Hydrostatic Pressure Gradient Research Articles

Estimation of the minimum fluidisation velocities in well-mixed bi-disperse fluidised beds

A method for estimating minimum fluidisation velocities in a well-mixed, bi-disperse fluidised bed of spherical particles is described where a drag model is combined with a particle packing model. The method described does not require empirical input about a specific particle mixture, and so these minimum fluidisation velocities can be estimated over wide ranges of size and density ratios. The treatment is fully non-dimensionalised. It is shown that two minimum fluidisation velocities may be defined for a well mixed bi-disperse bed: the gas speed at which fluidisation initiates determined from considering the bed as a whole, and a higher one corresponding to the balance of forces on an individual particle. The differences between bi- and mono-disperse beds are the change in particle volume fraction owing to packing, the difference in drag around individual particles compared with the average drag, and the action of the hydrostatic pressure gradient. The latter two effects tend to increase the difference between the two limits of minimum fluidisation velocity, while packing decreases it and intensifies the dependence on mass fraction of the minimum fluidisation velocities. The influence of inertia is determined from particle properties through an Archimedes number. Though the inertial effects are not large for a wide range of particles, they can start to dominate other influences on the minimum fluidisation velocities as particle diameter increases.

Peritoneal vasculopathy in the pathophysiology of long-term ultrafiltration failure: A hypothesis based on clinical observations .

Ultrafiltration failure in long-term peritoneal dialysis patients is a well-known and important, but poorly-explained complication of the treatment. Transcapillary ultrafiltration consists mainly of small-pore fluid transport and partly of free-water transport. The former is to a large extent dependent on the hydrostatic pressure gradient and on the number of perfused peritoneal microvessels. Free-water transport depends mainly on the crystalloid osmotic gradient. A longitudinal analysis of peritoneal transport has shown a dramatic decrease of net ultrafiltration and small-pore fluid transport after 4years of peritoneal dialysis. It will be argued that in contrast to common belief, a decrease of osmotically induced water transport cannot be the major contributor to long-term ultrafiltration failure. By exclusion of potential alternatives, the presence of vasculopathy in the peritoneal microcirculation is the most likely explanation. The resulting narrowing of vascular lumina will decrease the hydrostatic pressure gradient and thereby small-pore fluid transport and net ultrafiltration. Deposition of advanced glycosylation end products in peritoneal vessels may be important in the development of vasculopathy. This hypothesis is supported by morphological and functional results of dialysis with "biocompatible" solutions. .

Lymphatic Vessel Pumping.

The lymphatic system extends its network of vessels throughout most of the body. Lymphatic vessels carry a fluid rich in proteins, immune cells, and long-chain fatty acids known as lymph. It results from an excess of interstitial tissue fluid collected from the periphery and transported centrally against hydrostatic pressure and protein concentration gradients. Thus, this one-way transport system is a key component in the maintenance of normal interstitial tissue fluid volume, protein concentration and fat metabolism, as well as the mounting of adequate immune responses as lymph passes through lymph nodes. In most cases, lymph is actively propelled via rhythmical phasic contractions through a succession of valve-bordered chambers constituting the lymphatic vessels. This contraction/relaxation cycle, or lymphatic pumping, is initiated in the smooth muscle cells present in the vessel wall by a pacemaker mechanism generating voltage-gated Ca2+ channel-induced action potentials. The action potentials provide the depolarization and Ca2+ influx essential for the engagement of the contractile machinery leading to the phasic constrictions of the lymphatic chambers and forward movement of lymph. The spontaneous lymphatic constrictions can be observed in isolated vessels in the absence of any external stimulation, while they are critically regulated by physical means, such as lymph-induced transmural pressure and flow rate, as well as diffusible molecules released from the lymphatic endothelium, perivascular nerve varicosities, blood and surrounding tissues/cells. In this chapter, we describe the latest findings which are improving our understanding of the mechanisms underlying spontaneous lymphatic pumping and discuss current theories about their physiological initiation.

