Impact Of Nonuniformity Research Articles

Space‐time ambiguity functions for electronically scanned ISR applications

AbstractElectronically steerable array (ESA) technology has recently been applied to incoherent scatter radar (ISR) systems. These arrays allow for pulse‐to‐pulse steering of the antenna beam to collect data in a three‐dimensional region. This is in direct contrast to dish‐based antennas, where ISR acquisition is limited at any one time to observations in a two‐dimensional slice. This new paradigm allows for more flexibility in the measurement of ionospheric plasma parameters. Multiple ESA‐based ISR systems operate currently in the high‐latitude region where the ionosphere is highly variable in both space and time. Because of the highly dynamic nature of the ionosphere in this region, it is important to differentiate between measurement‐induced artifacts and the true behavior of the plasma. Often, three‐dimensional ISR data produced by ESA systems are fitted in a spherical coordinate space and then the parameters are interpolated to a Cartesian grid, potentially introducing error and impacting the reconstructions of the plasma parameters. To take advantage of the new flexibility inherent in ESA systems, we present a new way of analyzing ISR observations through use of the space‐time ambiguity function. The use of this new measurement ambiguity function allows us to pose the ISR observational problem in terms of a linear inverse problem whose goal is the estimate of the time domain lags of the intrinsic plasma autocorrelation function used for parameter fitting. The framework allows us to explore the impact of nonuniformity in plasma parameters in both time and space. We discuss examples of possible artifacts in high‐latitude situations and discuss possible ways of reducing them and improving the quality of data products from electronically steerable ISRs.

Concrete slab analyses with field-assigned non-uniform support conditions

Intelligent compaction (IC) technologies have been used to locate and identify areas of soft, weak or non-uniform subgrade support, which can be linked to pavement performance to set realistic limits on allowable non-uniformity as identified by IC. Based on field data, finite element analyses were performed to investigate the impact of non-uniformities on concrete slab tensile stresses. Non-uniform support cases were modelled by deterministically and randomly assigning field-correlated moduli of subgrade reaction (k-values) to specific spatial areas in the foundation layer. Stresses depended on the size of the non-uniform area, the stiffness change between adjacent non-uniform areas, load location and configuration, and temperature differential. Cases with randomly assigned k-values showed as much as a 39% increase in peak slab tensile stresses relative to a uniform support condition, which could lead to premature slab failures. The ability of IC to locate foundation non-uniformities could increase the reliability of concrete pavements.

Influence of Aggregate Base Layer Variability on Pavement Performance

The objective of this research was to investigate the variability of base layer construction in hot-mix asphalt (HMA) pavements and to assess the impact of base layer variability or nonuniformity on pavement performance. Subjective acceptance criteria of base layer construction may lead to variable pavement performance and may result in early pavement distresses and failure. Eleven existing HMA pavement projects with aggregate base course layers constructed in the past few years were selected for falling weight deflectometer (FWD) testing and visual distress surveys. In six of these projects, issues with aggregate base performance (stability and uniformity) had been observed and reported during paving of the HMA surface layer. Later, these pavements exhibited various levels of early distresses, including cracking (longitudinal, transverse, and alligator), aggregate base failure, and pavement surface roughness or irregularities (for ride quality). The remaining five HMA pavement projects, for which no issues related to aggregate base layer behavior were reported during construction, performed well after construction. A test section of approximately 1 mi on each project was subjected to FWD testing. The existing HMA pavements that showed early distresses exhibited high levels of spatial variability and nonuniformity in aggregate base course layers, as demonstrated by FWD testing and backcalculated base layer modulus values and distributions. The existing HMA pavements that performed well exhibited low levels of spatial variability and good uniformity in aggregate base course layers, as shown by the FWD test results and the backcalculated base layer modulus values and distributions.

Generalized Memristive Device SPICE Model and its Application in Circuit Design

This paper presents a SPICE model for memristive devices. It builds on existing models and is correlated against several published device characterization data with an average error of 6.04%. When compared to existing alternatives, the proposed model can more accurately simulate a wide range of published memristors. The model is also tested in large circuits with up to 256 memristors, and was less likely to cause convergence errors when compared to other models. We show that the model can be used to study the impact of memristive device variation within a circuit. We examine the impact of nonuniformity in device state variable dynamics and conductivity on individual memristors as well as a four memristor read/write circuit. These studies show that the model can be used to predict how variation in a memristor wafer may impact circuit performance.

