Dust in Supernovae and Supernova Remnants II: Processing and survival

Observations have recently shown that supernovae are efficient dust factories, as predicted for a long time by theoretical models. The rapid evolution of their stellar progenitors combined with their efficiency in precipitating refractory elements from the gas phase into dust grains make supernovae the major potential suppliers of dust in the early Universe, where more conventional sources like Asymptotic Giant Branch (AGB) stars did not have time to evolve. However, dust yields inferred from observations of young supernovae or derived from models do not reflect the net amount of supernova-condensed dust able to be expelled from the remnants and reach the interstellar medium. The cavity where the dust is formed and initially resides is crossed by the high velocity reverse shock which is generated by the pressure of the circumstellar material shocked by the expanding supernova blast wave. Depending on grain composition and initial size, processing by the reverse shock may lead to substantial dust erosion and even complete destruction. The goal of this review is to present the state of the art about processing and survival of dust inside supernova remnants, in terms of theoretical modelling and comparison to observations

Pyrimidine based hole-blocking materials with high triplet energy and glass transition temperature for blue phosphorescent OLEDs

We designed and synthesized new hole-blocking materials (HBMs), mPyrPPB and pPPyrPB, consisting of pyrimidine and phenylene segments for high-performance blue phosphorescent OLEDs. The thermal, electrochemical, and optical properties of mPyrPPB and pPPyrPB were systemically investigated. It was found that the Tg values of mPyrPPB and pPPyrPB were 118 and 137 °C, respectively. Especially, the triplet energy and highest occupied molecular orbital (HOMO) energy level of mPyrPPB were 2.77 eV and −6.86 eV, respectively, indicating that it had sufficiently high triplet energy and deep HOMO energy level for the hole-blocking layer (HBL) in blue phosphorescent OLED devices. It was found that all the meta conjugation of mPyrPPB molecular structure effectively prevented π-electron delocalization and thus increased the triplet energy and electron transport property. In addition, mPyrPPB exhibited higher electron-transporting property than pPPyrPB because mPyrPPB possessed effective intermolecular hydrogen bonds. When mPyrPPB was utilized as a HBM for a blue phosphorescent OLED device, external quantum efficiency (EQE), current efficiency (CE), and power efficiency (PE) values effectively increased to 16.4%, 36.7 cd/A, and 13.4 lm/W, respectively. Compared to the reference device without HBM, EQE, CE, and PE increased by 38%, 35%, and 54% respectively, mainly due to the confinement of triplet excitons and holes and improved electron-transporting ability. © 2018 Elsevier B.V.1

Macroline, akuammiline, sarpagine, and ajmaline alkaloids from Alstonia macrophylla

A total of seventeen alkaloids, comprising six macroline (including alstofolinine A, a macroline indole incorporating a butyrolactone ring-E), two ajmaline, one sarpagine, and eight akuammiline alkaloids, were isolated from the stem-bark and leaf extracts of the Malayan Alstonia macrophylla. The structure and relative configurations of these alkaloids were established using NMR, MS and in several instances, confirmed by X-ray diffraction analysis. Six of these alkaloids were effective in reversing multidrug-resistance(MDR) in vincristine-resistant KB cells

Gastric Lesions and Immune Responses caused by Long-term Infection with Helicobacter heilmannii in C57BL/6 Mice

Helicobacter heilmannii is a gastric micro-organism that can induce gastritis and B-cell MALT (mucosa-associated lymphoid tissue) lymphoma in mice, in a host-dependent manner. The present study was designed to examine gastric lesions and immune responses caused by intragastric H. heilmannii infection of an inbred mouse strain, C57BL/6. Long-term infection led to the formation of gastric nodules and increased mucosal thickness of the stomach, due to gastric epithelial proliferation. Infection also induced the formation of lymphoid follicles in the corpus mucosa and submucosa. The follicular cells were mainly CD45R+ cells that did not produce immunoglobulin. However, scattered in the lamina propria and corpus submucosa, numerous IgA+ cells were found in infected mice, but not in control mice. RT-PCR results showed that H. heilmannii infection led to increased mRNA expression for IFN-γ (a Th1 cytokine) and IL-10 (a Th2 cytokine) in the mouse stomach, suggesting that both Th1 and Th2 responses are associated with H. heilmannii infection. The mRNA of other cytokines and chemokines (IL-1β, IL-12p40, TNF-α, MCP-1, KC and MIP-2) was also increased by infection.This work was supported by the Brain Korea 21 project and the Korean Research Foundation (KRF-005-E00077). We thank Dr Christine McDonald (Department of Pathology, University of Michigan) for her kind advice

Raman characterization of strain and composition in small-sized self-assembled Si/Ge dots

A detailed Raman characterization of the structural properties of as-grown and annealed self-assembled Si/Ge dot multilayers is reported in this paper. Several new modes in as-grown or annealed Si/Ge dots and a frequency splitting of 4.2 cm(-1) between the longitudinal (LO) and transversal optical (TO) Ge-Ge modes in as-grown Si/Ge dots are observed in Raman spectra. An average Ge content of 0.8 and lateral strain of -3.4% are consistently obtained from these spectral features for as-grown Si/Ge dots with a lateral size of about 20 nm and a height of about 2 nm. It suggests that a certain amount of intermixing between Si spacer layers and Si/Ge dots takes place for the Si/Ge dot multilayers. The annealing behavior of the Ge-Si mode in Si/Ge dots indicates that the observed sharp Ge-Si mode is a Ge-Si alloy mode within the core regions of Si/Ge dots, rather than a Ge-Si interface mode in the interface regions of dots. The phonon strain-shift coefficients of the Ge-Ge and Ge-Si modes are determined for the small-sized Si/Ge dots with a high Ge content under a biaxial strain condition. The results show that the LO-TO frequency splitting of the Ge-Ge mode and the frequencies of the Ge-Ge and Ge-Si modes can be used as an efficient way to determine the average strain and composition in uncorrelated small-sized Si/Ge dot multilayers in which the mean strain field is close to the biaxial case

Active asymmetric plasmonic Bragg gratings

We discuss asymmetric reflectance in surface plasmon Bragg gratings incorporating optical gain, referred to as active asymmetric surface plasmon Bragg gratings. It is shown that balanced modulation of index and gain/loss with quarter pitch spatial shift causes unidirectional coupling between contra-propagating modes in long-range surface plasmon polariton Bragg gratings. Such gratings operate at the breaking threshold of parity-time symmetry (exceptional point). Two active asymmetric surface plasmon Bragg gratings designs are proposed and their performance is examined through modal and transfer matrix method computations