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Search Results: 1 - 10 of 19 matches for " Aylwyn Scally "
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Destruction of protoplanetary disks in the Orion Nebula Cluster
Aylwyn Scally,Cathie Clarke
Physics , 2000, DOI: 10.1046/j.1365-8711.2001.04274.x
Abstract: We use numerical N-body simulations of the Orion Nebula Cluster (ONC) to investigate the destruction of protoplanetary disks by close stellar encounters and UV radiation from massive stars. The simulations model a cluster of 4000 stars, and we consider separately cases in which the disks have fixed radii of 100 AU and 10 AU. In the former case, depending on a star's position and orbit in the cluster over 10^7 years, UV photoevaporation removes at least 0.01 Msol from its disk, and can remove up to 1 Msol. We find no dynamical models of the ONC consistent with the suggestion of Storzer and Hollenbach that the observed distribution and abundance of proplyds could be explained by a population of stars on radial orbits which spend relatively little time near Theta 1C Ori (the most massive star in the ONC). Instead the observations require either massive disks (e.g. a typical initial disk mass of 0.4 Msol) or a very recent birth for Theta 1C Ori. When we consider the photoevaporation of the inner 10 AU of disks in the ONC, we find that planet formation would be hardly affected. Outside that region, planets would be prevented from forming in about half the systems, unless either the initial disk masses were very high or they formed in less than ~ 2 Myr and Theta 1C Ori has only very recently appeared. We also present statistics on the distribution of minimum stellar encounter separations. This peaks at 1000 AU, with less than 10% of stars having had an encounter closer than 100 AU after 10^7 years. We conclude that stellar encounters are unlikely to play a significant role in destroying protoplanetary disks. In the absence of any disruption mechanism other than those considered here, we would thus predict planetary systems like our own to be common amongst stars forming in ONC-like environments.
Wide binaries in the Orion Nebula Cluster
Aylwyn Scally,Cathie Clarke,Mark J. McCaughrean
Physics , 1999, DOI: 10.1046/j.1365-8711.1999.02513.x
Abstract: Using proper motion data for 894 stars in the Orion Nebula Cluster (ONC) compiled by Jones & Walker in 1988, we search for binaries with apparent separations in the range 1000-5000 AU, and find an upper limit of three. Using a Monte Carlo method, we test the consistency of this result with two hypotheses: i) that the cluster contains a binary population identical to that found in the solar neighbourhood, and ii) that the cluster contains no binaries at all in this separation range. We obtain results strongly favouring the latter hypothesis. Star formation in the Galaxy is seen to occur in a variety of different environments, but it has been proposed that most stars may be formed in dense regions similar to the ONC, rather than in less dense groupings like that found in Taurus-Auriga. Since roughly 15 per cent of galactic field stars are known to be in binaries with separations greater than 1000 AU, the apparent absence of such binaries in the ONC places an upper limit on the contribution that dense clusters can make to galactic star formation.
Brown dwarf populations in open clusters
Tim Adams,Melvyn B. Davies,Richard F. Jameson,Aylwyn Scally
Physics , 2002, DOI: 10.1046/j.1365-8711.2002.05413.x
Abstract: We present the results of multiple simulations of open clusters, modelling the dynamics of a population of brown dwarf members. We consider the effects of a large range of primordial binary populations, including the possibilities of having brown dwarf members contained within a binary system. We also examine the effects of various cluster diameters and masses. Our examination of a population of wide binary systems containing brown dwarfs, reveals evidence for exchange reactions whereby the brown dwarf is ejected from the system and replaced by a heavier main-sequence star. We find that there exists the possibility of hiding a large fraction of the brown dwarfs contained within the primordial binary population. We conclude that it is probable that the majority of brown dwarfs are contained within primordial binary systems which then hides a large proportion of them from detection.
