Bactericidal strontium-releasing injectable bone cements based on bioactive glasses

Strontium-releasing injectable bone cements may have the potential to prevent implant-related infections through the bactericidal action of strontium, while enhancing bone formation in patients suffering from osteoporosis. A melt-derived bioactive glass (BG) series (SiO₂–CaO–CaF₂–MgO) with 0–50% of calcium substituted with strontium on a molar base were produced. By mixing glass powder, poly(acrylic acid) and water, cements were obtained which can be delivered by injection and set in situ, giving compressive strength of up to 35 MPa. Strontium release was dependent on BG composition with increasing strontium substitution resulting in higher concentrations in the medium. Bactericidal effects were tested on Staphylococcus aureus and Streptococcus faecalis; cell counts were reduced by up to three orders of magnitude over 6 days. Results show that bactericidal action can be increased through BG strontium substitution, allowing for the design of novel antimicrobial and bone enhancing cements for use in vertebroplasty or kyphoplasty for treating osteoporosis-related vertebral compression fractures.     

Modeling of Drying of Food Materials with Thickness of Several Centimeters by the Reaction Engineering Approach (REA)

Food materials are highly perishable. Drying is necessary to restrict biological and chemical activity to extend shelf life. A good drying model is useful for design of a better dryer, evaluation of dryer performance, prediction of product quality, and optimization. The reaction engineering approach (REA) is a simple-lumped parameter model revealed to be accurate and robust to model drying of various thin layers or small objects. Modeling drying behavior of different sizes is essential for a good drying model, yet it is still very challenging, even for a traditional diffusion-based model, which requires several sets of experiments to generate the diffusivity function. The REA is implemented in this study, for the first time, to model drying of rather thick samples of food materials. An approximate spatial distribution of sample temperature is introduced and combined with the REA to model drying kinetics. Results have indicated that the REA can model both moisture content and temperature profiles. The accuracy and effectiveness of the REA to model drying of thick samples of food materials are revealed in this study. This has extended the application of REA substantially. The application of the REA is currently not restricted for thin layesr or small objects but also for thick samples.     

Compaction studies of alternate solid forms of celecoxib

The aim of this study was to compare the compaction behavior of crystalline celecoxib (CryCEL), amorphous celecoxib (AmCEL) and celecoxib (CEL) – polyvinyl pyrolidone (PVP) – meglumine (MEG) solid dispersion (Ter-Mix) using texture analyzer and hydraulic press for low and high pressures, respectively. Pressure induced devitrification in the amorphous and ternary system was also studied using PXRD. Elastic energy/plastic energy (EE/PE) ratio of AmCEL, CryCEL and Ter-Mix was found to be 1.71, 2.32, and 1.91, respectively at 6.35 MPa. Similar trend was observed at all studied compaction pressures. AmCEL showed significant devitrification, while Ter-Mix showed degree of crystallinity (DOC) of 11.9%, when compacted at tableting pressures of 109 MPa. Parameters ‘a’, ‘1/b’, and ‘Py’ obtained using Kawakita equation and Heckel equation gave values of 0.86, 5.2, and 253.4 MPa for CryCEL, 0.89, 4.85, and 103 MPa for AmCEL and 0.68, 16.1, and 169.6 MPa for Ter-Mix, respectively. The study revealed significant differences in compaction properties of CryCEL, AmCEL, and Ter-Mix. AmCEL was not suitable for compacted solid dosage forms due to pressure induced devitrification. However, stabilized AmCEL in Ter-Mix showed relatively lesser devitrification and can be developed as compacted dosage forms.     

Impact of process parameters on critical performance attributes of a continuous blender—A DEM‐based study

A discrete element method‐based computational study carried out to study the effect of impeller design, speed, and input feed rate on the performance of a continuous powder blender is presented. The blender performance was characterized using the mean particle residence time, the residence time distribution, the number of blade passes experienced by the powder, and the mean centered variance. The powder residence time decreased with increasing impeller speed; however, the number of blade passes experienced a maximum at an intermediate speed. The effects of feed rate and impeller design were more prominent at lower speeds. Lower feed rate resulted in the powder experiencing higher number of blade passes. The number of blade passes was also higher for the alternate blade pattern when compared to the forward pattern. The computational findings were compared with an experimental study which showed that the model captured the essential flow dynamics well. © 2012 American Institute of Chemical Engineers AIChE J, 2012     

High‐Sensitivity p–n Junction Photodiodes Based on PbS Nanocrystal Quantum Dots

Chemically synthesized nanocrystal quantum dots (NQDs) are promising materials for applications in solution‐processable optoelectronic devices such as light emitting diodes, photodetectors, and solar cells. Here, we fabricate and study two types of p‐n junction photodiodes in which the photoactive p‐layer is made from PbS NQDs while the transparent n‐layer is fabricated from wide bandgap oxides (ZnO or TiO₂). By using a p–n junction architecture we are able to significantly reduce the dark current compared to earlier Schottky junction devices without reducing external quantum efficiency (EQE), which reaches values of up to ～80%. The use of this device architecture also allows us to significantly reduce noise and obtain high detectivity (>10¹² cm Hz^1/2 W^?1) extending to the near infrared past 1 μm. We observe that the spectral shape of the photoresponse exhibits a significant dependence on applied bias, and specifically, the EQE sharply increases around 500–600 nm at reverse biases greater than 1 V. We attribute this behavior to a “turn‐on” of an additional contribution to the photocurrent due to electrons excited to the conduction band from the occupied mid‐gap states.     

