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Search Results: 1 - 10 of 235017 matches for " George R. Hughes "
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Are Coastal Protected Areas Always Effective in Achieving Population Recovery for Nesting Sea Turtles?
Ronel Nel, André E. Punt, George R. Hughes
PLOS ONE , 2013, DOI: 10.1371/journal.pone.0063525
Abstract: Sea turtles are highly migratory and usually dispersed, but aggregate off beaches during the nesting season, rendering them vulnerable to coastal threats. Consequently, coastal Marine Protection Areas (MPAs) have been used to facilitate the recovery of turtle populations, but the effectiveness of these programs is uncertain as most have been operating for less than a single turtle generation (or<20 yr). South Africa, however, hosts one of the longest running conservation programs, protecting nesting loggerhead (Caretta caretta) and leatherback (Dermochelys coriacea) turtles since 1963 in a series of coastal MPAs. This provides a unique opportunity to evaluate the long-term effect of spatial protection on the abundance of two highly migratory turtle species with different life history characteristics. Population responses were assessed by modeling the number of nests over time in an index area (13 km) and an expanded monitoring area (53 km) with varying survey effort. Loggerhead abundance increased dramatically from~250 to>1700 nests pa (index area) especially over the last decade, while leatherback abundance increased initially~10 to 70 nests pa (index area), but then stabilized. Although leatherbacks have higher reproductive output per female and comparable remigration periods and hatching success to loggerheads, the leatherback population failed to expand. Our results suggest that coastal MPAs can work but do not guarantee the recovery of sea turtle populations as pressures change over time. Causes considered for the lack of population growth include factors in the MPA (expansion into unmonitored areas or incubation environment) of outside of the MPA (including carrying capacity and fishing mortality). Conservation areas for migratory species thus require careful design to account for species-specific needs, and need to be monitored to keep track of changing pressures.
Determining Photometric Metallicities of dSph Stellar Populations
Joanne Hughes,George Wallerstein
Physics , 2011,
Abstract: If there are so few upper red-giant branch stars in the SDSS-discovered dwarf galaxies, how can we find the true population structure without extensive spectroscopy? We review recent photometric and spectroscopic studies of the Ultra-Faint Dwarf Galaxies, and determine a new method of estimating [Fe/H] with a combination of Washington and Stromgren filters, using Bootes I dSph as an example. We can use the CT1by filters alone to achieve 0.3 dex resolution in [Fe/H], and 0.5 Gyr resolution in age. Both the Washington and Stromgren filters, C and v, are sensitive to CN-variations; however, in stars with a large deficiency of heavy elements the CN bands are weak and not important. The [Fe/H]-sensitivity of the Washington and Stromgren combination is at least twice as great as the SDSS filters, and this work maintains that resolution on the lower red-giant branch, where other calibrations fail.
Age and Metallicity Effects in Omega Centauri
Joanne Hughes,George Wallerstein
Physics , 1999,
Abstract: We have observed (with vby filters) a field north of the core of the most massive globular cluster in our galaxy, Omega Centauri. We have found a correlation of age and metallicity in a region which avoids the dense core and the inhomogeneous foreground dust emission shown by the IRAS satellite. Our observations show that the comparatively metal-rich stars (as defined by the (b-y) and m_1 colors) are younger than the metal-poor stars by at least 3 Gyr. This correlation of metallicity with age suggests that Omega Cen has enriched itself over a timescale of about 3 Gyr, and possibly longer. It is remarkable that ejecta from stellar winds combined with supernovae of type II failed to disperse the cluster's interstellar matter at an earlier epoch, but were captured by the cluster instead. Star formation would have ceased as type Ia supernovae dispersed the remaining interstellar matter. This work and other recent evidence suggests that Omega Cen could have been part of a small satellite galaxy in which all the activity occurred before it was captured by the Milky Way.
Fraser Syndrome: Two millennia of cryptophthalmos from Pliny the Elder to FRAS, FREM and GRIP: A historical perspective  [PDF]
George R. Fraser
Open Journal of Genetics (OJGen) , 2013, DOI: 10.4236/ojgen.2013.32A3001
Abstract:

From its first description in antiquity, the place of cryptophthalmos in the history of medical genetics is briefly set out until, in the twentieth century, this rare constellation of multiple congenital malformations of which cryptophthalmos is the most striking, even though not obligatory, component, was identified as an inherited autosomal recessive condition. It was given the name of Fraser syndrome and mutant alleles of the genes FRAS1, FREM2 and GRIP1 were identified as being responsible for a proportion of cases. In the remainder of cases, it may be supposed that mutant alleles of other genes, as yet unidentified, are responsible. In general, this association of multiple disparate malformations in an autosomal recessive condition may be expected to throw light on important aspects of gene action in embryogenesis. An aspect of medical genetics, which has become important with respect to the condition, is antenatal diagnosis with the prospect of abortion of affected fetuses.

Graphene as a tunable THz reservoir for shaping the Mollow triplet of an artificial atom via plasmonic effects
Ebrahim Forati,George W. Hanson,Stephen Hughes
Physics , 2014, DOI: 10.1103/PhysRevB.90.085414
Abstract: Using a realistic quantum master equation we show that the resonance fluorescence spectra of a two-level artificial atom (quantum dot) can be tuned by adjusting its photonic local density of states via biasing of one or more graphene monolayers. The structured photon reservoir is included using a photon Green function theory which fully accounts for the loss and dispersion. The field-driven Mollow triplet spectrum can be actively controlled by the graphene bias in the THz frequency regime. We also consider the effect of a dielectric support environment, and multiple graphene layers, on the emitted fluorescence. Finally, thermal bath effects are considered and shown to be important for low THz frequencies.
