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Flux Profiles (flux + profile)
Selected AbstractsImprovement and validation of a snow saltation model using wind tunnel measurementsEARTH SURFACE PROCESSES AND LANDFORMS, Issue 14 2008Andrew Clifton Abstract A Lagrangian snow saltation model has been extended for application to a wide variety of snow surfaces. Important factors of the saltation process, namely number of entrained particles, ejection angle and speed, have been parameterized from data in the literature. The model can now be run using simple descriptors of weather and snow conditions, such as wind, ambient pressure and temperature, snow particle sizes and surface density. Sensitivity of the total mass flux to the new parameterizations is small. However, the model refinements also allow concentration and mass flux profiles to be calculated, for comparison with measurements. Sensitivity of the profiles to the new parameterizations is considerable. Model results have then been compared with a complete set of drifting snow data from our cold wind tunnel. Simulation mass flux results agree with wind tunnel data to within the bounds of measurement uncertainty. Simulated particle sizes at 50 mm above the surface are generally larger than seen in the tunnel, probably as the model only describes particles in saltation, while additional smaller particles may be present in the wind tunnel at this height because of suspension. However, the smaller particles carry little mass, and so the impact on the mass flux is low. The use of simple input data, and parameterization of the saltation process, allows the model to be used predictively. This could include applications from avalanche warning to glacier mass balance. Copyright © 2008 John Wiley & Sons, Ltd. [source] Use of methyl salicylate as a simulant to predict the percutaneous absorption of sulfur mustardJOURNAL OF APPLIED TOXICOLOGY, Issue 2 2001Jim E. Riviere Abstract Exposure to chemical vesicants such as sulfur mustard (HD) continues to be a threat to military forces requiring protectant strategies to exposure to be evaluated. Methyl salicylate (MS) has historically been the simulant of choice to assess HD exposure. The purpose of this study was to compare the percutaneous absorption and skin deposition of MS to HD in the isolated perfused porcine skin flap (IPPSF). The HD data were obtained from a previously published study in this model wherein 400 ,g cm,2 of ]14C[-MS or ]14C[-HD in ethanol were topically applied to 16 IPPSFs and experiments were terminated at 2, 4 or 8 h. Perfusate was collected at increasing time intervals throughout perfusion. Radioactivity was determined in perfusate and skin samples. Perfusate flux profiles were fitted to a bi-exponential model Y(t) = A(e, , e,) and the area under the curve (AUC), peak flux and time to peak flux were determined. Sulfur mustard had more pronounced and rapid initial flux parameters (P < 0.05). The AUCs determined from observed and model-predicted parameters were not statistically different, although the mean HD AUC was 40,50% greater than MS. The HD skin and fat levels were up to twice those seen with MS, but had lower stratum corneum and residual skin surface concentrations (P < 0.05). Compared with other chemicals studied in this model, HD and MS cutaneous disposition were very similar, supporting the use of MS as a dermal simulant for HD exposure. Copyright © 2001 John Wiley & Sons, Ltd. [source] Computational study of staged membrane reactor configurations for methane steam reforming.AICHE JOURNAL, Issue 1 2010Abstract The present work complements part I of this article and completes a computational analysis of the performances of staged membrane reactors for methane steam reforming. The influence of the number of stages and catalyst amount is investigated by comparing the methane conversion and hydrogen recovery yield achieved by an equisized-staged reactor to those of an equivalent conventional membrane reactor for different furnace temperatures and flow configurations (co- and counter-current). The most relevant result is that the proposed configuration with a sufficiently high number of stages and a significantly smaller catalyst amount (up to 70% lower) can achieve performances very close to the ones of the conventional unit in all the operating conditions considered. This is equivalent to say that the staged configuration can compensate and in fact substitute a significant part of the catalyst mass of a conventional membrane reactor. To help the interpretation of these results, stage-by-stage