Internal Flows in Free Drops (IFFD)

Within the framework of an Earth-based research task investigating the internal flows within freely levitated drops, a low-gravity technology development experiment has been designed and carried out within the NASA Glovebox facility during the STS-83 and STS-94 Shuttle flights (MSL-1 mission). The goal was narrowly defined as the assessment of the capabilities of a resonant single-axis ultrasonic levitator to stably position free drops in the Shuttle environment with a precision required for the detailed measurement of internal flows. The results of this entirely crew-operated investigation indicate that the approach is fundamentally sound, but also that the ultimate stability of the positioning is highly dependent on the residual acceleration characteristic of the Spacecraft, and to a certain extent, on the initial drop deployment of the drop. The principal results are: the measured dependence of the residual drop rotation and equilibrium drop shape on the ultrasonic power level, the experimental evaluation of the typical drop translational stability in a realistic low-gravity environment, and the semi-quantitative evaluation of background internal flows within quasi-isothermal drops. Based on these results, we conclude that the successful design of a full-scale Microgravity experiment is possible, and would allow accurate the measurement of thermocapillary flows within transparent drops. The need has been demonstrated, however, for the capability for accurately deploying the drop, for a quiescent environment, and for precise mechanical adjustments of the levitator

Resolving the Azimuthal Ambiguity in Vector Magnetogram Data with the Divergence-Free Condition: Application to Discrete Data

We investigate how the divergence-free property of magnetic fields can be exploited to resolve the azimuthal ambiguity present in solar vector magnetogram data, by using line-of-sight and horizontal heliographic derivative information as approximated from discrete measurements. Using synthetic data we test several methods that each make different assumptions about how the divergence-free property can be used to resolve the ambiguity. We find that the most robust algorithm involves the minimisation of the absolute value of the divergence summed over the entire field of view. Away from disk centre this method requires the sign and magnitude of the line-of-sight derivatives of all three components of the magnetic field vector.Comment: Solar Physics, in press, 20 pages, 11 figure

Isolation and characterization of novel microsatellite markers and their application for diversity assessment in cultivated groundnut (Arachis hypogaea)

<p>Abstract</p> <p>Background</p> <p>Cultivated peanut or groundnut (<it>Arachis hypogaea </it>L.) is the fourth most important oilseed crop in the world, grown mainly in tropical, subtropical and warm temperate climates. Due to its origin through a single and recent polyploidization event, followed by successive selection during breeding efforts, cultivated groundnut has a limited genetic background. In such species, microsatellite or simple sequence repeat (SSR) markers are very informative and useful for breeding applications. The low level of polymorphism in cultivated germplasm, however, warrants a need of larger number of polymorphic microsatellite markers for cultivated groundnut.</p> <p>Results</p> <p>A microsatellite-enriched library was constructed from the genotype TMV2. Sequencing of 720 putative SSR-positive clones from a total of 3,072 provided 490 SSRs. 71.2% of these SSRs were perfect type, 13.1% were imperfect and 15.7% were compound. Among these SSRs, the GT/CA repeat motifs were the most common (37.6%) followed by GA/CT repeat motifs (25.9%). The primer pairs could be designed for a total of 170 SSRs and were optimized initially on two genotypes. 104 (61.2%) primer pairs yielded scorable amplicon and 46 (44.2%) primers showed polymorphism among 32 cultivated groundnut genotypes. The polymorphic SSR markers detected 2 to 5 alleles with an average of 2.44 per locus. The polymorphic information content (PIC) value for these markers varied from 0.12 to 0.75 with an average of 0.46. Based on 112 alleles obtained by 46 markers, a phenogram was constructed to understand the relationships among the 32 genotypes. Majority of the genotypes representing subspecies <it>hypogaea </it>were grouped together in one cluster, while the genotypes belonging to subspecies <it>fastigiata </it>were grouped mainly under two clusters.</p> <p>Conclusion</p> <p>Newly developed set of 104 markers extends the repertoire of SSR markers for cultivated groundnut. These markers showed a good level of PIC value in cultivated germplasm and therefore would be very useful for germplasm analysis, linkage mapping, diversity studies and phylogenetic relationships in cultivated groundnut as well as related <it>Arachis </it>species.</p

A variational problem on Stiefel manifolds

In their paper on discrete analogues of some classical systems such as the rigid body and the geodesic flow on an ellipsoid, Moser and Veselov introduced their analysis in the general context of flows on Stiefel manifolds. We consider here a general class of continuous time, quadratic cost, optimal control problems on Stiefel manifolds, which in the extreme dimensions again yield these classical physical geodesic flows. We have already shown that this optimal control setting gives a new symmetric representation of the rigid body flow and in this paper we extend this representation to the geodesic flow on the ellipsoid and the more general Stiefel manifold case. The metric we choose on the Stiefel manifolds is the same as that used in the symmetric representation of the rigid body flow and that used by Moser and Veselov. In the extreme cases of the ellipsoid and the rigid body, the geodesic flows are known to be integrable. We obtain the extremal flows using both variational and optimal control approaches and elucidate the structure of the flows on general Stiefel manifolds.Comment: 30 page

Efficient use of crop germplasm resources: identifying useful germplasm for crop improvement through core and mini-core collections and molecular marker approaches