First Time Lucky? Exploring Whether First-Time Offenders Should Be Sentenced More Leniently

This article explores the normative position and theoretical justifications for sentencing first-time offenders more leniently than repeat offenders, and examines whether such a practice is defensible. Those justifications include a lack of awareness of the gravity of criminal behaviour, a single lapse, that no censure has previously been communicated by the criminal justice system to that person, adolescent-limited offending, the impact of being in a minority group, and non-uniform impact. It examines whether various sentencing philosophies support sentence reductions for first-time offenders, and whether the justifiability of such practices depends on the theoretical basis and aims of sentencing, for instance the role of proportionality and deterrence.

Predicting Architectural Vulnerability on Multithreaded Processors under Resource Contention and Sharing

Architectural vulnerability factor (AVF) characterizes a processor's vulnerability to soft errors. Interthread resource contention and sharing on a multithreaded processor (e.g., SMT, CMP) shows nonuniform impact on a program's AVF when it is co-scheduled with different programs. However, measuring the AVF is extremely expensive in terms of hardware and computation. This paper proposes a scalable two-level predictive mechanism capable of predicting a program's AVF on a SMT/CMP architecture from easily measured metrics. Essentially, the first-level model correlates the AVF in a contention-free environment with important performance metrics and the processor configuration, while the second-level model captures the interthread resource contention and sharing via processor structures' occupancies. By utilizing the proposed scheme, we can accurately estimate any unseen program's soft error vulnerability under resource contention and sharing with any other program(s), on an arbitrarily configured multithreaded processor. In practice, the proposed model can be used to find soft error resilient thread-to-core scheduling for multithreaded processors.

Correlations Between Mapping Spectroscopic Ellipsometry Results and Solar Cell Performance for Evaluations of Nonuniformity in Thin-Film Silicon Photovoltaics

An understanding of the relationship between materials property and thin-film solar cell performance variations over large areas is of interest for evaluating the impact of macroscopic nonuniformities in scale-up from laboratory cells to production modules. In this study, we have spatially correlated the properties of the hydrogenated silicon (Si:H) i- and p-layers-as mapped over a 13 cm×13 cm substrate area-with device performance parameters from an array of a-Si:H based n-i-p dot cells. To evaluate materials and device nonuniformities, a 16 × 16 array of dot cells has been fabricated over the substrate area, and this same area has been mapped by spectroscopic ellipsometry (SE).Analysis of the SE data over the full area provides maps of i-layer thickness and band gap, p-layer thickness and band gap, and p-layer surface roughness thickness for the n-i-p solar cell structure. The mapped values adjacent to the devices have been correlated with photovoltaic (PV) device performance parameters. When sufficient nonuniformity exists, these correlations enable optimization based on specific values of the fundamental properties. Alternatively, if the optimum set of properties has been identified, the impact of deviations due to macroscopic uniformities can be evaluated.

Optical‐fiber microcoil waveguides and resonators and their applications for interferometry and sensing

AbstractIn this work, recent progress in the theoretical and experimental studies of optical‐fiber microcoil waveguides and resonators, as well as their various applications are reviewed. In particular, the focus is set on sensing and interferometry applications. It is shown that due to its inherently low propagation and fiber‐coupling losses, fiber‐microcoil based sensors and interferometers offer substantial enhancement of sensitivity and compactness compared to other types of devices. Recent progress in the realization and experimental characterization of such structures is presented and the theoretical tools to analyze the impact of real‐world nonuniformities on the characteristics of fiber‐microcoil structures are provided.

