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Sample records for avalanche quenching

  1. 400-ps time resolution with a passively quenched avalanche photodiode.

    Science.gov (United States)

    Grayson, T P; Wang, L J

    1993-06-01

    Avalanche photodiodes (APD's) operated in a single-photon-counting Geiger mode are becoming attractive alternatives to photomultiplier tubes for low-light-level detection and signal timing. By paying careful attention to the design and construction of a simple APD passive quenching circuit to reduce stray capacitances, we directly measured a time resolution of 410 ps FWHM for a commercial APD. A more detailed data analysis shows the actual time resolution to be ~ 390 ps FWHM. This is believed to be the most accurate time response for such a simple, inexpensive, and widely available device achieved to date. PMID:20829894

  2. Advanced active quenching circuits for single-photon avalanche photodiodes

    Science.gov (United States)

    Stipčević, M.; Christensen, B. G.; Kwiat, P. G.; Gauthier, D. J.

    2016-05-01

    Commercial photon-counting modules, often based on actively quenched solid-state avalanche photodiode sensors, are used in wide variety of applications. Manufacturers characterize their detectors by specifying a small set of parameters, such as detection efficiency, dead time, dark counts rate, afterpulsing probability and single photon arrival time resolution (jitter), however they usually do not specify the conditions under which these parameters are constant or present a sufficient description. In this work, we present an in-depth analysis of the active quenching process and identify intrinsic limitations and engineering challenges. Based on that, we investigate the range of validity of the typical parameters used by two commercial detectors. We identify an additional set of imperfections that must be specified in order to sufficiently characterize the behavior of single-photon counting detectors in realistic applications. The additional imperfections include rate-dependence of the dead time, jitter, detection delay shift, and "twilighting." Also, the temporal distribution of afterpulsing and various artifacts of the electronics are important. We find that these additional non-ideal behaviors can lead to unexpected effects or strong deterioration of the system's performance. Specifically, we discuss implications of these new findings in a few applications in which single-photon detectors play a major role: the security of a quantum cryptographic protocol, the quality of single-photon-based random number generators and a few other applications. Finally, we describe an example of an optimized avalanche quenching circuit for a high-rate quantum key distribution system based on time-bin entangled photons.

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

    International Nuclear Information System (INIS)

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

  4. Active quenching circuit for a InGaAs single-photon avalanche diode

    International Nuclear Information System (INIS)

    We present a novel gated operation active quenching circuit (AQC). In order to simulate the quenching circuit a complete SPICE model of a InGaAs SPAD is set up according to the I–V characteristic measurement results of the detector. The circuit integrated with aROIC (readout integrated circuit) is fabricated in an CSMC 0.5 μm CMOS process and then hybrid packed with the detector. Chip measurement results show that the functionality of the circuit is correct and the performance is suitable for practical system applications. (semiconductor integrated circuits)

  5. SiMPl-An avalanche diode array with bulk integrated quench resistors for single photon detection

    International Nuclear Information System (INIS)

    The so-called silicon photomultipliers (SiPMs, MPPCs, etc.) are already replacing photomultiplier tubes in many applications. Still the reproducibility and the cost requirements are not at the level required for the coverage of many square meters of detector area. Therefore a simple technology is desired which allows a high yield and keeps the detector costs in a reasonable range. In the existing devices the need of high ohmic polysilicon for the quench resistors is one of the most yield and cost driving technological issues. We are proposing a front-side illuminated detector structure with quench resistors integrated into the silicon bulk. In this concept other obstacles for light like metal lines or contacts can be omitted and therefore the fill factor is only limited by the gaps necessary for optical cross-talk suppression. Within the array the entire surface area remains non-structured and can be easily coated with an anti-reflective layer. Compared to existing devices the proposed detector has the potential of higher photon detection efficiency especially in the blue and the UV range, an improved hardness against ionizing radiation and a much simpler processing resulting in a higher production yield and lower costs. The quenching mechanism has been demonstrated in a proof-of-principle production performed in house. The second prototype fabrication on silicon on isolator substrates has been done and allows testing of the device performance. The results from the first measurements are presented.

  6. Single photon detection with self-quenching multiplication

    Science.gov (United States)

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

    2011-01-01

    A photoelectronic device and an avalanche self-quenching process for a photoelectronic device are described. The photoelectronic device comprises a nanoscale semiconductor multiplication region and a nanoscale doped semiconductor quenching structure including a depletion region and an undepletion region. The photoelectronic device can act as a single photon detector or a single carrier multiplier. The avalanche self-quenching process allows electrical field reduction in the multiplication region by movement of the multiplication carriers, thus quenching the avalanche.

  7. Nano-multiplication region avalanche photodiodes and arrays

    Science.gov (United States)

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

    2011-01-01

    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.

  8. Discharge quenching circuit for counters

    International Nuclear Information System (INIS)

    A circuit for quenching discharges in gas-discharge detectors with working voltage of 3-5 kV based on transistors operating in the avalanche mode is described. The quenching circuit consists of a coordinating emitter follower, amplifier-shaper for avalanche key cascade control which changes potential on the counter electrodes and a shaper of discharge quenching duration. The emitter follower is assembled according to a widely used flowsheet with two transistors. The circuit permits to obtain a rectangular quenching pulse with front of 100 ns and an amplitude of up to 3.2 kV at duration of 500 μm-8 ms. Application of the quenching circuit described permits to obtain countering characteristics with the slope less than or equal to 0.02%/V and plateau extent greater than or equal to 300 V

  9. Gallium-based avalanche photodiode optical crosstalk

    Science.gov (United States)

    Blazej, Josef; Prochazka, Ivan; Hamal, Karel; Sopko, Bruno; Chren, Dominik

    2006-11-01

    Solid-state single photon detectors based on avalanche photodiode are getting more attention in various areas of applied physics: optical sensors, quantum key distribution, optical ranging and Lidar, time-resolved spectroscopy, X-ray laser diagnostics, and turbid media imaging. Avalanche photodiodes specifically designed for single photon counting semiconductor avalanche structures have been developed on the basis of various materials: Si, Ge, GaP, GaAsP, and InGaP/InGaAs at the Czech Technical University in Prague during the last 20 years. They have been tailored for numerous applications. Trends in demand are focused on detection array construction recently. Even extremely small arrays containing a few cells are of great importance for users. Electrical crosstalk between individual gating and quenching circuits and optical crosstalk between individual detecting cells are serious limitation for array design and performance. Optical crosstalk is caused by the parasitic light emission of the avalanche which accompanies the photon detection process. We have studied in detail the optical emission of the avalanche photon counting structure in the silicon- and gallium-based photodiodes. The timing properties and spectral distribution of the emitted light have been measured for different operating conditions to quantify optical crosstalk. We conclude that optical crosstalk is an inherent property of avalanche photodiode operated in Geiger mode. The only way to minimize optical crosstalk in avalanche photodiode array is to build active quenching circuit with minimum response time.

  10. Negative feedback avalanche diode

    Science.gov (United States)

    Itzler, Mark Allen (Inventor)

    2010-01-01

    A single-photon avalanche detector is disclosed that is operable at wavelengths greater than 1000 nm and at operating speeds greater than 10 MHz. The single-photon avalanche detector comprises a thin-film resistor and avalanche photodiode that are monolithically integrated such that little or no additional capacitance is associated with the addition of the resistor.

  11. Quench limits

    International Nuclear Information System (INIS)

    With thirteen beam induced quenches and numerous Machine Development tests, the current knowledge of LHC magnets quench limits still contains a lot of unknowns. Various approaches to determine the quench limits are reviewed and results of the tests are presented. Attempt to reconstruct a coherent picture emerging from these results is taken. The available methods of computation of the quench levels are presented together with dedicated particle shower simulations which are necessary to understand the tests. The future experiments, needed to reach better understanding of quench limits as well as limits for the machine operation are investigated. The possible strategies to set BLM (Beam Loss Monitor) thresholds are discussed. (author)

  12. Test of micropixel avalanche photodiodes

    International Nuclear Information System (INIS)

    The micropixel avalanche photodiode (MAPD) is a novel photodetector with a multipixel intrinsic structure on the common silicon substrate. The typical size of each pixel is 20-30 μm and the density is about 103 mm-2. Each pixel works on the common load in the Geiger mode, where the discharge is limited by an individual quenching resistor (negative feedback like in the gas Geiger counter) included in each pixel feeding chain located on the common substrate. In the Geiger mode one can get an amplification factor for a single photoelectron at the level of 106 at room temperature. Measurements of gain, photon detection efficiency, one-photoelectron resolution, noise and dark current for different types of MAPD were performed and compared

  13. Pulse shape of the self quenching streamer counter in the coexistence region

    International Nuclear Information System (INIS)

    The pulse shape of the electrical signal out of the counter operating in the self-quenching streamer (SQS) mode is obtained and the time correlation between the primary avalanche and the SQS avalanche is measured and studied. The results yield more information in the coexistence region about the time jitters in the process of the SQS avalanche than that shown in our last paper. (orig.)

  14. Quenched pinning and collective dislocation dynamics.

    Science.gov (United States)

    Ovaska, Markus; Laurson, Lasse; Alava, Mikko J

    2015-01-01

    Several experiments show that crystalline solids deform in a bursty and intermittent fashion. Power-law distributed strain bursts in compression experiments of micron-sized samples, and acoustic emission energies from larger-scale specimens, are the key signatures of the underlying critical-like collective dislocation dynamics - a phenomenon that has also been seen in discrete dislocation dynamics (DDD) simulations. Here we show, by performing large-scale two-dimensional DDD simulations, that the character of the dislocation avalanche dynamics changes upon addition of sufficiently strong randomly distributed quenched pinning centres, present e.g. in many alloys as immobile solute atoms. For intermediate pinning strength, our results adhere to the scaling picture of depinning transitions, in contrast to pure systems where dislocation jamming dominates the avalanche dynamics. Still stronger disorder quenches the critical behaviour entirely. PMID:26024505

  15. Model of single-electron performance of micropixel avalanche photodiodes

    CERN Document Server

    Sadygov, Z; Akhmedov, G; Akhmedov, F; Khorev, S; Mukhtarov, R; Sadigov, A; Sidelev, A; Titov, A; Zerrouk, F; Zhezher, V

    2014-01-01

    An approximate iterative model of avalanche process in a pixel of micropixel avalanche photodiode initiated by a single photoelectron is presented. The model describes development of the avalanche process in time, taking into account change of electric field within the depleted region caused by internal discharge and external recharge currents. Conclusions obtained as a result of modelling are compared with experimental data. Simulations show that typical durations of the front and rear edges of the discharge current have the same magnitude of less than 50 ps. The front of the external recharge current has the same duration, however duration of the rear edge depends on value of the quenching micro-resistor. It was found that effective capacitance of the pixel calculated as the slope of linear dependence of the pulse charge on bias voltage exceeds its real capacitance by a factor of two.

  16. Time characteristics of a self quenching streamer in the coexistence region

    International Nuclear Information System (INIS)

    Experimental studies on the time correlation between electrical signals in the primary avalanche and optical signals which are emitted in the avalanches of the limited proportional mode and the self quenching streamer (SQS) mode have demonstrated that there exists a weak optical emission which is almost simultaneous with the limited proportional avalanche, that a streamer pulse in the SQS mode has a few nanoseconds delay relative to the primary avalanche, and that the spread of the delay (FWHM) is also a few nanoseconds. ((orig.))

  17. Forest damage and snow avalanche flow regime

    OpenAIRE

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

    2015-01-01

    Snow avalanches break, uproot and overturn trees causing damage to forests. The extent of forest damage provides useful information on avalanche frequency and intensity. However, impact forces depend on avalanche flow regime. In this paper, we define avalanche loading cases representing four different avalanche flow regimes: powder, intermittent, dry and wet. Using a numerical model that simulates both powder and wet snow avalanches, we study documented events with forest ...

  18. Characteristics of avalanche accidents and a overview of avalanche equipment

    Directory of Open Access Journals (Sweden)

    Mateusz Biela

    2015-12-01

    Full Text Available Avalanches are one of the most spectacular phenomena which may occur in the mountains. Unfortunately they are often caused by humans and pose for him a big danger. In the Polish Tatras alone they represent 18% of all causes of death among 1996-2013. One fourth of the people caught by an avalanche dies, and their chances of survival depends on the depth of burial, burial time, the presence of an air pocket and the degree of injuries. The most common cause of death is asphyxiation, the next is injuries and hypothermia is the rarest cause of death. The fate of the buried people depends on their equipment such as avalanche transceiver, ABS backpack and AvaLung, and also from the equipment of the people who are seeking (avalanche probes, avalanche transceiver and shovels, which has been proven in practice and research.

  19. Investigation of avalanche photodiodes

    International Nuclear Information System (INIS)

    Some characteristics and performances of a set of nine Hamamatsu avalanche photodiodes have been investigated. These APDs have equipped a small 3x3 PbWO4 crystal matrix in X3 beam during the summer of 1995. This note summarizes the main results of this work. An electromagnetic calorimeter with a high resolution is necessary to search for the Higgs if it has a mass between 80 and 160 GeV. A PbWO4 crystal option has been chosen by the CMS collaboration to achieve this task. The light is collected and converted into an electric charge by an Avalanche Photodiode (APD) followed by a fast preamplifier. The advantage of the APDs is that they are not sensitive to the strong magnetic field when compared to photomultipliers and they are a small nuclear counter effect when compared to PIN diodes. In this study, we have tested nine low capacitance Hamamatsu APDs (S5345) received in spring, 1995 with an area of 0.2 cm2. We have measured the capacitance and dark current for each APD. The gain measurements have also been done with gamma sources, continuous and pulsed light. The gain sensitivity versus bias and temperature have also been investigated succinctly. (author). 8 refs., 16 figs., 1 tab

  20. Investigation of avalanche photodiodes

    Energy Technology Data Exchange (ETDEWEB)

    Si Mohand, D.; Benhammou, Y.; Depasse, P.; Goyot, M.; Ille, B.; Linard, E.; Martin, F.; Musienko, Y.

    1996-06-01

    Some characteristics and performances of a set of nine Hamamatsu avalanche photodiodes have been investigated. These APDs have equipped a small 3x3 PbWO{sub 4} crystal matrix in X3 beam during the summer of 1995. This note summarizes the main results of this work. An electromagnetic calorimeter with a high resolution is necessary to search for the Higgs if it has a mass between 80 and 160 GeV. A PbWO{sub 4} crystal option has been chosen by the CMS collaboration to achieve this task. The light is collected and converted into an electric charge by an Avalanche Photodiode (APD) followed by a fast preamplifier. The advantage of the APDs is that they are not sensitive to the strong magnetic field when compared to photomultipliers and they are a small nuclear counter effect when compared to PIN diodes. In this study, we have tested nine low capacitance Hamamatsu APDs (S5345) received in spring, 1995 with an area of 0.2 cm{sup 2}. We have measured the capacitance and dark current for each APD. The gain measurements have also been done with gamma sources, continuous and pulsed light. The gain sensitivity versus bias and temperature have also been investigated succinctly. (author). 8 refs., 16 figs., 1 tab.

  1. Imaging findings of avalanche victims

    Energy Technology Data Exchange (ETDEWEB)

    Grosse, Alexandra B.; Grosse, Claudia A.; Anderson, Suzanne [University Hospital of Berne, Inselspital, Department of Diagnostic, Pediatric and Interventional Radiology, Berne (Switzerland); Steinbach, Lynne S. [University of California San Francisco, Department of Radiology, San Francisco, CA (United States); Zimmermann, Heinz [University Hospital of Berne, Inselspital, Department of Trauma and Emergency Medicine, Berne (Switzerland)

    2007-06-15

    Skiing and hiking outside the boundaries remains an attractive wilderness activity despite the danger of avalanches. Avalanches occur on a relatively frequent basis and may be devastating. Musculoskeletal radiologists should be acquainted with these injuries. Fourteen avalanche victims (11 men and 3 women; age range 17-59 years, mean age 37.4 years) were air transported to a high-grade trauma centre over a period of 2 years. Radiographs, CT and MR images were prospectively evaluated by two observers in consensus. Musculoskeletal findings (61%) were more frequent than extraskeletal findings (39%). Fractures were most commonly seen (36.6%), involving the spine (14.6%) more frequently than the extremities (9.8%). Blunt abdominal and thoracic trauma were the most frequent extraskeletal findings. A wide spectrum of injuries can be found in avalanche victims, ranging from extremity fractures to massive polytrauma. Asphyxia remains the main cause of death along with hypoxic brain injury and hypothermia. (orig.)

  2. Neuronal avalanches and coherence potentials

    Science.gov (United States)

    Plenz, D.

    2012-05-01

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

  3. Correcting for accidental correlations in saturated avalanche photodiodes

    CERN Document Server

    Grieve, James A; Tang, Zhongkan; Ling, Alexander

    2015-01-01

    In this paper we present a high-level numerical model for estimating rates of accidental correlations between a pair of passively quenched Geiger mode avalanche photodiodes operating in the saturated regime. By considering the recovery time of both the diodes and the detection circuit we introduce the concept of an "effective duty cycle" and show that it may be estimated by numeric simulation. The impact of effective duty cycle on the observed accidental rate is examined and we demonstrate that the updated model leads to an improved correction factor in actual experiments. This will improve the signal-to-noise ratio in applications depending on correlation measurements.

  4. Ultraviolet avalanche photodiodes

    Science.gov (United States)

    McClintock, Ryan; Razeghi, Manijeh

    2015-08-01

    The III-Nitride material system is rapidly maturing; having proved itself as a material for LEDs and laser, and now finding use in the area of UV photodetectors. However, many UV applications are still dominated by the use of photomultiplier tubes (PMT). PMTs are capable of obtaining very high sensitivity using internal electron multiplication gain (typically ~106). It is highly desirable to develop a compact semiconductor-based photodetector capable of realizing this level of sensitivity. In principle, this can be obtained in III-Nitrides by taking advantage of avalanche multiplication under high electric fields - typically 2.7 MV/cm, which with proper design can correspond to an external reverse bias of less than 100 volts. In this talk, we review the current state-of-the-art in III-Nitride solar- and visible-blind APDs, and present our latest results on GaN APDs grown on both conventional sapphire and low dislocation density free-standing c- and m-plane GaN substrates. Leakage current, gain, and single photon detection efficiency (SPDE) of these APDs were compared. The spectral response and Geiger-mode photon counting performance of UV APDs are studied under low photon fluxes, with single photon detection capabilities as much as 30% being demonstrated in smaller devices. Geiger-mode operation conditions are optimized for enhanced SPDE.

  5. Avalanche effects near nanojunctions

    Science.gov (United States)

    Nandigana, Vishal V. R.; Aluru, N. R.

    2016-07-01

    In this article, we perform a computational investigation of a nanopore connected to external fluidic reservoirs of asymmetric geometries. The asymmetry between the reservoirs is achieved by changing the cross-sectional areas, and the reservoirs are designated as the micropore reservoir and macropore reservoir. When an electric field is applied, which is directed from the macropore towards the micropore reservoir, we observe local nonequilibrium chaotic current oscillations. The current oscillations originate at the micropore-nanopore interface owing to the local cascade of ions; we refer to this phenomenon as the "avalanche effects." We mathematically quantify chaos in terms of the maximum Lyapunov exponent. The maximum Lyapunov exponent exhibits a monotonic increase with the applied voltage and the macropore reservoir diameter. The temporal power spectra maps of the chaotic currents depict a low-frequency "1 /f "-type dynamics for the voltage chaos and "1 /f2 "-type dynamics for the macropore reservoir chaos. The results presented here offer avenues to manipulate ionic diodes and fluidic pumps.

  6. Gas Quenching Small Components

    Institute of Scientific and Technical Information of China (English)

    Paul Stratton

    2004-01-01

    Gas quenching is an environmentally friendly and effective way of quenching components. However it has not been possible to apply it to small components because of the difficulties of jigging. A method of gas quenching such small components is described in which they are levitated in a confined gas stream. The method is suitable for quenching low alloy steel components that weigh between 1 and 10g.

  7. Quenches after LS1

    International Nuclear Information System (INIS)

    In this paper I will give an overview of the different types of quenches that occur in the LHC, followed by an estimate of the number of quenches that we can expect after LS1. Beam-induced quenches and false triggering of the QPS will be the main cause of those quenches that cause a beam dump. Possibly in total up to 10-20 per year. After consolidation of the 13 kA joints, the approach for the BLM settings can be less conservative than in 2010-2012 in order to maximize beam time. This will cause some quenches but, anyhow, a beam.induced quench is not more risky than a quench provoked by false triggering. It is not easy to predict the number of BLM triggered beam dumps, needed to avoid magnet quenches, because it is not sure how to scale beam losses and UFO's from 3.5 TeV to 6.5 TeV, and it is not sure if the thresholds at 3.5 TeV are correct. Quench events will be much more massive (ex: RB quench at 6 kA → 2 MJ, RB quench at 11 kA → 6-20 MJ), and as a result cryo recuperation much longer. There will also be more ramp induced quenches after a FPA in other circuits due to higher ramp rates and smaller temperature margins (mutual coupling)

  8. Study of high speed quenching circuits in photon counting imaging lidar system

    Science.gov (United States)

    Zheng, Xiangyang; Ding, Yuxing; Huang, Genghua; Shu, Rong

    2015-10-01

    Detection theory of single photon avalanche diodes(SPADs),which are applied in photon counting imaging light detection and ranging(LIDAR)system, is analyzed in detail in this paper. Four types of common quenching circuits based on SPADs, namely passive quenching, active quenching, gate-control quenching, and hybrid quenching circuits are studied. Furthermore,operational principle and performance characteristics of each of these four types of quenching circuits are fully discussed. Besides, an improved hybrid quenching circuit prone to be integrated with ASIC technology is brought up. Analysis shows that this new circuit can quench and reset SPADs with high speed, meeting the demands for qualities of quenching circuits in photon counting imaging LIDAR system. Also, results of theoretical study indicate that some performance indexes like response rate, quenching speed and dead time are satisfactory. Above all, this quenching circuit is simpler in structure and its cost is much smaller compared with common quenching circuits known to us in papers published so far. As a result, the prospect of this new circuit is probably good after more efforts are taken to integrate it with photon counting imaging LIDAR.

  9. A Single-Photon Avalanche Diode Imager for Fluorescence Lifetime Applications

    OpenAIRE

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

    2007-01-01

    A 64-by-64-pixel CMOS single-photon avalanche diode (SPAD) imager for time-resolved fluorescence detection features actively quenched and reset pixels, allowing gated detection to eliminate pile-up nonlinearities common to most time-correlated single-photon counting (TCSPC) approaches. Timing information is collected using an on-chip time-to-digital converter (TDC) based on a counter and a supply-regulated delay-locked loop (DLL).

  10. Neuronal avalanches and brain plasticity

    Science.gov (United States)

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

    2007-12-01

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

  11. Supersensitive avalanche silicon drift photodetector

    International Nuclear Information System (INIS)

    Physical principles of performance and main characteristics of a novel avalanche photodetector developed on the basis of MOS (metal-oxide-silicon) technology are presented. The photodetector contains a semitransparent gate electrode and a drain contact to provide a drift of multiplied charge carriers along the semiconductor surface. A high gain (more than 104) of the photocurrent was achieved due to the local negative feedback effect realized on the Si -- SiO2 boundary. Special attention is paid to the possibilities of the development of a supersensitive avalanche CCD (charge-coupled device) for the detection of individual photons in visible and ultraviolet spectral regions. The experimental results obtained with a two-element CCD prototype are discussed. (author)

  12. Avalanches, Scaling and Coherent Noise

    OpenAIRE

    Newman, M. E. J.; Sneppen, Kim

    1996-01-01

    We present a simple model of a dynamical system driven by externally-imposed coherent noise. Although the system never becomes critical in the sense of possessing spatial correlations of arbitrarily long range, it does organize into a stationary state characterized by avalanches with a power-law size distribution. We explain the behavior of the model within a time-averaged approximation, and discuss its potential connection to the dynamics of earthquakes, the Gutenberg-Richter law, and to rec...

  13. Avalanche ecology and large magnitude avalanche events: Glacier National Park, Montana, USA

    Science.gov (United States)

    Fagre, Daniel B.; Peitzsch, Erich H.

    2010-01-01

    Large magnitude snow avalanches play an important role ecologically in terms of wildlife habitat, vegetation diversity, and sediment transport within a watershed. Ecological effects from these infrequent avalanches can last for decades. Understanding the frequency of such large magnitude avalanches is also critical to avalanche forecasting for the Going-to-the-Sun Road (GTSR). In January 2009, a large magnitude avalanche cycle occurred in and around Glacier National Park, Montana. The study site is the Little Granite avalanche path located along the GTSR. The study is designed to quantify change in vegetative cover immediately after a large magnitude event and document ecological response over a multi-year period. GPS field mapping was completed to determine the redefined perimeter of the avalanche path. Vegetation was inventoried using modified U.S. Forest Service Forest Inventory and Analysis plots, cross sections were taken from over 100 dead trees throughout the avalanche path, and an avalanche chronology was developed. Initial results indicate that the perimeter of this path was expanded by 30%. The avalanche travelled approximately 1200 vertical meters and 3 linear kilometers. Stands of large conifers as old as 150 years were decimated by the avalanche, causing a shift in dominant vegetation types in many parts of the avalanche path. Woody debris is a major ground cover up to 3 m in depth on lower portions of the avalanche path and will likely affect tree regrowth. Monitoring and measuring the post-avalanche vegetation recovery of this particular avalanche path provides a unique dataset for determining the ecological role of avalanches in mountain landscapes.

  14. Avalanche Dynamics in Wet Granular Materials

    OpenAIRE

    Tegzes, P.; Vicsek, T.; P. Schiffer

    2002-01-01

    We have studied the dynamics of avalanching wet granular media in a rotating drum apparatus. Quantitative measurements of the flow velocity and the granular flux during avalanches allow us to characterize novel avalanche types unique to wet media. We also explore the details of viscoplastic flow (observed at the highest liquid contents) in which there are lasting contacts during flow, leading to coherence across the entire sample. This coherence leads to a velocity independent flow depth at h...

  15. Free-running InGaAs/InP single photon detector with feedback quenching IC

    International Nuclear Information System (INIS)

    InGaAs/InP avalanche photodiodes (APD) are usually employed as Geiger-mode single photon detector at near-infrared wavelength between 1.0 μm and 1.7 μm. In order to work in the free-running regime rather than gated regime, we demonstrate a feedback quenching integrated circuit to rapidly quench the avalanche and reset the APD. Because this IC is close to the APD, parasitic capacitance is largely reduced, thus reducing the quench-time, reset-time and also the afterpulsing probability. We investigated the free-running single photon detector's afterpulsing effect, de-trapping time, dark count rate and detection efficiency and also compared with gated regime operation. After corrected for deadtime and afterpulse, we found the free-running detector performance is comparable with gated regime

  16. Free-running InGaAs/InP single photon detector with feedback quenching IC

    Energy Technology Data Exchange (ETDEWEB)

    Zheng, Fu; Wang, Feilong [Key Laboratory of Electronics and Information Technology for Space Systems, Center for Space Sciences and Applied Research, Chinese Academy of Sciences, No. 1 Nanertiao, Zhongguancun, Haidian District, Beijing 100190 (China); University of Chinese Academy of Sciences, Beijing 100049 (China); Wang, Chao [Key Laboratory of Electronics and Information Technology for Space Systems, Center for Space Sciences and Applied Research, Chinese Academy of Sciences, No. 1 Nanertiao, Zhongguancun, Haidian District, Beijing 100190 (China); College of Physics, Beijing Institute of Technology, No. 5 Nandajie, Zhongguancun, Haidian District, Beijing 100081 (China); Sun, Zhibin [Key Laboratory of Electronics and Information Technology for Space Systems, Center for Space Sciences and Applied Research, Chinese Academy of Sciences, No. 1 Nanertiao, Zhongguancun, Haidian District, Beijing 100190 (China); Zhai, Guangjie, E-mail: gjzhai@nssc.ac.cn [Key Laboratory of Electronics and Information Technology for Space Systems, Center for Space Sciences and Applied Research, Chinese Academy of Sciences, No. 1 Nanertiao, Zhongguancun, Haidian District, Beijing 100190 (China)

    2015-11-01

    InGaAs/InP avalanche photodiodes (APD) are usually employed as Geiger-mode single photon detector at near-infrared wavelength between 1.0 μm and 1.7 μm. In order to work in the free-running regime rather than gated regime, we demonstrate a feedback quenching integrated circuit to rapidly quench the avalanche and reset the APD. Because this IC is close to the APD, parasitic capacitance is largely reduced, thus reducing the quench-time, reset-time and also the afterpulsing probability. We investigated the free-running single photon detector's afterpulsing effect, de-trapping time, dark count rate and detection efficiency and also compared with gated regime operation. After corrected for deadtime and afterpulse, we found the free-running detector performance is comparable with gated regime.

  17. Time Directed Avalanches in Invasion Models

    International Nuclear Information System (INIS)

    We define forward and backward time-directed avalanches for a broad class of self-organized critical models including invasion percolation, interface depinning, and a simple model of evolution. Although the geometrical properties of the avalanches do not change under time reversal, their stationary state statistical distribution does. The overall distribution of forward avalanches P(s)∼s-2 is superuniversal in this class of models. The power-law exponent π for the distribution of distances between subsequent active sites is derived from the properties of backward avalanches

  18. Silicon Geiger mode avalanche photodiodes

    Institute of Scientific and Technical Information of China (English)

    M. Mazzillo; S. Billotta; G. Bonanno; A. Campisi; L. Cosentino; P. Finocchiaro; F. Musumeci; S.Privitera; S. Tudisco; G. Condorelli; D. Sanfilippo; G. Fallica; E. Sciacca; S. Aurite; S. Lombardo; E. Rlmini; M. Belluso

    2007-01-01

    In this letter we present the results regarding the electrical and optical characterization of Geiger mode silicon avalanche photodiodes (GMAP) fabricated by silicon standard planar technology. Low dark count rates, negligible afterpulsing effects,good timing resolution and high quantum detection efficiency in all the visible range have been measured. The very good electro-optical performances of our photodiodes make them attractive for the fabrication of arrays with a large number of GMAP to be used both in the commercial and the scientific fields, as telecommunications and nuclear medical imaging.

  19. Production networks and failure avalanches

    CERN Document Server

    Weisbuch, G; Weisbuch, Gerard; Battiston, Stefano

    2005-01-01

    Although standard economics textbooks are seldom interested in production networks, modern economies are more and more based upon suppliers/customers interactions. One can consider entire sectors of the economy as generalised supply chains. We will take this view in the present paper and study under which conditions local failures to produce or simply to deliver can result in avalanches of shortage and bankruptcies across the network. We will show that a large class of models exhibit scale free distributions of production and wealth among firms and that metastable regions of high production are highly localised.

  20. 3D avalanche multiplication in Si-Ge lateral avalanche photodiodes

    Science.gov (United States)

    Jamil, Erum; Hayat, Majeed M.; Davids, Paul S.; Camacho, Ryan M.

    2016-05-01

    Si-Ge lateral avalanche photodiodes (Si-Ge LAPDs) are promising devices for single photon detection, but they also have technology challenges. Si-Ge LAPDs are CMOS compatible and capable of detecting photons near the 1550 nm telecommunications bands. However, the Si-Ge LAPD exhibits a unique avalanche multiplication process in silicon, where the electrons and holes follow curved paths in three-dimensional space. Traditional models for the analysis of the avalanche multiplication process assume one-dimensional paths for the carriers that undergo the chains of impact ionizations; therefore, they are not suitable for analyzing the avalanche properties of Si-Ge LAPDs. In this paper, the statistics of the avalanche process in the Si-Ge LAPD are modeled analytically using a method that was recently developed by our group for understanding the avalanche multiplication in nanopillar, core-shell GaAs avalanche photodiodes, for which the electric field is non-uniform in magnitude and direction. Specifically, the calculated mean avalanche gain and the excess noise are presented for the Si-Ge LAPD device. It is also shown that the avalanche characteristics depend upon the specific avalanche path taken by the carrier, which depends, in turn, on the lateral location where each photon is absorbed in the Ge absorber. This property can be exploited to achieve reduced excess noise as well as wavelength-sensitive single-photon detection.

  1. Tevatron quench pressure measurement

    International Nuclear Information System (INIS)

    The upcoming lower temperature/higher energy upgrade to the Fermilab Tevatron accelerator has raised questions concerning peak pressures during magnet system quenches. An experiment was performed to measure the pressure versus time at various quench energies in several devices in the Tevatron. A smaller study also looked at the temperature and mass flow rate versus time. Data was captured in a PC based circular buffer. The buffer captured ten seconds of data at 250 Hz for up to eight channels. Quenches ranging from 400 GeV to 1000 GeV were investigated. Peak pressures of 1.24 MPa (180 psia) were measured at 1000 GeV. Peak pressure increased linearly with quench energy up to 950 GeV, where it flattened off. Likewise, the time to reach peak pressure decreased linearly until 900 GeV, where it flattened off at 280 ms. The process appears to become heat transfer limited at about 900 GeV. This results in reasonable peak quench pressures at the expense of the coil reaching higher peak temperatures (not measured). The existing cryostats and relieving systems in the Tevatron will be sufficient for the new low temperature upgrade

  2. Temporal correlations in neuronal avalanche occurrence

    Science.gov (United States)

    Lombardi, F.; Herrmann, H. J.; Plenz, D.; de Arcangelis, L.

    2016-04-01

    Ongoing cortical activity consists of sequences of synchronized bursts, named neuronal avalanches, whose size and duration are power law distributed. These features have been observed in a variety of systems and conditions, at all spatial scales, supporting scale invariance, universality and therefore criticality. However, the mechanisms leading to burst triggering, as well as the relationship between bursts and quiescence, are still unclear. The analysis of temporal correlations constitutes a major step towards a deeper understanding of burst dynamics. Here, we investigate the relation between avalanche sizes and quiet times, as well as between sizes of consecutive avalanches recorded in cortex slice cultures. We show that quiet times depend on the size of preceding avalanches and, at the same time, influence the size of the following one. Moreover we evidence that sizes of consecutive avalanches are correlated. In particular, we show that an avalanche tends to be larger or smaller than the following one for short or long time separation, respectively. Our analysis represents the first attempt to provide a quantitative estimate of correlations between activity and quiescence in the framework of neuronal avalanches and will help to enlighten the mechanisms underlying spontaneous activity.

  3. Snow variability effect upon avalanching

    Directory of Open Access Journals (Sweden)

    P. A. Chernous

    2015-05-01

    Full Text Available Thickness, density, shearing strength, and temperature of snow on mountain slopes are considered as stochastic fields or processes. Parameters of these fields (processes were estimated in several geographical regions. Errors of snow stability estimation are shown to be depending on the above parameters, quantity of point measurements, and the measurement technique. Errors of different methods of space and time interpretation of measurements of the snow characteristics are discussed. Results of these studies performed on slope of the Khibiny Mountains, the Altai, the Baikal Mountains, and the Caucasus are presented in the article. Monitoring of the snow cover stability on slopes and the avalanche forecasting are the most difficult actions to be carried out in areas with great spatial variability of snow. The Khibiny Mountains are first of all such area among other ones. 

  4. The Quench Action

    Science.gov (United States)

    Caux, Jean-Sébastien

    2016-06-01

    We give a pedagogical introduction to the methodology of the Quench Action, which is an effective representation for the calculation of time-dependent expectation values of physical operators following a generic out-of-equilibrium state preparation protocol (for example a quantum quench). The representation, originally introduced in Caux and Essler (2013 Phys. Rev. Lett. 110 257203), is founded on a mixture of exact data for overlaps together with variational reasonings. It is argued to be quite generally valid and thermodynamically exact for arbitrary times after the quench (from short times all the way up to the steady state), and applicable to a wide class of physically relevant observables. Here, we introduce the method and its language, give an overview of some recent results, suggest a roadmap and offer some perspectives on possible future research directions.

  5. Catastrophic avalanches and methods of their control

    Directory of Open Access Journals (Sweden)

    N. A. Volodicheva

    2014-01-01

    Full Text Available Definition of such phenomenon as “catastrophic avalanche” is presented in this arti-cle. Several situations with releases of catastrophic avalanches in mountains of Caucasus, Alps, and Central Asia are investigated. Materials of snow-avalanche ob-servations performed since 1960s at the Elbrus station of the Lomonosov Moscow State University (Central Caucasus were used for this work. Complex-valued measures of engineering protection demonstrating different efficiencies are consid-ered.

  6. Rare-gas dependence of the self-quenching streamer

    International Nuclear Information System (INIS)

    The self-quenching streamer (SQS) mode is understood these days as one of the basic modes of gas counter operation. In the present work, the SQS transition is clearly observed for Ar-, Kr- and Xe-mixtures with CH4, C2H6, C3H8, isoC4H10 and CO2, and for He- and Ne-mixtures with C2H6, C3H8 and isoC4H10. For He- and Ne-mixtures with CH4 or CO2, the GM discharge is developed instead of the SQS transition. The avalanche size at the transition voltage decreases, in the order of He-, Ne-, Ar-, Kr- and Xe-mixtures, except for He-mixtures with CH4 or CO2. The mechanisms of the SQS transition proposed by Atac et al. and Zhang have disadvantages in explaining all these results. If the photo-ionization is assumed as in Atac's mechanism, energetic photons whose yield is sufficiently large are needed for the SQS transition. The interaction between metastable states of rare gases proposed by Zhang may be energetically capable of producing electrons for the transition; effects of quenching gas in mixtures cannot be explained by this mechanism. Further investigation is necessary for microscopic processes occurring in the avalanche development. More detailed information is required on the atomic reaction cross sections of photo-ionization, radiative recombination, etc. (N.K.)

  7. Quenched effective population size

    CERN Document Server

    Sagitov, Serik; Vatutin, Vladimir

    2010-01-01

    We study the genealogy of a geographically - or otherwise - structured version of the Wright-Fisher population model with fast migration. The new feature is that migration probabilities may change in a random fashion. Applying Takahashi's results on Markov chains with random transition matrices, we establish convergence to the Kingman coalescent, as the population size goes to infinity. This brings a novel formula for the coalescent effective population size (EPS). We call it a quenched EPS to emphasize the key feature of our model - random environment. The quenched EPS is compared with an annealed (mean-field) EPS which describes the case of constant migration probabilities obtained by averaging the random migration probabilities over possible environments.

  8. Quorum quenching enzymes.

    Science.gov (United States)

    Fetzner, Susanne

    2015-05-10

    Bacteria use cell-to-cell communication systems based on chemical signal molecules to coordinate their behavior within the population. These quorum sensing systems are potential targets for antivirulence therapies, because many bacterial pathogens control the expression of virulence factors via quorum sensing networks. Since biofilm maturation is also usually influenced by quorum sensing, quenching these systems may contribute to combat biofouling. One possibility to interfere with quorum sensing is signal inactivation by enzymatic degradation or modification. Such quorum quenching enzymes are wide-spread in the bacterial world and have also been found in eukaryotes. Lactonases and acylases that hydrolyze N-acyl homoserine lactone (AHL) signaling molecules have been investigated most intensively, however, different oxidoreductases active toward AHLs or 2-alkyl-4(1H)-quinolone signals as well as other signal-converting enzymes have been described. Several approaches have been assessed which aim at alleviating virulence, or biofilm formation, by reducing the signal concentration in the bacterial environment. These involve the application or stimulation of signal-degrading bacteria as biocontrol agents in the protection of crop plants against soft-rot disease, the use of signal-degrading bacteria as probiotics in aquaculture, and the immobilization or entrapment of quorum quenching enzymes or bacteria to control biofouling in membrane bioreactors. While most approaches to use quorum quenching as antivirulence strategy are still in the research phase, the growing number of organisms and enzymes known to interfere with quorum sensing opens up new perspectives for the development of innovative antibacterial strategies. PMID:25220028

  9. Universality of abrupt holographic quenches.

    Science.gov (United States)

    Buchel, Alex; Myers, Robert C; van Niekerk, Anton

    2013-11-15

    We make an analytic investigation of rapid quenches of relevant operators in d-dimensional holographic conformal field theories, which admit a dual gravity description. We uncover a universal scaling behavior in the response of the system, which depends only on the conformal dimension of the quenched operator in the vicinity of the ultraviolet fixed point of the theory. Unless the amplitude of the quench is scaled appropriately, the work done on a system during the quench diverges in the limit of abrupt quenches for operators with dimension (d/2)≤Δ

  10. Rock avalanches: significance and progress (Invited)

    Science.gov (United States)

    Davies, T. R.

    2013-12-01

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

  11. Deterministically Driven Avalanche Models of Solar Flares

    CERN Document Server

    Strugarek, Antoine; Joseph, Richard; Pirot, Dorian

    2014-01-01

    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...

  12. Maximal avalanches in the Bak-Sneppen model

    OpenAIRE

    Gillett, Alexis; Meester, Ronald; van der Wal, Peter

    2006-01-01

    We study the durations of the avalanches in the maximal avalanche decomposition of the Bak-Sneppen evolution model. We show that all the avalanches in this maximal decomposition have infinite expectation, but only `barely', in the sense that if we made the appropriate threshold a tiny amount smaller (in a certain sense), then the avalanches would have finite expectation. The first of these results is somewhat surprising, since simulations suggest finite expectations.

  13. Single-Photon Avalanche Diodes (SPAD) in CMOS 0.35 μm technology

    Science.gov (United States)

    Pellion, D.; Jradi, K.; Brochard, N.; Prêle, D.; Ginhac, D.

    2015-07-01

    Some decades ago single photon detection used to be the terrain of photomultiplier tube (PMT), thanks to its characteristics of sensitivity and speed. However, PMT has several disadvantages such as low quantum efficiency, overall dimensions, and cost, making them unsuitable for compact design of integrated systems. So, the past decade has seen a dramatic increase in interest in new integrated single-photon detectors called Single-Photon Avalanche Diodes (SPAD) or Geiger-mode APD. SPAD are working in avalanche mode above the breakdown level. When an incident photon is captured, a very fast avalanche is triggered, generating an easily detectable current pulse. This paper discusses SPAD detectors fabricated in a standard CMOS technology featuring both single-photon sensitivity, and excellent timing resolution, while guaranteeing a high integration. In this work, we investigate the design of SPAD detectors using the AMS 0.35 μm CMOS Opto technology. Indeed, such standard CMOS technology allows producing large surface (few mm2) of single photon sensitive detectors. Moreover, SPAD in CMOS technologies could be associated to electronic readout such as active quenching, digital to analog converter, memories and any specific processing required to build efficient calorimeters1

  14. Criticality and avalanches in neural networks

    International Nuclear Information System (INIS)

    Highlights: • Temporal criticality is used as criticality indicator. • The Mittag–Leffler function is proposed as a proper form of temporal complexity. • The distribution of avalanche size becomes scale free in the supercritical state. • The scale-free distribution of avalanche sizes is an epileptic manifestation. -- Abstract: Experimental work, both in vitro and in vivo, reveals the occurrence of neural avalanches with an inverse power law distribution in size and time duration. These properties are interpreted as an evident manifestation of criticality, thereby suggesting that the brain is an operating near criticality complex system: an attractive theoretical perspective that according to Gerhard Werner may help to shed light on the origin of consciousness. However, a recent experimental observation shows no clear evidence for power-law scaling in awake and sleeping brain of mammals, casting doubts on the assumption that the brain works at criticality. This article rests on a model proposed by our group in earlier publications to generate neural avalanches with the time duration and size distribution matching the experimental results on neural networks. We now refine the analysis of the time distance between consecutive firing bursts and observe the deviation of the corresponding distribution from the Poisson statistics, as the system moves from the non-cooperative to the cooperative regime. In other words, we make the assumption that the genuine signature of criticality may emerge from temporal complexity rather than from the size and time duration of avalanches. We argue that the Mittag–Leffler (ML) exponential function is a satisfactory indicator of temporal complexity, namely of the occurrence of non-Poisson and renewal events. The assumption that the onset of criticality corresponds to the birth of renewal non-Poisson events establishes a neat distinction between the ML function and the power law avalanches generating regime. We find that

  15. Bulk metallic glasses deform via slip avalanches.

    Science.gov (United States)

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

    2014-04-18

    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

  16. Relating rock avalanche morphology to emplacement processes

    Science.gov (United States)

    Dufresne, Anja; Prager, Christoph; Bösmeier, Annette

    2015-04-01

    The morphology, structure and sedimentological characteristics of rock avalanche deposits reflect both internal emplacement processes and external influences, such as runout path characteristics. The latter is mainly predisposed by topography, substrate types, and hydrogeological conditions. Additionally, the geological setting at the source slope controls, e.g. the spatial distribution of accumulated lithologies and hence material property-related changes in morphology, or the maximum clast size and amount of fines of different lithological units. The Holocene Tschirgant rock avalanche (Tyrol, Austria) resulted from failure of an intensely deformed carbonate rock mass on the southeast face of a 2,370-m-high mountain ridge. The initially sliding rock mass rapidly fragmented as it moved towards the floor of the Inn River valley. Part of the 200-250 x 106 m3 (Patzelt 2012) rock avalanche debris collided with and moved around an opposing bedrock ridge and flowed into the Ötz valley, reaching up to 6.3 km from source. Where the Tschirgant rock avalanche spread freely it formed longitudinal ridges aligned along motion direction as well as smaller hummocks. Encountering high topography, it left runup ridges, fallback patterns (i.e. secondary collapse), and compressional morphology (successively elevated, transverse ridges). Further evidence for the mechanical landslide behaviour is given by large volumes of mobilized valley-fill sediments (polymict gravels and sands). These sediments indicate both shearing and compressional faulting within the rock avalanche mass (forming their own morphological units through, e.g. in situ bulldozing or as distinctly different hummocky terrain), but also indicate extension of the spreading landslide mass (i.e. intercalated/injected gravels encountered mainly in morphological depressions between hummocks). Further influences on its morphology are given by the different lithological units. E.g. the transition from massive dolomite

  17. Design of Industrial Quenching Processes

    Institute of Scientific and Technical Information of China (English)

    Nikolai. I. KOBASKO; George .E. TOTTEN

    2004-01-01

    The method of designing industrial processes of quench cooling, in particular, the speed of the conveyor movement with regard to shape and sizes of parts to be quenched, thermal and physical properties of material and cooling capacity of quenchants has been developed. The suggested designing method and databases are the basis for the complete automation of industrial processes of quench cooling, especially for continuous conveyor lines, with the purpose of making high-strength materials. The process is controlled by infrared technique.

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

    Science.gov (United States)

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

    2011-11-01

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

  19. A double grid position sensitive avalanche chamber

    International Nuclear Information System (INIS)

    A double grid position sensitive avalanche chamber (DGAC) has been developed. Its sensitive area is 250 x 200 mm2. The properties of the DGAC were tested in flowing isobutylene gas at a pressure of 360 Pa. The position resolution of 4 mm in both x and y coordinates and the time resolution of 290 ps are obtained for 252Cf fission fragment source

  20. Avalanches in a Bose-Einstein condensate

    OpenAIRE

    Schuster, J; A. Marte; Amtage, S; Sang, B.; Rempe, G.; Beijerinck, HCW Herman

    2001-01-01

    Collisional avalanches are identified to be responsible for an 8-fold increase of the initial loss rate of a large 87-Rb condensate. We show that the collisional opacity of an ultra-cold gas exhibits a critical value. When exceeded, losses due to inelastic collisions are substantially enhanced. Under these circumstances, reaching the hydrodynamic regime in conventional BEC experiments is highly questionable.

  1. Rock avalanches caused by earthquakes: source characteristics.

    Science.gov (United States)

    Keefer, D K

    1984-03-23

    Study of a worldwide sample of historical earthquakes showed that slopes most susceptible to catastrophic rock avalanches were higher than 150 meters and steeper than 25 degrees. The slopes were undercut by fluvial or glacial erosion, were composed of intensely fractured rock, and exhibited at least one other indicator of low strength or potential instability. PMID:17759365

  2. Oscillatory regime of avalanche particle detectors

    International Nuclear Information System (INIS)

    We describe the model of an avalanche high energy particle detector consisting of two pn-junctions, connected through an intrinsic semiconductor with a reverse biased voltage applied. We show that this detector is able to generate the oscillatory response on the single particle passage through the structure. The possibility of oscillations leading to chaotic behaviour is pointed out. (author). 15 refs, 7 figs

  3. Passive Quenching Electronics for Geiger Mode 4H-SiC Avalanche Photodiodes

    Science.gov (United States)

    Liu, Fei; Zhou, Dong; Lu, Hai; Chen, Dun-Jun; Ren, Fang-Fang; Zhang, Rong; Zheng, You-Dou

    2015-12-01

    Not Available Supported by the National Basic Research Program of China under Grant Nos 2011CB301900 and 2011CB922100, and the Priority Academic Program Development of Jiangsu Higher Education Institutions.

  4. Quantum quenches of holographic plasmas

    CERN Document Server

    Buchel, Alex; Myers, Robert C; van Niekerk, Anton

    2013-01-01

    We employ holographic techniques to study quantum quenches at finite temperature, where the quenches involve varying the coupling of the boundary theory to a relevant operator with an arbitrary conformal dimension $2\\leq\\D\\leq4$. The evolution of the system is studied by evaluating the expectation value of the quenched operator and the stress tensor throughout the process. The time dependence of the new coupling is characterized by a fixed timescale and the response of the observables depends on the ratio of the this timescale to the initial temperature. The observables exhibit universal scaling behaviours when the transitions are either fast or slow, i.e. when this ratio is very small or very large. The scaling exponents are smooth functions of the operator dimension. We find that in fast quenches, the relaxation time is set by the thermal timescale regardless of the operator dimension or the precise quenching rate.

