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Sample records for advanced avalanche photodiode

  1. Some tests of avalanche photodiodes produced by Advanced Photonix, Inc.

    SciTech Connect

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

    1995-08-01

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

  2. Characterization of Advanced Avalanche Photodiodes for Water Vapor Lidar Receivers

    NASA Technical Reports Server (NTRS)

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

    2000-01-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2016-05-01

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

  4. Integrated avalanche photodiode arrays

    DOEpatents

    Harmon, Eric S.

    2015-07-07

    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.

  5. Ultraviolet avalanche photodiodes

    NASA Astrophysics Data System (ADS)

    McClintock, Ryan; Razeghi, Manijeh

    2015-08-01

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

  6. Gallium-based avalanche photodiode optical crosstalk

    NASA Astrophysics Data System (ADS)

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

    2006-11-01

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

  7. Avalanche Photodiode Statistics in Triggered-avalanche Detection Mode

    NASA Technical Reports Server (NTRS)

    Tan, H. H.

    1984-01-01

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

  8. Why small avalanche photodiodes are beautiful

    NASA Astrophysics Data System (ADS)

    Rees, Graham J.; David, John P. R.

    2003-07-01

    Conventional wisdom suggests that, for low avalanche noise, avalanche photodiodes should operate at low electric fields, where electron and hole ionisation coefficients can differ widely. However, the associated weak ionization requires long multiplication regions, which in turn demand high bias voltages and result in long carrier transit times, reducing device speed. Moreover, multiplication is particularly sensitive to temperature in this region. In this paper we discuss the effects of dead space on reducing noise in short devices and on the associated benefits in predicted response time and reduced temperature sensitivity. The paper is illustrated with work from the Sheffield group.

  9. Nano-multiplication region avalanche photodiodes and arrays

    NASA Technical Reports Server (NTRS)

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

    2011-01-01

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

  10. Type-II Superlattice Avalanche Photodiodes

    NASA Astrophysics Data System (ADS)

    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

  11. Highly enhanced avalanche probability using sinusoidally-gated silicon avalanche photodiode

    SciTech Connect

    Suzuki, Shingo; Namekata, Naoto Inoue, Shuichiro; Tsujino, Kenji

    2014-01-27

    We report on visible light single photon detection using a sinusoidally-gated silicon avalanche photodiode. Detection efficiency of 70.6% was achieved at a wavelength of 520 nm when an electrically cooled silicon avalanche photodiode with a quantum efficiency of 72.4% was used, which implies that a photo-excited single charge carrier in a silicon avalanche photodiode can trigger a detectable avalanche (charge) signal with a probability of 97.6%.

  12. Cooled avalanche photodiode used for photon detection

    NASA Technical Reports Server (NTRS)

    Robinson, Deborah L.; Metscher, Brian D.

    1987-01-01

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

  13. Photon detection with cooled avalanche photodiodes

    NASA Technical Reports Server (NTRS)

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

    1987-01-01

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

  14. Avalanche Photodiode Arrays for Optical Communications Receivers

    NASA Technical Reports Server (NTRS)

    Srinivasan, M.; Vilnrotter, V.

    2001-01-01

    An avalanche photodiode (APD) array for ground-based optical communications receivers is investigated for the reception of optical signals through the turbulent atmosphere. Kolmogorov phase screen simulations are used to generate realistic spatial distributions of the received optical field. It is shown that use of an APD array for pulse-position modulation detection can improve performance by up to 4 dB over single APD detection in the presence of turbulence, but that photon-counting detector arrays yield even greater gains.

  15. A cooled avalanche photodiode with high photon detection probability

    NASA Technical Reports Server (NTRS)

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

    1986-01-01

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

  16. Characterization of avalanche photodiodes for lidar atmospheric return signal detectors

    NASA Technical Reports Server (NTRS)

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

    1988-01-01

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

  17. Relative degradation of near infrared avalanche photodiodes from proton irradiation

    NASA Technical Reports Server (NTRS)

    Becker, Heidi; Johnston, Allan H.

    2004-01-01

    InGaAs and Ge avalanche photodiodes are compared for the effects of 63-MeV protons on dark current. Differences in displacement damage factors are discussed as they relate to structural differences between devices.

  18. Optimum Receiver Structure for PPM Signals with Avalanche Photodiode Statistics

    NASA Technical Reports Server (NTRS)

    Vilnrotter, V.; Srinivasan, M.

    1998-01-01

    The maximum likelihood decision statistic for detection of pulse-position modulated signals with an avalanche photodiode is derived, using the more accurate Webb density rather than Poisson or Gaussian approximations for the distribution of avalanche photodiode output electrons. It is shown that for Webb-distributed output electtrons, the maximum likelihood rule is to choose the PPM word corresponding to the slot with the maximum electron count.

  19. Measuring atmospheric dispersion employing avalanche photodiodes

    NASA Astrophysics Data System (ADS)

    Schreiber, Ulrich; Maier, Wolfgang; Riepl, Stefan

    1994-12-01

    The accuracy of today's satellite laser ranging system is limited to a few cm. A significant part of this range error is due to the limitations of the atmospheric correction model. A dual color ranging experiment has been designed to investigate this source of error. When ranging to satellites at the fundamental and second harmonic frequency of a Nd:YAG laser, two different pulse round trip times are obtained simultaneously. The infrared pulse is detected by an avalanche photodiode, operated in the `Geiger mode', while the green pulse is recorded by a microchannel plate photomultiplier. For a given satellite pass, the jitter in recording the time of flight of the pulse is too high to calculate an atmospheric correction from individual measurements. Due to the many shots per satellite pass, the scatter can be significantly reduced by applying a nonlinear least squares fitting procedure to the data. The results of a large number of satellite passes are compared with the predictions of the Marini-Murray model.

  20. III-V alloy heterostructure high speed avalanche photodiodes

    NASA Technical Reports Server (NTRS)

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

    1979-01-01

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

  1. 3D avalanche multiplication in Si-Ge lateral avalanche photodiodes

    NASA Astrophysics Data System (ADS)

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

    2016-05-01

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

  2. Study on avalanche photodiode influence on heterodyne laser interferometer linearity

    NASA Astrophysics Data System (ADS)

    Budzyn, Grzegorz; Podzorny, Tomasz

    2016-06-01

    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.

  3. Receiver characteristics of laser altimeters with avalanche photodiodes

    NASA Technical Reports Server (NTRS)

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

    1992-01-01

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

  4. Geiger-mode avalanche photodiodes, history, properties and problems

    NASA Astrophysics Data System (ADS)

    Renker, D.

    2006-11-01

    Geiger-mode avalanche photodiodes (G-APDs) have been developed during recent years and promise to be an alternative to photomultiplier tubes. They have many advantages like single photon response, high detection efficiency, high gain at low bias voltage and very good timing properties but some of their properties, the dark count rate for example, can be a problem. Several types of G-APDs are on the market and should be selected carefully for a given application.

  5. Avalanche photodiode photon counting receivers for space-borne lidars

    NASA Technical Reports Server (NTRS)

    Sun, Xiaoli; Davidson, Frederic M.

    1991-01-01

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

  6. Radiation hard avalanche photodiodes for CMS ECAL

    NASA Astrophysics Data System (ADS)

    Grahl, J.; Kronquist, I.; Rusack, R.; Singovski, A.; Kuznetsov, A.; Musienko, Y.; Reucroft, S.; Swain, J.; Deiters, K.; Ingram, Q.; Renker, D.; Sakhelashvili, T.

    2003-05-01

    The photo detectors of the CMS electromagnetic calorimeter have to operate in a rather hostile environment, in a strong magnetic field of 4 T and under unprecedented radiation levels. Avalanche Photo Diodes (APDs) have been chosen to detect the scintillation light of the 62,000 lead tungstate crystals in the barrel part of the calorimeter. After a 6 year long R&D work Hamamatsu Photonics produces APDs with a structure that is basically radiation hard. Only a few percent of the delivered APDs are weak due to defects at the surface caused by dust particles in the production process. Since a reliability of 99.9% is required, a method to detect weak APDs before they are built into the detector had to be developed. The described screening method is a combination of 60Co irradiations and annealing under bias of all APDs and irradiations with hadrons on a sampling basis.

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

    NASA Astrophysics Data System (ADS)

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

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

  8. Silicon avalanche photodiode operation and lifetime analysis for small satellites.

    PubMed

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

    2013-07-15

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

  9. Reliability assessment of multiple quantum well avalanche photodiodes

    NASA Technical Reports Server (NTRS)

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

    1995-01-01

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

  10. Photon counting modules using RCA silicon avalanche photodiodes

    NASA Technical Reports Server (NTRS)

    Lightstone, Alexander W.; Macgregor, Andrew D.; Macsween, Darlene E.; Mcintyre, Robert J.; Trottier, Claude; Webb, Paul P.

    1989-01-01

    Avalanche photodiodes (APD) are excellent small area, solid state detectors for photon counting. Performance possibilities include: photon detection efficiency in excess of 50 percent; wavelength response from 400 to 1000 nm; count rate to 10 (exp 7) counts per sec; afterpulsing at negligible levels; timing resolution better than 1 ns. Unfortunately, these performance levels are not simultaneously available in a single detector amplifier configuration. By considering theoretical performance predictions and previous and new measurements of APD performance, the anticipated performance of a range of proposed APD-based photon counting modules is derived.

  11. Initial results from the Sherbrooke avalanche photodiode positron tomograph

    SciTech Connect

    Lecomte, R.; Cadorette, J.; Rodrigue, S.; Lapointe, D.; Rouleau, D.; Bentourkia, M.; Yao, R.; Msaki, P.

    1996-06-01

    The design features and engineering constraints of a PET system based on avalanche photodiode (APD) detectors have been described in a previous report. In this paper, the authors present the initial results obtained with the Sherbrooke APD-PET scanner, a very high spatial resolution device designed for dynamic imaging of small and medium-sized laboratory animals such as rats, cats, rabbits and small monkeys. Its physical performance has been evaluated in terms of resolution, sensitivity, count rate, random and scatter fractions, contrast and relative activity recovery as a function of object size. The capabilities of the scanner for biomedical research applications have been demonstrated using phantom and animal studies.

  12. A 1.06 micrometer avalanche photodiode receiver

    NASA Technical Reports Server (NTRS)

    Eden, R. C.

    1975-01-01

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

  13. 400-ps time resolution with a passively quenched avalanche photodiode.

    PubMed

    Grayson, T P; Wang, L J

    1993-06-01

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

  14. Recent progress in high gain InAs avalanche photodiodes (Presentation Recording)

    NASA Astrophysics Data System (ADS)

    Bank, Seth; Maddox, Scott J.; Sun, Wenlu; Nair, Hari P.; Campbell, Joe C.

    2015-08-01

    InAs possesses nearly ideal material properties for the fabrication of near- and mid-infrared avalanche photodiodes (APDs), which result in strong electron-initiated impact ionization and negligible hole-initiated impact ionization [1]. Consequently, InAs multiplication regions exhibit several appealing characteristics, including extremely low excess noise factors and bandwidth independent of gain [2], [3]. These properties make InAs APDs attractive for a number of near- and mid-infrared sensing applications including remote gas sensing, light detection and ranging (LIDAR), and both active and passive imaging. Here, we discuss our recent advances in the growth and fabrication of high gain, low noise InAs APDs. Devices yielded room temperature multiplication gains >300, with much reduced (~10x) lower dark current densities. We will also discuss a likely key contributor to our current performance limitations: silicon diffusion into the intrinsic (multiplication) region from the underlying n-type layer during growth. Future work will focus on increasing the intrinsic region thickness, targeting gains >1000. This work was supported by the Army Research Office (W911NF-10-1-0391). [1] A. R. J. Marshall, C. H. Tan, M. J. Steer, and J. P. R. David, "Electron dominated impact ionization and avalanche gain characteristics in InAs photodiodes," Applied Physics Letters, vol. 93, p. 111107, 2008. [2] A. R. J. Marshall, A. Krysa, S. Zhang, A. S. Idris, S. Xie, J. P. R. David, and C. H. Tan, "High gain InAs avalanche photodiodes," in 6th EMRS DTC Technical Conference, Edinburgh, Scotland, UK, 2009. [3] S. J. Maddox, W. Sun, Z. Lu, H. P. Nair, J. C. Campbell, and S. R. Bank, "Enhanced low-noise gain from InAs avalanche photodiodes with reduced dark current and background doping," Applied Physics Letters, vol. 101, no. 15, pp. 151124-151124-3, Oct. 2012.

  15. Avalanche photodiode based detector for beam emission spectroscopy

    SciTech Connect

    Dunai, D.; Zoletnik, S.; Sarkoezi, J.; Field, A. R.

    2010-10-15

    An avalanche photodiode based (APD) detector for the visible wavelength range was developed for low light level, high frequency beam emission spectroscopy (BES) experiments in fusion plasmas. This solid state detector has higher quantum efficiency than photomultiplier tubes, and unlike normal photodiodes, it has internal gain. This paper describes the developed detector as well as the noise model of the electronic circuit. By understanding the noise sources and the amplification process, the optimal amplifier and APD reverse voltage setting can be determined, where the signal-to-noise ratio is the highest for a given photon flux. The calculations are compared to the absolute calibration results of the implemented circuit. It was found that for a certain photon flux range, relevant for BES measurements ({approx_equal}10{sup 8}-10{sup 10} photons/s), the new detector is superior to both photomultipliers and photodiodes, although it does not require cryogenic cooling of any component. The position of this photon flux window sensitively depends on the parameters of the actual experimental implementation (desired bandwidth, detector size, etc.) Several detector units based on these developments have been built and installed in various tokamaks. Some illustrative results are presented from the 8-channel trial BES system installed at Mega-Ampere Spherical Tokamak (MAST) and the 16-channel BES system installed at the Torus Experiment for Technology Oriented Research (TEXTOR).

  16. Development of high gain avalanche photodiodes for UV imaging applications

    NASA Astrophysics Data System (ADS)

    Sood, Ashok K.; Zeller, John W.; Welser, Roger E.; Puri, Yash R.; Dupuis, Russell D.; Ji, Mi-Hee; Kim, Jeomoh; Detchprohm, Theeradetch; Dhar, Nibir K.; Lewis, Jay S.; Peters, Roy L.

    2015-08-01

    High-resolution imaging in ultraviolet (UV) bands has many applications in defense and commercial systems. The shortest wavelength is desired for increased spatial resolution, which allows for small pixels and large formats. The next frontier is to develop UV avalanche photodiode (UV-APD) arrays with high gain to demonstrate high-resolution imaging. We compare performance characteristics of front-illuminated Al0.05Ga0.95N UV-APDs grown on a free-standing (FS) GaN substrate and a GaN/sapphire template. UV-APDs grown on a FS-GaN substrate show lower dark current densities for all fabricated mesa sizes than similar UV-APDs grown on a GaN/sapphire template. In addition, stable avalanche gain higher than 5×105 and a significant increase in the responsivity of UV-APDs grown on a FS-GaN substrate are observed as a result of avalanche multiplication at high reverse bias. We believe that the high crystalline quality of Al0.05Ga0.95N UVAPDs grown on a FS-GaN substrate with low dislocation density is responsible for the observed improvement of low leakage currents, high performance photodetector characteristics, and reliability of the devices.

  17. Temperature Control of Avalanche Photodiode Using Thermoelectric Cooler

    NASA Technical Reports Server (NTRS)

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

    1999-01-01

    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.

  18. High resolution, low energy avalanche photodiode X-ray detectors

    NASA Technical Reports Server (NTRS)

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

    1991-01-01

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

  19. Studies of avalanche photodiodes for scintillating fibre tracking readout

    SciTech Connect

    Fenker, H; Thomas, J

    1993-01-01

    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.

  20. Avalanche photodiode based time-of-flight mass spectrometry

    SciTech Connect

    Ogasawara, Keiichi Livi, Stefano A.; Desai, Mihir I.; Ebert, Robert W.; McComas, David J.; Walther, Brandon C.

    2015-08-15

    This study reports on the performance of Avalanche Photodiodes (APDs) as a timing detector for ion Time-of-Flight (TOF) mass spectroscopy. We found that the fast signal carrier speed in a reach-through type APD enables an extremely short timescale response with a mass or energy independent <2 ns rise time for <200 keV ions (1−40 AMU) under proper bias voltage operations. When combined with a microchannel plate to detect start electron signals from an ultra-thin carbon foil, the APD comprises a novel TOF system that successfully operates with a <0.8 ns intrinsic timing resolution even using commercial off-the-shelf constant-fraction discriminators. By replacing conventional total-energy detectors in the TOF-Energy system, APDs offer significant power and mass savings or an anti-coincidence background rejection capability in future space instrumentation.

  1. Correcting for accidental correlations in saturated avalanche photodiodes.

    PubMed

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

    2016-02-22

    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. PMID:26907016

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

    NASA Astrophysics Data System (ADS)

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

    2006-11-01

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

  3. Characterization of midwave infrared InSb avalanche photodiode

    SciTech Connect

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

    2015-06-28

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

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

    PubMed Central

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

    2008-01-01

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

  5. Nano-Multiplication-Region Avalanche Photodiodes and Arrays

    NASA Technical Reports Server (NTRS)

    Zheng, Xinyu; Pain, Bedabrata; Cunningham, Thomas

    2008-01-01

    Nano-multiplication-region avalanche photodiodes (NAPDs), and imaging arrays of NAPDs integrated with complementary metal oxide/semiconductor (CMOS) active-pixel-sensor integrated circuitry, are being developed for applications in which there are requirements for high-sensitivity (including photoncounting) detection and imaging at wavelengths from about 250 to 950 nm. With respect to sensitivity and to such other characteristics as speed, geometric array format, radiation hardness, power demand of associated circuitry, size, weight, and robustness, NAPDs and arrays thereof are expected to be superior to prior photodetectors and arrays including CMOS active-pixel sensors (APSs), charge-coupled devices (CCDs), traditional APDs, and microchannelplate/ CCD combinations. Figure 1 depicts a conceptual NAPD array, integrated with APS circuitry, fabricated on a thick silicon-on-insulator wafer (SOI). Figure 2 presents selected aspects of the structure of a typical single pixel, which would include a metal oxide/semiconductor field-effect transistor (MOSFET) integrated with the NAPD. The NAPDs would reside in silicon islands formed on the buried oxide (BOX) layer of the SOI wafer. The silicon islands would be surrounded by oxide-filled insulation trenches, which, together with the BOX layer, would constitute an oxide embedding structure. There would be two kinds of silicon islands: NAPD islands for the NAPDs and MOSFET islands for in-pixel and global CMOS circuits. Typically, the silicon islands would be made between 5 and 10 m thick, but, if necessary, the thickness could be chosen outside this range. The side walls of the silicon islands would be heavily doped with electron-acceptor impurities (p+-doped) to form anodes for the photodiodes and guard layers for the MOSFETs. A nanoscale reach-through structure at the front (top in the figures) central position of each NAPD island would contain the APD multiplication region. Typically, the reach-through structure would be

  6. High performance waveguide-coupled Ge-on-Si linear mode avalanche photodiodes.

    PubMed

    Martinez, Nicholas J D; Derose, Christopher T; Brock, Reinhard W; Starbuck, Andrew L; Pomerene, Andrew T; Lentine, Anthony L; Trotter, Douglas C; Davids, Paul S

    2016-08-22

    We present experimental results for a selective epitaxially grown Ge-on-Si separate absorption and charge multiplication (SACM) integrated waveguide coupled avalanche photodiode (APD) compatible with our silicon photonics platform. Epitaxially grown Ge-on-Si waveguide-coupled linear mode avalanche photodiodes with varying lateral multiplication regions and different charge implant dimensions are fabricated and their illuminated device characteristics and high-speed performance is measured. We report a record gain-bandwidth product of 432 GHz for our highest performing waveguide-coupled avalanche photodiode operating at 1510nm. Bit error rate measurements show operation with BER< 10-12, in the range from -18.3 dBm to -12 dBm received optical power into a 50 Ω load and open eye diagrams with 13 Gbps pseudo-random data at 1550 nm. PMID:27557187

  7. Development of Fuses for Protection of Geiger-Mode Avalanche Photodiode Arrays

    NASA Astrophysics Data System (ADS)

    Grzesik, Michael; Bailey, Robert; Mahan, Joe; Ampe, Jim

    2015-11-01

    Current-limiting fuses composed of Ti/Al/Ni were developed for use in Geiger-mode avalanche photodiode arrays for each individual pixel in the array. The fuses were designed to burn out at ˜4.5 × 10-3 A and maintain post-burnout leakage currents less than 10-7 A at 70 V sustained for several minutes. Experimental fuse data are presented and successful incorporation of the fuses into a 256 × 64 pixel InP-based Geiger-mode avalanche photodiode array is reported.

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

    SciTech Connect

    Diepold, Marc Franke, Beatrice; Götzfried, Johannes; Hänsch, Theodor W.; Krauth, Julian J.; Mulhauser, Françoise; Nebel, Tobias; Pohl, Randolf; Fernandes, Luis M. P.; Amaro, Fernando D.; Gouvea, Andrea L.; Monteiro, Cristina M. B.; Santos, Joaquim M. F. dos; Machado, Jorge; Amaro, Pedro; Santos, José Paulo; and others

    2015-05-15

    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.

  9. Extracting dark current components and characteristics parameters for InGaAs/InP avalanche photodiodes

    NASA Astrophysics Data System (ADS)

    Xu, Jiao; Chen, Xiaoshuang; Wang, Wenjuan; Lu, Wei

    2016-05-01

    The dark current of separate absorption grading charge multiplication (SAGCM) InGaAs/InP avalanche photodiodes has been numerical analyzed. SRH current, TAT current, BBT current and avalanche amplification combined together as the dark current have been extracted by simulation separately. The trend of punch-through voltage and breakdown voltage have been discussed, meanwhile the influence of structure parameters also has been investigated.

  10. Impact ionization engineered avalanche photodiode arrays for free space optical communication

    NASA Astrophysics Data System (ADS)

    Ferraro, Mike S.; Rabinovich, William S.; Clark, William R.; Waters, William D.; Campbell, Joe C.; Mahon, Rita; Vaccaro, Kenneth; Krejca, Brian D.

    2016-03-01

    High sensitivity photodetectors serve two purposes in free space optical communication: data reception and position sensing for pointing, tracking, and stabilization. Because of conflicting performance criteria, two separate detectors are traditionally utilized to perform these tasks but recent advances in the fabrication and development of large area, low noise avalanche photodiode (APD) arrays have enabled these devices to be used both as position sensitive detectors (PSD) and as communications receivers. Combining these functionalities allows for more flexibility and simplicity in optical assembly design without sacrificing the sensitivity and bandwidth performance of smaller, single element data receivers. Beyond eliminating the need to separate the return beam into two separate paths, these devices enable implementation of adaptive approaches to compensate for focal plane beam wander and breakup often seen in highly scintillated terrestrial and maritime optical links. While the Naval Research Laboratory (NRL) and Optogration Inc, have recently demonstrated the performance of single period, InAlAs/InGaAs APD arrays as combined data reception and tracking sensors, an impact ionization engineered (I2E) epilayer design achieves even lower carrier ionization ratios by incorporating multiple multiplication periods engineered to suppress lower ionization rate carriers while enhancing the higher ionization rate carriers of interest. This work presents a three period I2E concentric, five element avalanche photodiode array rated for bandwidths beyond 1GHz with measured carrier ionization ratios of 0.05-0.1 at moderate APD gains. The epilayer design of the device will be discussed along with initial device characterization and high speed performance measurements.

  11. The blocking probability of Geiger-mode avalanche photo-diodes

    NASA Technical Reports Server (NTRS)

    Moision, Bruce; Srinivasan, Meera; Hamkins, Jon

    2005-01-01

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

  12. Photon Detection with Cooled Avalanche Photodiodes: Theory and Preliminary Experimental Results

    NASA Technical Reports Server (NTRS)

    Robinson, D. L.; Hays, D. A.

    1985-01-01

    Avalanche photodiodes (APDs) can be operated in a geiger-tube mode so that they can respond to single electron events and thus be used as photon counting detectors. Operational characteristics and theory of APDs while used in this mode are analyzed and assessed. Preliminary experimental investigation of several commercially available APDs has commenced, and initial results for dark count statistics are presented.

  13. Photoionization of Trapped Carriers in Avalanche Photodiodes to Reduce Afterpulsing During Geiger-Mode Photon Counting

    NASA Technical Reports Server (NTRS)

    Krainak, Michael A.

    2005-01-01

    We reduced the afterpulsing probability by a factor of five in a Geiger-mode photon-counting InGaAs avalanche photodiode by using sub-band-gap (lambda = 1.95 micron) laser diode illumination, which we believe photoionizes the trapped carriers.

  14. Geiger-Mode Avalanche Photodiode Arrays Integrated to All-Digital CMOS Circuits

    PubMed Central

    Aull, Brian

    2016-01-01

    This article reviews MIT Lincoln Laboratory's work over the past 20 years to develop photon-sensitive image sensors based on arrays of silicon Geiger-mode avalanche photodiodes. Integration of these detectors to all-digital CMOS readout circuits enable exquisitely sensitive solid-state imagers for lidar, wavefront sensing, and passive imaging. PMID:27070609

  15. AlInAsSb separate absorption, charge, and multiplication avalanche photodiodes

    NASA Astrophysics Data System (ADS)

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

    2016-05-01

    We report AlxIn1-xAsySb1-y separate absorption, charge, and multiplication avalanche photodiodes (APDs) that operate in the short-wavelength infrared spectrum. They exhibit excess noise factor less or equal to that of Si and the low dark currents typical of III-V compound APDs.

  16. Geiger-Mode Avalanche Photodiode Arrays Integrated to All-Digital CMOS Circuits.

    PubMed

    Aull, Brian

    2016-01-01

    This article reviews MIT Lincoln Laboratory's work over the past 20 years to develop photon-sensitive image sensors based on arrays of silicon Geiger-mode avalanche photodiodes. Integration of these detectors to all-digital CMOS readout circuits enable exquisitely sensitive solid-state imagers for lidar, wavefront sensing, and passive imaging. PMID:27070609

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

    NASA Technical Reports Server (NTRS)

    Arbel, D.; Schwartz, J. A.

    1991-01-01

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

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

    SciTech Connect

    Gullikson, E.M.; Gramsch, E. |; Szawlowski, M.

    1995-08-01

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

  19. Modeling of high-precision wavefront sensing with new generation of CMT avalanche photodiode infrared detectors.

    PubMed

    Gousset, Silvère; Petit, Cyril; Michau, Vincent; Fusco, Thierry; Robert, Clelia

    2015-12-01

    Near-infrared wavefront sensing allows for the enhancement of sky coverage with adaptive optics. The recently developed HgCdTe avalanche photodiode arrays are promising due to their very low detector noise, but still present an imperfect cosmetic that may directly impact real-time wavefront measurements for adaptive optics and thus degrade performance in astronomical applications. We propose here a model of a Shack-Hartmann wavefront measurement in the presence of residual fixed pattern noise and defective pixels. To adjust our models, a fine characterization of such an HgCdTe array, the RAPID sensor, is proposed. The impact of the cosmetic defects on the Shack-Hartmann measurement is assessed through numerical simulations. This study provides both a new insight on the applicability of cadmium mercury telluride (CMT) avalanche photodiodes detectors for astronomical applications and criteria to specify the cosmetic qualities of future arrays. PMID:26836674

  20. Dynamics of local micro-breakdown in the Geiger mode of avalanche photodiodes

    SciTech Connect

    Verhovtseva, A. V. Gergel, V. A.

    2009-07-15

    Mathematical modeling methods were used to study the dynamics of micro-breakdown development in structures of silicon avalanche photodiodes. The constructed model considers the locality of the avalanchexs multiplication region appearing during single photon absorption and the delay of the avalanchexs current spreading over the rear electrode of the diode. The calculations showed two different phases of transient process of the formation of the electrical signal, i.e., the rapid and slow ones due to current spreading and ordinary RC recharge, respectively. The load resistances required to implement the pulsed mode of operation of the structures of the avalanche photodiode were calculated for a series of actual diode capacitances and spreading resistances of the rear electrode.

  1. Traceable calibration of Si avalanche photodiodes using synchrotron radiation

    NASA Astrophysics Data System (ADS)

    Müller, I.; Klein, R. M.; Hollandt, J.; Ulm, G.; Werner, L.

    2012-04-01

    In this paper, we present a new substitution method based on the unique properties of synchrotron radiation and of the Metrology Light Source (MLS), the dedicated electron storage ring of the PTB. The MLS is used as a light source with a dynamic range of its photon flux of 11 orders of magnitude to bridge the gap in optical power measurement between a cryogenic electrical substitution radiometer and a single photon detector. Two single photon avalanche diodes were calibrated at 651 nm with combined relative uncertainties of 0.17% and 0.16% traceable to a primary standard, a cryogenic electrical substitution radiometer.

  2. Silicon Geiger-mode avalanche photodiode arrays for photon-starved imaging

    NASA Astrophysics Data System (ADS)

    Aull, Brian F.

    2015-05-01

    Geiger-mode avalanche photodiodes (GMAPDs) are capable of detecting single photons. They can be operated to directly trigger all-digital circuits, so that detection events are digitally counted or time stamped in each pixel. An imager based on an array of GMAPDs therefore has zero readout noise, enabling quantum-limited sensitivity for photon-starved imaging applications. In this review, we discuss devices developed for 3D imaging, wavefront sensing, and passive imaging.

  3. Al0.52In0.48P avalanche photodiodes for soft X-ray spectroscopy

    NASA Astrophysics Data System (ADS)

    Auckloo, A.; Cheong, J. S.; Meng, X.; Tan, C. H.; Ng, J. S.; Krysa, A.; Tozer, R. C.; David, J. P. R.

    2016-03-01

    The performance of Al0.52In0.48P avalanche photodiodes was assessed as soft X-ray detectors at room temperature. The effect of the avalanche gain improved the energy resolution and an energy resolution (FWHM) of 682 eV is reported for 5.9 keV X-rays.

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

    PubMed

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

    2011-11-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2015-12-01

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

  6. Signal-to-noise ratio of Geiger-mode avalanche photodiode single-photon counting detectors

    NASA Astrophysics Data System (ADS)

    Kolb, Kimberly

    2014-08-01

    Geiger-mode avalanche photodiodes (GM-APDs) use the avalanche mechanism of semiconductors to amplify signals in individual pixels. With proper thresholding, a pixel will be either "on" (avalanching) or "off." This discrete detection scheme eliminates read noise, which makes these devices capable of counting single photons. Using these detectors for imaging applications requires a well-developed and comprehensive expression for the expected signal-to-noise ratio (SNR). This paper derives the expected SNR of a GM-APD detector in gated operation based on gate length, number of samples, signal flux, dark count rate, photon detection efficiency, and afterpulsing probability. To verify the theoretical results, carrier-level Monte Carlo simulation results are compared to the derived equations and found to be in good agreement.

  7. Screening of Avalanche Photodiodes for the Cms Ecal

    NASA Astrophysics Data System (ADS)

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

    2004-07-01

    The Compact Muon Solenoid is one of two general purpose detectors currently being constructed for the Large Hadron Collider at CERN foreseen to begin data taking in 2007. Avalanche Photo Diodes (APDs) have been chosen to detect the scintillation light of the 61 200 lead tungstate crystals in the barrel part of the electromagnetic calorimeter of CMS. After a 8 years long R&D work Hamamatsu Photonics produces now APDs with a structure that is basically radiation resistant. Since a reliability of 99.9% is required, a method to detect weak APDs before they are built into the detector had to be developed. The described screening method is a combination of an irradiation with 60Co and annealing under bias of all APDs and on a sampling basis only an irradiation with hadrons.

  8. AlInAsSb/GaSb staircase avalanche photodiode

    NASA Astrophysics Data System (ADS)

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

    2016-02-01

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

  9. Development of Gated Pinned Avalanche Photodiode Pixels for High-Speed Low-Light Imaging.

    PubMed

    Resetar, Tomislav; De Munck, Koen; Haspeslagh, Luc; Rosmeulen, Maarten; Süss, Andreas; Puers, Robert; Van Hoof, Chris

    2016-01-01

    This work explores the benefits of linear-mode avalanche photodiodes (APDs) in high-speed CMOS imaging as compared to different approaches present in literature. Analysis of APDs biased below their breakdown voltage employed in single-photon counting mode is also discussed, showing a potentially interesting alternative to existing Geiger-mode APDs. An overview of the recently presented gated pinned avalanche photodiode pixel concept is provided, as well as the first experimental results on a 8 × 16 pixel test array. Full feasibility of the proposed pixel concept is not demonstrated; however, informative data is obtained from the sensor operating under -32 V substrate bias and clearly exhibiting wavelength-dependent gain in frontside illumination. The readout of the chip designed in standard 130 nm CMOS technology shows no dependence on the high-voltage bias. Readout noise level of 15 e - rms, full well capacity of 8000 e - , and the conversion gain of 75 µV / e - are extracted from the photon-transfer measurements. The gain characteristics of the avalanche junction are characterized on separate test diodes showing a multiplication factor of 1.6 for red light in frontside illumination. PMID:27537882

  10. Balanced InGaAs/InP avalanche photodiodes for single photon detection

    NASA Astrophysics Data System (ADS)

    Lu, Zhiwen; Sun, Wenlu; Zheng, Xiaoguang; Campbell, Joe; Jiang, Xudong; Itzler, Mark A.

    2012-10-01

    Abstract - We demonstrate a sinusoidally-gated InGaAs/InP photodiode pair operated at wavelength of 1310 nm with high photon detection efficiency (PDE) and low dark count rate (DCR). The photodiode pair is biased in a balanced scenario so that the common component of the output signal is cancelled. The concept of balanced photodiodes helps improve detection efficiency while canceling the common mode signal, which, in this case, is the capacitive response of the photodiodes. In conventional sinusoidal gating, an extra component, - an RF filter (or several) at the gating frequency, is utilized to filter out the gating signal and leave the avalanche signal for detection. For this configuration, sinusoidally-gated counting systems are restricted to a single frequency. With the balanced single photon diodes (SPAD), sinusoidal gating within a continuous frequency range is feasible. A printed circuit with symmetric layout of two bias tees was fabricated on a duroid board to enable the application of AC and DC signals for the dual SPADs. At a laser repletion rate of 1 MHz and temperature of 240 K the DCR and PDE were 58 kHz and 43%, respectively. Afterpulsing probability was lower compared with a sinusoidually-gated single SPAD. Jitter of 240 ps was achieved with 1 photon per pulse for an excess bias of 1.6%.

  11. Polarization engineering of back-illuminated separate absorption and multiplication AlGaN avalanche photodiodes

    NASA Astrophysics Data System (ADS)

    Yang, Guofeng; Wang, Fuxue

    2016-08-01

    The back-illuminated separate absorption and multiplication AlGaN avalanche photodiodes (APDs) with a p-type graded AlGaN layer have been designed to investigate the polarization engineering on the performance of the devices. The calculated results show that the APD with p-graded AlGaN layer exhibits lower avalanche breakdown voltage and increased maximum multiplication gain compared to the structure with conventional p-type AlGaN layer. The improved performance of the designed APD is numerically explained by the polarization-assisted enhancement of the ionization electric field in the multiplication region and polarization doping effect caused by the p-type graded layer.

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

    NASA Technical Reports Server (NTRS)

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

    1995-01-01

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

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

    SciTech Connect

    Mallick, Shubhrangshu; Banerjee, Koushik; Ghosh, Siddhartha; Plis, Elena; Rodriguez, Jean Baptiste; Krishna, Sanjay; Grein, Christoph

    2007-12-10

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

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

    NASA Astrophysics Data System (ADS)

    Mallick, Shubhrangshu; Banerjee, Koushik; Ghosh, Siddhartha; Plis, Elena; Rodriguez, Jean Baptiste; Krishna, Sanjay; Grein, Christoph

    2007-12-01

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

  15. The performance of photon counting imaging with a Geiger mode silicon avalanche photodiode

    NASA Astrophysics Data System (ADS)

    Qu, Hui-Ming; Zhang, Yi-Fan; Ji, Zhong-Jie; Chen, Qian

    2013-10-01

    In principle, photon counting imaging can detect a photon. With the development of low-level-light image intensifier techniques and low-level-light detection devices, photon counting imaging can now detect photon images under extremely low illumination. Based on a Geiger mode silicon avalanche photodiode single photon counter, an experimental system for photon counting imaging was built through two-dimensional scanning of a SPAD (single photon avalanche diode) detector. The feasibility of the imaging platform was validated experimentally. Two images with different characteristics, namely, the USAF 1951 resolution test panel and the image of Lena, were chosen to evaluate the imaging performance of the experimental system. The results were compared and analysed. The imaging properties under various illumination and scanning steps were studied. The lowest illumination limit of the SPAD photon counting imaging was determined.

  16. Germanium-tin multiple quantum well on silicon avalanche photodiode for photodetection at two micron wavelength

    NASA Astrophysics Data System (ADS)

    Dong, Yuan; Wang, Wei; Lee, Shuh Ying; Lei, Dian; Gong, Xiao; Khai Loke, Wan; Yoon, Soon-Fatt; Liang, Gengchiau; Yeo, Yee-Chia

    2016-09-01

    We report the demonstration of a germanium-tin multiple quantum well (Ge0.9Sn0.1 MQW)-on-Si avalanche photodiode (APD) for light detection near the 2 μm wavelength range. The measured spectral response covers wavelengths from 1510 to 2003 nm. An optical responsivity of 0.33 A W‑1 is achieved at 2003 nm due to the internal avalanche gain. In addition, a thermal coefficient of breakdown voltage is extracted to be 0.053% K‑1 based on the temperature-dependent dark current measurement. As compared to the traditional 2 μm wavelength APDs, the Si-based APD is promising for its small excess noise factor, less stringent demand on temperature stability, and its compatibility with silicon technology.

  17. Practical photon number detection with electric field-modulated silicon avalanche photodiodes.

    PubMed

    Thomas, O; Yuan, Z L; Shields, A J

    2012-01-01

    Low-noise single-photon detection is a prerequisite for quantum information processing using photonic qubits. In particular, detectors that are able to accurately resolve the number of photons in an incident light pulse will find application in functions such as quantum teleportation and linear optics quantum computing. More generally, such a detector will allow the advantages of quantum light detection to be extended to stronger optical signals, permitting optical measurements limited only by fluctuations in the photon number of the source. Here we demonstrate a practical high-speed device, which allows the signals arising from multiple photon-induced avalanches to be precisely discriminated. We use a type of silicon avalanche photodiode in which the lateral electric field profile is strongly modulated in order to realize a spatially multiplexed detector. Clearly discerned multiphoton signals are obtained by applying sub-nanosecond voltage gates in order to restrict the detector current. PMID:22273682

  18. Effective amplifier noise for an optical receiver based on linear mode avalanche photodiodes

    NASA Technical Reports Server (NTRS)

    Chen, C.-C.

    1989-01-01

    The rms noise charge induced by the amplifier for an optical receiver based on the linear-mode avalanche photodiode (APD) was analyzed. It is shown that for an amplifier with a 1-pF capacitor and a noise temperature of 100 K, the rms noise charge due to the amplifier is about 300. Since the noise charge must be small compared to the signal gain, APD gains on the order of 1000 will be required to operate the receiver in the linear mode.

  19. Dark Current Degradation of Near Infrared Avalanche Photodiodes from Proton Irradiation

    NASA Technical Reports Server (NTRS)

    Becker, Heidi N.; Johnston, Allan H.

    2004-01-01

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

  20. State-of-the-art performance of GaAlAs/GaAs avalanche photodiodes

    NASA Technical Reports Server (NTRS)

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

    1979-01-01

    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.

  1. A prototype avalanche photodiode array for scintillating-fiber tracking detectors

    NASA Astrophysics Data System (ADS)

    Yoshida, tracking detectors T.; Sora, T.

    2004-12-01

    We have evaluated the performance of a prototype 16-channel avalanche photodiode (APD) array developed primarily for scintillating-fiber (SCIFI) tracking detectors. The APD array was coupled to a 2.5 m long SCIFI array, and the detection efficiency was measured for minimum ionizing particles passing through the SCIFI array. The APD array was cooled to -50 °C to improve the S/N ratio. We have found that the APD array can read out each individual SCIFI with sufficiently high efficiency.

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

    PubMed

    Akiba, Makoto; Tsujino, Kenji; Sasaki, Masahide

    2010-08-01

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

  3. Active quenching circuit for single-photon detection with Geiger mode avalanche photodiodes.

    PubMed

    Stipcević, Mario

    2009-03-20

    In this paper a novel construction of an active quenching circuit intended for single-photon detection is presented, along with a few original methods for its evaluation. The circuit has been combined with a standard avalanche photodiode C30902S to form a single-photon detector. This detector has a dead time of 39 ns, maximum random counting frequency of 14 MHz, small afterpulsing probability, an estimated peak detection efficiency of over 20%, and a dark count rate of less than 100 Hz. This simple and robust active quenching circuit can be built from off-the-shelf electronic components and is presented with the detailed schematic diagram. PMID:19305468

  4. The 1.06 micrometer avalanche photodiode detectors with integrated circuit preamplifiers

    NASA Technical Reports Server (NTRS)

    Eden, R. C.

    1975-01-01

    The development of a complete solid state 1.06 micron optical receiver which can be used in optical communications at data rates approaching 1.5 Gb/s, or in other applications requiring sensitive, short-pulse detection, is reported. This work entailed both the development of a new type of heterojunction 3-5 semiconductor alloy avalanche photodiode and an extremely charge-sensitive wideband low-noise preamp design making use of GaAs Schottky barrier-gate field effect transistors.

  5. Wavelength-division-multiplexed InGaAs/InP avalanched photodiodes for quantum key distributions

    NASA Astrophysics Data System (ADS)

    Lee, Moon Hyeok; Ha, Changkyun; Jeong, Heung-Sun; Kim, Dong Wook; Lee, Seoung Hun; Lee, Min Hee; Kim, Kyong Hon

    2016-02-01

    We demonstrate improved single photon detection efficiencies of InGaAs/InP avalanche photodiodes (APDs) in a wavelength-division-multiplexed (WDM) scheme for high-capacity plug-and-play-type two-way quantum key distributions (QKDs). Single-photon detectors (SPDs) combined in the WDM APD scheme can be used to overcome the detection speed limit of a single SPD which is caused mainly by the afterpulse effect. The multiple SPDs combined in the parallel WDM scheme can increase the single photon detection capacity, although additional optical losses resulted from the WDM MUX and deMUX devices induce limited increases.

  6. Required energy for a laser radar system incorporating a fiber amplifier or an avalanche photodiode.

    PubMed

    Overbeck, J A; Salisbury, M S; Mark, M B; Watson, E A

    1995-11-20

    The transmitted energy required for an airborne laser radar system to be able to image a target at 20 km is investigated. Because direct detection is being considered, two methods of enhancing the received signal are discussed: (1) using an avalanche photodiode (APD) as the detector and (2) using a commercial fiber amplifier as a preamplifier before a photodetector. For this analysis a specified signal-to-noise ratio was used in conjunction with the radar range equation, which includes the effects of atmospheric transmission and turbulence. Theoretical analysis reveals that a system with a fiber amplifier performs nearly the same as a system incorporating an APD. PMID:21060654

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

    PubMed

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

    2007-06-01

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

  8. UV and blue-enhanced avalanche photodiodes for nuclear spectroscopy applications

    NASA Astrophysics Data System (ADS)

    Gramsch, Ernesto; Avila, R. E.

    Avalanche photodiodes of the bevel-edge type have been developed with improved blue and UV response. The detectors have been characterized for use in low-light level applications such as nuclear spectroscopy. An etching technique not used before in avalanche photodiodes has been used to obtain improved blue and UV response. Quantum efficiency up to 40% has been obtained above 200 nm. The gain and dark current are dependent on external voltage, and gains up to 400 are obtained at 1980 V without excess noise, and breakdown occurs at ˜2000 V. The detector exhibits low noise and fast response, necessary for use in nuclear spectroscopy systems. The energy resolution from a 57Co gamma-ray source was measured to be 942 eV (6.4 keV X-rays), which corresponds to 111 r.m.s. noise electrons at the input. We measured the energy resolution of the detector coupled with a 3×3×3 mm 3 BGO scintillator from a 22Na gamma-ray source. The energy resolution at the 511 keV line was 12.5%, which is comparable to photomultiplier tubes coupled to a scintillator of the same size. The resolution with a 3×3×25 mm 3 LSO scintillator was also measured, the energy resolution at 511 keV was 12.1%.

  9. Interplanetary space weather effects on Lunar Reconnaissance Orbiter avalanche photodiode performance

    NASA Astrophysics Data System (ADS)

    Clements, E. B.; Carlton, A. K.; Joyce, C. J.; Schwadron, N. A.; Spence, H. E.; Sun, X.; Cahoy, K.

    2016-05-01

    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).

  10. Linear mode photon counting with the noiseless gain HgCdTe e-avalanche photodiode

    NASA Astrophysics Data System (ADS)

    Beck, Jeffrey D.; Scritchfield, Richard; Mitra, Pradip; Sullivan, William W.; Gleckler, Anthony D.; Strittmatter, Robert; Martin, Robert J.

    2014-08-01

    A linear mode photon counting focal plane array using HgCdTe mid-wave infrared (MWIR) cutoff electron initiated avalanche photodiodes (e-APDs) has been designed, fabricated, and characterized. The broad spectral range (0.4 to 4.3 μm) is unique among photon counters, making this a "first of its kind" system spanning the visible to the MWIR. The low excess noise [F(M)≈1] of the e-APDs allows for robust photon detection while operating at a stable linear avalanche gain in the range of 500-1000. The readout integrated circuit (ROIC) design included a very high gain-bandwidth product resistive transimpedance amplifier (3×1013 Ω-Hz) and a 4 ns output digital pulse width comparator. The ROIC had 16 high-bandwidth analogs and 16 low-voltage differential signaling digital outputs. The 2×8 array was integrated into an LN2 Dewar with a custom leadless chip carrier and daughter board design that preserved high-bandwidth analog and digital signal integrity. The 2×8 e-APD arrays were fabricated on 4.3 μm cutoff HgCdTe and operated at 84 K. The measured dark currents were approximately 1 pA at 13 V bias where the measured avalanche photodiode gain was 500. This translates to a predicted dark current induced dark count rate of less than 20 KHz. Single photon detection was achieved with a photon pulse signal-to-noise ratio of 13.7 above the amplifier noise floor. A photon detection efficiency of 50% was measured at a photon background limited false event rate of about 1 MHz. The measured jitter was in the range of 550-800 ps. The demonstrated minimum time between distinguishable events was less than 10 ns.

  11. Single-Photon-Sensitive HgCdTe Avalanche Photodiode Detector

    NASA Technical Reports Server (NTRS)

    Huntington, Andrew

    2013-01-01

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

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

    PubMed

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

    2015-01-01

    Avalanche photodiodes (APDs) are essential components in quantum key distribution systems and active imaging systems requiring both ultrafast response time to measure photon time of flight and high gain to detect low photon flux. The internal gain of an APD can improve system signal-to-noise ratio (SNR). Excess noise is typically kept low through the selection of material with intrinsically low excess noise, using separate-absorption-multiplication (SAM) heterostructures, or taking advantage of the dead-space effect using thin multiplication regions. In this work we demonstrate the first measurement of excess noise and gain-bandwidth product in III-V nanopillars exhibiting substantially lower excess noise factors compared to bulk and gain-bandwidth products greater than 200 GHz. The nanopillar optical antenna avalanche detector (NOAAD) architecture is utilized for spatially separating the absorption region from the avalanche region via the NOA resulting in single carrier injection without the use of a traditional SAM heterostructure. PMID:26627932

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

    PubMed Central

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

    2015-01-01

    Avalanche photodiodes (APDs) are essential components in quantum key distribution systems and active imaging systems requiring both ultrafast response time to measure photon time of flight and high gain to detect low photon flux. The internal gain of an APD can improve system signal-to-noise ratio (SNR). Excess noise is typically kept low through the selection of material with intrinsically low excess noise, using separate-absorption-multiplication (SAM) heterostructures, or taking advantage of the dead-space effect using thin multiplication regions. In this work we demonstrate the first measurement of excess noise and gain-bandwidth product in III–V nanopillars exhibiting substantially lower excess noise factors compared to bulk and gain-bandwidth products greater than 200 GHz. The nanopillar optical antenna avalanche detector (NOAAD) architecture is utilized for spatially separating the absorption region from the avalanche region via the NOA resulting in single carrier injection without the use of a traditional SAM heterostructure. PMID:26627932

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

    NASA Astrophysics Data System (ADS)

    Ghosh, Sid

    2015-08-01

    photodiodes and some of the recent results on the work being done at Raytheon on SWIR avalanche photodiodes.

