Uniform Improvement Research Articles

A Numerical Investigation of Extrusion through Bezier Shaped Curved Die Profile

The die profile plays an important role in reduction of extrusion load, evolution of uniform micro-structure and overall improvement of surface integrity of extruded product. In the present investigation, a numerical analysis has been carried out for extrusion through cosine die profile using DEFORM software for plane strain deformation using rigid plastic material. The extrusion load has been predicted. The effective stress, strain, strain rate and velocity distribution have been determined. It is proposed to investigate the evolution of uniform microstructure and the effect of strain hardening in the extrusion process in future work.

Fabrication of bioceramic scaffolds with ordered pore structure by inverse replication of assembled particles

β-Tricalcium phosphate (β-TCP) scaffolds with an ordered pore structure were fabricated by ceramic slip casting using a particle-assembled template. An ordered pore structure is expected to enable uniform and accurate improvement in the topology of the porous structure of scaffolds. Monosized spherical polyethylene particles were self-assembled into an fcc lattice by close-packing with a pyramidal indentation and heat-treated for interparticle necking. β-TCP slurry was cast with this particle array, followed by heat treatments to burn out the particles and sinter the β-TCP frame. The sintered scaffold showed not only an ordered arrangement of uniform pores but also pore interconnection pathways, which faithfully replicated the particle-assembled structure. High porosity, high pore interconnectivity, and structural controllability, as well as high accessibility, were achieved by this process.

Scaling Capacity by Two Channels in IEEE 802.11 Ad Hoc Networks With an SIR Comparison Algorithm

When an IEEE 802.11 ad hoc network achieves a capacity C using a single channel, the targeted capacity using two channels should be 2 ·C. We believe that this should be used as the benchmark for capacity comparisons for multichannel schemes. However, most of the dual-channel 802.11 protocols proposed in the literature appear to achieve less than 60% of the 2 ·C targeted capacity. In previous work, we proposed a link-directionality-based dual-channel medium-access-control (MAC) protocol (DCP) to boost the network capacities by up to 78% of our targeted capacities, i.e., 78% × 2 ·C = 1.56 ·C. However, the DCP still fails to reach the 2 ·C capacity target due to the overheads incurred by the protocol. In this paper, we implement a signal-to-interference ratio (SIR) comparison algorithm (SCA) on top of the DCP in an attempt to further improve network capacity. This algorithm incurs relatively small overheads and can further relax the protocol constraints that are imposed by the virtual carrier-sensing mechanism. Interestingly, while the capacity of the pure DCP decreases when link lengths are short, the capacity of the pure SCA increases when link lengths are short. The two algorithms compensate for the downside of each other to bring about a more uniform capacity improvement. Simulations show that the proposed scheme [described as DCP with SCA (DCPwSCA)] can increase the network throughputs by 430% in lattice topologies and 213% in random topologies.

Plasma immersion ion implantation of cylindrical bore using self-excited radio-frequency glow discharge

Abstract Plasma immersion ion implantation (PIII) is an effective surface processing technique. However, it is still difficult to implant the inner wall of a cylindrical bore using this technique due to the internal small-volume effect. This paper presents a new approach based on self-excited radio-frequency (RF) glow discharge inside the tube. The tube which itself acts as a plasma source to generate the required plasma is biased negatively to conduct PIII. Steady discharge and plasma generation can be achieved and the plasma density is generally quite uniform in spite of the end effect of glow discharge. To demonstrate the technique, a stainless steel tube 30 mm in diameter and 200 mm long is implanted. The XPS results show that nitrogen PIII is indeed successful and phases such as Cr 2 O 3 , CrN, and FeN are formed from the nitrogen implanted layer which improves the wear resistance of the stainless steel tube. Our results reveal uniform improvement along the tube axis suggesting that this novel technique is an effective tool to implant the inner wall of a cylindrical bore.

