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High frequency ultraviolet - visible (UV-VIS) sensors offer a way of improving dissolved organic carbon (DOC) load estimates in rivers as they can be calibrated to DOC concentration. This is an improvement on periodic grab sampling, or the use of pumped sampling systems which store samples in-field before collection. We hypothesised that the move to high frequency measurements would increase the load estimate based on grab sampling due to systemic under-sampling of high flows. To test our hypotheses, we calibrated two sensors in contrasting catchments (Exe and Bow Brook, UK) against weekly grab sampled DOC measurements and then created an hourly time series of DOC for the two sites. Taking this measurement as a 'true' value of DOC load, we simulated 1,000 grab sampling campaigns at weekly, fortnightly and monthly frequency to understand the likely distribution of load and error estimates. We also performed an analysis of daily grab samples collected using a pumped storage sampling system with weekly collection. Our results show that: a) grab sampling systemically underestimates DOC loads and gives positively skewed distributions of results, b) this under-estimation and positive skew decreases with increasing sampling frequency, c) commonly used estimates of error in the load value are also systemically lowered by the oversampling of low, stable flows due to their dependence on the variance in the flow-weighted mean concentration, and d) that pumped storage systems may lead to under-estimation of DOC and over estimation of specific ultra-violet absorbance (SUVA), a proxy for aromaticity, due to biodegradation during storage.

CONTEXT Harassing and discriminating behaviors on the part of instructors or supervisors are known to affect the quality of work performed by medical students, influence their career decisions, and have other undetermined long-term consequences. OBJECTIVE To assess the prevalence and forms of harassment and discrimination experienced by 1996 medical school graduates. DESIGN A self-administered survey of harassment and discrimination mailed to graduating medical students. SETTING AND PARTICIPANTS A total of 1001 graduating medical students at 8 US medical schools (4 public and 4 private), chosen from each of the 4 regions designated by the Association of American Medical Colleges for geographic categorization. OUTCOME MEASURE The number of reported experiences of various forms of harassment and discrimination while attending medical school. RESULTS Of 1001 surveys, 548 (55%) were returned. Overall, 46% of the students reported experiencing some form of harassment and 41% some form of discrimination from instructors or supervisors while attending medical school. Nonsexual verbal harassment was reported by 41%; sexual verbal harassment was reported by 10%. Discrimination based on gender was reported by 29% of students; discrimination based on race was reported by 12%. CONCLUSIONS Harassment and discrimination of medical students by instructors and supervisors continue to occur frequently, and new approaches are needed to address these problems.

In November 1994, Oregon became the first US state to legalize physician-assisted suicide (PAS) as an option for end-of-life care.This study compares the attitudes and experiences of medical students in Oregon regarding PAS to those of fourth-year medical students in the United States outside Oregon.A survey of all students at the Oregon Health Sciences University and fourth-year medical students at 3 non-Oregonian US medical schools.Oregon medical students returned 227 questionnaires (58%), and 113 were returned from control schools (33%).A similar percentage of both study groups favored the legalization of PAS (64% vs 66%; P = .74). If the practice were legal, 55% of the total surveyed reported they "might be willing to write a lethal prescription," (50% Oregon students vs 60% control; P = .13 and 44% fourth-year Oregon students vs 60% control; P = .04). Among fourth-year students, 20% reported a request by a patient to the student or a preceptor for a lethal prescription in the past year (26% vs 16%; P = .09).This study demonstrates support for and willingness by many medical students to participate in PAS. Some medical students reported observation of PAS during their training experience. Fourth-year Oregon students reported significantly less willingness than other students to provide a patient with a lethal prescription, perhaps indicating hesitancy to include PAS in clinical practice.

