Standard<Emphasis Type="Italic">SU</Emphasis>(5) supergravity grand unification model and predictions

A review is given of the StandardSU(5) supergravity model. This model has passed an important check regarding unification of the electro-weak and the strong couplings using high precision LEP data. It is shown that for a significant domain of the parameter space the model also satisfies constraints on the SUSY spectrum from CDF and LEP, as well as proton stability and cosmological relic density constraints.     

Physics with large extra dimensions

The recent understanding of string theory opens the possibility that the string scale can be as low as a few TeV. The apparent weakness of gravitational interactions can then be accounted by the existence of large internal dimensions, in the sub-millimeter region. Furthermore, our world must be confined to live on a brane transverse to these large dimensions, with which it interacts only gravitationally. In my lecture, I describe briefly this scenario which gives a new theoretical framework for solving the gauge hierarchy problem and the unification of all interactions. I also discuss a minimal embedding of the standard model, gauge coupling unification and proton stability. On leave from: Centre de Physique Théorique, Ecole Polytechnique, 91128 Palaiseau, Cedex, France.     

Simulation and design of a bandpass filter on metasubstrates

This work presents an analysis of the microstrip bandpass filter on metamaterial substrates. The filter is composed of two ring resonators with quarter-wavelength side-coupled sections. The filter input is provided, as well as the output port, using a quarter-wavelength side-coupled microstrip line section. Simulations by finite element method have been carried out to verify the effect of the metamaterial substrate properties on the filter performance, and to compare these results to those obtained considering isotropic substrate.     

Mathematical modelling and numerical simulation of the morphological development of neurons

Background

The morphological development of neurons is a very complex process involving both genetic and environmental components. Mathematical modelling and numerical simulation are valuable tools in helping us unravel particular aspects of how individual neurons grow their characteristic morphologies and eventually form appropriate networks with each other.

Methods

A variety of mathematical models that consider (1) neurite initiation (2) neurite elongation (3) axon pathfinding, and (4) neurite branching and dendritic shape formation are reviewed. The different mathematical techniques employed are also described.

Results

Some comparison of modelling results with experimental data is made. A critique of different modelling techniques is given, leading to a proposal for a unified modelling environment for models of neuronal development.

Conclusion

A unified mathematical and numerical simulation framework should lead to an expansion of work on models of neuronal development, as has occurred with compartmental models of neuronal electrical activity.

     

X-ray topography, photopyroelectric and two-photon absorption studies on solution grown benzimidazole single crystal

Benzimidazole (BMZ) is an organic nonlinear optical material, and it is possible to grow it in the laboratory by a slow evaporation solution growth technique using methanol as the solvent. Its nonlinear optical harmonic generation efficiency is 4.5 times higher than that of standard potassium dihydrogen phosphate (KDP) single crystal. It crystallizes with orthorhombic structure, which is noncentrosymmetric in nature, with lattice parameters a=13.58 Å, b=6.85 Å, c=6.97 Å. The functional groups of the grown specimen are confirmed by heteronuclear chemical shift correlation (HETCOR) analysis and it is found that other elements are not incorporated in the compound. The crystalline perfection is examined by high resolution X-ray diffraction (HRXRD), and its topographic image was recorded for the as-grown single crystal indicates the presence of some grain boundaries in the grown specimen. Thermal parameters such as thermal diffusivity (α), thermal conductivity (k), thermal effusivity (e), and heat capacity (c _p ) have been determined by a photopyroelectric thermal wave method. In addition, piezoelectricity, birefringence, and third-order nonlinear optical properties have been examined. The two-photon absorption coefficient of the title compound is determined by the open-aperture Z-scan technique.     

Thermodynamic non-additivity in disordered systems with extended phase space

Non-additivity effects in coupled dynamic-stochastic systems are investigated. It is shown that there is a mapping of the replica approach to disordered systems with finite replica indexn on Tsallis non-extensive statistics, if the average thermodynamic entropy of the dynamic subsystem differs from the information entropy for the probability distribution in the stochastic subsystem. The entropic indexq is determined by the entropy difference ΔS. In the case of incomplete information, the entropic indexq=1−n is shown to be related to the degree of lost information.     

Turbulent flame visualization using direct numerical simulation

Combustion phenomena are of high scientific and technological interest, in particular for energy generation and transportation systems. Direct Numerical Simulations (DNS) have become an essential and well established research tool to investigate the structure of turbulent flames, since they do not rely on any approximate turbulence models. In this work two complementary DNS codes are employed to investigate different types of fuels and flame configurations. The code is π³ is a 3-dimensional DNS code using a low-Mach number approximation. Chemistry is described through a tabulation, using two coordinates to enter a database constructed for example with 29 species and 141 reactions for methane combustion. It is used here to investigate the growth of a turbulent premixed flame in a methane-air mixture (Case 1). The second code,Sider is an explicit three-dimensional DNS code solving the fully compressible reactive Navier-Stokes equations, where the chemical processes are computed using a complete reaction scheme, taking into account accurate diffusion properties. It is used here to compute a hydrogen/air turbulent diffusion flame (Case 2), considering 9 chemical species and 38 chemical reactions.     

Sensitization of spinal cord nociceptive neurons with a conjugate of substance P and cholera toxin

Background  

Several investigators have coupled toxins to neuropeptides for the purpose of lesioning specific neurons in the central nervous system. By producing deficits in function these toxin conjugates have yielded valuable information about the role of these cells. In an effort to specifically stimulate cells rather than kill them we have conjugated the neuropeptide substance P to the catalytic subunit of cholera toxin (SP-CTA). This conjugate should be taken up selectively by neurokinin receptor expressing neurons resulting in enhanced adenylate cyclase activity and neuronal firing.     

A 100 kHz Narrow-Pulse-Width Mid-Infrared Optical Parametric Oscillator Based on PPMgLN Crystal

We report a narrow pulse width optical parametric oscillator based on periodically poled MgO:LiNbO₃ (PPMgLN) with a high repetition rate under quasi-phase matched conditions. When the maximum pumping power of the 1,064-nm laser was 14.57 W, the acousto-optical (A-O) Q-switch repetition rate was 100 kHz, and the PPMgLN crystal grating period was 29.5 μm. A 1,474-nm signal light output power of 4.21 W and a 3,828 nm idler light output power of 1.547 W were obtained, corresponding to a pulse width of 9.52 ns and 9.65 ns, respectively. The overall optical–optical conversion efficiency was 39.5%. Additionally, by changing the temperature from 25°C to 150°C, a tunable signal wavelength of 1,474–1,499 nm and idler wavelength at 3,676–3,828 nm of the output laser were achieved.     

Analysis of Asymmetric Long-Range Surface-Plasmon Waveguide with High-Confinement Mode

We model and study the asymmetric long-range surface-plasmon waveguides using the finite-element method. We introduce two types of asymmetric structures and discuss their modal properties compared to traditional long-range surface-plasmon waveguides. Although the propagation distance is decreased, the energy-confinement capability is improved for asymmetric long-range waveguiding structures when the geometrical parameters are properly selected. Our simulation result offers guidance for tuning properties of plasmonic waveguides and providing ways for enhancing electromagnetic energy confinement in long-range surface-plasmon waveguides.