Air pollution is a major environmental concern during all seasons in the megacity of Beijing, China. Here we present the results from a winter study that was conducted from 21 November 2011 to 20 ...January 2012 with an Aerodyne Aerosol Chemical Speciation Monitor (ACSM) and various collocated instruments. The non-refractory submicron aerosol (NR-PM1) species vary dramatically with clean periods and pollution episodes alternating frequently. Compared to summer, wintertime submicron aerosols show much enhanced organics and chloride, which on average account for 52% and 5%, respectively, of the total NR-PM1 mass. All NR-PM1 species show quite different diurnal behaviors between summer and winter. For example, the wintertime nitrate presents a gradual increase during daytime and correlates well with secondary organic aerosol (OA), indicating a dominant role of photochemical production over gas–particle partitioning. Positive matrix factorization was performed on ACSM OA mass spectra, and identified three primary OA (POA) factors, i.e., hydrocarbon-like OA (HOA), cooking OA (COA), and coal combustion OA (CCOA), and one secondary factor, i.e., oxygenated OA (OOA). The POA dominates OA during wintertime, contributing 69%, with the other 31% being SOA. Further, all POA components show pronounced diurnal cycles with the highest concentrations occurring at nighttime. CCOA is the largest primary source during the heating season, on average accounting for 33% of OA and 17% of NR-PM1. CCOA also plays a significant role in chemically resolved particulate matter (PM) pollution as its mass contribution increases linearly as a function of NR-PM1 mass loadings. The SOA, however, presents a reverse trend, which might indicate the limited SOA formation during high PM pollution episodes in winter. The effects of meteorology on PM pollution and aerosol processing were also explored. In particular, the sulfate mass is largely enhanced during periods with high humidity because of fog processing of high concentration of precursor SO2. In addition, the increased traffic-related HOA emission at low temperature is also highlighted.
The amyloid-β protein (Aβ) protein plays a pivotal role in the pathogenesis of Alzheimer's disease (AD). It is believed that Aβ deposited in the brain originates from the brain tissue itself. ...However, Aβ is generated in both brain and peripheral tissues. Whether circulating Aβ contributes to brain AD-type pathologies remains largely unknown. In this study, using a model of parabiosis between APPswe/PS1dE9 transgenic AD mice and their wild-type littermates, we observed that the human Aβ originated from transgenic AD model mice entered the circulation and accumulated in the brains of wild-type mice, and formed cerebral amyloid angiopathy and Aβ plaques after a 12-month period of parabiosis. AD-type pathologies related to the Aβ accumulation including tau hyperphosphorylation, neurodegeneration, neuroinflammation and microhemorrhage were found in the brains of the parabiotic wild-type mice. More importantly, hippocampal CA1 long-term potentiation was markedly impaired in parabiotic wild-type mice. To the best of our knowledge, our study is the first to reveal that blood-derived Aβ can enter the brain, form the Aβ-related pathologies and induce functional deficits of neurons. Our study provides novel insight into AD pathogenesis and provides evidence that supports the development of therapies for AD by targeting Aβ metabolism in both the brain and the periphery.
Polycrystalline BiFeO3 nanoparticles (size 80–120 nm) are prepared by a simple sol–gel technique. Such nanoparticles are very efficient for photocatalytic decomposition of organic contaminants under ...irradiation from ultraviolet to visible frequencies. The BiFeO3 nanoparticles also demonstrate weak ferromagnetism of about 0.06 μB/Fe at room temperature, in good agreement with theoretical calculations.
Fully recrystallized CoCrFeMnNi high entropy alloys (HEAs) with different grain sizes ranging from 503nm to 88.9µm were fabricated by cold rolling and controlled annealing. Tensile tests were ...conducted at ambient temperature, and deformation microstructures were investigated using electron channeling contrast imaging (ECCI) and transmission electron microscopy (TEM) techniques. It is found that strain-hardening curves changed dramatically with grain refinement. Deformation twinning prevails when the grain size is coarse, but it is absent when the grain size falls in the ultrafine-grained (UFG) regime. The transition of twinning behavior is supposed to be determined by the increased twinning stress with grain refinement. It is indicated that the twinning behavior of the HEAs is strongly dependent on the competition between the flow stress and critical twinning stress with grain refinement.
In this study, the effect of strain rate on the tensile deformation behavior of Fe–22Mn–0.6C–(1.5Al) (wt%) twinning-induced plasticity (TWIP) steel was investigated. The experimental results ...indicated that the work hardening exponent (n), ultimate tensile strength (σu) and the uniform elongation (δu) decreased with increasing strain rates (from 10−4 to 100s−1). This phenomenon exhibited negative strain rate sensitivity (NSRS), and the strain rate sensitivity value (m) was observed to be higher in the aluminum added FeMnC TWIP steel. In order to gain an in-depth understanding of this sensitivity and the subsequent effect of aluminum, the present research focused on the deformation twins and conducted comparative studies on their influence in terms of fractions (F), thickness (t) and spacing (s). Additionally, a twin boundary affected zone (TBAZ) model was proposed, where the relation between higher strain rates were directly applicable to the reduction of interfaces between the matrix and deformation twins. These result indicated that fewer sessile dislocations could be accommodated at high strain rates, thus weakening the work hardening ability. Finally, model calculations were performed to validate the findings, where TBAZ region fractions in FeMnC–Al were observed to be higher than that in FeMnC, corresponding to the increased strain rate sensitivity.
