Search

1. In pregnant rabbits near term, cardiac output and its distribution were measured by injection of isotope-labelled microspheres into the left ventricle. Hypoxaemia (mean Pa,O2 35 mm Hg) caused a reduction in placental and renal flows, while myometrial flow was unchanged and coronary and cerebral blood flows increased. 2. In the lateral (ovarian) end of the uterine horn foetal and placental weight and absolute maternal placental blood flow were greater than in intermediate or medial positions. Placental flow (per 100 g placental tissue) was most in the most lateral placenta and decreased in the intermediate positions, especially when there were many placentas in the same horn. 3. Abortions and runts (more than 2 S.D. below the mean weight for their age) occurred most often in the medial end of the uterine horn, while oversize foetuses (more than 2 S.D. above the mean weight) usually occupied the most lateral position. 4. Ovarian blood flow (460 ml./100 g. min) was relatively large (e.g. compared with renal flow, 275 ml./100 g.min).

Lower absorption, lower refractive index and tunable resistance are three advantages of doped silicon oxide containing nanocrystalline silicon grains (nc-SiOx) compared to doped microcrystalline silicon, for the use as p- and n-type layers in thin-film silicon solar cells. In this study we show how optical, electrical and microstructural properties of nc-SiOx layers depend on precursor gas ratios and we propose a growth model to explain the phase separation in such films into Si-rich and O-rich regions as visualized by energy-filtered transmission electron microscopy. INTRODUCTION

Optical measurements made at the Arecibo Observatory during the 1987 heating campaign showed large temporal and spatial variations in 630.0-nm airglow enhancements during times of continuous power transmissions of high-power radio waves. Photometric data displayed fluctuations of 60 R or more in the red-line (630.0 nm) emission from atomic oxygen. These fluctuations were associated with heater-induced cavities which drifted and evolved in the modified ionosphere. Data from the Arecibo incoherent scatter radar were used in conjunction with airglow images to provide a physical interpretation of the modification process. Electrons were accelerated by large amplitude Langmuir waves excited by parametric decay instabilities occurring near the wave reflection points inside the density cavities. Inelastic collisions with oxygen atoms produced excited states which yielded enhanced 630.0-nm and 557.7-nm emissions. A numerical model has been used to relate the enhanced airglow intensities to the energy spectrum of the accelerated electrons. The measured airglow could have been produced by an isotropic source at 340 km altitude that accelerated 0.01% of the ambient electrons into a suprathermal Maxwellian distribution with a temperature of 2.05 eV. Experimental and theoretical studies suggest that airglow clouds were directly coupled to plasma density cavities because (1) these cavities trapped themore » HF radio beam and (2) electrons accelerated out into regions of reduced plasma concentration were less effectively thermalized and, consequently, were more effective for collisional excitation of neutral species.« less

Briefly describes a variety of minicourses designed to acquaint students with practical applications of chemistry in everyday experiences.

Measurements of transmittance through dust and debris clouds generated by explosions and moving vehicles from five field tests involving 120 trials were analyzed to determine the degree to which transmittance is wavelength dependent. Statistical tests to determine whether the amounts of time transmittance were reduced to specified levels that were significantly different for various wavelengths revealed, in general, no consistent wavelength dependence. Relationships between the extinction coefficient for IR spectral and visible regions have been established for specific explosive types and soil conditions involved in some of these tests.

The use of the pulse edge analysis technique to explain ionospheric modifications caused by high-power HF radio waves is discussed. The technique, implemented at the Arecibo Observatory, uses long radar pulses and very rapid data sampling. A comparison of the pulse leading and trailing edge characteristics is obtained and the comparison is used to estimate the relative changes in the interaction region height and layer width; an example utilizing this technique is provided. Main plasma line overshoot and miniovershoot were studied from the pulse edge observations; the observations at various HF pulsings and radar resolutions are graphically presented. From the pulse edge data the development and the occurrence of main plasma line overshoot and miniovershoot are explained. The theories of soliton formation and collapse, wave ducting, profile modification, and parametric instabilities are examined as a means of explaining main plasma line overshoots and miniovershoots.