272 research outputs found
Worlds of events: deduction with partial knowledge about causality
Interactions between internet users are mediated by their devices and the common support infrastructure in data centres. Keeping track of causality amongst actions that take place in this distributed system is key to provide a seamless interaction where effects follow causes. Tracking causality in large scale interactions is difficult due to the cost of keeping large quantities of metadata; even more challenging when dealing with resource-limited devices. In this paper, we focus on keeping partial knowledge on causality and address deduction from that knowledge.We provide the first proof-theoretic causality modelling for distributed partial knowledge. We prove computability and consistency results. We also prove that the partial knowledge gives rise to a weaker model than classical causality. We provide rules for offline deduction about causality and refute some related folklore. We define two notions of forward and backward bisimilarity between devices, using which we prove two important results. Namely, no matter the order of addition/ removal, two devices deduce similarly about causality so long as: (1) the same causal information is fed to both. (2) they start bisimilar and erase the same causal information. Thanks to our establishment of forward and backward bisimilarity, respectively, proofs of the latter two results work by simple induction on length.-This work was partially funded by the SyncFree project in the European Seventh Framework Programme under Grant Agreement 609551 and by the Erasmus Mundus Joint Doctorate Programme under Grant Agreement 2012-0030. Our special thanks to the SyncFree peers for their prolific comments on the early versions of this work. We would like to also thank the anonymous referees for their constructive discussion over the ICE forum.info:eu-repo/semantics/publishedVersio
Entanglement transfer from dissociated molecules to photons
We introduce and study the concept of a reversible transfer of the quantum
state of two internally-translationally entangled fragments, formed by
molecular dissociation, to a photon pair. The transfer is based on intracavity
stimulated Raman adiabatic passage and it requires a combination of processes
whose principles are well established.Comment: 5 pages, 3 figure
Selection Effects on the Observed Redshift Dependence of GRB Jet Opening Angles
Apparent redshift dependence of the jet opening angles () of
gamma-ray bursts (GRBs) is observed from current GRB sample. We investigate
whether this dependence can be explained with instrumental selection effects
and observational biases by a bootstrapping method. Assuming that (1) the GRB
rate follows the star formation history and the cosmic metallicity history and
(2) the intrinsic distributions of the jet-corrected luminosity () and are a Gaussian or a power-law function, we
generate a mock {\em Swift}/BAT sample by considering various instrumental
selection effects, including the flux threshold and the trigger probability of
BAT, the probabilities of a GRB jet pointing to the instrument solid angle and
the probability of redshift measurement. Our results well reproduce the
observed dependence. We find that in case of
good consistency between the mock and
observed samples can be obtained, indicating that both and
are degenerate for a flux-limited sample. The parameter set
gives the best consistency for the current {\em Swift} GRB sample.
Considering the beaming effect, the derived intrinsic local GRB rate
accordingly is Gpc yr, inferring that of Type Ib/c SNe may be accompanied by a GRB.Comment: 25pages, 7 figures. ApJ in pres
Economic analysis of the health impacts of housing improvement studies: a systematic review
Background: Economic evaluation of public policies
has been advocated but rarely performed. Studies from a
systematic review of the health impacts of housing
improvement included data on costs and some economic
analysis. Examination of these data provides an
opportunity to explore the difficulties and the potential
for economic evaluation of housing.
Methods: Data were extracted from all studies included
in the systematic review of housing improvement which
had reported costs and economic analysis (n=29/45).
The reported data were assessed for their suitability to
economic evaluation. Where an economic analysis was
reported the analysis was described according to pre-set
definitions of various types of economic analysis used in
the field of health economics.
Results: 25 studies reported cost data on the
intervention and/or benefits to the recipients. Of these,
11 studies reported data which was considered
amenable to economic evaluation. A further four studies
reported conducting an economic evaluation. Three of
these studies presented a hybrid ‘balance sheet’
approach and indicated a net economic benefit
associated with the intervention. One cost-effectiveness
evaluation was identified but the data were unclearly
reported; the cost-effectiveness plane suggested that the
intervention was more costly and less effective than the
status quo.
