Convective Supply Research Articles

Массопроводность дисперсных и листовых материалов в условиях термодинамического равновесия

The intensification of drying of wet capillary-porous bodies and their structural and deformation transformations is determined by the internal mechanism of moisture transfer in the material being dried. The scientific papers of A.V. Lykova, S.P. Rudobashty, B.S. Sazhina, E.N. Ochneva, N.V. Churaeva are devoted to the study of mass conductivity of various bodies. They confirm the importance to determine the characteristics of internal moisture transfer in the form of liquid and vapor to calculate the intensity of moisture exchange between the surface of a wet material and the coolant and to establish the ratio of moisture and heat flows not only during the drying process, but also during storage of materials. For dispersed and sheet capillary-porous materials of different composition and porous structure, determining the intensity of internal moisture transfer during their interaction with the environment is a relevant area of the research. It determines the drying method, thermal treatment conditions and energy efficiency. Dispersed and sheet capillary-porous materials of various shapes, sizes, structures, and humidity have been used as the objects of the study. To determine the mass conductivity parameters of a wet body during its interaction with a coolant, a thermodynamic method is used. It is based on the use of experimental desorption isotherms and calculated parameters characterizing the porous structure of the material. The authors have applied the method to calculate the mass conductivity coefficients of dispersed and sheet materials based on experimental data obtained under conditions of thermodynamic equilibrium of a wet body and gas. Calculated curves of the dependence of effective mass conductivity coefficients and the moisture content of the dried material are obtained considering environmental parameters. The data obtained on the patterns and the changes in mass conductivity coefficients makes it possible to establish the types of relationships between moisture and the material with the mechanisms of its transfer for a number of dispersed and sheet bodies. The data obtained can be used for the kinetic calculation of the drying process and to determine the conditions of their storage, as well as to identify the conditions for increasing the energy efficiency of dryers with convective supply.

Identification of the kinetic regularities of ectocarpus dehydration under convective supply of thermal energy

Identification of the kinetic regularities of ectocarpus dehydration under convective supply of thermal energy

Internal Mass Transport Induced Voltage Losses during Water Electrolysis on Interconnected Nickel Nanowire Mesh Electrodes

Nickel nanowire mesh electrodes offer great potential for water electrolysis in alkaline environment, given their high internal surface area, mechanical strength, and alkaline resistance. Here we use a nickel nanowire mesh with a specific area of 26 m2/cm3, resulting in ~100-fold area enhancement for a 4µm thick nanowire mesh, compared to planar nickel. This highly benefits geometric current density, potentially into a regime where mass transport is the main limiting factor. Therefore, we performed a systematic study of electrode behaviour under various mass transport conditions to decouple kinetic and mass transfer related contributions to electrode voltage losses.An electrochemical flow cell was designed to measure the nanowire mesh electrode performance under optimal mass transport conditions. The cell provided electrolyte flow through the nanomesh, enabling convective supply of reagent into the nanopores as well as convective removal of reaction products. Facilitated by the inherent strength of the nanowire mesh, superficial flow velocities up to 1 cm/s could be obtained, with which geometric current densities as high as 320 mA/cm2 could be measured in the kinetically limited (flowrate independent) regime.Internal mass transport limitations were isolated by use of an inverted rotating disk electrode (iRDE). Koutecky-Levich analysis was performed to compensate for external mass transfer contributions on both nanowire mesh electrodes and planar electrodes. The nanowire mesh as iRDE resembles operating conditions in an electrolyzer, whereas the planar electrode provides a well-defined benchmark area for the electrode surface activity.For both the oxygen evolution reaction as the hydrogen evolution reaction, mass transport limitations were studies as function of current density and electrolyte (NaOH) concentration. Nanowire mesh electrode operation in the presence of internal mass transport limitations was compared to the non-limited condition and planar benchmark, from which the electrode effectiveness factor could be calculated. A 1-d simplified model of the electrode was used to explain the observed phenomena and to provide guidance for design optimization.

