equation for various values of ambient electric field, have yielded the equilibrium ionization rates and energy distribution functions for the runaway electrons. The mean runaway electron energies and associated rates are employed here in two macroscopic treatments in order to set bounds on the expected radio emissions from runaway electron avalanches occuring in thunderstorms. The ambient electric field is that calculated from two disks of charge with sinusoidally varying charge density in altitude and peak charge density of +/- 10 nC/m3. An analytic expression for the radiatied electric field from a point-charge avalanche, including high-energy and low-energy electrons is shown to be highly dependent upon the ambient electric field strength and profile. For comparison, a one-dimensional numerical model of a runaway electron avalanche and the resulting radio emissions are presented. For the numerical case the runaway avalanche is dominated by production of high and low-energy electrons, relaxation, electron attachment, and high-energy electron loss. The radius of the 1-D electron avalanche is treated as an independent parameter and the resulting rise in the channel conductivity can limit the amplitude of the radio emissions, even in strong ambient electric fields. The peak electric-field amplitude and HF and VHF spectral amplitudes are compared with narrow bipolar pulse observations.

Tierney, H. E.; Roussel-Dupre, R. A.; Symbalisty, E. M.; Beasley, W. H.

2003-12-01

105

Avalanches in a Stochastic Model of Spiking Neurons  

PubMed Central

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.

Cowan, Jack D.; van Drongelen, Wim

2010-01-01

106

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

107

Physically-sound scaling laws for snow avalanche impact pressure  

NASA Astrophysics Data System (ADS)

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

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

2012-04-01

108

Frontal dynamics of powder snow avalanches  

NASA Astrophysics Data System (ADS)

We analyze frontal dynamics of dilute powder snow avalanches sustained by rapid blow-out behind the front. Such material injection arises as a weakly cohesive snow cover is fluidized by the very pore pressure gradient that the particle cloud induces within the snowpack. We model cloud fluid mechanics as a potential flow consisting of a traveling source of denser fluid thrust into a uniform airflow. Stability analysis of a mass balance involving snow cover and powder cloud yields relations among scouring depth, frontal height, speed, mixed-mean density, and impact pressure when the frontal region achieves a stable growth rate. We compare predictions with field measurements, show that powder clouds cannot reach steady frontal speed on a uniform snowpack with constant cloud width and derive a criterion for cloud ignition. Because static pressure is continuous across the mean air-cloud interface and deviatoric stresses are negligible, frontal acceleration is insensitive to local slope, but instead arises from a deficit of flow-induced suction in the wake. We calculate how far a powder cloud travels until its frontal mixed-mean density becomes stable, and show how topographic spread can hasten its collapse.

Carroll, C. S.; Louge, M. Y.; Turnbull, B.

2013-06-01

109

Soft collisions in relativistic runaway electron avalanches  

NASA Astrophysics Data System (ADS)

This paper reports the first application of the relativistic binary-encounter-Bethe (RBEB) electron impact ionization model for studies of relativistic runaway electron avalanches (RREA) phenomenon at different pressures in air, which is believed to be the root cause of the hard x-rays and terrestrial gamma-ray flashes observed in the Earth's atmosphere in association with lightning activity. The model allows robust and accurate description of ionization over a wide range of energies (from the ionization threshold to megaelectronvolts), that is especially important for studies of thermal runaway electrons. A direct comparison between RREA rates obtained using classic Møller and the new RBEB differential ionization cross sections demonstrates that the dipole interaction between primary electrons and K-shell electrons of oxygen and nitrogen has an impact on the rates for relatively low applied electric fields comparable to or higher than 20 kV cm-1 at ground pressure. Implications of non-similarity of the runaway process developing at different altitudes due to the Swann-Fermi density effect are discussed.

Celestin, Sebastien; Pasko, Victor P.

2010-08-01

110

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

111

OPTIMIZING THROUGH CO-EVOLUTIONARY AVALANCHES  

SciTech Connect

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

S. BOETTCHER; A. PERCUS

2000-08-01

112

Sediment Transport by Spring Avalanches in the Southern Swiss Alps  

NASA Astrophysics Data System (ADS)

Dense wet-snow avalanches breaking through to the base of the snow pack or overriding snow-free surfaces can entrain basal material and act as important agents of sediment transport in steep Alpine catchments. As part of an ongoing study, we investigated two debris fans in the Matter Valley of southern Switzerland during spring 2009 and 2010, with emphasis on quantifying avalanche sediment transport. Deposited debris ranged from soil parcels and plant material to cobbles and boulders greater than 1 m3. Large boulders were generally angular and fresh with clear signs of recent impacts. The seasonal sediment load transported by avalanches was estimated at one fan by sampling the debris content within a number of representative areas, and then extrapolating the cumulative volume. Results reveal a total transported sediment volume of ~150 m3 in 2009 and ~15 m3 in 2010, which likely reflects varying snowfall and avalanche frequency between years. When distributed over the deposition area on the fan, these results imply an average accumulated sediment thickness of 12 mm in 2009 and 3 mm in 2010. Calculated catchment-wide erosion rates are ~0.1 mm/yr for 2009 and ~0.01 mm/yr for 2010. Cross-sections through avalanche debris revealed that transported sediment generally resides on top of the snow surface. As the avalanches melt, entrained sediment is set down gently, often resulting in precariously balanced boulders and rows of blocks perched on the walls of the fan’s channels. In flat lying areas, snowmelt resulted in sparse sediment deposits with no clear structure or sorting. Observations show that the fan surface is usually protected from erosion by snow and older avalanche deposits, which provide a smooth gliding plane for new events. Within the bedrock gulley adjacent to the fan, and in the avalanche source region above, signs of abrasive wear were evident on exposed bedrock surfaces. These include rounded and scoured bedrock, fresh signs of boulder impacts, and scratch marks on the rock walls. Numerical modeling of avalanche flow dynamics, using the program RAMMS with realistic scenarios, revealed areas of predicted maximum pressure, which corresponded well with field observations of scoured bedrock.

Egloff, J. M.; Hunziker, M.; Moore, J. R.; Christen, M.

2010-12-01

113

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

114

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

115

Silicon avalanche photodiodes for particle detection  

NASA Astrophysics Data System (ADS)

The junction termination extension (JTE) avalanche photodiode (APD) with a ring structure around the active area was built with the use of planar technology processing of float zone silicon doped by neutron transmutation. The main junction and JTE structure have been processed simultaneously, by one implantation step followed by annealing. To set a difference in the doping levels of silicon in the main junction and in the ring structure, the single oxide mask was developed with openings gradually patterned on planar surface. To provide a contact with low resistivity the surface of the main junction was covered by a thin silicon p+-layer, grown with MBE (molecular beam epitaxy). The thickness of this "dead" layer no more than 100 nm was obtained. As have been found, the dark current is strongly dependent on the implanted dose, decreasing with decreasing dose from 5x1012 to 2x1012 cm-2. The detectors built with the lowest dose only have the level of dark currents suitable for the measurement of the gain resulted from carrier multiplication. The gain up to 25 was obtained for visible light (?=600 nm) and up to 7×103 for single 2.5 MeV ?-particles. For 4.3 MeV ?-particles the best energy resolution of 330 keV FWHM was obtained. For 22.16 keV x-ray from a 109Cd source the resolution of 4.7 keV FWHM have been measured, which corresponds to 560 rms electrons noise.

Chistokhin, I. B.; Pchelyakov, O. P.; Tishkovsky, E. G.; Obodnikov, V. I.; Maksimov, V. V.; Ivanov, A. A.; Gramsch, E.

2008-05-01

116

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.

117

Density and granulometric structure of wet and dry-snow avalanches  

NASA Astrophysics Data System (ADS)

We present several measurements of avalanche density, which were carried out in naturally and artificially released dry, and wet-snow avalanches at the Vallée de la Sionne test site in Switzerland. Measurements were performed using capacitance probes developed by M. Louge (Louge et al. 1997), which are installed at two heights along the instrumented pylon. The high frequency response of the sensor (7.5 kHz) allows capturing significantly different density variations, which can also be correlated to avalanche granulometry. We show that in dry-snow avalanches average density increases from head to tail presumably due to the actions of forces and temperature variations within the avalanche body. At the avalanche tail the density is the largest and it remains constant up to deposition. In the avalanche head and body, density is characterized by large fluctuations around the average, which decrease their frequency toward the tail. The granular structure changes accordingly from a more dilute flow at the avalanche head, to the high density, well-rounded granules of various sizes that dominate the avalanche tail. In contrast to the large density variations that characterize dry-snow avalanches, wet-snow avalanches exhibit a more constant density throughout the whole avalanche and a homogeneous structure constituted by well-sorted granules, with a predominance of large particles moving on the avalanche surface. These measurements show the avalanche structure of both wet and dry-snow avalanches, which has been inaccessible to measurements up to now and will lead to new and improved physical models of avalanche dynamics.

Sovilla, B.; Blaschke, B.

2012-04-01

118

Avalanche fatalities in the western United States: a comparison of three databases  

Microsoft Academic Search

Reported avalanche fatalities in the United States increased markedly through the latter half of the twentieth century, a\\u000a result of the increasing popularity of winter sports. Despite this increase, the literature concerning US avalanche fatalities\\u000a is sparse. This paper presents a comparison of three US databases containing avalanche fatality information: Storm Data, the West Wide Avalanche Network (WWAN) dataset, and

Jeremy M. SpencerWalker; Walker S. Ashley

2011-01-01

119

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

Microsoft Academic Search

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

Nate Furman; Wynn Shooter; Scott Schumann

2010-01-01

120

Avalanches in Interfacial Motion in a Model Porous Medium  

NASA Astrophysics Data System (ADS)

I report measurements of the dynamics of an air/water interface moving through a model porous medium composed of glass beads. At low capillary number, the interface does not move uniformly. Instead, some small regions stay pinned, while others move, at least for a short time. These bursts of motion are called avalanches. In several theoretical models, (See, for example, L.A.N. Amaral, A.-L. Barabasi, S.V. Buldyrev, S. Havlin, S.T. Harrington, R. Sadr, and H.E. Stanley, Phys. Rev. E, 51, 4655 (1995) and references therein.) for driving forces F close to the critical force F_c, the avalanches follow a power-law distribution. In contrast, I find that the number N(s) of moving regions of size s decays exponentially with s, even at very low capillary number. I will discuss some of the important features of the experiments and models that might help explain the different avalanche behavior.

Dougherty, Andrew

1997-03-01

121

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

SciTech Connect

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

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

2007-01-01

122

Wind may have driven avalanches on Martian dunes  

NASA Astrophysics Data System (ADS)

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

Balcerak, Ernie

2012-07-01

123

Distribution of Maximum Velocities in Avalanches Near the Depinning Transition  

NASA Astrophysics Data System (ADS)

We report exact predictions for universal scaling exponents and scaling functions associated with the distribution of the maximum collective avalanche propagation velocities vm in the mean field theory of the interface depinning transition. We derive the extreme value distribution P(vm|T) for the maximum velocities in avalanches of fixed duration T and verify the results by numerical simulation near the critical point. We find that the tail of the distribution of maximum velocity for an arbitrary avalanche duration, vm, scales as P(vm)˜vm-2 for large vm. These results account for the observed power-law distribution of the maximum amplitudes in acoustic emission experiments of crystal plasticity and are also broadly applicable to other systems in the mean-field interface depinning universality class, ranging from magnets to earthquakes.

LeBlanc, Michael; Angheluta, Luiza; Dahmen, Karin; Goldenfeld, Nigel

2012-09-01

124

Simultaneous resonant enhanced multiphoton ionization and electron avalanche ionization in gas mixtures  

SciTech Connect

Resonant enhanced multiphoton ionization (REMPI) and electron avalanche ionization (EAI) are measured simultaneously in Ar:Xe mixtures at different partial pressures of mixture components. A simple theory for combined REMPI+EAI in gas mixture is developed. It is shown that the REMPI electrons seed the avalanche process, and thus the avalanche process amplifies the REMPI signal. Possible applications are discussed.

Shneider, Mikhail N.; Zhang Zhili; Miles, Richard B. [Mechanical and Aerospace Engineering, Princeton University, Princeton, New Jersey 08544 (United States)

2008-07-15

125

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

126

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

127

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

Microsoft Academic Search

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

Z. Donkó

1995-01-01

128

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

NASA Astrophysics Data System (ADS)

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

Simonson, S.; Fassnacht, S. R.

2011-12-01

129

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

Microsoft Academic Search

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

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

2002-01-01

130

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

131

High gain multigap avalanche detectors for Cerenkov ring imaging  

SciTech Connect

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

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

1980-10-01

132

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

133

Particle Size Segregation In Granular Avalanches: A Study In Shocks  

NASA Astrophysics Data System (ADS)

In this thesis, we explore properties of shock wave solutions of the Gray-Thornton model for particle size segregation in granular avalanches. In these avalanches, particles segregate by size when subject to shear. As the particles roll across each other, other particles fall into the gaps that form, with smaller particles more likely to fit. These small particles fall to the bottom of the avalanche and force the larger particles upward. These processes are called kinetic sieving and squeeze expulsion. The Gray-Thornton model is a nonlinear scalar conservation law expressing conservation of mass under shear for the concentration of small particles in a bidisperse mixture. In this model, the velocity (and thus, shear) is a function of the height of the avalanche. We first discuss characteristic surfaces of the model, which are used in combination with shock waves to construct and analyze solutions of the model. . Shock waves are weak solutions of the partial differential equation across which the concentration of small particles jumps. For a linear velocity profile, we give criteria on smooth initial conditions under which a shock wave forms in the interior of the avalanche in finite time. Additionally, numerical simulations show how and when these shocks form, verifying our analysis. Shocks will often lose stability as they are sheared by the flow of the avalanche. Upon the loss of stability a complex structure develops in which a two-dimensional rarefaction wave interacts dynamically with a pair of shocks. This rarefaction represents a mixing zone in which small and large particles are mixed as they are transported up and down (respectively) through the zone. Under a linear velocity profile, the structure of this region twice changes over time before reaching the boundary of the avalanche. We also present a special case where the structure of the mixing region does not change over time. By introducing a scaling, we can find a similarity solution for this case. Linear velocity profiles are not always present in granular materials, especially in the case of boundary driven shear. Thus, we analyze shock formation from smooth initial data under a general increasing velocity profile. Additionally, we analyze the short time solution of the mixing zone under an increasing velocity profile. Here, we present several cases, with each case more general than the previous one. For each case, we analyze the structure of the mixing zone as much as possible, and discuss limitations to the more general cases. Numerical simulations show how the mixing region evolves for each case. We look at the evolution of an avalanche that is uniform in the downslope direction. Analysis of this solution is important because it appears in the most general version of the mixing zone problem.

Giffen, Nicholas J.

134

Microwave diagnostics of laser-induced avalanche ionization in air  

NASA Astrophysics Data System (ADS)

This work presents a simplified model of microwave scattering during the avalanche ionization stage of laser breakdown and corresponding experimental results of microwave scattering from laser breakdown in room air. The model assumes and measurements confirm that the breakdown regime can be viewed as a point dipole scatterer of the microwave radiation and thus directly related to the time evolving number of electrons. The delay between the laser pulse and the rise of the microwave scattering signal is a direct measure of the avalanche ionization process.

Zhang, Zhili; Shneider, Mikhail N.; Miles, Richard B.

2006-10-01

135

Extreme statistics of avalanches near the depinning transition  

NASA Astrophysics Data System (ADS)

Near the depinning transition, motion proceeds by avalanche fluctuations with power law distributed sizes and durations. We derive exact exponents and scaling functions for the statistics of maximum avalanche velocities in a mean field theory of the transition. We find a power law regime in the maximum velocity distribution with an exponent that agrees with the distribution of peak amplitudes observed in acoustic emission experiments of crystal plasticity. Our results should be applicable to the study of a number of systems considered to be in the mean field interface depinning universality class, ranging from magnets to earthquakes.

Leblanc, Michael; Angheluta, Luiza; Dahmen, Karin; Goldenfeld, Nigel

2013-03-01

136

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

PubMed

This article discusses mitigation strategies to protect traffic routes from snow avalanches. Up to now, mitigation of snow avalanches on many roads and railways in the Alps has relied on avalanche sheds, which require large initial investments resulting in high opportunity costs. Therefore, avalanche risk managers have increasingly adopted organizational mitigation measures such as warning systems and closure policies instead. The effectiveness of these measures is, however, greatly dependent on human decisions. In this article, we present a method for optimizing avalanche mitigation for traffic routes in terms of both their risk reduction impact and their net benefit to society. First, we introduce a generic framework for assessing avalanche risk and for quantifying the impact of mitigation. This allows for sound cost-benefit comparisons between alternative mitigation strategies. Second, we illustrate the framework with a case study from Switzerland. Our findings suggest that site-specific characteristics of avalanche paths, as well as the economic importance of a traffic route, are decisive for the choice of optimal mitigation strategies. On routes endangered by few avalanche paths with frequent avalanche occurrences, structural measures are most efficient, whereas reliance on organizational mitigation is often the most appropriate strategy on routes endangered by many paths with infrequent or fuzzy avalanche risk. Finally, keeping a traffic route open may be very important for tourism or the transport industry. Hence, local economic value may promote the use of a hybrid strategy that combines organizational and structural measures to optimize the resource allocation of avalanche risk mitigation. PMID:18808393

Rheinberger, Christoph M; Bründl, Michael; Rhyner, Jakob

2008-09-18

137

Model for domain wall avalanches in ferromagnetic thin films  

Microsoft Academic Search

The Barkhausen jumps or avalanches in magnetic domain-walls motion between successive pinned configurations, due the competition among magnetic external driving force and substrum quenched disorder, appear in bulk materials and thin films. We introduce a model based in rules for the domain wall evolution of ferromagnetic media with exchange or short-range interactions, that include disorder and driving force effects. We

R. C. Buceta; D. Muraca

2011-01-01

138

Silicon avalanche diodes for direct detection of nuclear particles  

Microsoft Academic Search

The junction termination extension (JTE) avalanche diode (AD) for direct detection of nuclear particles was built with the use of planar technology processing. The active area of the detector with JTE structure have been processed simultaneously, by one implantation of boron step followed by the diffusion up to the depth of 14 mum. The contact layer (p+ region) had the

I. B. Chistokhin; O. P. Pchelyakov; E. G. Tishkovsky; V. I. Obodnikov; V. V. Maksimov; A. A. Ivanov; E. I. Pinzhenin; E. Gramsch

2009-01-01

139

Quantum Detection Efficiency in Geiger Mode Avalanche Photodiodes  

Microsoft Academic Search

The fabrication of silicon shallow junction photodiodes is a relevant topic for the detection of blue and near ultraviolet weak photon fluxes. In this paper we present a simple model to calculate the quantum detection efficiency (QDE) of a Geiger mode avalanche photodiode (GMAP) as a function of the dead layer thickness above the junction depletion layer. A comparison between

Massimo Mazzillo; Alessandro Piazza; Giovanni Condorelli; Delfo Sanfilippo; Giorgio Fallica; Sergio Billotta; Massimiliano Belluso; Giovanni Bonanno; Luigi Cosentino; Alfio Pappalardo; Paolo Finocchiaro

2008-01-01

140

A model for frictional melt production beneath large rock avalanches  

Microsoft Academic Search

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

Fabio Vittorio De Blasio; Anders Elverhøi

2008-01-01

141

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

142

High quantum efficiency GaP avalanche photodiodes.  

PubMed

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

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

2011-09-26

143

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

144

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

145

Generalized excess noise factor for avalanche photodiodes of arbitrary structure  

Microsoft Academic Search

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

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

1990-01-01

146

Higher efficiency active quenching circuit for avalanche photodiodes  

SciTech Connect

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

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

1993-06-01

147

Studies of avalanche photodiodes for scintillating fibre tracking readout  

Microsoft Academic Search

Avalanche Photodiodes (APDs) operating in 'Geiger Mode' have been studied in a fibre tracking readout environment. A fast recharge circuit has been developed for high rate data taking, and results obtained from a model fibre tracker in the test beam at Brookhaven National Laboratory are presented. A high rate calibrated light source has been developed using a commercially available laser

H. Fenker; J. Thomas; C. Tatsch; M. Wright

1993-01-01

148

High-Gain Avalanche Rushing amorphous Photoconductor (HARP) detector  

Microsoft Academic Search

We have been studying a very sensitive image sensor since the early 1980s. In 1985, the author found for the first time that an experimental pickup tube with an amorphous selenium photoconductive target exhibits high sensitivity with excellent picture quality because of a continuous and stable avalanche multiplication phenomenon. We named the pickup tube with an amorphous photoconductive layer operating

K. Tanioka

2009-01-01

149

Ablation of avalanched and undisturbed snow, Himalaya Mountains, Pakistan  

SciTech Connect

Avalanche deposits represent a significant storage of winter snow on the south slope of the Himalaya Mountains, Pakistan, complicating the annual snowmelt cycle because of the differences in ablation of avalanche-transported snow and undisturbed snow. Measurements show very high rates of melting of both snow types, particularly of avalanche sow late in the melt season. The high rates are a function of the low latitude of the study area and the low elevation of the avalanche snow deposits, as well as heat release by condensation. Air temperature was closely correlated with daily snowmelt and appears to hold promise as a predictor, however, data constraints prevent an energy balance analysis of this relationship. Gravimetric measurements show that condensation is important in the snow surface energy exchange and can represent a significant source of energy for snowmelt. Rainfall during warm conditions also makes a more significant contribution to snowmelt than shown in previous studies. The derived temperature-based melt factors or coefficients compare well with published figures from other mountain areas, but their confidence limits are sufficiently wide to produce significant errors in the prediction of basin snowmelt runoff.

de Scally, F.A. (Okanagan College, Kelowna, British Columbia (Canada)); Gardner, J.S. (Univ. of Waterloo, Ontario (Canada))

1990-11-01

150

Avalanche breakdown of diffused silicon p-n junctions  

Microsoft Academic Search

Using impact ionization rates of Moll et al. [23] and Lee et al. [24], the avalanche breakdown voltages of diffused silicon p-n junctions were calculated by assuming an error function diffused impurity distribution. The theoretical results were verified experimentally with samples having breakdown voltages ranging from 100 volts to 9000 volts. Good agreement was found between the experimental breakdown voltages

R. A. Kokosa; R. L. Davies

1966-01-01

151

Reliability Assessment of Multiple Quantum Well Avalanche Photodiodes.  

National Technical Information Service (NTIS)

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 ...

I. Yun H. M. Menkara Y. Wang I. H. Oguzman J. Kolnik

1995-01-01

152

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

153

Submicron chip ESD protection schemes which avoid avalanching junctions  

Microsoft Academic Search

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

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

1995-01-01

154

Improving the performance of silicon single-photon avalanche diodes  

Microsoft Academic Search

Many applications require high performance Single Photon Avalanche Diodes (SPAD) either as single pixels or as small arrays of detectors. Although currently available silicon devices reached remarkable performance, nevertheless further improvements are needed in order to meet the requirements of most demanding time-resolved techniques. In this paper we present a new planar silicon technology for the fabrication of SPAD detectors,

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

2011-01-01

155

Gridded snow maps supporting avalanche forecasting in Norway  

NASA Astrophysics Data System (ADS)

We present gridded maps indicating key parameters for avalanche forecasting with a 1 km x 1 km resolution. Based on the HBV hydrology model, snow parameters are modeled based on observed and interpolated precipitation and temperature data. Modeled parameters include for example new snow accumulated the last 24 and 72 hours, snow-water equivalent, and snow-water content. In addition we use meteorological parameters from the UK weather prediction model "Unified Model" such as wind and radiation to model snow-pack properties. Additional loading in lee-slopes by wind-transport is modeled based on prevailing wind conditions, snow-water content and snow age. A depth hoar index accounts for days with considerable negative temperature gradients in the snow pack. A surface hoar index based on radiation and humidity is currently under development. The maps are tested against field reports from avalanche observers throughout Norway. All data is available via a web-platform that combines maps for geo-hazards such as floods, landslides and avalanches. The maps are used by the Norwegian avalanche forecasting service, which is currently in a test phase. The service will be operational by winter 2012/2013.

Müller, K.; Humstad, T.; Engeset, R. V.; Andersen, J.

2012-04-01

156

Rockfalls, Avalanches and Landslides at Augustine Volcano, 2003-2006  

Microsoft Academic Search

Rockfalls, avalanches, and landslides have been frequently recorded in seismic data at Augustine Volcano for many years. Typical years, such as 2003 or 2004, had several dozen such events that were strong enough to trigger the automatic event detection system. Seventeen rockfalls occurred in 2003, mostly in late summer when air temperatures were highest. In 2004, 28 events occurred --

N. Deroin; S. R. McNutt; C. Reyes; D. D. Sentman

2006-01-01

157

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

NASA Astrophysics Data System (ADS)

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

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

2013-05-01

158

The development of structures in analogue and natural debris avalanches  

NASA Astrophysics Data System (ADS)

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

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

2010-05-01

159

Electroded avalanche amorphous selenium (a-Se) photosensor.  

PubMed

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

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

2012-05-01

160

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

161

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

Microsoft Academic Search

The formation of terminal moraines mainly results from glacier changes in response to climate variations. But glaciers may also react sensitively to increased debris cover caused by large-scale failure of bedrock slopes. Catastrophic rock avalanches are a major source of sediment in active orogens like e.g. the Southern Alps, New Zealand (Shulmeister et al., 2009). They often occur as a

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

2010-01-01

162

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

163

Rescue missions for totally buried avalanche victims: conclusions from 12 years of experience.  

PubMed

The planning and execution of avalanche rescue missions to search for totally buried avalanche victims are mostly based on personal experience and preference, as evidence-based information from literature is almost completely missing. Hence, the aim of this study was to identify major factors determining the survival probability of totally buried victims during avalanche rescue missions carried out by organized rescue teams (Austrian Mountain Rescue Service, Tyrol). During the 12-year period studied, 109 totally buried persons (56 off-piste, 53 backcountry), were rescued or recovered; 18.3% survived to hospital discharge. Median depth of burial was 1.25 m; median duration of burial was 85 min. The majority (61.6%) of the rescue missions were conducted under considerably dangerous avalanche conditions. The probability of survival was highest when located visually and lowest for those located by avalanche transceiver; survival did not significantly differ between those found by rescue dogs and those located with avalanche probes. Multivariate analysis revealed short duration of burial and off-piste terrain to be the two independent predictors of survival. Whenever companion rescue fails, snow burial in an avalanche is associated with extraordinarily high mortality. Searching the avalanche debris with probe lines seems to be equally effective as compared to searching with rescue dogs. The potential hazard for rescuers during avalanche rescue missions comes mainly from self-triggered avalanches, hence thorough mission planning and critical risk-benefit assessment are of utmost importance for risk reduction. PMID:18800960

Hohlrieder, Matthias; Thaler, Stephanie; Wuertl, Walter; Voelckel, Wolfgang; Ulmer, Hanno; Brugger, Hermann; Mair, Peter

2008-01-01

164

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

165

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

Microsoft Academic Search

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

Christian Huggel; Jacqueline Caplan-Auerbach; Christopher F. Waythomas; Rick L. Wessels

2007-01-01

166

Anticrack Nucleation as Triggering Mechanism for Snow Slab Avalanches  

NASA Astrophysics Data System (ADS)

Snow slab avalanches are believed to begin by the gravity-driven shear failure of weak layers in stratified snow. The critical crack length for shear crack propagation along such layers should increase without bound as the slope decreases. However, recent experiments show that the critical length of artificially introduced cracks remains constant or, if anything, slightly decreases with decreasing slope. This surprising observation can be understood in terms of volumetric collapse of the weak layer during failure, resulting in the formation and propagation of mixed-mode anticracks, which are driven simultaneously by slope-parallel and slope-normal components of gravity. Such fractures may propagate even if crack-face friction impedes downhill sliding of the snowpack, indicating a scenario in which two separate conditions have to be met for slab avalanche release.

Heierli, J.; Gumbsch, P.; Zaiser, M.

2008-07-01

167

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

168

Photon avalanche up-conversion in holmium doped fluoride glasses  

SciTech Connect

Photon avalanche green up-conversion emission centered at 545 nm has been observed in Ho{sup 3+} doped and Ho{sup 3+}, Tm{sup 3+} co-doped ZrF{sub 4}-based fluoride glasses when excited near 585 nm which is off resonance with any ground state absorption bands of either Ho{sup 3+} or Tm{sup 3+} ions. Detailed spectral measurements and analysis suggest that the 545 nm emission occurs from the {sup 5}S{sub 2},{sup 5}F{sub 4} states of Ho{sup 3+} that are populated by excited state absorption from the {sup 5}I{sub 7} state of Ho{sup 3+}. Strong cross-relaxation that efficiently populates the {sup 5}I{sub 7} state makes the photon avalanche process possible in this system.

Chen, Y.H.; Liu, G.K.; Beitz, J.V. [Argonne National Lab., IL (United States). Chemistry Division; Jie Wang [Shanghai Institute of Optics and Fine Mechanics, Shanghai (China)

1996-08-01

169

Avalanche Breakdown Design Parameters in GaN  

NASA Astrophysics Data System (ADS)

We have studied the avalanche breakdown design parameters of GaN n+/p and p+/n junctions in the voltage range of 1.2 to 12 kV using numerical simulations and analytical calculations. Important analytical models regarding the relationships between breakdown voltages, depletion width, maximum junction electric field and doping concentrations have been extracted which shows very high consistency with the results from numerical simulations. These analytical models can be used as guidelines in the designing of GaN high voltage power devices. The multiplication factors Mn and Mp have also been obtained and the analytical models have been extracted. The results showed that in GaN, n+/p junction is better than p+/n for the main voltage blocking junction due to a sharper avalanche current increase.

