Sample records for avalanche gain feasibility

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

    International Nuclear Information System (INIS)

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


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

  2. TCAD simulation of Low Gain Avalanche Detectors

    Energy Technology Data Exchange (ETDEWEB)

    Dalal, Ranjeet; Jain, Geetika; Bhardwaj, Ashutosh, E-mail:; Ranjan, Kirti


    In the present work, detailed simulation using Technology Computer Aided Design (TCAD) tool, Silvaco for non-irradiated and irradiated LGAD (Low Gain Avalanche Detector) devices has been carried out. The effects of different design parameters and proton irradiation on LGAD operation are discussed in detail. An already published effective two trap bulk damage model is used to simulate the radiation damage without implementing any acceptor removal term. The TCAD simulation for irradiated LGAD devices produce decreasing gain with increasing fluence, similar to the measurement results. The space charge density and electric field distribution are used to illustrate the possible reasons for the degradation of gain of the irradiated LGAD devices.

  3. TCAD simulation of Low Gain Avalanche Detectors

    International Nuclear Information System (INIS)

    Dalal, Ranjeet; Jain, Geetika; Bhardwaj, Ashutosh; Ranjan, Kirti


    In the present work, detailed simulation using Technology Computer Aided Design (TCAD) tool, Silvaco for non-irradiated and irradiated LGAD (Low Gain Avalanche Detector) devices has been carried out. The effects of different design parameters and proton irradiation on LGAD operation are discussed in detail. An already published effective two trap bulk damage model is used to simulate the radiation damage without implementing any acceptor removal term. The TCAD simulation for irradiated LGAD devices produce decreasing gain with increasing fluence, similar to the measurement results. The space charge density and electric field distribution are used to illustrate the possible reasons for the degradation of gain of the irradiated LGAD devices.

  4. TCAD simulation of Low Gain Avalanche Detectors (United States)

    Dalal, Ranjeet; Jain, Geetika; Bhardwaj, Ashutosh; Ranjan, Kirti


    In the present work, detailed simulation using Technology Computer Aided Design (TCAD) tool, Silvaco for non-irradiated and irradiated LGAD (Low Gain Avalanche Detector) devices has been carried out. The effects of different design parameters and proton irradiation on LGAD operation are discussed in detail. An already published effective two trap bulk damage model is used to simulate the radiation damage without implementing any acceptor removal term. The TCAD simulation for irradiated LGAD devices produce decreasing gain with increasing fluence, similar to the measurement results. The space charge density and electric field distribution are used to illustrate the possible reasons for the degradation of gain of the irradiated LGAD devices.

  5. An amorphous selenium based positron emission mammography camera with avalanche gain. (United States)

    Reznik, A; Lui, B J M; Rowlands, J A


    Early diagnosis of breast cancer is crucial for effective treatment, and the need exists for greater detection ability and specificity than possible by screening x-ray mammography (currently the primary imaging technique for the detection of breast lesions). Positron Emission Tomography (PET) using the radiotracer 2-[fluorine-18]-fluoro-2-deoxy-D-glucose (FDG) offers a noninvasive, highly sensitive method for the diagnosis of breast cancer. Images from PET contain unique metabolic information that is not available from anatomical imaging techniques. We propose a Positron Emission Mammography (PEM) imaging system that maintains the established high specificity of FDG PET while providing improved collection efficiency for the radiotracer signal and the potential for images with better spatial resolution. This PEM system will enable detection of lesions that are considerably smaller than those that can be visualized using whole body PET imaging. The compact dual-head PEM camera will be based on an amorphous selenium (a-Se) avalanche photodetector and the scintillator lutetium oxyorthosilicate (LSO). The camera promises high collection efficiency by combining the fast scintillation light decay and high light yield of LSO with the excellent quantum efficiency, large avalanche gain, and rapid response time of a-Se. We have measured the gain and readout time of an 8 microm a-Se layer and demonstrated the feasibility of the proposed PEM camera.

  6. Study of gain homogeneity and radiation effects of Low Gain Avalanche Pad Detectors (United States)

    Gallrapp, C.; Fernández García, M.; Hidalgo, S.; Mateu, I.; Moll, M.; Otero Ugobono, S.; Pellegrini, G.


    Silicon detectors with intrinsic charge amplification implementing a n++-p+-p structure are considered as a sensor technology for future tracking and timing applications in high energy physics experiments. The performance of the intrinsic gain in Low Gain Avalanche Detectors (LGAD) after irradiation is crucial for the characterization of radiation hardness and timing properties in this technology. LGAD devices irradiated with reactor neutrons or 800 MeV protons reaching fluences of 2.3 × 1016 neq/cm2 were characterized using Transient Current Technique (TCT) measurements with red and infra-red laser pulses. Leakage current variations observed in different production lots and within wafers were investigated using Thermally Stimulated Current (TSC). Results showed that the intrinsic charge amplification is reduced with increasing fluence up to 1015 neq/cm2 which is related to an effective acceptor removal. Further relevant issues were charge collection homogeneity across the detector surface and leakage current performance before and after irradiation.

  7. Multiplication theory for dynamically biased avalanche photodiodes: new limits for gain bandwidth product. (United States)

    Hayat, Majeed M; Ramirez, David A


    Novel theory is developed for the avalanche multiplication process in avalanche photodiodes (APDs) under time-varying reverse-biasing conditions. Integral equations are derived characterizing the statistics of the multiplication factor and the impulse-response function of APDs, as well as their breakdown probability, all under the assumption that the electric field driving the avalanche process is time varying and spatially nonuniform. Numerical calculations generated by the model predict that by using a bit-synchronous sinusoidal biasing scheme to operate the APD in an optical receiver, the pulse-integrated gain-bandwidth product can be improved by a factor of 5 compared to the same APD operating under the conventional static biasing. The bit-synchronized periodic modulation of the electric field in the multiplication region serves to (1) produce large avalanche multiplication factors with suppressed avalanche durations for photons arriving in the early phase of each optical pulse; and (2) generate low avalanche gains and very short avalanche durations for photons arriving in the latter part of each optical pulse. These two factors can work together to reduce intersymbol interference in optical receivers without sacrificing sensitivity.

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

    International Nuclear Information System (INIS)

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


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

  9. Gas gain characteristics of parallel plate avalanche counter

    Energy Technology Data Exchange (ETDEWEB)

    Nishio, Katsuhisa; Yamamoto, Hideki; Kanno, Ikuo; Kimura, Itsuro [Kyoto Univ. (Japan). Faculty of Engineering; Nakagome, Y.


    In the conventional gas gain theory, the Townsend primary ionization coefficient is expressed as a function of S, which is the ratio of the electric field strength (E) to the gas density (N). In this paper, an experimental form of {alpha} is derived from the data and is compared with the formula so far. (J.P.N.)

  10. Low Gain Avalanche Detectors (LGAD) for particle physics and synchrotron applications (United States)

    Moffat, N.; Bates, R.; Bullough, M.; Flores, L.; Maneuski, D.; Simon, L.; Tartoni, N.; Doherty, F.; Ashby, J.


    A new avalanche silicon detector concept is introduced with a low gain in the region of ten, known as a Low Gain Avalanche Detector, LGAD. The detector's characteristics are simulated via a full process simulation to obtain the required doping profiles which demonstrate the desired operational characteristics of high breakdown voltage (500 V) and a gain of 10 at 200 V reverse bias for X-ray detection. The first low gain avalanche detectors fabricated by Micron Semiconductor Ltd are presented. The doping profiles of the multiplication junctions were measured with SIMS and reproduced by simulating the full fabrication process which enabled further development of the manufacturing process. The detectors are 300 μm thick p-type silicon with a resistivity of 8.5 kΩcm, which fully depletes at 116 V. The current characteristics are presented and demonstrate breakdown voltages in excess of 500 V and a current density of 40 to 100 nAcm‑2 before breakdown measured at 20oC. The gain of the LGAD has been measured with a red laser (660 nm) and shown to be between 9 and 12 for an external bias voltage range from 150 V to 300 V.

  11. On the high gain operation of low-pressure microdot gas avalanche chambers

    International Nuclear Information System (INIS)

    Breskin, A.


    Microdot avalanche chambers (MDOT) equipped with thin semitransparent Cr photocathodes, were characterized with UV photons at low gas pressure. Gains superior to 10 4 were reached with gas multiplication at the dots. In a mode where preamplification in the gas volume precedes the additional dot multiplication, gains superior to 10 6 were measured at 30-60 torr of propane. The fast amplification mechanism results in narrow high amplitude pulses with 2-3 ns rise time, visible with no further electronic amplification means. We present here our preliminary results and briefly discuss potential applications. (orig.)

  12. Analysis of single photon detection in avalanche photodetectors with multi-gain-stage multiplication region. (United States)

    Hosseinzadeh, Amir; Zavvari, Mahdi


    We report the design and analysis of a single photon avalanche detector (SPAD) with cascaded multiplication stages with asymmetric gain series for near-IR applications. The asymmetric gain profile allows us to selectively enhance the ionization coefficient for injected electrons and suppress the hole-initiated ionization by repetition of high and low field layers. The low field layer acts as a carrier relaxation region, which inhibits avalanche feedback between stages; hence, it is expected to have a lower dark count rate (DCR). The gain stage consists of three distinct layers with different electric fields, which can be adjusted by geometrical and mole fraction design. In this paper we study the effect of these layers' field and thickness on the single photon quantum efficiency (SPQE) and DCR of the proposed SPAD. Our results show that the high-field layer can better influence the performance of the detector rather than the others. In comparison with a conventional SPAD with a uniform multiplication region, our proposed structure shows lower DCR for a same SPQE.

  13. Gain and time resolution of 45 μm thin Low Gain Avalanche Detectors before and after irradiation up to a fluence of 1015 neq/cm2 (United States)

    Lange, J.; Carulla, M.; Cavallaro, E.; Chytka, L.; Davis, P. M.; Flores, D.; Förster, F.; Grinstein, S.; Hidalgo, S.; Komarek, T.; Kramberger, G.; Mandić, I.; Merlos, A.; Nozka, L.; Pellegrini, G.; Quirion, D.; Sykora, T.


    Low Gain Avalanche Detectors (LGADs) are silicon sensors with a built-in charge multiplication layer providing a gain of typically 10 to 50. Due to the combination of high signal-to-noise ratio and short rise time, thin LGADs provide good time resolutions. LGADs with an active thickness of about 45 μm were produced at CNM Barcelona. Their gains and time resolutions were studied in beam tests for two different multiplication layer implantation doses, as well as before and after irradiation with neutrons up to 1015 neq/cm2. The gain showed the expected decrease at a fixed voltage for a lower initial implantation dose, as well as for a higher fluence due to effective acceptor removal in the multiplication layer. Time resolutions below 30 ps were obtained at the highest applied voltages for both implantation doses before irradiation. Also after an intermediate fluence of 3×1014 neq/cm2, similar values were measured since a higher applicable reverse bias voltage could recover most of the pre-irradiation gain. At 1015 neq/cm2, the time resolution at the maximum applicable voltage of 620 V during the beam test was measured to be 57 ps since the voltage stability was not good enough to compensate for the gain layer loss. The time resolutions were found to follow approximately a universal function of gain for all implantation doses and fluences.

  14. Arctic avalanche dynamics (United States)

    Prokop, Alexander; Eiken, Mari; Ganaus, Kerstin; Rubensdotter, Lena


    Since the avalanche disaster December 19th, 2015 in Longyearbyen (Svalbard) happened, where two people were killed within settlements, the dynamic of avalanches in arctic regions is of increasing interest for hazard mapping in such areas. To investigate the flow behavior of arctic avalanches we focused on avalanches that occurred in Central Svalbard. In this regions historic avalanche events can be analyzed due to their deposition behavior visible on geomorphological maps in the run-out area of the avalanches. To get an idea about possible snow mass that was involved in the avalanches we measured the snow volume balance of recent avalanches (winters 2015/16) via terrestrial laser scanning. In this way we gained reasonable data to set calibration and input parameters for dynamic avalanche modeling. Using state of the art dynamic avalanche models allowed us to back calculate how much snow was involved in the historic avalanches that we identified on the geomorphological maps and what the return period of those events are. In our presentation we first explain our methodology; we discuss arctic avalanche behavior of the avalanches measured via terrestrial laser scanning and how the dynamic avalanche models performed for those case examples. Finally we conclude how our results can improve avalanche hazard mapping for arctic regions.

  15. Technology developments and first measurements on inverse Low Gain Avalanche Detector (iLGAD) for high energy physics applications

    CERN Document Server

    Carulla, M.; Fernández-Martínez, P.; IMB-CNM (CSIC); Flores, D.; IMB-CNM (CSIC); González, J.; Hidalgo, S.; Jaramillo, R.; Merlos, A.; Palomo, F.R.; Pellegrini, G; Quirion, D.; Vila, I.


    ABSTRACT: The first Inverse Low Gain Avalanche Detector (iLGAD) have been fabricated at IMB-CNM (CSIC). The iLGAD structure includes the multiplication diffusions at the ohmic contact side while the segmentation is implemented at the front side with multiple P + diffusions. Therefore, iLGAD is P on P position-sensitive detector with a uniform electric field all along the device area that guarantees the same signal amplification wherever a particle passes through the sensitive bulk solving the main draw of the LGAD microstrip detector. However, the detection current is dominated by holes flowing back from the multiplication junction with the subsequent transient current pulse duration increase in comparison with conventional LGAD counterparts. Applications of iLGAD range from tracking and timing applications like determination of primary interaction vertex to medical imaging. The paper addresses the optimization of the iLGAD structure with the aid of TCAD simul...

  16. arXiv Simulation of gain stability of THGEM gas-avalanche particle detectors

    CERN Document Server

    Correia, P.M.M.; Azevedo, C.D.R.; Breskin, A.; Bressler, S.; Oliveira, C.A.B.; Silva, A.L.M.; Veenhof, R.; Veloso, J.F.C.A.


    Charging-up processes affecting gain stability in Thick Gas Electron Multipliers (THGEM) were studied with a dedicated simulation toolkit. Integrated with Garfield++, it provides an effective platform for systematic phenomenological studies of charging-up processes in MPGD detectors. We describe the simulation tool and the fine-tuning of the step-size required for the algorithm convergence, in relation to physical parameters. Simulation results of gain stability over time in THGEM detectors are presented, exploring the role of electrode-thickness and applied voltage on its evolution. The results show that the total amount of irradiated charge through electrode's hole needed for reaching gain stabilization is in the range of tens to hundreds of pC, depending on the detector geometry and operational voltage. These results are in agreement with experimental observations presented previously.

  17. Pulse oximeter using a gain-modulated avalanche photodiode operated in a pseudo lock-in light detection mode (United States)

    Miyata, Tsuyoshi; Iwata, Tetsuo; Araki, Tsutomu


    We propose a reflection-type pulse oximeter, which employs two pairs of a light-emitting diode (LED) and a gated avalanche photodiode (APD). One LED is a red one with an emission wavelength λ = 635 nm and the other is a near-infrared one with that λ = 945 nm, which are both driven with a pulse mode at a frequency f (=10 kHz). Superposition of a transistor-transistor-logic (TTL) gate pulse on a direct-current (dc) bias, which is set so as not exceeding the breakdown voltage of each APD, makes the APD work in a gain-enhanced operation mode. Each APD is gated at a frequency 2f (=20 kHz) and its output signal is fed into a laboratory-made lock-in amplifier that works in synchronous with the pulse modulation signal of each LED at a frequency f (=10 kHz). A combination of the gated APD and the lock-in like signal detection scheme is useful for the reflection-type pulse oximeter thanks to the capability of detecting a weak signal against a large background (BG) light.

  18. Digitally grown AlInAsSb for high gain separate absorption, grading, charge, and multiplication avalanche photodiodes (United States)

    Lyu, Yuexi; Han, Xi; Sun, Yaoyao; Jiang, Zhi; Guo, Chunyan; Xiang, Wei; Dong, Yinan; Cui, Jie; Yao, Yuan; Jiang, Dongwei; Wang, Guowei; Xu, Yingqiang; Niu, Zhichuan


    We report on the growth of high quality GaSb-based AlInAsSb quaternary alloy by molecular beam epitaxy (MBE) to fabricate avalanche photodiodes (APDs). By means of high resolution X-ray diffraction (HRXRD) and scanning transmission electron microscope (STEM), phase separation phenomenon of AlInAsSb random alloy with naturally occurring vertical superlattice configuration was demonstrated. To overcome the tendency for phase segregation while maintaining a highly crystalline film, a digital alloy technique with migration-enhanced epitaxy growth method was employed, using a shutter sequence of AlSb, AlAs, AlSb, Sb, In, InAs, In, Sb. AlInAsSb digital alloy has proved to be reproducible and consistent with single phase, showing sharp satellite peaks on HRXRD rocking curve and smooth surface morphology under atomic force microscopy (AFM). Using optimized digital alloy, AlInAsSb separate absorption, grading, charge, and multiplication (SAGCM) APD was grown and fabricated. At room temperature, the device showed high performance with low dark current density of ∼14.1 mA/cm2 at 95% breakdown and maximum stable gain before breakdown as high as ∼200, showing the potential for further applications in optoelectronic devices.

  19. Proof-of-concept and feasibility demonstrations for an avalanche photodiode/photoelastic modulator-based imaging polarimeter (United States)

    National Aeronautics and Space Administration — Building on the successful heritage of JPL’s Multiangle SpectroPolarimetric Imager (MSPI), we propose infusing HgCdTe avalanche photodiode (APD) array technology...

  20. Avalanche risk assessment in Russia (United States)

    Komarov, Anton; Seliverstov, Yury; Sokratov, Sergey; Glazovskaya, Tatiana; Turchaniniva, Alla


    . The case studies of specific territories are performed using large-scale risk assessment methods. Thus, we discuss these problems by presenting an avalanche risk assessment approach on example of the developing but poorly researched ski resort areas in the North Caucasus. The suggested method includes the formulas to calculate collective and individual avalanche risk. The results of risk analysis are shown in quantitative data that can be used to determine levels of avalanche risk (acceptable, admissible and unacceptable) and to suggest methods to decrease the individual risk to acceptable level or better. It makes possible to compare risk quantitative data obtained from different mountain regions, analyze it and evaluate the economic feasibility of protection measures. At present, we are developing methods of avalanche risk assessment in economic performance. It conceder costs of objects located in avalanche prone area, traffic density values and probability of financial loss.

  1. Negative feedback avalanche diode (United States)

    Itzler, Mark Allen (Inventor)


    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.

  2. Assessing the importance of terrain parameters on glide avalanche release (United States)

    Peitzsch, Erich H.; Hendrikx, Jordy; Fagre, Daniel B.


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

  3. Electric field distribution and simulation of avalanche formation due ...

    Indian Academy of Sciences (India)

    Avalanche propagation; gas gain; parallel grid avalanche counter. PACS Nos 29.40.Cs, 51.50.+v, 52.80.Dy. 1. Introduction. Multiwire detectors have evolved into several configurations depending on the physics goal of the experiments. In the pioneering work of George Charpak et al [1], the detector was developed for high ...

  4. SiC Avalanche Photodiodes and Arrays Project (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 APDs...

  5. Synoptic atmospheric circulation patterns controlling avalanche activity in central Svalbard (United States)

    Hancock, Holt; Prokop, Alexander; Eckerstorfer, Markus; Hendrikx, Jordy


    Central Svalbard's avalanche activity is primarily controlled by the local and synoptic scale meteorological conditions characterizing the region's winter storms. Previous work has described Svalbard's direct-action snow climate as High-Arctic maritime based on the unique meteorological conditions and resulting snowpack stratigraphy observed in the region. To gain a better understanding of the broad-scale spatial controls on regional avalanche activity in Svalbard, this work investigates synoptic atmospheric circulation patterns associated with observed avalanche cycles during the 2007/2008 to 2015/2016 winter seasons. We use avalanche observations systematically recorded as part of the Cryoslope Svalbard project from 2007-2010 in combination with additional observations from notable avalanche events from 2010-2016 to develop a regional avalanche cycle history. We then compare the timing of these avalanche cycles to an existing daily calendar of synoptic types and NCEP/NCAR Reanalysis datasets to characterize the synoptic atmospheric circulation patterns influencing this avalanche activity. Our results indicate regional avalanche cycles are driven by cyclonic activity in the seas surrounding Svalbard under synoptic circulation patterns associated with warm air advection and moisture transport from lower latitudes to Svalbard. The character and spatial distribution of observed avalanche activity can be differentiated by atmospheric circulation type: mid-winter slushflow and wet slab avalanche cycles, for example, are typically associated with meridional southerly flow over the North Atlantic bringing warm air and heavy precipitation to Svalbard. Such analyses can provide a foundation upon which to improve the understanding of central Svalbard's snow climate to facilitate regional avalanche forecasting efforts.

  6. Thunder - adaptive avalanche airbag system


    Chen, Kan


    Skiing plays an important role in outdoor activities. It allows us to regain control of our body, makes us feel alive. However, in some cases, skiing comes with great risk. Avalanche is the worth thing a skier would like to encounter. Thunder is an adaptive avalanche airbag system. Usually, an avalanche airbag product can help you float on the snow in an avalanche circumstance. Thunder are more focusing on the human behavior, making this avalanche airbag system not only an effective safety eq...

  7. Gaining information about home visits in primary care: methodological issues from a feasibility study. (United States)

    Voigt, Karen; Taché, Stephanie; Klement, Andreas; Fankhaenel, Thomas; Bojanowski, Stefan; Bergmann, Antje


    Home visits are part of general practice work in Germany. Within the context of an expanding elderly population and a decreasing number of general practitioner (GPs), open questions regarding the organisation and adequacy of GPs' care in immobile patients remain. To answer these questions, we will conduct a representative primary data collection concerning contents and organisation of GPs' home visits in 2014. Because this study will require considerable efforts for documentation and thus substantial involvement by participating GPs, we conducted a pilot study to see whether such a study design was feasible. We used a mixed methods design with two study arms in a sample of teaching GPs of the University Halle. The quantitative arm evaluates participating GPs and documentation of home visits. The qualitative arm focuses on reasons for non-participation for GPs who declined to take part in the pilot study. Our study confirms previously observed reasons for non-response of GPs in the particular setting of home visits including lack of time and/or interest. In contrast to previous findings, monetary incentives were not crucial for GPs participation. Several factors influenced the documentation rate of home visits and resulted in a discrepancy between the numbers of home visits documented versus those actually conducted. The most frequently reported problem was related to obtaining patient consent, especially when patients were unable to provide informed consent due to cognitive deficits. The results of our feasibility study provide evidence for improvement of the study design and study instruments to effectively conduct a documentation-intensive study of GPs doing home visits. Improvement of instructions and questionnaire regarding time variables and assessment of the need for home visits will be carried out to increase the reliability of future data. One particularly important methodological issue yet to be resolved is how to increase the representativeness of home

  8. Feasibility of a controlled trial aiming to prevent excessive pregnancy-related weight gain in primary health care

    Directory of Open Access Journals (Sweden)

    Weiderpass Elisabete


    Full Text Available Abstract Background Excessive gestational weight gain and postpartum weight retention may predispose women to long-term overweight and other health problems. Intervention studies aiming at preventing excessive pregnancy-related weight gain are needed. The feasibility of implementing such a study protocol in primary health care setting was evaluated in this pilot study. Methods A non-randomized controlled trial was conducted in three intervention and three control maternity and child health clinics in primary health care in Finland. Altogether, 132 pregnant and 92 postpartum women and 23 public health nurses (PHN participated in the study. The intervention consisted of individual counselling on physical activity and diet at five routine visits to a PHN and of an option for supervised group exercise until 37 weeks' gestation or ten months postpartum. The control clinics continued their usual care. The components of the feasibility evaluation were 1 recruitment and participation, 2 completion of data collection, 3 realization of the intervention and 4 the public health nurses' experiences. Results 1 The recruitment rate was slower than expected and the recruitment period had to be prolonged from the initially planned three months to six months. The average participation rate of eligible women at study enrolment was 77% and the drop-out rate 15%. 2 In total, 99% of the data on weight, physical activity and diet and 96% of the blood samples were obtained. 3 In the intervention clinics, 98% of the counselling sessions were realized, their contents and average durations were as intended, 87% of participants regularly completed the weekly records for physical activity and diet, and the average participation percentage in the group exercise sessions was 45%. 4 The PHNs regarded the extra training as a major advantage and the high additional workload as a disadvantage of the study. Conclusion The study protocol was mostly feasible to implement, which

  9. GEM scintillation readout with avalanche photodiodes

    CERN Document Server

    Conceição, A S; Fernandes, L M P; Monteiro, C M B; Coelho, L C C; Azevedo, C D R; Veloso, J F C A; Lopesac, J A M; dos Santosa, J M F


    The use of the scintillation produced in the charge avalanches in GEM holes as signal amplification and readout is investigated for xenon. A VUV-sensitive avalanche photodiode has been used as photosensor. Detector gains of about 4 × 104 are achieved in scintillation readout mode, for GEM voltages of 490 V and for a photosensor gain of 150. Those gains are more than one order of magnitude larger than what is obtained using charge readout. In addition, the energy resolutions achieved with the scintillation readout are lower than those achieved with charge readout. The GEM scintillation yield in xenon was measured as a function of GEM voltage, presenting values that are about a half of those achieved for the charge yield, and reach about 730 photons per primary electron at GEM voltages of 490 V.

  10. Determination of all feasible robust PID controllers for open-loop unstable plus time delay processes with gain margin and phase margin specifications. (United States)

    Wang, Yuan-Jay


    This paper proposes a novel alternative method to graphically compute all feasible gain and phase margin specifications-oriented robust PID controllers for open-loop unstable plus time delay (OLUPTD) processes. This method is applicable to general OLUPTD processes without constraint on system order. To retain robustness for OLUPTD processes subject to positive or negative gain variations, the downward gain margin (GM(down)), upward gain margin (GM(up)), and phase margin (PM) are considered. A virtual gain-phase margin tester compensator is incorporated to guarantee the concerned system satisfies certain robust safety margins. In addition, the stability equation method and the parameter plane method are exploited to portray the stability boundary and the constant gain margin (GM) boundary as well as the constant PM boundary. The overlapping region of these boundaries is graphically determined and denotes the GM and PM specifications-oriented region (GPMSOR). Alternatively, the GPMSOR characterizes all feasible robust PID controllers which achieve the pre-specified safety margins. In particular, to achieve optimal gain tuning, the controller gains are searched within the GPMSOR to minimize the integral of the absolute error (IAE) or the integral of the squared error (ISE) performance criterion. Thus, an optimal PID controller gain set is successfully found within the GPMSOR and guarantees the OLUPTD processes with a pre-specified GM and PM as well as a minimum IAE or ISE. Consequently, both robustness and performance can be simultaneously assured. Further, the design procedures are summarized as an algorithm to help rapidly locate the GPMSOR and search an optimal PID gain set. Finally, three highly cited examples are provided to illustrate the design process and to demonstrate the effectiveness of the proposed method. Copyright © 2014 ISA. Published by Elsevier Ltd. All rights reserved.

  11. MO-AB-BRA-07: Low Dose Imaging with Avalanche Amorphous Selenium Flat Panel Imager

    Energy Technology Data Exchange (ETDEWEB)

    Scheuermann, J; Howansky, A; Goldan, A; Tanioka, K; Zhao, W [Stony Brook University, Stony Brook, New York (United States); Leveille, S; Tousignant, O [2Analogic Canada, Saint-laurent, Quebec (Canada)


    Purpose: We present the first active matrix flat panel imager (AMFPI) capable of producing x-ray quantum noise limited images at low doses by overcoming the electronic noise through signal amplification by photoconductive avalanche gain (gav). The indirect detector fabricated uses an optical sensing layer of amorphous selenium (a-Se) known as High-Gain Avalanche Rushing Photoconductor (HARP). The detector design is called Scintillator HARP (SHARP)-AMFPI. This is the first image sensor to utilize solid-state HARP technology. Methods: The detector’s electronic readout is a 24 × 30 cm{sup 2} array of thin film transistors (TFT) with a pixel pitch of 85 µm. The HARP structure consists of a 15 µm layer of a-Se isolated from the high voltage (HV) and signal electrode by a 2 µm thick hole blocking layer and electron blocking layer, respectively, to reduce dark current. A 150 µm thick structured CsI scintillator with reflective backing and a fiber optic faceplate (FOP) was coupled to the semi-transparent HV bias electrode of the HARP structure. Images were acquired using a 30 kVp Mo/Mo spectrum typically used in mammography. Results: Optical sensitivity measurements demonstrate that gav = 76 ± 5 can be achieved over the entire active area of the detector. At a constant dose to the detector of 6.67 µGy, image quality increases with gav until the effective electronic noise is negligible. Quantum noise limited images can be obtained with doses as low as 0.18 µGy. Conclusion: We demonstrate the feasibility of utilizing avalanche gain to overcome electronic noise. The indirect detector fabricated is the first solid-state imaging sensor to use HARP, and the largest active area HARP sensor to date. Our future work is to improve charge transport within the HARP structure and utilize a transparent HV electrode.

  12. Integrated avalanche photodiode arrays (United States)

    Harmon, Eric S.


    The present disclosure includes devices for detecting photons, including avalanche photon detectors, arrays of such detectors, and circuits including such arrays. In some aspects, the detectors and arrays include a virtual beveled edge mesa structure surrounded by resistive material damaged by ion implantation and having side wall profiles that taper inwardly towards the top of the mesa structures, or towards the direction from which the ion implantation occurred. Other aspects are directed to masking and multiple implantation and/or annealing steps. Furthermore, methods for fabricating and using such devices, circuits and arrays are disclosed.

  13. Neuronal avalanches and learning

    Energy Technology Data Exchange (ETDEWEB)

    Arcangelis, Lucilla de, E-mail: [Department of Information Engineering and CNISM, Second University of Naples, 81031 Aversa (Italy)


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

  14. Type-II Superlattice Avalanche Photodiodes (United States)

    Huang, Jun

    Type-II superlattice avalanche photodiodes have shown advantages compared to conventional mercury cadmium telluride photodiodes for infrared wavelength detection. However, surface or interface leakage current has been a major issue for superlattice avalanche photodiodes, especially in infrared wavelength region. First, passivation of the superlattice device with ammonium sulfide and thioacetamide was carried out, and its surface quality was studied by X-ray Photoelectron Spectroscopy. The study showed that both ammonium sulfide and thiacetamide passivation can actively remove the native oxide at the surface. Thiacetamide passivation combine more sulfur bonds with III-V elements than that of ammonium sulfide. Another X-ray photoelectron spectra of thiacetamide-treated atomic layer deposited zinc sulfide capped InAs/GaSb superlattice was performed to investigate the interface sulfur bond conditions. Sb--S and As--S bonds disappear while In-S bond gets enhanced, indicating that Indium Sulfide should be the major components at the interface after ZnS deposition. Second, the simulation of electrical characteristics for zinc sulfide, silicon nitride and silicon dioxide passivated superlattice devices was performed by SILVACO software to fit the experimental results and to discover the surface current mechanism. Different surface current mechanism strengths were found. Third, several novel dual-carrier avalanche photodiode structures were designed and simulated. The structures had alternate carrier multiplication regions, placed next to a wider electron multiplication region, creating dual-carrier multiplication feedback systems. Gain and excess noise factor of these structures were simulated and compared based on the dead space multiplication theory under uniform electric field. From the simulation, the applied bias can be greatly lowered or the thickness can be shrunk to achieve the same gain from the conventional device. The width of the thin region was the most

  15. First approximations in avalanche model validations using seismic information (United States)

    Roig Lafon, Pere; Suriñach, Emma; Bartelt, Perry; Pérez-Guillén, Cristina; Tapia, Mar; Sovilla, Betty


    Avalanche dynamics modelling is an essential tool for snow hazard management. Scenario based numerical modelling provides quantitative arguments for decision-making. The software tool RAMMS (WSL Institute for Snow and Avalanche Research SLF) is one such tool, often used by government authorities and geotechnical offices. As avalanche models improve, the quality of the numerical results will depend increasingly on user experience on the specification of input (e.g. release and entrainment volumes, secondary releases, snow temperature and quality). New model developments must continue to be validated using real phenomena data, for improving performance and reliability. The avalanches group form University of Barcelona (RISKNAT - UB), has studied the seismic signals generated from avalanches since 1994. Presently, the group manages the seismic installation at SLF's Vallée de la Sionne experimental site (VDLS). At VDLS the recorded seismic signals can be correlated to other avalanche measurement techniques, including both advanced remote sensing methods (radars, videogrammetry) and obstacle based sensors (pressure, capacitance, optical sender-reflector barriers). This comparison between different measurement techniques allows the group to address the question if seismic analysis can be used alone, on more additional avalanche tracks, to gain insight and validate numerical avalanche dynamics models in different terrain conditions. In this study, we aim to add the seismic data as an external record of the phenomena, able to validate RAMMS models. The seismic sensors are considerable easy and cheaper to install than other physical measuring tools, and are able to record data from the phenomena in every atmospheric conditions (e.g. bad weather, low light, freezing make photography, and other kind of sensors not usable). With seismic signals, we record the temporal evolution of the inner and denser parts of the avalanche. We are able to recognize the approximate position

  16. Reformulating partially hydrogenated vegetable oils to maximise health gains in India: is it feasible and will it meet consumer demand? (United States)


    Background The consumption of partially hydrogenated vegetable oils (PHVOs) high in trans fat is associated with an increased risk of cardiovascular disease and other non-communicable diseases. In response to high intakes of PHVOs, the Indian government has proposed regulation to set limits on the amount of trans fat permissible in PHVOs. Global recommendations are to replace PHVOs with polyunsaturated fatty acids (PUFAs) in order to optimise health benefits; however, little is known about the practicalities of implementation in low-income settings. The aim of this study was to examine the technical and economic feasibility of reducing trans fat in PHVOs and reformulating it using healthier fats. Methods Thirteen semi-structured interviews were conducted with manufacturers and technical experts of PHVOs in India. Data were open-coded and organised according to key themes. Results Interviewees indicated that reformulating PHVOs was both economically and technically feasible provided that trans fat regulation takes account of the food technology challenges associated with product reformulation. However, there will be challenges in maintaining the physical properties that consumers prefer while reducing the trans fat in PHVOs. The availability of input oils was not seen to be a problem because of the low cost and high availability of imported palm oil, which was the input oil of choice for industry. Most interviewees were not concerned about the potential increase in saturated fat associated with increased use of palm oil and were not planning to use PUFAs in product reformulation. Interviewees indicated that many smaller manufacturers would not have sufficient capacity to reformulate products to reduce trans fat. Conclusions Reformulating PHVOs to reduce trans fat in India is feasible; however, a collision course exists where the public health goal to replace PHVOs with PUFA are opposed to the goals of industry to produce a cheap alternative product that meets

  17. Aggregation of Marginal Gains in Cardiac Surgery: Feasibility of a Perioperative Care Bundle for Enhanced Recovery in Cardiac Surgical Patients. (United States)

    Fleming, Ian O; Garratt, Claire; Guha, Ranj; Desai, Jatin; Chaubey, Sanjay; Wang, Yanzhong; Leonard, Sara; Kunst, Gudrun


    The aim of this pilot study was to assess the feasibility of a perioperative care bundle for enhanced recovery after cardiac surgery (ERACS). A prospective, observational study. A major urban teaching and university hospital and tertiary referral center. The study included 53 patients undergoing cardiac surgery before implementation of an ERACS protocol (pre-ERACS group) and 52 patients undergoing cardiac surgery after implementation of an ERACS protocol (ERACS group). Based on recommendations from a consensus review in colorectal surgery, the following enhanced recovery perioperative care bundle was applied: detailed preoperative information, avoidance of prolonged fasting periods preoperatively, preoperative carbohydrate beverages, optimization of analgesia with avoidance of long-acting opioids, prevention of postoperative nausea and vomiting, early enteral nutrition postoperatively, and early mobilization. The authors hypothesized that length of hospital stay would be reduced with ERACS. Secondary outcome variables included a composite of postoperative complications and pain scores. Whereas the length of stay in the group of patients receiving the bundle of enhanced recovery interventions remained unchanged compared with the non-ERACS group, there was a statistically significant reduction in the number of patients in the ERACS group presenting with one or more postoperative complications (including hospital-acquired infections, acute kidney injury, atrial fibrillation, respiratory failure, postoperative myocardial infarction, and death). In addition, postoperative pain scores were improved significantly in the ERACS group. This pilot study demonstrated that ERACS is feasible and has the potential for improved postoperative morbidity after cardiac surgery. A larger multicenter quality improvement study implementing perioperative care bundles would be the next step to further assess outcomes in ERACS patients. Copyright © 2016 The Authors. Published by Elsevier

  18. Feasibility of a hospital-based, family-centered intervention to reduce weight gain in overweight children and adolescents. (United States)

    Dreimane, Daina; Safani, David; MacKenzie, Marsha; Halvorson, Mary; Braun, Sharon; Conrad, Barry; Kaufman, Francine


    To evaluate the effects of a hospital-based, family-centered lifestyle program (Kids N Fitness) on weight and health in overweight 7-17-year-old children. The Kids N Fitness program consisting of up to twelve 90-min sessions was conducted in an outpatient setting. The program comprised interactive nutrition and exercise sessions with behavior modification. Subjects completed a logbook and child's health questionnaire. Measures and surveys were taken before, during, and after the program. Two hundred and sixty-four overweight children (137 female, 73% Hispanic), mean age 11.5+/-2.1 years, with body mass index (BMI)=85th percentile, no physical limitations, and attendance of >or=50% of sessions. A subgroup of 115 children was observed for up to 6 months prior to program. INTERVENTION RESULTS: Weight and BMI velocity, and BMI, and BMI z-score were lower during the program than during the pre-program observation period. Compared, subjects in the 12-week program had significantly reduced gains in weight and greater losses in body mass index, than in 8 weeks. Improvements in emotional well-being and behavior correlated positively with weight loss (p=0.005). Positive health outcomes suggest that family-centered programs, stressing healthy eating strategies, participation in team-oriented physical activities, and behavior modification, are effective in improving weight dynamics and psychological functioning.

  19. Reducing financial avalanches by random investments (United States)

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


    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.

  20. Lumped transmission line avalanche pulser (United States)

    Booth, Rex


    A lumped linear avalanche transistor pulse generator utilizes stacked transistors in parallel within a stage and couples a plurality of said stages, in series with increasing zener diode limited voltages per stage and decreasing balanced capacitance load per stage to yield a high voltage, high and constant current, very short pulse.

  1. A microstrip gas avalanche chamber with two-dimensional readout

    International Nuclear Information System (INIS)

    Angelini, F.; Bellazzini, R.; Brez, A.; Massai, M.M.; Spandre, G.; Torquati, M.R.


    A microstrip gas avalanche chamber with a 200 μm anode pitch has been built and successfully tested in our laboratory. A gas gain of 10 4 and an energy resolution of 18% (FWHM) at 6 keV have been measured using a gas mixture of argon-CO 2 at atmospheric pressure. A preliminary measurement of the positional sensitivity indicates that a spatial resolution of 50 μm can be obtained. (orig.)

  2. Plasmonic field confinement for separate absorption-multiplication in InGaAs nanopillar avalanche photodiodes. (United States)

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


    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.



    塩澤, 孝哉


    In this paper, modeling for the simulation of the avalanche by a particle method is discussed. There are two kinds of the snow avalanches, one is the surface avalanche which shows a smoke-like flow, and another is the total-layer avalanche which shows a flow like Bingham fluid. In the simulation of the surface avalanche, the particle method in consideration of a rotation resistance model is used. The particle method by Bingham fluid is used in the simulation of the total-layer avalanche. At t...

  4. Velocity distribution in snow avalanches (United States)

    Nishimura, K.; Ito, Y.


    In order to investigate the detailed structure of snow avalanches, we have made snow flow experiments at the Miyanomori ski jump in Sapporo and systematic observations in the Shiai-dani, Kurobe Canyon. In the winter of 1995-1996, a new device to measure static pressures was used to estimate velocities in the snow cloud that develops above the flowing layer of avalanches. Measurements during a large avalanche in the Shiai-dani which damaged and destroyed some instruments indicate velocities increased rapidly to more than 50 m/s soon after the front. Velocities decreased gradually in the following 10 s. Velocities of the lower flowing layer were also calculated by differencing measurement of impact pressure. Both recordings in the snow cloud and in the flowing layer changed with a similar trend and suggest a close interaction between the two layers. In addition, the velocity showed a periodic change. Power spectrum analysis of the impact pressure and the static pressure depression showed a strong peak at a frequency between 4 and 6 Hz, which might imply the existence of either ordered structure or a series of surges in the flow.

  5. Feasibility and Potential Benefits of a Self-Monitoring Enhanced Lifestyle Intervention to Prevent Excessive Gestational Weight Gain in Women Who Are Overweight or Obese. (United States)

    Shieh, Carol; Yang, Ziyi; Haas, David M; Carpenter, Janet S

    To evaluate the feasibility and potential benefits of a self-monitoring enhanced lifestyle intervention to prevent excessive gestational weight gain in women who are overweight and obese. A one-group, prospective design involving 8 weeks of healthy eating and physical activity and self-monitoring of weight, nutrition, and walking. Recruitment and enrollment in prenatal clinics and self-monitoring at home. Women (N = 22) at 14 to 24 gestational weeks, with body mass indexes of 25 to 40 kg/m 2 , without medical and psychiatric diseases that affected cognition or walking. Participants self-monitored weight and nutrition intake for the first 4 weeks and weight, nutrition intake, and walking in the second 4 weeks. Feasibility data were collected weekly (attrition, self-monitoring adherence, program safety, participant feedback) or at the end of Week 8 (satisfaction ratings). Potential benefits included weight, nutrition, and physical activity, measured at baseline (T1), the end of Week 4 (T2), or the end of Week 8 (T3). Attrition rates were 27.3% by T2 and 40.9% by T3. Adherence to log return was 100%. No adverse effects were noted, but food craving was persistent, and stress levels were high. Program satisfaction was high. Trends for improved activity and reduced trans fat consumption were seen. Our findings indicate that the intervention is worthy of further development and testing with a randomized controlled trial. Copyright © 2017 AWHONN, the Association of Women’s Health, Obstetric and Neonatal Nurses. Published by Elsevier Inc. All rights reserved.

  6. Avalanches and Criticality in Driven Magnetic Skyrmions (United States)

    Díaz, S. A.; Reichhardt, C.; Arovas, D. P.; Saxena, A.; Reichhardt, C. J. O.


    We show using numerical simulations that slowly driven Skyrmions interacting with random pinning move via correlated jumps or avalanches. The avalanches exhibit power-law distributions in their duration and size, and the average avalanche shape for different avalanche durations can be scaled to a universal function, in agreement with theoretical predictions for systems in a nonequilibrium critical state. A distinctive feature of Skyrmions is the influence of the nondissipative Magnus term. When we increase the ratio of the Magnus term to the damping term, a change in the universality class of the behavior occurs, the average avalanche shape becomes increasingly asymmetric, and individual avalanches exhibit motion in the direction perpendicular to their own density gradient.

  7. Avalanche dynamics of elastic interfaces. (United States)

    Le Doussal, Pierre; Wiese, Kay Jörg


    Slowly driven elastic interfaces, such as domain walls in dirty magnets, contact lines wetting a nonhomogeneous substrate, or cracks in brittle disordered material proceed via intermittent motion, called avalanches. Here we develop a field-theoretic treatment to calculate, from first principles, the space-time statistics of instantaneous velocities within an avalanche. For elastic interfaces at (or above) their (internal) upper critical dimension d≥d(uc) (d(uc)=2,4 respectively for long-ranged and short-ranged elasticity) we show that the field theory for the center of mass reduces to the motion of a point particle in a random-force landscape, which is itself a random walk [Alessandro, Beatrice, Bertotti, and Montorsi (ABBM) model]. Furthermore, the full spatial dependence of the velocity correlations is described by the Brownian-force model (BFM) where each point of the interface sees an independent Brownian-force landscape. Both ABBM and BFM can be solved exactly in any dimension d (for monotonous driving) by summing tree graphs, equivalent to solving a (nonlinear) instanton equation. We focus on the limit of slow uniform driving. This tree approximation is the mean-field theory (MFT) for realistic interfaces in short-ranged disorder, up to the renormalization of two parameters at d=d(uc). We calculate a number of observables of direct experimental interest: Both for the center of mass, and for a given Fourier mode q, we obtain various correlations and probability distribution functions (PDF's) of the velocity inside an avalanche, as well as the avalanche shape and its fluctuations (second shape). Within MFT we find that velocity correlations at nonzero q are asymmetric under time reversal. Next we calculate, beyond MFT, i.e., including loop corrections, the one-time PDF of the center-of-mass velocity u[over ·] for dimension delasticity) and a=1-4/9(2-d)+... (long-ranged elasticity). We show how the dynamical theory recovers the avalanche-size distribution

  8. A probabilistic model for snow avalanche occurrence (United States)

    Perona, P.; Miescher, A.; Porporato, A.


    Avalanche hazard forecasting is an important issue in relation to the protection of urbanized environments, ski resorts and of ski-touring alpinists. A critical point is to predict the conditions that trigger the snow mass instability determining the onset and the size of avalanches. On steep terrains the risk of avalanches is known to be related to preceding consistent snowfall events and to subsequent changes in the local climatic conditions. Regression analysis has shown that avalanche occurrence indeed correlates to the amount of snow fallen in consecutive three snowing days and to the state of the settled snow at the ground. Moreover, since different type of avalanches may occur as a result of the interactions of different factors, the process of snow avalanche formation is inherently complex and with some degree of unpredictability. For this reason, although several models assess the risk of avalanche by accounting for all the involved processes with a great detail, a high margin of uncertainty invariably remains. In this work, we explicitly describe such an unpredictable behaviour with an intrinsic noise affecting the processes leading snow instability. Eventually, this sets the basis for a minimalist stochastic model, which allows us to investigate the avalanche dynamics and its statistical properties. We employ a continuous time process with stochastic jumps (snowfalls), deterministic decay (snowmelt and compaction) and state dependent avalanche occurrence (renewals) as a minimalist model for the determination of avalanche size and related intertime occurrence. The physics leading to avalanches is simplified to the extent where only meteorological data and terrain data are necessary to estimate avalanche danger. We explore the analytical formulation of the process and the properties of the probability density function of the avalanche process variables. We also discuss what is the probabilistic link between avalanche size and preceding snowfall event and

  9. Terrain Classification of Norwegian Slab Avalanche Accidents (United States)

    Hallandvik, Linda; Aadland, Eivind; Vikene, Odd Lennart


    It is difficult to rely on snow conditions, weather, and human factors when making judgments about avalanche risk because these variables are dynamic and complex; terrain, however, is more easily observed and interpreted. Therefore, this study aimed to investigate (1) the type of terrain in which historical fatal snow avalanche accidents in Norway…

  10. Towards an understanding of flows in avalanche transport phenomena (United States)

    Jin, Suying; Ramadan, Nikolas; van Compernolle, Bart; Poulos, Matt J.; Morales, George J.


    Recent heat transport experiments conducted in the Large Plasma Device (LAPD) at UCLA, studying avalanche phenomena at steep cross-magnetic field pressure gradients, suggest that flows play a critical role in the evolution of transport phenomena, motivating further characterization. A ring shaped electron beam source injects sub-ionization energy electrons along the strong background magnetic field within a larger quiescent plasma, creating a hollow, high pressure filament. Two distinct regimes are observed as the density decays; the first characterized by multiple small avalanches producing sudden relaxations of the pressure profile which then recovers under continued heating, and the second signaled by a permanent collapse of the density profile after a global avalanche event, then dominated by drift-Alfven waves. The source is modified from previous experiments to gain active control of the flows by controlling the bias between the emitting ring and surrounding carbon masks. The results of flow measurements obtained using a Mach probe and Langmuir/emissive probe are here presented and compared. An analytical model for the behavior of the electron beam source is also in development. Sponsored by NSF Grant 1619505 and by DOE/NSF at BaPSF.

  11. Frontal Dynamics of Powder Snow Avalanches (United States)

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


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

  12. Avalanche breakdown of the quantum hall effects

    CERN Document Server

    Komiyama, S


    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 ...

  13. Studies of light emission by continuously sensitive avalanche chambers

    International Nuclear Information System (INIS)

    Charpak, G.; Dominik, W.; Fabre, J.P.; Gaudaen, J.; Sauli, F.; Suzuki, M.


    The optimal conditions for the optical recording of images of electron avalanches between parallel meshes have been studied. The emission spectra of gas mixtures have been investigated, where triethylamine (TEA), tetrakis(dimethylamine)ethylene (TMAE), and nitrogen, are used as the photon-emitting agents. For a given charge gain, the photon intensity decreases with electric field. This favours amplification between parallel meshes instead of wires. The use of intensified CCD cameras permits the recording of the local energy loss along the tracks. (orig.)

  14. Energy and dissipated work in snow avalanches (United States)

    Bartelt, P.; Buser, O.


    Using the results of large scale avalanche experiments at the Swiss Vallée de la Sionne test site, the energy balance of several snow avalanches is determined. Avalanches convert approximately one-seventh of their potential energy into kinetic energy. The total potential energy depends strongly on the entrained snowcover, indicating that entrainment processes cannot be ignored when predicting terminal velocities and runout distances. We find energy dissipation rates on the order of 1 GW. Fluidization of the fracture slab can be identified in the experiments as an increase in dissipation rate, thereby explaining the initial and rapid acceleration of avalanches after release. Interestingly, the dissipation rates appear to be constant along the track, although large fluctuations in internal velocity exist. Thus, we can demonstrate within the context of non-equilibrium thermodynamics that -- in space -- granular snow avalanches are irreversible, dissipative systems that minimize entropy production because they appear to reach a steady-state non-equilibrium. A thermodynamic analysis reveals that fluctuations in velocity depend on the roughness of the flow surface and viscosity of the granular system. We speculate that this property explains the transition from flowing avalanches to powder avalanches.

  15. Avalanches in vanadium sesquioxide nanodevices (United States)

    Wang, Siming; Ramírez, Juan Gabriel; Schuller, Ivan K.


    The resistance versus temperature across the metal-insulator transition (MIT) of V2O3 nanodevices exhibits multiple discontinuous jumps. The jump sizes range over three orders of magnitude in resistance and their distribution follows a power law, implying that the MIT of V2O3 occurs through avalanches. While the maximum jump size depends on the device size, the power law exponent for V2O3 is independent of device geometry and different than the one found earlier in V O2 . A two-dimensional random percolation model exhibits a power law distribution different from the one found in V2O3 . Instead, the model gives a similar exponent found in another vanadium oxide, V O2 . Our results suggest that the MITs of V O2 and V2O3 are produced by different mechanisms.

  16. Continuum description of avalanches in granular media.

    Energy Technology Data Exchange (ETDEWEB)

    Aranson, I. S.; Tsimring, L. S.


    A continuum theory of partially fluidized granular flows is proposed. The theory is based on a combination of the mass and momentum conservation equations with the order parameter equation which describes the transition between flowing and static components of the granular system. We apply this model to the dynamics of avalanches in chutes. The theory provides a quantitative description of recent observations of granular flows on rough inclined planes (Daerr and Douady 1999): layer bistability, and the transition from triangular avalanches propagating downhill at small inclination angles to balloon-shaped avalanches also propagating uphill for larger angles.

  17. Statistical Distributions of Electron Avalanches and Streamers

    Directory of Open Access Journals (Sweden)

    T. Ficker


    Full Text Available A new theoretical concept of fractal multiplication of electron avalanches has resulted in forming a generalized distribution function whose multiparameter character has been subjected to detailed discussion. 

  18. Electromagnetic radiation field of an electron avalanche (United States)

    Cooray, Vernon; Cooray, Gerald


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

  19. Statistics of Electron Avalanches and Streamers

    Directory of Open Access Journals (Sweden)

    T. Ficker


    Full Text Available We have studied the severe systematic deviations of populations of electron avalanches from the Furry distribution, which has been held to be the statistical law corresponding to them, and a possible explanation has been sought. A  new theoretical concept based on fractal avalanche multiplication has been proposed and is shown to be a convenient candidate for explaining these deviations from Furry statistics. 

  20. Catastrophic avalanches and methods of their control

    Directory of Open Access Journals (Sweden)

    N. A. Volodicheva


    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.

  1. Creation of the snow avalanche susceptibility map of the Krkonoše Mountains using GIS

    Directory of Open Access Journals (Sweden)

    Petr Suk


    Full Text Available This article deals with the development of the snow avalanche susceptibility map in the Czech part of the Krkonoše Mountains using the free Geographic Information System (GIS GRASS. The area susceptibility map consists of two components: the morphological risk map, which is derived from the digital terrain model (DTM and describes the slope steepness, aspect and curvature of the slope, and the protecting vegetation influence map, which is based on supervised image classification (spectrozonal aerial photos and takes into consideration the importance of vegetation cover. The final map also includes starting zones calculated on the basis of significant changes in slope steepness and approximate shapes of avalanche paths based on these zones. In the map development, the layer of measured paths of avalanche cadastre in the Czech part of the Krkonoše Mountains was used, partly to gain the morphological characteristics of starting zones and partly to check the quality of the map.

  2. Erosion dynamics of powder snow avalanches - Observations (United States)

    Sovilla, Betty; Louge, Michel


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

  3. Mean secondary electron yield of avalanche electrons in the channels of a microchannel plate detector

    International Nuclear Information System (INIS)

    Funsten, H.O.; Suszcynsky, D.M.; Harper, R.W.


    By modeling the statistical evolution of an avalanche created by 20 keV protons impacting the input surface of a z-stack microchannel plate (MCP) detector, the mean secondary electron yield γ C of avalanche electrons propagating through a MCP channel is measured to equal 1.37 for 760 V per MCP in the z stack. This value agrees with other studies that used MCP gain measurements to infer γ C . The technique described here to measure γ C is independent of gain saturation effects and simplifying assumptions used in the segmented dynode model, both of which can introduce errors when inferring γ C through gain measurements. copyright 1996 American Institute of Physics

  4. Vulnerability assessment in avalanche hazardous areas (United States)

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


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

  5. Criticality and avalanches in neural networks

    International Nuclear Information System (INIS)

    Zare, Marzieh; Grigolini, Paolo


    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

  6. Thin Al1?x Ga x As0.56Sb0.44 diodes with extremely weak temperature dependence of?avalanche breakdown


    Zhou, Xinxin; Tan, Chee Hing; Zhang, Shiyong; Moreno, Manuel; Xie, Shiyu; Abdullah, Salman; Ng, Jo Shien


    When using avalanche photodiodes (APDs) in applications, temperature dependence of avalanche breakdown voltage is one of the performance parameters to be considered. Hence, novel materials developed for APDs require dedicated experimental studies. We have carried out such a study on thin Al1?x Ga x As0.56Sb0.44 p?i?n diode wafers (Ga composition from 0 to 0.15), plus measurements of avalanche gain and dark current. Based on data obtained from 77 to 297?K, the alloys Al1?x Ga x As0.56Sb0.44 ex...