Kinetic Regularities Research of the Convective Concentration Process of a Hexane-Paraffinic Composition for the Food Paraffin Production

Film structures, used for the production of biodegradable packaging materials, are hydrophilic in nature. Their paraffinization reduced the influence of external factors, primarily moisture, for them, i.e. applying a thin layer of molten food paraffin to the film surface for subsequent protection of packaged food products from moisture and sunlight. While producing the moisture-repellent compositions, a man pays much attention to the quality of the final food paraffin. One of its important safety indicators is the absence of carcinogenic aromatic hydrocarbons in it. The kinetic regularities study of the convective concentration processes of a technical paraffin solution in n-hexane is necessary to analyze their mechanism and speed, depending on the operating parameters, making possible to determine the rational duration of these procedures and the specific yield of the resulting product. To rationalize the convective concentration of a hexane solution, it is necessary to select such operating parameters enabling not only to remove hexane with toxic components dissolved in it from the study object in a relatively simple apparatus, but also to significantly reduce the time for this process. The study aim was to determine the rational modes of hexane-paraffin mixture concentration, as an object for the food paraffin production with convective energy supply. The concentration curve nature, although it is typical for the interacting materials, in particular n-hexane and paraffin, has a certain specificity, determined by the physicochemical parameters of the research object, which is a true solution included various toxic substances. The specific features of the study object are to be reflected not only on the solution concentration mechanism, but also on the temperature fields evolution in it and, as a result, determine the original approaches to modeling the process of removing the solvent together with toxic substances, particularly, benz-α-pyrene.

Solution of a mathematical model for the concentration of a hexane solution of technical paraffin to obtain its food modification

For pectin-containing film structures, which are used for the production of biodegradable packaging materials and are hydrophilic in nature, their paraffinization, i.e., applying a thin layer of molten food paraffin to the surface of the film for subsequent protection of packaged food products from moisture and sunlight, will reduce the influence of external factors, primarily moisture, To rationalize the convective preconcentration of a hexane solution, it is necessary to select such regime parameters that will allow not only the removal of hexane with toxic components dissolved in it from the object of study in a relatively simple apparatus, but also significantly reduce the time for the process within temperature restrictions. The latter condition, in view of the complexity of the empirical determination of the temperature distribution in a thin layer of the object of concentration, is advisable to implement by solving the system of equations for the transfer of thermal energy and mass in partial derivatives, however, we can restrict ourselves to one equation for the transfer of thermal energy, using empirical kinetic dependences that describe the removal of n-hexane from the composition. The aim of the study was to adapt paraffin to a hexane solution and solve the model of heat and mass transfer during its concentration in order to exclude the possibility of reducing its temperature below the value of possible preliminary crystallization. The model was implemented numerically by the finite difference method. As a result of the solution, the intensity of the temperature front advancement along the height of the film of the hexanoparaffin composition was found with varying the proportion of paraffin in the process of its concentration with convective supply of thermal energy to it, i.e., it was adapted to the resulting solution and a mathematical model of heat and mass transfer was solved during its concentration to eliminate the likelihood of a decrease in its temperature below the value of possible pre-crystallization. The data obtained do not conflict with the known results of other researchers and can be successfully used for operational calculation and design of the designated processes and units.

Analysis of the screw press mouthpiece parameters for 3D extrusion of peat pieces of tubular type

The results of theoretical and experimental studies on the creation of a screw press composite mouthpiece screw press for 3D-forming of peat pieces of a tubular type in the field for intensifying the process of field drying of material in a complex mechanized pit are presented. The main purpose of the study was to substantiate the geometric and design parameters of the screw press composite mouthpiece of the spread machine for the production of peat-agglomerated products of the tubular type. The parameters of the mouthpiece are selected based on the geometric characteristics of the peat pieces. An increase in moisture loss during drying of peat-agglomerated products is provided by forming a peat piece in the form of a thick-walled pipe made of a peat raw materials composed of low and high decomposition degrees in a ratio of 1:3. Additive production of polymer-fiber peat composites by extrusion allows to produce products with improved mechanical properties in comparison with non-reinforced raw materials. The vertical arrangement of the peat tubular piece on the drying field allows to increase the loading of the field area by 10 %, increase the convective heat supply to the piece and reduce the contact coefficient of the piece with the field by three times in comparison with the peat spreading of the pieces in the form of a horizontal tape. Based on the analysis of the shape and size of the agglomerated products, the design of a screw press composite mouthpiece consisting of two conditional molding zones of various configurations has been developed. The article presents a parametric analysis of the volumetric productivity of a screw press with a composite mouthpiece of a tubular type, the energy intensity of mechanical processing is determined, the degree of mechanical processing of peat raw materials is estimated with the optimization of the screw parameters for the production of agglomerated products of a tubular type.

