38 research outputs found
“Magnetic Force Microscopy and Energy Loss Imaging of Superparamagnetic Iron Oxide Nanoparticles”
We present quantitative, high spatially resolved magnetic force microscopy imaging of samples based on 11 nm diameter superparamagnetic iron oxide nanoparticles in air at room temperature. By a proper combination of the cantilever resonance frequency shift, oscillation amplitude and phase lag we obtain the tip-sample interaction maps in terms of force gradient and energy dissipation. These physical quantities are evaluated in the frame of a tip-particle magnetic interaction model also including the tip oscillation amplitude. Magnetic nanoparticles are characterized both in bare form, after deposition on a flat substrate, and as magnetically assembled fillers in a polymer matrix, in the form of nanowires. The latter approach makes it possible to reveal the magnetic texture in a composite sample independently of the surface topography
Magnetic properties and magneto-birefringence of magnetic fluids
Static magnetic properties of a large variety of magnetic fluids
with magnetite particles is studied. A qualitative study of
magnetization curves was performed to establish the influence of
interactions or the presence of agglomerations in each sample.
Improved equations for magneto-granulometric analysis, for ideal
ferrofluids, were proposed. Better results for the mean magnetic
diameter than in the case of using the known equations were
obtained. A quantitative study using several models for ideal and
interacting particles was performed to select the best method and
dimensional distribution function for magneto-granulometric
analysis as well as for accurately determining macroscopic
quantities of samples (initial susceptibility, saturation
magnetization, particle number density or magnetic volume fraction)
and properties of nanoparticles (mean magnetic diameter, thickness
of the nonmagnetic layer and particle distribution). A new model
for magneto-birefringence was proposed and discussed as well as
applied for diluted and concentrated ferrofluids. The Langevin
behaviour of samples was investigated and compared with the
investigation based on magnetic properties. Nanoparticles
parameters like mean "magneto-optical" diameter, effective
anisotropy constant, Shliomis diameter and the real part of the
electrical permittivity of particles were accurately determined
Some Functionals and Approximation Operators Associated with a Family of Discrete Probability Distributions
A certain discrete probability distribution was considered in [“A discrete probability distribution and some applications”, Mediterr. J. Math., 2023]. Its basic properties were investigated and some applications were presented. We now embed this distribution into a family of discrete distributions depending on two parameters and investigate the properties of the new distributions
Some Functionals and Approximation Operators Associated with a Family of Discrete Probability Distributions
A certain discrete probability distribution was considered in ["A discrete probability distribution and some applications", Mediterr. J. Math., 2023]. Its basic properties were investigated and some applications were presented. We now embed this distribution into a family of discrete distributions depending on two parameters and investigate the properties of the new distributions
Dilution series approach for investigation of microstructural properties and particle interactions in high-quality magnetic fluids
The aim of the paper is to study the deviation of
magnetic properties of the magnetic fluids prepared for this study,
from ideal (Langevin) behaviour, i.e. to estimate particle interaction
influence and dimensions and influence of particle aggregates, as well
as to explain the related effects observed. We also determine the
particle coupling parameter, the particle nonmagnetic layer thickness,
and the particle distribution, which are fundamental for sample
characterization. A comparison of the studied magnetic fluids with
each other, with respect to microstructure formation and particle
interaction strength is finally done. For these purposes, a
concentration dependence study, following the proposed “dilution
series approach”, is performed. Three series of dilutions of three
types of magnetic fluids were prepared and analyzed
On Markov operators preserving polynomials
The paper is concerned with a special class of positive
linear operators acting on the space C(K) of all continuous functions
defined on a convex compact subset K of R^d,
having non-empty interior. Actually, this class consists of all positive
linear operators T on C(K) which leave invariant the
polynomials of degree at most and which, in addition, map polynomials into polynomials
of the same degree. Among other things, we discuss the existence of such operators in the special
case where K is strictly convex by also characterizing them within the class of positive projections.
In particular we show that such operators exist if and only if the boundary of K is an ellipsoid. Furthermore, a characterization of
balls of R^d in terms of a special class of them is furnished. Additional results and illustrative examples are presented as well