DC Electrical Resistivity and Magnetic Property of Single-Phase α-Fe2O3 Nanopowder Synthesized by a Simple Chemical Method

Nanocrystalline pure α-Fe₂O₃ powder, with an average particle size of 35 nm, has been synthesized by using an aqueous solution-based synthetic route. DC electrical resistivity of the synthesized material was measured with respect to temperature by the two-probe method from 28° to 225°C. Room temperature resistivity of the nanopowder was ∼10⁸Ω·cm. Magnetic hysteresis measurement revealed that the synthesized α-Fe₂O₃ nanopowder exhibited ferromagnetic behavior at room temperature. The hysteretic features are high saturation magnetization of 5.1 emu/g, high remanence of 2.2 emu/g, and coercivity of 200.5 Oe.     

The Stabilizing Effects of Polyols and Sugars on Porcine Pancreatic Lipase

Porcine pancreatic lipase (PPL) has been used as a biocatalyst for many years and is one of the most widely used enzymes for biotechnological applications; however, it is a rather complex mixture with various active enzymes. The present study has been undertaken to determine the effects of polyols and sugars (cosolvents) on the thermal stability of PPL preparation. The thermal stability of PPL exposed to 60°C for 10 min was enhanced in the presence of cosolvents in terms of both residual specific activity and conformational stability. Thermal denaturation, changes in circular dichroism, fluorescence spectra, apparent kinetic parameters, activity, and preferential interaction parameter of PPL preparation are discussed in terms of contributions to the mechanism of thermal stability and the activity enhancement. Partial specific volume measurement of PPL in the presence of cosolvents is presented for the first time. The preferential interaction parameter (ξ ₃) was negative in all cosolvents used, and maximum hydration was observed in the presence of trehalose, where the preferential interaction parameter was −0.076 g/g. The observed increase in the thermal stability of PPL preparation in the presence of cosolvents is due to the preferential hydration of the enzyme.     

Direct <Emphasis Type="SmallCaps">d</Emphasis>-Glucose Oxidation over Noble Metal Nanoparticles Introduced on Polymer and Inorganic Supports

In the present work, nanocatalysts prepared on inorganic supports (zeolites) were investigated in d-glucose oxidation and compared to systems supported on polymer (hypercrosslinked polystyrene (HPS)) previously described. Catalytic activities and selectivities were measured under various reaction conditions. The selectivity of d-glucose oxidation and activity of both Pd-containing zeolites and HPS-Ru were similar (99.7% and TOF 0.013–0.014 mol/(mol Me s)). Physicochemical analysis X-ray photoelectron spectroscopy, liquid nitrogen physisorption, diffuse reflectance infrared Fourier transform spectroscopy of adsorbed CO for metal sites evaluation, CD₃CN for acid sites evaluation showed that Pd species were in oxidic form, while Ru species were in oxidic and reduced form. The catalytic activity decreased when acidic sites were present in Pd-containing zeolites.     

X-Ray Photoelectron Spectroscopy Investigation of Pd-Beta Zeolite Catalysts with Different Acidities

Three different H-Beta zeolites with SiO₂/Al₂O₃ molar ratios of 300, 150 and 25 were loaded with palladium by evaporation–impregnation method using Pd(NO₃)₂ as a precursor. Dependence between the electronic states of Pd as a function of the acidity of Beta zeolite was studied by XPS for calcined and reduced samples. The dependence of the electronic states of Pd on the support was detected to have a complicated character and to be influenced by various factors such as metal loading, density of the imperfections in the zeolitic framework and proton localization. In calcined zeolites mainly agglomerated PdO and AlPd _x O crystallites were detected referring to interaction of palladium with the support. Reduction of PdO led to formation of metallic Pd_n clusters, which further reduced to [Pd_n–H_m]^m+ complexes and AlPd _x O complexes. The increase of the reduction temperature seems to enhance interactions of Pd_n clusters with imperfect [AlO _x ⁻] components instead of protons, especially in less acidic samples due to enhanced agglomeration of palladium particles outside the pores of the zeolite. The fraction, size and shape of the formed species were detected to be sensitive to the acidity of the support.     

Evaporative heat loss and heat transfer for open- and closed-cycle systems of a floating tilted wick solar still

An analytical expression for the thermal efficiency of evaporative heat loss and heat transfer for a open- and closed-cycle systems of floating tilted wick solar stills in terms of system design and climatic parameters has been derived. The expression for open- and closed-cycle systems was validated by performing experiments for both systems. Optimization of the design of the still for evaporative cooling (open cycle) and the distillation unit (closed cycle) was obtained using the derived analytical expression for large-scale installation. Numerical calculations were also carried out for a typical summer day at the Sri Ramakrishna Mission Vidyalaya College of Arts and Science, Coimbatore, India, to predict the performance of the still.     

