Pressure dependence of the small-signal gain and saturation intensity of a copper vapor laser

The small-signal gain coefficient and the saturation intensity of a copper vapor laser have been measured for both 510.6- and 578.2-nm transitions through the implementation of a discharge driven oscillator-amplifier configuration. Pressure dependence of the gain and saturation property of the laser has been investigated.     

The Role of Dry Aero-acoustical Lubrication and Material Softening in Ultrasonically Assisted Milling of Difficult-to-Cut AISI 304 Steels

A recent and promising technique in advanced material processing techniques is the use of ultrasonic assistance in almost all cutting, forming and shaping processes. Optimizing manufacturing costs through reducing process forces and tool wears, improving machinability through enhancing surface finish and quality with minimal production time and energy, and delivering products with prolonged service life are some of the most important features of the vibration assisted manufacturing methods. To study the effect of ultrasonic vibrations on the milling process of the stainless steels, a series of experiments was designed and then implemented on a difficult-to-machine material. The result of the surface roughness and the cutting force tests has been comprised with and without processing by ultrasonic assistance. Experiments prove that under ultrasonic assistance, cutting forces are reduced, surface quality is improved and in all, a better machinability is achieved. It is concluded that dry aero-acoustical lubrication conditions and materials softening are of crucial importance in the machinability of difficult-to-cut AISI 304 materials.     

Polymer nanocomposites processed via self-assembly through introduction of nanoparticles,nanosheets, and nanofibers

Nanocomposites offer the theoretical potential to achieve mechanical properties surpassing those of conventional (micro-scale) composites. The underlying reasons for the high potential of nanocomposites include the uniquely high mechanical attributes of nano-scale reinforcement, effective control of defect size and growth by nano-spaced interfaces, and interactions between the polymer matrix and the large surface areas of nanomaterials. Attempts to produce nanocomposites via conventional processing techniques have encountered challenges associated with thorough dispersion and effective interfacial interactions of nano-scale reinforcement with the polymer matrix. In order to address these challenges, materials were processed into polymer nanocomposites via electrostatically driven layer-by-layer self-assembly. Electrostatically dispersed nanomaterials and oppositely charged polyelectrolytes were sequentially built upon a substrate (cellular scaffold). The self-assembled nanocomposites, after complementary cross-linking, provided a unique balance of strength and ductility, which surpassed those of conventional (micro-scale) composites. Self-assembly was found to be an effective approach to producing nanocomposites embodying uniformly dispersed nanomaterials with controlled interfacial interactions. This approach is highly versatile and enables introduction of diverse nanomaterials into polymer nanocomposites. The work reported herein evaluated introduction of diverse categories of nanomaterials incorporating nanoparticles, nanosheets, nanotubes, and nanofibers. This investigation also evaluated the potential for a biomimetic approach to processing of light-weight structural systems by self-assembly of polymer nanocomposites onto cellular scaffolds.     

Novel method for fast determination of ultra trace amounts of timolol maleate by continuous cyclic voltammetry at Au microelectrode in flowing injection systems

A novel method for easy and fast detection of timolol maleate in flow-injection system has been introduced. It was used for analysis of timolol maleate in pure form as well as in its pharmaceutical formulations. The reported method is simple, precise, accurate, time saving and economic as compared to all previously reported methods. The best performance for measurement of timolol maleate was obtained at, pH 2.0, scans rate 300 V s⁻¹, accumulation potential −500 mV and delay time 0.6 s. The advantages of the proposed detection method are, (1) the removal of oxygen from the test solution is not required any more, (2) the detection limit of the method is sub-micromolar, (3) this method is fast enough for determination of the drug compound, in a wide variety of chromatographic techniques. The potential waveform consists of potential steps for cleaning, accumulation and potential ramp that were continuously applied on an Au disk microelectrode (with a radius of 12.5 μm). The detection limit of the method for timolol maleate was 1.58 ng ml⁻¹. The relative standard deviation of the method at 1.0 × 10⁻⁹ M was 2.3% for 20 runs.     

Fabrication of a highly selective and sensitive Gd(III)-PVC membrane sensor based on N-(2-pyridyl)-N′-(4-nitrophenyl)thiourea

In this work we report the development of a highly selective and sensitive Gd(III) membrane based on N-(2-pyridyl)-N′-(4-nitrophenyl)thiourea (PyTu4NO₂) as an excellent neutral ion carrier. The Gd(III) sensor exhibits a Nernstian slope of 19.95 ± 0.3 mV per decade over the concentration range of 3.0 × 10⁻⁷ to 1.0 × 10⁻¹ M, and a detection limit of 3.0 × 10⁻⁷ M of Gd(III) ions. The potentiometric response of the sensor is independent of the solution pH in the range of 4.0–9.0. It manifests advantages of low detection limit, fast response time (10 s), and most significantly, very good selectivity with respect to a number of lanthanide ions (La, Ce, Sm, and Eu ions). It can be used at least for a period of 8 weeks without any significant divergences in its potential response. To assess its analytical applicability the proposed Gd(III) sensor was successfully applied as an indicator electrode in the titration of Gd(III) ion solutions with EDTA and for the determination of the fluoride ion in two mouth wash preparations. It was also used for the direct monitoring of Gd(III) ions in binary mixtures.     

