Influence of Intermetallic Particles on the Corrosion Properties of Extruded ZK60 Mg Alloy Containing Cu

The microstructure and corrosion behavior of the extruded ZK60 Mg alloys with different Cu content were comparatively investigated. The ZK60 alloy had a microstructure consisting of ??-Mg grains with intermetallic MgZn2 and Zn2Zr3 particles. The addition of 1 wt % Cu resulted in the additional presence of CuMgZn particles. In a 0.6 M NaCl solution at 25 ??C, the corrosion rate of the alloy with the added Cu appeared to be about 16% faster than that of the alloy without the addition of Cu. The factors affecting the degraded corrosion resistance of the Cu-added ZK60 alloy are discussed

Quantum-based Mechanical Force Realization in Pico-Newton Range

We propose mechanical force realization based on flux quantization in the pico-Newton range. By controlling the number of flux quantum in a superconducting annulus, a force can be created as integer multiples of a constant step. For a 50 nm-thick Nb annulus with the inner and outer radii of 5 $\mu$m and 10 $\mu$m, respectively, and the field gradient of 10 T/m the force step is estimated to be 184 fN. The stability against thermal fluctuations is also addressed.Comment: 5 pages; 4 figure

Reduction of metabolic waste products, ammonia and lactate, through the coupling of GS selection and LDH-A down-regulation in CHO cells

The cultivation of Chinese hamster ovary (CHO) cells for the production of therapeutic proteins inevitably accompanies the production of metabolic wastes, mostly ammonia and lactate. Ammonia alters cell growth, productivity and the glycosylation patterns of proteins, and lactate acidifies culture media, having negative effects on cell culture. A stable CHO cell line should be established for the manufacturing process of therapeutic proteins, and the development of stable cell lines is usually based on two expression systems: the dihydrofolate reductase (DHFR) system and the glutamine synthetase (GS) system. Compared to the DHFR system, the GS system produces a reduced level of ammonia because the GS protein uses ammonia to produce glutamine. In order to overcome the lactate accumulation problem, down-regulation of the lactate-producing enzyme, lactate dehydrogenase-A (LDH-A), has been shown to be effective. Engineering of the LDH-A gene has been applied for several CHO cell lines with the DHFR system, but there has been no trial which couples the ammonia reduction from the GS system and lactate reduction through cell engineering. In the present study, the GS system was used for the expression of therapeutic antibody in CHO cells, thereby reducing ammonia in the culture media. In addition, the LDH-A gene was down-regulated with shRNA to reduce lactate production. The antibody-producing cell line produces a reduced level of ammonia compared to the host cell line due to the over-expression of the GS protein. The down–regulation of the LDH-A gene in the antibody-producing cell line not only reduces the level of lactate but also further reduces the level of ammonia, accomplishing complete waste reduction. LDH-A down-regulation was also applied to the host cell lines of the GS system – the CHO-K1 cell line and the GS deficient CHO-K1 cell line. However, LDH-A down-regulated host cells could not survive the pool-selection process. Given that the GS system uses a glutamine-depleted condition as a form of selection pressure, enhanced glycolysis is inevitable and the down-regulation of LDH-A appears to hinder metabolic changes. Taken together, the application of LDH-A down-regulation in the producing cell line of the GS system successfully reduced both ammonia and lactate levels. However, LDH-A engineering could not be applied to the host cell lines because it inhibits the selection process of the GS system

Phase-field Models for Solidification and Solid/Liquid Interactions

The microstructure resulting from the solidification of alloys can greatly affect their properties, making the prediction of solidification phenomena under arbitrary conditions a very important tool in the field of computer-aided design of materials. Although considerable attention has been allocated to the understanding of this phenomenon in cases in which the solidification front advances freely into the liquid, the actual microstructure of solidification is strongly dependent of interfacial interactions. Over the past decade, the phase-field approach has been proved to be a quite effective tool for the simulation of solidification processes. In phase-field models, one or more phase fields ø (conserved and/or non-conserved) are introduced to describe the microstructure of a complex system. The behavior of a given microstructure over time is then simulated by solving evolution equations written in terms of the minimization of the free energy of the entire system, which is written as a functional of the field variables as well as their gradients and materials’ constitutive equations. With the given free energy functional, the governing equations (phase-field equation, diffusion equation, heat equation and so on) are solved throughout the entire space domain without having to track each of the interfaces formed or abrupt changes in the topology of the microstructure. In this work I will present phase-field models for solidification processes, solid/liquid interactions as well as their applications