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Rarefaction acceleration in magnetized gamma-ray burst jets
Get PDFRelativistic jets associated with long/soft gamma-ray bursts are formed and initially propagate in the interior of the progenitor star. Because of the subsequent loss of their external pressure support after they cross the stellar surface, these flows can be modelled as moving around a corner. A strong steady-state rarefaction wave is formed, and the sideways expansion is accompanied by a rarefaction acceleration. We investigate the efficiency and the general characteristics of this mechanism by integrating the steady-state, special relativistic, magnetohydrodynamic equations, using a special set of partial exact solutions in planar geometry (r self-similar with respect to the ‘corner’). We also derive analytical approximate scalings in the ultrarelativistic cold/magnetized, and hydrodynamic limits. The mechanism is more effective in magnetized than in purely hydrodynamic flows. It substantially increases the Lorentz factor without much affecting the opening of the jet; the resulting values of their product can be much greater than unity, allowing for possible breaks in the afterglow light curves. These findings are similar to the ones from numerical simulations of axisymmetric jets by Komissarov et al. and Tchekhovskoy et al., although in our approach we describe the rarefaction as a steady-state simple wave and self-consistently calculate the opening of the jet that corresponds to zero external pressure
Deregulation of calcium homeostasis mediates secreted aesynuclein - induced neurotoxicity
Get PDFα-Synuclein (AS) plays a crucial role in Parkinson's disease pathogenesis. AS is normally secreted from neuronal cells and can thus exert paracrine effects. We have previously demonstrated that naturally secreted AS species, derived from SH-SY5Y cells inducibly overexpressing human wild type AS, can be toxic to recipient neuronal cells. In the current study, we show that application of secreted AS alters membrane fluidity and increases calcium (Ca2+) entry. This influx is reduced on pharmacological inhibition of voltage-operated Ca2+ channels. Although no change in free cytosolic Ca2+ levels is observed, a significantly increased mitochondrial Ca2+ sequestration is found in recipient cells. Application of voltage-operated Ca2+ channel blockers or Ca2+ chelators abolishes AS-mediated toxicity. AS-treated cells exhibit increased calpain activation, and calpain inhibition greatly alleviates the observed toxicity. Collectively, our data suggest that secreted AS exerts toxicity through engagement, at least in part, of the Ca2+ homeostatic machinery. Therefore, manipulating Ca2+ signaling pathways might represent a potential therapeutic strategy for Parkinson's disease
Validity and reliability of the Greek version of the Satisfaction with Life Scale (SWLS): Evidence from physically active college students
Get PDFPhysical activity has been found to be positively related to life satisfaction (McAuley et al., 2006; 2008). Such studies frequently used the Satisfaction with Life Scale (SWLS) to assess life satisfaction, which is one of the most widely used instruments. Although this five-item scale has been established to have sound psychometric properties, the validity of this instrument has not been examined in Greece. Therefore, the aims of the current study were to examine the factorial validity and reliability of the SWLS
Sparse Nonlinear MIMO Filtering and Identification
Get PDFIn this chapter system identification algorithms for sparse nonlinear multi input multi output (MIMO) systems are developed. These algorithms are potentially useful in a variety of application areas including digital transmission systems incorporating power amplifier(s) along with multiple antennas, cognitive processing, adaptive control of nonlinear multivariable systems, and multivariable biological systems. Sparsity is a key constraint imposed on the model. The presence of sparsity is often dictated by physical considerations as in wireless fading channel-estimation. In other cases it appears as a pragmatic modelling approach that seeks to cope with the curse of dimensionality, particularly acute in nonlinear systems like Volterra type series. Three dentification approaches are discussed: conventional identification based on both input and output samples, semi–blind identification placing emphasis on minimal input resources and blind identification whereby only output samples are available plus a–priori information on input characteristics. Based on this taxonomy a variety of algorithms, existing and new, are studied and evaluated by simulation
Dosimetric accuracy of a deterministic radiation transport based 192Ir brachytherapy treatment planning system: Part III. Comparison to Monte Carlo simulation in voxelized anatomical computational models
Get PDFTo compare TG43-based and Acuros deterministic radiation transport-based calculations of the BrachyVision treatment planning system (TPS) with corresponding Monte Carlo (MC) simulation results in heterogeneous patient geometries, in order to validate Acuros and quantify the accuracy improvement it marks relative to TG43
On the stick-slip flow from slit and cylindrical dies of a Phan-Thien and Tanner fluid model. II. Linear stability analysis
Get PDFDuring extrusion of viscoelastic fluids various flow instabilities may arise resulting in
