Polarimetric variations of binary stars. II. Numerical simulations for circular and eccentric binaries in Mie scattering envelopes

We present numerical simulations of the periodic polarimetric variations produced by a binary star placed at the center of an empty spherical cavity inside a circumbinary ellipsoidal and optically thin envelope made of dust grains. Mie single-scattering is considered along with pre- and post-scattering extinction factors which produce a time-varying optical depth and affect the morphology of the periodic variations. We are interested in the effects that various parameters will have on the average polarization, the amplitude of the polarimetric variations, and the morphology of the variability. We show that the absolute amplitudes of the variations are smaller for Mie scattering than for Thomson scattering. Among the four grain types that we have studied, the highest polarizations are produced by grains with sizes in the range 0.1-0.2 micron. In general, the variations are seen twice per orbit. In some cases, because spherical dust grains have an asymmetric scattering function, the polarimetric curves produced also show variations seen once per orbit. Circumstellar disks produce polarimetric variations of greater amplitude than circumbinary envelopes. Another goal of these simulations is to see if the 1978 BME (Brown, McLean, & Emslie, ApJ, 68, 415) formalism, which uses a Fourier analysis of the polarimetric variations to find the orbital inclination for Thomson-scattering envelopes, can still be used for Mie scattering. We find that this is the case, if the amplitude of the variations is sufficient and the true inclinations is i_true > 45 deg. For eccentric orbits, the first-order coefficients of the Fourier fit, instead of second-order ones, can be used to find almost all inclinations.Comment: 23 pages, 5 figures, to be published in Astronomical Journa

Assessing the quantity of pulmonary edema in critically ill children

Measuring extravascular lung water may be useful for predicting outcome in adults with acute lung injury. The present commentary briefly reviews the potential role and limitations of extravascular lung water measurement in critically ill children

Comparison of Preparative Techniques for Scanning Electron Microscopy Examination of Soybean Seed Coats in Sectional View

Various scanning electron microscopy preparative techniques have been used by researchers to examine sectional views of dry, mature soybean (Glycine~ CL.) Merr.) seed coats. Such previously employed techniques were utilized In our preliminary investigations of seed coat structure, but often yielded unacceptable preservation. Consequently, eight preparative techniques were evaluated In an effort to define conditions required to obtain consistently high quality preservation of soybean seed coats In sectional view. Of the eight procedures tested with the cultivar Williams 82, razor sections and mechanical fractures of dry seed coats yielded the poorest definition of anatomical features. Samples soaked In water prior to preparation and those subjected to prolonged osmium fixation showed unacceptable alteration of the seed coat parenchyma. Best preservation was obtained with seed coats which were not subjected to chemical fixation, but which were sequentially dehydrated from 20% ethanol, cryofractured, and critical point dried. Results obtained via this protocol, with four additional soybean genotypes and cultivars, demonstrate Its applicability to comparative anatomical analysis

Influence of Deer Damage on Farmers\u27 Perceptions of Deer Population Trends: Important Implications for Managers

Farmers\u27 attitudes toward deer, their perceptions of deer depredations and their preferences for future deer population levels have been extensively studied in New York (Brown and Decker 1979; Brown et al. 1977a,1977b, 1978a,1978b, 1979,1980; Decker and Brown 1982; Decker et al. 1981a, 1981b). These studies have contributed to deer-population-management decisions that give consideration to farming interests. Nevertheless, farmers cannot be expected to support deer management efforts on their behalf if they do not understand the population changes such management is designed to achieve. Consequently, wildlife managers need to know whether or not the effects of such efforts are recognized. A direct indication of this, which had not been examined previously, is how well the farming community perceives changes in deer abundance over a reasonable period of time, say 5 years. Using data from the previous studies cited and a deer-population index, the authors sought an answer to the following question: Do farmers recognize managed increases or decreases in deer populations, or do they simply react to experience with deer damage

Dissecting eukaryotic translation and its control by ribosome density mapping

Translation of an mRNA is generally divided into three stages: initiation, elongation and termination. The relative rates of these steps determine both the number and position of ribosomes along the mRNA, but traditional velocity sedimentation assays for the translational status of mRNA determine only the number of bound ribosomes. We developed a procedure, termed Ribosome Density Mapping (RDM), that uses site-specific cleavage of polysomal mRNA followed by separation on a sucrose gradient and northern analysis, to determine the number of ribosomes associated with specified portions of a particular mRNA. This procedure allows us to test models for translation and its control, and to examine properties of individual steps of translation in vivo. We tested specific predictions from the current model for translational control of GCN4 expression in yeast and found that ribosomes were differentially associated with the uORFs elements and coding region under different growth conditions, consistent with this model. We also mapped ribosome density along the ORF of several mRNAs, to probe basic kinetic properties of translational steps in yeast. We found no detectable decline in ribosome density between the 5′ and 3′ ends of the ORFs, suggesting that the average processivity of elongation is very high. Conversely, there was no queue of ribosomes at the termination site, suggesting that termination is not very slow relative to elongation and initiation. Finally, the RDM results suggest that less frequent initiation of translation on mRNAs with longer ORFs is responsible for the inverse correlation between ORF length and ribosomal density that we observed in a global analysis of translation. These results provide new insights into eukaryotic translation in vivo

Turbulent Chemical Diffusion in Convectively Bounded Carbon Flames

It has been proposed that mixing induced by convective overshoot can disrupt the inward propagation of carbon deflagrations in super-asymptotic giant branch stars. To test this theory, we study an idealized model of convectively bounded carbon flames with 3D hydrodynamic simulations of the Boussinesq equations using the pseudospectral code Dedalus. Because the flame propagation timescale is much longer than the convection timescale, we approximate the flame as fixed in space, and only consider its effects on the buoyancy of the fluid. By evolving a passive scalar field, we derive a {\it turbulent} chemical diffusivity produced by the convection as a function of height, $D_{\rm t}(z)$. Convection can stall a flame if the chemical mixing timescale, set by the turbulent chemical diffusivity, $D_{\rm t}$, is shorter than the flame propagation timescale, set by the thermal diffusivity, $\kappa$, i.e., when $D_{\rm t}>\kappa$. However, we find $D_{\rm t}<\kappa$ for most of the flame because convective plumes are not dense enough to penetrate into the flame. Extrapolating to realistic stellar conditions, this implies that convective mixing cannot stall a carbon flame and that "hybrid carbon-oxygen-neon" white dwarfs are not a typical product of stellar evolution.Comment: Accepted to Ap

Accounting Hall of Fame 2000 induction: Shaun F. O\u27Malley

For the induction of Shaun f. O\u27Malley: Remarks by Robert L. Brown, PricewaterhouseCoopers; Citation prepared by Daniel L. Jensen, The Ohio State University, read by Robert L. Brown, PricewaterhouseCoopers; Response by Shaun f. O\u27Malley, PricewaterhouseCooper