Motion of compliant capsules on corrugated surfaces: A means of sorting by mechanical properties

We discuss a novel method for capturing the dynamic coupling between a fluid and an elastic solid, the so-called fluid–structure interaction. This method integrates a lattice Boltzmann model to capture the fluid dynamics with a lattice spring model to capture the micromechanics of the solid phase. We then examine the fluid-driven motion of microcapsules, which are modeled as fluid-filled, elastic shells, along a corrugated substrate. We show that the ability of the capsules to navigate along the surface depends critically on capsule's elastic modulus. In particular, we illustrate how this substrate can be utilized to design a device for sorting microcapsules by their mechanical properties. These results apply not only to polymeric microcapsules, but also describe the interaction between the substrate and certain biological cells (e.g., leukocytes and other cells with cytoskeletons). Hence, by isolating species of a certain stiffness, the device could be highly useful for applications in biotechnology and tissue engineering or in the quality control of fabricated microcapsules. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 2667–2678, 2006     

Ichthyosan in fish eye

Ichthyosan A and V are two highly elastoviscous glycan complexes present in the aqueus and vitreus [here aqueus and vitreus are used as nouns as was suggested by Balazs and Denlinger in The eye, vol 1A. Vegetative physiology and biochemistry, 3rd edn. Academic Press, New York, pp 533–589, 1984] of the fish eye. Ichthyosan A, with its high elastic properties, surrounds and stabilizes the lens of the eye. Ichthyosan V, within the collagen fibers, serves as a structure stabilizer of the gel vitreus. These two molecular complexes are non-covalent aggregates composed of hyaluronan, a chondroitin-proteoglycan (sulfate free), and a keratan-like molecule. The ratio of hyaluronan to chondroitin–proteoglycan varies in the two ichthyosans. Electrophoretic separation methods (both free and gel electrophoresis) demonstrate that the hyaluronan–proteoglycan aggregates move as one molecular entity. The average molecular weight of the ichthyosan varies from 5.2 to 13.0 million in various species. Aquatic mammals do not have ichthyosan in their eyes.     

Numerical simulation of multiple scattering for modeling speckle roughness analyses on vertical surface regions of silicon wafers

Laser speckle measurement methods enable the roughness analysis also for vertical regions of silicon wafers. However, we have to calculate upon disturbing intensities that are generated by multiple reflection from the surrounding surfaces. A numerical simulation will be described in this study by which the higher spatial frequency of multiple scattered speckle intensities can be shown. Since focused laser beam is generally used for this purpose the influences of convergent illumination will also be taken into account. The results confirm the feasibility of speckle measurement methods (speckle-contrast, speckle-correlation) for roughness analysis of inaccessible surface regions of microstructures (side walls of grooves, inside surfaces of borings). Also, practically undetectable effects can be analysed through the calculation algorithm.     

Typesetting of terahertz waveforms

We demonstrate programmable generation of temporally shaped terahertz waveforms in LiNbO3 by spatially shaping the beam profile of femtosecond excitation laser pulses with a spatial light modulator. The generated terahertz waveforms have amplitudes that are approximately proportional to the first spatial derivative of the excitation beam profile.     

Pattern formation in binary fluids confined between rough, chemically heterogeneous surfaces

Using a mesoscale model for hydrodynamics, we simulate driven flow of AB binary fluids past surfaces that contain well-defined roughness or asperities. The geometry and wetting properties of the asperities are found to have a dramatic effect on the flow patterns. We isolate conditions where the A fluid forms vertical bands that bridge the asperities and an imposed shear (or pressure gradient) drives the system to form monodisperse droplets of A within the B fluid. The size of the droplets can be tailored by varying the morphology of the asperities. The surfaces needed to create this rich dynamical behavior are used as the stamps in microcontact printing; thus, the parameter space can readily be accessed experimentally, and the predictions suggest an efficient method for forming emulsions with well-controlled morphologies.     

Almost All Finitely Generated Subgroups of the Nottingham Group are Free

It is proved that two random elements of the Nottingham groupgenerate a free group with probability 1. This answers a questionof A. Shalev. 2000 Mathematics Subject Classification 20E18,13F25.     

Local control of periodic pattern formation in binary fluids within microchannels

Simulations show that a local perturbation (a "hot spot") at the inlet of a microchannel can be a source of traveling concentration waves in a binary fluid and can be exploited to create periodic, oscillatory patterns within the channel. We isolate two distinctly different types of traveling periodic patterns and estimate the wavelength of the structures. Our findings provide the first example of how a local perturbation can be used to create well-defined periodic patterns in two-phase flow within a confined geometry and can lead to new routes for creating gradient materials.     

Can one derive the Schwartzschild line-element without the field equations?

In 1944 W.Lenz has conceived an ingenious derivation of the Schwartzschild line Element for weak gravitational fields, without using the field equations ofEinstein. The derivation is based only on the Principle of Equivalence and the conservation of energy in the Newtonian approximation. Later M.Köhler raised some doubts how far this derivation is correct. Our aim is to show thatKohler's criticism can be met andLenz's derivation is correct.