The use of two reactive elements to optimize oxidation performance of alumina-forming alloys

Abstract

Standard reactive element (RE) studies have characterized the behavior of single RE additions such as Y, La or Hf. However, several commercial alumina-forming alloys are “co-doped” with two or more RE additions which allows the total amount of RE dopant in the alloy to be reduced. The oxidation performance of both commercial and laboratory-made co-doped alloys shows better scale adhesion and/or slower scale growth rates than comparable alloys with one RE addition. Characterization of the alumina scales showed no significant change in the grain structure with co-doping; however, as the total RE addition was reduced in co-doped alloys, a smaller volume of RE-rich oxides was observed within the scale. Quantification of the amount of RE ionic segregation on alumina scale grain boundaries formed on single doped and co-doped alloys showed similar amounts of segregation.     

Low-temperature ozone exposure technique to modulate the stoichiometry of WOx nanorods and optimize the electrochromic performance

A low-temperature ozone exposure technique was employed for the post-treatment of WO(x) nanorod thin films fabricated from hot-wire chemical vapor deposition (HWCVD) and ultrasonic spray deposition (USD) techniques. The resulting films were characterized with x-ray diffraction (XRD), transmission electron microscopy (TEM), Raman spectroscopy, UV-vis-NIR spectroscopy and x-ray photoelectron spectroscopy (XPS). The stoichiometry and surface crystallinity of the WO(x) thin films were subsequently modulated upon ozone exposure and thermal annealing without particle growth. The electrochromic performance was studied in a LiClO(4)-propylene carbonate electrolyte, and the results suggest that the low-temperature ozone exposure technique is superior to the traditional high-temperature thermal annealing (employed to more fully oxidize the WO(x)). The optical modulation at 670?nm was improved from 35% for the as-deposited film to 57% for the film after ozone exposure at 150?°C. The coloration efficiency was improved and the switching speed to the darkened state was significantly accelerated from 18.0?s for the as-deposited film to 11.8?s for the film after the ozone exposure. The process opens an avenue for low-temperature and cost-effective manufacturing of electrochromic films, especially on flexible polymer substrates.     

Mixtures of silicon and aluminum oxides to optimize the performance of nanoporous thin films in concrete

This study explored the effect of two combinations of silicon and aluminum oxides, nanosilica–nanoboehmite and nanosilica–gibbsite, on the hydration reaction of cement and the porosity of the interfacial transition zone (ITZ). The influence of sols on the cement hydration reaction was investigated using isothermal calorimetry while their effect on the porosity of the aggregate–paste interface was validated using scanning electron microscopy. The nanosilica–nanoboehmite mixtures were found to accelerate the hydration reaction to a higher degree than the individual components, nanosilica and nanoboehmite. Further, the effect was also found to be dependent on the stoichiometry of the mixture of nanoparticles. The nanosilica–gibbsite combinations not only accelerated the reaction but also increased the cumulative heat of hydration. In this case, the enhancement is attributed to the seeding effect of the gibbsite particles, being more prominent at the smaller particle sizes. Lastly, when these materials were applied as nanoporous thin films on the aggregates, all sol mixtures not only helped to decrease the overall porosity but also contributed to refinement of the porosity in the cement paste adjacent to the aggregate. These effects were observed up to 250 μm away from the surface of the aggregate thus not restricted to the typical length of the interfacial transition zone in concrete (40–50 μm).     

Increasing the performance characteristics of a cutter used to saw diamond crystals

We show that the application of two-sided ultrasound charging to disks used to cut natural diamond crystals and further hardening of surfaces by depositing diamond-like film on them considerably raise the performance characteristics of a cutting instrument. A. N. Sevchenko Scientific-Research Institute of Applied Physical Problems at the Belarusian State University, Minsk, Belarus. Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 72, No. 5, pp. 1004–1007, September–October, 1999.     

Selection of excipient,solvent and packaging to optimize the performance of spray-dried formulations: case example fenofibrate

Context: Along with other options, solid dispersions prepared by spray drying offer the possibility of formulating poorly soluble drugs in a rapidly dissolving format. As a wide range of potential excipients and solvents is available for spray drying, it is usually necessary to carry out a comprehensive array of studies to arrive at an optimal formulation.

