Impression creep behavior of different zones in friction stir welded Mg–Zn–Mn wrought alloy

The friction stir welded joint of wrought ZM21 alloy was divided into five parts, and their localized creep behavior was studied via the impression method. The tests were carried out in the stress range of 300–450 MPa (σ_imp/G ≈ 0.02–0.03) and in the temperature range of 448–523 K. Optical and SEM micrographs and EDS taken before and after the impression tests were used to study the microstructure of various zones of the FS welded joint. Power law was found to satisfactorily relate the stress and strain rates. The steady-state impression velocity was found to vary significantly between the advancing and retreating sides of TMAZ and HAZ. For TMAZ, the creep exponent on the AS was 4.8, and on the RS, it was 7.8. The activation energy on the AS was ~?133 kJ/mol, and on the RS, it was ~?101 kJ/mol. Similarly, for HAZ, the creep exponent on the AS was found to be 5.5 and on the RS, it was 4.9. The activation energy on the AS was ~?86 kJ/mol and on the RS, it was ~?232 kJ/mol. The cross-over of steady-state impression velocity of different zones indicates that the weak zone was temperature and stress dependent. Within the stresses and temperatures studied, the weld zone's creep resistance (i.e., lower minimum impression velocity) was found to be better than the base material. As it is with most magnesium alloys, dislocation climb was found to be the operative mechanism in the FS weldments of ZM21 alloy. The rate-controlling mechanism remains to be identified because the wide variation in n and Q values suggests that different creep mechanisms are in operation in different zones.

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Impression Creep Behavior of an Mg–Zn–RE Alloy at Elevated Temperatures

Mg–Zn–RE alloys are promising candidates for automotive and aerospace applications as, among magnesium alloys, they have better corrosion and creep resistance abilities at elevated temperatures. This study evaluates the high-temperature creep behavior of ZE41 magnesium alloy, belonging to the Mg–Zn–RE family, using impression test. Impression tests were performed under a constant temperature and stress with a flat-ended cylindrical punch. Power law and Eyring relationships were used to analyze the creep mechanism. By applying the power-law relationship, it was found that the creep exponent decreased from 7.5 to 4 in the temperature range of 493 K to 593 K. Activation energy increased from 78.5 to 107.1 kJ/mol in the applied stress range of 350 to 500 MPa (normalized stress: 0.024 ≤ σ_imp/G ≥ 0.034). Using the Eyring relationship, a single activation energy of 25 kJ/mol for the entire stress and temperature range was obtained. Based on the creep exponent and activation energy, it is proposed that pipe-diffusion-controlled dislocation climb is the dominant mechanism, but grain boundary sliding also contributes at higher stresses.

     

Persuasive social features that promote knowledge sharing among tertiary students on social networking sites: An empirical study

Persuasive system features have been widely adopted to encourage attitude and behaviour change. Recently, most social networking sites (SNS) adopt some form of persuasive system features that leverage social influence to deliberately induce prescribed behaviours in their users. However, studies on how these features can be used to promote knowledge sharing are inadequate; particularly, regarding how SNS that have been developed solely for academic purposes can adopt these features to promote knowledge sharing. To address this knowledge gap, this study integrates constructs from the social capital theory and persuasive systems design model to investigate the impact of persuasive social features on knowledge sharing among students of tertiary institutions on academic social networking sites. Data are quantitatively gathered from 218 respondents from tertiary institutions and statistically analyzed. The results suggest that perceived dialogue support and perceived social support have strong influences on knowledge sharing behaviour.     

Equivalent circuit for broadband underwater transducers

A method is presented to determine the equivalent circuits of broadband transducers with 2 resonances in the frequency band of interest. The circuit parameters are refined by least-squares fitting the measured electrical conductance data with this model. The method is illustrated by computing the conductance and susceptance of the equivalent circuits of 3 types of broadband transducers and comparing them with the measured values. The equivalent circuit of a transducer is necessary for designing filters that match the impedances of the transducer and the power amplifier that drives the transducer.     

