Modeling accuracy of a fiber-optics test bed using MGF method

The absolute accuracy of modeling a high bit rate optical transmitter-receiver test-bed by using moment generating functions is investigated with extensive system measurements and component characterizations. We achieved a 0.5-dB average optical signal-to-noise ratio accuracy for a 10-Gb/s return-to-zero fiber-optics test bed. The methodology shown here can be very useful for both efficient and accurate component or system engineering.     

Analyzing and comparing Montgomery multiplication algorithms

Montgomery multiplication methods constitute the core of modular exponentiation, the most popular operation for encrypting and signing digital data in public-key cryptography. In this article, we study the operations involved in computing the Montgomery product, describe several high-speed, space-efficient algorithms for computing MonPro(a, b), and analyze their time and space requirements. Our focus is to collect several alternatives for Montgomery multiplication, three of which are new. However, we do not compare the Montgomery techniques to other modular multiplication approaches     

Lateral Confinement Needed to Suppress Softening of Concrete in Compression

Suppression of softening in the load-deflection diagram of concrete-filled tubular columns and spiral columns is proposed to serve as a design criterion helping to avoid the size effect and explosive brittle character of collapse. To this end, the recently developed “tube-squash” tests, in which a short concrete-filled steel tube is squashed to about a half of its original length and allowed to bulge, are conducted with tubes of different wall thicknesses. A finite-strain finite element computer code with a microplane constitutive model is used to simulate the tests. After its verification and calibration by tests, the code is used to analyze nonbuckling concrete-filled tubular columns and spirally reinforced columns. It is found that softening in the load-deflection diagram can be fully suppressed only if the reinforcement ratio (ratio of the tube volume or spiral volume to the total volume of column) exceeds about 14%. If mild softening is allowed, the reinforcement ratio must still exceed about 8%. These ratios are surprisingly high. If they are not used in design, one needs to pay attention to the localization of softening damage, accept the (deterministic) size effect engendered by it, and ensure safety margins appropriate for protecting against sudden explosive brittle collapse. This is of particular concern for the design of very large columns.     

Wear Behavior of Borided AISI D2 Steel under Linear Reciprocating Sliding Conditions

Protection of Metals and Physical Chemistry of Surfaces - AISI D2 steel is the most commonly used cold-work tool steel in its grade. In this study, micro-structural characterization and some...     

Preparation and characterization of chitosan/montmorillonite‐K10 nanocomposites films for food packaging applications

Chitosan (CS)/montmorillonite‐K10 (MMTK‐10) clay composite films with different amounts of the clay MMTK‐10 (0.5, 1, 2.5, and 5%) were prepared using a solution‐casting method, and their properties were determined. The objective of this study is to prepare CS/clay nanocomposites and then to investigate the effects of clay content on mechanical, barrier, and thermal properties of these nanocomposites. The prepared films were characterized by Fourier transform infrared spectroscopy, X‐ray diffraction analysis, transmission electron microscopy, and scanning electron microscopy. Barrier properties (oxygen and water permeability), mechanical properties (tensile strength and elongation), and thermal behaviors (thermogravimetric analysis) were investigated and compared. The water vapor and gas permeability values of the composite films decreased significantly with increasing filler concentration. Tensile strength of the composites increased significantly with the addition of clay, and elongation at break decreased with increasing clay concentration. The tensile strength of nanocomposites is up to 34.82 MPa for 5 wt% clay content, and the tensile modulus shows a 74.63% higher value than that of neat CS. The resulting films had an opaque appearance, which depended on the amount of MMTK‐10 added. The oxygen permeability decreased with the increase in MMTK‐10. The minimum oxygen permeability (1.54 cm³/m² day atm) was recorded for film with 5% MMTK‐10. The water permeability of the composite films decreased significantly between 13 and 22% when clay was added. The dispersed clay improves the thermal stability and enhances the hardness and elastic modulus of the matrix systematically with the increased loading of clay. POLYM. COMPOS., 33:1874–1882, 2012. © 2012 Society of Plastics Engineers     

Persistent left superior vena cava: Two case reports and a review from nephrologists’ perspective

Thoracic venous anomalies without congenital heart anomalies are present in minority of the population, but they are frequent enough to be encountered while placing hemodialysis catheters through the jugular or subclavian veins. Persistent left superior vena cava is the most commonly seen anomaly and it is rarely noticed before the observation of an unusual course of hemodialysis catheter or guidewire on chest X‐ray. We present two patients with previously unspotted persistent left superior vena cava and uncomplicated hemodialysis catheter insertions through the internal jugular veins with good catheter functions. Review of the relevant literature from a nephrologists’ perspective with technical aspects is provided.     

