Kind Of Dispersion Research Articles

Influence of Dispersant on the Dispersion Stability of Nano-CoFe<sub>2</sub>O<sub>4</sub> Refrigeration Oil

Abstract. Adding dispersants like surfactants and polymers to modify nanoparticles surface is an effective way to enhance the dispersion stability of nanoparticles in refrigeration oil. In this paper, many groups of nano-CoFe2O4refrigeration oil were prepared. In order to obtain the most effective kind of dispersant and the optimum additive amount, sedimentation observation method was employed for evaluation of the dispersion stability of CoFe2O4nanoparticles in 3GS mineral lubricant. The spectral behavior of the surface modified nano-CoFe2O4was studied by Fourier transform infrared (FT-IR) spectrometer. It was revealed that the optimized mass ratio between nano-CoFe2O4and dispersant ratio is 2 to 5; a relatively appropriate dispersant for nano-CoFe2O4would be Tween40, Tween60, Span80, Span80; Tween60 was the best. It was also illustrated in the infrared spectrum that nano-CoFe2O4particles surface modified by Tween60 was connected by organic groups in Tween60. Thus, the particles changed from hydrophilic to lipophilic and performed good dispersity and high stability when dispersed in mineral refrigeration oil.

Preparation of BME MLCC Powders by Aqueous Chemical Coating Method

High and large capacitance base–metal–electrode multilayer ceramic capacitors (BME MLCCs) for future application require much thinner dielectric layers (<l μm) than ever before, which means that grain size uniformity of BME MLCC powder should be effectively controlled. In this paper, high‐performance nanosized BME MLCC powder was developed by a novel and convenient aqueous chemical coating method. Various kinds of dispersants were used to disperse BaTiO3 particles in aqueous solutions. Poly(acrylic acid–comaleic acid) was found to be the best for dispersing. BaTiO3 particles were well coated by adding the doping elements into the uniform BaTiO3 slurry in the form of inorganic solutions and organic solutions under an appropriate pH value. Thermogravimetric analysis, transmission electron microscopy, and energy‐dispersive spectroscopy were utilized in the study of calcining, microstructures, and element analysis. The dielectric constants of the ceramics at room temperature could reach 2100, with low dielectric loss <1.0% and high insulation resistivity ∼1012 Ω·cm. The average grain size is as low as about 130 nm.

Blood compatibility of nano-hydroxyapatite dispersed using various agents

Nano-hydroxyapatite (nHAP), dispersed with three kinds of dispersants (heparin sodium, polyacrylic sodium and water), reacted with red blood cell, Bel-7402 tumor cell, to compare their dispersing efficiency against nHAP from one another. The blood compatibility of nHAP is also determined by blood solubility experiment so that the capability of different dispersant dispersing against nHAP of different concentration and the relation between nHAP and blood compatibility have been determined. The inhibiting function of Bel-7402 against tumor cells is determined with the MTT staining method. The study result shows that heparin sodium has the best dispersing efficiency for nHAP without the phenomenon of hemolysis.

Spatial variability of fusarium head blight pathogens and associated mycotoxins in wheat crops

The spatial pattern of Fusarium‐infected kernels and their mycotoxin contamination was studied in four wheat fields in Germany using geo‐referenced sampling grids (12–15 × 20–30 m, 28–30 samples per field) at harvest. For each sample, frequency of Fusarium‐infected kernels and spectrum of species were assessed microbiologically; mycotoxin contents were determined by HPLC‐MS/MS analysis. Spatial variability of pathogens and mycotoxins was analysed using various parameters including Spatial Analysis by Distance IndicEs (sadie®). Microdochium majus, the most frequent head blight pathogen in 1998, was less frequent in 1999 and could not be detected in kernels from two fields in 2004. Fusarium avenaceum, F. graminearum and F. poae were the most frequent Fusarium species, with 7–8 species per field. The frequency of Fusarium‐infected kernels was 3–15% and the incidence of species showed considerable within‐field variability. Spatial patterns varied among Fusarium species as well as from field to field. Although pathogens and mycotoxin were often distributed randomly in the field, F. avenaceum, F. graminearum, F. poae, F. sporotrichioides, F. tricinctum and the mycotoxin moniliformin had an aggregated pattern in at least one field. Patterns are discussed in relation to spread of Fusarium species depending on inoculum sources, spore type, kind of dispersal, availability of susceptible host tissue and micro‐climate. Sampling of wheat fields for representative assessment of mycotoxins is complicated by random patterns of Fusarium‐infected kernels, especially where the frequency of infection is small.

