Keratin filament suspensions show unique micromechanical properties.

All epithelial cells feature a prominent keratin intermediate filament (IF) network in their cytoplasm. Studies in transgenic mice and in patients with inherited epithelial fragility syndromes showed that a major function of keratin IFs is to provide mechanical support to epithelial cell sheets. Yet the micromechanical properties of keratin IFs themselves remain unknown. We used rheological methods to assess the properties of suspensions of epidermal type I and type II keratin IFs and of vimentin, a type III IF polymer. We find that both types of IFs form gels with properties akin to visco-elastic solids. With increasing deformation they display strain hardening and yield relatively rapidly. Remarkably, both types of gels recover their preshear properties upon cessation of the deformation. Repeated imposition of small deformations gives rise to a progressively stiffer gel for keratin but not vimentin IFs. The visco-elastic moduli of both gels show a weak dependence upon the frequency of the input shear stress and the concentration of the polymer, suggesting that both steric and nonsteric interactions between individual polymers contribute to the observed mechanical properties. In support of this, the length of individual polymers contributes only modestly to the properties of IF gels. Collectively these properties render IFs unique among cytoskeletal polymers and have strong implications for their function in vivo.     

Physical properties of microbial suspensions

Physical properties of suspensions of Saccharomyces cerevisiae, Candida utilis and Escherichia coli (density, viscosity and surface tension) were measured in synthetic suspensions formed of centrifuged biomass and supernatants from various stages of batch cultivation in the range from 0 to 10% w/v for yeasts and from 0 to 0.25% w/v for bacteria. Surface tension was also measured in native suspensions in the range of 0 less than or equal to Cm less than or equal to 2.0% w/v. All single cell suspensions were found to be Newtonian in behaviour. Densities strictly obey the mixing law, viscosities of Saccharomyces cerevisiae suspensions were correlated by an empirical relation in dependence of Cm and t, surface tensions were correlated graphically for suspensions of Saccharomyces cerevisiae and Escherichia coli, since experiments with both microorganisms have shown that the previously published approximate correlation can safely be used.     

Physical properties of microbial suspensions

A way of characterizing cell size distribution in suspensions of single-cell microorganisms is suggested, based on the first and second moments around origin. Suspension density may be predicted on the basis of the mixing law and the density of microbial dry matter, for suspensions ofSaccharomyces cerevisiae, Candida lipolytica, andAspergillus niger. Newtonian viscosities were correlated using regression analysis by η=Aexp(BC _m)exp(D/t); another correlation is presented for the calculation of surface tension in single-cell microbial suspensions. All the relations are valid in the range of concentrations up to 15% (w/v) and for temperatures between 15° and 35°C. The formulae presented may be used in other hydraulic studies.     

高效氟氯氰菊酯微胶囊悬浮剂对德国小蠊的防治效果

【目的】研究高效氟氯氰菊酯微胶囊悬浮剂对德国小蠊Blattella germanica的防治效果,为指导防治德国小蠊提供科学、合理的依据。【方法】参照国家标准GB/T 13917.1-2009《农药登记卫生用杀虫剂的室内药效试验及评价第1部分:喷射剂》的测试方法进行防治试验。【结果】0.8 m L/m2剂量的瓷砖和玻璃面板药效的持续时间分别为98 d、112 d;1.6 m L/m2剂量的瓷砖和玻璃面板药效的持续时间分别为112 d、119 d。【结论】相同剂量的瓷砖和玻璃面板相比较,玻璃面板的药效持续时间长,但稳定性低。     

A semi-empirical model for flow of blood and other particulate suspensions through narrow tubes

A semi-empirical model applicable to the flow of blood and other particulate suspensions through narrow tubes has been developed. It envisages a central core of blood surrounded by a wall layer of reduced hematocrit. With the help of this model the wall layer thickness and extent of plug flow may be calculated using pressure drop, flow rate and hematocrit reduction data. It has been found from the available data in the literature that for a given sample of blood the extent of plug flow increases with decreasing tube diameter. Also for a flow through a given tube it increases with hematocrit. The wall layer thickness is found to decrease with increase in blood hematocrit. A comparison between the results of rigid particulate suspensions and blood reveals that the thicker wall layer and smaller plug flow radius in the case of blood may be attributed to the deformability of the erythrocytes.     

Transient lateral transport of platelet-sized particles in flowing blood suspensions.