  5. A PMT-like high gain avalanche photodiode based on GaN/AlN periodical stacked structure

    CERN Document Server

    Zheng, Ji-yuan; Yang, Di; Yu, Jia-dong; Meng, Xiao; E, Yan-xiong; Wu, Chao; Hao, Zhi-biao; Sun, Chang-zheng; Xiong, Bing; Luo, Yi; Han, Yan-jian; Wang, Jian; Li, Hong-tao; Brault, Julien; Matta, Samuel; Khalfioui, Mohamed Al; Yan, Jian-chang; Wei, Tong-bo; Zhang, Yun; Wang, Jun-xi

    2016-01-01

    Avalanche photodiode (APD) has been intensively investigated as a promising candidate to replace photomultiplier tubes (PMT) for weak light detection. However, in conventional APDs, a large portion of carrier energy drawn from the electric field is thermalized, and the multiplication efficiencies of electron and hole are low and close. In order to achieve high gain, the device should work under breakdown bias, where carrier multiplication proceeds bi-directionally to form a positive feedback multiplication circle. However, breakdown is hard to control, in practice, APDs should work under Geiger mode as a compromise between sustainable detection and high gain. The complexity of system seriously restricts the application. Here, we demonstrate an avalanche photodiode holding high gain without breakdown, which means no quenching circuit is needed for sustainable detection. The device is based on a GaN/AlN periodically-stacked-structure (PSS), wherein electron holds much higher efficiency than hole to draw energy ...

  6. Modelling the evolution of temperature in avalanche flow

    Science.gov (United States)

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

    2013-04-01

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

  7. Hierarchical networks, power laws, and neuronal avalanches.

    Science.gov (United States)

    Friedman, Eric J; Landsberg, Adam S

    2013-03-01

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

  8. Avalanche dynamics of radio pulsar glitches

    CERN Document Server

    Melatos, A; Wyithe, J S B

    2007-01-01

    We test statistically the hypothesis that radio pulsar glitches result from an avalanche process, in which angular momentum is transferred erratically from the flywheel-like superfluid in the star to the slowly decelerating, solid crust via spatially connected chains of local, impulsive, threshold-activated events, so that the system fluctuates around a self-organised critical state. Analysis of the glitch population (currently 285 events from 101 pulsars) demonstrates that the size distribution in individual pulsars is consistent with being scale invariant, as expected for an avalanche process. The waiting-time distribution is consistent with being exponential in seven out of nine pulsars where it can be measured reliably, after adjusting for observational limits on the minimum waiting time, as for a constant-rate Poisson process. PSR J0537$-$6910 and PSR J0835$-$4510 are the exceptions; their waiting-time distributions show evidence of quasiperiodicity. In each object, stationarity requires that the rate $\\...

  9. Snow Avalanche Release, Scale Invariance and Criticallity

    Science.gov (United States)

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

    It is widely recognised that a number of geophysical phenomena as volcanic eruptions, landslides, etc, obey the so-called Gutenberg-Richter relation, first established for the frequency-magnitude statistics of earthquakes, where is the occurence frequency of earthquakes with a magnitude greater than m. This power law behaviour, character- istic of critical phenomena, is usually evidenced in the form of a linear distribution in a double logarithmic plot, in a way similar to the self organised criticality of a sand pile (2). We have shown very recently and for the first time that snow avalanche release exhibited such a behaviour (3). The only reliable parameter we had at that time was the amplitude of the acoustic emission associated with the avalanche release. Since it was not possible to record several events in the same gully, data were taken in sev- eral gullys of the same mountain range. Yet, the data aligned quite well on a unique straight line, with a critical exponent of about 1.6. This observation suggests that the very nature of the release mechanism is independent of the average slope and mor- phology of the gully. In order to understand the origin of this critical behaviour and to further investigate the mechanisms responsible for avalanche release, the avalanche release is studied in the present paper both by discrete elements simulations and cel- lular automata, and compared to further field data. The discrete elements simulations deal with a population of spheres on a slope, experiencing both a gravitational stress, interactions with the substrate, and mutual contact interactions. A gradual increase of the slope or a gradual change in contact forces (accounting for thermal snow mi- crostructure evolution) eventually result in avalanche release. The conditions are ad- justed until the frequency-magnitude of avalanches exhibit a critical behaviour. The cellular automaton is more or less similar to a game of life: a 2-d grid of boxes repre- sents the

  10. Communicators' perspective on snow avalanche risk communication

    Science.gov (United States)

    Charriere, M. K. M.; Bogaard, T.; Mostert, E.

    2014-12-01

    Among all the natural hazards, snow avalanches are the only ones for which a public danger scale is globally used. It consists of 5 levels of danger displayed with a given number and colour and for each of them, behavioural advices are provided. Even though this is standardized in most of the countries affected by this natural hazard, the tools (usually websites or smartphone applications) with which the information is disseminated to the general pubic differs, particularly in terms of target audience and level of details. This study aims at gathering the perspectives of several communicators that are responsible for these communication practices. The survey was created to assess how and why choices were made in the design process of the communication tools and to determine how their effectiveness is evaluated. Along with a review of existing avalanche risk communication tools, this study provides guidelines for communication and the evaluation of its effectiveness.

  11. Do Neural Avalanches Indicate Criticality After All?

    CERN Document Server

    Dehghani, Mohammad; Shahbazi, Farhad

    2016-01-01

    Neural avalanches in size and duration exhibit a power law distribution illustrating as a straight line when plotted on the logarithmic scales. The power-law exponent is interpreted as the signature of criticality and it is assumed that the resting brain operates near criticality. However, there is no clear evidence that supports this assumption, and even there are extensive research studies conflicting one another. The model of the current paper is an extension of a previous publication wherein we used an integrate-and-fire model on a regular lattice with periodic boundary conditions and introduced the temporal complexity as a genuine signature of criticality. However, in that model the power-law distribution of neural avalanches were manifestation of super-criticality rather than criticality. Here, however, we show that replacing the discrete noise in the model with a Gaussian noise and continuous time solution of the equation leads to coincidence of temporal complexity and spatiotemporal patterns of neural...

  12. Basic characteristics of the avalanche transistor

    International Nuclear Information System (INIS)

    The avalanche transistor is a useful device for a short-pulse generator of the thermionic electron-gun. However, some properties of the transistor have not been clear experimentally until now. In this report the following properties are presented: the thermal characteristics of the primary breakdown voltage, variations of the output pulse waveform according to the power supply voltage, and the estimated V-I curve of the secondary breakdown voltage. (author)

  13. Expert Fuzzy Model for Avalanche Prediction

    Directory of Open Access Journals (Sweden)

    Mohan Vizhakat

    2003-10-01

    Full Text Available It is imperative that the time required for the analysis and prediction of an extremely volatile event like avalanche needs to be reduced to the minimum. This is particularly critical because of the extremely fast and highly uncertain nature of the event itself. Another peculiar nature of such predictions is that these have to be based almost entirely on the long and intermediate-term data/infomation available, since there would hardly be any short-term warnings (unlike as in the case of a storm that could point towards an imminent prediction. Both the above-mentioned factors favour adoption of such techniques of automated analysis, which are fast, accurate, and employable even under uncertainvoids of information. Apart from empirical and statistical methods, one of the highly promising techniques for developing a practical model for prediction of avalanche is that based on rule-based expert systems. However, development of a realistic rule-based expert system based on conventional logic would imply that one has to firstly define the natural phenomenon being modelled at an extremely high resolution and accuracy. The process of defining a highly uncertain phenomenon like the avalanche at such high resolution, and thereafter, framing extensive rules for all the possibilities is likely to make the system extremely complex, and therefore, unmanageable in many ways. This study attempts tosimplify this problem by proposing a simpler and better technique using an algorithm based on fuzzy logic. This algorithm has the potential to handle even highly complex phenomenon, like that of an avalanche in a fundamentally simple manner. Such potential makes it capable of handling the higher levels of details and still contains the complexity within the manageable limits. Additional details would also make the system more accurate and realistic.

  14. Holographic Jet Quenching

    Science.gov (United States)

    Ficnar, Andrej

    In this dissertation we study the phenomenon of jet quenching in quark-gluon plasma using the AdS/CFT correspondence. We start with a weakly coupled, perturbative QCD approach to energy loss, and present a Monte Carlo code for computation of the DGLV radiative energy loss of quarks and gluons at an arbitrary order in opacity. We use the code to compute the radiated gluon distribution up to n=9 order in opacity, and compare it to the thin plasma (n=1) and the multiple soft scattering (n=infinity) approximations. We furthermore show that the gluon distribution at finite opacity depends in detail on the screening mass mu and the mean free path lambda. In the next part, we turn to the studies of how heavy quarks, represented as "trailing strings" in AdS/CFT, lose energy in a strongly coupled plasma. We study how the heavy quark energy loss gets modified in a "bottom-up" non-conformal holographic model, constructed to reproduce some properties of QCD at finite temperature and constrained by fitting the lattice gauge theory results. The energy loss of heavy quarks is found to be strongly sensitive to the medium properties. We use this model to compute the nuclear modification factor RAA of charm and bottom quarks in an expanding plasma with Glauber initial conditions, and comment on the range of validity of the model. The central part of this thesis is the energy loss of light quarks in a strongly coupled plasma. Using the standard model of "falling strings", we present an analytic derivation of the stopping distance of light quarks, previously available only through numerical simulations, and also apply it to the case of Gauss-Bonnet higher derivative gravity. We then present a general formula for computing the instantaneous energy loss in non-stationary string configurations. Application of this formula to the case of falling strings reveals interesting phenomenology, including a modified Bragg-like peak at late times and an approximately linear path dependence. Based

  15. Monte Carlo studies of electron avalanches in microdosimetric proportional counters

    International Nuclear Information System (INIS)

    We present preliminary results from a study of electron avalanches in a low pressure cylindrical microdosimetric counter. The technique is based on the Monte Carlo simulation of the motion of electrons in electric field and their interactions with the molecules of gas. All the electrons are traced simultaneously in time and their coordinates and velocities are recorded. It lets us study all temporal and space aspects of the electron avalanche development. In this work we have concentrated on a study of the dependence of gain, radial extent and time extent of the avalanche on the gas pressure. We explain our results by the existence of seeding region in the avalanche where a relatively small number of secondary electrons are created. Each of these electrons gives subsequently rise to a partial avalanche in the proper avalanche region. (orig.)

  16. Holographic Quenches with a Gap

    CERN Document Server

    da Silva, Emilia; Mas, Javier; Serantes, Alexandre

    2016-01-01

    In order to holographically model quenches with a gapped final hamiltonian, we consider a gravity-scalar theory in anti-de Sitter space with an infrared hard wall. We allow a time dependent profile for the scalar field at the wall. This induces an energy exchange between bulk and wall and generates an oscillating scalar pulse. We argue that such backgrounds are the counterpart of quantum revivals in the dual field theory. We perform a qualitative comparison with the quench dynamics of the massive Schwinger model, which has been recently analyzed using tensor network techniques. Agreement is found provided the width of the oscillating scalar pulse is inversely linked to the energy density communicated by the quench. We propose this to be a general feature of holographic quenches.

  17. Holographic quenches with a gap

    Science.gov (United States)

    da Silva, Emilia; Lopez, Esperanza; Mas, Javier; Serantes, Alexandre

    2016-06-01

    In order to holographically model quenches with a gapped final hamiltonian, we consider a gravity-scalar theory in anti-de Sitter space with an infrared hard wall. We allow a time dependent profile for the scalar field at the wall. This induces an energy exchange between bulk and wall and generates an oscillating scalar pulse. We argue that such backgrounds are the counterpart of quantum revivals in the dual field theory. We perform a qualitative comparison with the quench dynamics of the massive Schwinger model, which has been recently analyzed using tensor network techniques. Agreement is found provided the width of the oscillating scalar pulse is inversely linked to the energy density communicated by the quench. We propose this to be a general feature of holographic quenches.

  18. Studies of Electron Avalanche Behavior in Liquid Argon

    OpenAIRE

    Kim, J.G.; Dardin, S. M.; Jackson, K.H.; Kadel, R. W.(Lawrence Berkeley National Laboratory and University of California, 94720, Berkeley, California, USA); Kadyk, J. A.; Peskov, V.; Wenzel, W. A.

    2002-01-01

    Electron avalanching in liquid argon is being studied as a function of voltage, pressure, radiation intensity, and the concentrations of certain additives, especially xenon. The avalanches produced in an intense electric field at the tip of a tungsten needle are initiated by ionization from a moveable americium (241Am) gamma ray source. Photons from xenon excimers are detected as photomultiplier signals in coincidence with the current pulse from the needle. In pure liquid argon the avalanche ...

  19. Mathematical modeling of powder-snow avalanche flows

    OpenAIRE

    Dutykh, Denys; Acary-Robert, Céline; Bresch, Didier

    2009-01-01

    Powder-snow avalanches are violent natural disasters which represent a major risk for infrastructures and populations in mountain regions. In this study we present a novel model for the simulation of avalanches in the aerosol regime. The second scope of this study is to get more insight into the interaction process between an avalanche and a rigid obstacle. An incompressible model of two miscible fluids can be successfully employed in this type of problems. We allow for mass diffusion between...

  20. Improvements in quench factor modelling

    OpenAIRE

    Rometsch, P.A.; Starink, M.J.; Gregson, P.J.

    2003-01-01

    In this contribution, the validity of a number of key quench factor analysis (QFA) assumptions is discussed. It is shown that the incorporation of a square root dependency of yield strength on precipitate volume fraction provides a sounder physical basis for quench factor modelling. Peak-aged strength/hardness prediction accuracies are not affected, but C-curve positions are. It is also demonstrated that transformation kinetics are described more correctly by a modified Starink–Zahra equation...

  1. Modelling of snow avalanche dynamics: influence of model parameters

    Science.gov (United States)

    Bozhinskiy, A. N.

    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 value of the coefficient of entrainment me, we have a curve on a plane of the coefficients of dry and turbulent friction. It was found that the family of curves (me is a parameter) are crossed at the single point. The value of the coefficient of turbulent friction at the cross-point remained practically constant for the maximum and average avalanche run-outs. The conclusions obtained are confirmed by the results of modelling for six arbitrarily chosen avalanche sites: three in the Khibiny mountains, Kola Peninsula, Russia, two in the Elbrus region and one idealized site with an exponential longitudinal profile. The dependences of run-out on the coefficient of dry friction are constructed for all the investigated avalanche sites. The results are important for the statistical simulation of avalanche dynamics since they suggest the possibility of using only one random model parameter, namely, the coefficient of dry friction, in the model. The histograms and distribution functions of the coefficient of dry friction are constructed and presented for avalanche sites Nos 22 and 43 (Khibiny mountains) and 'Domestic', with the available series of field data.

  2. The quenching time scale and quenching rate of galaxies

    CERN Document Server

    Lian, Jianhui; Zhang, Kai; Kong, Xu

    2016-01-01

    The average star formation rate (SFR) in galaxies has been declining since redshift of 2. A fraction of galaxies quench and become quiescent. We constrain two key properties of the quenching process: the quenching time scale and the quenching rate among galaxies. We achieve this by analyzing the galaxy number density profile in NUV-u color space and the distribution in NUV-u v.s. u-i color-color diagram with a simple toy-model framework. We focus on galaxies in three mass bins between 10 to 10 and 10 to 10.6 solar mass. In the NUV-u v.s. u-i color-color diagram, the red u-i galaxies exhibit a different slope from the slope traced by the star-forming galaxies. This angled distribution and the number density profile of galaxies in NUV-u space strongly suggest that the decline of the SFR in galaxies has to accelerate before they turn quiescent. We model this color-color distribution with a two-phase exponential decline star formation history. The models with an e-folding time in the second phase (the quenching p...

  3. Bilayer avalanche spin-diode logic

    International Nuclear Information System (INIS)

    A novel spintronic computing paradigm is proposed and analyzed in which InSb p-n bilayer avalanche spin-diodes are cascaded to efficiently perform complex logic operations. This spin-diode logic family uses control wires to generate magnetic fields that modulate the resistance of the spin-diodes, and currents through these devices control the resistance of cascaded devices. Electromagnetic simulations are performed to demonstrate the cascading mechanism, and guidelines are provided for the development of this innovative computing technology. This cascading scheme permits compact logic circuits with switching speeds determined by electromagnetic wave propagation rather than electron motion, enabling high-performance spintronic computing

  4. Bilayer avalanche spin-diode logic

    Energy Technology Data Exchange (ETDEWEB)

    Friedman, Joseph S., E-mail: joseph.friedman@u-psud.fr; Querlioz, Damien [Institut d’Electronique Fondamentale, Univ. Paris-Sud, CNRS, 91405 Orsay (France); Fadel, Eric R. [Department of Materials Science, Massachusetts Institute of Technology, Cambridge, MA 02139 (United States); Wessels, Bruce W. [Department of Electrical Engineering & Computer Science, Northwestern University, Evanston, IL 60208 (United States); Department of Materials Science & Engineering, Northwestern University, Evanston, IL 60208 (United States); Sahakian, Alan V. [Department of Electrical Engineering & Computer Science, Northwestern University, Evanston, IL 60208 (United States); Department of Biomedical Engineering, Northwestern University, Evanston, IL 60208 (United States)

    2015-11-15

    A novel spintronic computing paradigm is proposed and analyzed in which InSb p-n bilayer avalanche spin-diodes are cascaded to efficiently perform complex logic operations. This spin-diode logic family uses control wires to generate magnetic fields that modulate the resistance of the spin-diodes, and currents through these devices control the resistance of cascaded devices. Electromagnetic simulations are performed to demonstrate the cascading mechanism, and guidelines are provided for the development of this innovative computing technology. This cascading scheme permits compact logic circuits with switching speeds determined by electromagnetic wave propagation rather than electron motion, enabling high-performance spintronic computing.

  5. Bilayer avalanche spin-diode logic

    Directory of Open Access Journals (Sweden)

    Joseph S. Friedman

    2015-11-01

    Full Text Available A novel spintronic computing paradigm is proposed and analyzed in which InSb p-n bilayer avalanche spin-diodes are cascaded to efficiently perform complex logic operations. This spin-diode logic family uses control wires to generate magnetic fields that modulate the resistance of the spin-diodes, and currents through these devices control the resistance of cascaded devices. Electromagnetic simulations are performed to demonstrate the cascading mechanism, and guidelines are provided for the development of this innovative computing technology. This cascading scheme permits compact logic circuits with switching speeds determined by electromagnetic wave propagation rather than electron motion, enabling high-performance spintronic computing.

  6. MPPC versus MRS APD in two-phase Cryogenic Avalanche Detectors

    International Nuclear Information System (INIS)

    Two-phase Cryogenic Avalanche Detectors (CRADs) with combined THGEM/GAPD multiplier have become an emerging potential technique for dark matter search and coherent neutrino-nucleus scattering experiments. In such a multiplier the THGEM hole avalanches are optically recorded in the Near Infrared (NIR) using a matrix of Geiger-mode APDs (GAPDs). To select the proper sensor, the performances of six GAPD types manufactured by different companies, namely by Hamamatsu (MPPCs), CPTA (MRS APDs) and SensL (SiPMs), have been comparatively studied at cryogenic temperatures when operated in two-phase CRADs in Ar at 87 K. While the GAPDs with ceramic packages failed to operate properly at cryogenic temperatures, those with plastic packages, namely MPPC S10931-100P and MRS APD 149-35, showed satisfactory performances at 87 K. In addition, MPPC S10931-100P turned out to be superior in terms of the higher detection efficiency, lower noise rate, lower pixel quenching resistor and better characteristics reproducibility

  7. MPPC versus MRS APD in two-phase Cryogenic Avalanche Detectors

    CERN Document Server

    Bondar, A; Dolgov, A; Shemyakina, E; Sokolov, A

    2015-01-01

    Two-phase Cryogenic Avalanche Detectors (CRADs) with combined THGEM/GAPD multiplier have become an emerging potential technique for dark matter search and coherent neutrino-nucleus scattering experiments. In such a multiplier the THGEM hole avalanches are optically recorded in the Near Infrared (NIR) using a matrix of Geiger-mode APDs (GAPDs). To select the proper sensor, the performances of six GAPD types manufactured by different companies, namely by Hamamatsu (MPPCs), CPTA (MRS APDs) and SensL (SiPMs), have been comparatively studied at cryogenic temperatures when operated in two-phase CRADs in Ar at 87 K. While the GAPDs with ceramic packages failed to operate properly at cryogenic temperatures, those with plastic packages, namely MPPC S10931-100P and MRS APD 149-35, showed satisfactory performances at 87 K. In addition, MPPC S10931-100P turned out to be superior in terms of the higher detection efficiency, lower nose rate, lower pixel quenching resistor and better characteristics reproducibility.

  8. MPPC versus MRS APD in two-phase Cryogenic Avalanche Detectors

    Science.gov (United States)

    Bondar, A.; Buzulutskov, A.; Dolgov, A.; Shemyakina, E.; Sokolov, A.; Bondar, A.; Buzulutskov, A.; Dolgov, A.; Shemyakina, E.; Sokolov, A.

    2015-04-01

    Two-phase Cryogenic Avalanche Detectors (CRADs) with combined THGEM/GAPD multiplier have become an emerging potential technique for dark matter search and coherent neu\\-tri\\-no-nucleus scattering experiments. In such a multiplier the THGEM hole avalanches are optically recorded in the Near Infrared (NIR) using a matrix of Geiger-mode APDs (GAPDs). To select the proper sensor, the performances of six GAPD types manufactured by different companies, namely by Hamamatsu (MPPCs), CPTA (MRS APDs) and SensL (SiPMs), have been comparatively studied at cryogenic temperatures when operated in two-phase CRADs in Ar at 87 K. While the GAPDs with ceramic packages failed to operate properly at cryogenic temperatures, those with plastic packages, namely MPPC S10931-100P and MRS APD 149-35, showed satisfactory performances at 87 K. In addition, MPPC S10931-100P turned out to be superior in terms of the higher detection efficiency, lower noise rate, lower pixel quenching resistor and better characteristics reproducibility.

  9. Universality in fast quantum quenches

    CERN Document Server

    Das, Sumit R; Myers, Robert C

    2014-01-01

    We expand on the investigation of the universal scaling properties in the early time behaviour of fast but smooth quantum quenches in a general $d$-dimensional conformal field theory deformed by a relevant operator of dimension $\\Delta$ with a time-dependent coupling. The quench consists of changing the coupling from an initial constant value $\\lambda_1$ by an amount of the order of $\\delta \\lambda$ to some other final value $\\lambda_2$, over a time scale $\\delta t$. In the fast quench limit where $\\delta t$ is smaller than all other length scales in the problem, $ \\delta t \\ll \\lambda_1^{1/(\\Delta-d)}, \\lambda_2^{1/(\\Delta-d)}, \\delta \\lambda^{1/(\\Delta-d)}$, the energy (density) injected into the system scales as $\\delta{\\cal E} \\sim (\\delta \\lambda)^2 (\\delta t)^{d-2\\Delta}$. Similarly, the change in the expectation value of the quenched operator at times earlier than the endpoint of the quench scales as $\\langle {\\cal O}_\\Delta\\rangle \\sim \\delta \\lambda\\, (\\delta t)^{d-2\\Delta}$, with further logarithmic...

  10. Validation of DEM prediction for granular avalanches on irregular terrain

    Science.gov (United States)

    Mead, Stuart R.; Cleary, Paul W.

    2015-09-01

    Accurate numerical simulation can provide crucial information useful for a greater understanding of destructive granular mass movements such as rock avalanches, landslides, and pyroclastic flows. It enables more informed and relatively low cost investigation of significant risk factors, mitigation strategy effectiveness, and sensitivity to initial conditions, material, or soil properties. In this paper, a granular avalanche experiment from the literature is reanalyzed and used as a basis to assess the accuracy of discrete element method (DEM) predictions of avalanche flow. Discrete granular approaches such as DEM simulate the motion and collisions of individual particles and are useful for identifying and investigating the controlling processes within an avalanche. Using a superquadric shape representation, DEM simulations were found to accurately reproduce transient and static features of the avalanche. The effect of material properties on the shape of the avalanche deposit was investigated. The simulated avalanche deposits were found to be sensitive to particle shape and friction, with the particle shape causing the sensitivity to friction to vary. The importance of particle shape, coupled with effect on the sensitivity to friction, highlights the importance of quantifying and including particle shape effects in numerical modeling of granular avalanches.

  11. High voltage short plus generation based on avalanche circuit

    International Nuclear Information System (INIS)

    Simulate the avalanche circuit in series with PSPICE module, design the high voltage short plus generation circuit by avalanche transistor in series for the sweep deflection circuit of streak camera. The output voltage ranges 1.2 KV into 50 ohm load. The rise time of the circuit is less than 3 ns. (authors)

  12. Avalanche Statistics of Driven Granular Slides in a Miniature Mound

    CERN Document Server

    Juanico, D E; Batac, R; Monterola, C

    2008-01-01

    We examine avalanche statistics of rain- and vibration-driven granular slides in miniature soil mounds using experimental and numerical approaches. A crossover from power-law to non power-law avalanche-size statistics is demonstrated as a generic driving rate $\

  13. Structural Measures for Controlling Avalanches in Formation Zone

    Directory of Open Access Journals (Sweden)

    Vinay Chaudhary

    2006-11-01

    Full Text Available Jammu-Srinagar national highway (NH-1A, a lifeline of the Kashmir valley, gains considerableimportance as being the only link between the Kashmir valley and the rest of the country. Astretch of 15 km is marred by 15 major avalanche sites, out of that D-10 avalanche site takes aheavy toll of life and property, besides bringing the busiest highway to a standstill for daystogether, year after year. Therefore, this avalanche site was selected for installation of avalanchecontrolstructures in formation zone and demonstration of technology thereof. A combinationof wind-control structures, supporting structures, and controlled release of avalanches usingexplosive, has been adopted to mitigate avalanche hazard. As a result, the D-10 site can boastof having become a school for live demonstration of the avalanche-control methods on themighty Pir Panjal range at more than 3200 m above the sea level. This paper deals with themethods used for control of avalanches in formation zone of D-10 avalanche site and brings outtheir effectiveness and site-specific applications.

  14. Avalanche behavior of power MOSFETs under different temperature conditions

    Institute of Scientific and Technical Information of China (English)

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

    2011-01-01

    The ability of high-voltage power MOSFETs to withstand avalanche events under different temperature conditions are studied by experiment and two-dimensional device simulation. The experiment is performed to investigate dynamic avalanche failure behavior of the domestic power MOSFETs which can occur at the rated maximum operation temperature range (-55 to 150 ℃). An advanced ISE TCAD two-dimensional mixed mode simulator with thermodynamic non-isothermal model is used to analyze the avalanche failure mechanism. The unclamped inductive switching measurement and simulation results show that the parasitic components and thermal effect inside the device will lead to the deterioration of the avalanche reliability of power MOSFETs with increasing temperature. The main failure mechanism is related to the parasitic bipolar transistor activity during the occurrence of the avalanche behavior.

  15. Avalanches and disorder-induced criticality in artificial spin ices

    International Nuclear Information System (INIS)

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

  16. Reducing financial avalanches by random investments.

    Science.gov (United States)

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

    2013-12-01

    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

  17. Townsend coefficients of gases in avalanche counters

    International Nuclear Information System (INIS)

    Though much work has been done by many authors in the last few years in the development and application of avalanche counters for ion radiation, it is based upon values of the Townsend coefficients as the essential gas parameter, which were determined many years ago for much lower reduced field strengths F/p than prevail in such counters. Therefore absolute determinations of α in vapours of methyl alcohol, cyclohexane, acetone, and n-heptene were performed under original conditions of avalanche counters. The values obtained do not differ by more than 30%-50% from the former values indeed, extrapolated over F/p for the first three mentioned substances, but the amounts of A and B in the usual representation α/p=A exp(-B(F/p)) are much greater for the stronger reduced fields. This is of importance for such counter properties as the dependence of pulse heights on pressure, voltage, electrode distance etc., which are governed by other combinations of A and B than α/p itself. A comparison of results for different ionic radiations shows a marked influence of the primary ionization density along the particle tracks which is hard to explain. (Auth.)

  18. Hot gas in massive halos drives both mass quenching and environment quenching

    CERN Document Server

    Gabor, Jared M

    2014-01-01

    Observations indicate that galaxies with high stellar masses or in dense environments have low specific star formation rates, i.e. they are quenched. Based on cosmological hydrodynamic simulations that include a prescription where quenching occurs in regions dominated by hot (>10^5 K) gas, we argue that this hot gas quenching in halos >10^12 Msun drives both mass quenching (i.e. central quenching) and environment quenching (i.e. satellite quenching). These simulations reproduce a broad range of locally observed trends among quenching, halo mass, stellar mass, environment, and distance to halo center. We show that mass quenching is independent of environment because 10^12-10^13 Msun "quenching halos" -- those where most mass quenching occurs -- inhabit a large range of environments. On the other hand, environment quenching is independent of stellar mass because galaxies of all stellar masses may live in dense environments as satellites of groups and clusters. Furthermore, satellite galaxies show signs of mass ...

  19. Quench anaylsis of MICE spectrometer superconducting solenoid

    Energy Technology Data Exchange (ETDEWEB)

    Kashikhin, Vladimir; Bross, Alan; /Fermilab; Prestemon, Soren; / /LBL, Berkeley

    2011-09-01

    MICE superconducting spectrometer solenoids fabrication and tests are in progress now. First tests of the Spectrometer Solenoid discovered some issues which could be related to the chosen passive quench protection system. Both solenoids do not have heaters and quench propagation relied on the 'quench back' effect, cold diodes, and shunt resistors. The solenoids have very large inductances and stored energy which is 100% dissipated in the cold mass during a quench. This makes their protection a challenging task. The paper presents the quench analysis of these solenoids based on 3D FEA solution of coupled transient electromagnetic and thermal problems. The simulations used the Vector Fields QUENCH code. It is shown that in some quench scenarios, the quench propagation is relatively slow and some areas can be overheated. They describe ways of improving the solenoids quench protection in order to reduce the risk of possible failure.

  20. Single-Photon Avalanche Diodes (SPAD) in CMOS 0.35 µm technology

    Energy Technology Data Exchange (ETDEWEB)

    Pellion, D.; Jradi, K.; Brochard, N. [Le2i – CNRS/Univ. de Bourgogne, Dijon (France); Prêle, D. [APC – CNRS/Univ. Paris Diderot, Paris (France); Ginhac, D. [Le2i – CNRS/Univ. de Bourgogne, Dijon (France)

    2015-07-01

    Some decades ago single photon detection used to be the terrain of photomultiplier tube (PMT), thanks to its characteristics of sensitivity and speed. However, PMT has several disadvantages such as low quantum efficiency, overall dimensions, and cost, making them unsuitable for compact design of integrated systems. So, the past decade has seen a dramatic increase in interest in new integrated single-photon detectors called Single-Photon Avalanche Diodes (SPAD) or Geiger-mode APD. SPAD are working in avalanche mode above the breakdown level. When an incident photon is captured, a very fast avalanche is triggered, generating an easily detectable current pulse. This paper discusses SPAD detectors fabricated in a standard CMOS technology featuring both single-photon sensitivity, and excellent timing resolution, while guaranteeing a high integration. In this work, we investigate the design of SPAD detectors using the AMS 0.35 µm CMOS Opto technology. Indeed, such standard CMOS technology allows producing large surface (few mm{sup 2}) of single photon sensitive detectors. Moreover, SPAD in CMOS technologies could be associated to electronic readout such as active quenching, digital to analog converter, memories and any specific processing required to build efficient calorimeters (Silicon PhotoMultiplier – SiPM) or high resolution imagers (SPAD imager). The present work investigates SPAD geometry. MOS transistor has been used instead of resistor to adjust the quenching resistance and find optimum value. From this first set of results, a detailed study of the dark count rate (DCR) has been conducted. Our results show a dark count rate increase with the size of the photodiodes and the temperature (at T=22.5 °C, the DCR of a 10 µm-photodiode is 2020 count s{sup −1} while it is 270 count s{sup −1} at T=−40 °C for a overvoltage of 800 mV). A small pixel size is desirable, because the DCR per unit area decreases with the pixel size. We also found that the adjustment

  1. Single-Photon Avalanche Diodes (SPAD) in CMOS 0.35 µm technology

    International Nuclear Information System (INIS)

    Some decades ago single photon detection used to be the terrain of photomultiplier tube (PMT), thanks to its characteristics of sensitivity and speed. However, PMT has several disadvantages such as low quantum efficiency, overall dimensions, and cost, making them unsuitable for compact design of integrated systems. So, the past decade has seen a dramatic increase in interest in new integrated single-photon detectors called Single-Photon Avalanche Diodes (SPAD) or Geiger-mode APD. SPAD are working in avalanche mode above the breakdown level. When an incident photon is captured, a very fast avalanche is triggered, generating an easily detectable current pulse. This paper discusses SPAD detectors fabricated in a standard CMOS technology featuring both single-photon sensitivity, and excellent timing resolution, while guaranteeing a high integration. In this work, we investigate the design of SPAD detectors using the AMS 0.35 µm CMOS Opto technology. Indeed, such standard CMOS technology allows producing large surface (few mm2) of single photon sensitive detectors. Moreover, SPAD in CMOS technologies could be associated to electronic readout such as active quenching, digital to analog converter, memories and any specific processing required to build efficient calorimeters (Silicon PhotoMultiplier – SiPM) or high resolution imagers (SPAD imager). The present work investigates SPAD geometry. MOS transistor has been used instead of resistor to adjust the quenching resistance and find optimum value. From this first set of results, a detailed study of the dark count rate (DCR) has been conducted. Our results show a dark count rate increase with the size of the photodiodes and the temperature (at T=22.5 °C, the DCR of a 10 µm-photodiode is 2020 count s−1 while it is 270 count s−1 at T=−40 °C for a overvoltage of 800 mV). A small pixel size is desirable, because the DCR per unit area decreases with the pixel size. We also found that the adjustment of overvoltage is

  2. Chiral logarithms in quenched QCD

    International Nuclear Information System (INIS)

    The quenched chiral logarithms are examined on a 163x28 lattice with Iwasaki gauge action and overlap fermions. The pion decay constant fpi is used to set the lattice spacing, a = 0.200(3) fm. With pion mass as low as ∼180 MeV, we see the quenched chiral logarithms clearly in mpi2/m and fP, the pseudoscalar decay constant. The authors analyze the data to determine how low the pion mass needs to be in order for the quenched one-loop chiral perturbation theory (chiPT) to apply. With the constrained curve-fitting method, they are able to extract the quenched chiral logarithmic parameter delta together with other low-energy parameters. Only for mpi<=300 MeV do we obtain a consistent and stable fit with a constant delta which they determine to be 0.24(3)(4) (at the chiral scale Lambdachi = 0.8 GeV). By comparing to the 123x28 lattice, they estimate the finite volume effect to be about 2.7% for the smallest pion mass. They also fitted the pion mass to the form for the re-summed cactus diagrams and found that its applicable region is extended farther than the range for the one-loop formula, perhaps up to mpi ∼500-600 MeV. The scale independent delta is determined to be 0.20(3) in this case. The authors study the quenched non-analytic terms in the nucleon mass and find that the coefficient C1/2 in the nucleon mass is consistent with the prediction of one-loop chiPT. They also obtain the low energy constant L5 from fpi. They conclude from this study that it is imperative to cover only the range of data with the pion mass less than ∼300 MeV in order to examine the chiral behavior of the hadron masses and decay constants in quenched QCD and match them with quenched one-loop chiPT

  3. Disordered artificial spin ices: Avalanches and criticality (invited)

    Science.gov (United States)

    Reichhardt, Cynthia J. Olson; Chern, Gia-Wei; Libál, Andras; Reichhardt, Charles

    2015-05-01

    We show that square and kagome artificial spin ices with disconnected islands exhibit disorder-induced nonequilibrium phase transitions. The critical point of the transition is characterized by a diverging length scale and the effective spin reconfiguration avalanche sizes are power-law distributed. For weak disorder, the magnetization reversal is dominated by system-spanning avalanche events characteristic of a supercritical regime, while at strong disorder, the avalanche distributions have subcritical behavior and are cut off above a length scale that decreases with increasing disorder. The different type of geometrical frustration in the two lattices produces distinct forms of critical avalanche behavior. Avalanches in the square ice consist of the propagation of locally stable domain walls separating the two polarized ground states, and we find a scaling collapse consistent with an interface depinning mechanism. In the fully frustrated kagome ice, however, the avalanches branch strongly in a manner reminiscent of directed percolation. We also observe an interesting crossover in the power-law scaling of the kagome ice avalanches at low disorder. Our results show that artificial spin ices are ideal systems in which to study a variety of nonequilibrium critical point phenomena as the microscopic degrees of freedom can be accessed directly in experiments.

  4. Disordered artificial spin ices: Avalanches and criticality (invited)

    Energy Technology Data Exchange (ETDEWEB)

    Reichhardt, Cynthia J. Olson, E-mail: cjrx@lanl.gov; Chern, Gia-Wei; Reichhardt, Charles [Center for Nonlinear Studies and Theoretical Division, Los Alamos National Laboratory, Los Alamos, New Mexico 87545 (United States); Libál, Andras [Faculty of Mathematics and Computer Science, Babes-Bolyai University, RO-400591 Cluj-Napoca (Romania)

    2015-05-07

    We show that square and kagome artificial spin ices with disconnected islands exhibit disorder-induced nonequilibrium phase transitions. The critical point of the transition is characterized by a diverging length scale and the effective spin reconfiguration avalanche sizes are power-law distributed. For weak disorder, the magnetization reversal is dominated by system-spanning avalanche events characteristic of a supercritical regime, while at strong disorder, the avalanche distributions have subcritical behavior and are cut off above a length scale that decreases with increasing disorder. The different type of geometrical frustration in the two lattices produces distinct forms of critical avalanche behavior. Avalanches in the square ice consist of the propagation of locally stable domain walls separating the two polarized ground states, and we find a scaling collapse consistent with an interface depinning mechanism. In the fully frustrated kagome ice, however, the avalanches branch strongly in a manner reminiscent of directed percolation. We also observe an interesting crossover in the power-law scaling of the kagome ice avalanches at low disorder. Our results show that artificial spin ices are ideal systems in which to study a variety of nonequilibrium critical point phenomena as the microscopic degrees of freedom can be accessed directly in experiments.

  5. Disordered artificial spin ices: Avalanches and criticality (invited)

    International Nuclear Information System (INIS)

    We show that square and kagome artificial spin ices with disconnected islands exhibit disorder-induced nonequilibrium phase transitions. The critical point of the transition is characterized by a diverging length scale and the effective spin reconfiguration avalanche sizes are power-law distributed. For weak disorder, the magnetization reversal is dominated by system-spanning avalanche events characteristic of a supercritical regime, while at strong disorder, the avalanche distributions have subcritical behavior and are cut off above a length scale that decreases with increasing disorder. The different type of geometrical frustration in the two lattices produces distinct forms of critical avalanche behavior. Avalanches in the square ice consist of the propagation of locally stable domain walls separating the two polarized ground states, and we find a scaling collapse consistent with an interface depinning mechanism. In the fully frustrated kagome ice, however, the avalanches branch strongly in a manner reminiscent of directed percolation. We also observe an interesting crossover in the power-law scaling of the kagome ice avalanches at low disorder. Our results show that artificial spin ices are ideal systems in which to study a variety of nonequilibrium critical point phenomena as the microscopic degrees of freedom can be accessed directly in experiments

  6. Non-Geiger-Mode Single-Photon Avalanche Detector with Low Excess Noise

    Science.gov (United States)

    Zhao, Kai; Lo, YuHwa; Farr, William

    2010-01-01

    This design constitutes a self-resetting (gain quenching), room-temperature operational semiconductor single-photon-sensitive detector that is sensitive to telecommunications optical wavelengths and is scalable to large areas (millimeter diameter) with high bandwidth and efficiencies. The device can detect single photons at a 1,550-nm wavelength at a gain of 1 x 10(exp 6). Unlike conventional single photon avalanche detectors (SPADs), where gain is an extremely sensitive function to the bias voltage, the multiplication gain of this device is stable at 1 x 10(exp 6) over a wide range of bias from 30.2 to 30.9 V. Here, the multiplication gain is defined as the total number of charge carriers contained in one output pulse that is triggered by the absorption of a single photon. The statistics of magnitude of output signals also shows that the device has a very narrow pulse height distribution, which demonstrates a greatly suppressed gain fluctuation. From the histograms of both pulse height and pulse charge, the equivalent gain variance (excess noise) is between 1.001 and 1.007 at a gain of 1 x 10(exp 6). With these advantages, the device holds promise to function as a PMT-like photon counter at a 1,550- nm wavelength. The epitaxial layer structure of the device allows photons to be absorbed in the InGaAs layer, generating electron/hole (e-h) pairs. Driven by an electrical field in InGaAs, electrons are collected at the anode while holes reach the multiplication region (InAlAs p-i-n structure) and trigger the avalanche process. As a result, a large number of e-h pairs are created, and the holes move toward the cathode. Holes created by the avalanche process gain large kinetic energy through the electric field, and are considered hot. These hot holes are cooled as they travel across a p -InAlAs low field region, and are eventually blocked by energy barriers formed by the InGaAsP/ InAlAs heterojunctions. The composition of the InGaAsP alloy was chosen to have an 80 me

  7. Statistical analyses support power law distributions found in neuronal avalanches.

    Directory of Open Access Journals (Sweden)

    Andreas Klaus

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

  8. Overspill avalanching in a dense reservoir network.

    Science.gov (United States)

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

    2012-05-01

    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

  9. A high-speed avalanche photodiode

    International Nuclear Information System (INIS)

    High-speed avalanche photodiodes are widely used in optical communication systems. Nowadays, separate absorption charge and multiplication structure is widely adopted. In this article, a structure with higher speed than separate absorption charge and multiplication structure is reported. Besides the traditional absorption layer, charge layer and multiplication layer, this structure introduces an additional charge layer and transit layer and thus can be referred to as separate absorption, charge, multiplication, charge and transit structure. The introduction of the new charge layer and transit layer brings additional freedom in device structure design. The benefit of this structure is that the carrier transit time and device capacitance can be reduced independently, thus the 3 dB bandwidth could be improved by more than 50% in contrast to the separate absorption charge and multiplication structure with the same size. (semiconductor devices)

  10. Avalanche photodiodes now and possible developments

    International Nuclear Information System (INIS)

    Avalanche Photodiodes (APDs) are now out of their infancy and are used in large numbers in the electromagnetic calorimeter of CMS where they have to stand the extremely hostile environment of LHC. This type--with smaller sensitive area and arranged in monolithic arrays--is an excellent candidate for the read out of scintillating crystals in medical imaging and a PET scanner operates already successfully since more than 3 years. We present the properties of the device used in CMS and possible improvements of the structure, which could open the door for new applications. Operating APDs at low temperatures or in Geiger mode will allow single photon counting and in future they could replace photomultiplier tubes

  11. Overspill avalanching in a dense reservoir network

    CERN Document Server

    Mamede, G L; Schneider, C M; de Araújo, J C; Herrmann, H J

    2012-01-01

    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 which 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.

  12. Radiation hard avalanche photodiodes for CMS ECAL

    CERN Document Server

    Kuznetsov, A; Britvitch, A; Deiters, K; Egeland, R; Gilbert, B; Godinovic, N; Ingram, Q; Lester, E; Musienko, Y; Puljak, I; Renker, D; Reucroft, S; Rusack, R W; Sakhelashvili, T M; Singovsky, A V; Soric, I; Swain, J D

    2003-01-01

    The photo detectors of the CMS electromagnetic calorimeter have to operate in a rather hostile environment, in a strong magnetic field of 4T and under unprecedented radiation levels. Avalanche Photo Diodes (APDs) have been chosen to detect the scintillation light of the 62,000 lead tungstate crystals in the barrel part of the calorimeter. After a 6 year long R&D work Hamamatsu Photonics produces APDs with a structure that is basically radiation hard. Only a few percent of the delivered APDs are weak due to defects at the surface caused by dust particles in the production process. Since a reliability of 99.9% is required, a method to detect weak APDs before they are built into the detector had to be developed. The described screening method is a combination of **6**0Co irradiations and annealing under bias of all APDs and irradiations with hadrons on a sampling basis.

  13. Avalanche photodiodes for the CMS detector

    CERN Document Server

    Deiters, K; Ingram, Q; Nicol, S; Musienko, I; Patel, B; Renker, D; Reucroft, S; Rusack, R W; Sakhelashvili, T M; Singovsky, A V; Swain, J D; Vikas, P

    2000-01-01

    The CERN LHC experiment CMS has selected for the readout of the barrel crystal calorimeter a 5*5 mm/sup 2/ avalanche photodiode (APD) manufactured by Hamamatsu Photonics. In the detector we will equip each crystal with two APDs for a total of 122400 diodes. As the calorimeter will be almost completely inaccessible during the life of the detector, the assurance that they will survive with a high probability in the intense radiation field is an essential part of the of the APD qualification process. In this paper the properties of the APD selected will be described, as well as the procedures we have developed to assure their radiation hardness and reliability. (2 refs).

  14. Avalanche photodiodes now and possible developments

    CERN Document Server

    Britvitch, I; Ingram, Q; Kuznetsov, A; Musienko, Y; Renker, D; Reucroft, S; Sakhelashvili, T M; Swain, J

    2004-01-01

    Avalanche Photodiodes (APDs) are now out of their infancy and are used in large numbers in the electromagnetic calorimeter of CMS where they have to stand the extremely hostile environment of LHC. This type - with smaller sensitive area and arranged in monolithic arrays - is an excellent candidate for the read out of scintillating crystals in medical imaging and a PET scanner operates already successfully since more than 3 years. We present the properties of the device used in CMS and possible improvements of the structure, which could open the door for new applications. Operating APDs at low temperatures or in Geiger mode will allow single photon counting and in future they could replace photomultiplier tubes.

  15. Avalanche of particles in evaporating coffee drops

    CERN Document Server

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

    2010-01-01

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

  16. Seeded excitation avalanches in off-resonantly driven Rydberg gases

    CERN Document Server

    Simonelli, Cristiano; Masella, Guido; Asteria, Luca; Arimondo, Ennio; Ciampini, Donatella; Morsch, Oliver

    2016-01-01

    We report an experimental investigation of the facilitated excitation dynamics in off-resonantly driven Rydberg gases by separating the initial off-resonant excitation phase from the facilitation phase, in which successive facilitation events lead to excitation avalanches. We achieve this by creating a controlled number of initial seed excitations. Greater insight into the avalanche mechanism is obtained from an analysis of the full counting distributions. We also present simple mathematical models and numerical simulations of the excitation avalanches that agree well with our experimental results.

  17. Seeded excitation avalanches in off-resonantly driven Rydberg gases

    Science.gov (United States)

    Simonelli, C.; Valado, M. M.; Masella, G.; Asteria, L.; Arimondo, E.; Ciampini, D.; Morsch, O.

    2016-08-01

    We report an experimental investigation of the facilitated excitation dynamics in off-resonantly driven Rydberg gases by separating the initial off-resonant excitation phase from the facilitation phase, in which successive facilitation events lead to excitation avalanches. We achieve this by creating a controlled number of initial seed excitations. Greater insight into the avalanche mechanism is obtained from an analysis of the full counting distributions. We also present simple mathematical models and numerical simulations of the excitation avalanches that agree well with our experimental results.

  18. Anthropogenic effect on avalanche and debris flow activity

    Directory of Open Access Journals (Sweden)

    S. A. Sokratov

    2015-04-01

    Full Text Available The paper presents examples of the change in snow avalanches and debris flows activity due to the anthropogenic pressure on vegetation and relief. The changes in dynamical characteristics of selected snow avalanches and debris flows due to the anthropogenic activity are quantified. The conclusion is made that the anthropogenic effects on the snow avalanches and debris flows activity are more pronounced than the possible effects of the climate change. The necessity is expressed on the unavoidable changes of the natural environment as the result of a construction and of use of the constructed infrastructure to be account for in corresponding planning of the protection measures.

  19. Quench Simulation Studies: Program documentation of SPQR

    CERN Document Server

    Sonnemann, F

    2001-01-01

    Quench experiments are being performed on prototypes of the superconducting magnets and busbars to determine the adequate design and protection. Many tests can only be understood correctly with the help of quench simulations that model the thermo-hydraulic and electrodynamic processes during a quench. In some cases simulations are the only method to scale the experimental results of prototype measurements to match the situation of quenching superconducting elements in the LHC. This note introduces the theoretical quench model and the use of the simulation program SPQR (Simulation Program for Quench Research), which has been developed to compute the quench process in superconducting magnets and busbars. The model approximates the heat balance equation with the finite difference method including the temperature dependence of the material parameters. SPQR allows the simulation of longitudinal quench propagation along a superconducting cable, the transverse propagation between adjacent conductors, heat transfer i...

  20. Quench/reflood modeling in MELCOR

    International Nuclear Information System (INIS)

    The authors describe the reactor accident simulation model MELCOR. It comprises hydrodynamic investigations on reactor core quenching, hydrogen generation in the reactor core vessel, quench front advances. Preliminary comparisons to data are reasonable but need further validation. (uke)

  1. Jet quenching and heavy quarks

    Science.gov (United States)

    Renk, Thorsten

    2014-05-01

    Jet quenching and more generally physics at high transverse momentum PT scales is a cornerstone of the heavy-ion physics program at both RHIC and LHC. In this work, the current understanding of jet quenching in terms of a QCD shower evolution being modified by the surrounding medium is reviewed along with the evidence for this picture from light parton high PT observables. Conceptually, the same QCD shower description should also be relevant for heavy quarks, but with several important modifications introduced by the quark masses. Thus especially in the limit of small jet energy over quark mass Ejet/mq, the relevant physics may be rather different from light quark jets, and several attempts to explain the observed phenomenology of heavy quarks at high PT are discussed here.