Heat and mass transfer in the blasted layer of vegetable materials with cyclic microwave power supply

The results of modeling and experimental study of heat and mass transfer in a dense blown layer of plant materials under cyclic microwave exposure are presented. The two-dimensional mathematical model consists of the equations of conservation of the mass of the gas phase, filtration, heat and mass transfer in phases, which take into account the internal resistance to heat and moisture transfer in the particles when determining the heat and mass transfer coefficients. In this case, the dependences of the heat of the phase transition on the humidity of the particles, their shrinkage during dehydration, and the dependences of the effective coefficients of thermal conductivity of the gas and vapor diffusion on the filtration rate are taken into account. The simulation results of drying chopped potatoes in a dense layer with a cyclic microwave convective energy supply are presented. The possibility of intensifying the process of moisture dehydration and reducing its duration compared with the convective method is shown. Comparison of calculated data with experimental data confirms the adequacy of the model.

COMPARATIVE ANALYSIS OF METHODS SUPPLIES THERMAL ENERGY IN HIGH-WATER BIOLOGICAL OBJECTS DURING DRYING

Object of research: the process of heating a biological object with various methods of supplying thermal energy, in particular, convective, direct electric and combined methods.
 Solved problem: intensification of heating of high-moisture biological objects during the drying process.
 Main scientific results. The expediency of using a combined (direct electric and convective) supply of thermal energy for intensifying heating of raw materials in the drying process has been established. In terms of the duration of the heating process, combined heating is much more effective than using purely convective or direct electric heating. Comparison of the values of the duration of the heating process for a body weighing 0.0028 kg shows that the combined heating occurs 1.5–2.5 times faster. At the same time, the consumption of electrical energy for the selected processing modes is 279–254 J, which is 80–87 % of the total required energy. It has been found that the main control factor in the combined heat supply is the applied voltage of direct electric heating.
 The area of practical application of the research results: enterprises of the processing industry, specializing in the production of dried products.
 Innovative technological product: a combined method of heating high-moisture objects during the drying process, which will provide intensive and energy-efficient processing modes while maintaining the established quality of the finished product.
 Scope of application of the innovative technological product: production of finished food products and semi-finished products.

Unsteady Mass Transfer of Nutrients in Gels with Channels of Different Spatial Structures

The dynamics of the development of immobilized cells in a gel under conditions of limited mass transfer of nutrients across the interface was considered. The goal of this study was to find methods for effective cultivation of living microorganisms in the gel due to the correct choice of the structure of internal channels, when nutrients are delivered to the gel by the convective-diffusion mechanism. The variation of the relative intensity of transmitted light along the height of the agarose gel sample with living yeast cells during nutrient solution diffusion from the surface with time was determined by spectroscopy. The depth of the gel layer at which the vital activity of microorganisms is provided was evaluated. The possibility of forming time-stable linear and branching channels in the gel was established experimentally. The possibility of their stable use for convective supply of nutrient in the volume was verified. The tendencies of diffusion of nutrients from the channels in the gel with immobilized cells were determined. The 3D structure of channels that provides an increase in the efficiency of cell nutrition in the gel volume was discussed.

System modelling of non-stationary drying processes

The kinetics of the drying process in continuous drum dryers differs from the drying of single objects in a batch mode. Drying process is affected by too many factors; hence, it is practically impossible to obtain an analyt- ical solution from the initial equations of heat and mass transfer, since the duration of drying depends on the opera- ting parameters. Therefore, it is of high theoretical and practical importance to create a highly efficient rotary drum dryer. Its design should be based on an integrated research of non-stationary processes of heat and mass transfer, hydrodynamics of fluidized beds, and drying kinetics in the convective heat supply. The experiment described in the present paper featured sunflower seeds. It was based on a systematic approach to modelling rotary convective drying processes. The approach allowed the authors to link together separate idealized models. Each model characterized a process of heat and mass transfer in a fluidized bed of wet solids that moved on a cylindrical surface. The experiment provided the following theoretical results: 1) a multimodel system for the continuous drying process of bulky mate- rials in a fluidized bed; 2) an effective coefficient of continuous drying, based on the mechanics of the fluidized bed and its continuous dehydration. The multimodel system makes it possible to optimize the drying process according to its material, heat-exchanger, and technological parameters, as well as to the technical and economic characteristics of the dryer.

