Energy Requirements For Transport Research Articles

Life cycle embodied, operational and mobility-related energy and greenhouse gas emissions analysis of a green development in Melbourne, Australia

At least 40% of total greenhouse gas emissions are related to the built environment, mostly because of energy coming from fossil fuels. In response, developments with an improved energy efficiency (e.g. so-called ‘green’ or ‘net-zero energy’ developments) have been built. Despite reductions in operational energy use in ‘green’ developments, previous studies have identified trade-offs in terms of embodied energy in construction materials and sometimes transport energy associated with the mobility of building users.This research reconsiders the evaluation of green environmental claims through a life cycle approach. A multi-scale life cycle energy assessment software tool is employed to quantify the energy use and greenhouse gas emissions of a case study medium-scale green development in Melbourne, Australia over 50 years. Results show that the total life cycle energy use and greenhouse gas emissions of the development are 1,492 TJ (2,688 GJ per capita and 107 GJ/m2 of GFA) and 81 ktCO2-e (146 tCO2-e per capita and 6 tCO2-e/m2 of GFA), respectively, compared to 2,220 TJ (4,001 GJ per capita and 159 GJ/m2 of GFA) and 177 ktCO2-e (318 tCO2-e per capita and 13 tCO2-e/m2 of GFA) for a business-as-usual development with the same geometry. In fact, each of the embodied, operational and transport energy requirements represents an important contribution to the life cycle energy: 31%, 35% and 34%, respectively. Therefore, all life cycle stages and scales of the built environment are relevant to the overall energy and greenhouse gas emissions performance of green developments.

Multiobjective optimization of thermophysical properties of indonesian fly-ash nanofluid

Nanofluids with thermal and viscous tunable properties are seen to be smart fluids of the future generation. In determining the viscous and heat transfer characteristics, the concentration of nanomaterials is important. Generally, an optimal concentration of nanomaterial is needed to design a sustainable and cost-effective heat transfer process. This study includes modeling and optimization of various thermal and viscous temperature-dependent characteristics for differing nanofluid concentrations. The nanofluids containing fly-ash nanoparticles dispersed in water are used in this work. The Response Surface Methodology (RSM) is used to model and optimize the thermophysical properties of nanofluids. The higher volume of nanoparticles in the solution not only increases the heat transfer but also increases the fluid's viscosity leading to higher energy requirements for transportation. The study's key objective is to find the optimal fly-ash nanoparticle concentration and thermophysical characteristics. Temperature and volume concentration were considered as input parameters, while viscosity, thermal conductivity, specific heat, and density were selected as a response. The optimum value for viscosity, thermal conductivity, specific heat, and density are estimated as 0.0466536 Pa.s, 0.686725 W/m °C, 4040 j/kg °C and 984.368 kg/m3 for the input value of 60 °C and 0.1041741 percent nanoparticle loading.

Boosting the Usage of Green Energy for EV Charging in Smart Buildings Managed by an Aggregator Through a Novel Renewable Usage Index

The growing trend of electric vehicles (EVs) and building integrated photovoltaics (BIPVs) is a promising means to reduce related climate change issues. EV loads can be managed via an aggregator to maximize the usage of green energy produced by photovoltaic units (PV) through smart charging strategies that exploit controllable EV demand connected to BIPV. Previous works have focused on the EV charging coordination in a smart BIPV, although without an optimization that encourages EV charging with the energy produced by the PV units. This paper proposes an aggregation strategy that maximizes a green energy index (GEI) for the smart charging coordination of EVs, which takes advantage of periods with high PV availability to charge the EV batteries; moreover, a post-processing stage for the GEI provides EV owners with information about the percentage of charged energy, period by period, that comes from PV generation. The results for a case study with 510 EVs integrated with 17 smart BIPVs show that the strategy effectively optimizes the usage of the energy produced by the PV units to charge the EVs, contributes to reduce non-renewable energy consumption of the building sector, and satisfies the EV owners’ energy requirements for transportation.

Energy costs of salt tolerance in crop plants.

