A second-order global solution of the ideal resonance problem     

Boris Garfinkel  Carol A. Williams 《Celestial Mechanics and Dynamical Astronomy》1974,9(1):105-125

The Ideal Resonance Problem, as formulated in 1966 (Paper I), is defined by the Hamiltonian Following the procedure adopted in the construction of a first-orderglobal solution (Papers II, III, and V), we derive a second-order solution from the von Zeipel-Bohlin recursive algorithm of Paper II. The singularities inherent in the Bohlin expansion in powers of μ have been suppressed by means of theregularizing function of Paper III, and the singularities in the coefficients atAB″=0 have been removed by thenormalization technique of Paper V. As a check, it is shown that the global solution includes asymptotically theclassical solution, expanded in powers ofμ ², and carrying thecritical divisor B′.  相似文献   

Preface     

Julio A. Fernández  Allan W. Harris  Iwan P. Williams 《Earth, Moon, and Planets》2005,97(3-4):177-99

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On the reduction of certain integrals occurring in Kopal's fourier theory of eclipsing binaries     

Igor Jurkevich  Williams B. Heard 《Astrophysics and Space Science》1977,52(1):237-238

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Drivers of afforestation in Northern Vietnam: Assessing local variations using geographically weighted regression   总被引：2，自引：0，他引：2  

Floriane Clement  Didier Orange  Meredith Williams  Corinne Mulley  Michael Epprecht 《Applied geography (Sevenoaks, England)》2009,29(4):561-576

This article identifies drivers of forest transition in a province of Northern Vietnam between 1993 and 2000 by applying geographically weighted regression (GWR) analysis to remotely sensed and statistical data. The regression model highlighted the spatial variation of the relationship between the percentage of land afforested and its proximate causes. Factors identified as having a major impact on afforestation are: the presence or proximity of a wood-processing industry, the distance to highways, and land allocation to households. Whereas the two former variables are in most areas of the province positively correlated with afforestation, an unexpected negative correlation was observed for the latter. The analysis of these results, supported by an in-depth knowledge of the area and of the political context, leads to the conclusion that, during the time period considered, afforestation was largely driven by state organisations on protected state-owned land, and forestry was not a significant component of household economic activities.  相似文献   

Measurements of meteor smoke particles during the ECOMA-2006 campaign: 2. Results     

Irina Strelnikova  Markus Rapp  Boris Strelnikov  Gerd Baumgarten  Alvin Brattli  Knut Svenes  Ulf-Peter Hoppe  Martin Friedrich  Jörg Gumbel  Bifford P. Williams 《Journal of Atmospheric and Solar》2009,71(3-4):486-496

The first sounding rocket of the European ECOMA-project (ECOMA, Existence and Charge state Of Meteoric smoke particles in the middle Atmosphere) was launched on 8 September 2006. Measurements with a new particle detector described in the companion paper by Rapp and Strelnikova [2008. Measurements of meteor smoke particles during the ECOMA-2006 campaign: 1. Particle detection by active photoionization. Journal of Atmospheric and Solar-Terrestrial Physics, this issue, doi:10.1016/j.jastp.2008.06.002] clearly showed meteor smoke particle (MSP) signatures in both data channels. The data channels measure particles directly impacting on the detector electrode and photoelectrons from the particles actively created using ionization by the UV-photons of a xenon-flashlamp. Measured photoelectron currents resemble model expectations of the shape of the MSP layer almost perfectly, whereas derived number densities in the altitude range 60–90 km are larger than model results by about a factor of 5. Given the large uncertainties inherent to both model and the analysis of our measurements (e.g., the composition of the particles is not known and must be assumed) we consider this a satisfactory agreement and proof that MSPs do extend throughout the entire mesosphere as predicted by models. The measurements of direct particle impacts revealed a confined layer of negative charge between 80 and 90 km. This limited altitude range, however, is quantitatively shown to be the consequence of the aerodynamics of the rocket flight and does not have any geophysical origin. Measured charge signatures are consistent with expectations of particle charging given our own measurements of the background ionization. Unfortunately, however, a contamination of these measurements from triboelectric charging cannot be excluded at this stage.  相似文献   

Fire effects on rangeland hydrology and erosion in a steep sagebrush‐dominated landscape     

