Since the 1960s, it has been a common practice worldwide to pursue a homogeneous distribution of reinforcements within a matrix material, discontinuous metal matrix composites (DMMCs) in particular. ...Taking an overview of the worldwide activities in DMMC research, despite many favourable attributes such as improved specific strength, stiffness and superior wear resistance, DMMCs with a homogeneous microstructure tend to exhibit a very low room temperature damage tolerance even with a highly ductile matrix material such as aluminium. In this review, a range of uniquely multi-scale hierarchical structures have been successfully designed and fabricated by tailoring reinforcement distribution for DMMCs in order to obtain superior performance. A variety of specific microstructures that were developed in Al, Mg, Cu, Fe, Co and TiAl matrices indicate that there must be adequate plastic regions among the reinforcements to blunt or deflect cracks if one wants to toughen DMMCs. Following this path, aided by theoretical analyses, the most recent success is the design and fabrication of a network distribution of in situ reinforcing TiB whiskers (TiBw) in titanium matrix composites (TMCs), where a tailored three-dimensional (3D) quasi-continuous network microstructure displays significant improvements in mechanical properties. This resolves the brittleness surrounding TMCs fabricated by powder metallurgy. It is the large reinforcement-lean regions that remarkably improve the composite's ductility by bearing strain, blunting the crack and decreasing the crack-propagation rate. The fracture, strengthening and toughening mechanisms are comprehensively elucidated in order to further understand the advantages of such an inhomogeneous microstructure, and to justify the development of novel techniques to produce such inhomogeneous microstructures. This approach opens up a new horizon of research and applications of DMMCs and can be easily extended to general multi-phase composites with enhanced physical and mechanical properties.
Although methanogenesis is considered a strictly anaerobic process, oxygen‐replete surface open‐ocean waters are usually supersaturated with methane (CH4), a phenomenon termed the oceanic methane ...paradox. Here, we report that abiotic methane photoproduction from chromophoric dissolved organic matter (CDOM) significantly contributes to this paradox. Methane photoproduction was observed during solar‐simulated irradiations of various waters collected along the land‐ocean continuum. Methane photoproduction rates decreased seaward, whereas its relative production efficiency and the methane‐to‐carbon‐monoxide (CO) photoproduction ratio (ΔCH4/ΔCO) both followed a reversed trend. Remote‐sensing modeling incorporating a ΔCH4/ΔCO–CDOM absorption relationship yielded an annual methane photoproduction of 118 Gg for the global open ocean, accounting for 20–60% of the open‐ocean methane efflux and being of comparable magnitude to the upper‐ocean methane microbial‐oxidation sink. The photodegradation of CDOM thus plays an important role in maintaining supersaturated methane concentrations in the oxygenated upper ocean and in sustaining oceanic methane emissions to the atmosphere.
Plain Language Summary
Methane is the second most important greenhouse gas after carbon dioxide, and the global ocean is a significant source of it to the atmosphere. In aquatic environments, methane is thought to be exclusively produced by microbes that degrade organic matter in the absence of oxygen. Contradictorily, the oxygen‐rich waters of the surface open ocean are almost always supersaturated with methane, containing higher concentrations than deeper in the water column. This apparent contradiction is often called the oceanic methane paradox. Here, we demonstrate that the degradation of dissolved organic matter by sunlight in the surface ocean represents an important mechanism of methane production that is capable of maintaining the supersaturation of methane in the surface ocean and of sustaining methane emissions to the atmosphere on a global scale. This study thus suggests that the photochemical production of methane is an important contributor to the oceanic methane paradox.
Key Points
Methane photoproduction from dissolved organic matter is a ubiquitous phenomenon in natural waters
The efficiency of methane photoproduction increases from the land to sea
Methane photoproduction is an important contributor to the oceanic methane paradox
Biodiesel is an alternative diesel fuel that can be produced from different kinds of vegetable oils. It is an oxygenated, non-toxic, sulphur-free, biodegradable, and renewable fuel and can be used in ...diesel engines without significant modification. However, the performance, emissions and combustion characteristics will be different for the same biodiesel used in different types of engine.
In this study, the biodiesel produced from soybean crude oil was prepared by a method of alkaline-catalyzed transesterification. The effects of biodiesel addition to diesel fuel on the performance, emissions and combustion characteristics of a naturally aspirated DI compression ignition engine were examined. Biodiesel has different properties from diesel fuel. A minor increase in brake specific fuel consumption (BSFC) and decrease in brake thermal efficiency (BTE) for biodiesel and its blends were observed compared with diesel fuel. The significant improvement in reduction of carbon monoxide (CO) and smoke were found for biodiesel and its blends at high engine loads. Hydrocarbon (HC) had no evident variation for all tested fuels. Nitrogen oxides (NOx) were slightly higher for biodiesel and its blends. Biodiesel and its blends exhibited similar combustion stages to diesel fuel. The use of transesterified soybean crude oil can be partially substituted for the diesel fuel at most operating conditions in terms of the performance parameters and emissions without any engine modification.
The Brownian motion of molecules at thermal equilibrium usually has a finite correlation time and will eventually be randomized after a long delay time, so that their displacement follows the ...Gaussian statistics. This is true even when the molecules have experienced a complex environment with a finite correlation time. Here, we report that the lateral motion of the acetylcholine receptors on live muscle cell membranes does not follow the Gaussian statistics for normal Brownian diffusion. From a careful analysis of a large volume of the protein trajectories obtained over a wide range of sampling rates and long durations, we find that the normalized histogram of the protein displacements shows an exponential tail, which is robust and universal for cells under different conditions. The experiment indicates that the observed non-Gaussian statistics and dynamic heterogeneity are inherently linked to the slow-active remodelling of the underlying cortical actin network.
