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Search Results: 1 - 10 of 462565 matches for " Eleanor A. Powell "
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HIV Infection of Hepatocytes Results in a Modest Increase in Hepatitis C Virus Expression In Vitro
Ling Kong, Jeffrey A. Welge, Eleanor A. Powell, Jason T. Blackard
PLOS ONE , 2014, DOI: 10.1371/journal.pone.0083728
Abstract: Previous studies demonstrate that soluble HIV proteins impact both hepatocyte function and HCV replication in vitro. It has also been reported that HIV can productively infect hepatocytes. We therefore investigated the impact of HIV infection of hepatocytes on HCV expression. The Huh7.5JFH1 cell line that constitutively expresses infectious HCV was infected with the lab-adapted strains HIVNL4-3 or HIVYK-JRCSF. HCV expression was quantified via HCV core antigen ELISA, Western blot, and strand-specific real-time PCR for positive-sense and negative-sense HCV RNA. After HIVNL4-3 infection of Huh7.5JFH1 cells, positive-sense and negative-sense HCV RNA levels were elevated compared to HIV uninfected cells. Increased HCV RNA synthesis was also observed after infection of Huh7.5JFH1 cells with HIVYK-JRCSF. HIV-induced HCV core production was decreased in the presence of the anti-HIV drugs AZT, T20, and raltegravir, although these medications had a minimal effect on HCV expression in the absence of HIV. HCV core, NS3, and NS5A protein expression were increased after HIV infection of Huh7.5JFH1 cells. Chemically inactivated HIV had a minimal effect on HCV expression in Huh7.5JFH1 cells suggesting that ongoing viral replication was critical. These data demonstrate that HIV induces HCV RNA synthesis and protein production in vitro and complement previous in vivo reports that HCV RNA levels are elevated in individuals with HIV/HCV co-infection compared to those with HCV mono-infection. These findings suggest that HIV suppression may be a critical factor in controlling liver disease, particularly if the underlying liver disease is not treated.
Effects of HCV on Basal and Tat-Induced HIV LTR Activation
Satarupa Sengupta, Eleanor Powell, Ling Kong, Jason T. Blackard
PLOS ONE , 2013, DOI: 10.1371/journal.pone.0064956
Abstract: Hepatitis C virus (HCV) co-infection occurs in ~30–40% of the HIV-infected population in the US. While a significant body of research suggests an adverse effect of HIV on HCV replication and disease progression, the impact of HCV on HIV infection has not been well studied. Increasing data suggest that hepatocytes and other liver cell populations can serve as reservoirs for HIV replication. Therefore, to gain insight into the impact of HCV on HIV, the effects of the HCV Core protein and infectious hepatitis C virions were evaluated on basal and Tat-induced activation of the HIV long terminal repeat (LTR) in hepatocytes. The HIV LTR was highly induced by the HIV transactivator protein Tat in hepatocytes. Activation varied according to the number of NF-kB binding sites present in the LTRs from different HIV subtypes. Involvement of the NF-kB binding pathway in LTR activation was demonstrated using an NF-kB inhibitor and deletion of the NF-kB binding sites. TNFα, a pro-inflammatory cytokine that plays an important role in HIV pathogenesis, also induced LTR activity in hepatocytes. However, HIV LTR activity was suppressed in hepatocytes in the presence of HCV Core protein, and the suppressive effect persisted in the presence of TNFα. In contrast, infectious hepatitis C virions upregulated HIV LTR activation and gene transcription. Core-mediated suppression remained unaltered in the presence of HCV NS3/4A protein, suggesting the involvement of other viral/cellular factors. These findings have significant clinical implications as they imply that HCV could accelerate HIV disease progression in HIV/HCV co-infected patients. Such analyses are important to elucidate the mechanisms by which these viruses interact and could facilitate the development of more effective therapies to treat HIV/HCV co-infection.
