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Search Results: 1 - 10 of 288779 matches for " W. R. Howard "
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Maternal and infant vitamin D status during lactation: Is latitude important?  [PDF]
Carol L. Wagner, Cynthia R. Howard, Thomas C. Hulsey, Ruth A. Lawrence, Myla Ebeling, Judy Shary, Pamela G. Smith, Kristen Morella, Sarah N. Taylor, Bruce W. Hollis
Health (Health) , 2013, DOI: 10.4236/health.2013.512271
Abstract:

Background: The effect of latitude on maternal and infant vitamin D status during lactation is presumed to be strongly associated with higher rates of deficiency in those living at higher latitudes, yet with lifestyle changes, this conclusion may no longer be correct. Objective: To ascertain if higher latitude adversely affects the vitamin D status of lactating women and their fully breastfeeding infants. Study Design/Methods: Fully breastfeeding women and their infants were eligible for participation in this study as part of a larger prospective vitamin D supplementation trial. Women were recruited from two sites of differing latitude: Charleston, SC at 32°N and Rochester, NY at latitude 43°N. Maternal and infant baseline vitamin D status, intact parathyroid hormone (IPTH), serum calcium and phosphorus as a function of site/latitude were measured. The primary outcome was maternal and infant total circulating 25(OH)D at baseline by center/latitude, and the secondary outcome was the percent of women and infants who had achieved a baseline concentration of at least 20 ng/mL, meeting the Institute of Medicine’s definition of sufficiency at 4 to 6 weeks postpartum. Statistical analysis was performed using SAS version 9.3. Results: Higher latitude adversely affected vitamin D status only in lactating Caucasian women. African American and Hispanic women and infants living in Rochester compared to Charleston had improved vitamin D status, an effect that was no longer significant when controlling for socioeconomic factors and season. Overall, there was a significant vitamin D deficiency at baseline in lactating mothers, and a far greater deficiency in their infants. Maternal baseline 25(OH)D concentration remained positively associated with being Caucasian, BMI and summer months. Breastfeeding infant vitamin D status mirrored maternal status and remained positively associated with being Caucasian and summer months. Those infants who had been on a vitamin D supplement at the time of enrollment in the study had markedly

The TRENDS High-Contrast Imaging Survey. IV. The Occurrence Rate of Giant Planets around M-Dwarfs
Benjamin T. Montet,Justin R. Crepp,John Asher Johnson,Andrew W. Howard,Geoffrey W. Marcy
Physics , 2013, DOI: 10.1088/0004-637X/781/1/28
Abstract: Doppler-based planet surveys have discovered numerous giant planets but are incomplete beyond several AU. At larger star-planet separations, direct planet detection through high-contrast imaging has proven successful, but this technique is sensitive only to young planets and characterization relies upon theoretical evolution models. Here we demonstrate that radial velocity measurements and high-contrast imaging can be combined to overcome these issues. The presence of widely separated companions can be deduced by identifying an acceleration (long-term trend) in the radial velocity of a star. By obtaining high spatial resolution follow-up imaging observations, we rule out scenarios in which such accelerations are caused by stellar binary companions with high statistical confidence. We report results from an analysis of Doppler measurements of a sample of 111 M-dwarf stars with a median of 29 radial velocity observations over a median time baseline of 11.8 yr. By targeting stars that exhibit a radial velocity acceleration ("trend") with adaptive optics imaging, we determine that 6.5% +/- 3.0% of M-dwarf stars host one or more massive companions with 1 < m/M_Jupiter < 13 and 0 < a < 20 AU. These results are lower than analyses of the planet occurrence rate around higher-mass stars. We find the giant planet occurrence rate is described by a double power law in stellar mass M and metallicity F = [Fe/H] such that f(M,F) = 0.039(+0.056,-0.028) M^(0.8(+1.1,-0.9)) 10^((3.8 +/- 1.2)F). Our results are consistent with gravitational microlensing measurements of the planet occurrence rate; this study represents the first model-independent comparison with microlensing observations.
