Average Size Parameters Research Articles

Preparation of surface modified magnetic Iron Oxide nanoparticles and study of their colloidal behavior

In this work, we report synthesis of surface modified superparamagnetic iron oxide nanoparticles (SPION) by co-precipitation method using FeSO4.7H2O and Fe2(SO4)3.5H2O as precursors and trisodium citrate dihydrate as surfactant. Surface modification of the as prepared samples was performed in pot by sol-gel precipitation method using tetraethoxysilane (TEOS). The structure, morphology, and magnetic properties of the products were characterized by X-ray powder diffraction (XRD), Scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FT-IR), and Vibrating sample magnetometer (VSM) at room temperature. The results revealed formation of iron oxide nanoparticles, with an average size parameter of 8.5 nm for naked and 37nm for silica coated particles, with a superparamagnetic behavior and fast response to applied magnetic fields with zero remanence and coercivity.

Theoretical study on the change of the particle extinction coefficient during the aerosol dynamic processes

In this study, the effects of aerosol dynamics on the aerosol optical properties were analytically investigated using an approximated expression for the overall extinction coefficient ( b ext ) , which was valid for a wide range of particle size. The processes of both coagulation and condensation in the continuum region were considered using the moment method, with an overall extinction coefficient obtained from the harmonic mean between the overall particle extinction coefficient of the Rayleigh scattering and geometric scattering regions. The derived analytical expressions were compared with the asymptotic expressions of the extinction coefficient, which showed that the obtained expressions ultimately approached the asymptotic expressions. Subsequently, this study showed a simple and straightforward method for estimating the changes in the extinction coefficient and visibility of polydispersed aerosols during aerosol dynamic processes. The accuracy of the approximated overall coefficient was dependent on a given aerosol refractive index and size parameter. Usually, the error was less than 8% for an average size parameter range of 0–80.

Effects of polydispersity of chainlike aggregates on light-scattering properties and data inversion.

A systematic evaluation of the effects of polydispersity of chainlike aggregates in terms of primary particle number density and size on the scattering quantities and data inversion is presented. For aggregates with refractive index in the range absolute value(m-1) = 0.8-1.2, average size parameter x < 0.40, and primary particle number Np < 20, it is shown that the effects of polydispersity of primary particle size on the light-scattering quantities are much stronger than the polydispersity of the number of primary particles per aggregate. For aggregates with polydisperse primary particle size, the assumption of monodispersity tends to underestimate the real and imaginary parts of the refractive index and the number of primary particles. Specifically, for values of the distribution width sigma greater than 0.10, the effect of polydispersity of the size of primary particles must be considered in the data inversion schemes. Furthermore, in the same range of values for the refractive index, particle size parameter, and primary particle number, the assumption of monodispersity for aggregates with polydisperse particle number tends to underestimate the value of the real part of the refractive index and overestimate the value of the imaginary part of the refractive index and primary particle size. However, for values of the distribution width sigma less than 0.60, the effects of polydispersity of primary particle number can be neglected. In addition, the suitable pairing sets of the measured scattering quantities for data inversion are presented and discussed.

CHARACTERIZATION OF POWDER PARTICLE MORPHOLOGY

Technological properties of powders depend on their granulometry and particle morphology. Most of the image analysis methods provide only average size parameters (diameter, area, perimeter, etc.) which are often inadequate for characterizing the morphology of the particles. For particle abrasivity characterization, angularity factors are more sensitive. This paper studies different parameters for describing the hardmetal powder granulometry and morphology. The main aim is to find numerical descriptors for the shape factors that adequately characterize the hardmetal powders produced by the mechanical method - milling in a disintegrator. For the characterization of the powder particle morphology, irregularity parameter IP (relation of the diameters of the maximum inscribed and minimum circumscribed circles) suits best, taking into account the ellipticity and irregularity of the particle form. For describing the angularity of ground powders, the so-called spike parameter - quadratic fit can be used.

