Accelerated formation of an ultrafine-grained structure in a two-phase Ti alloy during compression with decreasing temperatures

ABSTRACT

Ultrafine-grained (UFG) structure is beneficial for overcoming the strength-ductility trade-off and enhancing the superplasticity of two-phase Ti alloys. Recently, it has been demonstrated that compression with decreasing temperatures is effective for producing UFG two-phase Ti alloys initially with lamellar microstructures. However, the effect of lamellar thickness on the microstructural evolution during this process has not yet been fully elucidated. In this study, Ti-6Al-4V alloys with different lamellar thicknesses were compressed while the processing temperature was decreased from 800°C to 600°C. The thinner lamellar microstructure was preferable for preventing void/crack formation, while accelerating the continuous dynamic recrystallisation, thus providing a fully UFG structure at a relatively low strain of 1.4. In addition, the origin of different plastic flows in each sample was analysed in detail by analysing the microstructural evolution. These findings demonstrate that the processing method is effective for reducing the grain size of a two-phase Ti alloy without severe plastic deformation techniques, which require large strain (≥4). A reduction in the strain required to achieve the UFG structure would be beneficial because conventional metal-forming processes, i.e. rolling, extrusion, or forging, which are suitable for mass production, could be used.     

The origin of photoluminescence in Ge-implanted SiO2 layers

Ge ions were implanted at 100 keV with 3×10¹⁶ cm⁻² into a 300  nm thick SiO₂ layer on Si. Visible photoluminescence (PL) around 2.1 eV from an as-implanted sample is observed, and faded out by subsequent annealing at 900°C for 2 h. However, PL shows up again after annealing above 900°C at the same peak position. Compared with the as-implanted sample, significant increase of Ge–Ge bonds is measured in X-ray photoelectron spectroscopy, and the formation of Ge nanocrystals with a diameter of 5 nm are observed in transmission electron microscopy from the sample annealed at 1100°C. We conclude that the PL peak from the sample annealed above 900°C is caused by the quantum confinement effects from Ge nanocrystals, while the luminescence from the as-implanted sample is due to some radiative defects formed by Ge implantation.     

In Situ Self-Assembly of Quantum Dots at the Plasma Membrane Mediates Energy Transfer-Based Activation of Channelrhodopsin

The use of nanoparticle (NP) bioconjugates to control the activity of membrane ion channels has recently emerged as a new paradigm for the activation of electrically excitable cells. An NP-based strategy is reported for the specific activation of channelrhodopsin C1V1 (ChR-C1V1) expressed in the plasma membrane of HEK 293T/17 cells. Hydrophilic CdSe/ZnS core–shell semiconductor quantum dots (QDs) are self-assembled to the exofacial face of recombinantly expressed ChR-C1V1 by metal affinity-driven interaction of the QD ZnS shell with an N-terminal hexahistidine tag displayed on ChR-C1V1. This configuration enables the Förster resonance energy transfer (FRET)-based excitation and activation of the 11-cis-retinal moiety of ChR-C1V1 using the QD as a light harvesting transducer/energy donor. It is shown that the specific laser-induced opening of the ChR-C1V1 channel wherein the photoexcited QD (405 nm excitation, 530 nm emission) iteratively activates ChR-C1V1 channels as confirmed using the voltage-sensitive dye (VSD) bis-(1,3-diethylthiobarbituric acid)trimethine oxonol (DiSBAC ₂ (3)). In the absence of the QD transducer, excitation of ChR-C1V1-expressing cells at 405 nm results in no activation of ChR-C1V1. The results demonstrate the ability to controllably interface QDs with living cells for the activation of ChR membrane proteins and detail a new NP-bioconjugate hybrid system for the specific activation of ion channels.     

Finiteness theorems for positive definite -regular quadratic forms

An integral quadratic form of variables is said to be -regular if globally represents all quadratic forms of variables that are represented by the genus of . For any , it is shown that up to equivalence, there are only finitely many primitive positive definite integral quadratic forms of variables that are -regular. We also investigate similar finiteness results for almost -regular and spinor -regular quadratic forms. It is shown that for any , there are only finitely many equivalence classes of primitive positive definite spinor or almost -regular quadratic forms of variables. These generalize the finiteness result for 2-regular quaternary quadratic forms proved by Earnest (1994).

     

The reactionsK − p→π ∓ Σ(1385)± at 8.25 GeV/c

The reactionsK ^? p→π ^? Σ(1385)^± are studied at an incident laboratory momentum of 8.25 GeV/c using data from a high statistics (?180 events/μb) bubble chamber experiment. In the case of the reactionK ^? p→π ^? Σ(1385)⁺ an amplitude analysis is performed and the complete Σ(1385)⁺ spin density matrix is extracted as a function oft′. The results are compared with the predictions of the additive quark model. In the case of the reactionK ^? p→π ⁺ Σ(1385)^? the cross-sections for forward and backward production are determined.     

