Ejecta types on Ganymede and Callisto

Ejecta types on Ganymede and Callisto have been identified from Voyager 1 and 2 images. Image resolution used range from approx. 0.6 to approx. 4 km/pxl, which allowed the surveying of almost all of the mappable surface of the two satellites. Seven ejecta classes were identified on Voyager images of Ganymede on the basis of albedo pattern and type of terminus. The ejecta of different terrains on ejecta characteristics were investigated for the most populated ejecta types. Two major ejecta types were identified on Callisto; both have counterparts on Ganymede. Type C1 has a uniformly high albedo and a sharp terminus. Type C2 has a gradational terminus and a moderate albedo. The similarity in ejecta types on Ganymede and Callisto may indicate similarities in the near surface environment of the two satellites, with different ejecta types representing several possible conditions for the impact environment

Director ties, board experience, and firm strategic outcomes : board experience effects on post-acquisition performance

The entire dissertation/thesis text is included in the research.pdf file; the official abstract appears in the short.pdf file (which also appears in the research.pdf); a non-technical general description, or public abstract, appears in the public.pdf file.Title from title screen of research.pdf file (viewed on August 1, 2007)Vita.Thesis (Ph. D.) University of Missouri-Columbia 2006.This study examines the effects of board experience on firm outcomes. Using the resource-based view of the firm in complement with agency theory and the resource dependence perspective, theory development links the past experience of outside directors' strategic experiences at their home firms with similar strategies pursued by the focal firm. Hypotheses test the effects on both short-term and long-term performance of outside directors' experience with acquisitions by their home firms of the entire assets of target firms. Results generally do not support the notion that acquiring firms benefit through positive post-acquisition performance from the past experience of their outside directors. However, significant results with respect to board international experience and the acquisition experience of the audit committee provide empirical support for the strategic importance of board experience and of board committees and for their potential impact on firm performance. Discussion of the results address limitations of the study and provide some direction for future investigation into the effects of board experience on firm strategic outcomes.Includes bibliographical reference

A Support Vector Machine for the Discrimination of MicroRNA Precursors from Other Genomic Hairpin Structures

Motivation: MicroRNAs (miRNAs) are endogenous, small (~ 20 nt), single-stranded, non-coding RNAs (ncRNAs) that result from the nuclear and cytoplasmic processing of transcribed precursor hairpin structures. They are increasingly recognized as playing crucial roles as post-transcriptional antisense regulators of gene expression through regulation of mRNA stability or translational efficiency. miRNAs, first reported in Caenorhabditis elegans, have been identified in the genomes of most higher organisms, including worms, flies, plants, mammals and recently in viruses. Functional studies have shown that miRNAs play important roles in processes such as, cell proliferation, fat metabolism, apoptosis, neuronal cell fate, insulin secretion, haematopoietic differentiation and developmental regulation. The detection of homologs of known miRNAs through comparative genomic approaches has proved relatively tractable. However, the ab-initio prediction of miRNA precursors through computational methods poses several additional difficulties, not least the fact that not all thermodynamically plausible transcribed hairpins are processed to yield mature miRNAs. It has not until now been possible to identify conserved sequence or structural elements that define consensus recognition elements for the enzymes that process miRNA precursors. In the light of these observations we wished to develop and improve methods for the discrimination of true miRNA precursor hairpins from spurious hairpins Methods: We have developed a SVM (Support Vector Machine) that considers up to 74 features associated with the primary and secondary structures and thermodynamic characteristics of candidate hairpin structures. We use a standard heuristic approach to optimize combinations of features used and train the SVM with sets of characterized hairpin miRNA precursors and known non-miRNA hairpins. Results: Our SVM shows highly promising results in the discrimination of true miRNA precursors from \u201cspurious\u201d hairpins (typically around 95% sensitivity) in various species. In particular, our levels of false positive predictions appear to be low relative to comparable methods

A New Kinematic Distance Estimator to the LMC

The distance to the Large Magellanic Cloud (LMC) can be directly determined by measuring three of its properties, its radial-velocity field, its mean proper motion, and the position angle \phi_ph of its photometric line of nodes. Statistical errors of 2% are feasible based on proper motions obtained with any of several proposed astrometry satellites, the first possibility being the Full-Sky Astrometric Mapping Explorer (FAME). The largest source of systematic error is likely to be in the determination of \phi_ph. I suggest two independent methods to measure \phi_ph, one based on counts of clump giants and the other on photometry of clump giants. I briefly discuss a variety of methods to test for other sources of systematic errors.Comment: submitted to ApJ, 13 page

Physico-electrochemical Characterization of Pluripotent Stem Cells during Self-Renewal or Differentiation by a Multi-modal Monitoring System.

