Bufo microscaphus

Number of Pages: 3Integrative BiologyGeological Science

Measuring the quantum efficiency of single radiating dipoles using a scanning mirror

Using scanning probe techniques, we show the controlled manipulation of the radiation from single dipoles. In one experiment we study the modification of the fluorescence lifetime of a single molecular dipole in front of a movable silver mirror. A second experiment demonstrates the changing plasmon spectrum of a gold nanoparticle in front of a dielectric mirror. Comparison of our data with theoretical models allows determination of the quantum efficiency of each radiating dipole.Comment: 4 pages, 4 figure

Evaluation of positive G sub Z tolerance following simulated weightlessness (bedrest)

The magnitude of physiologic changes which are known to occur in human subjects exposed to varying levels of + G sub Z acceleration following bed rest simulation of weightlessness was studied. Bed rest effects were documented by fluid and electrolyte balance studies, maximal exercise capability, 70 deg passive tilt and lower body negative pressure tests and the ability to endure randomly prescribed acceleration profiles of +2G sub Z, +3G sub Z, and +4G sub Z. Six healthy male volunteers were studied during two weeks of bed rest after adequate control observations, followed by two weeks of recovery, followed by a second two-week period of bed rest at which time an Air Force cutaway anti-G suit was used to determine its effectiveness as a countermeasure for observed cardiovascular changes during acceleration. Results showed uniform and significant changes in all measured parameters as a consequence of bed rest including a reduced ability to tolerate +G sub Z acceleration. The use of anti-G suits significantly improved subject tolerance to all G exposures and returned measured parameters such as heart rate and blood pressure towards or to pre-bed-rest (control) values in four of the six cases

Effect of cluster exposure, berry contact and cultivar on cuticular membrane formation and occurrence of bunch rot (Botrytis cinerea PERS.: FR.) with 3 Vitis vinifera L. cultivars

Leaf removal treatments were applied to Riesling during 1990 and 1991,and to Cabernet franc and Optima in 1991. Shaded and exposed clusters of Riesling were sampled prior to veraison and shaded and exposed clusters of all 3 cultivars were sampled prior to their respective harvest dates. Clusters were sampled to examine the effect of berry exposure, berry contact, time of sampling, and cultivar on cuticular membrane formation and the occurrence of bunch rot (Botrytis cinerea PERS.: FR.). Non-contact and contact cuticle proper and epicuticular wax berry samples were examined qualitatively using cryogenic scanning electron miscroscopy and quantitatively using enzymatic separation and chloroform extraction. Exposed Riesling samples had 18.6 and 35.0 % more epicuticular wax and cuticle proper respectively than shaded samples. Non-contact Riesling samples had 15.7 and 35.0 % more epicuticular wax and cuticle proper than contact samples, and although significant, epicuticular wax and cuticle proper weights of Riesling increased by only 5.7 and 4.5 % respectively, between veraison and harvest. Although exposed cuticular membrane samples from all 3 cultivars had more epicuticular wax and cuticle proper than shaded samples, large differences between cultivars were present. Clusters from the hand leaf removal (i.e. exposed) treatment of all 3 cultivars examined had significantly less bunch rot than clusters from the control (i.e. shaded). Cabernet franc was the most tolerant and Optima the most susceptible of the 3 cultivars to bunch rot. Time of sampling and differences between years also influenced the occurrence of bunch rot for Riesling with less rot present at veraison compared to harvest and less rot present at the 1990 compared to the 1991 harvest. Exposure, cultivar and level of contact within the cluster are all important factors in the cuticular membrane formation process and contribute greatly to determining the overall susceptibility of a grape cultivar to bunch rot when grown in a temperate climate

Kinetics of Phase Separation in Thin Films: Simulations for the Diffusive Case

We study the diffusion-driven kinetics of phase separation of a symmetric binary mixture (AB), confined in a thin-film geometry between two parallel walls. We consider cases where (a) both walls preferentially attract the same component (A), and (b) one wall attracts A and the other wall attracts B (with the same strength). We focus on the interplay of phase separation and wetting at the walls, which is referred to as {\it surface-directed spinodal decomposition} (SDSD). The formation of SDSD waves at the two surfaces, with wave-vectors oriented perpendicular to them, often results in a metastable layered state (also referred to as ``stratified morphology''). This state is reminiscent of the situation where the thin film is still in the one-phase region but the surfaces are completely wet, and hence coated with thick wetting layers. This metastable state decays by spinodal fluctuations and crosses over to an asymptotic growth regime characterized by the lateral coarsening of pancake-like domains. These pancakes may or may not be coated by precursors of wetting layers. We use Langevin simulations to study this crossover and the growth kinetics in the asymptotic coarsening regime.Comment: 39 pages, 19 figures, submitted to Phys.Rev.

