Temperature-dependent crystal-plasticity model for magnesium: a bottom-up approach

A crystal-plasticity model is developed to account for temperature-dependent mechanical behaviour of magnesium in this paper. The constitutive description of plastic deformation accounts for crystalline slip and twining as well as their interactions. The temperature dependence is incorporated into the constitutive equations for both slip and twin modes based on experimental observations. A bottom-up computational modelling framework is proposed to validate the developed constitutive model. First, the crystal-plasticity model is calibrated with experimental results for plane compression at micro-scale. At meso-scale, a three-dimensional representative element volume was adopted to represent the microstructure of polycrystalline magnesium. In the combination with the proposed constitutive theory, the effects of temperature on mechanical response and evolution of twins and texture in polycrystalline magnesium were predicted. Comprehensive experimental validations at meso-scale were performed to consolidate further the developed crystal-plasticity model incorporating temperature dependence in terms of stress-strain curves, the Hall-Petch relationship and texture evolution. This work provides a useful modelling tool for understanding temperature-dependent behaviour of magnesium, which could be used to improve the formability of this family of materials

Micro-cutting of single-crystal metal: Finite-element analysis of deformation and material removal

This paper presents analysis of mechanics in a micro-cutting process of a single-crystal metal – mechanisms of deformation and material removal related to an anisotropic crystallographic structure of a work-piece. A crystal-plasticity theory was implemented in a finite-element (FE) modelling scheme to consider inherently anisotropic deformation of a single-crystal metal at micro-scale. A new shear-strain-based criterion and several conventional strain-based criteria were employed to simulate the material removal process, and their effect on the anisotropy of cutting forces was studied. Subsequently, the micro-cutting process of single-crystal copper was predicted using FE modelling by combining the crystal-plasticity theory and the proposed criterion of material removal. The validity of the present FE modelling methodology was corroborated through a comprehensive comparison between FE simulations and experimental data in terms of cutting forces, chip morphology, deformation field, pile-up patterns and misorientation angle in the work-piece

Paving the Way to Simulate and Understand the Radiochemical Damage of Porous Polymer Foam

The widespread and advanced application of polymers outshines the current ability to theoretically predict their radiation deterioration without much prior knowledge. This work presents a versatile methodology to simulate and forecast the radiochemical damage of polydimethylsiloxane (PDMS) foam. The radiolytic kinetics of PDMS foam in radiation-thermal environments is first studied by multiscale simulations with experimental verification. Then the radiolytic kinetic model of PDMS is developed via material informatics gained from experiments, reactive force field simulations, and density functional theory calculations, involving the paramount elementary reactions and other events in the physical, physicochemical, and chemical stages. The model configuration is designed to interactively couple with the service conditions and structural relationships, which enables the model to allow for the intricate radiation-thermal coupling effect, dose rate effect, and postradiation effect. To improve the adaptivity and accuracy of the model and further rationalize the radiolytic kinetics frame, the diffusion coefficients and reaction rate constants with temperature, topology, and morphology dependence are calculated. The developed radiolytic kinetic model can precisely predict the deteriorated PDMS system from various aspects simultaneously, including gas yields, radiation chemical yields, and damaged molecular structure and cross-linking network. The overall accuracy in view of the standard deviation calculated from the normalized data is less than 0.35. The proposed methodology has a promising future in nonempirical simulations, multiscale understanding, and goal-oriented harnessing of the structure–property relationships of polymers

Asymmetric Total Synthesis of Nannocystin A

Nannocystin A is a novel 21-membered macrolactone isolated from myxobacterium <i>Nanocystis</i> sp. It is a potent elongation factor 1 inhibitor and inhibits cancer cell line growth at nanomolar concentrations. In this work, a concise asymmetric total synthesis of nannocystin A has been developed, which features Sharpless epoxidation, Stille coupling, and final macrolactamization

Histone acetyltransferase (HAT) inhibitors and knockdown suppress HCV replication.

<p>HuH-7-HCV-2a J6/JFH-1(p7-rLuc2A) replicon cells were incubated with DMSO or different concentrations of p300i (<b>A</b>) or HATIIi (<b>B</b>) for 48 h. <i>Renilla</i> luciferase activity was measured and normalized to total protein amount. Statistical differences are indicated as * if <i>p</i> ≤ 0.05, *** if <i>p</i> ≤ 0.001, or <i>NS</i> for not significant. <b>(C)</b>. HuH-7-HCV-2a J6/JFH-1(p7-rLuc2A) replicon cells were transfected with non-silencing control or PCAF RNAi. At 24 h after transfection, <i>renilla</i> luciferase activity was measured and normalized to total protein amount. Statistical differences are indicated as * if <i>p</i> ≤ 0.05. <b>(D)</b>. To determine the transcript level of PCAF, RNA was extracted from HuH-7-HCV-2a J6/JFH-1(p7-rLuc2A) replicon cells 16 h after transfecting with non-silencing control or PCAF RNAi. After reverse transcription, real-time PCR experiment was performed using PCAF-specific primers. The transcript level of β-glucuronidase (GUSB) was determined in parallel and used for normalization. Statistical difference is indicated as * if <i>p</i> ≤ 0.05.</p

AnA inhibits HCV entry and release.