temperature and flux profiles are examined in detail. Then, the quantification of the performance losses with respect to the conventional reactor is carried out by evaluating the catalyst amount possibly saved and furnace temperature reduction. © 2009 American Institute of Chemical Engineers AIChE J, 2010 [source] Characterization of downflowing high velocity fluidized bedsAICHE JOURNAL, Issue 3 2000Chunshe Cao A downer-riser circulating high velocity fluidization apparatus was developed to study the fundamentals of downflowing gas-solid particle mixtures. The acceleration and deceleration of solids due to the influences of the entrance and exit sections result in a relatively uniform axial solids distribution. Radial solid density profiles detected with an X-ray imaging system in the downer show the existence of a core-annulus flow with a dilute core surrounded by a denser wall region. Local solids flux profiles were obtained with an aspirating probe device and the solid velocity profile obtained from the two measured quantities. These confirm that the majority of solids segregates in a wall region that flows faster than the dilute core region. Thus, the shorter residence time in the high-speed downer wall region is coupled with faster reaction rates due to the accompanying high concentration of catalyst, while the dilute core has slower reaction rates with longer residence time due to the lower catalyst concentration and flow velocity. This results in much more uniform reaction extent over the cross-sectional area of the downer and, therefore, should improve the product selectivity. [source] A search for circumstellar material around B-type stars in the Galactic haloMONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 4 2002H. R. M. Magee Abstract 19 B-type stars, selected from the Palomar,Green Survey, have been observed at infrared wavelengths to search for possible infrared excesses, as part of an ongoing programme to investigate the nature of early-type stars at high Galactic latitudes. The resulting infrared fluxes, along with Strömgren photometry, are compared with theoretical flux profiles to determine whether any of the targets show evidence of circumstellar material, which may be indicative of post-main-sequence evolution. Eighteen of the targets have flux distributions in good agreement with theoretical predictions. However, one star, PG 2120+062, shows a small near-infrared excess, which may be due either to a cool companion of spectral type F5,F7, or to circumstellar material, indicating that it may be an evolved object such as a post-asymptotic giant branch star, in the transition region between the asymptotic giant branch and planetary nebula phase, with the infrared excess due to recent mass loss during giant branch evolution. [source] A comparison of ammonium, nitrate and proton net fluxes along seedling roots of Douglas-fir and lodgepole pine grown and measured with different inorganic nitrogen sourcesPLANT CELL & ENVIRONMENT, Issue 3 2008B. J. HAWKINS ABSTRACT Significant spatial variability in NH4+, NO3, and H+ net fluxes was measured in roots of young seedlings of Douglas-fir (Pseudotsuga menziesii) and lodgepole pine (Pinus contorta) with ion-selective microelectrodes. Seedlings were grown with NH4+, NO3,, NH4NO3 or no nitrogen (N), and were measured in solutions containing one or both N ions, or no N in a full factorial design. Net NO3, and NH4+ uptake and H+ efflux were greater in Douglas-fir than lodgepole pine and in roots not exposed to N in pretreatment. In general, the rates of net NH4+ uptake were the same in the presence or absence of NO3,, and vice versa. The highest NO3, influx occurred 0,30 mm from the root apex in Douglas-fir and 0,10 mm from the apex in lodgepole pine. Net NH4+ flux was zero or negative (efflux) at Douglas-fir root tips, and the highest NH4+ influx occurred 5,20 mm from the root tip. Lodgepole pine had some NH4+ influx at the root tips, and the maximum net uptake 5 mm from the root tip. Net H+ efflux was greatest in the first 10 mm of roots of both species. This study demonstrates that nutrient uptake by conifer roots can vary significantly across different regions of the root, and indicates that ion flux profiles along the roots may be influenced by rates of root growth and maturation. [source] A consistent vertical Bowen ratio profile in the planetary boundary layerTHE QUARTERLY JOURNAL OF THE ROYAL METEOROLOGICAL SOCIETY, Issue 620 2006M. Hantel Abstract It has recently been suggested that the integrand b=,,,,, of the subgrid-scale conversion rate between available and