Disentanglement of the secrets of aluminium in acidophilic tea plant (Camellia sinensis L.) influenced by organic and inorganic amendments

Field experiment was carried out for four years in mature tea (Camellia sinensis L.) growing plot to investigate the impacts of different doses of inorganic and organic fertilizers on aluminium (Al) distribution pattern in soil and different parts of tea plant, leaf pigment concentration, gas exchange parameters, as well as the yield of tea. Results indicated that application of 6 × 103 kg compost ha−1 significantly increased the dry matter yields of tea. Pluckable shoot of tea plant were markedly stimulated in the presence of Al irrespective of treatment imposed. Furthermore, Al induced growth stimulation in tea plant was facilitated by higher photosynthesis rate as well as gas exchange parameters. For the present experiment, Tea Research Association Heavy Metal Contamination Index (TRAHMCI) decreases with increase the fertilizer dose and all the experimental soils were found non-polluted with respect to Al. Localization of Al in the root apex predominantly accumulated in the cortex. The translocation of Al from root to shoot was driven by the gradient in hydrostatic pressure and water potential. In all tea infusions influenced by different treatments, Al concentrations were within the maximum permissible limit of Al in drinking water by Provisional Tolerable Weekly Intake (PTWI) established by the Joint FAO/WHO Expert Committee on Food Additives (JECFA, 2 mg kg−1 bw−1) and the tolerable weekly intake (TWI) established by EFSA (European Food Safety Authority, 1 mg kg−1 bw−1). Application of stepwise multiple regression model indicates that around 75% of the variability in the yield of the crop can be expressed by the selected parameters under study. The Hierarchical cluster analysis reveals that two homogenous groups of treatment can be formed based on all the studied parameters.

Analysis of the stress field in the DeSoto canyon Salt Basin for ensuring safe offshore carbon storage

Offshore geologic CO2 storage offers an attractive option to reduce greenhouse gas emissions. Vast CO2 storage capacity exists in Cretaceous-Neogene sandstone in the DeSoto Canyon Salt Basin. Understanding the stress and pressure regimes in the basin can help evaluate the geomechanical integrity of the formations, thus minimizing the risk of CO2 migrating out of the storage complex. Borehole breakouts were identified using four-arm dipmeter logs. Elongation of the breakouts is aligned with the minimum horizontal compressive stress (Shmin), which tends to be oriented northeast-southwest. Vertical reservoir stresses are influenced by rock and fluid density. Lithostatic and hydrostatic stress each have a power-law relationship to depth. The average lithostatic stress (Sv) gradient is ∼21.4 kPa/m. Hydrostatic pressure gradient increases with brine density to a maximum of ∼12.2 kPa/m. Geometric mean of the Shmin-depth values correspond to an effective Shmin - effective Sv quotient of ∼0.5. Injection pressure can be maintained safely below the estimated effective minimum horizontal stress, thereby reducing the risk of cross-formational flow. Future study should focus on further constraint of geomechanical properties, reservoir integrity, and seal integrity.

Fluid accumulation in the staged Fontan procedure: the impact of colloid osmotic pressures.

Despite Fontan surgery showing improved results, fluid accumulation and oedema formation with pleural effusion are major challenges. Transcapillary fluid balance is dependent on hydrostatic and colloid osmotic pressure (COP) gradients; however, the COP values are not known for Fontan patients. The aim of this study was to evaluate the COP of plasma (COPp) and interstitial fluid (COPi) in children undergoing bidirectional cavopulmonary connection and total cavopulmonary connection. This study was designed as a prospective, observational study. Thirty-nine children (age 3 months-4.9 years) undergoing either bidirectional cavopulmonary connection or total cavopulmonary connection procedures were included. Blood samples and interstitial fluid were obtained prior to, during and after the preoperative cardiac catheterization and surgery with the use of cardiopulmonary bypass (CPB). Interstitial fluid was harvested using the wick method when the patient was under general anaesthesia. Plasma and interstitial fluid were measured by a colloid osmometer. Baseline values were compared with data from healthy controls. Baseline COPp was 20.6 ± 2.8 and 22.0 ± 3.2 mmHg and COPi was 11.3 ± 2.6 and 12.5 ± 3.5 mmHg in the bidirectional cavopulmonary connection group and the total cavopulmonary connection group, respectively. These values were significantly lower than in healthy controls. The COPp was slightly reduced throughout both procedures and normalized after surgery. The COPi increased slightly during the use of CPB and significantly decreased after surgery, resulting in an increased COP gradient and was correlated to pleural effusion. Fluid accumulation seen after Fontan surgery is associated with changes in COPs, determinants for fluid filtration and lymphatic flow. NCT 02306057: https://clinicaltrials.gov/ct2/results?cond=&term=NCT+02306057.

