516 research outputs found
Evidence for a Very Large-Scale Fractal Structure in the Universe from Cobe Measurements
In this work, we analyse the temperature fluctuations of the cosmic microwave
background radiation observed by COBE and show that the distribution can be
fitted by a fractal distribution with a fractal dimension .
This value is in close agreement with the fractal dimension obtained by Coleman
and Pietronero (1992) and Luo and Schramm (1992) from galaxy-galaxy and
cluster-cluster correlations up to . The fact that the
observed temperature fluctuations correspond to scales much larger than and are signatures of the primordial density fluctuations at the
recombination layer suggests that the structure of the matter at the early
universe was already fractal and thus non-homogeneous on those scales. This
result may have important consequences for the theoretical framework that
describes the universe.Comment: 11 pages, postscript file, 2 figures available upon request. To
appear in ApJ Letter
Baryon acoustic oscillations from Integrated Neutral Gas Observations: Radio frequency interference measurements and telescope site selection
The Baryon acoustic oscillations from Integrated Neutral Gas Observations
(BINGO) telescope is a new 40-m class radio telescope to measure the
large-angular-scale intensity of Hi emission at 980-1260 MHz to constrain dark
energy parameters. As it needs to measure faint cosmological signals at the
milliKelvin level, it requires a site that has very low radio frequency
interference (RFI) at frequencies around 1 GHz. We report on measurement
campaigns across Uruguay and Brazil to find a suitable site, which looked at
the strength of the mobile phone signals and other radio transmissions, the
location of wind turbines, and also included mapping airplane flight paths. The
site chosen for the BINGO telescope is a valley at Serra do Urubu, a remote
part of Paraiba in North-East Brazil, which has sheltering terrain. During our
measurements with a portable receiver we did not detect any RFI in or near the
BINGO band, given the sensitivity of the equipment. A radio quiet zone around
the selected site has been requested to the Brazilian authorities ahead of the
telescope construction.Comment: Preprint of an article accepted in the Journal of Astronomical
Instrumentation, copyright 2018 World Scientific Publishing Company
https://www.worldscientific.com/worldscinet/ja
Limitations of Climatic Data for Inferring Species Boundaries: Insights from Speckled Rattlesnakes
Phenotypes, DNA, and measures of ecological differences are widely used in species delimitation. Although rarely defined in such studies, ecological divergence is almost always approximated using multivariate climatic data associated with sets of specimens (i.e., the "climatic niche"); the justification for this approach is that species-specific climatic envelopes act as surrogates for physiological tolerances. Using identical statistical procedures, we evaluated the usefulness and validity of the climate-as-proxy assumption by comparing performance of genetic (nDNA SNPs and mitochondrial DNA), phenotypic, and climatic data for objective species delimitation in the speckled rattlesnake (Crotalus mitchellii) complex. Ordination and clustering patterns were largely congruent among intrinsic (heritable) traits (nDNA, mtDNA, phenotype), and discordance is explained by biological processes (e.g., ontogeny, hybridization). In contrast, climatic data did not produce biologically meaningful clusters that were congruent with any intrinsic dataset, but rather corresponded to regional differences in atmospheric circulation and climate, indicating an absence of inherent taxonomic signal in these data. Surrogating climate for physiological tolerances adds artificial weight to evidence of species boundaries, as these data are irrelevant for that purpose. Based on the evidence from congruent clustering of intrinsic datasets, we recommend that three subspecies of C. mitchellii be recognized as species: C. angelensis, C. mitchellii, and C. Pyrrhus
Reduction of health-related risks among female commercial sex workers: learning from their life and working experiences.
We performed this study to determine both positive and negative impacts on the health of sex workers working on the street. We conducted this study using key informant and focus group interviews in bars and streets in Mozambique. The interviewed sex workers were aware about the risks and protection against sexually transmitted infections (STIs), and they consistently used condoms. Most suffered from harmful behavior, including violence and assault by both customers and other commercial sex workers. We found that sex workers\u27 own skills and knowledge acquired through experience potentially could be developed into life skills that could save and protect their lives
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