Photometric Observations of Omega Centauri: Multi-Wavelength Observations of Evolved Stars
Joanne Hughes,George Wallerstein,Floor van Leeuwen
Physics , 2001,
Abstract: We present multi-wavelength observations of the northern population of Omega Cen from the main-sequence turn-off to high on the red giant branch. We show that the best information about the metallicity and age of the stars can be gained from combining vby, B-I and V-I colors (in the absence of spectroscopy). We confirm our results for the main-sequence turn-off stars: there is at least a 3 Gyr age spread. We use proper motion studies to confirm cluster membership at and above the level of the horizontal branch, and we show that the age spread is maintained amongst stars from the subgiant branch through the red giants. The available evidence suggests that Omega Cen is the core of a disrupted dwarf galaxy.
Some ancient and recent observations on Hyaenas
Alun R. Hughes
Koedoe : African Protected Area Conservation and Science , 1958, DOI: 10.4102/koedoe.v1i1.868
Abstract: Some ancient and recent observations on Hyaenas
Commentary on “A Modest Proposal for a Basic Agreement on Peaceful Cross-Strait Development” by Chang Ya-chung
Christopher R. Hughes
Journal of Current Chinese Affairs , 2010,
Abstract: This critique assesses Prof. Chang Ya-chung’s draft basic agreement for cross-Strait relations by arguing that it overstates changes in Beijing’s Taiwan policy, which is based on a strategy that has not seen substantial change since it was devised in the early 1990s to prevent the island’s democratization leading to the exercise of self-determination. By over-estimating Taiwan’s political, diplomatic, military, and economic vulnerability the proposal unnecessarily narrows down Taibei’s options to the point where it has to accept Beijing’s one-China principle. This merely closes off other options that Taiwan can just as readily pursue, such as continuing to develop cross-Strait relations through ad hoc solutions to practical problems or seeking more imaginative ways to create a durable modus vivendi with international support. Even more problematic is that a political framework for stability based on the principles of Chinese nationalism is unlikely to be acceptable for Taiwan’s liberaldemocratic politics and could thus amount to an unnecessary risk that would lead to a less durable cross-Strait status quo than that which has been maintained over the last two decades.
5-HT2A Receptor Activation Normalizes Exaggerated Fear Behavior in p-Chlorophenylalanine (PCPA)-Treated Rats  [PDF]
Cathryn R. Hughes, Lee Tran, N. Bradley Keele
Journal of Behavioral and Brain Science (JBBS) , 2012, DOI: 10.4236/jbbs.2012.24053
Abstract: Deficits in serotonin (5-hydroxytryptamine, 5-HT) neurotransmission are implicated in abnormal emotional behaviors such as aggression, anxiety, and depression. However, the specific 5-HT receptor mechanisms involved are not well understood. The role of 5-HT2 receptors in fear potentiated startle, (FPS) was examined in rats chronically treated with pchlorophenylalanine (PCPA) to reduce brain 5-HT. PCPA-treated rats show an enhanced magnitude of FPS. Systemic administration of the 5-HT2 receptor agonist (±)-2,5-Dimethoxy-4-iodoamphetamine hydrochloride (DOI) reduced FPS in both PCPA-treated and saline (SAL)-treated control animals, normalizing the exaggerated fear response in PCPA-treated rats. In both SAL- and PCPA-treated animals, the DOI-induced reduction of learned fear was reversed by the 5-HT2 antagonist ketanserin, but not by the 5-HT2B/2C antagonist SB 206553. Together, these findings suggest 5-HT2A receptors are critical regulators of learned fear, and that 5-HT2A receptors may be an important pharmacological target to normalize exaggerated learned fear resulting from chronic 5-HT-ergic disruption.
G+C content dominates intrinsic nucleosome occupancy
Desiree Tillo, Timothy R Hughes
BMC Bioinformatics , 2009, DOI: 10.1186/1471-2105-10-442
Abstract: We find that a simple linear combination of only 14 simple DNA sequence attributes (G+C content, two transformations of dinucleotide composition, and the frequency of eleven 4-bp sequences) explains nucleosome occupancy in vitro and in vivo in a manner comparable to the Kaplan model. G+C content and frequency of AAAA are the most important features. G+C content is dominant, alone explaining ~50% of the variation in nucleosome occupancy in vitro.Our findings provide a dramatically simplified means to predict and understand intrinsic nucleosome occupancy. G+C content may dominate because it both reduces frequency of poly-A-like stretches and correlates with many other DNA structural characteristics. Since G+C content is enriched or depleted at many types of features in diverse eukaryotic genomes, our results suggest that variation in nucleotide composition may have a widespread and direct influence on chromatin structure.The genomes of eukaryotes are packaged into nucleosomes, comprised of approximately 147 base pairs of double-stranded DNA wrapped around an octamer of the highly conserved histone subunits[1]. Histones are the most abundant DNA binding proteins in the cell, and occupy ~80% of the yeast genome in vivo[2]. In the past few decades, it has become clear that the biological roles of nucleosomes extend far beyond simple DNA packaging, to include replication, DNA repair, recombination, and transcriptional regulation[3,4]. Active regulatory sequences are often depleted of nucleosomes[5-7], presumably due to steric hindrance constraints between nucleosomes and binding of most other DNA-binding proteins. The interplay between histones, DNA, and other DNA-binding proteins is therefore critical to the orchestration of transcription and other functions of the genome.In S. cerevisiae, studies examining the relative incorporation of yeast genomic DNA into nucleosomes in vitro have demonstrated that nucleosome depletion at promoters is to a large extent programmed int
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