3,544 research outputs found
Publishing an E-journal on a shoe string: Is it a sustainaible project?.
The aim of this article is to report on an experiment in publishing an open access journal and learn from it about the larger field of open access publishing. The experiment is the launch of the European Journal of Comparative Economics (EJCE), an on-line refereed and open access journal, founded in 2004 by the European Association for Comparative Economic Studies and LIUC University in Italy. They embarked upon this project in part to respond to the rising concentration in the market for scientific publishing and the resulting use of market power to raise subscription prices and restrict access to scientific output. We had hoped that open access journals could provide some countervailing power and increase competition in the field. Our experience running a poorly endowed journal has shown that entry to the field may be easy, yet that making it a sustainable enterprise is not straightforward.Open-access publishing, online journals, scientific publication
Inequalities for quantum channels assisted by limited resources
The information capacities and ``distillability'' of a quantum channel are
studied in the presence of auxiliary resources. These include prior
entanglement shared between the sender and receiver and free classical bits of
forward and backward communication. Inequalities and trade-off curves are
derived. In particular an alternative proof is given that in the absence of
feedback and shared entanglement, forward classical communication does not
increase the quantum capacity of a channel.Comment: 8 pages, 4 figures (references updated, minor changes
Rashba effect induced localization in quantum networks
We study a quantum network extending in one-dimension (chain of square loops
connected at one vertex) made up of quantum wires with Rashba spin-orbit
coupling. We show that the Rashba effect may give rise to an electron
localization phenomenon similar to the one induced by magnetic field. This
localization effect can be attributed to the spin precession due to the Rashba
effect. We present results both for the spectral properties of the infinite
chain, and for linear transport through a finite-size chain connected to leads.
Furthermore, we study the effect of disorder on the transport properties of
this network.Comment: To appear in Phys. Rev. Let
Normal form decomposition for Gaussian-to-Gaussian superoperators
In this paper we explore the set of linear maps sending the set of quantum
Gaussian states into itself. These maps are in general not positive, a feature
which can be exploited as a test to check whether a given quantum state belongs
to the convex hull of Gaussian states (if one of the considered maps sends it
into a non positive operator, the above state is certified not to belong to the
set). Generalizing a result known to be valid under the assumption of complete
positivity, we provide a characterization of these Gaussian-to-Gaussian (not
necessarily positive) superoperators in terms of their action on the
characteristic function of the inputs. For the special case of one-mode
mappings we also show that any Gaussian-to-Gaussian superoperator can be
expressed as a concatenation of a phase-space dilatation, followed by the
action of a completely positive Gaussian channel, possibly composed with a
transposition. While a similar decomposition is shown to fail in the multi-mode
scenario, we prove that it still holds at least under the further hypothesis of
homogeneous action on the covariance matrix
Testing the assumptions for the analysis of survival data arising from a prevalent cohort study with follow-up
In a prevalent cohort study with follow-up subjects identified as prevalent cases are followed until failure (defined suitably) or censoring. When the dates of the initiating events of these prevalent cases are ascertainable, each observed datum point consists of a backward recurrence time and a possibly censored forward recurrence time. Their sum is well known to be the left truncated lifetime. It is common to term these left truncated lifetimes "length biased" if the initiating event times of all the incident cases (including those not observed through the prevalent sampling scheme) follow a stationary Poisson process. Statistical inference is then said to be carried out under stationarity. Whether or not stationarity holds, a further assumption needed for estimation of the incident survivor function is the independence of the lifetimes and their accompanying truncation times. That is, it must be assumed that survival does not depend on the calendar date of the initiating event. We show how this assumption may be checked under stationarity, even though only the backward recurrence times and their associated (possibly censored) forward recurrence times are\ud
observed. We prove that independence of the lifetimes and truncation times is equivalent to equality in distribution of the backward and forward recurrence times, and exploit this equivalence as a means of testing the former hypothesis. A simulation study is conducted to investigate the power and Type 1 error rate of our proposed tests, which include a bootstrap procedure that takes into account the pairwise dependence between the forward and backward recurrence times, as well as the potential censoring of only one of the members of each pair. We illustrate our methods using data from the Canadian Study of Health and Aging. We also point out an equivalence of the\ud
problem presented here to a non-standard changepoint problem
Rashba effect in quantum networks
We present a formalism to study quantum networks made up by single-channel
quantum wires in the presence of Rashba spin-orbit coupling and magnetic field.
