Thermionic microwave gun for terahertz and synchrotron light sources

Conventional thermionic microwave and radio frequency (RF) guns can offer high average beam current, which is important for synchrotron light and terahertz (THz) radiation source facilities, as well as for industrial applications. For example, the Advanced Photon Source at Argonne National Laboratory is a national synchrotron-radiation light source research facility that utilizes thermionic RF guns. However, these existing thermionic guns are bulky, difficult to handle and install, easily detuned, very sensitive to thermal expansion, and due for a major upgrade and replacement. In this paper, we present the design of a new, more stable, and reliable gun with optimized electromagnetic performance, improved thermal engineering, and a more robust cathode mounting technique, which is a critical step to improve the performance of existing and future light sources, industrial accelerators, and electron beam-driven THz sources. We will also present a fabricated gun prototype and show results of high-power and beam tests.

A short-pulse X-ray beamline for spectroscopy and scattering

Experimental facilities for picosecond X-ray spectroscopy and scattering based on RF deflection of stored electron beams face a series of optical design challenges. Beamlines designed around such a source enable time-resolved diffraction, spectroscopy and imaging studies in chemical, condensed matter and nanoscale materials science using few-picosecond-duration pulses possessing the stability, high repetition rate and spectral range of synchrotron light sources. The RF-deflected chirped electron beam produces a vertical fan of undulator radiation with a correlation between angle and time. The duration of the X-ray pulses delivered to experiments is selected by a vertical aperture. In addition to the radiation at the fundamental photon energy in the central cone, the undulator also emits the same photon energy in concentric rings around the central cone, which can potentially compromise the time resolution of experiments. A detailed analysis of this issue is presented for the proposed SPXSS beamline for the Advanced Photon Source. An optical design that minimizes the effects of off-axis radiation in lengthening the duration of pulses and provides variable X-ray pulse duration between 2.4 and 16 ps is presented.

Optical design of the Short Pulse Soft X-ray Spectroscopy beamline at the Advanced Photon Source

The Short Pulse X-ray facility planned for the Advanced Photon Source (APS) upgrade will provide two sectors with photon beams having picosecond pulse duration. The Short Pulse Soft X-ray Spectroscopy (SPSXS) beamline will cover the 150-2000 eV energy range using an APS bending magnet. SPSXS is designed to take full advantage of this new timing capability in addition to providing circular polarized radiation. Since the correlation between time and electron momentum is in the vertical plane, the monochromator disperses in the horizontal plane. The beamline is designed to maximize flux and preserve the time resolution by minimizing the number of optical components. The optical design allows the pulse duration to be varied from 1.5 to 100 ps full width at half-maximum (FWHM) without affecting the energy resolution, and the resolution to be changed with minimal effect on the pulse duration. More than 10(9) photons s(-1) will reach the sample with a resolving power of 2000 and a pulse duration of ∼2 ps for photon energies between 150 and 1750 eV. The spot size expected at the sample position will vary with pulse duration and exit slit opening. At 900 eV and at a resolving power of 2000 the spot will be ∼10 µm × 10 µm with a pulse duration of 2.3 ps FWHM.

Optical design of the short pulse x-ray imaging and microscopy time-angle correlated diffraction beamline at the Advanced Photon Source

The short pulse x-ray imaging and microscopy beamline is one of the two x-ray beamlines that will take full advantage of the short pulse x-ray source in the Advanced Photon Source (APS) upgrade. A horizontally diffracting double crystal monochromator which includes a sagittally focusing second crystal will collect most of the photons generated when the chirped electron beam traverses the undulator. A Kirkpatrick-Baez mirror system after the monochromator will deliver to the sample a beam which has an approximately linear correlation between time and vertical beam angle. The correlation at the sample position has a slope of 0.052 ps/μrad extending over an angular range of 800 μrad for a cavity deflection voltage of 2 MV. The expected time resolution of the whole system is 2.6 ps. The total flux expected at the sample position at 10 keV with a 0.9 eV energy resolution is 5.7 × 10(12) photons/s at a spot having horizontal and vertical full width at half maximum of 33 μm horizontal by 14 μm vertical. This new beamline will enable novel time-dispersed diffraction experiments on small samples using the full repetition rate of the APS.

Paediatric acute asthma management in Australia and New Zealand: practice patterns in the context of clinical practice guidelines

OBJECTIVES

To compare clinical practice guideline (CPG) recommendations and reported physician management of acute paediatric asthma in the 11 largest paediatric emergency departments, all of which have CPGs, in Australia (n = 9) and New Zealand (n = 2). All 11 sites participate in the Paediatric Research in Emergency Departments International Collaborative (PREDICT) research network.

METHODS

(a) A review of CPGs for acute childhood asthma from all PREDICT sites. (b) A standardised anonymous survey of senior emergency doctors at PREDICT sites investigating management of acute childhood asthma.

