Multidimensional simulations of magnetic field amplification and electron acceleration to near-energy equipartition with ions by a mildly relativistic quasi-parallel plasma collision

The energetic electromagnetic eruptions observed during the prompt phase of gamma-ray bursts are attributed to synchrotron emissions. The internal shocks moving through the ultrarelativistic jet, which is ejected by an imploding supermassive star, are the likely source of this radiation. Synchrotron emissions at the observed strength require the simultaneous presence of powerful magnetic fields and highly relativistic electrons. We explore with one and three-dimensional relativistic particle-in-cell simulations the transition layer of a shock, that evolves out of the collision of two plasma clouds at a speed 0.9c and in the presence of a quasi-parallel magnetic field. The cloud densities vary by a factor of 10. The number densities of ions and electrons in each cloud, which have the mass ratio 250, are equal. The peak Lorentz factor of the electrons is determined in the 1D simulation, as well as the orientation and the strength of the magnetic field at the boundary of the two colliding clouds. The relativistic masses of the electrons and ions close to the shock transition layer are comparable as in previous work. The 3D simulation shows rapid and strong plasma filamentation behind the transient precursor. The magnetic field component orthogonal to the initial field direction is amplified in both simulations to values that exceed those expected from the shock compression by over an order of magnitude. The forming shock is quasi-perpendicular due to this amplification. The simultaneous presence of highly relativistic electrons and strong magnetic fields will give rise to significant synchrotron emissions.Comment: 8 pages, 5 figures. This work was presented at 21st International Conference on Numerical Simulation of Plasmas (ICNSP'09). Accepted for publication IEEE Trans. on Plasma Scienc

Particle-in-cell simulation of a mildly relativistic collision of an electron-ion plasma carrying a quasi-parallel magnetic field: Electron acceleration and magnetic field amplification at supernova shocks

Plasma processes close to SNR shocks result in the amplification of magnetic fields and in the acceleration of electrons, injecting them into the diffusive acceleration mechanism. The acceleration of electrons and the B field amplification by the collision of two plasma clouds, each consisting of electrons and ions, at a speed of 0.5c is investigated. A quasi-parallel guiding magnetic field, a cloud density ratio of 10 and a plasma temperature of 25 keV are considered. A quasi-planar shock forms at the front of the dense plasma cloud. It is mediated by a circularly left-hand polarized electromagnetic wave with an electric field component along the guiding magnetic field. Its propagation direction is close to that of the guiding field and orthogonal to the collision boundary. It has a low frequency and a wavelength that equals several times the ion inertial length, which would be indicative of a dispersive Alfven wave close to the ion cyclotron resonance frequency of the left-handed mode (ion whistler), provided that the frequency is appropriate. However, it moves with the super-alfvenic plasma collision speed, suggesting that it is an Alfven precursor or a nonlinear MHD wave such as a Short Large-Amplitude Magnetic Structure (SLAMS). The growth of the magnetic amplitude of this wave to values well in excess of those of the quasi-parallel guiding field and of the filamentation modes results in a quasi-perpendicular shock. We present evidence for the instability of this mode to a four wave interaction. The waves developing upstream of the dense cloud give rise to electron acceleration ahead of the collision boundary. Energy equipartition between the ions and the electrons is established at the shock and the electrons are accelerated to relativistic speeds.Comment: 16 pages, 18 figures, Accepted for publication by Astron & Astrophy

