Stochastic analysis of estuarine hydraulics     

R. Willis  B. A. Finney  M. McKee  A. Militello 《Stochastic Environmental Research and Risk Assessment (SERRA)》1989,3(2):71-84

A new methodology is presented for the solution of the stochastic hydraulic equations characterizing steady, one-dimensional estuarine flow. The methodology is predicated on quasi-linearization, perturbation methods, and the finite difference approximation of the stochastic differential operators. Assuming Manning's roughness coefficient is the principal source of uncertainty in the model, stochastic equations are presented for the water depths and flow rates in the estuarine system. Moment equations are developed for the mean and variance of the water depths. The moment equations are compared with the results of Monte Carlo simulation experiments. The results confirm that for any spatial location in the estuary that (1) as the uncertainty in the channel roughness increases, the uncertainty in mean depth increases, and (2) the predicted mean depth will decrease with increasing uncertainty in Manning'sn. The quasi-analytical approach requires significantly less computer time than Monte Carlo simulations and provides explicit  相似文献   

An Explicit Finite Difference Model for Unconfined Aquifers   总被引：2，自引：0，他引：2  

Wen-sen Chu  Robert Willis 《Ground water》1984,22(6):728-734

Most of the current simulation models for unconfined aquifers are based on the assumption that the free surface variation is small so that it can be combined with permeability to reduce the nonlinear Boussinesq equation to a linear partial differential equation (PDE). One of the most obvious reasons for using the linearization assumption is for the ease of numerical solution. This work presents a simpler alternative which permits an easy direct solution of the Boussinesq equation. A forward in time, central in space (FTCS) explicit finite difference method is used in the simulation model. The model was first validated by comparing its results with known analytical solution. It was then applied to an actual situation in which the short-term responses (from pumping) of an unconfined aquifer were simulated. The study shows that the stability of the model can be easily controlled, and because of the simple algorithm used, the code can be expeditiously developed and economically run on smaller machines. Due to the uncertainties in the calibration results, it is recommended here that more data be collected to improve the calibration before the model is used as a real-time simulation tool.  相似文献   

Optical observations of line profile variability in the WN5 star HD 50896     

Linda J. Smith  Allan J. Willis 《Astrophysics and Space Science》1994,221(1-2):189-196

The WN5 star HD 50896 is a well known variable star but the cause of the variations is uncertain. As part of an extensive observing campaign on HD 50896, 68 spectra were obtained with the AAT and UCL echelle spectrograph over three nights in January 1991. The variations seen in the emission line profiles of He II 4686, He II 4860, N V 4945 and N V 4603, 4620, sampling different regions of the wind, are described. Gross night-to-night changes are seen in the tops of all the emission lines, with the pattern of variability being different for each line, as a consequence of the different line formation regions. The edges of the emission line profiles are seen to shift but not in a systematic way, as expected for binary motion. In terms of hourly variations which monitor the propagation of instabilities in the wind, distinct blobs are seen moving outwards through the emission line profiles of the He II lines but are absent in NV 4945. This appears to indicate that, at least for the epoch of these observations, the instabilities develop farther out in the wind than the N V formation region and may well rule out photospheric-induced wind instabilities.  相似文献   

Storms in Space     

David M.  Willis 《Geophysical Journal International》2002,150(3):830-831

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Borehole drainage and its implications for the investigation of glacier hydrology: experiences from Haut Glacier d'Arolla,Switzerland     

Shulamit Gordon  Martin Sharp  Bryn Hubbard  Ian Willis  Chris Smart  Luke Copland  Jon Harbor  Bradley Ketterling 《水文研究》2001,15(5):797-813

Studies of glacier hydrology rely increasingly on measurements made in boreholes as a basis for reconstructing the character and behaviour of subglacial drainage systems. In temperate glaciers, in which boreholes remain open to the atmosphere following drilling, the interpretation of such data may be complicated by supraglacial or englacial water flows to and from boreholes. We report on a suite of techniques used to identify borehole water sources and to reconstruct patterns of water circulation within boreholes at Haut Glacier d'Arolla, Switzerland. Results are used to define a number of borehole ‘drainage’ types. Examples of each drainage type are presented, along with the manner in which they influence interpretations of borehole water‐levels, borehole water‐quality data, and borehole dye traces. The analysis indicates that a full understanding of possible borehole drainage modes is required for the correct interpretation of many borehole observations, and that those observations provide an accurate indication of subglacial conditions only under relatively restricted circumstances. Copyright © 2001 John Wiley & Sons, Ltd.  相似文献   

Transnational Migration and the Politics of Identity – Edited by Meenakshi Thapan     

