How can avalanche breakdown be avoided in fet

The SiGeC films can be biased for avalanche operation, as the required vertical electric field is confined to the region near the heterojunction interface, thereby not affecting the gate oxide of the adjacent NMOS. With suitable heterojunction and doping profiles, the avalanche region can also be bandgap engineered, allowing for avalanche breakdown voltages that are compatible with CMOS devices.

High frequency breakdown voltage. This report contains information about the effect of frequency on the breakdown voltage of an air gap at standard pressure and temperature, 76 mm Hg and O degrees C, respectively. The frequencies of interest are 47 MHz and 60 MHz.

Additionally, the breakdown in vacuum is briefly considered. The breakdown mechanism is explained on the basis of collision and ionization. The presence of the positive ions produced by ionization enhances the field in the gap, and thus determines the breakdown. When a low-frequency voltage is applied across the gap, the breakdown mechanism is the same as that caused by the DC or static voltage. However, when the frequency exceeds the first critical value f c , the positive ions are trapped in the gap, increasing the field considerably.

This makes the breakdown occur earlier; in other words, the breakdown voltage is lowered. As the frequency increases two decades or more, the second critical frequency, f ce , is reached. This time the electrons start being trapped in the gap.

Those electrons that travel multiple times across the gap before reaching the positive electrode result in an enormous number of electrons and positive ions being present in the gap. The result is a further decrease of the breakdown voltage. However, increasing the frequency does not decrease the breakdown voltage correspondingly. The reason is that the recombination rate increases and counterbalances the production rate, thus reducing the effect of the positive ions' concentration in the gap.

The theory of collision and ionization does not apply to the breakdown in vacuum. It seems that the breakdown in vacuum is primarily determined by the irregularities on the surfaces of the electrodes.

Therefore, the effect of frequency on the breakdown , if any, is of secondary importance. Automated identification of potential snow avalanche release areas based on digital elevation models. Full Text Available The identification of snow avalanche release areas is a very difficult task. The release mechanism of snow avalanches depends on many different terrain, meteorological, snowpack and triggering parameters and their interactions, which are very difficult to assess.

In many alpine regions such as the Indian Himalaya, nearly no information on avalanche release areas exists mainly due to the very rough and poorly accessible terrain, the vast size of the region and the lack of avalanche records. However avalanche release information is urgently required for numerical simulation of avalanche events to plan mitigation measures, for hazard mapping and to secure important roads.

By far the most reliable way to identify avalanche release areas is using historic avalanche records and field investigations accomplished by avalanche experts in the formation zones.

But both methods are not feasible for this area due to the rough terrain, its vast extent and lack of time. Such instruments can acquire spatially continuous data even over inaccessible terrain and cover large areas. We validate our tool using a database of historic avalanches acquired over 56 yr in the neighborhood of Davos, Switzerland, and apply this method for the avalanche tracks along the Rohtang tunnel access road. This tool, used by avalanche experts, delivers valuable input to identify focus areas for more-detailed investigations on avalanche release areas in remote regions such as the Indian Himalaya and is a precondition for large-scale avalanche hazard mapping.

The identification of snow avalanche release areas is a very difficult task. Investigation of dielectric breakdown in silica-epoxy nanocomposites using designed interfaces. Adding nano-sized fillers to epoxy has proven to be an effective method for improving dielectric breakdown strength DBS. Evidence suggests that dispersion state, as well as chemistry at the filler-matrix interface can play a crucial role in property enhancement.

Herein we investigate the contribution of both filler dispersion and surface chemistry on the AC dielectric breakdown strength of silica-epoxy nanocomposites. Surface initiated RAFT polymerization was used to synthesize multiple graft densities of PGMA chains, ultimately controlling the dispersion of the filler. Investigation of the synthesized multifunctional nanoparticles was effective in defining the maximum particle spacing or free space length L f that still leads to property enhancement, as well as giving insight into the effects of varying the electronic nature of the molecules at the interface on breakdown strength.

All rights reserved. Transient events in bright debris discs: Collisional avalanches revisited. A collisional avalanche is set off by the breakup of a large planetesimal, releasing vast amounts of small unbound grains that enter a debris disc located further away from the star, triggering there a collisional chain reaction that could potentially create detectable transient structures.