Li, Zhongda; Pala, Vipindas; Chow, T. Paul

2013-08-01

170

Universal Critical Dynamics in High Resolution Neuronal Avalanche Data  

NASA Astrophysics Data System (ADS)

The tasks of neural computation are remarkably diverse. To function optimally, neuronal networks have been hypothesized to operate near a nonequilibrium critical point. However, experimental evidence for critical dynamics has been inconclusive. Here, we show that the dynamics of cultured cortical networks are critical. We analyze neuronal network data collected at the individual neuron level using the framework of nonequilibrium phase transitions. Among the most striking predictions confirmed is that the mean temporal profiles of avalanches of widely varying durations are quantitatively described by a single universal scaling function. 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.

Friedman, Nir; Ito, Shinya; Brinkman, Braden A. W.; Shimono, Masanori; DeVille, R. E. Lee; Dahmen, Karin A.; Beggs, John M.; Butler, Thomas C.

2012-05-01

171

Model for domain wall avalanches in ferromagnetic thin films  

Microsoft Academic Search

The Barkhausen jumps or avalanches in magnetic domain-walls motion between\\u000asuccesive pinned configurations, due the competition among magnetic external\\u000adriving force and substrum quenched disorder, appear in bulk materials and thin\\u000afilms. We introduce a model based in rules for the domain wall evolution of\\u000aferromagnetic media with exchange or short-range interactions, that include\\u000adisorder and driving force effects. We

R. C. Bucetaand; D. Muraca

2010-01-01

172

Progress in Silicon Single-Photon Avalanche Diodes  

Microsoft Academic Search

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

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

2007-01-01

173

Development of a novel planar-construction avalanche photodiode  

Microsoft Academic Search

A deep-diffused large-area avalanche photodiode (APD) without bevel or grooves has been designed and built for use in low-light-level applications. The design does not incorporate a bevel edge or grooves to avoid early breakdown at the surface. The APD has been built using standard planar technology for silicon devices. Photodiodes with 2- and 3-mm diameter active area have been produced

Ernesto Gramsch; R. E. Avila; J. Ferrer

2001-01-01

174

A thermal neutron beam monitor based on avalanche counter  

NASA Astrophysics Data System (ADS)

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

Nakhostin, M.; Baba, M.

2013-05-01

175

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

Microsoft Academic Search

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

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

1998-01-01

176

Indirect flat-panel detector with avalanche gain  

Microsoft Academic Search

A new concept - an indirect flat-panel detector with avalanche gain - for low dose x-ray imaging has been proposed. The detector consists of an amorphous selenium (a-Se) photoconductor optically coupled to a structured cesium iodide (CsI) scintillator. Under an electric field ESe, the a-Se is sensitive to light and converts the optical photons emitted from CsI into electronic signal.

Wei Zhao; Dylan C. Hunt; Kenkichi Tanioka; John A. Rowlands

2004-01-01

177

Avalanche Dynamics and Trading Friction Effects on STOCK Market Returns  

NASA Astrophysics Data System (ADS)

We propose a model with heterogeneous interacting traders which can explain some of the stylized facts of stock market returns. A generalized version of the Random Field Ising Model (RFIM) is introduced to describe trading behavior. Imitation effects, which induce agents to trade, can generate avalanches in trading volume and large gaps in demand and supply. A trade friction is introduced which, by responding to price movements, creates a feedback mechanism on future trading and generates volatility clustering.

Iori, Giulia

178

Quantum Theory for Cold Avalanche Ionization in Solids  

SciTech Connect

A theory of photon-assisted impact ionization in solids is presented. Our theory makes a quantum description of the new impact ionization--cold avalanche ionization recently reported by P. P. Rajeev, M. Gertsvolf, P. B. Corkum, and D. M. Rayner [Phys. Rev. Lett. 102, 083001 (2009)]. The present theory agrees with the experiments and can be reduced to the traditional impact ionization expression in the absence of a laser.

Deng, H. X. [Department of Applied Physics, University of Electronic Science and Technology of China, Chengdu 610054 (China); Department of Materials Sciences and Engineering, University of Michigan, Ann Arbor, MI48109 (United States); Zu, X. T.; Xiang, X. [Department of Applied Physics, University of Electronic Science and Technology of China, Chengdu 610054 (China); Sun, K. [Department of Materials Sciences and Engineering, University of Michigan, Ann Arbor, MI48109 (United States)

2010-09-10

179

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

NASA Astrophysics Data System (ADS)

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

Kim, Hyun-Joo

180

Three advanced designs of micro-pixel avalanche photodiodes: Their present status, maximum possibilities and limitations  

NASA Astrophysics Data System (ADS)

Novel types of micro-pixel avalanche photodiodes (MAPDs) and their principle of performance are analyzed. The first design contains a common silicon wafer on which a matrix of independent p n junctions (micro-pixels) with individual surface resistors are created. The individual resistors provide a local suppression of the avalanche process and discharge each micro-pixel to a common metal grid (electrode). The second design is an avalanche photodiode with independent micro-pixels in which the local suppression of the avalanche process is carried out due to the limited conductivity of individual surface drift channels formed along the silicon silicon oxide boundary. This design is considered as a prototype for a future super-fast avalanche CCD matrix capable to work in a single-photon detection mode. The third design contains a matrix of deep buried multilayer pixels with an individual suppression of the avalanche process in independent vertical channels.

Sadygov, Z.; Olshevski, A.; Chirikov, I.; Zheleznykh, I.; Novikov, A.

2006-11-01

181

Modelling avalanche protection systems by Savage-Hutter theory  

NASA Astrophysics Data System (ADS)

Avalanches and other flow like natural catastrophes like mudflows and landslides caused important damage in the past. Settlements and important infrastructure, like streets or power plants have to be protected, which often demands major effort. The building of protection system is often very expensive, due to the difficult terrain where the constructions have to be placed. Optimizing the size and the positioning of groups of obstacles, relative to each other, in respect to efficiency and costs, is therefore of scientific and economical interest. In the last decades various models have been proposed. The Savage-Hutter theory is an attractive approach to simulate gravity driven free-surface flows. The model was extended to simulate avalanches in arbitrary topography, where a curvilinear coordinate system was used to create a generally twisted reference surface. Moreover, an elevation function was introduced, which accounts for the difference between the basal topography and its reference surface. In this way, local irregularities could be taken into consideration. This elevation function was also used to include obstacles for avalanche protection into the model. This method has some major weakness, causing too light impact of the obstacles in the model, when compared to laboratory experiments. In this work, the problem will be discussed in detail and an alternative approach will be proposed. Different kind of obstructions will be compared. Also computational results for groups of objects will be presented.

Wawra, M.; Wang, Y.; Pudasaini, S. P.; Wu, W.

2009-04-01

182

Model for domain wall avalanches in ferromagnetic thin films  

NASA Astrophysics Data System (ADS)

The Barkhausen jumps or avalanches in magnetic domain-walls motion between successive pinned configurations, due the competition among magnetic external driving force and substrum quenched disorder, appear in bulk materials and thin films. We introduce a model based in rules for the domain wall evolution of ferromagnetic media with exchange or short-range interactions, that include disorder and driving force effects. We simulate in 2-dimensions with Monte Carlo dynamics, calculate numerically distributions of sizes and durations of the jumps and find power-law critical behavior. The avalanche-size exponent is in excellent agreement with experimental results for thin films and is close to predictions of the other models, such as like random-field and random-bond disorder, or functional renormalization group. The model allows us to review current issues in the study of avalanches motion of the magnetic domain walls in thin films with ferromagnetic interactions and opens a new approach to describe these materials with dipolar or long-range interactions.

Buceta, R. C.; Muraca, D.

2011-11-01

183

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

184

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

185

Experimental investigation of plastic deformations before a granular avalanche.  

PubMed

We present an experimental study of the deformation inside a granular material that is progressively tilted. We investigate the deformation before the avalanche with a spatially resolved diffusive wave spectroscopy setup. At the beginning of the inclination process, we first observe localized and isolated events in the bulk, with a density which decreases with the depth. As the angle of inclination increases, series of microfailures occur periodically in the bulk, and finally a granular avalanche takes place. The microfailures are observed only when the tilt angles are larger than a threshold angle much smaller than the granular avalanche angle. We have characterized the density of reorganizations and the localization of microfailures. We have also explored the effect of the nature of the grains, the relative humidity conditions, and the packing fraction of the sample. We discuss those observations in the framework of the plasticity of granular matter. Microfailures may then be viewed as the result of the accumulation of numerous plastic events. PMID:23410323

Amon, Axelle; Bertoni, Roman; Crassous, Jérôme

2013-01-22

186

Avalanche photodiode detection statistics for direct detection laser radar  

NASA Astrophysics Data System (ADS)

The detection statistics of avalanche photodiode detectors when used in laser radar systems are examined. In the laser radar systems considered here, a diffuse hard target is illuminated by a transmitted laser beam and the photons subtended by the receiving aperture and focused onto the detector obey negative-binomial statistics. The specific negative-binomial distribution is determined by the coherence length of the laser and the angular subtense of the target. These received photons are converted into photoelectrons and amplified by the avalanche photodiode which is an imperfect device. Dark current, amplifier, and background-produced noise electrons must be exceeded by the avalanche photodiode output electron pulse for a detection to occur. The required mean number of signal photons from a given negative-binomial target as a function of probability of detection and probability of false alarm is calculated. For perfect photon counters, the probability of detection at high discrete false alarm probabilities is also calculated. It is shown that for probabilities of detection of 0.9, three to five times more laser power may be required than for the generally assumed Poisson signal photons case. At probabilities of detection of 0.3, corresponding to multipulse waveforms, the statistics are independent of the target photon distribution.

Youmans, Douglas G.

1992-06-01

187

First townsend coefficient of organic vapour in avalanche counters  

NASA Astrophysics Data System (ADS)

A new concept is presented in the paper for implementing the proven method of determining the first Townsend coefficient (?) of gases using an avalanche counter. The A and B gas constants, interrelated by the expression ?/p = A exp[-B/(K/p)], are analyzed. Parallel-plate avalanche counters (PPAC) with an electrode spacing d from 0.1 to 0.4 cm have been employed for the investigation, arranged to register low-energy alpha particles at n-heptane vapour pressures of p >= 5 Torr. An in-depth discussion is given, covering the veracity and the behaviour vs K/p, of the n-heptane A and B constants determined at reduced electric-field intensity values ranging from 173.5 to 940 V/cm Torr; the constants have been found to depend upon d. The results of the investigation are compared to available data of the ? coefficient of organic vapours used in avalanche counters. The PPAC method of determining ? reveals some imperfections at very low values of the pd product.

Sernicki, Jan

1990-03-01

188

Avalanche Noise from Schottky Barrier Diodes in the Frequency Range 75 - 115 GHz (Technical Notes)  

Microsoft Academic Search

Excess noise has been generated in the 75-115 GHz band, by reverse biasing GaAs Schottky barrier diodes into avalanche breakdown. Diodes with lower epi-layer doping yield lower excess noise, but provide stable avalanche noise, and are less liable to generate excess mixer noise. A sharp reverse bias characteristic appears to be a precondition for a stable avalanche noise output.

N. J. Keen; R. W. Haas; P. Zimmerman

1978-01-01

189

Landscape and sedimentary response to catastrophic debris avalanches, western Taranaki, New Zealand  

Microsoft Academic Search

Catastrophic volcanic debris avalanches reshape volcanic edifices with up to half of pre-collapse cone volumes being removed. Deposition from this debris avalanche deposit often fills and inundates the surrounding landscape and may permanently change the distribution of drainage networks. On the weakly-incised Mt. Taranaki ring-plain, volcanic debris avalanche deposits typically form a large, wedge shape (in plan view), over all

Jonathan N. Procter; Shane J. Cronin; Anke V. Zernack

2009-01-01

190

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

Microsoft Academic Search

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

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

2010-01-01

191

Snow Avalanche Disturbance Ecology: Examples From the San Juan Mountains, Colorado.  

NASA Astrophysics Data System (ADS)

We evaluated landscape ecology approaches to characterize snow avalanche paths based on patterns of plant species composition and evidence of disturbance. Historical records of avalanche incidents, patterns in the annual growth layers of woody plants, and distributions of plant species can be used to quantify and map the frequency and magnitude of snow slide events. Near Silverton, Colorado, a series of snow storms in January of 2005 resulted in many avalanche paths running full track at 30 and 100 year return frequency. Many avalanches cut fresh trimlines, widening their tracks by uprooting, stripping, and breaking mature trees. Powerful avalanches deposited massive piles of snow, rocks, and woody debris in their runout zones. We used cross-section discs and cores of representative downed trees to detect dendro-ecological signals of past snow avalanche disturbance. Avalanche signals included impact scars from the moving snow and associated wind blast, relative width of annual growth rings, and development of reaction wood in response to tilting. Initial measurements of plant diversity and disturbance along the elevation gradient of an avalanche path near Silverton indicate that avalanche activity influences patterns of forest cover, contributes to the high local plant species diversity, and provides opportunities for new seedling establishment.

Simonson, S.; Fassnacht, S. R.

2008-12-01

192

Snow avalanche regime and climatic conditions in the Chic-Choc Range, eastern Canada  

Microsoft Academic Search

Because snow avalanches occur at altitudes close to the 0°C isotherm in mountain environments, they should respond quickly\\u000a to climatic variations. This study provides tree-ring-based high-magnitude avalanche chronologies for 12 subalpine avalanche\\u000a paths in the Chic-Choc Range of Québec (eastern Canada). For the period covered by the chronologies, i.e., between 1895 and\\u000a 1999, high-magnitude avalanches occurred with an average return

Daniel Germain; Louise Filion; Bernard Hétu

2009-01-01

193

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

USGS Publications Warehouse

The community of Forest Falls, California, is frequently subject to relatively slow moving debris flows. Some 11 debris flow events that were destructive to property have been recorded between 1955 and 1998. On July 11 and 13, 1999, debris flows again occurred, produced by high-intensity, short-duration monsoon rains. Unlike previous debris flow events, the July 11 rainfall generated a high-velocity debris avalanche in Snow Creek, one of the several creeks crossing the composite, debris flow dominated, alluvial fan on which Forest Falls is located. This debris avalanche overshot the bank of the active debris flow channel of Snow Creek, destroying property in the near vicinity and taking a life. The minimum velocity of this avalanche is calculated to have been in the range of 40 to 55 miles per hour. Impact from high-velocity boulders removed trees where the avalanche overshot the channel bank. Further down the fan, the rapidly moving debris fragmented the outer parts of the upslope side of large pine trees and embedded rock fragments into the tree trunks. Unlike the characteristic deposits formed by debris flows, the avalanche spread out down-slope and left no deposit suggestive of a debris avalanche. This summer monsoon-generated debris avalanche is apparently the first recorded for Forest Falls. The best indications of past debris avalanches may be the degree of permanent scars produced by extensive abrasion and splintering of the outer parts of pine trees that were in the path of an avalanche.

Morton, Douglas M.; Hauser, Rachel M.

2001-01-01

194

Development of a Germanium Avalanche-Type Semiconductor Nuclear Particle Detector and Discussion of Avalanche Detector Arrays  

Microsoft Academic Search

Research on avalanche or high field types of semiconductor detectors has increased within the past two years, impelled, in part, by the great interest in the photo-detection field. We have concentrated on the surface contoured-deep junction diffusion approach while other investigators generally have pursued the use of a planar-oxide passivated-shallow diffused structures. Reported herein are results of studies of deep

Gerald C. Huth; Russell A. McKinney; Robert J. Locker

1968-01-01

195

Development in the design and performance of gas avalanche microdetectors  

NASA Astrophysics Data System (ADS)

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

Cho, Hyo-Sung

1997-12-01

196

Monitoring of snow avalanches using a seismic array: Location, speed estimation, and relationships to meteorological variables  

NASA Astrophysics Data System (ADS)

Monitoring snow avalanches is necessary in order to better understand their triggering mechanisms and ultimately improve forecast performance. Seismic monitoring has been developed by several groups over the last 20 years and holds great potential to detect, locate, and characterize snow avalanches. During the 2009-2010 winter, a seismic antenna was installed in the French Alps close to the village of Saint-Christophe-en-Oisans (1700 m above sea level). The array of seven sensors operated during 50 days in October and November 2009 under snow-free conditions and during 40 days in January and February 2010 in presence of snow. It recorded different types of seismic events including snow avalanches, rockfalls, shots, and regional and local microearthquakes. Eighty avalanche signals were visually identified. Using a beam-forming method, we were able to locate snow avalanches on slopes of various orientations in a radius of about 3 km and track their propagation. The location technique allowed for the estimation of avalanches' front speed, which ranged between 12 and 32 m s-1. The method can also distinguish dry and wet snow avalanches. Durations of avalanches can be as long as 380 s because of the length of the slopes in the area. Seismic monitoring provides a catalog of avalanches with precise times, which can be used to analyze the impact of meteorological forcings on the avalanche triggering. Snowfall is found to be the dominant forcing of avalanche activity during this period, as revealed by the strongest correlation. For the period of study, our results suggest that the impact of precipitation on the snowpack instability lasts for about 6 days.

Lacroix, P.; Grasso, J.-R.; Roulle, J.; Giraud, G.; Goetz, D.; Morin, S.; Helmstetter, A.

2012-03-01

197

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

198

Subsampling effects in neuronal avalanche distributions recorded in vivo  

PubMed Central

Background Many systems in nature are characterized by complex behaviour where large cascades of events, or avalanches, unpredictably alternate with periods of little activity. Snow avalanches are an example. Often the size distribution f(s) of a system's avalanches follows a power law, and the branching parameter sigma, the average number of events triggered by a single preceding event, is unity. A power law for f(s), and sigma = 1, are hallmark features of self-organized critical (SOC) systems, and both have been found for neuronal activity in vitro. Therefore, and since SOC systems and neuronal activity both show large variability, long-term stability and memory capabilities, SOC has been proposed to govern neuronal dynamics in vivo. Testing this hypothesis is difficult because neuronal activity is spatially or temporally subsampled, while theories of SOC systems assume full sampling. To close this gap, we investigated how subsampling affects f(s) and sigma by imposing subsampling on three different SOC models. We then compared f(s) and sigma of the subsampled models with those of multielectrode local field potential (LFP) activity recorded in three macaque monkeys performing a short term memory task. Results Neither the LFP nor the subsampled SOC models showed a power law for f(s). Both, f(s) and sigma, depended sensitively on the subsampling geometry and the dynamics of the model. Only one of the SOC models, the Abelian Sandpile Model, exhibited f(s) and sigma similar to those calculated from LFP activity. Conclusion Since subsampling can prevent the observation of the characteristic power law and sigma in SOC systems, misclassifications of critical systems as sub- or supercritical are possible. Nevertheless, the system specific scaling of f(s) and sigma under subsampling conditions may prove useful to select physiologically motivated models of brain function. Models that better reproduce f(s) and sigma calculated from the physiological recordings may be selected over alternatives.

Priesemann, Viola; Munk, Matthias HJ; Wibral, Michael

2009-01-01

199

The HgCdTe electron avalanche photodiode  

NASA Astrophysics Data System (ADS)

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

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

2004-10-01

200

Neuronal avalanches in the resting MEG of the human brain.  

PubMed

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

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

2013-04-17

201

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

202

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

Microsoft Academic Search

Snow avalanches pose a threat to settlements and infrastructure in alpine environments. Due to the catastrophic events in recent years, the public is more aware of this phenomenon. Alpine settlements have always been confronted with natural hazards, but changes in land use and in dealing with avalanche hazards lead to an altering perception of this threat. In this study, a

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

2006-01-01

203

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

Microsoft Academic Search

The 18 May 1980 eruption of Mount St. Helens was initiated by a massive rockslide-debris avalanche which completely transformed the upper 25 km of the North Fork Toutle River valley. The debris was generated by one of the largest gravitational mass movements ever recorded on Earth. Moving at an average velocity of 35 m\\/s, the debris avalanche buried approximately 60

G. L. Beach; D. Dzurisin

1984-01-01

204

SEX, DRUGS AND THE WHITE DEATH: LESSONS FOR AVALANCHE EDUCATORS FROM HEALTH AND SAFETY CAMPAIGNS  

Microsoft Academic Search

A common expectation of avalanche education is that it should reduce the frequency of avalanche deaths. But is this expectation realistic? After all, education campaigns aimed at reducing unsafe sex, illegal drug use, unsafe driving and other risky behaviors have met with very limited success, and in some cases have even worsened the problems they were intended to solve. This

Ian McCammon

205

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

206

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

207

A simplified approach to time-domain modeling of avalanche photodiodes  

Microsoft Academic Search

A simplified algorithm for calculating time response of avalanche photodiodes (APDs) is presented. The algorithm considers the time course of avalanche processes for the general case of position-dependent double-carrier multiplications including the dead space effect. The algorithm is based on a discrete time setting ideally suited for computer modeling and can be applied to any APD structure. It gives a

A. Bandyopadhyay; M. Jamal Deen; L. E. Tarof; W. Clark

1998-01-01

208

Supersmooth surface for low glide avalanche and low signal modulation media  

Microsoft Academic Search

This study investigates the effect of surface morphology and roughness on glide avalanche and signal amplitude modulation. Low glide avalanche and low signal modulation are obtained by the use of diamond or alumina texturing process. Diamond texturing process uses fine and tightly distributed diamond particles together with a microfiber texturing tape. The alumina texturing process which adds small amount of

A. H. Tan; J. S. Lin; C. M. Wang; C. Dong

1999-01-01

209

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

210

A photon-counting avalanche photodiode array with fully integrated active quenching and recharging circuit  

Microsoft Academic Search

The design of a 4 × 1 photon-counting avalanche photodiode array with fully integrated active bias controlling circuit is presented in this paper. The array uses highly sensitive Geiger mode avalanche photodiodes and is capable of detecting four single-photon-level optical signals simultaneously. The photodiode pixels can work either in parallel mode or independently because of the separate gate configuration. The

F. Lin; M. Mac Sweeney; M. M. Sheehan; A. Mathewson

2005-01-01

211

Lithologic, Structural, and Topographic Influences on Snow-Avalanche Path Location, Eastern Glacier National Park, Montana  

Microsoft Academic Search

We examine the roles of lithology, structure, and topography as determinants of the location and morphology of snow-avalanche paths in east-central Glacier National Park, Montana. Most models of avalanche path location emphsize topographic interactions with prevailing winds and ignore the role of geologic influences. Landsat Thematic Mapper digital data, covering the study area, were enhanced through a combination of directional

David R. Butler; Stephen J. Walsh

1990-01-01

212

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…

Purves, R. S.; Sanderson, M.

1998-01-01

213

Reduced gravity causes larger and lower-angle granular avalanches with less stratification  

Microsoft Academic Search

Granular materials avalanche when a static angle of repose is exceeded and freeze at a dynamic angle of repose. Such avalanches occur subaerially on hillslopes and wind dunes and subaqueously at the lee side of deltas and dunes. Their properties are important for the inference of present morphodynamics and past climate from surface morphology on rocky planetary bodies. The objective

S. J. de Vet; M. G. Kleinhans; H. Markies; A. C. in't Veld; F. N. Postema

2010-01-01

214

Energy Model of Increasing Radiation and the Size of an Electron Avalanche in a Streamer Chamber.  

National Technical Information Service (NTIS)

A qualitative model is proposed of increasing light radiation and the size of an avalanche with increased gas amplification N in a streamer chamber based on the proportion of the light radiation of electrostatic avalanche energy. From the model it follows...

N. S. Glagoleva A. T. Matyushin V. T. Matyushin N. N. Nupgozhin

1983-01-01

215

SEISMIC RECORDINGS OF ICE AND DEBRIS AVALANCHES OF ILIAMNA VOLCANO, ALASKA  

Microsoft Academic Search

Seismic data recorded on Iliamna Volcano, Alaska, indicate that Iliamna ice avalanches are preceded by up to several hours of p recursory seismicity. This precursory activity is represented by a 1-3 hour period of activity comprising a sequence of discrete repeatin g earthquakes and a period of continuous groundshaking that builds in amplitude. The avalanche itself is represented by a

Jacqueline Caplan-Auerbach; Stephanie G. Prejean; John A. Power

216

Precursory seismicity associated with frequent, large ice avalanches on Iliamna volcano, Alaska, USA  

Microsoft Academic Search

Since 1994, at least six major (volume >106 m3) ice and rock avalanches have occurred on Iliamna volcano, Alaska, USA. Each of the avalanches was preceded by up to 2 hours of seismicity believed to represent the initial stages of failure. Each seismic sequence begins with a series of repeating earthquakes thought to represent slip on an ice-rock interface, or

Jacqueline Caplan-Auerbach; Christian Huggel

2007-01-01

217

Perturbation avalanches and criticality in gene regulatory networks.  

PubMed

Boolean networks are simplified models of gene regulatory networks. We derive an approximation of the size distribution of perturbation avalanches in Boolean networks based on known results in the theory of branching processes. We show numerically that the approximation works well for different kinds of Boolean networks. It has been suggested that gene regulatory networks may be dynamically critical. To study this, as an application of the presented theory we present a novel method for estimating an order parameter from microarray data. According to the available data and our method, we find that gene regulatory networks appear to be stable and reside near the phase transition between order and chaos. PMID:16574157

Rämö, P; Kesseli, J; Yli-Harja, O

2006-03-30

218

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

219

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

220

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); Sdrulla, D. [Advanced Power Technology, Bend, OR (United States)

1998-06-01

221

Avalanches of dewetting holes in viscoelastic phase separation  

NASA Astrophysics Data System (ADS)

Textbook ideas fails regarding phase separation of polymer solutions, because of viscoelastic effects. Here with fluorescence microscopy we visualize in real time this process. Quasi two dimensional polymer solutions of polystyrene near the critical concentration are confined between non-wetting surfaces. Apart from a double phase separation induced by rapid hydrodynamic coarsening, we observe novel avalanched dewetting of solvent-enriched holes, not only in the polymer-enriched phase but also near the walls. Strikingly, this occurs at the late stage of the spinodal decomposition. These dewetting holes govern pattern evolution of the phase-separated polymer network.

Yu, Changqian; Bae, Sung Chul; Granick, Steve

2013-03-01

222

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

223

Silicon avalanche photodiode operation and lifetime analysis for small satellites.  

PubMed

Silicon avalanche photodiodes (APDs) are sensitive to operating temperature fluctuations and are also susceptible to radiation flux expected in satellite-based quantum experiments. We introduce a low power voltage adjusting mechanism to overcome the effects of in-orbit temperature fluctuations. We also present data on the performance of Si APDs after irradiation (?-ray and proton beam). Combined with an analysis of expected orbital irradiation, we propose that a Si APD in a 400 km equatorial orbit may operate beyond the lifetime of the satellite. PMID:23938543

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

2013-07-15

224

Silicon avalanche photodiode operation and lifetime analysis for small satellites  

NASA Astrophysics Data System (ADS)

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

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

2013-07-01

225

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

226

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

SciTech Connect

We report the scaling behavior of Barkhausen avalanches for every small field step along the hysteresis loop in CoCrPt alloy film having perpendicular magnetic anisotropy. Individual Barkhausen avalanche is directly observed utilizing a high-resolution soft X-ray microscopy that provides real space images with a spatial resolution of 15 nm. Barkhausen avalanches are found to exhibit power-law scaling behavior at all field steps along the hysteresis loop, despite their different patterns for each field step. Surprisingly, the scaling exponent of the power-law distribution of Barkhausen avalanches is abruptly altered from 1 {+-} 0.04 to 1.47 {+-} 0.03 as the field step is close to the coercive field. The contribution of coupling among adjacent domains to Barkhausen avalanche process affects the sudden change of the scaling behavior observed at the coercivity-field region on the hysteresis loop of CoCrPt alloy film.

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

2008-10-14

227

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

PubMed

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

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

2002-04-04

228

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

229

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

Microsoft Academic Search

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

Christian Huggel; Jacqueline Caplan-Auerbach; Christopher F. Waythomas; Rick L. Wessels

2007-01-01

230

High arctic snow avalanche observations and modeling in Svalbard 2007-2009  

NASA Astrophysics Data System (ADS)

Systematic snow avalanche observations, carried out by the Norklima CRYOSLOPE Svalbard research project 2007-2009, represent the first comprehensive study of periglacial slope processes and especially snow avalanches in a high arctic maritime landscape. The main focus is on snow avalanche types, their spatial distribution, timing and associated controlling meteorological and snow pack conditions. Another focus is on the classification of the snow pack in central Svalbard in terms of thickness, hardness, stratigraphy and most persistent weak layers that cause avalanching. As a result of increasing population and tourism, snow mobile transportation and other recreational use of the steep terrain has increased, especially during the last 10-15 years in Svalbard. Such winter activity takes place in a high relief, almost vegetation free landscape, affected by snow avalanches. We present results from the 3 years project period, as well as the methods used to collect observations on snow avalanches, the snow pack and the meteorological data along the most intensively used 70 km snow mobile tracks around Svalbard's main settlement Longyearbyen. This enables us to identify the main factors controlling snow avalanches. We have recorded the amount of traffic along the main snow mobile tracks in our snow avalanche affected study area by use of radar, for avalanche risk evaluation. We also exemplify the high arctic maritime snow climate as an important additional type of snow climate, and emphasize its characteristics. Along with the field work, numerical modeling of avalanche activity has been developed and tested during the winter 2008-2009, on a weekly basis. The modeling includes topography, geomorphology and vegetation as input data, along with daily meteorological observations on air temperature, wind, cloud cover and precipitation from two meteorological stations at different altitudes. Examples from this modeling experiment will be presented together with the collected, contemporary field observations for verification of the modeling.

