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Search Results: 1 - 10 of 454766 matches for " J. R. Tucker "
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Protection of Vaginal Epithelial Cells with Probiotic Lactobacilli and the Effect of Estrogen against Infection by Candida albicans  [PDF]
R. Doug Wagner, Shemedia J. Johnson, Danielle R. Tucker
Open Journal of Medical Microbiology (OJMM) , 2012, DOI: 10.4236/ojmm.2012.23008
Abstract: Some probiotic strains of lactobacilli appear to be protective against vulvovaginal candidiasis. The vaginal epithelial cell line (VK2 E6/E7) was used as a model to assess the protective mechanisms of probiotic lactobacilli for cells chal- lenged with Candida albicans. Co-culture of VK2 cells with Lactobacillus rhamnosus GR-1 and Lactobacillus reuteri RC-14 prior to C. albicans challenge showed reduced adherence of C. albicans to the VK2 cells and inhibition of C. albicans growth. H2O2 concentrations of 0.3 μg/ml, produced by lactobacilli and estrogen-primed VK2 cells, were inhi-bitory to C. albicans growth. C. albicans growth was also inhibited by 10 μg/ml lactic acid. C. albicans infection was increased by 17β-estradiol through induction of hyphal germination. L. reuteri RC-14, but not L. rhamnosus GR-1, H2O2, or lactic acid inhibited estrogen-stimulated hyphal germination. The results of this study support a role for H2O2 and lactic acid from probiotic bacteria in vaginal epithelial protection from candidiasis and a role for 17β-estradiol in the disease by induction of C. albicans hyphal germination.
The dynamics of Cosserat nets
J. Gratus,R. W. Tucker
Journal of Applied Mathematics , 2003, DOI: 10.1155/s1110757x03110224
Abstract: A formulation of the dynamics of a collection of connected simple 1-dimensional Cosserat continua and rigid bodies is presented in terms of sections of an SO(3) fibration over a 1-dimensional net. A large class of junction conditions is considered in a unified framework. All the equations of motion and junction conditions are derived as extrema of a constrained variational principle on the net and are analysed perturbatively for structures with Kirchhoff constitutive properties. The whole discussion is based on the notion of a Cosserat net and its contractions obtained by taking certain limits that transform Cosserat elements to rigid structures. Generalisations are briefly discussed within this framework.
An Intrinsic Approach to Forces in Magnetoelectric Media
R. W. Tucker,T. J. Walton
Physics , 2008, DOI: 10.1393/ncc/i2009-10342-7
Abstract: This paper offers a conceptually straightforward method for the calculation of stresses in polarisable media based on the notion of a drive form and its property of being closed in spacetimes with symmetry. After an outline of the notation required to exploit the powerful exterior calculus of differential forms, a discussion of the relation between Killing isometries and conservation laws for smooth and distributional drive forms is given. Instantaneous forces on isolated spacetime domains and regions with interfaces are defined, based on manifestly covariant equations of motion. The remaining sections apply these notions to media that sustain electromagnetic stresses, with emphasis on homogeneous magnetoelectric material. An explicit calculation of the average pressure exerted by a monochromatic wave normally incident on a homogeneous, magnetoelectric slab in vacuo is presented and the concluding section summarizes how this pressure depends on the parameters in the magnetoelectric tensors for the medium.
New Perspectives On the Relevance of Gravitation for the Covariant Description of Electromagnetically Polarizable Media
T. Dereli,J. Gratus,R. W. Tucker
Physics , 2006, DOI: 10.1088/1751-8113/40/21/016
Abstract: Electromagnetic properties of a simple polarisable medium may be parameterised in terms of a constitutive tensor whose properties can in principle be determined by experiments in non-inertial (accelerating) frames and in the presence of weak but variable gravitational fields. After establishing some geometric notation, discussion is given to basic concepts of stress, energy and momentum in the vacuum where the useful notion of a drive form is introduced in order to associate the conservation of currents involving the flux of energy, momentum and angular momentum with spacetime isometries. The definition of the stress-energy-momentum tensor is discussed with particular reference to its symmetry based on its role as a source of relativistic gravitation. General constitutive properties of material continua are formulated in terms of spacetime tensors including those that describe magneto-electric phenomena in moving media. This leads to a formulation of a self-adjoint constitutive tensor describing, in general, inhomogeneous, anisotropic, magneto-electric bulk matter in arbitrary motion. The question of an invariant characterisation of intrinsically magneto-electric media is explored. An action principle is established to generate the phenomenological Maxwell system and the use of variational derivatives to calculate stress-energy-momentum tensors is discussed in some detail. The relation of this result to tensors proposed by Abraham and others is discussed in the concluding section where the relevance of the whole approach to experiments on matter in non-inertial environments with variable gravitational and electromagnetic fields is stressed.
The Covariant Description of Electromagnetically Polarizable Media
T. Dereli,J. Gratus,R. W. Tucker
Physics , 2006, DOI: 10.1016/j.physleta.2006.10.060
Abstract: The form of the phenomenological stress-energy-momentum tensor for the electromagnetic field in a class of inhomogeneous, anisotropic magneto-electric media is calculated from first principles, leading to a coherent understanding of the phenomenological stresses and energy-momentum exchanges induced by electromagnetic interactions with such matter in terms of a fully relativistic covariant variational framework.
