Current Transport across the Grain Boundaries of High-Field High-Temperature Micro- and Nanocrystalline Superconductors

We have fabricated micro- and nanocrystalline YBa2Cu3O7, Bi2Sr2CaCu2O8 and Bi2Sr2Ca2Cu3O10 superconductors using mechanical ball milling, hot isostatic pressing and oxygen annealing. The fabricated materials were characterised using powder x-ray diffraction, differential scanning calorimetry, thermogravimetry, resistivity, V-I traces, a.c. magnetic susceptibility and d.c. magnetic hysteresis. A new approach for measuring the resistivity of grain boundaries in polycrystalline materials is presented. The average resistivities of the grain boundaries ρ_GB in micro- and nanocrystalline YBa2Cu3O7 are much higher than that of the grains (ρ_G) which leads to huge ρ_GB/ρ_G values of 2 × 10^3 and 1.6 × 10^5 respectively. For nanocrystalline Bi2Sr2CaCu2O8 and both micro- and nanocrystalline Bi2Sr2Ca2Cu3O10 samples, ρ_GB/ρ_G is at least 10^3. Only microcrystalline Bi2Sr2CaCu2O8 has a very low ρ_GB that is similar to ρ_G such that ρ_GB/ρ_G≈1. The values of grain boundary resistivity measured in our samples were used in conjunction with a theoretical framework developed in Durham, to quantitatively calculate how high grain boundary resistivities must be to account for the decrease by several orders of magnitude in transport critical current density J_c in polycrystalline YBa2Cu3O7 and Bi2Sr2Ca2Cu3O10. We conclude that the significant effort made by the research community in texturing samples and removing the grain boundaries is well-founded. For low-temperature superconducting intermetallics such as Nb3Sn, we demonstrate that increases in J_c by two orders of magnitude is still possible by completely removing the grain boundaries from these materials and incorporating additional artificial pinning. Only large-grained polycrystalline Bi2Sr2CaCu2O8 has sufficiently low grain boundary resistivity, that cost constraints for applications may yet lead to high J_c polycrystalline materials that have artificial pinning sites or pinning produced by irradiation

Transcriptomics of Gabra4 knockout mice reveals common NMDAR pathways underlying autism, memory, and epilepsy

Autism spectrum disorder (ASD) is a neuronal developmental disorder with impaired social interaction and communication, often with abnormal intelligence and comorbidity with epilepsy. Disturbances in synaptic transmission, including the GABAergic, glutamatergic, and serotonergic systems, are known to be involved in the pathogenesis of this disorder, yet we do not know if there is a common molecular mechanism. As mutations in the GABAergic receptor subunit gene GABRA4 are reported in patients with ASD, we eliminated the Gabra4 gene in mice and found that the Gabra4 knockout mice showed autistic-like behavior, enhanced spatial memory, and attenuated susceptibility to pentylenetetrazol-induced seizures, a constellation of symptoms resembling human high-functioning autism. To search for potential molecular pathways involved in these phenotypes, we performed a hippocampal transcriptome profiling, constructed a hippocampal interactome network, and revealed an upregulation of the NMDAR system at the center of the converged pathways underlying high-functioning autism-like and anti-epilepsy phenotypes

The Cause of ‘Weak-Link’ Grain Boundary Behaviour in Polycrystalline Bi2Sr2CaCu2O8 and Bi2Sr2Ca2Cu3O10 Superconductors

The detrimental effects of grain boundaries have long been considered responsible for the low critical current densities (J_c) in high temperature superconductors. In this paper, we apply the quantitative approach used to identify the cause of the 'weak-link' grain boundary behaviour in YBa2Cu3O7 [1], to the Bi2Sr2CaCu2O8 and Bi2Sr2Ca2Cu3O10 materials that we have fabricated. Magnetic and transport measurements are used to characterise the grain and grain boundary properties of micro- and nanocrystalline material. Magnetisation measurements on all nanocrystalline materials show non-Bean-like behaviour and are consistent with surface pinning. Bi2Sr2CaCu2O8: Our microcrystalline material has very low grain boundary resistivity (ρ_GB), which is similar to that of the grains (ρ_G) such that ρ_GB≈ρ_G=2×〖10〗^(-5) Ωm (assuming a grain boundary thickness (d) of 1 nm) equivalent to an areal resistivity of ρ_G=2×〖10〗^(-14) Ωm^2. The transport J_c values are consistent with well-connected grains and very weak grain boundary pinning. However, unlike low temperature superconductors in which decreasing grain size increases the pinning along the grain boundary channels, any increase in pinning produced by making the grains in our Bi2Sr2CaCu2O8 materials nanocrystalline was completely offset by a decrease in the depairing current density of the grain boundaries caused by their high resistivity. We suggest a different approach to increasing J_c from that used in LTS materials, namely incorporating additional strong grain and grain boundary pinning sites in microcrystalline materials to produce high J_c values. Bi2Sr2Ca2Cu3O10: Both our micro- and nanocrystalline samples have ρ_GB/ρ_G of at least 10^3. This causes strong suppression of J_c across the grain boundaries, which explains the low transport J_c values we find experimentally. Our calculations show that low J_c in untextured polycrystalline Bi2Sr2Ca2Cu3O10 material is to be expected and the significant effort in the community in texturing samples and removing grain boundaries altogether is well-founded