Protein stability function relations: native β‐lactoglobulin sulphhydryl–disulphide exchange with PDS

Intermolecular sulphhydryl–disulphide exchange with β‐lactoglobulin dimer occurs when this dissociates to form monomers exposing two SH groups. This notion is re‐evaluated in the light of recent structural data suggesting that the degree of SH group exposure in β‐lactoglobulin is unaffected by dissociation. β‐Lactoglobulin was treated with 2,2′‐dipyridyl disulphide (PDS). The rate of sulphhydryl–disulphide exchange was measured at sub‐denaturation temperatures of 25–60 ° C. Parallel studies were conducted by reacting PDS with reduced glutathione (GSH). The SH group of GSH was up to 31 000 times more reactive than β‐lactoglobulin. At pH 7 the reaction activation enthalpy (ΔH^#) and entropy (ΔS^#) was 26 kJ mol⁻¹ and −100 J mol⁻¹ K⁻¹ respectively for GSH. For β‐lactoglobulin, ΔH^# was 157.2 kJ mol⁻¹ and ΔS^# was 254 J mol⁻¹ K⁻¹. At pH 2.6, ΔH^# was 14.4 kJ mol⁻¹ and ΔS^# was −213 J mol⁻¹ K⁻¹ for GSH. The corresponding results for β‐lactoglobulin were 20.3 kJ mol⁻¹ and −147 J mol⁻¹ K⁻¹. These and other thermodynamic results are discussed in terms of the effects of β‐lactoglobulin conformational structure and stability on SH group reactivity. For native β‐lactoglobulin at neutral pH, intermolecular sulphhydryl–disulphide exchange appears to involve the dissociated monomer. SH group activation probably arises from the lower structural stability of the monomer relative to the dimer. At pH 2.6 the mechanism of SH–disulphide exchange does not require protein dissociation and probably involves breathing motions or localised changes in protein structure. © 2000 Society of Chemical Industry     

Does financial development lower energy intensity?

The growth-induced effects of financial development have been well-established in the empirical literature, as well as the significance of financial development to energy demand behavior. However, the empirical evidence on the relationship between financial development and energy intensity remains sparse in the literature. Given the multifaceted nature of the effects of financial development, the proposed relationship seems a complex one and warrants an empirical investigation. Using the case of Ghana, this study provides an empirical answer to the question: does financial development lower energy intensity? To provide solid grounds for either rejection or acceptance of the null hypothesis, this study performed several robustness checks. Generally, the evidence revealed that financial development lowers energy intensity. Further, the results revealed that the price of energy, trade liberalization and industry structure play significant roles. These results have important implications for the design of macro energy efficiency policies and the creation of a ‘Green Bank’.     

Long-term follow-up of joint stabilization procedures in the treatment of fixed deformities of feet in leprosy

Primate erythrocyte complement receptor type 1 (CR1) plays an essential role in complement-associated immune complex clearance by transporting complexes to macrophages in the liver and/or spleen. Antibody-bound hepatitis C virus, which consists of immune complexes, is observed in patients with chronic hepatitis C. The aim of this study was to clarify the pathophysiological roles of erythrocyte CR1 in hepatitis C virus-infected individuals. We quantified the expression of erythrocyte CR1 with a fluorescence-activated cell sorter system in 57 chronic hepatitis C and 37 chronic hepatitis B cases and 20 normal volunteers. Complement-bound immune complexes were quantified by means of an enzyme-linked immunosorbent assay using anti-C1q and anti-C3d antibodies. Hepatitis C virus-infected patients showed lower erythrocyte CR1 and higher C3d immune complex levels than volunteers (P < 0.01 and P < 0.05, respectively). An inverse correlation was observed between the erythrocyte CR1 and C3d immune complex levels in hepatitis C virus infection (r = -0.300, P = 0.032). The erythrocyte CR1 levels in hepatitis C virus infection were lower in patients with severe liver inflammation, cirrhosis, or hepatocellular carcinoma than in those with mild inflammation, whereas the levels did not differ regardless of the disease stage in hepatitis B virus infection. These findings demonstrate that the expression of erythrocyte CR1 is related to immune complex quantity and the severity of liver disease in hepatitis C virus infection.     

Surface tensions and contact angles due to lignin sulphonates in the system: Liquid sulphur,aqueous zinc sulphate and zinc sulphide

Surface tension and contact angle measurements were made in the liquid sulphur-aqueous zinc sulphate-zinc sulphide system at superatmospheric pressures, and showed that, in the absence of surfactants, the liquid sulphur-aqueous solution interfacial tension was 54.0 ± 1.0 mN/m, falling to 27.0-30.0 mN/m when 0.3 g/L or more of lignin sulphonate was added to the solution. At the same time, the contact angle between liquid sulphur and the same solution increased from 80 ± 5° to 148 ± 5°. As a result, the work of adhesion between liquid sulphur and zinc sulphide falls from 63.7 mJ/m² to about 5.3 mJ/m². The results indicate that adsorption of lignin sulphonate occurs on both the mineral-aqueous and the sulphur-aqueous interfaces.