5 results
A new frontier in laboratory physics: magnetized electron–positron plasmas
- M. R. Stoneking, T. Sunn Pedersen, P. Helander, H. Chen, U. Hergenhahn, E. V. Stenson, G. Fiksel, J. von der Linden, H. Saitoh, C. M. Surko, J. R. Danielson, C. Hugenschmidt, J. Horn-Stanja, A. Mishchenko, D. Kennedy, A. Deller, A. Card, S. Nißl, M. Singer, M. Singer, S. König, L. Willingale, J. Peebles, M. R. Edwards, K. Chin
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- Journal:
- Journal of Plasma Physics / Volume 86 / Issue 6 / December 2020
- Published online by Cambridge University Press:
- 18 November 2020, 155860601
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We describe here efforts to create and study magnetized electron–positron pair plasmas, the existence of which in astrophysical environments is well-established. Laboratory incarnations of such systems are becoming ever more possible due to novel approaches and techniques in plasma, beam and laser physics. Traditional magnetized plasmas studied to date, both in nature and in the laboratory, exhibit a host of different wave types, many of which are generically unstable and evolve into turbulence or violent instabilities. This complexity and the instability of these waves stem to a large degree from the difference in mass between the positively and the negatively charged species: the ions and the electrons. The mass symmetry of pair plasmas, on the other hand, results in unique behaviour, a topic that has been intensively studied theoretically and numerically for decades, but experimental studies are still in the early stages of development. A levitated dipole device is now under construction to study magnetized low-energy, short-Debye-length electron–positron plasmas; this experiment, as well as a stellarator device that is in the planning stage, will be fuelled by a reactor-based positron source and make use of state-of-the-art positron cooling and storage techniques. Relativistic pair plasmas with very different parameters will be created using pair production resulting from intense laser–matter interactions and will be confined in a high-field mirror configuration. We highlight the differences between and similarities among these approaches, and discuss the unique physics insights that can be gained by these studies.
Characterizing the inpatient care of young adults experiencing early psychosis
- R. Kamieniecki, B. Vaughn, J. Danielson, K. Bonnie, M. Carter, T. Mihic, S. Williams, J. Puyat
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- Journal:
- European Psychiatry / Volume 41 / Issue S1 / April 2017
- Published online by Cambridge University Press:
- 23 March 2020, p. S380
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Introduction/objectives
The available literature suggests that treatments and health services for psychosis are considered to be poorly organized and highly variable. Little is known, however, about how inpatient care is provided to individuals experiencing early psychosis. To facilitate quality improvement activities, we characterized the care this patient group receives in an inner city hospital.
MethodsWe performed chart reviews of individuals admitted to psychiatric inpatient units at St. Paul's Hospital, Vancouver, British Columbia between 01/04/2014 and 31/03/2016. Those who were 17–25 years of age and hospitalized for psychotic symptoms at the time of admission were included. Demographic and health service use were summarized using descriptive characteristics.
ResultsWe identified 73 inpatients (mean age = 22; males = 78%; Caucasian = 41%) that met study inclusion criteria, having a combined total of 102 care episodes and an average length of stay of 30.7 days (median = 18; min = 3; max = 268). Half of the care episodes were repeat admissions, with up to 30% of the patients readmitted within 28 days of discharge. Physical and mental status examinations (MSE) were performed in virtually all care episodes, although frequency is low (31.4% had daily physical examinations and 18.6% had MSE every nursing shift). In 49% and 50% of care episodes, patients were given oral antipsychotics and discharged on depot medications. Even when indicated, not all care episodes had follow-up appointments (60%) or referrals to income assistance (35%), community mental health teams (61%), and housing support (38%).
ConclusionsSpecific programs are needed to address current gaps in inpatient care for patients with early psychosis.
Disclosure of interestThe authors have not supplied their declaration of competing interest.
Experimental study of the stability and dynamics of a two-dimensional ideal vortex under external strain
- N. C. Hurst, J. R. Danielson, D. H. E. Dubin, C. M. Surko
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- Journal:
- Journal of Fluid Mechanics / Volume 848 / 10 August 2018
- Published online by Cambridge University Press:
- 01 June 2018, pp. 256-287
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The dynamics of two-dimensional (2-D) ideal fluid vortices is studied experimentally in the presence of an irrotational strain flow. Laboratory experiments are conducted using strongly magnetized pure electron plasmas, a technique which is made possible by the isomorphism between the drift–Poisson equations describing plasma dynamics transverse to the field and the 2-D Euler equations describing an ideal fluid. The electron plasma system provides an excellent opportunity to study the dynamics of a 2-D Euler fluid due to weak dissipation and weak 3-D effects, simple diagnosis and precise control. The plasma confinement apparatus used here was designed specifically to study vortex dynamics under the influence of external flow by applying boundary conditions in two dimensions. Additionally, vortex-in-cell simulations are carried out to complement the experimental results and to extend the parameter range of the studies. It is shown that the global dynamics of a quasi-flat vorticity profile is in good quantitative agreement with the theory of a piecewise-constant elliptical patch of vorticity, including the equilibria, dynamical orbits and stability properties. Deviations from the elliptical patch theory are observed for non-flat vorticity profiles; they include inviscid damping of the orbits and modified stability limits. The dependence of these phenomena on the flatness of the initial profile is discussed. The relationship of these results to other theoretical, numerical and experimental studies is also discussed.
