Non-uniform Rate Research Articles

Reliability Models for SEC/DED Memory With Scrubbing in FPGA-Based Designs

Block RAMs on field-programmable gate arrays (FPGAs) are susceptible to radiation-induced single-event upsets (SEUs) and are usually protected by fault-tolerant techniques such as single error correction/double error correction (SEC/DED) codes and/or scrubbing. Scrubbing can be divided into two categories based on the mechanism that controls the scrubbing interval. With deterministic scrubbing, each memory location is scrubbed (repaired) on a regular basis and the interval is fixed. With probabilistic scrubbing, a word is checked and corrected any time it is accessed (read or written). In this case, the scrubbing interval is exponentially distributed. This paper presents two mean-time-to-failure (MTTF) models for SEC/DED memory with scrubbing, which can be applied to general applications, including FPGA designs. The first one considers only probabilistic scrubbing but takes into account nonuniform scrub rates for different memory locations. The second model combines both deterministic scrubbing and probabilistic scrubbing into a single model. The proposed models provide more accurate MTTF estimates compared with prior models. An FPGA-based DSP application is studied as an example to show how the proposed models can be used for estimating memory reliability and to reveal the impact of probabilistic scrub rates and memory access distributions on memory reliability.

Naked eye observations of microstructurally short fatigue cracks

An experimental methodology is described whereby interactions between cracks and microstructural barriers, and the consequent non-uniform propagation rates are observed without the assistance of any microscopy technique. This experimental procedure consists in increasing the grain size of Al1050 and Al1100 aluminum alloys specimens until the centimeter scale by applying a series of mechanical and heat treatments. By properly adjusting the strains, temperatures and furnace times of both stages a very precise control of the microstructural size is achieved. Once the thermomechanical treatment is completed and the sought microstructural size is obtained, a small circular notch is machined on each specimen in order to initiate the cracks at the desired location, and the samples are subjected to mode I fatigue loading. The fluctuating crack growth rate, the twist and tilt angles of the crack-plane at grain boundaries and crack arrest and branching can be easily observed with the naked eye. Production of secondary crack branches caused by roughness induced closure has also been observed. Tests were performed varying grain size and notch diameter and it was observed that the distance between successive minima in crack growth rate correlates well with the grain size of the specimens. .

Some Analytical Properties of the Model for Stochastic Evolutionary Games in Finite Populations with Non-uniform Interaction Rate

Traditional evolutionary games assume uniform interaction rate, which means that the rate at which individuals meet and interact is independent of their strategies. But in some systems, especially biological systems, the players interact with each other discriminately. Taylor and Nowak (2006) were the first to establish the corresponding non-uniform interaction rate model by allowing the interaction rates to depend on strategies. Their model is based on replicator dynamics which assumes an infinite size population. But in reality, the number of individuals in the population is always finite, and there will be some random interference in the individuals' strategy selection process. Therefore, it is more practical to establish the corresponding stochastic evolutionary model in finite populations. In fact, the analysis of evolutionary games in a finite size population is more difficult. Just as Taylor and Nowak said in the outlook section of their paper, “The analysis of non-uniform interaction rates should be extended to stochastic game dynamics of finite populations." In this paper, we are exactly doing this work. We extend Taylor and Nowak's model from infinite to finite case, especially focusing on the infiuence of non-uniform connection characteristics on the evolutionary stable state of the system. We model the strategy evolutionary process of the population by a continuous ergodic Markov process. Based on the limit distribution of the process, we can give the evolutionary stable state of the system. We make a complete classification of the symmetric 2 × 2 games. For each case game, the corresponding limit distribution of the Markov-based process is given when noise intensity is small enough. In contrast with most literatures in evolutionary games using the simulation method, all our results obtained are analytical. Especially, in the dominant-case game, coexistence of the two strategies may become evolutionary stable states in our model. This result can be used to explain the emergence of cooperation in the Prisoner is Dilemma Games to some extent. Some specific examples are given to illustrate our results.

Effect of the header pressure drop induced flow maldistribution on the microchannel evaporator performance

This paper presents an experimental and numerical investigation of the flow maldistribution caused by the pressure drop in headers and its impact on the performance of a microchannel evaporator with horizontal headers and vertically oriented tubes. Experimental results show that the flash gas bypass method almost eliminates the quality induced maldistribution. However, refrigerant flow maldistribution caused by the header pressure drop still exists. This is mainly because the pressure drop along the headers results in uneven pressure difference and therefore non-uniform liquid refrigerant mass flow rate across each microchannel tube. A microchannel evaporator model validated by experimental results is employed to quantify header pressure drop induced flow maldistribution. Parametric analysis reveals that such maldistribution impact is significantly reduced by enlarging the outlet header size, increasing heat exchanger aspect ratio, or reducing the microchannel size while other parameters are kept constant. When ratio of outlet header to the total evaporator pressure drop is less than 30%, the cooling capacity reduction is limited below 3%.