Eckerstorfer, Markus; Christiansen, Hanne H.; Humlum, Ole

2010-05-01

231

Infrasonic and seismic signals of snow avalanches and debris flow  

NASA Astrophysics Data System (ADS)

Infrasonic and seismic signals generated by debris flows and snow avalanches are observed by microphones and seismometers, respectively, in near field. The properties of the signals obtained are presented. For debris flows, infrasonic and seismic signals are correlated and their amplitudes show a relationship with flow depth and precipitation data. During the passing of a debris flow several surges identified by ultrasonic gauges are observed in the time series and in the running spectra of infrasonic and seismic data. Both sensors detect the debris flow phenomena before reaching the sensors. Analyses in the time and frequency domains of seismic and acoustic signals from snow avalanches provide information on these natural phenomena. Although time series behaviour of infrasonic and seismic waves is similar, the time series present some differences in the information supplied. Complementarity and peculiarities of the use of these sensors for monitoring purposes are discussed in the paper. During the execution of this study infrasonic signals emitted from helicopters, airplanes and thunder were also identified and are presented

Kogelnig, Arnold; Suriñach, Emma; Hübl, Johannes; Vilajosana, Ignasi; Hiller, Martin; Dufour, Francois; McArdell, Brian W.

2010-05-01

232

Modeling of debris crushing during rock avalanche motion  

NASA Astrophysics Data System (ADS)

Study of numerous rock avalanches (RA) worldwide revealed that most of them are characterized by intensive comminution of debris that forms lower/internal parts of RA deposits and, at the same time, by retention of structure of the source rock massifs in RA debris despite that had passed a long distance from its source zone. The latter results in formation of pseudo-stratified bodies with unmixed 'layers' of debris that can be traced for several kilometers. Such internal structure excludes turbulence during rapid motion of dry granular flow typical of RA. It differs significantly from the style of motion of debris flows, which include significant amount of fluid obligatorily. Since such combination of crushing and of crushed material unmixing is typical, it must be reproduced both by physical and by numerical models of RA motion pretending to be reliable. Simple physical experiments demonstrate that intensive undamped crushing with retention of the initial structure of the material during its crushing can be achieved under repeated static loading with shearing - combination of mechanical processes quite reliable during RA motion, while similar loading without shearing results in crushing that fades much faster. The undamped crushing could be achieved by repeated loading with forced mixing too but in this case the original structure of the affected material can not retain. It allows assumption that mechanism simulated - static loading combined with shearing really act during motion of large-scale rock avalanches.

Strom, Alexander; Pernik, Leonid

2013-04-01

233

Collective Dislocation Dynamics and Avalanches during Fatigue of Aluminum  

NASA Astrophysics Data System (ADS)

We present a study of collective dislocation dynamics and plasticity during fatigue of pure Aluminum from the analysis of continuous and discrete acoustic emission (AE). The three stages of macroscopic fatigue behavior (strain-hardening, shakedown, and strain softening) are clearly differentiated in terms of AE. During the first loading cycles, collective dislocation dynamics consists in dislocation avalanches of various sizes and clustered in time. Once a microstructure of dislocation cells and walls is formed, the spreading of such avalanches is restrained, and the discrete AE strongly decreases. Instead, a symmetrical (tension-compression) continuous AE, maximal at plastic yield, is observed, likely associated to a superposition of numerous, small and uncorrelated motions such as dislocation loops initiation from cell walls. However, some discrete AE activity remains during shakedown, a possible signature of sudden rearrangements of the microstructure occurring at scales larger than its wavelength. Finally, the onset of strain softening is associated to a strong increase of discrete AE, in relation with microcracking. Our results suggest that collective dislocation instabilities and the emergence of a dislocation microstructure are interrelated, and challenge future numerical modeling developments of dislocation assemblies.

Rhouma, W. Ben; Deschanel, S.; Weiss, J.

2011-09-01

234

Avalanche mechanism for the enhanced loss of ultracold atoms  

NASA Astrophysics Data System (ADS)

In several experiments with ultracold trapped atoms, a narrow loss feature has been observed near an atom-dimer resonance, at which there is an Efimov trimer at the atom-dimer threshold. The conventional interpretation of these loss features is that they are produced by the avalanche mechanism, in which the energetic atom and dimer from three-body recombination undergo secondary elastic collisions that produce additional atoms with sufficient energy to escape from the trapping potential. We use Monte Carlo methods to calculate the average number of atoms lost and the average heat generated by recombination events in a Bose-Einstein condensate and in a thermal gas. We improve on previous models by taking into account the energy dependence of the cross sections, the spatial structure of the atom cloud, and the elastic scattering of the atoms. We show that the avalanche mechanism cannot produce a narrow loss feature near the atom-dimer resonance. The number of atoms lost from a recombination event can be more than twice as large as the three that would be obtained in the absence of secondary collisions. However, the resulting loss feature is broad and its peak is at a scattering length that is larger than the atom-dimer resonance and depends on the trap depth.

Langmack, Christian; Smith, D. Hudson; Braaten, Eric

2013-02-01

235

L-I-H Transition with Avalanche Noise  

NASA Astrophysics Data System (ADS)

Discharges have been observed to persist in a state subcritical to the H-mode, called I-phase, for extended periods. L-H transitions occur spontaneously in this state. I-phase edges are excited by noise, due to the statistical variability of core heat avalanches arriving at the edge. This suggests that the L-H transition problem should be formulated statistically, given an ensemble of colored noise tied to the mean heat flux. In this paper, we study the L-H transition in the presence of a noisy mean heat flux using 0D multi-field models, with special attention on the marginally subcritical state. The transition problem is formulated of the ``waiting time'' variety, studied as a function of margin below mean threshold, noise spectrum, and noise strength. Results indicate that 1/f noise, as expected for avalanche-induced flux perturbations, is more effective at triggering transitions. Our analyses of crossing rates and the effects of temporal coherence extend beyond a related analysis by Bian (PoP 2010). The effects of noise characteristics on reverse H-L transition dynamics is also investigated and related 1D modeling will be discussed.

Lee, C. J.; Diamond, P. H.; Miki, K.

2012-10-01

236

Enhanced Avalanche Ionization by RF Fields Creating an Ultracold Plasma  

NASA Astrophysics Data System (ADS)

Ultracold plasmas have been shown to evolve from initially frozen Rydberg gases held in magneto-optical traps.(M.P. Robinson, B. Laburthe Tolra, Michael W. Noel, T.F. Gallagher, and P. Pillet, Phys. Rev. Lett. 85), 4466 (2000) We report the enhancement of the avalanche ionization process by application of radiofrequency fields. An initial slow ionization rate is observed in the Rydberg sample due to black body ionization and ionizing collisions with hot Rydberg atoms. This produces an overall posititve space charge of cold ions as the hot electrons leave the sample. Once a threshold density of positive charges is built up, the hot electrons become trapped to the sample, leading to avalance ionization due to electron-Rydberg collisions. The mechanism of the ionization remains unclear. However, the application of radiofrequency fields, in the 1 V/cm, 100 MHz range, dramatically enhances the rate of avalanche ionization without changing the threshold density at which it occurs. Apparently, the limiting parameter is the rate of collisional ionization of Rydberg atoms by electrons.

Robinson, M. P.; Gallagher, T. F.; Laburthe Tolra, B.; Pillet, P.

2001-05-01

237

The occurrence of avalanches in a single crystal of Mn12-acetate  

NASA Astrophysics Data System (ADS)

Recent studies of Mn12-acetate have focused on the possible observation of superradiance triggered by avalanches of the magnetic relaxation [J. Tejada, E. M. Chudnovsky, J. M. Hernandez, and R. Amigo, Appl. Phys. Lett. 84, 2373 (2004); M. Bal et al., Phys. Rev. B, 70, 140403 (2004)]. It is therefore of interest to determine the conditions for such avalanches. For several single crystals of Mn12-acetate of different dimensions, the distribution of magnetic fields at which magnetic avalanches occur at different temperatures is reported for field sweep rates of 5 and 10 mT/s. No avalanches were observed above 0.8 K for these conditions. For temperatures below 0.8 K, avalanches were found between 2.0 and 4.2 T, with about half occurring below the field (3.2 T) above which appreciable relaxation proceeds by ground state tunneling. At the level of statistics accumulated in these experiments, there appears to be no clear preference for an avalanche to occur at or near a resonant magnetic field, and a surprising number occur at fields below the expected onset of appreciable ground state tunneling in the absence of avalanches.

Suzuki, Yoko; Sarachik, M. P.; Avraham, N.; Myasoedov, Y.; Shtrikman, H.; Zeldov, E.; Rumberger, E. M.; Hendrickson, D. N.; Christou, G.

2005-05-01

238

The rock avalanche sediment in moraines and its implication for palaeoclimate reconstruction  

NASA Astrophysics Data System (ADS)

Rock avalanches mobilise a large quantity of sediment that after deposition on a glacier may cause its regime to alter. The glacier response includes change of mass balance after the rock avalanche emplacement followed by re-deposition of the rock avalanche sediment as moraine (Reznichenko et al., 2010; Reznichenko et al., 2011). Such aclimatic glacier response to a supraglacial rock avalanche deposit can confound apparent climatic signals extracted from moraine chronologies, which are widely used to infer regional climate change and are often correlated globally. Therefore, the origin of any particular dated moraine must be clarified before that date can be used for paleoclimatic interpretation. We present a new method that identifies the presence of rock avalanche sediment in moraines, based on the characteristics of the finest sediment fraction which contrast with those of non-rock-avalanche-derived glacial sediment. Under the dry, high-stress conditions during rock avalanche emplacement, fragmenting grains form agglomerates, which are absent in the wet, lower-stress processes of sub- and en-glacial environments. We show that these agglomerates are present in some moraines in the Southern Alps of New Zealand that have been attributed to climate fluctuation. This technique has the potential to resolve long-standing arguments about the role of rock avalanches in moraine formation and to enhance the use of moraines in palaeoclimatological studies. Reznichenko, N.V., Davies, T.R.H., Shulmeister, J. and McSaveney, M.J., 2010. Effects of debris on ice-surface melting rates: an experimental study. Journal of Glaciology, Vol. 56, No. 197, 384-394 Reznichenko, N.V., Davies, T.R.H. and Alexander, D.J., 2011. Effects of rock avalanches on glacier behaviour and moraine formation. Geomorphology, v. 132, is.3-4, p. 327-338

Reznichenko, N.; Davies, T. R. H.; Shulmeister, J.; Winkler, S.

2012-04-01

239

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

NASA Astrophysics Data System (ADS)

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.

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

2013-08-01

240

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

Sze, R.C.

1979-10-10

241

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

242

Modeling the gain and bandwidth of submicron active layer n+-i-p+ avalanche photodiode  

NASA Astrophysics Data System (ADS)

The electron initiated avalanche gain and bandwidth are calculated for thin submicron GaAs n+-i-p+ avalanche photodiode. A model is used to estimate the avalanche build-up of carriers in the active multiplication layer considering the dead-space effect. In the model, the carriers are identified both by their energy and position in the multiplication region. The excess energy of the carriers above threshold is assumed to be equally distributed among the carriers generated after impact ionization. The gain versus bias and bandwidth versus gain characteristics of the device are also demonstrated for different active layer thicknesses of the APD.

Majumder, Kanishka; Das, N. R.

2012-10-01

243

Single Photon Avalanche Diodes: Towards the Large Bidimensional Arrays  

PubMed Central

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

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

2008-01-01

244

Subnanosecond timing with large area avalanche photodiodes and LSO scintillator  

SciTech Connect

The detection properties of 10 mm and 16 mm diameter beveled-edge avalanche photodiodes fitted with LSO crystal were measured using {gamma}-sources. Among the properties measured were the electron-hole pair yield, time resolution and energy resolution. These detectors provide excellent time resolution of 570 {+-} 17 ps for {sup 60}Co {gamma}-rays with the energy threshold set at 1 MeV. The energy resolution of the 662 keV {gamma}-peak from a {sup 137}Cs source was measured to be 11% FWHM with a shaping time constant of 0.1 {micro}s. A comparative discussion of the observed time resolution of these large area APDs emphasizes that APD gain, its quantum efficiency, and capacitance are important in timing applications.

Moszynski, M.; Ludziejewski, T.; Wolski, D. [Soltan Inst. for Nuclear Studies, Swierk-Otwock (Poland); Klamra, W. [Royal Inst. of Tech., Stockholm (Sweden). Dept. of Physics; Szawlowski, M. [Advanced Photonix, Inc., Camarillo, CA (United States); Kapusta, M. [Univ. of Warsaw (Poland). Inst. of Experimental Physics

1996-06-01

245

10 Gbps silicon waveguide-integrated infrared avalanche photodiode.  

PubMed

We have fabricated monolithic silicon avalanche photodiodes capable of 10 Gbps operation at a wavelength of 1550 nm. The photodiodes are entirely CMOS process compatible and comprise a p-i-n junction integrated with a silicon-on-insulator (SOI) rib waveguide. Photo-generation is initiated via the presence of deep levels in the silicon bandgap, introduced by ion implantation and modified by subsequent annealing. The devices show a small signal 3 dB bandwidth of 2.0 GHz as well as an open eye pattern at 10 Gbps. A responsivity of 4.7 ± 0.5 A/W is measured for a 600 µm device at a reverse bias of 40 V. PMID:24105500

Ackert, Jason J; Karar, Abdullah S; Paez, Dixon J; Jessop, Paul E; Cartledge, John C; Knights, Andrew P

2013-08-26

246

Polychromatic flow cytometry with an avalanche photodiode array  

NASA Astrophysics Data System (ADS)

Multi parameter flow cytometry enables detailed identification of cell type and function based on fluorescence of antibody conjugated dye labels. Current instruments use photomultiplier tube detectors to measure up to eight fluorescent labels from a single excitation source. We demonstrate polychromatic flow cytometry using a 14-element avalanche photodiode (APD) array coupled with a dispersive optical grating. Forward scatter, side scatter, and 14 fluorescence channels over the 530 to 800 nm spectral range are recorded using a 16 channel electronics console for simultaneous event capture. The APD detector elements have a working spectral range from 400 nm to 1050 nm. Results are presented for flow cytometry measurements of Spherotech UltraRainbow test beads, quantum dot labeled polystyrene spheres, and cells with antibody conjugated dye labels. The flow cytometry test bead measurements illustrate the sensitivity and spectral resolution of the APD detector array. The application of the instrument is demonstrated by identifying CD4 positive lymphocyte populations in normal human whole blood samples.

Lawrence, William G.; Varadi, Gyula; Entine, Gerald; Podniesinski, Edward; Wallace, Paul K.

2008-03-01

247

Parallel adaptive numerical simulation of dry avalanches over natural terrain  

NASA Astrophysics Data System (ADS)

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 model of the conservation laws and an adaptive grid Godunov solver to solve the resulting equations. The software is designed to run on distributed memory supercomputers and makes use of digital elevation data dynamically, i.e., refine the grid and input data to finer resolutions to better capture flow features as the flow evolves. Our simulations are validated using quantitative and qualitative comparisons to tabletop experiments and data from field observations. Our software is freely available and uses only publicly available libraries and hence can be used on a wide range of hardware and software platforms.

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

2005-01-01

248

Development of scintillation detectors based on avalanche microchannel photodiodes  

NASA Astrophysics Data System (ADS)

Avalanche Microchannel PhotoDiodes (AMPDs) are solid state photodetectors with high internal gain and a density of independent channels up to 104/mm2. They are potential substitutes for photomultiplier tubes in a wide variety of applications in nuclear physics and nuclear medicine, especially when fine segmentation of the detectors and their operation in high magnetic fields is required. In this work, we study the performance of a detector based on a LYSO (2×2×10 mm3) scintillation crystal and AMPD at detection of 511 keV ?-quanta. The detector shows linear energy response, an energy resolution of ˜12%, and sub-nanosecond time resolution. These characteristics are encouraging for using AMPDs in detector systems of positron emission tomographs (PET) of the next generation.

Britvitch, I.; Lorenz, E.; Olshevski, A.; Renker, D.; Sadygov, Z.; Scheuermann, R.; Stoykov, A.; Werner, A.; Zheleznykh, I.

2007-02-01

249

Avalanche Photodiode for liquid xenon scintillation: quantum efficiency and gain  

NASA Astrophysics Data System (ADS)

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

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

2009-01-01

250

Design and reliability of mesa-etched InP-based Geiger-mode avalanche photodiodes  

Microsoft Academic Search

Design modifications to InP-based Geiger-mode avalanche photodiodes are described that improve reliability. Geiger-mode aging at multiple conditions can cause significant degradation in some design variants while linear mode (below breakdown) aging does not.

G. M. Smith; J. P. Donnelly; K. A. McIntosh; E. K. Duerr; C. J. Vineis; D. C. Shaver; S. Verghese; J. E. Funk; J. M. Mahan; P. I. Hopman; L. J. Mahoney; K. M. Molvar; F. J. O'Donnell; D. C. Oakley; K. G. Ray

2006-01-01

251

Temperature dependence of avalanche breakdown for epitaxial diodes in 4H silicon carbide  

NASA Astrophysics Data System (ADS)

The temperature dependence of avalanche breakdown is investigated for uniform and microplasma-related breakdown in epitaxial 4H SiC p-n junctions. P-n mesa diodes fabricated with positive angle beveling and oxide passivation can withstand temperatures of up to 300-400 °C in the breakdown regime. Uniform avalanche breakdown in 4H silicon carbide appears to have a positive temperature coefficient, in contrast to the 6H polytype, where the temperature coefficient is negative. The influence of deep levels on avalanche breakdown in epitaxial diodes is of minor importance for uniform breakdown, but appears to be significant for breakdown through microplasmas. A negative temperature coefficient for the avalanche breakdown voltage can be observed even for 4H SiC if the breakdown is dominated by microplasmas.

Konstantinov, A. O.; Nordell, N.; Wahab, Q.; Lindefelt, U.

1998-09-01

252

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

253

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

Wegrzecka, I.; Wegrzecki, M.

1999-04-01

254

Observation of the Avalanche of Runaway Electrons in Air in a Strong Electric Field  

NASA Astrophysics Data System (ADS)

The generation of an avalanche of runaway electrons is demonstrated for the first time in a laboratory experiment. Two flows of runaway electrons are formed sequentially in an extended air discharge gap at the stage of delay of a pulsed breakdown. The first, picosecond, runaway electron flow is emitted in the cathode region where the field is enhanced. Being accelerated in the gap, this beam generates electrons due to impact ionization. These secondary electrons form a delayed avalanche of runaway electrons if the field is strong enough. The properties of the avalanche correspond to the existing notions about the runaway breakdown in air. The measured current of the avalanche exceeds up to an order the current of the initiating electron beam.

Gurevich, A. V.; Mesyats, G. A.; Zybin, K. P.; Yalandin, M. I.; Reutova, A. G.; Shpak, V. G.; Shunailov, S. A.

2012-08-01

255

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

SciTech Connect

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

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

2010-08-15

256

Some results on the use of avalanche photodiodes for scintillating fiber readout.  

National Technical Information Service (NTIS)

We have measured the properties of avalanche photodiodes (APDs) for possible use in conjunction with scintillating fibers as charged particle detectors. The quantities measured so far have been the gain of the APDs, the amplitude distribution of pulses fr...

M. Salomon J. Kitching

1990-01-01

257

Observation of the avalanche of runaway electrons in air in a strong electric field.  

PubMed

The generation of an avalanche of runaway electrons is demonstrated for the first time in a laboratory experiment. Two flows of runaway electrons are formed sequentially in an extended air discharge gap at the stage of delay of a pulsed breakdown. The first, picosecond, runaway electron flow is emitted in the cathode region where the field is enhanced. Being accelerated in the gap, this beam generates electrons due to impact ionization. These secondary electrons form a delayed avalanche of runaway electrons if the field is strong enough. The properties of the avalanche correspond to the existing notions about the runaway breakdown in air. The measured current of the avalanche exceeds up to an order the current of the initiating electron beam. PMID:23002751

Gurevich, A V; Mesyats, G A; Zybin, K P; Yalandin, M I; Reutova, A G; Shpak, V G; Shunailov, S A

2012-08-20

258

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

NASA Astrophysics Data System (ADS)

We probe the dynamics of intermittent avalanches caused by steady addition of grains to a quasi-two-dimensional heap. To characterize the time-dependent average avalanche flow speed v(t) , we image the top free surface. To characterize the grain fluctuation speed ?v(t) , we use speckle-visibility spectroscopy. During an avalanche, we find that the fluctuation speed is approximately one-tenth the average flow speed, ?v?0.1v , and that these speeds are largest near the beginning of an event. We also find that the distribution of event durations is peaked, and that event sizes are correlated with the time interval since the end of the previous event. At high rates of grain addition, where successive avalanches merge into smooth continuous flow, the relationship between average and fluctuation speeds changes to ??v1/2 .

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

2007-12-01

259

Emplacement mechanisms of contrasting debris avalanches at Volcán Mombacho (Nicaragua), provided by structural and facies analysis  

NASA Astrophysics Data System (ADS)

We study the lithology, structure, and emplacement of two debris-avalanche deposits (DADs) with contrasting origins and materials from the Quaternary-Holocene Mombacho Volcano, Nicaragua. A clear comparison is possible because both DADs were emplaced onto similar nearly flat (3° slope) topography with no apparent barrier to transport. This lack of confinement allows us to study, in nature, the perfect case scenario of a freely spreading avalanche. In addition, there is good evidence that no substratum was incorporated in the events during flow, so facies changes are related only to internal dynamics. Mombacho shows evidence of at least three large flank collapses, producing the two well-preserved debris avalanches of this study; one on its northern flank, “Las Isletas,” directed northeast, and the other on its southern flank, “El Crater,” directed south. Other south-eastern features indicate that the debris-avalanche corresponding to the third collapse (La Danta) occurred before Las Isletas and El Crater events. The materials involved in each event were similar, except in their alteration state and in the amount of substrata initially included in the collapse. While “El Crater” avalanche shows no signs of substratum involvement and has characteristics of a hydrothermal weakening-related collapse, the “Las Isletas” avalanche involves significant substratum and was generated by gravity spreading-related failure. The latter avalanche may have interacted with Lake Nicaragua during transport, in which case its run-out could have been modified. Through a detailed morphological and structural description of the Mombacho avalanches, we provide two contrasting examples of non-eruptive volcanic flank collapse. We show that, remarkably, even with two distinct collapse mechanisms, the debris avalanches developed the same gross stratigraphy of a coarse layer above a fine layer. This fine layer provided a low friction basal slide layer. Whereas DAD layering and the run-outs are roughly similar, the distribution of structures is different and related to lithology: Las Isletas has clear proximal faults replaced distally by inter-hummock depressions where basal unit zones are exhumed, whereas El Crater has faults throughout, but the basal layer is hidden in the distal zone. Hummocky forms depend on material type, with steep hummocks being formed of coherent lava units, and low hummocks by matrix-rich units. In both avalanches, extensional structures predominate; the upper layers exclusively underwent longitudinal and lateral extension. This is consistent with evidence of only small amounts of block-to-block interactions during bulk horizontal spreading. The base of the moving mass accommodated transport by large amounts of simple shear. We suggest that contractional structures and inter-block collisions seen in many other avalanches are artifacts related to topographic confinement.

Shea, Thomas; van Wyk de Vries, Benjamin; Pilato, Martín

2008-07-01

260

A CMOS 3-D Imager Based on Single Photon Avalanche Diode  

Microsoft Academic Search

A 64-pixel linear array aimed at 3-D vision applications is implemented in a high-voltage 0.8 mum CMOS technology. The detection of the incident light signals is performed using photodiodes biased above breakdown voltage so that an extremely high sensitivity can be achieved exploiting the intrinsic multiplication effect of the avalanche phenomenon. Each 38times180-mum2 pixel includes, besides the single photon avalanche

David Stoppa; Lucio Pancheri; Mauro Scandiuzzo; Lorenzo Gonzo; Gian-Franco Dalla Betta; Andrea Simoni

2007-01-01

261

Avalanching in single-event-upset charge collection in semiconductor diodes  

NASA Astrophysics Data System (ADS)

The one-dimensional computer program DIODE has been used to calculate charge collection in single ionizing events in silicon and gallium arsenide diodes. Avalanche multiplication is calculated to occur above a threshold of 3 V in a silicon diode, in agreement with published measurements. Since avalanching may lead to burnout in very large integration semiconductors, it is a greater danger than the funneling effect of space charge. Carrier recombination is found to be important in gallium arsenide.

Ward, Alford L.

1987-02-01

262

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

263

Intrinsic optical bistability in Tm-doped laser crystal pumped at 648nm avalanche wavelength  

Microsoft Academic Search

Intrinsic optical bistability and dynamic hysteresis phenomenon, induced by nonlinear excitation and energy level coupling, are predicted theoretically in single Tm-doped laser crystal pumped at 648nm avalanche wavelength. Taking into account the dominant energy transfer processes including excited state absorption, cross relaxation, energy transfer up-conversion and decay of the metastable level Tm3+ 3F4, the analytical formula of avalanche threshold condition

Li Li; Xinlu Zhang; Lixue Chen

2007-01-01

264

IMPROVEMENTS IN THE APPLICATION OF THE SNOWMICROPEN TO DERIVE STABILITY INFORMATION FOR AVALANCHE FORECASTING  

Microsoft Academic Search

Local snowpack measurements and local stability tests are currently the basis for the assessment of snowpack stability in most avalanche warning operations. The SnowMicroPen (SMP), a high-resolution penetrometer for snow, measures penetration resistance of snow. In order for SMP measurements to be useful for stability evaluation (or avalanche forecasting purposes), stability information needs to be derived from the SMP signal.

Christine Pielmeier; Jürg Schweizer; Hans Peter Marshall

265

Low dark current InGaAs\\/InAlAs\\/InP avalanche photodiode  

Microsoft Academic Search

The performance of uncooled InGaAs\\/InAlAs\\/InP avalanche photodiodes operating near 1.5 mum has been studied theoretically. Device modelling based on advanced drift and diffusion model with commercial software, the Crosslight APSYS, has been performed. Separate absorption, grading, charge and multiplication avalanche photodiodes with a relatively thick undepleted p-type InGaAs absorption region and thin InAlAs multiplication layer have been considered. Basic physical

J. Muszalski; J. Kaniewski; K. Kalinowski

2009-01-01

266

Delta-doped avalanche photodiodes for high bit-rate lightwave receivers  

Microsoft Academic Search

The authors estimate the GB (grain bandwidth) product limits and the noise performance of a new SAGM-APD (separate avalanche, grating, and multiplication avalanche photodiode) structure: the ?-doped SAGM-APD. It is shown that GB products in excess of 140 GHz for a 0.2-?m-thick multiplication layer and possibly larger GB products for smaller widths can be obtained. While recent calculations have predicted

Ravi Kuchibhotla; Joe C. Campbell

1991-01-01

267

Distinguishing volcanic debris avalanche deposits from their reworked products: the Perrier sequence (French Massif Central)  

Microsoft Academic Search

Debris avalanches associated with volcanic sector collapse are usually high-volume high-mobility phenomena. Debris avalanche\\u000a deposit remobilisation by cohesive debris flows and landslides is common, so they can share textural characteristics such\\u000a as hummocks and jigsaw cracks. Distinguishing original deposits from reworked products is critical for geological understanding\\u000a and hazard assessment because of their different origin, frequency and environmental impact. We

Benjamin Bernard; Benjamin van Wyk de Vries; Hervé Leyrit

2009-01-01

268

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

NASA Astrophysics Data System (ADS)

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

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

2013-04-01

269

Digital X-Ray Imaging Using Avalanche aSe Photoconductor  

Microsoft Academic Search

This work presents the development of a novel detector comprised of an avalanche amorphous selenium (a-Se) photoconductor and an amorphous silicon (a-Si:H) passive pixel sensor for digital X-ray imaging, in particular, for low exposure imaging applications. Electrical compatibility of a high voltage (~1000 V) avalanche a-Se photoconductor with a low voltage (~25 V) a-Si:H pixel sensor is demonstrated. Single pixel

Afrin Sultana; Matthew M. Wronski; Karim S. Karim; J. A. Rowlands

2010-01-01

270

Investigation of avalanche silicon detectors for low energy single ion implantation applications  

Microsoft Academic Search

Avalanche silicon photodiodes have potential applications to detect low energy single ions for counting single ion impacts in shallow implant depths for the deterministic doping of nanoscale electronic devices. This paper reports the investigation of avalanche photodiode detectors in the linear operation mode for detection of 0.5–2MeV helium ions. The measured charge gain was found to be up to 100

Changyi Yang; David Jamieson

2010-01-01

271

Comparison of risk assessment methods: multiple perspectives of flood and avalanche hazards in North East France  

NASA Astrophysics Data System (ADS)

Mountainous areas are exposed to several natural hazards such as snow avalanches, debris flows or floods. Such processes may be more frequent and intense in high mountains but they occur in medium-high mountains as well causing loss of life and materials. Thus, the Vosges range, a medium-high mountain located in the north-east of France, is concerned by two kind of natural hazards namely avalanches and floods. While the avalanches constitute the most murderous natural risk in Alsace, its management is paradoxically not a priority. Because it causes more material damages and affects larger places with multiple and complex consequences, the flood risk is more worrying for the administrators. They didn't have the same approach toward these two kinds of risk. So, two different approaches used to assess risk and two study cases are presented: flood risk in the river Bruche (located in the north of the Vosges range, Alsace) and avalanche risk in the Vosges range. The first one is mainly focused on economic aspects of risk. Flood risk analyses are discussed from a hydro-economical perspective. The second one focuses the analysis on human, material and environmental vulnerabilities. Avalanche risk analysis is discussed from a geo-historical point of view. About 300 avalanche events have been reported since the end of the 18th century. The two approaches that we describe illustrate the complementarity of human and physical science to improve the understanding and assessment of hazardous processes in medium-high mountain range. On the one hand, the geo-historical method developed for the avalanche risk could be extended to the flood hazard. Indeed, contrary to high mountains, no service is in charge of the systematic inventory of floods and avalanches in the Vosges mountains. The geo-historical approach could address this lack of data. On the other hand, the methods of damages assessment and vulnerability characterization could be a good tool for the human science.