Multiple scattering of narrow light beams in aerosols

A multiple scattering propagation model of narrow light beams in aerosol media is described. It is based on a paraxial approximation of the radiative transfer equation in which the flux normal to the incident beam direction is modeled by a diffusion process. The model solutions are the forward- and backscattered intensity profiles for the specified geometry and receiver aperture and field of view. The required inputs are the system parameters, and the aerosol single scattering angular phase function and extinction and scattering coefficients which are allowed to vary along the beam axis. Good agreement is shown with measurements performed in the laboratory over scales ranging from a few tens of mm to a few m, and in the atmosphere over a scale of the order of 1 km. The solutions are valid for optical depths smaller than ≈ 10, for phase functions corresponding to average size parameters of order one or greater, and for off-axis positions not exceeding ≈ 25% of the reciprocal of the scattering coefficient.

Extinction efficiency in the infrared (2–18 μm) of laboratory ice clouds: observations of scattering minima in the Christiansen bands of ice

Extinction measurements with a laser diode (0.685 µm) and a Fourier transform infrared spectrometer (2-18 µm) were performed on laboratory ice clouds (5 µm ≤ D ≤ 70 µm) grown at a variety of temperatures, and thus at a variety of crystal habits and average projected crystal area. Ice clouds were grown by nucleation of a supercooled water droplet cloud with a rod cooled with liquid nitrogen. The ice crystals observed were mainly plates and dendrites at the coldest temperatures (≈-15 °C) and were mainly columns and needles at warmer temperatures (≈-5 °C). The crystals were imaged with both a novel microscope equipped with a video camera and a heated glass slide and a continuously running Formvar replicator. The IR spectral optical-depth measurements reveal a narrow (0.5-µm-width) extinction minimum at 2.84 µm and a wider (3-µm-width) minimum at 10.5 µm. These partial windows are associated with wavelengths where the real part of the index of refraction for bulk ice has a relative minimum so that extinction is primarily due to absorption rather than scattering (i.e., the Christiansen effect). Bulk ice has absorption maxima near the window wavelengths. IR extinction efficiency has a noticeable wavelength dependence on the average projected crystal area and therefore on the temperaturedependent crystal properties. The average-size parameters in the visible for different temperatures ranged from 64 to 128, and in the IR they ranged from 2.5 to 44. The extinction efficiency and the single-scatter albedo for ice spheres as computed from Mie scattering also show evidence of the Christiansen effect.

Effects of diethylenetriamine and Aerosol OT on the stability of oil-in-water emulsion stabilized by interfacial polyurea film.

The stability of oil-in-water emulsions containing a triisocyanate soluble in the oil phase and an amine in the water phase was investigated. The oil component was di-n-butyl phthalate (DBP) containing Aerosol OT as an emulsifier. The time required for the average size parameter to reach a constant value was studied. It was found that the polyurea film produced by an interfacial polymerization reaction between the amine and the triisocyanate contributed to forming a stable emulsion at a lower Aerosol OT concentration, but at a higher Aerosol OT concentration the amine did not show any effect on the emulsion stability.

EFFECTS OF INTERFACIAL POLYUREA FILM ON THE STABILITY OF OIL IN WATER EMULSIONS

ABSTRACT The stability of oil in water emulsions containing a triisocyanate soluble in the oil phase was investigated. The oil component was either di-n-butyl phthalate (DBP) or a mixture of DBP with liquid paraffin. The time required for the average size parameter to reach a constant value was studied. It was found that the polyurea film produced by an interfacial polymerization reaction between water and a triisocyanate contributed to make the stable emulsions. The effects of drop size, temperature, polarity of oil phase, triisocyanate concentration, and mechanical stirring on the stability of the emulsions were established in this study. The film thickness at the point where the average size parameter reached a constant value was found to be of the order of 0. 002 ∼ 0. 004μ.

