1,301 research outputs found
Protein sequence entropy is closely related to packing density and hydrophobicity
We investigated the correlation between the Shannon information entropy, âsequence entropyâ, with respect to the local flexibility of native globular proteins as described by inverse packing density. These are determined at each residue position for a total set of 130 query proteins, where sequence entropies are calculated from each set of aligned residues. For the accompanying aggregate set of 130 alignments, a strong linear correlation is observed between the calculated sequence entropy and the corresponding inverse packing density determined at an associated residue position. This region of linearity spans the range of Cα packing densities from 12 to 25 amino acids within a sphere of 9 Ă
radius. Three different hydrophobicity scales all mimic the behavior of the sequence entropies. This confirms the idea that the ability to accommodate mutations is strongly dependent on the available space and on the propensity for each amino acid type to be buried. Future applications of these types of methods may prove useful in identifying both core and flexible residues within a protein
Chandra Observations of the Optically Dark GRB030528
The X-ray-rich GRB030528 was detected by the HETE satellite and its
localization was rapidly disseminated. However, early optical observations
failed to detect a counterpart source. In a 2-epoch ToO observation with
Chandra, we discovered a fading X-ray source likely counterpart to GRB030528.
The source brightness was typical of X-ray afterglows observed at similar
epochs. Other observers detected an IR source at a location consistent with the
X-ray source. The X-ray spectrum is not consistent with a large absorbing
column.Comment: 4 pages, 1 figures, to appear in Santa Fe GRB Conference Proceedings,
200
Previously Claimed(/Unclaimed) X-ray Emission Lines in High Resolution Afterglow Spectra
We review the significance determination for emission lines in the Chandra
HETGS spectrum for GRB020813, and we report on a search for additional lines in
high resolution Chandra spectra. No previously unclaimed features are found. We
also discuss the significance of lines sets reportedly discovered using XMM
data for GRB011211 and GRB030227. We find that these features are likely of
modest, though not negligible, significance.Comment: 4 pages, 1 figures, to appear in Santa Fe GRB Conference Proceedings,
200
Optical and X-ray Observations of the Afterglow to XRF030723
The X-ray-flash XRF030723 was detected by the HETE satellite and rapidly
disseminated, allowing for an optical transient to be detected ~1 day after the
burst. We discuss observations in the optical with Magellan, which confirmed
the fade of the optical transient. In a 2-epoch ToO observation with Chandra,
we discovered a fading X-ray source spatially coincident with the optical
transient. We present spectral fits to the X-ray data. We also discuss the
possibility that the source underwent a rebrightening in the X-rays, as was
observed in the optical. We find that the significance of a possible
rebrightening is very low (~1 sigma).Comment: 4 pages, 2 figures, to appear in Santa Fe GRB Conference Proceedings,
200
Color-dependent learning in restrained africanized honey bees
Q2Q1Associative color learning has been demonstrated to be very poor using restrained European honey bees unless the antennae are amputated. Consequently, our understanding of proximate mechanisms in visual information processing is handicapped. Here we test learning performance of Africanized honey bees under restrained conditions with visual and olfactory stimulation using the proboscis extension response (PER) protocol. Restrained individuals were trained to learn an association between a color stimulus and a sugarâwater reward. We evaluated performance for âabsoluteâ learning (learned association between a stimulus and a reward) and âdiscriminantâ learning (discrimination between two stimuli). Restrained Africanized honey bees (AHBs) readily learned the association of color stimulus for both blue and green LED stimuli in absolute and discriminatory learning tasks within seven presentations, but not with violet as the rewarded color. Additionally, 24-h memory improved considerably during the discrimination task, compared with absolute association (15â55%). We found that antennal amputation was unnecessary and reduced performance in AHBs. Thus color learning can now be studied using the PER protocol with intact AHBs. This finding opens the way towards investigating visual and multimodal learning with application of neural techniques commonly used in restrained honey bees.https://scienti.minciencias.gov.co/cvlac/visualizador/generarCurriculoCv.do?cod_rh=0000002842Revista Nacional - Indexad
Assessment of studentsâ crisis communications skill increase based on classroom instruction and Second Lifeâą training
Crisis communication training and skill development are critical to ensure the sustainability of the agriculture industry. The purpose of this study was to assess studentsâ perceptions of knowledge, ability, and skills on select crisis-related skills, tasks, and activities in order to identify the potential effectiveness of a Second LifeTM (SL) simulation. Pre- and post-test data were collected to determine the potential changes in skill in the seven crisis communication constructs of (a) related knowledge; (b) mass, group, and intrapersonal communications; (c) contingency planning; (d) use of related supplies and tools; (e) identifying learning and training needs; (f) related areas of expertise; and (g) personality traits. Participants also identified their SL Performance Expectancy as it pertained to crisis communications training. Of the population of study (N = 15), 12 usable pairs (n = 12) were analyzed and described in the findings. Participants identified their current competency level in each of the crisis communication skill areas using a 6-point Likert-type scale that ranged from âno knowledge/experienceâ to âexpertâ. A grand mean was calculated for each construct with differences between pre- and post-test scores being examined. The resulting difference in each of the seven crisis communication constructs represented a large effect when comparing pre-test/post-test scores. Based on data, participants increased in knowledge, ability, and skills on associated items. Each item could be used to improve a communicatorâs ability to effectively manage a crisis. Virtual worlds appear to be an effective training mechanism and additional research should be focused in this area
Imaging and burst location with the EXIST high-energy telescope
The primary instrument of the proposed EXIST mission is a coded mask high
energy telescope (the HET), that must have a wide field of view and extremely
good sensitivity. It will be crucial to minimize systematic errors so that even
for very long total integration times the imaging performance is close to the
statistical photon limit. There is also a requirement to be able to reconstruct
images on-board in near real time in order to detect and localize gamma-ray
bursts. This must be done while the spacecraft is scanning the sky. The
scanning provides all-sky coverage and is key to reducing systematic errors.
The on-board computational problem is made even more challenging for EXIST by
the very large number of detector pixels. Numerous alternative designs for the
HET have been evaluated. The baseline concept adopted depends on a unique coded
mask with two spatial scales. Monte Carlo simulations and analytic analysis
techniques have been used to demonstrate the capabilities of the design and of
the proposed two-step burst localization procedure
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