Giacona, Florie; Eleuterio, Julian

2010-05-01

272

Negative resistance in p-n junctions under avalanche breakdown conditions, part II  

Microsoft Academic Search

The small-signal impedance of the space-charge region of p-n junctions under avalanche breakdown conditions is calculated using reasonably realistic dependences of electron and hole ionization rates and drift velocities upon electric field. Two structures are analyzed: one is p+?n+structure which has a fairly uniform distribution of avalanche multiplication, and the other is a singly diffused junction which is a hybrid

T. Misawa

1966-01-01

273

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

274

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

275

Rockfall and snow avalanche impacts leave different anatomical signatures in tree rings of juvenile Larix decidua.  

PubMed

Rockfall and snow avalanche events often cause injury to European larch (Larix decidua Mill.) trees, giving rise to the formation of callus tissue and tangential rows of traumatic resin ducts (TRDs). We analyzed and quantified anatomical reactions of juvenile trees injured before the start of the growing season by snow avalanches (15 trees, 324 cross sections) or rockfalls (18 trees, 270 cross sections). Traumatic resin ducts were observed in the growth ring formed following injury in 94.3% of the rockfall samples and 87.3% of the snow avalanche samples. Traumatic resin ducts were formed at the beginning of the new annual ring around wounds caused by rockfalls. In contrast, in trees injured by snow avalanches, TRDs were not formed until after the formation of several rows of early earlywood (EE) tracheids (mean +/- SD = 4.19 +/- 2.56 rows). The dimensions of the EE tracheids observed in the snow avalanche samples were greatly reduced in the tissues bordering the wound, with radial width reaching an average of only 50% and lumen cross-sectional area an average of only 46% of pre-event values. It is therefore possible to differentiate injuries due to past snow avalanches from injuries due to rockfall based on anatomical growth reactions in the tissues bordering scars. PMID:18765376

Stoffel, Markus; Hitz, Oliver M

2008-11-01

276

Snow Avalanche Risk and Decision Support For Clear-cut Harvested Terrain  

NASA Astrophysics Data System (ADS)

The destruction of mature and regenerating forest stands by snow avalanches that initiate on terrain exposed by clear-cut logging is a significant problem in the Coast and Columbia Mountains of British Columbia, Canada. The purpose of this presentation is to discuss the development of a risk-based decision support system formulated to address issues of risk related to snow avalanches initiating within the boundaries of clear-cut logged terrain. The analysis of variables collected from 91 areas from which avalanches have initiated was used to characterize terrain associated with destructive snow avalanches. The relations of these variables to avalanche frequency and magnitude are then developed from past studies and physical reasoning. Using these relations aframework has been developed to guide a decision maker through the collection of variables for the case at hand and then through the assessment of the given scenario by considering information collected from similar cases in past. The outcome is an estimate of the chance an event will be of a given acceptable frequency and the chance it will be of a given acceptable size (based on the Canadian Snow Avalanche Size Classification System). These estimates are then used to estimate risk and aid in logging decisions.

Stitzinger, K. R.; McClung, D.

277

Geomorphological consequences of a glacier advance across a paraglacial rock avalanche deposit  

NASA Astrophysics Data System (ADS)

Glacial reworking of paraglacial rock slope sediment has been inferred from long-deglaciated terrains to contribute significantly to glacial sediment transfer. At Feegletscher, Switzerland, we provide the first description of the geomorphological consequences of glacier advance across paraglacial rock avalanche sediment. This produced a small arcuate end moraine that encloses a zone of hummocky debris. The sedimentology of these landforms is conditioned by rock avalanche sediment and can be differentiated from purely glacial sediments, indicating that the contribution of glacially reworked rock avalanche debris may be recognisable in deglaciated terrain. Remarkably, much of the overridden rock avalanche debris has maintained its angularity and delicate brecciation features, despite up to 40 years of glacial action. We suggest that the surface 'carapace facies' of the rock avalanche deposit, comprising large openwork blocks, limited the effectiveness of glacial erosion processes. The carapace facies will have resisted significant erosion by the relatively thin glacier because of its high shear strength and because it was able to transmit subglacial meltwater efficiently. Thus, enhanced debris transfer associated with reworking of paraglacial rock avalanche sediment should not necessarily be expected during the initial stages of glacier advance.

Cook, Simon J.; Porter, Philip R.; Bendall, Charles A.

2013-05-01

278

Segregation in a quasi-stationary avalanche on an inclined conveyor-belt  

NASA Astrophysics Data System (ADS)

We have carried out laboratory experiments to determine the internal structure of segregating dense granular avalanches and test the recent theoretical predictions of the existence of breaking size-segregation waves [Thornton & Gray, 2008]. Measurements were performed on a quasi-stationary avalanche that flows down an inclined upward-moving conveyor-belt. In this configuration the bottom layers of the flow are dragged upslope while upper layers are avalanching downslope due to gravity; effectively, as if the observer were moving along with an avalanche. We show that a breaking size-segregation wave is located in the flow, recirculating the particles, and causing large particles to accumulate downslope and fines upslope. The large particles at the downslope end, after being deposited and overrun, are carried upslope through the lower layers, segregate to the free-surface, and avalanche down again. Small particles segregate downwards and are dragged upslope when reaching the lower layers. Imaging of a cross-section of the bulk flow, far from the side-wall, is made possible by combining a laser light sheet and an interstitial liquid that has a matched refractive index with the particles. Thornton, A. R. & Gray, J. M. N. T. 2008 Breaking size-segregation waves and particle recirculation in granular avalanches. J. Fluid Mech. 596, 261-284.

van der Vaart, Kasper; Gray, Nico; Ancey, Christophe

2013-04-01

279

A Real Two-Phase Mechanical Model for Rock-Ice Avalanches  

NASA Astrophysics Data System (ADS)

Rock-ice avalanches in high mountain permafrost environments are a hazardous and poorly understood process. Their hazard potential derives from the large volume, high velocities, the potential entrainment of large amounts of rock-debris, ice, snow and water during the flow, high impact pressures, and unpredictable flow paths and deposition patterns. In contrast to the usual single-phase model of rock avalanches, the solid phase (ice) in rock-ice avalanches can transform to fluid (water or slurry) during the course of the debris-avalanche and fundamentally alter the multiple mechanical processes. We postulate that a real two-phase debris flow model could much better address the dynamic interaction of solid (rock and ice) and fluid (water, snow, slurry and fine particles) rather than a simple single-phase Voellmy- or Coulomb-type model. For this, we enhance the general two-phase debris flow model proposed by Pudasaini (2011) by additionally introducing two new mechanical aspects typical for the rock-ice avalanches: (a) the dynamic strength weakening including the internal fluidization and basal lubrication, as well as (b) the internal mass and momentum exchanges between the phases. In these models, the effective basal and internal friction angles are variable and are described in terms of evolving effective solid volume fraction (rock and ice), friction factors, volume fraction of the ice, true friction coefficients and the lubrication and fluidization factors. These factors are functions of several physical parameters and mechanical and dynamical variables, including the volume fractions of the solid, shear-rate and the normal stresses. Rock-ice avalanches are a unique scenario in geophysical mass flows, where phase exchange and material strength weakening occurs and can dominate the flow dynamics. Here, we present an innovative approach to model and simulate these two special aspects. Additionally, in the model, the inertial terms include the hydraulic pressure gradients and the virtual mass. The source in the solid momentum includes gravity, the Coulomb friction, slope gradient, buoyancy, and the generalized drag. The source term for the fluid momentum includes gravity, fluid pressure and topographic gradients, enhanced non-Newtonian viscous stresses, and the drag. There are strong couplings between the solid and fluid momentum transfer. The new enhanced two-phase model can better explain dynamically changing frictional properties of rock-ice avalanches that occur internally and along the flow path. Both mass and momentum exchanges allow for a much more realistic simulation, especially during the critical initial and final stages of avalanche propagation. Benchmark numerical simulations demonstrate that the dynamics of permafrost rock-ice avalanche is fundamentally different form that of pure rock avalanches. The model simulations reveal special features of rock-ice avalanche propagation form and dynamics, similar to those observed, e.g., in the 2007 Bliggspitze rock-ice avalanche event. Numerical results also reveal that mass and momentum exchange between the phases and the associated internal and basal strength weakening offer a new explanation for the exceptionally long run-out distances leading to higher flow mobility typical for high-mountain rock-ice avalanches. These new results substantially improve modelling run-out distances and inundation areas, and could significantly contribute to hazard prediction and mitigation in high-mountain permafrost environments. Here we show that the new two-phase rock-ice avalanche model can yield a novel and enhanced representation of multiple processes that lead to the high and changing mobility of rock-ice-avalanches.

Pudasaini, S. P.; Krautblatter, M.

2012-04-01

280

Snow and weather conditions fostering avalanche releases in forests: Rare situations with decreasing trends during the last 41 years  

NASA Astrophysics Data System (ADS)

Snow avalanche formation is a complex interaction between terrain, snowpack and meteorological conditions. So far, research on meteorological contributory factors focused mainly on avalanches in open unforested terrain, since the occurrence of avalanches in forests is not primarily a meteorological phenomena. Furthermore, mountain forests play a crucial role in avalanche control by preventing avalanche formation. The main effect of forests is the modification of the snow's mechanical properties and, therefore, the reduction of forming unstable continues snow layers. Nevertheless, snow avalanches may occur in forests and these so-called 'forest avalanches' are important disturbances that affect mountain ecosystems and can pose hazard to human settlements and infrastructures. Therefore, an improved understanding of snow and weather conditions which increase the probability of forest avalanche releases could be highly valuable for avalanche warning and forest services. We present a comprehensive analysis of snow and weather conditions fostering avalanche releases in forests and their potential changes during the last decades. We applied a hierarchical clustering method based on 21 snow and weather variables in order to best reproduce the potential underlying structure in our dataset on 189 observed forest avalanche events. Two types can be defined: Type 1 avalanches are 'new snow forest avalanches' releasing in periods of heavy snowfall (3-day new snow sum > 50 cm) and under stormy (3-day maximum wind speed > 17 m/s) and permanently cold conditions (1-, 3- and 5-day mean air temperature < 0°C). They mainly occur in open coniferous forest at the upper treeline at elevations above 1700 masl and are concentrated on north-exposed slopes. Forest avalanches of type 2 ('old snow forest avalanches') tend to release at all expositions below 1700 masl after periods of high insolation (5-day sum of sunshine duration > 240 min) and an increase in air temperature. Snow and weather conditions of type 1, but not of type 2 avalanches, are rare and clearly distinguishable by classification trees from those of avalanches released in open unforested terrain. In the next step, we analysed if the occurrence of these two typical snow and weather situations did change during the last 41 years (1970/71-2010/11). Therefore, we counted the number of days between November and May where forest avalanches are likely to occur using data of 14 snow and weather stations which are well distributed regarding the different climatic regions of the Swiss Alps. Then, we used logistic regression to test for long-term trends in the occurrence of favourable conditions for forest avalanches at each station. The number of days with meteorological conditions which foster the occurrence of new snow forest avalanches decreased at 11 stations during the last 41 years; also trends for old snow forest avalanches are negative at 12 stations independent from altitude and climatic region. The past negative trends in the occurrence of snow and weather conditions which foster forest avalanche releases suggest a further decrease under a changing climate. Nevertheless, such events will also occur in the future and the presented combinations of meteorological parameters could support avalanche warning and forest services in forecasting forest avalanches.

Teich, M.; Marty, C.; Gollut, C.; Grêt-Regamey, A.; Bebi, P.

2012-04-01

281

Paleomagnetic estimate of the emplacement temperature of the long-runout Nevado de Colima volcanic debris avalanche deposit, Mexico  

Microsoft Academic Search

Stoopes and Sheridan have mapped a volcanic debris avalanche of Nevado de Colima which has an exceptionally long runout (120 km) and low fall-height to length ratio (H\\/L = 0.04). We present paleomagnetic results from this volcanic debris avalanche deposit which provide evidence that this avalanche was emplaced at elevated temperatures. The majority of samples, collected from lithic clasts in

Bradford M. Clement; Charles B. Connor; Grenville Graper

1993-01-01

282

Rheology of a wet, fragmenting granular flow and the riddle of the anomalous friction of large rock avalanches  

Microsoft Academic Search

The effective friction coefficient of rock avalanches diminishes gradually as a function of the avalanche volume. Large rock\\u000a avalanches can reach run-out distances as long as ten times the fall height, despite the fact that the physics of friction\\u000a would indicate a run-out only a little greater than the fall height. Numerous suggestions have been put forward to explain\\u000a this

Fabio Vittorio De Blasio

2009-01-01

283

Enhanced Red and Near Infrared Detection in Flow Cytometry Using Avalanche Photodiodes  

PubMed Central

Background Polychromatic flow cytometry enables detailed identification of cell phenotype using multiple fluorescent parameters. The photomultiplier tubes used to detect fluorescence in current instruments limit the sensitivity in the long wavelength spectral range. We demonstrate the flow cytometric applications of silicon avalanche photodiodes, which have improved red sensitivity and a working fluorescence detection range beyond 1000 nm. Methods A comparison of the wavelength dependent performance of the avalanche photodiode and photomultiplier tube was carried out using pulsed light emitting diode sources, calibrated test beads and biological samples. A breadboard flow cytometer test bench was constructed to compare the performance of photomultiplier tubes and avalanche photodiode detectors. The avalanche photodiode used an additional amplifier stage to match the internal gain of the photomultiplier tube. Results The resolution of the avalanche photodiode and photomultiplier tube was compared for flow cytometry applications using a pulsed light emitting diode source over the 500 nm to 1060 nm spectral range. These measurements showed the relative changes in the signal to noise performance of the APD and PMT over a broad spectral range. Both the avalanche photodiode and photomultiplier tubes were used to measure the signal to noise response for a set of 6 peak calibration beads over the 530 to 800 nm wavelength range. CD4 positive cells labeled with antibody conjugated phycoerythrin or 800 nm quantum dots were identified by simultaneous detection using the avalanche photodiode and the photomultiplier tube. The ratios of the intensities of the CD4? and CD4+ populations were found to be similar for both detectors in the visible wavelengths, but only the avalanche photodiode was able to separate these populations at wavelengths above 800 nm. Conclusions These measurements illustrate the differences in APD and PMT performance at different wavelengths and signal intensity levels. While the APD and PMT show similar signal to noise performance in the visible spectral range, the dark noise of the APD detector reduces the sensitivity at low signal levels. At wavelengths longer than 650 nm, the high quantum efficiency of the avalanche photodiode contributes to better signal-to-noise performance. The avalanche photodiode detector provides enhanced performance in the long wavelength region and may be used to extend the working range of the flow cytometer beyond 1000 nm.

Lawrence, William G.; Varadi, Gyula; Entine, Gerald; Podniesinski, Edward; Wallace, Paul K.

2008-01-01

284

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

NASA Astrophysics Data System (ADS)

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 areas of abyssal plains. Based on the small scale topographic elements, we reinvestigated the distribution areas and emplacement styles of the debris-avalanche deposits, which differ from those previously proposed from GLORIA images without benefit of detailed bathymetric data or direct seafloor observations. There are several types of small scale topographic elements in the debris-avalanche deposits previously proposed: source amphitheater, toppled blocks, marginal levee, slide-emplaced blocks, chute, mud wave, hummocky terrain. They are very similar to those appeared in subaerial volcanic debris-avalanche fields. However, no correlation between the collapse height and runout distance are observed in the submarine debris-avalanche deposits. The hummocky terrains can be classified into two types: FLAT-TYPE, which is distributed in the nearly flat abyssal plain, less than 0.5 degree, and SLOPE-TYPE, which located on the lower part of the submarine flanks, greater than 1 degree. The size of hummocks in a slope-type hummocky terrain have an unimodal distribution pattern with a broad peak in the number of hummocks versus height category diagram. On the contrary, the size of hummocks in flat-type hummocky terrains have a power law distribution pattern in the same diagram. The fractal dimensions calculated from these diagrams are 1.19 (Nuuanu landslide), 2.32 (Ka Lae landslide) and 2.96 (Alika 2 debris-avalanche), respectively. They are expected to reflect the processes and degree of fragmentation. Therefore, among the debris_]avalanche deposits proposed previously around Hawaiian ridge, only three debris-avalanche deposits, Nuuanu, Alika 2, Ka Lae, could be a huge landslide deposits accompanied with huge tsunamis. Because fractal dimension indicates degree of the fragmentation, Alika 2 debris flow could be the most powerful turbulent flow among others. The bending trend in the power law distribution pattern of the Nuuanu landslide imply that the hummocks were produced by two different fragmentation: turbulent flows at the toe of the debris-avalanche and translational disruption at proximal part. The hummocks without a power law distribution in the terrain have been produced by a overlapping of small scale debris flow deposits rather than a huge landslide failure. Unimodal size distribution with a broad peak may be interpreted as a gravel-rich submarine fans rather than a huge landslide deposit.

Yokose, H.; Yamato, S.

2005-12-01

285

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

USGS Publications Warehouse

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

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

1991-01-01

286

Submarine evidence for large-scale debris avalanches in the Lesser Antilles Arc  

NASA Astrophysics Data System (ADS)

Results from a recent marine geophysical survey demonstrate the importance of the process of flank collapse in the growth and evolution of volcanoes along an island arc. The Aguadomar cruise, aboard the French R/V L'Atalante, surveyed the flanks of the Lesser Antilles Arc between the islands of Montserrat and St. Lucia. Analysis of the data shows that flank collapse events occurred on active volcanoes all along the arc and resulted in debris avalanches, some of them being of large magnitude. The debris avalanche deposits display hummocky topography on the swath bathymetry, speckled pattern on backscatter images, hyperbolic facies on 3.5 kHz echosounder data and chaotic units on air gun seismic profiles. They extend from horseshoe-shaped structures previously identified on the subaerial part of the volcanoes. In the southern part of the arc, large-scale debris avalanche deposits were identified on the floor of the Grenada Basin west of active volcanoes on Dominica, Martinique and St. Lucia. The extent of debris avalanche deposits off Dominica is about 3500 km2. The debris avalanches have resulted from major flank collapse events which may be mainly controlled by the large-scale structure of the island arc and the presence of the deep Grenada Basin. In the northern part of the arc, several debris avalanche deposits were also identified around the island of Montserrat. With smaller extent (20-120 km2), they are present on the east, south and west submarine flanks of Soufriere Hills volcano which has been erupting since July 1995. Flank collapse is thus a recurrent process in the recent history of this volcano. The marine data are also relevant for a discussion of the transport mechanisms of debris avalanches on the seafloor surrounding a volcanic island arc.

Deplus, C.; Le Friant, A.; Boudon, G.; Komorowski, J.-C.; Villemant, B.; Harford, C.; Ségoufin, J.; Cheminée, J.-L.

2001-10-01

287

Emplacement of rock avalanche material across saturated sediments, Southern Alp, New Zealand  

NASA Astrophysics Data System (ADS)

The spreading of material from slope failure events is not only influenced by the volume and nature of the source material and the local topography, but also by the materials encountered in the runout path. In this study, evidence of complex interactions between rock avalanche and sedimentary runout path material were investigated at the 45 x 106 m3 long-runout (L: 4.8 km) Round Top rock avalanche deposit, New Zealand. It was sourced within myolinitic schists of the active strike-slip Alpine Fault. The narrow and in-failure-direction elongate source scarp is deep-seated, indicating slope failure was triggered by strong seismic activity. The most striking morphological deposit features are longitudinal ridges aligned radially to source. Trenching and geophysical surveys show bulldozed and sheared substrate material at ridge termini and laterally displaced sedimentary strata. The substrate failed at a minimum depth of 3 m indicating a ploughing motion of the ridges into the saturated material below. Internal avalanche compression features suggest deceleration behind the bulldozed substrate obstacle. Contorted fabric in material ahead of the ridge document substrate disruption by the overriding avalanche material deposited as the next down-motion hummock. Comparison with rock avalanches of similar volume but different emplacement environments places Round Top between longer runout avalanches emplaced over e.g. playa lake sediments and those with shorter travel distances, whose runout was apparently retarded by topographic obstacles or that entrained high-friction debris. These empirical observations indicate the importance of runout path materials on tentative trends in rock avalanche emplacement dynamics and runout behaviour.

Dufresne, A.; Davies, T. R.; McSaveney, M. J.

2012-04-01

288

Modelling dispersive pressure, fluidization and density variations in mixed flowing/powder snow avalanches  

NASA Astrophysics Data System (ADS)

In this presentation we will derive a system of depth-averaged partial differential equations to model snow avalanche flow with granular turbulence and density variations. The primary application of the model is to simulate mixed flowing/powder snow avalanches exhibiting highly fluidized flow at the avalanche front. These avalanches are characterized by snow mass in the form of snow granules and ice particles which visibly undergo strong, explosive-like slope perpendicular movements. Sudden transitions from a collisional to a frictional flow regime can occur after the front passage depending on the rate of turbulent energy production, which is responsible for maintaining fluidization of the flow body. Fluidization cannot occur without the interaction of the turbulent kinetic energy with the basal boundary, which expands the avalanche flow volume. We capture this effect by solving a third-order energy/momentum equation for the vertical velocities, vertical accelerations and time rate of change of the accelerations. Avalanche mass will work against these vertical movements which produces strong gradients in density depending on the overburden pressure. Thus, we are able to model not only the dispersive pressure induced by the particle interactions of the basal boundary but also the rate of change of dispersive pressure which is responsible for the collisional/frictional flow regime transitions and longitudinal density variations. We no longer assume a hydrostatic pressure distribution. We apply the model to several observed avalanches at the Vallée de la Sionne test site, demonstrating how we can model measured front velocities, front arrival times, flow heights and impact pressures.

Bartelt, Perry; Buser, Othmar

2013-04-01

289

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

290

Particle trajectories in 2D granular avalanches with imposed vibrations  

NASA Astrophysics Data System (ADS)

We study particle trajectories of photoelastic grains in a 2D circular rotating drum subjected to imposed vertical vibrations in order to characterize the jamming behavior of granular materials. Jamming appears in many systems (grain silos & chutes, landslides, mixing industrial materials, etc.) and vibration (granular temperature) is a primary factor in the jamming/unjamming transition. Images are taken and each particle's position is found for every frame then compared between frames to find the velocities. Particle tracking allows us to quantitatively measure the flow and mixing properties in our experiment. We present data on avalanching statistics, mean flow, the width of the shear band, and properties related to mixing (fluctuations and trajectories of neighboring grains). We find that vibrations induce more rearrangements of the grains and cause the pile of grains to become more compact over time. At constant peak acceleration we find that low frequency/high amplitude caused more grain movement than high frequency/low amplitude in both the stationary and rotating case.

Swisher, Nora; Utter, Brian

2011-03-01

291

Fluctuations and Avalanche Statistics in Sheared Systems of Elliptical Particles  

NASA Astrophysics Data System (ADS)

We have performed a series of 2D Couette shear experiment on a system of granular particles near jamming. In these experiments, the particles, which are photoelastic ellipses with aspect ratio 2, are confined between an inner rotating wheel and a fixed outer ring. The inner wheel rotation rate was varied between 0.01 and 0.1 rpm. Using photoelastic properties of the particles and two synchronized cameras, we are able to track the position, orientation and contact forces of each particle through the entire experiment. We determined the local mean, fluctuations, and correlations for various system properties, such as density (Voronoi volume), pressure, orientational order parameter and shear rate. A striking finding of this study is the fact that near jamming, the system can exist in an effectively shear jammed metastable state for very long times before relaxing to an unjammed state. We have also studied the dynamics of avalanches by analyzing the time series of global stress. This study gives us insight to the nature of failure in sheared systems of asymmetrical particles.

Farhadi, Somayeh; Behringer, Robert P.

2012-02-01

292

The opening of Sirte basin: Result of slab avalanching?  

NASA Astrophysics Data System (ADS)

North Africa's Sirte basin opening is an enigmatic feature in the complex Meso-Cenozoic rearrangement of Mediterranean tectonics. New borehole data inversion constrains its deformation history showing a stretching event starting ~ 70 Ma and terminating in a further abrupt increase at ~ 50 Ma, rapidly fading afterwards. The timing of this event hardly reconciles with the Mesozoic major plates reorganization following the spreading of the Atlantic, and the Neogene Central Mediterranean tectonics, active at different times. Here, we propose that Sirte rifting could have been driven by the pull exerted by the Hellenic subduction. Reconstructions of Hellenic convergence and slab deep subduction, as constrained by plate kinematics and tomography, show that large slab mass accumulates in the upper mantle by late Cretaceous-Paleogene, eventually forcing further sinking in the lower mantle, coeval to the growing strain evolution recorded in Sirte. Furthermore, the ~ 20 m.y. phase of large pull here recorded, the consequent rapid growth over ~ 10 m.y. and following decay are compatible with the dynamics of slab avalanche as revealed by numerical models, showing that the Sirte basin opened in response to the large pull force developed during the mass flush, and transferred from deep slab to surface.

Capitanio, F. A.; Faccenna, C.; Funiciello, R.

2009-07-01

293

The opening of Sirte basin:Result of slab avalanching?  

NASA Astrophysics Data System (ADS)

NorthAfrica's Sirtebasin opening is an enigmatic feature in the complex Meso-Cenozoic rearrangement of Mediterranean tectonics. New borehole data inversion constrains its deformation history showing a stretching event starting ~70Ma and terminating in a further abrupt increase at ~50Ma, rapidly fading afterwards. The timing of this event hardly reconciles with the Mesozoic major plates reorganization following the spreading of the Atlantic, and the Neogene Central Mediterranean tectonics, active at different times. Here, we propose that Sirte rifting could have been driven by the pull exerted by the Hellenic subduction. Reconstructions of Hellenic convergence and slab deep subduction, as constrained by plate kinematics and tomography, show that large slab mass accumulates in the upper mantle by late Cretaceous- Paleogene, eventually forcing further sinking in the lower mantle, coeval to the grow in strain evolution recorded in Sirte. Furthermore, the~20m.y. phase of large pull here recorded, the consequent rapid growth over ~10m.y. and following decay are compatible with the dynamics of slab avalanche as revealed by numerical models, showing that the Sirte basin opened in response to the large pull force developed during the mass flush, and transferred from deep slab to surface.

Capitanio, F. A.; Faccenna, C.

2009-12-01

294

Single photon counting linear mode avalanche photodiode technologies  

NASA Astrophysics Data System (ADS)

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

Williams, George M.; Huntington, Andrew S.

2011-09-01

295

Profilometry using two-photon absorption of silicon avalanche photodiode  

NASA Astrophysics Data System (ADS)

Though silicon photodetectors are usually insensitive to near infrared light of the wavelength longer than 1100 nm, they become sensitive to it with high intensity, producing photocurrent in proportion to the square of the intensity. This is due to two-photon absorption (TPA) process. So far, the TPA process in silicon photodetectors has mainly been applied to measuring the waveform of optical short pulses, since it can give the intensity correlation of incident light signals. In this paper, as a new application of the TPA process in photodetectors, we propose a novel profilometry based on Michelson interferometer with optical microwave as a light source and avalanche photodiode as a two-photon absorber. In contrast to the classical heterodyne profilometer that measures the optical path length difference from the phase of the modulated optical signal, the dynamic range of the TPA method is not limited by the bandwidth of a photodetector and attached electronic devices. The TPA method can realize the dynamic range of several millimeters to several ten meters with simple setup. The principle of the TPA based profilometry is experimentally demonstrated using fiber optic Michelson interferometer.

Tanaka, Yusuke; Kurokawa, Takashi

2002-09-01

296

The Importance of Damage Potential for Avalanche Risk Assessments  

NASA Astrophysics Data System (ADS)

Risk is normally expressed as a function of recurrence probability of a process and its related damage potential. Various physical and empirical models describing the process aspect of the risk formula exist in the field of avalanche risk management while studies on damage potential are rare. Due to the changes of the socio-economic structures in mountain regions (urban sprawl, population growth, increased mobility and tourism) these studies are mandatory. This study focuses on different possibilities to obtain obligatory input parameters for multitemporal studies in settlement areas. A conceptual method that records the damage potential (probability of presence, evaluation of buildings) was developed and applied in Tyrol, Austria. A second approach, working with real-time insurance values for buildings and population growth, was tested in Grison, Switzerland. The different developments of the damage potential in the two alpine study areas are highlighted; their influences on the risk formula are discussed. The results of both studies show the advantages and disadvantages of each method, such as precision, amount of time needed and possibilities of implementing in a GIS. The results serve to improve risk determination and point out an unnoticed increase of damage potential and risk in apparently safe settlement areas.

Keiler, M.; Fuchs, S.

2003-04-01

297

A protein biosensor using Geiger mode avalanche photodiodes  

NASA Astrophysics Data System (ADS)

A compact optical sensor specifically designed for protein detection is introduced in this work. The sensor takes advantage of avalanche photodiode's ultra-high sensitivity when operated in Geiger mode and is capable of detecting and quantifying very low light levels down to the single photons. The sensor has been tested with a luciferase gene reporter molecule detection system in Escherichia coli samples. The luciferase production is monitored via the APD and the luminescence amount detected is directly proportional to the amount of protein being produced. This reporter system will allow us to elucidate specific sources of proteins and to monitor the dynamics of protein activity within the cell in a real-time setting. The significant increase of photodiode breakdowns after the samples are applied to the sensor is the mechanism of detecting the bioluminescence. The degree of increase can be used to estimate the quantity of protein molecules. The sensor is packaged in a Teflon lightproof container to form a compact detection system.

