Assessing the mechanical,phase inversion,and rheological properties of poly-[(R)-3-hydroxybutyrate-co-(R)-3-hydroxyvalerate] (PHBV) blended with poly-(l-lactic acid) (PLA)

Poly-(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) and poly-(l-lactic acid) (PLA) have attracted much interest in recent years since they are biodegradable, thus can replace synthetic non-degradable materials. In this study, improvements of PHBV, mechanical, phase inversions, and rheological properties were investigated after blending with PLA in varying ratio’s. Three different blends of commercially available PLAs with 92–98% l-lactide units and one grade of PHB with 5% valerate content were blended using a micro-compounder at 175 °C. The composition of PHBV in blends ranged from 50% to 80%. With the addition of PLA, increases in the flexural strength and elastic modulus were observed for several blends, while minor to no changes were detected in the elongation at break and tensile strength as compared to pure PHBV material. Like many conventional plastics, the complex viscosity decreased with increasing rotational frequency due to decreasing entanglements and molecular weight. The complex viscosity with respect to time was very stable for the blends, but no improvements in the PHBV viscosity were observed with the addition of PLA at 170 °C. Three phase inversion models were used to predict the continuity of the blends, and the results showed both dual- and PLA-continuity phase for the blends. In summary, the mechanical results showed improvements in the tensile and flexural properties, while the rheological observation showed minor improvements in the complex viscosity for numerous concentrations.     

Pressure distribution on a roof in presence of the Moving Surface Boundary-layer Control

The paper studies effect of momentum injection, accomplished through circular cylindrical rotating elements, on the pressure distribution at the roof of a model house. Extensive wind tunnel tests, complemented by flow visualization, suggest that such Moving Surface Boundary-layer Control (MSBC) effectively delays separation and significantly increases the pressure, both on leeward and windward surfaces. This would assist in protection of the roof against wind storms and snow accumulation.     

On the effect of SHI irradiation on dielectric properties of Y3+xFe5−xO12 (x=0.0–0.6) system

The present work aims to investigate the pre- and post-effect of 50 MeV Li³⁺ ion irradiation at a fluence of 5×10¹³ ions/cm² on the dielectric properties of Y_3+xFe_5?xO₁₂, x=0.0, 0.2, 0.4 and 0.6, garnet system over broad temperature, 300–673 K, and frequency, 100 Hz–13 MHz, ranges. Thermal variation of ac resistivity measurements suggests that the mechanism responsible for conduction in the system is polaron hopping. The observed modifications in dielectric properties after swift heavy ion irradiation are mainly due to the modifications of the metal–insulator contacts due to radiation damage-induced disorder and irradiation-induced point/cluster of defects in the material and also compressive strain generated in the lattice structure. The electric modulus presentation and the complex impedance spectral analysis have been employed to study the relaxation process. The YFeO₃ phase is found to be irradiation hard phase as compared with the garnet phase.     

Bent-shaped mesogenic oxadiazoles and thiadiazoles with terminal methyl group

Rod-shaped 4-methylbenzoic acid-N′-(4′-n-alkoxybenzoyl) hydrazide (series I) have been synthesized by the Schotten–Baumann reaction of 4-methylbenzhydrazide with 4-n-alkoxy benzoyl chloride using dry pyridine, as a solvent. The series I compounds have been cyclized to bent-shaped mesogenic 2-(4′-methylphenyl)-5-(4″-n-alkoxyphenyl)-1,3,4-oxadiazoles (series II) and 2-(4′-methylphenyl)-5-(4″-n-alkoxyphenyl)-1,3,4-thiadiazole (series III) using POCl₃ and Lawesson's reagent, respectively. The synthesized compounds are characterized by the combination of elemental analysis and standard spectroscopic methods. In series II, lower and middle members are non-mesogenic. n-Dodecyloxy to n-hexadecyloxy derivatives exhibit enantiotropic nematic mesophase. In series III, all the compounds synthesized exhibit enantiotropic nematic mesophase. n-Tetradecyloxy and n-hexadecyloxy derivatives also exhibit enantiotropic SmA mesophase. The mesomorphic properties of the series II and III used in this study are compared with each other and with other structurally related compound to evaluate the effect of different heterocyclic moieties as well as terminal substituents on mesomorphism.     

Effect of surface roughness on multilayer film growth

NbC/Si multilayers grown on silicon substrates of different roughness have been used to study the influence of surface quality on growth characteristics. Surface morphology of substrate and multilayer film are characterized by topographic measurements using atomic force microscopy (AFM) technique and power spectral density analysis (PSD). Grazing incidence x-ray reflectivity (GIXR) technique in combination with PSD analysis reveals a growth characteristic of multilayer film on substrates of different roughness. It is revealed that the stochastic growth of NbC on rough substrate leads to formation of clusters of varying size depending on initial substrate roughness. Details of growth characteristic are discussed.     

Influence of the core‐hole effect on optical properties of magnesium oxide (MgO) near the Mg L‐edge region

The influence of the core‐hole effect on optical properties of magnesium oxide (MgO) is established through experimental determination of optical constants and first‐principles density functional theory studies. Optical constants (δ and β) of MgO thin film are measured in the spectral region 40–300 eV using reflectance spectroscopy techniques at the Indus‐1 synchrotron radiation source. The obtained optical constants show strong core exciton features near the Mg L‐edge region, causing significant mismatch with Henke's tabulated values. On comparing the experimentally obtained optical constants with Henke's tabulated values, an edge shift of ～3.0 eV is also observed. Distinct evidence of effects of core exciton on optical constants (δ and β) in the near Mg L‐edge absorption spectra are confirmed through first‐principles simulations.     

Study of SHI-induced ion beam mixing in Y3+: YIG employing X-ray diffraction and Mössbauer spectroscopy

The consequences of swift heavy ion (SHI) irradiation (Li^3?+?, 50 MeV, fluence =?5 × 10¹³ ions/cm²) on the structural and microscopic magnetic properties of Y^3?+?-substituted yttrium iron garnet (Y_3?+?x Fe_5???x O₁₂, x = 0.0, 0.2 and 0.4) have been studied at 300 K. It is found that an additional YFeO₃-phase observed along with bcc garnet phase, is completely removed for x = 0.2 composition while its percentage formation considerably reduces for x = 0.4 composition after irradiation. Similar effect has been observed for specimens sintered at 1,500°C. The SHI-induced ion beam mixing has been revealed through X-ray diffraction and Mössbauer spectroscopy.     

An alternative givens ordering

Summary A new Givens ordering is shown, empirically and by an approximate theoretical analysis, to take appreciably fewer stages than the standard scheme. Sharper error bounds than Gentleman's ensue, and the scheme is better suited to parallel computation. Other schemes, less efficient but more easily analysed, are discussed. The effect of a possible limit in practice on the number of simultaneous computations is considered.     

Analytical solution of attitude motion for spacecraft with a slewing appendage

This paper investigates pitch motion and in orbital plane elastic vibration of a spacecraft with a flexible beam type appendage undergoing prescribed slew maneuver. The governing equations are transformed into a standard quasi-linear form, and then solved by Butenin's variation of parameters approach. Validity of the analytical solutions is assessed over a range of system parameters and initial conditions by comparing them with the results of numerical integration. The results show that they are very good approximations and provide extensive insight into the dynamical response of the system.