  2. Jet quenching and heavy quarks

    International Nuclear Information System (INIS)

    Jet quenching and more generally physics at high transverse momentum PT scales is a cornerstone of the heavy-ion physics program at both RHIC and LHC. In this work, the current understanding of jet quenching in terms of a QCD shower evolution being modified by the surrounding medium is reviewed along with the evidence for this picture from light parton high PT observables. Conceptually, the same QCD shower description should also be relevant for heavy quarks, but with several important modifications introduced by the quark masses. Thus especially in the limit of small jet energy over quark mass Ejet/mq, the relevant physics may be rather different from light quark jets, and several attempts to explain the observed phenomenology of heavy quarks at high PT are discussed here

  3. Quenched QCD at finite density

    International Nuclear Information System (INIS)

    Simulations of quenched QCD at relatively small but nonzero chemical potential μ on 32 x 163 lattices indicate that the nucleon screening mass decreases linearly as μ increases predicting a critical chemical potential of one third the nucleon mass, MN/3, by extrapolation. The meson spectrum does not change as μ increases over the same range, from zero to mπ/2. Past studies of quenched lattice QCD have suggested that there is phase transition at μ=mπ/2. The authors provide alternative explanations for these results, and find a number of technical reasons why standard lattice simulation techniques suffer from greatly enhanced fluctuations and finite size effects for μ ranging from mπ/2 to mN/3. They find evidence for such problems in their simulations, and suggest that they can be surmounted by improved measurement techniques

  4. Quenched Reinforcement Exposed to Fire

    DEFF Research Database (Denmark)

    Hertz, Kristian Dahl

    2006-01-01

    Idealized data are derived for the tensile strength of quenched and tempered prestressing steel and of quenched and self-tempered reinforcing bars for fire safety design. 0.2% stresses are derived as a function of the maximum temperature and in addition, 2.0% stresses are provided. A strain of 2.......0% is seldom found in “slack” (not prestressed) reinforcement, but 2.0% stresses might be relevant for reinforcement in T shaped cross sections and for prestressed structures, where large strains can be applied. All data are provided in a “HOT” condition during a fire and in a “COLD” condition after a...... fire. The COLD condition is relevant for analyses of residual load bearing capacity of a structure after a fire exposure. It is also relevant for analyses of concrete structures exposed to fully developed fire courses. The reason is that compression zones of concrete are always the weakest in the...

  5. Quenched Reinforcement Exposed to Fire

    DEFF Research Database (Denmark)

    Hertz, Kristian Dahl

    2006-01-01

    investigated. Therefore, two test series have been made, which are presented in the present paper. In one test series, transient properties are found in a HOT condition during a fire and in the other, residual properties are found in a COLD condition after a fully developed fire course.......Idealized data are derived for the tensile strength of quenched and tempered prestressing steel and of quenched and self-tempered reinforcing bars for fire safety design. 0.2% stresses are derived as a function of the maximum temperature and in addition, 2.0% stresses are provided. A strain of 2.......0% is seldom found in “slack” (not prestressed) reinforcement, but 2.0% stresses might be relevant for reinforcement in T shaped cross sections and for prestressed structures, where large strains can be applied. All data are provided in a “HOT” condition during a fire and in a “COLD” condition after a...

  6. Holographic quenches and anomalous transport

    CERN Document Server

    Ammon, Martin; Jimenez-Alba, Amadeo; Macedo, Rodrigo P; Melgar, Luis

    2016-01-01

    We study the response of the chiral magnetic effect due to continuous quenches induced by time dependent electric fields within holography. Concretely, we consider a holographic model with dual chiral anomaly and compute the electric current parallel to a constant, homogeneous magnetic field and a time dependent electric field in the probe approximation. We explicitly solve the PDEs by means of pseudospectral methods in spatial and time directions and study the transition to an universal "fast" quench response. Moreover, we compute the amplitudes, i.e.,~residues of the quasi normal modes, by solving the (ODE) Laplace transformed equations. We investigate the possibility of considering the asymptotic growth rate of the amplitudes as a well defined notion of initial time scale for linearized systems. Finally, we highlight the existence of Landau level resonances in the electrical conductivity parallel to a magnetic field at finite frequency and show explicitly that these only appear in presence of the anomaly. ...

  7. Jet-quenching and correlations

    Indian Academy of Sciences (India)

    Fuqiang Wang

    2015-05-01

    This article reviews recent advances in our understanding of the experimental aspects of jet-quenching and correlations in relativistic heavy-ion collisions at RHIC and LHC. Emphasis is put on correlation measurements, namely jet-like correlations with anisotropic flow subtraction in heavy-ion collisions and long-range pseudorapidity correlations in small systems. Future path on correlation studies is envisioned which may elucidate jet–medium interactions and the properties of the hot dense medium in QCD.

  8. TASK 2: QUENCH ZONE SIMULATION

    Energy Technology Data Exchange (ETDEWEB)

    Fusselman, Steve

    2015-09-30

    Aerojet Rocketdyne (AR) has developed an innovative gasifier concept incorporating advanced technologies in ultra-dense phase dry feed system, rapid mix injector, and advanced component cooling to significantly improve gasifier performance, life, and cost compared to commercially available state-of-the-art systems. A key feature of the AR gasifier design is the transition from the gasifier outlet into the quench zone, where the raw syngas is cooled to ~ 400°C by injection and vaporization of atomized water. Earlier pilot plant testing revealed a propensity for the original gasifier outlet design to accumulate slag in the outlet, leading to erratic syngas flow from the outlet. Subsequent design modifications successfully resolved this issue in the pilot plant gasifier. In order to gain greater insight into the physical phenomena occurring within this zone, AR developed a cold flow simulation apparatus with Coanda Research & Development with a high degree of similitude to hot fire conditions with the pilot scale gasifier design, and capable of accommodating a scaled-down quench zone for a demonstration-scale gasifier. The objective of this task was to validate similitude of the cold flow simulation model by comparison of pilot-scale outlet design performance, and to assess demonstration scale gasifier design feasibility from testing of a scaled-down outlet design. Test results did exhibit a strong correspondence with the two pilot scale outlet designs, indicating credible similitude for the cold flow simulation device. Testing of the scaled-down outlet revealed important considerations in the design and operation of the demonstration scale gasifier, in particular pertaining to the relative momentum between the downcoming raw syngas and the sprayed quench water and associated impacts on flow patterns within the quench zone. This report describes key findings from the test program, including assessment of pilot plant configuration simulations relative to actual

  9. The LHC quench protection system

    CERN Multimedia

    2009-01-01

    The new quench protection system (QPS) has the crucial roles of providing an early warning for any part of the superconducting coils and busbars that develop high resistance, as well as triggering the switch-off of the machine. Over 2000 new detectors will be installed around the LHC to make sure every busbar segment between magnets is monitored and protected. One of the major consolidation activities for the LHC is the addition of two new detectors to the quench protection system. A magnet quench occurs when part of the superconducting cable becomes normally-conducting. When the protection system detects an increased resistance the huge amount of energy stored in the magnet chains is safely extracted and ‘dumped’ into specially designed resistors. In the case of the main dipole chain, the stored energy in a single LHC sector is roughly the same as the kinetic energy of a passenger jet at cruising speed. The first new detector is designed to monitor the superconducting...

  10. How to quench a galaxy

    CERN Document Server

    Pontzen, Andrew; Roth, Nina; Peiris, Hiranya V; Saintonge, Amélie; Volonteri, Marta; Quinn, Tom; Governato, Fabio

    2016-01-01

    We show how the interplay between active galactic nuclei (AGN) and merger history determines whether a galaxy quenches star formation at high redshift. We first simulate, in a full cosmological context, a galaxy of total dynamical mass $10^{12}\\,M_{\\odot}$ at $z=2$. Then we systematically alter the accretion history of the galaxy by minimally changing the linear overdensity in the initial conditions. This "genetic modification" approach allows the generation of three sets of $\\Lambda$CDM initial conditions leading to maximum merger ratios of 1:10, 1:5 and 2:3 respectively. The changes leave the final halo mass, large scale structure and local environment unchanged, providing a controlled numerical experiment. Interaction between the AGN physics and mergers in the three cases lead respectively to a star-forming, temporarily-quenched and permanently-quenched galaxy. However the differences do not primarily lie in the black hole accretion rates, but in the kinetic effects of the merger: the galaxy is resilient a...

  11. SiC Avalanche Photodiodes and Arrays Project

    Data.gov (United States)

    National Aeronautics and Space Administration — Aymont Technology, Inc. (Aymont) will demonstrate the feasibility of SiC p-i-n avalanche photodiodes (APD) arrays. Aymont will demonstrate 4 x 4 arrays of 2 mm2...

  12. Discrimination capability of avalanche counters detecting different ionizing particles

    International Nuclear Information System (INIS)

    The discrimination capability of avalanche counters to detect different ionizing particles has been studied using a 252Cf source. Pulse height, pulse-height resolution and timing properties have been measured as a function of the reduced applied voltage for parallel-plate and parallel-grid avalanche counters. At the highest applied voltages, space charge effects shift the pulse-height signal of the avalanche counter away from being linearly proportional to the stopping power of the detected particles and cause the pulse-height resolution to deteriorate. To optimize the avalanche counter capability, without loss of time resolution, it appears better to operate the detector at voltages well below the breakdown threshold. Measurements with 32S ions are also reported. (orig.)

  13. Avalanche dynamics in evolution, growth, and depinning models

    Science.gov (United States)

    Paczuski, Maya; Maslov, Sergei; Bak, Per

    1996-01-01

    The dynamics of complex systems in nature often occurs in terms of punctuations, or avalanches, rather than following a smooth, gradual path. A comprehensive theory of avalanche dynamics in models of growth, interface depinning, and evolution is presented. Specifically, we include the Bak-Sneppen evolution model, the Sneppen interface depinning model, the Zaitsev flux creep model, invasion percolation, and several other depinning models into a unified treatment encompassing a large class of far from equilibrium processes. The formation of fractal structures, the appearance of 1/f noise, diffusion with anomalous Hurst exponents, Lévy flights, and punctuated equilibria can all be related to the same underlying avalanche dynamics. This dynamics can be represented as a fractal in d spatial plus one temporal dimension. The complex state can be reached either by tuning a parameter, or it can be self-organized. We present two exact equations for the avalanche behavior in the latter case. (1) The slow approach to the critical attractor, i.e., the process of self-organization, is governed by a ``gap'' equation for the divergence of avalanche sizes. (2) The hierarchical structure of avalanches is described by an equation for the average number of sites covered by an avalanche. The exponent γ governing the approach to the critical state appears as a constant rather than as a critical exponent. In addition, the conservation of activity in the stationary state manifests itself through the superuniversal result η=0. The exponent π for the Lévy flight jumps between subsequent active sites can be related to other critical exponents through a study of ``backward avalanches.'' We develop a scaling theory that relates many of the critical exponents in this broad category of extremal models, representing different universality classes, to two basic exponents characterizing the fractal attractor. The exact equations and the derived set of scaling relations are consistent with

  14. Seeded excitation avalanches in off-resonantly driven Rydberg gases

    OpenAIRE

    Simonelli, Cristiano; Valado, Maria Martinez; Masella, Guido; Asteria, Luca; Arimondo, Ennio; Ciampini, Donatella; Morsch, Oliver

    2016-01-01

    We report an experimental investigation of the facilitated excitation dynamics in off-resonantly driven Rydberg gases by separating the initial off-resonant excitation phase from the facilitation phase, in which successive facilitation events lead to excitation avalanches. We achieve this by creating a controlled number of initial seed excitations. Greater insight into the avalanche mechanism is obtained from an analysis of the full counting distributions. We also present simple mathematical ...

  15. Avalanche dynamics in evolution, growth, and depinning models

    Energy Technology Data Exchange (ETDEWEB)

    Paczuski, M.; Maslov, S.; Bak, P. [Department of Physics, Brookhaven National Laboratory, Upton, New York 11973 (United States)]|[Department of Physics, State University of New York at Stony Brook, Stony Brook, New York 11794 (United States)

    1996-01-01

    Dynamics of complex systems in nature often occurs in terms of punctuations, or avalanches, rather than following a smooth, gradual path. Theory of avalanche dynamics in models of growth, interface depinning, and evolution is presented. Specifically, we include the Bak-Sneppen evolution model, Sneppen interface depinning model, Zaitsev flux creep model, invasion percolation, and several other depinning models into a unified treatment encompassing a large class of far from equilibrium processes. The formation of fractal structures, the appearance of 1/{ital f} noise, diffusion with anomalous Hurst exponents, L{acute e}vy flights, and punctuated equilibria can all be related to the same underlying avalanche dynamics. This dynamics can be represented as a fractal in {ital d} spatial plus one temporal dimension. The complex state can be reached either by tuning a parameter, or it can be self-organized. We present two {ital exact} equations for the avalanche behavior in the latter case. (1) The slow approach to the critical attractor, i.e., the process of self-organization, is governed by a ``gap`` equation for divergence of avalanche sizes. (2) The hierarchical structure of avalanches is described by an equation for the average number of sites covered by an avalanche. The exponent {gamma} governing the approach to the critical state appears as a constant rather than as a critical exponent. In addition, the conservation of activity in the stationary state manifests itself through the superuniversal result {eta}=0. The exponent {pi} for the L{acute e}vy flight jumps between subsequent active sites can be related to other critical exponents through a study of {open_quote}{open_quote}backward avalanches.{close_quote}{close_quote} We develop a scaling theory that relates many of the critical exponents in this broad category of extremal models, representing different universality classes, to two basic exponents characterizing the fractal attractor. (Abstract Truncated)

  16. Predictive Capabilities of Avalanche Models for Solar Flares

    OpenAIRE

    Strugarek, Antoine; Charbonneau, Paul

    2014-01-01

    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 a...

  17. Neuronal Avalanches in the Resting MEG of the Human Brain

    OpenAIRE

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

    2013-01-01

    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 para...

  18. Spatio-temporal avalanche forecasting with Support Vector Machines

    Directory of Open Access Journals (Sweden)

    A. Pozdnoukhov

    2011-02-01

    Full Text Available 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.

  19. Avalanches, plasticity, and ordering in colloidal crystals under compression

    Science.gov (United States)

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

    2016-06-01

    Using numerical simulations we examine colloids with a long-range Coulomb interaction confined in a two-dimensional trough potential undergoing dynamical compression. As the depth of the confining well is increased, the colloids move via elastic distortions interspersed with intermittent bursts or avalanches of plastic motion. In these avalanches, the colloids rearrange to minimize their colloid-colloid repulsive interaction energy by adopting an average lattice constant that is isotropic despite the anisotropic nature of the compression. The avalanches take the form of shear banding events that decrease or increase the structural order of the system. At larger compression, the avalanches are associated with a reduction of the number of rows of colloids that fit within the confining potential, and between avalanches the colloids can exhibit partially crystalline or anisotropic ordering. The colloid velocity distributions during the avalanches have a non-Gaussian form with power-law tails and exponents that are consistent with those found for the velocity distributions of gliding dislocations. We observe similar behavior when we subsequently decompress the system, and find a partially hysteretic response reflecting the irreversibility of the plastic events.

  20. Quenching star formation in cluster galaxies

    CERN Document Server

    Taranu, Dan S; Balogh, Michael L; Smith, Russell J; Power, Chris; Krane, Brad

    2012-01-01

    In order to understand the processes that quench star formation within rich clusters, we construct a library of subhalo orbits drawn from lambdaCDM cosmological N-body simulations of four rich clusters. The orbits are combined with models of star formation followed by quenching in the cluster environment to predict colours and spectroscopic line indices of satellite galaxies. Simple models with only halo mass-dependent quenching and without environmental (i.e. cluster-dependent) quenching fail to reproduce the observed cluster-centric colour and absorption linestrength gradients. Models in which star formation is instantly quenched at the virial radius also fail to match the observations. Better matches to the data are achieved by more complicated bulge-disc models in which the bulge stellar populations depend only on the galaxy subhalo mass while the disc quenching depends on the cluster environment. In the most successful models quenching begins at pericentre, operating on an exponential timescale of 2 -- 3...

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

    Directory of Open Access Journals (Sweden)

    A. Kogelnig

    2011-08-01

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

  2. Avalanche outbreaks emerging in cooperative contagions

    Science.gov (United States)

    Cai, Weiran; Chen, Li; Ghanbarnejad, Fakhteh; Grassberger, Peter

    2015-11-01

    The spreading of contagions can exhibit a percolation transition, which separates transitory prevalence from outbreaks that reach a finite fraction of the population. Such transitions are commonly believed to be continuous, but empirical studies have shown more violent spreading modes when the participating agents are not limited to one type. Striking examples include the co-epidemic of the Spanish flu and pneumonia that occurred in 1918 (refs , ), and, more recently, the concurrent prevalence of HIV/AIDS and a host of diseases. It remains unclear to what extent an outbreak in the presence of interacting pathogens differs from that due to an ordinary single-agent process. Here we study a mechanistic model for understanding contagion processes involving inter-agent cooperation. Our stochastic simulations reveal the possible emergence of a massive avalanche-like outbreak right at the threshold, which is manifested as a discontinuous phase transition. Such an abrupt change arises only if the underlying network topology supports a bottleneck for cascaded mutual infections. Surprisingly, all these discontinuous transitions are accompanied by non-trivial critical behaviours, presenting a rare case of hybrid transition. The findings may imply the origin of catastrophic occurrences in many realistic systems, from co-epidemics to financial contagions.

  3. OPTIMIZING THROUGH CO-EVOLUTIONARY AVALANCHES

    Energy Technology Data Exchange (ETDEWEB)

    S. BOETTCHER; A. PERCUS

    2000-08-01

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

  4. The structure of powder snow avalanches

    Science.gov (United States)

    Sovilla, Betty; McElwaine, Jim N.; Louge, Michel Y.

    2015-01-01

    Powder snow avalanches (PSAs) can be hundreds of metres high and descend at astonishing speeds. This review paints a composite picture of PSAs from data acquired at the Vallée de la Sionne test site in Switzerland, including time-histories of snow cover thickness from buried RADAR and, at several elevations on a pylon, impact pressures from load cells, air pressure, particle velocity from optical sensors, and cloud density and particle cluster size from capacitance probes. PSAs feature distinct flow regions with stratification in mean density. At the head, highly fluctuating impact pressures weaken with elevation, while vertical velocity profiles evolve rapidly along the flow, suggesting that surface snow layers of light, cold, cohesionless snow erupt into a turbulent, inhomogeneous, recirculating frontal cloud region. For hundreds of metres behind the head, cloud stratification sharpens with the deposition of suspended cloud particles, while a denser basal flow of increasing thickness forms as deeper, warmer and heavier parts of the weakened snow cover are entrained. Toward the tail, vertical velocity profiles are more uniform, impact pressures become lower and steadier as the flow becomes thinner, and snow pack entrainment is negligible.

  5. Multi-scale modelling of granular avalanches

    Science.gov (United States)

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

    2013-06-01

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

  6. Avalanche breakdown of the quantum hall effects

    CERN Document Server

    Komiyama, S

    1999-01-01

    Heat stability of two-dimensional electron gas (2DEG) systems in the integer quantum hall effect (IQHE) regime is discussed, and a heat instability is suggested to be the intrinsic mechanism behind the breakdown of the IQHE. Phenomenological argument is provided to suggest that the 2DEG system in the IQHE state becomes thermally unstable when the Hall electric field E sub y reaches a threshold value E sub b. Above E sub b , excited nonequilibrium electrons (holes), which are initially present in the conductor as the temperature fluctuation, are accelerated by E sub y and the 2DEG thereby undergoes a transition to a warm dissipative state. The critical field, E sub b , of this abrupt transition is theoretically estimated and shown to be in fare agreement with experimentally reported values. Consideration of the dynamics of electrons suggests that the transition is a process of avalanche electron-hole pair multiplication, in which a small number of non-equilibrium carriers, gains kinetic energy within a Landau ...

  7. Jet Quenching via Jet Collimation

    CERN Document Server

    Casalderrey-Solana, Jorge; Wiedemann, Urs Achim

    2011-01-01

    The ATLAS Collaboration recently reported strong modifications of dijet properties in heavy ion collisions. In this work, we discuss to what extent these first data constrain already the microscopic mechanism underlying jet quenching. Simple kinematic arguments lead us to identify a frequency collimation mechanism via which the medium efficiently trims away the soft components of the jet parton shower. Through this mechanism, the observed dijet asymmetry can be accomodated with values of $\\hat{q}\\, L$ that lie in the expected order of magnitude.

  8. Rapid Quench in an Electrostatic Levitator

    Science.gov (United States)

    SanSoucie, Michael P.; Rogers, Jan R.; Matson, Douglas M.

    2016-01-01

    The Electrostatic Levitation (ESL) Laboratory at the NASA Marshall Space Flight Center (MSFC) is a unique facility for investigators studying high-temperature materials. The ESL laboratory's main chamber has been upgraded with the addition of a rapid quench system. This system allows samples to be dropped into a quench vessel that can be filled with a low melting point material, such as a gallium or indium alloy, as a quench medium. Thereby allowing rapid quenching of undercooled liquid metals. Up to eight quench vessels can be loaded into a wheel inside the chamber that is indexed with control software. The system has been tested successfully with samples of zirconium, iron-cobalt alloys, titanium-zirconium-nickel alloys, and a silicon-cobalt alloy. This new rapid quench system will allow materials science studies of undercooled materials and new materials development. In this presentation, the system is described and some initial results are presented.

  9. Sediment Transport by Spring Avalanches in the Southern Swiss Alps

    Science.gov (United States)

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

    2010-12-01

    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

  10. THE EFFECT OF AVALANCHING IN A TWO-SPECIES RIPPLE MODEL

    OpenAIRE

    Hoyle, Rebecca B; ANITA MEHTA

    2001-01-01

    This paper discusses a simple two-species ripple model with avalanching. The effect of the avalanching term is investigated numerically, and is found to be crucial in producing realistic ripple profiles.

  11. Universality in the mean spatial shape of avalanches

    Science.gov (United States)

    Thiery, Thimothée; Le Doussal, Pierre

    2016-05-01

    Quantifying the universality of avalanche observables beyond critical exponents is of current great interest in theory and experiments. Here, we compute the spatial shape of avalanches in the universality class of the depinning of elastic interfaces in random media. We provide for the first time an analytically tractable definition of the spatial shape, accessible in experiments, and study the mean spatial shape of avalanches at fixed size centered around their starting point (seed). We calculate the associated universal scaling functions, both in a mean-field model and beyond. Notably, they are predicted to exhibit a cusp singularity near the seed. The results are in good agreement with a numerical simulation of an elastic line.

  12. Dynamic rock fragmentation: thresholds for long runout rock avalanches

    Directory of Open Access Journals (Sweden)

    E.T. Bowman

    2014-10-01

    Full Text Available The dynamic fragmentation of rock within rock avalanches is examined using the fragmentation concepts introduced by Grady and co-workers. The analyses use typical material values for weak chalk and limestone in order to determine theoretical strain rate thresholds for dynamic fragmentation and resulting fragment sizes. These are found to compare favourably with data obtained from field observations of long runout rock avalanches and chalk cliff collapses in spite of the simplicity of the approach used. The results provide insight as to the energy requirements to develop long runout behaviour and hence may help to explain the observed similarities between large rock avalanches and much smaller scale chalk cliff collapses as seen in Europe.

  13. Avalanche dynamics in evolution, growth, and depinning models

    CERN Document Server

    Paczuski, M; Bak, P

    1995-01-01

    The dynamics of complex systems in nature often occurs in terms of punctuations, or avalanches, rather than following a smooth, gradual path. A comprehensive theory of avalanche dynamics in models of growth, interface depinning, and evolution is presented. Specifically, we include the Bak-Sneppen evolution model, the Sneppen interface depinning model, the Zaitsev flux creep model, invasion percolation, and several other depinning models into a unified treatment encompassing a large class of far from equilibrium processes. The formation of fractal structures, the appearance of 1/f noise, diffusion with anomalous Hurst exponents, Levy flights, and punctuated equilibria can all be related to the same underlying avalanche dynamics. This dynamics can be represented as a fractal in d spatial plus one temporal dimension. We develop a scaling theory that relates many of the critical exponents in this broad category of extremal models, representing different universality classes, to two basic exponents characterizing ...

  14. Communicators' perspective on snow avalanche risk communication using smartphone applications

    Science.gov (United States)

    Charrière, Marie; Bogaard, Thom; Junier, Sandra; Mostert, Erik

    2015-04-01

    Among all the natural hazards, snow avalanches are the only ones for which a public danger scale is used globally. It consists of 5 levels of danger displayed with a given number and colour, and for each of them behavioural advices are provided. Even though this is standardized in most of the countries affected by this natural hazard, the smartphone applications with which the information is disseminated to the general public differ, particularly in terms of target audience and level of details. This study aims to gather the perspectives of several persons that are responsible for these avalanche risk communication practices. The survey was created to assess how and why choices were made in the design process of the applications and to determine how their effectiveness is evaluated. Along with a review of existing avalanche risk communication smartphone applications, this study provides guidelines for communication and the evaluation of its effectiveness.

  15. Spectral analysis of colour-quenched and chemically quenched C-14 samples

    International Nuclear Information System (INIS)

    In this paper pairs of pulse height distribution curves, of C-14 samples, colour-quenched and chemically quenched was obtained. The possibility to choose a counting window in order to obtain the counting efficiency curves, for both type of quenching was studied. (Author) 7 refs

  16. Avalanche shape and exponents beyond mean-field theory

    Science.gov (United States)

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

    2014-12-01

    Elastic systems, such as magnetic domain walls, density waves, contact lines, and cracks, are pinned by substrate disorder. When driven, they move via avalanches, with power law distributions of size, duration and velocity. Their exponents, and the shape of an avalanche, defined as its mean velocity as a function of time, were studied. They are known approximatively from experiments and simulations, and were predicted from mean-field models, such as the Brownian force model (BFM), where each point of the elastic interface sees a force field which itself is a random walk. As we showed in EPL, 97 (2012) 46004, the BFM is the starting point for an \\varepsilon = d\\text{c}-d expansion around the upper critical dimension, with d\\text{c}=4 for short-ranged elasticity, and d\\text{c}=2 for long-ranged elasticity. Here we calculate analytically the O}(\\varepsilon) , i.e. 1-loop, correction to the avalanche shape at fixed duration T, for both types of elasticity. The exact expression, though different from the phenomenological form presented by Laurson et al. in Nat. Commun., 4 (2013) 2927, is well approximated by ≤ft_T≃ [ Tx(1-x)]γ-1 \\exp≤ft( A}≤ft[\\frac12-x\\right]\\right) , 0 < x < 1. The asymmetry A}≈ - 0.336 (1-d/d\\text{c}) is negative for d close to d\\text{c} , skewing the avalanche towards its end, as observed in numerical simulations in d = 2 and 3. The exponent γ=(d+\\zeta)/z is given by the two independent exponents at depinning, the roughness ζ and the dynamical exponent z. We propose a general procedure to predict other avalanche exponents in terms of ζ and z. We finally introduce and calculate the shape at fixed avalanche size, not yet measured in experiments or simulations.

  17. Geophysical investigation of the Sandalp rock avalanche deposits

    Science.gov (United States)

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

    2010-04-01

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

  18. A new method for avalanche hazard mapping using a combination of statistical and deterministic models

    OpenAIRE

    M. Barbolini; Keylock, C. J.

    2002-01-01

    The purpose of the present paper is to propose a new method for avalanche hazard mapping using a combination of statistical and deterministic modelling tools. The methodology is based on frequency-weighted impact pressure, and uses an avalanche dynamics model embedded within a statistical framework. The outlined procedure provides a useful way for avalanche experts to produce hazard maps for the typical case of avalanche sites where histor...

  19. Different hierarchy of avalanches observed in the Bak-Sneppen evolution model

    CERN Document Server

    Li, W

    2000-01-01

    We introduce a new quantity, average fitness, into the Bak-Sneppen evolution model. Through the new quantity, a different hierarchy of avalanches is observed. The gap equation, in terms of the average fitness, is presented to describe the self-organization of the model. It is found that the critical value of the average fitness can be exactly obtained. Based on the simulations, two critical exponents, avalanche distribution and avalanche dimension, of the new avalanches are given.

  20. Magnetar Outbursts from Avalanches of Hall Waves and Crustal Failures

    CERN Document Server

    Li, Xinyu; Belovorodov, Andrei M

    2016-01-01

    We explore the interaction between Hall waves and mechanical failures inside a magnetar crust, using detailed one-dimentional models that consider temperature-sensitive plastic flow, heat transport and cooling by neutrino emission, as well as the coupling of the crustal motion to the magnetosphere. We find that the dynamics is enriched and accelerated by the fast, short-wavelength Hall waves that are emitted by each failure. The waves propagate and cause failures elsewhere, triggering avalanches. We argue that these avalanches are the likely sources of outbursts in transient magnetars.

  1. A general model for the gain of gas avalanche counters

    International Nuclear Information System (INIS)

    A simple, general model of the avalanche process in gas counters is described. Applicable to all the common forms of gas avalanche detector - wire, microstrip, point anode and parallel gap, the model describes the gain process in terms of two pseudo-physical constants which are effectively invariant over the working range of any given detector configuration. For counter operation over a wide range of conditions (e.g. very different gas pressures) the model is extended so that four parameters are required to model the gain. Applications of the model to the characterisation, operation and design of a variety of counter types are given. (author)

  2. Test of BESⅢ RPC in the avalanche mode

    Institute of Scientific and Technical Information of China (English)

    HAN Ji-Feng; ZHANG Jia-Wen; CHEN Jin; ZHANG Qing-Min; LIU Qian; XIE Yu-Guang; QIAN Sen; MA Lie-Hua

    2008-01-01

    The installation of the BESⅢ RPC system has been completed.Cosmic ray test results show that they perform very well in streamer mode and meet the BESⅢ requirements.We have tested several RPCs in the avalanche mode with the addition of extra SF6 in the gas mixture.We find an efficiency plateau that reaches~95%.and a time resolution of 1.8 ns.This demonstrates that the BESⅢ-type RPC can work in the avalanche mode as well.

  3. SNOW AVALANCHE ACTIVITY IN PARÂNG SKI AREA REVEALED BY TREE-RINGS

    Directory of Open Access Journals (Sweden)

    F. MESEȘAN

    2014-11-01

    Full Text Available Snow Avalanche Activity in Parâng Ski Area Revealed by Tree-Rings. Snow avalanches hold favorable conditions to manifest in Parâng Mountains but only one event is historically known, without destructive impact upon infrastructure or fatalities and this region wasn’t yet the object of avalanche research. The existing ski infrastructure of Parâng resort located in the west of Parâng Mountains is proposed to be extended in the steep slopes of subalpine area. Field evidence pinpoints that these steep slopes were affected by snow avalanches in the past. In this study we analyzed 11 stem discs and 31 increment cores extracted from 22 spruces (Picea abies (L. Karst impacted by avalanches, in order to obtain more information about past avalanches activity. Using the dendrogeomorphological approach we found 13 avalanche events that occurred along Scărița avalanche path, since 1935 until 2012, nine of them produced in the last 20 years. The tree-rings data inferred an intense snow avalanche activity along this avalanche path. This study not only calls for more research in the study area but also proves that snow avalanches could constitute an important restrictive factor for the tourism infrastructure and related activities in the area. It must be taken into consideration by the future extension of tourism infrastructure. Keywords: snow avalanche, Parâng Mountains, dendrogeomorphology, ski area.

  4. Quenched Chiral Perturbation Theory to one loop

    NARCIS (Netherlands)

    Colangelo, G.; Pallante, E.

    1998-01-01

    The divergences of the generating functional of quenched Chiral Perturbation theory (qCHPT) to one loop are computed in closed form. We show how the quenched chiral logarithms can be reabsorbed in the renormalization of the B0 parameter of the leading order Lagrangian. Finally, we do the chiral powe

  5. MSFC Electrostatic Levitator (ESL) Rapid Quench System

    Science.gov (United States)

    SanSoucie, Michael P.; Craven, Paul D.; Rogers, Jan R.

    2014-01-01

    The NASA Marshall Space Flight Center (MSFC) Electrostatic Levitator (ESL) Laboratory is a unique facility for investigators studying high-temperature materials. The laboratory boasts two levitators in which samples can be levitated, heated, melted, undercooled, and resolidified, all without the interference of a container or data-gathering instrument. The ESL main chamber has been upgraded with the addition of a rapid quench system. This system allows samples to be dropped into a quench vessel that can be filled with a low melting point material, such as a gallium or indium alloy. Thereby allowing rapid quenching of undercooled liquid metals. Up to 8 quench vessels can be loaded into the quench wheel, which is indexed with LabVIEW control software. This allows up to 8 samples to be rapidly quenched before having to open the chamber. The system has been tested successfully on several zirconium samples. Future work will be done with other materials using different quench mediums. Microstructural analysis will also be done on successfully quench samples.

  6. QUENCHING ON BOUNDARY TO THE NEWTON FILTRATION EQUATION (Ⅰ)

    Institute of Scientific and Technical Information of China (English)

    段志文; 谢春红; 卢伟明

    2003-01-01

    This paper discusses the global existence and quenching of the solution to the Newton filtration equation with the nonlinear boundary condition.The authors also discuss the profile of the quenching solution in the quenching time and obtain the quenching rate of the quenching solution.

  7. QUENCH STUDIES AND PREHEATING ANALYSIS OF SEAMLESS

    Energy Technology Data Exchange (ETDEWEB)

    Palczewski, Ari [JLAB; Geng, Rongli [JLAB; Eremeev, Grigory [JLAB

    2013-09-01

    One of the alternative manufacturing technologies for SRF cavities is hydroforming from seamless tubes. Although this technology has produced cavities with gradient and Q-values comparable to standard EBW/EP cavities, a few questions remain. One of these questions is whether the quench mechanism in hydroformed cavities is the same as in standard electron beam welded cavities. Towards this effort Jefferson Lab performed quench studies on 2 9 cell seamless hydroformed cavities. These cavities include DESY's - Z163 and Z164 nine-cell cavities hydroformed at DESY. Initial Rf test results Z163 were published in SRF2011. In this report we will present post JLAB surface re-treatment quench studies for each cavity. The data will include OST and T-mapping quench localization as well as quench location preheating analysis comparing them to the observations in standard electron beam welded cavities.

  8. Quench Heater Studies for the LHC Magnets

    CERN Document Server

    Rodríguez-Mateos, F

    2001-01-01

    About 2000 LHC (CERN's Large Hadron Collider) superconducting magnets will be protected with quench heaters against development of excessive voltage and overheating after a resistive transition. The quench heater strips are powered by capacitor bank discharge power supplies. The strips are made of stainless steel partially plated with copper to reduce their resistance and to allow for the connection of quench heaters in series. The strips are embedded in between two polyimide foils. The initial power density and the current decay time determine the quench heater effectiveness. Since only one type of heater power supply will be available, the copper plating cycle is adapted for the various magnet types to keep the resistance of the heater circuit constant. Different quench heater designs have been tested on various prototype magnets to optimise the copper-plating cycle and the electric insulation of the heater strip. This paper summarises the experimental results and computations that allowed to finalise the h...

  9. Finite Element Simulation of Metal Quenching

    Institute of Scientific and Technical Information of China (English)

    方刚; 曾攀

    2004-01-01

    The evolution of the phase transformation and the resulting internal stresses and strains in metallic parts during quenching were modeled numerically. The numerical simulation of the metal quenching process was based on the metallo-thermo-mechanical theory using the finite element method to couple the temperature, phase transformation, and stress-strain fields. The numerical models are presented for the heat treatment and kinetics of the phase transformation. The finite element models and the phase transition kinetics accurately predict the distribution of the microstructure volume fractions, the temperature, the distortion, and the stress-strain relation during quenching. The two examples used to validate the models are the quenching of a small gear and of a large turbine rotor. The simulation results for the martensite phase volume fraction, the stresses, and the distortion in the gear agree well with the experimental data. The models can be used to optimize the quenching conditions to ensure product quality.

  10. Quenching and anisotropy of hydromagnetic turbulent transport

    International Nuclear Information System (INIS)

    Hydromagnetic turbulence affects the evolution of large-scale magnetic fields through mean-field effects like turbulent diffusion and the α effect. For stronger fields, these effects are usually suppressed or quenched, and additional anisotropies are introduced. Using different variants of the test-field method, we determine the quenching of the turbulent transport coefficients for the forced Roberts flow, isotropically forced non-helical turbulence, and rotating thermal convection. We see significant quenching only when the mean magnetic field is larger than the equipartition value of the turbulence. Expressing the magnetic field in terms of the equipartition value of the quenched flows, we obtain for the quenching exponents of the turbulent magnetic diffusivity about 1.3, 1.1, and 1.3 for Roberts flow, forced turbulence, and convection, respectively. However, when the magnetic field is expressed in terms of the equipartition value of the unquenched flows, these quenching exponents become about 4, 1.5, and 2.3, respectively. For the α effect, the exponent is about 1.3 for the Roberts flow and 2 for convection in the first case, but 4 and 3, respectively, in the second. In convection, the quenching of turbulent pumping follows the same power law as turbulent diffusion, while for the coefficient describing the Ω×J effect nearly the same quenching exponent is obtained as for α. For forced turbulence, turbulent diffusion proportional to the second derivative along the mean magnetic field is quenched much less, especially for larger values of the magnetic Reynolds number. However, we find that in corresponding axisymmetric mean-field dynamos with dominant toroidal field the quenched diffusion coefficients are the same for the poloidal and toroidal field constituents.

  11. Electric field distribution and simulation of avalanche formation due to the passage of heavy ions in a parallel grid avalanche counter

    Indian Academy of Sciences (India)

    D Kanjilal; S Saha

    2009-05-01

    Electric field distributions and their role in the formation of avalanche due to the passage of heavy ions in parallel grid avalanche type wire chamber detectors are evaluated using a Monte Carlo simulation. The relative merits and demerits of parallel and crossed wire grid configurations are studied. It is found that the crossed grid geometry has marginally higher gain at larger electric fields close to the avalanche region. The spatial uniformity of response in the two wire grid configurations is also compared.

  12. Multi-step avalanche chambers for FNAL experiment E605

    International Nuclear Information System (INIS)

    Physical processes in multi-step avalanche chambers, detector properties, and difficulties in operation are discussed. Advantages of multi-step chambers over classical MWPC for specific experimental problems encountered in experiment E605 (high-flux environment and CERENKOV imaging) are described. Some details of detector design are presented

  13. Positron camera with high-density avalanche chambers

    International Nuclear Information System (INIS)

    The results of an extensive investigation of the properties of high-density avalanche chambers (HIDAC) are presented. This study has been performed in order to optimize the layout of HIDAC detectors, since they are intended to be applied as position sensitive detectors for annihilation radiation in a positron emission tomograph being under construction. (author)

  14. A high current, high speed pulser using avalanche transistors

    International Nuclear Information System (INIS)

    A high current, high speed pulser for the beam pulsing of a linear accelerator is described. It uses seven avalanche transistors in cascade. Design of a trigger circuit to obtain fast rise time is discussed. The characteristics of the pulser are : (a) Rise time = 0.9 ns (FWHM) and (d) Life time asymptotically equals 2000 -- 3000 hr (at 50 Hz). (author)

  15. Properties of the avalanche photodiodes for the CMS electromagnetic calorimeter

    International Nuclear Information System (INIS)

    The electromagnetic calorimeter of the CMS experiment at CERN's Large Hadron Collider will use 122 400 Avalanche Photodiodes from Hamamatsu Photonics. The design of this APD type is the result of a long R and D program performed by Hamamatsu Photonics and the CMS collaboration. The APD parameters including the behavior under irradiation are discussed in view of our application

  16. Properties of the avalanche photodiodes for the CMS electromagnetic calorimeter

    CERN Document Server

    Deiters, K; Musienko, Yu V; Nicol, S; Patel, P; Renker, D; Reucroft, S; Rusack, R W; Sakhelashvili, T M; Swain, J D; Vikas, P

    2000-01-01

    The electromagnetic calorimeter of the CMS experiment at CERN's Large Hadron Collider will use 122400 avalanche photodiodes from Hamamatsu Photonics. The design of this APD type is the result of a long R&D program performed by Hamamatsu photonics and the CMS Collaboration. The APD parameters including the behavior under irradiation are discussed in view of our application. (4 refs).

  17. Timing properties of parallel plate avalanche counters with light particles

    International Nuclear Information System (INIS)

    We have operated a 15 cm2 parallel plate avalanche counter (PPAC) with protons and α-particles. Time resolution of 140 psec (FWHM) has been measured with 5.5 MeV α-particles at 30 Torr of isobutane. (author)

  18. Optical fibers and avalanche photodiodes for scintillator counters

    International Nuclear Information System (INIS)

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

  19. Catastrophic debris avalanche deposit of Socompa volcano, northern Chile

    Science.gov (United States)

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

    1985-01-01

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

  20. Avalanches in dry and saturated disordered media at fracture

    Science.gov (United States)

    Milanese, Enrico; Yılmaz, Okan; Molinari, Jean-François; Schrefler, Bernhard

    2016-04-01

    This paper analyzes fracturing in inhomogeneous media under dry and fully saturated conditions. We adopt a central force model with continuous damage to study avalanche behavior in a two-dimensional truss lattice undergoing dilation. Multiple fractures can develop at once and a power-law distribution of the avalanche size is observed. The values for the power-law exponent are compared with the ones found in the literature and scale-free behavior is suggested. The fracture evolves intermittently in time because only some avalanches correspond to fracture advancement. A fully saturated model with continuous damage based on the extended Biot's theory is developed and avalanche behavior is studied in the presence of fluid, varying the fluid boundary conditions. We show that power-law behavior is destroyed when the fluid flux governs the problem. Fluid pressure behavior during intermittent crack tip advancement is studied for the continuous-damage fully saturated model. It is found that when mechanical loading prevails, the pressure rises when the crack advances, while when fluid loading prevails, the pressure drops when the crack advances.

  1. Exact velocity of dispersive flow in the asymmetric avalanche process

    OpenAIRE

    Ivashkevich, E. V.; Povolotsky, A. M.; Priezzhev, V.B.

    2000-01-01

    Using the Bethe ansatz we obtain the exact solution for the one-dimensional asymmetric avalanche process. We evaluate the velocity of dispersive flow as a function of driving force and the density of particles. The obtained solution shows a dynamical transition from intermittent to continuous flow.

  2. Avalanches in dry and saturated disordered media at fracture.

    Science.gov (United States)

    Milanese, Enrico; Yılmaz, Okan; Molinari, Jean-François; Schrefler, Bernhard

    2016-04-01

    This paper analyzes fracturing in inhomogeneous media under dry and fully saturated conditions. We adopt a central force model with continuous damage to study avalanche behavior in a two-dimensional truss lattice undergoing dilation. Multiple fractures can develop at once and a power-law distribution of the avalanche size is observed. The values for the power-law exponent are compared with the ones found in the literature and scale-free behavior is suggested. The fracture evolves intermittently in time because only some avalanches correspond to fracture advancement. A fully saturated model with continuous damage based on the extended Biot's theory is developed and avalanche behavior is studied in the presence of fluid, varying the fluid boundary conditions. We show that power-law behavior is destroyed when the fluid flux governs the problem. Fluid pressure behavior during intermittent crack tip advancement is studied for the continuous-damage fully saturated model. It is found that when mechanical loading prevails, the pressure rises when the crack advances, while when fluid loading prevails, the pressure drops when the crack advances. PMID:27176380

  3. Current oscillations in avalanche particle detectors with PNIPN-structure

    International Nuclear Information System (INIS)

    The model of an avalanche high energy particle detector consisting of two pn-junctions, connected through an intrinsic semiconductor with a reverse biased voltage applied. This detector is able to generate the oscillatory response on the single particle passage through the structure. The possibility of oscillations leading to chaotic behaviour is pointed out

  4. SIMULATION OF AVALANCHE PHOTODIODE CONSTRUCTION WITH GUARD AREAS

    Directory of Open Access Journals (Sweden)

    N. N. Koritko

    2015-04-01

    Full Text Available Construction and breakdown voltage of avalanche photodiode with Read diode structure was simulated by computer. It was shown that the guard area construction composed of the metal electrode and guard rings influences on the electrical quantities of n+-p junction breakdown region.

  5. Jet quenching from QCD evolution

    Science.gov (United States)

    Chien, Yang-Ting; Emerman, Alexander; Kang, Zhong-Bo; Ovanesyan, Grigory; Vitev, Ivan

    2016-04-01

    Recent advances in soft-collinear effective theory with Glauber gluons have led to the development of a new method that gives a unified description of inclusive hadron production in reactions with nucleons and heavy nuclei. We show how this approach, based on the generalization of the DGLAP evolution equations to include final-state medium-induced parton shower corrections for large Q2 processes, can be combined with initial-state effects for applications to jet quenching phenomenology. We demonstrate that the traditional parton energy loss calculations can be regarded as a special soft-gluon emission limit of the general QCD evolution framework. We present phenomenological comparison of the SCETG -based results on the suppression of inclusive charged hadron and neutral pion production in √{sNN }=2.76 TeV lead-lead collisions at the Large Hadron Collider to experimental data. We also show theoretical predictions for the upcoming √{sNN }≃5.1 TeV Pb +Pb run at the LHC.

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

    Science.gov (United States)

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

    2009-01-01

    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

  7. Soil erosion and organic carbon export by wet snow avalanches

    Directory of Open Access Journals (Sweden)

    O. Korup

    2014-01-01

    Full Text Available 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.

  8. The dominance of quenching through cosmic times

    Science.gov (United States)

    Renzini, Alvio

    2016-07-01

    The evolution with cosmic time of the star formation rate density (SFRD) and of the main-sequence star formation rate-stellar mass relations are two well-established observational facts. In this Letter, the implications of these two relations combined are analytically explored, showing that quenching of star formation must start already at very early cosmic times and the quenched fraction then dominates ever since over the star-forming one. Thus, a simple picture of the cosmic evolution of the global SFRD is derived, in terms of the interplay between star formation and its quenching.

  9. Quenching phenomena in natural circulation loop

    Energy Technology Data Exchange (ETDEWEB)

    Umekawa, Hisashi; Ozawa, Mamoru [Kansai Univ., Osaka (Japan); Ishida, Naoki [Daihatsu Motor Company, Osaka (Japan)

    1995-09-01

    Quenching phenomena has been investigated experimentally using circulation loop of liquid nitrogen. During the quenching under natural circulation, the heat transfer mode changes from film boiling to nucleate boiling, and at the same time flux changes with time depending on the vapor generation rate and related two-phase flow characteristics. Moreover, density wave oscillations occur under a certain operating condition, which is closely related to the dynamic behavior of the cooling curve. The experimental results indicates that the occurrence of the density wave oscillation induces the deterioration of effective cooling of the heat surface in the film and the transition boiling regions, which results in the decrease in the quenching velocity.

  10. Forensic Analysis of the May 2014 West Salt Creek Rock Avalanche in Western Colorado

    Science.gov (United States)

    Coe, J. A.; Baum, R. L.; Allstadt, K.; Kochevar, B. F.; Schmitt, R. G.; Morgan, M. L.; White, J. L.; Stratton, B. T.; Hayashi, T. A.; Kean, J. W.

    2015-12-01

    The rain-on-snow induced West Salt Creek rock avalanche occurred on May 25, 2014 on the northern flank of Grand Mesa. The avalanche was rare for the contiguous U.S. because of its large size (59 M m3) and high mobility (Length/Height=7.2). To understand the avalanche failure sequence, mechanisms, and mobility, we conducted a forensic analysis using large-scale (1:1000) structural mapping and seismic data. We used high-resolution, Unmanned Aircraft System (UAS) imagery as a base for our field mapping and analyzed seismic data from 22 broadband stations (distances <656 km) and one short-period network. We inverted broadband data to derive a time series of forces that the avalanche exerted on the earth and tracked these forces using curves in the avalanche path. Our results revealed that the rock avalanche was a cascade of landslide events, rather than a single massive failure. The sequence began with a landslide/debris flow that started about 10 hours before the main avalanche. The main avalanche lasted just over 3 minutes and traveled at average velocities ranging from 15 to 36 m/s. For at least two hours after the avalanche ceased movement, a central, hummock-rich, strike-slip bound core continued to move slowly. Following movement of the core, numerous shallow landslides, rock slides, and rock falls created new structures and modified topography. Mobility of the main avalanche and central core were likely enhanced by valley floor material that liquefied from undrained loading by the overriding avalanche. Although the base was likely at least partially liquefied, our mapping indicates that the overriding avalanche internally deformed predominantly by sliding along discrete shear surfaces in material that was nearly dry and had substantial frictional strength. These results indicate that the West Salt Creek avalanche, and probably other long-traveled avalanches, could be modeled as two layers: a liquefied basal layer; and a thicker and stronger overriding layer.

  11. Avalanche Debris Detection Using Satellite- and Drone Based Radar and Optical Remote Sensing

    Science.gov (United States)

    Eckerstorfer, M.; Malnes, E.; Vickers, H.; Solbø, S. A.; Tøllefsen, A.

    2014-12-01

    The mountainous fjord landscape in the county of Troms, around its capital Tromsø in Northern Norway is prone to high avalanche activity during the snow season. Large avalanches pose a hazard to infrastructure, such as buildings and roads, located between the steep mountainsides and the fjords. A prolonged cold spell during January and February 2014 was followed by rapid new-snow loading during March 2014, inducing a significant avalanche cycle with many spontaneous, size D4 avalanches that affected major transport veins. During and shortly after the avalanche cycle of March 2014, we obtained 11 Radarsat-2 Ultrafine mode scenes, chosen according to reported avalanche activity. We further collected four Radarsat-2 ScanSAR mode scenes and two Landsat-8 scenes covering the entire county of Troms. For one particular avalanche, we obtained a drone-based orthophoto, from which a DEM of the avalanche debris surface was derived, using structure-from-motion photogrammetry. This enabled us to calculate the debris volume accurately. We detected avalanche debris in the radar images visually, by applying two detection algorithms that make use of the increased backscatter in avalanche debris. This backscatter increase is a product of increased snow water equivalent and surface roughness, roughly of the order of 3 dB. In addition, we applied a multi-temporal approach by repeatedly detecting avalanche debris at different acquisition times, as well as a multi-sensor approach, covering similar areas with different sensors. This multi-temporal and multi-sensor approach enabled us to map the spatial extent and magnitude of the March 2014 avalanche cycle in the county Troms. With ESA's Sentinel-1 satellite, providing high-resolution, large swath radar images with a short repeat cycle, a complete avalanche record for a forecasting region could become feasible. In this first test season, we detected more than 550 avalanches that were released during a one-month period over an area of

  12. Torus CLAS12-Superconducting Magnet Quench Analysis

    Energy Technology Data Exchange (ETDEWEB)

    Kashikhin, V. S. [Fermilab; Elouadhiri, L. [Jefferson Lab; Ghoshal, P. K. [Jefferson Lab; Kashy, D. [Jefferson Lab; Makarov, A. [Fermilab; Pastor, O. [Jefferson Lab; Quettier, L. [Jefferson Lab; Velev, G. [Fermilab; Wiseman, M. [Jefferson Lab

    2014-01-01

    The JLAB Torus magnet system consists of six superconducting trapezoidal racetrack-type coils assembled in a toroidal configuration. These coils are wound with SSC-36 Nb-Ti superconductor and have the peak magnetic field of 3.6 T. The first coil manufacturing based on the JLAB design began at FNAL. The large magnet system dimensions (8 m diameter and 14 MJ of stored energy) dictate the need for quench protection. Each coil is placed in an aluminum case mounted inside a cryostat and cooled by 4.6 K supercritical helium gas flowing through a copper tube attached to the coil ID. The large coil dimensions and small cryostat thickness drove the design to challenging technical solutions, suggesting that Lorentz forces due to transport currents and eddy currents during quench and various failure scenarios are analyzed. The paper covers the magnet system quench analysis using the OPERA3d Quench code.

