Boron nitride coatings of steel and graphite produced with a low pressure r.f. plasma

Boron nitride (BN) coatings were deposited onto die steel and graphite substrates with a low pressure r.f. plasma. The coatings were deposited onto substrates at temperatures of 550–620 °C from a gas mixture of argon, NH₃ and BCl₃. X-ray diffraction and scanning electron microscopy were employed to identify and to characterize the coatings. The coatings are mostly amorphous; however, the existence of small amounts of hexagonal BN was identified. The influence on the growth rate of the deposition time and the pressure in the reactor is described.     

A multi-layer sampler for the study of detailed hydrochemical profiles in groundwater

A modular multi-layer sampler was developed and utilized for sampling undisturbed groundwater chemical profiles. Sampling at 3 cm depth intervals is based on the dialysis-cell method and has no depth limitations. The sampler may be used for water quality monitoring and research, both in existing or specially drilled screened wells     

Experimental Investigation of Thermal and Hydrodynamic Effects on Radially Grooved Thrust Washer Bearings

In this study, an experimental investigation on the effects of grooves on thrust washer bearings is investigated. Eight equally sized grooves are machined about 100 μ m deep into one side of a flat-faced steel washer. This thrust washer bearing is located between a helical gear and its carrier and is tested on a test rig capable of measuring frictional torque and the temperature of the bearing at different speeds. It is found that the grooved washers had lower bearing temperatures and failed at significantly higher loads than the control washer with no grooves. For a test procedure with varying operating conditions, the coefficient of friction is also significantly lower for the grooved washers. However, the grooved washers had about the same coefficient of friction as the control washers at each step when the speeds are very high. The results from various tests suggest that the increased amount of lubricant passing through the grooved surface of the washer removes heat from the washer bearing by convection. This decrease in stored heat conducted from friction deters thermoelastic instabilities and the reduction of hydrodynamic stiffness due to the decrease in viscosity. Enhanced hydrodynamic load-carrying capacity is also evident in the grooved washers test results.     

A statistical model of elasto-plastic asperity contact between rough surfaces

This work models statistically elasto-plastic contact between two rough surfaces using the results of a previous finite element analysis of an elasto-plastic sphere in contact with a rigid flat. The individual asperity contact model used accounts for a varying geometrical hardness effect that has recently been documented in previous works (where geometrical hardness is defined as the uniform pressure found during fully plastic contact). The contact between real surfaces with known material and surface properties, such as the elastic modulus, yield strength, and roughness are modeled. The asperity is modeled as an elastic-perfectly plastic material. The model produces predictions for contact area, contact force, and surface separation. The results of this model are compared to other existing models of asperity contact. Agreement exists in some cases and in other cases it corrects flaws, especially at large deformations. The model developed by Chang, Etsion and Bogy is also shown to have serious flaws when compared to the others. This work also identifies significant limitations of the statistical models (including that of Greenwood and Williamson).     

Deposition of silicon carbide coatings on titanium alloy with a low pressure R.F. plasma

A low pressure r.f. plasma was applied to deposit SiC coatings onto Ti6A14V substrates. The coatings were deposited onto substrates at temperatures of 140–390°C from a gas mixture of tetramethylsilane (TMS), argon and hydrogen. Scanning electron microscopy, X-ray diffraction and transmission electron microscopy were employed to identify and to characterize the coatings obtained. It was found that the coatings were hexagonal α-SiC of type III. The coating thickness approximately follows a parabolic time law. A maximum rate of deposition was observed in the pressure range 5–6 mbar. The rate of deposition increases with concentration of TMS up to 0.05% and remains approximately constant up to 0.12%     

Perceptual Issues in Music Pattern Recognition: Complexity of Rhythm and Key Finding

We consider several perceptual issues in the context of machine recognition ofmusic patterns. It is argued that a successful implementation of a musicrecognition system must incorporate perceptual information and error criteria.We discuss several measures of rhythm complexity which are used fordetermining relative weights of pitch and rhythm errors. Then, a new methodfor determining a localized tonal context is proposed. This method is based onempirically derived key distances. The generated key assignments are then usedto construct the perceptual pitch error criterion which is based on noterelatedness ratings obtained from experiments with human listeners.     

Complexity of the consistency problem for certain Post classes

The complexity of the consistency problem for several important classes of Boolean functions is analyzed. The classes of functions under investigation are those which are closed under function composition or superposition. Several of these so-called Post classes are considered within the context of machine learning with an application to breast cancer diagnosis. The considered Post classes furnish a user-selectable measure of reliability. It is shown that for realistic situations which may arise in practice, the consistency problem for these classes of functions is polynomial-time solvable.     

Combinatorial Optimization and Performance Analysis of a Multi-arm Cartesian Robotic Fruit Harvester—Extensions of Graph Coloring

A mobile melon robotic harvester consisting of multiple Cartesian manipulators, each with three degrees of freedom, is being developed. In order to design an optimal robot in terms of number of arms, manipulator capabilities, and robot speed, a method of allocating the fruits to be picked by each manipulator in a way that yields the maximum harvest has been developed. Such a method has already been devised for a multi-arm robot with 2DOF each. The maximum robotic harvesting problem was shown there to be an example of the maximum k-colorable subgraph problem (MKCSP) on an interval graph. However, for manipulators with 3DOF, the additional longitudinal motion results in variable intervals. To overcome this issue, we devise a new model based on the color-dependent interval graph (CDIG). This enables the harvest by multiple robotic arms to be modeled as a modified version of the MKCSP. Based on previous research, we develop a greedy algorithm that solves the problem in polynomial time, and prove its optimality using induction. As with the multi-arm 2DOF robot, when simulated numerous times on a field of randomly distributed fruits, the algorithm yields a nearly identical percentage of fruit harvested for given robot parameters. The results of the probabilistic analysis developed for the 2DOF robot was modified to yield a formula for the expected harvest ratio of the 3DOF robot. The significance of this method is that it enables selecting the most efficient actuators, number of manipulators, and robot forward velocity for maximal robotic fruit harvest.