Distributed Random Process for a Large-Scale Peer-to-Peer Lottery

Most online lotteries today fail to ensure the verifiability of the random process and rely on a trusted third party. This issue has received little attention since the emergence of distributed protocols like Bitcoin that demonstrated the potential of protocols with no trusted third party. We argue that the security requirements of online lotteries are similar to those of online voting, and propose a novel distributed online lottery protocol that applies techniques developed for voting applications to an existing lottery protocol. As a result, the protocol is scalable, provides efficient verification of the random process and does not rely on a trusted third party nor on assumptions of bounded computational resources. An early prototype confirms the feasibility of our approach

Improving the mass determination of Galactic Cepheids

We have selected a sample of Galactic Cepheids for which accurate estimates of radii, distances, and photometric parameters are available. The comparison between their pulsation masses, based on new Period-Mass-Radius (PMR) relations, and their evolutionary masses, based on both optical and NIR Color-Magnitude (CM) diagrams, suggests that pulsation masses are on average of the order of 10% smaller than the evolutionary masses. Current pulsation masses show, at fixed radius, a strongly reduced dispersion when compared with values published in literature.The increased precision in the pulsation masses is due to the fact that our predicted PMR relations based on nonlinear, convective Cepheid models present smaller standard deviations than PMR relations based on linear models. At the same time, the empirical radii of our Cepheid sample are typically accurate at the 5% level. Our evolutionary mass determinations are based on stellar models constructed by neglecting the effect of mass-loss during the He burning phase. Therefore, the difference between pulsation and evolutionary masses could be intrinsic and does not necessarily imply a problem with either evolutionary and/or nonlinear pulsation models. The marginal evidence of a trend in the difference between evolutionary and pulsation masses when moving from short to long-period Cepheids is also briefly discussed. The main finding of our investigation is that the long-standing Cepheid mass discrepancy seems now resolved at the 10% level either if account for canonical or mild convective core overshooting evolutionary models.Comment: 14 pages, 4 postscript figures, accepted for publication on ApJ Letter

The escape problem under stochastic volatility: the Heston model

We solve the escape problem for the Heston random diffusion model. We obtain exact expressions for the survival probability (which ammounts to solving the complete escape problem) as well as for the mean exit time. We also average the volatility in order to work out the problem for the return alone regardless volatility. We look over these results in terms of the dimensionless normal level of volatility --a ratio of the three parameters that appear in the Heston model-- and analyze their form in several assymptotic limits. Thus, for instance, we show that the mean exit time grows quadratically with large spans while for small spans the growth is systematically slower depending on the value of the normal level. We compare our results with those of the Wiener process and show that the assumption of stochastic volatility, in an apparent paradoxical way, increases survival and prolongs the escape time.Comment: 29 pages, 12 figure

Reverse wedge osteotomy of the distal radius in Madelung's deformity

Madelung\u27s deformity results from a growth defect in the palmar and ulnar region of the distal radius. It presents as an excessively inclined radial joint surface, inducing "spontaneous progressive palmar subluxation of the wrist". The principle of reverse wedge osteotomy (RWO) consists in the reorientation of the radial joint surface by taking a circumferential bone wedge, the base of which is harvested from the excess of the radial and dorsal cortical bone of the distal radius, then turning it over and putting back this reverse wedge into the osteotomy so as to obtain closure on the excess and opening on the deficient cortical bone. RWO corrects the palmar subluxation of the carpus and improves distal radio-ulnar alignment. All five bilaterally operated patients were satisfied, esthetically and functionally. Its corrective power gives RWO a place apart among the surgical techniques currently available in Madelung\u27s deformity

Peer-to-Peer Secure Multi-Party Numerical Computation Facing Malicious Adversaries

We propose an efficient framework for enabling secure multi-party numerical computations in a Peer-to-Peer network. This problem arises in a range of applications such as collaborative filtering, distributed computation of trust and reputation, monitoring and other tasks, where the computing nodes is expected to preserve the privacy of their inputs while performing a joint computation of a certain function. Although there is a rich literature in the field of distributed systems security concerning secure multi-party computation, in practice it is hard to deploy those methods in very large scale Peer-to-Peer networks. In this work, we try to bridge the gap between theoretical algorithms in the security domain, and a practical Peer-to-Peer deployment. We consider two security models. The first is the semi-honest model where peers correctly follow the protocol, but try to reveal private information. We provide three possible schemes for secure multi-party numerical computation for this model and identify a single light-weight scheme which outperforms the others. Using extensive simulation results over real Internet topologies, we demonstrate that our scheme is scalable to very large networks, with up to millions of nodes. The second model we consider is the malicious peers model, where peers can behave arbitrarily, deliberately trying to affect the results of the computation as well as compromising the privacy of other peers. For this model we provide a fourth scheme to defend the execution of the computation against the malicious peers. The proposed scheme has a higher complexity relative to the semi-honest model. Overall, we provide the Peer-to-Peer network designer a set of tools to choose from, based on the desired level of security.Comment: Submitted to Peer-to-Peer Networking and Applications Journal (PPNA) 200

