Exhaustion Regime Research Articles

Atomistic processes controlling flow stress scaling during compression of nanoscale face-centered-cubic crystals

The size dependence of strength observed in submicrometer face-centered-cubic (fcc) metallic crystals under uniform deformation depends on the interaction of pre-existing dislocations with surfaces. To date, however, the dislocation processes controlling flow stress scaling in fcc crystals less than 100 nm in size have remained an open question due to limited knowledge on microstructural evolution during deformation in such small volumes. Here, molecular dynamics computer simulations employing a technique of high-temperature annealing and quenching on porous crystals were used to generate complex dislocation microstructures in sub-75 nm Cu pillars with high initial dislocation densities of 10 16 m −2, which made it possible to quantitatively examine their evolution during compression as a function of pillar diameter. These simulations reveal a transition from a state of dislocation exhaustion, where mobile dislocations are lost at the free surface and the dislocation density steadily decreases, to a regime of intermittent plastic flow between elastic loading and source-limited activation inside the pillars. It is shown that plastic flow stresses predicted during dislocation exhaustion regime exhibit little to no size dependence, while pronounced size effects are found during source-limited activation. Remarkably, the relationship between flow stress predicted at 5% strain and diameter is found to follow closely the power-law dependence reported in past experiments with larger Cu crystals and smaller densities. A deformation mechanism map, expressed in terms of diameter, is developed and used to elucidate the origin of size-dependent plasticity in nanoscale fcc crystals.

Controlling the level of the sonic boom generated by a flying vehicle by means of cryogenic forcing. 2. Distributed injection of a supercooled gas from the vehicle surface

The possibility of improving the efficiency of cryogenic forcing on the parameters of the hanging shock determining the length of the region of minimization of the sonic boom (middle zone) generated by a modified power-law body is studied. The effect of distributed injection of the coolant from the body surface on the formation of a perturbed flow near the body and at large distances from the body is considered. The scheme of distributed injection and the regime of coolant exhaustion are demonstrated to exert a significant effect on the length of the middle zone of the sonic boom. A scheme of cryogenic forcing is determined, which ensures reduction of bow shock wave intensity by more than 40% at distances corresponding to 7000 body diameters. The mechanism of cryogenic forcing on the flow structure near the body is discussed.

Expected waiting time in symmetric polling systems with correlated walking times

Polling systems have been extensively studied, and have found many applications. They have often been used for studying wired local area networks such as token passing rings and wireless local area networks such as bluetooth. In this contribution we relax one of the main restrictions on the statistical assumptions under which polling systems have been analyzed. Namely, we allow correlation between walking times. We consider (i) the gated regime where a gate closes whenever the server arrives at a queue. It then serves at that queue all customers who were present when the gate closes. (ii) The exhaustive regime in which the server remains at a queue till it empties. Our analysis is based on stochastic recursive equations related to branching processes with migration with a random environment. In addition to our derivation of expected waiting times for polling systems with correlated walking times, we set the foundations for computing second order statistics of the general multi-dimensional stochastic recursions.

Price Regulation and Public Service Obligations under International Arbitrage

National regulation generates price differentials between countries stimulating arbitrage by international distributors. Harmed manufacturers counteract using vertical price-squeeze or non-price discrimination. We show that: (i) either under regulatory commitment or discretion, there are non-linear relationships between technology/market conditions and the first-mover’s pricing strategy; (ii) public service obligations on distributors allow regulators to manipulate parallel exports so as to improve national welfare; (iii) to prevent sabotage, regulation should provide manufacturers with adequate countervailing incentives; (iv) coordinating national agencies alleviates negative regulatory and market externalities. Therefore, static and dynamic efficiency concerns may arise within a regional exhaustion regime of intellectual property rights.

The European Union’s Trade Mark Exhaustion Regime

The European Union’s Trade Mark Exhaustion Regime

4H-SiC Material for Hall Effect and High-Temperature Sensors Working in Harsh Environments

We report electrical and optical measurements performed on low-doped, n-type 4H-SiC. We show that below a typical carrier concentration of similar to5 10(15) cm(-3) at room temperature, they work in the so-called exhaustion regime from 300 K. The carrier concentration remains constant and the resistivity increases linearly at a rate of 3400 ppm/K from 500 to 800 K. This establishes low doped SiC as a good candidate to produce high performance Hall sensors, working in harsh environment, with a large sensitivity and a low thermal drift.

4H-SiC: a material for high temperature Hall sensor

Abstract In this work, we show that progress made in the crystal growth and device processing technology of 4H-SiC open the way to the development of Hall sensors presenting a low thermal drift with a large sensitivity (930 V/(A T)) in a wide temperature range. Above 300 K, low doped 4H-SiC epilayers are working in the exhaustion regime. Transport measurements show a constant value of the carrier density from 300 to 800 K. Simultaneously, the resistivity increases linearly at a rate of 3400 ppm/K between 500 and 800 K leading to the possibility to use the same samples as temperature sensor.