  13. History of Giant Resonances and Quenching

    CERN Document Server

    Arima, A

    1999-01-01

    The history of nuclear magnetic moments and Gamow-Teller transitions is reviewed. The importance of configuration mixing and core polarization to explain the quenching phenomena is shown, and discussed in the context of the recent measurement of the Gamow-Teller strength in sup 9 sup 0 Nb. It is confirmed that the contribution of the DELTA-hole excitation to the quenching of spin matrix elements is small.

  14. The surprising inefficiency of dwarf satellite quenching

    CERN Document Server

    Wheeler, Coral; Cooper, Michael C; Boylan-Kolchin, Mike; Bullock, James S

    2014-01-01

    We study dwarf satellite galaxy quenching using observations from the Geha et al. (2012) NSA/SDSS catalog together with LCDM cosmological simulations to facilitate selection and interpretation. We show that fewer than 30% of dwarfs (M* ~ 10^8.5-10^9.5 Msun) identified as satellites within massive host halos (Mhost ~ 10^12.5-10^14 Msun) are quenched, in spite of the expectation from simulations that half of them should have been accreted more than 6 Gyr ago. We conclude that whatever the action triggering environmental quenching of dwarf satellites, the process must be highly inefficient. We investigate a series of simple, one-parameter quenching models in order understand what is required to explain the low quenched fraction and conclude that either the quenching timescale is very long (> 9.5 Gyr, a "slow starvation" scenario) or that the environmental trigger is not well matched to accretion within the virial volume. We discuss these results in light of the fact that most of the low mass dwarf satellites in ...

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

    Science.gov (United States)

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

    2013-12-01

    Two-dimensional avalanche simulation software operating in three-dimensional terrain are widely used for hazard zoning and engineering to predict runout distances and impact pressures of snow avalanche events. Mountain forests are an effective biological protection measure; however, the protective capacity of forests to decelerate or even to stop avalanches that start within forested areas or directly above the treeline is seldom considered in this context. In particular, runout distances of small- to medium-scale avalanches are strongly influenced by the structural conditions of forests in the avalanche path. This varying decelerating effect has rarely been addressed or implemented in avalanche simulation. We present an evaluation and operationalization of a novel forest detrainment modeling approach implemented in the avalanche simulation software RAMMS. The new approach accounts for the effect of forests in the avalanche path by detraining mass, which leads to a deceleration and runout shortening of avalanches. The extracted avalanche mass caught behind trees stops immediately and, therefore, is instantly subtracted from the flow and the momentum of the stopped mass is removed from the total momentum of the avalanche flow. This relationship is parameterized by the empirical detrainment coefficient K [Pa] which accounts for the braking power of different forest types per unit area. To define K dependent on specific forest characteristics, we simulated 40 well-documented small- to medium-scale avalanches which released in and ran through forests with varying K-values. Comparing two-dimensional simulation results with one-dimensional field observations for a high number of avalanche events and simulations manually is however time consuming and rather subjective. In order to process simulation results in a comprehensive and standardized way, we used a recently developed automatic evaluation and comparison method defining runout distances based on a pressure

  16. A new web-based system to improve the monitoring of snow avalanche hazard in France

    Science.gov (United States)

    Bourova, Ekaterina; Maldonado, Eric; Leroy, Jean-Baptiste; Alouani, Rachid; Eckert, Nicolas; Bonnefoy-Demongeot, Mylene; Deschatres, Michael

    2016-05-01

    Snow avalanche data in the French Alps and Pyrenees have been recorded for more than 100 years in several databases. The increasing amount of observed data required a more integrative and automated service. Here we report the comprehensive web-based Snow Avalanche Information System newly developed to this end for three important data sets: an avalanche chronicle (Enquête Permanente sur les Avalanches, EPA), an avalanche map (Carte de Localisation des Phénomènes d'Avalanche, CLPA) and a compilation of hazard and vulnerability data recorded on selected paths endangering human settlements (Sites Habités Sensibles aux Avalanches, SSA). These data sets are now integrated into a common database, enabling full interoperability between all different types of snow avalanche records: digitized geographic data, avalanche descriptive parameters, eyewitness reports, photographs, hazard and risk levels, etc. The new information system is implemented through modular components using Java-based web technologies with Spring and Hibernate frameworks. It automates the manual data entry and improves the process of information collection and sharing, enhancing user experience and data quality, and offering new outlooks to explore and exploit the huge amount of snow avalanche data available for fundamental research and more applied risk assessment.

  17. Custom single-photon avalanche diode with integrated front-end for parallel photon timing applications.

    Science.gov (United States)

    Cammi, C; Panzeri, F; Gulinatti, A; Rech, I; Ghioni, M

    2012-03-01

    Emerged as a solid state alternative to photo multiplier tubes (PMTs), single-photon avalanche diodes (SPADs) are nowadays widely used in the field of single-photon timing applications. Custom technology SPADs assure remarkable performance, in particular a 10 counts/s dark count rate (DCR) at low temperature, a high photon detection efficiency (PDE) with a 50% peak at 550 nm and a 30 ps (full width at half maximum, FWHM) temporal resolution, even with large area devices, have been obtained. Over the past few years, the birth of novel techniques of analysis has led to the parallelization of the measurement systems and to a consequent increasing demand for the development of monolithic arrays of detectors. Unfortunately, the implementation of a multidimensional system is a challenging task from the electrical point of view; in particular, the avalanche current pick-up circuit, used to obtain the previously reported performance, has to be modified in order to enable high parallel temporal resolution, while minimizing the electrical crosstalk probability between channels. In the past, the problem has been solved by integrating the front-end electronics next to the photodetector, in order to reduce the parasitic capacitances and consequently the filtering action on the current signal of the SPAD, leading to an improvement of the timing jitter at higher threshold. This solution has been implemented by using standard complementary metal-oxide-semiconductor (CMOS) technologies, which, however, do not allow a complete control on the SPAD structure; for this reason the intrinsic performance of CMOS SPADs, such as DCR, PDE, and afterpulsing probability, are worse than those attainable with custom detectors. In this paper, we propose a pixel architecture, which enables the development of custom SPAD arrays in which every channel maintains the performance of the best single photodetector. The system relies on the integration of the timing signal pick-up circuit next to the

  18. Custom single-photon avalanche diode with integrated front-end for parallel photon timing applications

    Science.gov (United States)

    Cammi, C.; Panzeri, F.; Gulinatti, A.; Rech, I.; Ghioni, M.

    2012-03-01

    Emerged as a solid state alternative to photo multiplier tubes (PMTs), single-photon avalanche diodes (SPADs) are nowadays widely used in the field of single-photon timing applications. Custom technology SPADs assure remarkable performance, in particular a 10 counts/s dark count rate (DCR) at low temperature, a high photon detection efficiency (PDE) with a 50% peak at 550 nm and a 30 ps (full width at half maximum, FWHM) temporal resolution, even with large area devices, have been obtained. Over the past few years, the birth of novel techniques of analysis has led to the parallelization of the measurement systems and to a consequent increasing demand for the development of monolithic arrays of detectors. Unfortunately, the implementation of a multidimensional system is a challenging task from the electrical point of view; in particular, the avalanche current pick-up circuit, used to obtain the previously reported performance, has to be modified in order to enable high parallel temporal resolution, while minimizing the electrical crosstalk probability between channels. In the past, the problem has been solved by integrating the front-end electronics next to the photodetector, in order to reduce the parasitic capacitances and consequently the filtering action on the current signal of the SPAD, leading to an improvement of the timing jitter at higher threshold. This solution has been implemented by using standard complementary metal-oxide-semiconductor (CMOS) technologies, which, however, do not allow a complete control on the SPAD structure; for this reason the intrinsic performance of CMOS SPADs, such as DCR, PDE, and afterpulsing probability, are worse than those attainable with custom detectors. In this paper, we propose a pixel architecture, which enables the development of custom SPAD arrays in which every channel maintains the performance of the best single photodetector. The system relies on the integration of the timing signal pick-up circuit next to the

  19. Silicon photomultipliers with bulk-integrated quenching resistor: first results of characterization

    International Nuclear Information System (INIS)

    For future experiments in high energy physics detectors with high photon detection efficiencies (PDE) and ability to work in high magnetic fields are in the focus of research. Silicon photomultipliers (SiPM), arrays of Geiger-mode avalanche photodiodes, tend to replace conventional photomultiplier tubes in many applications. Conventional SiPMs use high-ohmic polysilicon as quenching resistor, which forms a barrier for incident light, thus decreasing the PDE. Furthermore it's also one of the cost driving technological issues in fabrication. By integrating the quenching resistor into the silicon bulk obstacles for light within the active area can be omitted and the fill factor of the device is only limited by the gaps necessary for optical crosstalk suppression. So this device is a promising candidate to achieve maximum PDE of up to 70%. In addition the absence of lateral high field regions on surface should improve the radiation hardness of the device. Results of the characterization of the in-house prototype production are presented.

  20. Stability of the discretization of the electron avalanche phenomenon

    Energy Technology Data Exchange (ETDEWEB)

    Villa, Andrea, E-mail: andrea.villa@rse-web.it [Ricerca Sul Sistema Energetico (RSE), Via Rubattino 50, 20134, Milano (Italy); Barbieri, Luca, E-mail: luca.barbieri@rse-web.it [Ricerca Sul Sistema Energetico (RSE), Via Rubattino 50, 20134, Milano (Italy); Gondola, Marco, E-mail: marco.gondola@rse-web.it [Ricerca Sul Sistema Energetico (RSE), Via Rubattino 50, 20134, Milano (Italy); Leon-Garzon, Andres R., E-mail: andresricardo.leon@polimi.it [CMIC Department “Giulio Natta”, Politecnico di Milano, Piazza Leonardo da Vinci 32, 20133, Milano (Italy); Malgesini, Roberto, E-mail: roberto.malgesini@rse-web.it [Ricerca Sul Sistema Energetico (RSE), Via Rubattino 50, 20134, Milano (Italy)

    2015-09-01

    The numerical simulation of the discharge inception is an active field of applied physics with many industrial applications. In this work we focus on the drift-reaction equation that describes the electron avalanche. This phenomenon is one of the basic building blocks of the streamer model. The main difficulty of the electron avalanche equation lies in the fact that the reaction term is positive when a high electric field is applied. It leads to exponentially growing solutions and this has a major impact on the behavior of numerical schemes. We analyze the stability of a reference finite volume scheme applied to this latter problem. The stability of the method may impose a strict mesh spacing, therefore a proper stabilized scheme, which is stable whatever spacing is used, has been developed. The convergence of the scheme is treated as well as some numerical experiments.

  1. Plasma simulation of electron avalanche in a linear thyratron

    International Nuclear Information System (INIS)

    Thyratrons typically operate at sufficiently small PD (pressure x electrode separation) that holdoff is obtained by operating on the near side of the Paschen curve, and by shielding the slot in the control grid so there is no straight line path for electrons to reach the anode from the cathode. Electron avalanche is initiated by pulsing the control grid to a high voltage. Upon collapse of voltage in the cathode-control grid space, the discharge is sustained by penetration of potential through the control grid slot into the cathode-control grid region. To better understand the electron avalanche process in multi-grid and slotted structures such as thyratrons, a plasma simulation code has been constructed. This effort is in support of a companion program in which a linear thyratron is being electrically and spectroscopically characterized

  2. Avalanche effect and gain saturation in high harmonic generation

    CERN Document Server

    Serrat, Carles; Budesca, Josep M; Seres, Jozsef; Seres, Enikoe; Aurand, Bastian; Hoffmann, Andreas; Namba, Shinichi; Kuehl, Thomas; Spielmann, Christian

    2015-01-01

    Optical amplifiers in all ranges of the electromagnetic spectrum exhibit two essential characteristics: i) the input signal during the propagation in the medium is multiplied by the avalanche effect of the stimulated emission to produce exponential growth and ii) the amplification saturates at increasing input signal. We demonstrate that the strong-field theory in the frame of high harmonic generation fully supports the appearance of both the avalanche and saturation effects in the amplification of extreme ultraviolet attosecond pulse trains. We confirm that the amplification takes place only if the seed pulses are perfectly synchronized with the driving strong field in the amplifier. We performed an experimental study and subsequent model calculation on He gas driven by intense 30-fs-long laser pulses, which was seeded with an attosecond pulse train at 110 eV generated in a separated Ne gas jet. The comparison of the performed calculations with the measurements clearly demonstrates that the pumped He gas med...

  3. A compact gas-filled avalanche counter for DANCE

    International Nuclear Information System (INIS)

    A compact gas-filled avalanche counter for the detection of fission fragments was developed for a highly segmented 4π γ-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 α-decay rate up to ∼2.4×108/s are described.

  4. Stability of the discretization of the electron avalanche phenomenon

    International Nuclear Information System (INIS)

    The numerical simulation of the discharge inception is an active field of applied physics with many industrial applications. In this work we focus on the drift-reaction equation that describes the electron avalanche. This phenomenon is one of the basic building blocks of the streamer model. The main difficulty of the electron avalanche equation lies in the fact that the reaction term is positive when a high electric field is applied. It leads to exponentially growing solutions and this has a major impact on the behavior of numerical schemes. We analyze the stability of a reference finite volume scheme applied to this latter problem. The stability of the method may impose a strict mesh spacing, therefore a proper stabilized scheme, which is stable whatever spacing is used, has been developed. The convergence of the scheme is treated as well as some numerical experiments

  5. A compact gas-filled avalanche counter for DANCE

    Science.gov (United States)

    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

    A compact gas-filled avalanche counter for the detection of fission fragments was developed for a highly segmented 4π γ-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 α-decay rate up to ˜2.4×108/s are described.

  6. A compact gas-filled avalanche counter for DANCE

    Energy Technology Data Exchange (ETDEWEB)

    Wu, C.Y., E-mail: wu24@llnl.gov [Lawrence Livermore National Laboratory, Livermore, CA 94551 (United States); Chyzh, A.; Kwan, E.; Henderson, R.A.; Gostic, J.M.; Carter, D. [Lawrence Livermore National Laboratory, Livermore, CA 94551 (United States); Bredeweg, T.A.; Couture, A.; Jandel, M.; Ullmann, J.L. [Los Alamos National Laboratory, Los Alamos, NM 87545 (United States)

    2012-12-01

    A compact gas-filled avalanche counter for the detection of fission fragments was developed for a highly segmented 4{pi} {gamma}-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 {sup 235}U, {sup 238}Pu, {sup 239}Pu, and {sup 241}Pu 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 {sup 252}Cf. The design and performance of this avalanche counter for targets with extreme {alpha}-decay rate up to {approx}2.4 Multiplication-Sign 10{sup 8}/s are described.

  7. Origin of the Avalanche-Like Photoluminescence from Metallic Nanowires

    Science.gov (United States)

    Ma, Zongwei; Yu, Ying; Shen, Shaoxin; Dai, Hongwei; Yao, Linhua; Han, Yibo; Wang, Xia; Han, Jun-Bo; Li, Liang

    2016-01-01

    Surface plasmonic systems provide extremely efficient ways to modulate light-matter interaction in photon emission, light harvesting, energy conversion and transferring, etc. Various surface plasmon enhanced luminescent behaviors have been observed and investigated in these systems. But the origin of an avalanche-like photoluminescence, which was firstly reported in 2007 from Au and subsequently from Ag nanowire arrays/monomers, is still not clear. Here we show, based on systematic investigations including the excitation power/time related photoluminescent measurements as well as calculations, that this avalanche-like photoluminescence is in fact a result of surface plasmon assisted thermal radiation. Nearly all of the related observations could be perfectly interpreted with this concept. Our finding is crucial for understanding the surface plasmon mediated thermal and photoemission behaviors in plasmonic structures, which is of great importance in designing functional plasmonic devices.

  8. 40 CFR 86.327-79 - Quench checks; NOX analyzer.

    Science.gov (United States)

    2010-07-01

    ... 40 Protection of Environment 18 2010-07-01 2010-07-01 false Quench checks; NOX analyzer. 86.327-79... Quench checks; NOX analyzer. (a) Perform the reaction chamber quench check for each model of high vacuum... capillary, and if used, dilution capillary. (c) Quench check as follows: (1) Calibrate the NOX analyzer...

  9. Radiation hard avalanche photodiodes for the CMS detector

    International Nuclear Information System (INIS)

    The avalanche photodiodes, developed by Hamamatsu Photonics in collaboration with CMS, which are to be used to read out the lead tungstate crystals in the barrel part of the CMS electromagnetic calorimeter, are described. The procedures taken to ensure their long-term reliability in the radiation environment expected in CMS are outlined, as well as the studies made to verify the very high reliability required

  10. Simulation of neutron radiation effects in silicon avalanche photodiodes

    OpenAIRE

    Osborne, Mark David

    2000-01-01

    This thesis was submitted for the degree of Doctor of Philosophy and awarded by Brunel University. A new one-dimensional device simulation package developed for the simulation of neutron radiatiol! effects in silicon avalanche photodiodes is described. The software uses a finite difference technique to solve the time-independent semiconductor equations across a user specified structure. Impact ionisation and illumination are included, allowing accurate simulation with minimal assumptions a...

  11. Numerical simulation of neutron radiation effects in avalanche photodiodes

    OpenAIRE

    Osborne, M.; Hobson, PR; Watts, SJ

    2000-01-01

    A new one-dimensional (1-D) device model developed for the simulation of neutron radiation effects in silicon avalanche photodiodes is described. The model uses a finite difference technique to solve the time-independent semiconductor equations across a user specified structure. The model includes impact ionization and illumination allowing accurate simulation with minimal assumptions. The effect of neutron radiation damage is incorporated via the introduction of deep acceptor levels subject ...

  12. Radiation Hard Avalanche Photo-Diodes for the CMS detector

    CERN Document Server

    Antunovic, Z; Deiters, K; Godinovic, N; Ingram, Q; Kuznetsov, A; Musienko, Y; Puljak, I; Reucroft, S; Rusack, R W; Sakhelashvili, T M; Singovsky, A V; Soric, I; Swain, J D

    2003-01-01

    The avalanche photo-diodes, developed by Hamamatsu Photonics in collaboration with CMS, which are to be used to read out the lead tungstate crystals in the barrel part of the CMS electromagnetic calorimeter, are described. The procedures taken to ensure their long term reliability in the radiation environment expected in CMS are outlined, as well as the studies made to verify the very high reliability required.

  13. Radiation hard avalanche photodiodes for the CMS detector

    CERN Document Server

    Antunovic, Z; Deiters, K; Godinovic, N; Ingram, Q; Kuznetsov, A; Musienko, Y; Puljak, I; Renker, D; Reucroft, S; Rusack, R; Sakhelashvili, T M; Singovsky, A V; Soric, I; Swain, J

    2005-01-01

    The avalanche photodiodes, developed by Hamamatsu Photonics in collaboration with CMS, which are to be used to read out the lead tungstate crystals in the barrel part of the CMS electromagnetic calorimeter, are described. The procedures taken to ensure their long-term reliability in the radiation environment expected in CMS are outlined, as well as the studies made to verify the very high reliability required.

  14. Azimuthal spread of the avalanche in proportional chambers

    International Nuclear Information System (INIS)

    The angular distribution of the avalanche around the anode wire in the gas proportional counter is determined by measuring the distribution of positive ions arriving on cathode strips surrounding the anode wire for each single event. The shape and width of the distribution depend on such factors as the gas gain, the anode diameter, the counting gas and the primary ionization density. Effects of these factors are studied systematically, and their importance for practical counter applications is discussed

  15. Automated characterization of single-photon avalanche photodiode

    OpenAIRE

    Aina Mardhiyah M. Ghazali; Audun Nystad Bugge; Sebastien Sauge; Vadim Makarov

    2012-01-01

    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 µW), dark count rate and photon detection efficiency at different bias voltages. The automated characterization routine is implemented in C++ running on a Linux computer. ABSTRAK: Kami melaporkan pencirian pengesan foton tunggal secara automatik b...

  16. A New Positioning Algorithm for Position-Sensitive Avalanche Photodiodes

    OpenAIRE

    Zhang, Jin; Olcott, Peter D.; Levin, Craig S

    2007-01-01

    We are using a novel position sensitive avalanche photodiode (PSAPD) for the construction of a high resolution positron emission tomography (PET) camera. Up to now most researchers working with PSAPDs have been using an Anger-like positioning algorithm involving the four corner readout signals of the PSAPD. This algorithm yields a significant non-linear spatial “pin-cushion” distortion in raw crystal positioning histograms. In this paper, we report an improved positioning algorithm, which com...

  17. Investigation of avalanche photodiodes radiation hardness for baryonic matter studies

    International Nuclear Information System (INIS)

    Modern avalanche photodiodes (APDs) with high gain are good device candidates for light readout from detectors applied in relativistic heavy-ion collision experiments. The results of the investigations of the APDs properties from Zecotek, Ketek, and Hamamatsu manufacturers after irradiation using secondary neutrons from U120M cyclotron facility at NPI of ASCR in Rez are presented. The results of the investigations can be used for the design of the detectors for the experiments at NICA and FAIR

  18. Avalanche multiplication of electrons and holes in cadmium telluride

    CERN Document Server

    Demich, N V

    2001-01-01

    Determination of the ratio of the coefficients of the electrons and holes of the diode structures impact ionization is carried out with the purpose of optimizing the parameters of the avalanche diodes from the cadmium telluride. It is shown experimentally, that the process of the impact ionization in the cadmium telluride is stimulated by holes. The ratio of the coefficients of the holes and electrons impact ionization constitutes approx = 30-40

  19. Avalanche photodiodes as large dynamic range detectors for synchrotron radiation

    International Nuclear Information System (INIS)

    We investigated silicon-based avalanche photodiodes (APDs) as X-ray detectors in terms of their linearity, maximum counting rates, and dynamic range with 8.4 keV synchrotron radiation. Measurements resulted in counting rates that extend from the APD's noise level of 10-2 Hz to saturation counting rates in excess of 108 Hz. In addition, by monitoring the APD's noise level and photon counting efficiency between synchrotron bursts, we demonstrate nine orders of magnitude dynamic range. ((orig.))

  20. Avalanche Merging and Continuous Flow in a Sandpile Model

    OpenAIRE

    Corral, Alvaro; Paczuski, Maya

    1999-01-01

    A dynamical transition separating intermittent and continuous flow is observed in a sandpile model, with scaling functions relating the transport behaviors between both regimes. The width of the active zone diverges with system size in the avalanche regime but becomes very narrow for continuous flow. The change of the mean slope, Delta z, on increasing the driving rate, r, obeys Delta z ~ r^{1/theta}. It has nontrivial scaling behavior in the continuous flow phase with an exponent theta given...

  1. Signal and Noise Properties of Position-Sensitive Avalanche Photodiodes

    OpenAIRE

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

    2011-01-01

    After many years of development, position-sensitive avalanche photodiodes (PSAPDs) are now being incorporated into a range of scintillation detector systems, including those used in high-resolution small-animal PET and PET/MR scanners. In this work, the signal, noise, signal-to-noise ratio (SNR), flood histogram and timing resolution were measured for lutetium oxyorthosilicate (LSO) scintillator arrays coupled to PSAPDs ranging in size from 10–20 mm, and the optimum bias voltage and working t...

  2. Quench Protection of DI-BSCCO Coil

    Science.gov (United States)

    Yamaguchi, T.; Ueno, E.; Kato, T.; Hayashi, K.

    Quench protection is one of the most important requirements for the practical application of high-temperature-superconducting (HTS) coils. Quench protection requires that early detection of a developing quench event is followed by rapid reduction of the operating current. However, such quench detection is very difficult because HTS wire produces heat only locally due to the very slow propagation velocity of a normal zone. Excellent high voltage insulation performance is required if the current is to be reduced rapidly in a large-scale superconducting application with very large inductance. Thus it is important to investigate the behavior of coils with various decay time constants, and to detect voltages on very short time scales. This goal remains to be achieved. In the present study we built test coil and a full-scale pole coil for a 20 MW motor for use in experiments on quench protection, and parameterized the relation between the decay time constant and the detecting voltage, using a conventional balance circuit to detect the quench, which was generated by gradually raising the temperature of the coils. The results verify that a balance circuit can be used for quench detection. For example, when the current decay time constant is 4 seconds, the test coil can be protected even with a detecting voltage of 0.15 volts, despite a significant heat production rate of 126 W. We also confirmed that the full-scale pole coil, with a decay time constant of 20 seconds, can be protected with a detecting voltage of 0.06 V.

  3. Wave form of current quench during disruptions in tokamaks

    International Nuclear Information System (INIS)

    The time dependence of the current decay during the current quench phase of disruptions, which can significantly influence the electro-magnetic force on the in-vessel components due to the induced eddy currents, is investigated using data obtained in JT-60U experiments in order to derive a relevant physics guideline for the predictive simulations of disruptions in ITER. It is shown that an exponential decay can fit the time dependence of current quench for discharges with large quench rate (fast current quench). On the other hand, for discharges with smaller quench rate (slow current quench), a linear decay can fit the time dependence of current quench better than exponential. (author)

  4. Automated Characterization of Single-Photon Avalanche Photodiode

    Directory of Open Access Journals (Sweden)

    Aina Mardhiyah M. Ghazali

    2012-01-01

    Full Text Available 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 µW, dark count rate and photon detection efficiency at different bias voltages. The automated characterization routine is implemented in C++ running on a Linux computer. ABSTRAK: Kami melaporkan pencirian pengesan foton tunggal secara automatik berdasarkan kepada diod foto runtuhan silikon (silicon avalanche photodiode (PerkinElmer C30902SH komersial. Pencirian  diod foto adalah berdasarkan kepada plot arus-voltan (I-V pada tahap pencahayaan yang berbeza (kelam - tanpa cahaya, 10pW, dan 10µW, kadar bacaan latar belakang, kecekapan pengesanan foton pada voltan picuan yang berbeza. Pengaturcaraan C++ digunakan di dalam rutin pencirian automatik melalui komputer dengan sistem pengendalian LINUX.KEYWORDS: avalanche photodiode (APD; single photon detector; photon counting; experiment automation

  5. First Townsend coefficient of organic vapour in avalanche counters

    International Nuclear Information System (INIS)

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

  6. Effects of quenching and partial quenching on QCD penguin matrix elements

    NARCIS (Netherlands)

    Golterman, Maarten; Pallante, Elisabetta

    2002-01-01

    We point out that chiral transformation properties of penguin operators change in the transition from unquenched to (partially) quenched QCD. The way in which this affects the lattice determination of weak matrix elements can be understood in the framework of (partially) quenched chiral perturbation

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

    International Nuclear Information System (INIS)

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

  8. Degraded core quench: a status report

    International Nuclear Information System (INIS)

    An important accident management measure for controlling severe accident transients in light water reactors (LWRs) is the injection of water to cool the degrading core. This report for the CSNI summarises the status of experimental and theoretical knowledge of fuel behaviour aspects concerning the quench of degraded cores, where the fuel rods are in a mainly rod-like geometry at the time of quench; consideration of quench of late phase core configurations such as debris beds is outside its scope. Initially the review addresses thermal hydraulic aspects of reflood and quenching in non-degraded reactor cores, this is relevant because the models developed here are often extrapolated into the severe accident regime. The review then considers the phenomena exhibited in the bundle experiments LOFT LP-FP-2, PBF SFD-ST, and the CORA tests 12, 13 and 17. Following this, the extent to which the experimental knowledge has been translated into computer models is considered by reviewing the status of the treatment of quench in four major code systems; SCDAP/RELAP5, ICARE/CATHARE, ATHLET-CD/KESS and MELCOR

  9. Thermodynamic analysis of pressure-quenching process

    International Nuclear Information System (INIS)

    Pressure-induced amorphization of metal alloy is a new subject which has just begun at the Institute of Solid Physics (Russia). The Cd-Sb system has three stoichiometric compounds at atmospheric pressure. CdSb is a stable phase, while Cd3Sb2 and Cd4Sb3 are metastable at room temperature. The addition of Sb to Cd makes the melting temperature of the alloy fall as the pressure increases at lower pressure. So, there exists a critical pressure, which increases with the increasing of content of Sb, and if Sb > 50%, the melting point decreases with an increase of pressure throughout the process. In this study, a Cd43Sb57 matrix alloy was prepared by melting pure cadmium (99.99%) and antimony (99.99%) in an evacuated silica tube. The tube with the alloy was heated to 943K, kept for 5 min at this temperature, then quenched in water to avoid segregation. The specimen was annealed at 523 K for 100 h. The phase transformation of the pressure-quenched specimen was examined by a micro-area diffraction unit at different times, which shows the crystalline samples, treated by the pressure quenching technique, were amorphizated spontaneously at room temperature. It can be seen that the pressure-quenched metastable phase (PQMP) is different from the original phase, and the pressure quenching process results in a new phase transformation different from that at atmospheric pressure

  10. The quenched spectrum with staggered fermions

    International Nuclear Information System (INIS)

    In this paper we present results for the hadron spectrum in the quenched approximation using staggered fermions. Pinning down the quenched spectrum is an important step in the program of using lattice calculations to extract physically useful quantities. If we cannot extract the masses of the lightest few states with small errors, and make reliable extrapolations to zero quark mass, then calculations of more complicated quantities are suspect. Furthermore, we would like to know how well the quenched approximation reproduces the physical spectrum, for this gives us some indication of the trustworthiness of other quenched calculations. We present results for the spectrum of QCD in the quenched approximation using staggered fermions at β = 5.7, 6.0 and 6.2. We use extended wall sources, which give a better projection onto the ground state, and allow us to study many non-local pion and rho states, as well as the Delta baryon. Staggered flavor symmetry breaking reduces dramatically from β = 5.7 to 6.2. For β = 6, the ratio mN/mp lies significantly below 1.5 for mq s. At β = 6 we study finite volume effects using 163 x 40 and 243 x 40 lattices. We reanalyze our old data at β = 6.2 and resolve the problem of the anomalously light scalar state. 20 refs., 19 figs., 11 tabs

  11. Spatial aspects of vulnerability and risk resulting from snow avalanches

    Science.gov (United States)

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

    2012-04-01

    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

  12. Estimating bulk rheological properties of flowing snow avalanches from field data

    OpenAIRE

    Ancey, C.; Meunier, M.

    2004-01-01

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

  13. On possibilities of application of Miller formula for determination of parameters of Micropixel Avalanche Photodiodes

    CERN Document Server

    Sadygov, Z; Akhmedov, G; Akhmedov, F; Mukhtarov, R; Sadygov, A; Titov, A; Zhezher, V

    2014-01-01

    Miller formula modified to take into account voltage drop on serial resistor of an avalanche photodiode is considered. It is proven by experimental data that modified Miller formula can describe operation of both regular and micropixel avalanche photodiodes with good enough precision. It is shown that operation parameters of the devices can be determined using a linear extrapolation of the voltage-current curve for both regular avalanche photodiode and the one operating in Geiger mode.

  14. Avalanche dynamics in Bak-Sneppen evolution model observed with standard distribution width of fitness

    OpenAIRE

    Lee, Chaohong; Zhu, Xiwen; Gao, Kelin

    2001-01-01

    We introduce the standard distribution width of fitness to characterize the global and individual features of a ecosystem in the Bak-Sneppen evolution model. Through tracking this quantity in evolution, a different hierarchy of avalanche dynamics, $w_{0}$ avalanche is observed. The corresponding gap equation and the self-organized threshold $w_{c}$ are obtained. The critical exponents $\\tau ,$ $\\gamma $and $\\rho $, which describe the behavior of the avalanche size distribution, the average av...

  15. Magnitude-Frequency Distribution of Hummocks on Rockslide-Debris Avalanche Deposits and Its Geomorphological Significance

    OpenAIRE

    Hidetsugu Yoshida

    2016-01-01

    A magnitude-frequency analysis of rockslide-debris avalanche deposits was performed. Hummocks are conical mounds formed in debris avalanche deposits from the catastrophic sector collapse of a mountain (often volcanic) that represent relatively cohesive fragments of the mountain edifice. Examination of 17 debris avalanche deposits in Japan and the Philippines showed that, in general, the larger the magnitude of the hummocks, the smaller their frequency. Hummocks followed an exponential distrib...

  16. Estimating the avalanche contribution to the mass balance of debris covered glaciers

    OpenAIRE

    Banerjee, A.; Shankar, R.

    2014-01-01

    Avalanche from high head walls dominates the net accumulation in many debris covered glaciers in the Himalaya. These avalanche contributions are difficult to directly measure and may cause a systematic bias in glaciological mass balance measurements. In this paper we develop a method to estimate the avalanche contribution using available data, within the context of an idealised flowline model of the glacier. We focus on Hamtah glacier in Western Himalaya ...

  17. Smoothing of sandpile surfaces after intermittent and continuous avalanches: three models in search of an experiment

    OpenAIRE

    Biswas, Parthapratim; Majumdar, Arnab; Mehta, Anita; Bhattacharjee, J K

    1997-01-01

    We present and analyse in this paper three models of coupled continuum equations all united by a common theme: the intuitive notion that sandpile surfaces are left smoother by the propagation of avalanches across them. Two of these concern smoothing at the `bare' interface, appropriate to intermittent avalanche flow, while one of them models smoothing at the effective surface defined by a cloud of flowing grains across the `bare' interface, which is appropriate to the regime where avalanches ...

  18. Dynamical quenching of tunneling in molecular magnets

    International Nuclear Information System (INIS)

    It is shown that a single molecular magnet placed in a rapidly oscillating magnetic field displays the phenomenon of quenching of tunneling processes. The results open a way to manipulate the quantum states of molecular magnets by means of radiation in the terahertz range. Our analysis separates the time evolution into slow and fast components thereby obtaining an effective theory for the slow dynamics. This effective theory presents quenching of the tunnel effect, in particular, stands out its difference with the so-called coherent destruction of tunneling. We support our prediction with numerical evidence based on an exact solution of Schrödinger's equation. - Highlights: • Single molecular magnets under rapidly oscillating magnetic fields is studied. • It is shown that this system displays the quenching of tunneling processes. • Our findings provide a control of quantum molecular magnets via terahertz radiation

  19. Dynamical quenching of tunneling in molecular magnets

    Energy Technology Data Exchange (ETDEWEB)

    José Santander, María, E-mail: maria.jose.noemi@gmail.com [Recursos Educativos Quántica, Santiago (Chile); Departamento de Física, Universidad de Santiago de Chile and CEDENNA, Avda. Ecuador 3493, Santiago (Chile); Nunez, Alvaro S., E-mail: alnunez@dfi.uchile.cl [Departamento de Física, Facultad de Ciencias Físicas y Matemáticas, Universidad de Chile, Casilla 487-3, Santiago (Chile); Roldán-Molina, A. [Instituto de Física, Pontificia Universidad Católica de Valparaíso, Avenida Universidad 330, Curauma, Valparaíso (Chile); Troncoso, Roberto E., E-mail: r.troncoso.c@gmail.com [Centro para el Desarrollo de la Nanociencia y la Nanotecnología, CEDENNA, Avda. Ecuador 3493, Santiago 9170124 (Chile); Departamento de Física, Universidad Técnica Federico Santa María, Avenida España 1680, Valparaíso (Chile)

    2015-12-15

    It is shown that a single molecular magnet placed in a rapidly oscillating magnetic field displays the phenomenon of quenching of tunneling processes. The results open a way to manipulate the quantum states of molecular magnets by means of radiation in the terahertz range. Our analysis separates the time evolution into slow and fast components thereby obtaining an effective theory for the slow dynamics. This effective theory presents quenching of the tunnel effect, in particular, stands out its difference with the so-called coherent destruction of tunneling. We support our prediction with numerical evidence based on an exact solution of Schrödinger's equation. - Highlights: • Single molecular magnets under rapidly oscillating magnetic fields is studied. • It is shown that this system displays the quenching of tunneling processes. • Our findings provide a control of quantum molecular magnets via terahertz radiation.

  20. Thermal quench at finite 't Hooft coupling

    Directory of Open Access Journals (Sweden)

    H. Ebrahim

    2016-03-01

    Full Text Available Using holography we have studied thermal electric field quench for infinite and finite 't Hooft coupling constant. The set-up we consider here is D7-brane embedded in (α′ corrected AdS-black hole background. It is well-known that due to a time-dependent electric field on the probe brane, a time-dependent current will be produced and it will finally relax to its equilibrium value. We have studied the effect of different parameters of the system on equilibration time. As the most important results, for massless fundamental matter, we have observed a universal behaviour in the rescaled equilibration time in the very fast quench regime for different values of the temperature and α′ correction parameter. It seems that in the slow quench regime the system behaves adiabatically. We have also observed that the equilibration time decreases in finite 't Hooft coupling limit.

  1. IFKIS - a basis for managing avalanche risk in settlements and on roads in Switzerland

    Directory of Open Access Journals (Sweden)

    M. Bründl

    2004-01-01

    Full Text Available After the avalanche winter of 1999 in Switzerland, which caused 17 deaths and damage of over CHF 600 mill. in buildings and on roads, the project IFKIS, aimed at improving the basics of organizational measures (closure of roads, evacuation etc. in avalanche risk management, was initiated. The three main parts of the project were the development of a compulsory checklist for avalanche safety services, a modular education and training course program and an information system for safety services. The information system was developed in order to improve both the information flux between the national centre for avalanche forecasting, the Swiss Federal Institute for Snow and Avalanche Research SLF, and the local safety services on the one hand and the communication between avalanche safety services in the communities on the other hand. The results of this project make a valuable contribution to strengthening organizational measures in avalanche risk management and to closing the gaps, which became apparent during the avalanche winter of 1999. They are not restricted to snow avalanches but can also be adapted for dealing with other natural hazard processes and catastrophes.

  2. Fluorescence quenching of flavins by reductive agents

    Science.gov (United States)

    Penzkofer, A.; Bansal, A. K.; Song, S.-H.; Dick, B.

    2007-07-01

    The fluorescence behaviour of the flavins riboflavin, flavin mononucleotide (FMN), flavin adenine dinucleotide (FAD), and lumiflavin in aqueous solution at pH 8 in the presence of the reducing agents β-mercaptoethanol (β-ME), dithiothreitol (DTT), and sodium nitrite (NaNO 2) is studied under aerobic conditions. The fluorescence quantum yields and fluorescence lifetimes are determined as a function of the reducing agent concentration. For all three reducing agents diffusion controlled dynamic fluorescence quenching is observed which is thought to be due to photo-induced reductive electron transfer. For DTT additionally static fluorescence quenching occurs.

  3. Soliton splitting in quenched classical integrable systems

    Science.gov (United States)

    Gamayun, O.; Semenyakin, M.

    2016-08-01

    We take a soliton solution of a classical non-linear integrable equation and quench (suddenly change) its non-linearity parameter. For that we multiply the amplitude or the width of a soliton by a numerical factor η and take the obtained profile as a new initial condition. We find the values of η for which the post-quench solution consists of only a finite number of solitons. The parameters of these solitons are found explicitly. Our approach is based on solving the direct scattering problem analytically. We demonstrate how it works for Korteweg–de Vries, sine-Gordon and non-linear Schrödinger integrable equations.

  4. Fluorescence quenching of flavins by reductive agents

    Energy Technology Data Exchange (ETDEWEB)

    Penzkofer, A. [Institut II - Experimentelle und Angewandte Physik, Universitaet Regensburg, Universitaetsstrasse 31, D-93053 Regensburg (Germany)], E-mail: alfons.penzkofer@physik.uni-regensburg.de; Bansal, A.K. [Institut II - Experimentelle und Angewandte Physik, Universitaet Regensburg, Universitaetsstrasse 31, D-93053 Regensburg (Germany); Song, S.-H.; Dick, B. [Institut fuer Physikalische und Theoretische Chemie, Universitaet Regensburg, Universitaetsstrasse 31, 93053 Regensburg (Germany)

    2007-07-09

    The fluorescence behaviour of the flavins riboflavin, flavin mononucleotide (FMN), flavin adenine dinucleotide (FAD), and lumiflavin in aqueous solution at pH 8 in the presence of the reducing agents {beta}-mercaptoethanol ({beta}-ME), dithiothreitol (DTT), and sodium nitrite (NaNO{sub 2}) is studied under aerobic conditions. The fluorescence quantum yields and fluorescence lifetimes are determined as a function of the reducing agent concentration. For all three reducing agents diffusion controlled dynamic fluorescence quenching is observed which is thought to be due to photo-induced reductive electron transfer. For DTT additionally static fluorescence quenching occurs.

  5. Event-Shape Engineering and Jet Quenching

    CERN Document Server

    Christiansen, Peter

    2016-01-01

    Event-Shape Engineering (ESE) is a tool that enables some control of the initial geometry in heavy-ion collisions in a similar way as the centrality enables some control of the number of participants. Utilizing ESE, the path length in and out-of plane can be varied while keeping the medium properties (centrality) fixed. In this proceeding it is argued that this provides additional experimental information about jet quenching. Finally, it is suggested that if ESE studies are done in parallel for light and heavy quarks one can determine, in a model independent way, if the path-length dependence of their quenching differs.

  6. Laser surface quench processing of zirconium alloys

    International Nuclear Information System (INIS)

    Zircaloys (Zr-Sn alloys) undergo, in high temperature aqueous medium, a non-uniform corrosion of nodular form. Numerous works show that a best behavior can be got with quench structures. They show meanwhile less good characteristics than structures of α work-hardening type; superficial thermal process is a good compromise. Laser beams allow localized depositions of large quantities of energy in particularly short times. In this study, thermal process conditions are given, together with a parametric study (beam-matter interaction), an application to the surface process of thin products, and a complete characterization of the quenched structures

  7. Entanglement negativity after a global quantum quench

    International Nuclear Information System (INIS)

    We study the time evolution of the logarithmic negativity after a global quantum quench. In a 1 + 1-dimensional conformal invariant field theory, we consider the negativity between two intervals which can be either adjacent or disjoint. We show that the negativity follows the quasi-particle interpretation for the spreading of entanglement. We check and generalise our findings with a systematic analysis of the negativity after a quantum quench in the harmonic chain, highlighting two peculiar lattice effects: the late birth and the sudden death of entanglement. (paper)

  8. Quenching of hadron spectra in media

    International Nuclear Information System (INIS)

    We determine how the yield of large transverse momentum hadrons is modified due to induced gluon radiation off a hard parton traversing a QCD medium. The quenching factor is formally a collinear- and infrared-safe quantity and can be treated perturbatively. In spite of that, in the pperpendicular region of practical interest, its value turns out to be extremely sensitive to large distances and can be used to unravel the properties of dense quark-gluon final states produced in heavy ion collisions. We also find that the quenching is not given by a simple shift of the hard parton cross section by the mean energy loss. (author)

  9. Probing Klein tunnelling through quantum quenches

    International Nuclear Information System (INIS)

    We study the interplay between an inhomogeneous quantum quench of the external potential in a system of relativistic fermions in one-dimension and the well-known Klein tunneling. We find that the large time evolution is characterized by particle production at a constant rate which we derive analytically. The produced particles can be physically interpreted according to a semiclassical picture and the state reached in the long time limit can be classified as a non-equilibrium-steady-state. Such a quantum quench can be used in order to observe macroscopic effects of Klein tunneling in transport, with potential implementations with current experimental setups. (paper)

  10. Experimental study of stable imbibition displacements in a model open fracture. I. Local avalanche dynamics

    Science.gov (United States)

    Clotet, Xavier; Ortín, Jordi; Santucci, Stéphane

    2016-01-01

    We report the results of an experimental investigation of the spatiotemporal dynamics of stable imbibition fronts in a disordered medium, in the regime of capillary disorder, for a wide range of experimental conditions. We have used silicone oils of various viscosities μ and nearly identical oil-air surface tension and forced them to slowly invade a model open fracture at different constant flow rates v . In this first part of the study we have focused on the local dynamics at a scale below the size of the quenched disorder. Changing μ and v independently, we have found that the dynamics is not simply controlled by the capillary number Ca˜μ v . Specifically, we have found that the wide statistical distributions of local front velocities, and their large spatial correlations along the front, are indeed controlled by the capillary number Ca. However, local velocities exhibit also very large temporal correlations, and these correlations depend more strongly on the mean imposed velocity v than on the viscosity μ of the invading fluid. Correlations between local velocities lead to a burstlike dynamics. Avalanches, defined as clusters of large local velocities, follow power-law distributions—both in size and duration—with exponential cutoffs that diverge as Ca→0 , the pinning-depinning transition of stable imbibition displacements. Large data sets have led to reliable statistics, from which we have derived accurate values of critical exponents of the relevant power-law distributions. We have investigated also the dependence of their cutoffs on μ and v and related them to the autocorrelations of local velocities in space and time.

  11. Fluorescence quenching of TMR by guanosine in oligonucleotides

    Institute of Scientific and Technical Information of China (English)

    QU Peng; CHEN XuDong; ZHOU XiaoXue; LI Xun; ZHAO XinSheng

    2009-01-01

    Nucleotide-specific fluorescence quenching in fluorescently labeled DNA has many applications in biotechnology. We have studied the inter- and intra-molecular quenching of tetramethylrhodamine (TMR) by nucleotides to better understand their quenching mechanism and influencing factors. In agreement with previous work, dGMP can effectively quench TMR, while the quenching of TMR by other nucleotides is negligible. The Stern-Volmer plot between TMR and dGMP delivers a bimolecular quenching constant of Ks= 52.3 M~(-1). The fluorescence of TMR in labeled oligonucleotides decreases efficiently through photoinduced electron transfer by guanosine. The quenching rate constant between TMR and guanosine was measured using fluorescence correlation spectroscopy (FCS). In addition, our data show that the steric hindrance by bases around guanosine has significant effect on the G-quenching. The availability of these data should be useful in designing fluorescent oligonucleotides and understanding the G-quenching process.

  12. Fluorescence quenching of TMR by guanosine in oligonucleotides

    Institute of Scientific and Technical Information of China (English)

    2009-01-01

    Nucleotide-specific fluorescence quenching in fluorescently labeled DNA has many applications in biotechnology. We have studied the inter-and intra-molecular quenching of tetramethylrhodamine (TMR) by nucleotides to better understand their quenching mechanism and influencing factors. In agreement with previous work, dGMP can effectively quench TMR, while the quenching of TMR by other nucleotides is negligible. The Stern-Volmer plot between TMR and dGMP delivers a bimolecular quenching constant of Ks=52.3 M-1. The fluorescence of TMR in labeled oligonucleotides decreases efficiently through photoinduced electron transfer by guanosine. The quenching rate constant between TMR and guanosine was measured using fluorescence correlation spectroscopy (FCS). In addition, our data show that the steric hindrance by bases around guanosine has significant effect on the G-quenching. The availability of these data should be useful in designing fluorescent oligonucleotides and understanding the G-quenching process.

  13. Quench detection and behaviour in case of quench in the ITER magnet systems

    International Nuclear Information System (INIS)

    The quench of one of the ITER magnet system is an irreversible transition from superconducting to normal resistive state, of a conductor. This normal zone propagates along the cable in conduit conductor dissipating a large power. The detection has to be fast enough to dump out the magnetic energy and avoid irreversible damage of the systems. The primary quench detection in ITER is based on voltage detection, which is the most rapid detection. The very magnetically disturbed environment during the plasma scenario makes the voltage detection particularly difficult, inducing large inductive components in the coils and voltage compensations have to be designed to discriminate the resistive voltage associated with the quench. A conceptual design of the quench detection based on voltage measurements is proposed for the three majors magnet systems of ITER. For this, a clear methodology was developed. It includes the classical hot spot criterion, the quench propagation study using the commercial code Gandalf and the careful estimation of the inductive disturbances by developing the TrapsAV code. Specific solutions have been proposed for the compensation in the three ITER magnet systems and for the quench detection parameters, which are the voltage threshold (in the range of 0.1 V - 0.55 V) and the holding time (in the range of 1-1.4 s). The selected values, in particular the holding time, are sufficiently high to ensure the reliability of the system and avoid fast safety discharges not induced by a quench, which is a classical problem. (author)

  14. Validation of Quench Simulation and Simulation of the TWIN Solenoid

    CERN Document Server

    Pots, Rosalinde Hendrika

    2015-01-01

    For the Future Circular Collider at CERN a multi-purpose detector is proposed. The 6T TWIN Solenoid, a very large magnet system with a stored energy of 53 GJ, is being designed. It is important to protect the magnet against quenches in the system. Therefore several existing quench protection systems are evaluated and simulations have be performed on quenches in the TWIN Solenoid. The simulations on quenches in the TWIN Solenoid have been performed with promising results; the hotspot temperatures do not exceed 120 K and layer to layer voltages stay below 500 V. Adding quench heaters to the system might improve the quench protection system further.

  15. LHC BFPP Quench Test with Ions (2015)

    CERN Document Server

    Schaumann, Michaela; Bahamonde Castro, Cristina; Auchmann, Bernhard; Chetvertkova, Vera; Giachino, Rossano; Jowett, John; Kalliokoski, Matti; Lechner, Anton; Mertens, Tom; Ponce, Laurette; CERN. Geneva. ATS Department

    2016-01-01

    The 2015 Pb-Pb collision run of the LHC operated at a beam energy of 6.37Z TeV. The power of the secondary beams emitted from the interaction point by the bound-free pair production (BFPP) process reached new levels while the propensity of the bending magnets to quench is higher at the new magnetic field levels. This beam power is about 70 times greater than that contained in the luminosity debris and is focussed on a specific location. As long foreseen, orbit bumps were introduced in the dispersion suppressors around the highest luminosity experiments to mitigate the risk of quenches by displacing and spreading out these losses. Because the impact position and intensity of these secondary beams is well known and can be tracked easily with the Beam Loss Monitors (BLMs), the BFPP1 beam (208Pb81+ ions), which is the most intense, provides a tool to accurately measure the steady state quench limit of the LHC main dipoles. At the moment the exact quench limit is not known, but this knowledge is important to asses...

