Dependence of Microstructures and Mechanical Properties on the Growth Rate and Composition in Directionally Solidified Mg-Gd Alloys

Microstructures and mechanical properties of directionally solidified Mg-xGd (5.21, 7.96 and 9.58 wt.%) alloys were investigated at a wide range of growth rates (V = 10-200 μm/s) under the constant temperature gradient (G = 30 K/mm). The results showed that when the growth rate was 10 μm/s, different interface morphologies were observed in three tested alloys: cellular morphology for Mg-5.21Gd alloy, a mixed morphology of cellular structure and dendritic structure for Mg-7.96Gd alloy and dendrite morphology for Mg-9.58Gd alloy, respectively. Upon further increasing the growth rate, only dendrite morphology was exhibited in all experimental alloys. The microstructural parameters (λ1, λ2) decreased with increasing the growth rate for all the experimental alloy, and the measured λ1 and λ2 values were in good agreement with Trivedi model and Kattamis-Flemings model, respectively. Vickers hardness and the ultimate tensile strength increased with the increase of the growth rate and Gd content, while the elongation decreased gradually. Furthermore, the relationships between the hardness, ultimate tensile strength, the growth rate and the microstructural parameters were discussed and compared with the previous experimental results.

Carboxypeptidase E Independently Changes Microtubule Glutamylation, Dendritic Branching, and Neuronal Migration

Neuronal migration and dendritogenesis are dependent on dynamic changes to the microtubule (MT) network. Among various factors that regulate MT dynamics and stability, post-translational modifications (PTMs) of MTs play a critical role in conferring specificity of regulatory protein binding to MTs. Thus, it is important to understand the regulation of PTMs during brain development as multiple developmental processes are dependent on MTs. In this study, we identified that carboxypeptidase E (CPE) changes tubulin polyglutamylation, a major PTM in the brain, and we examine the impact of CPE-mediated changes to polyglutamylation on cortical neuron migration and dendrite morphology. We show, for the first time, that overexpression of CPE increases the level of polyglutamylated α-tubulin while knockdown decreases the level of polyglutamylation. We also demonstrate that CPE-mediated changes to polyglutamylation are dependent on the CPE zinc-binding motif and that this motif is necessary for CPE action on p150Glued localization. However, overexpression of a CPE mutant that does not increase MT glutamylation mimics the effects of overexpression of wild type CPE on dendrite branching. Furthermore, although overexpression of wild type CPE does not alter cortical neuron migration, overexpression of the mutant may act in a dominant-negative manner as it decreases the number of neurons that reach the cortical plate (CP), as we previously reported for CPE knockdown. Overall, our data suggest that CPE changes MT glutamylation and redistribution of p150Glued and that this function of CPE is independent of its role in shaping dendrite development but plays a partial role in regulating cortical neuron migration.

The Mammalian Kalrn Locus Gives Rise to Several Novel Long Non-coding RNAs

The Kalrn gene encodes several multi-domain protein isoforms that localise to neuronal synapses, and play dynamic roles in shaping axonal outgrowth, dendrite morphology and dendritic spine re-modelling. The genomic locus is implicated in several neurodevelopmental and neuropsychiatric diseases including autism, schizophrenia and bipolar disease. Mutations in the coding regions, inherited in a classical Mendelian manner, have also been implicated in certain forms of autism and intellectual disability. At the molecular level, the protein isoforms, encoded by reported transcript isoforms, share some core domains arising from the central exons, while other domains, especially towards the C terminal may be selectively incorporated. This heterogeneity seems to confer the ability to grow and retract dendritic spines, thus making Kalirin a critical and dynamic player in dendritogenesis. We have previously shown that in the zebrafish genome, a novel brain specific non-coding RNA arising from the 5’ end of the Kalirin gene, durga regulates neuronal morphology. In search of the mammalian equivalent, we characterized the mammalian Kalrn loci in detail, annotating multiple novel non-coding RNAs, including linear and circular variants, through analysis of transcriptomics data and experimental approaches. By comparing the mouse and human loci and studying the expression of the novel lncRNAs arising from the locus during differentiation of primary cortical neurons in culture, we show that certain non-coding RNAs arising from the locus show a temporal expression profile that coincides with a subset of Kalirin protein coding isoforms. In humans, mouse and zebrafish the 5’end of the Kalrn locus gives rise to a chromatin associated lncRNA that is present in adult ovaries besides being expressed during brain development and in certain regions of the adult brain. Besides correcting some of the annotations available in public databases, we propose that this lncRNA arising from the 5’end of the Kalrn locus is the mammalian ortholog of zebrafish lncRNA durga.

