Concentration polarization phenomenon in the case of mechanical pressure difference on the membrane

We analyzed the transport of KCl solutions through the bacterial cellulose membrane and concentration boundary layers (CBLs) near membrane with pressure differences on the membrane. The membrane was located in horizontal-plane between two chambers with different KCL solutions. The membrane was located in horizontal-plane between two chambers with different KCL solutions. As results from the elaborated model, gradient of KCL concentration in CBLs is maximal at membrane surfaces in the case when pressure difference on the membrane equals zero. The amplitude of this maximum decreases with time of CBLs buildup. Application of mechanical pressure gradient in the direction of gradient of osmotic pressure on the membrane causes a shift of this maximum into the chamber with lower concentration. In turn, application of mechanical pressure gradient directed opposite to the gradient of osmotic pressure causes the appearance of maximum of concentration gradient in chamber with higher concentration. Besides, the increase of time of CBLs buildup entails a decrease of peak height and shift of this peak further from the membrane. Similar behavior is observed for distribution of energy dissipation in CBLs but for pressure difference on the membrane equal to zero the maximum of energy dissipation is observed in the chamber with lower concentration. We also measured time characteristics of voltage in the membrane system with greater KCl concentrations over the membrane. We can state that mechanical pressure difference on the membrane can suppress or strengthen hydrodynamic instabilities visible as pulsations of measured voltage. Additionally, time of appearance of voltage pulsations, its amplitude, and frequency depend on mechanical pressure differences on the membrane and initial quotient of KCl concentrations in chambers.     

Reduced Pressure Ice Fog Technique for Controlled Ice Nucleation during Freeze-Drying

A method to achieve controlled ice nucleation during the freeze-drying process using an ice fog technique was demonstrated in an earlier report. However, the time required for nucleation was about 5 min, even though only one shelf was used, which resulted in Ostwald ripening (annealing) in some of the vials that nucleated earlier than the others. As a result, the ice structure was not optimally uniform in all the vials. The objective of the present study is to introduce a simple variation of the ice fog method whereby a reduced pressure in the chamber is utilized to allow more rapid and uniform freezing which is also potentially easier to scale up. Experiments were conducted on a lab scale freeze dryer with sucrose as model compound at different concentration, product load, and fill volume. Product resistance during primary drying was measured using manometric temperature measurement. Specific surface area of the freeze-dried cake was also determined. No difference was observed either in average product resistance or specific surface area for the different experimental conditions studied, indicating that with use of the reduced pressure ice fog technique, the solutions nucleated at very nearly the same temperature (−10°C). The striking feature of the “Reduced Pressure Ice Fog Technique” is the rapid ice nucleation (less than a minute) under conditions where the earlier procedure required about 5 min; hence, effects of variable Ostwald ripening were not an issue.     

Mechanical aspects of CO2 angiography

The aim of this paper is to clarify some physical–mechanical aspects involved in the carbon dioxide angiography procedure (CO₂ angiography), with a particular attention to a possible damage of the vascular wall.CO₂ angiography is widely used on patients with iodine intolerance. The injection of a gaseous element, in most cases manually performed, requires a long training period. Automatic systems allow better control of the injection and the study of the mechanical behaviour of the gas.CO₂ injections have been studied by using manual and automatic systems. Pressures, flows and jet shapes have been monitored by using a cardiovascular mock. Photographic images of liquid and gaseous jet have been recorded in different conditions, and the vascular pressure rises during injection have been monitored.The shape of the liquid jet during the catheter washing phase is straight in the catheter direction and there is no jet during gas injection. Gas bubbles are suddenly formed at the catheter’s hole and move upwards: buoyancy is the only governing phenomenon and no bubbles fragmentation is detected. The pressure rise in the vessel depends on the injection pressure and volume and in some cases of manual injection it may double the basal vascular pressure values.CO₂ angiography is a powerful and safe procedure which diffusion will certainly increase, although some aspects related to gas injection and chamber filling are not jet well known. The use of an automatic system permits better results, shorter training period and limitation of vascular wall damage risk.     

