New digital divergence

Meeting: 6th International Conference on Information Technology and Applications (ICITA 2009),9 - 12 November 2009, Hanoi, VNThe paper summarizes the rise of digital technology, focusing on mobile phones and their impact on developing countries. For the first time the mass of the developing world, including the poor, have access to a technology that they can afford, know how to use and that has great potential to affect their poverty outcomes. The authors raise questions about how the “poor-people's technology” of the mobile phone can play a central role in information and communications technologies for development.À la fin du XXe siècle, on a assisté à la commercialisation d’Internet à titre de grande technologie transformatrice ayant d’importantes répercussions sur la société et sur l’économie, surtout dans les pays industrialisés. Au XXIe siècle, une nouvelle transformation se produit du fait de l’omniprésence du téléphone mobile. Les auteurs font ressortir deux nouvelles tendances. En premier lieu, ils mentionnent la croissance divergente de la téléphonie mobile et d’Internet, en particulier dans les pays en développement. Quant à la deuxième tendance, il s’agit de l’essor de l’utilisation partagée de matériel informatique et de logiciels. Faisant état de ces deux tendances et de plusieurs autres, les auteurs se demandent comment la technologie des pauvres, soit celle du téléphone mobile, peut jouer un rôle crucial parmi les technologies de l’information et de la communication au service du développement

Flory-Huggins theory for athermal mixtures of hard spheres and larger flexible polymers

A simple analytic theory for mixtures of hard spheres and larger polymers with excluded volume interactions is developed. The mixture is shown to exhibit extensive immiscibility. For large polymers with strong excluded volume interactions, the density of monomers at the critical point for demixing decreases as one over the square root of the length of the polymer, while the density of spheres tends to a constant. This is very different to the behaviour of mixtures of hard spheres and ideal polymers, these mixtures although even less miscible than those with polymers with excluded volume interactions, have a much higher polymer density at the critical point of demixing. The theory applies to the complete range of mixtures of spheres with flexible polymers, from those with strong excluded volume interactions to ideal polymers.Comment: 9 pages, 4 figure

Conformal Orbifold Partition Functions from Topologically Massive Gauge Theory

We continue the development of the topological membrane approach to open and unoriented string theories. We study orbifolds of topologically massive gauge theory defined on the geometry $[0,1]\times\Sigma$, where $\Sigma$ is a generic compact Riemann surface. The orbifold operations are constructed by gauging the discrete symmetries of the bulk three-dimensional field theory. Multi-loop bosonic string vacuum amplitudes are thereby computed as bulk correlation functions of the gauge theory. It is shown that the three-dimensional correlators naturally reproduce twisted and untwisted sectors in the case of closed worldsheet orbifolds, and Neumann and Dirichlet boundary conditions in the case of open ones. The bulk wavefunctions are used to explicitly construct the characters of the underlying extended Kac-Moody group for arbitrary genus. The correlators for both the original theory and its orbifolds give the expected modular invariant statistical sums over the characters.Comment: 47 pages LaTeX, 3 figures, uses amsfonts and epsfig; v2: Typos corrected, reference added, clarifying comments on modular invariance inserted; v3: Further comments on modular invariance added; to be published in JHE

On quantum coding for ensembles of mixed states

We consider the problem of optimal asymptotically faithful compression for ensembles of mixed quantum states. Although the optimal rate is unknown, we prove upper and lower bounds and describe a series of illustrative examples of compression of mixed states. We also discuss a classical analogue of the problem.Comment: 23 pages, LaTe

Interfacial tension and nucleation in mixtures of colloids and long ideal polymer coils

Mixtures of ideal polymers with hard spheres whose diameters are smaller than the radius of gyration of the polymer, exhibit extensive immiscibility. The interfacial tension between demixed phases of these mixtures is estimated, as is the barrier to nucleation. The barrier is found to scale linearly with the radius of the polymer, causing it to become large for large polymers. Thus for large polymers nucleation is suppressed and phase separation proceeds via spinodal decomposition, as it does in polymer blends.Comment: 4 pages (v2 includes discussion of the scaling of the interfacial tension along the coexistence curve and its relation to the Ginzburg criterion

Effects of black tea on body composition and metabolic outcomes related to cardiovascular disease risk: a randomized controlled trial

