Stabilization of Linear Dynamic Objects According to the Measured-Error State Under Constraints on the Phase and Control Variables

Journal of Computer and Systems Sciences International - We consider the problem of estimating the region of admissible initial states of a linear dynamic system for which the linear controller...     

Pareto Optimal Decentralized Control of a Rotor in Electromagnetic Bearings

Journal of Computer and Systems Sciences International - The problem of the optimal stabilization of a vertical rigid rotor rotating in two electromagnetic bearings is considered. A quantitative...     

Nanophononics: phonon engineering in nanostructures and nanodevices

Phonons, i.e., quanta of lattice vibrations, manifest themselves practically in all electrical, thermal and optical phenomena in semiconductors and other material systems. Reduction of the size of electronic devices below the acoustic phonon mean free path creates a new situation for phonon propagation and interaction. From one side, it complicates heat removal from the downscaled devices. From the other side, it opens up an exciting opportunity for engineering phonon spectrum in nanostructured materials and achieving enhanced operation of nanodevices. This paper reviews the development of the phonon engineering concept and discusses its device applications. The review focuses on methods of tuning the phonon spectrum in acoustically mismatched nano- and heterostructures in order to change the phonon thermal conductivity and electron mobility. New approaches for the electron-phonon scattering rates suppression, formation of the phonon stopbands and phonon focusing are also discussed. The last section addresses the phonon engineering issues in biological and hybrid bio-inorganic nanostructures.     

Synthesis of linear quadratic control laws on basis of linear matrix inequalities

Classic problems of control law construction for a linear dynamic object that is optimal by the quadratic criterion in the determinate and stochastic cases are reduced, as is known, to solving nonlinear matrix Riccati equations. It is shown that the notion of H ₂-norm of a system transfer matrix makes it possible to formulate and solve the stated problems in terms of linear matrix inequalities.     

Synthesis of a suboptimal controller by output for dampening limited disturbances

In the framework of the method of invariant ellipsoids, for a linear dynamic object a suboptimal linear dynamic controller by output is synthesized, at which the upper estimate of a maximum value of the norm of the controllable output reaches a minimum at all initial states of a system from a certain domain and at any disturbances bounded by the norm.     

Graphene-multilayer graphene nanocomposites as highly efficient thermal interface materials

We found that the optimized mixture of graphene and multilayer graphene, produced by the high-yield inexpensive liquid-phase-exfoliation technique, can lead to an extremely strong enhancement of the cross-plane thermal conductivity K of the composite. The "laser flash" measurements revealed a record-high enhancement of K by 2300% in the graphene-based polymer at the filler loading fraction f = 10 vol %. It was determined that the relatively high concentration of the single-layer and bilayer graphene flakes (~10-15%) present simultaneously with the thicker multilayers of large lateral size (~1 μm) were essential for the observed unusual K enhancement. The thermal conductivity of the commercial thermal grease was increased from an initial value of ~5.8 W/mK to K = 14 W/mK at the small loading f = 2%, which preserved all mechanical properties of the hybrid. Our modeling results suggest that graphene-multilayer graphene nanocomposite used as the thermal interface material outperforms those with carbon nanotubes or metal nanoparticles owing to graphene's aspect ratio and lower Kapitza resistance at the graphene-matrix interface.     

Interferometer for Testing of Convex Mirrors of Optical and Radio Telescopes Constructed by the Scheme of Orthogonal Rays

Journal of Communications Technology and Electronics - An interferometer for testing of convex spherical and aspherical mirrors has been developed and manufactured, operating according to the...     

Low flicker-noise GaN/AlGaN heterostructure field-effecttransistors for microwave communications

We report a detailed investigation of flicker noise in novel GaN/AlGaN heterostructure field-effect transistors (GaN HFET). Low values of 1/f noise found in these devices (i.e., the Hooge parameter is on the order of 10^-1) open up the possibility for applications in communication systems. We have examined the scaling of the noise spectral density with the device dimensions in order to optimize their performance. It was also found that the slope γ of the 1/f^γ noise density spectrum is in the 1.0-1.3 range for all devices and decreases with the decreasing (i.e., more negative) gate bias. The results are important for low-noise electronic technologies requiring a low phase-noise level     

Flicker noise in GaN/Al0.15Ga0.85N dopedchannel heterostructure field effect transistors

We have investigated noise characteristics of novel GaN/Al_0.15Ga_0.85N doped channel heterostructure field effect transistors designed for high-power density applications. The measurements were carried out for various gate bias voltages V_GS and with the drain voltage V_DS varying from the linear to the saturation regions of operation V_DS>5 V. Our results show that flicker, e.g., 1/f noise, is the dominant limiting noise of these devices; and the Hooge parameter is of the order of 10 ^-5-10^-4. The gate voltage dependence of 1/f noise was observed in the linear region for all examined V_GS and in the saturation region for V_GS>0. These results indicating low values of the Hooge parameter are important for microwave applications