  7. Real time avalanche detection for high risk areas. (United States)


    Avalanches routinely occur on State Highway 21 (SH21) between Lowman and Stanley, Idaho each winter. The avalanches pose : a threat to the safety of maintenance workers and the traveling public. A real-time avalanche detection system will allow the :...

  8. Nanopillar Optical Antenna Avalanche Detectors (United States)


    of the device in terms of accurately predicting the punch through voltage, the shape of the CV characteristic and the saturation capacitance Csat ~ 9...characterized for excess noise gain characteristics using custom setup built at UCLA. The schematic of the excess noise setup is shown in Fig XX below. The main

  9. Studies of neutron irradiation of avalanche photodiodes using sup 2 sup 5 sup 2 Cf

    CERN Document Server

    Musienko, Y; Ruuska, D; Swain, J D


    Results on the radiation hardness of photodiodes to fast neutrons are presented. Four photodiodes (three avalanche photodiodes from two manufacturers, and one PIN photodiode) were exposed to neutrons from a sup 2 sup 5 sup 2 Cf source at Oak Ridge National Laboratory. The effects of this radiation on many parameters such as gain, intrinsic dark current, quantum efficiency, noise, capacitance, and voltage and temperature coefficients of the gain for these devices for fluences up to approx 2x10 sup 1 sup 3 neutrons/cm sup 2 are shown and discussed. While degradation of APDs occurred during neutron irradiation, they remained photosensitive devices with gain.

  10. Oscillatory regime of avalanche particle detectors

    International Nuclear Information System (INIS)

    Lukin, K.A.; Cerdeira, H.A.; Colavita, A.A.


    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

  11. Avalanche photodiodes for the CMS electromagnetic calorimeter

    CERN Document Server

    Organtini, G


    Avalanche Photodiodes (APDs) will be used as photodetectors for the CMS crystal barrel calorimeter, made of lead tungstate (PWO) scintillating crystals. After two years of strong R&D effort a significant progress was achieved, in collaboration with manufacturers, in the relevant properties of the device for LHC applications. Quantum efficiency, noise contributions and radiation resistance measurements of APDs are presented.

  12. Temperature Control of Avalanche Photodiode Using Thermoelectric Cooler (United States)

    Refaat, Tamer F.; Luck, William S., Jr.; DeYoung, Russell J.


    Avalanche photodiodes (APDS) are quantum optical detectors that are used for visible and near infrared optical detection applications. Although APDs are compact, rugged, and have an internal gain mechanism that is suitable for low light intensity; their responsivity, and therefore their output, is strongly dependent on the device temperature. Thermoelectric coolers (TEC) offers a suitable solution to this problem. A TEC is a solid state cooling device, which can be controlled by changing its current. TECs are compact and rugged, and they can precisely control the temperature to within 0.1 C with more than a 150 C temperature gradient between its surfaces. In this Memorandum, a proportional integral (PI) temperature controller for APDs using a TEC is discussed. The controller is compact and can successfully cool the APD to almost 0 C in an ambient temperature environment of up to 27 C.

  13. Nano-multiplication region avalanche photodiodes and arrays (United States)

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


    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.

  14. X-ray spectrometry with Peltier-cooled large area avalanche photodiodes

    International Nuclear Information System (INIS)

    Fernandes, L.M.P.; Lopes, J.A.M.; Santos, J.M.F. dos; Conde, C.A.N.


    Performance characteristics of the response of a Peltier-cooled large-area avalanche photodiode are investigated. Detector gain, energy linearity, energy resolution and minimum detectable energy are studied at different operation temperatures. Detector energy resolution and lowest detectable X-ray energy present a strong improvement as the operation temperature is reduced from 25 to 15 deg. C and slower improvements are achieved for temperatures below 10 deg. C

  15. Avalanches and generalized memory associativity in a network model for conscious and unconscious mental functioning (United States)

    Siddiqui, Maheen; Wedemann, Roseli S.; Jensen, Henrik Jeldtoft


    We explore statistical characteristics of avalanches associated with the dynamics of a complex-network model, where two modules corresponding to sensorial and symbolic memories interact, representing unconscious and conscious mental processes. The model illustrates Freud's ideas regarding the neuroses and that consciousness is related with symbolic and linguistic memory activity in the brain. It incorporates the Stariolo-Tsallis generalization of the Boltzmann Machine in order to model memory retrieval and associativity. In the present work, we define and measure avalanche size distributions during memory retrieval, in order to gain insight regarding basic aspects of the functioning of these complex networks. The avalanche sizes defined for our model should be related to the time consumed and also to the size of the neuronal region which is activated, during memory retrieval. This allows the qualitative comparison of the behaviour of the distribution of cluster sizes, obtained during fMRI measurements of the propagation of signals in the brain, with the distribution of avalanche sizes obtained in our simulation experiments. This comparison corroborates the indication that the Nonextensive Statistical Mechanics formalism may indeed be more well suited to model the complex networks which constitute brain and mental structure.

  16. CMOS-based avalanche photodiodes for direct particle detection

    International Nuclear Information System (INIS)

    Stapels, Christopher J.; Squillante, Michael R.; Lawrence, William G.; Augustine, Frank L.; Christian, James F.


    Active Pixel Sensors (APSs) in complementary metal-oxide-semiconductor (CMOS) technology are augmenting Charge-Coupled Devices (CCDs) as imaging devices and cameras in some demanding optical imaging applications. Radiation Monitoring Devices are investigating the APS concept for nuclear detection applications and has successfully migrated avalanche photodiode (APD) pixel fabrication to a CMOS environment, creating pixel detectors that can be operated with internal gain as proportional detectors. Amplification of the signal within the diode allows identification of events previously hidden within the readout noise of the electronics. Such devices can be used to read out a scintillation crystal, as in SPECT or PET, and as direct-conversion particle detectors. The charge produced by an ionizing particle in the epitaxial layer is collected by an electric field within the diode in each pixel. The monolithic integration of the readout circuitry with the pixel sensors represents an improved design compared to the current hybrid-detector technology that requires wire or bump bonding. In this work, we investigate designs for CMOS APD detector elements and compare these to typical values for large area devices. We characterize the achievable detector gain and the gain uniformity over the active area. The excess noise in two different pixel structures is compared. The CMOS APD performance is demonstrated by measuring the energy spectra of X-rays from 55 Fe

  17. Avalanches in functional materials and geophysics

    CERN Document Server

    Saxena, Avadh; Planes, Antoni


    This book provides the state-of-the art of the present understanding of avalanche phenomena in both functional materials and geophysics. The main emphasis of the book is analyzing these apparently different problems within the common perspective of out-of-equilibrium phenomena displaying spatial and temporal complexity that occur in a broad range of scales. Many systems, when subjected to an external force, respond intermittently in the form of avalanches that often span over a wide range of sizes, energies and durations. This is often related to a class of critical behavior characterized by the absence of characteristic scales. Typical examples are magnetization processes, plastic deformation and failure occuring in functional materials. These phenomena share many similarities with seismicity arising from the earth crust failure due to stresses that originate from plate tectonics.

  18. Avalanche Dynamics of Radio Pulsar Glitches (United States)

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


    We test statistically the hypothesis that radio pulsar glitches result from an avalanche process, in which angular momentum is transferred erratically from the flywheel-like superfluid in the star to the slowly decelerating, solid crust via spatially connected chains of local, impulsive, threshold-activated events, so that the system fluctuates around a self-organized critical state. Analysis of the glitch population (currently 285 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 measured power-law exponents fall in the range -0.13 age. The rate distribution itself is fitted reasonably well by an exponential for λ >= 0.25 yr-1, with langle λ rangle = 1.3+ 0.7-0.6 yr-1. For λ 0.25 yr-1 must exceed ~70%.

  19. Avalanches in Mn12-Acetate: ``Magnetic Burning" (United States)

    McHugh, Sean; Suzuki, Y.; Graybill, D.; Sarachik, M. P.; Avraham, N.; Myasoedov, Y.; Shtrikman, H.; Zeldov, E.; Bagai, R.; Chakov, N. E.; Christou, G.


    From local time-resolved measurements of fast reversal of the magnetization in single crystals of the molecular magnet Mn12-acetate, we have shown[1] that the magnetization avalanche spreads as a narrow interface that propagates through the crystal at a constant velocity roughly two orders of magnitude smaller than the speed of sound. This phenomenon is closely analogous to the propagation of a flame front (deflagration) through a flammable chemical substance. The propagation speed of the avalanche depends on the energy stored in each molecule, which can be controlled and tuned using an external magnetic field. We report studies of propagation speed with different external fields in Mn12-acetate. [1] Yoko Suzuki, M.P. Sarachik, E.M. Chudnovsky, S. McHugh, R. Gonzalez-Rubio, N. Avraham, Y. Myasoedov, H. Shtrikman, E. Zeldov, N.E. Chakov and G. Christou, Phys. Rev. Lett. 95, 147201 (2005).

  20. Assessing the value of real-time snow and avalanche information (United States)

    Zeidler, Antonia; Adams, Marc; Schuster, Martin; Berner, Martin; Nagy, Wilhelm


    This poster presentation shows first results from a pilot study on exploring the possibilities of using existing and new information and communication technologies (ICT) for snow and avalanche assessments. Today, ICT solutions allow the utilisation of information at a high spatiotemporal resolution, due to the widespread availability of internet access, high computing power and affordable mobile devices. Therefore, there is an increasing request for up to date information on snow and avalanche decision-making. However, there are challenges that need to be addressed from different view points. These include topics in the field of technological feasibility of providing a stable network, exchanging trustworthy information and motivation of experts to participate. This contribution discusses the lessons-learnt, from the establishment of a platform to the user-experience.

  1. A position sensitive parallel plate avalanche counter

    International Nuclear Information System (INIS)

    Lombardi, M.; Tan Jilian; Potenza, R.; D'amico, V.


    A position sensitive parallel plate avalanche counter with a distributed constant delay-line-cathode (PSAC) is described. The strips formed on the printed board were served as the cathode and the delay line for readout of signals. The detector (PSAC) was operated in isobutane gas at the pressure range from 10 to 20 torr. The position resolution is better than 1 mm and the time resolution is about 350 ps, for 252 Cf fission-spectrum source

  2. State-of-the-art performance of GaAlAs/GaAs avalanche photodiodes (United States)

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


    Ga(0.15)Al(0.85)As/GaAs avalanche photodiodes have been successfully fabricated. The performance of these detectors is characterized by a rise time of less than 35 ps, an external quantum efficiency with an antireflection coating of 95% at 0.53 microns, and a microwave optical gain of 42 dB. The dark current density is in the low range (10 to the minus A/sq cm) at one-half the breakdown voltages, and rises to 0.0001 A/sq cm at 42 dB optical gain.

  3. New advances for modelling the debris avalanches (United States)

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


    Flow-like landslides are a major global hazard and they occur worldwide causing a large number of casualties, significant structural damages to property and infrastructures as well as economic losses. When involving open slopes, these landslides often occur in triangular source areas where initial slides turn into avalanches through further failures and/or eventual soil entrainment. This paper deals with the numerical modelling of the propagation stage of debris avalanches which provides information such as the propagation pattern of the mobilized material, its velocity, thickness and run-out distance. In the paper, a "depth integrated" model is used which allows: i) adequately taking into account the irregular topography of real slopes which greatly affect the propagation stage and ii) using a less time consuming model than fully 3D approaches. The used model is named "GeoFlow_SPH" and it was formerly applied to theoretical, experimental and real case histories (Pastor et al., 2009; Cascini et al., 2012). In this work the behavior of debris avalanches is analyzed with special emphasis on the apical angle, one of the main features of this type of landslide, in relation to soil rheology, hillslope geometry and features of triggering area. Furthermore, the role of erosion has been investigated with reference to the uppermost parts of open slopes with a different steepness. These analyses are firstly carried out for simplified benchmark slopes, using both water-like materials (with no shear strength) and debris type materials. Then, three important case studies of Campania region (Cervinara, Nocera Inferiore e Sarno) are analyzed where debris avalanches involved pyroclastic soils originated from the eruptive products of Vesusius volcano. The results achieved for both benchmark slopes and real case histories outline the key role played by the erosion on the whole propagation stage of debris avalanches. The results are particularly satisfactory since they indicate the

  4. Anthropogenic effect on avalanche and debris flow activity


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


    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 unavoida...

  5. Setting best practice criteria for self-differencing avalanche photodiodes in quantum key distribution (United States)

    Koehler-Sidki, Alexander; Dynes, James F.; Lucamarini, Marco; Roberts, George L.; Sharpe, Andrew W.; Savory, Seb J.; Yuan, Zhiliang; Shields, Andrew J.


    In recent years, the security of avalanche photodiodes as single photon detectors for quantum key distribution has been subjected to much scrutiny. The most prominent example of this surrounds the vulnerability of such devices to blinding under strong illumination. We focus on self-differencing avalanche photodiodes, single photon detectors that have demonstrated count rates exceeding 1 GCounts/s resulting in secure key rates over 1 MBit/s. These detectors use a passive electronic circuit to cancel any periodic signals thereby enhancing detection sensitivity. However this intrinsic feature can be exploited by adversaries to gain control of the devices using illumination of a moderate intensity. Through careful experimental examinations, we define here a set of criteria for these detectors to avoid such attacks.

  6. Potential health gains and health losses in eleven EU countries attainable through feasible prevalences of the life-style related risk factors alcohol, BMI, and smoking: a quantitative health impact assessment. (United States)

    Lhachimi, Stefan K; Nusselder, Wilma J; Smit, Henriette A; Baili, Paolo; Bennett, Kathleen; Fernández, Esteve; Kulik, Margarete C; Lobstein, Tim; Pomerleau, Joceline; Boshuizen, Hendriek C; Mackenbach, Johan P


    Influencing the life-style risk-factors alcohol, body mass index (BMI), and smoking is an European Union (EU) wide objective of public health policy. The population-level health effects of these risk-factors depend on population specific characteristics and are difficult to quantify without dynamic population health models. For eleven countries-approx. 80 % of the EU-27 population-we used evidence from the publicly available DYNAMO-HIA data-set. For each country the age- and sex-specific risk-factor prevalence and the incidence, prevalence, and excess mortality of nine chronic diseases are utilized; including the corresponding relative risks linking risk-factor exposure causally to disease incidence and all-cause mortality. Applying the DYNAMO-HIA tool, we dynamically project the country-wise potential health gains and losses using feasible, i.e. observed elsewhere, risk-factor prevalence rates as benchmarks. The effects of the "worst practice", "best practice", and the currently observed risk-factor prevalence on population health are quantified and expected changes in life expectancy, morbidity-free life years, disease cases, and cumulative mortality are reported. Applying the best practice smoking prevalence yields the largest gains in life expectancy with 0.4 years for males and 0.3 year for females (approx. 332,950 and 274,200 deaths postponed, respectively) while the worst practice smoking prevalence also leads to the largest losses with 0.7 years for males and 0.9 year for females (approx. 609,400 and 710,550 lives lost, respectively). Comparing morbidity-free life years, the best practice smoking prevalence shows the highest gains for males with 0.4 years (342,800 less disease cases), whereas for females the best practice BMI prevalence yields the largest gains with 0.7 years (1,075,200 less disease cases). Smoking is still the risk-factor with the largest potential health gains. BMI, however, has comparatively large effects on morbidity. Future

  7. Multiphonon absorption and photon avalanche criterion in erbium doped materials

    International Nuclear Information System (INIS)

    Auzel, F.


    The photon avalanche effect has been recently observed at room temperature in erbium doped fluoride glasses and crystals, in a particularly clear way, displaying simultaneously all the typical features of this effect: (i) existence of a threshold for transmission at the excitation wavelength, (ii) up-conversion excitation threshold, (iii) long delay for threshold establishment. Analysing the first step of the avalanche effect as an anti-Stokes multiphonon absorption, it can be shown why this effect is so clearly observed at room temperature in our erbium studies. Our results are compared with other cases of avalanche, with cases which have been called ''looping effects'' and ''quasi-avalanche'' ones. (author)

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

    International Nuclear Information System (INIS)

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


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

  9. Assessment and mapping of snow avalanche risk in Russia (United States)

    Seliverstov, Yuri; Glazovskaya, Tatiana; Shnyparkov, Alexander; Vilchek, Yana; Sergeeva, Ksenia; Martynov, Alexei

    The term 'risk' can be defined as the probability of unfavourable consequences or negative effects. Risk can be expressed by means of various indices, such as collective or social risk (possible number of dead), individual risk (probability of a person's death within a certain territory during 1 year), probability of losses, etc. This paper is a case study of the small-scale assessment and mapping of individual avalanche risk focused on the two regions of Russia with the highest levels of avalanche activity: the northern Caucasus and the mountainous parts of Sakhalin island. The basic indices applied for individual avalanche risk estimation are: recurrence interval of avalanches (avalanche frequency), percentage of the whole investigated territory that is occupied by avalanche-prone areas, duration of avalanche danger period, probability of a person's stay in an avalanche-prone area during 1 day (24 hours) and during 1 year, total population of the area and its density. The results of individual avalanche risk assessment, undertaken for the territory of Russia as a whole, show that its values generally do not exceed the admissible level (from 1 × 10-6 to 1 × 10-4). However, some areas of the northern Caucasus, including famous alpine skiing resorts (Krasnaya Poliana, Dombai, the Mount Elbrus region, etc.), and of Sakhalin, including the environs of towns (Kholmsk, Nevel'sk) and other smaller human settlements, are characterized by an unacceptable level of risk. In the aggregate, areas with an unacceptable (>1 × 10-4) level of individual avalanche risk comprise about 7% of the whole avalanche-prone territory of the northern Caucasus, those with an admissible level comprise 52% and those with an acceptable level (<1 × 10-6) 41%. The corresponding values for Sakhalin are 0.1%, 14.8% and 85.1%.

  10. The 2002 rock/ice avalanche at Kolka/Karmadon, Russian Caucasus: assessment of extraordinary avalanche formation and mobility, and application of QuickBird satellite imagery (United States)

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


    A massive rock/ice avalanche of about 100x106m3 volume took place on the northern slope of the Kazbek massif, North Ossetia, Russian Caucasus, on 20 September 2002. The avalanche started as a slope failure, that almost completely entrained Kolka glacier, traveled down the Genaldon valley for 20km, was stopped at the entrance of the Karmadon gorge, and was finally succeeded by a distal mudflow which continued for another 15km. The event caused the death of ca. 140 people and massive destruction. Several aspects of the event are extraordinary, i.e. the large ice volume involved, the extreme initial acceleration, the high flow velocity, the long travel distance and particularly the erosion of a valley-type glacier, a process not known so far. The analysis of these aspects is essential for process understanding and worldwide glacial hazard assessments. This study is therefore concerned with the analysis of processes and the evaluation of the most likely interpretations. The analysis is based on QuickBird satellite images, field observations, and ice-, flow- and thermo-mechanical considerations. QuickBird is currently the best available satellite sensor in terms of ground resolution (0.6 m) and opens new perspectives for assessment of natural hazards. Evaluation of the potential of QuickBird images for assessment of high-mountain hazards shows the feasibility for detailed avalanche mapping and analysis of flow dynamics, far beyond the capabilities of conventional satellite remote sensing. It is shown that the avalanche was characterized by two different flows. The first one was comparable to a hyperconcentrated flow and was immediately followed by a flow with a much lower concentration of water involving massive volumes of ice. The high mobility of the avalanche is likely related to fluidization effects at the base of the moving ice/debris mass with high pore pressures and a continuous supply of water due to frictional melting of ice. The paper concludes with

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

    Directory of Open Access Journals (Sweden)

    C. Huggel


    Full Text Available A massive rock/ice avalanche of about 100x106m3 volume took place on the northern slope of the Kazbek massif, North Ossetia, Russian Caucasus, on 20 September 2002. The avalanche started as a slope failure, that almost completely entrained Kolka glacier, traveled down the Genaldon valley for 20km, was stopped at the entrance of the Karmadon gorge, and was finally succeeded by a distal mudflow which continued for another 15km. The event caused the death of ca. 140 people and massive destruction. Several aspects of the event are extraordinary, i.e. the large ice volume involved, the extreme initial acceleration, the high flow velocity, the long travel distance and particularly the erosion of a valley-type glacier, a process not known so far. The analysis of these aspects is essential for process understanding and worldwide glacial hazard assessments. This study is therefore concerned with the analysis of processes and the evaluation of the most likely interpretations. The analysis is based on QuickBird satellite images, field observations, and ice-, flow- and thermo-mechanical considerations. QuickBird is currently the best available satellite sensor in terms of ground resolution (0.6 m and opens new perspectives for assessment of natural hazards. Evaluation of the potential of QuickBird images for assessment of high-mountain hazards shows the feasibility for detailed avalanche mapping and analysis of flow dynamics, far beyond the capabilities of conventional satellite remote sensing. It is shown that the avalanche was characterized by two different flows. The first one was comparable to a hyperconcentrated flow and was immediately followed by a flow with a much lower concentration of water involving massive volumes of ice. The high mobility of the avalanche is likely related to fluidization effects at the base of the moving ice/debris mass with high pore pressures and a continuous supply of water due to frictional melting of ice. The paper

  12. Tuning magnetization avalanches in Mn12-acetate (United States)

    Wen, Bo; McHugh, S.; Ma, Xiang; Sarachik, M. P.; Myasoedov, Y.; Shtrikman, H.; Zeldov, E.; Bagai, R.; Christou, G.


    We report the results of a systematic study of magnetic avalanches (abrupt magnetization reversals) in the molecular magnet Mn12-acetate using a micron-sized Hall sensor array. Measurements were taken for: (a) fixed magnetic field (constant barrier against spin reversal); and (b) fixed energy release obtained by adjusting the barrier and δM. A detailed comparison with the theory of magnetic deflagration of Garanin and Chudnovsky [1] will be presented and discussed. [1] D. A. Garanin and E. M. Chudnovsky, Phys. Rev. B 76, 054410 (2007)

  13. Validation of DEM prediction for granular avalanches on irregular terrain (United States)

    Mead, Stuart R.; Cleary, Paul W.


    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.

  14. High voltage short plus generation based on avalanche circuit

    International Nuclear Information System (INIS)

    Hu Yuanfeng; Yu Xiaoqi


    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)

  15. Electric field distribution and simulation of avalanche formation due ...

    Indian Academy of Sciences (India)

    Abstract. 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 ...

  16. Electric field distribution and simulation of avalanche formation due ...

    Indian Academy of Sciences (India)

    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 ...

  17. Avalanche transmission and critical behaviour in load-bearing ...

    Indian Academy of Sciences (India)

    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 ...

  18. Townsend coefficients of gases in avalanche counters

    International Nuclear Information System (INIS)

    Brunner, G.


    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.)

  19. Similar Hamiltonian Between Avalanche-effect & Sociophysics (United States)

    Maksoed, Ssi, Wh-


    Of similar Hamiltonian concerned in ``sociophysics'', there were RandomFieldIsingModel/RFIM in external field retrieved in S. Sabhapandit:``Hysteresis & Avalanche in RandomFieldIsingModel'',2002:'' earthquake, it is an energy release and in case of ferromagnet, it is the size of the domain flips''. Following the extremes & compromises curve in Serge Galam: ``Sociophysics: a Review of Galam Model'', 2008 fig. 12, h 9 whereas it seems similar with ``heating curve''-Prof. Ir. Abdul Kadir: ``Mesin Arus Searah'', h 192 when the heat sources are continuous denote continuous opinion dynamics. Further, hysteresis as duties in ``Kajian Analisis Model Mikromagnetik dari Struktur Magnet Nanokomposit'', 2007 [ UI file no. S29286 ] also sought:'' calculate the probability that `one more site became unstable' causes an avalanche of the spin flips...'' usually found in Per Bak sand-pile fractal characters experiment exhibits. Great acknowledgment to HE. Mr. LieutGen-TNI[rtd]. H. TUK SETYOHADI, +62-21-7220385, Jl. Sriwijaya Raya 3, Kebayoran Baru, South-Jakarta.

  20. III-V strain layer superlattice based band engineered avalanche photodiodes (Presentation Recording) (United States)

    Ghosh, Sid


    Laser detection and ranging (LADAR)-based systems operating in the Near Infrared (NIR) and Short Wave Infrared (SWIR) have become popular optical sensors for remote sensing, medical, and environmental applications. Sophisticated laser-based radar and weapon systems used for long-range military and astronomical applications need to detect, recognize, and track a variety of targets under a wide spectrum of atmospheric conditions. Infrared APDs play an important role in LADAR systems by integrating the detection and gain stages in a single device. Robust silicon-APDs are limited to visible and very near infrared region ( 3um) infrared photon detection applications. Recently, various research groups (including Ghosh et. al.) have reported SWIR and MWIR HgCdTe APDs on CdZnTe and Si substrates. However, HgCdTe APDs suffer from low breakdown fields due to material defects, and excess noise increases significantly at high electric fields. During the past decade, InAs/GaSb Strain Layer Superlattice (SLS) material system has emerged as a potential material for the entire infrared spectrum because of relatively easier growth, comparable absorption coefficients, lower tunneling currents and longer Auger lifetimes resulting in enhanced detectivities (D*). Band engineering in type II SLS allows us to engineer avalanche properties of electrons and holes. This is a great advantage over bulk InGaAs and HgCdTe APDs where engineering avalanche properties is not possible. The talk will discuss the evolution of superlattice based avalanche photodiodes and some of the recent results on the work being done at Raytheon on SWIR avalanche photodiodes.

  1. Gain limits of a Thick GEM in high-purity Ne, Ar and Xe

    CERN Document Server

    Miyamoto, J; Peskov, V


    The dependence of the avalanche charge gain in Thick Gas Electron Multipliers (THGEM) on the purity of Ne, Ar and Xe filling gases was investigated. The gain, measured with alpha-particles in standard conditions (atmospheric pressure, room temperature), was found to considerably drop in gases purified by non-evaporable getters. On the other hand, small N2 admixtures to noble gases resulted in high reachable gains. The results are of general relevance in the operation of gas-avalanche detectors in noble gases, particularly that of two-phase cryogenic detectors for rare events.

  2. Avalanche situation in Turkey and back calculation of selected events (United States)

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


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

  3. Impulse response measurement in the HgCdTe avalanche photodiode (United States)

    Singh, Anand; Pal, Ravinder


    HgCdTe based mid-wave infrared focal plane arrays (MWIR FPAs) are being developed for high resolution imaging and range determination of distant camouflaged targets. Effect of bandgap grading on the response time in the n+/ν/p+ HgCdTe electron avalanche photodiode (e-APD) is evaluated using impulse response measurement. Gain normalized dark current density of 2 × 10-9 A/cm2 at low reverse bias for passive mode and 2 × 10-4 A/cm2 at -8 V for active mode is measured in the fabricated APD device, yielding high gain bandwidth product of 2.4 THZ at the maximum gain. Diffusion of carriers is minimized to achieve transit time limited impulse response by introducing composition grading in the HgCdTe epilayer. The noise equivalent photon performance less than one is achievable in the FPA that is suitable for active cum passive imaging applications.

  4. Anthropogenic effect on avalanche and debris flow activity

    Directory of Open Access Journals (Sweden)

    S. A. Sokratov


    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.

  5. Avalanche localization and its effects in proportional counters

    International Nuclear Information System (INIS)

    Fischer, J.; Okuno, H.; Walenta, A.H.


    Avalanche development around the anode wire in a gas proportional counter is investigated. In the region of proportional gas amplification, the avalanche is found to be well localized on one side of the anode wire, where the electrons arrive along the field lines from the point of primary ionization. Induced signals on electrodes surrounding the anode wire are used to measure the azimuthal position of the avalanche on the anode wire. Practical applications of the phenomena such as left-right assignment in drift chambers and measurement of the angular direction of the primary ionization electrons drifting towards the anode wire are discussed


    Energy Technology Data Exchange (ETDEWEB)

    Lauer, E J


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

  7. Relation of the runaway avalanche threshold to momentum space topology (United States)

    McDevitt, Christopher J.; Guo, Zehua; Tang, Xian-Zhu


    The underlying physics responsible for the formation of an avalanche instability due to the generation of secondary electrons is studied. A careful examination of the momentum space topology of the runaway electron population is carried out with an eye toward identifying how qualitative changes in the momentum space of the runaway electrons is correlated with the avalanche threshold. It is found that the avalanche threshold is tied to the merger of an O and X point in the momentum space of the primary runaway electron population. Such a change of the momentum space topology is shown to be accurately described by a simple analytic model, thus providing a powerful means of determining the avalanche threshold for a range of model assumptions.

  8. Discrimination capability of avalanche counters detecting different ionizing particles

    International Nuclear Information System (INIS)

    Prete, G.; Viesti, G.; Padua Univ.


    The discrimination capability of avalanche counters to detect different ionizing particles has been studied using a 252 Cf 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 32 S ions are also reported. (orig.)

  9. Random walk theory applied to electron avalanche formation (United States)

    Englert, G. W.


    Use of microscopic detail in random walk theory describing the initial formations of a large number of avalanches shows that concomitant electron transport coefficients quickly relax to equilibrium values. This enables the use of random walks having step sizes and probabilities based only on local electric field strengths and densities. A self-consistent avalanche solution which accounts for collective long range Coulomb interactions as well as short range elastic and inelastic collisions between electrons and background atoms is demonstrated for helium. Avalanche growth retardation followed by an abrupt growth augmentation as time proceeds is shown to be associated with the formation of regions of charge density extrema near the avalanche axis and within the axial distance covered by the electron swarm.

  10. Non-linear behaviour of large-area avalanche photodiodes

    CERN Document Server

    Fernandes, L M P; Monteiro, C M B; Santos, J M; Morgado, R E


    The characterisation of photodiodes used as photosensors requires a determination of the number of electron-hole pairs produced by scintillation light. One method involves comparing signals produced by X-ray absorptions occurring directly in the avalanche photodiode with the light signals. When the light is derived from light-emitting diodes in the 400-600 nm range, significant non-linear behaviour is reported. In the present work, we extend the study of the linear behaviour to large-area avalanche photodiodes, of Advanced Photonix, used as photosensors of the vacuum ultraviolet (VUV) scintillation light produced by argon (128 nm) and xenon (173 nm). We observed greater non-linearities in the avalanche photodiodes for the VUV scintillation light than reported previously for visible light, but considerably less than the non-linearities observed in other commercially available avalanche photodiodes.

  11. Noiseless Near-Infrared Photon Counting Avalanche Photodiode Detectors (United States)

    National Aeronautics and Space Administration — This proposal concerns the research and development of a mercury cadmium telluride (HgCdTe) Avalanche Photodiode (APD) array for use as a low-noise science detector...

  12. Transient events in bright debris discs: Collisional avalanches revisited (United States)

    Thebault, P.; Kral, Q.


    Context. A collisional avalanche is set off by the breakup of a large planetesimal, releasing vast amounts of small unbound grains that enter a debris disc located further away from the star, triggering there a collisional chain reaction that could potentially create detectable transient structures. Aims: We investigate this mechanism, using for the first time a fully self-consistent code coupling dynamical and collisional evolutions. We also quantify for the first time the photometric evolution of the system and investigate whether or not avalanches could explain the short-term luminosity variations recently observed in some extremely bright debris discs. Methods: We use the state-of-the-art LIDT-DD code. We consider an avalanche-favoring A6V star, and two set-ups: a "cold disc" case, with a dust release at 10 au and an outer disc extending from 50 to 120 au, and a "warm disc" case with the release at 1 au and a 5-12 au outer disc. We explore, in addition, two key parameters: the density (parameterized by its optical depth τ) of the main outer disc and the amount of dust released by the initial breakup. Results: We find that avalanches could leave detectable structures on resolved images, for both "cold" and "warm" disc cases, in discs with τ of a few 10-3, provided that large dust masses (≳1020-5 × 1022 g) are initially released. The integrated photometric excess due to an avalanche is relatively limited, less than 10% for these released dust masses, peaking in the λ 10-20 μm domain and becoming insignificant beyond 40-50 μm. Contrary to earlier studies, we do not obtain stronger avalanches when increasing τ to higher values. Likewise, we do not observe a significant luminosity deficit, as compared to the pre-avalanche level, after the passage of the avalanche. These two results concur to make avalanches an unlikely explanation for the sharp luminosity drops observed in some extremely bright debris discs. The ideal configuration for observing an

  13. Influence of snow-cover properties on avalanche dynamics (United States)

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


    Snow avalanches with the potential of reaching traffic routes and settlements are a permanent winter threat for many mountain communities. Snow safety officers have to take the decision whether to close a road, a railway line or a ski slope. Those decisions are often very difficult as they demand the ability to interpret weather forecasts, to establish their implication for the stability and the structure of the snow cover and to evaluate the influence of the snow cover on avalanche run-out distances. In the operational programme 'Italy-Switzerland, project STRADA' we focus on the effects of snow cover on avalanche dynamics, and thus run-out distance, with the aim to provide a better understanding of this influence and to ultimately develop tools to support snow safety officers in their decision process. We selected five avalanches, measured at the Vallée de la Sionne field site, with similar initial mass and topography but different flow dynamics and run-out distances. Significant differences amongst the individual avalanches could be observed for front and internal velocities, impact pressures, flow regimes, deposition volumes and run-out distances. For each of these avalanches, the prevailing snow conditions at release were reconstructed using field data from local snowpits or were modeled with SNOWPACK. Combining flow dynamical data with snow cover properties shows that erodible snow depth, snow density and snow temperature in the snow pack along the avalanche track are among the decisive variables that appear to explain the observed differences. It is further discussed, how these influencing factors can be quantified and used for improved predictions of site and time specific avalanche hazard.

  14. Physical vulnerability of reinforced concrete buildings impacted by snow avalanches

    Directory of Open Access Journals (Sweden)

    D. Bertrand


    Full Text Available This paper deals with the assessment of physical vulnerability of civil engineering structures to snow avalanche loadings. In this case, the vulnerability of the element at risk is defined by its damage level expressed on a scale from 0 (no damage to 1 (total destruction. The vulnerability of a building depends on its structure and flow features (geometry, mechanical properties, type of avalanche, topography, etc.. This makes it difficult to obtain vulnerability relations. Most existing vulnerability relations have been built from field observations. This approach suffers from the scarcity of well documented events. Moreover, the back analysis is based on both rough descriptions of the avalanche and the structure. To overcome this problem, numerical simulations of reinforced concrete structures loaded by snow avalanches are carried out. Numerical simulations allow to study, in controlled conditions, the structure behavior under snow avalanche loading. The structure is modeled in 3-D by the finite element method (FEM. The elasto-plasticity framework is used to represent the mechanical behavior of both materials (concrete and steel bars and the transient feature of the avalanche loading is taken into account in the simulation. Considering a reference structure, several simulation campaigns are conducted in order to assess its snow avalanches vulnerability. Thus, a damage index is defined and is based on global and local parameters of the structure. The influence of the geometrical features of the structure, the compressive strength of the concrete, the density of steel inside the composite material and the maximum impact pressure on the damage index are studied and analyzed. These simulations allow establishing the vulnerability as a function of the impact pressure and the structure features. The derived vulnerability functions could be used for risk analysis in a snow avalanche context.

  15. La Carte de Localisation Probable des Avalanches (CPLA

    Directory of Open Access Journals (Sweden)

    Gilles BORREL


    Full Text Available La Carte de Localisation Probable des Avalanches (CPLA indique l’enveloppe des limites extrêmes connues atteintes par les avalanches, ainsi que les travaux de protection associés. Il s’agit d’un document informatif et non d’une carte de risque. Depuis 1990, les données thématiques sont numérisées.

  16. Avalanches driven by pressure gradients in a magnetized plasma (United States)

    Van Compernolle, B.; Morales, G. J.


    The results are presented for a basic heat transport experiment involving an off-axis heat source in which avalanche events occur. The configuration consists of a long, hollow, cylindrical region of elevated electron temperature embedded in a colder plasma, and far from the device walls [Van Compernolle et al. Phys. Rev. E 91, 031102(R) (2015)]. The avalanche events are identified as sudden rearrangements of the pressure profile following the growth of fluctuations from ambient noise. The intermittent collapses of the plasma pressure profile are associated with unstable drift-Alfvén waves and exhibit both radial and poloidal dynamics. After each collapse, the plasma enters a quiescent phase in which the pressure profile slowly recovers and steepens until a threshold is exceeded, and the process repeats. The use of reference probes as time markers allows for the visualization of the 2D spatio-temporal evolution of the avalanche events. Avalanches are observed only for a limited combination of heating powers and magnetic fields. At higher heating powers, the system transits from the avalanche regime into a regime dominated by sustained drift-Alfvén wave activity. This manuscript focuses on new results that illustrate the individual contributions to the avalanche process from density and temperature gradients in the presence of zero-order, sheared flows.

  17. The parallel plate avalanche counter: a simple, rugged, imaging X-ray counter

    International Nuclear Information System (INIS)

    Joensen, K.D.; Budtz-Joergensen, C.; Bahnsen, A.; Madsen, M.M.; Olesen, C.; Schnopper, H.W.


    A two-dimensional parallel gap proportional counter has been developed at the Danish Space Research Institute. Imaging over the 120 mm diameter active area is obtained using the positive ion component of the avalanche signals as recorded by a system of wedge- and strip-electrodes. An electronically simple, but very effective background rejection is obtained by using the fast electron component of the avalanche signal. Gas gains up to 8x10 5 have been achieved. An energy-resolution of 16% and a sub-millimeter spatial resolution have been measured at 5.9 keV for an operating gas gain of 10 5 . In principle, the position coordinates are linear functions of electronic readouts. The present model, however, exhibits non-linearities, caused by imperfections in the wedge and strip-electrode pattern. These non-linearities are corrected by using a bilinear correction algorithm. We conclude that the rugged construction, the simple electronics, the effectiveness of the background rejection and the actual imaging performance makes this a very attractive laboratory detector for low and intermediate count rate imaging applications. ((orig.))

  18. Skier triggering of backcountry avalanches with skilled route selection (United States)

    Sinickas, Alexandra; Haegeli, Pascal; Jamieson, Bruce


    Jamieson (2009) provided numerical estimates for the baseline probabilities of triggering an avalanche by a backcountry skier making fresh tracks without skilled route selection as a function of the North American avalanche danger scale (i.e., hazard levels Low, Moderate, Considerable, High and Extreme). Using the results of an expert survey, he showed that triggering probabilities while skiing directly up, down or across a trigger zone without skilled route selection increase roughly by a factor of 10 with each step of the North American avalanche danger scale (i.e. hazard level). The objective of the present study is to examine the effect of skilled route selection on the relationship between triggering probability and hazard level. To assess the effect of skilled route selection on triggering probability by hazard level, we analysed avalanche hazard assessments as well as reports of skiing activity and triggering of avalanches from 11 Canadian helicopter and snowcat operations during two winters (2012-13 and 2013-14). These reports were submitted to the daily information exchange among Canadian avalanche safety operations, and reflect professional decision-making and route selection practices of guides leading groups of skiers. We selected all skier-controlled or accidentally triggered avalanches with a destructive size greater than size 1 according to the Canadian avalanche size classification, triggered by any member of a guided group (guide or guest). These operations forecast the avalanche hazard daily for each of three elevation bands: alpine, treeline and below treeline. In contrast to the 2009 study, an exposure was defined as a group skiing within any one of the three elevation bands, and consequently within a hazard rating, for the day (~4,300 ratings over two winters). For example, a group that skied below treeline (rated Moderate) and treeline (rated Considerable) in one day, would receive one count for exposure to Moderate hazard, and one count for


    Energy Technology Data Exchange (ETDEWEB)



    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.

  20. Avalanches Near the Onset of Jamming (United States)

    Schwarz, J. M.; Chakrabarti, Bismayan


    As the jamming transition is approached from the liquid-like side, experiments and simulations demonstrate that a random assembly of particles exhibits avalanche-like behaviour in response to a probe particle being dragged through it. To better understand this response, we construct a lattice model with active and inactive particles occupying some fraction of the lattice, with each site being occupied by at most one particle. Only the active particles can hop to empty neighboring sites and can activate k neighboring inactive particles at some rate λk. Also, active particles can become inactive at some rate γ. When lambdak>=2=0 , this model is closely related to the conserved lattice gas model which is thought to belong to the universality class of absorbing phase transitions with a conserved field, i.e. conserved stochastic sandpile models. To mimic the approach towards jamming, an increasingly more crowded environment, we study this model for λk>=1>0 and search for a new universality class as λk=1 approaches zero.

  1. Guiding thermomagnetic avalanches with soft magnetic stripes

    Energy Technology Data Exchange (ETDEWEB)

    Vlasko-Vlasov, V. K.; Colauto, F.; Benseman, T.; Rosenmann, D.; Kwok, W. -K.


    We demonstrate the potential for manipulating the ultrafast dynamics of thermomagnetic flux avalanches (TMA) in superconducting films with soft magnetic stripes deposited on the film. By tuning the in-plane magnetization of the stripes, we induce lines of strong magnetic potentials for Abrikosov vortices, resulting in guided slow motion of vortices along the stripe edges and preferential bursts of TMA along the stripes. Furthermore, we show that transversely polarized stripes can reduce the TMA size by diverting magnetic flux away from the major trunk of the TMA into interstripe gaps. Our data indicate that TMAs are launched from locations with enhanced vortex entry barrier, where flux accumulation followed by accelerated vortex discharge significantly reduces the threshold of the applied field ramping speed required for the creation of TMAs. Finally, vortex-antivortex annihilation at the moving front of an expanding TMA can account for the enhanced TMA activity in the receding branches of the sample's magnetization cycle and the preferred propagation of TMAs into maximum trapped flux regions.

  2. Measurement-based characterization of multipixel avalanche photodiodes for scintillating detectors

    CERN Document Server

    Dziewiecki, M


    Multipixel avalanche photodiodes (MAPD) are recently gaining popularity in high energy physics experiments as an attractive replacement for photomultiplier tubes, which have been extensively used for many years as a part of various scintillating detectors. Their low price, small dimensions and another features facilitating their use (like mechanical shock resistance, magnetic field immunity or moderate supply voltage) make the MAPDs a good choice for commercial use as well, what is reflected in growing number of producers as well as MAPD models available on the market. This dissertation presents Author’s experience with MAPD measurements and modelling, gained during his work on the T2K (Tokai-to-Kamioka) long-baseline neutrino experiment, carried out by an international collaboration in Japan. First, operation principle of the MAPD, definitions of various parameters and measurement methods are discussed. Then, a device for large-scale MAPD measurements and related data processing methods are described. Fina...

  3. Development and performance of a deep-diffused, planar construction avalanche photodiode

    CERN Document Server

    Gramsch, E; Ferrer, J


    A deep-diffused, large-area avalanche photodiode (APD) without bevel has been designed and built for use in low-light level applications. 2 and 3 mm diameter active area APDs have been built using standard planar technology for silicon devices, and a gain of 6 is obtained at 1300 V. The dark current is dependent on external voltage and it is only 50 to 80 nA below breakdown, which is much lower than standard bevel edge devices. The energy resolution of a sup 1 sup 3 sup 7 Cs source with an APD coupled to a CsI (Tl) scintillator was 14.5%. We have also performed simulations of the gain and breakdown voltage that correlate well with the results. (Author)

  4. Update on Linear Mode Photon Counting with the HgCdTe Linear Mode Avalanche Photodiode (United States)

    Beck, Jeffrey D.; Kinch, Mike; Sun, Xiaoli


    The behavior of the gain-voltage characteristic of the mid-wavelength infrared cutoff HgCdTe linear mode avalanche photodiode (e-APD) is discussed both experimentally and theoretically as a function of the width of the multiplication region. Data are shown that demonstrate a strong dependence of the gain at a given bias voltage on the width of the n- gain region. Geometrical and fundamental theoretical models are examined to explain this behavior. The geometrical model takes into account the gain-dependent optical fill factor of the cylindrical APD. The theoretical model is based on the ballistic ionization model being developed for the HgCdTe APD. It is concluded that the fundamental theoretical explanation is the dominant effect. A model is developed that combines both the geometrical and fundamental effects. The model also takes into account the effect of the varying multiplication width in the low bias region of the gain-voltage curve. It is concluded that the lower than expected gain seen in the first 2 × 8 HgCdTe linear mode photon counting APD arrays, and higher excess noise factor, was very likely due to the larger than typical multiplication region length in the photon counting APD pixel design. The implications of these effects on device photon counting performance are discussed.

  5. Segregation induced fingering instabilities in granular avalanches (United States)

    Woodhouse, Mark; Thornton, Anthony; Johnson, Chris; Kokelaar, Pete; Gray, Nico


    It is important to be able to predict the distance to which a hazardous natural granular flows (e.g. snow slab avalanches, debris-flows and pyroclastic flows) might travel, as this information is vital for accurate assessment of the risks posed by such events. In the high solids fraction regions of these flows the large particles commonly segregate to the surface, where they are transported to the margins to form bouldery flow fronts. In many natural flows these bouldery margins experience a much greater frictional force, leading to frontal instabilities. These instabilities create levees that channelize the flow vastly increasing the run-out distance. A similar effect can be observed in dry granular experiments, which use a combination of small round and large rough particles. When this mixture is poured down an inclined plane, particle size segregation causes the large particles to accumulate near the margins. Being rougher, the large particles experience a greater friction force and this configuration (rougher material in front of smoother) can be unstable. The instability causes the uniform flow front to break up into a series of fingers. A recent model for particle size-segregation has been coupled to existing avalanche models through a particle concentration dependent friction law. In this talk numerical solutions of this coupled system are presented and compared to both large scale experiments carried out at the USGS flume and more controlled small scale laboratory experiments. The coupled depth-averaged model captures the accumulation of large particles at the flow front. We show this large particle accumulation at the head of the flow can lead to the break-up of the initially uniform front into a series of fingers. However, we are unable to obtain a fully grid-resolved numerical solution; the width of the fingers decreases as the grid is refined. By considering the linear stability of a steady, fully-developed, bidisperse granular layer it is shown that

  6. Intermittent flow under constant forcing: Acoustic emission from creep avalanches (United States)

    Salje, Ekhard K. H.; Liu, Hanlong; Jin, Linsen; Jiang, Deyi; Xiao, Yang; Jiang, Xiang


    While avalanches in field driven ferroic systems (e.g., Barkhausen noise), domain switching of martensitic nanostructures, and the collapse of porous materials are well documented, creep avalanches (avalanches under constant forcing) were never observed. Collapse avalanches generate particularly large acoustic emission (AE) signals and were hence chosen to investigate crackling noise under creep conditions. Piezoelectric SiO2 has a strong piezoelectric response even at the nanoscale so that we chose weakly bound SiO2 spheres in natural sandstone as a representative for the study of avalanches under time-independent, constant force. We found highly non-stationary crackling noise with four activity periods, each with power law distributed AE emission. Only the period before the final collapse shows the mean field behavior (ɛ near 1.39), in agreement with previous dynamic measurements at a constant stress rate. All earlier event periods show collapse with larger exponents (ɛ = 1.65). The waiting time exponents are classic with τ near 2.2 and 1.32. Creep data generate power law mixing with "effective" exponents for the full dataset with combinations of mean field and non-mean field regimes. We find close agreement with the predicted time-dependent fiber bound simulations, including events and waiting time distributions. Båth's law holds under creep conditions.

  7. Feasibility tests of a high resolution sampling radial drift chamber

    International Nuclear Information System (INIS)

    Huth, J.


    The design concept and results of feasibility tests for a vertex detector intended for use in the TPC-PEP4/9 experiment are presented. The detector is based on a slow radial drift in dimethyl ether. High resolution localization of the avalanches at the sense wire is accomplished with nearby pickup wires and the utilization of waveform sampling electronics. The avalanche angular coordinate measurements, combined with knowledge of the electric field distribution and drift velocity permit reconstruction of the trajectory using essentially all track information. Measurements with a test chamber constructed to study characteristics of avalanche localization indicate that the recoverable track information in one centimeter of dimethyl ether at 1.5 atm is equivalent to 30 measurements of 40 μm accuracy. (orig.)

  8. Fast transmission avalanche counter for charged particle detection

    International Nuclear Information System (INIS)

    Nojbert, V.; Dubbers, F.


    A new type of detectors, an avalanche transmission-type counter has been developed to record charged particles. It consists of two very thin tightened films between which high voltage is applied. Structurally the avalanche counter is made in the form of round small polyamide frames on which a FORMAVAR film of 15-30 μgxcm -2 thick is tightened. The latter is then covered with gold (approximately 40 μgxcm -2 ). As a working gas the avalanche counter uses vapours of acetone or n-heptane at a pressure ranging from 2 to 10 mm Hg. The basic circuits of detector-preamplifier connection is given, and the dependence of the detector signal amplitude on the counter anode-cathode voltage is presented. When recording α-particles the proper time resolution of the developed counter constitutes 475 ps

  9. The diversity of flux avalanche patterns in superconducting films (United States)

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


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

  10. Precise method for determining avalanche breakdown voltage of silicon photomultipliers (United States)

    Chirikov-Zorin, I.


    A physically motivated method is proposed for determining the avalanche breakdown voltage of silicon photomultipliers (SiPM). The method is based on measuring the dependence of the relative photon detection efficiency (PDErel) on the bias voltage when one type of carriers (electron or hole) is injected into the avalanche multiplication zone of the p-n junction. The injection of electrons or holes from the base region of the SiPM semiconductor structure is performed using short-wave or long-wave light. At a low overvoltage (1-2 V) the detection efficiency is linearly dependent on the bias voltage; therefore, extrapolation to zero PDErel value determines the SiPM avalanche breakdown voltage with an accuracy within a few millivolts.

  11. Experimental method to predict avalanches based on neural networks

    Directory of Open Access Journals (Sweden)

    V. V. Zhdanov


    Full Text Available The article presents results of experimental use of currently available statistical methods to classify the avalanche‑dangerous precipitations and snowfalls in the Kishi Almaty river basin. The avalanche service of Kazakhstan uses graphical methods for prediction of avalanches developed by I.V. Kondrashov and E.I. Kolesnikov. The main objective of this work was to develop a modern model that could be used directly at the avalanche stations. Classification of winter precipitations into dangerous snowfalls and non‑dangerous ones was performed by two following ways: the linear discriminant function (canonical analysis and artificial neural networks. Observational data on weather and avalanches in the gorge Kishi Almaty in the gorge Kishi Almaty were used as a training sample. Coefficients for the canonical variables were calculated by the software «Statistica» (Russian version 6.0, and then the necessary formula had been constructed. The accuracy of the above classification was 96%. Simulator by the authors L.N. Yasnitsky and F.М. Cherepanov was used to learn the neural networks. The trained neural network demonstrated 98% accuracy of the classification. Prepared statistical models are recommended to be tested at the snow‑avalanche stations. Results of the tests will be used for estimation of the model quality and its readiness for the operational work. In future, we plan to apply these models for classification of the avalanche danger by the five‑point international scale.

  12. Avalanche boron fusion by laser picosecond block ignition with magnetic trapping for clean and economic reactor

    International Nuclear Information System (INIS)

    Hora, H.; Nissim, N.


    Measured highly elevated gains of proton–boron (HB11) fusion (Picciottoet al., Phys. Rev. X4, 031030 (2014)) confirmed the exceptional avalanche reaction process (Lalousiset al., Laser Part. Beams 32, 409 (2014); Horaet al., Laser Part. Beams33, 607 (2015)) for the combination of the non-thermal block ignition using ultrahigh intensity laser pulses of picoseconds duration. The ultrahigh acceleration above 10 20  cm s −2 for plasma blocks was theoretically and numerically predicted since 1978 (Hora,Physics of Laser Driven Plasmas(Wiley, 1981), pp. 178 and 179) and measured (Sauerbrey, Phys. Plasmas3, 4712 (1996)) in exact agreement (Horaet al., Phys. Plasmas14, 072701 (2007)) when the dominating force was overcoming thermal processes. This is based on Maxwell’s stress tensor by the dielectric properties of plasma leading to the nonlinear (ponderomotive) force f NL resulting in ultra-fast expanding plasma blocks by a dielectric explosion. Combining this with measured ultrahigh magnetic fields and the avalanche process opens an option for an environmentally absolute clean and economic boron fusion power reactor. Finally, this is supported also by other experiments with very high HB11 reactions under different conditions (Labauneet al., Nature Commun.4, 2506 (2013)).

  13. Design and analysis of CMOS single photon counting avalanche photodiodes integrated with active quenching circuits

    International Nuclear Information System (INIS)

    Kim, Kwang Hyun; Kim, Young Soo


    The CMOS SPADs (Single Photon Avalanche Diodes) integrated with active quenching circuits were fabricated on same chip using AMIS 0.7 μm high voltage CMOS process without any process modifications. The SPADs have N+/P-substrate structure and their diameter of photo sensing area are 25 μm, 50 μm, 100 μm, 400 μm, and 800 μm. The avalanche multiplication is occurred at 10.7 V, and the photocurrent gain at 11 V reverse bias voltage is about 1000. In zero bias condition, the maximum quantum efficiency appears at 650 nm wavelength, and it corresponds to around 30%. The active quenching circuit is composed to a comparator, three monostable, and two MOS switch. As a circuit simulation results, the comparator and the monostable generate ∼22 nsec and ∼1 nsec delayed output pulse, respectively. The dead time of the active quenching circuits integrated with SPADs is about 100 nsec as a measured result. (author)

  14. Investigations of single-electron avalanches in a proportional drift tube

    International Nuclear Information System (INIS)

    Anderson, W.S.; Armitage, J.C.; Chevreau, P.; Heinrich, J.G.; Lu, C.; McDonald, I.; McDonald, K.T.; Miller, B.; Secrest, D.; Weckel, J.


    Detailed information on single-electron drift and avalanche behavior has a basic interest in an investigation of gas-chamber performance. Its timing, avalanche distribution, attachment by the working gas mixtures, etc., provide various criteria for choosing the best suitable gas mixture under a specific experimental circumstance. Investigations of single-electron avalanches in a proportional drift tube have been carried out with a pulsed N 2 laser. The study consists of two aspects: timing properties, and fluctuations in the gas avalanche

  15. Neutron irradiation studies of avalanche photodiodes using californium-252 (United States)

    Reucroft, S.; Rusack, R.; Ruuska, D.; Swain, J.


    Californium-252 is a convenient and copious source of neutrons of energies around 1 MeV, and provides many advantages over reactors for neutron irradiation studies of detector components. We describe here an experimental setup at Oak Ridge National Laboratory which has been constructed to study the performance of avalanche photodiodes in neutron fluences up to 10 13 neutrons/cm 2, similar to what is expected in parts of the CMS detector at the LHC. An irradiation study of some avalanche photodiodes is discussed, followed by a brief summary of results obtained.

