Detection of Carbon Dioxide in Air Using Difference-Frequency Generation Based Infrared Spectrometer

Spectroscopic detection of carbon dioxide (CO₂) in ambient air was performed using a continuous-wave mid-infrared spectrometer based on difference-frequency generation in an AgGaS₂ crystal. Significant improvement in nonlinear optical frequency conversion efficiency was achieved by Gaussian beam optical design consideration. CO₂ concentration was determined from direct-absorption spectral measurement.     

Analysis of aperture-coupled microstrip antenna using thesegmentation method

The authors present an original analysis of an aperture-coupled microstrip antenna. The theory is based on the segmentation method, which considers the patch as a multiport network whose impedance matrix is deduced from a hybrid matrix, and the use of analytical expressions of the cavity admittance at the slot centre. The theory is presented for the first time, and the theoretical results are in good agreement with previous published measurements     

Should Russia increase domestic prices for natural gas?

Previous analyses of Russia's dual pricing system and hidden subsidies for natural gas, have neglected to assess the dual pricing system as a domestic environmental policy. If dual pricing is considered as a policy to reduce conventional air pollutants, it is more than economically justified in Russia on the basis of avoided health risks. In the short term, the substitution of coal for natural gas may result in significant additional human health risk, which translates into economic damage. An alternative abatement possibility is expensive and unlikely enforceable, due to weak environmental regulation. The authors conclude that while the price differential can be expected to diminish over time, as Russia increasingly moves to a market economy, in the near-term, dual pricing of natural gas remains the most efficient environmental policy for Russia.     

Lead-acid battery capacity in solar home systems—Field tests and experiences in Lundazi, Zambia

Batteries in solar home systems can cause problems and costs for the users and/or operators of the systems. In Zambia the Lundazi Energy Service Company (LESCO) operates 150 solar home systems on a fee for service basis. The aim of the study was to investigate how the capacity of lead-acid flat plate batteries had changed after one year of operation under real conditions. The results indicate that the batteries capacity has been significantly reduced in comparison to new unused batteries of the same type. Changes in battery management and maintenance, along with additional education of customers on correct use of SHS is advised in order to improve the life span of batteries in practical use.     

Multiobjective optimisation of integrated energy systems for remote communities considering economics and CO2 emissions

The methods for designing, planning and managing integrated energy systems, while holistically considering the major economic and environmental factors, are still embryonic. However, the first phase of the design is often crucial if we want to manage resources better and reduce energy consumption and pollution. Considering integrated energy systems implies dealing with complex systems in which the synergy between the various components is best exploited (for example the thermal energy of a diesel engine produced during the night is complimented by the Rankine organic cycle of a solar thermal plant). The context of isolated communities further increases the difficulties when considering the long distance of transport required to supply fossil fuels. These sites are often located in very precarious environments, with limited or nonexistent resources except for solar energy, and with frequent additional needs for desalination (in arid zones).This paper illustrates a holistic method to rationalize the design of energy integrated systems. It is based on a superstructure (collection of models of all envisaged technologies) and a multi-objective optimisation (resources, demand, energy, emission, costs) using an evolutionary algorithm. The approach proposed allows the identification of more complete and more coherent integrated configurations characterizing the most promising designs (also taking into account the time dependency aspects). It also allows to better structure the information in view of a participative decision approach. The study shows that the economic implementation of renewable energy (solar) is even more difficult, compared to diesel based solutions, in cases of isolated communities with high load variations. New infrastructure or retrofit cases are considered.     

Simulations of electric field domain suppression in a superlattice oscillator device using a distributed circuit model

We present a method for simulating static domain formation in distributed negative differential resistance devices using a distributed circuit array model coupled with quantum transport simulations. This simulation method is applied to the case of a superlattice Bloch oscillator to ascertain the efficacy of electric field domain wall suppression by micro shunt side walls. Two independent simulation mechanisms using the same basic distributed circuit model are employed to separate simulation artifacts from true physical trends. Simulations are presented, suggesting that the presence of the micro shunt can suppress domain formation above a critical device bias voltage. The simulated dependence of this critical voltage on macroscopic device parameters is presented.     

