Study on the microstructural evolution of different component alloys consisting of B2-NiSc intermetallics

Ni-50%Sc and Ni-51%Sc alloy were prepared with a vacuum arc smelting and water cooled copper mold suction-casting machine. The results showed that the two component alloys consisted of the primary phase B2-NiSc and lamellar (Ni2Sc+NiSc)eutectic due to the loss of Sc duringmelting. Two groups of alloys underwent (970 ℃, 72 h) homogenization heat treatment, and spherical or plate shape Ni2Sc particles were dispersed on the B2-NiSc matrix. With the increase of Sc content from50% to 51%, the amount of the second phase in the alloy decreases, the microstructure becomes uniform, and the grain gradually changes from long bar to a spherical particle. According to the Jackson boundary theory, the Jackson factor α of B2-NiSc =0.5 < 2, so the interface is rough, which explains that the growth pattern of the B2-NiSc phase is anon-faceted growth. It is consistent with the dendritic growth pattern of the B2-NiSc phase, which is observed from the experiment. After a longheat treatment, the number of vacancies decreases and the microstructure became uniform. The loss rate of Sc in rapidly quenched solidification was higher than that after the heat treatment

Analytical Solution of Poisson's Equation with Application to VLSI Global Placement

Poisson's equation has been used in VLSI global placement for describing the potential field caused by a given charge density distribution. Unlike previous global placement methods that solve Poisson's equation numerically, in this paper, we provide an analytical solution of the equation to calculate the potential energy of an electrostatic system. The analytical solution is derived based on the separation of variables method and an exact density function to model the block distribution in the placement region, which is an infinite series and converges absolutely. Using the analytical solution, we give a fast computation scheme of Poisson's equation and develop an effective and efficient global placement algorithm called Pplace. Experimental results show that our Pplace achieves smaller placement wirelength than ePlace and NTUplace3. With the pervasive applications of Poisson's equation in scientific fields, in particular, our effective, efficient, and robust computation scheme for its analytical solution can provide substantial impacts on these fields

Effect of cooling rate on microstructure of B2-NiSc intermetallics

Ni-50at%Sc alloy was prepared by centrifugal casting method. Volume fraction, the actual content of B2-NiSc and second phase Ni2Sc in alloy were analyzed with an Image-Pro Plus software. The cooling rates for the solidified thin plate with thickness of 2.65mm, 1.2mm, 0.75mm and 0.35 mm are 1164, 2570, 4112 and 8811 K·s- 1, respectively. It is found that d=0.5 mm was an critical dimension which corresponds to an abrupt change in the solidification rate. It is also found that (Ni2Sc+NiSc)eutectic was dispersed at grain boundary or between dendritic arms due to the loss of Sc element during melting. While d＞ 0.5mm (corresponding to the thin plate with thickness of 0.75mm, 1.20mm and 2.65 mm), the solidification structure consists of primary phase B2-NiSc and (Ni2Sc+NiSc)eutectic. While d ＜ 0.5mm (corresponding to the thin plate with thickness of 0.35 mm), the solidification structure is composed of fine globular B2-NiSc and relatively small amounts of (Ni2Sc+NiSc)eutectic. Based on the phase volumetric analyzing of the microstructure with an Image-Pro Plus software, the loss of Sc element during melting was about 3.01~3.10 at%. The eutectic NiSc in the lamellar eutectic structure together with the primary phase B2-NiSc form a larger single phase NiSc, while Ni2Sc with the form of particles is distributed on the grain boundaries after (970 ℃, 72 h) homogenization heat treatment

A new grinding force model for micro grinding RB-SiC ceramic with grinding wheel topography as an input

The ability to predict grinding force for hard and brittle materials is important to optimize and control the grinding process. However, it is a difficult task to establish a comprehensive grinding force model that takes into account of brittle fracture, grinding conditions and random distribution of grinding wheel topography. Therefore, this study developed a new grinding force model for micro-grinding of RB-SiC ceramics. First, the grinding force components and grinding trajectory were analyzed based on the critical depth of rubbing, ploughing and brittle fracture. Afterwards, the corresponding individual grain force were established and the total grinding force was derived through incorporating the single grain force with dynamic cutting grains. Finally, a series of calibration and validation experiments were conducted to obtain the empirical coefficient and verify the accuracy of the model. It was found that ploughing and fracture were the dominate removal modes, which illustrate the force components decomposed is correct. Furthermore, the values predicted according to proposed model are consistent with the experimental data, with the average deviation of 6.793% and 8.926% for the normal and tangential force, respectively. This suggests that the proposed model is acceptable and can be used to simulate the grinding force for RB-SiC ceramics in practical