Agriculture is expanding into regions that are affected by salinity. This review considers the energetic costs of salinity tolerance in crop plants and provides a framework for a quantitative assessment of costs. Different sources of energy, and modifications of root system architecture that would maximize water vs ion uptake are addressed. Energy requirements for transport of salt (NaCl) to leaf vacuoles for osmotic adjustment could be small if there are no substantial leaks back across plasma membrane and tonoplast in root and leaf. The coupling ratio ofthe H+ -ATPase also is a critical component. One proposed leak, that of Na+ influx across the plasma membrane through certain aquaporin channels, might be coupled to water flow, thus conserving energy. For the tonoplast, control of two types of cation channels is required for energy efficiency. Transporters controlling the Na+ and Cl- concentrations in mitochondria and chloroplasts are largely unknown and could be a major energy cost. The complexity of the system will require a sophisticated modelling approach to identify critical transporters, apoplastic barriers and root structures. This modelling approach will inform experimentation and allow a quantitative assessment of the energy costs of NaCl tolerance to guide breeding and engineering of molecular components.

Assessing Electric Vehicle storage, flexibility, and Distributed Energy Resource potential

The emergence of Plug in Battery Electric Vehicles (BEV) is a process which will bring a large aggregate source of distributed energy storage into the electricity industry. The potential exists for this storage to bring benefits from the ability to shift net BEV demand (both charging and vehicle to the grid export) in response to electricity industry needs. The potential for BEV flexibility to act as a Distributed Energy Resource (DER) is however constrained by a range of factors including their mobility, need to serve transport energy requirements, and the locational/temporal availability of physical charging opportunity.This paper addresses the challenge of characterizing the availability of this new storage resource and aims to be of use to policy makers and electricity industry planners in developing strategies for maximizing the value of BEV integration for the electricity industry. In particular it: presents a general discussion of, and framework for understanding the manner in which BEV storage gives rise to charging/discharging flexibility, presents a method for simply characterizing the factors which constrain this flexible resource, introduces a method for empirically establishing a benchmark DER potential which fully accounts for relevant constraints, and applies these methods to a case study of vehicle use in the Sydney Greater Metropolitan area.Results show that, in respect of vehicle transport in Sydney, charging speed and the need to reserve energy in respect of transport needs is a lesser constraint than the impact of charging infrastructure availability. While the DER potential declines during the day in all cases, access to additional charging infrastructure minimizes this decline. Investment in additional non-residential charging infrastructure may therefore be particularly important in maximizing the DER potential arising from BEV storage flexibility, in particular for the opportunity to manage the integration of high future PV generation levels.

Cost optimal energy sector planning: a Pinch Analysis approach

Renewable energy sources can contribute to the increasing energy demand as well as reduction of green-house gas emissions and pollutants. It is desirable to find the optimum mix between renewable and non-renewable energy sources, based on carbon emissions or cost of electricity constraints. In this paper, a Pinch Analysis based method for allocating different energy sources to different demands of a region is proposed. The proposed approach determines the cost optimum mix of various energy sources. Applicability of the method is demonstrated through an illustrative case study of Lakshadweep Islands, India. These islands are too remote to have inter-connections with the mainland and depend on imports of oil for electrical, process, and transport energy requirements. The locally available renewable energy sources can be used to solve problems of energy security, higher energy cost, and environmental pollution. Additionally, the Government of India provides a significant amount of subsidy to supply electricity in Lakshadweep Islands. The proposed method helps in reducing the burden of subsidy significantly by appropriately utilizing locally available renewable energy sources. The proposed Pinch Analysis formulation consider energy as flow, cost of energy as quality, and minimizes subsidized diesel based power generation (formulated as resource). Based on the current acceptable price of electricity, the use of renewable energy sources leads to saving in the subsidy of 317.08 × 106 Rs./y and reduction in emissions from diesel generator set by about 58%. The policy implications for subsidy are also discussed in this paper and therefore, the work is useful to guide policy makers.

Life cycle energy and cost analysis of embodied, operational and user-transport energy reduction measures for residential buildings

Few studies have evaluated the overall life cycle energy demand of residential buildings, including their embodied, operational and user-transport requirements. To our knowledge, none has quantified the life cycle cost associated with reducing each of the aforementioned energy demands. It is critical to evaluate both energy and financial requirements in order to provide effective energy saving solutions for actors of the built environment.This study quantifies the life cycle energy and cost requirements associated with 22 different energy reduction measures targeting embodied, operational and user-transport requirements. It evaluates a case study apartment building in Sehaileh, Lebanon. Embodied, operational and transport energy requirements are calculated over 50years using a comprehensive approach. Life cycle costs are quantified using the net present value technique.Results identify the most cost effective energy reduction measures and discard some others which are financially prohibitive, namely the installation of photovoltaic panels and the use of hybrid cars. A number of recommendations for building designers, occupants, urban designers and planners and decision makers are provided based on the quantified benefits of each measure. This demonstrates the need for assessments with a broad scope and their potential to inform energy reduction strategies in the built environment.

