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Search Results: 1 - 10 of 449761 matches for " S. E. Walker "
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Productivity of maize-bean intercropping in a semi-arid region of South Africa
M Tsubo, E Mukhala, HO Ogindo, S Walker
Water SA , 2003,
Abstract: Food shortage is known to have been caused by overpopulation, natural disasters and poor food distribution. In areas facing food insecurity, such as Africa, peasants or small-scale farmers have practised intercropping since old times. In this study, an investigation was carried out to determine whether intercropping increased production for small-scale farming in a semi-arid region (Free State, South Africa). Crop productivity of maize and bean intercropping systems was evaluated in terms of crop yield and growth. The effect of radiation and water utilisation by these systems was measured to determine their productivity. Field trials were carried out during three summer crop growing seasons (plant densities, row orientation and sowing date trials. In all growing seasons, rainfall was below normal, and air temperatures were normal. The total land equivalent ratios for yield and growth ranged between 1.06 to 1.58 and 1.38 to 1.86 respectively, showing yield and growth advantage of intercropping. Concerning radiation and water use, the intercropping of maize and beans had both radiation and water use efficiencies (RUE and WUE, respectively) as high as maize sole cropping, and intercropping RUE and WUE were greater than bean sole cropping. >From these results, it has been concluded that maize-bean intercropping can be recommended to small-scale farmers in this semi-arid region. Water SA Vol.29(4): 381-388
Diving for the Sedimentary Record of Multiyear Sea Ice
Molly Fritz Miller,Samuel S. Bowser,Sally E. Walker
Oceanography , 2012,
Abstract: How is sediment transported to the seafloor along coastlines where the sea ice rarely melts? Are there distinctive characteristics of the resulting deposits that label them as accumulating in this setting that is so sensitive to climate change?
Systematics of two-component superconductivity in $YBa_{2}Cu_{3}O_{6.95}$ from microwave measurements of high quality single crystals
H. Srikanth,Z. Zhai,S. Sridhar,A. Erb,E. Walker
Physics , 1997, DOI: 10.1103/PhysRevB.57.7986
Abstract: Systematic microwave surface impedance measurements of YBCO single crystals grown in $BaZrO_3$ crucibles reveal new properties that are not directly seen in similar measurements of other YBCO samples. Two key observations obtained from complex conductivity are: a new normal conductivity peak at around 80K and additional pairing below 65K. High pressure oxygenation of one of the crystals still yields the same results ruling out any effect of macroscopic segregation of O-deficient regions. A single complex order parameter cannot describe these data, and the results suggest at least two superconducting components. Comparisons with model calculations done for various decoupled two-component scenarios (i.e. s+d, d+d) are presented. Systematics of three single crystals show that the 80K quasiparticle peak is correlated with the normal state inelastic scattering rate. Close to Tc, the data follow a mean-field behavior. Overall, our results strongly suggest the presence of multiple pairing temperature and energy scales in $YBa_{2}Cu_{3}O_{6.95}$.
The Diffuse Source at the Center of LMC SNR 0509-67.5 is a Background Galaxy at z = 0.031
Ashley Pagnotta,Emma S. Walker,Bradley E. Schaefer
Physics , 2014, DOI: 10.1088/0004-637X/788/2/173
Abstract: Type Ia supernovae (SNe Ia) are well-known for their use in the measurement of cosmological distances, but our continuing lack of concrete knowledge about their progenitor stars is both a matter of debate and a source of systematic error. In our attempts to answer this question, we presented unambiguous evidence that LMC SNR 0509-67.5, the remnant of an SN Ia that exploded in the Large Magellanic Cloud 400 +/- 50 years ago, did not have any point sources (stars) near the site of the original supernova explosion, from which we concluded that this particular supernova must have had a progenitor system consisting of two white dwarfs (Schaefer & Pagnotta 2012). There is, however, evidence of nebulosity near the center of the remnant, which could have been left over detritus from the less massive WD, or could have been a background galaxy unrelated to the supernova explosion. We obtained long-slit spectra of the central nebulous region using GMOS on Gemini South to determine which of these two possibilities is correct. The spectra show H-alpha emission at a redshift of z = 0.031, which implies that the nebulosity in the center of LMC SNR 0509-67.5 is a background galaxy, unrelated to the supernova.