Size distribution and average size parameters of casein micelles determined by electron microscopy in bovine milk between pH 5·5 and 6·7. A comparison of several evaluation methods

SummaryThe conversion of the two-dimensional size distribution of casein micelles, observed by electron microscopy in a plane section, to the three dimensional distribution is discussed and the average size parameters evaluated by several methods are compared. It is shown that parameters containing the −1 moment of the two-dimensional distribution, i.e. Dn, the number of micelles per unit volume and the width of the size distribution, are sometimes uncertain. The occurrence of negative numbers in some of the classes of the distribution is discussed and remedies are suggested. Sections were made by freeze-fracturing skim milk samples; the pH of the milk was between 5·5 and 6·7.

Characteristics of Mesoscale Precipitation Bands in Southern Finland

A large amount of observational material, consisting of more than 3000 hours of radar measurements from about 1 50 cyclones has been analyzed to discover the characteristic features of banded structures in extratropical cyclones in southern Finland. All previously classified types of rain- and snowbands have been observed. The most common rainband types were warm frontal aloft, postfrontal, warm sector and occluded warm frontal bands. The average size parameters of different rainband types showed only slight variations from type to type. A distinct annual variation in the echo top height, rainband width and wavelength has been found. The average echo top heights were 3 and 6.5 km, the wavelengths 29 and 77 km, and the widths 18 and 35 km in winter and summer, respectively. The monthly values of the ratio of wavelength to height were relatively constant. They varied between 6 and 14, averaging 11.

Semiphenomenological studies of the ground state binding energies of hypernuclei.

We show that the binding energies of $_{\mathrm{\ensuremath{\Lambda}}}^{5}\mathrm{He}$ and p-shell hypernuclei can be satisfactorily explained in the folding model approach using a density dependent effective \ensuremath{\Lambda}N interaction. Our analysis predicts a very reasonable value of the range of the \ensuremath{\Lambda}N interaction. The calculated value of ${B}_{\ensuremath{\Lambda}}$ of $_{\mathrm{\ensuremath{\Lambda}}}^{7}\mathrm{Li}$ using the cluster model density for $^{6}\mathrm{Li}$ and the best fit parameters of this potential supports the view that $^{6}\mathrm{Li}$ possesses an \ensuremath{\alpha}-d cluster structure. Using this potential we also determine the average size parameter (${a}_{0}$) of the oscillator shell model density of nucleons in N\ensuremath{\ne}Z core nuclei from fitting the ${B}_{\ensuremath{\Lambda}}$ values of the corresponding hypernuclei. The effect of different forms of density distribution of core nuclei on the values of potential parameters is investigated and is found to be very small. As regards the form of density dependence, a ${\ensuremath{\rho}}^{2/3}$ form is found to be the most appropriate for this purpose and is used throughout this work. Other forms do not give a satisfactory account of the data.

The relation of raindrop size to intensity of rainfall in different types of tropical rain using a simple raindrop recorder

The paper give3 the results of studies of raindrop size characteristics in three other different types of tropical rain to what Sivaramakrishnan had earlier studied {1961), using the simple raindrop recorder. The study of raindropsize characteristics refers to analysis of raindrop samples taken at Poona in (1) typical shower types of rain without thunder (cumuliform clouds), (2) continuous type of rain with occasional thunder (cumuliform and stratiform clouds mixed) and (3) non freezing rain during typical monsoon from stratiform clouds. Regression equations connecting the intensity of rainfall with the various rainfall parameters such as median drop size Dn, liquid water content W, radar reflectivity Z have been developed and compared with findings of other investigators all over the world. Best's formula is found to represent the size distribution of raindrops in the tropics also but with suitable changes in the constants. It is also shown in agreement with results obtained earlier by Sivaramakrishnan (1961),Blanchard (1953), Best (1951), Atlas and Chmela (1957) and Spilhaus (1948) that the median drop diameter is the most suitable parameter for describing the average size of the drop size distribution in preference to other average size parameters such as mean diameter Dm, mode diameter Dd , mean volume diameter Dv and predominant diameter Dp.&#x0D;