LHS6343C: A Transiting Field Brown Dwarf Discovered by the Kepler Mission
John Asher Johnson,Kevin Apps,J. Zachary Gazak,Justin R. Crepp,Ian J. Crossfield,Andrew W. Howard,Geoff W. Marcy,Timothy D. Morton,Carly Chubak,Howard Isaacson
Physics , 2010, DOI: 10.1088/0004-637X/730/2/79
Abstract: We report the discovery of a brown dwarf that transits one member of the M+M binary system LHS6343AB every 12.71 days. The transits were discovered using photometric data from the Kelper public data release. The LHS6343 stellar system was previously identified as a single high-proper-motion M dwarf. We use high-contrast imaging to resolve the system into two low-mass stars with masses 0.45 Msun and 0.36 Msun, respectively, and a projected separation of 55 arcsec. High-resolution spectroscopy shows that the more massive component undergoes Doppler variations consistent with Keplerian motion, with a period equal to the transit period and an amplitude consistent with a companion mass of M_C = 62.8 +/- 2.3 Mjup. Based on an analysis of the Kepler light curve we estimate the radius of the companion to be R_C = 0.832 +/- 0.021 Rjup, which is consistent with theoretical predictions of the radius of a > 1 Gyr brown dwarf.
The TRENDS High-Contrast Imaging Survey. V. Discovery of an Old and Cold Benchmark T-dwarf Orbiting the Nearby G-star HD 19467
Justin R. Crepp,John Asher Johnson,Andrew W. Howard,Geoffrey W. Marcy,John Brewer,Debra A. Fischer,Jason T. Wright,Howard Isaacson
Physics , 2013, DOI: 10.1088/0004-637X/781/1/29
Abstract: The nearby Sun-like star HD 19467 shows a subtle radial velocity (RV) acceleration of -1.37+/-0.09 m/s/yr over an 16.9 year time baseline (an RV trend), hinting at the existence of a distant orbiting companion. We have obtained high-contrast adaptive optics images of the star using NIRC2 at Keck Observatory and report the direct detection of the body that causes the acceleration. The companion, HD 19467 B, is dK=12.57+/-0.09 mag fainter than its parent star (contrast ratio of 9.4e-6), has blue colors J-K_s=-0.36+/-0.14 (J-H=-0.29+/-0.15), and is separated by 1.653+/-0.004" (51.1+/-1.0 AU). Follow-up astrometric measurements obtained over an 1.1 year time baseline demonstrate physical association through common parallactic and proper motion. We calculate a firm lower-limit of m>51.9^{+3.6}_{-4.3}Mjup for the companion mass from orbital dynamics using a combination of Doppler observations and imaging. We estimate a model-dependent mass of m=56.7^{+4.6}_{-7.2}Mjup from a gyrochronological age of 4.3^{+1.0}_{-1.2} Gyr. Isochronal analysis suggests a much older age of $9\pm1$ Gyr, which corresponds to a mass of m=67.4^{+0.9}_{-1.5}Mjup. HD 19467 B's measured colors and absolute magnitude are consistent with a late T-dwarf [~T5-T7]. We may infer a low metallicity of [Fe/H]=-0.15+/-0.04 for the companion from its G3V parent star. HD 19467 B is the first directly imaged benchmark T-dwarf found orbiting a Sun-like star with a measured RV acceleration.
The TRENDS High-Contrast Imaging Survey. II. Direct Detection of the HD 8375 Tertiary
Justin R. Crepp,John Asher Johnson,Andrew W. Howard,Geoff W. Marcy,Debra A. Fischer,Scott M. Yantek,Jason T. Wright,Howard Isaacson,Ying Feng
Physics , 2012, DOI: 10.1088/0004-637X/771/1/46
Abstract: We present the direct imaging detection of a faint tertiary companion to the single-lined spectroscopic binary HD 8375 AB. Initially noticed as an 53 m/s/yr Doppler acceleration by Bowler et al. 2010, we have obtained high-contrast adaptive optics observations at Keck using NIRC2 that spatially resolve HD 8375 C from its host(s). Astrometric measurements demonstrate that the companion shares a common proper-motion. We detect orbital motion in a clockwise direction. Multiband relative photometry measurements are consistent with a spectral-type of M1V. Our combined Doppler and imaging observations place a lower-limit of m>0.297Msun on its dynamical mass. We also provide a refined orbit for the inner pair using recent RV measurements obtained with HIRES. HD 8375 is one of many triple-star systems that are apparently missing in the solar neighborhood.
