Surface Area-volume Relationships Research Articles

Micro-scale experimental investigations of CO2-WAG injection and Ostwald ripening analysis in carbonate rocks with different pore structures

Carbonate reservoirs are rich in hydrocarbon resources. However, carbonate reservoirs usually have strong pore structure heterogeneity, and thus it is necessary to understand the effect of heterogeneity on pore-scale fluid distributions during CO2 enhanced oil recover (CO2-EOR) process. We thus conducted water-alternating-gas (CO2-WAG) injection in the three carbonate samples with strong to weak heterogeneity. The 15 sets of images showed that the fractured-vuggy carbonate with the strongest heterogeneity had the highest additional oil recovery. CO2-WAG injection significantly changed the residual oil distribution, and further oil production can be achieved by increasing the number of CO2-WAG cycles. For CO2 geological storage, with the increase of carbonate heterogeneity, CO2 capillary-trapping capacity decreased, CO2 dissolution trapping potentiality decreased, but the stability of CO2 capillary trapping enhanced. These key parameters related to CO2 storage were described through the saturation of trapped gas, the types of trapped gas, and the surface area-volume relationship of CO2 clusters. For example, the higher amount of network gas is detrimental to the stability of CO2 capillary trapping because the network gas is easily displaced when the hydrodynamic force is enhanced. The specific surface area of CO2 cluster determines dissolution dynamics, and a higher specific surface area is beneficial for CO2 dissolution. Another interesting phenomenon - Ostwald ripening, is related to long-term CO2 transport. The CO2 concentration gradient in aquifer generates a vertically upward diffusive flux, causing CO2 remobilization. By calculating the height of the transition zone and the time to reach gravity-capillary pressure equilibrium, we found that as carbonate heterogeneity increased, the height of transition zone (the area where CO2 is trapped by capillary pressure) increased, while equilibrium time shortened. By comparing the results of previous gas-water two-phase flow experiments, we believe that the relationship between CO2 storage characteristics and carbonate heterogeneity summarized in this paper are universally applicable.

Short-term movement is different in two syntopic Tropidurus (Squamata, Tropiduridae) species in a semiarid habitat

ABSTRACT Displacement occurs during the movement of an organism and can be defined as a change in spatial position, being influenced by biotic and abiotic factors. Measuring the displacement of organisms within their home range is relevant for understanding their use of space and can reveal possible causes and consequences of their movements. During part of the dry season in a semi-arid region of Northeastern Brazil, we marked and observed syntopic Tropidurus hispidus and Tropidurus semitaeniatus individuals in a rocky habitat, and compared their locomotive parameters. We also evaluated the existence of relationships between locomotion and morphometry (snout–vent length and body mass) and abiotic factors (air temperature and relative humidity) of these species. A total of 25.33 hours of observations showed that T. semitaeniatus is clearly less sedentary in relation to T. hispidus, in terms of short-term movements. There was a tendency of smaller individuals to perform a greater number of displacement movements per minute, and displacement distance per minute increased in accordance with an increase in relative humidity for T. semitaeniatus. The movement pattern of the less sedentary T. semitaeniatus may reflect their greater dependence on rocky outcrops and, consequently, they demonstrate better morphological and behavioural adaptations. The surface area–volume relationship, which influences thermoregulatory behaviour, may explain the relationship between morphology and displacement distance in T. semitaeniatus. Furthermore, this species appears to control their movements with the aim of avoiding dehydration caused by restrictions of relative low humidity in their microhabitats. This study has important implications for future research on biomechanics, ecophysiology and modelling of the potential distribution of Tropiduridae lizards under climate change.

Experimental pore-scale analysis of carbon dioxide hydrate in sandstone via X-Ray micro-computed tomography

Carbon dioxide geo-sequestration (CGS) into sediments in the form of (gas) hydrates is one proposed method for reducing anthropogenic carbon dioxide emissions to the atmosphere and, thus reducing global warming and climate change. However, there is a serious lack of understanding of how such CO2 hydrate forms and exists in sediments. We thus imaged CO2 hydrate distribution in sandstone, and investigated the hydrate morphology and cluster characteristics via x-ray micro-computed tomography in 3D in-situ. A substantial amount of gas hydrate (∼17% saturation) was observed, and the stochastically distributed hydrate clusters followed power-law relations with respect to their size distributions and surface area-volume relationships. The layer-like hydrate configuration is expected to reduce CO2 mobility in the reservoir, and the smaller than expected hydrate surface-area/volume ratio will reduce methane production and CO2 storage capacities. These findings will aid large-scale implementation of industrial CGS projects via the hydrate route.