Observation of interlayer phonon modes in van der Waals heterostructures

We have investigated the vibrational properties of van der Waals heterostructures of monolayer transition metal dichalcogenides (TMDs), specifically MoS2/WSe2 and MoSe2/MoS2 heterobilayers as well as twisted MoS2 bilayers, by means of ultralow-frequency Raman spectroscopy. We discovered Raman features (at 30 ~ 40 cm-1) that arise from the layer-breathing mode (LBM) vibrations between the two incommensurate TMD monolayers in these structures. The LBM Raman intensity correlates strongly with the suppression of photoluminescence that arises from interlayer charge transfer. The LBM is generated only in bilayer areas with direct layer-layer contact and atomically clean interface. Its frequency also evolves systematically with the relative orientation between of the two layers. Our research demonstrates that LBM can serve as a sensitive probe to the interface environment and interlayer interactions in van der Waals materials

Laser-assisted grinding of reaction-bonded SiC

The paper presents development of a novel laser-assisted grinding process to reduce surface roughness and subsurface damage in grinding reaction-bonded (RB)-SiC. A thermal control approach is proposed to facilitate the process development, in which a two-temperature model is applied to control the required laser power to thermal softening of RB-SiC prior to grinding operation without melting the workpiece or leaving undesirable microstructural alteration, while Fourier's law is adopted to obtain the thermal gradient for verification. An experimental comparison of conventional grinding and laser-assisted grinding shows significant reduction of machined surface roughness (37%-40%) and depth of subsurface damage (SSD) layer (22%-50.6%) using the thermal control approach under the same grinding conditions. It also shows high specific grinding energy 1.5 times that in conventional grinding at the same depth of cut which accounts for the reduction of subsurface damage as it provides enough energy to promote ductile-regime material removal

Effects of α-lipoic acid on growth performance, body composition, antioxidant status and lipid catabolism of juvenile Chinese mitten crab Eriocheir sinensis fed different lipid percentage

This manuscript version is made available under the CC-BY-NC-ND 4.0 license http://creativecommons.org/licenses/by-nc-nd/4.0/ This author accepted manuscript is made available following 24 month embargo from date of publication (Sept 2017) in accordance with the publisher’s archiving policyThis study evaluates the effects of dietary lipid percentage (7% and 13%) on growth performance, body composition, antioxidative status and hepatopancreas lipid catabolism of Chinese mitten crab Eriocheir sinensis. Each lipid diet was supplemented with three concentrations of α-lipoic acid at 0, 700 and 1400 mg/kg, and fed to E. sinensis juveniles for eight weeks. The weight gain and specific growth rate of crabs fed the diets supplemented with α-LA were significantly higher than those fed the control diet without α-LA, regardless of dietary lipid percentage. The α-LA significantly increased lipid accumulation in the whole body and hepatopancreas in a dose-dependent manner. Crabs fed 13% lipid showed a significantly higher hepatosomatic index than those fed 7% lipid. The mRNA expressions of triacylglycerol lipase and intracellular lipase increased with the increase of α-LA concentration in crabs fed 7% lipid. No significant difference was found in the CPT-1 mRNA expression among all treatments. The α-LA supplementation at 1400 mg/kg significantly improved oxidative stress due to lipid accumulation in the hepatopancreas of crabs fed 7% lipid as indicated by the high activity of superoxide dismutase and glutathione peroxidase and a low level of malondialdehyde. The diet with 13% lipid increased the lipid content in the hepatopancreas but suppressed glutathione peroxidase. Meanwhile, the total antioxidant capacity increased with the increase of α-LA concentration in crabs fed 13% lipid. This study indicates that α-LA supplementation can improve growth performance and accelerate lipid accumulation in the hepatopancreas by increasing lipid utilization efficiency. Furthermore, α-LA can relieve hepatopancreas oxidative damage induced by lipid accumulation and improve the health of E. sinensis

Material removal mechanism of laser-assisted grinding of RB-SiC ceramics and process optimization