  16. Meteorological variables associated with deep slab avalanches on persistent weak layers (United States)

    Marienthal, Alex; Hendrikx, Jordy; Birkeland, Karl; Irvine, Kathryn M.


    Deep slab avalanches are a particularly challenging avalanche forecasting problem. These avalanches are typically difficult to trigger, yet when they are triggered they tend to propagate far and result in large and destructive avalanches. For this work we define deep slab avalanches as those that fail on persistent weak layers deeper than 0.9m (3 feet), and that occur after February 1st. We utilized a 44-year record of avalanche control and meteorological data from Bridger Bowl Ski Area to test the usefulness of meteorological variables for predicting deep slab avalanches. As in previous studies, we used data from the days preceding deep slab cycles, but we also considered meteorological metrics over the early months of the season. We utilized classification trees for our analyses. Our results showed warmer temperatures in the prior twenty-four hours and more loading over the seven days before days with deep slab avalanches on persistent weak layers. In line with previous research, extended periods of above freezing temperatures led to days with deep wet slab avalanches on persistent weak layers. Seasons with either dry or wet avalanches on deep persistent weak layers typically had drier early months, and often had some significant snow depth prior to those dry months. This paper provides insights for ski patrollers, guides, and avalanche forecasters who struggle to forecast deep slab avalanches on persistent weak layers late in the season.


    Directory of Open Access Journals (Sweden)



    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.

  18. Characterizing the nature and variability of avalanche hazard in western Canada (United States)

    Shandro, Bret; Haegeli, Pascal


    The snow and avalanche climate types maritime, continental and transitional are well established and have been used extensively to characterize the general nature of avalanche hazard at a location, study inter-seasonal and large-scale spatial variabilities and provide context for the design of avalanche safety operations. While researchers and practitioners have an experience-based understanding of the avalanche hazard associated with the three climate types, no studies have described the hazard character of an avalanche climate in detail. Since the 2009/2010 winter, the consistent use of Statham et al. (2017) conceptual model of avalanche hazard in public avalanche bulletins in Canada has created a new quantitative record of avalanche hazard that offers novel opportunities for addressing this knowledge gap. We identified typical daily avalanche hazard situations using self-organizing maps (SOMs) and then calculated seasonal prevalence values of these situations. This approach produces a concise characterization that is conducive to statistical analyses, but still provides a comprehensive picture that is informative for avalanche risk management due to its link to avalanche problem types. Hazard situation prevalence values for individual seasons, elevations bands and forecast regions provide unprecedented insight into the inter-seasonal and spatial variability of avalanche hazard in western Canada.

  19. Charge Gain, Voltage Gain, and Node Capacitance of the SAPHIRA Detector Pixel by Pixel (United States)

    Pastrana, Izabella M.; Hall, Donald N. B.; Baker, Ian M.; Jacobson, Shane M.; Goebel, Sean B.


    The University of Hawai`i Institute for Astronomy has partnered with Leonardo (formerly Selex) in the development of HgCdTe linear mode avalanche photodiode (L-APD) SAPHIRA detectors. The SAPHIRA (Selex Avalanche Photodiode High-speed Infra-Red Array) is ideally suited for photon-starved astronomical observations, particularly near infrared (NIR) adaptive optics (AO) wave-front sensing. I have measured the stability, and linearity with current, of a 1.7-um (10% spectral bandpass) infrared light emitting diode (IR LED) used to illuminate the SAPHIRA and have then utilized this source to determine the charge gain (in e-/ADU), voltage gain (in uV/ADU), and node capacitance (in fF) for each pixel of the 320x256@24um SAPHIRA. These have previously only been averages over some sub-array. Determined from the ratio of the temporal averaged signal level to variance under constant 1.7-um LED illumination, I present the charge gain pixel-by-pixel in a 64x64 sub-array at the center of the active area of the SAPHIRA (analyzed separately as four 32x32 sub-arrays) to be about 1.6 e-/ADU (σ=0.5 e-/ADU). Additionally, the standard technique of varying the pixel reset voltage (PRV) in 10 mV increments and recording output frames for the same 64x64 subarray found the voltage gain per pixel to be about 11.7 uV/ADU (σ=0.2 uV/ADU). Finally, node capacitance was found to be approximately 23 fF (σ=6 fF) utilizing the aforementioned charge and voltage gain measurements. I further discuss the linearity measurements of the 1.7-um LED used in the charge gain characterization procedure.

  20. Avalanche transmission and critical behaviour in load-bearing ...

    Indian Academy of Sciences (India)

    Synchronization, Coupled Systems and Networks Volume 77 Issue 5 November 2011 pp 873-879 ... ... 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 ...

  1. Positron camera with high-density avalanche chambers

    International Nuclear Information System (INIS)

    Manfrass, D.; Enghardt, W.; Fromm, W.D.; Wohlfarth, D.; Hennig, K.


    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)

  2. Electron avalanche structure determined by random walk theory (United States)

    Englert, G. W.


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

  3. A Hidden Markov Model for avalanche forecasting on Chowkibal ...

    Indian Academy of Sciences (India)

    ... different states of the model and Avalanche Activity Index (AAI) of a day, derived from the model input variables, as an observation. Validation of the model with independent data of two winters (2008–2009, 2009–2010) gives 80% accuracy for both day-1 and day-2. Comparison of various forecasting quality measures and ...

  4. Dimensional reduction, avalanches and disorder in artificial kagome spin ice (United States)

    Hugli, Remo V.; Duff, Gerard; Braun, Hans-Benjamin


    In collaboration with an experimental team at the Swiss Light Source we have recently demonstrated that emergent monopoles and associated Dirac strings can directly be observed in real space via x-ray circular dichroism in a kagome lattice geometry. Here we build on the fact that the experimental results are in excellent agreement with MC simulations of a lattice of point dipoles with disorder realized in the form of random switching fields. We demonstrate that within a large range of physical parameters such as interdipolar coupling and randomness, magnetization reversal proceeds via a novel 1D avalanche behaviour whose hallmark is an exponential avalanche size distribution. After presenting simple arguments for the origin of such dimensional reduction we demonstrate that such 1D avalanche behavior also occurs in a model where the dipoles are stretched into magnetic charge dumbbells which provides a more realistic model for nanolithographic islands. Finally we demonstrate how a judicious design of the island anisotropy can be used to achieve controlled switching and avalanche propagation which paves the way for spintronic applications

  5. Snow avalanche hazard of the Krkonose National Park, Czech Republic

    Czech Academy of Sciences Publication Activity Database

    Blahůt, Jan; Klimeš, Jan; Balek, Jan; Hájek, P.; Červená, L.; Lysák, J.


    Roč. 13, č. 2 (2017), s. 86-90 ISSN 1744-5647 R&D Projects: GA MV VG20132015115 Institutional support: RVO:67985891 Keywords : snow avalanches * hazard * inventory * hazard mitigation * Krkonoše Subject RIV: DE - Earth Magnetism, Geodesy, Geography OBOR OECD: Physical geography Impact factor: 2.174, year: 2016

  6. heat flow in a finite isolated pulsed avalanche semiconductor diode ...

    African Journals Online (AJOL)

    ES Obe


    Mar 1, 1981 ... high-power high-efficiency avalanche semiconductor devices. The temperature rise as a function of the heat sink size is computed, and useful practical design curves for a specified operation time presented. ... 2.1 THE PHYSICAL MODEL. Figure 1 shows a basic structure of a diode,-radius R, mounted on.

  7. Imaging of ionizing radiations from electronic avalanches, limited, in gases

    International Nuclear Information System (INIS)

    Charpak, G.


    This work deals with the imaging of ionizing radiations from electronic avalanches in gases. Some applications realized with the help of physical instruments like : fog chambers, Geiger-Mueller counters, proportional counters, scintillation counters, semiconductor detectors, nuclear emulsions, bubble chambers, drift chambers, wire spark chambers and calorimeters are described and their performances compared. (O.L.). 5 refs., 10 figs

  8. Large Format Geiger Mode Avalanche Photodiode Arrays and Readout Circuits (United States)


    efficiency. The pixels in early CMOS designs effectively contained a “stop watch ” – circuitry operating at fast clock frequencies required to...Ghioni, A. Lacaita, C. Samori, and F. Zappa, "Avalanche photodiodes and quenching circuits for single-photon detection," Appl . Opt. 35, 1956-1976

  9. Application of avalanche photodiodes as a readout for scintillator tile-fiber systems

    CERN Document Server

    Cheshkov, C V; Gouchtchine, E; Litov, L; Mandjoukov, I; Spassov, V


    The application of reach-through avalanche photodiodes (R'APD) as a photodetector for scintillator tiles has been investigated. The light collected by WLS fibers (0.84mm and 1mm diameter) embedded in the scintillator has been transmited to the 0.5mm2 active surface of APD by clear optical fibers and optical connectors. A low noise charge sensitive preamplifier (approximately 400 electrons equivalent noise charge) has been used to gain the photodiode signal. Various configurations of tile-fibre systems, suitable for CMS and LHCb experiments at LHC have been studied using cosmic muons and muon beam at SPS at CERN. In order to optimize the performance of APD, measurments in the temperature range from -10C to +25C have been done. The MIP detection efficiency and electron/MIP separation have been estimated in order to determine applicability of the readout for LHCb preshower.

  10. Linear Mode HgCdTe Avalanche Photodiodes for Photon Counting Applications (United States)

    Sullivan, William, III; Beck, Jeffrey; Scritchfield, Richard; Skokan, Mark; Mitra, Pradip; Sun, Xiaoli; Abshire, James; Carpenter, Darren; Lane, Barry


    An overview of recent improvements in the understanding and maturity of linear mode photon counting with HgCdTe electron-initiated avalanche photodiodes is presented. The first HgCdTe LMPC 2x8 format array fabricated in 2011 with 64 micron pitch was a remarkable success in terms of demonstrating a high single photon signal to noise ratio of 13.7 with an excess noise factor of 1.3-1.4, a 7 ns minimum time between events, and a broad spectral response extending from 0.4 micron to 4.2 micron. The main limitations were a greater than 10x higher false event rate than expected of greater than 1 MHz, a 5-7x lower than expected APD gain, and a photon detection efficiency of only 50% when greater than 60% was expected. This paper discusses the reasons behind these limitations and the implementation of their mitigations with new results.

  11. Laboratory study of avalanches in a magnetized plasma (United States)

    van Compernolle, Bart


    Results of a basic heat transport experiment [] involving an off-axis heat source are presented. Experiments are performed in the Large Plasma Device (LAPD) at UCLA. A ring-shaped electron beam source injects low energy electrons (below ionization energy) along a strong magnetic field into a preexisting, large and cold plasma. The injected electrons are thermalized by Coulomb collisions within a short distance and provide an off-axis heat source that results in a long, hollow, cylindrical region of elevated electron temperature embedded in a colder plasma, and far from the machine walls. It is demonstrated that this heating configuration provides an ideal environment to study avalanche phenomena under controlled conditions. The avalanches are identified as sudden rearrangements of the pressure profile following the growth of fluctuations from ambient noise. The intermittent collapses of the plasma pressure profile are associated with unstable drift-Alfvén waves and exhibit both radial and azimuthal dynamics. After each collapse the plasma enters a quiescent phase in which the pressure profile slowly recovers and steepens until a threshold is exceeded, and the process repeats. The use of reference probes as time markers allows for the visualization of the 2D spatio-temporal evolution of the avalanche events. Avalanches are only observed for a limited combination of heating powers and magnetic fields. At higher heating powers the system transitions from the avalanche regime into a regime dominated by sustained drift-Alfvén wave activity. The pressure profile then transitions to a near steady-state in which anomalous transport balances the external pressure source. Performed at the Basic Plasma Science Facility at UCLA, supported jointly by DOE and NSF.

  12. Dealing with the white death: avalanche risk management for traffic routes. (United States)

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


    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.

  13. Meteorological variables to aid forecasting deep slab avalanches on persistent weak layers (United States)

    Marienthal, Alex; Hendrikx, Jordy; Birkeland, Karl; Irvine, Kathryn M.


    Deep slab avalanches are particularly challenging to forecast. These avalanches are difficult to trigger, yet when they release they tend to propagate far and can result in large and destructive avalanches. We utilized a 44-year record of avalanche control and meteorological data from Bridger Bowl ski area in southwest Montana to test the usefulness of meteorological variables for predicting seasons and days with deep slab avalanches. We defined deep slab avalanches as those that failed on persistent weak layers deeper than 0.9 m, and that occurred after February 1st. Previous studies often used meteorological variables from days prior to avalanches, but we also considered meteorological variables over the early months of the season. We used classification trees and random forests for our analyses. Our results showed seasons with either dry or wet deep slabs on persistent weak layers typically had less precipitation from November through January than seasons without deep slabs on persistent weak layers. Days with deep slab avalanches on persistent weak layers often had warmer minimum 24-hour air temperatures, and more precipitation over the prior seven days, than days without deep slabs on persistent weak layers. Days with deep wet slab avalanches on persistent weak layers were typically preceded by three days of above freezing air temperatures. Seasonal and daily meteorological variables were found useful to aid forecasting dry and wet deep slab avalanches on persistent weak layers, and should be used in combination with continuous observation of the snowpack and avalanche activity.

  14. A multi path, weather independent avalanche monitoring tool using distributed acoustic fiber optic sensing (United States)

    Prokop, Alexander; Wirbel, Anna


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

  15. Application of statistical and dynamics models for snow avalanche hazard assessment in mountain regions of Russia (United States)

    Turchaninova, A.


    The estimation of extreme avalanche runout distances, flow velocities, impact pressures and volumes is an essential part of snow engineering in mountain regions of Russia. It implies the avalanche hazard assessment and mapping. Russian guidelines accept the application of different avalanche models as well as approaches for the estimation of model input parameters. Consequently different teams of engineers in Russia apply various dynamics and statistical models for engineering practice. However it gives more freedom to avalanche practitioners and experts but causes lots of uncertainties in case of serious limitations of avalanche models. We discuss these problems by presenting the application results of different well known and widely used statistical (developed in Russia) and avalanche dynamics models for several avalanche test sites in the Khibini Mountains (The Kola Peninsula) and the Caucasus. The most accurate and well-documented data from different powder and wet, big rare and small frequent snow avalanche events is collected from 1960th till today in the Khibini Mountains by the Avalanche Safety Center of "Apatit". This data was digitized and is available for use and analysis. Then the detailed digital avalanche database (GIS) was created for the first time. It contains contours of observed avalanches (ESRI shapes, more than 50 years of observations), DEMs, remote sensing data, description of snow pits, photos etc. Thus, the Russian avalanche data is a unique source of information for understanding of an avalanche flow rheology and the future development and calibration of the avalanche dynamics models. GIS database was used to analyze model input parameters and to calibrate and verify avalanche models. Regarding extreme dynamic parameters the outputs using different models can differ significantly. This is unacceptable for the engineering purposes in case of the absence of the well-defined guidelines in Russia. The frequency curves for the runout distance

  16. Magnetic avalanches in manganese-acetate, "magnetic deflagration" (United States)

    Suzuki, Yoko

    Mn12-acetate, first synthesized in 1980 by Lis, is one example of a class of many molecules called single molecule magnets (SMMs) or molecular nanomagnets. These molecules have several atomic spins strongly coupled together within each molecule. They exhibit interesting quantum mechanical phenomena at low temperatures such as quantum tunneling of magnetization, which was first found with Mn12-acetate in 1996 by Friedman, et al. , and Berry phase oscillations which were measured in Fe8 (another SMM) in 1999 by Wernsdorfer, et al. In addition to possible application as memory storage and qubits for quantum computers, these systems provide the means for studies of mesoscopic physics as well as the interactions of the molecules with their environment, such as phonon, photon, nuclear spin, intermolecular dipole, and exchange interactions. Mn12-acetate has twelve Mn ions magnetically coupled in the center of the molecule yielding a giant spin of S = 10 at low temperature. It also has a large uniaxial anisotropy of 65 K. Below 3 K, magnetization curves show strong hysteresis due to the anisotropy barrier. At thesis temperatures, the spin relaxes through the barrier by quantum tunneling of magnetization, which produces regularly-spaced multiple resonant steps in the hysteresis curve. Magnetic avalanches, first detected by Paulsen et al., also occur for some samples only at low temperature, leading to a very fast single-step reversal of the full magnetization, which clearly differs from relaxation by tunneling. In this thesis, I present the results of detailed experimental studies of two aspects of magnetic avalanche phenomenon: "conditions for the triggering of avalanches" and "propagation of the avalanche front". In the first study, we find the magnetic fields at which avalanches occur are stochastically distributed in a particular range of fields. For the second study, we conducted local time-resolved measurements. The results indicate the magnetization avalanches spread

  17. A New Method for the Estimation of Avalanche Distance Exceeded Probabilities (United States)

    Barbolini, Massimiliano; Cappabianca, Federica; Savi, Fabrizio


    A crucial point in any methodology for avalanche hazard assessment is the evaluation of avalanche distance exceeded probability, i.e., the annual probability that any assigned location along a given path is reached or exceeded by an avalanche. Typically this problem is faced by estimating the snow volume in the starting zone that is likely to accumulate an average every T years by statistical analysis of snowfall record, and then using this volume as input to an appropriately calibrated avalanche dynamics model to determine the runout distances for this design event. This methodology identifies the areas that can be affected by an avalanche for the considered value of the return period (i.e. the average interval of time for a certain event to repeat itself), T. However, it does not allow us to evaluate the actual avalanche encounter probability for any given point in the runout zone. In the present work this probability is computed by numerical integration of the expression P(x) = ∫0∞ P*(V)f(V) dV, where f is the probability density function (PDF) of the avalanche release volume V, and P* is the probability of the point x being reached or passed by an avalanche if the release volume is V; this latter probability is calculated by avalanche dynamics simulations. The procedure is implemented using a one-dimensional hydraulic-continuum avalanche dynamic model, calibrated on data from different Italian Alpine ranges, and is applied to a real world hazard mapping problem.

  18. Erosion dynamics of powder snow avalanches - model of frontal entrainment (United States)

    Louge, Michel; Sovilla, Betty


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

  19. Stability of the discretization of the electron avalanche phenomenon

    Energy Technology Data Exchange (ETDEWEB)

    Villa, Andrea, E-mail: [Ricerca Sul Sistema Energetico (RSE), Via Rubattino 50, 20134, Milano (Italy); Barbieri, Luca, E-mail: [Ricerca Sul Sistema Energetico (RSE), Via Rubattino 50, 20134, Milano (Italy); Gondola, Marco, E-mail: [Ricerca Sul Sistema Energetico (RSE), Via Rubattino 50, 20134, Milano (Italy); Leon-Garzon, Andres R., E-mail: [CMIC Department “Giulio Natta”, Politecnico di Milano, Piazza Leonardo da Vinci 32, 20133, Milano (Italy); Malgesini, Roberto, E-mail: [Ricerca Sul Sistema Energetico (RSE), Via Rubattino 50, 20134, Milano (Italy)


    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.

  20. Plasma simulation of electron avalanche in a linear thyratron

    International Nuclear Information System (INIS)

    Kushner, M.J.


    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

  1. Anticrack nucleation as triggering mechanism for snow slab avalanches. (United States)

    Heierli, J; Gumbsch, P; Zaiser, M


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

  2. Kinetic modelling of runaway electron avalanches in tokamak plasmas.

    Czech Academy of Sciences Publication Activity Database

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


    Roč. 57, č. 9 (2015), č. článku 095006. ISSN 0741-3335 EU Projects: European Commission(XE) 633053 - EUROfusion Institutional support: RVO:61389021 Keywords : plasma physics * runaway electrons * knock-on collisions * tokamak * Fokker-Planck * runaway avalanches Subject RIV: BL - Plasma and Gas Discharge Physics OBOR OECD: Fluids and plasma physics (including surface physics) Impact factor: 2.404, year: 2015

  3. Avalanche fluctuations within the multigap resistive plate chamber

    International Nuclear Information System (INIS)

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


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

  4. Particle-based Powder-snow Avalanche Simulation Using GPU


    Yndestad, Leif Kåre Hornnes


    The main focus of this thesis was the simulation of a powder-snow avalanche flow. The simulation were implemented using the particle-based simulation solution SPH, from a mathematical model describing powder-snow flow dynamics. The simulation was accelerated by applying the computational power of the GPU, in order to provide a faster simulation time than would have been achieved on the CPU.

  5. About possibility of application of avalanche photodiodes during radioecological monitoring

    International Nuclear Information System (INIS)

    Huseynaliyev, Y.H.


    Full text : This article includes all necessary information about possibility of application of avalanche photodiodes during radioecological surveys. It is shown that at present these devices can be operated in every field of our life. Mostly their operation is based on different types of crystals, which have different characteristics. These photodiodes have a great importance in production of tomographs for conducting of diagnostics and forecasting. Further additional diagram of connection to work of this photodiode is explained [az

  6. Tuning magnetic avalanches in the molecular magnet Mn12 -acetate (United States)

    McHugh, S.; Wen, Bo; Ma, Xiang; Sarachik, M. P.; Myasoedov, Y.; Zeldov, E.; Bagai, R.; Christou, G.


    Using micron-sized Hall sensor arrays to obtain time-resolved measurements of the local magnetization, we report a systematic study in the molecular magnet Mn12 acetate of magnetic avalanches controllably triggered in different fixed external magnetic fields and for different values of the initial magnetization. The speeds of propagation of the spin-reversal fronts are in good overall agreement with the theory of magnetic deflagration of Garanin and Chudnovsky [Phys. Rev. B 76, 054410 (2007)].

  7. Propagation of avalanches in Mn12-acetate: magnetic deflagration. (United States)

    Suzuki, Yoko; Sarachik, M P; Chudnovsky, E M; McHugh, S; Gonzalez-Rubio, R; Avraham, Nurit; Myasoedov, Y; Zeldov, E; Shtrikman, H; Chakov, N E; Christou, G


    Local time-resolved measurements of fast reversal of the magnetization of single crystals of Mn12-acetate indicate that the magnetization avalanche spreads as a narrow interface that propagates through the crystal at a constant velocity that is roughly 2 orders of magnitude smaller than the speed of sound. We argue that this phenomenon is closely analogous to the propagation of a flame front (deflagration) through a flammable chemical substance.

  8. Avalanches in the Bean critical-state model (United States)

    Barford, W.


    A macroscopic equation of motion for the flux density in dirty type-II superconductors is introduced. The flux density is subject to various types of spatially varying pinning force. When there is no stick-slip dynamics, i.e., when the static pinning force equals the dynamic pinning force, it is shown that in both one and two dimensions an increase in the surface magnetic field leads to an overall height change and hence to a change in magnetization equal to the change in the surface magnetic field. More interesting behavior occurs on introducing stick-slip dynamics, i.e., when the static pinning force exceeds the dynamic pinning force. In this limit a distribution of avalanche sizes over four orders of magnitude is found for a 100×100 lattice. Apart from the anomalous behavior at large sizes, this is shown to fit a distribution of the form P(s)~s-ν exp(-s/α), where s is the avalanche size. The anomalous behavior for large sizes corresponds to avalanches which involve most of the lattice and, hence, cause the flux to ``slide over the edge,'' as detected by a change in the edge magnetization.

  9. Avalanches and power-law behaviour in lung inflation (United States)

    Suki, Béla; Barabási, Albert-László; Hantos, Zoltán; Peták, Ferenc; Stanley, H. Eugene


    WHEN lungs are emptied during exhalation, peripheral airways close up1. For people with lung disease, they may not reopen for a significant portion of inhalation, impairing gas exchange2,3. A knowledge of the mechanisms that govern reinflation of collapsed regions of lungs is therefore central to the development of ventilation strategies for combating respiratory problems. Here we report measurements of the terminal airway resistance, Rt , during the opening of isolated dog lungs. When inflated by a constant flow, Rt decreases in discrete jumps. We find that the probability distribution of the sizes of the jumps and of the time intervals between them exhibit power-law behaviour over two decades. We develop a model of the inflation process in which 'avalanches' of airway openings are seen-with power-law distributions of both the size of avalanches and the time intervals between them-which agree quantitatively with those seen experimentally, and are reminiscent of the power-law behaviour observed for self-organized critical systems4. Thus power-law distributions, arising from avalanches associated with threshold phenomena propagating down a branching tree structure, appear to govern the recruitment of terminal airspaces.

  10. First Townsend coefficient of organic vapour in avalanche counters

    International Nuclear Information System (INIS)

    Sernicki, J.


    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.)

  11. Automated Characterization of Single-Photon Avalanche Photodiode

    Directory of Open Access Journals (Sweden)

    Aina Mardhiyah M. Ghazali


    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

  12. Noise Fluctuations and Avalanche Statistics of Skyrmions with Quenched Disorder (United States)

    Diaz, Sebastian; Olson Reichhardt, Cynthia; Reichhardt, Charles; Saxena, Avadh

    Magnetic skyrmions are nanoscopic magnetic textures that enjoy topologically-protected stability and exhibit particle-like behavior. Their novel transport properties have generated extensive basic research and show great potential for using skyrmions as information carriers in future high-density magnetic storage and logic devices. At the particle level, both magnetic skyrmions and superconducting vortices - another kind of topological excitations that also behave as particles - admit a common theoretical description. While in real materials, superconducting vortex dynamics is dissipation-dominated, the so-called Magnus force dominates the dynamics of magnetic skyrmions. Using a particle-based model, we simulate two different systems in the presence of quenched disorder: velocity noise fluctuations of current-driven skyrmions and avalanche statistics of flux-driven skyrmions. We obtain the power spectral density, dynamical phase diagram, as well as the avalanche critical exponents as a function of the Magnus force strength. Our results show that both the noise and avalanche properties of skyrmions depart significantly from the known case of superconducting vortices.

  13. The transitional behaviour of avalanches in cohesive granular materials (United States)

    Quintanilla, M. A. S.; Valverde, J. M.; Castellanos, A.


    We present a statistical analysis of avalanches of granular materials that partially fill a slowly rotated horizontal drum. For large sized noncohesive grains the classical coherent oscillation is reproduced, consisting of a quasi-periodic succession of regularly sized avalanches. As the powder cohesiveness is increased by decreasing the particle size, we observe a gradual crossover to a complex dynamics that resembles the transitional behaviour observed in fusion plasmas. For particle size below ~50 µm, avalanches lose a characteristic size, retain a short term memory and turn gradually decorrelated in the long term as described by a Markov process. In contrast, large grains made cohesive by coating them with adhesive microparticles display a distinct phenomenology, characterized by a quasi-regular succession of well defined small precursors and large relaxation events. The transition from a one-peaked distribution (noncohesive large beads) to a flattened distribution (fine cohesive beads) passing through the two-peaked distribution of cohesive large beads had already been predicted using a coupled-map lattice model, as the relaxation mechanism of grain reorganization becomes dominant to the detriment of inertia.

  14. Self-organization without conservation: are neuronal avalanches generically critical? (United States)

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


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

  15. Particle-size segregation in dense granular avalanches (United States)

    Gray, John Mark Nicholas Timm; Gajjar, Parmesh; Kokelaar, Peter


    Particles of differing sizes are notoriously prone to segregate, which is a chronic problem in the manufacture of a wide variety of products that are used by billions of people worldwide every day. Segregation is the single most important factor in product non-uniformity, which can lead to significant handling problems as well as complete batches being discarded at huge financial loss. It is generally regarded that the most important mechanism for segregation is the combination of kinetic sieving and squeeze expulsion in shallow granular avalanches. These free-surface flows are more common than one might expect, often forming part of more complicated flows in drums, heaps and silos, where there is mass exchange with underlying regions of static or slowly moving grains. The combination of segregation and solid-fluid granular phase transitions creates incredibly complicated and beautiful patterns in the resulting deposits, but a full understanding of such effects lies beyond our capabilities at present. This paper reviews recent advances in our ability to model the basic segregation processes in a single avalanche (without mass exchange) and the subtle feedback effects that they can have on the bulk flow. This is particularly important for geophysical applications, where segregation can spontaneously self-channelize and lubricate the flow, significantly enhancing the run-out of debris-flows, pyroclastic flows, rock-falls and snow-slab avalanches.

  16. Rock-avalanche dynamics revealed by large-scale field mapping and seismic signals at a highly mobile avalanche in the West Salt Creek valley, western Colorado (United States)

    Coe, Jeffrey A.; Baum, Rex L.; Allstadt, Kate E.; Kochevar, Bernard; Schmitt, Robert G.; Morgan, Matthew L.; White, Jonathan L.; Stratton, Benjamin T.; Hayashi, Timothy A.; Kean, Jason W.


    On 25 May 2014, a rain-on-snow–induced rock avalanche occurred in the West Salt Creek valley on the northern flank of Grand Mesa in western Colorado (United States). The avalanche mobilized from a preexisting rock slide in the Green River Formation and traveled 4.6 km down the confined valley, killing three people. The avalanche was rare for the contiguous United States because of its large size (54.5 Mm3) and high mobility (height/length = 0.14). 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 imagery as a base for field mapping, and analyzed seismic data from 22 broadband stations (distances central, hummock-rich core continued to move slowly. Since 25 May 2014, numerous shallow landslides, rock slides, and rock falls have created new structures and modified avalanche topography. Mobility of the main avalanche and central core was 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 thin, liquefied basal layer, and a thicker and stronger overriding layer.

  17. Design and Development of 256x256 Linear Mode Low-Noise Avalanche Photodiode Arrays (United States)

    Yuan, Ping; Sudharsanan, Rengarajan; Bai, Xiaogang; Boisvert, Joseph; McDonald, Paul; Chang, James


    A larger format photodiode array is always desirable for many LADAR imaging applications. However, as the array format increases, the laser power or the lens aperture has to increase to maintain the same flux per pixel thus increasing the size, weight and power of the imaging system. In order to avoid this negative impact, it is essential to improve the pixel sensitivity. The sensitivity of a short wavelength infrared linear-mode avalanche photodiode (APD) is a delicate balance of quantum efficiency, usable gain, excess noise factor, capacitance, and dark current of APD as well as the input equivalent noise of the amplifier. By using InA1As as a multiplication layer in an InP-based APD, the ionization coefficient ratio, k, is reduced from 0.40 (lnP) to 0.22, and the excess noise is reduced by about 50%. An additional improvement in excess noise of 25% was achieved by employing an impact-ionization-engineering structure with a k value of 0.15. Compared with the traditional InP structure, about 30% reduction in the noise-equivalent power with the following amplifier can be achieved. Spectrolab demonstrated 30-um mesa APD pixels with a dark current less than 10 nA and a capacitance of 60 fF at gain of 10. APD gain uninformity determines the usable gain of most pixels in an array, which is critical to focal plane array sensitivity. By fine tuning the material growth and device process, a break-down-voltage standard deviation of 0.1 V and gain of 30 on individual pixels were demonstrated in our 256x256 linear-mode APD arrays.

  18. The Tancitaro Debris Avalanche: Characterization, propagation and modeling (United States)

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


    The Tancitaro volcano (3860 m) is an andesitic-dacitic stratovolcano located in the western portion of the Trans-Mexican Volcanic Belt within the state of Michoacán (Mexico). The tectonic activity of this area has likely contributed to a large sector collapse of the volcano. The first findings of a multidisciplinary investigation into this debris avalanche are presented here. Geomorphological analyses, based on the interpretation of orthophotos, satellite imagery and on GIS elaborations, had the objective of determining the main morphometric features of the landslide. The collapse structure is an east-facing horseshoe-shaped crater (4 km wide and 5.3 km long), while the deposit forms a large fan that is 66 km long, covers an area of approximately 1155 km 2 and has an estimated volume of 18 km 3. Event volume was established by reconstructing the paleo-edifice in a GIS and taking into account volumetric expansion. Cross sections measured in the field were also used for this purpose. Field investigations also highlighted the presence of two texturally distinct units, which are referred to as the "block facies" and the "matrix facies", respectively. The first is responsible for the typical hummock morphologies found in the proximal area. A transitional zone contains a "mixed block and matrix facies" while in the distal portion blocks and megablocks, some of which have a jigsaw puzzle texture, gradually decrease in size until they disappear entirely. A number of matrix samples were collected to conduct direct shear tests, granulometric analyses and classification of the materials. The data and analyses described above were used to discuss the mechanism controlling the long runout of the avalanche. Based on the comparison between the Tancitaro debris avalanche and similar events we propose that mechanical fluidization was the mechanism responsible for the remarkable mobility of the landslide. The predisposing factors leading to the collapse were also considered. Field

  19. Statistical evaluation of waveform collapse reveals scale-free properties of neuronal avalanches

    Directory of Open Access Journals (Sweden)

    Aleena eShaukat


    Full Text Available Neural avalanches are a prominent form of brain activity characterized by network-wide bursts whose statistics follow a power-law distribution with a slope near 3/2. Recent work suggests that avalanches of different durations can be rescaled and thus collapsed together. This collapse mirrors work in statistical physics where it is proposed to form a signature of systems evolving in a critical state. However, no rigorous statistical test has been proposed to examine the degree to which neuronal avalanches collapse together. Here, we describe a statistical test based on functional data analysis, where raw avalanches are first smoothed with a Fourier basis, then rescaled using a time-warping function. Finally, an F ratio test combined with a bootstrap permutation is employed to determine if avalanches collapse together in a statistically reliable fashion. To illustrate this approach, we recorded avalanches from cortical cultures on multielectrode arrays as in previous work. Analyses show that avalanches of various durations can be collapsed together in a statistically robust fashion. However, a principal components analysis revealed that the offset of avalanches resulted in marked variance in the time-warping function, thus arguing for limitations to the strict fractal nature of avalanche dynamics. We compared these results with those obtained from cultures treated with an AMPA/NMDA receptor antagonist (APV/DNQX, which yield a power-law of avalanche durations with a slope greater than 3/2. When collapsed together, these avalanches showed marked misalignments both at onset and offset time-points. In sum, the proposed statistical evaluation suggests the presence of scale-free avalanche waveforms and constitutes an avenue for examining critical dynamics in neuronal systems.

  20. Information processing occurs via critical avalanches in a model of the primary visual cortex (United States)

    Bortolotto, G. S.; Girardi-Schappo, M.; Gonsalves, J. J.; Pinto, L. T.; Tragtenberg, M. H. R.


    We study a new biologically motivated model for the Macaque monkey primary visual cortex which presents power-law avalanches after a visual stimulus. The signal propagates through all the layers of the model via avalanches that depend on network structure and synaptic parameter. We identify four different avalanche profiles as a function of the excitatory postsynaptic potential. The avalanches follow a size-duration scaling relation and present critical exponents that match experiments. The structure of the network gives rise to a regime of two characteristic spatial scales, one of which vanishes in the thermodynamic limit.

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

    Directory of Open Access Journals (Sweden)

    M. Bründl


    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. Readout of plastic scintillators with cooled large-area avalanche photodiodes

    Energy Technology Data Exchange (ETDEWEB)

    Mykulyak, A.; Kapusta, M.; Lynen, U.; Moszynski, M.; Mueller, W.F.J.; Orth, H.; Schwarz, C.; Szawlowski, M.; Trautmann, W.; Trzcinski, A.; Wolski, D.; Zwieglinski, B. E-mail:


    Time-of-flight measurements in multifragmentation of heavy, relativistic projectiles require very good time resolution and at the same time the detecting system must cope with a dynamic range of up to 8000:1. We look into the possibility of application of large-area avalanche photodiodes (LAAPDs) as alternative light sensors to meet the above requirements. The paper presents the results of our amplitude and time response studies of a plastic scintillator BC-408 readout with a phi16 mm LAAPD using radioactive sources. The measurements were performed using two different setups. The best time resolution has been obtained by exploiting LAAPD cooling to increase its gain beyond that accessible at room temperature. We reach 610 ps (FWHM) at -26 deg. C for the corresponding LAAPD gain of {approx}900 and the {sup 90}Sr/{sup 90}Y {beta}-ray source. We hope to reach below the desired 400 ps with the latter setup at the higher light levels available with multifragmentation products.

  3. Radiation Detection Measurements with a New 'Buried Junction' Silicon Avalanche Photodiode

    CERN Document Server

    Lecomte, R; Rouleau, D; Dautet, H; McIntyre, R J; McSween, D; Webb, P


    An improved version of a recently developed 'Buried Junction' avalanche photodiode (APD), designed for use with scintillators, is described and characterized. This device, also called the 'Reverse APD', is designed to have a wide depletion layer and thus low capacitance, but to have high gain only for e-h pairs generated within the first few microns of the depletion layer. Thus it has high gain for light from scintillators emitting in the 400-600 nm range, with relatively low dark current noise and it is relatively insensitive to minimum ionizing particles (MIPs). An additional feature is that the metallurgical junction is at the back of the wafer, leaving the front surface free to be coupled to a scintillator without fear of junction contamination. The modifications made in this device, as compared with the earlier diode, have resulted in a lower excess noise factor, lower dark current, and much-reduced trapping. The electrical and optical characteristics of this device are described and measurements of ener...

  4. Subsampling effects in neuronal avalanche distributions recorded in vivo

    Directory of Open Access Journals (Sweden)

    Munk Matthias HJ


    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

  5. Micro-pixels avalanche photodiodes as radiation detector

    International Nuclear Information System (INIS)

    Ahmadov, F.; Garibov, A.; Madatov, R.; Naghiyev, J.; Sadigov, A; Suleymanov, S.; Sadygov, Z.; Ahmadov, G.; Sadygov, Z.; Zhezher, V.; Mukhtarov, R.; Guliyev, E.; Zerrouk, F.


    Full text: In this work it was reported the results of gamma-ray, alpha particle and neutron detecting measurements performed using LFS scintillation crystal by micro-pixels avalanche photodiodes. The gamma ray detection performance investigated in the range of energy 59.6 keV - 1.3 MeV at room temperature. For this measurements Am-241 and Cd-109 sources placed together in front of the detector. Obtained results showed these detectors could be used in many fields e.g. geology of monitoring and exploration of oil and gas fields, medicine, border security and monitoring of contamination areas

  6. Study on avalanche photodiode influence on heterodyne laser interferometer linearity (United States)

    Budzyn, Grzegorz; Podzorny, Tomasz


    In the paper we analyze factors reducing the possible accuracy of the heterodyne laser interferometers. The analysis is performed for the avalanche-photodiode input stages but is in main points valid also for stages with other type of photodetectors. Instrumental error originating from optical, electronic and digital signal processing factors is taken into consideration. We stress factors which are critical and those which can be neglected at certain accuracy requirements. In the work we prove that it is possible to reduce errors of the laser instrument below 1 nm point for multiaxial APD based interferometers by precise control of incident optical power and the temperature of the photodiode.

  7. 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


    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.

  8. 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


    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.

  9. Double screening tests of the CMS ECAL avalanche photodiodes

    International Nuclear Information System (INIS)

    Deiters, K.; Ingram, Q.; Renker, D.; Sakhelashvili, T.; Britvitch, I.; Kuznetsov, A.; Musienko, Y.; Singovsky, A.


    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

  10. Hole-Initiated-Avalanche, Linear-Mode, Single-Photon-Sensitive Avalanche Photodetector with Reduced Excess Noise and Low Dark Count Rate, Phase I (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...

  11. Performance Analysis of Spectral Amplitude Coding Based OCDMA System with Gain and Splitter Mismatch (United States)

    Umrani, Fahim A.; Umrani, A. Waheed; Umrani, Naveed A.; Memon, Kehkashan A.; Kalwar, Imtiaz Hussain


    This paper presents the practical analysis of the optical code-division multiple-access (O-CDMA) systems based on perfect difference codes. The work carried out use SNR criterion to select the optimal value of avalanche photodiodes (APD) gain and shows how the mismatch in the splitters and gains of the APD used in the transmitters and receivers of network can degrade the BER performance of the system. The investigations also reveal that higher APD gains are not suitable for such systems even at higher powers. The system performance, with consideration of shot noise, thermal noise, bulk and surface leakage currents is also investigated.

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


    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 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.

  13. Low power wide spectrum optical transmitter using avalanche mode LEDs in SOI CMOS technology

    NARCIS (Netherlands)

    Agarwal, Vishal Vishal; Dutta, Satadal; Annema, Anne J.; Hueting, Raymond Josephus Engelbart; Steeneken, P.G.; Nauta, Bram


    This paper presents a low power monolithically integrated optical transmitter with avalanche mode light emitting diodes in a 140 nm silicon-on-insulator CMOS technology. Avalanche mode LEDs in silicon exhibit wide-spectrum electroluminescence (400 nm < λ < 850 nm), which has a significant overlap

  14. Low power wide spectrum optical transmitter using avalanche mode LEDs in SOI CMOS technology

    NARCIS (Netherlands)

    Agarwal, V.; Dutta, S; Annema, AJ; Hueting, RJE; Steeneken, P.G.; Nauta, B


    This paper presents a low power monolithically integrated optical transmitter with avalanche mode light emitting diodes in a 140 nm silicon-on-insulator CMOS technology. Avalanche mode LEDs in silicon exhibit wide-spectrum electroluminescence (400 nm < λ < 850 nm), which has a significant

  15. Feasibility study

    International Nuclear Information System (INIS)

    Gibbs, P.; Kalas, P.


    The feasibility study itself examines the technical, economic and financial implications of a nuclear power station in depth so as to make sure that nuclear power is the right course to take. This means that it is quite an expensive operation and it is to avoid wasting this money that a pre-feasibility study is carried out. This preliminary study should eliminate cases where the electrical system cannot absorb the capacity of a nuclear station of commercial size, where other sources of power such as hydro-electricity, gas or cheap coal would make nuclear obviously uneconomic or where no suitable sites exist. If this first rather simple survey shows that nuclear power is a credible solution to a utilities need for electricity or heat production plant, then the next stage is a full feasibility study. (orig./TK) [de

  16. Apparatus and method for recharging a string a avalanche transistors within a pulse generator (United States)

    Fulkerson, E. Stephen


    An apparatus and method for recharging a string of avalanche transistors within a pulse generator is disclosed. A plurality of amplification stages are connected in series. Each stage includes an avalanche transistor and a capacitor. A trigger signal, causes the apparatus to generate a very high voltage pulse of a very brief duration which discharges the capacitors. Charge resistors inject current into the string of avalanche transistors at various points, recharging the capacitors. The method of the present invention includes the steps of supplying current to charge resistors from a power supply; using the charge resistors to charge capacitors connected to a set of serially connected avalanche transistors; triggering the avalanche transistors; generating a high-voltage pulse from the charge stored in the capacitors; and recharging the capacitors through the charge resistors.

  17. Antidepressants and Weight Gain (United States)

    Antidepressants and weight gain: What causes it? Can antidepressants cause weight gain? Answers from Daniel K. Hall- ... is a possible side effect of nearly all antidepressants. However, each person responds to antidepressants differently. Some ...

  18. Infrasonic and seismic signals of snow avalanches and debris flow (United States)

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


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

  19. Supershort avalanche electron beam in SF6 and krypton (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


    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.

  20. From an electron avalanche to the lightning discharge (United States)

    Zalikhanov, B. Zh.


    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.

  1. Does Avalanche Shovel Shape Affect Excavation Time: A Pilot Study

    Directory of Open Access Journals (Sweden)

    Kurt Schindelwig


    Full Text Available In Europe and North America, approximately 150 fatalities occur as a result of avalanches every year. However, it is unclear whether certain shovel shapes are more effective than others in snow removal during avalanche victim recovery. The objective was to determine the performance parameters with a developed standardized test using different shovel shapes and to determine sex-specific differences. Hence, several parameters were determined for clearing the snow from a snow filled box (15 men, 14 women. A flat (F and a deep (D shovel blade with the shaft connected straight (S or in clearing mode (C were used for the investigation of the shovel shapes FS, DC and the subsequent use of DC&DS. Mean snow mass shifted per unit time increased significantly from 1.50 kg/s with FS to 1.71 kg/s (14% with DS and further to 1.79 kg/s (4% with DC&DS for all participants. Snow mass shifted per unit time was 44% higher (p < 0.05 for men than for women. In excavation operations, the sex-specific physical performance should be taken into account. The results were limited to barely binding snow, because only with this snow did the tests show a high reliability.

  2. Scale-free avalanche dynamics in crystal plasticity (United States)

    Ispanovity, Pater Dusan; Laurson, Lasse; Zaiser, Michael; Zapperi, Stefano; Groma, Istvan; Alava, Mikko


    We investigate the properties of strain bursts (dislocation avalanches) occurring during plastic deformation of crystalline matter using two dimensional discrete dislocation dynamics (DDD). We perform quasistatic stress-controlled simulations with three DDD models differing in the spatiotemporal discretization and the mobility law assumed for individual dislocations. We find that each model exhibits identical avalanche dynamics with the following properties: (i) strain burst sizes follow a power law distribution characterized by an exponent τ ~ 1 . 0 and (ii) the distribution in truncated at a cutoff that diverges with increasing system size at any applied stress level. It has been proposed earlier that plastic yielding can be described in terms of a continuous phase transition of depinning type and its critical point is at the yield stress. We will demonstrate, however, that our results are inconsistent with cutoff scaling in depinning systems (like magnetic domain walls or earthquakes) and that the system behaves as critical at every stress level. We, therefore, conclude that in the models studied plastic yielding cannot be associated with a continuous phase transition. Financial supports of the Hungarian Scientific Research Fund (OTKA) under Contract Numbers PD-105256 and K-105335 and of the European Commission under Grant Agreement No. CIG-321842 are acknowledged.

  3. Vortex Avalanches with Periodic Arrays of Pinning Sites (United States)

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


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

  4. Avalanche photo-detection for high data rate applications

    International Nuclear Information System (INIS)

    Coldenstrodt-Ronge, H B; Silberhorn, C


    Avalanche photo-detection is commonly used in applications which require single-photon sensitivity. We examine the limits of using avalanche photo-diodes (APD) for characterizing photon statistics at high data rates. To identify the regime of linear APD operation, we employ a ps-pulsed diode laser with variable repetition rates between 0.5 MHz and 80 MHz. We modify the mean optical power of the coherent pulses by applying different levels of well-calibrated attenuation. The linearity at high repetition rates is limited by the APD dead time and a nonlinear response arises at higher photon-numbers due to multiphoton events. Assuming Poissonian input-light statistics we ascertain the effective mean photon-number of the incident light with high accuracy. Time multiplexed detectors allow us to accomplish photon-number resolution by 'photon chopping'. This detection setup extends the linear response function to higher photon-numbers and statistical methods may be used to compensate for nonlinearity. We investigate this effect, compare it to the single APD case and show the validity of the convolution treatment in the TMD data analysis

  5. Validating numerical simulations of snow avalanches using dendrochronology: the Cerro Ventana event in Northern Patagonia, Argentina

    Directory of Open Access Journals (Sweden)

    A. Casteller


    Full Text Available The damage caused by snow avalanches to property and human lives is underestimated in many regions around the world, especially where this natural hazard remains poorly documented. One such region is the Argentinean Andes, where numerous settlements are threatened almost every winter by large snow avalanches. On 1 September 2002, the largest tragedy in the history of Argentinean mountaineering took place at Cerro Ventana, Northern Patagonia: nine persons were killed and seven others injured by a snow avalanche. In this paper, we combine both numerical modeling and dendrochronological investigations to reconstruct this event. Using information released by local governmental authorities and compiled in the field, the avalanche event was numerically simulated using the avalanche dynamics programs AVAL-1D and RAMMS. Avalanche characteristics, such as extent and date were determined using dendrochronological techniques. Model simulation results were compared with documentary and tree-ring evidences for the 2002 event. Our results show a good agreement between the simulated projection of the avalanche and its reconstructed extent using tree-ring records. Differences between the observed and the simulated avalanche, principally related to the snow height deposition in the run-out zone, are mostly attributed to the low resolution of the digital elevation model used to represent the valley topography. The main contributions of this study are (1 to provide the first calibration of numerical avalanche models for the Patagonian Andes and (2 to highlight the potential of Nothofagus pumilio tree-ring records to reconstruct past snow-avalanche events in time and space. Future research should focus on testing this combined approach in other forested regions of the Andes.

  6. Snow-avalanche hazard forecasting in the Krkonoše Mountains, Czechia (United States)

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


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

  7. Wet-snow avalanche interaction with a deflecting dam: field observations and numerical simulations in a case study

    Directory of Open Access Journals (Sweden)

    B. Sovilla


    Full Text Available In avalanche-prone areas, deflecting dams are widely used to divert avalanches away from endangered objects. In recent years, their effectiveness has been questioned when several large and multiple avalanches have overrun such dams.

    In 2008, we were able to observe a large wet-snow avalanche, characterized by an high water content, that interacted with a deflecting dam and overflowed it at its lower end. To evaluate the dam's performance, we carried out an airborne laser scanning campaign immediately after the avalanche. This data, together with a video sequence made during the avalanche descent, provided a unique data set to study the dynamics of a wet dense snow avalanche and its flow behavior along a deflecting dam.

    To evaluate the effect of the complex flow field of the avalanche along the dam and to provide a basis for discussion of the residual risk, we performed numerical simulations using a two-dimensional dense snow avalanche dynamics model with entrainment.

    In comparison to dry dense snow avalanches, we found that wet-snow avalanches, with high water content, seem to be differently influenced by the local small-scale topography roughness. Rough terrain close to the dam deflected the flow to produce abrupt impacts with the dam. At the impact sites, instability waves were generated and increased the already large flow depths. The complex flow dynamics around the dam may produce large, local snow deposits. Furthermore, the high water content in the snow may decrease the avalanche internal friction angle, inducing wet-snow avalanches to spread further laterally than dry-snow avalanches.

    Based on our analysis, we made recommendations for designing deflecting dams and for residual risk analysis to take into account the effects of wet-snow avalanche flow.

  8. Timing of wet snow avalanche activity: An analysis from Glacier National Park, Montana, USA. (United States)

    Peitzsch, Erich H.; Hendrikx, Jordy; Fagre, Daniel B.


    Wet snow avalanches pose a problem for annual spring road opening operations along the Going-to-the-Sun Road (GTSR) in Glacier National Park, Montana, USA. A suite of meteorological metrics and snow observations has been used to forecast for wet slab and glide avalanche activity. However, the timing of spring wet slab and glide avalanches is a difficult process to forecast and requires new capabilities. For the 2011 and 2012 spring seasons we tested a previously developed classification tree model which had been trained on data from 2003-2010. For 2011, this model yielded a 91% predictive rate for avalanche days. For 2012, the model failed to capture any of the avalanche days observed. We then investigated these misclassified avalanche days in the 2012 season by comparing them to the misclassified days from the original dataset from which the model was trained. Results showed no significant difference in air temperature variables between this year and the original training data set for these misclassified days. This indicates that 2012 was characterized by avalanche days most similar to those that the model struggled with in the original training data. The original classification tree model showed air temperature to be a significant variable in wet avalanche activity which implies that subsequent movement of meltwater through the snowpack is also important. To further understand the timing of water flow we installed two lysimeters in fall 2011 before snow accumulation. Water flow showed a moderate correlation with air temperature later in the season and no synchronous pattern associated with wet slab and glide avalanche activity. We also characterized snowpack structure as the snowpack transitioned from a dry to a wet snowpack throughout the spring. This helped to assess potential failure layers of wet snow avalanches and the timing of avalanches compared to water moving through the snowpack. These tools (classification tree model and lysimeter data), combined with

  9. Risk analysis for dry snow slab avalanche release by skier triggering (United States)

    McClung, David


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

  10. Optimization of eyesafe avalanche photodiode lidar for automobile safety and autonomous navigation systems (United States)

    Williams, George M.


    Newly emerging accident-reducing, driver-assistance, and autonomous-navigation technology for automobiles is based on real-time three-dimensional mapping and object detection, tracking, and classification using lidar sensors. Yet, the lack of lidar sensors suitable for meeting application requirements appreciably limits practical widespread use of lidar in trucking, public livery, consumer cars, and fleet automobiles. To address this need, a system-engineering perspective to eyesafe lidar-system design for high-level advanced driver-assistance sensor systems and a design trade study including 1.5-μm spot-scanned, line-scanned, and flash-lidar systems are presented. A cost-effective lidar instrument design is then proposed based on high-repetition-rate diode-pumped solid-state lasers and high-gain, low-excess-noise InGaAs avalanche photodiode receivers and focal plane arrays. Using probabilistic receiver-operating-characteristic analysis, derived from measured component performance, a compact lidar system is proposed that is capable of 220 m ranging with 5-cm accuracy, which can be readily scaled to a 360-deg field of regard.

  11. Characterization and quality control of avalanche photodiode arrays for the Clear-PEM detector modules

    Energy Technology Data Exchange (ETDEWEB)

    Abreu, Conceicao [LIP, Av Elias Garcia 14, 1000-149 Lisbon (Portugal); UALG, Campus de Gambelas, 8000-117 Faro (Portugal); Amaral, Pedro [LIP, Av Elias Garcia 14, 1000-149 Lisbon (Portugal); Carrico, Bruno [LIP, Av Elias Garcia 14, 1000-149 Lisbon (Portugal)]. E-mail:; Ferreira, Miguel [LIP, Av Elias Garcia 14, 1000-149 Lisbon (Portugal); Luyten, Joan [LIP, Av Elias Garcia 14, 1000-149 Lisbon (Portugal); Moura, Rui [LIP, Av Elias Garcia 14, 1000-149 Lisbon (Portugal); Ortigao, Catarina [LIP, Av Elias Garcia 14, 1000-149 Lisbon (Portugal); Rato, Pedro [LIP, Av Elias Garcia 14, 1000-149 Lisbon (Portugal); Varela, Joao [LIP, Av Elias Garcia 14, 1000-149 Lisbon (Portugal); IST, Av Rovisco Pais, 1049-001 Lisbon (Portugal)


    Clear-PEM is a Positron Emission Mammography (PEM) prototype being developed in the framework of the Crystal Clear Collaboration at CERN. This device is a dedicated PET camera for mammography, based on LYSO:Ce scintillator crystals, Avalanche PhotoDiodes (APD) and a fast, low-noise electronics readout system, designed to examine both the breast and the axillary lymph node areas, and aiming at the detection of tumors down to 2 mm in diameter. The prototype has two planar detector heads, each composed of 96 detector modules. The Clear-PEM detector module is composed of a matrix of 32 identical 2x2x20 mm{sup 3} LYSO:Ce crystals read at both ends by Hamamatsu S8550 APD arrays (4x8) for Depth-of-Interaction (DoI) capability. The APD arrays were characterized by the measurement of gain and dark current as a function of bias voltage, under controlled temperature conditions. Two independent setups were used. The full set of 398 APD arrays followed a well-defined quality control (QC) protocol, aiming at the rejection of arrays not complying within defined specifications. From a total of 398 arrays, only 2 (0.5%) were rejected, reassuring the trust in these detectors for prototype assembly and future developments.

