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Search Results: 1 - 10 of 198173 matches for " Dunstone N. "
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Status and Distribution of Otters In the Amboro National Park, Bolivia
Dunstone N.,Strachan R.
IUCN Otter Specialist Group Bulletin , 1988,
Abstract: Otters have not fared well in the presence of man, both species have been extensively hunted for their pelts. In recent years an even greater threat is posed by the dynamiting and poisoning of rivers and clearance of bankside vegetation. Amboro is a relatively new National Park and should be regarded as a showpiece for Bolivia. The foresight of the Government, C.D.F., Prodena Bolivia, and particularly Reginald Hardy and Robin Clarke in getting this venture off the ground and for their continuing support is commendable. Considerable problems remain however, paramount of which, is the hunting of animals for food, for live export or for skins. Ample evidence of this practise has been found on both visits to Amboro. Pteronura brasiliensis occurred commonly in the Park up until 10 years ago, and was hunted for its pelt until 15 years ago. The species of otter which was commonly encountered was the neotropical river otter (Lutra longicaudis). As far as the otter populations are concerned, direct persecution is now minimal since there is no market for their skins. However the practise of fishing using dynamite or poison should be actively discouraged if the good populations of these animals are to be maintained.
Spectropolarimetric multi line analysis of stellar magnetic fields
J. C. Ramirez Velez,M. Semel,M. Stift,M. J. Martinez Gonzalez,P. Petit,N. Dunstone
Physics , 2010, DOI: 10.1051/0004-6361/200810484
Abstract: In this paper we study the feasibility of inferring the magnetic field from polarized multi-line spectra using two methods: The pseudo line approach and The PCA-ZDI approach. We use multi-line techniques, meaning that all the lines of a stellar spectrum contribute to obtain a polarization signature. The use of multiple lines dramatically increases the signal to noise ratio of these polarizations signatures. Using one technique, the pseudo-line approach, we construct the pseudo-line as the mean profile of all the individual lines. The other technique, the PCA-ZDI approach proposed recently by Semel et al. (2006) for the detection of polarized signals, combines Principle Components Analysis (PCA) and the Zeeman Do ppler Imaging technique (ZDI). This new method has a main advantage: the polarized signature is extracted using cross correlations between the stellar spectra nd functions containing the polarization properties of each line. These functions are the principal components of a database of synthetic spectra. The synthesis of the spectra of the database are obtained using the radiative transfer equations in LTE. The profiles built with the PCA-ZDI technique are denominated Multi-Zeeman-Signatures. The construction of the pseudo line as well as the Multi-Zeeman-Signatures is a powerful tool in the study of stellar and solar magnetic fields. The information of the physical parameters that governs the line formation is contained in the final polarized profiles. In particular, using inversion codes, we have shown that the magnetic field vector can be properly inferred with both approaches despite the magnetic field regime.
Magnetic fields and differential rotation on the pre-main sequence III: The early-G star HD 106506
I. A. Waite,S. C. Marsden,B. D. Carter,R. Hart,J. -F. Donati,J. C. Ramírez Vélez,M. Semel,N. Dunstone
Physics , 2011, DOI: 10.1111/j.1365-2966.2011.18366.x
Abstract: We present photometry and spectropolarimetry of the pre-main sequence star HD 106506. A photometric rotational period of ~1.416 +/- 0.133 days has been derived using observations at Mount Kent Observatory (MKO). Spectropolarimetric data taken at the 3.9-m Anglo-Australian Telescope (AAT) were used to derive spot occupancy and magnetic maps of the star through the technique of Zeeman Doppler imaging (ZDI). The resulting brightness maps indicate that HD 106506 displays photospheric spots at all latitudes including a predominant polar spot. Azimuthal and radial magnetic images of this star have been derived, and a significant azimuthal magnetic field is indicated, in line with other active young stars. A solar-like differential rotation law was incorporated into the imaging process. Using Stokes I information the equatorial rotation rate, $\Omega_{eq}$, was found to be 4.54 +/- 0.01 rad/d, with a photospheric shear $\delta\Omega$ of $0.21_{-0.03}^{+0.02}$ rad/d. This equates to an equatorial rotation period of ~1.39 +/- 0.01 days, with the equatorial region lapping the poles every ~$30_{-3}^{+5}$ days. Using the magnetic features, the equatorial rotation rate, $\Omega_{eq}$, was found to be 4.51 +/- 0.01 rad/d, with a photospheric shear $\delta\Omega$ of 0.24 +/- 0.03 rad/d. This differential rotation is approximately 4 times that observed on the Sun.
