Unit Volume Of Suspension Research Articles

Angular reflectance of suspended gold, aluminum and silver nanospheres on a gold film: Effects of concentration and size distribution

In this article, we describe a parametric study of the effects of the size distribution (SD) and the concentration of nanospheres in ethanol on the angular reflectance. Calculations are based on an effective medium approach in which the effective dielectric constant of the mixture is obtained using the Maxwell–Garnett formula. The detectable size limits of gold, aluminum, and silver nanospheres on a 50-nm-thick gold film are calculated to investigate the sensitivity of the reflectance to the SD and the concentration of the nanospheres. The following assumptions are made: (1) the total number of particles in the unit volume of suspension is constant, (2) the nanospheres in the suspension on a gold film have a SD with three different concentrations, and (3) there is no agglomeration and the particles have a log-normal SD, where the effective diameter, deff and the effective variance, νeff are given. The dependence of the reflectance on the deff, νeff, and the width of the SD are also investigated numerically. The angular variation of the reflectance as a function of the incident angle shows a strong dependence on the effective size of the metallic nanospheres. The results confirm that the size of the nanospheres (deff <100 nm) can be detected by reflected light from the bottom surface of a gold film with a reasonable sensitivity if a proper angle of incidence is chosen based on the type of metallic particles on a gold thin film at λ = 632 nm. We show that the optimum incident angle to characterize the size of nanospheres on a gold film is between 70° and 75° for a given concentration with a particular SD.

The Kinetics of Cell Adhesion to Solid Scaffolds: An Experimental and Theoretical Approach

The process of cell seeding on biocompatible scaffolds has a major impact on the morphological evolution of an engineered tissue because it involves all the key factors of tissue formation: cells, matrix, and their mutual interactions. In order to characterize the efficiency of cell seeding techniques, mainly static parameters are used such as cell density, cell distribution, and cell viability. Here, we present an experimental model that incorporates an optical density meter providing real-time information on the cell seeding velocity, a relevant dynamic parameter of cell-matrix interaction. Our setup may be adapted to fit various cell seeding protocols. A modified fluorimetric cuvette is used as bioreactor culture flask. The optical density of the magnetically stirred cell suspension is recorded by a digital optoelectronic device. We performed calibration experiments in order to prove that, in our experimental conditions, optical density depends linearly on the number of cells in the unit volume of suspension. Control studies showed that, during the time course of a typical experiment (up to 10 h), the cells (murine 3T3 fibroblasts) neither aggregated nor adhered significantly to the walls of the cuvette. Hence, our setup yields the number of cells attached to the scaffold as a function of time. In order to analyze the experimental seeding curves, we built a kinetic model based on Langmuir's adsorption theory, which was extended to include a preliminary step of integrin function recovery. We illustrate the proposed approach by two sets of experiments that involved trypsin-EDTA or only EDTA treatment (no trypsin) used to detach the cells from the culture flasks. The data indicate that in both cases cell-matrix adhesion has a sequential, two-step dynamics, but kinetic parameters and attachment site availability depend on the experimental protocol.

Rheological Characterization of Suspension and Gel Prepared from Colloidal Silica for Sealed Lead-Acid Batteries by Small Amplitude Dynamic Oscillation Measurement

Gelation behaviors of silica suspensions, prepared from 6 grades of commercial colloidal silica (Ludox® series) and sulfuric acid, were investigated rheologically by a small amplitude dynamic oscillation measurement method in which storage and loss moduli were monitored with time. To date, the gel strength of silica suspension/gel in sulfuric acid and its progress with time have not been properly defined, because of their complex rheological behavior such as their weak structure. For the purpose of a quantitative investigation, the time evolution of the storage modulus was measured for the representation of gel strength and its progress related to fluidity decline with time for application to battery manufacture.A suspension prepared from small-sized silica particles showed high gel strength and accelerated gelation. It was demonstrated that the total surface area in a unit volume of suspension determines the gelation behavior, regardless of particle size in different grades of silica. This implies that high gel strength can be achieved with low content of silica of small particle size.It was also found that deionized colloidal silica enhances gel strength. This means that sodium ions in the Ludox®, which play a stabilizing role, should be removed in order to form a strong gel. A positively charged surface and chloride stabilizing ions are not suitable for gelled electrolyte, since they accelerate gelation but do not enhance gel strength.In conclusion, colloidal silica particles of small size and negative surface charge without stabilizing ions should be used for achieving high gel strength in application to batteries.

