735 research outputs found
Isocurvature fluctuations in Affleck-Dine mechanism and constraints on inflation models
We reconsider the Affleck-Dine mechanism for baryogenesis and show that the
baryonic isocurvature fluctuations are generated in many inflation models in
supergravity. The inflationary scale and the reheating temperature must satisfy
certain constraints to avoid too large baryonic isocurvature fluctuations.Comment: 18 pages, 1 figur
Non-Gaussianity from isocurvature perturbations
We develop a formalism to study non-Gaussianity in both curvature and
isocurvature perturbations. It is shown that non-Gaussianity in the
isocurvature perturbation between dark matter and photons leaves distinct
signatures in the CMB temperature fluctuations, which may be confirmed in
future experiments, or possibly, even in the currently available observational
data. As an explicit example, we consider the QCD axion and show that it can
actually induce sizable non-Gaussianity for the inflationary scale, H_{inf} =
O(10^9 - 10^{11})GeV.Comment: 24 pages, 6 figures; references added; version to appear in JCA
Seasonal particulate organic carbon dynamics of the Kolyma River tributaries, Siberia
Arctic warming is causing permafrost thaw and release of organic carbon (OC) to fluvial systems. Permafrost-derived OC can be transported downstream and degraded into greenhouse gases that may enhance climate warming. Susceptibility of OC to decomposition depends largely upon its source and composition, which vary throughout the seasonally distinct hydrograph. Most studies on carbon dynamics to date have focused on larger Arctic rivers, yet little is known about carbon cycling in lower-order rivers and streams. Here, we characterize the composition and sources of OC, focusing on less studied particulate OC (POC), in smaller waterways within the Kolyma River watershed. Additionally, we examine how watershed characteristics control carbon concentrations. In lower-order systems, we find rapid initiation of primary production in response to warm water temperatures during spring freshet, shown by decreasing δ13C-POC, in contrast to larger rivers. This results in CO2 uptake by primary producers and microbial degradation of mainly autochthonous OC. However, if terrestrially derived inorganic carbon is assimilated by primary producers, part of it is returned via CO2 emissions if the autochthonous OC pool is simultaneously degraded. As Arctic warming and hydrologic changes may increase OC transfer from smaller waterways to larger river networks, understanding carbon dynamics in smaller waterways is crucial.</p
Chlamydia trachomatis samples testing falsely negative in the Aptima Combo 2 test in Finland, 2019
Since February 2019, over 160 Chlamydia trachomatis (CT) cases testing negative or equivocal by Aptima Combo 2 (AC2) but positive by Aptima CT test run with Panther instruments occurred in Finland. The AC2 test targets chlamydial 23S rRNA while the CT test targets 16S rRNA. Sequencing of 10 strains revealed a nucleotide substitution in 23S rRNA. The significance of this for the failure of the AC2 test to detect the variant is not yet known.Peer reviewe
Development and characterization of the readout system for POLARBEAR-2
POLARBEAR-2 is a next-generation receiver for precision measurements of the
polarization of the cosmic microwave background (Cosmic Microwave Background
(CMB)). Scheduled to deploy in early 2015, it will observe alongside the
existing POLARBEAR-1 receiver, on a new telescope in the Simons Array on Cerro
Toco in the Atacama desert of Chile. For increased sensitivity, it will feature
a larger area focal plane, with a total of 7,588 polarization sensitive
antenna-coupled Transition Edge Sensor (TES) bolometers, with a design
sensitivity of 4.1 uKrt(s). The focal plane will be cooled to 250 milliKelvin,
and the bolometers will be read-out with 40x frequency domain multiplexing,
with 36 optical bolometers on a single SQUID amplifier, along with 2 dark
bolometers and 2 calibration resistors. To increase the multiplexing factor
from 8x for POLARBEAR-1 to 40x for POLARBEAR-2 requires additional bandwidth
for SQUID readout and well-defined frequency channel spacing. Extending to
these higher frequencies requires new components and design for the LC filters
which define channel spacing. The LC filters are cold resonant circuits with an
inductor and capacitor in series with each bolometer, and stray inductance in
the wiring and equivalent series resistance from the capacitors can affect
bolometer operation. We present results from characterizing these new readout
components. Integration of the readout system is being done first on a small
scale, to ensure that the readout system does not affect bolometer sensitivity
or stability, and to validate the overall system before expansion into the full
receiver. We present the status of readout integration, and the initial results
and status of components for the full array.Comment: Presented at SPIE Astronomical Telescopes and Instrumentation 2014:
Millimeter, Submillimeter, and Far-Infrared Detectors and Instrumentation for
Astronomy VII. Published in Proceedings of SPIE Volume 915
The impact of MK-467 on plasma drug concentrations, sedation and cardiopulmonary changes in sheep treated with intramuscular medetomidine and atipamezole for reversal
The effect of MK‐467, a peripheral α2‐adrenoceptor antagonist, on plasma drug concentrations, sedation and cardiopulmonary changes induced by intramuscular (IM) medetomidine was investigated in eight sheep. Additionally, the interactions with atipamezole (ATI) used for reversal were also evaluated. Each animal was treated four times in a randomized prospective crossover design with 2‐week washout periods. Medetomidine (MED) 30 μg/kg alone or combined in the same syringe with MK‐467 300 μg/kg (MMK) was injected intramuscular, followed by ATI 150 μg/kg (MED + ATI and MMK + ATI) or saline intramuscular 30 min later. Plasma was analysed for drug concentrations, and sedation was subjectively assessed with a visual analogue scale. Systemic haemodynamics and blood gases were measured before treatments and at intervals thereafter. With MK‐467, medetomidine plasma concentrations were threefold higher prior to ATI, which was associated with more profound sedation and shorter onset. No significant differences were observed in early cardiopulmonary changes between treatments. Atipamezole reversed the medetomidine‐related cardiopulmonary changes after both treatments. Sedation scores decreased more rapidly when MK‐467 was included. In this study, MK‐467 appeared to have a pronounced effect on the plasma concentration and central effects of medetomidine, with minor cardiopulmonary improvement. </p
Bayes in the sky: Bayesian inference and model selection in cosmology
The application of Bayesian methods in cosmology and astrophysics has
flourished over the past decade, spurred by data sets of increasing size and
complexity. In many respects, Bayesian methods have proven to be vastly
superior to more traditional statistical tools, offering the advantage of
higher efficiency and of a consistent conceptual basis for dealing with the
problem of induction in the presence of uncertainty. This trend is likely to
continue in the future, when the way we collect, manipulate and analyse
observations and compare them with theoretical models will assume an even more
central role in cosmology.