  12. Gain uniformity experimental study performed on triple-GEM gas detector

    International Nuclear Information System (INIS)

    Dong Liyuan; Qi Huirong; Lu Xinyu; Ouyang Qun; Chen Yuanbo; Li Yuhong


    With the application of the two-dimensional GEM gaseous detector in X-ray imaging, the correction method of gain uniformity caused by triple-GEM avalanche structures and electric field uniformity should be studied. The paper reported the study of the triple-GEM detector with effective area 100 mm × 100 mm used the Pad's size of 9.5 mm × 9.5 mm. In the test, 100 readout channels were designed. Results showed that gain remained stable over time; at air flow increases, gain from increases obviously to changes very little. Particularly, triple-GEM's gain uniformity was very good (more than 80%) and the range of energy resolution was from 0.18 to 0.2. To improve gain consistency of results, the difference value revised was obtained to be about 0.1 by the least square method. It provided a better method to improve gain uniformity of GEM detector. (authors)

  13. Avalanche situation in Turkey and back-calculation of selected events (United States)

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


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

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

    International Nuclear Information System (INIS)

    Mahajan, S.M.; Sudarshan, T.S.; Department of Electrical and Computer Engineering, University of South Carolina, Columbia, South Carolina 29208)


    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

  15. Modeling the influence of snow cover temperature and water content on wet-snow avalanche runout (United States)

    Valero, Cesar Vera; Wever, Nander; Christen, Marc; Bartelt, Perry


    Snow avalanche motion is strongly dependent on the temperature and water content of the snow cover. In this paper we use a snow cover model, driven by measured meteorological data, to set the initial and boundary conditions for wet-snow avalanche calculations. The snow cover model provides estimates of snow height, density, temperature and liquid water content. This information is used to prescribe fracture heights and erosion heights for an avalanche dynamics model. We compare simulated runout distances with observed avalanche deposition fields using a contingency table analysis. Our analysis of the simulations reveals a large variability in predicted runout for tracks with flat terraces and gradual slope transitions to the runout zone. Reliable estimates of avalanche mass (height and density) in the release and erosion zones are identified to be more important than an exact specification of temperature and water content. For wet-snow avalanches, this implies that the layers where meltwater accumulates in the release zone must be identified accurately as this defines the height of the fracture slab and therefore the release mass. Advanced thermomechanical models appear to be better suited to simulate wet-snow avalanche inundation areas than existing guideline procedures if and only if accurate snow cover information is available.


    Directory of Open Access Journals (Sweden)

    Aleksandr Shnyparkov


    Full Text Available In recent years, the Government of the Russian Federation considerably increased attention to the exploitation of the Russian Arctic territories. Simultaneously, the evaluation of snow avalanches danger was enhanced with the aim to decrease fatalities and reduce economic losses. However, it turned out that solely reporting the degree of avalanche danger is not sufficient. Instead, quantitative information on probabilistic parameters of natural hazards, the characteristics of their effects on the environment and possibly resulting losses is increasingly needed. Such information allows for the estimation of risk, including risk related to snow avalanches. Here, snow avalanche risk is quantified for the Khibiny Mountains, one of the most industrialized parts of the Russian Arctic: Major parts of the territory have an acceptable degree of individual snow avalanche risk (<1×10-6. The territories with an admissible (10-4–10-6 or unacceptable (>1×10-4 degree of individual snow avalanche risk (0.5 and 2% of the total area correspond to the Southeast of the Khibiny Mountains where settlements and mining industries are situated. Moreover, due to an increase in winter tourism, some traffic infrastructure is located in valleys with an admissible or unacceptable degree of individual snow avalanches risk.

  17. Slab entrainment and surge dynamics of the 2015 Valleé de la Sionne avalanches (United States)

    Köhler, Anselm; McElwaine, Jim; Sovilla, Betty


    On 3 February 2015 five avalanches were artificially released at the Valleé de la Sionne test site in the west of Switzerland. The dense parts of the avalanches were tracked by the GEODAR Mark 2 radar system at 111 Hz framerate with 0.75 m down slope resolution. The data show that these avalanche contain several internal surges and that the avalanche front is repeatedly overtaken by some of these surges. We show that these surges exist on different scale. While the major surges originates from secondary triggered slab releases and occur all over the avalanche. The minor surges are only found in the energetic part of a well developed powder snow avalanche. The mass of the major surges can be as huge as the initial released mass, this has a dramatic effect on the mass distribution inside the avalanche and effects the front velocity and run out. Furthermore, the secondary released snow slabs are an important entrainment mechanism and up to 50 percent of the mass entered the avalanche via slab entrainment. We analyse the dynamics of the leading edge and the minor surges in more detail using a simple one dimensional model with frictional resistance and quadratic velocity dependent drag. These models fit the data well for the start and middle of avalanche but cannot capture the slowing and overtaking of the minor surge. We find much higher friction coefficients to describe the surging. We propose that this data can only be explained by changes in the snow surface. These effects are not included in current models yet, but the data presented here will enable the development and verification of such models.

  18. SWIR HgCdTe avalanche photiode focal plane array performances evaluation (United States)

    de Borniol, E.; Rothman, J.; Salveti, F.; Feautrier, P.


    One of the main challenges of modern astronomical instruments like adaptive optics (AO) systems or fringe trackers is to deal with the very low photons flux detection scenarios. The typical timescale of atmospheric turbulences being in the range of some tens of milliseconds, infrared wavefront sensors for AO systems needs frame rates higher than 1 KHz leading to integration times lower than 1 ms. This integration time associated with a low irradiance results in a few number of integrated photons per frame per pixel. To preserve the information coming from this weak signal, the focal plane array (FPA) has to present a low read out noise, a high quantum efficiency and a low dark current. Up to now, the output noise of high speed near infrared sensors is limited by the silicon read out circuit noise. The use of HgCdTe avalanche photodiodes with high gain at moderate reverse bias and low excess noise seems then a logical way to reduce the impact of the read noise on images signal to noise ratio. These low irradiance passive imaging applications with integration times in the millisecond range needs low photodiode dark current and low background current. These requirements lead to the choice of the photodiode cut off wavelength. The short wave infrared (SWIR) around 3 μm is a good compromise between the gain that can be obtain for a given APD bias and the background and dark current. The CEA LETI HgCdTe APD technology, and a fine analysis of the gain curve characteristic are presented in [1] and won't be detailed here. The response time of the APD is also a key factor for a high frame rate FPA. This parameter has been evaluated in [2] and the results shows cut off frequencies in the GHz range. In this communication we report the performances of a SWIR APD FPA designed and fabricated by CEA LETI and SOFRADIR for astrophysical applications. This development was made in the frame of RAPID, a 4 years R&D project funded by the French FUI (Fond Unique Interministériel). This

  19. Avalanche dynamics for active matter in heterogeneous media (United States)

    Reichhardt, C. J. O.; Reichhardt, C.


    Using numerical simulations, we examine the dynamics of run-and-tumble disks moving in a disordered array of fixed obstacles. As a function of increasing active disk density and activity, we find a transition from a completely clogged state to a continuous flowing phase, and in the large activity limit, we observe an intermittent state where the motion occurs in avalanches that are power law distributed in size with an exponent of β =1.46. In contrast, in the thermal or low activity limit we find bursts of motion that are not broadly distributed in size. We argue that in the highly active regime, the system reaches a self-jamming state due to the activity-induced self-clustering, and that the intermittent dynamics is similar to that found in the yielding of amorphous solids. Our results show that activity is another route by which particulate systems can be tuned to a nonequilibrium critical state.

  20. Snow drift: acoustic sensors for avalanche warning and research

    Directory of Open Access Journals (Sweden)

    M. Lehning


    Full Text Available Based on wind tunnel measurements at the CSTB (Jules Verne facility in Nantes and based on field observations at the SLF experimental site Versuchsfeld Weissfluhjoch, two acoustic wind drift sensors are evaluated against different mechanical snow traps and one optical snow particle counter. The focus of the work is the suitability of the acoustic sensors for applications such as avalanche warning and research. Although the acoustic sensors have not yet reached the accuracy required for typical research applications, they can, however, be useful for snow drift monitoring to help avalanche forecasters. The main problem of the acoustic sensors is a difficult calibration that has to take into account the variable snow properties. Further difficulties arise from snow fall and high wind speeds. However, the sensor is robust and can be operated remotely under harsh conditions. It is emphasized that due to the lack of an accurate reference method for snow drift measurements, all sensors play a role in improving and evaluating snow drift models. Finally, current operational snow drift models and snow drift sensors are compared with respect to their usefulness as an aid for avalanche warning. While drift sensors always make a point measurement, the models are able to give a more representative drift index that is valid for a larger area. Therefore, models have the potential to replace difficult observations such as snow drift in operational applications. Current models on snow drift are either only applicable in flat terrain, are still too complex for an operational application (Lehning et al., 2000b, or offer only limited information on snow drift, such as the SNOWPACK drift index (Lehning et al., 2000a. On the other hand, snow drift is also difficult to measure. While mechanical traps (Mellor 1960; Budd et al., 1966 are probably still the best reference, they require more or less continuous manual operation and are thus not suitable for remote locations

  1. Studies of avalanche photodiodes for scintillating fibre tracking readout

    International Nuclear Information System (INIS)

    Fenker, H.; Thomas, J.


    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

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

    Directory of Open Access Journals (Sweden)

    Emilio Sciacca


    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.

  3. Correcting for accidental correlations in saturated avalanche photodiodes. (United States)

    Grieve, J A; Chandrasekara, R; Tang, Z; Cheng, C; Ling, A


    In this paper we present a general method for estimating rates of accidental coincidence between a pair of single photon detectors operated within their saturation regimes. By folding the effects of recovery time of both detectors and the detection circuit into an "effective duty cycle" we are able to accomodate complex recovery behaviour at high event rates. As an example, we provide a detailed high-level model for the behaviour of passively quenched avalanche photodiodes, and demonstrate effective background subtraction at rates commonly associated with detector saturation. We show that by post-processing using the updated model, we observe an improvement in polarization correlation visibility from 88.7% to 96.9% in our experimental dataset. This technique will be useful in improving the signal-to-noise ratio in applications which depend on coincidence measurements, especially in situations where rapid changes in flux may cause detector saturation.

  4. Application of Ultraviolet Light in Dental Identification of Avalanche Victims. (United States)

    Agrawal, Nitin Kumar; Dahal, Samarika; Wasti, Harihar; Soon, Alistair


    In any disaster, it becomes important to identify the deceased for ethical, social and legal causes.Out of the numerous methods of identification, dental comparison is considered to be one of the scientific methods in a Disaster Victim Identification process. The two victims of avalanche in Nepal were identified using dental comparison. The two bodies brought for examination were unidentifiable visually. To aid identification of tooth coloured restorations, ultraviolet light was used. The ultraviolet light made the tooth coloured restorations appear distinct from the adjacent tooth structure in one of the cases. This helped in post-mortem charting of dental examination with greater accuracy. When the ante-mortem dental records and the post-mortem dental findings were compared, positive identification was made for both the cases. The bodies were then handed over to their respective kin. These cases highlighted the importance of ultraviolet light in post-mortem dental examination and the significance of forensic dentistry in identification process.

  5. TCAD simulations for a novel single-photon avalanche diode (United States)

    Jin, Xiangliang; Yang, Jia; Yang, Hongjiao; Tang, Lizhen; Liu, Weihui


    A single-photon avalanche diode (SPAD) device with P+-SEN junction, and a low concentration of N-type doping circular virtual guard-ring was presented in this paper. SEN layer of the proposed SPAD has high concentration of N-type doping, causing the SPAD low breakdown voltage (~14.26 V). What's more, an efficient and narrow (about 2μm) guard-ring of the proposed SPAD not only can withstand considerably higher electric fields for preventing edge breakdown, but also offers a little increment in fill factor compared with existing SPADs due to its small area. In addition, some Silvaco TCAD simulations have been done and verify characteristics and performance of the design in this work.

  6. Mechanics of debris flows and rock avalanches: Chapter 43 (United States)

    Iverson, Richard M.; Fernando, Harindra Joseph


    Debris flows are geophysical phenomena intermediate in character between rock avalanches and flash floods. They commonly originate as water-laden landslides on steep slopes and transform into liquefied masses of fragmented rock, muddy water, and entrained organic matter that disgorge from canyons onto valley floors. Typically including 50%–70% solid grains by volume, attaining speeds >10 m/s, and ranging in size up to ∼109 m3, debris flows can denude mountainsides, inundate floodplains, and devastate people and property (Figure 43.1). Notable recent debris-flow disasters resulted in more than 20,000 fatalities in Armero, Colombia, in 1985 and in Vargas state, Venezuela, in 1999.

  7. Interevent Correlations from Avalanches Hiding Below the Detection Threshold (United States)

    Janićević, Sanja; Laurson, Lasse; Mâløy, Knut Jørgen; Santucci, Stéphane; Alava, Mikko J.


    Numerous systems ranging from deformation of materials to earthquakes exhibit bursty dynamics, which consist of a sequence of events with a broad event size distribution. Very often these events are observed to be temporally correlated or clustered, evidenced by power-law-distributed waiting times separating two consecutive activity bursts. We show how such interevent correlations arise simply because of a finite detection threshold, created by the limited sensitivity of the measurement apparatus, or used to subtract background activity or noise from the activity signal. Data from crack-propagation experiments and numerical simulations of a nonequilibrium crack-line model demonstrate how thresholding leads to correlated bursts of activity by separating the avalanche events into subavalanches. The resulting temporal subavalanche correlations are well described by our general scaling description of thresholding-induced correlations in crackling noise.

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

    Directory of Open Access Journals (Sweden)

    Edda Bjork Thordardottir


    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.

  9. XeCl avalanche discharge laser employing Ar as a diluent (United States)

    Sze, R.C.


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

  10. Avalanche diode having reduced dark current and method for its manufacture (United States)

    Davids, Paul; Starbuck, Andrew Lee; Pomerene, Andrew T. S.


    An avalanche diode includes an absorption region in a germanium body epitaxially grown on a silicon body including a multiplication region. Aspect-ratio trapping is used to suppress dislocation growth in the vicinity of the absorption region.

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

  12. Readout of scintillator light with avalanche photodiodes for positron emission tomography

    International Nuclear Information System (INIS)

    Chen, Ruru; Fremout, A.; Tavernier, S.; Bruyndonckx, P.; Clement, D.; Loude, J.-F.; Morel, C.


    The noise properties and other relevant characteristics of avalanche photodiodes have been investigated with the perspective of replacing photomultiplier tubes in positron emission tomography. It is clearly demonstrated that they are a valid alternative to photomultiplier tubes in this application

  13. Observation of the Avalanche of Runaway Electrons in Air in a Strong Electric Field (United States)

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


    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.

  14. Extended Wavelength InP Based Avalanche Diodes for MWIR Response, Phase I (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...

  15. Analysis of the dynamic avalanche of punch through insulated gate bipolar transistor (PT-IGBT) (United States)

    Lefranc, P.; Planson, D.; Morel, H.; Bergogne, D.


    In the paper proposed here, we are studying the dynamic avalanche from experimental results first, dynamic avalanche is identified on a punch through insulated gate bipolar transistor (PT-IGBT) module 1200 V-300 A from Mitsubishi. Secondly, the phenomenon is analysed thanks to simple solid state devices equations. Numerical simulations are used to confirm experimental results. Simulation results allows us locating the active area of the dynamic avalanche during turn-off under over-current conditions. A PT-IGBT cell is described with MEDICI™, a finite element simulator. A mixed-mode simulation is performed thanks to MEDICI™ and SPICE™. The circuit simulated here is a buck topology with an inductive load. Finally, a thermal analysis is performed to estimate temperature increase due to dynamic avalanche.

  16. Backcountry snowmobilers' risk perceptions, avalanche related information seeking behaviours, preparedness and decision-making processes (United States)

    Baker, Jennifer

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

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

    International Nuclear Information System (INIS)

    Diamond, P.H.; Champeaux, S.; Malkov, M.


    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)

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

    Directory of Open Access Journals (Sweden)

    Tiago L Ribeiro


    Full Text Available Scale-invariant neuronal avalanches have been observed in cell cultures and slices as well as anesthetized and awake brains, suggesting that the brain operates near criticality, i.e. within a narrow margin between avalanche propagation and extinction. In theory, criticality provides many desirable features for the behaving brain, optimizing computational capabilities, information transmission, sensitivity to sensory stimuli and size of memory repertoires. However, a thorough characterization of neuronal avalanches in freely-behaving (FB animals is still missing, thus raising doubts about their relevance for brain function.To address this issue, we employed chronically implanted multielectrode arrays (MEA to record avalanches of 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.Altogether, the data provide a comprehensive link between behavior

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

    International Nuclear Information System (INIS)

    Brenning, N.; Axnaes, I.; Nilsson, J.O.; Eninger, J.E.


    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 N st.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 N st.p ∝ p 21/4 τ -3/4 . This pressure scaling disagrees with the p 3/2 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 n e of free electrons becomes larger than the density N st.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

  20. Multiwire proportional chamber and multistage avalanche chamber with low concentration photoionization gas

    International Nuclear Information System (INIS)

    Zhao Pingde; Xu Zhiqing; Tang Xiaowei


    The characteristics of multiwire proportional chamber and multistage avalanche chamber filled with argon and photoionization gas (C 2 H 5 ) 3 N were measured. The spatial resolution curves and output pulse height spectra were measured as well. Low concentration (C 2 H 5 ) 3 N can play an effective part in quenching. At very low concentration, the phenomena of avalanche transverse expansion was observed obviously

  1. Noise Performance of Millimeter-wave Silicon Based Mixed Tunneling Avalanche Transit Time(MITATT) Diode


    Aritra Acharyya; Moumita Mukherjee; J. P. Banerjee


    A generalized method for small-signal simulation of avalanche noise in Mixed Tunneling Avalanche Transit Time (MITATT) device is presented in this paper where the effect of series resistance is taken into account. The method is applied to a millimeter-wave Double Drift Region (DDR) MITATT device based on Silicon to obtain noise spectral density and noise measure as a function of frequency for different values of series resistance. It is found that noise measure of the dev...

  2. Parameters of an avalanche of runaway electrons in air under atmospheric pressure (United States)

    Oreshkin, E. V.


    The features of runaway-electron avalanches developing in air under atmospheric pressures are investigated in the framework of a three-dimensional numerical simulation. The simulation results indicate that an avalanche of this type can be characterized, besides the time and length of its exponential growth, by the propagation velocity and by the average kinetic energy of the runaway electrons. It is shown that these parameters obey the similarity laws applied to gas discharges.

  3. Statistical analysis and trends of wet snow avalanches in the French Alps over the period 1959-2010 (United States)

    Naaim, Mohamed


    Since an avalanche contains a significant proportion of wet snow, its characteristics and its behavior change significantly (heterogeneous and polydisperse). Even if on a steep given slope, wet snow avalanches are slow. They can flow over gentle slopes and reach the same extensions as dry avalanches. To highlight the link between climate warming and the proliferation of wet snow avlanches, we crossed two well-documented avalanche databases: the permanent avalanche chronicle (EPA) and the meteorological re-analyzes. For each avalanche referenced in EPA, a moisture index I is buit. It represents the ratio of the thickness of the wet snow layer to the total snow thickness, at the date of the avalanche on the concerned massif at 2400 m.a.s.l. The daily and annual proportion of avalanches exceeding a given threshold of I are calculated for each massif of the French alps. The statistical distribution of wet avalanches per massif is calculated over the period 1959-2009. The statistical quantities are also calculated over two successive periods of the same duration 1959-1984 and 1984-2009, and the annual evolution of the proportion of wet avalanches is studied using time-series tools to detect potential rupture or trends. This study showed that about 77% of avalanches on the French alpine massif mobilize dry snow. The probability of having an avalanche of a moisture index greater than 10 % in a given year is 0.2. This value varies from one massif to another. The analysis between the two successive periods showed a significant growth of wet avalanches on 20 massifs and a decrease on 3 massifs. The study of time-series confirmed these trends, which are of the inter-annual variability level.

  4. Granular avalanches across irregular three-dimensional terrain: 2. Experimental tests (United States)

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


    Scaling considerations indicate that miniature experiments can be used to test models of granular avalanches in which the effects of intergranular fluid and cohesion are negligible. To test predictions of a granular avalanche model described in a companion paper, we performed bench top experiments involving avalanches of dry sand across irregular basal topography that mimicked the complexity of natural terrain. The experiments employed a novel method of laser-assisted cartography to map the three-dimensional morphology of rapidly moving avalanches, thereby providing high-resolution data for comparison with model output. Model input consisted of two material properties (angles of internal and basal Coulomb friction of the sand), which were measured in independent tests, and of initial and boundary conditions that characterized the geometry of the experimental apparatus. Experimental results demonstrate that the model accurately predicts not only the gross behavior but also many details of avalanche motion, from initiation to deposition. We attribute this accuracy to a mathematical and computational formulation that conserves mass and momentum in three-dimensional physical space and satisfies the Coulomb equation in three-dimensional stress space. Our results support the hypothesis that a Coulomb proportionality between shear and normal stresses applies in moderately rapid granular flows and that complicated constitutive postulates are unnecessary if momentum conservation is strictly enforced in continuum avalanche models. Furthermore, predictions of our Coulomb continuum model contrast with those of a Coulomb point mass model, illustrating the importance of multidimensional modeling and model testing.

  5. Is extracorporeal rewarming indicated in avalanche victims with unwitnessed hypothermic cardiorespiratory arrest? (United States)

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


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

  6. Gain control mechanisms in spinal motoneurons

    Directory of Open Access Journals (Sweden)

    Michael David Johnson


    Full Text Available Motoneurons provide the only conduit for motor commands to reach muscles. For many years, motoneurons were in fact considered to be little more than passive wires. Systematic studies in the past 25 years however have clearly demonstrated that the intrinsic electrical properties of motoneurons are under strong neuromodulatory control via multiple sources. The discovery of potent neuromodulation from the brainstem and its ability to change the gain of motoneurons shows that the passive view of the motor output stage is no longer tenable. A mechanism for gain control at the motor output stage makes good functional sense considering our capability of generating an enormous range of forces, from very delicate (e.g. putting in a contact lens to highly forceful (emergency reactions. Just as sensory systems need gain control to deal with a wide dynamic range of inputs, so to might motor output need gain control to deal with the wide dynamic range of the normal movement repertoire. Two problems emerge from the potential use of the brainstem monoaminergic projection to motoneurons for gain control. First, the projection is highly diffuse anatomically, so that independent control of the gains of different motor pools is not feasible. In fact, the system is so diffuse that gain for all the motor pools in a limb likely increases in concert. Second, if there is a system that increases gain, probably a system to reduce gain is also needed. In this review, we summarize recent studies that show local inhibitory circuits within the spinal cord, especially reciprocal and recurrent inhibition, have the potential to solve both of these problems as well as constitute another source of gain modulation.

  7. Monitoring snow avalanches in the medium range by a network of infrasonic arrays: first results (United States)

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


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

  8. Fractal dimension of debris-avalanche deposits in the Hawaiian submarine landslide deposits (United States)

    Yokose, H.; Yamato, S.


    17 landslide deposits on the flanks of the southern Hawaiian Ridge have been classified into two major types: SLUMPS, which moved slowly as a coherent mass, and DEBRIS AVALANCHES, which moved quickly.The debris-avalanche deposits are predominant on submarine flanks of volcanic ocean islands elsewhere in the world. Such huge landslides are considered to produce giant tsunamis and megaturbidites covering large areas of abyssal plains. Based on the small scale topographic elements, we reinvestigated the distribution areas and emplacement styles of the debris-avalanche deposits, which differ from those previously proposed from GLORIA images without benefit of detailed bathymetric data or direct seafloor observations. There are several types of small scale topographic elements in the debris-avalanche deposits previously proposed: source amphitheater, toppled blocks, marginal levee, slide-emplaced blocks, chute, mud wave, hummocky terrain. They are very similar to those appeared in subaerial volcanic debris-avalanche fields. However, no correlation between the collapse height and runout distance are observed in the submarine debris-avalanche deposits. The hummocky terrains can be classified into two types: FLAT-TYPE, which is distributed in the nearly flat abyssal plain, less than 0.5 degree, and SLOPE-TYPE, which located on the lower part of the submarine flanks, greater than 1 degree. The size of hummocks in a slope-type hummocky terrain have an unimodal distribution pattern with a broad peak in the number of hummocks versus height category diagram. On the contrary, the size of hummocks in flat-type hummocky terrains have a power law distribution pattern in the same diagram. The fractal dimensions calculated from these diagrams are 1.19 (Nuuanu landslide), 2.32 (Ka Lae landslide) and 2.96 (Alika 2 debris-avalanche), respectively. They are expected to reflect the processes and degree of fragmentation. Therefore, among the debris_]avalanche deposits proposed previously

  9. The September 1988 intracaldera avalanche and eruption at Fernandina volcano, Galapagos Islands (United States)

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


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

  10. Multi-level modelling of the response of the ultraminiature proportional counter: gas gain phenomena and pulse height spectra

    International Nuclear Information System (INIS)

    Olko, P.; Moutarde, C.; Segur, P.


    The ultraminiature proportional counters, UMC, unique radiation detectors for monitoring high intensity therapy fields, designed by Kliauga and operated at Columbia University (USA), have yielded a number of pulse height distributions for photons, neutrons and ions at simulated diameters of 5-50 nm. Monte Carlo calculations of the gas gain in such a counter questioned the possibility of achieving proportionally at such low simulated diameters. The response of the UMC has now been modelled taking into account both fluctuations of energy deposited in the counter volume and its calculated gas gain. Energy deposition was calculated using the MOCA-14, MOCA-8 and TRION codes, whereby distributions of ionisations d(j) after irradiations with 137 Cs, 15 MeV neutrons and 7 MeV.amu -1 deuterons were obtained. Monte Carlo calculations of electron avalanches in UMC show that the size of the single-electron avalanche P(n) reaching the anode depends strongly on the location of the primary ionisation within the counter volume. Distributions of the size of electron avalanches for higher numbers of primary ionisations, P *j (n), were obtained by successive convolutions of P(n). Finally, the counter response was obtained by weighting P *j (n) over d(j) distributions. On comparing the measured and calculated spectra it was concluded that the previously proposed single-electron peak calibration method might not be valid for the UMC due to the excessive width and overlap of electron avalanche distributions. Better agreement between the measured and calculated spectra is found if broader electron avalanche distributions than those used in the present calculations, are assumed. (author)

  11. The Importance of Damage Potential for Avalanche Risk Assessments (United States)

    Keiler, M.; Fuchs, S.


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

  12. Laser annealing heals radiation damage in avalanche photodiodes

    Energy Technology Data Exchange (ETDEWEB)

    Lim, Jin Gyu [University of Waterloo, Institute for Quantum Computing, Waterloo, ON (Canada); University of Waterloo, Department of Electrical and Computer Engineering, Waterloo, ON (Canada); Anisimova, Elena; Higgins, Brendon L.; Bourgoin, Jean-Philippe [University of Waterloo, Institute for Quantum Computing, Waterloo, ON (Canada); University of Waterloo, Department of Physics and Astronomy, Waterloo, ON (Canada); Jennewein, Thomas [University of Waterloo, Institute for Quantum Computing, Waterloo, ON (Canada); University of Waterloo, Department of Physics and Astronomy, Waterloo, ON (Canada); Canadian Institute for Advanced Research, Quantum Information Science Program, Toronto, ON (Canada); Makarov, Vadim [University of Waterloo, Institute for Quantum Computing, Waterloo, ON (Canada); University of Waterloo, Department of Electrical and Computer Engineering, Waterloo, ON (Canada); University of Waterloo, Department of Physics and Astronomy, Waterloo, ON (Canada)


    Avalanche photodiodes (APDs) are a practical option for space-based quantum communications requiring single-photon detection. However, radiation damage to APDs significantly increases their dark count rates and thus reduces their useful lifetimes in orbit. We show that high-power laser annealing of irradiated APDs of three different models (Excelitas C30902SH, Excelitas SLiK, and Laser Components SAP500S2) heals the radiation damage and several APDs are restored to typical pre-radiation dark count rates. Of nine samples we test, six APDs were thermally annealed in a previous experiment as another solution to mitigate the radiation damage. Laser annealing reduces the dark count rates further in all samples with the maximum dark count rate reduction factor varying between 5.3 and 758 when operating at -80 C. This indicates that laser annealing is a more effective method than thermal annealing. The illumination power to reach these reduction factors ranges from 0.8 to 1.6 W. Other photon detection characteristics, such as photon detection efficiency, timing jitter, and afterpulsing probability, fluctuate but the overall performance of quantum communications should be largely unaffected by these variations. These results herald a promising method to extend the lifetime of a quantum satellite equipped with APDs. (orig.)

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

    CERN Document Server

    Ng, J S


    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 ...

  14. Analysis of the dynamic avalanche of carrier stored trench bipolar transistor (CSTBT) during clamped inductive turn-off transient (United States)

    Xue, Peng; Fu, Guicui


    The dynamic avalanche has a huge impact on the switching robustness of carrier stored trench bipolar transistor (CSTBT). The purpose of this work is to investigate the CSTBT's dynamic avalanche mechanism during clamped inductive turn-off transient. At first, with a Mitsubishi 600 V/150 A CSTBT and a Infineon 600 V/200 A field stop insulated gate bipolar transistor (FS-IGBT) utilized, the clamped inductive turn-off characteristics are obtained by double pulse test. The unclamped inductive switching (UIS) test is also utilized to identify the CSTBT's clamping voltage under dynamic avalanche condition. After the test data analysis, it is found that the CSTBT's dynamic avalanche is abnormal and can be triggered under much looser condition than the conventional buffer layer IGBT. The comparison between the FS-IGBT and CSTBT's experimental results implies that the CSTBT's abnormal dynamic avalanche phenomenon may be induced by the carrier storage (CS) layer. Based on the semiconductor physics, the electric field distribution and dynamic avalanche generation in the depletion region are analyzed. The analysis confirms that the CS layer is the root cause of the CSTBT's abnormal dynamic avalanche mechanism. Moreover, the CSTBT's negative gate capacitance effect is also investigated to clarify the underlying mechanism of the gate voltage bump observed in the test. In the end, the mixed-mode numerical simulation is utilized to reproduce the CSTBT's dynamic avalanche behavior. The simulation results validate the proposed dynamic avalanche mechanisms.

  15. 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


    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.

  16. Relational Information Gain

    DEFF Research Database (Denmark)

    Lippi, Marco; Jaeger, Manfred; Frasconi, Paolo


    We introduce relational information gain, a refinement scoring function measuring the informativeness of newly introduced variables. The gain can be interpreted as a conditional entropy in a well-defined sense and can be efficiently approximately computed. In conjunction with simple greedy general......-to-specific search algorithms such as FOIL, it yields an efficient and competitive algorithm in terms of predictive accuracy and compactness of the learned theory. In conjunction with the decision tree learner TILDE, it offers a beneficial alternative to lookahead, achieving similar performance while significantly...

  17. Receiver Gain Modulation Circuit (United States)

    Jones, Hollis; Racette, Paul; Walker, David; Gu, Dazhen


    A receiver gain modulation circuit (RGMC) was developed that modulates the power gain of the output of a radiometer receiver with a test signal. As the radiometer receiver switches between calibration noise references, the test signal is mixed with the calibrated noise and thus produces an ensemble set of measurements from which ensemble statistical analysis can be used to extract statistical information about the test signal. The RGMC is an enabling technology of the ensemble detector. As a key component for achieving ensemble detection and analysis, the RGMC has broad aeronautical and space applications. The RGMC can be used to test and develop new calibration algorithms, for example, to detect gain anomalies, and/or correct for slow drifts that affect climate-quality measurements over an accelerated time scale. A generalized approach to analyzing radiometer system designs yields a mathematical treatment of noise reference measurements in calibration algorithms. By treating the measurements from the different noise references as ensemble samples of the receiver state, i.e. receiver gain, a quantitative description of the non-stationary properties of the underlying receiver fluctuations can be derived. Excellent agreement has been obtained between model calculations and radiometric measurements. The mathematical formulation is equivalent to modulating the gain of a stable receiver with an externally generated signal and is the basis for ensemble detection and analysis (EDA). The concept of generating ensemble data sets using an ensemble detector is similar to the ensemble data sets generated as part of ensemble empirical mode decomposition (EEMD) with exception of a key distinguishing factor. EEMD adds noise to the signal under study whereas EDA mixes the signal with calibrated noise. It is mixing with calibrated noise that permits the measurement of temporal-functional variability of uncertainty in the underlying process. The RGMC permits the evaluation of EDA by

  18. Derivation of a simple analytical expression of the gain of pure argon filled CAT proportional counters

    CERN Document Server

    Chaplier, G; Megtert, S


    In previous publications, we described the intrinsic properties of CAT detectors, formed as a unique or a collection of individual single holes (gas proportional pixel detector). In our last paper, we have shown that the calculated gain of the avalanche along the electric field lines was dependent on the distance of photon absorption with respect to the symmetry axis of a single hole. On the contrary, the measured gain did not follow this dependence and it was suggested that the gain of the detector was similar to the one measured along the hole symmetry axis, irrespective of the shape of the off-axis electric field lines. We present here a simple calculation of the on-axis gain of such structures that corresponds to the measurements and takes into account the detector geometry.

  19. Nonlinear response and avalanche behavior in metallic glasses (United States)

    Riechers, B.; Samwer, K.


    The response to different stress amplitudes at temperatures below the glass transition temperature is analyzed by mechanical oscillatory excitation of Pd40Ni40P20 metallic glass samples in single cantilever bending geometry. While low amplitude oscillatory excitations are commonly used in mechanical spectroscopy to probe the relaxation spectrum, in this work the response to comparably high amplitudes is investigated. The strain response of the material is well below the critical yield stress even for highest stress amplitudes, implying the expectation of a linear relation between stress and strain according to Hooke's Law. However, a deviation from the linear behavior is evident, which is analyzed in terms of temperature dependence and influence of the applied stress amplitude by two different approaches of evaluation. The nonlinear approach is based on a nonlinear expansion of the stress-strain-relation, assuming an intrinsic nonlinear character of the shear or elastic modulus. The degree of nonlinearity is extracted by a period-by-period Fourier-analysis and connected to nonlinear coefficients, describing the intensity of nonlinearity at the fundamental and higher harmonic frequencies. The characteristic timescale to adapt to a significant change in stress amplitude in terms of a recovery timescale to a steady state value is connected to the structural relaxation time of the material, suggesting a connection between the observed nonlinearity and primary relaxation processes. The second approach of evaluation is termed the incremental analysis and relates the observed response behavior to avalanches, which occur due to the activation and correlation of local microstructural rearrangements. These rearrangements are connected with shear transformation zones and correspond to localized plastic events, which are superimposed on the linear response behavior of the material.

  20. Characterizing wet slab and glide slab avalanche occurrence along the Going-to-the-Sun Road, Glacier National Park, Montana, USA (United States)

    Peitzsch, Erich H.; Hendrikx, Jordy; Fagre, Daniel B.; Reardon, Blase


    Wet slab and glide slab snow avalanches are dangerous and yet can be particularly difficult to predict. Both wet slab and glide slab avalanches are thought to depend upon free water moving through the snowpack but are driven by different processes. In Glacier National Park, Montana, both types of avalanches can occur in the same year and affect the Going-to-the-Sun Road (GTSR). Both wet slab and glide slab avalanches along the GTSR from 2003-2010 are investigated. Meteorological data from two high-elevation weather stations and one SNOTEL site are used in conjunction with an avalanche database and snowpit profiles. These data were used to characterize years when only glide slab avalanches occurred and those years when both glide slab and wet slab avalanches occurred. Results of 168 glide slab and 57 wet slab avalanches along the GTSR suggest both types of avalanche occurrence depend on sustained warming periods with intense solar radiation (or rain on snow) to produce free water in the snowpack. Differences in temperature and net radiation metrics between wet slab and glide slab avalanches emerge as one moves from one day to seven days prior to avalanche occurrence. On average, a more rapid warming precedes wet slab avalanche occurrence. Glide slab and wet slab avalanches require a similar amount of net radiation. Wet slab avalanches do not occur every year, while glide slab avalanches occur annually. These results aim to enhance understanding of the required meteorological conditions for wet slab and glide slab avalanches and aid in improved wet snow avalanche forecasting.

  1. Layer number dependence of flux avalanches in superconducting shifted strip array

    International Nuclear Information System (INIS)

    Mine, A.; Tsuchiya, Y.; Miyano, S.; Pyon, S.; Tamegai, T.; Nagasawa, S.; Hidaka, M.


    Highlights: • We have fabricated superconducting shifted strip arrays (SSAs) up to 4 layers. • Flux penetrations into SSAs are observed by using magneto-optical imaging. • Linear flux avalanches are observed in a wider range of overlap in the 4-layer SSAs than in the 2- or 3-layer SSAs. - Abstract: We have fabricated multi-layer superconducting shifted strip arrays (SSAs) of Nb up to 4 layers and systematically studied the vortex penetrations into these structures. We observed the vortex penetration as a function of the number of layers and the ratio of overlap between neighboring layers by using magneto-optical (MO) imaging. In the case of 2- and 3-layer SSAs, spot-like avalanches occur when the overlap is small, while linear avalanches occur when the overlap is large, consistent with our previous reports. In the 4-layer SSAs, the smallest limit of the overlap between the neighboring layers for the linear avalanche is lower. Flux penetrations parallel to the strip which were observed in the 3-layer SSA were also observed in the 4-layer SSAs with smaller ratio of overlap. Larger demagnetization effects in the middle two layers in 4-layer SSA help to make avalanches larger and more extended.

  2. Analysis of avalanche risk factors in backcountry terrain based on usage frequency and accident data in Switzerland (United States)

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


    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 - and 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

  3. Learn and gain

    CERN Document Server

    Al-Alami, Suhair Eyad Jamal


    Initiating the slogan ""love it, live it"", Learn and Gain includes eight short stories, chosen to illustrate various modes of narration, as well as to provoke reflection and discussion on a range of issues. All texts utilized here illustrate how great writers can, with their insight and gift for words, help us to see the world we live in, in new probing and exciting ways. What characterises the book, the author believes, is the integration of the skills of literary competence, communicative c...

  4. Note: An avalanche transistor-based nanosecond pulse generator with 25 MHz repetition rate. (United States)

    Beev, Nikolai; Keller, Jonas; Mehlstäubler, Tanja E


    We have developed an avalanche transistor-based pulse generator for driving the photocathode of an image intensifier, which comprises a mainly capacitive load on the order of 100 pF. The circuit produces flat-top pulses with a rise time of 2 ns, a FWHM of 10 ns, and an amplitude of tens of V at a high repetition rate in the range of tens of MHz. The generator is built of identical avalanche transistor sections connected in parallel and triggered in a sequence, synchronized to a reference rf signal. The described circuit and mode of operation overcome the power dissipation limit of avalanche transistor generators and enable a significant increase of pulse repetition rates. Our approach is naturally suited for synchronized imaging applications at low light levels.

  5. Note: An avalanche transistor-based nanosecond pulse generator with 25 MHz repetition rate (United States)

    Beev, Nikolai; Keller, Jonas; Mehlstäubler, Tanja E.


    We have developed an avalanche transistor-based pulse generator for driving the photocathode of an image intensifier, which comprises a mainly capacitive load on the order of 100 pF. The circuit produces flat-top pulses with a rise time of 2 ns, a FWHM of 10 ns, and an amplitude of tens of V at a high repetition rate in the range of tens of MHz. The generator is built of identical avalanche transistor sections connected in parallel and triggered in a sequence, synchronized to a reference rf signal. The described circuit and mode of operation overcome the power dissipation limit of avalanche transistor generators and enable a significant increase of pulse repetition rates. Our approach is naturally suited for synchronized imaging applications at low light levels.

  6. 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


    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.

  7. Avalanches and Dimensional Reduction Breakdown in the Critical Behavior of Disordered Systems (United States)

    Tarjus, Gilles; Baczyk, Maxime; Tissier, Matthieu


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

  8. Possible deviations from Griffith’s criterion in shallow slabs, and consequences on slab avalanche release

    Directory of Open Access Journals (Sweden)

    F. Louchet


    Full Text Available Possible reasons for deviations from Griffith’s criterion in slab avalanche triggerings are examined. In the case of a major basal crack, we show (i that the usual form of Griffith’s criterion is valid if elastic energy is stored in a shallow and hard slab only, and (ii that rapid healing of broken ice bonds may lead to shear toughnesses larger than expected from tensile toughness experiments. In the case of avalanches resulting from failure of multi-cracked weak layers, where a simple Griffith’s criterion cannot be applied, frequency/size plots obtained from discrete elements and cellular automata simulations are shown to obey scale invariant power law distributions. These findings are confirmed by both frequency/acoustic emission duration and frequency/size plots obtained from field data, suggesting that avalanche triggerings may be described using the formalism of critical phenomena.

  9. Chaos and Correlated Avalanches in Excitatory Neural Networks with Synaptic Plasticity (United States)

    Pittorino, Fabrizio; Ibáñez-Berganza, Miguel; di Volo, Matteo; Vezzani, Alessandro; Burioni, Raffaella


    A collective chaotic phase with power law scaling of activity events is observed in a disordered mean field network of purely excitatory leaky integrate-and-fire neurons with short-term synaptic plasticity. The dynamical phase diagram exhibits two transitions from quasisynchronous and asynchronous regimes to the nontrivial, collective, bursty regime with avalanches. In the homogeneous case without disorder, the system synchronizes and the bursty behavior is reflected into a period doubling transition to chaos for a two dimensional discrete map. Numerical simulations show that the bursty chaotic phase with avalanches exhibits a spontaneous emergence of persistent time correlations and enhanced Kolmogorov complexity. Our analysis reveals a mechanism for the generation of irregular avalanches that emerges from the combination of disorder and deterministic underlying chaotic dynamics.

  10. Error diagrams and temporal correlations in a fracture model with characteristic and power-law distributed avalanches

    DEFF Research Database (Denmark)

    Moreno, Y.; Vázquez-Prada, M.; Pacheco, A.F.


    to the heterogeneity of the system. In one regime, a characteristic event is observed while for the second regime a power-law spectrum of avalanches is obtained reminiscent of self-organized criticality. We find that both regimes are different when predicting large avalanches and that, in the second regime...

  11. Forecasting for natural avalanches during spring opening of Going-to-the-Sun Road, Glacier National Park, Montana, USA (United States)

    Reardon, Blase; Lundy, Chris


    The annual spring opening of the Going-to-the-Sun Road in Glacier National Park presents a unique avalanche forecasting challenge. The highway traverses dozens of avalanche paths mid-track in a 23-kilometer section that crosses the Continental Divide. Workers removing seasonal snow and avalanche debris are exposed to paths that can produce avalanches of destructive class 4. The starting zones for most slide paths are within proposed Wilderness, and explosive testing or control are not currently used. Spring weather along the Divide is highly variable; rain-on-snow events are common, storms can bring several feet of new snow as late as June, and temperature swings can be dramatic. Natural avalanches - dry and wet slab, dry and wet loose, and glide avalanches - present a wide range of hazards and forecasting issues. This paper summarizes the forecasting program instituted in 2002 for the annual snow removal operations. It focuses on tools and techniques for forecasting natural wet snow avalanches by incorporating two case studies, including a widespread climax wet slab cycle in 2003. We examine weather and snowpack conditions conducive to wet snow avalanches, indicators for instability, and suggest a conceptual model for wet snow stability in a northern intermountain snow climate.

  12. Self-organized criticality induced by quenched disorder: Experiments on flux avalanches in NbHx films

    NARCIS (Netherlands)

    Welling, M.S.; Aegerter, C.M.; Wijngaarden, R.J.


    We present an experimental study of the influence of quenched disorder on the distribution of flux avalanches in type-II superconductors. In the presence of much quenched disorder, the avalanche sizes are powerlaw distributed and show finite-size scaling, as expected from self-organized criticality

  13. Measurement and modeling of microlenses fabricated on single-photon avalanche diode arrays for fill factor recovery

    NARCIS (Netherlands)

    Mata Pavia, J.; Wolf, M.; Charbon, E.


    Single-photon avalanche diode (SPAD) imagers typically have a relatively low fil factor, i.e. a low proportion of the pixel’s surface is light sensitive, due to in-pixel circuitry. We present a microlens array fabricated on a 128x128 single-photon avalanche diode (SPAD) imager to enhance its

  14. Avalanche dynamics, surface roughening, and self-organized criticality: Experiments on a three-dimensional pile of rice

    NARCIS (Netherlands)

    Aegerter, C.M.; Gunther, R.; Wijngaarden, R.J.


    The results of both the avalanche and the roughening behavior of an experimental self-organized criticality (SOC) system are presented. In addition, simple arguments for universal scaling relations, derived by Paczuski et al. on general grounds, connecting the avalanche and the roughening behavior

  15. Modelling wet snow avalanche runout to assess road safety at a high-altitude mine in the central Andes (United States)

    Valero, Cesar Vera; Wever, Nander; Bühler, Yves; Stoffel, Lukas; Margreth, Stefan; Bartelt, Perry


    Mining activities in cold regions are vulnerable to snow avalanches. Unlike operational facilities, which can be constructed in secure locations outside the reach of avalanches, access roads are often susceptible to being cut, leading to mine closures and significant financial losses. In this paper we discuss the application of avalanche runout modelling to predict the operational risk to mining roads, a long-standing problem for mines in high-altitude, snowy regions. We study the 35 km long road located in the "Cajón del rio Blanco" valley in the central Andes, which is operated by the Codelco Andina copper mine. In winter and early spring, this road is threatened by over 100 avalanche paths. If the release and snow cover conditions can be accurately specified, we find that avalanche dynamics modelling is able to represent runout, and safe traffic zones can be identified. We apply a detailed, physics-based snow cover model to calculate snow temperature, density and moisture content in three-dimensional terrain. This information is used to determine the initial and boundary conditions of the avalanche dynamics model. Of particular importance is the assessment of the current snow conditions along the avalanche tracks, which define the mass and thermal energy entrainment rates and therefore the possibility of avalanche growth and long runout distances.

  16. Smartphone applications for communicating avalanche risk information : a study on how they are developed and evaluated by their providers

    NARCIS (Netherlands)

    Charriere, M.K.M.; Bogaard, T.A.


    Every year, people are victims of avalanches. It is commonly assumed that one way to decrease those losses is to inform about danger levels. This paper presents a study on current practices in the development and evaluation of smartphones applications that are dedicated to avalanche risk

  17. A mineralogical and granulometric study of Cayambe volcano debris avalanche deposit (United States)

    Detienne, M.; Delmelle, P.; Guevara, A.; Samaniego, P.; Bustillos, J.; Sonnet, P.; Opfergelt, S.


    Volcano flank/sector collapse represents one of the most catastrophic volcanic hazards. Various volcanic and non-volcanic processes are known to decrease the stability of a volcanic cone, eventually precipitating its gravitational failure. Among them, hydrothermal alteration of volcanic rocks leading to clay mineral formation is recognized as having a large negative impact on rock strength properties. Furthermore, the presence of hydrothermal clays in the collapsing mass influences the behavior of the associated volcanic debris avalanche. In particular, clay-containing debris avalanches seem to travel farther and spread more widely than avalanches of similar volume but which do not incorporate hydrothermally-altered materials. However, the relationship between hydrothermal alteration, flank collapse and debris avalanche behavior is not well understood. The objective of this study is to better determine the volume and composition of hydrothermal clay minerals in the poorly characterized debris avalanche deposit (DAD) of Cayambe composite volcano, located in a densely populated area ~70 km northeast of Quito, Ecuador. Cayambe DAD originated from a sector collapse, which occurred less than 200 ka ago. The DAD is 10-20 m thick and has an estimated total volume of ~0.85 Km3. The H/L ratio (where H is the vertical drop and L is the travel distance of the avalanche) for Cayambe DAD is ~0.095, suggesting a high mobility. In the medial-distal zone, at 9-20 km from its source, the DAD consists of an unstratified and unsorted matrix supporting millimetric to metric clasts. It has a matrix facies (i.e. rich in particles DAD behaved as a cohesive debris flow. Analysis of 13 matrix samples reveals a large variability in particle size distribution. This may reflect poor mixing of the collapsed material during transport. The clay fraction content in the matrix ranges from 15 to 30 wt.%, and does not show a relationship with the sample position in the DAD. Mineralogical

  18. Improved x-ray detection and particle identification with avalanche photodiodes

    Energy Technology Data Exchange (ETDEWEB)

    Diepold, Marc, E-mail:; Franke, Beatrice; Götzfried, Johannes; Hänsch, Theodor W.; Krauth, Julian J.; Mulhauser, Françoise; Nebel, Tobias; Pohl, Randolf [Max Planck Institute of Quantum Optics, 85748 Garching (Germany); Fernandes, Luis M. P.; Amaro, Fernando D.; Gouvea, Andrea L.; Monteiro, Cristina M. B.; Santos, Joaquim M. F. dos [LIBPhys, Physics Department, Universidade de Coimbra, 3004-516 Coimbra (Portugal); Machado, Jorge [Laboratório de Instrumentação, Engenharia Biomédica e Física da Radiação (LIBPhys-UNL) e Departamento de Física da Faculdade de Ciências e Tecnologia da Universidade Nova de Lisboa, Monte da Caparica, 2892-516 Caparica (Portugal); Laboratoire Kastler Brossel, UPMC-Sorbonne Universités, CNRS, ENS-PSL Research University, Collège de France, 4 place Jussieu, case 74, 75005 Paris (France); Amaro, Pedro; Santos, José Paulo [Laboratório de Instrumentação, Engenharia Biomédica e Física da Radiação (LIBPhys-UNL) e Departamento de Física da Faculdade de Ciências e Tecnologia da Universidade Nova de Lisboa, Monte da Caparica, 2892-516 Caparica (Portugal); and others


    Avalanche photodiodes are commonly used as detectors for low energy x-rays. In this work, we report on a fitting technique used to account for different detector responses resulting from photoabsorption in the various avalanche photodiode layers. The use of this technique results in an improvement of the energy resolution at 8.2 keV by up to a factor of 2 and corrects the timing information by up to 25 ns to account for space dependent electron drift time. In addition, this waveform analysis is used for particle identification, e.g., to distinguish between x-rays and MeV electrons in our experiment.

  19. Diffusion correction to the Raether Meek criterion for the avalanche-to-streamer transition (United States)

    Montijn, Carolynne; Ebert, Ute


    Space-charge dominated streamer discharges can emerge in free space from single electrons. We reinvestigate the Raether-Meek criterion and show that streamer emergence depends not only on ionization and attachment rates and gap length, but also on electron diffusion. Motivated by simulation results, we derive an explicit quantitative criterion for the avalanche-to-streamer transition both for pure non-attaching gases and for air, under the assumption that the avalanche emerges from a single free electron and evolves in a homogeneous field.

  20. A new crack propagation criterion for skier-triggered snow slab avalanches


    Gaume Johan; Reuter Benjamin; van Herwijnen Alec; Schweizer Jürg


    Dry snow slab avalanches begin with a local failure in a weak snowpack layer buried below cohesive slab layers. If the size of the failed zone exceeds a critical length rapid crack propagation occurs possibly followed by slab release if the slope is steep enough. The probability to trigger a slab avalanche by a skier or a snowmobile is generally described by classical stability indices which do not account for crack propagation. In this study we propose a new model to evaluate the conditions ...

  1. Ultralow-noise readout circuit with an avalanche photodiode: toward a photon-number-resolving detector. (United States)

    Tsujino, Kenji; Akiba, Makoto; Sasaki, Masahide


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

  2. A multiple parallel-plate avalanche counter for fission-fragment detection

    Energy Technology Data Exchange (ETDEWEB)

    Wu, C.Y., E-mail: [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)


    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.

  3. Characterization of new hexagonal large area Geiger Avalanche Photodiodes

    International Nuclear Information System (INIS)

    Boccone, V.; Aguilar, J.A.; Della Volpe, D.; Christov, A.; Montaruli, T.; Rameez, M.; Basili, A.


    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 mm 2 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 (V ov ). Optical crosstalk and

  4. Extending the Astronomical Application of Photon Counting HgCdTe Linear Avalanche Photo-Diode Arrays to Low Background Space Observations. (United States)

    Hall, Donald

    The high quantum efficiency and very low dark current, together with the ability to set the wavelength cutoff from one to far beyond 5.5 microns, of large format HAWAII HgCdTe arrays have already made them the workhorse for NASA space astronomy (and related) observations in the 1 to 5.5 micron infrared. They have performed outstandingly on Hubble Wide Field Camera 3 and WISE (and also Deep Impact/EPOXI and OCO-2) and are crucial to the two major NASA Astrophysics missions, JWST and WFIRST, and to Euclid. The proposed investigation seeks to extend these benefits to the most demanding observations those that seek to wring information from only a few photons (starved due to either the intrinsic faintness of the source or the need for high spectral or time resolution) or to discriminate a weak signature against a bright source. We will characterize, and optimize for space astronomy observations, the unique linear avalanche properties of HgCdTe photo-diodes (HgCdTe L-APDs) that allow noiseless (i.e. faithfully preserves the Poisson statistics of the incoming photons) avalanche multiplication of individual photo-electrons. 2.5 micron HgCdTe L-APD technology, developed for infrared eye-safe LIDAR and range gated imaging, is already benefiting infrared wavefront sensing for ground based adaptive optics. In HgCdTe the L-APD gain and the onset voltage for tunneling current are exponential functions of bandgap while also varying with cryogenic operating temperature. The unique HgCdTe bandgap engineering that allows tuning of the cutoff wavelength can be used to critically improve avalanche performance for specific applications. We will thoroughly evaluate avalanche performance at several representative bandgaps so as to allow model prediction of performance over the critical 1 to 5 micron spectral interval. The proposed investigation will hybridize modest 32x32 arrays of HgCdTe L-APDs to photon counting readouts already developed under another award and characterize their

  5. Gaining Relational Competitive Advantages

    DEFF Research Database (Denmark)

    Hu, Yimei; Zhang, Si; Li, Jizhen


    Establishing strategic technological partnerships (STPs) with foreign partners is an increasingly studied topic within the innovation management literature. Partnering firms can jointly create sources of relational competitive advantage. Chinese firms often lack research and development (R......&D) capabilities but are increasingly becoming preferred technological partners for transnational corporations. We investigate an STP between a Scandinavian and a Chinese firm and try to explore how to gain relational competitive advantage by focusing on its two essential stages: relational rent generation...... and appropriation. Based on an explorative case study, we develop a conceptual framework that consists of process, organizational alliance factors, and coordination modes that we propose lead to relational competitive advantage....

  6. Collisional avalanche exponentiation of runaway electrons in electrified plasmas

    International Nuclear Information System (INIS)

    Jayakumar, R.; Fleischmann, H.H.; Zweben, S.J.