  15. Linear Mode HgCdTe Avalanche Photodiodes for Photon Counting Applications

    NASA Technical Reports Server (NTRS)

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

    2015-01-01

    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.

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

    NASA Technical Reports Server (NTRS)

    Kenimer, R. L.

    1988-01-01

    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.

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

    NASA Technical Reports Server (NTRS)

    Eppeldauer, G.; Schaefer, A. R.

    1988-01-01

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

  18. A method to precisely identify the afterpulses when using the S9717 avalanche photodiode

    NASA Astrophysics Data System (ADS)

    Rusu, Alexandru; Rusu, Lucian

    2015-12-01

    The detection ratio of an avalanche photodiode (APD) biased in Geiger-mode increases versus the excess voltage; the afterpulsing rate increases too. The last one can be reduced by inserting an artificial dead time and accepting a lower measuring top rate. So, in order to tune a single-photon detector system, it is necessary to exactly identify afterpulses and measure their rate; the experimental results are presented. When using the S9717 APD in Geiger-mode, the cathode to ground voltage waveform reveals the existence of a particular sequence of pulses: a usual one followed, within 1μs, by a least one appearing to have been generated for negative excess voltage values. All these characteristics are the signature of the afterpulsing generation. Based on this observation, we were able to precisely measure the afterpulsing rate.

  19. A method to precisely identify the afterpulses when using the S9717 avalanche photodiode

    SciTech Connect

    Rusu, Alexandru Rusu, Lucian

    2015-12-07

    The detection ratio of an avalanche photodiode (APD) biased in Geiger-mode increases versus the excess voltage; the afterpulsing rate increases too. The last one can be reduced by inserting an artificial dead time and accepting a lower measuring top rate. So, in order to tune a single-photon detector system, it is necessary to exactly identify afterpulses and measure their rate; the experimental results are presented. When using the S9717 APD in Geiger-mode, the cathode to ground voltage waveform reveals the existence of a particular sequence of pulses: a usual one followed, within 1μs, by a least one appearing to have been generated for negative excess voltage values. All these characteristics are the signature of the afterpulsing generation. Based on this observation, we were able to precisely measure the afterpulsing rate.

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

    NASA Astrophysics Data System (ADS)

    Vilella, E.; Diéguez, A.

    2011-12-01

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

  1. Properties of avalanche photodiodes for applications in high energy physics, astrophysics and medical imaging

    NASA Astrophysics Data System (ADS)

    Renker, Dieter

    2002-06-01

    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 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&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.

  2. Ultra-low noise charge sensitive preamplifier for scintillation detection with avalanche photodiodes in PET applications

    SciTech Connect

    Schmitt, D.; Lecomte, R.; Lapointe, M.; Martel, G.; Carrier, C.; Karuta, B.; Duval, F.

    1987-02-01

    The need for compact, fast, low-noise front-end electronics in high resolution positron emission tomography (PET) has prompted this effort to design a preamplifier suitable for avalanche photodiode-based scintillation detectors. Due to the small signals from the detectors (< .03 rhoC/meV), a preamplifier with ultra-low noise performance in the 5 to 20 MHz range is essential to achieve the timing resolution required by the PET application. Out of many available technologies, a new third generation MOSFET was selected and implemented as input transistor in an original charge sensitive (CSP) design. Performance among the best reported to date are obtained. The new design was implemented as a dual-channel preamplifier in high density hybrid (thick film) technology.

  3. Hybridization process for back-illuminated silicon Geiger-mode avalanche photodiode arrays

    NASA Astrophysics Data System (ADS)

    Schuette, Daniel R.; Westhoff, Richard C.; Loomis, Andrew H.; Young, Douglas J.; Ciampi, Joseph S.; Aull, Brian F.; Reich, Robert K.

    2010-04-01

    We present a unique hybridization process that permits high-performance back-illuminated silicon Geiger-mode avalanche photodiodes (GM-APDs) to be bonded to custom CMOS readout integrated circuits (ROICs) - a hybridization approach that enables independent optimization of the GM-APD arrays and the ROICs. The process includes oxide bonding of silicon GM-APD arrays to a transparent support substrate followed by indium bump bonding of this layer to a signal-processing ROIC. This hybrid detector approach can be used to fabricate imagers with high-fill-factor pixels and enhanced quantum efficiency in the near infrared as well as large-pixel-count, small-pixel-pitch arrays with pixel-level signal processing. In addition, the oxide bonding is compatible with high-temperature processing steps that can be used to lower dark current and improve optical response in the ultraviolet.

  4. Numerical analysis of single photon detection avalanche photodiodes operated in the Geiger mode

    NASA Astrophysics Data System (ADS)

    Sugihara, K.; Yagyu, E.; Tokuda, Y.

    2006-06-01

    For a wide range of the thicknesses of the charge and the multiplication layers, detection efficiency and dark count probability are numerically investigated for GaInAs/InP single photon detection avalanche photodiodes (APD's) which are operated in the Geiger mode. Breakdown probability and dark currents are calculated to evaluate detection efficiency and dark count probability. The result shows that dark count probability can be significantly reduced by increasing the thickness of the charge layer, whereas detection efficiency is expected to decline steeply at some thickness of the charge layer. Moreover, increasing the thickness of the multiplication layer does not continue to reduce dark count probability, which increases when the multiplication layer is thicker than a critical thickness. Finally, we show a design guideline of single photon detection APD's with higher detection efficiency and lower dark count probability.

  5. Micropixel avalanche photodiodes and the possibility for their application in positron-emission tomography

    NASA Astrophysics Data System (ADS)

    Anfimov, N. V.; Selyunin, A. S.

    2012-12-01

    Micropixel avalanche photodiodes (MAPDs) are new instruments for detecting low-intensity light. They consist of many microcounters (pixels integrated on a common silicon wafer). A unique design by the Joint Institute for Nuclear Research (JINR) (Z. Sadygov)—deep-microwell MAPD—provides an order of larger pixel densities without losses in photon-detection efficiency. These instruments are beginning to find use in precision electromagnetic calorimetry. MAPDs can be most widely applied as photodetectors in scanners for positron-emission tomographs (PETs), particularly the time-of-flight PETs becoming popular now. The possibility of using MAPDs in PETs is shown, and the time resolution of a pair of quanta detected by Lutetium Fine Silicate scintillation crystals with MAPD readout is obtained at the level of 400 ps.

  6. Numerical Examination of Silicon Avalanche Photodiodes Operated in Charge Storage Mode

    NASA Technical Reports Server (NTRS)

    Parks, Joseph W., Jr.; Brennan, Kevin F.

    1998-01-01

    The behavior of silicon-based avalanche photodiodes (APD's) operated in the charge storage mode is examined. In the charge storage mode, the diodes are periodically biased to a sub-breakdown voltage and then open-circuited. During this integration period, photo-excited and thermally generated carriers are accumulated within the structure. The dynamics of this accumulation and its effects upon the avalanching of the diode warrants a detailed, fully numerical analysis. The salient features of this investigation include device sensitivity to the input photo-current including the self-quenching effect of the diode and its limitations in sensing low light levels, the dependence of the response on the bulk lifetime and hence on the generation current within the device, the initial gain, transient response, dependence of the device uniformity upon performance, and the quantity of storable charge within the device. To achieve these tasks our device simulator, STEBS-2D, was utilized. A modified current-controlled boundary condition is employed which allows for the simulation of the isolated diode after the initial reset bias has been applied. With this boundary condition, it is possible to establish a steady-state voltage on the ohmic contact and then effectively remove the device from the external circuit while still including effects from surface recombination, trapped surface charge, and leakage current from the read-out electronics.

  7. Hybrid AlGaN-SiC Avalanche Photodiode for Deep-UV Photon Detection

    NASA Technical Reports Server (NTRS)

    Aslam, Shahid; Herrero, Federico A.; Sigwarth, John; Goldsman, Neil; Akturk, Akin

    2010-01-01

    The proposed device is capable of counting ultraviolet (UV) photons, is compatible for inclusion into space instruments, and has applications as deep- UV detectors for calibration systems, curing systems, and crack detection. The device is based on a Separate Absorption and Charge Multiplication (SACM) structure. It is based on aluminum gallium nitride (AlGaN) absorber on a silicon carbide APD (avalanche photodiode). The AlGaN layer absorbs incident UV photons and injects photogenerated carriers into an underlying SiC APD that is operated in Geiger mode and provides current multiplication via avalanche breakdown. The solid-state detector is capable of sensing 100-to-365-nanometer wavelength radiation at a flux level as low as 6 photons/pixel/s. Advantages include, visible-light blindness, operation in harsh environments (e.g., high temperatures), deep-UV detection response, high gain, and Geiger mode operation at low voltage. Furthermore, the device can also be designed in array formats, e.g., linear arrays or 2D arrays (micropixels inside a superpixel).

  8. A new method to improve multiplication factor in micro-pixel avalanche photodiodes with high pixel density

    NASA Astrophysics Data System (ADS)

    Sadygov, Z.; Ahmadov, F.; Khorev, S.; Sadigov, A.; Suleymanov, S.; Madatov, R.; Mehdiyeva, R.; Zerrouk, F.

    2016-07-01

    Presented is a new model describing development of the avalanche process in time, taking into account the dynamics of electric field within the depleted region of the diode and the effect of parasitic capacitance shunting individual quenching micro-resistors on device parameters. Simulations show that the effective capacitance of a single pixel, which defines the multiplication factor, is the sum of the pixel capacitance and a parasitic capacitance shunting its quenching micro-resistor. Conclusions obtained as a result of modeling open possibilities of improving the pixel gain in micropixel avalanche photodiodes with high pixel density (or low pixel capacitance).

  9. Development of novel technologies to enhance performance and reliability of III-Nitride avalanche photodiodes

    NASA Astrophysics Data System (ADS)

    Suvarna, Puneet Harischandra

    Solar-blind ultraviolet avalanche photodiodes are an enabling technology for applications in the fields of astronomy, communication, missile warning systems, biological agent detection and particle physics research. Avalanche photodiodes (APDs) are capable of detecting low-intensity light with high quantum efficiency and signal-to-noise ratio without the need for external amplification. The properties of III-N materials (GaN and AlGaN) are promising for UV photodetectors that are highly efficient, radiation-hard and capable of visible-blind or solar-blind operation without the need for external filters. However, the realization of reliable and high performance III-N APDs and imaging arrays has several technological challenges. The high price and lack of availability of bulk III-N substrates necessitates the growth of III-Ns on lattice mismatched substrates leading to a high density of dislocations in the material that can cause high leakage currents, noise and premature breakdown in APDs. The etched sidewalls of III-N APDs and high electric fields at contact edges are also detrimental to APD performance and reliability. In this work, novel technologies have been developed and implemented that address the issues of performance and reliability in III-Nitride based APDs. To address the issue of extended defects in the bulk of the material, a novel pulsed MOCVD process was developed for the growth of AlGaN. This process enables growth of high crystal quality AlxGa1-xN with excellent control over composition, doping and thickness. The process has also been adapted for the growth of high quality III-N materials on silicon substrate for devices such as high electron mobility transistors (HEMTs). A novel post-growth defect isolation technique is also discussed that can isolate the impact of conductive defects from devices. A new sidewall passivation technique using atomic layer deposition (ALD) of dielectric materials was developed for III-N APDs that is effective in

  10. Studies of Avalanche Photodiodes (APDS) as Readout Devices for Scintillating Fibers for High Energy Gamma-Ray Astronomy Telescopes

    NASA Technical Reports Server (NTRS)

    Vasile, Stefan; Shera, Suzanne; Shamo, Denis

    1998-01-01

    New gamma ray and charged particle telescope designs based on scintillating fiber arrays could provide low cost, high resolution, lightweight, very large area and multi radiation length instrumentation for planned NASA space exploration. The scintillating fibers low visible light output requires readout sensors with single photon detection sensitivity and low noise. The sensitivity of silicon Avalanche Photodiodes (APDS) matches well the spectral output of the scintillating fibers. Moreover, APDs have demonstrated single photon capability. The global aim of our work is to make available to NASA a novel optical detector concept to be used as scintillating fiber readouts and meeting the requirements of the new generations of space-borne gamma ray telescopes. We proposed to evaluate the feasibility of using RMD's small area APDs ((mu)APD) as scintillating fiber readouts and to study possible alternative (mu)APD array configurations for space borne readout scintillating fiber systems, requiring several hundred thousand to one million channels. The evaluation has been conducted in accordance with the task description and technical specifications detailed in the NASA solicitation "Studies of Avalanche Photodiodes (APD as readout devices for scintillating fibers for High Energy Gamma-Ray Astronomy Telescopes" (#8-W-7-ES-13672NAIS) posted on October 23, 1997. The feasibility study we propose builds on recent developments of silicon APD arrays and light concentrators advances at RMD, Inc. and on more than 5 years of expertise in scintillating fiber detectors. In a previous program we carried out the initial research to develop a high resolution, small pixel, solid-state, silicon APD array which exhibited very high sensitivity in the UV-VIS spectrum. This (mu)APD array is operated in Geiger mode and results in high gain (greater than 10(exp 8)), extremely low noise, single photon detection capability, low quiescent power (less than 10 (mu)W/pixel for 30 micrometers sensitive

  11. A new type of thermal-neutron detector based on ZnS(Ag)/LiF scintillator and avalanche photodiodes

    NASA Astrophysics Data System (ADS)

    Marin, V. N.; Sadykov, R. A.; Trunov, D. N.; Litvin, V. S.; Aksenov, S. N.; Stolyarov, A. A.

    2015-09-01

    A high-efficiency thermal-neutron detector based on ZnS(Ag)/LiF scintillator is described, which employs a new technique of signal pick-up with the aid of a light guide and avalanche photodiodes instead of optical fibers and photomultipliers. Results of tests on the RADEX pulsed neutron source are presented, in which neutron diffraction patterns of test objects have been obtained.

  12. HgCdTe MWIR Back-Illuminated Electron-Initiated Avalanche Photodiode Arrays

    NASA Astrophysics Data System (ADS)

    Reine, M. B.; Marciniec, J. W.; Wong, K. K.; Parodos, T.; Mullarkey, J. D.; Lamarre, P. A.; Tobin, S. P.; Gustavsen, K. A.; Williams, G. M.

    2007-08-01

    This paper reports data for back-illuminated planar n-on-p HgCdTe electron-initiated avalanche photodiode (e-APD) 4 × 4 arrays with large unit cells (250 × 250 μm2). The arrays were fabricated from p-type HgCdTe films grown by liquid phase epitaxy (LPE) on CdZnTe substrates. The arrays were bump-mounted to fanout boards and characterized in the back-illuminated mode. Gain increased exponentially with reverse bias voltage, and the gain versus bias curves were quite uniform from element to element. The maximum gain measured was 648 at -11.7 V for a cutoff wavelength of 4.06 μm at 160 K. For the same reverse-bias voltage, the gains measured at 160 K for elements with two different cutoff wavelengths (3.54 μm and 4.06 μm at 160 K) show an exponential increase with increasing cutoff wavelength, in agreement with Beck’s empirical model for gain versus voltage and cutoff wavelength in HgCdTe e-APDs. Spot scan data show that both the V = 0 response and the gain at V = -5.0 V are spatially uniform over the large junction area. To the best of our knowledge, these are the first spot scan data for avalanche gain ever reported for HgCdTe e-APDs. Capacitance versus voltage data are consistent with an ideal abrupt junction having a donor concentration equal to the indium concentration in the LPE film.

  13. Slot clock recovery in optical PPM communication systems with avalanche photodiode photodetectors

    NASA Technical Reports Server (NTRS)

    Davidson, Frederic M.; Sun, Xiaoli

    1989-01-01

    Slot timing recovery in a direct-detection optical PPM communication system can be achieved by processing the photodetector output waveform with a nonlinear device whose output forms the input to a phase-locked loop. The choice of a simple transition detector as the nonlinearity is shown to give satisfactory synchronization performance. The rms phase error of the recovered slot clock and the effect of slot timing jitter on the bit error probability were directly measured. The experimental system consisted of an AlGaAs laser diode (wavelength = 834 nm) and a silicon avalanche photodiode photodetector. The system used Q = 4 PPM signaling and operated at a source data rate of 25 Mbits/s. The mathematical model developed to compute the rms phase error of the recovered clock is shown to be in good agreement with results of actual measurements of phase errors. The use of the recovered slot clock in the receiver resulted in no significant degradation in receiver sensitivity compared to a system with perfect slot timing. The system achieved a bit error probability of 10 to the -6th at a received optical signal energy of 55 detected photons per information bit.

  14. Update on Linear Mode Photon Counting with the HgCdTe Linear Mode Avalanche Photodiode

    NASA Technical Reports Server (NTRS)

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

    2014-01-01

    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.

  15. Multihit mode direct-detection laser radar system using a Geiger-mode avalanche photodiode.

    PubMed

    Oh, Min Seok; Kong, Hong Jin; Kim, Tae Hoon; Hong, Keun Ho; Kim, Byung Wook; Park, Dong Jo

    2010-03-01

    In this paper, a direct-detection laser radar system that uses a Geiger-mode avalanche photodiode (GAPD) of relatively short dead time (45 ns) is described. A passively Q-switched microchip laser is used as a laser source and a compact peripheral component interconnect system, which includes a time-to-digital converter (TDC), is set up for fast signal processing. With both the GAPD and the TDC functioning multistop acquisition, the system operates in a multihit mode. The software for the three-dimensional visualization and an algorithm for the removal of noise are developed. It is shown that the single-shot precision of the system is approximately 10 cm (sigma) and the precision is improved by increasing the number of laser pulses to be averaged so that the precision of approximately 1 cm (sigma) was acquired with more than 150 laser pulses scattered from the target. The accuracy of the system is measured to be 12 cm when the energy of the emitted laser pulse varies with a factor of 7. PMID:20370163

  16. A comparison of avalanche photodiode and photomultiplier tube detectors for flow cytometry

    NASA Astrophysics Data System (ADS)

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

    2008-02-01

    Commercial flow cytometers use photomultiplier tubes (PMTs) for fluorescence detection. These detectors have high linear gain and broad dynamic range, but have limited sensitivity in the red and near infrared spectral regions. We present a comparison of avalanche photodiodes (APDs) and PMTs as detectors in flow cytometry instruments, and demonstrate improved sensitivity and resolution in the red and near infrared spectral regions using the APD. The relative performance of the PMT and APD were evaluated by simultaneously measuring the mean fluorescence intensity and coefficient of variation for emission from light emitting diode pulses, flow cytometry test beads, and fluorescently labeled cells. The relative signal to noise performance of the APD and PMT was evaluated over the 500 nm to 1050 nm wavelength range using pulsed light emitting diode light sources. While APDs have higher quantum efficiency but lower internal gain than PMTs, with appropriate external amplification the APD has signal to noise response that is comparable to PMTs in the 500 nm to 650 nm range and improved response in the 650 nm to 850 nm range The data demonstrates that the APD had performance comparable to the PMT in the spectral region between 500 to 650 nm and improved performance in the range of 650 to 1000 nm, where the PMT performance is quite poor. CD4 positive lymphocyte populations were easily identified in normal human blood both by APD and PMT using phycoerythrin labeled antibodies. In contrast, only the APD detector could resolve CD4 positive populations using 800 nm Quantum dot labeled antibodies.

  17. Impact ionization in AlxGa1-xAsySb1-y avalanche photodiodes

    NASA Astrophysics Data System (ADS)

    Grzesik, M.; Donnelly, J.; Duerr, E.; Manfra, M.; Diagne, M.; Bailey, R.; Turner, G.; Goodhue, W.

    2014-04-01

    Avalanche photodiodes (APDs) have been fabricated in order to determine the impact ionization coefficients of electrons (α) and holes (β) in AlxGa1-xAsySb1-y lattice matched to GaSb for three alloy compositions: (x = 0.40, y = 0.035), (x = 0.55, y = 0.045), and (x = 0. 65, y = 0.054). The impact ionization coefficients were calculated from photomultiplication measurements made on specially designed APDs, which allowed for both pure electron and pure hole injection in the same device. Photo-multiplication measurements were made at temperatures ranging from 77 K to 300 K for all three alloys. A quasi-physical model with an explicit temperature dependence was used to express the impact ionization coefficients as a function of electric-field strength and temperature. For all three alloys, it was found that α < β at any given temperature. In addition, the values of the impact ionization coefficients were found to decrease as the aluminum concentration of the AlGaAsSb alloy was increased. A value between 1.2 and 4.0 was found for β/α, which is dependent on temperature, alloy composition, and electric-field strength.

  18. Response of large area avalanche photodiodes to low energy x rays

    SciTech Connect

    Gentile, T. R.; Bales, M.; Arp, U.; Dong, B.; Farrell, R.

    2012-05-15

    For an experiment to study neutron radiative beta-decay, we operated large area avalanche photodiodes (APDs) near liquid nitrogen temperature to detect x rays with energies between 0.2 keV and 20 keV. Whereas there are numerous reports of x ray spectrometry using APDs at energies above 1 keV, operation near liquid nitrogen temperature allowed us to reach a nominal threshold of 0.1 keV. However, due to the short penetration depth of x rays below 1 keV, the pulse height spectrum of the APD become complex. We studied the response using monochromatic x ray beams and employed phenomenological fits of the pulse height spectrum to model the measurement of a continuum spectrum from a synchrotron. In addition, the measured pulse height spectrum was modelled using a profile for the variation in efficiency of collection of photoelectrons with depth into the APD. The best results are obtained with the collection efficiency model.

  19. High-speed bridge circuit for InGaAs avalanche photodiode single-photon detector

    NASA Astrophysics Data System (ADS)

    Hashimoto, Hirofumi; Tomita, Akihisa; Okamoto, Atsushi

    2014-02-01

    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.

  20. Fast single photon avalanche photodiode-based time-resolved diffuse optical tomography scanner

    PubMed Central

    Mu, Ying; Niedre, Mark

    2015-01-01

    Resolution in diffuse optical tomography (DOT) is a persistent problem and is primarily limited by high degree of light scatter in biological tissue. We showed previously that the reduction in photon scatter between a source and detector pair at early time points following a laser pulse in time-resolved DOT is highly dependent on the temporal response of the instrument. To this end, we developed a new single-photon avalanche photodiode (SPAD) based time-resolved DOT scanner. This instrument uses an array of fast SPADs, a femto-second Titanium Sapphire laser and single photon counting electronics. In combination, the overall instrument temporal impulse response function width was 59 ps. In this paper, we report the design of this instrument and validate its operation in symmetrical and irregularly shaped optical phantoms of approximately small animal size. We were able to accurately reconstruct the size and position of up to 4 absorbing inclusions, with increasing image quality at earlier time windows. We attribute these results primarily to the rapid response time of our instrument. These data illustrate the potential utility of fast SPAD detectors in time-resolved DOT. PMID:26417526

  1. Progress in the use of avalanche photodiodes for readout for calorimeters

    SciTech Connect

    Fenker, H.; Morgan, K.; Regan, T.

    1991-09-01

    During the past year the Superconducting Super Collider Tracking Group has progressed from acquisition of its first avalanche photodiode (APD) to installation of a 96-channel array of the devices. The work was motivated by the desire to learn how to use APDs as the sensitive elements in a fiber tracking detector, moderated by the presence of limited resources and the absence of activity within groups outside the SSC Laboratory on such a project. We chose, therefore, to team up with an ongoing research effort which intended to evaluate both pre-shower and shower-maximum detectors and various means of sensing the light produced. The pre-shower detector is made of layers of scintillating fibers similar to a fiber tracker. The shower-maximum detector uses optical fibers to transmit the light from scintillating plates to the readout devices. Our contribution has been to develop the APD array for use in this test from concept to operation. Currently, the equipment is installed in Fermilab's MP beamline awaiting delivery to the final 36 APDs and exposure to the beam. 9 refs., 18 figs.

  2. Radiation detection measurements with a new ``Buried Junction'' silicon avalanche photodiode

    NASA Astrophysics Data System (ADS)

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

    1999-02-01

    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 energy and timing resolution of this device with several scintillators (BGO, LSO and GSO) of potential interest in high-energy physics and PET imaging systems are presented.

  3. All AlGaN epitaxial structure solar-blind avalanche photodiodes with high efficiency and high gain

    NASA Astrophysics Data System (ADS)

    Wu, Hualong; Wu, Weicong; Zhang, Hongxian; Chen, Yingda; Wu, Zhisheng; Wang, Gang; Jiang, Hao

    2016-05-01

    Solar-blind avalanche photodiodes were fabricated with an all AlGaN-based epitaxial structure on sapphire by metal–organic chemical vapor deposition. The devices demonstrate a maximum responsivity of 114.1 mA/W at 278 nm and zero bias, corresponding to an external quantum efficiency (EQE) of 52.7%. The EQE improves to 64.8% under a bias of ‑10 V. Avalanche gain higher than 2 × 104 was obtained at a bias of ‑140 V. The high performance is attributed to the all AlGaN-based p–i–n structure comprised of undoped and Si-doped n-type Al0.4Ga0.6N on a high quality AlN layer and highly conductive p-type AlGaN grown with In-surfactant-assisted Mg-delta doping.

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

    SciTech Connect

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

    2014-06-16

    In this study, we demonstrate the avalanche multiplication phenomenon in a crystalline-selenium (c-Se)-based heterojunction photodiode. The carrier injection from an external electrode, which is considered to be the major factor contributing to dark current at a high electric field, was significantly decreased by employing a thin n-type Ga{sub 2}O{sub 3} layer with a high hole-injection barrier. The fabricated Ga{sub 2}O{sub 3}/c-Se diode exhibited extremely high external quantum efficiency of over 100% in the short-wavelength region at a relatively low reverse-bias voltage of ∼20 V. Furthermore, Sn-doping of the Ga{sub 2}O{sub 3} layer increases the carrier concentration; hence, the resulting device has a lower threshold voltage for avalanche multiplication.

  5. Linear arrays of InGaAs/InP avalanche photodiodes for 1.0-1.7 micron

    NASA Technical Reports Server (NTRS)

    Ackley, D. E.; Hladky, J.; Lange, M. J.; Mason, S.; Erickson, G.; Olsen, G. H.; Ban, V. S.; Forrest, S. R.; Staller, C.

    1990-01-01

    Separate absorption and multiplication InGaAs/InP avalanche photodiodes (SAM-APDs) with a floating guard ring structure that is well-suited to array applications have been successfully demonstrated. Individual APDs have breakdown voltages greater than 80 V, multiplications over 40 at 100 nA dark current, and uniform spatial gain profiles. Uniform I-V characteristics and gains have been measured over linear dimensions as large as 1.2 cm. Gains over 10 at low multiplied dark currents were measured on 21 consecutive devices at the wafer level.

  6. Effects of Displacement Damage on the Time-Resolved Gain and Bandwidth of a Low Breakdown Voltage Si Avalanche Photodiode

    NASA Technical Reports Server (NTRS)

    Laird, Jamie S.; Onoda, Shinobu; Hirao, Toshio; Becker, Heidi; Johnston, Allan; Laird, Jamie S.; Itoh, Hisayoshi

    2006-01-01

    Effects of displacement damage and ionization damage induced by gamma irradiation on the dark current and impulse response of a high-bandwidth low breakdown voltage Si Avalanche Photodiode has been investigated using picosecond laser microscopy. At doses as high as 10Mrad (Si) minimal alteration in the impulse response and bandwidth were observed. However, dark current measurements also performed with and without biased irradiation exhibit anomalously large damage factors for applied biases close to breakdown. The absence of any degradation in the impulse response is discussed as are possible mechanisms for higher dark current damage factors observed for biased irradiation.

  7. Characterization of the Hamamatsu S8664 avalanche photodiode for X-ray and VUV-light detection

    NASA Astrophysics Data System (ADS)

    Lux, T.; Freitas, E. D. C.; Amaro, F. D.; Ballester, O.; Jover-Manas, G. V.; Martín, C.; Monteiro, C. M. B.; Sánchez, F.; Rico, J.

    2012-09-01

    We present the first operation of the VUV-sensitive avalanche photodiode (APD) from Hamamatsu to xenon scintillation light and to direct X-rays of 22.1 keV and 5.9 keV. A large non-linear response was observed for the direct X-ray detection. At 415 V APD bias voltage it was of about 30% for 22.1 keV and about 45% for 5.9 keV. The quantum efficiency for 172 nm photons has been measured to be 69±15%.

  8. Evaluation of a fast single-photon avalanche photodiode for measurement of early transmitted photons through diffusive media.

    PubMed

    Mu, Ying; Valim, Niksa; Niedre, Mark

    2013-06-15

    We tested the performance of a fast single-photon avalanche photodiode (SPAD) in measurement of early transmitted photons through diffusive media. In combination with a femtosecond titanium:sapphire laser, the overall instrument temporal response time was 59 ps. Using two experimental models, we showed that the SPAD allowed measurement of photon-density sensitivity functions that were approximately 65% narrower than the ungated continuous wave case at very early times. This exceeds the performance that we have previously achieved with photomultiplier-tube-based systems and approaches the theoretical maximum predicted by time-resolved Monte Carlo simulations. PMID:23938989

  9. Betabox: a beta particle imaging system based on a position sensitive avalanche photodiode

    NASA Astrophysics Data System (ADS)

    Dooraghi, A. A.; Vu, N. T.; Silverman, R. W.; Farrell, R.; Shah, K. S.; Wang, J.; Heath, J. R.; Chatziioannou, A. F.

    2013-06-01

    A beta camera has been developed that allows planar imaging of the spatial and temporal distribution of beta particles using a 14 × 14 mm2 position sensitive avalanche photodiode (PSAPD). This camera system, which we call Betabox, can be directly coupled to microfluidic chips designed for cell incubation or other biological applications. Betabox allows for imaging the cellular uptake of molecular imaging probes labeled with charged particle emitters such as 18F inside these chips. In this work, we investigate the quantitative imaging capabilities of Betabox for 18F beta particles, in terms of background rate, efficiency, spatial resolution, and count rate. Measurements of background and spatial resolution are considered both at room temperature (21 °C ± 1 °C) and at an elevated operating temperature (37 °C ± 1 °C), as is often required for biological assays. The background rate measured with a 4 keV energy cutoff is below 2 cph mm-2 at both 21 and 37 °C. The absolute efficiency of Betabox for the detection of 18F positron sources in contact with a PSAPD with the surface passivated from ambient light and damage is 46% ± 1%. The lower detection limit is estimated using the Rose Criterion to be 0.2 cps mm-2 for 1 min acquisitions and a 62 × 62 µm2 pixel size. The upper detection limit is approximately 21 000 cps. The spatial resolution at both 21 and 37 °C ranges from 0.4 mm FWHM at the center of the field of view (FOV), and degrades to 1 mm at a distance of 5 mm away from center yielding a useful FOV of approximately 10 × 10 mm2. We also investigate the effects on spatial resolution and sensitivity that result from the use of a polymer based microfluidic chip. For these studies we place varying layers of low-density polyethylene (LDPE) between the detector and the source and find that the spatial resolution degrades by ˜180 µm for every 100 µm of LDPE film. Sensitivity is reduced by half with the inclusion of ˜200 µm of additional LDPE film. Lastly

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

    NASA Astrophysics Data System (ADS)

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

    2004-09-01

    Avalanche photodiodes (APDs) have proven to be useful as light detectors for high resolution positron emission tomography (PET). Their compactness makes these devices excellent candidates for replacing bulky photomultiplier tubes (PMTs) in PET systems where space limitations are an issue. The readout of densely packed, 10 × 10 lutetium oxyorthosilicate (LSO) block detectors (crystal size 2.0 × 2.0 × 12 mm3) with custom-built monolithic 3 × 3 APD arrays was investigated. The APDs had a 5 × 5 mm2 active surface and were arranged on a 6.25 mm pitch. The dead space on the edges of the array was 1.25 mm. The APDs were operated at a bias voltage of approximately 380 V for a gain of 100 and a dark current of 10 nA per APD. The standard deviation in gain between the APDs in the array ranged from 1.8 to 6.5% as the gain was varied from 50 to 108. A fast, low-noise, multi-channel charge sensitive preamplifier application-specific integrated circuit (ASIC) was developed for the APD readout. The amplifier had a rise time of 8 ns, a noise floor of 515 e- rms and a 9 e- pF-1 noise slope. An acquired flood image showed that all 100 crystals from the block detector could be resolved. Timing measurements with single-channel LSO-APD detectors, as well as with the array, against a plastic scintillator and PMT assembly showed a time resolution of 1.2 ns and 2.5 ns, respectively. The energy resolution measured with a single 4.0 × 4.0 × 10 mm3 LSO crystal, wrapped in four-layer polytetrafluoroethylene (PTFE) tape and coupled with optical grease on a single APD of the array, yielded 15% (full width at half maximum, FWHM) at 511 keV. Stability tests over 9 months of operation showed that the APD arrays do not degrade appreciably. These results demonstrate the ability to decode densely packed LSO scintillation blocks with compact APD arrays. The good timing and energy resolution makes these detectors suitable for high resolution PET.

  11. Betabox: a beta particle imaging system based on a position sensitive avalanche photodiode

    PubMed Central

    Dooraghi, AA; Vu, NT; Silverman, RW; Farrell, R; Shah, KS; Wang, J; Heath, JR; Chatziioannou, AF

    2013-01-01

    A beta camera has been developed that allows planar imaging of the spatial and temporal distribution of beta particles using a 14 × 14 mm2 position sensitive avalanche photodiode (PSAPD). This camera system, which we call Betabox, can be directly coupled to microfluidic chips designed for cell incubation or other biological applications. Betabox allows for imaging the cellular uptake of molecular imaging probes labeled with charged particle emitters such as 18F inside these chips. In this work, we investigate the quantitative imaging capabilities of Betabox for 18F beta particles, in terms of background rate, efficiency, spatial resolution, and count rate. Measurements of background and spatial resolution are considered both at room temperature (21 °C ± 1 °C) and at an elevated operating temperature (37 °C ± 1 °C), as is often required for biological assays. The background rate measured with a 4 keV energy cutoff is below 2 cph mm−2 at both 21 and 37 °C. The absolute efficiency of Betabox for the detection of 18F positron sources in contact with a PSAPD with the surface passivated from ambient light and damage is 46% ± 1%. The lower detection limit is estimated using the Rose Criterion to be 0.2 cps mm−2 for 1 min acquisitions and a 62 × 62 µm2 pixel size. The upper detection limit is approximately 21 000 cps. The spatial resolution at both 21 and 37 °C ranges from 0.4 mm FWHM at the center of the field of view (FOV), and degrades to 1 mm at a distance of 5 mm away from center yielding a useful FOV of approximately 10 × 10 mm2. We also investigate the effects on spatial resolution and sensitivity that result from the use of a polymer based microfluidic chip. For these studies we place varying layers of low-density polyethylene (LDPE) between the detector and the source and find that the spatial resolution degrades by ~180 µm for every 100 µm of LDPE film. Sensitivity is reduced by half with the inclusion of ~200 µm of additional LDPE film

  12. Conception d'un circuit d'etouffement pour photodiodes a avalanche en mode geiger pour integration heterogene 3d

    NASA Astrophysics Data System (ADS)

    Boisvert, Alexandre

    Le Groupe de Recherche en Appareillage Medical de Sherbrooke (GRAMS) travaille actuellement sur un programme de recherche portant sur des photodiodes a avalanche mono-photoniques (PAMP) operees en mode Geiger en vue d'une application a la tomographie d'emission par positrons (TEP). Pour operer dans ce mode; la PAMP, ou SPAD selon l'acronyme anglais (Single Photon Avalanche Diode), requiert un circuit d'etouffement (CE) pour, d'une part, arreter l'avalanche pouvant causer sa destruction et, d'autre part. la reinitialiser en mode d'attente d'un nouveau photon. Le role de ce CE comprend egalement une electronique de communication vers les etages de traitement avance de signaux. La performance temporelle optimale du CE est realisee lorsqu'il est juxtapose a la PAMP. Cependant, cela entraine une reduction de la surface photosensible ; un element crucial en imagerie. L'integration 3D, a base d'interconnexions verticales, offre une solution elegante et performante a cette problematique par l'empilement de circuits integres possedant differentes fonctions (PAMP, CE et traitement avance de signaux). Dans l'approche proposee, des circuits d'etouffement de 50 pm x 50 pm realises sur une technologie CMOS 130 mn 3D Tezzaron, contenant chacun 112 transistors, sont matrices afin de correspondre a une matrice de PAMP localisee sur une couche electronique superieure. Chaque circuit d'etouffement possede une gigue temporelle de 7,47 ps RMS selon des simulations faites avec le logiciel Cadence. Le CE a la flexibilite d'ajuster les temps d'etouffement et de recharge pour la PAMP tout en presentant une faible consommation de puissance (~ 0,33 mW a 33 Mcps). La conception du PAMP necessite de supporter des tensions superieures aux 3,3 V de la technologie. Pour repondre a ce probleme, des transistors a drain etendu (DEMOS) ont ete realises. En raison de retards de production par Ies fabricants, les circuits n'ont pu etre testes physiquement par des mesures. Les resultats de ce memoire

  13. Epitaxial growth of HgCdTe 1.55-um avalanche photodiodes by molecular beam epitaxy

    NASA Astrophysics Data System (ADS)

    de Lyon, Terence J.; Baumgratz, B.; Chapman, G. R.; Gordon, E.; Hunter, Andrew T.; Jack, Michael D.; Jensen, John E.; Johnson, W.; Johs, Blaine D.; Kosai, K.; Larsen, W.; Olson, G. L.; Sen, M.; Walker, B.

    1999-04-01

    Separate absorption and multiplication avalanche photodiode (SAM-APD) device structures, operating in the 1.1 - 1.6 micrometer spectral range, have been fabricated in the HgCdTe material system by molecular-beam epitaxy. These HgCdTe device structures, which offer an alternative technology to existing III-V APD detectors, were grown on CdZnTe(211)B substrates using CdTe, Te, and Hg sources with in situ In and As doping. The alloy composition of the HgCdTe layers was adjusted to achieve both efficient absorption of IR radiation in the 1.1 - 1.6 micrometer spectral range and low excess-noise avalanche multiplication. To achieve resonant enhancement of hole impact ionization from the split-off valence band, the Hg(subscript 1-x)Cd(subscript x)Te alloy composition in the gain region of the device, x equals 0.73, was chosen to achieve equality between the bandgap energy and spin-orbit splitting. The appropriate value of this alloy composition was determined from analysis of the 300 K bandgap and spin-orbit splitting energies of a set of calibration layers, using a combination of IR transmission and spectroscopic ellipsometry measurements. MBE-grown APD epitaxial wafers were processed into passivated mesa-type discrete device structures and diode mini-arrays using conventional HgCdTe process technology. Device spectral response, dark current density, and avalanche gain measurements were performed on discrete diodes and diode mini- arrays on the processed wafers. Avalanche gains in the range of 30 - 40 at reverse bias of 85 - 90 V and array-median dark current density below 2 X 10(superscript -4) A/cm(superscript 2) at 40 V reverse bias have been demonstrated.

  14. Analysis and modeling of optical crosstalk in InP-based Geiger-mode avalanche photodiode FPAs

    NASA Astrophysics Data System (ADS)

    Chau, Quan; Jiang, Xudong; Itzler, Mark A.; Entwistle, Mark; Piccione, Brian; Owens, Mark; Slomkowski, Krystyna

    2015-05-01

    Optical crosstalk is a major factor limiting the performance of Geiger-mode avalanche photodiode (GmAPD) focal plane arrays (FPAs). This is especially true for arrays with increased pixel density and broader spectral operation. We have performed extensive experimental and theoretical investigations on the crosstalk effects in InP-based GmAPD FPAs for both 1.06-μm and 1.55-μm applications. Mechanisms responsible for intrinsic dark counts are Poisson processes, and their inter-arrival time distribution is an exponential function. In FPAs, intrinsic dark counts and cross talk events coexist, and the inter-arrival time distribution deviates from purely exponential behavior. From both experimental data and computer simulations, we show the dependence of this deviation on the crosstalk probability. The spatial characteristics of crosstalk are also demonstrated. From the temporal and spatial distribution of crosstalk, an efficient algorithm to identify and quantify crosstalk is introduced.

  15. Performance of Ce-doped (La, Gd)2Si2O7 scintillator with an avalanche photodiode

    NASA Astrophysics Data System (ADS)

    Kurosawa, Shunsuke; Shishido, Toetsu; Suzuki, Akira; Pejchal, Jan; Yokota, Yuui; Yoshikawa, Akira

    2014-04-01

    Scintillation properties of Ce-doped (La, Gd)2Si2O7 (Ce:La-GPS) crystal were measured with Si avalanche photodiode (APD, Hamamatsu S8664-55). Since Ce:La-GPS is a novel scintillator, its scintillation properties have been evaluated using the APD for the first time. This crystal grown by floating zone method had a good light output of 41,000±1000 photons/MeV and FWHM energy resolution at 662 keV was 4.4±0.1% at 23.0±0.2 °C. The photon non-proportional response (PNR) of Ce:La-GPS was approximately 65% at 32 keV, where light output at 662 keV was normalized to 100%. Moreover, the temperature dependence of the light outputs was determined to be approximately 0.15%/°C from -10 to 30 °C.

  16. Design of resonant cavity structure for efficient high-temperature operation of single-photon avalanche photodiodes.

    PubMed

    Zavvari, Mahdi; Abedi, Kambiz; Karimi, Mohammad

    2014-05-20

    A novel design of a single-photon avalanche photodiode (SPAD) is proposed based on resonant cavity (RC) structure, and its performance is studied. In the proposed structure, InAlAs/InGaAs distributed Bragg reflectors (DBRs) are employed as top and bottom mirrors and the quantum efficiency (QE) of the absorption region is calculated considering the effect of the RC. Results show that using 12 periods of DBRs as a bottom reflector without incorporation of a top mirror can enhance the QE to about 90% at room temperature. For this RC-enhanced SPAD, a single-photon quantum efficiency (SPQE) is obtained of about 0.35 at T=300  K. For temperatures lower than T=260  K, SPQE is about 1. Results show that although the RC doesn't affect the dark current, for a given SPQE the dark count rate is lower for the RC-SPAD. PMID:24922220

  17. CMOS integrated avalanche photodiodes and frequency-mixing optical sensor front end for portable NIR spectroscopy instruments.

    PubMed

    Yun, Ruida; Sthalekar, Chirag; Joyner, Valencia M

    2011-01-01

    This paper presents the design and measurement results of two avalanche photodiode structures (APDs) and a novel frequency-mixing transimpedance amplifier (TIA), which are key building blocks towards a monolithically integrated optical sensor front end for near-infrared (NIR) spectroscopy applications. Two different APD structures are fabricated in an unmodified 0.18 \\im CMOS process, one with a shallow trench isolation (STI) guard ring and the other with a P-well guard ring. The APDs are characterized in linear mode. The STI bounded APD demonstrates better performance and exhibits 3.78 A/W responsivity at a wavelength of 690 nm and bias voltage of 10.55 V. The frequency-mixing TIA (FM-TIA) employs a T-feedback network incorporating gate-controlled transistors for resistance modulation, enabling the simultaneous down-conversion and amplification of the high frequency modulated photodiode (PD) current. The TIA achieves 92 dS Ω conversion gain with 0.5 V modulating voltage. The measured IIP(3) is 10.6/M. The amplifier together with the 50 Ω output buffer draws 23 mA from a1.8 V power supply. PMID:22254238

  18. Geiger-mode operation of ultraviolet avalanche photodiodes grown on sapphire and free-standing GaN substrates

    NASA Astrophysics Data System (ADS)

    Cicek, E.; Vashaei, Z.; McClintock, R.; Bayram, C.; Razeghi, M.

    2010-06-01

    GaN avalanche photodiodes (APDs) were grown on both conventional sapphire and low dislocation density free-standing (FS) c-plane GaN substrates. Leakage current, gain, and single photon detection efficiency (SPDE) of these APDs were compared. At a reverse-bias of 70 V, APDs grown on sapphire substrates exhibited a dark current density of 2.7×10-4 A/cm2 whereas APDs grown on FS-GaN substrates had a significantly lower dark current density of 2.1×10-6 A/cm2. Under linear-mode operation, APDs grown on FS-GaN achieved avalanche gain as high as 14 000. Geiger-mode operation conditions were studied for enhanced SPDE. Under front-illumination the 625-μm2-area APD yielded a SPDE of ˜13% when grown on sapphire substrates compared to more than 24% when grown on FS-GaN. The SPDE of the same APD on sapphire substrate increased to ˜30% under back-illumination—the FS-GaN APDs were only tested under front illumination due to the thick absorbing GaN substrate.

  19. Model of turn-on characteristics of InP-based Geiger-mode avalanche photodiodes suitable for circuit simulations

    NASA Astrophysics Data System (ADS)

    Jordy, George; Donnelly, Joseph

    2015-05-01

    A model for the turn-on characteristics of separate-absorber-multiplier InP-based Geiger-mode Avalanche Photodiodes (APDs) has been developed. Verilog-A was used to implement the model in a manner that can be incorporated into circuit simulations. Rather than using SPICE elements to mimic the voltage and current characteristics of the APD, Verilog-A can represent the first order nonlinear differential equations that govern the avalanche current of the APD. This continuous time representation is fundamentally different than the piecewise linear characteristics of other models. The model is based on a driving term for the differential current, which is given by the voltage overbias minus the voltage drop across the device's space-charge resistance RSC. This drop is primarily due to electrons transiting the separate absorber. RSC starts off high and decreases with time as the initial breakdown filament spreads laterally to fill the APD. With constant bias voltage, the initial current grows exponentially until space charge effects reduce the driving function. With increasing current the driving term eventually goes to zero and the APD current saturates. On the other hand, if the APD is biased with a capacitor, the driving term becomes negative as the capacitor discharges, reducing the current and driving the voltage below breakdown. The model parameters depend on device design and are obtained from fitting the model to Monte-Carlo turn-on simulations that include lateral spreading of the carriers of the relevant structure. The Monte-Carlo simulations also provide information on the probability of avalanche, and jitter due to where the photon is absorbed in the APD.

  20. A discrete model of the development and relaxation of a local microbreakdown in silicon avalanche photodiodes operating in the Geiger mode

    SciTech Connect

    Vanyushin, I. V. Gergel, V. A.; Gontar', V. M.; Zimoglyad, V. A.; Tishin, Yu. I.; Kholodnov, V. A. Shcheleva, I. M.

    2007-06-15

    A new discrete theoretical model of the development and relaxation of a local microbreakdown in silicon avalanche photodiodes operating in the Geiger mode is developed. It is shown that the spreading resistance in the substrate profoundly affects both the amplitude of a single-photon electrical pulse and the possibility of attaining the steady-state form of the avalanche breakdown excluding the Geiger mode of the photodiode's operation. The model is employed to interpret the experimental data obtained using test single-photon cells of avalanche photodiodes fabricated on the basis of the 0.25-{mu}m silicon technology with the use of deep implantation to form the region of avalanche multiplication for the charge carriers. Excellent functional properties of the studied type of the single-photon (Geiger) cell are noted. A typical amplitude characteristic of the cell for optical radiation with the wavelength {lambda} = 0.56 {mu}m in the irradiance range of 10{sup -3}-10{sup 2} lx is presented; this characteristic indicates that the quantum efficiency of photoconversion is extremely high.

  1. Detection of the Light Produced in Scintillating Tiles by Means of a Wls Fiber and AN Avalanche Photodiode Working in the Geiger Mode

    NASA Astrophysics Data System (ADS)

    Akindinov, A.; Mal'Kevich, D.; Martemiyanov, A.; Smirnitsky, A.; Voloshin, K.; Grigoriev, E.; Golovin, V.; Bondarenko, G.

