Characterization and modeling of hardware imperfections in Schottky diode based six‐port modulator

This article presents digital correction for hardware imperfection in mixer‐less six‐port modulator. A passive six‐port network correlates radio frequency carrier reflected from its different ports. If the reflection coefficients at these ports are controlled by in‐phase and quadrature‐phase baseband data, the modulated information is translated directly over the radio frequency carrier without any mixing action. However, the six‐port modulator has several hardware impairments resulting into linear and nonlinear distortion. This article presents a digital characterization and distortion mitigation scheme for six‐port modulator using new quadrature interference memory polynomial model and its variant. As a proof of concept, a prototype of digitally assisted six‐port modulator is designed to modulate QAM data to radio frequency carrier at 2.0 GHz. The measurement results show the capability of modulating 16 and 64 QAM data with very low EVM less than 1.2% after employing proposed digital correction scheme.     

Information-sharing and decision-making in networks of radiation detectors

A network of sensors observes a time-inhomo-geneous Poisson signal and within a fixed time interval has to decide between two hypotheses regarding the signal’s intensity. The paper reveals an interplay between network topology, essentially determining the quantity of information available to different sensors, and the quality of individual sensor information as captured by the sensor’s likelihood ratio. Armed with analytic expressions of bounds on the error probabilities associated with the binary hypothesis test regarding the intensity of the observed signal, the insight into the interplay between sensor communication and data quality helps in deciding which sensor is better positioned to make a decision on behalf of the network, and links the analysis to network centrality concepts. The analysis is illustrated on networked radiation detection examples, first in simulation and then on cases utilizing field measurement data available through a U.S. Domestic Nuclear Detection Office (dndo) database.     

Novel Analog Calibration Technique for Current-Steering DACs’ Dynamic Performance

This paper reports the post-layout dynamic performance of a novel calibration technique for current-steering digital-to-analog converter that was proposed previously. This technique not only improves the linearity, but it does so with low power as well as a very low area. It uses an analog feedback loop consisting of four transistors to calibrate each bit of the DAC, and the same feedback circuit is used for all the bits, thus significantly saving the chip area. Layout of the 10-bit calibrated CS DAC circuit was done in a 180-nm technology; the total area of the DAC and the calibration circuit together was 0.16 \(\hbox {mm}^{2}\). Simulation results show that the spurious free dynamic range is 62 dB for signals of 1 MHz at a sampling frequency of 100 MS/s.     

Constraints for Using Lambert W Function-Based Explicit Colebrook–White Equation

We analyze the general applicability of a recent explicit expression of the Colebrook–White equation for turbulent flow friction factor calculation. This explicit expression, which is based on the Lambert W function, is characterized by an exponential term which imposes restrictions on its use. These constraints have been expressed in terms of pipe roughness (ε/D) and the Reynolds number R that are required for friction factor calculation. These constraints were determined as 8.0666?ln(R)+(ε/D)R<721.97 and 8.0666?ln(R)+(ε/D)R<5731.83, respectively, for machines using single precision and double precision computations. Using the Lambert W function, an explicit equation relating R and ε/D was derived at the limiting case which allowed for a graphical representation of the applicability of the explicit form of the Colebrook–White equation in the R versus ε/D space. Before computing friction factors using the explicit Colebrook–White equation, a quick check must be performed to see if the desired combination of R and ε/D values satisfies the applicable constraint mentioned above.     

Use of Case Studies in Engineering Education: Assessment of Changes in Cognitive Skills

Industry, educational institutions, government bodies, and academic accreditation entities have all stressed the need to incorporate sound assessment techniques into educational programs. However, many of the items listed in the Accreditation Board for Engineering and Technology 3(a–k) criteria are not commonly addressed in engineering programs. Literature has shown that case study methodology is an effective way to bridge this gap, particularly with regard to improving higher-cognitive skills. In this paper we discuss the various approaches to assessing cognitive improvements when case study methods are implemented in classrooms, along with a literature review, and the various methods are illustrated with examples. The limitations of these methods are examined and the paper concludes by stressing the need to conduct further research to identify the optimum way to assess the effectiveness of the case study methodology in engineering classrooms.     

