The two-phase approximation for black hole collisions: Is it robust?

Recently Abrahams and Cook devised a method of estimating the total radiated energy resulting from collisions of distant black holes by applying Newtonian evolution to the holes up to the point where a common apparent horizon forms around the two black holes and subsequently applying Schwarzschild perturbation techniques . Despite the crudeness of their method, their results for the case of head-on collisions were surprisingly accurate. Here we take advantage of the simple radiated energy formula devised in the close-slow approximation for black hole collisions to test how strongly the Abrahams-Cook result depends on the choice of moment when the method of evolution switches over from Newtonian to general relativistic evolution. We find that their result is robust, not depending strongly on this choice.Comment: 4 pages, 3 figures, submitted to Classical and Quantum Gravit

Reactivity Boundaries to Separate the Fate of a Chemical Reaction Associated with an Index-two saddle

Reactivity boundaries that divide the destination and the origin of trajectories are of crucial importance to reveal the mechanism of reactions. We investigate whether such reactivity boundaries can be extracted for higher index saddles in terms of a nonlinear canonical transformation successful for index-one saddles by using a model system with an index-two saddle. It is found that the true reactivity boundaries do not coincide with those extracted by the transformation taking into account a nonlinearity in the region of the saddle even for small perturbations, and the discrepancy is more pronounced for the less repulsive direction of the index-two saddle system. The present result indicates an importance of the global properties of the phase space to identify the reactivity boundaries, relevant to the question of what reactant and product are in phase space, for saddles with index more than one

En bici a la UA

Exposición que se realizó desde el 20 de Mayo hasta el 4 de Junio de 2013 en la Biblioteca de la Universidad de Alicante por el servicio de PUNTBIU

Child protection procedures in emergency departments

Background: Emergency departments (EDs) may be the first point at which children who have been subject to abuse or neglect come into contact with professionals who are able to act for their protection. In order to ascertain current procedures for identifying and managing child abuse, we conducted a survey of EDs in England and Northern Ireland. Methods: Questionnaires were sent to the lead professionals in a random sample of 81 EDs in England and 20 in Northern Ireland. Departments were asked to provide copies of their procedures for child protection. These were analysed qualitatively using a structured template. Results: A total of 74 questionnaires were returned. 91.3% of departments had written protocols for child protection. Of these, 27 provided copies of their protocols for analysis. Factors judged to improve the practical usefulness of protocols included: those that were brief; were specific to the department; incorporated both medical and nursing management; included relevant contact details; included a single page flow chart which could be accessed separately. 25/71 (35.2%) departments reported that they used a checklist to highlight concerns. The most common factors on the checklists included an inconsistent history or one which did not match the examination; frequent attendances; delay in presentation; or concerns about the child’s appearance or behaviour, or the parent–child interaction. Conclusions: There is a lack of consistency in the approach to identifying and responding to child abuse in EDs. Drawing on the results of this survey, we are able to suggest good practice guidelines for the management of suspected child abuse in EDs. Minimum standards could improve management and facilitate clinical audit and relevant training

Reactivity Boundaries to Separate the Fate of a Chemical Reaction Associated with Multiple Saddles

Reactivity boundaries that divide the origin and destination of trajectories are crucial of importance to reveal the mechanism of reactions, which was recently found to exist robustly even at high energies for index-one saddles [Phys. Rev. Lett. 105, 048304 (2010)]. Here we revisit the concept of the reactivity boundary and propose a more general definition that can involve a single reaction associated with a bottleneck made up of higher index saddles and/or several saddle points with different indices, where the normal form theory, based on expansion around a single stationary point, does not work. We numerically demonstrate the reactivity boundary by using a reduced model system of the $H^+_5$ cation where the proton exchange reaction takes place through a bottleneck made up of two index-two saddle points and two index-one saddle points. The cross section of the reactivity boundary in the reactant region of the phase space reveals which initial conditions are effective in making the reaction happen, and thus sheds light on the reaction mechanism.Comment: 12 pages, 7 figure