Persistence of magnetic field driven by relativistic electrons in a plasma

The onset and evolution of magnetic fields in laboratory and astrophysical plasmas is determined by several mechanisms, including instabilities, dynamo effects and ultra-high energy particle flows through gas, plasma and interstellar-media. These processes are relevant over a wide range of conditions, from cosmic ray acceleration and gamma ray bursts to nuclear fusion in stars. The disparate temporal and spatial scales where each operates can be reconciled by scaling parameters that enable to recreate astrophysical conditions in the laboratory. Here we unveil a new mechanism by which the flow of ultra-energetic particles can strongly magnetize the boundary between the plasma and the non-ionized gas to magnetic fields up to 10-100 Tesla (micro Tesla in astrophysical conditions). The physics is observed from the first time-resolved large scale magnetic field measurements obtained in a laser wakefield accelerator. Particle-in-cell simulations capturing the global plasma and field dynamics over the full plasma length confirm the experimental measurements. These results open new paths for the exploration and modelling of ultra high energy particle driven magnetic field generation in the laboratory

The Curious Adventure of the Ultrahigh Energy Cosmic Rays

These lectures discuss the mysteries involving the production and extragalactic propagation of ultrahigh energy cosmic rays and suggested possible solutions.Comment: Lectures given at the D. Chalonge Euroschool, Erice, Italy, November 2000, 25 pages, 7 ps figs., expanded revision with color fig.

VHE γ\gamma-ray observations of Markarian 501

Markarian 501, a nearby (z=0.033) X-ray selected BL Lacertae object, is a well established source of Very High Energy (VHE, E>=300 GeV) gamma rays. Dramatic variability in its gamma-ray emission on time-scales from years to as short as two hours has been detected. Multiwavelength observations have also revealed evidence that the VHE gamma-ray and hard X-ray fluxes may be correlated. Here we present results of observations made with the Whipple Collaboration's 10 m Atmospheric Cerenkov Imaging Telescope during 1999 and discuss them in the context of observations made on Markarian 501 during the period from 1996-1998

Cosmic rays and molecular clouds

This paper deals with the cosmic-ray penetration into molecular clouds and with the related gamma--ray emission. High energy cosmic rays interact with the dense gas and produce neutral pions which in turn decay into two gamma rays. This makes molecular clouds potential sources of gamma rays, especially if they are located in the vicinity of a powerful accelerator that injects cosmic rays in the interstellar medium. The amplitude and duration in time of the cosmic--ray overdensity around a given source depend on how quickly cosmic rays diffuse in the turbulent galactic magnetic field. For these reasons, gamma-ray observations of molecular clouds can be used both to locate the sources of cosmic rays and to constrain the properties of cosmic-ray diffusion in the Galaxy.Comment: To appear in the proceedings of the San Cugat Forum on Astrophysics 2012, 27 pages, 10 figure

Recent Results from the VERITAS Collaboration

A decade after the discovery of TeV gamma-rays from the blazar Mrk 421 (Punch et al. 1992), the list of TeV blazars has increased to five BL Lac objects: Mrk 421 (Punch et al. 1992; Petry et al. 1996; Piron et al. 2001), Mrk 501 (Quinn et al. 1996; Aharonian et al. 1999; Djannati-Atai et al. 1999), 1ES2344+514 (Catanese et al. 1998), H1426+428 (Horan et al. 2000, 2002; Aharonian et al. 2002; Djannati-Atai et al. 2002) and 1ES1959+650 (Nishiyama et al. 1999; Konopelko et al. 2002; Holder et al. 2002). In this paper we report results from recent observations of Mrk 421, H1426+428 and 1ES1959+650 using the Whipple Observatory 10 m telescope

Lorentz violation and Crab synchrotron emission: a new constraint far beyond the Planck scale

Special relativity asserts that physical phenomena appear the same for all inertially moving observers. This symmetry, called Lorentz symmetry, relates long wavelengths to short ones: if the symmetry is exact it implies that spacetime must look the same at all length scales. Several approaches to quantum gravity, however, suggest that there may be a Lorentz violating microscopic structure of spacetime, for example discreteness, non-commutativity, or extra dimensions. Here we determine a very strong constraint on a type of Lorentz violation that produces a maximum electron speed less than the speed of light. We use the observation of 100 MeV synchrotron radiation from the Crab nebula to improve the previous limits by a factor of 40 million, ruling out this type of Lorentz violation, and thereby providing an important constraint on theories of quantum gravity.Comment: 12 pages. Presentation shortened and revised for letter to Nature. New title "A strong astrophysical constraint on the violation of special relativity by quantum gravity". Maximum observed synchrotron frequency lowered, resulting in weakening the constraint from E_QG>4.5*10^27 GeV to E_QG>10^26 GeV. The role of the effective field theory assumptions underlying the analysis is highlighte