Concentration profiles of 2.5 microns latex beads were measured to demonstrate lateral transport of platelet-sized objects in flows of blood suspensions; the flows had equivalent Poiseuille wall shear rates (WSRs) from 250 to 1220 s-1. Each experimental trial began with a steady flow of suspension without beads in a thin-walled capillary tube (219 microns ID; 10.2 microns SD). The tube entrance was then switched to a reservoir containing suspension of equal hematocrit, but with beads, for a short interval of flow at the same WSR. This process established a paraboloidal tongue of labeled suspension with a transient concentration gradient at its surface. The tube and contents were rapidly frozen to fix the suspended particles in flow-determined locations. Segments of frozen tube were collected at distances from the entrance corresponding to 13%, 39%, and 65% of the axial extent of the ideal paraboloidal tongue. Concentration profiles were estimated from distances measured on fluorescence microscope images of cross-cut tube segments. Experiments used tubes either 40 or 50 cm long, suspension hematocrits of 0, 15, or 40%, and bead concentrations in the range of 1.5-2.2 x 10(5)/mm3. Profiles for 0% hematocrit suspension, a dilute, single-component suspension, had features expected in normal diffusive mixing in a flow. Distinctly different profiles and more lateral transport occurred when the suspensions contained red cells; then, all profiles for 13% extent had regions of excess bead concentration near the wall. Suspension flows with 40% hematocrit exhibited the largest amount of lateral transport. A case is made that, to a first approximation, the rate of lateral transport grew linearly with WSR; however, statistical analysis showed that for 40% hematocrit, less lateral transport occurred when the WSR was 250 s-1 or 1220 s-1 than 560 s-1, thus indicating that the rate behavior is more complex.     

Theory of filtration of mixed blood suspensions

A theory is developed for the flow of suspensions of blood cells through filters in which the properties of the cells are defined by statistical distributions. It is shown that conditions are generally transient, and computational procedures are developed to compute the pressure drop and the fraction of the pores of the filter containing cells of various types as a function of time. The computations show a large influence of very small concentrations of stiff cells which gradually collect in the filter and effectively plug the filter during the time of a typical test. It is also shown that the mean value of the resistance offered by a cell population with a limited distribution of resistances is more important than dispersion of resistances about the mean in determining the observable pressure curve. Experimental data are presented demonstrating that the drug pentoxifylline reduces the stiffness of leukocytes.     

The linear cable theory as a model of gill blood flow

The vascular organization of the teleost gill suggests that blood flow distribution from the filamental artery to the respiratory lamellae is governed by relationships analogous to the cable conduction properties of a nerve axon. The space constant (λ) by definition is the distance along the gill filament at which the in-series resistance of the afferent filament artery equals the in-parallel resistance of the afferent lamellar arteriolar, lamellar, efferent lamellar arteriolar (ALA-L-ELA) segments. Constriction of the afferent filamental artery or uniform dilation of the ALA-L-ELA will decrease λ. As λ decreases, flow through the proximal (basal) lamellae greatly increases at the expense of distal lamellar perfusion. When λ increases in a system of finite length the flow profile must account for reflected pressures within the main vessel. The λ calculated from corrosion casts of gill vasculature is $\text{1}\text{4}$ to $\text{1}\text{2}$ the filament length. This favors blood flow through the proximal lamellae and when cardiac output increases, the proportion of cardiac output perfusing the proximal areas increases at the expense of distal lamellar blood flow. To offset these changes it is proposed that increased distal lamellar perfusion is achieved by simultaneous vasodilatation of distal and constriction of proximal ALA-L-ELA segments and dilation of the afferent filamental artery.     

Effects of aggregation on the flow properties of red blood cell suspensions in narrow vertical tubes

The flow properties of aggregating red cell suspensions flowing at low rates through vertical tubes with diameters from 30 microns to 150 microns are analyzed using a theoretical model. Unidirectional flow is assumed, and the distributions of velocity and red cell concentration are assumed to be axisymmetric. A three-layer approximation is used for the distribution of red cells, with a cylindrical central core of aggregated red cells moving with uniform velocity, a cell-free marginal layer near the tube wall, and an annular region located between the core and the marginal layer containing suspended non-aggregating red cells. This suspension is assumed to behave approximately as a Newtonian fluid whose viscosity increases exponentially with red cell concentration. Physical arguments concerning the mechanics of red cell attachment to, and detachment from the aggregated core lead to a kinetic equation for core formation. From this kinetic equation and the equation for conservation of red cell volume flux, a relationship between core radius and pressure gradient is obtained. Then the relative viscosity is calculated as a function of pseudo-shear rate. At low flow rates, it is shown that the relative viscosity decreases with decreasing flow and that the dependence of relative viscosity on shear rates is more pronounced in larger tubes. It is also found that the relative viscosity decreases with increasing aggregation tendency of suspension. These theoretical predictions are in good qualitative and quantitative agreement with experimental results.     