Rheological Behavior of Kaolin and Montmorillonite Suspensions at Low Concentrations

The rheological behavior of kaolin and montmorillonite suspensions at low concentrations in water and polymer solutions has been investigated. An influence of the polymer concentration on the viscosity of suspension for the kaolin suspension in the presence of diethylenetriaminomethylated polyacrylamide and for the montmorillonite suspension in the presence of polyacrylic acid has been demonstrated. The dependence between the shear stress and the cross-sectional area of particles and the number of particles in a unit volume of the suspension has been shown. Mathematical equations for the number of aggregates in the unit volume of suspension and the number of initial particles in aggregate at the different polymer concentrations in mixture are proposed.

The use of ultrasound in food technology I: inactivation of peroxidase by thermosonication

The combined effect of high power ultrasound and temperature on the activity of peroxidase type VI from horseradish suspended in water was studied. The tests were performed at 80°C using power ultrasounds having frequencies of 20, 40, and 60 kHz. Accordingly, the actual ultrasonic powers varied in the range from 0 to 120 W. Combined treatments were carried out by using a laboratory scale plant operating in continuous and in batch mode. In continuous experiments, 46 ml of suspension was circulated in the plant having a sanitation chamber of 20 ml. In the other case, two sets of experiments were carried out by using a sanitation chamber of 100 ml treating 40 or 80 ml of suspensions, respectively. It was found that the decimal reduction time of peroxidase at 80°C, D 80, reduces from 65 to 10 min ca. when ultrasounds are applied. In particular, D 80 varies with ultrasonic power, sonotrode geometry and volume of suspensions submitted to the treatment. It has been demonstrated that the influence of these variables on the decimal reduction time can be grouped by considering the ultrasound power density, i.e. the ultrasound power per unit area of tip of the probe and unit volume of suspension.

Characterization of red blood cell aggregate formation using an analytical model of the ultrasonic backscattering coefficient.

Ultrasound backscattering is well adapted to study the red blood cell (RBC) aggregation phenomenon and growth of RBC aggregates since the backscattered ultrasonic intensity depends on the sixth power of the mean radius of the scattering centers when considered as spherical. Thus, small variations of aggregate size induce large variations of the backscattered intensity. From measurements of the ultrasonic backscattering coefficient (ultrasonic backscattering cross section per unit volume of suspension), an analytical model describing its variation versus time, for human aggregated red blood cells in sedimentation, is proposed. Results given by the model allow to define three phases in the phenomenon: 1) a starting phase characterized by a duration ts; 2) a stationary final phase beginning at time tf; 3) a growing intermediate phase characterized by its duration tf - ts. The analytical model has been applied to describe RBC aggregation in dextran 70,000 dalton of different concentrations, and at various hematocrits. Knowledge of the durations ts, tf and the maximum slope s of the curve during the intermediate phase, determined with the model, allows a means to study RBC aggregate growth.

Ultrasonic standing wave removal of microorganisms from suspension in small batch systems

Cells in suspension in an ultrasonic standing wave can be manipulated in both batch and flow systems. The removal of log phase Saccharomyces cerevisiae and Escherichia coli from culture medium in a 5 ml cylindrical tube containing a 3 MHz standing wave with a Bessel shaped pressure profile at right angles to the tube axis is reported here. A chamber and transducer/reflector alignment system was developed to provide a high quality standing wave. Cells in the ultrasonic field were first concentrated in a column of clumps along the axis of the sonication chamber. They were collected by controlled sedimentation using pulsed ultrasound. The cell concentration dependent yeast recovery reached 97% (from 7×10 7 cell·ml −1) in a 5.5 min experiment. The yield for the smaller bacteria was 72% at best (from 4×10 9 cells·ml −1) in 11 min. The optimum cell concentrations for harvesting of both types of cell were similar when expressed as cell volume per unit volume of suspension. The results provide insight into the requirements of achieving high on-line cell recovery using ultrasound.