Cordycepin Ameliorates Synaptic Dysfunction and Dendrite Morphology Damage of Hippocampal CA1 via A1R in Cerebral Ischemia

Cordycepin exerted significant neuroprotective effects and protected against cerebral ischemic damage. Learning and memory impairments after cerebral ischemia are common. Cordycepin has been proved to improve memory impairments induced by cerebral ischemia, but its underlying mechanism has not been revealed yet. The plasticity of synaptic structure and function is considered to be one of the neural mechanisms of learning and memory. Therefore, we investigated how cordycepin benefits dendritic morphology and synaptic transmission after cerebral ischemia and traced the related molecular mechanisms. The effects of cordycepin on the protection against ischemia were studied by using global cerebral ischemia (GCI) and oxygen-glucose deprivation (OGD) models. Behavioral long-term potentiation (LTP) and synaptic transmission were observed with electrophysiological recordings. The dendritic morphology and histological assessment were assessed by Golgi staining and hematoxylin-eosin (HE) staining, respectively. Adenosine A1 receptors (A1R) and adenosine A2A receptors (A2AR) were evaluated with western blotting. The results showed that cordycepin reduced the GCI-induced dendritic morphology scathing and behavioral LTP impairment in the hippocampal CA1 area, improved the learning and memory abilities, and up-regulated the level of A1R but not A2AR. In the in vitro experiments, cordycepin pre-perfusion could alleviate the hippocampal slices injury and synaptic transmission cripple induced by OGD, accompanied by increased adenosine content. In addition, the protective effect of cordycepin on OGD-induced synaptic transmission damage was eliminated by using an A1R antagonist instead of A2AR. These findings revealed that cordycepin alleviated synaptic dysfunction and dendritic injury in ischemic models by modulating A1R, which provides new insights into the pharmacological mechanisms of cordycepin for ameliorating cognitive impairment induced by cerebral ischemia.

Multi-scale simulation of the dendrite growth during selective laser melting of rare earth magnesium alloy

The solidification microstructure of the alloy fabricated by the selective-laser-melting (SLM) process can significantly impact its mechanical properties. In this study, a multi-scale model which couples the macroscale model for thermal-fluid and microscale cellular automata (CA) was proposed to simulate the complex solidification evolution and the dendrite growth (from planar to cellular to dendritic growth) during the SLM process. The solid–liquid interface of CA was dispersed with the bilinear interpolation method. On that basis, the curvature was accurately determined, and the calculation result was well verified by employing the Kurz–Giovanola–Trivedi analytical solution. The dendrite morphology, solute distribution, and primary dendrite arm spacing during the solidification of the SLM molten pool were quantitatively analyzed with the proposed model, well consistent with the experiment. The distribution of the undercooling field and the concentration field at the tip of dendrites different orientations were analyzed, and the two competing growth mechanisms of converging and diverging growth were revealed. Moreover, the research also indicates that during the growth of dendrites, the result of dendrite competition is determined by the height of the dendrite tip position in the direction of the thermal gradient, while the distribution of the concentration field (symmetrical or asymmetric) at the tip of the dendrite critically impacted the competing growth form of dendrites.

Effect of Ti on the Structure and Mechanical Properties of TixZr2.5-xTa Alloys

To determine the effects of Ti and mixing entropy (ΔSmix) on the structure and mechanical proper-ties of Zr-Ta alloys and then find a new potential energetic structural material with good me-chanical properties and more reactive elements, TixZr2.5−xTa (x = 0, 0.5, 1.0, 1.5, 2.0) alloys were investigated. The XRD experimental results showed that the phase transformation of TixZr2.5−xTa nonequal-ratio ternary alloys depended not on the value of ΔSmix, but on the amount of Ti atoms. With the addition of Ti, the content of the HCP phase decreased gradually. SEM analyses revealed that dendrite morphology and component segregation increasingly developed and then weakened gradually. When x increases to 2.0, TixZr2.5−xTa with the best mechanical properties can be ob-tained. The yield strength, compressive strength and fracture strain of Ti2.0Zr0.5Ta reached 883 MPa, 1568 MPa and 34.58%, respectively. The dependence of the phase transformation and me-chanical properties confirms that improving the properties of Zr-Ta alloys by doping Ti is feasible.

