Synthesis of 4-Alkyl-4-alkoxybutenolides Having Unsaturated Side Chains via Chromium Carbene Complex Photochemistry: (+)-Cerulenin

The photochemical reaction between optically active ene carbamates and chromium alkoxycarbene complexes containing unsaturated aliphatic side chains was further developed. Although remote olefinic groups, including conjugated dienes, were tolerated, a homoallylic side chain underwent intramolecular reaction to give a strained cyclobutanone. (+)-Cerulenin was synthesized utilizing the photochemical reaction of an alkynylcarbene complex with an optically active ene carbamate and the bis(pi-crotyl)nickel halide alkylation of a vinyl bromide as key steps.     

Quantification of β-Sitosterol in Hairy Root Cultures and Natural Plant Parts of Butterfly Pea (Clitoria ternatea L.)

JPC – Journal of Planar Chromatography – Modern TLC - A simple normal-phase high-performance thin-layer chromatography (HPTLC) method has been developed for the quantification of...     

Permutation-symmetric multicritical points in random antiferromagnetic spin chains

We present a general theory of a class of multicritical points in the phase diagrams of random antiferromagnetic spin chains. We show that low-energy properties of these points are almost completely determined by a permutation symmetry of the effective theory not shared by the microscopic Hamiltonian. One case provides an analytic theory of the quantum critical point in the random spin-3/2 chain, studied in a recent work by Refael, Kehrein, and Fisher.     

Fractional spin textures in the frustrated magnet SrCr(9p)Ga(12-9p)O₁₉

We consider the archetypal frustrated antiferromagnet SrCr(9p)Ga(12-9p)O?? in its well-known spin-liquid state, and demonstrate that a Cr(3+) spin S=3/2 ion in direct proximity to a pair of vacancies (in disordered p<1 samples) is cloaked by a spatially extended spin texture that encodes the correlations of the parent spin liquid. In this spin-liquid regime, our analytic theory predicts that the combined object has a magnetic response identical to a classical spin of length S/2=3/4, which dominates over the small intrinsic susceptibility of the pure system. This fractional-spin texture leaves an unmistakable imprint on the measured ?1Ga nuclear magnetic resonance line shapes, which we compute using Monte Carlo simulations and compare with experimental data.     

Effect of gadolinium substitution on the linear thermal expansion of barium sodium niobate

Ba₂NaNb₅O₁₅ (BSN) exhibits a large thermal contraction in its c-axis between 350° and 750°C. This behaviour contributes to a serious cracking problem during its crystal growth. The substitutions of Gd for Ba and/or Na in BSN can be made with either anion or cation compensation. The former, namely, type A, compositions were found to eliminate the thermal contraction behaviors, and had small variations in their linear thermal expansion coefficients, α, between 50° and 650°C. With good ferroelectric and dielectric properties, they showed potentials to replace the BSN crystal in electro-optic devices.     

Application of thermogravimetric equations in the thermal decomposition of manganese(II) soaps

Summary Thermal decomposition of manganese(II) soaps of general composition, Mn(O₂CR)₂ (where R = C₁₇H₃₃, C₁₁H₂₃, C₉H₁₉, C₇H₁₅) has been studied by t.g.a. and a probable mechanism of decomposition is proposed. The activation energies have been determined using the different equations of Horowitz and Metzger and of Coats and Redfern. The results obtained are consistent.     

Multi-Fidelity High-Throughput Optimization of Electrical Conductivity in P3HT-CNT Composites

Combining high-throughput experiments with machine learning accelerates materials and process optimization toward user-specified target properties. In this study, a rapid machine learning-driven automated flow mixing setup with a high-throughput drop-casting system is introduced for thin film preparation, followed by fast characterization of proxy optical and target electrical properties that completes one cycle of learning with 160 unique samples in a single day, a > 10 ×  improvement relative to quantified, manual-controlled baseline. Regio-regular poly-3-hexylthiophene is combined with various types of carbon nanotubes, to identify the optimum composition and synthesis conditions to realize electrical conductivities as high as state-of-the-art 1000 S cm⁻¹. The results are subsequently verified and explained using offline high-fidelity experiments. Graph-based model selection strategies with classical regression that optimize among multi-fidelity noisy input-output measurements are introduced. These strategies present a robust machine-learning driven high-throughput experimental scheme that can be effectively applied to understand, optimize, and design new materials and composites.     

Charge state distribution studies of pure and oxygen mixed krypton ECR plasma – signature of isotope anomaly and gas mixing effect

We report the charge state distributions of the pure, 25% and 50% oxygen mixed krypton plasma to shed more light on the understanding of the gas mixing and the isotope anomaly [A. G. Drentje, Rev. Sci. Instrum. 63 (1992) 2875 and Y Kawai, D Meyer, A Nadzeyka, U Wolters and K Wiesemann, Plasma Sources Sci. Technol. 10 (2001) 451] in the electron cyclotron resonance (ECR) plasmas. The krypton plasma was produced using a 10 GHz all‐permanent‐magnet ECR ion source. The intensities of the highly abundant four isotopes, viz. ⁸²Kr (~11.58%), ⁸³Kr (~11.49%), ⁸⁴Kr (~57%) and ⁸⁶Kr (17.3%) up to ~ +14 charge state have been measured by extracting the ions from the plasma and analysing them in the mass and the energy using a large acceptance analyzer‐cum‐switching dipole magnet. The influence of the oxygen gas mixing on the isotopic krypton ion intensities is clearly evidenced beyond +9 charge state. With and without oxygen mixing, the charge state distribution of the krypton ECR plasma shows the isotope anomaly with unusual trends. The anomaly in the intensities of the isotopes having quite closer natural abundance, viz. ⁸²Kr, ⁸⁶Kr and ⁸³Kr, ⁸⁶Kr is prominent, whereas the intensity ratio of ⁸⁶Kr to ⁸⁴Kr shows a weak signature of it. The isotope anomaly tends to disappear with increasing oxygen mixing in the plasma. The observed trends in the intensities of the krypton isotopes do not follow the prediction of linear Landau wave damping in the plasma. Copyright © 2016 John Wiley & Sons, Ltd.