5,427 research outputs found
Magnetic substructure in the northern Fermi Bubble revealed by polarized WMAP emission
We report a correspondence between giant, polarized microwave structures
emerging north from the Galactic plane near the Galactic center and a number of
GeV gamma-ray features, including the eastern edge of the recently-discovered
northern Fermi Bubble. The polarized microwave features also correspond to
structures seen in the all-sky 408 MHz total intensity data, including the
Galactic center spur. The magnetic field structure revealed by the polarization
data at 23 GHz suggests that neither the emission coincident with the Bubble
edge nor the Galactic center spur are likely to be features of the local ISM.
On the basis of the observed morphological correspondences, similar inferred
spectra, and the similar energetics of all sources, we suggest a direct
connection between the Galactic center spur and the northern Fermi Bubble.Comment: Accepted for publication in The Astrophysical Journal Letters after
minor change
Masculinity in Adolescent Males’ Early Romantic and Sexual Heterosexual Relationships
There is a need to understand better the complex interrelationship between the adoption of masculinity during adolescence and the development of early romantic and sexual relationships. The purpose of this study was to describe features of adolescent masculinity and how it is expressed in the contexts of early to middle adolescent males’ romantic and sexual relationships. Thirty-three 14- to 16-year-old males were recruited from an adolescent clinic serving a community with high sexually transmitted infection rates and were asked open-ended questions about their relationships—how they developed, progressed, and ended. Participants described a high degree of relationally oriented beliefs and behaviors related to romantic and sexual relationships, such as a desire for intimacy and trust. The males also described a more limited degree of conventionally masculine beliefs and behaviors. These beliefs and behaviors often coexisted or overlapped. Implications for the clinical care of similar groups of adolescents are described
Constant Approximation for -Median and -Means with Outliers via Iterative Rounding
In this paper, we present a new iterative rounding framework for many
clustering problems. Using this, we obtain an -approximation algorithm for -median with outliers, greatly
improving upon the large implicit constant approximation ratio of Chen [Chen,
SODA 2018]. For -means with outliers, we give an -approximation, which is the first -approximation for
this problem. The iterative algorithm framework is very versatile; we show how
it can be used to give - and -approximation
algorithms for matroid and knapsack median problems respectively, improving
upon the previous best approximations ratios of [Swamy, ACM Trans.
Algorithms] and [Byrka et al, ESA 2015].
The natural LP relaxation for the -median/-means with outliers problem
has an unbounded integrality gap. In spite of this negative result, our
iterative rounding framework shows that we can round an LP solution to an
almost-integral solution of small cost, in which we have at most two
fractionally open facilities. Thus, the LP integrality gap arises due to the
gap between almost-integral and fully-integral solutions. Then, using a
pre-processing procedure, we show how to convert an almost-integral solution to
a fully-integral solution losing only a constant-factor in the approximation
ratio. By further using a sparsification technique, the additive factor loss
incurred by the conversion can be reduced to any
ALMA Multi-line Imaging of the Nearby Starburst Galaxy NGC 253
We present spatially resolved (50 pc) imaging of molecular gas species
in the central kiloparsec of the nearby starburst galaxy NGC 253, based on
observations taken with the Atacama Large Millimeter/submillimeter Array
(ALMA). A total of 50 molecular lines are detected over a 13 GHz bandwidth
imaged in the 3 mm band. Unambiguous identifications are assigned for 27 lines.
Based on the measured high CO/CO isotopic line ratio (350), we
show that CO(1-0) has moderate optical depths. A comparison of the HCN
and HCO with their C-substituted isotopologues shows that the
HCN(1-0) and HCO(1-0) lines have optical depths at least comparable to
CO(1-0). HCN/HCO (and HCN/HNC) line ratios
provide tighter constraints on dense gas properties in this starburst. SiO has
elevated abundances across the nucleus. HNCO has the most distinctive
morphology of all the bright lines, with its global luminosity dominated by the
outer parts of the central region. The dramatic variation seen in the HNCO/SiO
line ratio suggests that some of the chemical signatures of shocked gas are
being erased in the presence of dominating central radiation fields (traced by
CH and CN). High density molecular gas tracers (including HCN, HCO,
and CN) are detected at the base of the molecular outflow. We also detect
hydrogen recombination lines that, like their counterparts,
show compact, centrally peaked morphologies, distinct from the molecular gas
tracers. A number of sulfur based species are mapped (CS, SO, NS, CS,
HCS and CHSH) and have morphologies similar to SiO.Comment: 20 pages, 10 figures, accepted to the Astrophysical Journa
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Metabolic reprogramming of human CD8+ memory T cells through loss of SIRT1.
