10,556 research outputs found
Origins of the GATT: British Resistance to American Multilateralism
Fiftieth-anniversary explanations for the efficacy of the GATT imply that the institution's longevity is testimony to the free trade principles upon which it is based. In this light, the predominantly American architects of the system figure as free trade visionaries who benevolently imposed postwar institutions of international cooperation on their war-torn allies. This paper takes issue with such a characterization. Instead, the success of the GATT has been crucially dependent upon its ability to generate pragmatic and detailed policy via a uniquely inclusive forum. An effective institutional procedure, not free trade dogma, has proved key to its endurance—and this feature has been in place since the institution's inception.
"Origins of the GATT - British Resistance to American Multilateralism"
Fiftieth-anniversary explanations for the efficacy of the GATT imply that the institution's longevity is testimony to the free trade principles upon which it is based. In this light, the predominantly American architects of the system figure as free trade visionaries who benevolently imposed postwar institutions of international cooperation on their war-torn allies. This paper takes issue with such a characterization. Instead, the success of the GATT has been crucially dependent upon its ability to generate pragmatic and detailed policy via a uniquely inclusive forum. An effective institutional procedure, not free trade dogma, has proved key to its endurance--and this feature has been in place since the institution's inception.
Inventory of Non-Energy Sources of Greenhouse Gas Emissions in Hawaii Phase I
International concern for global climate change has stimulated a wide range of data gathering and analysis efforts worldwide. The recognition that certain atmospheric gases, many of which are anthropogenic in origin, have the capacity to absorb infrared radiation-and thus trap heat in the atmosphere--has focused research efforts on these so-called "greenhouse" gases. In order for a country to assess its contribution to such global warming, it must first develop an emissions inventory of greenhouse gas sources and sinks. In the United States, the U.S. Environmental Protection Agency (EPA) has recently published such an inventory (U.S. EPA, 1994) and has been funding the efforts of each state to develop their own inventories of sources of greenhouse gas emissions (U.S. EPA, 1995, hereafter titled the State Phase I Workbook). It is this latter document which serves as the basis for the present report by providing the bulk of its overall methodology.Clean Air Branch, Department of Health, State of Hawai
Fluorescence of thermal control coatings on S0069 and A0114
Many of the thermal control surfaces exposed to the space environment during the 5.8 year LDEF mission experienced changes in fluorescence. All of the thermal control coatings flown on LDEF experiments S0069 and A0114 were characterized for fluorescence under ambient conditions. Some of the black coatings, having protective overcoats, appear bright yellow under ultraviolet exposure. Urethane based coatings exhibited emission spectra shifts toward longer wavelengths in the visible range. Zinc oxide pigment based coatings experienced a quenching of fluorescence, while zinc orthotitanate pigment based and other ceramic type coatings had no measurable fluorescence
Stochastic Electron Acceleration by Cascading Fast Mode Waves in Impulsive Solar Flares
We present a model for the acceleration of electrons from thermal to ultrarelativistic energies during an energy release fragment in an impulsive solar flare. Long-wavelength low-amplitude fast mode waves are assumed to be generated during the initial flare energy release (by, for example, large-scale restructuring of the magnetic field). These waves nonlinearly cascade to higher wavenumbers and eventually reach the dissipation range, whereupon they are transit-time damped by electrons in the tail of the thermal distribution. The electrons, in turn, are energized out of the tail and into substantially higher energies. We find that for turbulence energy densities much smaller than the ambient magnetic field energy density and comparable to the thermal particle energy density, and for a wide range of initial wavelengths, a sufficient number of electrons are accelerated to hard X-ray-producing energies on observed timescales. We suggest that MHD turbulence unifies electron and proton acceleration in impulsive solar flares, since a preceding study established that a second MHD mode (the shear Alfven wave) preferentially accelerates protons from thermal to gamma-ray line-producing energies
New Promise for Electron Bulk Energization in Solar Flares: Preferential Fermi Acceleration of Electrons over Protons in Reconnection-driven Magnetohydrodynamic Turbulence
