oalib

Publish in OALib Journal

ISSN: 2333-9721

APC: Only $99

Submit

Any time

2020 ( 2 )

2019 ( 364 )

2018 ( 522 )

2017 ( 493 )

Custom range...

Search Results: 1 - 10 of 328480 matches for " D. E. Ross "
All listed articles are free for downloading (OA Articles)
Page 1 /328480
Display every page Item
Infectious Disease, Endangerment, and Extinction
Ross D. E. MacPhee,Alex D. Greenwood
International Journal of Evolutionary Biology , 2013, DOI: 10.1155/2013/571939
Abstract:
Infectious Disease, Endangerment, and Extinction
Ross D. E. MacPhee,Alex D. Greenwood
International Journal of Evolutionary Biology , 2013, DOI: 10.1155/2013/571939
Abstract: Infectious disease, especially virulent infectious disease, is commonly regarded as a cause of fluctuation or decline in biological populations. However, it is not generally considered as a primary factor in causing the actual endangerment or extinction of species. We review here the known historical examples in which disease has, or has been assumed to have had, a major deleterious impact on animal species, including extinction, and highlight some recent cases in which disease is the chief suspect in causing the outright endangerment of particular species. We conclude that the role of disease in historical extinctions at the population or species level may have been underestimated. Recent methodological breakthroughs may lead to a better understanding of the past and present roles of infectious disease in influencing population fitness and other parameters. 1. Background Although lethal epi- or panzootics are obvious risk factors that can lead to population fluctuation or decline in particular circumstances, infectious diseases are seldom considered as potential drivers of extirpation or extinction—that is, of the complete loss of all populations or subunits comprising a given biological species. For example, in conservation biology, infectious disease is usually regarded as having only a marginal or contributory influence on extinction, except perhaps in unusual circumstances (e.g., [1–4]). In their examination of 223 instances of critically endangered species listed by the IUCN (International Union for Conservation of Nature) as allegedly threatened by infectious disease, Smith et al. [4] found that in the overwhelming majority of cases there was no conclusive evidence to support infectious disease as a contributing threat. Although this record should improve with increasing awareness of the effects of infectious diseases on wildlife, as this paper illustrates progress has so far been slow. Both of the authors of this paper are primarily concerned with mammals, which is the group that will receive the bulk of attention here. However, at the pragmatic, data-gathering level, the issues concerned with properly accounting for and evaluating the effects of infectious diseases on natural populations differ little from one phylogenetic grouping to another. First, narrowing down extinction events or even catastrophic population declines to single causes is almost always problematic. In most real cases, extinction is multicausational, even if one cause can be identified as being predominantly responsible [5]. Habitat fragmentation and climate change are
Higgs mass bounds in a Triplet Model
J. R. Forshaw,D. A. Ross,B. E. White
Physics , 2001, DOI: 10.1088/1126-6708/2001/10/007
Abstract: We perform a global fit to high energy precision electroweak data in a Higgs model containing the usual isospin doublet plus a real isospin triplet. The analysis is performed in terms of the oblique parameters S, T and U and we show that the mass of the lightest Higgs boson can be as large as 2 TeV.
Peak Power Effect on Skin Rejuvenation Using IPL: Lumecca IPL Evaluation  [PDF]
E. V. Ross, Michael Kreindel
Advances in Aging Research (AAR) , 2016, DOI: 10.4236/aar.2016.53008
Abstract: A high peak power IPL system (Lumecca) was tested to determine the correlation between a high peak power and the successful treatment of pigmented and vascular lesions. Short pulse duration in the millisecond range and high peak power of 3.3 kW/cm2 enabled selective and effective destruction, not only of pigment, but also of vessels in a comparable manner to a pulsed dye laser. Only one treatment session at a low fluence (8 - 16 J/cm2) was sufficient to achieve the desired results.
A Gravitational Redshift Determination of the Mean Mass of White Dwarfs. DA Stars
Ross E. Falcon,D. E. Winget,M. H. Montgomery,Kurtis A. Williams
Physics , 2010, DOI: 10.1088/0004-637X/712/1/585