Cold-pressed rapeseed cake or full fat rapeseed to organic dairy cows—milk production and profitability

The interest in growing and feeding locally produced feeds is increasing. Case studies in Sweden have shown that feeds grown on-farm are more environmentally favourable than imported feeds, partly due to the lower energy requirements for transport. Full fat rapeseed (FFRS) and its co-product cold-pressed rapeseed cake (CRC) can both be locally produced, and CRC has been proven to be suitable for dairy cows. In both feeds, fat content limits the amount that can be supplemented in the diet, and less FFRS than CRC can be used. However, in a previous study with scenario calculations, CRC showed lower profitability than FFRS. The present study examined how milk yield and milk composition were influenced by feeding FFRS compared with CRC in organic diets and calculated the farm profitability on each occasion. The study was performed using 56 Swedish Holstein cows in different lactation stages. Diets were 100 % organic, including a mixed ration (silage, grains and minerals) fed ad libitum and a restricted amount of concentrates (field beans together with either CRC or ground FFRS). There were no significant differences in milk yield and composition between the diets. However, cows fed FFRS had a higher intake of the mixed ration than cows fed CRC. Cows fed CRC had the highest profitability in later lactation, whereas the diets were economically similar during early lactation.

Reducing the total life cycle energy demand of recent residential buildings in Lebanon

Buildings require a substantive amount of energy for their operation. Recent studies have found that indirect requirements, such as the embodied energy associated with their construction and the transport-related energy of their users can be even more significant. A complete life cycle energy analysis of buildings in a Mediterranean context has seldom been undertaken.This paper relies on a multi-scale life cycle energy analysis framework to determine the energy use profile of recent residential buildings in Lebanon by taking into account embodied, operational and user transport energy requirements. It studies a representative case study building in Sehaileh, a suburb of the capital Beirut, over 50 years and identifies the most effective ways to reduce energy use across the different life cycle stages and scales of the built environment.Results show that the life cycle energy demand is dominated by transport energy (49%) followed by operational (33%) and embodied (18%) requirements. The main ways to reduce this life cycle energy demand comprise relocating jobs outside of the capital, putting in place an adequate public transport network, improving town planning to favour pedestrians and rely on gas or renewable energy sources instead of electricity when possible, notably for domestic hot water.

Assessing viability of bio-ethanol production from sweet sorghum in India

To meet the energy requirement for transport, blending automotive fuels with ethanol has been mandated in India like several other countries across the globe. The entire blending requirement has to come from molasses (by-product of sugarcane). Ethanol produced from molasses will not be able to meet the blending targets due to cyclical nature of sugar cane production resulting in shortage of molasses and its competing uses (potable and pharmaceutical use). This has promoted research efforts to augment energy sources that are sustainable and economically viable. One such source that can be commercially exploited for ethanol production is sweet sorghum. The sugars in the stalks of sweet sorghum can be crushed to produce juice, which can be processed into ethanol for blending. An attempt is made in this paper to assess viability of ethanol production from sweet sorghum. Net Present Value (NPV), the indicator of economic viability assessment, is negative and would thus be difficult for the industry to take off under the current scenario of ethanol price, feedstock price and ethanol recovery rate. Hence, an enabling environment and policy support for bio-ethanol production from sweet sorghum is crucial to meet future blending requirements.

The effect of uncertainty on US transport-related GHG emissions and fuel consumption out to 2050

The future of US transport energy requirements and emissions is uncertain. Transport policy research has explored a number of scenarios to better understand the future characteristics of US light-duty vehicles. Deterministic scenario analysis is, however, unable to identify the impact of uncertainty on the future US vehicle fleet emissions and energy use. Variables determining the future fleet emissions and fuel use are inherently uncertain and thus the shortfall in understanding the impact of uncertainty on the future of US transport needs to be addressed. This paper uses a stochastic technology and fleet assessment model to quantify the uncertainties in US vehicle fleet emissions and fuel use for a realistic yet ambitious pathway which results in about a 50% reduction in fleet GHG emissions in 2050. The results show the probability distribution of fleet emissions, fuel use, and energy consumption over time out to 2050. The expected value for the fleet fuel consumption is about 450 and 350 billion litres of gasoline equivalent with standard deviations of 40 and 80 in 2030 and 2050, respectively. The expected value for the fleet GHG emissions is about 1360 and 850 Mt CO 2 equivalent with standard deviation of 130 and 230 in 2030 and 2050 respectively. The parameters that are major contributors to variations in emissions and fuel consumption are also identified and ranked through the uncertainty analysis. It is further shown that these major contributors change over time, and include parameters such as: vehicle scrappage rate, annual growth of vehicle kilometres travelled in the near term, total vehicle sales, fuel economy of the dominant naturally-aspirated spark ignition vehicles, and percentage of gasoline displaced by cellulosic ethanol. The findings in this paper demonstrate the importance of taking uncertainties into consideration when choosing amongst alternative fuel and emissions reduction pathways, in the light of their possible consequences.

