Scattering of electron stream waves on metal-dielectric periodic structures

The results of the theoretical and experimental research of the surface waves scattering of an electron stream and a planar dielectric waveguide on metal-dielectric structures of the dielectric prism — band diffraction grating-type are presented. Within the approximation of the given current there has been carried out a numerical analysis of energy characteristics of diffraction-Cerenkov radiation for a wide interval of the main system parameters change. The results of numerical analysis are confirmed by the data of experimental simulation.     

Adaptive OFDM Techniques With One-Bit-Per-Subcarrier Channel-State Feedback

In the orthogonal frequency-division multiplexing (OFDM) scheme, some subcarriers may be subject to a deep fading. Adaptive techniques can be applied to mitigate this effect if the channel-state information (CSI) is available at the transmitter. In this paper, we study the performance of an OFDM-based communication system whose transmitter has only one bit of CSI per subcarrier, obtained through a low-rate feedback. Three adaptive approaches are considered to exploit such a CSI feedback: adaptive subcarrier selection; adaptive power allocation (APA); and adaptive modulation selection (AMS). Under the conditions of a constant raw data rate and perfect feedback channel, the performance of these approaches are analyzed and compared in terms of raw bit-error rate. It is shown that one-bit CSI feedback can greatly enhance the system performance. Moreover, imperfections of the feedback channel are considered, and their impact on the performance of these techniques is studied. It is shown that by exploiting the knowledge that the feedback channel is imperfect, the performance of the APA and AMS techniques can be substantially improved     

Principles of minimum variance robust adaptive beamforming design

Robustness is typically understood as an ability of adaptive beamforming algorithm to achieve high performance in the situations with imperfect, incomplete, or erroneous knowledge about the source, propagation media, and antenna array. It is also desired to achieve high performance with as little as possible prior information. In the last decade, several fruitful principles to minimum variance distortionless response (MVDR) robust adaptive beamforming (RAB) design have been developed and successfully applied to solve a number of problems in a wide range of applications. Such principles of MVDR RAB design are summarized here in a single paper. Prof. Gershman has actively participated in the development and applications of a number of such MVDR RAB design principles.     

Tunable quasioptical power dividers operating in the millimeter wavelength range

Circuits and principle of operation of quasioptical power dividers based on two-row periodic structures, formed by grids of metal bars and a dielectric waveguide placed along their longitudinal axis, are described. The experimental studies of power divider prototypes in a frequency range of 60–80 GHz have shown a possibility of regulating the emitted power level in the main divider arm by changing longitudinal and angular coordinates of the two-row periodic structure, which can be used for designing quasioptical attenuators.     

Weak combined magnetic field affects basic and morphine-induced rat's EEG

The present study was undertaken to find out, whether weak combined magnetic field (CMF) with intensity comparable to that of the Earth's static magnetic field can influence the EEG activity of the rat's brain at normal (non-treated animals) conditions and after intraperitoneal (i.p.) and intracerebroventricular (i.c.v.) administration of morphine in experimental animals bearing chronically implanted electrodes and cannules. Most of the experiments were performed using CMF containing co-linear static (20.9 microT) and alternating sinusoidal (20.9 microT, 48 Hz) components, i.e., tuned for Ca2+-resonance. The effects of the field were estimated by comparison of the averaged EEG frequency spectra in the range of frequencies between 0.8-23 Hz in experimental and control animals. Statistically significant effects of CMF were observed both in non-treated and morphine-treated rats. However, the most profound effect-the drastic power reduction at most EEG frequencies-appeared in the animals subjected to the i.p.-injection of morphine. These results show that weak CMF can influence the spontaneous electrical brain activity. The data obtained are consistent with the findings of other groups demonstrating that weak magnetic fields may drastically modify the effects of both exogenous and endogenous opioids on different basic functions in vertebrates and invertebrates. Possible mechanisms for the observed effects are discussed.     

Measuring the magnetic moments of short-lived particles using channeling in bent crystals

A recent demonstration of spin precession using channeling in a bent crystal offers the interesting possibility of a technique to measure magnetic moments of short-lived charm baryons. There are significant differences among theoretical models of these moments. Accumulating experimental evidence indicates the tools used for hyperon magnetic moment measurements, polarized production and decay asymmetries, may also be available with heavier baryons. Useful measurements may be possible using the channeling technique but they will require challenging beam conditions.     

Collaborative beamforming for wireless sensor networks with Gaussian distributed sensor nodes

Collaborative beamforming has been recently introduced in the context of wireless sensor networks (WSNs) to increase the transmission range of individual sensor nodes. The challenge in using collaborative beamforming in WSNs is the uncertainty regarding the sensor node locations. However, the actual sensor node spatial distribution can be modeled by a properly selected probability density function (pdf). In this paper, we model the spatial distribution of sensor nodes in a cluster of WSN using Gaussian pdf. Gaussian pdf is more suitable in many WSN applications than, for example, uniform pdf which is commonly used for flat ad hoc networks. The average beampattern and its characteristics, the distribution of the beampattern level in the sidelobe region, and the distribution of the maximum sidelobe peak are derived using the theory of random arrays. We show that both the uniform and Gaussian sensor node deployments behave qualitatively in a similar way with respect to the beamwidths and sidelobe levels, while the Gaussian deployment gives wider mainlobe and has lower chance of large sidelobes.