Monitoring pluripotent stem cell behaviors (self-renewal and differentiation to specific lineages/phenotypes) is critical for a fundamental understanding of stem cell biology and their translational applications. In this study, a multi-modal stem cell monitoring system was developed to quantitatively characterize physico-electrochemical changes of the cells in real time, in relation to cellular activities during self-renewal or lineage-specific differentiation, in a non-destructive, label-free manner. The system was validated by measuring physical (mass) and electrochemical (impedance) changes in human induced pluripotent stem cells undergoing self-renewal, or subjected to mesendodermal or ectodermal differentiation, and correlating them to morphological (size, shape) and biochemical changes (gene/protein expression). An equivalent circuit model was used to further dissect the electrochemical (resistive and capacitive) contributions of distinctive cellular features. Overall, the combination of the physico-electrochemical measurements and electrical circuit modeling collectively offers a means to longitudinally quantify the states of stem cell self-renewal and differentiation

Towards an integrated pipeline for the in-silico prediction of plant microRNAs and their precursors

MicroRNAs (miRNAs) are endogenous, small (~ 20 nt), single-stranded, non-coding RNAs that result from the processing of transcribed precursor hairpin structures. They are increasingly recognized as playing crucial roles as post-transcriptional antisense regulators of gene expression through regulation of mRNA stability or translational efficiency. The detection of homologs of known miRNAs through comparative genomic approaches has proved relatively tractable. However, the ab-initio prediction of potentially lineage-specific miRNA precursors through computational methods poses several additional difficulties, not least the fact that not all thermodynamically plausible transcribed hairpins are processed to yield mature miRNAs. We have developed a Support Vector Machine that considers up to 78 features associated with the primary and secondary structures and thermodynamic characteristics of candidate hairpin structures. Our SVM is highly specific in the discrimination of true miRNA precursors from “spurious” hairpins with levels of false positive predictions that are low relative to comparable methods. We also show how our SVM functions as part of an in-silico pipeline for the prediction of novel miRNA precursors in plant genomes

Bionomics of the Spider Metaphidippus Galathea (Walckenaer) and Its Significance as a Biological Control Agent in Sorghum

Entomolog

The planets around NN Serpentis : still there

We present 25 new eclipse times of the white dwarf binary NN Ser taken with the high-speed camera ULTRACAM on the William Herschel Telescope and New Technology Telescope, the RISE camera on the Liverpool Telescope and HAWK-I on the Very Large Telescope to test the two-planet model proposed to explain variations in its eclipse times measured over the last 25 yr. The planetary model survives the test with flying colours, correctly predicting a progressive lag in eclipse times of 36 s that has set in since 2010 compared to the previous 8 yr of precise times. Allowing both orbits to be eccentric, we find orbital periods of 7.9 ± 0.5 and 15.3 ± 0.3 yr, and masses of 2.3 ± 0.5 and 7.3 ± 0.3 MJ. We also find dynamically long-lived orbits consistent with the data, associated with 2:1 and 5:2 period ratios. The data scatter by 0.07 s relative to the best-fitting model, by some margin the most precise of any of the proposed eclipsing compact object planet hosts. Despite the high precision, degeneracy in the orbit fits prevents a significant measurement of a period change of the binary and of N-body effects. Finally, we point out a major flaw with a previous dynamical stability analysis of NN Ser, and by extension, with a number of analyses of similar systems

Simulations of AGN feedback in galaxy clusters and groups: impact on gas fractions and the Lx-T scaling relation

Recently, rapid observational and theoretical progress has established that black holes (BHs) play a decisive role in the formation and evolution of individual galaxies as well as galaxy groups and clusters. In particular, there is compelling evidence that BHs vigorously interact with their surroundings in the central regions of galaxy clusters, indicating that any realistic model of cluster formation needs to account for these processes. This is also suggested by the failure of previous generations of hydrodynamical simulations without BH physics to simultaneously account for the paucity of strong cooling flows in clusters, the slope and amplitude of the observed cluster scaling relations, and the high-luminosity cut-off of central cluster galaxies. Here we use high-resolution cosmological simulations of a large cluster and group sample to study how BHs affect their host systems. We focus on two specific properties, the halo gas fraction and the X-ray luminosity-temperature scaling relation, both of which are notoriously difficult to reproduce in self-consistent hydrodynamical simulations. We show that BH feedback can solve both of these issues, bringing them in excellent agreement with observations, without alluding to the `cooling only' solution that produces unphysically bright central galaxies. By comparing a large sample of simulated AGN-heated clusters with observations, our new simulation technique should make it possible to reliably calibrate observational biases in cluster surveys, thereby enabling various high-precision cosmological studies of the dark matter and dark energy content of the universe.Comment: 4 pages, 2 figures, minor revisions, ApJL in pres