Wide-band photonically phased array antenna using vector sum phase shifting approach

In this paper, a wide-band photonically phased array antenna is demonstrated. The array configuration consists of a 4 /spl times/ 1 Vivaldi single-polarization antenna array and an independent photonic phasing system for each element. The phasing network of this array is implemented using two novel photonic phase shifters based on the vector summation approach. A vector sum phase shifter (VSPS), which exhibits a frequency-linear characteristic from dc to 15 GHz and can be continuously tuned from 0 to 100/spl deg/, is presented. A second-order VSPS (SO-VSPS), a modification of the VSPS that is capable of 0-430/spl deg/ phasing range, is also demonstrated. This paper presents the operation and characterization of each component of the array, including the radiating elements and the various photonic phase shifters and, finally, a demonstration of the combined system. A discussion on the practicality of this system for airborne applications is presented, along with suggestions for simplification and improvement.     

Resolution of near-infrared spectral data from distillation of binary mixtures and calculation of band boundaries of feasible solutions for species profiles

In this work, mean centering, ordinary and incomplete rank annihilation based methods were applied to estimate concentration profiles (g/mL) and pure spectra of components from an evolutionary near infrared spectral data for successive condensates from distillation process of binary mixtures. Constraints such as non-negativity, selectivity of some spectral regions and density of condensates were applied during the resolution of some series of data. Fixed size moving window evolving factor analysis (FSMWEFA) and orthogonal projection analysis (OPA) were the applied chemometrics methods for assigning the selective regions. No pure spectrum from any of components or calibration samples was necessary for performing the analysis. Three binary mixtures containing toluene:n-hexane, toluene:cyclohexene and toluene:ethanol were investigated using the proposed method. Band boundaries of feasible solutions for pure absorption spectra and species concentration profiles for the mixture of components were successfully estimated in presence of high spectral overlap. In the first case the solution was unique, but in the second and third distillations a number of acceptable solutions were obtained as band boundaries.     

Estimating the distribution of external causes in hospital data from injury diagnosis

Hospital discharge datasets are a key source for estimating the incidence of non-fatal injuries. While hospital records usually document injury diagnosis (e.g. traumatic brain injury, femur fracture, etc.) accurately, they often contain poor quality information on external causes (e.g. road traffic crashes, falls, fires, etc.), if such data is recorded at all. However, estimating incidence by external causes is essential for designing effective prevention strategies. Thus, we developed a method for estimating the number of hospital admissions due to each external cause based on injury diagnosis. We start with a prior probability distribution of external causes for each case (based on victim age and sex) and use Bayesian inference to update the probabilities based on the victim's injury diagnoses. We validate the method on a trial dataset in which both external causes and injury diagnoses are known and demonstrate application to two problems: redistribution of cases classified to ill-defined external causes in one hospital data system; and, estimation of external causes in another hospital data system that only records nature of injuries. In comparison with age–sex proportional distribution (the method usually employed), we found the Bayesian method to be a significant improvement for generating estimates of incidence for many external causes (e.g. fires, drownings, poisonings). But the method, performed poorly in distinguishing between falls and road traffic injuries, both of which are characterized by similar injury codes in our datasets. While such stop gap methods can help derive additional information, hospitals need to incorporate accurate external cause coding in routine record keeping.     

The use of positron annihilation lifetime technique to study the effect of doping metal salts on polyhydroxamic acid polymers

Polyhydroxamic acid (PHA) from polymethacrylamide (PMAA) was prepared. Chromium chloride (CrCl₃) and ferric chloride (FeCl₃) salts were added to the polymer in order to increase its electrical conductivity, i.e., the dopants help produce semiconducting properties. The positron annihilation lifetime technique spectroscopy (PALS) was used to study the changes in the free volume as a function of FeCl₃ and CrCl₃ concentrations. ortho-Positronium lifetime components were used to estimate the free volume parameters. It was found that the hole size and the total free volume fraction decreased with FeCl₃ concentration. On the other hand, the hole size increased slightly with CrCl₃ concentration and then decreased, while the total free volume fraction increased continuously. The free volume distributions were determined from ortho-positronium distributions. The electric conductivity as a function of FeCl₃ and CrCl₃ concentrations showed fluctuation behavior and showed a continuous increase with the increase in temperature. The correlation between positron annihilation parameters and electric conductivity were discussed. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 81: 2095–2101, 2001     

Electrocatalytic activities of gold-5-amino-2-mercaptobenzimidazole-M self-assembled monolayer complexes (M: Ag, Cu) for hydroquinone oxidation investigated by CV and EIS

