Polarized thermal emission from X-ray Dim Isolated Neutron Stars: the case of RX J1856.5-3754

The observed polarization properties of thermal radiation from isolated, cooling neutron stars depend on both the emission processes at the surface and the effects of the magnetized vacuum which surrounds the star. Here we investigate the polarized thermal emission from X-ray Dim Isolated Neutron Stars, taking RX J1856.5-3754 as a representative case. The physical conditions of the star outermost layers in these sources is still debated, and so we consider emission from a magnetized atmosphere and a condensed surface, accounting for the effects of vacuum polarization as the radiation propagates in the star magnetosphere. We have found that, for a significant range of viewing geometries, measurement of the phase-averaged polarization fraction and phase-averaged polarization angle at both optical and X-ray wavelengths allow us to determine whether this neutron star has an atmosphere or a condensed surface. Our results may therefore be relevant in view of future developments of soft X-ray polarimeters.Comment: 12 pages, 12 figures, accepted for publication in MNRA

Youth under the gun : violence, fear, and resistance in urban Guatemala

textThis study examines how violence affects youth in marginalized urban communities, focusing on the experiences of three groups of young people: gang members, activists, and the “jóvenes encerrados”, youth who live confined to their homes due to fear. Based on 14 months of ethnographic research in El Mezquital, an extensive marginalized urban area in Guatemala City, I explore the socio-economic conditions that trigger violence in these communities, the responses of young people and the community to violence, and the State’s role in exacerbating violence in impoverished neighborhoods. In this dissertation I argue that gang members and activists are expressing a deep-seated social discontent against the exclusion, humiliation, and social stigmatization faced by young people in marginalized urban neighborhoods. However, the two groups express their discontent in significantly different ways. Initially, gangs used violence to express their discontent, but they gradually resorted to a perverse game of crime, in complicity with the police, and they distanced themselves from their own communities; in this work I analyze gangs’ process of transformation and the circumstances that led to this change. Activists express their discontent through community art and public protest, but their demonstrations have limited social impact, since public attention continues to focus on gangs; here I examine activists’ motivations, struggles, and obstacles. However, the vast majority of young people live in a state of fear, preferring to keep quiet and withdraw into their homes; here I show how violence, fear, and distrust affect the generation born into postwar Guatemala. This study illustrates the perverse role of the State in impoverished urban neighborhoods and its responsibility for the escalation of urban violence in Guatemala. On the one hand, the State shuns residents from these neighborhoods and systematically denies them basic services; it criminalizes and abuses young people, even forming social cleansing groups to eliminate gang members. On the other hand, the State fosters crime in these communities and acts as gangs’ accomplice in extortions, drug trade, and robberies. As in many other Latin American countries, the Guatemalan State penalizes crime, but simultaneously encourages and benefits from it; the State is complicit in crime.Anthropolog

On the Reachability Problem in Cryptographic Protocols

We study the verification of secrecy and authenticity properties for cryptogra- phic protocols which rely on symmetric shared keys. The verification can be reduced to check whether a certain parallel program which models the protocol and the specification can reach an erroneous state while interacting with the environment. Assuming finite principals, we present a simple decision procedure for the reachability problem which is based on a symbolic' reduction system

vibration fatigue tests by tri axis shaker design of an innovative system for uncoupled bending torsion loading

Abstract An innovative system for bending-torsion fatigue tests by tri-axis shaker is designed and presented. The system mounts a cylindrical specimen with eccentric tip mass, excited by horizontal and vertical base accelerations. A lateral thin plate prevents specimen horizontal displacement and allows torsional and bending deformations to be controlled independently. A lumped-mass model is first used to verify if input accelerations and resultant dynamic forces, required in testing, comply with shaker specifications. A finite element model is then used to perform both modal and harmonic analyses, necessary to determine the system natural frequencies and the dynamic response under horizontal and vertical accelerations. Experimental measures on a prototype are finally used to gather preliminary information for validating the numerical model and to verify that the proposed testing system can control bending and torsion loadings independently

On the Symbolic Reduction of Processes with Cryptographic Functions

We study the reachability problem for cryptographic protocols represented as processes relying on perfect cryptographic functions. We introduce a symbolic reduction system that can handle hashing functions, symmetric keys, and public keys. Desirable properties such as secrecy or authenticity are specified by inserting logical assertions in the processes. We show that the symbolic reduction system provides a flexible decision procedure for finite processes and a reference for sound implementations. The symbolic reduction system can be regarded as a variant of syntactic unification which is compatible with certain set-membership constraints. For a significant fragment of our formalism, we argue that a dag implementation of the symbolic reduction system leads to an algorithm running in NPTIME thus matching the lower bound of the problem. In the case of iterated or finite control processes, we show that the problem is undecidable in general and in NPTIME for a subclass of iterated processes that do not rely on pairing. Our technique is based on rational transductions of regular languages and it applies to a class of processes containing the ping-pong protocols presented in [DolevEK-IC82]

Análise do segmento exportador da avicultura brasileira no período de 1996 a 2004

This paper has the main goal of analyzing and evaluating the structure and dynamics of the market from the exporting section of Brazilian chicken raising, from 1996 to 2004. Concentration rates were calculated in order to measure the market share which are dominated by the main companies. The dynamics of the sector position (turnover) was also checked. The reached results point that the sector concentration is higt, and great investments are necessary to the performance in the international market; the placement of the companies was changed mainly due to the ones which had lost positions compared to the first year. However, the concentration has decreased, and there is evidence that the market power hasn’t been used by the companies in a sense of reducing the consumers’ well being.Aviculture, Exports, Market concentration, Sector dynamics, International Relations/Trade,