ИССЛЕДОВАНИЕ ИНТЕНСИВНОСТИ КОНВЕКТИВНОЙ ПЕНОСУШКИ ЖЕЛАТИНОВОГО БУЛЬОНА ИЗ ОТХОДОВ ПЕРЕРАБОТКИ РЫБ ЧАСТИКОВЫХ ПОРОД

The intensity of the process of convective foam drying of gelatinized broth prepared from ordinary fish waste in the Astrakhan region was studied experimentally. The product was dried in a foamed state in a layer with a unilateral convective energy supply, as well as in the foamed and natural state in the form of round bars with a uniform convective energy supply. The ranges of variation of the main factors influencing the process were selected and substantiated, and their effect on the objective function (yield of dry gelatin per unit time per unit area) was analyzed. Approximating dependencies of the objective function on the main factors are obtained. According to the results of the research, application of a uniform convective energy supply in the course of drying gelatin broth under rational regimes allows to increase specific productivity of the process by 1.5 times, compared to drying with a unilateral energy supply, and to shorten the drying time from 4.2 to 2.3 hours. In this case, foaming the product results in more than a twofold increase in productivity while reducing the drying time by almost twice. The rational regimes for carrying out the process of convective drying of gelatinized broth in producing dry gelatin are determined: convective drying of the gelatinized broth should be conducted in a foamed state, with a uniform power supply, in the form of bars with circular cross section under the following conditions: initial diameter dn of a round bar = 0.004 m, initial moisture wn of product = 75%, flow rate v of the drying agent not less than 4.5 m/s, temperature T of the drying agent = 293-295 K. The indicated regimes provide the highest specific yield of the dry product G = 0.33 kg/(m2·h) and are recommended for practical use in order to increase the intensity of the process while maintaining the quality of dry gelatin.

Study of diffusive- and convective-transport mediated microtumor growth in a controlled microchamber.

In this paper, we report on using mass transport to control nutrition supply of colorectal cancer cells for developing a microtumor in a confined microchamber. To mimic the spatial heterogeneity of a tumor, two microfluidic configurations based on resistive circuits are designed. One has a convection-dominated microchamber to simulate the tumor region proximal to leaky blood vessels. The other has a diffusion-dominated microchamber to mimic the tumor core that lacks blood vessels and nutrient supply. Thus, the time for nutrition to fill the microchamber can vary from tens of minutes to several hours. Results show that cells cultured under a diffusive supply of nutrition have a high glycolytic rate and a nearly constant oxygen consumption rate. In contrast, cells cultured under convective supply of nutrition have a gradual increase of oxygen consumption rate with a low glycolytic rate. This suggests that cancer cells have distinct reactions under different mass transport and nutrition supply. Using these two microfluidic platforms to create different rate of nutrition supply, it is found that a continuous microtumor that almost fills the mm-size microchamber can be developed under a low-nutrient supply environment, but not for the convective condition. It also is demonstrated that microchannels can simulate the delivery of anti-cancer drugs to the microtumor under controlled mass-transport. This method provides a means to develop a larger scale microtumor in a lab-on-a-Chip system for post development and stimulations, and microchannels can be applied to control the physical and chemical environment for anti-cancer drug screening.