Aims: We investigate this mechanism , using for the first time a fully self-consistent code coupling dynamical and collisional evolutions. We also quantify for the first time the photometric evolution of the system and investigate whether or not avalanches could explain the short-term luminosity variations recently observed in some extremely bright debris discs.

We consider an avalanche -favoring A6V star, and two set-ups: a "cold disc" case, with a dust release at 10 au and an outer disc extending from 50 to au, and a "warm disc" case with the release at 1 au and a au outer disc.

Likewise, we do not observe a significant luminosity deficit, as compared to the pre- avalanche level, after the passage of the avalanche. These two results concur to make avalanches an unlikely explanation for the sharp luminosity drops observed in some extremely bright debris discs.

The ideal configuration for observing an. The breakdown mechanism in each of these regions is explained. An extensive bibliography on AC breakdown in gases is included.

Avalanche risk assessment in Russia. The constant growth of economic activity, especially in the North Caucasus region and therefore the increased avalanche hazard lead to the demand of the large-scale avalanche risk assessment methods development.

Such methods are needed for the determination of appropriate avalanche protection measures as well as for economic assessments during all stages of spatial planning of the territory.

The requirement of natural hazard risk assessments is determined by the Federal Law of Russian Federation. A great size of Russia territory, vast diversity of natural conditions and large variations in type and level of economic development of different regions cause significant variations in avalanche risk values. At the first stage of research the small scale avalanche risk assessment was performed in order to identify the most common patterns of risk situations and to calculate full social risk and individual risk.

The full social avalanche risk for the territory of country was estimated at 91 victims. Within these territories the safety of population can be achieved mainly by organizational activities.

The whole specter of mitigation measures is required in order to minimize risk. The future development of such areas is not recommended. 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.

Advantages include, visible-light blindness, operation in harsh environments e. Furthermore, the device can also be designed in array formats, e. The mechanism of runaway electron generation at gas pressures from a few atmospheres to several tens of atmospheres is proposed.

According to this mechanism , the electrons pass into the runaway mode in the enhanced field zone that arises between a cathode micropoint—a source of field-emission electrons—and the region of the positive ion space charge accumulated near the cathode in the tails of the developing electron avalanches. As a result, volume gas ionization by runaway electrons begins with a time delay required for the formation of the enhanced field zone. This process determines the delay time of breakdown.

The influence of the gas pressure on the formation dynamics of the space charge region is analyzed. At gas pressures of a few atmospheres, the space charge arises due to the avalanche multiplication of the very first field-emission electron, whereas at pressures of several tens of atmospheres, the space charge forms as a result of superposition of many electron avalanches with a relatively small number of charge carriers in each.

Effects of the intrinsic layer width on the band-to-band tunneling current in p-i-n GaN-based avalanche photodiodes. Dark current is critical for GaN-based avalanche photodiodes because it significantly increases the noise current and limits the multiplication factor.

It has been found that the band-to-band tunneling current is the dominant origin of the dark current for avalanche photodiodes at the onset of breakdown voltage. Experimentally, for GaN-based avalanche photodiodes with a thinner intrinsic layer, the dark current increases nearly exponentially with the applied voltage even at a lower bias voltage.

In this paper, the intrinsic layer i-layer width of GaN-based avalanche photodiodes has been varied to study its effect on the band-to-band tunneling current. A widely used equation was used to calculate the band-to-band tunneling current of avalanche photodiodes with different i-layer widths i-layer 0.

Then, GaN-based avalanche photodiodes i-layer 0. Also, the measurement of dark current of all three different structures was performed, and their multiplication factors were given.

A numerical simulation was developed for magnetic nanoparticles in a liquid dielectric to investigate the AC breakdown voltage of the magnetic nanofluids according to the volume concentration of the magnetic nanoparticles. In prior research, we found that the dielectric breakdown voltage of the transformer oil-based magnetic nanofluids was positively or negatively affected according to the amount of magnetic nanoparticles under a testing condition of dielectric fluids, and the trajectory of the magnetic nanoparticles in a fabricated chip was visualized to verify the related phenomena via measurements and computations.

In this study, a numerical simulation of magnetic nanoparticles in an insulating fluid was developed to model particle tracing for AC breakdown mechanisms happened to a sphere-sphere electrode configuration and to propose a possible mechanism regarding the change in the breakdown strength due to the behavior of the magnetic nanoparticles with different applied voltages. A probabilistic model for snow avalanche occurrence. 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. Photon-counting monolithic avalanche photodiode arrays for the super collider.

