Multi-Pulse Laser Wakefield Acceleration: A New Route to Efficient, High-Repetition-Rate Plasma Accelerators and High Flux Radiation Sources

Laser-driven plasma accelerators can generate accelerating gradients three orders of magnitude larger than radio-frequency accelerators and have achieved beam energies above 1 GeV in centimetre long stages. However, the pulse repetition rate and wall-plug efficiency of plasma accelerators is limited by the driving laser to less than approximately 1 Hz and 0.1% respectively. Here we investigate the prospects for exciting the plasma wave with trains of low-energy laser pulses rather than a single high-energy pulse. Resonantly exciting the wakefield in this way would enable the use of different technologies, such as fibre or thin-disc lasers, which are able to operate at multi-kilohertz pulse repetition rates and with wall-plug efficiencies two orders of magnitude higher than current laser systems. We outline the parameters of efficient, GeV-scale, 10-kHz plasma accelerators and show that they could drive compact X-ray sources with average photon fluxes comparable to those of third-generation light source but with significantly improved temporal resolution. Likewise FEL operation could be driven with comparable peak power but with significantly larger repetition rates than extant FELs

Instructional Discussion: The Most Important Area of Training for New Basic Course Instructors

In order to determine the most important concept to teach new basic course instructors, it is important to know what we want students to be able to do as a result of the basic course and what teaching method will best reach that outcome. One main goal of the basic course is to teach students to communicate orally and give them practice doing so. This can be accomplished through what Muller (2014) defines as instructional discussion, or “an instructional interaction where teachers and students engage together in an exploration of problems, ideas, and questions in ways that incorporate the knowledge of all participants to generate a collective wisdom or understanding that would not have emerged without the interaction” (p. 326). This definition illustrates the importance of engagement and interaction, both important goals within the basic communication course. Additionally, instructional discussion highlights the central role of communication in the teaching and learning process. Thus, it is imperative that training programs for basic course instructors address how to plan, facilitate, and assess an instructional discussion as well as teach students how to engage in the process

Interseeded cover crops, soil health, and nitrogen supply for grain corn in Ontario

Non-Peer ReviewedInterseeded cover crops are a promising option for improving environmental sustainability in corn-based rotations. Field plots were established in 2015 under conventional tillage and regional corn N fertilization practices and repeated over two seasons at three sites in southern Ontario: Ridgetown, Elora, and Peterborough. The objectives were to evaluate the effects of interseeded annual ryegrass (ARG) and red clover (RCL) on grain corn yield and N uptake; soil mineral N (Nmin); and soil biological parameters. At each site, ARG, RCL, an ARG/RCl blend (MIX), and a no-cover control (BARE) were arranged in a RCBD replicated four times. The cover crops were seeded between the corn rows at the 5-leaf stage using an InterSeederTM drill. Cover crops accumulated 15 - 860 kg C ha-1 and 1.3 - 77 kg N ha-1 per season, and their yields were significantly correlated with soil microbial biomass, β-Glucosidase activity, and particulate organic matter. Community-level physiological profiling (BIOLOG EcoplatesTM) showed that microbial community diversity was significantly greater in ARG than BARE. Grain N concentration (10.8 - 11.2 g kg-1) and aboveground corn N uptake (100 - 154 kg ha-1) were not significantly reduced by cover crops at all sites. Although residual Nmin levels measured at grain corn harvest (0-30 cm) and the following spring (0-15 cm) were generally low (2.4 - 9.3 mg kg-1) at all sites, ARG had 48% lower Nmin than BARE. The effects of cover crops on soil health parameters, corn N uptake and Nmin were more affected by site and seasonal variability than by cover crop treatments. However, the results indicate the potential for improving soil health when there is successful establishment of interseeded annual ryegrass or red clover

Zoonotic disease risk perceptions and infection control practices of Australian veterinarians: Call for change in work culture

