Experimental demonstration of a W-band gyroklystron amplifier

The experimental demonstration of a four cavity W-band (93 GHz) gyroklystron amplifier is reported. The gyroklystron has produced 67 kW peak output power and 28% efficiency in the TE011 mode using a 55 kV, 4.3 A electron beam. The full width at half maximum instantaneous bandwidth is greater than 460 MHz, a significant increase over the bandwidth demonstrated in previous W-band gyroklystron amplifier experiments. The amplifier is unconditionally stable at this operating point. Experimental results are in good agreement with theoretical predictions

Harmonic operation of a free-electron laser

Harmonic operation of a free-electron-laser amplifier is studied. The key issue investigated here is suppression of the fundamental. For a tapered amplifier with the right choice of parameters, it is found that the presence of the harmonic mode greatly reduces the growth rate of the fundamental. A limit on the reflection coefficient of the fundamental mode that will ensure stable operation is derived. The relative merits of tripling the frequency by operating at the third harmonic versus decreasing the wiggler period by a factor of 3 are discussed

Arctic HYCOS – 1st Workshop on Improved Monitoring, Accuracy and Data Availability in the Arctic Drainage Basin: Meeting Summary Report and Implementation Plan

The World Hydrological Cycle Observing System (WHYCOS) is a global programme, developed in response to the scarcity or absence of accurate, timely and accessible data and information in real or near real time on freshwater resources in many parts of the world. The programme is implemented through various components (HYCOSs) at the regional and/or basin scale. It is guided by the WHYCOS International Advisory Group (WIAG). The Arctic-HYCOS program is being promoted through this Workshop. For more information on the WHYCOS, please see http://www.whycos.org/cms/. The main goal of the Arctic-HYCOS program is to improve monitoring, data accuracy, availability and dissemination of information in the pan-arctic drainage basin. This project is science-driven and is aimed at monitoring freshwater fluxes and pollutants into the Arctic Ocean with the objective of improving climate predictions in the Northern Hemisphere and assessing the pollution of the Arctic coastal areas and the open Arctic Ocean. Arctic-HYCOS is currently organized along three main activities. 1. Develop and optimal design fro hydro-meteorological monitoring networks to capture the essential variability of the Arctic hydrological system and to enable accurate and efficient assessment of change 2. Estimate uncertainty of available in situ and possible remote sensing data including analysis of accuracy and systematic errors of new observation technology 3. Develop an integrated pan-arctic data consolidation and analysis system for the water cycle uniting data from various in-situ and other sources

High power operation of an X-band gyrotwistron

We report the first experimental verification of a gyrotwistron amplifier. The device utilized a single 9.858 GHz, TE011 cavity, a heavily attenuated drift tube, and a long tapered output waveguide section. With a 440 kV, 200-245 A, 1 μs electron beam and a sharply tapered axial magnetic field, peak powers above 21 MW were achieved with a gain near 24 dB. Performance was limited by competition from a fundamental TE11 mode. A multimode code was developed to analyze this system, and simulations were in good agreement with the experiment

Particle Dark Energy

We explore the physics of a gas of particles interacting with a condensate that spontaneously breaks Lorentz invariance. The equation of state of this gas varies from 1/3 to less than -1 and can lead to the observed cosmic acceleration. The particles are always stable. In our particular class of models these particles are fermions with a chiral coupling to the condensate. They may behave as relativistic matter at early times, produce a brief period where they dominate the expansion with w<0 today, and behave as matter at late time. There are no small parameters in our models, which generically lead to dark energy clustering and, depending on the choice of parameters, smoothing of small scale power.Comment: 8 pages, 5 figures; minor update with added refs; version appearing in Phys. Rev.

Post-decisional accounts of biases in confidence

Most models of decision-making suggest that confidence, the 'feeling of knowing' that accompanies our choices, is constructed as the decision unfolds. However, more recent studies have noted that processes occurring after we commit to a particular choice also affect this subjective belief. This leads to the following question: when are we better judges of ourselves? If, after a decision, evidence continues to accumulate in an unbiased manner, then our confidence judgements should improve. Conversely, if post-decisional information processing is biased, our sense of confidence could be distorted, and so our confidence judgements should degrade with time. We briefly discuss recently proposed models of post-decisional evidence accumulation, and explore whether, and how, biases in confidence could arise

Efficient operation of a high-power X-band gyroklystron

Experimental studies of amplification in a two-cavity X-band gyroklystron are reported. The system utilizes a thermionic magnetron injection gun at voltages up to 440 kV and currents up to 190 A in 1-μs pulses. Optimum performance is achieved by tapering the magnetic-field profile. Peak powers of 20 MW in the TE01 mode at 9.87 GHz are measured with calibrated crystals and with methanol calorimetry. Resultant efficiencies are in excess of 31% and large-signal gains surpass 26 dB. The experimental results are in good agreement with simulated results from a partially self-consistent, nonlinear, steady-state code

Field Measurements of Penetrator Seismic Coupling in Sediments and Volcanic Rocks

Field experiments were conducted to determine how well a seismometer installed using a penetrator would be coupled to the ground. A dry-lake bed and a lava bed were chosen as test sites to represent geological environments of two widely different material properties. At each site, two half-scale penetrators were fired into the ground, a three-component geophone assembly was mounted to the aft end of each penetrator, and dummy penetrators were at various distances to generate seismic signals. These signals were detected by the penetrator-mounted geophone assembly and by a reference geophone assembly buried or anchored to surface rock and 1-m from the penetrator. The recorded signals were digitized, and cross-spectral analyses were performed to compare the observed signals in terms of power spectral density ratio, coherence, and phase difference. The analyses indicate that seismometers deployed by penetrators will be as well coupled to the ground as are seismometers installed by conventional methods for the frequency range of interest in earthquake seismology

Nutrition planning and policy for African countries: summary report of a seminar held 2-19 June, 1976

This paper is the summary report of a seminar which was held at the Institute for Development Studies from 2 to 19 June 1976, The seminar was sponsored by USAID through a contract to Cornell University in Ithaca, New York. Participants were government officers and employees of nongovernment agencies from ten English-speaking African countries whose responsibilities are clearly related to nutrition planning and policy making. The report includes short summaries of the sessions conducted by the seminar staff members. Some of these sessions were devoted to the salient nutritional problems of Africa and their complex causes, to sociocultural factors that influence the condition and its alleviation, and to the basic economic considerations relating to the cause and control of malnutrition and food shortages. However, much more time was devoted to planning and policy relating to nutrition. The participants formed working groups and prepared short reports on nutrition planning for Tanzania's Ujamaa villages, on nutrition activities and goals in Kenya, on increased wheat consumption and the trend toward bottle feeding in West Africa, and on nutrition actitivities in the Sudan. The working group reports are also included in this paper