A recycle flow flotation machine model     

C.C Harris  A Chakravarti  S.N Degaleesan 《International Journal of Mineral Processing》1975,2(1):39-58

Residence time measurements were made on a Denver laboratory flotation machine with and without the DR ring assembly. Soluble and insoluble tracers were used (a dye and fine quartz, respectively), and the variables studied were tank liquid volume, $\text{V}$, water and air volumetric flow rates, Q and Q_A respectively, and some geometric and design variables.By analogy with nominal residence time, $\text{t}{}_{\mathrm{<mtext>N</mtext>}}\text{(=}\text{V}\text{Q}\text{)}$, a term “effective residence time” $\text{t}{}_{\mathrm{<mtext>E</mtext>}}$ is defined by: where f(t) is the fraction of tracer remaining in the tank at time t. Perfect mixing is indicated if and only if: (i) data satisfies the exponential relationship; and (ii) $\text{t}{}_{\mathrm{<mtext>E</mtext>}}\text{t}{}_{\mathrm{<mtext>N</mtext>}}\text{= 1}$.Using the soluble tracer the machine behaved substantially as a perfect mixer under all operating conditions, except with the DR ring at values of Q_A nearly double the natural aeration capacity of the machine; condition (i) above was satisfied, but $\text{t}{}_{\mathrm{<mtext>E</mtext>}}\text{t}{}_{\mathrm{<mtext>N</mtext>}}\text{～ 1.1}$.With the insoluble tracer the machine behaved as a perfect mixer only without air. As Q_A increased, $\text{t}{}_{\mathrm{<mtext>E</mtext>}}\text{t}{}_{\mathrm{<mtext>N</mtext>}}$ increased from unity to about 1.2, and the effect was emphasized by the DR ring. In all cases condition (i) above was satisfied.A model in which the flow pattern in the tank includes a large component of pulp recirculation through the impeller region is developed. This model can account for the experimental findings but the details remain to be elucidated.  相似文献   

The petrology and petrogenesis of some muscovite granite sills from the Barousse Massif,Central Pyrenees     

N. B. W. Harris 《Contributions to Mineralogy and Petrology》1974,45(3):215-230

The mineralogy, petrology and Rb-Sr isotope compositions of muscovite granite sills and associated pegmatites from the Barousse Massif, Central Pyrenees, are described. The petrogenesis of the granites is discussed with respect to their structure, mineral assemblages, mineral compositions and initial ⁸⁷Sr/⁸⁶Sr ratio. It is concluded that the muscovite granite sills have been intruded as magma, formed from the partial melting of continental crust at 276 million years. Progressive crystallisation of the siliceous magma has concentrated the aqueous phase in the remaining melt, and the associated pegmatites are the final expression of the crystallising intrusion.  相似文献   

Studies of the reaction between diamond and heated kimberlite     

Dr. J. W. Harris  Dr. E. R. Vance 《Contributions to Mineralogy and Petrology》1974,47(4):237-244

At temperatures above about 1100° C degassed molten kimberlites were found to attack diamond, producing both graphite and metallic iron on the diamond surface. Using ordinary kimberlites in experiments performed at 1 Kb in a closed system, diamonds developed etch features (at temperatures above about 1000° C), consistent with attack by wet CO₂, but no graphite or iron was formed on the surfaces of the diamonds.  相似文献   

Induced graphitisation around crystalline inclusions in diamond     

J. W. Harris  E. R. Vance 《Contributions to Mineralogy and Petrology》1972,35(3):227-234

In an external vacuum and at temperatures between 900° C and 1650° C internal graphitisation takes place on or around mineral inclusions in diamond, and appears to be responsible for similar features previously reported in diamond from several localities. Several mechanisms are proposed and discussed for internal graphitisation at temperatures as low as 900° C: it is proposed that at low external pressures CO₂ exsolves from inclusions and causes internal graphitisation. The results also indicate that immediately after pressure release arising from volcanic breakthrough of kimberlites of different geological ages at several localities in West and South Africa, the temperature was not in excess of 800° C to 900° C in certain regions of the diatremes.  相似文献   

Amazonian forest dieback under climate-carbon cycle projections for the 21st century   总被引：10，自引：0，他引：10  

P. M. Cox  R. A. Betts  M. Collins  P. P. Harris  C. Huntingford  C. D. Jones 《Theoretical and Applied Climatology》2004,78(1-3):137-156

Summary The first GCM climate change projections to include dynamic vegetation and an interactive carbon cycle produced a very significant amplification of global warming over the 21st century. Under the IS92a business as usual emissions scenario CO₂ concentrations reached about 980ppmv by 2100, which is about 280ppmv higher than when these feedbacks were ignored. The major contribution to the increased CO₂ arose from reductions in soil carbon because global warming is assumed to accelerate respiration. However, there was also a lesser contribution from an alarming loss of the Amazonian rainforest. This paper describes the phenomenon of Amazonian forest dieback under elevated CO₂ in the Hadley Centre climate-carbon cycle model.  相似文献   

A Note on Second Species Solutions Generated from p–q Resonant Orbits     

Esther Barrabés  Gerard Gómez 《Celestial Mechanics and Dynamical Astronomy》2004,88(3):229-244

The first image under the flow of the restricted three-body problem of the p—q resonant strips — that appear in the study of the p—q resonant orbits — do not have, in general, intersection with the strip. In this paper we show some particular situations in which the above intersections exist for some very simple p—q resonant orbits which, at the same time, are periodic second species solutions.This revised version was published online in October 2005 with corrections to the Cover Date.  相似文献   