Studies on Mechano-Perception in Characeae: Decrease in Electrical Membrane Resistance in Receptor Potentials

A polyacrylate chamber with three pools was developed to measurethe changes in electrical membrane resistance during generationof receptor potentials upon mechanical stimulation in Charainternodal cells. The membrane resistance decreased at the peakof the receptor potentials. The present results support thehypothesis that the receptor potential is generated by activationof ion channel(s). This is the first success in demonstratinga change in the membrane resistance in receptor potential inducedmechanically in plants. (Received June 17, 1997; Accepted September 12, 1997)     

Variability observed in mechano-regulated in vivo tissue differentiation can be explained by variation in cell mechano-sensitivity

Computational simulations of tissue differentiation have been able to capture the main aspects of tissue formation/regeneration observed in animal experiments-except for the considerable degree of variability reported. Understanding and modelling the source of this variability is crucial if computational tools are to be developed for clinical applications. The objective of this study was to test the hypothesis that differences in cell mechano-sensitivity between individuals can explain the variability of tissue differentiation patterns observed experimentally. Simulations of an experiment of tissue differentiation in a mechanically loaded bone chamber were performed. Finite element analysis was used to determine the biophysical environment, and a lattice-modelling approach was used to simulate cell activity. Differences in cell mechano-sensitivity among individuals were modelled as differences in cell activity rates, with the activation of cell activities regulated by the mechanical environment. Predictions of the tissue distribution in the chambers produced the two different classes of results found experimentally: (i) chambers with a layer of bone across the chamber covered by a layer of cartilage on top and (ii) chambers with almost no bone, mainly fibrous tissue and small islands of cartilage. This indicates that the differing cellular response to the mechanical environment (i.e., subject-specific mechano-sensitivity) could be a reason for the different outcomes found when implants (or tissue engineered constructs) are used in a population.     

A Krypton Diffusion Porometer for the Direct Field Measurement of Stomatal Resistance

A stomatal diffusion porometer is described which measures directlythe diffusion of radioactive krypton through amphistomatousleaves. The porometer is relatively small and portable and iseasily used under field conditions. It consists of a miniaturediffusion chamber above an acrylic plastic reservoir which contains1200 cm³ of air enriched with ⁸⁵Kr. Geiger tubes in the diffusionchamber and in the reservoir monitor the relative concentrationsof 85Kr. Krypton is allowed to diffuse from the larger reservoirthrough the leaf into the diffusion chamber and the time forits concentration in relation to that in the reservoir to changebetween two fixed values is recorded. When this time lapse wascalibrated against known resistances a linear relationship,independent of temperature was found. Sources of error are analysedand some experiments are described in which the porometer wasused to measure diurnal changes in stomatal resistance. Resistancesof potted sunflower plants (Helianthus annuus L.) grown in agreenhouse were measured with both the krypton diffusion porometerand a condensation-type porometer and the results were usedto calculate both cuticular and stomatal resistances. Demonstrationof field measurements with the porometer include data from eucalyptustrees {Eucalyptus camaldulensis Dehn) and from an unirrigatedcotton crop {Gossypium hirsutum var. SJ 2) growing under semi-aridconditions. Stomatal conductance of the cotton crop during theopening phase was linearly related to solar radiation.     