In VitroAdsorption of Phenobarbital, Chlorpheniramine Maleate, and Theophylline by Four Commercially Available Activated Charcoal Suspensions

Four commercially available antidotal activated charcoal suspensions (Actidose Aqua, InstaChar, LiquiChar, and CharcoAid 2000) were evaluated with respect to their abilities to adsorb three test drugs in vitro from simulated gastric fluid. Different volumes of each suspension were added to glass vials containing 20 mL of stock solutions of each drug. The vials were shaken for a time more than sufficient to ensure adsorption equilibrium, then the charcoal was removed from the samples by filtration. The filtrates were analyzed by ultraviolet spectroscopy to determine the residual drug concentrations. The product containing a 2000 m2/g charcoal (CharcoAid 2000) adsorbed more drug per unit volume of suspension than did the other three products, which contained 900 m2/g charcoal and which were all similar in performance.

疎水性多孔質膜によるクロレラ懸濁液における炭酸ガスおよび酸素の物質移動特性

The absorption of CO2 and O2 gas into the chlorella suspension and the stripping of O2 gas generated by photosynthesis of chlorella through the hydrophobic microporous hollow fiber membrane of polypropylene took place. The chlorella suspension flowed inside the hollow fibers and the gas mixture of CO2 and air flowed outside them. The following results were obtained :(1) Overall mass transfer coefficient of CO2 and O2 gas for absorption did not depend on the flow rate of gas mixture, the total pressure of gas mixture, the CO2 concentration of gas mixture and the chlorella concentration, but only on the flow rate of suspension, (2) Overall mass transfer coefficient was correlated by the dimensionless equation given below, Sh=A (Pe) 1/3The value of A in equation was smaller than that obtained in the previous papers using the similar type of membrane module. This difference in A was explained by the apparant decrease in interfacial area of membrane per unit volume of suspension due to the dence packing of hollow fibers per unit cross-sectional area of shell in our module as compared with the others, and(3) The supply of CO2 gas and the stripping of O2 gas generated by photosynthesis could be taken place at the same time through the one membrane module.

FACTORS INFLUENCING RESPIRATORY MEASUREMENTS USING OXYGEN ELECTRODES AND CARTESIAN‐DIVER MICRORESPIROMETRY

SummaryThe dark respiration rates of primary leaf mesophyll protoplasts of barley (Hordeum vulgare L. cv. Patty) were measured by a Clark‐type oxygen electrode and Cartesian‐diver microrespirometry, in order to compare the two techniques. Factors found to be important in determinations of respiratory rates of protoplasts were the numbers of protoplasts per unit volume of suspension, the age of protoplast preparations and the stirring speed of the magnetic follower when using the oxygen electrode. Increases in numbers of protoplasts per unit volume caused a marked decrease in respiration using both techniques. Below 2000 protoplasts μl−1 both techniques provided rates of dark respiration within the same range until 1000 protoplasts μl−1, below which a marked increase in respiration occurred. Respiratory rates of protoplasts declined by 32 % from initial values over a 30 h period after isolation in the dark. In addition, an increase in the stirring rate in the reaction vessel of the oxygen electrode had the effect of reducing both the viability of protoplasts and their rates of oxygen uptake. It is suggested that consistent standardization of procedures, especially in terms of numbers of protoplasts per unit volume, is necessary for assay techniques for respiration in protoplasts. The advantages and disadvantages of using Cartesian‐diver microrespirometry compared to oxygen electrodes are also discussed.

Nucleation and growth kinetics for the crystallization of ice from dextrose solutions in a continuous stirred tank crystallizer with supercooled feed

AbstractThe crystallization of ice in aqueous dextrose solutions is studied in an adiabatic continuous stirred tank crystallizer with a supercooled feed stream. The effective diameter of the ice crystals was determined for various values of mean crystal residence time, feed supercooling, magma density, stirring rate, and dextrose concentration. For all process conditions the supercooling was measured at 9‐12 different locations in the crystallizer. These local supercoolings were averaged algebraically to yield the bulksupercooling.From the experimental results growth and nucleation rates have been calculated. By comparing the experimental growth rates to growth rates calculated by means of a mathematical model kinetics for the inbuilding of water molecules into the ice lattice have been determined. The growth rate appears to be directly proportional to the interface supercooling. The rate constant decreases exponentially with increasing weight percentage of dextrose in the solution.The nucleation rate was found to be directly proportional to total crystal surface per unit volume of suspension and proportional to the bulksupercooling to the power 2.1. Nucleation is believed to occur by breakage of dendrites from the surface of parent crystals.

