Magnetized Kelvin-Helmholtz instability in the presence of a radiation field

The purpose of this study is to analyze the dynamical role of a radiation field on the growth rate of the unstable Kelvin - Helmholtz (KH) perturbations. As a first step toward this purpose, the analyze is done in a general way, irrespective of applying the model to a specific astronomical system. The transition zone between the two layers of the fluid is ignored. Then, we perform a linear analysis and by imposing suitable boundary conditions and considering a radiation field, we obtain appropriate dispersion relation. Unstable modes are studied by solving the dispersion equation numerically, and then growth rates of them are obtained. By analyzing our dispersion relation, we show that for a wide range of the input parameters, the radiation field has a destabilizing effect on KH instability. In eruptions of the galaxies or supermassive stars, the radiation field is dynamically important and because of the enhanced KH growth rates in the presence of the radiation; these eruptions can inject more momentum and energy into their environment and excite more turbulent motions.Comment: Accepted for publication in Astrophysics and Space Scienc

Control of star formation by supersonic turbulence

Understanding the formation of stars in galaxies is central to much of modern astrophysics. For several decades it has been thought that stellar birth is primarily controlled by the interplay between gravity and magnetostatic support, modulated by ambipolar diffusion. Recently, however, both observational and numerical work has begun to suggest that support by supersonic turbulence rather than magnetic fields controls star formation. In this review we outline a new theory of star formation relying on the control by turbulence. We demonstrate that although supersonic turbulence can provide global support, it nevertheless produces density enhancements that allow local collapse. Inefficient, isolated star formation is a hallmark of turbulent support, while efficient, clustered star formation occurs in its absence. The consequences of this theory are then explored for both local star formation and galactic scale star formation. (ABSTRACT ABBREVIATED)Comment: Invited review for "Reviews of Modern Physics", 87 pages including 28 figures, in pres

Theory of disk accretion onto supermassive black holes

Accretion onto supermassive black holes produces both the dramatic phenomena associated with active galactic nuclei and the underwhelming displays seen in the Galactic Center and most other nearby galaxies. I review selected aspects of the current theoretical understanding of black hole accretion, emphasizing the role of magnetohydrodynamic turbulence and gravitational instabilities in driving the actual accretion and the importance of the efficacy of cooling in determining the structure and observational appearance of the accretion flow. Ongoing investigations into the dynamics of the plunging region, the origin of variability in the accretion process, and the evolution of warped, twisted, or eccentric disks are summarized.Comment: Mostly introductory review, to appear in "Supermassive black holes in the distant Universe", ed. A.J. Barger, Kluwer Academic Publishers, in pres

Discovery of Pulsations from the Pulsar J0205+6449 in SNR 3C 58 with the Fermi Gamma-Ray Space Telescope

We report the discovery of gamma-ray pulsations (> 0.1 GeV) from the young radio and X-ray pulsar PSR J0205+6449 located in the Galactic supernova remnant 3C 58. Data in the gamma-ray band were acquired by the Large Area Telescope aboard the Fermi Gamma-ray Space Telescope (formerly GLAST), while the radio rotational ephemeris used to fold gamma-rays was obtained using both the Green Bank Telescope and the Lovell telescope at Jodrell Bank. The light curve consists of two peaks separated by 0.49 +/- 0.01 +/- 0.01 cycles which are aligned with the X-ray peaks. The first gamma-ray peak trails the radio pulse by 0.08 +/- 0.01 +/- 0.01, while its amplitude decreases with increasing energy as for the other gamma-ray pulsars. Spectral analysis of the pulsed gamma-ray emission suggests a simple power law of index -2.1 +/- 0.1 +/- 0.2 with an exponential cut-off at 3.0 +1.1 -0.7 +/- 0.4 GeV. The first uncertainty is statistical and the second is systematic. The integral gamma-ray photon flux above 0.1 GeV is (13.7 +/- 1.4 +/- 3.0) x 10^(-8) /cm2/s, which implies for a distance of 3.2 kpc and assuming a broad fan-like beam a luminosity of 8.3 x 10^(34) ergs/s and an efficiency eta of 0.3%. Finally, we report a 95% upper limit on the flux of 1.7 x 10^(-8) /cm2/s for off-pulse emission from the object.Comment: 7 pages, 1 figure, accepted for publication in Astrophysical Journal Letters, contact author: Damien Paren

