Influence of interfacial reactions on the fiber-matrix interfacial shear strength in sapphire fiber-reinforced Nial(Yb) composites

The influence of microstructure of the fiber-matrix interface on the interfacial shear strength, measured using a fiber-pushout technique, has been examined in a sapphire-fiber-reinforced NiAl(Yb) matrix composite under the following conditions: (1) as-fabricated powder metallurgy (PM) composites, (2) PM composites after solid-state heat treatment (HT), and (3) PM com-posites after directional solidification (DS). The fiber-pushout stress-displacement behavior con-sisted of an initial “pseudoelastic” region, wherein the stress increased linearly with displacement, followed by an “inelastic” region, where the slope of the stress-displacement plot decreased until a maximum stress was reached, and the subsequent gradual stress decreased to a “fric-tional” stress. Energy-dispersive spectroscopy (EDS) and X-ray analyses showed that the inter-facial region in the PM NiAl(Yb) composites was comprised of Yb₂O₃,O-rich NiAl and some spinel oxide (Yb₃Al₅O₁₂), whereas the interfacial region in the HT and DS composites was comprised mainly of Yb₃Al₅O₁₂. A reaction mechanism has been proposed to explain the pres-ence of interfacial species observed in the sapphire-NiAl(Yb) composite. The extent of inter-facial chemical reactions and severity of fiber surface degradation increased progressively in this order: PM < HT < DS. Chemical interactions between the fiber and the NiAl(Yb) matrix resulted in chemical bonding and higher interfacial shear strength compared to sapphire-NiAl composites without Yb. Unlike the sapphire-NiAl system, the frictional shear stress in the sap-phire-NiAl(Yb) composites was strongly dependent on the processing conditions. Formerly Research Associate, Department of Chemical Engineering, Cleveland State University     

Novel method for characterisation of single-mode fibres and prediction of crossover wavelength and bandpass in nonidentical fibre directional couplers

We present here a novel and accurate method for the characterisation of single-mode fibres from a measurement of the wavelength dependence of the Petermann spot size. We also show its applicability in the prediction of the crossover wave length and bandpass in wavelength filters using nonidentical fibre directional couplers.     

A second phase III multicenter placebo controlled study of 2 dosages of modified release tamsulosin in patients with symptoms of benign prostatic hyperplasia. United States 93-01 Study Group

PURPOSE: In a double-blind, phase III clinical trial we evaluate the safety and efficacy of 0.4 and 0.8 mg. tamsulosin daily for the treatment of patients with symptoms of moderate to severe benign prostatic hyperplasia. MATERIALS AND METHODS: Patients meeting the basic requirements of the study underwent a 4-week single-blind placebo evaluation period. A total of 735 patients were randomized to double-blind therapy with tamsulosin or placebo. Treatment duration was 13 weeks. Efficacy and safety were evaluated at 5 visits during the double-blind treatment period. RESULTS: When efficacy data between baseline and end point were compared there was a significant reduction in total American Urological Association symptom score (25%) in each tamsulosin group compared with placebo (p = 0.01) and the percentage of patients with a 30% or more reduction in peak urinary flow rate was significantly greater in the tamsulosin versus placebo group (p <0.05). Improvements in American Urological Association symptom scores and maximum flow rate occurred at 1 week of treatment. None of the patients experienced a first dose effect. There were no significant changes in blood pressure on standing at any visit during the study except for a decrease in systolic blood pressure of 20 mm. Hg or more between the 0.8 mg. dose and placebo groups at visit 4 (p = 0.036). Positive orthostatic tests were significantly more frequent in the 0.8 mg. group compared with placebo at visit 4 (p = 0.012). The treatment groups did not differ significantly in incidence of electrocardiogram abnormalities at each post-baseline visit and at end point. CONCLUSIONS: Tamsulosin was safe and effective, and clinically and statistically superior to placebo in relieving symptoms of benign prostatic hyperplasia in men with moderate to severe symptoms at baseline. There was no evidence of a first dose effect and no clinically significant orthostatic hypertension. In addition, response to treatment was rapid.     

Dainty—A screen editor for data entry

Earth scientists generally handle large arrays of multivariate data (tabular form) which have to be entered into a computer for further processing. This paper is concerned with a user-friendly screen data editor named DAINTY, developed by the authors to serve the needs of data entry and printing. Whereas column operations are required for tabular data, text data entry requires row operations. DAINTY provides a number of column operations which generally are not present in commercial editors. These operations are discussed.     

Mechanical property anisotropy in superalloy El-929 directionally solidified by an exothermic technique

Directional solidification of the nickel-based superalloy El-929 was carried out by employing the exothermic technique for preparing several 150mm long × 55mm diameter rods. Specimens machined from the blanks cut at 0°, 45°, 75° and 90° to the chill surface were tensile and stress-rupture tested at different temperatures. The air-melted DS alloy, when loaded parallel to the growth direction, shows considerable improvement in stress-rupture life and tensile ductility as compared with the vacuum induction melted, forged and heat-treated alloy. However, these property advantages rapidly degrade with the increasing deviation of the load axis from the growth direction.     

