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1

Avalanches!  

NSDL National Science Digital Library

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

Payne, Laura X.

1999-01-01

2

Avalanche!  

NSDL National Science Digital Library

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

3

Avalanche  

NSDL National Science Digital Library

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

Rathjen, Don

2005-01-01

4

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 Weather Forecasting  

NSDL National Science Digital Library

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

Comet

2010-09-30

6

Avalanche speed in thin avalanche photodiodes  

NASA Astrophysics Data System (ADS)

The duration of the avalanche multiplication process in thin GaAs avalanche photodiodes is investigated using a full band Monte Carlo (FBMC) model. The results are compared with those of a simple random path length (RPL) model which makes the conventional assumptions of a displaced exponential for the ionization path length probability distribution function and that carriers always travel at their saturated drift velocities. We find that the avalanche duration calculated by the RPL model is almost twice of that predicted by the FBMC model, although the constant drift velocities used in the former model are estimated using the latter. The faster response predicted by FBMC model arises partly from the reduced dead space but mainly from the velocity overshoot of ionizing carriers. While the feedback multiplication processes forced by the effects of dead space extend the avalanche duration in short structures, the effects of velocity overshoot in the realistic model more than compensate, significantly improving multiplication bandwidth.

Ong, D. S.; Rees, G. J.; David, J. P. R.

2003-04-01

7

Avalanche!: Slip Sliding Away  

NSDL National Science Digital Library

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

8

Reuyl Crater Dust Avalanches  

NASA Technical Reports Server (NTRS)

(Released 13 May 2002) The Science The rugged, arcuate rim of the 90 km crater Reuyl dominates this THEMIS image. Reuyl crater is at the southern edge of a region known to be blanketed in thick dust based on its high albedo (brightness) and low thermal inertia values. This thick mantle of dust creates the appearance of snow covered mountains in the image. Like snow accumulation on Earth, Martian dust can become so thick that it eventually slides down the face of steep slopes, creating runaway avalanches of dust. In the center of this image about 1/3 of the way down is evidence of this phenomenon. A few dozen dark streaks can be seen on the bright, sunlit slopes of the crater rim. The narrow streaks extend downslope following the local topography in a manner very similar to snow avalanches on Earth. But unlike their terrestrial counterparts, no accumulation occurs at the bottom. The dust particles are so small that they are easily launched into the thin atmosphere where they remain suspended and ultimately blow away. The apparent darkness of the avalanche scars is due to the presence of relatively dark underlying material that becomes exposed following the passage of the avalanche. Over time, new dust deposition occurs, brightening the scars until they fade into the background. Although dark slope streaks had been observed in Viking mission images, a clear understanding of this dynamic phenomenon wasn't possible until the much higher resolution images from the Mars Global Surveyor MOC camera revealed the details. MOC images also showed that new avalanches have occurred during the time MGS has been in orbit. THEMIS images will allow additional mapping of their distribution and frequency, contributing new insights about Martian dust avalanches. The Story The stiff peaks in this image might remind you of the Alps here on Earth, but they really outline the choppy edge of a large Martian crater over 50 miles wide (seen in the context image at right). While these aren't the Alps, you will find quite a few avalanches. Avalanches of dust, however, not snow. Martian dust can become so thick in this area that it eventually slides down the steep slopes, creating runaway avalanches of dust. No dedicated, Swiss-like avalanche rescue teams would be needed much on Mars, however. Unlike snow, the dust doesn't pile up and accumulate at the bottom. Instead, dust particles are so small that they get launched into the atmosphere where they remain suspended until . . . poof! They are blown away and distributed lightly elsewhere. For evidence of past avalanches, check out the dark streaks running down the bright, sunlit slopes (western side of the peaks about 1/3 of the way down the image). These avalanche scars are dark because the underlying surface is not as bright as the removed dust. Eventually, new dust will settle over these scars, and the streaks will brighten until they fade into the background. The neat thing is that we'll be able to see all of these changes happening over time. Our current two Mars orbiters (called Mars Global Surveyor and 2001 Mars Odyssey) are showing that avalanche action is happening right now, all of the time on Mars. For example, the camera on Mars Global Surveyor has already taken pictures of the Martian surface in some areas that showed no avalanches - the first time the picture was snapped, that is. The next time around, the camera took a picture of the same area, only voila! New streaks, meaning new avalanches! That's why it can be so exciting to look at the Martian landscape over time to see how it changes. The THEMIS camera on Odyssey will continue to map out the places where the avalanches occur and how often. This information will really help scientists understand how dust is works to shape the terrain and to influence the Martian climate as it constantly swings into the atmosphere, falls down to the ground, and rises back up again. Stay tuned to see if you too can pick out the changes over time!

2002-01-01

9

Laboratory singing sand avalanches.  

PubMed

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

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

2010-02-01

10

Avalanches in UGe 2  

NASA Astrophysics Data System (ADS)

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

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

2004-05-01

11

Technological advances in avalanche survival.  

PubMed

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

Radwin, Martin I; Grissom, Colin K

2002-01-01

12

SiC Avalanche Photodiodes  

Microsoft Academic Search

In summary, 4H- and 6HSiC avalanche photodiodes have been fabricated and characterized. These APDs exhibit low dark current, high uniform gain, low excess noise, and external quantum efficiency in excess of 50%

Joe C. Campbell; Xiangyi Guo; Han-Din Liu; Dion McIntosh

2006-01-01

13

Recent advances in avalanche photodiodes  

Microsoft Academic Search

In this paper we review recent advancements in the performance of avalanche photodiodes (APDs). APDs designed for fiber optic receivers, low-level ultra-violet detection, and Geiger-mode single photon detectors will be discussed.

J. C. Campbell

2008-01-01

14

Kinetic description of avalanching systems.  

PubMed

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

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

2005-09-01

15

Avalanche Collapse of Interdependent Network  

E-print Network

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

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

2012-07-02

16

AVALANCHE PROTECTION FOR ROSA KHUTOR  

Microsoft Academic Search

2 RDM Resort Development and Management Consultants ABSTRACT: The 2014 Winter Olympics have been awarded to Sochi, Russia. The Alpine skiing venue will be the new ski area now being built at Rosa Khutor, above the village of Krasnaya Polyana. Planning and implementation of the avalanche protection program is an important part of the development given that the area is

Chris Stethem; Roger McCarthy

2008-01-01

17

SiC avalanche photodiodes  

Microsoft Academic Search

Ultraviolet detectors are becoming increasingly important in medical, military, and environmental applications, including biological agent detection and non-line-of-sight (NLOS) communications. SiC avalanche photodiodes (APDs) are an attractive candidate for those applications that place a premium on detectors that are compact, rugged, and inexpensive. This paper presents an overview of 4H-SiC APDs.

J. C. Campbell; Han-Din Liu; D. Mcintosh; Xiaogang Bai

2007-01-01

18

Computational snow avalanche simulation in forested terrain  

NASA Astrophysics Data System (ADS)

Two-dimensional avalanche simulation software operating in three-dimensional terrain is widely used for hazard zoning and engineering to predict runout distances and impact pressures of snow avalanche events. Mountain forests are an effective biological protection measure against avalanches; however, the protective capacity of forests to decelerate or even to stop avalanches that start within forested areas or directly above the treeline is seldom considered in this context. In particular, runout distances of small- to medium-scale avalanches are strongly influenced by the structural conditions of forests in the avalanche path. We present an evaluation and operationalization of a novel detrainment function implemented in the avalanche simulation software RAMMS for avalanche simulation in forested terrain. The new approach accounts for the effect of forests in the avalanche path by detraining mass, which leads to a deceleration and runout shortening of avalanches. The relationship is parameterized by the detrainment coefficient K [kg m-1 s-2] accounting for differing forest characteristics. We varied K when simulating 40 well-documented small- to medium-scale avalanches, which were released in and ran through forests of the Swiss Alps. Analyzing and comparing observed and simulated runout distances statistically revealed values for K suitable to simulate the combined influence of four forest characteristics on avalanche runout: forest type, crown closure, vertical structure and surface cover, for example, values for K were higher for dense spruce and mixed spruce-beech forests compared to open larch forests at the upper treeline. Considering forest structural conditions within avalanche simulations will improve current applications for avalanche simulation tools in mountain forest and natural hazard management.

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

2014-08-01

19

Recent advances in avalanche photodiodes  

Microsoft Academic Search

The development of high-performance optical receivers has been a primary driving force for research on III-V compound avalanche photodiodes (APDs). The evolution of fiber optic systems toward higher bit rates has pushed APD performance toward higher bandwidths, lower noise, and higher gain-bandwidth products. Utilizing thin multiplication regions has reduced the excess noise. Further noise reduction has been demonstrated by incorporating

Joe C. Campbell; Stephane Demiguel; Feng Ma; Ariane Beck; Xiangyi Guo; Shuling Wang; Xiaoguang Zheng; Xiaowei Li; Jeffrey D. Beck; Michael A. Kinch; Andrew Huntington; Larry A. Coldren; Jean Decobert; Nadine Tscherptner

2004-01-01

20

GIS-aided avalanche warning in Norway  

NASA Astrophysics Data System (ADS)

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

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

2014-05-01

21

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

NASA Astrophysics Data System (ADS)

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

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

2014-05-01

22

On the temporal organization of neuronal avalanches  

PubMed Central

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

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

2014-01-01

23

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

24

Dynamic avalanche in bipolar power devices  

Microsoft Academic Search

In bipolar power devices, remaining plasma is extracted during turn-off. In high-voltage devices, even at moderate conditions dynamic avalanche caused by the free carriers appears. Strong dynamic avalanche leads to filament formation. The effect must not be destructive as long as the filaments can move. Effects which are common in the bipolar devices GTO, GCT, IGBT and power diode are

Josef Lutz; Roman Baburske

25

Avalanche in Adhesion at Metal Interfaces  

NASA Technical Reports Server (NTRS)

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

Banerjea, Amitava; Good, Brian S.

1994-01-01

26

Frontal Dynamics of Powder Snow Avalanches  

NASA Astrophysics Data System (ADS)

We model the dynamics of the head of dilute powder snow avalanches sustained by a massive frontal blow-out, arising as a weakly cohesive snow cover is fluidized by the very pore pressure gradients that the avalanche induces within the snow pack. Such material eruption just behind the front acts as a source of denser fluid thrust into a uniform ambient air flow at high Reynolds number. In such "eruption current", fluidization depth is inversely proportional to a bulk Richardson number representing avalanche height. By excluding situations in which the snow cover is not fluidized up to its free surface, we derive a criterion combining snow pack friction and density indicating which avalanches can produce a sustainable powder cloud. A mass balance involving snow cover and powder cloud sets avalanche height and mean density. By determining which solution of the mass balance is stable, we find that avalanches reach constant growth and acceleration rates for fixed slope and avalanche width. Under these conditions, we calculate the fraction of the fluidized cover that is actually scoured and blown-out into the cloud, and deduce from a momentum balance on the head that the avalanche accelerates at a rate only 14% of the gravitational component along the flow. We also calculate how far a powder cloud travels until its mean density becomes constant. Finally, we show that the dynamics of powder snow avalanches are crucially affected by the rate of change of their width, for example by reaching an apparent steady speed as their channel widens. If such widening is rapid, or if slope inclination vanishes, we calculate where and how powder clouds collapse. Predictions agree well with observations of powder snow avalanches carried out at the Vallee de la Sionne (Switzerland).

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

2012-04-01

27

High Arctic avalanche climate in Central Svalbard  

NASA Astrophysics Data System (ADS)

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

Eckerstorfer, Markus; Christiansen, Hanne H.

2010-05-01

28

Hummock alignment in Japanese volcanic debris avalanches controlled by pre-avalanche slope of depositional area  

NASA Astrophysics Data System (ADS)

This paper investigates the relationship of hummock orientation to the flow dynamics of volcanic debris avalanches. There are opposing views on whether hummocks are systematically aligned along debris avalanche paths, or not. To investigate this geomorphologically fundamental question, I investigated hummock orientation for six Japanese debris avalanches of two simple styles: four “freely spreading” debris avalanches, and two “valley-filling” debris avalanches. Quantitative GIS-based data analysis revealed that hummock orientation along the avalanche flow path alternated between dominantly parallel to and dominantly perpendicular to the flow direction. These changes of alignment reflect dynamic changes of the local stress field within the avalanche, alternating between extensional and compressional in response to changes of the slope of the pre-avalanche ground surface. Changes of hummock alignment from perpendicular to parallel indicate that the local stress regime has changed from compressional to extensional. Conversely, changes of hummock alignment from parallel to perpendicular indicate that the local stress regime has changed from extensional to compressional. Thus, this research demonstrated a clear relationship between hummock orientation and dynamic changes of stress regime within avalanches that are related to changes of the slope of the pre-avalanche ground surface.

Yoshida, Hidetsugu

2014-10-01

29

Initiation of immersed granular avalanches  

NASA Astrophysics Data System (ADS)

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

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

2014-05-01

30

Photon counting with passively quenched germanium avalanche.  

PubMed

We demonstrate photon counting in germanium avalanche photodiodes biased beyond breakdown and quenched with a simple series resistance circuit. The devices show moderate (> 7%) quantum efficiency with limited afterpulsing and dark counts and subnanosecond jitter. PMID:20941236

Owens, P C; Rarity, J G; Tapster, P R; Knight, D; Townsend, P D

1994-10-20

31

Electrothermal simulation of superconducting nanowire avalanche photodetectors  

E-print Network

We developed an electrothermal model of NbN superconducting nanowire avalanche photodetectors (SNAPs) on sapphire substrates. SNAPs are single-photon detectors consisting of the parallel connection of N superconducting ...

Marsili, Francesco

32

Monitoring and modelling snow avalanches in Svalbard  

NASA Astrophysics Data System (ADS)

Monitoring and modelling snow avalanches in Svalbard Ole Humlum 1,3, Hanne H. Christiansen 1, Ulrich Neumann 1, Markus Eckerstorfer 1, Anna Sjöblom 1, Knut Stalsberg 2 and Lena Rubensdotter 2. 1: The University Centre in Svalbard (UNIS). 2: Geological Survey of Norway (NGU) 3: University of Oslo Ground based transportation in Svalbard landscape all takes place across mountainous terrain affected by different geomorphological slope processes. Traffic in and around the Svalbard settlements is increasing, and at the same time global climate models project substantial increases in temperature and precipitation in northern high latitudes for coming century. Therefore improved knowledge on the effect of climatic changes on slope processes in such high arctic landscapes is becoming increasingly important. Motivated by this, the CRYOSLOPE Svalbard research project since 2007 has carried out field observations on snow avalanche frequency and associated meteorological conditions. Snow avalanches are important geomorphic agents of erosion and deposition, and have long been a source of natural disasters in many mid-latitude mountain areas. Avalanches as a natural hazard has thereby been familiar to inhabitants of the Alps and Scandinavia for centuries, while it is a more recent experience in high arctic Svalbard. In addition, overall climate, topography and especially high winter wind speeds makes it difficult to apply snow avalanche models (numerical or empirical) developed for use at lower latitudes, e.g. in central Europe. In the presentation we examplify results from the ongoing (since winter 2006-07) monitoring of snow avalanches in Svalbard along a 70 km long observational route in the mountains. In addition, we present observations on the geomorphological impact of avalanches, with special reference to the formation of rock glaciers. Finally, we also present some initial results from numerical attempts of snow avalanche risk modelling within the study area.

Humlum, O.; Christiansen, H.; Neumann, U.; Eckerstorfer, M.; Sjöblom, A.; Stalsberg, K.; Rubensdotter, L.

2009-04-01

33

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

34

Erosion dynamics of powder snow avalanches - Observations  

NASA Astrophysics Data System (ADS)

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

Sovilla, Betty; Louge, Michel

2013-04-01

35

Deterministically Driven Avalanche Models of Solar Flares  

E-print Network

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

Strugarek, Antoine; Joseph, Richard; Pirot, Dorian

2014-01-01

36

Advances in Cryogenic Avalanche Detectors (review)  

E-print Network

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

A. Buzulutskov

2011-12-28

37

Bulk Metallic Glasses Deform via Slip Avalanches  

E-print Network

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

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

2013-12-21

38

Bulk Metallic Glasses Deform via Slip Avalanches  

E-print Network

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

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

2013-01-01

39

Modelling of snow avalanche dynamics: influence of model parameters  

Microsoft Academic Search

The three-parameter hydraulic model of snow avalanche dynamics including the coefficients of dry and turbulent friction and the coefficient of new-snow-mass entrainment was investigated. The 'Domestic' avalanche site in Elbrus region, Caucasus, Russia, was chosen as the model avalanche range. According to the model, the fixed avalanche run-out can be achieved with various combinations of model parameters. At the fixed

A. N. Bozhinskiy

2008-01-01

40

Bulk metallic glasses deform via slip avalanches.  

PubMed

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

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

2014-04-18

41

Assessing the importance of terrain parameters on glide avalanche release  

NASA Astrophysics Data System (ADS)

Glide snow avalanches are dangerous and difficult to predict. Despite recent research there is still a lack of understanding regarding the controls of glide avalanche release. Glide avalanches often occur in similar terrain or the same locations annually and observations suggest that topography may be critical. Thus, to gain an understanding of the terrain component of these types of avalanches we examined terrain parameters associated with glide avalanche release as well as areas of consistent glide crack formation but no subsequent avalanches. Glide avalanche occurrences visible from the Going-to-the-Sun Road corridor in Glacier National Park, Montana from 2003-2013 were investigated using an avalanche database derived of daily observations each year from April 1 to June 15. This yielded 192 glide avalanches in 53 distinct avalanche paths. Each avalanche occurrence was digitized in a GIS using satellite, oblique, and aerial imagery as reference. Topographical parameters such as area, slope, aspect, elevation and elevation were then derived for the entire dataset utilizing GIS tools and a 10m DEM. Land surface substrate and surface geology were derived from National Park Service Inventory and Monitoring maps and U.S. Geological Survey surface geology maps, respectively. Surface roughness and glide factor were calculated using a four level classification index. . Then, each avalanche occurrence was aggregated to general avalanche release zones and the frequencies were compared. For this study, glide avalanches released in elevations ranging from 1300 to 2700 m with a mean aspect of 98 degrees (east) and a mean slope angle of 38 degrees. The mean profile curvature for all glide avalanches was 0.15 and a plan curvature of -0.01, suggesting a fairly linear surface (i.e. neither convex nor concave). The glide avalanches occurred in mostly bedrock made up of dolomite and limestone slabs and talus deposits with very few occurring in alpine meadows. However, not all glide avalanches failed as cohesive slabs on this bedrock surface. Consequently, surface roughness proved to be a useful descriptive variable to discriminate between slopes that avalanched and those that did not. Annual 'repeat offender' glide avalanche paths were characterized by smooth outcropping rock plates with stratification planes parallel to the slope. Combined with aspect these repeat offenders were also members of the highest glide category. Using this understanding of the role of topographic parameters on glide avalanche activity, a spatial terrain based model was developed to identify other areas with high glide avalanche potential outside of our immediate observation area.

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

2013-12-01

42

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

43

Nano-multiplication region avalanche photodiodes and arrays  

NASA Technical Reports Server (NTRS)

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

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

2011-01-01

44

High mantle temperature during Cretaceous avalanche  

NASA Astrophysics Data System (ADS)

A new sequence of axisymmetrical spherical mantle convection simulations has been computed to monitor the influence of mantle avalanches on the mantle thermal state. During an avalanche that is characterized by a high rate of mixing between upper mantle and lower mantle, a complex perturbation of the thermal field occurs due to the advection of cold upper mantle into the lower mantle, and the hot return flows from the lower mantle. The computation shows that the avalanches trigger global upper mantle warming of several tens of degrees and make it possible to explain both core-mantle boundary and transition zone origins for mantle plumes. Recently, the chemical compositions of DSDP/ODP drill holes on crust older than 80 Myr have been interpreted to reflect a higher mean mantle temperature during the Mesozoic [Humler et al., Earth Planet. Sci. Lett. 173 (1999) 7-23]. Here, we have used and extended the data set for oceanic crust younger than 80 Myr. Combining the mean chemistry for old oceanic crust and the mean depth of the ocean basin versus the square root of age, we propose a continuous curve for the temperature evolution of the upper mantle for the last 130 Myr. It shows a mantle thermal high around 125 Ma with amplitude (50 K) and duration (30 Myr) comparable with those obtained from theoretical convection models. It is proposed that such a high mantle temperature may be due to the thermal effects of an avalanche which may have started 180 Myr ago.

Machetel, Philippe; Humler, Eric

2003-03-01

45

Assessment of snow transport in avalanche terrain  

Microsoft Academic Search

A local to regional assessment of transported snow during snow storms or subsequent periods of strong winds is a prerequisite to reliably estimate avalanche danger. Despite the fact that it has received continuing attention for decades, the problem of quantifying snow transport persists. Systems from point measurements to full three-dimensional simulations have been tested but all have their respective weaknesses.

Michael Lehning; Charles Fierz

2008-01-01

46

Colloquium: Experiments in vortex avalanches E. Altshuler*  

E-print Network

) Avalanche dynamics are found in many phenomena, from earthquakes to the evolution of species. They can also be found in vortex matter when a type-II superconductor is externally driven, for example, by an increasing the self-organization of a complex system of vortices. These are not empty words. They call attention

Johansen, Tom Henning

47

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

48

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

49

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

50

Threshold Model for Triggered Avalanches on Networks  

E-print Network

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

Ausloos, Marcel

2014-01-01

51

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

52

Predictive Capabilities of Avalanche Models for Solar Flares  

NASA Astrophysics Data System (ADS)

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

Strugarek, A.; Charbonneau, P.

2014-11-01

53

Viscoelastic Effects in Avalanche Dynamics: A Key to Earthquake Statistics  

NASA Astrophysics Data System (ADS)

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

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

2014-05-01

54

Predictive Capabilities of Avalanche Models for Solar Flares  

E-print Network

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

Strugarek, Antoine

2014-01-01

55

A climatology of major avalanche winters in Western Canada  

Microsoft Academic Search

A nearly continuous record of avalanches on the Canadian Pacific Railway for the 70 years from 1910 is used to identify four major avalanche winters (1919–20, 1932–33, 1934–35 and 1971–72). The selection is based on the frequency and mass of avalanche snow, and the length of rail line affected near Rogers Pass, British Columbia. Daily weather data are compiled for

B. B. Fitzharris

1987-01-01

56

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

57

Optimization of 4H-SiC separated-absorption-charge-multiplication (SACM) avalanche photodiode with low avalanche breakdown voltage  

Microsoft Academic Search

H-SiC avalanche photodiode with a separated absorption region, a charge adjustment region and a multiplication region is proposed and its optoelectronic performance is modeled. By properly designing the doping concentration of each layer, the avalanche breakdown voltage and photo-response of the device is found to be dependent of the thickness of the multiplication region. The avalanche breakdown voltage shows a

Rongdun Hong; Xiaping Chen; Mingkun Zhang; Zhengyun Wu; Yi Zhou

2011-01-01

58

Lifetime of bubble rafts: cooperativity and avalanches.  

PubMed

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

Ritacco, Hernán; Kiefer, Flavien; Langevin, Dominique

2007-06-15

59

Lifetime of Bubble Rafts: Cooperativity and Avalanches  

NASA Astrophysics Data System (ADS)

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

Ritacco, Hernán; Kiefer, Flavien; Langevin, Dominique

2007-06-01

60

A rockfall avalanche in a sandstone landscape, Nattai North, NSW  

Microsoft Academic Search

Rockfall avalanches are commonly associated with the alpine regions of Europe, South America and north?western Canada, but modern examples have only been reported very recently in Australia (Pells et al. 1987). The Nattai North rockfall avalanche is located on the Burragorang Walls escarpment in the sandstone landscape of the Sydney Basin. The volume of rock involved in the failure had

David M. Cunningham

1988-01-01

61

Development of Snow Avalanche Forecasting System in Japan  

Microsoft Academic Search

We describe the development of an avalanche warning system in Japan. Study area was set on southern part of Niigata prefecture, where we had huge amount of snow in winter 2005-2006 and the snow depth exceeded 4 m in February. The snow cover model SNOWPACK, which was developed at the Swiss Federal Institute for Snow and Avalanche Research, was used.

Kouichi Nishimura; Hiroyuki Hirashima; Satoru Yamaguchi; Kenji Kosugi; Atsushi Sato; Kaoru Izumi; Keisuke Suzuki; Masaaki Hanaoka; Michael Lehning

2006-01-01

62

Gene Transfer to Rabbit Retina with Electron Avalanche Transfection  

E-print Network

Gene Transfer to Rabbit Retina with Electron Avalanche Transfection Thomas W. Chalberg,1 Alexander clinically acceptable methods for efficient gene transfer. Electroporation is widely used for transfection for the eye. METHODS. A novel method for nonviral DNA transfer, called electron avalanche transfection

Palanker, Daniel

63

Avalanche behavior of low-voltage power MOSFETs  

Microsoft Academic Search

This letter addresses the behavior of low voltage power MOSFETs under avalanche, with a paralleling point of view. It is shown that during avalanche, up-to-date technology MOSFET transistors exhibit a resistance far in excess of their on-state resistance (RDSon). A novel test setup is proposed to measure \\

Cyril Buttay; Tarek Ben Salah; Dominique Bergogne; Bruno Allard; Hervé Morel; Jean-Pierre Chante

2004-01-01

64

Mountain Snowmobilers and Avalanches: An Examination of Precautionary Behaviour  

E-print Network

to investigate the circumstances surrounding the accidents. One of the overarching conclusions of the panel, experience, training, trip details, etc.), and identify what factors affect their avalanche risk perception to those who have lost friends or loved ones in avalanche accidents. #12;vii Acknowledgements I would like

65

ORIGINAL PAPER Amateur decision-making in avalanche terrain with  

E-print Network

that affect people's decision to evacuate. Such research can help emergency planners design effective+Business Media B.V. 2009 Abstract Avalanches pose a serious threat to recreational backcountry travelers in mountainous terrain. This study explores how the three main amateur user groups of avalanche terrain

66

A cooled avalanche photodiode with high photon detection probability  

NASA Technical Reports Server (NTRS)

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

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

1986-01-01

67

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

68

Age of Palos Verdes submarine debris avalanche, southern California  

USGS Publications Warehouse

The Palos Verdes debris avalanche is the largest, by volume, late Quaternary mass-wasted deposit recognized from the inner California Borderland basins. Early workers speculated that the sediment failure giving rise to the deposit is young, taking place well after sea level reached its present position. A newly acquired, closely-spaced grid of high-resolution, deep-tow boomer profiles of the debris avalanche shows that the Palos Verdes debris avalanche fills a turbidite leveed channel that extends seaward from San Pedro Sea Valley, with the bulk of the avalanche deposit appearing to result from a single failure on the adjacent slope. Radiocarbon dates from piston-cored sediment samples acquired near the distal edge of the avalanche deposit indicate that the main failure took place about 7500 yr BP. ?? 2003 Elsevier B.V. All rights reserved.

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

2004-01-01

69

Reducing financial avalanches by random investments  

NASA Astrophysics Data System (ADS)

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

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

2013-12-01

70

Avalanches of Singing Sand in the Laboratory  

NASA Astrophysics Data System (ADS)

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

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

2011-03-01

71

Reducing financial avalanches by random investments.  

PubMed

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

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

2013-12-01

72

Germanium avalanche receiver for low power interconnects  

NASA Astrophysics Data System (ADS)

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

Virot, Léopold; Crozat, Paul; Fédéli, Jean-Marc; Hartmann, Jean-Michel; Marris-Morini, Delphine; Cassan, Eric; Boeuf, Frédéric; Vivien, Laurent

2014-09-01

73

Avalanche situation in Turkey and back calculation of selected events  

NASA Astrophysics Data System (ADS)

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

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

2014-05-01

74

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

2009-05-01

75

ELECTRON AVALANCHE MODEL OF DIELECTRIC-VACUUM SURFACE BREAKDOWN  

SciTech Connect

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

Lauer, E J

2007-02-21

76

Avalanche behavior in yield stress fluids  

NASA Astrophysics Data System (ADS)

We show that above a critical stress, typical yield stress fluids (gels, clay suspensions) and soft glassy materials (the colloidal glass of Laponite) start flowing abruptly and subsequently accelerate, leading to avalanches that are remarkably similar to those of granular materials. Rheometrical tests reveal that this is associated to a bifurcation in rheological behavior: for small stresses, the viscosity increases in time: the material ``ages,'' and eventually stops flowing. For slightly larger stresses the viscosity decreases continuously in time: the flow accelerates and we observe a 1 ``rejuvenation'' of the material by the flow. We show that for the Laponite system, both the aging and the shear rejuvenation can be observed directly using Diffusive Wave Spectroscopy. We propose a simple physical model capable of reproducing the rheological observations. These results may have some implication in geophysics: they shed some light on certain landslides of clayey soils, and the way quicksand works.

Bonn, Daniel

2005-03-01

77

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. PMID:22529343

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

2012-01-01

78

Modeling Advanced Avalanche Effects for Bipolar Transistor Circuit Design  

E-print Network

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

Technische Universiteit Delft

79

Low dark current 4H-SiC avalanche photodiodes  

Microsoft Academic Search

In this paper, we study the mechanisms of the 4H-SiC avalanche photodiode (APD) dark current and find that the mesa sidewall leakage current is the primary contributor. Improving the sidewall passivation decreases the device dark current.

X. Guo; A. Beck; B. Yang; J. C. Campbell

2003-01-01

80

Avalanche Multiplication as a Gain Mechanism in Photodiodes.  

National Technical Information Service (NTIS)

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

H. W. Ruegg

1966-01-01

81

Effect of volume fraction on granular avalanche dynamics  

NASA Astrophysics Data System (ADS)

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

Gravish, Nick; Goldman, Daniel I.

2014-09-01

82

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

83

Spatio-temporal avalanche forecasting with Support Vector Machines  

NASA Astrophysics Data System (ADS)

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

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

2011-02-01

84

Avalanches and hysteresis in frustrated superconductors and XY spin glasses  

NASA Astrophysics Data System (ADS)

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

Sharma, Auditya; Andreanov, Alexei; Müller, Markus

2014-10-01

85

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

86

Dead Time of Single Photon Avalanche Diodes  

NASA Astrophysics Data System (ADS)

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

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

2011-06-01

87

The formation and propagation of flux avalanches in tailored MgB2 films  

NASA Astrophysics Data System (ADS)

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

Treiber, S.; Albrecht, J.

2010-09-01

88

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

NASA Astrophysics Data System (ADS)

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

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

2013-12-01

89

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

90

Arrest of Avalanche Propagation by Discontinuities on Snow Cover  

NASA Astrophysics Data System (ADS)

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

Frigo, B.; Chiaia, B.

2009-04-01

91

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

92

Superelevation of flowing avalanches around curved channel bends  

NASA Astrophysics Data System (ADS)

Flowing avalanches are those with a dense core of flowing granular material at the base, which dominates the dynamics causing friction. Sometimes when avalanches descend, they encounter curved channel bends, which cause the flowing material to superelevate or climb up on the wall of the channel bend so that the level of the flowing snow is higher on the outside of the bend than at the center of the channel. This can provide important information about avalanche speeds. The conventional approach for estimating speeds is mathematically equivalent to one developed from equations based on fluid mechanics with a balance between fluid pressure force and centrifugal force to yield a simple expression which relates channel radius, avalanche speed, and superelevation geometry. In this paper, the conventional theory is replaced by one which relates avalanche speed to basal friction (as appropriate for flowing snow), passive snow pressure (accounting for friction between snow particles), channel radius, and superelevation geometry. It is shown that the conventional theory is physically unrealistic for flowing snow modeled as a frictional material. Also, the conventional theory will result in lower speed estimates than the new formulation for the same amount of superelevation.

McClung, D. M.

2001-01-01

93

Avalanche multiplication and impact ionization in amorphous selenium photoconductive target  

NASA Astrophysics Data System (ADS)

The avalanche multiplication factor and the hole ionization coefficient in the amorphous selenium (a-Se) high-gain avalanche rushing amorphous photoconductor (HARP) target depend on the electric field. The phenomenon of avalanche multiplication and impact ionization in the 0.4-µm-thick a-Se HARP target is investigated. The hot carrier energy in the 0.4-µm-thick a-Se HARP target increases linearly as the target voltage increases. The energy relaxation length of hot carriers in the a-Se photoconductor of the 0.4-µm-thick HARP target saturates as the electric field increases. The average energy Eav of a hot carrier and the energy relaxation length ?E in the a-Se photoconductor of the 0.4-µm-thick HARP target at 1 × 108 V/m were 0.25 eV and 2.5 nm, respectively. In addition, the hole ionization coefficient ? and the avalanche multiplication factor M are derived as a function of the electric field, the average energy of a hot carrier, and the impact ionization energy. The experimental hole ionization coefficient ? and the avalanche multiplication factor M in the 0.4-µm-thick a-Se HARP target agree with the theoretical results.