Route Effects in I-ECAP of AZ31B Magnesium Alloy

An AZ31B wrought magnesium alloy was processed by incremental equal channel angular pressing (I-ECAP) using routes A and BC. Despite the fact that the measured grain size for both routes was very similar, the mechanical properties were different. Tensile strength was improved using route A comparing to route BC, without ductility loss, while tension-compression anisotropy observed for route A was significantly suppressed when using route BC. Moreover, billet shape evolution resulting from subsequent passes of I-ECAP was studied. Significant distortion after processing using route BC and no occurrence of such effect for route A were observed. Results of a finite element analysis showed that non-uniform strain rate sensitivity might be responsible for different billet shapes. The conclusion is drawn that processing route has a strong influence on the billet shape and mechanical properties when processing magnesium alloys by I-ECAP.

Investigations of afterpulsing and detection efficiency recovery in superconducting nanowire single-photon detectors

We report on the observation of a non-uniform dark count rate in Superconducting Nanowire Single Photon Detectors (SNSPDs), specifically focusing on an afterpulsing effect present when the SNSPD is operated at a high bias current regime. The afterpulsing exists for real detection events (triggered by input photons) as well as for dark counts (no laser input). In our standard set-up, the afterpulsing is most likely to occur at around 180 ns following a detection event, for both real counts and dark counts. We characterize the afterpulsing behavior and speculate that it is not due to the SNSPD itself but rather the amplifiers used to boost the electrical output signal from the SNSPD. We show that the afterpulsing indeed disappears when we use a different amplifier with a better low frequency response. We also examine the short-lived enhancement of detection efficiency during the recovery of the SNSPD due to temporary perturbation of the bias and grounding conditions.

The role of parasitoids in regulation of Polistes wasp population (Hymenoptera, Vespidae: Polistinae)

The study conducted in 2005–2010 analyzes the behavioral response of the parasitoids Latibulus argiolus (Rossi) (Hymenoptera, Ichneumonidae) and Elasmus schmitti Ruschka (Hymenoptera, Eulophidae) to the distribution of their host, Polistes wasps (Hymenoptera, Vespidae). Various conditions of the parasitoid-host system and conditions of regulation of the host abundance are discussed. The parasitoid females are more active in wasp colony clusters and tend to infest larger nests. If the parasitoids are abundant, infestation of host colonies starts earlier, sometimes before the worker emergence; therefore, density-dependent behavioral response of parasitoids is caused primarily by the impact of the aggregation component. Thus, the host population density factor appears to be mediated not only by the non-uniform development rates of colonies and their spatial distribution, but also by the seasonal (temporal) aspect of their development. Low density of the host population, at which the parasitoids regulate the wasp abundance, corresponds to a certain phase of the seasonal colony development, namely to the period before the emergence of workers. On the whole, we are dealing with a host-parasitoid system in which the spatial and temporal factors are closely interrelated.

Fast‐rate output feedback control system design with adaptive output estimator for nonuniformly sampled multirate systems

SUMMARYMultirate sampled system can be seen in many industries and several kinds of control method using lifting method have been proposed. Unfortunately, it was difficult to deal with nonuniformly sampled multirate systems. In this paper, we will propose a design scheme of output feedback control with a simple structure for nonuniformly sampled systems based on almost strictly positive real properties. A design method of a fast‐rate output feedback control system for nonuniformly sampled multirate systems with a fast uniform input updating rate and slow nonuniform output sampling rates. An adaptive output estimator will be proposed so as to realize a fast‐rate output feedback control for nonuniformly sampled systems at the fast sampling period of the input updating rate, and then, a design scheme of a fast‐rate adaptive output feedback control at the fast sampling period of the input updating rate will be proposed for nonuniformly sampled systems utilizing the proposed adaptive output estimator. We also analyze the stability of the obtained fast‐rate output feedback control system based on almost strictly positive real properties of the controlled system. Copyright © 2013 John Wiley & Sons, Ltd.

