Surface detonation in type Ia supernova explosions?

We explore the evolution of thermonuclear supernova explosions when the progenitor white dwarf star ignites asymmetrically off-center. Several numerical simulations are carried out in two and three dimensions to test the consequences of different initial flame configurations such as spherical bubbles displaced from the center, more complex deformed configurations, and teardrop-shaped ignitions. The burning bubbles float towards the surface while releasing energy due to the nuclear reactions. If the energy release is too small to gravitationally unbind the star, the ash sweeps around it, once the burning bubble approaches the surface. Collisions in the fuel on the opposite side increase its temperature and density and may -- in some cases -- initiate a detonation wave which will then propagate inward burning the core of the star and leading to a strong explosion. However, for initial setups in two dimensions that seem realistic from pre-ignition evolution, as well as for all three-dimensional simulations the collimation of the surface material is found to be too weak to trigger a detonation.Comment: 5 pages, 3 figures, in: Proceedings of the SciDAC 2006 Meeting, Denver June 25-26 2006, also available at http://herald.iop.org/jpcs46/m51/gbr//link/40

Monitoring prohemostatic treatment in bleeding patients

Acutely bleeding patients are commonly found in the trauma and major surgery scenarios. They require prompt and effective treatment to restore an adequate hemostatic pattern, to avoid serious and sometimes life-threatening complications.Different prohemostatic treatments are available, including allogeneic blood derivatives (fresh frozen plasma, platelet concentrates, and cryoprecipitates), prothrombin complex concentrates, specific coagulation factors (fibrinogen, recombinant factor XIII, recombinant activated factor VII), and drugs (protamine for patients under heparin treatment, desmopressin, antifibrinolytics).For decades, prohemostatic treatment of the acutely bleeding patient was based on empirical strategies and clinical judgment, both in terms of a correct diagnosis of the mechanism(s) leading to bleeding, and of an assessment of the effects of the treatment. This empirical strategy may lead to excessive or unnecessary use of allogeneic blood products, as well as to an incorrect, inefficacious, or even dangerous treatment. Different monitoring devices are nowadays available for guiding the diagnostic and therapeutic decision-making process in an acutely bleeding patient. This review addresses the available tools for monitoring prohemostatic treatment of the bleeding patient, with a specific respect for point-of-care tests (thromboelastography, thromboelastometry, platelet function tests, and heparin monitoring systems) at the light of the existing evidence

Effect of preoperative P2Y12 and thrombin platelet receptor inhibition on bleeding after cardiac surgery

BACKGROUND: Drugs that act on the platelet P2Y12 receptor are responsible for postoperative bleeding in cardiac surgery. However, protease-activated receptor (PAR) that reacts to thrombin stimulation might still be active in patients treated with P2Y12 inhibitors. Preoperative platelet function testing could possibly guide the timing of surgery. We investigated the association between P2Y12 receptor and PAR inhibition and bleeding after cardiac surgery. METHODS: A retrospective cohort study of 361 patients undergoing cardiac surgery and treated with P2Y12 anti-platelet agents was undertaken. All patients received a preoperative multiplate electrode aggregometry testing of platelet P2Y12 receptor activity (ADPtest) and PAR reactivity with thrombin receptor-activating peptide (TRAP) stimulation. ADPtest and TRAPtest data measured before surgery were analysed for association with postoperative bleeding (ml per 12 h) and severe postoperative bleeding. RESULTS: Both the ADPtest and the TRAPtest were significantly (P=0.001) associated with postoperative bleeding. A threshold of 22 U for the ADPtest yielded a negative predictive value (NPV) of 94% and a positive predictive value (PPV) of 20%, and a threshold of 75 U for the TRAPtest yielded an NPV of 95% and a PPV of 23%. In the subgroup of patients with ADPtest <22 U, TRAPtest ≥75 U was not associated with severe bleeding (NPV of 100% and PPV of 37%). CONCLUSIONS: In patients taking P2Y12 receptor inhibitors, residual platelet reactivity to thrombin stimulation limits the risk of severe postoperative bleeding

Multidimensional hydrodynamic simulations of the hydrogen injection flash

The injection of hydrogen into the convection shell powered by helium burning during the core helium flash is commonly encountered during the evolution of metal-free and extremely metal-poor low-mass stars. With specifically designed multidimensional hydrodynamic simulations, we aim to prove that an entropy barrier is no obstacle for the growth of the helium-burning shell convection zone in the helium core of a metal-rich Pop I star, i.e. convection can penetrate into the hydrogen-rich layers for these stars, too. We further study whether this is also possible in one-dimensional stellar evolutionary calculations. Our hydrodynamical simulations show that the helium-burning shell convection zone in the helium core moves across the entropy barrier and reaches the hydrogen-rich layers. This leads to mixing of protons into the hotter layers of the core and to a rapid increase of the nuclear energy production at the upper edge of the helium-burning convection shell - the hydrogen injection flash. As a result a second convection zone appears in the hydrogen-rich layers. Contrary to 1D models, the entropy barrier separating the two convective shells from each other is largely permeable to chemical transport when allowing for multidimensional flow, and consequently, hydrogen is continuously mixed deep into the helium core. We find it difficult to achieve such a behavior in one-dimensional stellar evolutionary calculations.Comment: 8 pages, 8 figures - accepted for publication in Astronomy and Astrophysics. Animations related to the manuscript can be downloaded from http://www-astro.ulb.ac.be/~mocak/index.php/Main/AnimationsHeFlas