Un'esperienza in un gruppo di auto-mutuo-aiuto con detenuti alcolisti

In contemporary society the eddying succession of objects, persons, situations leads to relationships with others being lived in a contracted time. Sentiments therefore have a short time for being developed and deepened. And because of that, in interchanges the affective logic of substitution prevails that produces a kind of dispersion of the experience with grave repercussions on the structure of the Self. Perhaps, in this context, the invitation of Plato can be precious: for containing the erosive force of time lived in that way, we need to make use of study and of memory. The author maintains that, in respect to an identity which is precipitously transient, produced by mass education, personal education can constitute a bulwark to the dispersion and a possibility for a more solid structuring of the Self and of human relationships.

Physical Model of Aluminium Refining Process in the Batch and Continuous Reactors

Both primary and secondary aluminium need to be refined. The most popular methods of aluminium refining is barbotage. This method is based on the introduction of refining gas bubbles into liquid metal. It can be done in batch or continuous reactors. The refining gas can be introduced to the metal by lances, ceramic porous plugs or rotary impellers. The gas bubbles generated in this way are then mixed with the liquid metal and the level of mixing depends on the processing parameters such as the flow rate of refining gas or the impeller speed. Five patterns of the refining gas dispersion in the liquid metal are known: no dispersion, minimal dispersion, intimate dispersion, uniform dispersion and over-dispersion. Physical modelling is the best way to visualize these kinds of dispersion. It also helps to choose the adequate processing parameters. However, it is also important to keep the dynamic and geometrical similarities to the refining process. In the paper the physical modelling of the aluminium refining process is presented. Two reactors: URO-200 batch reactor with a rotary impeller and URC-7000 continuous reactor with ceramic porous plugs were taken into consideration.

Turing bifurcation in a reaction–diffusion system with density-dependent dispersal

Motivated by the recent finding [N. Kumar, G.M. Viswanathan, V.M. Kenkre, Physica A 388 (2009) 3687] that the dynamics of particles undergoing density-dependent nonlinear diffusion shows sub-diffusive behaviour, we study the Turing bifurcation in a two-variable system with this kind of dispersal. We perform a linear stability analysis of the uniform steady state to find the conditions for the Turing bifurcation and compare it with the standard Turing condition in a reaction–diffusion system, where dispersal is described by simple Fickian diffusion. While activator–inhibitor kinetics are a necessary condition for the Turing instability as in standard two-variable systems, the instability can occur even if the diffusion constant of the inhibitor is equal to or smaller than that of the activator. We apply these results to two model systems, the Brusselator and the Gierer–Meinhardt model.

Price Dispersion: An Empirical Analysis in the Tour Operating Industry

Price dispersion refers to the existence of a nondegenerated distribution of prices by the sellers of a product or service with similar features. Price dispersion is a clear reality in the tour operating market, although very little attention has been given to an analysis of this kind of dispersion and price oscillations in package holidays. In this article, the existence of inter- and intrafirm price dispersion and its persistence over time are analyzed. For the purpose of the analysis, a dataset of package holiday prices for the Balearic Islands is used from a sample of British and German tour operators. The results show the existence of persistent differences in the mean prices of tour operators and price distributions with different dispersions and shapes for tour operators and markets. Nevertheless these distributions are not static, showing a swift response to market demands. Although the article is presented as an empirical investigation, the results can be interpreted in the context of theoretical literature on price dispersion.