    2004-07-01

    Plates of an organic scintillator BC408, 50 × 50 × 5 mm3, with a wavelength-shifting (WLS) fiber Kuraray Y11, embedded in circular grooves inside the plastic, were used in combination with 1 mm2 avalanche photodiodes working in the Geiger mode (APDg or MRS-APD). Beam tests with minimum ionizing particles (MIP), performed at the ITEP synchrotron, have shown high detection efficiencies (about 13 photo-electrons).

  2. The 1.06 optical receiver. [avalanche photodiodes for laser range finders

    NASA Technical Reports Server (NTRS)

    Tomasetta, L. R.; Law, H. D.; Nakano, K.; Scholl, F. W.; Harris, J. S., Jr.

    1978-01-01

    High performance 1.06 micron m avalanche photodetectors (APDs), fabricated in the GaAlSb system, have high quantum efficiency (90 percent), high speed (risetime less than 60 ps) and low leakage currents (less than 50 na). The dark current represents more than an order of magnitude reduction compared to previously reported results. The high speed avalanche gain of these devices is between 20 and 50. The area uniformity is better than + or - 10 percent. GaAlAs APDs at 0.53 micron m have even faster speed, lower dark currents, and high speed gains of 100 to 200. Optical rangefinders based on measured APD performance parameters have far superior performance when compared to even ideal photomultiplier tubes in either a one color or two color rangefinder system. For a one color system, f factor of two lower time jitter can be achieved with identical transmitted power. The superiority of the APD based two color receiver is significant and exists in the entire range of desired time jitters (less than 100 ps) and received power levels.

  3. Word timing recovery in direct detection optical PPM communication systems with avalanche photodiodes using a phase lock loop

    NASA Technical Reports Server (NTRS)

    Sun, Xiaoli; Davidson, Frederic M.

    1990-01-01

    A technique for word timing recovery in a direct-detection optical PPM communication system is described. It tracks on back-to-back pulse pairs in the received random PPM data sequences with the use of a phase locked loop. The experimental system consisted of an 833-nm AlGaAs laser diode transmitter and a silicon avalanche photodiode photodetector, and it used Q = 4 PPM signaling at source data rate 25 Mb/s. The mathematical model developed to describe system performance is shown to be in good agreement with the experimental measurements. Use of this recovered PPM word clock with a slot clock recovery system caused no measurable penalty in receiver sensitivity. The completely self-synchronized receiver was capable of acquiring and maintaining both slot and word synchronizations for input optical signal levels as low as 20 average detected photons per information bit. The receiver achieved a bit error probability of 10 to the -6th at less than 60 average detected photons per information bit.

  4. Performance Dependences of Multiplication Layer Thickness for InP/InGaAs Avalanche Photodiodes Based on Time Domain Modeling

    NASA Technical Reports Server (NTRS)

    Xiao, Yegao; Bhat, Ishwara; Abedin, M. Nurul

    2005-01-01

    InP/InGaAs avalanche photodiodes (APDs) are being widely utilized in optical receivers for modern long haul and high bit-rate optical fiber communication systems. The separate absorption, grading, charge, and multiplication (SAGCM) structure is an important design consideration for APDs with high performance characteristics. Time domain modeling techniques have been previously developed to provide better understanding and optimize design issues by saving time and cost for the APD research and development. In this work, performance dependences on multiplication layer thickness have been investigated by time domain modeling. These performance characteristics include breakdown field and breakdown voltage, multiplication gain, excess noise factor, frequency response and bandwidth etc. The simulations are performed versus various multiplication layer thicknesses with certain fixed values for the areal charge sheet density whereas the values for the other structure and material parameters are kept unchanged. The frequency response is obtained from the impulse response by fast Fourier transformation. The modeling results are presented and discussed, and design considerations, especially for high speed operation at 10 Gbit/s, are further analyzed.

  5. Design and performance testing of an avalanche photodiode receiver with multiplication gain control algorithm for intersatellite laser communication

    NASA Astrophysics Data System (ADS)

    Yu, Xiaonan; Tong, Shoufeng; Dong, Yan; Song, Yansong; Hao, Shicong; Lu, Jing

    2016-06-01

    An avalanche photodiode (APD) receiver for intersatellite laser communication links is proposed and its performance is experimentally demonstrated. In the proposed system, a series of analog circuits are used not only to adjust the temperature and control the bias voltage but also to monitor the current and recover the clock from the communication data. In addition, the temperature compensation and multiplication gain control algorithm are embedded in the microcontroller to improve the performance of the receiver. As shown in the experiment, with the change of communication rate from 10 to 2000 Mbps, the detection sensitivity of the APD receiver varies from -47 to -34 dBm. Moreover, due to the existence of the multiplication gain control algorithm, the dynamic range of the APD receiver is effectively improved, while the dynamic range at 10, 100, and 1000 Mbps is 38.7, 37.7, and 32.8 dB, respectively. As a result, the experimental results agree well with the theoretical predictions, and the receiver will improve the flexibility of the intersatellite links without increasing the cost.

  6. Temporal dependence of transient dark counts in an avalanche photodiode: A solution for power-law behavior of afterpulsing

    NASA Astrophysics Data System (ADS)

    Akiba, M.; Tsujino, K.

    2016-08-01

    This paper offers a theoretical explanation of the temperature and temporal dependencies of transient dark count rates (DCRs) measured for a linear-mode silicon avalanche photodiode (APD) and the dependencies of afterpulsing that were measured in Geiger-mode Si and InGaAs/InP APDs. The temporal dependencies exhibit power-law behavior, at least to some extent. For the transient DCR, the value of the DCR for a given time period increases with decreases in temperature, while the power-law behavior remains unchanged. The transient DCR is attributed to electron emissions from traps in the multiplication layer of the APD with a high electric field, and its temporal dependence is explained by a continuous change in the electron emission rate as a function of the electric field strength. The electron emission rate is calculated using a quantum model for phonon-assisted tunnel emission. We applied the theory to the temporal dependence of afterpulsing that was measured for Si and InGaAs/InP APDs. The power-law temporal dependence is attributed to the power-law function of the electron emission rate from the traps as a function of their position across the p-n junction of the APD. Deviations from the power-law temporal dependence can be derived from the upper and lower limits of the electric field strength.

  7. Monolithically integrated avalanche photodiode receiver in 0.35 μm bipolar complementary metal oxide semiconductor

    NASA Astrophysics Data System (ADS)

    Jukić, Tomislav; Steindl, Bernhard; Enne, Reinhard; Zimmermann, Horst

    2015-11-01

    We present the first optoelectronic integrated bipolar complementary metal oxide semiconductor (BiCMOS) receiver chip with an avalanche photodiode (APD). A large 200-μm-diameter APD connected to a high-speed transimpedance amplifier designed for a 2-Gbps optical wireless communication system is proposed. The complete chip was realized in a 0.35-μm silicon BiCMOS technology. Due to the thick intrinsic zone and multiplication gain, the responsivity of the APD reaches a value of up to 120 A/W for a wavelength of 675 nm. Furthermore, the capacitance of the APD is <500 fF for reverse bias voltages above 18 V. The receiver has a supply voltage of 3.3 V with a current consumption of 76 mA. The delivered 50-Ω single-ended output swing is 550 mVpp and the overall transimpedance is 260 kΩ with 1.02-GHz bandwidth. The achieved data rate is 2 Gbps with a sensitivity of -30.3 dBm at a bit error rate <10-9.

  8. Study of gain and photoresponse characteristics for back-illuminated separate absorption and multiplication GaN avalanche photodiodes

    SciTech Connect

    Wang, Xiaodong; Pan, Ming; Hou, Liwei; Xie, Wei; Hu, Weida Xu, Jintong; Li, Xiangyang; Chen, Xiaoshuang Lu, Wei

    2014-01-07

    The gain and photoresponse characteristics have been numerically studied for back-illuminated separate absorption and multiplication (SAM) GaN avalanche photodiodes (APDs). The parameters of fundamental models are calibrated by simultaneously comparing the simulated dark and light current characteristics with the experimental results. Effects of environmental temperatures and device dimensions on gain characteristics have been investigated, and a method to achieve the optimum thickness of charge layer is obtained. The dependence of gain characteristics and breakdown voltage on the doping concentration of the charge layer is also studied in detail to get the optimal charge layer. The bias-dependent spectral responsivity and quantum efficiency are then presented to study the photoresponse mechanisms inside SAM GaN APDs. It is found the responsivity peak red-shifts at first due to the Franz-Keldysh effect and then blue-shifts due to the reach-through effect of the absorption layer. Finally, a new SAM GaN/AlGaN heterojunction APD structure is proposed for optimizing SAM GaN APDs.

  9. Ge/graded-SiGe multiplication layers for low-voltage and low-noise Ge avalanche photodiodes on Si

    NASA Astrophysics Data System (ADS)

    Miyasaka, Yuji; Hiraki, Tatsurou; Okazaki, Kota; Takeda, Kotaro; Tsuchizawa, Tai; Yamada, Koji; Wada, Kazumi; Ishikawa, Yasuhiko

    2016-04-01

    A new structure is examined for low-voltage and low-noise Ge-based avalanche photodiodes (APDs) on Si, where a Ge/graded-SiGe heterostructure is used as the multiplication layer of a separate-absorption-carrier-multiplication structure. The Ge/SiGe heterojunction multiplication layer is theoretically shown to be useful for preferentially enhancing impact ionization for photogenerated holes injected from the Ge optical-absorption layer via the graded SiGe, reflecting the valence band discontinuity at the Ge/SiGe interface. This property is effective not only for the reduction of operation voltage/electric field strength in Ge-based APDs but also for the reduction of excess noise resulting from the ratio of the ionization coefficients between electrons and holes being far from unity. Such Ge/graded-SiGe heterostructures are successfully fabricated by ultrahigh-vacuum chemical vapor deposition. Preliminary pin diodes having a Ge/graded-SiGe multiplication layer act reasonably as photodetectors, showing a multiplication gain larger than those for diodes without the Ge/SiGe heterojunction.

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

    NASA Astrophysics Data System (ADS)

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

    2012-06-01

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

  11. Pulse-resolved multi-photon X-ray detection at 31 MHz based on a quadrant avalanche photodiode.

    PubMed

    Reusch, Tobias; Osterhoff, Markus; Agricola, Johannes; Salditt, Tim

    2014-07-01

    The technical realisation and the commissioning experiments of a high-speed X-ray detector based on a quadrant avalanche silicon photodiode and high-speed digitizers are described. The development is driven by the need for X-ray detectors dedicated to time-resolved diffraction and imaging experiments, ideally requiring pulse-resolved data processing at the synchrotron bunch repetition rate. By a novel multi-photon detection scheme, the exact number of X-ray photons within each X-ray pulse can be recorded. Commissioning experiments at beamlines P08 and P10 of the storage ring PETRA III, at DESY, Hamburg, Germany, have been used to validate the pulse-wise multi-photon counting scheme at bunch frequencies ≥ 31 MHz, enabling pulse-by-pulse readout during the PETRA III 240-bunch mode with single-photon detection capability. An X-ray flux of ≥ 3.7 × 10(9) photons s(-1) can be detected while still resolving individual photons at low count rates. PMID:24971964

  12. Detection efficiency calibration of single-photon silicon avalanche photodiodes traceable using double attenuator technique

    PubMed Central

    López, Marco; Hofer, Helmuth; Kück, Stefan

    2015-01-01

    A highly accurate method for the determination of the detection efficiency of a silicon single-photon avalanche diode (Si-SPAD) is presented. This method is based on the comparison of the detected count rate of the Si-SPAD compared to the photon rate determined from a calibrated silicon diode using a modified attenuator technique, in which the total attenuation is measured in two attenuation steps. Furthermore, a validation of this two-step method is performed using attenuators of higher transmittance. The setup is a tabletop one, laser-based, and fully automated. The measurement uncertainty components are determined and analyzed in detail. The obtained standard measurement uncertainty is < 0.5%. Main contributions are the transmission of the neutral density filters used as attenuators and the spectral responsivity of the calibrated analog silicon diode. Furthermore, the dependence of the detection efficiency of the Si-SPAD on the mean photon number of the impinging laser radiation with Poissonian statistics is investigated. PMID:25892852

  13. In Orbit Performance of Si Avalanche Photodiode Single Photon Counting Modules in the Geoscience Laser Altimeter System on ICESat

    NASA Technical Reports Server (NTRS)

    Sun, X.; Jester, P. L.; Palm, S. P.; Abshire, J. B.; Spinhime, J. D.; Krainak, M. A.

    2006-01-01

    Si avalanche photodiode (APD) single photon counting modules (SPCMs) are used in the Geoscience Laser Altimeter System (GLAS) on Ice, Cloud, anti land Elevation Satellite (ICESat), currently in orbit measuring Earth surface elevation and atmosphere backscattering. These SPCMs are used to measure cloud and aerosol backscatterings to the GLAS laser light at 532-nm wavelength with 60-70% quantum efficiencies and up to 15 millions/s maximum count rates. The performance of the SPCMs has been closely monitored since ICESat launch on January 12, 2003. There has been no measurable change in the quantum efficiency, as indicated by the average photon count rates in response to the background light from the sunlit earth. The linearity and the afterpulsing seen from the cloud and surface backscatterings profiles have been the same as those during ground testing. The detector dark count rates monitored while the spacecraft was in the dark side of the globe have increased almost linearly at about 60 counts/s per day due to space radiation damage. The radiation damage appeared to be independent of the device temperature and power states. There was also an abrupt increase in radiation damage during the solar storm in 28-30 October 2003. The observed radiation damage is a factor of two to three lower than the expected and sufficiently low to provide useful atmosphere backscattering measurements through the end of the ICESat mission. To date, these SPCMs have been in orbit for more than three years. The accumulated operating time to date has reached 290 days (7000 hours). These SPCMs have provided unprecedented receiver sensitivity and dynamic range in ICESat atmosphere backscattering measurements.

  14. Comparative Performance of the Photomultiplier Tube and the Silicon Avalanche Photodiode When Used as Detectors in Angular Scattering Measurements

    NASA Astrophysics Data System (ADS)

    Kroner, D. O.; Nelson, R. M.; Boryta, M. D.; Hapke, B. W.; Manatt, K.; Smythe, W. D.

    2014-12-01

    We report the results of a comparative study of two types of photometric detectors that are commonly used for, spacecraft, ground-based telescope, and laboratory observations in support of precise angular scattering investigations of the type described in a companion paper (Nelson et al., this meeting). The performance of the state of the art Hamamatsu C12703-01 Silicon Avalanche photodiode (SAD) was compared to that of the Hamamatsu R928 Photomultiplier tube (PMT). The Hamamatsu R928 evolved from a sequence of photometric detectors with a long history of use in support of laboratory and remote sensing studies, tracing backwards to include the RCA 1P21 and the RCA 931A. Two newly acquired SADs were bench tested along with a new R928 photomultiplier tube that was thermoelectrically cooled to -10 deg C. The SAD's employed electronic thermal compensation supplied by the manufacturer. The SADs and PMT measured electromagnetic radiation from solid-state lasers of wavelength 635 nm after the radiation was reflected from diffusely-scattering surfaces of varying albedos. The SADs were housed on tripods that were co-aligned with the PMT and laser. The photometric detectors were placed 4.3 meters from a reflecting disk. The disk was rotated to reduce the effect of laser speckle. All detectors in the experiment were equipped with notch filters that transmit light only of the wavelength emitted by the laser. Three SR830 DSP Lock-in Amplifiers were connected to the detectors and various setting configurations were compared in order to optimize signal to noise. Neutral Density filters (ND 0,3 and ND 0,9) were placed in the light path to determine the linearity in the response function of the detectors. We conclude that in this application SADs and PMTs produce comparable photometric precision and fidelity. SADs offer greater convenience because thermal compensation circuitry is integrated with the detector. This work was partially supported by NASA's Cassini Science

  15. Optimization of a guard ring structure in Geiger-mode avalanche photodiodes fabricated at National NanoFab Center

    NASA Astrophysics Data System (ADS)

    Lim, K. T.; Kim, H.; Cho, M.; Kim, Y.; Kim, C.; Kim, M.; Lee, D.; Kang, D.; Yoo, H.; Park, K.; Sul, W. S.; Cho, G.

    2016-01-01

    A typical Geiger-mode avalanche photodiode (G-APD) contains a guard ring that protects the structure from having an edge breakdown due to the lowering of electric fields at junction curvatures. In this contribution, G-APDs with a virtual guard ring (vGR) merged with n-type diffused guard ring (nGR) in various sizes were studied to find the optimal design for G-APDs fabricated at National NanoFab Center (NNFC) . The sensors were fabricated via a customized CMOS process with a micro-cell size of 65× 65 μm2 on a 200 mm p-type epitaxial layer wafer. I-V characteristic curves for proposed structures were measured on a wafer-level with an auto probing system and plotted together to compare their performance. A vGR width of 1.5 μm and a nGR width of 1.5 μm with an overlapping between vGR and nGR of 1.5 μm showed the lowest leakage current before the breakdown voltage while suppressing the edge breakdown. Furthermore, the current level of the lowest-leakage-current structure was as low as that of only vGR with a width of 2.0 μm, indicating that the structure is also area efficient. Based on these results, the design with vGR, nGR, and OL with width of 1.5 μm is determined to be the optimal structure for G-APDs fabricated at NNFC.

  16. Linear mode photon counting from visible to MWIR with HgCdTe avalanche photodiode focal plane arrays

    NASA Astrophysics Data System (ADS)

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

    2015-05-01

    Results of characterization data on linear mode photon counting (LMPC) HgCdTe electron-initiated avalanche photodiode (e-APD)focal plane arrays (FPA) are presented that reveal an improved understanding and the growing maturity of the technology. The first successful 2x8 LMPC FPA was fabricated in 2010 [1]. Since then a process validation lot of 2x8 arrays was fabricated. Five arrays from this lot were characterized that replicated the previous 2x8 LMPC array performance. In addition, it was unambiguously verified that readout integrated circuit (ROIC) glow was responsible for most of the false event rate (FER) of the 2010 array. The application of a single layer metal blocking layer between the ROIC and the detector array and optimization of the ROIC biases reduced the FER by an order of magnitude. Photon detection efficiencies (PDEs) of greater than 50% were routinely demonstrated across 5 arrays, with one array reaching a PDE of 70%. High resolution pixel-surface spot scans were performed and the junction diameters of the diodes were measured. The junction diameter was decreased from 31 μm to 25 μm resulting in a 2x increase in E-APD gain from 470 on the 2010 array to 1100 on one of the 2013 FPAs. Mean single photon signal to noise ratios of >12 were demonstrated at excess noise factors of 1.2-1.3. NASA Goddard Space Flight Center (GSFC) performed measurements on the delivered FPA that verified the PDE and FER data.

  17. Restraint of range walk error in a Geiger-mode avalanche photodiode lidar to acquire high-precision depth and intensity information.

    PubMed

    Xu, Lu; Zhang, Yu; Zhang, Yong; Yang, Chenghua; Yang, Xu; Zhao, Yuan

    2016-03-01

    There exists a range walk error in a Geiger-mode avalanche photodiode (Gm-APD) lidar because of the fluctuation in the number of signal photoelectrons. To restrain this range walk error, we propose a new returning-wave signal processing technique based on the Poisson probability response model and the Gaussian functions fitting method. High-precision depth and intensity information of the target at the distance of 5 m is obtained by a Gm-APD lidar using a 6 ns wide pulsed laser. The experiment results show that the range and intensity precisions are 1.2 cm and 0.015 photoelectrons, respectively. PMID:26974630

  18. Design of a back-illuminated, crystallographically etched, silicon-on-sapphire avalanche photodiode with monolithically integrated microlens, for dual-mode passive & active imaging arrays

    NASA Astrophysics Data System (ADS)

    Stern, Alvin G.; Cole, Daniel C.

    2008-12-01

    There is a growing need in space and environmental research applications for dual-mode, passive and active 2D and 3D ladar imaging methods. To fill this need, an advanced back-illuminated avalanche photodiode (APD) design is presented based on crystallographically etched (100) epitaxial silicon on R-plane sapphire (SOS), enabling single photon sensitive, solid-state focal plane arrays (FPAs) with wide dynamic range, supporting passive and active imaging capability in a single FPA. When (100) silicon is properly etched with KOH:IPA:H2O solution through a thermally grown oxide mask, square based pyramidal frustum or mesa arrays result with the four mesa sidewalls of the APD formed by (111) silicon planes that intersect the (100) planes at a crystallographic angle, Φc = 54.7°. The APD device is fabricated in the mesa using conventional silicon processing technology. Detectors are back-illuminated through light focusing microlenses fabricated in the thinned, AR-coated sapphire substrate. The APDs share a common, front-side anode contact, made locally at the base of each device mesa. A low resistance (Al) or (Cu) metal anode grid fills the space between pixels and also inhibits optical cross-talk. SOS-APD arrays are indium bump-bonded to CMOS readout ICs to produce hybrid FPAs. The quantum efficiency for the square 27 µm pixels exceeds 50% for 250 nm < λ < 400 nm and exceeds 80% for 400 nm < λ < 700 nm. The sapphire microlenses compensate detector quantum efficiency loss resulting from the mesa geometry and yield 100% sensitive-area-fill-factor arrays, limited in size only by the wafer diameter.

  19. Effect of variations in the doping profiles on the properties of doped multiple quantum well avalanche photodiodes

    NASA Technical Reports Server (NTRS)

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

    1996-01-01

    The purpose of this study is to use both theoretical and experimental evidence to determine the impact of doping imbalance and symmetry on the physical and electrical characteristics of doped multiple quantum well avalanche photodiodes (APD). Theoretical models have been developed to calculate the electric field valence and conduction bands, capacitance-voltage (CV), and carrier concentration versus depletion depth profiles. The models showed a strong correlation between the p- and n-doping balance inside the GaAs wells and the number of depleted stages and breakdown voltage of the APD. A periodic doping imbalance in the wells has been shown to result in a gradual increase (or decrease) in the electric field profile throughout the device which gave rise to partially depleted devices at low bias. The MQW APD structures that we modeled consisted of a 1 micron top p(+)-doped (3 x 10(exp 18) cm(exp -3)) GaAs layer followed by a 1 micron region of alternating layers of GaAs (500 A) and Al(0.42)Ga(0.58)As (500 A), and a 1 micron n(+) back layer (3 x 10(exp 18) cm(exp -3)). The GaAs wells were doped with p-i-n layers placed at the center of each well. The simulation results showed that in an APD with nine doped wells, and where the 50 A p-doped layer is off by 10% (p = 1.65 x 10(exp 18) cm(exp -3), n = 1.5 x 10(exp 18) cm(exp -3)), almost half of the MQW stages were shown to be undepleted at low bias which was a result of a reduction in the electric field near the p(+) cap layer by over 50% from its value in the balanced structure. Experimental CV and IV data on similar MBE grown MQW structures have shown very similar depletion and breakdown characteristics. The models have enabled us to better interpret our experimental data and to determine both the extent of the doping imbalances in the devices as well as the overall p- or n-type doping characteristics of the structures.

  20. Receiver Performance of CO2 and CH4 Lidar with Low Noise HgCdTe Avalanche Photodiodes

    NASA Astrophysics Data System (ADS)

    Sun, X.; Abshire, J. B.

    2012-12-01

    NASA Goddard Space Flight Center (GSFC) is currently developing CO2 lidars at 1.57 μm wavelength for the Active Sensing of CO2 Emission over Days, Nights, and Seasons (ASCENDS) mission. One of the major technical challenges is the photodetectors that have to operate in short wave infrared (SWIR) wavelength region and sensitive to received laser pulses of only a few photons. We have been using InGaAs photocathode photomultiplier tubes (PMT) in our airborne simulator of the CO2 lidar that can detect single photon with up to 10% quantum efficiency at <1.6 μm wavelength. However it was difficult to maintain a sufficiently wide signal dynamic range and single photon sensitivity at the same time with the PMTs. There may also be a lifetime limitation with the InGaAs photocathode PMT for a multi-year space mission. We have been developing HgCdTe avalanche photodiode (APD) SWIR detector systems with DRS Technologies, Reconnaissance, Surveillance and Target Acquisition (RSTA) Division as an alternative photodetector for our CO2 lidars. The new HgCdTe APDs have typically a >50% quantum efficiency, including the effect of fill-factor, from 0.9 to 4.5 μm wavelength. DRS RSTA will integrate a low noise read-out integrated circuit (ROIC) with the HgCdTe APD array into a low noise analog SWIR detector with near single photon sensitivity. The new HgCdTe APD SWIR detector assembly is expected to improve the receiver sensitivity of our CO2 lidar by at least a factor of two and provide a sufficient wide signal dynamic range. The new SWIR detector systems can also be used in the CH4 lidars at 1.65 μm wavelength currently being developed at GSFC. The near infrared PMTs have diminishing quantum efficiency as the wavelength exceeds 1.6 μm. InGaAs APDs have a high quantum efficiency but too high an excess noise factor to achieve near quantum limited performance. The new HgCdTe APDs is expected to give a much superior performance than the PMTs and the InGaAs APDs. In this paper, we

  1. MBE growth of HgCdTe avalanche photodiode structures for low-noise 1.55 μm photodetection

    NASA Astrophysics Data System (ADS)

    de Lyon, T. J.; Baumgratz, B.; Chapman, G.; Gordon, E.; Hunter, A. T.; Jack, M.; Jensen, J. E.; Johnson, W.; Johs, B.; Kosai, K.; Larsen, W.; Olson, G. L.; Sen, M.; Walker, B.; Wu, O. K.

    1999-05-01

    Molecular-beam epitaxy (MBE) has been utilized to fabricate HgCdTe heterostructure separate absorption and multiplication avalanche photodiodes (SAM-APD) sensitive to infrared radiation in the 1.1-1.6 μm spectral range, as an alternative technology to existing III-V APD detectors. Device structures were grown on CdZnTe(211)B substrates using CdTe, Te, and Hg sources with in situ In and As doping. The composition of the HgCdTe alloy layers was adjusted to achieve both efficient absorption of IR radiation in the 1.1-1.6 μm spectral range and low excess-noise avalanche multiplication. The Hg 1- xCd xTe alloy composition in the gain region of the device, x=0.73, was selected to achieve equality between the bandgap energy and spin-orbit splitting to resonantly enhance the impact ionization of holes in the split-off valence band. The appropriate value of this alloy composition was determined from analysis of the 300 K bandgap and spin-orbit splitting energies of a set of calibration layers, using a combination of IR transmission and spectroscopic ellipsometry measurements. MBE-grown APD epitaxial wafers were processed into passivated mesa-type discrete device structures and diode mini-arrays using conventional HgCdTe process technology. Device spectral response, dark current density, and avalanche gain measurements were performed on the processed wafers. Avalanche gains in the range of 30-40 at reverse bias of 85-90 V and array-median dark current density below 2×10 -4 A/cm 2 at 40 V reverse bias have been demonstrated.

  2. Impact of a New Highly Sensitive HgCdTe Avalanche Photodiode Detector on Receiver Performance for the CO2 Sounder Lidar for the ASCENDS Mission

    NASA Astrophysics Data System (ADS)

    Sun, X.; Abshire, J. B.

    2013-12-01

    NASA Goddard Space Flight Center (GSFC) is currently developing a CO2 lidar as a candidate for the NASA's planned ASCENDS mission under the support of Earth Science Technology Office (ESTO) Instrument Incubator Program (IIP). As part of this work we have demonstrated new type of lower noise HgCdTe avalanche photodiode (APD) multi-element detector for the lidar receiver. This significantly improves the receiver sensitivity, lower the laser power, and reduce the receiver telescope size compared to InGaAs photomultiplier tubes (PMT) and APDs currently used. The HgCdTe APD arrays were designed and manufactured by DRS Technologies, Reconnaissance, Surveillance and Target Acquisition (RSTA) Division, which combines their mature HgCdTe APD detector in a hybrid package with a new custom cryogenic silicon preamplifier. The new detectors were specially designed for our airborne CO2 lidar and operate at ~ 77K inside a turn-key closed-cycle cooler. The detector has 80 μm square pixels in a 4x4 array, and >70% fill factor and was custom designed to match the optics of our airborne and eventually space-based CO2 lidar. The initial results of evaluating the detector at NASA GSFC showed the HgCdTe APD assembly has a quantum efficiency of ~90% near 1550-nm, >500 APD gain, 8-10 MHz electrical bandwidth, and an average noise equivalent power of <1fW/Hz1/2. The detector also has a much wider linear dynamic range than PMTs, since it operates in a linear analog mode and has variable gain. Given the wide range of surface reflectivities this is important for ASCENDS. The new detector also greatly improves our CO2 lidar's receiver sensitivity. Calculations show it enables us to reduce the laser transmitter power by half for the space borne instrument while staying with a conventional reasonably sized (~1.2 m) diameter receiver telescope. We will show analysis and laboratory test results of the CO2 lidar performance using a receiver with this new detector. We are also funded by NASA ESTO

  3. Single-photon property characterization of 1.3 μm emissions from InAs/GaAs quantum dots using silicon avalanche photodiodes

    PubMed Central

    Zhou, P. Y.; Dou, X. M.; Wu, X. F.; Ding, K.; Li, M. F.; Ni, H. Q.; Niu, Z. C.; Jiang, D. S.; Sun, B. Q.

    2014-01-01

    We developed a new approach to test the single-photon emissions of semiconductor quantum dots (QDs) in the optical communication band. A diamond-anvil cell pressure device was used for blue-shifting the 1.3 μm emissions of InAs/GaAs QDs to 0.9 μm for detection by silicon avalanche photodiodes. The obtained g(2)(0) values from the second-order autocorrelation function measurements of several QD emissions at 6.58 GPa were less than 0.3, indicating that this approach provides a convenient and efficient method of characterizing 1.3 μm single-photon source based on semiconductor materials. PMID:24407193

  4. A theory study of the multiplication characteristics of InP/InGaAs avalanche photodiodes with double multiplication layers and double charge layers

    NASA Astrophysics Data System (ADS)

    Liu, Guipeng; Chen, Wenjie; Liu, Linsheng; Jin, Peng; Tian, Yonghui; Yang, Jianhong

    2016-09-01

    An In0.53Ga0.47As/InP avalanche photodiodes (APD) structure with double multiplication layers and double charge layers has been proposed. The calculated results with considering the dead space effect show that a thin 2nd multiplication layer will reduce the excess noise factor F in this structure for a fixed mean gain . And its performances will reach the best when the 2nd multiplication layer is 0.01 μm, which will reduce the excess noise factor 7% compared to a conventional APD for =10. The effects of 1st and 2nd charge layers on the APD have also been studied in this paper.

  5. Ultrahigh-sensitivity high-linearity photodetection system using a low-gain avalanche photodiode with an ultralow-noise readout circuit.

    PubMed

    Akiba, Makoto; Fujiwara, Mikio; Sasaki, Masahide

    2005-01-15

    A highly sensitive photodetection system with a detection limit of 1 photon/s was developed. This system uses a commercially available 200-microm-diameter silicon avalanche photodiode (APD) and an in-house-developed ultralow-noise readout circuit, which are both cooled to 77 K. When the APD operates at a low gain of approximately 10, it has a high-linearity response to the number of incident photons and a low excess noise factor. The APD also has a high quantum efficiency and a dark current of less than 1 e/s at 77 K. This photodetection system will shorten measurement time and permit higher spatial and wavelength resolution for near-field scanning optical microscopes. PMID:15675687

  6. Single-photon property characterization of 1.3 μm emissions from InAs/GaAs quantum dots using silicon avalanche photodiodes.

    PubMed

    Zhou, P Y; Dou, X M; Wu, X F; Ding, K; Li, M F; Ni, H Q; Niu, Z C; Jiang, D S; Sun, B Q

    2014-01-01

    We developed a new approach to test the single-photon emissions of semiconductor quantum dots (QDs) in the optical communication band. A diamond-anvil cell pressure device was used for blue-shifting the 1.3 μm emissions of InAs/GaAs QDs to 0.9 μm for detection by silicon avalanche photodiodes. The obtained g((2))(0) values from the second-order autocorrelation function measurements of several QD emissions at 6.58 GPa were less than 0.3, indicating that this approach provides a convenient and efficient method of characterizing 1.3 μm single-photon source based on semiconductor materials. PMID:24407193

  7. Nuclear resonant scattering measurements on {sup 57}Fe by multichannel scaling with a 64-pixel silicon avalanche photodiode linear-array detector

    SciTech Connect

    Kishimoto, S. Haruki, R.; Mitsui, T.; Yoda, Y.; Taniguchi, T.; Shimazaki, S.; Ikeno, M.; Saito, M.; Tanaka, M.

    2014-11-15

    We developed a silicon avalanche photodiode (Si-APD) linear-array detector for use in nuclear resonant scattering experiments using synchrotron X-rays. The Si-APD linear array consists of 64 pixels (pixel size: 100 × 200 μm{sup 2}) with a pixel pitch of 150 μm and depletion depth of 10 μm. An ultrafast frontend circuit allows the X-ray detector to obtain a high output rate of >10{sup 7} cps per pixel. High-performance integrated circuits achieve multichannel scaling over 1024 continuous time bins with a 1 ns resolution for each pixel without dead time. The multichannel scaling method enabled us to record a time spectrum of the 14.4 keV nuclear radiation at each pixel with a time resolution of 1.4 ns (FWHM). This method was successfully applied to nuclear forward scattering and nuclear small-angle scattering on {sup 57}Fe.

  8. Count rate studies of a box-shaped PET breast imaging system comprised of position sensitive avalanche photodiodes utilizing monte carlo simulation.

    PubMed

    Foudray, Angela M K; Habte, Frezghi; Chinn, Garry; Zhang, Jin; Levin, Craig S

    2006-01-01

    We are investigating a high-sensitivity, high-resolution positron emission tomography (PET) system for clinical use in the detection, diagnosis and staging of breast cancer. Using conventional figures of merit, design parameters were evaluated for count rate performance, module dead time, and construction complexity. The detector system modeled comprises extremely thin position-sensitive avalanche photodiodes coupled to lutetium oxy-orthosilicate scintillation crystals. Previous investigations of detector geometries with Monte Carlo indicated that one of the largest impacts on sensitivity is local scintillation crystal density when considering systems having the same average scintillation crystal densities (same crystal packing fraction and system solid-angle coverage). Our results show the system has very good scatter and randoms rejection at clinical activity ranges ( approximately 200 muCi). PMID:17645997

  9. Negative feedback avalanche diode

    NASA Technical Reports Server (NTRS)

    Itzler, Mark Allen (Inventor)

    2010-01-01

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

  10. Voltage sharing effect and interface state calculation of a wafer-bonding Ge/Si avalanche photodiode with an interfacial GeO2 insulator layer.

    PubMed

    Ke, Shaoying; Lin, Shaoming; Li, Xin; Li, Jun; Xu, Jianfang; Li, Cheng; Chen, Songyan

    2016-02-01

    The tunneling effect and interface state in the p-Ge/GeO2p-Si structure of a wafer-bonding Ge/Si avalanche photodiode (APD) are investigated. It is found that the thin interfacial GeO2 layer (1-2 nm) formed by the hydrophilic reaction at the wafer-bonding interface significantly affects the performance of the Ge/Si APD. With the increase of the GeO2 thickness, the dark current of the Ge/Si APD decreases enormously due to the blocking effect of this GeO2 layer. Owing to the carrier accumulation in Ge layer under illumination condition, the voltage sharing effect of the GeO2 layer (thicker) becomes serious, leading to the absence of the electric field in Ge layer. The photon-generated electrons at Ge/GeO2 interface can be captured and released by the interface states at certain reverse bias. This can adjust the avalanche current of the Ge/Si APD. The stronger interface recombination induced by the larger interface state density (ISD) results in the decrease of the electric field in Ge layer. This increases the transit time of carriers, which in turn decreases the 3dB-bandwidth. Due to the drastic increase of the dark current (larger ISD), the gain of the Ge/Si APD decreases. PMID:26906771

  11. In-flight verification of avalanche photodiodes: avenue to a low-cost solution to measure suprathermal particles for future missions

    NASA Astrophysics Data System (ADS)

    Ogasawara, K.; Bonnell, J. W.; Christian, E. R.; Desai, M. I.; Grubbs, G. A., II; Jahn, J. M.; Livi, S. A.; Kanekal, S. G.; Llera, K.; McComas, D. J.; Michell, R.; Samara, M.; Vines, S. K.

    2014-12-01

    Flight operation results and plans of Avalanche Photodiodes (APDs) to measure suprathermal particles (a ~few keV up to ~100s of keV) are summarized in this presentation. Ions and electrons in this energy range play crucial roles in many fundamental processes of space plasmas including particle heating and acceleration, providing source material for the energetic particles accelerated near the Sun, the heliosphere, and in geospace. Characterizing these populations poses serious technical challenges because this energy region lies between the two most commonly used particle detection techniques, i.e., that used by thermal or plasma instruments and by Solid-State Detector (SSD)-based energetic particle telescopes, which are limited by typical SSD threshold energies of >10s keV. Our previous work has already demonstrated that a new type of low-noise, low-threshold Avalanche Photo-Diode (APD) has an intrinsic noise level of 0.9 keV, and can therefore enable high-energy resolution measurements of suprathermal electrons and ions. In addition, APDs provide suitable solutions for space plasma detectors in low-cost missions/platform because of their light-weight, small-size, power-saving features. This study presents two low-cost missions (a sounding rocket and a CubeSat) that implement APDs as particle detectors: (1) The Medium-energy Electron SPectrometer (MESP) sensor aboard a sounding rocket was launched from Poker Flat Research Range on 3 March 2014 as a part of Ground-to-Rocket Electrodynamics-Electrons Correlative Experiment (GREECE) mission. MESP successfully measured the precipitating electrons from 2 to 200 keV in 100-ms time resolution by using 2 APDs and 1 SSD. We show the overall results and the comparison with an MCP-based instrument results. (2) The Miniaturized Electron and pRoton Telescope (MERiT) on the Compact Radiation bElt Explorer (CeREs) to study charged particle dynamics in the Earth's radiation belts. CeREs will be flown as part of a 3U CubeSat in a

  12. Pulse-resolved multi-photon X-ray detection at 31 MHz based on a quadrant avalanche photodiode

    PubMed Central

    Reusch, Tobias; Osterhoff, Markus; Agricola, Johannes; Salditt, Tim

    2014-01-01

    The technical realisation and the commissioning experiments of a high-speed X-ray detector based on a quadrant avalanche silicon photodiode and high-speed digitizers are described. The development is driven by the need for X-ray detectors dedicated to time-resolved diffraction and imaging experiments, ideally requiring pulse-resolved data processing at the synchrotron bunch repetition rate. By a novel multi-photon detection scheme, the exact number of X-ray photons within each X-ray pulse can be recorded. Commissioning experiments at beamlines P08 and P10 of the storage ring PETRA III, at DESY, Hamburg, Germany, have been used to validate the pulse-wise multi-photon counting scheme at bunch frequencies ≥31 MHz, enabling pulse-by-pulse readout during the PETRA III 240-bunch mode with single-photon detection capability. An X-ray flux of ≥3.7 × 109 photons s−1 can be detected while still resolving individual photons at low count rates. PMID:24971964

  13. Fast scintillation timing detector using proportional-mode avalanche photodiode for nuclear resonant scattering experiments in high-energy synchrotron X-ray region

    NASA Astrophysics Data System (ADS)

    Inoue, Keisuke; Kishimoto, Shunji

    2016-01-01

    To obtain both a high count rate of >107 s-1 and a detection efficiency sufficient for high-energy X-rays of >30 keV, we propose a scintillation timing detector using a proportional-mode silicon avalanche photodiode (Si-APD) for synchrotron radiation nuclear resonant scattering. We here present results obtained with a prototype detector using a lead-loaded plastic scintillator (EJ-256) mounted on a proportional-mode Si-APD (active area size: 3 mm in diameter). The detector was operated at ‒35 °C for a better signal-to-noise ratio. Using synchrotron X-rays of 67.41 keV, which is the same energy as the first excited level of 61Ni, we successfully measured pulse-height and time spectra of the scintillation light. A good time resolution of 0.50±0.06 ns (full width at half-maximum) was obtained for 67.41 keV X-rays with a scintillator 3 mm in diameter and 2 mm thick.

  14. Impact ionization in Al{sub x}Ga{sub 1−x}As{sub y}Sb{sub 1−y} avalanche photodiodes

    SciTech Connect

    Grzesik, M.; Donnelly, J.; Duerr, E.; Manfra, M.; Diagne, M.; Bailey, R.; Turner, G.; Goodhue, W.

    2014-04-21

    Avalanche photodiodes (APDs) have been fabricated in order to determine the impact ionization coefficients of electrons (α) and holes (β) in Al{sub x}Ga{sub 1−x}As{sub y}Sb{sub 1−y} lattice matched to GaSb for three alloy compositions: (x = 0.40, y = 0.035), (x = 0.55, y = 0.045), and (x = 0. 65, y = 0.054). The impact ionization coefficients were calculated from photomultiplication measurements made on specially designed APDs, which allowed for both pure electron and pure hole injection in the same device. Photo-multiplication measurements were made at temperatures ranging from 77 K to 300 K for all three alloys. A quasi-physical model with an explicit temperature dependence was used to express the impact ionization coefficients as a function of electric-field strength and temperature. For all three alloys, it was found that α < β at any given temperature. In addition, the values of the impact ionization coefficients were found to decrease as the aluminum concentration of the AlGaAsSb alloy was increased. A value between 1.2 and 4.0 was found for β/α, which is dependent on temperature, alloy composition, and electric-field strength.

  15. InGaAs/InP Avalanche Photodiode for Single Photon Detection with Zinc Diffusion Process Using Metal Organic Chemical Vapor Deposition.

    PubMed

    Lee, In Joon; Lee, Min Soo; Kim, Min Su; Jun, Dong-Hwan; Jeong, Hae Yong; Kim, Sangin; Han, Sang-wook; Moon, Sung

    2016-05-01

    In this paper, we describe a design, simulation, and fabrication of an InGaAs/InP single photon avalanche photodiode (SPAD), which requires a much higher gain, compared to APD's for conventional optical communications. To achieve a higher gain, an efficient multiplication width control is essential because it significantly affects the overall performance including not only gain but also noise characteristics. Normally, the multiplication layer width is controlled by the Zinc diffusion process. For the reliable and controllable diffusion process, we used metal organic chemical vapor deposition (MOCVD). The controllability of the proposed diffusion process is proved by the diffusion depth measurement of the fabricated devices which show the proportional dependence on the square root of the diffusion time. As a result, we successfully implemented the SPAD that exhibits a high gain enough to detect single photons and a very low dark current level of about 0.1 nA with 0.95 breakdown voltage. The single photon detection efficiency of 15% was measured at the 100 kHz gate pulse rate and the temperature of 230 K. PMID:27483891

  16. Characterization of a CsI(Tl) array coupled to avalanche photodiodes for the Barrel of the CALIFA calorimeter at the NEPTUN tagged gamma beam facility

    NASA Astrophysics Data System (ADS)

    Gascón, M.; Schnorrenberger, L.; Pietras, B.; Álvarez-Pol, H.; Cortina-Gil, D.; Díaz Fernández, P.; Duran, I.; Glorius, J.; González, D.; Perez-Loureiro, D.; Pietralla, N.; Savran, D.; Sonnabend, K.

    2013-10-01

    Among the variety of crystal calorimeters recently designed for several physics facilities, CALIFA (CALorimeter for In-Flight emitted gAmmas and light-charged particles) has especially demanding requirements since it must perform within a very complicated energy domain (gamma-ray energies from 0.1 to 20 MeV and up to 300 MeV protons). As part of the R&D program for the Barrel section of CALIFA, a reduced geometry prototype was constructed. This prototype consisted of a 3 × 5 array of CsI(Tl) crystals of varying dimensions, coupled to large area avalanche photodiodes. Here reported are the details regarding the construction of the prototype and the experimental results obtained at the NEPTUN tagged gamma beam facility, reconstructing gamma energies up to 10 MeV. Dedicated Monte Carlo simulations of the setup were also performed, enabling a deeper understanding of the experimental data. The experimental results demonstrate the effectiveness of the reconstruction method and helped to establish the most suitable crystal geometry to be employed within the forthcoming calorimeter.

  17. Pixel multiplexing technique for real-time three-dimensional-imaging laser detection and ranging system using four linear-mode avalanche photodiodes.

    PubMed

    Xu, Fan; Wang, Yuanqing; Li, Fenfang

    2016-03-01

    The avalanche-photodiode-array (APD-array) laser detection and ranging (LADAR) system has been continually developed owing to its superiority of nonscanning, large field of view, high sensitivity, and high precision. However, how to achieve higher-efficient detection and better integration of the LADAR system for real-time three-dimensional (3D) imaging continues to be a problem. In this study, a novel LADAR system using four linear mode APDs (LmAPDs) is developed for high-efficient detection by adopting a modulation and multiplexing technique. Furthermore, an automatic control system for the array LADAR system is proposed and designed by applying the virtual instrumentation technique. The control system aims to achieve four functions: synchronization of laser emission and rotating platform, multi-channel synchronous data acquisition, real-time Ethernet upper monitoring, and real-time signal processing and 3D visualization. The structure and principle of the complete system are described in the paper. The experimental results demonstrate that the LADAR system is capable of achieving real-time 3D imaging on an omnidirectional rotating platform under the control of the virtual instrumentation system. The automatic imaging LADAR system utilized only 4 LmAPDs to achieve 256-pixel-per-frame detection with by employing 64-bit demodulator. Moreover, the lateral resolution is ∼15 cm and range accuracy is ∼4 cm root-mean-square error at a distance of ∼40 m. PMID:27036763

  18. Four-layer depth-of-interaction PET detector for high resolution PET using a multi-pixel S8550 avalanche photodiode

    NASA Astrophysics Data System (ADS)

    Nishikido, Fumihiko; Inadama, Naoko; Oda, Ichiro; Shibuya, Kengo; Yoshida, Eiji; Yamaya, Taiga; Kitamura, Keishi; Murayama, Hideo

    2010-09-01

    Avalanche photodiodes (APDs) are being used as photodetectors in positron emission tomography (PET) because they have many advantages over photomultipliers (PMTs) typically used in PET detectors. We have developed a PET detector that consists of a multi-pixel APD and a 6×6×4 array of 1.46×1.46 mm 2×4.5 m LYSO crystals for a small animal PET scanner. The detector can identify four-layer depth of interaction (DOI) with a position-sensitive APD coupled to the backside of a crystal array by just an optimized reflector arrangement. Since scintillation lights are shared among many pixels by the method, weaker signals in APD pixels far from the interacting crystals are affected by noise. To evaluate the performance of the four-layer DOI detector with the APD and the influence of electrical noise on our method, we constructed a prototype DOI detector and tested its performance. We found, except for crystal elements on the edge of the crystal array, all crystal elements could be identified from the 2D position histogram. An energy resolution of 16.9% was obtained for the whole crystal array of the APD detector. The results of noise dependence of detector performances indicated that the DOI detector using the APD could achieve sufficient performance even when using application-specific integrated circuits.

  19. Time-resolved non-contact fluorescence diffuse optical tomography measurements with ultra-fast time-correlated single photon counting avalanche photodiodes

    NASA Astrophysics Data System (ADS)

    Bérubé-Lauzière, Yves; Robichaud, Vincent; Lapointe, Éric

    2007-07-01

    The design and fabrication of time-correlated single photon counting (TCSPC) avalanche photodiodes (APDs) and associated quenching circuits have made significant progresses in recent years. APDs with temporal resolutions comparable to microchannel plate photomultiplier tubes (MCP-PMTs) are now available. MCP-PMTs were until these progresses the best TCSPC detectors with timing resolutions down to 30ps. APDs can now achieve these resolutions at a fraction of the cost. Work is under way to make the manufacturing of TCSPC APDs compatible with standard electronics fabrication practices. This should allow to further reduce their cost and render them easier to integrate in complex multi-channel TCSPC electronics, as needed in diffuse optical tomography (DOT) systems. Even if their sensitive area is much smaller than that of the ubiquitous PMT used in TCSPC, we show that with appropriate selection of optical components, TCSPC APDs can be used in time-domain DOT. To support this, we present experimental data and calculations clearly demonstrating that comparable measurements can be obtained with APDs and PMTs. We are, to our knowledge, the first group using APDs in TD DOT, in particular in non-contact TD fluorescence DOT.