This review is an introduction to Bayesian methods in cosmology and
astrophysics and recent results in the field. I first present Bayesian
probability theory and its conceptual underpinnings, Bayes' Theorem and the
role of priors. I discuss the problem of parameter inference and its general
solution, along with numerical techniques such as Monte Carlo Markov Chain
methods. I then review the theory and application of Bayesian model comparison,
discussing the notions of Bayesian evidence and effective model complexity, and
how to compute and interpret those quantities. Recent developments in
cosmological parameter extraction and Bayesian cosmological model building are
summarized, highlighting the challenges that lie ahead.Comment: Invited review to appear in Contemporary Physics. 41 pages, 6
figures. Expanded references wrt published versio
Residual noise covariance for Planck low-resolution data analysis
Aims: Develop and validate tools to estimate residual noise covariance in Planck frequency maps. Quantify signal error effects and compare different techniques to produce low-resolution maps. Methods: We derive analytical estimates of covariance of the residual noise contained in low-resolution maps produced using a number of map-making approaches. We test these analytical predictions using Monte Carlo simulations and their impact on angular power spectrum estimation. We use simulations to quantify the level of signal errors incurred in different resolution downgrading schemes considered in this work. Results: We find an excellent agreement between the optimal residual noise covariance matrices and Monte Carlo noise maps. For destriping map-makers, the extent of agreement is dictated by the knee frequency of the correlated noise component and the chosen baseline offset length. The significance of signal striping is shown to be insignificant when properly dealt with. In map resolution downgrading, we find that a carefully selected window function is required to reduce aliasing to the sub-percent level at multipoles, ell > 2Nside, where Nside is the HEALPix resolution parameter. We show that sufficient characterization of the residual noise is unavoidable if one is to draw reliable contraints on large scale anisotropy. Conclusions: We have described how to compute the low-resolution maps, with a controlled sky signal level, and a reliable estimate of covariance of the residual noise. We have also presented a method to smooth the residual noise covariance matrices to describe the noise correlations in smoothed, bandwidth limited maps.Peer reviewe
Contrasts in dissolved, particulate, and sedimentary organic carbon from the Kolyma River to the East Siberian Shelf
Arctic rivers will be increasingly affected by the
hydrological and biogeochemical consequences of thawing permafrost. During
transport, permafrost-derived organic carbon (OC) can either accumulate in
floodplain and shelf sediments or be degraded into greenhouse gases prior to
final burial. Thus, the net impact of permafrost OC on climate will
ultimately depend on the interplay of complex processes that occur along the
source-to-sink system. Here, we focus on the Kolyma River, the largest
watershed completely underlain by continuous permafrost, and marine
sediments of the East Siberian Sea, as a transect to investigate the fate of
permafrost OC along the land–ocean continuum. Three pools of riverine OC
were investigated for the Kolyma main stem and five of its tributaries:
dissolved OC (DOC), suspended particulate OC (POC), and riverbed sediment OC
(SOC). They were compared with earlier findings in marine sediments. Carbon isotopes
(δ13C, Δ14C), lignin phenol, and lipid biomarker
proxies show a contrasting composition and degradation state of these
different carbon pools. Dual C isotope source apportionment calculations
imply that old permafrost-OC is mostly associated with sediments (SOC;
contribution of 68±10 %), and less dominant in POC (38±8 %), whereas autochthonous primary production contributes around 44±10 % to POC in the main stem and up to 79±11 % in tributaries.
Biomarker degradation indices suggest that Kolyma DOC might be relatively
degraded, regardless of its generally young age shown by previous studies.
In contrast, SOC shows the lowest Δ14C value (oldest OC), yet
relatively fresh compositional signatures. Furthermore, decreasing mineral
surface area-normalised OC- and biomarker loadings suggest that SOC might be
reactive along the land–ocean continuum and almost all parameters were
subjected to rapid change when moving from freshwater to the marine
environment. This suggests that sedimentary dynamics play a crucial role
when targeting permafrost-derived OC in aquatic systems and support earlier
studies highlighting the fact that the land–ocean transition zone is an efficient
reactor and a dynamic environment. The prevailing inconsistencies between
freshwater and marine research (i.e. targeting predominantly DOC and SOC
respectively) need to be better aligned in order to determine to what degree
thawed permafrost OC may be destined for long-term burial, thereby
attenuating further global warming.</p
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