    In contrast to earlier expectations, it is estimated that generation of runaway electrons from close collisions of existing runaways with cold plasma electrons can be significant even for small electric fields, whenever runaways can gain energies of about 20 MeV or more. In that case, the runaway population will grow exponentially with the energy spectrum showing an exponential decrease towards higher energies. Energy gains of the required magnitude may occur in large tokamak devices as well as in cosmic-ray generation. (orig.)

  7. Regional snow-avalanche detection using object-based image analysis of near-infrared aerial imagery

    Directory of Open Access Journals (Sweden)

    K. Korzeniowska


    Full Text Available Snow avalanches are destructive mass movements in mountain regions that continue to claim lives and cause infrastructural damage and traffic detours. Given that avalanches often occur in remote and poorly accessible steep terrain, their detection and mapping is extensive and time consuming. Nonetheless, systematic avalanche detection over large areas could help to generate more complete and up-to-date inventories (cadastres necessary for validating avalanche forecasting and hazard mapping. In this study, we focused on automatically detecting avalanches and classifying them into release zones, tracks, and run-out zones based on 0.25 m near-infrared (NIR ADS80-SH92 aerial imagery using an object-based image analysis (OBIA approach. Our algorithm takes into account the brightness, the normalised difference vegetation index (NDVI, the normalised difference water index (NDWI, and its standard deviation (SDNDWI to distinguish avalanches from other land-surface elements. Using normalised parameters allows applying this method across large areas. We trained the method by analysing the properties of snow avalanches at three 4 km−2 areas near Davos, Switzerland. We compared the results with manually mapped avalanche polygons and obtained a user's accuracy of > 0.9 and a Cohen's kappa of 0.79–0.85. Testing the method for a larger area of 226.3 km−2, we estimated producer's and user's accuracies of 0.61 and 0.78, respectively, with a Cohen's kappa of 0.67. Detected avalanches that overlapped with reference data by > 80 % occurred randomly throughout the testing area, showing that our method avoids overfitting. Our method has potential for large-scale avalanche mapping, although further investigations into other regions are desirable to verify the robustness of our selected thresholds and the transferability of the method.

  8. Regional snow-avalanche detection using object-based image analysis of near-infrared aerial imagery (United States)

    Korzeniowska, Karolina; Bühler, Yves; Marty, Mauro; Korup, Oliver


    Snow avalanches are destructive mass movements in mountain regions that continue to claim lives and cause infrastructural damage and traffic detours. Given that avalanches often occur in remote and poorly accessible steep terrain, their detection and mapping is extensive and time consuming. Nonetheless, systematic avalanche detection over large areas could help to generate more complete and up-to-date inventories (cadastres) necessary for validating avalanche forecasting and hazard mapping. In this study, we focused on automatically detecting avalanches and classifying them into release zones, tracks, and run-out zones based on 0.25 m near-infrared (NIR) ADS80-SH92 aerial imagery using an object-based image analysis (OBIA) approach. Our algorithm takes into account the brightness, the normalised difference vegetation index (NDVI), the normalised difference water index (NDWI), and its standard deviation (SDNDWI) to distinguish avalanches from other land-surface elements. Using normalised parameters allows applying this method across large areas. We trained the method by analysing the properties of snow avalanches at three 4 km-2 areas near Davos, Switzerland. We compared the results with manually mapped avalanche polygons and obtained a user's accuracy of > 0.9 and a Cohen's kappa of 0.79-0.85. Testing the method for a larger area of 226.3 km-2, we estimated producer's and user's accuracies of 0.61 and 0.78, respectively, with a Cohen's kappa of 0.67. Detected avalanches that overlapped with reference data by > 80 % occurred randomly throughout the testing area, showing that our method avoids overfitting. Our method has potential for large-scale avalanche mapping, although further investigations into other regions are desirable to verify the robustness of our selected thresholds and the transferability of the method.

  9. Study of gain variation as a function of physical parameters of GEM foil

    CERN Document Server

    Das, Supriya


    The ALICE experiment at LHC has planned to upgrade the TPC by replacing the MWPC with GEM based detecting elements to restrict the IBF to a tolerable value. However the variation of the gain as a function of physical parameters of industrially produced large size GEM foils is needed to be studied as a part of the QA procedure for the detector. The size of the electron avalanche and consequently the gain for GEM based detectors depend on the electric field distribution inside the holes. Geometry of a hole plays an important role in defining the electric field inside it. In this work we have studied the variation of the gain as a function of the hole diameters using Garfield++ simulation package.

  10. Using GIS and Google Earth for the creation of the Going-to-the-Sun Road Avalanche Atlas, Glacier National Park, Montana, USA (United States)

    Peitzsch, Erich H.; Fagre, Daniel B.; Dundas, Mark


    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.

  11. Cosmic Ray Measurements by Scintillators with Metal Resistor Semiconductor Avalanche Photo Diodes (United States)

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


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

  12. Automatic scanning of Cerenkov light photograms from a multistep avalanche chamber using a television digitizer

    International Nuclear Information System (INIS)

    Vascon, M.; Zanella, G.


    A television digitizer and its application to automatic scanning of Cerenkov imaging using the multistep avalanche chamber in front of optical spark chamber are described. The results are of interest in the adoption of the automatic scanning of photographic plates of these events or for the on-line application of the television digitizer itself. (orig.)

  13. Calorimeter detector consisting of a KMgF3 scintillator and parallel-plate avalanche chamber

    International Nuclear Information System (INIS)

    Buzulutskov, A.F.; Turchanovich, L.K.; Vasil'chenko, V.G.


    Scintillations of a KMgF 3 crystal have been detected in the parallel-plate avalanche chamber with a TEA gaseous photocathode, the scintillation signal is shown to be much higher than the direct ionization one. The characteristic properties of the calorimeters on the basis of such structure with electrical and optical readout are discussed. 10 refs.; 4 figs

  14. Smartphone applications for communicating avalanche risk information - a review of existing practices (United States)

    Charrière, M. K. M.; Bogaard, T. A.


    Every year, in all mountainous regions, people are victims of avalanches. One way to decrease those losses is believed to be informing about danger levels. The paper presents a study on current practices in the development of smartphones applications that are dedicated to avalanche risk communication. The analysis based on semi-structured interviews with developers of smartphone apps highlights the context of their development, how choices of content and visualization were made as well as how their effectiveness is evaluated. It appears that although the communicators agree on the message to disseminate, its representation triggers debate. Moreover, only simple evaluation processes are conducted but there is a clear awareness that further scientific efforts are needed to analyze the effectiveness of the smartphone apps. Finally, the current or planned possibility for non-experts users to report feedback on the snow and avalanches conditions open the doors to a transition of these apps from one-way communication tools to two-ways communication platforms. This paper also indicates the remaining challenges that avalanche risk communication is facing, although it is disputably the most advanced and standardized practice compared to other natural hazards. Therefore, this research is of interest for the entire field of natural hazards related risk communication.

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

    Czech Academy of Sciences Publication Activity Database

    Klimeš, Jan; Vilímek, V.; Omelka, M.


    Roč. 50, č. 1 (2009), s. 193-209 ISSN 0921-030X Institutional research plan: CEZ:AV0Z30460519 Keywords : rock debris avalanches * natural hazards * Huascaran Subject RIV: DE - Earth Magnetism, Geodesy, Geography Impact factor: 1.217, year: 2009

  16. Experimental multi-photon-resolving detector using a single avalanche photodiode

    Czech Academy of Sciences Publication Activity Database

    Haderka, Ondřej; Hamar, M.; Peřina ml., Jan


    Roč. 28, - (2004), s. 149-154 ISSN 1434-6060 R&D Projects: GA MŠk LN00A015 Keywords : multichannel detector * avalanche photodiode Subject RIV: BH - Optics, Masers, Lasers Impact factor: 1.692, year: 2004

  17. A new single-photon avalanche diode in 90nm standard CMOS technology

    NARCIS (Netherlands)

    Karami, M.A.; Gersbach, M.; Charbon, E.


    A single-photon avalanche diode (SPAD) fabricated in a 90nm standard CMOS process is reported. The detector comprises an octagonal multiplication region and a guard ring to prevent premature edge breakdown using exclusively standard layers. The proposed structure is the result of a systematic study

  18. Characterization of Single-Photon Avalanche Diodes in Standard 140-nm SOI CMOS Technology

    NARCIS (Netherlands)

    Lee, M.J.; Sun, P.; Charbon, E.


    We report on the characterization of single-photon avalanche diodes (SPADs) fabricated in standard 140-nm silicon on insulator (SOI) complementary metal-oxide-semiconductor (CMOS) technology. As a methodology for SPAD optimization, a test structure array, called SPAD farm, was realized with several

  19. A simple and accurate method for bidimensional position read-out of parallel plate avalanche counters

    International Nuclear Information System (INIS)

    Breskin, A.; Zwang, N.


    A simple method for bidimensional position read-out of Parallel Plate Avalanche counters (PPAC) has been developed, using the induced charge technique. An accuracy better than 0.5 mm (FWHM) has been achieved for both coordinates with 5.5. MeV α-particles at gas pressures of 10-40 torr. (author)

  20. Flexible ultrathin-body single-photon avalanche diode sensors and CMOS integration

    NARCIS (Netherlands)

    Sun, P.; Ishihara, R.; Charbon, E.


    We proposed the world’s first flexible ultrathin-body single-photon avalanche diode (SPAD) as photon counting device providing a suitable solution to advanced implantable bio-compatible chronic medical monitoring, diagnostics and other applications. In this paper, we investigate the Geiger-mode

  1. Massive Formation of Equiaxed Crystals by Avalanches of Mushy Zone Segments (United States)

    Ludwig, A.; Stefan-Kharicha, M.; Kharicha, A.; Wu, M.


    It is well known that the growth and motion of equiaxed crystals govern important microstructural features, especially in larger castings such as heavy ingots. To determine the origin of the equiaxed crystals, heterogeneous nucleation, and/or fragmentation of dendrite arms from columnar regions are often discussed. In the present study, we demonstrate that under certain conditions relatively large areas of mushy regions slide downward and form spectacular crystal avalanches. These avalanches crumble into thousands of dendritic fragments, whereby the larger fragments immediately sediment and the smaller proceed to behave as equiaxed crystals. Traces of such crystal avalanches can be seen by conspicuous equiaxed layers in the lower part of the casting. From the arguments in the discussion, it is believed that such a phenomenon may occur in alloys which reveal an upward solutal buoyancy in the interdendritic mush. This would include certain steels and other alloys such as Cu-Al, Pb-Sn, or Ni-Al-alloys. Moreover, the occurrence of crystal avalanches contribute to the formation of V-segregations.

  2. A parallel plate avalanche detector system for the localization of relativistic heavy ions

    International Nuclear Information System (INIS)

    Burgei, R.; Demoulins, M.; Cavata, C.; Fanet, H.; Gosset, J.; Le Merdy, A.; L'Hote, D.; Lucas, B.; Lugol, J.C.; Poitou, J.; Valette, O.


    Parallel plate avalanche counters have been designed and used for the localization of relativistic heavy ions. They have been tested with alpha particles from a 241 Am source. They have been used with the heavy-ion beams from Saturne in conjunction with the 4π detector Diogene. They provide an accurate measurement of the vertex position with high efficiency. (orig.)

  3. Development of an integrated four-channel fast avalanche-photodiode detector system with nanosecond time resolution (United States)

    Li, Zhenjie; Li, Qiuju; Chang, Jinfan; Ma, Yichao; Liu, Peng; Wang, Zheng; Hu, Michael Y.; Zhao, Jiyong; Alp, E. E.; Xu, Wei; Tao, Ye; Wu, Chaoqun; Zhou, Yangfan


    A four-channel nanosecond time-resolved avalanche-photodiode (APD) detector system is developed at Beijing Synchrotron Radiation. It uses a single module for signal processing and readout. This integrated system provides better reliability and flexibility for custom improvement. The detector system consists of three parts: (i) four APD sensors, (ii) four fast preamplifiers and (iii) a time-digital-converter (TDC) readout electronics. The C30703FH silicon APD chips fabricated by Excelitas are used as the sensors of the detectors. It has an effective light-sensitive area of 10 × 10 mm2 and an absorption layer thickness of 110 μm. A fast preamplifier with a gain of 59 dB and bandwidth of 2 GHz is designed to readout of the weak signal from the C30703FH APD. The TDC is realized by a Spartan-6 field-programmable-gate-array (FPGA) with multiphase method in a resolution of 1ns. The arrival time of all scattering events between two start triggers can be recorded by the TDC. The detector has been used for nuclear resonant scattering study at both Advanced Photon Source and also at Beijing Synchrotron Radiation Facility. For the X-ray energy of 14.4 keV, the time resolution, the full width of half maximum (FWHM) of the detector (APD sensor + fast amplifier) is 0.86 ns, and the whole detector system (APD sensors + fast amplifiers + TDC readout electronics) achieves a time resolution of 1.4 ns.

  4. Progress in high gain inertial confinement fusion

    International Nuclear Information System (INIS)

    Sun Jingwen


    The author reviews the progress in laboratory high gain inertial confinement fusion (ICF), including ICF capsule physics, high-energy-density science, inertial fusion energy, the National Ignition Facility (NIF) and its design of ignition targets and the peta watt laser breakthrough. High power laser, particle beam, and pulsed power facilities around the world have established the new laboratory field of high-energy- density plasma physics and have furthered development of inertial fusion. New capabilities such as those provided by high-brightness peta watt lasers have enabled the study of matter feasible in conditions previously unachievable on earth. Science and technology developed in inertial fusion research have found near-term commercial use and have enabled steady progress toward the goal of fusion ignition and high gain in the laboratory, and have opened up new fields of study for the 21 st century

  5. New Very Low Noise Multilayer And Graded-Gap Avalanche Photodiodes For The 0.8 To 1 .8 μm Wavelength Region (United States)

    Capasso, F.; Tsang, W. T.; Williams, G. F.


    Recent experimental and theoretical results on a new class of low noise avalanche photo-diodes are reviewed. A large enhancement of the impact ionization rates ratio (a/(3=10) has been demonstrated in AlGaAs/GaAs superlattices and graded band gap detector structures. In addition two novel photodiodes ("staircase" and "channeling" APDs) where only electrons multiply, have been proposed. The staircase APD is the solid state analog of the photo-multiplier with discrete dynodes. It has a low operating voltage (5-20 volts) and a lower excess noise factor, in the ideal case, than that of an ideal conventional APD The channeling APD is instead the solid state analog of a channeltron photomultiplier and has the unique feature of an ultrahigh a/β, ratio (≍∞) compatible with high gain (>100).

  6. Developing an Experimental Simulation Method for Rock Avalanches: Fragmentation Behavior of Brittle Analogue Material (United States)

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


    Gravitational mass movement on earth and other planets show a scale dependent behavior, of which the physics is not fully understood. In particular, the runout distance for small to medium sized landslides (volume dynamics control small and large landslides/rock avalanches. Several mechanisms have been proposed to explain this scale dependent behavior, but no consensus has been reached. Experimental simulations of rock avalanches usually involve transport of loose granular material down a chute. Though such granular avalanche models provide important insights into avalanche dynamics, they imply that the material fully disintegrate instantaneously. Observations from nature, however, suggests that a transition from solid to "liquid" occurs over some finite distance downhill, critically controlling the mobility and energy budget of the avalanche. Few experimental studies simulated more realistically the material failing during sliding and those were realized in a labscale centrifuge, where the range of volumes/scales is limited. To develop a new modeling technique to study the scale dependent runout behavior of rock avalanches, we designed, tested and verified several brittle materials allowing fragmentation to occur under normal gravity conditions. According to the model similarity theory, the analogue material must behave dynamically similar to the rocks in natural rock avalanches. Ideally, the material should therefore deform in a brittle manner with limited elastic and ductile strains up to a certain critical stress, beyond which the material breaks and deforms irreversibly. According to scaling relations derived from dimensional analysis and for a model-to-prototype length ratio of 1/1000, the appropriate yield strength for an analogue material is in the order of 10 kPa, friction coefficient around 0.8 and stiffness in the order of MPa. We used different sand (garnet, quartz) in combination with different matrix materials (sugar, salt, starch, plaster) to cement

  7. Volcanic avalanche fault zone with pseudotachylite and gouge in French Massif Central (United States)

    Bernard, Karine; van Wyk de Vries, Benjamin


    Structures and textures with sedimentological variations at different scales of the lithofacies assemblage help us to constrain the basal kinematic transition from non-depositional to depositional conditions during volcanic avalanche emplacement. In the well-exposed impact-sheared contact along volcanic avalanche fault zone in the French Massif Central, we observe how the granular textures of the pseudotachylite and fault gouge have recorded the propagation of shock wave with granular oscillatory stress. Sequential events of basal aggradation along avalanche fault zone have been established related to fractal D-values, temperature pressure regime and oscillatory stress during slow wave velocity. A typical lithofacies assemblage with a reverse grading shows the pseudotachylite and fault gouge. A cataclastic gradient is characterised by the fractal D-values from 2.7 in jigsaw breccias with pseudotachylite partial melt, to 2.6 in the polymodal gouge. Shock, brecciation and comminution produce cataclastic shear bands in the pseudotachylite and quartz microstructures along the basal contact of the volcanic debris-avalanche deposit. Gouge microstructures show granular segregation, cataclasis with antithetic rotational Riedel shear, and an arching effect between the Riedel shear bands. X-ray microtomography provided 3D microfabrics along the clastic vein in the sandy-gouge. From the available statistical dataset, a few equations have been developed implicating the same cataclastic origin with a co-genetic evolution of lithofacies. An impact wave during primary shear propagation may contribute to produce hydroclastic matrix, pseudotachylite partial melt and proximal gouge thixotropy with v 50m/s and a T < 654 °C. The interseismic period with oscillatory stress is related to crushed clasts and basaltic melt around 800 °C, Riedel shear bands with granular segregation along the fault gouge. The secondary shock by matrix-rich avalanche (ΔP = 10GPa, T ≥ 1000-1500

  8. Study of multi anode photo multiplier tubes at low gains

    CERN Document Server

    Eisenhardt, S; Bibby, J; Libby, J


    We describe a preliminary study of the signal shape of the Multianode Photo Multiplier Tubes (MaPMT) at low gain. We investigate the feasibility of running the MaPMT at gains of around 30000 e which would allow to use front-end chips that have been developed for silicon detectors or micro strip gas chambers. In addition we have investigated the focusing properties of an improved design of the MaPMT.

  9. Operational gain : measuring the capture of genetic gain ...

    African Journals Online (AJOL)

    Operational gain : measuring the capture of genetic gain : operational deployment of technology. ... The concept of operational gain is more than the weighted average of the genetic quality of planted hectares, and encompasses tree breeding efficiencies, propagation efficiencies, matching of species and genotype to site, ...

  10. Wet and full-depth glide snow avalanche onset monitoring and detection with ground based Ku-band radar (United States)

    Lucas, Célia; Bühler, Yves; Leinss, Silvan; Hajnsek, Irena


    Wet and full-depth glide snow avalanches can be of considerable danger for people and infrastructure in alpine regions. In Switzerland avalanche hazard predictions are performed by the Institute for Snow and Avalanche Research SLF. However these predictions are issued on regional scale and do not yield information about the current status of particular slopes of interest. To investigate the potential of radar technology for avalanche prediction on the slope scale, we performed the following experiment. During the winter seasons 2015/2016 and 2016/2017, a ground-based Ku-band radar was placed in the vicinity of Davos (GR) in order to monitor the Dorfberg slope with 4-minute measurement intervals [1]. With Differential Interferometry [2] line of sight movements on the order of a fraction of the radar wavelength (1.7 cm) can be measured. Applying this technique to the Dorfberg scenario, it was possible to detect snowpack displacement of up to 0.4 m over 3 days in the avalanche release area prior to a snow avalanche event. A proof of concept of this approach was previously made by [3-5]. The analysis of the snowpack displacement history of such release areas shows that an avalanche is generally released after several cycles of acceleration and deceleration of a specific area of the snowpack, followed by an abrupt termination of the movement at the moment of the avalanche release. The acceleration and deceleration trends are related to thawing and refreezing of the snowpack induced by the daily temperature variations. The proposed method for the detection of snowpack displacements as indication for potential wet and full-depth glide snow avalanches is a promising tool to increase avalanche safety on specific slopes putting infrastructure or people at risk. The identification of a singular signature to discriminate the time window immediately prior to the release is still under investigation, but the ability to monitor snowpack displacement allows for mapping of zones

  11. Advanced radiation detector development mercuric iodide, silicon with internal gain, hybrid scintillator/semiconductor detectors. Comprehensive summary report, 1976-1985

    International Nuclear Information System (INIS)

    Huth, G.C.; Dabrowski, A.J.


    Accomplishments are reported in the development of a compound semi-insulator mercuric iodide (HgI 2 ) for nuclear radiation detection and spectroscopy, early lung cancer detection and localization in the uranium miner/worker population, computer digital image processing and image reconstruction research, and a concept for multiple, filtered x-ray computed tomography scanning to reveal chemical compositional information. Another area of interest is the study of new advances in the area of silicon detectors with internal gain (''avalanche'')

  12. The mobility of rock avalanches: disintegration, entrainment and deposition - a conceptual approach (United States)

    Knapp, Sibylle; Mamot, Philipp; Krautblatter, Michael


    Massive rock slope failures cause more than 60% of all catastrophic landslide disasters. Failures usually progress through three consecutive phases: detachment, disintegration and flow. While significant advances have been achieved in modelling Rock Avalanche Phase 1 "Detachment" and Phase 3 "Flow", the crucial link between both during Phase 2 "Disintegration", is still poorly understood. Disintegration of the detached rock mass is often initiated by its first major impact with the ground surface. This is a preliminary setup of a PhD project in which we aim at understanding the importance of disintegration and on site conditions at the impact site on fluidization and mobilization. The TUM Landslides Group is experienced in near surface geophysics of rockwalls and under Alpine conditions and has also developed laboratory experience in testing resistivity and P-/S-wave velocity of anisotropic and fractured rocks in the laboratory. In addition, there is a more than ten year experience in the analysis of different magnitudes of rock slope failure. Many of these studies took part in the Wetterstein Mountains and close to the Zugspitze. In this project we plan to compare one very small (Steingerümpel, Rein valley, Germany, with 0.003 km³) and two larger test sites (Eibsee, Zugspitze area, Germany, with 0.3 km³ and Flims, Grisons, Switzerland, with 12 km³) situated in limestone rocks. From our preliminary work we know that the Steingerümpel bergsturz shows a low degree of fracturing in spite of a high impact; the latter ones are high-magnitude rock slope failures which both partially collapsed into a lake and were highly disintegrated and fluidized. We intend to use the smaller Eibsee rock avalanche as a training site where we can try to understand the full dynamics of the flow using sedimentology, geophysics and surface geomorphology which indicated compressive and extensional flow, superelevation and runups. Regarding entrainment processes, we will carry out a

  13. First characterisation of the "Rumi-Pana" rock avalanche deposits (Famatina Range, La Rioja, Argentina) (United States)

    Santiago Pullarello, José; Derron, Marc-Henri; Penna, Ivanna; Leiva, Alicia; Jaboyadoff, Michel


    Active mountain fronts are subject to large scale slope collapses which have the capacity to run long distances on piedmont areas. Along time, fluvial activity and other gravitatory processes can intensively erode and mask primary features related to the collapses. Therefore, to reconstruct the history of their occurrence, further analyses are needed, e.g. sedimentologic analyses. This work focuses on the occurrence of large rock avalanches in the Vinchina region, La Rioja (28°43'27.81'' S / 68°00'25.42'' W) on the western side of the Famatina range(Argentina). Here, photointerpretation of high resolution satellite images (Google Earth) allowed us to identify two rock avalanches, main scarps developed at 2575 and 2750 m a.s.l. . There are no absolute ages for these deposits, however, comparing their preservation degree with those dated further north (in similar climatic and landscape dynamics contexts [i]), we can suggest these rock avalanches took place during the Pleistocene. We carried out a fieldwork survey in this remote area, including classical landslide mapping, structural analysis, deposits characterization and sampling. The deposits reach the valley bottom (at around 1700 m a.s.l.) with runouts about 5 and 5.3 km long. In one of the cases, the morphology of the deposit is well preserved, allowing to reconstruct accurately its extension. However, in the second case, the deposits are strongly eroded by courses draining the mountain front, therefore further analyses should be done to reconstruct its extension. In addition to morphologic interpretations, a multiscale grain-size analysis was done to differentiate rock avalanches from other hillslope deposits: (1) 3D surface models of surface plots (5x5m) have been built by SfM photogrammetry; 2) classical sieving and 3) laser grain-size analysis of deposits. Samples were collected on different parts of the slope, but also along cross sections through the avalanche deposit. This deposits characterization will

  14. A simulated avalanche search and rescue mission induces temporary physiological and behavioural changes in military dogs. (United States)

    Diverio, Silvana; Barbato, Olimpia; Cavallina, Roberta; Guelfi, Gabriella; Iaboni, Martina; Zasso, Renato; Di Mari, Walter; Santoro, Michele Matteo; Knowles, Toby G


    Saving human lives is of paramount importance in avalanche rescue missions. Avalanche military dogs represent an invaluable resource in these operations. However, their performance can be influenced by several environmental, social and transport challenges. If too severe, these are likely to activate a range of responses to stress, which might put at risk the dogs' welfare. The aim of this study was to assess the physiological and behavioural responses of a group of military dogs to a Simulated Avalanche Search and Rescue mission (SASR). Seventeen avalanche dogs from the Italian Military Force Guardia di Finanza (SAGF dogs) were monitored during a simulated search for a buried operator in an artificial avalanche area (SASR). Heart rate (HR), body temperature (RBT) and blood samples were collected at rest the day before the trial (T0), immediately after helicopter transport at the onset of the SASR (T1), after the discovery of the buried operator (T2) and 2h later (T3). Heart rate (HR), rectal body temperature (RBT), cortisol, aspartate aminotransferase (AST), creatine kinase (CK), non-esterified fatty acids (NEFA) and lactate dehydrogenase (LDH) were measured. During the search mission the behaviour of each SAGF dog was measured by focal animal sampling and qualitatively assessed by its handler and two observers. Inter-rater agreement was evaluated. Snow and environmental variables were also measured. All dogs successfully completed their search for the buried, simulated victim within 10min. The SASR was shown to exert significant increases on RBT, NEFA and cortisol (Pdog's search mission ability was found only for motivation, signalling behaviour, signs of stress and possessive reward playing. More time signalling was related to shorter search time. In conclusion, despite extreme environmental and training conditions only temporary physiological and behavioural changes were recorded in the avalanche dogs. Their excellent performance in successful simulated SASR

  15. Ultraviolet AlGaN-based Avalanche Photo Diode Grown over Single Crystal Bulk AlN Substrates, Phase I (United States)

    National Aeronautics and Space Administration — Premature breakdown is a key obstacle in developing AlGaN-based avalanche photo diodes (APD) for ultraviolet (UV) light detection. Novel materials growth techniques,...

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

    Directory of Open Access Journals (Sweden)

    R. Sailer


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

  17. GaN-based, low-voltage avalanche photodiodes for robust and compact UV imagers, Phase I (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...

  18. Intrinsic Bistability and Critical Slowing in Tm3+/Yb3+ Codoped Laser Crystal with the Photon Avalanche Mechanism

    International Nuclear Information System (INIS)

    Li, Li; Li-Xue, Chen; Xin-Lu, Zhang


    We present theoretically a novel intrinsic optical bistability (IOB) in the Tm 3+ /Yb 3+ codoped system with a photon avalanche mechanism. Numerical simulations based on the rate equation model demonstrate distinct IOB hysteresis and critical slowing dynamics around the avalanche thresholds. Such an IOB characteristic in Tm 3+ /Yb 3+ codoped crystal has potential applications in solid-state bistable optical displays and luminescence switchers in visible-infrared spectra. (fundamental areas of phenomenology (including applications))

  19. Sudden gains versus gradual gains in a psychotherapy training clinic. (United States)

    Greenfield, Michael F; Gunthert, Kathleen C; Haaga, David A F


    Sudden gains are abrupt and substantial improvements in symptoms. This study used the Outcome Questionnaire-45 (OQ-45; Lambert et al., 1996) to characterize sudden gains occurring in a cognitive-behavioral therapy training clinic. Also, gradual gainers were identified and used as a comparison group. Sudden gains were identified in 23% of patients and in 29% of those who entered treatment in the clinical range on the OQ, within the range of prevalence established by previous sudden gain studies in the context of randomized controlled trials (RCT's). As in earlier research, sudden gains tended to occur early in therapy. However, sudden gains were more likely to be reversed than in RCT's. Gradual gains occurred for 54% of nonsudden gainers; they were of similar magnitude to sudden gains but occurred later in therapy. Sudden gainers showed significantly better outcomes at the end of treatment than did gradual gainers. Sudden gains have clear prognostic significance, but more research is needed to determine why they may be more transient in naturalistic studies or studies involving less experienced therapists than they are in RCT's. © 2010 Wiley Periodicals, Inc.

  20. Snow-avalanche modeling and hazard level assessment using statistical and physical modeling, DSS and WebGIS: case study from Czechia (United States)

    Blahut, J.; Balek, J.; Juras, R.; Klimes, J.; Klose, Z.; Roubinek, J.; Pavlasek, J.


    Snow-avalanche modeling and hazard level assessment are important issues to be solved within mountain regions worldwide. In Czechia, there are two mountain ranges (Krkonoše and Jeseníky Mountains), which suffer from regular avalanche activity every year. Mountain Rescue Service is responsible for issuing avalanche bulletins. However, its approaches are still lacking objective assessments and procedures for hazard level estimations. This lack is mainly caused by missing expert avalanche information system. This paper presents preliminary results from a project funded by the Ministry of Interior of the Czech Republic. This project is focused on development of an information system for snow-avalanche hazard level forecasting. It is composed of three main modules, which should act as a Decision Support System (DSS) for the Mountain Rescue Service. Firstly, snow-avalanche susceptibility model is used for delimiting areas where avalanches can occur based on accurate statistical analyses. For that purpose a waste database is used, containing more than 1100 avalanche events from 1961/62 till present. Secondly, a physical modeling of the avalanches is being performed on avalanche paths using RAMMS modeling code. Regular paths, where avalanches occur every year, and irregular paths are being assessed. Their footprint is being updated using return period information for each path. Thirdly, snow distribution and stability models (distributed HBV-ETH, Snowtran 3D, Snowpack and Alpine 3D) are used to assess the critical conditions for avalanche release. For calibration of the models data about meteo/snow cover data and snowpits is used. Those three parts are being coupled in a WebGIS platform used as the principal component of the DSS in snow-avalanche hazard level assessment.

  1. Exploring the significance of the fluidized flow regime for avalanche hazard mapping (United States)

    Issler, Dieter; Gauer, Peter

    Observational and experimental evidence suggests that it is important to explicitly account for the fluidized flow regime in avalanche hazard mapping due to its high mobility, intermediate density and high velocity. We explore the differences from conventional runout modelling by implementing an extension of the Norem-Irgens-Schieldrop (NIS) rheology in a simple mass-point model. When the dispersive stresses and the excess pore pressure equal the overburden pressure, the flow height increases and the density diminishes until a new equilibrium is reached, determined by the different density dependencies of the two parameters of the dispersive stresses. Fluidization requires sufficiently steep terrain; when it occurs it leads to substantially higher velocities than compared to the dense-flow regime. The model parameters are strongly constrained by their physical meaning and vary little between widely different avalanches. However, in all test cases we obtained better agreement between simulated and observed runout distances and pressure effects than with conventional models.

  2. Mapping snow avalanche risk using GIS technique and 3D modeling in Ceahlau Mountain (United States)

    Covasnianu, A.; Grigoras, I. R.; State, L. E.; Balin, D.; Hogas, S.; Balin, I.


    This study consisted in a precise mapping project (GPS field campaign and on-screen digitization of the topographic maps at 1:5.000 scale) of the Ceahlau mountain area in Romanian Carpathians in order to address the snow avalanche risk management, surveying and monitoring. Thus we considered the slope, aspect, altitude, landforms and roughness derived from a high resolute numerical terrain model (31 km2 at 1: 5.000 scale resulted in a spatial resolution of 3 m by the help of Topo to Raster tool). These parameters were classified according to a model applied into Tatra Mountains and used over Ceahlau Massive. The results were adapted and interpreted considering to the European Avalanche Hazard Scale. This work was made in the context of the elaboration of Risk Map and is directly concerning both the security of tourism activities but also the management of the Natural Park Ceahlau. The extension of this method to similar mountain areas is ongoing.

  3. Modelling results of avalanche multiplication in AlGaAs soft X-ray APDs

    Energy Technology Data Exchange (ETDEWEB)

    Barnett, A.M., E-mail: [Space Research Centre, Department of Physics and Astronomy, Michael Atiyah Building, University of Leicester, Leicester LE1 7RH (United Kingdom); Lees, J.E.; Bassford, D.J. [Space Research Centre, Department of Physics and Astronomy, Michael Atiyah Building, University of Leicester, Leicester LE1 7RH (United Kingdom); Ng, J.S.; Tan, C.H.; Gomez, R.B. [Department of Electronic and Electrical Engineering, University of Sheffield, Mappin Street, Sheffield S1 3JD (United Kingdom)


    First results from a new simple simulation of X-ray spectroscopy with an Al{sub 0.8}Ga{sub 0.2}As p{sup +}-p{sup -}-n{sup +} spectroscopic X-ray photon counting avalanche photodiode are presented and compared with experimentally obtained data. Particular attention is paid to the experimentally observed phenomenon of an additional peak being present in the spectrum from a radioisotope source that, whilst previously reported, had not been fully explained. The additional peak is shown to result from the unequal distributions of multiplications undergone by the charge carriers created by photons absorbed in the p{sup +} and p{sup -} layers. The consequences of this effect for future AlGaAs X-ray photon counting avalanche photodiode designs are discussed.

  4. Performance and simulation of a double-gap resistive plate chamber in the avalanche mode

    CERN Document Server

    Ahn Sung Hwan; Hong Byung Sik; Hong Seong Jong; Ito, M; Kang, T I; Kim, B I; Kim, J H; Kim, Y J; Kim, Y U; Koo, D G; Lee Hyup Woo; Lee, K B; Lee Kyong Sei; Lee Seok Jae; Lim, J K; Moon, D H; Nam, S K; Park, S; Park, W J; Rhee June Tak; Ryu, M S; Sim Kwang Souk


    We present a detailed analysis of the time and the charge signals of a prototype double-gap resistive plate chamber for the endcap region of the Compact Muon Solenoid (CMS) detector at the Large Hadron Collider (LHC). The chamber was built with relatively low-resistivity bakelite. The time and the charge results demonstrate that the high- voltage plateau, which satisfies various CMS requirements for the efficiency, the noise cluster rate, the fraction of the large signal, and the streamer probability, can be extended at least up to 400 V with the present design. In addition, a simple avalanche multiplication model is studied in detail. The model can reproduce the experimental charge spectra reasonably well. The charge information enables us to estimate the effective Townsend coefficient in avalanche-mode operation.

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

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


    The Tancitaro is an andesitic-dacitic stratovolcano located in the Michoacán Guanajuato volcanic field within the west-central portion of the trans-Mexican Volcanic Belt. The volcanism in this area is characterized by two composite volcanoes, the highest of which is the Tancitaro volcanic edifice (3840 m), some low angle lava cones and more than 1,000 monogenetic cinder cones. The distribution of the cinder cones is controlled by NE-SW active faults, although there are also additional faults with NNW-SSE trends along which some cones are aligned. The Tancitaro stratovolcano is located at the intersection of the tectonical structures that originate these alignments. All this geological activity has contributed to the gravitational instability of the volcano, leading to a huge sector collapse which produced the investigated debris avalanche. The collapse structure is an east-facing horseshoe-shaped crater (4 km wide and 5.3 km long), related with a large fan that was deposited within the Tepalcatepec depression. The deposit starts only 7 km downslope from the failure scar, it is 66 km long and covers an area of approximately 1155 km2. The landslide magnitude is about 20 km3 and it was firstly determined by the reconstruction of the paleo-edifice using a GIS software and then validated by the observation of significant outcrops. The fan was primarily formed by the deposit of this huge debris avalanche and subsequently by debris flow and fluvial deposits. Field investigations on the fan area highlighted the presence of two texturally distinct parts, which are referred to the 'block facies' and the 'matrix facies'. The first sedimentary structure is responsible for the typical hummock morphologies in the proximal area, as seen in many other debris avalanche deposits. Instead in the distal zones, the deposit is made up by the 'mixed block and matrix facies'. Blocks and megablocks, some of which are characterized by a jigsaw puzzle texture, gradually decrease in size

  6. Increasing power-law range in avalanche amplitude and energy distributions (United States)

    Navas-Portella, Víctor; Serra, Isabel; Corral, Álvaro; Vives, Eduard


    Power-law-type probability density functions spanning several orders of magnitude are found for different avalanche properties. We propose a methodology to overcome empirical constraints that limit the range of truncated power-law distributions. By considering catalogs of events that cover different observation windows, the maximum likelihood estimation of a global power-law exponent is computed. This methodology is applied to amplitude and energy distributions of acoustic emission avalanches in failure-under-compression experiments of a nanoporous silica glass, finding in some cases global exponents in an unprecedented broad range: 4.5 decades for amplitudes and 9.5 decades for energies. In the latter case, however, strict statistical analysis suggests experimental limitations might alter the power-law behavior.

  7. Change in snow avalanche and debris flow hazards in the region of Krasnaya Polyana as the result of anthropogenic activity (United States)

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


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

  8. Gain characteristics of a 100 μm thick GEM in Krypton-CO2 mixtures (United States)

    Roque, R. C.; Natal da Luz, H.; Carramate, L. F. N. D.; Azevedo, C. D. R.; Mir, J. A.; Amaro, F. D.


    The operation of a Micropattern Gaseous Detector (MPGD) comprising a cascade of two non-standard Gas Electron Multipliers (GEM) made from a 100 μm kapton foil was evaluated in pure krypton and in krypton-CO2 mixtures. The final avalanche charge was collected in a 2D strip readout, providing an active area of 10×10 cm2 for the entire detection system. For each mixture, the effective gain and energy resolution were measured as a function of the electric field in the drift, transfer and induction regions. Using X-rays from a 55Fe radioactive source (5.9 keV), gains close to 104 and energy resolution of 22% (FWHM) were achieved in pure krypton under stable conditions, showing the potential of the experimental setup for the following imaging studies.

  9. In-situ observations of the April 2014 Mount Everest Avalanche (United States)

    Moore, Kent; Cristofanelli, Paolo; Bonasoni, Paolo; Pietro Verza, Gian; Semple, John


    Instrumental records indicate a warming of approximately 0.8oC has occurred in the Everest region since the 1980s that has resulted in a 100-300m rise in the height at which the ground is permanently frozen as well as a retreat and thinning of Everest's glaciers. This period of warming has coincided with Mount Everest becoming an increasingly important destination for both climbers and trekkers. For some time, there have been concerns that this warming and the resultant changes in the region's glaciers may be increasing the risks for both travellers to Mount Everest as well as the indigenous populations who support them. On April 18 2014, an avalanche caused by the collapse of a large serac swept down Mount Everest's Khumbu Ice Fall resulting in the deaths of 16 Sherpa. Although satellite imagery has been used to estimate the size of the serac, in-situ data on the avalanche itself has not been available. Here we show that this event was of a sufficient size as to result in the excitation of a 20 min long 'avalanche wind' that was observed at the Nepal Climate Observatory-Pyramid situated 12 km from Mount Everest. We use these observations to estimate that the winds at Everest Base Camp during this event were of hurricane strength. As a result of the destabilization of the region's glaciers due to the climate change, there are concerns that such events may become more frequent. These results provide the basis for a method to estimate the frequency and severity of avalanches in this region.

  10. Performances of Resistive Plate chamber Operated in Avalanche Mode under 137Cs Irradiation

    CERN Document Server

    Abbrescia, Marcello; Gianini, Gabriele; Iaselli, Giuseppe; Maggi, Marcello; Marangelli, Bartolomeo; Natali, Sergio; Nuzzo, Salvatore; Ranieri, Antonio; Ratti, Sergio P; Romano, Francesco; Vitulo, Paolo


    A 2 mm gas RPC with bakelite plates has been operated in avalanche mode under 137Cs source irradiation. We report on measurements of the efficiency in cosmic rays detection and of the charge developed in the gap, performed for different gas mixtures. We show that C2H2F4 based mixtures exhibit a wide full efficiency plateau with low streamer probability, while the argon based mixtures allow to reduce the detector power consumption

  11. Light from electron avalanches and background rejection in X-ray astronomy

    International Nuclear Information System (INIS)

    Siegmund, O.H.W.; Sanford, P.W.; Mason, I.M.; Culhane, J.L.; Cockshott, R.


    A modified version of the parallel plate imaging proportional counter, developed to register images of cosmic x-ray sources in the focal planes of x-ray telescopes, has been constructed to investigate the application of risetime discrimination to the scintillation pulses caused by the electron avalanche process. It is shown that efficient background event rejection (> 90%) is achieved and the application of this system for x-ray astronomy is discussed. (U.K.)

  12. Network dynamics in nociceptive pathways assessed by the neuronal avalanche model

    Directory of Open Access Journals (Sweden)

    Wu José


    Full Text Available Abstract Background Traditional electroencephalography provides a critical assessment of pain responses. The perception of pain, however, may involve a series of signal transmission pathways in higher cortical function. Recent studies have shown that a mathematical method, the neuronal avalanche model, may be applied to evaluate higher-order network dynamics. The neuronal avalanche is a cascade of neuronal activity, the size distribution of which can be approximated by a power law relationship manifested by the slope of a straight line (i.e., the α value. We investigated whether the neuronal avalanche could be a useful index for nociceptive assessment. Findings Neuronal activity was recorded with a 4 × 8 multichannel electrode array in the primary somatosensory cortex (S1 and anterior cingulate cortex (ACC. Under light anesthesia, peripheral pinch stimulation increased the slope of the α value in both the ACC and S1, whereas brush stimulation increased the α value only in the S1. The increase in α values was blocked in both regions under deep anesthesia. The increase in α values in the ACC induced by peripheral pinch stimulation was blocked by medial thalamic lesion, but the increase in α values in the S1 induced by brush and pinch stimulation was not affected. Conclusions The neuronal avalanche model shows a critical state in the cortical network for noxious-related signal processing. The α value may provide an index of brain network activity that distinguishes the responses to somatic stimuli from the control state. These network dynamics may be valuable for the evaluation of acute nociceptive processes and may be applied to chronic pathological pain conditions.

  13. 1000-V, 300-ps pulse-generation circuit using silicon avalanche devices (United States)

    Benzel, D. M.; Pocha, M. D.


    A Marx configured avalanche transistor string and a pulse rise-time peaking diode are used to generate pulses of >1000 V into a 50-Ω load with rise times of less than 300 ps. The trigger delay of this circuit is about 7-10 ns, with jitter <100 ps. This circuit has been used to generate pulses at a repetition rate up to 5 kHz.

  14. Rock avalanche and rock glacier: A compound landform study from Hornsund, Svalbard

    Czech Academy of Sciences Publication Activity Database

    Hartvich, Filip; Blahůt, Jan; Stemberk, Josef


    Roč. 276, JAN 1 (2017), s. 244-256 ISSN 0169-555X R&D Projects: GA MŠk(CZ) LM2015079; GA MŠk(CZ) LG15007 Institutional support: RVO:67985891 Keywords : ERT * TLS (LiDAR) * lichenometry * morphometry * rock avalanche * rock glacier * Schmidt hammer * Svalbard * Hornsund Subject RIV: DB - Geology ; Mineralogy OBOR OECD: Geology Impact factor: 2.958, year: 2016

  15. Snow fracture in relation to slab avalanche release: critical state for the onset of crack propagation


    J. Gaume; A. van Herwijnen; G. Chambon; N. Wever; J. Schweizer


    The failure of a weak snow layer buried below cohesive slab layers is a necessary, but insufficient, condition for the release of a dry-snow slab avalanche. The size of the crack in the weak layer must also exceed a critical length to propagate across a slope. In contrast to pioneering shear-based approaches, recent developments account for weak layer collapse and allow for better explaining typical observations of remote triggering from low-angle terrain. However, these new...

  16. Burial duration, depth and air pocket explain avalanche survival patterns in Austria and Switzerland. (United States)

    Procter, Emily; Strapazzon, Giacomo; Dal Cappello, Tomas; Zweifel, Benjamin; Würtele, Andreas; Renner, Andreas; Falk, Markus; Brugger, Hermann


    To calculate the first Austrian avalanche survival curve and update a Swiss survival curve to explore survival patterns in the Alps. Avalanche accidents occurring between 2005/06 and 2012/13 in Austria and Switzerland were collected. Completely buried victims (i.e. burial of the head and chest) in open terrain with known outcome (survived or not survived) were included in the analysis. Extrication and survival curves were calculated using the Turnbull algorithm, as in previous studies. 633 of the 796 completely buried victims were included (Austria n=333, Switzerland n=300). Overall survival was 56% (Austria 59%; Switzerland 52%; p=0.065). Time to extrication was shorter in Austria for victims buried ≤60min (p15min. The survival curves resembled those previously published and support the idea that underlying survival patterns are reproducible. The results are in accordance with current recommendations for management of avalanche victims and serve as a reminder that expedient companion rescue within a few minutes is critical for survival. An air pocket was shown to be a positive prognostic factor for survival. Copyright © 2016 Elsevier Ireland Ltd. All rights reserved.

  17. Prediction of electromagnetic pulse generation by picosecond avalanches in high-pressure air

    International Nuclear Information System (INIS)

    Mayhall, D.J.; Yee, J.H.


    The gas avalanche switch is a laser-activated, high-voltage switch, consisting of a set of pulse-charged electrodes in a high-pressure gas. Induced electrons from a picosecond-scale laser pulse initiate an avalanche discharge between high-voltage and grounded electrodes. If the voltage, pressure, and dimensions are correct, the rapid avalanche, fueled by the immense number of electrons available in the gas, collapses the applied voltage in picoseconds and generates electromagnetic pulses with widths as short as 1-10 ps and 3 dB bandwidths of 20-120 GHz. With proper voltage or pressure detuning, wider pulses and lower bandwidths occur. In addition to picosecond electromagnetic pulse generation, application of this switch should result in ultra-fast Marx bank pulsers. A number of versions of the switch are possible. The simplest is a parallel plate capacitor, consisting of a gas between two parallel plate conductors. High voltage is applied across the two plates. A parallel plate, Blumlein geometry features a center electrode between two grounded parallel plates. This geometry emits a single pulse in each direction along the parallel plates. A frozen wave geometry with multiple, oppositely charged center electrodes will emit AC pulses. Series switches consisting of gas gaps between two electrodes are also possible

  18. Comparison of measurements and modeling of beam ion loss during TAE avalanches in NSTX (United States)

    Darrow, Douglass; Crocker, N.; Fredrickson, E.; Gorelenkov, N.; Podesta, M.; Shi, L.; White, R.


    Brief `avalanches' of toroidal Alfvén eigenmodes (TAEs) are observed in NSTX plasmas having several different n numbers simultaneously present. All are accompanied by a drop in the neutron rate, indicating likely loss of beam ions. However, the scintillator fast ion loss detector at the wall on NSTX registers losses only for some avalanches and not others. When losses are seen, they cover a wide range of pitch angles, suggesting that the modes cause stochasticity in the beam ion phase space. A 16 channel array of microwave reflectometers provides a radial profile of the structure of each n TAE, which can then be used to produce an absolute amplitude for a TAE mode structure computed by the NOVA code for the plasma at the time of interest. Using the equilibrium plus the TAE modes structures in the guiding center code ORBIT then allows modeling of the effect of the avalanches on beam ion orbits. The modeling does reveal stochastic behavior and loss of some classes of orbits that are populated by the neutral beams on NSTX, with an amplitude threshold for loss that is close to that observed in the experiments. This work supported by US DoE contract DE-ACO2-09CH11466 and the China Scholarship Council.

  19. Neural avalanches at the critical point between replay and non-replay of spatiotemporal patterns.

    Directory of Open Access Journals (Sweden)

    Silvia Scarpetta

    Full Text Available We model spontaneous cortical activity with a network of coupled spiking units, in which multiple spatio-temporal patterns are stored as dynamical attractors. We introduce an order parameter, which measures the overlap (similarity between the activity of the network and the stored patterns. We find that, depending on the excitability of the network, different working regimes are possible. For high excitability, the dynamical attractors are stable, and a collective activity that replays one of the stored patterns emerges spontaneously, while for low excitability, no replay is induced. Between these two regimes, there is a critical region in which the dynamical attractors are unstable, and intermittent short replays are induced by noise. At the critical spiking threshold, the order parameter goes from zero to one, and its fluctuations are maximized, as expected for a phase transition (and as observed in recent experimental results in the brain. Notably, in this critical region, the avalanche size and duration distributions follow power laws. Critical exponents are consistent with a scaling relationship observed recently in neural avalanches measurements. In conclusion, our simple model suggests that avalanche power laws in cortical spontaneous activity may be the effect of a network at the critical point between the replay and non-replay of spatio-temporal patterns.

  20. Snow instability evaluation in skier-triggered snow slab avalanches: combining failure initiation and crack propagation (United States)

    Gaume, Johan; Reuter, Benjamin


    Dry-snow slab avalanches start with a local failure in a weak snowpack layer buried below cohesive snow slab layers. If the size of the failed zone exceeds a critical size, rapid crack propagation occurs possibly followed by slab release if the slope is steep enough. The probability of skier-triggering a slab avalanche is generally characterized by classical stability indices that do not account for crack propagation. In this study, we propose a new model to evaluate the conditions for the onset of crack propagation in skier-triggered slab avalanches. For a given weak layer, the critical crack length characterizing crack propagation propensity was compared to the size of the area where the skier-induced stress exceeds the shear strength of the weak layer. The ratio between both length scales yields a stability criterion combining the processes of failure initiation and crack propagation. The critical crack length was calculated from a recently developed model based on numerical simulations. The skier-induced stress was computed from analytical solutions and finite element simulations to account for slab layering. A detailed sensitivity analysis was performed for simplified snow profiles to characterize the influence of snowpack properties and slab layering on crack propagation propensity. Finally, we applied our approach for manually observed snow profiles and compared our results to rutschblock stability tests.

  1. Memory effect in gated single-photon avalanche diodes: a limiting noise contribution similar to afterpulsing (United States)

    Contini, D.; Dalla Mora, A.; Di Sieno, L.; Cubeddu, R.; Tosi, A.; Boso, G.; Pifferi, A.


    In recent years, emerging applications, such as diffuse optical imaging and spectroscopy (e.g., functional brain imaging and optical mammography), in which a wide dynamic range is crucial, have turned the interest towards Single-Photon Avalanche Diode (SPAD). In these fields, the use of a fast-gated SPAD has proven to be a successful technique to increase the measurement sensitivity of different orders of magnitude. However, an unknown background noise has been observed at high illumination during the gate-OFF time, thus setting a limit to the maximum increase of the dynamic range. In this paper we describe this noise in thin-junction silicon single-photon avalanche diode when a large amount of photons reaches the gated detector during the OFF time preceding the enabling time. This memory effect increases the background noise with respect to primary dark count rate similarly to a classical afterpulsing process, but differently it is not related to a previous avalanche ignition in the detector. We discovered that memory effect increases linearly with the power of light impinging on the detector and it has an exponential trend with time constants far different from those of afterpulsing and independently of the bias voltage applied to the junction. For these reasons, the memory effect is not due to the same trapping states of afterpulsing and must be described as a different process.

  2. Drainage evolution in the debris avalanche deposits near Mount Saint Helens, Washington (United States)

    Beach, G. L.; Dzurisin, D.


    The 18 May 1980 eruption of Mount St. Helens was initiated by a massive rockslide-debris avalanche which completely transformed the upper 25 km of the North Fork Toutle River valley. The debris was generated by one of the largest gravitational mass movements ever recorded on Earth. Moving at an average velocity of 35 m/s, the debris avalanche buried approximately 60 sq km of terrain to an average depth of 45 m with unconsolidated, poorly sorted volcaniclastic material, all within a period of 10 minutes. Where exposed and unaltered by subsequent lahars and pyroclastic flows, the new terrain surface was characterized predominantly by hummocks, closed depressions, and the absence of an identifiable channel network. Following emplacement of the debris avalanche, a complex interrelationship of fluvial and mass wasting processes immediately began operating to return the impacted area to an equilibrium status through the removal of material (potential energy) and re-establishment of graded conditions. In an attempt to chronicle the morphologic evolution of this unique environmental setting, a systematic series of interpretative maps of several selected areas was produced. These maps, which document the rate and character of active geomorphic processes, are discussed.

  3. Synaptic plasticity and neuronal refractory time cause scaling behaviour of neuronal avalanches (United States)

    Michiels van Kessenich, L.; de Arcangelis, L.; Herrmann, H. J.


    Neuronal avalanches measured in vitro and in vivo in different cortical networks consistently exhibit power law behaviour for the size and duration distributions with exponents typical for a mean field self-organized branching process. These exponents are also recovered in neuronal network simulations implementing various neuronal dynamics on different network topologies. They can therefore be considered a very robust feature of spontaneous neuronal activity. Interestingly, this scaling behaviour is also observed on regular lattices in finite dimensions, which raises the question about the origin of the mean field behavior observed experimentally. In this study we provide an answer to this open question by investigating the effect of activity dependent plasticity in combination with the neuronal refractory time in a neuronal network. Results show that the refractory time hinders backward avalanches forcing a directed propagation. Hebbian plastic adaptation plays the role of sculpting these directed avalanche patterns into the topology of the network slowly changing it into a branched structure where loops are marginal.

  4. Small-scale laboratory tests on granular avalanches around an obstacle (United States)

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


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

  5. Experimental and numerical investigation of a RC wall loaded by snow-like avalanche pressure signal (United States)

    Ousset, Isabelle; Bertrand, David; Brun, Michaël; Limam, Ali; Naaïm, Mohamed


    Nowadays, civil engineering structures exposed to snow avalanches are mostly designed considering static loadings involving large safety factors. These latters highlight the lack of knowledge about the effects of the loading generated by a snow flow, and generally lead to oversize the civil structure. Indeed, the transient nature of the loading signal and also the composition of the snow flow can generate dynamic phenomena which cannot be taken into account considering only static loadings. The case of the avalanche of the Taconnaz (France), which occurred in 1999 and where important parts of the defense structure were destroyed, showed that static design approaches can lead to underestimate the potential effect of the snow flow. Thus, in order to give some new insights about this issue, the effect of the temporal variations of the snow loading on the mechanical behavior of an idealized defense structure is investigated. Therefore, a reinforced concrete (RC) wall with a L-like shape has been considered which is supposed to represent a part of the defense structure situated in Taconnaz. Static pushover tests, carried out in laboratory conditions on 1/6 scale physical model of the RC structure, allowed obtaining the capacity of the tested structure (Berthet-Rambaud et al. (2007)). Finite Element (FE) models have been developed and calibrated from the previous experimental data. The FE approach allows simulating the dynamic mechanical response of the structure. The effect of the transient nature of the loading of the avalanche has been explored applying out-of-plan dynamic loadings on the RC wall. In order to be as close as possible of a "field" snow avalanche, the imposed time evolution of the loading has been generated from in situ measurements recorded at the French experimental site "le col du Lautaret" (Thibert et al. (2008)). The RC mechanical behaviour has been described by four nonlinear constitutive laws. The four behaviour laws are compared and analyzed for

  6. Cataclysmic Rock Avalanche from El Capitan, Yosemite Valley, circa 3.6 ka (United States)

    Stock, G. M.