  20. Pixel multiplexing technique for real-time three-dimensional-imaging laser detection and ranging system using four linear-mode avalanche photodiodes

    NASA Astrophysics Data System (ADS)

    Xu, Fan; Wang, Yuanqing; Li, Fenfang

    2016-03-01

    The avalanche-photodiode-array (APD-array) laser detection and ranging (LADAR) system has been continually developed owing to its superiority of nonscanning, large field of view, high sensitivity, and high precision. However, how to achieve higher-efficient detection and better integration of the LADAR system for real-time three-dimensional (3D) imaging continues to be a problem. In this study, a novel LADAR system using four linear mode APDs (LmAPDs) is developed for high-efficient detection by adopting a modulation and multiplexing technique. Furthermore, an automatic control system for the array LADAR system is proposed and designed by applying the virtual instrumentation technique. The control system aims to achieve four functions: synchronization of laser emission and rotating platform, multi-channel synchronous data acquisition, real-time Ethernet upper monitoring, and real-time signal processing and 3D visualization. The structure and principle of the complete system are described in the paper. The experimental results demonstrate that the LADAR system is capable of achieving real-time 3D imaging on an omnidirectional rotating platform under the control of the virtual instrumentation system. The automatic imaging LADAR system utilized only 4 LmAPDs to achieve 256-pixel-per-frame detection with by employing 64-bit demodulator. Moreover, the lateral resolution is ˜15 cm and range accuracy is ˜4 cm root-mean-square error at a distance of ˜40 m.

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

    NASA Astrophysics Data System (ADS)

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

    2013-05-01

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

  2. Extending the Astronomical Application of Photon Counting HgCdTe Linear Avalanche Photo-Diode Arrays to Low Background Space Observations.

    NASA Astrophysics Data System (ADS)

    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

  3. Design of a silicon avalanche photodiode pixel with integrated laser diode using back-illuminated crystallographically etched silicon-on-sapphire with monolithically integrated microlens for dual-mode passive and active imaging arrays

    NASA Astrophysics Data System (ADS)

    Stern, Alvin G.

    2010-08-01

    There is a growing need in scientific research applications for dual-mode, passive and active 2D and 3D LADAR imaging methods. To fill this need, an advanced back-illuminated silicon avalanche photodiode (APD) design is presented using a novel silicon-on-sapphire substrate incorporating a crystalline aluminum nitride (AlN) antireflective layer between the silicon and R-plane sapphire. This allows integration of a high quantum efficiency silicon APD with a gallium nitride (GaN) laser diode in each pixel. The pixel design enables single photon sensitive, solid-state focal plane arrays (FPAs) with wide dynamic range, supporting passive and active imaging capability in a single FPA. When (100) silicon is properly etched with TMAH solution, square based pyramidal frustum or mesa arrays result with the four mesa sidewalls of the APD formed by (111) silicon planes that intersect the (100) planes at a crystallographic angle, φ c = 54.7°. The APD device is fabricated in the mesa using conventional silicon processing technology. The GaN laser diode is fabricated by epitaxial growth inside of an inverted, etched cavity in the silicon mesa. Microlenses are fabricated in the thinned, and AR-coated sapphire substrate. The APDs share a common, front-side anode contact, and laser diodes share a common cathode. A low resistance (Al) or (Cu) metal anode grid fills the space between pixels and also inhibits optical crosstalk. SOS-APD arrays are flip-chip bump-bonded to CMOS readout ICs to produce hybrid FPAs. The square 27 μm emitter-detector pixel achieves SNR > 1 in active detection mode for Lambert surfaces at 1,000 meters.

  4. Recent Advances of The Sh-theory of Avalanching Motions

    NASA Astrophysics Data System (ADS)

    Pudasaini, S. P.; Hutter, K.

    The Savage-Hutter (SH)-Theory of the gravity driven avalanching motion of a finite mass of cohesionless granular material has in 1989 been derived for 2D chute flows with free surface. Its physical basis is the density preserving fluid obeying Mohr- Coulomb internal friction and an equivalent law for basal sliding. The internal friction angle, , and the basal friction angle, , with are the only phenomenological coefficients of the model. The governing equations are formulated in a curvilinear co- ordinate system, and a von Karman-Polhausen procedure is used to deduce thickness ´ ´ averaged equations for the time and space evolution of the avalanche depth and the velocity profile. Extensions of the SH-theory to model 3D free surface flows subject to gravity have been derived for generalisations using an orthogonal metric in which the coordinate lines in the downhill direction are curved but not twisted. These formulations allow reproduction of the flow down a straight channel merging into a horizontal plane and yield a fair reproduction when being compared with laboratory experiments. We have recently derived model equations for a free gravity flow of granular mate- rials down a chute whose talweg follows a helical curve with constant pitch as well as channels generated by arbitrary space curves with slowly varying curvature and torsion. These are very important extensions to the original SH-theory. Two different metrics are used. For the first case we use a non-orthogonal and for the second an orthogonal metric. The depth averaged equations are deduced for both cases. Semi- analytical similarity solutions have been found to test the model equations. All equations derived from these extensions of the SH model are a hyperbolic system of PDEs with possibly discontinuous coefficients. Numerical integration schemes must be shock-capturing. We explain the integration procedure and shall present the results (provided the program works by the time of the conference).

  5. Development of long-wavelength avalanche photodiodes and vertical-cavity lasers for epitaxial integration as a vertical-cavity photon number amplifier

    NASA Astrophysics Data System (ADS)

    Huntington, Andrew Sumika

    The goal of this research was to develop technology for building a vertical-geometry photon number amplifier (vertical PNA) that operates at a wavelength in the low-absorption window for optical fibers near 1.55 mum. An optical amplifier of this design would provide electrically-tappable low-noise polarization-independent optical amplification of laser pulses and serve as a stepping stone toward development of a tunable amplifying wavelength converter. The vertical PNA design consists of a multiple active region (MAR) VCSEL integrated with an avalanche photodiode of the separate absorption, charge, and multiplication layer design (SACM APD): the VCSEL is intended to operate continuous wave (CW), modulated by the APD. Both components were selected for their high gain: in excess of 10 electrons out per photon in for the APD, and slightly more than 1 photon out per electron in for the MAR VCSEL under ideal circumstances. In working toward the vertical PNA, significant technical challenges were addressed: (1) Development of a long-wavelength MAR VCSEL capable of high-temperature CW operation. Although this goal was never achieved, efforts directed to this end resulted in an investigation of basic material science issues that are vital to future improvements of the device. Better DBR and active region designs were developed, the overall thermal impedance of the structure was reduced significantly, a rudimentary optical aperture compatible with InP-based materials was tested, and loss estimates for the device were put on solid ground. (2) Development of a low-noise SACM APD capable of modulating the MAR VCSEL at high speed. Here the vital relationships between growth conditions, material quality, and APD performance were established. Other achievements include demonstration of highly uniform arrays of these devices, extremely low-noise operation, and the largest area long-wavelength APDs ever reported. (3) Successful demonstration of the epitaxial integration of these

  6. Development of the HgCdTe Avalanche Photodiode Detectors and the Improvement in the CO2 Lidar Performance for the ASCENDS Mission

    NASA Astrophysics Data System (ADS)

    Sun, X.; Abshire, J. B.; Chen, J. R.; Ramanathan, A. K.; Mao, J.

    2015-12-01

    NASA Goddard Space Flight Center (GSFC) is developing the CO2 lidar as a candidate for the NASA's planned ASCENDS mission under the support of Earth Science Technology Office (ESTO) IIP and ATI-QRS programs. A new type of HgCdTe avalanche photodiode (APD) detector has been developed by the DRS Technologies under the IIP program. The new detectors achieved >70% quantum efficiency, including the effect of the fill factor, over the spectral range from 0.4 to 4.3 μm, which significantly improves the receiver performance of our CO2 lidar and enabled other remote sending measurements. The HgCdTe APD arrays have 80 μm square pixels in a 4x4 array along with a bank of 16 preamplifiers on the same chip carrier. Test results at both DRS and GSFC showed the HgCdTe APD array has achieved, an APD gain of 500-1000, 8-10 MHz electrical bandwidth, and an average noise equivalent power (NEP) of <0.5 fW/Hz1/2. It has demonstrated at least a 3 orders of magnitude dynamic range at a fixed APD gain setting. The gains of the APD and the preamplifier can also be adjusted to further extend the receiver dynamic range. During summer 2014 we successfully demonstrated airborne lidar measurements of column CO2 using one of these detectors. The Aerospace Corporation is currently building a 3U CubeSat with one of these detectors in a small closed-cycle cryocooler as the primary payload under the ESTO In-space Validation of Earth Science Technology (InVEST) program. The CubeSat is scheduled to be launched in late 2016 and will fly in a low Earth orbit and monitor the performance for at least a year. We have also updated the performance analysis of a space-based version of our CO2 lidar with the new HgCdTe APD detector. For the retrievals, a least-square-error method is used to fit the measured transmittances to a predetermined line shape function using 8 to 16 sampling wavelengths. The error in the derived total optical depth and the CO2 mixing ratio are estimated via the standard error

  7. Performance of OOK and low-order PPM modulations in optical communications when using APD-based receivers. [Off-On Keying and Pulse Position Modulation using Avalanche PhotoDiodes

    NASA Technical Reports Server (NTRS)

    Abshire, J. B.

    1984-01-01

    The paper computes direct detection laser communications receiver performance when using avalanche photodiode (APD) detectors. The performances are compared in terms of bit error probability vs average signal required per bit when the transmitter uses either on-off keying (OOK) or low-order PPM formats. It is shown that QPPM requires 3 dB less signal than OOK, while BPPM requires the same or slightly more than OOK for the same performance. Optimum APD gain values range from 200 to 400. When using QPPM, k(eff) = 0.006, and optimum gain, 60 signal counts/bit are required at 500 Mbits/s for a 0.000001 bit error probability. It is concluded that QPPM may be an attractive signaling format for some fiber or free space laser communication applications.

  8. An Acoustic Charge Transport Imager for High Definition Television Applications: Reliability Modeling and Parametric Yield Prediction of GaAs Multiple Quantum Well Avalanche Photodiodes. Degree awarded Oct. 1997

    NASA Technical Reports Server (NTRS)

    Hunt, W. D.; Brennan, K. F.; Summers, C. J.; Yun, Ilgu

    1994-01-01

    Reliability modeling and parametric yield prediction of GaAs/AlGaAs multiple quantum well (MQW) avalanche photodiodes (APDs), which are of interest as an ultra-low noise image capture mechanism for high definition systems, have been investigated. First, the effect of various doping methods on the reliability of GaAs/AlGaAs multiple quantum well (MQW) avalanche photodiode (APD) structures fabricated by molecular beam epitaxy is investigated. Reliability is examined by accelerated life tests by monitoring dark current and breakdown voltage. Median device lifetime and the activation energy of the degradation mechanism are computed for undoped, doped-barrier, and doped-well APD structures. Lifetimes for each device structure are examined via a statistically designed experiment. Analysis of variance shows that dark-current is affected primarily by device diameter, temperature and stressing time, and breakdown voltage depends on the diameter, stressing time and APD type. It is concluded that the undoped APD has the highest reliability, followed by the doped well and doped barrier devices, respectively. To determine the source of the degradation mechanism for each device structure, failure analysis using the electron-beam induced current method is performed. This analysis reveals some degree of device degradation caused by ionic impurities in the passivation layer, and energy-dispersive spectrometry subsequently verified the presence of ionic sodium as the primary contaminant. However, since all device structures are similarly passivated, sodium contamination alone does not account for the observed variation between the differently doped APDs. This effect is explained by the dopant migration during stressing, which is verified by free carrier concentration measurements using the capacitance-voltage technique.

  9. Effect of atmospheric turbulence on the bit error probability of a space to ground near infrared laser communications link using binary pulse position modulation and an avalanche photodiode detector

    NASA Technical Reports Server (NTRS)

    Safren, H. G.

    1987-01-01

    The effect of atmospheric turbulence on the bit error rate of a space-to-ground near infrared laser communications link is investigated, for a link using binary pulse position modulation and an avalanche photodiode detector. Formulas are presented for the mean and variance of the bit error rate as a function of signal strength. Because these formulas require numerical integration, they are of limited practical use. Approximate formulas are derived which are easy to compute and sufficiently accurate for system feasibility studies, as shown by numerical comparison with the exact formulas. A very simple formula is derived for the bit error rate as a function of signal strength, which requires only the evaluation of an error function. It is shown by numerical calculations that, for realistic values of the system parameters, the increase in the bit error rate due to turbulence does not exceed about thirty percent for signal strengths of four hundred photons per bit or less. The increase in signal strength required to maintain an error rate of one in 10 million is about one or two tenths of a db.

  10. Performance assessment of simulated 3D laser images using Geiger-mode avalanche photo-diode: tests on simple synthetic scenarios

    NASA Astrophysics Data System (ADS)

    Coyac, Antoine; Hespel, Laurent; Riviere, Nicolas; Briottet, Xavier

    2015-10-01

    In the past few decades, laser imaging has demonstrated its potential in delivering accurate range images of objects or scenes, even at long range or under bad weather conditions (rain, fog, day and night vision). We note great improvements in the conception and development of single and multi infrared sensors, concerning embedability, circuitry reading capacity, or pixel resolution and sensitivity, allowing a wide diversity of applications (i.e. enhanced vision, long distance target detection and reconnaissance, 3D DSM generation). Unfortunately, it is often difficult to dispose of all the instruments to compare their performance for a given application. Laser imaging simulation has shown to be an interesting alternative to acquire real data, offering a higher flexibility to perform this sensors comparison, plus being time and cost efficient. In this paper, we present a 3D laser imaging end-to-end simulator using a focal plane array with Geiger mode detection, named LANGDOC. This work aims to highlight the interest and capability of this new generation of photo-diodes arrays, especially for airborne mapping and surveillance of high risk areas.

  11. Germanium avalanche receiver for low power interconnects

    NASA Astrophysics Data System (ADS)

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

    2014-09-01

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

  12. Low-cost SWIR sensors: advancing the performance of ROIC-integrated colloidal quantum dot photodiode arrays

    NASA Astrophysics Data System (ADS)

    Klem, Ethan J. D.; Lewis, Jay; Gregory, Chris; Temple, Dorota; Wijewarnasuriya, Priyalal S.; Dhar, Nibir

    2014-06-01

    RTI has developed a novel photodiode technology based on solution-processed PbS colloidal quantum dots (CQD) capable of providing low-cost, high performance detection across the Vis-SWIR spectral range. The most significant advantages of the CQD technology are ease of fabrication, small pixel size, and extended wavelength range. The devices are fabricated directly onto the ROIC substrate at low temperatures compatible with CMOS, and arrays can be fabricated at wafer scale. We will discuss recent advances in device architecture and processing that result in measured dark currents of 15 nA/cm2 at room temperature and enhanced SWIR responsivity from the UV to ~1.7 μm, compare these results to InGaAs detectors, and present measurements of the CQD detectors temperature dependent dark current.

  13. A wide spectral range single-photon avalanche diode fabricated in an advanced 180 nm CMOS technology.

    PubMed

    Mandai, Shingo; Fishburn, Matthew W; Maruyama, Yuki; Charbon, Edoardo

    2012-03-12

    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 4 V, with 30 % PDP at wavelengths from 520 nm to 720 nm. Dark count rates (DCR) are at most 5 kHz, which is 30 Hz/μm2, at an excess bias of 4V when we measure 10 μm diameter active area structure. Afterpulsing probability, timing jitter, and temperature effects on DCR are also presented. PMID:22418462

  14. Laser Light Scattering, from an Advanced Technology Development Program to Experiments in a Reduced Gravity Environment

    NASA Technical Reports Server (NTRS)

    Meyer, William V.; Tscharnuter, Walther W.; Macgregor, Andrew D.; Dautet, Henri; Deschamps, Pierre; Boucher, Francois; Zuh, Jixiang; Tin, Padetha; Rogers, Richard B.; Ansari, Rafat R.

    1994-01-01

    Recent advancements in laser light scattering hardware are described. These include intelligent single card correlators; active quench/active reset avalanche photodiodes; laser diodes; and fiber optics which were used by or developed for a NASA advanced technology development program. A space shuttle experiment which will employ aspects of these hardware developments is previewed.

  15. Advanced modeling of electron avalanche process in polymeric dielectric voids: Simulations and experimental validation

    NASA Astrophysics Data System (ADS)

    Testa, L.; Serra, S.; Montanari, G. C.

    2010-08-01

    This paper deals with aging phenomena in polymers under electric stress. In particular, we focus our efforts on the development of a novel theoretical method accounting for the discharge process (partial discharge) in well known defects present in polymers, which are essentially tiny air gaps embedded in a polymeric matrix. Such defects are believed to act as trigger points for the partial discharges and their induced aging process. The model accounts for the amplitude as well as the energy distribution of the electrons during their motion, particularly at the time in which they impact on the polymer surface. The knowledge of the number of generated electrons and of their energy distributions is fundamental to evaluate the amount of damage caused by an avalanche on the polymer-void interface and get novel insights of the basic phenomena underlying the relevant aging processes. The calculation of such quantities would require generally the combined solution of the Boltzmann equation in the energy and space/time domains. The proposed method simplifies the problem, taking into account only the main phenomena involved in the process and provides a partial discharge (PD) model virtually free of adjustable parameters. This model is validated by an accurate experimental procedure aimed at reproducing the same conditions of the simulations and regarding air gaps embedded in polymeric dielectrics. The experimental results confirm the validity and accuracy of the proposed approach.

  16. High-optical-power handling InGaAs photodiodes and balanced receivers for high-spurious free dynamic range (SFDR) analog photonic links

    NASA Astrophysics Data System (ADS)

    Joshi, Abhay M.; Wang, Xinde; Mohr, Dan; Becker, Donald; Patil, Ravikiran

    2004-08-01

    We have developed 20 mA or higher photocurrent handling InGaAs photodiodes with 20 GHz bandwidth, and 10 mA or higher photocurrent handling InGaAs photodiodes with >40 GHz bandwidth. These photodiodes have been thoroughly tested for reliability including Bellcore GR 468 standard and are built to ISO 9001:2000 Quality Management System. These Dual-depletion InGaAs/InP photodiodes are surface illuminated and yet handle such large photocurrent due to advanced band-gap engineering. They have broad wavelength coverage from 800 nm to 1700 nm, and thus can be used at several wavelengths such as 850 nm, 1064 nm, 1310 nm, 1550 nm, and 1620 nm. Furthermore, they exhibit very low Polarization Dependence Loss of 0.05dB typical to 0.1dB maximum. Using above high current handling photodiodes, we have developed classical Push-Pull pair balanced photoreceivers for the 2 to 18 GHz EW system. These balanced photoreceivers boost the Spurious Free Dynamic Range (SFDR) by almost 3 dB by eliminating the laser RIN noise. Future research calls for designing an Avalanche Photodiode Balanced Pair to boost the SFDR even further by additional 3 dB. These devices are a key enabling technology in meeting the SFDR requirements for several DoD systems.

  17. Using Photodiodes in the Laboratory.

    ERIC Educational Resources Information Center

    Jenkins, T. E.

    1995-01-01

    Describes the most popular optical detector in the design of photodiode detector circuits. Discusses how a photodiode works, points to consider in the design of a photodiode, and photodiode hybrids. (AIM)

  18. [Avalanche accidents and treatment of avalanche victims].

    PubMed

    Skaiaa, Sven Christjar; Thomassen, Øyvind

    2016-03-15

    Avalanches may be provoked spontaneously or as a result of human activity, and they trigger the need for considerable rescue resources. Avalanche search and rescue operations are complex and characterised by physical and mental stress. The guidelines for resuscitation of avalanche victims may be perceived as complex and abstruse, which can lead to suboptimal treatment and an increased strain on rescue teams. The purpose of this article is to summarise the principles for medical treatment of avalanche victims. PMID:26983147

  19. Dust Avalanches

    NASA Technical Reports Server (NTRS)

    2003-01-01

    [figure removed for brevity, see original site]

    Crater wall dust avalanches in southern Arabia Terra.

    Note: this THEMIS visual image has not been radiometrically nor geometrically calibrated for this preliminary release. An empirical correction has been performed to remove instrumental effects. A linear shift has been applied in the cross-track and down-track direction to approximate spacecraft and planetary motion. Fully calibrated and geometrically projected images will be released through the Planetary Data System in accordance with Project policies at a later time.

    NASA's Jet Propulsion Laboratory manages the 2001 Mars Odyssey mission for NASA's Office of Space Science, Washington, D.C. The Thermal Emission Imaging System (THEMIS) was developed by Arizona State University, Tempe, in collaboration with Raytheon Santa Barbara Remote Sensing. The THEMIS investigation is led by Dr. Philip Christensen at Arizona State University. Lockheed Martin Astronautics, Denver, is the prime contractor for the Odyssey project, and developed and built the orbiter. Mission operations are conducted jointly from Lockheed Martin and from JPL, a division of the California Institute of Technology in Pasadena.

    Image information: VIS instrument. Latitude 10.3, Longitude 24.5 East (335.5 West). 19 meter/pixel resolution.

  20. Seismic signal of avalanches

    NASA Astrophysics Data System (ADS)

    Pesaresi, Damiano; Ravanat, Xavier; Thibert, Emmanuel

    2010-05-01

    The characterization of avalanches with seismic signals is an important task. For risk mitigation, estimating remotely avalanche activity by means of seismic signals is a good alternative to direct observations that are often limited by visual conditions and observer's availability. In seismology, the main challenge is to discriminate avalanche signals within the natural earth seismic activity and background noise. Some anthropogenic low frequency (infra-sound) sources like helicopters also generate seismic signals. In order to characterize an avalanche seismic signal, a 3-axis broad band seismometer (Guralp 3T) has been set-up on a real scale avalanche test site in Lautaret (France). The sensor is located in proximity of 2 avalanche paths where avalanches can be artificially released. Preliminary results of seismic records are presented, correlated with avalanche physical parameters (volume released, velocity, energy).

  1. Negative Avalanche Feedback Detectors for Photon-Counting Optical Communications

    NASA Technical Reports Server (NTRS)

    Farr, William H.

    2009-01-01

    Negative Avalanche Feedback photon counting detectors with near-infrared spectral sensitivity offer an alternative to conventional Geiger mode avalanche photodiode or phototube detectors for free space communications links at 1 and 1.55 microns. These devices demonstrate linear mode photon counting without requiring any external reset circuitry and may even be operated at room temperature. We have now characterized the detection efficiency, dark count rate, after-pulsing, and single photon jitter for three variants of this new detector class, as well as operated these uniquely simple to use devices in actual photon starved free space optical communications links.

  2. Characterization of an advanced harmonic subtraction single-photon detection system based on an InGaAs/InP avalanche diode

    NASA Astrophysics Data System (ADS)

    Bienfang, Joshua C.; Restelli, Alessandro

    2016-05-01

    We discuss the performance of a 1.25 GHz gated single-photon avalanche diode (SPAD) with bias gates of 150 ps FWHM and AC amplitude up to 25 V, a high-efficiency, high-speed SPAD system. This system uses an interferometric readout technique known as harmonic subtraction, and recent development efforts have enabled the use of up to the 4th harmonic of the gate to discriminate avalanche signals from the gate transient. With an improved design of the RF control system we have been able to demonstrate an ultra-low minimum detectable charge. We discuss the performance of this system, particularly its afterpulsing performance when counting at rates > 108 s-1. Systems of this type require unique characterization techniques, and we will discuss the methods we have developed for this purpose.

  3. Compact model for non-local avalanche effect in advanced bipolar transistors: An assessment of the relaxation length and its temperature dependence

    NASA Astrophysics Data System (ADS)

    Setekera, Robert; van der Toorn, Ramses

    2016-05-01

    We present a physics based compact model formulation for non-local avalanche effects. It is explicit and in terms of elementary functions, hence suitable for implementation in existing compact transistor models. The formulation has only two material coefficients as parameters: the energy relaxation length and its temperature coefficient. We present a detailed verification of our model against measured avalanche characteristics, as a function of both bias and temperature, for Si and SiGe industrial bipolar transistors. We demonstrate that the model is complete and accurate enough for the parameter extraction to be taken as an in situ measurement for both the electron energy relaxation length and its temperature coefficient: values obtained correspond to the values published earlier in the semiconductor literature.

  4. Angle sensitive single photon avalanche diode

    SciTech Connect

    Lee, Changhyuk Johnson, Ben Molnar, Alyosha

    2015-06-08

    An ideal light sensor would provide exact information on intensity, timing, location, and angle of incoming photons. Single photon avalanche diodes (SPADs) provide such desired high (single photon) sensitivity with precise time information and can be implemented at a pixel-scale to form an array to extract spatial information. Furthermore, recent work has demonstrated photodiode-based structures (combined with micro-lenses or diffraction gratings) that are capable of encoding both spatial and angular information of incident light. In this letter, we describe the implementation of such a grating structure on SPADs to realize a pixel-scale angle-sensitive single photon avalanche diode (A-SPAD) built in a standard CMOS process. While the underlying SPAD structure provides high sensitivity, the time information of the two layers of diffraction gratings above offers angle-sensitivity. Such a unique combination of SPAD and diffraction gratings expands the sensing dimensions to pave a path towards lens-less 3-D imaging and light-field time-of-flight imaging.

  5. Dune Avalanche Scars

    NASA Technical Reports Server (NTRS)

    2004-01-01

    05 August 2004 This Mars Global Surveyor (MGS) Mars Orbiter Camera (MOC) image shows large, low albedo (dark) sand dunes in Kaiser Crater near 47.2oS, 340.4oW. The dunes are--ever so slowly--moving east to west (right to left) as sand avalanches down the steeper, slip face slopes of each. Avalanching sand in the Kaiser dune field has left deep scars on these slopes, suggesting that the sand is not loose but is instead weakly cemented. The image covers an area approximately 3 km (1.9 mi) wide and is illuminated by sunlight from the upper left.

  6. Avalanches in Wood Compression.

    PubMed

    Mäkinen, T; Miksic, A; Ovaska, M; Alava, Mikko J

    2015-07-31

    Wood is a multiscale material exhibiting a complex viscoplastic response. We study avalanches in small wood samples in compression. "Woodquakes" measured by acoustic emission are surprisingly similar to earthquakes and crackling noise in rocks and laboratory tests on brittle materials. Both the distributions of event energies and of waiting (silent) times follow power laws. The stress-strain response exhibits clear signatures of localization of deformation to "weak spots" or softwood layers, as identified using digital image correlation. Even though material structure-dependent localization takes place, the avalanche behavior remains scale-free. PMID:26274428

  7. Inverse avalanches on Abelian sandpiles

    SciTech Connect

    Chau, H.F. Department of Physics, University of Illinois at Urbana-Champaign, 1110 West Green Street, Urbana, Illinois 61801-3080 )

    1994-11-01

    A simple and computationally efficient way of finding inverse avalanches for Abelian sandpiles, called the inverse particle addition operator, is presented. In addition, the method is shown to be optimal in the sense that it requires the minimum amount of computation among methods of the same kind. The method is also conceptually succinct because avalanche and inverse avalanche are placed in the same footing.

  8. Reuyl Crater Dust Avalanches

    NASA Technical Reports Server (NTRS)

    2002-01-01

    (Released 13 May 2002) The Science The rugged, arcuate rim of the 90 km crater Reuyl dominates this THEMIS image. Reuyl crater is at the southern edge of a region known to be blanketed in thick dust based on its high albedo (brightness) and low thermal inertia values. This thick mantle of dust creates the appearance of snow covered mountains in the image. Like snow accumulation on Earth, Martian dust can become so thick that it eventually slides down the face of steep slopes, creating runaway avalanches of dust. In the center of this image about 1/3 of the way down is evidence of this phenomenon. A few dozen dark streaks can be seen on the bright, sunlit slopes of the crater rim. The narrow streaks extend downslope following the local topography in a manner very similar to snow avalanches on Earth. But unlike their terrestrial counterparts, no accumulation occurs at the bottom. The dust particles are so small that they are easily launched into the thin atmosphere where they remain suspended and ultimately blow away. The apparent darkness of the avalanche scars is due to the presence of relatively dark underlying material that becomes exposed following the passage of the avalanche. Over time, new dust deposition occurs, brightening the scars until they fade into the background. Although dark slope streaks had been observed in Viking mission images, a clear understanding of this dynamic phenomenon wasn't possible until the much higher resolution images from the Mars Global Surveyor MOC camera revealed the details. MOC images also showed that new avalanches have occurred during the time MGS has been in orbit. THEMIS images will allow additional mapping of their distribution and frequency, contributing new insights about Martian dust avalanches. The Story The stiff peaks in this image might remind you of the Alps here on Earth, but they really outline the choppy edge of a large Martian crater over 50 miles wide (seen in the context image at right). While these aren

  9. High speed, high performance /Hg,Cd/Te photodiode detectors.

    NASA Technical Reports Server (NTRS)

    Soderman, D. A.; Pinkston, W. H.

    1972-01-01

    The current performance of high speed photodiode detectors for the 1 to 10 micron spectral region is discussed. The (Hg,Cd)Te photodiode configuration, detector properties, integration in laser receiver modules, and frequency response are considered for near infrared and far infrared wavelengths. The recent advances in (Hg,Cd)Te material and device development are indicated by the realization not only of exceptionally high speed detectors but of detectors that exhibit excellent detectivities. The performance improves substantially when the detector is cooled. This detector junction technology has been extended to other compositions of (Hg,Cd)Te for peak spectral responses at 5 and 10 micron.

  10. Hebes Chasma Dust Avalanches

    NASA Technical Reports Server (NTRS)

    2005-01-01

    [figure removed for brevity, see original site]

    Dust avalanches, also called slope streaks, occur on many Martian terrains. The deposition of airborne dust on surfaces causes a bright tone in the THEMIS VIS images. Any movement of the dust downhill, a dust avalanche, will leave behind a streak where the darker, dust-free surface is exposed.

    These dust avalanches are located in Hebes Chasma.

    Image information: VIS instrument. Latitude -1.4, Longitude 286.6 East (73.4 West). 17 meter/pixel resolution.

    Note: this THEMIS visual image has not been radiometrically nor geometrically calibrated for this preliminary release. An empirical correction has been performed to remove instrumental effects. A linear shift has been applied in the cross-track and down-track direction to approximate spacecraft and planetary motion. Fully calibrated and geometrically projected images will be released through the Planetary Data System in accordance with Project policies at a later time.

    NASA's Jet Propulsion Laboratory manages the 2001 Mars Odyssey mission for NASA's Office of Space Science, Washington, D.C. The Thermal Emission Imaging System (THEMIS) was developed by Arizona State University, Tempe, in collaboration with Raytheon Santa Barbara Remote Sensing. The THEMIS investigation is led by Dr. Philip Christensen at Arizona State University. Lockheed Martin Astronautics, Denver, is the prime contractor for the Odyssey project, and developed and built the orbiter. Mission operations are conducted jointly from Lockheed Martin and from JPL, a division of the California Institute of Technology in Pasadena.

  11. Supraglacial rock avalanches and their effect on glacial deposition

    NASA Astrophysics Data System (ADS)

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

    2012-04-01

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

  12. 10Be cosmic-ray exposure dating of moraines and rock avalanches in the Upper Romanche valley (French Alps): Evidence of two glacial advances during the Late Glacial/Holocene transition

    NASA Astrophysics Data System (ADS)

    Chenet, Marie; Brunstein, Daniel; Jomelli, Vincent; Roussel, Erwan; Rinterknecht, Vincent; Mokadem, Fatima; Biette, Melody; Robert, Vincent; Léanni, Laëtitia

    2016-09-01

    Cosmic-ray exposure (CRE) dating of moraines allow glacier fluctuations and past climate change reconstructions. In the French Alps, there is a lack of moraine dating for the Late Glacial/Holocene transition period. Here we present a chronology of glacier advances in the Upper Romanche valley (French Alps - Massif des Ecrins) based on 10Be CRE dating. CRE ages of moraines of 13.0 ± 1.1 ka and 12.4 ± 1.5 ka provide evidence for two stages of glacial advance or standstill at the end of the Late Glacial. The CRE dating of a rock avalanche deposit at 12.2 ± 1.5 ka is attributed to post-glacial debuttressing and reveals rapid deglaciation at the end of the Late Glacial. A CRE age of 7.1 ± 0.7 ka of a second mass-wasting, whose triggering factor is unidentified so far, indicates that up to an altitude of 2300 m a.s.l., the valley was ice-free as of ∼7 kyr at the latest. The re-evaluation of 21 moraine 10Be CRE ages from nine glacial valleys across the Alps shows multiple glacial advances occurring at the Late Glacial/Holocene transition. These results lead to a re-evaluation of the importance of cooling events during the Allerød and the Younger Dryas in the Alps.

  13. Advanced Atmospheric Water Vapor DIAL Detection System

    NASA Technical Reports Server (NTRS)

    Refaat, Tamer F.; Elsayed-Ali, Hani E.; DeYoung, Russell J. (Technical Monitor)

    2000-01-01

    Measurement of atmospheric water vapor is very important for understanding the Earth's climate and water cycle. The remote sensing Differential Absorption Lidar (DIAL) technique is a powerful method to perform such measurement from aircraft and space. This thesis describes a new advanced detection system, which incorporates major improvements regarding sensitivity and size. These improvements include a low noise advanced avalanche photodiode detector, a custom analog circuit, a 14-bit digitizer, a microcontroller for on board averaging and finally a fast computer interface. This thesis describes the design and validation of this new water vapor DIAL detection system which was integrated onto a small Printed Circuit Board (PCB) with minimal weight and power consumption. Comparing its measurements to an existing DIAL system for aerosol and water vapor profiling validated the detection system.

  14. A theoretical study of improved front-illuminated avalanche drift detectors

    NASA Astrophysics Data System (ADS)

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

    2013-06-01

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

  15. Tikhonravov Crater Dust Avalanches

    NASA Technical Reports Server (NTRS)

    2005-01-01

    [figure removed for brevity, see original site]

    Dust avalanches, also called slope streaks, occur on many Martian terrains. The deposition of airborne dust on surfaces causes a bright tone in the THEMIS VIS images. Any movement of the dust downhill, a dust avalanche, will leave behind a streak where the darker, dust-free surface is exposed.

    These dust avalanches are located within a small crater inside Tikhonravov Crater.

    Image information: VIS instrument. Latitude 12.6, Longitude 37.1 East (322.9 West). 36 meter/pixel resolution.

    Note: this THEMIS visual image has not been radiometrically nor geometrically calibrated for this preliminary release. An empirical correction has been performed to remove instrumental effects. A linear shift has been applied in the cross-track and down-track direction to approximate spacecraft and planetary motion. Fully calibrated and geometrically projected images will be released through the Planetary Data System in accordance with Project policies at a later time.

    NASA's Jet Propulsion Laboratory manages the 2001 Mars Odyssey mission for NASA's Office of Space Science, Washington, D.C. The Thermal Emission Imaging System (THEMIS) was developed by Arizona State University, Tempe, in collaboration with Raytheon Santa Barbara Remote Sensing. The THEMIS investigation is led by Dr. Philip Christensen at Arizona State University. Lockheed Martin Astronautics, Denver, is the prime contractor for the Odyssey project, and developed and built the orbiter. Mission operations are conducted jointly from Lockheed Martin and from JPL, a division of the California Institute of Technology in Pasadena.

  16. Lycus Sulci Dust Avalanches

    NASA Technical Reports Server (NTRS)

    2005-01-01

    [figure removed for brevity, see original site]

    Dust avalanches, also called slope streaks, occur on many Martian terrains. The deposition of airborne dust on surfaces causes a bright tone in the THEMIS VIS images. Any movement of the dust downhill, a dust avalanche, will leave behind a streak where the darker, dust-free surface is exposed.

    These dust avalanches occur on the slopes of Lycus Sulci near Olympus Mons.

    Image information: VIS instrument. Latitude 28.1, Longitude 220.4 East (139.6 West). 18 meter/pixel resolution.

    Note: this THEMIS visual image has not been radiometrically nor geometrically calibrated for this preliminary release. An empirical correction has been performed to remove instrumental effects. A linear shift has been applied in the cross-track and down-track direction to approximate spacecraft and planetary motion. Fully calibrated and geometrically projected images will be released through the Planetary Data System in accordance with Project policies at a later time.

    NASA's Jet Propulsion Laboratory manages the 2001 Mars Odyssey mission for NASA's Office of Space Science, Washington, D.C. The Thermal Emission Imaging System (THEMIS) was developed by Arizona State University, Tempe, in collaboration with Raytheon Santa Barbara Remote Sensing. The THEMIS investigation is led by Dr. Philip Christensen at Arizona State University. Lockheed Martin Astronautics, Denver, is the prime contractor for the Odyssey project, and developed and built the orbiter. Mission operations are conducted jointly from Lockheed Martin and from JPL, a division of the California Institute of Technology in Pasadena.

  17. Crater Dust Avalanches

    NASA Technical Reports Server (NTRS)

    2005-01-01

    [figure removed for brevity, see original site]

    Dust avalanches, also called slope streaks, occur on many Martian terrains. The deposition of airborne dust on surfaces causes a bright tone in the THEMIS VIS images. Any movement of the dust downhill, a dust avalanche, will leave behind a streak where the darker, dust-free surface is exposed.

    These dust avalanches are located in a small canyon within a crater rim northeast of Naktong Vallis.

    Image information: VIS instrument. Latitude 7.1, Longitude 34.7 East (325.3 West). 17 meter/pixel resolution.

    Note: this THEMIS visual image has not been radiometrically nor geometrically calibrated for this preliminary release. An empirical correction has been performed to remove instrumental effects. A linear shift has been applied in the cross-track and down-track direction to approximate spacecraft and planetary motion. Fully calibrated and geometrically projected images will be released through the Planetary Data System in accordance with Project policies at a later time.

    NASA's Jet Propulsion Laboratory manages the 2001 Mars Odyssey mission for NASA's Office of Space Science, Washington, D.C. The Thermal Emission Imaging System (THEMIS) was developed by Arizona State University, Tempe, in collaboration with Raytheon Santa Barbara Remote Sensing. The THEMIS investigation is led by Dr. Philip Christensen at Arizona State University. Lockheed Martin Astronautics, Denver, is the prime contractor for the Odyssey project, and developed and built the orbiter. Mission operations are conducted jointly from Lockheed Martin and from JPL, a division of the California Institute of Technology in Pasadena.

  18. Crater Dust Avalanches

    NASA Technical Reports Server (NTRS)

    2005-01-01

    [figure removed for brevity, see original site]

    Dust avalanches, also called slope streaks, occur on many Martian terrains. The deposition of airborne dust on surfaces causes a bright tone in the THEMIS VIS images. Any movement of the dust downhill, a dust avalanche, will leave behind a streak where the darker, dust-free surface is exposed.

    This region of dust avalanches is located in and around a crater to the west of yesterday's image.

    Image information: VIS instrument. Latitude 14.7, Longitude 32.7 East (327.3 West). 18 meter/pixel resolution.

    Note: this THEMIS visual image has not been radiometrically nor geometrically calibrated for this preliminary release. An empirical correction has been performed to remove instrumental effects. A linear shift has been applied in the cross-track and down-track direction to approximate spacecraft and planetary motion. Fully calibrated and geometrically projected images will be released through the Planetary Data System in accordance with Project policies at a later time.

    NASA's Jet Propulsion Laboratory manages the 2001 Mars Odyssey mission for NASA's Office of Space Science, Washington, D.C. The Thermal Emission Imaging System (THEMIS) was developed by Arizona State University, Tempe, in collaboration with Raytheon Santa Barbara Remote Sensing. The THEMIS investigation is led by Dr. Philip Christensen at Arizona State University. Lockheed Martin Astronautics, Denver, is the prime contractor for the Odyssey project, and developed and built the orbiter. Mission operations are conducted jointly from Lockheed Martin and from JPL, a division of the California Institute of Technology in Pasadena.

  19. ASIC Readout Circuit Architecture for Large Geiger Photodiode Arrays

    NASA Technical Reports Server (NTRS)

    Vasile, Stefan; Lipson, Jerold

    2012-01-01

    The objective of this work was to develop a new class of readout integrated circuit (ROIC) arrays to be operated with Geiger avalanche photodiode (GPD) arrays, by integrating multiple functions at the pixel level (smart-pixel or active pixel technology) in 250-nm CMOS (complementary metal oxide semiconductor) processes. In order to pack a maximum of functions within a minimum pixel size, the ROIC array is a full, custom application-specific integrated circuit (ASIC) design using a mixed-signal CMOS process with compact primitive layout cells. The ROIC array was processed to allow assembly in bump-bonding technology with photon-counting infrared detector arrays into 3-D imaging cameras (LADAR). The ROIC architecture was designed to work with either common- anode Si GPD arrays or common-cathode InGaAs GPD arrays. The current ROIC pixel design is hardwired prior to processing one of the two GPD array configurations, and it has the provision to allow soft reconfiguration to either array (to be implemented into the next ROIC array generation). The ROIC pixel architecture implements the Geiger avalanche quenching, bias, reset, and time to digital conversion (TDC) functions in full-digital design, and uses time domain over-sampling (vernier) to allow high temporal resolution at low clock rates, increased data yield, and improved utilization of the laser beam.

  20. Synchronous Photodiode-Signal Sampler

    NASA Technical Reports Server (NTRS)

    Primus, Howard K.

    1988-01-01

    Synchronous sampling circuit increases signal-to-noise ratio of measurements of chopped signal of known phase and frequency in presence of low-frequency or dc background noise. Used with linear array of photoelectric sensors for locating edge of metal plate. Multiplexing circuit cycles through 16 light-emitting-diode/photodiode pairs, under computer control. Synchronized with multiplexer so edge detector makes one background-subtracted signal measurement per emitter/detector pair in turn.

  1. Neuronal avalanches and learning

    NASA Astrophysics Data System (ADS)

    de Arcangelis, Lucilla

    2011-05-01

    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.

  2. Neuronal avalanches and coherence potentials

    NASA Astrophysics Data System (ADS)

    Plenz, D.

    2012-05-01

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

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

    PubMed

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

    2016-04-01

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

  4. Avalanches in dry and saturated disordered media at fracture

    NASA Astrophysics Data System (ADS)

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

    2016-04-01

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

  5. Recent advances in cardiac SPECT instrumentation and system design.

    PubMed

    Smith, Mark F

    2013-08-01

    Recent advances in clinical cardiac SPECT instrumentation are reviewed from a systems perspective. New hardware technologies include pixelated scintillator and semiconductor detector elements; photodetectors such as position-sensitive photomultiplier tubes (PSPMT), avalanche photodiodes (APD) and silicon photomultipliers (SiPM); and novel cardiac collimation methods. There are new approaches for positioning detectors and controlling their motion during cardiac imaging. Software technology advances include iterative image reconstruction with modeling of Poisson statistics and depth-dependent collimator response. These new technologies enable faster acquisitions, the lowering of administered activity and radiation dose, and improved image resolution. Higher sensitivity collimators are a significant factor enabling faster acquisitions. Several clinical systems incorporating new technologies are discussed and different system designs can achieve similar performance. With detector elements such as APDs, SiPMs and semiconductors that are insensitive to magnetic fields, the potential for cardiac SPECT imagers that are MRI compatible opens up new frontiers in clinical cardiac research and patient care. PMID:23832650

  6. Avalanche effects near nanojunctions

    NASA Astrophysics Data System (ADS)

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

    2016-07-01

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

  7. Avalanche effects near nanojunctions.

    PubMed

    Nandigana, Vishal V R; Aluru, N R

    2016-07-01

    In this article, we perform a computational investigation of a nanopore connected to external fluidic reservoirs of asymmetric geometries. The asymmetry between the reservoirs is achieved by changing the cross-sectional areas, and the reservoirs are designated as the micropore reservoir and macropore reservoir. When an electric field is applied, which is directed from the macropore towards the micropore reservoir, we observe local nonequilibrium chaotic current oscillations. The current oscillations originate at the micropore-nanopore interface owing to the local cascade of ions; we refer to this phenomenon as the "avalanche effects." We mathematically quantify chaos in terms of the maximum Lyapunov exponent. The maximum Lyapunov exponent exhibits a monotonic increase with the applied voltage and the macropore reservoir diameter. The temporal power spectra maps of the chaotic currents depict a low-frequency "1/f"-type dynamics for the voltage chaos and "1/f^{2}"-type dynamics for the macropore reservoir chaos. The results presented here offer avenues to manipulate ionic diodes and fluidic pumps. PMID:27575159

  8. Controlling avalanche criticality in 2D nano arrays

    NASA Astrophysics Data System (ADS)

    Zohar, Y. C.; Yochelis, S.; Dahmen, K. A.; Jung, G.; Paltiel, Y.

    2013-05-01

    Many physical systems respond to slowly changing external force through avalanches spanning broad range of sizes. Some systems crackle even without apparent external force, such as bursts of neuronal activity or charge transfer avalanches in 2D molecular layers. Advanced development of theoretical models describing disorder-induced critical phenomena calls for experiments probing the dynamics upon tuneable disorder. Here we show that isomeric structural transitions in 2D organic self-assembled monolayer (SAM) exhibit critical dynamics with experimentally tuneable disorder. The system consists of field effect transistor coupled through SAM to illuminated semiconducting nanocrystals (NCs). Charges photoinduced in NCs are transferred through SAM to the transistor surface and modulate its conductivity. Avalanches of isomeric structural transitions are revealed by measuring the current noise I(t) of the transistor. Accumulated surface traps charges reduce dipole moments of the molecules, decrease their coupling, and thus decrease the critical disorder of the SAM enabling its tuning during experiments.

  9. Assessing wet snow avalanche activity using detailed physics based snowpack simulations

    NASA Astrophysics Data System (ADS)

    Wever, N.; Vera Valero, C.; Fierz, C.

    2016-06-01

    Water accumulating on microstructural transitions inside a snowpack is often considered a prerequisite for wet snow avalanches. Recent advances in numerical snowpack modeling allow for an explicit simulation of this process. We analyze detailed snowpack simulations driven by meteorological stations in three different climate regimes (Alps, Central Andes, and Pyrenees), with accompanying wet snow avalanche activity observations. Predicting wet snow avalanche activity based on whether modeled water accumulations inside the snowpack locally exceed 5-6% volumetric liquid water content is providing a higher prediction skill than using thresholds for daily mean air temperature, or the daily sum of the positive snow energy balance. Additionally, the depth of the maximum water accumulation in the simulations showed a significant correlation with observed avalanche size. Direct output from detailed snow cover models thereby is able to provide a better regional assessment of dangerous slope aspects and potential avalanche size than traditional methods.

  10. Correlations in avalanche critical points.

    PubMed

    Cerruti, Benedetta; Vives, Eduard

    2009-07-01

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

  11. X-ray spectroscopy with silicon pin and avalanche photo diodes

    NASA Technical Reports Server (NTRS)

    Desai, U. D.

    1992-01-01

    Results of an evaluation of silicon P-Intrinsic-N (PIN) photodiodes and Avalanche Photodiodes (APD) for the direct detection of soft x rays from 1 to 20 keV and for the detection of scintillation light output from CsI(TI) for higher x ray energies (30 to 1000 keV) are presented. About one keV resolution was achieved at room temperature for both the PIN and APD detectors for soft x rays (1 to 20 keV). Commercially available, low power (18 mV), low noise, hybrid preamplifiers, were used. These photodiodes were also coupled to CsI(TI) scintillator and obtained about 6 resolution at 662 keV. The photodiode frequency response matches well with the emission spectrum of the CsI(TI) scintillator providing good spectral resolution and a higher signal than NaI(TI) when viewed by conventional photomultipliers. A PIN-CsI(TI) combination provides a low energy threshold of around 60 keV while for the APD-CsI(TI) it is 15 keV.

