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Search Results: 1 - 10 of 150095 matches for " H. Walters "
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Predicting numerically the large increases in extra pressure drop when boger fluids flow through  [PDF]
H. R. Tamaddon-Jahromi, M. F. Webster, K. Walters
Natural Science (NS) , 2010, DOI: 10.4236/ns.2010.21001
Abstract: Recent numerical studies on pressure-drops in contraction flows have introduced a variety of constitutive models to compare and contrast the competing influences of extensional vis-cosity, normal stress and shear-thinning. Early work on pressure-drops employed the constant viscosity Oldroyd-B and Upper Convected Max- well (UCM) models to represent the behavior of so-called Boger fluids in axisymmetric contrac-tion flows, in (unsuccessful) attempts to predict the very large enhancements that were ob-served experimentally. In more recent studies, other constitutive models have been employed to interpret observed behavior and some pro-gress has been made, although finding a (re-spectable) model to describe observed contrac-tion-flow behavior, even qualitatively, has been frustratingly difficult. With this in mind, the present study discusses the ability of a well- known FENE type model (the so-called FENE- CR model) to describe observed behavior. For various reasons, an axisymmetric (4:1:4) con-traction/expansion geometry, with rounded corners, is singled out for special attention, and a new hybrid finite element/volume algo-rithm is utilized to conduct the modeling, which reflects an incremental pressure-correction time-stepping structure. New to this algo-rithmic formulation are techniques in time discretization, discrete treatment of pressure terms, and compatible stress/velocity-gradient representation. We shall argue that the current simulations for the FENE-CR model have re-sulted in a major improvement in the sort-for agreement between theory and experiment in this important bench-mark problem.
Clinical presentation and outcome of Tuberculosis in Human Immunodeficiency Virus infected children on anti-retroviral therapy
Elisabetta Walters, Mark F Cotton, Helena Rabie, H Simon Schaaf, Lourens O Walters, Ben J Marais
BMC Pediatrics , 2008, DOI: 10.1186/1471-2431-8-1
Abstract: We performed a comprehensive file review of all children who commenced HAART at Tygerberg Children's Hospital from January 2003 through December 2005.Data from 290 children were analyzed; 137 TB episodes were recorded in 136 children; 116 episodes occurred before and 21 after HAART initiation; 10 episodes were probably related to immune reconstitution inflammatory syndrome (IRIS). The number of TB cases per 100 patient years were 53.3 during the 9 months prior to HAART initiation, and 6.4 during post HAART follow-up [odds ratio (OR) 16.6; 95% confidence interval (CI) 12.5–22.4]. A positive outcome was achieved in 97/137 (71%) episodes, 6 (4%) cases experienced no improvement, 16 (12%) died and the outcome could not be established in 18 (13%). Mortality was less in children on HAART (1/21; 4.8%) compared to those not on HAART (15/116; 12.9%).We recorded an extremely high incidence of TB among HIV-infected children, especially prior to HAART initiation. Starting HAART at an earlier stage is likely to reduce morbidity and mortality related to TB, particularly in TB-endemic areas. Management frequently deviated from standard guidelines, but outcomes in general were good.The tuberculosis (TB) epidemic is poorly controlled in sub-Saharan Africa; the region that reports the highest TB incidence rates and highest prevalence of human immunodeficiency virus (HIV) infection [1,2]. Prevention of mother to child transmission (PMTCT) programs are poorly established in many countries and in many instances fail to use potent antiretroviral regimens, resulting in huge numbers of HIV-infected children.Childhood TB contributes significantly to the global TB case load (15–20% of cases), [3-5] especially in Africa where TB has been identified as a major respiratory cause of death in children [6]. The high disease burden results from ongoing TB transmission (poor epidemic control) and increased vulnerability as a result of HIV-induced immune compromise. Compared to HIV-uninfected childre
