342 research outputs found
Bayesian estimation applied to multiple species
Observed data are often contaminated by undiscovered interlopers, leading to biased parameter estimation. Here we present BEAMS (Bayesian estimation applied to multiple species) which significantly improves on the standard maximum likelihood approach in the case where the probability for each data point being âpureâ is known. We discuss the application of BEAMS to future type-Ia supernovae (SNIa) surveys, such as LSST, which are projected to deliver over a million supernovae light curves without spectra. The multiband light curves for each candidate will provide a probability of being Ia (pure) but the full sample will be significantly contaminated with other types of supernovae and transients. Given a sample of N supernovae with mean probability, âšPâ©, of being Ia, BEAMS delivers parameter constraints equal to NâšPâ© spectroscopically confirmed SNIa. In addition BEAMS can be simultaneously used to tease apart different families of data and to recover properties of the underlying distributions of those families (e.g. the type-Ibc and II distributions). Hence BEAMS provides a unified classification and parameter estimation methodology which may be useful in a diverse range of problems such as photometric redshift estimation or, indeed, any parameter estimation problem where contamination is an issue
General Relativistic effects in preheating
General relativistic effects in the form of metric perturbations are usually
neglected in the preheating era that follows inflation. We argue that in
realistic multi-field models these effects are in fact crucial, and the fully
coupled system of metric and quantum field fluctuations needs to be considered.
Metric perturbations are resonantly amplified, breaking the scale-invariance of
the primordial spectrum, and in turn stimulate scalar field resonances via
gravitational rescattering. This non-gravitationally dominated nonlinear growth
of gravitational fluctuations may have significant effects on the Doppler peaks
in the cosmic background radiation, primordial black hole formation,
gravitational waves and nonthermal symmetry restoration.Comment: 10 pages. 1 .ps fig. Matches version to appear in Phys Lett
Racial/ethnic heterogeneity in associations of blood pressure and incident cardiovascular disease by functional status in a prospective cohort: the Multi-Ethnic Study of Atherosclerosis.
OBJECTIVES:Research has demonstrated that the association between high blood pressure and outcomes is attenuated among older adults with functional limitations, compared with healthier elders. However, it is not known whether these patterns vary by racial/ethnic group. We evaluated race/ethnicity-specific patterns of effect modification in the association between blood pressure and incident cardiovascular disease (CVD) by functional status. SETTING:We used data from the Multi-Ethnic Study of Atherosclerosis (2002-2004, with an average of 8.8 years of follow-up for incident CVD). We assessed effect modification of systolic blood pressure and cardiovascular outcomes by self-reported physical limitations and by age. PARTICIPANTS:The study included 6117 participants (aged 46 to 87; 40% white, 27% black, 22% Hispanic and 12% Chinese) who did not have CVD at the second study examination (when self-reported physical limitations were assessed). OUTCOME MEASURES:Incident CVD was defined as an incident myocardial infarction, coronary revascularisation, resuscitated cardiac arrest, angina, stroke (fatal or non-fatal) or death from CVD. RESULTS:We observed weaker associations between systolic blood pressure (SBP) and CVD among white adults with physical limitations (incident rate ratio (IRR) per 10âmm Hg higher SBP: 1.09 (95% CI 0.99 to 1.20)) than those without physical limitations (IRR 1.29 (1.19, 1.40); P value for interaction <0.01). We found a similar pattern among black adults. Poor precision among the estimates for Hispanic or Chinese participants limited the findings in these groups. The attenuated associations were consistent across both multiplicative and additive scales, though physical limitations showed clearer patterns than age on an additive scale. CONCLUSION:Attenuated associations between high blood pressure and incident CVD were observed for blacks and whites with poor function, though small sample sizes remain a limitation for identifying differences among Hispanic or Chinese participants. Identifying the characteristics that distinguish those in whom higher SBP is associated with less risk of morbidity or mortality may inform our understanding of the consequences of hypertension among older adults
Unbroken supersymmetry in the Aharonov-Casher effect
We consider the problem of the bound states of a spin 1/2 chargless particle
in a given Aharonov-Casher configuration. To this end we recast the description
of the system in a supersymmetric form. Then the basic physical requirements
