Constraints on the Bulk Lorentz Factor of GRB 990123

GRB 990123 was a long, complex gamma-ray burst accompanied by an extremely bright optical flash. We present the collective constraints on the bulk Lorentz factor for this burst based on estimates from burst kinematics, synchrotron spectral decay, prompt radio flash observations, and prompt emission pulse width. Combination of these constraints leads to an average bulk Lorentz factor for GRB 990123 of Gamma_0=1000 +/- 100 which implies a baryon loading of M_jet=8 (+17/-2) x 10^-8 Msolar. We find these constraints to be consistent with the speculation that the optical light is emission from the reverse shock component of the external shock. In addition, we find the implied value of M_jet to be in accordance with theoretical estimates: the baryonic loading is sufficiently small to allow acceleration of the outflow to Gamma > 100.Comment: 4 pages, 2 postscript figures, to appear in "Gamma-Ray Burst and Afterglow Astronomy 2001", Woods Hole; 5-9 Nov, 200

Flaring up: radio diagnostics of the kinematic, hydrodynamic and environmental properties of gamma-ray bursts

The specific incidence of radio flares appears to be significantly larger than that of the prompt optical emission. This abundance, coupled with the reverse shock interpretation, suggests that radio flares add a unique probe on the physics of gamma-ray burst (GRB) shocks. Motivated thus, we estimate the strength of the reverse shock expected for bursts in which multiwavelength observations have allowed the physical parameters of the forward shock to be determined. We use all six bursts (980519, 990123, 990510, 991208, 991216, 000418) which are found to be adiabatic and thus are predicted to have a strong reverse shock. We aim to constrain the hydrodynamic evolution of the reverse shock and the initial bulk Lorentz factor — which we found to be between 10² and 10³ and well above the lower limits derived from the requirement that GRBs be optically thin to high-energy photons. In half of the cases we improve the description of the early afterglow light curves by adding a contribution from the reverse shock. Modelling of this early emission provides the opportunity to investigate the immediate surroundings of the burst. For 991216 and 991208, the expected 1/r² density structure for a stellar wind is not compatible with the early afterglow light curves. Considering the radial range relevant to these GRBs, we discuss the conditions under which the inclusion of a wind termination shock may resolve the absence of a 1/r² density profile

Was GRB 990123 a unique optical flash?

GRB 990123 was a long, complex gamma-ray burst accompanied by an extremely bright optical flash. We find different constraints on the bulk Lorentz of this burst to be consistent with the speculation that the optical light is emission from the reverse shock component of the external shock. Motivated by this currently favoured idea, we compute the prompt reverse shock emission to be expected for bursts in which multi-wavelength observations allow the physical parameters to be constrained. We find that for reasonable assumptions about the velocity of source expansion, a strong optical flash of approximately m_V=9 was expected from the reverse shocks, which were usually found to be mildly relativistic. The best observational prospects for detecting these prompt flashes are highlighted, along with the possible reasons for the absence of optical prompt detections in ongoing observations.Comment: 6 pages, 4 figures; final version to be published in MNRA

Mitochondrial Localization of Vitamin D Receptor in Human Platelets and Differentiated Megakaryocytes

Background: Like other steroid hormones, vitamin D elicits both transcriptional events and rapid non genomic effects. Vitamin D receptor (VDR) localization and mechanisms of VDR-triggered non genomic responses are still controversial. Although anticoagulant effects of vitamin D have been reported and VDR signalling has been characterized in monocytes and vascular cells, nothing is known about VDR expression and functions in human platelets, anucleated fragments of megakaryocytes which are known targets of other steroids. Methodology/Principal Findings: In this study we characterized the expression and cellular localization of VDR in human platelets and in a megakaryocyte lineage. Human platelets and their TPA-differentiated precursors expressed a classical 50 kDa VDR protein, which increased with megakaryocytes maturation. By biochemical fractionation studies we demonstrated the presence of the receptor in the soluble and mitochondrial compartment of human platelets, and the observation was confirmed by immunoelectron microscopy analysis. Similar localization was found in mature megakaryocytes, where besides its classical nuclear localization the receptor was evident as soluble and mitochondria resident protein. Conclusions: The results reported here suggest that megakaryocytopoiesis and platelet activation, which are calciumdependent events, might be modulated by a mitochondrial non genomic activity of VDR. These data open challengin

