Estimation and Minimization of the Cramer-Rao lower bound for radio direction-finding on the azimuth and elevation of planar antenna arrays

In this paper an approach of obtaining optimal planar antenna arrays consisting of omnidirectional sensors is proposed. The novelty of the proposed approach is to apply an exact expression of the Cramer-Rao lower bound for an arbitrary planar antenna array consisting of a number of omnidirectional elements which has been presented in the further chapters of the paper. The obtained formula describes the influence of antenna elements locations on the direction-of-arrival estimation accuracy. It has been shown that the direction-of-arrival accuracy via planar antenna arrays is determined as the sum of squares of differences between all omnidirectional elements coordinates along x- and y-axis. Thus knowing an expected area or sector of signal source it is very easy to calculate optimal arrangement of antenna elements in order to reduce direction-finding errors, because obtained by that way positions gives the best match according to the maximum likelihood criterion. It is worth nothing that such antenna arrays are useful in the way that they allow estimating the coordinates of radio emission sources in the three-dimensional coordinate space, i.e. in azimuth and elevation. In order to confirm the proposed methodology optimal antenna arrays constructed after minimization of the new formulas are researched. It is found out that the new shapes of antenna arrays based on the analytical expressions have better direction-of-arrival accuracy in comparison with the circular ones

The use of finely ground slag in portland cement with mineral additives

The method of introducing of finely ground granulated blast furnace slag (GBFS) in the composition of the cement as a result of dry mixing of the material with the additive is considered. The aim of the research was to study the effect of the addition of finely ground slag on the construction, technical, physical, mechanical, and structural characteristics of cement with mineral additives. The setting time was studied, the normal density of the cement paste with the addition of finely ground slag was determined. The dependences of the strength and porosity of the cement stone on the time of hydration of samples are built. The strength of the cement was determined by the national standard GOST 30744-2001. The porosity of the cement stone was determined by saturating the samples with an inert liquid. It has been established that the introduction of 3–5% of slag 1 and 1–3% of slag 2 provides an increase in the strength of cement stone during the first days of hardening on average by 37–44%; at the grade age - by 26–30%, decrease in porosity — by 17–28%. It is shown that the introduction of finely ground slag additives compacts and strengthens the structure of the cement stone. It has been established that grinding GBFS to a size of 1 μm (slag 1) is impractical because the obtained research results are comparable with the results when slag 2 is introduced into the cement composition

Ideal two-dimensional electron systems with a giant Rashba-type spin splitting in real materials: Surfaces of bismuth tellurohalides

Spintronics is aimed at actively controlling and manipulating the spin degrees of freedom in semiconductor devices. A promising way to achieve this goal is to make use of the tunable Rashba effect that relies on the spin-orbit interaction in a two-dimensional electron system immersed in an inversion-asymmetric environment. The spin-orbit-induced spin splitting of the two-dimensional electron state provides a basis for many theoretically proposed spintronic devices. However, the lack of semiconductors with large Rashba effect hinders realization of these devices in actual practice. Here we report on a giant Rashba-type spin splitting in two-dimensional electron systems that reside at tellurium-terminated surfaces of bismuth tellurohalides. Among these semiconductors, BiTeCl stands out for its isotropic metallic surface-state band with the Γ̄-point energy lying deep inside the bulk band gap. The giant spin splitting of this band ensures a substantial spin asymmetry of the inelastic mean free path of quasiparticles with different spin orientations. © 2012 American Physical Society.We acknowledge partial support by the University of the Basque Country (Project No. GV-UPV/EHU, Grant No. IT-366-07) and Ministerio de Ciencia e Inovación (Grant No. FIS2010-19609-C02-00).Peer Reviewe

Space-charge mechanism of aging in ferroelectrics: an exactly solvable two-dimensional model

A mechanism of point defect migration triggered by local depolarization fields is shown to explain some still inexplicable features of aging in acceptor doped ferroelectrics. A drift-diffusion model of the coupled charged defect transport and electrostatic field relaxation within a two-dimensional domain configuration is treated numerically and analytically. Numerical results are given for the emerging internal bias field of about 1 kV/mm which levels off at dopant concentrations well below 1 mol%; the fact, long ago known experimentally but still not explained. For higher defect concentrations a closed solution of the model equations in the drift approximation as well as an explicit formula for the internal bias field is derived revealing the plausible time, temperature and concentration dependencies of aging. The results are compared to those due to the mechanism of orientational reordering of defect dipoles.Comment: 8 pages, 4 figures. accepted to Physical Review

DFT study of dihydrogen addition to molybdenum π-heteroaromatic complexes: a prerequisite step for the catalytic hydrodenitrogenation process