    El Capitan in Yosemite Valley is one of the largest and most iconic granite faces in the world. Despite glacially steepened walls exceeding 90 degrees, a historic database shows relatively few rock falls from El Capitan in the past 150 years. However, a massive bouldery deposit beneath the southeast face suggests an earlier rock avalanche of unusually large size. Spatial analysis of airborne LiDAR data indicate that the rock avalanche deposit has a volume of ~2.70 x 106 m3, a maximum thickness of 18 m, and a runout distance of 660 m, roughly twice the horizontal extent of the adjacent talus. The deposit is very coarse on its distal edge, with individual boulder volumes up to 2500 m3. Cosmogenic 10Be exposure dates from boulders distributed across the deposit confirm this interpretation. Four 10Be samples are tightly clustered between 3.5 and 3.8 ka, with a mean age of 3.6 +/- 0.6 ka. A fifth sample gives a much older age of 22.0 ka, but a glacier occupied Yosemite Valley at this time, prohibiting deposition; thus, the older age likely results from exposure on the cliff face prior to failure. The similarity of ages and overall morphology suggest that the entire deposit formed during a single event. The mean exposure age coincides with inferred Holocene rupture of the northern Owens Valley and/or White Mountain fault(s) between 3.3 and 3.8 ka (Lee et al., 2001; Bacon and Pezzopane, 2007). This time coincidence, combined with the fact that historic rupture of the Owens Valley fault in A.D. 1872 generated numerous large rock falls in Yosemite Valley, strongly suggests that the El Capitan rock avalanche was triggered by a seismic event along the eastern margin of the Sierra Nevada circa 3.6 ka. As there is not an obvious "scar" on the expansive southeast face, the exact source area of the rock avalanche is not yet known. Detrital apatite U-Th/(He) thermochronometry can determine the elevation(s) from which rock fall boulders originate, but significant inter-sample age

  7. High Gain Advanced GPS Receiver

    National Research Council Canada - National Science Library

    Brown, Alison; Zhang, Gengsheng


    NAVSYS High Gain Advanced GPS Receiver (HAGR) uses a digital beam-steering antenna array to enable up to eight GPS satellites to be tracked, each with up to 10 dBi of additional antenna gain over a conventional receiver solution...

  8. Examining spring wet slab and glide avalanche occurrence along the Going-to-the-Sun Road corridor, Glacier National Park, Montana, USA (United States)

    Peitzsch, Erich H.; Hendrikx, Jordy; Fagre, Daniel B.; Reardon, Blase


    Wet slab and glide snow avalanches are dangerous and yet can be particularly difficult to predict. Wet slab and glide avalanches are presumably triggered by free water moving through the snowpack and the subsequent interaction with layer or ground interfaces, and typically occur in the spring during warming and subsequent melt periods. In Glacier National Park (GNP), Montana, both types of avalanches can occur in the same year and affect the spring opening operations of the Going-to-the-Sun Road (GTSR).

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

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


    The present study concerns the numerical modeling of debris avalanches on the Nevado de Toluca Volcano (Mexico) using TITAN2D simulation software, and its application to create hazard maps. Nevado de Toluca is an andesitic to dacitic stratovolcano of Late Pliocene-Holocene age, located in central México near to the cities of Toluca and México City; its past activity has endangered an area with more than 25 million inhabitants today. The present work is based upon the data collected during extensive field work finalized to the realization of the geological map of Nevado de Toluca at 1:25,000 scale. The activity of the volcano has developed from 2.6 Ma until 10.5 ka with both effusive and explosive events; the Nevado de Toluca has presented long phases of inactivity characterized by erosion and emplacement of debris flow and debris avalanche deposits on its flanks. The largest epiclastic events in the history of the volcano are wide debris flows and debris avalanches, occurred between 1 Ma and 50 ka, during a prolonged hiatus in eruptive activity. Other minor events happened mainly during the most recent volcanic activity (less than 50 ka), characterized by magmatic and tectonic-induced instability of the summit dome complex. According to the most recent tectonic analysis, the active transtensive kinematics of the E-W Tenango Fault System had a strong influence on the preferential directions of the last three documented lateral collapses, which generated the Arroyo Grande and Zaguàn debris avalanche deposits towards E and Nopal debris avalanche deposit towards W. The analysis of the data collected during the field work permitted to create a detailed GIS database of the spatial and temporal distribution of debris avalanche deposits on the volcano. Flow models, that have been performed with the software TITAN2D, developed by GMFG at Buffalo, were entirely based upon the information stored in the geological database. The modeling software is built upon equations

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

    Directory of Open Access Journals (Sweden)

    C. Mitterer


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

  11. The electromagnetic radiation fields of a relativistic electron avalanche with special attention to the origin of narrow bipolar pulses (United States)

    Cooray, G. V.; Cooray, G. K.


    Gurevich et al. [1] postulated that the source of narrow bipolar pulses, a class of high energy pulses that occur during thunderstorms, could be a runaway electron avalanche driven by the intense electric fields of a thunderstorm. Recently, Watson and Marshall [2] used the modified transmission line model to test the mechanism of the source of narrow bipolar pulses. In a recent paper, Cooray and Cooray [3] demonstrated that the electromagnetic fields of accelerating charges could be used to evaluate the electromagnetic fields from electrical discharges if the temporal and spatial variation of the charges in the discharge is known. In the present study, those equations were utilized to evaluate the electromagnetic fields generated by a relativistic electron avalanche. In the analysis it is assumed that all the electrons in the avalanche are moving with the same speed. In other words, the growth or the decay of the number of electrons takes place only at the head of the avalanche. It is shown that the radiation is emanating only from the head of the avalanche where electrons are being accelerated. It is also shown that an analytical expression for the radiation field of the avalanche at any distance can be written directly in terms of the e-folding length of the avalanche. This makes it possible to extract directly the spatial variation of the e-folding length of the avalanche from the measured radiation fields. In the study this model avalanche was used to investigate whether it can be used to describe the measured electromagnetic fields of narrow bipolar pulses. The results obtained are in reasonable agreement with the two station data of Eack [4] for speeds of propagation around (2 - 2.5) x 10^8 m/s and when the propagation effects on the electric fields measured at the distant station is taken into account. [1] Gurevich et al. (2004), Phys. Lett. A., 329, pp. 348 -361. [2] Watson, S. S. and T. C. Marshall (2007), Geophys. Res. Lett., Vol. 34, L04816, doi: 10

  12. Diversity Gain through Antenna Blocking

    Directory of Open Access Journals (Sweden)

    V. Dehghanian


    Full Text Available As part of the typical usage mode, interaction between a handheld receiver antenna and the operator's RF absorbing body and nearby objects is known to generate variability in antenna radiation characteristics through blocking and pattern changes. It is counterintuitive that random variations in blocking can result in diversity gain of practical applicability. This diversity gain is quantified from a theoretical and experimental perspective. Measurements carried out at 1947.5 MHz verify the theoretical predictions, and a diversity gain of 3.1 dB was measured through antenna blocking and based on the utilized measurement setup. The diversity gain can be exploited to enhance signal detectability of handheld receivers based on a single antenna in indoor multipath environments.

  13. Particulate kinematic simulations of debris avalanches: interpretation of deposits and landslide seismic signals of Mount Saint Helens, 1980 May 18 (United States)

    Ward, Steven N.; Day, Simon


    We construct a new class of granular landslide models in which avalanches are simulated with large numbers of independent particles moving under the influence of topographically derived gravitational and centripetal acceleration. Concurrently, the particles suffer deceleration due to basal and dynamic friction. The novel aspect of the calculation is that complex particle-to-particle interactions, fluctuating basal contacts, and unresolved topographic roughness within and below the deforming flow are mimicked by random perturbations in along-track and cross-slope acceleration. We apply the method to the 1980 May 18 Mount Saint Helens debris avalanche by constraining the initial geometry and structure of the slide mass from geological data, and the initial failure sequence from eyewitness accounts. After tuning coefficients of mechanical friction and random accelerations, the landslide simulation generates a final deposit whose extent, thickness, morphological structure and lithological variation closely replicate those observed. Moreover, the model avalanche is consistent kinematically with mapped patterns of bedrock scouring, deposit superelevation, and net force history implied from seismic records. To be successful, the slide mass must be divided into upper, high-friction and lower, low-friction members. This division corresponds to fresh, water-unsaturated and hydrothermally altered, water-saturated rock units and points to a mechanical explanation of the kinematics of the debris avalanche. Success in reproducing many features of the Mount Saint Helens avalanche indicates that debris-deposit data may be used to determine the kinematic histories of less well-observed landslides.

  14. Developmental gains in visuospatial memory predict gains in mathematics achievement.

    Directory of Open Access Journals (Sweden)

    Yaoran Li

    Full Text Available Visuospatial competencies are related to performance in mathematical domains in adulthood, but are not consistently related to mathematics achievement in children. We confirmed the latter for first graders and demonstrated that children who show above average first-to-fifth grade gains in visuospatial memory have an advantage over other children in mathematics. The study involved the assessment of the mathematics and reading achievement of 177 children in kindergarten to fifth grade, inclusive, and their working memory capacity and processing speed in first and fifth grade. Intelligence was assessed in first grade and their second to fourth grade teachers reported on their in-class attentive behavior. Developmental gains in visuospatial memory span (d = 2.4 were larger than gains in the capacity of the central executive (d = 1.6 that in turn were larger than gains in phonological memory span (d = 1.1. First to fifth grade gains in visuospatial memory and in speed of numeral processing predicted end of fifth grade mathematics achievement, as did first grade central executive scores, intelligence, and in-class attentive behavior. The results suggest there are important individual differences in the rate of growth of visuospatial memory during childhood and that these differences become increasingly important for mathematics learning.

  15. Developmental gains in visuospatial memory predict gains in mathematics achievement. (United States)

    Li, Yaoran; Geary, David C


    Visuospatial competencies are related to performance in mathematical domains in adulthood, but are not consistently related to mathematics achievement in children. We confirmed the latter for first graders and demonstrated that children who show above average first-to-fifth grade gains in visuospatial memory have an advantage over other children in mathematics. The study involved the assessment of the mathematics and reading achievement of 177 children in kindergarten to fifth grade, inclusive, and their working memory capacity and processing speed in first and fifth grade. Intelligence was assessed in first grade and their second to fourth grade teachers reported on their in-class attentive behavior. Developmental gains in visuospatial memory span (d = 2.4) were larger than gains in the capacity of the central executive (d = 1.6) that in turn were larger than gains in phonological memory span (d = 1.1). First to fifth grade gains in visuospatial memory and in speed of numeral processing predicted end of fifth grade mathematics achievement, as did first grade central executive scores, intelligence, and in-class attentive behavior. The results suggest there are important individual differences in the rate of growth of visuospatial memory during childhood and that these differences become increasingly important for mathematics learning.

  16. Developmental Gains in Visuospatial Memory Predict Gains in Mathematics Achievement (United States)

    Li, Yaoran; Geary, David C.


    Visuospatial competencies are related to performance in mathematical domains in adulthood, but are not consistently related to mathematics achievement in children. We confirmed the latter for first graders and demonstrated that children who show above average first-to-fifth grade gains in visuospatial memory have an advantage over other children in mathematics. The study involved the assessment of the mathematics and reading achievement of 177 children in kindergarten to fifth grade, inclusive, and their working memory capacity and processing speed in first and fifth grade. Intelligence was assessed in first grade and their second to fourth grade teachers reported on their in-class attentive behavior. Developmental gains in visuospatial memory span (d = 2.4) were larger than gains in the capacity of the central executive (d = 1.6) that in turn were larger than gains in phonological memory span (d = 1.1). First to fifth grade gains in visuospatial memory and in speed of numeral processing predicted end of fifth grade mathematics achievement, as did first grade central executive scores, intelligence, and in-class attentive behavior. The results suggest there are important individual differences in the rate of growth of visuospatial memory during childhood and that these differences become increasingly important for mathematics learning. PMID:23936154

  17. Investigation on properties of ultrafast switching in a bulk gallium arsenide avalanche semiconductor switch

    International Nuclear Information System (INIS)

    Hu, Long; Su, Jiancang; Ding, Zhenjie; Hao, Qingsong; Yuan, Xuelin


    Properties of ultrafast switching in a bulk gallium arsenide (GaAs) avalanche semiconductor switch based on semi-insulating wafer, triggered by an optical pulse, were analyzed using physics-based numerical simulations. It has been demonstrated that when a voltage with amplitude of 5.2 kV is applied, after an exciting optical pulse with energy of 1 μJ arrival, the structure with thickness of 650 μm reaches a high conductivity state within 110 ps. Carriers are created due to photons absorption, and electrons and holes drift to anode and cathode terminals, respectively. Static ionizing domains appear both at anode and cathode terminals, and create impact-generated carriers which contribute to the formation of electron-hole plasma along entire channel. When the electric field in plasma region increases above the critical value (∼4 kV/cm) at which the electrons drift velocity peaks, a domain comes into being. An increase in carrier concentration due to avalanche multiplication in the domains reduces the domain width and results in the formation of an additional domain as soon as the field outside the domains increases above ∼4 kV/cm. The formation and evolution of multiple powerfully avalanching domains observed in the simulations are the physical reasons of ultrafast switching. The switch exhibits delayed breakdown with the characteristics affected by biased electric field, current density, and optical pulse energy. The dependence of threshold energy of the exciting optical pulse on the biased electric field is discussed

  18. Efficient numerical schemes for viscoplastic avalanches. Part 2: The 2D case (United States)

    Fernández-Nieto, Enrique D.; Gallardo, José M.; Vigneaux, Paul


    This paper deals with the numerical resolution of a shallow water viscoplastic flow model. Viscoplastic materials are characterized by the existence of a yield stress: below a certain critical threshold in the imposed stress, there is no deformation and the material behaves like a rigid solid, but when that yield value is exceeded, the material flows like a fluid. In the context of avalanches, it means that after going down a slope, the material can stop and its free surface has a non-trivial shape, as opposed to the case of water (Newtonian fluid). The model involves variational inequalities associated with the yield threshold: finite volume schemes are used together with duality methods (namely Augmented Lagrangian and Bermúdez-Moreno) to discretize the problem. To be able to accurately simulate the stopping behavior of the avalanche, new schemes need to be designed, involving the classical notion of well-balancing. In the present context, it needs to be extended to take into account the viscoplastic nature of the material as well as general bottoms with wet/dry fronts which are encountered in geophysical geometries. Here we derive such schemes in 2D as the follow up of the companion paper treating the 1D case. Numerical tests include in particular a generalized 2D benchmark for Bingham codes (the Bingham-Couette flow with two non-zero boundary conditions on the velocity) and a simulation of the avalanche path of Taconnaz in Chamonix-Mont-Blanc to show the usability of these schemes on real topographies from digital elevation models (DEM).

  19. 3D Silicon Coincidence Avalanche Detector (3D-SiCAD) for charged particle detection (United States)

    Vignetti, M. M.; Calmon, F.; Pittet, P.; Pares, G.; Cellier, R.; Quiquerez, L.; Chaves de Albuquerque, T.; Bechetoille, E.; Testa, E.; Lopez, J.-P.; Dauvergne, D.; Savoy-Navarro, A.


    Single-Photon Avalanche Diodes (SPADs) are p-n junctions operated in Geiger Mode by applying a reverse bias above the breakdown voltage. SPADs have the advantage of featuring single photon sensitivity with timing resolution in the picoseconds range. Nevertheless, their relatively high Dark Count Rate (DCR) is a major issue for charged particle detection, especially when it is much higher than the incoming particle rate. To tackle this issue, we have developed a 3D Silicon Coincidence Avalanche Detector (3D-SiCAD). This novel device implements two vertically aligned SPADs featuring on-chip electronics for the detection of coincident avalanche events occurring on both SPADs. Such a coincidence detection mode allows an efficient discrimination of events related to an incoming charged particle (producing a quasi-simultaneous activation of both SPADs) from dark counts occurring independently on each SPAD. A 3D-SiCAD detector prototype has been fabricated in CMOS technology adopting a 3D flip-chip integration technique, and the main results of its characterization are reported in this work. The particle detection efficiency and noise rejection capability for this novel device have been evaluated by means of a β- strontium-90 radioactive source. Moreover the impact of the main operating parameters (i.e. the hold-off time, the coincidence window duration, the SPAD excess bias voltage) over the particle detection efficiency has been studied. Measurements have been performed with different β- particles rates and show that a 3D-SiCAD device outperforms single SPAD detectors: the former is indeed capable to detect particle rates much lower than the individual DCR observed in a single SPAD-based detectors (i.e. 2 to 3 orders of magnitudes lower).

  20. Relating Silicon Carbide Avalanche Breakdown Diode Design to Pulsed-Energy Capability (United States)


    parameters specifically for each ABD. The focus of this paper is to present results from pulsed-current tests of the 4 ABD designs and to draw conclusions...shown in figure 3. Component values of 2 kΩ, 90 µF, and 24 µH were used for R, C, and L, respectively. With the capacitor charged by the DC supply...The capacitor voltage and the inductor charging time, were adjusted for each ABD to control the peak avalanche current and its negative slope

  1. An Ion Beam Tracking System based on a Parallel Plate Avalanche Counter

    Directory of Open Access Journals (Sweden)

    Carter I. P.


    Full Text Available A pair of twin position-sensitive parallel plate avalanche counters have been developed at the Australian National University as a tracking system to aid in the further rejection of unwanted beam particles from a 6.5 T super conducting solenoid separator named SOLEROO. Their function is to track and identify each beam particle passing through the detectors on an event-by-event basis. In-beam studies have been completed and the detectors are in successful operation, demonstrating the tracking capability. A high efficiency 512-pixelwide-angle silicon detector array will then be integrated with the tracking system for nuclear reactions studies of radioactive ions.

  2. Measurements of electron avalanche formation time in W-band microwave air breakdown (United States)

    Cook, Alan M.; Hummelt, Jason S.; Shapiro, Michael A.; Temkin, Richard J.


    We present measurements of formation times of electron avalanche ionization discharges induced by a focused 110 GHz millimeter-wave beam in atmospheric air. Discharges take place in a free volume of gas, with no nearby surfaces or objects. When the incident field amplitude is near the breakdown threshold for pulsed conditions, measured formation times are ˜0.1-2 μs over the pressure range 5-700 Torr. Combined with electric field breakdown threshold measurements, the formation time data shows the agreement of 110 GHz air breakdown with the similarity laws of gas discharges.

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

    International Nuclear Information System (INIS)

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


    Recent results on Al and Zn superheated superconducting granules (SSG) embedded into varnish GE 7031, and operated at very low temperature (down to 40 mK) are presented. The observed signals exhibit possible evidence for avalanche phenomena that could be due to thermal exchanges inside the detector. Such a result may confirm previous claims based on tests with Cd granules at T < 300 mK. Present observations indeed suggest that the SSG colloid should be dealt with as a composite medium rather than as an assembly of single grains

  4. Measurements of electron avalanche formation time in W-band microwave air breakdown

    International Nuclear Information System (INIS)

    Cook, Alan M.; Hummelt, Jason S.; Shapiro, Michael A.; Temkin, Richard J.


    We present measurements of formation times of electron avalanche ionization discharges induced by a focused 110 GHz millimeter-wave beam in atmospheric air. Discharges take place in a free volume of gas, with no nearby surfaces or objects. When the incident field amplitude is near the breakdown threshold for pulsed conditions, measured formation times are ∼0.1-2 μs over the pressure range 5-700 Torr. Combined with electric field breakdown threshold measurements, the formation time data shows the agreement of 110 GHz air breakdown with the similarity laws of gas discharges.

  5. Fluorescence excited in a thunderstorm atmosphere by relativistic runaway electron avalanches (United States)

    Babich, L. P.; Bochkov, E. I.


    The spectrum and spatiotemporal evolution of the fluorescence of an atmospheric discharge developing in the regime of relativistic runaway electron avalanche (RREA) generation have been calculated without involving the relativistic feedback. The discharges generating narrow bipolar pulses, along with the discharges responsible for terrestrial gamma-ray flashes, are shown to be relatively dark. Nevertheless, the fluorescence excited by a discharge involving RREAs can be recorded with cameras used to record high-altitude optical phenomena. A possible connection between a certain class of optical phenomena observed at the tops of thunderclouds and RREA emission is pointed out.

  6. Space-qualified silicon avalanche-photodiode single-photon-counting modules (United States)

    Sun, Xiaoli; Krainak, Michael A.; Abshire, James B.; Spinhirne, James D.; Trottier, Claude; Davies, Murray; Dautet, Henri; Allan, Graham R.; Lukemire, Alan T.; Vandiver, James C.


    A space-qualified silicon avalanche-photodiode (APD) based single-photon-counting-module (SPCM) was developed for the Geoscience Laser Altimeter System (GLAS) on board NASA's Ice, Cloud, and Land Elevation Satellite (ICESat). Numerous improvements were made over the commercially available SPCMs in both performance and reliability. The measured optoelectronic parameters include, 65% photon detection efficiency at the 532 nm wavelength, 15-17 mega-counts per second (Mcps) maximum count rate and less than 200 s-1 dark counts before exposure to space radiation.

  7. Cosmogenic Nuclide Exposure Dating of the Tiltill Rock Avalanche, Yosemite National Park (United States)

    Ford, K. R.; Pluhar, C. J.; Stone, J. O.; Stock, G. M.; Zimmerman, S. R.


    Yosemite National Park serves as an excellent natural laboratory for studying rock falls and rock avalanches because these are the main processes modifying the nearly vertical slopes of this recently glaciated landscape. Mass wasting represents a significant hazard in the region and the database of previous rock falls and other mass wasting events in Yosemite is extensive, dating back to the mid-1800s. However, this record is too short to capture the recurrence characteristics and triggering mechanisms of the very largest events, necessitating studies of the geologic record of mass wasting. Rock falls and rock avalanches are readily dated by cosmogenic nuclide methods due to their instantaneous formation, and results can be tied to triggering events such as seismic activity (e.g. Stock et al., 2009). Here, we apply exposure dating to the Holocene Tiltill rock avalanche north of Hetch Hetchy Reservoir. The deposit comprises what appear to be two separate lobes of rock and debris, yielding a total volume of ~3.1 x 106 m3. Assuming an erosion rate of 0.0006 cm/yr and neglecting snowpack shielding, preliminary data suggest a mean exposure age of 11,000 + 600 year B.P. for both deposits, indicating that they were emplaced in a single event. The age of the Tiltill 'slide' is similar to earthquakes on the Owens Valley Fault between 10,800 + 600 and 10,200 + 200 cal year B.P. (Bacon, 2007) and the White Mountain Fault, ~10,000 cal year B.P. (Reheis, 1996; DePolo, 1989). Given that movement on the Owens Valley fault in 1872 caused a number of rock falls in Yosemite and the coincidence of ages between the Tiltill 'slide' and paleoseismic events, a large earthquake in Eastern Sierra Nevada may have triggered this event. Other trigger events are also possibilities, but only through compilation of a database of large rock avalanches can statistically significant groupings of events begin to demonstrate whether seismic triggering is a dominant process.

  8. Pulse-Shape Discrimination of Alpha Particles of Different Specific Energy-Loss With Parallel-Plate Avalanche Counters (United States)

    Nakhostin, M.; Baba, M.


    Parallel-plate avalanche counters have long been recognized as timing detectors for heavily ionizing particles. However, these detectors suffer from a poor pulse-height resolution which limits their capability to discriminate between different ionizing particles. In this paper, a new approach for discriminating between charged particles of different specific energy-loss with avalanche counters is demonstrated. We show that the effect of the self-induced space-charge in parallel-plate avalanche counters leads to a strong correlation between the shape of output current pulses and the amount of primary ionization created by the incident charged particles. The correlation is then exploited for the discrimination of charged particles with different energy-losses in the detector. The experimental results obtained with α-particles from an 241Am α-source demonstrate a discrimination capability far beyond that achievable with the standard pulse-height discrimination method.

  9. The effect of a low-frequency noise signal on a single-frequency millimeter-band oscillator based on an avalanche-transit diode (United States)

    Kotov, V. D.; Myasin, E. A.


    Noise-wave generation in a single-frequency oscillator based on a 7-mm-band avalanche-transit diode has been implemented for the first time under the action of a low-frequency narrow-band ( 3 MHz) noise signal on an avalanche-transit-diode feed circuit.

  10. Avalanche analysis from multi-electrode ensemble recordings in cat, monkey and human cerebral cortex during wakefulness and sleep.

    Directory of Open Access Journals (Sweden)

    Nima eDehghani


    Full Text Available Self-organized critical states are found in many natural systems, from earthquakes to forest fires, they have also been observed in neural systems, particularly, in neuronal cultures. However, the presence of critical states in the awake brain remains controversial. Here, we compared avalanche analyses performed on different in vivo preparations during wakefulness, slow-wave sleep and REM sleep, using high-density electrode arrays in cat motor cortex (96 electrodes, monkey motor cortex and premotor cortex and human temporal cortex (96 electrodes in epileptic patients. In neuronal avalanches defined from units (up to 160 single units, the size of avalanches never clearly scaled as power-law, but rather scaled exponentially or displayed intermediate scaling. We also analyzed the dynamics of local field potentials (LFPs and in particular LFP negative peaks (nLFPs among the different electrodes (up to 96 sites in temporal cortex or up to 128 sites in adjacent motor and pre-motor cortices. In this case, the avalanches defined from nLFPs displayed power-law scaling in double logarithmic representations, as reported previously in monkey. However, avalanche defined as positive LFP (pLFP peaks, which are less directly related to neuronal firing, also displayed apparent power-law scaling. Closer examination of this scaling using the more reliable cumulative distribution function (CDF and other rigorous statistical measures, did not confirm power-law scaling. The same pattern was seen for cats, monkey and human, as well as for different brain states of wakefulness and sleep. We also tested other alternative distributions. Multiple exponential fitting yielded optimal fits of the avalanche dynamics with bi-exponential distributions. Collectively, these results show no clear evidence for power-law scaling or self-organized critical states in the awake and sleeping brain of mammals, from cat to man.

  11. Smartphone applications for communicating avalanche risk information - a study on how they are developed and evaluated by their providers (United States)

    Charrière, Marie K. M.; Bogaard, Thom A.


    Every year, people are victims of avalanches. It is commonly assumed that one way to decrease those losses is to inform about danger levels. This paper presents a study on current practices in the development and evaluation of smartphones applications that are dedicated to avalanche risk communication. The analysis based on semi-structured interviews with developers of six smartphone apps highlights the context of their development, how choices of content and visualization were made and how their effectiveness is evaluated by the developers themselves. It appears that all these communicators agree on the message to disseminate and the general representation concepts (i.e., use of the international avalanche danger scale and of a tiered approach). However, the specific ways this message is presented (e.g., maps, icons) is not uniform. Moreover, only simple evaluation processes (e.g., usage monitoring) are conducted by the developers. However, they are well aware that further efforts need to be made in order to thoroughly analyze the effectiveness of the smartphone apps in terms of their real impact (e.g., increase in awareness or change in behavior). This work also highlighted that the smartphone applications are in transition from being one-way communication tools to becoming two-way communication platforms, with the possibility for non-experts users to report on snow and avalanche conditions. This paper indicates challenges that avalanche risk communication is facing, although it is indisputably the most advanced and standardized practice compared to communication tools for other natural hazards. In addition to being relevant for the avalanche risk communication community, this research is therefore of interest for scientists and practitioners working on risk communication related to natural hazards.

  12. Mapping flux avalanches in MgB2 films-equivalence between magneto-optical imaging and magnetic measurements

    International Nuclear Information System (INIS)

    Colauto, F; Choi, E M; Lee, J Y; Lee, S I; Yurchenko, V V; Johansen, T H; Ortiz, W A


    Vortex avalanches are known to occur in MgB 2 films within a certain range of temperatures and magnetic fields. These events, resulting from a thermomagnetic instability, were first revealed by real-time magneto-optical imaging, which exposed dendritic paths of abrupt flux propagation. This very powerful technique has, however, a practical limitation, since sensors that are currently available cannot be used at high magnetic fields. This letter shows that results obtained using dc magnetometry are in good correspondence with those furnished by magneto-optical imaging, demonstrating that the two techniques can be efficiently used as complementary tools to map vortex avalanches in superconducting films. (rapid communication)

  13. 14-plex Feasibility Report

    Energy Technology Data Exchange (ETDEWEB)

    Kotongan, Victoria Hazel [Native Village of Unalakleet


    The Native Village of Unalakleet project was a feasibility study for a retrofit of a “tribally owned” three story, 14 apartment complex located in Unalakleet, Alaska. The program objective and overall goal was to create a plan for retrofitting to include current appraised value and comparable costs of new construction to determine genuine feasibility as low-income multi-family housing for tribal members.

  14. An amorphous silicon photodiode with 2 THz gain-bandwidth product based on cycling excitation process (United States)

    Yan, Lujiang; Yu, Yugang; Zhang, Alex Ce; Hall, David; Niaz, Iftikhar Ahmad; Raihan Miah, Mohammad Abu; Liu, Yu-Hsin; Lo, Yu-Hwa


    Since impact ionization was observed in semiconductors over half a century ago, avalanche photodiodes (APDs) using impact ionization in a fashion of chain reaction have been the most sensitive semiconductor photodetectors. However, APDs have relatively high excess noise, a limited gain-bandwidth product, and high operation voltage, presenting a need for alternative signal amplification mechanisms of superior properties. As an amplification mechanism, the cycling excitation process (CEP) was recently reported in a silicon p-n junction with subtle control and balance of the impurity levels and profiles. Realizing that CEP effect depends on Auger excitation involving localized states, we made the counter intuitive hypothesis that disordered materials, such as amorphous silicon, with their abundant localized states, can produce strong CEP effects with high gain and speed at low noise, despite their extremely low mobility and large number of defects. Here, we demonstrate an amorphous silicon low noise photodiode with gain-bandwidth product of over 2 THz, based on a very simple structure. This work will impact a wide range of applications involving optical detection because amorphous silicon, as the primary gain medium, is a low-cost, easy-to-process material that can be formed on many kinds of rigid or flexible substrates.

  15. The Effect of Electron versus Hole Photocurrent on Optoelectric Properties of p+-p-n-n+ Wz-GaN Reach-Through Avalanche Photodiodes

    Directory of Open Access Journals (Sweden)

    Moumita Ghosh


    Full Text Available The authors have made an attempt to investigate the effect of electron versus hole photocurrent on the optoelectric properties of p+-p-n-n+ structured Wurtzite-GaN (Wz-GaN reach-through avalanche photodiodes (RAPDs. The photo responsivity and optical gain of the devices are obtained within the wavelength range of 300 to 450 nm using a novel modeling and simulation technique developed by the authors. Two optical illumination configurations of the device such as Top Mounted (TM and Flip Chip (FC are considered for the present study to investigate the optoelectric performance of the device separately due to electron dominated and hole dominated photocurrents, respectively, in the visible-blind ultraviolet (UV spectrum. The results show that the peak unity gain responsivity and corresponding optical gain of the device are 555.78 mA W−1 and 9.4144×103, respectively, due to hole dominated photocurrent (i.e., in FC structure; while those are 480.56 mA W−1 and 7.8800×103, respectively, due to electron dominated photocurrent (i.e., in TM structure at the wavelength of 365 nm and for applied reverse bias of 85 V. Thus, better optoelectric performance of Wz-GaN RAPDs can be achieved when the photocurrent is made hole dominated by allowing the UV light to be shined on the n+-layer instead of p+-layer of the device.

  16. Large-area NbN superconducting nanowire avalanche photon detectors with saturated detection efficiency (United States)

    Murphy, Ryan P.; Grein, Matthew E.; Gudmundsen, Theodore J.; McCaughan, Adam; Najafi, Faraz; Berggren, Karl K.; Marsili, Francesco; Dauler, Eric A.


    Superconducting circuits comprising SNSPDs placed in parallel—superconducting nanowire avalanche photodetectors, or SNAPs—have previously been demonstrated to improve the output signal-to-noise ratio (SNR) by increasing the critical current. In this work, we employ a 2-SNAP superconducting circuit with narrow (40 nm) niobium nitride (NbN) nanowires to improve the system detection efficiency to near-IR photons while maintaining high SNR. Additionally, while previous 2-SNAP demonstrations have added external choke inductance to stabilize the avalanching photocurrent, we show that the external inductance can be entirely folded into the active area by cascading 2-SNAP devices in series to produce a greatly increased active area. We fabricated series-2-SNAP (s2-SNAP) circuits with a nanowire length of 20 μm with cascades of 2-SNAPs providing the choke inductance necessary for SNAP operation. We observed that (1) the detection efficiency saturated at high bias currents, and (2) the 40 nm 2-SNAP circuit critical current was approximately twice that for a 40 nm non-SNAP configuration.

  17. Photon-counting monolithic avalanche photodiode arrays for the super collider

    International Nuclear Information System (INIS)

    Ishaque, A.N.; Castleberry, D.E.; Rougeot, H.M.


    In fiber tracking, calorimetry, and other high energy and nuclear physics experiments, the need arises to detect an optical signal consisting of a few photons (in some cases a single photoelectron) with a detector insensitive to magnetic fields. Previous attempts to detect a single photoelectron have involved avalanche photodiodes (APDs) operated in the Geiger mode, the visible light photon counter, and a photomultiplier tube with an APD as the anode. In this paper it is demonstrated that silicon APDs, biased below the breakdown voltage, can be used to detect a signal of a few photons with conventional pulse counting circuitry at room temperature. Moderate cooling, it is further argued, could make it possible to detect a single photoelectron. Monolithic arrays of silicon avalanche photodiodes fabricated by Radiation Monitoring Devices, Inc. (RMD) were evaluated for possible use in the Super Collider detector systems. Measurements on 3 element x 3 element (2 mm pitch) APD arrays, using pulse counting circuitry with a charge sensitive amplifier (CSA) and a Gaussian filter, are reported and found to conform to a simple noise model. The model is used to obtain the optimal operating point. Experimental results are described in Section II, modeling results in Section III, and the conclusions are summarized in Section IV

  18. Efficient numerical schemes for viscoplastic avalanches. Part 1: The 1D case

    Energy Technology Data Exchange (ETDEWEB)

    Fernández-Nieto, Enrique D., E-mail: [Departamento de Matemática Aplicada I, Universidad de Sevilla, E.T.S. Arquitectura, Avda, Reina Mercedes, s/n, 41012 Sevilla (Spain); Gallardo, José M., E-mail: [Departamento de Análisis Matemático, Universidad de Málaga, F. Ciencias, Campus Teatinos S/N (Spain); Vigneaux, Paul, E-mail: [Unitée de Mathématiques Pures et Appliquées, Ecole Normale Supérieure de Lyon, 46 allée d' Italie, 69364 Lyon Cedex 07 (France)


    This paper deals with the numerical resolution of a shallow water viscoplastic flow model. Viscoplastic materials are characterized by the existence of a yield stress: below a certain critical threshold in the imposed stress, there is no deformation and the material behaves like a rigid solid, but when that yield value is exceeded, the material flows like a fluid. In the context of avalanches, it means that after going down a slope, the material can stop and its free surface has a non-trivial shape, as opposed to the case of water (Newtonian fluid). The model involves variational inequalities associated with the yield threshold: finite-volume schemes are used together with duality methods (namely Augmented Lagrangian and Bermúdez–Moreno) to discretize the problem. To be able to accurately simulate the stopping behavior of the avalanche, new schemes need to be designed, involving the classical notion of well-balancing. In the present context, it needs to be extended to take into account the viscoplastic nature of the material as well as general bottoms with wet/dry fronts which are encountered in geophysical geometries. We derived such schemes and numerical experiments are presented to show their performances.

  19. Mapping and evaluation of snow avalanche risk using GIS technique in Rodnei National Park (United States)

    Covǎsnianu, Adrian; Grigoraş, Ioan-Rǎducu; Covǎsnianu, Liliana-Elena; Iordache, Iulian; Balin, Daniela


    The study consisted in a precise mapping project (GPS field campaign, on-screen digitization of the topographic maps at 1:25.000 scale and updated with ASTER mission) of the Rodnei National Park area (Romanian Carpathians) with a focus on snow avalanche risk survey. Parameters taken into account were slope, aspect, altitude, landforms and roughness resulted from a high resolute numerical terrain model obtained by ASTER (Advanced Spaceborne Thermal Emission and Reflection Radiometer) mission. The resulted digital surface model with a spatial resolution of 10 m covered a total area of 187 square kilometers and was improved by the help of Topo to Raster tool. All these parameters were calibrated after a model applied onto Tatra Massive and also Ceahlău Mountain. The results were adapted and interpreted in accordance with European avalanche hazard scale. This work was made in the context of the elaboration of Risk Map and is directly concerning both the security of tourism activities but also the management of the Rodnei Natural Park. The extension of this method to similar mountain areas is ongoing.

  20. Interplanetary Space Weather Effects on Lunar Reconnaissance Orbiter Avalanche Photodiode Performance (United States)

    Clements, E. B.; Carlton, A. K.; Joyce, C. J.; Schwadron, N. A.; Spence, H. E.; Sun, X.; Cahoy, K.


    Space weather is a major concern for radiation-sensitive space systems, particularly for interplanetary missions, which operate outside of the protection of Earth's magnetic field. We examine and quantify the effects of space weather on silicon avalanche photodiodes (SiAPDs), which are used for interplanetary laser altimeters and communications systems and can be sensitive to even low levels of radiation (less than 50 cGy). While ground-based radiation testing has been performed on avalanche photodiode (APDs) for space missions, in-space measurements of SiAPD response to interplanetary space weather have not been previously reported. We compare noise data from the Lunar Reconnaissance Orbiter (LRO) Lunar Orbiter Laser Altimeter (LOLA) SiAPDs with radiation measurements from the onboard Cosmic Ray Telescope for the Effects of Radiation (CRaTER) instrument. We did not find any evidence to support radiation as the cause of changes in detector threshold voltage during radiation storms, both for transient detector noise and long-term average detector noise, suggesting that the approximately 1.3 cm thick shielding (a combination of titanium and beryllium) of the LOLA detectors is sufficient for SiAPDs on interplanetary missions with radiation environments similar to what the LRO experienced (559 cGy of radiation over 4 years).

  1. An accurate behavioral model for single-photon avalanche diode statistical performance simulation (United States)

    Xu, Yue; Zhao, Tingchen; Li, Ding


    An accurate behavioral model is presented to simulate important statistical performance of single-photon avalanche diodes (SPADs), such as dark count and after-pulsing noise. The derived simulation model takes into account all important generation mechanisms of the two kinds of noise. For the first time, thermal agitation, trap-assisted tunneling and band-to-band tunneling mechanisms are simultaneously incorporated in the simulation model to evaluate dark count behavior of SPADs fabricated in deep sub-micron CMOS technology. Meanwhile, a complete carrier trapping and de-trapping process is considered in afterpulsing model and a simple analytical expression is derived to estimate after-pulsing probability. In particular, the key model parameters of avalanche triggering probability and electric field dependence of excess bias voltage are extracted from Geiger-mode TCAD simulation and this behavioral simulation model doesn't include any empirical parameters. The developed SPAD model is implemented in Verilog-A behavioral hardware description language and successfully operated on commercial Cadence Spectre simulator, showing good universality and compatibility. The model simulation results are in a good accordance with the test data, validating high simulation accuracy.

  2. Snow fracture in relation to slab avalanche release: critical state for the onset of crack propagation (United States)

    Gaume, Johan; van Herwijnen, Alec; Chambon, Guillaume; Wever, Nander; Schweizer, Jürg


    The failure of a weak snow layer buried below cohesive slab layers is a necessary, but insufficient, condition for the release of a dry-snow slab avalanche. The size of the crack in the weak layer must also exceed a critical length to propagate across a slope. In contrast to pioneering shear-based approaches, recent developments account for weak layer collapse and allow for better explaining typical observations of remote triggering from low-angle terrain. However, these new models predict a critical length for crack propagation that is almost independent of slope angle, a rather surprising and counterintuitive result. Based on discrete element simulations we propose a new analytical expression for the critical crack length. This new model reconciles past approaches by considering for the first time the complex interplay between slab elasticity and the mechanical behavior of the weak layer including its structural collapse. The crack begins to propagate when the stress induced by slab loading and deformation at the crack tip exceeds the limit given by the failure envelope of the weak layer. The model can reproduce crack propagation on low-angle terrain and the decrease in critical length with increasing slope angle as modeled in numerical experiments. The good agreement of our new model with extensive field data and the ease of implementation in the snow cover model SNOWPACK opens a promising prospect for improving avalanche forecasting.

  3. The Acheron rock avalanche deposit, Canterbury, New Zealand : age and implications for dating landslides

    International Nuclear Information System (INIS)

    Smith, G.M.; Bell, D.H.; Davies, T.R.H.


    New radiocarbon ages for wood samples retrieved from the base of the Acheron rock avalanche near Porters Pass, Canterbury, show a clustering of ages between 1370 and 1101 yr BP. This is significantly dissimilar to the established radiocarbon age of 500 ± 69 yr BP (NZ547), from weathering-rind thickness measurements and from lichen studies. This contradiction impacts on current calibrations of lichenometric and weathering-rind dating methods, which has serious implications for landslide and earthquake dates based on them. A 500-600 yr BP earthquake event along the Porters Pass-Amberley Fault Zone has been dated in an adjacent trench and is consistent with previous dates but does not correspond to the Acheron rock avalanche emplacement as previously proposed. The landslide may have been caused by either a Porters Pass Fault event (1100-800 yr BP) or by the better-constrained Round Top event (1010 ± 50 yr BP) on the Alpine Fault. (author). 30 refs., 13 figs., 2 tabs.

  4. An avalanche counter and encoder system for counting and mapping radioactive specimens

    International Nuclear Information System (INIS)

    Britten, R.J.


    A parallel plate counter utilizes avalanche event counting over a large area with the ability to locate radioactive sources in two dimensions. One novel embodiment comprises a gas-filled chamber formed by a stretched stainless steel window cathode spaced from a flat semiconductive anode surface between which a high voltage is applied. When a beta ray, for example, enters the chamber, an ionization event occurs and the avalanche effect multiplies the event and results in charge collection on the anode surface for a limited period of time before the charge leaks away. An encoder system, comprising a symmetrical array of planar conductive surfaces separated from the anode by a dielectric material, couples charge currents the amplitude of which define the relative position of the ionization event. A number of preferred encoder system embodiments are disclosed including a novel matrix or grid pattern of electrical paths connected to voltage dividers and charge sensitive integrating amplifiers. The amplitude of coupled current delivered to the amplifiers defines the location of the event, and spatial resolution for a given signal-to-noise ratio can be controlled by changing the number of such amplifiers. (author) 11 figs

  5. Observing and characterizing avalanche activity in the Khumbu Himal, Nepal, using Pleiades and airborne HDR imagery (United States)

    Thompson, Sarah; Nicholson, Lindsey; Klug, Christoph; Rieg, Lorenzo; Sailer, Rudolf; Bucher, Tilman; Brauchle, Jörg


    In the high, steep terrain of the Khumbu Himal, Nepal, snow avalanches play an important role in glacier mass balance, and rockfall supplies much of the rock material that forms the extensive debris covers on glaciers in the region. Information on the frequency and size of gravitational mass movements is helpful for understanding current and future glacier behaviour but currently lacking. In this study we use a combination of high resolution Pleiades optical satellite imagery in conjunction with airborne HDR imagery of slopes in deep shadow or overexposed snow slopes, provided by the German Aerospace Center (DLR) MACS system (see Brauchle et al., MM3.2/GI2.12/GMPV6.4/HS11.13/NH8.9/SSS12.24), to undertake a qualitative observational study of the gravitational processes evident in these sets of imagery. We classify the features found and discuss their likely frequency in the context of previously published research findings. Terrain analysis based upon digital terrain models derived from the same Pleiades imagery is used to investigate the slope angle, degree of confinement, curvature and aspect of observed avalanche and rock fall tracks. This work presents a first overview of the types of gravitational slides affecting glaciers of the Khumbu Himal. Subsequent research efforts will focus on attempting to quantify volumes of mass movement using repeat satellite imagery.

  6. Storage and methyl jasmonate in postharvest conservation of roses cv. Avalanche

    Directory of Open Access Journals (Sweden)

    Elka Fabiana Aparecida Almeida


    Full Text Available The use of methyl jasmonate has demonstrated its efficiency to extend the vase life of cut flowers. The objective of this study was to evaluate the effect of methyl jasmonate associated with storage at low temperatures on the postharvest quality of Rosa cv. Avalanche stems. The treatments consisted of 125, 250, 500 and 1000 μM of methyl jasmonate, besides the control with distilled water. The flower buds were sprayed with 4 mL of the solution, according to the treatments, and then kept in a cold chamber (1 °C for periods of 2 and 6 days. Subsequently, the stems were taken to the postharvest laboratory at a temperature of 16 °C. Better quality, higher fresh weight and water absorption were observed in flower stems stored for 2 days. The application of methyl jasmonate caused less turgescence and greater darkening of roses. It was possible to conclude that two days is the best storage time at 1 °C and the use of methyl jasmonate does not maintain the quality of roses cv. Avalanche after harvest.

  7. A novel 4H-SiC lateral bipolar junction transistor structure with high voltage and high current gain (United States)

    Deng, Yong-Hui; Xie, Gang; Wang, Tao; Sheng, Kuang


    In this paper, a novel structure of a 4H-SiC lateral bipolar junction transistor (LBJT) with a base field plate and double RESURF in the drift region is presented. Collector-base junction depletion extension in the base region is restricted by the base field plate. Thin base as well as low base doping of the LBJT therefore can be achieved under the condition of avalanche breakdown. Simulation results show that thin base of 0.32 μm and base doping of 3 × 1017 cm-3 are obtained, and corresponding current gain is as high as 247 with avalanche breakdown voltage of 3309 V when the drift region length is 30 μm. Besides, an investigation of a 4H-SiC vertical BJT (VBJT) with comparable breakdown voltage (3357 V) shows that the minimum base width of 0.25 μm and base doping as high as 8 × 1017 cm-3 contribute to a maximum current gain of only 128.

  8. Heritability of gestational weight gain

    DEFF Research Database (Denmark)

    Andersson, Elina Scheers; Silventoinen, Karri; Tynelius, Per


    Gestational weight gain (GWG) is a complex trait involving intrauterine environmental, maternal environmental, and genetic factors. However, the extent to which these factors contribute to the total variation in GWG is unclear. We therefore examined the genetic and environmental influences on the...

  9. Yield gains in leafy vegetables (United States)

    Yield of all crops have increased during the past century through improved cultural practices and plant breeding. We reviewed gains in yield of lettuce and spinach in the U.S., principally California and Arizona. We proposed several genetic models for yield of lettuce based on the market type: whole...

  10. Feasible mathematics II

    CERN Document Server

    Remmel, Jeffrey


    Perspicuity is part of proof. If the process by means of which I get a result were not surveyable, I might indeed make a note that this number is what comes out - but what fact is this supposed to confirm for me? I don't know 'what is supposed to come out' . . . . 1 -L. Wittgenstein A feasible computation uses small resources on an abstract computa­ tion device, such as a 'lUring machine or boolean circuit. Feasible math­ ematics concerns the study of feasible computations, using combinatorics and logic, as well as the study of feasibly presented mathematical structures such as groups, algebras, and so on. This volume contains contributions to feasible mathematics in three areas: computational complexity theory, proof theory and algebra, with substantial overlap between different fields. In computational complexity theory, the polynomial time hierarchy is characterized without the introduction of runtime bounds by the closure of certain initial functions under safe composition, predicative recursion on nota...

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

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


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

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

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


    The Andean bent which coincides with the Peruvian-Chilean border region is characterised by one of the largest relief contrasts on earth with depth of the subduction trench ranging from 5000 to 6000 m below sea level and mountain tops ranging from 5500 to 6300 m a.s.l.. The western flank of the Andes is subdivided in 4 major geologic zones (i.e. Coastal Cordillera, longitudinal Basin or depression, the Precordillera or western escarpment and western Cordillera). Local relief contrasts are also pronounced due to the incision of deep canyons into several million old uplifted surfaces, preserved because of the extremely dry climate with precipitation averaging a few mm and less per year. The Lluta collapse (minimum age of 2.5 Ma; volume 26 km3) is one of the largest non-volcanic non-marine landslides on Earth and has been mapped in that area (Wörner et al., 2002). Systematic mapping in northern Chile and Southern Peru has revealed that this is not the only gigantic landslide in the area but that further landslides of similar size occurred in the area, located both along the canyon slopes and along the western escarpment of the Cordillera. This suggests that landsliding has been a major factor in controlling erosion. This contribution describes first results on mapping a giant landslide complex in southern Perù called the Cerro Caquilluco - Cerrillos Negros Tomasiri rock slide - avalanche complex. The systematic mapping we have carried out in the area is presented in a further contribution to this conference. The Cerro Caquilluco - Cerrillos Negros Tomasiri rock slide - avalanche complex affected the upper part of a SW dipping paleosurface (8° to 9°) cut by a disconnected and regular primitive drainage network organized in a series of SW trending parallel valleys. This network developed within the lower Miocene pinkish tuffaceous deposits of the Huaylillas formation, whereas the main landslide scarp lies within the conglomerates of the Upper Moquegua formation

  13. Avalanche risk assessment for mountain roads - a comparison of case studies from Iceland and the Alps (United States)

    Wastl, M.; Stötter, J.


    While the management of alpine natural hazards in settlements follows highly developed operational standardised procedures in many countries, there are very few approaches for a systematic survey and assessment of these natural hazard processes and the related risks and for a sustainable planning of measures for roads. This is even more surprising against the background of the ongoing increase of traffic in Europe and its economic importance. This contribution compares the results of a regional scale assessment of the avalanche risk on mountain roads for case studies from Austria, Italy and Iceland. It provides the first assessment of the natural hazard situation for roads outside closed settlements in Iceland and discusses the applicability of regional scale risk based approaches developed in the Alps to the specific natural, economic and social situation. It also compares the role of risk in the assessment and management of natural hazards in these countries. The assessment of the risk by natural hazard processes for roads follows approaches developed by Wilhelm (1997, 1998, 1999) and Borter (1999a, 1999b) in the Alps adapted to comply with the data availability of the regional scale. These approaches distinguish between the individual risk on the one hand and the collective risk for the society on the other hand for each process area as well as the cumulative risk for the investigated road section. As the spatial and temporal distribution of avalanches is relatively well documented in some of the Alpine countries practical approaches have been developed for the assessment of this natural hazard process. These have been successfully applied e.g. to roads in inner Oetz and inner Stubai Valley, Tyrol, Austria by Huttenlau (2004) and Gufler (2007) and Sulden road, Ortles Alps, Southern Tyrol, Italy by Zischg et al. (2004). On the basis of these investigations the individual, collective and cumulative death risk for avalanches was determined for Siglufjar

  14. Avalanche consumption and the stationary regions of the density profile around the droplets in the theory of condensation


    Kurasov, V.


    The contradiction between the stationary aproach to the density profile and the avalanche character of the metastable phase consumption is investigated. The exact solution for the metastable phase profile is obtained. The reconsidered value for the special parameter responsible for the hierarchy in the structure of the density profile around the droplet is presented.

  15. A wide spectral range single-photon avalanche diode fabricated in an advanced 180 nm CMOS technology

    NARCIS (Netherlands)

    Mandai, S.; Fishburn, M.W.; Maruyama, Y.; Charbon, E.


    We present a single-photon avalanche diode (SPAD) with a wide spectral range fabricated in an advanced 180 nm CMOS process. The realized SPAD achieves 20 % photon detection probability (PDP) for wavelengths ranging from 440 nm to 820 nm at an excess bias of 4V, with 30 % PDP at wavelengths from 520

  16. On weak solutions to the 2D Savage-Hutter model of the motion of a gravity driven avalanche flow

    Czech Academy of Sciences Publication Activity Database

    Feireisl, Eduard; Gwiazda, P.; Swierczewska-Gwiazda, A.


    Roč. 41, č. 5 (2016), s. 759-773 ISSN 0360-5302 EU Projects: European Commission(XE) 320078 - MATHEF Institutional support: RVO:67985840 Keywords : avalanche flow * convex integration * Savage-Hutter system Subject RIV: BA - General Mathematics Impact factor: 1.608, year: 2016

  17. Posttraumatic stress and other health consequences of catastrophic avalanches: A 16-year follow-up of survivors. (United States)

    Thordardottir, Edda Bjork; Valdimarsdottir, Unnur Anna; Hansdottir, Ingunn; Resnick, Heidi; Shipherd, Jillian C; Gudmundsdottir, Berglind


    To date, no study has investigated the effects of avalanches on survivor's health beyond the first years. The aim of this study was to examine long-term health status 16 years after exposure to avalanches using a matched cohort design. Mental health, sleep quality and somatic symptoms among avalanche survivors (n=286) and non-exposed controls (n=357) were examined. Results showed that 16% of survivors currently experience avalanche-specific PTSD symptoms (PDS score>14). In addition, survivors presented with increased risk of PTSD hyperarousal symptoms (>85th percentile) (aRR=1.83; 98.3% CI [1.23-2.74]); sleep-related problems (PSQI score>5) (aRR=1.34; 95% CI [1.05-1.70]); PTSD-related sleep disturbances (PSQI-A score≥4) (aRR=1.86; 95% CI [1.30-2.67]); musculoskeletal and nervous system problems (aRR 1.43; 99% CI 1.06-1.93) and gastrointestinal problems (aRR 2.16; 99% CI 1.21-3.86) compared to the unexposed group. Results highlight the need for treatment for long-term PTSD symptoms and sleep disruption in disaster communities. Copyright © 2015 Elsevier Ltd. All rights reserved.

