Valence-band discontinuity between GaN and AIN measured by x-ray photoemission spectroscopy

The valence-band discontinuity at a wurtzite GaN/AIN (0001) heterojunction is measured by means of x-ray photoemission spectroscopy. The method first measures the core level binding energies with respect to the valence-band maximum in both GaN and A1N bulk films. The precise location of the valenceb and maximum is determined by aligning prominent features in the valenceb and spectrum with calculated densities of states. Subsequent measurements of separations between Ga and Al core levels for thin overlayers of GaN film grown on A1N and vice versa yield a valence-band discontinuity of ΔE_v = 0.8+- 0.3 eV in the standard Type I heterojunction alignment.     

PIE: A Programming and Instrumentation Environment for Parallel Processing

The issues of performance-efficient programs and system support for parallel programming are the focus of this project to integrate functionality with performance concerns.     

Reference database of the main physiological parameters in Sprague-Dawley rats from 6 to 32 months

Human immunodeficiency virus (HIV) infection is a major public health problem worldwide, but particularly in subsaharan Africa and Asia. Numerous observational studies report inverse associations between vitamin status, measured biochemically or as levels of dietary intake, and the risk of disease progression or vertical transmission. Evidence to support these findings has been obtained from a few randomized placebo-controlled trials. In this paper, we review studies that examined the role of vitamins A, B, C, D, and E in HIV disease progression and transmission, and we discuss the potential mechanisms of action of these vitamins. Adequate vitamin intake leads to enhancement of epithelial integrity and systemic immunity and could contribute to improved clinical condition among HIV-infected subjects and reduce vertical transmission by reducing the risk and severity of opportunistic infection and reducing viral load in blood. Adequate vitamin status may also reduce vertical transmission through the intrapartum and breastfeeding routes by reducing HIV viral load in lower genital secretions and breast milk, respectively. Vitamin supplements may be one of a few potential treatments that are inexpensive enough to be made available to HIV-infected persons in developing countries.     

Visual analysis of quality-related manufacturing data using fractal geometry

Improving manufacturing quality is an important challenge in various industrial settings. Data mining methods mostly approach this challenge by examining the effect of operation settings on product quality. We analyze the impact of operational sequences on product quality. For this purpose, we propose a novel method for visual analysis and classification of operational sequences. The suggested framework is based on an Iterated Function System (IFS), for producing a fractal representation of manufacturing processes. We demonstrate our method with a software application for visual analysis of quality-related data. The proposed method offers production engineers an effective tool for visual detection of operational sequence patterns influencing product quality, and requires no understanding of mathematical or statistical algorithms. Moreover, it enables to detect faulty operational sequence patterns of any length, without predefining the sequence pattern length. It also enables to visually distinguish between different faulty operational sequence patterns in cases of recurring operations within a production route. Our proposed method provides another significant added value by enabling the visual detection of rare and missing operational sequences per product quality measure. We demonstrate cases in which previous methods fail to provide these capabilities.     

Effect of Plasma-Polymerized Primers on the Durability of Aluminum/Epoxy Adhesive Bonds

The durability of aluminum/epoxy adhesive joints prepared from substrates pretreated by plasma etching and then deposition of plasma-polymerized primers was determined using the wedge crack testing method. Plasma etching and polymerization were conducted using both direct current (DC) and microwave (2.45 GHz) driven plasma systems. Plasma-polymerized primers were deposited using trimethysilane (TMS) and hexa-methyldisiloxane (HMDSO) to form siloxane-like and silica-like films, respectively. Plasma etching with argon and argon/hydrogen plasmas was used as a substrate pre-treatment. In some cases etching with an oxygen plasma was used as a post-treatment to give a silica-like surface to siloxane-like films deposited from TMS. Adhesive joints were prepared using two different epoxy adhesives, Cytec FM-300 and FM-123-2. Differences in initial adhesion were observed for primer films with chemical differences. Siloxane-like primer films were not wetted by the adhesive and resulted in poor wedge test results. Silica-like primer films were not wetted by the adhesive and resulted in poor wedge test results. Silica-like primer films deposited onto aluminum substrates resulted in wedge specimens with good adhesion and durability. The initial crack was cohesive within the adhesive. However, crack growth occurred at the interface between the adhesive and silica-like primer. Durability of the wedge specimens was essentially invariant of the type of microwave plasma pretreatment for grit-blasted aluminum substrates that were coated with silica-like primers before bonding with FM-123-2.     

On the Bonding Mechanism in Cold Spray of Deformable hex-BN-Ni Clusters

Bond strength and the lubrication potential of coatings made of 7 µm Hexagonal Boron Nitride particles encapsulated with nickel (hBN-Ni), and deposited onto aluminum 6061 substrates via cold spray were examined; for all tests, N₂ was used as the carrier gas at a temperature of 480 °C and pressure of 2.4 MPa. Results showed significant improvement in both wear resistance and reduced surface friction. Coated samples also demonstrated unexpected high bond strength, which was much greater than pure nickel cold sprayed onto aluminum. However, while the results were truly promising, the primary reason for the observed high bond strength could not be explained using existing cold spray theories which were primarily developed for pure metal particles. Based on the present findings compared to cold-sprayed layers of composite nickel-nickel (nickel particles encapsulated with nickel), a mechanism for bonding of hBN-Ni particles to aluminum based on the level of plastic deformation and hardenability is proposed. Indeed, the high bond strength between the coating and substrate is related to the relatively high initial ductility of the nickel encapsulation, compliance of the hBN, as well as the ensuing significant plastic deformation of the composite particles during cold spray deposition.     

Effects of physical workload on cognitive task performance and situation awareness

Sixteen participants performed a military operations simulation directing loading of helicopters to weight capacity within an allotted timeframe and subject to a set of decision rules. The participants stood, walked or jogged on a treadmill while performing the simulated cognitive task. Task performance was measured in terms of helicopter loading rate and accuracy. Situation awareness (SA) was measured using a simulation freeze technique and SA queries. Subjective workload was measured using the NASA-TLX. Results indicated a general trend of decreasing SA with increasing physical workload for perceptual knowledge, comprehension and overall SA. Results also revealed higher subjective workload during jogging than during the walking and standing conditions. However, the physical workload manipulations did not appear to affect cognitive task performance. This study has practical implications for defining physical and cognitive workloads in specific dynamic, complex work environments to support operator SA and performance.     

Interfacial load transfer in carbon nanotube/ceramic microfiber hybrid polymer composites

Growing carbon nanotubes (CNTs) on the surface of fibers has the potential to modify fiber–matrix interfacial adhesion, enhance the composite delamination resistance, and possibly improve its toughness and any matrix-dominated elastic property as well. In the present work aligned CNTs were grown upon ceramic fibers (silica and alumina) by chemical vapor deposition (CVD) at temperatures of 650 °C and 750 °C. Continuously-monitored single fiber composite (SFC) fragmentation tests were performed on pristine as well as on CNT-grown fibers embedded in epoxy. The critical fragment length, fiber tensile strength at critical length, and interfacial shear strength were evaluated. Significant increases (up to 50%) are observed in the fiber tensile strength and in the interfacial adhesion (which was sometimes doubled) with all fiber types upon which CNTs are CVD-grown at 750 °C. We discuss the likely sources of these improvements as well as their implications.