3,376 research outputs found
The sources of sex differences in aging in annual fishes
Intersexual differences in life span (age at death) and aging (increase in mortality risk associated with functional deterioration) are widespread among animals, from nematodes to humans. Males often live shorter than females, but there is substantial unexplained variation among species and populations. Despite extensive research, it is poorly understood how life span differences between the sexes are modulated by an interplay among genetic, environmental and social factors. The goal of our study was to test how sex differences in life span and ageing are modulated by social and environmental factors, and by intrinsic differences between males and females. To disentangle the complex basis of sex differences in life span and aging, we combined comparative data from sex ratios in 367 natural populations of four species of African annual killifish with experimental results on sex differences in life span and aging from eight laboratory populations tested in treatments that varied social and environmental conditions. In the wild, females consistently outlived males. In captivity, sex-specific mortality depended on social conditions. In social-housed experimental groups, male-biased mortality persisted in two aggressive species, but ceased in two placid species. When social and physical contacts were prevented by housing all fish individually, male-biased mortality ceased in all four species. This outcome held across benign and challenging environmental conditions. Fitting demographic survival models revealed that increased baseline mortality was primarily responsible for a shorter male life span in social-housing conditions. The timing and rate of aging were not different between the sexes. No marker of functional aging we recorded in our study (lipofuscin accumulation, proliferative changes in kidney and liver) differed between males and females, despite their previously confirmed association with functional aging in Nothobranchius killifish. We show that sex differences in life span and aging in killifish are driven by a combination of social and environmental conditions, rather than differential functional aging. They are primarily linked to sexual selection but precipitated through multiple processes (predation, social interference). This demonstrates how sex-specific mortality varies among species even within an ecologically and evolutionary discrete lineage and explains how external factors mediate this difference
Reconstruction of the optical potential from scattering data
We propose a method for reconstruction of the optical potential from
scattering data. The algorithm is a two-step procedure. In the first step the
real part of the potential is determined analytically via solution of the
Marchenko equation. At this point we use a diagonal Pad\'{e} approximant of the
corresponding unitary -matrix. In the second step the imaginary part of the
potential is determined via the phase equation of the variable phase approach.
We assume that the real and the imaginary parts of the optical potential are
proportional. We use the phase equation to calculate the proportionality
coefficient. A numerical algorithm is developed for a single and for coupled
partial waves. The developed procedure is applied to analysis of
, , and data.Comment: 26 pages, 8 figures, results of nucl-th/0410092 are refined, some new
results are presente
Analyzing Femorotibial Cartilage Thickness Using Anatomically Standardized Maps: Reproducibility and Reference Data.
Alterations in cartilage thickness (CTh) are a hallmark of knee osteoarthritis, which remain difficult to characterize at high resolution, even with modern magnetic resonance imaging (MRI), due to a paucity of standardization tools. This study aimed to assess a computational anatomy method producing standardized two-dimensional femorotibial CTh maps. The method was assessed with twenty knees, processed following three common experimental scenarios. Cartilage thickness maps were obtained for the femorotibial cartilages by reconstructing bone and cartilage mesh models in tree-dimension, calculating three-dimensional CTh maps, and anatomically standardizing the maps. The intra-operator accuracy (median (interquartile range, IQR) of -0.006 (0.045) mm), precision (0.152 (0.070) mm), entropy (7.02 (0.71) and agreement (0.975 (0.020))) results suggested that the method is adequate to capture the spatial variations in CTh and compare knees at varying osteoarthritis stages. The lower inter-operator precision (0.496 (0.132) mm) and agreement (0.808 (0.108)) indicate a possible loss of sensitivity to detect differences in a setting with multiple operators. The results confirmed the promising potential of anatomically standardized maps, with the lower inter-operator reproducibility stressing the need to coordinate operators. This study also provided essential reference data and indications for future research using CTh maps
The Duck Redux: An Improved Proper Motion Upper Limit for the Pulsar B1757-24 Near the Supernova Remnant G5.4-1.2
"The Duck" is a complicated non-thermal radio system, consisting of the
energetic radio pulsar B1757-24, its surrounding pulsar wind nebula G5.27-0.90
and the adjacent supernova remnant (SNR) G5.4-1.2. PSR B1757-24 was originally
claimed to be a young (~15 000 yr) and extreme velocity (>~1500 km/s) pulsar
which had penetrated and emerged from the shell of the associated SNR G5.4-1.2,
but recent upper limits on the pulsar's motion have raised serious difficulties
with this interpretation. We here present 8.5 GHz interferometric observations
of the nebula G5.27-0.90 over a 12-year baseline, doubling the time-span of
previous measurements. These data correspondingly allow us to halve the
previous upper limit on the nebula's westward motion to 14 milliarcseconds/yr
(5-sigma), allowing a substantive reevaluation of this puzzling object. We rule
out the possibility that the pulsar and SNR were formed from a common supernova
explosion ~15 000 yrs ago as implied by the pulsar's characteristic age, but
conclude that an old (>~70 000 yr) pulsar / SNR association, or a situation in
which the pulsar and SNR are physically unrelated, are both still viable
explanations.Comment: 9 pages, including 1 color and 1 B/W figure. Minor changes following
referee's report. ApJ, in pres
Supersymmetric Flavor Models and the B --> phi K_S Anomaly
We consider the flavor structure of supersymmetric theories that can account
for the deviation of the observed time-dependent CP asymmetry in B --> phi K_S
from the standard model prediction. Assuming simple flavor symmetries and
effective field theory, we investigate possible correlations between sizable
supersymmetric contributions to b --> s transitions and to flavor changing
processes that are more tightly constrained. With relatively few assumptions,
we determine the properties of minimal Yukawa and soft mass textures that are
compatible with the desired supersymmetric flavor-changing effect and
constraints. We then present explicit models that are designed (at least
approximately) to realize these textures. In particular, we present an Abelian
model based on a single U(1) factor and a non-trivial extra-dimensional
topography that can explain the CP asymmetry in B --> phi K_S, while
suppressing other supersymmetric flavor changing effects through a high degree
of squark-quark alignment.Comment: 18 pages LaTeX, 3 eps figure
An Alternative Yukawa Unified SUSY Scenario
Supersymmetric SO(10) Grand Unified Theories with Yukawa unification
represent an appealing possibility for physics beyond the Standard Model.