Park, Wug-Dong; Tanioka, Kenkichi

2014-03-01

94

Friction and dynamics of rock avalanches travelling on glaciers  

NASA Astrophysics Data System (ADS)

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

De Blasio, Fabio Vittorio

2014-05-01

95

Underwater Sand Avalanches Linked to Sea-Level Changes in Gulf of Mexico  

NSF Publications Database

... Sand Avalanches Linked to Sea-Level Changes in Gulf of Mexico The drillship JOIDES Resolution at ... sand avalanches to rapid sea-level changes in deep waters of the Gulf of Mexico, according to marine ...

96

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

97

Looking for Self-Organized Critical Behavior in Avalanches of Slightly Cohesive Powders  

NASA Astrophysics Data System (ADS)

We report results from a statistical analysis of avalanches of cohesive powders in a slowly rotated drum. Interparticle adhesion, which diminishes the effect of inertia and whose magnitude strongly fluctuates in a local scale, makes avalanches in slightly cohesive powders eligible for displaying self-organized criticality. However, the results show that avalanche sizes, time interval between avalanches, and maximum stable angle do not follow a power-law distribution. Otherwise, these parameters scale with powder cohesiveness.

Quintanilla, M. A.; Valverde, J. M.; Castellanos, A.; Viturro, R. E.

2001-11-01

98

On the formation of glide-snow avalanches  

NASA Astrophysics Data System (ADS)

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

Mitterer, C.; Schweizer, J.

2012-12-01

99

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

100

Release of Wet Snow Avalanches: A Grain-scale Approach  

NASA Astrophysics Data System (ADS)

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

Gan, Yixiang; Faug, Thierry; Einav, Itai

2014-05-01

101

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

E-print Network

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

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

2012-04-26

102

Hybrid avalanche photodiode ranging and photon-counting altimeter  

NASA Astrophysics Data System (ADS)

Avalanche photodiodes are very well suited and extensively used for low light application. In this paper we present a devise using avalanche photodiodes in conjunction with a pulsed laser-source to be used as an optical altimeter. The extreme sensitivity of a dedicated silicon SPAD array is combined with a versatile standard CMOS readout circuit to achieve unique performances. This imaging device is able to perform ranging with four centimeters accuracy over five kilometers distance. It is also capable of delivering quantum limited images. Development of the readout circuit will be disclosed as well as measurement results performed on the final device.

Dierickx, B.; Bellis, S.; Witvrouwen, N.; Dupont, B.; Defernez, A.; Jackson, C.

2010-10-01

103

Thermoelastic model for the descent of avalanches and landslides  

NASA Astrophysics Data System (ADS)

A wedge-shaped mass of snow or soil on a flat mountain slope is simulated in a connected formulation by a thermoelastic medium acted upon by gravity, a uniform surface load, and a heat flux. An exact solution of the problem of equilibrium of the mass is obtained. Two criteria for the descent of an avalanche or a landslide are derived from the conditions of impossibility of equilibrium. This result can be used to predict soil landslides and the descent of avalanches in the mountains.

Chernyshov, A. D.

2012-11-01

104

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

105

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

E-print Network

crystals can form weak layers or interfaces that are common sources of failure for avalanches nonpersistent, whereas persistent crystals maintain their form even deep within the snowpack and can remain 2012 Keywords: Snow Avalanche Anticrack Storm snow often avalanches before crystals metamorphose

Dozier, Jeff

106

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

E-print Network

Quantum-dot based avalanche photodiodes for mid-infrared sensing Majeed M. Hayat a , Oh-Hyun Kwon b ABSTRACT A mid-infrared sensor is proposed in which an intersubband quantum-dot (QD) detector is integrated temperatures. Keywords: Quantum dots, avalanche photodiodes, infrared, sensors, mid-wave infrared, avalanche

Hayat, Majeed M.

107

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

108

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

E-print Network

Avalanche spin-valve transistor K. J. Russell,a) Ian Appelbaum,b) Wei Yi, D. J. Monsma, F. Capasso, California 93106 (Received 11 June 2004; accepted 10 September 2004) A spin-valve transistor with a Ga allow fabrication of spin-valve transistors with high gain in a variety of materials. © 2004 American

Russell, Kasey

109

Group Dynamics and Decision Making: Backcountry Recreationists in Avalanche Terrain  

ERIC Educational Resources Information Center

The purpose of this study was to describe and determine the prevalence of decision-making characteristics of recreational backcountry groups when making a decision of where to travel and ride in avalanche terrain from the perspective of individuals. Decision-making characteristics encompassed communication, decision-making processes, leadership,…

Bright, Leslie Shay

2010-01-01

110

Teaching Avalanche Safety Courses: Instructional Techniques and Field Exercises.  

ERIC Educational Resources Information Center

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

Watters, Ron

111

Some studies of avalanche photodiode readout of fast scintillators  

SciTech Connect

Photomultipliers (PMs) are the classical readout element for scintillation detectors in high energy particle physics, nuclear physics, medical physics, industrial radiation monitors etc. Here, large area avalanche photodiodes with high performance, narrow operation tolerances and high reliability have recently become available. The authors report on some tests of their performance in the readout of fast scintillators.

Holl, I.; Lorenz, E. [Max-Planck-Inst. fuer Physik, Muenchen (Germany)] [Max-Planck-Inst. fuer Physik, Muenchen (Germany); Natkaniez, S. [Inst. of Nuclear Physics, Krakow (Poland)] [Inst. of Nuclear Physics, Krakow (Poland); Renker, D. [Paul Scherrer Inst., Villigen (Switzerland)] [Paul Scherrer Inst., Villigen (Switzerland); Schmelz, C. [Max-Planck-Inst. fuer Physik, Muenchen (Germany)] [Max-Planck-Inst. fuer Physik, Muenchen (Germany); [Technische Univ. Muenchen (Germany). Nuklearmedizinische Klinik Rechts der Isar; Schwartz, B. [Budger Institute of Nuclear Physics, Novosibirsk (Russian Federation)] [Budger Institute of Nuclear Physics, Novosibirsk (Russian Federation)

1995-08-01

112

Fracture energy applicable to dry snow slab avalanche release  

Microsoft Academic Search

Dry slab avalanches release by a sequence of propagating fractures: first by shear fracture (mode II and mode III) in a weak layer at the base of the slab and second by tensile fracture through the crown after which release of the slab is imminent. The fracture energy is the energy which must be provided to produce a unit area

D. M. McClung

2007-01-01

113

Avalanches in breakdown and fracture processes Stefano Zapperi,1  

E-print Network

Avalanches in breakdown and fracture processes Stefano Zapperi,1 Purusattam Ray,2 H. Eugene Stanley and Department of Physics, Boston University, Boston, Massachusetts 02215 4 The Abdus Salam International Centre, corresponding to the spinodal point, the system becomes un- stable. The nature of the nucleation process

Stanley, H. Eugene

114

Electron avalanche structure determined by random walk theory  

NASA Technical Reports Server (NTRS)

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

Englert, G. W.

1973-01-01

115

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

E-print Network

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

Buldyrev, Sergey

116

Some recent advances in snow and avalanche science 1. Introduction  

E-print Network

of topics in current avalanche science, including advances in modeling thermal and mechanical processes be used to monitor changes in snow structure when different thermal conditions are applied. Large presentations when the meeting was last held in the Lake Tahoe area in 1986. The ISSW meeting has become

Marshall, Hans-Peter

117

High-Power, Low-Noise Avalanche Diode Oscillators  

Microsoft Academic Search

An approach to higher-power generation with avalanche diodes is described which uses (1) passivated devices in order to avoid the use of conventional packages, (2) multiple-diode chips for reducing the thermal resistance, and (3) cascading waveguide oscillator mounts for efficient power combining.

Ferdo Ivanek; V. Gopala; K. Reddi

1971-01-01

118

Structural Control of Giant Rock Avalanches in Argentina  

NSDL National Science Digital Library

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

Tewksbury, Barb

119

Self-pulsed high-efficiency avalanche-diode oscillators  

Microsoft Academic Search

Self-pulsed microwave power outputs have been generated from avalanche diodes operating in the anomalous mode. A delay line has been used in achieving self-pulsed oscillation with rectangular pulse shape. L-band power outputs of 12 W peak at 50 percent duty cycle have been obtained, with 22 percent efficiency. CW oscillation has also been obtained from the same diodes.

S. G. Liu; J. J. Risko

1970-01-01

120

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

2009-01-01

121

Soil erosion and organic carbon export by wet snow avalanches  

NASA Astrophysics Data System (ADS)

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

Korup, O.; Rixen, C.

2014-01-01

122

Soil erosion and organic carbon export by wet snow avalanches  

NASA Astrophysics Data System (ADS)

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

Korup, O.; Rixen, C.

2014-04-01

123

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

NASA Astrophysics Data System (ADS)

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

Prokop, Alexander; Wirbel, Anna

2013-04-01

124

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

125

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

NASA Astrophysics Data System (ADS)

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

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

2014-09-01

126

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

NASA Technical Reports Server (NTRS)

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

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

1977-01-01

127

Wave motion resulting from adhesive avalanche between metallic surfaces  

NASA Astrophysics Data System (ADS)

Atomistic simulations of impacting copper surfaces were performed using a many-body potential defined by the embedded-atom method. In the course of impact, as the impact surfaces approach each other, an adhesive avalanche occurs. That is, at a separation of roughly 2 Å beyond the bulk interplanar spacing, one or both surface layers becomes unstable and abruptly moves towards the other. The adhesive avalanche signals a transition from an initial system with two distinct surfaces (at the impact interface) to one possessing no identifiable surfaces. This motion generates a brief (<1 psec) but strong (10 GPa) tensile wave ahead of a compressive shock wave, which propagate away from the interface into the bulk. The tensile wave appears at impact velocities as low as 10 m/sec. Similar dynamic effects appear in a broad range of materials, and indeed may be of fundamental importance in phenomena underlying adhesion, friction, and wear.

Taylor, Paul A.

1991-12-01

128

Erosion dynamics of powder snow avalanches - model of frontal entrainment  

NASA Astrophysics Data System (ADS)

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

Louge, Michel; Sovilla, Betty

2013-04-01

129

Pushing technologies: single-photon avalanche diode arrays  

Microsoft Academic Search

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

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

2004-01-01

130

CMOS silicon avalanche photodiodes for NIR light detection: a survey  

Microsoft Academic Search

This paper surveys recent research on CMOS silicon avalanche photodiodes (SiAPD) and presents the design of a SiAPD based\\u000a photoreceiver dedicated to near-infrared spectroscopy (NIRS) application. Near-infrared spectroscopy provides an inexpensive,\\u000a non-invasive, and portable means to image brain function, and is one of the most efficient diagnostic techniques of different\\u000a neurological diseases. In NIRS system, brain tissue is penetrated by

Ehsan Kamrani; Mohamad Sawan

131

4H-SiC PIN Recessed Window Avalanche Photodiode  

Microsoft Academic Search

We report 4H-SiC p-i-n recessed window avalanche photodiodes with low dark current and high quantum efficiency. For a circular device of 250 mum diameter, the device demonstrated a responsivity of ~135.5 mW\\/A (external quantum efficiency = ~64%), a dark current ~90 pA (~0.183 mum\\/cm2) at a photocurrent gain of 1000, and an excess noise factor k of slightly less than

Han-Din Liu; Dion McIntosh; Xiaogang Bai; Huapu Pan; Mingguo Liu; Joe C. Campbell

2007-01-01

132

Avalanche localization and crossover scaling in amorphous plasticity  

NASA Astrophysics Data System (ADS)

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

Budrikis, Zoe; Zapperi, Stefano

2013-12-01

133

Large area silicon avalanche photodiodes for scintillation detectors  

NASA Astrophysics Data System (ADS)

Large area (?1 cm 2) silicon avalanche photodiodes (SiAPDs) have been fabricated and their performance as optical detectors for use with scintillating crystals has been measured. Light sensitivity is measured for hexagonal SiAPDs of 1.57 cm 2 total package area, and the energy and timing resolution is measured for these devices coupled to CsI(Tl) scintillators operating as gamma spectrometers.

Farrell, R.; Olschner, F.; Frederick, E.; McConchie, L.; Vanderpuye, K.; Squillante, M. R.; Entine, G.

1990-03-01

134

Large area silicon avalanche photodiodes for scintillation detectors  

Microsoft Academic Search

Large area (~1 cm2) silicon avalanche photodiodes (SiAPDs) have been fabricated and their performance as optical detectors for use with scintillating crystals has been measured. Light sensitivity is measured for hexagonal SiAPDs of 1.57 cm2 total package area, and the energy and timing resolution is measured for these devices coupled to CsI(Tl) scintillators operating as gamma spectrometers.

R. Farrell; F. Olschner; E. Frederick; L. McConchie; K. Vanderpuye; M. R. Squillante; G. Entine

1990-01-01

135

Theory of electron-avalanche breakdown in solids  

Microsoft Academic Search

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

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

1981-01-01

136

The Tancitaro Debris Avalanche: Characterization, propagation and modeling  

Microsoft Academic Search

The Tancitaro volcano (3860m) is an andesitic–dacitic stratovolcano located in the western portion of the Trans-Mexican Volcanic Belt within the state of Michoacán (Mexico). The tectonic activity of this area has likely contributed to a large sector collapse of the volcano. The first findings of a multidisciplinary investigation into this debris avalanche are presented here.Geomorphological analyses, based on the interpretation

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

2010-01-01

137

A short-wavelength selective reach-through avalanche photodiode  

Microsoft Academic Search

A new reach-through avalanche photodiode, designed for use with sources of short-wavelength light such as scintillators, is described. The device has a double junction p+-p-n-p--n+ structure in which the central three layers, which comprise about 99% of the device thickness, are fully depleted. The p+ light-entry surface extends across the whole device and can be placed in contact with a

R. J. McIntyre; P. P. Webb; H. Dautet

1996-01-01

138

Automated characterization of single-photon avalanche photodiode  

E-print Network

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

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

2012-02-08

139

Avalanche-photodiode-based photon counter echo photon number resolving  

NASA Astrophysics Data System (ADS)

The solid state photodetectors based on silicon avalanche photodiodes operated in Geiger mode are used for detection of echo signal in laser ranging experiments. The avalanche process nonlinearity enhance the influence of starting conditions to avalanche grow of photodiode output signal. This is the reason why the internal delay of this type of detectors is depended on detected signal intensity, i.e. in case of weak signal it is depended on number of detected photons. The dependence is in the range of 0-200 ps for photon numbers 1-1000 photons. The active quenching and gating circuit with time walk compensation has been constructed to eliminate this effect (Kirchner, 1998). In our experiment, we have used the outputs of the compensation circuit to estimate the photon numbers detected on a shot by shot basis simultaneously with original required time interval estimation. The mutual time difference between the compensated and uncompensated output pulses corresponds to the photon number. Monitoring this time difference by the picosecond event timing device enabled us to monitor the echo signal strength fluctuation on a shot by shot basis in a laser ranging. The experimental results will be presented.

Blazej, Josef; Prochazka, Ivan; Hamal, Karel

2004-01-01

140

Solar flares and avalanches in driven dissipative systems  

NASA Technical Reports Server (NTRS)

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

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

1993-01-01

141

Avalanche Defence Strategies and Monitoring of Two Sites in Mountain Permafrost Terrain, Pontresina, Eastern Swiss Alps  

Microsoft Academic Search

Snow-supporting avalanche defence structures are increasingly being built at high altitudes in potential permafrost areas.\\u000a Special construction methods and guidelines have been developed to ensure a minimal stability of the structures, which have\\u000a a vital role in the protection of underlying settlements and transport infrastructure against snow avalanches. If the avalanche\\u000a slopes are located on ice-rich permafrost terrain, as is

Marcia Phillips

2006-01-01

142

Repetitive avalanche cycling of low-voltage power trench n-MOSFETs  

Microsoft Academic Search

Low voltage discrete power trench n-MOSFETs in TO-220 packages have been subjected to over 200 million cycles of repetitive unclamped inductive switching (UIS) at a mounting base temperature of 150° C and at different avalanche currents. Hot-hole injection into the gate dielectric during avalanche conduction causes a reduction in the threshold voltage as the number of avalanche cycles increase. The

Olayiwola Alatise; Ian Kennedy; George Petkos; K. Heppenstall; K. Khan; J. Parkin; A. Koh; P. Rutter

2010-01-01

143

Spatial aspects of vulnerability and risk resulting from snow avalanches  

NASA Astrophysics Data System (ADS)

Mountain regions provide a significant proportion of areas used for human settlements, economic purpose, and recreation. Simultaneously, due to steep vertical gradients mountain areas are prone to mass movement processes. The intersection of such processes with areas used by human action turns them into hazards. In particular in arctic regions, which show a greater susceptibility to disturbances than many landscapes, considerable efforts have been undertaken in recent decades to reduce the adverse effects of mountain hazards. The concept of risk supplemented the traditional engineering approaches of technical mitigation since the 1990s to comprehensively manage these threats, and to develop strategies for a sustainable use of these areas. The concept of risk is based on a mathematical combination of hazards and consequences, but is static over time. However, three major dynamic systems interact in the field of mountain hazard risk management: the physical environment, which includes hazardous events; the social and demographic characteristics of the communities that experience them; and the values at risk such as buildings, roads, and other components of the built environment. These dynamics have not sufficiently been taken into account so far in natural hazard risk management, in particular with respect to industrialised artic regions. Within the city of Kirovsk, Kola Peninsula, Russian Federation, these dynamics were assessed by taking snow avalanche risk as an example. The test site is exposed to multiple avalanche tracks with repeated releases during individual winter seasons, endangering the built environment and any kind of infrastructure lines. The aim was to contribute to the development of a spatial risk model for mountain regions on different temporal scales. The spatial characteristics of the long-term avalanche risk, as a result of the evolution of the built environment, was analysed on an annual as well as inter-annual level. This long-term development was superimposed by short-term fluctuations due to the spatiotemporal movement of people and mobile values into and within areas endangered by avalanche hazards. As a result, individual system dynamics and the evolution of the entire risk system were specifically assessed. Furthermore, insights in spatiotemporal aspects of vulnerability of elements at risk exposed to snow avalanches were gained. The overall purpose of the study was to develop concepts and methods for an enhanced natural hazard risk management applicable in mountain regions.

Fuchs, S.; Koltermann, P.; Sokratov, S.; Seliverstov, Y.; Shnyparkov, A.

2012-04-01

144

Avalanche-diode oscillator circuit with tuning at multiple frequencies  

NASA Technical Reports Server (NTRS)

Detailed theoretical analysis of three different modes or types of high efficiency oscillation in a PIN diode are presented. For the TRAPATT mode in a PIN diode, it is shown that a traveling avalanche zone is not necessary to generate a dense trapped plasma. An economical computer program for TRAPATT oscillations in a PIN diode is described. Typical results of diode power, dc-to-RF conversion efficiency, and required circuit impedances are presented for several different current waveforms. A semianalytical solution for a second type of high efficiency mode in a PIN diode is derived assuming a rectangular current waveform. A quasi-static approximation is employed to derive a semianalytical solution for the voltage across a PIN diode in a third mode, where avalanching occurs during a major portion of a half cycle. Calculations for this mode indicate that the power increases proportionally to the magnitude of the drive current with a small decrease in efficiency relative to the ordinary TRAPATT mode. An analytical solution is also given for a PIN diode, where it is assumed that the ionization coefficient is a step function. It is shown that the step-ionization approximation permits one to draw possible patterns of avalanche region in the depletion layer as a function of time. A rule governing admissible patterns is derived and an example solution given for one admissible pattern. Preliminary experimental results on the high-efficiency oscillations are presented and discussed. Two different experimental circuits, which used channel-dropping filters to provide independent harmonic tuning, are described. Simpler circuits used to produce high-efficiency oscillations are discussed. Results of experiments using inexpensive Fairchild FD300 diodes are given.

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

1971-01-01

145

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. PMID:23595765

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

2013-01-01

146

Avalanche contribution to shear modulus of granular materials  

NASA Astrophysics Data System (ADS)

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

Otsuki, Michio; Hayakawa, Hisao

2014-10-01

147

A 1.06 micrometer avalanche photodiode receiver  

NASA Technical Reports Server (NTRS)

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

Eden, R. C.

1975-01-01

148

Operation of silicon single photon avalanche diodes at cryogenic temperature.  

PubMed

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

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

2007-06-01

149

Reliability assessment of multiple quantum well avalanche photodiodes  

NASA Technical Reports Server (NTRS)

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

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

1995-01-01

150

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

151

Demonstration of the first 4H-SiC avalanche photodiodes  

Microsoft Academic Search

4H-SiC visible-blind reach-through avalanche photodiodes (RAPDs) were designed and fabricated with mesa edge termination and thermal oxide passivation techniques. The devices show “hard” avalanche breakdown with a positive temperature coefficient. The photo response spectra, measured at different biases, displayed a maximum responsivity of 106 A\\/W, and a corresponding optical gain of about 500.

Feng Yan; Jian H Zhao; Gregory H Olsen

2000-01-01

152

Demonstration of the first 4H-SiC avalanche photodiodes  

NASA Astrophysics Data System (ADS)

4H-SiC visible-blind reach-through avalanche photodiodes (RAPDs) were designed and fabricated with mesa edge termination and thermal oxide passivation techniques. The devices show "hard" avalanche breakdown with a positive temperature coefficient. The photo response spectra, measured at different biases, displayed a maximum responsivity of 106 A/W, and a corresponding optical gain of about 500.

Feng Yan; Zhao, Jian H.; Olsen, Gregory H.

2000-02-01

153

Improvements in avalanche-transistor sweep circuitry for electrooptic streak cameras  

Microsoft Academic Search

The performance of the avalanche transistor deflector driver (sweep) circuitry used in the high speed, electrooptic streak camera was improved. In the previous design for the sweep circuit, trigger to output delay time drifted on some cameras. This delay drift is a function of a somewhat randomly unstable breakdown voltage of some avalanche transistors. Both temperature and differences in manufacturing

S. W. Thomas; R. L. Griffith; W. R. McDonald

1984-01-01

154

Scenario-specific observations for regional snow avalanche warnings Dave Gauthier and Bruce Jamieson  

E-print Network

. 1 INTRODUCTION Snow avalanches are one of the most deadly slope hazards affecting Canadians their lives in 98 separate recreational avalanche accidents in Canada, mostly while skiing/snowboarding or snowmobiling. In contrast, over the same period there were 7 accidents resulting in 16 fatalities in non

Jamieson, Bruce

155

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

PubMed

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

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

2005-07-15

156

Geomorphology of snow avalanche impact landforms in the southern Canadian Cordillera  

E-print Network

Geomorphology of snow avalanche impact landforms in the southern Canadian Cordillera ALEXIS L@uvic.ca) Snow avalanche impact landforms (SAILs) are typically elliptical-shaped depressions bounded impact events over many hundreds of years. All three landforms share common morphologies: a water

Smith, Dan

157

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

158

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

Microsoft Academic Search

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

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

2011-01-01

159

Two examples of expert knowledge based system for avalanche forecasting and protection  

NASA Astrophysics Data System (ADS)

In avalanche modelling and control and in avalanche forecasting, most of the knowledge is based on scientific theory but the experience of specialists (field practitioners, forecasters...) plays a large role. This paper presents two French computer-based systems dedicated to avalanche modelling and control and to avalanche forecasting. They are both based on expert knowledge. ELSA (Etude et Limites de Sites d'Avalanches), is a computer system dedicated to the modelling of the knowledge of avalanche experts and to the integration of new symbolic computer models with classical numerical models. The basic aim of integration is to build a unique computer system incorporating all these models. After a description of the terrain representation, we present the different scenarios that ELSA takes into account. Then, the methods which deal with some phenomena occurring in avalanches are described. The problems involved in the integration of these methods close this first part. MEPRA is an expert system built to create an objective tool in avalanche risk forecasting. This development allowed us to imagine a processing system for 2 of the most important problems in avalanche risk forecasting: representation of the present snow cover characteristics and evaluation of avalanche instability and risk. In this way, mechanics and thermodynamics play a major role in the system. After a punctual validation at the location of a snow weather station and in order to describe the great variability of the snow pack and the avalanche risk in a massif, the MEPRA expert system was connected with a meteorological analysis system, SAFRAN and a numerical model to simulate the snow cover CROCUS. Then, every day, a MEPRA expert analysis is carried out in different locations with different orientations, slopes and altitudes. Its results were used successfully during the Winter Olympic Games of Albertville and by avalanche forecasters during the 92/93 winter season. The daily avalanche risks estimated by MEPRA are also compared with the observed avalanche activity during the 10 last winters. For a better description of local phenomena like wind slab or snow accumulation, a local version of this tool should be developed to integrate field characteristics.

Buisson, Laurent; Giraud, Gérald

1995-11-01

160

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

161

Spike Avalanches Exhibit Universal Dynamics across the Sleep-Wake Cycle  

E-print Network

Scale-invariant neuronal avalanches have been observed in cell cultures and slices as well as anesthetized and awake brains, suggesting that the brain operates near criticality, i.e. within a narrow margin between avalanche propagation and extinction. In theory, criticality provides many desirable features for the behaving brain, optimizing computational capabilities, information transmission, sensitivity to sensory stimuli and size of memory repertoires. However, a thorough characterization of neuronal avalanches in freely-behaving (FB) animals is still missing, thus raising doubts about their relevance for brain function. To address this issue, we employed chronically implanted multielectrode arrays (MEA) to record avalanches of spikes from the cerebral cortex (V1 and S1) and hippocampus (HP) of 14 rats, as they spontaneously traversed the wake-sleep cycle, explored novel objects or were subjected to anesthesia (AN). We then modeled spike avalanches to evaluate the impact of sparse MEA sampling on their sta...

Ribeiro, Tiago L; Caixeta, Fábio; Belchior, Hindiael; Chialvo, Dante R; Nicolelis, Miguel A L; Ribeiro, Sidarta; 10.1371/journal.pone.0014129

2011-01-01

162

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

NASA Technical Reports Server (NTRS)

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

Blonski, Slawomir

2007-01-01

163

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

164

International Snow Science Workshop Grenoble Chamonix Mont-Blanc -2013 Impressions from Applying ISO 31000 to an Avalanche Mitigation Project  

E-print Network

ABSTRACT: ISO 31000 is an international standard for risk management. It offers standard risk con- cepts, avalanche risk, avalanche mitigation 1 INTRODUCTION ISO 31000 is an international standard for risk ISO 31000 to an Avalanche Mitigation Project Bruce Jamieson1 and Alan Jones2 1 Dept. of Civil

Jamieson, Bruce

165

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

166

Snow-avalanche hazard forecasting in the Krkonoše Mountains, Czechia  

NASA Astrophysics Data System (ADS)

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

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

2014-05-01

167

Silicon Avalanche Pixel Sensor for High Precision Tracking  

E-print Network

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

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

2013-11-30

168

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

169

Tuned critical avalanche scaling in bulk metallic glasses.  

PubMed

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

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

2014-01-01

170

Spontaneous avalanche ionization of a strongly blockaded Rydberg gas.  

PubMed

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

Robert-de-Saint-Vincent, M; Hofmann, C S; Schempp, H; Günter, G; Whitlock, S; Weidemüller, M

2013-01-25

171

First-principles derivation of static avalanche-size distributions  

NASA Astrophysics Data System (ADS)

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

Le Doussal, Pierre; Wiese, Kay Jörg

2012-06-01

172

First-principles derivation of static avalanche-size distributions.  

PubMed

We study the energy minimization problem for an elastic interface in a random potential plus a quadratic well. As the position of the well is varied, the ground state undergoes jumps, called shocks or static avalanches. We introduce an efficient and systematic method to compute the statistics of avalanche sizes and manifold displacements. The tree-level calculation, i.e., mean-field limit, is obtained by solving a saddle-point equation. Graphically, it can be interpreted as the sum of all tree graphs. The 1-loop corrections are computed using results from the functional renormalization group. At the upper critical dimension the shock statistics is described by the Brownian force model (BFM), the static version of the so-called Alessandro-Beatrice-Bertotti-Montorsi (ABBM) model in the nonequilibrium context of depinning. This model can itself be treated exactly in any dimension and its shock statistics is that of a Lévy process. Contact is made with classical results in probability theory on the Burgers equation with Brownian initial conditions. In particular we obtain a functional extension of an evolution equation introduced by Carraro and Duchon, which recursively constructs the tree diagrams in the field theory. PMID:23005046

Le Doussal, Pierre; Wiese, Kay Jörg

2012-06-01

173

First-principle derivation of static avalanche-size distribution  

E-print Network

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

Pierre Le Doussal; Kay Joerg Wiese

2011-11-14

174

Silicon avalanche pixel sensor for high precision tracking  

NASA Astrophysics Data System (ADS)

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

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

2014-03-01

175

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

NASA Astrophysics Data System (ADS)

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

Laute, Katja; Beylich, Achim A.

2013-04-01

176

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

NASA Astrophysics Data System (ADS)

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 flat-lying fans. Following volcanic debris avalanches a period of intense re-sedimentation commonly begins on ring-plain areas, particularly in wet or temperate climates. This is exacerbated by large areas of denuded landscape, ongoing instability in the scarp/source region, damming of river/stream systems, and in some cases inherent instability of the volcanic debris avalanche deposits. In addition, on Mt. Taranaki, the collapse of a segment of the cone by volcanic debris avalanche often generates long periods of renewed volcanism, generating large volumes of juvenile tephra onto unstable and unvegetated slopes, or construction of new domes with associated rock falls and block-and-ash flows. The distal ring-plain impact from these post-debris avalanche conditions and processes is primarily accumulation of long run-out debris flow and hyperconcentrated flow deposits with a variety of lithologies and sedimentary character. Common to these post-debris avalanche units is evidence for high-water-content flows that are typically non-cohesive. Hence sedimentary variations in these units are high in lateral and longitudinal exposure in relation to local topography. The post-collapse deposits flank large-scale fans and hence similar lithological and chronological sequences can form on widely disparate sectors of the ring plain. These deposits on Mt. Taranaki provide a record of landscape response and ring-plain evolution in three stages that divide the currently identified Warea Formation: 1) the deposition of broad fans of material adjacent to the debris avalanche unit; 2) channel formation and erosion of Stage 1 deposits, primarily at the contact between debris avalanche deposits and the Stage 1 deposits and the refilling of these channels; and 3) the development of broad tabular sheet flows on top of the debris avalanche, leaving sediments between debris avalanche mounds. After a volcanic debris avalanche, these processes represent an ever changing and evolving hazard-scape with hazard maps needing to be regularly updated to take account of which stage the sedimentary system is in.

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

2009-10-01

177

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

SciTech Connect

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

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

2013-01-15

178

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

PubMed Central

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

2014-01-01

179

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

NASA Astrophysics Data System (ADS)

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

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

2002-11-01

180

Entraining avalanches on slopes: results from experiments using PIV on viscoplastic gravity currents  

NASA Astrophysics Data System (ADS)

In order to conduct experiments simulating entrainment by avalanches on slopes, it was necessary to select a material which could act as both a stationary entrainable layer, mimicking undisturbed mud or snow, and a flowing mass, representing the flowing avalanche. Carbopol Ultrez 10, a viscoplastic "micro-gel" exhibiting a yield stress does just that: it remains plastic on a slope until an avalanche arrives and increases the shear within, reducing the viscosity in some or all of the material which may begin to flow as a fluid. Carbopol is transparent and easily seeded with fluorescent tracking micro-particles, without significantly changing the material rheology. We take advantage of its properties to perform Particle Imaging Velocimetry (PIV) on an idealized avalanche, which flows into an entrainment zone where it interacts with a layer of stationary bed material. The internal velocity field is obtained for the flow as it passes over the loose material, showing the entrainment mechanisms active at different slope angles. At the shallowest slope the avalanche is slower and mobilizes the bed almost entirely, causing it to slip along the base and buckle downstream of the front. At steeper slopes the avalanche shears the bed, yet appears to glide over it more easily with a smaller effect downstream. Increasing the concentration of the Carbopol and thus increasing the apparent yield stress leads to more destruction of the bed layer by the avalanche. Three flow phases are identified, beginning with a "rolling phase" where the avalanche has minimal effect on the bed and seems to roll onto it as the front moves forward, then a "gliding phase" where the deposited fluid is pushed downwards and glides downstream, shearing the bed material. Finally, on the shallower slopes and at higher Carbopol concentration, the avalanche digs down to the rigid base, and completely displaces the bed material downstream, with its front riding atop an entirely mobilized plug-flow layer.