Transglutaminase-Mediated Semen Coagulation Controls Sperm Storage in the Malaria Mosquito
David W. Rogers,Francesco Baldini,Francesca Battaglia,Maria Panico,Anne Dell,Howard R. Morris,Flaminia Catteruccia
PLOS Biology , 2012, DOI: 10.1371/journal.pbio.1000272
Abstract: Insect seminal fluid proteins are powerful modulators of many aspects of female physiology and behaviour including longevity, egg production, sperm storage, and remating. The crucial role of these proteins in reproduction makes them promising targets for developing tools aimed at reducing the population sizes of vectors of disease. In the malaria mosquito Anopheles gambiae, seminal secretions produced by the male accessory glands (MAGs) are transferred to females in the form of a coagulated mass called the mating plug. The potential of seminal fluid proteins as tools for mosquito control demands that we improve our limited understanding of the composition and function of the plug. Here, we show that the plug is a key determinant of An. gambiae reproductive success. We uncover the composition of the plug and demonstrate it is formed through the cross-linking of seminal proteins mediated by a MAG-specific transglutaminase (TGase), a mechanism remarkably similar to mammalian semen coagulation. Interfering with TGase expression in males inhibits plug formation and transfer, and prevents females from storing sperm with obvious consequences for fertility. Moreover, we show that the MAG-specific TGase is restricted to the anopheline lineage, where it functions to promote sperm storage rather than as a mechanical barrier to re-insemination. Taken together, these data represent a major advance in our understanding of the factors shaping Anopheles reproductive biology.
International Stem Cell Collaboration: How Disparate Policies between the United States and the United Kingdom Impact Research
Jingyuan Luo,Jesse M. Flynn,Rachel E. Solnick,Elaine Howard Ecklund,Kirstin R. W. Matthews
PLOS ONE , 2012, DOI: 10.1371/journal.pone.0017684
Abstract: As the scientific community globalizes, it is increasingly important to understand the effects of international collaboration on the quality and quantity of research produced. While it is generally assumed that international collaboration enhances the quality of research, this phenomenon is not well examined. Stem cell research is unique in that it is both politically charged and a research area that often generates international collaborations, making it an ideal case through which to examine international collaborations. Furthermore, with promising medical applications, the research area is dynamic and responsive to a globalizing science environment. Thus, studying international collaborations in stem cell research elucidates the role of existing international networks in promoting quality research, as well as the effects that disparate national policies might have on research. This study examined the impact of collaboration on publication significance in the United States and the United Kingdom, world leaders in stem cell research with disparate policies. We reviewed publications by US and UK authors from 2008, along with their citation rates and the political factors that may have contributed to the number of international collaborations. The data demonstrated that international collaborations significantly increased an article's impact for UK and US investigators. While this applied to UK authors whether they were corresponding or secondary, this effect was most significant for US authors who were corresponding authors. While the UK exhibited a higher proportion of international publications than the US, this difference was consistent with overall trends in international scientific collaboration. The findings suggested that national stem cell policy differences and regulatory mechanisms driving international stem cell research in the US and UK did not affect the frequency of international collaborations, or even the countries with which the US and UK most often collaborated. Geographical and traditional collaborative relationships were the predominate considerations in establishing international collaborations.