A note on residual-based empirical likelihood kernel density estimation

In general the empirical likelihood method can improve the performance of estimators by including additional information about the underlying data distribution. Application of the method to kernel density estimation based on independent and identically distributed data always improves the estimation in second order. In this paper we consider estimation of the error density in nonparametric regression by residual-based kernel estimation. We investigate whether the estimator is improved when additional information is included by the empirical likelihood method. We show that the convergence rate is not effected, but in comparison to the residual-based kernel estimator we observe a change in the asymptotic bias of the empirical likelihood estimator in first order and in the asymptotic variance in second order. Those changes do not result in a general uniform improvement of the estimation, but in typical examples we demonstrate the good performance of the residual-based empirical likelihood estimator in asymptotic theory as well as in simulations.

A New Gaussian Mixture Algorithm for GMTI Tracking Under a Minimum Detectable Velocity Constraint

This paper introduces a new methodology to account for Doppler blind zone constraints, arising, for example, in ground moving target indicator (GMTI) tracking applications. In such problems, target measurements are suppressed when the range rate (Doppler) of the target drops below a specified threshold in magnitude (the minimum detectable velocity). The proposed method, employing Gaussian mixture approximations to the filtering density, differs from earlier Gaussian mixture approaches in the way missed measurements are modelled. The distinctive feature of the algorithm, as compared with other Gaussian mixture filters, is that it is based on an exact calculation of the filtering density when a measurement is not recorded. Algorithms that result from applying this methodology are simple to implement and computationally undemanding. Simulation results indicate a uniform improvement in estimation accuracy over that of earlier proposed analytic techniques, and a tracking performance comparable to that of state-of-the-art particle filters.

A meta-analysis of interventions to promote mammography among ethnic minority women.

Although many studies have been focused on interventions designed to promote mammography screening among ethnic minority women, few summaries of the effectiveness of the interventions are available. The aim of this study was to determine the effectiveness of the interventions for improving mammography screening among asymptomatic ethnic minority women. A meta-analysis was performed on intervention studies designed to promote mammography use in samples of ethnic minority women. Random-effects estimates were calculated for interventions by measuring differences in intervention and control group screening rates postintervention. The overall mean weighted effect size for the 23 studies was 0.078 (Z = 4.414, p < .001), indicating that the interventions were effective in improving mammography use among ethnic minority women. For mammography intervention types, access-enhancing strategies had the biggest mean weighted effect size of 0.155 (Z = 4.488, p < .001), followed by 0.099 (Z = 6.552, p < .001) for individually directed approaches such as individual counseling or education. Tailored, theory-based interventions resulted in a bigger effect size compared with nontailored interventions (effect sizes = 0.101 vs. 0.076, respectively; p < .05 for all models). Of cultural strategies, ethnically matched intervention deliveries and offering culturally matched intervention materials had effect sizes of 0.067 (Z = 2.516, p = .012) and 0.051 (Z = 2.365, p = .018), respectively. Uniform improvement in mammography screening is a goal to address breast cancer disparities in ethnic minority communities in this country. The results of this meta-analysis suggest a need for increased use of a theory-based, tailored approach with enhancement of access.

A realisable non-linear eddy viscosity/diffusivity model for confined swirling flows

A non-linear eddy viscosity/diffusivity model for turbulent flows is presented, featuring quadratic constitutive relationships for both Reynolds stresses and scalar fluxes. Model coefficients are defined by enforcing compliance with fundamental experimental evidence, and realizability of both the velocity and scalar fields, which is achieved by making coefficients depend upon an appropriately defined strain parameter. The model is also shown to satisfy joint-realizability. The model is extensively tested against experimental results for confined swirling flows, encompassing a wide range of values of the swirl number, momentum and density ratios. The results unambiguously indicate a remarkable, uniform improvement over standard modelling. Further, previous work on the subject of nonlinear models is reviewed.

