Showing papers by "Beihang University published in 1997"

Analysis of the time-varying pricing of a bottleneck with elastic demand using optimal control theory

Abstract: In this paper, a time-varying pricing model of a road bottleneck with elastic traffic demand is formulated using the optimal control theory. It is assumed that the optimal use of the bottleneck is achieved when social benefit over the whole time horizon of study is maximized. The necessary conditions for optimal solution are derived and their economic interpretations are given. Different from conventional analyses, queuing is not pre-assumed to be zero when obtaining the optimal time-varying toll, and the exit capacity of the bottleneck is assumed either to be constant or to vary with queue length. An approximate iterative algorithm is proposed for solving the model in a discrete time version. Three numerical examples are presented to demonstrate the applications of the proposed model and algorithm.

Generalized tanh method with symbolic computation and generalized shallow water wave equation

Abstract: We report that symbolic computation with the generalized tanh method leads to new soliton-like solutions for a (2+1)-dimensional generalization of the shallow water wave equations.

Conducting IPN based on polyaniline and crosslinked cellulose

Abstract: Polyaniline/crosslinked cellulose conductive interpenetrating polymer networks (IPNs) were prepared by oxidative polymerization of aniline within the self-synthesized cellulose network using ammonium persulphate as oxidant. The conductivity of the IPN increases and then decreases with decrease in the aniline/(NH 4 ) 2 S 2 O 8 ratio, with increase in the HCl/aniline ratio, with increase in aniline content, as well as with increase in reaction time. In addition, the conductivity of the films strongly depends on the amount of tetraethyl orthosilicate crosslinker. In comparison with polyaniline/cellulose acetate composites, the conductivity increases by an order of one to two magnitudes in spite of the lower polyaniline content in this work.

Towards a Computer-Supported Cooperative Environment for Concurrent Engineering:

Abstract: Computer-supported cooperative work has been the focus of attention in a concurrent engineering environment for some time. This paper studies this cooperative team environment from three perspectives: (a) the infrastructure of communication and information model viewpoint; (b) the planning and control of workflow viewpoint, and (c) some implementation viewpoints Implementation viewpoints in- dude constraints' management, negotiation, and memory capture and management. A set of enabling technology in each perspective area and its rationale are discussed. Finally, a structure of the whole system environment including definitions of an architecture and a global user interface are introduced.

Origin of phonon anomalies in La 2 CuO 4

Abstract: The experimentally observed softening of the oxygen breathing mode at the X point, ${\mathrm{O}}_{\mathrm{X}}^{\mathrm{B}}$, and of a second CuO bond stretching mode of ${\mathrm{\ensuremath{\Delta}}}_{1}$ symmetry at the wave vector q=(0.5,0,0) in the doped metallic phase of La-Cu-O is investigated and shown to be driven by long-range, nonlocal electron-phonon interaction effects of monopole charge-redistribution type. The amplification of softening for both modes by about 1 THz, recently found in inelastic neutron scattering for an optimally doped ${\mathrm{La}}_{1.85}$${\mathrm{Sr}}_{0.15}$${\mathrm{CuO}}_{4}$ probe as compared with an underdoped ${\mathrm{La}}_{1.9}$${\mathrm{Sr}}_{0.1}$${\mathrm{CuO}}_{4}$ crystal is explained by the growing importance of the more extended orbitals in the charge response in particular at the Cu ion. Such an enlarged contribution of the more extended orbitals leads to a reduction of the dominant self-interaction, U, of the electrons mainly at the Cu and allows for an enhancement of the monopole charge redistributions whose magnitude determines the softening of the phonon modes. The existence of a specific mixture of localized and more extended states at the Fermi energy is crucial for the appearance of the strong nonlocal electron-phonon coupling of ionic origin and for the reinforcement of the phonon mediated part of pairing in the high-temperature superconductors.

Sliding wear properties of TiAl alloys with/without TiN coatings

Abstract: Dry sliding wear behavior of TiAl alloys, with and without TiN coatings, has been studied by using the block-on-ring wear test. The TiAl alloys were coated with TiN and a multilayer of TiN and TiCN using multi-arc ion plating and plasma chemical vapor deposition, respectively. The results show that wear resistance of the TiAl has been enhanced with the presence of the coatings. It is interesting that the wear rate as a function of the normal load is quite different from general observations, i.e., the wear rate decreased with an increase in the normal load. The properties of the alloy with and without the coatings have been related to microstructural features using X-ray diffraction and scanning electron microscopy.

Crack Initiation Mechanisms for Corrosion Fatigue of Austenitic Stainless Steel

Abstract: Corrosion fatigue tests on annealed type 316 (UNS S31600) stainless steel (SS) showed the maximum stress level for failure in 0.5 M sodium chloride (NaCl) aqueous solution at pH = 4.2 was ...

Design and synthesis of conducting secondary crosslinked interpenetrating polymer network

Abstract: A new conducting composite of a secondary crosslinked interpenetrating polymer network (IPN) was first designed and synthesized by chemically incorporating a rigid conducting polymer within the flexible crosslinked network and forming the link between them. The new conducting composite produced with a low content of polypyrrole exhibited unusually good conductivity, processability, and mechanical properties, and the conductivity was not influenced by the formation of an IPN.