Comparative life cycle assessment of centralized and distributed biomass processing systems combined with mixed feedstock landscapes

Lignocellulosic biofuels can help fulfill escalating demands for liquid fuels and mitigate the environmental impacts of petroleum-derived fuels. Two key factors in the successful large-scale production of lignocellulosic biofuels are pretreatment (in biological conversion processes) and a consistent supply of feedstock. Cellulosic biomass tends to be bulky and difficult to handle, thereby exacerbating feedstock supply challenges. Currently, large biorefineries face many logistical problems because they are fully integrated, centralized facilities in which all units of the conversion process are present in a single location. The drawbacks of fully integrated biorefineries can potentially be dealt by a network of distributed processing facilities called ‘Regional Biomass Processing Depots’ (RBPDs) which procure, preprocess/pretreat, densify and deliver feedstock to the biorefinery and return by-products such as animal feed to end users. The primary objective of this study is to perform a comparative life cycle assessment (LCA) of distributed and centralized biomass processing systems. Additionally, we assess the effect that apportioning land area to different feedstocks within a landscape has on the energy yields and environmental impacts of the overall systems. To accomplish these objectives, we conducted comparative LCAs of distributed and centralized processing systems combined with farm-scale landscapes of varying acreages allocated to a ‘corn-system’ consisting of corn grain, stover and rye (grown as a winter double crop) and two perennial grasses, switchgrass and miscanthus. The distributed processing system yields practically the same total energy and generates 3.7% lower greenhouse gas emissions than the centralized system. Sensitivity analyses identified perennial grass yields, biomass densification and its corresponding energy requirements, transport energy requirements and carbon sequestration credits for conversion from annual to perennial crops as key parameters that significantly affect the overall results.

Food or fuel? What European farmers can contribute to Europe's transport energy requirements and the Doha Round

Farm support in higher income countries is a testament to the fundamental social and economic importance of agriculture, yet domestic efforts to support this sector can arouse multilateral discord in a world of global food markets. In this paper, we argue that the advent of biofuels offers a new opportunity for agriculture to contribute to society, and to do so in a way that reduces trade rivalry and improves energy security. Holding current agricultural production constant, we find that the EU has the potential to reduce oil imports between 6% and 28% by converting eligible agricultural crops into biofuels under two differing conversion scenarios. Further, 33% of food support could be removed with no net farm revenue loss, using the biofuel premia (compared with food value) of corn and rapeseed to compensate for subsidy reductions. These results can help overcome the current impasse in global trade negotiations by reconciling the needs of EU farmers with those who would gain from more liberal international trade.

Energy requirements for transport and surface application of liquid pig manure in Manitoba, Canada

The objective of this study was to conduct a thorough accounting of energy used to transport liquid pig manure from farm storage to the field and to surface-apply the manure. Energy consumption was determined using both energy data from the literature plus data from field-scale research. Energy consumption was compared between two manure application systems (the drag hose and the slurry wagon systems) and two application timing treatments (single vs. twice-annual manure application). The single annual application of liquid pig manure applied at 81.5 m 3 ha −1 and transported 1.8 km from storage to field consumed 2180 MJ ha −1 with the drag hose system and 2185 MJ ha −1 with the slurry wagon system. The twice-annual manure application regime used 2726 and 2209 MJ ha −1 for the drag hose and slurry wagon systems, respectively. When energy use was calculated on the basis of MJ per kg of available N, liquid pig manure applied once annually with the slurry wagon system provided N at 17.76 MJ kg −1 of available N, which was 33% of the energy cost of N from anhydrous ammonia and 23% of the energy cost of N from urea. Manure transport distance could be increased to 8.4 km before the energy cost per kg of available N from pig manure was equivalent to anhydrous ammonia, and up to 12.3 km before the energy cost of manure N was equivalent to urea N. Despite the high energy cost to deliver liquid pig manure from storage to field, the much lower cost per kg of available N compared to inorganic fertilizer N highlights the opportunities that exist for improving the energy efficiency of industrial agriculture by replacing inorganic fertilizers with manure.