Lin, F.; MacSweeney, M.; Sheehan, M. M.; Mathewson, A.

2005-01-01

298

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

299

Non depth-averaged continuum models for avalanche motions  

NASA Astrophysics Data System (ADS)

We present a continuum mechanical non depth-averaged model (N-DAM) for rapid motion of granular materials such as snow avalanches, landslides and debris flows. In contrast to the commonly used depth-averaged models (DAM), which are appropriate for smooth changes of flow variables, the motion perpendicular to the topography is taken into account and calculated by the N-DAM. This is important in the initiation and deposition regions and particularly, when the flow hits an obstacle or a defense structure. The primary challenge in modeling a complete three-dimensional flow is to construct an appropriate closure for the stress tensor, and in this talk we present various approaches to relate the stress and the strain-rate tensors. Since advancing from DAM to N-DAM requires fundamental changes in the traditional numerical simulation technique, a numerical method based on the Non Oscillatory Central-Total Variation Diminishing (NOC-TVD), coupled with the Marker And Cell (MAC), is introduced and simulation results are presented.

Domnik, B.; Kroener, C.; Pudasaini, S. P.

2009-04-01

300

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

PubMed

Power-law behaviors in brain activity in healthy animals, in the form of neuronal avalanches, potentially benefit the computational activities of the brain, including information storage, transmission and processing. In contrast, power-law behaviors associated with seizures, in the form of epileptic quakes, potentially interfere with the brain's computational activities. This review draws attention to the potential roles played by homeostatic mechanisms and multistable time-delayed recurrent inhibitory loops in the generation of power-law phenomena. Moreover, it is suggested that distinctions between health and disease are scale-dependent. In other words, what is abnormal and defines disease it is not the propagation of neural activity but the propagation of activity in a neural population that is large enough to interfere with the normal activities of the brain. From this point of view, epilepsy is a disease that results from a failure of mechanisms, possibly located in part in the cortex itself or in the deep brain nuclei and brainstem, which truncate or otherwise confine the spatiotemporal scales of these power-law phenomena. PMID:22805061

Milton, John G

2012-07-01

301

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

302

Avalanches in the raise and peel model in the presence of a wall  

NASA Astrophysics Data System (ADS)

We investigate a non-equilibrium one-dimensional model known as the raise and peel model describing a growing surface which grows locally and has non-local desorption. For specific values of adsorption (ua) and desorption (ud) rates, the model shows interesting features. At ua = ud, the model is described by a conformal field theory (with conformal charge c = 0) and its stationary probability can be mapped onto the ground state of the XXZ quantum chain. Moreover, for the regime ua ? ud, the model shows a phase in which the avalanche distribution is scale-invariant. In this work, we study the surface dynamics by looking at avalanche distributions using a finite-sized scaling formalism and explore the effect of adding a wall to the model. The model shows the same universality for the cases with and without a wall for an odd number of tiles removed, but we find a new exponent in the presence of a wall for an even number of tiles released in an avalanche. New insights into the effect of parity on avalanche distributions are discussed and we provide a new conjecture for the probability distribution of avalanches with a wall obtained by using an exact diagonalization of small lattices and Monte Carlo simulations.

Antillon, Edwin; Wehefritz-Kaufmann, Birgit; Kais, Sabre

2013-07-01

303

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

304

Relative influence of mechanical and meteorological factors on avalanche release depth distributions. Application to French Alps.  

NASA Astrophysics Data System (ADS)

This study sheds new lights on the properties of avalanche size distributions and discusses the universality sometimes postulated in the litterature. A full-scale mechanical model integrating weak layer heterogeneity and redistribution of stresses by elasticity of the overlying slab is developed. Considering that an avalanche can occur only if the snowfall depth exceeds the limit given by the mechanical criterion, release depth distributions obtained by the mechanical model are rigorously coupled with the distribution of 3-day extreme snowfalls. It is shown that this coupled mechanical-meteorological model is able to reproduce with excellent accuracy field data from 369 natural slab avalanches in La Plagne (France). Not only the power-law tail of the distribution, corresponding to large slab depths, but also the body of the distribution for lower slab depths, are well replicated. Small to intermediate size avalanches appear to be controled mainly by mechanics, whereas large avalanches and the associated power-law exponent, are influenced by a strong mechanical-meteorological coupling. Finally, using a rigorous interpolation formalism, this model is used to obtain release depth maps for given return periods, leading to a powerfull operational tool.

Gaume, J.; Chambon, G.; Eckert, N.; Naaim, M.

2012-04-01

305

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

306

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

307

A statistical analysis of tree-ring dating in conjunction with snow avalanches: Comparison of on-path versus off-path responses  

Microsoft Academic Search

Tree-rings were collected from snow-avalanche paths in Colorado, and from positions away from avalanche paths. The rings were examined for morphological responses to avalanche-induced trauma. Use of the Chi-square statistic revealed a significant difference in the number of morphological responses from on-path versus off-path positions. A high number of on-path trees were definitely damaged by avalanche impact in 1973; a

Carl L. Bryant; David R. Butler; John D. Vitek

1989-01-01

308

The most recent megalandslides of the Canary Islands: El Golfo debris avalanche and Canary debris flow, west El Hierro Island  

Microsoft Academic Search

Two major landsliding events have been identified west of the island of El Hierro: The El Golfo debris avalanche and the Canary debris flow. These landslides were identified from swath bathymetry, seismic reflection, and TOpographic PArametric Sonar (TOPAS) data obtained in December 1994 during a cruise on board the Spanish R\\/V Hesperides. The El Golfo debris avalanche originated subaerially on

Roger Urgeles; Miquel Canals; Jesús Baraza; Belén Alonso; Doug Masson

1997-01-01

309

Calculation of the diffusion curvature related avalanche breakdown in high-voltage planar p-n junctions  

Microsoft Academic Search

Avalanche multiplication calculations are performed in high-voltage planar p-n junctions to determine breakdown voltage limitations imposed by curvature effects. The issue of choice of ionization coefficient for avalanche multiplication is discussed. From the calculations, a series of design curves and equations are generated which relate the breakdown voltage and peak electric field to those of an ideal junction of the

V. A. K. Temple; M. S. Adler

1975-01-01

310

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

311

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

NASA Astrophysics Data System (ADS)

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

2013-04-01

312

Full-depth avalanches and soil erosion: an experimental site in NW Italy  

NASA Astrophysics Data System (ADS)

In the future the combined effect of changes in climate and land use could contribute to the intensification of soil erosion, related to snowpack movements as snow gliding and full-depth avalanches. Often, with particular meteorological conditions, the snow movement along a slope is associated with erosion and transport of the upper soil horizons, with the release of significant amount of material in the runout zone. Moreover the chemical composition of the snow in the deposition zone is usually different from the snow in the starting zone, revealing a potential release of ionic species mainly by the organic debris transported by the avalanche itself. The aim of this work is to characterize the quantity and quality of the material released by full-depth avalanches in the deposition zone. The study area is located in Aosta Valley (NW-Italy), on a SW exposed avalanche path, running from 2000 m a.s.l. of the triggering zone to 1200 m a.s.l. of the deposition zone. At this site, snow gliding and glide cracks, generally followed by full-depth avalanches, have been frequently observed. In the starting area, two plots located at the same elevation, slope and aspect, but with different soil moisture content, are equipped with moisture and temperature sensors, located at different depth in the soil, at the snow-soil interface and in the basal snowpack layer, and with glide shoes. The recorded data are related to the snow physical properties, measured by periodical investigations. In the deposition area, after a full-depth avalanche event occurred in March 2009, the mixed material was collected through snow avalanche coring, and a snow pit was dug in the deposit, in order to evaluate the quantity and the distribution of the material transported by the avalanche. First results show that the average density of the snow in the deposition zone was 624 kg m-3. The solid material was distributed mainly in the upper 5 cm of the avalanche deposit, with a mean concentration of the material equal to 187 kg m-3. The accumulation of sediments in the runout zone was estimated equal to 93 Mg ha-1. The concentration of cations and anions in the avalanche snow was higher on the deposit surface (e.g. NH4+: 85.6 µeq L-1 in the surface and 1.5 µeq L-1 along the profile) and was significantly higher than the mean concentrations observed for alpine snowpacks (e.g. NH4+: ~ 5 µeq L-1). By redistributing snow, avalanches not only redistribute water, but also nutrients, that can be available for plants in the growing season. Moreover avalanche tracks are places where soil accumulates in some areas and erodes in others, contributing to potentially unique pedo-environmental conditions. This project is carried out as part of "DYNAVAL", a EU Interreg Project.

Ceaglio, Elisabetta; Freppaz, Michele; Maggioni, Margherita; Filippa, Gianluca; Godone, Danilo; Zanini, Ermanno

2010-05-01

313

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

PubMed

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

Tarjus, Gilles; Baczyk, Maxime; Tissier, Matthieu

2013-03-26

314

A 20th century calendar of snow avalanche activity within the Bødalen valley, inner Nordfjord, western Norway  

NASA Astrophysics Data System (ADS)

The forest-covered valley floor of the Bødalen valley located in the inner Nordfjord, western Norway offers the great opportunity for snow-avalanche reconstruction using tree rings. By sampling at different points within the forest stand, both on birch (Betula pubescens) and alder (Alnus), we are able to extract the magnitude and return period of major snow-avalanche events in the valley. The years of 1967, 1974, 1985, 1994 and 2001 appear like very avalanche-rich, and the years of 1992 and 2007 appear as extreme, with snow-avalanche signals being recorded at the majority of the trees. Although the investigated valley is quite remote during the winter time, the gained knowledge of the recent snow-avalanche history provides a picture of the potential activity that can be expected also elsewhere in the Nordfjord region, and escpecially in the inhabited areas as well as along important transportation corridors that do not have such records available.

Decaulne, A.; Eggertsson, O.; Laute, K.; Beylich, A. A.

2012-04-01

315

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

PubMed

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

Tsujino, Kenji; Akiba, Makoto; Sasaki, Masahide

2007-03-01

316

Electron dominated impact ionization and avalanche gain characteristics in InAs photodiodes  

NASA Astrophysics Data System (ADS)

An experimental investigation into impact ionization in InAs photodiodes is presented. Photomultiplication measurements on p-i-n and n-i-p diodes show that while high avalanche gains can be obtained for electron initiated multiplication, there is virtually no gain with hole initiated multiplication. This indicates that the electron ionization coefficient is significantly greater than the hole ionization coefficient raising the possibility of extremely low noise InAs avalanche photodiodes when gain is initiated by electrons. The onset of electron initiated impact ionization was detectable at electric fields below 10 kV cm-1 with useful gain observed at biases below 10 V.

Marshall, A. R. J.; Tan, C. H.; Steer, M. J.; David, J. P. R.

2008-09-01

317

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

SciTech Connect

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

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

2007-03-15

318

Developing an Experimental Simulation Method for Rock Avalanches: Fragmentation Behavior of Brittle Analogue Material  

NASA Astrophysics Data System (ADS)

Gravitational mass movement on earth and other planets show a scale dependent behavior, of which the physics is not fully understood. In particular, the runout distance for small to medium sized landslides (volume < 106m3) can be predicted by a simple Coulomb friction law consistent with a constant kinetic coefficient of friction at the landslide base. This implies that the runout can be considered independent of volume. Large volume landslides (rock avalanches), however, show a dependence of runout on volume. This break in scaling behavior suggests that different dynamics control small and large landslides/rock avalanches. Several mechanisms have been proposed to explain this scale dependent behavior, but no consensus has been reached. Experimental simulations of rock avalanches usually involve transport of loose granular material down a chute. Though such granular avalanche models provide important insights into avalanche dynamics, they imply that the material fully disintegrate instantaneously. Observations from nature, however, suggests that a transition from solid to "liquid" occurs over some finite distance downhill, critically controlling the mobility and energy budget of the avalanche. Few experimental studies simulated more realistically the material failing during sliding and those were realized in a labscale centrifuge, where the range of volumes/scales is limited. To develop a new modeling technique to study the scale dependent runout behavior of rock avalanches, we designed, tested and verified several brittle materials allowing fragmentation to occur under normal gravity conditions. According to the model similarity theory, the analogue material must behave dynamically similar to the rocks in natural rock avalanches. Ideally, the material should therefore deform in a brittle manner with limited elastic and ductile strains up to a certain critical stress, beyond which the material breaks and deforms irreversibly. According to scaling relations derived from dimensional analysis and for a model-to-prototype length ratio of 1/1000, the appropriate yield strength for an analogue material is in the order of 10 kPa, friction coefficient around 0.8 and stiffness in the order of MPa. We used different sand (garnet, quartz) in combination with different matrix materials (sugar, salt, starch, plaster) to cement it. The deformation behavior and strength of the samples was tested using triaxial compression tests at atmospheric confining pressures. Proper material properties were obtained using well-sorted, well-rounded, medium grained quartz sand with gypsum plaster as matrix. The favored analogue material is produced by thoroughly mixing the quartz sand with gypsum and water. Afterwards, sufficient time is given to allow cementation by the gypsum. The material typically exhibits elastic deformation up to 0.3% strain and additionally

Thordén Haug, Øystein; Rosenau, Matthias; Leever, Karen; Oncken, Onno

2013-04-01

319

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

320

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

321

Generation efficiency of single-photon current pulses in the Geiger mode of silicon avalanche photodiodes  

SciTech Connect

Statistical fluctuations of the avalanche's multiplication efficiency were studied as applied to the single-photon (Geiger) mode of avalanche photodiodes. The distribution function of partial multiplication factors with an anomalously wide (of the order of the average) dispersion was obtained. Expressions for partial feedback factors were derived in terms of the average gain and the corresponding dependences on the diode's overvoltage were calculated. Final expressions for the photon-electric pulse's conversion were derived by averaging corresponding formulas over the coordinate of initiating photoelectron generation using the functions of optical photon absorption in silicon.

Verkhovtseva, A. V., E-mail: alevteena@gmail.com; Gergel, V. A., E-mail: gergel@mail.cplire.ru [Russian Academy of Sciences, Kotel'nikov Institute of Radio Engineering and Electronics (Russian Federation)

2009-09-15

322

New insights on Mafate - Saint Gilles debris avalanche deposits (westward Piton des Neiges volcano Réunion Island)  

NASA Astrophysics Data System (ADS)

Studies of debris avalanche deposits on Reunion Island (southwestern Indian Ocean) have been started in the last decade with the bathymetric surveys offshore Piton de la Fournaise and the identification of giant submarine landslides (Lénat et al., 1989; Cochonnat et al., 1990). Since this discovery, new field investigations have been driven to characterise and understand the role of debris avalanche phenomena in the evolution of volcanic island like Reunion. The first aerial outcrop of debris avalanche deposits has been identified in the west part of Piton des Neiges volcano in 1996. It has been described has a succession of breccia events interbedded by lava flows, and localised in St Gilles area (Bachèlery et al, 2003). In the last two years, the breccia problematic has been revisited and new outcrops have been found in the northern and southern part of St Gilles area (Bret et al., 2003). In the light of new geological surveys, new debris avalanche deposits outcrops have been identified around the St Gilles area. Most of these new outcrops are situated in the main riverbeds of the western Piton des Neiges flank (Rivière des Galets, Ravine Divon, Ravine Bernica and Ravine Trois Bassins). Furthermore, similar breccia outcrops has been identified down the Maïdo cliff, in the walls of Mafate cirque, uphill St Gilles area. All these formations show common characters of debris avalanche deposits with (i) a “block facies” consisting of plurimetric to decametric shattered lava flow and dykes segments with typical jigsaw fractures packed in (ii) a “matrix facies” composed of silty to sandy heterogeneous elements. This tends to prove that previous authors have underestimated the St Gilles event lateral extent. Our new field surveys point out the new extension (obvious landslide scars) of the St Gilles well known debris avalanche deposits. These scars start in the Mafate cirque (where the landslide head is located), then continue through the Mafate wall in the north of Maïdo place and go down to the sea from Ravine Trois Bassins in the south to Rivière des Galets in the north. These discoveries associated to recent submarine DEM interpretation (Oehler, 2001) allow us to consider a new global evolution sketch of the whole Piton des Neiges west flank with a large debris-avalanche (now called Mafate - St Gilles debris avalanche deposits) that has recovered the former basaltic Piton des Neiges topography at the end of the shield building stage (around: 0.45 My).

Fèvre, F.; Bret, B.; Odon, O.; Arnaud, A.; Bachèlery, B.

2003-04-01

323

Sensitivity Analysis of a Spatio-Temporal Avalanche Forecasting Model Based on Support Vector Machines  

NASA Astrophysics Data System (ADS)

The recent progress in environmental monitoring technologies allows capturing extensive amount of data that can be used to assist in avalanche forecasting. While it is not straightforward to directly obtain the stability factors with the available technologies, the snow-pack profiles and especially meteorological parameters are becoming more and more available at finer spatial and temporal scales. Being very useful for improving physical modelling, these data are also of particular interest regarding their use involving the contemporary data-driven techniques of machine learning. Such, the use of support vector machine classifier opens ways to discriminate the ``safe'' and ``dangerous'' conditions in the feature space of factors related to avalanche activity based on historical observations. The input space of factors is constructed from the number of direct and indirect snowpack and weather observations pre-processed with heuristic and physical models into a high-dimensional spatially varying vector of input parameters. The particular system presented in this work is implemented for the avalanche-prone site of Ben Nevis, Lochaber region in Scotland. A data-driven model for spatio-temporal avalanche danger forecasting provides an avalanche danger map for this local (5x5 km) region at the resolution of 10m based on weather and avalanche observations made by forecasters on a daily basis at the site. We present the further work aimed at overcoming the ``black-box'' type modelling, a disadvantage the machine learning methods are often criticized for. It explores what the data-driven method of support vector machine has to offer to improve the interpretability of the forecast, uncovers the properties of the developed system with respect to highlighting which are the important features that led to the particular prediction (both in time and space), and presents the analysis of sensitivity of the prediction with respect to the varying input parameters. The purpose of the sensitivity analysis is to shed light on the particular abilities of the model in assessing the likelihood of avalanche releases under evolving meteorological/snowpack conditions. Both spatial resolution (the abilities to produce reliable forecasts for individual avalanche paths) and temporal behaviour of the model are explored in details. Based on the sensitivity analysis, the uncertainty estimation for the provided forecasts is discussed. Particularly, the ensembles of prediction models are run and analysed in order to estimate the variability of the provided forecast and assess the uncertainty coming from the variety of sources: imprecise input data, uncertainty in weather forecast, sub-optimal parameters of the prediction model and variability in the choice of the training dataset.

Matasci, G.; Pozdnoukhov, A.; Kanevski, M.

2009-04-01

324

Rockfalls, Avalanches and Landslides at Augustine Volcano, 2003-2006  

NASA Astrophysics Data System (ADS)

Rockfalls, avalanches, and landslides have been frequently recorded in seismic data at Augustine Volcano for many years. Typical years, such as 2003 or 2004, had several dozen such events that were strong enough to trigger the automatic event detection system. Seventeen rockfalls occurred in 2003, mostly in late summer when air temperatures were highest. In 2004, 28 events occurred -- also in late summer. Typical events lasted about 30 sec, had frequencies greater than 6 Hz, and were well recorded on summit stations, suggesting that they were rockfalls from the steep summit dome into the adjacent moat area. In 2005, both the rate and the occurrence pattern changed. Rockfall activity began in April 2006 and continued through fall and early winter, after peaking in May and June. Overall there were more than 340 rockfalls in 2005, including both small and large events. The 2005 rockfall activity increased at nearly the same time as both earthquake activity and ground heating, suggesting that higher temperatures and steaming contributed to mechanical instabilities of the surface dome rocks. We examined relative amplitudes and frequency contents at station pairs to determine relative locations of the rockfalls by assuming both higher amplitudes and higher frequencies are associated with events closer to a given station. When a low-light camera was installed at Augustine in January 2006, we were able to confirm these relations because of the clear correlation between rockfalls, debris flows, and pyroclastic flows to the east (towards the camera) and higher amplitudes and frequencies at east station AUE. Other events had higher amplitudes and frequencies at west station AUW with no material seen moving eastward. Still other events moved towards the north, with amplitudes being nearly equivalent at both AUE and AUW. Compound events also occurred, with mass flow in several directions simultaneously. As the new steep-sided and unstable dome grew in spring 2006, rockfalls and related signals dominated the seismograms. The systematic patterns in amplitude and frequency, verified by data form the low-light camera, make it possible to estimate mass flow in various directions using seismic data. This work is in progress and will be compared with geologic maps of deposits from the 2006 eruptions. The increased rockfall rate of 2005 is a new class of precursory signal that may be incorporated into long-term monitoring strategies at Augustine and elsewhere.

Deroin, N.; McNutt, S. R.; Reyes, C.; Sentman, D. D.

2006-12-01

325

Snow avalanche incidents in north-western Anatolia, Turkey during December 1992  

Microsoft Academic Search

Snow avalanches take place in the mountainous regions of Turkey mostly in the eastern Anatolia Region with an average annual death toll of 23 people and much damage to property. However, in the mountainous areas of the Kastamonu and Sinop provinces in the western part of the Black Sea Region of Turkey between 25 and 30 December 1992, blizzards with

IBRAHIM GISIRER; Harun Tunçel; Ö. Murat Yava?; Tarhan Erenb?lge; Ayhan Sayin

1995-01-01

326

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

SciTech Connect

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

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

1990-09-05

327

A solar blind, hybrid III-nitride\\/silicon, ultraviolet avalanche photodiode  

Microsoft Academic Search

A novel, hybrid III-Nitride\\/Si, ultraviolet (UV) avalanche photodiode (APD) is proposed. The device combines the favorable short wavelength interband absorption properties of the direct bandgap III-Nitride material with the unique impact ionization characteristics of silicon. Solar blind response is achieved through optical isolation of the multiplication region of the device

P. Paul Ruden; Subash Krishnankutty

1999-01-01

328

Avalanche frontiers in the dissipative Abelian sandpile model and off-critical Schramm-Loewner evolution.  

PubMed

Avalanche frontiers in Abelian sandpile model (ASM) are random simple curves whose continuum limit is known to be a Schramm-Loewner evolution with diffusivity parameter ?=2. In this paper we consider the dissipative ASM and study the statistics of the avalanche and wave frontiers for various rates of dissipation. We examine the scaling behavior of a number of functions, such as the correlation length, the exponent of distribution function of loop lengths, and the gyration radius defined for waves and avalanches. We find that they do scale with the rate of dissipation. Two significant length scales are observed. For length scales much smaller than the correlation length, these curves show properties close to the critical curves, and the corresponding diffusivity parameter is nearly the same as the critical limit. We interpret this as the ultraviolet limit where ?=2 corresponding to c=-2. For length scales much larger than the correlation length, we find that the avalanche frontiers tend to self-avoiding walk, and the corresponding driving function is proportional to the Brownian motion with the diffusivity parameter ?=8/3 corresponding to a field theory with c=0. We interpret this to be the infrared limit of the theory or at least a crossover. PMID:23004700

Najafi, M N; Moghimi-Araghi, Saman; Rouhani, S

2012-05-03

329

Lutetium oxyorthosilicate block detector readout by avalanche photodiode arrays for high resolution animal PET  

Microsoft Academic Search

Avalanche photodiodes (APDs) have proven to be useful as light detectors for high resolution positron emission tomography (PET). Their compactness makes these devices excellent candidates for replacing bulky photomultiplier tubes (PMTs) in PET systems where space limitations are an issue. The readout of densely packed, 10 × 10 lutetium oxyorthosilicate (LSO) block detectors (crystal size 2.0 × 2.0 × 12

B. J. Pichler; B. K. Swann; J. Rochelle; R. E. Nutt; S. R. Cherry; S. B. Siegel

2004-01-01

330

Effect of Soft Dead Space on the Mean Gain of Avalanche Photodiodes in Submicron Ranges  

Microsoft Academic Search

A novel modified model which accounts for both the effect of dead space and soft ionization rate in the multiplication process of avalanche photodiodes (APDs) is proposed. The application of the suggested model is intended to be mainly beneficial in simulating gain characteristics of thin APDs in which considering the realistic ionization events and physical multiplication phenomena is inevitable. Based

Saeedeh Jahanmiri Nejad; M. H. Sheikhi

2007-01-01

331

Single p-type/intrinsic/n-type silicon nanowires as nanoscale avalanche photodetectors.  

PubMed

We report the controlled synthesis of axial modulation-doped p-type/intrinsic/n-type (p-i-n) silicon nanowires with uniform diameters and single-crystal structures. The p-i-n nanowires were grown in three sequential steps: in the presence of diborane for the p-type region, in the absence of chemical dopant sources for the middle segment, and in the presence of phosphine for the n-type region. The p-i-n nanowires were structurally characterized by transmission electron microscopy, and the spatially resolved electrical properties of individual nanowires were determined by electrostatic force and scanning gate microscopies. Temperature-dependent current-voltage measurements recorded from individual p-i-n devices show an increase in the breakdown voltage with temperature, characteristic of band-to-band impact ionization, or avalanche breakdown. Spatially resolved photocurrent measurements show that the largest photocurrent is generated at the intrinsic region located between the electrode contacts, with multiplication factors in excess of ca. 30, and demonstrate that single p-i-n nanowires function as avalanche photodiodes. Electron- and hole-initiated avalanche gain measurements performed by localized photoexcitation of the p-type and n-type regions yield multiplication factors of ca. 100 and 20, respectively. These results demonstrate the significant potential of single p-i-n nanowires as nanoscale avalanche photodetectors and open possible opportunities for studying impact ionization of electrons and holes within quasi-one-dimensional semiconductor systems. PMID:17163733

Yang, Chen; Barrelet, Carl J; Capasso, Federico; Lieber, Charles M

2006-12-01

332

Evaluation of a Junction Termination Extension Avalanche Photodiode for X-Ray Detection  

Microsoft Academic Search

An avalanche photodiode (APD) with a ring structure around the active area was built. The junction termination extension (JTE) APD has three diffused rings around the main junction to reduce the electric field at the surface. This design has the advantage that it does not need a sharp bevel edge or grooves to avoid early breakdown at the surface. The

Ernesto Gramsch; Oleg P. Pchelyakov; Igor B. Chistokhin; Eugene G. Tishkovsky

2007-01-01

333

Numerical modeling of debris avalanches at Nevado de Toluca (Mexico): implications for hazard evaluation and mapping  

Microsoft Academic Search

The present study concerns the numerical modeling of debris avalanches on the Nevado de Toluca Volcano (Mexico) using TITAN2D simulation software, and its application to create hazard maps. Nevado de Toluca is an andesitic to dacitic stratovolcano of Late Pliocene-Holocene age, located in central México near to the cities of Toluca and México City; its past activity has endangered an

F. Grieco; L. Capra; G. Groppelli; G. Norini

2007-01-01

334

Study of the wavefield generated by a gas exploder used for artificial avalanche release  

Microsoft Academic Search

A study of the entire wavefield (3D) generated by the detonation of a Gazex® device performed on the Gamsleiten slope, at Obertauern, Austria is presented. The main aim of the study was to determine whether the detonation can trigger snow avalanches in remote locations. A linear array of sensors in the vicinity of the blasting point combining six 1D and

E. Suriñach; I. Vilajosana; K. Kleemayr; L. Rammer

2011-01-01

335

The net benefit of public expenditures on avalanche defence structures in the municipality of Davos, Switzerland  

NASA Astrophysics Data System (ADS)

Avalanches pose a threat to settlements as well as industrial and recreational areas in the Alps. As a counter measure, technical mitigation measures have been implemented since the 19th century, resulting in a raise in value of formerly endangered areas. This increase in value can be considered as a benefit due to prevented damage. This paper compares the total costs and benefits of technical mitigation measures in the municipality of Davos, Switzerland as a basis for evaluating their net social benefit. The benefit of avalanche defence structures is determined using two different approaches. First, the replacement value of buildings protected by mitigation measures is quantified. Second, the number of protected persons is monetarily assessed by means of a human capital approach. The quantified benefit is compared with the present value of cumulative capital expenditures on avalanche mitigation measures. In addition, distributional effects of the public expenditures on technical mitigation measures are discussed based on the average future tax revenues within protected areas. Depending on whether benefits are calculated in terms of protected buildings or protected persons, the results show a large range of cost-benefit ratios. Critical issues of cost-benefit analyses in the context of alpine natural hazards are highlighted, including problems related to the human capital approach and the sensitivity of results to how benefits are calculated. The applicability of cost-benefit analyses for evaluating avalanche mitigation measures is discussed.

Fuchs, S.; McAlpin, M. C.

2005-04-01

336

Neuronal avalanches differ from wakefulness to deep sleep--evidence from intracranial depth recordings in humans.  

