A new mathematical model is proposed for time-independent laminar flow through a rigid isotropic and consolidated porous medium of spatially varying porosity. The model is based upon volumetric averaging concepts. Explicit assumptions regarding the mean geometric properties of the porous microstructure lead to a relationship between tortuosity and porosity. Microscopic inertial effects are introduced through consideration of flow development within the pores. A momentum transport equation is derived in terms of the fluid properties, the porous medium porosity and a characteristic length of the microstructure. In the limiting cases of porosity unity and zero, the model yields the required Navier-Stokes equation for free flow and no flow in a solid, respectively.

Mathematical Modelling of Flow Through Consolidated Isotropic Porous Media

The effect of electrolyte concentration and co-ion type on the ζ-potential of polystyrene latices

Resistive flex sensors can be used to measure bending or flexing with relatively little effort and a
relativelylow budget. Their lightness, compactness, robustness, measurement effectiveness and
low power consumption make these sensors useful for manifold applications in diverse fields.
Here, we provide a comprehensive survey of resistive flex sensors, taking into account their
working principles, manufacturing aspects, electrical characteristics and equivalent models,
useful front-end conditioning circuitry, and physic-bio-chemical aspects. Particular effort is
devoted to reporting on and analyzing several applications of resistive flex sensors, related to the
measurement of body position and motion, and to the implementation of artificial devices. In
relation to the human body, we consider the utilization of resistive flex sensors for the
measurement of physical activity and for the development of interaction/interface devices driven
by human gestures. Concerning artificial devices, we deal with applications related to the
automotive field, robots, orthosis and prosthesis, musical instruments and measuring tools. The
presented literature is collected from different sources, including bibliographic databases,
company press releases, patents, master’s theses and PhD theses.

https://iopscience.iop.org/article/10.1088/0964-1726/25/1/013001/pdf

Resistive flex sensors: a survey

Theories of electrokinetics of soft particles, which are particles covered with an ion-penetrable surface layer of polyelectrolytes, are reviewed. Approximate analytic expressions are given, which describe various electrokinetics of soft particles both in dilute and concentrated suspensions, that is, electrophoretic mobility, electrical conductivity, sedimentation velocity and potential, dynamic electrophoretic mobility, colloid vibration potential, and electrophoretic mobility under salt-free condition.

Electrokinetics of soft particles

Electrokinetic equations for electrophoresis of a soft particle (that is, a hard particle covered with a layer of polyelectrolytes) have been solved previously under the conditions that the net force acting on the soft particle as a whole (the particle core plus the polyelectrolyte layer) must be zero and that the electrical force acting on the polymer segment is balanced with a frictional force exerted by the liquid flow (J. Colloid Interface Sci.163, 474 (1994)). In the present work we replaced the latter condition by the alternative and more appropriate condition that pressure is continuous at the boundary between the surface layer and the surrounding electrolyte solution to solve the electrokinetic equations and obtained the general mobility expression for the electrophoretic mobility of a spherical soft particle. It is found that the general mobility expression thus obtained reproduces all of the approximate mobility expressions derived previously and, in addition, that the continuous pressure condition leads to the correct limiting behavior of the electrophoretic mobility in the case where the frictional coefficient tends to zero (this behavior cannot be derived from the force balance condition for the polyelectrolyte layer).

On the General Expression for the Electrophoretic Mobility of a Soft Particle

Creeping flow over a composite sphere: Solid core with porous shell

A method for synthetizing nanorods, comprising using self-assembled defect free nanotubes formed in water at room temperature and the nanorods are synthesised within the nanotubes in water at room temperature. The size of the nanorods obtained is well defined due to the well-defined size of the self-assembled nanotubes. In addition, the nanorods synthesised by this method may be doped to improve the conductivity and to obtain p and n nanowires.

Method for Fabricating Intrinsically Conducting Polymer Nanorods

This article presents alternative ways to produce efficient custom force or pressure sensors using cellulose paper filled with carbon-black pigments. We have produced several prototypes of force sensors to observe and compare their response with applied forces with those of commercial sensors, as well as those of other conductive materials. Advantages of custom sensors are presented through the description of various examples of music controllers using several kinds of paper touch sensors with a large variety of size and shape. Our goal is to provide digital musical instrument designers with new strategies to circumvent the limited offering of commercial sensors, and to propose ways to exploit these concepts through a dedicated Web site.

In-house development of paper force sensors for musical applications

Pressure and position sensors are usual components of many electronic devices. They equip cars and planes for security and presence sensing, industrial automated systems and many other Human-Interface Devices for medicine and kinesiology robotics, video games, etc. We present alternative ways to develop our selves these sensors using a low cost material: conductive paper loaded with carbon black pigments. We show that such a paper can be easily used to develop position, pressure and flexion sensors and that it is a good basis to develop more refined sensors such as accelerometers or tilt sensors for shock sensing with smart packaging. We last compare a few trials to produce oneself this paper using conventional fibers such as TMP, chemical or recycled pulp using classic laboratory handsheet formers and mixing those with industrial carbon black loaded papers.

Carbon Black Loaded Paper: an intelligent substrate for Electronic Sensors Design

Numerical calculations have been made of the spin friction coefficient of both an infinite array of suspended parallel cylinders and an array of cylinders sandwiched between two plates. At low cylinder volume fractions the results can be expressed in terms of a virial expansion in volume fraction and the first and second virial coefficients have been determined. The results for an infinite array are compared to a cell model in which the flow around a reference cylinder is calculated. The agreement between both methods is excellent. For spheres, the results of the rotary friction coefficient, calculated using a similar cell model, differ from literature data obtained using a cluster expansion. These results have a bearing on the concentration dependence of the rotary friction and rotary diffusion coefficients of spherical and non-spherical particles.

Theodorus G. M. van de Ven

Papers

Creeping flow over a composite sphere: Solid core with porous shell

Method for Fabricating Intrinsically Conducting Polymer Nanorods

In-house development of paper force sensors for musical applications

Carbon Black Loaded Paper: an intelligent substrate for Electronic Sensors Design

Concentration dependence of spin friction coefficients in suspensions of parallel cylinders and spheres