Opening the terahertz window with integrated diode circuits

The terahertz region of the electromagnetic spectrum, spanning from 100 GHz through 10 THz, is of increasing importance for a wide range of scientific, military and commercial applications. This interest is spurred by the unique properties of this spectral band and the very recent development of convenient terahertz sources and detectors. However, the terahertz band is also extremely challenging, in large part because it spans the transition from traditional electronics to photonics. This paper reviews the importance of this frequency band and summarizes the efforts of scientists and engineers to span the "terahertz technology gap." The emphasis is on solid-state circuits that use nonlinear diodes to translate the functionality of microwave technology to much higher frequencies.     

On replacement models via a fuzzy set theoretic framework

Uncertainty is present in virtually all replacement decisions due to unknown future events, such as revenue streams, maintenance costs, and inflation. Fuzzy sets provide a mathematical framework for explicitly incorporating imprecision into the decision making model, especially when the system involves human subjectivity. This paper illustrates the use of fuzzy sets and possibility theory to explicitly model uncertainty in replacement decisions via fuzzy variables and numbers. In particular, a fuzzy set approach to economic life of an asset calculation as well as a finite-horizon single asset replacement problem with multiple challengers is discussed. Because the use of triangular fuzzy numbers provides a compromise between computational efficiency and realistic modeling of the uncertainty, this discussion emphasizes fuzzy numbers. The algorithms used to determine the optimal replacement policy incorporate fuzzy arithmetic, dynamic programming (DP) with fuzzy rewards, the vertex method, and various ranking methods for fuzzy numbers. A brief history of replacement analysis, current conventional techniques, the basic concepts of fuzzy sets and possibility theory, and the advantages of the fuzzy generalization are also discussed     

A 5 mW and 5% efficiency 210 GHz InP-based heterostructure barrier varactor quintupler

This letter reviews the design, construction, and measurement of a 210 GHz heterostructure barrier varactor frequency quintupler. The quintupler utilizes planar heterostructure barrier varactors (HBVs) based on the InGaAs/InAlAs/AlAs material system and has produced a measured output power of 5.2 mW with 5.2% conversion efficiency at 210 GHz. This performance is comparable to the state-of-the-art results reported in the literature for HBV frequency triplers operating at millimeter and submillimeter wavelengths.     

Iris Recognition Using Wavelet Features

The traditional iris recognition systems require equal high quality human iris images. A cheap image acquisition system has difficulty in capturing equal high quality iris images. This paper describes a new feature representation method for iris recognition robust to noises. The disc-shaped iris image is first convolved with a low pass filter along the radial direction. Then, the radially smoothed iris image is decomposed in the angular direction using a one-dimensional continuous wavelet transform. Each decomposed one-dimensional waveform is approximated by an optimal piecewise linear curve connecting a small set of node points. The set of node points is used as a feature vector. The optimal approximation procedure reduces the feature vector size while maintaining recognition accuracy. The similarity between two iris images is measured by the normalized cross-correlation coefficients between optimal curves. The similarity between two iris images is estimated using mid-frequency bands. The rotation of one-dimensional signals due to the head tilt is estimated using the lowest frequency component. Experimentally we show the proposed method produces superb performance in iris recognition.     

Transistor oscillator and amplifier grids

Although quasi-optical techniques are applicable to a large variety of solid-state devices, special attention is given to transistors, which are attractive because they can be used as either amplifiers or oscillators. Experimental results for MESFET bar-grid and planar grid oscillators are presented. A MESFET grid amplifier that receives only vertically polarized waves at the input and radiates horizontally polarized waves at the output is discussed. These planar grids can be scaled for operation at millimeter- and submillimeter-wave frequencies. By using modern IC fabrication technology, planar grid oscillators and amplifiers containing thousands of devices can be built, thereby realizing an efficient means for large-scale power combining     

Bilateral Laplace Transforms on Time Scales: Convergence, Convolution, and the Characterization of Stationary Stochastic Time Series