Black-Scholes Option Pricing Model Modified to Admit a Miniscule Drift Can Reproduce the Volatility Smile  [PDF]
Matthew C. Modisett, James A. Powell
Applied Mathematics (AM) , 2012, DOI: 10.4236/am.2012.36093
Abstract: This paper develops a closed-form solution to an extended Black-Scholes (EBS) pricing formula which admits an implied drift parameter alongside the standard implied volatility. The market volatility smiles for vanilla call options on the S&P 500 index are recreated fitting the best volatility-drift combination in this new EBS. Using a likelihood ratio test, the implied drift parameter is seen to be quite significant in explaining volatility smiles. The implied drift parameter is sufficiently small to be undetectable via historical pricing analysis, suggesting that drift is best considered as an implied parameter rather than a historically-fit one. An overview of option-pricing models is provided as background.
Mathematical Model of Seed Dispersal by Frugivorous Birds and Migration Potential of Pinyon and Juniper in Utah  [PDF]
Ram C. Neupane, James A. Powell
Applied Mathematics (AM) , 2015, DOI: 10.4236/am.2015.69135
Abstract: Seed dispersal of juniper and pinyon is a process in which frugivorous birds play an important role. Birds either consume and digest seeds or carry and cache them at some distance from the source tree. These transported and settled seeds can be described by a dispersal kernel, which captures the probability that the seed will move a certain distance by the end of the process. To model active seed dispersal of this nature, we introduce handling time probabilities into the dispersal model to generate a seed digestion kernel. In the limit of no variability in handling time the seed digestion kernel is Gaussian, whereas for uniform variability in handling time the kernel approaches a Laplace distribution. This allows us to standardize spatial movement (diffusion) and handling time (peak settling rate) parameters for all three distributions and compare. Analysis of the tails indicates that the seed digestion kernel decays at a rate intermediate between Gaussian and Laplace seed kernels. Using this seed digestion kernel, we create an invasion model to estimate the speed at which juniper and pinyon forest boundaries move. We find that the speed of seed invasion corresponding to the digestion kernel was faster than seeds resulting from Laplace and Gaussian kernels for more rapidly digested seeds. For longer handling times the speeds are bounded between the Laplace (faster) and Gaussian (slower) speeds. Using parameter values from the literature we evaluate the migration potential of pinyon and juniper, finding that pinyon may be able to migrate up to two orders of magnitude more rapidly, consistent with observations of pine migration during the Holocene.
Seed improvement by selection and invigoration
Powell, A.A.;
Scientia Agricola , 1998, DOI: 10.1590/S0103-90161998000500023
Abstract: the basis of differences in seed quality are described for two groups of crops, grain legumes and vegetables and approaches to the improvement of quality are proposed. in grain legumes the major factors affecting seed quality are imbibition damage, seed ageing and their interaction. it is proposed that use of seed vigour tests, specifically the electrical conductivity test, to identify the incidence of imbibition damage and ageing allows the selection of seed lots for sale and for use under different field conditions. alternatively in grain legume species in which there is a genotypic influence on predisposition to imbibition damage the approach to seed improvement may lie through selection in breeding programmes. thus identification of testa characteristics that favour slow imbibition would enable selection for these characteristics. seed ageing is also the major cause of reduced seed quality in vegetable species, leading to slow and asynchronous germination. an approach to their seed improvement has been the development of seed invigoration treatments based on seed hydration. the principle of these treatments is described and several treatments outlined, with emphasis being given to aerated hydration, a treatment completed within 36h. the physiological basis of improvement by invigoration is discussed.
Seed improvement by selection and invigoration
Powell A.A.
Scientia Agricola , 1998,
Abstract: The basis of differences in seed quality are described for two groups of crops, grain legumes and vegetables and approaches to the improvement of quality are proposed. In grain legumes the major factors affecting seed quality are imbibition damage, seed ageing and their interaction. It is proposed that use of seed vigour tests, specifically the electrical conductivity test, to identify the incidence of imbibition damage and ageing allows the selection of seed lots for sale and for use under different field conditions. Alternatively in grain legume species in which there is a genotypic influence on predisposition to imbibition damage the approach to seed improvement may lie through selection in breeding programmes. Thus identification of testa characteristics that favour slow imbibition would enable selection for these characteristics. Seed ageing is also the major cause of reduced seed quality in vegetable species, leading to slow and asynchronous germination. An approach to their seed improvement has been the development of seed invigoration treatments based on seed hydration. The principle of these treatments is described and several treatments outlined, with emphasis being given to aerated hydration, a treatment completed within 36h. The physiological basis of improvement by invigoration is discussed.