Hicks theorem: Effects of technological improvement in the Ricardian model

Using the Ricardian model, we formally prove Hicks' [Hicks, John (1953), “An Inaugural Lecture,” Oxford Economic Papers 5(2), 117–135.] insight into the effects of technological improvement: uniform technological improvement at home benefits all countries (or at least does not hurt); export-biased technological improvement at home benefits the foreign country (or at least does not hurt), but import-biased technological improvement at home can hurt the foreign country as long as the comparative advantage is not reversed. We then study optimal strategies of technological improvement and show that for a small country it is optimal to choose export-biased technological improvement. For a large country, it is optimal to improve technology in both sectors at a rate proportional to the consumers' expenditure share. Therefore, if the expenditure share of the import sector is larger than that of the export sector, a large country will choose a relatively import-biased technological improvement, which will hurt its trading partner.

A Uniform Improvement of Bonferroni-Type Tests by Sequential Tests

We propose a new method to uniformly improve cutoff tests (as, e.g., the Bonferroni test) by replacing them with a sequential testing procedure. The proposed procedure provides a uniform improvement—that is, it rejects the null hypothesis at least in all cases where the original procedure does, has level α, and never requires a sample size larger than that of the original procedure. Information on the often-unknown joint distribution of the test statistics across the hypotheses is not required. We discuss the applications to one- and two-sided tests for the intersection of multiple hypotheses, as well as to tests of elementary hypotheses. For the wide class of asymptotically linear test statistics and under unknown nuisance parameters, we propose an asymptotic approximation to our improved procedure and show that it exhausts the nominal type I error rate asymptotically. We present an application in a clinical study with multiple endpoints where the null hypothesis of no effect is tested against the alternative that at least one endpoint shows an effect, and give a real data example.

Preparation of poly(vinylidene fluoride) microfiltration membrane with uniform surface-copolymerized poly(ethylene glycol) methacrylate and improvement of blood compatibility

This work describes the surface modification and characterization of poly(vinylidene fluoride) (PVDF) microfiltration (MF) membranes grafted with poly(ethylene glycol) methacrylate (PEGMA) via surface-activated ozone treatment and thermally induced graft copolymerization. The chemical composition and microstructure of the surface-modified PVDF membranes were characterized by Fourier transform infrared spectroscopy (FT-IR), contact angle, and atomic force microscopy (AFM) measurements. Blood compatibility of the modified membranes was evaluated by the biofouling property of the platelet adhesion observed by scanning electron microscopy (SEM) and the plasma protein adsorption determined by an enzyme-linked immunosorbent assay (ELISA). In general, the grafting density of the copolymerized PEGMA and the hydrophilicity on the surface of PVDF MF membranes increase with increasing macromonomer concentration of PEGMA in the reaction solution. The grafting distribution of PEGMA on the resulting membranes was found to form a uniform polymer hydrogel-like layer controlled by sufficient high content of PEGMA in the reaction solution, while their surface roughness was kept lower than that of the virgin membrane. For the platelet adhesion test, a remarkable suppression of the platelets adhered to the PVDF MF membranes grafted with PEGMA polymer was observed. In the water flux experiments, the PEGMA-grafted hydrophilic PVDF MF membranes exhibited good anti-fouling properties to substantially reduce the irreversible membrane fouling caused by platelet adhering and plasma protein adsorption as compared with the virgin hydrophobic PVDF MF membranes.

An Evaluation of Image Noise Variance for Time-of-Flight PET

We describe a simple theoretical framework for linear time-of-flight (TOF) PET reconstruction and evaluate several alternative TOF filters. We implement a capability for direct computation of TOF noise variance images and evaluate the gain in image variance for TOF vs. non-TOF for 1.26 nsec TOF resolution on the Siemens biograph HiRez PET/CT. The variance calculation is validated by comparing to pixel variances computed from replicated synthetic data. TOF reconstruction does not give a uniform improvement in image noise variance, but reduces variance more toward the periphery of an object than at its center. The TOF performance gain depends in part on how random coincidences are processed, and is greater when the randoms fraction is higher, or when randoms smoothing is not employed. We confirm that the TOF gain is greater for larger objects than for smaller ones, but find discrepancies with the D/Deltax rule of thumb. With 1.26 nsec resolution on the HiRez, TOF image noise gain factors (non-TOF/TOF variance) range from 1.5 to 2.2 on the measured data at hand. We predict that an improvement in TOF resolution by a factor of 2 (to 600 psec) could improve image variance on this machine by an additional factor of 1.8. We find that confidence weighted TOF reconstruction under-performs non-TOF reconstruction for objects whose diameters are small compared to the TOF resolution.