In fiber tracking, calorimetry, and other high energy and nuclear physics experiments, the need arises to detect an optical signal consisting of a few photons in some cases a single photoelectron with a detector insensitive to magnetic fields. Previous attempts to detect a single photoelectron have involved avalanche photodiodes APDs operated in the Geiger mode, the visible light photon counter, and a photomultiplier tube with an APD as the anode.

In this paper it is demonstrated that silicon APDs, biased below the breakdown voltage, can be used to detect a signal of a few photons with conventional pulse counting circuitry at room temperature.

Moderate cooling, it is further argued, could make it possible to detect a single photoelectron. Monolithic arrays of silicon avalanche photodiodes fabricated by Radiation Monitoring Devices, Inc. RMD were evaluated for possible use in the Super Collider detector systems.

Measurements on 3 element x 3 element 2 mm pitch APD arrays, using pulse counting circuitry with a charge sensitive amplifier CSA and a Gaussian filter, are reported and found to conform to a simple noise model. The model is used to obtain the optimal operating point. Spatial shape of avalanches. In disordered elastic systems, driven by displacing a parabolic confining potential adiabatically slowly, all advance of the system is in bursts, termed avalanches. Avalanches have a finite extension in time, which is much smaller than the waiting time between them.

We establish scaling relations governing the behavior close to the boundary. We then give analytic results for the Brownian force model, in which the microscopic disorder for each degree of freedom is a random walk. Finally, we confirm these results with numerical simulations. To do this properly we elucidate the influence of discretization effects, which also confirms the assumptions entering into the scaling ansatz.

This allows us to reach the scaling limit already for avalanches of moderate size. We find excellent agreement for the universal shape and its fluctuations, including all amplitudes. Supershort avalanche electron beam in SF6 and krypton.

Zhang, Cheng; Tarasenko, Victor F. Runaway electrons play an important role in the avalanche formation in nanosecond- and subnanosecond- pulse discharges. In this paper, characteristics of a supershort avalanche electron beam SAEB generated at the subnanosecond and nanosecond breakdown in sulfur hexafluoride SF6 in an inhomogeneous electric field were studied. Experimental results showed that SAEB currents appeared during the rise-time of the voltage pulse for both pulsers.

Moreover, amplitudes of the SAEB current in SF6 and Kr approximately ranged from several to tens of milliamps at atmospheric pressure, which were smaller than those in N2 and air ranging from hundreds of milliamps to several amperes.

Barrier breakdown mechanism in nano-scale perpendicular magnetic tunnel junctions with ultrathin MgO barrier. Lv, Hua; Leitao, Diana C. Recently, the perpendicular magnetic tunnel junctions p-MTJs arouse great interest because of its unique features in the application of spin-transfer-torque magnetoresistive random access memory STT-MRAM , such as low switching current density, good thermal stability and high access speed.

We observe that the extrinsic breakdown mechanism dominates, since the resistance of our p-MTJs decreases gradually with the increasing current. From the statistical analysis of differently sized p-MTJs, we observe that the breakdown voltage Vb of 1. Using Simmons' model, we find that the steady state is related with the barrier height of the MgO layer.

Furthermore, our study suggests a more efficient method to evaluate the MTJ stability under high bias rather than measuring Vb.

Calibration of snow avalanche mathematical models using the data of real avalanches in the Ile Zailiyskiy Alatau Range. Full Text Available The calibration of the dry friction and turbulent friction coefficients is necessary for computer simulation of avalanches. The method of back calculation based on data on actual avalanches is used for this purpose. The range is located in Kazakhstan. The data on six avalanches in the same avalanche site were used.

Five avalanches were dry, and one avalanche was wet. Avalanches volume varied from to m3. The calibrated coefficients were chosen under condition of the best fit with real avalanches. Avalanches and Criticality in Driven Magnetic Skyrmions. We show using numerical simulations that slowly driven Skyrmions interacting with random pinning move via correlated jumps or avalanches. The avalanches exhibit power-law distributions in their duration and size, and the average avalanche shape for different avalanche durations can be scaled to a universal function, in agreement with theoretical predictions for systems in a nonequilibrium critical state.

