Icing and De-Icing of a Propeller with Internal Electric Blade Heaters

An investigation has been made in the NACA Cleveland icing research tunnel to determine the de-icing effectiveness of an experimental configuration of an Internal electric propeller-blade heater. Two atmospheric Icing conditions and two propeller operating conditions were Investigated, In experiments with unheated blades and with heat applied to the blades both continuously and cyclically. Data are presented to show the effect of propeller speed., ambient air temperature and liquid-water concentration, and the duration of the heat-on and cycle times on the power requirements and de-Icing performance of the blade heaters. The extent of ice-covered area on the blades for various icing ax4 operating conditions has been determined. The largest iced area was obtained at the higher ambient-air temperatures and at low propeller speed. The ohord.wise extent of Icing In practically every case was greater than that covered by blade heaters. Adequate de-icing in the heated area with continuous application of heat was obtained with the power available but a maximum power, input of 1250 watts per blade was insufficient for cyclic de-Icing for the range of conditions investigated. Blade-surface temperature rates of rise of 0.2 to 0.7 F per second were obtained and the minimum cooling period for cyclic de-icing was found to be approximately 2-1/2 times the heating period

Wage and Occupational Differences Between Black and White Men: Labor Market Discrimination in the Rural South

The existence of labor market discrimination based on race is well established.However, study continues into a variety of aspects of discrimination-among them the extent to which it exists in different regions. Gwartney has estimated the ratio of black to white earnings to be between .83 and .88 for the North and between .68 and .74 for the South. Masters, in a study of earnings differentials between black and white men, found a ratio of .79 for the non-South and .69 for the South. Although considerable literature has developed concerning earnings differentials, wage discrimination in rural areas is one topic which has received relatively little attention. In an attempt to eliminate this oversight this paper concentrates on the extent of wage differences between black and white men in the rural South attributable to labor market discrimination

Undergraduate Public Health Education: Does it Meet Public Health Workforce Needs?

The professional bachelor’s degree [Bachelor of Public Health (BPH) or Bachelor of Science (BS) in Public Health] provides a cadre of trained individuals to fill entry-level positions in American public health agencies. The traditional Bachelors of Arts or Science degrees with majors in public health produce an informed citizenry, but may not provide sufficient public health course content to enable graduates of such programs to effectively enter the public health workforce

Undergraduate Public Health Education: Does it Meet Public Health Workforce Needs?

The professional bachelor’s degree [Bachelor of Public Health (BPH) or Bachelor of Science (BS) in Public Health] provides a cadre of trained individuals to fill entry-level positions in American public health agencies. The traditional Bachelors of Arts or Science degrees with majors in public health produce an informed citizenry, but may not provide sufficient public health course content to enable graduates of such programs to effectively enter the public health workforce

Regulation of Synthesis and Secretion of Pineal Hormonal Principles

Physiological Science

Metabolism of a tropical rainforest stream

Gradients in photosynthesis (P) and respiration (R) were measured on an unperturbed portion of the Rio Mameyes, a tropical stream in the Luquillo Experimental Forest, northeastern Puerto Rico. Rates of P, which were similar to those of streams in temperate-deciduous forests, were low in the heavily canopied headwaters (\u3c70 g O2 m−2 y−1) and were higher (453–634 g O2 m−2 y−1) in middle and lower reaches. Periphyton biomass did not show the expected increase as the canopy opened downstream, probably because of increasing herbivory in downstream reaches. Rates of R, which were much higher than in most temperate streams, also were lower in the headwaters (767 g O2 m−2 y−1) than in the middle and lower reaches (1550–1660 g O2 m−2 y−1). High rates of R and suppressed periphyton abundance caused annual P/R to be \u3c\u3c1 from headwaters to lower reaches. Results for the Rio Mameyes suggest that intense herbivory, which is favored by the presence of large herbivores and consistently high temperatures, may be more typical of tropical than temperate streams. Results also show that the tropical rainforest provides the stream with sufficient amounts of labile organic C to support high rates of respiration over long distances across the basin

The Solar-System-Scale Disk Around AB Aurigae

The young star AB Aurigae is surrounded by a complex combination of gas-rich and dust dominated structures. The inner disk which has not been studied previously at sufficient resolution and imaging dynamic range seems to contain very little gas inside a radius of least 130 astronomical units (AU) from the star. Using adaptive-optics coronagraphy and polarimetry we have imaged the dust in an annulus between 43 and 302 AU from the star, a region never seen before. An azimuthal gap in an annulus of dust at a radius of 102 AU, along with a clearing at closer radii inside this annulus, suggests the formation of at least one small body at an orbital distance of about 100 AU. This structure seems consistent with crude models of mean motion resonances, or accumulation of material at two of the Lagrange points relative to the putative object and the star. We also report a low significance detection of a point source in this outer annulus of dust. This source may be an overdensity in the disk due to dust accreting onto an unseen companion. An alternate interpretation suggests that the object's mass is between 5 and 37 times the mass of Jupiter. The results have implications for circumstellar disk dynamics and planet formation.Comment: 11 pages, 5 figures, accepted for publication in Astrophysical Journal, V. 680, June 10, 200

Preliminary Survey of Chemical Contaminants in Water, Sediment, and Aquatic Biota at Selected Sites in Northeastern Florida Bay and Canal C-111

Several actions are under way to alter water management capabilities and practices in south Florida in order to restore a more natural hydroperiod for the Everglades. Because relatively little research has been conducted on contaminants entering Florida Bay, we undertook a preliminary study in June 1995 to determine contaminant concentrations in surface water, sediment, and biota prior to major changes in water management. The areas studied were the C-111 canal (five sites) beginning just above water control structure S-197 and extending to Manatee Bay (part of the Biscayne Bay system), Shell Creek (three sites), the mouth of Taylor River, Trout Creek (two sites), and a site near the Key Largo Ranger Station. Hydrographic observations were made at each site, and samples of water and sediment were collected at each of the five areas except the Key Largo site. Bioresidues were determined for indigenous oysters collected from the C-111 canal and Shell Creek and for transplanted oysters exposed at the Key Largo site, the C-111 canal, Shell Creek, Taylor River, and Trout Creek for 5-29 days. Water samples were analyzed for selected organochlorine pesticides and metals; sediments were analyzed for the same compounds and for polycyclic aromatic hydrocarbons (PAHs). Fish filets and shucked oysters were analyzed for selected organochlorine pesticides, polychlorinated biphenyl (PCB) congeners, and metals. Other than low dissolved oxygen at some C-111 canal sites, water quality was generally good. Most contaminants were below water and sediment quality guidelines designed to protect aquatic life, and contaminant concentrations in oysters were low. Threshold effect levels were exceeded for some organochlorine pesticides and PAHs in some sediment samples, but all values measured were below probable effect levels. Low concentrations of organochlorine pesticides were detected in sediments from the C-111 canal, Shell Creek, Taylor River, and Trout Creek; except for Taylor River, low concentrations of PCB congeners and PAHs were detected from the same areas. The only organochlorine pesticide detected in filets from seven fish was 3.2 v-g DDE/kg (wet weight) in a sea catfish. Total mercury concentrations in filets of four species of fishes ranged from 0.53 to 1.3 μg/g, wet weight, which falls within a limited consumption advisory by the State of Florida