Pitting Corrosion of Amorphous Ni–Zr Alloys in Chloride Ion Containing Sulfuric Acid Solutions

Abstract: The pitting corrosion behavior of the melt-spun amorphous Ni-Zr alloys with 30-75 at% zirconium, the crystalline arc-melted counterparts and the sputter-deposited Ni-Zr alloys with 20-84 at% zirconium was examined by electrochemical measurements in deaerated 0.5 kmol/ m 3 H 2 SO 4 with and without 0.1 kmol/m 3 NaCl at 303 K. In the sulfuric acid solution without Cl - , these alloys were spontaneously passive and their potentiodynamic behavior was similar to each other. In the Cl - -containing solution, all the melt-spun amorphous alloys suffered pitting during anodic polarization and the pitting potential decreased with an increase in zirconium content. On the other hand, the crystalline arc-melted low zirconium alloys suffered pitting but no pitting observed for the crystalline alloys containing 70 at% zirconium or more. In addition, the pitting potential increased with the zirconium content of crystalline alloys. All the sputter-deposited alloys did not suffer pitting regardless of the amorphous and crystalline structures. Therefore, the melt-spun amorphous alloys were the most susceptible to pitting corrosion. A marked difference was observed in the pitting behavior between the shiny side (top side) and the dull side (wheel side) surfaces of the melt-spun ribbon. The pits initiated from the dull side surface. Thus, the dull side surface could be responsible for such an unusual pitting behavior of the melt spun ribbon.

Prescribing Gaussian curvature on $R^2$

Abstract: We derive a sufficient condition for a radially symmetric function K(x) which is positive somewhere to be a conformal curvature on R2. In particular, we show that every nonnegative radially symmetric continuous function K(x) on R2 is a conformal curvature. In this paper, we consider the prescribing Gaussian curvature problem. Let (M, g) be a Riemannian manifold of dimension 2 with Gaussian curvature k. Given a function K on M , one may ask the following question: Can we find a new conformal metric g1 on M (i.e., there exists u on M such that g1 = e g) such that K is the Gaussian curvature of g1? This is equivalent to the problem of solving the elliptic equation ∆u − k +Ke = 0 (0) on M , where ∆ is the Laplacian of (M, g). This problem has been considered by many authors. In case M is compact, we refer to [6] for details and references. In case M = R, equation (0) becomes ∆u+K(x)e = 0 (1) and this problem is well understood if K(x) is nonpositive; in particular, if |K(x)| decays slower than |X |−2 at infinity, then equation (1) has no solution (see [11], [13]). However, if K(x) is positive at some point, the situation is totally different. If K(x0) > 0 for some x0 ∈ R, R. C. McOwen [10] proved that, for K(x) = O(r−l) as r → ∞, equation (1) has a C solution, where l is a positive constant. Also, it is not difficult to see that equation (1) has solutions for every positive constant K(x) = C. Since there is no known nonexistence result for K ≥ 0 on R, one may propose the following Problem 1. Is it true that every nonnegative function (smooth enough) on R is a conformal Gaussian curvature function? Received by the editors May 10, 1996. 1991 Mathematics Subject Classification. Primary 58G30; Secondary 53C21.

Variational principles of nonlinear dynamical fluid-solid interaction systems

Abstract: Based on the fundamental equations of continuum mechanics, the concept of Hamilton's principle and the adoption of Eulerian and Lagrangian descriptions of fluid and solid, respectively,variational principles admitting variable boundary conditions are developed to model mathematically the nonlinear dynamical behaviour of the responses and interactions between fluid and solid. The nonlinearity of the fluid is introduced through nonlinear field equations and nonlinear boundary conditions on the free surface and fluid–solid interaction interface. The structure is treated as a nonlinear elastic body. This model assumes the fluid inviscid, incompressible or compressible and the fluid motion irrotational or rotational but isentropic along the flow path of each fluid particle. The stationary conditions of the variational principles include the governing equations of nonlinear elastic dynamics, fluid dynamics and those relating to the fluid-structure interaction interface as well as the imposed boundary conditions. A family of variational principles are obtained depending on the assumptions introduced into the mathematical model (i.e. fluid incompressible, motion irrotational, etc.) and these provide a foundation to construct numerical schemes of study to assess the dynamical behaviour of nonlinear fluid–solid interaction systems. Two simple illustrative examples are presented demonstrating the applicability of the proposed theoretical approach.

Study of gelation using differential scanning calorimetry (DSC)

Abstract: A new method for determining the degree of conversion of gelation (αgel) and gel time (tgel) at gel point using a single technology, DSC, is discussed in this work. Four kinds of thermoset resins are evaluated. It is found that the mutation points of reduced reaction rate (Vr) vs. reaction conversion (α) curves, corresponding with the changes of reaction mechanism, represents the gelation of the reaction. The α at the mutation point is defined as αgel. From isothermal DSC curves, the point at αgel is defined astgel. Traditional techniques (ASTM D3532 and DSC method) are also used to determine αgel andtgel in order to demonstrate this new method. We have found that the results obtained from this new method are very consistent with the results obtained from traditional methods.