Resistance Thermometer for Heat Transfer Measurements in a Shock Tube

This report describes a method for the application of the well-known principle of the resistance thermometer to the problem of measuring surface temperatures and heat transfer rates under highly transient conditions, such as are experienced in a shock tube. By using a thin platinum film sputtered on glass, a resistance thermometer gage is obtained which has a response lag of less than 1 µ sec, a linear output of 2-3 mv/°c, repeatability and durability. The gage preparation, including the sputtering technique, calibration method, and response characteristics are discussed, and some measurements of surface temperatures and heat transfer rates on models in the shock tube are presented in order to illustrate the performance that can be expected from this instrument

The distance upon contact: Determination from roughness profile

The point at which two random rough surfaces make contact takes place at the contact of the highest asperities. The distance upon contact d_0 in the limit of zero load has crucial importance for determination of dispersive forces. Using gold films as an example we demonstrate that for two parallel plates d_0 is a function of the nominal size of the contact area L and give a simple expression for d_0(L) via the surface roughness characteristics. In the case of a sphere of fixed radius R and a plate the scale dependence manifests itself as an additional uncertainty \delta d(L) in the separation, where the scale L is related with the separation d via the effective area of interaction L^2\sim\pi Rd. This uncertainty depends on the roughness of interacting bodies and disappears in the limit L\to \infty.Comment: 5 pages, 4 figures, to be published in PR

Body-assisted van der Waals interaction between two atoms

Using fourth-order perturbation theory, a general formula for the van der Waals potential of two neutral, unpolarized, ground-state atoms in the presence of an arbitrary arrangement of dispersing and absorbing magnetodielectric bodies is derived. The theory is applied to two atoms in bulk material and in front of a planar multilayer system, with special emphasis on the cases of a perfectly reflecting plate and a semi-infinite half space. It is demonstrated that the enhancement and reduction of the two-atom interaction due to the presence of a perfectly reflecting plate can be understood, at least in the nonretarded limit, by using the method of image charges. For the semi-infinite half space, both analytical and numerical results are presented.Comment: 17 pages, 9 figure

Single nucleotide polymorphisms for assessing genetic diversity in castor bean (Ricinus communis)

<p>Abstract</p> <p>Background</p> <p>Castor bean (<it>Ricinus communis</it>) is an agricultural crop and garden ornamental that is widely cultivated and has been introduced worldwide. Understanding population structure and the distribution of castor bean cultivars has been challenging because of limited genetic variability. We analyzed the population genetics of <it>R. communis </it>in a worldwide collection of plants from germplasm and from naturalized populations in Florida, U.S. To assess genetic diversity we conducted survey sequencing of the genomes of seven diverse cultivars and compared the data to a reference genome assembly of a widespread cultivar (Hale). We determined the population genetic structure of 676 samples using single nucleotide polymorphisms (SNPs) at 48 loci.</p> <p>Results</p> <p>Bayesian clustering indicated five main groups worldwide and a repeated pattern of mixed genotypes in most countries. High levels of population differentiation occurred between most populations but this structure was not geographically based. Most molecular variance occurred within populations (74%) followed by 22% among populations, and 4% among continents. Samples from naturalized populations in Florida indicated significant population structuring consistent with local demes. There was significant population differentiation for 56 of 78 comparisons in Florida (pairwise population ϕ_PTvalues, <it>p </it>< 0.01).</p> <p>Conclusion</p> <p>Low levels of genetic diversity and mixing of genotypes have led to minimal geographic structuring of castor bean populations worldwide. Relatively few lineages occur and these are widely distributed. Our approach of determining population genetic structure using SNPs from genome-wide comparisons constitutes a framework for high-throughput analyses of genetic diversity in plants, particularly in species with limited genetic diversity.</p

Anomalous density dependence of static friction in sand

We measured experimentally the static friction force $F_s$ on the surface of a glass rod immersed in dry sand. We observed that $F_s$ is extremely sensitive to the closeness of packing of grains. A linear increase of the grain-density yields to an exponentially increasing friction force. We also report on a novel periodicity of $F_s$ during gradual pulling out of the rod. Our observations demonstrate the central role of grain bridges and arches in the macroscopic properties of granular packings.Comment: plain tex, 6 pages, to appear in Phys.Rev.