Reproducibility of oligonucleotide arrays using small samples
Jeanette N McClintick, Ronald E Jerome, Charles R Nicholson, David W Crabb, Howard J Edenberg
BMC Genomics , 2003, DOI: 10.1186/1471-2164-4-4
Abstract: The standard Affymetrix protocol can be used starting with only 2 micrograms of total RNA, with results equivalent to the recommended 10 micrograms. Biological variability is much greater than the technical variability introduced by this change. A simple amplification protocol described here can be used for samples as small as 0.1 micrograms of total RNA. This amplification protocol allows detection of a substantial fraction of the significant differences found using the standard protocol, despite an increase in variability and the 5' truncation of the transcripts, which prevents detection of a subset of genes.Biological differences in a typical experiment are much greater than differences resulting from technical manipulations in labeling and hybridization. The standard protocol works well with 2 micrograms of RNA, and with minor modifications could allow the use of samples as small as 1 micrograms. For smaller amounts of starting material, down to 0.1 micrograms RNA, differential gene expression can still be detected using the single cycle amplification protocol. Comparisons of groups of four arrays detect many more significant differences than comparisons of three arrays.The ability to measure the expression of thousands of genes at once using microarrays has opened new areas of research, including global examination of the effects of perturbations on cells or animals and the classification of tumors by their pattern of gene expression. Microarrays using cDNAs [1,2] and oligonucleotides [3-5] have both proven valuable.Commercially available oligonucleotide microarrays provide a standardized tool that allows assay of thousands of mRNAs at one time. Affymetrix GeneChips? contain pairs of 25-nucleotide sequences (probe pairs) synthesized on silica wafers; one of each pair exactly matches the sequence of interest and the other contains a single mismatching nucleotide in the center [6,7]. A single sequence is queried by a group of 8 to 16 probe pairs that constitute a
Interannual variability of pteropod shell weights in the high-CO2 Southern Ocean
D. Roberts,W. R. Howard,A. D. Moy,J. L. Roberts
Biogeosciences Discussions , 2008,
Abstract: Anthropogenic inputs of CO2 are altering ocean chemistry and may alter the role of marine calcifiers in ocean ecosystems. CO2 emissions over the coming centuries may produce changes in ocean pH not seen for millions of years. Laboratory evidence has shown decreased calcification in some species of coccolithophores, foraminifera, corals and pteropods in response to CO2 enrichment. However, in situ observations of calcification in marine organisms are limited, especially for the aragonitic pteropods. This group of pelagic molluscs are likely to be more sensitive to changes in carbonate chemistry than calcite producers such as foraminifera and coccolithophores. Here we present observations of pteropod shell-weight and flux from 1997–2006 in sediment traps deployed at 47° S, 142° E at 2000 meters below sea surface in the Southern Ocean. A decadal trend of –1.17±0.47 μg yr 1 (P=0.02) in mean shell weight in the pteropod Limacina helicina antarctica forma antarctica suggests a small but detectable reduction in calcification. Gaps in the data make it difficult to state with certainty the significance of the trend. However, this data set represents the first attempt to estimate interannual variations in pteropod calcification and establish a benchmark against which future impacts of ocean acidification may be detected. Contributions of Limacina helicina antarctica morphotypes to the total pteropod flux were also reduced over the decade. We suggest these small though discernible trends are due to changing carbonate chemistry in the Subantarctic, as other oceanographic variables show no clear decadal trends. With CO2 continuing to enter the ocean such impacts on pteropods and other marine calcifiers could result in changes to the distribution of species and the structure of Southern Ocean ecosystems.
Giant Planet Occurrence in the Stellar Mass-Metallicity Plane
John Asher Johnson,Kimberly M. Aller,Andrew W. Howard,Justin R. Crepp
Physics , 2010, DOI: 10.1086/655775
Abstract: Correlations between stellar properties and the occurrence rate of exoplanets can be used to inform the target selection of future planet search efforts and provide valuable clues about the planet formation process. We analyze a sample of 1194 stars drawn from the California Planet Survey targets to determine the empirical functional form describing the likelihood of a star harboring a giant planet as a function of its mass and metallicity. Our stellar sample ranges from M dwarfs with masses as low as 0.2 Msun to intermediate-mass subgiants with masses as high as 1.9 Msun. In agreement with previous studies, our sample exhibits a planet-metallicity correlation at all stellar masses; the fraction of stars that harbor giant planets scales as f \propto 10^{1.2 [Fe/H]}. We can rule out a flat metallicity relationship among our evolved stars (at 98% confidence), which argues that the high metallicities of stars with planets are not likely due to convective envelope "pollution." Our data also rule out a constant planet occurrence rate for [Fe/H]< 0, indicating that giant planets continue to become rarer at sub-Solar metallicities. We also find that planet occurrence increases with stellar mass (f \propto Mstar), characterized by a rise from 3.5% around M dwarfs (0.5 Msun) to 14% around A stars (2 Msun), at Solar metallicity. We argue that the correlation between stellar properties and giant planet occurrence is strong supporting evidence of the core accretion model of planet formation.
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