4,241 research outputs found
Object Distribution Networks for World-wide Document Circulation
This paper presents an Object Distribution System (ODS), a distributed system inspired by the ultra-large scale distribution models used in everyday life (e.g. food or newspapers distribution chains). Beyond traditional mechanisms of approaching information to readers (e.g. caching and mirroring), this system enables the publication, classification and subscription to volumes of objects (e.g. documents, events). Authors submit their contents to publication agents. Classification authorities provide classification schemes to classify objects. Readers subscribe to topics or authors, and retrieve contents from their local delivery agent (like a kiosk or library, with local copies of objects). Object distribution is an independent process where objects circulate asynchronously among distribution agents. ODS is designed to perform specially well in an increasingly populated, widespread and complex Internet jungle, using weak consistency replication by object distribution, asynchronous replication, and local access to objects by clients. ODS is based on two independent virtual networks, one dedicated to the distribution (replication) of objects and the other to calculate optimised distribution chains to be applied by the first network
Pulsations powered by hydrogen shell burning in white dwarfs
In the absence of a third dredge-up episode during the asymptotic giant
branch phase, white dwarf models evolved from low-metallicity progenitors have
a thick hydrogen envelope, which makes hydrogen shell burning be the most
important energy source. We investigate the pulsational stability of white
dwarf models with thick envelopes to see whether nonradial -mode pulsations
are triggered by hydrogen burning, with the aim of placing constraints on
hydrogen shell burning in cool white dwarfs and on a third dredge-up during the
asymptotic giant branch evolution of their progenitor stars. We construct
white-dwarf sequences from low-metallicity progenitors by means of full
evolutionary calculations, and analyze their pulsation stability for the models
in the range of effective temperatures
K. We demonstrate that, for white dwarf models with masses M_{\star} \lesssim
0.71\,\rm M_{\sun} and effective temperatures K that evolved from low-metallicity progenitors (,
, and ) the dipole () and quadrupole ()
modes are excited mostly due to the hydrogen-burning shell through the
-mechanism, in addition to other modes driven by either the
or the convective driving mechanism. However, the
mechanism is insufficient to drive these modes in white dwarfs evolved from
solar-metallicity progenitors. We suggest that efforts should be made to
observe the dipole mode in white dwarfs associated with low-metallicity
environments, such as globular clusters and/or the galactic halo, to place
constraints on hydrogen shell burning in cool white dwarfs and the third
dredge-up episode during the preceding asymptotic giant branch phase.Comment: 6 pages, 4 figures, 1 table. To be published in Astronomy and
Astrophysic
Screening of Obstructive Sleep Apnea with Empirical Mode Decomposition of Pulse Oximetry
Detection of desaturations on the pulse oximetry signal is of great
importance for the diagnosis of sleep apneas. Using the counting of
desaturations, an index can be built to help in the diagnosis of severe cases
of obstructive sleep apnea-hypopnea syndrome. It is important to have automatic
detection methods that allows the screening for this syndrome, reducing the
need of the expensive polysomnography based studies. In this paper a novel
recognition method based on the empirical mode decomposition of the pulse
oximetry signal is proposed. The desaturations produce a very specific wave
pattern that is extracted in the modes of the decomposition. Using this
information, a detector based on properly selected thresholds and a set of
simple rules is built. The oxygen desaturation index constructed from these
detections produces a detector for obstructive sleep apnea-hypopnea syndrome
with high sensitivity () and specificity () and yields better
results than standard desaturation detection approaches.Comment: Accepted in Medical Engineering and Physic
Unitarity of theories containing fractional powers of the d'Alembertian operator
We examine the unitarity of a class of generalized Maxwell U(1) gauge
theories in (2+1) D containing the pseudodifferential operator
, for . We show that only Quantum
Electrodynamics (QED) and its generalization known as Pseudo Quantum
Electrodynamics (PQED), for which and , respectively,
satisfy unitarity. The latter plays an important role in the description of the
electromagnetic interactions of charged particles confined to a plane, such as
in graphene or in hetero-junctions displaying the quantum Hall effect.Comment: 6 pages, no figure
Interaction Induced Quantum Valley Hall Effect in Graphene
We use Pseudo Quantum Electrodynamics (PQED) in order to describe the full
electromagnetic interaction of the p-electrons of graphene in a consistent 2D
formulation. We first consider the effect of this interaction in the vacuum
polarization tensor or, equivalently, in the current correlator. This allows us
to obtain the dc conductivity after a smooth zero-frequency limit is taken in
Kubo's formula.Thereby, we obtain the usual expression for the minimal
conductivity plus corrections due to the interaction that bring it closer to
the experimental value. We then predict the onset of an interaction-driven
spontaneous Quantum Valley Hall effect (QVHE) below a critical temperature of
the order of K. The transverse (Hall) valley conductivity is evaluated
exactly and shown to coincide with the one in the usual Quantum Hall effect.
Finally, by considering the effects of PQED, we show that the electron
self-energy is such that a set of P- and T- symmetric gapped electron energy
eigenstates are dynamically generated, in association with the QVHE.Comment: 5 pages + supplemental materia
Revisiting the axion bounds from the Galactic white dwarf luminosity function
It has been shown that the shape of the luminosity function of white dwarfs
(WDLF) is a powerful tool to check for the possible existence of DFSZ-axions, a
proposed but not yet detected type of weakly interacting particles. With the
aim of deriving new constraints on the axion mass, we compute in this paper new
theoretical WDLFs on the basis of WD evolving models that incorporate for the
feedback of axions on the thermal structure of the white dwarf. We find that
the impact of the axion emission into the neutrino emission can not be
neglected at high luminosities () and that the axion
emission needs to be incorporated self-consistently into the evolution of the
white dwarfs when dealing with axion masses larger than meV (i.e. axion-electron coupling constant ). We went beyond previous works by including 5 different derivations
of the WDLF in our analysis. Then we have performed -tests to have a
quantitative measure of the assessment between the theoretical WDLFs
---computed under the assumptions of different axion masses and normalization
methods--- and the observed WDLFs of the Galactic disk. While all the WDLF
studied in this work disfavour axion masses in the range suggested by
asteroseismology ( meV; ) lower axion masses can not be discarded from our current knowledge
of the WDLF of the Galactic Disk. A larger set of completely independent
derivations of the WDLF of the galactic disk as well as a detailed study of the
uncertainties of the theoretical WDLFs is needed before quantitative
constraints on the axion-electron coupling constant can be made.Comment: 17 pages, 6 figures, accepted for publication in the Journal of
Cosmology and Astroparticle Physic
Robust-fidelity atom-photon entangling gates in the weak-coupling regime
We describe a simple entangling principle based on the scattering of photons
off single emitters in one-dimensional waveguides (or extremely-lossy
cavities). The scheme can be applied to photonic qubits encoded in polarization
or time-bin, and features a filtering mechanism that works effectively as a
built-in error-correction directive. This automatically maps imperfections from
weak couplings, atomic decay into undesired modes, frequency mismatches, or
finite bandwidths of the incident photonic pulses, into heralded losses instead
of infidelities. The scheme is thus adequate for high-fidelity maximally
entangling gates even in the weak-coupling regime. These, in turn, can be
directly applied to store and retrieve photonic-qubit states, thereby
completing an atom-photon interface toolbox, or to sequential measurement-based
quantum computations with atomic memories.Comment: 5 pages, 2 figure
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