two basin filling boxes the convection induced by turbulent buoyant plumes in a rectangular filling box baines and turner 1969 is extended to situations where the lower depths of the box are divided into two basins by a vertical barrier the barrier restricts horizontal spreading and allows the interbasin exchange of water to occur only in the common region above the barrier height one and two plume systems are considered in the two plume case it is assumed that each of the plumes arises from an independent buoyancy source above each basin the resulting two basin circulation is characterized by different stratifications in each basin and by an overflow from one basin into the other the spreading depths of the plumes and ambient stratification depend on the barrier height relative basin sizes and in the two plume case the relative strengths of the two buoyancy fluxes these results may be of relevance to multibasin seas and oceans where the circulation produced by near surface sources of intermediate and deep water is influenced by underwater ridges

multiphase plumes in a stratified ambient we report on experiments of turbulent particle laden plumes descending through a stratified environment we show that provided the characteristic plume speed b 0 n 1 4 exceeds the particle fall speed where the plume buoyancy flux is b 0 and the brunt vaisala frequency is n then the plume is arrested by the stratification and initially intrudes at the neutral height associated with a single phase plume of the same buoyancy flux if the original fluid phase in the plume has density equal to that of the ambient fluid at the source then as the particles sediment from the intruding fluid the fluid finds itself buoyant and rises ultimately intruding at a height of about 0 58 pm 0 03 of the original plume height consistent with new predictions we present based on classical plume theory we generalise this result and show that if the buoyancy flux at the source is composed of a fraction f s associated with the buoyancy of the source fluid and a fraction 1 f s from the particles then following the sedimentation of the particles the plume fluid intrudes at a height 0 58 0 22f s pm 0 03 h t where h t is the maximum plume height this is key for predictions of the environmental impact of any material dissolved in the plume water which may originate from the particle load we also show that the particles sediment at their fall speed through the fluid below the maximum depth of the plume as a cylindrical column whose area scales as the ratio of the particle flux at the source to the fall speed and concentration of particles in the plume at the maximum depth of the plume before it is arrested by the stratification we demonstrate that there is negligible vertical transport of fluid in this cylindrical column but a series of layers of high and low particle concentration develop in the column with a vertical spacing which is given by the ratio of the buoyancy of the particle load and the background buoyancy gradient small fluid intrusions develop at the side of the column associated with these layers as dense parcels of particle laden fluid convect downwards and then outward once the particles have sedimented from the fluid with a lateral return flow drawing in ambient fluid as a result the pattern of particle rich and particle poor layers in the column gradually migrates upwards owing to the convective transport of particles between the particle rich layers superposed on the background sedimentation we consider the implications of the results for mixing by bubble plumes for submarine blowouts of oil and gas and for the fate of plumes of waste particles discharged at the ocean surface during deep sea mining

filling box flows in porous media we report upon a theoretical and experimental investigation of a porous medium filling box flow by specifically examining the details of the laminar descending plume and its outflow in a control volume having an impermeable bottom boundary and sidewalls the plume outflow initially comprises a pair of oppositely directed gravity currents the gravity currents propagate horizontally until they reach the lateral sidewalls at y pm l the flow then becomes of filling box type with a vertically ascending first front separating discharged plume fluid below from ambient fluid above the flow details are described analytically by first deriving a new similarity solution for darcy plumes with mathit pe o 1 where mathit pe is the peclet number from the similarity solution so obtained we then derive expressions for the plume volume flux and mean reduced gravity as functions of the vertical distance from the source regarding the plume outflow a similarity solution adopted from huppert woods j fluid mech vol 292 1995 pp 55 69 describes the height and front speed of the gravity currents whereas a semi implicit finite difference scheme is used to predict the first front elevation versus time and horizontal distance as with high reynolds number filling box flows that studied here is an example of a coupled problem the gravity current source conditions are prescribed by the plume volume flux and mean reduced gravity conversely discharged plume fluid may be re entrained into the plume be it soon or long after reaching the bottom impermeable boundary to corroborate our model predictions analogue laboratory experiments are performed with fresh water and salt water as the working fluids our experiments consider as independent variables the porous medium bead diameter and the plume source volume flux and reduced gravity predictions for the gravity current front position and height compare favourably against analogue measured data good agreement is likewise noted when considering either the mean elevation or the profile of the first front results from this study may be adopted in modelling geological plumes for example our equations can be used to predict the time required for discharged plume fluid to return to the point of injection in the case of aquifers closed on the sides and below by impermeable boundaries