Evaluation of drilling parameters in gas hydrate exploration wells

Gas hydrates are crystalline ice-like structures formed from water and gas molecules at high pressure and low temperature conditions. They are considered as near-future energy resources. Recently, there have been many drilling activities in gas hydrates in both permafrost regions (mainly Mallik wells, Canada; Ignik Sikumi #1 well, Alaska; Mount Elbert #1, Alaska) and marine sediments (the wells drilled in Gulf of Mexico and India drilling expeditions). In this study, it is aimed to evaluate and analyze logging-while drilling data (LWD) and other drilling data of these drilling activities. Initially, all drilling parameters (i.e. rate of penetration, weight on bit, torques, mud logs, etc.) of these wells were collected and drawn to see the change in parameters with depths. In order to indicate the changes in drilling parameters in the sediments containing gas hydrates, gas hydrate saturations were estimated from resistivity logs and NMR logs in this study. High resistivity log values and methane peaks in drilling fluid were good indicators of gas hydrate existence. During the drilling of permafrost formations and gas hydrates deposited in coarse sands as pore filling, the rate of penetration generally decreased. Differently, there was not almost any change in the rate of penetration during the drilling of fracture-filling gas hydrates within silts/clay in India. Borehole enlargements (washouts) were commonly seen in the wells drilled in marine sediments (Gulf of Mexico and Indian expeditions). However, this effect was minimum during the drilling of the wells in permafrost regions. This difference is due to the loose sediments in marine environment. Furthermore, gamma and density logs were seriously affected by washouts, mainly in marine sediments. It was observed that pore-filling gas hydrates affect the rate of penetration and keep the sediments stable because well collapses mainly occurred in the sediments without any gas hydrates. However, the temperature of drilling fluid should be close to the temperature of gas hydrate zones to reduce the effect of drilling on gas hydrate dissociation for the wells both in permafrost and marine sediments. In Gulf Mexico and Indian drilling expeditions, riser and wellhead equipment were not used. However, the usage of surface casing might decrease the risk of borehole collapses due to very loose sediments close to sea floor. Another important outcome of this study is that the pressure gradient follows hydrostatic pressure gradients according to the pressure analysis within gas hydrate stability zones of marine sediments. Finally, the analyses of drilling parameters revealed that drilling through gas hydrate bearing strata is not as risky as it might have been considered. The key is hidden in appropriate drilling design.

Abstract 5039: The relationship between interstitial fluid pressure, collective invasion and YAP activation in engineered human breast tumors

Abstract The tumor microenvironment exhibits increased interstitial fluid pressure (IFP) due to combined effects of vascular leakage and inefficient drainage. Elevated IFP affects the transition of metastatic cells from the tumor to the healthy tissue. However, the complex architecture of the heterogeneous tumor tissues has made it difficult to correlate IFP with chemical and physical tumor responses that regulate invasion and metastasis. To overcome these limitations, we have engineered 3D breast tumor models for the quantitative characterization of biophysical and biochemical features that delineate its transition from a passive non-invasive to a metastatic state. In brief, we embed MDA-MB-231 human breast cancer cells in a collagen type I cavity molded within polydimethylsiloxane (PDMS) channels. The multicellular aggregates are subject to gradients of hydrostatic pressure through opposing reservoirs of culture media that are located at the base (Pbase) and the tip (Ptip) of the tumor. The pressure differential |Pbase – Ptip| defines the IFP gradient across the tumor. We found that the morphology of the engineered breast tumor models varies in response to the differential pressure gradients. For Pbase = Ptip and Pbase > Ptip, the engineered tumors displayed limited invadopodia formation. In contrast, for Pbase < Ptip, the engineered tumors displayed enhanced invadopodia formation. Moreover, we found that IFP affected cellular motility and invasion. Tumor cells demonstrated the highest average speed and directionality and were most invasive for Pbase < Ptip. Furthermore, we found that IFP-induced collective invasion coincides with the elevated expression of epithelial-mesenchymal transition (EMT) markers (vimentin, E-cadherin, Snail and keratin-8) in the engineered breast tumor models. In contrast with the previously demonstrated tumor suppressive activity of E-cadherin, engineered tumors that overexpressed E-cadherin developed a more invasive phenotype. The IFP-induced invasion through EMT in our engineered breast tumors motivated an investigation into the role of Yes-associated protein (YAP). YAP activation is implicated in EMT and regulated by fluid shear stress. Immunofluorescence staining for nuclear YAP suggests that YAP activation modulates the invasion and cell motility responses to IFP. Traction force microscopy will be used to further examine the relationship between IFP, force transduction into the surrounding microenvironment, and YAP activation. Citation Format: Andreas P. Kourouklis, Allison K. Simi, Alexandra Piotrowski-Daspit, Joe Tien, Celeste M. Nelson. The relationship between interstitial fluid pressure, collective invasion and YAP activation in engineered human breast tumors [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 5039.