A member of the peptidase M48 superfamily of Porphyromonas gingivalis is associated with virulence in vitro and in vivo
Sheila Walters,Myriam Bélanger,Paulo H. Rodrigues,Joan Whitlock
Journal of Oral Microbiology , 2009, DOI: 10.3402/jom.v1i0.2021
Abstract: Background: In vivo-induced antigen technology was previously used to identify 115 genes induced in Porphyromonas gingivalis W83 during human infection. One of these, PG2197, a conserved hypothetical protein which has homology to a Zn-dependent protease, was examined with respect to a role in disease. Design: The expression of PG2197 in human periodontitis patients was investigated, but as there is increasing evidence of a direct relationship between P. gingivalis and cardiovascular disease, a mutation was constructed in this gene to also determine its role in adherence, invasion, and persistence within human coronary artery endothelial cells (HCAEC) and neutrophil killing susceptibility. Results: Plaque samples from 20 periodontitis patients were analyzed by real-time PCR, revealing that PG2197 was expressed in 60.0% of diseased sites compared to 15.8% of healthy sites, even though P. gingivalis was detected in equal numbers from both sites. The expression of this gene was also found to be up-regulated in microarrays at 5 and 30 min of invasion of HCAEC. Interestingly, a PG2197 mutant displayed increased adherence, invasion, and persistence within HCAEC when compared to the wild-type strain. Conclusion: This gene appears to be important for the virulence of P. gingivalis, both in vivo and in vitro.
Vibrational interference of Raman and high-harmonic generation pathways
Zachary B. Walters,Stefano Tonzani,Chris H. Greene
Physics , 2009, DOI: 10.1016/j.chemphys.2009.09.022
Abstract: Experiments have shown that the internal vibrational state of a molecule can affect the intensity of high harmonic light generated from that molecule. This paper presents a model which explains this modulation in terms of interference between different vibrational states occurring during the high harmonic process. In addition, a semiclassical model of the continuum electron propagation is developed which connects with rigorous treatments of the electron-ion scattering.
Limits of the Plane Wave Approximation in the Measurement of Molecular Properties
Zachary B. Walters,Stefano Tonzani,Chris H. Greene
Physics , 2008,
Abstract: Rescattering electrons offer great potential as probes of molecular properties on ultrafast timescales. The most famous example is molecular tomography, in which high harmonic spectra of oriented molecules are mapped to ``tomographic images'' of the relevant molecular orbitals. The accuracy of such reconstructions may be greatly affected by the distortion of scattering wavefunctions from their asymptotic forms due to interactions with the parent ion. We investigate the validity of the commonly used plane wave approximation in molecular tomography, showing how such distortions affect the resulting orbital reconstructions.
High Harmonic Generation in SF$_{6}$: Raman-excited Vibrational Quantum Beats
Zachary B. Walters,Stefano Tonzani,Chris H. Greene
Physics , 2007, DOI: 10.1088/0953-4075/40/18/F01
Abstract: In a recent experiment (N. Wagner et al., PNAS v103, p13279) on SF$_{6}$, a high-harmonic generating laser pulse is preceded by a pump pulse which stimulates Raman-active modes in the molecule. Varying the time delay between the two pulses modulates high harmonic intensity, with frequencies equal to the vibration frequencies of the Raman-active modes. We propose an explanation of this modulation as a quantum interference between competing pathways that occur via adjacent vibrational states of the molecule. The Raman and high harmonic processes act as beamsplitters, producing vibrational quantum beats among the Raman-active vibrational modes that are excited by the first pulse. We introduce a rigorous treatment of the electron-ion recombination process and the effect of the ionic Coulomb field in the electron propagation outside the molecule, improving over the widely-used three-step model.
