•COVID-19 presents unprecedented challenge to all facets of human endeavour.•A critical review of the negative and positive impacts of the pandemic is presented.•The danger of relying on ...pandemic-driven benefits to achieving SDGs is highlighted.•The pandemic and its interplay with circular economy (CE) approaches is examined.•Sector-specific CE recommendations in a resilient post-COVID-19 world are outlined.
The World Health Organization declared COVID-19 a global pandemic on the 11th of March 2020, but the world is still reeling from its aftermath. Originating from China, cases quickly spread across the globe, prompting the implementation of stringent measures by world governments in efforts to isolate cases and limit the transmission rate of the virus. These measures have however shattered the core sustaining pillars of the modern world economies as global trade and cooperation succumbed to nationalist focus and competition for scarce supplies. Against this backdrop, this paper presents a critical review of the catalogue of negative and positive impacts of the pandemic and proffers perspectives on how it can be leveraged to steer towards a better, more resilient low-carbon economy. The paper diagnosed the danger of relying on pandemic-driven benefits to achieving sustainable development goals and emphasizes a need for a decisive, fundamental structural change to the dynamics of how we live. It argues for a rethink of the present global economic growth model, shaped by a linear economy system and sustained by profiteering and energy-gulping manufacturing processes, in favour of a more sustainable model recalibrated on circular economy (CE) framework. Building on evidence in support of CE as a vehicle for balancing the complex equation of accomplishing profit with minimal environmental harms, the paper outlines concrete sector-specific recommendations on CE-related solutions as a catalyst for the global economic growth and development in a resilient post-COVID-19 world.
Dissimilar FSW of immiscible materials: Steel/magnesium Kasai, H.; Morisada, Y.; Fujii, H.
Materials science & engineering. A, Structural materials : properties, microstructure and processing,
01/2015, Letnik:
624
Journal Article
Recenzirano
Odprti dostop
The dissimilar joint between a light metal and a strong metal such as steel, is necessary for reducing the weight of vehicles. Friction Stir Welding (FSW) is a useful process to obtain several kinds ...of dissimilar joints and many studies have already been reported. However, the joint between steel and magnesium has not been aggressively studied, because it is an immiscible system. Aluminum is one of the most popular alloying elements for magnesium, and the iron-aluminum system has many intermetallic compounds due to their strong interactions. In this study, the Fe-Al intermetallic compound layer was successfully formed at the joint interface between iron and magnesium using aluminum in the magnesium alloys. The joint strength increased with the increasing aluminum content of the magnesium alloy due to the depletion of aluminum at the magnesium side near the interface.
A
bstract
We consider a hybrid Monte Carlo algorithm which is applicable to lattice theories defined on Lefschetz thimbles. In the algorithm, any point (field configuration) on a thimble is ...parametrized uniquely by the flow-direction and the flow-time defined at a certain asymptotic region close to the critical point, and it is generated by solving the gradient flow equation downward. The associated complete set of tangent vectors is also generated in the same manner. Molecular dynamics is then formulated as a constrained dynamical system, where the equations of motion with Lagrange multipliers are solved by the second-order constraint-preserving symmetric integrator. The algorithm is tested in the λ
ϕ
4
model at finite density, by choosing the thimbles associated with the classical vacua for subcritical and supercritical values of chemical potential. For the lattice size
L
= 4, we find that the residual sign factors average to not less than 0.99 and are safely included by reweighting and that the results of the number density are consistent with those obtained by the complex Langevin simulations.
The microstructures of Al alloy 6061 subjected to very-high-power ultrasonic additive manufacturing were systematically examined to understand the underlying ultrasonic welding mechanism. The ...microstructure of the weld interface between the metal tapes consisted of fine, equiaxed grains resulting from recrystallization, which is driven by simple shear deformation along the ultrasonically vibrating direction of the tape surface. Void formation at the weld interface is attributed to surface asperities resulting from pressure induced by the sonotrode at the initial tape deposition. Transmission electron microscopy revealed that Al–Al metallic bonding without surface oxide layers was mainly achieved, although some oxide clusters were locally observed at the original interface. The results suggest that the oxide layers were broken up and then locally clustered on the interface by ultrasonic vibration.
Display omitted
Recrystallization, which is mainly caused by the induced strain, is one of the most important factors of Friction Stir Welding. In this study, strain and strain rate are directly ...obtained by the change in the material flow velocity which is observed by three-dimensional visualization of the material flow. The grain size of the pure aluminum in the stir zone estimated by the Zener–Hollomon parameter using the obtained strain rate shows good agreement with that observed by Electron Back-Scatter Diffraction mapping.
► The micro-scaled SiC particles can be uniformly distributed in copper plates during the friction stir welding process. ► Bonded structure consisting of particle-rich region and particle-free region ...formed in the stir zone. ► The SiC particle stimulated nucleation for the dynamic recrystallization of copper was confirmed. ► The SiC dispersed copper joint exhibits hardness 40
HV higher than pure copper joints without SiC addition.
The SiC particles with mean size of 5
μm were introduced into the pure Cu joints during the friction stir welding process. After one pass processing, the distribution of SiC particle is not uniform and some pores formed around the aggregation of SiC particles. However, the particle distribution became rather uniform after two passes processing and the previous pores can be refilled. In addition, banded structure consisting of particle-rich and particle-free region can be observed in the stir zone. The particle-rich region has an average grain size of less than 2
μm, much smaller than that of about 8
μm in the particle-free region. Microstructural observation confirmed that the SiC particles can act as the heterogeneous nucleation site in the dynamic recrystallization of Cu grains. The SiC dispersed Cu joints exhibit a Vickers hardness of 110
HV, much higher than 70
HV in the stir zone without SiC particles.