compositional differences in enstatite chondrites based on carbon and nitrogen stable isotope measurements carbon and nitrogen abundance and isotopic compositions from four eh4 one eh5 five el6 chondrites and one aubrite were determined by using stepped pyrolysis n only and combustion n and c extractions in attempts to distinguish the components present carbon contents range from 0 15 to 0 70 wt with no systematic relationship between carbon content and meteorite group or petrologic type whole rock 13c values range from 28 5 to 4 1 most c occurs as graphite and when temperature steps above 700 c are considered there is a difference between eh4 5 13c 9 1 to 5 8 and el6 chondrites 13c 6 7 to 4 2 carbon in bustee aubrite is isotopically lighter 13c 24 than in any enstatite chondrite nitrogen occurs as osbornite sinoite and in isostructural substitution for oxygen in silicate lattice sites nitrogen abundances and isotopic compositions are more variable than c due to the heterogenous distribution of n bearing minerals three el6 s containing osbornite have higher n concentrations than other type 6 enstatite chondrites sinoite where present is depleted in 15n relative to osbornite nitrogen in the bustee aubrite has a similar abundance and 15n value to those of el6 s again dominated by the presence of osbornite in addition to the refractory c and n bearing minerals there is also organic material largely terrestrial contamination and evidence for at least two exotic components the first is a host for xe hl and is characterized by 13c 47 and 15n 73 whereas the second is less well defined but is marked by 15n 269

the variable carbon isotopic composition of type 3 ordinary chondrites a survey of bulk carbon isotopic compositions has been carried out for a suite of h l and ll ordinary chondrites from the most unequilibrated type 3 to the metamorphosed type 6 the isotopic composition of the higher petrologic types 4 6 is lighter in the range 25 to 30 and less variable than specimens of type 3 11 to 28 there is no simple relationship between bulk carbon and its isotopic composition several carbon phases of different 13c may be present in the meteorites in variable proportions to characterize the variability of type 3 chondrites a selection has been treated with orthophosphoric acid to test for the presence of terrestrial weathering products of high 13c some contamination and weathering products seem to be present but such an interpretation is less than straightforward the heavier isotopic composition and variability of type 3 meteorites may also be due in part to the presence of a component of graphite magnetite matrix in the h and l group samples

alh85085 a unique volatile poor carbonaceous chondrite with possible implications for nebular fractionation processes abstract allan hills 85085 is a unique chondrite with affinities to the al rais renazzo clan of carbonaceous chondrites its constituents are less than 50 m in mean size chondrules and microchondrules of all textures are present nonporphyritic chondrules are unusually abundant the mean compositions of porphyritic nonporphyritic and barred olivine chondrules resemble those in ordinary chondrites except that they are depleted in volatile elements ca al rich inclusions are abundant and largely free of nebular alteration they comprise types similar to those in cm and co chondrites as well as unique types calcium dialuminate occurs in several inclusions metal silicate and sulfide compositions are close to those in cm co chondrites and al rais and renazzo c1 chondrite clasts and metal rich reduced clasts are present but opaque matrix is absent siderophile abundances in alh85085 are extremely high e g fe si 1 7 solar and volatiles are depleted e g na si 0 25 solar s si 0 03 solar nonvolatile lithophile abundances are similar to those in al rais renazzo and cm and co chondrites alh85085 agglomerated when temperatures in the nebula were near 1000 k in the same region where renazzo al rais and the ci chondrites formed agglomeration of high temperature material may thus be a mechanism by which the fractionation of refractory lithophiles occurred in the nebula chondrule formation must have occurred at high temperatures when clumps of precursors were small after agglomeration alh85085 was annealed and lightly shocked c1 and other clasts were subsequently incorporated during late stage brecciation