Rheological properties of Aspergillus niger pellet suspensions

Summary Shear diagrams for Aspergillus niger pellet suspensions were obtained using a helical ribbon impeller system. Experimental results concerning the effects of pellet size and surface nature on the rheological behaviour are given. In addition, the influence of the quantity of biomass was studied; it can be quantified by the model proposed by R. Wittler et al. (1983).Symbols b Fitting parameter eq. 5 (-) - C Fitting parameter eq. 5 (Pa s)^0.5 - c Maximum tangential velocity (-) - d _R Diameter of the ribbon impeller (mm) - Em Fitting parameter eq. 5 (-) - Ex Pellet volume fraction (or P.V.F.) (-) - H Height of the ribbon impeller (mm) - K Consistency index (Pa) (s) ⁿ - M Torque (arbitrary unit) - N Rotational speed (l) (s)^-1 - n Flow behaviour index (-) - _s Apparent viscosity of pellet suspension (Pa s) - p Width of the ribbon (mm) - s Pitch of the ribbon impeller (mm) - t Vessel diameter for the impeller-vessel system (mm) - Shear rate (s)^-1 - Shear stress (Pa)     

Flocculation properties of pectin in various suspensions

Pectin had a flocculating activity and its flocculating activities in various suspensions were investigated. Flocculating activity of pectin in a kaolin suspension was markedly stimulated by the addition of Al3+ and Fe3+ to the suspension. Optimum temperature for flocculating activity of pectin in the kaolin suspension was around 30 degrees C and high flocculating activity was obtained when 30 mg/l of pectin and 0.2 mM Fe3+ were added to the suspension. Other inorganic suspensions of activated carbon and acid clay were flocculated by pectin in the presence of Al3+ or Fe3+. Flocculation of organic suspensions such as cellulose and yeast by pectin occurred when 0.1-0.2 mM Fe3+ was present in the suspensions.     

Theoretical modeling of filtration of blood cell suspensions

A theoretical model of filtration of suspensions containing red blood cells (RBCs) and white blood cells (WBCs) has been developed. Equations are written for the pressure drop, the filtration flow and the fractions of filter pores containing RBCs (alpha) and WBCs (alpha*). Because the relative resistances (ratios of resistance of cell to resistance of suspending fluid) of RBCs (beta) and WBCs (beta*) through the filter pore are greater than one, the transit of these cells (especially WBCs) through the filter is slower than that of suspending fluid; this leads to values of alpha and alpha* higher than those simply expected from the hematocrit and leukocrit, respectively, in the entering and exiting suspensions. In the absence of pore plugging by the cells (steady flow), the pressure drop can be computed from alpha, alpha*, beta and beta*. In order to model unsteady flow, differential equations are written to include pore plugging and the subsequent unplugging by the rising filtration pressure at a constant flow. By specifying the fractions of entering RBCs (epsilon) and WBCs (epsilon*) which would plug the pores and the rate at which the plugged pores would unplug in response to pressure rise (epsilon u), as well as the fractions of entering RBCs (epsilon p) and WBCs (epsilon p*) that would plug the pores permanently, theoretical pressure-time curves can be generated by numerical integration, and the results fit the experimental data well. From such fitting of theoretical curve to experimental data, information can be deduced for epsilon, epsilon*, epsilon u, epsilon p and epsilon* p.     

Flow injection analysis of blood L-lactate by using a Prussian Blue-based biosensor as amperometric detector

An amperometric l-lactate biosensor was fabricated by confining lactate oxidase in a Prussian Blue-modified electrode with a Nafion membrane. The detector was assembled in a flow injection apparatus and operated at -0.1 V. Conditions for optimal electrode response were determined by investigating the influence of the amount of immobilized enzyme, the sample volume, and the flow rate. At the established operational conditions, the biosensor exhibited negligible response from interfering species usually present in biological fluids. The stability of the biosensor was also investigated, and its sensitivity was maintained unchanged at certain experimental conditions. l-Lactate was determined in blood samples, and the influence of physical exercise on the results was clearly evidenced, demonstrating that the proposed amperometric detector is suitable for monitoring changes in the l-lactate levels in biological fluids.     

Hydrodynamic properties of a double-helical model for DNA.

The translational and rotational diffusion coefficients of very short DNA fragments have been calculated using a double-helical bead model in which each nucleotide is represented by one bead. The radius of the helix is regarded as an adjustable parameter. The translational coefficient and the perpendicular rotation coefficient agree very well with experimental values for oligonuclotides with 8, 12, and 20 base pairs, for a single value of the helical radius of about 10 A. We have also calculated a nuclear magnetic resonance relaxation time in which the coefficient for rotation about the main axis is involved. As found previously with cylindrical models, the results deviate from experimental values, indicating that the internal motion of the bases has a remarkable amplitude. An attempt to quantify the extent of internal motions is presented.     

Physical properties of resistance vessel wall in peripheral blood flow regulation--I. Mathematical model

A mathematical model is introduced to investigate the influence of the physical properties of the resistance vessel wall on the metabolic and myogenic mechanisms. The resistance vessel wall is assumed to have an elastic property and the elastic modulus to be a function of pressure (myogenic) and flow (metabolic). Blood is Poiseuille's flow. The resulting mathematical equations for pressure-flow, pressure-diameter, pressure-wall tension and pressure-wall elastic modulus relationships introduced obey Laplace's law. Poiseuille's law and Hooke's law. In comparison with the experimental data (pressure diameter), the mathematical model is confirmed to explain well the dynamic behavior of the resistance vessel wall in vivo.