Фізичні основи очищення газових сумішей з допомогою фільтрування

Розглянуто форми подрібнених дисперсних матеріалів. Наведено формули визначення еквівалентного діаметра. Подано класифікацію сучасних фільтрів, розкрито їхні особливості. Показано основні чинники, що впливають на роботу фільтрів. Відомо, що сушильні апарати для подрібненої деревини, які часто використовують у виробництві деревостружкових і деревоволокнистих плит, для конвективного підведення тепла до стружки, як об'єкта сушіння, потребують уважного ставлення до енергоощадності. Варто зазначити, що специфічні властивості подрібненої деревини (малі розміри частинок, мала насипна маса, рухомість, парусність) дають змогу використовувати різноманітні способи сушіння: сушіння у щільному, киплячому, розпушеному шарі, а також безпосередній контакт об'єкта сушіння із нагрітою металевою поверхнею. Незважаючи на конструкційне розмаїття сушильних агрегатів для подрібненої деревини, найпоширенішими є конвективні сушарки із пневмомеханічним переміщенням подрібненого матеріалу. Наведені нижче формули дають змогу залежно від форми та розмірів подрібнених частинок і породи деревини зробити правильний вибір типу фільтру. Останнє дає змогу оцінити роботу самих фільтрувальних пристроїв. Адже за мірою накопичення пиловловлюваних подрібнених частинок значно зростає ступінь їх вловлюваності.

Hot Surface Ignition of A Composite Fuel Droplet

The present study examines the characteristics of conductive heating (up to ignition temperature) of a composite fuel droplet based on coal, liquid petroleum products, and water. In this paper, we have established the difference between heat transfer from a heat source to a fuel droplet in case of conductive (hot surface) and convective (hot gas) heat supply. The Leidenfrost effect influences on heat transfer characteristics significantly due to the gas gap between a composite fuel droplet and a hot surface.

An assessment of the vertical diffusive flux of iron and other nutrients to the surface waters of the subpolar North Atlantic Ocean

Abstract. In this study we report diapycnal diffusive fluxes of dissolved iron (dFe), dissolved aluminium (dAl) and the major macronutrients to the surface waters of the North Atlantic subpolar gyre. Turbulent diffusivities at the base of the summer mixed layer ranged from 0.01 to 0.5 (median 0.07) cm2 s−1 and daily macronutrient fluxes into the surface mixed layer typically represented < 0.5% of integrated mixed layer inventories, although fluxes were highly variable. Elevated nutrient fluxes of up to 4% of mixed layer inventories were identified on the Greenland Shelf, where integrated nutrient pools were lowest due to localised shoaling of the mixed layer. Diffusive fluxes of dFe and dAl were typically <0.1% of mixed layer inventories but were also highly variable between stations. Approximations of daily phytoplankton nutrient and Fe uptake indicate that the diffusive flux may at best represent <10% of phytoplankton macronutrient uptake, and only 1% of daily phytoplankton Fe uptake. The daily turbulent diffusive flux of dFe was comparable in magnitude to coincident estimates of aeolian Fe supply but despite shallower than normal convective mixing in winter 2010 the diffusive supply was 22 and 59 times smaller than the annual convective supply of Fe to the Irminger and Iceland basins respectively. The general picture obtained from this study is one of small magnitude diffusive nutrient and Fe fluxes to the subpolar North Atlantic during the period of annual nutrient minima and indicates that the diffusive supply mechanism is unlikely to alleviate the recently identified presence of seasonal iron limitation within the North Atlantic subpolar gyre; a condition exacerbated by low dFe:NO3− ratios in subsurface source waters.

Mass transport in a boundary layer and in an ion exchange membrane: Mechanism of concentration polarization and water dissociation