Controlled shot peening simulation for realistic impact pattern characterisation

Representative shot peening (SP) patterns as function of SP process parameters are calculated and presented. The work scrutinises the SP process parameters affecting the development of coverage and residual stresses (RS) by tackling the following phenomena: shot interactions into the shot stream, distribution of coverage on a reference plate surface, probability of non-uniform impact and relationship of adjacent impacts with RS development. The shot stream is simulated with a 2D kinematic model and the real distribution of the two most important SP parameters, i.e., shot velocity and angle are calculated. The effect of adjacent impacts on RS built-up is examined via a finite element (FE) model, resulting to a criterion about the minimum shot distance that affects the RS field. Finally, a stochastic simulation is performed via a germ-grain Boolean model, which simulates the stochastic nature of the process and results to the definition of realistic SP impact patterns.

Low Day 30 Total Donor Chimerism After Reduced-Intensity Conditioning Allogeneic Hematopoietic Stem Cell Transplantation Is Associated with Poorer Overall Survival In Myeloid but Not Lymphoid Disorders

AbstractAbstract 1325While some studies associated an increased relapse rate and poorer progression-free survival with lower donor T-cell chimerism after reduced-intensity conditioning (RIC) allogeneic hematopoietic stem cell transplantation (HSCT); early total donor cell chimerism, despite its use as a clinical trial endpoint, is not established as a predictor of survival. In part this may reflect its non-uniform impact across hematologic malignancies. Clarifying the survival impact of early donor chimerism could help identify patients who may benefit from additional interventions; and also define its value as a disease-specific endpoint.We undertook a retrospective analysis of adult patients undergoing 8/8 HLA-matched RIC HSCT from 2002–2008 with available day 30 total donor cell chimerism (range, 20–50 days; PB or marrow). All received fludarabine/busulfan-based conditioning with sirolimus- and/or tacrolimus-based GVHD prophylaxis. Umbilical cord blood transplants; ex-/in-vivo T-cell depletion (e.g. ATG); or malignant relapse/progression at or prior to day 30 chimerism were excluded. 414 patients with a median age of 58 years (range, 41–69) and median follow-up among survivors of 34 months (range, 6–80) were analyzed. Patient characteristics: 211 myeloid (116 AML, 63 MDS, 20 CML, 12 MPD); 203 lymphoid (70 NHL, 66 CLL, 39 HD, 21 MM, 6 ALL); 343 (83%) with high-risk disease; 265 (64%) were males; 404 (98%) received peripheral blood stem cells; 234 (57%) had matched-unrelated donors; and 132 (32%) had prior transplants.Day 30 total donor cell chimerism was <50% in 32 patients (8%); 50–89% in 99 patients (24%); and ≥90% in 283 patients (68%). Factors predictive of lower day 30 chimerism were high-risk disease (p<0.01), no prior transplant (p<0.01), male sex (p=0.02) and myeloid diagnosis (p=0.03). In univariable analyses patients with lower day 30 chimerism had worse 3-year progression-free and overall survival (PFS, OS) (p<0.0001; p=0.003). The cumulative incidence of chronic GVHD correlated with the degree of day 30 chimerism (p=0.049). Stratified by diagnosis, lower day 30 chimerism was associated with poorer 3-year PFS and OS in myeloid (p<0.0001; p<0.001) but not in lymphoid disorders (p=0.09; p=0.66) (Figure). For both myeloid and lymphoid disorders, lower day 30 chimerism was associated with increased incidence of relapse (p<0.0001; p=0.02) but not of non-relapse mortality (p=0.24; p=0.41).In multivariable Cox-models, day 30 chimerism <50% was associated with lower PFS and OS (HR 3.13, 95% CI 2.04–5, p<0.0001; HR 2.27, 95% CI 1.41–3.57, p<0.001). For myeloid disorders, day 30 chimerism <50% was associated with poorer PFS and OS (HR 6.25, 95% CI 3.23–11.11, p<0.0001; HR 3.33, 95% CI 1.82–6.25, p=0.0001). For lymphoid disorders, day 30 chimerism <50% was associated with poorer PFS (HR 2.13, 95% CI 1.09–4.17, p=0.03) but not OS (HR 1.44, 95% CI 0.65–3.23, p=0.36), that may reflect in-part longer survival after lymphoid compared to myeloid relapse. However, there may also be disease-specific differences. For instance, low day 30 chimerism was highly associated with poorer PFS and OS in AML/MDS (HR 4.54, 95% CI 2.13–10, p<0.0001; HR 3.33, 95% CI 1.67–10, p=0.001); had a trend of PFS impairment in CLL/NHL (HR 2.17, 95% CI 0.97–5, p=0.06); but had no impact in HD or myeloma.In conclusion day 30 total donor chimerism <50% is an independent predictor of poor survival after T-cell replete RIC HSCT. Routine assessment of day 30 chimerism in myeloid disorders helps identify a patient subset with significantly worse RIC HSCT outcomes, who may be candidates for trials of additional therapies to improve survival. Conversely, it may be a less relevant RIC HSCT endpoint in lymphoid disorders, where its survival impact appears more limited. [Display omitted] Disclosures:No relevant conflicts of interest to declare.

