Optical follow-up of GRB 970508

We report on the results of optical follow-up observations of the counterpart of the gamma-ray burst GRB 970508, starting 7 hr after the event. Multicolor U-, B-, V-, R-c-, and I-c-band observations were obtained during the first three consecutive nights. The counterpart was monitored regularly in R-c, until similar to 4 months after the burst. The light curve after the maximum follows a decline that can be fitted with a power law with exponent alpha = -1.141 +/- 0.014. Deviations from a smooth power-law decay are moderate (rms = 0.15 mag). We find no flattening of the light curve at late times. The optical afterglow fluence is a significant fraction, similar to 5%, of the GRB fluence. The optical energy distribution can be well represented by a power law, the slope of which changed at the time of the maximum (the spectrum became redder).

Environmental pricing of externalities from different sources of electricity generation in Chile

The rapid increase in electricity demand in Chile means a choice must be made between major investments in renewable or non-renewable sources for additional production. Current projects to develop large dams for hydropower in Chilean Patagonia impose an environmental price by damaging the natural environment. On the other hand, the increased use of fossil fuels entails an environmental price in terms of air pollution and greenhouse gas emissions contributing to climate change. This paper studies the debate on future electricity supply in Chile by investigating the preferences of households for a variety of different sources of electricity generation such as fossil fuels, large hydropower in Chilean Patagonia and other renewable energy sources. Using Double Bounded Dichotomous Choice Contingent Valuation, a novel advanced disclosure method and internal consistency test are used to elicit the willingness to pay for less environmentally damaging sources. Policy results suggest a strong preference for renewable energy sources with higher environmental prices imposed by consumers on electricity generated from fossil fuels than from large dams in Chilean Patagonia. Policy results further suggest the possibility of introducing incentives for renewable energy developments that would be supported by consumers through green tariffs or environmental premiums. Methodological findings suggest that advanced disclosure learning overcomes the problem of internal inconsistency in SB-DB estimates.

TEMPORALLY AND SPATIALLY-RESOLVED PLASMA PARAMETERS AND EEDF MEASUREMENTS IN A LOW-FREQUENCY DISCHARGE

A time-resolved Langmuir probe technique is used to measure the dependence of the electron density, electron temperature, plasma potential and electron energy distribution function (EEDF) on the phase of the driving voltage in a RF driven parallel plate discharge. The measurements were made in a low-frequency (100-500 kHz), symmetrically driven, radio frequency discharge operating in H-2, D-2 and Ar at gas pressures of a few hundred millitorr. The EEDFs could not be represented by a single Maxwellian distribution and resembled the time averaged EEDFs reported in 13.56 MHz discharges. The measured parameters showed structure in their spatial and temporal dependence, generally consistent with a simple oscillating sheath model. Electron temperatures of less than 0.1 eV were measured during the phase of the RF cycle when both electrodes are negative with respect to the plasma.

ENHANCED VOLUME PRODUCTION OF NEGATIVE-IONS IN THE POST DISCHARGE OF A MULTICUSP HYDROGEN DISCHARGE

In this paper we demonstrate a new concept in the production of negative hydrogen ions in a low-pressure multicusp discharge. The discharge voltage is modulated to produce a non-Maxwellian, hot-electron plasma during the current pulse, followed by a cool Maxwellian electron plasma in the post discharge. This procedure, of separating in time the required hot and cold electron plasmas required for volume H- production, is called a temporal filter. The time evolution of the electron energy distribution function is measured using the time-resolved second derivative of a Langmuir probe characteristic. Time-resolved measurements of the negative ion density are made using laser photodetachment. The measurements show that the negative ion density in the center of the source, at a gas pressure of 0.07 Pa, increases by a factor of 2 when the discharge is switched off. At this low pressure the average H- beam current extracted from the source, when operated with a discharge current of 1 A in the pulse modulated mode exceeds the H- beam current from a 5 A continuously operated source. The increase in efficiency of the pulsed source is explained in terms of a two-step H- production mechanism.

Enhancement of positron annihilation on molecules due to vibrational Feshbach resonances

The zero-range potential model is used to investigate positron collisions and annihilation with molecules. The Kr dimer is considered as an example. It is shown that (i) although positrons do not bind to individual Kr atoms, they do form bound states with Kr. (ii) A sequence of vibrationally excited states of the positron-molecule complex extends into the positron continuum, where it manifests as vibrational Feshbach resonances. (iii) These resonances give a very large contribution to the positron annihilation rate. Even after averaging over the thermal positron energy distribution, the contribution of the lowest Feshbach resonance exceeds that of the non-resonant background by an order of magnitude. © 2002 Elsevier Science B.V. All rights reserved.

Addressing the technical and market challenges to high wind power integration in Ireland

Over the last decade there has been a rapid global increase in wind power stimulated by energy and climate policies. However, as wind power is inherently variable and stochastic over a range of time scales, additional system balancing is required to ensure system reliability and stability. This paper reviews the technical, policy and market challenges to achieving ambitious wind power penetration targets in Ireland’s All-Island Grid and examines a number of measures proposed to address these challenges. Current government policy in Ireland is to address these challenges with additional grid reinforcement, interconnection and open-cycle gas plant. More recently smart grid combined with demand side management and electric vehicles have also been presented as options to mitigate the variability of wind power. In addition, the transmission system operators have developed wind farm specific grid codes requiring improved turbine controls and wind power forecasting techniques.

EMAS and ISO 14001 in the German industry – complements or substitutes?

The two environmental management system (EMS) standards EMAS and ISO 14001 have been available in Europe for the last 15 years. ISO 14001 has been taken up at a much larger scale but many firms in the German automotive and engineering industry have certified their EMSs according to both standards. Two research questions are addressed: (i) What explains why companies adopt both EMAS and ISO 14001? (ii) Are EMAS and ISO 14001 complements or substitutes? Based on 21 interviews with industrial and institutional representatives, this study finds that, first, the two standards are adopted for completely different reasons: while ISO 14001 is often done as a response to external pressure, EMAS tends to be motivated internally. Second, it is argued that EMAS and ISO 14001 are likely in a situation of direct competition at present which may well turn into complementarity in the future.

Analysis of Two-Speed Wind Farm Operation From Grid-Side Measurements

This paper analyzes data captured by a phasor measurement unit at a wind farm, employing two-speed induction generators, and investigates aspects of the control system's interaction with the power system. Composite superimposed transient events are proposed as a method to improve the quality of the analysis and reduce errors caused by unknowns, such as wind speed variation. A Mathworks SimPowerSystems model validates the inertia contribution of the wind farm, which is an important parameter in power systems with high wind penetration. Transients caused by turbine speed transitions are identified and explained. The analysis also highlights areas where wind farm control should be improved if useful inertia contribution is to be provided.