Conservation of crop germplasm diversity involves the establishment of in situ and ex situ genebanks. The major activities for ex situ genebanks include assembling, conserving, characterizing and providing easy access to germplasm for scientists. More than six million accessions are currently assembled in over 1300 genebanks worldwide. ICRISAT is one of the 15 CGIAR centres, with headquarters at Patancheru, India, and conserves genetic resources of sorghum, pearl millet, chickpea, pigeonpea, groundnut, and six small millets. The ICRISAT genebank holds 114,870 accessions from 130 countries, including both archival materials from various organizations throughout the world, and from fresh collections resulting from 213 missions in 62 countries. The ICRISAT genebank supplies annually over 40,000 germplasm samples to scientists worldwide. Sixty-six varieties selected from the basic germplasm have been released for cultivation in 44 countries, and ICRISAT has restored/repatriated crop germplasm to eight countries. The research focus is on germplasm diversity assessment, developing core and mini-core collections, and using a molecular characterization approach to both enhance the utilization of germplasm in research and improve the efficiency of germplasm management. Following these approaches, we have been able to identify a significant number of accessions with traits potentially relevant for crop improvement

NEXUS/Physics: An interdisciplinary repurposing of physics for biologists

In response to increasing calls for the reform of the undergraduate science curriculum for life science majors and pre-medical students (Bio2010, Scientific Foundations for Future Physicians, Vision & Change), an interdisciplinary team has created NEXUS/Physics: a repurposing of an introductory physics curriculum for the life sciences. The curriculum interacts strongly and supportively with introductory biology and chemistry courses taken by life sciences students, with the goal of helping students build general, multi-discipline scientific competencies. In order to do this, our two-semester NEXUS/Physics course sequence is positioned as a second year course so students will have had some exposure to basic concepts in biology and chemistry. NEXUS/Physics stresses interdisciplinary examples and the content differs markedly from traditional introductory physics to facilitate this. It extends the discussion of energy to include interatomic potentials and chemical reactions, the discussion of thermodynamics to include enthalpy and Gibbs free energy, and includes a serious discussion of random vs. coherent motion including diffusion. The development of instructional materials is coordinated with careful education research. Both the new content and the results of the research are described in a series of papers for which this paper serves as an overview and context.Comment: 12 page

Tunneling through a multigrain system: deducing the sample topology from the nonlinear conductance

We study a current transport through a system of a few grains connected with tunneling links. The exact solution is given for an arbitrarily connected double-grain system with a shared gate in the framework of the orthodox model. The obtained result is generalized for multigrain systems with strongly different tunneling resistances. We analyse the large-scale nonlinear conductance and demonstrate how the sample topology can be unambiguously deduced from the spectroscopy pattern (differential conductance versus gate-bias plot). We present experimental data for a multigrain sample and reconstruct the sample topology. A simple selection rule is formulated to distinguish samples with spectral patterns free from spurious disturbance caused by recharging of some grains nearby. As an example, we demonstrate experimental data with additional peaks in the spectroscopy pattern, which can not be attributed to coupling to additional grains. The described approach can be used to judge the sample topology when it is not guaranteed by fabrication and direct imaging is not possible.Comment: 13 pages (including 8 figures

Correlation and symmetry effects in transport through an artificial molecule

Spectral weights and current-voltage characteristics of an artificial diatomic molecule are calculated, considering cases where the dots connected in series are in general different. The spectral weights allow us to understand the effects of correlations, their connection with selection rules for transport, and the role of excited states in the experimental conductance spectra of these coupled double dot systems (DDS). An extended Hubbard Hamiltonian with varying interdot tunneling strength is used as a model, incorporating quantum confinement in the DDS, interdot tunneling as well as intra- and interdot Coulomb interactions. We find that interdot tunneling values determine to a great extent the resulting eigenstates and corresponding spectral weights. Details of the state correlations strongly suppress most of the possible conduction channels, giving rise to effective selection rules for conductance through the molecule. Most states are found to make insignificant contributions to the total current for finite biases. We find also that the symmetry of the structure is reflected in the I-V characteristics, and is in qualitative agreement with experiment.Comment: 25 figure files - REVTEX - submitted to PR

Separation of v-Src-induced mitogenesis and morphological transformation by inhibition of AP-1

v-Src activity results in both morphological transformation and reentry of quiescent chick embryo fibroblasts (CEF) into cell cycle. We have previously used temperature-sensitive v-Src mutants to show that enhanced activity of cellular AP-1 in the first few hours after activation of v-Src invariably precedes the biological consequences. Here we have investigated whether the early activation of AP-1 is essential for any or all of the v-Src responses by using a mutant c-Fos that comprises the leucine zipper and a disrupted basic region. Expression of the c-Fos mutant partially reduced cellular AP-1 activity in exponentially growing cells. However, in CEF that had been made quiescent by serum deprivation, v-Src-induced stimulation of AP-1 DNA binding activity was substantially reduced. In addition, quiescent CEF stably transfected with this mutant show an impaired mitogenic response to v-Src, indicating that the AP-1 stimulation is a necessary prerequisite for cell-cycle reentry. The ability of v-Src to morphologically transform quiescent CEF was not impaired by the inhibition of AP-1 stimulation, indicating that the mitogenic and morphological consequences of v-Src have distinguishable biochemical mediators. Focal adhesion kinase, a recently identified determinant of cell morphology, undergoes a gel mobility shift, characteristic of its hyperphosphorylated state, in response to v-Src activation in cells expressing the inhibitory AP-1 protein. This provides further evidence that the pathways that regulate morphological transformation are independent of AP-1