The Slurry for Glass Polishing by Micro Abrasive Suspension Jets

The influence of different dispersants and suspending agents of CeO2 polishing powder was investigated, including sodium hexametaphosphate, polyethyleneglycoll, polyacrylic acid, anionic polyacrylamide, and their mixtures. The suspension stability of ceria particles in slurries and the pH dependence were examined by the measurement of zeta potential, sedimentation and viscosity, etc. The material removal rate and surface roughness of different slurries for K9 glass polishing were studied. The slurry mixed by three kinds of dispersants can achieved the maximum material removal rate and the minimum surface roughness.

Effect of dispersant on preparation of barium–strontium titanate powders through oxalate co-precipitation method

The quantitative precipitation of barium–strontium titanyl oxalate: (Ba 0.6Sr 0.4TiO(C 2O 4) 2·4H 2O, BSTO) precursor powders were successfully prepared through oxalate co-precipitation method. The pyrolysis of BSTO at 800 °C/4 h produced the barium–strontium titanate (Ba 0.6Sr 0.4TiO 3, BST) powders. Two kinds of dispersants namely ammonium salt of poly mathacrylic acid (PMAA-NH 4) and polyethylene glycol (PEG) were added respectively during the co-precipitation procedure. The powders were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM), etc. Experimental results show that the addition of the dispersants reduced the productive rate of BST powders. The BSTO and BST powders obtained by aforementioned technique without dispersants were homogeneous with quasi-orbicular morphology. The particles grew into spindle shape with the effect of PEG. The morphology homogeneity was broke with small grains as well as large agglomerated particles concurrent when PMAA-NH 4 was added. The mechanism of the effect of the two dispersants was investigated in detail.

Solid Dispersions of Chitosan Glutamate for the Local Delivery of Miconazole: Characterization and In Vitro Activity

The incorporation of miconazole nitrate (MCN) in mucoadhesive microparticles made of a water-soluble chito- san salt, chitosan glutamate (CHG) was studied. These solid systems may be proposed for buccal or vaginal applications against mycotic infections, taking advantage of the muco-adhesive and permeation enhancing properties of this polymer. Two series of solid dispersions were obtained by either spray-drying and lyophilization, under different formulation vari- ables. The in vitro release of MCN from both the series of microparticles was analyzed at pH simulating the mouth or vaginal environments. A high amount (60 to 85%) of the loaded MCN was released quickly within the first 30 min both at pH 5.0 and 6.6 from all the systems, while the release did not further increase in the following 4 h. These results suggest that the released drug was the fraction of drug desorbed from the CHG particle surface, while a residual amount of drug remained associated or entrapped within them. An in vitro microbiological assay was carried out against different strains of Candida. MCN- CHG lyophilized solid dis- persions gave enhanced inhibitory activity on yeast growth compared to the free drug, whereas the inclusion of MCN in spray-dried microparticles generally did not improve the activity of the drug. The different physical properties of the two kinds of dispersions seemed to be at the basis of the observed different in vitro antimycotic activity.

Synthesis of biocompatible and biodegradable polymer particles in supercritical carbon dioxide

The free radical copolymerization of N-vinyl-2-pyrrolidone and 2-methylene-1,3-dioxepane was carried out in supercritical carbon dioxide (scCO2) using three kinds of dispersants and 2,2′-azobisisobutyronitrile as the initiator. Polymerization was performed with fluorinated polymeric dispersants synthesized in scCO2 using the solution polymerization method and commercially available siloxane-based surfactant. Spherical biocompatible and biodegradable polymeric particles were prepared within the sub-micron size range. The effect of various ratios of the comonomer, reaction temperature, and concentration of initiator, in addition to the types and concentrations of the dispersants, on the particle size and morphology was investigated. The particle size and particle size distribution of copolymer particles were controlled using the above mentioned experimental parameters. Glass transition temperatures of copolymers were varied according to the comonomer ratios used.