Laser-assisted grinding (LAG) is a promising method for cost-effective machining of hard and brittle materials. Knowledge of material removal mechanism and attainable surface integrity are crucial to the development of this new technique. This paper focusing on the application of LAG to Reaction Bonded (RB)-SiC ceramics investigate the material removal mechanism, grinding force ratio and specific grinding energy as well as workpiece surface temperature and surface integrity, together with those of the conventional grinding for comparison. Response surface method and genetic algorithm were used to optimize the machining parameters, achieving minimum surface roughness and subsurface damage, maximum material removal rate. The experiments results revealed that the structural changes and hardness decrease enhanced the probability of plastic removal in LAG, therefore obtained better surface integrity. The error of 3-D finite element simulation model that developed to predict the temperature gradient produced by the laser radiation is found to be within 2.7%-15.8%

Prevailing I292V PB2 mutation in avian influenza H9N2 virus increases viral polymerase function and attenuates IFN-β induction in human cells

Adaptation of PB2 protein is important for the establishment of avian influenza viruses in mammalian hosts. Here, we identify I292V as the prevalent mutation in PB2 of circulating avian H9N2 and pandemic H1N1 viruses. The same dominant PB2 mutation is also found in most human isolates of emergent avian H7N9 and H10N8 viruses. In human cells, PB2-292V in H9N2 virus has the combined ability of conferring higher viral polymerase activity and stronger attenuation of IFN-β induction than that of its predecessor PB2-292I. IFN-β attenuation is accompanied by higher binding affinity of PB2-292V for host mitochondrial antiviral signalling protein, an important intermediary protein in the induction of IFN-β. In the mouse in vivo model, PB2-292V mutation increases H9N2 virus replication with ensuing increase in disease severity. Collectively, PB2-292V is a new mammalian adaptive marker that promotes H9N2 virus replication in mammalian hosts with the potential to improve transmission from birds to humans

Magnons and magnetic fluctuations in atomically thin MnBi2Te4

MnBi2Te4, referred to as MBT, is a van der Waals material combining topological electron bands with magnetic order. Here, Lujan et al study collective spin excitations in MBT, and show that magnetic fluctuations increase as samples reduce in thickness, implying less robust magnetic order. Electron band topology is combined with intrinsic magnetic orders in MnBi2Te4, leading to novel quantum phases. Here we investigate collective spin excitations (i.e. magnons) and spin fluctuations in atomically thin MnBi2Te4 flakes using Raman spectroscopy. In a two-septuple layer with non-trivial topology, magnon characteristics evolve as an external magnetic field tunes the ground state through three ordered phases: antiferromagnet, canted antiferromagnet, and ferromagnet. The Raman selection rules are determined by both the crystal symmetry and magnetic order while the magnon energy is determined by different interaction terms. Using non-interacting spin-wave theory, we extract the spin-wave gap at zero magnetic field, an anisotropy energy, and interlayer exchange in bilayers. We also find magnetic fluctuations increase with reduced thickness, which may contribute to a less robust magnetic order in single layers.We thank Chao Lei, B. Wieder, A. Ernst, and M. G. Vergniory for helpful discussions. This research was primarily supported by the National Science Foundation through the Center for Dynamics and Control of Materials: an NSF MRSEC under Cooperative Agreement No. DMR-1720595, which also supported the facility used in sample preparation. Additional support from NSF DMR-1949701 and DMR-2114825 is gratefully acknowledged by G.A.F. This work was performed in part at the Aspen Center for Physics, which is supported by the National Science Foundation grant PHY-1607611. A.L. acknowledges support from the funding grant: PID2019-105488GB-I00. Z.Y. and R.H. acknowledge support by the NSF CAREER Grant No. DMR-1760668 and NSF Grant No. DMR-2104036. X.L. gratefully acknowledges the Welch Foundation grant F-1662 for support in sample preparation. Work at ORNL was supported by the U.S. Department of Energy, Office of Science, Basic Energy Sciences, Materials Sciences and Engineering Division. M. R-V. was supported by LANL LDRD Program and by the U.S. Department of Energy, Office of Science, Basic Energy Sciences, Materials Sciences and Engineering Division, Condensed Matter Theory Program. L.-J.C. and S.-F.L. were primarily funded by the Ministry of Science and Technology 105-2112-M-001-031-MY3 in Taiwan, and the collaboration with UT-Austin is facilitated by the Air Force Office of Scientific Research under award number FA2386-21-1-4067. Partial funding for L.-J.C. while visiting UT-Austin was provided by a Portugal-UT collaboration grant