CD8 T cell response in a phase I study of therapeutic vaccination of advanced NSCLC with allogeneic tumor cells secreting endoplasmic reticulum-chaperone gp96-Ig-peptide complexes  [PDF]
Luis E. Raez, Gail R. Walker, Paulette Baldie, Eva Fisher, Jorge E. Gomez, Khaled Tolba, Edgardo S. Santos, Eckhard R. Podack
Advances in Lung Cancer (ALC) , 2013, DOI: 10.4236/alc.2013.21002
Abstract: Antigen containing, allogeneic cells secreting the genetically modified protein and peptide-chaperone gp96-Ig cross, prime and expand antigen specific CD8 T cells with therapeutic antitumor activity in mice. In a first in man phase I study, we now report the results of therapeutic vaccination of non-small cell lung cancer (NSCLC) patients with an established, allogeneic non-small cell lung adenocarcinoma cell line secreting gp96-Ig. Advanced NSCLC-patients stage IIIB or IV of any histological subtype were enrolled and treated with up to 36 vaccinations over the course of 18 weeks. Primary endpoint was safety, secondary endpoints tumor response and overall survival. Measurement of tumor antigen specific CD8 CTL responses is precluded by the lack of known NSCLC associated antigens. Therefore, we measured patient CD8 T cell-IFN-γ responses to allo-antigens of the vaccine cells as surrogate for tumor antigen specific CD8 CTL. In 7 of 18 treated patients tumor growth was stabilized, however none of the 18 patients had an objective tumor response by RECIST criteria. Of 15 patients evaluable for immune response, 11 responded to vaccination with more than twofold increase in CD8-IFN-γ frequency above baseline. These patients had a median survival time of 16.5 months. Four patients who had no CD8 response above base line had survival times from 2.1 to 6.7 months. Our data are consistent with the concept that generation of CD8 CTL by therapeutic vaccination may delay tumor growth and progression and mediate prolonged survival even in the absence of objective tumor responses. Further studies will be required to test this concept and promising result.
Using genetic data to estimate diffusion rates in heterogeneous landscapes
L. Roques,E. Walker,P. Franck,S. Soubeyrand,E. K. Klein
Quantitative Biology , 2015,
Abstract: Having a precise knowledge of the dispersal ability of a population in a heterogeneous environment is of critical importance in agroecology and conservation biology as it can provide management tools to limit the effects of pests or to increase the survival of endangered species. In this paper, we propose a mechanistic-statistical method to estimate space-dependent diffusion parameters of spatially-explicit models based on stochastic differential equations, using genetic data. Dividing the total population into subpopulations corresponding to different habitat patches with known allele frequencies, the expected proportions of individuals from each subpopulation at each position is computed by solving a system of reaction-diffusion equations. Modelling the capture and genotyping of the individuals with a statistical approach, we derive a numerically tractable formula for the likelihood function associated with the diffusion parameters. In a simulated environment made of three types of regions, each associated with a different diffusion coefficient, we successfully estimate the diffusion parameters with a maximum-likelihood approach. Although higher genetic differentiation among subpopulations leads to more accurate estimations, once a certain level of differentiation has been reached, the finite size of the genotyped population becomes the limiting factor for accurate estimation.
Nestin Reporter Transgene Labels Multiple Central Nervous System Precursor Cells
Avery S. Walker,Gwendolyn E. Goings,Yongsoo Kim,Richard J. Miller,Anjen Chenn,Francis G. Szele
Neural Plasticity , 2010, DOI: 10.1155/2010/894374
Abstract: Embryonic neuroepithelia and adult subventricular zone (SVZ) stem and progenitor cells express nestin. We characterized a transgenic line that expresses enhanced green fluorescent protein (eGFP) specified to neural tissue by the second intronic enhancer of the nestin promoter that had several novel features. During embryogenesis, the dorsal telencephalon contained many and the ventral telencephalon few eGFP+ cells. eGFP+ cells were found in postnatal and adult neurogenic regions. eGFP+ cells in the SVZ expressed multiple phenotype markers, glial fibrillary acidic protein, Dlx, and neuroblast-specific molecules suggesting the transgene is expressed through the lineage. eGFP+ cell numbers increased in the SVZ after cortical injury, suggesting this line will be useful in probing postinjury neurogenesis. In non-neurogenic regions, eGFP was strongly expressed in oligodendrocyte progenitors, but not in astrocytes, even when they were reactive. This eGFP+ mouse will facilitate studies of proliferative neuroepithelia and adult neurogenesis, as well as of parenchymal oligodendrocytes. 