PubMed

Neuronal activity differs between wakefulness and sleep states. In contrast, an attractor state, called self-organized critical (SOC), was proposed to govern brain dynamics because it allows for optimal information coding. But is the human brain SOC for each vigilance state despite the variations in neuronal dynamics? We characterized neuronal avalanches--spatiotemporal waves of enhanced activity--from dense intracranial depth recordings in humans. We showed that avalanche distributions closely follow a power law--the hallmark feature of SOC--for each vigilance state. However, avalanches clearly differ with vigilance states: slow wave sleep (SWS) shows large avalanches, wakefulness intermediate, and rapid eye movement (REM) sleep small ones. Our SOC model, together with the data, suggested first that the differences are mediated by global but tiny changes in synaptic strength, and second, that the changes with vigilance states reflect small deviations from criticality to the subcritical regime, implying that the human brain does not operate at criticality proper but close to SOC. Independent of criticality, the analysis confirms that SWS shows increased correlations between cortical areas, and reveals that REM sleep shows more fragmented cortical dynamics. PMID:23555220

Priesemann, Viola; Valderrama, Mario; Wibral, Michael; Le Van Quyen, Michel

2013-03-21

337

Development of a superthermal electron avalanche and tearing mode suppression during electron cyclotron resonant heating  

Microsoft Academic Search

The critical velocity, for electron acceleration up to the superthermal region, is expressed in terms of the heating power per particle, instead of the inductively applied electric field. This expression is used to evaluate the superthermal electron production rate in a superthermal electron avalanche during electron cyclotron resonant heating (ECRH). The comparison between the predicted growth time of the superthermal

Avrilios Lazaros

2001-01-01

338

Fast-ion Energy Loss During TAE Avalanches in the National Spherical Torus Experiment  

SciTech Connect

Strong TAE avalanches on NSTX, the National Spherical Torus Experiment [M. Ono, et al., Nucl. Fusion 40 (2000) 557] are typically correlated with drops in the neutron rate in the range of 5% - 15%. In previous studies of avalanches in L-mode plasmas, these neutron drops were found to be consistent with modeled losses of fast ions. Here we expand the study to TAE avalanches in NSTX H-mode plasmas with improved analysis techniques. At the measured TAE mode amplitudes, simulations with the ORBIT code predict that fast ion losses are negligible. However, the simulations predict that the TAE scatter the fast ions in energy, resulting in a small (? 6%) drop in fast ion ?. The net decrease in energy of the fast ions is sufficient to account for the bulk of the drop in neutron rate, even in the absence of fast ion losses. This loss of energy from the fast ion population is comparable to the estimated energy lost by damping from the Alfven wave during the burst. The previously studied TAE avalanches in L-mode are re-evaluated using an improved calculation of the potential fluctuations in the ORBIT code.

Fredrickson, E D; Darrow, D S; Gorelenkov, N N; Kramer, G J; Kubota, S; Podesta, M; White, R B; Bortolon, A; Gerhardt, S P; Bell, R E; Diallo, A; LeBlanc, B; Levinton, F M

2012-07-11

339

Profilometry based on two-photon absorption in a silicon avalanche photodiode.  

PubMed

A novel profilometry method based on two-photon absorption in a silicon avalanche photodiode is proposed. This method has a wide dynamic range, from millimeters to tens of meters. The principle is experimentally confirmed with a fiber-optic Mach-Zehnder interferometer. PMID:12659260

Tanaka, Yosuke; Sako, Naoya; Kurokawa, Takashi; Tsuda, Hiroyuki; Takeda, Mitsuo

2003-03-15

340

Mobility Statistics and Automated Hazard Mapping for Debris Flows and Rock Avalanches.  

National Technical Information Service (NTIS)

Power-law equations that are physically motivated and statistically tested and calibrated provide a basis for forecasting areas likely to be inundated by debris flows, rock avalanches, and lahars with diverse volumes. The equations A=a1V2/3 and B=a2V2/3 a...

J. P. Griswold R. M. Iverson

2007-01-01

341

Wind Tunnel Experiments and Numerical Simulation of Snow Drifting around an Avalanche Protecting Dam  

Microsoft Academic Search

To learn about wind flow and snow drifting around avalanche dams, experiments were done in the Jules Verne Climatic Wind Tunnel. The paper reports the results from numerical wind flow simulations that were done to support the findings from the wind tunnel. Satisfying the model similitude criteria for the wind tunnel configuration was difficult due to the inevitable small geometric

Skuli Thordarson

2002-01-01

342

Basal shear and normal stresses of dry and wet snow avalanches after a slope deviation  

Microsoft Academic Search

Basal shear and normal force measurements of dry and wet snow avalanches and slush flows from the Weissfluhjoch snow chute are presented. This chute contains two slope angle transitions in order to measure the effect of slope deviations on the normal and shear force distributions. Slope deviations are typically encountered near snow sheds and the dynamic forces resulting from them

K. Platzer; P. Bartelt; C. Jaedicke

2007-01-01

343

Fast-ion energy loss during TAE avalanches in the National Spherical Torus Experiment  

NASA Astrophysics Data System (ADS)

Strong toroidal Alfvén eigenmode (TAE) avalanches on NSTX, the National Spherical Torus Experiment (Ono et al 2000 Nucl. Fusion 40 557) are typically correlated with drops in the neutron rate in the range 5-15%. In previous studies of avalanches in L-mode plasmas, these neutron drops were found to be consistent with modelled losses of fast ions. Here we expand the study to TAE avalanches in NSTX H-mode plasmas with improved analysis techniques. At the measured TAE mode amplitudes, simulations with the ORBIT code predict that fast ion losses are negligible. However, the simulations predict that the TAE scatter the fast ions in energy, resulting in a small (?5-6%) drop in fast ion ?. The net decrease in energy of the fast ions is sufficient to account for about 50% of the drop in neutron rate, redistribution for ?40%, and fast ion losses account for only ?10%. This loss of energy from the fast ion population is comparable to the estimated energy lost by damping from the Alfvén wave during the burst. The previously studied TAE avalanches in L-mode are re-evaluated using an improved calculation of the potential fluctuations in the ORBIT code near the separatrix.

Fredrickson, E. D.; Crocker, N. A.; Darrow, D. S.; Gorelenkov, N. N.; Kramer, G. J.; Kubota, S.; Podesta, M.; White, R. B.; Bortolon, A.; Gerhardt, S. P.; Bell, R. E.; Diallo, A.; LeBlanc, B.; Levinton, F. M.; Yuh, H.

2013-01-01

344

Avalanche frontiers in the dissipative Abelian sandpile model and off-critical Schramm-Loewner evolution  

NASA Astrophysics Data System (ADS)

Avalanche frontiers in Abelian sandpile model (ASM) are random simple curves whose continuum limit is known to be a Schramm-Loewner evolution with diffusivity parameter ?=2. In this paper we consider the dissipative ASM and study the statistics of the avalanche and wave frontiers for various rates of dissipation. We examine the scaling behavior of a number of functions, such as the correlation length, the exponent of distribution function of loop lengths, and the gyration radius defined for waves and avalanches. We find that they do scale with the rate of dissipation. Two significant length scales are observed. For length scales much smaller than the correlation length, these curves show properties close to the critical curves, and the corresponding diffusivity parameter is nearly the same as the critical limit. We interpret this as the ultraviolet limit where ?=2 corresponding to c=-2. For length scales much larger than the correlation length, we find that the avalanche frontiers tend to self-avoiding walk, and the corresponding driving function is proportional to the Brownian motion with the diffusivity parameter ?=8/3 corresponding to a field theory with c=0. We interpret this to be the infrared limit of the theory or at least a crossover.

Najafi, M. N.; Moghimi-Araghi, Saman; Rouhani, S.

2012-05-01

345

Effect of dead space on gain and noise of double-carrier-multiplication avalanche photodiodes  

Microsoft Academic Search

The effect of dead space on the statistics of the gain in a double-carrier-multiplication avalanche photodiode (APD) is determined using a recurrence method. The dead space is the minimum distance that a newly generated carrier must travel in order to acquire sufficient energy to become capable of causing an impact ionization. Recurrence equations are derived for the first moment, the

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

1992-01-01

346

Mixed-magma pyroclastic surge deposits associated with debris avalanche deposits at Colima volcanoes, Mexico  

Microsoft Academic Search

The transition between the terminal cones and the ancestral edifices of Nevado de Colima and Fuego de Colima volcanoes is marked by the deposits of gigantic volcanic debris avalanches of the Mount St. Helens (MSH) or Bezymianny type. Unusual mafic juvenile fragments and cauliflower bombs as well as juvenile fragments of mixed and more evolved composition are abundant in dune-bedded

Claude Robin; Jean-Christophe Komorowski; Christian Boudal; Philippe Mossand

1990-01-01

347

A ring-oscillator-based active quenching and active recharge circuit for single photon avalanche diodes  

Microsoft Academic Search

This paper proposes a new active quenching and active recharge circuit for single photon avalanche diodes (SPADs). Thanks to the simple ring oscillator architecture, the circuit is one of the most compact active quenching circuits published in the literature. Additionally, a simple modification to the basic version of the circuit allows to measure the hold-off delay and the recharge pulse

M. Gronholm; J. Poikonen; M. Laiho

2009-01-01

348

A method to quench and recharge avalanche photo diodes for use in high rate situations  

SciTech Connect

We present a new method of using Avalanche Photo Diodes (APDS) for low level light detection in Geiger mode in high rate situations such as those encountered at the Superconducting Super Collider (SSC). The new technique is readily adaptable to implementation in CMOS VLSI.

Regan, T.O.; Fenker, H.C.; Thomas, J. [Superconducting Super Collider Lab., Dallas, TX (United States); Oliver, J. [Harvard Univ., Cambridge, MA (United States). High Energy Physics Lab.

1992-06-01

349

High-Speed and Compact Quenching Circuit for Single-Photon Avalanche Diodes  

Microsoft Academic Search

In this paper, an innovative active-quenching and recharging circuit for single-photon avalanche diodes is presented. The proposed driver is very fast and extremely compact. It is based on a novel quenching paradigm that heavily reduces dead time, which now is only limited by the sensor rather than the circuit itself. To test speed performance, we designed the circuit with a

Rosario Mita; Gaetano Palumbo

2008-01-01

350

An avalanche-mode amorphous Selenium photoconductive layer for use as a camera tube target  

Microsoft Academic Search

It was found for the first time that an evaporated amorphous photoconductive layer of selenium produced the phenomenon of avalanche multiplication, and an amorphous photoconductive layer was used as the target in an experimental camera tube. The camera tube shows high sensitivity, greatly in excess of a quantum efficiency of unity, the upper limit of the sensitivity of a conventional

K. Tanioka; J. Yamazaki; K. Shidara; K. Taketoshi; T. Kawamura; S. Ishioka; Y. Takasaki

1987-01-01

351

Bunch-purity measurements of synchrotron X-ray beams with an avalanche photodiode detector  

Microsoft Academic Search

The bunch purity of synchrotron X-ray beams has been measured with an avalanche photodiode (APD) detector. The APD detector has several advantages for measurements of the bunch structure in a storage ring: the detector has a good time resolution of 100 ps (FWHM) and very low noise level. Moreover, the peak profile by the present APD device has only a

Shunji Kishimoto

1994-01-01

352

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

SciTech Connect

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

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

2006-09-15

353

Electron injection into SiO2 from an avalanching p-n junction  

Microsoft Academic Search

The current injected into SiO2 as a result of avalanche breakdown of an underlying p-n junction, with doping typically used in MOSTS, has been investigated. By use of a simple model, an expression has been derived for the dependence of this current on the gate and reverse voltages; reasonable agreement with experiment is obtained.

M. Pepper

1973-01-01

354

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

PubMed

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

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

2006-09-01

355

Modelling snow avalanches dynamics by Cellular Automata: a case study in Davos (Swiss Alps)  

Microsoft Academic Search

A Cellular Automata model was developed for modelling the flow of snow avalanches. The model is based on SCIDDICA SS2, a numerical code recently developed for the simulation of subaerial and subaqueous flow-like landslides. Basically, the model is based on a regular division of the space in cells, each one embedding an identical finite automaton (fa), whose state accounts for

Alessia Errera; Paolo Mazzanti; Maria Vittoria Avolio; Dieter Issler; Valeria Lupiano; Salvatore di Gregorio

2010-01-01

356

Two-dimensional electronic readout system for multi-step-avalanche chambers  

Microsoft Academic Search

We present prototype studies of a new technical solution of detector readout for measurements of charged particles at very high particle densities. In particular, this paper describes a readout system for Multi-Step Avalanche Chambers designed for the WA98 experiment at the CERN SPS. Results from the prototype studies are used for the design parameters of a readout chip containing both

L. Carlén; S. Garpman; H.-Å Gustafsson; H. Löhner; J. Nystrand; A. Oskarsson; I. Otterlund; T. Svensson; E. Stenlund; K. Söderström; H. J Whitlow

1997-01-01

357

Estimation of noise figure for conventional and multilayered avalanche photodiodes using the lucky drift model  

Microsoft Academic Search

A new technique for estimating the excess noise factor in conventional and multilayered avalanche photodiodes has been developed. It is based upon a computer simulation of carrier motion using lucky drift concepts. In conventional photodiodes the importance of the dead space is demonstrated. In multilayered photodiodes preliminary results show good agreement with other theoretical work.

J. S. Marsland; R. C. Woods; C. A. Brownhill; S. Gould

1990-01-01

358

Rock avalanches that travel onto glaciers and related developments, Karakoram Himalaya, Inner Asia  

Microsoft Academic Search

Catastrophic rock slope failures in rugged terrain commonly generate rock avalanches. When these occur in glacier basins the extent of landslide run out and its emplacement geometry are affected by movement over ice. Substantial modifications of glacier activity and sedimentation can follow. Ice activity leads to rapid modification, transport and dispersal of landslide debris. The nature of these interactions is

Kenneth Hewitt

2009-01-01

359

Precise measurement of first Townsend coefficient, using parallel plate avalanche chamber  

NASA Astrophysics Data System (ADS)

By employing iso-C4H10 gas, we have studied the effective parameters in the first Townsend coefficient measurement using parallel plate avalanche chamber (PPAC). Obtained results are free from space charge and gap deformation effects, which have seriously affected previous PPAC-based measurements. The required conditions for a reliable Townsend coefficient measurement are presented as well.

Nakhostin, Mohammad; Baba, Mamoru; Ohtsuki, Tsutomu; Oishi, Takuji; Itoga, Toshiro

2007-03-01

360

Cosmic Ray Measurements by Scintillators with Metal Resistor Semiconductor Avalanche Photo Diodes  

ERIC Educational Resources Information Center

|An educational set-up for cosmic ray physics experiments is described. The detector is based on scintillator tiles with a readout through metal resistor semiconductor (MRS) avalanche photo diode (APD) arrays. Typical measurements of the cosmic angular distribution at sea level and a study of the East-West asymmetry obtained by such a device are…

Blanco, Francesco; La Rocca, Paola; Riggi, Francesco; Akindinov, Alexandre; Mal'kevich, Dmitry

2008-01-01

361

An Assessment of Snow Avalanche Paths and Forest Dynamics Using Ikonos Satellite Data  

Microsoft Academic Search

Ikonos panchromatic and multispectral satellite data were acquired in October 2000 and August 2002 for a test area along US Highway 2, the southern border of Glacier National Park (GNP), Montana, USA. The research goals were to map snow avalanche paths and to characterize vegetation patterns in selected paths for longitudinal (i.e., source, track, and runout) and transverse (i.e., inner,

Stephen J. Walsh; Daniel J. Weiss; David R. Butler; George P. Malanson

2004-01-01

362

Pseudo-Encopresis: From Avalanche to Victory, from Vicious to Virtuous Cycles  

Microsoft Academic Search

In this paper, encopresis is considered from the perspective of Second Cybernetics (7). In families where these symptoms feature, all members are considered to be inadvertently participating in an uncontrolled avalanche of events. All members appear powerless to affect the course of these events, and experience the symptoms of encopresis as oppressive.

Michael White

1984-01-01

363

Shear Fracture Precipitated by Strain Softening as a Mechanism of Dry Slab Avalanche Release  

Microsoft Academic Search

.Snow stratigraphy studies at the fracture lines of dry slab avalanches often indicate a situation that consists of a harder thick layer overlying a thin weak layer. Prefracture stress conditions and progressive fracture of snow slabs are discussed here from the point of view that slow shear failure in the weak layer results in Griffith-like critical lengths there, resulting in

David M. McClung

1979-01-01

364

Debris Avalanches and Debris Flows Transformed from Collapses in the Trans-Mexican Volcanic Belt, México  

Microsoft Academic Search

Volcanoes of the Trans-Mexican Volcanic Belt (TMVB) have yielded numerous sector and flank collapses during Pleistocene and Holocene time. Sector collapses associated with magmatic activity have yielded debris avalanches with generally limited runout extent (e.g. Popocatépetl, Jocotitlán, and Colima volcanoes). In contrast, flank collapses (smaller failures not involving the volcano summit), both associated and unassociated with magmatic activity and correlated

L. Capra; J. Macias; K. Scott; M. Abrams

2001-01-01

365

TCN dating of Holocene rock avalanches in the Karakoram Himalaya, northern  

Microsoft Academic Search

This paper re-examines seven field sites where blocky, cross-valley deposits have been important in interpretations of Quaternary events. The deposits are products of run out and emplacement of rock slide - rock avalanches. Each of the events dammed the river where it occurred and impounded large parts of the Upper Indus drainage for some centuries at least. The landslide barriers

K. Hewitt; J. Gosse; J. J. Clague

2009-01-01

366

From deep seated slope deformation to rock avalanche: Destabilization and transportation models of the Sierre landslide (Switzerland)  

NASA Astrophysics Data System (ADS)

Sackung is a widespread post-glacial morphological feature affecting Alpine mountains and creating characteristic geomorphological expression that can be detected from topography. Over long time evolution, internal deformation can lead to the formation of rapidly moving phenomena such as a rock-slide or rock avalanche. In this study, a detailed description of the Sierre rock-avalanche (SW Switzerland) is presented. This convex-shaped postglacial instability is one of the larger rock-avalanche in the Alps, involving more than 1.5 billion m3 with a run-out distance of about 14 km and extremely low Fahrböschung angle. This study presents comprehensive analyses of the structural and geological characteristics leading to the development of the Sierre rock-avalanche. In particular, by combining field observations, digital elevation model analyses and numerical modelling, the strong influence of both ductile and brittle tectonic structures on the failure mechanism and on the failure surface geometry is highlighted. The detection of pre-failure deformation indicates that the development of the rock avalanche corresponds to the last evolutionary stage of a pre-existing deep seated gravitational slope instability. These analyses accompanied by the dating and the characterization of rock avalanche deposits, allow the proposal of a destabilization model that clarifies the different phases leading to the development of the Sierre rock avalanche.

Pedrazzini, Andrea; Jaboyedoff, Michel; Loye, Alexandre; Derron, Marc-Henry

2013-10-01

367

Impact of the Rayleigh number and endothermic phase transition on the time behaviour of mantle avalanches  

NASA Astrophysics Data System (ADS)

There has been a long history of studying the endothermic phase change at a depth of 660 km in the Earth's mantle. The goal of the present study is to determine the transition between one-layered convection and two-layered circulation and to analyze the dynamics of mantle avalanches using simple two-dimensional numerical models. A series of numerical calculations have been investigated using different Rayleigh numbers (Ra) and Clapeyron slopes (?d). It has been established that the Rayleigh number effectively influences the dynamics of the phase transition. At higher Rayleigh numbers the hindering effect is stronger; at ?d < 0 mantle convection is shifted from one-layered towards a partially layered flow system. From calculating the vertical mass flux at 660 km and analysing its time series three types of mantle flow were found. The first type is whole mantle convection (one-layered), namely below Ra = 105 and for ?d = -3, -4.5, -6, -9 MPa/K. The second type is an intermittently layered mantle convection, where the convection is mainly layered but there is a significant, episodically huge mass transfer between the two layers, i.e. above Ra = 5 × 105 and for ?d = -3, -4.5, -6 MPa/K. The third type covers isolated upper and lower mantle convection at ?d = -9 MPa/K and from Ra = 105, within which range all of the simulations resulted in two-layered convection. Systematic investigation has been carried out to map the region in the second group where avalanche events can appear. Mantle avalanches have been detected in 12 models from Ra = 5 × 105 to Ra = 107 and at ?d = -3, -4.5, -6 MPa/K. As a result of a Fourier analysis the characteristic time periods of mantle avalanches have been calculated. Analysing the amplitude spectrum of the vertical mass flux at a depth of 660 km two specific time periods were determined. The larger one, at about 580 Myr, may correspond to the large mantle overturns. The shorter period represents smaller, more frequent mantle avalanches. Studying the influence of the Rayleigh number and the Clapeyron slopes systematically, it has been shown that the characteristic time period of these smaller avalanches depends on Ra, but is independent of ?d. As Ra increases the time period decreases; the relationship can be well described with a power function. The characteristic time period of small avalanches for mantle-like parameters (Ra ˜ 107, ?d = -3 MPa/K) is about 80-150 Myr, which can be compared to the average time period of episodic flood basalt activity.

Herein, Mátyás; Galsa, Attila; Lenkey, László

2013-05-01

368

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

SciTech Connect

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

Wronski, M. M.; Rowlands, J. A. [Imaging Research, Sunnybrook Health Sciences Centre, Department of Medical Biophysics, University of Toronto, 2075 Bayview Avenue, Toronto, Ontario M4N 3M5 (Canada)

2008-12-15

369

Debris avalanches at Somma-Vesuvius volcano (Italy) and implications for hazard evaluation  

NASA Astrophysics Data System (ADS)

Catastrophic landslides associated with eruptions are a normal event in the life of many volcanoes. Slope failure of major portions of a volcanic edifice can trigger explosive activity by the sudden pressure release of hydrothermal-magmatic systems. Pumiceous pyroclastic flows are often erupted late in the paroxymal phase of eruptions associated with breached crater formation, following the removal of material overlying the central vent, and mantle debris avalanche deposits. Several historic breached crater eruptions have resulted in fatalities, many from tsunamis produced by debris avalanches entering the sea from coastal volcanoes. Somma-Vesuvius, located in southern Italy, is an active volcano with a breached crater close to the continental shelf of Naples Bay. The Somma-Vesuvius volcanic succession mainly consists of lava flows and minor scoria fall deposits (25 ka < age < 20 ka), overlain by the deposits of four main plinian eruptions: the "Pomici di Base" (18,000 years BP); the "Mercato Pumice" (8,000 years BP); the "Avellino Pumice"(3,400 years BP); and the "Pompei Pumice" (A.D. 79). The interpretation of core, well data and high-resolution seismic profiles offshore of Somma-Vesuvius documents interlayered volcanic and marine units in the Late Quaternary succession. Stratigraphic analysis permitted the identification and mapping of two thick debris avalanche deposits located on the continental shelf. With a volume of 2.9 km3, the older debris avalanche is linked to the 18 ka-old Pomici di Base plinian eruption. The younger debris avalanche has a volume of approximately 1 km3 and is linked to the 3.4 ka-old Avellino plinian eruption. The identification of two debris avalanches originating from Somma-Vesuvius has important implications for the hazard evaluation: i) the occurrence of two sector collapses in the history of Somma-Vesuvius volcano; ii) a potential volcano slope failure and consequent tsunamis produced by the entry of a debris avalanche into Naples Bay should be considered in the volcanic hazard evaluation of this densely populated area.

Milia, A.; Marsella, E.; Molisso, F.; Sacchi, M.; Torrente, M. M.

2003-04-01

370

Rock avalanche deposits in Alai Valley, Central Asia: misinterpretation of glacial record  

NASA Astrophysics Data System (ADS)

The reconstruction of Quaternary glaciations has been restricted by conventional approaches with resulting contradictions in interpretation of the regional glacial record, that recently have been subjected to critical re-evaluation. Along with uncertainties in dating techniques and their applicability to particular landforms (Kirkbride and Winkler, 2012), it has recently been demonstrated that the presence of rock avalanche debris in a landform can be unequivocally detected; this allows for the first time definitive identification of and distinction between glacial moraines and landslide deposits. It also identifies moraines that have formed due to rock avalanche deposition on glaciers, possibly with no associated climatic signal (Reznichenko et al., 2012). Confusion between landslide deposits and moraines is evident for ranges in Central Asia (e.g., Hewitt, 1999) where the least-studied glacial record is selectively correlated with established glacial chronologies in Alpine ranges, which in turn masks the actual glacial extent and their responses to climate change, tectonics and landsliding activity. We describe examples in the glaciated Alai Valley, large intermountain depression between the Zaalay Range of the Northern Pamir and the Alay Range of the Southern Tien-Shan, showing that some large Quaternary deposits classically interpreted as moraines are of rock avalanche origin. Sediment from these deposits has been tested for the presence of agglomerates that are only produced under high stress conditions during rock avalanche motion, and are absent from glacial sediments (Reznichenko et al., 2012). This reveals that morphologically-similar deposits have radically different geneses: rock avalanche origin for a deposit in the Komansu river catchment and glacial origin for deposits in the Ashiktash and Kyzylart catchments. The enormous Komansu rock avalanche deposit, probably triggered by a rupture of the Main Pamir thrust, currently covers about 100 km2 with a minimum estimated volume more than 1 x 109 m3. Another smaller rock avalanche deposit rests on the Lenin Glacial sediment in the neighbour Ashiktash river catchment, which was previously suggested to originate from Mt. Lenin (7134 m). The revised origin of these deposits highlights the role of rock avalanches in glacial activity and in the resulting glacial record in this valley and other actively tectonic areas of Central Asia. Although further investigation is required to detail the geneses, magnitudes and ages for these and other landforms in the valley, this study contributes explicit evidence for contamination of palaeoclimate proxies with data from non-climatic events, and reinforces the urgent need for revised interpretation of the glacial chronologies. Hewitt, K., 1999. Quaternary moraines vs. catastrophic rock avalanches in the Karakoram Himalaya, Northern Pakistan. Quaternary Research, v. 51, p. 220-237. Kirkbride, M.P., and Winkler, S., 2012. Correlation of Late Quaternary moraines: impact of climate variability, glacier response, and chronological resolution: Quaternary Science Reviews, v. 46, p. 1-29. Reznichenko, N.V., Davies, T.R.H., Shulmeister, J. and Larsen S.H, 2012. A new technique for identifying rock-avalanche-sourced sediment in moraines and some paleoclimatic implications. Geology, v. 40, p. 319-322.

Reznichenko, Natalya; Davies, Tim; Robinson, Tom; De Pascale, Gregory

2013-04-01

371

Direct Measurement of Microstructural Avalanches during the Martensitic Transition of Cobalt Using Coherent X-Ray Scattering  

SciTech Connect

Heterogeneous microscale dynamics in the martensitic phase transition of cobalt is investigated with real-time x-ray scattering. During the transformation of the high-temperature face-centered cubic phase to the low-temperature hexagonal close-packed phase, the structure factor evolution suggests that an initial rapid local transformation is followed by a slower period during which strain relaxes. Coherent x-ray scattering measurements performed during the latter part of the transformation show that the kinetics is dominated by discontinuous sudden changes-avalanches. The spatial size of observed avalanches varies widely, from 100 nm to 10{mu}m, the size of the x-ray beam. An empirical avalanche amplitude quantifies this behavior, exhibiting a power-law distribution. The avalanche rate decreases with inverse time since the onset of the transformation.

Sanborn, Christopher; Ludwig, Karl F.; Rogers, Michael C.; Sutton, Mark (McGill); (BU)

2011-09-06

372

Recalculation of an artificially released avalanche with SAMOS and validation with measurements from a pulsed Doppler radar  

NASA Astrophysics Data System (ADS)

A joint experiment was carried out on 10 February 1999 by the Swiss Federal Institute for Snow and Avalanche Research (SFISAR) and the Austrian Institute for Avalanche and Torrent Research (AIATR, of the Federal Office and Re-search Centre for Forests, BFW) to measure forces and velocities at the full scale experimental site CRÊTA BESSE in VALLÉE DE LA SIONNE, Canton du Valais, Switzerland. A huge avalanche could be released artificially, which permitted extensive investigations (dynamic measurements, im-provement of measurement systems, simulation model verification, design of protective measures, etc.). The results of the velocity measurements from the dual frequency pulsed Doppler avalanche radar of the AIATR and the recalculation with the numerical simulation model SAMOS are explained in this paper.

Sailer, R.; Rammer, L.; Sampl, P.

373

Numerical modeling of the Mount Steller rock-ice avalanche and of the associated landquake  

NASA Astrophysics Data System (ADS)

Gravitational instabilities, such as landslides, avalanches or debris flows play a key role in erosion processes and represent one of the major natural hazards in mountainous, coastal or volcanic regions. Despite the great amount of field, experimental and numerical work devoted to this problem, the understanding of the physical processes at work in gravitational flows is still an open issue, in particular due to the lack of observations relevant to their dynamics. In this context, the seismic signal generated by gravitational flows (i. e. landquake) is a unique opportunity to get information on their dynamics. Indeed, as shown recently by Favreau et al. (2010), simulation of the seismic signal generated by landslides makes it possible to discriminate different flow scenarios and estimate the rheological parameters during the flow. However, the feasibility of this method was only proved for one landslide (i. e. the Thurwieser landslide) recorded by two seismic stations. We simulate here the 2005 rock-ice avalanche occurring on the Mount Steller, Alaska, that has been recorded by more than ten seismic stations. This 40-60 million of cubic meters rock-ice avalanche traveled about 10 km and stopped on the Bering glacier. Field survey showed that a significant part of this mass result of ice eroded from the glacier by the flow (Huggel et al., 2008). By simulating the avalanche and the generated seismic signal, the aim is to constrain the flow dynamics and in particular, to assess the role of erosion processes on the avalanche behavior. As a result, simulation shows that the presence of the glacier as well as erosion processes have to be taken into account to reproduce the seismic signal generated by the avalanche. Comparison between simulated and observed seismic signals makes it possible to constrain the volume of eroded material and more generally to discriminate different landslide scenarios. Because gravitational instabilities are continuously recorded by global and regional seismic networks, this new method will help gathering new data on landslide behavior. 2D simulations of this landslide have also been performed to investigate how the 3D topography affect the seismic signal. Favreau, P., Mangeney, A., Lucas, A., Crosta, G., and Bouchut, F., 2010. Numerical modeling of landquakes, Geophys. Res. Lett., 37, L15305. Huggel, C. et al., 2008. Ninth International Conference on Permafrost.