Influence of repeated firings on the color parameters of two different all‐ceramic materials

All‐ceramics materials have been widely used in dental practice due to advantages of esthetic outcome. Color parameters, one of the major factors for the esthetic outcome, are affected from different factors such as repeated firings, chemical composition and thickness. In clinical practice, ceramics were frequently subjected to the repeated firings, but the effects of the repeated firings on the color parameters have been underestimated or unknown, so the aim of the study was to evaluate the effects of the repeated firings on the color parameters of all‐ceramic materials. Two commercially available A2 shaded all‐ceramic systems were used in this study (lithium disilicate pressable ceramics and computer aided design/computer aided manufacturing [CAD/CAM] fabricated zirconia). Ten samples for each group (zirconia and lithium disilicate) were prepared and subjected to repeated firings, respectively (1st, 3rd, 5th). Color measurements were performed after each repeated firings using a colorimeter (Minolta CR 321, Konica Minolta, Tokyo, Japan). The perceptibility threshold and acceptability threshold for color changes (ΔE₀₀) was defined as 0.8 and 1.8, respectively. Statistical analysis of the results was performed by using repeated measures ANOVA for color parameters and using non‐parametric Kruskal‐Wallis and Mann‐Whitney‐U test for ΔE₀₀ values (P < .05). L*, a* values showed statistically significant differences for lithium disilicate pressable ceramics and were not significant the zirconia specimens. ΔE₀₀ values were above the perceptibility level for both lithium disilicate and zirconia specimens. Repeated firings affect the color parameters of the lithium disilicate specimens. As a result of repeated firings, lithium disilicate ceramics become lighter and greener.     

Activity–Composition Relations in MnCr2O4–CoCr2O4 Solid Solutions and Stabilities of MnCr2O4 and CoCr2O4 at 1300°C

Phase equilibria in the system MnO–CoO–Cr₂O₃ were investigated at 1300°C under controlled oxygen partial pressures by using the gas equilibration technique. The CoO activities in various phase assemblages of the system were measured by determining the partial pressures of oxygen in the gas phase for coexistence with metallic cobalt. The activity data revealed that at 1300°C, MnO–CoO and MnCr₂O₄–CoCr₂O₄ solid solutions exhibit mild positive departures from ideal behavior. The activities in the stoichiometric spinel solutions were found to be in good agreement with those predicted from a model based on cation distribution equilibria. The standard free energy of formation of the compound CoCr₂O₄ from its oxide components at 1300°C was determined as −37 636 J/mol, while that for MnCr₂O₄ was found as −44 316 J/mol.     

Synthesis and characterization of γ-Bi2O3 based solid electrolyte doped with Nb2O5

γ-phase bismuth oxide is a well known high oxygen ion conductor and can be used as an electrolyte for intermediate temperature solid oxide fuel cells (IT-SOFCs). This study aims to determine new phases of Bi₂O₃-Nb₂O₅ binary system and the temperature dependence of the electrical transport properties. The reaction products obtained in open air atmosphere were characterized by X-ray powder diffractions (XRD). The unit cell parameters were defined from the indexes of the powder diffraction patterns. The γ-Bi₂O₃ crystal system were obtained by doping 0.01 < mole% Nb₂O₅ < 0.04 at 750 °C for 48 and 96 h. Thermal behaviour and thermal stability of the phases were investigated by thermal analysis techniques. Surface and grain properties of the related phases were determined by SEM analysis. The temperature dependence of the electrical properties of γ-Bi₂O₃ solid solution was measured by four-point probe d.c. conductivity method. In the investigated system, the highest value of conductivity was observed for σ _T = 0.016 ohm^?1 cm^?1 at 650 °C on 4 mole% Nb₂O₅ addition. The electrical conductivity curves of studied materials revealed regular increase with temperature in the form of the Arrhenius type conductivity behaviour.