Step-Ladder Expansive Cranioplasty after Decompressive Craniotomy and Expansive Duraplasty: Discussing Possibilities on a Mathematical Model

<b>Background</b> Role of decompressive craniectomy in reducing intracranial pressure is well established. However, it comes with a cost of requiring a second surgery in the form of cranioplasty without which unacceptable hemodynamic consequences occur. It is generally felt that a credible alternative is required. <b>Objective</b> The aim of the study is to devise a mathematical model, which closely represents the cranium and intracranial contents, on which various alternatives can be evaluated with reproducible results, and to work out the effects of a novel technique of expansive cranioplasty on that model. <b>Methods</b> A mathematical model was designed based on the presumption that dura forms a watertight bag-containing brain, floating in cerebrospinal fluid (CSF). A model for an expansive cranioplasty was designed, and its ability to provide the space required to allow volume expansion and to achieve adequate reduction in intracranial pressure (ICP) was evaluated on this model. <b>Results</b> The mathematical model could closely reproduce the surface area–volume relationships in the published literature. Based on the calculations on the model, it was found that a projection of dural outpouching of 0.83 cm beyond the craniectomy margin on either side of a bilateral 12 × 15 cm elliptical craniectomy defect is required to achieve and accommodate a volume expansion of 157 cm³, which was recorded to be the maximum volume expansion in the reviewed literature. A two-step step-ladder cranioplasty can be constructed to achieve an increase in cranial width by 1.1 to 1.3 cm on each side. <b>Conclusion</b> Calculations based on the present model indicate that a two-step expansive cranioplasty can accommodate adequate volume expansion while alleviating the ill effects of a craniectomy and necessity of a second surgery. However, these are discussions on mathematical model, based on multitude of assumptions and approximations, and hence these discussions require clinical trials to validate the findings.

Surface area-volume relationships for the mastoid air cell system and tympanum in adult humans: Implications for mastoid function

Conclusions: The middle ear (ME) surface area/volume ratio (SA/V) is greater than that of the tympanum. The rate of ME pressure decrease is proportional to the ME SA/V. The mastoid air-cell system (MACS) will not function as an ME gas reserve unless the blood perfusion/surface area is much greater for the tympanum than the MACS and decreases as MACS volume increases. Objective: To measure the MACS and tympanum surface areas and volumes and ascertain whether the MACS could function as an ME gas reserve. Methods: Twenty adult subjects with a wide range of MACS volumes underwent CT of their MEs. The left and right surface areas and volumes of the tympanum and MACS were reconstructed and entered into a simple perfusion-limited model of transmucosal gas exchange. In this model the MACS would be a gas reserve if ME SA/V was less than the tympanum SA/V or equivalently, if their ratio was less than a critical value of 1. Results: Both MACS and tympanum SA were linearly related to their volumes. MACS SA/V and the ME SA/V were significantly greater than those for the tympanum. Inputting the measured values into the model yielded a critical value of 1.4, which was significantly greater than 1.

Comment on "A Surface Area-Volume Relationship for Prairie Wetlands in the Upper Assiniboine River Basin, Saskatchewan" by L.H. Wiens, Canadian Water Resources Journal 26(4): 503–514

(2002). Comment on 'A Surface Area-Volume Relationship for Prairie Wetlands in the Upper Assiniboine River Basin, Saskatchewan' by L.H. Wiens, Canadian Water Resources Journal 26(4): 503–514. Canadian Water Resources Journal / Revue canadienne des ressources hydriques: Vol. 27, No. 2, pp. 229-231.

A Surface Area-Volume Relationship for Prairie Wetlands in the Upper Assiniboine River Basin, Saskatchewan

The proliferation of geographical information system applications in hydrology and spatially distributed hydrologic models, all using areal input data, has created a need for a simple technique for estimating the storage volumes of wetland areas. Prompted by a hydrologic basin study in support of a Federal/Provincial study of the upper Assiniboine River basin in Saskatchewan, surface area-volume data sets for 177 wetland sites were analysed using regression analysis techniques. A composite relationship was derived, made up of two regression formulae, one for use with wetland areas under 70 hectares and a second for wetland areas between 70 and 500 hectares. A comparison was made between the composite area-volume relationship resulting from this study and similar area-volume relationships derived for two Iowa river basins in 1967. Although the two Iowa regression formulae compare reasonably well with the results of this study for wetland areas under six hectares, volumes derived by the three relationships diverge rapidly for areas greater than six hectares. Further analyses of wetland area-volume relationships using data from other areas of the prairie region could lead to the development of a suite of formulae which could eventually be consolidated and distributed into regional zones of application for use by the water resource community.

Alveolar epithelial surface area-volume relationship in isolated rat lungs.