Energized Uptake of Ascorbate and Dehydroascorbate From the Apoplast of Intact Leaves in Relation to Apoplastic Steady State Concentrations of Ascorbate

Abstract: Transport of ascorbate (AA) and dehydroascorbate (DHA) through the petiole into detached leaves of Lepidium sativum and other plant species via the transpiration stream, and energized uptake into leaf tissue, were measured indirectly by recording changes in membrane potential and apoplastic pH simultaneously with substrate‐stimulated respiration and transpiratory water loss. When 25 mM AA or DHA was fed to the leaves, steady state respiration at 25 °C was transiently increased by more than 50 % with AA and 70 % with DHA. Stimulation of respiration was accompanied by a transient breakdown of membrane potential followed by alkalinization of the leaf apoplast suggesting energized uptake at the expense of the transmembrane proton motive force. The average CO2/AA ratio calculated from stimulated respiration during ascorbate uptake was 0.76 ± 0.26 (n = 17). The corresponding ratio for DHA was 1.38 ± 0.28 (n = 11). Far lower CO2/substrate ratios were observed when NaCl or KCl were fed to leaves. The differences indicate either partial metabolism of AA and DHA in addition to energized transport, or less likely, higher energy requirement for transport of AA and DHA than for the inorganic salts. Maximum rates of energized AA transport into leaf tissue (deduced from maxima of extra respiration and calculated on the basis of CO2/AA = 0.76) were close to 650 nmol m‐2 leaf area s‐1, i.e. far higher than most previously reported rates of transport. When the apoplastic concentration of AA was decreased below steady state levels during infiltration/centrifugation experiments, AA was released from leaf cells into the apoplast. This suggests that AA oxidation to DHA in the apoplast (as occurs during extracellular ozone detoxification) triggers energized transport of the DHA into the symplast and simultaneously AA release from the symplast into the apoplast, perhaps together with protons in a reversal of the energized uptake process.

Metabolic depletion inhibits the uptake of nontransferrin-bound iron by K562 cells.

The effect of metabolic inhibitors on nontransferrin bound iron transport by K562 cells was investigated. Incubation with 1 microM rotenone, 10 microM antimycin, or 0.5 mM 2,4-dinitrophenol effectively reduced ATP levels by approximately 50%. Both the rate and extent of Fe+3 uptake were impaired in ATP-depleted cells, which display a reduced Vmax for uptake. K562 cell ferrireductase activity was also lowered by metabolic inhibitors, suggesting that the apparent energy requirements for transport reside in the reduction of Fe+3 to Fe+2. However, ATP depletion was found to inhibit the rate and extent of Fe+2 uptake as well. Thus, the transbilayer passage of Fe+2 and/or Fe+3 appears to be an energy-requiring process. These features possibly reflect properties of the transport mechanism associated with a recently identified K562 cell transport protein, called SFT for "Stimulator of Fe Transport," since exogenous expression of its activity is also affected by ATP depletion.

Effect of Extracellular Potassium on Ouabain‐Sensitive Consumption of High‐Energy Phosphate by Crayfish Giant Axons: A Study of the Energy Requirement for Transport in the Steady State

Crayfish axons exposed to a high or low extracellular K+ concentration ([K+]o) maintain intracellular Na+ and K+ concentrations constant, for up to 3 h, by adjusting both the Na+/K+ transport "coupling ratio" and turnover rate in compensation for changes in ion fluxes due to altered electrochemical gradients. These findings give rise to the prediction that the steady-state consumption of high-energy phosphate (approximately P) [ATP and phospho-L-arginine (Arg-P)] is inversely proportional to the [K+]o, i.e., directly proportional to the product of membrane conductance and magnitude of the transmembrane electrochemical gradients for Na+ and K+. This investigation was designed to test this hypothesis. The [K+]o did not influence total approximately P consumption (Q approximately P) of the axon. For a [K+]o between 0.5 and 21.6 mM, Q approximately P averaged 52.8 +/- 4.7%/h (n = 44) of the initial [ATP] + [Arg-P]. Unlike total Q approximately P, the ouabain-sensitive portion of Q approximately P was markedly influenced by [K+]o. In 0.5 mM K+o, ouabain poisoning reduced Q approximately P to 8%/h, a result indicating that 85% of the total Q approximately P was ouabain sensitive. For 1.35 mM K+o, the ouabain-sensitive portion was 66%; at 5.4 mM K+o, 45%; and at 13.5 mM K+o, 41%. There was a small but significant increase in the ouabain-sensitive Q approximately P at 21.6 mM K+o, compared with Q approximately P at 5.4 mM K+o. The pattern of effect of [K+]o on Q approximately P was similar to its effect on the electrical power content of the Na+ and K+ electrochemical gradients. In contrast to the generally accepted Na+ flux (JNa)/approximately P stoichiometry of 3, an actual ratio of JNa/approximately P stoichiometry of approximately 33:1 was calculated for the experiments reported here, a result suggesting that cells in a zero-membrane current steady state utilize efficient energy conservation mechanisms that may not operate under non-steady-state conditions.