In this paper, we report the use of cold-sample rolling (CSR) processing, which induced a high fraction of double twins and a substantial texture-weakening effect in an Al-concentrated commercial ...Mg-6Al-1Zn (mass%) alloy sheet. A CSR-processed and subsequently annealed sheet showed a weak basal texture with a broad distribution of the (0001) poles toward the rolling and transverse directions. This led to moderate stretch formability with a limiting dome height of 5.5 mm. High-temperature rolling (HTR) processing has been reported to weaken the basal texture in Mg-Al-based alloy sheets because of the activation of non-basal <c+a> dislocations, resulting in texture weakening. However, the processing induced a relatively low fraction of double twins. Consequently, CSR processing led to a relatively high texture-weakening effect. The results showed that twinning-mediated static recrystallization is essential for texture weakening in Al-concentrated Mg-alloy sheets.
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•A unique cold-sample rolling (CSR) process is proposed.•CSR processing induced a high fraction of double twins in basal-textured AZ61.•The high fraction of twins contributed to significant texture weakening.•The (0001) planes in the CSR-processed sheet were weakly aligned in the RD and TD.•The texture weakening improved the room-temperature formability.
An experimental investigation is conducted to evaluate the effects of using diethyl ether and ethanol as additives to biodiesel/diesel blends on the performance, emissions and combustion ...characteristics of a direct injection diesel engine. The test fuels are denoted as B30 (30% biodiesel and 70% diesel in vol.), BE-1 (5% diethyl ether, 25% biodiesel and 70% diesel in vol.) and BE-2 (5% ethanol, 25% biodiesel and 70% diesel in vol.) respectively. The results indicate that, compared with B30, there is slightly lower brake specific fuel consumption (BSFC) for BE-1. Drastic reduction in smoke is observed with BE-1 and BE-2 at higher engine loads. Nitrogen oxide (NOx) emissions are found slightly higher for BE-2. Hydrocarbon (HC) emissions are slightly higher for BE-1 and BE-2, but carbon monoxide (CO) are slightly lower. The peak pressure, peak pressure rise rate and peak heat release rate of BE-1 are almost similar to those of B30, and higher than those of BE-2 at lower engine loads. At higher engine loads the peak pressure, peak pressure rise rate and peak heat release rate of BE-1 are the highest and those of B30 are the lowest. BE-1 reflects better engine performance and combustion characteristics than BE-2 and B30.
We revisit the classical relation between the strangeness content of the nucleon, the pion–nucleon sigma term and the SU(3)F breaking of the baryon masses in the context of Lorentz covariant chiral ...perturbation theory with explicit decuplet-baryon resonance fields. We find that a value of the pion–nucleon sigma term of ∼60 MeV is not necessarily at odds with a small strangeness content of the nucleon, in line with the fulfillment of the OZI rule. Moreover, this value is indeed favored by our next-to-leading order calculation. We compare our results with earlier ones and discuss the convergence of the chiral series as well as the uncertainties of chiral approaches to the determination of the sigma terms.
In this study, the biodiesel produced from soybean crude oil was prepared by a method of alkaline-catalyzed transesterification. The important properties of biodiesel were compared with those of ...diesel. Diesel and biodiesel were used as fuels in the compression ignition engine, and its performance, emissions and combustion characteristics of the engine were analyzed. The results showed that biodiesel exhibited the similar combustion stages to that of diesel, however, biodiesel showed an earlier start of combustion. At lower engine loads, the peak cylinder pressure, the peak rate of pressure rise and the peak of heat release rate during premixed combustion phase were higher for biodiesel than for diesel. At higher engine loads, the peak cylinder pressure of biodiesel was almost similar to that of diesel, but the peak rate of pressure rise and the peak of heat release rate were lower for biodiesel. The power output of biodiesel was almost identical with that of diesel. The brake specific fuel consumption was higher for biodiesel due to its lower heating value. Biodiesel provided significant reduction in CO, HC, NO
x
and smoke under speed characteristic at full engine load. Based on this study, biodiesel can be used as a substitute for diesel in diesel engine.
An experimental investigation was conducted to evaluate the effects of using methanol as additive to biodiesel–diesel blends on the engine performance, emissions and combustion characteristics of a ...direct injection diesel engine under variable operating conditions. BD50 (50% biodiesel and 50% diesel in vol.) was prepared as the baseline fuel. Methanol was added to BD50 as an additive by volume percent of 5% and 10% (denoted as BDM5 and BDM10). The results indicate that the combustion starts later for BDM5 and BDM10 than for BD50 at low engine load, but is almost identical at high engine load. At low engine load of 1500
r/min, BDM5 and BDM10 show the similar peak cylinder pressure and peak of pressure rise rate to BD50, and higher peak of heat release rate than that of BD50. At low engine load of 1800
r/min, the peak cylinder pressure and the peak of pressure rise rate of BDM5 and BDM10 are lower than those of BD50, and the peak of heat release rate is similar to that of BD50. The crank angles at which the peak values occur are later for BDM5 and BDM10 than for BD50. At high engine load, the peak cylinder pressure, the peak of pressure rise rate and peak of heat release rate of BDM5 and BDM10 are higher than those of BD50, and the crank angle of peak values for all tested fuels are almost same. The power and torque outputs of BDM5 and BDM10 are slightly lower than those of BD50. BDM5 and BDM10 show dramatic reduction of smoke emissions. CO emissions are slightly lower, and NO
x
and HC emissions are almost similar to those of BD50 at speed characteristic of full engine load.
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