On the interplay between inertial and viscoelastic effects for the flow in weakly modulated channels

The flow inside a spatially modulated channel is examined for viscoelastic fluids of the Oldroyd‐B type. The lower wall is flat and the upper wall is sinusoidally modulated. The modulation amplitude is assumed to be small. Thus, a regular perturbation expansion of the flow field coupled to a variable‐step finite‐difference scheme is used to solve the problem. Convergence and accuracy assessment against earlier experimental results indicate that there is a significant range of validity of the perturbation approach. The influences of wall geometry, inertia and viscoelasticity on the flow kinematics and stresses are investigated systematically. In particular, the interplay between the flow and fluid parameters effects on the conditions for the onset of backflow, number of vortices, their size and location is revealed. The distance between the flow separation and reattachment locations identifies the vortex size. Non‐monotonic dependence of the vortex size on elasticity is reported. The critical conditions for the onset of negative elasticity effects on vortex size are identified. The critical Reynolds number for the onset of backflow initially decreases then levels off or even increases as elasticity increases. For highly elastic fluid and large enough Reynolds number, more than one vortex appear near the lower wall. Copyright © 2005 John Wiley & Sons, Ltd.     

Spectral Properties of Bifunctional Schiff Bases, [Bis (X-Phenyl)-Ethane Diimine]

Electronic spectra of five (Bis(X-phenyl)-Ethane diimine] compounds I-V, have been investigated in various organic solvents and aqueous buffer solutions of varying pH's. The observed visible band is assigned to intramolecular CT transition. Furthermore, it is deduced that structure of the o-hydroxy derivative is not entirely planar. The acid dissociation constant values of the hydroxy derivatives have been determined and are discussed.     

Convergence Dynamics of Delayed Hopfield-Type Neural Networks Under Almost Periodic Stimuli

Convergence dynamics of Hopfield-type neural networks subjected to almost periodic external stimuli are investigated. In this article, we assume that the network parameters vary almost periodically with time and we incorporate variable delays in the processing part of the network architectures. By employing Halanay inequalities, we obtain delay independent sufficient conditions for the networks to converge exponentially toward encoded patterns associated with the external stimuli. The networks are guaranteed to have exponentially hetero-associative stable encoding of the external stimuli.     

Microchip electrophoresis for specific gene detection of the pathogenic bacteria V. cholerae by circle-to-circle amplification.

We have developed a new method for a fast and precise analysis of circle-to-circle amplification (C2CA) product for specific gene detection by microchip electrophoresis. In this method, we have added a new enzymatic step to the C2CA reaction, which could be carried out isothermally at 37 degrees C. Compared to the original single-stranded DNA, the double-stranded DNA that is produced by this enzymatic reaction is more reliable for analysis by microchip electrophoresis. C2CA product was detected within 55 s with high reproducibility by this method which was successfully applied to the detection of 10-ng genomic DNA of the pathogenic bacteria Vibrio. cholerae within 110 s. Purification was found to be an indispensable step for the analysis of the C2CA product of genomic DNA samples.     

Free‐radical‐promoted cationic photopolymerization under visible light in aerated media: New and highly efficient silane‐containing initiating systems

New systems for the visible‐light‐induced polymerization of cationic resins working through a free‐radical‐promoted process are presented. They are based on a photoinitiator (camphorquinone, isopropylthioxanthone, Eosin), a silane, and a diphenyl iodonium salt, the new compound being the silane. The overall efficiency is strongly affected by the silane structure. The rates of polymerization and final percent conversion are noticeably higher than those obtained in the presence of already studied reference systems. Moreover, contrary to previously investigated free‐radical‐promoted cationic polymerizations, oxygen does not inhibit the process and an unusual enhancement of the polymerization kinetics is found in aerated conditions: such an observation seems to have never been reported so far. The excited state processes and the role of oxygen as revealed by laser flash photolysis are discussed. The particular behavior of the silyl radicals is outlined. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 2008–2014, 2008     

Sonochemical synthesis of stable hydrosol of Fe3O4 nanoparticles

The sonolysis of an aqueous solution of Fe(CO)(5) in the presence of sodium dodecyl sulfate leads to the formation of a stable hydrosol of amorphous Fe(3)O(4) nanoparticles. The amorphicity of iron oxide nanoparticles was determined by X-ray diffraction and differential scanning calorimetry. The nanoparticles were characterized by elemental analysis, EDX, transmission electron microscopy, dynamic light scattering, Raman spectroscopy, XPS, and spot test.     

On the Filling Invariants at Infinity of Hadamard Manifolds

We study the filling invariants at infinity div _k for Hadamard manifolds defined by Brady and Farb [ Trans. Am. Math. Soc. 350(8) (1998), 3393–3405]. Among other results, we give a positive answer to the question they posed: whether these invariants can be used to detect the rank of a symmetric space of noncompact type.     

Acoustic emission from domain wall motion in ferroelectric lead germanate

Simultaneous visual observation and monitoring of the ultrasonic signals show that acoustic emission (AE) produced as Pb₅Ge₃O₁₁c-plate crystals undergo the ferroelectric hysteresis cycle results from domain wall nucleation and collapse. AE activity takes place predominantly at applied electric fields large enough to bring a crystal substantially towards its saturation polarisation. A notable feature observed in Pb₅Ge₃O₁₁ and Pb_5?xBa_xGe₃O₁₁ alloys is the existence of an abrupt threshold electric field, denoted by E_∞ in the high gain limit, for production of AE: as the electric field is increased beyond the threshold value, the amount of AE observed increases by several orders of magnitude. E_∞ depends linearly on the inverse of the c-plate sample thickness (1/d) and also upon sample temperature—falling to a minimum at about 70°C for Pb₅Ge₃O₁₁ and then rising steeply as the Curie temperature (178°C) is approached. E_∞ is also dependent on the rate of change of the applied electric field and as this is increased extrapolates to the high frequency limit of the coercive field. Measurements of crystal polarisation indicate a one-to-one correspondence between AE and the electrical Barkhausen pulses which occur during polarisation reversal—further evidence for domain nucleation and collapse as the source of AE. Optical and AE studies made simultaneously on gadolinium molybdate add confirmation that these particular processes are responsible for the AE produced by ferroelectric crystals.     

Determination of nanomolar levels of guanine by differential-pulse adsorptive cathodic stripping voltammetry of its copper(II) complex

Guanine is determined at the 5.0×10^–10 –2.0×10^–7 mol/l level by differential-pulse adsorptive stripping voltammetry at a hanging mercury drop electrode using the reduction peak of its copper (II) complex at –0.21 V vs. Ag-AgCl electrode. The optimum analytical conditions were found to be Britton-Robinson buffer solution (pH 4.8), an accumulation potential of 0.0 V and an accumulation time of 3 min. Under these conditions, the detection limit is 5.0×10^–10 mol/l and the relative standard deviation 2.6% for 1.0×10^–7 mol/l guanine. The method is compared with the previous voltammetric methods. The presence of some purine derivatives does not interfere.     

Decatungstate (W10O)/Silane: A New and Promising Radical Source Under Soft Light Irradiation

The use of decatungstate in combination with silanes to generate silyl radicals under green fluorescence bulb irradiation as well as sunlight exposure is described. The mechanisms are investigated by ESR and laser flash photolysis experiments. The high potential of this reaction is evidenced here when using a decatungstate/silane/diphenyl iodonium salt combination as an initiating system for the ring opening photopolymerization of epoxides.