Conductivity Induced by High-Field Terahertz Waves in Dielectric Material.

An intense, subpicosecond, relativistic electron beam traversing a dielectric-lined waveguide generates very large amplitude electric fields at terahertz (THz) frequencies through the wakefield mechanism. In recent work employing this technique to accelerate charged particles, the generation of high-power, narrow-band THz radiation was demonstrated. The radiated waves contain fields with measured amplitude exceeding 2 GV/m, orders of magnitude greater than those available by other THz generation techniques at a narrow bandwidth. For fields approaching the GV/m level, a strong damping has been observed in SiO_{2}. This wave attenuation with an onset near 850 MV/m is consistent with changes to the conductivity of the dielectric lining and is characterized by a distinctive latching mechanism that is reversible on longer timescales. We describe the detailed measurements that serve to clarify the underlying physical mechanisms leading to strong field-induced damping of THz radiation (hω=1.59 meV, f=0.38 THz) in SiO_{2}, a bulk, wide band-gap (8.9 eV) dielectric.

Observation of acceleration and deceleration in gigaelectron-volt-per-metre gradient dielectric wakefield accelerators.

There is urgent need to develop new acceleration techniques capable of exceeding gigaelectron-volt-per-metre (GeV m(-1)) gradients in order to enable future generations of both light sources and high-energy physics experiments. To address this need, short wavelength accelerators based on wakefields, where an intense relativistic electron beam radiates the demanded fields directly into the accelerator structure or medium, are currently under intense investigation. One such wakefield based accelerator, the dielectric wakefield accelerator, uses a dielectric lined-waveguide to support a wakefield used for acceleration. Here we show gradients of 1.347±0.020 GeV m(-1) using a dielectric wakefield accelerator of 15 cm length, with sub-millimetre transverse aperture, by measuring changes of the kinetic state of relativistic electron beams. We follow this measurement by demonstrating accelerating gradients of 320±17 MeV m(-1). Both measurements improve on previous measurements by and order of magnitude and show promise for dielectric wakefield accelerators as sources of high-energy electrons.

Observation of narrow-band terahertz coherent Cherenkov radiation from a cylindrical dielectric-lined waveguide.

We report experimental observation of narrow-band coherent Cherenkov radiation driven by a subpicosecond electron bunch traveling along the axis of a hollow cylindrical dielectric-lined waveguide. For an appropriate choice of dielectric wall thickness, a short-pulse beam current profile excites only the fundamental mode of the structure, producing energetic pulses in the terahertz range. We present detailed measurements showing a narrow emission spectrum peaked at 367 + or - 3 GHz from a 1 cm long fused silica capillary tube with submillimeter transverse dimensions, closely matching predictions. We demonstrate a 100 GHz shift in the emitted central frequency when the tube wall thickness is changed by 50 microm. Calibrated measurements of the radiated energy indicate up to 10 microJ per 60 ps pulse for an incident beam charge of 200 pC, corresponding to a peak power of approximately 150 kW.

Making assessment relevant to treatment planning: the STS Clinician Rating Form. Systemic Treatment Selection.

This article reports on the development of a computerized, clinician-based method of assessing patient variables that contribute to differential assignment of psychotherapy models. In the current health care environment, omnibus personality tests and current state measures are both expensive and insensitive to most of the empirically defined patient characteristics that have been identified as indicators of different treatment qualities. Moreover, reliance on patient self-report introduces a variety of distortions and limits predictive studies and follow-up assessments to those who are cooperative. These factors limit the usefulness of the currently available procedures. Aptitude-Treatment-Interaction (ATI) research has revealed differential effects of manualized cognitive, interpersonal, and insight-oriented treatments as a function on a select number of relatively specific personality and symptom qualities. A cost- and time-efficient method of measuring these dimensions could increase the power of treatment by identifying in advance those that are likely to be most effective for a given patient. The STS (Systematic Treatment Selection) Clinician Rating Form is a relatively brief, clinician-based measure of a variety of patient dimensions, including subjective distress, various aspects of coping style, and resistance traits. Current data reveal good interrater reliability and adequate levels of discriminant and convergent validity.

Staff attitudes that impede the implementation of behavioral treatment programs.

Staff who have negative attitudes about behavioral treatments are less likely to implement them. Previous research suggests that negative attitudes are associated with staff burnout and perceived collegial support. A path analysis is conducted in this study to determine the direction of these effects. Ninety staff members who work in treatment programs for severely mentally ill adults completed measures of attitudes about behavior therapy, experience with behavior therapy, burnout, and collegial support. Results of the path analysis yielded a model with good fit that confirmed our hypotheses; namely, burnout leads to negative attitudes and experience with behavior therapy yields positive attitudes. Insufficient collegial support leads to negative attitudes through burnout. Implications of these findings for improving the use of behavior treatments in real-world programs are discussed.

The differential effects of parental alcoholism and mental illness on their adult children.

Growing up in a household with alcoholic or mentally ill parents is more likely to produce lower self-esteem, greater dysphoria, and more anxiety in adulthood. To test this hypothesis, 139 undergraduate and graduate students completed measures of anxiety, depression, social avoidance, self-esteem, and social support. Results showed that adult children of alcoholics, adult children of mentally ill, and adult children of substance-abusing mentally ill had lower self-esteem and were more socially anxious than normal controls. Adult children of mentally ill parents were more depressed and showed greater trait anxiety than did adult children of alcoholics and controls. The impact of parental pathology is diminished when the adult child has a large and/or satisfactory social support network.

Principles and application of extracorporeal shock wave lithotripsy.

The physics, instrumentation, and patient-care aspects of extracorporeal shock wave lithotripsy (ESWL) in the treatment of kidney stone disease are described. The kidney stone is located through the use of two integrated roentgenographic imaging systems. The x-ray tubes, fixed on either side of a tub of water in which the patient is partially immersed, are directed upward. The patient is maneuvered until the imaging systems indicate the kidney stone is within the second focus of the reflector and within the 1.5-cu cm target area. Once within this alignment, the stone is ready for shock wave treatment; general or regional anesthesia is used to immobilize the patient so that the position of the stone can be maintained within the focus of the shock wave. When the stone is repeatedly subjected to this high-energy force, it begins to disintegrate until fragments of less than 1 mm are left. ESWL can (1) disintegrate kidney stones of all types, (2) be efficiently transmitted over distances that allow the shock wave source to be outside the body, (3) safely pass through living tissue, and (4) be precisely controlled and focused into a small target area. ESWL is a safe, effective, and cost-saving treatment that can be used for 90% of all kidney stone disease that previously required surgery.

Deep vein thrombosis in a Queensland hospital.

Investigation in the postoperative period of 75 patients by means of the radioiodinated fibrinogen uptake method, by the use of the Doppler ultrasonic flow detector, and by clinical assessment revealed an incidence of deep vein thrombosis of only 12%. This is distinctly lower than has been reported by other investigators using the same techniques both in Australia and elsewhere. It appears from this study and associated work that the Doppler ultrasonic technique is sufficiently accurate to be of value in the clinical diagnosis of significant deep vein thrombosis.