Abstract Previous data demonstrate that traumatic brain injury (TBI) activates autophagy, and increases microtubule-associated protein 1 light chain 3 (LC3) immunostaining mainly in neurons. However, ...the role of autophagy in traumatic brain damage remains elusive. The aim of the present study was to investigate the autophagic mechanisms participating in traumatic brain injury. The autophagy inhibitors 3-methyladenine (3-MA) and bafliomycin A1 (BFA) were administered with a single i.c.v. injection before TBI. We first examined the protein levels of Beclin-1 and LC3 II, which have been found to promote autophagy previously. Immunoblotting analysis showed that 3-MA pretreatment reduced post-TBI Beclin-1 and LC3-II levels, and maintained p62/SQSTM1 (p62) levels. In addition, double immunolabeling showed that the increased punctate LC3-II dots colocalizing with Propidium Iodide (PI)-stained nuclei at 24 h after injury, were partially inhibited by 3-MA pretreatment. Furthermore, inhibition of autophagy could reduce TBI-induced cell injury assessed with i.p. injection of PI and lesion volume, and attenuate behavioral outcome evaluated by motor test and Morris water maze. The neuroprotective effects were associated with an inhibition on TBI-induced up-regulation of LC3, Beclin-1, cathepsin B, caspase-3 and the Beclin-1/Bcl-2 ratio. Taken together, these data imply that the autophagy pathway is involved in the pathophysiologic responses after TBI, and inhibition of this pathway may help attenuate traumatic damage and functional outcome deficits.
The strength of polycrystalline materials increases with decreasing grain size. Below a critical size, smaller grains might lead to softening, as suggested by atomistic simulations. The strongest ...size should arise at a transition in deformation mechanism from lattice dislocation activities to grain boundary-related processes. We investigated the maximum strength of nanotwinned copper samples with different twin thicknesses. We found that the strength increases with decreasing twin thickness, reaching a maximum at 15 nanometers, followed by a softening at smaller values that is accompanied by enhanced strain hardening and tensile ductility. The strongest twin thickness originates from a transition in the yielding mechanism from the slip transfer across twin boundaries to the activity of preexisting easy dislocation sources.
Abstract
Understanding the competition between superconductivity and other ordered states (such as antiferromagnetic or charge-density-wave (CDW) state) is a central issue in condensed matter ...physics. The recently discovered layered kagome metal
A
V
3
Sb
5
(
A
= K, Rb, and Cs) provides us a new playground to study the interplay of superconductivity and CDW state by involving nontrivial topology of band structures. Here, we conduct high-pressure electrical transport and magnetic susceptibility measurements to study CsV
3
Sb
5
with the highest
T
c
of 2.7 K in
A
V
3
Sb
5
family. While the CDW transition is monotonically suppressed by pressure, superconductivity is enhanced with increasing pressure up to P1 ≈ 0.7 GPa, then an unexpected suppression on superconductivity happens until pressure around 1.1 GPa, after that,
T
c
is enhanced with increasing pressure again. The CDW is completely suppressed at a critical pressure P2 ≈ 2 GPa together with a maximum
T
c
of about 8 K. In contrast to a common dome-like behavior, the pressure-dependent
T
c
shows an unexpected double-peak behavior. The unusual suppression of
T
c
at P1 is concomitant with the rapidly damping of quantum oscillations, sudden enhancement of the residual resistivity and rapid decrease of magnetoresistance. Our discoveries indicate an unusual competition between superconductivity and CDW state in pressurized kagome lattice.
The super acidity of the unsolvated Al(C6F5)3 enabled isolation of the elusive silane–alane complex SiH⋅⋅⋅Al, which was structurally characterized by spectroscopic and X‐ray diffraction methods. The ...Janus‐like nature of this adduct, coupled with strong silane activation, effects multifaceted frustrated‐Lewis‐pair‐type catalysis. When compared with the silane–borane system, the silane–alane system offers unique features or clear advantages in the four types of catalytic transformations examined in this study, including: ligand redistribution of tertiary silanes into secondary and quaternary silanes, polymerization of conjugated polar alkenes, hydrosilylation of unactivated alkenes, and hydrodefluorination of fluoroalkanes.