  16. Calculating Quench Propagation with ANSYS(regsign)

    International Nuclear Information System (INIS)

    A commercial Finite-Element-Analysis program, ANSYS(regsign), is widely used in structural and thermal analysis. With the program's ability to include non-linear material properties and import complex CAD files, one can generate coil geometries and simulate quench propagation in superconducting magnets. A 'proof-of-principle' finite element model was developed assuming a resistivity that increases linearly from zero to its normal value at a temperature consistent with the assumed B magnetic field. More sophisticated models could easily include finer-grained coil, cable, structural, and circuit details. A quench is provoked by raising the temperature of an arbitrary superconducting element above its Tc. The time response to this perturbation is calculated using small time-steps to allow convergence between steps. Snapshots of the temperature and voltage distributions allow examination of longitudinal and turn-to-turn quench propagation, quench-front annihilation, and cryo-stability. Modeling details are discussed, and a computed voltage history was compared with measurements from a recent magnet test.

  17. An Iodine Fluorescence Quenching Clock Reaction

    Science.gov (United States)

    Weinberg, Richard B.; Muyskens, Mark

    2007-01-01

    Clock reactions based upon competing oxidation and reduction reactions of iodine and starch as the most popular type of chemistry example is presented to illustrate the redox phenomena, reaction kinetics, and principles of chemical titration. The examination of the photophysical principles underlying the iodine fluorescence quenching clock…

  18. Partial quenching and chiral symmetry breaking

    OpenAIRE

    Creutz, Michael

    2014-01-01

    Partially quenched chiral perturbation theory assumes that valence quarks propagating on gauge configurations prepared with sea quarks of different masses will form a chiral condensate as the valence quark mass goes to zero. I present a counterexample involving non-degenerate sea quarks where the valence condensate does not form.

  19. Martian Dust Devil Electron Avalanche Process and Associated Electrochemistry

    Science.gov (United States)

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

    2010-01-01

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

  20. Subsampling effects in neuronal avalanche distributions recorded in vivo

    Directory of Open Access Journals (Sweden)

    Munk Matthias HJ

    2009-04-01

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

  1. Electron-avalanche amplifier based on the electronic Venturi effect

    Science.gov (United States)

    Taubert, D.; Schinner, G. J.; Tranitz, H. P.; Wegscheider, W.; Tomaras, C.; Kehrein, S.; Ludwig, S.

    2010-10-01

    Scattering of otherwise ballistic electrons far from equilibrium is investigated in a cold two-dimensional electron system. The interaction between excited electrons and the degenerate Fermi liquid induces a positive charge in a nanoscale region which would be negatively charged for diffusive transport at local thermal equilibrium. In a three-terminal device we observe avalanche amplification of electrical current, resulting in a situation comparable to the Venturi effect in hydrodynamics. Numerical calculations using a random-phase approximation are in agreement with our data and suggest Coulomb interaction as the dominant scattering mechanism.

  2. Avalanches properties in a self-organized critical transport model

    International Nuclear Information System (INIS)

    We have proposed a one-dimensional transport model based on critical-gradient fluctuation dynamics to describe some of the properties of plasma turbulence induced transport. This model has the characteristic properties of a self-organized critical (SOC) system. In this model, the flux is self-regulated by the stability properties of the fluctuations. A high-gradient edge region emerges where transport dynamics is close to marginal stability. The core remains at the subcritical gradient that is typical of a SOC system. Avalanches are quasi-periodic events triggered mostly near the edge region. (author)

  3. Low-temperature performance of a large area avalanche photodiode

    International Nuclear Information System (INIS)

    A Large Area Avalanche Photodiode was studied, aiming to access its performance as light detector at low temperatures, down to -80 deg. C. The excess noise factor, F, was measured and found to be approximately independent of the temperature. A linear dependence of F on the APD gain with a slope of 0.00239±0.00008 was observed for gains >100. The detection of low intensity light pulses, producing only a few primary electron-hole pairs in the photodiode, is reported

  4. Simulation of a flowing snow avalanche using molecular dynamics

    OpenAIRE

    Güçer, Denizhan; ÖZGÜÇ, Halil Bülent

    2014-01-01

    This paper presents an approach for the modeling and simulation of a flowing snow avalanche, which is formed of dry and liquefied snow that slides down a slope, using molecular dynamics and the discrete element method. A particle system is utilized as a base method for the simulation and marching cubes with real-time shaders are employed for rendering. A uniform grid-based neighbor search algorithm is used for collision detection for interparticle and particle-terrain interactions. A mass-spr...

  5. AvaDrone: An Autonomous Drone for Avalanche Victim Recovery

    OpenAIRE

    Dickensheets, Benjamin D.

    2015-01-01

    For the 179 Americans that are caught in avalanches each year, timely recovery often means the difference between life and death. The goal of this project was to design and build a prototype drone for a system to quickly and automatically locate a buried victim, using an on-board antenna to receive a signal from industry standard transmitting beacons. The design was based on a quad-rotor platform and uses Arduino hardware to receive a beacon signal and navigate the craft. In broad strokes...

  6. Parallel-plate avalanche detectors with anode wire grids

    International Nuclear Information System (INIS)

    A fission-fragment detection system was designed and built at The George Washington University, to be used in photofission experiments at the Saskatchewan Accelerator Laboratory and the Jefferson Laboratory. The fission fragments were detected using parallel-plate avalanche detectors with anode wire grids. An array of several target-detector pairs was mounted inside a low-pressure reaction chamber. The results of calibrations of the detectors using a 252Cf source and their performance with a bremsstrahlung photon beam during the experiments are presented

  7. Parallel-plate avalanche detectors with anode wire grids

    CERN Document Server

    Sanabria, J C; Cetina, C; Cole, P L; Dodge, W R; Nedorezov, V G; Sudov, A S; Kezerashvili, G Ya

    2000-01-01

    A fission-fragment detection system was designed and built at The George Washington University, to be used in photofission experiments at the Saskatchewan Accelerator Laboratory and the Jefferson Laboratory. The fission fragments were detected using parallel-plate avalanche detectors with anode wire grids. An array of several target-detector pairs was mounted inside a low-pressure reaction chamber. The results of calibrations of the detectors using a sup 2 sup 5 sup 2 Cf source and their performance with a bremsstrahlung photon beam during the experiments are presented.

  8. Double screening tests of the CMS ECAL avalanche photodiodes

    International Nuclear Information System (INIS)

    Specially developed avalanche photodiodes (APDs) will be used to measure the light from the 61,200 lead tungstate crystals in the barrel part of the CMS electromagnetic calorimeter. To ensure the reliability over the lifetime of the detector, every APD is screened by irradiation and burn-in before it is accepted for CMS. As part of the establishment of the screening procedure and to determine its effectiveness, a large number of APDs were screened twice. The results of these tests suggest that the required reliability will be achieved

  9. Double Screening Tests of the CMS ECAL Avalanche Photodiodes

    CERN Document Server

    Deiters, Konrad; Renker, Dieter; Sakhelashvili, Tariel; Britvitch, Ilia; Kuznetsov, Andrey; Musienko, Yuri; Singovsky, Alexander

    2005-01-01

    Specially developed avalanche photo-diodes (APDs) will be used to measure the light from the 61,200 lead tungstate crystals in the barrel part of the CMS electromagnetic calorimeter. To ensure the reliability over the lifetime of the detector, every APD is screened by irradiation and burn-in before it is accepted for CMS. As part of the establishment of the screening procedure and to determine its effectiveness, a large number of APDs were screened twice. The results of these tests suggest that the required reliability will be achieved.

  10. Comment on "Avalanche dynamics in evolution, growth and depinning models"

    CERN Document Server

    Dahlbom, M; Dahlbom, Mats; Irback, Anders

    1996-01-01

    In a recent paper Paczuski, Maslov and Bak present a comprehensive theory of avalanche dynamics in models of growth, interface depinning and evolution. One of their main results is the so-called gamma equation, which is claimed to be exact. In this note it is shown that this equation requires a numerical correction factor in order to become exact. The exactness is needed when using the equation to determine the exponent \\gamma. The correct equation is tested against numerical results for the Bak-Sneppen evolution model and two closely related models, and it turns out that it improves the description of data in a statistically significant way.

  11. Breakdown voltage in thin III-V avalanche photodiodes

    Science.gov (United States)

    Saleh, Mohammad A.; Hayat, Majeed M.; Kwon, Oh-Hyun; Holmes, Archie L.; Campbell, Joe C.; Saleh, Bahaa E. A.; Teich, Malvin C.

    2001-12-01

    The dead-space multiplication theory of Hayat and Saleh [J. Lightwave Technol. 10, 1415 (1992)], in conjunction with the multiplication-width-independent ionization-coefficient model developed by Saleh et al. [IEEE Trans. Electron Devices 47, 625 (2000)], are shown to accurately predict breakdown voltages for thin avalanche photodiodes of GaAs, InP, In0.52Al0.48As, and Al0.2Ga0.8As, over a broad range of device widths. The breakdown voltage is determined from the analytical expression for the impulse-response-function decay rate.

  12. Avalanches of rearrangements in quasi-2D emulsion hopper flow

    OpenAIRE

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

    2015-01-01

    We experimentally study the flow of a quasi-two-dimensional emulsion through a constricting hopper shape. Our area fractions range from 0.83 to 0.99, such that the droplets are always in contact with one another and are in many cases highly deformed. At the lowest flow rates, the droplets exit the hopper via intermittent avalanches. At the highest flow rates, the droplets exit continuously. The transition between these two types of behaviors is a fairly smooth function of the mean strain rate...

  13. Avalanche proton-boron fusion based on elastic nuclear collisions

    Science.gov (United States)

    Eliezer, Shalom; Hora, Heinrich; Korn, Georg; Nissim, Noaz; Martinez Val, Josè Maria

    2016-05-01

    Recent experiments done at Prague with the 600 J/0.2 ns PALS laser interacting with a layer of boron dopants in a hydrogen enriched target have produced around 109 alphas. We suggest that these unexpected very high fusion reactions of proton with 11B indicate an avalanche multiplication for the measured anomalously high nuclear reaction yields. This can be explained by elastic nuclear collisions in the broad 600 keV energy band, which is coincident with the high nuclear p-11B fusion cross section, by the way of multiplication through generation of three secondary alpha particles from a single primarily produced alpha particle.

  14. Quench simulation of SMES consisting of some superconducting coils

    Energy Technology Data Exchange (ETDEWEB)

    Noguchi, S., E-mail: noguchi@ssi.ist.hokudai.ac.jp [Graduate School of Information Science and Technology, Hokkaido University, Kita 14 Nishi 9, Kita-ku, Sapporo 060-0814 (Japan); Oga, Y.; Igarashi, H. [Graduate School of Information Science and Technology, Hokkaido University, Kita 14 Nishi 9, Kita-ku, Sapporo 060-0814 (Japan)

    2011-11-15

    A chain of quenches may be caused by a quench of one element coil when SMES is consists of many element coils. To avoid the chain of quenches, the energy stored in element coil has to be quickly discharged. The cause of the chain of the quenches is the short time constant of the decreasing current of the quenched coil. In recent years, many HTS superconducting magnetic energy storage (HTS-SMES) systems are investigated and designed. They usually consist of some superconducting element coils due to storing excessively high energy. If one of them was quenched, the storage energy of the superconducting element coil quenched has to be immediately dispersed to protect the HTS-SMES system. As the result, the current of the other element coils, which do not reach to quench, increases since the magnetic coupling between the quenched element coil and the others are excessively strong. The increase of the current may cause the quench of the other element coils. If the energy dispersion of the element coil quenched was failed, the other superconducting element coil would be quenched in series. Therefore, it is necessary to investigate the behavior of the HTS-SMES after quenching one or more element coils. To protect a chain of quenches, it is also important to investigate the time constant of the coils. We have developed a simulation code to investigate the behavior of the HTS-SMES. By the quench simulation, it is indicated that a chain of quenches is caused by a quench of one element coil.

  15. Simulation of the Quench-06 experiment with Scdapsim; Simulacion del experimento Quench-06 con Scdapsim

    Energy Technology Data Exchange (ETDEWEB)

    Angel M, E. del; Nunez C, A.; Amador G, R. [CNSNS, Dr. Barragan No. 779, 03020 Mexico D.F. (Mexico)]. e-mail: edangelm@cnsns.gob.mx

    2003-07-01

    The present work describes the pattern of the called Quench installation developed and used by the National Commission of Nuclear Security and Safeguards (CNSNS) for their participation in the International Standard Problem 45 (ISP), organized by the Nuclear Energy Agency (NEA). The exercise consisted on the simulation of the denominated experiment Quench-06 carried out in the experimental installation Quench located in the Forschungszentrum laboratory in Karlsruhe, Germany. The experiment Quench-06 consisted on simulating the sudden and late injection of water in a fuel assemble for a pressurized reactor (PWR). The CNSNS uses the version bd of the SCDAPSIM code developed by the company Innovative Software Systems (ISS) to simulate this experiment. The obtained results showed that the code is able to predict the experiment partially when overestimating the hydrogen production and of the partial fused of some fuel pellets, but predicting correctly the damage in the shroud. (Author)

  16. Hole-Initiated-Avalanche, Linear-Mode, Single-Photon-Sensitive Avalanche Photodetector with Reduced Excess Noise and Low Dark Count Rate Project

    Data.gov (United States)

    National Aeronautics and Space Administration — A radiation hard, single photon sensitive InGaAs avalanche photodiode (APD) receiver technology will be demonstrated useful for long range space based optical...

  17. Knowledge-Based System for Forecasting Snow Avalanches of Chowkibal-Tangdhar Axis (J&K

    Directory of Open Access Journals (Sweden)

    Praveen Naresh

    1999-12-01

    Full Text Available In this paper an attempt has been made to use artificial intelligence in avalanche forecasting and to develop arule-based expert system for predicting direct action avalanches of Chowkibal-Tangdhar axis (JLK. Using C-language integrated production system (CLIPS, procedural knowledge is represented in the form of rules. Thecondition attributes of the rulebased system are 28 variables selected from 1 154 samples of snow-met and snowprofile data.The relative contribution of each variable on avalanche days and non-avalanche days and their influence on sitewise release of avalanche was studied to formulate 358 rules. These rules, which include 173decision rules, were finally implemented and validated for running the model. Sixty-three samples of snow-metdata and pit profile data attributing to avalanche days and 54 samples of non-avalanche days were run on themodel. The results show that the knowledge-based model can predict avalanche days with 76 per cent efficiency.The misclassified results accounted for 28.2 percent of 117 test samples.

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

    Science.gov (United States)

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

    2013-09-01

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

  19. Quench Protection for the MICE Cooling Channel Coupling Magnet

    Energy Technology Data Exchange (ETDEWEB)

    Guo, Xing Long; Xu, Feng Yu; Wang, Li; Green, Michael A.; Pan, Heng; Wu, Hong; Liu, X.K.; Jia, Lin Xiang; Amm, Kathleen

    2008-08-02

    This paper describes the passive quench protection system selected for the muon ionization cooling experiment (MICE) cooling channel coupling magnet. The MICE coupling magnet will employ two methods of quench protection simultaneously. The most important method of quench protection in the coupling magnet is the subdivision of the coil. Cold diodes and resistors are put across the subdivisions to reduce both the voltage to ground and the hot-spot temperature. The second method of quench protection is quench-back from the mandrel, which speeds up the spread of the normal region within the coils. Combining quench back with coil subdivision will reduce the hot spot temperature further. This paper explores the effect on the quench process of the number of coil sub-divisions, the quench propagation velocity within the magnet, and the shunt resistance.

  20. Simulation of bundle test Quench-12 with integral code MELCOR

    International Nuclear Information System (INIS)

    The past NRI analyses cover the Quench-01, Quench-03 and Quench-06 with version MELCOR 1.8.5 (including reflood model), and Quench-01 and Quench-11 tests with the latest version MELCOR 1.8.6. The Quench-12 test is specific, because it has different bundle configuration related to the VVER bundle configuration with hexagonal grid of pins and also used E110 cladding material. Specificity of Quench-12 test is also in the used material of fuel rod cladding - E110. The test specificities are a reason for the highest concern, because the VVER reactors are operated in the Czech Republic. The new input model was developed with the taking into account all experience from previous simulations of the Quench bundle tests. The recent version MELCOR 1.8.6 YU2911 was used for the simulation with slightly modified ELHEAT package. Sensitivity studies on input parameters and oxidation kinetics were performed. (author)

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

    Energy Technology Data Exchange (ETDEWEB)

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

    2008-10-14

    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.

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

    International Nuclear Information System (INIS)

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

  3. Modelling of pressure tube Quench using PDETWO

    International Nuclear Information System (INIS)

    Transient two-dimensional heat conduction calculations have been carried out to determine the time-dependent temperature distribution in an overheated pressure tube during quenching with water. The purpose of the calculations is to provide input for evaluation of thermal (secondary) stresses in the pressure tube due to quench. The quench phenomenon in pressure tubes could occur in several hypothetical accident scenarios, including incidents involving intermittent buoyancy-induced flow during outages. In these scenarios, there will be two (radial and axial) or three dimensional temperature gradients, resulting in thermal stresses in the pressure tube, as the water front reaches and starts to cool down the hot pressure tube. The transient, two-dimensional heat conduction equation in the pressure tube during quench is solved using a FORTRAN package called PDETWO, available in the open literature for solving time-dependent coupled systems of non-linear partial differential equations over a two-dimensional rectangular region. This routine is based on finite difference solution of coupled, non-linear partial differential equations. Temperature gradient in the circumferential gradient is neglected for conservatism and convenience. The advancing water front is not modelled explicitly, and assumed to be at a uniform temperature and moving at a constant velocity inferred from experimental data. For outer surface and both ends of the pressure tube in the axial direction, a zero-heat flux boundary condition is assumed, while for the inner surface a moving water-quench front is assumed by appropriately varying the fluid temperature and the heat transfer coefficient. The pressure tube is assumed to be at a uniform temperature of 400oC initially, to represent conditions expected during an intermittent buoyancy-influenced flow scenario. The results confirm the expectations that axial temperature gradients and associated heat fluxes are small in comparison with those in the radial

  4. Characterization of midwave infrared InSb avalanche photodiode

    International Nuclear Information System (INIS)

    This paper focuses on the InSb material potential for the elaboration of Avalanche Photodiodes (APD) for high performance infrared imaging applications, both in passive or active mode. The first InSb electron-APD structure was grown by molecular beam epitaxy, processed and electrically characterized. The device performances are at the state of the art for the InSb epi-diode technology, with a dark current density J(−50 mV) = 32 nA/cm2 at 77 K. Then, a pure electron injection was performed, and an avalanche gain, increasing exponentially, was observed with a gain value near 3 at −4 V at 77 K. The Okuto–Crowell model was used to determine the electron ionization coefficient α(E) in InSb, and the InSb gain behavior is compared with the one of InAs and MCT APDs

  5. Characterization of midwave infrared InSb avalanche photodiode

    Energy Technology Data Exchange (ETDEWEB)

    Abautret, J., E-mail: johan.abautret@ies.univ-montp2.fr; Evirgen, A. [Université Montpellier, IES, UMR 5214, F-34095 Montpellier (France); CNRS, IES, UMR 5214, F-34095 Montpellier (France); SOFRADIR, BP 21, 38113 Veurey-Voroize (France); Perez, J. P.; Christol, P. [Université Montpellier, IES, UMR 5214, F-34095 Montpellier (France); CNRS, IES, UMR 5214, F-34095 Montpellier (France); Rothman, J. [CEA-LETI, 17 rue des Martyrs, 38054 Grenoble Cedex 9 (France); Cordat, A. [SOFRADIR, BP 21, 38113 Veurey-Voroize (France)

    2015-06-28

    This paper focuses on the InSb material potential for the elaboration of Avalanche Photodiodes (APD) for high performance infrared imaging applications, both in passive or active mode. The first InSb electron-APD structure was grown by molecular beam epitaxy, processed and electrically characterized. The device performances are at the state of the art for the InSb epi-diode technology, with a dark current density J(−50 mV) = 32 nA/cm{sup 2} at 77 K. Then, a pure electron injection was performed, and an avalanche gain, increasing exponentially, was observed with a gain value near 3 at −4 V at 77 K. The Okuto–Crowell model was used to determine the electron ionization coefficient α(E) in InSb, and the InSb gain behavior is compared with the one of InAs and MCT APDs.

  6. Plasma simulation of electron avalanche in a linear thyratron

    International Nuclear Information System (INIS)

    The plasma simulation code models, in 2-1/2 spatial dimensions, an electron avalanche in a tetrode thyratron (cathode, auxiliary grid, control grid, and anode). Electron trajectories are modeled using the Monte-Carlo method. Individual particles in the simulation are treated as macro-particles with each individual electron having the effective weight of many electrons. Collisions and electron multiplication are included. The weights of the individual particles are dynamically rescaled to enable simulation of an avalanche having an electron density range of 106 cm-3 to 1013cm-3. Poisson's equation is solved to obtain electric fields within the grid structure. The excited states of the gas and ion motion are modeled using rate and fluid transport equations. Excitation and ionization rates are obtained directly from the rate of collisions of the electron macro-particles. A modified null-collision technique is used to include electron-electron, electron-ion, electron-neutral excited state collisions. Inclusion of electron-ion collisions is important in thyratrons because the current to the anode may be limited by electron ion collisions in the control grid slot. A circuit is also included in the simulation to model the effects of external parameters such as inductance and the auxiliary grid priming current

  7. From an electron avalanche to the lightning discharge

    Science.gov (United States)

    Zalikhanov, B. Zh.

    2016-01-01

    The goal of this work is to describe qualitatively the physics of processes which begin with an electron avalanche and finish in a lightning discharge. A streamer model is considered that is based on studies of the recently discovered processes occurring in the prestreamer region. The investigation and analysis of these processes enabled making the conclusion that they are, in essence, the attendant processes, which ensure the electron avalanche-to-streamer transition, and may be interpreted as a manifestation of properties of a double charge layer exposed to the external electric field. The pressing problems of physical processes which form a lightning discharge are considered from the standpoint of new ideas about the mechanism of the streamer formation and growth. Causes of the emergence of coherent super-high-frequency radiation of a leader and the neutron production in a lightning discharge are revealed that have not been explained so far in the theory of gas discharge. Based also on new ideas about the lightning discharge, a simple ball-lightning model, providing answers to almost allquestions formulated from numerous observations on the behavior of ball lightning, is offered, and the need of a new design of lightning protection instead of the traditional rod is discussed.

  8. Scale-free avalanche dynamics in the stock market

    CERN Document Server

    Bartolozzi, M; Thomas, A W

    2006-01-01

    Self-organized criticality has been claimed to play an important role in many natural and social systems. In the present work we empirically investigate the relevance of this theory to stock-market dynamics. Avalanches in stock-market indices are identified using a multi-scale wavelet-filtering analysis designed to remove Gaussian noise from the index. Here new methods are developed to identify the optimal filtering parameters which maximize the noise removal. The filtered time series is reconstructed and compared with the original time series. A statistical analysis of both high-frequency Nasdaq E-mini Futures and daily Dow Jones data is performed. The results of this new analysis confirm earlier results revealing a robust power law behaviour in the probability distribution function of the sizes, duration and laminar times between avalanches. This power law behavior holds the potential to be established as a stylized fact of stock market indices in general. While the memory process, implied by the power law ...

  9. Supershort avalanche electron beam in SF6 and krypton

    Science.gov (United States)

    Zhang, Cheng; Tarasenko, Victor F.; Gu, Jianwei; Baksht, Evgeni Kh.; Beloplotov, Dmitry V.; Burachenko, Alexander G.; Yan, Ping; Lomaev, Mikhail I.; Shao, Tao

    2016-03-01

    Runaway electrons play an important role in the avalanche formation in nanosecond- and subnanosecond- pulse discharges. In this paper, characteristics of a supershort avalanche electron beam (SAEB) generated at the subnanosecond and nanosecond breakdown in sulfur hexafluoride (SF6 ) in an inhomogeneous electric field were studied. One pulser operated at negative polarity with voltage pulse amplitude of ˜130 kV and rise time of 0.3 ns. The other pulser operated at negative polarity with voltage pulse amplitude of 70 kV and rise time of ˜1.6 ns . SAEB parameters in SF6 are compared with those obtained in krypton (Kr), nitrogen (N2 ), air, and mixtures of SF6 with krypton or nitrogen. Experimental results showed that SAEB currents appeared during the rise-time of the voltage pulse for both pulsers. Moreover, amplitudes of the SAEB current in SF6 and Kr approximately ranged from several to tens of milliamps at atmospheric pressure, which were smaller than those in N2 and air (ranging from hundreds of milliamps to several amperes). Furthermore, the concentration of SF6 additive could significantly reduce the SAEB current in N2-SF6 mixture, but it slightly affected the SAEB current in Kr -SF6 mixture because of the atomic/molecular ionization cross section of the gas had a much greater impact on the SAEB current rather than the electronegativity.

  10. Scaling of avalanche queues in directed dissipative sandpiles

    Science.gov (United States)

    Tadic; Priezzhev

    2000-09-01

    Using numerical simulations and analytical methods we study a two-dimensional directed sandpile automaton with nonconservative random defects (concentration c) and varying driving rate r. The automaton is driven only at the top row and driving rate is measured by the number of added particles per time step of avalanche evolution. The probability distribution of duration of elementary avalanches at zero driving rate is exactly given by P1(t,c)=t(-3/2) exp[t ln(1-c)]. For driving rates in the interval 0 server queue in the queue theory. We study scaling properties of the busy period and dissipated energy of sequences of noninterrupted activity. In the limit c-->0 and varying linear system size Lqueues are characterized by a multifractal scaling and we determine the corresponding spectral functions. For L>1/c increasing the driving rate somewhat compensates for the energy losses at defects above the line r approximately sqrt[c]. The scaling exponents of the distributions in this region of phase diagram vary approximately linearly with the driving rate. Using properties of recurrent states and the probability theory we determine analytically the exact upper bound of the probability distribution of busy periods. In the case of conservative dynamics c=0 the probability of a continuous flow increases as F(infinity) approximately r(2) for small driving rates. PMID:11088824

  11. Avalanche Structure in the Kadanoff Sand Pile Model

    CERN Document Server

    Perrot, Kevin

    2011-01-01

    Sand pile models are dynamical systems emphasizing the phenomenon of Self Organized Criticality (SOC). From N stacked grains, iterating evolution rules leads to some critical configuration where a small disturbance has deep consequences on the system, involving numerous steps of grain fall. Physicists L. Kadanoff et al. inspire KSPM, a model presenting a sharp SOC behavior, extending the well known Sand Pile Model. In KSPM with parameter D we start from a pile of N stacked grains and apply the rule: D-1 grains can fall from column i onto the D-1 adjacent columns to the right if the difference of height between columns i and i+1 is greater or equal to D. We propose an iterative study of KSPM evolution where one single grain addition is repeated on a heap of sand. The sequence of grain falls following a single grain addition is called an avalanche. From a certain column precisely studied for D=3, we provide a plain process describing avalanches.

  12. Quenched Chiral Behavior of Hadrons with Overlap Fermions

    International Nuclear Information System (INIS)

    We study the quenched chiral behavior of hadrons with the pseudoscalar mass as low as ∼ 280 MeV. We look for quenched chiral logs in the pion mass, determine the renormalized quark mass, and observe quenched artifacts in the a0 and N* propagators. The calculation is done on a quenched lattice of size 204 and a = 0.148(2) fm using overlap fermions and an improved gauge action

  13. Comparison of seismic and infrasound wave fields generated by snow avalanches

    Science.gov (United States)

    Suriñach, Emma; Tapia, Mar; Pérez-Guillén, Cristina; Khazaradze, Giorgi; Roig, Pere

    2016-04-01

    Snow avalanches are a source of waves that are transmitted through the ground and the air. These wave fields are detected by seismic and infrasound sensors. During the winter seasons 2008 -2016, a good quality database of avalanches was obtained at the VdlS test site with an accurate instrumentation. These avalanches were both natural and artificially triggered and were of varying types and sizes. Distances involved were 0.5 -3 km. Seismic signals were acquired using three seismometers (3-components, 1Hz) spaced 600 m apart along the avalanche track. One infrasound sensor (0.1Hz) and one seismometer (3-components, 1Hz) were placed one next to the other with a common base of time on the slope opposite the path. The database obtained enables us to compare the different signals generated. Differences in the frequency content and shape of the signals depending on the type and size of the avalanche are detected. A clear evolution of the recorded seismic signals along the path is observed. The cross correlation of the infrasound and seismic signals generated by the avalanches allows us to determine different characteristics for powder, transitional and wet avalanches concerning their wave fields. The joint analysis of infrasound and seismic waves enables us to obtain valuable information about the internal parts of the avalanche as a source of each wave field. This study has repercussions on avalanche dynamics and on the selection of the appropriate avalanche detection system. This study is supported by the Spanish Ministry of Science and Innovation project CHARMA: CHAracterization and ContRol of MAss Movements. A Challenge for Geohazard Mitigation (CGL2013-40828-R), and RISKNAT group (2014GR/1243).

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

    Science.gov (United States)

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

    2010-05-01

    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

  15. Quench simulation of SMES consisting of some superconducting coils

    Science.gov (United States)

    Noguchi, S.; Oga, Y.; Igarashi, H.

    2011-11-01

    In recent years, many HTS superconducting magnetic energy storage (HTS-SMES) systems are investigated and designed. They usually consist of some superconducting element coils due to storing excessively high energy. If one of them was quenched, the storage energy of the superconducting element coil quenched has to be immediately dispersed to protect the HTS-SMES system. As the result, the current of the other element coils, which do not reach to quench, increases since the magnetic coupling between the quenched element coil and the others are excessively strong. The increase of the current may cause the quench of the other element coils. If the energy dispersion of the element coil quenched was failed, the other superconducting element coil would be quenched in series. Therefore, it is necessary to investigate the behavior of the HTS-SMES after quenching one or more element coils. To protect a chain of quenches, it is also important to investigate the time constant of the coils. We have developed a simulation code to investigate the behavior of the HTS-SMES. By the quench simulation, it is indicated that a chain of quenches is caused by a quench of one element coil.

  16. Conformal quantum mechanics and holographic quench

    CERN Document Server

    Järvelä, Jarkko; Keski-Vakkuri, Esko

    2015-01-01

    Recently, there has been much interest in holographic computations of two-point non-equilibrium Green functions from AdS-Vaidya backgrounds. In the strongly coupled quantum field theory on the boundary, the dual interpretation of the background is an equilibration process called a holographic quench. The two dimensional AdS-Vaidya spacetime is a special case, dual to conformal quantum mechanics. We study how the quench is incorporated into a Hamiltonian $H + \\theta(t) \\Delta H$ and into correlation functions. With the help of recent work on correlation functions in conformal quantum mechanics, we first rederive the known two point functions, and then compute non-equilibrium 3- and 4-point functions. We also compute the 3-point function Witten diagram in the two-dimensional AdS-Vaidya background, and find agreement with the conformal quantum mechanics result.

  17. Triangular Ising antiferromagnets with quenched nonmagnetic impurities.

    Science.gov (United States)

    Tang, Huai-Lei; Zhu, Yi; Yang, Guo-Hong; Jiang, Ying

    2010-05-01

    In a random spin system, the cooperation of randomness and frustration will lead to a spin-glass phase. However, in geometrically frustrated spin systems, quenched nonmagnetic impurities lift frustration locally. This makes randomness and frustration in these systems as competitors rather than cooperators. By mapping the dilute triangular Ising antiferromagnetic system to elastic array of noncrossing strings, we find that the nonmagnetic impurities in the spin system play roles of pinning centers in the string system. Calculation shows that in the ground state of this system, the spin-glass correlation is power-law decayed, quite different from the standard behavior of spin glass in which spin-glass correlation between two spins at infinite distance tends to a finite value. This indicates that triangular Ising antiferromagnets with quenched nonmagnetic impurities cannot be a spin glass. Instead, in the ground states, they present properties of vortex glass. PMID:20866185

  18. Conformal quantum mechanics and holographic quench

    Science.gov (United States)

    Järvelä, Jarkko; Keränen, Ville; Keski-Vakkuri, Esko

    2016-02-01

    Recently, there has been much interest in holographic computations of two-point nonequilibrium Green functions from anti-de Sitter- (AdS-)Vaidya backgrounds. In the strongly coupled quantum field theory on the boundary, the dual interpretation of the background is an equilibration process called a holographic quench. The two-dimensional AdS-Vaidya spacetime is a special case, dual to conformal quantum mechanics. We study how the quench is incorporated into a Hamiltonian H +θ (t )Δ H and into correlation functions. With the help of recent work on correlation functions in conformal quantum mechanics, we first rederive the known two-point functions, and then compute nonequilibrium three- and four-point functions. We also compute the three-point function Witten diagram in the two-dimensional AdS-Vaidya background, and find agreement with the conformal quantum mechanics result.

  19. Collapse and Revival in Holographic Quenches

    CERN Document Server

    da Silva, Emilia; Mas, Javier; Serantes, Alexandre

    2014-01-01

    We study holographic models related to global quantum quenches in finite size systems. The holographic set up describes naturally a CFT, which we consider on a circle and a sphere. The enhanced symmetry of the conformal group on the circle motivates us to compare the evolution in both cases. Depending on the initial conditions, the dual geometry exhibits oscillations that we holographically interpret as revivals of the initial field theory state. On the sphere, this only happens when the energy density created by the quench is small compared to the system size. However on the circle considerably larger energy densities are compatible with revivals. Two different timescales emerge in this latter case. A collapse time, when the system appears to have dephased, and the revival time, when after rephasing the initial state is partially recovered. The ratio of these two times depends upon the initial conditions in a similar way to what is observed in some experimental setups exhibiting collapse and revivals.

  20. Collapse and revival in holographic quenches

    Science.gov (United States)

    da Silva, Emilia; Lopez, Esperanza; Mas, Javier; Serantes, Alexandre

    2015-04-01

    We study holographic models related to global quantum quenches in finite size systems. The holographic set up describes naturally a CFT, which we consider on a circle and a sphere. The enhanced symmetry of the conformal group on the circle motivates us to compare the evolution in both cases. Depending on the initial conditions, the dual geometry exhibits oscillations that we holographically interpret as revivals of the initial field theory state. On the sphere, this only happens when the energy density created by the quench is small compared to the system size. However on the circle considerably larger energy densities are compatible with revivals. Two different timescales emerge in this latter case. A collapse time, when the system appears to have dephased, and the revival time, when after rephasing the initial state is partially recovered. The ratio of these two times depends upon the initial conditions in a similar way to what is observed in some experimental setups exhibiting collapse and revivals.

  1. Quench from Mott Insulator to Superfluid

    Energy Technology Data Exchange (ETDEWEB)

    Zurek, Wojciech H. [Los Alamos National Laboratory; Dziarmaga, Jacek [Instytut Fizyki Uniwersytetu Jagiello´nskiego; Tylutki, Marek [Instytut Fizyki Uniwersytetu Jagiello´nskiego

    2012-06-01

    We study a linear ramp of the nearest-neighbor tunneling rate in the Bose-Hubbard model driving the system from the Mott insulator state into the superfluid phase. We employ the truncated Wigner approximation to simulate linear quenches of a uniform system in 1...3 dimensions, and in a harmonic trap in 3 dimensions. In all these setups the excitation energy decays like one over third root of the quench time. The -1/3 scaling is explained by an impulse-adiabatic approximation - a variant of the Kibble-Zurek mechanism - describing a crossover from non-adiabatic to adiabatic evolution when the system begins to keep pace with the increasing tunneling rate.

  2. Energy upgrade as regards quench performance

    Energy Technology Data Exchange (ETDEWEB)

    MacKay, W.W.; Tepikian, S.

    2011-01-01

    Since the cross section for W production increases rapidly with energy, we consider the possibility of increasing the collision energy of polarized protons at RHIC. The limits of present hardware are examined with a particular emphasis on the quench training performance of magnets. Ignoring the limits of the DX magnets, the short-sample currents for the main arc (8 cm) dipoles could allow an increase of more than 30%, however we estimate 400 to 500 training quenches for the just 8 cm dipoles to reach this level. We propose that a 10% increase in energy might be achieved with the present hardware configuration. Raising the beam energy to 275 GeV ({radical}s = 550 GeV) should increase the W production rate by almost 50% from the 250 GeV level for the same optics with identical {beta}*'s at the collision points.

  3. The "Perfect" Fluid Quenches Jets Almost Perfectly

    CERN Document Server

    Müller, Berndt

    2008-01-01

    The QCD matter produced in nuclear collisions at the Relativistic Heavy Ion Collider (RHIC) has been found to have a very low shear viscosity, which is close to the lower bound allowed by unitarity. The matter has also been found to strongly suppress the emission of energetic hadrons. This phenomenon, called "jet quenching" is interpreted to be the result of a large energy loss by the precursor parton on its path through the dense matter, primarily due to gluon radiation. I discuss how the two phenomena are related. The RHIC data suggest, in some scenarios of jet quenching, that the quark-gluon plasma created in nuclear collisions is characterized by strong coupling, but still admits a quasi-particle description.

  4. Light emission in nanogaps: overcoming quenching

    CERN Document Server

    Yang, Jianji; Lalanne, Philippe

    2015-01-01

    Very large spontaneous-emission-rate enhancements (~1000) are obtained for quantum emitters coupled with tiny plasmonic resonance, especially when emitters are placed in the mouth of nanogaps formed by metal nanoparticles that are nearly in contact. This fundamental effect of light emission at subwavelength scales is well documented and understood as resulting from the smallness of nanogap modes. In contrasts, it is much less obvious to figure out whether the radiation efficiency is high in these gaps, or if the emission is quenched by metal absorption especially for tiny gaps a few nanometers wide; the whole literature only contains scattered electromagnetic calculations on the subject, which suggest that absorption and quenching can be kept at a small level despite the emitter proximity to metal. Thus through analytical derivations in the limit of small gap thickness, it is our objective to clarify why quantum emitters in nanogap antennas offer good efficiencies, what are the circumstances in which high eff...

  5. Dynamics of Surface Roughening with Quenched Disorder

    OpenAIRE

    Havlin, S.; L. A. N. Amaral; Buldyrev, S V; Harrington, S. T.; Stanley, H. E.

    1994-01-01

    We study the dynamical exponent $z$ for the directed percolation depinning (DPD) class of models for surface roughening in the presence of quenched disorder. We argue that $z$ for $(d+1)$ dimensions is equal to the exponent $d_{\\rm min}$ characterizing the shortest path between two sites in an isotropic percolation cluster in $d$ dimensions. To test the argument, we perform simulations and calculate $z$ for DPD, and $d_{\\rm min}$ for percolation, from $d = 1$ to $d = 6$.

  6. Jet quenching and direct photon production

    OpenAIRE

    Liu, Fu-Ming; Hirano, Tetsufumi; Werner, Klaus; Zhu, Yan

    2008-01-01

    Jet quenching effect has been investigated in the direct photon production, based on a realistic data-constrained (3+1) dimensional hydrodynamic description of the expanding hot and dense matter, a reasonable treatment of the propagation of partons and their energy loss in the fluid, and a systematic study of the main sources of direct photons. Our resultant $\\pt$ spectra agree with recent PHENIX data in a broad $\\pt$ range. Parton energy loss in the plasma eventually effect significantly dir...

  7. The QUENCH programme at Forschungszentrum Karlsruhe (FZK)

    International Nuclear Information System (INIS)

    The QUENCH programme at FZK was launched to investigate the hydrogen source term during reflood of an overheated reactor core. It consists of large scale bundle experiments, separate-effects tests, modelling activities and application and validation of severe fuel damage (SFD) code systems. The paper describes the experimental part of the programme, namely the experimental facilities and test rigs as well as selected results obtained during the recent years. (author)

  8. Dynamical Multiscaling in Quenched Skyrme Systems

    OpenAIRE

    Rutenberg, Andrew D.; Zakrzewski, Wojtek J.; Zapotocky, Martin

    1997-01-01

    Strong dynamical scaling violations exist in quenched two-dimensional systems with vector O(3) order parameters. These systems support non-singular topologically stable configurations (skyrmions). By tuning the stability of isolated skyrmions to expand or shrink, we find dramatic differences in the dynamical multiscaling spectrum of decaying moments $$ of the topological charge density distribution and in particular in the decay of the energy-density $\\epsilon \\sim $. We...

  9. Photon structure functions from quenched lattice QCD

    International Nuclear Information System (INIS)

    We calculate the first moment of the photon structure function, γ=∫01dxF2γ(x,Q2), on the quenched lattices with β=6.0 using the formalism developed by the authors recently. In this exploratory study, we take into account only the connected contractions. The result is compared with the experimental data as well as model predictions

  10. Readout circuitry for continuous high-rate photon detection with arrays of InP Geiger-mode avalanche photodiodes

    Science.gov (United States)

    Frechette, Jonathan; Grossmann, Peter J.; Busacker, David E.; Jordy, George J.; Duerr, Erik K.; McIntosh, K. Alexander; Oakley, Douglas C.; Bailey, Robert J.; Ruff, Albert C.; Brattain, Michael A.; Funk, Joseph E.; MacDonald, Jason G.; Verghese, Simon

    2012-06-01

    An asynchronous readout integrated circuit (ROIC) has been developed for hybridization to a 32x32 array of single-photon sensitive avalanche photodiodes (APDs). The asynchronous ROIC is capable of simultaneous detection and readout of photon times of arrival, with no array blind time. Each pixel in the array is independently operated by a finite state machine that actively quenches an APD upon a photon detection event, and re-biases the device into Geiger mode after a programmable hold-off time. While an individual APD is in hold-off mode, other elements in the array are biased and available to detect photons. This approach enables high pixel refresh frequency (PRF), making the device suitable for applications including optical communications and frequency-agile ladar. A built-in electronic shutter that de-biases the whole array allows the detector to operate in a gated mode or allows for detection to be temporarily disabled. On-chip data reduction reduces the high bandwidth requirements of simultaneous detection and readout. Additional features include programmable single-pixel disable, region of interest processing, and programmable output data rates. State-based on-chip clock gating reduces overall power draw. ROIC operation has been demonstrated with hybridized InP APDs sensitive to 1.06-μm and 1.55-μm wavelength, and fully packaged focal plane arrays (FPAs) have been assembled and characterized.

  11. Successful magnet quench test for CAST.

    CERN Multimedia

    Brice Maximilien

    2002-01-01

    The CERN Axion Solar Telescope (CAST) consists of a prototype LHC dipole magnet with photon detectors at each end. It searches for very weakly interacting neutral particles called axions, which should originate in the core of the Sun. The telescope, located at Point 8, can move vertically within its wheeled platform, which travels horizontally along tracks in the floor. In this way, the telescope can view the Sun at sunrise through one end and at sunset through the other end. It has been cooled down to below 1.8 K and reached ~95% of its final magnetic field of 9 tesla before a quench was induced to test the whole cryogenic system under such conditions. The cryogenic system responded as expected to the magnet quench and CAST is now ready to start its three-year search for solar axions. Photos 01 & 02 : Members of the LHC cryogenics team pose in front of the axion telescope on the day of the first quench test, together with some of the CAST collaboration.

  12. Avalanche dynamics in the Bak-Sneppen evolution model observed with a standard distribution width of fitness

    Science.gov (United States)

    Lee, Chaohong; Zhu, Xiwen; Gao, Kelin

    2003-01-01

    We introduce the standard distribution width of fitness to characterize the global and individual features of an ecosystem described by the Bak-Sneppen evolution model. Through tracking this quantity in evolution, a different hierarchy of avalanche dynamics, the w0 avalanche, is observed. The corresponding gap equation and the self-organized threshold wc are obtained. The critical exponents τ, γ and ρ, which describe the behaviour of the avalanche size distribution, the average avalanche size and the relaxation to attractor, respectively, are calculated by numerical simulation. The exact master equation and γ equation are derived, and the scaling relations are established among the critical exponents of this new avalanche.

  13. La carte de localisation des phénomènes d'avalanche (CLPA) : enjeux et perspectives

    OpenAIRE

    Bonnefoy, M.; Borrel, G.; Richard, D.; Bélanger, L; Naaïm, M.

    2010-01-01

    The Localization Map of Avalanche Phenomena (CLPA in French) was created in 1971 as a response to the deadly avalanche occurred in Val d'Isère (February 1970, 39 persons killed). The aim is to inventory and to memorize areas where avalanches occurred in the past in order to keep in memory precisely greatest limits of those avalanches. The CLPA was rapidly considered as an essential element for developing plan in mountain areas. After the other catastrophic avalanche, which occurred in the Mon...

  14. Smooth and fast versus instantaneous quenches in quantum field theory

    OpenAIRE

    Das, Sumit; Galante, Damián; Myers, Robert

    2015-01-01

    We examine in detail the relationship between smooth fast quantum quenches, characterized by a time scale $\\delta t$, and {\\em instantaneous quenches}, within the framework of exactly solvable mass quenches in free scalar field theory. Our earlier studies \\cite{dgm1,dgm2} highlighted that the two protocols remain distinct in the limit $\\delta t \\rightarrow 0$ because of the relation of the quench rate to the UV cut-off, i.e., $1/\\delta t\\ll\\Lambda$ always holds in the fast smooth quenches whi...

  15. Cryogenic Quenching Process for Electronic Part Screening

    Science.gov (United States)

    Sheldon, Douglas J.; Cressler, John

    2011-01-01

    The use of electronic parts at cryogenic temperatures (less than 100 C) for extreme environments is not well controlled or developed from a product quality and reliability point of view. This is in contrast to the very rigorous and well-documented procedures to qualify electronic parts for mission use in the 55 to 125 C temperature range. A similarly rigorous methodology for screening and evaluating electronic parts needs to be developed so that mission planners can expect the same level of high reliability performance for parts operated at cryogenic temperatures. A formal methodology for screening and qualifying electronic parts at cryogenic temperatures has been proposed. The methodology focuses on the base physics of failure of the devices at cryogenic temperatures. All electronic part reliability is based on the bathtub curve, high amounts of initial failures (infant mortals), a long period of normal use (random failures), and then an increasing number of failures (end of life). Unique to this is the development of custom screening procedures to eliminate early failures at cold temperatures. The ability to screen out defects will specifically impact reliability at cold temperatures. Cryogenic reliability is limited by electron trap creation in the oxide and defect sites at conductor interfaces. Non-uniform conduction processes due to process marginalities will be magnified at cryogenic temperatures. Carrier mobilities change by orders of magnitude at cryogenic temperatures, significantly enhancing the effects of electric field. Marginal contacts, impurities in oxides, and defects in conductor/conductor interfaces can all be magnified at low temperatures. The novelty is the use of an ultra-low temperature, short-duration quenching process for defect screening. The quenching process is designed to identify those defects that will precisely (and negatively) affect long-term, cryogenic part operation. This quenching process occurs at a temperature that is at least

  16. Kinetic modelling of runaway electron avalanches in tokamak plasmas

    Science.gov (United States)

    Nilsson, E.; Decker, J.; Peysson, Y.; Granetz, R. S.; Saint-Laurent, F.; Vlainic, M.

    2015-09-01

    Runaway electrons can be generated in tokamak plasmas if the accelerating force from the toroidal electric field exceeds the collisional drag force owing to Coulomb collisions with the background plasma. In ITER, disruptions are expected to generate runaway electrons mainly through knock-on collisions (Hender et al 2007 Nucl. Fusion 47 S128-202), where enough momentum can be transferred from existing runaways to slow electrons to transport the latter beyond a critical momentum, setting off an avalanche of runaway electrons. Since knock-on runaways are usually scattered off with a significant perpendicular component of the momentum with respect to the local magnetic field direction, these particles are highly magnetized. Consequently, the momentum dynamics require a full 3D kinetic description, since these electrons are highly sensitive to the magnetic non-uniformity of a toroidal configuration. For this purpose, a bounce-averaged knock-on source term is derived. The generation of runaway electrons from the combined effect of Dreicer mechanism and knock-on collision process is studied with the code LUKE, a solver of the 3D linearized bounce-averaged relativistic electron Fokker-Planck equation (Decker and Peysson 2004 DKE: a fast numerical solver for the 3D drift kinetic equation Report EUR-CEA-FC-1736, Euratom-CEA), through the calculation of the response of the electron distribution function to a constant parallel electric field. The model, which has been successfully benchmarked against the standard Dreicer runaway theory now describes the runaway generation by knock-on collisions as proposed by Rosenbluth (Rosenbluth and Putvinski 1997 Nucl. Fusion 37 1355-62). This paper shows that the avalanche effect can be important even in non-disruptive scenarios. Runaway formation through knock-on collisions is found to be strongly reduced when taking place off the magnetic axis, since trapped electrons can not contribute to the runaway electron population. Finally, the

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

    Directory of Open Access Journals (Sweden)

    F. Techel

    2014-08-01

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

  18. Novel radiation detectors based on multi pixels avalanche photodiodes: their status and perspectives of application

    International Nuclear Information System (INIS)

    Full text: Different versions of silicon avalanche photodiodes (APD), as well as new multi pixel avalanche photodiodes (MAPD) have been discussed widely during the last decade as an advanced photon counter for various applications. The sensitive area of a MAPD contains a matrix of independent micro-pixels with individual passive elements, which are created on a common silicon wafer. The individual passive elements provide local suppression of the avalanche process and discharge each micro-pixel to a common conducting or metal electrode. The advanced properties of a MAPD are connected with a local negative feedback (LNF) effect, which result in a local self-suppression of the avalanche gain due to individual passive elements with necessary resistivity and capacitance and, consequently, significantly reduces the influence of crystal non-uniformities on the characteristics of the avalanche multiplication process. The LNF effect is achieved by forming a specific matrix in the multilayer silicon structure which ensures a localisation of the avalanche processes and limits them in frames of independent micro-regions of 3-50 m in size, depending of the MAPD design. Thus, the micro-pixel structure in a MAPD results in a unique combination of high signal amplification and uniform avalanche multiplication over the entire sensitive area of the device. Each pixel has a sandwich like structure like a metal-resistive layer-semiconductor (MRS). This device is made in a very simple technology and it may demonstrate very good parameters in the red and near infrared regions of spectrum.