Conformationally constrained PNA analogues: structural evolution toward DNA/RNA binding selectivity

Since its discovery 12 years ago, aminoethylglycyl peptide nucleic acid (aeg-PNA) has emerged as one of the successful DNA mimics for potential therapeutic and diagnostic applications. An important requisite for in vivo applications that has received inadequate attention is engineering PNA analogues for able discrimination between DNA and RNA as binding targets. Our approach toward this aim is based on structural preorganization of the backbone to hybridization-competent conformations to impart binding selectivity. This strategy has allowed us to design locked PNAs to achieve specific hybridization with DNA or RNA with aims to increase the binding strength without losing the binding specificity. This Account presents results of our rationale in design of different conformationally constrained PNA analogues, their synthesis, and evaluation of hybridization specificities.     

Hydrogenolysis of Hydroxymatairesinol Over Carbon-Supported Palladium Catalysts

The natural lignan hydroxymatairesinol was hydrogenolysed to a potential anticarcinogenic substance matairesinol over different carbon-supported palladium catalysts. The reaction was conducted in 2-propanol at 70 °C under hydrogen flow in a stirred glass reactor. The catalysts were characterised by N₂-physisorption, CO pulse chemisorption and pH measurement of aqueous catalyst slurries. The most active catalyst (Degussa-Hüls) gave yields of matairesinol over 90% in 4 h. It was concluded that the acidity of the catalyst had a profound influence on the reaction rate.     

Degradation in Thermal Properties and Morphology of Polyetheretherketone-Alumina Composites Exposed to Gamma Radiation

Sheets of polyetheretherketone (PEEK) and PEEK-alumina composites with micron-sized alumina powder with 5, 10, 15, 20, and 25% by weight were fabricated, irradiated with gamma rays up to 10 MGy and the degradation in their thermal properties and morphology were evaluated. The radicals generated during irradiation get stabilized by chain scission and crosslinking. Chain scission is predominant on the surface and crosslinking is predominant in the bulk of the samples. Owing to radiation damage, the glass transition temperature, T _g increased for pure PEEK from 136 to 140.5?°C, whereas the shift in T _g for the composites decreased with increase in alumina content and for PEEK-25% alumina, the change in T _g was insignificant, as alumina acts as an excitation energy sink and reduces the crosslinking density, which in turn decreased the shift in T _g towards higher temperature. Similarly, the melting temperature, T _m and enthalpy of melting, ??H _m of PEEK and PEEK-alumina composites decreased on account of radiation owing to the restriction of chain mobility and disordering of structures caused by crosslinks. The decrease in T _m and ??H _m was more pronounced in pure PEEK and the extent of decrease in T _m and ??H _m was less for composites. SEM images revealed the formation of micro-cracks and micro-pores in PEEK due to radiation. The SEM image of irradiated PEEK-alumina (25%) composite showed negligible micro-cracks and micro-pores, because of the reinforcing effect of high alumina content in the PEEK matrix which helps in reducing the degradation in the properties of the polymer. Though alumina reduces the degradation of the polymer matrix during irradiation, an optimum level of ceramic fillers only have to be loaded to the polymer to avoid the reduction in toughness.     

GA Approach for Optimization of Surface Roughness Parameters in Machining of Al Alloy SiC Particle Composite

Experiments were carried out using carbide turning inserts on AA7075/10?wt.% SiC (particle size 10-20???m) composites to get actual input values to the optimization problem, so that the optimized results are realistic. By using experimental data, the regression model was developed. This model was used to formulate the fitness function of the genetic algorithm (GA). This investigation attempts to perform the application of GA for finding the optimal solution of the cutting conditions minimum value of surface roughness. The analysis of this investigation shows that the GA technique is capable of estimating the optimal cutting conditions that yield the minimum surface roughness value. With the highest speed, the lowest feed rate, the lowest depth of cut, and the highest nose radius of the cutting conditions' scale, the GA technique recommends 1.039???m as the best minimum predicted surface roughness value. This means that the GA technique has decreased the minimum surface roughness value of the experimental sample data, regression modeling and desirability analysis by about 3%, 1%, and 2.8%, respectively.     

Effect of Thermal Oxidation on Corrosion Resistance of Commercially Pure Titanium in Acid Medium

This article addresses the characteristics of commercially pure titanium (CP-Ti) subjected to thermal oxidation in air at 650?°C for 48?h and its corrosion behavior in 0.1 and 4?M HCl and HNO₃ mediums. Thermal oxidation of CP-Ti leads to the formation of thick oxide scales (~20???m) throughout its surface without any spallation. The oxide layer consists of rutile- and oxygen-diffused titanium as predominant phases with a hardness of 679?±?43?HV_1.96. Electrochemical studies reveal that the thermally oxidized CP-Ti offers a better corrosion resistance than its untreated counterpart in both HCl and HNO₃ mediums. The uniform surface coverage and compactness of the oxide layer provide an effective barrier toward corrosion of CP-Ti. The study concludes that thermal oxidation is an effective approach to engineer the surface of CP-Ti so as to increase its corrosion resistance in HCl and HNO₃ mediums.