Surface magnetic fields on two accreting T Tauri stars: CV Cha and CR Cha
G. A. J. Hussain,A. Collier Cameron,M. M. Jardine,N. Dunstone,J. Ramirez Velez,H. C. Stempels,J. -F. Donati,M. Semel,G. Aulanier,T. Harries,J. Bouvier,C. Dougados,J. Ferreira,B. D. Carter,W. A. Lawson
Physics , 2009, DOI: 10.1111/j.1365-2966.2009.14881.x
Abstract: We have produced brightness and magnetic field maps of the surfaces of CV Cha and CR Cha: two actively accreting G and K-type T Tauri stars in the Chamaeleon I star-forming cloud with ages of 3-5 Myr. Our magnetic field maps show evidence for strong, complex multi-polar fields similar to those obtained for young rapidly rotating main sequence stars. Brightness maps indicate the presence of dark polar caps and low latitude spots -- these brightness maps are very similar to those obtained for other pre-main sequence and rapidly rotating main sequence stars. Only two other classical T Tauri stars have been studied using similar techniques so far: V2129 Oph and BP Tau. CV Cha and CR Cha show magnetic field patterns that are significantly more complex than those recovered for BP Tau, a fully convective T Tauri star. We discuss possible reasons for this difference and suggest that the complexity of the stellar magnetic field is related to the convection zone; with more complex fields being found in T Tauri stars with radiative cores (V2129 Oph, CV Cha and CR Cha). However, it is clearly necessary to conduct magnetic field studies of T Tauri star systems, exploring a wide range of stellar parameters in order to establish how they affect magnetic field generation, and thus how these magnetic fields are likely to affect the evolution of T Tauri star systems as they approach the main sequence.
Magnetic fields and differential rotation on the pre-main sequence II: The early-G star HD 141943 - coronal magnetic field, H-alpha emission and differential rotation
S. C. Marsden,M. M. Jardine,J. C. Ramírez Vélez,E. Alecian,C. J. Brown,B. D. Carter,J. F. Donati,N. Dunstone,R. Hart,M. Semel,I. A. Waite
Physics , 2011, DOI: 10.1111/j.1365-2966.2011.18272.x
Abstract: Spectropolarimetric observations of the pre-main sequence early-G star HD 141943 were obtained at three observing epochs (2007, 2009 and 2010). The observations were obtained using the 3.9-m Anglo-Australian telescope with the UCLES echelle spectrograph and the SEMPOL spectropolarimeter visitor instrument. The brightness and surface magnetic field topologies (given in Paper I) were used to determine the star's surface differential rotation and reconstruct the coronal magnetic field of the star. The coronal magnetic field at the 3 epochs shows on the largest scales that the field structure is dominated by the dipole component with possible evidence for the tilt of the dipole axis shifting between observations. We find very high levels of differential rotation on HD 141943 (~8 times the solar value for the magnetic features and ~5 times solar for the brightness features) similar to that evidenced by another young early-G star, HD 171488. These results indicate that a significant increase in the level of differential rotation occurs for young stars around a spectral type of early-G. Also we find for the 2010 observations that there is a large difference in the differential rotation measured from the brightness and magnetic features, similar to that seen on early-K stars, but with the difference being much larger. We find only tentative evidence for temporal evolution in the differential rotation of HD 141943.