Investigation on the photocatalytic behaviors of europium carbonate and oxide nanoparticles prepared based on statistically optimized carbonation and calcination routes

This study is focused on evaluating the photocatalytic properties of the europium carbonate and oxide nanoparticles synthesized via optimizing the direct precipitation and decomposition of the precipitate as a precursor into europium oxide by thermal decomposition. The emphasis was directed towards determining the optimal reaction conditions. To this end, the Taguchi method was used to determine the best parameters for the reaction. The carbonate product at this stage, was used in a further step where it underwent a one-step calcinations treatment leading to its decomposition into europium oxide nanoparticles. The nanoparticles were next characterized using X-ray diffraction, SEM, FT-IR and thermal analysis techniques. Then, the photocatalytic behaviors of the europium carbonate and oxide nanoparticles for the photocatalytic degradation of methyl orange under ultraviolet light was investigated and the results exhibited efficient degradation of the target in the presence of both nanoparticles as photocatalysts.     

Highly selective ratiometric fluorescence determination of Eu3+ ion based on (4E)-4-(2-phenyldiazenyl)-2-((E)-(2-aminoethylimino)methyl)phenol

(4E)-4-(2-phenyldiazenyl)-2-((E)-(2-aminoethylimino)methyl)phenol (PAMP) was synthesized for the first time and used as a ratiometric fluorescent chemosensor for recognition of Eu³⁺ ions in acetonitrile solution. PAMP shows a fluorescent emission at 536 nm. When it forms a complex with Eu³⁺ ion, two new fluorescent enhancements at 418 and 496 nm appeared. In acetonitrile solution, the blue shift of fluorescent emission upon europium binding is due to the formation of a 1:1 metal ligand complex. The chemosensor shows a linear response toward Eu³⁺ in the range of 8.3 × 10^? 8 M to 8.3 × 10^? 6 M. The new fluorescent probe exhibits high selectivity toward Eu³⁺ ions over a large number of interfering cations.     

DIRECT ELECTROCHEMICAL POWER GENERATION FROM CARBON IN FUEL CELLS WITH MOLTEN HYDROXIDE ELECTROLYTE

Historically, despite its compelling cost and performance advantages, the use of a molten metal hydroxide electrolyte has been ignored by direct carbon fuel cell (DCFC) researchers, primarily due to the potential for formation of carbonate salt in the cell. This article describes the electrochemistry of a patented medium-temperature DCFC based on a molten hydroxide electrolyte, which overcomes the historical carbonate formation.

An important technique discovered for significantly reducing carbonate formation in the DCFC is to ensure a high water content of the electrolyte. To date, four successive generations of DCFC prototypes have been built and tested to demonstrate the technology - all using graphite rods as their fuel source. These cells all used a simple design in which the cell containers served as the air cathodes and successfully demonstrated the ability to deliver more than 40 A with the current density exceeding 250 mA/cm². Conversion efficiency greater than 60% was achieved.     

An innovative bed temperature-oriented modeling and robust control of a circulating fluidized bed combustor

Circulating fluidized bed (CFB) combustion systems are increasingly used as superior coal burning systems in power generation due to their higher efficiency and lower emissions. However, because of their non-linearity and complex behavior, it is difficult to build a comprehensive model that incorporates all the system dynamics. In this paper, a mathematical model of the circulating fluidized bed combustion system based on mass and energy conservation equations was successfully extracted. Using these correlations, a state space dynamical model oriented to bed temperature has been obtained based on subspace method. Bed temperature, which influences boiler overall efficiency and the rate of pollutants emission, is one of the most significant parameters in the operation of these types of systems. Having dynamic and parametric uncertainties in the model, a robust control algorithm based on linear matrix inequalities (LMI) have been applied to control the bed temperature by input parameters, i.e. coal feed rate and fluidization velocity. The controller proposed properly sets the temperature to our desired range with a minimum tracking error and minimizes the sensitivity of the closed-loop system to disturbances caused by uncertainties such as change in feeding coal, while the settling time of the system is significantly decreased.