An Experimental Study of the Run-Up Process of Breaking Bores Generated by Dam-Break Under Dry- and Wet-Bed Conditions

In this study, a series of dam-break laboratory experiments were carried out to investigate the run-up process of breaking bores under dry- and wet-bed conditions. Detailed measurements were conducted to reveal differences in the run-up hydrodynamic characteristics under these two conditions, e.g. the bore front profile, the maximum run-up height and duration, and the instantaneous bore front velocity. Two successive bores were observed under the wet-bed run-up process, while multiple bores (three bores in general) were generated during the dry-bed run-up process due to the significant bottom friction effect. A linear relationship with the uniform gradient is found between the maximum run-up height and the initial water head for both dry- and wet-bed conditions, indicating that difference in the maximum run-up height between the dry- and specified wet-bed cases or among various wet-bed cases is not sensitive to the initial water head. Under the same initial water head, although the dry-bed run-up process takes a longer duration than that of wet-bed cases, the maximum run-up height is smallest for the dry-bed case and gradually increases with the increase of the initial downstream water depth for wet-bed cases. Under the wet-bed conditions, temporal variation of the bore front run-up velocity can be classified into two stages, i.e. the acceleration stage induced by the relatively large incident bore front water depth (large onshore hydrostatic pressure gradient) and the deceleration stage governed by the offshore-directed gravity force and bottom friction. Nevertheless, due to the small incident bore front water depth, run-up process under the dry-bed conditions does not show the acceleration stage.

Pulmonary endothelial permeability and tissue fluid balance depend on the viscosity of the perfusion solution.

Fluid filtration in the pulmonary microcirculation depends on the hydrostatic and oncotic pressure gradients across the endothelium and the selective permeability of the endothelial barrier. Maintaining normal fluid balance depends both on specific properties of the endothelium and of the perfusing blood. Although some of the essential properties of blood needed to prevent excessive fluid leak have been identified and characterized, our understanding of these remains incomplete. The role of perfusate viscosity in maintaining normal fluid exchange has not previously been examined. We prepared a high-viscosity perfusion solution (HVS) with a relative viscosity of 2.5, i.e., within the range displayed by blood flowing in vessels of different diameters in vivo (1.5-4.0). Perfusion of isolated murine lungs with HVS significantly reduced the rate of edema formation compared with perfusion with a standard solution (SS), which had a lower viscosity similar to plasma (relative viscosity 1.5). HVS did not alter capillary filtration pressure. Increased endothelial shear stress produced by increasing flow rates of SS, to mimic the increased shear stress produced by HVS, did not reduce edema formation. HVS significantly reduced extravasation of Evans blue-labeled albumin compared with SS, indicating that it attenuated endothelial leak. These findings demonstrate for the first time that the viscosity of the solution perfusing the pulmonary microcirculation is an important physiological property contributing to the maintenance of normal fluid exchange. This has significant implications for our understanding of fluid homeostasis in the healthy lung, edema formation in disease, and reconditioning of donor organs for transplantation.

Cardiac performance is influenced by rotational changes of position in the transversal plane, both in the horizontal and in the 60̊ head-up postures.