This study was conducted to determine the perceptions of zoonotic disease risk among Australian veterinarians, the infection control practices they use to protect themselves from zoonotic diseases, and the factors influencing their use of these protective practices. A questionnaire was designed and piloted prior to its administration to veterinarians at the annual Australian Veterinary Association Conference in May 2011. The questionnaire comprised 21 closed, semi-closed and open questions. Data from the questionnaire were analyzed using ordinal logistic regression analyses to determine significant factors for veterinarians’ use of personal protective equipment (PPE). A total of 344 veterinarians completed the questionnaire of which 63.7% were women, 63.2% worked in small/companion animal practice, and 79.9% worked in private veterinary practice. Of the respondents, 44.9% reported contracting a zoonosis during their careers with 19.7% reporting a suspected case and 25.2% reporting a confirmed incidence. Around 40–60% of veterinarians perceived exposure to zoonosis likely or very likely in a variety of situations. With reference to current national industry guidelines, the reported use of PPE was less than “adequate” for most scenarios except for performing postmortems, surgery or dental procedures. No PPE was used by 60–70% of veterinarians for treating respiratory and neurological cases and by 40–50% when treating gastrointestinal and dermatological cases. Workplace conditions need improvement as 34.8% of workplaces did not have isolation units for infected animals, 21.1% did not have separate eating areas for staff, and 57.1% did not have complete PPE kits for use. Veterinarians were more likely to use PPE if they had undertaken postgraduate education, perceived that zoonosis exposure from animals and procedures was likely, consciously considered PPE use for every case they dealt with and believed that liability issues and risks encouraged use of PPE. In contrast, those working in private practices, those who tended to ‘just hope for the best’ when trying to avoid zoonotic diseases, and those who were not aware of industry guidelines were less likely to use PPE. The results suggest that veterinarians’ perceptions and workplace policies and culture substantially influence their use of PPE. Efforts should be made to encourage veterinarians and their workplaces to use infection control practices to protect themselves and their staff from zoonotic diseases

Bright X-ray radiation from plasma bubbles in an evolving laser wakefield accelerator

We show that the properties of the electron beam and bright x-rays produced by a laser wakefield accelerator can be predicted if the distance over which the laser self-focuses and compresses prior to self-injection is taken into account. A model based on oscillations of the beam inside a plasma bubble shows that performance is optimised when the plasma length is matched to the laser depletion length. With a 200~TW laser pulse this results in an x-ray beam with median photon energy of \unit[20]{keV}, $> 6\times 10^{8}$ photons above \unit[1]{keV} per shot and a peak brightness of \unit[3 \times 10^{22}]{photons~s^{-1}mrad^{-2}mm^{-2} (0.1\% BW)^{-1}}.Comment: 5 pages, 4 figure

Experimental philosophy leading to a small scale digital data base of the conterminous United States for designing experiments with remotely sensed data

Research using satellite remotely sensed data, even within any single scientific discipline, often lacked a unifying principle or strategy with which to plan or integrate studies conducted over an area so large that exhaustive examination is infeasible, e.g., the U.S.A. However, such a series of studies would seem to be at the heart of what makes satellite remote sensing unique, that is the ability to select for study from among remotely sensed data sets distributed widely over the U.S., over time, where the resources do not exist to examine all of them. Using this philosophical underpinning and the concept of a unifying principle, an operational procedure for developing a sampling strategy and formal testable hypotheses was constructed. The procedure is applicable across disciplines, when the investigator restates the research question in symbolic form, i.e., quantifies it. The procedure is set within the statistical framework of general linear models. The dependent variable is any arbitrary function of remotely sensed data and the independent variables are values or levels of factors which represent regional climatic conditions and/or properties of the Earth's surface. These factors are operationally defined as maps from the U.S. National Atlas (U.S.G.S., 1970). Eighty-five maps from the National Atlas, representing climatic and surface attributes, were automated by point counting at an effective resolution of one observation every 17.6 km (11 miles) yielding 22,505 observations per map. The maps were registered to one another in a two step procedure producing a coarse, then fine scale registration. After registration, the maps were iteratively checked for errors using manual and automated procedures. The error free maps were annotated with identification and legend information and then stored as card images, one map to a file. A sampling design will be accomplished through a regionalization analysis of the National Atlas data base (presently being conducted). From this analysis a map of homogeneous regions of the U.S.A. will be created and samples (LANDSAT scenes) assigned by region

Optical Characterisation of Suspended Particles in the Mackenzie River Plume (Canadian Arctic Ocean) and Implications for Ocean Colour Remote Sensing