Bates, Belinda; Ancey, Christophe

2014-05-01

181

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

NASA Astrophysics Data System (ADS)

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

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

2012-12-01

182

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

NASA Astrophysics Data System (ADS)

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

de Arcangelis, L.

2012-05-01

183

Nanoscale avalanche photodiode with self-quenching and ultrahigh ultraviolet/visible rejection ratio.  

PubMed

A 4H-SiC based separate-absorption-multiplication (SAM) avalanche photodiode with a nanoscale multiplication region and a bulk absorption region is proposed and its optoelectronic performance is modeled. The results show that the avalanche breakdown voltage of the device is found to be dependent on the illumination condition. This is attributed to the existence of an illumination-dependent hole potential well in the upper center of the absorption region. Based on the illumination-dependence of avalanche breakdown voltage, a self-quenching and an ultrahigh UV/visible rejection ratio have been realized in this structure. PMID:22940979

Hong, Rongdun; Zhou, Yi; Xie, Yannan; Chen, Xiaping; Zhang, Zifeng; Wang, Kang L; Wu, Zhengyun

2012-09-01

184

MACY: A Multi-wire Avalanche Counter at Yale  

NASA Astrophysics Data System (ADS)

MACY (a Multi-wire Avalanche Counter at Yale) has recently been built in the WNSL at Yale. It is a position-sensitive proportional detector that will be used at the focal plane of the gas-filled recoil spectrometer SASSYER to detect heavy ions produced in nuclear reactions. This detector comprises of an anode plane, a cathode plane, and two position-sensitive wire planes that are kept on ground potential. Its primary purpose is to distinguish recoiling nuclei of interest from scattered beam particles. It provides information on energy loss and it also serves as an efficient start detector for a time-of-flight measurement. In addition, MACY measures the X and Y position of the transmitted particle. Design and first experimental results are presented. This work has been supported by the DOE under grant numbers DE-FG02-91ER-40609 and DE-FG02-88ER-40417

Qian, J.; Heinz, A.; Sciacchitano, M.; Willams, E. T.; Ai, H.; Amro, H.; Beausang, C. W.; Casten, R. F.; McCutchan, E. A.; Meyer, D.; Millman, E. M.; Plettner, C.; Swarson, D.; Vinson, J.; Winkler, R.; Zamfir, N. V.; Gurdal, G.; Thomas, N. J.

2004-10-01

185

Construction and Testing of MACY: Multiwire Avalanche Counter at Yale  

NASA Astrophysics Data System (ADS)

The Multiwire Avalanche Counter at Yale (MACY) is a position-sensitive, gas-filled detector for use in the magnetic separator SASSYER. MACY will measure the position and time of flight of recoil nuclei -- produced in fusion evaporation reactions in the target position in Yrast Ball -- as they pass through the focal plane of SASSYER. Construction and preliminary tests using a ^241Am alpha source have been completed with promising results. Exploration of the effects of applied voltage and isobutane pressure on signal height has been done, and this data will be used to determine the optimal operating parameters. Continued testing will determine more thoroughly the limits of the detector, including position resolution, and results will be presented. Supported by the US DOE under grants DE-FG02-91ER-40609 and DE-FG02-88ER-40417.

Meyer, Deseree; Beausang, C. W.; Krücken, R. L.; Barton, C. W.; Zyromski, K. R.; Parker, P. D.; Casten, R. F.; Zamfir, N. V.; Pietralla, N.; Caprio, M. A.; Novak, J. R.; Cooper, J. R.; Hecht, A. A.; Gurdal, G.

2001-10-01

186

Elastic-Plastic-Brittle Transitions and Avalanches in Disordered Media  

NASA Astrophysics Data System (ADS)

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

Kale, Sohan; Ostoja-Starzewski, Martin

2014-01-01

187

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

PubMed

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

Kale, Sohan; Ostoja-Starzewski, Martin

2014-01-31

188

Avalanches on a conical bead pile: scaling with tuning parameters  

E-print Network

Uniform spherical beads were used to explore the behavior of a granular system near its critical angle of repose on a conical bead pile. We found two tuning parameters that could take the system to a critical point where a simple power-law described the avalanche size distribution as predicted by self-organized criticality, which proposed that complex dynamical systems self-organize to a critical point without need for tuning. Our distributions were well described by a simple power-law with the power {\\tau} = 1.5 when dropping beads slowly onto the apex of a bead pile from a small height. However, we could also move the system from the critical point using either of two tuning parameters: the height from which the beads fell onto the top of the pile or the region over which the beads struck the pile. As the drop height increased, the system did not reach the critical point yet the resulting distributions were independent of the bead mass, coefficient of friction, or coefficient of restitution. All our apex-dropping distributions for any type of bead (glass, stainless steel, zirconium) showed universality by scaling onto a common curve with {\\tau} = 1.5 and {\\sigma} = 1.0, where 1/{\\sigma} is the power of the tuning parameter. From independent calculations using the moments of the distribution, we find values for {\\tau} = 1.6 \\pm 0.1 and {\\sigma} = 0.91 \\pm 0.15. When beads were dropped across the surface of the pile instead of solely on the apex, then the system also moved from the critical point and again the avalanche size distributions fell on a common curve when scaled similarly using the same values of {\\tau} and {\\sigma}. We also observed that an hcp structure on the base of the pile caused an emergent structure in the pile that had six faces with some fcc or hcp structure.

S. Y. Lehman; Elizabeth Baker; Howard A. Henry; Andrew J. Kindschuh; Larry C. Markley; Megan B. Browning; Mary E. Mills; R. Michael Winters IV; D. T. Jacobs

2012-01-02

189

Critical Scaling of Avalanche Dynamics in Sheared Amorphous Solids with Inertia  

NASA Astrophysics Data System (ADS)

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

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

2013-03-01

190

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

NASA Astrophysics Data System (ADS)

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

Baker, Jennifer

191

RF SMALL SIGNAL AVALANCHE CHARACTERIZATION AND REPERCUSSIONS ON BIPOLAR TRANSISTOR CIRCUIT DESIGN  

E-print Network

RF SMALL SIGNAL AVALANCHE CHARACTERIZATION AND REPERCUSSIONS ON BIPOLAR TRANSISTOR CIRCUIT DESIGN transistor circuits, electronic circuit designers are exploring regimes of transistor operation that meet on some important transistor properties like unilateral and maximum available power gain, as well

Technische Universiteit Delft

192

Two-phase argon and xenon avalanche detectors based on Gas Electron Multipliers  

E-print Network

We study the performance of two-phase avalanche detectors based on Gas Electron Multipliers (GEMs) and operated in an electron-avalanching mode in Ar and Xe. Emission, gain, energy resolution and stability characteristics of the detectors were studied. Rather high gains, reaching 5000, and stable operation for several hours were observed in the two-phase Ar avalanche detector using a triple-GEM multiplier. The signals induced by X-rays, beta-particles and gamma-rays were successfully recorded. Preliminary results were obtained in the two-phase Xe avalanche detector: the maximum gain of the triple-GEM in two-phase Xe and Xe+2%CH4 was about 200. The results obtained are relevant in the field of two-phase detectors for dark matter searches, coherent neutrino scattering, PET and digital radiography.

Bondar, A; Grebenuk, A; Pavlyuchenko, D; Snopkov, R; Tikhonov, Yu A

2006-01-01

193

{Road Traffic and Avalanches - Methods for Risk Evaluation and Risk Management  

NASA Astrophysics Data System (ADS)

This paper considers the methods for risk analysis and management in connection with avalanches and road traffic. Examples with calculations of encounter probability and quantification of uncertainty are given, along with suggestions for risk management in Norway.

Kristensen, Krister; Kristensen, Carl Bonnevie; Harbitz, Alf

2003-11-01

194

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

E-print Network

States of America, 2 Laboratory of Mathematical Physics, The Rockefeller University, New York, New York systems, such as earthquakes or sandpile avalanches, permanently evolve at a phase transition point

Destexhe, Alain

195

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

196

Time-varying force from dense granular avalanches on a wall Benoit Chanut, Thierry Faug  

E-print Network

. It also drives the residual force corresponding to the avalanche tail until its standstill whatever in industrial processes [1] as well as protection dams against geophysical flows [2­6]. Granular drag on objects

Paris-Sud XI, Université de

197

Regional comparison of old-deep slab avalanches David Tracz1  

E-print Network

régions. 1 INTRODUCTION Deep slab avalanches are a unique and difficult to forecast natural hazard. Little usually makes human triggering less frequent. The long burial time of the weak layer as well as the large

Jamieson, Bruce

198

4H-SiC Nano-Pillar Avalanche Photodiode With Illumination-Dependent Characteristics  

Microsoft Academic Search

A 4H-SiC nano-pillar-based avalanche photodiode (NAPD) with a separate absorption region and a multiplication region is proposed and its optoelectronic performance is modeled. By properly designing the device geometry and the doping con- centration of each layer, the avalanche breakdown voltage of the NAPD is found to be dependent of the incident wavelength and power density, which are explained by

Rongdun Hong; Yi Zhou; Kang Long Wang; Zhengyun Wu

2011-01-01

199

Nonlocal effects in thin 4H-SiC UV avalanche photodiodes  

Microsoft Academic Search

The avalanche multiplication and excess noise characteristics of 4H-SiC avalanche photodiodes with i-region widths of 0.105 and 0.285 ?m have been investigated using 230-365-nm light, while the responsivities of the photodiodes at unity gain were examined for wavelengths up to 375 nm. Peak unity gain responsivities of more than 130 mA\\/W at 265 nm, equivalent to quantum efficiencies of more

B. K. Ng; John P. R. David; Richard C. Tozer; Graham J. Rees; Feng Yan; Jian H. Zhao; Maurice Weiner

2003-01-01

200

High-performance SiC avalanche photodiode for single ultraviolet photon detection  

Microsoft Academic Search

Sensitive ultraviolet photodetectors are essential components for a growing number of civilian and military applications. In this paper, we report 4H Silicon Carbide (SiC) avalanche photodiodes (APDs) with a p-i-n structure. These APDs, range in diameter from 180 mum to 250mum, exhibit very low dark current (10s of pA at avalanche gain of 1000) and high gain in linear-mode operation.

Xiaogang Bai; Han-din Liu; Dion McIntosh; Joe C. Campbell

2008-01-01

201

High single photon detection efficiency 4H-SiC avalanche photodiodes  

Microsoft Academic Search

Detection of low-level ultraviolet (UV) light has been the focus of numerous research and development efforts in recent years. To date, the most promising solid-state solution is SiC avalanche photodiodes. We report 4H-SiC avalanche photodiodes with low dark current and high gain. Geiger mode operation with high single photon detection efficiency and low dark count probability has been achieved. The

Xiaogang Bai; Dion McIntosh; Han-Din Liu; Joe C. Campbell

2009-01-01

202

4H-SiC PIN Recessed-Window Avalanche Photodiode With High Quantum Efficiency  

Microsoft Academic Search

We report a 4H-SiC PIN recessed-window avalanche photodiode with a peak responsitivity of 136 mA\\/W (external quantum efficiency = 60%) at lambda = 262 nm, corresponding to more than a 50% increase in external quantum efficiency compared to nonrecessed structures. The dark current was 90 pA at a photocurrent gain of 1000. Avalanche gains of over 106, k ~ 0.1,

Handin Liu; Dion McIntosh; Xiaogang Bai; Huapu Pan; Mingguo Liu; Joe C. Campbell; Ho Young Cha

2008-01-01

203

Ultraviolet Single Photon Detection With Geiger-Mode 4H-SiC Avalanche Photodiodes  

Microsoft Academic Search

We report 4H-SiC avalanche photodiodes operated in Geiger mode for single photon detection at 265 nm. At room temperature, the single photon detection efficiency is 14% with a dark count probability of 1.7 x 10-4. Since the external quantum efficiency is 21% at 265 nm, it follows that 65% of the absorbed photons are counted as avalanche events. The jitter

Xiaogang Bai; Dion McIntosh; Handin Liu; Joe C. Campbell

2007-01-01

204

Multiplication and excess noise characteristics of thin 4H-SiC UV avalanche photodiodes  

Microsoft Academic Search

The avalanche multiplication and excess noise characteristics of thin 4H-SiC avalanche photodiodes with an i-region width of 0.1 ?m have been investigated. The diodes are found to exhibit multiplication characteristics which change significantly when the wavelength of the illuminating light changes from 230 to 365 nm. These multiplication characteristics show unambiguously that ?>? in 4H-SiC and that the ?\\/? ratio

B. K. Ng; F. Yan; J. P. R. David; R. C. Tozer; G. J. Rees; C. Qin; J. H. Zhao

2002-01-01

205

Improvements in avalanche-transistor sweep circuitry for electro-optic streak cameras  

Microsoft Academic Search

The authors have improved the performance of the avalanche-transistor deflector-driver (sweep) circuitry used in the high-speed, electro-optic streak camera at Lawrence Livermore National Laboratory. In the previous design for the sweep circuit, trigger-to-output delay time drifted on some cameras. This delay drift is a function of a somewhat randomly unstable breakdown voltage of some avalanche transistors. Both temperature and differences

S. W. Thomas; R. L. Griffith; W. R. McDonald

1986-01-01

206

Classical analogy for the deflection of flux avalanches by a metallic layer  

NASA Astrophysics Data System (ADS)

Sudden avalanches of magnetic flux bursting into a superconducting sample undergo deflections of their trajectories when encountering a conductive layer deposited on top of the superconductor. Remarkably, in some cases the flux is totally excluded from the area covered by the conductive layer. We present a simple classical model that accounts for this behaviour and considers a magnetic monopole approaching a semi-infinite conductive plane. This model suggests that magnetic braking is an important mechanism responsible for avalanche deflection.

Brisbois, J.; Vanderheyden, B.; Colauto, F.; Motta, M.; Ortiz, W. A.; Fritzsche, J.; Nguyen, N. D.; Hackens, B.; Adami, O.-A.; Silhanek, A. V.

2014-10-01

207

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

PubMed

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

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

2013-07-15

208

Bayesian stochastic modelling for avalanche predetermination: from a general system framework to return period computations  

Microsoft Academic Search

Stochastic models are recent but unavoidable tools for snow avalanche hazard mapping that can be described in a general system\\u000a framework. For the computation of design return periods, magnitude and frequency have to be evaluated. The magnitude model\\u000a consists of a set of physical equations for avalanche propagation associated with a statistical formalism adapted to the input–output\\u000a data structure. The

N. Eckert; E. Parent; M. Naaim; D. Richard

2008-01-01

209

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

NASA Astrophysics Data System (ADS)

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

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

2012-04-01

210

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

211

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

PubMed

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

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

2014-08-01

212

Foliage penetration optimization for Geiger-mode avalanche photodiode lidar  

NASA Astrophysics Data System (ADS)

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

Johnson, Steven E.

2013-05-01

213

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

214

Radiation tests of single photon avalanche diode for space applications  

NASA Astrophysics Data System (ADS)

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

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

2013-05-01

215

Avalanches in compressed porous SiO2-based materials  

NASA Astrophysics Data System (ADS)

The failure dynamics in SiO2-based porous materials under compression, namely the synthetic glass Gelsil and three natural sandstones, has been studied for slowly increasing compressive uniaxial stress with rates between 0.2 and 2.8 kPa/s. The measured collapsed dynamics is similar to Vycor, which is another synthetic porous SiO2 glass similar to Gelsil but with a different porous mesostructure. Compression occurs by jerks of strain release and a major collapse at the failure point. The acoustic emission and shrinking of the samples during jerks are measured and analyzed. The energy of acoustic emission events, its duration, and waiting times between events show that the failure process follows avalanche criticality with power law statistics over ca. 4 decades with a power law exponent ? ? 1.4 for the energy distribution. This exponent is consistent with the mean-field value for the collapse of granular media. Besides the absence of length, energy, and time scales, we demonstrate the existence of aftershock correlations during the failure process.

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

2014-08-01

216

Characterization of Advanced Avalanche Photodiodes for Water Vapor Lidar Receivers  

NASA Technical Reports Server (NTRS)

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

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

2000-01-01

217

Avalanche photodiode photon counting receivers for space-borne lidars  

NASA Technical Reports Server (NTRS)

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

Sun, Xiaoli; Davidson, Frederic M.

1991-01-01

218

Dynamic behavior of magnetic avalanches in the spin-ice compound Dy2Ti2O7  

NASA Astrophysics Data System (ADS)

Avalanches of the magnetization, that is to say an abrupt reversal of the magnetization at a given field, have been previously reported in the spin-ice compound Dy2Ti2O7. This out-of-equilibrium process, induced by magnetothermal heating, is quite usual in low-temperature magnetization studies. A key point is to determine the physical origin of the avalanche process. In particular, in spin-ice compounds, the origin of the avalanches might be related to the monopole physics inherent to the system. We have performed a detailed study of the avalanche phenomena in three single crystals, with the field oriented along the [111] direction, perpendicular to [111], and along the [100] directions. We have measured the changing magnetization during the avalanches and conclude that avalanches in spin ice are quite slow compared to the avalanches reported in other systems such as molecular magnets. Our measurements show that the avalanches trigger after a delay of about 500 ms and that the reversal of the magnetization then occurs in a few hundreds of milliseconds. These features suggest an unusual propagation of the reversal, which might be due to the monopole motion. The avalanche fields seem to be reproducible in a given direction for different samples, but they strongly depend on the initial state of magnetization and on how the initial state was achieved.

Jackson, M. J.; Lhotel, E.; Giblin, S. R.; Bramwell, S. T.; Prabhakaran, D.; Matsuhira, K.; Hiroi, Z.; Yu, Q.; Paulsen, C.

2014-08-01

219

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

NASA Astrophysics Data System (ADS)

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

Bartelt, Perry; Buser, Othmar; Glover, James

2014-05-01

220

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

221

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

SciTech Connect

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

Glicken, H.

1985-01-01

222

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

USGS Publications Warehouse

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

Crandell, Dwight Raymond; Fahnestock, Robert K.

1965-01-01

223

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

224

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

PubMed Central

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

Jenkinson, Garrett; Goutsias, John

2014-01-01

225

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

226

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

NASA Astrophysics Data System (ADS)

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

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

2010-05-01

227

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

NASA Technical Reports Server (NTRS)

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

2003-01-01

228

Short-Wave Infrared HgCdTe Avalanche Photodiodes  

NASA Astrophysics Data System (ADS)

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

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

2012-10-01

229

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

NASA Astrophysics Data System (ADS)

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

Deline, Philip; Kirkbride, Martin P.

2009-01-01

230

Transmission of packets on a hierarchical network: Avalanches, statistics and explosive percolation  

E-print Network

We discuss transport on load bearing branching hierarchical networks which can model diverse systems which can serve as models of river networks, computer networks, respiratory networks and granular media. We study avalanche transmissions and directed percolation on these networks, and on the V lattice, i.e., the strongest realization of the lattice. We find that typical realizations of the lattice show multimodal distributions for the avalanche transmissions, and a second order transition for directed percolation. On the other hand, the V lattice shows power - law behavior for avalanche transmissions, and a first order (explosive) transition to percolation. The V lattice is thus the critical case of hierarchical networks. We note that small perturbations to the V lattice destroy the power-law behavior of the distributions, and the first order nature of the percolation. We discuss the implications of our results.

Gupte, Neelima

2014-01-01

231

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

PubMed

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

Tarjus, Gilles; Baczyk, Maxime; Tissier, Matthieu

2013-03-29

232

Memory effects in avalanche dynamics: a key to the statistical properties of earthquakes  

E-print Network

Many complex systems respond to continuous input of energy by accumulation of stress over time and sudden energy releases in the form of avalanches. Avalanches are paradigmatic non-equilibrium phenomena displaying power law size distribution and involving all the length scales in the system. Conventional avalanche models disregard memory effects and thus miss basic features observed in real systems. Notable examples are aftershocks and the anomalous exponent of the Gutenberg-Richter law which characterize earthquake statistics. We propose a model which accounts for memory effects through the introduction of viscoelastic relaxation at an intermediate time scale. We demonstrate that in the resulting dynamics, coherent oscillations of the stress field emerge spontaneously without fine tuning of any parameter. Remarkably, in two dimensions, which is relevant in seismicity, these oscillations generate instability patterns that produce realistic earthquake dynamics with the correct Gutenberg-Richter exponent.

Jagla, E A; Rosso, Alberto

2013-01-01

233

Crossover behavior in the avalanche process of the fiber bundle model in local load sharing  

NASA Astrophysics Data System (ADS)

The crossover behavior near the catastrophic failure in the avalanche process of fiber bundle model in local load sharing condition is numerically investigated by dividing the tensile stretching process into several segments. In every segment of the tensile process, the fracture parameters, such as the number of fracture fibers, the energy emission, the avalanche size and its distribution, are calculated respectively. The results illustrate that the evolution of the fracture process from the initial tensile stage to the final fracture can be well described by a power law relationship or a simple quadratic polynomial. In the vicinity of the catastrophic failure, the avalanche size distribution appear crossover behavior with two different power law exponents, which provides a possible route for theoretically predicting the catastrophic fracture of materials.

Hao, Da-Peng; Tang, Gang; Xun, Zhi-Peng; Xia, Hui; Han, Kui

2014-12-01

234

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

SciTech Connect

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

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

2013-04-15

235

Recent results on avalanche phenomena for Al and Zn superconducting granule colloids  

NASA Astrophysics Data System (ADS)

The operation of Al and Zn superheated superconducting granules (SSGs) is studied to determine the existence of the avalanche phenomenon. The SSGs are operated at temperatures reaching a minimum of 40 mK embedded in a varnish GE 7031 coating. The signals in this range appear to duplicate the results of tests at 400 mK for 'avalanche' phenomena which can be related to latent heat exchanges. Because the cause of the avalanches is not confirmed, the mechanism of latent heat exchange cannot be conclusively described; further, it is not clear whether the phenomenon can be controlled for practical applications. The investigation does, however, lend evidence to the existence of collective effects within the SSG colloid, suggesting that an SSG colloid be treated as a collective or a composite medium and not as an assembly of single grains.

Freund, P.; Gebauer, J.; Boniface, J.; Gonzalez-Mestres, L.; Perret-Gallix, D.

236

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

237

How Burial Time of Avalanche Victims is Influenced by Rescue Method: An Analysis of Search Reports from the Alps  

Microsoft Academic Search

Two hundred and seventeen avalanche reports from Switzerland and the Tyrol were used to investigate the influence of rescue method on the survival and burial time of avalanche victims. The probability of survival for victims rescued by their companion was higher (75, n=113) than for people found by an organised search team (30, n=104). Burial time and burial depth are

Leopold Slotta-bachmayr

2005-01-01

238

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

239

High single photon detection efficiency 4H-SiC avalanche photodiodes  

NASA Astrophysics Data System (ADS)

Detection of low-level ultraviolet (UV) light has been the focus of numerous research and development efforts in recent years. To date, the most promising solid-state solution is SiC avalanche photodiodes. We report 4H-SiC avalanche photodiodes with low dark current and high gain. Geiger mode operation with high single photon detection efficiency and low dark count probability has been achieved. The dark current behavior of a 4x4 array of SiC APDs is also presented.

Bai, Xiaogang; McIntosh, Dion; Liu, Han-Din; Campbell, Joe C.

2009-05-01

240

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

241

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

NASA Technical Reports Server (NTRS)

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

Arbel, D.; Schwartz, J. A.

1991-01-01

242

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

PubMed

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

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

2011-06-01

243

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

NASA Astrophysics Data System (ADS)

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

Swartwout, M.

244

Depth Averaged Equations Applied To Study of Defense Structures Effects On Dense Avalanche Flows  

NASA Astrophysics Data System (ADS)

Avalanche zoning and protection devices are the complementary tools used to assess avalanche risk and protect persons and human activities in mountainous areas. Despite the intensive use of defense structures as protection against avalanches, their hydraulic and structural effects are not well known. Many structures were designed empirically using expert knowledge or knowledge developed in other domain such as hydraulic. Defence structures effects in terms of energy dissipation, deviation and snow retention are difficult to study in situ. The cost and difficulties of experiments, the danger and the weak annual number of avalanches in a given site, are the reasons why scientists oriented their research towards the use of numerical or laboratory physical models. This paper presents and discuss the possibilities to use depth averaged equations to study dense avalanche flows around defence structures. The used numerical resolu- tion method is based on an upwind numerical scheme. Equations are integrated on each cell of the mesh and the numerical fluxes are calculated thanks to a simplified Riemann solver where the retained solution is obtained as a combination of shock and rarefaction founctions. This allows taking into account the topography variation and jets and surges presence. These two characteristics are needed because both exper- imental and in situ observations showed a significant topography modifications and jets and surges formations during interaction between avalanche flows and structures. The case of vertical surfaces such as those made of concrete destined to deviate flows are treated by appropriated boundary condition functions. A discussion about the best way to integrate defence structures in such model is presented and discussed. This modelisation has, in a first time, been tested on analytical solutions and on experimen- tal laboratory scale model results. These tests have shown the capacity of this model, despite the strong hypothesis, to reproduce correctly some experimentally observed characteristics. In a second phase, this model was applied to study a well documented real case where a large avalanche flow interacted with a complex protection device composed of several types of defence structures. This comparison showed a good con- formity between the numerical results and in-situ observations concerning the global characteristics of the flows such as the deposit and the trajectory of the avalanche.

Naaim, M.; Bouvet-Naaim, F.; Faug, T.; Lachamp, P.

245

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

NASA Astrophysics Data System (ADS)

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

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

2012-06-01

246

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

E-print Network

: Snow avalanches threaten mountain communities worldwide: avalanches affect not only snow sport tourists, as it is generally done for snow sport tourists but also on avalanche dynamics and interaction with structures led to the construction of communication ties to mountain valleys, infrastructures to host people

Paris-Sud XI, Université de

247

Analysis of rock-fall and rock-fall avalanche seismograms in the French Alps  

E-print Network

/or rolling, with a very rapid to extremely rapid movement. After a free fall with a vertical drop Hf from1 Analysis of rock-fall and rock-fall avalanche seismograms in the French Alps J. Deparis, D reviews seismograms from 10 rock-fall events recorded between 1992 and 2001 by the permanent seismological

Paris-Sud XI, Université de

248

The blocking probability of Geiger-mode avalanche photo-diodes  

NASA Technical Reports Server (NTRS)

When a photo is detected by a Geiger-mode avalanche photo-diode (GMAPD), the detector is rendered inactive, or blocked, for a certain period of time. In this paper we derive the blocking probability for a GMAPD whose input is either an unmodulated, Benoulli modulated or pulse-position-modulated Poisson process.

Moision, Bruce; Srinivasan, Meera; Hamkins, Jon

2005-01-01

249

Two-phase Numerical Model of Powder Avalanche Theory and Application  

Microsoft Academic Search

In this paper the powder snow avalanche is considered as a two-phase flow (air and snow particles). The equations governing this flow are the fluid mechanics conservation laws. The mass and the momentum conservation are considered for each phase. The interaction between the two phases takes into account the drag force between the particle and the air. Owing to high

Mohamed Naaim; Ibrahim Gurer

1998-01-01

250

PHYSICAL REVIEW E 84, 061103 (2011) Avalanche spatial structure and multivariable scaling functions  

E-print Network

-Parisi-Zhang (qKPZ) equation. We fully characterize the spatial structure of these avalanches--we report universal scaling functions, including corrections to scaling and systematic error bars, facilitated by a novel be described by the same family of front-propagation models. In this paper, we study the spatial structures

Sethna, James P.

251

Silicon Avalanche Photodetectors Fabricated With Standard CMOS/BiCMOS Technology  

E-print Network

Silicon Avalanche Photodetectors Fabricated With Standard CMOS/BiCMOS Technology Myung-Jae Lee Photonics for High-Speed Interconnects .....1 1-2. Silicon Photodetectors in Standard CMOS/BiCMOS Technology/BiCMOS Technology for Photodetectors .......................................................7 2-2. Silicon

Choi, Woo-Young

252

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

253

First principles numerical model of avalanche-induced arc discharges in electron-irradiated dielectrics  

NASA Technical Reports Server (NTRS)

The model consists of four phases: single electron dynamics, single electron avalanche, negative streamer development, and tree formation. Numerical algorithms and computer code implementations are presented for the first three phases. An approach to developing a code description of fourth phase is discussed. Numerical results are presented for a crude material model of Teflon.

Beers, B. L.; Pine, V. W.; Hwang, H. C.; Bloomberg, H. W.; Lin, D. L.; Schmidt, M. J.; Strickland, D. J.

1979-01-01

254

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

E-print Network

Numerical simulations of dense clouds on steep slopes: Application to powder­snow avalanches of Glaciology, vol. 38 Abstract In this paper two­dimensional Direct Numerical Simulations (DNS) of dense clouds in the laboratory. Direct numerical simulations give, in addition to the overall flow structure, local density

Saramito, Pierre

255

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

E-print Network

Numerical simulations of dense clouds on steep slopes: Application to powder-snow avalanches of Glaciology, vol. 38 Abstract In this paper two-dimensional Direct Numerical Simulations (DNS) of dense clouds in the laboratory. Direct numerical simulations give, in addition to the overall flow structure, local density

Saramito, Pierre

256

Three-dimensional modeling and numerical simulations of avalanches over a real mountain topography  

NASA Astrophysics Data System (ADS)

For real three-dimensional numerical simulations of avalanches over mountain topography, we have developed a new preprocessor that generates the mesh and sets the initial conditions. In our approach, first we select the region of interest on which the preprocessor creates a colored overlay with possible starting positions, then we choose the initial sliding zone. Afterwards, the preprocessor creates an unstructured triangulated surface. Together with an initial hexahedral mesh, the utility, called the snappyHexMesh in the OpenFOAM software package [1], creates the final mesh. Our second reprocessing utility sets the initial conditions needed by the numerical solver for the avalanche flow simulation. In the next step, we calculate the flow dynamics with our numerical solver, which is based on interFoam [1]. Different rheological models and parameters can be chosen in this solver. We implement, for the first time, the Coulomb-type internal friction rheology with a Coulomb sliding law at the base in connection to the continuum dynamical model equations for the mass and momentum balances. We show good comparisons between our numerical solutions and published results of small scale laboratory experiments. We also present some preliminary results for avalanche flows down real mountain slopes. When calibrated with field measurements, our numerical simulations (based on the full three-dimensional flow dynamics) can provide a deeper understanding of the dynamics of real avalanches, with applications to proper hazard mapping and improved risk management. [1] http://www.openfoam.org/

Kröner, C.; Pudasaini, S. P.

2012-04-01

257

The Relative Importance of Snow Avalanche Disturbance and Thinning on Canopy Plant Populations  

E-print Network

; mortality; Picea engelmannii; Pinus contorta; plant populations; Rocky Mountains; Salix glauca; snow (Pinus contorta) and Engelmann spruce (Picea engelmannii) bend when small, but were broken by avalanches glauca) never grew large enough to break. Breakage was influenced by size rather than wood elasticity

Johnson, Edward A.

258

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

259

Ultraviolet separate absorption and multiplication 4H-SiC avalanche photodiodes  

Microsoft Academic Search

We report separate absorption and multiplication 4H-SiC avalanche photodiodes. An external quantum efficiency of 83% (187 mA\\/W) at 278 nm corresponding to unity gain after reach-through was achieved. Gain higher than 1000 was demonstrated without edge breakdown

Xiangyi Guo; Larry B. Rowland; Greg T. Dunne; Jody A. Fronheiser; Peter M. Sandvik; Ariane L. Beck; Joe C. Campbell

2005-01-01

260

Electrical characterization of 4H-SiC avalanche photodiodes containing threading edge and screw dislocations  

Microsoft Academic Search

The reverse voltage current characteristics and electroluminescence of small area 4H-SiC avalanche photodiodes were investigated and correlated with the presence of threading screw and edge dislocations. Localized electroluminescence was observed at threading dislocations at voltages close to breakdown whereas diodes without any extended defects exhibited uniform light emission in the active area. Diodes containing either edge or screw dislocations were

R. A. Berechman; M. Skowronski; S. Soloviev; P. Sandvik

2010-01-01

261

Demonstration of ultraviolet separate absorption and multiplication 4H-SiC avalanche photodiodes  

Microsoft Academic Search

We report ultraviolet separate absorption and multiplication 4H-SiC avalanche photodiodes. An external quantum efficiency of 83% (187 mA\\/W) at 278 nm, corresponding to unity gain after reach-through was achieved. A gain higher than 1000 was demonstrated without edge breakdown.

