221 research outputs found
Optimizing future dark energy surveys for model selection goals
We demonstrate a methodology for optimizing the ability of future dark energy
surveys to answer model selection questions, such as `Is acceleration due to a
cosmological constant or a dynamical dark energy model?'. Model selection
Figures of Merit are defined, exploiting the Bayes factor, and surveys
optimized over their design parameter space via a Monte Carlo method. As a
specific example we apply our methods to generic multi-fibre baryon acoustic
oscillation spectroscopic surveys, comparable to that proposed for SuMIRe PFS,
and present implementations based on the Savage-Dickey Density Ratio that are
both accurate and practical for use in optimization. It is shown that whilst
the optimal surveys using model selection agree with those found using the Dark
Energy Task Force (DETF) Figure of Merit, they provide better informed
flexibility of survey configuration and an absolute scale for performance; for
example, we find survey configurations with close to optimal model selection
performance despite their corresponding DETF Figure of Merit being at only 50%
of its maximum. This Bayes factor approach allows us to interpret the survey
configurations that will be good enough for the task at hand, vital especially
when wanting to add extra science goals and in dealing with time restrictions
or multiple probes within the same project.Comment: 12 pages, 16 figure
Accuracy of the Cosmed K5 portable calorimeter
Purpose The purpose of this study was to assess the accuracy of the Cosmed K5 portable metabolic system dynamic mixing chamber (MC) and breath-by-breath (BxB) modes against the criterion Douglas bag (DB) method. Methods Fifteen participants (mean age±SD, 30.6±7.4 yrs) had their metabolic variables measured at rest and during cycling at 50, 100, 150, 200, and 250W. During each stage, participants were connected to the first respiratory gas collection method (randomized) for the first four minutes to reach steady state, followed by 3-min (or 5-min for DB) collection periods for the resting condition, and 2-min collection periods for all cycling intensities. Collection periods for the second and third methods were preceded by a washout of 1–3 min. Repeated measures ANOVAs were used to compare metabolic variables measured by each method, for seated rest and each cycling work rate. Results For ventilation (VE) and oxygen uptake (VO2), the K5 MC and BxB modes were within 2.1 l/min (VE) and 0.08 l/min (VO2) of the DB (p≥0.05). Compared to DB values, carbon dioxide production (VCO2) was significantly underestimated by the K5 BxB mode at work rates ≥150W by 0.12–0.31 l/min (p\u3c0.05). K5 MC and BxB respiratory exchange ratio values were significantly lower than DB at cycling work rates ≥100W by 0.03–0.08 (p\u3c0.05). Conclusion Compared to the DB method, the K5 MC and BxB modes are acceptable for measuring VE and VO2 across a wide range of cycling intensities. Both K5 modes provided comparable values to each other
Recommended from our members
INSIGHT: A population-scale COVID-19 testing strategy combining point-of-care diagnosis with centralized high-throughput sequencing.
We present INSIGHT [isothermal NASBA (nucleic acid sequence-based amplification) sequencing-based high-throughput test], a two-stage coronavirus disease 2019 testing strategy, using a barcoded isothermal NASBA reaction. It combines point-of-care diagnosis with next-generation sequencing, aiming to achieve population-scale testing. Stage 1 allows a quick decentralized readout for early isolation of presymptomatic or asymptomatic patients. It gives results within 1 to 2 hours, using either fluorescence detection or a lateral flow readout, while simultaneously incorporating sample-specific barcodes. The same reaction products from potentially hundreds of thousands of samples can then be pooled and used in a highly multiplexed sequencing-based assay in stage 2. This second stage confirms the near-patient testing results and facilitates centralized data collection. The 95% limit of detection is <50 copies of viral RNA per reaction. INSIGHT is suitable for further development into a rapid home-based, point-of-care assay and is potentially scalable to the population level
Optimizing baryon acoustic oscillation surveys II: curvature, redshifts, and external datasets
We extend our study of the optimization of large baryon acoustic oscillation
(BAO) surveys to return the best constraints on the dark energy, building on
Paper I of this series (Parkinson et al. 2007). The survey galaxies are assumed
to be pre-selected active, star-forming galaxies observed by their line
emission with a constant number density across the redshift bin. Star-forming
galaxies have a redshift desert in the region 1.6 < z < 2, and so this redshift
range was excluded from the analysis. We use the Seo & Eisenstein (2007)
fitting formula for the accuracies of the BAO measurements, using only the
information for the oscillatory part of the power spectrum as distance and
expansion rate rulers. We go beyond our earlier analysis by examining the
effect of including curvature on the optimal survey configuration and updating
the expected `prior' constraints from Planck and SDSS. We once again find that
the optimal survey strategy involves minimizing the exposure time and
maximizing the survey area (within the instrumental constraints), and that all
time should be spent observing in the low-redshift range (z<1.6) rather than
beyond the redshift desert, z>2. We find that when assuming a flat universe the
optimal survey makes measurements in the redshift range 0.1 < z <0.7, but that
including curvature as a nuisance parameter requires us to push the maximum
redshift to 1.35, to remove the degeneracy between curvature and evolving dark
energy. The inclusion of expected other data sets (such as WiggleZ, BOSS and a
stage III SN-Ia survey) removes the necessity of measurements below redshift
0.9, and pushes the maximum redshift up to 1.5. We discuss considerations in
determining the best survey strategy in light of uncertainty in the true
underlying cosmological model.Comment: 15 pages, revised in response to referees remarks, accepted for
publication in MNRAS. 2nd paper in a series. Paper 1 is at
http://arxiv.org/abs/astro-ph/070204
INSIGHT: A population-scale COVID-19 testing strategy combining point-of-care diagnosis with centralized high-throughput sequencing.