emptying filling boxes the fluid mechanics of natural ventilation this paper describes the fluid mechanics of the natural ventilation of a space connected to a large body of stationary ambient fluid the flows are driven by buoyancy differences between the interior and exterior fluids connections with the ambient fluid are high level and low level openings two main forms of ventilation are identified mixing ventilation and displacement ventilation mixing ventilation occurs when the incoming ambient fluid mixes with the fluid within the space as is the case if dense fluid enters through a high level inlet in this case vertical stratification is weak displacement ventilation occurs when dense fluid enters at low levels and displaces the lighter fluid within the space out through high level openings a strong stable stratification develops in this case and there is little mixing between the incoming fluid and that in the interior both of these modes of ventilation are studied theoretically and the results are compared with laboratory experiments transient draining flows which occur when a space initially contains fluid of a density different from the ambient are examined the presence of internal sources of buoyancy allows steady states to be established and the effects of point line and vertically distributed sources are studied these steady states are extensions of filling box models with the addition of continuous exchange of fluid with the environment outside the space a major result of this work is that the form of the stratification within the space depends on the entrainment caused by the convective elements plumes produced by the buoyancy sources but is independent of the strength of the sources the strength of the stratification and the magnitudes of the velocities do however depend on the source strength the effects of opening size s and configurations are determined and criteria for producing a particular stratification within the space are established applications of this work to the ventilation of buildings are presented

physical weathering in arid landscapes due to diurnal variation in the direction of solar heating despite the prominent role of physical weathering in arid and semi arid landscapes there has been little study of the specifi c processes responsible for the rapid breakdown of subaerially exposed rocks for example many boulders and cobbles in deserts exhibit fi ne near vertical cracks although workers have hypothesized that these and other cracks are initiated by diurnal heating and cooling no convincing specifi c mechanism for their formation has been proposed we have characterized these cracks at eight sites on surfaces of different ages in the mojave sonoran and chihuahuan deserts and the high desert of central new mexico our data reveal four basic types of cracks longitudinal surfaceparallel fabric related and meridional the orientations of the fi rst three types are associated with clast shape and rock fabric the azimuths of meridional cracks however are preferentially aligned north south typically with a nonrandom multimodal distribution we propose that these cracks are caused by tensile stresses that arise in the interior of clasts due to strong radial gradients in temperature that evolve and rotate in alignment with the sun s rays we suggest that the multimodal nature of crack orientations may be in part attributable to the seasonally varying latitude dependent solar elevation angle over millennial time scales we suggest that this thermal cracking is an effi cient weathering process that together with cumulic soil epipedon development creates the key attributes of most desert pavements in addition to individual clasts exposed on desert surfaces this mechanism of cracking is potentially signifi cant in other climates and on other planets as well as for rock outcrops and for man made structures

turbulent fountains in an open chamber the flow and density distribution produced by injecting dense fluid upwards at the bottom of a homogeneous fluid have been investigated experimentally and theoretically both axisymmetric and line sources have been studied using small scale laboratory experiments in which salt water is injected into a tank of fresh water the turbulent fountain formed in this way rises to a maximum height which can be related to the froude number of the inflow and then falls back and spreads out along the floor continuing the inflow builds up a stable stratification in a similar manner to that discussed earlier for the plume filling box model of baines turner 1969 which is complementary to the present work the fountain flows considered here have the important new feature that the volume of the inflow is significant so the total volume of fluid in the open container increases with time the evolution is determined by the rate of entrainment into the fountain from its surroundings which is found directly by experiment re entrainment of fluid into the fountain continually changes the density profile in the mixed fluid collecting at the bottom of the chamber below the level of the fountain top and controls the rate of rise of a front of marked fluid the top of the fountain rises linearly in time at a rate which for axisymmetric fountains has been shown both experimentally and theoretically to be close to half the rate of rise of the free surface due to the inflow thus at a certain time the front rises above the top of the fountain once the mixed fluid at the bottom of the chamber has risen above the fountain its density profile remains unchanged the front velocity the fountain height and the density profile have all been obtained as functions of time using a theory which is in good agreement with the experimental results for a large range of input froude numbers for line fountains the results are less precise owing to an instability which causes the flow to switch irregularly from a symmetrical state to one in which the downflow occurs on one side only and with a smaller maximum height in concluding we discuss the applications which motivated the work particularly the development of a stratified hybrid layer in magma chambers replenished from below and the dynamically identical but inverted problem of heating large buildings through ducts located near the roof