A distinctive feature of Skyrmions is the influence of the nondissipative Magnus term. When we increase the ratio of the Magnus term to the damping term, a change in the universality class of the behavior occurs, the average avalanche shape becomes increasingly asymmetric, and individual avalanches exhibit motion in the direction perpendicular to their own density gradient.

Nano-multiplication region avalanche photodiodes and arrays. 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. Avalanches in insulating gases. Avalanches of charged particles in gases are often studied with the ''electrical method'', the measurement of the waveform of the current in the external circuit.

In this thesis a substantial improvement of the time resolution of the measuring setup, to be used for the electrical method, is reported. The avalanche is started by an N 2 -laser with a pulse duration of only 0. With the setup it is possible to analyze current waveforms with a time resolution down to 1. Furthermore it is possible to distinguish between the current caused by the electrons and the current caused by the ions in the avalanche and to monitor these currents simultaneously.

Depending on the nature of the gas and the experimental conditions, processes as diffusion, ionization, attachment, detachment, conversion and secondary emission are observed. Values of parameters with which these processes can be described, are derived from an analysis of the current waveforms. For this analysis already published theories and new theories described in this thesis are used. The drift velocity of both the electrons and the ions could be easily determined from measured avalanche currents.

Special attention is paid to avalanches in air becasue of the practical importance of air insulation. The Chimborazo sector collapse and debris avalanche : deposit characteristics as evidence of emplacement mechanisms. Bernard, B. Chimborazo is a Late Pleistocene to Holocene stratovolcano located at the southwest end of the main Ecuadorian volcanic arc.

It experienced a large sector collapse and debris avalanche DA of the initial edifice CH This left a 4 km wide scar, removing 8. The debris avalanche deposit DAD is abundantly exposed throughout the Riobamba Basin to the Rio Chambo, more than 35 km southeast of the volcano.

The DAD averages a thickness of 40 m, covers about km Two-dimensional nanowires on homoepitaxial interfaces: Atomic-scale mechanism of breakdown and disintegration.

We present a model for hole-mediated spontaneous breakdown of ahomoepitaxial two-dimensional 2D flat nanowire based exclusively on random, thermally-activated motion of atoms. The model suggests a consecutive three-step mechanism driving the rupture and complete disintegration of the nanowire on a crystalline surface. The breakdown scenario includes: i local narrowing of a part of the stripe to a monatomic chain, ii formation of a recoverable single vacancy or a 2D vacancy cluster that causes temporary nanowire rupture, iii formation of a non-recoverable 2D hole leading to permanent nanowire breakdown.

These successive events in the temporal evolution of the nanowire morphology bring the nanowire stripe into an irreversible unstable state, leading to a dramatic change in its peculiar physical properties and conductivity. The atomistic simulations also reveal a strong increase of the nanowire lifetime with an enlargement of its width and open up a way for a fine atomic-scale control of the nanowire lifetime and structural, morphological and thermodynamic stability. Study of the physical mechanisms involved in the femtosecond laser optical breakdown of dielectric materials.

We have carried out detailed time resolved experimental studies of the mechanism of electron excitation-relaxation, when an ultrashort 60 fs -1 ps laser UV and IR pulse interacts with a wide band gap dielectric material. This gives fundamental insight into the understanding of the laser damaging process taking place under our irradiation conditions.

The usage of time-resolved spectral interferometry technique allows to directly measure the electron density of the irradiated material under different excitation conditions and hence leads to quantification of the process. The measurements, carried out at the optical breakdown threshold utilizing different pulse durations, raise questions regarding the usage of critical excitation density as a universal ablation criterion.

A new criterion related to the exchanged energy is proposed. Additionally, the use of an experimental setup implementing a double pump pulse allows the identification of different excitation mechanisms taking place at time scales of the order of the pulse duration used. These differences are discussed in detail. Next, we measure the energy spectrum of excited electrons with a complementary technique: the photoemission spectroscopy.

These results allow us on one hand to show a crossed effect between the two 'pump' pulses and on the other hand to measure electron relaxation characteristic times, as a function of their kinetic energy. Finally, a morphological study of craters resulting from ablation in the case of a single pulse has been carried out for different irradiation parameters: number of shots, energy and pulse duration.