The convergence of Laplace transforms on time scales is generalized to the bilateral case. The bilateral Laplace transform of a signal on a time scale subsumes the continuous time bilateral Laplace transform, and the discrete time bilateral z-transform as special cases. As in the unilateral case, the regions of convergence (ROCs) time scale Laplace transforms are determined by the time scale’s graininess. ROCs for the bilateral Laplace transforms of double sided time scale exponentials are determined by two modified Hilger circles. The ROC is the intersection of points external to modified Hilger circle determined by behavior for positive time and the points internal to the second modified Hilger circle determined by negative time. Since graininess lies between zero and infinity, there can exist conservative ROCs applicable for all time scales. For continuous time (ℝ) bilateral transforms, the circle radii become infinite and results in the familiar ROC between two lines parallel to the imaginary z axis. Likewise, on ℤ, the ROC is an annulus. For signals on time scales bounded by double sided exponentials, the ROCs are at least that of the double sided exponential. The Laplace transform is used to define the box minus shift through which time scale convolution can be defined. Generalizations of familiar properties of signals on ℝ and ℤ include identification of the identity convolution operator, the derivative theorem, and characterizations of wide sense stationary stochastic processes for an arbitrary time scales including autocorrelation and power spectral density expressions.     

Phosphorous Levels in Peeled and Deveined Shrimp Treated with Sodium Tripolyphosphate

Using volumetric and spectrophotometric methods for the determination of phosphorous, untreated shrimp were shown to have high and variable phosphorous content. When peeled and deveined shrimp were treated with 0.5% and 1.0% sodium tripolyphosphate (STP) solutions, the STP uptake was shown to be low. At these low treatment concentrations the phosphorous content in the treated shrimp did not exceed the range of natural phosphorous found in untreated shrimp. When higher treatment concentrations were used, treated thrimp could be identified. The stability of STP in treated shrimp during frozen storage was investigated using a P³² STP isotope. After 2 wk of frozen storage at –26°C only 12% of the total activity could be attributed to STP. At the same time, pyrophosphate was present at a level of 25% and orthophosphate at 27%. During further frozen storage, the STP concentration remained at approxinately 12%, pyrophosphate dropped down to as low as 2% while orthophosphate gradually increased reaching 45% of total activity at the end of 10 wk storage period.     

Thermal Expansion of Alkaline‐Doped Lanthanum Ferrite Near the Néel Temperature

The thermal expansion and magnetic behaviors of divalent, alkaline‐doped lanthanum ferrites (La_0.9M_0.1FeO₃, M=Ca, Sr, Ba) were assessed using a combination of dilatometry, magnetometry, time‐of‐flight neutron diffraction, and high‐temperature X‐ray diffraction. Néel temperatures were determined through vibrating sample magnetometry and correlated well with changes in thermal expansion behavior observed during both dilatometry and X‐ray diffraction. The Néel temperatures observed for pure, Ca‐doped, Sr‐doped, and Ba‐doped lanthanum ferrites were 471°C, 351°C, 465°C, and 466°C, respectively. The effect of divalent substitutions on the magnetic behavior are attributed to charge compensation mechanisms and structural changes in the material.     

Penetration of Sodium Tripolyphosphate into Fresh and Prefrozen Peeled and Deveined Shrimp

The distribution of sodium tripolyphosphate (STP) in peeled and deveined shrimp tails after treatment was investigated using P³² labeled STP. Fresh and frozen brown (Penaeus aztecus) and fresh and frozen white (Penaeus setiferus) shrimp were used in the study. Shrimp were treated in solutions of either 0.5%, 1%, 5%, or 10% STP that had been prepared using P³² labeled STP diluted with “cold” STP. The duration of treatment was either 20 sec, 1 min, 5 min, or 20 min. When shrimp were treated in 0.5% and 1% STP solutions, a phosphate concentration gradient was evident in the shrimp muscle. After such treatments, STP was shown to accumulate on the surface of the muscle preventing further STP uptake. At higher STP concentrations (5% and 10% solutions) prolonged time treatments overcame the concentration gradient as STP became equally distributed through the shrimp muscle (4.8 mm). No difference in the STP penetration mechanism between fresh and prefrozen treated shrimo was evident.