Common–interest community agreements on private lands provide opportunity and scale for wildlife management
Powell, L. A.
Animal Biodiversity and Conservation , 2012,
Abstract: Private lands are critical to conservation planning for wildlife, worldwide. Agriculture subsidies, tax incentives, and conservation easements have been successfully used as tools to convert cropland to native vegetation. However, uncertain economies threaten the sustainability of these incentives. The wildlife management profession is in need of innovative models that support effective management of populations. I argue that biologists should consider the option of facilitating the development of private reserves to reduce the dependence of conservation on public investment. Private reserves can be enhanced by creating common–interest communities, which reduce the problem posed by limited size of individual properties. Cross–property agreements between landowners can provide economic incentives through forms of ecotourism, energy production, and/or enhanced agricultural production. I share two case studies that demonstrate how cross–property agreements may be beneficial to landowner’s finances and conservation of diverse wildlife communities, as well as providing an efficient structure for NGOs and management agencies to engage and support landowners.
Tensor Tilt from Primordial B-modes
Brian A. Powell
Physics , 2011, DOI: 10.1111/j.1365-2966.2011.19734.x
Abstract: A primordial cosmic microwave background B-mode is widely considered a "smoking gun" signature of an early period of inflationary expansion. However, competing theories of the origin of structure, including string gases and bouncing cosmologies, also produce primordial tensor perturbations that give rise to a B-mode. These models can be differentiated by the scale dependence of their tensor spectra: inflation predicts a red tilt ($n_T<0$), string gases and loop quantum cosmology predict a blue tilt ($n_T>0$), while a nonsingular matter bounce gives zero tilt ($n_T=0$). We perform a Bayesian analysis to determine how far $|n_T|$ must deviate from zero before a tilt can be detected with current and future B-mode experiments. We find that Planck in conjunction with QUIET (II) will decisively detect $n_T \neq 0$ if $|n_T| > 0.3$, too large to distinguish either single field inflation or string gases from the case $n_T=0$. While a future mission like CMBPol will offer improvement, only an ideal satellite mission will be capable of providing sufficient Bayesian evidence to distinguish between each model considered.
The resonant dynamics of arbitrarily-shaped meta-atoms
David A. Powell
Physics , 2014, DOI: 10.1103/PhysRevB.90.075108
Abstract: Meta-atoms, nano-antennas, plasmonic particles and other small scatterers are commonly modeled in terms of their modes. However these modal solutions are seldom determined explicitly, due to the conceptual and numerical difficulties in solving eigenvalue problems for open systems with strong radiative losses. Here these modes are directly calculated from Maxwell's equations expressed in integral operator form, by finding the complex frequencies which yield a homogenous solution. This gives a clear physical interpretation of the modes, and enables their conduction or polarization current distribution to be calculated numerically for particles of arbitrary shape. By combining the modal current distribution with a scalar impedance function, simple yet accurate models of scatterers are constructed which describe their response to an arbitrary incident field over a broad bandwidth. These models generalize both equivalent-dipole and and equivalent-circuit models to finite sized structures with multiple modes. They are applied here to explain the frequency-splitting for a pair of coupled split rings, and the accompanying change in radiative losses. The approach presented in this paper is made available in an open-source code.
Scalar runnings and a test of slow roll from CMB distortions
Brian A. Powell
Physics , 2012,
Abstract: A future measurement of cosmic microwave \mu-distortions by an experiment with the specifications of PIXIE will provide an equivalent 3-sigma detection of the running of running of the spectral index of scalar perturbations, \beta = d\alpha/dln(k), if \mu > 7.75 E-8, covering much of the PIXIE sensitivity range. This corresponds to a resolution limit of \beta > 0.015 which is relatively large given any presumption of slow roll, a result of the current tight constraints on \alpha < 0 on CMB scales. We show that a detection of \beta at this level is in conflict with slow roll conditions if the primordial signal can be distinguished from any post-inflationary contamination.
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