Fluoride-catalyzed hydroalkoxylation of hexafluoropropene with 2,2,2-trifluoroethanol

Trifluoroethoxylation of hexafluoropropene with 2,2,2-trifluoroethanol (TFE) were conducted using an alkali metal fluoride catalyst to produce CF₃CHFCF₂OCH₂CF₃. KF exhibited the highest yield and selectivity of CF₃CHFCF₂OCH₂CF₃, whereas LiF and NaF were inactive for the trifluoroethoxylation reaction. The same reaction also proceeded well in the presence of RbF or CsF, but yielded large amounts of olefinic and high molecular weight side products, implying that the size of alkali metal cation or the degree of MF dissociation plays an important role in determining the activity and the product composition. FT-IR and NMR experiments revealed that CsF interacts with TFE more strongly than KF through a hydrogen bonding. The experimental and spectroscopic results suggest that the degree of MF dissociation should be in the medium range for the selective production of CF₃CHFCF₂OCH₂CF₃ in high yield and selectivity.     

Angular intensity distribution of a molecular oxygen beam scattered from a graphite surface

The scattering of the oxygen molecule from a graphite surface has been studied using a molecular beam scattering technique. The angular intensity distributions of scattered oxygen molecules were measured at incident energies from 291 to 614 meV with surface temperatures from 150 to 500 K. Every observed distribution has a single peak at a larger final angle than the specular angle of 45° which indicates that the normal component of the translation energy of the oxygen molecule is lost by the collision with the graphite surface. The amount of the energy loss by the collision has been roughly estimated as about 30-41% based on the assumption of the tangential momentum conservation during the collision. The distributions have also been analyzed with two theoretical models, the hard cubes model and the smooth surface model. These results indicate that the scattering is dominated by a single collision event of the particle with a flat surface having a large effective mass. The derived effective mass of the graphite surface for the incoming oxygen is 9-12 times heavier than that of a single carbon atom, suggesting a large cooperative motion of the carbon atoms in the topmost graphene layer.     

KR-31543 reduces the production of proinflammatory molecules in human endothelial cells and monocytes and attenuates atherosclerosis in mouse model

KR-31543, (2S, 3R, 4S)-6-amino-4-[N-(4-chlorophenyl)-N-(2-methyl-2H-tetrazol-5-ylmethyl) amino]-3,4-dihydro-2-dimethyoxymethyl-3-hydroxy-2-methyl-2H-1-benz opyran is a new neuroprotective agent for ischemia-reperfusion damage. It has also been reported that KR-31543 has protective effects on lipid peroxidation and H₂O₂-induced reactive oxygen species production. In this study, we investigated the anti-inflammatory and anti-atherogenic properties of KR-31543. We observed that KR-31543 treatment reduced the production of MCP-1, IL-8, and VCAM-1 in HUVECs, and of MCP-1 and IL-6 in THP-1 human monocytes. We also examined the effect of KR-31543 on monocytes migration in vitro. KR-31543 treatment effectively reduced the migration of THP-1 human monocytes to the HUVEC monolayer in a dose-dependent manner. We next examined the effects of this compound on atherogenesis in LDL receptor deficient (Ldlr^-/-) mice. After 10 weeks of western diet, the formation of atherosclerotic lesion in aorta was reduced in the KR-31543-treated group compared to the control group. The accumulation of macrophages in lesion was also reduced in KR-31543 treated group. However, the plasma levels of total cholesterol, HDL, LDL, and triglyceride were not affected by KR-31543 treatment. Taken together, these results show that KR-31543 has anti-inflammatory properties on human monocytes and endothelial cells, and inhibits fatty streak lesion formation in mouse model of atherosclerosis, suggesting the potential of KR-31543 for the treatment for atherosclerosis.     

Plastic enzyme-linked immunosorbent assays (ELISA)-on-a-chip biosensor for botulinum neurotoxin A

A plastic ELISA-on-a-chip (EOC) employing the concept of cross-flow immuno-chromatographic analysis was applied to the measurement of botulinum neurotoxin A (BoNT/A) as agent for bio-terrorism. Two monoclonal antibodies specific to the heavy chain of the toxin were raised and identified to form sandwich binding complexes as the pair with the analyte. For the construction of an immuno-strip, one was utilized as the capture antibody immobilized onto nitrocellulose membrane and the other as the detection coupled to an enzyme, horseradish peroxidase. The two plates of EOC used in this study were fabricated by injection molding of polycarbonate to improve the reproducibility of manufacture and, after inclusion of the immuno-strip, bonded using a UV-sensitive adhesive. Under optimal conditions of analysis, the chip produced a color signal in proportion to the analyte dose and the signal was quantified using a detector equipped with a digital camera. From the dose-response curve, the detection limit of BoNT/A was 2.0 ng mL⁻¹, approximately five times more sensitive than a commercial-version detection kit employing colloidal gold tracer.