Transport of pantothenic acid in Lactobacillus plantarum.

The characteristics of pantothenic acid (PA) transport into nonproliferating cells of Lactobacillus plantarum were studied. These characteristics included the effects of pH and temperature variations and the energy requirement for transport and binding of the vitamin. At pH 7.5 and 38 °C the intracellular vitamin was in the form of phosphopantothenic acid (P-PA) and was not exchangeable with external PA. Vitamin transport appeared separate from phosphorylation since significant free PA was observed only at elevated temperatures (e.g. 45 °C) and at low pH values. PA uptake and accumulation were energy-dependent, being inhibited completely by 10−2 M iodoacetate and the absence of glucose, exhibited pH and temperature optima of 7.5 and 38 °C, respectively, and were linear with time for at least 60 min. PA uptake exhibited substrate saturation. No free PA was observed when cells were incubated in PA concentrations above saturation levels. Apparent Km and Vmax values of 7.85 × 10−7 M and 5.35 μmol of PA/mg cells (dry weight) per minute, respectively, were determined from Lineweaver–Burk plots. Competitive inhibition of transport was observed with panthenol and pantoyl taurine. Ki values were, respectively, 3.55 × 10−5 M and 3.07 × 10−6 M. Pantoyl lactone, at concentrations which inhibited growth by 78%, had no effect on transport. The data reported suggest that PA transport is an active, mediated process and that transport may limit the phosphorylation of PA into P-PA. Inhibitor studies showed that PA transport was at least 150 times more sensitive to analogue inhibition than was growth itself, suggesting that transport of PA was not a limiting factor in the growth of L. plantarum.

Glycerol uptake by the haustorial mycoparasite Tieghemiomyces parasiticus in axenic culture

Uptake of [14C]glycerol by 72-h-old resting cell suspensions of Tieghemiomyces parasiticus was linear with respect to time and had the characteristics of a protein-mediated system of transport. The uptake process obeyed Michaelis–Menten kinetics with an apparent Km of 8 × 10−4 M and Vmax of 5.26 nmol ∙ min−1 ∙ mg−1 dry wt. Glycerol uptake exhibited pH and temperature dependence with optima at pH 5 and 35 °C, respectively. The energy of activation (Ea) and Q10 for this uptake process were calculated to be 12 043 cal/mol and 1.98, respectively, between 20 and 30 °C. Glycerol uptake also exhibited substrate specificity and was inhibited by α-glycerolphosphate and 1,2-propanediol, while inhibition by 1,3-propanediol was negligible. Preexposing resting cell suspensions to sodium azide and 2,4-dinitrophenol (4 × 10−3 M) significantly inhibited glycerol uptake, possibly suggesting an energy requirement for transport. Cold osmotic shock treatment severely reduced glycerol uptake but did not destroy cell viability.

Concentration of urine in a central core model of the renal counterflow system

Concentration of urine in a central core model of the renal counterflow system. In this model descending Henle's limbs (DHL), ascending Henle's limbs (AHL) and collecting ducts (CD) exchange with a central vascular core (VC) formed by vasa recta loops—assumed so highly permeable that the core functions as a single tube, open at the cortical end and closed at the papillary end. Solute supplied to the VC primarily by AHL increases VC osmolality and so extracts water from DHL and CD, increasing their osmolality while diluting AHL fluid. This single effect multiplied by the counterflow arrangement leads to a high papillary osmolality in all structures. Some of the solute may enter DHL to be recycled. In single solute system energy requirements for transport out of AHL decrease from outer to inner medulla. In two solute systems (e.g. salt and urea) mixing in the central core can supply part of the energy for the final concentration of urine. Urea cycling, regulated by ADH, allows active Na + transport in the outer medulla and cortex to be used for concentration in the inner medulla.