Magnetic fields and differential rotation on the pre-main sequence I: The early-G star HD 141943 - brightness and magnetic topologies
S. C. Marsden,M. M. Jardine,J. C. Ramírez Vélez,E. Alecian,C. J. Brown,B. D. Carter,J. F. Donati,N. Dunstone,R. Hart,M. Semel,I. A. Waite
Physics , 2011, DOI: 10.1111/j.1365-2966.2011.18367.x
Abstract: Spectroscopic and spectropolarimetric observations of the pre-main sequence early-G star HD 141943 were obtained at four observing epochs (in 2006, 2007, 2009 and 2010). The observations were undertaken at the 3.9-m Anglo-Australian Telescope using the UCLES echelle spectrograph and the SEMPOL spectropolarimeter visitor instrument. Brightness and surface magnetic field topologies were reconstructed for the star using the technique of least-squares deconvolution to increase the signal-to-noise of the data. The reconstructed brightness maps show that HD 141943 had a weak polar spot and a significant amount of low latitude features, with little change in the latitude distribution of the spots over the 4 years of observations. The surface magnetic field was reconstructed at three of the epochs from a high order (l <= 30) spherical harmonic expansion of the spectropolarimetric observations. The reconstructed magnetic topologies show that in 2007 and 2010 the surface magnetic field was reasonably balanced between poloidal and toroidal components. However we find tentative evidence of a change in the poloidal/toroidal ratio in 2009 with the poloidal component becoming more dominant. At all epochs the radial magnetic field is predominantly non-axisymmetric while the azimuthal field is predominantly axisymmetric with a ring of positive azimuthal field around the pole similar to that seen on other active stars.
Trends and determinants of Comprehensive HIV and AIDS knowledge among urban young women in Kenya
Rhoune Ochako, Dunstone Ulwodi, Purity Njagi, Steven Kimetu, Aggrey Onyango
AIDS Research and Therapy , 2011, DOI: 10.1186/1742-6405-8-11
Abstract: Data used was drawn from the 1993, 1998, 2003 and 2008/09 Kenya Demographic & Health Surveys. Logistic regression was used for analysis.While comprehensive HIV and AIDS knowledge is low among urban young women in Kenya, the results show a significant increase in comprehensive knowledge from 9% in 1993 to 54% in 2008/09. The strongest predictors for having comprehensive knowledge were found to be 1) education; 2) having tested for HIV; 3) knowing someone with HIV, and/or 4) having a small or moderate to great risk perception.The response to HIV and AIDS can only be successful if individuals adopt behaviours that will protect against infection. Currently, efforts are underway in Kenya to ensure that young people have comprehensive knowledge. As evident from the results, comprehensive HIV and AIDS knowledge has increased over the 15 year period among urban young women from 9% in 1993 to 54% in 2008/09. Despite this improvement, a lot more needs to be done to attain the target of 90% threshold set by UNGASS. While both young women and men should be targeted with education on HIV prevention, concerted efforts should be directed at young women as many continue to get infected due to low levels of comprehensive HIV knowledge.Globally, sub-Saharan Africa (SSA) has been worst affected by HIV as it accounted for more than 68% the burden of the disease with more than 72% of all AIDS deaths recorded in 2008 [1,2]. New HIV infections were estimated at 1.7 million in 2007, accumulating to 22.5 million people living with the virus; of which, women accounted for 61% and young people aged 15-24 years accounted for an estimated 45% of the new HIV infections. In SSA region, Kenya is among countries worst affected by the AIDS pandemic [3], and this led to the declaration of AIDS as a national disaster in 1999. Since then, the National AIDS Control Council (NACC) was established to coordinate resources for prevention of HIV transmission and provision of care and support to the infected
The impact of fire on habitat use by the short-snouted elephant shrew (Elephantulus brachyrhynchus) in North West Province, South Africa
Richard W. Yarnell,Daniel J. Metcalfe,Nigel Dunstone,Niall Burnside
African Zoology , 2011,
