Recovery time of a plasma-wakefield accelerator.

The interaction of intense particle bunches with plasma can give rise to plasma wakes1,2 capable of sustaining gigavolt-per-metre electric fields3,4, which are orders of magnitude higher than provided by state-of-the-art radio-frequency technology5. Plasma wakefields can, therefore, strongly accelerate charged particles and offer the opportunity to reach higher particle energies with smaller and hence more widely available accelerator facilities. However, the luminosity and brilliance demands of high-energy physics and photon science require particle bunches to be accelerated at repetition rates of thousands or even millions per second, which are orders of magnitude higher than demonstrated with plasma-wakefield technology6,7. Here we investigate the upper limit on repetition rates of beam-driven plasma accelerators by measuring the time it takes for the plasma to recover to its initial state after perturbation by a wakefield. The many-nanosecond-level recovery time measured establishes the in-principle attainability of megahertz rates of acceleration in plasmas. The experimental signatures of the perturbation are well described by simulations of a temporally evolving parabolic ion channel, transferring energy from the collapsing wake to the surrounding media. This result establishes that plasma-wakefield modules could be developed as feasible high-repetition-rate energy boosters at current and future particle-physics and photon-science facilities.

High-resolution sampling of beam-driven plasma wakefields.

Plasma-wakefield accelerators driven by intense particle beams promise to significantly reduce the size of future high-energy facilities. Such applications require particle beams with a well-controlled energy spectrum, which necessitates detailed tailoring of the plasma wakefield. Precise measurements of the effective wakefield structure are therefore essential for optimising the acceleration process. Here we propose and demonstrate such a measurement technique that enables femtosecond-level (15 fs) sampling of longitudinal electric fields of order gigavolts-per-meter (0.8 GV m-1). This method-based on energy collimation of the incoming bunch-made it possible to investigate the effect of beam and plasma parameters on the beam-loaded longitudinally integrated plasma wakefield, showing good agreement with particle-in-cell simulations. These results open the door to high-quality operation of future plasma accelerators through precise control of the acceleration process.

FLASHForward: plasma wakefield accelerator science for high-average-power applications.

The FLASHForward experimental facility is a high-performance test-bed for precision plasma wakefield research, aiming to accelerate high-quality electron beams to GeV-levels in a few centimetres of ionized gas. The plasma is created by ionizing gas in a gas cell either by a high-voltage discharge or a high-intensity laser pulse. The electrons to be accelerated will either be injected internally from the plasma background or externally from the FLASH superconducting RF front end. In both cases, the wakefield will be driven by electron beams provided by the FLASH gun and linac modules operating with a 10 Hz macro-pulse structure, generating 1.25 GeV, 1 nC electron bunches at up to 3 MHz micro-pulse repetition rates. At full capacity, this FLASH bunch-train structure corresponds to 30 kW of average power, orders of magnitude higher than drivers available to other state-of-the-art LWFA and PWFA experiments. This high-power functionality means FLASHForward is the only plasma wakefield facility in the world with the immediate capability to develop, explore and benchmark high-average-power plasma wakefield research essential for next-generation facilities. The operational parameters and technical highlights of the experiment are discussed, as well as the scientific goals and high-average-power outlook. This article is part of the Theo Murphy meeting issue 'Directions in particle beam-driven plasma wakefield acceleration'.

Tunable Plasma-Based Energy Dechirper.

A tunable plasma-based energy dechirper has been developed at FLASHForward to remove the correlated energy spread of a 681 MeV electron bunch. Through the interaction of the bunch with wakefields excited in plasma the projected energy spread was reduced from a FWHM of 1.31% to 0.33% without reducing the stability of the incoming beam. The experimental results for variable plasma density are in good agreement with analytic predictions and three-dimensional simulations. The proof-of-principle dechirping strength of 1.8 GeV/mm/m significantly exceeds those demonstrated for competing state-of-the-art techniques and may be key to future plasma wakefield-based free-electron lasers and high energy physics facilities, where large intrinsic chirps need to be removed.

The effect of slurry on skin permeability to methylene blue dye in dairy cows with and without a history of digital dermatitis.

This study aimed to determine whether there was a difference in skin permeability to methylene blue dye or skin morphology between dairy cows that differed in their susceptibility to digital dermatitis (DD) and to assess the effect of contact with slurry on skin permeability. Twenty nine dairy cows were monitored for DD during the winter housing period and classed as DD+ (previous DD infection, n = 17), or DD- (no recorded infection, n = 12). The animals were culled and a skin sample was taken from above the heel of each hind foot and frozen. Samples were later defrosted and one sample from each cow was tested for permeability, whereas the other was treated with slurry for 24 h before permeability testing. To test permeability, methylene blue dye was applied to the skin surface in a Franz diffusion cell. After 48 h, the amount of dye that had passed through the skin was estimated. The stratum corneum thickness and the density of hair follicles were determined from additional heel skin samples. Skin permeability to methylene blue dye was significantly greater for samples that had been treated with slurry but did not differ between DD+ and DD- animals. No difference was found in the stratum corneum thickness or density of hair follicles between DD+ and DD- animals. These findings imply that individual differences in general skin permeability are not a major factor in determining DD susceptibility and suggest that contact with slurry could contribute to DD infection by increasing the permeability of the skin, which may facilitate pathogen entry. Further work is required to clarify the role played by slurry in the pathogenesis of DD.

