Secondary grain growth in ammonium nitrate crystallization

Crystallization and ageing of pure ammonium nitrate crystals was studied by scanning electron microscopy. Ageing the crystals beyond 1 h led to the growth of secondary grains along the grain boundaries of primary grains (140–200 m). After 6 h ageing secondary growth along grain boundaries was not observed; instead, distinct clusters with morphologies similar to the secondary grains were formed. The ancillary growth obeys approximately the parabolic relation L=(Kt)^1/n+1 where n=1 justifies grain growth in the pure crystals, and its formation is ascribed to the dissolution of dendrites, edges and corners. The high interfacial activity and interparticle voids can affect the storage and mechanical properties of the material.     

Classification of speech dysfluencies with MFCC and LPCC features

The goal of this paper is to discuss comparison of speech parameterization methods: Mel-Frequency Cepstrum Coefficients (MFCC) and Linear Prediction Cepstrum Coefficients (LPCC) for recognizing the stuttered events. Speech samples from UCLASS are used for our analysis. The stuttered events are identified through manual segmentation and used for feature extraction. Two simple classifiers are used for testing the proposed features. Conventional validation method is used for testing the reliability of the classifier. The experimental investigation elucidates MFCC and LPCC features which can be used for identifying the stuttered events and LPCC features were slightly outperformed than MFCC features.     

Experimental studies on flow and heat transfer characteristics of secondary refrigerant-based CNT nanofluids for cooling applications

ABSTRACT

The aim of the research work is to explore the convective heat transfer coefficient characteristics of propanol-based nanofluids for cooling applications. The stable suspension of the nanofluid with volume fractions of 0.15 and 0.3 is prepared and characterised. The measurement on the density shows that there is only a negligible increase in the density of the nanofluid and the specific heat of the nanofluid increases with the volumetric concentration of nanofluids. Furthermore, there is an enhancement in the convective heat transfer coefficient of 70% for the nanofluid containing 0.3% of CNT.

Abbreviations: CNT: carbon nanotubes; IPA: isopropyl alcohol; MWCNT: multi-walled carbon nanotubes; SDBS: sodium dodecyl benzene sulphate     

Composite polymer electrolyte based on (PEO)6:NaPO3 dispersed with BaTiO3

BACKGROUND: Polymer electrolytes have attracted considerable attention as regards portable solid‐state electrochemical device applications. The present investigation is focused on the characterization of a new Na⁺ ion conducting polymer electrolyte (PEO)₆:NaPO₃ dispersed with 3–10 wt% BaTiO₃ (0.7 µm) fillers. The composite polymer electrolytes (CPEs) were prepared by a solution‐casting method and characterized using various physical measurement techniques. RESULTS: Differential scanning calorimetry results indicate a maximum reduction in the degree of crystallinity of the polymer from 62.6% for uncomplexed poly(ethylene oxide) (PEO) to 27.6% for the CPE with 6 wt% BaTiO₃. This substantiates an enhancement in the amorphous phase of the polymer inferred from X‐ray diffraction and optical micrographs. The CPE dispersed with 6 wt% BaTiO₃ is found to be the best composition exhibiting a maximum ionic conductivity of 1.2 × 10^?6 S cm^?1 at 345 K with cationic transport number (t) of 0.33. CONCLUSIONS: An enhancement in the ionic conductivity of about two orders of magnitude is achieved for the composite electrolytes when compared to filler‐free solid polymer electrolyte. Correlation of the temperature‐dependent conductivity, activation energy for ion migration and transport number enables an understanding of the role played by the fillers in conduction characteristics of the CPEs. Copyright © 2007 Society of Chemical Industry     

Experimental heat transfer behavior of graphite–water microfluid in a coiled agitated vessel

Agitation is one of the widely used engineering operations in all of the chemical industries, which involves both material transport and heat transfer in the system. In order to conserve energy spent in heat transfer systems, enhancements to heating and cooling in industrial processes can be achieved by dispersing small‐sized particles having high thermal conductivity in a base fluid. This article reports an experimental study on the heat transfer characteristics of graphite–water microfluid in a coiled agitated vessel equipped with propeller and six bladed disc turbine impellers. The heat transfer coefficient for the graphite–water microfluid is found to be higher than that for the base fluid (water) and increased with higher volume concentrations of graphite and higher impeller speed. Comparison of the graphite–water microfluid and water is found to demonstrate a significant enhancement in the convective heat transfer coefficient. Empirical correlations for the calculation of Nusselt numbers are performed, and the calculated Nusselt number is found to be in good agreement with experimental values within ±10% deviation.     

