DETERMINATION OF MULLITE IN CLAY REFRACTORY PRODUCTS

<正> 莫来石(3Al_2O_3·2SiO_2)在粘土质耐火材料及陶瓷等制品中的形成和其晶体的发育,关系着制品的质量.由于莫来石在氢氟酸中的溶解度低,一般定量分析窑业制品中的莫来石含量,均采用氢氟酸处理试料而将残渣看成莫来石的方法.可是根据文献的记载,有关分析方法的条件,多属语焉不详,并且互有出入,兹综合于表1:     

DETERMINATION OF THE OPTIMUM PREPARATION CONDITION OF THE SOL-GEL SiO2 USING THE RESPONSE SURFAC METHODOLOGY

A typical sol - gel process consists of the liquid reaction, the solution gelation, and followed by the dehydration. The surface properties of silica gel such as surface area, pore volumes, and the pore diameter were affected by the manufacturing variables including pH values, gelation and dehydration temperatures. The objective of this study is to determine the optimum preparation conditions to maximize a response of surface area, or minimize its pore diameter. In addition, interactions between process variables were studied and their significance to the surface properties was also weighted. It was found that the surface area of silica gels increased with an increasing amount of NH₄OH to a maximum value and then decreased. As a drying temperature kept constant, the surface area and the pore volume increased with an increasing gelation temperature. However, the pore diameter was not influenced by this factor and the pore size was almost uniform at a low NH₄OH concentration. For a higher NH₄OH concentration, the pore volume and the pore diameter became larger but the surface area became smaller as the gelation temperature increased. By means of the response surface methodology analysis, the optimum processing condition was found to be 0.0155 mole of NH₄OH, 80,3°C for gelation temperature, and 63.2°C for the dehydration. As a result the maximum surface area corresponding to the optimum preparation conditions was 818.9 (m²/g) as expected.     

Robust control for linear systems with structured state space uncertainty

A recent sufficient condition for the stability robustness of linear systems with time-varying norm bounded state space uncertainty is extended to include the structure of the uncertainty. Our new result requires that the nominal eigenvalues lie to the left of a vertical line in the complex plane which is determined by a norm involving the structure of the uncertainty and the nominal closed-loop eigenvector matrix. Therefore, this robustness result is especially well suited to the design of control systems using eigenstructure assignment. When the uncertainty is time-invariant, our norm is also an upper bound on the incremental eigenvalue perturbations. We also consider the use of Perron weightings to reduce conservatism and the extension of the results to discrete time systems.     

Feature reasoning for sheet metal components

The objective of this paper is to develop a set of principles for extracting, recognizing and reasoning about features from sheet metal parts which are created in the CAD system. Recognition of such features will enable the automatic evaluation of designs and the development of process plans by among other things, mapping form features to tools needed to produce the form. The principles are developed by studying the face-oriented representations of features and deriving concepts which relate the features geometrically and topologically. Subsequently, the processes that relate to the geometrical forms are used to further uniquely identify the features.     

A LAGRANGIAN-EULERIAN METHOD WITH ADAPTIVELY LOCAL ZOOMING AND PEAK/VALLEY CAPTURING APPROACH TO SOLVE TWO-DIMENSIONAL ADVECTION-DIFFUSION TRANSPORT EQUATIONS