This work has. Magnetic avalanches in manganese-acetate, "magnetic deflagration". Mnacetate, first synthesized in by Lis, is one example of a class of many molecules called single molecule magnets SMMs or molecular nanomagnets. These molecules have several atomic spins strongly coupled together within each molecule.

They exhibit interesting quantum mechanical phenomena at low temperatures such as quantum tunneling of magnetization, which was first found with Mnacetate in by Friedman, et al. In addition to possible application as memory storage and qubits for quantum computers, these systems provide the means for studies of mesoscopic physics as well as the interactions of the molecules with their environment, such as phonon, photon, nuclear spin, intermolecular dipole, and exchange interactions.

It also has a large uniaxial anisotropy of 65 K. Below 3 K, magnetization curves show strong hysteresis due to the anisotropy barrier. At thesis temperatures, the spin relaxes through the barrier by quantum tunneling of magnetization, which produces regularly-spaced multiple resonant steps in the hysteresis curve. Magnetic avalanches , first detected by Paulsen et al. In this thesis, I present the results of detailed experimental studies of two aspects of magnetic avalanche phenomenon: "conditions for the triggering of avalanches " and "propagation of the avalanche front".

In the first study, we find the magnetic fields at which avalanches occur are stochastically distributed in a particular range of fields. For the second study, we conducted local time-resolved measurements. The results indicate the magnetization avalanches spread.

Full Text Available Runaway electrons play an important role in the avalanche formation in nanosecond- and subnanosecond- pulse discharges. Neuronal avalanches and learning. Arcangelis, Lucilla de, E-mail: dearcangelis na. 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.

However, the results of the IGBT show two different failure behaviors. But at low current mode, the main failure mechanism is related to the parasitic thyristor activity during the occurrence of the avalanche process and which is in good agreement with the experiment result.

Gallium-based avalanche photodiode optical crosstalk. 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. 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.

Energy and dissipated work in snow avalanches. Avalanches convert approximately one-seventh of their potential energy into kinetic energy. The total potential energy depends strongly on the entrained snowcover, indicating that entrainment processes cannot be ignored when predicting terminal velocities and runout distances.

We find energy dissipation rates on the order of 1 GW. Fluidization of the fracture slab can be identified in the experiments as an increase in dissipation rate, thereby explaining the initial and rapid acceleration of avalanches after release.

Interestingly, the dissipation rates appear to be constant along the track, although large fluctuations in internal velocity exist. Thus, we can demonstrate within the context of non-equilibrium thermodynamics that -- in space -- granular snow avalanches are irreversible, dissipative systems that minimize entropy production because they appear to reach a steady-state non-equilibrium. A thermodynamic analysis reveals that fluctuations in velocity depend on the roughness of the flow surface and viscosity of the granular system.

We speculate that this property explains the transition from flowing avalanches to powder avalanches. Necessary conditions for the homogeneous formation of a volume avalanche discharge with specific applications to rare gas-halide excimer laser discharges.

The major problem encountered in scaling experiments has been the formation of arc channels in the discharge volume. The presence of arcing can totally disrupt proper laser operation. This problem stems from a general lack of understanding of high pressure avalanche discharge phenomena. Therefore, clarifying the basic discharge formation process and establishing a set of criteria under which a homogeneous avalanche discharge can be obtained is of central importance in defining the scaling limits of avalanche discharge lasers.

This relationship was first explored by A. Palmer in The basic requirement of his model was that the preionization density be large enough to cause an appreciable overlap of the primary electron avalanches and hence smooth out the ensuing space-charge fields to the extent that individual streamer formation would be prevented.

This is the same basic model used in the more detailed discharge formation analysis developed here except that the effects of a time varying electric field caused by a finite voltage rise time and the effects due to the various electrochemical properties of the gas mixture are property taken into consideration. RF accelerating structures of the Compact Linear Collider CLIC require a material capable of sustaining high electric field with a low breakdown rate and low induced damage.

Because of the similarity of many aspects of DC and RF breakdown , a DC breakdown study is underway at CERN in order to test candidate materials and surface preparations, and have a better understanding of the breakdown mechanism under ultra-high vacuum in a simple setup. Conditioning speeds and breakdown fields of several metals and alloys have been measured. The results indicate clearly that the breakdown field is limited by the cathode.

