Convection in a vertical cavity submitted to crossed uniform heat fluxes

In this study, free convection in a vertical cavity heated from the four walls by uniform heat fluxes is considered. Analytical solutions are derived for a fully developed base flow, for which linear stability analysis predicts the growth of oblique, three-dimensional disturbances in general. A Hopf type bifurcation occurs at the critical Rayleigh number, over the entire range of Prandtl numbers and heat flux ratios considered, characterized by oscillating instabilities. Depending mostly on the value of the Prandtl number, either thermal, for Pr>1, or hydrodynamic, for Pr<1, instability modes are predicted. For small Prandtl numbers, both modes can occur at the codimension two intersection points of the critical branches.     

HYDROMAGNETIC NATURAL CONVECTION OF A BINARY FLUID IN A VERTICAL POROUS ENCLOSURE

An analytical and numerical investigation is conducted to study the effect of an electromagnetic field on natural convection in a vertical rectangular porous cavity saturated with an electrically conducting binary mixture. Uniform heat fluxes are applied to the vertical walls while the horizontal walls are adiabatic. Governing parameters of the problem under study are the thermal Rayleigh R_T, Hartmann number Ha, buoyancy ratio ?, Lewis number Le, and aspect ratio A. An analytical solution, valid for tall enclosures (A > > 1), is derived on the basis of the parallel flow approximation. In the range of the governing parameters considered in this study, a good agreement is found between the analytical predictions and the numerical results obtained by solving the full governing equations.     

Increased expression of a hemimethylated oriC binding protein, SeqA, in an aphA mutant

In Escherichia coli, the origin of DNA replication, oriC, becomes transiently hemimethylated at the GATC sequences immediately after initiation of replication and this hemimethylated state is prolonged because of its sequestration by a fraction of outer membrane. This sequestration is dependent on a hemimethylated oriC binding protein such as SeqA. We previously isolated a clone of phage lambda gt11 called hobH, producing a LacZ fusion protein which recognizes hemimethylated oriC DNA. Very recently, Thaller et al. (FEMS Microbiol. Lett. 146 (1997) 191-198) found that the same DNA segment encodes a non-specific acid phosphatase, and named the gene aphA. We show here that the interruption of the aphA reading frame by kanamycin resistance gene insertion, abolishes acid phosphatase (NAP) activity. Interestingly, in the membrane of the null mutant, the amount of SeqA protein is about six times higher than that in the parental strain, suggesting the existence of a regulatory mechanism between SeqA and NAP expression.     

A compact split step Padé scheme for higher-order nonlinear Schrödinger equation (HNLS) with power law nonlinearity and fourth order dispersion

In this paper we propose a compact split step Padé scheme (CSSPS) to solve the scalar higher-order nonlinear Schrödinger equation (HNLS) with higher-order linear and nonlinear effects such as the third and fourth order dispersion effects, Kerr dispersion, stimulated Raman scattering and power law nonlinearity. The stability of this method has been proved. It has been shown as well that the CSSPS method gives the same results as classical numerical methods like the split step Fourier method and Crank–Nicholson (CN) method but it presents many advantages over theme. It is more efficient. This proposed scheme is well suited to higher-order dispersion effects and readily generalized for nonlinear and dispersion managed fibers. We tested this scheme for the case of the quintic nonlinearity and confirmed that this effect has no significant role on the propagation of single solitons.     

Comparison of EEG signal decomposition methods in classification of motor-imagery BCI

A brain–computer interface (BCI) provides a link between the human brain and a computer. The task of discriminating four classes (left and right hands and feet) of motor imagery movements of a simple limb-based BCI is still challenging because most imaginary movements in the motor cortex have close spatial representations. We aimed to classify binary limb movements, rather than the direction of movement within one limb. We also investigated joint time-frequency methods to improve classification accuracies. Neither of these, to our knowledge, has been investigated previously in BCI. We recorded EEG data from eleven participants, and demonstrated the classification of four classes of simple-limb motor imagery with an accuracy of 91.46% using intrinsic time-scale decomposition and 88.99% using empirical mode decomposition. In binary classifications, we achieved average accuracies of 89.90% when classifying imaginary movements of left hand versus right hand, 93.1% for left hand versus right foot, 94.00% for left hand versus left foot, 83.82% for left foot versus right foot, 97.62% for right hand versus left foot, and 95.11% for right hand versus right foot. The results show that the binary classification performance is slightly better than that of four-class classification. Our results also show that there is no significant difference in terms of spatial distribution between left and right foot motor imagery movements. There is also no difference in classification performances involving left or right foot movement. This work demonstrates that binary and four-class movements of the left and right feet and hands can be classified using recorded EEG signals of the motor cortex, and an intrinsic time-scale decomposition (ITD) feature extraction method can be used for real time brain computer interface.

     

Structural characterisation and antibacterial activity of PP/TiO2 nanocomposites prepared by an in situ sol–gel method

Polypropylene/titanium dioxide (PP/TiO₂) nanocomposites can be prepared using a novel method based on the hydrolysis–condensation reactions (sol–gel method) of titanium alkoxide inorganic precursors that have been premixed with polypropylene under molten conditions. The resultant nanocomposites were characterised by transmission electronic microscopy (TEM), X-ray diffraction, Raman spectroscopy and X-ray photoelectron spectroscopy (XPS). These techniques showed the formation of the titanium oxi-hydroxide chemical structure (Ti_xO_y(OH)_z) with a diameter of approximately 10 nm in the polymer matrix. Furthermore, a condensation degree of around 17% was determined using XPS analysis. The antibacterial activity was tested according to the JIS Z 2801:2000 standard with Staphylococcus aureus (S. aureus) and Escherichia coli (E. coli) in the absence of light. Correlations between the microstructure and the chemical composition of PP/TiO₂ nanocomposites and the antibacterial properties of these nanocomposites were discussed. The structure of titanium oxi-hydroxide derivative particles (Ti_xO_y(OH)_z) within the polypropylene matrix has been shown to impact strongly on the antibacterial properties in comparison with the results obtained with a dispersion of anatase titanium dioxide into the PP.