Microsegregation in directionally solidified Pb-8.4 at. pct Au alloy

The dependence of microsegregation behavior on growth rate and thermal gradient has been examined in a Pb-8.4 at. pct Au alloy material partially directionally solidified and quenched. The composition of the quenched “liquid” at the dendrite tip (C _t), that of the eutectic-like solid phase freezing from the interdendritic liquid at the base of dendrite(C _se), the volume fraction of this eutectic-like region(f _e), and solute profiles in the interdendritic quenched liquid and ahead of the dendrite have been measured. Two dendritic growth models for solidification of a binary alloy melt in a positive thermal gradient at the liquid-solid interface, one for dendrites with “minimum undercooled dendrite tip” and the other for an Ivantsov type of dendrite with “marginally stable tip,” have been examined for a quantitative comparison with measured values ofC ₁, C_se, andf _e. Convection in the melt, possibly due to horizontal density gradients, is found to be a serious limitation for theoretical understanding of the observed experimental behavior and meaningful comparison of theories.     

Effect of undercooling on the microstructure of Ni-35 at. pct Mo (eutectic) and Ni-38 at. pct Mo (hypereutectic) alloys

Ni-35 at. pct Mo (eutectic) and Ni-38 at. pct Mo (hypereutectic) alloy specimens have been solidified from various levels of undercooling in the differential thermal analysis (DTA) and the electromagnetic levitation (EML) units in a pyrex/vycor bed. The evolution of the microstructure in the solidified specimens has been examined in terms of the degree of undercooling, the nature of the first phase to nucleate from the melt, and the specimen cooling rate. The melt has been observed to undercool more in the presence of intermetallic NiMo (β) phase as compared to that in the presence of nickel-rich solid solution (γ). The “anomalous eutectic” type of microstructure has been shown to result from the initial formation of the dendritic skeleton of either of the two phases, its segmentation due to convection and ripening, and the subsequent nucleation of the other phase in the interdendritic liquid regions. The recalescence behavior has been examined as a function of undercooling and the nature of the phase nucleating first in the melt.     

Influence of Cr and W alloying on the fiber-matrix interfacial shear strength in cast and directionally solidified sapphire nial composites

Sapphire-reinforced NiAl matrix composites with chromium or tungsten as alloying additions were synthesized using casting and zone directional solidification (DS) techniques and characterized by a fiber pushout test as well as by microhardness measurements. The sapphire-NiAl(Cr) specimens exhibited an interlayer of Cr rich eutectic at the fiber-matrix interface and a higher interfacial shear strength compared to unalloyed sapphire-NiAl specimens processed under identical conditions. In contrast, the sapphire-NiAl(W) specimens did not show interfacial excess of tungsten rich phases, although the interfacial shear strength was high and comparable to that of sapphire-NiAl(Cr). The postdebond sliding stress was higher in sapphire-NiAl(Cr) than in sapphire-NiAl(W) due to interface enrichment with chromium particles. The matrix microhardness progressively decreased with increasing distance from the interface in both DS NiAl and NiAl(Cr) specimens. The study highlights the potential of casting and DS techniques to improve the toughness and strength of NiAl by designing dual-phase microstructures in NiAl alloys reinforced with sapphire fibers. R. TIWARI, formerly Research Associate, Department of Chemical Engineering, Cleveland State University     

User-centric hybrid semi-autoencoder recommendation system

Recommendation System is one of such solutions to overcome information overload issues and to identify products most relevant to users and provide suggestions to users for items they might be interested in consuming or elements matching their needs. The significant challenge of several recommendation approaches is that they suggested a huge number of things to the target user. But the exciting items, according to the target user, are seen at the bottom of the recommended list. The proposed approach has improved the quality of recommendations by implementing some of the unique features in the new framework of auto encoder called semi-autoencoder, which contains the rating information as well as some additional information of users. Autoencoder is widely used in the recommender system because it gives the best result for feature extraction, dimensionality reduction, regeneration of data, and a better understanding of the user’s characteristics. The experimental results are compared with some established popular methods using precision, recall, and F-measure evaluation measures. Users generally don’t want to see lots of suggestions. With its six building blocks, the proposed approach gives better performance for the top 10 recommendations compared to other well-known methods.

     

Cryptanalysis of a novel ultra-lightweight mutual authentication protocol for IoT devices using RFID tags

Internet of Things (IoT) is an evolving architecture which connects multiple devices to Internet for communication or receiving updates from a cloud or a server. In future, the number of these connected devices will increase immensely making them an indistinguishable part of our daily lives. Although these devices make our lives more comfortable, they also put our personal information at risk. Therefore, security of these devices is also a major concern today. In this paper, we propose an ultra-lightweight mutual authentication protocol which uses only bitwise operation and thus is very efficient in terms of storage and communication cost. In addition, the computation overhead is very low. We have also compared our proposed work with the existing ones which verifies the strength of our protocol, as obtained results are promising. A brief cryptanalysis of our protocol that ensures untraceability is also presented.