Information dynamics based self-adaptive reservoir for delay temporal memory tasks

Recurrent neural networks of the reservoir computing (RC) type have been found useful in various time-series processing tasks with inherent non-linearity and requirements of variable temporal memory. Specifically for delayed response tasks involving the transient memorization of information (temporal memory), self-adaptation in RC is crucial for generalization to varying delays. In this work using information theory, we combine a generalized intrinsic plasticity rule with a local information dynamics based schema of reservoir neuron leak adaptation. This allows the RC network to be optimized in a self-adaptive manner with minimal parameter tuning. Local active information storage, measured as the degree of influence of previous activity on the next time step activity of a neuron, is used to modify its leak-rate. This results in RC network with non-uniform leak rate which depends on the time scales of the incoming input. Intrinsic plasticity (IP) is aimed at maximizing the mutual information between each neuron’s input and output while maintaining a mean level of activity (homeostasis). Experimental results on two standard benchmark tasks confirm the extended performance of this system as compared to the static RC (fixed leak and no IP) and RC with only IP. In addition, using both a simulated wheeled robot and a more complex physical hexapod robot, we demonstrate the ability of the system to achieve long temporal memory for solving a basic T-shaped maze navigation task with varying delay time scale.

Photon counting spectral breast CT: Effect of adaptive filtration on CT numbers, noise, and contrast to noise ratio

Photon counting spectral (PCS) computed tomography (CT) shows promise for breast imaging. An issue with current photon-counting detectors is low count rate capabilities, artifacts resulting from nonuniform count rate across the field of view, and suboptimal spectral information. These issues are addressed in part by using tissue-equivalent adaptive filtration of the x-ray beam. The purpose of the study was to investigate the effect of adaptive filtration on different aspects of PCS breast CT. The theoretical formulation for the filter shape was derived for different filter materials and evaluated by simulation and an experimental prototype of the filter was fabricated from a tissue-like material (acrylic). The PCS CT images of a glandular breast phantom with adipose and iodine contrast elements were simulated at 40, 60, 90, and 120 kVp tube voltages, with and without adaptive filter. The CT numbers, CT noise, and contrast-to-noise ratio (CNR) were compared for spectral CT images acquired with and without adaptive filters. Similar comparison was made for material-decomposed PCS CT images. The adaptive filter improved the uniformity of CT numbers, CT noise, and CNR in both ordinary and material decomposed PCS CT images. At the same tube output the average CT noise with adaptive filter, although uniform, was higher than the average noise without adaptive filter due to x-ray absorption by the filter. Increasing tube output, so that average skin exposure with the adaptive filter was same as without filter, made the noise with adaptive filter comparable to or lower than that without adaptive filter. Similar effects were observed when energy weighting was applied, and when material decompositions were performed using energy selective CT data. An adaptive filter decreases count rate requirements to the photon counting detectors which enables PCS breast CT based on commercially available detector technologies. Adaptive filter also improves image quality in PCS breast CT by decreasing beam hardening artifacts and by eliminating spatial nonuniformities of CT numbers, noise, and CNR.

Fabrication of 3D charged particle trap using through-silicon vias etched by deep reactive ion etching

Positrons are charged antiparticles that annihilate upon contact with electrons or any form of matter. Two of the authors (Lynn and Weber) have proposed a new approach to store large numbers of charged particles such as positrons. The proposed structure consists of thousands of 0.1-mm-diameter holes etched through silicon wafers, which are then stacked axially to form cylindrical microtubes to store a large number of positrons. The authors used deep reactive ion etching on the wafers to create the through-holes with smooth and straight sidewalls. To produce the best possible etching results, they iteratively modified the etching parameters, including the chamber pressure, temperature, radio frequency power, inductively coupled plasma power, SF6/O2 gas flow, and O2 gas content. These iterations addressed the fabrication issues that were encountered, such as bowing, notching, undercutting, nonuniform etch rates across the wafer, and preferential etching along certain crystal planes. The trench widths were calibrated to match the etch rates between all the wafer features. The final results enabled the etching of through-wafer vias with straight sidewalls (89.9–90.1°), smooth surfaces, and high aspect ratios (≥5:1) with minimal defects. This paper describes the etching process used to produce these vias.

Optimal Execution in Presence of Short-Term Trading

Starting from basic hypotheses on how footprints from hidden orders are interpreted by short-term traders, we derive a fair price model that predicts market impact for non-uniform participation rate schedules. We use this model to derive an optimal execution schedule for a risk-averse trader. The optimal schedule delays front-loading to avoid the information shock of an abrupt start. We also consider optimal strategies with respect to the Volume-Weighted Average Price (VWAP) benchmark. We show that the VWAP-optimized schedule for a large order is similar to the risk-averse one. In an example, we compute the cost of front-loading, and the additional cost of the information shock that results from an aggressive trade start.