A Genome-Wide Survey of Genetic Variation in Gorillas Using Reduced Representation Sequencing
Aylwyn Scally, Bryndis Yngvadottir, Yali Xue, Qasim Ayub, Richard Durbin, Chris Tyler-Smith
PLOS ONE , 2013, DOI: 10.1371/journal.pone.0065066
Abstract: All non-human great apes are endangered in the wild, and it is therefore important to gain an understanding of their demography and genetic diversity. Whole genome assembly projects have provided an invaluable foundation for understanding genetics in all four genera, but to date genetic studies of multiple individuals within great ape species have largely been confined to mitochondrial DNA and a small number of other loci. Here, we present a genome-wide survey of genetic variation in gorillas using a reduced representation sequencing approach, focusing on the two lowland subspecies. We identify 3,006,670 polymorphic sites in 14 individuals: 12 western lowland gorillas (Gorilla gorilla gorilla) and 2 eastern lowland gorillas (Gorilla beringei graueri). We find that the two species are genetically distinct, based on levels of heterozygosity and patterns of allele sharing. Focusing on the western lowland population, we observe evidence for population substructure, and a deficit of rare genetic variants suggesting a recent episode of population contraction. In western lowland gorillas, there is an elevation of variation towards telomeres and centromeres on the chromosomal scale. On a finer scale, we find substantial variation in genetic diversity, including a marked reduction close to the major histocompatibility locus, perhaps indicative of recent strong selection there. These findings suggest that despite their maintaining an overall level of genetic diversity equal to or greater than that of humans, population decline, perhaps associated with disease, has been a significant factor in recent and long-term pressures on wild gorilla populations.
A New Isolation with Migration Model along Complete Genomes Infers Very Different Divergence Processes among Closely Related Great Ape Species
Thomas Mailund ,Anders E. Halager,Michael Westergaard,Julien Y. Dutheil,Kasper Munch,Lars N. Andersen,Gerton Lunter,Kay Prüfer,Aylwyn Scally,Asger Hobolth,Mikkel H. Schierup
PLOS Genetics , 2012, DOI: 10.1371/journal.pgen.1003125
Abstract: We present a hidden Markov model (HMM) for inferring gradual isolation between two populations during speciation, modelled as a time interval with restricted gene flow. The HMM describes the history of adjacent nucleotides in two genomic sequences, such that the nucleotides can be separated by recombination, can migrate between populations, or can coalesce at variable time points, all dependent on the parameters of the model, which are the effective population sizes, splitting times, recombination rate, and migration rate. We show by extensive simulations that the HMM can accurately infer all parameters except the recombination rate, which is biased downwards. Inference is robust to variation in the mutation rate and the recombination rate over the sequence and also robust to unknown phase of genomes unless they are very closely related. We provide a test for whether divergence is gradual or instantaneous, and we apply the model to three key divergence processes in great apes: (a) the bonobo and common chimpanzee, (b) the eastern and western gorilla, and (c) the Sumatran and Bornean orang-utan. We find that the bonobo and chimpanzee appear to have undergone a clear split, whereas the divergence processes of the gorilla and orang-utan species occurred over several hundred thousands years with gene flow stopping quite recently. We also apply the model to the Homo/Pan speciation event and find that the most likely scenario involves an extended period of gene flow during speciation.
Breast-conserving therapy in breast cancer patients - a 12-year experience
Aylwyn Mannell
South African Journal of Surgery , 2005,
Abstract: Introduction: Twenty years ago prospective randomised controlled trials were initiated to compare conservative breast surgery plus radiation with radical mastectomy in the treatment of early-stage breast cancer. The results have shown no survival advantage for mastectomy over breast-conserving therapy (BCT). However, local recurrence of cancer after BCT has been reported to be as high as 14%, necessitating salvage mastectomy. Methods: This retrospective study was performed on 165 breast cancer patients undergoing BCT in the 12 years up to August 2002. Resection and intraoperative cytological assessment were used to achieve clear excision margins. Adjuvant therapy (hormones, chemotherapy) was undertaken, and the incidence and times of local recurrence and distant metastases were recorded. Results: Ninety-four per cent of patients had clear margins at the initial operation. This was achieved irrespective of ductal carcinoma in situ alone or surrounding the cancer in 62% of cases. At a median follow-up of 65 months one patient developed local recurrence (LR) in the breast synchronously with distant relapse. Two patients had non-nodal axillary recurrences but no patient suffered LR in isolation in the treated breast. Conclusion: BCT is a safe alternative to mastectomy provided that the tumour is completely excised. The segment containing the cancer should be resected from the nipple to the periphery of the breast. Intraoperative cytological assessment helps to ensure clear margins. Reexcision is recommended for patients with close/involved margins. South African Journal of Surgery Vol. 43(2) 2005: 28-32
Incidental Detection of a Unilateral Dilated Blind-Ending Ureter, Renal Agenesis, and a Dilated Seminal Vesicle
Michael St John Floyd Jr,John Scally,Paul Patrick Irwin
Urology Journal , 2012,
Abstract: No Abstract
Primary ciliary dyskinesia in a Staffordshire bull terrier : clinical communication
M. De Scally,R.G. Lobetti,E. Van Wilpe
Journal of the South African Veterinary Association , 2012, DOI: 10.4102/jsava.v75i3.471
Abstract: Primary ciliary dyskinesia (PCD) is a diverse group of inherited structural and functional abnormalities of the respiratory and other cilia, which results in recurrent respiratory tract infections. Primary ciliary dyskinesia was diagnosed in a 14-week old Staffordshire bull terrier that had a history of respiratory disease from 7 weeks of age. Pneumonia was diagnosed on thoracic radiographs and transtracheal aspirate. Transmission electron microscopy of the bronchi and trachea indicated the presence of both primary and secondary ciliary dyskinesia. The most prominent primary defects consisted of absent inner dyneim arms, absent radial spokes and absence of the central microtubules. These defects accounted for 62 % of the total number of cross-sections screened. Non-specific ciliary abnormalities encountered most often were compound cilia, swollen cilia, addition / deletion of peripheral doublets and disorganised axonemes (26 %). To the authors' knowledge, this is the first case of PCD described in the Staffordshire bull terrier and the first report of PCD in South Africa.