  12. Avalanche Collapse of Interdependent Networks

    NASA Astrophysics Data System (ADS)

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

    2012-12-01

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

  13. TCAD simulations of a novel UV and blue-extended photodiode

    NASA Astrophysics Data System (ADS)

    Chen, Chang-ping; Jin, Xiang-liang; Zhou, Xiao-ya; Yang, Hongjiao; Luo, Jun

    2013-08-01

    In this paper, a new UV and blue-extended photodiode with an octagon-ring-shaped structure is proposed, which have increased responsivity for the UV and blue light, high responsive speed with short rise and fall time and UV/blue selectivity. TCAD simulation approach is used to analyze the structural characteristics and photoelectric characteristics of this new photodiode. For the structural characteristics, doping profile, potential distribution and Electric field distribution are analyzed simply. For the photoelectric characteristics, the influences caused by doping concentration of n-well on dark current, avalanche breakdown voltage and transient response are discussed in detail. The finger distance (D) between two adjacent P+ anodes, the width (W) of P+ anode and the ratio of D/W are analyzed, witch affects the spectral response, DC characteristic and transient response obviously. The work of TCAD simulation in this paper is conducive to extract model parameters and process parameters of this new photodiode, which will further be used for numerical simulation to analyze its photoelectric characteristics, noise characteristics more accurately. This work is also a significant and helpful guide for device design and chip fabrication.

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

    PubMed

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

    2006-12-01

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

  15. Lumped transmission line avalanche pulser

    DOEpatents

    Booth, R.

    1995-07-18

    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. 8 figs.

  16. Lumped transmission line avalanche pulser

    DOEpatents

    Booth, Rex

    1995-01-01

    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.

  17. A branching process model for sand avalanches

    SciTech Connect

    Garcia-Pelayo, R.; Salazar, I.; Schieve, W.C. )

    1993-07-01

    An analytically solvable model for sand avalanches of noninteracting grains of sand, based on the Chapman-Kolmogorov equations, is presented. For a single avalanche, distributions of lifetimes, sizes of overflows and avalanches, and correlation functions are calculated. Some of these are exponentials, some are power laws. Spatially homogeneous distributions of avalanches are also studied. Computer simulations of avalanches of interacting grains of sand are compared to the solutions to the Chapman-Kolmogorov equations. It is found that within the range of parameters explored in the simulation, the approximation of noninteracting grains of sand is a good one. 20 refs., 4 figs.

  18. Photodiode-Based, Passive Ultraviolet Dosimeters

    NASA Technical Reports Server (NTRS)

    Vaughn, Jason A.; Gray, Perry

    2004-01-01

    Simple, passive instruments have been developed for measuring the exposure of material specimens to vacuum ultraviolet (VUV) radiation from the Sun. Each instrument contains a silicon photodiode and a coulometer. The photocharge generated in the photodiode is stored in the coulometer. The accumulated electric charge measured by use of the coulometer is assumed to be proportional to the cumulative dose of VUV radiation expressed in such convenient units as equivalent Sun hours (ESH) [defined as the number of hours of exposure to sunlight at normal incidence]. Intended originally for use aboard spacecraft, these instruments could also be adapted to such terrestrial uses as monitoring the curing of ultraviolet-curable epoxies. Each instrument includes a photodiode and a coulometer assembly mounted on an interface plate (see figure). The photodiode assembly includes an aluminum housing that holds the photodiode, a poly(tetrafluoroehylene) cosine receptor, and a narrow-band optical filter. The cosine receptor ensures that the angular response of the instrument approximates the ideal angular response (proportional to the cosine of the angle of incidence). The filter is chosen to pass the ultraviolet wavelength of interest in a specific experiment. The photodiode is electrically connected to the coulometer. The factor of proportionality between the charge stored in the coulometer and ultraviolet dosage (in units of ESH) is established, prior to use, in calibration experiments that involve the use of lamps and current sources traceable to the National Institute of Standards and Technology.

  19. Experimental Avalanches in a Rotating Drum

    NASA Astrophysics Data System (ADS)

    Hubard, Aline; O'Hern, Corey; Shattuck, Mark

    We address the question of universality in granular avalanches and the system size effects on it. We set up an experiment made from a quasi-two-dimensional rotating drum half-filled with a monolayer of stainless-steel spheres. We measure the size of the avalanches created by the increased gravitational stress on the pile as we quasi-statically rotate the drum. We find two kinds of avalanches determined by the drum size. The size and duration distributions of the avalanches that do not span the whole system follow a power law and the avalanche shapes are self-similar and nearly parabolic. The distributions of the avalanches that span the whole system are limited by the maximal amount of potential energy stored in the system at the moment of the avalanche. NSF CMMI-1462439, CMMI-1463455.

  20. Test of DEP hybrid photodiodes

    SciTech Connect

    Baumbaugh, A.; Binkley, M.; Elias, J.

    1997-08-01

    The goal of the measurement was to study some parameters of DEP HYBRID PHOTODIODES (HPD), and the check its performance for CMS calorimetry at LHC. The principal of the HPD operation is described. The schematic view of the HPD. The HPD is vacuum photo device composed of photocathode (PC) and a silicon PIN diode (Si) as multiplication system in a very close proximity geometry. The distance between PC and Si is of the order of several mm and has an electric field < 10 kV. The photoelectron emited by the photocathode multiply by a factor of several thousand in the silicon and the charge is collected on the HPD`s anode. Several types of HPD`s were tested. There was a single channel HPD, called {open_quotes}E-type{close_quotes} with p-side of the silicon facing the HPD`s photocathode and two multipixel HPD (DEP) namely a 25 pixel HPD and a 7 pixel HPD. Both were of {open_quotes}T-type{close_quotes} structure with n-side of silicon facing the photocathode.

  1. Retrieving avalanche basal friction law parameters from high rate positioning of avalanches

    NASA Astrophysics Data System (ADS)

    Pulfer, Gaëtan; Naaim, Mohamed; Thibert, Emmanuel; Soruco, Alvaro

    2015-04-01

    The Voellmy avalanche basal friction parameters are retrieved from high rate positioning of artificially released avalanches. Avalanche fronts were tracked thanks to an accurate photogrammetric system set up at the Lautaret full-scale avalanche test-site (French Alps). Couples of images were acquired at 1 frame per second with 2 APS-C DSLR synchronized cameras set at 800 meters from the avalanche track. The avalanche height and velocity are also measured at a fixed location in the avalanche track. Rheological parameters of the avalanche flow are reconstructed by an inverse optimization method using these in situ data. The direct model is a Saint-Venant type model were basal friction is parameterized according to the Voellmy's friction law. A Sensitivity analysis of the friction parameters is conducted and theirs uncertainty are determined. Finally the results obtained from different avalanches are compared and discussed.

  2. Post-processing Free Quantum Random Number Generator Based on Avalanche Photodiode Array

    NASA Astrophysics Data System (ADS)

    Yang, Li; Sheng-Kai, Liao; Fu-Tian, Liang; Qi, Shen; Hao, Liang; Cheng-Zhi, Peng

    2016-03-01

    Not Available Supported by the Chinese Academy of Sciences Center for Excellence and Synergetic Innovation Center in Quantum Information and Quantum Physics, Shanghai Branch, University of Science and Technology of China, and the National Natural Science Foundation of China under Grant No 11405172.

  3. Maximum detection range limitation of pulse laser radar with Geiger-mode avalanche photodiode array

    NASA Astrophysics Data System (ADS)

    Luo, Hanjun; Xu, Benlian; Xu, Huigang; Chen, Jingbo; Fu, Yadan

    2015-05-01

    When designing and evaluating the performance of laser radar system, maximum detection range achievable is an essential parameter. The purpose of this paper is to propose a theoretical model of maximum detection range for simulating the Geiger-mode laser radar's ranging performance. Based on the laser radar equation and the requirement of the minimum acceptable detection probability, and assuming the primary electrons triggered by the echo photons obey Poisson statistics, the maximum range theoretical model is established. By using the system design parameters, the influence of five main factors, namely emitted pulse energy, noise, echo position, atmospheric attenuation coefficient, and target reflectivity on the maximum detection range are investigated. The results show that stronger emitted pulse energy, lower noise level, more front echo position in the range gate, higher atmospheric attenuation coefficient, and higher target reflectivity can result in greater maximum detection range. It is also shown that it's important to select the minimum acceptable detection probability, which is equivalent to the system signal-to-noise ratio for producing greater maximum detection range and lower false-alarm probability.

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

    NASA Astrophysics Data System (ADS)

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

    2015-12-01

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

  5. Response of cooled PWO scintillators readout with avalanche photodiodes to low-energy gamma-rays

    NASA Astrophysics Data System (ADS)

    Melnychuk, D.; Czarnacki, W.; Kalicy, G.; Keşik, G.; Korman, A.; Kozlowski, T.; Mykulyak, A.; Novotny, R. W.; Wojtkowska, J.; Zwieglinski, B.

    2009-08-01

    Identification of π0 and η mesons by detecting both γ-rays from their decay is a prerequisite for suppressing undesired background in studies of photon transitions between the states of charmonium in the physics program of PANDA. To achieve this goal the detection threshold of the PANDA electromagnetic calorimeter (EMC) should be as low as possible. An experimental setup intended for measurements of the response of cooled PWO scintillators in the energy range 4.4-20 MeV has been designed and constructed. The setup uses γ-rays emitted in reactions induced by protons with light nuclei. Events with full-energy expended in PWO are selected by enclosing the studied 20×20×200 mm PWO-II scintillator in a cylinder of EJ-200 plastic scintillator, whose two halves are read out independently. A comparison of the relative Gaussian dispersions, σ/E, obtained by us for the three energies in the above energy range, indicates that a smooth dependence established at MAMI, for a matrix of 3×3 PWO-II scintillators between 40.9 and 674.5 MeV, also gives a valid extrapolation into the range of these very low energies.

  6. Quantitative Scaling of Magnetic Avalanches.

    PubMed

    Durin, G; Bohn, F; Corrêa, M A; Sommer, R L; Le Doussal, P; Wiese, K J

    2016-08-19

    We provide the first quantitative comparison between Barkhausen noise experiments and recent predictions from the theory of avalanches for pinned interfaces, both in and beyond mean field. We study different classes of soft magnetic materials, including polycrystals and amorphous samples-which are characterized by long-range and short-range elasticity, respectively-both for thick and thin samples, i.e., with and without eddy currents. The temporal avalanche shape at fixed size as well as observables related to the joint distribution of sizes and durations are analyzed in detail. Both long-range and short-range samples with no eddy currents are fitted extremely well by the theoretical predictions. In particular, the short-range samples provide the first reliable test of the theory beyond mean field. The thick samples show systematic deviations from the scaling theory, providing unambiguous signatures for the presence of eddy currents. PMID:27588876

  7. Quantitative Scaling of Magnetic Avalanches

    NASA Astrophysics Data System (ADS)

    Durin, G.; Bohn, F.; Corrêa, M. A.; Sommer, R. L.; Le Doussal, P.; Wiese, K. J.

    2016-08-01

    We provide the first quantitative comparison between Barkhausen noise experiments and recent predictions from the theory of avalanches for pinned interfaces, both in and beyond mean field. We study different classes of soft magnetic materials, including polycrystals and amorphous samples—which are characterized by long-range and short-range elasticity, respectively—both for thick and thin samples, i.e., with and without eddy currents. The temporal avalanche shape at fixed size as well as observables related to the joint distribution of sizes and durations are analyzed in detail. Both long-range and short-range samples with no eddy currents are fitted extremely well by the theoretical predictions. In particular, the short-range samples provide the first reliable test of the theory beyond mean field. The thick samples show systematic deviations from the scaling theory, providing unambiguous signatures for the presence of eddy currents.

  8. Neuronal avalanches and brain plasticity

    NASA Astrophysics Data System (ADS)

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

    2007-12-01

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

  9. Optical receivers with large-diameter photodiode

    NASA Astrophysics Data System (ADS)

    Swoboda, Robert; Schneider, Kerstin; Zimmermann, Horst

    2006-04-01

    This work presents two types of optical receivers with large-diameter photodiodes. Both are optoelectronic integrated circuits (OEICs) realized in 0.6μm BiCMOS Si technology integrating PIN photodiode, transimpedance amplifier (TIA) and output circuit on chip. The two circuits are an optocoupler with a photodiode diameter of 780μm and a rise- and falltime of 5ns and 4.9ns respectively at 850nm light and a plastic optical fiber (POF) receiver with a photodiode diameter of 500μm and upper -3dB cut-off frequencies of 165MHz at 660nm light and 148MHz at 850nm light. The measured rise- and falltime of the POF receiver was 1.78ns and 2.45ns at 660nm light and 1.94ns and 2.5ns at 850ns, respectively. The presented results combine the advantage of easier handling of large-diameter photodiode receivers and high performance.

  10. The development of structures in analogue and natural debris avalanches

    NASA Astrophysics Data System (ADS)

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

    2010-05-01

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

  11. Avalanche dynamics of elastic interfaces.

    PubMed

    Le Doussal, Pierre; Wiese, Kay Jörg

    2013-08-01

    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 d

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

    USGS Publications Warehouse

    Fagre, Daniel B.; Peitzsch, Erich H.

    2010-01-01

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

  13. Snowfall and avalanche synchronization: beyond observational statistics

    NASA Astrophysics Data System (ADS)

    Crouzy, Benoît; Forclaz, Romain; Sovilla, Betty; Corripio, Javier; Perona, Paolo

    2015-04-01

    We present a methodology for quantifying the synchronization between snowfall and avalanches in relation to slope and terrain properties at the detachment zone. Focusing on a particular field situation (SLF study site, Vallée de la Sionne, Valais, Switzerland), we present a dataset consisting of 549 avalanche events and use a stochastic framework (Perona et al., Proceedings of the Royal Society A, 2012) for capturing the avalanche statistics with a minimal number of ingredients. Over the observation period (7 years), meteorological data was collected and pictures of the slope were taken every 30 minutes. For the avalanche events, slope, aspect, coordinates and altitude of the detachment zone are available from georeferenced images, and the timing of the events can be obtained from selecting the images before and after avalanche events. All model parameters can directly be computed from meteorological data (snow depth evolution), except for one parameter: the state-dependent avalanche release rate, which aggregates the influence of slope and terrain properties. From the timing distribution of the precipitation events and of the avalanche events, we calibrate the model and fix the value of the missing parameter by maximizing the likelihood of the field observations, conditional to the value of the model parameter. We carefully discuss confidence intervals for our parameter estimation. The calibrated model allows us to obtain statistical properties of the avalanches in our study site, beyond observational statistics. We compute the synchronization between snowfall and avalanches for low and high slopes, which in turn allows us to derive the return period of avalanche events (dependent and independent on the release depth). We obtain the critical event magnitude above which the return period of avalanche events with release depth h* is shorter than the return period of snowfall with equal deposited snow depth h*. Finally, using the concept of information entropy, we

  14. Time Directed Avalanches in Invasion Models

    SciTech Connect

    Maslov, S. Department of Physics, SUNY at Stony Brook, Stony Brook, New York 11794 )

    1995-01-23

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

  15. A probabilistic model for snow avalanche occurrence

    NASA Astrophysics Data System (ADS)

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

    2009-04-01

    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

  16. Forest damage and snow avalanche flow regime

    NASA Astrophysics Data System (ADS)

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

    2015-01-01

    Snow avalanches break, uproot and overturn trees causing damage to forests. The extent of forest damage provides useful information on avalanche frequency and intensity. However, impact forces depend on avalanche flow regime. In this paper, we define avalanche loading cases representing four different avalanche flow regimes: powder, intermittent, dry and wet. In the powder regime, the blast of the cloud can produce large bending moments in the tree stem because of the impact area extending over the entire tree crown. We demonstrate that intermittent granular loadings are equivalent to low-density uniform dry snow loadings under the assumption of homogeneous particle distributions. In the wet snow case, avalanche pressure is calculated using a quasi-static model accounting for the motion of plug-like wet snow flows. Wet snow pressure depends both on avalanche volume and terrain features upstream of the tree. Using a numerical model that simulates both powder and wet snow avalanches, we study documented events with forest damage. We find (1) powder clouds with velocities over 20 m s-1 can break tree stems, (2) the intermittent regime seldom controls tree breakage and (3) quasi-static pressures of wet snow avalanches can be much higher than pressures calculated using dynamic pressure formulas.

  17. Vertical Isolation for Photodiodes in CMOS Imagers

    NASA Technical Reports Server (NTRS)

    Pain, Bedabrata

    2008-01-01

    In a proposed improvement in complementary metal oxide/semi conduct - or (CMOS) image detectors, two additional implants in each pixel would effect vertical isolation between the metal oxide/semiconductor field-effect transistors (MOSFETs) and the photodiode of the pixel. This improvement is expected to enable separate optimization of the designs of the photodiode and the MOSFETs so as to optimize their performances independently of each other. The purpose to be served by enabling this separate optimization is to eliminate or vastly reduce diffusion cross-talk, thereby increasing sensitivity, effective spatial resolution, and color fidelity while reducing noise.

  18. Current isolating epitaxial buffer layers for high voltage photodiode array

    DOEpatents

    Morse, Jeffrey D.; Cooper, Gregory A.

    2002-01-01

    An array of photodiodes in series on a common semi-insulating substrate has a non-conductive buffer layer between the photodiodes and the semi-insulating substrate. The buffer layer reduces current injection leakage between the photodiodes of the array and allows optical energy to be converted to high voltage electrical energy.

  19. A compact gas-filled avalanche counter for DANCE

    SciTech Connect

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

    2012-08-04

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

  20. A compact gas-filled avalanche counter for DANCE

    DOE PAGESBeta

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

    2012-08-04

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

  1. On the temporal organization of neuronal avalanches

    PubMed Central

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

    2014-01-01

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

  2. Gaussian Velocity Distributions in Avalanches

    NASA Astrophysics Data System (ADS)

    Shattuck, Mark

    2004-03-01

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

  3. Optical Demonstrations with a Scanning Photodiode Array.

    ERIC Educational Resources Information Center

    Turman, Bobby N.

    1980-01-01

    Describes the photodiode array and the electrical connections necessary for it. Also shows a few of the optical demonstration possibilities-shadowgraphs for measuring small objects, interference and diffraction effects, angular resolution of an optical system, and a simple spectrometer. (Author/DS)

  4. MRS photodiode in strong magnetic field

    SciTech Connect

    Beznosko, D.; Blazey, G.; Dyshkant, A.; Francis, K.; Kubik, D.; Rykalin, V.; Tartaglia, M.A.; Zutshi, v.; /Northern Illinois U.

    2004-12-01

    The experimental results on the performance of the MRS (Metal/Resistor/Semiconductor) photodiode in the strong magnetic field of 4.4T, and the possible impact of the quench of the magnet at 4.5T on sensor's operation are reported.

  5. Avalanche!--Teachable Moments in Outdoor Education

    ERIC Educational Resources Information Center

    Galloway, Shayne

    2005-01-01

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

  6. Forest damage and snow avalanche flow regime

    NASA Astrophysics Data System (ADS)

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

    2015-06-01

    Snow avalanches break, uproot and overturn trees causing damage to forests. The extent of forest damage provides useful information on avalanche frequency and intensity. However, impact forces depend on avalanche flow regime. In this paper, we define avalanche loading cases representing four different avalanche flow regimes: powder, intermittent, dry and wet. Using a numerical model that simulates both powder and wet snow avalanches, we study documented events with forest damage. First we show that in the powder regime, although the applied impact pressures can be small, large bending moments in the tree stem can be produced due to the torque action of the blast. The impact area of the blast extends over the entire tree crown. We find that, powder clouds with velocities over 20 m s-1 can break tree stems. Second we demonstrate that intermittent granular loadings are equivalent to low-density uniform dry snow loadings under the assumption of homogeneous particle distributions. The intermittent regime seldom controls tree breakage. Third we calculate quasi-static pressures of wet snow avalanches and show that they can be much higher than pressures calculated using dynamic pressure formulas. Wet snow pressure depends both on avalanche volume and terrain features upstream of the tree.

  7. Design of Advanced Atmospheric Water Vapor Differential Absorption Lidar (DIAL) Detection System

    NASA Technical Reports Server (NTRS)

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

    1999-01-01

    The measurement of atmospheric water vapor is very important for understanding the Earth's climate and water cycle. The lidar atmospheric sensing experiment (LASE) is an instrument designed and operated by the Langley Research Center for high precision water vapor measurements. The design details of a new water vapor lidar detection system that improves the measurement sensitivity of the LASE instrument by a factor of 10 are discussed. The new system consists of an advanced, very low noise, avalanche photodiode (APD) and a state-of-the-art signal processing circuit. The new low-power system is also compact and lightweight so that it would be suitable for space flight and unpiloted atmospheric vehicles (UAV) applications. The whole system is contained on one small printed circuit board (9 x 15 sq cm). The detection system is mounted at the focal plane of a lidar receiver telescope, and the digital output is read by a personal computer with a digital data acquisition card.

  8. Avalanche in Adhesion at Metal Interfaces

    NASA Technical Reports Server (NTRS)

    Banerjea, Amitava; Good, Brian S.

    1994-01-01

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

  9. Updated design for a low-noise, wideband transimpedance photodiode amplifier

    SciTech Connect

    Paul, S. F.; Marsala, R.

    2006-10-15

    The high-speed rotation diagnostic developed for Columbia's HBT-EP tokamak requires a high quantum efficiency, very low drift detector/amplifier combination. An updated version of the circuit developed originally for the beam emission spectroscopy experiment on TFTR is being used. A low dark current (2 nA at 15 V bias), low input source capacitance (2 pF) FFD-040 N-type Si photodiode is operated in photoconductive mode. It has a quantum efficiency of 40% at the 468.6 nm (He II line that is being observed). A low-noise field-effect transistor (InterFET IFN152 with e{sub Na}=1.2 nV/{radical}Hz) is used to reduce the noise in the transimpedance preamplifier (A250 AMPTEK op-amp) and a very high speed (unity-gain bandwidth=200 MHz) voltage feedback amplifier (LM7171) is used to restore the frequency response up to 100 kHz. This type of detector/amplifier is photon-noise limited at this bandwidth for incident light with a power of >{approx}2 nW. The circuit has been optimized using SIMETRIX 4.0 SPICE software and a prototype circuit has been tested successfully. Though photomultipliers and avalanche photodiodes can detect much lower light levels, for light levels >2 nW and a 10 kHz bandwidth, this detector/amplifier combination is more sensitive because of the absence of excess (internally generated) noise.

  10. Thermal energy in dry snow avalanches

    NASA Astrophysics Data System (ADS)

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

    2015-09-01

    Avalanches can exhibit many different flow regimes from powder clouds to slush flows. Flow regimes are largely controlled by the properties of the snow released and entrained along the path. Recent investigations showed the temperature of the moving snow to be one of the most important factors controlling the mobility of the flow. The temperature of an avalanche is determined by the temperature of the released and entrained snow but also increases by frictional processes with time. For three artificially released avalanches, we conducted snow profiles along the avalanche track and in the deposition area, which allowed quantifying the temperature of the eroded snow layers. This data set allowed to calculate the thermal balance, from release to deposition, and to discuss the magnitudes of different sources of thermal energy of the avalanches. For the investigated dry avalanches, the thermal energy increase due to friction was mainly depending on the effective elevation drop of the mass of the avalanche with a warming of approximately 0.3 °C per 100 vertical metres. Contrarily, the temperature change due to entrainment varied for the individual avalanches, from -0.08 to 0.3 °C, and depended on the temperature of the snow along the path and the erosion depth. Infrared radiation thermography (IRT) was used to assess the surface temperature before, during and just after the avalanche with high spatial resolution. This data set allowed to identify the warmest temperatures to be located in the deposits of the dense core. Future research directions, especially for the application of IRT, in the field of thermal investigations in avalanche dynamics are discussed.

  11. Particle-size segregation in dense granular avalanches

    NASA Astrophysics Data System (ADS)

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

    2015-01-01

    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.

  12. Temporal correlations in neuronal avalanche occurrence

    PubMed Central

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

    2016-01-01

    Ongoing cortical activity consists of sequences of synchronized bursts, named neuronal avalanches, whose size and duration are power law distributed. These features have been observed in a variety of systems and conditions, at all spatial scales, supporting scale invariance, universality and therefore criticality. However, the mechanisms leading to burst triggering, as well as the relationship between bursts and quiescence, are still unclear. The analysis of temporal correlations constitutes a major step towards a deeper understanding of burst dynamics. Here, we investigate the relation between avalanche sizes and quiet times, as well as between sizes of consecutive avalanches recorded in cortex slice cultures. We show that quiet times depend on the size of preceding avalanches and, at the same time, influence the size of the following one. Moreover we evidence that sizes of consecutive avalanches are correlated. In particular, we show that an avalanche tends to be larger or smaller than the following one for short or long time separation, respectively. Our analysis represents the first attempt to provide a quantitative estimate of correlations between activity and quiescence in the framework of neuronal avalanches and will help to enlighten the mechanisms underlying spontaneous activity. PMID:27094323

  13. Temporal correlations in neuronal avalanche occurrence.

    PubMed

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

    2016-01-01

    Ongoing cortical activity consists of sequences of synchronized bursts, named neuronal avalanches, whose size and duration are power law distributed. These features have been observed in a variety of systems and conditions, at all spatial scales, supporting scale invariance, universality and therefore criticality. However, the mechanisms leading to burst triggering, as well as the relationship between bursts and quiescence, are still unclear. The analysis of temporal correlations constitutes a major step towards a deeper understanding of burst dynamics. Here, we investigate the relation between avalanche sizes and quiet times, as well as between sizes of consecutive avalanches recorded in cortex slice cultures. We show that quiet times depend on the size of preceding avalanches and, at the same time, influence the size of the following one. Moreover we evidence that sizes of consecutive avalanches are correlated. In particular, we show that an avalanche tends to be larger or smaller than the following one for short or long time separation, respectively. Our analysis represents the first attempt to provide a quantitative estimate of correlations between activity and quiescence in the framework of neuronal avalanches and will help to enlighten the mechanisms underlying spontaneous activity. PMID:27094323

  14. Temporal correlations in neuronal avalanche occurrence

    NASA Astrophysics Data System (ADS)

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

    2016-04-01

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

  15. Interface Trap States in Organic Photodiodes

    PubMed Central

    Arca, Francesco; Tedde, Sandro F.; Sramek, Maria; Rauh, Julia; Lugli, Paolo; Hayden, Oliver

    2013-01-01

    Organic semiconductors are attractive for optical sensing applications due to the effortless processing on large active area of several cm2, which is difficult to achieve with solid-state devices. However, compared to silicon photodiodes, sensitivity and dynamic behavior remain a major challenge with organic sensors. Here, we show that charge trapping phenomena deteriorate the bandwidth of organic photodiodes (OPDs) to a few Hz at low-light levels. We demonstrate that, despite the large OPD capacitances of ~10 nF cm−2, a frequency response in the kHz regime can be achieved at light levels as low as 20 nW cm−2 by appropriate interface engineering, which corresponds to a 1000-fold increase compared to state-of-the-art OPDs. Such device characteristics indicate that large active area OPDs are suitable for industrial sensing and even match medical requirements for single X-ray pulse detection in the millisecond range. PMID:23429565

  16. Continuum description of avalanches in granular media.

    SciTech Connect

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

    2000-12-05

    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. Dynamics of Avalanche Activities in Financial Markets

    NASA Astrophysics Data System (ADS)

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

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

  18. Initiation of immersed granular avalanches

    NASA Astrophysics Data System (ADS)

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

    2014-05-01

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

  19. Initiation of immersed granular avalanches.

    PubMed

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

    2014-05-01

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

  20. Silicon photodiode as the two-color detector

    NASA Astrophysics Data System (ADS)

    Ponomarev, D. B.; Zakharenko, V. A.

    2015-11-01

    This paper describes a silicon photodiode as the two-color photodetector. The work of one photodiode in two spectral ranges is achieved due to the changes of the spectral sensitivity of the photodiodes in the transition from photodiode mode for photovoltaic in the short circuit mode. On the basis of silicon photodiode FD-256 the layout of the spectral ratio pyrometer was assembled and the results of theoretical calculations was confirmed experimentally. The calculated dependences of the coefficient of error of the spectral ratio pyrometer from temperature reverse voltage 10 and 100 V was presented. The calculated dependence of the instrumental error and the assessment of methodological errors of the proposed photodetector spectral ratio was done. According to the results of the presented research was set the task of development photodiode detectors which change the spectral sensitivity depending on the applied voltage.

  1. Avalanche control: Conservation Guide Series No. 5

    SciTech Connect

    Not Available

    1985-01-01

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

  2. Shocks generate crossover behavior in lattice avalanches.

    PubMed

    Burridge, James

    2013-11-22

    A spatial avalanche model is introduced, in which avalanches increase stability in the regions where they occur. Instability is driven globally by a driving process that contains shocks. The system is typically subcritical, but the shocks occasionally lift it into a near- or supercritical state from which it rapidly retreats due to large avalanches. These shocks leave behind a signature-a distinct power-law crossover in the avalanche size distribution. The model is inspired by landslide field data, but the principles may be applied to any system that experiences stabilizing failures, possesses a critical point, and is subject to an ongoing process of destabilization that includes occasional dramatic destabilizing events. PMID:24313528

  3. Avalanche grainflow on a simulated aeolian dune

    NASA Astrophysics Data System (ADS)

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

    2013-09-01

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

  4. Photodiodes for ten micrometer laser communication systems

    NASA Technical Reports Server (NTRS)

    Cohen, S. C.

    1972-01-01

    The performance is discussed of 10-micron mercury-cadmiumtelluride and lead-tin-telluride photodiodes in laser heterodyne communication systems. The dependence of detector quantum efficiency, resistance, frequency response, and signal-to-noise ratio on temperature, bias, and local oscillator power are examined. Included in the discussion is an analysis of the feasibility of high temperature operation, and ability of the detector to dissipate power to a heat sink is explored. Some aspects of direct detection response are considered and figures showing flux levels from a blackbody presented.

  5. Interference effects in Reticon photodiode array detectors

    NASA Astrophysics Data System (ADS)

    Mount, George H.; Sanders, Ryan W.; Brault, James W.

    1992-03-01

    A detector system incorporating the Reticon RL1024S photodiode array has been constructed as part of a double spectrograph to be used to study the earth's atmosphere from ground-based and aircraft-based platforms. To determine accurately the abundances of atmospheric trace gases, this new system must be able to measure spectral absorptions as small as 0.02 percent. The detector exhibits superior signal-to-noise characteristics at the light levels characteristic of scattered skylights, but interference in the passivating layer causes problems in achieving the required precision. The mechanism of the problems and the solution implemented are described in detail.

  6. Prehistoric rock avalanches in the Olympic Mountains, Washington

    USGS Publications Warehouse

    Schuster, R.L.; Logan, R.L.; Pringle, P.T.

    1992-01-01

    Rock avalanches blocked streams in the Olympic Mountains southwest of Puget Sound during the past few thousand years. Limiting radiocarbon ages indicated that three or four of six avalanches occurred from 1000 to 1300 years ago or shortly thereafter. Most of the dates were from the outer preserved rings of trees drowned behind avalanche dams. These three or four avalanches may be coeval not only with one another but also with abrupt tectonic deformation in western Washington. No rock avalanches in the Olympic Mountains are known to have resulted from storms or earthquakes during the past century. The avalanches strengthen the case that a large prehistoric earthquake occurred in the Puget Sound region.

  7. Rock avalanches: significance and progress (Invited)

    NASA Astrophysics Data System (ADS)

    Davies, T. R.

    2013-12-01

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

  8. LWIR HgCdTe barrier photodiode with Auger-suppression

    NASA Astrophysics Data System (ADS)

    Kopytko, M.; Kębłowski, A.; Gawron, W.; Pusz, W.

    2016-03-01

    This paper reports on advanced metalorganic chemical vapor deposition (MOCVD) grown HgCdTe barrier photodiodes for long wave infrared (LWIR) application. The n+p+Bp πN+ device is a concept of a specific barrier bandgap architecture integrated with Auger-suppression as a good solution for high operating temperature (HOT) infrared detectors with high detectivity and sub-nanosecond time constant. The design approach, growth aspects and detector characterization of HgCdTe n+p+Bp πN+ barrier photodiodes operated with thermoelectric cooling (230 K) have been discussed in the paper. The influence of absorber thickness on the device’s properties has been analyzed in the experiment.

  9. Electron avalanches in liquid argon mixtures

    SciTech Connect

    Kim, J.G.; Dardin, S.M.; Kadel, R.W.; Kadyk, J.A.; Wenzel, W.B.; Peskov, V.

    2004-03-19

    We have observed stable avalanche gain in liquid argon when mixed with small amounts of xenon in the high electric field (>7 MV/cm) near the point of a chemically etched needle in a point-plane geometry. We identify two gain mechanisms, one pressure dependent, and the other independent of the applied pressure. We conclude that the pressure dependent signals are from avalanche gain in gas bubbles at the tip of the needle, while the pressure independent pulses are from avalanche gain in liquid. We measure the decay time spectra of photons from both types of avalanches. The decay times from the pressure dependent pulses decrease (increase) with the applied pressure (high voltage), while the decay times from the pressure independent pulses are approximately independent of pressure or high voltage. For our operating conditions, the collected charge distribution from avalanches is similar for 60 keV or 122 keV photon sources. With krypton additives, instead of Xe, we measure behavior consistent with only the pressure dependent pulses. Neon and TMS were also investigated as additives, and designs for practical detectors were tested.

  10. Electron avalanches in liquid argon mixtures

    NASA Astrophysics Data System (ADS)

    Kim, J. G.; Dardin, S. M.; Kadel, R. W.; Kadyk, J. A.; Peskov, V.; Wenzel, W. A.

    2004-12-01

    We have observed stable avalanche gain in liquid argon when mixed with small amounts of xenon (xe) in the high electric field ( >7 MV/cm) near the point of a chemically etched needle in a point-plane geometry. We identify two gain mechanisms, one pressure dependent, and the other independent of the applied pressure. We conclude that the pressure-dependent signals are from avalanche gain in gas bubbles at the tip of the needle, while the pressure-independent pulses are from avalanche gain in liquid. We measure the decay time spectra of photons from both types of avalanches. The decay times from the pressure-dependent pulses decrease (increase) with the applied pressure (high voltage), while the decay times from the pressure-independent pulses are approximately independent of pressure or high voltage. For our operating conditions, the collected charge distribution from avalanches is similar for 60 or 122 keV photon sources. With krypton additives, instead of Xe, we measure behavior consistent with only the pressure-dependent pulses. Neon and TMS were also investigated as additives, and designs for practical detectors were tested.

  11. Analytical modeling for gamma radiation damage on silicon photodiodes

    NASA Astrophysics Data System (ADS)

    Jafari, H.; Feghhi, S. A. H.

    2016-04-01

    Radiation-induced damage in PIN silicon photodiode induces degradation of the photodiode parameters. In this work, by presenting an analytical model, the effect of gamma dose on the dark current in a PIN photodiode array was investigated. Geant4 was used to obtain the damage constant as a result of primary incident particle fluence and NIEL distribution calculations. Experimental measurements as well as numerical simulation of the semiconductor with ATLAS were carried out to verify and parameterize the analytical model calculations. A reasonable agreement has been found between analytical results and experimental data for BPX65 silicon photodiodes irradiated by a Co-60 gamma source at total doses up to 500 krad under different reverse voltages. Moreover, the results showed that the dark current of each photodiode array pixel has considerably increased by gamma dose irradiation.

  12. The application of Landsat data to mapping avalanche hazards

    NASA Technical Reports Server (NTRS)

    Waterman, S.

    1979-01-01

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

  13. Dynamic scaling for avalanches in disordered systems

    SciTech Connect

    Zheng, Guang-Ping; Li, Mo

    2001-03-01

    Dynamic scaling for fracture or breakdown process in disordered systems is investigated in a two-dimensional random field Ising model (RFIM). We find two evolving stages in the avalanche process in the RFIM. At the short-time regime, a power-law growth of the avalanche size {Delta}s is observed; and at late times, the conventional nucleation and growth process is found. At the critical point of the RFIM, the avalanche size is found to obey the dynamic scaling law {Delta}s{approx}t{sup (d-{beta}/{nu})/z}. From this dynamic scaling relation, the critical strength of the random field D{sub c} and the critical exponents, {beta}, {nu}, and z, are determined. The observed dynamics is explained by a simple nucleation theory of first-order phase transformations.

  14. Identifying single electron avalanches in streamer discharges

    NASA Astrophysics Data System (ADS)

    Wormeester, Gideon; Nijdam, Sander; Ebert, Ute

    2011-10-01

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

  15. Advances in SPECT and PET Hardware.

    PubMed

    Slomka, Piotr J; Pan, Tinsu; Berman, Daniel S; Germano, Guido

    2015-01-01

    There have been significant recent advances in single photon emission computed tomography (SPECT) and positron emission tomography (PET) hardware. Novel collimator designs, such as multi-pinhole and locally focusing collimators arranged in geometries that are optimized for cardiac imaging have been implemented to reduce imaging time and radiation dose. These new collimators have been coupled with solid state photon detectors to further improve image quality and reduce scanner size. The new SPECT scanners demonstrate up to a 7-fold increase in photon sensitivity and up to 2 times improvement in image resolution. Although PET scanners are used primarily for oncological imaging, cardiac imaging can benefit from the improved PET sensitivity of 3D systems without inter-plane septa and implementation of the time-of-flight reconstruction. Additionally, resolution recovery techniques are now implemented by all major PET vendors. These new methods improve image contrast, image resolution, and reduce image noise. Simultaneous PET/magnetic resonance (MR) hybrid systems have been developed. Solid state detectors with avalanche photodiodes or digital silicon photomultipliers have also been utilized in PET. These new detectors allow improved image resolution, higher count rate, as well as a reduced sensitivity to electromagnetic MR fields. PMID:25721706

  16. Laboratory study of avalanches in magnetized plasmas.

    PubMed

    Van Compernolle, B; Morales, G J; Maggs, J E; Sydora, R D

    2015-03-01

    It is demonstrated that a novel heating configuration applied to a large and cold magnetized plasma allows the study of avalanche phenomena under controlled conditions. Intermittent collapses of the plasma pressure profile, associated with unstable drift-Alfvén waves, exhibit a two-slope power-law spectrum with exponents near -1 at lower frequencies and in the range of -2 to -4 at higher frequencies. A detailed mapping of the spatiotemporal evolution of a single avalanche event is presented. PMID:25871044

  17. Phase avalanches in near-adiabatic evolutions

    SciTech Connect

    Vertesi, T.; Englman, R.

    2006-02-15

    In the course of slow, nearly adiabatic motion of a system, relative changes in the slowness can cause abrupt and high magnitude phase changes, ''phase avalanches,'' superimposed on the ordinary geometric phases. The generality of this effect is examined for arbitrary Hamiltonians and multicomponent (>2) wave packets and is found to be connected (through the Blaschke term in the theory of analytic signals) to amplitude zeros in the lower half of the complex time plane. Motion on a nonmaximal circle on the Poincare-sphere suppresses the effect. A spectroscopic transition experiment can independently verify the phase-avalanche magnitudes.

  18. Relating rock avalanche morphology to emplacement processes

    NASA Astrophysics Data System (ADS)

    Dufresne, Anja; Prager, Christoph; Bösmeier, Annette

    2015-04-01

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

  19. Avalanche mode of motion: Implications from lunar examples

    USGS Publications Warehouse

    Howard, K.A.

    1973-01-01

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

  20. Avalanche mode of motion - Implications from lunar examples.

    NASA Technical Reports Server (NTRS)

    Howard, K. A.

    1973-01-01

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

  1. A 64 single photon avalanche diode array in 0.18 µm CMOS standard technology with versatile quenching circuit for quick prototyping

    NASA Astrophysics Data System (ADS)

    Uhring, Wilfried; Le Normand, Jean-Pierre; Zint, Virginie; Dumas, Norbert; Dadouche, Foudil; Malasse, Imane; Scholz, Jeremy

    2012-04-01

    Several works have demonstrated the successfully integration of Single-photon avalanche photodiodes (SPADs) operating in Geiger mode in a standard CMOS circuit for the last 10 years. These devices offer an exceptional temporal resolution as well as a very good optical sensitivity. Nevertheless, it is difficult to predict the expected performances of such a device. Indeed, for a similar structure of SPAD, some parameter values can differ by two orders of magnitude from a technology to another. We proposed here a procedure to identify in just one or two runs the optimal structure of SPAD available for a given technology. A circuit with an array of 64 SPAD has been realized in the Tower-Jazz 0.18 μm CMOS image sensor process. It encompasses an array of 8 different structures of SPAD reproduced in 8 diameters in the range from 5 μm up to 40 μm. According to the SPAD structures, efficient shallow trench insulator and/or P-Well guard ring are used for preventing edge breakdown. Low dark count rate of about 100 Hz are expected thanks to the use of buried n-well layer and a high resistivity substrate. Each photodiode is embedded in a pixel which includes a versatile quenching circuitry and an analog output of its cathode voltage. The quenching system is configurable in four operation modes; the SPAD is disabled, the quenching is completely passive, the reset of the photodiode is active and the quenching is fully active. The architecture of the array makes possible the characterization of every single photodiode individually. The parameters to be measured for a SPAD are the breakdown avalanche voltage, the dark count rate, the dead time, the timing jitter, the photon detection probability and the after-pulsing rate.

  2. Note: Multi-confocal fluorescence correlation spectroscopy in living cells using a complementary metal oxide semiconductor-single photon avalanche diode array

    NASA Astrophysics Data System (ADS)

    Kloster-Landsberg, M.; Tyndall, D.; Wang, I.; Walker, R.; Richardson, J.; Henderson, R.; Delon, A.

    2013-07-01

    Living cells are heterogeneous and rapidly changing biological samples. It is thus desirable to measure molecular concentration and dynamics in many locations at the same time. In this note, we present a multi-confocal setup capable of performing simultaneous fluorescence correlation spectroscopy measurements, by focusing the spots with a spatial light modulator and acquiring data with a monolithic 32 × 32 single-photon avalanche photodiode array. A post-processing method is proposed to correct cross-talk effects between neighboring spots. We demonstrate the applicability of our system by simultaneously measuring the diffusion of free enhanced Green Fluorescent Protein (eGFP) molecules at nine different points in living cells.

  3. Diamond photodiodes for x-ray application

    SciTech Connect

    Distel, James R; Smedley, John; Keister, Jeffrey W; Muller, Erik; Jordan - Sweet, Jean; Bohon, Jen; Dong, Bin

    2009-01-01

    Single crystal high purity CVD diamonds have been metallized and calibrated as photodiodes at the National Synchrotron Light Source (NSLS). Current mode responsivity measurements have been made over a wide range (0.2-28 keV) of photon energies across several beamlines. Linear response has been achieved over ten orders of magnitude of incident flux, along with uniform spatial response. A simple model of responsivity has been used to describe the results, yielding a value of 13.3 {+-} 0.5 eV for the mean pair creation energy. The responsivity vs. photon energy data show a dip for photon energies near the carbon edge (284 eV), indicating incomplete charge collection for carriers created less than one micron from the metallized layer.

  4. Assessing the importance of terrain parameters on glide avalanche release

    USGS Publications Warehouse

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

    2014-01-01

    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

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

    SciTech Connect

    Hunt, D. C.; Tanioka, Kenkichi; Rowlands, J. A.

    2007-12-15

    The flat-panel detector (FPD) is the state-of-the-art detector for digital radiography. The FPD can acquire images in real-time, has superior spatial resolution, and is free of the problems of x-ray image intensifiers--veiling glare, pin-cushion and magnetic distortion. However, FPDs suffer from poor signal to noise ratio performance at typical fluoroscopic exposure rates where the quantum noise is reduced to the point that it becomes comparable to the fixed electronic noise. It has been shown previously that avalanche multiplication gain in amorphous selenium (a-Se) can provide the necessary amplification to overcome the electronic noise of the FPD. Avalanche multiplication, however, comes with its own intrinsic contribution to the noise in the form of gain fluctuation noise. In this article a cascaded systems analysis is used to present a modified metric related to the detective quantum efficiency. The modified metric is used to study a diagnostic x-ray imaging system in the presence of intrinsic avalanche multiplication noise independently from other noise sources, such as electronic noise. An indirect conversion imaging system is considered to make the study independent of other avalanche multiplication related noise sources, such as the fluctuations arising from the depth of x-ray absorption. In this case all the avalanche events are initiated at the surface of the avalanche layer, and there are no fluctuations in the depth of absorption. Experiments on an indirect conversion x-ray imaging system using avalanche multiplication in a layer of a-Se are also presented. The cascaded systems analysis shows that intrinsic noise of avalanche multiplication will not have any deleterious influence on detector performance at zero spatial frequency in x-ray imaging provided the product of conversion gain, coupling efficiency, and optical quantum efficiency are much greater than a factor of 2. The experimental results show that avalanche multiplication in a-Se behaves as

  6. Vortex avalanches in a type II superconductor

    SciTech Connect

    Behnia, K.; Capan, C.; Mailly, D.; Etienne, B.

    1999-12-01

    The authors report on a study of the spatiotemporal variation of magnetic induction in a superconducting niobium sample during a slow sweep of external magnetic field. A sizable fraction of the increase in the local vortex population occurs in abrupt jumps. They compare the size distribution of these avalanches with the predictions of self-organized-criticality models for vortex dynamics.

  7. Rock avalanches caused by earthquakes: Source characteristics

    USGS Publications Warehouse

    Keefer, D.K.

    1984-01-01

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

  8. Fractal avalanche ruptures in biological membranes

    NASA Astrophysics Data System (ADS)

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

    2010-11-01

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

  9. Rock avalanches caused by earthquakes: source characteristics.

    PubMed

    Keefer, D K

    1984-03-23

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

  10. Stable, high quantum efficiency silicon photodiodes for vacuum-UV applications

    NASA Technical Reports Server (NTRS)

    Korde, Raj; Canfield, L. Randall; Wallis, Brad

    1988-01-01

    Silicon photodiodes have been developed by defect-free phosphorus diffusion having practically no carrier recombination at the SiSiO2 interface or in the front diffused region. The quantum efficiency of these photodiodes was found to be around 120 percent at 100 nm. Unlike the previously tested silicon photodiodes, the developed photodiodes exhibit extremely stable quantum efficiency over extended periods of time. The possibility of using these photodiodes as vacuum ultraviolet detector standards is being currently investigated.

  11. Performance Analysis of OCDMA Based on AND Detection in FTTH Access Network Using PIN & APD Photodiodes

    NASA Astrophysics Data System (ADS)

    Aldouri, Muthana; Aljunid, S. A.; Ahmad, R. Badlishah; Fadhil, Hilal A.

    2011-06-01

    In order to comprise between PIN photo detector and avalanche photodiodes in a system used double weight (DW) code to be a performance of the optical spectrum CDMA in FTTH network with point-to-multi-point (P2MP) application. The performance of PIN against APD is compared through simulation by using opt system software version 7. In this paper we used two networks designed as follows one used PIN photo detector and the second using APD photo diode, both two system using with and without erbium doped fiber amplifier (EDFA). It is found that APD photo diode in this system is better than PIN photo detector for all simulation results. The conversion used a Mach-Zehnder interferometer (MZI) wavelength converter. Also we are study, the proposing a detection scheme known as AND subtraction detection technique implemented with fiber Bragg Grating (FBG) act as encoder and decoder. This FBG is used to encode and decode the spectral amplitude coding namely double weight (DW) code in Optical Code Division Multiple Access (OCDMA). The performances are characterized through bit error rate (BER) and bit rate (BR) also the received power at various bit rate.