Climate change significantly impacts Arctic shelf regions in terms of air temperature, ultraviolet radiation, melting of sea ice, precipitation, thawing of permafrost and coastal erosion. Direct consequences have been observed on the increasing Arctic river flow and a large amount of organic carbon sequestered in soils at high latitudes since the last glacial maximum can be expected to be delivered to the Arctic Ocean during the coming decade. Monitoring the fluxes and fate of this terrigenous organic carbon is problematic in such sparsely populated regions unless remote sensing techniques can be developed and proved to be operational. The main objective of this study is to develop an ocean colour algorithm to operationally monitor dynamics of suspended particulate matter (SPM) on the Mackenzie River continental shelf (Canadian Arctic Ocean) using satellite imagery. The water optical properties are documented across the study area and related to concentrations of SPM and particulate organic carbon (POC). Robust SPM and POC : SPM proxies are identified, such as the light backscattering and attenuation coefficients, and relationships are established between these optical and biogeochemical parameters. Following a semi-analytical approach, a regional SPM quantification relationship is obtained for the inversion of the water reflectance signal into SPM concentration. This relationship is reproduced based on independent field optical measurements. It is successfully applied to a selection of MODIS satellite data which allow estimating fluxes at the river mouth and monitoring the extension and dynamics of the Mackenzie River surface plume in 2009, 2010 and 2011. Good agreement is obtained with field observations representative of the whole water column in the river delta zone where terrigenous SPM is mainly constrained (out of short periods of maximum river outflow). Most of the seaward export of SPM is observed to occur within the west side of the river mouth. Future work will require the validation of the developed SPM regional algorithm based on match-ups with field measurements, then the routine application to ocean colour satellite data in order to better estimate the fluxes and fate of SPM and POC delivered by the Mackenzie River to the Arctic Ocean

Effect of abdominal binding on respiratory mechanics during exercise in athletes with cervical spinal cord injury

West CR, Goosey-Tolfrey VL, Campbell IG, Romer LM. Effect of abdominal binding on respiratory mechanics during exercise in athletes with cervical spinal cord injury. J Appl Physiol 117: 36–45, 2014. First published May 22, 2014; doi:10.1152/japplphysiol.00218.2014.—We asked whether elastic binding of the abdomen influences respiratory mechanics during wheelchair propulsion in athletes with cervical spinal cord injury (SCI). Eight Paralympic wheelchair rugby players with motor-complete SCI (C5-C7) performed submaximal and maximal incremental exercise tests on a treadmill, both with and without abdominal binding. Measurements included pulmonary function, pressure-derived indices of respiratory mechanics, operating lung volumes, tidal flow-volume data, gas exchange, blood lactate, and symptoms. Residual volume and functional residual capacity were reduced with binding (77 18 and 81 11% of unbound, P 0.05), vital capacity was increased (114 9%, P 0.05), whereas total lung capacity was relatively well preserved (99 5%). During exercise, binding introduced a passive increase in transdiaphragmatic pressure, due primarily to an increase in gastric pressure. Active pressures during inspiration were similar across conditions. A sudden, sustained rise in operating lung volumes was evident in the unbound condition, and these volumes were shifted downward with binding. Expiratory flow limitation did not occur in any subject and there was substantial reserve to increase flow and volume in both conditions. V ˙ O2 was elevated with binding during the final stages of exercise (8 –12%, P 0.05), whereas blood lactate concentration was reduced (16 –19%, P 0.05). V ˙ O2/heart rate slopes were less steep with binding (62 35 vs. 47 24 ml/beat, P 0.05). Ventilation, symptoms, and work rates were similar across conditions. The results suggest that abdominal binding shifts tidal breathing to lower lung volumes without influencing flow limitation, symptoms, or exercise tolerance. Changes in respiratory mechanics with binding may benefit O2 transport capacity by an improvement in central circulatory function.This article has been made available through the Brunel Open Access Publishing Fund

Nuclear structure beyond the neutron drip line: the lowest energy states in 9^9He via their T=5/2 isobaric analogs in 9^9Li

The level structure of the very neutron rich and unbound $^9$He nucleus has been the subject of significant experimental and theoretical study. Many recent works have claimed that the two lowest energy $^9$He states exist with spins $J^\pi=1/2^+$ and $J^\pi=1/2^-$ and widths on the order of hundreds of keV. These findings cannot be reconciled with our contemporary understanding of nuclear structure. The present work is the first high-resolution study with low statistical uncertainty of the relevant excitation energy range in the $^8$He$+n$ system, performed via a search for the T=5/2 isobaric analog states in $^9$Li populated through $^8$He+p elastic scattering. The present data show no indication of any narrow structures. Instead, we find evidence for a broad $J^{\pi}=1/2^+$ state in $^9$He located approximately 3 MeV above the neutron decay threshold

Enhanced He-alpha emission from "smoked" Ti targets irradiated with 400nm, 45 fs laser pulses

We present a study of He-like 1s(2)-1s2p line emission from solid and low-density Ti targets under similar or equal to 45 fs laser pulse irradiation with a frequency doubled Ti: Sapphire laser. By varying the beam spot, the intensity on target was varied from 10(15) W/cm(2) to 10(19) W/cm(2). At best focus, low density "smoked" Ti targets yield similar to 20 times more He-alpha than the foil targets when irradiated at an angle of 45 degrees with s-polarized pulses. The duration of He-alpha emission from smoked targets, measured with a fast streak camera, was similar to that from Ti foils