Abstract: We measure apparent velocities (v_app) of the Halpha and Hbeta Balmer line cores for 449 non-binary thin disk normal DA white dwarfs (WDs) using optical spectra taken for the ESO SN Ia Progenitor surveY (SPY; Napiwotzki et al. 2001). Assuming these WDs are nearby and co-moving, we correct our velocities to the Local Standard of Rest so that the remaining stellar motions are random. By averaging over the sample, we are left with the mean gravitational redshift, : we find = = 32.57 +/- 1.17 km/s. Using the mass-radius relation from evolutionary models, this translates to a mean mass of 0.647 +0.013 -0.014 Msun. We interpret this as the mean mass for all DAs. Our results are in agreement with previous gravitational redshift studies but are significantly higher than all previous spectroscopic determinations except the recent findings of Tremblay & Bergeron (2009). Since the gravitational redshift method is independent of surface gravity from atmosphere models, we investigate the mean mass of DAs with spectroscopic Teff both above and below 12000 K; fits to line profiles give a rapid increase in the mean mass with decreasing Teff. Our results are consistent with no significant change in mean mass: ^hot = 0.640 +/- 0.014 Msun and ^cool = 0.686 +0.035 -0.039 Msun.
The Nature and Origin of z_a~z_e Absorption Lines in the Redshift 0.20 Quasar, PKS 2135-147
Fred Hamann,E. A. Beaver,Ross D. Cohen,Vesa Junkkarinen,R. W. Lyons,E. M. Burbidge
Physics , 1997, DOI: 10.1086/304698
Abstract: We use new UV and optical spectra and an archival HST-WFPC2 image to study the z_a~z_e absorber in the z_e = 0.20 QSO PKS 2135-147. The UV spectra, obtained with HST-FOS, show strong z_a~z_e absorption lines of C IV, N V, O VI, Ly-alpha and Ly-beta. The z_a~z_e line profiles are resolved, with deconvolved FWHM of 270 to 450 km/s. Lower limits on the total column densities are of order 10^15 cm-2 for all ions. If the absorber is photoionized by the QSO and the derived relative columns in C IV and H I are roughly correct, then the metallicity must be at least solar. The location of the z_a~z_e absorber remains uncertain. Two ~L_* galaxies in a small cluster centered on PKS 2135-147 lie within 36h^{-1} kpc projected distance and have redshifts consistent with causing or contributing to the z_a~z_e lines. The extensive halo of the QSO's host galaxy could also contribute. Calculations show that the QSO is bright enough to photoionize gas up to O VI in the low-density halos of the host and nearby cluster galaxies. Nonetheless, there is indirect evidence for absorption much nearer the QSO, namely (1) the derived high (albeit uncertain) metallicity, (2) the relatively strong N V absorption lines, which might be caused by a higher nitrogen abundance in the metal-rich gas, and (3) strong, lobe-dominated steep-spectrum radio emission, which is known to correlate with a much higher incidence of (probably intrinsic) z_a~z_e lines. We propose that the CIV/NV/OVI line ratios can be used as a general diagnostic of intrinsic versus intervening absorption, as long as the line saturation effects are understood.
Variability in Hot Carbon-Dominated Atmosphere (hot DQ) White Dwarfs: Rapid Rotation?
Kurtis A. Williams,M. H. Montgomery,D. E. Winget,Ross E. Falcon,Michael Bierwagon
Physics , 2015,
Abstract: Hot white dwarfs with carbon-dominated atmospheres (hot DQs) are a cryptic class of white dwarfs. In addition to their deficiency of hydrogen and helium, most of these stars are highly magnetic, and a large fraction vary in luminosity. This variability has been ascribed to nonradial pulsations, but increasing data call this explanation into question. We present studies of short-term variability in seven hot DQ white dwarfs. Three (SDSS J1426+5752, SDSS J2200-0741, and SDSS J2348-0942) were known to be variable. Their photometric modulations are coherent over at least two years, and we find no evidence for variability at frequencies that are not harmonics. We present the first time-series photometry for three additional hot DQs (SDSS J0236-0734, SDSS J1402+3818, and SDSS J1615+4543); none are observed to vary, but the signal-to-noise is low. Finally, we present high speed photometry for SDSS J0005-1002, known to exhibit a 2.1 d photometric variation; we do not observe any short-term variability. Monoperiodicity is rare among pulsating white dwarfs, so we contemplate whether the photometric variability is due to rotation rather than pulsations; similar hypotheses have been raised by other researchers. If the variability is due to rotation, then hot DQ white dwarfs as a class contain many rapid rotators. Given the lack of companions to these stars, the origin of any fast rotation is unclear -- both massive progenitor stars and double degenerate merger remnants are possibilities. We end with suggestions on future work that would best clarify the nature of these rare, intriguing objects.
A Gravitational Redshift Determination of the Mean Mass of White Dwarfs. DBA and DB Stars
Ross E. Falcon,D. E. Winget,Michael H. Montgomery,Kurtis A. Williams