quasi steady states in natural displacement ventilation driven by periodic gusting of wind we investigate the natural displacement ventilation of a space connected to a body of warm fluid through high and low level vents the space is subject to discrete periodic gusts of wind entering at high level from a cold exterior the cold exterior air entering the space produces buoyancy differences between the space and the body of warm fluid driving a ventilation flow initially we examine the case of a series of identical gusts of wind modelled as turbulent buoyant thermals new laboratory experiments show that an approximately two layer stratification is established and the height of the interface is quasi steady if the period between thermals is much less than the draining time of the space but longer than the fall time of individual thermals experiments also show that the interface height depends on the average buoyancy flux associated with the wind gusts the time between thermals as well as the geometric properties of the vents this contrasts with the case of a continuous source of buoyancy where the interface height depends only on the geometric properties of the vents and is independent of the buoyancy flux we develop a quasi steady two layer model of the flow based on the classical theory of turbulent thermals and show that it is consistent with our new experimental data we generalize the model to explore the sensitivity of the results to temporal variations in the size of thermals we then extend the model to explore the effects of longer interval times between successive thermals and find a two layer stratification still develops but that the interface height now varies cyclically in time we then discuss the implications of these results for the ventilation of a shopping mall subject to gusts of wind

the carbon and oxygen isotopic composition of meteoritic carbonates the 13c12c and 18o16o isotopic ratios of carbonates from carbonaceous and ordinary chondrites have been measured on co2 released by the action of h3po4 on whole rock samples carbonates from ci cm and cr carbonaceous chondrites exhibit a range in 18o of ca 15 20 5 to 35 1 relative to smow limited data from co2 water equilibration experiments suggest that meteoritic carbonates do not possess grossly anomalous 17o isotopic compositions therefore they are truly enriched in 13c with 13c between 23 7 and 80 7 relative to pdb large internal variations in 13c and 18o were found in individual meteorites and suggest that two or more isotopically distinct carbonates of different origin may be present the abundance 13c and 18o of carbonate in cm2 chondrites may be related to the extent of aqueous alteration of the meteorites carbonates in ci and cr chondrites have a median 13c ca 50 to 60 whereas 13c of cm meteorites lie in the range 40 to 50 although exceptions exist in both sets of samples cv3 and co3 carbonaceous chondrites and unequilibrated ordinary chondrites release small amounts of co2 on acid treatment which might be from carbonate dissolution but which is not enriched in 13c exhibiting 13c values ca 0 10 the exception to this is bishunpur with 13c ca 23 5 the difference in 13c of the ci cm and cr vs cv co and ordinary chondrite carbonates may be a result of the progressive enrichment in 13c of percolating fluids brought about by increasing solubilization of exotic 13c enriched grains

emptying filling boxes free turbulent versus laminar porous media plumes we examine the transient evolution of a negatively buoyant laminar plume in an emptying filling box containing a uniform porous medium in the long time limit unicode stix x1d70f rightarrow infty the box is partitioned into two uniform layers of different densities however the approach towards steady state is characterized by a lower contaminated layer that is continuously stratified the presence of this continuous stratification poses non trivial analytical challenges we nonetheless demonstrate that it is possible to derive meaningful bounds on the range of possible solutions particularly in the limit of large unicode stix x1d707 where unicode stix x1d707 represents the ratio of the draining to filling time scales the validity of our approach is confirmed by drawing comparisons against the free turbulent plume case where unlike with porous media plumes an analytical solution that accounts for the time variable continuous stratification of the lower layer is available baines turner j fluid mech vol 37 1969 pp 51 80 germeles j fluid mech vol 71 1975 pp 601 623 a separate component of our study considers time variable forcing where the laminar plume source strength changes abruptly with time when the source is turned on and off with a half period unicode stix x0394 unicode stix x1d70f the depth and reduced gravity of the contaminated layer oscillate between two extrema after the first few cycles different behaviour is seen when the source is merely turned up or down for instance a change of the source reduced gravity leads to a permanent change of interface depth which is a qualitative point of difference from the free turbulent plume case