Echocardiography is usually performed with the subject/patient lying in the left lateral position (LLP), because the acoustic window is better in this than in the supine position (SP). The aim was to investigate cardiac responses to rotational changes of position in the transversal plane, from SP to LLP while horizontal, and from leaning on the back (HUT-LB) to leaning on the left side (HUT-LL) while tilted 60° head-up from the horizontal. Healthy men (n=12) underwent 10-min HUT provocations. Cardiac variables were measured using two-dimensional echocardiography, Doppler, tissue Doppler imaging and arterial pressures using a volume-clamp method. In horizontal posture, cardiac volumes were smaller in SP than in LLP: end-diastolic volume (EDV) by 14%, end-systolic volume (ESV) by 13%, stroke volume (SV) by 14%, and cardiac output (CO) by 16% (P<0·03). In addition, the mitral annular plane systolic excursion (MAPSE) was 11% smaller (P=0·001) and the left ventricle isovolumic relaxation time (IVRT) 27% longer in SP than in LLP. The ejection fraction, heart rate, arterial pressure and pulmonary ventilation were similar in SP and LLP. During HUT, EDV, SV, CO and MAPSE were smaller, and IVRT was longer, in HUT-LB than in HUT-LL, by -19%, -20%, -17%, -18% and +35%, respectively (P<0·04). Cardiac performance is enhanced in LLP versus SP and in HUT-LL versus HUT-LB, which can be attributed to improved venous return, conceivably, wholly or in part, due to increased hydrostatic pressure gradients between the caval veins and the heart in the LLP and HUT-LL positions.

On the dynamics of a thin viscous film spreading between a permeable horizontal plate and an elastic sheet

The two-dimensional dynamics of a thin film of viscous fluid spreading between a permeable horizontal plate and an overlying thin elastic sheet is explored. We use a lubrication model to describe the balance between the elastic stress, the hydrostatic pressure gradient and the viscous resistance of the flow, as fluid spreads laterally from a source and simultaneously drains through the plate. A family of asymptotic solutions are described in which the flow is dominated by either the hydrostatic pressure gradient or the elastic stress associated with the deformation of the sheet. In these solutions, although the deformation of the sheet above the porous plate arises from the fluid flow below the sheet, the fluid typically separates from the sheet a short distance upstream of the full extent of the draining zone, with the region of flow being driven purely by the hydrostatic pressure gradient. As a result, an air gap develops below the sheet up to the point where it touches back down onto the plate. With a very light or stiff elastic sheet, this touchdown point may extend far beyond the fluid draining zone, but otherwise it is similar to the extent of the draining zone.

The Arteriolar Vasodilatation Model of Vibrio cholerae Induced Diarrhoeal Disease

Secretory diarrhoeal disease caused by enterotoxins produced by pathogenic bacteria is characterised by severe fluid loss into the intestine. A prevalent explanation for such high rates of loss, such as occur in episodes of cholera, is that intestinal epithelial cells (enterocytes) actively secrete chloride ion into the lumen. Fluid is drawn into the lumen because of the osmotic pressure difference that is created across the mucosa. Widely proposed as the cause of many forms of secretory diarrhoea, the enterocyte based paradigm displaced an earlier model of secretion i.e. fluid filtration caused by increased capillary hydrostatic pressure, possibly coupled with increased hydraulic conductivity. This would be aggravated by any concurrent inhibition of fluid absorption if it occurred. In the earlier and alternative paradigm, pathophysiological reductions in smooth muscle tone elevate capillary pressure, thereby increasing the hydrostatic pressure gradient that forces fluid from the capillary into the interstitial space and thence into the lumen. In this review, the present and historical evidence for the vasodilatation view of secretory diarrhoeal disease is presented, together with past challenges of this concept, particularly those involving the erroneous equating of solute permeability with hydraulic conductivity. It can be seen that the physical forces model of altered Starling forces combined with enhanced fluid permeation explains more experimental findings than the cellular based enterocyte model can. Several key past papers advocating enterocyte secretion in which the capillary vasodilatation model was also discounted, were examined for the inherent fallacies within the arguments that were proposed. Where possible, quantitative arguments are proposed that indicate that is it the combination of capillary vasodilatation combined with increased tight junctional hydraulic conductivity that causes profuse secretion, made worse by any concurrent inability to absorb fluid. To assist the general physiological reader, an appendix reviews Bernoulli’s principle of flow within tubes and explains the arguably counter-intuitive phenomenon that vasodilatation increases capillary pressure because of a velocity reduction within a dilated segment.