RESULTS

CPGs for mild to moderate asthma were similar across sites and based on salbutamol delivery by metered dose inhaler with spacer and oral prednisolone. In severe to critical asthma, differences between sites were common and related to recommendations for: ipratropium use; metered-dose inhaler versus nebulised delivery of salbutamol in severe asthma; use of intravenous aminophylline, intravenous magnesium and dosing of intravenous salbutamol in critical asthma. The questionnaire (78 of 83 doctors responded) also revealed significant differences between doctors in the treatment of moderate to severe asthma. Ipratropium was used for moderate asthma by 42%. For severe to critical asthma, nebulised delivery of salbutamol was preferred by 79% of doctors over metered dose inhalers. For critical asthma, doctors reported using intravenous aminophylline in 45%, intravenous magnesium in 55%, and intravenous salbutamol in 87% of cases. Thirty-nine different dosing regimens for intravenous salbutamol were reported.

CONCLUSIONS

CPG recommendations and reported physician practice for mild to moderate paediatric asthma management were broadly similar across PREDICT sites and consistent with national guidelines. Practice was highly variable for severe to critical asthma and probably reflects limitations of available evidence. Areas of controversy, in particular the comparative efficacy of intravenous bronchodilators, would benefit from multi-centre trials. Collaborative development of CPGs should be considered.

Intranasal fentanyl is an equivalent analgesic to oral morphine in paediatric burns patients for dressing changes: a randomised double blind crossover study

INTRODUCTION

The ideal analgesic agent for burns wound dressings in paediatric patients would be one that is easy to administer, well tolerated, and produces rapid onset of analgesia with a short duration of action and minimal side-effects to allow rapid resumption of activities and oral intake. We compared our current treatment of oral morphine to intranasal fentanyl in an attempt to find an agent closer to the ideal.

METHODS

A randomised double blind two-treatment crossover study comparing intranasal administration of fentanyl (INF) to orally administered morphine (OM). Children with burn injury aged up to 15 years and weighing 10-75 kg were included. Primary end-point was pain scores. Secondary end-points were time to resumption of age-appropriate activities, time to resumption of fluid intake, sedation and cooperation. Routine observations and vital signs were also recorded.

RESULTS

Twenty-four patients were studied with a median age of 4.5 years (interquartile range 1.8-9.0 years) and a median weight of 18.4 kg (interquartile range 12.9-33.2kg). Mean pain difference scores (OM-INF) ranged from -0.500 (95% CI=-1.653 to 0.653) at baseline to -0.625 (05% CI=-1.863 to 0.613) for a retrospective rating of worst pain experienced during the dressing procedure. All measurements were within a pre-defined range of equivalent efficacy. The median time to resumption of fluid intake was 108 min (range 44-175 min) with OM and 140 min (range 60-210 min) with INF. These differences were not statistically significant. Fewer patients experienced mild side-effects with INF compared to OM (n=5 versus n=10). No patients experienced depressed respirations or oxygen saturations.

SUMMARY

Intranasal fentanyl was shown to be equivalent to oral morphine in the provision of analgesia for burn wound dressing changes in this cohort of paediatric patients. It was concluded that intranasal fentanyl is a suitable analgesic agent for use in paediatric burns dressing changes either by itself or in combination with oral morphine as a top up titratable agent.

Evidence for microbunching "sidebands" in a saturated free-electron laser using coherent optical transition radiation

We report the first measurements of z-dependent coherent optical transition radiation (COTR) due to electron-beam microbunching at high gains ( >10(4)) including saturation of a self-amplified spontaneous emission free-electron laser (FEL). In these experiments the fundamental wavelength was near 530 nm, and the COTR spectra exhibit the transition from simple spectra to complex spectra ( 5% spectral width) after saturation. The COTR intensity growth and angular distribution data are reported as well as the evidence for transverse spectral dependencies and an "effective" core of the beam being involved in microbunching.

Exponential Gain and Saturation of a Self-Amplified Spontaneous Emission Free-Electron Laser

Self-amplified spontaneous emission in a free-electron laser has been proposed for the generation of very high brightness coherent x-rays. This process involves passing a high-energy, high-charge, short-pulse, low-energy-spread, and low-emittance electron beam through the periodic magnetic field of a long series of high-quality undulator magnets. The radiation produced grows exponentially in intensity until it reaches a saturation point. We report on the demonstration of self-amplified spontaneous emission gain, exponential growth, and saturation at visible (530 nanometers) and ultraviolet (385 nanometers) wavelengths. Good agreement between theory and simulation indicates that scaling to much shorter wavelengths may be possible. These results confirm the physics behind the self-amplified spontaneous emission process and forward the development of an operational x-ray free-electron laser.

First Observation of z-Dependent Electron-Beam Microbunching Using Coherent Transition Radiation

We report the first measurements of the electron-beam microbunching z dependence in a self-amplified spontaneous-emission (SASE) free-electron laser (FEL) experiment by the observation of visible wavelength coherent transition radiation (CTR). In this case the fundamental SASE wavelength was at 537 nm, and the CTR exhibited an exponential intensity growth similar to the SASE radiation. In addition, we observed for the first time structure in the CTR angular distribution patterns that may be useful for optimizing SASE FEL performance.