List-mode-based reconstruction for respiratory motion correction in PET using non-rigid body transformations

Respiratory motion in emission tomography leads to reduced image quality. Developed correction methodology has been concentrating on the use of respiratory synchronized acquisitions leading to gated frames. Such frames, however, are of low signal-to-noise ratio as a result of containing reduced statistics. In this work, we describe the implementation of an elastic transformation within a list-mode-based reconstruction for the correction of respiratory motion over the thorax, allowing the use of all data available throughout a respiratory motion average acquisition. The developed algorithm was evaluated using datasets of the NCAT phantom generated at different points throughout the respiratory cycle. List-mode-data-based PET-simulated frames were subsequently produced by combining the NCAT datasets with Monte Carlo simulation. A non-rigid registration algorithm based on B-spline basis functions was employed to derive transformation parameters accounting for the respiratory motion using the NCAT dynamic CT images. The displacement matrices derived were subsequently applied during the image reconstruction of the original emission list mode data. Two different implementations for the incorporation of the elastic transformations within the one-pass list mode EM (OPL-EM) algorithm were developed and evaluated. The corrected images were compared with those produced using an affine transformation of list mode data prior to reconstruction, as well as with uncorrected respiratory motion average images. Results demonstrate that although both correction techniques considered lead to significant improvements in accounting for respiratory motion artefacts in the lung fields, the elastic-transformation-based correction leads to a more uniform improvement across the lungs for different lesion sizes and locations.

Extension of the reconstruction field of view and truncation correction using sinogram decomposition

We propose a novel truncation correction algorithm that completes unmeasured data outside of the scan field of view, which allows extending the reconstruction field of view. When a patient extends outside the detector coverage the projection data are transversely truncated, which causes severe artifacts. The proposed method utilizes the idea of sinogram decomposition, where we consider sinogram curves corresponding to image points outside the field of view. We propose two ways to estimate the truncated data, one based on the minimum value along the sinogram curve, and the other based on the data values near the edge of truncation. Both estimation methods are combined to achieve uniform image quality improvement from the edge of truncation to the outer side of the extended region. In our evaluation with simulated and real projection data we compare the proposed method with existing methods and investigate the dependence on the amount of truncation. The evaluation shows that the proposed method handles cases when truncation is present on both sides of the detector, or when a high-contrast object is located outside the field of view.

System-Optimal Stochastic Transportation Network Design

In transportation engineering, the network design problem (NDP) aims at finding an optimal link improvement in a network for given demand. Although traffic demand is essentially uncertain, many previous studies assumed it to be deterministic. The demand stochasticity is incorporated and formulas are developed for system-optimal (SO) flow stochastic NDP. The SO assumption is justified by comparing results from SO deterministic NDP with those of user-equilibrium NDP. The difference in social cost between the two approaches is found to be less than 5%. Two two-stage stochastic programs with recourse formulations are proposed: one with penalty function and the other without. The main advantage of the first formulation is that a planner can exert better control on improvement by appropriately weighing reduction in the congestion versus improvement costs. The challenge, however, lies in selecting an appropriate penalty function. A nonlinear penalty function is found suitable for the test network studied. The second formulation does not require penalty function but results in a large number of scenarios. Nonanticipativity constraints are introduced in the second formulation to arrive at uniform improvement over all scenarios. Both formulations are solved on a test network. It is found that necessary improvements and the total costs with both models are more than those for average demand.

Estimation of error variance in ANOVA model and order restricted scale parameters

We consider the estimation of error variance in the analysis of experiments using two level orthogonal arrays. We address the estimator which is the minimum of all the estimators which we obtain by pooling some sums of squares for factorial effects. Under squared error loss, we discuss whether or not this estimator uniformly improves upon the best positive multiple of error sum of squares. We show that when we have two factorial effects, we obtain uniform improvement. However, we show that when we have more than two factorial effects, we cannot necessarily obtain uniform improvement. Further, the above results are applied to the problem of estimating the smallest scale parameter of chi-square distributions.