The hard X-ray luminosity of impulsive solar flares indicates that electrons in the low corona are bulk energized to energies of order 25 keV. LaRosa & Moore pointed out that the required bulk energization could be produced by cascading MHD turbulence generated by Alfvénic outflows from sites of strongly driven reconnection. LaRosa, Moore, & Shore proposed that the compressive component of the cascading turbulence dissipates into the electrons via Fermi acceleration. However, for this to be a viable electron bulk energization mechanism, the rate of proton energization by the same turbulence cannot exceed the electron energization rate. In this paper we estimate the relative efficiency of electron and proton Fermi acceleration in the compressive MHD turbulence expected in the reconnection outflows in impulsive solar flares. We find that the protons pose no threat to the electron energization. Particles extract energy from the MHD turbulence by mirroring on magnetic compressions moving along the magnetic field at the Alfvén speed. The mirroring rate, and hence the energization rate, is a sensitive function of the particle velocity distribution. In particular, there is a lower speed limit Vmin ≍ VA, below which the pitch-angle distribution of the particles is so highly collapsed to the magnetic field in the frame of the magnetic compressions that there is no mirroring and hence no Fermi acceleration. For coronal conditions, the proton thermal speed is much less than the Alfvén speed and proton Fermi acceleration is negligible. In contrast, nearly all of the electrons are super-Alfvénic, so their pitch-angle distribution is nearly isotropic in the frame of the magnetic compressions. Consequently, the electrons are so vigorously mirrored that they are Fermi accelerated to hard X-ray energies in a few tenths of a second by the magnetic compressions on scales of 105-103 cm in the cascading MHD turbulence. We conclude that dissipation of reconnection-generated MHD turbulence by electron Fermi acceleration plausibly accounts for the electron bulk energization in solar flares
Single-shot gas-phase thermometry using purerotational hybrid femtosecond/picosecond coherent anti-Stokes Raman scattering
High-repetition-rate, single-laser-shot measurements are important for the investigation of unsteady flows where temperature and species concentrations can vary significantly. Here, we demonstrate singleshot, pure-rotational, hybrid femtosecond/picosecond coherent anti-Stokes Raman scattering (fs/ps RCARS) thermometry based on a kHz-rate fs laser source. Interferences that can affect nanosecond (ns) and ps CARS, such as nonresonant background and collisional dephasing, are eliminated by selecting an appropriate time delay between the 100-fs pump/Stokes pulses and the pulse-shaped 8.4-ps probe. A time- and frequency-domain theoretical model is introduced to account for rotational-level dependent collisional dephasing and indicates that the optimal probe-pulse time delay is 13.5 ps to 30 ps. This time delay allows for uncorrected best-fit N2- RCARS temperature measurements with ~1% accuracy. Hence, the hybrid fs/ps RCARS approach can be performed with kHz-rate laser sources while avoiding corrections that can be difficult to predict in unsteady flows
All-diode-pumped quasi-continuous burst-mode laser for extended high-speed planar imaging
An all-diode-pumped, multistage Nd:YAG amplifier is investigated as a means of extending the duration of high-power, burst-mode laser pulse sequences to an unprecedented 30 ms or more. The laser generates 120 mJ per pulse at 1064.3 nm with a repetition rate of 10 kHz, which is sufficient for a wide range of planar laser diagnostics based on fluorescence, Raman scattering, and Rayleigh scattering, among others. The utility of the technique is evaluated for image sequences of formaldehyde fluorescence in a lifted methane–air diffusion flame. The advantages and limitations of diode pumping are discussed, along with long-pulse diode-bar performance characteristics to guide future designs
Hybrid femtosecond/picosecond coherent anti-Stokes Raman scattering for high-speed gas-phase thermometry
We demonstrate hybrid femtosecond/picosecond (fs/ps) coherent anti-Stokes Raman scattering for high-speed thermometry in unsteady high-temperature flames, including successful comparisons with a time- and frequencyresolved theoretical model. After excitation of the N2 vibrational manifold with 100 fs broadband pump and Stokes beams, the Raman coherence is probed using a frequency-narrowed 2:5 ps probe beam that is time delayed to suppress the nonresonant background by 2 orders of magnitude. Experimental spectra were obtained at 500 Hz in steady and pulsed H2–air flames and exhibit a temperature precision of 2.2% and an accuracy of 3.3% up to 2400 K. Strategies for real-time gas-phase thermometry in high-temperature flames are also discussed, along with implications for kilohertz-rate measurements in practical combustion systems
- …