Observations of High Nitrate Concentrations in Forage Bermudagrass during Severe to Exceptional Drought Years  [PDF]
Dennis W. Hancock, Uttam K. Saha, Jennifer J. Tucker, R. Lawton Stewart Jr.
American Journal of Plant Sciences (AJPS) , 2016, DOI: 10.4236/ajps.2016.74062
Abstract: With the prediction of climate change-induced increases in drought frequency and severity in the southeastern USA, it is important to better understand the risks that drought may pose to NO3 accumulation in bermudagrass [Cynodon dactylon (L.) Pers.] forage. This report offers observations of NO3 concentration in Bermudagrass forage samples submitted to the University of Georgia’s Feed and Environmental Water Lab (FEWL) during the extreme to exceptional drought of 2007, the severe drought of 2008, and the four preceding seasons when drought stress was minimal or absent. The probability (P) of a sample being at high risk for nitrate toxicosis was the greatest for the extreme to exceptional drought of 2007 (P = 0.160), slightly lower in the severe drought year of 2008 (P = 0.105), and the lowest for samples from the 2003-2006 growing seasons (P = 0.082) when drought stress was minimal or absent.
Hydrodynamic forces on two moving discs
Burton D.A.,Gratus J.,Tucker R.W.
Theoretical and Applied Mechanics , 2004, DOI: 10.2298/tam0402153b
Abstract: We give a detailed presentation of a flexible method for constructing explicit expressions of irrotational and incompressible fluid flows around two rigid circular moving discs. We also discuss how such expressions can be used to compute the fluid-induced forces and torques on the discs in terms of Killing drives. Conformal mapping techniques are used to identify a meromorphic function on an annular region in C with a flow around two circular discs by a Mobius transformation. First order poles in the annular region correspond to vortices outside of the two discs. Inflows are incorporated by putting a second order pole at the point in the annulus that corresponds to infinity.
Simulation of Si:P spin-based quantum computer architecture
Angbo Fang,Yia-Chung Chang,J. R. Tucker
Physics , 2005, DOI: 10.1103/PhysRevB.72.075355
Abstract: We present a systematic and realistic simulation for single and double phosphorous donors in a silicon-based quantum computer design. A two-valley equation is developed to describe the ground state of phosphorous donors in strained silicon quantum well (QW), with the central cell effect treated by a model impurity potential. We find that the increase of quantum well confinement leads to shrinking charge distribution in all 3 dimensions. Using an unrestricted Hartree-Fock method with Generalized Valence Bond (GVB) single-particle wave functions, we are able to solve the two-electron Sch${\ddot o}$dinger equation with quantum well confinement and realistic gate potentials. The effects of QW width, gate voltages, donor separation, and donor position are calculated and analyzed. The gate tunability and gate fidelity are defined and evaluated, for a typical QC design. Estimates are obtained for the duration of $\sqrt{SWAP}$ gate operation and the required accuracy in voltage control. A strong exchange oscillation is observed as both donors are shifted along [001] axis but with their separation unchanged. Applying a gate potential tends to suppress the oscillation. The exchange oscillation as a function of donor position along [100] axis is found to be completely suppressed as the donor separation is decreased. The simulation presented in this paper is of importance to the practical design of an exchange-based silicon quantum computer.
Classical and Quantum Dynamics of Free Electromagnetic Laser Pulses
S. Goto,R. W. Tucker,T. J. Walton
Physics , 2015,
Abstract: We discuss the use of a class of exact finite energy solutions to the vacuum source free Maxwell equations as models for multi- and single cycle laser pulses in classical interaction with relativistic charged point particles. These solutions are classified in terms of their chiral content and their influence on particular charge configurations in space. The results of such classical interactions motivate a particular quantum description of a freely propagating laser pulse in terms of an effective quantum Hamiltonian. The classical chiral states that evolve according to the classical vacuum Maxwell equations are now replaced by quantized bi-qutrit elements satisfying the Schrodinger equation. This description may offer a means to control and manipulate qu-trit states encoded into such laser pulses.
Aspects of Quantum Energy and Stress in Inhomogeneous Unbounded Dielectric Continua
S. Goto,R. W. Tucker,T. J. Walton
Physics , 2014,
Abstract: This article addresses a number of issues associated with the problem of calculating contributions from the electromagnetic quantum induced energy and stress in a stationary material with an inhomogeneous polarizability. After briefly reviewing the conventional approaches developed by Lifshitz el al and more recent attempts by others, we emphasize the need to accommodate the effects due to the classical constitutive properties of the material in any experimental attempt to detect such contributions. Attention is then concentrated on a particular system composed of an ENZ-type (epsilon-near-zero) meta-material, chosen to have an anisotropic and inhomogeneous permittivity confined in an infinitely long perfectly conducting open waveguide. This permits us to deduce from the source-free Maxwell's equations a complete set of harmonic electromagnetic evanescent eigen-modes and eigen-frequencies. Since these solutions prohibit the existence of asymptotic scattering states in the guide an alternative regularization scheme, based on the Euler-Maclaurin formula, enables us to prescribe precise criteria for the extraction of finite quantum expectation values from regularized mode sums together with error bounds on these values. This scheme is used to derive analytic results for regularized energy densities in the guide. The criteria are exploited to construct a numerical scheme that is bench-marked by comparing its output with the analytic results derived from the special properties of the inhomogeneous ENZ medium.
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