Observation of self-amplified spontaneous emission and exponential growth at 530 nm

Experimental evidence for self-amplified spontaneous emission (SASE) at 530 nm is reported. The measurements were made at the low-energy undulator test line facility at the Advanced Photon Source, Argonne National Laboratory. The experimental setup and details of the experimental results are presented, as well as preliminary analysis. This experiment extends to shorter wavelengths the operational knowledge of a linac-based SASE free-electron laser and explicitly shows the predicted exponential growth in intensity of the optical pulse as a function of length along the undulator.

Injury and illness in a wilderness multisport endurance event

Our objective was to identify patterns of injury and illness and develop possible preventive strategies for competitors in a wilderness multisport endurance event. Using a prospective observational cohort study during the Winter Classic, a 2-day wilderness multisport endurance event held in rugged alpine terrain in Victoria, Australia, we sought details of demographics, pre-, intra-, and postrace injuries and illness. We employed chi-squared tests and iterative multivariate analysis. There were 33 respondents with 26 (78%) aged between 26 and 35 years. Seven (21%) developed symptoms consistent with exposure, and three (9%) developed asthma during the race. Competitors in the marathon pairs class had a 50% risk of exposure vs 12% for the individual class (p = 0.031). The number of times raced, nonsteroidal anti-inflammatory drug use, and increasing age were the other independent significant predictors of exposure. Twenty-three (70%) of the competitors were injured at some time during the race. The day 1 run was more commonly associated with injuries than other stages (39% injured, p = 0.0037). Increased amounts of training, previous musculoskeletal problems, and increased number of previous race attempts were all significant independent predictors of injury. Most competitors (67%) suffered musculoskeletal problems after the race, these typically being of the thighs and calves, but only two competitors required time off from their normal activities. We concluded that injuries in wilderness multisport endurance events are common, particularly in the run stages. These injuries are usually minor, but their frequency makes major injury an ever-present risk. Both injury and illness are more frequent in those who compete while carrying injuries. These events are high risk for the development of injuries and illness and require a high level of competitor preparation and readily available medical support.

A community quality initiative for health care reform

In 1989, the Madison Area Employers Health Care Coalition conducted a feasibility study for the purpose of finding solutions to common health care concerns. The study revealed three conclusions: (1) there was little or no price competition among providers; (2) employers lacked useful data and information regarding health care costs and outcomes; and (3) employers and employees lacked basic health care consumerism. These conclusions led to the development of a health care purchasing group in the spring of 1990 with the formation of the Employers Health Care Alliance Cooperative (The Alliance). The conclusions outlined above became the cornerstone of the services offered by The Alliance, which include provider contracting, data collection, and consumer education and advocacy. The Alliance also developed the community quality initiative, a partnership of employers, health care consumers, and providers committed to using continuous quality improvement methods.

Vaginal cones for the treatment of genuine stress incontinence

The value of vaginal cones for genuine stress incontinence was assessed in 34 women with this condition. Subjective and objective assessments were made before and after 6 weeks of treatment using urinary diaries, perineometry, 'home' pad test and cone weights with and without voluntary pelvic floor contraction. There was a subjective improvement in 23 of the 34 women (68%) after 6 weeks of cone use with 16 (47%) deciding that no additional treatment other than cone therapy was required at this time. Statistical analyses showed that there were significant improvements in the objective indices. There were no side-effects observed with cone use. When followed up 12-24 (mean 15.8) months from the start of the study, 14 women (41%) were still improved with either cone or pelvic floor exercises. Vaginal cones would seem to be a simple and practical means of improving both pelvic floor strength and genuine stress incontinence.

Application of a frequency definition of ventricular proarrhythmia

To differentiate spontaneous variability from proarrhythmia in patients with benign or potentially lethal ventricular arrhythmias, 495 patients with 2 or more Holter tracings during placebo therapy were evaluated. The Holter session with the highest frequency of ventricular premature complexes (VPCs) and ventricular tachycardia was compared with the first placebo recording. Patients were segregated by their baseline frequency of VPCs. The percent of patients taking placebo in this trial who had the same increase in VPC frequency as has been ascribed to those with proarrhythmia varied from 0 of 470 patients with a baseline frequency of ventricular arrhythmia of 10 to 50 VPCs/hour, 3 of 44 (7%) with 51 to 100 VPCs/hour, 1 of 139 (0.7%) with 101 to 300 VPCs/hour and 1 of 265 (0.04%) with more than 300 VPCs/hour. Overall, 5 of 496 (1%) patients would have been classified as having proarrhythmia using the algorithm although only placebo was given. A 10-fold or greater increase in ventricular tachycardia beats in patients taking placebo occurred in 9 of 274 patients (3%). Thus, a simple algorithm to define proarrhythmia in patients with mixed cardiac disease and chronic ventricular arrhythmias can be defined and differentiated from spontaneous variability. This arbitrary algorithm defines proarrhythmia as an increase of more than 3 times when baseline VPC frequency is more than 100 VPCs/hour and more than 10 times when that frequency is less than 100 VPCs/hour with a false-positive rate of only 1%.