Al does it all: The elusive silane–alane complex SiH⋅⋅⋅Al was isolated and structurally characterized by spectroscopic and X‐ray diffraction methods. The Janus‐like nature of this adduct, coupled with strong silane activation, effects multifaceted frustrated‐Lewis‐pair‐type catalysis. Its use in four different reactions is described.
Stereoselective polymerization of chiral or prochiral monomers is a powerful method to produce high-performance stereoregular crystalline polymeric materials. However, for monomers with two ...stereogenic centers, it is generally necessary to separate diastereomers before polymerization, resulting in substantial material loss and added energy cost associated with the separation and purification process. Here we report a diastereoselective polymerization methodology enabled by catalysts that directly polymerize mixtures of eight-membered diolide (8DL) monomers with varying starting ratios of chiral racemic (
) and achiral
diastereomers into stereosequenced crystalline polyhydroxyalkanoates with isotactic and syndiotactic stereodiblock or stereotapered block microstructures. These polymers show enhanced ductility and toughness relative to polymers of pure
-8DL, subject to tuning by variation of the diastereomeric ratio and structure of the 8DL monomers.
The effect of two-step homogenization treatments on the precipitation behavior of Al3Zr dispersoids was investigated by transmission electron microscopy (TEM) in 7150 alloys. Two-step treatments with ...the first step in the temperature range of 300–400°C followed by the second step at 470°C were applied during homogenization. Compared with the conventional one-step homogenization, both a finer particle size and a higher number density of Al3Zr dispersoids were obtained with two-step homogenization treatments. The most effective dispersoid distribution was attained using the first step held at 300°C. In addition, the two-step homogenization minimized the precipitate free zones and greatly increased the number density of dispersoids near dendrite grain boundaries. The effect of two-step homogenization on recrystallization resistance of 7150 alloys with different Zr contents was quantitatively analyzed using the electron backscattered diffraction (EBSD) technique. It was found that the improved dispersoid distribution through the two-step treatment can effectively inhibit the recrystallization process during the post-deformation annealing for 7150 alloys containing 0.04–0.09wt.% Zr, resulting in a remarkable reduction of the volume fraction and grain size of recrystallization grains.
•Effect of two-step homogenization on Al3Zr dispersoids was investigated by TEM.•Finer and higher number of dispersoids obtained with two-step homogenization•Minimized the precipitate free zones and improved the dispersoid distribution•Recrystallization resistance with varying Zr content was quantified by EBSD.•Effectively inhibit the recrystallization through two-step treatments in 7150 alloy
•Fabrication of superhydrophobic aluminum alloy surfaces by chemical etching followed by organic molecule passivation.•The formation of flake-like micro-nanostructure morphology of the low surface ...energy aluminum stearate on aluminum.•The complementary corrosion studies by polarization resistance and electrochemical impedance spectroscopy (EIS).•The modulus of impedanceis found to be 70 times larger for the superhydrophobic surfaces compared with the as-received aluminum alloy surface.
Superhydrophobic aluminum alloy surfaces are obtained by chemical etching using 1M NaOH solution followed by passivation using 0.01M ethanolic stearic acid (SA) solution. The formation of low surface energy aluminum stearate takes place during the passivation process between stearic acid and hydroxyl group-terminated aluminum alloy surfaces. A schematic model of the SA passivation process on the OH terminated Al-surfaces is presented in this work. The flake-like micro-nanostructure morphology of the low surface energy aluminum stearate increases the water contact angle by more than 150°, demonstrating the superhydrophobic properties. The corrosion current density reduces and polarization resistance increases systematically with increasing passivation time. The polarization resistance, calculated from the Tafel curve of the superhydrophobic surfaces prepared by stearic acid passivation for 60min, is determined to be 137 times larger than that of the as-received aluminum alloy substrate. Similarly, the modulus of impedance, as-determined from electrochemical impedance spectroscopy (EIS), is found to be 70 times larger for the superhydrophobic surfaces compared with the as-received aluminum alloy surface. These results demonstrate that the superhydrophobic aluminum alloy surfaces created by chemical etching followed by passivation have superior corrosion resistance properties than the as-receive aluminum alloy substrate.