  12. Experimental study on photodiode damage by millisecond pulse laser irradiation

    NASA Astrophysics Data System (ADS)

    Wei, Zhi; Jin, Guangyong; Tan, Yong; Wang, Di

    2015-10-01

    The photoelectric detector is a very significance part in laser and its application system, but when photoelectric detector irradiated by high energy laser, the laser may cause thermal damage to the photoelectric detector, when the temperature more than its melting point and vaporization point, there will be a permanent damage in PIN photodetector, leading to the failure of photoelectric detector. In order to study the photodiode damage mechanism by millisecond pulse laser irradiation, a set of experimental system has been built, choosing appropriate pulsed laser parameters to irradiate silicon-based PIN photodiode and monitoring the surface temperature in the process of irradiation, until the PIN photodiode complete failure. The measurement results of real-time temperature, responsivity change and damage morphology were analyzed to conclude the failure reason of the PIN photodiode. The results showed that with the increase of laser energy, the PIN photodiode surface temperature would be also increased accordingly. Before the laser irradiation, the responsivity of PIN photodiode was the same. But after the laser irradiation, the responsivity of the PIN photodiode would be changed and with the increase of laser energy, the decline extent of responsivity would be also increased. Judging from the ablation, crack and fold zone on the surface of PIN photodiode after the laser irradiation, the damage was for thermal stress effect. The continuity of material confined its free expansion. Therefore, the uneven thermal expansion induced the great thermal stress. At the same time, the silicon transited from brittle to ductile and the yield strength dramatically decreased. Once the maximum thermal stress exceeded the critical stress, the plastic deformation and the brittle cracks of silicon would be generated. With the increase of laser energy, the thermal stress damage extent of PIN photodiode would be also increased accordingly and the black area of laser ablation would be

  13. Smartphone applications for communicating avalanche risk information - a review of existing practices

    NASA Astrophysics Data System (ADS)

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

    2015-11-01

    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.

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

    SciTech Connect

    Hunt, D. C.; Tanioka, Kenkichi; Rowlands, J. A.

    2007-03-15

    The past decade has seen the swift development of the flat-panel detector (FPD), also known as the active matrix flat-panel imager, for digital radiography. This new technology is applicable to other modalities, such as fluoroscopy, which require the acquisition of multiple images, but could benefit from some improvements. In such applications where more than one image is acquired less radiation is available to form each image and amplifier noise becomes a serious problem. Avalanche multiplication in amorphous selenium (a-Se) can provide the necessary amplification prior to read out so as to reduce the effect of electronic noise of the FPD. However, in direct conversion detectors avalanche multiplication can lead to a new source of gain fluctuation noise called depth dependent avalanche noise. A theoretical model was developed to understand depth dependent avalanche noise. Experiments were performed on a direct imaging system implementing avalanche multiplication in a layer of a-Se to validate the theory. For parameters appropriate for a diagnostic imaging FPD for fluoroscopy the detective quantum efficiency (DQE) was found to drop by as much as 50% with increasing electric field, as predicted by the theoretical model. This drop in DQE can be eliminated by separating the collection and avalanche regions. For example by having a region of low electric field where x rays are absorbed and converted into charge that then drifts into a region of high electric field where the x-ray generated charge undergoes avalanche multiplication. This means quantum noise limited direct conversion FPD for low exposure imaging techniques are a possibility.

  15. Characterization and Modeling of Indium Gallium Antimonide Avalanche Photodiode and of Indium Gallium Arsenide Two-band Detector

    NASA Technical Reports Server (NTRS)

    2006-01-01

    A model of the optical properties of Al(x)Ga(1-x)As(y)Sb(1-y) and In(x)Ga(1-x)As(y)Sb(1-y) is presented, including the refractive, extinction, absorption and reflection coefficients in terms of the optical dielectric function of the materials. Energy levels and model parameters for each binary compound are interpolated to obtain the needed ternaries and quaternaries for various compositions. Bowing parameters are considered in the interpolation scheme to take into account the deviation of the calculated ternary and quaternary values from experimental data due to lattice disorders. The inclusion of temperature effects is currently being considered.

  16. Modelling the evolution of temperature in avalanche flow

    NASA Astrophysics Data System (ADS)

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

    2013-04-01

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

  17. Olokele rock avalanche, island of Kauai, Hawaii.

    USGS Publications Warehouse

    Jones, B.L.; Chinn, S.S.W.; Brice, J.C.

    1984-01-01

    In October 1981 a mass of rock and soil having an estimated volume of 500 000 m3 fell as a rock fall-avalanche from a steep slope 800 m high near the head of Olokele Canyon. Boulders were launched into the air from a bench on the slope for a downstream distance of about 850 m. The velocity of the avalanche was rapidly diminished by impact against the valley sides, and it became a muddy debris flow that traveled 4.6 km downstream, severely eroding the valley sides. The volume of debris deposited on the canyon bottom is estimated to be 2 500 000 m3, or about four times the volume derived from the slope. -from Authors

  18. Stochastic simulation of electron avalanches on supercomputers

    SciTech Connect

    Rogasinsky, S. V.; Marchenko, M. A.

    2014-12-09

    In the paper, we present a three-dimensional parallel Monte Carlo algorithm named ELSHOW which is developed for simulation of electron avalanches in gases. Parallel implementation of the ELSHOW was made on supercomputers with different architectures (massive parallel and hybrid ones). Using the ELSHOW, calculations of such integral characteristics as the number of particles in an avalanche, the coefficient of impact ionization, the drift velocity, and the others were made. Also, special precise computations were made to select an appropriate size of the time step using the technique of dependent statistical tests. Particularly, the algorithm consists of special methods of distribution modeling, a lexicographic implementation scheme for “branching” of trajectories, justified estimation of functionals. A comparison of the obtained results for nitrogen with previously published theoretical and experimental data was made.

  19. Communicators' perspective on snow avalanche risk communication

    NASA Astrophysics Data System (ADS)

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

    2014-12-01

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

  20. Hierarchical networks, power laws, and neuronal avalanches

    NASA Astrophysics Data System (ADS)

    Friedman, Eric J.; Landsberg, Adam S.

    2013-03-01

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

  1. Snow Avalanche Release, Scale Invariance and Criticallity

    NASA Astrophysics Data System (ADS)

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

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

  2. Teaching Natural Hazards: The Use of Snow Avalanches in Demonstrating and Addressing Geographic Topics and Principles.

    ERIC Educational Resources Information Center

    Butler, David R.

    1988-01-01

    Illustrates the importance of studying the snow avalanche as a natural hazard. Describes the various kinds of snow avalanches, the types of triggering mechanisms that produce them, the typical avalanche terrain, and the geomorphic and the vegetative evidence for snow avalanching. Depicts methods of human adjustment to the avalanche hazard.…

  3. Detection of short-term activity avalanches in human brain default mode network with ultrafast MR encephalography.

    PubMed

    Rajna, Zalán; Kananen, Janne; Keskinarkaus, Anja; Seppänen, Tapio; Kiviniemi, Vesa

    2015-01-01

    Recent studies pinpoint visually cued networks of avalanches with MEG/EEG data. Co-activation pattern (CAP) analysis can be used to detect single brain volume activity profiles and hemodynamic fingerprints of neuronal avalanches as sudden high signal activity peaks in classical fMRI data. In this study, we aimed to detect dynamic patterns of brain activity spreads with the use of ultrafast MR encephalography (MREG). MREG achieves 10 Hz whole brain sampling, allowing the estimation of spatial spread of an avalanche, even with the inherent hemodynamic delay of the BOLD signal. We developed a novel computational method to separate avalanche type fast activity spreads from motion artifacts, vasomotor fluctuations, and cardio-respiratory noise in human brain default mode network (DMN). Reproducible and classical DMN sources were identified using spatial ICA prior to advanced noise removal in order to assure that ICA converges to reproducible networks. Brain activity peaks were identified from parts of the DMN, and normalized MREG data around each peak were extracted individually to show dynamic avalanche type spreads as video clips within the DMN. Individual activity spread video clips of specific parts of the DMN were then averaged over the group of subjects. The experiments show that the high BOLD values around the peaks are mostly spreading along the spatial pattern of the particular DMN segment detected with ICA. With also the spread size and lifetime resembling the expected power law distributions, this indicates that the detected peaks are parts of activity avalanches, starting from (or crossing) the DMN. Furthermore, the split, one-sided sub-networks of the DMN show different spread directions within the same DMN framework. The results open possibilities to follow up brain activity avalanches in the hope to understand more about the system wide properties of diseases related to DMN dysfunction. PMID:26321936

  4. Monte Carlo simulations within avalanche rescue

    NASA Astrophysics Data System (ADS)

    Reiweger, Ingrid; Genswein, Manuel; Schweizer, Jürg

    2016-04-01

    Refining concepts for avalanche rescue involves calculating suitable settings for rescue strategies such as an adequate probing depth for probe line searches or an optimal time for performing resuscitation for a recovered avalanche victim in case of additional burials. In the latter case, treatment decisions have to be made in the context of triage. However, given the low number of incidents it is rarely possible to derive quantitative criteria based on historical statistics in the context of evidence-based medicine. For these rare, but complex rescue scenarios, most of the associated concepts, theories, and processes involve a number of unknown "random" parameters which have to be estimated in order to calculate anything quantitatively. An obvious approach for incorporating a number of random variables and their distributions into a calculation is to perform a Monte Carlo (MC) simulation. We here present Monte Carlo simulations for calculating the most suitable probing depth for probe line searches depending on search area and an optimal resuscitation time in case of multiple avalanche burials. The MC approach reveals, e.g., new optimized values for the duration of resuscitation that differ from previous, mainly case-based assumptions.

  5. Thermal avalanches near a Mott transition.

    PubMed

    Lashley, J C; Gofryk, K; Mihaila, B; Smith, J L; Salje, E K H

    2014-01-22

    We probe the volume collapse transition (ΔV/Vo ∼ 15%) between the isostructural γ and α phases (T ∼ 100 K) of Ce0.9Th0.1 using the Hall effect, three-terminal capacitive dilatometry, and electrical resistivity measurements. Hall effect measurements confirm the itinerant ground state as the carrier concentration increases by a factor of 7 in the α phase, γ phase (nH = 5.28 × 10(26) m(-3)), and the α phase (nH = 3.76 × 10(27) m(-3)). We were able to detect a noise spectrum consisting of avalanches while slowly varying the temperature through the hysteretic region. We surmise that the avalanches originate from intergranular stresses at the interfaces between partially transformed high-volume and low-volume phases. The statistical distribution of avalanches obey power laws with energy exponent ϵ ≃ 1.5. Hall effect measurements, combined with universal critical exponents, point to short electron mean-free percolation pathways and carrier localization at phase interfaces. Carrier localization was predicted many years ago for elemental cerium by Johansson (1974 Phil. Mag. 30 469). PMID:24351548

  6. Reversible Avalanches and Criticality in Amorphous Solids

    NASA Astrophysics Data System (ADS)

    Reichhardt, Charles

    2015-03-01

    Despite its importance for basic science and industry, the physical process that causes a solid to change its shape permanently under external deformation is still not well understood. In this paper we use molecular dynamics simulations of amorphous solids under oscillatory shear to study this phenomenon, and show that at a critical strain amplitude, the size of the cooperative atomic motion that allows for a permanent deformation diverges. We compare this non-equilibrium critical behavior to that of a ``front depinning'' transition. This viewpoint, based on fluctuations and statistics, is complementary to the dynamical ``transition to chaos'' which was previously identified at the same strain amplitude. Below this irreversibile-depinning transition, we observe large avalanches which are completely repetitive with each shear strain cycle. This suggests that while avalanches on their own do not cause irreversible deformation, it is likely that the irreversibility transition and the ``depinning-like'' transition are two aspects of the same phenomena. One implication is that the transition could be detected before the onset of irreversible flow by an analysis of the power spectra of avalanches. Work done in collaboration with Ido Regev, Karin Dahmen, John Weber, and Turab Lookman.

  7. Mechanisms of evolution of avalanches in regular graphs

    NASA Astrophysics Data System (ADS)

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

    2013-06-01

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

  8. Avalanches in tip-driven interfaces in random media

    NASA Astrophysics Data System (ADS)

    Aragón, L. E.; Kolton, A. B.; Le Doussal, P.; Wiese, K. J.; Jagla, E. A.

    2016-01-01

    We analyse by numerical simulations and scaling arguments the avalanche statistics of 1-dimensional elastic interfaces in random media driven at a single point. Both global and local avalanche sizes are power-law distributed, with universal exponents given by the depinning roughness exponent ζ and the interface dimension d, and distinct from their values in the uniformly driven case. A crossover appears between uniformly driven behaviour for small avalanches, and point-driven behaviour for large avalanches. The scale of the crossover is controlled by the ratio between the stiffness of the pulling spring and the elasticity of the interface; it is visible both in the global and local avalanche-size distributions, as in the average spatial avalanche shape. Our results are relevant to model experiments involving locally driven elastic manifolds at low temperatures, such as magnetic domain walls or vortex lines in superconductors.

  9. Avalanche in adhesion. [interfacial separation between two Ni crystals

    NASA Technical Reports Server (NTRS)

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

    1989-01-01

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

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

    NASA Astrophysics Data System (ADS)

    Bozhinskiy, A. N.

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

  11. Unambiguous reconstruction of network structure using avalanche dynamics.

    PubMed

    Leleu, Timothée; Aihara, Kazuyuki

    2015-02-01

    A robust method for inferring the structure of networks is presented based on the one-to-one correspondence between the expected composition of cascades of bursts of activity, called crackling noise or avalanches, and the weight matrix. Using a model of neuronal avalanches as a paradigmatic example, we derive this correspondence exactly by calculating the closed-form expression of the joint probability distribution of avalanche sizes obtained by counting separately the number of elements active in each subnetwork during avalanches. PMID:25768549

  12. Photodiode arrays having minimized cross-talk between diodes

    DOEpatents

    Guckel, Henry; McNamara, Shamus P.

    2000-10-17

    Photodiode arrays are formed with close diode-to-diode spacing and minimized cross-talk between diodes in the array by isolating the diodes from one another with trenches that are formed between the photodiodes in the array. The photodiodes are formed of spaced regions in a base layer, each spaced region having an impurity type opposite to that of the base layer to define a p-n junction between the spaced regions and the base layer. The base layer meets a substrate at a boundary, with the substrate being much more heavily doped than the base layer with the same impurity type. The trenches extend through the base layer and preferably into the substrate. Minority carriers generated by absorption of light photons in the base layer can only migrate to an adjacent photodiode through the substrate. The lifetime and the corresponding diffusion length of the minority carriers in the substrate is very short so that all minority carriers recombine in the substrate before reaching an adjacent photodiode.

  13. Long-wavelength photonic integrated circuits and avalanche photodetectors

    NASA Astrophysics Data System (ADS)

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

    2001-10-01

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

  14. Measurement of snow particle size and speed in powder snow avalanches

    NASA Astrophysics Data System (ADS)

    Ito, Yoichi; Nishimura, Kouichi; Naaim-Bouvet, Florence; Bellot, Hervé; Thibert, Emmanuel; Ravanat, Xavier; Fontaine, Firmin

    2015-04-01

    Generally snow avalanches consist a dense-flow layer at the bottom and a powder snow cloud on top. Snow particle size and speed are key parameters to describe the turbulent condition in the powder cloud, however, the information on the particles were not well investigated. In this study, we observed powder snow avalanches using a snow particle counter (SPC) to measure the particle size and speed. The SPC is an optical device consisting a laser diode and photodiode; a pulse signal proportional to its diameter is generated resulting from a snow particle passing through the sensing volume. In general use, the signals are sent to a transducer and divided into 32 size classes based on particle diameter to observe the snow particle size distribution and mass flux at 1-s intervals. In this study, the direct output signal from the transducer was also acquired at a high frequency to obtain the original pulse signal produced by each snow particle. Then the speed of each particle can be calculated using the peak of the pulse, which corresponds to particle diameter and the duration over which the particle passes through the sampling area. We also employed an ultrasonic anemometer to measure air flow speed. Both sensors were installed at the Col du Lautaret Pass in the French Alps. The results of the particle size and speed distribution were then compared with airflow movement in the powder cloud. The ratio of the particle and airflow speeds changed by the particle size distribution and the distance from the dense-flow layer.

  15. Analysis of the photodiode boundary layer transition indicator

    SciTech Connect

    Kuntz, D.W.; Wilken, A.C.; Payne, J.L.

    1994-01-01

    The photodiode transition indicator is a device which has been successfully used to determine the onset of boundary layer transition on numerous hypersonic flight vehicles. The exact source of the electromagnetic radiation detected by the photodiode at transition was not understood. In some cases early saturation of the device occurred, and the device failed to detect transition. Analyses have been performed to determine the source of the radiation producing the photodiode signal. The results of these analyses indicate that the most likely source of the radiation is blackbody emission from the heatshield material bordering the quartz window of the device. Good agreement between flight data and calculations based on this radiation source has been obtained. Analyses also indicate that the most probable source of the radiation causing early saturation is blackbody radiation from carbon particles which break away from the nosetip during the ablation process.

  16. Photonic microwave generation with high-power photodiodes.

    PubMed

    Fortier, Tara M; Quinlan, Franklyn; Hati, Archita; Nelson, Craig; Taylor, Jennifer A; Fu, Yang; Campbell, Joe; Diddams, Scott A

    2013-05-15

    We utilized and characterized high-power, high-linearity modified unitraveling carrier (MUTC) photodiodes for low-phase-noise photonic microwave generation based on optical frequency division (OFD). When illuminated with picosecond pulses from a repetition-rate-multiplied gigahertz Ti:sapphire modelocked laser, the photodiodes can achieve a 10 GHz signal power of +14 dBm. Using these diodes, we generated a 10 GHz microwave tone with less than 500 attoseconds absolute integrated timing jitter (1 Hz-10 MHz) and a phase noise floor of -177 dBc/Hz.We also characterized the electrical response, amplitude-to-phase conversion, saturation, and residual noise of the MUTC photodiodes. PMID:23938920

  17. Avalanche-like behavior in ciliary import

    PubMed Central

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

    2013-01-01

    Cilia and flagella are microtubule-based organelles that protrude from the cell body. Ciliary assembly requires intraflagellar transport (IFT), a motile system that delivers cargo from the cell body to the flagellar tip for assembly. The process controlling injections of IFT proteins into the flagellar compartment is, therefore, crucial to ciliogenesis. Extensive biochemical and genetic analyses have determined the molecular machinery of IFT, but these studies do not explain what regulates IFT injection rate. Here, we provide evidence that IFT injections result from avalanche-like releases of accumulated IFT material at the flagellar base and that the key regulated feature of length control is the recruitment of IFT material to the flagellar base. We used total internal reflection fluorescence microscopy of IFT proteins in live cells to quantify the size and frequency of injections over time. The injection dynamics reveal a power-law tailed distribution of injection event sizes and a negative correlation between injection size and frequency, as well as rich behaviors such as quasiperiodicity, bursting, and long-memory effects tied to the size of the localized load of IFT material awaiting injection at the flagellar base, collectively indicating that IFT injection dynamics result from avalanche-like behavior. Computational models based on avalanching recapitulate observed IFT dynamics, and we further show that the flagellar Ras-related nuclear protein (Ran) guanosine 5'-triphosphate (GTP) gradient can in theory act as a flagellar length sensor to regulate this localized accumulation of IFT. These results demonstrate that a self-organizing, physical mechanism can control a biochemically complex intracellular transport pathway. PMID:23431147

  18. Effects of the 9-T magnetic field on MRS photodiode

    SciTech Connect

    Beznosko, D.; Blazey, G.; Dyshkant, A.; Rykalin, V.; /Northern Illinois U.

    2005-10-01

    The experimental results on the performance of the MRS (Metal/Resistor/Semiconductor) photodiode in the strong magnetic field of 9T, and the possible impact of the quench of the magnet at 9.5T on sensor's operation are reported. The measurement method used is being described. The results of the work agree with the expectations that the MRS photodiode is not exhibiting sensitivity to the magnetic field presence. This result is essential for the design of the future electron-positron linear collider detector.

  19. Bilayer avalanche spin-diode logic

    SciTech Connect

    Friedman, Joseph S. Querlioz, Damien; Fadel, Eric R.; Wessels, Bruce W.; Sahakian, Alan V.

    2015-11-15

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

  20. Bilayer avalanche spin-diode logic

    NASA Astrophysics Data System (ADS)

    Friedman, Joseph S.; Fadel, Eric R.; Wessels, Bruce W.; Querlioz, Damien; Sahakian, Alan V.

    2015-11-01

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

  1. Single photon avalanche diode radiation tests

    NASA Astrophysics Data System (ADS)

    Kodet, Jan; Prochazka, Ivan; Blazej, Josef; Sun, Xiaoli; Cavanaugh, John

    2012-12-01

    The single photon counting diodes are recently planned for applications in deep space missions. That is why the proton radiation and gamma ray radiation tests of silicon based single photon avalanche diodes were measured and compared. The main characteristic that changed after the irradiation was effective dark count rate, which was measured using actively quenching and gating circuit. The radiation reached 6.5 krad at 53 MeV protons energy and 34 krad using gamma ray radiation source 60Co. The annealing rates were monitored at room temperature and at 60 °C.

  2. Novel Micro-pixel Avalanche Photo Diodes and their Possible Application in Cosmic Ray/Astrophysical Researches

    NASA Astrophysics Data System (ADS)

    Zheleznykh, I.M.; Sadygov, Z.Ya.; Khrenov, B.A.; Tkatchev, L.G.; Zerrouk, F.

    In 80th a new type of APDs with negative local feedback which significantly reduces the excess noise factor introduced by the avalanche process - the metal-resistive layer-semiconductor (MRS) APDs - were developed in INR (Moscow) by Sadygov et al. in the frameworks of the Soviet DUMAND program led by M.A. Markov. In 90th and during a few last years some new kinds of the Micro-pixel Avalanche PhotoDiodes (MAPDs), which have high signal gain (up to 106), were developed in INR and JINR (Dubna, Moscow region). The novel MAPDs with high photon detection efficiency and very good single electron resolution which were produced and tested by "Dubna APD" collaboration (JINR - INR - IP AZ - "Zecotek" Company - "Mikron" factory) are described. Sensitive area of a MAPD-------------------------- 1 mm2, 4 mm2 and 9 mm2; Spectral range of sensitivity --------------------- 250-650 nm; Photon detection efficiency (max.) ------------- 20-30 %; Operating voltage ----------------------------------- ~100 V. The excellent parameters of MAPDs are achieved due to forming an electric field with a specific geometry in the multilayer silicon structure, which ensures the localization of the avalanche processes and limits them to the micro regions (micro-pixels) with a diameter of 3 - 30 micron depending of the design. The multi channel modules of a mosaic type on the basis of MAPDs with the above mentioned (and improved!) parameters have a high potential for using as key elements for light detection in fields of Astronomy, Cosmic Ray Physics and Astroparticle Physics. Application of MAPDs in space imaging detectors observing the UV flashes in the atmosphere caused by ultra high energy cosmic ray particles (and other phenomena) is of special interest.

  3. Breakdown of avalanche critical behaviour in polycrystalline plasticity.

    PubMed

    Richeton, Thiebaud; Weiss, Jérôme; Louchet, François

    2005-06-01

    Acoustic emission experiments on creeping ice as well as numerical simulations argue for a self-organization of collective dislocation dynamics during plastic deformation of single crystals into a scale-free pattern of dislocation avalanches characterized by intermittency, power-law distributions of avalanche sizes, complex space-time correlations and aftershock triggering. Here, we address the question of whether such scale-free, close-to-critical dislocation dynamics will still apply to polycrystals. We show that polycrystalline plasticity is also characterized by intermittency and dislocation avalanches. However, grain boundaries hinder the propagation of avalanches, as revealed by a finite (grain)-size effect on avalanche size distributions. We propose that the restraint of large avalanches builds up internal stresses that push temporally the dynamical system into a supercritical state, off the scale-invariant critical regime, and trigger secondary avalanches in neighbouring grains. This modifies the statistical properties of the avalanche population. The results might also bring into question the classical ways of modelling plasticity in polycrystalline materials, based on homogenization procedures. PMID:15880114

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

    NASA Astrophysics Data System (ADS)

    Mead, Stuart R.; Cleary, Paul W.

    2015-09-01

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

  5. Coalescence avalanches in 2D emulsions: a stochastic approach

    NASA Astrophysics Data System (ADS)

    Masila, Danny Raj; Rengaswamy, Raghunathan

    2015-11-01

    One coalescence event in a 2D concentrated emulsion can trigger an avalanche resulting in the rapid destabilization of the drop-assembly. The sensitive dependence of this phenomenon on various factors that include surfactant concentration and viscosities of the fluid phases makes the avalanching problem appear probabilistic. We propose a stochastic framework- that utilizes a probability function to explain local coalescence events- to study the dynamics of the coalescence avalanches. A function that accounts for the local coalescence mechanism is used to fit the experimentally (from literature) measured probability data. A continuation parameter is introduced along with this function to account for the effect of system properties on the avalanche dynamics. Our analysis reveals that this behavior is a result of the inherent autocatalytic nature of the process. We discover that the avalanche dynamics shows critical behavior where two outcomes are favored: no avalanche and large avalanches that lead to destabilization. We study the effect of system size and fluid properties on the avalanche dynamics. A sharp transition from non-autocatalytic (stable emulsions) to autocatalytic (unstable) behavior is observed as parameters are varied.

  6. Age of Palos Verdes submarine debris avalanche, southern California

    USGS Publications Warehouse

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

    2004-01-01

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

  7. Avalanches and the distribution of solar flares

    NASA Technical Reports Server (NTRS)

    Lu, Edward T.; Hamilton, Russell J.

    1991-01-01

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

  8. Reducing financial avalanches by random investments.

    PubMed

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

    2013-12-01

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

  9. Similar Hamiltonian Between Avalanche-effect & Sociophysics

    NASA Astrophysics Data System (ADS)

    Maksoed, Ssi, Wh-

    2016-05-01

    Of similar Hamiltonian concerned in ``sociophysics'', there were RandomFieldIsingModel/RFIM in external field retrieved in S. Sabhapandit:``Hysteresis & Avalanche in RandomFieldIsingModel'',2002:'' ..in 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.

  10. Reducing financial avalanches by random investments

    NASA Astrophysics Data System (ADS)

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

    2013-12-01

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

  11. Avalanches and scaling in plastic deformation

    SciTech Connect

    Koslowski, M.

    2004-01-01

    Plastic deformation of crystalline materials is a complex non-homogeneous process characterized by avalanches in the motion of dislocations. We study the evolution of dislocations loops using an analytically solvable phase-field model of dislocations for ductile single crystals during monotonic loading. We present simulations of dislocations under slow external loading that generate scale-free avalanches and power-law behavior that are characteristics of self organized criticality. The distribution of dislocation loop sizes is given by P(A) {approx} A{sup -{sigma}}, with {sigma} = 1.8 {+-} 0.1. The power law exponent is in agreement with those found in acoustic emission measurements on stressed ice single crystals. In addition to the jerky character of dislocation motion, this model also predicts a range of macroscopic behaviors in agreement with observation, including hardening and dislocation multiplication with monotonic loading and a maximum in the acoustic emission signal at the onset of yielding. At sufficient large stress, the hardening rate drops and the stress-strain curve saturates. At the same time the acoustic emission as well as the dislocation production decreases in agreement with experimental observation.

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

    NASA Astrophysics Data System (ADS)

    Charrière, Marie K. M.; Bogaard, Thom A.

    2016-05-01

    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.

  13. The mobility of rock avalanches: disintegration, entrainment and deposition - a conceptual approach

    NASA Astrophysics Data System (ADS)

    Knapp, Sibylle; Mamot, Philipp; Krautblatter, Michael

    2015-04-01

    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

  14. Biostability of micro-photodiode arrays for subretinal implantation.

    PubMed

    Hämmerle, Hugo; Kobuch, Karin; Kohler, Konrad; Nisch, Wilfried; Sachs, Helmut; Stelzle, Martin

    2002-02-01

    Micro-photodiode arrays based on semiconductor chip technology are being developed to replace degenerated photoreceptor cells in the retina. Electric current is generated in tiny micro-photodiodes and delivered to the adjacent tissue by micro-electrodes. One of the main requirements of a sub-retinal implantable device is long-term stability versus corrosion in vivo (biostability). Biostability of micro-photodiode arrays (MPDA) was investigated in vitro and in vivo. No significant damage was found on chips immersed for up to 21 months in saline solution. Under in vivo conditions, however, the silicon oxide passivation layer of the chip was dissolved within a period of about 6-12 months. Subsequently, the underlying silicon was corroded. In contrast, stimulation electrodes consisting of titanium nitride were well preserved both in vitro and in vivo. The deterioration of the electrical properties of the micro-photodiodes correlated with the morphological damage observed. Strategies aiming at the development of an improved biostable encapsulation of neurotechnological implants have to be investigated and will be discussed briefly. PMID:11771699

  15. Increasing the dynamic range of CMOS photodiode imagers

    NASA Technical Reports Server (NTRS)

    Pain, Bedabrata (Inventor); Cunningham, Thomas J. (Inventor); Hancock, Bruce R. (Inventor)

    2007-01-01

    A multiple-step reset process and circuit for resetting a voltage stored on a photodiode of an imaging device. A first stage of the reset occurs while a source and a drain of a pixel source-follower transistor are held at ground potential and the photodiode and a gate of the pixel source-follower transistor are charged to an initial reset voltage having potential less that of a supply voltage. A second stage of the reset occurs after the initial reset voltage is stored on the photodiode and the gate of the pixel source-follower transistor and the source and drain voltages of the pixel source-follower transistor are released from ground potential thereby allowing the source and drain voltages of the pixel source-follower transistor to assume ordinary values above ground potential and resulting in a capacitive feed-through effect that increases the voltage on the photodiode to a value greater than the initial reset voltage.

  16. Novel vertical silicon photodiodes based on salicided polysilicon trenched contacts

    SciTech Connect

    Kaminski, Yelena; Shauly, Eitan; Paz, Yaron

    2015-12-07

    The classical concept of silicon photodiodes comprises of a planar design characterized by heavily doped emitters. Such geometry has low collection efficiency of the photons absorbed close to the surface. An alternative, promising, approach is to use a vertical design. Nevertheless, realization of such design is technologically challenged, hence hardly explored. Herein, a novel type of silicon photodiodes, based on salicided polysilicon trenched contacts, is presented. These contacts can be prepared up to 10 μm in depth, without showing any leakage current associated with the increase in the contact area. Consequently, the trenched photodiodes revealed better performance than no-trench photodiodes. A simple two dimensional model was developed, allowing to estimate the conditions under which a vertical design has the potential to have better performance than that of a planar design. At large, the deeper the trench is, the better is the vertical design relative to the planar (up to 10 μm for silicon). The vertical design is more advantageous for materials characterized by short diffusion lengths of the carriers. Salicided polysilicon trenched contacts open new opportunities for the design of solar cells and image sensors. For example, these contacts may passivate high contact area buried contacts, by virtue of the conformity of polysilicon interlayer, thus lowering the via resistance induced recombination enhancement effect.

  17. Modelisation de photodetecteurs a base de matrices de diodes avalanche monophotoniques pour tomographie d'emission par positrons

    NASA Astrophysics Data System (ADS)

    Corbeil Therrien, Audrey

    La tomographie d'emission par positrons (TEP) est un outil precieux en recherche preclinique et pour le diagnostic medical. Cette technique permet d'obtenir une image quantitative de fonctions metaboliques specifiques par la detection de photons d'annihilation. La detection des ces photons se fait a l'aide de deux composantes. D'abord, un scintillateur convertit l'energie du photon 511 keV en photons du spectre visible. Ensuite, un photodetecteur convertit l'energie lumineuse en signal electrique. Recemment, les photodiodes avalanche monophotoniques (PAMP) disposees en matrice suscitent beaucoup d'interet pour la TEP. Ces matrices forment des detecteurs sensibles, robustes, compacts et avec une resolution en temps hors pair. Ces qualites en font un photodetecteur prometteur pour la TEP, mais il faut optimiser les parametres de la matrice et de l'electronique de lecture afin d'atteindre les performances optimales pour la TEP. L'optimisation de la matrice devient rapidement une operation difficile, car les differents parametres interagissent de maniere complexe avec les processus d'avalanche et de generation de bruit. Enfin, l'electronique de lecture pour les matrices de PAMP demeure encore rudimentaire et il serait profitable d'analyser differentes strategies de lecture. Pour repondre a cette question, la solution la plus economique est d'utiliser un simulateur pour converger vers la configuration donnant les meilleures performances. Les travaux de ce memoire presentent le developpement d'un tel simulateur. Celui-ci modelise le comportement d'une matrice de PAMP en se basant sur les equations de physique des semiconducteurs et des modeles probabilistes. Il inclut les trois principales sources de bruit, soit le bruit thermique, les declenchements intempestifs correles et la diaphonie optique. Le simulateur permet aussi de tester et de comparer de nouvelles approches pour l'electronique de lecture plus adaptees a ce type de detecteur. Au final, le simulateur vise a

  18. Which Photodiode to Use: A Comparison of CMOS-Compatible Structures

    PubMed Central

    Murari, Kartikeya; Etienne-Cummings, Ralph; Thakor, Nitish; Cauwenberghs, Gert

    2010-01-01

    While great advances have been made in optimizing fabrication process technologies for solid state image sensors, the need remains to be able to fabricate high quality photosensors in standard CMOS processes. The quality metrics depend on both the pixel architecture and the photosensitive structure. This paper presents a comparison of three photodiode structures in terms of spectral sensitivity, noise and dark current. The three structures are n+/p-sub, n-well/p-sub and p+/n-well/p-sub. All structures were fabricated in a 0.5 μm 3-metal, 2-poly, n-well process and shared the same pixel and readout architectures. Two pixel structures were fabricated—the standard three transistor active pixel sensor, where the output depends on the photodiode capacitance, and one incorporating an in-pixel capacitive transimpedance amplifier where the output is dependent only on a designed feedback capacitor. The n-well/p-sub diode performed best in terms of sensitivity (an improvement of 3.5 × and 1.6 × over the n+/p-sub and p+/n-well/p-sub diodes, respectively) and signal-to-noise ratio (1.5 × and 1.2 × improvement over the n+/p-sub and p+/n-well/p-sub diodes, respectively) while the p+/n-well/p-sub diode had the minimum (33% compared to other two structures) dark current for a given sensitivity. PMID:20454596

  19. Enabling accurate photodiode detection of multiple optical traps by spatial filtering

    NASA Astrophysics Data System (ADS)

    Ott, Dino; Reihani, S. Nader S.; Oddershede, Lene B.

    2014-09-01

    Dual and multiple beam optical tweezers allow for advanced trapping geometries beyond single traps, however, these increased manipulation capabilities, usually complicate the detection of position and force. The accuracy of position and force measurements is often compromised by crosstalk between the detected signals, this crosstalk leading to a systematic error on the measured forces and distances. In dual-beam optical trapping setups, the two traps are typically orthogonal polarized and crosstalk can be minimized by inserting polarization optics in front of the detector, however, this method is not perfect because of the de-polarization of the trapping beam introduced by the required high numerical aperture optics. Moreover, the restriction to two orthogonal polarisation states limits the number of detectable traps to two. Here, we present an easy-to-implement simple method to efficiently eliminate cross-talk in dual beam setups.1 The technique is based on spatial filtering and is highly compatible with standard back-focal-plane photodiode based detection. The reported method significantly improves the accuracy of force-distance measurements, e.g., of single molecules, hence providing much more scientific value for the experimental efforts. Furthermore, it opens the possibility for fast and simultaneous photodiode based detection of multiple holographically generated optical traps.

  20. Topographic Avalanche Risk: DEM Sensitivity Analysis

    NASA Astrophysics Data System (ADS)

    Nazarkulova, Ainura; Strobl, Josef

    2015-04-01

    GIS-based models are frequently used to assess the risk and trigger probabilities of (snow) avalanche releases, based on parameters and geomorphometric derivatives like elevation, exposure, slope, proximity to ridges and local relief energy. Numerous models, and model-based specific applications and project results have been published based on a variety of approaches and parametrizations as well as calibrations. Digital Elevation Models (DEM) come with many different resolution (scale) and quality (accuracy) properties, some of these resulting from sensor characteristics and DEM generation algorithms, others from different DEM processing workflows and analysis strategies. This paper explores the impact of using different types and characteristics of DEMs for avalanche risk modeling approaches, and aims at establishing a framework for assessing the uncertainty of results. The research question is derived from simply demonstrating the differences in release risk areas and intensities by applying identical models to DEMs with different properties, and then extending this into a broader sensitivity analysis. For the quantification and calibration of uncertainty parameters different metrics are established, based on simple value ranges, probabilities, as well as fuzzy expressions and fractal metrics. As a specific approach the work on DEM resolution-dependent 'slope spectra' is being considered and linked with the specific application of geomorphometry-base risk assessment. For the purpose of this study focusing on DEM characteristics, factors like land cover, meteorological recordings and snowpack structure and transformation are kept constant, i.e. not considered explicitly. Key aims of the research presented here are the development of a multi-resolution and multi-scale framework supporting the consistent combination of large area basic risk assessment with local mitigation-oriented studies, and the transferability of the latter into areas without availability of

  1. Study of seismic signals generated by explosions triggering avalanches.

    NASA Astrophysics Data System (ADS)

    Surinach, Emma; Pérez-Guillén, Cristina; Tapia, Mar; Hiller, Martin; Dufour, François

    2014-05-01

    Our group is dedicated to the study of the seismic signals generated by avalanches. Through several years deploying seismic stations at the Vallée de la Sionne (VDLS) test site in Switzerland (operated by SLF) it has gathered a large amount of seismic signals forming a database. The database consists mainly on signals generated by snow avalanches descending the VDLS test site. However, signals corresponding to the explosions that triggered the avalanches and even earthquakes are also included in the database. Depending on the snowpack stability, some of the explosions, despite being of the same charge, are unable to trigger an avalanche. The explosion signals are recorded in 3-component seismometers placed at two or three sites separated a maximum distance of 2.5 km approx. from the release area of the avalanches. The seismic signals corresponding to the explosions recorded at different sites are analyzed and their characteristics compared. Amplitude and frequency content of the displacement, velocity and acceleration of the generated waves traveling into the ground and those of the blast (air) are calculated. These values are compared with those of the waves generated by avalanches and other seismic sources (earthquakes, helicopters, airplanes). These analyses allow us to quantify and evaluate parameters related to the possible triggering of secondary snow avalanches caused by the generated vibrations in air and ground. The results are related to the weather and snowpack conditions, when it is possible.

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

    SciTech Connect

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

    2015-05-07

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

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

    NASA Astrophysics Data System (ADS)

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

    2015-05-01

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

  4. A payload to evaluate photodiodes for the detection of soft and hard x rays in a space environment using a Get Away Special

    NASA Technical Reports Server (NTRS)

    Desai, Upendra D.; Stewart, Amyelizabeth C.

    1992-01-01

    We propose to use the Get Away Special (GAS) facility to evaluate P-intrinsic-N (PIN) detectors and avalanche photodiodes (APD's) for the detection of both solar and nonsolar soft and hard x rays. We would like to fly both types of silicon detectors for the direct detection of the x ray photons in the energy range from 1 to 30 keV with an energy resolution of about 1 keV. We would also like to use both types of photodiodes viewing CsI(Tl) scintillators to extend the energy range up to 1 MeV with -6 percent resolution at 660 keV. Solar flares would be detected with this instrumentation during periods of solar pointing providing high energy resolution spectra with high time resolution. Similar data would be obtained in the scanning mode on nonsolar transient and steady x ray sources with the same instrumentation. A commandable door over the detectors would be required to allow measurements to be made as low as 1 keV.

  5. Overspill avalanching in a dense reservoir network

    PubMed Central

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

    2012-01-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2016-08-01

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

  7. ELECTRON AVALANCHE MODEL OF DIELECTRIC-VACUUM SURFACE BREAKDOWN

    SciTech Connect

    Lauer, E J

    2007-02-21

    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.

  8. Comparison at the sub-100 fW optical power level of calibrating a single-photon detector using a high-sensitive, low-noise silicon photodiode and the double attenuator technique

    NASA Astrophysics Data System (ADS)

    Porrovecchio, G.; Šmid, M.; López, M.; Hofer, H.; Rodiek, B.; Kück, S.

    2016-08-01

    A comparison down to sub-100-fW optical power level was carried out between a low-noise Silicon photodiode and a low optical flux measurement facility based on a double attenuator technique. The comparison was carried out via a silicon single-photon avalanche diode (Si-SPAD), which acted as transfer standard. The measurements were performed at a wavelength of 770 nm using an attenuated laser as a radiation source at optical power levels between approximately 86 fW and approximately 1325 fW, corresponding to approximately 330 000 photons s‑1 and approximately 5.2  ×  106 photons s‑1, respectively. The mean relative deviation of the detection efficiencies of the Si-SPAD, determined by the Si-photodiode and the low optical flux measurement facility, i.e. between two completely independent traceability routes, was  <  0.2%, thus well within the combined standard uncertainty of the two measurements. To our knowledge, this is the first comparison for the detection efficiency of a single photon detector using a direct optical flux measurement by a conventional Si-photodiode at such low power levels.

  9. Photodiode-based sensor for flame sensing and combustion-process monitoring.

    PubMed

    Arias, Luis; Torres, Sergio; Sbarbaro, Daniel; Farias, Oscar

    2008-10-10

    A nonintrusive low-cost sensor based on silicon photodiode detectors has been designed to analyze the formation and behavior of excited CH(*) and C(2)(*) radicals in the combustion process by sensing the spectral emission of hydrocarbon flames. The sensor was validated by performing two sets of experiments for both nonconfined and confined flames. For a nonconfined oil flame, the sensor responses for the axial intensity were highly correlated with the measurements obtained with a radiometer. For confined gas flames the ratio between the signal corresponding to C(2)(*) and CH(*) was successfully correlated with the CO pollutant emissions and the combustion efficiency. These results give additional insight on how to prevent an incomplete combustion using spectral information. The fast response, the nonintrusive character, and the instantaneous measurement of the needed spectral information makes the proposed optical sensor a key element in the development of advanced control strategies for combustion processes. PMID:18846197

  10. Effects of scale-free avalanche walks on anomalous diffusions

    NASA Astrophysics Data System (ADS)

    Kim, Hyun-Joo

    2016-07-01

    Effects of scale-free avalanche walks on anomalous diffusions have been studied by introducing simple non-Markovian walk models. The scale-free avalanche walk is realized as a walker goes to one direction consistently in a time interval, the distribution of which follows a power-law. And it is applied to the memory models, in which the entire history of a walk process is memorized or the memory for the latest step is enhanced with time. The power-law avalanche walk with memory effects strengthens the persistence between steps and thus makes the Hurst exponent be larger than the cases without avalanche walks, while does not affect the anti-persistent nature.

  11. Quantitative Analysis of Spectral Impacts on Silicon Photodiode Radiometers: Preprint

    SciTech Connect

    Myers, D. R.

    2011-04-01

    Inexpensive broadband pyranometers with silicon photodiode detectors have a non-uniform spectral response over the spectral range of 300-1100 nm. The response region includes only about 70% to 75% of the total energy in the terrestrial solar spectral distribution from 300 nm to 4000 nm. The solar spectrum constantly changes with solar position and atmospheric conditions. Relative spectral distributions of diffuse hemispherical irradiance sky radiation and total global hemispherical irradiance are drastically different. This analysis convolves a typical photodiode response with SMARTS 2.9.5 spectral model spectra for different sites and atmospheric conditions. Differences in solar component spectra lead to differences on the order of 2% in global hemispherical and 5% or more in diffuse hemispherical irradiances from silicon radiometers. The result is that errors of more than 7% can occur in the computation of direct normal irradiance from global hemispherical irradiance and diffuse hemispherical irradiance using these radiometers.

  12. Quantitative measurement of body motion using Schottky barrier silicon photodiode.

    PubMed

    Yoo, J H; Suh, I H; Wallace, S; Hankla, J W; Wauters, K A

    1979-11-01

    A new motion detection system has been developed using a laser beam and a Schottky barrier silicon photodiode. The system broadens the scope of gravitational center stabilography by facilitating the quantitative assessment of tremors of body appendages such as the hands and even the head. The system also eliminates cumbersome platforms and wire attachments previously used in gravitational center stabilography. The subject is asked to aim the beam at the photodiode. A quantitative off-center variation parameter, ARDS (Average Radial Distance Squared multiplied by time), was utilized in units of cm2 sec. A preliminary evaluation of the system shows that it is suitable for rapidly screening large numbers of subjects for localised neuromuscular control. PMID:526517

  13. Photon counting photodiode array detector for far ultraviolet (FUV) astronomy

    NASA Technical Reports Server (NTRS)

    Hartig, G. F.; Moos, H. W.; Pembroke, R.; Bowers, C.

    1982-01-01

    A compact, stable, single-stage intensified photodiode array detector designed for photon-counting, far ultraviolet astronomy applications employs a saturable, 'C'-type MCP (Galileo S. MCP 25-25) to produce high gain pulses with a narrowly peaked pulse height distribution. The P-20 output phosphor exhibits a very short decay time, due to the high current density of the electron pulses. This intensifier is being coupled to a self-scanning linear photodiode array which has a fiber optic input window which allows direct, rigid mechanical coupling with minimal light loss. The array was scanned at a 250 KHz pixel rate. The detector exhibits more than adequate signal-to-noise ratio for pulse counting and event location. Previously announced in STAR as N82-19118

  14. Experimental verification of the photodiode theory of SIS mixers

    NASA Technical Reports Server (NTRS)

    Woody, David P.; Wengler, Michael J.

    1993-01-01

    The authors describe the characterization and interpretation of the performance of SIS receivers within the framework of the photodiode theory of mixing. The quantum efficiency plays a dominant role in the theory, and a simple method of accurately measuring this parameter is presented. It is demonstrated that the quantum efficiency measurements can be conveniently made on a standard radio astronomy receiver and combined with the usual hot and cold load characterization to improve the understanding of the receiver's performance. The measurements verify that the photodiode theory of mixing accurately describes the receiver noise even at local-oscillator power levels well above the linear response range. The results for receivers operating at 100 and 240 GHz verify the utility of this approach. These methods should also prove useful in evaluating submillimeter receivers.

  15. Flexible germanium nanomembrane metal-semiconductor-metal photodiodes

    NASA Astrophysics Data System (ADS)

    Kim, Munho; Seo, Jung-Hun; Yu, Zongfu; Zhou, Weidong; Ma, Zhenqiang

    2016-08-01

    We demonstrate flexible Ge nanomembrane (Ge NM) based metal-semiconductor-metal photodiodes. The effect of uniaxial tensile strain on Ge NM based photodiodes was investigated using bending fixtures. Dark current density is decreased from 21.5 to 4.8 mA/cm2 at 3 V by a tensile strain of 0.42% while photon responsivity is increased from 0.2 to 0.45 A/W at the wavelength of 1.5 μm. Enhanced responsivity is also observed at longer wavelengths up to 1.64 μm. The uniaxial tensile strain effectively reduces the direct bandgap energy of the Ge NM, leading to a shift of the absorption edge toward a longer wavelength.

  16. Spectral line-diode registry effects with photodiode array detectors

    SciTech Connect

    Winge, R.K.; Fassel, V.A.; Eckels, D.E.

    1986-05-01

    A limitation of photodiode array detectors for spectroscopic intensity measurements relates to the spacing of the diodes and the errors generated when a spectral line is not in exact registry with the diode or diodes from which its intensity is being measured. These misregistry intensity errors, which may be as high as 25 to 30%, are documented for a range of spectral bandwidths and for single diode (pixel) intensities and multiple diode summations of intensities.

  17. Potential for SPECT cameras utilizing photodiode readout of scintillator crystals

    SciTech Connect

    Moses, W.W.; Derenzo, S.E.; Gruber, G.J.; Huesman, R.H.

    1997-05-01

    We present a conceptual design for a SPECT detector consisting of an array of 3x3x5 mm CsI(Tl) scintillator crystals individually read out by an array of 3 mm square silicon photodiodes. The interaction position is not determined by Anger logic, but by the location of the individual crystal/photodiode element in which the gamma ray is observed. Since the design is modular (each module typically having 64 crystals, photodiodes, and charge amplifiers, and one multiplexer circuit to reduce the number of readout channels), a large variety of camera geometries can be realized. Advantages of this design over conventional cameras (NaI(Tl) scintillator/photomultiplier tube) are lower gain drift (i.e. higher stability), smaller size, significantly higher count rate capability, and potentially lower cost. For the 141 keV emissions of Tc-99m, both CsI(Tl) and NaI(Tl) have 85-90% photoelectric fraction, but CsI(TI) has an attenuation length of 3.0 mm as compared to 4.5 mm for NaI(Tl). Thus, a 5 mm thick CsI(Tl) camera has singular efficiency to a Nal(Tl) camera with a 7.5 mm thickness (between 1/4 and 3/8 inch). The light output of CsI(Tl) is 25% higher than that of Nal(Tl), and while its 565 nm emissions are not efficiently detected with photomultiplier tubes, they are well matched to photodiode detection.

