Performances of a magnetic particle driven micromixer are predicted numerically. This micromixer takes advantages of mixing enhancements induced by alternating actuation of magnetic particles suspended in the fluid. Effects of magnetic actuation force, switching frequency and channel's lateral dimension have been investigated. Numerical results show that the magnetic particle actuation at an appropriate frequency causes effective mixing and the optimum switching frequency depends on the channel's lateral dimension and the applied magnetic force. The maximum efficiency is obtained at a relatively high operating frequency for large magnetic actuation forces and narrow microchannels. If the magnetic particles are actuated with a much higher or lower frequency than the optimum switching frequency, they tend to add limited agitation to the fluid flow and do not enhance the mixing significantly. The optimum switching frequency obtained from the present numerical prediction is in good agreement with the theoretical analysis. The proposed mixing scheme not only provides an excellent mixing, even in simple microchannel, but also can be easily applied to lab-on-a-chip applications with a pair of external electromagnets. Keywords Magnetic particles Á Micromixing Á Microfluidic Á Magnetic actuationList of symbols A cross-section area of the microchannel (m 2 ) A p cross-section area of the particle (m 2 ) B magnetic flux density (Tesla)force (N) f switching frequency (Hz) f cr critical switching frequency (Hz) H channel height (m) H e magnetic field strength (A/m) H M electromagnet thickness (m) I current (A) L streamwise dimension or length (m) m particle mass (kg) M magnetization of the particle (A/m) P pressure (N/m 2 ) Pe peclet number (ReSc) r particle radius (m) Re Reynolds number (UWq f /g) Sc Schmidt number (g/q f D) St Strouhal number (Wf/U) S distance between two parallel electromagnets (m) t time (s) T period, 1/f (s) U relative velocity between the fluid and particle along y direction (m/s) V volume (m 3 ) V fluid's velocity vector v particles' velocity vector W lateral dimension or width (m)

Mold filling of a rectangular cavity of three different thick nesses fed from a reservoir is studied for unfilled and glass fiber‐filled polypropylene and polystyrene. The shapes of flow fronts studied by short‐shots are affected predominantly by the thickness of the cavity with other parameters playing a less important role. Pressure drop versus volumetric flow rate inside the thinnest cavity is studied experimentally and predictions are made from a computer simulation of mold filling. The orientation of fibers in the cavity is examined using a reflect‐type microscope and the orientation is found to depend on cavity thickness, melt temperature, fiber content, and to a lesser extent, on volumetric flow rate. In the thinnest cavity, where the flow is quasi‐unidirectional, the fibers remain in the plane of flow oriented either along the flow direction or perpendicular to it, except in the region near the flow front, where they follow a “fountain” flow behavior.

The results of several thousands of inelastic time history analyses, which have been made on single degree of freedom structures to assess P-delta effects induced in earthquakes, are reviewed. The principal factors influencing P-delta actions are shown to be the ductility, the duration of the severe ground motion, the level of damping and the period of the structure. A method of designing for P-delta effects for single degree of freedom structures is presented. A limited number of analyses of multi-storey frames and walls indicate that the approach may be used for multi-storey structures. This paper gives background information on the P-delta method of analysis given in an appendix to the commentary of the proposed loading code.

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The present study develops a new approach to minimize the weight of a radiating straight fin array so that the whole system of the fin array is optimized by minimizing the weight of the individual fin, which is subjected to radiation interaction with adjacent fins and base. The obtained system has the minimum weight possible, and also yields the best shape of the individual fins for a given total heat dissipation and uniform base temperature. Based on the present analysis, the optimum number of fins in a fin array is obtained.

A continuous exchange factor method for the analysis of radiative exchange in gray enclosures with absorbing-emitting and isotropically scattering media and diffuse surfaces is developed. In this method two types of exchange function are defined: the direct exchange function and the total exchange function. Certain integral equations relating total exchange functions to direct exchange functions are developed. These integral equations are solved using a Gaussian quadrature integration method. The results obtained based on the present approach are found to be more accurate than those of the zonal method. Unlike the zonal method, in the present approach, there is no need for evaluation of multiple integrations for calculating direct exchange factors.