The effects of Al(MnFe)Si dispersoids, with different sizes and number densities, on the evolution of microstructure and ambient/elevated-temperature mechanical properties of extruded AA6082 alloys, ...with varying Mn content, under T5 conditions, were investigated. Compared to the low density of coarse dispersoids formed during conventional homogenization, the high density of fine dispersoids formed during a new low-temperature homogenization was more effective in increasing the material’s resistance to plastic deformation during extrusion, resulting in the dissolution of more constituent Mg2Si particles into the α-Al matrix. A large amount of β", some β′ precipitates and fine dispersoids co-existed in the α-Al matrix of 0.5% Mn containing alloy, which afforded this alloy a substantial increase in ambient-temperature yield strength of 65–75 MPa under T5 conditions compared to the base alloy without dispersoids. A further increase in the Mn content decreased the number density of the β" precipitates, resulting in a decline in the mechanical properties. Upon thermal exposure at 300 °C for 100 h, β"/β′ fully transformed into an undesirable equilibrium β phase and lost their strengthening effect, while fine and dense dispersoids became the dominant strengthener, leading to a 55–70% increase in the elevated-temperature yield strength relative to the alloys either without dispersoids or with coarse dispersoids. Dispersoid strengthening was more pronounced at 0.7% Mn addition as further increasing the Mn content mainly contributed to the fraction of insoluble Mn-containing intermetallics.
•High density of fine, thermally stable Al(FeMn)Si dispersoids formed during new homogenization of AA6082 alloy.•Extrusion of alloy with fine dispersoids caused the dissolution of more Mg2Si into α-Al matrix.•Co-existence of fine dispersoids and β"/β’ precipitates render the alloy under T5 with high strength.•Upon exposure to 300 °C, β"/β’ transformed into undesirable β, while Al(FeMn)Si remained thermally stable.•High density of fine dispersoids has increased the yield strength at 300 °C of alloy by 55-70%.
Two well-known low-ceiling-temperature (LCT) monomers, γ-butyrolactone (γ-BL) toward ring-opening polymerization (ROP) to polyester and cyclohexene toward ring-opening metathesis polymerization ...(ROMP) to poly(cyclic olefin), are notoriously “nonpolymerizable”. Here we present a strategy to render not only polymerizability of both the γ-BL and cyclohexene sites, orthogonally, but also complete and orthogonal depolymerization, through creating an LCT/LCT hybrid, bicyclic lactone/olefin (BiL=). This hybrid monomer undergoes orthogonal polymerization between ROP and ROMP, depending on the catalyst employed, affording two totally different classes of polymeric materials from this single monomer: polyester P(BiL=)ROP via ROP and functionalized poly(cyclic olefin) P(BiL=)ROMP via ROMP. Intriguingly, both P(BiL=)ROP and P(BiL=)ROMP are thermally robust but chemically recyclable under mild conditions (25–40 °C), in the presence of a catalyst, to recover cleanly the same monomer via chain unzipping and scission, respectively. In the ROP, topological and stereochemical controls have been achieved and the structures characterized. Furthermore, the intact functional group during the orthogonal polymerization (i.e., the double bond in ROP and the lactone in ROMP) is utilized for postfunctionalization for tuning materials’ thermal and mechanical performances. The impressive depolymerization orthogonality further endows selective depolymerization of both the ROP/ROMP copolymer and the physical blend composites into the same starting monomer.
PDF