kinetic energy has a measurable impact upon the Lorenz energy cycle. Here we discuss a technique to estimate this quantity within the lower part of an atmospheric column by relating b to the subgrid-scale fluxes of sensible and latent heat in form of their sum (the total convective heat flux, c, to be diagnosed from the pertinent energy law) and their ratio (a generalized Bowen ratio, ,, to be specified a priori). We focus on the frequently observed case that c vanishes at or above the top of the boundary layer, which implies that , must be minus unity at the same level (referred to as ,critical pressure'). , at the earth's surface is taken as measured. Observations suggest that the vertical curvature of the , profile is negative in the boundary layer. We specify an analytic vertical profile ,(,) that interpolates these pieces of information; , is a non-dimensional vertical coordinate. The pertinent thermodynamic energy law from which the column profile c(,) is gained (referred to here as convection equation) is driven by the (observed) grid-scale budget; the solution c is over most of the boundary layer quite insensitive to ,. It is only in the immediate vicinity of the critical pressure that c(,) becomes sensitively dependent upon ,(,); it actually turns infinite at this level (a ,pole' of the convection equation). We remove the pole through adjusting the critical pressure by a uniquely determined (and actually quite small) amount. This makes the , profile consistent with the convection equation and with the other convective flux profiles, across the entire boundary layer. The remaining open parameter that cannot be fixed by our method is the curvature of the Bowen ratio profile. This exercise has implications for about a third of all atmospheric columns over the globe and thus may be relevant for the quantification of the global energy cycle. Copyright © 2006 Royal Meteorological Society [source] Modelling sources and sinks of CO2, H2O and heat within a Siberian pine forest using three inverse methodsTHE QUARTERLY JOURNAL OF THE ROYAL METEOROLOGICAL SOCIETY, Issue 590 2003M. Siqueira Abstract Source/sink distributions of heat, CO2 and water vapour in a Siberian Scots pine forest were estimated from measured concentration and temperature profiles using three inverse analysis methods. These methods include: a Eulerian second-order closure model (EUL); a localized near-field Lagrangian dispersion model (LNF); and a hybrid model (HEL) which uses the Eulerian second-order turbulence model to calculate the flow statistics combined with the regression analysis used with the Lagrangian model. Model predictions were compared to heat flux profiles measured at five levels in the canopy, and to CO2 and water-vapour fluxes measured close to the ground and above the forest. Predictions of sensible-heat flux profiles by the LNF and HEL schemes were systematically better than results from the EUL analysis. This improvement was attributed to the redundancy in the measured profile (scalar concentration and temperature) data for LNF and HEL and to the imposed smoothness condition used in the regression analyses, whereas the EUL approach calculates a source for each level without any redundancy. The LNF and HEL schemes were also better than EUL in predicting source distributions for CO2 and water vapour, although errors were larger than for sensible heat. The main novelty in our study is the use of EUL to decompose the vertical variability in scalar (or heat) sources into variability produced by the inhomogeneity in flow statistics and variability inferred from the measured mean scalar concentration (or temperature) profile. Hence, it is possible with this analysis to assess how much ,new information' about the source variability is attributed to vertical variation in the measured mean scalar concentration (or temperature) profiles. The analysis shows that measured water vapour concentration profiles provide little information on the inferred source distribution, whereas the CO2 profiles contain more information. Monte Carlo simulations show that computed sources from all three inverse methods have similar sensitivities to errors in measured temperatures. Errors are reduced when the reference temperature above the canopy is held fixed, implying that errors in this temperature propagate throughout the entire domain. When information content and error estimations are combined, a valuable tool to assess the quality of source prediction by inverse methods can be generated. Copyright © 2003 Royal Meteorological Society [source] | |||||||||||||