Xiangyi Guo; Larry B. Rowland; Greg T. Dunne; Jody A. Fronheiser; Peter M. Sandvik; Ariane L. Beck; Joe C. Campbell

2006-01-01

262

Geiger mode operation of ultraviolet 4H-SiC avalanche photodiodes  

Microsoft Academic Search

We report single photon counting in p-n junction 4H-SiC avalanche photodetectors. At 325 nm, the unity-gain external quantum efficiency was 10% and the single photon detection efficiency was 2.9%. This result represents ?30% of the maximum attainable detection efficiency.

A. L. Beck; G. Karve; S. Wang; J. Ming; X. Guo; J. C. Campbell

2005-01-01

263

Proton-Implantation-Isolated 4H-SiC Avalanche Photodiodes  

Microsoft Academic Search

We report 4H-SiC p-i-n structure avalanche photodiodes (APDs) isolated by proton implantation. These APDs achieved low dark current (670 nA\\/cm2 at a gain of 1000) and gains as high as 105. The external quantum efficiency was 44% at 278 nm.

Qiugui Zhou; Han-Din Liu; Dion C. McIntosh; Chong Hu; Xiaoguang Zheng; Joe C. Campbell

2009-01-01

264

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

E-print Network

of as a particular limit rk k>> =( ) 0 of the more general convective cell structure. In contrast to the familiar, and on streamers, or radially extended convective cells, as a possible concrete realization of the avalanche distribution function (pdf) of the transport flux are also identified. In particular, we show

Diamond, Patrick H.

265

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

E-print Network

­12], and as earthquakes driven by motion of tectonic plates [13­16]. Some features of the avalanche statistics, like size retardation effects. We show that under monotonous driving the particle moves forward at all times, as it does of earthquakes. We analyze quantitatively the limits of slow and fast relaxation for stationary driving

Wiese, Kay Jörg

266

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

E-print Network

argue that this phenomenon is closely analogous to the propagation of a flame front (deflagration) in which the initial relaxation of the magnetization toward the direction of the field results fields,9 have confirmed the thermal nature of the avalanches. More recently, the electromagnetic signal

Lombardi, John R.

267

On the effect of synchrotron radiation and magnetic fluctuations on the avalanche runaway growth rate  

E-print Network

reactors.2 The avalanche mechanism has been treated theoretically in several publications. In Ref. 3 levels b~ 10 3 . © 2000 American Institute of Physics. S1070-664X 00 02209-6 The generation process particles. The results were valid for the entire parameter range of interest and pro- vide good physical

Martín-Solís, José Ramón

268

Single-photon avalanche detectors for low-light-level imaging  

Microsoft Academic Search

Linear arrays of single photon avalanche detectors (SPADs) designed for use in low light level imaging applications were fabricated using a novel planar process that is compatible with standard CMOS technology. The device characteristics for these arrays are presented here to investigate their suitability for high efficiency low light level imaging. A new scheme is proposed to eliminate the problem

Alan P. Morrison; Vasileios S. Sinnis; Alan Mathewson; Franco Zappa; Laura Varisco; Massimo Ghioni; Sergio D. Cova

1997-01-01

269

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

270

Flood avalanches in a semiarid basin with a dense reservoir network  

NASA Astrophysics Data System (ADS)

This study investigates flood avalanches in a dense reservoir network in the semiarid north-eastern Brazil. The population living in this area strongly depends on the availability of the water from this network. Water is stored during intense wet-season rainfall events and evaporates from the reservoir surface during the dry season. These seasonal changes are the driving forces behind the water dynamics in the network. The reservoir network and its connectivity properties during flood avalanches are investigated with a model called ResNetM, which simulates each reservoir explicitly. It runs on the basis of daily calculated water balances for each reservoir. A spilling reservoir contributes with water to the reservoir downstream, which can trigger avalanches affecting, in some cases, large fractions of the network. The main focus is on the study of the relation between the total amount of water stored and the largest observable cluster of connected reservoirs that overspill in the same day. It is shown that the thousands of small and middle-sized reservoirs are eminent for the retention of water upstream the large ones. Therefore, they prevent large clusters at a low level of water. Concerning connectivity measures, the actual reservoir network, which evolved without an integrated plan, performed better (i.e., generated smaller avalanches for similar amount of stored water) than numerous stochastically generated artificial reservoir networks on the same river network.

Peter, Samuel J.; de Araújo, José Carlos; Araújo, Nuno A. M.; Herrmann, Hans Jürgen

2014-05-01

271

A Single Photon Avalanche Diode Array Fabricated in Deep-Submicron CMOS Technology  

Microsoft Academic Search

We report the first fully integrated single photon avalanche diode array fabricated in 0.35 mum CMOS technology. At 25 mum, the pixel pitch achieved by this design is the smallest ever reported. Thanks to the level of miniaturization enabled by this design, we were able to build the largest single photon streak camera ever built in any technology, thus proving

Cristiano Niclass; Maximilian Sergio; Edoardo Charbon

2006-01-01

272

A single photon avalanche diode array fabricated in deep-submicron CMOS technology  

Microsoft Academic Search

We report the first fully integrated single photon avalanche diode array fabricated in 0.35µm CMOS technology. At 25µm, the pixel pitch achieved by this design is the smallest ever reported. Thanks to the level of miniaturization enabled by this design, we were able to build the largest single photon streak camera ever built in any technology, thus proving the scalability

Cristiano Niclass; Maximilian Sergio; Edoardo Charbon

2006-01-01

273

The Oeschinensee rock avalanche: reconstruction and dating of a prehistoric event  

NASA Astrophysics Data System (ADS)

Some of the most dramatic examples of alpine rock avalanches can be found in the Kandersteg area of the central Swiss Alps. Most of these slope failures have been interpreted to be late- or postglacial in age, however the precise failure timing is rarely known. Here we present a case study of the prehistoric Oeschinensee rock avalanche, whose deposit dams the lake Oeschinen in the UNESCO world heritage site Jungfrau-Aletsch-Bietschhorn. Detailed field investigations revealed a deposit area of roughly 1.8 million m2, composed of scattered and fractured blocks and large boulders, which is in places more than 100 m thick. The release area consists of an inclined sliding plane (dipping about 35 degrees) and steep rock cliff on the southern side of the valley above the lake. Preliminary estimates show that the failure released roughly 135 million m3 of sedimentary rock, which travelled first across the valley then turned downstream. We investigate geomorphological features and the distribution of material within the rock avalanche deposit, and in addition reconstruct past topography and model the event runout to determine relevant physical and frictional flow parameters. We then use Cl-36 cosmogenic surface exposure dating of boulders on top of the deposit to determine the age of the failure. These results will help clarify when the rock avalanche occurred, the failure scenario in relation to deglaciation and changing climate, and the age of formation of the lake Oeschinen.

Köpfli, P.; Moore, J. R.; Ivy-Ochs, S.

2012-04-01

274

FlowCapt: a new acoustic sensor to measure snowdrift and wind velocity for avalanche forecasting  

Microsoft Academic Search

Wind can create even greater unstable accumulations of snow in mountainous areas than heavy snowfalls. But knowing wind conditions is not sufficient to predict these accumulations because their formations also depend on the snow quality of the snowpack surface upwind of the release zone. Consequently, assessment of snowdrift is required to improve avalanche forecasting. In accordance with this assumption, a

V Chritin; R Bolognesi; H Gubler

1999-01-01

275

Crosstalk analysis of integrated Geiger-mode avalanche photodiode focal plane arrays  

E-print Network

Arrays of photon-counting Geiger-mode avalanche photodiodes (APDs) sensitive to 1.06 and 1.55 µm wavelengths and as large as 256 x 64 elements on 50 µm pitch have been fabricated for defense applications. As array size, ...

Younger, Richard D.

276

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

277

Analysis and simulatin of rock avalanche sequence in the Cerro Caquilluco landslide (Tacna, Peru)  

NASA Astrophysics Data System (ADS)

The Cerro Caquilluco (Tacna, Peru) rock avalanche complex has a total volume of about 15 km3 and a length of 43 km, extending from 3900 m a.s.l to 530 m a.s.l.. Based on geomorphological interpretation and lithological evidences, we reconstructed a possible rock-avalanches sequence consisting of at least nine major events. For each event, we calculated the mobilized volumes through the comparison of pre- and post-failure morphology. We argue that the first rock avalanche event corresponds to the Cerrillos Negros rock avalanche, characterized by a distal tongue shaped lobe, 11 km long, 3 km wide and 25 to 60 m thick (rough volume estimate 1.15 km3), deposited along the piedmont surface (average slope: 2° ). The reconstruction of pristine pre-failure morphology was accomplished by mimicking the preserved morphology close to the source area, and by removing the deposited volumes from the rock avalanche path. For this, we made the hypothesis that the old paleosurface was already eroded by valleys progressively moving upstream during a wetter climate, as suggested by Hoke et al (2007) for similar conditions in northern Chile. The reconstruction of the pre-event morphology required several attempts to fit the eroded and the deposited volumes. Finally, a total mobilized volume of about 10.2 km2 was obtained for this event. For the successive scenarios of slide retrogression, we used the morphologies obtained by previous scenarios as pre-failure morphologies, and we calculated, by difference with current topography, the lobe volumes. The volumes of single rock avalanche episodes decrease from the first to the last event, roughly following a power-law decay. This behavior is comparable to that described by Utili and Crosta (2011) for retrogressive instabilities in rocky cliffs. The rock-avalanche events have been simulated, to verify the different scenarios in terms of spreading area and maximum runout, by using SPH (Smooth Particle Hydrodynamics) and Finite Element codes. Different equivalent fluid models were tested and a frictional rheology was finally selected. The results of numerical model are presented and compared with mapped runout. Hoke G D, Isacks B L, Jordan T E, Blanco N, Tomlinson A J, Ramezani J, (2007) Geomorphic evidence for post-10 Ma uplift of the western ?ank of the central Andes 18° 30'-22° S. Tectonics 26. Utili S, Crosta G B (2011) Modeling the evolution of natural cliffs subject to weathering: 1. Limit analysis approach. Journal of Geophysical Research: Earth Surface (2003-2012), 116(F1).

Crosta, Giovanni B.; Frattini, Paolo; Valbuzzi, Elena; Hermanns, Reginald L.

2014-05-01

278

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

279

Avalanche Upconversion in THULIUM:LITHIUM Yttrium Fluoride, THULIUM:YTTRIUM Aluminum Oxide and THULIUM:YAG.  

NASA Astrophysics Data System (ADS)

This thesis reports original observations and theory of strong, induced excited state absorption and emission, known as avalanche upconversion, in thulium doped crystals. The nonlinear dynamics responsible for this phenomenon and its characteristic threshold are studied in great detail, and shown to consist of two distinct cooperative processes, namely near-neighbor cross relaxation(s) and excitation migration among more distant ion pairs. The temperature dependence of avalanche upconversion and cross relaxation in these materials is explained for the first time. Also, phase conjugation with threshold behavior and potential motion sensitivity for novelty filtering is demonstrated utilizing an avalanche nonlinearity. Complex, transverse ring structures observed in Gaussian beam propagation through avalanche media are explained on the basis of numerical simulations of avalanche-induced absorption and dispersion. Evidence is presented of coherent delocalization in Tm-doped solids, in the form of unexpected oscillations in the transient response to incident light pulses. Two theoretical approaches for describing avalanche behavior were compared. A rate equation analysis suitable for weak-coupled impurity ions was used to predict basic avalanche features, including increasing absorption and upconversion emission above a threshold, temporal delay of absorption, and temperature dependence of avalanche threshold. A density matrix approach suitable for arbitrary coupling reproduced these features but also predicted oscillations in excited state populations in the presence of significant interion coherence. This theory incorporated both near -neighbor cross relaxation which gives rise to induced absorption, and excitation migration among distant pair ions necessary for immensely magnifying the effect, in a single formalism. Studies of the concentration and temperature dependence of fluorescence decays of Tm ions from ^1 G_4 and ^3 H_4 states provided firm evidence of pair-wise cross relaxations of ions in both these states. Transient four-wave mixing experiments directly revealed energy migration among ^3F _4 state Tm ions at a rate rapid enough to support the content ion that migration plays an important role in avalanche dynamics. Additional experiments yielded a temperature dependence of avalanche threshold in good agreement with theory, as well as avalanche phase conjugation and transverse propagation effects due to avalanche dynamics in accord with predictions.

Ni, Hui

1994-01-01

280

The Morsárjökull rock avalanche in the southern part of the Vatnajökull glacier, south Iceland  

NASA Astrophysics Data System (ADS)

On the 20th of March 2007 a large rock avalanche fell on Morsárjökull, one of the outlet glaciers from the southern part of the Vatnajökull ice cap, in south Iceland. This is considered to be one of the largest rock avalanches which have occurred in Iceland during the last decades. It is believed that it fell in two separate stages, the main part fell on the 20th of March and the second and smaller one, on the 17th of April 2007. The Morsárjökull outlet glacier is about 4 km long and surrounded by up to 1000 m high valley slopes. The outlet glacier is fed by two ice falls which are partly disconnected to the main ice cap of Vatnajökull, which indicates that the glacier is mainly fed by ice avalanches. The rock avalanche fell on the eastern side of the uppermost part of the Morsárjökull outlet glacier and covered about 1/5 of the glacier surface, an area of about 720,000 m2. The scar of the rock avalanche is located on the north face of the headwall above the uppermost part of the glacier. It is around 330 m high, reaching from about 620 m up to 950 m, showing that the main part of the slope collapsed. It is estimated that about 4 million m3 of rock debris fell on the glacier, or about 10 million tons. The accumulation lobe is up to 1.6 km long, reaching from 520 m a.s.l., to about 350 m a.s.l. Its width is from 125 m to 650 m, or on average 480 m. The total area which the lobe covers is around 720.000 m2 and its mean thickness 5.5 m. The surface of the lobe shows longitudinal ridges and grooves and narrow flow-like lobes, indicating that the debris mass evolved down glacier as a mixture of a slide and debris flow. The debris mass is coarse grained and boulder rich. Blocks over 5 to 8 m in diameter are common on the edges of the lobe up to 1.6 km from the source. No indication was observed of any deformation of the glacier surface under the debris mass. The first glaciological measurements of Morsárjökull outlet glacier were carried out in the year 1896 and it is evident that since that time the glacier has retreated considerably and during the last decade the melting has been very rapid. It is thought that undercutting of the mountain slope by glacial erosion and the retreat of the glacier are the main contributing factors leading to the rock avalanche. The glacial erosion has destabilized the slope, which is mainly composed of palagonite and dolerite rocks, affected by geothermal alteration. Hence a subsequent fracture formation has weakened the strength of the bedrock. However the exact triggering factor is not known. No seismic activity or meteorological signal such as heavy rainfall or intensive snowmelt recorded prior to the rock avalanche which could be interpreted as triggering factors. From 2007 considerable changes have been observed on the glacier. The ice-front has retreated considerably and the debris lobe of the rock avalanche has moved downward along with the glacier ice about 90-100 m per year. The rocky material, by insulating the ice, has reduced its melting, leading to a relative "thickening" of the ice beneath the rock avalanche debris up to 11-15 m per year. After three melting seasons the debris mass was about 29 m above the surrounding ice surface.

Sæmundsson, ?orsteinn; Sigur?sson, Ingvar A.; Pétursson, Halldór G.; Decaulne, Armelle; Jónsson, Helgi P.

2010-05-01

281

The effect of vegetation cover on the formation of glide-snow avalanches  

NASA Astrophysics Data System (ADS)

Glide snow avalanches release on steep, smooth slopes and can be prevented either by protection forests or by artificial defense structures. To minimize the risk for people and infrastructure, guidelines have been formulated concerning structure, height and distance between avalanche prevention bridges. These guidelines assure the major functions of the defense structures: first to prevent the release of avalanches and second to withstand the static and dynamic forces of the moving snow cover. The major functions of protection forests are generally similar and therefore guidelines on the maximum tolerable size of forest gaps exist in Switzerland. These guidelines are based on a static relationship between the pressure of the snow cover and the resistance of the defense structure and on empirical observations (forest). Whereas ground friction is only qualitatively taken into account, we assume it to play a crucial role in glide snow avalanche formation. To prove this assumption we collected data on the predominant vegetation cover of 67 release areas in the region of Davos, Switzerland. Our observations reveal a strong relationship between vegetation cover type, slope angle and slab length. We were able to quantify the Coulomb friction parameter ? by applying a physical model that accounts for the dynamic forces of the moving snow on the stauchwall, the fixed snow cover below the release area. The stauchwall resists the dynamic forces of the snow cover, until a critical strain rate is reached and then fails in brittle compression. This failure strongly depends on the friction between snow cover and soil. A typical value of ? for grassy slopes is 0.2. Snow characteristics like density are implemented in the model as constants. We compared the model results with the guidelines for defense structures and forest gap sizes and found accordance for certain friction parameter values. Forest gaps of 40 meter length and a 35° slope angle require friction values of 0.5 corresponding to stumps or tree regeneration to assure protection. Therefore forest gap guidelines in Switzerland imply a relatively rough surface to prevent avalanche formation. The calculated slope angle and slab length for smooth, grassy slopes corresponds to defense structure distances for shallow snow heights. Guidelines for defense structure distances correspond to a smooth surface like grass or low dwarf shrubs which are common vegetation types for regions above the tree line. Therefore we could confirm that artificial defense structures, built in accordance with guidelines prevent glide snow avalanche releases, even on smooth terrain.

Feistl, Thomas; Bebi, Peter; Bartelt, Perry

2014-05-01

282

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

283

Large scale mapping of forests with a protection function against rockfall and avalanches  

NASA Astrophysics Data System (ADS)

On mountain slopes, forest can play an important role to protect human lives and facilities against natural hazards. Silvicultural strategies and interventions to maintain or improve protection forest structures are of first interest. Up to now no large scale mapping of forest with a protection function against rockfalls and snow avalanches exist in France. The objectives of the study is to develop decision support tools for rockfall protection forest management. Two Geographic Information System based models which automatically map forests with a protection function against rockfalls and snow avalanches have been developed. These devices have been used to map forest with protection function in the French Alps. The first model, RollFree, calculates the maximum rockfall run out zone using the energy line principle. Forest with protection function are mapped crossing data on rockfall hazard, the forest cover and the socio-economical issues of a county. The second model, AvaLine, mapped the maximum run out zones of snow avalanches. Forests located in a departure zone of an avalanche that endangered an issue are mapped as protection forests. Results showed that forests with a protection function against rockfall can represent up to 30 percents of the forest cover in a county. In addition, forests with a protection function against avalanches can represent up to 7 percents of the total forested area. The two models developed present the advantages of a fast computational time and need only few input parameters such as a DEM, a map of the issues and a map of the forest cover. However it remain difficult to estimate precisely the error on the area mapped as protection forest on the all county. A first campaign of validation was done in the Vercor Regional natural park for forest with a protection function against rockfall. The study show that the model can overestimate the protection forest mapping up to 12 percent. Up to now no similar study was done for protection forest against avalanches. Despite uncertainty on the mapping illustrated in the Vercor Regional natural park, protection forests mapped by these models can be used as decisional tools by practitioners to develop adapted forest management strategies for large scale study.

Toe, David; Berger, Fréderic

2014-05-01

284

Direct measurement of microstructural avalanches during the martensitic transition of cobalt using coherent x-ray scattering.  

PubMed

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 ?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. PMID:21797551

Sanborn, Christopher; Ludwig, Karl F; Rogers, Michael C; Sutton, Mark

2011-07-01

285

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

286

Volcanic mixed avalanches: a distinct eruption-triggered mass-flow process at snow-clad volcanoes  

USGS Publications Warehouse

A generally unrecognized type of pyroclastic deposit was produced by rapid avalanches of intimately mixed snow and hot pyroclastic debris during eruptions at Mount St. Helens, Nevado del Ruiz, and Redoubt Volcano between 1982 and 1989. These "mixed avalanches' traveled as far as 14 km at velocities up to ~27 m/s, involved as much as 107 m3 of rock and ice, and left unmelted deposits of single flow units as thick as 5 m. During flow downslope, heat transfer from hot rocks to snow produced meltwater that partially saturated the mixtures, apparently giving these mixed avalanches mobilities equal to or greater than those of "dry' debris avalanches of similar volume. After melting and desiccation, the deposits are highly susceptible to erosion and unlikely to be well preserved in the stratigraphic record. -Authors

Pierson, T. C.; Janda, R. J.

1994-01-01

287

Simulation of the Avalanche Process in the G-APD and Circuitry Analysis of the SiPM  

Microsoft Academic Search

The discrete modeling of the Geiger-mode APD is considered. Results of modeling and experimental measurements with the SiPM show that the known formula for the charge of the avalanche pulse Q=dU*Cd underestimates its value. In addition, it is seen from the dynamic of the avalanche multiplication that the resistor Rq in photodiode, usually called a quenching resistor, in reality fulfills

V. M. Grebenyuk; A. I. Kalinin; Nguyen Manh Shat; A. K. Zhanusov; V. A. Bednyakov

2009-01-01

288

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

289

The Large-Scale Debris Avalanche From The Tancitaro Volcano (Mexico): Characterization And Modeling  

NASA Astrophysics Data System (ADS)

The Tancitaro is an andesitic-dacitic stratovolcano located in the Michoacán Guanajuato volcanic field within the west-central portion of the trans-Mexican Volcanic Belt. The volcanism in this area is characterized by two composite volcanoes, the highest of which is the Tancitaro volcanic edifice (3840 m), some low angle lava cones and more than 1,000 monogenetic cinder cones. The distribution of the cinder cones is controlled by NE-SW active faults, although there are also additional faults with NNW-SSE trends along which some cones are aligned. The Tancitaro stratovolcano is located at the intersection of the tectonical structures that originate these alignments. All this geological activity has contributed to the gravitational instability of the volcano, leading to a huge sector collapse which produced the investigated debris avalanche. The collapse structure is an east-facing horseshoe-shaped crater (4 km wide and 5.3 km long), related with a large fan that was deposited within the Tepalcatepec depression. The deposit starts only 7 km downslope from the failure scar, it is 66 km long and covers an area of approximately 1155 km2. The landslide magnitude is about 20 km3 and it was firstly determined by the reconstruction of the paleo-edifice using a GIS software and then validated by the observation of significant outcrops. The fan was primarily formed by the deposit of this huge debris avalanche and subsequently by debris flow and fluvial deposits. Field investigations on the fan area highlighted the presence of two texturally distinct parts, which are referred to the 'block facies' and the 'matrix facies'. The first sedimentary structure is responsible for the typical hummock morphologies in the proximal area, as seen in many other debris avalanche deposits. Instead in the distal zones, the deposit is made up by the 'mixed block and matrix facies'. Blocks and megablocks, some of which are characterized by a jigsaw puzzle texture, gradually decrease in size until they disappear entirely in the most distal reaches. The granulometric analysis and the comparison between the debris avalanche of the Tancitaro and other collapses with similar morphometric features (vertical relief during runout, travel distance, volume and area of the deposit) indicate that the collapse was most likely not primed by any type of eruption, but rather triggered by a strong seismic shock that could have induced the failure of a portion of the edifice, already deeply altered by intense hydrothermal fluid circulation. It is also possible to hypothesize that mechanical fluidization may have been the mechanism controlling the long runout of the avalanche, as has been determined for other well-known events. The behavior of the Tancitaro debris avalanche was numerically modeled using the DAN-W code. By opportunely modifying the rheological parameters of the different models selectable within DAN, it was determined that the two-parameter 'Voellmy model' provides the best approximation of the avalanche movement. The Voellmy model produces the most realistic results in terms of runout distance, velocity and spatial distribution of the failed mass. Since the Tancitaro event was not witnessed directly, it is possible to infer approximate velocities only from comparisons with similar and documented events, namely the Mt. St. Helens debris avalanche occurred on May 18, 1980.

Morelli, S.; Gigli, G.; Falorni, G.; Garduno Monroy, V. H.; Arreygue, E.

2008-12-01

290

Ultraviolet and white photon avalanche upconversion in Ho3+-doped nanophase glass ceramics  

NASA Astrophysics Data System (ADS)

Ho3+-doped fluoride nanophase glass ceramics have been synthesized from silica-based oxyfluoride glass. An intense white emission light is observed by the naked eye under near infrared excitation at 750nm. This visible upconversion is due to three strong emission bands in the primary color components, red, green, and blue. Besides, ultraviolet signals are also recorded upon the same excitation wavelength. The excitation mechanism of both the ultraviolet and the visible emissions is a photon avalanche process with a relatively low pump power threshold at about 20mW. The total upconverted emission intensity has been estimated to increase by about a factor of 20 in the glass ceramic compared to the precursor glass, in which an avalanche type mechanism is not generated.

Lahoz, F.; Martín, I. R.; Calvilla-Quintero, J. M.

2005-01-01

291

Ultraviolet and white photon avalanche upconversion in Ho{sup 3+}-doped nanophase glass ceramics  

SciTech Connect

Ho{sup 3+}-doped fluoride nanophase glass ceramics have been synthesized from silica-based oxyfluoride glass. An intense white emission light is observed by the naked eye under near infrared excitation at 750 nm. This visible upconversion is due to three strong emission bands in the primary color components, red, green, and blue. Besides, ultraviolet signals are also recorded upon the same excitation wavelength. The excitation mechanism of both the ultraviolet and the visible emissions is a photon avalanche process with a relatively low pump power threshold at about 20 mW. The total upconverted emission intensity has been estimated to increase by about a factor of 20 in the glass ceramic compared to the precursor glass, in which an avalanche type mechanism is not generated.

Lahoz, F.; Martin, I.R.; Calvilla-Quintero, J.M. [Departmento de Fisica Fundamental y Experimental, Electronica y Sistemas, University of La Laguna, 38206 La Laguna, Tenerife (Spain)

2005-01-31

292

Gain properties of doped GaAs/AlGaAs multiple quantum well avalanche photodiode structures  

NASA Technical Reports Server (NTRS)

A comprehensive characterization has been made of the static and dynamical response of conventional and multiple quantum well (MQW) avalanche photodiodes (APDs). Comparison of the gain characteristics at low voltages between the MQW and conventional APDs show a direct experimental confirmation of a structure-induced carrier multiplication due to interband impact ionization. Similar studies of the bias dependence of the excess noise characteristics show that the low-voltage gain is primarily due to electron ionization in the MQW-APDS, and to both electron and hole ionization in the conventional APDS. For the doped MQW APDS, the average gain per stage was calculated by comparing gain data with carrier profile measurements, and was found to vary from 1.03 at low bias to 1.09 near avalanche breakdown.

Menkara, H. M.; Wagner, B. K.; Summers, C. J.

1995-01-01

293

Design and realization of a facility for the characterization of Silicon Avalanche PhotoDiodes  

NASA Astrophysics Data System (ADS)

We present the design, construction, and performance of a facility for the characterization of Silicon Avalanche Photodiodes in the operating temperature range between ?2°C and 25°C. The system can simultaneously measure up to 24 photo-detectors, in a completely automatic way, within one day of operations. The measured data for each sensor are: the internal gain as a function of the bias voltage and temperature, the gain variation with respect to the bias voltage, and the dark current as a function of the gain. The systematic uncertainties have been evaluated during the commissioning of the system to be of the order of 1%. This paper describes in detail the facility design and layout, and the procedure employed to characterize the sensors. The results obtained from the measurement of the 380 Avalanche Photodiodes of the CLAS12-Forward Tagger calorimeter detector are then reported, as the first example of the massive usage of the facility.

Celentano, A.; Colaneri, L.; De Vita, R.; Fegan, S.; Minì, G.; Nobili, G.; Ottonello, G.; Parodi, F.; Rizzo, A.; Zonta, I.

2014-09-01

294

Fluctuations of particle motion in granular avalanches - from the microscopic to the macroscopic scales  

E-print Network

In this study, we have investigated the fluctuations of particle motion, i.e. the non-affine motion, during the avalanche process, discovering a rich dynamics from the microscopic to the macroscopic scales. We find that there is strong correlation between the magnitude of the velocity fluctuation and the velocity magnitude in the spatial and temporal domains. In addition the velocity magnitude of the system and the stress fluctuations of the system are strongly correlated temporally. Our finding will pose challenges to the development of more rigorous theories to describe the avalanche dynamics based on the microscopic approach. Moreover, our finding presents a plausible mechanism of the particle entrainment in a simple system.

Ziwei Wang; Jie Zhang

2014-10-23

295

Photon avalanche upconversion in Ho3+-Yb3+ co-doped transparent oxyfluoride glass-ceramics  

NASA Astrophysics Data System (ADS)

The Ho3+-Yb3+ co-doped transparent glass and glass-ceramics containing CaF2 nanocrystals have been prepared. Differential thermal analysis and X-ray diffraction measurements have been made to characterize thermal properties of glass and structural changes in glass-ceramics, respectively. Photon avalanche upconversion has been achieved by exciting the samples at 745 nm at room temperature. An intense green and a weak red upconverted emissions corresponding to the 5S2:5F4 ? 5I8 and 5F5 ? 5I8 transitions, respectively, have been observed. The upconversion intensity has been found to increase with the increase in the size of the fluoride nanocrystals in glass-ceramics. Experimental evidences confirm that the mechanism of upconversion is photon avalanche.

Babu, P.; Martín, I. R.; Venkata Krishnaiah, K.; Seo, Hyo Jin; Venkatramu, V.; Jayasankar, C. K.; Lavín, V.

2014-04-01

296

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

NASA Astrophysics Data System (ADS)

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 of this work is to determine whether the angles of repose depend on gravity; that is, are different on planet Mars or the Moon compared to Earth. Until now it has been assumed that the angles of repose are independent of gravitational acceleration because both mobilising force and friction theoretically depend linearly on gravity. During 33 parabolic flights in a well-controlled research aircraft we imaged avalanching granular materials in rotating drums and Hele-Shaw cells at effective gravitational accelerations of 0.10 g and 0.38 g. Control measurements were done at 1 g in flight and on the ground. The 9 drums had a diameter of 0.2 m and rotated slow enough for discontinuous avalanching. The granular materials had particle sizes of about 0.2, 0.6 or 2 mm, were rounded or angular and had air or water as interstitial fluid. Angles were measured at 25 Hz by image analyses on the digital videos and acceleration of the aircraft was measured at 50 Hz in three directions. Hele-shaw cells were used to study auto-organization processes in discontinuous avalanching bi-dispersed granular materials and their respective individual grain species. In both setups the angular materials had time-averaged angles of about 40 deg and rounded materials about 25 deg for all g, except the finest glass beads in air, which is explained by static electricity. For all materials, the static angle of repose increases about 5 deg with decreasing g (from 1 to 0.1 g), whereas the dynamic angle decreases with about 10 deg. Consequently, the avalanche size increases with decreasing g. The interstitial fluid hardly affected the results: subaqueous avalanches were smaller than subaerial but the lubrication did not decrease the angles of repose. The particle size hardly made a difference, ruling out effects of particle momentum, fluid drag and groundwater dynamics. Consequently, granular avalanches and their strata are larger at reduced g. Stratification patterns of the bidisperse materials were reduced and in some cases disappeared completely at lower gravity. The lower dynamic angle of repose is expected to be preserved more often at planetary surfaces following threshold triggering events such as earthquakes and impacts. Furthermore, sediment processing methods on future European and American Mars landers that depend on the mobilization angle should account for the difference between angles of repose in reduced-gravity.

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

2010-12-01

297

Three-dimensional nanostructuring of polymer materials by controlled avalanche using femtosecond laser pulses  

NASA Astrophysics Data System (ADS)

We report direct laser fabrication of free-standing 3D structures in a sol-gel photo-polymer SZ2080, poly(ethylene glycol) diacrylate (PEG-DA-700) and thermo-polymer polydimethylsiloxane (PDMS) without use of two-photon absorbing photo-sensitizers. By estimating the multi-photon and avalanche ionization rates in the focal volume it is shown that bulk structuring of pure materials was achieved via a controlled avalanche. It is shown that several non-photosesitized materials can be combined for fabrication of composite material structures evoking a possibility to create non-toxic biocompatible scaffolds for tissue engineering, transparent microoptical elements and higher damage threshold photonic devices.