Katie Willis 《Singapore journal of tropical geography》2007,28(3):364-365

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Sea lice treatments on salmon farms have no adverse effects on zooplankton communities: a case study     

Willis KJ  Gillibrand PA  Cromey CJ  Black KD 《Marine pollution bulletin》2005,50(8):806-816

The long-term effects of the sea lice treatment products Excis and Slice on zooplankton communities in a Scottish sea loch were investigated at a commercially operating salmon farm over 31 months. Cypermethrin and emamectin benzoate are the active ingredients in Excis and Slice respectively, which are widely used to control ectoparasitic sea lice on farmed salmon. Excis and Slice treatments did not cause basin-wide effects on the zooplankton community. For both formulations, no adverse affects on zooplankton were detected, instead observed changes in zooplankton abundance and community composition displayed natural seasonal cycles of abundance. Water column concentrations of cypermethrin and emamectin benzoate following sea lice treatments at the fish farm were predicted using models. Cypermethrin concentrations of 3000 ng/l were predicted for short periods immediately after each cage treatment assuming no particle adhesion. The 3-h and 24-h Environmental Quality Standards (EQS) were exceeded for 10 h and 32 h respectively on the second day when five cages were treated. However, cypermethrin concentrations higher than 0.5 ng/l (24-h EQS) were predicted to occur over <2% of the total basin area on each treatment day. The 3-h EQS (16 ng/l) was exceeded in <0.3% of the basin on each treatment day. The concentration of soluble emamectin benzoate present in the water column was predicted from modelled deposition footprints and sediment concentrations to be of order 10(-3) ng/l. Predicted concentrations of both chemicals were generally lower than those causing toxicity to copepods in previous laboratory studies and further support the results of this field study that environmental concentrations of Excis and Slice do not adversely impact zooplankton communities.  相似文献   

Statistics of the largest sunspot and facular areas per solar cycle     

D. M. Willis  Y. Kabasakal Tulunay 《Solar physics》1979,64(2):237-246

The statistics of extreme values is used to investigate the statistical properties of the largest areas of sunspots and photospheric faculae per solar cycle. The largest values of the synodic-solar-rotation mean areas of umbrae, whole spots and faculae, which have been recorded for nine solar cycles, are each shown to comply with the general form of the extreme value probability function. Empirical expressions are derived for the three extreme value populations from which the characteristic statistical parameters, namely the mode, median, mean and standard deviation, can be calculated for each population. These three extreme value populations are also used to find the expected ranges of the extreme areas in a group of solar cycles as a function of the number of cycles in the group. The extreme areas of umbrae and whole spots have a dispersion comparable to that found by Siscoe for the extreme values of sunspot number, whereas the extreme areas of faculae have a smaller dispersion which is comparable to that found by Siscoe for the largest geomagnetic storm per solar cycle. The expected range of the largest sunspot area per solar cycle for a group of one hundred cycles appears to be inconsistent with the existence of the prolonged periods of sunspot minima that have been inferred from the historical information on solar variability. This inconsistency supports the contention that there are temporal changes of solar-cycle statistics during protracted periods of sunspot minima (or maxima). Indeed, without such temporal changes, photospheric faculae should have been continually observable throughout the lifetime of the Sun.  相似文献   

Physical adsorption of hydrogen on interstellar graphite grain surfaces     

R. F. Willis  B. Fitton 《Astrophysics and Space Science》1975,34(1):57-71

We review existingsingle-particle theories concerning parameters of importance which determine the kinetics of hydrogen molecule formation and ejection from cold (T _gr?20K) graphite grain surfaces. The nature of thesingle-particle quantum states of low mass gas atoms and molecules in a periodic surface lattice potential is considered. Contributions to the physical adsorption potential due to dynamic polarizability effects arising from thelong-range collective valence-electron charge-density oscillations (plasmons) of the substrate are discussed.Short-range electron correlation effects at the surface may lead to the formation of a ‘quasimolecular state’ of adsorbed H₂ with a bond length ～3.5 Å and a reduced bond energy ～0.075 eV. It is proposed, that one consequence of this dynamical screening of the adsorbed molecules is that they are ejected normal to the grain surface with velocities ?20 km s^?1 and not necessarily in a high vibrational state. Similar dynamical effects could be important in determining activation processes and long-range ordering in monolayer films of adsorbed H₂. The astrophysical consequences of thesemany-body effects are discussed in the light of recent experimental and observational results.  相似文献   

The Microstructure of the Magnetopause     

D. M. Willis 《Geophysical Journal International》1975,41(3):355-389

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