Vertical Scanning Interferometry: A New Method to Measure the Dissolution Dynamics of Cementitious Minerals

The aqueous dissolution rate is a key indicator of a portland cement's reactivity, and is relevant in predicting the progress of reactions and property development in cementitious materials. Though a valuable material property, the dissolution rates of the individual cement phases and their mixtures have been seldom determined. This work for the very first time applies vertical scanning interferometry (VSI) as a new method, aptly suited to measure dissolution dynamics of cement relevant minerals. Special emphasis is placed on measuring the first dissolution rate (DR_F), i.e., when water initially and for a short duration (i.e., on the order of tens of seconds) contacts the mineral surface. DR_F, mol·m^?2·s^?1) are measured for a variety of fast and slower dissolving minerals including (1a) natural limestone (CaCO₃), (1b) reagent‐grade gypsum (CaSO₄·2H₂O); (2) alite (impure, MIII‐Ca₃SiO₅); and (3) an ASTM C150, Type I/II ordinary portland cement across a range of solution pHs. Detailed aspects of image acquisition, processing and interpretation are presented to emphasize the methodological and statistical treatment of the results. The outcomes develop quantifications of aqueous dissolution rates—inputs valuable in simulating cement hydration, and forward a new means to study correlations between chemical composition, crystallography, and the reactivity of cementitious materials.     

Propane Aromatization over HZSM‐5 and Ga/HZSM‐5 Catalysts

The selective transformation of light alkanes to aromatics that are more valuable and versatile feedstocks for the chemical industry is one of the major challenges of catalytic chemistry. The complexity of the aromatization chemistry makes it difficult to unravel reaction mechanisms and, mechanistic information is largely developed from observed product distributions. This article reviews the current mechanistic understanding for the conversion of propane to aromatic compounds over HZSM‐5 and Ga/HZSM‐5 catalysts based on experimental as well as theoretical studies.

Following a general discussion of acidity and confinement effects in these systems, this review focuses on understanding specific reactions occurring on Brønsted acid sites in HZSM‐5. Mechanistic details available from Density Functional Theory (DFT) calculations, as well as kinetic modeling efforts for various complex hydrocarbon systems are critically reviewed. A detailed, tabulated review of the literature compares the catalytic performance of gallium modified ZSM‐5 catalysts and subsequently the promotional effect of gallium as an additive is critically discussed in terms of the nature of the active sites, as well as the new reaction pathways introduced by gallium addition.     

An Assessment of Bulk Metallic Glasses for Microelectromechanical System Devices

Metallic glasses were born purely of academic interest and earlier commercial attempts were limited due to the low thickness of the samples. However, with the successful fabrication of bigger samples using multicomponent system, there has been renewed interest in the commercial applicability of bulk metallic glasses (BMGs) as they offer promising mechanical, tribological and other properties which make the commercialization aspect lucrative. Through this study, an attempt has been made to assess the applicability of bulk metallic glasses as a material for Microelectromechanical System (MEMS) applications. Ranking and comparison, with the current MEMS material set, has been made using multiple criteria decision making (MCDM) approach. Performance index (PIs) was calculated using Ashby approach and Technique for Order Preference by Similarity to Ideal Solution (TOPSIS) was used to rank the materials on a collective basis. Additional features have been investigated to assess their suitability as a MEMS material. It was observed that BMGs offer promising prospects as a suitable MEMS material based on their overall performance when compared to the current material set being used for MEMS applications.     

Effect of rhenium doping on various physical properties of single crystals of MoSe2

Effect of rhenium doping is examined in single crystals of MoSe₂ viz. MoRe_0.005Se_1.995, MoRe_0.001Se_1.999 and Mo_0.995Re_0.005Se₂, which is grown by using the direct vapor transport (DVT) technique. The grown crystals are structurally characterized by X-ray diffraction, by determining their lattice parameters a and c, and X-ray density. Also, the Hall effect and thermoelectric power (TEP) measurements show that the single crystals exhibit a p-type semiconducting nature. The direct and indirect band gap measurements are also undertaken on these semiconducting materials.     

Effect of rhenium doping on various physical properties of single crystals of MoSe2

正Effect of rhenium doping is examined in single crystals of MoSe_2 viz.MoRe_(0.005)Se_(1.995), MoRe_(0.001)Se_(1.999) and Mo_(0.995)Re_(0.005)Se_2,which is grown by using the direct vapor transport(DVT) technique. The grown crystals are structurally characterized by X-ray diffraction,by determining their lattice parameters a and c,and X-ray density.Also,the Hall effect and thermoelectric power(TEP) measurements show that the single crystals exhibit a p-type semiconducting nature.The direct and indirect band gap measurements are also undertaken on these semiconducting materials.