Maintainability Prediction in Department of Defense Development Programs

This paper outlines the need for maintainability prediction procedures which are applicable to systems and equipment, and outlines the scope and principle features of techniques included in the new Maintainability Prediction Handbook (MIL-HDBK-472). This handbook consolidates tri-service efforts in the field of maintainability prediction and furnishes guidelines for the selection, interpretation, and application of the procedures contained therein. The paper also describes how the Department of Defense and the procuring agencies are expected to use the handbook, the planned method of updating its contents, and additional techniques being considered for future incorporation.     

Predictive value of p63, ki‐67, and survivin expression in oral leukoplakia: A tissue microarray study

The aim of this study was to analyze the immunohistochemical expression of survivin, ki‐67, and p63 in oral leukoplakic lesions, histopathologically differentiated into dysplastic and nondysplastic. A tissue microarray containing 57 samples of biopsies from clinically classified lesions, such as leukoplakia, was immunolabeled for survivin, ki‐67, and p63. Samples were scored for percentage of positively stained. Scores were designated as follows: low = less than 25% of positive cells; and high = more than 25% of positive cells. On performing histopathological diagnosis, 20 dysplastic lesions and 37 nondysplastic lesions were seen, in which female patients (56.1%) were predominant with an average age of 58.27 years. The study showed a high expression of 37.5% for survivin, 43.7% for ki‐67, and 88.2% for p63 in dysplastic lesions. However, there was a high expression of 16.7% for survivin, 16.7% for ki‐67, and 92% for p63 in nondysplastic lesions. There is a positive correlation of expression among the three antibodies. In the association of immunoreactivity, in both dysplastic and nondysplastic lesions, increased expression of survivin reflects on the increased expression of ki‐67, and there is an overexpression of p63. In leukoplakia, the expression of survivin associated with that of ki‐67 reinforces the assumption that all these lesions are potentially malignant, regardless of histopathology; and the overexpression of p63 may indicate carcinogenic potential. These findings may help in the treatment of patients with this type of lesion.     

An MPEG‐4 Compliant Interactive Multimedia Streaming Platform Using Overlay Networks

This paper presents a multimedia streaming platform for efficiently transmitting MPEG‐4 content over IP networks. The platform includes an MPEG‐4 compliant streaming server and client, supporting object‐based representation of multimedia scenes, interactivity, and advanced encoding profiles defined by the ISO standard. For scalability purposes, we employ an application‐layer multicast scheme for media transmission using overlay networks. The overlay network, governed by the central entity of the network distribution manager, is dynamically deployed according to a set of pre‐defined criteria. The overlay network supports both broadcast delivery and video‐on‐demand content. The multimedia streaming platform is standards‐compliant and utilizes widespread multimedia protocols such as MPEG‐4, real‐time transport protocol, real‐time transport control protocol, and real‐time streaming protocol. The design of the overlay network was architected with the goal of transparency to both the streaming server and the client. As a result, many commercial implementations that use industry‐standard protocols can be plugged into the architecture relatively painlessly and can enjoy the benefits of the platform.     

Treatment of textile dyehouse wastewater by TiO2 photocatalysis

The oxidative degradation of an actual textile dyehouse wastewater was investigated by means of photocatalysis in the presence of TiO2. The UV-A-induced photocatalytic oxidation over TiO2 suspensions was capable of decolorizing the effluent completely, as well as reducing chemical oxygen demand (COD) sufficiently (COD reduction generally varied between about 40% and 90% depending on the operating conditions) after 4 h of treatment. Two crystalline forms of TiO2, viz. anatase and rutile, were tested for their photocatalytic activity and anatase was found to be more active than rutile. The extent of photocatalytic degradation was found to increase with increasing TiO2 concentration up to 0.5 g/L TiO2, above which degradation remained practically constant, reaching a plateau. Furthermore, textile effluent degradation was enhanced at acidic conditions (i.e. pH = 3) and in the presence of hydrogen peroxide. To assess catalyst activity on repeated use, experiments were performed where the catalyst was recovered and reused; after three successive uses, TiO2 had sufficiently retained its photocatalytic activity. Finally, the luminescent marine bacteria Vibrio fischeri was used to assess the acute ecotoxicity of samples prior to and after the photocatalytic treatment and it was found that ecotoxicity was fully eliminated following photocatalytic oxidation.     

