3,417 research outputs found
A formal method for identifying distinct states of variability in time-varying sources: SgrA* as an example
Continuously time variable sources are often characterized by their power
spectral density and flux distribution. These quantities can undergo dramatic
changes over time if the underlying physical processes change. However, some
changes can be subtle and not distinguishable using standard statistical
approaches. Here, we report a methodology that aims to identify distinct but
similar states of time variability. We apply this method to the Galactic
supermassive black hole, where 2.2 um flux is observed from a source associated
with SgrA*, and where two distinct states have recently been suggested. Our
approach is taken from mathematical finance and works with conditional flux
density distributions that depend on the previous flux value. The discrete,
unobserved (hidden) state variable is modeled as a stochastic process and the
transition probabilities are inferred from the flux density time series. Using
the most comprehensive data set to date, in which all Keck and a majority of
the publicly available VLT data have been merged, we show that SgrA* is
sufficiently described by a single intrinsic state. However the observed flux
densities exhibit two states: a noise-dominated and a source-dominated one. Our
methodology reported here will prove extremely useful to assess the effects of
the putative gas cloud G2 that is on its way toward the black hole and might
create a new state of variability.Comment: Submitted to ApJ; 33 pages, 4 figures; comments welcom
Tensor products of subspace lattices and rank one density
We show that, if is a subspace lattice with the property that the rank
one subspace of its operator algebra is weak* dense, is a commutative
subspace lattice and is the lattice of all projections on a separable
infinite dimensional Hilbert space, then the lattice is
reflexive. If is moreover an atomic Boolean subspace lattice while is
any subspace lattice, we provide a concrete lattice theoretic description of
in terms of projection valued functions defined on the set of
atoms of . As a consequence, we show that the Lattice Tensor Product Formula
holds for \Alg M and any other reflexive operator algebra and give several
further corollaries of these results.Comment: 15 page
Bosonic autonomous entanglement engines with weak bath coupling are impossible
Entanglement is a fundamental feature of quantum physics and a key resource
for quantum communication, computing and sensing. Entangled states are fragile
and maintaining coherence is a central challenge in quantum information
processing. Nevertheless, entanglement can be generated and stabilised through
dissipative processes. In fact, entanglement has been shown to exist in the
steady state of certain interacting quantum systems subject solely to
incoherent coupling to thermal baths. This has been demonstrated in a range of
bi- and multipartite settings using systems of finite dimension. Here we focus
on the steady state of infinite-dimensionsional bosonic systems. Specifically,
we consider any set of bosonic modes undergoing excitation-number-preserving
interactions of arbitrary strength and divided between an arbitrary number of
parties that each couple weakly to thermal baths at different temperatures. We
show that the steady state is always separable.Comment: 10 pages, 1 figur
Pandemic influenza control in Europe and the constraints resulting from incoherent public health laws
© 2010 Martin et al; licensee BioMed Central Ltd. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.Background: With the emergence of influenza H1N1v the world is facing its first 21st century global pandemic. Severe Acute Respiratory Syndrome (SARS) and avian influenza H5N1 prompted development of pandemic preparedness plans. National systems of public health law are essential for public health stewardship and for the implementation of public health policy[1]. International coherence will contribute to effective regional and global responses. However little research has been undertaken on how law works as a tool for disease control in Europe. With co-funding from the European Union, we investigated the extent to which laws across Europe support or constrain pandemic preparedness planning, and whether national differences are likely to constrain control efforts. Methods: We undertook a survey of national public health laws across 32 European states using a questionnaire designed around a disease scenario based on pandemic influenza. Questionnaire results were reviewed in workshops, analysing how differences between national laws might support or hinder regional responses to pandemic influenza. Respondents examined the impact of national laws on the movements of information, goods, services and people across borders in a time of pandemic, the capacity for surveillance, case detection, case management and community control, the deployment of strategies of prevention, containment, mitigation and recovery and the identification of commonalities and disconnects across states. Results: Results of this study show differences across Europe in the extent to which national pandemic policy