Electron acceleration in laboratory-produced turbulent collisionless shocks

Astrophysical collisionless shocks are among the most powerful particle accelerators in the Universe. Generated by violent interactions of supersonic plasma flows with the interstellar medium, supernova remnant shocks are observed to amplify magnetic fields and accelerate electrons and protons to highly relativistic speeds. In the well-established model of diffusive shock acceleration, relativistic particles are accelerated by repeated shock crossings. However, this requires a separate mechanism that pre-accelerates particles to enable shock crossing. This is known as the ‘injection problem’, which is particularly relevant for electrons, and remains one of the most important puzzles in shock acceleration. In most astrophysical shocks, the details of the shock structure cannot be directly resolved, making it challenging to identify the injection mechanism. Here we report results from laser-driven plasma flow experiments, and related simulations, that probe the formation of turbulent collisionless shocks in conditions relevant to young supernova remnants. We show that electrons can be effectively accelerated in a first-order Fermi process by small-scale turbulence produced within the shock transition to relativistic non-thermal energies, helping overcome the injection problem. Our observations provide new insight into electron injection at shocks and open the way for controlled laboratory studies of the physics underlying cosmic accelerators

Risk factors for cardiovascular disease in patients with COPD: mild-to-moderate COPD versus severe-to-very severe COPD

ABSTRACT Objective: To assess and compare the prevalence of comorbidities and risk factors for cardiovascular disease (CVD) in COPD patients according to disease severity. Methods: The study included 25 patients with mild-to-moderate COPD (68% male; mean age, 65 ± 8 years; mean FEV1, 73 ± 15% of predicted) and 25 with severe-to-very severe COPD (males, 56%; mean age, 69 ± 9 years; mean FEV1, 40 ± 18% of predicted). Comorbidities were recorded on the basis of data obtained from medical charts and clinical evaluations. Comorbidities were registered on the basis of data obtained from medical charts and clinical evaluations. The Charlson comorbidity index was calculated, and the Hospital Anxiety and Depression Scale (HADS) score was determined. Results: Of the 50 patients evaluated, 38 (76%) had been diagnosed with at least one comorbidity, 21 (42%) having been diagnosed with at least one CVD. Twenty-four patients (48%) had more than one CVD. Eighteen (36%) of the patients were current smokers, 10 (20%) had depression, 7 (14%) had dyslipidemia, and 7 (14%) had diabetes mellitus. Current smoking, depression, and dyslipidemia were more prevalent among the patients with mild-to-moderate COPD than among those with severe-to-very severe COPD (p < 0.001, p = 0.008, and p = 0.02, respectively). The prevalence of high blood pressure, diabetes mellitus, alcoholism, ischemic heart disease, and chronic heart failure was comparable between the two groups. The Charlson comorbidity index and HADS scores did not differ between the groups. Conclusions: Comorbidities are highly prevalent in COPD, regardless of its severity. Certain risk factors for CVD, themselves classified as diseases (including smoking, dyslipidemia, and depression), appear to be more prevalent in patients with mild-to-moderate COPD

The Very Energetic Radiation Imaging Telescope Array System (VERITAS)

We give an overview of the current status and scientific goals of VERITAS, a proposed hexagonal array of seven 10 m aperture imaging Cherenkov telescopes. The selected site is Montosa Canyon (1390 m a.s.l.) at the Whipple Observatory, Arizona. Each telescope, of 12 m focal length, will initially be equipped with a 499 element photomultiplier camera covering a 3.5 degree field of view. A central station will initiate the readout of 500 MHz FADCs upon receipt of multiple telescope triggers. The minimum detectable flux sensitivity will be 0.5% of the Crab Nebula flux at 200 GeV. Detailed simulations of the array's performance are presented elsewhere at this meeting. VERITAS will operate primarily as a gamma-ray observatory in the 50 GeV to 50 TeV range for the study of active galaxies, supernova remnants, pulsars and gamma-ray bursts

eIF2B bodies and their role in the integrated stress response

Eukaryotic initiation factor 2 (eIF2) is a G protein comprised of 3 subunits (α, β and γ) that is critical for translation. It is tightly regulated in the integrated stress response (ISR) via the phosphorylation of its α subunit following the induction of cellular stress. In its phosphorylated form eIF2α inhibits the guanine nucleotide exchange factor (GEF) eukaryotic initiation factor 2B (eIF2B), resulting in the attenuation of global protein synthesis. eIF2B is a multisubunit protein comprised of regulatory and catalytic subunits. The catalytic subunits are responsible for the GEF activity whereas the regulatory subunits mediate inhibition by phosphorylated eIF2α. Through studying the localisation of eIF2B subunits, cytoplasmic eIF2B bodies were identified in mammalian cells. A relationship between body size and the eIF2B subunits localising to them exists; larger bodies contain all subunits and smaller bodies contain predominantly catalytic subunits. eIF2 localises to eIF2B bodies and moves through these bodies in a manner that correlates with eIF2B GEF activity. Upon the induction of cellular stress phosphorylated eIF2α localises predominately to larger eIF2B bodies which contain regulatory subunits and a decrease in the movement of eIF2 through these bodies is observed. Interestingly, drugs that inhibit the ISR can rescue the movement of eIF2 through these eIF2B bodies, in a manner that correlates to cellular levels of phosphorylated eIF2α. In contrast, smaller eIF2B bodies, which contain predominately catalytic subunits, show increased movement of eIF2 during cellular stress. This increase in movement is accompanied by an increase in the localisation of eIF2Bδ to these bodies, suggesting the formation of a novel eIF2B subcomplex. This response is mimicked by ISR-inhibiting drugs, providing insight into their potential mechanisms of action. This study provides the first evidence that the composition and function of mammalian eIF2B bodies is regulated by the ISR and the drugs that control it