Design of optimal control under uncertain initial conditions: A minimax approach

The need for a game-theoretical formulation of the problem of linear-quadratic control under nonmeasurable plant state where the functional depends on the uncertain initial state was substantiated. The minimax output control law in terms of linear matrix inequalities that may be regarded as the optimal robust control law for the given set of the plant initial states was established assuming that the measurable components of the initial state were known and the nonmeasurable components take on values within the given ellipsoid. The results obtained were generalized to the plants with uncertain parameters.     

Giant enhancement of the carrier mobility in silicon nanowires with diamond coating

We show theoretically that the low-field carrier mobility in silicon nanowires can be greatly enhanced by embedding the nanowires within a hard material such as diamond. The electron mobility in the cylindrical silicon nanowires with 4-nm diameter, which are coated with diamond, is 2 orders of magnitude higher at 10 K and a factor of 2 higher at room temperature than the mobility in a free-standing silicon nanowire. The importance of this result for the downscaled architectures and possible silicon-carbon nanoelectronic devices is augmented by an extra benefit of diamond, a superior heat conductor, for thermal management.     

Investigation of Thermal Crosstalk Between SOI FETs by the Subthreshold Sensing Technique

Experimental-modeling investigation of the transient thermal crosstalk between the field-effect transistors implemented on a silicon-on-insulator substrate is reported. The measurements were performed using a high-speed electrical pulse-probe sampling technique, which allowed detection of thermally modulated subthreshold currents. The technique achieved a temperature resolution of ~50 mK, a time resolution of 5 ns, and a temperature sensitivity of ~0.6 muA/K. The finite-element method was used to solve the heat diffusion equation and to obtain the temperature profiles for the given device structures. The combined high-resolution experimental-simulation approach allowed the study of the thermal crosstalk between two adjacent devices and probe the local temperature at different locations of the structure. The effects of the interface quality, layer thickness, material selection, and interdevice spacing on the heat diffusion and device performance were investigated in detail.     

Robust H ∞ Control of Linear Uncertain Systems: Its Limiting Performance

The concept of a H norm is introduced for linear control systems with uncertain bounded parameters. A procedure for determining the lower estimate of the minimal robust H norm in the linear state feedback class is designed. An example of a system in which the estimate coincides with the minimal robust norm is given.     

Utilization of refinery effluent

Conclusions It is shown that refinery effluent may be used in beneficiation plants located near refineries; this would reduce the amount of effluent discharged.Translated from Khimiya i Tekhnologiya Topliv i Masel, No. 2, pp. 24–25, February, 1969.     

Interplay of confinement, strain, and piezoelectric effects in the optical spectrum of GaN quantum dots

We theoretically investigated excitonic states, energy and oscillator strength of optical transitions in GaN quantum dots characterized by different size, shape, interface, and substrate. On the basis of our multi-band model we determined that the piezoelectric field-induced red shift of the ground state transition, observed in recent experiments, can manifest itself only in strained GaN/AIN dots with the dot height larger than 3 nm. It was also established that the oscillator strength of the red-shifted transitions is small (< 0.05) and decreases fast with increasing the dot size, while the strength of ground state transitions in c-GaN/c-AIN and GaN/dielectric dots is large (approximately 0.4-0.7) and almost independent of the dot size.     

Vector spherical harmonics application to 3-D tomography problem

A method of series expansion with the aid of vector spherical harmonics intended for inverting line integrated data is proposed to investigate 3-D vector fields in the spherical plasmas. A set of numerical computations demonstrating the 3-D reconstruction of the model vector fields has been performed to assess the inversion method proposed.     

Optimal shock isolation of a two-component viscoelastic object

A limiting performance of shock isolation is studied for an object modeled by two rigid bodies connected by a viscoelastic element with a linear characteristic. The object is attached to a movable base by means of a shock isolator, which is regarded as a device that produces a control force between the base and the object. The base and the object move along the same straight line. The base is subject to an external shock excitation that is characterized by the time history of the acceleration of the base. A control law is defined for the shock isolator to minimize the maximum magnitude of the displacement of the object relative to the base, provided that the force of interaction between the components of the object does not exceed a prescribed value. An algorithm for constructing the exact solution of the problem under certain assumptions is presented. A technique for constructing an approximate solution for an object having high stiffness is described. The optimal control is shown to have impulse components. Examples are given. The two-component model considered in the paper is known to have been utilized to describe the mechanical response of a human body to a shock load along the spine or from thorax to back. Therefore, the problem under consideration can be regarded as a benchmark optimal control problem for a system that protects from injuries cased by shock loads. Solution of such problems is highly topical for development of safety systems for vehicles.