Objective: To study the influence of formulation parameters such as co-sprayed excipients, solvents and packaging on the manufacture, in vitro performance and stability of spray-dried oral drug products using fenofibrate as a model drug.

Materials and methods: Solid dispersions of fenofibrate with different amorphous polymers were manufactured from two solvent systems by spray drying. These were characterized in terms of physicochemical properties, crystalline content and dissolution behavior in biorelevant media upon production and after storage in two packaging systems (Glass and Activ-Vials^?).

Results and discussion: Spray drying the same formulation from two different solvents led to different physicochemical properties, dissolution behavior and long-term stability. The dissolution behavior and long-term stability also varied significantly among excipients. The viscosity of the polymer and the packaging material proved to be important to the long-term stability.

Conclusion: For spray-dried products containing fenofibrate, the excipients were ranked according to dissolution and stability performance as follows: PVP derivatives >> HPMC 2910/15, HPMCAS-MF, HP-β-CD >> PVP:PVA 2:8. EtOH 96% proved superior to acetone/water for spray drying with polymers. The results were used to propose a general approach to developing spray-dried formulations of poorly soluble drugs.     

Optical-irradiance performance investigation to optimize a solar still with internal reflectors and double external boosters

Forschung im Ingenieurwesen - This study was performed to optimize the single slope solar still with internally reflecting walls and externally reflecting, top and bottom, flat booster reflectors...     

Application of autoregressive spectral analysis to cepstral estimation of mean scatterer spacing

The problem of estimation of mean scatterer spacing in an object containing regularly spaced structures is addressed. An autoregressive (AR) spectral estimation method is compared with a conventional fast Fourier transform (FFT)-based approach for this task. Regularly spaced structures produce a periodicity in the power spectrum of ultrasonic backscatter. This periodicity is manifested as a peak in the cepstrum. A phantom was constructed for comparison of the two methods. It contained regularly spaced nylon filaments. It also contained randomly positioned glass spheres that produced incoherent backscatter. In an experiment in which this target was interrogated using broadband ultrasound, the AR spectral estimate offered considerable improvement over the FFT when the analysis gate length was on the order of the structural dimension. Advantages included improved resolution, reduction in bias and variance of scatterer spacing estimates, and greater resistance to ringing artifacts. Data were also acquired from human liver in vivo. AR spectral estimates on human data exhibited a decreased dependence on gate length. These results offer promise for enhanced spatial resolution and accuracy in ultrasonic tissue characterization and nondestructive evaluation of materials.     

Processing to optimize the strength of heavily drawn Cu-Nb alloys

Heavily drawn Cu-Nb alloys display quite high ultimate tensile strengths. A modification to the consumable arc-casting technique used to prepare these alloys is shown to decrease the as-cast niobium dendrite diameter,t ₀, and also increase strength. Evaluation of strength, niobium filament spacing and thickness data show that strength varies with as-cast niobium dendrite size as somewhere betweent _o ^–0.36 tot _o ^–0.50 . Splat-cooling techniques demonstrate that minimum niobium dendrite sizes as small as 0.22m are possible. These sizes are over a factor of 10 smaller than has been achieved by consumable arc casting, and it is therefore suggested that processing rapidly solidified powders of Cu-Nb alloys should have significant advantages for preparing high-strength heavily drawn Cu-Nb alloys.     

The application of the capacitor's physics to optimize capacitiveangular-position sensors

The distributions of the potential and charge density in a capacitive angular-position sensor with three electrode disks in an axis-symmetrical configuration have been found by creating a suitable physical model and solving Laplace's equation. The influences of geometrical parameters on the nonlinearity, which originates from the electric-field-bending effect, are discussed in detail for a capacitive angular-position sensor. The approximately analytical results are verified by a numerical analysis and are found to be very useful to predict the influences of geometrical nonidealities. The calculations are experimentally verified by using a novel, absolute angular-position sensor with a nonlinearity of less than ±17" and ±50" over measurement ranges of 15° and 90°, respectively     

An algorithm to optimize the equivalent network for dielectrics

An algorithm is derived to optimize the number of branches in the equivalent network representing dielectric dispersion with many relaxation times. The algorithm is characterized by deriving general normalized relations. Satisfactory results are obtained for a network with more than 50% reduction in the number of branches for dispersion data of perfluoropolyether dielectric. The method is directly applicable to dispersion relations featuring weakly overlapping arcs in the complex plane of the dielectric constant. The procedure is also extendible for relations with strong arcs overlapping, such as in polymers and composite materials. This revised version was published online in November 2006 with corrections to the Cover Date.     