In vitro studies of the alveolar epithelial response to deformation require knowledge of the in situ mechanical environment of these cells. Because of the presence of tissue folding and crumpling, previous measurements of the alveolar surface area available for gas exchange are not equivalent to the epithelial surface area. To identify epithelial deformations in uniformly inflated lungs representative of the in vivo condition, we studied isolated Sprague-Dawley rat lungs (n = 31) fixed by perfusion with glutaraldehyde on deflation after cycling three times at high lung volume (10-25 cmH2O). The epithelial basement membrane in 45 electron micrographs (x12,000)/rat was traced, digitally scanned, and analyzed. Epithelial basement membrane surface area (EBMSA) was computed from a morphometric relationship. EBMSA was found to increase 5, 16, 12, and 40% relative to EBMSA at 24% total lung capacity at lung volumes of 42, 60, 82, and 100% total lung capacity, respectively. The increases in EBMSA suggest that epithelial cells undergo significant deformations with large inflations and that alveolar basement membrane deformation may contribute to lung recoil at high lung pressures.

Sensitivity of Reservoir Sizing to Evaporation Estimates

Net reservoir evaporation is defined as the open water evaporation less the original evapotranspiration from the reservoir site. These rates are estimated on an average monthly basis by the method of Morton using sparse climtological data that include average annual precipitation, air temperature, dewpoint temperature, and sunshine ratio. Sunshine ratio data are substituted with the more generally available cloud cover data with little loss in accuracy. Generalized reservoir surface area-volume relationships are derived by regression analysis separately for large and small reservoirs in Australia. They represent the surface area-volume characteristics of a reservoir confined in a hypothetical valley whose shape is an averaging of the shapes of a large number of actual sites. The sensitivity of estimated storage sizes to errors in the evaporation rates and the reservoir surface area-volume relationships is tested for five catchments located in the southeastern extremity of Australia. With regard to these parameters, estimated reservoir sizes are shown to be surprisingly robust.

Effects of changes in extracellular ionic concentrations on aortic baroreceptors with nonmyelinated afferent fibers.

The effects of ionic change upon one of the two classes of aortic baroreceptors, those having unmyelinated axons or C-fibers, have not been examined heretofore. Differences from results in aortic baroreceptors with myelinated axons might be expected because of differences in accessible surface area-volume relationships. Recordings were obtained using an in vitro aortic arch-aortic nerve preparation from 21 aortic C-fibers in 15 normotensive Wistar-Kyoto rats (WKR) 13-17 weeks old. During a slow pressure ramp, the endings responded with an irregular discharge. However, if the discharge was averaged over 10-20 seconds, the average discharge correlated well with the pressure level in the arch. The maximal discharge increased with faster ramp rates but the threshold was not shifted over the range of ramp rates employed. The relationship between pressure and discharge was tested during alterations in the extracellular concentrations of Na, K, and Ca ([Na]0, [K]0, and [Ca]0). A 12% decrease in [Na]0 clearly decreased the firing in the aortic C-fibers during a ramp stimulus. During a pressure step, the initial discharge was not decreased but the steady state discharge was clearly depressed. When the aortic arch was perfused continuously at constant pressure, a decrease in Na of only 6% depressed the activity. Doubling [K]0 increased firing for a few minutes and was followed by a reduction of discharge. Previous reports have shown no effect on myelinated baroreceptor discharge by a 12% decrease in [Na]0, a change which significantly depressed firing in all C-fiber baroreceptors in this study. Thus, C-fiber baroreceptors are more sensitive to changes in extracellular ionic composition than are baroreceptors with myelinated axons.

Economies of Scale: Some Statistical Evidence: Comment

As engineers, working in the field of chemical economics, we appreciate Moore's analysis of the dubious statistical evidence behind the so-called power-rule relating size and cost.' However, we believe that more can and should be said about the matter. The fact is that in every case of our experience in the chemical and petroleum industries, large plants can be built at a lower unit cost than smaller ones. There are probably real cases outside of our experience where this rule does not hold. We can postulate conditions where it would not hold. But practically, these exceptions do not seem to be significant. Various reasons may be brought up as to why large plants cost less per unit of potential productive capacity than smaller ones (such as the surface area-volume relationship mentioned by Womer)?2 But these are only limited explanations, rather than proofs. There are obvious difficulties in defining or circumscribing both plant and Even if the terms could be circumscribed to some extent, the cost of a is a summation of many components so diverse that to expect them to follow the same mechanics would be absurd. Finally, the rule obviously fails at some high limit of capacity. In the face of these difficulties, one must conclude that any relationship between capacity and cost would be empirical, limited and highly approximate. The so-called power rule relationship C = KSn with C the cost, S the size and n an integer between zero and one, is a simple way of expressing the gross fact that large plants are built at lower unit cost. There are certainly more complex relationships which describe the fact more suitably; however, theory and data are insufficient to tell us what they are.3 But if the simple power rule relationship is to be used, its limitations must be clearly understood. The following example may assist such an understanding.