This article is licensed under a Creative Commons Attribution 3.0 Unported Licence (http://creativecommons.org/licenses/by/3.0/)There is increasing evidence that tea and its non-caffeine components (primarily flavonoids) contribute to cardiovascular health. Randomized controlled trials have shown that tea can improve cardiovascular disease risk factors. We have previously reported a non-caffeine associated beneficial effect of regular black tea consumption on blood pressure and its variation. Objective: To explore the non-caffeine associated effects of black tea on body weight and body fat distribution, and cardiovascular disease related metabolic outcomes. Design: regular tea-drinking men and women (n ¼ 111; BMI 20–35 kg m 2) were recruited to a randomized controlled double-blind 6 month parallel-designed trial. Participants consumed 3 cups per day of either powdered black tea solids (tea) or a flavonoid-free flavour- and caffeine-matched placebo (control). Body weight, waist- and hip-circumference, endothelial function and plasma biomarkers were assessed at baseline, 3 months and 6 months. Results: Compared to control, regular ingestion of black tea over 3 months inhibited weight gain ( 0.64 kg, p ¼ 0.047) and reduced waist circumference ( 1.88 cm, P ¼ 0.035) and waist-to-hip ratio ( 0.03, P ¼ 0.005). These effects were no longer significant at 6 months. There were no significant effects observed on fasting glucose, insulin, plasma lipids or endothelial function. Conclusion: Our study suggests that short-term regular ingestion of black tea over 3 months can improve body weight and body fat distribution, compared to a caffeine-matched control beverage. However, there was no evidence that these effects were sustained beyond 3 months

A Neutron Star with a Massive Progenitor in Westerlund 1

We report the discovery of an X-ray pulsar in the young, massive Galactic star cluster Westerlund 1. We detected a coherent signal from the brightest X-ray source in the cluster, CXO J164710.2-455216, during two Chandra observations on 2005 May 22 and June 18. The period of the pulsar is 10.6107(1) s. We place an upper limit to the period derivative of Pdot<2e-10 s/s, which implies that the spin-down luminosity is Edot<3e33 erg/s. The X-ray luminosity of the pulsar is L_X = 3(+10,-2)e33 (D/5 kpc)^2 erg/s, and the spectrum can be described by a kT = 0.61+/-0.02 keV blackbody with a radius of R_bb = 0.27+/-0.03 (D/5 kpc}) km. Deep infrared observations reveal no counterpart with K1 Msun. Taken together, the properties of the pulsar indicate that it is a magnetar. The rarity of slow X-ray pulsars and the position of CXO J164710.2-455216 only 1.6' from the core of Westerlund 1 indicates that it is a member of the cluster with >99.97% confidence. Westerlund 1 contains 07V stars with initial masses M_i=35 Msun and >50 post-main-sequence stars that indicate the cluster is 4+/-1 Myr old. Therefore, the progenitor to this pulsar had an initial mass M_i>40 Msun. This is the most secure result among a handful of observational limits to the masses of the progenitors to neutron stars.Comment: 4 pages, 5 figures. Final version to match ApJL (added one figure since v2

Ω-Arithmetization of Ellipses

International audienceMulti-resolution analysis and numerical precision problems are very important subjects in fields like image analysis or geometrical modeling. In the continuation of our previous works, we propose to apply the method of Ω-arithmetization to ellipses. We obtain a discrete multi-resolution representation of arcs of ellipses. The corresponding algorithms are completely constructive and thus, can be exactly translated into functional computer programs. Moreover, we give a global condition for the connectivity of the discrete curves generated by the method at every scale

A General Fidelity Limit for Quantum Channels

We derive a general limit on the fidelity of a quantum channel conveying an ensemble of pure states. Unlike previous results, this limit applies to arbitrary coding and decoding schemes, including nonunitary decoding. This establishes the converse of the quantum noiseless coding theorem for all such schemes.Comment: 14 pages, RevTeX. Submittted to Physical Review

Accessible information and optimal strategies for real symmetrical quantum sources

We study the problem of optimizing the Shannon mutual information for sources of real quantum states i.e. sources for which there is a basis in which all the states have only real components. We consider in detail the sources ${\cal E}_M$ of $M$ equiprobable qubit states lying symmetrically around the great circle of real states on the Bloch sphere and give a variety of explicit optimal strategies. We also consider general real group-covariant sources for which the group acts irreducibly on the subset of all real states and prove the existence of a real group-covariant optimal strategy, extending a theorem of Davies (E. B. Davies, IEEE. Inf. Theory {\bf IT-24}, 596 (1978)). Finally we propose an optical scheme to implement our optimal strategies, enough simple to be realized with present technology.Comment: RevTeX, 16 pages, 4 eps figures with psfig, submitted to Phys. Rev. A, corrected output error of Fig. 1 in the previous versio