Electrocatalytic activity of a new catalyst toward the oxidation reaction of hydroquinone as a model compound is described. The catalyst was formed by immobilizing metal cations on the topside of a gold-5-amino-2-mercaptobenzimidazole, self-assembled monolayer (Au-5A2MBI-Mⁿ⁺ SAM, Mⁿ⁺: Cu²⁺, Ag⁺) electrode. Preparation steps and the electrocatalytic activity of the catalyst were studied by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). The EIS data were approximated by appropriate electronic equivalent circuit models from which kinetic parameters, such as charge transfer resistance, double layer capacitance, and apparent rate constant (k_app), were estimated. Excellent activity was observed for Au-5A2MBI-Ag⁺ SAM with the following order: Au-5A2MBI-Ag⁺ > Au-5A2MBI-Cu²⁺ > Au-5A2MBI, after testing many modified electrodes. The increased activity originates from a modification of the Au-5A2MBI structure by mediating the effect of Ag⁺. This behavior was understood from significant increases in the k_app without significant changes in the double layer capacitance.     

Friction of Undulated Surfaces Coated with MoS2 by Pulsed Laser Deposition

Solid lubricants such as molybdenum disulfide can provide very low friction, but their effectiveness especially in the geometrically constrained sliding pairs is limited by plowing of coated surfaces by wear particles. Even in the presence of solid lubricants wear particles cause higher friction by plowing the interface. To minimize plowing, undulated surfaces with microgrooves perpendicular to the sliding direction can be used to trap wear particles. Smooth and undulated stainless steel surfaces were coated with molybdenum disulfide by pulsed laser deposition (PLD) and friction tested. Under identical test conditions, the friction coefficient of coated undulated surfaces is between 20–40 percent lower than that of coated smooth surfaces. The friction coefficient of undulated uncoated surfaces is about 100–350 percent less than that of smooth uncoated surfaces. Moreover, the entrapment of wear particles at the interfaces of geometrically constrained bearings may lead to seizure even when bearing surfaces are coated with solid lubricants. The use of undulated surf aces on these sliding systems has shown improved operating time and a reduced maintenance cycle.     

The role of different parameters on the stability and thermal conductivity of carbon nanotube/water nanofluids

It is obvious that the applicability and efficiency of nanofluids (suspensions contained nanoparticles) are related to their high heat transfer coefficients, especially thermal conductivity. Many parameters affect this property including size, shape and source of nanoparticles, surfactants, power of ultrasonic, time of ultrasonication, elapsed time after ultrasonication, pH, temperature, particle concentration and surfactant concentration. Some of these parameters may have interaction effects. An accepted way for obtaining the optimized condition is based on the design of experiments and statistical analysis. In this paper we investigate the stability and thermal conductivity of carbon nanotube (CNT)/water nanofluids and propose the optimum condition for the production and application of nanofluids. It has been shown that the significant factors on the thermal conductivity and stability are not precisely similar to one another.     

On the growth sequence of highly ordered nanoporous anodic aluminium oxide

Anodic aluminium oxide films were fabricated by well known two-step anodizing process in oxalic acid electrolyte. The ordering characteristics (ordered pore domains, average pore diameter size and through-pore arrangement) of anodic aluminium oxide films, obtained in different growth sequences, were identified by microscopic analysis such as ex situ contact-mode atomic force microcopy and scanning electron microscopy. Flattened areas in which some pits are seen mostly cover the electropolished surface of aluminium. Single anodizing of aluminium produces a broad distribution of nanopore size, whereas induces a highly ordered hemispherical pattern, which plays the ordered nucleation sites for the second anodizing step. Moreover, a quasi-linear growth behavior exists for the ordered domain growth versus the duration of first step anodizing. The through-pore arrangement of ideally grown membranes is not influenced by increasing the duration of second step anodizing.     

Developing a coordinated vendor–buyer model in two-stage supply chains with stochastic lead-times

This paper develops an approach to determine the optimal production and shipment policy for an integrated vendor–buyer problem. The vendor manufactures the product in batches at a finite rate and ships the output to the buyer. All shipments to the buyer are equal-sized batches. Despite previous papers in the literature, we assume that the supply lead-time between vendor and buyer is stochastic and shortage is also allowed. The objective is to minimize the expected total cost of both buyer and vendor. We derive the expected annual integrated total cost function and propose an analytic solution procedure to determine the optimal policy. To illustrate the significance of cost-reduction of the integrated approach in comparison with independent decisions by buyer or vendor, some numerical examples are also presented.