The presence of a thin cuprous oxide film at the surface of copper electrodes significantly increases the breakdown field. On the other hand, the conditioning speed of Mo is improved by removing oxides at t During pressurization of a wellbore a typical downhole pressure record shows the following regimes: first the applied wellbore pressure balances the reservoir pressure, then after the compressive circumferential hole stresses are overcome, tensile stresses are induced on the inside surface of the hole.

When the magnitude of these stresses reach the tensile failure stress of the surrounding rock medium, a fracture is initiated and propagates into the reservoir. However experimental investigations [2] show that the breakdown did not occur even if a fracture was initiated at the borehole wall. Drilling muds had the tendency to seal and stabilize fractures and prevent fracture propagation. Also fracture mechanics analysis of breakdown process in mini-frac or leak off tests [3] show that the breakdown pressure could be either equal or larger than the fracture initiation pressure.

In order to gain a deeper understanding of the breakdown process in reservoir rock, numerical investigations using the extended finite element method XFEM for hydraulic fracturing of porous materials [4] are discussed. The reservoir rock is assumed to be pre-fractured. During pressurization of the borehole, the injection pressure, the pressure distribution and the position of the highest flux along the fracture for different fracturing fluid viscosities are recorded and the influence of the aforementioned values on the stability of fracture propagation is discussed.

Imaging findings of avalanche victims. Grosse, Alexandra B. Skiing and hiking outside the boundaries remains an attractive wilderness activity despite the danger of avalanches. Avalanches occur on a relatively frequent basis and may be devastating. Musculoskeletal radiologists should be acquainted with these injuries.

Fourteen avalanche victims 11 men and 3 women; age range years, mean age Radiographs, CT and MR images were prospectively evaluated by two observers in consensus. Fractures were most commonly seen Blunt abdominal and thoracic trauma were the most frequent extraskeletal findings.

A wide spectrum of injuries can be found in avalanche victims, ranging from extremity fractures to massive polytrauma. Asked 6 years, 6 months ago. Active 6 years, 6 months ago. Viewed 2k times. Zulu Zulu 1, 10 10 silver badges 13 13 bronze badges. Add a comment. Active Oldest Votes.

For the classic scenario of driving something inductive, I can imagine multiple reasons why you use such a transistor: A bit of extra safety for when the flywheel diode fails. Your chosen transistor has it anyways already and you can shave off costs by omitting the diode You are so space constrained that you can't put a diode there. You have other sources of voltage spikes that you have little to no control over e. Sign up or log in Sign up using Google.

Sign up using Facebook. Sign up using Email and Password. Post as a guest Name. Email Required, but never shown. The Overflow Blog. In zener breakdown, electrons from the p-doped region cross the depletion region through tunneling. This happens in a controlled fashion at a well-established reverse-bias voltage.

In avalanche breakdown, the effect is similar, but the breakdown occurs as high-energy electrons propelled toward the depletion region by a high voltage crash into lattice molecules hard enough to break electron-hole pairs, thus freeing more electrons which, in turn, crash into other molecules and free yet more electrons, etc.

Thus, the effect is like an avalanche. Ka-fet-tea-air with stress on the 'fet'. Log in. Electronics Engineering. Study now. See Answer. Best Answer. Theoretically, you need to - dope less the junction region of your device like p-i-n diodes, the i intrinsic region is not doped in order to reduce E field peak, which occurs near the center of the device. At circuit design level, you can protect your devices with clamp diodes or something similar.

Study guides. Physics 20 cards. A wave has a frequency of hertz what is the period of the wave. In which material does sound travel the fastest. In this type of wave particles of the medium vibrate perpendicularly to the direction of the wave itself. A 5 ohm resistor a 10 ohm resistor and a 15 ohm resistor are connected in series to a volt power source What is the amount of current flowing between the 5 ohm resistor and the 10 ohm resistor.

Electrical Engineering 21 cards. Could you give me an example of a simple sentence. In what kind of circuit is the voltage the same across all branches. How is the wiring done in houses and other occupied buildings.

In a series circuit the is the same at every point. Q: How can avalanche breakdown be avoided in FET? Write your answer Related questions. Effect of temperature on zener breakdown and avalanche breakdown? What are the types of breakdown region in diode? Explain zener breakdown and avalanche breakdown? How will you differentiate the diodes whether it is Zener or avalanche when you are given two diodes of rating 6. Difference between zener breakdown and avalanche breakdown?