Application of adsorption potential theory to methane adsorption on organic-rich shales at above critical temperature

The characteristic curves for methane on organic-rich shales at above critical temperature were investigated. And the adsorption equation of methane on organic-rich shales at above critical temperature was deduced. The results show that the improved Amankwah’s method is applied to obtain the suitable pseudo-saturation pressure and then the optimal characteristic curve for methane on organic-rich shales can be determined based on the adsorption potential theory. The adsorption equation is constructed by combination of the D–A equation and characteristic curve, which could reliably predict the methane adsorption capacity on organic-rich shales at different temperatures and pressures. The methane adsorption capacity first increases to maximum and then decreases with increasing the depth. When the burial depth is lower than a depth corresponding to the maximum adsorption capacity, the adsorption capacity is determined by the hydrostatic pressure gradient combined with the geothermal gradient. The higher the hydrostatic pressure gradient is, the larger the maximum adsorption capacity is. However, when the burial depth exceeds the critical depth, the methane adsorption capacity is mainly affected by the geothermal gradient. The higher the geothermal gradient is, the faster the fall rate of the adsorption capacity is.

Influence of Normal and Shear Stress on the Hydraulic Transmissivity of Thin Cracks in a Tight Quartz Sandstone, a Granite, and a Shale

AbstractTransmissivity of fluids along fractures in rocks is reduced by increasing normal stress acting across them, demonstrated here through gas flow experiments on Bowland shale, and oil flow experiments on Pennant sandstone and Westerly granite. Additionally, the effect of imposing shear stress at constant normal stress was determined, until frictional sliding started. In all cases, increasing shear stress causes an accelerating reduction of transmissivity by 1 to 3 orders of magnitude as slip initiated, as a result of the formation of wear products that block fluid pathways. Only in the case of granite, and to a lesser extent in the sandstone, was there a minor amount of initial increase of transmissivity prior to the onset of slip. These results cast into doubt the commonly applied presumption that cracks with high resolved shear stresses are the most conductive. In the shale, crack transmissivity is commensurate with matrix permeability, such that shales are expected always to be good seals. For the sandstone and granite, unsheared crack transmissivity was respectively 2 and 2.5 orders of magnitude greater than matrix permeability. For these rocks crack transmissivity can dominate fluid flow in the upper crust, potentially enough to permit maintenance of a hydrostatic fluid pressure gradient in a normal (extensional) faulting regime.

Characterization of Mouse Mesenteric Lymphatic Valve Structure and Function.

Intraluminal valves of collecting lymphatic vessels ensure unidirectional lymph transport against hydrostatic pressure gradient. Mouse mesentery harbors up to 800 valves and represents a convenient model for lymphatic valve quantification, high resolution imaging of different stages of valve development as well as for analysis of valve function. The protocol describes embryonic and postnatal mesenteric lymphatic vessel preparation for whole-mount immunofluorescent staining and visualization of valve organization, quantification of main morphological parameters such as valve size and leaflet length, and the quantitative assessment of functional properties of adult valves using back-leak and closure tests.

The Lymphatic Fluid.

This review will highlight our current understanding of the formation, circulation, and immunological role of lymphatic fluid. The formation of the extracellular fluid depends on the net balance between the hydrostatic and osmotic pressure gradients effective in the capillary beds. Lymph originates from the extracellular fluid and its composition combines the ultrafiltrated plasma proteins with the proteome generated by the metabolic activities of each parenchymal tissue. Several analyses have indicated how the lymph composition reflects the organs' physiological and pathological states. The collected lymphatic fluid moves from the capillaries into progressively larger collectors toward the draining lymph node aided by the lymphangion contractility and unidirectional valves, which prevent backflow. The proteomic composition of the lymphatic fluid is reflected in the MHC II peptidome presented by nodal antigen-presenting cells. Taken together, the past few years have generated new interest in the formation, transport, and immunological role of the lymphatic fluid.

