Computer simulation of turbulence in internal combustion engines

The paper presents two- and three-dimensional computations of the in-cylinder turbulent flow in a diesel engine. The mathematical formulation is presented first, with emphasis on the modifications made to the standard k-ε model of turbulence, to account for rapid compression/expansion, and on the k-w model also used in the computations. Then, the results of two-and three-dimensional transient calculations are presented and compared with experimental data. It is realized that two-dimensional computations may be of little value to real engines, which would probably require three-dimensional analyses. However, two-dimensional studies are still useful in allowing the testing of new ideas easily and economically. It is concluded that the standard k-ε model may lead to poor predictions when used for internal combustion (IC) engine simulations, and that the modified model leads to more reasonable length-scale distributions, and it improves significantly the overall agreement of velocity predictions with experiment. The effect of the k-ε modification is apparent in both the two- and three-dimensional simulations. It is also demonstrated that the k-w model provides better turbulence predictions than the unmodified k-ε model, for the cases considered, and that a similar modification of the k-w model, to account for rapid compression/expansion, might improve its predictions even further.     

Measurement of surface wave transmission coefficient across surface-breaking cracks and notches in concrete

In this paper, a technique for measuring a surface wave transmission coefficient across surface-breaking cracks and notches in a heterogeneous but globally isotropic material (concrete) is presented. Once the transmission coefficient across a surface discontinuity is known, its depth may be estimated. There are many difficulties in measuring the transmission coefficient experimentally owing to effects of wave path dependence, unknown characteristics of the receiver and the wave source, and the variation of impact event or receiver coupling. To eliminate the undesired effects, a self-calibrating measurement scheme is applied to obtain the surface wave transmission coefficient across notches and surface-breaking cracks in concrete. The obtained signal transmission coefficient is not affected by the experimental setup or the heterogeneous nature of the material. The testing scheme is described and experimental results obtained from concrete specimens with notches and surface-breaking cracks are presented. Repeatable and reliable measurements of surface wave transmission coefficient are obtained, which demonstrate a strong relation to normalized discontinuity depth. A numerical study using the boundary element method is presented, which verifies the experimental findings.     

Dominance of radiative coupling over disorder in resonance Rayleigh scattering in semiconductor multiple quantum-well structures

Resonance Rayleigh scattering by periodic semiconductor multiple quantum-well structures is studied experimentally and theoretically. Polaritonic effects are found to dominate disorder in the secondary emission dynamics. The coexistence of several radiant polaritonic modes with different radiative decay times leads to polarization beating between modes, strongly influences the rise times, and determines the fast decay times of the resonance Rayleigh scattered signals.     

Unitarized hard-meson calculation of Kl3 form factors

K_l3 form factors are studied in the analytic hard-meson framework. The Gell-Mann-Oakes-Renner model for chiral SU(3) × SU(3) symmetry breaking is employed to determine the so called σ-terms and current divergences. PCAC is used for the π^? and K-mesons, and two-particle unitarity is used for the 1^? and 0⁺ channels. The results depend on the Kappa-meson mass. Results are presented for the slope of the divergence form factor λ₀, the ratio $\text{ξ =}\text{?}{}_{\mathrm{?}}\text{(0)}\text{?}{}_{\mathrm{+}}\text{(0)}$, and the width of the Kappa meson, for m_κ = 900 and 1100 MeV. It is found that the κ has a large width, and the prediction for λ₀ and ξ are in quantitative agreement with the recent experiments.     

On the zeros of univalent functions with univalent derivatives

Summary A family, E, consisting of normalised univalent functions with univalent derivatives is studied with regard to the zeros of these functions. Entrata in Redazione il 29 marzo 1978.     

Optical colours and polarization of a model reflection nebula. III. Composite and mixture of grains in the nebula with the star in the rear

The colour differences between the star and the associated reflection nebula and polarization caused by core mantle grains and mixture of grains have been given. They are based on homogeneous plane-parallel slab-model of the nebula with the star in the rear. The composite particles in the form of concentric spheres consist of homogeneous core of graphite, silicate or SiC and homogeneous mantle of ice. The effect of varying the core and mantle radii has been studied. The mixtures of grains composed of ice, silicate, graphite and SiC in various proportions have also been considered. Each of these grain species has been considered with exp(−a ³) type of size distribution function. The wavelength dependent indices of refraction have been used throughout.     

K−p elastic scattering at 14.3 GeV/c

Results are presented of a bubble chamber experiment on K^?p elastic scattering at 14.3 GeV/c, in four-momentum transfer range 0.04 < |t| < 2.74 GeV² using an initial set of 40 000 events. The total elastic cross section is (2.96 ± 0.10) mb. The results are compared with K⁺p elastic scattering data at 13.8 GeV/c, and the effective Regge trajectory is calculated using K^?p data from 5 to 100 GeV/c.     

Luminescence in high purity In0.53Ga0.47As

We have investigated luminescence processes in high purity In_0.53Ga_0.47As grown by liquid phase epitaxy on InP substrate. The origins of luminescence processes have been determined by studying the dependence of emission intensity and spectrum on temperature. We show that exciton-ionized donor complex dominates the luminescence at 2K. With increasing temperature, the luminescence spectrum is dominated by donor-valence band and free electron-free hole recombination. Spectrum and bandgap energy are found to be dependent on the excitation position.     

Nanocasting of carbon nanotubes: in-situ graphitization of a low-cost mesostructured silica templated by non-ionic surfactant micelles

The in-situ graphitization of an as-made, large pore silica mesostructure templated by nonionic Pluronic 123 surfactant micelles provides a low cost pathway to the nanocasting of linear carbon nanotubes.