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Search Results: 1 - 10 of 464403 matches for " D. S. Montgomery "
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An Uncertain Future for American Lauraceae: A Lethal Threat from Redbay Ambrosia Beetle and Laurel Wilt Disease (A Review)  [PDF]
Paul E. Kendra, Wayne S. Montgomery, Jerome Niogret, Nancy D. Epsky
American Journal of Plant Sciences (AJPS) , 2013, DOI: 10.4236/ajps.2013.43A092

Laurel wilt is a destructive vascular disease responsible for high mortality of American tree species in the family Lauraceae, particularly redbay (Persea borbonia) and swampbay (P. palustris), two dominant components of Coastal Plain forest communities in the southeastern United States. The disease syndrome emerged as a result of establishment of an exotic wood-boring beetle, Xyleborus glabratus, now known as the redbay ambrosia beetle. During gallery excavation, females of X. glabratus introduce a newly-described, obligatory fungal symbiont, Raffaelea lauricola. This fungus proliferates within the gallery and provides food for the beetles, but it has proven to be pathogenic to American lauraceous hosts, which have had no co-evolved history with R. lauricola. Presence of the foreign fungus elicits secretion of resins and formation of extensive parenchymal tyloses within xylem vessels. The extreme defensive response results in blockage of water transport, systemic wilt, and ultimately tree death. The beetle vector was first detected near Savannah, Georgia in 2002, and since has spread throughout the Southeast to become established in six states. The epidemic spread south through Florida more rapidly than predicted and currently threatens commercial production of avocado (Persea americana). Recent research indicates that California bay laurel (Umbellularia californica) can serve as a reproductive host for X. glabratus and is susceptible to laurel wilt disease. Thus, the US Pacific coastal forest ecosystems (and the California avocado industry) would be negatively impacted should the vector become established along the western coast. This review article summarizes our current understanding of the insect vector, the mycopathogen, and the susceptible host tree species. It also addresses elements of disease management and limitations with our current detection methods for redbay ambrosia beetle, which rely on manuka oil lures. Of the host-based attractants evaluated, cubeb oil shows the most promise as a potential new lure

Probing the core and envelope structure of DBV white dwarfs
T. S. Metcalfe,M. H. Montgomery,S. D. Kawaler
Physics , 2003, DOI: 10.1046/j.1365-8711.2003.07128.x
Abstract: We investigate the global pulsation properties of DBV white dwarf models that include both the double-layered envelope structure expected from time-dependent diffusion calculations, as well as a non-uniform C/O core expected from prior nuclear burning. We compare these models to otherwise identical models containing a pure C core to determine whether the addition of core structure leads to any significant improvement. Our double-layered envelope model fit to GD 358 that includes an adjustable C/O core is significantly better than our pure C core fit (7sigma improvement). We find a comparable improvement from fits to a second DBV star, CBS 114, though the values of the derived parameters may be more difficult to reconcile with stellar evolution theory. We find that our models are systematically cooler by 1,900 K relative to the similar models of Fontaine & Brassard (2002). Although a fit to their model reproduces the mass and envelope structure almost exactly, we are unable to reproduce the absolute quality of their fit to GD 358. Differences between the constitutive physics employed by the two models may account for both the temperature offset and the period residuals.
The effect of 3-He diffusion on the pulsational spectra of DBV models
M. H. Montgomery,T. S. Metcalfe,D. E. Winget
Physics , 2000,
Abstract: We consider envelopes of DB white dwarfs which are not composed of pure 4-He, but rather a mixture of 3-He and 4-He. Given this assumption, the same diffusive processes which produce a relatively pure H layer overlying a He layer in the DA's should work to produce a 3-He layer overlying a 4-He layer in the DB's. We examine the relevant timescales for diffusion in these objects, and compare them to the relevant evolutionary timescales in the context of the DBV white dwarfs. We then explore the consequences which 3-He separation has on the pulsational spectra of DBV models. Since GD 358 is the best-studied member of this class of variables, we examine fits to its observed pulsation spectrum. We find that the inclusion of a 3-He layer results in a modest improvement in a direct fit to the periods, while a fit to the period spacings is significantly improved.
The core/envelope symmetry in pulsating stars
M. H. Montgomery,T. S. Metcalfe,D. E. Winget
Physics , 2003, DOI: 10.1046/j.1365-8711.2003.06853.x
Abstract: We demonstrate that there is an inherent symmetry in the way high-overtone stellar pulsations sample the core and the envelope, which can potentially lead to an ambiguity in the asteroseismologically derived locations of internal structures. We provide an intuitive example of the source of this symmetry by analogy with a vibrating string. For the stellar case, we focus on the white dwarf stars, establishing the practical consequences for high-order white dwarf pulsations both analytically and numerically. In addition, we verify the effect empirically by cross-fitting two different structural models, and we discuss the consequences that this approximate symmetry may have for past and present asteroseismological fits of the pulsating DBV, GD 358. Finally, we show how the signatures of composition transition zones that are brought about by physically distinct processes may be used to help alleviate this potential ambiguity in our asteroseismological interpretation of the pulsation frequencies observed in white dwarf stars.