RekštytÄ--, Sima; Jonušauskas, Linas; Žukauskas, Albertas; Gervinskas, Gediminas; Malinauskas, Mangirdas; Juodkazis, Saulius

2014-03-01

298

Single-photon avalanche diode arrays for fast transients and adaptive optics  

Microsoft Academic Search

An instrumentation based on a silicon monolithic array of 60 photon counters [single-photon avalanche diode array (SPADA)] for state-of-the-art measurements of fast transient phenomena and adaptive optics (AO) is presented. The fabricated solid-state photon counters are rugged, easy to be integrated in the optical system, free from read-out noise, and provide very fast frame rates (> 10 kHz) and nanosecond

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

2006-01-01

299

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

300

Planar InP\\/InGaAs avalanche photodetectors with partial charge sheet in device periphery  

Microsoft Academic Search

A novel planar separate absorption, charge sheet, grading and multiplication avalanche photodiode (APD) structure incorporating a partial charge sheet in the device periphery is described, which allows for straightforward fabrication of APD devices without the use of guard rings. Metalorganic chemical vapor deposition grown, Zn-diffused InP\\/InGaAs APD devices have been fabricated. High dc gains well in excess of 100 and

L. E. Tarof; D. G. Knight; K. E. Fox; C. J. Miner; N. Puetz; H. B. Kim

1990-01-01

301

Planar InP-InGaAs single-growth avalanche photodiodes with no guard rings  

Microsoft Academic Search

A novel single-growth planar avalanche photodiode (APD) structure without guard rings is described. InP-InGaAs separate absorption, charge sheet, grading, and multiplication (SAGCM) APD's have been fabricated using the new edge breakdown suppression method. A very low, dark current of 0.6 nA at 0.98 of the breakdown voltage (BV) was measured for a 30-?m-diameter device. The maximum -3-dB electrical bandwidth was

L. E. Tarof; R. Bruce; D. G. Knight; J. Yu; H. B. Kim; T. Baird

1995-01-01

302

Reconnection and scale-free avalanching in a driven current-sheet model  

Microsoft Academic Search

Uritsky et al. [2002], through a study of Polar UVI auroral image sequences, have produced a set of scale-free probability distributions for several characteristic properties of the evolving bright emission regions in the nightside auroral oval. These distributions almost certainly reflect the dynamics of the plasma sheet. A scale-free avalanching process involving reconnection and\\/or current diversion over an exceptionally broad

Alex J. Klimas; Vadim M. Uritsky; Dimitris Vassiliadis; Daniel N. Baker

2004-01-01

303

Feasibility study of an avalanche photodiode readout for a high resolution PET with nsec time resolution  

SciTech Connect

A feasibility study for a high resolution positron emission tomograph, based on 9.5 x 4 x 4 mm{sup 3} LSO crystals viewed by 3 mm diameter avalanche photodiodes, has been carried out. Using a Na{sup 22} source the authors determined a spatial resolution of 2.3 {+-} 0.1 mm, an energy resolution around 15 % and a time resolution of 2.6 nsec. Possible configurations for larger scale tests and a tomograph are given.

Schmelz, C.; Ziegler, S. [Technische Univ. Muenchen (Germany). Nuklearmedizinische Klinik Rechts der Isar] [Technische Univ. Muenchen (Germany). Nuklearmedizinische Klinik Rechts der Isar; Bradbury, S.M.; Holl, I.; Lorenz, E. [Max-Planck-Inst. fuer Physik, Muenchen (Germany)] [Max-Planck-Inst. fuer Physik, Muenchen (Germany); Renker, D. [Paul Scherrer Inst., Villigen (Switzerland)] [Paul Scherrer Inst., Villigen (Switzerland)

1995-08-01

304

Performance of Deep Ultraviolet GaN Avalanche Photodiodes Grown by MOCVD  

Microsoft Academic Search

We report high-performance GaN ultraviolet (UV) p-i-n avalanche photodiodes (APDs) fabricated on bulk GaN substrates. The fabricated GaN p-i-n diodes demonstrated optical gains > 104 and low dark current densities operating at wavelengths from 280 to 360 nm. The result is among the highest III-N-based APD gains at the deep UV wavelength of 280 nm reported to date.

Shyh-Chiang Shen; Yun Zhang; Dongwon Yoo; Jae-Boum Limb; Jae-Hyun Ryou; Paul D. Yoder; Russell D. Dupuis

2007-01-01

305

Proton Irradiation of Ultraviolet 4H-SiC Single Photon Avalanche Diodes  

Microsoft Academic Search

The effects of proton irradiation on ultraviolet 4H-SiC single photon avalanche photodiodes (SPADs) are investigated for the first time. The SPADs, grown by chemical vapor deposition, were designed for operation in the ultraviolet having dark count rates (DCR) of about 30 kHz and single photon detection efficiency (SPDE) of 4.89%. The SPADs were irradiated with 2 MeV protons to a

Jun Hu; Xiaobin Xin; Jian H. Zhao; Brenda L. VanMil; Rachael Myers-Ward; Charles R. Eddy; David Kurt Gaskill

2011-01-01

306

Electrical characterization of 4H-SiC avalanche photodiodes containing threading edge and screw dislocations  

NASA Astrophysics Data System (ADS)

The reverse voltage current characteristics and electroluminescence of small area 4H-SiC avalanche photodiodes were investigated and correlated with the presence of threading screw and edge dislocations. Localized electroluminescence was observed at threading dislocations at voltages close to breakdown whereas diodes without any extended defects exhibited uniform light emission in the active area. Diodes containing either edge or screw dislocations were found to have excess leakage currents and breakdown prematurely compared to diodes without dislocations.

Berechman, R. A.; Skowronski, M.; Soloviev, S.; Sandvik, P.

2010-06-01

307

Electrical and Optical Modeling of 4H-SiC Avalanche Photodiodes  

NASA Astrophysics Data System (ADS)

Optimal physical models and material parameters for 4H-SiC avalanche photodiodes (APDs) were studied using a two-dimensional device simulation tool. In the models, we took account of temperature-dependent impact ionization and absorption coefficient as a function of wavelength. The absorption coefficient spectra derived in this work exhibited a rapid increase below ?300 nm, which can be qualitatively incorporated into indirect and direct band transition models. The simulated characteristics were in good agreement with the measured characteristics.

Cha, Ho-Young; Sandvik, Peter M.

2008-07-01

308

Electrical and Optical Modeling of 4H-SiC Avalanche Photodiodes  

Microsoft Academic Search

Optimal physical models and material parameters for 4H-SiC avalanche photodiodes (APDs) were studied using a two-dimensional device simulation tool. In the models, we took account of temperature-dependent impact ionization and absorption coefficient as a function of wavelength. The absorption coefficient spectra derived in this work exhibited a rapid increase below ˜300 nm, which can be qualitatively incorporated into indirect and

Ho-Young Cha; Peter M. Sandvik

2008-01-01

309

Silicon carbide photomultipliers and avalanche photodiode arrays for ultraviolet and solar-blind light detection  

Microsoft Academic Search

Silicon carbide is known for its large bandgap and suitability to make highly sensitive ultraviolet photo-detectors. These devices show appreciable quantum efficiencies in the 240 nm - 350 nm wavelength range in combination with low dark currents. We present recent results on 4H-SiC avalanche photodiode arrays and SiC-based solid-state photomultiplier arrays suitable for ultraviolet and solar-blind light detection. A novel

Alexey Vert; Stanislav Soloviev; Alexander Bolotnikov; Peter Sandvik

2009-01-01

310

Demonstration of 4H-SiC avalanche photodiodes linear array  

Microsoft Academic Search

4H-SiC visible blind avalanche photodiode (APD) linear arrays have been fabricated and successfully tested. A 40 pixel linear array with only one bad pixel has been demonstrated. The linear arrays show uniform breakdown voltage and low leakage current. The photoresponse and the excess noise factor of 4H-SiC APD pixels have been studied. A very high multiplication gain with very low

F. Yan; C Qin; J. H Zhao; M Bush; G Olsen; B. K Ng; J. P. R David; R. C Tozer; M Weiner

2003-01-01

311

Numerical modeling and design of single photon counter 4H-SiC avalanche photodiodes  

Microsoft Academic Search

We report device performance investigation of 4H-SiC avalanche photodiodes (APDs) with or without absorbing AlGaN cap layers, as 4H-SiCspsila potential use in single photon counter APDs have drawn interest. Wide bandgap 4H-SiC photodiodes have low dark current levels at high temperatures and under intense radiation compared to silicon, and the 4H-SiC APDs are ldquosolar blindrdquo - transparent to the sunpsilas

Akin Akturk; Neil Goldsman; Shahid Aslam; John Sigwarth; Fred Herrero

2008-01-01

312

Demonstration of Ultraviolet 6H-SiC PIN Avalanche Photodiodes  

Microsoft Academic Search

We report electrical and electrooptical characteristic of mesa-structure 6H-SiC PIN avalanche photodiodes. At a gain of 1000, the dark current density is 9.2 muA\\/cm2. The excess noise factor corresponds to a k value of ~0.1. In addition, peak responsivity of 80 mA\\/W was observed at 290 nm (external quantum efficiency of ~35%)

Han-Din Liu; Xiangyi Guo; Dion McIntosh; Joe C. Campbell

2006-01-01

313

Demonstration of 4H-SiC avalanche photodiodes linear array  

NASA Astrophysics Data System (ADS)

4H-SiC visible blind avalanche photodiode (APD) linear arrays have been fabricated and successfully tested. A 40 pixel linear array with only one bad pixel has been demonstrated. The linear arrays show uniform breakdown voltage and low leakage current. The photoresponse and the excess noise factor of 4H-SiC APD pixels have been studied. A very high multiplication gain with very low excess noise factors is reported.

Yan, F.; Qin, C.; Zhao, J. H.; Bush, M.; Olsen, G.; Ng, B. K.; David, J. P. R.; Tozer, R. C.; Weiner, M.

2003-02-01

314

4H-SiC Avalanche Photodiodes for 280nm UV Detection  

Microsoft Academic Search

We designed and fabricated 4H-SiC PIN avalanche photodiodes (APD) for UV detection. The thickness of an intrinsic layer in a PIN structure was optimized in order to achieve the highest quantum efficiency at the wavelength of interest. The optimized 4H-SiC PIN APDs exhibited a maximum external quantum efficiency of > 80% at the wavelength of 280nm and a gain greater

Ho-Young Cha; Hyuk-Kee Sung; Hyungtak Kim; Chun-Hyung Cho; Peter M. Sandvik

2010-01-01

315

A new Savage–Hutter type model for submarine avalanches and generated tsunami  

Microsoft Academic Search

In this paper, we present a new two-layer model of Savage–Hutter type to study submarine avalanches. A layer composed of fluidized granular material is assumed to flow within an upper layer composed of an inviscid fluid (e.g. water). The model is derived in a system of local coordinates following a non-erodible bottom and takes into account its curvature. We prove

E. D. Fernández-Nieto; F. Bouchut; D. Bresch; M. J. Castro Díaz; A. Mangeney

2008-01-01

316

Hydrogen migration under avalanche injection of electrons in Si metal-oxide-semiconductor capacitors  

Microsoft Academic Search

Aluminum\\/silicon dioxide\\/silicon capacitors in which the oxide has been grown thermally under ultra-dry (≲1 ppm H2O) conditions and subsequently treated by low temperature water diffusion have been characterized electrically and chemically. Avalanche injection of electrons has been observed to produce the complex charging behavior previously observed in similar systems, which includes electron trapping and interface positive charge generation. Secondary ion

R. Gale; F. J. Feigl; C. W. Magee; D. R. Young

1983-01-01

317

Avalanche photodiode array sensor with high-speed CCD delay line readout  

Microsoft Academic Search

A prototype solid-state multi-chip-module (MCM) optical sensor circuit is described. The MCM is designed to sample the optical signals from a fiber-optic array at rates up to 200 MHz. The fiber-optic inputs interface to the MCM avalanche-photodiode (APD) sensor array. The prototype 40 pixel MCM stores approximately 1000 samples from each fiber before readout. This is done on the MCM

Kevin L. Albright; Jeffrey M. Bradley

1999-01-01

318

Study of avalanche breakdown and impact ionization in 4H silicon carbide  

Microsoft Academic Search

Epitaxial p-n diodes in 4H SiC are fabricated with uniform avalanche multiplication and breakdown. Photomultiplication measurements\\u000a were performed to determine electron and hole ionization rates. Theoretical values of critical fields and breakdown voltages\\u000a in 4H SiC are calculated using the ionization rates obtained. We discuss ionization mechanisms in 4H SiC and make a comparison\\u000a between silicon carbide and gallium nitride.

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

1998-01-01

319

An integrated active-quenching circuit for single-photon avalanche diodes  

Microsoft Academic Search

We introduce the first integrated active quenching circuit (I-AQC) that drives an avalanche photodiode (APD) above its breakdown voltage, in order to detect single photons. Based on the I-AQC, we developed a compact and versatile photon-counting module suitable for applications in which very weak optical signals have to be detected, as for instance, photon correlation spectroscopy, luminescence measurements, and laser

Franco Zappa; Massimo Ghioni; Sergio Cova; Carlo Samori; Andrea Carlo Giudice

2000-01-01

320

Low Dark Count Single-Photon Avalanche Diode Structure Compatible With Standard Nanometer Scale CMOS Technology  

Microsoft Academic Search

A single-photon avalanche diode structure implemented in a 130-nm imaging process is reported. The device employs a p-well anode, rather than the commonly adopted p+, and a novel guard ring compatible with recent scaling trends in standard nanometer scale complementary metal-oxide-semiconductor technologies. The 50-mum 2 active area device exhibits a dark count rate of 25 Hz at 20 degC and

Justin A. Richardson; Lindsay A. Grant; Robert K. Henderson

2009-01-01

321

Fractures in weak snowpack layers in relation to slab avalanche release  

NASA Astrophysics Data System (ADS)

The vast majority of recreational avalanche incidents are caused by human-triggering of the slab avalanche. Specific snowpack characteristics, including hardness difference and difference in crystal size across the failure layer, associated with skier-triggered dry slab avalanches were identified. The relation of these snowpack variables with fracture initiation and fracture propagation, both of which are required for skier-triggering, was investigated. The properties of the slab overlying the weak layer, as well as the layer above the weak layer, were found to be important for fracture propagation in that the slab supplies the energy necessary to propagate the fracture through the weak layer. A classification system for fractures in stability tests was assessed. It was shown that incorporating such a descriptive classification system can improve the interpretation of these test results. Sudden fractures are more often the failure layer of slab avalanches than other fractures. Specific snowpack characteristics associated with the different fracture characters showed that sudden fractures are typically associated with snowpack conditions favouring both fracture initiation and fracture propagation. In-situ fractures in weak snowpack layers were photographed at 250 frames per second in 39 field tests. Displacement measurements of markers placed in the snow above weak layers showed that slope normal displacement (due to crushing of the weak layer) was observed in each fracture. The speed of propagating fractures was measured, ranging from 17 to 26 m/s. These observations were used to assess theoretical slab release models, suggesting that the fracture of the weak layer is coupled to a propagating flexural wave in the overlying slab that controls the speed of propagation.

van Herwijnen, Alec Francois Guillaume

322

Extremely large rockslides and rock avalanches in the Tien Shan Mountains, Kyrgyzstan  

Microsoft Academic Search

Most systematic research on large rock-slope failures is geographically biased towards reports from Europe, the Americas,\\u000a the Himalayas and China. Although reports exist on large rockslides and rock avalanches in the territory of the former Soviet\\u000a Union, they are not readily available, and few translations have been made. To begin closing this gap, we describe here preliminary\\u000a data from field

Alexander L. Strom; Oliver Korup

2006-01-01

323

A new silicon avalanche photodiode photon counting detector module for astronomy  

Microsoft Academic Search

A new silicon avalanche photodiode photon counting detector module with a peak detection efficiency of 45 percent and a maximum counting rate of more than 3,000,000 cts\\/sec is described and its performance assessed over a range of operating conditions. The module should prove ideal for a wide variety of astronomical instrumentation as it covers the spectral range 350-150 nm and

N. S. Nightingale

1991-01-01

324

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

NASA Technical Reports Server (NTRS)

The author has identified the following significant results. Interpretation of small scale LANDSAT imagery provides a means for determining the general location and distribution of avalanche paths. The accuracy and completeness of small scale mapping is less than is obtained from the interpretation of large scale color infrared photos. Interpretation of enlargement prints (18X) of LANDSAT imagery is superior to small scale imagery, because more detailed information can be extracted and annotated.

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

1975-01-01

325

Effect of inertia on sheared disordered solids: Critical scaling of avalanches in two and three dimensions  

NASA Astrophysics Data System (ADS)

Molecular dynamics simulations with varying damping are used to examine the effects of inertia and spatial dimension on sheared disordered solids in the athermal quasistatic limit. In all cases the distribution of avalanche sizes follows a power law over at least three orders of magnitude in dissipated energy or stress drop. Scaling exponents are determined using finite-size scaling for systems with 103-106 particles. Three distinct universality classes are identified corresponding to overdamped and underdamped limits, as well as a crossover damping that separates the two regimes. For each universality class, the exponent describing the avalanche distributions is the same in two and three dimensions. The spatial extent of plastic deformation is proportional to the energy dissipated in an avalanche. Both rise much more rapidly with system size in the underdamped limit where inertia is important. Inertia also lowers the mean energy of configurations sampled by the system and leads to an excess of large events like that seen in earthquake distributions for individual faults. The distribution of stress values during shear narrows to zero with increasing system size and may provide useful information about the size of elemental events in experimental systems. For overdamped and crossover systems the stress variation scales inversely with the square root of the system size. For underdamped systems the variation is determined by the size of the largest events.

Salerno, K. Michael; Robbins, Mark O.

2013-12-01

326

Flood avalanches in a semiarid basin with a dense reservoir network  

E-print Network

This study investigates flood avalanches in a dense reservoir network in the semiarid north-eastern Brazil. The population living in this area strongly depends on the availability of the water from this network. Water is stored during intense wet-season rainfall events and evaporates from the reservoir surface during the dry season. These seasonal changes are the driving forces behind the water dynamics in the network. The reservoir network and its connectivity properties during flood avalanches are investigated with a model called ResNetM, which simulates each reservoir explicitly. It runs on the basis of daily calculated water balances for each reservoir. A spilling reservoir contributes with water to the reservoir downstream, which can trigger avalanches affecting, in some cases, large fractions of the network. The main focus is on the study of the relation between the total amount of water stored and the largest observable cluster of connected reservoirs that overspill in the same day. It is shown that th...

Peter, Samuel J; Araújo, N A M; Herrmann, H J

2014-01-01

327

An analytical approach for calculating energy spectra of relativistic runaway electron avalanches in air  

NASA Astrophysics Data System (ADS)

Simplified equations describing the transport and energy spectrum of runaway electrons are derived from the basic kinematics of the continuity equations. These equations are useful in modeling the energy distribution of energetic electrons in strong electric fields, such as those found inside thunderstorms. Dwyer and Babich (2011) investigated the generation of low-energy electrons in relativistic runaway electron avalanches. The paper also developed simple analytical expressions to describe the detailed physics of Monte Carlo simulations of relativistic runaway electrons in air. In the current work, the energy spectra of the runaway electron population are studied in detail. Dependence of electron avalanche development on properties such as the avalanche length, radiation length, and the effective Møller scattering efficiency factor are discussed in detail. To describe the shapes of the electron energy spectra for a wide range of electric field strengths, the diffusion term responsible for random deviation of electron energy ionization loss from the mean value is added to the kinetic equation. We find that the diffusion in energy space helps maintain an exponential energy spectrum for electric fields that approach the runaway electron threshold field.

Cramer, E. S.; Dwyer, J. R.; Arabshahi, S.; Vodopiyanov, I. B.; Liu, N.; Rassoul, H. K.

2014-09-01

328

Single-Photon-Sensitive HgCdTe Avalanche Photodiode Detector  

NASA Technical Reports Server (NTRS)

The purpose of this program was to develop single-photon-sensitive short-wavelength infrared (SWIR) and mid-wavelength infrared (MWIR) avalanche photodiode (APD) receivers based on linear-mode HgCdTe APDs, for application by NASA in light detection and ranging (lidar) sensors. Linear-mode photon-counting APDs are desired for lidar because they have a shorter pixel dead time than Geiger APDs, and can detect sequential pulse returns from multiple objects that are closely spaced in range. Linear-mode APDs can also measure photon number, which Geiger APDs cannot, adding an extra dimension to lidar scene data for multi-photon returns. High-gain APDs with low multiplication noise are required for efficient linear-mode detection of single photons because of APD gain statistics -- a low-excess-noise APD will generate detectible current pulses from single photon input at a much higher rate of occurrence than will a noisy APD operated at the same average gain. MWIR and LWIR electron-avalanche HgCdTe APDs have been shown to operate in linear mode at high average avalanche gain (M > 1000) without excess multiplication noise (F = 1), and are therefore very good candidates for linear-mode photon counting. However, detectors fashioned from these narrow-bandgap alloys require aggressive cooling to control thermal dark current. Wider-bandgap SWIR HgCdTe APDs were investigated in this program as a strategy to reduce detector cooling requirements.

Huntington, Andrew

2013-01-01

329

Resonant- and avalanche-ionization amplification of laser-induced plasma in air  

NASA Astrophysics Data System (ADS)

Amplification of laser-induced plasma in air is demonstrated utilizing resonant laser ionization and avalanche ionization. Molecular oxygen in air is ionized by a low-energy laser pulse employing (2 + 1) resonance-enhanced multi-photon ionization (REMPI) to generate seed electrons. Subsequent avalanche ionization of molecular oxygen and nitrogen significantly amplifies the laser-induced plasma. In this plasma-amplification effect, three-body attachments to molecular oxygen dominate the electron-generation and -loss processes, while either nitrogen or argon acts as the third body with low electron affinity. Contour maps of the electron density within the plasma obtained in O2/N2 and O2/Ar gas mixtures are provided to show relative degrees of plasma amplification with respect to gas pressure and to verify that the seed electrons generated by O2 2 + 1 REMPI are selectively amplified by avalanche ionization of molecular nitrogen in a relatively low-pressure condition (?100 Torr). Such plasma amplification occurring in air could be useful in aerospace applications at high altitude.

Wu, Yue; Zhang, Zhili; Jiang, Naibo; Roy, Sukesh; Gord, James R.

2014-10-01

330

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

NASA Technical Reports Server (NTRS)

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 sq km of terrain to an average depth of 45 m with unconsolidated, poorly sorted volcaniclastic material, all within a period of 10 minutes. Where exposed and unaltered by subsequent lahars and pyroclastic flows, the new terrain surface was characterized predominantly by hummocks, closed depressions, and the absence of an identifiable channel network. Following emplacement of the debris avalanche, a complex interrelationship of fluvial and mass wasting processes immediately began operating to return the impacted area to an equilibrium status through the removal of material (potential energy) and re-establishment of graded conditions. In an attempt to chronicle the morphologic evolution of this unique environmental setting, a systematic series of interpretative maps of several selected areas was produced. These maps, which document the rate and character of active geomorphic processes, are discussed.

Beach, G. L.; Dzurisin, D.

1984-01-01

331

Predicting Solar Flares by Data Assimilation in Avalanche Models. I. Model Design and Validation  

E-print Network

Data assimilation techniques, developed in the last two decades mainly for weather prediction, produce better forecasts by taking advantage of both theoretical/numerical models and real-time observations. In this paper, we explore the possibility of applying the data-assimilation techniques known as 4D-VAR to the prediction of solar flares. We do so in the context of a continuous version of the classical cellular-automaton-based self-organized critical avalanche models of solar flares introduced by Lu and Hamilton (Astrophys. J., 380, L89, 1991). Such models, although a priori far removed from the physics of magnetic reconnection and magneto-hydrodynamical evolution of coronal structures, nonetheless reproduce quite well the observed statistical distribution of flare characteristics. We report here on a large set of data assimilation runs on synthetic energy release time series. Our results indicate that, despite the unpredictable (and unobservable) stochastic nature of the driving/triggering mechanism within the avalanche model, 4D-VAR succeeds in producing optimal initial conditions that reproduce adequately the time series of energy released by avalanches/flares. This is an essential first step towards forecasting real flares.

Eric Bélanger; Alain Vincent; Paul Charbonneau

2007-08-14

332

Indirect flat-panel detector with avalanche gain: Fundamental feasibility investigation for SHARP-AMFPI (scintillator HARP active matrix flat panel imager)  

Microsoft Academic Search

An indirect flat-panel imager (FPI) with avalanche gain is being investigated for low-dose x-ray imaging. It is made by optically coupling a structured x-ray scintillator CsI(Tl) to an amorphous selenium (a-Se) avalanche photoconductor called HARP (high-gain avalanche rushing photoconductor). The final electronic image is read out using an active matrix array of thin film transistors (TFT). We call the proposed

Wei Zhao; Li Dan; Alla Reznik; B. J. M. Lui; D. C. Hunt; J. A. Rowlands; Yuji Ohkawa; Kenkichi Tanioka

2005-01-01

333

Self-Oscillating Harmonic OptoElectronic Mixer Based on a CMOS-Compatible Avalanche Photodetector for Fiber-Fed 60GHz Self-Heterodyne Systems  

Microsoft Academic Search

A self-oscillating harmonic opto-electronic mixer based on a CMOS-compatible avalanche photodetector for fiber-fed 60-GHz self-heterodyne systems is demonstrated. The mixer is composed of an avalanche photodetector fabricated with 0.18-mum standard CMOS process and an electrical feedback loop for self oscillation. It simultaneously performs photodetection and frequency up-conversion of photodetected signals into the second harmonic self-oscillation frequency band. The avalanche photodetector

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

2008-01-01

334

Comparing the characteristics of rockfall talus and snow avalanche landforms in an Alpine environment using a new methodological approach: Massif des Ecrins, French Alps  

Microsoft Academic Search

The geometry and sedimentology of 49 talus slope deposits have been analysed in the French Alps to show the effects of snow avalanche activity on their characteristics. Twenty slopes are heavily avalanche-modified, 15 are snow-avalanche boulder tongues and 14 are rockfall-talus slopes. Slope angle, slope segmentation, longitudinal and sorting indices provide criteria to differentiate these deposits. Although the transition from

Vincent Jomelli; Bernard Francou

2000-01-01

335

LiDAR-based characterization of the Mt Shasta debris avalanche deposit  

NASA Astrophysics Data System (ADS)

The failure of destabilized volcano flanks, due either to tectonic activity on basement structures underlying the volcanic edifice, magmatic intrusion or external forcing (e.g. weather events), is a likely occurrence during the lifetime of a stratovolcano. Flank failure can generate large debris avalanches, and the significant hazards associated with volcanic debris avalanches in the Cascade range were demonstrated by the collapse of Mt St Helens (WA, USA), which triggered its devastating explosive eruption in May 1980. Mt Shasta is a 4,317 m high, snow-capped, steep-sloped stratovolcano located in Northern California. The most voluminous of the Cascade volcanoes, the current edifice began forming on the remnants of an ancestral Mt Shasta that collapsed approximately 300,000 to 380,000 years ago producing one of the largest debris avalanches known on Earth. The debris avalanche deposit (DAD) covers a surface of 450 km2 across the Shasta valley, for a total volume of approximately 26 km3. A LiDAR point cloud and orthophoto of the Shasta DAD surveyed by the NCALM consortium provides a new topographic dataset of the area with unprecedented resolution. This will permit the identification of subtle topographic features of the Shasta DAD not apparent in the field or in coarser resolution datasets. Statistical measures of the LiDAR-derived digital elevation model, such as surface texture, will be used to detect and characterize the hummock topography, differentiate between various DAD facies and geomorphic units, and extract the morphological parameters for subsequent analogue and numerical modeling of the debris avalanche. This work aims to improve our understanding of the Mt Shasta DAD morphology and its dynamics, and provide insight into the cause, timing of events and mode of emplacement of the DAD. The Cascade range includes numerous large extinct, dormant or active stratovolcanoes, and knowledge of the link between basement structures and the Mt Shasta DAD will elucidate the causes of edifice instability and may be used to target priority areas for volcanic hazard mapping.

Tortini, R.; Carn, S. A.; van Wyk de Vries, B.

2013-12-01

336

Mobility statistics and automated hazard mapping for debris flows and rock avalanches  

USGS Publications Warehouse

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=?1V2/3 and B=?2V2/3 are based on the postulate that the maximum valley cross-sectional area (A) and total valley planimetric area (B) likely to be inundated by a flow depend only on its volume (V) and the topography of the flow path. Testing of these equations involves determining whether or not they fit data for documented flows satisfactorily, and calibration entails determining best-fit values of the coefficients ?1 and ?2 for debris flows, rock avalanches, and lahars. This report describes statistical testing and calibration of the equations by using field data compiled from many sources, and it describes application of the equations to delineation of debris-flow hazard zones. Statistical results show that for each type of flow (debris flows, rock avalanches, and lahars), the dependence of A and B on V is described well by power laws with exponents equal to 2/3. This value of the exponent produces fits that are effectively indistinguishable from the best fits obtained by using adjustable power-law exponents. Statistically calibrated values of the coefficients ?1 and ?2 provide scale-invariant indices of the relative mobilities of rock avalanches (?1 = 0.2, ?2 = 20), nonvolcanic debris flows (?1 = 0.1, ?2 = 20), and lahars (?1 = 0.05, ?2 = 200). These values show, for example, that a lahar of specified volume can be expected to inundate a planimetric area ten times larger than that inundated by a rock avalanche or nonvolcanic debris flow of the same volume. The utility of the calibrated debris-flow inundation equations A=0.1V2/3 and B=20V2/3 is demonstrated by using them within the GIS program LAHARZ to delineate nested hazard zones for future debris flows in an area bordering the Umpqua River in the south-central Oregon Coast Range. This application requires use of high-resolution topographic data derived form LIDAR surveys, knowledge of local geology to specify a suitable range of prospective debris-flow volumes, and development and use of a new algorithm for identification of prospective debris-flow source areas in finely dissected terrain.

Griswold, Julia P.; Iverson, Richard M.

2008-01-01

337

Small-scale laboratory tests on granular avalanches around an obstacle  

NASA Astrophysics Data System (ADS)

In the framework of the European project DYNAVAL (Interreg Alcotra), experiments have been scheduled in order to improve the existing knowledge about the dynamics of dense snow avalanche flows around an obstacle and the induced forces exerted on it. In particular, small-scale laboratory tests on granular flows are performed at Cemagref. The granular properties and behaviour of flowing snow have been evidenced and studied in recent literature and, until now, the analogy with dry granular materials has been largely used when investigating the influence of obstacles on dense avalanche flows. The experimental device consists of an inclined plane equipped with a reservoir to store the granular material simulating the dense flow and feeding a channel of variable width whose slope can be modified among a large range of values. Flow height, surface velocity and impact forces are measured. Two main tests, with and without obstacle, are realized. The flow dynamics (velocity, height and eventually density as well) is first characterized by performing reference tests for which the granular material flows down the channel in the absence of obstacle. The temporal evolution of the flow height is detected using a laser technique correlating the deviation of the laser line proportionally to the flow height. The granular PIV method (Particle Image Velocimetry) allows surface velocity measurements. As a second step, an obstacle is set up at the end of the channel and measurements are pursued focusing on the hydrodynamic effects of the obstacle and the forces exerted on the obstacle. Impact forces are measured at high frequency thanks to two force sensors connected to the obstacle. The current obstacle has been designed to represent the simplest case: a flat structure of height typically close to the incident flow depth, normal to the flow direction and to the bottom, spanning the whole channel width. This geometry is similar to 2D discrete numerical simulations previously reported in steady and transient avalanche regime, and typically encountered when snow avalanches overflow dams. Results, showing two main flow regimes affecting the resulting force on the obstacle, will be presented. The results are consistent with the previous numerical simulations and a simple hydrodynamic model. These experiments will be then used to design more complex tests based on obstacles with a geometry similar to real retarding mounds built at the Taconnaz avalanche path, France.

Caccamo, Paolo; Chanut, Benoît.; Faug, Thierry; Bellot, Hervé; Naaim-Bouvet, Florence

2010-05-01

338

Analysis of the snow-atmosphere energy balance during wet-snow instabilities and implications for avalanche prediction  

NASA Astrophysics Data System (ADS)

Wet-snow avalanches are notoriously difficult to predict, as their formation mechanism is poorly understood and in-situ measurements closely related to instability are inexistent. Instead, air temperature is commonly used as predictor variable for days with high wet-snow avalanche danger - with limited success. As melt water is a major driver of wet-snow instability and snow melt depends on the energy input into the snow cover, we computed the energy balance and study whether it is a better proxy than meteorological parameters such as air temperature for predicting periods with high wet-snow avalanche activity. The energy balance was partly measured and partly modelled for virtual slopes at different elevations for the aspects south and north using the 1-D snow cover model SNOWPACK. We used measured meteorological variables and computed energy balance and its components to compare wet-snow avalanche days to non-avalanche days for four consecutive winter seasons in the surroundings of Davos, Switzerland. Air temperature, the net shortwave radiation and the energy input integrated over 3 or 5 days showed best results in discriminating event from non-event days. Multivariate statistics, however, revealed that for better predicting avalanche days, information on the cold content of the snowpack is necessary. Wet-snow avalanche activity was closely related to periods when large parts of the snowpack reached an isothermal state (0 °C) and energy input exceeded a maximum value of 200 kJ m-2 in one day, or the 3-day sum of positive energy input was larger than 1.2 MJ m-2. Prediction accuracy with measured meteorological variables was as good as with computed energy balance parameters, but simulated energy balance variables accounted better for different aspects, slopes and elevations than meteorological data.

