Studies suggest that dysfunction of brain-derived neurotrophic factor (BDNF) is a possible contributor to the pathology and symptoms of Alzheimer's disease (AD). Several studies report reduced ...peripheral blood levels of BDNF in AD, but findings are inconsistent. This study sought to quantitatively summarize the clinical BDNF data in patients with AD and mild cognitive impairment (MCI, a prodromal stage of AD) with a meta-analytical technique. A systematic search of Pubmed, PsycINFO and the Cochrane Library identified 29 articles for inclusion in the meta-analysis. Random-effects meta-analysis showed that patients with AD had significantly decreased baseline peripheral blood levels of BDNF compared with healthy control (HC) subjects (24 studies, Hedges' g=-0.339, 95% confidence interval (CI)=-0.572 to -0.106, P=0.004). MCI subjects showed a trend for decreased BDNF levels compared with HC subjects (14 studies, Hedges' g=-0.201, 95% CI=-0.413 to 0.010, P=0.062). No differences were found between AD and MCI subjects in BDNF levels (11 studies, Hedges' g=0.058, 95% CI=-0.120 to 0.236, P=0.522). Interestingly, the effective sizes and statistical significance improved after excluding studies with reported medication in patients (between AD and HC: 18 studies, Hedges' g=-0.492, P<0.001; between MCI and HC: 11 studies, Hedges' g=-0.339, P=0.003). These results strengthen the clinical evidence that AD or MCI is accompanied by reduced peripheral blood BDNF levels, supporting an association between the decreasing levels of BDNF and the progression of AD.
The present research was motivated by two unsettled questions. First, what are the detailed characteristics of the nanostructured interface in a nano-carbon/metal composite containing interfacial ...reaction products? Second, what other factors in interfacial carbide (not only its content) can influence the interface strength and mechanical properties, and if it is true? We developed a novel strategy to uncover these issues in graphite nano-flakes (GNFs)/Ti composites. Four GNFs/Ti samples with similar concentration of interfacial carbides were prepared under the guidance of DICTRA simulation. High-resolution transmission electron microscopy and precession assisted electron diffraction were applied to gain fundamental insight into the mechanisms that affect the characteristics of GNFs/Ti interfaces. The tensile results showed that the interfacial morphologies, GNFs-TiCx bonding strength, preferred orientation and growth defects were significant factors that were closely associated with the mesoscopic mechanical behavior. Interestingly, the heat-treated (HT) 1123K-600s GNFs/Ti composite exhibited the optimal tensile properties and superior GNFs-TiCx “synergetic” effect. The origin of such findings were explored from the viewpoint of nano-cracks/dislocation-interface interaction. This work provides a new insight in understanding the interfacial characteristics of GNFs/Ti composite, and underscores the importance of reaction interface design in strengthening of bulk GNFs/metal composite.
Display omitted
Graphene nanoplatelets (GNPs) and TiB whiskers (TiBw) hybrid reinforced Ti–6Al–4V (TC4) matrix composites ((GNPs + TiBw)/TC4) were fabricated by Fast Hot-Press Sintering (FHPS) and hot rolling (HR) ...method. The microstructure, mechanical properties and strengthening mechanisms were systematically studied with various TiBw contents. Microstructure observation results indicate that GNPs can be mostly preserved and TiBw are rarely obtained during the sintering process. HR process was applied to further densify the composites and obtain the in-situ TiBw. The high ductility of composites was achieved via designing network structure with reinforcements of GNPs and in-situ TiBw, which reduce the interface reaction of the GNPs/Ti and improved the interface bonding. The tensile ductility of the GNPs/TC4 composites were improved with the addition of TiB2 powders. As a result, 0.1 wt% GNPs/TC4 composites with the addition of 0.05 wt% TiB2 powders showed the best combination of ultimate tensile strength of 1158 MPa and a fracture elongation of 15.8%. Compared to the fracture elongation of pure TC4 alloy (15.2%), there was no sacrifice of ductility.
•GNPs and TiBs hybrid reinforced TC4 matrix composites were fabricated by Fast Hot-Press Sintering and hot rolling.•The network composites with 0.1 wt% GNPs and 0.05 wt% TiB2 showed improved performance on both strength and ductility.•The effects of TiBw on improving GNPs-Ti interface bonding and the mechanical properties of composites is discussed.
A flexible 3D porous magnet KCo7(OH)3(ip)6(H2O)4·12 H2O based on unprecedented trigonal‐prismatic heptanuclear CoII clusters (see figure) is reported to undergo a reversible ...single‐crystal‐to‐single‐crystal transformation on the desorption/adsorption of guest molecules, accompanied by reversible magnetic property changes. This might be applied for the sensing of coordinative, paramagnetic, small molecules such as O2 and NO.
Display omitted
► LSP can generate high-level compressive residual stresses and refine original grains. ► Massive LSP impacts can effectively prevent the SCC initiation of the U-bend sample. ► ...Mechanism of massive LSP impacts on SCC was also entirely revealed.
The effects of massive laser peening (LP) impacts on surface residual stress, micro-structure, and stress corrosion cracking (SCC) behaviour of U-bend samples were investigated by X-ray diffraction (XRD) technology, optical microscope (OM) and transmission electron microscope (TEM) observations. Two important factors to influence SCC initiation, residual stress and grain refinement, were discussed in detail by using different types of treatment processes. Results showed massive LP impacts can induce both deep compressive residual stress and refined grains in the surface layer of ANSI 304 stainless steel, and the corrosion mechanism of massive LP impacts on SCC was also analysed and revealed.