Impact of External Cue Validity on Driving Performance in Parkinson's Disease
Karen Scally,Judith L. Charlton,Robert Iansek,John L. Bradshaw,Simon Moss,Nellie Georgiou-Karistianis
Parkinson's Disease , 2011, DOI: 10.4061/2011/159621
Abstract: This study sought to investigate the impact of external cue validity on simulated driving performance in 19 Parkinson's disease (PD) patients and 19 healthy age-matched controls. Braking points and distance between deceleration point and braking point were analysed for red traffic signals preceded either by Valid Cues (correctly predicting signal), Invalid Cues (incorrectly predicting signal), and No Cues. Results showed that PD drivers braked significantly later and travelled significantly further between deceleration and braking points compared with controls for Invalid and No-Cue conditions. No significant group differences were observed for driving performance in response to Valid Cues. The benefit of Valid Cues relative to Invalid Cues and No Cues was significantly greater for PD drivers compared with controls. Trail Making Test (B-A) scores correlated with driving performance for PDs only. These results highlight the importance of external cues and higher cognitive functioning for driving performance in mild to moderate PD. 1. Introduction In addition to its cardinal motor signs (bradykinesia, postural instability, resting tremor, cogwheel rigidity), a distinctive profile of cognitive deficits has been well documented in Parkinson’s disease (PD) [1–10]. Although primarily dysexecutive in origin, cognitive impairment has been observed across a range of domains including attention, working memory, verbal and visual memory, visuoperception, visuospatial functioning, verbal fluency, planning, and organizational abilities [11–17]. PD has been characterised by a particular deficit in the volitional control or internal cueing of movement, with patients typically demonstrating significantly slower initiation and execution times as well as reduced accuracy of movement compared to age-matched controls [18–22]. This internal cueing deficit is also present on tasks that primarily demand cognition rather than motor performance, with impairment observed in the ability to use advance information to internally cue responses on Stroop colour naming and cognitive set-shifting tasks [23, 24]. Importantly, research findings have further demonstrated that provision of valid external cues compensates for defective internal initiation and improves performance on both motor and cognitive tasks in PD relative to controls [19, 20, 25–35]. Although invalid cues—providing incorrect information about the task requirements—have been found to prolong response times in neurologically normal subjects, the impact of invalid cues on performance in PD has generated conflicting
Molecular Evolutionary Analysis of ABCB5: The Ancestral Gene Is a Full Transporter with Potentially Deleterious Single Nucleotide Polymorphisms
Karobi Moitra,Mark Scally,Kate McGee,Germaine Lancaster,Bert Gold,Michael Dean
PLOS ONE , 2012, DOI: 10.1371/journal.pone.0016318
Abstract: ABCB5 is a member of the ABC protein superfamily, which includes the transporters ABCB1, ABCC1 and ABCG2 responsible for causing drug resistance in cancer patients and also several other transporters that have been linked to human disease. The ABCB5 full transporter (ABCB5.ts) is expressed in human testis and its functional significance is presently unknown. Another variant of this transporter, ABCB5 beta posses a “half-transporter-like” structure and is expressed in melanoma stem cells, normal melanocytes, and other types of pigment cells. ABCB5 beta has important clinical implications, as it may be involved with multidrug resistance in melanoma stem cells, allowing these stem cells to survive chemotherapeutic regimes.
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