  19. Avalanches near a solid insulator in nitrogen gas at atmospheric pressure

    International Nuclear Information System (INIS)

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

  20. Magnitude-Frequency Distribution of Hummocks on Rockslide-Debris Avalanche Deposits and Its Geomorphological Significance

    Directory of Open Access Journals (Sweden)

    Hidetsugu Yoshida

    2016-01-01

    Full Text Available A magnitude-frequency analysis of rockslide-debris avalanche deposits was performed. Hummocks are conical mounds formed in debris avalanche deposits from the catastrophic sector collapse of a mountain (often volcanic that represent relatively cohesive fragments of the mountain edifice. Examination of 17 debris avalanche deposits in Japan and the Philippines showed that, in general, the larger the magnitude of the hummocks, the smaller their frequency. Hummocks followed an exponential distribution: log10N(x = a – bx, where N(x is the cumulative number of hummocks with magnitude ≥ x and a and b are constants; x is equal to log10A, where A is the area of a hummock. The constants a and b were positively correlated. The value of b, which differs among avalanches and in this analysis ranged between 1 and 3, may be controlled by the mobility of the debris avalanche. Avalanches with higher mobility (relatively longer runout have higher b and potentially produce more numerous fragments forming hummocks (i.e., higher a. From the above correlation, the magnitude-frequency relationship can be used to roughly estimate the original height of the collapsed volcanic body, if the runout distance of the rockslide–debris avalanche can be estimated with sufficient accuracy.

  1. The mass dependence of dwarf satellite galaxy quenching

    International Nuclear Information System (INIS)

    We combine observations of the Local Group with data from the NASA-Sloan Atlas to show the variation in the quenched fraction of satellite galaxies from low-mass dwarf spheroidals and dwarf irregulars to more massive dwarfs similar to the Magellanic Clouds. While almost all of the low-mass (M * ≲ 107 M ☉) dwarfs are quenched, at higher masses the quenched fraction decreases to approximately 40%-50%. This change in the quenched fraction is large and suggests a sudden change in the effectiveness of quenching that correlates with satellite mass. We combine this observation with models of satellite infall and ram pressure stripping to show that the low-mass satellites must quench within 1-2 Gyr of pericenter passage to maintain a high quenched fraction, but that many more massive dwarfs must continue to form stars today even though they likely fell into their host >5 Gyr ago. We also characterize how the susceptibility of dwarfs to ram pressure must vary as a function of mass if it is to account for the change in quenched fractions. Though neither model predicts the quenching effectiveness a priori, this modeling illustrates the physical requirements that the observed quenched fractions place on possible quenching mechanisms.

  2. The mass dependence of dwarf satellite galaxy quenching

    Energy Technology Data Exchange (ETDEWEB)

    Slater, Colin T.; Bell, Eric F., E-mail: ctslater@umich.edu, E-mail: ericbell@umich.edu [Department of Astronomy, University of Michigan, 500 Church Street, Ann Arbor, MI 48109 (United States)

    2014-09-10

    We combine observations of the Local Group with data from the NASA-Sloan Atlas to show the variation in the quenched fraction of satellite galaxies from low-mass dwarf spheroidals and dwarf irregulars to more massive dwarfs similar to the Magellanic Clouds. While almost all of the low-mass (M {sub *} ≲ 10{sup 7} M {sub ☉}) dwarfs are quenched, at higher masses the quenched fraction decreases to approximately 40%-50%. This change in the quenched fraction is large and suggests a sudden change in the effectiveness of quenching that correlates with satellite mass. We combine this observation with models of satellite infall and ram pressure stripping to show that the low-mass satellites must quench within 1-2 Gyr of pericenter passage to maintain a high quenched fraction, but that many more massive dwarfs must continue to form stars today even though they likely fell into their host >5 Gyr ago. We also characterize how the susceptibility of dwarfs to ram pressure must vary as a function of mass if it is to account for the change in quenched fractions. Though neither model predicts the quenching effectiveness a priori, this modeling illustrates the physical requirements that the observed quenched fractions place on possible quenching mechanisms.

  3. Quench propagation and protection analysis of the ATLAS Toroids

    CERN Document Server

    Dudarev, A; ten Kate, H H J; Baynham, D Elwyn; Courthold, M J D; Lesmond, C

    2000-01-01

    The ATLAS superconducting magnet system consists of the Barrel Toroid, two End Cap Toroids and the Central Solenoid. However, the Toroids of eight coils each are magnetically separate systems to the Central Solenoid. The Toroids are electrically connected in series and energized by a single power supply. The quench protection system is based on the use of relatively small external dump resistances in combination with quench-heaters activated after a quench event detection to initiate the internal dump of stored energy in all the coils. A rather strong quench-back effect due to eddy-currents in the coil casings at the transport current decay is beneficial for the quench protection efficiency in the event of heater failures. The quench behaviour of the ATLAS Toroids was computer simulated for normal operation of the quench protection system and its complete non-operation (failure) mode. (3 refs).

  4. Single Photon Avalanche Diodes: Towards the Large Bidimensional Arrays

    Directory of Open Access Journals (Sweden)

    Emilio Sciacca

    2008-08-01

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

  5. Systematic afterpulsing-estimation algorithms for gated avalanche photodiodes

    CERN Document Server

    Wiechers, Carlos; Muñiz-Sánchez, Oscar R; Yépiz, Pablo Daniel; Arredondo-Santos, Alejandro; Hirsch, Jorge G; U'Ren, Alfred B

    2016-01-01

    We present a method designed to efficiently extract optical signals from InGaAs avalanche photodiodes (APDs) operated in gated mode. In particular, our method permits an estimation of the fraction of counts which actually results from the signal being measured, as opposed to being produced by noise mechanisms, specifically by afterpulsing. Our method in principle allows the use of InGaAs APDs at high detection efficiencies, with the full operation bandwidth, either with or without resorting to the application of a dead time. As we show below, our method can be used in configurations where afterpulsing exceeds the genuine signal by orders of magnitude, even near saturation. The algorithms which we have developed are suitable to be used either in real-time processing of raw detection probabilities or in post-processing applications, after a calibration step has been performed. The algorithms which we propose here can complement technologies designed for the reduction of afterpulsing.

  6. Investigation of a photon counting avalanche photodiode from Hamamatsu photonics

    Science.gov (United States)

    Britvitch, I.; Musienko, Y.; Renker, D.

    2006-11-01

    Multi-cell avalanche photodiodes (APDs) operating in Geiger mode have been shown to be a very promising alternative to photomultiplier tubes for the detection of single photons at room temperature. Like a photomultiplier they have high gain and a fast rise time and they are insensitive to pickup. Beyond it they operate in high magnetic fields, are compact and need a relatively low bias voltage. It is expected that the MOS production technique makes them cheap. Recently PSI and Hamamatsu Photonics worked together for the development of a radiation-hard APD for CMS ECAL and had very good success. The development continued based on a similar design for a photon counting multielement Geiger-mode APD with an area of 1×1 mm 2. The properties of this device have been measured and will be reported.

  7. Investigation of a photon counting avalanche photodiode from Hamamatsu photonics

    Energy Technology Data Exchange (ETDEWEB)

    Britvitch, I. [ETH Zuerich (Switzerland); Musienko, Y. [Northeastern University, Boston (United States); Renker, D. [Paul Scherrer Institute, Villigen PSI, 5232 Villigen (Switzerland)]. E-mail: dieter.renker@psi.ch

    2006-11-01

    Multi-cell avalanche photodiodes (APDs) operating in Geiger mode have been shown to be a very promising alternative to photomultiplier tubes for the detection of single photons at room temperature. Like a photomultiplier they have high gain and a fast rise time and they are insensitive to pickup. Beyond it they operate in high magnetic fields, are compact and need a relatively low bias voltage. It is expected that the MOS production technique makes them cheap. Recently PSI and Hamamatsu Photonics worked together for the development of a radiation-hard APD for CMS ECAL and had very good success. The development continued based on a similar design for a photon counting multielement Geiger-mode APD with an area of 1x1 mm{sup 2}. The properties of this device have been measured and will be reported.

  8. Self-aligned multi-channel superconducting nanowire avalanche photodetector

    CERN Document Server

    Cheng, Risheng; Ma, Xiaosong; Fan, Linran; Fong, King Y; Poot, Menno; Tang, Hong X

    2016-01-01

    We describe a micromachining process to allow the coupling of an array of single-mode telecommunication fibers to individual superconducting nanowire single photon detectors (SNSPDs). As proof of principle, we show the integration of four detectors on the same silicon chip, including two standard single-section nanowire detectors and two superconducting nanowire avalanche photodetectors (SNAPs) with modified series structure without external inductor, and their performances are compared. The SNAP shows saturated system detection efficiency of 16% while the dark count rate is less than 20 Hz, without the use of photon-recycling reflectors. The SNAP also demonstrates doubled signal-to-noise ratio, reduced reset time (~ 4.9 ns decay time) and improved timing jitter (62 ps FWHM) compared to standard SNSPDs.

  9. Investigation of a photon counting avalanche photodiode from Hamamatsu photonics

    International Nuclear Information System (INIS)

    Multi-cell avalanche photodiodes (APDs) operating in Geiger mode have been shown to be a very promising alternative to photomultiplier tubes for the detection of single photons at room temperature. Like a photomultiplier they have high gain and a fast rise time and they are insensitive to pickup. Beyond it they operate in high magnetic fields, are compact and need a relatively low bias voltage. It is expected that the MOS production technique makes them cheap. Recently PSI and Hamamatsu Photonics worked together for the development of a radiation-hard APD for CMS ECAL and had very good success. The development continued based on a similar design for a photon counting multielement Geiger-mode APD with an area of 1x1 mm2. The properties of this device have been measured and will be reported

  10. Studies of avalanche photodiodes for scintillating fibre tracking readout

    International Nuclear Information System (INIS)

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

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

    Science.gov (United States)

    Ispánovity, Péter Dusán; Groma, István; Györgyi, Géza; Csikor, Ferenc F.; Weygand, Daniel

    2010-08-01

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

  12. Design and characterization of avalanche photodiodes in submicron CMOS technologies

    Science.gov (United States)

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

    2014-03-01

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

  13. Minimum Quench Energy and Early Quench Development in NbTi Superconducting Strands

    CERN Document Server

    Breschi, M; Boselli, M; Bottura, Luca; Devred, Arnaud; Ribani, P L; Trillaud, F

    2007-01-01

    The stability of superconducting wires is a crucial task in the design of safe and reliable superconducting magnets. These magnets are prone to premature quenches due to local releases of energy. In order to simulate these energy disturbances, various heater technologies have been developed, such as coated tips, graphite pastes, and inductive coils. The experiments studied in the present work have been performed using a single-mode diode laser with an optical fiber to illuminate the superconducting strand surface. Minimum quench energies and voltage traces at different magnetic flux densities and transport currents have been measured on an LHC-type, Cu/NbTi wire bathed in pool boiling helium I. This paper deals with the numerical analysis of the experimental data. In particular, a coupled electromagnetic and thermal model has been developed to study quench development and propagation, focusing on the influence of heat exchange with liquid helium.

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

    Science.gov (United States)

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

    2013-08-01

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

  15. Triple SV: A Bit Level Symmetric Block-Cipher Having High Avalanche Effect

    Directory of Open Access Journals (Sweden)

    Rajdeep Chakraborty

    2011-08-01

    Full Text Available The prolific growth of network communication system entails high risk of breach in information security. This substantiates the need for higher security for electronic information. Cryptography is one of the ways to secure electronic documents. In this paper, we propose a new block cipher, TRIPLE SV (3SV, with 256-bit block size and 112-bit key length. Generally, stream ciphers produce higher avalanche effect but Triple SV shows a substantial rise in avalanche effect with a block cipher implementation. The CBC mode has been used to attain higher avalanche effect. The technique is implemented in C language and has been tested for feasibility

  16. Avalanche transmission and critical behaviour in load-bearing hierarchical networks

    Indian Academy of Sciences (India)

    Ajay Deep Kachhvah; Neelima Gupte

    2011-11-01

    The strength and stability properties of hierarchical load-bearing networks and their strengthened variants have been discussed in a recent work. Here, we study the avalanche time distributions on these load-bearing networks. The avalanche time distributions of the V-lattice, a unique realization of the networks, show power-law behaviour when tested with certain fractions of its trunk weights. All other avalanche distributions show Gaussian peaked behaviour. Thus the V-lattice is the critical case of the network. We discuss the implications of this result.

  17. A new hierarchy of avalanches observed in Bak-Sneppen evolution model

    OpenAIRE

    Li, W; Cai, X.

    1999-01-01

    A new quantity, average fitness, is introduced in Bak-Sneppen evolution model. Through this new quantity, a new hierarchy of avalanches is observed in the evolution of Bak-Sneppen model. An exact gap equation, governing the self-organization of the model, is presented. It is found that the self-organized threshold of the new quantity can be exactly obtained. Two basic exponents, avalanche distribution and avalanche dimension are given through simulations of one- and two-dimensional Bak-Sneppe...

  18. Bounds for avalanche critical values of the Bak-Sneppen model

    OpenAIRE

    Gillett, Alexis; Meester, Ronald; Nuyens, Misja

    2005-01-01

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

  19. Long-wavelength photonic integrated circuits and avalanche photodetectors

    Science.gov (United States)

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

    2001-10-01

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

  20. Avalanche-to-streamer transition near hydrometeors in thunderstorms

    Science.gov (United States)

    Rutjes, Casper; Dubinova, Anna; Ebert, Ute; Buitink, Stijn; Scholten, Olaf; Trinh, Gia

    2016-04-01

    In the early phase of lightning initiation, streamers must form near water droplets and or ice crystals, collectively called hydrometeors, as it is generally believed that the electric fields in a thunderstorm are below classical breakdown [1]. The hydrometeors, due to their dielectric property, electrically polarize and will enhance the thunderstorm electric field in localized areas just outside the surface, potentially above breakdown. Available electrons, from for example a cosmic ray event, are drawn towards the positive side of the polarized hydrometeor. Some electrons reach the localized area above breakdown, while oxygen molecules have absorbed others. In the area above breakdown electrons begin to multiply in number, creating electron avalanches towards the surface, leaving positive ions behind. This results in a charge separation, which potentially can initiate a positive streamer. The final outcome however strongly depends on several parameters, such as the strength of the thunderstorm electric field, the size and shape of the hydrometeor and the initial amount of electrons. In our letter [1] we introduced a dimensionless quantity M that we call the Meek number, based on the historical and well-used Reather-Meek criterion [2], as a measure of how likely it is to create an avalanche-to-streamer transition near a hydrometeor. Results from simulations showed that streamers can start in a field of only 15% of breakdown from large elongated shaped hydrometeors. Now we extended and generalized our method to arbitrary shaped hydrometeors and we take into account that potentially several electrons can reach the area above breakdown. Due to these effects we can predict smaller hydrometeors to be able to start streamers. We will present the latest results. [1] Dubinova, A., Rutjes, C., Ebert, U., Buitink, S., Scholten, O., & Trinh, G. T. N. (2015). Prediction of lightning inception by large ice particles and extensive air showers. Physical review letters, 115

  1. Sixteen-year follow-up of childhood avalanche survivors

    Directory of Open Access Journals (Sweden)

    Edda Bjork Thordardottir

    2016-08-01

    Full Text Available Background: Every year a substantial number of children are affected by natural disasters worldwide. However, data are scarce on long-term psychological impact of natural disasters on children's health. Identifying risk factors and outcomes associated with the long-term sequelae of posttraumatic stress disorder (PTSD can provide a gateway to recovery as well as enhancement of preventive measures. Objective: Among childhood avalanche survivors, we aimed to investigate risk factors for PTSD symptoms and the relationship between socioeconomic status (SES and PTSD symptoms in adulthood. Methods: Childhood survivors (aged 2–19 at the time of exposure of two avalanches were identified through nationwide registers 16 years later. The Posttraumatic Diagnostic Scale was used to assess current PTSD symptoms. One-way ANOVA was used to explore PTSD symptoms by background and trauma-specific factors, as well as associations with current SES. Predictors of PTSD symptoms were examined by multivariable regression analysis. Results: Response rate was 66% (108/163. Results from univariate ANOVA analysis revealed that female sex was associated with PTSD symptoms (F=5.96, p<0.05. When adjusted for age and sex, PTSD symptoms were associated with lower education (F=7.62, p<0.001, poor financial status (F=12.21, p<0.001, and unemployment and/or disability (F=3.04, p<0.05. In a multivariable regression model, when adjusting for age and sex, lack of social support (t=4.22, p<0.001 and traumatic reactions of caregivers (t=2.49, p<0.05 in the aftermath of the disaster independently predicted PTSD 16 years post-trauma. Conclusions: Lingering PTSD symptoms after childhood exposure to a disaster may negatively influence socioeconomic development in adulthood. Strengthening children's support systems post-disaster may prevent the long-term sequelae of symptoms.

  2. SARNET benchmark on QUENCH-11. Final report

    International Nuclear Information System (INIS)

    The QUENCH out-of-pile experiments at Forschungszentrum Karlsruhe (Karlsruhe Research Center) are set up to investigate the hydrogen source term that results from the water or steam injection into an uncovered core of a Light-Water Reactor, to examine the behavior of overheated fuel elements under different flooding conditions, and to create a database for model development and improvement of Severe Fuel Damage (SFD) code packages. The boil-off experiment QUENCH-11 was performed on December 8, 2005 as the second of two experiments in the frame of the EC-supported LACOMERA program. It was to simulate ceasing pumps in case of a small break LOCA or a station blackout with a late depressurization of the primary system, starting with boil-down of a test bundle that was partially filled with water. It is the first test to investigate the whole sequence of an anticipated reactor accident from the boil-off phase to delayed reflood of the bundle with a low water injection rate. The test is characterized by an interaction of thermal-hydraulics and material interactions that is even stronger than in previous QUENCH tests. It was proposed by INRNE Sofia (Bulgarian Academy of Sciences) and defined together with Forschungszentrum Karlsruhe. After the test, QUENCH-11 was chosen as a SARNET code benchmark exercise. Its task is a comparison between experimental data and analytical results to assess the reliability of the code prediction for different phases of an accident and the experiment. The SFD codes used were ASTEC, ATHLET-CD, ICARE-CATHARE, MELCOR, RATEG/SVECHA, RELAP/-SCDAPSIM, and SCDAP/RELAP5. The INRNE took responsibility as benchmark coordinator to compare the code results with the experimental data. As a basis of the present work, histories of temperatures, hydrogen production and other important variables were used. Besides, axial profiles at quench initiation and the final time of 7000 s, above all of temperatures, are presented. For most variables a mainstream of

  3. SARNET benchmark on QUENCH-11. Final report

    Energy Technology Data Exchange (ETDEWEB)

    Stefanova, A. [Bylgarska Akademiya na Naukite, Sofia (Bulgaria). Inst. for Nuclear Research and Nuclear Energy; Drath, T. [Ruhr-Univ. Bochum (Germany). Energy Systems and Energy Economics; Duspiva, J. [Nuclear Research Inst., Rez (CZ). Dept. of Reactor Technology] (and others)

    2008-03-15

    The QUENCH out-of-pile experiments at Forschungszentrum Karlsruhe (Karlsruhe Research Center) are set up to investigate the hydrogen source term that results from the water or steam injection into an uncovered core of a Light-Water Reactor, to examine the behavior of overheated fuel elements under different flooding conditions, and to create a database for model development and improvement of Severe Fuel Damage (SFD) code packages. The boil-off experiment QUENCH-11 was performed on December 8, 2005 as the second of two experiments in the frame of the EC-supported LACOMERA program. It was to simulate ceasing pumps in case of a small break LOCA or a station blackout with a late depressurization of the primary system, starting with boil-down of a test bundle that was partially filled with water. It is the first test to investigate the whole sequence of an anticipated reactor accident from the boil-off phase to delayed reflood of the bundle with a low water injection rate. The test is characterized by an interaction of thermal-hydraulics and material interactions that is even stronger than in previous QUENCH tests. It was proposed by INRNE Sofia (Bulgarian Academy of Sciences) and defined together with Forschungszentrum Karlsruhe. After the test, QUENCH-11 was chosen as a SARNET code benchmark exercise. Its task is a comparison between experimental data and analytical results to assess the reliability of the code prediction for different phases of an accident and the experiment. The SFD codes used were ASTEC, ATHLET-CD, ICARE-CATHARE, MELCOR, RATEG/SVECHA, RELAP/-SCDAPSIM, and SCDAP/RELAP5. The INRNE took responsibility as benchmark coordinator to compare the code results with the experimental data. As a basis of the present work, histories of temperatures, hydrogen production and other important variables were used. Besides, axial profiles at quench initiation and the final time of 7000 s, above all of temperatures, are presented. For most variables a mainstream of

  4. Inductive heating and quenching of planetary shafts

    Directory of Open Access Journals (Sweden)

    B. Kosec

    2010-04-01

    Full Text Available Purpose: High mechanical and temperature cyclic loading of the final products for automotive, construction, transport and agriculture mechanization industry, demands sufficient mechanical properties of all of their components during its exploitation. Majority of the components is made from steel, by different cold forming processes. Their main demanded characteristics are surface wear resistance and fatigue strength under pulsating stress in combination with cyclic temperature loading, which could be achieved only by appropriate heat treatment.Design/methodology/approach: In the experimental part of our work, the efficiency of the combined inductive heating and water quenching heat treatment and quality of the planetary shafts were analyzed, with the use of thermographic analysis, hardness measurements, and metallographic examination.Findings: Combination of inductive heating and water quenching is the most effective heat treatment process of carbon steel planetary shafts for the diesel engine starters.Research limitations/implications: Long life span of carbon steel planetary shafts it's essential for their economical production. The replacement of starter is expensive from both: money and working time point of view.Practical implications: Surface temperature measurements during the inductive heating process were realized in the industrial environment. The intensity and homogeneity of the planetary shaft surface temperature field was measured by thermographic camera.Originality/value: On the base of theoretical knowledge and measurements, a mathematical model for temperature conditions determination in the shaft during the entire process of heating and quenching was carried out. On the basis of developed mathematical model a computer program was worked out, and used for analyses and optimization of planetary shafts induction hardening process.

  5. Quenching simulation of steel grinding balls

    Energy Technology Data Exchange (ETDEWEB)

    Zapata-Hernandez, O.; Reyes, L. A.; Camurri, C.; Carrasco, C.; Garza-Monte-de-Oca, F.; Colas, R.

    2015-07-01

    The phase transformations of high carbon steel during quenching and equalizing were modelled using commercial computer packages based on the finite element method and the kinetic transformation of steel. The model was used to predict the temperature and microstructural changes taking place within balls of two different sizes that are used for grinding mineral ores. A good correlation between the temperatures measured by inserted thermocouples and those predicted by the model was obtained after modifying the thermal conductivity of the steel within the temperature domain at which mixed phases are present. The phase transformations predicted were confirmed by metallographic analyses. (Author)

  6. Intelligent temperature control system of quench furnace

    Institute of Scientific and Technical Information of China (English)

    胡燕瑜; 桂卫华; 唐朝晖; 唐玲

    2004-01-01

    A fuzzy-neural networks intelligent temperature control system of quench furnace was presented. Combined genetic algorithm with back-propagation algorithm, the weight values of neural networks, parameters of fuzzy membership functions and inference rules can be adjusted automatically, which realizes the optimal control of temperature. The results show that this control system can run effectively with satisfied temperature precision: in temperature uprising stage, overshot of temperature is under 4 ℃; in stable stage, the scope of temperature change is controlled within ±2 ℃, which meets the need of control veracity of temperature.

  7. The "Perfect" Fluid Quenches Jets Almost Perfectly

    OpenAIRE

    Müller, Berndt

    2008-01-01

    The QCD matter produced in nuclear collisions at the Relativistic Heavy Ion Collider (RHIC) has been found to have a very low shear viscosity, which is close to the lower bound allowed by unitarity. The matter has also been found to strongly suppress the emission of energetic hadrons. This phenomenon, called "jet quenching" is interpreted to be the result of a large energy loss by the precursor parton on its path through the dense matter, primarily due to gluon radiation. I discuss how the tw...

  8. Voltage Quench Dynamics of a Kondo System.

    Science.gov (United States)

    Antipov, Andrey E; Dong, Qiaoyuan; Gull, Emanuel

    2016-01-22

    We examine the dynamics of a correlated quantum dot in the mixed valence regime. We perform numerically exact calculations of the current after a quantum quench from equilibrium by rapidly applying a bias voltage in a wide range of initial temperatures. The current exhibits short equilibration times and saturates upon the decrease of temperature at all times, indicating Kondo behavior both in the transient regime and in the steady state. The time-dependent current saturation temperature connects the equilibrium Kondo temperature to a substantially increased value at voltages outside of the linear response. These signatures are directly observable by experiments in the time domain. PMID:26849606

  9. Minimum Quench Energies of LHC Strands

    CERN Document Server

    Bauer, P; Wolf, R

    1998-01-01

    Within the framework of the LHC Project a program has been initiated at CERN to establish the influence of various strand parameters (coating, Cu/Sc ratio, RRR, billet design, cooling) on the Minimum Quench Energy (MQE) of LHC prototype strands operating in superfluid helium at 1.9K in peak-fields of 9T. The experimental technique is based on a graphite-paste tip heater described in [1]. The analysis of the measurements was facilitated by a theoretical model based on the numerical solution of the one-dimensional heat balance equation.

  10. GaN-Based, Low-Voltage Avalanche Photodiodes for Robust and Compact UV Imagers Project

    Data.gov (United States)

    National Aeronautics and Space Administration — This Phase I SBIR program is directed toward the development of a novel low-voltage (~10V) AlGaN-based multi-quantum well (MQW) avalanche photodiode (APD) on...

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

    International Nuclear Information System (INIS)

    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 λ 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.

  12. Single Photon Sensitive HgCdTe Avalanche Photodiode Detector (APD) Project

    Data.gov (United States)

    National Aeronautics and Space Administration — A linear mode HgCdT electron-initiated avalanche photodiode (EAPD) capable of 1570nm photon detection efficiency (PDE) at >10 MHz will be developed. The Phase I...

  13. Loading-rate-independent delay of catastrophic avalanches in a bulk metallic glass

    Science.gov (United States)

    Chen, S. H.; Chan, K. C.; Wang, G.; Wu, F. F.; Xia, L.; Ren, J. L.; Li, J.; Dahmen, K. A.; Liaw, P. K.

    2016-02-01

    The plastic flow of bulk metallic glasses (BMGs) is characterized by intermittent bursts of avalanches, and this trend results in disastrous failures of BMGs. In the present work, a double-side-notched BMG specimen is designed, which exhibits chaotic plastic flows consisting of several catastrophic avalanches under the applied loading. The disastrous shear avalanches have, then, been delayed by forming a stable plastic-flow stage in the specimens with tailored distances between the bottoms of the notches, where the distribution of a complex stress field is acquired. Differing from the conventional compressive testing results, such a delaying process is independent of loading rate. The statistical analysis shows that in the specimens with delayed catastrophic failures, the plastic flow can evolve to a critical dynamics, making the catastrophic failure more predictable than the ones with chaotic plastic flows. The findings are of significance in understanding the plastic-flow mechanisms in BMGs and controlling the avalanches in relating solids.

  14. Avalanche criticality during compression of porcine cortical bone of different ages

    Science.gov (United States)

    Baró, Jordi; Shyu, Peter; Pang, Siyuan; Jasiuk, Iwona M.; Vives, Eduard; Salje, Ekhard K. H.; Planes, Antoni

    2016-05-01

    Crack events developed during uniaxial compression of cortical bones cut from femurs of developing pigs of several ages (4, 12, and 20 weeks) generate avalanches. These avalanches have been investigated by acoustic emission analysis techniques. The avalanche energies are power-law distributed over more than four decades. Such behavior indicates the absence of characteristic scales and suggests avalanche criticality. The statistical distributions of energies and waiting times depend on the pig age and indicate that bones become stronger, but less ductile, with increasing age. Crack propagation is equally age-dependent. Older pigs show, on average, larger cracks with a time distribution similar to those of aftershocks in earthquakes, while younger pigs show only statistically independent failure events.

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

    Institute of Scientific and Technical Information of China (English)

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

    2013-01-01

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

  16. Application of a New Rheological Model to Rock Avalanches: An SPH Approach

    Science.gov (United States)

    Manzanal, D.; Drempetic, V.; Haddad, B.; Pastor, M.; Martin Stickle, M.; Mira, P.

    2016-06-01

    Rock avalanches move large volumes of material causing a highly destructive power over large areas. In these events, it is possible to monitor the evolution of slopes but failure cannot be always prevented. For this reason, modelling of the propagation phase provides engineers with fundamental information regarding speed, track, runout and depth. From these data, it is possible to perform a better risk assessment and propose mitigation measures to reduce the potential hazard of specific area. The purpose of this paper is to present a depth integrated, SPH model, which can be used to simulate real rock avalanches and to assess the influence of the rheology on the avalanche properties. The paper compares the performance of different rheological models to reproduce the track, runout and depth of the final deposit for both, scale test and real events such as Frank and Thurwiesier rock avalanches. These sets of benchmarks provide information on the proposed model accuracy and limitations.

  17. Prediction of picosecond voltage collapse and electromagnetic wave generation in gas avalanche switches

    International Nuclear Information System (INIS)

    A picosecond speed switch, the Gas Avalanche Switch (GAS), has been proposed for GeV linear accelerators. The medium is gas at high pressure (100 - 700 atm). An avalanche discharge is induced between pulse-charged high voltage electrodes by electron deposition from a fast laser pulse. Avalanche electrons move to the positive electrode, causing the applied voltage to collapse in picoseconds. A two-dimensional (2D) electromagnetic electron fluid computer code calculates the avalanche evolution and voltage collapse in air for an infinite parallel plate capacitor with a 0.1 mm spacing. Calculations are done for an accelerator switch geometry consisting of a 0.7 mm wide by 0.8 mm high, rectangular, high voltage center electrode (CE) between the grounded plates of a parallel plate line of 2 mm spacing. Several variations of CE elevation and initial electron deposition are investigated The 2D character of the outgoing TEM waves is shown

  18. Investigation of the avalanche photodiodes for the CMS electromagnetic calorimeter operated at high gain

    CERN Document Server

    Deiters, K; Godinovic, N; Ingram, Q; Longo, E; Montecchi, M; Musienko, Yu V; Nicol, S; Patel, B; Renker, D; Reucroft, S; Rusack, R W; Sakhelashvili, T M; Singovsky, A V; Soric, I; Swain, J D; Vikas, P

    2001-01-01

    Avalanche photodiodes (APD) with improved characteristics were developed by Hamamatsu Photonics for the electromagnetic calorimeter of the CMS experiment. This report presents measurements of the latest generation of APDs, which are capable to operate at high gains (~2000). (5 refs).

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

    Science.gov (United States)

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

    2012-08-24

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

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

    Science.gov (United States)

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

    2012-08-01

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

  1. Design and performance of a position sensitive annular parallel plate avalanche counter

    International Nuclear Information System (INIS)

    Design considerations and characteristics of a parallel plate avalanche counter is presented. A short introduction to parallel plate detectors as well as the mechanical and electrical design is reported. Some results from experiments illustrate the performance of the detector

  2. Extended Wavelength InP Based Avalanche Diodes for MWIR Response Project

    Data.gov (United States)

    National Aeronautics and Space Administration — For this NASA STTR program, we propose to develop a novel superlattice-based near infrared to midwave infrared avalanche photodetector (APD) grown on InP substrates...

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

    Science.gov (United States)

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

    2013-03-01

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

  4. Prediction of steel quenching results depending on the efficiency of quenching fluids

    International Nuclear Information System (INIS)

    Quenching makes it possible to obtain, on previously austenitized steel parts, special structures and mechanical characteristics by making faster cooling than in calm air. To obtain this cooling, the austenitized part is plunged into a stirred fluid maintained at low temperature. After having recalled the methods making it possible to quantify the effectiveness of the quenching fluid and to foresee the aptitude of a steel grade for quenching (or hardenability), we will specify the method developed by UNIMETAL RECHERCHE : a) to control, on an instrumented furnace, the quenching parameters (mainly, fluid characteristics) b) to determine the cooling curves inside cylindrical steel test bars (Φ 10 to 60 mm) c) to measure cooling speeds (Vr) at specific points on the incident curves d) to establish of the relationship between Vr and the diameter Φ e) to enter these relations into the PREVER UNIMETAL model. This makes it possible to foresee the results of conventional tests defining hardenability (JOMINY test, U curves) This model, operational in 1993, makes it possible to avoid long and costly real tests. (orig.)

  5. Heat transfer model for quenching by submerging

    Energy Technology Data Exchange (ETDEWEB)

    Passarella, D N; Varas, F [Departamento de Matematica Aplicada II, E.T.S. de Ing. de Telecomunicacion, Universidad de Vigo, Campus Marcosende, 36310 Vigo (Spain); MartIn, E B, E-mail: diego@dma.uvigo.es, E-mail: fvaras@uvigo.es, E-mail: emortega@uvigo.es [Area de Mecanica de Fluidos, E.T.S. de Ing. Industriales, Universidad de Vigo, Campus Marcosende, 36310 Vigo (Spain)

    2011-05-01

    In quenching by submerging the workpiece is cooled due to vaporization, convective flow and interaction of both mechanisms. The dynamics of these phenomena is very complex and the corresponding heat fluxes are strongly dependent on local flow variables such as velocity of fluid and vapor fraction. This local dependence may produce very different cooling rates along the piece, responsible for inappropriate metallurgical transformations, variability of material properties and residual stresses. In order to obtain an accurate description of cooling during quenching, a mathematical model of heat transfer is presented here. The model is based on the drift-flux mixture-model for multiphase flows, including an equation of conservation of energy for the liquid phase and specific boundary conditions that account for evaporation and presence of vapor phase on the surface of the piece. The model was implemented on Comsol Multiphysics software. Generation of appropriate initial and boundary conditions, as well as numerical resolution details, is briefly discussed. To test the model, a simple flow condition was analyzed. The effect of vapor fraction on heat transfer is assessed. The presence of the typical vapor blanket and its collapse can be recovered by the model, and its effect on the cooling rates on different parts of the piece is analyzed. Comparisons between numerical results and data from literature are made.

  6. Holographic quenches towards a Lifshitz point

    Science.gov (United States)

    Camilo, Giancarlo; Cuadros-Melgar, Bertha; Abdalla, Elcio

    2016-02-01

    We use the holographic duality to study quantum quenches of a strongly coupled CFT that drive the theory towards a non-relativistic fixed point with Lifshitz scaling. We consider the case of a Lifshitz dynamical exponent z close to unity, where the non-relativistic field theory can be understood as a specific deformation of the corresponding CFT and, hence, the standard holographic dictionary can be applied. On the gravity side this amounts to finding a dynamical bulk solution which interpolates between AdS and Lishitz spacetimes as time evolves. We show that an asymptotically Lifshitz black hole is always formed in the final state. This indicates that it is impossible to reach the vacuum state of the Lifshitz theory from the CFT vacuum as a result of the proposed quenching mechanism. The nonequilibrium dynamics following the breaking of the relativistic scaling symmetry is also probed using both local and non-local observables. In particular, we conclude that the equilibration process happens in a top-down manner, i.e., the symmetry is broken faster for UV modes.

  7. Heat transfer model for quenching by submerging

    International Nuclear Information System (INIS)

    In quenching by submerging the workpiece is cooled due to vaporization, convective flow and interaction of both mechanisms. The dynamics of these phenomena is very complex and the corresponding heat fluxes are strongly dependent on local flow variables such as velocity of fluid and vapor fraction. This local dependence may produce very different cooling rates along the piece, responsible for inappropriate metallurgical transformations, variability of material properties and residual stresses. In order to obtain an accurate description of cooling during quenching, a mathematical model of heat transfer is presented here. The model is based on the drift-flux mixture-model for multiphase flows, including an equation of conservation of energy for the liquid phase and specific boundary conditions that account for evaporation and presence of vapor phase on the surface of the piece. The model was implemented on Comsol Multiphysics software. Generation of appropriate initial and boundary conditions, as well as numerical resolution details, is briefly discussed. To test the model, a simple flow condition was analyzed. The effect of vapor fraction on heat transfer is assessed. The presence of the typical vapor blanket and its collapse can be recovered by the model, and its effect on the cooling rates on different parts of the piece is analyzed. Comparisons between numerical results and data from literature are made.

  8. Fractionation method with quench liquid recycle

    Energy Technology Data Exchange (ETDEWEB)

    Skraba, F.W.

    1988-10-11

    This patent describes a method of fractionating a hot vapor containing feed, the steps comprising: (a) introducing a hot vapor containing feed into a fractionation zone at a vapor containing feed location near one end of the fractionation zone; (b) removing liquid from a liquid collection zone below the one end of the fractionation zone; (c) passing the thus removed liquid through a heat extraction zone to extract heat from the liquid to produce cooled liquid; (d) returning a first portion of the thus cooled liquid to the fractionation zone as a first reflux liquid at a location intermediate the vapor containing feed location and the other end of the fractionation zone; and (e) returning a second portion of the thus cooled liquid to the fractionation zone as a quench liquid at a location intermediate the vapor containing feed location and the surface of thee liquid in the liquid collection zone wherein the quench liquid is sprayed onto an inclined surface over which condensed liquid from the hot vapor containing feed passes from the fractionation zone and the vapor containing feed location to the surface of the liquid in the liquid collection zone to directly cool the condensed liquid.

  9. Quenching of dilute Be-H alloys

    International Nuclear Information System (INIS)

    Be is a relevant material in nuclear and reactor technology. It has recently gained additional prominence as a coating material for Tokamak fusion devices. In this latter context, the reactions of Be with the hydrogen isotopes are very important. Recently, rather precise hydrogen solubility measurements both in α-Be and in β-Be became available. This paper presents an adapted form the solubility of H in Be in the α-phase. The solubility in terms of the atom ratio H/M can be expressed by: S = 1.723 x 10-4 sq. root p exp(-16700/RT) [H][M] where p is the pressure in MPa, T the temperature and R the gas constant. Thus, α-Be is an endothermic occluder of hydrogen. Another endothermic occluder of H is, for instance, Cu where TEM techniques showed the quenching of dilute Cu-H alloys from high temperatures leads to the formation of hydrogen bubbles around room temperature. Matter is ejected from the growing bubble by prismatic dislocation loop punching. In other TEM studies, it was established that quenching of the exothermic occluder of hydrogen, Mg, does not lead to bubble precipitation but to the formation of small hydride particles

  10. Oxygen distributions within tissue by phosphorescence quenching

    Science.gov (United States)

    Wilson, David F.; Grosul, Pavel; Rozhkov, Vladimir; Dugan, Benjamin W.; Reitveld, Ivo; Vinogradov, Sergei A.

    2002-06-01

    Oxygen dependent quenching of phosphorescence is a powerful method for measuring oxygen. Phosphors are now available that absorb and emit in the near IR region of the spectrum, are nontoxic, and remain in the blood, allowing rapid measure of oxygen through out selected tissue volumes. In vivo measurements are non-invasive except for the need to inject phosphor into the blood, and phosphorescence lifetimes can be measured without interference by tissue pigments that absorb or fluorescence at the measurement wavelengths. Phosphorescence quenching is uniquely useful for: (1) imaging oxygen in optically clear media or in the surface layer of the tissue, such as in the retina of the eye; (2) determining the distribution of oxygen in media, such as tissue, which have heterogeneous distributions by deconvoluting phosphorescence decay dat. These can be used to calculate the corresponding oxygen histograms. Measurement in 2D grids can b used to construct contour maps of the fraction of the sampled tissue volume with any selected range of oxygen pressures. These maps accurately show the location and size of any regions of hypoxia within the sampled tissue.

  11. Exotic mesons in quenched lattice QCD

    CERN Document Server

    Bernard, C W; DeTar, C E; Gottlieb, S; Heller, U M; Hetrick, J E; McNeile, C; Rummukainen, K; Sugar, B; Toussaint, D; Wingate, M; Bernard, Claude; Grand, Thomas A. De; Tar, Carleton De; Gottlieb, Steven; Heller, Urs M.; Hetrick, James E.; Neile, Craig Mc; Rummukainen, Kari; Sugar, Bob; Toussaint, Doug; Wingate, Matthew

    1997-01-01

    Since gluons in QCD are interacting fundamental constituents just as quarks are, we expect that in addition to mesons made from a quark and an antiquark, there should also be glueballs and hybrids (bound states of quarks, antiquarks and gluons). In general, these states would mix strongly with the conventional q-bar-q mesons. However, they can also have exotic quantum numbers inaccessible to q-bar-q mesons. Confirmation of such states would give information on the role of "dynamical" color in low energy QCD. In the quenched approximation we present a lattice calculation of the masses of mesons with exotic quantum numbers. These hybrid mesons can mix with four quark (q-bar-q-bar-q-q) states. The quenched approximation partially suppresses this mixing. Nonetheless, our hybrid interpolating fields also couple to four quark states. Using a four quark source operator, we demonstrate this mixing for the 1-+ meson. Using the conventional Wilson quark action, we calculate both at reasonably light quark masses, intend...

  12. Investigation of volumetrically heated debris bed quenching

    Energy Technology Data Exchange (ETDEWEB)

    Konovalikhin, M.J.; Sehgal, B.R. [Royal Institute of Technology, Div. of Nuclear Power Safety, Stockholm (Sweden)

    2001-07-01

    A series of experiments were conducted at RIT (Royal Institute of Technology) in which hot homogeneous and stratified particle beds were quenched by establishing a column of water onto the top of the bed and by injection of water from the bottom delivered through downcomers from the water overlayer. For this experimental program the following approach was adopted. Since corium debris have a particle size distribution and are more like sand, the debris beds were built with sand of different particle size distributions, heated with a network of thin heaters, distributed uniformly in the sand bed to produce uniform volumetric heat generation. Low porosity beds were constructed, since they are the most difficult to quench with top flooding. The primary objective was to obtain data, which will provide a phenomenological basis for assessing margins for coolability of a degraded core debris bed in the lower head of an LWR vessel as well as steam generation rate from the interactions between core debris and water. This paper summarizes the experimental results along with related analysis. (authors)

  13. High pressure pulsed avalanche discharges: Scaling of required preionization rate for homogeneity

    International Nuclear Information System (INIS)

    Homogeneous high-pressure discharges can be formed by pulsed avalanche breakdown, provided that the individual avalanche heads have diffused to a large enough radius to overlap before streamer breakdown occurs. The overlap condition can be met by using an external mechanism to preionize the neutral gas, e.g., x-rays or uv radiation. There are several scenarios, (1) to preionize the gas, and then trigger the discharge by the sudden application of an electric field, (2) to apply an overvoltage over the discharge and trigger the discharge by external ionization, or (3) to have a continuous rate of external ionization and let the E field rise, with a comparatively long time constant τ, across the breakdown value (E/n)0. The authors here study the last of these scenarios, which gives a very efficient use of the preionization source because the avalanche startpoint can accumulate during the pre-avalanche phase. The authors have found that the required avalanche startpoint density Nst.p, defined as the density of individual single, or clusters of, electrons at the time when the electric field crosses the breakdown value, scales with pressure and rise time as Nst.p ∝ p21/4τ-3/4. This pressure scaling disagrees with the p3/2 scaling found by Levatter and Lin (J. Appl. Phys. 51(1), 210), while the rise time scaling agrees satisfactorily with their results. For an E field which rises slowly across the breakdown value, the pre-avalanche accumulation of electrons must be taken into account, as well as the fact that the density ne of free electrons becomes larger than the density Nst.p of independent avalanche heads: when electron impact ionization closely balances attachment, individual electrons are replaced by clusters of electrons which are too close to form individual avalanche heads

  14. Secondary instability in drift wave turbulence as a mechanism for avalanche and zonal flow formation

    International Nuclear Information System (INIS)

    We report on recent developments in the theory of secondary instability in drift-ITG turbulence. Specifically, we explore secondary instability as a mechanism for avalanche formation. A theory of radially extended streamer cell formation and self-regulation is presented. Aspects of streamer structure and dynamics are used to estimate the variance of the drift-wave induced flux. The relation between streamer cell structures and the avalanche concept is discussed, as are the implications of our results for transport modeling. (author)

  15. The design of avalanche protection dams Recent practical and theoretical developments

    OpenAIRE

    2009-01-01

    This book represents a capitalisation of knowledge from previous EC research projects in the field of Natural hazards and, in particular, the CADZIE and SATSIE projects addressing the problem of avalanches. It is about the design of dams and other protection measures in the run-out zones of wet- and dry-snow avalanches. The book summarises recent theoretical developments and the results of field and laboratory studies, combining them with traditional design guidelines and principles to formu...

  16. Exact equqations and scaling relations for f-avalanche in the Bak-Sneppen evolution model

    OpenAIRE

    Li, W; Cai, X.

    2000-01-01

    Infinite hierarchy of exact equations are derived for the newly-observed f-avalanche in the Bak-Sneppen evolution model. By solving the first order exact equation, we found that the critical exponent which governs the divergence of the average avalanche size, is exactly 1 (for all dimensions), confirmed by the simulations. Solution of the gap equation yields another universal exponent, denoting the the relaxation to the attractor, is exactly 1. We also establish some scaling relations among t...

  17. Driving rate effects in avalanche-mediated, first-order phase transitions

    OpenAIRE

    Pérez Reche, Francisco José; Tadic, Bosiljka; Mañosa, Lluís; Planes Vila, Antoni; Vives i Santa-Eulàlia, Eduard

    2004-01-01

    We have studied the driving rate and temperature dependence of the power-law exponents that characterize the avalanche distribution in first-order phase transitions. Measurements of acoustic emission in structural transitions in Cu-Zn-Al and Cu-Al-Ni are presented. We show how the observed behaviour emerges within a general framework of competing time scales of avalanche relaxation, driving rate, and thermal fluctuations. We have confirmed our findings by numerical simulations of a prototype ...

  18. Mean Field Theory of Sandpile Avalanches: from the Intermittent to the Continuous Flow Regime

    OpenAIRE

    Benza, V. G.; Nori, Franco; Pla, Oscar

    1993-01-01

    We model the dynamics of avalanches in granular assemblies in partly filled rotating cylinders using a mean-field approach. We show that, upon varying the cylinder angular velocity $\\omega$, the system undergoes a hysteresis cycle between an intermittent and a continuous flow regimes. In the intermittent flow regime, and approaching the transition, the avalanche duration exhibits critical slowing down with a temporal power-law divergence. Upon adding a white noise term, and close to the trans...

  19. Wave-like avalanche propagation in the continuum field model of self-organized criticality

    OpenAIRE

    Oh, Dong Keun; Jhang, Hogun

    2013-01-01

    Travelling wave is identified as the mechanism of avalanche propagation in the continuum SOC (self-organized critical) system. Recovering the hidden causality based on a generalization of Fick's law, we lead the equivalent continuum equation which has spatiotemporal nonlocality. Taking into account of the hyperbolicity from the retarded response of the nonlocal kernel, it is possible to capture the propagating avalanche in constant speed. Verifying the computation, we analyze the evolution of...

  20. Avalanche Process in Semiconductor Photo Detectors in the Context of the Feedback Theory

    Czech Academy of Sciences Publication Activity Database

    Kushpil, Vasilij

    Rijeka : InTech, 2012 - (Gateva, S.), s. 207-230 ISBN 978-953-51-0358-5. - (Electrical and Electronic Engineering) R&D Projects: GA MŠk LA08015 Institutional support: RVO:61389005 Keywords : avalanche process * photo detectors Subject RIV: BG - Nuclear, Atomic and Molecular Physics, Colliders http://www.intechopen.com/books/photodetectors/avalanche-process-in-semiconductor-photo-detectors-in-the-context-of-the-feedback- theory -

  1. New alpha particle counter based on micro-pixel avalanche photodiode

    International Nuclear Information System (INIS)

    Full text : The main goal of this work is study of possibility to detect alpha particles with micro-pixel avalanche photodiode which has very thin active volume. The obtained results show that alpha detectors based on the micro-pixel avalanche photodiodes can be used as alpha particle counter in many experiments : public security, radioactive contamination monitoring in various environments and detection of charged particles from nuclear reactions

  2. On-Chip Integrated, Silicon–Graphene Plasmonic Schottky Photodetector with High Responsivity and Avalanche Photogain

    Science.gov (United States)

    Goykhman, Ilya; Sassi, Ugo; Desiatov, Boris; Mazurski, Noa; Milana, Silvia; de Fazio, Domenico; Eiden, Anna; Khurgin, Jacob; Shappir, Joseph; Levy, Uriel; Ferrari, Andrea C.

    2016-05-01

    We report an on-chip integrated metal-graphene-silicon plasmonic Schottky photodetector with 85mA/W responsivity at 1.55 um and 7% internal quantum efficiency. This is one order of magnitude higher than metal-silicon Schottky photodetectors operated in the same conditions. At a reverse bias of 3V, we achieve avalanche multiplication, with 0.37A/W responsivity and avalanche photogain~2. This paves the way to graphene integrated silicon photonics.

  3. Different Avalanche Behaviors in Different Specific Areas of a System Based on Neural Networks

    Institute of Scientific and Technical Information of China (English)

    ZHAO Xiao-Wei; CHEN Tian-Lun

    2003-01-01

    Based on the standard self-organizing map (SOM) neural network model and an integrate-and-fire mecha-nism, we introduce a kind of coupled map lattice system to investigate scale-invariance behavior in the activity of modelneural populations. We find power-law distribution behavior of avalanche size in our model. But more importantly, wefind there are different avalanche distribution behaviors in different specific areas of our system, which are formed by thetopological learning process of the SOM net.