Mitterer, C.; Schweizer, J.

2012-07-01

339

Analysis of the snow-atmosphere energy balance during wet-snow instabilities and implications for avalanche prediction  

NASA Astrophysics Data System (ADS)

Wet-snow avalanches are notoriously difficult to predict; their formation mechanism is poorly understood since in situ measurements representing the thermal and mechanical evolution are difficult to perform. Instead, air temperature is commonly used as a predictor variable for days with high wet-snow avalanche danger - often with limited success. As melt water is a major driver of wet-snow instability and snow melt depends on the energy input into the snow cover, we computed the energy balance for predicting periods with high wet-snow avalanche activity. The energy balance was partly measured and partly modelled for virtual slopes at different elevations for the aspects south and north using the 1-D snow cover model SNOWPACK. We used measured meteorological variables and computed energy balance and its components to compare wet-snow avalanche days to non-avalanche days for four consecutive winter seasons in the surroundings of Davos, Switzerland. Air temperature, the net shortwave radiation and the energy input integrated over 3 or 5 days showed best results in discriminating event from non-event days. Multivariate statistics, however, revealed that for better predicting avalanche days, information on the cold content of the snowpack is necessary. Wet-snow avalanche activity was closely related to periods when large parts of the snowpack reached an isothermal state (0 °C) and energy input exceeded a maximum value of 200 kJ m-2 in one day, or the 3-day sum of positive energy input was larger than 1.2 MJ m-2. Prediction accuracy with measured meteorological variables was as good as with computed energy balance parameters, but simulated energy balance variables accounted better for different aspects, slopes and elevations than meteorological data.

Mitterer, C.; Schweizer, J.

2013-02-01

340

Quantification of basal friction for glide-snow avalanche mitigation measures in forested and non-forested terrain  

NASA Astrophysics Data System (ADS)

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

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

2014-04-01

341

Avalanche risk assessment for mountain roads - a comparison of case studies from Iceland and the Alps  

NASA Astrophysics Data System (ADS)

While the management of alpine natural hazards in settlements follows highly developed operational standardised procedures in many countries, there are very few approaches for a systematic survey and assessment of these natural hazard processes and the related risks and for a sustainable planning of measures for roads. This is even more surprising against the background of the ongoing increase of traffic in Europe and its economic importance. This contribution compares the results of a regional scale assessment of the avalanche risk on mountain roads for case studies from Austria, Italy and Iceland. It provides the first assessment of the natural hazard situation for roads outside closed settlements in Iceland and discusses the applicability of regional scale risk based approaches developed in the Alps to the specific natural, economic and social situation. It also compares the role of risk in the assessment and management of natural hazards in these countries. The assessment of the risk by natural hazard processes for roads follows approaches developed by Wilhelm (1997, 1998, 1999) and Borter (1999a, 1999b) in the Alps adapted to comply with the data availability of the regional scale. These approaches distinguish between the individual risk on the one hand and the collective risk for the society on the other hand for each process area as well as the cumulative risk for the investigated road section. As the spatial and temporal distribution of avalanches is relatively well documented in some of the Alpine countries practical approaches have been developed for the assessment of this natural hazard process. These have been successfully applied e.g. to roads in inner Oetz and inner Stubai Valley, Tyrol, Austria by Huttenlau (2004) and Gufler (2007) and Sulden road, Ortles Alps, Southern Tyrol, Italy by Zischg et al. (2004). On the basis of these investigations the individual, collective and cumulative death risk for avalanches was determined for Siglufjarðarvegur between Siglufjörður and Straumnes in northern Iceland (Wastl et al. 2008). The total length of the public road network in Iceland is ca. 13000 km, mostly low-volume roads outside built-up areas. Almost 10500 km of these roads are open all year. Substantial parts of the public road network e.g. in central northern Iceland, northwestern and eastern Iceland lie in alpine mountain areas and are affected by characteristic natural hazard processes. Though the resulting road maintenance costs are considerable there is no general overview of the natural hazard situation up to now. The case study for Siglufjarðarvegur shows that a regional scale risk based approach is practical to determine, analyse and assess the natural hazard situation on mountain roads in Iceland and helps to assign priorities in following detailed investigations and the planning of measures. Thus road sections of a high risk level which should be given priority for possible protective measures can be identified and distinguished from areas of avalanche hazard where the collective avalanche death risk is low and acceptable according to international practice. The calculated risks can further be reduced by measures like temporary closing of parts of the road, which can bring the risk to an acceptable level almost everywhere in the investigated road section. This requires, however, a systematic monitoring of the development of the natural hazard situation along the road. The cumulative risk for the investigated section of Siglufjarðarvegur, for the case that no measures of avalanche prevention or control or temporary closing of the road are taken, agrees well with values determined for mountain roads in the Alps. References Borter P. (1999a) Risikoanalyse bei gravitativen Naturgefahren - Methode. Bundesamt für Umwelt, Wald und Landschaft (ed) Umwelt-Materialien 107/I Naturgefahren, Bern. Borter P. (1999b) Risikoanalyse bei gravitativen Naturgefahren - Fallbeispiele und Daten. Bundesamt für Umwelt, Wald und Landschaft (ed) Umwelt-Materialien 107/II Naturgefahren, Bern. Gufler B. (2007) Vergleichen

Wastl, M.; Stötter, J.

2009-04-01

342

Geiger-mode avalanche photodiode focal plane arrays for three-dimensional imaging LADAR  

NASA Astrophysics Data System (ADS)

We report on the development of focal plane arrays (FPAs) employing two-dimensional arrays of InGaAsP-based Geiger-mode avalanche photodiodes (GmAPDs). These FPAs incorporate InP/InGaAs(P) Geiger-mode avalanche photodiodes (GmAPDs) to create pixels that detect single photons at shortwave infrared wavelengths with high efficiency and low dark count rates. GmAPD arrays are hybridized to CMOS read-out integrated circuits (ROICs) that enable independent laser radar (LADAR) time-of-flight measurements for each pixel, providing three-dimensional image data at frame rates approaching 200 kHz. Microlens arrays are used to maintain high fill factor of greater than 70%. We present full-array performance maps for two different types of sensors optimized for operation at 1.06 ?m and 1.55 ?m, respectively. For the 1.06 ?m FPAs, overall photon detection efficiency of >40% is achieved at <20 kHz dark count rates with modest cooling to ~250 K using integrated thermoelectric coolers. We also describe the first evalution of these FPAs when multi-photon pulses are incident on single pixels. The effective detection efficiency for multi-photon pulses shows excellent agreement with predictions based on Poisson statistics. We also characterize the crosstalk as a function of pulse mean photon number. Relative to the intrinsic crosstalk contribution from hot carrier luminescence that occurs during avalanche current flows resulting from single incident photons, we find a modest rise in crosstalk for multi-photon incident pulses that can be accurately explained by direct optical scattering.

Itzler, Mark A.; Entwistle, Mark; Owens, Mark; Patel, Ketan; Jiang, Xudong; Slomkowski, Krystyna; Rangwala, Sabbir; Zalud, Peter F.; Senko, Tom; Tower, John; Ferraro, Joseph

2010-09-01

343

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

SciTech Connect

Large-rock avalanche deposits are a common component of the basin fill within the extensional tectonic terrain of the Basin and Range; these deposits recently have been interpreted to host oil and gas within the Railroad Valley area of eastern Nevada. Large blocks of brecciated bedrock are a primary component of these avalanche deposits and are potentially excellent oil and gas reservoirs. Our work provides further insight into the emplacement and economic potential of these deposits. Exposed large-rock avalanche deposits of the Miocene Oak City Formation on the western margin of the Canyon Range, Utah, contain coherent breccia blocks up to 3.5 km long, 1 km wide, and 200 m thick. These deposits were derived from the near-vertical dipping bed rock of the adjacent Canyon Range and now are exposed as much as 5.5 km from the range front within the Sevier Desert basin. Emplacement was relatively rapid, as indicated by three well-developed breccia facies within the carbonate breccia blocks. Stratigraphically, from the base the facies include (1) matrix-rich breccia, (2) jigsaw breccia, and (3) crackle breccia. The deposits were cut and segmented by a series of syn-depositional normal faults that developed during late Miocene and post-Miocene extension. Primary porosity was reduced by cement soon after burial. Cathodoluminescence cement patterns indicate that initially the basinward breccia blocks were more deeply buried relative to the water table than the breccia blocks proximal to the Canyon Range. After initial cementation, the basinward blocks were uplifted relative to the water table. Secondary porosity approaches 8% in the carbonate blocks and is greater than 14% within the jigsaw breccia. The size and porosity of these breccia blocks indicate their potential as reservoir targets.

Morris, T.H.; Hebertson, G.F. [Brigham Young Univ., Provo, Utah (United States)

1996-07-01

344

Metastability and microscopic avalanche dynamics in charge-density waves of chromium  

NASA Astrophysics Data System (ADS)

We have measured the relaxation of charge-density waves in chromium from out-of-equilibrium states achieved through rapid thermal quenching. Although pinned density waves have been predicted to relax through stick-slip dynamics, in which long-lived metastable states are linked by abrupt rearrangements of the microscopic structure, these microscopic behaviors have not been observed. Using synchrotron x rays, we have measured metastability of the order parameter and microscopic pinning phenomena including an avalanche of the charge-density wave phase. Molecular dynamical simulations based on the Fukuyama-Lee-Rice model show that these behaviors may be attributed to nucleation, pinning, and propagation of phase solitons.

Kim, Hyekyung Clarisse; Logan, Jonathan Michael; Shpyrko, O. G.; Littlewood, P. B.; Isaacs, E. D.

2013-10-01

345

Study of 144-channel hybrid avalanche photo-detector for Belle II RICH counter  

NASA Astrophysics Data System (ADS)

For the upgrade of the Belle detector at the KEKB collider, we are developing a proximity focusing ring imaging Cherenkov detector using a silica aerogel as a radiator. An array of 144 channel HAPD (Hybrid Avalanche Photo Detector) will be used as the photo-detector. We have measured performance of the HAPDs, and succeeded to read out single-photon signals from the HAPD using custom-made ASICs that have been developed for this purpose. We have also performed a beam test with a 2 GeV/ c electron beam and demonstrated more than 4?K/? separation performance at 4 GeV/ c.

Shiizuka, Susumu; Adachi, Ichiro; Dolenec, Rok; Hara, Koji; Iijima, Toru; Ikeda, Hirokazu; Imamura, Miki; Iwata, Syuuichi; Korpar, Samo; Krizan, Peter; Kumita, Tetsuro; Kuroda, Eiryo; Nishida, Shohei; Ogawa, Satoru; Pestotnik, Rok; Santelj, Luka; Sumiyoshi, Takayuki; Tabata, Makoto; Tagai, Rie

2011-02-01

346

TGF electron avalanches and gamma-ray emission - a new detailed simulation software package  

NASA Astrophysics Data System (ADS)

In designing the MXGS coded mask imager of the ASIM mission to detect and locate gamma-rays from Terrestrial Gamma-ray Flashes it has been necessary to simulate the expansion of gamma-ray photons from 15-20 km altitudes to make some estimate of TGF spectra and the diffuse extent of a TGF beam observed at orbital altitudes. From this a new detailed simulation software package has been developed to take into account not just electron scattering via Bremsstrahlung and ionization, but also a range of spatial electric field distributions which can drive the runaway electron avalanche process, and the evolution of electron and ion spatial density which might choke avalanche growth or stimulate a quasi-simultaneous lightning discharge. The software package uses the standard physics of keV-MeV photon interactions, Bremsstrahlung scattering and photon emission, with Elwert modifications, including the Sommerfeld-Maue electron wave function variation and electron shielding effects. It also includes the physics of close range Moller electron ionization scattering, distant electron Coulomb ionization, Binary-Electron-Bethe models of electron scattering, and positron Bhabha scattering and annihilation. It also uses a superparticle spatial mesh system to control particle-momentum densities, electric field evolution, and any exponential avalanche growth. Results will be presented of simulations using macro electric fields expected in storm clouds and the micro fields expected around streamer tips, and will include videos showing the detailed time evolution of electron and photon flux fields, local ion densities and, particularly, induced local electric fields and their effect in inhibiting or stopping a TGF particle avalanche. The software is script driven and intended for users who wish to concentrate on the effect of local electric fields on TGF origin and avoid the additional GEANT4 type overheads and complexities of all the scattering processes involved. It will also provide specific subroutines which will take care of all particle tracking, scattering and scattering products, for users who wish to develop their own Monte Carlo simulation methods.

Connell, Paul

2013-04-01

347

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

PubMed

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) approximately S;{-3/2}e;{-S4S_{m}} , where S_{m} is a large-scale cutoff, in some cases calculable. Resumming all one-loop contributions, we find P(S) approximately S;{-tau}exp(C(SS_{m});{1/2}-B/4(S/S_{m});{delta}) , where B , C , delta , and tau are obtained to first order in =4-d . Our result is consistent to O() with the relation tau=tau_{zeta}:=2-2/d+zeta , where zeta 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 tau=2-1/d+zeta 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 tau=tau_{zeta} 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) approximately K_{13}(S)S , where K is the Bessel- K function, thus tau_{hyperplane}=4/3 . PMID:19518415

Le Doussal, Pierre; Wiese, Kay Jörg

2009-05-01

348

Ultrahigh-sensitivity single-photon detection with linear-mode silicon avalanche photodiode.  

PubMed

We developed an ultrahigh-sensitivity single-photon detector using a linear-mode avalanche photodiode (APD) with a cryogenic low-noise readout circuit; the APD is operated at 78K. The noise-equivalent power of the detector is as low as 2.2x10(-20)W/Hz(1/2) at a wavelength of 450nm. The photon-detection efficiency and dark-count rate (DCR) are 0.72 and 0.0008counts/s, respectively. A low DCR is achieved by thermal treatment for reducing the trapped carriers when the thermal treatment temperature is above 100K. PMID:20680078

Akiba, Makoto; Tsujino, Kenji; Sasaki, Masahide

2010-08-01

349

4H-SiC Avalanche Photodiodes for 280nm UV Detection  

NASA Astrophysics Data System (ADS)

We designed and fabricated 4H-SiC PIN avalanche photodiodes (APD) for UV detection. The thickness of an intrinsic layer in a PIN structure was optimized in order to achieve the highest quantum efficiency at the wavelength of interest. The optimized 4H-SiC PIN APDs exhibited a maximum external quantum efficiency of > 80% at the wavelength of 280nm and a gain greater than 40000. Both electrical and optical characteristics of the fabricated APDs were in agreement with those predicted from simulation.

Cha, Ho-Young; Sung, Hyuk-Kee; Kim, Hyungtak; Cho, Chun-Hyung; Sandvik, Peter M.

350

Debris avalanches and slumps on the margins of volcanic domes on Venus: Characteristics of deposits  

NASA Technical Reports Server (NTRS)

Modified volcanic domes, referred to as collapsed margin domes, have diameters greater than those of terrestrial domes and were therefore thought to have no suitable terrestrial analogue. Comparison of the collapsed debris using the Magellan SAR images with volcanic debris avalanches on Earth has revealed morphological similarities. Some volcanic features identified on the seafloor from sonar images have diameters similar to those on Venus and also display scalloped margins, indicating modification by collapse. Examination of the SAR images of collapsed dome features reveals a number of distinct morphologies to the collapsed masses. Ten examples of collapsed margin domes displaying a range of differing morphologies and collapsed masses have been selected and examined.

Bulmer, M. H.; Guest, J. E.; Beretan, K.; Michaels, Gregory A.; Saunders, R. Stephen

1992-01-01

351

Characterization of a commercially available large area, high detection efficiency single-photon avalanche diode  

E-print Network

We characterize a new commercial, back-illuminated reach-through silicon single-photon avalanche photo diode (SPAD) SAP500 (Laser Components. Inc.), operated in Geiger-mode for purpose of photon counting. We show that for this sensor a significant interplay exists between dark counts, detection efficiency, afterpulsing, excess voltage and operating temperature, sometimes requiring a careful optimization tailored for a specific application. We find that a large flat plateau of sensitive area of about 0.5 mm in diameter, a peak quantum efficiency of 73% at 560 nm and timing precision down to 150 ps FWHM are the main distinguishing characteristics of this SPAD.

Mario Stip?evi?; Daqing Wang; Rupert Ursin

2013-11-08

352

InGaAs-InP avalanche photodiodes with dark current limited by generation-recombination.  

PubMed

Separate absorption grading charge multiplication avalanche photodiodes (SAGCM APDs) are widely accepted in photon starved optical communication systems due to the presence of large photocurrent gain. In this work, we present a detailed analysis of dark currents of planar-type SAGCM InGaAs-InP APDs with different thicknesses of multiplication layer. The effect of the diffusion process, the generation-recombination process, the tunneling process and the multiplication process on the total leakage current is discussed. A new empirical formula has been established to predict the optimal multiplication layer thickness of SAGCM APDs with dark current limited by generation-recombination at multiplication gain of 8. PMID:21643105

Zhao, Yanli; Zhang, Dongdong; Qin, Long; Tang, Qi; Wu, Rui Hua; Liu, Jianjun; Zhang, Youping; Zhang, Hong; Yuan, Xiuhua; Liu, Wen

2011-04-25

353

Scaling trends of single-photon avalanche diode arrays in nanometer CMOS technology  

NASA Astrophysics Data System (ADS)

A family of scaleable single photon avalanche diode (SPAD) structures in 130nm and 90nm CMOS is presented. Performance trends such as dark count rate (DCR), jitter and breakdown voltage are studied versus active diameter for devices ranging from 32?m down to 2?m. To address pixel pitch we introduce a shared buried n-well approach allowing compact arrays containing both NMOS-transistor readout circuitry and SPAD devices. A pixel pitch of 5?m has been achieved in 90nm CMOS technology, offering the potential for future megapixel single photon image sensors.

Richardson, Justin A.; Webster, Eric A. G.; Grant, Lindsay A.; Henderson, Robert K.

2011-05-01

354

Detection of Nanopipes in GaN Films by Localized Avalanche Breakdown Using NaOH Electrolyte  

NASA Astrophysics Data System (ADS)

Nanopipes in high-quality GaN films grown by metalorganic chemical vapor deposition (MOCVD) on a sapphire substrate were investigated by generating hollow etch pits. Hollow etch pits were formed on the surface of GaN films by localized avalanche breakdown using NaOH electrolyte. Using scanning electron microscopy (SEM) and atomic force microscopy (AFM), the relationship between hollow etch pits and crystalline defects in GaN films was investigated. It was found that hollow etch pits were formed at the nanopipes and electrical discharge occurred through these nanopipes at high electric fields, resulting in localized avalanche breakdown. Defect etching by localized avalanche breakdown was found to be a simple method to detect nanopipes in GaN films.

Ohkubo, Mitsugu

2001-11-01

355

Avalanches, loading and finite size effects in 2D amorphous plasticity: results from a finite element model  

E-print Network

Crystalline plasticity is strongly interlinked with dislocation mechanics and nowadays is relatively well understood. Concepts and physical models of plastic deformation in amorphous materials on the other hand - where the concept of linear lattice defects is not applicable - still are lagging behind. We introduce an eigenstrain-based finite element lattice model for simulations of shear band formation and strain avalanches. Our model allows us to study the influence of surfaces and finite size effects on the statistics of avalanches. We find that even with relatively complex loading conditions and open boundary conditions, critical exponents describing avalanche statistics are unchanged, which validates the use of simpler scalar lattice-based models to study these phenomena.

Stefan Sandfeld; Zoe Budrikis; Stefano Zapperi; David Fernandez Castellanos

2014-11-10

356

Proceedings of the 2008 International Snow Science Workshop, Whistler, British Columbia SNOW SLOPE STABILITY MODELING OF DIRECT-ACTION AVALANCHES IN A  

E-print Network

on naturally released avalanches on the Blue Point slide path on Red Mountain Pass, as this site is known STABILITY MODELING OF DIRECT-ACTION AVALANCHES IN A CONTINENTAL CLIMATE: RED MOUNTAIN PASS, COLORADO Hans Investigation of the Shallow Subsurface, Boise State University, Boise, ID 2 Cold Regions Research

Marshall, Hans-Peter

357

Chronology of Holocene rock-avalanche deposits based on Schmidt-hammer relative dating and dust stratigraphy in nearby bog deposits, Vora, inner Nordfjord, Norway  

Microsoft Academic Search

A number of large rock avalanches from the northern slope of the 1435 m high mountain of Vora in Breim, inner Nordfjord have been mapped. The avalanche tongues dam the 4 km long Sandalsvatnet, they cover an area of 3 km 2 and the volume exceeds 100 million m3. Age estimates have been obtained by radiocarbon datings of rock dust

Asbjørn Rune Aa; Jan Sjåstad; Eivind Sønstegaard; Lars Harald Blikra

2007-01-01

358

Undersampled Critical Branching Processes on Small-World and Random Networks Fail to Reproduce the Statistics of Spike Avalanches  

PubMed Central

The power-law size distributions obtained experimentally for neuronal avalanches are an important evidence of criticality in the brain. This evidence is supported by the fact that a critical branching process exhibits the same exponent . Models at criticality have been employed to mimic avalanche propagation and explain the statistics observed experimentally. However, a crucial aspect of neuronal recordings has been almost completely neglected in the models: undersampling. While in a typical multielectrode array hundreds of neurons are recorded, in the same area of neuronal tissue tens of thousands of neurons can be found. Here we investigate the consequences of undersampling in models with three different topologies (two-dimensional, small-world and random network) and three different dynamical regimes (subcritical, critical and supercritical). We found that undersampling modifies avalanche size distributions, extinguishing the power laws observed in critical systems. Distributions from subcritical systems are also modified, but the shape of the undersampled distributions is more similar to that of a fully sampled system. Undersampled supercritical systems can recover the general characteristics of the fully sampled version, provided that enough neurons are measured. Undersampling in two-dimensional and small-world networks leads to similar effects, while the random network is insensitive to sampling density due to the lack of a well-defined neighborhood. We conjecture that neuronal avalanches recorded from local field potentials avoid undersampling effects due to the nature of this signal, but the same does not hold for spike avalanches. We conclude that undersampled branching-process-like models in these topologies fail to reproduce the statistics of spike avalanches. PMID:24751599

Ribeiro, Tiago L.; Ribeiro, Sidarta; Belchior, Hindiael; Caixeta, Fabio; Copelli, Mauro

2014-01-01

359

Simulation of the Avalanche Process in the G-APD and Circuitry Analysis of the SiPM  

Microsoft Academic Search

The discrete modeling of the Geiger-mode APD is considered. Results of\\u000amodeling and experimental measurements with the SiPM show that the known\\u000aformula for the charge of the avalanche pulse Q=dU*Cd underestimates its value.\\u000aIn addition, it is seen from the dynamic of the avalanche multiplication that\\u000athe resistor Rq in photodiode, usually called a quenching resistor, in reality\\u000afulfills

V. M. Grebenyuk; A. I. Kalinin; Nguyen Manh Shat; A. K. Zhanusov; V. A. Bednyakov

2009-01-01

360

InGaAs/InP avalanche photodiode for infrared single photon detection using a time-to-voltage converter  

NASA Astrophysics Data System (ADS)

We demonstrated an efficient and robust technique for weak avalanche discrimination by using a time-to-voltage converter circuit for the infrared single photon detection based on InGaAs/InP single photon avalanche photodiodes (SPADs), which enabled a strong suppression of the afterpulse noise. At a gating frequency of 10 MHZ, a detection efficiency of 20.1% was obtained with a dark count probability of 1.2×10-5 and an afterpulse probability of 1.22% without dead time, paving the way for the low-noise fast detection of infrared single photons.

Bouzid, Abdessattar; Nahhas, Ahmed M.; Guedri, Kamel

2014-10-01

361

Proton radiation damage effects on the response of high speed communication avalanche photodiodes  

NASA Astrophysics Data System (ADS)

This paper discusses the radiation dependent characteristics of avalanche photodiodes (APDs). The reliability, of semiconductor detectors, is very dependent on the degradation modes. In this study, we present the main irradiation effects such as the multiplication gain, minority carrier life time, illumination, and radiation damage coefficient. Protons radiation effects, on the model of two different silicon avalanche photodiode structures, has been investigated. The results demonstrate that the model can accurately calculate the internal parameters of the APDs and produce data that can be directly compared with measurements. The fluence effects of 51 MeV proton irradiation, on the photosensitivity and signal to noise ratio, are also investigated. The objective was to analyze the effect depletion region volume and carrier concentration, of the i-region of APDs, on radiation hardness. Moreover, we have investigated, deeply, some of the degradation performance and capabilities of typical APDs, currently used in many communication and sensing systems, over wide range of the affecting parameters. APDs are used in systems that require coherent, and often single mode, light such as high data rate communications and sensing applications. APDs are an attractive receiver choice for low signal applications because their internal gain mechanism can improve signal to noise ratio. Additionally, we have taken into account the harmful effects of proton radiation on the device performance such as signal to noise ratio, bit error rate, gain, sensitivity, device responsitivity and operating efficiency.

Rashed, Ahmed Nabih Zaki; El-Halawany, Mohamed M. E.

2013-01-01

362

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

SciTech Connect

In this paper, the authors propose and demonstrate a new kind of optical bistable scheme which is based on an AHPT (avalanche hetero-junction phototransistor) and an LD. The operating principles of the AHPT and the completed bistable devices are discussed in details. A simple assumption is made to simplify the analysis. When the AHPT-LD-BOD works in the steady state, it presents four operating modes, which are linear amplification, avalanche gain, optical bistability, as well as optoelectronic switching. When it is in the mode of the optical bistability, the critical triggering optical power is no more than 10 ..mu..W and the output power at ON state is larger than 1 mW. The ratio of the output optical power at ON state to that at OFF state is greater than 4 dB. Based on the good performance of the AHPT, they can realize five elementary optical logic gates, which are OR, AND, INVERTER, NOR, and NAND. The advantage of this kind of bistable system over the conventional ones is that neither external optical nor electrical feedback is needed. Therefore, it is possible and convenient to realize either monolithic or hybrid integration.

Jie, D.; Xiao-Kang, H.; Bao-Yin, S.

1987-11-01

363

Experimental measurements on a powder avalanche impacting an obstacle: 3D velocity field and exerted pressures  

NASA Astrophysics Data System (ADS)

In the framework of the Alcotra DYNAVAL Interreg project, this experimental study aims at investigating the dynamical behaviour of a powder snow avalanche impacting an obstacle. Tests have been realised in a water tank where a salty water solution (rho=1.2kg m-3) flows down in a channel and impacts an obstacle at a distance d=1m from the releasing gate. The set-up geometry reproduces a simplified small-scale model of the real avalanche site of Taconnaz (Chamonix, France). A high-resolution acoustic velocimeter allows measurements on the 3D flow velocity. By measuring the velocity just upstream and downstream of the obstacle, it is possible to determine the influence of the obstacle on the flow. In a lack of suitable sensors, the pressure exerted on the obstacle is calculated using the classical formula P=1/2rhoU2. Then, density values are required. A new method to measure the flow density is advanced and preliminary results are presented.

Caccamo, P.; Naaim-Bouvet, F.; Bellot, H.; Ousset, F.; Faug, T.

2012-04-01

364

High-performance SiC avalanche photodiode for single ultraviolet photon detection  

NASA Astrophysics Data System (ADS)

Sensitive ultraviolet photodetectors are essential components for a growing number of civilian and military applications. In this paper, we report 4H Silicon Carbide (SiC) avalanche photodiodes (APDs) with a p-i-n structure. These APDs, range in diameter from 180 ?m to 250?m, exhibit very low dark current (10s of pA at avalanche gain of 1000) and high gain in linear-mode operation. An external quantum efficiency of 48% at 280 nm is achieved at unity gain with a recessed-window structure. The differential resistance of a 250 ?m recessed-window device at zero bias is estimated to be 6×1014 ohms. As a result of high external quantum efficiency, large area, and large differential resistance, a record high specific detectivity of 4.1×1014 cmHz 1/2 W-1, has been achieved. Single ultraviolet photon detection in Geiger-mode operation with gated quenching is also described. In this paper, we report single photon detection efficiency (SPDE) of 30% at 280 nm with a dark count probability (DCP) of 8×10-4.

Bai, Xiaogang; Liu, Han-din; McIntosh, Dion; Campbell, Joe C.

2008-08-01

365

Identification of Criticality in Neuronal Avalanches: I. A Theoretical Investigation of the Non-driven Case  

PubMed Central

In this paper, we study a simple model of a purely excitatory neural network that, by construction, operates at a critical point. This model allows us to consider various markers of criticality and illustrate how they should perform in a finite-size system. By calculating the exact distribution of avalanche sizes, we are able to show that, over a limited range of avalanche sizes which we precisely identify, the distribution has scale free properties but is not a power law. This suggests that it would be inappropriate to dismiss a system as not being critical purely based on an inability to rigorously fit a power law distribution as has been recently advocated. In assessing whether a system, especially a finite-size one, is critical it is thus important to consider other possible markers. We illustrate one of these by showing the divergence of susceptibility as the critical point of the system is approached. Finally, we provide evidence that power laws may underlie other observables of the system that may be more amenable to robust experimental assessment. PMID:23618010

2013-01-01

366

A study of the runaway relativistic electron avalanche and the feedback theory using GEANT4  

NASA Astrophysics Data System (ADS)

This study investigate the Runaway Relativistic Electron Avalanche (RREA) and the feedback process as well as the production of Bremsstrahlung photons from Runaway Electrons (REs). These processes are important to understand the production of the intense bursts of gamma-rays known as Terrestrial Gamma-Ray Flashes (TGFs). Results are obtained from Monte Carlo (MC) simulations using the GEometry ANd Tracking 4 (GEANT4) programming toolkit. The simulations takes into account the effects of electron ionisation, electron by electron scattering (Møller scattering) as well as positron and photon interactions, in the 250 eV-100 GeV energy range. Several physics libraries or 'physics lists' are provided with GEANT4 to implement these physics processes in the simulations. We give a detailed analysis of the electron and the feedback multiplication, in particular the avalanche lengths, ?, the energy distribution and the feedback factor, ?. We also find that our results vary significantly depending on which physics list we implement. In order to verify our results and the GEANT4 programming toolkit, we compare them to previous results from existing models. In addition we present the ratio of the production of bremsstrahlung photons to runaway electrons. From this ratio we obtain the parameter, ?, which describe the electron to photon relation.

Broberg Skeltved, Alexander; Østgaard, Nikolai; Carlson, Brant; Gjesteland, Thomas

2014-05-01

367

Effect of dissipation on avalanches in a two-dimensional sheared foam  

NASA Astrophysics Data System (ADS)

We study the response of a foam to a steady shear using a model(D.J. Durian, Phys. Rev. Lett. 75), 4780 (1995). of foams that incorporates elasticity and viscous dissipation in a polydisperse random array of gas bubbles. In the limit of small shear rates the elastic storage of energy in the system is dissipated intermittently through sudden avalanche-like rearrangements of the bubbles. We study the distribution and statistics of energy releases, or avalanches, for systems of different size and liquid content, and find that the nature of dissipation strongly influences the results. A ``mean-field'' dissipation that depends on the velocity of a bubble relative to an average imposed flow field gives a distribution ? E-0.7 that is cut off exponentially at large events. As the liquid content is increased toward the melting point, the cut-off moves towards larger events that are limited by the system size. By contrast, a dissipation that depends on the actual velocity difference of a bubble with respect to each of its neighbors shows a deviation from power law behavior for the smallest events. In either case, our predictions differ from those of models that find a power law in the distribution of event sizes, but either do not include dissipation or are only defined in the limit of zero liquid content.

Tewari, Shubha; Durian, D. J.; Langer, Stephen A.