for unbroken supersymmetry are established. We comment on the possibility of
neutron confinement in this system
Acid-base changes and acetate metabolism during routine and high-efficiency hemodialysis in children
Acid-base changes and acetate metabolism during routine and high-efficiency hemodialysis in children. Changes in acid-base status and plasma acetate concentrations were studied in eight children during 11 hemodialysis sessions. During dialysis, the blood bicarbonate concentration fell (20.5 ± 0.7 to 19.6 ± 0.8 mEq/liter), the PCO2 fell (33.4 ± 0.8 to 27.5 ± 1.4 mm Hg), and the pH rose (7.42 ± 0.01 to 7.48 ± 0.02). During the hour after dialysis, the bicarbonate concentration rose to normal (23.4 ± 0.7 mEq/liter), the PCO2 rose (32.8 ± 0.8 mm Hg), and the pH remained unchanged. The half-life of plasma acetate, measured after dialysis, was 8.7 min. During five âhigh-efficiencyâ dialysis sessions (urea clearance, > 3.0 ml/min/kg), blood bicarbonate concentration fell 3.2 mEq/liter, PCO2 fell 8.7 mm Hg, and plasma acetate rose to 7.51 mmoles/liter, whereas during six âroutine efficiencyâ dialysis sessions (urea clearance, 1.5 to 3.0 ml/min/kg), blood bicarbonate rose 1.0 mEq/liter, PCO2 fell 36 mm Hg, and plasma acetate rose to 3.52 mmoles/liter. At 1 hour after the end of dialysis, blood bicarbonate, PCO2, and plasma acetate concentrations were similar in the two groups. Clinical problems occurred more frequently in the high-efficiency group during dialysis although the difference was not significant. The data indicate that (1) dialysis with acetate buffer effectively corrects pre-dialysis metabolic acidosis, (2) although children have a high rate of acetate metabolism, during high-efficiency dialysis this rate is exceeded by the influx of acetate, and acid-base abnormalities occur. These abnormalities are transient but may cause clinical problems.Modifications acido-basiques et mĂ©tabolisme de l'acĂ©tate au cours de l'hĂ©modialyse de routine ou Ă efficacitĂ© Ă©levĂ©e chez l'enfant. Les modifications de l'Ă©tat acido-basique et des concentrations plasmatiques d'acĂ©tate ont Ă©tĂ© Ă©tudiĂ©es chez huit enfants au cours de 11 sĂ©ances d'hĂ©modialyse. Au cours de la dialyse les bicarbonates diminuent (20,5 ± 0,7 Ă 19,6 ± 0,8 mEq/ litre), la PCO2 diminue (33,4 ± 0,8 Ă 27,5 ± 1,4 mm Hg), et le pH augmente (7,42 ± 0,01 Ă 7,48 ± 0,02). Au cours de l'heure qui suit la dialyse les bicarbonates s'Ă©lĂšvent Ă une valeur normale, 23,4 ± 0,07 mEq/litre, la PCO2 s'Ă©lĂšve Ă 32,8 ± 0,8 mm Hg, et le pH est inchangĂ©. La demi vie de l'acĂ©tate plasmatique, mesurĂ©e aprĂšs la dialyse, Ă©tait de 8,7 min. Au cours de cinq sĂ©ances de dialyse Ă haute efficacitĂ© (clearance de l'urĂ©e, > 3,0 ml/min/kg) les bicarbonates baissent de 3,2 mEq/litre, la PCO2 de 8,7 mm Hg, et l'acĂ©tate plasmatique s'est Ă©levĂ© Ă 7,51 mmoles/litre alors qu'au cours de six sĂ©ances de dialyse d'efficacitĂ© moyenne (clearance de l'urĂ©e, 1,5 Ă 3,0 ml/min/kg) les bicarbonates ont augmentĂ© de 1,0 mEq/litre, la PCO2 a diminuĂ© de 3,6 mm Hg, et l'acĂ©tate plasmatique s'est Ă©levĂ© Ă 3,52 mmoles/litre. Une heure aprĂšs la fin de la dialyse les bicarbonates, la PCO2 et l'acĂ©tate plasmatique Ă©taient semblables dans les deux groupes. Des problĂšmes cliniques sont survenus plus souvent au cours de la dialyse dans le groups Ă haute efficacitĂ© bien que la diffĂ©rence ne soit pas significative. Ces rĂ©sultats indiquent que (1) la dialyse avec le tampon acĂ©tate corrige efficacement l'acidose mĂ©tabolique prĂ©-dialytique, (2) bien que l'enfant ait une capacitĂ© Ă©levĂ©e de mĂ©taboliser l'acĂ©tate, cette capacitĂ© est dĂ©bordĂ©e, au cours de la dialyse Ă haute efficacitĂ©, par l'entrĂ©e d'acĂ©tate et des anomalies acidobasiques surviennent. Ces anomalies sont transitoires et peuvent dĂ©terminer des problĂšmes cliniques
Massless Metric Preheating
Can super-Hubble metric perturbations be amplified exponentially during
preheating ? Yes. An analytical existence proof is provided by exploiting the
conformal properties of massless inflationary models. The traditional conserved
quantity \zeta is non-conserved in many regions of parameter space. We include
backreaction through the homogeneous parts of the inflaton and preheating
fields and discuss the role of initial conditions on the post-preheating
power-spectrum. Maximum field variances are strongly underestimated if metric
perturbations are ignored. We illustrate this in the case of strong
self-interaction of the decay products. Without metric perturbations,
preheating in this case is very inefficient. However, metric perturbations
increase the maximum field variances and give alternative channels for the
resonance to proceed. This implies that metric perturbations can have a large
impact on calculations of relic abundances of particles produced during
preheating.Comment: 8 pages, 4 colour figures. Version to appear in Phys. Rev. D.