Interaction of intense vuv radiation with large xenon clusters
Zachary B. Walters,Robin Santra,Chris H. Greene
Physics , 2005, DOI: 10.1103/PhysRevA.74.043204
Abstract: The interaction of atomic clusters with short, intense pulses of laser light to form extremely hot, dense plasmas has attracted extensive experimental and theoretical interest. The high density of atoms within the cluster greatly enhances the atom--laser interaction, while the finite size of the cluster prevents energy from escaping the interaction region. Recent technological advances have allowed experiments to probe the laser--cluster interaction at very high photon energies, with interactions much stronger than suggested by theories for lower photon energies. We present a model of the laser--cluster interaction which uses non-perturbative R-matrix techniques to calculate inverse bremsstrahlung and photoionization cross sections for Herman-Skillman atomic potentials. We describe the evolution of the cluster under the influence of the processes of inverse bremsstrahlung heating, photoionization, collisional ionization and recombination, and expansion of the cluster. We compare charge state distribution, charge state ejection energies, and total energy absorbed with the Hamburg experiment of Wabnitz {\em et al.} [Nature {\bf 420}, 482 (2002)] and ejected electron spectra with Laarmann {\em et al.} [Phys. Rev. Lett. {\bf 95}, 063402 (2005)].
Ionization of hydrogen and ionized helium by slow antiprotons
S Sahoo,S C Mukherjee,H R J Walters
Physics , 2004,
Abstract: We study the ionization process involving antiproton and hydrogen in the energy range between 0.1 keV to 500 keV, using single center close coupling approximation. We construct the scattering wave function using B-spline bases. The results obtained for ionization of atomic hydrogen are compared with other existing theoretical calculations as well as with the available experimental data. The present results are found to be encouraging. We also employed this method to study the ionization of ionized helium in the energy range between 1 and 500 keV. On comparision, the present results are found to interpret well the cross section values calculated using other theories.
Enhanced Satellite Cell Activity in Aging Skeletal Muscle after Manual Acupuncture-Induced Injury  [PDF]
Sonya K. Sobrian, Eric Walters
Chinese Medicine (CM) , 2014, DOI: 10.4236/cm.2014.51004

Skeletal muscle injury stimulates normally quiescent resident satellite (stem) cells to re-enter the cell cycle and execute the myogenic program to restore muscle structure and function. Previously, we reported that manual acupuncture needling of the tibialis anterior (TA) (ST36 = Zusanli) muscle of young male rats produced focal injury and morphological changes that accompanied the presence of activated satellite cells (SC) 72 hours post-needling. To investigate whether aging TA muscle responds in a similar fashion to acupuncture needling, 17-month-old female rats were subjected to a single insertion and manual manipulation of an acupuncture needle. At 72 hours’ post-needling, hematoxylin staining of the TA revealed increased mononuclear cell infiltration that was indicative of localized injury. Moreover, this was accompanied by a four-fold increase in the expression of proliferating cell nuclear antigen within cells of needled tissues. Heightened immunofluorescence for MyoD was found within SC in the needled muscle, which correlated with a 6- and 10-fold increase in two MyoD isoforms (~38 and 42 kDa, respectively), when analyzed by Western blotting. An additional 56 kDa MyoD immunoreactive species was observed in both needled and control muscle of the aging rats. The present study in pre-senile female rats, in conjunction with our previous study in young male rats, suggests that muscle remodeling and restructuring after injury may constitute the initial cellular and molecular mechanisms that underlie the benefits associated with acupuncture throughout the life-span.

Positronium-Atom Collisions
H R J Walters,A C H Yu,S Sahoo,Sharon Gilmore
Physics , 2004, DOI: 10.1016/j.nimb.2004.03.047
Abstract: New results are presented for Ps(1s) scattering by H(1s), He(1$^1$S) and Li(2s). Calculations have been performed in a coupled state framework, usually employing pseudostates, and allowing for excitation of both the Ps and the atom. In the Ps(1s)-H(1s) calculations the H$^-$ formation channel has also been included using a highly accurate H$^-$ wave function. Resonances resulting from unstable states in which the positron orbits H$^-$ have been calculated and analysed. The new Ps(1s)-He(1$^1$S) calculations still fail to resolve existing discrepancies between theory and experiment at very low energies. The possible importance of the Ps$^-$ formation channel in all three collision systems is discussed.
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