Investigation of the electroluminescence spectrum shift of InGaN/GaN multiple quantum well light-emitting diodes under direct and pulsed currents

Electroluminescence (EL) spectra of InGaN/GaN multiple quantum well light emitting diodes with different piezoelectric polarization fields were investigated under pulsed and direct currents. We find a positive correlation between the piezoelectric polarization field and the thermally induced red-shift of the EL spectra at high direct currents above 25 A/cm2. Under pulsed current, when thermal effects are negligible, a non-uniform EL spectrum blue-shift rate as a function of injection level is observed and compared with numerical results obtained by both self-consistent and non-self-consistent K·P methods. We conclude that the screening effect is positively related to the piezoelectric polarization field, but the band filling-induced blue-shift is almost independent from the piezoelectric field. The electrostatic fields induced by free carriers in the quantum wells increase rapidly with current but tend to saturate at higher injection where the band filling effect becomes the dominant mechanism for the blue-shift. Finally, at high injection above 30 A/cm2, an increase in Auger recombination and carrier leakage holds the spectral peaks almost constant in position.

Modeling Pedestrian Delay and Level of Service at Signalized Intersection Crosswalks under Mixed Traffic Conditions

The objectives of this study were to identify the factors affecting pedestrian level of service (LOS) at signalized intersection crosswalks under mixed traffic conditions and to propose a suitable method for estimating pedestrian LOS. The study attempted to develop a pedestrian LOS model for signalized intersection crosswalks in Mumbai, India, by using pedestrians’ perceptions of various influencing factors. The important factors considered to develop the model were turning traffic, through traffic, number of pedestrians, and pedestrian delay. Pedestrian delay is one of the key performance indicators for signalized intersection crosswalks; it is necessary to estimate delays accurately to assess LOS. As in the Highway Capacity Manual method, pedestrian delay can be calculated with the help of Webster's delay model, which assumes pedestrians arrive at a uniform rate at an intersection and all will comply with the signal; however, that assumption is not true for the Indian scenario. A pedestrian delay model for Indian conditions was developed by considering nonuniform arrival rate and signal noncompliance behavior. A video graphic technique was conducted for six selected crosswalks. A questionnaire survey was conducted to obtain the perceived LOS of pedestrians. Pedestrian delay was found with the use of the new model. A Pearson correlation analysis was done to find the significant factors that affect LOS. With perceived LOS as a dependent variable and significant factors as independent variables, stepwise regression was done to develop the model that fit for urban mixed traffic conditions.

On Nonuniform Convergence Rate Estimates in the Central Limit Theorem

We sharpen the upper bounds for the absolute constant in nonuniform convergence rate estimates in the central limit theorem for sums of independent identically distributed random variables possessing absolute moments of the order $2+\delta$ with some $0<\delta\le1$. In particular, it is demonstrated that under the existence of the third moment this constant does not exceed $18.2$. Also it is shown that the absolute constant in the estimates under consideration can be replaced by a function $C^*(|x|,\delta)$ of the argument $x$ of the difference of the prelimit and limit normal distribution functions for which a positive bounded nonincreasing majorant is found. Moreover, for $\delta=1$ this majorant is asymptotically exact (unimprovable) as $x\to\infty$ and sharpens the estimates due to Nikulin [preprint, arXiv:1004.0552v1 [math.ST], 2010] for all $x$. For the first time a similar result is obtained for the case $\delta\in(0,1)$. As a corollary, we obtain upper estimates for the Kolmogorov functions which are the analogues of the exact and the asymptotically exact constants in the (uniform) Berry--Esseen inequality.

Direct observation of concentration profiles induced by drying of a 2D colloidal dispersion drop

We report experimental results on the drying of a colloidal dispersion drop in a circular thin cell. This confined geometry is well adapted to quantify concentration profiles inside the drop using fluorescence microscopy. Two stages have been identified in the drop evolution. In the first one the drop is shrinking such as if a pure drop, keeping axisymmetry. In the second one strong distortions occur and result in the appearance of a local depression at the drop surface. This process results in the spontaneous formation of a complex drop shape with both concave and convex interfaces. The influence of the interface concavity on the concentration profiles inside the drop and the drying kinetics are investigated. Particularly, concentration profiles are related to the nonuniform evaporation rate at the distorted drop surface.