1. Introduction Expression of the intermediate filament protein nestin has been used as a marker for neural stem and progenitor cells in the ventricular and subventricular zones [1–3]. Nestin is also expressed by radial glia [1] which are substrates for migration and which can give rise to neurons [4, 5]. The second intronic enhancer of nestin specifies expression of the gene to neural tissues [6]. We generated a transgenic mouse using the second intronic enhancer of the nestin gene and the thymidine kinase minimal promoter to drive enhanced green fluorescent protein (eGFP+), an approach similar to what has been successfully used by others (Table 1) [7–12]. Several useful nestin-Cre mice have also been made allowing lineage studies and functional studies [13–15]; however for space constraints, we did not include them in Table 1. Table 1: Comparison of nestin-reporter mice. Transgenic reporter mice, even when generated identically, can have widely divergent expression of the transgene [16]. Indeed, we discovered some aspects of eGFP expression that differed from previously reported lines. In our transgenic mouse, eGFP was expressed more robustly in the pallium than the subpallium during embryogenesis. In the adult SVZ, eGFP+ cells expressed markers of multiple cell subtypes. Interestingly, in the ventral lateral ventricle, eGFP was primarily expressed by ependymal cells. Unexpectedly, eGFP was also detected in oligodendrocytes in the parenchyma throughout development and in the
Value of Protein Supplementation for Lambs and Meat Goat Kids Grazing Bermudagrass in Central Oklahoma
E.L. Walker,S.A. Nusz,D.H. Keisler,M.A. Brown
Journal of Animal and Veterinary Advances , 2012, DOI: 10.3923/javaa.2011.2582.2587
Abstract: Bermudagrass (Cynodon dactylon) is a high quality, abundant warm-season grass grown in temperate regions of the United States. While research data exists to support protein supplementation of steers grazing bermudagrass pastures, no such data exists for management of lambs and meat goat kids. The objective was to evaluate growth response of lambs and meat goat kids grazing bermudagrass with or without access to a commercial 21% CP protein tub (PT vs. NPT). Two trials were conducted in El Reno, Oklahoma, starting in June and ending in August in 2007 and 2008. In 2007 and 2008, respectively 29 and 54 meat goat kids (90±5 days of age) and 68 and 62 lambs of wool and hair breeds (and reciprocal crosses; 100±5 days of age) were utilized. Animals were stratified by weight, breed and gender and randomly assigned to 1.2 ha of common bermudagrass pasture with (n = 2) or without (n = 2) access to a commercial 21% CP protein tub. Growth of animals was assessed by change in body weights and serum concentrations of leptin every 2 weeks during grazing periods of 71 days for 2007 and 56 days for 2008. Sheep had greater ADG than goats (p<0.05) and breeds of sheep differed in ADG (p≤0.05). Ad libitum protein supplementation tubs had no effect on ADG or serum leptin of either lambs or kids grazing bermudagrass. These data do not support the need for protein supplementation of lambs and meat goat kids grazing bermudagrass.
Letter to the Editor: First complementary observations by ionospheric tomography, the EISCAT Svalbard radar and the CUTLASS HF radar
C. N. Mitchell,I. K. Walker,S. E. Pryse,I. Kersley
Annales Geophysicae (ANGEO) , 2003,
Abstract: Experimental results are presented from ionospheric tomography, the EISCAT Svalbard radar and the CUTLASS HF radar. Tomographic measurements on 10 October 1996, showing a narrow, field-aligned enhancement in electron density in the post-noon sector of the dayside auroral zone, are related to a temporal increase in the plasma concentration observed by the incoherent scatter radar in the region where the HF radar indicated a low velocity sunwards convection. The results demonstrate the complementary nature of these three instruments for polar-cap ionospheric studies. Key words. Ionosphere · Auroral ionosphere · Polar ionosphere · Radio science (ionospheric physics)
The spatial structure of the dayside ionospheric trough
S. E. Pryse,L. Kersley,M. J. Williams,I. K. Walker
Annales Geophysicae (ANGEO) , 2003,
Abstract: Tomographic imaging provides a powerful technique for obtaining images of the spatial distribution of ionospheric electron density at polar latitudes. The method, which involves monitoring radio transmissions from the Navy Navigation Satellite System at a meridional chain of ground receivers, has particular potential for complementing temporal measurements by other observing techniques such as the EISCAT incoherent-scatter radar facility. Tomographic reconstructions are presented here from a two-week campaign in November 1995 that show large-scale structuring of the polar ionosphere. Measurements by the EISCAT radar confirm the authenticity of the technique and provide additional information of the plasma electron and ion temperatures. The dayside trough, persistently observed at high latitudes during a geomagnetically quiet period but migrating to lower latitudes with increasing activity, is discussed in relationship to the pattern of the polar-cap convection. Key words. Ionosphere-magnetosphere interactions · Polar ionosphere · Radio science · Ionospheric propagation
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