1,666 research outputs found
Software Management Environment (SME) release 9.4 user reference material
This document contains user reference material for the Software Management Environment (SME) prototype, developed for the Systems Development Branch (Code 552) of the Flight Dynamics Division (FDD) of Goddard Space Flight Center (GSFC). The SME provides an integrated set of management tools that can be used by software development managers in their day-to-day management and planning activities. This document provides an overview of the SME, a description of all functions, and detailed instructions concerning the software's installation and use
RFX2 is a candidate downstream amplifier of A-MYB regulation in mouse spermatogenesis
<p>Abstract</p> <p>Background</p> <p>Mammalian spermatogenesis involves formation of haploid cells from the male germline and then a complex morphological transformation to generate motile sperm. Focusing on meiotic prophase, some tissue-specific transcription factors are known (A-MYB) or suspected (RFX2) to play important roles in modulating gene expression in pachytene spermatocytes. The current work was initiated to identify both downstream and upstream regulatory connections for <it>Rfx2</it>.</p> <p>Results</p> <p>Searches of pachytene up-regulated genes identified high affinity RFX binding sites (X boxes) in promoter regions of several new genes: <it>Adam5</it>, <it>Pdcl2</it>, and <it>Spag6</it>. We confirmed a strong promoter-region X-box for <it>Alf</it>, a germ cell-specific variant of general transcription factor TFIIA. Using <it>Alf </it>as an example of a target gene, we showed that its promoter is stimulated by RFX2 in transfected cells and used ChIP analysis to show that the promoter is occupied by RFX2 in vivo. Turning to upstream regulation of the <it>Rfx2 </it>promoter, we identified a cluster of three binding sites (MBS) for the MYB family of transcription factors. Because testis is one of the few sites of <it>A-myb </it>expression, and because spermatogenesis arrests in pachytene in <it>A-myb </it>knockout mice, the MBS cluster implicates <it>Rfx2 </it>as an <it>A-myb </it>target. Electrophoretic gel-shift, ChIP, and co-transfection assays all support a role for these MYB sites in <it>Rfx2 </it>expression. Further, <it>Rfx2 </it>expression was virtually eliminated in <it>A-myb </it>knockout testes. Immunohistology on testis sections showed that A-MYB expression is up-regulated only after pachytene spermatocytes have clearly moved away from the tubule wall, which correlates with onset of RFX2 expression, whereas B-MYB expression, by contrast, is prevalent only in earlier spermatocytes and spermatogonia.</p> <p>Conclusion</p> <p>With an expanding list of likely target genes, RFX2 is potentially an important transcriptional regulator in pachytene spermatocytes. <it>Rfx2 </it>itself is a good candidate to be regulated by A-MYB, which is essential for meiotic progression. If <it>Alf </it>is a genuine RFX2 target, then <it>A-myb</it>, <it>Rfx2</it>, and <it>Alf </it>may form part of a transcriptional network that is vital for completion of meiosis and preparation for post-meiotic differentiation.</p
TeV Gamma Rays from Geminga and the Origin of the GeV Positron Excess
The Geminga pulsar has long been one of the most intriguing MeV-GeV gamma-ray
point sources. We examine the implications of the recent Milagro detection of
extended, multi-TeV gamma-ray emission from Geminga, finding that this reveals
the existence of an ancient, powerful cosmic-ray accelerator that can plausibly
account for the multi-GeV positron excess that has evaded explanation. We
explore a number of testable predictions for gamma-ray and electron/positron
experiments (up to ~100 TeV) that can confirm the first "direct" detection of a
cosmic-ray source.Comment: 4 pages and 3 figures; Minor revisions, accepted for publication in
Physical Review Letter
A Survey About Nothing: Monitoring a Million Supergiants for Failed Supernovae
Extragalactic transient searches have historically been limited to looking
for the appearance of new sources such as supernovae. It is now possible to
carry out a new kind of survey that will do the opposite, that is, search for
the disappearance of massive stars. This will entail the systematic observation
of galaxies within a distance of 10 Mpc in order to watch ~10^6 supergiants.
