Radioactive contamination of bukhtas and bays on the Kola Peninsula and Novaya Zemlya and in the Far East

The characteristics of the radioactive contamination of bukhtas and bays are determined: the nonuniformity of the radionuclide distribution in the water and bottom deposits, the rate of accumulation of sediments, the distribution ratio, and the turbulent diffusion coefficient. A characteristic feature is the strong nonuniformity of the radionuclide distribution in bottom sediments. A mathematical model is proposed for radionuclide transport and water of bukhtas taking account of flow, turbulent diffusion, and settling of suspensions. Possible explanations are proposed for the characteristics of the radionuclide distribution in bukhtas. The reason for weak turbulent diffusion in bukhtas is examined. __________ Translated from Atomnaya énergiya, Vol. 103, No. 10, pp. 263–268, October, 2007.     

ID-based threshold decryption secure against adaptive chosen-ciphertext attack

This paper proposes an identity-based threshold decryption scheme IB-ThDec and reduces its security to the Bilinear Diffie-Hellman problem. Compared with previous work, this conceals two pairing computations in the ciphertext validity verification procedure. The formal proof of security of this scheme is provided in the random oracle model. Additionally, we show that IB-ThDec can be applied to the threshold key escrow and the mediated cryptosystems.     

Analysis of the formation of structures and chaotic dynamics in a nonrelativistic electron beam with a virtual cathode in the presence of a decelerating field

A nonrelativistic electron beam with a virtual cathode situated in the diode gap with a decelerating field is experimentally and theoretically studied. A 1D model of the electron beam in the presence of a decelerating field is constructed. Nonlinear nonstationary processes in this system are investigated by means of numerical analysis of the model. The processes are described and interpreted with regard to formation and interaction of structures in the electron flow. The theoretical results are qualitatively confirmed by the experimental data showing that the system under study can be considered as a promising controlled source of chaotic oscillations in the microwave range.     

Influence of the method of mixing of pigments with a polymer on the structure and properties of polyurethane compositions

The effect of the nature of pigments and the method of their addition on the properties of polyurethanes based on diphenylmethane diisocyanate and polyester is studied. Technical carbon black and titanium dioxide, which are added to a polyurethane composition in the presence of surfactants, are used as pigments. It is established that, upon the addition of pigments, the viscosity changes nonmonotonically, maximal values of viscosity being observed at a 20% concentration of technical carbon black. Optimal concentration of surface-active substances is found whose magnitude for technical carbon black is 0.25–0.5%. With an increase in surfactant concentration, they act as plasticizers abruptly lowering the intermolecular interaction. The effect of different surfactants on the rheological properties of polyurethane compositions is studied. It is shown that the addition of pigments makes it possible to enhance mechanical properties and to decrease internal stresses in films.     

Spatial spectra non-quadratic regularization method with false component filtering

A non-quadratic regularization algorithm modification is proposed. It ensures identifying and filtering angular spectrum false components by choosing regularizing functional parameters. The algorithm efficiency was proved by modeling while solving the problem of multibeam wavefield division using one input data realization.     

Construction and stratification of the stability domains of the linear dynamic systems with PID controllers

The regularities of motion of a point on the plane (in the space) of adjustable controller parameters at variations of the phase margin under a fixed crossover frequency were analyzed. The problem of decomposition of the stability domain into the zones with simple and complex Nyquist plots and subsequent construction of the point subset where all points satisfying the requirements on the system frequency characteristics was solved. Examples were presented.     

Mathematical modeling and optimization of intratumor drug transport

A pseudohyperbolic problem of optimal control of intratumoral drug distribution is formulated. It takes into account the heterogeneity of tumor tissues and effects of convection diffusion in a fissured porous medium. A mathematical model constructed and the corresponding optimal control problem are shown to be correct. __________ Translated from Kibernetika i Sistemnyi Analiz, No. 6, pp. 147–154, November–December 2007.     

On the E.S. Pyatnitskii principle of decomposition

The main notions and facts of the geometrical decomposition theory were characterized in brief. The E.S. Pyatnitskii principle of decomposition was treated as the solution of the problem of assignment of feedback controls so that the controlled system admits a decomposition suitable for realization of the control objectives. It was hypothesized that this method of control is advisable if the complexity of the controlled system exceeds a certain limit.     

Parallelization of the global extremum searching process

The parallel algorithm for searching the global extremum of the function of several variables is designed. The algorithm is based on the method of nonuniform coverings proposed by Yu.G. Evtushenko for functions that comply with the Lipschitz condition. The algorithm is realized in the language C and message passing interface (MPI) system. To speed up computations, auxiliary procedures for founding the local extremum are used. The operation of the algorithm is illustrated by the example of atomic cluster structure calculations.     

基于Mega8单片机和AD9833的正弦波信号发生器

正弦波信号作为一种基准信号广泛应用于各种电路中，产生正弦波信号的方法有很多种，DDS（Direct Digital Frequency Synthesis直接数字频率舍成器）作为一种新型技术，具有相对带宽宽，频率转换时间短，频率分辨率高，控制灵活方便等优点，成为现代频率合成技术中的佼佼者。AD公司生产的AD9833是一款低功耗、可编程波形发生器，在Mega8单片机的控制下可生成0-12．5MHz的正弦波，还可以生成三角波和方波。经现场验证，基于Mega8单片机和AD9833的正弦波信号发生器，可以非常方便地生成各种频率的正弦波。