Formation Of Laminar Structure Research Articles

Evaluation of whisker alignment and anisotropic mechanical properties of ZK60 alloy reinforced with SiCw during KOBO extrusion method

In current study, microstructure and high-temperature mechanical properties of ZK60 magnesium alloy reinforced by SiC whiskers were investigated after casting, the KOBO extrusion and aging processes. For this purpose, ZK60/SiCw composite specimens were prepared by stir casting technique. In order to achieve a laminar structure and improve the strength, the samples were subjected to KOBO extrusion technique and precipitation hardening, resulting in improved strength and increased ductility. The former is due to grain refining and formation of precipitates in the microstructure, while the latter is attributed to grain refining and formation of laminar structure. To evaluate the strength of the specimens, tensile test was carried out at ambient and high temperatures. It was found that the alignment of whiskers and crystalline orientation during the KOBO extrusion process increased the anisotropic strength along with improvement of elastic modulus specially in the extrusion direction. Moreover, characterization results after the hot tensile test determined that with increasing the test temperature, yield stress, ultimate tensile strength (UTS), and elastic modulus declined nonlinearly. At last, fracture surfaces of the composite samples were investigated and it was confirmed that the applied load caused the fracture of the whiskers and, on the other side; cavity nucleation resulted in significant elongation in the specimens.

Preparation of Ti2C MXene phase by ion beam sputtering and ion irradiation

Thin titanium carbide films were prepared by ion beam sputtering of titanium and graphite targets followed by thermal annealing at 600 °C in vacuum and irradiation by Ar+ ions up to a fluence of 1015 ions/cm2. The stoichiometry of the films was analyzed by RBS and NRA methods, it was found to be Ti2.2C. The crystalline structure of the films was analyzed by STEM and EELS microscopic methods: before irradiation it was mostly amorphous with crystalline parts and visible network of micro-voids, crystallization and formation of laminar structure was observed after irradiation. The irradiated part showed corrugated surface morphology and a dense network of nano-openings. The thickness of the films increased from ca 67 nm to ca 83 nm. Obviously, the effect of the ion irradiation promoted the recrystallization and self-organization of the structure, resulting in the nano-laminar phase of Ti2C.

Phosphorylation of Connexin 43 by Cdk5 Modulates Neuronal Migration During Embryonic Brain Development.

The gap junction protein, connexin 43 (Cx43), is only present and abundantly expressed in astrocytes but is absent in neurons in the mature brain tissues. However, both the expression and function of Cx43 in neurons during brain embryonic development remain largely unexplored. In the present study, we confirmed that Cx43 is expressed in the migrating neurons in the embryonic stage of the brain. Neuron-specific Cx43 conditional knockout (cKO) using Cre-loxP technique impairs neuronal migration and formation of laminar structure in cerebral cortex during brain embryonic development. The animal behavior tests demonstrated that, at the adult stage, neuronal Cx43 cKO mice exhibit normal learning and memory functions but increased anxiety-like behavior. We also found that during the embryonic development, the gradually decreased Cx43 expression in the cortex is closely correlated with the upregulation of cyclin-dependent kinase 5 (Cdk5) activity. Cdk5 directly phosphorylates Cx43 at Ser279 and Ser282, which, in consequence, inhibits the membrane targeting of Cx43 and promotes its proteasome-dependent degradation. In summary, our findings revealed that the embryonic expression of Cx43 in neurons regulates processes of neuronal migration and positioning in the developing brain by controlling astrocyte-neuron interactions during brain embryonic development, and Cdk5 directly phosphorylates Cx43, which regulates the membrane localization and degradation of Cx43 in neurons.

Nanosegregation of ternary Cr–Ni–Fe alloy deposits electrodeposited from a Cr3+-based bath

A laminar structure with nanosized segregation was observed in Cr–Ni–Fe alloy deposits electroplated in a Cr3+-based bath with Ni2+ and Fe2+ ions. The formation of laminar structure could be attributed to the depletion of preferentially reduced ions, or cathodic polarization, adjacent to the cathodic surface. This nanosized segregation could be clearly observed with scanning-transmission-electron microscope in high-angle angular dark-field (HAADF) mode. A crystalline Fe-rich alloy deposit with a grain size of 4nm can be achieved with an electroplating current density of 15Adm−2, whereas an amorphous Cr-rich alloy deposit was produced with 25Adm−2. Owing to the approach toward thermal equilibrium in the two-phase field, uphill diffusion took place in the Cr-rich alloy deposit during annealing at 500°C, forming a Cr- and Fe-rich multilayer.

Orientation Mapping Study on the Inhomogeneous Microstructure Evolution during Annealing of 6013 Aluminum Alloy

Orientation mapping in transmission electron microscope was successfully applied to study microstructural changes at the initial stage of recrystallization in the aluminum alloy with a bimodal second-phase particle distribution. The alloy samples were reversibly cold rolled resulting in the formation of laminar structure with zones of localized strain around large second-phase particles. Orientation mapping and in-situ investigations carry information about the processes which are active in the deformation zones during annealing.

Synthesis of laminar wurtzite CdSe nanocrystals from CdO at room temperature

The conversion of CdO to laminar wurtzite CdSe nanocrystals was achieved in a mixture of ethylenediamine and hydrazine hydrate at room temperature. The mechanism of reaction and the formation of laminar structure were discussed, and it was found that the mixed solvent played a crucial role in conversion.

Landau intermediate state structure in type I superconductors

Landau laminar structures are discussed for cases where the normal-superconducting (N-S) boundary is curved and where it is straight throughout a sample. A numerical calculation shows that the free energy for a curved N-S boundary is less than that for a straight one, except for values ofd/Δ less than about 8 and a small region of magnetic fields close toh ⊥. Here Δ is the surface energy parameter andh ⊥ is the perpendicular critical field corresponding to a sample thicknessd. The expression forh ⊥ for the straight N-S boundary is different from that obtained by Simonin and Lopez. It is shown that the data ofh ⊥ reported to date are insufficient to verify the formation of laminar structures with a straight N-S boundary.