  18. Reforestation and land use change as drivers for a decrease of avalanche damage in mid-latitude mountains (NW Spain) (United States)

    García-Hernández, Cristina; Ruiz-Fernández, Jesús; Sánchez-Posada, Covadonga; Pereira, Susana; Oliva, Marc; Vieira, Gonçalo


    Natural conditions that explain the triggering of snow avalanches are becoming better-known, but our understanding of how socio-environmental changes can influence the occurrence of damaging avalanches is still limited. This study analyses the evolution of snow avalanche damage in the Asturian Massif (NW Spain) between 1800 and 2015, paying special attention to changes in land-use and land-cover patterns. A damage index has been performed using historical sources, photointerpretation and fieldwork-based data, which were introduced in a GIS and processed by means of statistical analysis. Mapping allowed connecting spatiotemporal variations of damage and changes in human-environment interactions. The total number of victims was 342 (192 dead and 150 injured). Results show stability in the number of avalanches during the study period, but a progressive decrease in the damage per avalanche. Changes in land use explain the evolution of damage and its spatial/temporal behaviour. The role played by vegetation cover is at the root of this process: damage was the highest during the late 19th and early 20th centuries, when a massive deforestation process affected the protective forest. This deforestation was the result of demographic growth and intensive grazing, disentailment laws and emerging coal mining. Since the mid-20th century, the transformation of a traditional land-management system based on overexploitation into a system based on land marginalization and reforestation, together with the decline of deforestation due to industrial and legal causes, resulted in the decrease of avalanches that affected settlements (mostly those released below the potential timberline). The decrease of damage has been sharper in the western sector of the Asturian Massif, where oak deforestation was very intense in the past and where lithology allows for a more successful ecological succession at present. Taking into account that reforestation can be observed in mountain environments of

  19. Characteristics of debris avalanche deposits inferred from source volume estimate and hummock morphology around Mt. Erciyes, central Turkey (United States)

    Hayakawa, Yuichi S.; Yoshida, Hidetsugu; Obanawa, Hiroyuki; Naruhashi, Ryutaro; Okumura, Koji; Zaiki, Masumi; Kontani, Ryoichi


    Debris avalanches caused by volcano sector collapse often form characteristic depositional landforms such as hummocks. Sedimentological and geomorphological analyses of debris avalanche deposits (DADs) are crucial to clarify the size, mechanisms, and emplacement of debris avalanches. We describe the morphology of hummocks on the northeastern flank of Mt. Erciyes in Kayseri, central Turkey, likely formed in the late Pleistocene. Using a remotely piloted aircraft system (RPAS) and the structure-from-motion and multi-view stereo (SfM-MVS) photogrammetry, we obtained high-definition digital elevation model (DEM) and orthorectified images of the hummocks to investigate their geometric features. We estimated the source volume of the DAD by reconstructing the topography of the volcano edifice using a satellite-based DEM. We examined the topographic cross sections based on the slopes around the scar regarded as remnant topography. Spatial distribution of hummocks is anomalously concentrated at a certain distance from the source, unlike those that follow the distance-size relationship. The high-definition land surface data by RPAS and SfM revealed that many of the hummocks are aligned toward the flow direction of the debris avalanche, suggesting that the extensional regime of the debris avalanche was dominant. However, some displaced hummocks were also found, indicating that the compressional regime of the flow contributed to the formation of hummocks. These indicate that the flow and emplacement of the avalanche were constrained by the topography. The existing caldera wall forced the initial eastward flow to move northward, and the north-side caldera wall forced the flow into the narrow and steepened outlet valley where the sliding debris underwent a compressional regime, and out into the unconfined terrain where the debris was most likely emplaced on an extensional regime. Also, the estimated volume of 12-15 × 108 m3 gives a mean thickness of 60-75 m, which is much

  20. Characteristics of debris avalanche deposits inferred from source volume estimate and hummock morphology around Mt. Erciyes, central Turkey

    Directory of Open Access Journals (Sweden)

    Y. S. Hayakawa


    Full Text Available Debris avalanches caused by volcano sector collapse often form characteristic depositional landforms such as hummocks. Sedimentological and geomorphological analyses of debris avalanche deposits (DADs are crucial to clarify the size, mechanisms, and emplacement of debris avalanches. We describe the morphology of hummocks on the northeastern flank of Mt. Erciyes in Kayseri, central Turkey, likely formed in the late Pleistocene. Using a remotely piloted aircraft system (RPAS and the structure-from-motion and multi-view stereo (SfM–MVS photogrammetry, we obtained high-definition digital elevation model (DEM and orthorectified images of the hummocks to investigate their geometric features. We estimated the source volume of the DAD by reconstructing the topography of the volcano edifice using a satellite-based DEM. We examined the topographic cross sections based on the slopes around the scar regarded as remnant topography. Spatial distribution of hummocks is anomalously concentrated at a certain distance from the source, unlike those that follow the distance–size relationship. The high-definition land surface data by RPAS and SfM revealed that many of the hummocks are aligned toward the flow direction of the debris avalanche, suggesting that the extensional regime of the debris avalanche was dominant. However, some displaced hummocks were also found, indicating that the compressional regime of the flow contributed to the formation of hummocks. These indicate that the flow and emplacement of the avalanche were constrained by the topography. The existing caldera wall forced the initial eastward flow to move northward, and the north-side caldera wall forced the flow into the narrow and steepened outlet valley where the sliding debris underwent a compressional regime, and out into the unconfined terrain where the debris was most likely emplaced on an extensional regime. Also, the estimated volume of 12–15 × 108 m3 gives a mean thickness of

  1. Comparing thixotropic and Herschel–Bulkley parameterizations for continuum models of avalanches and subaqueous debris flows

    Directory of Open Access Journals (Sweden)

    C.-H. Jeon


    Full Text Available Avalanches and subaqueous debris flows are two cases of a wide range of natural hazards that have been previously modeled with non-Newtonian fluid mechanics approximating the interplay of forces associated with gravity flows of granular and solid–liquid mixtures. The complex behaviors of such flows at unsteady flow initiation (i.e., destruction of structural jamming and flow stalling (restructuralization imply that the representative viscosity–stress relationships should include hysteresis: there is no reason to expect the timescale of microstructure destruction is the same as the timescale of restructuralization. The non-Newtonian Herschel–Bulkley relationship that has been previously used in such models implies complete reversibility of the stress–strain relationship and thus cannot correctly represent unsteady phases. In contrast, a thixotropic non-Newtonian model allows representation of initial structural jamming and aging effects that provide hysteresis in the stress–strain relationship. In this study, a thixotropic model and a Herschel–Bulkley model are compared to each other and to prior laboratory experiments that are representative of an avalanche and a subaqueous debris flow. A numerical solver using a multi-material level-set method is applied to track multiple interfaces simultaneously in the simulations. The numerical results are validated with analytical solutions and available experimental data using parameters selected based on the experimental setup and without post hoc calibration. The thixotropic (time-dependent fluid model shows reasonable agreement with all the experimental data. For most of the experimental conditions, the Herschel–Bulkley (time-independent model results were similar to the thixotropic model, a critical exception being conditions with a high yield stress where the Herschel–Bulkley model did not initiate flow. These results indicate that the thixotropic relationship is promising for

  2. Sedimentary control of volcanic debris-avalanche structures and transformation into lahars (United States)

    Bernard, Karine; van Wyk de Vries, Benjamin; Thouret, Jean-Claude; Roche, Olivier; Samaniego Eguiguren, Pablo


    Volcanic debris avalanche structures and related transformations into lahars have been extensively analysed in order to establish a sedimentary classification of the deposits. Textural and structural variations of eight debris-avalanche deposits (DADs) have been correlated with Shape Preferred Orientation of 30,000 clasts together with grain-size distributions and statistical parameters from 156 sieved matrix samples. Granular segregation patterns have been observed with structural fault controls: proximal granular-segregation structures of the Tutupaca DAD ridges in Peru, basal sheared bands along overthrust lateral levee (Mt. Dore, France), mixing and cataclasis of fault-controlled deposits in half-graben during lateral spreading of distal thrust lobe (Pichu-Pichu, Peru), neo-cataclasis at the frontal thrust lobe (Meager, Canada and Mt. Dore, France). A logarithmic regression characterises the % matrix vs. matrix/gravels showing proximal and primary cataclasis, hybrid DADs with polymodal matrix and mixed facies up to transformations into lahar (Misti, Mt Dore). The sequential fragmentation helps to distinguish DAD that belong to Andean and Cascade Volcanic arcs (Tutupaca and Misti, Peru; Meager, Canada) to the hybrid DADs, before distal transformation into lahars (Pichu-Pichu); and hydrovolcanic fragmentation characterises the transformed lahar deposits (Misti). The fractal values of 150 sieved samples range between 2.3 and 2.7, implying extensional fractures with granular disaggregation. Skewness vs. kurtosis values help to distinguish the proximal mass wasting deposits and the transformed deposits by dilution. The sorting vs. median values enable us to differentiate the hybrid DADs with the transformed deposits by dilution. The sedimentological statistical parameters with Shape Preferred Orientation analysis that have been correlated with textural and structural observations show textural fabrics resulting from kinematic processes: cataclasis, hybrid matrix

  3. r.avaflow, the GIS simulation model for avalanche and debris flows: new developments and challenges (United States)

    Mergili, Martin; Queiroz de Oliveira, Gustavo; Fischer, Jan-Thomas; Krenn, Julia; Kulisch, Helmut; Malcherek, Andreas; Pudasaini, Shiva P.


    We present the latest developments and discuss some of the key challenges with regard to the novel and unified computational tool r.avaflow, representing an advanced, comprehensive, GIS-based open source simulation environment for two-phase geophysical mass flows such as avalanches of snow or rock, flows of debris or mud, and related process chains. r.avaflow is freely available and adoptable as a raster module of the GRASS GIS software ( We focus on the following issues: (1) We back-calculate a laboratory-scale debris flow experiment with r.avaflow and thereby show that different types of drag may govern the evolving flow dynamics, depending on the initial flow configuratiuon. In particular, it appears necessary to consider viscous ambient drag in order to achieve simulation results in line with experimentally measurements. (2) We employ a set of well-documented rock avalanche events to illustrate the use of a built-in functionality for parameter sensitivity analysis and optimization. To do so, we demonstrate possible strategies going beyond the deficient one-at-a-time simulation approach. They allow us to test three or more parameters at once with a limited number of model runs. Computational times are kept at an acceptable level by multi-core processing strategies and use of the Vienna Scientific Cluster. We further discuss a number of key issues with regard to (i) arbitrary mountain topography; and (ii) entrainment and deposition of material. Most tests indicate a good model performance when the affected areas predicted for a late stage of the flow simulation are compared with observed affected areas. However, we note that such a validation is not fully justified without the implementation of a physically correct model for the deposition process. Acknowledgement: The work was conducted as part of the international cooperation project "A GIS simulation model for avalanche and debris flows (avaflow)" supported by the Austrian Science Fund

  4. Improved Gain Microstrip Patch Antenna (United States)


    frequency selective structure (FSS) as a layer above a microstrip patch antenna. This is done to filter undesirable frequencies. For this purpose the used for isolating the antenna from the filtered frequency, not improving the gain of the antenna. [0008] Thus, there is a need for microstrip...selective surface applied. The passband is generally indicated as the region where the curve passes below a VSWR of 3. These results indicate a

  5. Optical gain in silicon nanocrystals

    Czech Academy of Sciences Publication Activity Database

    Pelant, Ivan


    Roč. 208, č. 3 (2011), s. 625-630 ISSN 1862-6300 R&D Projects: GA AV ČR KAN400100701; GA AV ČR(CZ) IAA101120804; GA MŠk LC510 Institutional research plan: CEZ:AV0Z10100521 Keywords : experimental approach * luminescence * nanocrystals * optical gain * silicon Subject RIV: BM - Solid Matter Physics ; Magnetism Impact factor: 1.463, year: 2011

  6. An aluminum influence on root circumnutation in dark revealed by a new super-HARP (high-gain avalanche rushing amorphous photoconductor) camera. (United States)

    Hayashi, Yoshitake; Nishiyama, Hiroki; Tanoi, Keitaro; Ohya, Tomoyuki; Nihei, Naoto; Tanioka, Kenkichi; Nakanishi, Tomoko M


    The circumnutation of a rice root under dark conditions was observed using a highly sensitive camera, a new super-HARP camera. A rice root showed regular rhythmic movement with fixed angle. When treated with Al (5 microM AlCl3), the rotation angle of the root tip was drastically decreased and then the movement was resumed again, whereas the root elongation rate was constant. With the increase of Al concentration, the cycle-fading period became shorter. This is the first report to show that an Al treatment ceased the rotation movement of the root but not elongation.

  7. Increasing rock-avalanche size and mobility in Glacier Bay National Park and Preserve, Alaska detected from 1984 to 2016 Landsat imagery (United States)

    Coe, Jeffrey A.; Bessette-Kirton, Erin; Geertsema, Marten


    In the USA, climate change is expected to have an adverse impact on slope stability in Alaska. However, to date, there has been limited work done in Alaska to assess if changes in slope stability are occurring. To address this issue, we used 30-m Landsat imagery acquired from 1984 to 2016 to establish an inventory of 24 rock avalanches in a 5000-km2 area of Glacier Bay National Park and Preserve in southeast Alaska. A search of available earthquake catalogs revealed that none of the avalanches were triggered by earthquakes. Analyses of rock-avalanche magnitude, mobility, and frequency reveal a cluster of large (areas ranging from 5.5 to 22.2 km2), highly mobile (height/length < 0.3) rock avalanches that occurred from June 2012 through June 2016 (near the end of the 33-year period of record). These rock avalanches began about 2  years after the long-term trend in mean annual maximum air temperature may have exceeded 0 °C. Possibly more important, most of these rock avalanches occurred during a multiple-year period of record-breaking warm winter and spring air temperatures. These observations suggested to us that rock avalanches in the study area may be becoming larger because of rock-permafrost degradation. However, other factors, such as accumulating elastic strain, glacial thinning, and increased precipitation, may also play an important role in preconditioning slopes for failure during periods of warm temperatures.

  8. Influence of weak layer heterogeneity and slab properties on slab tensile failure propensity and avalanche release area (United States)

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


    Dry-snow slab avalanches are generally caused by a sequence of fracture processes, including failure initiation in a weak snow layer underlying a cohesive slab followed by crack propagation within the weak layer (WL) and tensile fracture through the slab. During past decades, theoretical and experimental work has gradually increased our knowledge of the fracture process in snow. However, our limited understanding of crack propagation and fracture arrest propensity prevents the evaluation of avalanche release sizes and thus impedes hazard assessment. To address this issue, slab tensile failure propensity is examined using a mechanically based statistical model of the slab-WL system based on the finite element method. This model accounts for WL heterogeneity, stress redistribution by slab elasticity and possible tensile failure of the slab. Two types of avalanche release are distinguished in the simulations: (1) full-slope release if the heterogeneity is not sufficient to stop crack propagation and trigger a tensile failure within the slab; (2) partial-slope release if fracture arrest and slab tensile failure occur due to the WL heterogeneity. The probability of these two release types is presented as a function of the characteristics of WL heterogeneity and the slab. One of the main outcomes is that, for realistic values of the parameters, the tensile failure propensity is mainly influenced by slab properties. Hard and thick snow slabs are more prone to wide-scale crack propagation and thus lead to larger avalanches (full-slope release). In this case, the avalanche size is mainly influenced by topographical and morphological features such as rocks, trees, slope curvature and the spatial variability of the snow depth as often claimed in the literature.

  9. Axial InGaAs/GaAs nanowire separate absorption-multiplication avalanche photodetectors (Conference Presentation) (United States)

    Huffaker, Diana L.


    In0.53Ga0.47As/InP single photon avalanche detectors (SPADs) have a high photon detection efficiency in the near-IR, however the dark count rate is prohibitively high at room temperature. A nanowire-based In0.3Ga0.7As/GaAs SPAD can significantly reduce the DCR through a nearly three order of magnitude reduction in bulk InGaAs volume, as well as by reducing the indium composition for operation at 1064 nm. As a first step, we have successfully grown axial InGaAs/GaAs heterostructures using catalyst-free selective-area epitaxy. We will present the electrical characterization of a vertically oriented nanowire array InGaAs/GaAs SPADs operating at 1064 nm and use 3-dimensional modeling to aid in the analysis.

  10. Comparative study of afterpulsing behavior and models in single photon counting avalanche photo diode detectors. (United States)

    Ziarkash, Abdul Waris; Joshi, Siddarth Koduru; Stipčević, Mario; Ursin, Rupert


    Single-photon avalanche diode (SPAD) detectors, have a great importance in fields like quantum key distribution, laser ranging, florescence microscopy, etc. Afterpulsing is a non-ideal behavior of SPADs that adversely affects any application that measures the number or timing of detection events. Several studies based on a few individual detectors, derived distinct mathematical models from semiconductor physics perspectives. With a consistent testing procedure and statistically large data sets, we show that different individual detectors - even if identical in type, make, brand, etc. - behave according to fundamentally different mathematical models. Thus, every detector must be characterized individually and it is wrong to draw universal conclusions about the physical meaning behind these models. We also report the presence of high-order afterpulses that are not accounted for in any of the standard models.

  11. Parameters of a supershort avalanche electron beam generated in atmospheric-pressure air (United States)

    Tarasenko, V. F.


    Conditions under which the number of runaway electrons in atmospheric-pressure air reaches ˜5 × 1010 are determined. Recommendations for creating runaway electron accelerators are given. Methods for measuring the parameters of a supershort avalanche electron beam and X-ray pulses from gas-filled diodes, as well as the discharge current and gap voltage, are described. A technique for determining the instant of runaway electron generation with respect to the voltage pulse is proposed. It is shown that the reduction in the gap voltage and the decrease in the beam current coincide in time. The mechanism of intense electron beam generation in gas-filled diodes is analyzed. It is confirmed experimentally that, in optimal regimes, the number of electrons generated in atmospheric-pressure air with energies T > eU m , where U m is the maximum gap voltage, is relatively small.

  12. Two-dimensional simulation research of secondary electron emission avalanche discharge on vacuum insulator surface (United States)

    Cai, Libing; Wang, Jianguo; Zhu, Xiangqin; Wang, Yue; Zhang, Dianhui


    Based on the secondary electron emission avalanche (SEEA) model, the SEEA discharge on the vacuum insulator surface is simulated by using a 2D PIC-MCC code developed by ourselves. The evolutions of the number of discharge electrons, insulator surface charge, current, and 2D particle distribution are obtained. The effects of the strength of the applied electric field, secondary electron yield coefficient, rise time of the pulse, length of the insulator on the discharge are investigated. The results show that the number of the SEEA electrons presents a quadratic dependence upon the applied field strength. The SEEA current, which is on the order of Ampere, is directly proportional to the field strength and secondary electron yield coefficient. Finally, the electron-stimulated outgassing is included in the simulation code, and a three-phase discharge curve is presented by the simulation, which agrees with the experimental data.

  13. Supershort avalanche electron beams and x-ray in high-pressure nanosecond discharges

    International Nuclear Information System (INIS)

    Tarasenko, V F; Baksht, E H; Kostyrya, I D; Lomaev, M I; Rybka, D V


    The properties of a supershort avalanche electron beam (S AEB) and X-ray radiation produced using a nanosecond volume discharge are examined. An electron beam of the runaway electrons with amplitude of ∼ 50 A has been obtained in air atmospheric pressure. It is reported that S AEB is formed in the angle above 2π sr. Three groups of the runaway electrons are formed in a gas diode under atmospheric air pressure, when nanosecond voltage pulses with amplitude of hundreds of kilovolts are applied. The electron beam has been generated behind a 45 μm thick AlBe foil in SF 6 and Xe under the pressure of 2 arm, and in He under the pressure of about 12 atm. The paper gives the analysis of a generation mechanism of SAEB.

  14. Two-dimensional simulation research of secondary electron emission avalanche discharge on vacuum insulator surface

    International Nuclear Information System (INIS)

    Cai, Libing; Wang, Jianguo; Zhu, Xiangqin; Wang, Yue; Zhang, Dianhui


    Based on the secondary electron emission avalanche (SEEA) model, the SEEA discharge on the vacuum insulator surface is simulated by using a 2D PIC-MCC code developed by ourselves. The evolutions of the number of discharge electrons, insulator surface charge, current, and 2D particle distribution are obtained. The effects of the strength of the applied electric field, secondary electron yield coefficient, rise time of the pulse, length of the insulator on the discharge are investigated. The results show that the number of the SEEA electrons presents a quadratic dependence upon the applied field strength. The SEEA current, which is on the order of Ampere, is directly proportional to the field strength and secondary electron yield coefficient. Finally, the electron-stimulated outgassing is included in the simulation code, and a three-phase discharge curve is presented by the simulation, which agrees with the experimental data

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

    CERN Document Server

    Hayashi, K; Matsubara, E I; Kishimoto, S; Mori, T; Tanaka, M


    A high counting rate X-ray detector with an appropriate energy resolution is desired for high quality X-ray fluorescence hologram measurements because a holographic pattern is detected as extremely small intensity variations of X-ray fluorescence on a large intensity background. A cooled avalanche photodiode (APD), which has about 10% energy resolution and is designed for a high counting rate, fits the above requirements. Reconstructed atomic images from experimental holograms using the APD system provide us a clear view of the first and second neighbor atoms around an emitter. The present result proved that a combination of this APD system and a synchrotron X-ray source enables us to measure a high quality hologram for a reasonable measurement time.

  16. Performance Analysis of Single Photon Avalanche Diode Underwater VLC System Using ARQ

    KAUST Repository

    Shafiqu, Taniya


    Single photon avalanche diode (SPAD) has recently been introduced as a powerful detector for long distance underwater visible light (UVLC) communication. In this paper, the performance of the SPAD detector in UVLC is analyzed considering the effect of the turbulence induced fading resulting from air bubbles in addition to the combined effect of attenuation and scattering. Automatic repeat request (ARQ) system is adopted to mitigate different underwater impairments and reduce the error probability at the receiver side. Approximate packet error rate (PER) expressions are derived using Laguerre Gauss polynomial for a finite number of transmission. Next, the average energy efficiency and throughput are analyzed to account for the increased energy consumption cost and the decreased effective transmission rate, which results from adopting the ARQ scheme. Finally, different numerical results are introduced to verify the derived PER expressions, demonstrate the ability of the proposed ARQ system in extending the transmission range, and show the trade-off between energy efficiency (EE) and throughput.

  17. Predictions of silicon avalanche photodiode detector performance in water vapor differential absorption lidar (United States)

    Kenimer, R. L.


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

  18. A Single-Photon Avalanche Diode Array for Fluorescence Lifetime Imaging Microscopy (United States)

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


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

  19. Memory effect in silicon time-gated single-photon avalanche diodes

    Energy Technology Data Exchange (ETDEWEB)

    Dalla Mora, A.; Contini, D., E-mail:; Di Sieno, L. [Dipartimento di Fisica, Politecnico di Milano, Piazza Leonardo da Vinci 32, I-20133 Milano (Italy); Tosi, A.; Boso, G.; Villa, F. [Dipartimento di Elettronica, Informazione e Bioingegneria, Politecnico di Milano, Piazza Leonardo da Vinci 32, I-20133 Milano (Italy); Pifferi, A. [Dipartimento di Fisica, Politecnico di Milano, Piazza Leonardo da Vinci 32, I-20133 Milano (Italy); CNR, Istituto di Fotonica e Nanotecnologie, Piazza Leonardo da Vinci 32, I-20133 Milano (Italy)


    We present a comprehensive characterization of the memory effect arising in thin-junction silicon Single-Photon Avalanche Diodes (SPADs) when exposed to strong illumination. This partially unknown afterpulsing-like noise represents the main limiting factor when time-gated acquisitions are exploited to increase the measurement dynamic range of very fast (picosecond scale) and faint (single-photon) optical signals following a strong stray one. We report the dependences of this unwelcome signal-related noise on photon wavelength, detector temperature, and biasing conditions. Our results suggest that this so-called “memory effect” is generated in the deep regions of the detector, well below the depleted region, and its contribution on detector response is visible only when time-gated SPADs are exploited to reject a strong burst of photons.

  20. Properties of avalanche photodiodes for applications in high energy physics, astrophysics and medical imaging

    CERN Document Server

    Renker, D


    Avalanche Photodiodes (APDs) with reverse structure and very good sensitivity to visible light are the first time used in large scale for the readout of PbWO sub 4 crystals in the barrel of the CMS electromagnetic calorimeter. They have to operate in a rather hostile environment, in a magnetic field of 4 T and under unprecedented radiation levels for a minimum of 10 years with a failure rate substantially lower than 1%. After an extensive R and D work the mass production started recently. The properties of the APDs and the possibilities for modifications of some parameters for other applications will be discussed. Particularly interesting is the status of APD arrays and the prospects of their development for PET scanners and for X-ray imaging.

  1. Post-processing Free Quantum Random Number Generator Based on Avalanche Photodiode Array

    International Nuclear Information System (INIS)

    Li Yang; Liao Sheng-Kai; Liang Fu-Tian; Shen Qi; Liang Hao; Peng Cheng-Zhi


    Quantum random number generators adopting single photon detection have been restricted due to the non-negligible dead time of avalanche photodiodes (APDs). We propose a new approach based on an APD array to improve the generation rate of random numbers significantly. This method compares the detectors' responses to consecutive optical pulses and generates the random sequence. We implement a demonstration experiment to show its simplicity, compactness and scalability. The generated numbers are proved to be unbiased, post-processing free, ready to use, and their randomness is verified by using the national institute of standard technology statistical test suite. The random bit generation efficiency is as high as 32.8% and the potential generation rate adopting the 32 × 32 APD array is up to tens of Gbits/s. (paper)

  2. The Avalanche Hypothesis and Compression of Morbidity: Testing Assumptions through Cohort-Sequential Analysis.

    Directory of Open Access Journals (Sweden)

    Jordan Silberman

    Full Text Available The compression of morbidity model posits a breakpoint in the adult lifespan that separates an initial period of relative health from a subsequent period of ever increasing morbidity. Researchers often assume that such a breakpoint exists; however, this assumption is hitherto untested.To test the assumption that a breakpoint exists--which we term a morbidity tipping point--separating a period of relative health from a subsequent deterioration in health status. An analogous tipping point for healthcare costs was also investigated.Four years of adults' (N = 55,550 morbidity and costs data were retrospectively analyzed. Data were collected in Pittsburgh, PA between 2006 and 2009; analyses were performed in Rochester, NY and Ann Arbor, MI in 2012 and 2013. Cohort-sequential and hockey stick regression models were used to characterize long-term trajectories and tipping points, respectively, for both morbidity and costs.Morbidity increased exponentially with age (P<.001. A morbidity tipping point was observed at age 45.5 (95% CI, 41.3-49.7. An exponential trajectory was also observed for costs (P<.001, with a costs tipping point occurring at age 39.5 (95% CI, 32.4-46.6. Following their respective tipping points, both morbidity and costs increased substantially (Ps<.001.Findings support the existence of a morbidity tipping point, confirming an important but untested assumption. This tipping point, however, may occur earlier in the lifespan than is widely assumed. An "avalanche of morbidity" occurred after the morbidity tipping point-an ever increasing rate of morbidity progression. For costs, an analogous tipping point and "avalanche" were observed. The time point at which costs began to increase substantially occurred approximately 6 years before health status began to deteriorate.

  3. GAIN Technology Workshops Summary Report

    International Nuclear Information System (INIS)

    Braase, Lori Ann


    National and global demand for nuclear energy is increasing and United States (U.S.) global leadership is eroding. There is a sense of urgency with respect to the deployment of the innovative nuclear energy technologies. The Gateway for Accelerated Innovation in Nuclear (GAIN) initiative is based on the simultaneous achievement of three strategic goals. The first is maintaining global technology leadership within the U.S. Department of Energy (DOE). The second is enabling global industrial leadership for nuclear vendors and suppliers. The third is focused on utility optimization of nuclear energy within the clean energy portfolio. An effective public-private partnership is required to achieve these goals. DOEs recognizes the recent sense of urgency new developers and investors have in getting their concepts to market. They know that time to market for nuclear technology takes too long and the facilities needed to conduct the necessary research, development and demonstration (RD&D) activities are very expensive to develop and maintain. Early technologies, in the lower technology readiness levels (TRL) need materials testing, analysis, modeling, code development, etc., most of which currently exists in the DOE national laboratory system. However, mature technologies typically need large component testing and demonstration facilities, which are expensive and long-lead efforts. By understanding the needs of advanced nuclear technology developers, GAIN will connect DOE national laboratory capabilities (e.g., facilities, expertise, materials, and data) with industry RD&D needs. In addition, GAIN is working with the Nuclear Regulatory Commission (NRC) to streamline processes and increase understanding of the licensing requirements for advanced reactors.

  4. GAIN Technology Workshops Summary Report

    Energy Technology Data Exchange (ETDEWEB)

    Braase, Lori Ann [Idaho National Lab. (INL), Idaho Falls, ID (United States)


    National and global demand for nuclear energy is increasing and United States (U.S.) global leadership is eroding. There is a sense of urgency with respect to the deployment of the innovative nuclear energy technologies. The Gateway for Accelerated Innovation in Nuclear (GAIN) initiative is based on the simultaneous achievement of three strategic goals. The first is maintaining global technology leadership within the U.S. Department of Energy (DOE). The second is enabling global industrial leadership for nuclear vendors and suppliers. The third is focused on utility optimization of nuclear energy within the clean energy portfolio. An effective public-private partnership is required to achieve these goals. DOEs recognizes the recent sense of urgency new developers and investors have in getting their concepts to market. They know that time to market for nuclear technology takes too long and the facilities needed to conduct the necessary research, development and demonstration (RD&D) activities are very expensive to develop and maintain. Early technologies, in the lower technology readiness levels (TRL) need materials testing, analysis, modeling, code development, etc., most of which currently exists in the DOE national laboratory system. However, mature technologies typically need large component testing and demonstration facilities, which are expensive and long-lead efforts. By understanding the needs of advanced nuclear technology developers, GAIN will connect DOE national laboratory capabilities (e.g., facilities, expertise, materials, and data) with industry RD&D needs. In addition, GAIN is working with the Nuclear Regulatory Commission (NRC) to streamline processes and increase understanding of the licensing requirements for advanced reactors.

  5. A gain-coefficient switched Alexandrite laser

    International Nuclear Information System (INIS)

    Lee, Chris J; Van der Slot, Peter J M; Boller, Klaus-J


    We report on a gain-coefficient switched Alexandrite laser. An electro-optic modulator is used to switch between high and low gain states by making use of the polarization dependent gain of Alexandrite. In gain-coefficient switched mode, the laser produces 85 ns pulses with a pulse energy of 240 mJ at a repetition rate of 5 Hz.

  6. Estimating the potential gains from mergers

    DEFF Research Database (Denmark)

    Bogetoft, Peter; Wang, Dexiang


    We introduce simple production economic models to estimate the potential gains from mergers. We decompose the gains into technical ef¿ciency, size (scale) and harmony (mix) gains, and we discuss alternative ways to capture these gains. We propose to approximate the production processes using...

  7. Understanding weight gain at menopause. (United States)

    Davis, S R; Castelo-Branco, C; Chedraui, P; Lumsden, M A; Nappi, R E; Shah, D; Villaseca, P


    The aim of this review was to summarize the literature regarding the impact of the menopause transition on body weight and body composition. We conducted a search of the literature using Medline (Ovid, 1946-present) and PubMed (1966-2012) for English-language studies that included the following search terms: 'menopause', 'midlife', 'hormone therapy' or 'estrogen' combined with 'obesity', 'body weight' or 'body composition'. Whereas weight gain per se cannot be attributed to the menopause transition, the change in the hormonal milieu at menopause is associated with an increase in total body fat and an increase in abdominal fat. Weight excess at midlife is not only associated with a heightened risk of cardiovascular and metabolic disease, but also impacts adversely on health-related quality of life and sexual function. Animal and human studies indicate that this tendency towards central abdominal fat accumulation is ameliorated by estrogen therapy. Studies mostly indicate a reduction in overall fat mass with estrogen and estrogen-progestin therapy, improved insulin sensitivity and a lower rate of development of type 2 diabetes. The hormonal changes across the perimenopause substantially contribute to increased abdominal obesity which leads to additional physical and psychological morbidity. There is strong evidence that estrogen therapy may partly prevent this menopause-related change in body composition and the associated metabolic sequelae. However, further studies are required to identify the women most likely to gain metabolic benefit from menopausal hormone therapy in order to develop evidence-based clinical recommendations.

  8. Estimating the potential gains from mergers

    DEFF Research Database (Denmark)

    Bogetoft, Peter; Wang, Dexiang


    We introduce simple production economic models to estimate the potential gains from mergers. We decompose the gains into technical ef¿ciency, size (scale) and harmony (mix) gains, and we discuss alternative ways to capture these gains. We propose to approximate the production processes using...... the non-parametric. Data Envelopment Analysis (DEA) approach, and we use the resulting operational approach to estimate the potential gains from merging agricultural extension of¿ces in Denmark....

  9. Evaluating the Feasibility of Using Remote Technology for Cochlear Implants (United States)

    Goehring, Jenny L.; Hughes, Michelle L.; Baudhuin, Jacquelyn L.


    The use of remote technology to provide cochlear implant services has gained popularity in recent years. This article contains a review of research evaluating the feasibility of remote service delivery for recipients of cochlear implants. To date, published studies have determined that speech-processor programming levels and other objective tests…

  10. A nineteenth century avalanche episode reconstruction via historic newspapers: from unstructured information to standardized information (United States)

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


    Several climatic risks studies based on the analysis of data recorded in newspapers have been published to date. These studies deal with both general (Moltó, 2000; García y Martí, 2000; Hernández Varela et al., 2003; Olcina, 2005) and specific risks such as landslides (Domínguez et al., 1999; Devoli et al., 2007; Polemio y Petrucci, 2010) seastorms (Yanes y Marzol, 2009) and snowstorms (Olcina y Moltó, 2002) among others. The purpose of this paper is to report on the methodology and results of the study of an extreme historical event happened in the Asturian Massif (Northern Spain) in 1888. Special attention has been paid to methodological aspects and to the difficulties found in the goal of devising a method that would enable the reconstruction of this kind of phenomena on the basis of nivometheorogical conditions, geographical location and socio-economic impact. To a great deal we focused our efforts on designing a logical database structure and a set of tables that would allow us to store and cross the information for statistical analysis. This includes outlier detection in order to ensure the quality of the results. The information sources used in our study have been the issues of the daily newspaper 'El Carbayón' and the weekly newspaper 'El Oriente de Asturias' published in Oviedo and Llanes (Asturias) between the 20th of January and 30th of May 1888. A total of 92 issues have been collected via the hard copy microfilm housed in the Central Library of Asturias. We reviewed 70 reports relating to avalanche events happened in the aforementioned period of time. We grouped the consequences of the events into 3 main categories (personal injuries, material damages and absence of both) and 5 child categories (deaths, wounded, house and attached building damage, livestock injuries, damage to infrastructures and communications). We gathered data about the thickness of snow-cover, the number of consecutive snowstorms and, in order to facilitate a territorial

  11. Le déclenchement des avalanches de plaque de neige:
    De l'approche mécanique à l'approche statistique.


    Faillettaz, Jerome


    The present work aims at understanding the mechanisms responsible forsnow slab avalanche formation.A first approach consists in applying to snow well known concepts of Fracture Mechanics. Experimental measurements of fracture toughness, are interpreted in terms of the particular structure of snow.A statistical approach is then used, based on databases provided by La Plagne and Tignes ski resorts. We show for the first time that avalanche sizes are scale invariant.Models used to describe such ...

  12. Gain attenuation of gated framing camera

    International Nuclear Information System (INIS)

    Xiao Shali; Liu Shenye; Cao Zhurong; Li Hang; Zhang Haiying; Yuan Zheng; Wang Liwei


    The theoretic model of framing camera's gain attenuation is analyzed. The exponential attenuation curve of the gain along the pulse propagation time is simulated. An experiment to measure the coefficient of gain attenuation based on the gain attenuation theory is designed. Experiment result shows that the gain follows an exponential attenuation rule with a quotient of 0.0249 nm -1 , the attenuation coefficient of the pulse is 0.00356 mm -1 . The loss of the pulse propagation along the MCP stripline is the leading reason of gain attenuation. But in the figure of a single stripline, the gain dose not follow the rule of exponential attenuation completely, instead, there is a gain increase at the stripline bottom. That is caused by the reflection of the pulse. The reflectance is about 24.2%. Combining the experiment and theory, which design of the stripline MCP can improved the gain attenuation. (authors)

  13. A remotely piloted aircraft system in major incident management: concept and pilot, feasibility study. (United States)

    Abrahamsen, Håkon B


    Major incidents are complex, dynamic and bewildering task environments characterised by simultaneous, rapidly changing events, uncertainty and ill-structured problems. Efficient management, communication, decision-making and allocation of scarce medical resources at the chaotic scene of a major incident is challenging and often relies on sparse information and data. Communication and information sharing is primarily voice-to-voice through phone or radio on specified radio frequencies. Visual cues are abundant and difficult to communicate between teams and team members that are not co-located. The aim was to assess the concept and feasibility of using a remotely piloted aircraft (RPA) system to support remote sensing in simulated major incident exercises. We carried out an experimental, pilot feasibility study. A custom-made, remotely controlled, multirotor unmanned aerial vehicle with vertical take-off and landing was equipped with digital colour- and thermal imaging cameras, a laser beam, a mechanical gripper arm and an avalanche transceiver. We collected data in five simulated exercises: 1) mass casualty traffic accident, 2) mountain rescue, 3) avalanche with buried victims, 4) fisherman through thin ice and 5) search for casualties in the dark. The unmanned aerial vehicle was remotely controlled, with high precision, in close proximity to air space obstacles at very low levels without compromising work on the ground. Payload capacity and tolerance to wind and turbulence were limited. Aerial video, shot from different altitudes, and remote aerial avalanche beacon search were streamed wirelessly in real time to a monitor at a ground base. Electromagnetic interference disturbed signal reception in the ground monitor. A small remotely piloted aircraft can be used as an effective tool carrier, although limited by its payload capacity, wind speed and flight endurance. Remote sensing using already existing remotely piloted aircraft technology in pre

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

    International Nuclear Information System (INIS)

    Rameika, R.; Cox, B.; Jenkins, C.M.


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

  15. Best-Practice Criteria for Practical Security of Self-Differencing Avalanche Photodiode Detectors in Quantum Key Distribution (United States)

    Koehler-Sidki, A.; Dynes, J. F.; Lucamarini, M.; Roberts, G. L.; Sharpe, A. W.; Yuan, Z. L.; Shields, A. J.


    Fast-gated avalanche photodiodes (APDs) are the most commonly used single photon detectors for high-bit-rate quantum key distribution (QKD). Their robustness against external attacks is crucial to the overall security of a QKD system, or even an entire QKD network. We investigate the behavior of a gigahertz-gated, self-differencing (In,Ga)As APD under strong illumination, a tactic Eve often uses to bring detectors under her control. Our experiment and modeling reveal that the negative feedback by the photocurrent safeguards the detector from being blinded through reducing its avalanche probability and/or strengthening the capacitive response. Based on this finding, we propose a set of best-practice criteria for designing and operating fast-gated APD detectors to ensure their practical security in QKD.

  16. Thermodynamics of the Heat-Flux Avalanches at the First-Order Magnetic Transition in Magnetocaloric Materials (United States)

    Piazzi, Marco; Bennati, Cecilia; Basso, Vittorio


    We investigate the kinetics of first-order magnetic phase transitions by measuring and modeling the heat-flux avalanches corresponding to the irreversible motion of the phase-boundary interface separating the coexisting low- and high-temperature stable magnetic phases. By means of out-of-equilibrium thermodynamics, we encompass the damping mechanisms of the boundary motion in a phenomenological parameter αs. By analyzing the time behavior of the heat-flux signals measured on La (Fe -Mn -Si )13-H magnetocaloric compounds through Peltier calorimetry temperature scans performed at low rates, we relate the linear rise of the individual avalanches to the intrinsic-damping parameter αs.

  17. Laser-enhanced ionization of mercury atoms in an inert atmosphere with avalanche amplification of the signal. (United States)

    Clevenger, W L; Matveev, O I; Cabredo, S; Omenetto, N; Smith, B W; Winefordner, J D


    A new method for laser-enhanced ionization detection of mercury atoms in an inert gas atmosphere is described. The method, which is based on the avalanche amplification of the signal resulting from the ionization from a selected Rydberg level reached by a three-step laser excitation of mercury vapor in a simple quartz cell, can be applied to the determination of this element in various matrices by the use of conventional cold atomization techniques. The overall (collisional + photo) ionization efficiency is investigated at different temperatures, and the avalanche amplification effect is reported for Ar and P-10 gases at atmospheric pressure. It is shown that the amplified signal is related to the number of charges produced in the laser-irradiated volume. Under amplifier noise-limited conditions, a detection limit of ∼15 Hg atoms/laser pulse in the interaction region is estimated.

  18. Imaging Findings of a Survivor of Avalanche without Any Life Support at Very High Altitude and Extreme Low Temperatures

    Directory of Open Access Journals (Sweden)

    Abhishek Dwivedi


    Full Text Available Survival at high altitude is very challenging and in spite of adequate training and acclimatization, injuries are frequent. The fate of mountaineers and soldiers at such areas largely depends on the mercy of the climate. An avalanche causes physical trauma, cold injury and asphyxia to the victim. The patient in our report had diffuse cerebral edema, bilateral pulmonary consolidation and pneumothorax. In spite of the best efforts the victim succumbed to the injuries. There are many incidents of high altitude accidents in India. This case report is of a soldier deployed at the high altitude, is a lone ever reported survivor above 5000 meters, under 35 feet snow and below - 45°C for greater than 5 days of exposure to an avalanche

  19. Near-Saturation Single-Photon Avalanche Diode Afterpulse and Sensitivity Correction Scheme for the LHC Longitudinal density Monitor

    CERN Document Server

    Bravin, E; Palm, M


    Single-Photon Avalanche Diodes (SPADs) monitor the longitudinal density of the LHC beams by measuring the temporal distribution of synchrotron radiation. The relative population of nominally empty RF-buckets (satellites or ghosts) with respect to filled bunches is a key figure for the luminosity calibration of the LHC experiments. Since afterpulsing from a main bunch avalanche can be as high as, or higher than, the signal from satellites or ghosts, an accurate correction algorithm is needed. Furthermore, to reduce the integration time, the amount of light sent to the SPAD is enough so that pile-up effects and afterpulsing cannot be neglected. The SPAD sensitivity has also been found to vary at the end of the active quenching phase. We present a method to characterize and correct for SPAD deadtime, afterpulsing and sensitivity variation near saturation, together with laboratory benchmarking.

  20. Investigation of the performance of alpha particle counting and alpha-gamma discrimination by pulse shape with micro-pixel avalanche photodiode

    International Nuclear Information System (INIS)

    Ahmadov, G.; Madatov, R.; Sadigov, A.; Sadygov, Z.; Jafarova, E.; Ahmadov, G.; Sadygov, Z.; Olshevski, A.; Zerrouk, F.; Mukhtarov, R.


    Being capable measuring small lights gives possibility to use micro-pixel avalanche photodiodes with scintillators. It is shown two prototypes to use micro-pixel avalanche photodiodes with and without scintillators as alpha and gamma counters in this paper. First prototype is to use two micro-pixel avalanche photodiodes. One for detecting alpha particles and closer to it, the second one with a thin plastic scintillator for detecting gamma rays. Second prototype is called two-layers configuration in which it is used only one micro-pixel avalanche photodiode, but two scntillators with different decay times. One can distinquish alpha particle and gamma ray events by using pulse shape discrimination techniques in the two-layer configuration. In this work an alpha particle and gamma ray counting performance of micro-pixel avalanche photodiodes without scintillators and its combination of plastic and BGO+ plastic scintillators was investigated. Obtained results showed the detection performance of the micro-pixel avalanche photodiodes in combination with plastic scintillator was about the same as conventional semiconductor detectors

  1. Increasing rock-avalanche size and mobility in Glacier Bay National Park and Preserve, Alaska detected from 1984 to 2016 Landsat imagery (United States)

    Coe, Jeffrey A.; Bessette-Kirton, Erin; Geertsema, Marten


    In the USA, climate change is expected to have an adverse impact on slope stability in Alaska. However, to date, there has been limited work done in Alaska to assess if changes in slope stability are occurring. To address this issue, we used 30-m Landsat imagery acquired from 1984 to 2016 to establish an inventory of 24 rock avalanches in a 5000-km2 area of Glacier Bay National Park and Preserve in southeast Alaska. A search of available earthquake catalogs revealed that none of the avalanches were triggered by earthquakes. Analyses of rock-avalanche magnitude, mobility, and frequency reveal a cluster of large (areas ranging from 5.5 to 22.2 km2), highly mobile (height/length period of record). These rock avalanches began about 2  years after the long-term trend in mean annual maximum air temperature may have exceeded 0 °C. Possibly more important, most of these rock avalanches occurred during a multiple-year period of record-breaking warm winter and spring air temperatures. These observations suggested to us that rock avalanches in the study area may be becoming larger because of rock-permafrost degradation. However, other factors, such as accumulating elastic strain, glacial thinning, and increased precipitation, may also play an important role in preconditioning slopes for failure during periods of warm temperatures.

  2. Feasibility studies and technological innovation

    DEFF Research Database (Denmark)

    Hvelplund, Frede Kloster; Lund, Henrik; Sukkumnoed, Decharut


    The chapter offers a tool to conduct feasibility studies and focuses on how to make feasibility studies in a situation with environmental concerns, in which technological innovation and institutional chnages are among the objectives.......The chapter offers a tool to conduct feasibility studies and focuses on how to make feasibility studies in a situation with environmental concerns, in which technological innovation and institutional chnages are among the objectives....

  3. Application of avalanche photodiode for soft X-ray pulse-height analyses in the Ht-7 tokamak

    CERN Document Server

    Shi Yue Jiang; Hu Li Qun; Sun Yan Jun; LiuSheng; Ling Bil


    An avalanche photodiode (APD) has been used as soft X-ray energy pulse-height analysis system for the measurement of the electron temperature on the HT-7 tokamak. The experimental results obtained with the APD with its inferior energy resolution show a little difference compared to the conventional high energy-resolution Si (Li) detector. Both numerical analysis and experimental results prove that the APD is good enough for application of the electron temperature measurement in tokamaks.

  4. High speed quantitative digital beta autoradiography using a multi-step avalanche detector and an Apple-II microcomputer

    International Nuclear Information System (INIS)

    Bateman, J.E.; Connolly, J.F.; Stephenson, R.


    The development of an electronic, digital beta autoradiography system is described. Using a Multi-Step Avalanche/Multi-Wire Proportional Counter (MSA/MWPC) detector system fitted with delay line readout, high speed digital imaging is demonstrated with sub-millimeter spatial resolution. Good proportionality of observed counting rate relative to the known tritium activity is demonstrated. The application of the system to autoradiography in immunoelectrophoresis, histopathology and DNA sequencing is described. (author)

  5. Radiation hardness investigation of avalanche photodiodes for the Projectile Spectator Detector readout at the Compressed Baryonic Matter experiment

    Czech Academy of Sciences Publication Activity Database

    Kushpil, Vasilij; Mikhaylov, Vasily; Kushpil, Svetlana; Tlustý, Pavel; Svoboda, Ondřej; Kugler, Andrej


    Roč. 787, JUL (2015), s. 117-120 ISSN 0168-9002 R&D Projects: GA MŠk LG12007; GA MŠk LG14004; GA MŠk(CZ) LM2011019 Institutional support: RVO:61389005 Keywords : avalanche photodiodes * single protons detection * radiation hardness * neutron irradiation tests * compressed Baryonic Matter experiment * Projectile Spectator Detector Subject RIV: BG - Nuclear , Atomic and Molecular Physics, Colliders Impact factor: 1.200, year: 2015

  6. A distinct element approach to model the interaction between debris avalanches and embankments (United States)

    Salciarini, Diana; Tamagnini, Claudio; Conversini, Pietro; Rapinesi, Silvia


    Protective measures against hazards associated with debris flows and debris avalanches, include a variety of barriers such as rock/boulder fences, deflection berms, gabions and earthfill barriers, which are placed along the potential flow path where the debris is transported and deposited or close to infrastructures potentially at risk. Recent progress in the field of numerical methods for the lagrangian analysis of discrete particulate systems provides an opportunity to develop a rational design strategy for earthfill barriers as well as other protection methods against debris avalanches. In this work, the Discrete Element Method (DEM) has been used to model the interaction between such natural phenomena and embankments. In the DEM approach, the motion of a granular mass subject to gravity is simulated by numerically solving Newton's equation of motion for each particle considered as an individual body. A parametric study based on a case-history from a marginally stable rock slope near Assisi, in central Italy, has been conducted. The embankment has been simulated in two different ways. In the first case, the embankment acts as a rigid body. In this case, a series of DEM simulations has been conducted to investigate the effect of the influence of the geometry of the sliding mass, slope and barrier, and strength properties of the granular mass on the main design parameters for the barrier. Results show that the barriers considered are all effective in retaining the debris mass; less than 6% of the initial rock mass passes the barrier. The predicted efficiency of the barriers is primarily affected by: i) barrier height; ii) run-out distance; iii) macroscopic friction angle of the debris; and, iv) size of the storage area left between the barrier and the slope base. For the limited range of values considered, the slope angle has only a minor impact on the computed results. In the second case the embankment has been treated as a deformable body, which can slide at the

  7. Custom single-photon avalanche diode with integrated front-end for parallel photon timing applications (United States)

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


    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

  8. Transmission line pulse system for avalanche characterization of high power semiconductor devices (United States)

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


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

  9. Effects of ground freezing and snow avalanche deposits on debris flows in alpine environments

    Directory of Open Access Journals (Sweden)

    E. Bardou


    Full Text Available Debris flows consist of a mixture of water and sediments of various sizes. Apart from few exceptions, the water is usually contributed directly from precipitation. In a high mountain environment like the Alps, it appears necessary to consider infiltration of water into the ground during rainfall events, the runoff characteristics and the potential supply of sediment as a function of a multitude of climatic and hydrogeological factors. This paper outlines several new processes - either linked to ice formation in the ground before an event, or to the presence of snow avalanche deposits - that change the probability of observing an event. These processes were identified during field observations connected with extreme weather events that occurred recently in the Valais Alps (south-western Switzerland: they can be seen as factors either amplifying or reducing the potential of slope instability caused by the precipitation event. An intense freezing of the ground during the week preceding the exceptional rainfall event in mid-October 2000 amplified the probability of triggering debris flows between roughly 1800 and 2300m asl. Both growth of ice needles and superficial ground freezing destroyed soil aggregates (increasing the availability of sediments and/or, a deeper ground freezing resulted in decreased infiltration rate (increased runoff during the first hours of heavy rainfall. The presence of snow avalanche deposits in a gully could be simultaneously an amplifying factor (the snow deposits increase the base flow and create a sliding plane for the sediments, mainly at the time of summer storms or a reducing factor (reduction in the impact energy of the raindrops, mainly at the time of winter storms of the risk of triggering debris flows. If it is not currently possible to establish rainfall threshold values for debris flow triggering, the knowledge and the implementation of these processes in the analysis of the potential triggering (for example by

  10. Reinforced concrete structures loaded by snow avalanches : numerical and experimental approaches. (United States)

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


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

  11. PWR decontamination feasibility study

    International Nuclear Information System (INIS)

    Silliman, P.L.


    The decontamination work which has been accomplished is reviewed and it is concluded that it is worthwhile to investigate further four methods for decontamination for future demonstration. These are: dilute chemical; single stage strong chemical; redox processes; and redox/chemical in combination. Laboratory work is recommended to define the agents and processes for demonstration and to determine the effect of the solvents on PWR materials. The feasibility of Indian Point 1 for decontamination demonstrations is discussed, and it is shown that the system components of Indian Point 1 are well suited for use in demonstrations

  12. Computational and experimental progress on laser-activated gas avalanche switches for broadband, high-power electromagnetic pulse generation

    International Nuclear Information System (INIS)

    Mayhall, D.J.; Yee, J.H.; Villa, F.


    This paper discusses the gas avalanche switch, a high-voltage, picosecond-speed switch, which has been proposed. The basic switch consists of pulse-charged electrodes, immersed in a high-pressure gas. An avalanche discharge is induced in the gas between the electrodes by ionization from a picosecond-scale laser pulse. The avalanching electrons move toward the anode, causing the applied voltage to collapse in picoseconds. This voltage collapse, if rapid enough, generates electromagnetic waves. A two-dimensional (2D), finite difference computer code solves Maxwell's equations for transverse magnetic modes for rectilinear electrodes between parallel plate conductors, along with electron conservation equations for continuity, momentum, and energy. Collision frequencies for ionization and momentum and energy transfer to neutral molecules are assumed to scale linearly with neutral pressure. Electrode charging and laser-driven electron deposition are assumed to be instantaneous. Code calculations are done for a pulse generator geometry, consisting of an 0.7 mm wide by 0.8 mm high, beveled, rectangular center electrode between grounded parallel plates at 2 mm spacing in air

  13. Can Beta Blockers Cause Weight Gain? (United States)

    Beta blockers: Do they cause weight gain? Can beta blockers cause weight gain? Answers from Sheldon G. ... can occur as a side effect of some beta blockers, especially the older ones, such as atenolol ( ...

  14. 75 FR 63763 - Program Integrity: Gainful Employment (United States)


    ... CFR Part 668 RIN 1840-AD04 Program Integrity: Gainful Employment AGENCY: Office of Postsecondary... Proposed Rulemaking on Program Integrity: Gainful Employment, published in the Federal Register on July 26... determining whether a postsecondary educational program provides training that leads to gainful employment in...

  15. Maternal Weight Gain Biosocial Characteristics And Perinatal ...

    African Journals Online (AJOL)

    Two perinatal deaths occurred, with a perinatal mortality rate of 9.52/ 1000.Their mother's weight gains were not attributable to the deaths. Conclusion The study has shown that parity and social class significantly affect maternal weight gain in pregnancy. Even though the mean weight gain in this study was 8.58 ± 3.61kg, ...

  16. The Flynn effect in Korea: Large gains

    NARCIS (Netherlands)

    te Nijenhuis, J.; Cho, S.H.; Murphy, R.; Lee, K.H.


    Secular gains in IQ test scores have been reported for many Western countries. This is the first study of secular IQ gains in South Korea, using various datasets. The first question is what the size of the Flynn effect in South Korea is. The gains per decade are 7.7 points for persons born between

  17. The sound of avalanches: from a global to a local perspective.

    Directory of Open Access Journals (Sweden)

    Dubourg Florine


    Full Text Available We present an experimental study aiming to understand the local origin of the acoustic bursts recorded globally during a two-dimensional shear experiment of a granular medium. In order to explain the power-law distribution of energy of these events (also called avalanches, the analysis focuses on their acoustic frequencies. Experiments with single grains have also been performed, trying to separate the contributions related to collision between neighbours from shear movements between grains. Preliminary results indicate that both frictional sliding and collision-like mechanisms are involved in the origin of the acoustic bursts. The evolution of the structure of the medium around a large acoustic burst is analysed both with high resolution and high-speed imaging. The energy of the acoustic bursts seems related to single and well-localised events with very large variations in energy. However, these local reorganisation processes may eventually bring the global relaxation of the system, which is also captured by a force drop in the resistance to shear.