In particular, linear transport through one-dimensional and two-dimensional
finite-size networks is studied by means of the scattering formalism. In some
particular quantum networks, the action of the magnetic field or of the Rashba
spin-orbit coupling induces localization of the electron wave function. This
phenomenon, which relies on both the quantum-mechanical interference and the
geometry of the network, is manifested through the suppression of the
conductance for specific values of the spin-orbit-coupling strength or of the
magnetic field. Furthermore, the interplay of the Aharonov-Bohm phases and of
the non-Abelian phases introduced by spin-orbit coupling, is discussed in a
number of cases.Comment: 8 pages and 6 figure
Sources of H0 -tension in dark energy scenarios
By focusing on a simple extension of Lambda cold dark matter (ÎCDM) in which the dark energy equation of state is allowed to vary, we assess which epoch(s) possibly source the H0-tension. We consider cosmic microwave background (CMB) data in three possible ways: (i) complete CMB data; (ii) excluding the low-l+lowE (l<30 temperature and polarization) likelihoods; (iii) imposing early Universe priors, which allow us to disentangle early- and late-time physics. Through a joint analysis with low-redshift supernovae type-Ia and gravitationally lensed time delay datasets, and neglecting galaxy clustering baryonic acoustic oscillation (BAO) data, we find that the inclusion of early Universe CMB priors is consistent with local estimate of H0, while excluding the low-l+lowE likelihoods mildly relaxes the tension. This is in contrast to joint analyses with the complete CMB data. Our simple implementation of contrasting the effect of different CMB priors on the H0 estimate shows that the early Universe information from the CMB data when decoupled from late-time physics could be in agreement with a higher value of H0, even for ÎCDM model with no necessary modification. We also find no evidence for the early dark energy model using only the early Universe physics within the CMB data. Finally, using the BAO data in different redshift ranges to perform inverse distance ladder analysis, we find that the early Universe modifications, while perfectly capable of alleviating the H0-tension when including the BAO galaxy clustering data, would be at odds with the Ly-α BAO data due to the difference in rd vs H0 correlation between the two BAO datasets. We therefore infer and speculate that source for the H0-tension between CMB and local estimates could possibly originate in the modeling of late-time physics within the CMB analysis. This in turn recasts the H0-tension as an effect of late-time physics in CMB, instead of the current early-time CMB vs local late-time physics perspective
The Planck Surveyor mission: astrophysical prospects
Although the Planck Surveyor mission is optimized to map the cosmic microwave
background anisotropies, it will also provide extremely valuable information on
astrophysical phenomena. We review our present understanding of Galactic and
extragalactic foregrounds relevant to the mission and discuss on one side,
Planck's impact on the study of their properties and, on the other side, to
what extent foreground contamination may affect Planck's ability to accurately
determine cosmological parameters. Planck's multifrequency surveys will be
unique in their coverage of large areas of the sky (actually, of the full sky);
this will extend by two or more orders of magnitude the flux density interval
over which mm/sub-mm counts of extragalactic sources can be determined by
instruments already available (like SCUBA) or planned for the next decade (like
the LSA-MMA or the space mission FIRST), which go much deeper but over very
limited areas. Planck will thus provide essential complementary information on
the epoch-dependent luminosity functions. Bright radio sources will be studied
over a poorly explored frequency range where spectral signatures, essential to
understand the physical processes that are going on, show up. The
Sunyaev-Zeldovich effect, with its extremely rich information content, will be
observed in the direction of a large number of rich clusters of Galaxies.
Thanks again to its all sky coverage, Planck will provide unique information on
the structure and on the emission properties of the interstellar medium in the
Galaxy. At the same time, the foregrounds are unlikely to substantially limit
Planck's ability to measure the cosmological signals. Even measurements of
polarization of the primordial Cosmic Microwave background fluctuations appear
to be feasible.Comment: 20 pages, Latex (use aipproc2.sty, aipproc2.cls, epsfig.sty), 10
PostScript figures; invited review talk, Proc. of the Conference: "3 K
Cosmology", Roma, Italy, 5-10 October 1998, AIP Conference Proc, in press
Note: Figures 6 and 7 have been replaced by new and correct version
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