Decisions about life-sustaining treatment. Impact of physicians' behaviors on the family.

BACKGROUND: Despite the growing availability of advance directives, most patients in the intensive care unit lack written directives, and, therefore, consultation with families about treatment decisions remains the rule. In the context of decision making about withdrawing life-sustaining treatments, we investigated which physician and nurse behaviors families find supportive and which behaviors increase the family's burden. METHODS: We conducted intensive 1- to 2-hour-long individual interviews using a semistructured interview protocol with 32 family members of patients without advance directives whose deaths followed a stay in the intensive care unit and withdrawal of treatment. We analyzed more than 700 pages of verbatim interview data using content analysis techniques and achieved more than 90% interrater agreement on data codes. RESULTS: Themes emerged as families identified selected physician and nursing behaviors as helpful: encouraging advanced planning, timely communication, clarification of families' roles, facilitating family consensus, and accommodating family's grief. Behaviors that made families feel excluded or increased their burden included postponing discussions about treatment withdrawal, delaying withdrawal once scheduled, placing the full burden of decision making on one person, withdrawing from the family, and defining death as a failure. CONCLUSIONS: Study findings provide an increased understanding of the unmet needs of families and serve to guide physicians and nurses in reducing actions that increase families' burdens as they participate in treatment withdrawal decisions.

Principles of clinical medicine: an interdisciplinary integrated 2-year longitudinal course.

In keeping with the Report of the Panel on the General Professional Education of the Physician (Association of American Medical Colleges 1984), Oregon Health Sciences University (OHSU) School of Medicine is in the midst of revising its curriculum. After a 4-year process, the Curriculum Committee mandated development of the Principles of Clinical Medicine course, a 2-year longitudinal course integrating input from both basic and clinical science departments. We describe the steps leading to the course's implementation, its administrative and organizational structure, the evaluation of student performance, teacher training, course curriculum, and the use of interdisciplinary teaching. This course embodies many of the changes called for in the AAMC Report and serves as a model for interdisciplinary education.

Factors that influence clinicians' assessment and management of family violence.

OBJECTIVES: High rates of family violence and low rates of detection, report, and therapeutic intervention by health professionals are well documented. This study was undertaken to determine what factors influence clinicians' decision making about identifying abuse and intervening with victims. METHODS: Survey data about clinicians' experiences with and attitudes toward family violence were gathered by mailed questionnaire from a random sample of practicing clinicians in six disciplines (n = 1521). RESULTS: Data showed similarities within and wide differences among three groups of subjects: dentists/dental hygienists, nurses/physicians, and psychologists/social workers. Overall, a third of subjects reported having received no educational content on child, spouse, or elder abuse in their professional training programs. Subjects with education on the topic more commonly suspected abuse in their patients than those without; among all subjects, spouse abuse was suspected more often than child abuse while elder abuse was suspected infrequently. Significant numbers of subjects did not view themselves as responsible for dealing with problems of family violence. Subjects indicated low confidence in and low compliance with mandatory reporting laws. CONCLUSIONS: There is a need for educators to expand curricula on family violence and for legislators to reexamine mandatory reporting laws.

Health care in common: setting priorities in Oregon.

KIE: This is one of a set of six short articles, grouped under the umbrella title "Grassroots bioethics revisited: health care priorities and community values," with a very brief introduction by Bruce Jennings. The articles focus on the involvement of community health decisions projects with public policy issues of access to health care, allocation of resources, setting health care priorities, cost containment, and rationing.^ieng

Oregon Health Decisions. An experiment with informed community consent.

Oregon Health Decisions is a citizen-based project intended to develop statewide awareness of severe bioethical dilemmas. The project has set in motion civic means for addressing and resolving problems in Oregon's health provision system associated with personal autonomy, equity of access, prevention of illness, and humane cost containment. The process of civic involvement with consequent results is described together with the implications for future health policy in Oregon and elsewhere.

KIE: Oregon Health Decisions is a citizen-based nonprofit organization, established in the early 1980s to develop statewide awareness of bioethical issues and to encourage citizen participation in resolving such dilemmas. Operating through community agencies, the project recruited volunteers, held interdisciplinary workshops, and conducted 300 meetings involving more than 5,000 people. Resolutions were developed in five areas: autonomy and dignity of patients, disease prevention, access to health care, cost control, and resource allocation. The primary results have been heightened awareness within Oregon about bioethical issues, funding for other bioethics educational activities, new tasks for health planning agencies, and national media coverage that has fostered an interest in similar projects by other states and organizations.

Integrating cost awareness with ethics in the undergraduate medical curriculum.

The challenge to train medical students in cost awareness regarding medical care led to a program at the Oregon Health Sciences University that integrates concern for costs with medical ethics. Cost awareness is a perspective that balances the physician's ethical obligations toward individual patients with their duties toward society whose pooled resources pay for medical services. The program integrates the subject of cost awareness into major required courses spanning the four-year curriculum. First-year students see costs in the context of an overview of social aspects of medical care. For second-year students, cost awareness is incorporated into training in basic clinical skills. Third- and fourth-year students are shown the bill for one of their patients and analyze their ward experiences from the perspective of resource utilization. Junior and senior students examine the impact of the legal system and professional ethics on health care costs. Elective course work on cost awareness is also available.