Study of phase coexistence in YVO3 and LaVO3

The coexistence at low temperature in YVO₃ and LaVO₃ of two competing phases with defined orbital and spin orientations is studied by Raman spectroscopy. The temperature evolution of the phonons indicates that phase coexistence, due to strain in YVO₃ and fluctuations in LaVO₃, is not restricted to small R ionic radius in RVO₃ compounds. Also, a typical temperature at 50 K is inferred from the temperature dependence of the intensities in LaVO₃. Copyright © 2015 John Wiley & Sons, Ltd.     

Vernodalidimers A and B, novel orthoester elemanolide dimers from seeds of Vernonia anthelmintica

Two novel elemanolide dimers, vernodalidimers A (1) and B (2), possessing a rare tricyclic ortho ester moiety, were isolated from the seeds of Vernonia anthelmintica. Their structures were elucidated by 1D and 2D NMR data and CD spectra. Vernodalidimers A (1) and B (2) exhibited potent cell growth inhibitory activity against HL-60 cells (IC₅₀ 0.72 and 0.47 μM, respectively).     

X-ray emission from clusters of galaxies and cosmological parameters

Clusters of galaxies are excellent probes of cosmic structure and evolution. X-ray studies of clusters provide some of their key parameters, viz., temperature of the hot intra-cluster gas, its metallicity, X-ray luminosity and surface brightness giving mass distribution and mass-flow rate in the case of cooling flows. X-ray measurements for a large sample of clusters have lead to estimates of the total gravitating mass in them, which can be compared to the virial masses derived from dynamical considerations and gravitational lensing in some of them. X-ray derived total masses are consistent with masses obtained from the other methods after the effects due to the presence of cooling flows are taken into account in the analyses. Estimated virial masses, lack of evolution in X-ray properties, and detection of several very hot clusters at high redshifts indicate a Universe with a low value (≤ 0.3) for the Ω parameter.     

Pseuduvarines A and B, two new cytotoxic dioxoaporphine alkaloids from Pseuduvaria rugosa

Pseuduvarines A (1) and B (2), two new dioxoaporphine alkaloids with an amino moiety, were isolated from the stem bark of Pseuduvaria rugosa and their structures were elucidated by combination of 2D-NMR spectroscopic analysis. Pseuduvarines A (1) and B (2) showed cytotoxicity against MCF7, HepG2, and HL-60 (1: IC??, 0.9, 21.7, and >50.0 μM, respectively, 2: IC?? >50.0, 15.7, and 12.4 μM, respectively).     

Synthesis and Structure Analysis of Aurivillius Phases Pb1‐xBi4‐+Ti1‐xMnxO15

Synthesis Pb_1‐xBi_4+xTi_4‐xMn_xO₁₅ compounds (0 ≤ × ≤ 1) were carried out by molten salts method using eutectic mixture of Na₂SO₄/K₂SO₄ salts (1:1 molar ratio) as the flux. The samples were characterized by X‐ray powder diffraction and refined by Le Bail method using Rietica program. The refinement results revealed that the compounds with the composition 0 ≤ x ≤ 0.6 formed Aurivillius phase with the space group A2₁am while the other composition (x ≥ 0.8) showed another phase beside A2₁am. The ratio b/a of the lattices constants for all the samples are larger than 1 indicating the direction of the orthorhombic along the b axis of their cells. The lattice parameters and volume of the unit cells decrease as the Mn content increasing from x = 0 to 0.6, for x ≥ 0.8 a second phase were observed. The morphologies of Pb_1‐xBi_4+xTi_4‐xMn_xO₁₅ samples were observed by SEM and show plate‐like aggregate crystals, typical of layered compounds belonging to the Aurivillius phase.     

Micro‐Raman study of orbiton–phonon coupling in YbVO3

First‐order and multiphonon Raman active excitations are studied in YbVO₃ as a function of temperature in the orthorhombic and monoclinic phases. Below T ≃ 170 K, a G‐type orbital ordering with a concomitant monoclinic transition occurs. They enhance the phonon polarizabilities, allowing the resolution of room‐temperature bands, and activate new excitations around 700 cm⁻¹. Below T ∼ 65 K, the 700 cm⁻¹ excitations disappear, indicating a C‐type orbital ordering and a return to the orthorhombic structure. The observed phonon combinations around 1400 cm⁻¹ with a dominant Jahn‐Teller vibration at ∼690 cm⁻¹ reflect a possible orbiton‐phonon coupling. Copyright © 2011 John Wiley & Sons, Ltd.     

Crossing the gap from p- to n-type doping: nature of the states near the chemical potential in La(2)-(x)Sr(x)CuO(4) and Nd(2-x)Ce(x)CuO(4-delta)

We report on an x-ray absorption and resonant photoemission study on single crystals of the high-T(c) cuprates La2-xSrxCuO4 and Nd(2-x)Ce(x)CuO(4-delta). Using an intrinsic energy reference, we find that the chemical potential of La2-xSrxCuO4 lies near the top of the La2CuO4 valence band whereas in Nd(2-x)Ce(x)CuO(4-delta) it is situated near the bottom of the Nd2CuO4 conduction band. The data clearly establish that the introduction of Ce in Nd2CuO4 results in electrons being doped into the CuO2 planes. We infer that the states closest to the chemical potential have a Cu 3d(10) singlet origin in Nd(2-x)Ce(x)CuO(4-delta) and a 3d(9)L singlet origin in La2-xSrxCuO4.     

Ceramicines E-I, new limonoids from Chisocheton ceramicus

Five new limonoids, ceramicines E-I (1-5), have been isolated from the bark of Chisocheton ceramicus. The structures and relative stereochemistry of them were fully elucidated based on 1D- and 2D-NMR data. Ceramicines E-I (1-5) exhibited moderate cell growth inhibitory activities on a range of cell lines (HL-60, A549, MCF7, and HCT116). The absolute structure of previously isolated ceramicine B (6) was also elucidated by circular dichroism (CD) and X-ray analysis.     

Simulation of basic characteristics of single-shot full-field optical coherence tomography using spatially phase-modulated reference light

For the single-shot full-field optical coherence tomography (OCT) using spatially phase-modulated reference light, the basic characteristics have been simulated. At low spatial frequencies, the OCT signal intensity is enhanced twofold owing to subtractions, and with increasing the spatial frequency, the OCT signal intensity decreases 0.636 times at half the Nyquist frequency. OCT signal intensities also depend on orientations in images. Residual noninterference components of signal intensities between adjacent uniform areas increase background noise and reduce the system sensitivity. In the reference light, the optimum phase difference between adjacent uniform areas is 180 deg. Deviations from 180 deg reduce subtracted interference components. It is important that interference intensity, noninterference components and phases between adjacent uniform areas be approximately the same to obtain the OCT image with the reduction of background noise stably.     

Rupestines F-M, new guaipyridine sesquiterpene alkaloids from Artemisia rupestris

Eight new guaipyridine sesquiterpene alkaloids, rupestines F-M (1-8) were isolated from the leaves of Artemisia rupestris and their structures were elucidated on the basis of 2D-NMR data. The absolute configurations of 1-8 have been assigned by comparison of their experimental and calculated circular dichroism (CD) spectra.