In an unforced flowing NaCl solution in bulk, gravitational or electro convection supplies ions from bulk toward the membrane surface through a boundary layer. In a boundary layer formed on an anion exchange membrane, the convection converts to migration and diffusion and carries an electric current. In a boundary layer formed on a cation exchange membrane, the convection converts to migration and carry an electric current. In a forced flowing solution in bulk, the boundary layer thickness is reduced and gravitation or electro convection is disappeared. An electric current is carried by diffusion and migration on the anion exchange membrane and by migration on the cation exchange membrane. Ion transport in a boundary layer on the cation exchange membrane immersed in a NaCl solution is more restricted comparing to the phenomenon on the anion exchange membrane. This is due to lower counter-ion mobility in the boundary layer and the restricted water dissociation reaction in the membrane. The water dissociation reaction is generated in an ion exchange membrane and promoted due to the increased forward reaction rate constant. However, the current efficiency for the water dissociation reaction is generally low. The intensity of the water dissociation is more suppressed in the strong acid cation exchange membrane comparing to the phenomenon in the strong base anion exchange membrane due to lower forward reaction rate constant in the cation exchange membrane. In the strong acid cation exchange membrane, the intensity of electric potential is larger than the values in the strong base anion exchange membrane. Accordingly, the stronger repulsive force is developed between ion exchange groups (SO3• groups) and co-ions (OH− ions) in the cation exchange membrane, and the water dissociation reaction is suppressed. In the strong base anion exchange membrane, the repulsive force between ion exchange groups (N+(CH3)3 groups) and co-ions (H+ ions) is relatively low, and the water dissociation reaction is not suppressed. Violent water dissociation is generated in metallic hydroxides precipitated on the desalting surface of the cation exchange membrane. This phenomenon is caused by a catalytic effect of metallic hydroxides. Such violent water dissociation does not occur on the anion exchange membrane.

Experimental investigation of adiabatic evaporation waves in superheated refrigerants

Propagation of adiabatic evaporation waves arising while refrigerants R-11 rapidly transit to metastable state due to depressurization in the rarefaction wave is experimentally investigated. New regularities of the interphase surface dynamics and the influence of interphase heat and mass transfer in propagation of adiabatic evaporation waves are obtained. It has been found that the phase transition in metastable liquid occurs in the conditions of developing multiscale turbulence in liquid and vapor phases under dynamic action of a vapor flow on the interphase surface and convective heat supply to the zone of high-intensity phase transition. The surface phase transition was visualized by a rapid video camera, its pulsating character is revealed and its properties are determined.

Elevated haematocrit – when too much of a good thing wreaks havoc on the endothelial surface layer

The convective supply of oxygen through the microcirculation to the tissues is the product of blood flow and oxygen content of the blood and depends on red blood cells (RBCs) in two ways. The RBCs contain the oxygen-binding protein haemoglobin so that the oxygen content is proportional to the concentration of RBCs or haematocrit (Hct). Thus increasing Hct leads to an increase in the capacity for the blood to carry oxygen. However, the rheological properties of the blood depend critically on Hct and the viscosity of the blood increases exponentially with Hct. Since blood flow depends inversely on viscosity, increasing Hct leads to a reduction in blood flow. The balance between these two opposing effects of Hct on oxygen supply leads to the concept of optimal haematocrit at which oxygen supply is maximum, usually near a Hct of about 50% (Birchard, 1997). What happens when systemic Hct rises substantially above the optimal level? Elevated Hct or polycythaemia results as an adaptive physiological response to sojourn at high altitude. A pathological condition known as polycythaemia vera results from an unwanted overproduction of RBCs and is associated with increased cardiovascular risk. Because of the obvious link between elevated Hct and increased blood viscosity, it is generally thought that the increased cardiovascular risk is due to pathological changes in haemodynamics, often resulting in peripheral ischaemia, which lead to increased total peripheral resistance and arterial blood pressure. In an article in a recent issue of The Journal of Physiology, Richter et al. (2011) suggest that the origin of cardiovascular problems associated with chronically elevated Hct lies rather with interactions between the RBCs and the glycocalyx or endothelial surface layer (ESL). The animal model used in the study of Richter et al. (2011) was that of a transgenic mouse (tg6) line which overexpressed human erythropoietin (Vogel & Gassmann, 2011). The systemic Hct of the tg6 mice was 85% compared with 46% for the control mice. Interestingly, mean arterial pressure was not significantly different between the two groups, being 77 ± 5 mmHg for the tg6 group and 69 ± 2 mmHg for the control group. However, there is a dramatic difference in average lifespan between the two groups: the tg6 mice live an average of 7.4 months compared with 26.7 months for the control mice. This study emphasized microcirculatory measurements, carried out on venules of the cremaster muscle. The endothelial surface layer or glycocalyx represents the interface between the flowing blood and the endothelial surface. Under normal conditions the thickness of this gel-like structure varies between 0.4 and 1.2 μm depending on several factors. The thickness of this layer has been quantified by several different approaches, and in the study of Richter et al. (2011), the microviscometric method developed by Damiano et al. (2004) was employed to analyse velocity profile data collected using the μ-PIV technique. In the μ-PIV method, the cross-sectional velocity distribution of 0.5 μm diameter fluorescent microspheres was measured and interpreted by the microviscometric method, which provided calculated data on a variety of key microhaemodynamic variables. The results of the study of Richter et al. (2011) in regard to the ESL were that the thickness of the ESL in tg6 mice was 0.13 μm compared with the more usual value of 0.52 μm for the control mice. Thus, the substantially elevated Hct found for the tg6 mice was associated with a significantly thinner ESL. There are several consequences of this thinner ESL. Haemodynamically, the calibre of the microvessel lumen will be increased by about twice the difference in ESL thickness or about 0.8 μm, leading to a smaller contribution to vascular resistance to blood flow. Results of a flow simulation model are presented by Richter et al. (2011) which show the incremental contributions of Hct and ESL thickness to vascular resistance. A thinner ESL barrier in the tg6 mice also means that platelets and leukocytes could come closer to the endothelial surface, making it a more prothrombogenic surface than in control mice. The question arises as to whether the high Hct chronically degrades the ESL or whether another mechanism associated with high Hct might be responsible for the much lower ESL thickness. The authors investigated this issue by reducing Hct in both the tg6 and control mice using isovolaemic haemodilution. When the tg6 mice were haemodiluted to the same Hct as the control mice, there was no significant difference in ESL thickness, indicating that the thin ESL in tg6 mice could result from a readily reversible, compressive mechanical effect of RBCs on the ESL. The involvement of alterations in endothelial glycocalyx or ESL (e.g. from damage or degradation) has been invoked to account, at least in part, for a number of pathological conditions and the article by Richter et al. (2011) provides a novel addition to this growing list.