<p>(<b>A)</b>. HuH-7.5 cells were pretreated with DMSO and different concentrations of AnA for 12 h and infected with HCVpp-Luc for 4 h. followed by replacement by fresh medium. Luciferase activity was measured 48 h after infection and normalized to total protein amount. Statistical differences between samples are indicated as * if <i>p</i> ≤ 0.05, and ** if <i>p</i> ≤ 0.01. (<b>B)</b>. Viability of cells treated as in (<b>A)</b> was determined by MTT. <i>NS</i> = not significant. <b>(C)</b>. HuH-7-HCV-2a J6/JFH-1(p7-rLuc2A) cells were treated with DMSO and different concentrations of AnA for 5 h. After removal of inhibitors in the supernatant, HuH-7.5 cells were infected with the supernatant for 4 h followed by replacement of fresh medium. <i>Renilla</i> luciferase activity was measured 72 h after infection and normalized to total protein amount. Statistical differences are indicated as ** if <i>p</i> ≤ 0.01, or <i>NS</i> for not significant. <b>(D)</b>. Viability of cells treated as in (<b>C)</b> was determined by MTT. <i>NS</i> = not significant.</p

Vegetation and Climate Change during the Last Deglaciation in the Great Khingan Mountain, Northeastern China

<div><p>The Great Khingan Mountain range, Northeast China, is located on the northern limit of modern East Asian Summer Monsoon (EASM) and thus highly sensitive to the extension of the EASM from glacial to interglacial modes. Here, we present a high-resolution pollen record covering the last glacial maximum and the early Holocene from a closed crater Lake Moon to reconstruct vegetation history during the glacial-interglacial transition and thus register the evolution of the EASM during the last deglaciation. The vegetation history has gone through distinct changes from subalpine meadow in the last glacial maximum to dry steppe dominated by <i>Artemisia</i> from 20.3 to 17.4 ka BP, subalpine meadow dominated by Cyperaceae and <i>Artemisia</i> between 17.4 and 14.4 ka BP, and forest steppe dominated by <i>Betula</i> and <i>Artemisia</i> after 14.4 ka BP. The pollen-based temperature index demonstrates a gradual warming trend started at around 20.3 ka BP with interruptions of several brief events. Two cold conditions occurred around at 17.2–16.6 ka BP and 12.8–11.8 ka BP, temporally correlating to the Henrich 1 and the Younger Dryas events respectively, 1and abrupt warming events occurred around at 14.4 ka BP and 11.8 ka BP, probably relevant to the beginning of the Bølling-Allerød stages and the Holocene. The pollen-based moisture proxy shows distinct drought condition during the last glacial maximum (20.3–18.0 ka BP) and the Younger Dryas. The climate history based on pollen record of Lake Moon suggests that the regional temperature variability was coherent with the classical climate in the North Atlantic, implying the dominance of the high latitude processes on the EASM evolution from the Last Glacial Maximum (LGM) to early Holocene. The local humidity variability was influenced by the EASM limitedly before the Bølling-Allerød warming, which is mainly controlled by the summer rainfall due to the EASM front covering the Northeast China after that.</p></div

Direct Olefination at the C‑4 Position of Tryptophan via C–H Activation: Application to Biomimetic Synthesis of Clavicipitic Acid

The first Pd-catalyzed method for direct olefination at the C4 position of tryptophan derivatives has been developed via C–H activation to prepare 4-substituted tryptophans, which could be used for the synthesis of many hemiterpenoid indole alkaloids. This reaction proceeds under mild reaction conditions and with exceptional tolerance to a variety of functional groups. Furthermore, the efficiency of this method is demonstrated by the rapid and biomimetic synthesis of clavicipitic acid

Comparison of pollen records with the δ¹⁸O records from Greenland ice core and Chinese stalagmite.

<p>(a) The δ¹⁸O records of the Greenland ice cores [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0146261#pone.0146261.ref047" target="_blank">47</a>,<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0146261#pone.0146261.ref048" target="_blank">48</a>] (the light blue line is NGRIP δ¹⁸O profile, the dark blue line is GRIP δ¹⁸O profile), (b) the common logarithm transformation of pollen-based Temperature index (to outweigh strong variations caused by percentage maxima of <i>Betula</i> and Cyperaceae), (c) pollen percentages of arboreal (green line), steppe (orange line) and meadow (blue line) taxa, (d) pollen-based Moisture index, (e) the stalagmite δ¹⁸O records from Hulu cave [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0146261#pone.0146261.ref010" target="_blank">10</a>].</p

Simplified pollen percentage and concentration diagram of Lake Moon.

<p>Exaggeration (×10) is indicated by light-colored shading (adapted from <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0146261#pone.0146261.g002" target="_blank">Fig 2</a> of [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0146261#pone.0146261.ref029" target="_blank">29</a>]).</p