Terahertz gyrotrons with quasi-regular cavities
We describe two ways of the use in high-harmonic gyrotrons of quasi-regular cavities with short irregularities formed by the widening of cavity radius. The first one is a significant improvement of the selectivity of the second-harmonic gyrotrons due to the supression of parasitic near-cutoff fundamental-harmonic waves. The second approach is aimed to solve a typical problem of weakly-relativistic high-harmonics gyrotrons, namely, the use of long cavities ensuring extremely high diffraction Q-factors and a great share of Ohmic losses. We propose a quasi-regular cavity with periodic phase correctors, where a far-from-cutoff axial mode with a decreased diffraction Q-factor is excited in a gyrotron-like regime.
Sub-THz gyrotrons with special functions of frequency control for applications to DNP-NMR spectroscopy
Sub-THz gyrotrons with the functions of frequency control are useful for application to high power sub-THz spectroscopy including a DNP enhanced high-sensitive NMR spectroscopy. Continuous frequency tunability, frequency modulation and frequency step-changing will be achieved for our Gyrotron FU CW Series and such special functions of frequency control are applied for additional enhancement of NMR sensitivity. In this paper, it will be presented how such functions are achieved and how about the advantages of them for sensitivity enhancement of NMR spectroscopy.
Experimental study of water fluxes in a residential area: 2. Road infiltration, runoff and evaporation
Lack of accurate data has led some hydrologists and city planners to assume that urban infiltration is zero and runoff is 100% of the rainfall. These assumptions lead to an over estimation of road runoff volume and an underestimation of direct recharge to groundwater, which is already rising under some UK cities. This study investigates infiltration and runoff processes and quantifies the percentage of rainfall that contributes to storm drainage, and that which infiltrates through different types of road surface. Access tubes were installed for measuring soil water content using a neutron probe in three car parks, a road and a grass site at the Centre for Ecology and Hydrology, Crowmarsh Gifford, Wallingford. Storm drainage was recorded at the exit of the Thamesmead Estate in Crowmarsh Gifford, just before the drain joins the River Thames at Wallingford. Rainfall and water table depth were also recorded. Weekly measurements of soil moisture content indicated that the top 40 cm layer is not influenced by water‐table fluctuations and, therefore, positive changes in soil moisture could be attributed to infiltration of rainfall through the surface. Depending on the nature of the surface, subsurface layers, level of traffic, etc., between 6 and 9% of rainfall was found to infiltrate through the road surfaces studied. The storm drainage generated by road runoff revealed a flow pattern similar to that of the receiving watercourse (River Thames) and increased with the increase of infiltration and soil water content below the road surface. The ratio of runoff to rainfall was 0·7, 0·9 and 0·5 for annual, winter (October–March) and summer (April–September) respectively. As the results of the infiltration indicated that 6 to 9% of annual rainfall infiltrates through the road surface, this means that evaporation represents, 21–24% of annual rainfall, with more evaporation taking place during summer than winter. Copyright © 2003 John Wiley & Sons, Ltd.