Similarity of Stress-Singularity Problems for Materials with Linear and Bilinear Behaviors

An analogy is established between the solutions of the problems of singularities of stresses in linear and bilinear elastic isotropic media. It is shown that the distributions of stresses and displacements in the vicinity of singular points on the boundary of the body (characterized by the singularities of stresses) are described, in both cases, by the same functional dependences on the space coordinates but with different characteristics of the material. We deduce expressions for the effective moduli of elasticity and Poisson's ratio of the bielastic medium including the parameter of hardening of the material. The solution of the problem of singularities of stresses in bilinear materials is obtained from the solution of the corresponding problem for the linear elastic medium by replacing the elastic constants with the corresponding effective values depending on the parameter of hardening of the material. The cases of wedge-shaped notches (for various boundary conditions imposed on their edges), two-component wedges, plane wedge-shaped cracks, and circular conic notches or rigid inclusions in the bielastic space are studied in detail.     

Controlled linear system with delayed relay output under impulse random disturbances

The paper is devoted to the first order delayed linear system with relay output controlled by the proportional-integral (PI) regulator. The deterministic system exhibits stable oscillations, and, since the system itself is stable, it can be suitable to switch off the controller if there are no disturbances during a long time interval. In the present work, the random disturbances are modelled by a Poisson stream of impulses, and the goal is to determine the instants of switching on (off) of the PI controller. After several assumptions and quantization of the time axis, we construct the new optimal control problem which is successfully solved with the help of the dynamic programming approach.     

Semi-solid rapid compression testing of spray-formed hypereutectic Al-Si alloys

The rheology of Al-30Si-5Cu and Al-30Si-5Cu-2Mg spray-formed alloys has been characterized after holding at various times and temperatures, using semisolid rapid compression to obtain load-displacement curves. Microstructures were examined after partial remelting and compression in an attempt to understand the flow behavior. The initial resistance to flow generally increased with holding time at temperature. This increase was attributed to the increased strength of a three-dimensional (3-D) solid silicon network present in these alloys in the semisolid state, with the initial resistance to flow smaller in the magnesium-containing alloys. With increased temperature, the initial resistance decreased due to increased liquid content and grain spheroidization. The viscosity vs shear rate response was studied using the approach of Laxmanan and Flemings. The materials shear thinned rapidly during the test conditions, in which the shear rate rapidly increased from approximately 2.5 to 92 s⁻¹. The results were fitted to a power-law model, and the viscosities showed a drop of approximately two to four orders of magnitude when extrapolated to a shear rate of 1000 s⁻¹ (a typical value in actual component manufacture). The rapid compression test, which is close to conditions present in component manufacture, was shown to have more in common with a shear rate jump experiment, rather than steady-state viscometry.     

Finite sample properties of estimators of spatial autoregressive models with autoregressive disturbances

The article investigates the finite sample properties of estimators for spatial autoregressive models where the disturbance terms may follow a spatial autoregressive process. In particular we investigate the finite sample behavior of the feasible generalized spatial two-stage least squares (FGS2SLS) estimator introduced by Kelejian and Prucha (1998), the maximum likelihood (ML) estimator, as well as that of several other estimators. We find that the FGS2SLS estimator is virtually as efficient as the ML estimator. This is important because the ML estimator is computationally burdensome, and may even be forbidding in large samples, while the FGS2SLS estimator remains computationally feasible in large samples. Received: 20 January 2001 / Accepted: 31 August 2001     

Assessment of a Flexible Architecture for Distributed Control*

Production pipelines of manufactory industries present several machines and robots in which the movements of interpolated axes are managed by computerized numerical controls (CNCs). These are typically synchronized with several other simpler actuators along the pipeline of production. CNCs have to be flexible, easily expandable, and reusable, when pipelines of production are frequently reconfigured to realize different arranged pipelines with different technical requirements. In this paper, the assessment of a flexible CNC for such reconfigurable pipelines is presented. The analysis has been focused on defining objective metrics that can be applied for assessing performance and feasibility of distributed controls for pipelines. The method proposed has been applied on the distributed control architecture defined in the MUPAAC ESPRIT HPCN (Multi Processor Architecture for Automatic Control, High Performance Computer Networking of the European Commission). MUPAAC architecture and prototype has been assessed in order to identify the critical configurations and the limits of the architecture.     

Formation and electronic structure of interface

In the present work the formation of the interface between polycrystalline silver and thin films of titanium oxide was studied with photoelectron spectroscopy (XPS, UPS) and time-of-flight secondary ion mass spectrometry (TOF-SIMS). Titanium oxide was deposited stepwise on 100 nm thick silver films by reactive magnetron sputtering allowing to study the evolution of the interface formation process. The process involves two steps: formation of thin layer of silver oxide and subsequent growth of the TiO₂ film. For better understanding of the silver oxidation process, pure silver films were exposed to a low temperature Ar/O plasma for different time intervals providing a possibility to investigate early stages of the oxide film growth.     

Physicochemical principles of preparation of emulsion fuels

The basic physicochemical principles of preparation of emulsion fuel compositions based on heavy and extra-heavy crude cuts were analyzed with consideration of the nature and content of the phases constituting the emulsion, type of chemical additives — emulsifiers and stabilizers, and type of equipment for production of emulsion fuels. __________ Translated from Khimiya i Tekhnologiya Topliv i Masel, No. 5, pp. 51–56, September–October, 2007.