a distorted free surface. In order to investigate the factors generating these instabilities
we performed a linear stability analysis at zero Reynolds number around the steady
solution of the cylindrical or planar stick-slip flowfor a viscoelastic fluid following the
affine exponential Phan-Thien Tanner (PTT) model. Stick-slip flow is an important
special case of the extrudate swell problem, since the latter reduces to it in the limit
of infinite surface tension but avoids the complications of a free-boundary flow. The
linear stability analysis is performed for various values of the rheological parameters
of the PTT model in order to determine the effects of all material properties. It is
found that the flow becomes unstable as the Weissenberg number increases above
a critical value, due to a Hopf bifurcation suggesting that the flow will become
periodic in time. Both the critical value of theWeissenberg number and the frequency
of the instability depend strongly on the rheological parameters of the viscoelastic
model. The corresponding eigenvectors indicate that the perturbed flow field has a
spatially periodic structure, initiated at the rim of the die, extending for up to 5–7 die
gaps downstream, but confined close to the surface of the extrudate, in qualitative
agreement with existing experiments. This suggests that instability is generated by
the combination of the singularity in the velocity and stress fields at the die lip and the
strong extension that the extruded polymer undergoes near its surface. The elasticity
alone can be responsible for the appearance of instabilities in the extrusion process
of viscoelastic fluids and the often used assumptions of wall slip or compressibility,
although they might be present, are not required. Finally, the mechanisms that produce
these instabilities are examined through energy analysis of the disturbance flo
Gaspard Monge 1795-1799: Η ανέκδοτη αλληλογραφία ενός πολιτικά στρατευμένου μαθηματικού την περίοδο της Γαλλικής Επανάστασης.
Get PDFPoverty at the local level: The case of Athens
Get PDFThis article is based on the results of the sample survey of the year 2012, carried out in order to examine poverty in selected municipalities of Attica.
The method of data collection is in part based on the EU-SILC, annually conducted by the Hellenic Statistical Authority. However, there are specific questions concerning the living conditions at local level as well as questions about how households deal with the crisis.
We are going mainly to analyze and discuss questions relating to the municipality of Athens focusing on the phenomenon of poverty with a descriptive and comparative perspective using data from the sample survey, which was conducted at the second half of 2012 (800 questionnaires). The research questions are: what are the extent and the depth of poverty in Athens municipality? What are the risk groups? Who are those mostly affected by the crisis? Are there any differences with the pattern of the total population in Greece?
The analysis -mainly descriptive- is based on simple relative poverty and material deprivation indices aimed to reflect the size, the intensity and the extent of the phenomenon.
It is especially highlighted that the risk of poverty in Athens is high (20.1%) and slightly lower than that of the whole country (year 2011: 21.4%). It is also indicated that among high-risk groups are the unemployed, people with low educational level and the elderly
Κυτταρική βιολογία του σήματος των γλυκοκορτικοειδών: In vitro μελέτες
No full textΣκοπός της παρούσας διδακτορικής διατριβής είναι η διερεύνηση του ρόλου του µοτίβου 663YLCMKTLLL671 στη µεµβρανική εντόπιση του υποδοχέα των γλυκοκορτικοειδών, στο συνεντοπισµό µε την καβεολίνη-1 και στις ταχείες µη γενωµικές δράσεις των γλυκοκορτικοειδών µέσω ενεργοποίησης των µονοπατιών των MAPK και της PI3K. Επίσης, η διδακτορική διατριβή αυτή θα απαντήσει στο ερώτηµα εάν ο υποδοχέας των γλυκοκορτικοειδών παλµιτυλιώνεται.
The aim of this thesis is to determine the role of the motif 663YLCMKTLLL671 in mediating rapid non-genomic glucocorticoid signaling following translocation and binding to the plasma membrane
Grid reconstruction and skew angle estimation in integral images produced using circular microlenses
Get PDFNowadays a number of different three-dimensional (3D) systems compete in the field of capturing and delivering autostereoscopic (ASt) 3D content. Integral Imaging (InI) is a promising ASt technique that provides both horizontal and vertical parallax as well as high quality realistic 3D content. In this work we propose an InI preprocessing method for identification and accurate segmentation of the grid structure in Integral Images (InIms) generated using lens arrays (LAs) containing circular lenses. In the proposed method we utilize the gradient augmented circular hough transform to accurately detect circular regions in the acquired integral image (InIm). Subsequently by using a triangulation scheme followed by a statistical approach we accurately estimate the grid line structure of the utilized LA. This results in the accurate segmentation of the circular shaped elemental images (EIs) contained in the InIm, a process vital for the effectiveness of the InI methodology. We provide experimental results over artificial as well as optically acquired InIms to evaluate the accuracy of the method using objective metrics