Resistance Thermometer for Transient High-Temperature Studies

Current interest in ultra-high-speed flight has stimulated the development of the shock tube as a device for simulating high stagnation temperatures in supersonic flow. The main difficulty in these tests is the extremely short duration of uniform flow, of the order of 100-500 µsec. This time interval dictates extremely fast response of any measuring instrument applied to shock tube research

Elastic flexure controls magma trajectories and explains the offset of primary volcanic activity upstream of mantle plume axis at la Réunion and Hawaii hotspot islands

Surface volcanism at la Réunion and Hawaii occurs with an offset of 150–180 km upstream to the plume axis with respect to the plate motion. This striking observation raises questions about the forcing of plume-lithosphere thermo-mechanical interactions on melt trajectories beneath these islands. Based on visco-elasto-plastic numerical models handled at kilometric resolution, we propose to explain this offset by the development of compressional stresses at the base of the lithosphere, that result from elastic plate bending above the upward load exerted by the plume head. This horizontal compression adopts a disc shape centered around the plume axis: (i) it is 20 km thick, (ii) it has a 150 km radius, (iii) it lays at the base of the elastic part of the lithosphere, i.e., around ∼50–70 km depth where the temperature varies from ∼600 °C to ∼750 °C, (iv) it lasts for 5 to 10 My in an oceanic plate of age greater than 70 My, and (vi) it is controlled by the visco-elastic relaxation time at ∼50–70 km depth. This period of time exceeds the time during which both the Somalian/East-African and Pacific plates drift over the Reunion and Hawaii plumes, respectively. This indicates that this basal compression is actually a persistent feature. It is inferred that the buoyant melts percolating in the plume head pond below this zone of compression and eventually spread laterally until the most compressive principal elastic stresses reverse to the vertical, i.e., ∼150 km away from the plume head. There, melts propagate through dikes upwards to ∼35 km depth, where the plate curvature reverses and ambient compression diminishes. This 30–35 km depth may thus host a magmatic reservoir where melts transported by dykes pond. Only after further magmatic differentiation can dykes resume their ascension up to the surface and begin forming a volcanic edifice. As the volcano grows because of melt accumulation at the top of the plate, the lithosphere is flexed downwards, inducing extra tensile stress at 30–35 km depth and compression at ∼15 km depth (induced by the edifice load). It implies that now the melts pond at ∼15 km and form another magmatic reservoir lying just underneath the crust. These processes explain the ponding of primary (shield) melts at ∼35 km and ∼15 km depths as recorded below La Reunion, Mauritius or Hawaii volcanoes, all shifted by ∼150 km with respect to the plume axis

Insights into the role of DNA methylation in diatoms by genome-wide profiling in Phaeodactylum tricornutum

DNA cytosine methylation is a widely conserved epigenetic mark in eukaryotes that appears to have critical roles in the regulation of genome structure and transcription. Genome-wide methylation maps have so far only been established from the supergroups Archaeplastida and Unikont. Here we report the first whole-genome methylome from a stramenopile, the marine model diatom Phaeodactylum tricornutum. Around 6% of the genome is intermittently methylated in a mosaic pattern. We find extensive methylation in transposable elements. We also detect methylation in over 320 genes. Extensive gene methylation correlates strongly with transcriptional silencing and differential expression under specific conditions. By contrast, we find that genes with partial methylation tend to be constitutively expressed. These patterns contrast with those found previously in other eukaryotes. By going beyond plants, animals and fungi, this stramenopile methylome adds significantly to our understanding of the evolution of DNA methylation in eukaryotes.Fil: Veluchamy, Alaguraj. Institut de Biologie de l'École Normale Supérieure; FranciaFil: Lin, Xin. Institut de Biologie de l'École Normale Supérieure; Francia. Xiamen University; ChinaFil: Maumus, Florian.Fil: Rivarola, Maximo Lisandro.Fil: Bhavsar, Jaysheel.Fil: Creasy, Todd.Fil: O'Brien, Kimberly.Fil: Sengamalay, Naomi A..Fil: Tallon, Luke J..Fil: Smith, Andrew D..Fil: Rayko, Edda.Fil: Ahmed, Ikhlak.Fil: Crom, Stéphane Le.Fil: Farrant, Gregory K..Fil: Sgro, Jean-Yves.Fil: Olson, Sue A..Fil: Bondurant, Sandra Splinter.Fil: Allen, Andrew.Fil: Rabinowicz, Pablo D..Fil: Sussman, Michael R..Fil: Bowler, Chris.Fil: Tirichine, Leïla