natural ventilation in interconnected chambers ventilation of adjacent connected chambers forced in one chamber by an isolated point source of buoyancy is investigated there are floor and ceiling level external openings in the forced and unforced chambers respectively while the partition between the chambers has both a floor and ceiling level opening the flow evolves on the time scale over which the volume flux associated with the plume at the ceiling would fill both chambers the steady state in the forced chamber is analogous to the single chamber flow described by linden lane serff smeed j fluid mech vol 212 1990 p 309 with a well mixed buoyant upper layer which is deeper than in the single chamber flow due to the extra pressure drop at the upper interior opening the steady state in the unforced chamber inevitably exhibits vertical stratification and depends on the transient flow all the opening areas and the relative plan area of the two chambers as is verified by laboratory experiments when the upper interior opening is relatively large the buoyant layer in the unforced chamber is deeper than the buoyant layer in the forced chamber which contradicts model predictions based on the assumption that the layers are always well mixed

merging of two or more plumes arranged around a circle a model is presented of merging turbulent plumes from sources evenly spaced around a horizontal circle in a quiescent unstratified background this follows the previously developed method of i identifying the boundaries of interacting plumes with velocity potential contours of line sinks and ii closing the generalised plume equations with an entrainment assumption based on the integrated flux across the plume boundaries it includes the simplest case of two merging plumes as well as being applicable to plume flows in restricted corner configurations the model is shown to display the expected limiting behaviour for the source plumes and the merged plume consideration of the plume fluxes in the merging region leads to a revision of the entrainment assumption the resulting revised model compares satisfactorily with previous estimates of volume flux in two merging plumes

the ventilated filling box containing a vertically distributed source of buoyancy this paper describes the fluid mechanics within a box containing a vertical plane distributed source of buoyancy a theoretical analysis is presented that models the development of plumes from such sources in an unconfined ambient of uniform density two extensions are considered the first concerns a sealed box and the second involves the more general situation where the box is ventilated by openings at top and bottom in the sealed box the stratification develops in much the same way as for a filling box containing a single point source of buoyancy on the floor an initial front descends from the ceiling of the box and an asymptotic stratification eventually develops which is continuous in the vertical direction in the case of the ventilated box it is found that a complex stratification develops where one or more horizontal intrusions are formed by detachment of the plume boundary layer from the vertically distributed source where the buoyancy of the plume is less than or equal to that of the stratified ambient at a given height experimental results are presented to demonstrate the validity of the theory the findings are relevant to both forced and naturally ventilated buildings containing non adiabatic vertical surfaces

the formation and evolution of stratification during transient mixing ventilation we investigate the buoyancy driven ventilation of an enclosed volume of buoyant fluid which is connected to the exterior through two openings at the top of the enclosure an exchange flow becomes established with outflow through one opening being matched by an equal and opposite inflow through the other vent the inflowing flux of dense exterior fluid develops a turbulent buoyant plume which mixes with the interior fluid as it cascades to the base of the fluid volume an upward return flow gradually stratifies the confined volume of fluid with a first front of relatively dense plume fluid advancing to the top of the space initially the exchange flow is steady but as the first front rises above the inflow opening the flow rate wanes the initial development of the exchange flow and interior stratification follows the classical filling box work of baines turner j fluid mech vol 37 1969 p 51 with a plume of constant buoyancy flux once the first front exits the space the volume flux rapidly asymptotes to the form q q0 t from the initial value q0 where is the buoyancy driven draining time based on the initial density contrast with the environment the vertical structure of the interior density stratification asymptotes to a profile of constant shape whose amplitude decays in time as t 2 and we identify conditions under which the vertical variation in density is comparable to the difference between mean interior density and the exterior this generalises the analysis presented by linden lane serff smeed j fluid mech vol 212 1990 p 309 who assumed that the interior fluid is well mixed new laboratory experiments of the process are shown to be consistent with our predictions of the evolution of the flow the interior stratification and the migration of contaminants we also develop our analysis for situations where there are multiple stacks and show how this improves the mixing efficiency for a given ventilation flow the model has relevance for the design of transient mixing ventilation in a building especially when the effect of vertical stratification is important for ensuring thermal comfort

