Comparative Large Eddy Simulation study of a large-scale buoyant fire

A fully-coupled Large Eddy Simulation model which incorporates all essential combustion, radiation and soot chemistry considerations have been developed to simulate the temporal vortical structure of a large-scale buoyant fire. Numerical results are validated and compared against a full-scale fire measurements and predictions from other LES models. Quantitative comparisons against experimental data suggested that the present model successfully captured the vortical structures and the puffing behaviour of a buoyant fire.     

The properties of liquid nitrogen

The light-scattering ‘anisotropy’ spectrum of liquid nitrogen has been measured for the liquid along the liquid-vapour coexistence line from 69·4 K (almost the triple point) to near the critical point at 125 K and for the gas under pressure at 128 K. The spectrum is very broad (HWHH～50 cm^-1) due to rapid molecular reorientation. The molecular anisotropy spectrum is approximately gaussian, corresponding to a correlation time for molecular reorientation of order 2 × 10^-13 s at 80 K which is comparable with that obtained from nuclear magnetic resonance. A gaussian rather than a lorentzian form arises because molecular reorientation is not a ‘slow’ variable.

Above the critical temperature the molecular anisotropy spectrum can be roughly described as a collision-broadened rotational line spectrum.

The spectrum and its time Fourier Transform are analysed in terms of the dynamical correlation of orientation of the molecules.

A component of the spectrum due to induced polarization is separated from the anisotropy contribution by a study of the far wing of the spectrum and is observed on the Stokes side out to about 250 cm^-1. This depends exponentially on frequency shift and is interpreted in terms of molecular collision dynamics. The correlation time for this motion is about a factor three shorter than that for molecular reorientation.

The spectra are markedly asymmetric after all experimental corrections for asymmetry have been made. The asymmetry is shown to correspond to the detailed balance factor. It is pointed out that this factor should be allowed for in the case of induced scattering, in particular.

A theoretical analysis is given of the effect of correlation of molecular orientation on the light-scattering spectrum for centrosymmetric linear molecules. In particular it is shown that the normalized second moment of the spectrum is unaffected by correlation of orientation.     

The properties of liquid nitrogen

A Molecular Dynamics simulation of liquid nitrogen has been carried out using an atom-atom potential together with a point quadrupole-quadrupole interaction. The changes in the properties of the model fluid compared to a previous simulation [1] using the atom-atom potential alone are small but significant. The structure factor is notably closer to experiment. The properties associated with reorientation motion are also closer to experiment but discrepancies remain especially at high temperatures.     

Trefftz法中的自锁现象及变量减缩法

用Trefftz型边界解法分析了中厚板弯曲问题,发现了一类新的、因Trefftz函数溢机引起的"自锁现象",并提出了一种消除这类自锁问题的"变量减缩法".     

Determination of pesticides in soy-based infant formula using liquid chromatography with electrospray ionization tandem mass spectrometry

A sensitive method using liquid chromatography with electrospray ionization tandem mass spectrometry (LC/ESI-MS/MS) was developed and validated to quantify and confirm 13 pesticides, including aldicarb sulfoxide, aldicarb sulfone, oxamyl, methomyl, formetanate, 3-hydroxycarbofuran, carbendazim, thiabendazole, aldicarb, propoxur, carbofuran, carbaryl, and methiocarb, in soy-based infant formula. Data acquisition under MS/MS was achieved by applying multiple reaction monitoring of 2 fragment ion transitions to provide a high degree of sensitivity and selectivity for both quantitation and confirmation. Different approaches to constructing calibration curves were compared and discussed to address issues of the extraction efficiency or recovery, and matrix effects. Matrix-matched standard calibration curves with the use of isoprocarb as an internal standard were finally used to achieve the best accuracy of the method. Under most circumstances, recoveries of 13 pesticides, spiked at 5.0, 25.0, and 45.0 microg/kg, were close to 100%. The method detection limits (signal-to-noise ratio > or =3:1; microg/kg) of 13 pesticides were 0.2 for thiabendazole and methiocarb, 0.6 for aldicarb, and 0.1 for the others.     

A companion matrix approach to the study of zeros and critical points of a polynomial

In this paper, we introduce a new type of companion matrices, namely, D-companion matrices. By using these D-companion matrices, we are able to apply matrix theory directly to study the geometrical relation between the zeros and critical points of a polynomial. In fact, this new approach will allow us to prove quite a number of new as well as known results on this topic. For example, we prove some results on the majorization of the critical points of a polynomial by its zeros. In particular, we give a different proof of a recent result of Gerhard Schmeisser on this topic. The same method allows us to prove a higher order Schoenberg-type conjecture proposed by M.G. de Bruin and A. Sharma.     

Facets of the independent path-matching polytope

Cunningham and Geelen introduced the independent path-matching problem as a common generalization of the weighted matching problem and the weighted matroid intersection problem. Associated with an independent path-matching is an independent path-matching vector. The independent path-matching polytope of an instance of the independent path-matching problem is the convex hull of all the independent path-matching vectors. Cunningham and Geelen described a system of linear inequalities defining the independent path-matching polytope. In this paper, we characterize which inequalities in this system induce facets of the independent path-matching polytope, generalizing previous results on the matching polytope and the common independent set polytope.     

Application of a heuristic search technique for the improvement of spray zones cooling conditions in continuously cast steel billets

The process of casting occupies an important place in the metallurgical industry, and the entire world of the metal user. In the past, the ingot casting–rolling (slabbing, blooming, or billeting) process was commonly used. The continuous casting process has largely replaced this earlier method because of the inherent advantages of energy savings, enhanced productivity, higher yield and reduced costs. However, continuous casting process is not without of its problems. Considerable effort has been made by many researches to establish adequate design, operation and maintenance of continuous casting machine to ensure metallurgical quality of the final product. One of the most severe defects in continuous casting products is concerned with the cracks provoked by improper design of the spray cooling system. The aim of this work is to develop a two dimensional heat transfer model based on the finite difference method in order to calculate the strand temperatures and the solid shell profile along the machine. An Artificial Intelligence heuristic search procedure interacts with the numerical model to determine the improved cooling conditions for the sprays zones of a real continuous caster for the production of quality billets.