A semi-Markov model with memory for price changes

We study the high frequency price dynamics of traded stocks by a model of returns using a semi-Markov approach. More precisely we assume that the intraday returns are described by a discrete time homogeneous semi-Markov which depends also on a memory index. The index is introduced to take into account periods of high and low volatility in the market. First of all we derive the equations governing the process and then theoretical results have been compared with empirical findings from real data. In particular we analyzed high frequency data from the Italian stock market from first of January 2007 until end of December 2010

Mesoporous matrices for quantum computation with improved response through redundance

We present a solid state implementation of quantum computation, which improves previously proposed optically driven schemes. Our proposal is based on vertical arrays of quantum dots embedded in a mesoporous material which can be fabricated with present technology. The redundant encoding typical of the chosen hardware protects the computation against gate errors and the effects of measurement induced noise. The system parameters required for quantum computation applications are calculated for II-VI and III-V materials and found to be within the experimental range. The proposed hardware may help minimize errors due to polydispersity of dot sizes, which is at present one of the main problems in relation to quantum dot-based quantum computation. (c) 2007 American Institute of Physics

Weighted-indexed semi-Markov models for modeling financial returns

In this paper we propose a new stochastic model based on a generalization of semi-Markov chains to study the high frequency price dynamics of traded stocks. We assume that the financial returns are described by a weighted indexed semi-Markov chain model. We show, through Monte Carlo simulations, that the model is able to reproduce important stylized facts of financial time series as the first passage time distributions and the persistence of volatility. The model is applied to data from Italian and German stock market from first of January 2007 until end of December 2010.Comment: arXiv admin note: substantial text overlap with arXiv:1109.425

Discovery of short-period binary millisecond pulsars in four globular clusters

We report the discovery using the Parkes radio telescope of binary millisecond pulsars in four clusters for which no associated pulsars were previously known. The four pulsars have pulse periods lying between 3 and 6 ms. All are in circular orbits with low-mass companions and have orbital periods of a few days or less. One is in a 1.7-hour orbit with a companion of planetary mass. Another is eclipsed by a wind from its companion for 40% of the binary period despite being in a relatively wide orbit. These discoveries result from the use of improved technologies and prove that many millisecond pulsars remain to be found in globular clusters.Comment: 4 pages, 2 figs, 1 table - Accepted by Astrophysical Journal Letter

Intrinsic electric field effects on few-particle interactions in coupled GaN quantum dots

We study the multi-exciton optical spectrum of vertically coupled GaN/AlN quantum dots with a realistic three-dimensional direct-diagonalization approach for the description of few-particle Coulomb-correlated states. We present a detailed analysis of the fundamental properties of few-particle/exciton interactions peculiar of nitride materials. The giant intrinsic electric fields and the high electron/hole effective masses give rise to different effects compared to GaAs-based quantum dots: intrinsic exciton-exciton coupling, non-molecular character of coupled dot exciton wavefunction, strong dependence of the oscillator strength on the dot height, large ground state energy shift for dots separated by different barriers. Some of these effects make GaN/AlN quantum dots interesting candidates in quantum information processing.Comment: 23 pages, 8 figures, 1 tabl

Long Term Studies of Z sources with HEXTE/RXTE

We have analyzed the long pointed observations of the Z sources in the Rossi X-Ray Timing Explorer (RXTE) public archive to study the high energy emission in those sources. Our analysis is concentrated on the High Energy X--Ray Timing Experiment (HEXTE) waveband, since we are primarily interested in studying the hard X-ray (i.e., E > 20 keV) production in those sources. We give here the preliminary results of this ongoing study. We have found no hard X-ray tails (besides Sco X-1) in our database from any of the Z sources, i.e., GX 349+2 (< 7.9 x 10^-5 photons cm^-2 s^-1, 3 sigma, 50-150 keV), Cyg X-2 (< 8.4 x 10^-5 photons cm^-2 s^-1, 3 sigma, 50-150 keV), GX 17+2 (< 4.2 x 10^-5 photons cm^-2 s^-1, 3 sigma, 50-150 keV), GX 5-1 (< 2.1 x 10^-5 photons cm^-2 s^-1, 3 sigma, 50-150 keV), and Gx 340+0 (< 6.0 x 10^-5 photons cm^-2 s^-1, 3 sigma, 50-150 keV). From the point of view of HEXTE/RXTE observations shown here, the production of hard X-ray tails in Z sources is a process triggered when special conditions are fulfilled. One of these conditions, as derived from our analysis, is a threshold of ~ 4 x 10^36 erg s^-1 for the luminosity of the source's thermal component.Comment: LaTeX, 4 pages, all styles included. Presented at COSPAR Symposium on SNRs and NSs (Houston, Texas, October 10-19, 2002). To appear in Advances in Space Research (volume editors: Werner Becker and Wim Hermsen

Speedy Techniques to Evaluate Seismic Site Effects in Particular Geomorphologic Conditions: Faults, Cavities, Landslides and Topographic Irregularities

The ground motion that can be recorded at the free surface of a terrain is the final result of a series of phenomena that can be grouped into three fundamental typologies: the source mechanism, the seismic wave propagation till the bedrock interface below the investigated site and the site effects (Fig. 1). The first two features define the kind of seismic input whereas the third represents all modifications that can occur as a consequence of the interaction between seismic waves and local characteristics of the investigated site. The physical and mechanical properties of terrains as well as their morphologic and stratigraphic features appreciably affect the characteristics of the ground motion observed at the surface. The whole process of modifications undergone by a given seismic input in terms of amplitude, frequency content and duration, as a consequence of local characteristics, is generally termed the “local seismic response”. It is indeed well known that the spectral composition of a seismic event is modified first during the source-bedrock path (attenuation function), and second, when the seismic input interacts with the soft terrains layered between the bedrock and the free surface (Fig. 1a). This latter effect, significantly changes the spectral content so that it is extremely important for estimating the final input to which all structures built in the study area will be subjected.peer-reviewe