CONTEXT In November 1994, Oregon became the first US state to legalize physician-assisted suicide (PAS) as an option for end-of-life care. OBJECTIVE This study compares the attitudes and experiences of medical students in Oregon regarding PAS to those of fourth-year medical students in the United States outside Oregon. DESIGN A survey of all students at the Oregon Health Sciences University and fourth-year medical students at 3 non-Oregonian US medical schools. PARTICIPANTS Oregon medical students returned 227 questionnaires (58%), and 113 were returned from control schools (33%). RESULTS A similar percentage of both study groups favored the legalization of PAS (64% vs 66%; P = .74). If the practice were legal, 55% of the total surveyed reported they "might be willing to write a lethal prescription," (50% Oregon students vs 60% control; P = .13 and 44% fourth-year Oregon students vs 60% control; P = .04). Among fourth-year students, 20% reported a request by a patient to the student or a preceptor for a lethal prescription in the past year (26% vs 16%; P = .09). CONCLUSIONS This study demonstrates support for and willingness by many medical students to participate in PAS. Some medical students reported observation of PAS during their training experience. Fourth-year Oregon students reported significantly less willingness than other students to provide a patient with a lethal prescription, perhaps indicating hesitancy to include PAS in clinical practice.

A 30-cm-diam mercury ion thruster, using two or three grid ion accelerating systems, is operated at increased values of beam current. Comparisons with the SEP (Solar Electric Propulsion) and EPSEP (Extended Performance SEP) baseline thrusters are made with respect to performance and lifetime. It is found that when a third, or decelerator, grid is added to the conventional two-grid optics of a SEP-like thruster, the ion beam focusing properties are improved, as expected from theoretical considerations. The total thruster efficiency as a function of specific impulse, is increased for values of specific impulse in the range 1200-2800 sec. Lifetime test results predict a thruster lifetime, under space conditions, not less than that of the baseline SEP thruster.

ANEW propulsion concept which may have particular usefulness for transfer of loads from low Earth orbit (LEO) to geosynchronou s Earth orbit (GEO) is presented. Electrical energy in the form of microwaves is used to heat a propellant gas, thus providing thrust. An outline of the concept and experimental results in support of it are presented. Contents A variety of possible future space missions involve the transfer of substantial masses from LEO to GEO. 1 A crucial factor in propulsion systems designed to meet this need is the ratio of total mass required in LEO to payload mass in GEO, due to the fact that Earth-to-orbit cost is a major fraction of total cost. Systems presently considered for such missions include chemical systems and electrostatic ion propulsion systems. Figure 1 presents payload mass ratio as a function of specific impulse for these systems. Chemical systems provide short trip times at the expense of mass ratios of 3 or greater. Electrostatic ion propulsion systems can achieve mass ratios of 1.25-2.5, but require trip times of 50 days or longer. There is an intermediate range of specific impulse not accessible to present systems which would allow moderate trip times while maintaining mass ratios similar to those of electrostatic systems. The free radical propulsion concept presented here may prove capable of operating in that regime. The concept is illustrated schematically in Fig. 2. Electric power from solar panels is used to operate a microwave generator, and microwave energy is coupled to a propellant gas by means of a resonant cavity. The gas is ionized partially by the microwave fields, and inelastic collisions of gas molecules with the resultant electrons serve to dissociate the gas. The gas is allowed to recombine downstream, with the recombination energy heating the gas. The hot gas is expanded through a nozzle to produce thrust. Molecular hydrogen, with a theoretical specific impulse of 2100 s (100% conversion), is the most attractive propellant. Sample calculations on a hydrogen thruster for a thrust of 1 N and a specific impulse of 1500 s yield the following results: mass flow rate, 6.8xlO~ 5 kg/s; minimum input power, 7.3 kW; minimum flow area (nozzle throat), 4x 10 ~2 to 4x 10 ~4 m2 for pressures of 13.3 to 1330 N/m2, respectively; and thrust densities of the order of 100 N/m2. Attractive features of the free radical propulsion concept in comparison to electrostatic ion propulsion or similar systems are increased thrust, thrust density, and thrust-to-power ratio.