Frederick B. Pierson  Peter R. Robichaud  Corey A. Moffet  Kenneth E. Spaeth  Stuart P. Hardegree  Patrick E. Clark  C. Jason Williams 《水文研究》2008,22(16):2916-2929

Post‐fire runoff and erosion from wildlands has been well researched, but few studies have researched the degree of control exerted by fire on rangeland hydrology and erosion processes. Furthermore, the spatial continuity and temporal persistence of wildfire impacts on rangeland hydrology and erosion are not well understood. Small‐plot rainfall and concentrated flow simulations were applied to unburned and severely burned hillslopes to determine the spatial continuity and persistence of fire‐induced impacts on runoff and erosion by interrill and rill processes on steep sagebrush‐dominated sites. Runoff and erosion were measured immediately following and each of 3 years post‐wildfire. Spatial and temporal variability in post‐fire hydrologic and erosional responses were compared with runoff and erosion measured under unburned conditions. Results from interrill simulations indicate fire‐induced impacts were predominantly on coppice microsites and that fire influenced interrill sediment yield more than runoff. Interrill runoff was nearly unchanged by burning, but 3‐year cumulative interrill sediment yield on burned hillslopes (50 g m^?2) was twice that of unburned hillslopes (25 g m^?2). The greatest impact of fire was on the dynamics of runoff once overland flow began. Reduced ground cover on burned hillslopes allowed overland flow to concentrate into rills. The 3‐year cumulative runoff from concentrated flow simulations on burned hillslopes (298 l) was nearly 20 times that measured on unburned hillslopes (16 l). The 3‐year cumulative sediment yield from concentrated flow on burned and unburned hillslopes was 20 400 g m^?2 and 6 g m^?2 respectively. Fire effects on runoff generation and sediment were greatly reduced, but remained, 3 years post‐fire. The results indicate that the impacts of fire on runoff and erosion from severely burned steep sagebrush landscapes vary significantly by microsite and process, exhibiting seasonal fluctuation in degree, and that fire‐induced increases in runoff and erosion may require more than 3 years to return to background levels. Published in 2008 by John Wiley & Sons, Ltd.  相似文献   

Axisymmetric annulus convection at unit Prandtl number     

Gareth P. Williams 《地球物理与天体物理流体动力学》2013,107(3-4):357-369

Abstract

We examine the role played in annulus flows by mechanisms dependent upon the Prandtl number, σ. Solutions are obtained at σ = 1 for both the real annulus system and for the hypothetical “free annulus” system (free slip lateral boundaries). These solutions are compared with previously obtained solutions at σ = 7.

In the free annulus, the solution at σ = 1 differs radically from that at σ = 7. The σ = 1 solution appears to be essentially a finite amplitude mode due to Solberg instability whereas the solution at σ = 7 manifests a flow caused by the diffusive overturning mechanism.

The variation with σ of the real annulus flow is not so fundamental but some differences in the dynamical structures are noted.  相似文献   

Geochemical,mineralogical and microbiological characteristics of sediment from a naturally reduced zone in a uranium-contaminated aquifer     

K.M. Campbell  R.K. Kukkadapu  N.P. Qafoku  A.D. Peacock  E. Lesher  K.H. Williams  J.R. Bargar  M.J. Wilkins  L. Figueroa  J. Ranville  J.A. Davis  P.E. Long 《Applied Geochemistry》2012

Localized zones or lenses of naturally reduced sediments have the potential to play a significant role in the fate and transport of redox-sensitive metals and metalloids in aquifers. To assess the mineralogy, microbiology and redox processes that occur in these zones, several cores from a region of naturally occurring reducing conditions in a U-contaminated aquifer (Rifle, CO) were examined. Sediment samples from a transect of cores ranging from oxic/suboxic Rifle aquifer sediment to naturally reduced sediment were analyzed for U and Fe content, oxidation state, and mineralogy; reduced S phases; and solid-phase organic C content using a suite of analytical and spectroscopic techniques on bulk sediment and size fractions. Solid-phase U concentrations were higher in the naturally reduced zone, with a high proportion of the U present as U(IV). The sediments were also elevated in reduced S phases and Fe(II), indicating it is very likely that U(VI), Fe(III), and SO₄ reduction has occurred or is occurring in the sediment. The microbial community was assessed using lipid- and DNA-based techniques, and statistical redundancy analysis was performed to determine correlations between the microbial community and the geochemistry. Increased concentrations of solid-phase organic C and biomass in the naturally reduced sediment suggests that natural bioreduction is stimulated by a zone of increased organic C concentration associated with fine-grained material and lower permeability to groundwater flow. Characterization of the naturally bioreduced sediment provides an understanding of the natural processes that occur in the sediment under reducing conditions and how they may impact natural attenuation of radionuclides and other redox sensitive materials. Results also suggest the importance of recalcitrant organic C for maintaining reducing conditions and U immobilization.  相似文献   

