65 research outputs found

    Microstructure control in Sn-0.7mass%Cu alloys

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    Soldering alloys based oft the Sn-Cu alloy system are amongst the most favourable lead-free alternatives due to a range of attractive properties. Trace additions of Ni have been found to significantly improve the soldering characteristics of these alloys (reduced bridging etc.). This paper examines the mechanisms underlying the improvement in soldering properties of Sn-0.7 mass%Cu eutectic alloys modified with concentrations of Ni ranging front 0 to 1000 ppm. The alloys were investigated by thermal analysis during solidification, as well as optical/SEM microanalyses of fully solidified samples anti samples quenched during solidification. It is concluded that Ni additions dramatically alter the nucleation patterns and solidification behaviour of the Sn-Cu6Sn5 eutectic anti that these changes are related to the superior soldering characteristics of the Ni-modified Sn-0.7 mass%Cu alloys

    Elicitin-responsive lectin-like receptor kinase genes in BY-2 cells

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    The inhibition of elicitor-induced plant defense responses by the protein kinase inhibitors K252a and staurosporine indicates that defense responses require protein phosphorylation. We isolated a cDNA clone encoding Nicotiana tabacum lectin-like receptor protein kinase 1 ( NtlecRK1), an elicitor-responsive gene; in tobacco bright yellow ( BY-2) cells by a differential display method. NtlecRK forms a gene family with at least three members in tobacco. All three NtlecRK genes potentially encode the N-terminal legume lectin domain, transmembrane domain and C-terminal Ser/Thr-type protein kinase domain. Green fluorescent protein ( GFP) fusion showed that the NtlecRK1 protein was located on the plasma membrane. In addition, NtlecRK1 and 3 were responsive to INF1 elicitin and the bacterial elicitor harpin. These results indicate that NtlecRKs are membrane-located protein kinases that are induced during defense responses in BY-2 cells.</p

    Suppression of Cdc27B expression induces plant defence responses

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    Non-host resistance is the most general form of disease resistance in plants because it is effective against most phytopathogens. The importance of hypersensitive responses (HRs) in non-host resistance of Nicotiana species to the oomycete Phytophthora is clear. INF1 elicitin, an elicitor obtained from the late-blight pathogen Phytophthora infestans, is sufficient to induce a typical HR in Nicotiana species. The molecular mechanisms that underlie the non-host resistance component of plant defence responses have been investigated using differential-display polymerase chain reaction (PCR) in a model HR system between INF1 elicitin and tobacco BY-2 cells. Differential-display PCR has revealed that Cdc27B is down-regulated in tobacco BY- 2 cells after treatment with INF1 elicitin. Cdc27B is one of 13 essential components of the anaphase- promoting complex or cyclosome ( APC/ C)-type E3 ubiquitin ligase complex in yeast. This APC/C-type E3 ubiquitin ligase complex regulates G2-to-M phase transition of the cell cycle by proteolytic degradation. In this study, we investigated the roles of this gene, NbCdc27B, in plant defence responses using virus-induced gene silencing. Suppression of NbCdc27B in Nicotiana benthamiana plants induced defence responses and a gain of resistance to Colletotrichum lagenarium fungus. Elicitin-induced hypersensitive cell death (HCD) was inhibited mildly in plants silenced with tobacco rattle virus:: Cdc27B. Cdc27B could manage the signalling pathways of plant defence responses as a negative regulator without HCD.</p

    Effect of intermetallic stabilization on the impact resistance of joints to BGA packages

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    To the extent that it provides a potential low energy route for crack propagation the intermetallic compound that forms at the interface between a tin-based solder and the substrate can play a critical role in determining the likelihood of joint failure in impact loading such as can occur when portable devices are accidentally dropped. While it has been clearly documented in the standard equilibrium phase diagrams the implication of the allotropic change in the Cu6Sn5 intermetallic from a closepacked hexagonal to monoclinic crystal structure at 186° C with an accompanying 2.15% increase in volume has been found to have implications for the mechanical integrity of the interfacial intermetallic that were not previously recognized. In this paper the authors report the effect of a trace addition of Ni in permanently stabilizing the high-temperature form of the Cu6Sn5 to room temperature on the response to high speed shear of Sn-0.7Cu spheres reflowed to a copper substrate. By reducing the incidence of incipient cracking in the intermetallic layer the stress required to initiate cracking and the energy required for crack propagation are significantly increased with consequent benefits for the impact resistance of the solder joint

    The influence of solder composition on the impact strength of lead-free solder BGA joints

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    At the interface between Sn-based solders and substrates, intermetallic compounds (IMCs) form and grow during soldering operations and subsequent use. Such IMCs provide a metallurgical bond, and their interface microstructure has a critical effect on solder joint mechanical reliability. In the present study, the impact strength of BGA solder joints between (i) Cu substrates and Sn-Cu solders and (ii) Cu substrates and Sn-Cu-Ni solders has been evaluated using shear and tensile ball tests and Finite Element Modelling. In both tests, connections made using Sn-Cu-Ni solders show consistently better properties than those made using Sn-Cu solders, particularly at high displacement rates. Microstructural analysis and fractography are used to interpret the results and develop the FEM

    Synthesis and structure–activity studies of simplified analogues of aplysiatoxin with antiproliferative activity like bryostatin-1

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    Protein kinase C (PKC) isozymes are promising targets for anticancer therapy. Bryostatin-1 (bryo-1), a unique PKC activator with little tumor-promoting activity, is currently in clinical trials for the treatment of cancer. However, its limited availability from natural sources and its synthetic complexity have hampered studies of its mode of action and structural optimization as a therapeutic agent. The development of synthetically more accessible compounds with bryo-1-like activities is thus needed. Recently, we developed a simple and less lipophilic analogue of tumor-promoting aplysiatoxin (ATX) (aplog-1) as a promising lead for bryo-1-like anticancer drugs. Structure–activity studies suggested that local hydrophobicity around the spiroketal moiety of aplog-1 is a crucial determinant of its antiproliferative activity. The hydrophobic analogue (12,12-dimethyl-aplog-1) displayed more potent antiproliferative activity. Moreover, it showed little tumor-promoting activity and even suppressed the tumor promotion by 12-O-tetradecanoylphorbol 13-acetate (TPA) in vivo and in vitro. Aplog-1 and bryo-1 bound selectively to novel PKC isozymes (δ, η, and θ) while tumor promoters bound to both conventional and novel PKC isozymes. These results suggest that the unique biological activities of aplog-1 and bryo-1 are ascribable in part to the ability to bind to PKCδ, but weak binding to conventional PKC isozymes might also be important
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