petrology of alh85085 a chondrite with unique characteristics abstract alh85085 has several characteristics which set it apart from any known chondritic group its chondrules are smaller 25 75 m the majority are cryptocrystalline and all are volatile na k s depleted feni metal is more abundant 40 9 wt than in any other chondrite and sulfide abundance is low 1 1 matrix material does not surround the chondrules and fragments but occurs as lithic clasts lumps up to 300 m across the bulk composition of alh85085 is lower in na si and s si and higher in ni si fe si and mg si than in other chondritic groups the ca si al si and mg si ratios are closest to those of the renazzo chondrite grouplet cr matrix lumps are most similar to cr and murchison group cm chondrite matrices survival of this fragile matrix material as lithic clasts indicates that they were added just prior to the agglomeration of the chondrite all components chondrules fragments matrix lumps fall within a narrow size range which may be the result of aerodynamic sorting if so the sorting must have occurred after chondrule solidification and following a period of chondrule breakage since fragments from larger chondrules are present the ni vs co trend in the feni metal overlaps that of metal in cr chondrites and bencubbin these trends are similar to those of calculated nebular condensation paths indicating a nebular origin the cryptocrystalline texture and volatile depletion of the chondrules indicate that most chondrules were heated to temperatures above the liquidus although alh85085 cannot now be assigned to any known chondrite group it shares many similarities with cr chondrites and the bencubbin metal silicate chondritic assemblage and may be part of a chondritic group closely related to these meteorites

scalings for submarine melting at tidewater glaciers from buoyant plume theory abstractrapid dynamic changes at the margins of the greenland ice sheet synchronous with ocean warming have raised concern that tidewater glaciers can respond sensitively to ocean forcing understanding of the processes encompassing ocean forcing nevertheless remains embryonic the authors use buoyant plume theory to study the dynamics of proglacial discharge plumes arising from the emergence of subglacial discharge into a fjord at the grounding line of a tidewater glacier deriving scalings for the induced submarine melting focusing on the parameter space relevant for high discharge tidewater glaciers the authors suggest that in an unstratified fjord the often quoted relationship between total submarine melt volume and subglacial discharge raised to the power is appropriate regardless of plume geometry provided discharge lies below a critical value in these cases it is then possible to formulate a simple equation estimating total submarine melt volume as a function of discharge fjord temperature

alh 85085 nitrogen isotope analysis of a highly unusual primitive chondrite alh 85085 is an unusual fine grained primitive chondrite which does not fit into any of the known meteorite classes it shows many chemical similarities to the equally unusual meteorites bencubbin weatherford and renazzo nitrogen isotope analysis shows that alh 85085 like bencubbin weatherford and renazzo contains highly 15 n enriched nitrogen indeed alh 85085 has the highest 15 n measured in any whole rock meteorite totalling to 858 but reaching 1497 in the 850 875 c temperature increment however the distribution of isotopically heavy nitrogen in alh 85085 is different from that observed for bencubbin thus precluding a direct relationship between these meteorites isotopically heavy nitrogen occurs in alh 85085 in two sites carbonaceous material 15 n ca 860 13 c ca 1 c n ca 65 75 and in fine grained fe ni metal or opaque chondritic matrix clasts 15 n ca 990 a third very 15 n enriched nitrogen carrier with 15 n 1500 might also be located in the matrix it is probable that there is only a single component with elevated 15 n 1500 and that it occurs in at least three discrete sites mixed with varying amounts of nitrogen having more isotopically normal 15 n 0 50 the identity of the hosts of the isotopically heavy nitrogen have not been fully determined but it is becoming clear that an increasing number of brecciated meteorites some of which do not seem to be related in other ways show evidence of having sampled a reservoir rich in 15 n this may be a result of the introduction of heavy nitrogen during brecciation its 15 n values and distribution throughout the meteorites brought about by mixing with variable amounts of more isotopically normal nitrogen and subsequent vaporization and re condensation processes