The surface energy balance at the Huygens landing site and the moist surface conditions on Titan     

Kaj E. Williams  Christopher P. McKay  Fredrik Persson 《Planetary and Space Science》2012,60(1):376-385

The Huygens Probe provided a wealth of data concerning the atmosphere of Titan. It also provided tantalizing evidence of a small amount of surface liquid. We have developed a detailed surface energy balance for the Probe landing site. We find that the daily averaged non-radiative fluxes at the surface are 0.7 W m^?2, much larger than the global average value predicted by McKay et al. (1991) of 0.037 W m^?2. Considering the moist surface, the methane and ethane detected by the Probe from the surface is consistent with a ternary liquid of ethane, methane, and nitrogen present on the surface with mole fractions of methane, ethane, and nitrogen of 0.44, 0.34, and 0.22, respectively, and a total mass load of ～0.05 kg m^?2. If this liquid is included in the surface energy balance, only a small fraction of the non-radiative energy is due to latent heat release (～10^?3 W m^?2). If the amount of atmospheric ethane is less than 0.6×10^?5, the surface liquid is most likely evaporating over timescales of 5 Titan days, and the moist surface is probably a remnant of a recent precipitation event. If the surface liquid mass loading is increased to 0.5 kg m^?2, then the liquid lifetime increases to ～56 Titan days. Our modeling results indicate a dew cycle is unlikely, given that even when the diurnal variation of liquid is in equilibrium, the diurnal mass variation is only 3% of the total liquid. If we assume a high atmospheric mixing ratio of ethane (>0.6×10^?5), the precipitation of liquid is large (38 cm/Titan year for an ethane mixing ratio of 2×10^?5). Such a flux is many orders of magnitude in excess of the photochemical production rate of ethane.  相似文献   

Effects of tunnelling on existing support systems of perpendicularly crossing tunnels     

H.Y. Liu  J.C. Small  J.P. Carter  D.J. Williams 《Computers and Geotechnics》2009

The interactions between perpendicularly crossing tunnels in the Sydney region are investigated using a full three-dimensional (3D) finite element analysis coupled with elasto-plastic material models. Special attention is paid to the effect of subsequent tunnelling on the support system, i.e. the shotcrete lining and rock bolts, of the existing tunnel. The results of the analysis show that in a region such as Sydney, with relatively high horizontal stresses, installation of the new tunnel causes the shotcrete lining of the existing tunnel to be in tension in the side facing towards the tunnel opening and in compression at the crown and invert. The pre-stressed rock bolts are usually tensioned more in the sections closest to the tunnel opening. For this particular study, if a new tunnel is driven perpendicularly beneath an existing tunnel, significant increases are induced in the bending moments in the shotcrete lining at the lateral sides of the existing tunnel and in the axial forces at its crown and invert. The increase in side bending moments causes further tensile cracking but the crown and invert stresses remain within the thresholds for both compressive failure and tensile cracking for shotcrete lining of typical concrete quality. Moreover, the driving of the new tunnel causes the tensile forces in the existing side rock bolts to increase and those in the existing crown rock bolts to decrease. In contrast, if the new tunnel is driven perpendicularly above the existing tunnel, compressive failure of the existing shotcrete lining is induced at the crown of the deeper tunnel for concrete of typical capacity and a significant tensile force increase of the existing rock bolts around the crown. It is concluded that in order to ensure the stability of the existing tunnel, local thickening is needed at the sides of the existing shotcrete lining if the shallow tunnel is installed first and local thickening is needed at the crown if the deep tunnel is installed first.  相似文献