Moretti, Laurent; Mangeney, Anne; Capdeville, Yann; Stutzmann, Éléonore; Huggel, Christian; Schneider, Demian; Bouchut, François

2013-04-01

374

Numerical modeling of the Mount Steller rock-ice avalanche and of the associated landquake  

NASA Astrophysics Data System (ADS)

Gravitational instabilities, such as landslides, avalanches or debris flows play a key role in erosion processes and represent one of the major natural hazards in mountainous, coastal or volcanic regions. Despite the great amount of field, experimental and numerical work devoted to this problem, the understanding of the physical processes at work in gravitational flows is still an open issue, in particular due to the lack of observations relevant to their dynamics. In this context, the seismic signal generated by gravitational flows (i. e. landquake) is a unique opportunity to get information on their dynamics. Indeed, as shown recently by Favreau et al. (2010), simulation of the seismic signal generated by landslides makes it possible to discriminate different flow scenarios and estimate the rheological parameters during the flow. However, the feasibility of this method was only proved for one landslide (i. e. the Thurwieser landslide) recorded by two seismic stations. We simulate here the 2005 rock-ice avalanche occurring on the Mount Steller, Alaska, that has been recorded by more than ten seismic stations. This 40-60 million of cubic meters rock-ice avalanche traveled about 10 km and stopped on the Bering glacier. Field survey showed that a significant part of this mass result of ice eroded from the glacier by the flow (Huggel et al., 2008). By simulating the avalanche and the generated seismic signal, the aim is to constrain the flow dynamics and in particular, to assess the role of erosion processes on the avalanche behavior. As a result, simulation shows that the presence of the glacier as well as erosion processes have to be taken into account to reproduce the seismic signal generated by the avalanche. Comparison between simulated and observed seismic signals makes it possible to constrain the volume of eroded material and more generally to discriminate different landslide scenarios. Because gravitational instabilities are continuously recorded by global and regional seismic networks, this new method will help gathering new data on landslide behavior. Favreau, P., Mangeney, A., Lucas, A., Crosta, G., and Bouchut, F., 2010. Numerical modeling of landquakes, Geophys. Res. Lett., 37, L15305. Huggel, C. et al., 2008. Ninth International Conference on Permafrost.

Moretti, L.; Mangeney, A.; Capdeville, Y.; Stutzmann, E.; Huggel, C.; Schneider, D.; Favreau, P.

2011-12-01

375

Evaluating TITAN2D mass-flow model using the 1963 Little Tahoma Peak avalanches, Mount Rainier, Washington  

Microsoft Academic Search

The TITAN2D geophysical mass-flow model that is currently under development is evaluated by comparing simulation results with those obtained from another flow model, FLOW3D, and the published data on the 1963 Little Tahoma Peak avalanches on Mount Rainier, Washington. The avalanches, totaling approximately 10 x 106 m3 of brecciated lava flows and other debris, traveled 6.8 km horizontally and fell

M. F. Sheridan; A. J. Stinton; A. Patra; B. Pitman; A. Bauer; C. Nichita

2003-01-01

376

Effect of flux avalanches on activation energy in type-II superconductors: Evidence for self-organized criticality  

Microsoft Academic Search

The behavior of thermally activated flux avalanches is studied for both high-Tc superconductors (single crystals of Bi2Sr2CaCu2Ox and YBa2Cu3Ox) and a conventional type-II superconductor (Nb3Sn multifilamentary wire). By combining two different mechanisms, namely, thermally activated and avalanche flux motion, we have developed a U(j) relationship in a large regime of driving force for type-II superconductors. As a result of flux

Zuning Wang; Donglu Shi

1993-01-01

377

Evaluating Titan2D mass-flow model using the 1963 Little Tahoma Peak avalanches, Mount Rainier, Washington  

Microsoft Academic Search

The Titan2D geophysical mass-flow model is evaluated by comparing its simulation results and those obtained from another flow model, FLOW3D, with published data on the 1963 Little Tahoma Peak avalanches on Mount Rainier, Washington. The avalanches, totaling approximately 10×106 m3 of broken lava blocks and other debris, traveled 6.8 km horizontally and fell 1.8 km vertically (H\\/L=0.246). Velocities calculated from

M. F. Sheridan; A. J. Stinton; A. Patra; E. B. Pitman; A. Bauer; C. C. Nichita

2005-01-01

378

Time-resolved studies of the C-A transition in avalanche discharges; Fluorescence and gain-loss studies  

SciTech Connect

Time-resolved XeF {ital C}-{ital A} fluorescence and gain-loss studies are conducted in an avalanche discharge using arc-type UV preionization in a variety of devices that deliver peak powers from 1 to 13 MW/cm{sup 3} in time intervals from 10 to 30 ns. The results coupled with extensive fluorescence measurements give indications about the possibility of developing a successful XeF {ital C}-{ital A} transition avalanche discharge laser.

Sze, R.C. (Los Alamos National Lab., Los Alamos, NM (US)); Sakai, T. (Rice Univ., Houston, TX (US)); Vannini, M. (Inst. di Elletronica Quantistica, Florence (IT)); Sentis, M.L. (Inst. de Mecanique des Fluides, Marseille (FR))

1991-01-01

379

Based simulation of high gain and low breakdown voltage InGaAs\\/InP avalanche photodiode  

Microsoft Academic Search

The InGaAs\\/InP avalanche photodiode (APD) of thin heterostructure charge layer has studied. Apsys software is used for simulation. For reducing the dark current and achieving higher avalanche gain, a 30 nm InP charge layer and 100 nm InGaAsP grade charge layer used between 400 nm multiplication and absorption layers. Simulation results demonstrated that the low dark current properties and low

W. Lei; F. M. Guo; W. Lu; D. Y. Xiong; Z. Q. Zhu; J. H. Chu

2008-01-01

380

InP\\/InGaAsP\\/InGaAs avalanche photodiodes grown by chemical beam epitaxy  

Microsoft Academic Search

InP\\/InGaAsP\\/InGaAs avalanche photodiodes with separate absorption, grading, and multiplication regions (SAGM-APD's) have been fabricated from wafers grown by chemical beam epitaxy (CBE). These APD's exhibit low dark current (<25 nA at 90 percent of breakdown), low capacitance (?0.2 pF), and good responsivity (0.75 A\\/ W at 1.3 µm). The pulse response, which is relatively independent of avalanche gain, is characterized

Won-Tien Tsang; J. C. Campbell; G.J. Qua

1987-01-01

381

Stratigraphic reconstruction of two debris avalanche deposits at Colima Volcano (Mexico): Insights into pre-failure conditions and climate influence  

Microsoft Academic Search

Throughout its history, Colima Volcano has experienced numerous partial edifice collapses with associated emplacement of debris avalanche deposits of contrasting volume, morphology and texture. A detailed stratigraphic study in the south-eastern sector of the volcano allowed the recognition of two debris avalanche deposits, named San Marcos (>28,000calyr BP, V=~1.3km3) and Tonila (15,000–16,000calyr BP, V=~1km3 ). This work sheds light on

M. Roverato; L. Capra; R. Sulpizio; G. Norini

2011-01-01

382

Change in snow avalanche and debris flow hazards in the region of Krasnaya Polyana as the result of anthropogenic activity  

NASA Astrophysics Data System (ADS)

The first evaluations of the snow avalanches and debris flow danger in the region of Krasnaya Polyana (Winter Olympic Games 2014 site) were made by the staff of LSADF in 1960s. In those times the danger was estimated as medium and low. Active development of the region started in 2000, when the ski (mountain climatic health) resort Alpika Service was constructed at the north slope of Aibga mountain range. Then the Alpine resorts Rosa Khutor and Gornaya Karusel [Mountain Carousel] were put into operation on the same slope. OAO Gazprom was also developing its own ski resort at the neighbouring Psekhako ridge. As the result of deforestation the quantity of small snow avalanches increased on the Aibga slopes. Skiers were caught several times by avalanches initiated by them in the reported avalanche events. The construction of ski runs, motorways, roads, as well as building of other related infrastructure has resulted in considerable change in relief. The sediment capping was dumped into stream canals, which resulted in the formation of debris flows, threatening the infrastructure of the ski resorts. The relief change related to the on going Olympic constructions is especially pronounced, when newly formed landfilling on some slopes becomes the material for landslides and debris flows and beds for avalanches. Thus, the degree of snow avalanche and debris flows danger increased considerably in the recent years, requiring originally unplanned mitigation measures.

Shnyparkov, A. L.; Seliverstov, Y. G.; Sokratov, S. A.; Koltermann, K. P.

2012-04-01

383

Large-area avalanche photodiodes for the detection of soft x rays  

SciTech Connect

The charge-collection efficiency of beveled-edge-type silicon avalanche photodiodes has been determined for soft x rays in the 50--300-eV range. An efficiency of greater than 80% is measured for energies below the Si {ital L} absorption edge. The measured efficiency is well described by a model that accounts for absorption in an oxide overlayer and recombination at the front surface of the diode. The avalanche photodiodes are shown to be significantly more sensitive compared with other detectors for pulsed sources such as a laser-produced plasma source. These results are also very encouraging for soft-x-ray/extreme-UV applications involving synchrotron radiation.{ital PACS} {ital numbers}: 29.40.Wk, 07.85.+n, 85.60.Dw.

Gullikson, E.M. [Center for X-Ray Optics, Materials Sciences Division, Lawrence Berkeley Laboratory, Berkeley, California 94720 (United States); Gramsch, E. [Advance Photonix Inc., 1240 Avenida Acaso, California 93012 (United States)]|[Department of Physics, Universidad de Santiago, Avda. Ecuador 3493, Casilla 307, Santiago (Chile); Szawlowski, M. [Advance Photonix Inc., 1240 Avenida Acaso, California 93012 (United States)

1995-08-01

384

Performance evaluation of new large-area avalanche photodiodes for scintillation spectroscopy  

NASA Astrophysics Data System (ADS)

Avalanche photodiodes (APDs) appear promising for certain applications as a solid state replacement for the photomultiplier tube. The increase in leakage current and capacitance noise with device active area has in the past kept the size of commercially available devices to < 1 mm2. Recent advances in fabrication technology have, however, resulted in relatively low-noise devices of up to 1 in. in diameter. We have recently evaluated the performance as scintillation spectroscopy detectors of two commercial large-area avalanche photodiodes. These APDs exhibit exceptional performance: at 662 keV a 1-in. diameter device coupled to a CsI(Tl) scintillator and operating at room temperature yielded 6.9% resolution and a 1-cm device coupled to CsI(Tl) and cooled to 260 K gave 4.4% resolution, which is believed to be the best resolution ever recorded for a scintillation spectrometer.

James, K. M.; Masterson, M. J.; Farrell, R.

1992-03-01

385

Performance evaluation of new large-area avalanche photodiodes for scintillation spectroscopy  

NASA Astrophysics Data System (ADS)

Avalanche photodiodes (APD's) appear promising for certain applications as a solid state replacement for the photomultiplier tube. The increase in leakage current and capacitance noise with device active area has in the past kept the size of commercially available devices to less than 1 mm (exp 2). Recent advances in fabrication technology have, however, resulted in relatively low noise devices of up to 1 inch in diameter. We have recently evaluated the performance as scintillation spectroscopy detectors of two commercial large area avalanche photodiodes. These APD's exhibit exceptional performance: at 662 KeV a 1 inch diameter device coupled to a CsI(Tl) scintillator and operating at room temperature yielded 6.9 pct. resolution and a 1 cm device coupled to CsI(Tl) and cooled to 260 K gave 4.4 pct. resolution, which is believed to be the best resolution ever recorded for a scintillation spectrometer.

James, K. M.; Masterson, M. J.; Farrell, R.

386

Evaluating avalanche generation by 2-D finite element analysis at Pico de Orizaba, Mexico  

NASA Astrophysics Data System (ADS)

Pico de Orizaba, at the eastern Mexican Volcanic Belt, has collapse twice during its evolution (250 ka and 20 ka ago). In case of collapse of the present day cone, the run out distance of the moving mass represents a hazard for the surrounding population. We evaluate, by using finite element, two geological aspects that have been recognized in the present cone of Pico de Orizaba as possible triggering mechanisms for avalanches: 1) Extensive hydrothermal alteration (argillic), and 2) normal faulting at the volcano basement. Two dimensional finite element analyses were carried out in a profile trending NE40SW, perpendicular to the trend of dikes and volcanic flank eruptions. We evaluate effects of extension of hydrothermal alteration and amount of fault displacement needed for triggering the avalanche. We compare the shape of failure surface (which reflects the volume of the resulting failing mass) through distribution of velocity contours and displacement vectors.

Concha Dimas, A.; Watters, R. J.

2003-04-01

387

Avalanche mechanism for atom loss near an atom-dimer Efimov resonance  

NASA Astrophysics Data System (ADS)

An Efimov trimer near the atom-dimer threshold can increase the atom loss rate in ultracold trapped atoms through the avalanche mechanism proposed by Zaccanti A three-body recombination event creates an energetic atom and dimer, whose subsequent elastic collisions produce additional atoms with sufficient energy to escape from the trapping potential. We use Monte Carlo methods to calculate the average number of atoms lost and the average heat generated by recombination events in both a Bose-Einstein condensate and a thermal gas. We take into account the energy-dependence of the cross sections and the spatial structure of the atom cloud. While the number of atoms lost in a recombination event can be much larger than the value 3, we find that the avalanche mechanism does not produce a narrow loss feature near the atom-dimer resonance.

Langmack, Christian; Smith, D. Hudson; Braaten, Eric

2012-08-01

388

A GaN p—i—p—i—n Ultraviolet Avalanche Photodiode  

NASA Astrophysics Data System (ADS)

A separated absorption and multiplication GaN p—i—p—i—n avalanche photo-diode (APD) with a 25 ?m diameter mesa is proposed and demonstrated. Compared to the conventional p—i—n APD, the p—i—p—i—n structure reduces the probability of premature micro-plasma breakdown, raises the gain from 30 to 400 and reduces the work voltage from 93 to 48 V. The temperature test is set on p—i—p—i—n APDs, and the positive coefficient of 30 mV/K shows that avalanche breakdown happens in the devices. The peak responsivity of p—i—p—i—n APDs is 0.11 A/W under a wavelength of 358 nm.

Zheng, Ji-Yuan; Wang, Lai; Hao, Zhi-Biao; Luo, Yi; Wang, Lan-Xi; Chen, Xue-Kang

2012-09-01

389

Effects of triggering mechanism on snow avalanche slope angles and slab depths from field data  

NASA Astrophysics Data System (ADS)

Field data from snow avalanche fracture lines for slope angle and slab depth (measured perpendicular to the weak layer) were analyzed for different triggering mechanisms. For slope angle, the results showed that the same probability density function (pdf) (of log-logistic type) and range (25 - 55 degrees) apply independent of triggering mechanism. For slab depth, the same pdf (generalized extreme value) applies independent of triggering mechanism. For both slope angle and slab depth, the data skewness differentiated between triggering mechanism and increased with applied triggering load. For slope angle, skewness is lowest for natural triggering by snow loads and highest for triggering from human intervention. For slab depth, the skewness is lowest for natural triggering and highest for a mix of triggers including explosive control with skier triggering being intermediate. The results reveal the effects of triggering mechanism which are important for risk analyses and to guide avalanche forecasting.

McClung, David M.

2013-04-01

390

Ultralow noise midwave infrared InAs-GaSb strain layer superlattice avalanche photodiode  

SciTech Connect

Eye-safe midwavelength infrared InAs-GaSb strain layer superlattice p{sup +}-n{sup -}-n homojunction avalanche photodiodes (APDs) grown by solid source molecular beam epitaxy were fabricated and characterized. Maximum multiplication gain of 1800 was measured at -20 V at 77 K. Excess noise factors between 0.8 and 1.2 were measured up to gain of 300. Gain of 200 was measured at 120 K. Exponential nature of the gain as a function of reverse bias along with low excess noise factor at higher gain confirms single carrier electron-only impact ionization in the avalanche regime. Decrease in the multiplication gain at higher temperatures correlates with standard APD characteristics.

Mallick, Shubhrangshu; Banerjee, Koushik; Ghosh, Siddhartha; Plis, Elena; Rodriguez, Jean Baptiste; Krishna, Sanjay; Grein, Christoph [Laboratory for Photonics and Magnetics, ECE Department, University of Illinois, 851 S. Morgan Street, Chicago, Illinois 60607 (United States); Center for High Technology Materials, University of New Mexico, 1313 Goddard Street SE, MSC04 2710 Albuquerque, New Mexico 87106 (United States); Microphysics Laboratory, Physics Department, University of Illinois, 845 W. Taylor Street, Chicago, Illinois 60607 (United States)

2007-12-10

391

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

PubMed

We discuss avalanche and finite-size fluctuations in a mesoscopic model to describe the shear plasticity of amorphous materials. Plastic deformation is assumed to occur through series of local reorganizations. Yield stress criteria are random while each plastic slip event induces a quadrupolar long-range elastic stress redistribution. The model is discretized on a regular square lattice. Shear plasticity can be studied in this context as a depinning dynamic phase transition. We show evidence for a scale-free distribution of avalanches P(s) ? S(-?) with a nontrivial exponent ??1.25 significantly different from the mean field result ?=1.5. Finite-size effects allow for a characterization of the scaling invariance of the yield stress fluctuations observed in small samples. We finally identify a population of precursors of plastic activity and characterize its spatial distribution. PMID:21867265

Talamali, Mehdi; Petäjä, Viljo; Vandembroucq, Damien; Roux, Stéphane

2011-07-29

392

Geiger-mode avalanche photodiodes for laser communications and laser radar  

Microsoft Academic Search

Arrays of photon-counting avalanche photodiodes (APDs) enable laser-communications and laser-radar receivers with unprecedented sensitivity at 1.06-mum wavelength. Near room temperature, the best detectors have: 50% photon detection efficiency, 30-kHz dark count rate, and a 1-mus reset time to avoid after-pulsing. Arrays with 64 elements were fabricated in the InGaAsP\\/InP materials system and were bump-bonded to a custom CMOS integrated circuit

B. F. Aull; J. C. Aversa; E. A. Dauler; J. P. Donnelly; E. K. Duerr; J. P. Frechette; J. E. Funk; S. H. Groves; P. I. Hopman; K. E. Jensen; Z.-L. Liau; J. M. Mahan; L. J. Mahoney; K. A. McIntosh; A. Napoleone; D. C. Oakley; E. J. Ouellette; D. C. Shaver; G. M. Smith; S. Verghese; C. J. Vineis

2006-01-01

393

A two-phase argon avalanche detector operated in a single electron counting mode  

Microsoft Academic Search

The performance of a two-phase Ar avalanche detector in a single electron counting mode was studied, with regard to potential application in coherent neutrino-nucleus scattering and dark matter search experiments. The detector comprised a 1cm thick liquid Ar layer and a triple-GEM multiplier operated in the saturated vapour above the liquid phase. Successful operation of the detector in single electron

A. Bondar; A. Buzulutskov; A. Grebenuk; D. Pavlyuchenko; R. Snopkov; Y. Tikhonov; V. A. Kudryavtsev; P. K. Lightfoot; N. J. C. Spooner

2007-01-01

394

SPICE macro model of a spryton with MOSFETs in the avalanche mode  

SciTech Connect

A SPICE macro model for a triggered vacuum gap, a sprytron, intended for use in rapid discharge circuits such as Exploding Bridge Wire (EBW) applications, is presented. Power MOSFETs in the avalanche mode are utilized as the active switching elements in the model. The macro model is compared for accuracy in predicting the time dependent switching current, switch resistance and voltage drop across the switch using several test circuits. Techniques for extracting model parameters are discussed.

Raney, C.W.

1994-08-01

395

Dark current degradation of near infrared avalanche photodiodes from proton irradiation  

Microsoft Academic Search

InGaAs and Ge avalanche photodiodes (APDs) are examined for the effects of 63-MeV protons on dark current. Dark current increases were large and similar to prior results for silicon APDs, despite the smaller size of InGaAs and Ge devices. Bulk dark current increases from displacement damage in the depletion regions appeared to be the dominant contributor to overall dark current

Heidi N. Becker; Allan H. Johnston

2004-01-01

396

Plasma Enhanced CVD Si3N4 Film Applied to InP Avalanche Photodiodes  

Microsoft Academic Search

Si3N4 films fabricated by plasma CVD process were examined for suitability as a preferential diffusion mask and antireflection coating for InP avalanche photodiodes. Planar type InP APDs with low leakage currents were obtained by applying the Si3N4 mask in Cd preferential diffusion at 480°C. The Si3N4 film on InP with an optimized thickness showed surface reflection reduction to as low

Nobuhiko Susa; Hiroshi Kanbe; Hiroaki Ando; Yoshiro Ohmachi

1980-01-01

397

Infrared light emission from GaAs MESFETs operating at avalanche breakdown conditions  

Microsoft Academic Search

Visible and infrared light emission bands arising from avalanche breakdown between gate and drain contacts of high-frequency high-power GaAs field effect transistors have been studied. The decay time of the mid-infrared (mid-IR) light (photon energies in the range 0.25–0.5 eV) is considerably less than 25 ms, while light with photon energies below 0.25 eV decays in a few seconds after

K S Zhuravlev; V A Kolosanov; A G Milekhin; V G Polovinkin; T S Shamirzaev; Yu N Rakov; Yu B Myakishev; J Fryar; E McGlynn; M O Henry

2004-01-01

398

Influence of traps on avalanche triggering during breakdown of gallium phosphide p-n junctions  

Microsoft Academic Search

Deep centers are found to strongly influence the statistical delay of microplasma breakdown in gallium phosphide red LEDs.\\u000a It is postulated that this effect is caused by Shockley electrons triggering an avalanche or by subthreshold mechanisms of\\u000a impact ionization. It is shown that the statistical delay in the microplasma breakdown can be used to determine the parameters\\u000a of the deep

S. V. Bulyarskii; Yu. N. Serezhkin; V. K. Ionychev

1999-01-01

399

Size distributions of shocks and static avalanches from the functional renormalization group  

NASA Astrophysics Data System (ADS)

Interfaces pinned by quenched disorder are often used to model jerky self-organized critical motion. We study static avalanches, or shocks, defined here as jumps between distinct global minima upon changing an external field. We show how the full statistics of these jumps is encoded in the functional-renormalization-group fixed-point functions. This allows us to obtain the size distribution P(S) of static avalanches in an expansion in the internal dimension d of the interface. Near and above d=4 this yields the mean-field distribution P(S)˜S-3/2e-S/4Sm , where Sm is a large-scale cutoff, in some cases calculable. Resumming all one-loop contributions, we find P(S)˜S-?exp(C(S/Sm)1/2-(B)/(4)(S/Sm)?) , where B , C , ? , and ? are obtained to first order in ?=4-d . Our result is consistent to O(?) with the relation ?=???2-(2)/(d+?) , where ? is the static roughness exponent, often conjectured to hold at depinning. Our calculation applies to all static universality classes, including random-bond, random-field, and random-periodic disorders. Extended to long-range elastic systems, it yields a different size distribution for the case of contact-line elasticity, with an exponent compatible with ?=2-(1)/(d+?) to O(?=2-d) . We discuss consequences for avalanches at depinning and for sandpile models, relations to Burgers turbulence and the possibility that the relation ?=?? be violated to higher loop order. Finally, we show that the avalanche-size distribution on a hyperplane of codimension one is in mean field (valid close to and above d=4 ) given by P(S)˜K1/3(S)/S , where K is the Bessel- K function, thus ?hyperplane=(4)/(3) .

Le Doussal, Pierre; Wiese, Kay Jörg

2009-05-01

400

Development of avalanche risk between 1950 and 2000 in the Municipality of Davos, Switzerland  

NASA Astrophysics Data System (ADS)

In recent years, risk assessment has become increasingly important for the protection of settlements against natural hazards because the public authorities have to economise their budgets and therefore to legitimate their investments. To quantify risk, information is needed on both, recurrence intervals of the potentially damaging natural processes and on the associated damage potential. In the past, high efforts were undertaken to assess the former, while the latter was almost ignored. The aim of this study was to determine the development of the avalanche risk in the inhabited areas of the municipality of Davos, canton of Grisons, Switzerland, for the period between 1950 and 2000. The extent of avalanche prone areas was quantified using the numerical avalanche model AVAL-1D and the current legal hazard maps. The damage potential was quantified by the number and reinstatement values of buildings and by the number of persons per building. It has been demonstrated that, contrary to the frequently expressed statement that the vulnerability of communities has increased, the risk for this settlement in fact decreased substantially. This can mainly be attributed to the realisation of mitigation measures, such as defence structures in avalanche starting zones. The only exception regarding the development of risk was in the category of residential buildings, were an increase in risk was already detectable at medium recurrence intervals. This is remarkable because methods of land use planning, such as hazard mapping, are intended to protect residential buildings from the impact of hazardous processes. However, general statements referring to a larger area (region, country) might be difficult to make, since small-scale disparities have a very important influence on the diversification of risk and risk management. Furthermore, it has to be emphasized that the results are highly dependent on the assumptions made in this study.

Fuchs, S.; Bründl, M.; Stötter, J.

2004-04-01

401

A sub-ns time-gated CMOS single photon avalanche diode detector for Raman spectroscopy  

Microsoft Academic Search

A time-gated single photon avalanche diode (SPAD) has been designed and fabricated in a standard high voltage 0.35 µm CMOS technology for Raman spectroscopy. The sub-ns time gating window is used to suppress the fluorescence background typical of Raman studies, and also to minimize the dark count rate in order to maximize the signal-to-noise ratio of the Raman signal. The

I. Nissinen; J. Nissinen; A. K. Lansman; L. Hallman; A. Kilpela; J. Kostamovaara; M. Kogler; M. Aikio; J. Tenhunen

2011-01-01

402

Monolithic active-quenching and active-reset circuit for single-photon avalanche detectors  

Microsoft Academic Search

A monolithic circuit has been designed for ac- tive-quenching and active-reset of single-photon avalanche diodes (SPADs), which operate above the breakdown voltage for detecting single photons. To the best of our knowledge, this is the first fully integrated circuit of this kind ever reported. It can operate with any available SPAD device, since it generates pulses high enough to quench

F. Zappa; A. Lotito; A. C. Giudice; S. Cova; M. Ghioni

2003-01-01

403

Study of avalanche photodiodes for soft X-ray detection below 20 keV  

Microsoft Academic Search

The performance of the large area reach-through avalanche photodiode (APD), manufactured by Hamamatsu Photonics, K.K. as a high resolution X-ray detector is presented. The mentioned APD has an area of 3mm ?, a fast time response for signal carrier collection and its thick depletion layer of 130?m shows a potential to be used as an effective X-ray absorber below 20keV.

Y. Yatsu; Y. Kuramoto; J. Kataoka; J. Kotoku; T. Saito; T. Ikagawa; R. Sato; N. Kawai; S. Kishimoto; K. Mori; T. Kamae; Y. Ishikawa; N. Kawabata

2006-01-01

404

Multiplication in separate absorption, grading, charge, and multiplication InP-InGaAs avalanche photodiodes  

Microsoft Academic Search

Planar separate absorption, grading, charge, and multiplication (SAGCM) InP-InGaAs avalanche photodiodes (APD's) are ideal for studying the multiplication (photogain) versus bias voltage (M-V) characteristics. In this paper, the M-V characteristics-in SAGCM InP-InGaAs APD's are investigated both experimentally and theoretically. The self-calibrated nature of M and the bias-voltage independent quantum efficiency make it possible to compare theory and experiment accurately in

C. L. F. Ma; M. J. Deen; L. E. Tarof

1995-01-01

405

Monte Carlo simulation of the effect of multiplication layer thickness in wide-bandwidth avalanche photodiodes  

Microsoft Academic Search

Summary form only given. The impact ionization process was studied in thin multiplication layers used in wide-bandwidth SAGM-APDs (separate absorption, grading, and multiplication avalanche photodiodes) using wave-vector-dependent threshold energies for impact ionization and a full-band Monte Carlo model. Results show that the number of ionizing collisions is reduced in thin layers, leading to an increase in the effective ?\\/? ratio

V. Chandramouli; C. M. Maziar; J. C. Campbell

1993-01-01

406

High gain-bandwidth-product avalanche photodiodes for multigigabit\\/s data rates  

Microsoft Academic Search

For long-wavelength (1.3 ?m and 1.5 ?m) high-bit-rate (?400 Mbit\\/s) lightwave systems the highest receiver sensitivities have been achieved with III-V compound avalanche photodiodes with separate absorption and multiplication regions (SAM-APDs). Initial APDs of this type exhibited poor frequency response owing to charge accumulation at the heterojunction interfaces. A significant improvement in the bandwidth was achieved by introducing a transition

J. C. Campbell

1987-01-01

407

High gain-bandwidth-product avalanche photodiodes for multigigabit\\/s data rates  

Microsoft Academic Search

For long-wavelength (1.3 mum and 1.5 mum) high-bit-rate (>~400 Mbit\\/s) lightwave systems the highest receiver sensitivities have been achieved with III-V compound avalanche photodiodes with separate absorption and multiplication regions (SAM-APDs). Initial APDs of this type exhibited poor frequency response owing to charge accumulation at the heterojunction interfaces. A significant improvement in the bandwidth was achieved by introducing a transition

J. C. Campbell

1987-01-01

408

Depth of interaction resolution measurements for a high resolution PET detector using position sensitive avalanche photodiodes  

Microsoft Academic Search

We explore dual-ended read out of LSO arrays with two position sensitive avalanche photodiodes (PSAPDs) as a high resolution, high efficiency depth-encoding detector for PET applications. Flood histograms, energy resolution and depth of interaction (DOI) resolution were measured for unpolished LSO arrays with individual crystal sizes of 1.0, 1.3 and 1.5 mm, and for a polished LSO array with 1.3

Yongfeng Yang; Purushottam A. Dokhale; Robert W. Silverman; Kanai S. Shah; Mickel A. McClish; Richard Farrell; Gerald Entine; Simon R. Cherry

2006-01-01

409

Further measurements of electron transmission and avalanche gain in narrow lead glass tubing  

SciTech Connect

Measurements of electron transmission and multiplication in lead glass tube arrays, in which a resistive field shaping electrode is provided by reduction of a surface layer of lead oxide, have been continued. The transmission losses have been successfully modeled allowing the true avalanche gains to be extracted. Gains of up to 100 have been observed. Applications as a photon shield in Cherenkov imaging detectors are discussed. 8 refs., 7 figs.

