Waves in multilayer ferrite-dielectric transversely magnetized waveguides with an electrically controlled slowing factor

Multilayer wave-guiding structures comprising transversely magnetized ferrites are studied. A numerical theoretical model is constructed with the Galerkin method. An experimental investigation technique is developed. Theoretical and experimental results are found to be in good agreement. Such structures offer a high phase activity and may provide a basis for small-size millimeter-wave phase shifters and a new class of antenna systems, namely, integrated phased arrays.     

Well-Defined Oxide Core-Poly(vinyl pyrrolidone) Shell Nanoparticles: Interactions and Multi-Modal Glass Transition Dynamics at Interfaces

Interfacial interactions and dynamics were studied in silica and alumina core-poly(vinyl pyrrolidone) (PVP) shell nanoparticles with different shell thicknesses starting from 1-2 nm (monolayer); their geometry and structural organization were comprehensively characterized by several techniques. Far- and mid-IR spectroscopy, combined with DSC activation analysis of the glass transition, allowed to register hydrogen bonding and Lewis/Brønsted interactions, and the multi-modal glass transition dynamics in PVP nanoshells, as well as their interrelationship. For PVP monolayer, only a few “abnormal” modes constituted glass transition which covered the temperature range from 80 to 230 °C, with varying the activation energy by an order of magnitude.     

Study of interaction of proteins with fumed silica in aqueous suspensions by adsorption and photon correlation spectroscopy methods

The interaction of fumed silica A-300 (S(BET) = 297 m2 g(-1)) with bovine serum albumin (prepared by different methods), ovalbumin, human hemoglobin, and gelatin as a function of pH, salinity, and concentrations of components in aqueous medium was studied by adsorption and photon correlation spectroscopy (PCS) methods. Comparison of equilibrium (incubation time t(i) approximately 1 h) adsorption of proteins on A-300, minute (t(i) approximately 1 min) flocculation rate, and the particle size distributions measured by the PCS method shows different rearrangement of particle swarms depending on pH, salinity, and concentration of proteins, especially at pH close to IEP of silica or proteins. The electrokinetic mobility of protein/silica swarms is greater than that of individual components at pH far from the IEP of proteins. Changes in the Gibbs free energy (DeltaG) on protein adsorption depend on pH (-DeltaG is minimal at pH 2, close to the IEP of silica, and maximal at pH between the IEP of protein and silica), concentration (-DeltaG is maximal at C(p) between 1 and 6 mg/ml), type of proteins, and their preparation technique.     

Adaptive tuning of feedback gain in time-delayed feedback control

We demonstrate that time-delayed feedback control can be improved by adaptively tuning the feedback gain. This adaptive controller is applied to the stabilization of an unstable fixed point and an unstable periodic orbit embedded in a chaotic attractor. The adaptation algorithm is constructed using the speed-gradient method of control theory. Our computer simulations show that the adaptation algorithm can find an appropriate value of the feedback gain for single and multiple delays. Furthermore, we show that our method is robust to noise and different initial conditions.     

Stability and performance analysis of a block elimination solver for bordered linear systems

A new block elimination method for bordered systems is proposedand its numerical properties are analysed. In the case wherethe leading principal block is ill-conditioned or singular andthe method becomes unstable a perturbation approach is usedto enhance the stability. Results of experiments performed onthe SGI Power Challenge 8000 and on the Cray J-9x illustratethe performance of the new algorithm and compare it with thecurrent best approach. It is shown that the new method worksfaster while preserving stability.     

Sorption Modification of Fine Silica with Polyvinylpyrrolidone

The interaction of fine silica with polyvinylpyrrolidone in aqueous medium was studied by IR spectroscopy.     

Mathematical modeling in the development of indicator tubes for determining chromium(VI) in natural waters

The adsorption dynamics of the chromium(VI) complex of 1,5-diphenylcarbazide on the KU-2-8 strongly acidic cation exchanger was studied. A mathematical model was developed that adequately describes the processes in the system and provides recommendations on the procedure for determining chromium(VI) in natural water using an indicator tube. The experimental data were evaluated by processing model solutions of the composition of natural surface waters.     

Adsorption equilibriums in a silica-poly(vinyl alcohol)-gelatin system

The interaction of gelatin with nonporous nanosized amorphous silica containing poly(vinyl alcohol) (PVA) preliminarily adsorbed on its surface is studied. It is established that the modification of the nanosilica via PVA adsorption does not influence its ability to adsorb the protein. It is shown that, during adsorption, gelatin partly displaces PVA molecules from the silica surface. It is assumed that hydroxyl groups of strongly retained PVA macromolecules may play the role of active sites of protein adsorption along with free silanol groups.     

True reference nanosensor realized with silicon nanowires

Conventional gate oxide layers (e.g., SiO(2), Al(2)O(3), or HfO(2)) in silicon field-effect transistors (FETs) provide highly active surfaces, which can be exploited for electronic pH sensing. Recently, great progress has been achieved in pH sensing using compact integrateable nanowire FETs. However, it has turned out to be much harder to realize a true reference electrode, which--while sensing the electrostatic potential--does not respond to the proton concentration. In this work, we demonstrate a highly effective reference sensor, a so-called reference FET, whose proton sensitivity is suppressed by as much as 2 orders of magnitude. To do so, the Al(2)O(3) surface of a nanowire FET was passivated with a self-assembled monolayer of silanes with a long alkyl chain. We have found that a full passivation can be achieved only after an extended period of self-assembling lasting several days at 80 °C. We use this slow process to measure the number of active proton binding sites as a function of time by a quantitative comparison of the measured nonlinear pH-sensitivities to a theoretical model (site-binding model). Furthermore, we have found that a partially passivated surface can sense small changes in the number of active binding sites reaching a detection limit of δN(s) ≈ 170 μm(-2) Hz(-1/2) at 10 Hz and pH 3.     

“Mariya” experiment on the analysis of the electronpositron component of cosmic rays onboard the salyut 7, soyuz T-13, kosmos 1669 orbital complex

Measurement results for electron and positron flows with energies in the range of 30–150 MeV are given for different latitudes in the area of the Brazilian anomaly that were made with the Mariya magnetic spectrometer on the Salyut 7, Soyuz T-13, Kosmos 1669 orbital complex.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 9, pp. 19–24, September, 1986.The authors express their gratitude to V. A. Dzhanibekov and V. P. Savinye for active participation in conducting the experiments onboard the orbital complex and to V. B. Zotov and N. I. Shvets for help in preparing the experiment.