A simulation-intensive approach for checking hierarchical models

Recent computational advances have made it feasible to fit hierarchical models in a wide range of serious applications. In the process, the question of model adequacy arises. While model checking usually addresses the entire model specification, model failures can occur at each hierarchical stage. Such failures include outliers, mean structures errors, dispersion misspecification, and inappropriate exchangeabilities. We propose an approach which is entirely simulation based. Given a model specification and a dataset, we need only be able to simulate draws from the resultant posterior. By replicating a posterior of interest using data obtained under the model we can “see” the extent of variability in such a posterior. Then, we can compare the posterior obtained under the observed data with this medley of posterior replicates to ascertain whether the former is in agreement with them and accordingly, whether it is plausible that the observed data came from the proposed model. Many such comparisons can be run, each focusing on a different potential model failure. Focusing on generalized linear mixed models, we explore the questions of when hierarchical model stages are separable and checkable and illustrate the approach with both real and simulated data. Research supported in part by NSF SCREMS grant DMS-9506557, NSF grant DMS-9301316 and by the Natural Sciences and Engineering Research Council of Canada     

Laser melting treatment by overlapping passes of preheated nickel electrodeposited coatings on Al−Si alloy

Microstructure improvements of a nickel electrodeposited Al−Si alloy were studied after high-power laser melting treatment through a single pass or partially overlapping successive adjacent passes. In some cases, laser melting treatment was preceded by a 5-hour heating of the specimens at 500°C in argon atmosphere furnace. Microstructure observations and microhardness measurements were carried out on the specimens before and after laser melting treatment with and without preheating. Best results concerning microhardness, microstructural homogeneity, and porosity elimination, as well as adhesion of the nickel coating on the Al−Si alloy, were achieved when the specimens were first subjected to heating at 500°C in an argon atmosphere furnace for 5 hours and then submitted to a laser melting treatment through successive adjacent laser passes with an overlapping rate of 70 pct. Microstructure studies were carried out employing X-ray diffraction analysis (XRD) and energy-dispersive spectrometry (EDS). AlNi and Al₃Ni phases were detected in the diffusion area which resulted from the 5-hour heating. AlNi, Al₃Ni, and Al₃Ni₂ phases were identified in the laser melted zones (LMZs). Each one of the above phase was found to be the main phase under different conditions.     

Stochastic model predictive control for constrained discrete-time Markovian switching systems

In this paper we study constrained stochastic optimal control problems for Markovian switching systems, an extension of Markovian jump linear systems (MJLS), where the subsystems are allowed to be nonlinear. We develop appropriate notions of invariance and stability for such systems and provide terminal conditions for stochastic model predictive control (SMPC) that guarantee mean-square stability and robust constraint fulfillment of the Markovian switching system in closed-loop with the SMPC law under very weak assumptions. In the special but important case of constrained MJLS we present an algorithm for computing explicitly the SMPC control law off-line, that combines dynamic programming with parametric piecewise quadratic optimization.     

Image registration based on lifting process: an application to digital subtraction radiography.

In this paper, a digital subtraction radiology scheme is presented based on a new method for the automatic registration of dental radiographs acquired with or without rigorous a priori standardization. The scheme is comprised of an automatic registration method and a subtraction process. The proposed registration method can be considered as an object-based registration method without imposing the prerequisite of image segmentation in order to detect the boundary of the objects of interest or the automatic detection of matching landmarks. This is achieved by augmenting the dimensionality of the problem from two-dimensional gray-level matching to three-dimensional surface matching using the process of lifting in combination with a surface-matching technique. The pseudo three-dimensional affine transformation that matches the lifted images incorporates advantageous characteristics including spatial alignment of the surfaces, anisotropic correction of brightness/contrast differences, and stable convergence of the similarity function to its optimal value. The performance of the proposed automatic registration method is assessed against a manual method based on the projective transformation. The qualitative and quantitative assessments of the experiments have shown advantageous performance of the proposed automatic registration method against the manual one. Finally, the proposed registration method has been further improved in terms of execution time by the implementation of a surface decimation process.     

Comparative study of toughness between the AH 40 fatigue crack arrester steel and its weld metal in the case of robotic metal-cored arc welding

The current investigation aims to scrutinize the impact and fracture toughness of the AH 40 fatigue crack arrester (FCA) steel and its weld metal, when welded with the metal-cored arc welding technique (MCAW). Initially, macroscopic observation and microstructural characterization were carried out in the areas of interest. Subsequently, the impact toughness was determined with the use of the Charpy V-notch test (CVN) at various temperatures, while the values of the absorbed energy (KV), the percentage of shear fracture (PSF), and the lateral expansion (LE) were recorded. Moreover, the ruptured surfaces were examined with a scanning electron microscope (SEM). Finally, the crack tip opening displacement (δ) parameter was estimated at room temperature by fracture toughness testing. The obtained data led to the quantification of the toughness parameters, when dynamic or quasistatic load is applied, while the combined effect of several factors to the degradation of the weld metal toughness was elucidated. The ductile to brittle transition curve and the crack tip opening displacement in the weld metal appeared to be lower than inside the unaffected material. Nevertheless, fracture toughness properties were evaluated within acceptable limits in all cases.