Reaching this critical number ensures that something will occur yearly, since
these massive stars must end their lives with a core collapse within ~10^6
years. Using deep imaging and image subtraction it is possible to determine the
fates of these stars whether they end with a bang (supernova) or a whimper
(fall out of sight). Such a survey would place completely new limits on the
total rate of all core collapses, which is critical for determining the
validity of supernova models. It would also determine the properties of
supernova progenitors, better characterize poorly understood optical
transients, such as eta Carina-like mass ejections, find and characterize large
numbers of Cepheids, luminous blue variables and eclipsing binaries, and allow
the discovery of any new phenomena that inhabit this relatively unexplored
parameter space.Comment: final version, 7 pages, 5 figures, ApJ in pres
An Unexpectedly Swift Rise in the Gamma-ray Burst Rate
The association of long gamma-ray bursts with supernovae naturally suggests
that the cosmic GRB rate should trace the star formation history. Finding
otherwise would provide important clues concerning these rare, curious
phenomena. Using a new estimate of Swift GRB energetics to construct a sample
of 36 luminous GRBs with redshifts in the range z=0-4, we find evidence of
enhanced evolution in the GRB rate, with ~4 times as many GRBs observed at z~4
than expected from star formation measurements. This direct and empirical
demonstration of needed additional evolution is a new result. It is consistent
with theoretical expectations from metallicity effects, but other causes remain
possible, and we consider them systematically.Comment: 4 pages, 4 figures; minor changes to agree with published versio
Characteristics and Motivational Factors of Effective Extension Advisory Leaders: Implications for Building Strong Extension Advisory Councils
The purpose of this study was to determine the characteristics and motivational factors of effective Extension advisory leaders. This Delphi study was conducted with a selected group of County Extension Directors and a group of Extension State Advisory Leaders. The study identified 10 characteristics that distinguish an effective Extension advisory leader. Some of these characteristics are explicit and easy to observe, while others are implicit and difficult to directly observe. Therefore, it is practical to use directly observable characteristics of effective advisory leaders when selecting volunteers. Once potential volunteers are spotted in the community, implicit characteristics of effective advisory leaders should be used to further screen them before they are selected. The study also identified the eight most important factors motivating individuals to volunteer as effective advisory leaders. Understanding these motivational factors is helpful for creating an environment for attracting and retaining effective volunteers. Understanding their motivation for volunteer work and creating an environment for them to meet the motivating factors for volunteering will lead to volunteer satisfaction and retention. The findings of this study can be used to build strong Extension advisory councils
Identification of Current Proficiency Level of Extension Competencies and the Competencies Needed for Extension Agents to Be Successful in the 21st Century
In this era of globalization, competency is an issue of concern to any field of professionals and their clients. Competency is an integrated set of skills, knowledge, and attitudes that allow one to effectively carry out the activities of a given work to the standards expected in the employment context. The purpose of this descriptive survey study was to determine the current proficiency level of North Carolina Cooperative Extension agents’ competencies and the other competencies they need to develop to be successful in Cooperative Extension. Findings indicate that the current proficiency level of competency for Extension agents in North Carolina Cooperative Extension varies from moderate to high in all 42 items listed in the survey. Multiple regression analysis confirmed that Extension agents’ years of Extension experience and age were major determinants of their overall proficiency level. Extension agents’ proficiency levels did not vary with gender, level of education, professional association affiliation, job position, or area of job responsibility. The research revealed that emotional intelligence, interpersonal skills, flexibility for adapting to changing environments, and ability to manage resources were the most significant other competencies needed for Extension agents to be successful in current context
Mathematical Formulations of Hebbian Learning
Several formulations of correlation-based Hebbian learning are reviewed. On the presynaptic side, activity is described either by a firing rate or by presynaptic spike arrival. The state of the postsynaptic neuron can be described by its membrane potential, its firing rate, or the timing of backpropagating action potentials (BPAPs). It is shown that all of the above formulations can be derived from the point of view of an expansion. In the absence of BPAPs potentials, it is natural to correlate presynaptic spikes with the postsynaptic membrane potential. Time windows of spike time dependent plasticity arise naturally, if the timing of postsynaptic spikes is available at the site of the synapse as it is the case in the presence of BPAPs. With an appropriate choice of parameters, Hebbian synaptic plasticity has intrinsic normalization properties that stabilizes postsynaptic firing rates and leads to subtractive weight normalization
A reduced version of the NMC DERF 2 data set
The National Meterological Center (NMC) Dynamical Extended Range Forecast (DERF 2) data represents a major computational effort to better ascertain the potential for extended range forecasts and to develop a strategy for performing operational extended range forecasts using dynamical models. A major stumbling block for using this data has been the sheer volume of data that must be processed to perform even simple calculations. The product of the data reduction described is a manageable data set that fits comfortably on five magnetic tapes or on one compact disc. The document outlines the data reduction process of the second phase of DERF data. It contains the description of the fields and the resolution of both the original and final fields. In order to assist the users of this data set, maps of selected fields, using both the original truncation at rhomboidal 30 and the truncation of the final data at triangular 20, are displayed
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