  18. Pulse-periodic generation of supershort avalanche electron beams and X-ray emission (United States)

    Baksht, E. Kh.; Burachenko, A. G.; Erofeev, M. V.; Tarasenko, V. F.


    Pulse-periodic generation of supershort avalanche electron beams (SAEBs) and X-ray emission in nitrogen, as well as the transition from a single-pulse mode to a pulse-periodic mode with a high repetition frequency, was studied experimentally. It is shown that, in the pulse-periodic mode, the full width at halfmaximum of the SAEB is larger and the decrease rate of the gap voltage is lower than those in the single-pulse mode. It is found that, when the front duration of the voltage pulse at a nitrogen pressure of 90 Torr decreases from 2.5 to 0.3 ns, the X-ray exposure dose in the pulse-periodic mode increases by more than one order of magnitude and the number of SAEB electrons also increases. It is shown that, in the pulse-periodic mode of a diffuse discharge, gas heating in the discharge gap results in a severalfold increase in the SAEB amplitude (the number of electrons in the beam). At a generator voltage of 25 kV, nitrogen pressure of 90 Torr, and pulse repetition frequency of 3.5 kHz, a runaway electron beam was detected behind the anode foil.

  19. Avalanche dynamics of structural phase transitions in shape memory alloys by acoustic emission spectroscopy

    International Nuclear Information System (INIS)

    Ludwig, Benno


    In this work the avalanche dynamics of five shape memory samples has been analyzed by acoustic emission spectroscopy. The acoustic emission spectroscopy is particularly suitable for this analysis as it couples with high sensitivity to small structural changes caused by nucleation processes, interface movements, or variant rearrangements [91]. Owing to its high time resolution it provides a statistical approach to describe the jerky and intermittent character of the avalanche dynamics [20]. Rate-dependent cooling and heating runs have been conducted in order to study time-dependent aspects of the transition dynamics of the single crystals Ni 63 Al 37 , Au 50.5 Cd 49.5 , and Fe 68.8 Pd single 31.2 , and the polycrystalline sample Fe 68.8 Pd poly 31.2 . Moreover, a ferromagnetic Ni 52 Mn 23 Ga 25 single crystal has been studied by temperature cycles under an applied magnetic field and additionally by magnetic-field cycles at a constant temperature in the martensitic phase. All samples analyzed in this work show power law behavior in the acoustic emission features amplitude, energy, and duration, which indicates scale-free behavior. The access to these power law spectra allows an investigation of energy barriers separating the metastable states, which give rise to avalanche transition dynamics. By performing rate-dependent experiments the importance of thermal fluctuations and the impact of martensite respectively twin stabilization processes have been examined. In the case of the Ni 52 Mn 23 Ga 25 sample, the magnetic-field-induced variant rearrangement at slow field cycles leads to stronger signals than the rearrangement at quick cycles. This behavior can be explained by twin stabilization processes, which are accompanied by a reduction of the twin boundary mobility. For Ni 63 Al 37 , the combination of relevant thermal fluctuations, different involved time scales, and a high degree of intrinsic disorder leads to a lower acoustic activity and weaker signals under

  20. Avalanche dynamics of structural phase transitions in shape memory alloys by acoustic emission spectroscopy

    Energy Technology Data Exchange (ETDEWEB)

    Ludwig, Benno


    In this work the avalanche dynamics of five shape memory samples has been analyzed by acoustic emission spectroscopy. The acoustic emission spectroscopy is particularly suitable for this analysis as it couples with high sensitivity to small structural changes caused by nucleation processes, interface movements, or variant rearrangements [91]. Owing to its high time resolution it provides a statistical approach to describe the jerky and intermittent character of the avalanche dynamics [20]. Rate-dependent cooling and heating runs have been conducted in order to study time-dependent aspects of the transition dynamics of the single crystals Ni{sub 63}Al{sub 37}, Au{sub 50.5}Cd{sub 49.5}, and Fe{sub 68.8}Pd{sup single}{sub 31.2}, and the polycrystalline sample Fe{sub 68.8}Pd{sup poly}{sub 31.2}. Moreover, a ferromagnetic Ni{sub 52}Mn{sub 23}Ga{sub 25} single crystal has been studied by temperature cycles under an applied magnetic field and additionally by magnetic-field cycles at a constant temperature in the martensitic phase. All samples analyzed in this work show power law behavior in the acoustic emission features amplitude, energy, and duration, which indicates scale-free behavior. The access to these power law spectra allows an investigation of energy barriers separating the metastable states, which give rise to avalanche transition dynamics. By performing rate-dependent experiments the importance of thermal fluctuations and the impact of martensite respectively twin stabilization processes have been examined. In the case of the Ni{sub 52}Mn{sub 23}Ga{sub 25} sample, the magnetic-field-induced variant rearrangement at slow field cycles leads to stronger signals than the rearrangement at quick cycles. This behavior can be explained by twin stabilization processes, which are accompanied by a reduction of the twin boundary mobility. For Ni{sub 63}Al{sub 37}, the combination of relevant thermal fluctuations, different involved time scales, and a high degree of

  1. Single-Photon Avalanche Diode with Enhanced NIR-Sensitivity for Automotive LIDAR Systems. (United States)

    Takai, Isamu; Matsubara, Hiroyuki; Soga, Mineki; Ohta, Mitsuhiko; Ogawa, Masaru; Yamashita, Tatsuya


    A single-photon avalanche diode (SPAD) with enhanced near-infrared (NIR) sensitivity has been developed, based on 0.18 μm CMOS technology, for use in future automotive light detection and ranging (LIDAR) systems. The newly proposed SPAD operating in Geiger mode achieves a high NIR photon detection efficiency (PDE) without compromising the fill factor (FF) and a low breakdown voltage of approximately 20.5 V. These properties are obtained by employing two custom layers that are designed to provide a full-depletion layer with a high electric field profile. Experimental evaluation of the proposed SPAD reveals an FF of 33.1% and a PDE of 19.4% at 870 nm, which is the laser wavelength of our LIDAR system. The dark count rate (DCR) measurements shows that DCR levels of the proposed SPAD have a small effect on the ranging performance, even if the worst DCR (12.7 kcps) SPAD among the test samples is used. Furthermore, with an eye toward vehicle installations, the DCR is measured over a wide temperature range of 25-132 °C. The ranging experiment demonstrates that target distances are successfully measured in the distance range of 50-180 cm.

  2. Single-Photon Avalanche Diode with Enhanced NIR-Sensitivity for Automotive LIDAR Systems

    Directory of Open Access Journals (Sweden)

    Isamu Takai


    Full Text Available A single-photon avalanche diode (SPAD with enhanced near-infrared (NIR sensitivity has been developed, based on 0.18 μm CMOS technology, for use in future automotive light detection and ranging (LIDAR systems. The newly proposed SPAD operating in Geiger mode achieves a high NIR photon detection efficiency (PDE without compromising the fill factor (FF and a low breakdown voltage of approximately 20.5 V. These properties are obtained by employing two custom layers that are designed to provide a full-depletion layer with a high electric field profile. Experimental evaluation of the proposed SPAD reveals an FF of 33.1% and a PDE of 19.4% at 870 nm, which is the laser wavelength of our LIDAR system. The dark count rate (DCR measurements shows that DCR levels of the proposed SPAD have a small effect on the ranging performance, even if the worst DCR (12.7 kcps SPAD among the test samples is used. Furthermore, with an eye toward vehicle installations, the DCR is measured over a wide temperature range of 25–132 °C. The ranging experiment demonstrates that target distances are successfully measured in the distance range of 50–180 cm.

  3. Studies of a hybrid avalanche photo-detector in magnetic field

    Energy Technology Data Exchange (ETDEWEB)

    Šantelj, L., E-mail: [High Energy Accelerator Research Organization (KEK) (Japan); Adachi, I. [High Energy Accelerator Research Organization (KEK) (Japan); Sokendai University (Japan); Hataya, K. [Tokyo Metropolitan University (Japan); Iori, S. [Toho University (Japan); Iwata, S.; Kakuno, H. [Tokyo Metropolitan University (Japan); Kataura, R. [Niigata University (Japan); Kawai, H. [Chiba University (Japan); Kindo, H. [Sokendai University (Japan); Korpar, S. [University of Maribor (Slovenia); Jožef Stefan Institute, Ljubljana (Slovenia); Križan, P. [Jožef Stefan Institute, Ljubljana (Slovenia); University of Ljubljana (Slovenia); Mrvar, M. [Jožef Stefan Institute, Ljubljana (Slovenia); Nath, K. [Indian Institute of Technology Guwahati (India); Nishida, S. [High Energy Accelerator Research Organization (KEK) (Japan); Sokendai University (Japan); Ogawa, S. [Niigata University (Japan); Pestotnik, R.; Stanovnik, A.; Seljak, A. [Jožef Stefan Institute, Ljubljana (Slovenia); Sumiyoshi, T. [Tokyo University of Science, Tokyo (Japan); Tabata, M. [Chiba University (Japan); and others


    For the Belle II spectrometer a proximity focusing RICH counter with an aerogel radiator (ARICH) will be employed as a PID system in the forward endcap region of the spectrometer. The main challenge was the development of a reliable multichannel sensor for single photons that operates in the high magnetic field of the spectrometer (1.5 T) and withstands the radiation levels expected at the experiment. A 144-channel Hybrid Avalanche Photo-Detector (HAPD) was developed with Hamamatsu Photonics K.K. and the mass production of ∼480 HAPDs was completed recently. While our first tests of HAPD performance in the magnetic field (before mass production) showed no issues, we lately observed a presence of very large signal pulses (∼5000× single photon signal), generated internally within about 20% of HAPDs, while operating in the magnetic field. The rate of these pulses varies from sample to sample. These pulses impact the HAPD performance in two ways: they introduce periods of dead time and, in some cases, damage to the front-end electronics was observed. Here we present conditions under which such large pulses are generated, their properties and impact on HAPD performance, and discuss possible mechanism of their origin.

  4. Application of Townsend avalanche theory to tokamak startup by coaxial helicity injection (United States)

    Hammond, K. C.; Raman, R.; Volpe, F. A.


    The Townsend avalanche theory is employed to model and interpret plasma initiation in NSTX by Ohmic heating and coaxial helicity injection (CHI). The model is informed by spatially resolved vacuum calculations of electric field and magnetic field line connection length in the poloidal cross-section. The model is shown to explain observations of Ohmic startup including the duration and location of breakdown. Adapting the model to discharges initiated by CHI offers insight into the causes of upper divertor (absorber) arcs in cases where the discharge fails to start in the lower divertor gap. Finally, upper and lower limits are established for vessel gas fill based on requirements for breakdown and radiation. It is predicted that CHI experiments on NSTX-U should be able to use as much as four times the amount of prefill gas employed in CHI experiments in NSTX. This should provide greater flexibility for plasma start-up, as the injector flux is projected to be increased in NSTX-U.

  5. Performance trade-offs in single-photon avalanche diode miniaturization (United States)

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


    Single-photon avalanche diodes (SPADs) provide photons' time of arrival for various applications. In recent years, attempts have been made to miniaturize SPADs in order to facilitate large-array integration and in order to reduce the dead time of the device. We investigate the benefits and drawbacks of device miniaturization by characterizing a new fast SPAD in a commercial 0.18μm complementary metal oxide semiconductor technology. The device employs a novel and efficient guard ring, resulting in a high fill factor. Thanks to its small size, the dead time is only 5ns, resulting in the fastest reported SPAD to date. However, the short dead time is accompanied by a high after-pulsing rate, which we show to be a limiting parameter for SPAD miniaturization. We describe a new and compact active-recharge scheme which improves signal-to-noise tenfold compared with the passive configuration, using a fraction of the area of state-of-the-art active-recharge circuits, and without increasing the dead time. The performance of compact SPADs stands to benefit such applications as high-resolution fluorescence-lifetime imaging, active-illumination three-dimensional imagers, and quantum key distribution systems.

  6. Transition from avalanche dominated transport to drift-wave dominated transport in a basic laboratory experiment (United States)

    van Compernolle, Bart; Morales, George; Maggs, James; Sydora, Richard


    Results of a basic heat transport experiment involving an off-axis heat source are presented. Experiments are performed in the Large Plasma Device (LAPD) at UCLA. A ring-shaped electron beam source injects low energy electrons (below ionization energy) along a strong magnetic field into a preexisting, large and cold plasma. The injected electrons are thermalized by Coulomb collisions within a short distance and provide an off-axis heat source that results in a long, hollow, cylindrical region of elevated plasma pressure embedded in a colder plasma, and far from the machine walls. The off-axis source is active for a period long compared to the density decay time, i.e. as time progresses the power per particle increases. Two distinct regimes are observed to take place, an initial regime dominated by avalanches, identified as sudden intermittent rearrangements of the pressure profile, and a second regime dominated by sustained drift-Alfvén wave activity. The transition between the two regimes is sudden, affects the full radial profile and is preceded by the growth of drift Alfvén waves. Langmuir probe data will be shown on the evolution of the density, temperature and flow profiles during the transition. The character of the sustained drift wave activity will also be presented. Work supported by NSF/DOE Grant 1619505, and performed at the Basic Plasma Science Facility, sponsored jointly by DOE and NSF.

  7. Studies of a hybrid avalanche photo-detector in magnetic field (United States)

    Šantelj, L.; Adachi, I.; Hataya, K.; Iori, S.; Iwata, S.; Kakuno, H.; Kataura, R.; Kawai, H.; Kindo, H.; Korpar, S.; Križan, P.; Mrvar, M.; Nath, K.; Nishida, S.; Ogawa, S.; Pestotnik, R.; Stanovnik, A.; Seljak, A.; Sumiyoshi, T.; Tabata, M.; Tahirovič, E.; Yusa, Y.


    For the Belle II spectrometer a proximity focusing RICH counter with an aerogel radiator (ARICH) will be employed as a PID system in the forward endcap region of the spectrometer. The main challenge was the development of a reliable multichannel sensor for single photons that operates in the high magnetic field of the spectrometer (1.5 T) and withstands the radiation levels expected at the experiment. A 144-channel Hybrid Avalanche Photo-Detector (HAPD) was developed with Hamamatsu Photonics K.K. and the mass production of ∼480 HAPDs was completed recently. While our first tests of HAPD performance in the magnetic field (before mass production) showed no issues, we lately observed a presence of very large signal pulses (∼5000× single photon signal), generated internally within about 20% of HAPDs, while operating in the magnetic field. The rate of these pulses varies from sample to sample. These pulses impact the HAPD performance in two ways: they introduce periods of dead time and, in some cases, damage to the front-end electronics was observed. Here we present conditions under which such large pulses are generated, their properties and impact on HAPD performance, and discuss possible mechanism of their origin.

  8. Studies of a hybrid avalanche photo-detector in magnetic field

    International Nuclear Information System (INIS)

    Šantelj, L.; Adachi, I.; Hataya, K.; Iori, S.; Iwata, S.; Kakuno, H.; Kataura, R.; Kawai, H.; Kindo, H.; Korpar, S.; Križan, P.; Mrvar, M.; Nath, K.; Nishida, S.; Ogawa, S.; Pestotnik, R.; Stanovnik, A.; Seljak, A.; Sumiyoshi, T.; Tabata, M.


    For the Belle II spectrometer a proximity focusing RICH counter with an aerogel radiator (ARICH) will be employed as a PID system in the forward endcap region of the spectrometer. The main challenge was the development of a reliable multichannel sensor for single photons that operates in the high magnetic field of the spectrometer (1.5 T) and withstands the radiation levels expected at the experiment. A 144-channel Hybrid Avalanche Photo-Detector (HAPD) was developed with Hamamatsu Photonics K.K. and the mass production of ∼480 HAPDs was completed recently. While our first tests of HAPD performance in the magnetic field (before mass production) showed no issues, we lately observed a presence of very large signal pulses (∼5000× single photon signal), generated internally within about 20% of HAPDs, while operating in the magnetic field. The rate of these pulses varies from sample to sample. These pulses impact the HAPD performance in two ways: they introduce periods of dead time and, in some cases, damage to the front-end electronics was observed. Here we present conditions under which such large pulses are generated, their properties and impact on HAPD performance, and discuss possible mechanism of their origin.

  9. Biological modelling of a computational spiking neural network with neuronal avalanches (United States)

    Li, Xiumin; Chen, Qing; Xue, Fangzheng


    In recent years, an increasing number of studies have demonstrated that networks in the brain can self-organize into a critical state where dynamics exhibit a mixture of ordered and disordered patterns. This critical branching phenomenon is termed neuronal avalanches. It has been hypothesized that the homeostatic level balanced between stability and plasticity of this critical state may be the optimal state for performing diverse neural computational tasks. However, the critical region for high performance is narrow and sensitive for spiking neural networks (SNNs). In this paper, we investigated the role of the critical state in neural computations based on liquid-state machines, a biologically plausible computational neural network model for real-time computing. The computational performance of an SNN when operating at the critical state and, in particular, with spike-timing-dependent plasticity for updating synaptic weights is investigated. The network is found to show the best computational performance when it is subjected to critical dynamic states. Moreover, the active-neuron-dominant structure refined from synaptic learning can remarkably enhance the robustness of the critical state and further improve computational accuracy. These results may have important implications in the modelling of spiking neural networks with optimal computational performance. This article is part of the themed issue `Mathematical methods in medicine: neuroscience, cardiology and pathology'.

  10. Radiation hardness of semiconductor avalanche detectors for calorimeters in future HEP experiments (United States)

    Kushpil, V.; Mikhaylov, V.; Kugler, A.; Kushpil, S.; Ladygin, V. P.; Svoboda, O.; Tlustý, P.


    During the last years, semiconductor avalanche detectors are being widely used as the replacement of classical PMTs in calorimeters for many HEP experiments. In this report, basic selection criteria for replacement of PMTs by solid state devices and specific problems in the investigation of detectors radiation hardness are discussed. The design and performance of the hadron calorimeters developed for the future high energy nuclear physics experiments at FAIR, NICA, and CERN are discussed. The Projectile Spectator Detector (PSD) for the CBM experiment at the future FAIR facility, the Forward Calorimeter for the NA61 experiment at CERN and the Multi Purpose Detector at the future NICA facility are reviewed. Moreover, new methods of data analysis and results interpretation for radiation experiments are described. Specific problems of development of detectors control systems and possibilities of reliability improvement of multi-channel detectors systems are shortly overviewed. All experimental material is based on the investigation of SiPM and MPPC at the neutron source in NPI Rez.

  11. High-speed bridge circuit for InGaAs avalanche photodiode single-photon detector (United States)

    Hashimoto, Hirofumi; Tomita, Akihisa; Okamoto, Atsushi


    Because of low power consumption and small footprint, avalanche photodiodes (APD) have been commonly applied to photon detection. Recently, high speed quantum communication has been demonstrated for high bit-rate quantum key distribution. For the high speed quantum communication, photon detectors should operate at GHz-clock frequencies. We propose balanced detection circuits for GHz-clock operation of InGaAs-APD photon detectors. The balanced single photon detector operates with sinusoidal wave gating. The sinusoidal wave appearing in the output is removed by the subtraction from APD signal without sharp band-elimination filters. Omission of the sharp filters removes the constraint on the operating frequency of the single photon detector. We present two designs, one works with two identical APDs, the other with one APD and a low-pass filter. The sinusoidal gating enables to eliminate the gating noise even with the simple configuration of the latter design. We demonstrated the balanced single photon detector operating with 1.020GHz clock at 233 K, 193 K, and 186.5 K. The dark count probability was 4.0 x 10-4 counts/pulse with the quantum efficiency of 10% at 233K, and 1.6 x 10-4 counts/pulse at 186.5 K. These results were obtained with easily available APDs (NR8300FP-C.C, RENESASS) originally developed for optical time-domain reflectmeters.

  12. High-efficiency integrated readout circuit for single photon avalanche diode arrays in fluorescence lifetime imaging (United States)

    Acconcia, G.; Cominelli, A.; Rech, I.; Ghioni, M.


    In recent years, lifetime measurements by means of the Time Correlated Single Photon Counting (TCSPC) technique have led to a significant breakthrough in medical and biological fields. Unfortunately, the many advantages of TCSPC-based approaches come along with the major drawback of a relatively long acquisition time. The exploitation of multiple channels in parallel could in principle mitigate this issue, and at the same time it opens the way to a multi-parameter analysis of the optical signals, e.g., as a function of wavelength or spatial coordinates. The TCSPC multichannel solutions proposed so far, though, suffer from a tradeoff between number of channels and performance, and the overall measurement speed has not been increased according to the number of channels, thus reducing the advantages of having a multichannel system. In this paper, we present a novel readout architecture for bi-dimensional, high-density Single Photon Avalanche Diode (SPAD) arrays, specifically designed to maximize the throughput of the whole system and able to guarantee an efficient use of resources. The core of the system is a routing logic that can provide a dynamic connection between a large number of SPAD detectors and a much lower number of high-performance acquisition channels. A key feature of our smart router is its ability to guarantee high efficiency under any operating condition.

  13. High-efficiency dynamic routing architecture for the readout of single photon avalanche diode arrays in time-correlated measurements (United States)

    Cominelli, A.; Acconcia, G.; Peronio, P.; Rech, I.; Ghioni, M.


    In recent years, the Time-Correlated Single Photon Counting (TCSPC) technique has gained a prominent role in many fields, where the analysis of extremely fast and faint luminous signals is required. In the life science, for instance, the estimation of fluorescence time-constants with picosecond accuracy has been leading to a deeper insight into many biological processes. Although the many advantages provided by TCSPC-based techniques, their intrinsically repetitive nature leads to a relatively long acquisition time, especially when time-resolved images are obtained by means of a single detector, along with a scanning point system. In the last decade, TCSPC acquisition systems have been subjected to a fast trend towards the parallelization of many independent channels, in order to speed up the measure. On one hand, some high-performance multi-module systems have been already made commercially available, but high area and power consumption of each module have limited the number of channels to only some units. On the other hand, many compact systems based on Single Photon Avalanche Diodes (SPAD) have been proposed in literature, featuring thousands of independent acquisition chains on a single chip. The integration of both detectors and conversion electronic in the same pixel area, though, has imposed tight constraints on power dissipation and area occupation of the electronics, resulting in a tradeoff with performance, both in terms of differential nonlinearity and timing jitter. Furthermore, in the ideal case of simultaneous readout of a huge number of channels, the overall data rate can be as high as 100 Gbit/s, which is nowadays too high to be easily processed in real time by a PC. Typical adopted solutions involve an arbitrary dwell time, followed by a sequential readout of the converters, thus limiting the maximum operating frequency of each channel and impairing the measurement speed, which still lies well below the limit imposed by the saturation of the

  14. Rock avalanche occurrence in the San Juan province (Argentina): an analysis of their spatial distribution and main forcing factors (United States)

    Penna, Ivanna; Tonini, Marj; Vega Orozco, Carmen D.; Longchamp, Céline; Derron, Marc-Henri; Jaboyedoff, Michel


    Rock avalanches are frequent phenomena in the Argentinean Andes and a particular high concentration of these events is observed in the Northwest (~25°S) and in the Central Andes from 30°S until the transition with the Patagonian Andes (~38°S). Tectonic deformation and seismicity are generally proposed as main driving factors, with weather and lithologic conditions playing a subordinate role. From 28°S to 33°S, the subhorizontal subduction of the Nazca plate drives higher shortening rates than in the surrounding areas, and an intense seismicity. Main morphotectonic units in this regions are the Cordillera and Precordillera, separated by the Barreal-Calingasta depression. In the southern central part of the flat subduction area (30°30'°-32°30'S), it is observed high valley incision and maximum local relief of 2900 m, while in the Precordillera main fluvial courses developed in the inter-thrust valleys, where local relief is up to 2400 m. In both mountain ranges, we recognized 34 rock avalanches deposits with volumes up to 0.3 km3. There is no apparent lithologic control on detachments, which involved sedimentary, volcanic and granite rocks, even though ~20% of them were favored by layering orientation. However, about 50% of the inventoried rock avalanches with the greatest volumes, developed along tectonic structures or less than 1 km far from them. The main objective of the present study is to explore the spatial distribution of rock avalanche deposits, and compare it with the instrumental seismicity and landscape conditions by means of statistical tools (e.g. exploratory data analyses, Ripley's K-function). Those analyses allow to highlight the spatial correlation between the geological events. Moreover, to visually display the detected cluster spatial patterns we elaborated kernel density maps. Our findings revealed that most of the rock avalanches show a high spatial aggregation mainly between 31°20'S-31°50'S. Main concentration of bedrock landslides

  15. The Devdorak ice-rock avalanche and consequent debris flow from the slope of Mt. Kazbek (Caucasus, Georgia) in 2014 (United States)

    Chernomorets, Sergey; Savernyuk, Elena; Petrakov, Dmitry; Dokukin, Mikhail; Gotsiridze, George; Gavardashvili, Givi; Drobyshev, Valery; Tutubalina, Olga; Zaporozhchenko, Eduard; Kamenev, Nikolay; Kamenev, Vladimir; Kääb, Andreas; Kargel, Jeffrey; Huggel, Christian


    We have studied catastrophic glacial events of 2014 in the Kazbek-Dzhimaray massif, Caucasus Mts., Georgia. The first event is a so called "Kazbek blockage" of the Georgian Military Road, on 17 May 2014, which formed as a result of an ice-rock avalanche onto the Devdorak Glacier, and is similar to blockages which occurred in the same location in the 18th-19th century. The second event is a consequent debris flow on 20 August 2014. In May, June 2014 and September 2015 we conducted three field investigations of the disaster zone, which includes Devdorak Glacier, Amilishka and Kabakhi river valleys, the Terek River valley near the Kabakhi River mouth, and a temporary lake.We analyzed field research data, interpreted SPOT 6, Landsat-8 OLI, Terra ASTER, and Pleiades satellite imagery, as well as post-disaster helicopter imagery. To assess dynamic features of the ice-rock flow on 17 May 2014, we measured valley crossections with Bushnell laser ranger. In 2015 we have marked a 180-m baseline for ground stereosurvey and made a stereopair of the Devdorak glacier terminus from a distance of 700 m. The 17 May 2014 ice-rock avalanche initiated at 4500 m. a.s.l. It collapsed onto the tongue of the Devdorak Glacier which reaches down to 2300 m a.s.l. Downstream of the tongue, the avalanche transformed into an ice-rock "avalanche flow" which blocked the Terek River valley. The traffic on Military Georgian Road (part of E117 highway) which connects Russia with Georgia was stopped. 7 people were killed in their vehicles. The total length of the ice-rock avalanche and the subsequent flow was over 10 km. A temporary lake formed in the Terek river valley, reaching 300 m in length, and over 10 m in depth. For several hours, the lake was threatening another debris flow downstream the Terek river valley. According to field estimates at the Devdorak glacier tongue and in Amilishka, Kabakhi and Terek river valleys, the volume of the transported ice-rock avalanche mass, which deposited in

  16. Multi-layer Thick Gas Electron Multiplier (M-THGEM) Simulations at Low Pressure for High-Gain Operation (United States)

    Fritsch, Adam; Cortesi, Marco; Mittig, Wolfgang


    The Multi-layer Thick Gaseous Electron Multiplier (M-THGEM) is a novel hole-type gaseous electron multiplier produced by multi-layer printed circuit board technology; it consists of a densely perforated assembly of multiple insulating substrate sheets sandwiched between thin metallic-electrode layers. The electron avalanche processes occur along the successive multiplication stages within the M-THGEM holes, under the action of strong dipole fields resulting from the application of suitable potential differences between the electrodes. Using ANSYS Maxwell and Garfield, Monte Carlo simulations have been performed to find geometries that maximize the achievable gain, electron collection efficiency, ion feedback, energy resolution of M-THGEM devices at low pressure with pure gases. Comparisons of the calculations with measurements of a prototype device are ongoing. Preliminary results will be presented.

  17. High-gain ring FEL as a master oscillator for X-ray generation

    Energy Technology Data Exchange (ETDEWEB)

    Vinokurov, N.A. E-mail:; Shevchenko, O.A


    High-gain free electron laser (FEL) with bends between undulator sections is discussed. Such FEL configuration may be used for the mirror-free master oscillator in X-ray band. The oscillator linewidth is estimated. Results of computation for the state-of-art electron beam parameters show the feasibility of the X-ray oscillator FEL.

  18. Gain characteristics of erbium doped fiber amplifier (United States)

    Zhang, Lihua; Du, Yungang; Xi, Ying; Li, Jijun; Zhao, Chunwang


    In the design of Erbium Doped Fiber Amplifier (EDFA), improving flat-gain has great important significance. The working principle and gain characteristics of EDFA are introduced briefly, the influence of the factors such as Erbium doped fiber (EDF) length and pump power on the gain of EDFA is analyzed in detail, and the simulation experiments were carried out with Optisystem software. The result shows that, when pump power is constant, with EDF length departing the optimal value, the gain of each channel decreases at different degrees; when EDF length is constant, with pump power departing the optimal value, the gain of each channel changes at different degrees. Moreover, Er3+ concentration has significant effect on the gain, and there is an optimal Er3+ concentration to get the largest gain.

  19. Cherenkov luminescence measurements with digital silicon photomultipliers: a feasibility study

    Energy Technology Data Exchange (ETDEWEB)

    Ciarrocchi, Esther; Belcari, Nicola; Guerra, Alberto Del [Department of Physics, University of Pisa, Pisa (Italy); INFN, section of Pisa, Pisa (Italy); Cherry, Simon R. [Department of Biomedical Engineering, University of California, Davis, CA (United States); Lehnert, Adrienne; Hunter, William C. J.; McDougald, Wendy; Miyaoka, Robert S.; Kinahan, Paul E. [Department of Radiology, University of Washington, Seattle, WA (United States)


    A feasibility study was done to assess the capability of digital silicon photomultipliers to measure the Cherenkov luminescence emitted by a β source. Cherenkov luminescence imaging (CLI) is possible with a charge coupled device (CCD) based technology, but a stand-alone technique for quantitative activity measurements based on Cherenkov luminescence has not yet been developed. Silicon photomultipliers (SiPMs) are photon counting devices with a fast impulse response and can potentially be used to quantify β-emitting radiotracer distributions by CLI. In this study, a Philips digital photon counting (PDPC) silicon photomultiplier detector was evaluated for measuring Cherenkov luminescence. The PDPC detector is a matrix of avalanche photodiodes, which were read one at a time in a dark count map (DCM) measurement mode (much like a CCD). This reduces the device active area but allows the information from a single avalanche photodiode to be preserved, which is not possible with analog SiPMs. An algorithm to reject the noisiest photodiodes and to correct the measured count rate for the dark current was developed. The results show that, in DCM mode and at (10–13) °C, the PDPC has a dynamic response to different levels of Cherenkov luminescence emitted by a β source and transmitted through an opaque medium. This suggests the potential for this approach to provide quantitative activity measurements. Interestingly, the potential use of the PDPC in DCM mode for direct imaging of Cherenkov luminescence, as a opposed to a scalar measurement device, was also apparent. We showed that a PDPC tile in DCM mode is able to detect and image a β source through its Cherenkov radiation emission. The detector’s dynamic response to different levels of radiation suggests its potential quantitative capabilities, and the DCM mode allows imaging with a better spatial resolution than the conventional event-triggered mode. Finally, the same acquisition procedure and data processing could

  20. Stacked Transformer for Driver Gain and Receive Signal Splitting (United States)

    Driscoll, Kevin R.


    In a high-speed signal transmission system that uses transformer coupling, there is a need to provide increased transmitted signal strength without adding active components. This invention uses additional transformers to achieve the needed gain. The prior art uses stronger drivers (which require an IC redesign and a higher power supply voltage), or the addition of another active component (which can decrease reliability, increase power consumption, reduce the beneficial effect of serializer/deserializer preemphasis or deemphasis, and/or interfere with fault containment mechanisms), or uses a different transformer winding ratio (which requires redesign of the transformer and may not be feasible with high-speed signals that require a 1:1 winding ratio). This invention achieves the required gain by connecting the secondaries of multiple transformers in series. The primaries of these transformers are currently either connected in parallel or are connected to multiple drivers. There is also a need to split a receive signal to multiple destinations with minimal signal loss. Additional transformers can achieve the split. The prior art uses impedance-matching series resistors that cause a loss of signal. Instead of causing a loss, most instantiations of this invention would actually provide gain. Multiple transformers are used instead of multiple windings on a single transformer because multiple windings on the same transformer would require a redesign of the transformer, and may not be feasible with high-speed transformers that usually require a bifilar winding with a 1:1 ratio. This invention creates the split by connecting the primaries of multiple transformers in series. The secondary of each transformer is connected to one of the intended destinations without the use of impedance-matching series resistors.

  1. Tribal Utility Feasibility Study

    Energy Technology Data Exchange (ETDEWEB)

    Engel, R. A.; Zoellick, J. J.


    The Schatz Energy Research Center (SERC) assisted the Yurok Tribe in investigating the feasibility of creating a permanent energy services program for the Tribe. The original purpose of the DOE grant that funded this project was to determine the feasibility of creating a full-blown Yurok Tribal electric utility to buy and sell electric power and own and maintain all electric power infrastructure on the Reservation. The original project consultant found this opportunity to be infeasible for the Tribe. When SERC took over as project consultant, we took a different approach. We explored opportunities for the Tribe to develop its own renewable energy resources for use on the Reservation and/or off-Reservation sales as a means of generating revenue for the Tribe. We also looked at ways the Tribe can provide energy services to its members and how to fund such efforts. We identified opportunities for the development of renewable energy resources and energy services on the Yurok Reservation that fall into five basic categories: • Demand-side management – This refers to efforts to reduce energy use through energy efficiency and conservation measures. • Off-grid, facility and household scale renewable energy systems – These systems can provide electricity to individual homes and Tribal facilities in areas of the Reservation that do not currently have access to the electric utility grid. • Village scale, micro-grid renewable energy systems - These are larger scale systems that can provide electricity to interconnected groups of homes and Tribal facilities in areas of the Reservation that do not have access to the conventional electric grid. This will require the development of miniature electric grids to serve these interconnected facilities. • Medium to large scale renewable energy development for sale to the grid – In areas where viable renewable energy resources exist and there is access to the conventional electric utility grid, these resources can be

  2. Metastability and avalanche dynamics in strongly correlated gases with long-range interactions (United States)

    Hruby, Lorenz; Dogra, Nishant; Landini, Manuele; Donner, Tobias; Esslinger, Tilman


    We experimentally study the stability of a bosonic Mott insulator against the formation of a density wave induced by long-range interactions and characterize the intrinsic dynamics between these two states. The Mott insulator is created in a quantum degenerate gas of 87-Rubidium atoms, trapped in a 3D optical lattice. The gas is located inside and globally coupled to an optical cavity. This causes interactions of global range, mediated by photons dispersively scattered between a transverse lattice and the cavity. The scattering comes with an atomic density modulation, which is measured by the photon flux leaking from the cavity. We initialize the system in a Mott-insulating state and then rapidly increase the global coupling strength. We observe that the system falls into either of two distinct final states. One is characterized by a low photon flux, signaling a Mott insulator, and the other is characterized by a high photon flux, which we associate with a density wave. Ramping the global coupling slowly, we observe a hysteresis loop between the two states—a further signature of metastability. A comparison with a theoretical model confirms that the metastability originates in the competition between short- and global-range interactions. From the increasing photon flux monitored during the switching process, we find that several thousand atoms tunnel to a neighboring site on the timescale of the single-particle dynamics. We argue that a density modulation, initially forming in the compressible surface of the trapped gas, triggers an avalanche tunneling process in the Mott-insulating region.

  3. Elementary theory of bed-sediment entrainment by debris flows and avalanches (United States)

    Iverson, Richard M.


    Analyses of mass and momentum exchange between a debris flow or avalanche and an underlying sediment layer aid interpretations and predictions of bed-sediment entrainment rates. A preliminary analysis assesses the behavior of a Coulomb slide block that entrains bed material as it descends a uniform slope. The analysis demonstrates that the block's momentum can grow unstably, even in the presence of limited entrainment efficiency. A more-detailed, depth-integrated continuum analysis of interacting, deformable bodies identifies mechanical controls on entrainment efficiency, and shows that entrainment rates satisfy a jump condition that involves shear-traction and velocity discontinuities at the flow-bed boundary. Explicit predictions of the entrainment rateEresult from making reasonable assumptions about flow velocity profiles and boundary shear tractions. For Coulomb-friction tractions, predicted entrainment rates are sensitive to pore fluid pressures that develop in bed sediment as it is overridden. In the simplest scenario the bed sediment liquefies completely, and the entrainment-rate equation reduces toE = 2μ1gh1 cos θ(1 − λ1)/ , where θ is the slope angle, μ1 is the flow's Coulomb friction coefficient, h1 is its thickness, λ1 is its degree of liquefaction, and is its depth-averaged velocity. For values ofλ1ranging from 0.5 to 0.8, this equation predicts entrainment rates consistent with rates of 0.05 to 0.1 m/s measured in large-scale debris-flow experiments in which wet sediment beds liquefied almost completely. The propensity for bed liquefaction depends on several factors, including sediment porosity, permeability, and thickness, and rates of compression and shear deformation that occur when beds are overridden.

  4. Behaviour of Belle II ARICH Hybrid Avalanche Photo-Detector in magnetic field (United States)

    Kindo, H.; Adachi, I.; Dolenec, R.; Hataya, K.; Iori, S.; Iwata, S.; Kakuno, H.; Kataura, R.; Kawai, H.; Kobayashi, T.; Konno, T.; Korpar, S.; Kriz˘an, P.; Kumita, T.; Mrvar, M.; Nishida, S.; Ogawa, K.; Ogawa, S.; Pestotnik, R.; Šantelj, L.; Sumiyoshi, T.; Tabata, M.; Yonenaga, M.; Yusa, Y.


    The proximity-focusing Aerogel Ring-Imaging Cherenkov detector (ARICH) has been designed to separate kaons from pions in the forward end-cap of the Belle II spectrometer. The detector will be placed in 1.5 T magnetic field and must have immunity to it. In ARICH R&D, we solve the problem with new equipment called Hybrid Avalanche Photo-Detector (HAPD) which developed by Hamamatsu Photonics. Recently the production of about 500 HAPDs was completed. We test HAPDs in magnetic field in KEK. We found some HAPDs have significant amount of dead time, which reaches up to 30% in the worst case. The dead time is caused by very large (more than 10,000 times larger than a single photon signal) and frequent (∼5 Hz) signals, which make electronics paralysed. The huge signals are observed in about 30% of HAPDs. To identify the origin and understand the mechanism, we perform some extra test of HAPDs. We find a strange dependence of the huge signals to the APD bias voltage. If we reduce the bias voltage applied to one of the 4 APDs by 10 V, the frequency of the huge signals is much reduced. On the other hand, if we reduce the voltage of all the 4 HAPDs, huge signals do not decrease, or even increase in some case. We also find the huge signals seems to be related to the vacuum inside HAPD. We present about the observation of the huge signals of HAPDs in the magnetic field, and our strategy to manage it.

  5. Augmented Lagrangian Method and Compressible Visco-plastic Flows: Applications to Shallow Dense Avalanches (United States)

    Bresch, D.; Fernández-Nieto, E. D.; Ionescu, I. R.; Vigneaux, P.

    In this paper we propose a well-balanced finite volume/augmented Lagrangian method for compressible visco-plastic models focusing on a compressible Bingham type system with applications to dense avalanches. For the sake of completeness we also present a method showing that such a system may be derived for a shallow flow of a rigid-viscoplastic incompressible fluid, namely for incompressible Bingham type fluid with free surface. When the fluid is relatively shallow and spreads slowly, lubrication-style asymptotic approximations can be used to build reduced models for the spreading dynamics, see for instance [N.J. Balmforth et al., J. Fluid Mech (2002)]. When the motion is a little bit quicker, shallow water theory for non-Newtonian flows may be applied, for instance assuming a Navier type boundary condition at the bottom. We start from the variational inequality for an incompressible Bingham fluid and derive a shallow water type system. In the case where Bingham number and viscosity are set to zero we obtain the classical Shallow Water or Saint-Venant equations obtained for instance in [J.F. Gerbeau, B. Perthame, DCDS (2001)]. For numerical purposes, we focus on the one-dimensional in space model: We study associated static solutions with sufficient conditions that relate the slope of the bottom with the Bingham number and domain dimensions. We also propose a well-balanced finite volume/augmented Lagrangian method. It combines well-balanced finite volume schemes for spatial discretization with the augmented Lagrangian method to treat the associated optimization problem. Finally, we present various numerical tests.

  6. Particle-size segregation and diffusive remixing in shallow granular avalanches (United States)

    Gray, J. M. N. T.; Chugunov, V. A.


    Segregation and mixing of dissimilar grains is a problem in many industrial and pharmaceutical processes, as well as in hazardous geophysical flows, where the size-distribution can have a major impact on the local rheology and the overall run-out. In this paper, a simple binary mixture theory is used to formulate a model for particle-size segregation and diffusive remixing of large and small particles in shallow gravity-driven free-surface flows. This builds on a recent theory for the process of kinetic sieving, which is the dominant mechanism for segregation in granular avalanches provided the density-ratio and the size-ratio of the particles are not too large. The resulting nonlinear parabolic segregation remixing equation reduces to a quasi-linear hyperbolic equation in the no-remixing limit. It assumes that the bulk velocity is incompressible and that the bulk pressure is lithostatic, making it compatible with most theories used to compute the motion of shallow granular free-surface flows. In steady-state, the segregation remixing equation reduces to a logistic type equation and the ‘S’-shaped solutions are in very good agreement with existing particle dynamics simulations for both size and density segregation. Laterally uniform time-dependent solutions are constructed by mapping the segregation remixing equation to Burgers equation and using the Cole Hopf transformation to linearize the problem. It is then shown how solutions for arbitrary initial conditions can be constructed using standard methods. Three examples are investigated in which the initial concentration is (i) homogeneous, (ii) reverse graded with the coarse grains above the fines, and, (iii) normally graded with the fines above the coarse grains. Time-dependent two-dimensional solutions are also constructed for plug-flow in a semi-infinite chute.

  7. Spatial and temporal analysis of fatal off-piste and backcountry avalanche accidents in Austria with a comparison of results in Switzerland, France, Italy and the US (United States)

    Pfeifer, Christian; Höller, Peter; Zeileis, Achim


    In this article we analyzed spatial and temporal patterns of fatal Austrian avalanche accidents caused by backcountry and off-piste skiers and snowboarders within the winter periods 1967/1968-2015/2016. The data were based on reports of the Austrian Board for Alpine Safety and reports of the information services of the federal states. Using the date and the location of the recorded avalanche accidents, we were able to carry out spatial and temporal analyses applying generalized additive models and Markov random-field models. As a result of the trend analysis we noticed an increasing trend of backcountry and off-piste avalanche fatalities within the winter periods 1967/1968-2015/2016 (although slightly decreasing in recent years), which is in contradiction to the widespread opinion in Austria that the number of fatalities is constant over time. Additionally, we compared Austrian results with results of Switzerland, France, Italy and the US based on data from the International Commission of Alpine Rescue (ICAR). As a result of the spatial analysis, we noticed two hot spots of avalanche fatalities (Arlberg-Silvretta and Sölden). Because of the increasing trend and the rather narrow regional distribution of the fatalities, initiatives aimed at preventing avalanche accidents were highly recommended.

  8. Assessing the interaction between mountain forests and snow avalanches at Nevados de Chillán, Chile and its implications for ecosystem-based disaster risk reduction (United States)

    Casteller, Alejandro; Häfelfinger, Thomas; Cortés Donoso, Erika; Podvin, Karen; Kulakowski, Dominik; Bebi, Peter


    Gravitational natural hazards such as snow avalanches, rockfalls, shallow landslides and volcanic activity represent a risk to mountain communities around the world. In particular, where documentary records about these processes are rare, decisions on risk management and land-use planning have to be based on a variety of other sources including vegetation, tree-ring data and natural hazard process models. We used a combination of these methods in order to evaluate dynamics of natural hazards with a focus on snow avalanches at Valle Las Trancas, in the Biobío region in Chile. Along this valley, natural hazards threaten not only the local human population, but also the numerous tourists attracted by outdoor recreational activities. Given the regional scarcity of documentary records, tree-ring methods were applied in order to reconstruct the local history of snow avalanches and debris flow events, which are the most important weather-related processes at respective tracks. A recent version of the model Rapid Mass MovementS (RAMMS), which includes influences of forest structure, was used to calculate different avalanche parameters such as runout distances and maximum pressures, taking into consideration the presence or absence of forest along the tracks as well as different modeled return periods. Our results show that local Nothofagus broadleaf forests contribute to a reduction of avalanche runout distances as well as impact pressure on present infrastructure, thus constituting a valuable ecosystem disaster risk reduction measure that can substitute or complement other traditional measures such as snow sheds.


    Directory of Open Access Journals (Sweden)

    A. D. Oleynikov


    Full Text Available Currently, due to the global climate change and increasing frequency of weather events focus is on prediction of climate extremes. Large-scale meteorological anomalies can cause long-term paralysis of social and economic infrastructure of the major mountain regions and even individual states. In winter periods, these anomalies are associated with prolonged heavy snowfalls and associated with them catastrophic avalanches which cause significant social and economic damage. The climate system maintains a certain momentum during periods of adjustment and transition to other conditions in the ratio of heat and moisture and contains a climate «signal» of the climates of the past and the future. In our view seasonal and yearly extremes perform the role of these indicators, study of which enables for a deeper understanding and appreciation of the real situation of the climate periods related to the modern ones. The paper provides an overview of the criteria for selection of extreme winters. Identification of extremely cold winters during the period of instrumental observation and assessment of their snowiness and avalanche activity done for the Elbrus region, which is a model site for study of the avalanche regime in the Central Caucasus. The studies aim to identify the extreme winters in the Greater Caucasus, assess their frequency of occurrence, characterize the scale and intensity of the avalanche formation. The data obtained can be used to identify winter-analogues in the reconstruction and long-term forecast of avalanches

  10. Energy Gaining Windows for Residental Buildings

    DEFF Research Database (Denmark)

    Kragh, Jesper; Laustsen, Jacob Birck; Svendsen, Svend


    This paper presents some of the research done during the last 8 years at the Technical University of Denmark developing improved low-energy window solutions. The focus has been on maximizing the net energy gain of windows for residential buildings. The net energy gain of windows is the solar gain...... minus the heat loss integrated over the heating season. It is assumed that in northern cold climates all of the solar gain during the heating season can be utilized for space heating. Problems with overheating in the summer period must be solved with overhang or moveable solar shading devices. Two...... and longer durability of the window. The glazing in these fiber reinforced polyester windows is both unsealed and sealed triple glazing units. To increase the net energy gain slim frame profiles have been developed to increase the glazing area and thereby the solar gain. The challenge when developing slim...

  11. Feasibility studies for decommissioning

    International Nuclear Information System (INIS)

    Hladky, E.


    In this presentation author deals with planning of decommission of the NPPs A1, V1 and V2 Bohunice and Mochovce. It was concluded that: Used model for decommissioning parameters assessment has been suitable for elaboration of initial decommissioning plans (feasibility studies); Basic assessment of main decommissioning parameters and basic comparison of various decommissioning options have been possible; Improvement of the model and corresponding software is desirable and works on software improvement began one year ago; V1-NPP initial decommissioning plan should be actualized, because initial decommissioning plan does not correspond by its content and structure to requirements of Act No. 130/98 and Nuclear Regulatory Authority Degree No. 246/99; Strategy of radioactive wastes treatment and conditioning together with technical provisions at Jaslovske Bohunice site was changed in comparison with the assumptions in 1991-92; Considered V1 NPP decommissioning options are necessary to be re-evaluated in accordance with latest development of knowledge and approaches to NPP decommissioning in the world; Specific unit costs are substantially and differentially changed in comparison with the assumptions in 1991-92; Necessity to take into account technical changes resulted from V1 NPP reconstruction. (author)

  12. Single Photon Sensitive HgCdTe Avalanche Photodiode Detector (APD), Phase II (United States)

    National Aeronautics and Space Administration — Leveraging Phase I SBIR successes, in Phase II, a single photon sensitive LIDAR receiver will be fabricated and delivered to NASA. In Phase I, high-gain,...

  13. Controlling noise in plasmonic structures with gain (United States)

    Vyshnevyy, A. A.; Fedyanin, D. Yu.


    Loss compensation by gain medium gives the possibility to exploit subwavelength confinement of light in plasmonic nanostructures and construct nanoscale plasmonic circuits. However, due to fundamentally unavoidable spontaneous emission from the gain medium, lossless waveguides suffer from strong photonic noise, which limits their practical applications. Here we demonstrate the possibility of significant decrease of the noise level while preserving physical dimensions of lossless plasmonic waveguides with gain. Our findings are aimed at extending the communication capabilities of on-chip plasmonic networks.

  14. Weight gain during pregnancy :the characteristics of women who experience excess weight gain /1990.


    Ling, Carol Carlson


    Weight gain during pregnancy, relationships among body image, body weight standards, and attitudes toward weight gain were investigated. Weight gain recommendations, based on preconceptional weight status (PCWS) reflected current practices in prenatal care at Sentara Norfolk General Hospital, Norfolk, VA, and provided a basis on which to categorize weight gain as inadequate, appropriate, and excess. Women who experienced excess weight gain (EWG) were compared to those who ex...

  15. Measurement of Antenna Bore-Sight Gain (United States)

    Fortinberry, Jarrod; Shumpert, Thomas H.


    The absolute or free-field gain of a simple antenna can be approximated using standard antenna theory formulae or for a more accurate prediction, numerical methods may be employed to solve for antenna parameters including gain. Both of these methods will result in relatively reasonable estimates but in practice antenna gain is usually verified and documented via measurements and calibration. In this paper, a relatively simple and low-cost, yet effective means of determining the bore-sight free-field gain of a VHF/UHF antenna is proposed by using the Brewster angle relationship.

  16. Dual-Doppler Feasibility Study (United States)

    Huddleston, Lisa L.


    radar geometry issues at the NWS MLB radar, such as the "cone of silence" or beam blockage. In the event of a radar outage at one of the sites, the multi-radar algorithms would provide continuing coverage of the area through use of the data from the remaining operational radar sites. There are several options to collect, edit, synthesize and display dual-Doppler data sets. These options include commercial packages available for purchase and a variety of freeware packages available from the National Center for Atmospheric Research (NCAR) for processing raw radar data. However, evaluation of the freeware packages revealed that they do not have sufficient documentation and configuration control to be certified for 45 SW use. Additionally, a TI data line must be installed/leased from the NWS MLB office and CCAFS to enable the receipt of NWS MLB raw radar data to use in the dual-Doppler synthesis. Integration of the TI data line into the Eastern Range infrastructure that will meet the security requirements necessary for 45 SW use is time-consuming and costly. Overall evaluation indicates that establishment of the dual-Doppler capability using the existing operational radar systems is desirable and feasible with no technical concerns. Installation of such a system represents a significant enhancement to forecasting capabilities at the 45 WS and at NWS MLB. However, data security and cost considerations must be evaluated in light of current budgetary constraints. In any case, gaining the dual-Doppler capability will provide opportunities for better visualization of the wind field and better forecasting of the onset of convection and severe weather events to support space launch operations at KSC and CCAFS.

  17. Behaviour of large-area avalanche photodiodes under intense magnetic fields for VUV- visible- and X-ray photon detection

    International Nuclear Information System (INIS)

    Fernandes, L.M.P.; Antognini, A.; Boucher, M.; Conde, C.A.N.; Huot, O.; Knowles, P.; Kottmann, F.; Ludhova, L.; Mulhauser, F.; Pohl, R.; Schaller, L.A.; Santos, J.M.F. dos; Taqqu, D.; Veloso, J.F.C.A.


    The behaviour of large-area avalanche photodiodes for X-rays, visible and vacuum-ultra-violet (VUV) light detection in magnetic fields up to 5 T is described. For X-rays and visible light detection, the photodiode pulse amplitude and energy resolution were unaffected from 0 to 5 T, demonstrating the insensitivity of this type of detector to strong magnetic fields. For VUV light detection, however, the photodiode relative pulse amplitude decreases with increasing magnetic field intensity reaching a reduction of about 24% at 5 T, and the energy resolution degrades noticeably with increasing magnetic field

  18. Amplitude-temporal characteristics of a supershort avalanche electron beam generated during subnanosecond breakdown in air and nitrogen (United States)

    Tarasenko, V. F.; Baksht, E. Kh.; Beloplotov, D. V.; Burachenko, A. G.; Lomaev, M. I.


    The amplitude-temporal characteristics of a supershort avalanche electron beam (SAEB) with an amplitude of up to 100 A, as well as of the breakdown voltage and discharge current, are studied experimentally with a picosecond time resolution. The waveforms of discharge and SAEB currents are synchronized with those of the voltage pulses. It is shown that the amplitude-temporal characteristics of the SAEB depend on the gap length and the designs of the gas diode and cathode. The mechanism for the generation of runaway electron beams in atmospheric-pressure gases is analyzed on the basis of the obtained experimental data.

  19. Study on the realization of a minimum ionizing particle detector: development of a PPAC (Parallel-plate Avalanche Chamber)

    International Nuclear Information System (INIS)

    Heil, C.


    Parallel-Plate Avalanche Chamber (PPAC) detectors are used currently to observe nuclear disintegrations in nuclear physics. The work that has been done here shows PPAC can be used in high energy physics under certain conditions to detect minimum ionizing particles. Their advantage is to join good time resolution with low matter density. A PPAC prototype has been made with 90% efficiency, 3 NS jitter, 2 NS rise time, 20 mg/cm 2 mass, 1.5 mm spatial accuracy. The parameters studied were electrodes design, choice of gas filling, electronics and anode strips. The detector is to be used as a hodoscope with high flux of particles [fr

  20. Characterization of a rock avalanche deposit for risk assessment in the town of Celano (Fucino Basin, Central Italy

    Directory of Open Access Journals (Sweden)

    A. Rinaldini


    Full Text Available This paper describes multidisciplinary investigations carried out in the urban centre of Celano, a small town located at the northern edge of the Fucino Basin (Central Italy. The town lies upon a wide debris body that was recognized in this study as a rock avalanche deposit estimated to date to the Holocene. Geomorphologic studies and geophysical investigations led to a detailed characterization of the landslide deposit and the surrounding units. The information obtained was used to assess the vulnerability of the Celano municipal area, by evaluating the stability of the landslide body and the behaviour of its lithologies under seismic loads.