General Overview of Black Hole Accretion Theory

I provide a broad overview of the basic theoretical paradigms of black hole accretion flows. Models that make contact with observations continue to be mostly based on the four decade old alpha stress prescription of Shakura & Sunyaev (1973), and I discuss the properties of both radiatively efficient and inefficient models, including their local properties, their expected stability to secular perturbations, and how they might be tied together in global flow geometries. The alpha stress is a prescription for turbulence, for which the only existing plausible candidate is that which develops from the magnetorotational instability (MRI). I therefore also review what is currently known about the local properties of such turbulence, and the physical issues that have been elucidated and that remain uncertain that are relevant for the various alpha-based black hole accretion flow models.Comment: To be published in Space Science Reviews and as hard cover in the Space Sciences Series of ISSI: The Physics of Accretion on to Black Holes (Springer Publisher

Propositions for Innovative Forms of Digital Interactive Storytelling Based on Narrative Theories and Practices

This paper takes a look at narrative forms as of yet unexplored in the field of digital interactive storytelling, and proposes methods for how they can be used in engaging ways for the user. Digital Interactive Storytelling, while nearly two decades old as a field of research, has yet to produce a tool capable of producing masses of narratively interesting and engaging pieces for the end user. Although the various prototypes available produce several different story genres, they stem from the same classic narrative form. With this paper, we aim to introduce narrative techniques that have successfully been used in cinema, literature and the gaming world, and show how they can be adapted to DIS. We believe that by presenting these techniques authors can gain a better understanding of how to use existing systems

Developing A "Toolkit" To Measure Implementation Of Concurrent Palliative Care In Rural Community Cancer Centers

Objective: Despite national guidelines recommending early concurrent palliative care for individuals newly diagnosed with metastatic cancer, few community cancer centers, especially those in underserved rural areas do so. We are implementing an early concurrent palliative care model, ENABLE (Educate, Nurture, Advise, Before Life Ends) in four, rural-serving community cancer centers. Our objective was to develop a "toolkit" to assist community cancer centers that wish to integrate early palliative care for patients with newly diagnosed advanced cancer and their family caregivers. Method: Guided by the RE-AIM (Reach, Effectiveness-Adoption, Implementation, Maintenance) framework, we undertook an instrument-development process based on the literature, expert and site stakeholder review and feedback, and pilot testing during site visits. Results: We developed four instruments to measure ENABLE implementation: (1) the ENABLE RE-AIM Self-Assessment Tool to assess reach, adoption, implementation, and maintenance; (2) the ENABLE General Organizational Index to assess institutional implementation; (3) an Implementation Costs Tool; and (4) an Oncology Clinicians' Perceptions of Early Concurrent Oncology Palliative Care survey. Significance of results: We developed four measures to determine early palliative care implementation. These measures have been pilot-tested, and will be integrated into a comprehensive "toolkit" to assist community cancer centers to measure implementation outcomes. We describe the lessons learned and recommend strategies for promoting long-term program sustainability.WoSScopu

Effects of ibuprofen on the physiology and survival of hypothermic sepsis

OBJECTIVESThe objective was to compare the clinical and physiologic characteristics of febrile septic patients with hypothermic septic patients; and to examine plasma levels of cytokines tumor necrosis factor alpha (TNF-alpha) and interleukin 6 (IL-6) and the lipid mediators thromboxane B2 (TxB2) and prostacyclin in hypothermic septic patients in comparison with febrile patients. Most importantly, we wanted to report the effect of ibuprofen treatment on vital signs, organ failure, and mortality in hypothermic sepsis. SETTINGThe study was performed in the intensive care units (ICUs) of seven clinical centers in the United States and Canada. PATIENTSFour hundred fifty-five patients admitted to the ICU who met defined criteria for severe sepsis and were suspected of having a serious infection. INTERVENTIONIbuprofen at a dose of 10 mg/kg (maximum 800 mg) was administered intravenously over 30 to 60 mins every 6 hrs for eight doses vs. placebo (glycine buffer vehicle). MEASUREMENTS AND MAIN RESULTSForty-four (10%) septic patients met criteria for hypothermia and 409 were febrile. The mortality rate was significantly higher in hypothermic patients, 70% vs. 35% for febrile patients. At study entry, urinary metabolites of TxB2, prostacyclin, and serum levels of TNF-alpha and IL-6 were significantly elevated in hypothermic patients compared with febrile patients. In hypothermic patients treated with ibuprofen, there was a trend toward an increased number of days free of major organ system failures and a significant reduction in the 30-day mortality rate from 90% (18/20 placebo-treated patients) to 54% (13/24 ibuprofen-treated patients). CONCLUSIONSHypothermic sepsis has an incidence of [similar]10% and an untreated mortality twice that of severe sepsis presenting with fever. When compared with febrile patients, the hypothermic group has an amplified response with respect to cytokines TNF-alpha and IL-6 and lipid mediators TxB2 and prostacyclin. Treatment with ibuprofen may decrease mortality in this select group of septic patients. (Crit Care Med 1999; 27:699-707