Kazuo Maki

Theory and numerical calculation of pattern formation in shrinking gels

We discuss pattern formation in three-dimensional gels with cylindrical shapes during their shrinking such as volume phase transition. A Ginzburg–Landau theory is given for the pattern formation in shrinking gels. A characteristic feature in shrinking gels is the dense layer formed around the gel surface in the early stage of phase transition. This layer reduce considerably permeation of solvent and the shrinkage practically stops. We introduce the external osmotic pressure and the external elastic stress acting on the gel surface in order to take account of the effect of the layer. Patterns are classified according to the anisotropy and the incompressibility of gels by the linearized stability analysis of the theory. It appears that the external stress term suppresses the growth of the fluctuation with short wavelength. The results obtained by a numerical calculation for the evolution of patterns are also shown.

Practical human abdominal fat imaging utilizing electrical impedance tomography.

The fundamental cause of metabolic syndrome is thought to be abdominal obesity. Accurate diagnosis of abdominal obesity can be done by an x-ray computed tomography (CT) scan. But CT is expensive, bulky and entails the risks involved with radiation. To overcome such disadvantages, we attempted to develop a measuring device that could apply electrical impedance tomography to abdominal fat imaging. The device has 32 electrodes that can be attached to a subjects abdomen by a pneumatic mechanism. That way, electrode position data can be acquired simultaneously. An applied alternating current of 1.0 mArms was used at a frequency of 500 kHz. Sensed voltage data were carefully filtered to remove noise and processed to satisfy the reciprocal theorem. The image reconstruction software was developed concurrently, applying standard finite element methods and the Marquardt method to solve the mathematical inverse problem. The results of preliminary experiments showed that abdominal subcutaneous fat and the muscle surrounding the viscera could be imaged in humans. While our imaging of visceral fat was not of sufficient quality, it was suggested that we will be able to develop a safe and practical abdominal fat scanner through future improvements.

Evaluation of a magnetic dispersion by interparticle interactions

Abstract The magnetic, rheological and electrical effects of interparticle interactions in a metal particle dispersion have been investigated experimentally with the aim of understanding the state of the dispersion through such interactions. Samples of different degrees of dispersion were obtained by varying the duration of a sand milling operation. The magnetic interactions were assessed from the hysteresis and remanence curves of frozen dispersion samples. The coercivity and remanence coercivity of the dispersion samples were found to increase with increasing milling time, while the switching field distribution calculated from both the hysteresis and remanence curves decreased. The first normal stress difference, N 1 , of the dispersion was measured as a rheological indicator of magnetic interactions. N 1 decreased with increasing milling time. The dielectric constant and the ac conductivity were investigated for possible electrical particle interactions. Both parameters decreased with increasing milling time, but the results were found to be due to polymer-particle rather than particle-particle interactions.

Surface properties and particle interactions of metal magnetic powders

Abstract Two types of metal magnetic powders, referred to as powder A and powder B, were analyzed in terms of their surface properties and interparticle interaction characteristics. Surface chemical compositions were determined by using electron spectroscopy for chemical analysis. The major distinction in the surface compositions was that particles of powder A had excess aluminum, whereas those of powder B had excess silicon and carbon. Wettability of powder A as measured by the contact angle method and capillary penetration method was better than powder B. Dielectric properties, magnetic hysteresis and remanence curves were measured to identify the values of electric and magnetic interparticle interaction parameters. Electric particle interactions as given by the polarizability was greater for powder A than for powder B. Average values of parameters indicating magnetic particle interactions were nearly equal for both powders. A comparison of electric versus magnetic interaction parameters of individual samples indicated that these two different types of particle interactions correlated with each other.