Enhanced Magnetism in Highly Ordered Magnetite Nanoparticle‐Filled Nanohole Arrays

A new approach to develop highly ordered magnetite (Fe₃O₄) nanoparticle‐patterned nanohole arrays with desirable magnetic properties for a variety of technological applications is presented. In this work, the sub‐100 nm nanohole arrays are successfully fabricated from a pre‐ceramic polymer mold using spin‐on nanoprinting (SNAP). These nanoholes a then filled with monodispersed, spherical Fe₃O₄ nanoparticles of about 10 nm diameter using a novel magnetic drag and drop procedure. The nanohole arrays filled with magnetic nanoparticles a imaged using magnetic force microscopy (MFM). Magnetometry and MFM measurements reveal room temperature ferromagnetism in the Fe₃O₄‐filled nanohole arrays, while the as‐synthesized Fe₃O₄ nanoparticles exhibit superparamagnetic behavior. As revealed by MFM measurements, the enhanced magnetism in the Fe₃O₄‐filled nanohole arrays originates mainly from the enhanced magnetic dipole interactions of Fe₃O₄ nanoparticles within the nanoholes and between adjacent nanoholes. Nanoparticle filled nanohole arrays can be highly beneficial in magnetic data storage and other applications such as microwave devices and biosensor arrays that require tunable and anisotropic magnetic properties.     

A proximity effect model for superconductivity in titanium-transition metal alloys

We present a unified model for the variation in superconducting transition temperature T _c of quenched titanium-transition metal alloys with intermediate-temperature aging. Experimental results on T _c and the low-temperature resistivity of -quenched Ti-27 at % Nb solid solution, a representative system, measured as a function of annealing are given. It is shown that the enrichment of the matrix in Nb as a result of precipitation of a Ti-rich phase is too small to be of any consequence in influencing T _c. Our resistivity data give, for the first time, evidence for the formation of athermal phase in this system. In the light of the present investigation a clear picture has emerged for the interpretation of T _c in terms of varying extent of superconducting proximity effect, which is shown to be intimately related to the microstructural evolution. The result is shown to be general, applicable to any Ti-transition metal alloy system.     

Evaluation of yield criteria for forming simulations based on residual stress measurement

Process induced anisotropy in sheet metal is accounted for in analytical modeling by anisotropic yield criteria. The suitability of a yield criterion for predicting sheet metal forming process is generally validated by way of its ability to predict surface strains. However, the sensitivity of surface strains to yield criteria is dependent upon strain modes, with plane strain mode exhibiting higher sensitivity. To eliminate dependency on strain modes, stresses are used to evaluate yield criteria, since forming stresses are less sensitive to strain modes. In the study, the residual stresses remaining in a hemispherical cup formed in plain strain mode is predicted using Hill48 and Barlat89 criteria. The residual stresses are experimentally characterized by using X-Ray diffraction method. Suitable yield criterion for forming simulation is validated based on the correlation of theoretical predictions with experimental residual stress values.     

Real-time separation of perfusion and oxygenation signals for an implantable sensor using adaptive filtering

In this paper, an adaptive filtering algorithm to separate signals due to perfusion and oxygenation has been developed using an 810-nm source, in addition to 660-nm and 940-nm sources, as an internal reference due to its limited oxygen sensitivity. The newly developed algorithm was tested using Monte Carlo simulated data to prove the effectiveness of the 810-nm reference and adaptive algorithm. Following the simulation, an in vitro model was developed to test the algorithm that used a blood flow through system wrapped with tissue. The system had the ability to isolate the effects of perfusion and oxygenation and the algorithm accurately captured the changes in these signals with reliable consistency. Using the serosal surface of the swine jejunum, in vivo data was also taken to analyze the algorithms response to fluctuating perfusion levels like that seen in hemorrhaging or failing transplants. The algorithm was able to extract the perfusion information from the oxygenation information in this in vivo study. Overall, it was shown that an adaptive filtering algorithm using an 810-nm reference has provided a means to separate oxygenation and perfusion.