Asymptotic stabilization of the position of a rigid body with fixed point without velocity measurements

The problem of stabilization of a rigid body with a fixed point in reference to its velocity and position is considered. It is assumed that the rigid body is controlled by three external torques. The proposed controlling torques need neither the measurements of the velocity nor the information about the inertial parameters. Such a control may be realized by the on-line solution of the auxiliary differential equations.The stability of the closed loop nonlinear system is established by means of the Lyapunov function and Barbashin's theorem. The proposed control may be applied to stabilize the satellites controlled by the reactive jets.     

Optimal bus sizing in migration of processor design

The effect of wire delay on circuit timing typically increases when an existing layout is migrated to a new generation of process technology, because wire resistance and cross capacitances do not scale well. Hence, careful sizing and spacing of wires is an important task in migration of a processor to next generation technology. In this paper, timing optimization of signal buses is performed by resizing and spacing individual bus wires, while the area of the whole bus structure is regarded as a fixed constraint. Four different objective functions are defined and their usefulness is discussed in the context of the layout migration process. The paper presents solutions for the respective optimization problems and analyzes their properties. In an optimally-tuned bus layout, after optimizing the most critical signal delay, all signal delays (or slacks) are equal. The optimal solution of the MinMax problem is always bounded by the solution of the corresponding sum-of-delays problem. An iterative algorithm to find the optimally-tuned bus layout is presented. Examples of solutions are shown, and design implications are derived and discussed.     

The characteristics of the spinal trauma in catapulted pilots

The article discusses the peculiarities of spinal fractures in catapulted pilots: mechanism of fracture--indirect axial load in combination with front or front-lateral bending; morphological picture--wedge-shaped compression fracture of vertebral body; type of fracture--stable; clinic peculiarities--scanty clinic picture as a rule; localization--mid-thorax section and thoracolumbar zone; number of vertebrae affected--1 as a rule. Diagnostic and treatment recommendations are enclosed. The author also deals with a phenomenon which accompanies the emergency abandon of an aircraft--microlesion of spongy osseous tissue of vertebrae without fracture signs under the influence of shock overload, which later can be the reason of degenerative and dystrophic diseases of spine. Preventive and medical measures are described which assure an adequate rehabilitation of functional state of spine.     

The optical properties of high-porosity calcium fluoride ceramics

The effective absorption coefficient and the radiation diffusion coefficient are determined for high-porosity calcium fluoride ceramics. A laser photometer designed for recording low transmissions is used for measuring the normal hemispherical transmissivity of cylindrical samples of different thicknesses. Results are given for wavelengths of 0.63, 1.15, 3.39, and 5.25 μm. The thus obtained data are used to calculate the dependence of the bihemispherical reflectivity of a plane layer on the layer thickness.     

Temperature dependence of fracture stress in the brittle fracture region

The temperature dependence of the fracture stress of bcc metals in the brittle fracture region is examined. A model taking into account the effect of local plastic deformation of the crack tip on transition to brittle fracture is proposed. The model is then used to derive analytical expression for the temperature dependence of the fracture stress in the material with an initial crack or notch.Translated from Problemy Prochnosti, No. 11, pp. 57–62, November, 1991.     

Scanning electron microscopy of long-wavelength laser structures

New possibilities of scanning electron microscopy, using secondary-and reflected-electron signals, for determining the position of heteroboundaries in long-wavelength laser structures are reported. The formation of the indicated signals in structures of mid-infrared-range lasers of a new type based on type-II GaInAsSb/InGaAsSb heterostructures as well as in the conventional InAsSb/InAsSbP heterostructures is analyzed. The observed characteristic features of the formation of secondary-and reflected-electron signals in these structures as compared with the well-studied AlGaAs/GaAs structures are explained. The results obtained are necessary for accurate determination of an important laser parameter — the position of the p-n junction. It is shown that it is best to use the reflected-electron signal. Fiz. Tekh. Poluprovodn. 32, 1300–1305 (November 1998)