Use of chemometrics to optimize the operation of an ion source

A chemometric approach has been used to optimize the Agilent multimode ion source. Initial factorial experimental design studies indicated that there was a significant degree of curvature in the experimental region, so further central composite design experiments were performed. Optimum conditions were found using statistical optimization tools, and these results were then validated. As a result, recommendations have been made for the value of each operational parameter in order to optimize response.     

A linear programming model to optimize the decision-making to managing cogeneration system

A mathematical linear programming (LP) model was developed to optimize the decision-making for managing a cogeneration facility as a potential clean-development mechanism project in a hospital in Palestine. The model was developed to optimize the cost of energy and the cost of installation of a small cogeneration plant under constraints on electricity-and-heat supply and demand balances. In the model, the sources of electricity are either from cogeneration or public utilities and it was calculated the least cost to supply electricity and heat to the hospital. The hospital is using heat for their operation and that made the application for the cogeneration to be attractive and feasible. In this study, we will develop the LP model and will show the results and the time schedule for the cogeneration. This developed LP model can be used and run to any cogeneration application with little modification.     

General and self-consistent method for the calibration of polarization modulators, polarimeters, and mueller-matrix ellipsometers

Calibration of polarization-state generators (PSG's), polarimeters, and Mueller-matrix ellipsometers (MME's) is an important factor in the practical use of these instruments. A new general procedure, the eigenvalue calibration method (ECM), is presented. It can calibrate any complete MME consisting of a PSG and a polarimeter that generate and measure, respectively, all the states of polarization of light. In the ECM, the PSG and the polarimeter are described by two 4 x 4 matrices W and A, and their 32 coefficients are determined from three or four measurements performed on reference samples. Those references are smooth isotropic samples and perfect linear polarizers. Their optical characteristics are unambiguously determined during the calibration from the eigenvalues of the measured matrices. The ECM does not require accurate alignment of the various optical elements and does not involve any first-order approximation. The ECM also displays an efficient error control capability that can be used to improve the MME behavior. The ECM is illustrated by an experimental calibration, at two wavelengths (458 and 633 nm), of a MME consisting of a coupled phase modulator associated with a prism division-of-amplitude polarimeter.     

多孔介质模型的纤维过滤器优化模拟

用CFD软件FLUENT对纤维过滤器内部流场进行数值模拟,以熔体静电纺丝纤维膜为原型,探究纤维过滤器出口位置对过滤效率的影响,从速度分布、过滤压降及颗粒分布等方面进行对比.结果表明:过滤器压降随速度的增大而增大,随孔隙率的增大而减小,且膜后压力随速度增大成减小趋势;对多种纤维膜对比模拟发现,侧出口模型具有死水区,且颗粒分布不均,降低了膜使用率,将出口置于容器底部可有效减缓这种缺点;下出口模型较侧出口模型更能发挥纤维多孔介质的优势.     

Mine surface subsidence monitoring due to impacts of underground mining using persistent scatterer interferometry

The Singhbhum shear zone in India is well known for its historical underground copper mining activity. As a consequence, today some abandoned underground mines pose a serious risk to the local people and property. Thus it is essential for a long-term wide-range monitoring technique to map the surface subsidence over the mining areas. In this study, it has been tried to establish occurrence of ground subsidence with an advanced differential interferometric synthetic aperture radar technology called persistent scatterer interferometry, which is known for its capability of high-precision monitoring. The results clearly indicate trends of surface subsidence over abandoned mining regions.     