  18. Influence of snow-cover properties on avalanche dynamics

    NASA Astrophysics Data System (ADS)

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

    2012-04-01

    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.

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

    NASA Astrophysics Data System (ADS)

    Paczuski, Maya; Maslov, Sergei; Bak, Per

    1996-01-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2016-06-01

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

  1. Repertoires of Spike Avalanches Are Modulated by Behavior and Novelty.

    PubMed

    Ribeiro, Tiago L; Ribeiro, Sidarta; Copelli, Mauro

    2016-01-01

    Neuronal avalanches measured as consecutive bouts of thresholded field potentials represent a statistical signature that the brain operates near a critical point. In theory, criticality optimizes stimulus sensitivity, information transmission, computational capability and mnemonic repertoires size. Field potential avalanches recorded via multielectrode arrays from cortical slice cultures are repeatable spatiotemporal activity patterns. It remains unclear whether avalanches of action potentials observed in forebrain regions of freely-behaving rats also form recursive repertoires, and whether these have any behavioral relevance. Here, we show that spike avalanches, recorded from hippocampus (HP) and sensory neocortex of freely-behaving rats, constitute distinct families of recursive spatiotemporal patterns. A significant number of those patterns were specific to a behavioral state. Although avalanches produced during sleep were mostly similar to others that occurred during waking, the repertoire of patterns recruited during sleep differed significantly from that of waking. More importantly, exposure to novel objects increased the rate at which new patterns arose, also leading to changes in post-exposure repertoires, which were significantly different from those before the exposure. A significant number of families occurred exclusively during periods of whisker contact with objects, but few were associated with specific objects. Altogether, the results provide original evidence linking behavior and criticality at the spike level: spike avalanches form repertoires that emerge in waking, recur during sleep, are diversified by novelty and contribute to object representation. PMID:27047341

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

    PubMed

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

    2016-06-01

    Using numerical simulations we examine colloids with a long-range Coulomb interaction confined in a two-dimensional trough potential undergoing dynamical compression. As the depth of the confining well is increased, the colloids move via elastic distortions interspersed with intermittent bursts or avalanches of plastic motion. In these avalanches, the colloids rearrange to minimize their colloid-colloid repulsive interaction energy by adopting an average lattice constant that is isotropic despite the anisotropic nature of the compression. The avalanches take the form of shear banding events that decrease or increase the structural order of the system. At larger compression, the avalanches are associated with a reduction of the number of rows of colloids that fit within the confining potential, and between avalanches the colloids can exhibit partially crystalline or anisotropic ordering. The colloid velocity distributions during the avalanches have a non-Gaussian form with power-law tails and exponents that are consistent with those found for the velocity distributions of gliding dislocations. We observe similar behavior when we subsequently decompress the system, and find a partially hysteretic response reflecting the irreversibility of the plastic events. PMID:27415320

  3. Nucleation and development of dendritic flux avalanches in superconducting films

    NASA Astrophysics Data System (ADS)

    Vestgården, Jørn Inge; Shantsev, Daniil; Galperin, Yuri; Henning Johansen, Tom

    2012-02-01

    The stability of superconducting films is threatened by thermomagnetic runaways commonly observed as abrupt dendritic flux avalanches. We report numerical simulations of the electrodynamics and thermal behavior of superconducting films, where the gradual flux penetration is interrupted by such avalanches. The simulation formalism is based on an efficient method for treating the nonlinear and nonlocal electrodynamics, and it handles both the slow flux creep dynamics prior to the avalanches and the transition to the many orders of magnitude faster instability regime. Then the temperature rises quickly above the critical temperature, and the avalanche develops fully in less than 100 nanoseconds, with an initial velocity of approximately 100 km/s. Both the morphology and speed of the avalanches are in excellent agreement with results from magneto-optical imaging experiments. The sample is seeded with randomly distributed disorder, which results in a significantly reduced threshold for onset of avalanches. Interaction with the material disorder also contributes to branching and irreprodusibility of the flux structures. However, disorder is not the main mechanism behind branching and dendritic structures are also found to develop in completely uniform samples.

  4. Avalanche risk assessment for the link Osh - Bishkek, Kyrgyzstan

    NASA Astrophysics Data System (ADS)

    Nazarkulova, Kydyr

    2015-04-01

    The Bishkek-Osh road is main North-South ground transportation connection between the two major cities of Kyrgyzstan. One of the causes for frequent interruptions and closures between November and May is the avalanche risk due to local terrain characteristics and orographically induced precipitation maxima during winter. As a first step towards more effective prediction and implementation of mitigating measures the development of a digital avalanche inventory ('avalanche cadastre') has been initiated. This is aiming at modeling regional risk, and prioritizes the implementation of protective infrastructures in the most avalanche-prone zones. In addition, this helps with continuous monitoring of avalanche behaviour and the assessment of potential influence of climate change. For the parameterisation of models and support of decisions, details about avalanche incidences need to be collected. Historical data collected during Soviet time serve as an important baseline, complemented by more recent data. Overall, developing such a geo database shall be useful and effective for future planning at the Ministry of Emergency Services. This paper demonstrates important parameters to be collected and critical role of historical data as a baseline. Geodatabases are being developed on ArcGIS and used locally for planning preventive measures.

  5. Improving detection of avalanches on a conical bead pile

    NASA Astrophysics Data System (ADS)

    Vajpeyi, Avi; Lehman, Susan; Dahmen, Karin; Leblanc, Michael; Uhl, Jonathan

    A conical bead pile subject to slow driving and an external magnetic field is used as a simple system to investigate the variations in the avalanche size probability distribution function. Steel beads are dropped onto the pile from different heights and at different strengths of applied magnetic field. Avalanches are recorded by the change in mass as beads fall off the pile. Experimentally we observe an increasing deviation from power law behavior as the field and thus cohesion between the beads increases. We compare our experimental results for the probability distribution function to the results of an analytic theory from a mean-field model of slip avalanches [Dahmen, Nat Phys 7, 554 (2011)]. The model also makes predictions for avalanche duration, which is not measurable with the existing system. To more fully characterize the avalanching behavior of the pile over time, a high-speed camera has been added to the system to record the largest avalanches and allow more detailed analysis. The conical pile geometry presents a challenge for observation and particle tracking over the full pile. Our implementation scheme and preliminary results from the video analysis are presented. Research supported by NSF CBET 1336116 and 1336634.

  6. Dense Granular Avalanches: Mathematical Description and Experimental Validation

    NASA Astrophysics Data System (ADS)

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

    Snow avalanches, landslides, rock falls and debris flows are extremely dangerous and destructive natural phenomena. The frequency of occurrence and amplitudes of these disastrous events appear to have increased in recent years perhaps due to recent climate warming. The events endanger the personal property and infra-structure in mountainous regions. For example, from the winters 1940/41 to 1987/88 more than 7000 snow avalanches occurred in Switzerland with damaged property leading to a total of 1269 deaths. In February 1999, 36 people were buried by a single avalanche in Galtür, Austria. In August 1996, a very large debris flow in middle Taiwan resulted in 51 deaths, 22 lost and an approximate property damage of more than 19 billion NT dollars (ca. 600 million US dollars) [18]. In Europe, a suddenly released debris flow in North Italy in August 1998 buried 5 German tourists on the Superhighway "Brenner-Autobahn". The topic has gained so much significance that in 1990 the United Nations declared the International Decade for Natural Disasters Reduction (IDNDR); Germany has its own Deutsches IDNDR-Komitee für Katastrophenvorbeugung e.V. Special conferences are devoted to the theme, e.g., the CALAR conference on Avalanches, Landslides, Rock Falls and Debris Flows (Vienna, January 2000), INTERPRAEVENT, annual conferences on the protection of habitants from floods, debris flows and avalanches, special conferences on debris flow hazard mi tigation and those exclusively on Avalanches.

  7. Avalanches and hysteresis in frustrated superconductors and XY spin glasses.

    PubMed

    Sharma, Auditya; Andreanov, Alexei; Müller, Markus

    2014-10-01

    We study avalanches along the hysteresis loop of long-range interacting spin glasses with continuous XY symmetry, which serves as a toy model of granular superconductors with long-range and frustrated Josephson couplings. We identify sudden jumps in the T=0 configurations of the XY phases as an external field is increased. They are initiated by the softest mode of the inverse susceptibility matrix becoming unstable, which induces an avalanche of phase updates (or spin alignments). We analyze the statistics of these events and study the correlation between the nonlinear avalanches and the soft mode that initiates them. We find that the avalanches follow the directions of a small fraction of the softest modes of the inverse susceptibility matrix, similarly as was found in avalanches in jammed systems. In contrast to the similar Ising spin glass (Sherrington-Kirkpatrick) studied previously, we find that avalanches are not distributed with a scale-free power law but rather have a typical size which scales with the system size. We also observe that the Hessians of the spin-glass minima are not part of standard random matrix ensembles as the lowest eigenvector has a fractal support. PMID:25375434

  8. Repertoires of Spike Avalanches Are Modulated by Behavior and Novelty

    PubMed Central

    Ribeiro, Tiago L.; Ribeiro, Sidarta; Copelli, Mauro

    2016-01-01

    Neuronal avalanches measured as consecutive bouts of thresholded field potentials represent a statistical signature that the brain operates near a critical point. In theory, criticality optimizes stimulus sensitivity, information transmission, computational capability and mnemonic repertoires size. Field potential avalanches recorded via multielectrode arrays from cortical slice cultures are repeatable spatiotemporal activity patterns. It remains unclear whether avalanches of action potentials observed in forebrain regions of freely-behaving rats also form recursive repertoires, and whether these have any behavioral relevance. Here, we show that spike avalanches, recorded from hippocampus (HP) and sensory neocortex of freely-behaving rats, constitute distinct families of recursive spatiotemporal patterns. A significant number of those patterns were specific to a behavioral state. Although avalanches produced during sleep were mostly similar to others that occurred during waking, the repertoire of patterns recruited during sleep differed significantly from that of waking. More importantly, exposure to novel objects increased the rate at which new patterns arose, also leading to changes in post-exposure repertoires, which were significantly different from those before the exposure. A significant number of families occurred exclusively during periods of whisker contact with objects, but few were associated with specific objects. Altogether, the results provide original evidence linking behavior and criticality at the spike level: spike avalanches form repertoires that emerge in waking, recur during sleep, are diversified by novelty and contribute to object representation. PMID:27047341

  9. Using eCognition to automatically detect and map avalanche deposits from the spring 2009 avalanche cycle in the Tatra mts., Slovakia

    NASA Astrophysics Data System (ADS)

    Frauenfelder, R.; Lato, M. J.; Biskupic, M.

    2015-04-01

    Here we present results from ongoing work where we apply an object oriented mapping algorithm developed in eCognition in order to automatically identify and digitally map avalanche deposits. The algorithm performance is compared with respect to a selected number of manually digitized avalanche outlines mapped by avalanche experts.

  10. Thick detection zone single-photon avalanche diode fabricated in 0.35 μm complementary metal-oxide semiconductors

    NASA Astrophysics Data System (ADS)

    Steindl, Bernhard; Enne, Reinhard; Zimmermann, Horst

    2015-05-01

    An avalanche photodiode (APD) fabricated in 0.35 μm high-voltage complementary metal-oxide semiconductor (CMOS) technology, which was originally optimized for linear mode applications, is characterized in Geiger mode operation. This work shows that the used design concept is also suitable for single-photon detection applications and achieves a photon detection efficiency of 22.1% at 785 nm due to a thick detection zone and 3.5 V excess bias. At this operation point, the single-photon APD achieves good results regarding afterpulsing probability (3.4%) and dark count rate (46 kHz) with respect to the large active diameter of 86 μm.

  11. Avalanche mode of high-voltage overloaded p{sup +}–i–n{sup +} diode switching to the conductive state by pulsed illumination

    SciTech Connect

    Kyuregyan, A. S.

    2015-07-15

    A simple analytical theory of the picosecond switching of high-voltage overloaded p{sup +}–i–n{sup +} photodiodes to the conductive state by pulsed illumination is presented. The relations between the parameters of structure, light pulse, external circuit, and main process characteristics, i.e., the amplitude of the active load current pulse, delay time, and switching duration, are derived and confirmed by numerical simulation. It is shown that the picosecond light pulse energy required for efficient switching can be decreased by 6–7 orders of magnitude due to the intense avalanche multiplication of electrons and holes. This offers the possibility of using pulsed semiconductor lasers as a control element of optron pairs.

  12. Combined hydrogen and lithium beam emission spectroscopy observation system for Korea Superconducting Tokamak Advanced Research.

    PubMed

    Lampert, M; Anda, G; Czopf, A; Erdei, G; Guszejnov, D; Kovácsik, Á; Pokol, G I; Réfy, D; Nam, Y U; Zoletnik, S

    2015-07-01

    A novel beam emission spectroscopy observation system was designed, built, and installed onto the Korea Superconducting Tokamak Advanced Research tokamak. The system is designed in a way to be capable of measuring beam emission either from a heating deuterium or from a diagnostic lithium beam. The two beams have somewhat complementary capabilities: edge density profile and turbulence measurement with the lithium beam and two dimensional turbulence measurement with the heating beam. Two detectors can be used in parallel: a CMOS camera provides overview of the scene and lithium beam light intensity distribution at maximum few hundred Hz frame rate, while a 4 × 16 pixel avalanche photo-diode (APD) camera gives 500 kHz bandwidth data from a 4 cm × 16 cm region. The optics use direct imaging through lenses and mirrors from the observation window to the detectors, thus avoid the use of costly and inflexible fiber guides. Remotely controlled mechanisms allow adjustment of the APD camera's measurement location on a shot-to-shot basis, while temperature stabilized filter holders provide selection of either the Doppler shifted deuterium alpha or lithium resonance line. The capabilities of the system are illustrated by measurements of basic plasma turbulence properties. PMID:26233377

  13. The circuit of polychromator for Experimental Advanced Superconducting Tokamak edge Thomson scattering diagnostic.

    PubMed

    Zang, Qing; Hsieh, C L; Zhao, Junyu; Chen, Hui; Li, Fengjuan

    2013-09-01

    The detector circuit is the core component of filter polychromator which is used for scattering light analysis in Thomson scattering diagnostic, and is responsible for the precision and stability of a system. High signal-to-noise and stability are primary requirements for the diagnostic. Recently, an upgraded detector circuit for weak light detecting in Experimental Advanced Superconducting Tokamak (EAST) edge Thomson scattering system has been designed, which can be used for the measurement of large electron temperature (T(e)) gradient and low electron density (n(e)). In this new circuit, a thermoelectric-cooled avalanche photodiode with the aid circuit is involved for increasing stability and enhancing signal-to-noise ratio (SNR), especially the circuit will never be influenced by ambient temperature. These features are expected to improve the accuracy of EAST Thomson diagnostic dramatically. Related mechanical construction of the circuit is redesigned as well for heat-sinking and installation. All parameters are optimized, and SNR is dramatically improved. The number of minimum detectable photons is only 10. PMID:24089826

  14. Combined hydrogen and lithium beam emission spectroscopy observation system for Korea Superconducting Tokamak Advanced Research

    SciTech Connect

    Lampert, M.; Anda, G.; Réfy, D.; Zoletnik, S.; Czopf, A.; Erdei, G.; Guszejnov, D.; Kovácsik, Á.; Pokol, G. I.; Nam, Y. U.

    2015-07-15

    A novel beam emission spectroscopy observation system was designed, built, and installed onto the Korea Superconducting Tokamak Advanced Research tokamak. The system is designed in a way to be capable of measuring beam emission either from a heating deuterium or from a diagnostic lithium beam. The two beams have somewhat complementary capabilities: edge density profile and turbulence measurement with the lithium beam and two dimensional turbulence measurement with the heating beam. Two detectors can be used in parallel: a CMOS camera provides overview of the scene and lithium beam light intensity distribution at maximum few hundred Hz frame rate, while a 4 × 16 pixel avalanche photo-diode (APD) camera gives 500 kHz bandwidth data from a 4 cm × 16 cm region. The optics use direct imaging through lenses and mirrors from the observation window to the detectors, thus avoid the use of costly and inflexible fiber guides. Remotely controlled mechanisms allow adjustment of the APD camera’s measurement location on a shot-to-shot basis, while temperature stabilized filter holders provide selection of either the Doppler shifted deuterium alpha or lithium resonance line. The capabilities of the system are illustrated by measurements of basic plasma turbulence properties.

  15. The circuit of polychromator for Experimental Advanced Superconducting Tokamak edge Thomson scattering diagnostic

    SciTech Connect

    Zang, Qing; Zhao, Junyu; Chen, Hui; Li, Fengjuan; Hsieh, C. L.

    2013-09-15

    The detector circuit is the core component of filter polychromator which is used for scattering light analysis in Thomson scattering diagnostic, and is responsible for the precision and stability of a system. High signal-to-noise and stability are primary requirements for the diagnostic. Recently, an upgraded detector circuit for weak light detecting in Experimental Advanced Superconducting Tokamak (EAST) edge Thomson scattering system has been designed, which can be used for the measurement of large electron temperature (T{sub e}) gradient and low electron density (n{sub e}). In this new circuit, a thermoelectric-cooled avalanche photodiode with the aid circuit is involved for increasing stability and enhancing signal-to-noise ratio (SNR), especially the circuit will never be influenced by ambient temperature. These features are expected to improve the accuracy of EAST Thomson diagnostic dramatically. Related mechanical construction of the circuit is redesigned as well for heat-sinking and installation. All parameters are optimized, and SNR is dramatically improved. The number of minimum detectable photons is only 10.

  16. Study of EUV and x-ray radiation hardness of silicon photodiodes

    NASA Astrophysics Data System (ADS)

    Zabrodsky, Vladimir V.; Aruev, Pavel; Filimonov, Vladimir V.; Sobolev, Nikolay A.; Sherstnev, Evgeniy V.; Belik, Viktor P.; Nikolenko, Anton D.; Ivlyushkin, Denis V.; Pindyurin, Valery F.; Shadrin, Nikita S.; Soldatov, Artem E.; Mashkovtsev, Mikhail R.

    2013-05-01

    This work presents the results of long-term observation of the silicon photodiodes spatial profile response and the silicon photodiodes dark current after their exposure to 10.2 eV quanta and in the spectral range of 150-300 eV. Exposure of the photodiodes to quanta of an energy of 10.2 eV was repeated. Several other photodiodes have been irradiated in the spectral range of 700-1800 eV with a dose of 8 J/cm2. The spatial profile of the irradiated photodiodes was studied with 3.49 eV, 10.2 eV and 100 eV quanta. The effect of the recovery of the response spatial profile has been proved for the p+-n diode. An additional useful method of visualization of irradiated photodiode area is also presented.

  17. OPTIMIZING THROUGH CO-EVOLUTIONARY AVALANCHES

    SciTech Connect

    S. BOETTCHER; A. PERCUS

    2000-08-01

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

  18. Multi-scale modelling of granular avalanches

    NASA Astrophysics Data System (ADS)

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

    2013-06-01

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

  19. The structure of powder snow avalanches

    NASA Astrophysics Data System (ADS)

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

    2015-01-01

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

  20. Avalanche outbreaks emerging in cooperative contagions

    NASA Astrophysics Data System (ADS)

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

    2015-11-01

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

  1. Dead Time of Single Photon Avalanche Diodes

    NASA Astrophysics Data System (ADS)

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

    2011-06-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2012-03-01

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

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

    PubMed

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

    2012-03-01

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

  4. High-Performance, Fullerene-Free Organic Photodiodes Based on a Solution-Processable Indigo.

    PubMed

    Kim, Il Ku; Li, Xin; Ullah, Mujeeb; Shaw, Paul E; Wawrzinek, Robert; Namdas, Ebinazar B; Lo, Shih-Chun

    2015-11-01

    A solution-processable dibromoindigo with an alkyoxyphenyl solubilizing group is developed and used as a new electron acceptor in organic photodiodes. The solution-processed fullerene-free organic photodiodes show an almost spectrally flat response with a high responsivity (0.4 A W(-1) ) and a high detectivity (1 × 10(12) Jones). These values are comparable to silicon-based photodiodes. PMID:26392063

  5. Record-breaking avalanches in driven threshold systems.

    PubMed

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

    2013-05-01

    Record-breaking avalanches generated by the dynamics of several driven nonlinear threshold models are studied. Such systems are characterized by intermittent behavior, where a slow buildup of energy is punctuated by an abrupt release of energy through avalanche events, which usually follow scale-invariant statistics. From the simulations of these systems it is possible to extract sequences of record-breaking avalanches, where each subsequent record-breaking event is larger in magnitude than all previous events. In the present work, several cellular automata are analyzed, among them the sandpile model, the Manna model, the Olami-Feder-Christensen (OFC) model, and the forest-fire model to investigate the record-breaking statistics of model avalanches that exhibit temporal and spatial correlations. Several statistical measures of record-breaking events are derived analytically and confirmed through numerical simulations. The statistics of record-breaking avalanches for the four models are compared to those of record-breaking events extracted from the sequences of independent and identically distributed (i.i.d.) random variables. It is found that the statistics of record-breaking avalanches for the above cellular automata exhibit behavior different from that observed for i.i.d. random variables, which in turn can be used to characterize complex spatiotemporal dynamics. The most pronounced deviations are observed in the case of the OFC model with a strong dependence on the conservation parameter of the model. This indicates that avalanches in the OFC model are not independent and exhibit spatiotemporal correlations. PMID:23767588

  6. InGaAsP Avalanche Photodetectors for Non-Gated 1.06 micrometer Photon-Counting Receivers

    NASA Technical Reports Server (NTRS)

    Itzler, Mark A.; Jiang, Xudong; Ben-Michael, Rafael; Slomkowski, Krystyna; Krainak, Michael A.

    2007-01-01

    The efficient detection of single photons at 1.06 micron is of considerable interest for lidar/ladar systems designed for remote sensing an d ranging as well as for free-space optical transmission in photon-st arved applications. However, silicon-based single photon avalanche diodes (SPADs) used at shorter wavelengths have very low single photon d etection efficiency (approximately 1 - 2%) at 1.06 micron, and InP/In GaAs SPADs designed for telecommunications wavelengths near 1.5 micro n exhibit high dark count rates that generally inhibit non-gated (free-running) operation. To bridge this "single photon detection gap" for wavelengths just beyond 1 micron, we have developed high performance , large area (80 - 200 micron diameter) InP-based InGaAsP quaternary absorber SPADs optimized for operation at 1.06 micron and based on a highly reliable planar geometry avalanche photodiode structure. We wil l show that dark count rates are sufficiently low to allow for non-ga ted operation while achieving detection efficiencies far surpassing t hose found for Si SPADs. At a detection efficiency of 10%, 80 micron diameter devices exhibit dark count rates below 1000 Hz and count rate s of at least 3 MHz when operated at -40 C. Significantly higher dete ction efficiencies (30 - 50%) are achievable with acceptable tradeoff s in dark count rate. In this paper, we will also discuss performance modeling for these devices and compare their behavior with longer wav elength InP-based InGaAs ternary absorber SPADs fabricated on a relat ed device design platform.

  7. Development of a testbed for flexible a-Si:H photodiode sensing arrays

    NASA Astrophysics Data System (ADS)

    Dominguez, Alfonso; Kunnen, George; Vetrano, Michael; Smith, Joseph; Marrs, Michael; Allee, David R.

    2013-05-01

    Large area, flexible sensing arrays for imaging, biochemical sensing and radiation detection are now possible with the development of flexible active matrix display technology. In particular, large-area flexible imaging arrays can provide considerable advancement in defense and security industries because of their inherent low manufacturing costs and physical plasticity that allows for increased adaptability to non-planar mounting surfaces. For example, a flexible array of photodetectors and lenslets formed into a cylinder could image simultaneously with a 360 degree view without the need for expensive bulky optics or a gimbaled mount. Here we report the design and development of a scalable 16x16 pixel testbed for flexible sensor arrays using commercial-off-the-shelf (COTS) parts and demonstrate the capture of a shadow image with an array of photodiodes and active pixel sensors on a plastic substrate. The image capture system makes use of an array of low-noise, InGaZnO active pixel amplifiers to detect changes in current in 2.4 μm-thick reverse-biased a-Si:H PIN diodes. A thorough characterization of the responsivity, detectivity, and optical gain of an a- Si:H photodiode is also provided. At the back end, analog capture circuitry progressively scans the array and constructs an image based on the electrical activity in each pixel. The use of correlated-double-sampling to remove fixed pattern noise is shown to significantly improve spatial resolution due to process variations. The testbed can be readily adapted for the development of neutron, alpha-particle, or X-ray detection arrays given an appropriate conversion layer.

  8. Measuring snow properties relevant to slab avalanche release

    NASA Astrophysics Data System (ADS)

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

    2014-05-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2010-12-01

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

  10. The Sentinel Rock Avalanche of Zion National Park, Utah

    NASA Astrophysics Data System (ADS)

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

    2014-12-01

    Blocking the mouth of Zion Canyon over a distance of 2.3 km, the prehistoric Sentinel rock avalanche has had long-lasting impact on the spectacular scenery of Zion National Park, once damming a large lake that filled the rocky canyon with sediment. Today few of Zion's nearly 3 million annual visitors appreciate that the gentle and inviting, flat valley floor amidst great sandstone cliffs owes its origin to a massive landslide. In addition to representing an extreme-magnitude natural hazard with potentially devastating consequences, we also point out the constructive geomorphic and anthropogenic significance of large rock avalanches in this steep desert landscape. We combine new mapping of rock avalanche and related lacustrine deposits to reconstruct topography before and after the landslide, comment on failure kinematics, and determine new, refined volume estimates for the event. Cosmogenic nuclide surface exposure dating of deposited rock avalanche boulders allows us to date the landslide, determine subsequent rates of deposit erosion, and propose potential triggering mechanisms. Evidence suggests that boulders from across the slide surface were deposited simultaneously, yielding similar exposure ages and indicating a single massive and catastrophic rock slope failure. Rich anthropogenic use of the slide-dammed canyon attests to the long-lasting and diverse impacts of large rock avalanches.

  11. Avalanche multiplication and impact ionization in amorphous selenium photoconductive target

    NASA Astrophysics Data System (ADS)

    Park, Wug-Dong; Tanioka, Kenkichi

    2014-03-01

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

  12. Solid-state flat panel imager with avalanche amorphous selenium

    NASA Astrophysics Data System (ADS)

    Scheuermann, James R.; Howansky, Adrian; Goldan, Amir H.; Tousignant, Olivier; Levéille, Sébastien; Tanioka, K.; Zhao, Wei

    2016-03-01

    Active matrix flat panel imagers (AMFPI) have become the dominant detector technology for digital radiography and fluoroscopy. For low dose imaging, electronic noise from the amorphous silicon thin film transistor (TFT) array degrades imaging performance. We have fabricated the first prototype solid-state AMFPI using a uniform layer of avalanche amorphous selenium (a-Se) photoconductor to amplify the signal to eliminate the effect of electronic noise. We have previously developed a large area solid-state avalanche a-Se sensor structure referred to as High Gain Avalanche Rushing Photoconductor (HARP) capable of achieving gains of 75. In this work we successfully deposited this HARP structure onto a 24 x 30 cm2 TFT array with a pixel pitch of 85 μm. An electric field (ESe) up to 105 Vμm-1 was applied across the a-Se layer without breakdown. Using the HARP layer as a direct detector, an X-ray avalanche gain of 15 +/- 3 was achieved at ESe = 105 Vμm-1. In indirect mode with a 150 μm thick structured CsI scintillator, an optical gain of 76 +/- 5 was measured at ESe = 105 Vμm-1. Image quality at low dose increases with the avalanche gain until the electronic noise is overcome at a constant exposure level of 0.76 mR. We demonstrate the success of a solid-state HARP X-ray imager as well as the largest active area HARP sensor to date.

  13. Debris avalanche deposits: emplacement dynamics, morphology and hazards (Invited)

    NASA Astrophysics Data System (ADS)

    Davies, T. R.; Dufresne, A.

    2013-12-01

    Debris avalanches from volcanoes form some of the largest subaerial and submarine landslide deposits on Earth, covering vast areas (10s to 100s km2) and displaying typically hummocky surface topography. Numerical models have been developed that can identify the area threatened by an event of known volume from a known volcano, if the runout mechanics can be understood. Better understanding the hazards from these enormous events requires realistic parameterization of models, which must be able to explain debris avalanche deposit geometries under water, in air, on Mars and in vacuo on the Moon. We have shown that the complex deposit geometry of the 25 km3 Socompa deposit in Chile can be explained by the effects of basal debris fragmenting during runout. The hummocky surface morphology of many debris avalanche deposits again indicates that the emplacement process involved a very mobile basal layer, above which the travelling mass passively extends, leading to lateral and longitudinal disaggregation of the mass into discrete blocks whose dimension reflects the mass depth. Submarine debris avalanches can also be modelled on this basis, because the presence of ambient water does not fundamentally alter the fragmentation process; to assess the additional hazards of debris avalanches entering into water, models are available to simulate the tsunami generated by such events.

  14. The effectiveness of mean-field theory for avalanche distributions

    NASA Astrophysics Data System (ADS)

    Lee, Edward; Raju, Archishman; Sethna, James

    We explore the mean-field theory of the pseudogap found in avalanche systems with long-range anisotropic interactions using analytical and numerical tools. The pseudogap in the density of low-stability states emerges from the competition between stabilizing interactions between spins in an avalanche and the destabilizing random movement towards the threshold caused by anisotropic couplings. Pazmandi et al. have shown that for the Sherrington-Kirkpatrick model, the pseudogap scales linearly and produces a distribution of avalanche sizes with exponent t=1 in contrast with that predicted from RFIM t=3/2. Lin et al. have argued that the scaling exponent ? of the pseudogap depends on the tail of the distribution of couplings and on non-universal values like the strain rate and the magnitude of the coupling strength. Yet others have argued that the relationship between the pseudogap scaling and the distribution of avalanche sizes is dependent on dynamical details. Despite the theoretical arguments, the class of RFIM mean-field models is surprisingly good at predicting the distribution of avalanche sizes in a variety of different magnetic systems. We investigate these differences with a combination of theory and simulation.

  15. Investigation of a clinical PET detector module design that employs large-area avalanche photodetectors

    NASA Astrophysics Data System (ADS)

    Peng, Hao; Olcott, Peter D.; Spanoudaki, Virginia; Levin, Craig S.

    2011-06-01

    We investigated the feasibility of designing an Anger-logic PET detector module using large-area high-gain avalanche photodiodes (APDs) for a brain-dedicated PET/MRI system. Using Monte Carlo simulations, we systematically optimized the detector design with regard to the scintillation crystal, optical diffuser, surface treatment, layout of large-area APDs, and signal-to-noise ratio (SNR, defined as the 511 keV photopeak position divided by the standard deviation of noise floor in an energy spectrum) of the APD devices. A detector prototype was built comprising an 8 × 8 array of 2.75 × 3.00 × 20.0 mm3 LYSO (lutetium-yttrium-oxyorthosilicate) crystals and a 22.0 × 24.0 × 9.0 mm3 optical diffuser. From the four designs of the optical diffuser tested, two designs employing a slotted diffuser are able to resolve all 64 crystals within the block with good uniformity and peak-to-valley ratio. Good agreement was found between the simulation and experimental results. For the detector employing a slotted optical diffuser, the energy resolution of the global energy spectrum after normalization is 13.4 ± 0.4%. The energy resolution of individual crystals varies between 11.3 ± 0.3% and 17.3 ± 0.4%. The time resolution varies between 4.85 ± 0.04 (center crystal), 5.17 ± 0.06 (edge crystal), and 5.18 ± 0.07 ns (corner crystal). The generalized framework proposed in this work helps to guide the design of detector modules for selected PET system configurations, including scaling the design down to a preclinical PET system, scaling up to a whole-body clinical scanner, as well as replacing APDs with other novel photodetectors that have higher gain or SNR such as silicon photomultipliers.

  16. Compact multispectral photodiode arrays using micropatterned dichroic filters

    NASA Astrophysics Data System (ADS)

    Chandler, Eric V.; Fish, David E.

    2014-05-01

    The next generation of multispectral instruments requires significant improvements in both spectral band customization and portability to support the widespread deployment of application-specific optical sensors. The benefits of spectroscopy are well established for numerous applications including biomedical instrumentation, industrial sorting and sensing, chemical detection, and environmental monitoring. In this paper, spectroscopic (and by extension hyperspectral) and multispectral measurements are considered. The technology, tradeoffs, and application fits of each are evaluated. In the majority of applications, monitoring 4-8 targeted spectral bands of optimized wavelength and bandwidth provides the necessary spectral contrast and correlation. An innovative approach integrates precision spectral filters at the photodetector level to enable smaller sensors, simplify optical designs, and reduce device integration costs. This method supports user-defined spectral bands to create application-specific sensors in a small footprint with scalable cost efficiencies. A range of design configurations, filter options and combinations are presented together with typical applications ranging from basic multi-band detection to stringent multi-channel fluorescence measurement. An example implementation packages 8 narrowband silicon photodiodes into a 9x9mm ceramic LCC (leadless chip carrier) footprint. This package is designed for multispectral applications ranging from portable color monitors to purpose- built OEM industrial and scientific instruments. Use of an eight-channel multispectral photodiode array typically eliminates 10-20 components from a device bill-of-materials (BOM), streamlining the optical path and shrinking the footprint by 50% or more. A stepwise design approach for multispectral sensors is discussed - including spectral band definition, optical design tradeoffs and constraints, and device integration from prototype through scalable volume production

  17. MRS Photodiode, LED and extruded scintillator performance in magnetic field

    SciTech Connect

    Beznosko, D.; Blazey, G.; Dyshkant, A.; Francis, K.; Kubik, D.; Rykalin, V.; Zutshi, V.; /Northern Illinois U.

    2005-05-01

    The experimental results on the performance of the MRS (Metal/Resistor/Semiconductor) photodiode in the strong magnetic field of 4.4T, and the possible impact of the quench of the magnet at 4.5T on sensor's operation are reported. In addition, the experimental results on the performance of the extruded scintillator and WLS fiber, and various LEDs in the magnetic fields of 1.8T and 2.3T respectively, are detailed. The measurement method used is being described.

  18. Application of photodiodes to the detection of electromagnetic bursts

    NASA Technical Reports Server (NTRS)

    Fukushima, Y.; Saito, T.; Sakata, M.; Shima, M.; Yamamoto, Y.

    1985-01-01

    A new type of photodiode + scintillator (1 m2 x 1 cm) detector is developed to detect the large electro-magnetic burst under an EX-chamber. The threshold burst size is found to be 4.3 x 10 the 5 particles at the center of the scintillator. Therefore a gamma-ray family of 10 TeV is detectable by it, when it is set under 14 r.1. of iron. In addition, a very fast (2.4 nsec width) and very bright (correspond to 10 to the 6 particles) scintillation pulse has become avarable for this study.

  19. Polarization sensitive silicon photodiodes using nanostructured metallic grids

    NASA Astrophysics Data System (ADS)

    Guillaumée, M.; Dunbar, L. A.; Santschi, Ch.; Grenet, E.; Eckert, R.; Martin, O. J. F.; Stanley, R. P.

    2009-05-01

    In this paper, we present the design, fabrication, and characterization of wire grid polarizers. These polarizers show high extinction ratios and high transmission with structure dimensions that are compatible with current complementary metal-oxide-semiconductor (CMOS) technology. To design these wire grids, we first analyze the transmission properties of single apertures. From the understanding of a single aperture, we apply a modal expansion method to model wire grids. The most promising grids are fabricated on both a glass substrate and CMOS photodiode. An extinction ratio higher than 200 is measured.

  20. A hybrid solid-liquid polymer photodiode for the bioenvironment

    NASA Astrophysics Data System (ADS)

    Antognazza, M. R.; Ghezzi, D.; Musitelli, D.; Garbugli, M.; Lanzani, G.

    2009-06-01

    We demonstrate that a prototypical semiconducting polymer, poly[2-methoxy-5-(2'-ethylhexyloxy)-p-phenylene vinylene] (MEH-PPV) maintains unaltered its optoelectronic properties throughout the various steps for neural preparation. Films of MEH-PPV, after prolonged immersion in water or buffer solution, are characterized by linear and nonlinear optical spectroscopy. Based on this result, we introduce a hybrid solid-liquid photodiode based on MEH-PPV, in which we use culturing media as liquid, ionic cathodes. The hybrid device is proposed as an active interface between living tissue and conducting polymers for cell diagnostic and neural implants.

  1. Mobility of large rock avalanches: evidence from Valles Marineris, Mars

    USGS Publications Warehouse

    McEwen, A.S.

    1989-01-01

    Measurements of H/L (height of drop/length of runout) vs. volume for landslides in Valles Marineris on Mars show a trend of decreasing H/L with increasing volume. This trend, which is linear on a log-log plot, is parallel to but lies above the trend for terrestrial dry rock avalanches. This result and estimates of 104 to 105 Pa yield strength suggest that the landslides were not water saturated, as suggested by previous workers. The offset between the H/L vs. volume trends shows that a typical Martian avalanche must be nearly two orders of magnitude more voluminous than a typical terrestrial avalance in order to achieve the same mobility. This offset might be explained by the effects of gravity on flows with high yield strengths. These results should prove useful to future efforts to resolve the controversy over the mechanics of long-runout avalanches. -Author

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

    SciTech Connect

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

    2007-01-01

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

  3. [Death by avalanche in the minor mountain range].

    PubMed

    Geisenberger, Dorothee; Kramer, Lena; Pircher, Rebecca; Pollak, Stefan

    2015-01-01

    On 30 Jan 2015, two avalanche accidents happened in the Black Forest (at the foot of the 1493 m high Feldberg and the Herzogenhorn situated next to it), in which experienced ski tourers--a 58-year-old woman and a 20-year-old man--were completely buried by snow masses. Both victims were recovered dead after nearly 2 hours under the snow. The avalanches were promoted by strong snowfalls, snowdrift by the wind and steep downwind slopes. One of the victims, the 20-year-old man, underwent a forensic autopsy. The findings suggested death by protracted asphyxiation with agonal hypothermia. A mechanical traumatization with internal injuries suspected by the emergency doctor at the scene could not be confirmed at autopsy. The possible causes of death in the avalanche are discussed using the reported case as an example and in reference to the relevant literature. PMID:26548036

  4. Avalanche Dynamics of Crackle Sound in the Lung

    SciTech Connect

    Alencar, Adriano M.; Buldyrev, Sergey V.; Majumdar, Arnab; Stanley, H. Eugene; Suki, Bela

    2001-08-20

    We analyze a sequence of short transient sound waves, called 'crackles,' which are associated with explosive openings of airways during lung inflation. The distribution of time intervals between consecutive crackles {Delta}t shows two regimes of power law behavior. We develop an avalanche model which fits the data over five decades of {Delta}t. We find that the regime for large {Delta}t is related to the dynamics of distinct avalanches in a Cayley tree, and the regime for small {Delta}t is determined by the dynamics of crackle propagation within a single avalanche. We also obtain a mean-field solution of the model which provides information about lung inflation.

  5. Universality in the mean spatial shape of avalanches

    NASA Astrophysics Data System (ADS)

    Thiery, Thimothée; Le Doussal, Pierre

    2016-05-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2015-04-01

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

  7. Comparative analysis of high-performance infrared avalanche InxGa1-xAsyP1-y and Hg1-xCdxTe heterophotodiodes

    NASA Astrophysics Data System (ADS)

    Kholodnov, Viacheslav; Drugova, Albina; Nikitin, Mikhail; Chekanova, Galina

    2012-10-01

    Technology of infrared (IR) avalanche photodiodes (APDs) gradually moves from simple single element APD to 2D focal plane arrays (FPA). Spectral covering of APDs is expanded continuously from classic 1.3 μm to longer wavelengths due to using of narrow-gap semiconductor materials like Hg1-xCdxTe. APDs are of great interest to developers and manufacturers of different optical communication, measuring and 3D reconstruction thermal imaging systems. Major IR detector materials for manufacturing of high-performance APDs became heteroepitaxial structures InxGa1-xAsyP1-y and Hg1-xCdxTe. Progress in IR APD technology was achieved through serious improvement in material growing techniques enabling forming of multilayer heterostuctures with separate absorption and multiplication regions (SAM). Today SAM-APD design can be implemented both on InxGa1-xAsyP1-y and Hg1-xCdxTe multilayer heteroepitaxial structures. To create the best performance optimal design avalanche heterophotodiode (AHPD) it is necessary to carry out a detailed theoretical analysis of basic features of generation, avalanche breakdown and multiplication of charge carriers in proper heterostructure. Optimization of AHPD properties requires comprehensive estimation of AHPD's pixel performance depending on pixel's multi-layer structure design, layers doping, distribution of electric field in the structure and operating temperature. Objective of the present article is to compare some features of 1.55 μm SAM-AHPDs based on InxGa1-xAsyP1-y and Hg1-xCdxTe.

  8. Avalanche shape and exponents beyond mean-field theory

    NASA Astrophysics Data System (ADS)

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

    2014-12-01

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

  9. Geophysical investigation of the Sandalp rock avalanche deposits

    NASA Astrophysics Data System (ADS)

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

    2010-04-01

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

  10. Modeling and monitoring avalanches caused by rain-on-snow events

    NASA Astrophysics Data System (ADS)

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

    2014-12-01

    Direct-action avalanches occur during large storm cycles in mountainous regions, when stresses on the snowpack increase rapidly due to the load of new snow and outpace snow strengthening due to compaction. If temperatures rise above freezing during the storm and snowfall turns to rain, the near-surface snow undergoes rapid densification caused by the introduction of liquid water. This shock to the snowpack, if stability is near critical, can cause widespread immediate avalanching due to the large induced strain rates in the slab, followed by secondary delayed avalanches due to both the increased load as well as water percolation to the depth of a weak layer. We use the semi-empirical SNOow Slope Stability model (SNOSS) to estimate the evolution of stability prior to large avalanches during rain-on-snow events on Highway 21 north of Boise, Idaho. We have continuously monitored avalanche activity using arrays of infrasound sensors in the avalanche-prone section of HW21 near Stanley, in collaboration with the Idaho Transportation Department's avalanche forecasting program. The autonomous infrasound avalanche monitoring system provides accurate timing of avalanche events, in addition to capturing avalanche dynamics during some major releases adjacent to the array. Due to the remote location and low winter traffic volume, the highway is typically closed for multiple days during major avalanche cycles. Many major avalanches typically release naturally and reach the road, but due the complex terrain and poor visibility, manual observations are often not possible until several days later. Since most avalanche programs typically use explosives on a regular basis to control slope stability, the infrasound record of avalanche activity we have recorded on HW21 provides a unique opportunity to study large naturally triggered avalanches. We use a first-order physically based stability model to estimate the importance of precipitation phase, amount, and rate during major rain

  11. Low noise, IR-blind organohalide perovskite photodiodes for visible light detection and imaging.

    PubMed

    Lin, Qianqian; Armin, Ardalan; Lyons, Dani M; Burn, Paul L; Meredith, Paul

    2015-03-25

    Solution-processed organohalide perov-skite photodiodes that have performance metrics matching silicon, but are infrared-blind are reported. The perovskite photodiodes operate in the visible band, have low dark current and noise, high specific detectivity, large linear dynamic range, and fast temporal response. Their properties make them promising candidates for imaging applications. PMID:25677496

  12. 4H-SiC photodiode model for DC SPICE circuit simulation

    NASA Astrophysics Data System (ADS)

    Kociubiński, Andrzej; Duk, Mariusz; Korona, Mateusz; Muzyka, Krzysztof

    2015-09-01

    Technology, characterization and in particularly modeling of 4H-SiC photodiode have been presented in this paper. Modeling and simulation has been performed using PSPICE environment. Comparison of simulation with real results for electrical characteristic (I-V) of circular SiC photodiodes has been also presented.

  13. Free-electron THz-reabsorption in distributed photodiode structures

    NASA Astrophysics Data System (ADS)

    Calle, V. H.; Michael, E. A.

    2015-10-01

    Ultra-fast photodiodes based on vertical p-i-n or uni-traveling (UTC) mesa structures require a highly doped base layer that makes a well-conducting transverse connection between the mesa bottom layer and the bottom metal contacts. To reach the lowest possible THz loss, the question arises on what doping levels would be optimal for this layer. Doping levels of up to ≈ 5× {{10}19} cm-3 can be reached in InP, corresponding to conductivities of around 8× {{10}5} S m-1, which is still much lower than those of metal conductors. A full-wave analysis, which is executed in HFSS™ and CST Microwave Studio™ and reported here, shows that a valley of low loss exists around a conductivity of 5× {{10}4} S m-1 (estimated doping value ≈ 2× {{10}18} cm-3), in the middle of a conductivity range of excessive terahertz absorption, making this value the best choice for the whole frequency range up to 2000 GHz. The results are supported by an analytical solution in a simplified transmission line model. The results are expected to be significant for designing future distributed photonic devices such as traveling-wave (TW) photodiodes.

  14. Gamma ray spectroscopy and timing using LSO and PIN photodiodes

    SciTech Connect

    Moses, W.W.; Derenzo, S.E.; Melcher, C.L.; Manente, R.A.

    1994-11-01

    The high density, high light output, and short decay time of LSO (lutetium orthosilicate, Lu{sub 2}SiO{sub 5}:Ce) make it an attractive scintillator for gamma ray spectroscopy. The low cost, small size, high quantum efficiency, and ruggedness of silicon photodiodes make them attractive photodetectors for this same application, although their high noise (Compared to a photomultiplier tube) reduces their appeal. In this work the authors measure the gamma ray energy resolution, timing accuracy, and conversion factor from gamma energy to number of electron-hole pairs produced with a 3 x 3 x 22 mm{sup 3} LSO scintillator crystal read out with a 3 x 3 mm{sup 2} silicon PIN photodiode. When the detector is excited with 511 keV photons, a photopeak centered at 1,940 e{sup {minus}} with 149 keV fwhm is observed and a timing signal with 35 ns fwhm jitter is produced. When the detector is excited with 1,275 keV photons, a photopeak centered at 4,910 e{sup {minus}} with 149 keV fwhm is observed and a timing signal with 25 ns fwhm jitter is produced. While these performance measures are inferior to those obtained with photomultiplier tubes, they are acceptable for some applications.

  15. Stochastic Equation of Fragmentation and Branching Processes Related to Avalanches

    NASA Astrophysics Data System (ADS)

    Beznea, Lucian; Deaconu, Madalina; Lupaşcu, Oana

    2016-02-01

    We give a stochastic model for the fragmentation phase of an avalanche. We construct a fragmentation-branching process related to the avalanches, on the set of all fragmentation sizes introduced by Bertoin. A fractal property of this process is emphasized. We also establish a specific stochastic differential equation of fragmentation. It turns out that specific branching Markov processes on finite configurations of particles with sizes bigger than a strictly positive threshold are convenient for describing the continuous time evolution of the number of the resulting fragments. The results are obtained by combining analytic and probabilistic potential theoretical tools.