Comparison of Spectral Method and Lattice Boltzmann Simulations of Two-Dimensional Hydrodynamics
D. O. Martinez,W. H. Matthaeus,S. Chen,D. C. Montgomery
Physics , 1993, DOI: 10.1063/1.868296
Abstract: We present numerical solutions of the two-dimensional Navier-Stokes equations by two methods; spectral and the novel Lattice Boltzmann Equation (LBE) scheme. Very good agreement is found for global quantities as well as energy spectra. The LBE scheme is, indeed, providing reasonably accurate solutions of the Navier-Stokes equations with an isothermal equation of state, in the nearly incompressible limit. Relaxation to a previously reported ``sinh-Poisson'' state is also observed for both runs.
Local Inflammation Exacerbates the Severity of Staphylococcus aureus Skin Infection
Christopher P. Montgomery, Melvin D. Daniels, Fan Zhao, Brad Spellberg, Anita S. Chong, Robert S. Daum
PLOS ONE , 2013, DOI: 10.1371/journal.pone.0069508
Abstract: Staphylococcus aureus is the leading cause of skin infections. In a mouse model of S. aureus skin infection, we found that lesion size did not correlate with bacterial burden. Athymic nude mice had smaller skin lesions that contained lower levels of myeloperoxidase, IL-17A, and CXCL1, compared with wild type mice, although there was no difference in bacterial burden. T cell deficiency did not explain the difference in lesion size, because TCR βδ (-/-) mice did not have smaller lesions, and adoptive transfer of congenic T cells into athymic nude mice prior to infection did not alter lesion size. The differences observed were specific to the skin, because mortality in a pneumonia model was not different between wild type and athymic nude mice. Thus, the clinical severity of S. aureus skin infection is driven by the inflammatory response to the bacteria, rather than bacterial burden, in a T cell independent manner.
The High Magnetic Field Phase Diagram of a Quasi-One Dimensional Metal
J. S. Qualls,C. H. Mielke,J. S. Brooks,L. K. Montgomery,D. G. Rickel,N. Harrison,S. Y. Han
Physics , 2000, DOI: 10.1103/PhysRevB.62.12680
Abstract: We present a unique high magnetic field phase of the quasi-one dimensional organic conductor (TMTSF)$_2$ClO$_4$. This phase, termed "Q-ClO$_4$", is obtained by rapid thermal quenching to avoid ordering of the ClO$_4$ anion. The magnetic field dependent phase of Q-ClO$_4$ is distinctly different from that in the extensively studied annealed material. Q-ClO$_4$ exhibits a spin density wave (SDW) transition at $\approx$ 5 K which is strongly magnetic field dependent. This dependence is well described by the theoretical treatment of Bjelis and Maki. We show that Q-ClO$_4$ provides a new B-T phase diagram in the hierarchy of low-dimensional organic metals (one-dimensional towards two-dimensional), and describe the temperature dependence of the of the quantum oscillations observed in the SDW phase.
Randomized Controlled Trial of Fish Oil and Montelukast and Their Combination on Airway Inflammation and Hyperpnea-Induced Bronchoconstriction
Sandra Tecklenburg-Lund,Timothy D. Mickleborough,Louise A. Turner,Alyce D. Fly,Joel M. Stager,Gregory S. Montgomery
PLOS ONE , 2012, DOI: 10.1371/journal.pone.0013487
Abstract: Both fish oil and montelukast have been shown to reduce the severity of exercise-induced bronchoconstriction (EIB). The purpose of this study was to compare the effects of fish oil and montelukast, alone and in combination, on airway inflammation and bronchoconstriction induced by eucapnic voluntary hyperpnea (EVH) in asthmatics.
The Physics of Crystallization from Globular Cluster White Dwarf Stars in NGC 6397
D. E. Winget,S. O. Kepler,Fabiola Campos,M. H. Montgomery,Leo Girardi,P. Bergeron,Kurtis Williams
Physics , 2009, DOI: 10.1088/0004-637X/693/1/L6
Abstract: We explore the physics of crystallization in the deep interiors of white dwarf stars using the color-magnitude diagram and luminosity function constructed from proper motion cleaned Hubble Space Telescope photometry of the globular cluster NGC 6397. We demonstrate that the data are consistent with the theory of crystallization of the ions in the interior of white dwarf stars and provide the first empirical evidence that the phase transition is first order: latent heat is released in the process of crystallization as predicted by van Horn (1968). We outline how this data can be used to observationally constrain the value of Gamma = E_{Coulomb}/E_{thermal} near the onset of crystallization, the central carbon/oxygen abundance, and the importance of phase separation.
Demonstration of an optical mixing technique to drive Kinetic Electrostatic Electron Nonlinear waves in laser produced plasmas
J. L. Kline,B. Afeyan,W. A. Bertsche,N. A. Kurnit,D. S. Montgomery,R. P. Johnson,C. Niemann
Physics , 2012,
Abstract: A nitrogen gas Raman cell system has been constructed to shift a 70 J 527 nm laser beam to 600 nm with 20 J of energy. The 600 nm probe and a 200J, 527 nm pump beam were optically mixed in a laser produced (gas jet) plasma. The beating of the two laser beams formed a ponderomotive force that can drive Kinetic Electrostatic Electron Nonlinear (KEEN) waves discovered in Vlasov-Poisson simulations by Afeyan et al [1,2]. KEEN waves were detected in these experiments where traditional plasma theory would declare there to be a spectral gap (ie no linear waves possible). The detection was done using Thomson scattering with probe wavelengths of both 351 nm and 263.5 nm.
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