Overcoming challenges in large-core SI-POF-based system-level modeling and simulation

The application areas for plastic optical fibers such as in-building or aircraft networks usually have tight power budgets and require multiple passive components. In addition, advanced modulation formats are being considered for transmission over plastic optical fibers (POFs) to increase spectral efficiency. In this scenario, there is a clear need for a flexible and dynamic system-level simulation framework for POFs that includes models of light propagation in POFs and the components that are needed to evaluate the entire system performance. Until recently, commercial simulation software either was designed specifically for single-mode glass fibers or modeled individual guided modes in multimode fibers with considerable detail, which is not adequate for large-core POFs where there are millions of propagation modes, strong mode coupling and high variability. These are some of the many challenges involved in the modeling and simulation of POF-based systems. Here, we describe how we are addressing these challenges with models based on an intensity-vs-angle representation of the multimode signal rather than one that attempts to model all the modes in the fiber. Furthermore, we present model approaches for the individual components that comprise the POF-based system and how the models have been incorporated into system-level simulations, including the commercial software packages SimulinkTM and ModeSYSTM

The European Reference Network for Rare Neurological Diseases

European reference network; Rare neurological diseases; Virtual healthcareXarxa europea de referència; Malalties neurològiques rares; Assistència sanitària virtualRed europea de referencia; Enfermedades neurologicas raras; Asistencia sanitaria virtualWhile rare diseases (RDs) are by definition of low prevalence, the total number of patients suffering from an RD is high, and the majority of them have neurologic manifestations, involving central, peripheral nerve, and muscle. In 2017, 24 European Reference Networks (ERNs), each focusing on a specific group of rare or low-prevalence complex diseases, were formed to improve the care for patients with an RD. One major aim is to have “the knowledge travel instead of the patient,” which has been put into practice by the implementation of the Clinical Patient Management System (CPMS) that enables clinicians to perform pan-European virtual consultations. The European Reference Network for Rare Neurological Diseases (ERN-RND) provides an infrastructure for knowledge sharing and care coordination for patients affected by a rare neurological disease (RND) involving the most common central nervous system pathological conditions. It covers the following disease groups: (i) Cerebellar Ataxias and Hereditary Spastic Paraplegias; (ii) Huntington's disease and Other Choreas; (iii) Frontotemporal dementia; (iv) Dystonia, (non-epileptic) paroxysmal disorders, and Neurodegeneration with Brain Iron Accumulation; (v) Leukoencephalopathies; and (vi) Atypical Parkinsonian Syndromes. At the moment, it unites 32 expert centers and 10 affiliated partners in 21 European countries, as well as patient representatives, but will soon cover nearly all countries of the European Union as a result of the ongoing expansion process. Disease expert groups developed and consented on diagnostic flowcharts and disease scales to assess the different aspects of RNDs. ERN-RND has started to discuss diagnostically unclear patients in the CPMS, is one of four ERNs that serve as foundation of Solve-RD, and has established an RND training and education program. The network will facilitate trial readiness through the establishment of an ERN-RND registry with a minimal data of all patients seen at the ERN-RND centers, thus providing a unique overview of existing genotype-based cohorts. The overall aim of the ERNs is to improve access for patients with RDs to quality diagnosis, care, and treatment. Based on this objective, ERNs are monitored by the European Commission on a regular basis to provide transparency and reassurance to the RD community and the general public.This work is generated within the European Reference Network for Rare Neurological Diseases—Project ID No. 739510