natural ventilation of an enclosure containing two buoyancy sources this paper describes experiments and theoretical modelling of a naturally ventilated enclosure containing two point sources of buoyancy previous work on the flow and stratification that develop in a space owing to the presence of a single source of buoyancy has been extended to cover two sources of positive or negative buoyancy in an attempt to produce more realistic models of practical problems examples include naturally ventilated buildings and industrial or medical processes involving dispersal of contaminants by air currents the experimental technique involves the use of a water filled enclosure with salt solution injected at two points these sources of negative buoyancy form turbulent plumes within the enclosure two sources of unequal strength are found to produce a vertical density profile consisting of three distinct fully mixed layers the paper describes a theoretical model that successfully predicts the depths and densities of these layers the positions of the interfaces between the three layers were found to be a function only of the effective area a of the enclosure openings the height of the enclosure h and the ratio of the strengths of the two sources of buoyancy b 1 b 2 the behaviour of a system with one source of positive buoyancy at the lower boundary and one of negative buoyancy at the upper boundary of the enclosure is also examined this case has particular relevance to the prediction of thermal stratification in rooms with both cold and warm surfaces present again the height of the interfaces is dependent only on the geometry of the enclosure and the source strength ratio three distinct types of flow pattern are predicted and observed

buoyancy driven unbalanced exchange flow through a horizontal opening buoyancy driven exchange flows occur in a variety of natural and industrial situations including nuclear and hydraulic engineering oceanography and building ventilation balanced exchange flows whereby there is simultaneously an equal volume flux transferred vertically upwards and downwards through a horizontal opening have previously been described theoretically however until now there has been no theoretical description of unbalanced exchange flows whereby the volume flux in one direction through an opening exceeds that in the other the model developed herein examines the growth of perturbations on the density interface at an opening made in a horizontal plane that connects buoyant fluid below with denser fluid above by considering the interface as it is advected away from the plane of the opening by a bulk flow imposed in the vertical we quantify the exchange for the unbalanced case the model successfully predicts the froude number criterion which corresponds directly to the minimum dimensionless flow rate of the imposed flow for the onset of unbalanced exchange across circular openings found experimentally additionally comparisons made between the exchanges predicted and measured show excellent agreement across the entire range of possible flows from unidirectional flow through unbalanced exchange to balanced exchange consideration is given to applications of the model to ocean outfall design and to the prediction of building ventilation flows for natural ventilation the theoretical model we derive for unbalanced exchange bridges the gap in the prediction of air flow rates between displacement flows where the flow is unidirectional and balanced exchange flows

noble gases in e chondrites noble gas data are reported for 12 e chondrites combined with literature data they show that k ar ages are 4 ae for 14 out of 18 meteorites yet u th he ages are often shorter perhaps due to late mild reheating cosmic ray exposure ages differ systematically between types 4 and 6 with e4 s mostly below 16 myr and e6 s above 30 myr this may mean that the e chondrite parent body contains predominantly a single petrologic type on the 1 km scale of individual impacts in contrast to the more thoroughly mixed parent bodies of the ordinary chondrites the heavy noble gases consist of at least two primordial components the usual planetary component 36ar132xe 80 and a less fractionated subsolar component 2700 36ar132xe 3800 the latter is found in highest concentration in the e4 chondrite south oman 36ar 760 10 8cc g 36ar132xe 2700 the isotopic compositions of both components are similar to typical planetary values indicating that some factor other than mass controlled the noble gas elemental ratios the heavy xe isotopes occasionally show some of the lowest 134xe132xe and 136xe132xe ratios measured in bulk chondrites suggestive of nearly fission free xe e g 136xe132xe 0 3095 0 0020 amounts of planetary gas in e4 e6 chondrites fall in the range for ordinary chondrites of types 4 6 but in contrast to the ordinary chondrites fail to correlate with petrologic type or volatile trace element contents another unusual feature of e chondrites is that primordial ne is present even in most 4 s and 5 s 20nep 1 to 7 10 8cc g with an isotopic composition consistent with planetary ne analyses of mineral separates show that the planetary gases are concentrated in an hf and hcl insoluble mineral similar to phase q the poorly characterized hno3 soluble carrier of primordial gases in carbonaceous and ordinary chondrites the subsolar gases on the other hand are located in an hcl and hno3 resistant phase possibly enstatite or a minor phase included in enstatite much of the 129xer 50 for e4 s 70 for e6 s is in hcl resistant but hf soluble sites suggestive of a silicate a similar subsolar component may be responsible for the high 36ar132xe ratios of some c3 s unequilibrated ordinary chondrites and the unique aubrite shallowater the planet venus also has a high arkr ratio well above the planetary range and hence may have acquired its noble gases from an e chondrite like material similar to south oman