For the purpose of relating microscopic interface characteristics to macroscopic dynamic properties in carbon/metal nano-composites, the graphene nano-flakes (GNFs)/Ti composites were fabricated by ...spark plasma sintering (SPS) and subsequent 723K, 923K, 23K and 1323K hot-rolling. The dynamic properties (∼3000s−1) and interface failure processes were investigated by introducing Spilt Hopkinson Pressure Bar (SHPB) and stop-ring technology. A superior strength without losing ductility was realized by 1123K as-rolled GNFs/Ti composite. Observations provide new insights into the unique and effective load transfer process of interfacial TiC nano-layer on partially reacted GNFs, which appears to be responsible for the extraordinary dynamic property.
A laminated architecture with uniform dispersed graphene nanoflakes (GNFs) was elaborated in pure Ti matrix via a novel spray deposition method in conjunction with low-temperature consolidation ...strategy. The intrinsic structure of the aligned interlaminar GNFs was well-retained in the whole fabrication processes, and the appropriate interface reaction introduced a strong bonding between GNFs and Ti layers. In particular, the as-designed composite with 0.23 vol% GNFs exhibited the enhanced strength (+48.8% compared with the pure Ti laminates) without sacrifice in ductility. In-situ tensile tests indicated that the GNFs and interfacial TiC could effectively inhibited cracks propagation and relieved the strain concentration. The strengthening and toughening effects were induced by the synergetic effect of uniform dispersion, firmly interface bonding and laminated architecture. Together they act in concert to render outstanding mechanical performance. This study will highlight a simple and feasible route towards well balance between strength and ductility in Ti-based composites, and informative for achieving high-performance in nano-carbon/Ti system.
Display omitted
•The deposition of nickel nanoparticles is closely associated with the original nano-defects on the GNFs.•The interfacial microstructure of Ni-GNFs/Ti composites could be manipulated by controlling ...the nickel coating on GNFs.•Partially Ni-coated GNFs have better strengthening effect than fully Ni-coated GNFs in TMCs.•A good strength-plasticity compatibility was achieved in the TMCs with partially Ni-coated GNFs.
Display omitted
Graphene nanoflakes (GNFs) surface metallization is a potential method to simultaneously achieve homogeneous GNFs dispersion and suitable interfacial bonding in metal matrix composites (MMCs). In this study, the effect of nickel coating microstructure of GNFs on strengthening titanium matrix composites (TMCs) was investigated. To this end, nickel-coated graphene nanoflakes (Ni-GNFs) with two different states were produced via electroless plating. The Ni-GNFs/Ti bulk composites were consolidated by combining short-time ball milling, spark plasma sintering (SPS) and hot rolling (HR). Results showed that the reinforcements were well dispersed in the Ni-GNFs/Ti composites coupled with remarkably strength improvement, which resulted from the precipitation of NiTi2 intermetallic compound and strong interfacial bonding. The partially Ni-coated GNFs have a better strengthening effect than fully Ni-coated GNFs in TMCs, which was closely associated with the formation of a special interfacial microstructure. As a result, the composite with partially Ni-coated GNFs exhibited the highest tensile strength of 821 MPa, as well as excellent ductility (~18.3%). This finding may provide new strategies for the preparation of high-performance TMCs through interfacial microstructure design.
The uncontrollable interface reaction has always been a difficult issue in fabricating graphene reinforced titanium matrix composites during high temperature processing. To overcome the graphene ...nanoflakes (GNFs) agglomeration and relieve the severe C–Ti interface reaction, electroless plating method was applied to synthesize high-quality nickel coated graphene nanoflakes (Ni-GNFs) as reinforcements in Ti matrix. In the present work, the Ni-GNFs/Ti composites were fabricated by spark plasma sintering (SPS) and subsequent heat treatment (HT). The investigations of microstructure revealed that nickel-plating layer played an important role in controlling the degree of interface reaction, and the intrinsic nanostructure of GNFs was maintained after HT at 1123 K for 15min. Feather-shaped NiTi2 precipitation was generated when the nickel layer diffused into Ti matrix. A special crystallographic orientation relation of NiTi2 (1¯33)//Ti (100) and NiTi2 (51¯1¯)//Ti (1¯11) was found between NiTi2 and Ti matrix, which accounted for the improvement of load transfer capability. The compressive tests showed that the yield strength reached to 873 MPa when the composites containing only 0.05 wt% GNFs, which was an increase of 30.1% compared to the pure titanium. This work provides a new strategy for the interface microstructure design of bulk nano-carbon/titanium composites.
Display omitted
•High-quality nickel coating was obtained on the surface of graphene by electroless plating.•The interfacial evolution between nickel coated graphene and Ti matrix of composite was observed under thermal influence.•There exists special crystallographic orientation relation: NiTi2 (1¯33)//Ti (100) and NiTi2 (51¯1¯)//Ti (1¯11) in interface.
•The coarse and ultra-fine TiC grains are observed on GNFs/Ti interface.•The interfacial TiC phase induces significant strength and ductility improvement in GNFs/Ti composite.•The interfacial TiC can ...efficiently accumulate dislocations on TiC/Ti interface and store the micro-cracks.
This study aims to explain the failure mechanism of graphene nanoflakes/titanum (GNFs/Ti) composites with physical and chemical bonded interface. Formation of suitable titanium carbides (TiC) by interfacial chemical reaction is a promising approach for the interface bonding enhancement. We find that nano-TiC layer (consists of multi-sized grains) will simultaneously accumulate abundant dislocations on TiC/Ti interface and store the micro-cracks on GNFs-TiC interface, which greatly improve the strength and failure tolerance compared with physical-bonding interface. Tensile tests show that the interface chemical bonding lead to the excellent combination of high strength (849 MPa) and well ductility (a superior elongation of 20%) in 0.23 vol% GNFs/Ti composites.