However Yukawa unification is made difficult by large threshold corrections to
the bottom mass. Generally one is led to consider models where the sfermion
masses are large in order to suppress these corrections. Here we present
another possibility, in which the top and bottom GUT scale Yukawa couplings are
equal to a component of the charged lepton Yukawa matrix at the GUT scale in a
basis where this matrix is not diagonal. Physically, this weak eigenstate
Yukawa unification scenario corresponds to the case where the charged leptons
that are in the 16 of SO(10) containing the top and bottom quarks mix with
their counterparts in another SO(10) multiplet. Diagonalizing the resulting
Yukawa matrix introduces mixings in the neutrino sector. Specifically we find
that for a large region of parameter space with relatively light sparticles,
and which has not been ruled out by current LHC or other data, the mixing
induced in the neutrino sector is such that , in
agreement with data. The phenomenological implications are analyzed in some
detail.Comment: 32 pages, 22 Figure
Wide-field Multi-object Spectroscopy to Enhance Dark Energy Science from LSST
LSST will open new vistas for cosmology in the next decade, but it cannot
reach its full potential without data from other telescopes. Cosmological
constraints can be greatly enhanced using wide-field ( deg total
survey area), highly-multiplexed optical and near-infrared multi-object
spectroscopy (MOS) on 4-15m telescopes. This could come in the form of
suitably-designed large surveys and/or community access to add new targets to
existing projects. First, photometric redshifts can be calibrated with high
precision using cross-correlations of photometric samples against spectroscopic
samples at that span thousands of sq. deg. Cross-correlations of
faint LSST objects and lensing maps with these spectroscopic samples can also
improve weak lensing cosmology by constraining intrinsic alignment systematics,
and will also provide new tests of modified gravity theories. Large samples of
LSST strong lens systems and supernovae can be studied most efficiently by
piggybacking on spectroscopic surveys covering as much of the LSST
extragalactic footprint as possible (up to square degrees).
Finally, redshifts can be measured efficiently for a high fraction of the
supernovae in the LSST Deep Drilling Fields (DDFs) by targeting their hosts
with wide-field spectrographs. Targeting distant galaxies, supernovae, and
strong lens systems over wide areas in extended surveys with (e.g.) DESI or MSE
in the northern portion of the LSST footprint or 4MOST in the south could
realize many of these gains; DESI, 4MOST, Subaru/PFS, or MSE would all be
well-suited for DDF surveys. The most efficient solution would be a new
wide-field, highly-multiplexed spectroscopic instrument in the southern
hemisphere with m aperture. In two companion white papers we present gains
from deep, small-area MOS and from single-target imaging and spectroscopy.Comment: Submitted to the call for Astro2020 science white papers; tables with
estimates of telescope time needed for a supernova host survey can be seen at
http://d-scholarship.pitt.edu/id/eprint/3604
Feeling our way: academia, emotions and a politics of care
This paper aims to better understand the role of emotions in academia, and their part in producing, and challenging, an increasingly normalized neoliberal academy. It unfolds from two narratives that foreground emotions in and across academic spaces and practices, to critically explore how knowledges and positions are constructed and circulated. It then moves to consider these issues through the lens of care as a political stance towards being and becoming academics in neoliberal times. Our aim is to contribute to the burgeoning literature on emotional geographies, explicitly bringing this work into conversation with resurgent debates surrounding an ethic of care, as part of a politic of critiquing individualism and managerialism in (and beyond) the academy. We consider the ways in which neoliberal university structures circulate particular affects, prompting emotions such as desire and anxiety, and the internalisation of competition and audit as embodied scholars. Our narratives exemplify how attendant emotions and affect can reverberate and be further reproduced through university cultures, and diffuse across personal and professional lives. We argue that emotions in academia matter, mutually co-producing everyday social relations and practices at and across all levels. We are interested in their political implications, and how neoliberal norms can be shifted through practices of caring-with
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