Three-Dimensional p–q Resonant Orbits Close to Second Species Solutions     

Esther Barrabés  Gerard Gómez 《Celestial Mechanics and Dynamical Astronomy》2003,85(2):145-174

The purpose of this paper is to study, for small values of , the three-dimensional p–q resonant orbits that are close to periodic second species solutions (SSS) of the restricted three-body problem. The work is based on an analytic study of the in- and out-maps. These maps are associated to follow, under the flow of the problem, initial conditions on a sphere of radius around the small primary, and consider the images of those initial points on the same sphere. The out-map is associated to follow the flow forward in time and the in-map backwards. For both mappings we give analytical expressions in powers of the mass parameter. Once these expressions are obtained, we proceed to the study of the matching equations between both, obtaining initial conditions of orbits that will be 'periodic' with an error of the order ^1–, for some (1/3,1/2). Since, as 0, the inner solution and the outer solution will collide with the small primary, these orbits will be close to SSS.  相似文献   

Morphology and geotechnique of active-layer detachment failures in discontinuous and continuous permafrost, northern Canada   总被引：3，自引：1，他引：3  

Antoni G. Lewkowicz  Charles Harris 《Geomorphology》2005,69(1-4):275-297

Fifty active-layer detachment failures triggered after forest fire in the discontinuous permafrost zone (central Mackenzie Valley, 65° N.) are compared to several hundred others caused by summer meteorological triggers in continuous permafrost (Fosheim Peninsula, Ellesmere Island, 80°N). Most failures fall into compact or elongated morphological categories. The compact type occur next to stream channels and have little internal disturbance of the displaced block, whereas the elongated types can develop on any part of the slope and exhibit greater internal deformation. Frequency distributions of length-to-width and length-to-depth ratios are similar at all sites. Positive pore pressures, expected theoretically, were measured in the field at the base of the thawing layer. Effective stress analysis could predict the instability of slopes in both areas, providing cohesion across the thaw plane was set to zero and/or residual strength parameters were employed. The location of the shear planes or zones in relation to the permafrost table and the degree of post-failure secondary movements (including headwall recession and thermokarst development within the failure track) differed between the localities, reflecting dissimilarity in the environmental triggers and in the degree of ground thermal disturbance.  相似文献   

The role of ecosystem-atmosphere interactions in simulated Amazonian precipitation decrease and forest dieback under global climate warming   总被引：2，自引：0，他引：2  

R. A. Betts  P. M. Cox  M. Collins  P. P. Harris  C. Huntingford  C. D. Jones 《Theoretical and Applied Climatology》2004,78(1-3):157-175

Summary A suite of simulations with the HadCM3LC coupled climate-carbon cycle model is used to examine the various forcings and feedbacks involved in the simulated precipitation decrease and forest dieback. Rising atmospheric CO₂ is found to contribute 20% to the precipitation reduction through the physiological forcing of stomatal closure, with 80% of the reduction being seen when stomatal closure was excluded and only radiative forcing by CO₂ was included. The forest dieback exerts two positive feedbacks on the precipitation reduction; a biogeophysical feedback through reduced forest cover suppressing local evaporative water recycling, and a biogeochemical feedback through the release of CO₂ contributing to an accelerated global warming. The precipitation reduction is enhanced by 20% by the biogeophysical feedback, and 5% by the carbon cycle feedback from the forest dieback. This analysis helps to explain why the Amazonian precipitation reduction simulated by HadCM3LC is more extreme than that simulated in other GCMs; in the fully-coupled, climate-carbon cycle simulation, approximately half of the precipitation reduction in Amazonia is attributable to a combination of physiological forcing and biogeophysical and global carbon cycle feedbacks, which are generally not included in other GCM simulations of future climate change. The analysis also demonstrates the potential contribution of regional-scale climate and ecosystem change to uncertainties in global CO₂ and climate change projections. Moreover, the importance of feedbacks suggests that a human-induced increase in forest vulnerability to climate change may have implications for regional and global scale climate sensitivity.  相似文献   

Calibration of a land-surface model using data from primary forest sites in Amazonia     

P. P. Harris  C. Huntingford  J. H. C. Gash  M. G. Hodnett  P. M. Cox  Y. Malhi  A. C. Araújo 《Theoretical and Applied Climatology》2004,78(1-3):27-45

Summary A land-surface model (MOSES) was tested against observed fluxes of heat, water vapour and carbon dioxide for two primary forest sites near Manaus, Brazil. Flux data from one site (called C14) were used to calibrate the model, and data from the other site (called K34) were used to validate the calibrated model. Long-term fluxes of water vapour at C14 and K34 simulated by the uncalibrated model were good, whereas modelled net ecosystem exchange (NEE) was poor. The uncalibrated model persistently underpredicted canopy conductance (g _c ) from mid-morning to mid-afternoon due to saturation of the response to solar radiation at low light levels. This in turn caused a poor simulation of the diurnal cycles of water vapour and carbon fluxes. Calibration of the stomatal conductance/photosynthesis sub-model of MOSES improved the simulated diurnal cycle of g _c and increased the diurnal maximum NEE, but at the expense of degrading long-term water vapour fluxes. Seasonality in observed canopy conductance due to soil moisture change was not captured by the model. Introducing realistic depth-dependent soil parameters decreased the amount of moisture available for transpiration at each depth and led to the model experiencing soil moisture limitation on canopy conductance during the dry season. However, this limitation had only a limited effect on the seasonality in modelled NEE.  相似文献