Leading Edge Area Research Articles

Changes in Gypsy Moth (Lepidoptera: Lymantriidae) Fecundity and Male Wing Length Resulting from Defoliation

The influence of defoliation on gypsy moth fecundity and male moth wing length and the relationship between male moth wing length and egg mass density were investigated. Male pupae and egg masses were collected from plots located in the leading edge area of the gypsy moth infestation in Virginia and Maryland. Defoliation and egg mass density estimates were made in each plot. Male pupae were allowed to emerge, and the left forewings of 2,636 moths were measured to determine wing length. Fecundity was determined volumetrically for 767 egg masses. Gypsy moth fecundity and male wing length decreased substantially only when defoliation exceeded a threshold level of ≍40%. There was a minimal change in fecundity and male wing length due to increasing levels of defoliation above or below this threshold. Thus, the effect of defoliation on male wing length and fecundity is essentially binomial (i.e., male wing lengthy is either large or small and fecundity is either high or low). Wing length of male moths explained only ≍10% of the variation in egg mass density in the area where pupae were collected. The wing length of moths captured in pheromone traps used in conjunction with the number of moths captured may be useful for monitoring gypsy moth populations.

Cavitation noise studies on marine propellers

Experimental observations are described of cavitation inception and noise from five model propellers, three basic and two modified, tested in the open jet section of the Indian Institute of Science high-speed water tunnel facility. Extensive experiments on the three basic propellers of different design, which included visualization of cavitation and measurements of noise, showed that the dominant type of cavitation was in the form of tip vortex cavitation, accompanied by leading edge suction side sheet cavitation in its close vicinity, and the resultant noise depended on parameters such as the advance coefficient, the cavitation number, and the propeller geometry. Of these, advance coefficient was found to have the maximum influence not only on cavitation noise but also on the inception of cavitation. Noise levels and frequencies of spectra obtained from all the three basic propellers at conditions near inception and different advance coefficient values, when plotted in the normalized form as suggested by Blake, resulted in a universal spectrum which would be useful for predicting cavitation noise at prototype scales when a limited extent of cavitation is expected in the same form as observed on the present models. In an attempt to delay the onset of tip vortex cavitation, the blades of two of the three basic propellers were modified by drilling small holes in the tip and leading edge areas. Studies on the modified propellers showed that the effectiveness of the blade modification was apparently stronger at low advance coefficient values and depended on the blade sectional profile. Measurements of cavitation noise indicated that the modification also improved the acoustic performance of the propellers as it resulted in a complete attenuation of the low-frequency spectral peaks, which were prominent with the basic propellers. In addition to the above studies, which were conducted under uniform flow conditions, one of the basic propellers was tested in the simulated wake of a typical single screw ship. The wake was simulated by using a wire screen technique. Observations of cavitation and measurement of noise clearly showed that the presence of the wake had a strong influence on the propeller cavitation and noise performance. Cavitation was found to be of the cloud type, which generated very intense noise compared to that generated by tip vortex cavitation along with leading edge suction side sheet cavitation in the uniform flow conditions. The noise spectra obtained with wake simulation also are presented in a normalized form to be of general utility.

Value of needle aspiration in bacteriologic diagnosis of cellulitis in adults.

We prospectively studied 30 adult patients with cellulitis, including many who were hospitalized with significant underlying medical problems. Needle aspiration of both central and leading edge areas of their lesions was performed in an attempt to establish a bacteriologic diagnosis. Potential pathogens were isolated by this technique in only 10% of the patients. Neither site of aspiration was clearly superior in terms of culture yield. Because aspirate Gram stains and cultures so rarely provided useful bacteriologic information, they were seldom helpful in guiding antibiotic selection or in influencing the outcome of treatment in most patients. However, clinical information, as well as results of primary lesion cultures when obtainable, may be used to successfully select therapy in most cases of adult cellulitis. On the basis of our results, needle aspiration may not be justified as a routine diagnostic procedure for all adults with cellulitis, though it may still be useful in selected patients.

Thermal barrier coatings for thermal insulation and corrosion resistance in industrial gas turbine engines

Four thermal barrier coatings were subjected to a 500 h gas turbine engine test. The coatings were two Y 2O 3-stabilized ZrO 2 composites, Ca 2SiO 4 and CaTiO 3. The Ca 2SiO 4 coating exhibited significant spalling. Y 2O 3-stabilized ZrO 2 and CaTiO 3 coatings showed little degradation except in blade leading edge areas. Post- test examination showed variations in the coating due to manual application techniques. Improved process control is required if engineering quality coatings are to be developed. The results indicate that some leading edge loss of the coating can be expected near the tip.