4,979 research outputs found
The Local Group: The Ultimate Deep Field
Near-field cosmology -- using detailed observations of the Local Group and
its environs to study wide-ranging questions in galaxy formation and dark
matter physics -- has become a mature and rich field over the past decade.
There are lingering concerns, however, that the relatively small size of the
present-day Local Group ( Mpc diameter) imposes insurmountable
sample-variance uncertainties, limiting its broader utility. We consider the
region spanned by the Local Group's progenitors at earlier times and show that
it reaches co-moving Mpc in linear size (a volume of ) at . This size at early cosmic epochs is large enough
to be representative in terms of the matter density and counts of dark matter
halos with . The Local
Group's stellar fossil record traces the cosmic evolution of galaxies with
(reaching
at ) over a region that is comparable to or larger than
the Hubble Ultra-Deep Field (HUDF) for the entire history of the Universe. It
is highly complementary to the HUDF, as it probes much fainter galaxies but
does not contain the intrinsically rarer, brighter sources that are detectable
in the HUDF. Archaeological studies in the Local Group also provide the ability
to trace the evolution of individual galaxies across time as opposed to
evaluating statistical connections between temporally distinct populations. In
the JWST era, resolved stellar populations will probe regions larger than the
HUDF and any deep JWST fields, further enhancing the value of near-field
cosmology.Comment: 6 pages, 5 figures; MNRAS Letters, in pres
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Retinal Artery and Vein Occlusions Successfully Treated with Hyperbaric Oxygen
We present six cases of central retinal artery occlusion (CRAO) and central retinal vein occlusion (CRVO) that we recently treated with hyperbaric oxygen (HBO2). Patients in three of the six cases, including the CRVO case, experienced near to complete restoration of their vision. Another case had marked improvement. Our findings are similar to other case studies with approximately 65-70% improvement in patients treated for CRAO. Physicians should be aware that rapid referral of CRAO and CRVO patients to HBO2 is efficacious. Such patients should be placed on 100% oxygen by non-rebreather mask as soon as the diagnosis is suspected, pending transportation to HBO2
Efficacy of Dog Training With and Without Remote Electronic Collars vs. A Focus on Positive Reinforcement
We assessed the efficacy of dog training with and without remote electronic collars compared to training with positive reinforcement. A total of 63 dogs with known off-lead behavioral problems such as poor recall were allocated to one of three training groups (each n = 21), receiving up to 150min of training over 5 days to improve recall and general obedience. The 3 groups were: E-collar—manufacturer-nominated trainers who used electronic stimuli as part of their training program; Control 1—the same trainers following practices they would apply when not using electronic stimuli; and Control 2—independent, professional trainers who focused primarily on positive reinforcement for their training. Data collection focused on dogs’ response to two commands: “Come” (recall to trainer) and “Sit” (place hindquarters on ground). These were the two most common commands used during training, with improving recall being the target behavior for the subject dogs. Measures of training efficacy included number of commands given to elicit the response and response latency. Control 2 achieved significantly better responses to both “Sit” and “Come” commands after a single instruction in the allocated time. These dogs also had shorter response latencies than the E-collar group. There was no significant difference in the proportion of command disobeyed between the three groups, although significantly fewer commands were given to the dogs in Control 2. There was no difference in the number of verbal cues used in each group, but Control 2 used fewer hand and lead signals, and Control 1 made more use of these signals than E-collar group. These findings refute the suggestion that training with an E-collar is either more efficient or results in less disobedience, even in the hands of experienced trainers. In many ways, training with positive reinforcement was found to be more effective at addressing the target behavior as well as general obedience training. This method of training also poses fewer risks to dog welfare and quality of the human-dog relationship. Given these results we suggest that there is no evidence to indicate that E-collar training is necessary, even for its most widely cited indication
Towards models for the oxygen evolving centre of photosystem II and analysis of Lewis acidic metals within novel salen derivatives
The synthesis and characterisation of a range of ligands capable of binding four or five transition metals has been explored in an attempt to synthesise a model for the oxygen evolving centre of photosystem II. Difficulty was encountered in isolating the pure, deprotected ligands. A ligand based on 1,4,7-triazacyclononane containing three alcohol donors was isolated, investigated and compared against similar ligands. A series of copper N-oxide Bis(N,N'-Disalicylalethylenediamine) derivatives were synthesised and fully characterised. The electron paramagnetic resonance spectra (EPR) of these complexes were measured and compared in order to determine the relative Lewis acidity of the central metal. Electron nuclear double resonance (ENDOR) spectra were recorded of the complexes they revealed the catalytic activity of these complexes towards cyclopropanation was tested with a variety of styrene derivatives. A zinc N-oxide Bis(N,N'-Disalicylalethylenediamine) derivative was extensively studied for enantiomeric discrimination of a small amine, methylbenzyl amine (MBA). This was monitored via lH NMR titrations in three different solvents, CDCI3, CD3CN and CD3OD. The ability of MBA to displace a solvent molecule from the coordination sites was investigated and the data inserted into a kinetic model. Chloroform was found to have the weakest interaction while methanol had the strongest. The difference in affinity of ii-complex for i-MBA over S-MBA was also investigated and a preference for the heterochiral mixture was revealed.EThOS - Electronic Theses Online ServiceGBUnited Kingdo
Wolbachia in the Drosophila yakuba Complex: Pervasive Frequency Variation and Weak Cytoplasmic Incompatibility, but No Apparent Effect on Reproductive Isolation