How fishes find the shore: evidence for orientation to bathymetry from the non-homing sea lamprey

Orientation to a shoreline is the critical first step for aquatic organisms that navigate to coastal waters, estuaries, and rivers to feed or reproduce. Most studies of animal migration have focused on homing-based navigation while non-homing navigation is poorly understood. We quantified the navigation behavior of sea lamprey during their non-homing return migration to a coastline in the Laurentian Great Lakes. Acoustically tagged sea lamprey were displaced 3.3 km from shore into the center of an acoustic listening array that provided high-resolution (30 s intervals, &lt;5 m accuracy) three-dimensional paths. Eighty-one percent of individuals arrived at the nearest coast by moving towards shallower water. A biphasic sequence of movement was documented for most individuals, a more tortuous movement closer to the bottom associated with orientation, and a faster more linear movement we associate with directed search. Sea lamprey oriented to shallow water even when that was not the shoreward direction, and did not appear to rely on memory or recognition of the nearest coast. We postulate that individuals specifically performed barokinesis, whereby individuals assessed the gradient in absolute hydrostatic pressure on the bottom and to choose a heading towards shallower water. Repeated excursions to the bottom may confirm progress, while time spent at the surface is likely associated with surface-linked olfactory cues that indicate proximity to river water entrained along the coast. This is the first evidence that suggests the shoreward gradient in hydrostatic pressure may be used during shoreward orientation, and may represent a class of sensory information not previously considered in aquatic animal navigation.

Aquaporin 0 Modulates Lens Gap Junctions in the Presence of Lens-Specific Beaded Filament Proteins.

PurposeThe objective of this study was to understand the molecular and physiologic mechanisms behind the lens cataract differences in Aquaporin 0-knockout-Heterozygous (AQP0-Htz) mice developed in C57 and FVB (lacks beaded filaments [BFs]) strains.MethodsLens transparency was studied using dark field light microscopy. Water permeability (Pf) was measured in fiber cell membrane vesicles. Western blotting/immunostaining was performed to verify expression of BF proteins and connexins. Microelectrode-based intact lens intracellular impedance was measured to determine gap junction (GJ) coupling resistance. Lens intracellular hydrostatic pressure (HP) was determined using a microelectrode/manometer system.ResultsLens opacity and spherical aberration were more distinct in AQP0-Htz lenses from FVB than C57 strains. In either background, compared to wild type (WT), AQP0-Htz lenses showed decreased Pf (approximately 50%), which was restored by transgenic expression of AQP1 (TgAQP1/AQP0-Htz), but the opacities and differences between FVB and C57 persisted. Western blotting revealed no change in connexin expression levels. However, in C57 AQP0-Htz and TgAQP1/AQP0-Htz lenses, GJ coupling resistance decreased approximately 2.8-fold and the HP gradient decreased approximately 1.9-fold. Increased Pf in TgAQP1/AQP0-Htz did not alter GJ coupling resistance or HP.ConclusionsIn C57 AQP0-Htz lenses, GJ coupling resistance decreased. HP reduction was smaller than the coupling resistance reduction, a reflection of an increase in fluid circulation, which is one reason for the less severe cataract in C57 than FVB. Overall, our results suggest that AQP0 modulates GJs in the presence of BF proteins to maintain lens transparency and homeostasis.

On Thermodiffusion and Gauge Transformations for Thermodynamic Fluxes and Driving Forces

We discuss the molecular diffusion transport in infinitely dilute liquid solutions under non-isothermal conditions. This discussion is motivated by an occurring misinterpretation of thermodynamic transport equations written in terms of chemical potential in the presence of temperature gradient. The transport equations contain the contributions owned by a gauge transformation related to the fact that chemical potential is determined up to the summand of form (AT+B) with arbitrary constants A and B, where constant A is owned by the entropy invariance with respect to shifts by a constant value and B is owned by the potential energy invariance with respect to shifts by a constant value. The coefficients of the cross-effect terms in thermodynamic fluxes are contributed by this gauge transformation and, generally, are not the actual cross-effect physical transport coefficients. Our treatment is based on consideration of the entropy balance and suggests a promising hint for attempts of evaluation of the thermal diffusion constant from the first principles. We also discuss the impossibility of the "barodiffusion" for dilute solutions, understood in a sense of diffusion flux driven by the pressure gradient itself. When one speaks of "barodiffusion" terms in literature, these terms typically represent the drift in external potential force field (e.g., electric or gravitational fields), where in the final equations the specific force on molecules is substituted with an expression with the hydrostatic pressure gradient this external force field produces. Obviously, the interpretation of the latter as barodiffusion is fragile and may hinder the accounting for the diffusion fluxes produced by the pressure gradient itself.