The Photometric and Kinematic Structure of Face-On Disk Galaxies. I. Sample Definition, H-alpha Integral Field Spectroscopy, and HI Line-Widths

We present a survey of the photometric and kinematic properties of 39 nearby, nearly face-on disk galaxies. Our approach exploits echelle-resolution integral-field spectroscopy of the H-alpha regions, obtained with DensePak on the WIYN 3.5m telescope Bench Spectrograph. This data is complemented by HI line-profiles observed with the Nancay radio telescope for 25 of these sample galaxies. Twelve additional line-widths are available for sample galaxies from the literature. In this paper, we introduce the goals of this survey, define the sample selection algorithm, and amass the integral field spectroscopic data and HI line-widths. We establish spatially-integrated H-alpha line-widths for the sample. We test the veracity of these spatially-integrated line profiles by convolving narrow-band imaging data with velocity field information for one of the sample galaxies, PGC 38268, and also by comparing to HI line profiles. We find HI and H-alpha line profiles to be similar in width but different in shape, indicating we are observing different spatial distributions of ionized and neutral gas in largely axisymmetric systems with flat outer rotation-curves. We also find vertical velocity dispersions of the ionized disk gas within several disk scale-lengths have a median value of 18 km/s and an 80% range of 12-26 km/s. This is only a factor of ~2 larger than what is observed for neutral atomic and molecular gas. With standard assumptions for intrinsic and thermal broadening for H-alpha, this translates into a factor of three range in turbulent velocities, between 8 and 25 km/s.Comment: 29 pages, 20 figures; accepted for publication in ApJ Supplement Serie

A Wide Field Survey of Satellite Galaxies around the Spiral Galaxy M106

We present a wide field survey of satellite galaxies in M106 (NGC 4258) covering a 1.7\degr \times 2\degr field around M106 using Canada-France-Hawaii Telescope/MegaCam. We find 16 satellite galaxy candidates of M106. Eight of these galaxies are found to be dwarf galaxies that are much smaller and fainter than the remaining galaxies. Four of these galaxies are new findings. Surface brightness profiles of 15 out of 16 satellite galaxies can be represented well by an exponential disk profile with varying scale length. We derive the surface number density distribution of these satellite galaxies. The central number density profile (d $<100$ kpc) is well fitted by a power-law with a power index of $-2.1\pm0.5$, similar to the expected power index of isothermal distribution. The luminosity function of these satellites is represented well by the Schechter function with a faint end slope of $-1.19^{+0.03}_{-0.06}$. Integrated photometric properties (total luminosity, total colour, and disk scale length) and the spatial distribution of these satellite galaxies are found to be roughly similar to those of the Milky Way and M31.Comment: Accepted by MNRA

Near-Infrared Photometric Survey of Proto-Planetary Nebula Candidates

We present JHK' photometric measurements of 78 objects mostly consisting of proto-planetary nebula candidates. Photometric magnitudes are determined by means of imaging and aperture photometry. Unlike the observations with a photometer with a fixed-sized beam, the method of imaging photometry permits accurate derivation of photometric values because the target sources can be correctly identified and confusion with neighboring sources can be easily avoided. Of the 78 sources observed, we report 10 cases in which the source seems to have been misidentified or confused by nearby bright sources. We also present nearly two dozen cases in which the source seems to have indicated a variability which prompts a follow-up monitoring. There are also a few sources that show previously unreported extendedness. In addition, we present H band finding charts of the target sources.Comment: 3 tables, 1 figur

The Kr85 s-process Branching and the Mass of Carbon Stars

We present new spectroscopic observations for a sample of C(N)-type red giants. These objects belong to the class of Asymptotic Giant Branch stars, experiencing thermal instabilities in the He-burning shell (thermal pulses). Mixing episodes called third dredge-up enrich the photosphere with newly synthesized C12 in the He-rich zone, and this is the source of the high observed ratio between carbon and oxygen (C/O > 1 by number). Our spectroscopic abundance estimates confirm that, in agreement with the general understanding of the late evolutionary stages of low and intermediate mass stars, carbon enrichment is accompanied by the appearance of s-process elements in the photosphere. We discuss the details of the observations and of the derived abundances, focusing in particular on rubidium, a neutron-density sensitive element, and on the s-elements Sr, Y and Zr belonging to the first s-peak. The critical reaction branching at Kr85, which determines the relative enrichment of the studied species, is discussed. Subsequently, we compare our data with recent models for s-processing in Thermally Pulsing Asymptotic Giant Branch stars, at metallicities relevant for our sample. A remarkable agreement between model predictions and observations is found. Thanks to the different neutron density prevailing in low and intermediate mass stars, comparison with the models allows us to conclude that most C(N) stars are of low mass (M < 3Mo). We also analyze the C12/C13 ratios measured, showing that most of them cannot be explained by canonical stellar models. We discuss how this fact would require the operation of an ad hoc additional mixing, currently called Cool Bottom Process, operating only in low mass stars during the first ascent of the red giant branch and, perhaps, also during the asymptotic giant branch.Comment: 54 pages + 6 figures + 6 tables. ApJ accepte