We present INSIGHT [isothermal NASBA (nucleic acid sequence-based amplification) sequencing-based high-throughput test], a two-stage coronavirus disease 2019 testing strategy, using a barcoded isothermal NASBA reaction. It combines point-of-care diagnosis with next-generation sequencing, aiming to achieve population-scale testing. Stage 1 allows a quick decentralized readout for early isolation of presymptomatic or asymptomatic patients. It gives results within 1 to 2 hours, using either fluorescence detection or a lateral flow readout, while simultaneously incorporating sample-specific barcodes. The same reaction products from potentially hundreds of thousands of samples can then be pooled and used in a highly multiplexed sequencing-based assay in stage 2. This second stage confirms the near-patient testing results and facilitates centralized data collection. The 95% limit of detection is <50 copies of viral RNA per reaction. INSIGHT is suitable for further development into a rapid home-based, point-of-care assay and is potentially scalable to the population level
Model selection as a science driver for dark energy surveys
A key science goal of upcoming dark energy surveys is to seek time evolution
of the dark energy. This problem is one of {\em model selection}, where the aim
is to differentiate between cosmological models with different numbers of
parameters. However, the power of these surveys is traditionally assessed by
estimating their ability to constrain parameters, which is a different
statistical problem. In this paper we use Bayesian model selection techniques,
specifically forecasting of the Bayes factors, to compare the abilities of
different proposed surveys in discovering dark energy evolution. We consider
six experiments -- supernova luminosity measurements by the Supernova Legacy
Survey, SNAP, JEDI, and ALPACA, and baryon acoustic oscillation measurements by
WFMOS and JEDI -- and use Bayes factor plots to compare their statistical
constraining power. The concept of Bayes factor forecasting has much broader
applicability than dark energy surveys.Comment: 10 pages, 15 figures included. Updated to match MNRAS accepted
versio
Domesticating Urban Theory? US Concepts, British Cities and the Limits of Cross-national Applications
The efficacy of the urban regime and growth machine concepts beyond the US remains a matter of considerable debate. Some argue that these frameworks retain considerable value so long as they are 'properly' applied and that recent concerns about the limits to these frameworks result from no more than their 'misapplication'. I critically examine this argument through a review of recent work on the mobilisation of business interests in British cities. The central claim is that, even when focused on the 'right' issues and questions, US frameworks quickly exhaust their explanatory capacity. In the context of a widening diversity of alternative approaches, I suggest that it is time to move squarely beyond growth coalition and regime accounts. The paper makes a number of suggestions for ways in which this new phase of theory building might proceed.Yeshttps://us.sagepub.com/en-us/nam/manuscript-submission-guideline
Super-horizon perturbations and preheating
We discuss the evolution of linear perturbations about a
Friedmann-Robertson-Walker background metric, using only the local conservation
of energy-momentum. We show that on sufficiently large scales the curvature
perturbation on spatial hypersurfaces of uniform-density is constant when the
non-adiabatic pressure perturbation is negligible. We clarify the conditions
under which super-horizon curvature perturbations may vary, using preheating as
an example.Comment: 4 pages, talk presented at "Cosmology and Particle Physics 2000",
Verbier (Switzerland), 17-28 July 200
On Perturbations in Warm Inflation
Warm inflation is an interesting possibility of describing the early
universe, whose basic feature is the absence, at least in principle, of a
preheating or reheating phase. Here we analyze the dynamics of warm inflation
generalizing the usual slow-roll parameters that are useful for characterizing
the inflationary phase. We study the evolution of entropy and adiabatic
perturbations, where the main result is that for a very small amount of
dissipation the entropy perturbations can be neglected and the purely adiabatic
perturbations will be responsible for the primordial spectrum of
inhomogeneities. Taking into account the COBE-DMR data of the cosmic microwave
background anisotropy as well as the fact that the interval of inflation for
which the scales of astrophysical interest cross outside the Hubble radius is
about 50 e-folds before the end of inflation, we could estimate the magnitude
of the dissipation term. It was also possible to show that at the end of
inflation the universe is hot enough to provide a smooth transition to the
radiation era.Comment: 12 pages, no figures, requires revtex4. Further explanation on the
origin of the entropy perturbation, reference added and minor notation
change. Version accepted for publication in Phys. Rev.
Nanodiamond emulsions for enhanced quantum sensing and click-chemistry conjugation
Nanodiamonds containing nitrogen-vacancy (NV) centers can serve as colloidal
quantum sensors of local fields in biological and chemical environments.
However, nanodiamond surfaces are challenging to modify without degrading their
colloidal stability or the NV center's optical and spin properties. Here, we
report a simple and general method to coat nanodiamonds with a thin emulsion
layer that preserves their quantum features, enhances their colloidal
stability, and provides functional groups for subsequent crosslinking and
click-chemistry conjugation reactions. To demonstrate this technique, we
decorate the nanodiamonds with combinations of carboxyl- and azide-terminated
amphiphiles that enable conjugation using two different strategies. We study
the effect of the emulsion layer on the NV center's spin lifetime, and we
quantify the nanodiamonds' chemical sensitivity to paramagnetic ions using
relaxometry. This general approach to nanodiamond surface
functionalization will enable advances in quantum nanomedicine and biological
sensing.Comment: 52 pages, 42 figures (main text plus supplementary information
- …