Timing of Millisecond Pulsars in NGC 6752: Evidence for a High Mass-to-Light Ratio in the Cluster Core

Using pulse timing observations we have obtained precise parameters, including positions with about 20 mas accuracy, of five millisecond pulsars in NGC 6752. Three of them, located relatively close to the cluster center, have line-of-sight accelerations larger than the maximum value predicted by the central mass density derived from optical observation, providing dynamical evidence for a central mass-to-light ratio >~ 10, much higher than for any other globular cluster. It is likely that the other two millisecond pulsars have been ejected out of the core to their present locations at 1.4 and 3.3 half-mass radii, respectively, suggesting unusual non-thermal dynamics in the cluster core.Comment: Accepted by ApJ Letter. 5 pages, 2 figures, 1 tabl

Nuevos registros de la mosca endémica de la nieve Chionea (Spaeconopilus) pyrenaea (Bourne, 1981) y actualización de la distribución de las especies de mosca de nieve en los Pirineos

Wingless snow flies Chionea spp are highly specialized winter active arthropods of the supranivean fauna, for which little is known yet about their life history and ecology. Of the seven European species of the subgenus Chionea (Sphaeconophilus), four are known from or can be expected to occur in the Pyrenees: C. pyrenaea Bourne 1981, C. bezzii Oosterbroek & Reusch 2008, C. alpina Bezzi 1908 and C. lutescens Lundström 1907. The former two are possible endemic species only known from one location and only from male individuals. In this paper we update the distribution and illustrate for the first time the habitus of the female of C. pyrenaea and give a new synthesis of the current distribution of snow flies in the Pyrenees. In the context of a projected increase in temperature and snowpack reduction in depth and duration, we point the vulnerability of these species to global climate change.Las moscas sin alas del género Chionea spp son artrópodos especializados de la fauna supranivea, de los cuales se tiene escasa información ecológica. De las siete especies europeas del subgénero Chionea (Sphaeconophilus), se sabe que al menos cuatro se distribuirían en los Pirineos: C. pyrenaea Bourne 1981, C. bezzii Oosterbroek & Reusch 2008, C. alpina Bezzi 1908 and C. lutescens Lundström 1907. Las dos últimas serían, posiblemente, endémicas ya que están descritas en una única localización y solamente individuos macho. En este trabajo hemos ilustrado por primera vez el habitus de la hembra de C. pyrenaea proporcionando además una distribución actualizada de las moscas alpinas en los Pirineos. En el contexto futuro de una subida generalizada de las temperaturas y una reducción de la cubierta de la profundidad y duración de la cubierta de nieve, estos resultados indican la vulnerabilidad de estas especies al cambio climático

Las poblaciones Nor-pirenaicas de Megabunus diadema (Fabricius, 1779) (Aracnidos: Opiliones) se caracterizan por una proporción de machos altamente sesgada

Megabunus diadema (Fabricius, 1779) is an Atlantic and European harvestman species characterized by a discontinuous distribution from Scandinavia to the Iberian Peninsula. With very few male individuals ever observed in the field until now, the biological uniqueness of the species lies in its reproduction mode, hitherto regarded as asexual, facultative parthenogenesis. Based on a large sample of 741 sexed individuals, the study indicates a sex ratio much higher than what was formerly known, equal to 65.58% of males. Locally varying from 0 to 100% (median 75.5% of males), the sex ratio depends indeed on the altitude and the phenological cycle: the proportion of males decreases with increasing altitude and increases gradually during the spring to reach a plateau in summer. By describing populations locally dominated by male individuals and providing new information on the spatial and temporal patterns of tertiary sex ratio, we question the currently admitted reproduction mode of the species which could be normally sexual, at least locally, rather than asexual. A distribution map of the species on the northern slope of the Pyrenees is provided for the first time. Our study also complements the distribution for the southern slopes of the Pyrenees and the rest of the Iberian Peninsula published recently by Merino-Sáinz et al. (2013).Megabunus diadema (Fabricius 1779) es una especie de opilión Atlántica y Europea, caracterizada por una distribución discontinua desde Escandinavia a la Península Ibérica. La singularidad biológica de la especie se encuentra en el modo de reproducción, la partenogénesis facultativa, hasta ahora considerada como asexual. De hecho, hasta el momento se han observado muy pocos individuos masculinos en el campo. Los resultados de este estudio muestran, sobre una amplia muestra (741 individuos sexuados), que la proporción de sexo masculino es muy superior a lo conocido hasta ahora (65%). Localmente este porcentaje puede variar entre 0 y 100% (mediana del 75,5% para los machos). Los resultados muestran que la proporción de sexos depende de la altitud y del ciclo fenológico: la proporción de machos disminuye con la altitud y aumenta gradualmente durante la primavera hasta llegar a una meseta en verano. Para describir las poblaciones dominadas localmente por individuos masculinos y proporcionar nueva información sobre los patrones espaciales y temporales de la proporción de sexos en poblaciones adultas, cuestionamos el modo de reproducción actualmente admitido de la especie que podría ser normalmente sexual, al menos localmente, en lugar de asexual. Se proporciona, por primera vez, un mapa de distribución de la especie en la vertiente norte de los Pirineos. Nuestro estudio también complementa el estudio publicado recientemente por Merino-Sáinz et al. (2013) sobre su distribución en la vertiente sur de los Pirineos y en el resto de la Península Ibérica