Weakly ferromagnetic microspheres bearing paramagnetic CrBO3 core and nonmagnetic polyvinylbutyral shell

A new class of core–shell microspheres was prepared through a modified solvent evaporation technique by coating chromium orthoborate (CrBO₃) particles with a commercial resin, namely Mowital®B30HH (polyvinyl butyral, PVB). Well‐shaped spherical particles were obtained in diameters ranging from 40 to 420 µm. The morphological, structural, thermal, and magnetic properties were characterized by SEM, FTIR, UV–Vis, VSM (Vibrating Sample Magnetometry), and thermal analysis techniques. Uncoated CrBO₃ is paramagnetic at room temperature and antiferromagnetic at low temperatures (T_N = 12 K) while PVB itself is nonmagnetic at room temperature. The results indicated that the microspheres having a paramagnetic core and nonmagnetic shell displayed weakly ferromagnetic properties at room temperature. The observed ferromagnetism was correlated with the particle size and higher saturation magnetization values were achieved with smaller microspheres. This unconventional magnetic behavior can be tuned by varying the particle size and may allow CrBO₃/PVB microspheres to serve as a smart material in future applications. Copyright © 2009 John Wiley & Sons, Ltd.     

Very-low-pressure pyrolysis (VLPP) of group IV (A) tetramethyls: Neopentane and tetramethyltin

The decomposition of neopentane was studied using the very-low-pressure pyrolysis (VLPP) technique at temperatures from 1000 to 1260 K. The derived Arrhenius parameters are consistent with δH_f⁰(t-butyl) = 8.4 kcal/mol. Using the above A factor, data on the decomposition of tetramethyltin yield DH⁰(Sn(CH₃)₃ - CH₃) = 69 ± 2 kcal/mol.     

Comparative studies on some metrics for external validation of QSPR models

Quantitative structure-property relationship (QSPR) models used for prediction of property of untested chemicals can be utilized for prioritization plan of synthesis and experimental testing of new compounds. Validation of QSPR models plays a crucial role for judgment of the reliability of predictions of such models. In the QSPR literature, serious attention is now given to external validation for checking reliability of QSPR models, and predictive quality is in the most cases judged based on the quality of predictions of property of a single test set as reflected in one or more external validation metrics. Here, we have shown that a single QSPR model may show a variable degree of prediction quality as reflected in some variants of external validation metrics like Q2(F1), Q2(F2), Q2(F3), CCC, and r2(m) (all of which are differently modified forms of predicted variance, which theoretically may attain a maximum value of 1), depending on the test set composition and test set size. Thus, this report questions the appropriateness of the common practice of the "classic" approach of external validation based on a single test set and thereby derives a conclusion about predictive quality of a model on the basis of a particular validation metric. The present work further demonstrates that among the considered external validation metrics, r2(m) shows statistically significantly different numerical values from others among which CCC is the most optimistic or less stringent. Furthermore, at a given level of threshold value of acceptance for external validation metrics, r2(m) provides the most stringent criterion (especially with Δr2(m) at highest tolerated value of 0.2) of external validation, which may be adopted in the case of regulatory decision support processes.     

Experimental observation of preferential solvation on a radical ion pair using MARY spectroscopy

The effect of preferential solvation on the exciplex luminescence detected magnetic field effect has been studied using magnetic-field-effect-on-reaction-yield (MARY) spectroscopy. By designing solvent mixtures which can provide a micro-environment around the magneto-sensitive radical ion pair (RIP) from highly heterogeneous to quasi-homogenous, the effect of the polarity scan on an absolute magnetic field effect (χ(E)) and B(1/2) (the field value marking half saturation) has been studied on the system 9,10-dimethylanthracene (fluorophore)/N,N'-dimethylaniline (quencher). While the trend in χ(E) (although with subtle differences) follows the usual norm of passing through maxima with increasing polarity, the B(1/2) values show either a large monotonic decrease (for heterogeneous solvents) or remain constant (for quasi-homogenous systems) with increasing polarity. The observations have been interpreted invoking the concept of amplification of the "cage-effect" as a result of preferential solvation in binary solvents and its influence on the decaying exciplex. The use of ternary solvents further confirms the proposed mechanism. Additionally electron hopping from the radical ion pair to the surrounding neutral donor molecules could also possibly contribute to the observed trend.     