The role of voucher sale in advance for a capital-constrained supply chain

This paper studies voucher sale as an operational method to raise working capital for a supply chain, which consists of a supplier and a capital-constrained retailer. The retailer takes advantage of an online platform to sell vouchers and to get access to borrowing from a bank. By formulating a Stackelberg game model, we show the retailer’s possible order quantities in the cases without and with bank loan and analyze the impact of voucher sale on the retailer’s optimal choice of order quantity and the supplier’s optimal wholesale price. We find that a smaller voucher’s price induces the retailer to be more likely to order with loan from a bank while a larger voucher’s value induces an order quantity with the loan more difficult to be repaid. In addition, if voucher’s price is large, the supplier decides a wholesale price which leads the retailer not to borrow from a bank; and if voucher’s price is small, the supplier’s optimal decision is obtained by anticipating the retailer to borrow from a bank. We also analyze the impact of voucher sale in the presence of trade credit financing on the firms’ decisions. The results show that the voucher’s price should be small so that the large; otherwise, the retailer either does not borrow from the supplier or may not repay the supplier. Besides, the supplier decides a wholesale price so that the retailer does not borrow or can repay the supplier, except that the voucher’s value is large and the voucher’s price is medium

Hiding or sharing? Technology upgrade, technology spillover and information asymmetry

One giant manufacturer (M1) upgrades a common supplier’s production technology through investments, while the supplier (it), holding the technology spillover information privately, may spill the upgraded technology over to a rival manufacturer (M2). This study examines whether the supplier should share the information of technology spillover with M1. We first find technology spillover hurts not only M1 but also the supplier and M2, when the production cost is high and the investment cost is low at a high level of the real technology spillover degree, no matter whether the supplier shares the technology spillover information or not. As such, it may be unwise for the supplier to implement technology spillover and unprofitable for M2 to take a free ride of technology spillover conditionally. Furthermore, when the supplier can receive more payoffs by spilling the upgraded technology over to M2 under certain conditions, it should share (hide) the technology spillover information, and such sharing (hiding) strategy may create a “win-win-win”’ outcome for the three players, if the supplier is of low (high)-spillover type and the real degree of technology spillover falls into a high range

Isolation and Characterization of a Novel Four-Transmembrane Protein PMP22CD Specifically Expressed in the Testis

PMP22_Claudin family proteins play important roles in cell tight junction. In thisstudy, we have identified a novel member of this family, PMP22CD. Human PMP22CD wasfirst discovered by database sequence mining and analysis, and verified by cloning andsequencing. PMP22CD was isolated from the human testis cDNA library and mapped tochromosome 11q24.1 by browsing the UCSC genomic database. It contains an ORF with alength of 675bp, encoding a protein that contains a putative PMP22_Claudin domain withfour transmembrane helices. Its molecular weight and isoelectric point are predicted to be25.8kDa and 8.42, respectively. The PMP22CD protein is highly conservative in mammalanimals. Phylogenetic tree analysis indicated that PMP22CD stands for a new subgroup inthe PMP22/EMP/Claudin family. RT-PCR analysis showed that PMP22CD was specificallyexpressed in the testis. Green fluorescence protein localization analysis showed thatPMP22CD mainly surrounded the nuclear membrane, with a minority distribution in thecytoplasm. These results suggested that PMP22CD is a distant member of thePMP22/EMP/Claudin family and that it may have a novel function that does not involve celltight junction because it is not located at the cell membrane