Dielectric spectroscopy of fresh fruit and vegetable tissues from 10 to 1800 MHz.

Dielectric spectroscopy data from measurements on tissue samples of nine fresh fruits and vegetables were used to study their dielectric behavior over the frequency range from 10 MHz to 1.8 GHz at 5 to 65 degrees C. Dielectric constant and loss-factor data are presented graphically for apple, avocado, banana, cantaloupe, carrot, cucumber, grape, orange, and potato, showing dielectric constants ranging from values of several hundred at 10 MHz to less than 100 at 1.8 GHz and loss factors on the order of one thousand at 10 MHz to less than 20 at 1.8 GHz. The dielectric loss factor increased consistently with increasing temperature at frequencies below 1 GHz. The dielectric constant increased with temperature at lower frequencies, but it decreased with temperature at the higher frequencies. This reversal of the sign of the temperature coefficient occurred at some point in the frequency range between 20 and 120 MHz where the temperature dependence of the dielectric constant was zero. At frequencies below this point, ionic conduction dominates the dielectric behavior, but above that point dipolar relaxation appears to control the behavior. Multiple linear regression provided equations for calculation of the loss factor in the frequency range from 10 to 300 MHz at temperatures from 5 to 65 degrees C. The data provide new information useful in understanding dielectric heating behavior and evaluating dielectric properties of such agricultural products for quality sensing applications.     

Distortions of the low frequency signal by Martian ionosphere at vertical propagation

A mathematical tool is described that takes into account signal distortions caused by phase dispersion and signal absorption in the Mars ionosphere during reflection from the Mars surface below the orbiter. This tool is used to estimate the distortion of the cross-correlation function by phase dispersion and signal absorption caused during a double traverse of the radio signal through the Mars nighttime ionosphere on frequencies used for the radar experiment MARSIS. Ionospheric absorption reduces the cross-correlation function distortions caused by ionospheric dispersion. It is shown, that the value of signal absorption depends on free electron number density in the lower part of an ionosphere.     

Convergence acceleration and accuracy improvement in power bus impedance calculation with a fast algorithm using cavity modes

Based on the cavity-mode model, we have developed a fast algorithm for calculating power bus impedance in multilayer printed circuit boards. The fast algorithm is based on a closed-form expression for the impedance Z matrix of a rectangular power bus structure; this expression was obtained by reducing the original double infinite series into a single infinite series under an approximation. The convergence of the single series is further accelerated analytically. The accelerated single summation enables much faster computation, since use of only a few terms is enough to obtain good accuracy. In addition, we propose two ways to compensate for the error due to the approximation involved in the process of reducing the double series to the single series, and have demonstrated that these two techniques are almost equivalent.     

10W continuous-wave monolithically integrated master-oscillator power-amplifier

A semiconductor-based master-oscillator power-amplifier operating at 977 nm is demonstrated to emit more than 10 W continuous wave in a nearly diffraction limited beam with a narrow spectral bandwidth. The device consists of a distributed Bragg reflector laser and a flared amplifier monolithically integrated on a single chip     

Development of a Cyclogyro-Based Flying Robot With Variable Attack Angle Mechanisms

This paper presents an experimental study on the development of a cyclogyro-based flying robot with a new variable angle of attack mechanism. A cyclogyro is a flying machine supported in the air by power-driven rotors that rotate about a horizontal axis, like the paddle-wheels of a steamboat. Machines of this type have been designed by some companies but there has been no record of any successful flights. Our design starts with a new variable angle of attack mechanism with an eccentric (rotational) point in addition to a rotational point connecting to a motor. The main feature of the mechanism with the eccentric rotational point is the ability to change attack of angles in accordance with the wing positions (as determined by the rotational angles of the cyclogyro) without actuators. The design parameters (wing span, the number of wings, and eccentric distance) of the flying robot are determined through a series of experiments. Experimental results show that the cyclogyro-based flying robot with the new variable angle of attack mechanism is capable of generating sufficient lift force for flying.     