Small-scale convection beneath oceans and continents

Small-scale convection supplies heat flow of ∼17 mW m−2 to the base of stable continents where xenolith studies resolve the geotherm. However, effects of small-scale convection are difficult to resolve in ocean basins. On first pass, most seafloor appears to subside to an asymptote compatible with ∼40 mW m−2 convective heat flow. These common regions are tracked by hotspots so uplift associated with ponded mantle material is an attractive alternative. Unaffected seafloor in the North and South Atlantic continues to subside with the square root of age as expected from pure conduction. The theory of stagnant-lid convection provides good scaling relationships for heat flow. For linear viscosity, heat flow is proportional to the underlying “half-space” viscosity to the −1/3 power and the temperature to change viscosity by a factor of e to the 4/3 power. The formalism is easily modified to represent convection beneath a lid of highly viscous and buoyant cratonal lithosphere and to represent transient convection beneath thickening oceanic lithosphere. Asthenospheric mantle with linear, strongly temperature-dependent, and weakly depth-dependent viscosity is compatible with both oceanic and continental data. More complicated rheology may allow vigorous small-scale convection under most but not all old ocean basins. Still viable hypotheses require poorly understood global features, including lateral variations of asthenospheric temperature. Seismological studies have the potential to resolve the lithosphere-asthenosphere boundary, including local variations of its depth associated with small-scale convection.

One-arm maximal strength training improves work economy and endurance capacity but not skeletal muscle blood flow

Maximal strength training with a focus on maximal mobilization of force in the concentric phase improves endurance performance that employs a large muscle mass. However, this has not been studied during work with a small muscle mass, which does not challenge convective oxygen supply. We therefore randomized 23 adult females with no arm-training history to either one-arm maximal strength training or a control group. The training group performed five sets of five repetitions of dynamic arm curls against a near-maximal load, 3 days a week for 8 weeks. This training increased maximal strength by 75% and improved rate of force development during both strength and endurance exercise, suggesting that each arm curl became more efficient. This coincided with a 17–18% reduction in oxygen cost at standardized submaximal workloads (work economy), and a 21% higher peak oxygen uptake and 30% higher peak load during maximal arm endurance exercise. Blood flow assessed by Doppler ultrasound in the axillary artery supplying the working biceps brachii and brachialis muscles could not explain the training-induced adaptations. These data suggest that maximal strength training improved work economy and endurance performance in the skeletal muscle, and that these effects are independent of convective oxygen supply.