and pandemic plans have been integrated with public health laws. We found significant differences in legislation and in the legitimacy of strategic plans. States differ in the range and the nature of intervention measures authorized by law, the extent to which borders could be closed to movement of persons and goods during a pandemic, and access to healthcare of non-resident persons. Some states propose use of emergency powers that might potentially override human rights protections while other states propose to limit interventions to those authorized by public health laws. Conclusion: These differences could create problems for European strategies if an evolving influenza pandemic results in more serious public health challenges or, indeed, if a novel disease other than influenza emerges with pandemic potential. There is insufficient understanding across Europe of the role and importance of law in pandemic planning. States need to build capacity in public health law to support disease prevention and control policies. Our research suggests that states would welcome further guidance from the EU on management of a pandemic, and guidance to assist in greater commonality of legal approaches across states.Peer reviewe
Analysis of complex interactions between mechanical elements using ansys and simulink
Modelling and computer simulation play an important role in all engineering disciplines. For the coupling of different simulation tools interface are necessary, including both aspects of physics, numerical methods, software engineering, etc. This paper describes the development of the interface between MATLAB (as a topology optimisation tool) and ANSYS (computer aided engineering software used for finite element analysis). The setting of the project application in Workbench (ANSYS toolbox)
using APDL programming is described and then the ANSYS results are imported into SIMULINK
Emission lines in the atmosphere of the irradiated brown dwarf WD0137â349B
ESL acknowledges the support of STFC studentship. SLC acknowledges support from the University of Leicester College of Science and Engineering. CH highlights the financial support of the European community under the FP7 ERC starting grant 257431. This work was supported by the Science and Technology Facilities Council [ST/M001040/1].We present new optical and near-infrared spectra of WD0137â349; a close white dwarfâbrown dwarf non-interacting binary system with a period of â114âmin. We have confirmed the presence of Hâα emission and discovered He, Na, Mg, Si, K, Ca, Ti and Fe emission lines originating from the brown-dwarf atmosphere. This is the first brown-dwarf atmosphere to have been observed to exhibit metal emission lines as a direct result of intense irradiation. The equivalent widths of many of these lines show a significant difference between the day-side and night-side of the brown dwarf. This is likely an indication that efficient heat redistribution may not be happening on this object, in agreement with models of hot Jupiter atmospheres. The Hâα line strength variation shows a strong phase dependency as does the width. We have simulated the Caâii emission lines using a model that includes the brown-dwarf Roche geometry and limb darkening, and we estimate the mass ratio of the system to be 0.135 ± 0.004. We also apply a gas-phase equilibrium code using a prescribed drift-phoenix model to examine how the chemical composition of the brown-dwarf upper atmosphere would change given an outward temperature increase, and discuss the possibility that this would induce a chromosphere above the brown-dwarf atmosphere.Publisher PDFPeer reviewe
The determinants of credit spreads changes in global shipping bonds.
yesThis paper investigates whether bond, issuer, industry and macro-specific variables
account for the observed variation of credit spreadsâ changes of global shipping bond issues
before and after the onset of the subprime financial crisis. Results show that conclusions as
to the significant variables of spreads depend significantly on whether two-way clusteradjusted
standard errors are utilized, thus rendering results in the extant literature ambigious.
The main determinants of global cargo-carrying companiesâ shipping bond spreads
are found in this paper to be: the liquidity of the bond issue, the stock marketâs volatility,
the bond marketâs cyclicality, freight earnings and the credit rating of the bond issue
Bleeding related to disturbed fibrinolysis
The components and reactions of the fibrinolysis system are well understood. The pathway has fewer reactants and interactions than coagulation, but the generation of a complete quantitative model is complicated by the need to work at the solidâliquid interface of fibrin. Diagnostic tools to detect disease states due to malfunctions in the fibrinolysis pathway are also not so well developed as is the case with coagulation. However, there are clearly a number of inherited or acquired pathologies where hyperfibrinolysis is a serious, potentially lifeâthreatening problem and a number of antifibrinolytc drugs are available to treat hyperfibrinolysis. These topics will be covered in the following review
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