Effects of low-chloride solutions on action potentials of sheep cadiac purkinje fibers

The rapid repolarization during phase 1 of the action potential of sheep cardiac purkinje fibers has been attributed to a time- and voltage-dependent chloride current. In part, this conclusion was based on experiments that showed a substantial slowing of phase 1 when larger, presumably impermeant, anions were substituted for chloride in tyrode’s solution. We have re- examined the electrical effects of low-chloride solutions. We recorded action potentials of sheep cardiac purkinje fibers in normal tyrode’s solution and in low-chloride solutions made by substituting sodium propionate, acetylglycinate, methylsulfate, or methanesulfonate for the NaCl of Tyrode’s solution. Total calcium was adjusted to keep calcium ion activity of test solutions equal to that of control solutions. Propionate gave qualitatively variable results in preliminary experiments; it was not tested further. Low-chloride solutions made with the other anions gave much more consistent results: phase 1 and the notch that often occurs between phases 1 and 2 were usually unaffected, and the action potential duration usually increased. The only apparent change in the resting potential was a transient 3-6 mV depolarization when low-chloride solution was first admitted to the chamber, and a symmetrical transient hyperpolarization when chloride was returned to normal. If a time- and voltage-dependent chloride current exists in sheep cardiac purkinje fibers, our results suggest that it plays little role in generating phase 1 of the action potential.     

Oxygen uptake during mineralization of photosynthesized carbon from phytoplankton of the Barra Bonita reservoir: a mesocosm study.

This study aimed to discuss and describe the oxygen consumption during aerobic mineralization of organic products (cells and excretion products) from five unialgal cultures: Cryptomonas sp., Microcystis aeruginosa, Anabaena spiroides, Thalassiosira sp. and Aulacoseira granulata. These species were isolated from Barra Bonita reservoir (22 degrees 29' S and 48 degrees 34' W) and cultivated in the laboratory. From each culture, two decomposition chambers were prepared; each chamber contained about 130 mg.L(-1) of carbon from water samples of the reservoir. The chambers were aerated and incubated in the dark at 20.0 degrees C. The concentration of dissolved oxygen, pH values and electrical conductivity of the solutions were determined during a period of 10 days. The results indicated increases in oxygen consumption for all the solutions studied and also for electrical conductivity. The pH values presented a decreasing tendency throughout the experiment. Oxygen consumption varied from 43 (Aulacoseira granulata chamber) to 345 mg O2 g(-1) C (Anabaena spiroides chamber). Decrease in pH values was probably due to increase in CO2 concentration from microbial respiration. Increase in electrical conductivity might be due to the liberation of ions during decomposition. The results demonstrate the potentiality of the studied genera in influencing oxygen availability followed by a die-off event. It also indicates the possibility of changing of the electrical conductivity and pH values in the water column due the aerobic algae mineralization.     

A microstructural finite element simulation of mechanically induced bone formation.

A finite element method to simulate the formation of an interconnected trabectular bone microstructure oriented with respect to applied in vivo mechanical forces is introduced and quantitatively compared to experimental data from a hydraulic bone chamber implant model. Randomly located 45 microm mineralized nodules were used as the initial condition for the model simulations to represent an early stage of intramembranous bone formation. Boundary conditions were applied consistent with the mechanical environment provided by the in vivo bone chamber model. A two-dimensional repair simulation algorithim that incorporated strain energy density (SED), SED gradient, principal strain, or principal strain gradient as the local objective criterion was utilized to simulate the formation of an oriented trabecular bone microstructure. The simulation solutions were convergent, unique, and relatively insensitive to the assumed initial distribution of mineralized nodules. Model predictions of trabecular bone morphology and anisotropy were quantitatively compared to experimental results. All simulations produced structures that qualitatively resembled oriented trabecular bone. However only simulations utilizing a gradient objective criterion yielded results quantitatively similar to in vivo observations. This simulation approach coupled with an experimental model that delivers controlled in vivo mechanical stimuli can be utilized to study the relationship between physical factors and microstructural adaptation during bone repair.     

Quick Staining Method For Frozen Sections

Since the advent and general acceptance of frozen sections in histological and pathological laboratories it has been necessary to devise methods for staining these sections. The usual method is fixing the tissue to a slide by the use of celloidin. This paper is an attempt to describe a permanent, quick method of staining frozen sections without distortion or mechanical tearing of the tissues.     