Fujieda, I.; Mulera, T.A.; Perez-Mendez, V.; del Guerra, A.

1985-10-01

410

STI-Bounded Single-Photon Avalanche Diode in a Deep-Submicrometer CMOS Technology  

Microsoft Academic Search

This letter presents a novel and compact CMOS Geiger-mode single-photon avalanche diode (SPAD) device with an efficient guard ring structure for preventing edge breakdown. The new guard ring can withstand considerably higher electric fields than existing structures, and results in pixels which are an order of magnitude smaller and offer a nine-fold increase in fill factor compared with existing SPADs.

Hod Finkelstein; Mark J. Hsu; Sadik C. Esener

2006-01-01

411

Performance trade-offs in single-photon avalanche diode miniaturization  

Microsoft Academic Search

Single-photon avalanche diodes (SPADs) provide photons' time of arrival for various applications. In recent years, attempts have been made to miniaturize SPADs in order to facilitate large-array integration and in order to reduce the dead time of the device. We investigate the benefits and drawbacks of device miniaturization by characterizing a new fast SPAD in a commercial 0.18 mum complementary

Hod Finkelstein; Mark J. Hsu; Sanja Zlatanovic; Sadik Esener

2007-01-01

412

A fast active quenching and recharging circuit for single-photon avalanche diodes  

Microsoft Academic Search

This paper presents a fast active quenching and recharging circuit (AQRC) for single-photon avalanches diodes (SPAD). The proposed circuit topology exhibits an overall quenching time lower than 1.5ns and quiescent power dissipation equal to about 5mW. Moreover, the circuit allows tunable excess voltage from 5V to 12V. The circuit was design by using the DIB12 BiCMOS 2 ?m technology supply

Rosario Mita; G. Palumbot; Giorgio Fallica

2005-01-01

413

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

Microsoft Academic Search

During 14–16 September 1988, a large intracaldera avalanche and an eruption of basaltic tephra and lava at Fernandina volcano, Galapagos, produced the most profound changes within the caldera since its collapse in 1968. A swarm of eight earthquakes (mb 4.7–5.5) occurred in a 14 h period on 24 February 1988 at Fernandina, and two more earthquakes of this size followed

William W. Chadwick; Tui Roy; Alfredo Carrasco

1991-01-01

414

Study of avalanche microchannel photodiodes for use in a scintillating fiber muon beam profile monitor  

NASA Astrophysics Data System (ADS)

We report a study on the use of avalanche microchannel photodiodes (AMPDs) with sensitive area 0.75×0.75mm, density of microchannels 10/mm, and maximum gain of 3×10, in a scintillating fiber muon beam detector. We show that an AMPD-based detector is efficient for 29 MeV/c muons at count rates up to several MHz and is operational in magnetic fields up to a few Tesla.

Stoykov, A.; Scheuermann, R.; Prokscha, T.; Buehler, Ch.; Sadygov, Z. Ya.

2006-11-01

415

High time resolution x-ray measurements with an avalanche photodiode detector  

Microsoft Academic Search

An avalanche photodiode (APD) detector has been developed for x-ray timing measurements with a subnanosecond time resolution. The performance of the APD detector was investigated with synchrotron x-ray beams in multi- and single-bunch runs at the Photon Factory (PF) ring. A time resolution of 0.28 ns (FWHM) and a peak-to-background ratio of more than 107 were obtained from the main

Shunji Kishimoto; Photon Factory

1992-01-01

416

X-ray fluorescence hologram data collection with a cooled avalanche photodiode  

Microsoft Academic Search

A high counting rate X-ray detector with an appropriate energy resolution is desired for high quality X-ray fluorescence hologram measurements because a holographic pattern is detected as extremely small intensity variations of X-ray fluorescence on a large intensity background. A cooled avalanche photodiode (APD), which has about 10% energy resolution and is designed for a high counting rate, fits the

Kouichi Hayashi; Yukio Takahashi; Ei-Ichiro Matsubara; Shunji Kishimoto; Takeharu Mori; Masahiko Tanaka

2002-01-01

417

Recent developments in the avalanche photodiode x-ray detector for timing and fast counting measurements  

Microsoft Academic Search

An avalanche photodiode (APD) detector using a new silicon device has been developed for x-ray timing measurements. The device, Model No. S5343 (Hamamatsu Photonics), has an excellent time resolution of 0.10 ns and has only a short tail, or a full width of 1.41 ns at 10?5 maximum, in the response function for the time spectrum. Measurements of the purity

Shunji Kishimoto

1995-01-01

418

Avalanche multiplication in AlGaN based solar-blind photodetectors  

SciTech Connect

Avalanche multiplication has been observed in solar-blind AlGaN-based p-i-n photodiodes. Upon ultraviolet illumination, the optical gain shows a soft breakdown starting at relatively low electric fields, eventually saturating without showing a Geiger mode breakdown. The devices achieve a maximum optical gain of 700 at a reverse bias of 60 V. By modeling the device, it is found that this corresponds to an electric-field strength of 1.7 MV/0008.

McClintock, R.; Yasan, A.; Minder, K.; Kung, P.; Razeghi, M. [Center for Quantum Devices, Department of Electrical Engineering and Computer Science, Northwestern University, Evanston, Illinois 60208 (United States)

2005-12-12

419

Negative resistance in p-n junctions under avalanche breakdown conditions, part I  

Microsoft Academic Search

A one-dimensional, small-signal analysis of the space-charge region of a p-n junction in which avalanche occurs uniformly is presented. The impedance is found to have a negative real part. The impedance is Well represented by a parallel connection of the depletion layer capacitance, an inductance, and a negative resistance. The admittance of the latter two is proportional to the bias

T. Misawa

1966-01-01

420

Development and Calibration of a Preliminary Cellular Automata Model for Snow Avalanches  

Microsoft Academic Search

\\u000a Numerical modelling is a major challenge in the prevention of risks related to the occurrence of catastrophic phenomena. A\\u000a Cellular Automata methodology was developed for modelling large scale (extended for kilometres) dangerous surface flows of\\u000a different nature such as lava flows, pyroclastic flows, debris flows, rock avalanches, etc. This paper presents VALANCA, a\\u000a first version of a Cellular Automata model,

Maria Vittoria Avolio; Alessia Errera; Valeria Lupiano; Paolo Mazzanti; Salvatore Di Gregorio

2010-01-01

421

Charge carrier avalanche multiplication in high-voltage diodes triggered by ionizing radiation  

Microsoft Academic Search

Non-destructive strong carrier avalanche multiplication reaching levels up to four orders of magnitude as compared to the initially deposited charge was investigated in high-voltage diodes for a variety of initiating high-energy ions and for high-energy protons. Current levels of several amperes were detected with the current flowing only over time periods up to 50 ns. This indicates that no internal

Gerald Soelkner; Peter Voss; Winfried Kaindl; Gerhard Wachutka; K. H. Maier; H.-W. Becker

2000-01-01

422

Experimental diagnostics of an avalanche discharge excited HgBr\\/HgBr2 dissociation laser  

Microsoft Academic Search

The effects of discharge power and nitrogen partial pressure on small signal gain, fluorescence, and discharge driver efficiency have been investigated for an avalanche discharge Ne\\/N2\\/HgBr2 laser. This work helps clarify the role of nitrogen in these lasers, as well as presenting the first experimental evidence for bottlenecking in the HgBr laser. An optimum intrinsic laser efficiency of 2.0 percent

T. M. Shay; D. Gookin; M. C. Jordan; F. E. Hanson; E. J. Schimitschek

1985-01-01

423

Snow avalanche speed determination using wireless accelerometers at the Weissfluhjoch Snow Chute  

NASA Astrophysics Data System (ADS)

Experiments using a network of wireless accelerometers were carried out at the snow chute operated by the SLF at Weissfluhjoch (Switzerland) with an attempt to study internal dynamics of flowing snow. Several 2D and 3D wireless accelerometers placed in the starting zone prior to the experiments travelled within the flow when the avalanche was released. The characteristics of the sensors (size and density) allow the units to evolve like active particle tracers. Acceleration readings obtained at 85 Hz in 3 different experiments were analysed. The analysis methods used include Empirical Mode Decomposition and Kalman Filtering techniques to obtain reliable speed and position measurements from the single 2D and 3D acceleration measurements. The results are in agreement with those obtained from independent speed measurements from optical sensors and Video Images. The results although preliminary are promising. The information extracted could provide valuable information related to the internal dynamics of the avalanche. Small scale chutes are the ideal scenario for this type of experiment and new experiments using improved sensors are envisaged. Moreover, the potential of wireless technologies and wireless sensors to study natural phenomena such snow avalanches has been demonstrated. JAVA SUN Spot Project and The Spanish Ministerio de Educación y Ciencia Projects: CGL2006-06596/BTE and HU-2007-11 supported this research.

Vilajosana, I.; Schaefer, M.; Llosa, J.; Suriñach, E.; Marquès, J. M.; Kern, M. A.; Khazaradze, G.

2009-04-01

424

Laser Induced Avalanche Ionization in Gases with REMPI or Femtosecond Pre-Ionization  

NASA Astrophysics Data System (ADS)

Results of a theoretical study regarding the minimal requirements for the first pre-ionizing pulse to initiate avalanche ionization and essential gas heating by the second pulse are presented. The problem of minimal gas component density for the REMPI (Resonanse Enhanced Multi-Photon Ionization) pre-ionization with subsequent avalanche ionization in a bulk gas is explored on the basis of the theoretical model developed for the Ar:Xe mixture, where during the initial portion of the pulse (3+1) REMPI of Ar atoms starts the ionization, which subsequently continues to grow with an avalanche in the buffer Xe gas [1]. Note, that this method of plasma generation at intensities much lower than required for breakdown is very close to one considered in ref. [2] with femtosecond pre-ionizing laser pulse. Scaling parameters for gas mixtures, laser pulse shape, focusing and frequency are studied. Possible applications for improving of the detection sensitivity of Radar REMPI diagnostic technique and laser initiated ignition are discussed. [4pt] 1. M.N. Shneider, Z.Zhang, R.B. Miles, J.Appl.Phys. 104, 023302 (2008); 2. Z. Henis, G. Milikh, K. Papadopoulos, A. Zigler, J.Appl.Phys. 103, 103111 (2008)

Shneider, Mikhail; Miles, Richard

2009-10-01

425

Influence of roughness bottom on the dynamics of a buoyant cloud : application to a powder avalanche  

NASA Astrophysics Data System (ADS)

A powder avalanche is referred to as a turbulent flow of snow particles in air. In the past such avalanches have been modelled by buoyant cloud in a watertank: buoyant clouds flow along an inclined plane from a small immersed tank with a release gate (injection is of short duration). The powder avalanches are simulated by a heavy fluid (salt water + colorant or kaolin) which is dispersing in a lighter one. Such experiments allow studies for the influence of roughness bottoms on the dynamics of a buoyant clouds. The authors studied the flows of buoyant clouds on an uniform slope of 20° with different roughness: smooth PVC, abrasive paper, bottom covered with glued particles of PMMA or with glued glass beads of different sizes arranged in a compact way. The released volume varies between 2 to 4 liters and the density of salted water is 1.2. Two cameras are used to obtain the height together with the front velocity. Inside the study area the front velocity is approximately constant and the height of the clouds varies linearly with the distance from the released gate as usually observed in previous experiments. So for each roughness a front velocity and height growth can be defined. It was shown from the experiments that: As the bottom increases in roughness, the front speed increases and the height growth decreases. Nevertheless the height of glued elements does not seem to be the most appropriate parameter to characterize the roughness.

Brossard, D.; Naaim-Bouvet, F.; Naaim, M.; Caccamo, P.

2009-04-01

426

Statistics of avalanches with relaxation and Barkhausen noise: A solvable model  

NASA Astrophysics Data System (ADS)

We study a generalization of the Alessandro-Beatrice-Bertotti-Montorsi (ABBM) model of a particle in a Brownian force landscape, including retardation effects. We show that under monotonous driving the particle moves forward at all times, as it does in absence of retardation (Middleton's theorem). This remarkable property allows us to develop an analytical treatment. The model with an exponentially decaying memory kernel is realized in Barkhausen experiments with eddy-current relaxation and has previously been shown numerically to account for the experimentally observed asymmetry of Barkhausen pulse shapes. We elucidate another qualitatively new feature: the breakup of each avalanche of the standard ABBM model into a cluster of subavalanches, sharply delimited for slow relaxation under quasistatic driving. These conditions are typical for earthquake dynamics. With relaxation and aftershock clustering, the present model includes important ingredients for an effective description of earthquakes. We analyze quantitatively the limits of slow and fast relaxation for stationary driving with velocity v>0. The v-dependent power-law exponent for small velocities, and the critical driving velocity at which the particle velocity never vanishes, are modified. We also analyze nonstationary avalanches following a step in the driving magnetic field. Analytically, we obtain the mean avalanche shape at fixed size, the duration distribution of the first subavalanche, and the time dependence of the mean velocity. We propose to study these observables in experiments, allowing a direct measurement of the shape of the memory kernel and tracing eddy current relaxation in Barkhausen noise.

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

2013-09-01

427

Local cortical circuit model inferred from power-law distributed neuronal avalanches.  

PubMed

How cortical neurons process information crucially depends on how their local circuits are organized. Spontaneous synchronous neuronal activity propagating through neocortical slices displays highly diverse, yet repeatable, activity patterns called "neuronal avalanches". They obey power-law distributions of the event sizes and lifetimes, presumably reflecting the structure of local circuits developed in slice cultures. However, the explicit network structure underlying the power-law statistics remains unclear. Here, we present a neuronal network model of pyramidal and inhibitory neurons that enables stable propagation of avalanche-like spiking activity. We demonstrate a neuronal wiring rule that governs the formation of mutually overlapping cell assemblies during the development of this network. The resultant network comprises a mixture of feedforward chains and recurrent circuits, in which neuronal avalanches are stable if the former structure is predominant. Interestingly, the recurrent synaptic connections formed by this wiring rule limit the number of cell assemblies embeddable in a neuron pool of given size. We investigate how the resultant power laws depend on the details of the cell-assembly formation as well as on the inhibitory feedback. Our model suggests that local cortical circuits may have a more complex topological design than has previously been thought. PMID:17226088

Teramae, Jun-Nosuke; Fukai, Tomoki

2007-01-17

428

Avalanche of flux jumps in polycrystalline MgB2 superconductor  

NASA Astrophysics Data System (ADS)

Dc magnetization studies were carried out on a polycrystalline MgB2 superconductor, which was synthesized at 750 °C in Fe tube encapsulation under a vacuum of 10-5 Torr. Zero resistances at H=0 and 8 T are obtained at 38 and 22 K, respectively. The material possesses a sharp diamagnetic transition in the zero-field-cooled branch, whereas the field-cooled branch exhibits the paramagnetic-Meissner-effect-like phenomenon below Tc, indicating strong pinning in this compound. The critical current density at 20 K and 2 T, estimated by the Bean model is higher than 105 A/cm2. Due to the strong pinning, we observed the presence of flux avalanches below H=2 T at temperatures below 20 K. The magnetization M(H) grows (as usual) slowly with H and falls sharply to near zero moment value, and further grows again in a common way. The flux avalanches were seen quite symmetric in both increasing/decreasing the field in all four quadrants of the M(H) loops. The dynamics behavior of sinusoidal-like symmetric reproducible flux avalanches is discussed.

Felner, I.; Awana, V. P. S.; Mudgel, Monika; Kishan, H.

2007-05-01

429

Hysteresis, avalanches, and disorder-induced critical scaling: A renormalization-group approach  

SciTech Connect

Hysteresis loops are often seen in experiments at first-order phase transformations, when the system goes out of equilibrium. They may have a macroscopic jump (roughly as in the supercooling of liquids) or they may be smoothly varying (as seen in most magnets). We have studied the nonequilibrium zero-temperature random-field Ising-model as a model for hysteretic behavior at first-order phase transformations. As disorder is added, one finds a transition where the jump in the magnetization (corresponding to an infinite avalanche) decreases to zero. At this transition we find a diverging length scale, power-law distributions of noise (avalanches), and universal behavior. We expand the critical exponents about mean-field theory in 6{minus}{epsilon} dimensions. Using a mapping to the pure Ising model, we Borel sum the 6{minus}{epsilon} expansion to {ital O}({epsilon}{sup 5}) for the correlation length exponent. We have developed a method for directly calculating avalanche distribution exponents, which we perform to {ital O}({epsilon}). Our analytical predictions agree with numerical exponents in two, three, four, and five dimensions [Perkovi{acute c} {ital et} {ital al}., Phys. Rev. Lett. {bold 75}, 4528 (1995)]. {copyright} {ital 1996 The American Physical Society.}

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

1996-06-01

430

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

NASA Astrophysics Data System (ADS)

Sandpile-based models have successfully shed light on key features of nonlinear relaxational processes in nature, particularly the occurrence of fat-tailed magnitude distributions and exponential return times, from simple local stress redistributions. In this work, we extend the existing sandpile paradigm into an inter-sandpile cascade, wherein the avalanches emanating from a uniformly-driven sandpile (first layer) is used to trigger the next (second layer), and so on, in a successive fashion. Statistical characterizations reveal that avalanche size distributions evolve from a power-law p(S)?S?1.3 for the first layer to gamma distributions p(S)?S?exp(?S/S0) for layers far away from the uniformly driven sandpile. The resulting avalanche size statistics is found to be associated with the corresponding waiting time distribution, as explained in an accompanying analytic formulation. Interestingly, both the numerical and analytic models show good agreement with actual inventories of non-uniformly driven events in nature.

Batac, Rene; Longjas, Anthony; Monterola, Christopher

2012-02-01

431

Radio frequency emissions from a runaway electron avalanche model compared with intense, transient signals from thunderstorms  

NASA Astrophysics Data System (ADS)

We present a one-dimensional model of a runaway electron avalanche in a thunderstorm electric field. Previous simulations have calculated the ionization rates and energy distribution functions for runaway electrons, for various atmospheric values of E/p, through the solution of the modified relativistic Boltzmann equation. We use the field- and pressure-dependent ionization rates in a hydrodynamic macroscopic treatment. The runaway electron avalanche modeled here includes the production of runaway and low-energy electrons, electric field relaxation, electron attachment, and runaway electron loss. The model ambient electric field is established from two disks of charge with a sinusoidally spatially varying charge density of 9 nC/m3 peak amplitude. The peak ambient electric field from this configuration is 538 kV/m at 5 km. The numerically calculated radio frequency radiation exhibits relativistic effects. We hypothesize that runaway electron avalanches are sources of intense HF/VHF impulses radiated from within electrified clouds. The results from this case study are compared with ground-based and FORTE satellite observations of HF and VHF radiation observed during the rise portion of narrow bipolar pulses (NBP). Given the specified rates and ambient environment, the radiation electric field HF and VHF spectra covering 3-25, 26-48, and 60-66 MHz are in agreement with observations for limited angular ranges. The modeled peak radiation electric field in the time domain is just below one standard deviation from the observed mean for NBPs.

Tierney, Heidi E.; Roussel-Dupré, Robert A.; Symbalisty, Eugene M. D.; Beasley, William H.

2005-06-01

432

Measurement results from an avalanche amplifying pnCCD for single photon imaging  

NASA Astrophysics Data System (ADS)

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 from the CCDs’ depleted buried channel. The pixel-structure has been derived from pnCCDs and was optimized for lowest leakage current and for compatibility with the avalanche structures. All advantages of the pnCCDs are maintained, including high quantum efficiency (between 80% and 100%), high frame rate (up to 1000 frames/s) and low leakage current. Possible applications are in the field of High Time Resolution Astrophysics (HTRA). There, fast imaging of faint objects in the visible, such as, e.g. close binary stars or fast rotating neutron stars, requires single photon sensitivity and high frame rates. We present results from proof-of-principle tests carried out on first laboratory prototypes of such devices.

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

2010-12-01

433

Monitoring of full-depth avalanches contaminated by soil and rocks - their origin and consequences, (Krkonose/Karkonosze Mts.- High Sudetes)  

NASA Astrophysics Data System (ADS)

Monitoring of full-depth avalanches contaminated by soil and rocks - their origin and consequences, (Krkonose/Karkonosze Mts.- High Sudetes) Milena Kocianova Valerian Spusta, Irena Spatenkova, Alena Tondrova, Igor Jan Dvorak, Vlastimil Pilous Krkonoše National Park Administration, Dobrovskeho 3, 543 01 Vrchlabi, Czech republic Monitoring of snow avalanches is provided in Czech part of the Krkonose/Karkonosze Mountains since the winter season 1961/62. The full-depth avalanches contaminated by soil and rocks represent about 4% of the monitored number. There are six bigger avalanches of this type recorded during last 10 years. The areas of snutched weathering mantles reached at about 3000 - 23 000 m2 per individual avalanche track. In deposit zones the areas from 2600 to 18700 m2 were covered by soil, sods and small rock fragments whose volume ranged from about 130 to 880 m3 per individual avalanche track. The volume of large rock fragments in one concrete track was counted up to 144 m3. The great influence of full depth avalanches on relief and slope development is evident. Based on monitoring the speed of snutched areas overgrowing by vegetation and on comparison of space design of plant communities out off and on the avalanche tracks respectively, it would be possible to estimate the period of such bigger events. Very important thing is that four avalanche events were triggered by water, which infiltrated the base of snowpack within upper or central parts of avalanche slopes. Water origin was probably either a) in mires on adjacent summit plateau (ground water flown on inclined bedrock layers to the avalanche slopes) and b) in thawing water of snow patches situated on the cryoplanation terraces above the avalanche slopes. More detailed study of these phenomena is needed in the future.

Kocianova, M.

2009-04-01

434

GaN ultraviolet avalanche photodiodes with optical gain greater than 1000 grown on GaN substrates by metal-organic chemical vapor deposition  

Microsoft Academic Search

We report the performance of GaN p-i-n ultraviolet avalanche photodiodes grown on bulk GaN substrates by metal-organic chemical vapor deposition. The low dislocation density in the devices enables low reverse-bias dark currents prior to avalanche breakdown for ~30 mum diameter mesa photodetectors. The photoresponse is relatively independent of the bias voltage prior to the onset of avalanche gain which occurs

J. B. Limb; D. Yoo; J. H. Ryou; W. Lee; S. C. Shen; R. D. Dupuis; M. L. Reed; C. J. Collins; M. Wraback; D. Hanser; E. Preble; N. M. Williams; K. Evans

2006-01-01

435

Jerky elasticity: Avalanches and the martensitic transition in Cu74.08Al23.13Be2.79 shape-memory alloy  

NASA Astrophysics Data System (ADS)

Jerky elasticity was observed by dynamical mechanical analyzer measurements in a single crystal of the shape memory alloy Cu74.08Al23.13Be2.79. Jerks appear as spikes in the dissipation of the elastic response function and relate to the formation of avalanches during the transformation between the austenite and the martensite phase. The statistics of the avalanches follows the predictions of avalanche criticality P(E)~E-? where P(E) is the probability of finding an avalanche with the energy E. This result reproduces, within experimental uncertainties, previous findings by acoustic emission techniques.

Salje, Ekhard K. H.; Koppensteiner, Johannes; Reinecker, Marius; Schranz, Wilfried; Planes, Antoni

2009-12-01

436

Numerical modeling of debris avalanches at Nevado de Toluca (Mexico): implications for hazard evaluation and mapping  

NASA Astrophysics Data System (ADS)

The present study concerns the numerical modeling of debris avalanches on the Nevado de Toluca Volcano (Mexico) using TITAN2D simulation software, and its application to create hazard maps. Nevado de Toluca is an andesitic to dacitic stratovolcano of Late Pliocene-Holocene age, located in central México near to the cities of Toluca and México City; its past activity has endangered an area with more than 25 million inhabitants today. The present work is based upon the data collected during extensive field work finalized to the realization of the geological map of Nevado de Toluca at 1:25,000 scale. The activity of the volcano has developed from 2.6 Ma until 10.5 ka with both effusive and explosive events; the Nevado de Toluca has presented long phases of inactivity characterized by erosion and emplacement of debris flow and debris avalanche deposits on its flanks. The largest epiclastic events in the history of the volcano are wide debris flows and debris avalanches, occurred between 1 Ma and 50 ka, during a prolonged hiatus in eruptive activity. Other minor events happened mainly during the most recent volcanic activity (less than 50 ka), characterized by magmatic and tectonic-induced instability of the summit dome complex. According to the most recent tectonic analysis, the active transtensive kinematics of the E-W Tenango Fault System had a strong influence on the preferential directions of the last three documented lateral collapses, which generated the Arroyo Grande and Zaguàn debris avalanche deposits towards E and Nopal debris avalanche deposit towards W. The analysis of the data collected during the field work permitted to create a detailed GIS database of the spatial and temporal distribution of debris avalanche deposits on the volcano. Flow models, that have been performed with the software TITAN2D, developed by GMFG at Buffalo, were entirely based upon the information stored in the geological database. The modeling software is built upon equations solved by a parallel and adaptive mesh, that can concentrate computing power in region of special interest. First of all, simulations of known past events, were compared with the geological data validating the effectiveness of the method. Afterwards, numerous simulations have been executed varying input parameters as friction angles, starting point and initial volume, in order to obtain a global perspective over the possible expected debris avalanche scenarios. The input parameters were selected considering the geological, structural and topographic factors controlling instability of the volcanic cone, especially in case of renewed eruptive activity. The interoperability between TITAN2D and GIS softwares permitted to draw a semi-quantitative hazard map by crossing simulation outputs with the distribution of deposits generated by past episodes of instability, mapped during the field work.

Grieco, F.; Capra, L.; Groppelli, G.; Norini, G.

2007-05-01

437

InAlAs-InGaAs based avalanche photodiodes for next generation eye-safe optical receivers  

NASA Astrophysics Data System (ADS)

This paper presents results of three research and development efforts on the subject of avalanche photodiodes with InGaAs absorbers and InAlAs multiplication layers. The first portion of the paper presents results on 256x256 arrays of InAlAs-InGaAs APDs. These spanned more than 1.5 cm x 1.5 cm, had breakdown voltage variation of less than 2.5 volts and a dark current range between 1.5 and 3.5 nA at a gain of 10. The second portion of the paper presents single photon detection results of a receiver with a 50 micron aperture avalanche photodiode biased into sub-Geiger mode and a Maxim MAX3658 transimpedance amplifier. At temperatures of 200K and average avalanche gains approaching 1000 single photon detection efficiencies greater than 5% were observed with dark count rates of less than 500 kHz. At 175 K detection rates were as high as 14%. Finally, in the third portion of this paper, performance results of a novel impact ionization engineered InGaAs-InAlAs based avalanche photodiode are presented showing excess noise values lower than any previously published InGaAs based avalanche photodiode.

Clark, William R.; Vaccaro, Kenneth; Waters, William D.

2007-10-01

438

Reinventing germanium avalanche photodetector for nanophotonic on-chip optical interconnects.  

PubMed

Integration of optical communication circuits directly into high-performance microprocessor chips can enable extremely powerful computer systems. A germanium photodetector that can be monolithically integrated with silicon transistor technology is viewed as a key element in connecting chip components with infrared optical signals. Such a device should have the capability to detect very-low-power optical signals at very high speed. Although germanium avalanche photodetectors (APD) using charge amplification close to avalanche breakdown can achieve high gain and thus detect low-power optical signals, they are universally considered to suffer from an intolerably high amplification noise characteristic of germanium. High gain with low excess noise has been demonstrated using a germanium layer only for detection of light signals, with amplification taking place in a separate silicon layer. However, the relatively thick semiconductor layers that are required in such structures limit APD speeds to about 10 GHz, and require excessively high bias voltages of around 25 V (ref. 12). Here we show how nanophotonic and nanoelectronic engineering aimed at shaping optical and electrical fields on the nanometre scale within a germanium amplification layer can overcome the otherwise intrinsically poor noise characteristics, achieving a dramatic reduction of amplification noise by over 70 per cent. By generating strongly non-uniform electric fields, the region of impact ionization in germanium is reduced to just 30 nm, allowing the device to benefit from the noise reduction effects that arise at these small distances. Furthermore, the smallness of the APDs means that a bias voltage of only 1.5 V is required to achieve an avalanche gain of over 10 dB with operational speeds exceeding 30 GHz. Monolithic integration of such a device into computer chips might enable applications beyond computer optical interconnects-in telecommunications, secure quantum key distribution, and subthreshold ultralow-power transistors. PMID:20203606

Assefa, Solomon; Xia, Fengnian; Vlasov, Yurii A

2010-03-01

439

Powder avalanche and catching dam interaction : influence of upstream dam slope ?  

NASA Astrophysics Data System (ADS)

The influence of an obstacle on the dynamics of a finite-volume density current modelling a