Three hybridizing species—the clade [(Drosophila yakuba, D. santomea), D. teissieri]—comprise the yakuba complex in the D. melanogaster subgroup. Their ranges overlap on Bioko and São Tomé, islands off west Africa. All three species are infected with Wolbachia—maternally inherited, endosymbiotic bacteria, best known for manipulating host reproduction to favor infected females. Previous analyses reported no cytoplasmic incompatibility (CI) in these species. However, we discovered that Wolbachia from each species cause intraspecific and interspecific CI. In D. teissieri, analyses of F1 and backcross genotypes show that both host genotype and Wolbachia variation modulate CI intensity. Wolbachia-infected females seem largely protected from intraspecific and interspecific CI, irrespective of Wolbachia and host genotypes. Wolbachia do not affect host mating behavior or female fecundity, within or between species. The latter suggests little apparent effect of Wolbachia on premating or gametic reproductive isolation (RI) between host species. In nature, Wolbachia frequencies varied spatially for D. yakuba in 2009, with 76% (N = 155) infected on São Tomé, and only 3% (N = 36) infected on Bioko; frequencies also varied temporally in D. yakuba and D. santomea on São Tomé between 2009 and 2015. These temporal frequency fluctuations could generate asymmetries in interspecific mating success, and contribute to postzygotic RI. However, the fluctuations in Wolbachia frequencies that we observe also suggest that asymmetries are unlikely to persist. Finally, we address theoretical questions that our empirical findings raise about Wolbachia persistence when conditions fluctuate, and about the stable coexistence of Wolbachia and host variants that modulate Wolbachia effects
Assessing and Improving the Ecological Function of Linear Parks Along the Lower Los Angeles River Channel, Los Angeles County, California, US
Long overlooked by conservation groups and ecologists, urban open spaces are now seen as important contributors to biodiversity at various scales. Urban greenspaces often represent the only “nature” millions of human residents around the world ever interact with, and provide cooling and aesthetic relief from the urban hardscape. In the Los Angeles Metropolitan area, over the past three decades, non-profit advocacy groups and institutions have established a network of bike paths, neighborhood access points, habitat restoration, and recreational amenities along the Los Angeles River, a major urban waterway. We investigated the environmental contribution provided by numerous linear landscaped parks along the river, focusing on climate amelioration (i.e., cooling within heat islands) in the parks and surrounding neighborhoods, and on their contribution to local biodiversity, utilizing an indicator species approach. We conducted plant surveys of the parks, documenting locally native, non-local California native, and non-native species, and examined the occurrence of 15 riparian indicator species of wildlife in the parks and in 500-meter buffer zones surrounding each park utilizing citizen science data. We then explore correlations between indicator species richness and environmental variables. We note important occurrences of relict riparian vegetation in several linear parks, as well as both planted and naturally-occurring special-status plant and wildlife species. Finally, we discuss challenges to managing natural habitat in highly-urban parks, many of which support important relict vegetation and/or special-status species, and offer suggestions on how they may be improved
A Predicted Correlation Between Age Gradient and Star Formation History in FIRE Dwarf Galaxies
We explore the radial variation of star formation histories in dwarf galaxies
simulated with Feedback In Realistic Environments (FIRE) physics. The sample
contains 9 low-mass field dwarfs with M_ star = 10^5 - 10^7 M_sun from previous
FIRE results, and a new suite of 17 higher mass field dwarfs with M_star = 10^7
- 10^9 M_sun introduced here. We find that age gradients are common in our
dwarfs, with older stars dominant at large radii. The strength of the gradient
correlates with overall galaxy age such that earlier star formation produces a
more pronounced gradient. The relation between formation time and strength of
the gradient is driven by both mergers and star-formation feedback. Mergers can
both steepen and flatten the age gradient depending on the timing of the merger
and star formation history of the merging galaxy. In galaxies without
significant mergers, early feedback pushes stars to the outskirts at early
times. Interestingly, among galaxies without mergers, those with large dark
matter cores have flatter age gradients because these galaxies have more
late-time feedback. If real galaxies have age gradients as we predict, stellar
population studies that rely on sampling a limited fraction of a galaxy can
give a biased view of its global star formation history. We show that central
fields can be biased young by a few Gyrs while outer fields are biased old.
Fields positioned near the 2D half-light radius will provide the least biased
measure of a dwarf galaxy's global star formation history.Comment: 13 pages, 8 figures. Submitted to MNRAS, comments welcom
The landscape of viral associations in human cancers
Here, as part of the Pan-Cancer Analysis of Whole Genomes (PCAWG) Consortium, for which whole-genome and—for a subset—whole-transcriptome sequencing data from 2,658 cancers across 38 tumor types was aggregated, we systematically investigated potential viral pathogens using a consensus approach that integrated three independent pipelines. Viruses were detected in 382 genome and 68 transcriptome datasets. We found a high prevalence of known tumor-associated viruses such as Epstein–Barr virus (EBV), hepatitis B virus (HBV) and human papilloma virus (HPV; for example, HPV16 or HPV18). The study revealed significant exclusivity of HPV and driver mutations in head-and-neck cancer and the association of HPV with APOBEC mutational signatures, which suggests that impaired antiviral defense is a driving force in cervical, bladder and head-and-neck carcinoma. For HBV, HPV16, HPV18 and adeno-associated virus-2 (AAV2), viral integration was associated with local variations in genomic copy numbers. Integrations at the TERT promoter were associated with high telomerase expression evidently activating this tumor-driving process. High levels of endogenous retrovirus (ERV1) expression were linked to a worse survival outcome in patients with kidney cancer
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