7 - When sinks rescue sources in dynamic environments
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- By Matthew R. Falcy, Iowa State University, Brent J. Danielson, Iowa State University
- Edited by Jianguo Liu, Michigan State University, Vanessa Hull, Michigan State University, Anita T. Morzillo, Oregon State University, John A. Wiens
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- Book:
- Sources, Sinks and Sustainability
- Published online:
- 05 July 2011
- Print publication:
- 30 June 2011, pp 139-154
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Summary
Many species of conservation concern occur in spatially heterogeneous landscapes composed of different patches that function as population sources and population sinks. Temporal variation in habitat quality, due to a cycle of habitat disturbance and subsequent recovery, can create relatively underappreciated source–sink dynamics. A cycle of disturbance and recovery can cause a given patch to alternate between functioning as a population source and a population sink. During “good” years, this patch can conceivably sustain another nearby patch that is always sink habitat. However, after a disturbance, the putative source patch may then depend upon individuals from that sink for recolonization. Thus, the metapopulation can depend upon the presence of sink populations for long-term persistence, provided that the sink is relatively unaffected by disturbance. We developed a simple, two-patch model of source–sink dynamics in order to explore the sensitivity of long-term metapopulation persistence to the temporal scale of habitat disturbance, recovery in a putative source patch, and the rate of population decline in the sink. We found that management directed at decelerating the rate of population decline in the sink can have a much greater affect on metapopulation persistence than management targeted at increasing the rate of habitat recovery in the source. This result is magnified as disturbance frequency increases. It is hoped that sinks crucial to metapopulation survival are given appropriate conservation status.
Contributors
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- By Jennifer Alvarez, Ananda B. Amstadter, Metin Başoğlu, David M. Benedek, Charles C. Benight, George A. Bonanno, Evelyn J. Bromet, Richard A. Bryant, Barbara Lopes Cardozo, M. L. Somchai Chakkraband, Claude Chemtob, Roman Cieslak, Lauren M. Conoscenti, Joan M. Cook, Judith Cukor, Carla Kmett Danielson, JoAnn Difede, Charles DiMaggio, Anja J.E. Dirkzwager, Cristiane S. Duarte, Jon D. Elhai, Diane L. Elmore, Yael L.E. Errera, Julian D. Ford, Carol S. Fullerton, Sandro Galea, Freya Goodhew, Neil Greenberg, Lindsay Greene, Linda Grievink, Michael J. Gruber, Sumati Gupta, Johan M. Havenaar, Alesia O. Hawkins, Clare Henn-Haase, Kimberly Eaton Hoagwood, Christina W. Hoven, Sabra S. Inslicht, Krzysztof Kaniasty, Ronald C. Kessler, Rachel Kimerling, Richard V. King, Rolf J. Kleber, Jessica Mass Levitt, Brett T. Litz, Maria Livanou, Katelyn P. Mack, Paula Madrid, Shira Maguen, Paul Maguire, Donald J. Mandell, Charles R. Marmar, Andrea R. Maxwell, Shannon E. McCaslin, Alexander C. McFarlane, Thomas J. Metzler, Summer Nelson, Yuval Neria, Elana Newman, Thomas C. Neylan, Fran H. Norris, Carol S. North, Lawrence A. Palinkas, Benjaporn Panyayong, Maria Petukhova, Betty Pfefferbaum, Marleen Radigan, Beverley Raphael, James Rodriguez, G. James Rubin, Kenneth J. Ruggiero, Ebru Şalcıoğlu, Nancy A. Sampson, Arieh Y. Shalev, Bruce Shapiro, Laura M. Stough, Prawate Tantipiwatanaskul, Warunee Thienkrua, Phebe Tucker, J. Blake Turner, Robert J. Ursano, Bellis van den Berg, Peter G. van der Velden, Frits van Griensven, Miranda Van Hooff, Edward Waldrep, Philip S. Wang, Simon Wessely, Leslie H. Wind, C. Joris Yzermans, Heidi M. Zinzow
- Edited by Yuval Neria, Columbia University, New York, Sandro Galea, University of Michigan, Ann Arbor, Fran H. Norris
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- Book:
- Mental Health and Disasters
- Published online:
- 07 May 2010
- Print publication:
- 20 July 2009, pp xi-xvi
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