Cellulose acetate microspheres as floating depot systems to increase gastric retention of antidiabetic drug: formulation, characterization and in vitro-in vivo evaluation

Gastric emptying is a complex process that is highly variable and makes the in vivo performance of drug delivery systems uncertain. In order to avoid this variability, efforts have been made to increase the retention time of the drug delivery systems for more than 12 hours utilizing floating or hydrodynamically controlled drug delivery systems. The objective of this investigation was to develop a floating, depot-forming drug delivery system for an antidiabetic drug based on microparticulate technology to maintain constant plasma drug concentrations over a prolonged period of time for effective control of blood sugar levels. Formulations were optimized using cellulose acetate as the polymer and evaluated in vitro for physicochemical characteristics and drug release in phosphate buffered saline (pH 7.4), and evaluated in vivo in healthy male albino mice. The shape and the surface morphology of the prepared microspheres were characterized by optical microscopy and scanning electron microscopy. In vitro drug release studies were performed and drug release kinetics were calculated using the linear regression method. Effects of stirring rate during preparation and polymer concentration on the size of microspheres and drug release were observed. The prepared microspheres exhibited prolonged drug release (more than 10 hours) and remained buoyant for over 10 hours. Spherical and smooth-surfaced microspheres with encapsulation efficiency ranging from 73% to 98% were obtained. The release rate decreased and the mean particle size increased at higher polymer concentrations. Stirring speed affected the morphology of the microspheres. This investigation revealed that upon administration, the biocompatible depot-forming polymeric microspheres controlled the drug release and plasma sugar levels more efficiently than plain orally given drug. These formulations, with their reduced frequency of administration and better control over drug disposition, may provide an economic benefit to the user compared with products currently available for diabetes control.     

Direct impregnation method for preparing sulfated zirconia supported on mesoporous silica

A new method has been developed to prepare sulfated zirconia (S–ZrO₂) supported on mesoporous silica. With direct exchange of metal containing precursors for the surfactants in the as-synthesized MCM-41 materials, the problem of fill-up of the mesoporous structure was avoided and high sulfur content was achieved. By using this method, the composite of S–ZrO₂/MCM-41 with ZrO₂ content higher than 60 wt.% can be easily obtained without serious blockage of the pore structure of MCM-41. Nevertheless, the pore size and pore volume of the resultant S–ZrO₂/MCM-41 composites were found to vary markedly with the loading of ZrO₂. The strong acidic character of the obtained composites was examined by using them as catalysts in n-butane isomerization. Introduction of other metals such as aluminum as promoter into S–ZrO₂/MCM-41 can be easily conducted by the direct impregnation method.     

Rapid extraction and detection of trace Chlorpyrifos-methyl in orange juice by surface-enhanced Raman spectroscopy

It is estimated that 20–50% of crops are saved from infestation through the use of pesticides. However, US inspectors find that more than 4% of fruits and vegetables imported exceed concentration levels considered safe for human consumption. This represents millions of tons of food brought to market annually that cannot be inspected using current hour-long laboratory methods. In an effort to provide inspectors with a simple, fast, field-usable analyzer and method, we have been developing a sampling device that includes surface-enhanced Raman spectroscopy (SERS) to detect, identify, and quantify pesticides below part-per-million (μg/mL) concentrations in approximately 10 min using a portable Raman analyzer. The entire method, including solvent extraction, solid-phase extraction, and SERS-detection, was used to detect 50 parts-per-billion (ppb) Chlorpyrifos-methyl (CPM) artificially added to orange juice in 12 min. The same method and analyzer can be readily adapted to other pesticides and foods.     

Teaching Real-World Issues through Case Studies*

Engineering students are expected to be not only technically proficient, but, also to exhibit a sound awareness of real-world issues such as marketing, finance, communications, and interpersonal relations. We found that this is best learned by participating in a case study method of instruction. This paper describes the results of a research undertaken by the authors to develop a teaching methodology to bring real-world issues into engineering classrooms. It describes the steps taken in developing an engineering-management case study, administering this case study in a classroom, and results of evaluating the effectiveness of this method of instruction. In particular, it focuses on the students' and professional engineers' perceptions on the utility of the case study method of instruction in engineering classes. The results of the research lead to recommendations to funding agencies and educators on the need to develop interdisciplinary technical case studies so that the innovations happening in the engineering world can be communicated to the students in the classrooms.     

Structured Model for Batch Culture Growth of Lactobacillus bulgaricus

Batch fermentation kinetics of Lactobacillus bulgaricus were examined in detail using the methodology of cybernetic modelling. The effect of pH and lactate ion on the activity of the enzyme β-galactosidase was simulated. Cybernetic modelling is mainly used for simulation of growth on multiple substrates. Here, it has been incorporated in a model which simulates pH effects on single-substrate batch growth. The expression of active enzyme is crucial for substrate and growth. It was seen that the effect of lactate ion on the activity of the enzyme was dependant on the system pH. A semi-empirical expression was obtained for the relative amount of active enzyme present in the organism and used to model the enzyme, biomass, substrate and lactic acid concentrations for the batch fermentation. The rate of biomass formation and product formation depended on the amount of enzyme synthesised, which in turn was dependant on the pH value of the system. The model developed simulates the effect of pH and lactate concentration on the expression and degradation of the enzyme. © 1997 SCI.