Application of statistical design strategies to optimize the conductivity of electrosynthesized polypyrrole

Fractional factorial design (FFD) and response surface methodology (RSM) coupled with central composite design (CCD) were used to optimize the electrical conductivity of polypyrrole (PPy) synthesized through an electrochemical route and constant current electrolysis. Current density of polymerization, monomer concentration, electrolyte (lithium perchlorate) concentration and temperature were selected as variables to study the effect on electronic conductivity of PPy through FFD. The temperature and concentration of the electrolyte are identified as the key variables which influence the conductivity of PPy. An empirical equation for the conductivity of PPy with variables is obtained via regression analysis. A contour plot is generated which predicts that a high value for the conductivity for PPy (ca. 34.3 S cm⁻¹) can be obtained with the LiClO₄ concentration of 0.826 M and a temperature of 14.9 °C. The results from confirmation experiments justify the prediction from the statistical approach.     

Techniques to generate and optimize the load spectra for an aircraft

In this article, described the various techniques to generate the load spectra for an aircraft and optimize the generated loading sequence. The generation of loading sequence is carried out from the Flight Data Recorder (FDR), which records various parameters in flight. In this article main focus is on ‘g’ accelerations as these are used for load spectra generation. This article describes the techniques viz., (i) Peak-trough counting, (ii) Level cross counting algorithms to count the number of exceedances. After implementing and using these techniques, listed the advantages and disadvantages of these techniques. For a successful usage of generated load sequence for a test/analysis, it is necessary to optimize the generated loading sequence or turning points. The optimization of generated load sequence is carried out by filtering small cycle amplitudes of load/‘g’ ranges. At different range levels the filtering has been carried out, to arrive at an optimum range level of filtering. In order to be certain that the optimized spectra has not lost its severity and shape it has been re-plotted with the original spectra on the same graph. This optimization exercise useful in reducing the testing time.     

Numerical method to optimize the polar-azimuthal orientation of infrared superconducting-nanowire single-photon detectors

A finite-element method for calculating the illumination-dependence of absorption in three-dimensional nanostructures is presented based on the radio frequency module of the Comsol Multiphysics software package (Comsol AB). This method is capable of numerically determining the optical response and near-field distribution of subwavelength periodic structures as a function of illumination orientations specified by polar angle, φ, and azimuthal angle, γ. The method was applied to determine the illumination-angle-dependent absorptance in cavity-based superconducting-nanowire single-photon detector (SNSPD) designs. Niobium-nitride stripes based on dimensions of conventional SNSPDs and integrated with ~ quarter-wavelength hydrogen-silsesquioxane-filled nano-optical cavity and covered by a thin gold film acting as a reflector were illuminated from below by p-polarized light in this study. The numerical results were compared to results from complementary transfer-matrix-method calculations on composite layers made of analogous film-stacks. This comparison helped to uncover the optical phenomena contributing to the appearance of extrema in the optical response. This paper presents an approach to optimizing the absorptance of different sensing and detecting devices via simultaneous numerical optimization of the polar and azimuthal illumination angles.     

Tuning the pK(a) of fluorescein to optimize binding assays

The phenolic pKa of fluorescein varies depending on its environment. The fluorescence of the dye varies likewise. Accordingly, a change in fluorescence can report on the association of a fluorescein conjugate to another molecule. Here, we demonstrate how to optimize this process with chemical synthesis. The fluorescence of fluorescein-labeled model protein, bovine pancreatic ribonuclease (RNase A), decreases upon binding to its cognate inhibitor protein (RI). Free and RI-bound fluorescein-RNase A have pKa values of 6.35 and 6.70, respectively, leaving the fluorescein moiety largely unprotonated at physiological pH and thus limiting the sensitivity of the assay. To increase the fluorescein pKa and, hence, the assay sensitivity, we installed an electron-donating alkyl group ortho to each phenol group. 2',7'-Diethylfluorescein (DEF) has spectral properties similar to those of fluorescein but a higher phenolic pKa. Most importantly, free and RI-bound DEF-RNase A have pKa values of 6.68 and 7.29, respectively, resulting in a substantial increase in the sensitivity of the assay. Using DEF-RNase A rather than fluorescein-RNase A in a microplate assay at pH 7.12 increased the Z'-factor from -0.17 to 0.69. We propose that synthetic "tuning" of the pKa of fluorescein and other pH-sensitive fluorophores provides a general means to optimize binding assays.