1997-03-01

368

Dry granular avalanche down a flume: Choice of discrete element simulation parameters  

NASA Astrophysics Data System (ADS)

This paper presents a method to assign soft-sphere contact model parameters in a discrete-element simulation with which we can reproduce the experimentally measured avalanche dynamics of finite dry granular mass down a flume. We adopt the simplest linear model in which interaction force is decomposed along or tangent to the contact normal. The model parameters are chosen uniquely to satisfy theoretical models or to meet experimental evidences at either the particle or the bulk size level. The normal mode parameters are chosen specifically to ensure Hertzian contact time (but not its force-displacement history) and the resulting loss of particle kinetic energy, characterized by a measured coefficient of restitution, for each pair of colliding surfaces. We follow the literature to assign the tangential spring constant according to an elasticity model but propose a method to assign the friction coefficient using a measured bulk property that characterizes the bulk discharge volume flow rate. The linear contact model with the assigned parameters are evaluated by comparing the simulated bulk avalanche dynamics down three slopes to the experimental data, including instantaneous particle trajectories and bulk unsteady velocity profile. Satisfying quantitative agreement can be obtained except at the free surface and the early-time front propagation velocity.

Yang, F.-L.; Chang, W. T.; Huang, Y. T.; Hsieh, S. H.; Chen, C. S.

2013-12-01

369

Adherence of backcountry winter recreationists to avalanche prevention and safety practices in northern Italy.  

PubMed

Backcountry recreationists account for a high percentage of avalanche fatalities, but the total number of recreationists and relative percentage of different recreation types are unknown. The aim of this study was to collect the first comprehensive survey of backcountry skiers and snowshoers in a region in the European Alps to quantify adherence to basic prevention and safety practices. Over a 1-week period in February 2011 in South Tyrol, Italy, 5576 individuals (77.7% skiers, 22.3% snowshoers) in 1927 groups were surveyed. Significantly more skiers than snowshoers could report the avalanche danger level (52.5% vs 28.0% of groups) and carried standard rescue equipment (transceiver, probe, and shovel) (80.6% vs 13.7% of individuals). Complete adherence to minimum advisable practices (i.e., an individual being in a group with one member correctly informed about the danger level and carrying personal standard rescue equipment) was 41.5%, but was significantly higher in skiers (51.1% vs 8.7% snowshoers) and in individuals who were younger, reported more tours per season, traveled in larger groups, and started earlier. A transnational survey over a complete winter season would be required to obtain total participation prevalence, detect regional differences, and assess the influence of prevention and safety practices on relative reduction in mortality. PMID:23815413

Procter, E; Strapazzon, G; Dal Cappello, T; Castlunger, L; Staffler, H P; Brugger, H

2014-10-01

370

Assessment and prevention of the avalanche risk on medium-high mountain from a geo-historical point of view. The Vosges range (France) as a case study.  

NASA Astrophysics Data System (ADS)

To mention avalanche risks in the Vosges generally causes certain disbelief because of its modest height. Moreover, as far as natural risks are concerned, and especially the avalanche risk, medium-high mountains are not usually studied. The attention is more focused on the spectacular and destructive phenomena that occur in highest mountains such as the Alps or the Pyrenees. However, in January and February 2000, fifteen people were victims of avalanches and three of them died. These accidents have suddenly drawn attention to the fact that avalanche risk is underestimated. In opposition to the Alps and Pyrenees there is no study or systematic inventory of avalanches in the medium-high mountain ranges. Moreover, the many research and methodological articles dedicated to studies on avalanches in the high mountain ranges do not, unfortunately, raise any concerns about medium-high mountain ranges. So, we had to develop a new research method based on handwritten, printed, and oral sources as well as on observations. The results of this historical research exceeded all expectations. About 300 avalanche events have been reported since the end of the 18th century; they happened in about 90 avalanche paths. Spatial and temporal distributions of the avalanche events can be explained by climate, vulnerability and land use evolutions. The vulnerability has evolved since the 18th century: material vulnerability decreased whereas human vulnerability increased due to the expansion of winter sports. Finally we focus our study on the perception of the avalanche risk by the winter sports adepts in the Vosges mountains. Indeed, at the beginning of this research, we were directly confronted to a lack of knowledge, or even to an ignorance, of the avalanche risk. Several factors contribute to this situation among which the topography. Even though some places in the Vosges mountains look like the alpine topography, most of the summits are rounded. Furthermore, this mountain presents an annual and seasonal variability of snowfall and snow height. And the summits and slopes which present an avalanche risk can be easily reached in wintertime thanks to car parks close to the summits and the clearing of snow from the roads. A study is therefore being carried out in order to understand the mechanisms of perception and awareness of the avalanche risk. This is the first step towards the development of a new prevention method adapted to the recreational public in medium-high mountains.

Giacona, Florie; Martin, Brice; David, Pierre-Marie

2010-05-01

371

Influence of avalanche-photodiode dead time on the security of high-speed quantum-key distribution systems  

E-print Network

-speed quantum key distribution (QKD) systems in short-distance fiber networks, such as local area networks (LANsInfluence of avalanche-photodiode dead time on the security of high-speed quantum-key distribution photodiodes (APDs) in quantum cryptographic systems. A simultaneous hold-off of the APDs (SHA) technique

372

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

E-print Network

­12], and as earthquakes driven by motion of tectonic plates [13­16]. Some features of the avalanche statistics, like size that under monotonous driving the particle moves forward at all times, as it does in absence of retardation quantitatively the limits of slow and fast relaxation for stationary driving with velocity v > 0. The v

Wiese, Kay Jörg

373

Integrated snow and avalanche monitoring system for Indian Himalaya using multi-temporal satellite imagery and ancillary data  

Microsoft Academic Search

The variations in the local climate, environment and altitude as well as fast snow cover build up and rapid changes in snow characteristics with passage of winter are major contributing factors to make snow avalanches as one of the threatening problems in the North West Himalaya. For sustainable development of these mountainous areas, a number of multi-purpose projects are being

S. S. Sharma; Sneh Mani; P. Mathur

2004-01-01

374

Integrated snow and avalanche monitoring syatem for Indian Himalaya using multi-temporal satellite imagery and ancillary data  

Microsoft Academic Search

The variations in the local climate, environment and altitude as well as fast snow cover build up and rapid changes in snow characteristics with passage of winter are major contributing factors to make snow avalanches as one of the threatening problems in the North West Himalaya. For sustainable development of these mountainous areas, a number of multi-purpose projects are being

S. S. Sharma; Sneh Mani; P. Mathur

2004-01-01

375

Decades of snow-avalanche activity documented by tree rings on three colluvial cones in Northern Iceland  

NASA Astrophysics Data System (ADS)

Tree rings were used in Northern Iceland to infer snow avalanche activity (lateral extent, runout distance, frequency and return period) in three U-shaped valleys of Northern Iceland, within the Suður-Þingeyjarsýsla, east of the town of Akureyri: Dalsmynni, Ljósavatnsskarð and Fnjóskadalur. From summer 2006 to summer 2010, a total of 121 trees were sampled (either one cross section per trees, either two cores per tree - 39 trees on the cone investigated in Fnjóskadalur; 27 in Dalsmynni; 55 in Ljósavatnnsskarð). The analysis of the series of annual increment rings reveals the stress the trees suffer from during the dormant season and the growth disturbances the trees develop during the following growing season to cope with winter damage. The dendrochronologic approach enables the extraction of the chronology of snow avalanches back to the 50s in Dalsmynni, back to the 30s in Ljósavatnsskarð, and back to the 20's in Fnjóskadalur. Results emphasize the great impact of snow avalanche winters 1974 and 1995, which were dreadfull over the island and resulted in severe losses of lives. In addition, several other winters, undocumented in the written archives, are highlighted in tree rings, offering an opportunity to derive the snow-avalanche return period at each site.

Decaulne, Armelle; Eggertsson, Ólafur; Sæmundsson, Þorsteinn

2014-05-01

376

Electric field induced avalanche breakdown and non-volatile resistive switching in the Mott Insulators AM4Q8  

NASA Astrophysics Data System (ADS)

The Mott insulator compounds AM4Q8 exhibit a new type of volatile and non volatile resistive switchings that are of interest for RRAM application. We found that above a threshold electric field ETH of the order of a few kV/cm these compounds undergo a volatile resistive switching based on an avalanche process. For electric field much higher than the threshold avalanche breakdown field, the resistive switching turns non volatile. Our EDXS and STEM analyses show that the non volatile resistive switching originating from the avalanche breakdown can neither be ascribed to local chemical modifications nor to a local phase change with symmetry breaking at a resolution better than a few nanometer. This is in strong contrast with non volatile resistive switching reported so far that are all based on chemical or structural changes. Conversely, our results suggest that the avalanche breakdown induce the collapse of the Mott insulating state at the local scale and the formation of a granular conductive filament formed by compressed metallic domains and expanded “superinsulating” domains.

Corraze, B.; Janod, E.; Cario, L.; Moreau, P.; Lajaunie, L.; Stoliar, P.; Guiot, V.; Dubost, V.; Tranchant, J.; Salmon, S.; Besland, M.-P.; Phuoc, V. Ta; Cren, T.; Roditchev, D.; Stéphant, N.; Troadec, D.; Rozenberg, M.

2013-07-01

377

Electric field induced avalanche breakdown and non-volatile resistive switching in the Mott Insulators AM4Q8  

NASA Astrophysics Data System (ADS)

The Mott insulator compounds AM4Q8 exhibit a new type of volatile and non volatile resistive switchings that are of interest for RRAM application. We found that above a threshold electric field E TH of the order of a few kV/cm these compounds undergo a volatile resistive switching based on an avalanche process. For electric field much higher than the threshold avalanche breakdown field, the resistive switching turns non volatile. Our EDXS and STEM analyses show that the non volatile resistive switching originating from the avalanche breakdown can neither be ascribed to local chemical modifications nor to a local phase change with symmetry breaking at a resolution better than a few nanometer. This is in strong contrast with non volatile resistive switching reported so far that are all based on chemical or structural changes. Conversely, our results suggest that the avalanche breakdown induce the collapse of the Mott insulating state at the local scale and the formation of a granular conductive filament formed by compressed metallic domains and expanded "superinsulating" domains.

Corraze, B.; Janod, E.; Cario, L.; Moreau, P.; Lajaunie, L.; Stoliar, P.; Guiot, V.; Dubost, V.; Tranchant, J.; Salmon, S.; Besland, M.-P.; Phuoc, V. Ta; Cren, T.; Roditchev, D.; Stéphant, N.; Troadec, D.; Rozenberg, M.

2013-07-01

378

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

NASA Astrophysics Data System (ADS)

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 (> 28,000 cal yr BP, V = ~ 1.3 km 3) and Tonila (15,000-16,000 cal yr BP, V = ~ 1 km 3 ). This work sheds light on the pre-failure conditions of the volcano based primarily on a detailed textural study of debris avalanche deposits and their associated pyroclastic and volcaniclastic successions. Furthermore, we show how the climate at the time of the Tonila collapse influenced the failure mechanisms. The > 28,000 cal yr BP San Marcos collapse was promoted by edifice steep flanks and ongoing tectonic and volcanotectonic deformation, and was followed by a magmatic eruption that emplaced pyroclastic flow deposits. In contrast, the Tonila failure occurred just after the Last Glacial Maximum (22,000-18,000 cal BP) and, in addition to the typical debris avalanche textural characteristics (angular to sub-angular clasts, coarse matrix, jigsaw fit) it shows a hybrid facies characterized by debris avalanche blocks embedded in a finer, homogenous and partially cemented matrix, a texture more characteristic of debris flow deposits. The Tonila debris avalanche is directly overlain by a 7-m thick hydromagmatic pyroclastic succession. Massive debris flow deposits, often more than 10 m thick and containing large amounts of tree trunk logs, represent the top unit in the succession. Fluvial deposits also occur throughout all successions; these represent periods of highly localized stream reworking. All these lines of evidence point to the presence of water in the edifice prior to the Tonila failure, suggesting it may have been a weakening factor. The Tonila failure appears to represent an anomalous event related to the particular climatic conditions at the time of the collapse. The presence of extensive water at the onset of deglaciation modified the mobility of the debris avalanche, and led to the formation of a thick sequence of debris flows. The possibility that such a combination of events can occur, and that their probability is likely to increase during the rainy season, should be taken into consideration when evaluating hazards associated with future collapses at Colima volcano.

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

2011-10-01

379

Monte Carlo simulations of compact gamma cameras based on avalanche photodiodes.  

PubMed

Avalanche photodiodes (APDs), and in particular position-sensitive avalanche photodiodes (PSAPDs), are an attractive alternative to photomultiplier tubes (PMTs) for reading out scintillators for PET and SPECT. These solid-state devices offer high gain and quantum efficiency, and can potentially lead to more compact and robust imaging systems with improved spatial and energy resolution. In order to evaluate this performance improvement, we have conducted Monte Carlo simulations of gamma cameras based on avalanche photodiodes. Specifically, we investigated the relative merit of discrete and PSAPDs in a simple continuous crystal gamma camera. The simulated camera was composed of either a 4 x 4 array of four channels 8 x 8 mm2 PSAPDs or an 8 x 8 array of 4 x 4 mm2 discrete APDs. These configurations, requiring 64 channels readout each, were used to read the scintillation light from a 6 mm thick continuous CsI:Tl crystal covering the entire 3.6 x 3.6 cm2 photodiode array. The simulations, conducted with GEANT4, accounted for the optical properties of the materials, the noise characteristics of the photodiodes and the nonlinear charge division in PSAPDs. The performance of the simulated camera was evaluated in terms of spatial resolution, energy resolution and spatial uniformity at 99mTc (140 keV) and 125I ( approximately 30 keV) energies. Intrinsic spatial resolutions of 1.0 and 0.9 mm were obtained for the APD- and PSAPD-based cameras respectively for 99mTc, and corresponding values of 1.2 and 1.3 mm FWHM for 125I. The simulations yielded maximal energy resolutions of 7% and 23% for 99mTc and 125I, respectively. PSAPDs also provided better spatial uniformity than APDs in the simple system studied. These results suggest that APDs constitute an attractive technology especially suitable to build compact, small field of view gamma cameras dedicated, for example, to small animal or organ imaging. PMID:17505089

Després, Philippe; Funk, Tobias; Shah, Kanai S; Hasegawa, Bruce H

2007-06-01

380

Shallow-trench-isolation bounded single-photon avalanche diodes in commercial deep submicron CMOS technologies  

NASA Astrophysics Data System (ADS)

This dissertation describes the first single-photon detection device to be manufactured in a commercial deep-submicron CMOS technology. It also describes novel self-timed peripheral circuits which optimize the performance of the new device. An extension of the new device for dual-color single-photon detection is investigated. Finally, an area- and power-efficient method for single-photon frequency upconversion is presented, analyzed, and experimentally examined. Single-photon avalanche diodes have been used in diverse applications, including three-dimensional laser radar, three-dimensional facial mapping, fluorescence-correlation techniques and time-domain tomography. Due to the high electric fields which these devices must sustain, they have traditionally been manufactured in custom processes, severely limiting their speed and the ability to integrate them in high-resolution imagers. By utilizing a process module originally designed to enhance the performance of CMOS transistors, we achieve highly planar junctions in an area-efficient manner. This results in SPADs exhibiting high fill factors, small pitch and ultrafast operation. Device miniaturization is accompanied by excessive noise, which was shown to emanate from trapped avalanche charges. Due to the fast recharging of the device, these charges are released in a subsequent charged phase of the device, causing correlated after-pulses. We present electrostatic and electrical simulation results, as well as a comprehensive characterization of the new device. We also show for the first time that by utilizing the two junctions included in the device, we can selectively detect photons of different wavelengths in the same pixel, as is desirable in cross-correlation experiments. This dissertation also describes an efficient new method for single-photon frequency upconversion. This is desirable for applications including quantum-key distribution and high-resolution near-infrared imaging. The new technique is based on electroluminescence in or near the multiplication region of the device, resulting from hot-carrier recombination. We model a proposed hybrid device and deduce the critical parameters for efficient upconversion. Lastly, we experimentally demonstrate that the electroluminescence yield from an InGaAs/InAlAs avalanche diode is sufficient for highly-efficient upconversion.

Finkelstein, Hod

381

The role of Thurwieser rock avalanche in the geomorphological evolution of Zebrù Valley (Italian Central Alps)  

NASA Astrophysics Data System (ADS)

On September 18th, 2004 a rock avalanche with an estimated volume of 2.5 M m3 propagated from the southern flank of Punta Thurwieser, affecting the Marè Valley, a tributary located in upper part of Zebrù Valley, 30 Km East from Bormio, in the Italian Central Alps. The landslide event deposited a thick debris cover on the pre-landslide morphology up to 2.2 Km from the source area. In this contribution, we aim at studying the role of the rock avalanche on the geomorphological evolution of the valley and in particular in controlling the evolution of the drainage system, the sediment budget and the mass balance of Zebrù glacier. In fact, after ten years it is possible to appreciate and valuate how such an event could modify the landscape and the geomorphology of an alpine valley. First, the landslide body formed a robust obstacle splitting the original watershed into two different sub-units. This caused a different distribution of the sediment yield rate in the upper part of the valley. As a consequence, an extremely rapid excavation of a new channel took place, ending in a new debris fan along the Zebrù valley bottom. A consistent groundwater flow still occurs within the rock avalanche deposit along the old valley axis, excepted for periods characterized by intense precipitation and snow melting events, which are able to activate the recently developed drainage channel. Thus implies that the main transport of sediments will occur along the new channel, during periods of high discharge. In the middle part of the landslide deposit, a sediment trap formed, collecting the material eroded by the surrounding ridges and by the upper sector of the deposit itself, forming a small plain under constant accretion. From this temporary trap, it was possible to estimate the periglacial sediment transport yield of the basin. The Zebrù glacier, flowing from the Mt Zebrù peak, was partially interested from the landslide, which covered a portion of the ice tongue with a shallow layer of blocks and finer matrix. The Thurwieser debris acted as a thermal insulation, preserving a significant ice volume and building up a steep bound, in the order of 10 m high, between non-covered and covered glacier surface. Topographic data collected since 2004 are presented and analyzed in this contribution to study the evolution both at a large and small scale.

Riva, Federico; Frattini, Paolo; Greggio, Luca; Crosta, Giovanni B.

2014-05-01

382

Volcano-tectonic controls and emplacement kinematics of the Iriga debris avalanches (Philippines)  

NASA Astrophysics Data System (ADS)

Mt Iriga in southeastern Luzon is known for its spectacular collapse scar that was possibly created in 1628 ad by a 1.5-km3 debris avalanche. The debris avalanche deposit (DAD) covered 70 km2 and dammed the Barit River to form Lake Buhi. The collapse has been ascribed to a non-volcanic trigger related to a major strike-slip fault under the volcano. Using a combination of fieldwork and remote sensing, we have identified a similar size, older DAD to the southwest of the edifice that originated from a sector oblique to the underlying strike-slip fault. Both deposits cover wide areas of low, waterlogged plains, to a distance of about 16 km for the oldest and 12 km for the youngest. Hundreds of metre-wide and up to 50-m-high hummocks of intact conglomerate, sand and clay units derived from the base of the volcano show that the initial failure planes cut deep into the substrata. In addition, large proportions of both DAD consist of ring-plain sediments that were incorporated by soft-sediment bulking and extensive bulldozing. An ignimbrite unit incorporated into the younger DAD forms small (less than 5 m high) discrete hummocks between the larger ones. Both debris avalanches slid over water-saturated soft sediment or ignimbrite and spread out on a basal shear zone, accommodated by horst and graben formation and strike-slip faults in the main mass. The faults are listric and flatten into a well-developed basal shear zone. This shear zone contains components from the substrate and has a diffuse contact with the intact substrata. Long, transport-normal ridges in the distal parts are evidence of compression related to deceleration and bulldozing. The collapse orientation and structure on both sectors and DAD constituents are consistent with collapse being a response to combined transtensional faulting and gravity spreading. Iriga can serve as a model for other volcanoes, such as Mayon, that stand in sedimentary basins undergoing transtensional strike-slip faulting.

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

2012-11-01

383

Avalanches, branching ratios, and clustering of attractors in random Boolean networks and in the segment polarity network of Drosophila  

NASA Astrophysics Data System (ADS)

We discuss basic features of emergent complexity in dynamical systems far from equilibrium by focusing on the network structure of their state space. We start by measuring the distributions of avalanche and transient times in random Boolean networks (RBNs) and in the Drosophila polarity network by exact enumeration. A transient time is the duration of the transient from a starting state to an attractor. An avalanche is a special transient which starts as a single Boolean element perturbation of an attractor state. Significant differences at short times between the avalanche and the transient times for RBNs with small connectivity K—compared to the number of elements N—indicate that attractors tend to cluster in configuration space. In addition, one bit flip has a non-negligible chance to put an attractor state directly onto another attractor. This clustering is also present in the segment polarity gene network of Drosophila melanogaster, suggesting that this may be a robust feature of biological regulatory networks. We also define and measure a branching ratio for the state space networks and find evidence for a new timescale that diverges roughly linearly with N for 2<=KLtN. Analytic arguments show that this timescale does not appear in the random map nor can the random map exhibit clustering of attractors. We further show that for K=2 the branching ratio exhibits the largest variation with distance from the attractor compared to other values of K and that the avalanche durations exhibit no characteristic scale within our statistical resolution. Hence, we propose that the branching ratio and the avalanche duration are new indicators for scale-free behavior that may or may not be found simultaneously with other indicators of emergent complexity in extended, deterministic dynamical systems.

Berdahl, Andrew; Shreim, Amer; Sood, Vishal; Davidsen, Jörn; Paczuski, Maya

2008-06-01

384

A Single-Photon Avalanche Diode Array for Fluorescence Lifetime Imaging Microscopy  

PubMed Central

We describe the design, characterization, and demonstration of a fully integrated single-photon avalanche diode (SPAD) imager for use in time-resolved fluorescence imaging. The imager consists of a 64-by-64 array of active SPAD pixels and an on-chip time-to-digital converter (TDC) based on a delay-locked loop (DLL) and calibrated interpolators. The imager can perform both standard time-correlated single-photon counting (TCSPC) and an alternative gated-window detection useful for avoiding pulse pile-up when measuring bright signal levels. To illustrate the use of the imager, we present measurements of the decay lifetimes of fluorescent dyes of several types with a timing resolution of 350 ps. PMID:23976789

Schwartz, David Eric; Charbon, Edoardo; Shepard, Kenneth L.

2013-01-01

385

Two-dimensional photo-mapping on CMOS single-photon avalanche diodes.  

PubMed

Two-dimensional (2-D) photo-count mapping on CMOS single photon avalanche diodes (SPADs) has been demonstrated. Together with the varied incident wavelengths, the depth-dependent electric field distribution in active region has been investigated on two SPADs with different structures. Clear but different non-uniformity of photo-response have been observed for the two studied devices. With the help of simulation tool, the non-uniform photo-counts arising from the electric field non-uniformity have been well explained. As the quasi-3D distribution of electric field in the active region can be mapped, our method is useful for engineering the device structure to improve the photo-response of SPADs. PMID:24977896

Wu, Jau-Yang; Lu, Ping-Keng; Lin, Sheng-Di

2014-06-30

386

Stochastic Orbit Loss of Neutral Beam Ions From NSTX Due to Toroidal Alfven Eigenmode Avalanches  

SciTech Connect

Short toroidal Alfven eigenmode (TAE) avalanche bursts in the National Spherical Torus Experiment (NSTX) cause a drop in the neutron rate and sometimes a loss of neutral beam ions at or near the full injection energy over an extended range of pitch angles. The simultaneous loss of wide ranges of pitch angle suggests stochastic transport of the beam ions occurs. When beam ion orbits are followed with a guiding center code that incorporates plasma's magnetic equilibrium plus the measured modes, the predicted ranges of lost pitch angle are similar to those seen in the experiment, with distinct populations of trapped and passing orbits lost. These correspond to domains where the stochasticity extends in the orbit phase space from the region of beam ion deposition to the loss boundary.

Darrow, D S; Fredrickson, E D; Gorelenkov, N N; Gorelenkova, M; Kubota, S; Medley, S S; Podesta, M; Shi, L

2012-07-11

387

Stochastic orbit loss of neutral beam ions from NSTX due to toroidal Alfvén eigenmode avalanches  

NASA Astrophysics Data System (ADS)

Short toroidal Alfvén eigenmode (TAE) avalanche bursts in the National Spherical Torus Experiment (NSTX) cause a drop in the neutron rate and sometimes a loss of neutral beam ions at or near the full injection energy over an extended range of pitch angles. The simultaneous loss of wide ranges of pitch angle suggests stochastic transport of the beam ions occurs. When beam ion orbits are followed with a guiding centre code that incorporates the plasma's magnetic equilibrium plus the measured modes, the predicted ranges of lost pitch angle are similar to those seen in the experiment, with distinct populations of trapped and passing orbits lost. These correspond to domains where the stochasticity extends in the orbit phase space from the region of beam ion deposition to the loss boundary and the trajectories along which modes may transport particles extend from the deposition volume to the loss boundary.

Darrow, D. S.; Crocker, N.; Fredrickson, E. D.; Gorelenkov, N. N.; Gorelenkova, M.; Kubota, S.; Medley, S. S.; Podestà, M.; Shi, L.; White, R. B.

2013-01-01

388

The blocking probability of Geiger-mode avalanche photo-diodes  

NASA Astrophysics Data System (ADS)

When a photon is detected by a Geiger-mode avalanche photo-diode (GMAPD), the detector is rendered inactive, or blocked, for a certain period of time. In this paper we derive the blocking probability for a GMAPD whose input is either an unmodulated, Bernoulli modulated or pulse-position-modulated (PPM) Poisson process. We demonstrate how the PPM and Bernoulli cases differ, illustrating that the PPM blocking probability is larger than the Bernoulli. The blocking rates may be decreased by focusing the incident light on an array of detectors. We show that the binomial output statistics of an array of GMAPDs may be modeled as Poisson and measure the error in this approximation via the relative entropies of the two distributions.

Moision, Bruce; Srinivasan, Meera; Hamkins, Jon

2005-08-01

389

Detection performance improvement of chirped amplitude modulation ladar based on Gieger-mode avalanche photoelectric detector.  

PubMed

This paper presents an improved system structure of photon-counting chirped amplitude modulation (AM) ladar based on the Geiger-mode avalanche photoelectric detector (GmAPD). The error-pulse probability is investigated with statistical method. The research shows that most of the error pulses that are triggered by noise are distributed in the intensity troughs of the chirped AM waveform. The error-pulse probability is lowered with the sliding window and the threshold. With the average intensity of noise and signal being 0.3 count/sample and 1 count/sample, respectively, the probability of error pulses is reduced from 12% to 1.0%, and the SNR is improved by 2.2 dB in the improved system. PMID:22193131

Zhang, Zijing; Wu, Long; Zhang, Yu; Zhao, Yuan; Sun, Xiudong

2011-12-10

390

Cramer-Rao lower bound on range error for LADARs with Geiger-mode avalanche photodiodes.  

PubMed

The Cramer-Rao lower bound (CRLB) on range error is calculated for laser detection and ranging (LADAR) systems using Geiger-mode avalanche photodiodes (GMAPDs) to detect reflected laser pulses. For the cases considered, the GMAPD range error CRLB is greater than the CRLB for a photon-counting device. It is also shown that the GMAPD range error CRLB is minimized when the mean energy in the received laser pulse is finite. Given typical LADAR system parameters, a Gaussian-envelope received pulse, and a noise detection rate of less than 4 MHz, the GMAPD range error CRLB is minimized when the quantum efficiency times the mean number of received laser pulse photons is between 2.2 and 2.3. PMID:20733630

Johnson, Steven E

2010-08-20

391

Avoiding sensor blindness in Geiger mode avalanche photodiode arrays fabricated in a conventional CMOS process  

NASA Astrophysics Data System (ADS)

The need to move forward in the knowledge of the subatomic world has stimulated the development of new particle colliders. However, the objectives of the next generation of colliders sets unprecedented challenges to the detector performance. The purpose of this contribution is to present a bidimensional array based on avalanche photodiodes operated in the Geiger mode to track high energy particles in future linear colliders. The bidimensional array can function in a gated mode to reduce the probability to detect noise counts interfering with real events. Low reverse overvoltages are used to lessen the dark count rate. Experimental results demonstrate that the prototype fabricated with a standard HV-CMOS process presents an increased efficiency and avoids sensor blindness by applying the proposed techniques.

Vilella, E.; Diéguez, A.

2011-12-01

392

Optimization of MOCVD-diffused p-InP for planar avalanche photodiodes  

NASA Astrophysics Data System (ADS)

We investigate the materials properties and dark currents of planar InP/InGaAs avalanche photodiodes (APDs) in which the p-dopant, Zn, is introduced by diffusion in an MOCVD reactor using dimethylzinc (DMZn) as the source. APD dark currents are compared with low-temperature photoluminescence (PL), electrochemical capacitance-voltage (ECV) and secondary ion mass spectroscopy (SIMS) measurements of layers diffused under the same set of conditions. Device dark currents exhibit both surface-related and bulk contributions, with the bulk contribution appearing as a step increase in the current near the punch-through voltage. The bulk dark current contribution depends on the diffusion process parameters and is correlated with the total Zn incorporation and the intensities of the InP and InGaAs PL peaks. A variation of three orders of magnitude is observed in the bulk dark current contribution as diffusion conditions are varied.

Pitts, O. J.; Hisko, M.; Benyon, W.; Raymond, S.; SpringThorpe, A. J.

2014-05-01

393

Application of PN and avalanche silicon photodiodes to low-level optical  

NASA Technical Reports Server (NTRS)

New approaches to the discovery of other planetary systems require very sensitive and stable detection techniques in order to succeed. Two methods in particular, the astrometric and the photometric methods, require this. To begin understanding the problems and limitations of solid state detectors regarding this application, preliminary experiments were performed at the National Bureau of Standards and a low light level detector characterization facility was built. This facility is briefly described, and the results of tests conducted in it are outlined. A breadboard photometer that was used to obtain stellar brightness ratio precision data is described. The design principles of PN and avalanche silicon photodiodes based on low light level measuring circuits are discussed.

Eppeldauer, G.; Schaefer, A. R.

1988-01-01

394

Predictions of silicon avalanche photodiode detector performance in water vapor differential absorption lidar  

NASA Technical Reports Server (NTRS)

Performance analyses are presented which establish that over most of the range of signals expected for a down-looking differential absorption lidar (DIAL) operated at 16 km the silicon avalanche photodiode (APD) is the preferred detector for DIAL measurements of atmospheric water vapor in the 730 nm spectral region. The higher quantum efficiency of the APD's, (0.8-0.9) compared to a photomultiplier's (0.04-0.18) more than offsets the higher noise of an APD receiver. In addition to offering lower noise and hence lower random error the APD's excellent linearity and impulse recovery minimize DIAL systematic errors attributable to the detector. Estimates of the effect of detector system parameters on overall random and systematic DIAL errors are presented, and performance predictions are supported by laboratory characterization data for an APD receiver system.

Kenimer, R. L.

1988-01-01

395

Avalanches, hardening and softening in dense cross-linked actin networks  

NASA Astrophysics Data System (ADS)

Actin filament networks enable the cytoskeleton to adjust to internal and external forcing. These active networks can adapt to changes by dynamically adjusting their crosslinks. Here, we study actin filaments as elastic fibers having finite dimensions. We employ a full three-dimensional model to study the elastic properties of actin networks by computer simulations. We model a dense actin network with the crosslinks being approximately 1?m apart. The results show that dense actin networks, without any pre-straining, are characterized by (a) strain hardening without entropic elasticity, (b) 'viscotic' hysteresis in the case of strong crosslinks, (c) avalanches of crosslink slippage leading to strain softening in the case of breakable crosslinks, and (d) spontaneous formation of stress fibers in the case of active crosslink formation and destruction. We will discuss the relation to recent experimental observations.

Astrom, Jan; Kumar, Sunil; Vattulainen, Ilpo; Karttunen, Mikko

2008-03-01

396

Moisture proof columnar Cesium Iodide (CsI) layers for gas avalanche microdetectors  

SciTech Connect

Cesium iodide columnar layers having a diameter of 3 {micro}m, and wall spacing of {approx} 1 {micro}m act as secondary electron emitters and can be used for detection of radiation: charged particles, X-rays and gamma rays. With a large enough electric field across the columnar layers, {approx} 400 {micro}m in thickness, gas avalanche gain is evident when placed in a suitable gas, such as P10 or argon-ethane mixtures. The cesium iodide columns are damaged by ambient moisture. This damage can be prevented by evaporating protective layers of insoluble, low boiling point inorganic materials, such as mercuric iodide. Columnar layers with 20 nm coatings of mercuric iodide yield more than 30,000 electrons on average when traversed by electrons from a {sup 90}Sr beta source.