Growth of lithium-indium dendrites in all-solid-state lithium-based batteries with sulfide electrolytes

All-solid-state lithium-based batteries with inorganic solid electrolytes are considered a viable option for electrochemical energy storage applications. However, the application of lithium metal is hindered by issues associated with the growth of mossy and dendritic Li morphologies upon prolonged cell cycling and undesired reactions at the electrode/solid electrolyte interface. In this context, alloy materials such as lithium-indium (Li-In) alloys are widely used at the laboratory scale because of their (electro)chemical stability, although no in-depth investigations on their morphological stability have been reported yet. In this work, we report the growth of Li-In dendritic structures when the alloy material is used in combination with a Li6PS5Cl solid electrolyte and Li(Ni0.6Co0.2Mn0.2)O2 positive electrode active material and cycled at high currents (e.g., 3.8 mA cm−2) and high cathode loading (e.g., 4 mAh cm−2). Via ex situ measurements and simulations, we demonstrate that the irregular growth of Li-In dendrites leads to cell short circuits after room-temperature long-term cycling. Furthermore, the difference between Li and Li-In dendrites is investigated and discussed to demonstrate the distinct type of dendrite morphology.

The Morphology and Solute Segregation of Dendrite Growth in Ti-4.5% Al Alloy: A Phase-Field Study

Ti-Al alloys have excellent high-temperature performance and are often used in the manufacture of high-pressure compressors and low-pressure turbine blades for military aircraft engines. However, solute segregation is easy to occur in the solidification process of Ti-Al alloys, which will affect their properties. In this study, we used the quantitative phase-field model developed by Karma to study the equiaxed dendrite growth of Ti-4.5% Al alloy. The effects of supersaturation, undercooling and thermal disturbance on the dendrite morphology and solute segregation were studied. The results showed that the increase of supersaturation and undercooling will promote the growth of secondary dendrite arms and aggravate the solute segregation. When the undercooling is large, the solute in the root of the primary dendrite arms is seriously enriched, and when the supersaturation is large, the time for the dendrite tips to reach a steady-state will be shortened. The thermal disturbance mainly affects the morphology and distribution of the secondary dendrite arms but has almost no effect on the steady-state of the primary dendrite tips. This is helpful to understand the cause of solute segregation in Ti-Al alloy theoretically.

Overexpression of Lin28A in neural progenitor cells in vivo does not lead to brain tumor formation but results in reduced spine density

LIN28A overexpression has been identified in malignant brain tumors called embryonal tumors with multilayered rosettes (ETMR) but its specific role during brain development remains largely unknown. Radial glia cells of the ventricular zone (VZ) are proposed as a cell of origin for ETMR. We asked whether an overexpression of LIN28A in such cells might affect brain development or result in the formation of brain tumors.Constitutive overexpression of LIN28A in hGFAP-cre::lsl-Lin28A (GL) mice led to a transient increase of proliferation in the cortical VZ at embryonic stages but no postnatal brain tumor formation. Postnatally, GL mice displayed a pyramidal cell layer dispersion of the hippocampus and altered spine and dendrite morphology, including reduced dendritic spine densities in the hippocampus and cortex. GL mice displayed hyperkinetic activity and differential quantitative MS-based proteomics revealed altered time dependent molecular functions regarding mRNA processing and spine morphogenesis. Phosphoproteomic analyses indicated a downregulation of mTOR pathway modulated proteins such as Map1b being involved in microtubule dynamics.In conclusion, we show that Lin28A overexpression transiently increases proliferation of neural precursor cells but it is not sufficient to drive brain tumors in vivo. In contrast, Lin28A impacts on protein abundancy patterns related to spine morphogenesis and phosphorylation levels of proteins involved in microtubule dynamics, resulting in decreased spine densities of neurons in the hippocampus and cortex as well as in altered behavior. Our work provides new insights into the role of LIN28A for neuronal morphogenesis and development and may reveal future targets for treatment of ETMR patients.

Microstructure and Microsegregation Characterization of Laser Surfaced Remelted Al-3wt%Cu Alloys

Solidification rates during laser remelting of solid metals occur under solidification conditions that are far from equilibrium conditions. The microstructural evolution and microsegregation behaviors are affected by these conditions. This study comprised an experimental characterization of the ultra-fine microstructure and microsegregation in laser surface remelted regions of a hypoeutectic Al-Cu alloy. The laser scan speed, which controls the cooling rate within the remelted region, was observed to have a significant effect on microstructural features and microsegregation. Dendrite arm spacing was determined to decrease with increasing scan speed and depended on location within the melt pool. A transition of the dendrite morphology was also observed in the melt pools. This transition, which is attributed to the grain orientation change influenced by the laser beam movement, was experimentally characterized. The measured microsegregation profiles show decreasing microsegregation as cooling rate increases which is typically of increasing undercooling and non-equilibrium solidification.