Ingestible capsule for impedance and pH monitoring in the esophagus

Twenty-four-hour ambulatory pH monitoring is an essential tool for diagnosing gastroesophageal reflux disease (GERD). Simultaneous impedance and pH monitoring of the esophagus improves the detection and characterization of GERD. Conventional catheter-based monitoring systems are uncomfortable and interfere with the normal activity of the patient. To overcome these disadvantages, different wireless esophageal monitoring systems have been proposed. A capsule containing sensors for impedance and pH monitoring with wireless communication capabilities is presented. A low cost miniature microcontroller was utilized for interfacing between the sensors and a wireless transmitter. The microcontroller program allowed efficient management of the electric power provided by a 3-V battery. Magnetic holding is proposed as an alternative to surgical affixation of the monitoring capsule. Permanent neodymium magnets separated by 27 cm successfully held the capsule in a test tube. Experimental results demonstrated that friction force can aid magnetic holding to overcome peristalsis. The proposed design efficiently detected acid and nonacid reflux. More research regarding the holding method and capsule packaging are necessary to optimize the mechanical performance of the proposed design in order to facilitate clinical testing on human subjects.     

Resistivity dependence of minority carrier lifetime and cell performance in p-type dendritic web silicon ribbon

This study shows that the bulk lifetime in 95 μm thick p-type dendritic web silicon solar cells is a strong function of bulk resistivity. The higher the resistivity, the greater the bulk lifetime. This behavior is explained on the basis of dopant–defect interaction, which increases the lifetime limiting trap concentration with the addition of dopant atoms. Model calculations show that in the absence of doping dependence of bulk lifetime (τ), 2 Ω cm web should give the best cell efficiency for bulk lifetimes below 30 μs. However, strong doping dependence of bulk lifetime in p-web cells shifts the optimum resistivity from 2 to 15 Ω cm. Bulk lifetime in the as-grown web material was found to be less than 1 μs for all the resistivities. After the cell processing which involves phosphorus gettering, aluminum gettering, and SiN induced hydrogen passivation of defects, the bulk lifetime increased to 6.68, 11, 31 and 68.9 μs in 0.62, 1.37, 6.45 and 15 Ω cm p-type web material, respectively. Therefore, cell process induced recovery of lifetime in web is doping dependent, which favors high resistivity. Solar cells fabricated on 95 μm thick web silicon by a manufacturable process involving screen-printing and belt-line processing gave 14.5% efficient 4 cm² cells on 15 Ω cm resistivity. This represents a record efficiency for such a thin manufacturable screen-printed cell on a low-cost PV grade Si ribbon that requires no wafering or etching.     

Théorie géométrique de la diffraction et réciprocité

We examine how the geometrical theory of diffraction complies with reciprocity theorem. To this end, we consider two sets of problems involving a smooth, convex, perfectly conducting obstacle S, related by the reciprocity theorem. We show that it is not obvious that the GTD formulas satisfy reciprocity. However, we show that they may be recast in forms that are indeed reciprocal in nature.     

Determination and occurrence of oxofatty acids in fats and oils

A relatively simple method is detailed for the routine isolation and estimation of oxofatty acids (OFA) in lipids. The lipid in cyclohexane is transmethylated in a two-phase, 3.5 min procedure, and the carbonyls in the methyl ester fraction are derivatized with 2,4-dinitrophenylhydrazine (DNPH) in the presence of monochloroacetic acid (MCA). The derivatives are fractionated on alumina, and the OFA fraction is obtained and evaluated spectrophotometrically. A large variety of animal, plant, and marine lipids contained OFA ranging from <1 to >50 μmoles/g. Data also show that (a) OFA are formed in naturally oxidizing fats and oils, and (b) strongly acidic conditions can cause elaboration of OFA in hydroperoxidized fats and oils.