The expansion of CD8+CD28- T cells, a population of terminally differentiated memory T cells, is one of the most consistent immunological changes in humans during aging. CD8+CD28- T cells are highly cytotoxic, and their frequency is linked to many age-related diseases. As they do not accumulate in mice, many of the molecular mechanisms regulating their fate and function remain unclear. In this paper, we find that human CD8+CD28- T cells, under resting conditions, have an enhanced capacity to use glycolysis, a function linked to decreased expression of the NAD+-dependent protein deacetylase SIRT1. Global gene expression profiling identified the transcription factor FoxO1 as a SIRT1 target involved in transcriptional reprogramming of CD8+CD28- T cells. FoxO1 is proteasomally degraded in SIRT1-deficient CD8+CD28- T cells, and inhibiting its activity in resting CD8+CD28+ T cells enhanced glycolytic capacity and granzyme B production as in CD8+CD28- T cells. These data identify the evolutionarily conserved SIRT1-FoxO1 axis as a regulator of resting CD8+ memory T cell metabolism and activity in humans
Condoms and developmental contexts in younger adolescent boys
BACKGROUND:
Condom use is a key part of sexually transmitted infection (STI) prevention for young men. Yet little is known about how younger adolescent boys initially learn about and use condoms. We examined sources of information, attitudes towards, acquisition, practice and early use of condoms among 14-16-year-old boys.
METHODS:
Thirty 14-16-year-old boys were recruited from a teen clinic serving a community with high STI rates and were asked open-ended questions about condoms, such as, "Where did you learn about condoms?" and "In what situations would you/would you not, use condoms." Interviews were audio recorded, transcribed and coded. Qualitative analysis focused upon key concepts and shared social cognitions related to condom use.
RESULTS:
Both sexually inexperienced and experienced participants perceived that sex feels or would feel less pleasurable with condoms. For almost all participants, families were the primary source of both information about condoms and of condoms themselves. This information focused on pregnancy prevention, with STIs secondary. Participants' views of condoms fell into three developmental groups: not interested in condoms and equating their use with interest in sex; exploring condoms out of either curiosity or in preparation for sex; and experienced with condom use. Exploring included behaviours such as checking condoms out and trying them on.
CONCLUSIONS:
Our findings of existing negative perceptions of condoms, the importance of families in learning about condoms and the developmental need to test and try on condoms before use have implications for adolescent STI prevention programmes
Diffuse HI Disks in Isolated Galaxies
In order to investigate the contribution of diffuse components to their total
HI emission, we have obtained high precision HI line flux densities with the
100m Green Bank Telescope for a sample of 100 isolated spiral and irregular
galaxies which we have previously observed with the 43m telescope. A comparison
of the observed HI line fluxes obtained with the two different telescopes,
characterized by half-power beam widths of 9 arcmin and 21 arcmin respectively,
exploits a ``beam matching'' technique to yield a statistical determination of
the occurrence of diffuse HI components in their disks. A simple model of the
HI distribution within a galaxy well describes ~75 % of the sample and accounts
for all of the HI line flux density. The remaining galaxies are approximately
evenly divided into two categories: ones which appear to possess a
significantly more extensive HI distribution than the model predicts, and ones
for which the HI distribution is more centrally concentrated than predicted.
Examples of both extremes can be found in the literature but little attention
has been paid to the centrally concentrated HI systems. Our sample has
demonstrated that galaxies do not commonly possess extended regions of low
surface brightness HI gas which is not accounted for by our current
understanding of the structure of HI disks. Eight HI-rich companions to the
target objects are identified, and a set of extragalactic HI line flux density
calibrators is presented.Comment: 26 page
Bifurcations of periodic and chaotic attractors in pinball billiards with focusing boundaries
We study the dynamics of billiard models with a modified collision rule: the
outgoing angle from a collision is a uniform contraction, by a factor lambda,
of the incident angle. These pinball billiards interpolate between a
one-dimensional map when lambda=0 and the classical Hamiltonian case of elastic
collisions when lambda=1. For all lambda<1, the dynamics is dissipative, and
thus gives rise to attractors, which may be periodic or chaotic. Motivated by
recent rigorous results of Markarian, Pujals and Sambarino, we numerically
investigate and characterise the bifurcations of the resulting attractors as
the contraction parameter is varied. Some billiards exhibit only periodic
attractors, some only chaotic attractors, and others have coexistence of the
two types.Comment: 30 pages, 17 figures. v2: Minor changes after referee comments.
Version with some higher-quality figures available at
http://sistemas.fciencias.unam.mx/~dsanders/publications.htm
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