Stress response and hypothetical genes in Desulfovibrio vulgaris Hildenborough

The entire dissertation/thesis text is included in the research.pdf file; the official abstract appears in the short.pdf file (which also appears in the research.pdf); a non-technical general description, or public abstract, appears in the public.pdf file.Thesis advisor: Dr. Judy D. Wall."December 2008"Thesis (M.S.) University of Missouri-Columbia 2008.The sulfate-reducing bacteria have a significant impact on the environment and the economy, necessitating further investigation of their physiology to harness their positive attributes and to minimize the damaging byproducts. Through the use of in vitro and in silico experiments, I have examined some of the metabolic pathways of Desulfovibrio vulgaris Hildenborough. The information obtained may contribute to an application of the SRB, D. vulgaris in particular, as an effective and economical means of bioremediation and also may play a role in controlling their activity in corrosion of metals and concrete. During my work on this project, I have developed software tools to expedite the creation of targeted deletion mutants through marker exchange, protein tagging, and to identify the insertion sites of randomly integrated transposons. A substantial amount of microarray data from stressed cultures has been generated by our collaborators that I have analyzed for trends across the experimental conditions. My analysis has yielded new insights to the general and specific stress response systems of D. vulgaris. An interesting subset of data, the massive subset of hypothetical genes, offers many tantalizing opportunities for further study with the hints revealed by my analysis. Evidence for the translation of hypothetical genes, revised annotations of the functional descriptions, and clustering according to gene activation was compiled and used to assist in clarification of the role of some of the hypothetical genes identified within the genome sequence. Finally, physiological characterization of select deletion mutants that I constructed has also revealed interesting involvement of the specific gene products in the stress responses. The tools that have been developed and the studies undertaken have yielded immediate results that have increased the knowledge base of the SRB. In addition, further questions became evident whose answers will hopefully lead to critical breakthroughs to reach the ultimate goal of a natural bioremediation tool.Includes bibliographical reference

Cosmic ray diffusive acceleration at shock waves with finite upstream and downstream escape boundaries

In the present paper we discuss the modifications introduced into the first-order Fermi shock acceleration process due to a finite extent of diffusive regions near the shock or due to boundary conditions leading to an increased particle escape upstream and/or downstream the shock. In the considered simple example of the planar shock wave we idealize the escape phenomenon by imposing a particle escape boundary at some distance from the shock. Presence of such a boundary (or boundaries) leads to coupled steepening of the accelerated particle spectrum and decreasing of the acceleration time scale. It allows for a semi-quantitative evaluation and, in some specific cases, also for modelling of the observed steep particle spectra as a result of the first-order Fermi shock acceleration. We also note that the particles close to the upper energy cut-off are younger than the estimate based on the respective acceleration time scale. In Appendix A we present a new time-dependent solution for infinite diffusive regions near the shock allowing for different constant diffusion coefficients upstream and downstream the shock.Comment: LaTeX, 14 pages, 4 postscript figures; Solar Physics (accepted

Listen to the band! How sound can realize group identity and enact intergroup domination

Recent research suggests that sound appraisal can be moderated by social identity. We validate this finding, and also extend it, by examining the extent to which sound can also be understood as instrumental in intergroup relations. We interviewed nine members of a Catholic enclave in predominantly Protestant East Belfast about their experiences of an outgroup (Orange Order) parade, where intrusive sound was a feature. Participants reported experiencing the sounds as a manifestation of the Orange Order identity and said that it made them feel threatened and anxious because they felt it was targeted at them by the outgroup (e.g., through aggressive volume increases). There was also evidence that the sounds produced community disempowerment, which interviewees explicitly linked to the invasiveness of the music. Some interviewees described organising to collectively ‘drown out’ the bands’ sounds, an activity which appeared to be uplifting. These findings develop the elaborated social identity model of empowerment, by showing that intergroup struggle and collective self-objectification can operate through sound as well as through physical actions

A survey of UK Special School Speech & Language Therapists (SLT) and school staff regarding the use of mealtime mats to provide eating and drinking guidelines

Purpose: A survey of UK Special School Speech & Language Therapists (SLT) and school staff regarding the use of mealtime mats to provide eating and drinking guidelines. Method: Two questionnaires were developed to collect experiences of creating and using mealtime mats within UK special schools including benefits and disadvantages of this method, training provided and improvement suggestions. SLTs (11) completed an online survey and education staff members of a UK special school (25) completed a paper questionnaire. The data was analysed using descriptive statistics and reviewing the free text comments. Results: SLTs reported usage of mealtime mats with many utilising similar formats and areas of advice covered. Some aspects received less focus e.g. communication and environment. SLTs reported difficulties in continuing to provide mealtime mats, despite being positive about their usage, due to increased service pressures. This was often without active evaluation of the effectiveness of mealtime mats. Only 2 school staff members reported using mealtime mat and they had a different name. Other school staff were aware of the mats but did not support children with complex dysphagia. However they reported that a mealtime mat resource for children with autism would be useful. Conclusions: This survey has shown that mealtime mats are being utilised within UK special schools and are viewed positively. However there is variety in usage in terms of name, format, content and evaluation. Research to determine the effectiveness of mealtime mats in special schools and other settings, including how to implement them, would be beneficial