Abstract: Several studies have investigated the response of small mammal populations to fire, but few have investigated behavioural responses to habitat modification. In this study we investigated the impact of fire on home range, habitat use and activity patterns of the short-snouted elephant shrew ( highlights the importance of considering the landscape mosaic in fire management and allowing sufficient island patches to remain post-fire ensures the persistence of the small mammal fauna.Elephantulus brachyrhynchus) by radio-tracking individuals before and after a fire event. All animals survived the passage of fire in termite mound refugia. Before the fire, grassland was used more than thickets, but habitat utilization shifted to thickets after fire had removed the grass cover. Thickets were an important refuge both pre- and post-fire, but the proportion of thicket within the home range was greater post-fire. We conclude that fire-induced habitat modification resulted in a restriction of E. brachyrhynchus movements to patches of unburned vegetation. This may be a behavioural response to an increase in predation pressure associated with a reduction in cover, rather than a lack of food. This study
A New Model for Pore Formation by Cholesterol-Dependent Cytolysins
Cyril F. Reboul,James C. Whisstock,Michelle A. Dunstone
PLOS Computational Biology , 2014, DOI: doi/10.1371/journal.pcbi.1003791
Abstract: Cholesterol Dependent Cytolysins (CDCs) are important bacterial virulence factors that form large (200–300 ?) membrane embedded pores in target cells. Currently, insights from X-ray crystallography, biophysical and single particle cryo-Electron Microscopy (cryo-EM) experiments suggest that soluble monomers first interact with the membrane surface via a C-terminal Immunoglobulin-like domain (Ig; Domain 4). Membrane bound oligomers then assemble into a prepore oligomeric form, following which the prepore assembly collapses towards the membrane surface, with concomitant release and insertion of the membrane spanning subunits. During this rearrangement it is proposed that Domain 2, a region comprising three β-strands that links the pore forming region (Domains 1 and 3) and the Ig domain, must undergo a significant yet currently undetermined, conformational change. Here we address this problem through a systematic molecular modeling and structural bioinformatics approach. Our work shows that simple rigid body rotations may account for the observed collapse of the prepore towards the membrane surface. Support for this idea comes from analysis of published cryo-EM maps of the pneumolysin pore, available crystal structures and molecular dynamics simulations. The latter data in particular reveal that Domains 1, 2 and 4 are able to undergo significant rotational movements with respect to each other. Together, our data provide new and testable insights into the mechanism of pore formation by CDCs.
Perforin evolved from a gene duplication of MPEG1, followed by a complex pattern of gene gain and loss within Euteleostomi
Michael E D'Angelo, Michelle A Dunstone, James C Whisstock, Joseph A Trapani, Phillip I Bird
BMC Evolutionary Biology , 2012, DOI: 10.1186/1471-2148-12-59
Abstract: We identified orthologs and homologs of human perforin in all but one species analysed from Euteleostomi, and present evidence for an earlier ortholog in Gnathostomata but not in more primitive chordates. In placental mammals perforin is a single copy gene, but there are multiple perforin genes in all lineages predating marsupials, except birds. Our comparisons of these many-to-one homologs of human perforin show that they mainly arose from lineage-specific gene duplications in multiple taxa, suggesting acquisition of new roles or different modes of regulation. We also present evidence that perforin arose from duplication of the ancient MPEG1 gene, and that it shares a common ancestor with the functionally related complement proteins.The evolution of perforin in vertebrates involved a complex pattern of gene, as well as intron, gain and loss. The primordial perforin gene arose at least 500 million years ago, at around the time that the major histocompatibility complex-T cell receptor antigen recognition system was established. As it is absent from primitive chordates and invertebrates, cytotoxic cells from these lineages must possess a different effector molecule or cytotoxic mechanism.
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