Conclusions: Future studies planning an economic
evaluation need to (i) make best use of available data
and (ii) ensure that all relevant data are collected. To
facilitate this, economic evaluations should be planned
alongside the intervention with input from health
economists from the outset of the study. When
undertaken appropriately, economic evaluation provides
the potential to make significant contributions to
housing policy
Quantum advantage in postselected metrology
Abstract: In every parameter-estimation experiment, the final measurement or the postprocessing incurs a cost. Postselection can improve the rate of Fisher information (the average information learned about an unknown parameter from a trial) to cost. We show that this improvement stems from the negativity of a particular quasiprobability distribution, a quantum extension of a probability distribution. In a classical theory, in which all observables commute, our quasiprobability distribution is real and nonnegative. In a quantum-mechanically noncommuting theory, nonclassicality manifests in negative or nonreal quasiprobabilities. Negative quasiprobabilities enable postselected experiments to outperform optimal postselection-free experiments: postselected quantum experiments can yield anomalously large information-cost rates. This advantage, we prove, is unrealizable in any classically commuting theory. Finally, we construct a preparation-and-postselection procedure that yields an arbitrarily large Fisher information. Our results establish the nonclassicality of a metrological advantage, leveraging our quasiprobability distribution as a mathematical tool
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A compendium of time series measurements from moored instrumentation during the MAM '77 phase of JOINT-II
Low-Luminosity Gamma-Ray Bursts as a Distinct GRB Population:A Firmer Case from Multiple Criteria Constraints
The intriguing observations of Swift/BAT X-ray flash XRF 060218 and the
BATSE-BeppoSAX gamma-ray burst GRB 980425, both with much lower luminosity and
redshift compared to other observed bursts, naturally lead to the question of
how these low-luminosity (LL) bursts are related to high-luminosity (HL)
bursts. Incorporating the constraints from both the flux-limited samples
observed with CGRO/BATSE and Swift/BAT and the redshift-known GRB sample, we
investigate the luminosity function for both LL- and HL-GRBs through
simulations. Our multiple criteria, including the log N - log P distributions
from the flux-limited GRB sample, the redshift and luminosity distributions of
the redshift-known sample, and the detection ratio of HL- and LL- GRBs with
Swift/BAT, provide a set of stringent constraints to the luminosity function.
Assuming that the GRB rate follows the star formation rate, our simulations
show that a simple power law or a broken power law model of luminosity function
fail to reproduce the observations, and a new component is required. This
component can be modeled with a broken power, which is characterized by a sharp
increase of the burst number at around L < 10^47 erg s^-1}. The lack of
detection of moderate-luminosity GRBs at redshift ~0.3 indicates that this
feature is not due to observational biases. The inferred local rate, rho_0, of
LL-GRBs from our model is ~ 200 Gpc^-3 yr^-1 at ~ 10^47 erg s^-1, much larger
than that of HL-GRBs. These results imply that LL-GRBs could be a separate GRB
population from HL-GRBs. The recent discovery of a local X-ray transient
080109/SN 2008D would strengthen our conclusion, if the observed non-thermal
emission has a similar origin as the prompt emission of most GRBs and XRFs.Comment: 22 pages, 9 figures, 3 tables; MNRAS, in press; Updated analysis and
figure
The source counts of submillimetre galaxies detected at 1.1 mm
The source counts of galaxies discovered at sub-millimetre and millimetre
wavelengths provide important information on the evolution of infrared-bright
galaxies. We combine the data from six blank-field surveys carried out at 1.1
mm with AzTEC, totalling 1.6 square degrees in area with root-mean-square
depths ranging from 0.4 to 1.7 mJy, and derive the strongest constraints to
date on the 1.1 mm source counts at flux densities S(1100) = 1-12 mJy. Using
additional data from the AzTEC Cluster Environment Survey to extend the counts
to S(1100) ~ 20 mJy, we see tentative evidence for an enhancement relative to
the exponential drop in the counts at S(1100) ~ 13 mJy and a smooth connection
to the bright source counts at >20 mJy measured by the South Pole Telescope;
this excess may be due to strong lensing effects. We compare these counts to
predictions from several semi-analytical and phenomenological models and find
that for most the agreement is quite good at flux densities > 4 mJy; however,
we find significant discrepancies (>3sigma) between the models and the observed
1.1 mm counts at lower flux densities, and none of them are consistent with the
observed turnover in the Euclidean-normalised counts at S(1100) < 2 mJy. Our
new results therefore may require modifications to existing evolutionary models
for low luminosity galaxies. Alternatively, the discrepancy between the
measured counts at the faint end and predictions from phenomenological models
could arise from limited knowledge of the spectral energy distributions of
faint galaxies in the local Universe.Comment: 16 pages, 3 figures, 4 tables; accepted for publication in MNRA
Observing the Evolution of the Universe
How did the universe evolve? The fine angular scale (l>1000) temperature and
polarization anisotropies in the CMB are a Rosetta stone for understanding the
evolution of the universe. Through detailed measurements one may address
everything from the physics of the birth of the universe to the history of star
formation and the process by which galaxies formed. One may in addition track
the evolution of the dark energy and discover the net neutrino mass.
We are at the dawn of a new era in which hundreds of square degrees of sky
can be mapped with arcminute resolution and sensitivities measured in
microKelvin. Acquiring these data requires the use of special purpose
telescopes such as the Atacama Cosmology Telescope (ACT), located in Chile, and
the South Pole Telescope (SPT). These new telescopes are outfitted with a new
generation of custom mm-wave kilo-pixel arrays. Additional instruments are in
the planning stages.Comment: Science White Paper submitted to the US Astro2010 Decadal Survey.
Full list of 177 author available at http://cmbpol.uchicago.ed
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