Contains substantial new analysis of the ranges of parameter space for which
large changes to the inflation-produced power spectrum are expecte
UV Absorption Lines from High-Velocity Gas in the Vela Supernova Remnant: New insights from STIS Echelle Observations of HD72089
The star HD72089 is located behind the Vela supernova remnant and shows a
complex array of high and low velocity interstellar absorption features arising
from shocked clouds. A spectrum of this star was recorded over the wavelength
range 1196.4 to 1397.2 Angstroms at a resolving power lambda/Delta lambda =
110,000 and signal-to-noise ratio of 32 by STIS on the Hubble Space Telescope.
We have identified 7 narrow components of C I and have measured their relative
populations in excited fine-structure levels. Broader features at heliocentric
velocities ranging from -70 to +130 km/s are seen in C II, N I, O I, Si II, S
II and Ni II. In the high-velocity components, the unusually low abundances of
N I and O I, relative to S II and Si II, suggest that these elements may be
preferentially ionized to higher stages by radiation from hot gas immediately
behind the shock fronts.Comment: 11 pages, 2 figures, Latex. Submitted for the special HST ERO issue
of the Astrophysical Journal Letter
Inflationary Reheating in Grand Unified Theories
Grand unified theories may display multiply interacting fields with strong
coupling dynamics. This poses two new problems: (1) What is the nature of
chaotic reheating after inflation, and (2) How is reheating sensitive to the
mass spectrum of these theories ? We answer these questions in two interesting
limiting cases and demonstrate an increased efficiency of reheating which
strongly enhances non-thermal topological defect formation, including monopoles
and domain walls. Nevertheless, the large fluctuations may resolve this
monopole problem via a modified Dvali-Liu-Vachaspati mechanism in which
non-thermal destabilsation of discrete symmetries occurs at reheating.Comment: 4 pages, 5 ps figures - 1 colour, Revtex. Further (colour & 3-D)
figures available from http://www.sissa.it/~bassett/reheating/ . Matched to
version to appear in Phys. Rev. let
Dark energy reflections in the redshift-space quadrupole
We show that the redshift-space quadrupole will be a powerful tool for
constraining dark energy even if the baryon oscillations are missing from the
usual monopole power spectrum and even if bias is scale- and time-dependent. We
calculate the accuracy with which a next-generation galaxy survey based on KAOS
will measure the quadrupole power spectrum, which gives the leading
anisotropies in the power spectrum in redshift space due to the linear
velocity, Finger of God and Alcock-Paczynski effects. Combining the monopole
and quadrupole power spectra breaks the degeneracies between the multiple bias
parameters and dark energy both in the linear and nonlinear regimes and, in the
complete absence of baryon oscillations (), leads to a roughly 500%
improvement in constraints on dark energy compared with those from the monopole
spectrum alone. As a result the worst case - with no baryon oscillations - has
dark energy errors only mildly degraded relative to the ideal case, providing
insurance on the robustness of next-generation galaxy survey constraints on
dark energy.Comment: 6 pages, 3 colour figure
Restoring the sting to metric preheating
The relative growth of field and metric perturbations during preheating is
sensitive to initial conditions set in the preceding inflationary phase. Recent
work suggests this may protect super-Hubble metric perturbations from resonant
amplification during preheating. We show that this possibility is fragile and
sensitive to the specific form of the interactions between the inflaton and
other fields. The suppression is naturally absent in two classes of preheating
in which either (1) the vacua of the non-inflaton fields during inflation are
deformed away from the origin, or (2) the effective masses of non-inflaton
fields during inflation are small but during preheating are large. Unlike the
simple toy model of a coupling, most realistic particle
physics models contain these other features. Moreover, they generically lead to
both adiabatic and isocurvature modes and non-Gaussian scars on super-Hubble
scales. Large-scale coherent magnetic fields may also appear naturally.Comment: 6 pages, 3 ps figures, RevTex, revised discussion of backreaction and
new figure. To appear Phys. Rev. D (Rapid Communication
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