Nonuniform fiber networks and fiber-based composites: Pore size distributions and elastic moduli

An excluded-volume approach is developed for modeling the distribution of pore sizes and the specific surface area in isotropic networks of cylindrical fibers. The effect of accounting for nonuniformities in the spatial distribution of the fibers upon the mean pore size and effective surface area is examined. Fluctuations in the fiber volume fraction are shown to increase the mean pore radius and to reduce the specific surface area relative to their values for a spatially uniform network. A method is suggested for addressing the impact of spatial nonuniformities in the fiber volume fraction within mean-field and semiempirical models for the elastic moduli of fiber-based composites.

Modeling of parallel-plate regenerators with non-uniform plate distributions

A two-dimensional finite element model describing the performance of parallel-plate regenerators with arbitrary channel width distributions has been developed in order to investigate the effect of non-uniform plate spacing on the performance of regenerators. Results for a series of hypothetical plate spacing distributions are presented in order to understand the impact of spacing non-uniformity. Simulations of more realistic distributions where the plate spacings follow normal distributions are then discussed in order to describe the deviation of the performance of a regenerator relative to one with uniform spacing as a function of the standard deviation of the plate distribution. It has been shown that the most significant reduction in performance occurs when a volume of fluid between 100% and 200% of the regenerator void volume is displaced in a single blow.

Techniques for pixel response nonuniformity correction of CCD in interferential imaging spectrometer

Based on in-depth analysis of the relative radiation scaling theorem and acquired scaling data of pixel response nonuniformity correction of CCD (charge-coupled device) in spaceborne visible interferential imaging spectrometer, a pixel response nonuniformity correction method of CCD adapted to visible and infrared interferential imaging spectrometer system was studied out, and it availably resolved the engineering technical problem of nonuniformity correction in detector arrays for interferential imaging spectrometer system. The quantitative impact of CCD nonuniformity on interferogram correction and recovery spectrum accuracy was given simultaneously. Furthermore, an improved method with calibration and nonuniformity correction done after the instrument is successfully assembled was proposed. The method can save time and manpower. It can correct nonuniformity caused by other reasons in spectrometer system besides CCD itself's nonuniformity, can acquire recalibration data when working environment is changed, and can also more effectively improve the nonuniformity calibration accuracy of interferential imaging

Investment in Greek manufacturing under irreversibility and uncertainty: the message in used capital expenditures

This article contributes to the existing literature by showing that uncertainty produces a nonuniform impact to the extent that different types of capital goods exhibit heterogeneous irreversibility, which we define as asset-specific irreversibility. Hence, asset-specific irreversibility is responsible for asymmetries in responses across types of capital goods to uncertainty. We also show that for a given type of capital good, uncertainty produces a variety of responses across sectors, which we define sector-specific irreversibility. In other words, sectoral differences in terms of the ability to substitute a given type of capital with labour, introduce a second-order effect of uncertainty on investment.

Measuring structures of different scale in investigating nonuniform impact strength

Measuring structures of different scale in investigating nonuniform impact strength

Non-uniform impact excitation of a cylindrical bar

An experimental and numerical study of a non-uniform impact excitation of a circular bar is reported. In experiments, nine strikers with different contact area were accelerated against a circular bar. Axial surface strain of the impacted bar was measured at several distances from the impinged end to include the near and the far fields. The same experimental conditions were solved numerically using a commercial finite element code. It was demonstrated that the far-field response is insensitive to both the size and the form of the striker's colliding end. The distance at which such insensitivity is set is estimated to be approximately one and a half bar diameters.