Physics , 2012, DOI: 10.1088/0004-637X/757/2/116
Abstract: We measure apparent velocities (v_app) of absorption lines for 36 white dwarfs (WDs) with helium-dominated atmospheres -- 16 DBAs and 20 DBs -- using optical spectra taken for the European Southern Observatory SN Ia progenitor survey (SPY). We find a difference of 6.9+/-6.9 km/s in the average apparent velocity of the H-alpha lines versus that of the HeI 5876AA for our DBAs. This is a measure of the blueshift of this He line due to pressure effects. By using this as a correction, we extend the gravitational redshift method employed by Falcon et al. (2010) to use the apparent velocity of the HeI 5876AA line and conduct the first gravitational redshift investigation of a group of WDs without visible hydrogen lines. We use biweight estimators to find an average apparent velocity, _BI, (and hence average gravitational redshift, _BI) for our WDs; from that we derive an average mass, _BI. For the DBAs, we find _BI = 40.8+/-4.7 km/s and derive _BI = 0.71 +0.04 -0.05 Msun. Though different from of DAs (32.57 km/s) at the 91% confidence level and suggestive of a larger DBA mean mass than that for normal DAs derived using the same method (0.647 +0.013 -0.014 Msun; Falcon et al. 2010), we do not claim this as a stringent detection. Rather, we emphasize that the difference between _BI of the DBAs and of normal DAs is no larger than 9.2 km/s, at the 95% confidence level; this corresponds to roughly 0.10 Msun. For the DBs, we find ^He_BI = 42.9+/-8.49 km/s after applying the blueshift correction and determine _BI = 0.74 +0.08 -0.09 Msun. The difference between ^He_BI of the DBs and of DAs is less than or equal to 11.5 km/s (~0.12 Msun), at the 95% confidence level. The gravitational redshift method indicates much larger mean masses than the spectroscopic determinations of the same sample by Voss et al. (2007)...
Investigation of Arctic ozone depletion sampled over midlatitudes during the Egrett Campaign of spring/summer 2000
D. E. M. Ross,J. A. Pyle,N. R. P. Harris,J. D. McIntyre
Atmospheric Chemistry and Physics Discussions , 2004,
Abstract: A unique halocarbon dataset has been obtained using the Australian high altitude research aircraft, the Grob G520T Egrett, during May–June 2000 with GC instrument (DIRAC), which has been previously deployed on balloon platforms. The halocarbon data generally shows a good anticorrelation with ozone data obtained simultaneously from commercial sensors. On 5 June 2000, at 380 K, the Egrett entered a high latitude tongue of air over the UK CFC-11 and O3 data obtained on the flight show evidence of this feature. The dataset has been used, in conjunction with a 3D chemical transport model, to infer ozone depletion encountered in the midlatitude lower stratosphere during the flight. We calculate that ozone is depleted by 20% relative to its winter value in the higher latitude airmass. A suite of ozone loss tracers in the model have been used to track ozone depletion according to location relative to the vortex and chemical cycle responsible. The model, initialised on 9 December, indicates that 50% of the total chemical ozone destruction encountered in June in the middle latitudes occurred between the 90–70° N equivalent latitude band and that 70% was due to halogen chemistry.
Investigation of Arctic ozone depletion sampled over midlatitudes during the Egrett campaign of spring/summer 2000
D. E. M. Ross,J. A. Pyle,N. R. P. Harris,J. D. McIntyre
Atmospheric Chemistry and Physics (ACP) & Discussions (ACPD) , 2004,
Abstract: A unique halocarbon dataset has been obtained using the Australian high altitude research aircraft, the Grob G520T Egrett, during May-June 2000 with GC instrument (DIRAC), which has been previously deployed on balloon platforms. The halocarbon data generally shows a good anticorrelation with ozone data obtained simultaneously from commercial sensors. On 5 June 2000, at 380K, the Egrett entered a high latitude tongue of air over the U.K. CFC-11 and O3 data obtained on the flight show evidence of this feature. The dataset has been used, in conjunction with a 3D chemical transport model, to infer ozone depletion encountered in the midlatitude lower stratosphere during the flight. We calculate that ozone is depleted by 20% relative to its winter value in the higher latitude airmass. A suite of ozone loss tracers in the model have been used to track ozone depletion according to location relative to the vortex and chemical cycle responsible. The model, initialised on 9 December, indicates that 50% of the total chemical ozone destruction encountered in June in the middle latitudes occurred in the 90-70°N equivalent latitude band and that 70% was due to halogen chemistry.
Page 1 /328480
Display every page Item


Home
Copyright © 2008-2017 Open Access Library. All rights reserved.