International audienceThe range of molybdenum hydride complexes that are sought to participate in the important catalytic hydrodenitrogenation process (HDN) of nitrogen containing polycyclic aromatic hydrocarbons were evaluated by DFT studies. The previously synthesized stable (η6-quinoline)Mo(PMe3)3 complex 1N, in which molybdenum is bonded to the heterocyclic ring, was chosen as a model. The hydrogenation of the quinone heterocycle, which was postulated as the initial step in the overall HDN reaction, is found to occur via three consecutive steps of the oxidative addition of dihydrogen to Mo in 1N. Successive transfer of hydrogen atoms from the metal to the heterocycle leads to the ultimate formation of the tetrahydrido molybdenum intermediate Mo(PMe3)4H413 and 2,2,3,3-tetrahydroquinoline C9H11N 14. All the involved intermediates and transition states have been fully characterized by DFT. This computational modeling of the hydrogenation of quinoline, as a part of extended HDN catalytic processes, provides a fundamental understanding of such mechanism

Role of surface passivation in the formation of Dirac states at polar surfaces of topological crystalline insulators: The case of SnTe(111)

We present ab initio density functional theory (DFT) calculation results for electronic and spin structures of both the Te- and Sn-terminated SnTe(111) polar surfaces. Rocksalt narrow-gap semiconductor SnTe belongs to the recently discovered class of topological crystalline insulators in which the topological nature of surface electronic states arises from the crystal symmetry combined with band inversion at the L point. We demonstrate that in contrast to earlier model calculations only trivial spin-split states propagating over the entire two-dimensional Brillouin zone emerge at the SnTe(111) surfaces owing to the surface potential effect which destroys weakly protected topological states. We show that the surface passivation eradicates the trivial surface states and recovers the even number of the helical spin-polarized topological Dirac cones centered at the Γ¯¯¯ and M¯¯¯ points prescribed for the topological crystalline insulator by the crystal symmetry.We acknowledge partial support from the Basque Country government, Departamento de Educacion, Universidades e Investigacion (Grant No. IT-366-07), the Spanish Ministerio de Ciencia e Innovación (Grant No. FIS2010-19609-C02-00), the Ministry of Education and Science of the Russian Federation (Grant No. 2.8575.2013), and the Russian Foundation for Basic Research (Grant No. 13-02-12110-ofi-m).Peer Reviewe

Background free imaging of upconversion nanoparticle distribution in human skin

Widespread applications of nanotechnology materials have raised safety concerns due to their possible penetration through skin and concomitant uptake in the organism. This calls for systematic study of nanoparticle transport kinetics in skin, where high-resolution optical imaging approaches are often preferred. We report on application of emerging luminescence nanomaterial, called upconversion nanoparticles (UCNPs), to optical imaging in skin that results in complete suppression of background due to the excitation light back-scattering and biological tissue autofluorescence. Freshly excised intact and microneedle-treated human skin samples were topically coated with oil formulation of UCNPs and optically imaged. In the first case, 8- and 32-nm UCNPs stayed at the topmost layer of the intact skin, stratum corneum. In the second case, 8-nm nanoparticles were found localized at indentations made by the microneedle spreading in dermis very slowly (estimated diffusion coefficient, D-np = 3-7 x 10(-12) cm(2) . s(-1)). The maximum possible UCNP-imaging contrast was attained by suppressing the background level to that of the electronic noise, which was estimated to be superior in comparison with the existing optical labels. (C) 2012 Society of Photo-Optical Instrumentation Engineers (SPIE)

Measuring of False Peaks Occurring via Planar Antenna Arrays DOA Estimation

Direction-of-arrival (DOA) of radio signals takes a great scientific interest for radar, sonar and wireless communication tasks. In this paper the problem of DOA estimation methods for circular and concentric circular antenna arrays is considered. The super-resolution method MUSIC is researched. The performances are estimated in various noise environments and for various geometries of antenna arrays. Additionally, the problem of false peaks occurring in spatial spectrum is closely considered. Probability of occurring false peaks after computer simulations is presented

Measuring of False Peaks Occurring via Planar Antenna Arrays DOA Estimation

Direction-of-arrival (DOA) of radio signals takes a great scientific interest for radar, sonar and wireless communication tasks. In this paper the problem of DOA estimation methods for circular and concentric circular antenna arrays is considered. The super-resolution method MUSIC is researched. The performances are estimated in various noise environments and for various geometries of antenna arrays. Additionally, the problem of false peaks occurring in spatial spectrum is closely considered. Probability of occurring false peaks after computer simulations is presented