Degradation Induced by X-Ray Irradiation and Channel Hot Carrier Stresses in 130-nm NMOSFETs With Enclosed Layout

We present new experimental results about channel hot carrier degradation of enclosed layout transistors as a function of previous accumulated total ionizing dose, stress temperature, and transistor geometry. We show that the parametric degradation follows a power law, whose exponent is higher than in conventional open layout transistors, possibly due to a different diffusion geometry of hydrogen. Through physical simulation we attribute this effect to the electric field at the device corners, which leads to a non-uniform impact ionization. Previous irradiation reduces the channel hot carrier degradation in MOSFETs with 5.2-nm gate oxide, while having a minor influence with 2.2-nm gate dielectric.

Biological Response to Nonuniform Distributions of210Po in Multicellular Clusters

Radionuclides are distributed nonuniformly in tissue. The present work examined the impact of nonuniformities at the multicellular level on the lethal effects of (210)Po. A three-dimensional (3D) tissue culture model was used wherein V79 cells were labeled with (210)Po-citrate and mixed with unlabeled cells, and multicellular clusters were formed by centrifugation. The labeled cells were located randomly in the cluster to achieve a uniform distribution of radioactivity at the macroscopic level that was nonuniform at the multicellular level. The clusters were maintained at 10.5 degrees C for 72 h to allow alpha-particle decays to accumulate and then dismantled, and the cells were seeded for colony formation. Unlike typical survival curves for alpha particles, two-component exponential dose-response curves were observed for all three labeling conditions. Furthermore, the slopes of the survival curves for 100, 10 and 1% labeling were different. Neither the mean cluster absorbed dose nor a semi-empirical multicellular dosimetry approach could accurately predict the lethal effects of (210)Po-citrate.

Numerical Modeling of PEM Fuel Cells Under Partially Hydrated Membrane Conditions

In proton-exchange membrane fuel cells it is particularly important to maintain appropriate water content and temperature in the electrolyte membrane. The water balance depends on the coupling between diffusion of water, pressure variation, and the electro-osmotic drag in the membrane. In this paper we apply conservation laws for water and current, in conjunction with an empirical relationship between electro-osmotic drag and water content, to obtain a transport equation for water molar concentration and to derive a new equation for the electric potential that strictly accounts for variable water content and is more accurate than the conventionally used Laplace’s equation. The model is coupled with a computational fluid dynamics model that includes the porous gas diffusion electrodes and the reactant flow channels. The resulting coupled model accounts for multi-species diffusion (Stefan-Maxwell equation); first-order reaction kinetics (Butler-Volmer equation); proton transport (Nernst-Planck equation); and water transport in the membrane (Schlo¨gl equation). Numerical simulations for a two-dimensional cell are performed over nominal current densities ranging from i=0.4 to i=1.2 A/cm2. The relationship between humidification and the membrane potential loss is investigated, and the impact and importance of two-dimensionality, temperature, and pressure nonuniformities are analyzed and discussed.

Class Size and Educational Policy: Who Benefits from Smaller Classes?

ABSTRACT The impact of class size on student achievement remains an open question despite hundreds of empirical studies and the perception among parents, teachers, and policymakers that larger classes are a significant detriment to student development. This study sheds new light on this ambiguity by utilizing nonparametric tests for stochastic dominance to analyze unconditional and conditional test score distributions across students facing different class sizes. Analyzing the conditional distributions of test scores (purged of observables using class-size specific returns), we find that there is little causal effect of marginal reductions in class size on test scores within the range of 20 or more students. However, reductions in class size from above 20 students to below 20 students, as well as marginal reductions in classes with fewer than 20 students, increase test scores for students below the median, but decrease test scores above the median. This nonuniform impact of class size suggests that compensatory school policies, whereby lower-performing students are placed in smaller classes and higher-performing students are placed in larger classes, improves the academic achievement of not just the lower-performing students but also the higher-performing students.