Structural,magnetic and XPS studies of Sn0.95Co0.05O2-0.05 and Sn0.95Fe0.05O2-0.05 nanoparticles

Structural, microstructural, X-ray photoemission spectra (XPS) and magnetic properties of transition metal ion [5 mol% of Co (SC5) and Fe (SF5)]-doped SnO₂ nanoparticles have been studied. The SC5 and SF5 nanoparticles were synthesized by a chemical route using polyvinyl alcohol as surfactant. The doped SnO₂ crystallites were found to exhibit a tetragonal rutile structure and the average grains size was measured by the Scherer relation of X-ray diffraction. Transmission electron micrographs showed that the average grain size of SC5 is smaller than SF5. SC5 nanoparticles showed strong ferromagnetic behaviour but SF5 exhibited an F-centre exchange (FCE) mechanism. Temperature-dependent magnetization showed the values of phase transition temperature. XPS confirmed the presence of Sn–O–Co and Sn–O–Fe bonds in these SC5 and SF5 nanoparticles. The oxidation states of Sn, Co and Fe were found to be +4, +2 and +2, respectively, while the core level XPS peaks of Sn 3d, O 1s, Co 2p and Fe 2p were analyzed.     

Effect of 100 keV N+ ion irradiation on the organic single crystal of hippuric acid for nonlinear optical applications

The potential organic nonlinear optical material of hippuric acid (HA) single crystal has been grown by the slow evaporation solution growth technique using N, N-dimethylformamide as the solvent. Single crystals of pure HA were irradiated at room temperature with 100 keV Nitrogen (N⁺) ions at fluence 1×10¹⁶ and 5×10¹⁶ ions/cm². The pure and irradiated HA single crystals were characterized by different characterization technique. The photoluminescence and UV–visible absorption were performed at room temperature. The crystalline perfection of the pure and irradiated single crystals has been examined by high-resolution X-ray diffraction. Vickers microhardness technique was used to study the effect on the mechanical strength of the crystal at different ion fluences. The structural changes were analyzed by powder X-ray diffraction analysis. The functional groups of the synthesized compound have been identified by Fourier transform infrared spectroscopy. The dielectric constant and dielectric loss as a function of frequency were analyzed at room temperature.     

Compressions of ta10w alloy kennertium w-2, and beryllium oxide to 4.5 GPa

Abstract

The volume compressions of a tantalum alloy, tungsten alloy, and beryllium oxide (BeO) have been derived from the measurements of axial shortenings of cylindrical specimens of these materials to 4.5 GPa at room temperature. These measurements were carried out in a solid pressure medium piston- cylinder apparatus.     

An Experimental Study for Enhanced Availability of Free-Space Optics Systems over Hybrid Free-Space Optics/Radio Frequency Systems Using Switching Scheme Based on On–Off Keying and Multiple Pulse Position Modulation Schemes with Variable Data Rates

Abstract

Free-space optic links are degraded by such weather conditions as rain, fog, and atmospheric scintillation. The inherent advantages of free-space optic communication—providing higher data rates, security, and easy redeployment ability—motivate the avoidance of switching over free-space optic links to low bandwidth radio frequency links. This article establishes viable alternatives over free-space optics/radio frequency hybrid links to achieve higher capacity operation exploiting on–off keying and multiple pulse position modulation schemes with variable data rates to overcome the effect of fading due to adverse weather conditions. Results of an experimental free-space optical link at 1,550 nm are presented.     

A Rapid and Simple UPLC-MS–MS based Simultaneous Determination of the Medicinally Important E- and Z-Guggulsterone from Oleogum-Resins of Naturally Occurring Commiphora wightii Plants

A fast and simple method for simultaneous detection and quantification of the medicinally important E- and Z-guggulsterone from raw oleogum-resin of Commiphora wightii by UPLC was developed. Both E- and Z-guggulsterone were extracted from naturally occurring resin samples using ethyl acetate and methanol. Chromatographic separation of the analytes and their respective standards were performed on an Acquity UPLC BEH C₁₈ column followed by UV as well as a triple quadrupole detector in positive ionization mode. A linear gradient elution profile followed; mobile phase consisted of acetonitrile and 2 mM ammonium acetate in water. The method was validated over a range of 6.25 to 100 ng mL^?1 for both the guggulsterones. The calibration curves were linear with correlation coefficients of 0.9998 for E-guggulsterone and 0.9999 for Z-guggulsterone. The LOD and LOQ were 1.65 and 5.02 ng mL^?1 for E-guggulsterone and 2.57 and 7.79 ng mL^?1 for Z-guggulsterone respectively. The average recovery of E-guggulsterone (104.63%) and Z-guggulsterone (104.33%) achieved from spiked samples were consistent and reproducible. The intra- and inter-day assay precision of the analytes over the entire concentration range was less than 2%. The developed method required only 6 min to complete a run including 1 min to equilibrate the system and hence suitable for high throughput applications. Efficiency, reliability and accuracy of the developed method were evaluated by analyzing resin sample from different C. wightii populations. The result of this study offers improvement in terms of speed and sensitivity as compared to previously reported methods.     

Bose-Fermi mixtures in one dimension

We analyze the phase stability and the response of a mixture of bosons and spin-polarized fermions in one dimension (1D). Unlike in 3D, phase separation happens for low fermion densities. The dynamics of the mixture at low energy is independent of the spin-statistics of the components, and the modes are essentially undamped.