High rate particle tracking and ultra-fast timing with a thin hybrid silicon pixel detector

The Gigatracker (GTK) is a hybrid silicon pixel detector designed for the NA62 experiment at CERN. The beam spectrometer, made of three GTK stations, has to sustain high and non-uniform particle rate (∼1GHz in total) and measure momentum and angles of each beam track with a combined time resolution of 150ps. In order to reduce multiple scattering and hadronic interactions of beam particles, the material budget of a single GTK station has been fixed to 0.5% X0. The expected fluence for 100 days of running is 2×1014 1MeVneq/cm2, comparable to the one foreseen in the inner trackers of LHC detectors during 10 years of operation. To comply with these requirements, an efficient and very low-mass (<0.15%X0) cooling system is being constructed, using a novel microchannel cooling silicon plate. Two complementary read-out architectures have been produced as small-scale prototypes: one is based on a Time-over-Threshold circuit followed by a TDC shared by a group of pixels, while the other makes use of a constant-fraction discriminator followed by an on-pixel TDC. The read-out ASICs are produced in 130nm IBM CMOS technology and will be thinned down to 100μm or less. An overview of the Gigatracker detector system will be presented. Experimental results from laboratory and beam tests of prototype bump-bonded assemblies will be described as well. These results show a time resolution of about 170ps for single hits from minimum ionizing particles, using 200μm thick silicon sensors.

Progressive damage and failure strength of notched woven fabric composites under axial loading with varying strain rates

This study investigated the failure of notched and un-notched plain weave composite specimens subjected to varying strain rate loading. Different strain rate axial loads were applied to observe the rate effect on the failure. Both uniform and non-uniform strain rate loads were applied to the notched and un-notched composite specimens, respectively. Notched specimens showed initial cracks at the edge of the hole before final fracture. The initial crack under tensile loading became smaller as the strain rate increased. The initial crack length was predicted using the finite element analysis of the non-homogeneous, micromechanics-based model. The predicted length agreed well with the experimental measurement. Application of the initial crack size for the characteristic distance of the Average Stress failure criterion yielded acceptable tensile notch strengths. The compressive notch strength was less sensitive to the tensile notch strength. The non-constant, varying strain rate loading showed that the failure strength and stiffness depend on the history of the applied loading rates. The effects of the varying strain rates on both notched and un-notched specimens were different qualitatively. However, the strength ratios of the notched to un-notched specimens under varying rates were greater than those under constant rates regardless of tensile or compressive loading.

Solid phase epitaxy of ultra-shallow Sn implanted Si observed using high-resolution Rutherford backscattering spectrometry

We present detailed observations of the solid phase epitaxy process in Sn-implanted Si samples with nanometric depth resolution within a 50 nm ultra-shallow region beneath the surface. Measurements were made using high-resolution Rutherford backscattering spectrometry coupled with the ion channeling technique. Samples with Sn ions implanted onto Si substrates with and without prior Si+ self-amorphization implantation process show different crystal regrowth characteristics during annealing. Regrowth proceeds at a non-uniform rate up to a certain depth before stopping, and an Arrhenius-type defect density limiting model of crystal regrowth is proposed to account for this effect.

Study of Solder/Copper Interface Behavior Under Varying Strain Rates

This paper investigates the mechanical behavior of a copper–solder interface when subjected to varying strain rate loading between 0.05 s−1 and 10.0 s−1. The copper is alloy 101, and the solder is lead-free type with a composition of 96% tin and 4% silver. Both uniform and nonuniform two-level strain rate loadings were applied. For the two-level strain rate loading, the strain rate was changed from one level to another during the loading process as a step change. The strain rate tests were performed at room temperature as well as at an elevated temperature of 65 °C. The test results showed significant effects of uniform and nonuniform strain rates as well as temperature on fracture surface, peak stress, fracture strain, modulus, and stored energy density until fracture. Generally, a higher strain rate increased the peak stress and fracture strain, but decreased the modulus. The heated specimens showed significantly reduced strength and fracture strain at high strain rates when compared to the specimens tested at room temperature. For the two-level strain rates, the sequence of the loading rates affected the material behavior significantly. The peak stress under the two-level strain rates might be located outside the range that was determined by the two individual uniform strain rates occurring in the two-level rates. On the other hand, the fracture strain under two-level strain rate loading always fell inside that range. An expression was proposed to predict the interface fracture strains for the case of a two-level strain rate loading based on the data of each respective single-level strain test. The prediction was reasonable when compared to the experimental data with an average absolute error of 10%.