Talbot bands and temporal processing of optical signals

Talbot’s bands can be observed in one of the diffraction orders of a grating spectrometer with a partially phase-shifted input beam. This experiment has long been considered as a curiosity. Here, we look at it from a new perspective: we discuss the Talbot band experiment as a combination of two kinds of dispersion, refractive and diffractive. This may be of interest for various tasks of temporal optical signal processing such as dispersion management and the shaping of ps/fs-pulses. For this purpose, we demonstrate the use of micromachined optical elements to alter the performance of the classical Talbot band setup. A theoretical description and experimental results are presented.

Dispersion of barium titanate in aqueous media

Four kinds of dispersants including poly(acrylic acid-co-maleic acid), poly- dl-aspartic acid, polyacrylic acid and ammonium citrate were chosen from more than seventy kinds of dispersants by screening experiments concerning their dispersing abilities for barium titanate (BT) suspension in aqueous media. Sediment experiments, rheology characterization and particle distribution measurements were conducted through orthogonal experiments. The optimum concentrations of dispersants, pH value and ball-milling time have been obtained. Judging from the results of both rheological behavior and particle distribution curves, we can conclude that the best effective dispersant for BT particles in aqueous media is poly(acrylic acid-co-maleic acid), while the least effective one is ammonium citrated among these four kinds of dispersants.

Study of interaction of EP and AW additives with dispersants using XANES

The chemical interaction of two kinds of dispersants (bis-succinimide dispersant and borated bis-succinimide dispersant) with four kinds of antiwear (AW) and extreme pressure (EP) additives (zinc dialkyldithiophosphate, dialkyldithiophosphate ester, diphenylphosphate ester and dialkyldithiocarbamate) has been investigated under different contact pressures. The chemical compositions of the tribofilms have been studied by B, N, P and S X-ray absorption near edge structure (XANES) spectroscopy. The N K-edge XANES analysis has been used to follow the reaction pathway of amine and imide functional groups in the dispersants and their interactions with EP and AW additives. It has been found that AW additives react with amine to form amine phosphate at low load. However, at high load, there is a good evidence for the formation of a nitrate phase in the tribofilms, the first direct observation of oxidative dispersant loss in the rubbing contact. On the other hand, EP additives behave differently and in general are less reactive. The B K-edge XANES has been employed to follow the interaction of borated dispersant with the EP and AW additive. In general, boron originally in the trigonal coordination, is converted to a tetrahedral coordination form in the process of tribofilm formation.

Influence of Different Pre-treatments on Grain-size Measurement of Lake Sediments

As an important environmental index, grain-size character of lake sediments has been widely used in the lake sediment and environmental change studies, accurate measurement is an indispensable requisition for its application. In the depositing process of the lake sediments, chemical and physical change can be taken place and some organic matter, some carbonate may form, organic matter and carbonate can make the sediments cement, and the cementation is not helpful for the grain-size measurement , so pre-treatments is very necessary to get accurate grain-size data. There are some differences in the pre-treatments of lake sediments measurement in different laboratories. Here we present our experimental data of lake sediment grain-size measurement from two different lakes. Based on different pre-treatments, the results of the measurements were analyzed and compared, and two preferable pre-treatment methods were presented. The results indicate that the sediments from different lakes have different responds to different pre-treatment, it can be seen from the whole samples that the pre-treatment that dipping in the distilled water and dispersed by ultrasonic( method F-10 in the text) obtained the best dispersing effect, and the traditional pre-treatment (method E-3 in the text) , which is also the most common use one, also got rather good results. Whereas pre-treated by (NaPO3 )6could make the sediment particles easily to be shattered by ultrasonic and then another very thin particle peak appeared, possibly (NaPO3 )6 , as a kind of dispersant, decreasing the flocculation effect between the particles and then the direct striking effect to the particles of the ultrasonic strengthened, under the strong striking, particles can be broken up. We believe that the bimodal distribution curves do not reflect the real condition of the samples, and this kind of abnormal distribution can bring false environmental information, more attention need to pay to this phenomena when measuring the grain-size of the lake sediments.