Longitudinal EEG Studies in a Kindred with Lafora Disease

We reviewed 18 EEG studies in four members of a family with the Lafora form of progressive myoclonic epilepsy. Each patient was the product of a consan-guinous marriage and presented as a teenager with progressive seizures, myoclonus, dementia, and ataxia, and had biopsy proven disease. The EEG early in Lafora disease has spike-wave activity resembling that seen in a primary generalized epilepsy; the background slowing is more typical of a secondary generalized epilepsy. With disease progression, there is increased epileptiform activity, and a striking change in the spike-wave complexes, with a marked increase in frequency up to 6–12 Hz, and many more short duration poly spike components. Unlike some other forms of secondarily generalized epilepsy, the EEG in Lafora disease is distinguished by an increased frequency of the spike-wave complexes with disease progression. RESUME Les auteurs ont revu 18 enregistrements EEG pratiquÉs chez 4 membres d'une famille prÉsentant une maladie de Lafora. Chaque patient Était issu d'un manage consanguin et a prÉsentÉ dans adolescence association progressive de crises, d'un myoclonus, d'une dÉmence et d'une ataxie; le diagnostic de la maladie a ÉtÉ confirmÉ par une biopsie. EEG prÉsente, À la phase initiale de la maladie de Lafora, un aspect comparable À celui de Épilepsie gÉnÉralisÉe idiopathique, mais le ralentissement de activitÉ de fond Évoque davantage EEG des Épilepsies gÉnÉi-alisÉes symptomatiques (EGS). Pendant la progression de la maladie, les auteurs ont constatÉ une augmentation de activitÉÉp-ileptique EEG, avec modification importante de la morphologie des PO, qui ont augmentÉ de frÉquence, jusqu'À 6–12 c/s, avec composantes accrues en Polypointes rapides. Contrairement À d'autres formes d'EGS, EEG de la maladie de Lafora se distingue par une augmentation de frÉquence des PO au cours de Évolution. RESUMEN Se revisan 18 estudios de EEG en 4 miembros de una familia con la forma de Lafora de una epilepsÍa mioclÓnica progresiva. Cada paciente fue producto de un matrimonio consanguÍneo y en su adolescencia presentaron ataques progresivos, mioclonÍas, demencia y ataxia, y se les practiceÓ una biopsia que confirmÓ la enfermedad. Los EEGs practicados precozmente en la enfer-medad de Lafora tienen una actividad de punta-onda que semeja la que se observa en epilepsÍa generalizada primaria y la lentifi-caciÓn de la actividad de fondo es mÁs tÍpica de epilepsÍa generalizada sencundaria. A medida que la enfermedad progresa se observÓ un incremento de la actividad epileptiforme y un cambio sorprendente en los complejos punta-onda con marcado incremento de la frecuencia hasta 6–12 Hz. y muchos mÁs compo-nentes de polipuntas de breve duraciÓn. Contrariamente a otras formas de epilepsÍa generalizada secundaria el EEG en la enfermedad de Lafora se caracteriza por un incremento de la frecuencia de los complejos punta-onda a medida que la enfermedad progresa. ZUSAMMENFASSUNG Wir beurteilten 18 EEG-Untersuchungen bei 4 Mitgliedern einer Familie mit der Lafora-Form der progressiven Myoklonus-Epilepsie. Jeder Patient entstammte einer konsanguinen Ehe und wurde als Teenager mit progressiven AnfÄllen, Myoklonus, De-menz und Ataxie auffÄllig; die Diagnose wurde durch Biopsie bestÄtigt. Das EEG im frÜhen Verlauf einer Lafora-Erkrankung zeigt Spike Wave AktivitÄt, die der bei primÄr generalisierter Epilepsie Ähnelt, wÄhrend die HintergrundaktivitÄt mehr fÜr eine sekundÄr generaliserte Epilepsie typisch ist. Mit fortschreitender Erkrankung tritt vermehrt epileptische AktivitÄt und ein deutli-cher Wechsel der Spike Wave Komplexe mit starkem Ansteigen der Frequenz auf 6–12 Hz und vermehrten kurzdauernden Polyspike-Komponenten auf. Im Gegensatz zu anderen Formen sekundÄr generalisierter Epilepsien zeigt das EEG bei der Lafora-Erkrankung mit Erkrankungsfortgang eine zunehmende Frequenz der Spike Wave Komplexe.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/65436/1/j.1528-1157.1991.tb05548.x.pd