A Lagrangian–Eulerian method with adaptively local ZOOMing and Peak/valley Capturing approach (LEZOOMPC), consisting of advection–diffusion decoupling, backward particle tracking, forward particle tracking, adaptively local zooming, peak/valley capturing and slave point utilization, is presented to solve two-dimensional advection–diffusion transport equations. This approach and the associated computer code, 2DLEZOOMPC, were developed to circumvent the difficulties associated with the EPCOF scheme, developed earlier by the authors, when it was extended from a one-dimensional space to a multi- dimensional space. In EPCOF, all the nodes, including global nodes and fine-grid nodes, of the previous time are forward tracked for both determining rough elements and exactly capturing peaks and valleys. After kicking off those unnecessary nodes, a subset of the forward-tracked nodes are activated to preserve the shape of spatial distribution of the quantity of interest (e.g. concentration in the solute transport). The accurate results of applying EPCOF to solving two one-dimensional bench-mark problems under a variety of conditions have shown the capability of this scheme to eliminate all types of numerical errors associated with the advection term and to keep the maximum computational error to be within the prescribed error tolerance. However, difficulties arose when the EPCOF scheme was extended to a multi-dimensional space mainly due to the geometric difference between a one-dimensional space and a multi-dimensional space. To avoid these geometric difficulties, we modified the EPCOF scheme and named the modified scheme LEZOOMPC. LEZOOMPC uses regularly local zooming for rough elements and peak/valley capturing within subelements to resolve the problems of triangulation and boundary source as well as to preserve the shape of concentration distribution. In addition, LEZOOMPC employs the concept of slave points to deal with the compatibility problem associated with the diffusion zooming in a multi-dimensional space. As a result, not only is the geometrical problem resolved, but also the spirit of EPCOF is retained. Application of 2DLEZOOMPC to solving three two-dimensional bench-mark problems indicates it yields extremely accurate results for all the test cases. 2DLEZOOMPC could solve advection–diffusion transport problems accurately to within any prescribed error tolerance by using mesh Peclet numbers ranging from 0 to ∞ and very large time-step sizes as well as coarse global grid sizes. The size of time-step is related to both the diffusion coefficients and mesh sizes. Hence, it is limited only by the diffusion solver. Extension of this approach to a three-dimensional space will contain only implementation complexity but neither conceptual nor implementation difficulties. Details of the three-dimensional computer code, 3DLEZOOMPC, is to be presented in the companion paper.     

ANTIMICROBIAL AND PHYSICOCHEMICAL PROPERTIES OF METHYLCELLULOSE AND CHITOSAN FILMS CONTAINING A PRESERVATIVE

The methylcellulose was mixed with chitosan as well as 4% of sodium benzoate or potassium sorbate to form a film. Investigations of the antimycotic activity of the film on Penicillium notatum and Rhodotorula rubra revealed that it possessed significant antifungal properties. At 25C, approximately 43–45% of the preservatives were released from the film to the glycerol-water mixture in the first 30 min. The maximum amount of preservative that could be released from the film at 25C was approximately 57–65%. At 4C, 38–39% of preservatives were released from the film within 30 min, and reached a maximum amount of 49% in approximately 6h. The FT-IR spectrum showed that the ionic interaction between -COO of preservatives and -NH₃+ of chitosan existed in the film. However, the incorporation of preservatives did not affect the tensile strength and elongation property of the methylcellulose/chitosan film.     

Dynamic initiation and propagation behaviour of sub-interfacial cracks in PMMA/aluminium bi-material system

The paper describes studies on the dynamic initiation and growth of sub‐interfacial cracks in a PMMA/aluminium bi‐material system using high‐speed photography combined with the method of caustics. Dynamic fracture phenomena such as crack propagation trajectories, crack velocity, phase angle and stress intensity factor were determined from recordings of a series of dynamic caustic patterns surrounding the propagating sub‐interfacial crack tip.. There is a considerable influence of the distance between the interface and the crack on fracture characterization.     

Extremal control of pulse-width-modulated systems via an extended maximum principle

This paper considers the optimization of a class of pulse-width-modulated (PWM) control systems via an extended maximum principle. The technique developed here is applicable to single-input-single-output systems with linear plants. The amplitude of the control pulses, as well as the sign and width of each control pulse, is subject to optimization. The resulting optimization problem is shown to be a sequence of suboptimizations via a simple dual choice direct enumeration embedded in the TPBV problem.     

以人为本的人行系统城市设计

以CBD、购物区和旅游区的行人道路指示系统和全天候行人交通系统这两个重要细节问题为例,探讨如何进行以人为本的城市设计,从而建立一个充满人文关怀的城市形象,提高城市的吸引力和竞争力。     

Investigation of fracture characterizations of functionally graded materials

In this paper, the mode I crack problem of functionally gradient materials (FGMs) with the gradient direction parallel to the crack is discussed, and the differences of stress distribution between the gradient materials and the homogeneous materials are analyzed. It is shown that a mode I crack problem of FGMs with the gradient direction parallel to the crack direction can become a mixed‐mode crack problem. In FGMs, the crack initiation angles are determined by the fracture toughness gradient, elastic modulus and crack mode. If the gradient coefficients are small, the crack initiation angles in FGMs are the same as those in homogeneous materials. If the elastic modulus gradient is large, the principal stress terms without the gradient coefficients can be ignored in obtaining the crack initiation angle. In this study, all the above results are generalized to the mixed‐mode crack problems with arbitrary angle between the gradient direction and the crack direction.