Multidrug-resistant Opportunistic and Pathogenic Bacteria Contaminate Algerian Banknotes Currency

Currency is one of the most exchanged items in human communities as it is used daily in exchange for goods and services. It is handled by persons with different hygiene standards and can transit in different environments. Hence, money can constitute a reservoir for different types of human pathogens. This study aimed to evaluate the potential of Algerian banknotes to shelter opportunistic pathogenic and multiresistant bacteria. To that end, 200 circulating notes of four different denominations were collected from various places and analyzed for their bacterial loads and contents. Besides, predominant strains were identified and characterized by biochemical and molecular methods, and their resistance profiles against 34 antibiotics were determined. Our results indicated that 100% of the studied banknotes were contaminated with bacteria. The total bacterial concentrations were relatively high, and different bacterial groups were grown, showing important diversity. In total, 48 predominant strains were identified as belonging to 17 genera. Staphylococcus and Micrococcus were the most prevalent genera, followed by Bacillus, Pseudomonas, and Acinetobacter. Antibiotic susceptibility testing showed that all the isolates harbored resistance to at least two molecules, and worrying resistance levels were observed. These findings prove that Algerian currency harbors opportunistic multiresistant bacteria and could potentially act as a vehicle for the spread of bacterial diseases and as a reservoir for antibiotic resistance genes among the community. Therefore, no cash payment systems should be developed and generalized to minimize cash handling and subsequent potential health risks.Key words: currency, Algeria, opportunistic bacteria, antibiotic resistance, circulating resistance genes     

An energy dissipation and cross shear time dependent computational wear model for the analysis of polyethylene wear in total knee replacements

The cost and time efficiency of computational polyethylene wear simulations may enable the optimization of total knee replacements for the reduction of polyethylene wear. The present study proposes an energy dissipation wear model for polyethylene which considers the time dependent molecular behavior of polyethylene, aspects of tractive rolling and contact pressure. This time dependent – energy dissipation wear model was evaluated, along with several other wear models, by comparison to pin-on-disk results, knee simulator wear test results under various kinematic conditions and knee simulator wear test results that were performed following the ISO 14243-3 standard. The proposed time dependent – energy dissipation wear model resulted in improved accuracy for the prediction of pin-on-disk and knee simulator wear test results compared with several previously published wear models.     

Two Monthly Continuous Dynamic Model Based on Nash Bargaining Theory for Conflict Resolution in Reservoir System

So far many optimization models based on Nash Bargaining Theory associated with reservoir operation have been developed. Most of them have aimed to provide practical and efficient solutions for water allocation in order to alleviate conflicts among water users. These models can be discussed from two viewpoints: (i) having a discrete nature; and (ii) working on an annual basis. Although discrete dynamic game models provide appropriate reservoir operator policies, their discretization of variables increases the run time and causes dimensionality problems. In this study, two monthly based non-discrete optimization models based on the Nash Bargaining Solution are developed for a reservoir system. In the first model, based on constrained state formulation, the first and second moments (mean and variance) of the state variable (water level in the reservoir) is calculated. Using moment equations as the constraint, the long-term utility of the reservoir manager and water users are optimized. The second model is a dynamic approach structured based on continuous state Markov decision models. The corresponding solution based on the collocation method is structured for a reservoir system. In this model, the reward function is defined based on the Nash Bargaining Solution. Indeed, it is used to yield equilibrium in every proper sub-game, thereby satisfying the Markov perfect equilibrium. Both approaches are applicable for water allocation in arid and semi-arid regions. A case study was carried out at the Zayandeh-Rud river basin located in central Iran to identify the effectiveness of the presented methods. The results are compared with the results of an annual form of dynamic game, a classical stochastic dynamic programming model (e.g. Bayesian Stochastic Dynamic Programming model, BSDP), and a discrete stochastic dynamic game model (PSDNG). By comparing the results of alternative methods, it is shown that both models are capable of tackling conflict issues in water allocation in situations of water scarcity properly. Also, comparing the annual dynamic game models, the presented models result in superior results in practice. Furthermore, unlike discrete dynamic game models, the presented models can significantly reduce the runtime thereby avoiding dimensionality problems.     