Park, I.J.; Cho, H.S.; Hong, W.S.; Perez-Mendez, V.; Kadyk, J.

1999-05-05

397

IONIZATION IN ATMOSPHERES OF BROWN DWARFS AND EXTRASOLAR PLANETS. I. THE ROLE OF ELECTRON AVALANCHE  

SciTech Connect

Brown dwarf and extrasolar planet atmospheres form clouds which strongly influence the local chemistry and physics. These clouds are globally neutral obeying dust-gas charge equilibrium which is, on short timescales, inconsistent with the observation of stochastic ionization events of the solar system planets. We argue that a significant volume of the clouds in brown dwarfs and extrasolar planets is susceptible to local discharge events. These are electron avalanches triggered by charged dust grains. Such intra-cloud discharges occur on timescales shorter than the time needed to neutralize the dust grains by collisional processes. An ensemble of discharges is likely to produce enough free charges to suggest a partial and stochastic coupling of the atmosphere to a large-scale magnetic field.

Helling, Ch.; Jardine, M. [SUPA, School of Physics and Astronomy, University of St. Andrews, North Haugh, St. Andrews, KY16 9SS (United Kingdom); Witte, S. [Hamburger Sternwarte, Gojenbergsweg 112, 21029 Hamburg (Germany); Diver, D. A., E-mail: ch80@st-andrews.ac.uk [School of Physics and Astronomy, University of Glasgow, Glasgow G12 8QQ (United Kingdom)

2011-01-20

398

Practical fast gate rate InGaAs/InP single-photon avalanche photodiodes  

E-print Network

We present a practical and easy-to-implement method for high-speed near infrared single-photon detection based on InGaAs/InP single-photon avalanche photodiodes (SPADs), combining aspects of both sine gating and self-differencing techniques. At a gating frequency of 921 MHz and temperature of -30 $^{\\circ}$C we achieve: a detection efficiency of 9.3 %, a dark count probability of 2.8$\\times10^{-6}$ ns$^{-1}$, while the afterpulse probability is 1.6$\\times10^{-4}$ ns$^{-1}$, with a 10 ns "count-off time" setting. In principle, the maximum count rate of the SPAD can approach 100 MHz, which can significantly improve the performance for diverse applications.

Jun Zhang; Rob Thew; Claudio Barreiro; Hugo Zbinden

2009-08-16

399

A new non linear mechanism able to generate avalanches based on soil mechanics  

E-print Network

We propose a general mechanism based on soil mechanics concepts, such as dilatancy and friction, to explain the fact that avalanches stop at an angle smaller than they start: the mechanism involved is linked to the fact that the stress field near the free surface of a pile built with inclined strata obeys always the plasticity criteria, even when the slope is smaller than the friction angle. It results from this that the larger the slope angle the smaller the mean stress and the smaller the maximum principal stress. So when the pile rotates to generate the next instability the granular material is submitted to a decrease of the mean stress, resulting in an increase of its yielding angle, which becomes larger than the friction angle. The slope starts then flowing at an angle larger than the friction angle.

P. Evesque

2005-07-04

400

Identification of Criticality in Neuronal Avalanches: II. A Theoretical and Empirical Investigation of the Driven Case.  

PubMed

The observation of apparent power laws in neuronal systems has led to the suggestion that the brain is at, or close to, a critical state and may be a self-organised critical system. Within the framework of self-organised criticality a separation of timescales is thought to be crucial for the observation of power-law dynamics and computational models are often constructed with this property. However, this is not necessarily a characteristic of physiological neural networks-external input does not only occur when the network is at rest/a steady state. In this paper we study a simple neuronal network model driven by a continuous external input (i.e. the model does not have an explicit separation of timescales from seeding the system only when in the quiescent state) and analytically tuned to operate in the region of a critical state (it reaches the critical regime exactly in the absence of input-the case studied in the companion paper to this article). The system displays avalanche dynamics in the form of cascades of neuronal firing separated by periods of silence. We observe partial scale-free behaviour in the distribution of avalanche size for low levels of external input. We analytically derive the distributions of waiting times and investigate their temporal behaviour in relation to different levels of external input, showing that the system's dynamics can exhibit partial long-range temporal correlations. We further show that as the system approaches the critical state by two alternative 'routes', different markers of criticality (partial scale-free behaviour and long-range temporal correlations) are displayed. This suggests that signatures of criticality exhibited by a particular system in close proximity to a critical state are dependent on the region in parameter space at which the system (currently) resides. PMID:24872924

Hartley, Caroline; Taylor, Timothy J; Kiss, Istvan Z; Farmer, Simon F; Berthouze, Luc

2014-01-01

401

Scintillating fibers readout by Single Photon Avalanche Diodes (SPAD) for space applications  

NASA Astrophysics Data System (ADS)

We present the design and performances of a radiation detector based on plastic scintillating fibers with doubleside readout by means of large-area Single Photon Avalanche Diodes (SPAD). This can be the basic step toward the realization of a large-area, cost-effective position sensitive detector to be employed in future space gammaray observatories. SPADs are silicon devices operated above the junction breakdown voltage (with the typical overvoltage of 5V), for which a single photon interacting in the active region is sufficient to trigger a selfsustainable avalanche discharge. SPADs can thus be used for the detection of very low light levels with a fast time response around 50ps FWHM for single photon detection, without spectroscopic capabilities. Large-area SPAD (500 ?m in diameter) have been designed and fabricated at the CNR-IMM facility, with an intrinsic noise lower than 10kHz at -15°C, and are optically coupled to both ends of 3-meter long scintillating fibers, with the same diameter. Double-side readout is required to operate the devices in coincidence (10ns coincidence window), in order to reduce the rate of false detections to the level of 1Hz. The detectors have been tested with minimum ionizing particles at CERN PS demonstrating a detection efficiency larger than 90% and a moderate position resolution along the fiber due to the difference in time of arrival between the two photodetectors. Radiation hardness tests on SPADs have also been carried out, showing that large-area SPADs can be safely employed in low-inclination low Earth orbits.

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

2012-09-01

402

Identification of Criticality in Neuronal Avalanches: II. A Theoretical and Empirical Investigation of the Driven Case  

PubMed Central

The observation of apparent power laws in neuronal systems has led to the suggestion that the brain is at, or close to, a critical state and may be a self-organised critical system. Within the framework of self-organised criticality a separation of timescales is thought to be crucial for the observation of power-law dynamics and computational models are often constructed with this property. However, this is not necessarily a characteristic of physiological neural networks—external input does not only occur when the network is at rest/a steady state. In this paper we study a simple neuronal network model driven by a continuous external input (i.e. the model does not have an explicit separation of timescales from seeding the system only when in the quiescent state) and analytically tuned to operate in the region of a critical state (it reaches the critical regime exactly in the absence of input—the case studied in the companion paper to this article). The system displays avalanche dynamics in the form of cascades of neuronal firing separated by periods of silence. We observe partial scale-free behaviour in the distribution of avalanche size for low levels of external input. We analytically derive the distributions of waiting times and investigate their temporal behaviour in relation to different levels of external input, showing that the system’s dynamics can exhibit partial long-range temporal correlations. We further show that as the system approaches the critical state by two alternative ‘routes’, different markers of criticality (partial scale-free behaviour and long-range temporal correlations) are displayed. This suggests that signatures of criticality exhibited by a particular system in close proximity to a critical state are dependent on the region in parameter space at which the system (currently) resides. PMID:24872924

2014-01-01

403

arXiv:0803.1142v1[cond-mat.dis-nn]7Mar2008 Statistics of static avalanches in a random pinning landscape  

E-print Network

to the Burgers equation and to dynamic avalanches are discussed. In numerous systems, the equilibrium or non] the optimal energy and u(x; w) the optimal interface position. The force per unit volume exerted by the spring

Wiese, Kay Jörg

404

Indirect flat-panel detector with avalanche gain: Fundamental feasibility investigation for SHARP-AMFPI (scintillator HARP active matrix flat panel imager)  

SciTech Connect

An indirect flat-panel imager (FPI) with avalanche gain is being investigated for low-dose x-ray imaging. It is made by optically coupling a structured x-ray scintillator CsI(Tl) to an amorphous selenium (a-Se) avalanche photoconductor called HARP (high-gain avalanche rushing photoconductor). The final electronic image is read out using an active matrix array of thin film transistors (TFT). We call the proposed detector SHARP-AMFPI (scintillator HARP active matrix flat panel imager). The advantage of the SHARP-AMFPI is its programmable gain, which can be turned on during low dose fluoroscopy to overcome electronic noise, and turned off during high dose radiography to avoid pixel saturation. The purpose of this paper is to investigate the important design considerations for SHARP-AMFPI such as avalanche gain, which depends on both the thickness d{sub Se} and the applied electric field E{sub Se} of the HARP layer. To determine the optimal design parameter and operational conditions for HARP, we measured the E{sub Se} dependence of both avalanche gain and optical quantum efficiency of an 8 {mu}m HARP layer. The results were used in a physical model of HARP as well as a linear cascaded model of the FPI to determine the following x-ray imaging properties in both the avalanche and nonavalanche modes as a function of E{sub Se}: (1) total gain (which is the product of avalanche gain and optical quantum efficiency); (2) linearity; (3) dynamic range; (4) gain nonuniformity resulting from thickness nonuniformity; and (5) effects of direct x-ray interaction in HARP. Our results showed that a HARP layer thickness of 8 {mu}m can provide adequate avalanche gain and sufficient dynamic range for x-ray imaging applications to permit quantum limited operation over the range of exposures needed for radiography and fluoroscopy.

Zhao Wei; Li Dan; Reznik, Alla; Lui, B.J.M.; Hunt, D.C.; Rowlands, J.A.; Ohkawa, Yuji; Tanioka, Kenkichi [Department of Radiology, State University of New York at Stony Brook, L-4, 120 Health Sciences Center Stony Brook, New York 11793-8460 (United States); Imaging Research, Sunnybrook and Women's Health Sciences Center, 2075 Bayview Avenue, Toronto, Ontario, M4N 3M5 (Canada); Advanced Imaging Devices Research Division, Science and Technical Research Laboratories, Japan Broadcasting Corporation, 1-10-11 Kinuta, Setagaya-ku, Tokyo 157-8510 (Japan)

2005-09-15

405

A nineteenth century avalanche episode reconstruction via historic newspapers: from unstructured information to standardized information  

NASA Astrophysics Data System (ADS)

Several climatic risks studies based on the analysis of data recorded in newspapers have been published to date. These studies deal with both general (Moltó, 2000; García y Martí, 2000; Hernández Varela et al., 2003; Olcina, 2005) and specific risks such as landslides (Domínguez et al., 1999; Devoli et al., 2007; Polemio y Petrucci, 2010) seastorms (Yanes y Marzol, 2009) and snowstorms (Olcina y Moltó, 2002) among others. The purpose of this paper is to report on the methodology and results of the study of an extreme historical event happened in the Asturian Massif (Northern Spain) in 1888. Special attention has been paid to methodological aspects and to the difficulties found in the goal of devising a method that would enable the reconstruction of this kind of phenomena on the basis of nivometheorogical conditions, geographical location and socio-economic impact. To a great deal we focused our efforts on designing a logical database structure and a set of tables that would allow us to store and cross the information for statistical analysis. This includes outlier detection in order to ensure the quality of the results. The information sources used in our study have been the issues of the daily newspaper 'El Carbayón' and the weekly newspaper 'El Oriente de Asturias' published in Oviedo and Llanes (Asturias) between the 20th of January and 30th of May 1888. A total of 92 issues have been collected via the hard copy microfilm housed in the Central Library of Asturias. We reviewed 70 reports relating to avalanche events happened in the aforementioned period of time. We grouped the consequences of the events into 3 main categories (personal injuries, material damages and absence of both) and 5 child categories (deaths, wounded, house and attached building damage, livestock injuries, damage to infrastructures and communications). We gathered data about the thickness of snow-cover, the number of consecutive snowstorms and, in order to facilitate a territorial analysis of this episode, we also gathered data about the event locations. The primary difficulties we found were lack of information about some details (dates, geographic locations and frequently inaccurate quantification of damage), fuzzy terms or sentences (such as 'heavy snow', 'we have never seen a snowfall like this', 'huge snowslide', etc.) difficult to turn into crisp data, and difficulties in defining categories and allocating every incident into one of the categories. Many of these problems are limitations inherent to work with an information source whose purpose is to describe events for general public and not to write about them for scientific purposes. Others are due to the nature of the climate phenomenon associated to these events. These difficulties are increased, on the other hand, by the lack of development existing at the time which often resulted in villages being isolated by the storms with the ensuing, delays in communication, transportation, etc. The results of our study show the importance of the 1888 avalanche events, caused by three linked and consecutive snowstorms that took place between the 14th of February 1888 and the 22th of March 1888, creating snow covers with a depth ranging between 5 and 7 meters. Sixty six avalanches were documented, 60 of them causing material damage. The number of dead and wounded reached 37 and 23 respectively. The consequences of the event were felt throughout the Asturian Massif; 14 high- and mid-elevation mountain municipalities, were affected by avalanches, some of which displaced 40.000 m3 of snow. In this research, historical media has turned out to be a particularly valuable source of information for the study of this kind of episodes, because it enables us to understand the scope of events that occurred in the distant past in remote locations whose socio-economic impact cannot be directly inferred from instrumental data. On the other hand, we consider studies like the present one as preliminary steps for avalanche episodes modelling. Indeed, the information gathered with this kind of methods has to b

García, Cristina; Ruíz, Jesús; Gallinar, David; Sánchez de Posada, Covadonga

2014-05-01

406

Integrated snow and avalanche monitoring system for Indian Himalaya using multi-temporal satellite imagery and ancillary data  

NASA Astrophysics Data System (ADS)

The variations in the local climate, environment and altitude as well as fast snow cover build up and rapid changes in snow characteristics with passage of winter are major contributing factors to make snow avalanches as one of the threatening problems in the North West Himalaya. For sustainable development of these mountainous areas, a number of multi-purpose projects are being planned. In recent times, the danger of natural and man-made hazards is increasing and the availability of water is fluctuating; and thus, making the project implementation difficult. To overcome these difficulties to a great extent, an integrated monitoring system is required for short term as well as long term assessment of snowcover variation and avalanche hazard. In order to monitor the spatial extent of snow cover, satellite data can be employed on an operational basis. Spectral settings as well as the temporal and spatial resolution make time series NOAA-AVHHR and MODIS sensor data well suited for operational snow cover monitoring at regional or continental scale; Indian Remote Sensing Satellite (IRS) LISS, WiFS and AWiFS sensor data suitable for studies at larger scale; and microwave data for extraction of snow wetness information.. In the present paper, an attempt is made to study the trends of changes in snow characteristics and related avalanche phenomenon using time series multi-temporal, multi-resolution satellite data with respect to different ranges in Western Himalaya, namely Pir Panjal range, Great Himalaya range, Zanskar range, Ladakh range and Great Karakoram range. The operational processing of these data included geocoding, calibration, terrain normalization, classification, statistical post classification and derivation of snow cover statistics. The calibration and normalization of imageries allowed the application of physically based classification thresholds possible for albedo, brightness temperature and the Normalized Difference Snow Index (NDSI) parameters. Different methods have been used for the analysis of the temporal changes in satellite images. Multi-sensor data fusion techniques have been applied to increase the accuracy of classification, and also for extraction of necessary information about characteristics of snow and avalanches and the ground conditions. The results of the analysis of time series of last two winters are reported. The study confirms that significant changes in snow characteristics and wetness are mainly due to large variations in temperature at these altitudes, which contribute towards avalanche activities in early winter. A definite relationship has been observed between snow wetness, altitude and period of the year with respect to the probability of an avalanche occurrence. Snow wetness is found to be inversely proportional to the altitude, whereas probability of an avalanche is directly proportional to the wetness of snow, lying either over thin grass or boulder-covered ground. The results were verified through extensive field measurements. The emphasis has been laid on establishment of a dense network of Automatic Weather Stations (AWS), Upper Air Stations (UAS) and observatories in entire Himalaya; development of GIS based data bases using satellite imageries and other ancillary data for weather, snow and land cover monitoring. Records of past years will provide base information for realistic estimation of the impact of climatic changes and confidence to predict the weather and avalanches in various regions of Himalaya. Key Words: Integrated Monitoring System, Time series multi-sensor/multi-temporal Satellite Imageries, Multi-sensor Data Fusion, Change Detection, Snow characteristics

Sharma, S. S.; Mani, Sneh; Mathur, P.

407

Integrated snow and avalanche monitoring syatem for Indian Himalaya using multi-temporal satellite imagery and ancillary data  

NASA Astrophysics Data System (ADS)

The variations in the local climate, environment and altitude as well as fast snow cover build up and rapid changes in snow characteristics with passage of winter are major contributing factors to make snow avalanches as one of the threatening problems in the North West Himalaya. For sustainable development of these mountainous areas, a number of multi-purpose projects are being planned. In recent times, the danger of natural and man-made hazards is increasing and the availability of water is fluctuating; and thus, making the project implementation difficult. To overcome these difficulties to a great extent, an integrated monitoring system is required for short term as well as long term assessment of snowcover variation and avalanche hazard. In order to monitor the spatial extent of snow cover, satellite data can be employed on an operational basis. Spectral settings as well as the temporal and spatial resolution make time series NOAA-AVHHR and MODIS sensor data well suited for operational snow cover monitoring at regional or continental scale; Indian Remote Sensing Satellite (IRS) LISS, WiFS and AWiFS sensor data suitable for studies at larger scale; and microwave data for extraction of snow wetness information.. In the present paper, an attempt is made to study the trends of changes in snow characteristics and related avalanche phenomenon using time series multi-temporal, multi-resolution satellite data with respect to different ranges in Western Himalaya, namely Pir Panjal range, Great Himalaya range, Zanskar range, Ladakh range and Great Karakoram range. The operational processing of these data included geocoding, calibration, terrain normalization, classification, statistical post classification and derivation of snow cover statistics. The calibration and normalization of imageries allowed the application of physically based classification thresholds possible for albedo, brightness temperature and the Normalized Difference Snow Index (NDSI) parameters. Different methods have been used for the analysis of the temporal changes in satellite images. Multi-sensor data fusion techniques have been applied to increase the accuracy of classification, and also for extraction of necessary information about characteristics of snow and avalanches and the ground conditions. The results of the analysis of time series of last two winters are reported. The study confirms that significant changes in snow characteristics and wetness are mainly due to large variations in temperature at these altitudes, which contribute towards avalanche activities in early winter. A definite relationship has been observed between snow wetness, altitude and period of the year with respect to the probability of an avalanche occurrence. Snow wetness is found to be inversely proportional to the altitude, whereas probability of an avalanche is directly proportional to the wetness of snow, lying either over thin grass or boulder-covered ground. The results were verified through extensive field measurements. The emphasis has been laid on establishment of a dense network of Automatic Weather Stations (AWS), Upper Air Stations (UAS) and observatories in entire Himalaya; development of GIS based data bases using satellite imageries and other ancillary data for weather, snow and land cover monitoring. Records of past years will provide base information for realistic estimation of the impact of climatic changes and confidence to predict the weather and avalanches in various regions of Himalaya. Key Words: Integrated Monitoring System, Time series multi-sensor/multi-temporal Satellite Imageries, Multi-sensor Data Fusion, Change Detection, Snow characteristics

Sharma, S. S.; Mani, Sneh; Mathur, P.

408

Measurement of electromagnetic shower position and size with a saturated avalanche tube hodoscope and a fine grained scintillation hodoscope  

NASA Astrophysics Data System (ADS)

A hodoscope has been constructed from 100 ?m diameter wires and brass tubes (1.2 × 0.7 cm 2 cross section) filled with a mixture of argon, ethane and ethyl alcohol. It has been tested in the saturated avalanche mode in an SCG1-C electromagnetic shower detector to determine its properties for the measurement of the position and size of electromagnetic showers. Two of these tube hodoscopes were positioned 3.5 radiation lengths deep in the detector and the profiles of 1-25 GeV electromagnetic showers were measured. Simultaneous measurements were performed using a plane of twenty, 0.5 cm wide scintillation counters positioned immediately behind the gas tube hodoscope. In addition the transition between saturated avalanche and limited streamer modes was observed for the tube hodoscopes.

Rameika, R.; Cox, B.; Jenkins, C. M.; Judd, D. J.; Hale, G.; Mazur, P. O.; Murphy, C. T.; Turkot, F.; Wagoner, D. E.; Conetti, S.; Haire, M.; Lebrun, P.; Leroy, C.; Ryan, T.; Turnbull, L.; Gearhart, R. A.; Shen, C.

1985-05-01

409

Low-voltage-operation avalanche photodiode based on n-gallium oxide/p-crystalline selenium heterojunction  

NASA Astrophysics Data System (ADS)

In this study, we demonstrate the avalanche multiplication phenomenon in a crystalline-selenium (c-Se)-based heterojunction photodiode. The carrier injection from an external electrode, which is considered to be the major factor contributing to dark current at a high electric field, was significantly decreased by employing a thin n-type Ga2O3 layer with a high hole-injection barrier. The fabricated Ga2O3/c-Se diode exhibited extremely high external quantum efficiency of over 100% in the short-wavelength region at a relatively low reverse-bias voltage of ˜20 V. Furthermore, Sn-doping of the Ga2O3 layer increases the carrier concentration; hence, the resulting device has a lower threshold voltage for avalanche multiplication.

Imura, S.; Kikuchi, K.; Miyakawa, K.; Ohtake, H.; Kubota, M.

2014-06-01

410

Inverted-U profile of dopamine-NMDA-mediated spontaneous avalanche recurrence in superficial layers of rat prefrontal cortex.  

PubMed

Prefrontal cortex (PFC) functions, such as working memory, attention selection, and memory retrieval, depend critically on dopamine and NMDA receptor activation by way of an inverted-U-shaped pharmacological profile. Although single neuron responses in the PFC have shown some aspects of this profile, a network dynamic that follows the dopamine-NMDA dependence has not been identified. We studied neuronal network activity in acute medial PFC slices of adult rats by recording local field potentials (LFPs) with microelectrode arrays. Bath application of dopamine or the dopamine D1 agonist SKF38393 [(+/-)-1-phenyl-2,3,4,5-tetrahydro-(1H)-3-benzazepine-7,8-diol hydrochloride] in combination with NMDA induced spontaneous LFPs predominantly in superficial cortex layers. The LFPs at single electrodes were characterized by sharp negative peaks that were clustered in time across electrodes revealing diverse spatiotemporal patterns on the array. The pattern formation required fast GABAergic transmission, coactivation of the dopamine D1 and NMDA receptor, and depended in an inverted-U profile on dopamine. At moderate concentrations of dopamine or the dopamine D1 agonist, the pattern size distribution formed a power law with exponent alpha = -1.5, indicating that patterns are organized in the form of neuronal avalanches, thereby maximizing spatial correlations in the network. At lower or higher concentrations, alpha was more negative than -1.5, indicating reduced spatial correlations. Likewise, at moderate dopamine concentrations, the avalanche rate and recurrence of specific avalanches was maximal with recurrence frequencies after a "power law"-like heavy-tail distribution with a slope of -2.4. We suggest that the dopamine-NMDA-dependent spontaneous recurrence of specific avalanches in superficial cortical layers might facilitate integrative and associative aspects of PFC functions. PMID:16885228

Stewart, Craig V; Plenz, Dietmar

2006-08-01

411

Comparison of 4H-SiC Separate Absorption and Multiplication Region Avalanche Photodiodes Structures for UV Detection  

Microsoft Academic Search

We designed and fabricated silicon carbide (SiC) separate absorption multiplication region avalanche photodiodes (SAM-APDs) for UV detection in harsh environment applications. Two variations of device types were compared. Type I was designed to achieve reach-through (i.e. multiplication, charge, and absorption layers are depleted) prior to reaching high gain while Type II was designed not to achieve reach-through (i.e. only the

Ho-Young Cha; S. Soloviev; G. Dunne; L. Rowland; S. Zelakiewicz; P. Waldrab; P. Sandvik

2006-01-01

412

Large rock avalanches triggered by the M 7.9 Denali Fault, Alaska, earthquake of 3 November 2002  

Microsoft Academic Search

The moment magnitude (M) 7.9 Denali Fault, Alaska, earthquake of 3 November 2002 triggered thousands of landslides, primarily rock falls and rock slides, that ranged in volume from rock falls of a few cubic meters to rock avalanches having volumes as great as 20×106 m3. The pattern of landsliding was unusual: the number and concentration of triggered slides was much

Randall W. Jibson; Edwin L. Harp; William Schulz; David K. Keefer

2006-01-01

413

Reinforced concrete structures loaded by snow avalanches : numerical and experimental approaches.  

NASA Astrophysics Data System (ADS)

Today, due to the extension of occupied areas in mountainous regions, new strategies for risk mitigation have to be developed. In the framework of risk analysis, these latter have to take into account not only the natural hazard description but also the physical vulnerability of the exposed structures. From a civil engineering point of view, the dynamic behavior of column or portico was widely investigated especially in the case of reinforced concrete and steel. However, it is not the case of reinforced concrete walls for which only the in-plan dynamic behavior (shear behavior) has been studied in detail in the field of earthquake engineering. Therefore, the aim of this project is to study the behavior of reinforced concrete civil engineering structures submitted to out-of-plan dynamic loadings coming from snow avalanche interaction. Numerical simulations in 2D or 3D by the finite element method (FEM) are presented. The approach allows solving mechanical problems in dynamic condition involving none linearities (especially none linear materials). Thus, the structure mechanical response can be explored in controlled conditions. First, a reinforced concrete wall with a L-like shape is considered. The structure is supposed to represent a French defense structure dedicated to protect people against snow avalanches. Experimental pushover tests have been performed on a physical model. The experimental tests consisted to apply a uniform distribution of pressure until the total collapse of the wall. A 2D numerical model has been developed to simulate the mechanical response of the structure under quasi-static loading. Numerical simulations have been compared to experimental datas and results gave a better understanding of the failure mode of the wall. Moreover, the influence of several parameters (geometry and the mechanical properties) is also presented. Secondly, punching shear experimental tests have also been carried out. Reinforced concrete slabs simply supported have been considered. A concentrated load is monotonously applied on the center of the slab until its perforation. A 3D numerical model has been developed in order to explore the response of the RC slab. The model is based on multi-layered plate theory. Numerical and experimental results are compared.

Ousset, I.; Bertrand, D.; Brun, M.; Limam, A.; Naaim, M.

2012-04-01

414

An ultra low noise telecom wavelength free running single photon detector using negative feedback avalanche diode  

NASA Astrophysics Data System (ADS)

It is challenging to implement genuine free running single-photon detectors for the 1550 nm wavelength range with simultaneously high detection efficiency (DE), low dark noise, and good time resolution. We report a novel read out system for the signals from a negative feedback avalanche diode (NFAD) [M. A. Itzler, X. Jiang, B. Nyman, and K. Slomkowski, "Quantum sensing and nanophotonic devices VI," Proc. SPIE 7222, 72221K (2009), 10.1117/12.814669; X. Jiang, M. A. Itzler, K. ODonnell, M. Entwistle, and K. Slomkowski, "Advanced photon counting techniques V," Proc. SPIE 8033, 80330K (2011), 10.1117/12.883543; M. A. Itzler, X. Jiang, B. M. Onat, and K. Slomkowski, "Quantum sensing and nanophotonic devices VII," Proc. SPIE 7608, 760829 (2010), 10.1117/12.843588], which allows useful operation of these devices at a temperature of 193 K and results in very low darkcounts (˜100 counts per second (CPS)), good time jitter (˜30 ps), and good DE (˜10%). We characterized two NFADs with a time-correlation method using photons generated from weak coherent pulses and photon pairs produced by spontaneous parametric down conversion. The inferred detector efficiencies for both types of photon sources agree with each other. The best noise equivalent power of the device is estimated to be 8.1 × 10-18 W Hz-1/2, more than 10 times better than typical InP/InGaAs single photon avalanche diodes (SPADs) show in free running mode. The afterpulsing probability was found to be less than 0.1% per ns at the optimized operating point. In addition, we studied the performance of an entanglement-based quantum key distribution (QKD) using these detectors and develop a model for the quantum bit error rate that incorporates the afterpulsing coefficients. We verified experimentally that using these NFADs it is feasible to implement QKD over 400 km of telecom fiber. Our NFAD photon detector system is very simple, and is well suited for single-photon applications where ultra-low noise and free-running operation is required, and some afterpulsing can be tolerated.

Yan, Zhizhong; Hamel, Deny R.; Heinrichs, Aimee K.; Jiang, Xudong; Itzler, Mark A.; Jennewein, Thomas

2012-07-01

415

An ultra low noise telecom wavelength free running single photon detector using negative feedback avalanche diode.  

PubMed

It is challenging to implement genuine free running single-photon detectors for the 1550 nm wavelength range with simultaneously high detection efficiency (DE), low dark noise, and good time resolution. We report a novel read out system for the signals from a negative feedback avalanche diode (NFAD) [M. A. Itzler, X. Jiang, B. Nyman, and K. Slomkowski, "Quantum sensing and nanophotonic devices VI," Proc. SPIE 7222, 72221K (2009); X. Jiang, M. A. Itzler, K. ODonnell, M. Entwistle, and K. Slomkowski, "Advanced photon counting techniques V," Proc. SPIE 8033, 80330K (2011); M. A. Itzler, X. Jiang, B. M. Onat, and K. Slomkowski, "Quantum sensing and nanophotonic devices VII," Proc. SPIE 7608, 760829 (2010)], which allows useful operation of these devices at a temperature of 193 K and results in very low darkcounts (?100 counts per second (CPS)), good time jitter (?30 ps), and good DE (?10%). We characterized two NFADs with a time-correlation method using photons generated from weak coherent pulses and photon pairs produced by spontaneous parametric down conversion. The inferred detector efficiencies for both types of photon sources agree with each other. The best noise equivalent power of the device is estimated to be 8.1 × 10(-18) W?Hz(-1/2), more than 10 times better than typical InP/InGaAs single photon avalanche diodes (SPADs) show in free running mode. The afterpulsing probability was found to be less than 0.1% per ns at the optimized operating point. In addition, we studied the performance of an entanglement-based quantum key distribution (QKD) using these detectors and develop a model for the quantum bit error rate that incorporates the afterpulsing coefficients. We verified experimentally that using these NFADs it is feasible to implement QKD over 400 km of telecom fiber. Our NFAD photon detector system is very simple, and is well suited for single-photon applications where ultra-low noise and free-running operation is required, and some afterpulsing can be tolerated. PMID:22852669

Yan, Zhizhong; Hamel, Deny R; Heinrichs, Aimee K; Jiang, Xudong; Itzler, Mark A; Jennewein, Thomas

2012-07-01

416

Transmission line pulse system for avalanche characterization of high power semiconductor devices  

NASA Astrophysics Data System (ADS)

Because of the increasing in power density of electronic devices for medium and high power application, reliabilty of these devices is of great interest. Understanding the avalanche behaviour of a power device has become very important in these last years because it gives an indication of the maximum energy ratings which can be seen as an index of the device ruggedness. A good description of this behaviour is given by the static IV blocking characteristc. In order to avoid self heating, very relevant in high power devices, very short pulses of current have to be used, whose value can change from few milliamps up to tens of amps. The most used method to generate short pulses is the TLP (Transmission Line Pulse) test, which is based on charging the equivalent capacitance of a transmission line to high value of voltage and subsequently discharging it onto a load. This circuit let to obtain very short square pulses but it is mostly used for evaluate the ESD capability of semiconductor and, in this environment, it generates pulses of low amplitude which are not high enough to characterize the avalanche behaviour of high power devices . Advanced TLP circuit able to generate high current are usually very expensive and often suffer of distorption of the output pulse. In this article is proposed a simple, low cost circuit, based on a boosted-TLP configuration, which is capable to produce very square pulses of about one hundreds of nanosecond with amplitude up to some tens of amps. A prototype is implemented which can produce pulses up to 20A of amplitude with 200 ns of duration which can characterize power devices up to 1600V of breakdown voltage. Usage of microcontroller based logic make the circuit very flexible. Results of SPICE simulation are provided, together with experimental results. To prove the effectiveness of the circuit, the I-V blocking characteristics of two commercial devices, namely a 600V PowerMOS and a 1200V Trench-IGBT, are measured at different operating temperature.

Riccio, Michele; Ascione, Giovanni; De Falco, Giuseppe; Maresca, Luca; De Laurentis, Martina; Irace, Andrea; Breglio, Giovanni

2013-05-01

417