On δ-Equivalence With the Best in k-Sample Models

In recent work we introduced a general, a weak, and a strong partitioning principles for the construction of multiple decision procedures as multiple testing or selection procedures. Partitioning principles can be viewed as natural extensions of the closure principle and sometimes yield more powerful decision procedures. In this article we consider the problem of establishing equivalence with the best with respect to k treatment means, where equivalence is defined in terms of a threshold value δ > 0. We reformulate the original selection problem as a multiple testing problem and develop various step-down and step-up procedures by applying the closure principle and partitioning principles. The new step-down procedure is shown to provide a uniform improvement over procedures currently in use. Moreover, we propose some projection methods that yield confidence intervals being compatible with stepwise tests and selection procedures.

Magnetic resonance image findings in the early post-operative period after anterior cervical discectomy

If early neurological deterioration occurs following anterior cervical discectomy, the patient should be evaluated by urgent MRI scanning. In order to interpret such a scan it is essential to know what the normal post-operative MRI appearance is following an uncomplicated procedure. In the lumbar spine it is well recognized that early post-operative imaging following discectomy is difficult to interpret with a high rate of false positive scans. The normal appearance of MRI in the early post-operative period was evaluated prospectively in 15 patients undergoing anterior cervical discectomy without fusion for either cervical radiculopathy or myelopathy. MRI was performed on the first post-operative day, at 6 weeks and 6 months. The successful outcome of the procedure was validated by uniform improvement of Visual Analogue Scale measurement for neck and arm pain, the Neck Disability Index and European Myelopathy Score as appropriate. In contrast to the established findings following lumbar discectomy, only two cases showed a persistent epidural mass in the first post-operative scan and this had completely resolved at 6 months. All patients had foraminal narrowing and root or cord compression pre-operatively. Sixty six percent of cases showed persistent foraminal narrowing on sequential imaging up to 6 months despite showing good symptomatic improvement. All cases demonstrated high signal in the operated disc space on T2 weighted imaging on the first post-operative day and this finding persisted in 13 of 15 scans performed at 6 weeks. Post contrast imaging demonstrated no enhancement of operated disc space and adjacent vertebral body on the first post-operative day, whereas all scans at 6 weeks showed enhancement and such enhancement persisted at 6 months in 50%. Persistent epidural filling defects are uncommon following successful anterior cervical discectomy but persistence of foraminal narrowing is common despite successful outcome. Enhancement of the disc space is also common and does not in itself imply infection.

Influence Diagrams for Team Decision Analysis

We consider the representation and evaluation of team decision making under uncertainty using influence diagrams. We assume that all team members agree on common beliefs and preferences, but complete sharing of information is generally impossible. As a result, the team can be represented as a single rational individual with imperfect recall, and the optimal solution with perfect recall might not be achievable, except in special cases we can recognize. An alternative solution concept is a stable solution that integrates the notion of optimality with that of equilibrium from game theory. We extend this concept from individual decisions to sets of decisions, and introduce the Strategy Improvement and its variation, Uniform Strategy Improvement, as the corresponding solution methods. We also provide a variety of simplifying transformations to the influence diagram by exploiting its graphical structure. The result is a requisite influence diagram, one that requires minimum assessment and creates additional opportunities for optimality.

A Model of How Children Acquire Computing Skills from Hole-in-the-Wall Computers in Public Places

This paper explores the possibility of constructing a minimally invasive learning model from the results of a Graphical User Interface (GUI) Icon Association Inventory (devised by Dangwal and Inamdar [Mitra 2003]). We discuss the results obtained from four playground (hole-in-the-wall) computer kiosk sites in southern India, made freely available to children, without supervision, for nine months. Computing skills acquisition, as measured by the Icon Association Inventory, was plotted for each month and the learning curves are reported in the paper. The observed curves were fitted to predicted curves to understand the rates and stages of learning. Results indicate uniform improvement in the computing skills of the children who used these kiosks.