Single-phase equiatomic CoCrFeMnNi high-entropy alloy (HEA) specimens with three different grain sizes (0.65 μm, 2.1 μm and 105 μm) were processed by cold rolling and annealing treatment. Tensile ...properties were investigated over a broad temperature range from 77 K to 873 K. Superior strength-ductility balance can be achieved by refining grain size and decreasing temperature. The Hall-Petch relationship was well fitted, and the fitting parameters have a negative relation with temperature. The thermal and athermal contributions to the yield strength were revealed. This work has unveiled the superior mechanical property of HEAs at cryogenic temperatures.
•The Hall-Petch relationships for CoCrFeMnNi high-entropy alloys (HEAs) were well fitted in large temperature range.•The Hall-Petch slope and friction stress of the CoCrFeMnNi HEAs have a negative relation with temperature.•Athermal contribution and grain size (d) follow a Hall-Petch relation, while thermal part is related to temperature and d.•Superior strength and ductility for CoCrFeMnNi HEAs were achieved by refining grain size and decreasing temperature.
By combining scanning tunneling microscopy and spectroscopy, angle-resolved photoemission spectroscopy, and density functional theory band calculations, we directly observe and resolve the ...one-dimensional edge states of single bilayer (BL) Bi(111) islands on clean Bi(2)Te(3) and Bi(111)-covered Bi(2)Te(3) substrates. The edge states are localized in the vicinity of step edges having an ∼2 nm wide spatial distribution in real space and reside in the energy gap of the Bi(111) BL. Our results demonstrate the existence of nontrivial topological edge states of single Bi(111) bilayer as a two-dimensional topological insulator.
CoCrFeMnNi high-entropy alloys (HEAs) with partially recrystallized (PR) structure were fabricated by cold rolling and annealing. The microstructures were characterized and the tensile properties ...were tested at 77 K and 293 K, respectively. In contrast to the early necking at 293 K, an ultrahigh yield strength of 1692 MPa and a considerable uniform elongation of 10.3% were obtained at 77 K. The notable uniform elongation at 77 K can be attributed to the enhanced strain-hardening capability via introducing multiple deformation mechanisms in the recrystallized grains. This work provides a strategy to design high-strength high-ductility HEAs for applications at cryogenic environments.
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•Synthesis of Mg-doping ZnO by facile polyacrylamide gel method.•Tailoring ZnO band gap and surface properties by alloying with 5 at.% Mg2+.•MZO decomposes 95% MB solution within ...45min under solar irradiation.•MZO maintains more than 95% photodegradation after nine cycles.•Lowest oxygen vacancies of MZO favor for preventing electron-hole recombination.
The photocatalytic performance of Mg-doped ZnO (MZO) nanoparticles, synthesized through the polyacrylamide polymer method, was investigated by the photodegradation of the methylene blue (MB) solution. The nanoparticles were characterized by X-ray diffractometry, X-ray photoelectron spectroscopy, and UV–vis absorption spectrum. The results demonstrate that the catalysts present different photodegradation performances with varying calcination temperatures of the as-synthesized Mg-doped ZnO precursor. It is found that the highest photodegradation of the MB solution was achieved by the catalyst with a 47nm particle size, which had the lowest oxygen vacancies. The influence of operational parameters of pH and initial dye concentration was evaluated. Catalyst activity remained at 95% of its initial value even after the photodegradation process was repeated for nine times. Moreover, three intermediate products, possessing the OH, O2− and h+ groups were detected in the photodegradation processes. Hence, we attribute the enhanced photocatalytic properties of the ZnO nanoparticles to the lower amount of oxygen vacancies, which are a consequence of Mg-doping preventing electron-hole recombination.
Superelastic conducting fibers with improved properties and functionalities are needed for diverse applications. Here we report the fabrication of highly stretchable (up to 1320%) sheath-core ...conducting fibers created by wrapping carbon nanotube sheets oriented in the fiber direction on stretched rubber fiber cores. The resulting structure exhibited distinct short- and long-period sheath buckling that occurred reversibly out of phase in the axial and belt directions, enabling a resistance change of less than 5% for a 1000% stretch. By including other rubber and carbon nanotube sheath layers, we demonstrated strain sensors generating an 860% capacitance change and electrically powered torsional muscles operating reversibly by a coupled tension-to-torsion actuation mechanism. Using theory, we quantitatively explain the complementary effects of an increase in muscle length and a large positive Poisson's ratio on torsional actuation and electronic properties.
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