Dynamical characteristics of bacteria clustering by self-generated attractants

Motivated by the recent work on Escherichia coli bacteria clustering [Park, S., Wolanin, P.M., Yuzbashyan, E.A., Lin, H., Darnton, N.C., Stock, J.B., Silberzan, P., Austin, R., 2003. Proc. Natl. Acad. Sci. U.S.A. 100 (24), 13910], we have conducted a computer simulation of E. coli chemotaxis induced by a self-excreted attractant and investigated how bacteria clusters interact through a self-excreted attractant. By modeling the variation of tumbling frequency in the context of phosphorylation rate change, we have investigated the dependency of clustering behavior on the sensitivity of cells to the attractant. We have found that there exists an optimal sensitivity leading to bigger clusters and that the geometry surrounding the cells also plays an important role in localizing the cluster formation. This result suggests that bacterial cluster formation can be reduced by making bacteria more sensitive to attractants, which is opposite to an instinctive way (making them retarded to attractants). In addition, we have studied the effect of an initial cell distribution on clustering.     

Fluorometric analysis of borohydrides based on reductive aldehyde-to-alcohol conversion of arylaldehydes

Fluorometric analysis of borohydride (BH₄^–) species by the reduction of arylaldehydes to the corresponding arylmethanols was investigated. 9-Anthracenecarboxaldehyde (9-AA) exhibited pronounced ratiometric fluorescence signaling behavior toward borohydride in alkaline aqueous media. The borohydride-selective signaling of 9-AA was unaffected by the presence of commonly encountered metal ions and anions. 1-Pyrenecarboxaldehyde (1-PA) also showed comparable borohydride signaling behavior. The detection limit was found to be 7.4?μM (0.11?ppm) for 9-AA and 15.7?μM (0.23?ppm) for 1-PA. The utility of the probe with μPAD as a convenient tool for the determination of borohydrides was demonstrated.     

Preparation of Functionalized Polysilsesquioxane and Polysilsesquioxane‐Metal Nanoparticle Composite Spheres

Summary: Network polysilsesquioxane spheres made solely of poly(vinylsilsesquioxane) (PVSQ) and poly(3‐mercaptopropylsilsesquioxane) (PMPSQ) were prepared from heterogeneous mixtures of triethylamine (TEA), water, and either vinyltrimethoxysilane (VTMS), or 3‐mercaptopropyltrimethoxysilane (MPTMS). The microscopic, macroscopic observations, and the relationship between the diameters of spheres and the amount of each ingredient in the reaction system, showed that spheres formed via a mechanism similar to emulsion polymerization and suspension polymerization, depending on the reaction conditions. Diameters of spheres could be controlled from tens of nanometers to a few micrometers by adjusting the amounts of TEA, water, and a surfactant. Heating aqueous solutions of metal ions with these spheres produced polysilsesquioxanes (PSQ)‐metal nanoparticle composite spheres. The spheres prepared in this study were characterized by scanning electron microscopy, transmission electron microscopy, solid state NMR spectroscopy, IR spectroscopy, elemental analysis, and differential thermal analysis. These spheres would be useful in recovering metals from their ionic solutions and probes after chemical modifications.

An image of the spheres of poly(vinylsilsesquioxane)‐gold nanoparticle composite.     

Simple Patterning of Cells on a Biocompatible Nonchemically Amplified Resist

Summary: A simple lithographic process in conjunction with a novel biocompatible nonchemically amplified photoresist material was successfully used for cell patterning. UV light irradiation on selected regions of the nonchemically amplified resist film renders the exposed regions hydrophilic by the formation of carboxylic groups. Mouse fibroblast cells were found to be preferentially aligned and proliferated on the UV light exposed regions of the nonchemically amplified resist film where carboxylic groups were present.

Schematic representation of the simplified lithographic process used for cell patterning.     

Core/Shell Structured PCM Nanocapsules Obtained by Resin Fortified Emulsion Process

Phase change material (PCM, octadecane) nanocapsules were successfully prepared by resin fortified emulsion (RFE) polymerization using the alkali soluble resin (ASR) of poly(ethylene‐co‐acrylic acid) (EAA) and poly(styrene‐co‐acrylic acid) (SAA). Stable PCM nanocapsules were obtained by resin fortified emulsion polymerization, which could be attributed to the prevention of Ostwald ripening due to PCM being hydrophobic. Analysis of online FTIR measurements throughout the reaction confirmed that the nanocapsules contained octadecane as a PCM. TEM imaging of the PCM nanocapsules showed spherical and core/shell morphology. The characteristics of PCM nanocapsules can be controlled by process parameters. As a result, the particle size and particle size distribution (i.e., polydispersity index (Dw/Dn)) of the PCM nanocapsules were created by adjusting manufacturing conditions. The PCM nanocapsules exhibited thermal energy storage (～49.8 J/g) and release (～47.9 J/g) behavior.     

Curvature measurement using phase shifting in-line interferometry,single shot off-axis geometry and Zernike's polynomial fitting

This paper describes the difference between phase shifting in-line interferometry, single shot off-axis geometry and Zernike's polynomial fitting methods for measuring the curvature of a spherical smooth surface by using the Michelson interferometer. In phase shifting in-line interferometry, four interferograms shifted by a piezoelectric actuator (PZT) were captured by a digital detector and corrected by using the flat fielding method. In off-axis geometry, single shot off-axis interferogram was obtained by tilting the reference and the object wave of the off-axis interferogram was reconstructed in the central region of the observation plane by using the digital reference wave concept. The demodulated phase map was obtained and unwrapped to remove the 2π ambiguity. The unwrapped phase map was converted to height and the sagittal length that used for curvature measurement was calculated accurately. The results extracted from phase shifting in-line interferometry and single shot off-axis geometry methods were compared with the results extracted from single shot Zernike's polynomial fitting method and the results were in excellent agreement. A new trial was done to overcome the fringes produced from the object interfaces. Some factors of uncertainty which affected on the measurement were estimated in the order of 6.0 × 10^?5 mm or 0.003 dioptre (▽).     

A convergence study of a new partitioned fluid–structure interaction algorithm based on fictitious mass and damping

We develop, analyze and validate a new method for simulating fluid–structure interactions (FSIs), which is based on fictitious mass and fictitious damping in the structure equation. We employ a partitioned method for the fluid and structure motions in conjunction with sub-iteration and Aitken relaxation. In particular, the use of such fictitious parameters requires sub-iterations in order to reduce the induced error in addition to the local temporal truncation error. To this end, proper levels of tolerance for terminating the sub-iteration procedure have been obtained in order to recover the formal order of temporal accuracy. For the coupled FSI problem, these fictitious terms have a significant effect, leading to better convergence rate and hence substantially smaller number of sub-iterations. Through analysis we identify the proper range of these parameters, which we then verify by corresponding numerical tests. We implement the method in the context of spectral element discretization, which is more sensitive than low-order methods to numerical instabilities arising in the explicit FSI coupling. However, the method we present here is simple and general and hence applicable to FSI based on any other discretization. We demonstrate the effectiveness of the method in applications involving 2D vortex-induced vibrations (VIV) and in 3D flexible arteries with structural density close to blood density. We also present 3D results for a patient-specific aneurysmal flow under pulsatile flow conditions examining, in particular, the sensitivity of the results on different values of the fictitious parameters.     

Reduction of the squeal noise from an automotive water pump

Nonlinear Dynamics - This paper presents a method to reduce the squeal noise generated by an automotive water pump. The noise and vibration of the water pump were analyzed through experiments, from...