Dispersion of parameters characterizing the Landau levelsin crystals with cubic symmetry

AbstractBroadening of the Landau levels due to the presence of a crystal cubic lattice is examined on a semi‐classical basis for not too strong magnetic fields. The energies of the Landau levels remain discrete also in case of the presence of the lattice potential, but an essential broadening occurs in the momentum space of the electron motion when this motion is limited to a plane being transversal to the applied field. The broadening in the momentum space, attained without any electron–electron interaction admitted for the Landau levels, is described in terms of the band structure parameters characteristic for the presence of the magnetic field. Moreover, for a magnetic field tilted to the crystallographic axes, the broadening is dependent on the inclination angle of the field. Different crystal lattices exhibit different kinds of dispersion. In particular, for the Landau levels of tightly‐bound s‐electrons in a simple cubic and body‐centred cubic lattice there is no dispersion in the electron gyration frequency and degeneracy number of the level area over the value of the wavevector component parallel to the magnetic field. On the other hand, this kind of dispersion exists in the case of the face‐centred cubic lattice.

Diffraction effects in few-cycle optical pulses.

Basic concepts of three-dimensional wave packets are applied to the description of transverse effects on the propagation of ultrashort (femtosecond) pulses. The frequency-dependent nature of diffraction acts as a kind of dispersion that modifies the pulse front surface, its group velocity, the envelope form, and the carrier frequency. If the diffracted field in the monochromatic case is known, these changes can be straightforwardly quantified. Finding the propagated pulsed beam field reduces to a well-known and simpler problem of one-dimensional pulse propagation with group velocity dispersion. The method is applied to pulsed Gaussian beams and pulsed Bessel beams. Anomalous pulse front behavior, including superluminality in pulsed Gaussian beams is found. The carrier phase at any point of space is calculated.

An experimental and theoretical study of shock-wave propagation through reactive gases under conditions causing a transformation of the flow structure

Experimental observations of the transformation of the structure of shock waves entering the discharge gap of either a transverse or decaying glow discharge are presented. It is found that the total impulse of the shock wave pressure remains constant. A variation in the speed of sound, that is, the shock wave velocity, at which total dispersion of the wave occurs is found to be nonmonotonous across the discharge gap. The times over which the wave structure keeps changing after switching off the discharge have been more accurately determined. On the basis of the obtained experimental data and earlier results, a conclusion on the mechanism of this effect has been drawn. This mechanism is related to the dispersion of disturbances making up the wave structure in a relaxing medium (such as the glow discharge plasma). On the basis of a theory of this kind of dispersion, using the experimental data, and comparing energetic and temporal characteristics of the internal states of the plasma under study and the mode of sound disturbances (which according to the experiment, are responsible for the effect), we have succeeded in determining the O2(a1Δg) state whose relaxation brings about this effect.

Optimal Sex Ratios in Structured Populations

In this paper, we develop a general method to determine evolutionary equilibrium sex ratios and to check evolutionary stability, continuous stability and invadability in exact genetic models with or without dominance. This method is then applied to three kinds of models for structured populations: the first one concerns Hamilton's LMC model, except that only a fraction β of female offspring mate with male offspring born in the same colonies, while a fraction 1−β mate with male offspring chosen at random within the whole population; in the second model, it is assumed that partial dispersal of inseminated females occurs after mating; in the third model, partial dispersal of male and female offspring occurs before mating. In the first model, the effect of population regulation is studied while, in the other models, two kinds of dispersal are considered: proportional and uniform.