Review of methods for deriving areal reduction factors

The design of hydraulic structures requires knowledge of how much rain is likely to fall within a certain amount of time, and over a specific area. Point rainfalls are only representative for a very limited area, and for larger areas the areal average rainfall depth is likely to be much smaller than at the point of maximum observed depth. The estimation of areal reduction factors is concerned with the relationship between the point and areal rainfalls. This relationship has been found to vary with, for example, predominant weather type, season and return period. Methods for estimation of areal reduction factors include empirical and analytical methods. The current design guidelines in the United Kingdom are based on an empirical method, but since they were issued in 1975, several new analytical methods have been proposed. These methods are discussed, and recommendations for an update suitable for United Kingdom conditions are made

Large-scale attribution of trend in UK flood flow data

The objective of this study is to undertake a preliminary investigation of trend in annual maximum series of peak flood data in the United Kingdom, as a precursor to developing a more complete procedure for non-stationary flood frequency estimation. A fifth of the trends in series that are at least 20 years long are significant at the 5% level (of in total 388 series). Most of the significant trends are positive, and are located in the north and west. The largest positive trends occur for short records in the most recent decades. Trends were also investigated for various subsets of the data, based on different catchment characteristics. There is an indication that the range of trend values observed for urban catchments is larger than the range observed for the rural subset, and that storage of water, whether in lakes and reservoirs or in permeable geology, has an ameliorating effect on trend magnitude

Simulations of Sisyphus cooling including multiple excited states

We extend the theory for laser cooling in a near-resonant optical lattice to include multiple excited hyperfine states. Simulations are performed treating the external degrees of freedom of the atom, i.e., position and momentum, classically, while the internal atomic states are treated quantum mechanically, allowing for arbitrary superpositions. Whereas theoretical treatments including only a single excited hyperfine state predict that the temperature should be a function of lattice depth only, except close to resonance, experiments have shown that the minimum temperature achieved depends also on the detuning from resonance of the lattice light. Our results resolve this discrepancy.Comment: 7 pages, 6 figure

Redundant actuator development program

Two concepts of redundant secondary actuator mechanization, applicable to future advanced flight control systems, were studied to quantitatively assess their design applicability to an AST. The two actuator concepts, a four-channel, force summed system and a three-channel, active/standby system have been developed and evaluated through analysis, analog computer simulation, and piloted motion simulation. The quantitative comparison of the two concepts indicates that the force summed concept better meet performance requirements, although the active/standby is superior in other respects. Both concepts are viable candidates for advanced control application dependent on the specific performance requirements

Trends and challenges in VLSI technology scaling towards 100 nm

Summary form only given. Moore's Law drives VLSI technology to continuous increases in transistor densities and higher clock frequencies. This tutorial will review the trends in VLSI technology scaling in the last few years and discuss the challenges facing process and circuit engineers in the 100nm generation and beyond. The first focus area is the process technology, including transistor scaling trends and research activities for the 100nm technology node and beyond. The transistor leakage and interconnect RC delays will continue to increase. The tutorial will review new circuit design techniques for emerging process technologies, including dual Vt transistors and silicon-on-insulator. It will also cover circuit and layout techniques to reduce clock distribution skew and jitter, model and reduce transistor leakage and improve the electrical performance of flip-chip packages. Finally, the tutorial will review the test challenges for the 100nm technology node due to increased clock frequency and power consumption (both active and passive) and present several potential solution

Capital Flows, Investment, and Exchange Rates

This paper incorporates international capital flows into a two-country, monetary-general-equilibrium model of asset prices with investment and production. We use the model to calculate theoretical covariances between investment, the current account, the exchange rate, and the terms of trade.These covariances depend upon the coefficient of relative risk-aversion, the magnitude and sign of a country's net international indebtedness, other properties of tastes and technologies, and the stochastic processes on disturbances to productivity and monetary growth rates. International capital flows arise from changes in world wealth and its relative composition in foreign and domestic assets. The dynamic, stochastic relations between capital flows, exchange rates, investment, and the terms of trade are critically dependent on optimal portfolio allocations and the stochastic behavior of asset prices on international financial markets.

Steep Slopes and Preferred Breaks in GRB Spectra: the Role of Photospheres and Comptonization

The role of a photospheric component and of pair breakdown is examined in the internal shock model of gamma-ray bursts. We discuss some of the mechanisms by which they would produce anomalously steep low energy slopes, X-ray excesses and preferred energy breaks. Sub-relativistic comptonization should dominate in high comoving luminosity bursts with high baryon load, while synchrotron radiation dominates the power law component in bursts which have lower comoving luminosity or have moderate to low baryon loads. A photosphere leading to steep low energy spectral slopes should be prominent in the lowest baryon loadComment: ApJ'00, in press; minor revs. 10/5/99; (uses aaspp4.sty), 15 pages, 3 figure