  16. Effect of volume fraction on granular avalanche dynamics.

    PubMed

    Gravish, Nick; Goldman, Daniel I

    2014-09-01

    We study the evolution and failure of a granular slope as a function of prepared volume fraction, ϕ(0). We rotated an initially horizontal layer of granular material (0.3-mm-diam glass spheres) to a 45° angle while we monitor the motion of grains from the side and top with high-speed video cameras. The dynamics of grain motion during the tilt process depended sensitively on ϕ(0)∈[0.58-0.63] and differed above or below the granular critical state, ϕ(c), defined as the onset of dilation as a function of increasing volume fraction. For ϕ(0)-ϕ(c)<0, slopes experienced short, rapid, precursor compaction events prior to the onset of a sustained avalanche. Precursor compaction events began at an initial angle θ(0)=7.7±1.4° and occurred intermittently prior to the onset of an avalanche. Avalanches occurred at the maximal slope angle θ(m)=28.5±1.0°. Granular material at ϕ(0)-ϕ(c)>0 did not experience precursor compaction prior to avalanche flow, and instead experienced a single dilational motion at θ(0)=32.1±1.5° prior to the onset of an avalanche at θ(m)=35.9±0.7°. Both θ(0) and θ(m) increased with ϕ(0) and approached the same value in the limit of random close packing. The angle at which avalanching grains came to rest, θ(R)=22±2°, was independent of ϕ(0). From side-view high-speed video, we measured the velocity field of intermittent and avalanching flow. We found that flow direction, depth, and duration were affected by ϕ(0), with ϕ(0)-ϕ(c)<0 precursor flow extending deeper into the granular bed and occurring more rapidly than precursor flow at ϕ(0)-ϕ(c)>0. Our study elucidates how initial conditions-including volume fraction-are important determinants of granular slope stability and the onset of avalanches. PMID:25314432

  17. Microwave diagnostics of laser-induced avalanche ionization in air

    SciTech Connect

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

    2006-10-01

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

  18. Effect of volume fraction on granular avalanche dynamics

    NASA Astrophysics Data System (ADS)

    Gravish, Nick; Goldman, Daniel I.

    2014-09-01

    We study the evolution and failure of a granular slope as a function of prepared volume fraction, ϕ0. We rotated an initially horizontal layer of granular material (0.3-mm-diam glass spheres) to a 45∘ angle while we monitor the motion of grains from the side and top with high-speed video cameras. The dynamics of grain motion during the tilt process depended sensitively on ϕ0∈[0.58-0.63] and differed above or below the granular critical state, ϕc, defined as the onset of dilation as a function of increasing volume fraction. For ϕ0-ϕc<0, slopes experienced short, rapid, precursor compaction events prior to the onset of a sustained avalanche. Precursor compaction events began at an initial angle θ0=7.7±1.4∘ and occurred intermittently prior to the onset of an avalanche. Avalanches occurred at the maximal slope angle θm=28.5±1.0∘. Granular material at ϕ0-ϕc>0 did not experience precursor compaction prior to avalanche flow, and instead experienced a single dilational motion at θ0=32.1±1.5∘ prior to the onset of an avalanche at θm=35.9±0.7∘. Both θ0 and θm increased with ϕ0 and approached the same value in the limit of random close packing. The angle at which avalanching grains came to rest, θR=22±2∘, was independent of ϕ0. From side-view high-speed video, we measured the velocity field of intermittent and avalanching flow. We found that flow direction, depth, and duration were affected by ϕ0, with ϕ0-ϕc<0 precursor flow extending deeper into the granular bed and occurring more rapidly than precursor flow at ϕ0-ϕc>0. Our study elucidates how initial conditions—including volume fraction—are important determinants of granular slope stability and the onset of avalanches.

  19. Assessing risk based on uncertain avalanche activity patterns

    NASA Astrophysics Data System (ADS)

    Zeidler, Antonia; Fromm, Reinhard

    2015-04-01

    Avalanches may affect critical infrastructure and may cause great economic losses. The planning horizon of infrastructures, e.g. hydropower generation facilities, reaches well into the future. Based on the results of previous studies on the effect of changing meteorological parameters (precipitation, temperature) and the effect on avalanche activity we assume that there will be a change of the risk pattern in future. The decision makers need to understand what the future might bring to best formulate their mitigation strategies. Therefore, we explore a commercial risk software to calculate risk for the coming years that might help in decision processes. The software @risk, is known to many larger companies, and therefore we explore its capabilities to include avalanche risk simulations in order to guarantee a comparability of different risks. In a first step, we develop a model for a hydropower generation facility that reflects the problem of changing avalanche activity patterns in future by selecting relevant input parameters and assigning likely probability distributions. The uncertain input variables include the probability of avalanches affecting an object, the vulnerability of an object, the expected costs for repairing the object and the expected cost due to interruption. The crux is to find the distribution that best represents the input variables under changing meteorological conditions. Our focus is on including the uncertain probability of avalanches based on the analysis of past avalanche data and expert knowledge. In order to explore different likely outcomes we base the analysis on three different climate scenarios (likely, worst case, baseline). For some variables, it is possible to fit a distribution to historical data, whereas in cases where the past dataset is insufficient or not available the software allows to select from over 30 different distribution types. The Monte Carlo simulation uses the probability distribution of uncertain variables

  20. Safety on the Hills in Winter: Avalanche Risk--Snow Formation.

    ERIC Educational Resources Information Center

    Grant, Frank

    2003-01-01

    This compact training session on avalanche risk reviews snow crystal formations and common generalities about avalanches. Two types of avalanches--loose and slab--are described, and the characteristics of each are given along with danger signs that accompany each one. Three books are highly recommended for further information. (TD)

  1. Meteorological variables associated with deep slab avalanches on persistent weak layers

    USGS Publications Warehouse

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

    2014-01-01

    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.

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

    SciTech Connect

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

    2008-07-15

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

  3. Complementary Metal Oxide Semiconductor-Compatible Back-Side-Illuminated Photodiode for Optoelectronic Integrated Circuit Devices

    NASA Astrophysics Data System (ADS)

    Shin, Sang-Baie; Sekiguchi, Hiroto; Okada, Hiroshi; Wakahara, Akihiro

    2013-04-01

    In this study, the prototype optoelectronic integrated circuits (OEICs) operating with optical input signals were designed and fabricated. A back-side-illuminated (BSI) photodiode was designed and demonstrated by a newly proposed practical method, utilizing micro-electromechanical systems (MEMS) and postcomplement metal oxide semiconductor (CMOS) processes. Additional fabrication processes for the BSI photodiode were proposed and described in detail in this paper. The operational amplifier for amplification of the optical current by the BSI photodiode as the transimpedance amplifier was designed and fabricated. And the pulse width modulation (PWM) wave generator was implemented for modulating optical signals as the prototype OEIC device. The maximum quantum efficiency of 28.4% was obtained from the fabricated BSI photodiode. Output signals of PWM were successfully controlled by the generated optical current of the BSI photodiode.

  4. Modeling and measurement of a whole-cell bioluminescent biosensor based on a single photon avalanche diode.

    PubMed

    Daniel, Ramiz; Almog, Ronen; Ron, Amit; Belkin, Shimshon; Diamand, Yosi Shacahm

    2008-12-01

    Whole-cell biosensors are potential candidates for on-line and in situ environmental monitoring. In this work we present a new design of a whole-cell bioluminescence biosensor for water toxicity detection, based on genetically engineered Escherichia coli bacteria, carrying a recA::luxCDABE promoter-reporter fusion. Sensitive optical detection is achieved using a single photon avalanche photodiode (SPAD) working in the Geiger mode. The present work describes a simple mathematical model for the kinetic process of the bioluminescence based SOS toxin response of E. coli bacteria. We find that initially the bioluminescence signal depends on the time square and we show that the spectral intensity of the bioluminescence signal is inverse proportional to the frequency. We get excellent agreement between the theoretical model and the measured light signal. Furthermore, we present experimental results of the bioluminescent signal measurement using a SPAD and a photomultiplier, and demonstrate improvement of the measurement by applying a matched digital filter. Low intensity bioluminescence signals were measured after the whole-cell sensors were exposed to various toxicant concentrations (5, 15 and 20ppm). PMID:18774705

  5. Refractive index matched suspensions as a tool for investigating entrainment by avalanches and debris flows

    NASA Astrophysics Data System (ADS)

    Bates, Belinda; Ancey, Christophe

    2015-04-01

    Geophysical gravity flows such as avalanches and debris flows are complicated mixtures of fluid and solids, often containing particle sizes of many orders of magnitude. In a debris flow, for example, the composition varies from head to tail, and from bottom to top due to particle size segregation and recirculation. In addition the solid components may have different masses and mechanical properties. For this reason, a complete understanding of substrate entrainment by this type of flow is still out of reach. A common strategy for advancing our understanding of the physics of processes like entrainment is to use a greatly simplified laboratory model of a debris flow, and take internal and bulk measurements. This idealized technique forms the basis of this study, in which a two-phase, monodisperse suspension of PMMA beads in a refractive-index matched suspending fluid flowed down a flume, encountering an entrainable region of the same suspension on the way. This study represents the first attempt of taking continuous internal velocity measurements inside a flowing, entraining model avalanche or debris flow in the laboratory. Interior PIV measurements of flow velocity were taken in the entrainable region, along with surface height measurements, to shed some light on the entrainment mechanisms and to see how the bulk flow responded. Further, some differential pressure measurements were made in the entrainable bed to see if pore-pressure peaks had any correlation with significant events during entrainment. We present our preliminary findings and discuss the suitability of the method to entrainment investigations.

  6. Cold seeps associated with a submarine debris avalanche deposit at Kick'em Jenny volcano, Grenada (Lesser Antilles)

    NASA Astrophysics Data System (ADS)

    Carey, Steven; Ballard, Robert; Bell, Katherine L. C.; Bell, Richard J.; Connally, Patrick; Dondin, Frederic; Fuller, Sarah; Gobin, Judith; Miloslavich, Patricia; Phillips, Brennan; Roman, Chris; Seibel, Brad; Siu, Nam; Smart, Clara

    2014-11-01

    Remotely operated vehicle (ROV) exploration at the distal margins of a debris avalanche deposit from Kick'em Jenny submarine volcano in Grenada has revealed areas of cold seeps with chemosynthetic-based ecosystems. The seeps occur on steep slopes of deformed, unconsolidated hemipelagic sediments in water depths between 1952 and 2042 m. Two main areas consist of anastomosing systems of fluid flow that have incised local sediments by several tens of centimeters. No temperature anomalies were observed in the vent areas and no active flow was visually observed, suggesting that the venting may be waning. An Eh sensor deployed on a miniature autonomous plume recorder (MAPR) recorded a positive signal and the presence of live organisms indicates at least some venting is still occurring. The chemosynthetic-based ecosystem included giant mussels (Bathymodiolus sp.) with commensal polychaetes (Branchipolynoe sp.) and cocculinid epibionts, other bivalves, Siboglinida (vestimentiferan) tubeworms, other polychaetes, and shrimp, as well as associated heterotrophs, including gastropods, anemones, crabs, fish, octopods, brittle stars, and holothurians. The origin of the seeps may be related to fluid overpressure generated during the collapse of an ancestral Kick'em Jenny volcano. We suggest that deformation and burial of hemipelagic sediment at the front and base of the advancing debris avalanche led to fluid venting at the distal margin. Such deformation may be a common feature of marine avalanches in a variety of geological environments especially along continental margins, raising the possibility of creating large numbers of ephemeral seep-based ecosystems.

  7. Si/Ge photodiodes for coherent and analog communication

    NASA Astrophysics Data System (ADS)

    Piels, Molly

    High-speed photodiodes have diverse applications in wireless and fiber communications. They can be used as output stages for antenna systems as well as receivers for fiber optic networks. Silicon is an attractive substrate material for photonic components for a number of reasons. Low cost manufacturing in CMOS fabrication facilities, low material loss at telecommunications wavelengths, and relatively simple co-packaging with electronics are all driving interest in silicon photonic devices. Since silicon does not absorb light at telecommunications wavelengths, photodetector fabrication requires the integration of either III-V materials or germanium. Recent work on germanium photodetectors has focused on low-capacitance devices suitable for integration with silicon electronics. These devices have excellent bandwidth and efficiency, but have not been designed for the levels of photocurrent required by coherent and analog systems. This thesis explores the design, fabrication, and measurement of photodetectors fabricated on silicon with germanium absorbing regions for high speed and high power performance. There are numerous design trade-offs between speed, efficiency, and output power. Designing for high bandwidth favors small devices for low capacitance. Small devices require abrupt absorption profiles for good efficiency, but design for high output power favors large devices with dilute absorption. The absorption profile can be controlled by the absorber layer thickness, but this will also affect the bandwidth and power handling. This work quantifies the trade-offs between high speed, high efficiency, and high power design. Intrinsic region thickness and absorption profile are identified as the most important design variables. For PIN structures, the absorption profile and intrinsic region thickness are both functions of the Ge thickness, but in uni-traveling carrier (UTC) structures the absorption profile and intrinsic region can be designed independently. This

  8. Group Dynamics and Decision Making: Backcountry Recreationists in Avalanche Terrain

    ERIC Educational Resources Information Center

    Bright, Leslie Shay

    2010-01-01

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

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

    NASA Technical Reports Server (NTRS)

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

    1985-01-01

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

  10. Hybrid phase transition into an absorbing state: Percolation and avalanches.

    PubMed

    Lee, Deokjae; Choi, S; Stippinger, M; Kertész, J; Kahng, B

    2016-04-01

    Interdependent networks are more fragile under random attacks than simplex networks, because interlayer dependencies lead to cascading failures and finally to a sudden collapse. This is a hybrid phase transition (HPT), meaning that at the transition point the order parameter has a jump but there are also critical phenomena related to it. Here we study these phenomena on the Erdős-Rényi and the two-dimensional interdependent networks and show that the hybrid percolation transition exhibits two kinds of critical behaviors: divergence of the fluctuations of the order parameter and power-law size distribution of finite avalanches at a transition point. At the transition point global or "infinite" avalanches occur, while the finite ones have a power law size distribution; thus the avalanche statistics also has the nature of a HPT. The exponent β_{m} of the order parameter is 1/2 under general conditions, while the value of the exponent γ_{m} characterizing the fluctuations of the order parameter depends on the system. The critical behavior of the finite avalanches can be described by another set of exponents, β_{a} and γ_{a}. These two critical behaviors are coupled by a scaling law: 1-β_{m}=γ_{a}. PMID:27176256

  11. Teaching Avalanche Safety Courses: Instructional Techniques and Field Exercises.

    ERIC Educational Resources Information Center

    Watters, Ron

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

  12. Reducing the Odds: Backcountry Powder Skiing in Avalanche Terrain.

    ERIC Educational Resources Information Center

    Daffern, Tony

    This paper provides information and strategies to reduce the risk of encountering an avalanche when skiing or climbing on steep slopes. Skiers must recognize that the risk exists, be aware of their own tolerance for risk, and not allow companions to pressure them into taking more risk than they can tolerate. Ideally, one should ski with a small…

  13. Multi-step avalanche chambers for final experiment E605

    NASA Astrophysics Data System (ADS)

    Hubbard, J. R.; Coutrakon, G.; Cribier, M.; Mangeot, Ph.; Martin, H.; Mullié, J.; Palanque, S.; Pelle, J.

    1980-10-01

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

  14. Electron avalanche structure determined by random walk theory

    NASA Technical Reports Server (NTRS)

    Englert, G. W.

    1973-01-01

    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.

  15. Preliminary simulation study of a coincidence Avalanche Pixel Sensor

    NASA Astrophysics Data System (ADS)

    Vignetti, M. M.; Calmon, F.; Cellier, R.; Pittet, P.; Quiquerez, L.; Savoy-Navarro, A.

    2015-06-01

    In this paper a preliminary study of coincidence Avalanche Pixel Sensors (APiX) for High Energy Physics (HEP) applications is presented. In this preliminary work, some PEB prevention techniques found in literature have been studied by TCAD simulations adopting 2D Cylindrical geometrical models and 130nm CMOS process technological data.

  16. Hybrid phase transition into an absorbing state: Percolation and avalanches

    NASA Astrophysics Data System (ADS)

    Lee, Deokjae; Choi, S.; Stippinger, M.; Kertész, J.; Kahng, B.

    2016-04-01

    Interdependent networks are more fragile under random attacks than simplex networks, because interlayer dependencies lead to cascading failures and finally to a sudden collapse. This is a hybrid phase transition (HPT), meaning that at the transition point the order parameter has a jump but there are also critical phenomena related to it. Here we study these phenomena on the Erdős-Rényi and the two-dimensional interdependent networks and show that the hybrid percolation transition exhibits two kinds of critical behaviors: divergence of the fluctuations of the order parameter and power-law size distribution of finite avalanches at a transition point. At the transition point global or "infinite" avalanches occur, while the finite ones have a power law size distribution; thus the avalanche statistics also has the nature of a HPT. The exponent βm of the order parameter is 1 /2 under general conditions, while the value of the exponent γm characterizing the fluctuations of the order parameter depends on the system. The critical behavior of the finite avalanches can be described by another set of exponents, βa and γa. These two critical behaviors are coupled by a scaling law: 1 -βm=γa .

  17. A new approach to investigate leakage current mechanisms in infrared photodiodes from illuminated current-voltage characteristics

    SciTech Connect

    Gopal, Vishnu

    2014-08-28

    This paper presents a new approach to investigate leakage current mechanisms in infrared photodiodes from the illuminated current–voltage characteristics. The example of mid-wave mercury cadmium telluride photodiodes is presented to illustrate the new approach. The new method is suitable for evaluating diodes in an array environment as advance knowledge of any of the material or device parameters are not required. The thermal saturation current is estimated from the observed open circuit voltage and zero-bias current (photo-current) of the diode. The ohmic shunt resistance is estimated from the observed maximum dynamic impedance of the diode. The experimentally observed reverse bias diode current in excess of thermal current, photo-current, and ohmic shunt current is reported to be best described by an exponential function of the type, I{sub excess} = I{sub r0} + K{sub 1} exp (K{sub 2} V), where I{sub r0}, K{sub 1}, and K{sub 2} are fitting parameters and V is the applied bias voltage. Our investigations reveal a close link between the excess current and the sources of ohmic currents in the diode. Exponential growth of excess current with the applied bias voltage has been interpreted as an indication of soft breakdown of the diodes.

  18. Meteorological variables to aid forecasting deep slab avalanches on persistent weak layers

    USGS Publications Warehouse

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

    2015-01-01

    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.

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

    PubMed

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

    2009-01-01

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

  20. Use of a magnetic field to modify and detect avalanche behavior on a conical bead pile

    NASA Astrophysics Data System (ADS)

    Johnson, Nathan; Lehman, Susan

    2015-03-01

    A conical bead pile subject to slow driving and an external magnetic field is used to test the effects of drop height and cohesion on avalanche statistics. Magnetically susceptible beads were dropped onto a pile from different heights and into different strengths of magnetic field. Avalanches were recorded by the change in mass as beads fall off the pile. For beads dropped from a low drop height with no cohesion, the avalanche size distribution follows a power law. As cohesion increases, we observe an increase in the probability of very large avalanches and decreases in the mid-size avalanches. The resulting bump in the avalanche distribution moves to larger avalanche size as the cohesion in the system is increased, matching the prediction by an analytic theory from a mean-field model of slip avalanches. The model also makes predictions for avalanche duration, which is not measurable with our current system. Since the steel beads are magnetized while in the applied magnetic field, their motion during an avalanche creates a change in magnetic flux. To detect this motion, we have placed a large-diameter pick-up coil around the pile. Results of the testing and calibration of this coil to measure avalanche duration are presented.

  1. Snow avalanche detection and identification for near real-time application

    NASA Astrophysics Data System (ADS)

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

    2013-12-01

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

  2. Electroded avalanche amorphous selenium (a-Se) photosensor

    PubMed Central

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

    2012-01-01

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

  3. Laboratory study of avalanches in a magnetized plasma

    NASA Astrophysics Data System (ADS)

    van Compernolle, Bart

    2015-11-01

    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.

  4. Responsivity of Diamond X-ray Photodiodes Calibrated at NSLS

    SciTech Connect

    Keister,J.W.; Smedley, J.; Muller, E. M.; Bohon, J.

    2009-09-27

    Single crystal, high purity synthetic diamond is used as photoabsorption and carrier transport medium in x-ray photodiodes. While the thermal / mechanical robustness and high x-ray transmission of diamond make such devices attractive for synchrotron instrumentation, state-of-the-art quality material and electrical interfaces further make such detectors feasible. The present work develops methodology for attaining calculable responsivity (photocurrent yield) over a wide range of photon energies (0.2 to 28 keV) to within 5% accuracy. These methods achieve linear response for up to 0.2 W absorbed x-ray power and response time as low as 1 ns. Details of contact formation / robustness and bias configuration are explored.

  5. Colored adaptive compressed imaging with a single photodiode.

    PubMed

    Yan, Yiyun; Dai, Huidong; Liu, Xingjiong; He, Weiji; Chen, Qian; Gu, Guohua

    2016-05-10

    Computational ghost imaging is commonly used to reconstruct grayscale images. Currently, however, there is little research aimed at reconstructing color images. In this paper, we theoretically and experimentally demonstrate a colored adaptive compressed imaging method. Benefiting from imaging in YUV color space, the proposed method adequately exploits the sparsity of the U, V components in the wavelet domain, the interdependence between luminance and chrominance, and human visual characteristics. The simulation and experimental results show that our method greatly reduces the measurements required and offers better image quality compared to recovering the red (R), green (G), and blue (B) components separately in RGB color space. As the application of a single photodiode increases, our method shows great potential in many fields. PMID:27168280

  6. Perpendicular hot electron transport in the spin-valve photodiode

    NASA Astrophysics Data System (ADS)

    Huang, Biqin; Appelbaum, Ian

    2006-08-01

    The spin-valve photodiode is a ferromagnetic metal multilayer/n-type semiconductor Schottky device operated by photoexciting hot electrons in the metal and causing internal photoemission (IPE) into the semiconductor. Simple IPE theory predicts that the magnitude of the spin-valve effect (modulation of the photocurrent) should monotonically increase as a metallic capping layer thickness increases. Experimentally, however, we observe a nonmonotonic behavior with cap layer thickness, where the magnetocurrent reaches an optimum value and then decreases. The disagreement between this experimental result and the previous theoretical model is discussed, leading to an alternative interpretation of transport including reflection from the air-metal interface. Calculations with this model are consistent with the observed phenomena.

  7. Light induced tunnel effect in CNT-Si photodiode

    NASA Astrophysics Data System (ADS)

    Aramo, C.; Ambrosio, M.; Bonavolontà, C.; Boscardin, M.; Castrucci, P.; Crivellari, M.; De Crescenzi, M.; de Lisio, C.; Fiandrini, E.; Grossi, V.; Maddalena, P.; Passacantando, M.; Santucci, S.; Scarselli, M.; Valentini, A.; Valentino, M.

    2016-07-01

    Negative differential resistance (NDR), for which the current is a decreasing function of the voltage, has been observed in the current-voltage curves of several types of structures. We measured tunnelling current and NDR by illuminating large area heterojunction obtained by growing Multi Wall Carbon Nanotubes on the surface of n-doped Silicon substrate. In the absence of light, the current flow is null until a junction threshold of about 2.4 V is reached, beyond which the dark current flows at room temperature with a very low intensity of few nA. When illuminated, a current of tens nA is observed at a drain voltage of about 1.5 V. At higher voltage the current intensity decreases according to a negative resistance of the order of MΩ. In the following we report details of tunneling photodiode realized and negative resistance characteristics.

  8. Detector telescope array: silicon--CsI(Tl)--photodiode

    NASA Astrophysics Data System (ADS)

    Norbeck, E.; Yang, L. B.; Pogodin, P.; Ingram, F. D.

    1999-10-01

    A closely packed array of 60 telescopes was developed for use at forward angles in the 4π Array at the National Superconducting Cyclotron Laboratory at Michigan State University. The telescopes resolve isotopes and cover nearly 100% of the solid angle assigned to the array. These requirements and limitations of space and funding resulted in a number of novel features, some of which will be useful in other applications. These features include: photodiodes of arbitrary shape with no frame around the edge, replacement of aluminized Mylar with aluminum leaf, an inexpensive silicon diode leakage current monitor that presents a graph of leakage current vs detector number, and a low noise but inexpensive preamplifier chip. Experience with the array showed that compounds in the outer insulation layer of some types of coax cable can seriously contaminate a vacuum system. The use of computer aided design and computer controlled machine tools reduced the cost of the structural parts by orders of magnitude.

  9. Innovative Detection System of Ochratoxin A by Thin Film Photodiodes

    PubMed Central

    Caputo, Domenico; de Cesare, Giampiero; Fanelli, Corrado; Nascetti, Augusto; Ricelli, Alessandra; Scipinotti, Riccardo

    2007-01-01

    In this work we present, for the first time, a rapid, compact and innovative method for detection of Ochratoxin A (OTA) based on hydrogenated amorphous silicon (a-Si:H) sensors. 2 μl of acidified toluene containing OTA at different concentrations were spotted on the silica side of a High Performance Thin Layer Cromatography plate and aligned with a a-Si:H p-i-n photodiode deposited by Plasma Enhanced Chemical Vapor Deposition on a different glass substrate. As an UV radiation excites the mycotoxin, the re-emitted light is detected by the a-Si:H sensor. Results show a very good linearity between OTA concentration and the sensor photocurrent over almost three orders of magnitude. The minimum detected OTA concentration is equal to 0.1ng, showing that the presented system has the potential for a low cost system suitable for the early detection of toxins in foods.

  10. Performance limitations of InGaAs photodiodes

    NASA Astrophysics Data System (ADS)

    Rogalski, Antoni

    1999-04-01

    The carrier lifetimes in InxGa1-xAs (InGaAs) ternary alloys for radiative and Auger recombination are calculated for temperature 300 K in the short wavelength range 1.5 < (lambda) < 3.7 micrometers . Due to photon recycling, an order of magnitude enhancements in the radiative lifetimes over those obtained from the standard van Roosbroeck and Shockley expression, has been assumed. The possible Auger recombination mechanisms (CHCC, CHLH and CHSH processes) in direct-gap semiconductors are investigated. In n-type and p-type materials the carrier lifetimes are similar. It is clearly shown that in the range of low doping concentration, the carrier lifetime is determined by radiative recombination. For n-type material in the range of higher doping level, a competition between radiative and CHCC processes take place; instead for p-type materials the most effective channel of Auger mechanisms is the CHSH process. A special attention has been put on discussion of the carrier lifetimes in both types of In0.53Ga0.47As materials. Consequence of enhancement in the radiative lifetime leads to higher ultimate performance of photodiodes. The performance (RoA product) of heterostructure InGaAs photovoltaic devices are analyzed. Both the n-on-p (with p-type active region) as well as p-on- n (with n-type active region) are considered. Finally, theoretically predicted performance of InGaAs photodiodes are compared with experimental data reported by other authors.

  11. Geomorphology of the Arteara Holocene rock-avalanche deposit, Gran Canaria Island

    NASA Astrophysics Data System (ADS)

    Yepes, Jorge; Lomoschitz, Alejandro

    2010-05-01

    side, where some remains can still be recognised. This was later covered by a layer of ordered rubble from the left bank. Blockage of the main course gave rise to an alluvial-torrential plain of boulders and gravels along the section upstream from Arteara. A network of braided channels has developed on this plain. At present, the advance of the rising erosion has cut through the slope deposit and is dismantling the alluvial-torrential plain. The rock avalanche defines an elongated tongue in the direction of flow, of varying thickness (1-15m) and L/H = 2.47 (displacement/total fall=1325m/535m), reappearing at the foot (Hr=15m). In general, the rock avalanche is adapted to the previous slide, although it has small overspill lobes on the lateral flanks. The low angle of friction deduced (=21.47°) agrees with the high mobility estimated from the L/H ratio and is due to the existence of a previous relief defined by the rock slide and the lubrication provided by the ignimbrite. This easily weathered material must have made up the gravel layer over which the lava blocks moved. The rock avalanche deposit varies widely in size and is structured in bands of loose blocks with a bimodal distribution (0.1-3m3; 10.30m3) and low selection. The blocks lie on a layer of loose, flat, angular gravels. The blocks are angular and show numerous signs of impact, including split and fragmented blocks, faces with conchoidal fractures, chipped edges and broken corners. The movement of the rock avalanche would have been a swift, dry granular flow. The avalanche would have had a leap component at the head, turbulent flow in the intermediate corridor and laminar flow in the distal zone. The leap component is identified by the accumulation of blocks in crests transversal to the flow and the presence of megablocks aligned with the flow. The turbulent component is identified by the chaotic accumulation of blocks in the palaeochannels and overspill lobes covering the flanks. The laminar component

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

    NASA Astrophysics Data System (ADS)

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

    2010-05-01

    The formation of terminal moraines mainly results from glacier changes in response to climate variations. But glaciers may also react sensitively to increased debris cover caused by large-scale failure of bedrock slopes. Catastrophic rock avalanches are a major source of sediment in active orogens like e.g. the Southern Alps, New Zealand (Shulmeister et al., 2009). They often occur as a result of earthquakes, and also due to slope failure driven in the longer term by regional uplift. Rock avalanche deposits can drastically alter glacier mass balance through reduced ablation and consequential altered flow rates, and can contribute to glacier moraine formation (see e.g. Hewitt, 2005, 2009; Shulmeister et al., 2009). Consequently, the frequently-assumed linkage between terminal moraine formation and climate forcing may need to be reconsidered. Especially for the investigation of the regional Holocene glacier and climate chronologies it is essential to separate and assess the tectonic/coseismic impact on terminal moraine formation. In order to investigate the role of catastrophic landslide events in moraine formation, Ground Penetrating Radar (GPR) surveys of rock avalanche deposits on the Tasman and Hooker Glaciers, Southern Alps, New Zealand, were compared with laboratory experiments of the debris cover effect on underlying ice ablation. The 1991 Mt. Cook rock avalanche deposit on the Tasman Glacier is up to 10 m thick and has caused a 25 m high ridge to form at the upvalley edge of the deposit. The smaller 2004 Mt. Beatrice rock avalanche onto Hooker Glacier has formed an elevated plateau with similar raised edges because of reduced ice melting under the rock avalanche deposit. The reduction of ice-surface ablation on the glaciers is compared with laboratory data on ice ablation rates under various thickness of debris-cover, under controlled conditions with replication of diurnal temperature, radiation cycles and rainfall conditions. The latest results are presented

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

    NASA Astrophysics Data System (ADS)

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

    2015-12-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2014-12-01

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

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

    NASA Astrophysics Data System (ADS)

    Prokop, Alexander; Wirbel, Anna

    2013-04-01

    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

  16. A motion gesture sensor using photodiodes with limited field-of-view.

    PubMed

    Kim, Yong Sin; Baek, Kwang-Hyun

    2013-04-22

    This paper presents a low-power and small-size motion gesture sensor (MGS) based on an active infrared (IR) proximity sensor. While conventional proximity-based MGSs require two LEDs (the most power-hungry components) and one photodiode, the proposed MGS eliminates one of LEDs at the expense of an additional photodiode as a separate channel. In conjunction with an optical block that limits the field-of-view of each photodiode, the power consumption and area of the proposed MGS can be reduced by up to 52% and 69%, respectively, compared with conventional proximity-based MGSs. Optical simulation and test results validate theoretical analysis presented. PMID:23609631

  17. Maximum speeds and alpha angles of flowing avalanches

    NASA Astrophysics Data System (ADS)

    McClung, David; Gauer, Peter

    2016-04-01

    A flowing avalanche is one which initiates as a slab and, if consisting of dry snow, will be enveloped in a turbulent snow dust cloud once the speed reaches about 10 m/s. A flowing avalanche has a dense core of flowing material which dominates the dynamics by serving as the driving force for downslope motion. The flow thickness typically on the order of 1 -10 m which is on the order of about 1% of the length of the flowing mass. We have collected estimates of maximum frontal speed um (m/s) from 118 avalanche events. The analysis is given here with the aim of using the maximum speed scaled with some measure of the terrain scale over which the avalanches ran. We have chosen two measures for scaling, from McClung (1990), McClung and Schaerer (2006) and Gauer (2012). The two measures are the √H0-;√S0-- (total vertical drop; total path length traversed). Our data consist of 118 avalanches with H0 (m)estimated and 106 with S0 (m)estimated. Of these, we have 29 values with H0 (m),S0 (m)and um (m/s)estimated accurately with the avalanche speeds measured all or nearly all along the path. The remainder of the data set includes approximate estimates of um (m/s)from timing the avalanche motion over a known section of the path where approximate maximum speed is expected and with either H0or S0or both estimated. Our analysis consists of fitting the values of um/√H0--; um/√S0- to probability density functions (pdf) to estimate the exceedance probability for the scaled ratios. In general, we found the best fits for the larger data sets to fit a beta pdf and for the subset of 29, we found a shifted log-logistic (s l-l) pdf was best. Our determinations were as a result of fitting the values to 60 different pdfs considering five goodness-of-fit criteria: three goodness-of-fit statistics :K-S (Kolmogorov-Smirnov); A-D (Anderson-Darling) and C-S (Chi-squared) plus probability plots (P-P) and quantile plots (Q-Q). For less than 10% probability of exceedance the results show that

  18. Design and fabrication of an optimum peripheral region for low gain avalanche detectors

    NASA Astrophysics Data System (ADS)

    Fernández-Martínez, Pablo; Flores, D.; Hidalgo, S.; Greco, V.; Merlos, A.; Pellegrini, G.; Quirion, D.

    2016-06-01

    Low Gain Avalanche Detectors (LGAD) represent a remarkable advance in high energy particle detection, since they provide a moderate increase (gain ~10) of the collected charge, thus leading to a notable improvement of the signal-to-noise ratio, which largely extends the possible application of Silicon detectors beyond their present working field. The optimum detection performance requires a careful implementation of the multiplication junction, in order to obtain the desired gain on the read out signal, but also a proper design of the edge termination and the peripheral region, which prevents the LGAD detectors from premature breakdown and large leakage current. This work deals with the critical technological aspects required to optimize the LGAD structure. The impact of several design strategies for the device periphery is evaluated with the aid of TCAD simulations, and compared with the experimental results obtained from the first LGAD prototypes fabricated at the IMB-CNM clean room. Solutions for the peripheral region improvement are also provided.

  19. Advanced MCT technologies in France

    NASA Astrophysics Data System (ADS)

    Destefanis, Gérard; Tribolet, Philippe

    2007-04-01

    In this paper we present an overview of the very recent developments of the HgCdTe infrared detector technology developed by CEA-LETI and industrialized by Sofradir in France. Today Sofradir uses in production for more than 15years a very mature, reproducible, well mastered and fully understood, planar n on p ion implanted technology. This process that allows very high yields to be achieved in all infrared bands from SWIR to LWIR uses the very conventional approach of LPE growth of MCT on lattice-matched CdZnTe substrates. Progress in this field is continuous from 20years and has recently leaded to the fabrication of high performance VLWIR FPA (320x256 with cut off wavelengths as high as 20μm). Moreover, thanks to the design of the epitaxial structure and to the substrate removal step MCT FPAs present the unique features to have very high quantum efficiency (above 70%) from the cut off wavelength down to the UV. This effect, which opens new application fields, was recently demonstrated in SWIR 320x256 FPAs with cut off wavelength of 2.5μm. Very high quality FPAs (1280x1024) with pitches as small as 15μm have already been demonstrated last year using the MBE growth of MWIR MCT epilayers on 4 inches germanium substrates, n on p ion implanted photodiodes and the hot welding indium bump hybridization technique. At the same time, with the MBE growth, bicolor and dual band FPAs which uses more complex multi hetero-junctions architectures (both 4 layers npn and 'pseudo planar' structures and extrinsically doped MCT layers) were fabricated with formats of 320x256 and pitches as small as 25μm. A very new area of development concerns avalanche photodiodes (APD) made with MCT. This semiconductor presents a unique feature among all the over semiconductors. Extremely high avalanche gains can be obtained on n on p photodiodes without absolutely any noise excess (F(K)=1): MCT APDs act as perfect amplifiers. These results open new interesting fields of investigation for low

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

    NASA Astrophysics Data System (ADS)

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

    2013-12-01

    Hummocks are topographic features of large landslides and rockslide-debris avalanches common in volcanic settings. We use scaled analog models to study hummock formation and explore their importance in understanding landslide kinematics and dynamics. The models are designed to replicate large-scale volcanic collapses but are relevant also to non-volcanic settings. We characterize hummocks in terms of their evolution, spatial distribution, and internal structure from slide initiation to final arrest. Hummocks initially form by extensional faulting as a landslide begins to move. During motion, individual large blocks develop and spread, creating an initial distribution, with small hummocks at the landslide front and larger ones at the back. As the mass spreads, hummocks remain as discrete entities. They can get wider but may decrease in height, break up, or merge to form bigger and long anticlinal hummocks when confined. In areas of transverse movement within a landslide, elongate hummocks develop between strike-slip flower structures. Absence of hummocks and fault-like features in the deposit may imply a more fluidal flow of emplacement or very low cohesion of lithologies. Hummock size depends on their position in the initial mass, modified by subsequent breakup or coalescence. Hummock size, shape and spatial distribution vary between and within deposits. Such a universal structure with clear connection to the deformation process should provide a framework with which to study avalanche emplacement dynamics and conditions. We study well-preserved and well-sectioned hummocks in the Mt Iriga rockslide-debris avalanches (Philippines), to characterise the internal structure and relate hummocks to the landslide-avalanche behaviour. All the model structures are consistent with field observations and suggest a general brittle-slide emplacement for most landslide avalanches. The upper and outer hummock surface is destabilised by minor slumps and scree formation forming a

  1. Structural vulnerability assessment using reliability of slabs in avalanche area

    NASA Astrophysics Data System (ADS)

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

    2013-04-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2013-12-01

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

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

    NASA Technical Reports Server (NTRS)

    Knepper, D. H., Jr. (Principal Investigator)

    1977-01-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2016-05-01

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

  5. Arrest of Avalanche Propagation by Discontinuities on Snow Cover

    NASA Astrophysics Data System (ADS)

    Frigo, B.; Chiaia, B.

    2009-04-01

    Considering the spatial variability of the snow cover, the paper analyses, in the framework of Fracture Mechanics, the Mode II fracture propagation on snow cover that leads to large dry slab avalanches. Under the hypothesis of a perfectly brittle phenomenon, avalanche triggering is usually investigated numerically by means of Linear Elastic Fracture Mechanics (McClung, 1979; Chiaia et al., 2008). Since, however, the real phenomenon is intrinsically dynamical, another aspect to investigate is represented by dynamic fracture propagation. In this paper, we model dynamic crack propagation into a dry snow slab, to assess the possibility of crack arrest due to the presence of weak zones distributed along the snow slope. As a consequence of the first triggering mechanism (the Mode II fracture propagation on the weak plane), the secondary Mode I crack propagation in the crown is studied by means of numerical simulations based on Dynamic Elastic Fracture Mechanics and on the theory of crack arresters. By taking into account kinetic energy and using the FEM software FRANC 2D (Wawrzynek and Ingraffea, 1993), several paths of crown fracture propagation and their stability have been investigated. The snowpack is considered as a linear-elastic plate (2D problem), whose physical and mechanical parameters are chosen according to classical literature values. To investigate the possible arrest of crown fracture, we apply the theory of crack arresters, usually adopted for pipelines and perforated steel sheets fracture problems. To study crack arrest, different crack paths are simulated, in discontinuous (equipped with different shapes and geometries of artificial voids) snowpacks. The simulations show the effectiveness of these weak zones, to reduce substantially the crack driving force of the propagating fracture. This means that, increasing spatial variability tends to stabilize the snow slope, eventually splitting a major avalanche event into smaller, independent avalanches. Our

  6. Demonstration of highly reliable nonhermetic planar InGaAs/InP photodiodes

    NASA Astrophysics Data System (ADS)

    Osenbach, John W.; Evanosky, T. L.; Phatak, Suniel B.; Comizzoli, Robert B.; Chand, Naresh

    1996-01-01

    Reliable non-hermetic photodiodes are expected to reduce the cost of optoelectronics used in fiber to the home and cable TV system. However, all reports to date indicate non-hermetic InGaAs/InP photodiodes do not have sufficient reliability for use in the systems. In this paper, we report the first data that conclusively shows, properly designed and manufactured non- hermetic InGaAs/InP photodiodes can be made with reliability sufficient to use in telecommunication systems. We have produced non-hermetic photodiodes whose hazard rate at 15 years of field use at 45 degrees Celsius and 50% RH is less than 100 FITs, the requirement for telecommunication systems.

  7. Macroscopic control parameter for avalanche models for bursty transport

    SciTech Connect

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

    2009-01-15

    Similarity analysis is used to identify the control parameter R{sub A} for the subset of avalanching systems that can exhibit self-organized criticality (SOC). This parameter expresses the ratio of driving to dissipation. The transition to SOC, when the number of excited degrees of freedom is maximal, is found to occur when R{sub A}{yields}0. This is in the opposite sense to (Kolmogorov) turbulence, thus identifying a deep distinction between turbulence and SOC and suggesting an observable property that could distinguish them. A corollary of this similarity analysis is that SOC phenomenology, that is, power law scaling of avalanches, can persist for finite R{sub A} with the same R{sub A}{yields}0 exponent if the system supports a sufficiently large range of lengthscales, necessary for SOC to be a candidate for physical (R{sub A} finite) systems.

  8. Weathering processes implied from analysis of small Martian avalanche chutes

    NASA Technical Reports Server (NTRS)

    Sullivan, R.

    1992-01-01

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

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

    PubMed Central

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

    2016-01-01

    Surface plasmonic systems provide extremely efficient ways to modulate light-matter interaction in photon emission, light harvesting, energy conversion and transferring, etc. Various surface plasmon enhanced luminescent behaviors have been observed and investigated in these systems. But the origin of an avalanche-like photoluminescence, which was firstly reported in 2007 from Au and subsequently from Ag nanowire arrays/monomers, is still not clear. Here we show, based on systematic investigations including the excitation power/time related photoluminescent measurements as well as calculations, that this avalanche-like photoluminescence is in fact a result of surface plasmon assisted thermal radiation. Nearly all of the related observations could be perfectly interpreted with this concept. Our finding is crucial for understanding the surface plasmon mediated thermal and photoemission behaviors in plasmonic structures, which is of great importance in designing functional plasmonic devices. PMID:26728439

  10. Photon avalanche up-conversion in holmium doped fluoride glasses

    SciTech Connect

    Chen, Y.H.; Liu, G.K.; Beitz, J.V.; Jie Wang

    1996-08-01

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

  11. Universal critical dynamics in high resolution neuronal avalanche data.

    PubMed

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

    2012-05-18

    The tasks of neural computation are remarkably diverse. To function optimally, neuronal networks have been hypothesized to operate near a nonequilibrium critical point. However, experimental evidence for critical dynamics has been inconclusive. Here, we show that the dynamics of cultured cortical networks are critical. We analyze neuronal network data collected at the individual neuron level using the framework of nonequilibrium phase transitions. Among the most striking predictions confirmed is that the mean temporal profiles of avalanches of widely varying durations are quantitatively described by a single universal scaling function. We also show that the data have three additional features predicted by critical phenomena: approximate power law distributions of avalanche sizes and durations, samples in subcritical and supercritical phases, and scaling laws between anomalous exponents. PMID:23003192

  12. Stability of the discretization of the electron avalanche phenomenon

    SciTech Connect

    Villa, Andrea; Barbieri, Luca; Gondola, Marco; Leon-Garzon, Andres R.; Malgesini, Roberto

    2015-09-01

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

  13. Elastic collapse and avalanche criticality near a Mott transition

    NASA Astrophysics Data System (ADS)

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

    2011-03-01

    We study some dynamic aspects of a Mott transition in a rare-earth alloy Ce 0.90 Th 0.10 by resonant-ultrasound spectroscopy (RUS), electrical-transport, and thermal-expansion measurements. In the temperature range spanning the first-order transition, we observe a stiffening of the elastic response that is associated with a continuous front propagation (e . g . solitons). A defining characteristic of a mixed phase regime, slow scanning rates (0.01 K/min) show these solitons to be superimposed with jerks and avalanches in all three data sets: RUS, resistivity, and thermal expansion data. Analysis of the avalanche data give power law distributions with critical exponents P (E) =En for energy, in the case of thermal expansion data and length, in the case of electrical transport data. Work performed under the auspices of the U.S. Dept. of Energy.

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

    NASA Astrophysics Data System (ADS)

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

    2016-01-01

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

  15. High performance Ge-on-Si avalanche photodetector

    NASA Astrophysics Data System (ADS)

    Jang, Ki-Seok; Kim, Sanghoon; Kim, In Gyoo; Oh, Jin Hyuk; Kim, Sun Ae; Joo, Jiho; Kim, Gyungock

    2016-03-01

    We present high performance vertical-illumination type Ge-on-Si avalanche photodetectors and photoreceiver modules operating up to 25 Gb/s. The Ge avalanche photodetectors were grown on a bulk-silicon wafer by RPCVD, and fabricated with CMOS-compatible process. The fabricated devices show a -3dB bandwidth greater than 13 GHz at operational biases (gain> 20) for λ ~ 1550 nm. The measured maximum gain-bandwidth (GB) product is ~ 493 GHz. Two types of Ge-on-Si APD receiver modules exhibit high sensitivities of better than -20.7 dBm for a 25 Gb/s operation at a BER = 10-12 and λ ~ 1310 nm, and -27.75 dBm for a 10 Gb/s operation at a BER = 10-12 and λ ~ 1550nm, respectively.

  16. The wiper model: avalanche dynamics in an exclusion process

    NASA Astrophysics Data System (ADS)

    Politi, Antonio; Romano, M. Carmen

    2013-10-01

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

  17. Stability of Granular Packings Jammed under Gravity: Avalanches and Unjamming

    NASA Astrophysics Data System (ADS)

    Merrigan, Carl; Birwa, Sumit; Tewari, Shubha; Chakraborty, Bulbul

    Granular avalanches indicate the sudden destabilization of a jammed state due to a perturbation. We propose that the perturbation needed depends on the entire force network of the jammed configuration. Some networks are stable, while others are fragile, leading to the unpredictability of avalanches. To test this claim, we simulated an ensemble of jammed states in a hopper using LAMMPS. These simulations were motivated by experiments with vibrated hoppers where the unjamming times followed power-law distributions. We compare the force networks for these simulated states with respect to their overall stability. The states are classified by how long they remain stable when subject to continuous vibrations. We characterize the force networks through both their real space geometry and representations in the associated force-tile space, extending this tool to jammed states with body forces. Supported by NSF Grant DMR1409093 and DGE1068620.

  18. Athermal avalanche in bilayer superconducting nanowire single-photon detectors

    NASA Astrophysics Data System (ADS)

    Verma, V. B.; Lita, A. E.; Stevens, M. J.; Mirin, R. P.; Nam, S. W.

    2016-03-01

    We demonstrate that two superconducting nanowires separated by a thin insulating barrier can undergo an avalanche process. In this process, Joule heating caused by a photodetection event in one nanowire and the associated production of athermal phonons which are transmitted through the barrier cause the transition of the adjacent nanowire from the superconducting to the normal state. We show that this process can be utilized in the fabrication of superconducting nanowire single photon detectors to improve the signal-to-noise ratio, reduce system jitter, maximize device area, and increase the external efficiency over a very broad range of wavelengths. Furthermore, the avalanche mechanism may provide a path towards a superconducting logic element based on athermal gating.

  19. Application of a photodiode-array optical turbulence sensor to wind studies in complex terrain

    SciTech Connect

    Porch, W.M.; Green, T.J.

    1980-04-01

    A digital photodiode-array optical turbulence sensor was used to gather data simultaneously with analog optical anemometer measurements during the July 1979 ASCOT experiment. This system provided useful information regarding the uniformity of optical turbulence used by the optical anemometer to derive cross-path wind speeds. Wind speeds derived from digital analysis of the photodiode-array intensities also provided an independent measure of the cross-path wind speed. Close agreement was found between these two measures of the wind.

  20. Flux avalanches in superconducting films with periodic arrays of holes.

    SciTech Connect

    Vlasko-Vlasov, V.; Welp, U.; Metlushko, V.; Crabtree, G. W.; Materials Science Division; Inst. of Solid State Physics RAS

    2000-01-01

    The magnetic flux dynamics in Nb films with periodic hole arrays is studied magneto-optically. Flux motion in the shape of microavalanches along {l_brace}100{r_brace} and {l_brace}110{r_brace} directions of the hole lattice is observed. At lower temperatures anisotropic large scale thermo-magnetic avalanches dominate flux entry and exit. At T-T{sub c} critical-state-like field patterns periodically appear at fractions of the matching field.