  4. Spike avalanches exhibit universal dynamics across the sleep-wake cycle.

    Directory of Open Access Journals (Sweden)

    Tiago L Ribeiro

    Full Text Available BACKGROUND: 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. METHODOLOGY/PRINCIPAL FINDINGS: To address this issue, we employed chronically implanted multielectrode arrays (MEA to record avalanches of action potentials (spikes from the cerebral cortex and hippocampus 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 statistics. We found that the size distribution of spike avalanches are well fit by lognormal distributions in FB animals, and by truncated power laws in the AN group. FB data surrogation markedly decreases the tail of the distribution, i.e. spike shuffling destroys the largest avalanches. The FB data are also characterized by multiple key features compatible with criticality in the temporal domain, such as 1/f spectra and long-term correlations as measured by detrended fluctuation analysis. These signatures are very stable across waking, slow-wave sleep and rapid-eye-movement sleep, but collapse during anesthesia. Likewise, waiting time distributions obey a single scaling function during all natural behavioral states, but not during anesthesia. Results are equivalent for neuronal ensembles recorded from visual and tactile areas of the cerebral cortex, as well as the hippocampus. CONCLUSIONS

  5. Avalanches, Breathers and Flow Reversal in a Continuous Lorenz-96 Model

    CERN Document Server

    Blender, Richard; Lucarini, Valerio

    2013-01-01

    For the discrete model suggested by Lorenz in 1996 a one-dimensional long wave approximation with nonlinear excitation and diffusion is derived. The model is energy conserving but non-Hamiltonian. In a low order truncation weak external forcing of the zonal mean flow induces avalanche-like breather solutions which cause reversal of the mean flow by a wave-mean flow interaction. The mechanism is an outburst-recharge process similar to avalanches in a sand pile model.

  6. Variation of Quench Propagation Velocities in YBCO Cables

    CERN Document Server

    Härö, E.; Stenvall, A.; 10.1007/s10948-015-2976-y

    2015-01-01

    changes during the quench. Due to the large temperature margin between the operation and the current sharing temperatures, the normal zone does not propagate with the temperature front. This means that the temperature will rise in a considerably larger volume when compared to the quenched volume. Thus, the evolution of the temperature distribution below current sharing temperature Tcs after the quench onset affects the normal zone propagation velocity in HTS more than in LTS coils. This can be seen as an acceleration of the quench propagation velocities while the quench evolves when margin to Tcs is high. In this paper we scrutinize quench propagation in a stack of YBCO cables with an in-house finite element method software which solves the heat diffusion equation. We compute the longitudinal and transverse normal zone propagation velocities at various distances from the hot spot to demonstrate the distance-variation...

  7. Generalized Kadanoff-Baym relation in nonequilibrium quenched models

    CERN Document Server

    Britto, A L M; Frenkel, J

    2016-01-01

    In the context of a broad class of quenched models, we derive a generalized differential form of the Kadanoff-Baym (KB) ansatz which relates the out of equilibrium correlated and spectral Green's functions. This relation holds at any time both before the quench (when it coincides with the fluctuation-dissipation theorem) as well as after it. We also examine, in the context of exactly soluble quenched models, the validity of some of the earlier alternative extensions of the KB ansatz.

  8. Holographic study on the jet quenching parameter in anisotropic systems

    CERN Document Server

    Wang, Luying

    2016-01-01

    We first calculate the jet quenching parameter of an anisotropic plasma with a U(1) chemical potential via the AdS/CFT duality. The effects of charge, anisotropy parameter and quark motion direction on the jet quenching parameter are investigated. We then discuss the situation of anisotropic black brane in the IR region. We study both the jet quenching parameters along the longitudinal direction and transverse plane.

  9. Optimising Gas Quenching Technology through Modelling of Heat Transfer

    Institute of Scientific and Technical Information of China (English)

    FiorentChaffotte; LindaLefevre; DidierDomergue; AymericGoidsteinas; XavierDoussot; QingfeiZhang

    2004-01-01

    Gas Quenching represents an environmentally friendly alternative to more commonly-used oil quenching. Yet,the performances of this technology remain limited in terms of cooling rates reached compared to oil quenching. Distortion and process homogeneity also have to be controlled carefully. The efficiency of the gas quenching process fully depends on the heat transfer between the gas and the quenched parts. The goal of this study is the optimisation of the gas quenching process efficiency through a better understanding of the heat transfer phenomena involved. The study has been performed with modelling means and validated by an experimental approach. ThE configuration of the gas flow has a major influence on the heat transfer phenomena between the gas and the parts. The fluid dynamics modelling approach performed in this study allows to optimise the heat transfer phenomena. New gas quenching processes allowing enhanced gas quenching performance through higher cooling rates can be thereby identified. The new solutions have been validated in experimental and industrial conditions. Results obtained allow to expect significant improvement of high pressure gas quenching technology.

  10. Optimising Gas Quenching Technology through Modelling of Heat Transfer

    Institute of Scientific and Technical Information of China (English)

    Florent Chaffotte; Linda L(e)fevre; Didier Domergue; Aymeric Goldsteinas; Xavier Doussot; Qingfei Zhang

    2004-01-01

    Gas Quenching represents an environmentally friendly alternative to more commonly-used oil quenching. Yet,the performances of this technology remain limited in terms of cooling rates reached compared to oil quenching. Distortion and process homogeneity also have to be controlled carefully. The efficiency of the gas quenching process fully depends on the heat transfer between the gas and the quenched parts. The goal of this study is the optimisation of the gas quenching process efficiency through a better understanding of the heat transfer phenomena involved. The study has been performed with modelling means and validated by an experimental approach. The configuration of the gas flow has a major influence on the heat transfer phenomena between the gas and the parts. The fluid dynamics modelling approach performed in this study allows to optimise the heat transfer phenomena. New gas quenching processes allowing enhanced gas quenching performance through higher cooling rates can be thereby identified. The new solutions have been validated in experimental and industrial conditions. Results obtained allow to expect significant improvement of high pressure gas quenching technology.

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

    Science.gov (United States)

    Pudasaini, S. P.; Krautblatter, M.

    2012-04-01

    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

  12. Experimental methods for quenching structures in lunar-analog silicate melts - Variations as a function of quench media and composition

    International Nuclear Information System (INIS)

    Compositions analogous to lunar green, orange, and brown glasses were synthesized under consistent conditions, then quenched into a variety of different media when the samples were removed from the furnace. Iron valence and coordination are a direct function of quench media used, spanning the range from brine/ice (most effective quench), water, butyl phthalate, silicone oil, liquid nitrogen, highly reducing CO-CO2 gas, to air (least efficient quench). In the green and brown glasses, Fe(3+) in four-fold and six-fold coordination is observed in the slowest-quenched samples Fe(2+) coordination varies directly with quench efficiency. Less pronounced changes were observed in the Ti-rich orange glass. Therefore the remote-sensed spectrum of a glass-bearing regolith on the moon may be influenced by the process by which the glass cooled, and extreme caution must be used when comparing spectra of synthetic glass analogs with real lunar glasses

  13. Modified Methodology for the Quench Temperature Selection in Quenching and Partitioning (Q&P) Processing of Steels

    Science.gov (United States)

    Seo, Eun Jung; Cho, Lawrence; De Cooman, Bruno C.

    2016-08-01

    The original method to select the optimum quench temperature for quenching and partitioning (Q&P) processing aims to determine the quench temperature which yields a maximum volume fraction of retained austenite. In the present study, the original method was reviewed and refined by comparison with experimental results. The proposed methodology is based on the use of a modified Koistinen-Marburger equation for the kinetics of the athermal martensite transformation of steels containing C, Mn, Si, Cr, and B.

  14. Quenched scaling of Wilson twisted mass fermions

    International Nuclear Information System (INIS)

    We investigate the scaling behaviour of quenched Wilson twisted mass fermions at maximal twist applying two definitions of the critical mass. The first definition uses the vanishing of the pseudoscalar meson mass mPS while the second employs the vanishing of the PCAC quark mass mPCAC. We confirm in both cases the expected O(a) improvement. In addition, we show that the PCAC quark mass definition leads to substantially reduced O(a2) cut-off effects even when the pseudoscalar meson mass mPS is as small as 270 MeV. At a fixed value of mPS we perform continuum limits for the vector meson mass mV and for the pseudoscalar decay constant fPS and discuss the renormalisation constant ZV of the vector current. (orig.)

  15. Quenched scaling of Wilson twisted mass fermions

    International Nuclear Information System (INIS)

    We investigate the scaling behaviour of quenched Wilson twisted mass fermions at maximal twist applying two definitions of the critical mass. The first definition uses the vanishing of the pseudoscalar meson mass mPS while the second employs the vanishing of the PCAC quark mass mPCAC. We confirm in both cases the expected O(a) improvement. In addition, we show that the PCAC quark mass definition leads to substantially reduced O(a2) cut-off effects even when the pseudoscalar meson mass mPS is as small as 270 MeV. At a fixed value of mPS we perform continuum limits for the vector meson mass mV and for the pseudoscalar decay constant fPS and discuss the renormalisation constant ZV of the vector current

  16. Collisional quenching of highly rotationally excited HF

    CERN Document Server

    Yang, Benhui; Forrey, R C; Stancil, P C; Balakrishnan, N

    2015-01-01

    Collisional excitation rate coefficients play an important role in the dynamics of energy transfer in the interstellar medium. In particular, accurate rotational excitation rates are needed to interpret microwave and infrared observations of the interstellar gas for nonlocal thermodynamic equilibrium line formation. Theoretical cross sections and rate coefficients for collisional deexcitation of rotationally excited HF in the vibrational ground state are reported. The quantum-mechanical close-coupling approach implemented in the nonreactive scattering code MOLSCAT was applied in the cross section and rate coefficient calculations on an accurate 2D HF-He potential energy surface. Estimates of rate coefficients for H and H$_2$ colliders were obtained from the HF-He collisional data with a reduced-potential scaling approach. The calculation of state-to-state rotational quenching cross sections for HF due to He with initial rotational levels up to $j=20$ were performed for kinetic energies from 10$^{-5}$ to 15000...

  17. Quenching Simulation of PM Coated Tools

    Institute of Scientific and Technical Information of China (English)

    AxelHoftert; WernerTheisen; ChristophBroeckmann

    2004-01-01

    HIP cladding is a powder metallurgical coating technique used in the production of wear parts and tools. In many cases the composite components consist of carbide-free hot-work steel as base material and wear resistant carbide-rich PM cold-work steel as coating material. To ensure operativeness a heat tleatment matched to the substrate and coating material is required. Dissimilar phase tlansformation behaviour and different thermal expansion coefficients of layer and substrate entail inner stresses affecting the tlansformation kinetics in tam. In order to get a deeper insight into these effects Finite Element simulation tools are used. On the one hand, the tlansient heat conduction problem of the quenching process has to be solved. Non-linear boundary conditions and phase transformation of both, substrate and layer are considered. On the other hand, the mechanical response is calculated. The overall aim of the investigation is an improvement of common heat treatment techniques used for HIP cladded wear parts.

  18. Holography of radiation and jet quenching

    International Nuclear Information System (INIS)

    We study the on-linear propagation of radiation in N=4 SYM at zero and finite temperature using the refined radius/scale duality in AdS/CFT. We find that at finite temperature, the radiation stalls at a distance of 1/πT with a natural geometric and holographic interpretation. Indeed, the stalling is the holographic analogue of the gravitational in-fall of light towards the black hole in the bulk. We show that in the strongly interacting finite temperature medium, radiation can reach much farther than the static force. We suggest that these results are relevant for jet quenching by a strongly coupled quark-gluon liquid as currently probed in heavy ion colliders at RHIC. In particular, colored jets cannot make it beyond 1/3 fin at RHIC whatever their energy. (author)

  19. A perturbative framework for jet quenching

    CERN Document Server

    Zapp, Korinna C; Wiedemann, Urs A

    2013-01-01

    We present a conceptually new framework for describing jet evolution in the dense medium produced in ultra-relativistic nucleus-nucleus collisions using perturbative QCD and its implementation into the Monte Carlo event generator JEWEL. The rescattering of hard partons in the medium is modelled by infrared continued pQCD matrix elements supplemented with parton showers. The latter approximate higher order real-emission matrix elements and thus generate medium-induced gluon emissions. The interplay between different emissions is governed by their formation times. The destructive interference between subsequent scattering processes, the non-Abelian version of the Landau-Pomeranchuk-Migdal effect, is also taken into account. In this way the complete radiation pattern is consistently treated in a uniform way. Results obtained within this minimal and theoretically well constrained framework are compared with a variety of experimental data susceptible to jet-quenching effects at both RHIC and the LHC. Overall, a go...

  20. Thermal quenching of fluorescence in condensed media

    Science.gov (United States)

    Lagos, Miguel; Paredes, Rodrigo

    2016-09-01

    Environmental factors strongly affect the features of the electromagnetic spectra of fluorescent compounds hosted by material media. The shape of the absorption and emission peaks, their characteristic asymmetry and breadth, the Stokes shift and quantum yield are generally temperature dependent and heavily influenced by both the local and extended physical properties of the medium. The theoretical method used before to obtain the lineshape function is extended here to other terms of the interaction energy between the optically sensitive orbital and the hosting medium, which become significant when the spectral feature is broad. An analytical expression for the temperature dependent decay rate by non-radiative processes is obtained by this way. Comparison with experiment on thermal quenching gives agreement within the experimental uncertainty. The solvent polarity, its protic or aprotic character, hydrogen bonds, proximity effects and presence of quenchers are expected to enter through the coupling constants of the corresponding energy terms.

  1. How Cosmic Web Detachment Drives Galaxy Quenching

    CERN Document Server

    Aragon-Calvo, Miguel A; Silk, Joseph

    2016-01-01

    We present the Cosmic Web Detachment (CWD) model, a conceptual framework to interpret galaxy evolution in a cosmological context, providing a direct link between the star formation history of galaxies and the cosmic web. The CWD model unifies several mechanism known to disrupt or stop star formation into one single physical process and provides a natural explanation for a wide range of galaxy properties. Galaxies begin accreting star-forming gas at early times via a network of primordial highly coherent filaments. The efficient star formation phase ends when non-linear interactions with other galaxies or elements of the cosmic web detach the galaxy from its network of primordial filaments, thus ending the efficient accretion of cold gas. The stripping of the filamentary web around galaxies is the physical process responsible of star formation quenching in gas stripping, harassment, strangulation and starvation. Being a purely gravitational/mechanical process CWD acts at a more fundamental level than internal ...

  2. Thermal quenching of luminescence processes in feldspars

    DEFF Research Database (Denmark)

    Poolton, N.R.J.; Bøtter-Jensen, L.; Duller, G.A.T.

    1995-01-01

    The technique of optically stimulated luminescence has important uses in the dose evaluation of irradiated feldspars. The luminescence process involves the eviction of electrons from donor traps, charge transfer through the conduction band, and recombination at acceptor sites; each...... of these processes is, in general, thermally dependent, and leads either to enhancement or quenching of the luminescence with increasing temperature. Previous studies have measured the combined thermal activation characteristics of all three processes, and show a strong dependence on stimulation energy....... In this article, an initial attempt is made to isolate only the recombination part of the luminescence cycle, and determine its thermal characteristics separately. A Variety of luminescence transitions are examined in a range of both alkali and plagioclase feldspars; three distinct emission types are identified...

  3. Quenching Simulation of PM Coated Tools

    Institute of Scientific and Technical Information of China (English)

    Axel H(o)fter; Werner Theisen; Christoph Broeckmann

    2004-01-01

    HIP cladding is a powder metallurgical coating technique used in the production of wear parts and tools. In many cases the composite components consist of carbide-free hot-work steel as base material and wear resistant carbide-rich PM cold-work steel as coating material. To ensure operativeness a heat treatment matched to the substrate and coating material is required. Dissimilar phase transformation behaviour and different thermal expansion coefficients of layer and substrate entail inner stresses affecting the transformation kinetics in turn. In order to get a deeper insight into these effects Finite Element simulation tools are used. On the one hand, the transient heat conduction problem of the quenching process has to be solved. Non-linear boundary conditions and phase transformation of both, substrate and layer are considered. On the other hand, the mechanical response is calculated. The overall aim of the investigation is an improvement of common heat treatment techniques used for HIP cladded wear parts.

  4. The Role of Quench-back in the Passive Quench Protection of Long Solenoids with Coil Sub-division

    Energy Technology Data Exchange (ETDEWEB)

    Green, Michael A.; Guo, XingLong; Wang, Li; Pan, Heng; Wu, Hong

    2009-10-19

    This paper describes how a passive quench protection system can be applied to long superconducting solenoid magnets. When a solenoid coil is long compared to its thickness, the magnet quench process will be dominated by the time needed for uench propagation along the magnet length. Quench-back will permit a long magnet to quench more rapidly in a passive way. Quenchback from a conductive (low resistivity) mandrel is essential for spreading the quench along the length of a magnet. The andrel must be inductively coupled to the magnet circuit that is being quenched. Current induced in the mandrel by di/dt in the magnet produces heat in the mandrel, which in turn causes the superconducting coil wound on the mandrel to quench. Sub-divisions often employed to reduce the voltages to ground within the coil. This paper explores when it is possible for quench-back to be employed for passive quench protection. The role of sub-division of the coil is discussed for long magnets.

  5. Corium quench in deep pool mixing experiments

    International Nuclear Information System (INIS)

    The results of two recent corium-water thermal interaction (CWTI) tests are described in which a stream of molten corium was poured into a deep pool of water in order to determine the mixing behavior, the corium-to-water heat transfer rates, and the characteristic sizes of the quenched debris. The corium composition was 60% UO2, 16% ZrO2, and 24% stainless steel by weight; its initial temperature was 3080 K, approx.160 K above the oxide phase liquidus temperature. The corium pour stream was a single-phase 2.2 cm dia liquid column which entered the water pool in film boiling at approx.4 m/s. The water subcooling was 6 and 75C in the two tests. Test results showed that with low subcooling, rapid steam generation caused the pool to boil up into a high void fraction regime. In contrast, with large subcooling no net steam generation occurred, and the pool remained relatively quiescent. Breakup of the jet appeared to occur by surface stripping. In neither test was the breakup complete during transit through the 32 cm deep water pool, and molten corium channeled to the base where it formed a melt layer. The characteristic heat transfer rates measured 3.5 MJ/s and 2.7 MJ/s during the fall stage for small and large subcooling, respectively; during the initial stage of bed quench, the surface heat fluxes measured 2.4 MW/m2 and 3.7 MW/m2, respectively. A small mass of particles was formed in each test, measuring typically 0.1 to 1 mm and 1 to 5 mm dia for the large and small subcooling conditions, respectively. 9 refs., 13 figs., 1 tab

  6. AlInAsSb/GaSb staircase avalanche photodiode

    Science.gov (United States)

    Ren, Min; Maddox, Scott; Chen, Yaojia; Woodson, Madison; Campbell, Joe C.; Bank, Seth

    2016-02-01

    Over 30 years ago, Capasso and co-workers [IEEE Trans. Electron Devices 30, 381 (1982)] proposed the staircase avalanche photodetector (APD) as a solid-state analog of the photomultiplier tube. In this structure, electron multiplication occurs deterministically at steps in the conduction band profile, which function as the dynodes of a photomultiplier tube, leading to low excess multiplication noise. Unlike traditional APDs, the origin of staircase gain is band engineering rather than large applied electric fields. Unfortunately, the materials available at the time, principally AlxGa1-xAs/GaAs, did not offer sufficiently large conduction band offsets and energy separations between the direct and indirect valleys to realize the full potential of the staircase gain mechanism. Here, we report a true staircase APD operation using alloys of a rather underexplored material, AlxIn1-xAsySb1-y, lattice-matched to GaSb. Single step "staircase" devices exhibited a constant gain of ˜2×, over a broad range of applied bias, operating temperature, and excitation wavelengths/intensities, consistent with Monte Carlo calculations.

  7. Interaction of Avalanche Photodiodes (APDs Devices With Thermal Irradiation Environments

    Directory of Open Access Journals (Sweden)

    Ahmed Nabih Zaki Rashed

    2012-04-01

    Full Text Available This paper has been examined the high temperature irradiation variations testing in order to be used to determine avalanche photodiode lifetime, even though APD failure mechanisms are more sensitive to increases in current density. As a measured parameter of degradation, the current density is of great significance when searching for failure modes in APD. Raising the current density however, is not really indicative of lifetime since it is more likely a situation to be avoided than one that simulates normal lifetime degradation. The reliability of semiconductor detectors is very dependent on the degradation modes. This paper has 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 photon-starved (low signal applications, because their internal gain mechanism can improve signal to noise ratio. An optical receiver must also be appropriate for the laser wavelength being used. The near infrared is the preferred wavelength regime for deep space optical communications largely due to the wavelengths of available laser technologies that meet the optical power requirements of a deep space optical link

  8. Parallel plate avalanche detector PPAD construction and testing

    International Nuclear Information System (INIS)

    A multi-step two dimentsioned postion sensitive parallel plate avalanche detector (PPAD) was constructed locally to be later used in ion-atom collision experiments. The constructed detector was tested using a 1- 2.5 MeV He + beam, supplied from the University of Jordan Van de Graaff accelerator (JOVAC), under several grid voltages and detecting gas pressures (4 -10 mbar). A new data acquisition system MPDAS, interfaced with an ATARI-ST microcomputer was used during on-line measurements. The data were collected in List-mode so that they can be retrieved later in off-line mode analysis using LISA-ST program code. The 1-D and 2-D spectra reveal that good energy and position resolutions are obtaained at high pressures. The limstations on the postion resoulution are governed by the nonliearities of the W and S-anode and are explained to be due to partition noise arising from the fluctuation of the charge distribution falling on the anode. The energy spectra exhibit also energy peak shifts. The results are explained within the framework of ion-atom collisions processes and stopping effects. The data also suggest that some refinements are required to carry out ion-collision experiments to get a better understanding about the ion-atom interactions and its governing mechanisms.(author). 28 refs., 30 figs., 4 Tabs

  9. Influence of snow properties on dense avalanche friction parameters

    Science.gov (United States)

    Mohamed, Naaim

    2013-04-01

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

  10. Transport, hysteresis and avalanches in artificial spin ice systems

    Energy Technology Data Exchange (ETDEWEB)

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

    2010-01-01

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

  11. Novel micropixel avalanche photodiodes (MAPD) with superhigh pixel density

    International Nuclear Information System (INIS)

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

  12. Impact ionisation measurement and modelling of long wavelength avalanche photodiodes

    CERN Document Server

    Ng, J S

    2003-01-01

    Impact ionisation coefficients are measured in In sub 0 sub . sub 5 sub 3 Ga sub 0 sub . sub 4 sub 7 As and excess noise characteristics are measured in sub-micron ln sub 0 sub . sub 5 sub 2 Al sub 0 sub . sub 4 sub 8 As. Photomultiplication measurements performed on a series of In sub 0 sub . sub 5 sub 3 Ga sub 0 sub . sub 4 sub 7 As p-i-n diodes are reported. Taking careful account of factors which could give rise to erroneous results at low fields, ln sub 0 sub . sub 5 sub 3 Ga sub 0 sub . sub 4 sub 7 As ionisation coefficients are deduced at room temperature as a function of electric field. The results confirm the low field ionisation behaviour of alpha and the conventional field dependence of beta. Excess avalanche noise factors of In sub 0 sub . sub 5 sub 2 Al sub 0 sub . sub 4 sub 8 As p-i-n diodes, with i-region thicknesses ranging from 1.0 mu m to 0.1 mu m, are reported. The results indicate effective beta/alpha values lying between 0.15 and 0.23, comparable with or lower than the values reported in ...

  13. A protein biosensor using Geiger mode avalanche photodiodes

    International Nuclear Information System (INIS)

    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

  14. Kinetic modelling of runaway electron avalanches in tokamak plasmas

    CERN Document Server

    Nilsson, E; Peysson, Y; Granetz, R S; Saint-Laurent, F; Vlainic, M

    2015-01-01

    Runaway electrons (REs) can be generated in tokamak plasmas if the accelerating force from the toroidal electric field exceeds the collisional drag force due to Coulomb collisions with the background plasma. In ITER, disruptions are expected to generate REs mainly through knock-on collisions, where enough momentum can be transferred from existing runaways to slow electrons to transport the latter beyond a critical momentum, setting off an avalanche of REs. Since knock-on runaways are usually scattered off with a significant perpendicular component of the momentum with respect to the local magnetic field direction, these particles are highly magnetized. Consequently, the momentum dynamics require a full 3-D kinetic description, since these electrons are highly sensitive to the magnetic non-uniformity of a toroidal configuration. A bounce-averaged knock-on source term is derived. The generation of REs from the combined effect of Dreicer mechanism and knock-on collision process is studied with the code LUKE, a s...

  15. Computer simulation of quenched and tempered steel properties

    Directory of Open Access Journals (Sweden)

    B. Smoljan

    2011-06-01

    Full Text Available Purpose: The algorithm of estimation of mechanical properties based on steel hardness has been established.Design/methodology/approach: Numerical modelling of hardness distribution in as-quenched steel specimen was performed by involving the results of simple experimental test, i.e., Jominy-test. Hardness of quenched and tempered steel has been expressed as function of maximal hardness of actual steel and hardness of actual steel with 50% of martensite in microstructure, according to the time and temperature of tempering. After that distribution of other relevant mechanical properties was predicted based on predicted as-quenched and tempered hardness of steel. Experimental investigation has been performed on low alloy steel. The established procedure for estimation of quenched and tempered properties of steel has been applied in computer simulation of mechanical properties of quenched and tempered steel workpiece of complex form.Findings: Algorithm of estimation of hardness of quenched and tempered steel was improved. It can be concluded that working stress of quenched and tempered shaft can be successfully predicted by proposed method. The proposed computer simulation method could be applied in failure prevention.Research limitations/implications: The research was focused only on carbon and low alloyed heat treatable steels.Practical implications: The established algorithms can be used for prediction of mechanical properties in heat treating practice. Estimation of as-quenched hardness distribution is based on time, relevant for structure transformation, i.e., time of cooling from 800 to 500°C (t8/5. The hardness in the quenched and tempered state is estimated from the as-quenched hardness. The prediction of yield strength and toughness of steel is based on steel hardness.Originality/value: Hardness distribution is predicted by involving the results of simple experimental test, i.e., Jominy-test in numerical modelling of steel quenching.

  16. Temporal trends in avalanche activity in the French Alps and subregions: from occurrences and runout altitudes to unsteady return periods.

    OpenAIRE

    2013-01-01

    We present an analysis of temporal trends in ∼55 000 avalanches recorded between 1946 and 2010 in the French Alps and two north/south subregions. First, Bayesian hierarchical modelling is used to isolate low-, intermediate- and high-frequency trends in the mean avalanche occurrence and runout altitude per year/winter. Variables are then combined to investigate their correlation and the recent evolution of large avalanches. Comparisons are also made to climatic and flow regime covariates. The ...

  17. Discrimination of hot versus cold avalanche deposits: Implications for hazard assessment at Mount Meager, B.C.

    Directory of Open Access Journals (Sweden)

    M. L. Stewart

    2003-01-01

    Full Text Available The surficial deposits surrounding the Mount Meager volcanic complex include numerous avalanche deposits. These deposits share many attributes: (a they are nearly monolithologic and comprise mainly intermediate volcanic rock clasts, (b they lack internal structure, and (c they are very poorly sorted. Despite these similarities, the avalanche deposits represent two distinct processes. Mass wasting of the Mount Meager volcanic edifice has produced cold rock avalanche deposits, whereas gravitational collapse of active lava domes and flows has produced hot block and ash avalanche deposits. The ability to discriminate between these "hot" and "cold" avalanche deposits is a critical component in the assessment of hazards in volcanic terranes. Hot block and ash avalanche deposits can be distinguished by the presence of radially-oriented joints, breadcrust textures, and incipient welding, which are features indicative of high emplacement temperatures. Conversely, rock avalanche deposits resulting from mass wasting events may be distinguished by the presence of clasts that preserve pre-depositional weathering and jointing surfaces. Volcanic avalanches are mechanically similar to rock avalanches but pose a greater hazard due to high temperatures, increased fluidization from degassing and the potential to decouple highly mobile elutriated ash clouds. The increasing use of hazardous regions such as the Lillooet River valley requires more reliable risk assessment in order to minimize losses from future hazardous events.

  18. Rock-avalanche geomorphological and hydrological impact on an alpine watershed

    Science.gov (United States)

    Frattini, P.; Riva, F.; Crosta, G. B.; Scotti, R.; Greggio, L.; Brardinoni, F.; Fusi, N.

    2016-06-01

    Rock avalanches are large flow-like movements of fragmented rock that can cause extensive and rapid topographic changes, for which very few quantitative data are available. This paper analyses the geomorphological and hydrological impact of the 3 million m3 Thurwieser rock avalanche (2004, Italian Central Alps) by using Terrestrial Laser Scanner, airborne Lidar and GNSS data collected from 2005 to 2014. Sediment yield with respect to the normal valley regime, the dynamic and mass balance of affected glaciers, and the reorganization of superficial and groundwater flow networks are quantified. In the middle portion of the avalanche deposit, a natural sediment trap collected sediments from a new stream channel developed along the upper portion of the deposit and from a lateral drainage basin. This made possible to assess the 10-year impact of the rock avalanche on the sediment yield, which increased from about 120 to about 400 t km- 2·a- 1. The rock avalanche partially covered a glacier with a shallow debris layer that acted as a thermal insulator, limiting ice ablation and producing a 10-m high scarp between the free surface of the glacier and the debris-covered portion. A reduction of 75% of ice ablation was observed due to thermal insulation. The rock avalanche filled a tributary valley, splitting the original drainage basin in two. Under ordinary flows, seepage occurs within the avalanche deposit along the old valley axis. During high flow conditions, a new stream channel is activated along the middle and lower margin of the deposit, which has produced a new alluvial fan on the main valley floor. The fan evolution is described up to the present volume of about 2000 m3.

  19. Development of solid-state avalanche amorphous selenium for medical imaging

    Energy Technology Data Exchange (ETDEWEB)

    Scheuermann, James R., E-mail: James.Scheuermann@stonybrook.edu; Goldan, Amir H.; Zhao, Wei [Stony Brook University School of Medicine, Stony Brook, New York 11794 (United States); Tousignant, Olivier; Léveillé, Sébastien [Analogic Canada, Montreal, Ontario H4R 2P1 (Canada)

    2015-03-15

    Purpose: Active matrix flat panel imagers (AMFPI) have limited performance in low dose applications due to the electronic noise of the thin film transistor (TFT) array. A uniform layer of avalanche amorphous selenium (a-Se) called high gain avalanche rushing photoconductor (HARP) allows for signal amplification prior to readout from the TFT array, largely eliminating the effects of the electronic noise. The authors report preliminary avalanche gain measurements from the first HARP structure developed for direct deposition onto a TFT array. Methods: The HARP structure is fabricated on a glass substrate in the form of p-i-n, i.e., the electron blocking layer (p) followed by an intrinsic (i) a-Se layer and finally the hole blocking layer (n). All deposition procedures are scalable to large area detectors. Integrated charge is measured from pulsed optical excitation incident on the top electrode (as would in an indirect AMFPI) under continuous high voltage bias. Avalanche gain measurements were obtained from samples fabricated simultaneously at different locations in the evaporator to evaluate performance uniformity across large area. Results: An avalanche gain of up to 80 was obtained, which showed field dependence consistent with previous measurements from n-i-p HARP structures established for vacuum tubes. Measurements from multiple samples demonstrate the spatial uniformity of performance using large area deposition methods. Finally, the results were highly reproducible during the time course of the entire study. Conclusions: We present promising avalanche gain measurement results from a novel HARP structure that can be deposited onto a TFT array. This is a crucial step toward the practical feasibility of AMFPI with avalanche gain, enabling quantum noise limited performance down to a single x-ray photon per pixel.

  20. Quench Module Insert Capabilities and Development Test Results

    Science.gov (United States)

    Carswell, B.; Crouch, M.; Farmer, J.; Breeding, S.; Rose, F.; Whitaker, Ann F. (Technical Monitor)

    2001-01-01

    Quench Module Insert is a directional solidification furnace, which will fly in the Materials Science Research Facility. The QMI provides high thermal gradient and quench capabilities for processing metals and alloys in microgravity. This paper will describe the capabilities and present of on-going analysis and development testing.

  1. Chiral and continuum extrapolation of partially quenched lattice results

    Energy Technology Data Exchange (ETDEWEB)

    C.R. Allton; W. Armour; D.B. Leinweber; A.W. Thomas; R.D. Young

    2005-04-01

    The vector meson mass is extracted from a large sample of partially quenched, two-flavor lattice QCD simulations. For the first time, discretization, finite-volume and partial quenching artifacts are treated in a unified chiral effective field theory analysis of the lattice simulation results.

  2. Water-soluble polymer quenching medium VPZS-1

    International Nuclear Information System (INIS)

    Water-soluble polymer quenching medium VPZS-1 representing the solution of carboxymethyl cellulose sodium salt (Na-KMTs) is tested. Fire safety, nontoxicability, nondeficiency, easy producing and performance security give evidence of economical advisability of VPZS-1 application in steel quenching (9Kh2MF, 40Kh13, 34KhN1MA a.o.)

  3. 40 CFR 63.7295 - What requirements must I meet for quenching?

    Science.gov (United States)

    2010-07-01

    ... each quench tower and backup quench station at a new or existing coke oven battery. (1) For the... quenching. (b) For each quench tower at a new or existing coke oven battery and each backup quench station at a new coke oven battery, you must meet each of the requirements in paragraphs (b)(1) through...

  4. Dynamics of Holographic Entanglement Entropy Following a Local Quench

    CERN Document Server

    Rangamani, Mukund; Vincart-Emard, Alexandre

    2015-01-01

    We discuss the behaviour of holographic entanglement entropy following a local quench in 2+1 dimensional strongly coupled CFTs. The entanglement generated by the quench propagates along an emergent light-cone, reminiscent of the Lieb-Robinson light-cone propagation of correlations in non-relativistic systems. We find the the speed of propagation is bounded from below by the entanglement tsunami velocity obtained earlier for global quenches in holographic systems, and from above by the speed of light. The former is realized for sufficiently broad quenches, while the latter pertains for well localized quenches. The non-universal behavior in the intermediate regime appears to stem from finite-size effects. We also note that the entanglement entropy of subsystems reverts to the equilibrium value exponentially fast, in contrast to a much slower equilibration seen in certain spin models.

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

    Science.gov (United States)

    2003-01-01

    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

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

    Science.gov (United States)

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

    2013-07-01

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

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

    International Nuclear Information System (INIS)

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

  8. Non-Markovian property of afterpulsing effect in single-photon avalanche detector

    CERN Document Server

    Wang, Fang-Xiang; Li, Ya-Ping; He, De-Yong; Wang, Chao; Han, Yun-Guang; Wang, Shuang; Yin, Zhen-Qiang; Han, Zheng-Fu

    2016-01-01

    The single-photon avalanche photodiode(SPAD) has been widely used in research on quantum optics. The afterpulsing effect, which is an intrinsic character of SPAD, affects the system performance in most experiments and needs to be carefully handled. For a long time, afterpulsing has been presumed to be determined by the pre-ignition avalanche. We studied the afterpulsing effect of a commercial InGaAs/InP SPAD (The avalanche photodiode model is: Princeton Lightwave PGA-300) and demonstrated that its afterpulsing is non-Markovian, with a memory effect in the avalanching history. Theoretical analysis and experimental results clearly indicate that the embodiment of this memory effect is the afterpulsing probability, which increases as the number of ignition-avalanche pulses increase. This conclusion makes the principle of the afterpulsing effect clearer and is instructive to the manufacturing processes and afterpulsing evaluation of high-count-rate SPADs. It can also be regarded as a fundamental premise to handle ...

  9. Lowering effect of radioactive irradiation on breakdown voltage and electron avalanche pulse characteristics

    International Nuclear Information System (INIS)

    In the time resolving measurement of the growing process and breakdown of electron avalanche in a gap of uniform electric field, the phenomenon that DC breakdown voltage slightly lowered was observed when β ray was irradiated as the initial electron source, as compared with unirradiated condition. Beta source used is 90Sr-90Y of 2 mCi in radiative equilibrium. The experimental results and the examination are described in detail. In brief, the remarkable superposition of succeeding avalanche pulse over the preceeding avalanche pulse waveform was observed under the gap condition in which the breakdown voltage decreased in β-ray irradiation. Thus this superposition of avalanche pulses is considered as one of the causes of the breakdown voltage reduction. When β source is used as the initial electron source, the number of supplied initial electrons is very large as compared with unity, and at the same time, a great number of initial electrons can be supplied within the diffusion radius r of avalanche. Then the effect of initial electron number n0 was considered by employing a diagram for breakdown scheme. The transition from Townsend type breakdown to streamer type breakdown occurs owing to increasing n0, and in that condition, the breakdown voltage lowers slightly. (Wakatsuki, Y)

  10. Avalanche Hazard Mapping with Satellite Data and a Digital Elevation Model

    Directory of Open Access Journals (Sweden)

    Urs Gruber

    1995-04-01

    Full Text Available Today avalanche hazard mapping is a very time-consuming affair. To map large remote areas, a method based on satellite imagery and digital elevation model has been developed. For this purpose, two test-sites in the Swiss Apls were selected. To simulate the avalanche hazard, the existing Salm-Voellmy model was modified to the computer environment and extended to the characteristics of avalanches within forested terrain. The forests were classified with Landsat-TM data. So far, only a single forest-class was established. The separation of forest, shrub, and non-forested area along the timberline poses a problem. On the other hand, a classification of small openings and avalanche tracks within the forest could be achieved. A comparison with the existing avalanche cadastral map revealed that 85 per cent of the risk areas were correctly classified. On the other hand, the separation into the defined red and blue danger zones was not satisfactory. For the model's application to become operational, further improvements are needed. However, the general approach is very promising, and should lead to more reliable hazard maps for planning purposes, as well as to new and better insights into the mutual effects between snow and forest.

  11. A debris avalanche at Süphan stratovolcano (Turkey) and implications for hazard evaluation

    Science.gov (United States)

    Özdemir, Yavuz; Akkaya, İsmail; Oyan, Vural; Kelfoun, Karim

    2016-02-01

    The Quaternary Süphan debris avalanche deposit is located in Eastern Anatolia, Turkey. The avalanche formed by the sector collapse of a major stratovolcano towards the north, possibly during a single catastrophic event. The deposit has an estimated volume of 4 km3 and ran out over 25 km to cover an area of approximately 200 km2. Products of the collapse are overlain by younger eruptive units from the Süphan volcano. We have tested the numerical code VolcFlow to first reproduce the emplacement of the Quaternary Süphan debris avalanche and then to develop a hazard assessment for potential future sector collapses and subsequent emplacement of debris avalanches and associated tsunami. The numerical model captures the main features of the propagation process, including travel distance, lateral spread, and run up. The best fit obtained for the existing flow has a constant retarding stress of 50 kPa and a collapse scar volume of 4 km3. Analysis of potential future collapse scenarios reveals that northern sector debris avalanches (up to 6 km3) could affect several towns. In the case of a sector collapse towards the south, a tsunami will reach the city of Van and several of the biggest towns on the southern shoreline of Lake Van. Cities most affected by the larger amplitude waves would be Van, Edremit, Gevaş, Tatvan, and, to a lesser extent, Erciş, with wave amplitudes (first waves after the onset of the collapse) between 8 and 10 m.

  12. Analysis of avalanche risk factors in backcountry terrain based on usage frequency and accident data in Switzerland

    Science.gov (United States)

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

    2015-09-01

    Recreational activities in snow-covered mountainous terrain in the backcountry account for the vast majority of avalanche accidents. Studies analyzing avalanche risk mostly rely on accident statistics without considering exposure (or the elements at risk), i.e., how many, when and where people are recreating, as data on recreational activity in the winter mountains are scarce. To fill this gap, we explored volunteered geographic information on two social media mountaineering websites - bergportal.ch and camptocamp.org. Based on these data, we present a spatiotemporal pattern of winter backcountry touring activity in the Swiss Alps and compare this with accident statistics. Geographically, activity was concentrated in Alpine regions relatively close to the main Swiss population centers in the west and north. In contrast, accidents occurred equally often in the less-frequented inner-alpine regions. Weekends, weather and avalanche conditions influenced the number of recreationists, while the odds to be involved in a severe avalanche accident did not depend on weekends or weather conditions. However, the likelihood of being involved in an accident increased with increasing avalanche danger level, but also with a more unfavorable snowpack containing persistent weak layers (also referred to as an old snow problem). In fact, the most critical situation for backcountry recreationists and professionals occurred on days and in regions when both the avalanche danger was critical and when the snowpack contained persistent weak layers. The frequently occurring geographical pattern of a more unfavorable snowpack structure also explains the relatively high proportion of accidents in the less-frequented inner-alpine regions. These results have practical implications: avalanche forecasters should clearly communicate the avalanche danger and the avalanche problem to the backcountry user, particularly if persistent weak layers are of concern. Professionals and recreationists, on the

  13. Quenching parameter in a holographic thermal QCD

    CERN Document Server

    Patra, Binoy Krishna

    2016-01-01

    We have calculated the quenching parameter, $\\hat{q}$ in a model-independent way using the gauge-gravity duality. In earlier calculations, the geometry in the gravity side at finite temperature was usually taken as the pure AdS blackhole metric for which the dual gauge theory becomes conformally invariant unlike QCD. Therefore we use a metric which incorporates the fundamental quarks by embedding the coincident D7 branes in the Klebanov-Tseytlin background and a finite temperature is switched on by inserting a black hole into the background, known as OKS-BH metric. Further inclusion of an additional UV cap to the metric prepares the dual gauge theory to run similar to thermal QCD. Moreover $\\hat{q}$ is usually defined in the literature from the Glauber-model perturbative QCD evaluation of the Wilson loop, which has no reasons to hold if the coupling is large and is thus against the main idea of gauge-gravity duality. Thus we use an appropriate definition of $\\hat{q}$: $\\hat{q} L^- = 1/L^2$, where $L$ is the s...

  14. Equilibrium gold nanoclusters quenched with biodegradable polymers.

    Science.gov (United States)

    Murthy, Avinash K; Stover, Robert J; Borwankar, Ameya U; Nie, Golay D; Gourisankar, Sai; Truskett, Thomas M; Sokolov, Konstantin V; Johnston, Keith P

    2013-01-22

    Although sub-100 nm nanoclusters of metal nanoparticles are of interest in many fields including biomedical imaging, sensors, and catalysis, it has been challenging to control their morphologies and chemical properties. Herein, a new concept is presented to assemble equilibrium Au nanoclusters of controlled size by tuning the colloidal interactions with a polymeric stabilizer, PLA(1k)-b-PEG(10k)-b-PLA(1k). The nanoclusters form upon mixing a dispersion of ~5 nm Au nanospheres with a polymer solution followed by partial solvent evaporation. A weakly adsorbed polymer quenches the equilibrium nanocluster size and provides steric stabilization. Nanocluster size is tuned from ~20 to ~40 nm by experimentally varying the final Au nanoparticle concentration and the polymer/Au ratio, along with the charge on the initial Au nanoparticle surface. Upon biodegradation of the quencher, the nanoclusters reversibly and fully dissociate to individual ~5 nm primary particles. Equilibrium cluster size is predicted semiquantitatively with a free energy model that balances short-ranged depletion and van der Waals attractions with longer-ranged electrostatic repulsion, as a function of the Au and polymer concentrations. The close spacings of the Au nanoparticles in the clusters produce strong NIR extinction over a broad range of wavelengths from 650 to 900 nm, which is of practical interest in biomedical imaging. PMID:23230905

  15. Mechanical properties of dual phase steel quenched in bitumen medium

    Directory of Open Access Journals (Sweden)

    Adeolu A. ADEDIRAN

    2015-05-01

    Full Text Available The mechanical properties of a dual phase steel treated in different intercritical windows and subjected to bitumen as the quenching medium was investigated. The viscosity of the quenchant was altered at several rate, the morphology of phases formed was characterized. Also, the quenched samples produced ferrite-martensite phases obtained at different intercritical windows. The tensile and hardness behaviour of the structures was examined; and the microstructures were characterized. It was observed that samples intercriticaly heat treated at 790°C and held for 60mins, bitumen quenched at 125°C, offers the highest impact toughness, while its counterpart at 730°C soaked for 30mins, bitumen quenched at 125°C offered the least impact toughness value. Sample intercriticaly treated at 790°C and held for 45mins in a 150°C quenching, offered the peak hardness factor. However, samples at 790°C held at 45mins and bitumen quenched at 150°C possessed relatively the best combination of tensile properties, hardness and impact energy. The water quenched samples at 790°C held for 60mins has the peak hardness value. The micrographs as well showed a uniformly distributed dual phase structure of ferrite and martensite at various volume fractions.

  16. Overlap distributions for quantum quenches in the anisotropic Heisenberg chain

    Science.gov (United States)

    Mazza, Paolo P.; Stéphan, Jean-Marie; Canovi, Elena; Alba, Vincenzo; Brockmann, Michael; Haque, Masudul

    2016-01-01

    The dynamics after a quantum quench is determined by the weights of the initial state in the eigenspectrum of the final Hamiltonian, i.e. by the distribution of overlaps in the energy spectrum. We present an analysis of such overlap distributions for quenches of the anisotropy parameter in the one-dimensional anisotropic spin-1/2 Heisenberg model (XXZ chain). We provide an overview of the form of the overlap distribution for quenches from various initial anisotropies to various final ones, using numerical exact diagonalization. We show that if the system is prepared in the antiferromagnetic Néel state (infinite anisotropy) and released into a non-interacting setup (zero anisotropy, XX point) only a small fraction of the final eigenstates gives contributions to the post-quench dynamics, and that these eigenstates have identical overlap magnitudes. We derive expressions for the overlaps, and present the selection rules that determine the final eigenstates having nonzero overlap. We use these results to derive concise expressions for time-dependent quantities (Loschmidt echo, longitudinal and transverse correlators) after the quench. We use perturbative analyses to understand the overlap distribution for quenches from infinite to small nonzero anisotropies, and for quenches from large to zero anisotropy.

  17. The Mass Dependence of Dwarf Satellite Galaxy Quenching

    CERN Document Server

    Slater, Colin T

    2014-01-01

    We combine observations of the Local Group with data from the NASA-Sloan Atlas to show the variation in the quenched fraction of satellite galaxies from low mass dwarf spheroidals and dwarf irregulars to more massive dwarfs similar to the Magellanic clouds. While almost all of the low mass ($M_\\star \\lesssim 10^7$ $M_\\odot$) dwarfs are quenched, at higher masses the quenched fraction decreases to approximately 40-50%. This change in the quenched fraction is large, and suggests a sudden change in the effectiveness of quenching that correlates with satellite mass. We combine this observation with models of satellite infall and ram pressure stripping to show that the low mass satellites must quench within 1-2 Gyr of pericenter passage to maintain a high quenched fraction, but that many more massive dwarfs must continue to form stars today even though they likely fell in to their host >5 Gyr ago. We also characterize how the susceptibility of dwarfs to ram pressure must vary as a function of mass if it is to acco...

  18. Collimation quench test with 4 TeV proton beams

    CERN Document Server

    Salvachua, B; Cauchi, M; Deboy, D; Hofle, W; Holzer, EB; Jacquet, D; Lari, L; Nebot, E; Mirarchi, D; Quaranta, E; Redaelli, S; Sapinski, M; Schmidt, R; Valentino, G; Valuch, D; Wenniger, J; Wollmann, D; Zerlauth, M; CERN. Geneva. ATS Department

    2014-01-01

    In 2013, at the end of the LHC physics run I, several quench tests took place with the aim to measure the quench limit of the LHC superconducting magnets. The LHC superconducting magnets in the dispersion suppressor of IR7 are the most exposed to beam losses leaking from the betatron collimation system and represent the main limitation for the halo cleaning. A collimation quench test was performed with 4 TeV proton beams to improve the quench limit estimates, which determine the maximum allowed beam loss rate for a given collimation cleaning. The main goal of the collimation quench test was to try to quench the magnets by increasing losses at the collimators. This note describes the procedure during the test and the first results with the data. Losses of up to 1 MW over a few seconds were generated by blowing up the beam, achieving total losses of about 5.8 MJ. These controlled losses exceeded by a factor 2 the collimation design value, and the magnets did not quench.

  19. Fluorescence quenching of fulvic acids by fullerene in water

    International Nuclear Information System (INIS)

    Fullerene can be suspended in water as nanoscaled-fullerene-aggregates (nC60). However, little is known about its biogeochemical cycling in natural waters. In this paper, the interactions between nC60 and fulvic acids were investigated using fluorescence spectroscopy and fluorescence quenching titration. The results show that the intrinsic fluorescence of fulvic acids was static quenched by adding nC60. The association constants (log K) of fulvic acids and nC60 were estimated using a modified Ryan–Weber nonlinear model, and ranged from 6.76 to 7.41 l/mol. The log K was not significantly affected by the concentration levels of fulvic acids from 5.0 to 20.0 mg/l. The log K increased at low pH 3–5, but remained constant at high pH ranging from 5 to 11. The hydrophobic and π–π interactions were the likely primary mechanisms. The present observation will be helpful in understanding the environmental behavior of fullerene in natural aquatic ecosystems. - Highlights: ► Fluorescence of fulvic acids can be quenched by nanoscaled-fullerene-aggregates. ► Static quenching was the main fluorescence quenching mechanism. ► Association constants were estimated with fluorescence quenching titration. ► Hydrophobic and π–π interactions control the interaction. - Interactions between nanoscaled-fullerene-aggregates and fulvic acids in water were quantitatively investigated by fluorescence quenching titration.

  20. Systematic study of particle quenching in organic scintillators

    International Nuclear Information System (INIS)

    Among the different factors that affect measurements by organic scintillators, the majority of attention has been focused on those related to the scintillator (i.e., ionization, chemical, color and optical quenching), and less attention has been paid to the loss of energy before the particle (i.e., alpha or beta) arrives at the scintillator (i.e., particle quenching). This study evaluates the effect of particle quenching in different scintillation methods (i.e., using two plastic scintillation microspheres (PSm1 and PSm2), liquid scintillator and gel scintillator) by measuring solutions that contain increasing concentrations of NaCl, BaCl2 and glycerin. The results show the importance of particle quenching in PSm measurements because detection efficiency decreases with increasing concentrations of the quenching component, although the spectrum position and external standard parameter remain constant. The results have shown evidence of particle quenching, although at a lower magnitude, in the liquid scintillation or gel scintillation measurements. Moreover, the use of two PSm with different diameters and salty compound that alters the equilibrium of the liquid and gel emulsions also exemplified the importance of the transmission of optical photons through different scintillation media (i.e., optical quenching). Improvement and deterioration of the optical conditions on the scintillation media is manifested as a movement of the spectrum to higher and lower energies, respectively. The results obtained with PSm were confirmed by Monte Carlo simulation.

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

    Energy Technology Data Exchange (ETDEWEB)

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

    2009-11-09

    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.