Mass-loaded spherical accretion flows

We have calculated the evolution of spherical accretion flows undergoing mass-loading from embedded clouds through either conduction or hydrodynamical ablation. We have observed the effect of varying the ratios of the mass-loading timescale and the cooling timescale to the ballistic crossing timescale through the mass-loading region. We have also varied the ratio of the potential energy of a particle injected into the flow near the outer region of mass-loading to the temperature at which a minimum occurs in the cooling curve. The two types of mass-loading produce qualitatively different types of behaviour in the accretion flow, since mass-loading through conduction requires the ambient gas to be hot, whereas mass ablation from clumps occurs throughout the flow. Higher ratios of injected to accreted mass typically occur with hydrodynamical ablation, in agreement with previous work on wind-blown bubbles and supernova remnants. We find that mass-loading damps the radiative overstability of such flows, in agreement with our earlier work. If the mass-loading is high enough it can stabilize the accretion shock at a constant radius, yielding an almost isothermal subsonic post-shock flow. Such solutions may be relevant to cooling flows onto massive galaxies. Mass-loading can also lead to the formation of isolated shells of high temperature material, separated by gas at cooler temperatures

Model-based Identification of Alternative Bidding Zone Configurations from Clustering Algorithms Applied on Locational Marginal Prices

This paper deals with the application of clustering methods to assist the bidding zone review processes in Italy, considering the Locational Marginal Prices (LMPs) as the relevant features. A novel approach based on the definition of the input data for clustering, depending on a number of scenarios defined by the Transmission System Operator, is exploited. The problem under analysis requires additional procedures to solve the challenging issue of incorporating node connection constraints in the clustering algorithm. A dedicated procedure, based on the definition of specific functions, is then applied to develop customised versions of k-means and hierarchical clustering. The customised procedures implemented can identify both wide clusters and outliers, whose location depends on the assessed scenarios

Management of self-inflicted orchiectomy in psychiatric patient. Case report and non-systematic review of the literature.

INTRODUCTION: Self-inflicted orchidectomy and auto-castration, also known as "Eshmun complex" is a rare phenomenon. The aim of our study it to present the management of a patient who performed a self orchiectomy and propose a non-systematic review of literature about self-orchiectomy. MATERIAL AND METHOD: A 27-years old male Patient with psychiatric disorder was admitted to our ward to have been cutted his scrotum with scissors and cut away his left testicle causing active bleeding from the left spermatic artery. The patient underwent emergency surgery with clamping of the spermatic cord and hemostasis of the wound. RESULTS: After surgery the clinical condition of the patient remained good during whole hospitalization. Urgent psychiatric evaluation was performed in order to administer proper therapy for acute management. To best of our knowledge, only 11 cases of self-orchidectomy are reported in literature and all of them except 1 case, underwent surgical exploration. CONCLUSIONS: Self-orchidectomy is an extremely rare phenomenon, often associated with psychiatric disorders, compounded by the use of drugs. In our opinion, emergency surgery should be the first choice of treatment, offering diagnostic and hemostatic purpose in a single act, aimed to prevent acute and postacute complications

New Relativistic Effects in the Dynamics of Nonlinear Hydrodynamical Waves

In Newtonian and relativistic hydrodynamics the Riemann problem consists of calculating the evolution of a fluid which is initially characterized by two states having different values of uniform rest-mass density, pressure and velocity. When the fluid is allowed to relax, one of three possible wave-patterns is produced, corresponding to the propagation in opposite directions of two nonlinear hydrodynamical waves. New effects emerge in a special relativistic Riemann problem when velocities tangential to the initial discontinuity surface are present. We show that a smooth transition from one wave-pattern to another can be produced by varying the initial tangential velocities while otherwise maintaining the initial states unmodified. These special relativistic effects are produced by the coupling through the relativistic Lorentz factors and do not have a Newtonian counterpart.Comment: 4 pages, 5 figure

Exact Foldy-Wouthuysen transformation for spin 0 particle in curved space

Up to now, the only known exact Foldy- Wouthuysen transformation (FWT) in curved space is that concerning Dirac particles coupled to static spacetime metrics. Here we construct the exact FWT related to a real spin-0 particle for the aforementioned spacetimes. This exact transformation exists independently of the value of the coupling between the scalar field and gravity. Moreover, the gravitational Darwin term written for the conformal coupling is one third of the relevant term in the fermionic case.Comment: 10 pages, revtex, improved version to appear in Phys. Rev.