[en] A subgrid-scale model is discussed for the scalar dissipation rate in nonpremixed turbulent reacting flows. The model contains a coefficient which is determined by assuming a form for the scalar energy spectrum. The model is tested a priori using Direct Numerical Simulation (DNS) results for a temporal reacting mixing layer. The estimated dissipation rates are in good agreement with dissipation rates computed directly from the DNS data. Furthermore, the assumed spectrum methodology is found to accurately predict the model coefficient, including its spatial and temporal variations. copyright 1999 American Institute of Physics

[en] Rigorous upper bounds are derived for large-scale turbulent flame speeds in a prototypical model problem. This model problem consists of a reaction-diffusion equation with KPP chemistry with random advection consisting of a turbulent unidirectional shear flow. When this velocity field is fractal with a Hurst exponent H with 0< H<1, the almost sure upper bounds suggest that there is an accelerating large-scale turbulent flame front with the enhanced anomalous propagation law y = C_Ht^1+H for large renormalized times. In contrast, a similar rigorous almost sure upper bound for velocity fields with finite energy yields the turbulent flame propagation law y = C_Ht within logarithmic corrections. Furthermore, rigorous theorems are developed here which show that upper bounds for turbulent flame speeds with fractal velocity fields are not self-averaging, i.e., bounds for the ensemble-averaged turbulent flame speed can be extremely pessimistic and misleading when compared with the bounds for every realization

No abstract available

No abstract available

No abstract available

[en] A stepwise scheme is described for screening chemicals on the basis of their expected behaviour in the environment. The chemicals are subjected to experimental conditions in the laboratory believed to represent the critical environmental factors. The first step (requiring up to three weeks) is study of the behaviour of the chemical under abiotic conditions: evaporation, heat stability, interaction with soil and water, liability to oxidation, binding and leaching properties, and stability in the presence of enzymes in vitro. The second step (requiring up to three months) involves biological tests: plant sorption from air and soil, biodegradation, self-cleansing processes and effects on biota. (author)

[en] The modelling of the formation of transport barrier requires a quantitative prediction as to how much flux is reduced by zonal flows (ZFs). Here, I will consider a few simple turbulence models to discuss the scaling of turbulent transport with (mean or RMS) shearing rate and then to examine the model dependence of such scalings. In particular, I will examine the effects of ZFs with different frequency spectra on turbulent transport, by comparing the results obtained for high-frequency ZFs and those for low-frequency random ZFs, and identify different physical mechanisms responsible for the reduction in transport and turbulence amplitude. Furthermore, I will discuss the effects of fluctuating magnetic fields on the transport of particles and momentum in high β plasmas, indicating the possibility of quenching turbulent transport without much effect on turbulence amplitude with small normalized flux (the so-called cross-phase). (author)

[en] Random orientation of molecules within a sample leads to blurred observations of chemical reactions studied from the laboratory perspective. Methods developed for the dynamic imaging of molecular structures and processes struggle with this, as measurements are optimally made in the molecular frame. Here we use laser alignment to transiently fix CS2 molecules in space long enough to elucidate, in the molecular reference frame, details of ultrafast electronic vibrational dynamics during a photochemical reaction. These three-dimensional photoelectron imaging results, combined with ongoing efforts in molecular alignment and orientation, presage a wide range of insights obtainable from time-resolved studies in the molecular frame

[en] This paper presents experimental results of source identification for a non-minimum phase system. Generally, a causal linear system may be described by matrix form. The inverse problem is considered as a matrix inversion. Direct inverse method cannot be applied for a non-minimum phase system, because the system has ill-conditioning. Therefore, in this study the SVD inverse technique is introduced to execute an effective inversion. In a non-minimum phase system, its system matrix may be singular or near-singular and has very small singular values. These very small singular values have information about a phase of the system and ill-conditioning. Using this property, we could solve the ill-conditioned problem of the system and then verify it for the practical system (cantilever beam). The experimental results show that the SVD inverse technique works well for a non-minimum phase system. This inverse technique can be applied to the estimation of the magnitude of impact force, which becomes often a cause of damage to a mechanical system

[en] Recently a variety of electrochemical techniques have been used for the measurement of under-film corrosion of coated steel. Each method has its own characteristic and is suitable to determine some kinds of anti-corrosive mechanisms of coating film. We developed a new under-film corrosion tester (UFCT) which a doped current interrupter technique in principle. Electrochemical parameters can be measured by UFCT. It is possible for the novel under-film corrosion tester to evaluate under-film corrosion of steel covered with high electric resistance coating film which has no defect and is not easy to evaluate it by other methods. Finally some experimental results of protective coating performance obtained by UFCT were discussed