  2. Plasmonic field confinement for separate absorption-multiplication in InGaAs nanopillar avalanche photodiodes

    Science.gov (United States)

    Farrell, Alan C.; Senanayake, Pradeep; Hung, Chung-Hong; El-Howayek, Georges; Rajagopal, Abhejit; Currie, Marc; Hayat, Majeed M.; Huffaker, Diana L.

    2015-12-01

    Avalanche photodiodes (APDs) are essential components in quantum key distribution systems and active imaging systems requiring both ultrafast response time to measure photon time of flight and high gain to detect low photon flux. The internal gain of an APD can improve system signal-to-noise ratio (SNR). Excess noise is typically kept low through the selection of material with intrinsically low excess noise, using separate-absorption-multiplication (SAM) heterostructures, or taking advantage of the dead-space effect using thin multiplication regions. In this work we demonstrate the first measurement of excess noise and gain-bandwidth product in III-V nanopillars exhibiting substantially lower excess noise factors compared to bulk and gain-bandwidth products greater than 200 GHz. The nanopillar optical antenna avalanche detector (NOAAD) architecture is utilized for spatially separating the absorption region from the avalanche region via the NOA resulting in single carrier injection without the use of a traditional SAM heterostructure.

  3. Metal frame as local protection of superconducting films from thermomagnetic avalanches

    Science.gov (United States)

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

    2016-03-01

    Thermomagnetic avalanches in superconducting films propagating extremely fast while forming unpredictable patterns, represent a serious threat for the performance of devices based on such materials. It is shown here that a normal-metal frame surrounding a selected region inside the film area can provide efficient protection from the avalanches during their propagation stage. Protective behavior is confirmed by magneto-optical imaging experiments on NbN films equipped with Cu and Al frames, and also by performing numerical simulations. Experimentally, it is found that while conventional flux creep is not affected by the frames, the dendritic avalanches are partially or fully screened by them. The level of screening depends on the ratio of the sheet conductance of the metal and the superconductor in the resistive state, and for ratios much larger than unity the screening is very efficient.

  4. Metal frame as local protection of superconducting films from thermomagnetic avalanches

    Directory of Open Access Journals (Sweden)

    P. Mikheenko

    2016-03-01

    Full Text Available Thermomagnetic avalanches in superconducting films propagating extremely fast while forming unpredictable patterns, represent a serious threat for the performance of devices based on such materials. It is shown here that a normal-metal frame surrounding a selected region inside the film area can provide efficient protection from the avalanches during their propagation stage. Protective behavior is confirmed by magneto-optical imaging experiments on NbN films equipped with Cu and Al frames, and also by performing numerical simulations. Experimentally, it is found that while conventional flux creep is not affected by the frames, the dendritic avalanches are partially or fully screened by them. The level of screening depends on the ratio of the sheet conductance of the metal and the superconductor in the resistive state, and for ratios much larger than unity the screening is very efficient.

  5. Information Measure for Size Distribution of Avalanches in the Bak-Sneppen Evolution Model

    Science.gov (United States)

    Li, Wei; Cai, Xu

    2003-01-01

    Information of avalanche size distribution is measured by calculating information entropy (IE) in the Bak-Sneppen evolution model. It is found that the IE increases as the model evolves. Specifically, we establish the relation between the IE and the self-organized threshold fc. The variation of the IE near the critical point yields an exponent entropy index E = (tau-1)/sigma, where tau and sigma represent the critical exponents for avalanche size distribution and avalanche size cutoff, respectively. A new quantity Dtau(g) (g = 1-(fc-G)(tau-1)/sigma, where G is the gap of the current state), defined as 1-Itau(g)/Itau(1), with Itau(g) and Itau(1) being the IE for the current state and the critical one respectively, is suggested that it represents the distance between the state with gap G and the critical one.

  6. Flux avalanches triggered by AC magnetic fields in superconducting thin films

    International Nuclear Information System (INIS)

    Flux avalanches are known to occur as a consequence of thermomagnetic instabilities. Some of their fingerprints are jumps in magnetization curves, or a paramagnetic reentrance in AC susceptibility measurements. In this work we have studied flux avalanches triggered by an AC field cycle by means of AC susceptibility and residual magnetization after an applied AC field measured as a function of an AC excitation field (h). These measurements allow comparing both results with magneto-optical imaging carried out in similar conditions. The results show a correspondence for the onset of the avalanche activity, as well as between the residual magnetic moment and the mean gray value calculated from the magneto-optical images in the remanent state.

  7. Information Measure for Size Distribution of Avalanches in the Bak-Sneppen Evolution Model

    Institute of Scientific and Technical Information of China (English)

    LI Wei; CAI Xu

    2003-01-01

    Information of avalanche size distribution is measured by calculating information entropy (IE) in the Bak-Sneppen evolution model. It is found that the IE increases as the model evolves. Specifically, we establish the relation between the IE and the self-organized threshold fc ? The variation of the IE near the critical point yields an exponent entropy index E = (T - l)/avalanche size distribution and avalanche size cutoff, respectively. A new quantity DT(g) (g = 1 - (fc - G)'r-1' , where G is the gap of the current state), denned as 1 - IT(g)/IT(l), with IT(g) and /T(l) being the IE for the current state and the critical one respectively, is suggested that it represents the distance between the state with gap G and the critical one.

  8. Numerical simulation of powder-snow avalanche interaction with an obstacle

    CERN Document Server

    Dutykh, Denys; Bresch, Didier

    2009-01-01

    In this paper we present direct numerical simulations of a sliding avalanche in aerosol regime. The second scope of this study is to get more insight into the interaction process between an avalanche and a rigid obstacle. An incompressible model of two miscible fluids can be successfully employed in this type of problems. We allow for mass diffusion between two phases according to the Fick's law. It is shown that the present model is consistent in the sense of kinetic energy. Some connections with Brenner-Navier-Stokes and Kazhikhov-Smagulov systems are revealed. The governing equations are discretized with a contemporary fully implicit finite volume scheme. The solver is able to deal with arbitrary density ratios. Encouraging numerical results are presented. Impact pressure profiles, avalanche front position and velocity field are extracted from numerical simulations and discussed. The influence of the bottom boudary condition onto propagation and impact processes is discussed. Finally we give some ideas of ...

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

    Science.gov (United States)

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

    2010-05-01

    In the future the combined effect of changes in climate and land use could contribute to the intensification of soil erosion, related to snowpack movements as snow gliding and full-depth avalanches. Often, with particular meteorological conditions, the snow movement along a slope is associated with erosion and transport of the upper soil horizons, with the release of significant amount of material in the runout zone. Moreover the chemical composition of the snow in the deposition zone is usually different from the snow in the starting zone, revealing a potential release of ionic species mainly by the organic debris transported by the avalanche itself. The aim of this work is to characterize the quantity and quality of the material released by full-depth avalanches in the deposition zone. The study area is located in Aosta Valley (NW-Italy), on a SW exposed avalanche path, running from 2000 m a.s.l. of the triggering zone to 1200 m a.s.l. of the deposition zone. At this site, snow gliding and glide cracks, generally followed by full-depth avalanches, have been frequently observed. In the starting area, two plots located at the same elevation, slope and aspect, but with different soil moisture content, are equipped with moisture and temperature sensors, located at different depth in the soil, at the snow-soil interface and in the basal snowpack layer, and with glide shoes. The recorded data are related to the snow physical properties, measured by periodical investigations. In the deposition area, after a full-depth avalanche event occurred in March 2009, the mixed material was collected through snow avalanche coring, and a snow pit was dug in the deposit, in order to evaluate the quantity and the distribution of the material transported by the avalanche. First results show that the average density of the snow in the deposition zone was 624 kg m-3. The solid material was distributed mainly in the upper 5 cm of the avalanche deposit, with a mean concentration of the

  10. Al0.52In0.48P avalanche photodiodes for soft X-ray spectroscopy

    International Nuclear Information System (INIS)

    The performance of Al0.52In0.48P avalanche photodiodes was assessed as soft X-ray detectors at room temperature. The effect of the avalanche gain improved the energy resolution and an energy resolution (FWHM) of 682 eV is reported for 5.9 keV X-rays

  11. Rotational quenching of CS in ultracold 3He collisions

    Science.gov (United States)

    Kaur, Rajwant; Dhilip Kumar, T. J.

    2016-08-01

    Quantum mechanical scattering calculations of rotational quenching of CS (v = 0) collision with 3He are performed at ultracold temperatures and results are compared with isotopic 4He collision. Rotational quenching cross sections and rate coefficients have been calculated in the ultracold region for rotational levels up to j = 10 using the He-CS potential energy surface computed at the CCSD(T)/aug-cc-pVQZ level of theory. The quenching cross sections are found to be two orders of magnitude larger for the 3He than the 4He isotope under ultracold conditions. Wigner threshold law is found to be valid below 10-3 K temperature.

  12. Spontaneous symmetry breaking in annealed and quenched gauge field models

    International Nuclear Information System (INIS)

    The structure of annealed and quenched models with local U(1) gauge invariance is studied in terms of the Helmholtz free energy. The first non-trivial, or one-loop, account of fluctuations in the annealed model suggests that spontaneous symmetry breaking occurs in two and three dimensions, through a first-order phase transition. Within the same approximation scheme, the quenched model displays a continuous phase transition. A more complete account of the fluctuations in the annealed model changes the nature of the transition to a continuous one, whereas spontaneous symmetry breaking is then absent with quenched disorder. (author)

  13. Dynamical quenching with non-local alpha and downward pumping

    CERN Document Server

    Brandenburg, A; Käpylä, P J

    2014-01-01

    In light of new results, the one-dimensional mean-field dynamo model of Brandenburg & Kapyla (2007) with dynamical quenching and a nonlocal Babcock-Leighton alpha effect is re-examined for the solar dynamo. We extend the one-dimensional model to include the effects of turbulent downward pumping (Kitchatinov & Olemskoy 2011), and to combine dynamical quenching with shear. We use both the conventional dynamical quenching model of Kleeorin & Ruzmaikin (1982) and the alternate one of Hubbard & Brandenburg (2011), and confirm that with varying levels of non-locality in the alpha effect, and possibly shear as well, the saturation field strength can be independent of the magnetic Reynolds number.

  14. Sensing detection and quenching metho d for InGaAs single-photon detector%InGaAs单光子探测器传感检测与淬灭方式∗

    Institute of Scientific and Technical Information of China (English)

    郑丽霞; 吴金; 张秀川; 涂君虹; 孙伟锋; 高新江

    2014-01-01

    A gated operation dynamic bias control strategy of InGaAs single-photon avalanche diode (SPAD) and circuit implementation are proposed based on the research of the SPAD performances. By the gated operation active quenching method the quenching time can be lowered, also dark count and afterpulsing effect are inhibited. The circuit fabricated by standard complementary metal oxide semiconductor (CMOS) technology and SPAD fabricated by non-standard CMOS technology are interconnected through the indium column interconnection hybrid packaging process. In the low temperature (−30 ◦C) test conditions, the avalanche current signal triggered by light is extracted and avalanche phenomenon is quickly quenched. Studies in this paper are the sensing resistance and critical sensing voltage effect on electrical performance of the detector and the implementation method of the detection circuit. The recovery time and transfer delay of the SPAD are 575 and 563 ps, respectively and the quenching time is 1.88 ns. These characteristics meet the requirements for the nanosecond precision sensor detection application.%针对InGaAs单光子雪崩光电二极管(SPAD)的光电感应特性,研究了基于门控主动式淬灭的SPAD动态偏置控制和电路实现的策略.采用门控主动淬灭控制可降低淬灭时间,有效抑制暗计数和后脉冲效应.接口感应检测电路采用标准互补金属氧化物半导体(CMOS)工艺进行制造,而SPAD则采用非标准CMOS工艺.利用铟柱互连混合封装工艺实现SPAD与感应接口电路的协同工作.在低温−30◦C的条件下,实现了SPAD光触发雪崩电流信号的提取和快速淬灭.研究了感应电阻和临界检测电压对传感检测电性能的影响,并采用简单电路结构实现状态检测,实测得到的SPAD恢复时间、传输延时分别为575,563 ps,淬灭时间为1.88 ns,满足纳秒级精度传感检测应用的需要.

  15. A multiple parallel-plate avalanche counter for fission-fragment detection

    Energy Technology Data Exchange (ETDEWEB)

    Wu, C.Y., E-mail: wu24@llnl.gov [Lawrence Livermore National Laboratory, Livermore, CA 9455 (United States); Henderson, R.A. [Lawrence Livermore National Laboratory, Livermore, CA 9455 (United States); Haight, R.C.; Lee, H.Y.; Taddeucci, T.N. [Los Alamos National Laboratory, Los Alamos, MN 87545 (United States); Bucher, B.; Chyzh, A. [Lawrence Livermore National Laboratory, Livermore, CA 9455 (United States); Devlin, M.; Fotiades, N. [Los Alamos National Laboratory, Los Alamos, MN 87545 (United States); Kwan, E. [Lawrence Livermore National Laboratory, Livermore, CA 9455 (United States); National Superconducting Cyclotron Laboratory, East Lansing, MI 48824 (United States); O’Donnell, J.M.; Perdue, B.A.; Ullmann, J.L. [Los Alamos National Laboratory, Los Alamos, MN 87545 (United States)

    2015-09-11

    A new low-mass multiple gas-filled parallel-plate avalanche counter for the fission-fragment detection has been developed to mark the fission occurrence in measurements of the prompt fission neutron energy spectrum as a function of incident neutron energy. It was used successfully for the neutron-induced fission of {sup 235}U and {sup 239}Pu with a total mass near 100 mg each and the spontaneous fission of {sup 252}Cf. Both the incident neutron energy and the prompt fission neutron energy are measured by using the time-of-flight method. The design and performance of this avalanche counter are described.

  16. Gas sampling calorimeter studies in proportional, saturated avalanche, and streamer modes

    International Nuclear Information System (INIS)

    Recently, satisfactory new results were obtained at SLAC from gas sampling calorimeters running in the saturated avalanche mode within the energy range of 1.5 to 17.5 GeV. To study the higher energy behavior of this mode, more tests were carried out in the M4 beamline at Fermilab. This paper contains results obtained from the MAC prototype electromagnetic and hadronic calorimeters running in the proportional, saturated avalanche, and the streamer regions for energies between 12 and 150 GeV

  17. Avalanche-ion back-flow reduction in gaseous electron multipliers based on GEM/MHSP

    OpenAIRE

    Maia, J. M.; Mörmann, D.; Breskin, A.; Chechik, R.; Veloso, J. F. C. A.; Santos, J. M. F. dos

    2004-01-01

    We report on avalanche-ion back-flow measurements in the novel Micro-Hole and Strip-Plate (MHSP) multiplier and in gaseous photomultipliers comprising Gas Electron Multipliers (GEMs) followed by an MHSP. In a 3-GEMs/MHSP photomultiplier with reflective photocathode, avalanche-ion back-flow fraction of ~7% and ~2% were recorded for respective effective gains of 107 and 106, in Ar/CH4 (95/5) at 760 Torr. This is about one order of magnitude reduction in ion back-flow compared to the best values...

  18. Development of Fuses for Protection of Geiger-Mode Avalanche Photodiode Arrays

    Science.gov (United States)

    Grzesik, Michael; Bailey, Robert; Mahan, Joe; Ampe, Jim

    2015-11-01

    Current-limiting fuses composed of Ti/Al/Ni were developed for use in Geiger-mode avalanche photodiode arrays for each individual pixel in the array. The fuses were designed to burn out at ˜4.5 × 10-3 A and maintain post-burnout leakage currents less than 10-7 A at 70 V sustained for several minutes. Experimental fuse data are presented and successful incorporation of the fuses into a 256 × 64 pixel InP-based Geiger-mode avalanche photodiode array is reported.

  19. A method to harness global crowd-sourced data to understand travel behavior in avalanche terrain.

    Science.gov (United States)

    Hendrikx, J.; Johnson, J.

    2015-12-01

    To date, most studies of the human dimensions of decision making in avalanche terrain has focused on two areas - post-accident analysis using accident reports/interviews and, the development of tools as decision forcing aids. We present an alternate method using crowd-sourced citizen science, for understanding decision-making in avalanche terrain. Our project combines real-time GPS tracking via a smartphone application, with internet based surveys of winter backcountry users as a method to describe and quantify travel practices in concert with group decision-making dynamics, and demographic data of participants during excursions. Effectively, we use the recorded GPS track taken within the landscape as an expression of the decision making processes and terrain usage by the group. Preliminary data analysis shows that individual experience levels, gender, avalanche hazard, and group composition all influence the ways in which people travel in avalanche terrain. Our results provide the first analysis of coupled real-time GPS tracking of the crowd while moving in avalanche terrain combined with psychographic and demographic correlates. This research will lead to an improved understanding of real-time decision making in avalanche terrain. In this paper we will specifically focus on the presentation of the methods used to solicit, and then harness the crowd to obtain data in a unique and innovative application of citizen science where the movements within the terrain are the desired output data (Figure 1). Figure 1: Example GPS tracks sourced from backcountry winter users in the Teton Pass area (Wyoming), from the 2014-15 winter season, where tracks in red represent those recorded as self-assessed experts (as per our survey), and where tracks in blue represent those recorded as self-assessed intermediates. All tracks shown were obtained under similar avalanche conditions. Statistical analysis of terrain metrics showed that the experts used steeper terrain than the

  20. On-Chip Integrated, Silicon-Graphene Plasmonic Schottky Photodetector with High Responsivity and Avalanche Photogain.

    Science.gov (United States)

    Goykhman, Ilya; Sassi, Ugo; Desiatov, Boris; Mazurski, Noa; Milana, Silvia; de Fazio, Domenico; Eiden, Anna; Khurgin, Jacob; Shappir, Joseph; Levy, Uriel; Ferrari, Andrea C

    2016-05-11

    We report an on-chip integrated metal graphene-silicon plasmonic Schottky photodetector with 85 mA/W responsivity at 1.55 μm and 7% internal quantum efficiency. This is one order of magnitude higher than metal-silicon Schottky photodetectors operated in the same conditions. At a reverse bias of 3 V, we achieve avalanche multiplication, with 0.37A/W responsivity and avalanche photogain ∼2. This paves the way to graphene integrated silicon photonics. PMID:27053042

  1. On-Chip Integrated, Silicon–Graphene Plasmonic Schottky Photodetector with High Responsivity and Avalanche Photogain

    Science.gov (United States)

    2016-01-01

    We report an on-chip integrated metal graphene–silicon plasmonic Schottky photodetector with 85 mA/W responsivity at 1.55 μm and 7% internal quantum efficiency. This is one order of magnitude higher than metal–silicon Schottky photodetectors operated in the same conditions. At a reverse bias of 3 V, we achieve avalanche multiplication, with 0.37A/W responsivity and avalanche photogain ∼2. This paves the way to graphene integrated silicon photonics. PMID:27053042

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

    International Nuclear Information System (INIS)

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

  3. Gain and noise in very high gain avalanche photodiodes: Theory and experiment

    International Nuclear Information System (INIS)

    Large area silicon avalanche photodiodes (APDs) have been fabricated with maximum avalanche gains exceeding 10,000 and excellent signal to noise ratios. A model of device performance has been developed in which previously developed general expressions are numerically integrated using actual fabrication parameters. The gain, statistical fluctuations in the gain, electronic noise, and total peak broadening have been computed using this model. The results are in good agreement with measurements. The parameter keff was found to be 7.2 x 10-4, allowing a high signal to noise ratio at gains of several thousand

  4. Silicon avalanche photodiodes on the base of metal-resistor-semiconductor (MRS) structures

    International Nuclear Information System (INIS)

    The development of a high quantum efficiency, fast photodetector, with internal gain amplification for the wavelength range 450-600 nm is one of the critical issues for experimental physics - registration of low-intensity light photons flux. The new structure of Silicon Avalanche Detectors with high internal amplification (105-106) has been designed, manufactured and tested for registration of visible light photons and charge particles. The main features of Metal-Resistor-Semiconductor (MRS) structures are the high charge multiplication in nonuniform electric field near the 'needle' pn-junction and negative feedback for stabilization of avalanche process due to resistive layer

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

    Science.gov (United States)

    Swartwout, M.

    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.

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

    Science.gov (United States)

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

    2009-04-01

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

  7. A multiple parallel-plate avalanche counter for fission-fragment detection

    International Nuclear Information System (INIS)

    A new low-mass multiple gas-filled parallel-plate avalanche counter for the fission-fragment detection has been developed to mark the fission occurrence in measurements of the prompt fission neutron energy spectrum as a function of incident neutron energy. It was used successfully for the neutron-induced fission of 235U and 239Pu with a total mass near 100 mg each and the spontaneous fission of 252Cf. Both the incident neutron energy and the prompt fission neutron energy are measured by using the time-of-flight method. The design and performance of this avalanche counter are described

  8. Different Avalanche Behaviors in Different Specific Areas of a System Based on Neural Networks

    Institute of Scientific and Technical Information of China (English)

    ZHAOXiao-Wei; CHENTian-Lun

    2003-01-01

    Based on the standard self-organizing map (SOM) neural network model and an integrate-and-fire mecha-nism, we introduce a kind of coupled map lattice system to investigate scale-invariance behavior in the activity of model neural populations. We find power-law distribution behavior of avalanche size in our model. But more importantly, we find there are different avalanche distribution behaviors in different specific areas of our system, which are formed by the topological learning process of the SOM net.

  9. Off-state avalanche breakdown induced degradation in 20 V NLDMOS devices

    International Nuclear Information System (INIS)

    Degradation behaviors of 20 V NLDMOS operated under off-state avalanche breakdown conditions are presented. A constant current pulse stressing test is applied to the device. Two different degradation mechanisms are identified by analysis of electrical data, technology computer-aided design (TCAD) simulations and charge pumping measurements. The first mechanism is attributed to positive oxide-trapped charges in the N-type drift region, and the second one is due to decreased electron mobility upon interface state formation in the drift region. Both of the mechanisms are enhanced with increasing avalanche breakdown current. (semiconductor devices)

  10. Quenching simulation of steel grinding balls

    Directory of Open Access Journals (Sweden)

    Zapata-Hernández, Oscar

    2015-09-01

    Full Text Available The phase transformations of high carbon steel during quenching and equalizing were modelled using commercial computer packages based on the finite element method and the kinetic transformation of steel. The model was used to predict the temperature and microstructural changes taking place within balls of two different sizes that are used for grinding mineral ores. A good correlation between the temperatures measured by inserted thermocouples and those predicted by the model was obtained after modifying the thermal conductivity of the steel within the temperature domain at which mixed phases are present. The phase transformations predicted were confirmed by metallographic analyses.Las transformaciones de fase en aceros de alto carbono durante su temple y un posterior periodo de estabilización fueron modelizadas por medio del uso de paquetes computacionales basados en el método del elemento finito y de la transformación cinética de los aceros. El modelo se usó para predecir los cambios de temperatura y microestructura que se presentan en bolas de dos diferentes tamaños empleadas en estaciones de molienda de minerales. Se encontró una buena correlación entre las temperaturas medidas mediante la inserción de termopares y aquellas predichas por el modelo una vez que se modificó la conductividad térmica del acero en el intervalo mixto de fases. La predicción de las transformaciones de fase se confirmó a través del análisis metalográfico.

  11. Nano-Multiplication-Region Avalanche Photodiodes and Arrays

    Science.gov (United States)

    Zheng, Xinyu; Pain, Bedabrata; Cunningham, Thomas

    2008-01-01

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

  12. Characterization of new hexagonal large area Geiger Avalanche Photodiodes

    International Nuclear Information System (INIS)

    Photomultipliers (PMTs) are the standard detector for construction of the current generation of imaging Atmospheric Cherenkov Telescopes (IACTs). Despite impressive improvements in QE and reliability in the last years, these devices suffer from the limitation of being unable to operate in the partially illuminated sky (during full or partial moon periods) as the excess light leads to a significant increase in the rate of ageing of the devices themselves and consequently limit the life of the camera. A viable alternative is the large area Geiger-mode avalanche photodiodes (G-APDs also known as Silicon Photomultipliers or SiPMs) that are commercially available from different producers in various types and dimensions. The sufficiency of the maturity of this technology for application to Cherenkov Astronomy has already been demonstrated by the FACT telescope. One of the camera designs under study for the 4 m Davies Cotton Telescope foresees the utilization of a large area G-APDs coupled to non imaging light concentrators. In collaboration with Hamamatsu and deriving from their current technology, we have designed a new hexagonal shaped large area G-APD HEX S12516 which when coupled to a Winston cone of 24 degrees cutting angle allows for a pixel angular resolution of 0.25 degrees for a f/D 1.4 telescope with a diameter of 4 m. The device, available in 2 different cell size configurations (50 μm and 100 μm), is divided into 4 different channels powered in common cathode mode. A temperature sensor was included for a better temperature evaluation in the characterization phase. The first 3 prototypes were fully characterized and the results are compared to the larger area devices commercially available such as the S10985-050C (2x2 array of 3x3 mm2 G-APDs). The photo-detection efficiency is measured applying the Poisson statistics method using pulsed LED at 7 different wavelengths from 355 to 670 nm and for different bias over-voltages (Vov). Optical crosstalk and after

  13. Debris avalanche triggered by sill intrusions in basaltic volcanoes (Piton des Neiges, La Réunion Island)

    Science.gov (United States)

    Berthod, C.; Famin, V.; Bascou, J.; Michon, L.; Ildefonse, B.

    2014-12-01

    Debris avalanches derived from the flanks of volcanic islands are among the largest on Earth. Debris avalanches are rare, catastrophic destabilizations that still keep geologists debating about the mechanisms that initiate them and make them travel huge runout distances. To shed light on the trigger of such destabilizations, we studied the inland scar of a debris avalanche deposit cropping out at Piton des Neiges, a dormant and eroded basaltic volcano of La Réunion Island. The avalanche deposit rests on a pile of 50-70 sill intrusions with a shallow northward dip, i.e. toward the sea. We measured the anisotropy of magnetic susceptibility in a transect across the uppermost sill of the pile in contact with the avalanche deposit. This transect reveals a strongly asymmetric magnetic fabric, consistent with a north-directed shear movement of the upper intrusion wall. This suggests that the upper sill induced a co-intrusive shear displacement of the volcano flank toward the sea. The upper sill margin in contact with the avalanche is striated, showing that this intrusion is older than the avalanche. Striae indicate a northward direction of avalanche runout. The upper sill margin also displays a magmatic lineation consistent with a magma flow in the intrusion toward the north. There is thus a striking kinematic consistency between the directions of intrusion propagation and avalanche runout, both oriented toward the sea. From the above results, we propose that repeated sill intrusions, such as observed on Piton des Neiges, increase the instability of a volcanic edifice. Each injection induces an incremental slip of the overlying rock mass, which may eventually end up into a landslide. Sill intrusions associated with seaward displacements of volcano flank, such as inferred for the April 2007 eruption of Piton de la Fournaise (also in La Réunion), should therefore be considered as a potential trigger of debris avalanches.

  14. Low-lying Fermion modes: Dynamical versus quenched

    International Nuclear Information System (INIS)

    We compare the low-lying eigenmodes of the O(a) improved Wilson-Dirac operator on quenched and dynamical configurations and investigate methods of probing the topological properties of gauge configurations. (orig.)

  15. Measurement of cell volume changes by fluorescence self-quenching

    DEFF Research Database (Denmark)

    Hamann, Steffen; Kiilgaard, J.F.; Litman, Thomas; Alvarez-Leefmans, F.J.; Winther, B. R.; Zeuthen, Thomas

    2002-01-01

    At high concentrations, certain fluorophores undergo self-quenching, i.e., fluorescence intensity decreases with increasing fluorophore concentration. Accordingly, the self-quenching properties can be used for measuring water volume changes in lipid vesicles. In cells, quantitative determination of...... concentrations of the fluorophore calcein suitable for measurement of changes in cell water volume by self-quenching. The relationship between calcein fluorescence intensity, when excited at 490 nm (its excitation maximum), and calcein concentration was investigated in vitro and in various cultured cell types...... corresponded to a decrease in calcein fluorescence with high signal-to-noise ratio (>15). Similar results were obtained with the fluorophore BCECF when excited at its isosbestic wavelength (436 nm). The present results demonstrate the usefulness of fluorescence self-quenching to measure rapid changes in cell...

  16. Anthracene Fluorescence Quenching by a Tetrakis (Ketocarboxamide Cavitand

    Directory of Open Access Journals (Sweden)

    Tibor Zoltan Janosi

    2014-01-01

    Full Text Available Quenching of both fluorescence lifetime and fluorescence intensity of anthracene was investigated in the presence of a newly derived tetrakis (ketocarboxamide cavitand at various concentrations. Time-correlated single photon counting method was applied for the lifetime measurements. A clear correlation between the fluorescence lifetime of anthracene as a function of cavitand concentration in dimethylformamide solution was observed. The bimolecular collisional quenching constant was derived from the decrease of lifetime. Fluorescence intensity was measured in the emission wavelength region around 400 nm as a result of excitation at 280 nm. Effective quenching was observed in the presence of the cavitand. The obtained Stern-Volmer plot displayed upward curvature. The results did not follow even extended Stern-Volmer behavior, often used to describe deviations from static bimolecular quenching. To explain our results we adopted the Smoluchowski model and obtained a reasonable estimate for the molecular radius of the cavitand in solution.

  17. Carbonated aqueous media for quench heat treatment of steels

    Science.gov (United States)

    Nayak, U. Vignesh; Rao, K. M. Pranesh; Pai, M. Ashwin; Prabhu, K. Narayan

    2016-07-01

    Distilled water and polyalkylene glycol (PAG)-based aqueous quenchants of 5 and 10 vol.% with and without carbonation were prepared and used as heat transfer media during immersion quenching. Cooling curves were recorded during quenching of an inconel 600 cylindrical probe instrumented with multiple thermocouples. It was observed that the vapor stage duration was prolonged and the wetting front ascended uniformly for quenching with carbonated media. The cooling data were analyzed by determining the critical cooling parameters and by estimating the spatially dependent probe/quenchant interfacial heat flux transients. The study showed significantly reduced values of heat transfer rate for carbonated quenchants compared to quenchants without carbonation. Further, the reduction was more pronounced in the case of PAG-based carbonated quenchants than carbonated distilled water. The results also showed the dependence of heat transfer characteristics of the carbonated media on polymer concentration. The effect of quench uniformity on the microstructure of the material was assessed.

  18. Quenched moderate deviations principle for random walk in random environment

    Institute of Scientific and Technical Information of China (English)

    2010-01-01

    We derive a quenched moderate deviations principle for the one-dimensional nearest random walk in random environment,where the environment is assumed to be stationary and ergodic.The approach is based on hitting time decomposition.

  19. Time Evolution of Entanglement Entropy in Quenched Holographic Superconductors

    CERN Document Server

    Bai, Xiaojian; Li, Li; Sun, Jia-Rui; Zhang, Hai-Qing

    2014-01-01

    We investigate the dynamical evolution of entanglement entropy in a holographic superconductor model by quenching the source term of dual charged scalar operator. By access to the full background geometry, the holographic entanglement entropy is calculated for a strip geometry at AdS boundary. It is found that the entanglement entropy versus time exhibits a robust non-monotonic behaviour, independent of the strength of Gaussian quench and the size of strip: it first displays a small dip, then grows linearly, and finally saturates. The linear growth velocity has an upper bound for strip with large width. The value of this non-local probe at late time equilibrium shows interesting scaling behaviour with respect to quench strength. The response of entanglement entropy uncovers the dynamical transition at some critical quench strength which just coincides with the one obtained form the dynamical evolution of scalar order parameter.

  20. Computer simulations of phase separation in quenched polymer solutions

    OpenAIRE

    Geeter, de, Bastiaan Alexander

    2002-01-01

    This thesis describes the computational study of phase separation in polymer solutions after a temperature quench. For the simulation of this process Cahn-Hilliard simulations and Bond-Fluctuation Monte Carlo simulations were performed.

  1. Response of fermions in Chern bands to spatially local quenches

    Science.gov (United States)

    Grushin, Adolfo G.; Roy, Sthitadhi; Haque, Masudul

    2016-08-01

    We study the dynamical evolution of Chern-band systems after subjecting them to local quenches. For open-boundary systems, we show for half-filling that the chiral nature of edge states is manifested in the time-dependent chiral response to local density quenches on the edge. In the presence of power-law traps, we show how to mimic the half-filling situation by choosing the appropriate number of fermions depending on the trap size, and explore chiral responses of edges to local quenches in such a configuration. We find that perturbations resulting from the quenches propagate at smaller group velocities as the gap controlling the spatial extent of the edge modes decreases. Our results provide different routes to check dynamically the non-trivial nature of Chern bands.

  2. Effects of austenitizing temperature in quenched niobium steels

    International Nuclear Information System (INIS)

    Three steel compositions with varying Nb content were austenitized at different temperatures and quenched in cold water. Metallographic examination and hardness measurements provided a basis for explaining the hardening mechanism and the role of Nb on the process. (Author)

  3. Tryptophan and ATTO 590: Mutual Fluorescence Quenching and Exciplex Formation

    Energy Technology Data Exchange (ETDEWEB)

    Bhattacharjee, Ujjal [Ames Laboratory; Beck, Christie [Ames Laboratory; Winter, Arthur [Iowa State University; Wells, Carson [Iowa State University; Petrich, Jacob W [Ames Laboratory

    2014-07-24

    Investigation of fluorescence quenching of probes, such as ATTO dyes, is becoming an increasingly important topic owing to the use of these dyes in super-resolution microscopies and in single-molecule studies. Photoinduced electron transfer is their most important nonradiative pathway. Because of the increasing frequency of the use of ATTO and related dyes to investigate biological systems, studies are presented for inter- and intramolecular quenching of ATTO 590 with tryptophan. In order to examine intramolecular quenching, an ATTO 590–tryptophan conjugate was synthesized. It was determined that tryptophan is efficiently quenching ATTO 590 fluorescence by excited-state charge transfer and two charge transfer complexes are forming. In addition, it was discovered that an exciplex (whose lifetime is 5.6 ns) can be formed between tryptophan and ATTO 590, and it is suggested that the possibility of such exciplex formation should be taken into account when protein fluorescence is monitored in a system tagged with ATTO dyes.

  4. Simulation of the Quench-06 experiment with Scdapsim

    International Nuclear Information System (INIS)

    The present work describes the pattern of the called Quench installation developed and used by the National Commission of Nuclear Security and Safeguards (CNSNS) for their participation in the International Standard Problem 45 (ISP), organized by the Nuclear Energy Agency (NEA). The exercise consisted on the simulation of the denominated experiment Quench-06 carried out in the experimental installation Quench located in the Forschungszentrum laboratory in Karlsruhe, Germany. The experiment Quench-06 consisted on simulating the sudden and late injection of water in a fuel assemble for a pressurized reactor (PWR). The CNSNS uses the version bd of the SCDAPSIM code developed by the company Innovative Software Systems (ISS) to simulate this experiment. The obtained results showed that the code is able to predict the experiment partially when overestimating the hydrogen production and of the partial fused of some fuel pellets, but predicting correctly the damage in the shroud. (Author)

  5. Mechanical properties of dual phase steel quenched in bitumen medium

    OpenAIRE

    Adeolu A.ADEDIRAN; Aribo, Sunday; Muhammed Olalekan Hakeem AMUDA

    2015-01-01

    The mechanical properties of a dual phase steel treated in different intercritical windows and subjected to bitumen as the quenching medium was investigated. The viscosity of the quenchant was altered at several rate, the morphology of phases formed was characterized. Also, the quenched samples produced ferrite-martensite phases obtained at different intercritical windows. The tensile and hardness behaviour of the structures was examined; and the microstructures were characterized. It was obs...

  6. Application of Quenching and Partitioning Processing to Medium Mn Steel

    Science.gov (United States)

    Seo, Eun Jung; Cho, Lawrence; De Cooman, Bruno C.

    2015-01-01

    The present work analyzes the application of quenching and partitioning processing to medium Mn steel to obtain a new type of ultra-high-strength multiphase medium Mn steel. The selection of the quench temperature makes it possible to vary the ultimate tensile strength within a range of 500 MPa. The processing leads to low-carbon lath martensite matrix with a controlled volume fraction of retained austenite.

  7. Prediction Of Mechanical Properties Of Quench Hardening Steel*

    OpenAIRE

    Chotěborský R.; Linda M.

    2015-01-01

    The present study investigated the application of finite element method for prediction of mechanical properties of quench hardening steel. Based on the experimental results obtained, a numerical model for simulation of continuous cooling of quench hardening steel was developed. For the simulation of the kinetics of diffusion phase transformations, the Avrami equation and additive rule were applied. A new model was also developed for martensitic transformation which was validated using metallo...

  8. Chemical and colour quenching in liquid scintillation counting

    International Nuclear Information System (INIS)

    Chemical and colour quenching for H-3 and C-14 was studied. The method includes spectral analysis of colouring agents; methyl red, (4'-dimethylamine-azobenzene 2-carboxylic acid) dimethyl yellow (4'-dimethylamine-azobenzene) and malachite green (methane, bis .(4-dimethyl aminophenyl) - (phenyl)). External standard channels ratio was applied for the liquid scintillation counting of samples. The introduction of an isolated external standard seems to be a strong tool for the correction of chemical and colour quenching curves. (Author) 12 refs

  9. A reexamination of quenches in Helium 4 and Helium 3

    OpenAIRE

    Karra, G.; Rivers, R. J.

    1998-01-01

    In the light of recent difficulties in observing vortices in quenches of liquid helium 4 to its superfluid state we re-examine the Zurek scenario for their production. We argue that experiments in helium 4 are unlikely to produce true vortices in the numbers originally anticipated, if at all, because of the wide Ginzberg regime and the slowness of the mechanical quenches. On the other hand, the observed production of unambiguous vortices in neutron-bombarded helium 3, with its narrow Ginzberg...

  10. Positronium quenching in liquid and solid octanol and benzene

    DEFF Research Database (Denmark)

    Shantarovich, V.P.; Mogensen, O.E.; Goldanskii, V.I.

    1970-01-01

    The lifetimes of orthopositronium in several solutions in liquid and solid octanol and benzene have been measured. The Ps-quenching constant was found to be two to thirty times higher in the solid than in the liquid phase.......The lifetimes of orthopositronium in several solutions in liquid and solid octanol and benzene have been measured. The Ps-quenching constant was found to be two to thirty times higher in the solid than in the liquid phase....

  11. Oxygen quenching in LAB based liquid scintillator and nitrogen bubbling

    CERN Document Server

    Hua-Lin, Xiao

    2009-01-01

    Oxygen quenching effect in Linear Alkl Benzne (LAB) based liquid scintillator (LAB+3g/L POPOP+ 15 mg Bis--MSB) was studied by measuring the light yield as the function of nitrogen bubbling time. it shows that the light yield of fully purged liquid scintillator would increase of nearly 11% in room temperature and room atmosphere pressure. A simple model of nitrogen bubbling was built to describe the relationship between relative light yield (oxygen quenching factor) and bubbling time.

  12. Quenching histories of galaxies and the role of AGN feedback

    Science.gov (United States)

    Smethurst, Rebecca Jane; Lintott, Chris; Simmons, Brooke; Galaxy Zoo Team

    2016-01-01

    Two open issues in modern astrophysics are: (i) how do galaxies fully quench their star formation and (ii) how is this affected - or not - by AGN feedback? I present the results of a new Bayesian-MCMC analysis of the star formation histories of over 126,000 galaxies across the colour magnitude diagram showing that diverse quenching mechanisms are instrumental in the formation of the present day red sequence. Using classifications from Galaxy Zoo we show that the rate at which quenching can occur is morphologically dependent in each of the blue cloud, green valley and red sequence. We discuss the nature of these possible quenching mechanisms, considering the influence of secular evolution, galaxy interactions and mergers, both with and without black hole activity. We focus particularly on the relationship between these quenched star formation histories and the presence of an AGN by using this new Bayesian method to show a population of type 2 AGN host galaxies have recently (within 2 Gyr) undergone a rapid (τ 2 Gyr) quenching rates dominate for high stellar mass (log10[M*/M⊙] > 10.75) hosts of AGN with both early- and late-type morphology. We discuss how these results show that both merger-driven and non-merger processes are contributing to the co-evolution of galaxies and supermassive black holes across the entirety of the colour magnitude diagram.

  13. First experience with the new Coupling Loss Induced Quench system

    CERN Document Server

    Ravaioli, E; Dudarev, A V; Kirby, G; Sperin, K A; ten Kate, H H J; Verweij, A P

    2014-01-01

    New-generation high-field superconducting magnets pose a challenge relating to the protection of the coil winding pack in the case of a quench. The high stored energy per unit volume calls for a very efficient quench detection and fast quench propagation in order to avoid damage due to overheating. A new protection system called Coupling-Loss Induced Quench (CLIQ) was recently, developed and tested at CERN. This method provokes a fast change in the magnet transport current by means of a capacitive discharge. The resulting change in the local magnetic field induces inter-filament and inter-strand coupling losses which heat up the superconductor and eventually initiate a quench in a large fraction of the coil winding pack. The method is extensively tested on a Nb-Ti single-wire test solenoid magnet in the CERN Cryogenic Laboratory in order to assess its performance, optimize its operating parameters, and study new electrical configurations. Each parameter is thoroughly analyzed and its impact on the quench effi...

  14. Thermal quenching of thermoluminescence in quartz samples of various origin

    Energy Technology Data Exchange (ETDEWEB)

    Subedi, B. [Aristotle University of Thessaloniki, Nuclear Physics Laboratory, 54124-Thessaloniki (Greece); Oniya, E. [Archaeometry Laboratory, Cultural and Educational Technology Institute (C.E.T.I.), R.C. ' Athena' , Tsimiski 58, 67100 Xanthi (Greece); Physics and Electronics Department, Adekunle Ajasin University, PMB 01, Akungba Akoko (Nigeria); Polymeris, G.S. [ISIK University, Physics Department, Faculty of Science and Arts, 34980-Sile, Istanbul (Turkey); Afouxenidis, D.; Tsirliganis, N.C. [Archaeometry Laboratory, Cultural and Educational Technology Institute (C.E.T.I.), R.C. ' Athena' , Tsimiski 58, 67100 Xanthi (Greece); Kitis, G., E-mail: gkitis@auth.g [Aristotle University of Thessaloniki, Nuclear Physics Laboratory, 54124-Thessaloniki (Greece)

    2011-03-15

    The effect of thermal quenching stands among the most important properties in the thermoluminescence (TL) of quartz on which many applications of TL are based. Since the quartz samples used in various applications are all of different origin it is useful to investigate whether the values of the thermal quenching parameters, i.e. the activation energy for thermal quenching W and a parameter C which describes the ratio of non-radiative to radiative luminescence transitions, evaluated mainly in specific quartz samples can be extrapolated to quartz samples of unknown origin as well as to quartz samples which are annealed at high temperatures. In the present work the TL glow curve of a series of un-annealed and annealed natural and synthetic quartz samples were studied as a function of the heating rate between 0.25 K/s and 16 K/s. Using an indirect fitting method it was found that the thermal quenching parameters W and C in most of the quartz samples are very similar to the values accepted in the literature. Furthermore, in some cases the thermal quenching parameters W and C are not the same for all TL glow-peaks in the same glow-curve. Finally, the strong external treatment of annealing the quartz samples at very high temperature can also influence at least one of the thermal quenching parameters.

  15. Thermal quenching of thermoluminescence in quartz samples of various origin

    International Nuclear Information System (INIS)

    The effect of thermal quenching stands among the most important properties in the thermoluminescence (TL) of quartz on which many applications of TL are based. Since the quartz samples used in various applications are all of different origin it is useful to investigate whether the values of the thermal quenching parameters, i.e. the activation energy for thermal quenching W and a parameter C which describes the ratio of non-radiative to radiative luminescence transitions, evaluated mainly in specific quartz samples can be extrapolated to quartz samples of unknown origin as well as to quartz samples which are annealed at high temperatures. In the present work the TL glow curve of a series of un-annealed and annealed natural and synthetic quartz samples were studied as a function of the heating rate between 0.25 K/s and 16 K/s. Using an indirect fitting method it was found that the thermal quenching parameters W and C in most of the quartz samples are very similar to the values accepted in the literature. Furthermore, in some cases the thermal quenching parameters W and C are not the same for all TL glow-peaks in the same glow-curve. Finally, the strong external treatment of annealing the quartz samples at very high temperature can also influence at least one of the thermal quenching parameters.

  16. New Fast Response Thin Film-Based Superconducting Quench Detectors

    CERN Document Server

    Dudarev, A; van de Camp, W; Ravaioli, E; Teixeira, A; ten Kate, H H J

    2014-01-01

    Quench detection on superconducting bus bars and other devices with a low normal zone propagation velocity and low voltage build-up is quite difficult with conventional quench detection techniques. Currently, on ATLAS superconducting bus bar sections, superconducting quench detectors (SQD) are mounted to detect quench events. A first version of the SQD essentially consists of an insulated superconducting wire glued to a superconducting bus line or windings, which in the case of a quench rapidly builds up a relatively high resistance that can be easily and quietly detected. We now introduce a new generation of drastically improved SQDs. The new version makes the detection of quenches simpler, more reliable, and much faster. Instead of a superconducting wire, now a superconducting thin film is used. The layout of the sensor shows a meander like pattern that is etched out of a copper coated 25 mu m thick film of Nb-Ti glued in between layers of Kapton. Since the sensor is now much smaller and thinner, it is easi...

  17. Smooth and fast versus instantaneous quenches in quantum field theory

    CERN Document Server

    Das, Sumit R; Myers, Robert C

    2015-01-01

    We examine in detail the relationship between smooth fast quantum quenches, characterized by a time scale $\\delta t$, and instantaneous quenches, within the framework of exactly solvable mass quenches in free scalar field theory. We study UV finite quantities like correlators at finite spatial distances and the excess energy produced above the final ground state energy. We show that at late times and large distances (compared to the quench time scale) the correlator approaches the instantaneous quench correlator. At early times, we find that for small spatial separation and small $\\delta t$, the correlator scales universally with $\\delta t$, exactly as in the scaling of renormalized one point functions found in earlier work. At larger separation, the dependence on $\\delta t$ drops out. The excess energy also scales in a universal fashion: in the $m\\delta t \\rightarrow0$ limit it is finite for $d \\leq 3$ and agrees with the instantaneous quench, while it is divergent in higher dimensions. We argue that similar...

  18. NASA MSFC Electrostatic Levitator (ESL) Rapid Quench System

    Science.gov (United States)

    SanSoucie, Michael P.; Craven, Paul D.

    2014-01-01

    Electrostatic levitation, a form of containerless processing, is an important tool in materials research. Levitated specimens are free from contact with a container; therefore, heterogeneous nucleation on container walls is not possible. This allows studies of deeply undercooled melts. Furthermore, studies of high-temperature, highly reactive materials are also possible. Studies of the solidification and crystallization of undercooled melts is vital to the understanding of microstructure development, particularly the formation of alloys with unique properties by rapid solidification. The NASA Marshall Space Flight Center (MSFC) Electrostatic Levitator (ESL) lab has recently been upgraded to allow for rapid quenching of levitated materials. The ESL Rapid Quench System uses a small crucible-like vessel that can be partially filled with a low melting point material, such as a Gallium alloy, as a quench medium. An undercooled sample can be dropped into the vessel to rapidly quench the sample. A carousel with nine vessels sits below the bottom electrode assembly. This system allows up to nine rapid quenches before having to break vacuum and remove the vessels. This new Rapid Quench System will allow materials science studies of undercooled materials and new materials development. In this presentation, the system is described and initial results are presented.

  19. Using GIS and Google Earth for the creation of the Going-to-the-Sun Road Avalanche Atlas, Glacier National Park, Montana, USA

    Science.gov (United States)

    Peitzsch, Erich H.; Fagre, Daniel B.; Dundas, Mark

    2010-01-01

    Snow avalanche paths are key geomorphologic features in Glacier National Park, Montana, and an important component of mountain ecosystems: they are isolated within a larger ecosystem, they are continuously disturbed, and they contain unique physical characteristics (Malanson and Butler, 1984). Avalanches impact subalpine forest structure and function, as well as overall biodiversity (Bebi et al., 2009). Because avalanches are dynamic phenomena, avalanche path geometry and spatial extent depend upon climatic regimes. The USGS/GNP Avalanche Program formally began in 2003 as an avalanche forecasting program for the spring opening of the ever-popular Going-to-the-Sun Road (GTSR), which crosses through 37 identified avalanche paths. Avalanche safety and forecasting is a necessary part of the GTSR spring opening procedures. An avalanche atlas detailing topographic parameters and oblique photographs was completed for the GTSR corridor in response to a request from GNP personnel for planning and resource management. Using ArcMap 9.2 GIS software, polygons were created for every avalanche path affecting the GTSR using aerial imagery, field-based observations, and GPS measurements of sub-meter accuracy. Spatial attributes for each path were derived within the GIS. Resulting products include an avalanche atlas book for operational use, a geoPDF of the atlas, and a Google Earth flyover illustrating each path and associated photographs. The avalanche atlas aids park management in worker safety, infrastructure planning, and natural resource protection by identifying avalanche path patterns and location. The atlas was created for operational and planning purposes and is also used as a foundation for research such as avalanche ecology projects and avalanche path runout modeling.

  20. Design considerations of high-performance InGaAs/InP single-photon avalanche diodes for quantum key distribution

    CERN Document Server

    Ma, Jian; Wang, Liu-Jun; Tong, Cun-Zhu; Jin, Ge; Zhang, Jun; Pan, Jian-Wei

    2016-01-01

    InGaAs/InP single-photon avalanche diodes (SPADs) are widely used in practical applications requiring near-infrared photon counting such as quantum key distribution (QKD). Photon detection efficiency and dark count rate are the intrinsic parameters of InGaAs/InP SPADs, due to the fact that their performances cannot be improved using different quenching electronics given the same operation conditions. After modeling these parameters and developing a simulation platform for InGaAs/InP SPADs, we investigate the semiconductor structure design and optimization. The parameters of photon detection efficiency and dark count rate highly depend on the variables of absorption layer thickness, multiplication layer thickness, excess bias voltage and temperature. By evaluating the decoy-state QKD performance, the variables for SPAD design and operation can be globally optimized. Such optimization from the perspective of specific applications can provide an effective approach to design high-performance InGaAs/InP SPADs.