Minimal size of a barchan dune

Barchans are dunes of high mobility which have a crescent shape and propagate under conditions of unidirectional wind. However, sand dunes only appear above a critical size, which scales with the saturation distance of the sand flux [P. Hersen, S. Douady, and B. Andreotti, Phys. Rev. Lett. {\bf{89,}} 264301 (2002); B. Andreotti, P. Claudin, and S. Douady, Eur. Phys. J. B {\bf{28,}} 321 (2002); G. Sauermann, K. Kroy, and H. J. Herrmann, Phys. Rev. E {\bf{64,}} 31305 (2001)]. It has been suggested by P. Hersen, S. Douady, and B. Andreotti, Phys. Rev. Lett. {\bf{89,}} 264301 (2002) that this flux fetch distance is itself constant. Indeed, this could not explain the proto size of barchan dunes, which often occur in coastal areas of high litoral drift, and the scale of dunes on Mars. In the present work, we show from three dimensional calculations of sand transport that the size and the shape of the minimal barchan dune depend on the wind friction speed and the sand flux on the area between dunes in a field. Our results explain the common appearance of barchans a few tens of centimeter high which are observed along coasts. Furthermore, we find that the rate at which grains enter saltation on Mars is one order of magnitude higher than on Earth, and is relevant to correctly obtain the minimal dune size on Mars.Comment: 11 pages, 10 figure

Alkali and Alkaline Earth Metal Compounds: Core-Valence Basis Sets and Importance of Subvalence Correlation

Core-valence basis sets for the alkali and alkaline earth metals Li, Be, Na, Mg, K, and Ca are proposed. The basis sets are validated by calculating spectroscopic constants of a variety of diatomic molecules involving these elements. Neglect of $(3s,3p)$ correlation in K and Ca compounds will lead to erratic results at best, and chemically nonsensical ones if chalcogens or halogens are present. The addition of low-exponent $p$ functions to the K and Ca basis sets is essential for smooth convergence of molecular properties. Inclusion of inner-shell correlation is important for accurate spectroscopic constants and binding energies of all the compounds. In basis set extrapolation/convergence calculations, the explicit inclusion of alkali and alkaline earth metal subvalence correlation at all steps is essential for K and Ca, strongly recommended for Na, and optional for Li and Mg, while in Be compounds, an additive treatment in a separate `core correlation' step is probably sufficient. Consideration of $(1s)$ inner-shell correlation energy in first-row elements requires inclusion of $(2s,2p)$ `deep core' correlation energy in K and Ca for consistency. The latter requires special CCV$n$Z `deep core correlation' basis sets. For compounds involving Ca bound to electronegative elements, additional $d$ functions in the basis set are strongly recommended. For optimal basis set convergence in such cases, we suggest the sequence CV(D+3d)Z, CV(T+2d)Z, CV(Q+$d$)Z, and CV5Z on calcium.Comment: Molecular Physics, in press (W. G. Richards issue); supplementary material (basis sets in G98 and MOLPRO formats) available at http://theochem.weizmann.ac.il/web/papers/group12.htm

Electron correlation in the second Landau level; a competition between many, nearly degenerate quantum phases

At a very low temperature of 9mK, electrons in the 2nd Landau level of an extremely high mobility two-dimensional electron system exhibit a very complex electronic behavior. With varying filling factor, quantum liquids of different origins compete with several insulating phases leading to an irregular pattern in the transport parameters. We observe a fully developed $\nu=2+2/5$ state separated from the even-denominator $\nu=2+1/2$ state by an insulating phase and a $\nu=2+2/7$ and $\nu=2+1/5$ state surrounded by such phases. A developing plateau at $\nu=2+3/8$ points to the existence of other even-denominator states

A Multicenter Study Of Students Sensitivity To Screen-Update Delay

In a climate of shrinking educational budgets, online learning courses offer many advantages; however there are several possible problems associated with electronic learning. There may be problems associated with learning style preferences, student apathy, instructional support, accessibility, and problems with technology. This paper examines a technological problem associated with the effects of screen-update-delay and student enjoyment, student self-reported comprehension, and student objective comprehension. In particular, this paper attempts to identify the point at which longer screen updates will be detrimental to the students enjoyment and/or have a significant negative impact on the students self-reported comprehension and retention of material