Transfer of Complex Skill Learning from Virtual to Real Rowing

Simulators are commonly used to train complex tasks. In particular, simulators are applied to train dangerous tasks, to save costs, and to investigate the impact of different factors on task performance. However, in most cases, the transfer of simulator training to the real task has not been investigated. Without a proof for successful skill transfer, simulators might not be helpful at all or even counter-productive for learning the real task. In this paper, the skill transfer of complex technical aspects trained on a scull rowing simulator to sculling on water was investigated. We assume if a simulator provides high fidelity rendering of the interactions with the environment even without augmented feedback, training on such a realistic simulator would allow similar skill gains as training in the real environment. These learned skills were expected to transfer to the real environment. Two groups of four recreational rowers participated. One group trained on water, the other group trained on a simulator. Within two weeks, both groups performed four training sessions with the same licensed rowing trainer. The development in performance was assessed by quantitative biomechanical performance measures and by a qualitative video evaluation of an independent, blinded trainer. In general, both groups could improve their performance on water. The used biomechanical measures seem to allow only a limited insight into the rowers'' development, while the independent trainer could also rate the rowers'' overall impression. The simulator quality and naturalism was confirmed by the participants in a questionnaire. In conclusion, realistic simulator training fostered skill gains to a similar extent as training in the real environment and enabled skill transfer to the real environment. In combination with augmented feedback, simulator training can be further exploited to foster motor learning even to a higher extent, which is subject to future work.     

Interaction between the septum and the left (right) ventricular free wall in order to evaluate the effects on coronary blood flow: numerical simulation

Mathematical modelling of the cardiovascular system (CVS) can help in understanding the complex interactions between both the ventricles and the septum. By describing the behaviour of the left (right) ventricular free wall, atria and septum using the variable elastance models, it is possible to reproduce their interactions. By relating the mechanical properties of both atria and both ventricles to the electrocardiogram (ECG) signal, it is possible to analyse the effects produced by different ECG delay on haemodynamic parameters. In the cardiovascular field, the incorrect interactions between septum and both ventricular free walls are based on many pathological conditions, i.e. symptomatic heart failure resulting from systolic dysfunction, ischemic dilated cardiomyopathy, and so on. The possible corrections that can be induced on the QRS complex duration in the ECG signal (i.e. cardiac resynchronisation therapy, CRT) can produce benefits improving the clinical status of the patient. The aim of this work was to evaluate, using our numerical simulator of the CVS, the effects induced on coronary blood flow (CBF) and aortic pressure using different ECG times, intra-ventricular and inter-ventricular delays. The results were obtained by reproducing the circulatory baseline and CRT conditions of seven patients described in literature. Haemodynamic simulated results are in accordance with literature data. Also the controversial results on CBF, in presence of CRT, are consistent with those described in the literature.     

Interaction between the septum and the left (right) ventricular free wall in order to evaluate the effects on coronary blood flow: numerical simulation

Mathematical modelling of the cardiovascular system (CVS) can help in understanding the complex interactions between both the ventricles and the septum. By describing the behaviour of the left (right) ventricular free wall, atria and septum using the variable elastance models, it is possible to reproduce their interactions. By relating the mechanical properties of both atria and both ventricles to the electrocardiogram (ECG) signal, it is possible to analyse the effects produced by different ECG delay on haemodynamic parameters. In the cardiovascular field, the incorrect interactions between septum and both ventricular free walls are based on many pathological conditions, i.e. symptomatic heart failure resulting from systolic dysfunction, ischemic dilated cardiomyopathy, and so on. The possible corrections that can be induced on the QRS complex duration in the ECG signal (i.e. cardiac resynchronisation therapy, CRT) can produce benefits improving the clinical status of the patient. The aim of this work was to evaluate, using our numerical simulator of the CVS, the effects induced on coronary blood flow (CBF) and aortic pressure using different ECG times, intra-ventricular and inter-ventricular delays. The results were obtained by reproducing the circulatory baseline and CRT conditions of seven patients described in literature. Haemodynamic simulated results are in accordance with literature data. Also the controversial results on CBF, in presence of CRT, are consistent with those described in the literature.     