Extended Pilot‐Based Coding for Lossless Bit Rate Reduction of MPEG Surround

Pilot‐based coding (PBC), which is used for lossless bit rate reduction of audio coding, has been recently proposed for MPEG Surround. We propose extended PBC for further lossless bit rate reduction of MPEG Surround. Extended PBC selects the number of pilots depending on the parameter band number and the type of spatial parameter. It then encodes the pilots and the relevant difference data. Experiments show that extended PBC is more effective than the original PBC, especially for high bit rate modes, with a negligible complexity increase on the decoder side.     

Lithographic tuning of a two-dimensional photonic crystal laserarray

One attraction of photonic crystals is the ability to control optical device characteristics by lithographically varying the geometry. In this letter, we demonstrate a 10×10 array of optically pumped two-dimensional (2-D) photonic crystal defect lasers with varying lattice parameters. By adjusting the photonic crystal interhole spacing as well as the hole diameter we are able to tune the laser wavelength from 1500 to 1625 nm on a monolithic InP-InGaAsP wafer. A wavelength resolution of 10 nm from device to device was obtainable, limited by the lithography and etching tolerances of our fabrication method     

Wavelength-graded horizontal cavity laser array with postgrowthadjustment of wavelength

Wavelength-graded emission from a visible red GaInP-AlGaInP laser diode array has been achieved with the contradirectional surface-mode coupling technique. The wavelength control is attained by postgrowth adjustment of the thickness of the surface waveguide. The horizontal cavity lasers show both edge and surface emission (beam divergence 0.12°). The thermal red-shift of the wavelength is 0.028±0.002 nm/K. They show single-mode emission with a typical spectral linewidth of 0.09 nm and a sidemode suppression ratio up to 29 dB. The wavelength spacing between the individual lasers is 0.76±0.08 nm yielding a total range across the array of 5.4 nm (from 681.5 to 686.9 nm)     

Diversity Performance of a Wavelet-Packet-Based Multicarrier Multicode CDMA Communication System

In this paper, we propose and analyze a novel multicarrier (MC) multicode (MCD) code-division multiple-access (CDMA) system employing wavelet packets (WPs) for modulation. This system can achieve robust performance against multipath fading due to the localization of WPs in the time and frequency domains. The analytical framework is presented, and the system performance with diversity is evaluated by means of bit error rates and the outage probability . Since WPs have lower sidelobes compared to sinusoidal carriers, our system is very effective in reducing the problem of intercarrier interference. The effects of system parameters (e.g., order of diversity, fading parameters, and WP type) were investigated. The major contribution is to compare the performance of the system to that of the MC/MCD-CDMA system that is based on sinusoidal carriers. The results reveal a considerable performance improvement of our proposed system over the MC/MCD-CDMA system.     

Reading the footprints of strained islands

We report on recent advances in the understanding of surface processes occurring during growth and post-growth annealing of strained islands which may find application as self-assembled quantum dots. We investigate the model system SiGe/Si(0 0 1) by a new approach based on “reading the footprints” which islands leave on the substrate during their growth and evolution. Such footprints consist of trenches carved in the Si substrate. We distinguish between surface footprints and footprints buried below the islands. The former allow us to discriminate islands which are in the process of growing from those which are shrinking. Islands with steep morphologies grow at the expense of smaller and shallower islands, consistent with the kinetics of anomalous coarsening. While shrinking, islands change their shape according to thermodynamic predictions. Buried footprints are investigated by removing the SiGe epilayer by means of selective wet chemical etching. Their reading shows that: (i) during post-growth annealing islands move laterally because of surface-mediated Si–Ge intermixing; (ii) a tree-ring structure of trenches is created by dislocated islands during their “cyclic” growth. This allows us to distinguish coherent from dislocated islands and to establish whether the latter are the result of island coalescence.