289 Note: A New Table for the Estimation of Particle Density

SUMMARY A table for estimatinig directly the number of organisms in virus or other biological assays done by the dilution method, where the response is quantal, is given for several dilution factors and for any number of dilution levels. Fisher [1922] proposed a method for estimating the average number, m, of organisms in a unit volume of suspension that is particularly suitable in cases, such as quantal virus assays, in which the presence or absence of organisms can be determined but in which counts cannot be made. The estimation is based on counting the total number, T, in the dilution series with n replicates at each dilution level. If m is the average number of organisms per plate at the highest concentration, the estimated value of m is given by the following equation, obtained by equating the observed total number of sterile plates to its expected value, T = n(e-m + e-fia + ema2 + ... + e m/a5), (1) where a = the dilution factor s = the number of levels n = the number of replicates T = the total number of sterile plates.

Effect of Light Intensity and Thickness of Culture Solution on Oxygen Production by Algae

Data from a small cylindrical culture unit with variable annular culture chambers indicate that (i) the rate of oxygen evolution by an algal culture in the linear phase of growth is a logarithmic function of light intensity, and (ii) the rate of oxygen evolution per unit volume of suspension is linearly related to the reciprocal of culture thickness. These two relationships have been combined in an empirical equation which gives the expected variation of the oxygen production rate with light intensity, culture thickness, and suspension volume. The applicability of this equation has been tested on a larger, multilight culture unit in this laboratory. The agreement between the experimental and calculated oxygen production rates was very satisfactory, suggesting that the equation is not limited to a particular culture unit but may have wide applicability. The efficiency of the culture unit from the standpoint of oxygen output (chemical energy) relative to electrical energy to supply the light source has been calculated, and the maximum value of 0.51% was obtained. The energy to run auxiliary equipment was not a factor in these calculations. The maximum efficiency in converting light energy to chemical energy was approximately 12%. An extrapolation of the experimental results suggests that approximately 2 ft 3 and 30 kw would be required to provide the oxygen needs of one man.

Effect of Light Intensity and Thickness of Culture Solution on Oxygen Production by Algae

Data from a small cylindrical culture unit with variable annular culture chambers indicate that (i) the rate of oxygen evolution by an algal culture in the linear phase of growth is a logarithmic function of light intensity, and (ii) the rate of oxygen evolution per unit volume of suspension is linearly related to the reciprocal of culture thickness. These two relationships have been combined in an empirical equation which gives the expected variation of the oxygen production rate with light intensity, culture thickness, and suspension volume. The applicability of this equation has been tested on a larger, multilight culture unit in this laboratory. The agreement between the experimental and calculated oxygen production rates was very satisfactory, suggesting that the equation is not limited to a particular culture unit but may have wide applicability. The efficiency of the culture unit from the standpoint of oxygen output (chemical energy) relative to electrical energy to supply the light source has been calculated, and the maximum value of 0.51% was obtained. The energy to run auxiliary equipment was not a factor in these calculations. The maximum efficiency in converting light energy to chemical energy was approximately 12%. An extrapolation of the experimental results suggests that approximately 2 ft and 30 kw would be required to provide the oxygen needs of one man.

A generalized theory of sedimentation

A theoretical relationship between the concentration and the sedimentation velocity of non-flocculated suspensions of particles is derived. It is shown that the settling velocity relative to that of a single particle in the suspension is (1 - c)β where β is a function of particle shape, size distribution and Reynolds number and c is the volume of solid per unit volume of suspension. The expression is shown to satisfy the experimental results of other workers. An empirical relationship between β and the Reynolds number is suggested.