Cellular Immunity of Mice Infected with Listeria monocytogenes in Diffusion Chambers

The importance of bringing live bacteria into intimate contact with macrophages as a prerequisite for establishing cellular immunity was investigated. The bacterium Listeria monocytogenes was shown to replicate and survive in diffusion chambers implanted in the peritoneal cavities of mice. Humoral substances accruing from host responses to diffusing soluble antigens of the microorganism were unable to inactivate the bacteria. The resistance of mice immunized by subcutaneous inoculation of the live organism always exceeded the resistance of mice with Listeria diffusion chamber implants. Animals with sham diffusion chambers were more resistant to a challenge by L. monocytogenes than were normal mice. Host resistance was not significantly different between Listeria diffusion chamber implant groups and sham diffusion chamber implant groups. The results suggested that direct involvement of macrophages with the parasite is necessary to achieve cellular immunity.     

A new chamber design for measuring community metabolism in a Michigan stream

We designed an open-ended community metabolism chamber to simultaneously measure surface and hyporheic metabolism. Our chamber design eliminated reaeration, compartmentalized metabolism, maintained ambient conditions and included hyporheic respiration. We compared results from our hyporheic chamber to results obtained from: (1) closed benthic community metabolism chambers constructed as recommended by Bott et al. (1978), and (2) whole-stream metabolism techniques as modified by Marzolf et al. (1994). Simultaneous comparisons of all three procedures were made for a 35 m riffle section of Augusta Creek, a 3rd-order Michigan stream, in July 1997 and repeated in July 1998. Simultaneous comparisons of all three procedures were also made for a 30 m sandy run section of Augusta Creek in September 1997, and repeated in September 1998. Our hyporheic chamber estimates for community respiration (CR₂₄) were similar to those obtained using the whole-stream metabolism procedure but were considerably higher than estimates obtained using the closed benthic chambers in three of the four experiments. These data suggest that our chamber design provided estimates of community metabolism which included both benthic and hyporheic respiration. The chamber incorporates several positive aspects of both closed chambers and the whole-stream method. This new method can be replicated, eliminates the need for a reaeration coefficient, ambient conditions are better approximated since it remains an open system, and it appears to provide more realistic estimates of whole-stream metabolism compared to the traditional chamber approach.     

Spatial and temporal patterns of green fluorescent protein (GFP) fluorescence during leaf canopy development in transgenic oilseed rape,<Emphasis Type="Italic"> Brassica napus</Emphasis> L.

The green fluorescent protein (GFP) holds promise as a field-level transgene marker. One obstacle to the use of GFP is fluorescence variability observed within leaf canopies. In growth chamber and field experiments, GFP fluorescence in transgenic oilseed rape (Brassica napus) was shown to be variable at each leaf position over time and among different leaves on the same plant. A leaf had its highest GFP fluorescence after emergence and, subsequently, its fluorescence intensity decreased. GFP fluorescence intensity was directly correlated with the concentration of soluble protein. The concentration of the genetically linked recombinant Bacillus thuringiensis (Bt) cry1Ac endotoxin protein also was examined, and GFP fluorescence was positively correlated with Bt throughout development. The results show that GFP can be used as an accurate transgene marker but that aspects of plant developmental should be taken into account when interpreting fluorescence measurements.Communicated by M.C. Jordan