Simultaneous and accurate measurement of the dielectric constant at many frequencies spanning a wide range

We present an innovative technique which allows the simultaneous measurement of the dielectric constant of a material at many frequencies, spanning a four orders of magnitude range chosen between 10 --2 Hz and 10 4 Hz. The sensitivity and accuracy are comparable to those obtained using standard single frequency techniques. The technique is based on three new and simple features: a) the precise real time correction of the amplication of a current amplier; b) the specic shape of the excitation signal and its frequency spectrum; and c) the precise synchronization between the generation of the excitation signal and the acquisition of the dielectric response signal. This technique is useful in the case of relatively fast dynamical measurements when the knowledge of the time evolution of the dielectric constant is needed

Atmosphere of strongly magnetized neutron stars heated by particle bombardment

The magnetosphere of strongly magnetized neutron stars, such as magnetars, can sustain large electric currents. The charged particles return to the surface with large Lorentz factors, producing a particle bombardment. We investigate the transport of radiation in the atmosphere of strongly magnetized neutron stars, in the presence of particle bombardment heating. We solve the radiative transfer equations for a gray atmosphere in the Eddington approximation, accounting for the polarization induced by a strong magnetic field. The solutions show the formation of a hot external layer and a low (uniform) temperature atmospheric interior. This suggests that the emergent spectrum may be described by a single blackbody with the likely formation of a optical/infrared excess (below ~ 1 eV). We also found that the polarization is strongly dependent on both the luminosity and penetration length of the particle bombardment. Therefore, the thermal emission from active sources, such as transient magnetars, in which the luminosity decreases by orders of magnitude, may show a substantial variation in the polarization pattern during the outburst decline. Our results may be relevant in view of future X-ray polarimetric missions such as IXPE and eXTP.Comment: 16 pages, 9 figures, accepted for publication in MNRA

Focal epilepsy with ictal abdominal pain: a case report

Focal epilepsy with ictal abdominal pain is an unusual partial epilepsy characterized by paroxysmal episodes of abdominal or visceral pain, disturbance of awareness and electroencephalographic abnormalities. We describe a new case of ictal abdominal pain in which gastrointestinal complaints were the only manifestation of seizures and review the previously described pediatric patients. In our patient clinical findings, ictal EEG abnormalities, and a good response to antiepileptic drugs allowed us to make a diagnosis of focal epilepsy with ictal abdominal pain. This is a rare epileptic phenomenon that should be suspected in patients with unexplained paroxysmal abdominal pain and migraine-like symptoms. We suggest that, after the exclusion of more common etiologies, focal epilepsy with ictal abdominal pain should be considered in patients with paroxysmal abdominal pain and ictal EEG abnormalities

The innovation challenge in micro and small enterprises (MSE) An exploratory study at São Paulo metropolitan region

Purpose – This study aims to measure the degree of innovation of micro and small industrial companies in the West and Southwest metropolitan regions of the city of São Paulo, through a survey with 203 firms in the metallurgy sector. Design/methodology/approach – The research had a quantitative and descriptive focus and used as methodology the validated and international approach known as Innovation Radar. Findings – The degree of innovation in these micro and small companies is low; thus, the authors could not characterize them as systemic innovators. Most of them are little innovative, although some were classified as occasional innovators. The dimensions organization, processes, presence, supply chain and added value were the least developed. Research limitations/implications – To carry out similar studies in other Brazilian regions, to compare results and draw new conclusions, or even check if the degree of innovation present in micro-firms of these regions would not be even lower; to monitor the evolution of companies through a longitudinal study, to detect improvements in the degree of innovation; and to conduct a qualitative research that can deepen questions on the results of our study, such as the reasons why this type of company does not adopt innovative practices, or even the real suitability of the Innovation Radar model for micro and small enterprises (MSEs). We observed that some dimensions proved to be too sophisticated for these companies, such as R&D investments and the adoption of technological advances. Practical implications – The study shows that the degree of innovation measured by the Innovation Radar is a useful and initial measure to check an innovative attitude in micro and small companies. It can also drive the actions that should be prioritized to stimulate the culture of innovation in SME. However, it does not allow to answer why this type of organization does not adopt innovative practices as a management attitude. Regarding its contribution, the authors expect that the paper may bring an awareness of managers and owners of micro and small companies for the need to foster innovative practices that can help increase the competitiveness and survival of this type of organization Social implications – In Brazil, despite the fact that MSEs represent 98 per cent of the existing companies, and are mainly responsible for job creation, their leaders have a low concern for innovative practices. Originality/value – The study contributes to identify the degree of innovation of these firms, which comprise a representative and strategic segment of the city’s economy, by checking to what extent an innovative attitude is effectively present in this sector. The theoretical contribution of this study regards the appropriateness of mechanisms or methodologies created to measure the degree of innovation in large organizations. Dimensions such as technological platform, brand, innovative ambience, degree of organization or systematization of processes, which are frequently considered for companies in general, and especially for large ones, are not sufficient or, instead, too sophisticated to allow an effective measurement of the degree of innovation in MSE. Thus, this study provides information for designing more effective ways to evaluate the degree of innovation that take into account MSE’s specificities, which can be considered innovation efforts, such as simple process improvements, professional development of teams, and actions to seize ideas and opportunities, among others