Two-Queue Polling Models with a Patient Server

We consider two-queue polling models with the special feature that a timer mechanism is employed at Q1: whenever the server polls Q1 and finds it empty, it activates a timer and remains dormant, waiting for the first arrival. If such an arrival occurs before the timer expires, a busy period starts in accordance with Q1's service discipline. However, if the timer is shorter than the interarrival time to Q1, the server does not wait any more and switches back to Q2. We consider three configurations: (i) Q1 is controlled by the 1-limited protocol while Q2 is served exhaustively, (ii) Q1 employs the exhaustive regime while Q2 follows the 1-limited procedure, and (iii) both queues are served exhaustively. In all cases, we assume Poisson arrivals and allow general service and switchover time distributions. Our main results include the queue length distributions at polling instants, the waiting time distributions and the distribution of the total workload in the system.

Effect of thermal blooming in second-harmonic generation in nonlinear crystals with a regular domain structure

Analytical expressions are obtained for the power of the second harmonic in nonlinear crystals having a regular domain structure with allowance for thermal blooming for a Gaussian beam of basic radiation in the quasi-stationary plane-wave approximation. Calculations were carried out in both the approximation of an assigned field of basic radiation and a substantially nonlinear regime of exhaustion of basic radiation.

Theoretical Analysis of a Blocking‐Electrode Oxygen Sensor for Combustion‐Gas Streams

The currently employed oxygen sensor for internal combustion engines, which is used to control the intake air‐to‐fuel ratio , performs well near the stoichiometric , but cannot provide precise control during fuel‐lean or fuel‐rich operation. We propose an alternate oxygen‐sensor design, which is based on an established concept of a blocking electrode, and mathematically simulate the sensor response to a typical engine exhaust regime. Mathematical modeling of this device is particularly helpful since (i) the experiments required for the device characterization are difficult and (ii) the differential equations governing the device operation apply to electron, hole, and gas transport, all of which are well understood.

Stationary burning: Analysis of profile effects on the required exhaust efficiency and the permitted helium particle confinement time

In order to define the requirements on the helium exhaust system and on the permitted helium particle confinement, the burn condition for D-T plasmas had been derived in a recent paper [D. Reiter et al., to be published in Nucl. Fusion], taking the ratio ρ of the global α-particle confinement time τ α * to the energy confinement time τ E as a figure of merit which characterizes the prevailing confinement and exhaust regime. There it was shown that for an ignited and stationary burning D-T plasma, the value of ρ needs to remain sufficiently below 15 without any other impurities or below 10 for typical impurity concentrations. In the present paper, the effect of different radial profile shapes for densities and temperatures is analysed by applying appropriate shape factors. It is shown that the above condition remains valid over a wide range of realistic plasma profiles. Therefore, the values of ρ given above can be used as a realistic criterium to assess the quality of specific exhaust schemes and confinement regimes experimentally.

Burn condition, helium particle confinement and exhaust efficiency**This paper was presented orally at the Eighth European Tokamak Programme Workshop, Gut Ising, Federal Republic of Germany, December 1989.

The burn condition for D-T plasmas is derived in a form which accounts for the stationary helium concentration determined by the coupling of the fusion power and helium production. The ratio of the global alpha particle confinement timeto the energy confinement time τE is taken as a quantity characterizing the prevailing confinement and exhaust regime. For an ignited and stationary burning D-T plasma this ratio needs to remain sufficiently below 15 or below 10 for typical impurity concentrations. This poses a lower limit on the required helium exhaust efficiency and indicates that operational regimes are needed where the particle confinement time does not diverge too far from the energy confinement time. Applied to the D-3He fusion reaction, the analysis leads to even more stringent limits on the ratio,which must be smaller by a factor of three to four compared to the D-T case. It is found that, for any given temperature (and for otherwise equal exhaust and recycling conditions), in general burning can be achieved at two different values of the fusion parameter n T τE and ash concentration.

Numerical modeling of processes in a continuous chemical HF laser resonator on the basis of the Navier-Stokes equations

An effective finite-difference method for numerical integration of the complete system of Navier-Stokes equations is proposed for multicomponent chemically reacting gas mixtures in the presence of relaxation processes and coherent radiation. This method is used to investigate processes proceeding in a continuous supersonic chemical laser resonator using HF molecules. The problem is formulated using five assumptions regarding flow-mixture, diffusion, vibration level, and generation. Within this framework the system of Navier-Stokes equations is written out. Special questions of the mechanism, in particular the degree of influence on the local stream parameters and the output energetic characteristics of the laser effects associated with the off-design of the exhaust regime of the supersonic jets of reagents and with the origination of transverse pressure gradients in the stream due to heat liberation during the exothermal chemical reactions were investigated.