► Dissimilar Al/Fe joint was obtained by flat spot friction stir welding technique. ► The surface of the sound Al/Fe joint is smooth without any internal defects. ► No intermetallic compound layer ...but amorphous area is formed at the weld interface. ► The sound Al/Fe welds show high shear tensile load and fracture through plug mode. ► The probe length exerts little effect on the welds’ microstructure and properties.
The 6061-T6 Al alloy and mild steel plate with a thickness of 1mm were successfully welded by the flat spot friction stir welding technique, which contains two steps during the entire welding process. The rotating tools with different probe lengths of 1.0, 1.3 and 1.5mm were used in the first step, during which a conventional spot FSW was conducted above a round dent previously made on the back plate. However, sound Al/Fe welds with similar microstructure and mechanical properties can still be obtained after the second step, during which a probe-less rotating tool was used to flatten the weld surface. The sound welds have smooth surface without keyholes and other internal welding defects. No intermetallic compound layer but some areas with amorphous atomic configuration was formed along the Al/Fe joint interface due to the lower heat input. The shear tensile failure load can reach a maximum value of 3607N and fracture through plug mode. The probe length has little effect on the weld properties, which indicates that the tool life can be significantly extended by this new spot welding technique.
Hydrogen embrittlement of austenitic stainless steels has been examined with respect to deformation microstructures and lattice defects created during plastic deformation. Two types of austenitic ...stainless steels, SUS 304 and SUS 316L, uniformly hydrogen-precharged to 30 mass ppm in a high-pressure hydrogen environment, are subjected to tensile straining at room temperature. A substantial reduction of tensile ductility appears in hydrogen-charged SUS 304 and the onset of fracture is likely due to plastic instability. Fractographic features show involvement of plasticity throughout the crack path, implying the degradation of the austenitic phase. Electron backscatter diffraction analyses revealed prominent strain localization enhanced by hydrogen in SUS 304. Deformation microstructures of hydrogen-charged SUS 304 were characterized by the formation of high densities of fine stacking faults and ε-martensite, while tangled dislocations prevailed in SUS 316L. Positron lifetime measurements have revealed for the first time hydrogen-enhanced creation of strain-induced vacancies rather than dislocations in the austenitic phase and more clustering of vacancies in SUS 304 than in SUS 316L. Embrittlement and its mechanism are ascribed to the decrease in stacking fault energies resulting in strain localization and hydrogen-enhanced creation of strain-induced vacancies, leading to premature fracture in a similar way to that proposed for ferritic steels.
Essentials
The role of C‐type lectin‐like receptor‐2 (CLEC‐2) in cancer progression is unclear.
CLEC‐2‐depleted mouse model is generated by using a rat anti‐mouse CLEC‐2 monoclonal antibody.
CLEC‐2 ...depletion inhibits hematogenous tumor metastasis of podoplanin‐expressing B16F10 cells.
CLEC‐2 depletion prolongs cancer survival by suppressing thrombosis and inflammation.
Summary
Background
C‐type lectin‐like receptor 2 (CLEC‐2) is a platelet activation receptor of sialoglycoprotein podoplanin, which is expressed on the surface of certain types of tumor cells. CLEC‐2–podoplanin interactions facilitate hematogenous tumor metastasis. However, direct evidence of the role of CLEC‐2 in hematogenous metastasis and cancer progression is lacking.
Objective and methods
We generated immunological CLEC‐2‐depleted mice by using anti‐mouse CLEC‐2 monoclonal antibody 2A2B10 and investigated whether CLEC‐2 promoted hematogenous tumor metastasis and tumor growth and exacerbated the prognosis of mice bearing podoplanin‐expressing B16F10 melanoma cells.
Results
Our results showed that hematogenous metastasis was significantly inhibited in CLEC‐2‐depleted mice. B16F10 cells co‐cultured with wild‐type platelets, but not with CLEC‐2‐deficient platelets, showed increased proliferation. However, B16F10 cell proliferation was not inhibited in CLEC‐2‐depleted mice. Histological analysis showed that thrombus formation in tumor vessels was significantly inhibited and functional vessel density was significantly increased in CLEC‐2‐depleted mice. These data suggest that CLEC‐2 deficiency may inhibit thrombus formation in tumor vessels and increase the density of functional vessels, thus improving oxygen and nutrient supply to tumors, indirectly promoting tumor proliferation. Furthermore, the overall survival of CLEC‐2‐depleted mice was significantly prolonged, which may be due to the suppression of thrombus formation in the lungs and subsequent inhibition of systemic inflammation and cachexia.
Conclusions
These data provide a rationale for the targeted inhibition of CLEC‐2 as a new strategy for preventing hematogenous tumor metastasis and for inhibiting cancer‐related thromboembolism.
The defect formation mechanism during friction stir welding (FSW) was investigated by the three-dimensional visualisation of material flow around a tool. The three-dimensional flow patterns under ...various FSW conditions were obtained using two pairs of X-ray transmission real time imaging systems. The flow patterns revealed that the tilt of horizontal material flow around the tool and the stagnation of material flow on the advancing side (AS) of the tool were significantly correlated to the formation of defects. The material flow velocity during FSW was directly calculated based on the results of three-dimensional visualisation. The material flow velocity on the AS obviously decreased under the condition where defects were formed.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, UILJ, UKNU, UL, UM, UPUK
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