Dendritic Size Research Articles

Quantitative characterisation of ipRGCs in retinal degeneration using a computation platform for extracting and reconstructing single neurons in 3D from a multi-colour labeled population.

Light has a profound impact on mammalian physiology and behavior. Intrinsically photosensitive retinal ganglion cells (ipRGCs) express the photopigment melanopsin, rendering them sensitive to light, and are involved in both image-forming vision and non-image forming responses to light such as circadian photo-entrainment and the pupillary light reflex. Following outer photoreceptor degeneration, the death of rod and cone photoreceptors results in global re-modeling of the remnant neural retina. Although ipRGCs can continue signaling light information to the brain even in advanced stages of degeneration, it is unknown if all six morphologically distinct subtypes survive, or how their dendritic architecture may be affected. To answer these questions, we generated a computational platform-BRIAN (Brainbow Analysis of individual Neurons) to analyze Brainbow labeled tissues by allowing objective identification of voxels clusters in Principal Component Space, and their subsequent extraction to produce 3D images of single neurons suitable for analysis with existing tracing technology. We show that BRIAN can efficiently recreate single neurons or individual axonal projections from densely labeled tissue with sufficient anatomical resolution for subtype quantitative classification. We apply this tool to generate quantitative morphological information about ipRGCs in the degenerate retina including soma size, dendritic field size, dendritic complexity, and stratification. Using this information, we were able to identify cells whose characteristics match those reported for all six defined subtypes of ipRGC in the wildtype mouse retina (M1-M6), including the rare and complex M3 and M6 subtypes. This indicates that ipRGCs survive outer retinal degeneration with broadly normal morphology. We additionally describe one cell in the degenerate retina which matches the description of the Gigantic M1 cell in Humans which has not been previously identified in rodent.

Computational simulation of thermo-mechanical field and fluid flow and their effect on the solidification process in TWIP steel welds

The primary austenitic solidification mode of Twinning Induced Plasticity (TWIP) steel weld joints is one of the most important issues limiting its weldability. In order to gain knowledge on this topic, a comprehensive study was carried out through numerical simulation of diffusive-convective phenomena of fluid flow and heat transfer of the melted material in the weld pool of TWIP steel weld joints. Weldments were performed using different heat inputs and constraint conditions. The predictions of convective motion, thermal history and cooling rates estimated by finite element (FE) and finite volume (FV) simulations were correlated with chemical species segregation (Mn, C, Al and Si) and the solidification mode in the fusion zone. The microstructural characterization of weld joints and the numerical results provided a full analysis of the weld pool solidification process. Results revealed a relationship between both the dendrite size and Mn segregation with the estimated velocity field of liquid material in the melted zone. Moreover, the presence of δ-ferrite was experimentally detected in some weld joints and associated with the convective movement of melted material and chemical segregation. The cellular dendritic growth mode found in some weld joints contributed to the formation of δ-ferrite and promoted the transition of the solidification mode from austenitic to ferritic-austenitic. As well δ-ferrite allowed to mitigate hot-cracking and interrupted the Mn-enriched liquid film migration towards the heat-affected zone, avoiding the formation of liquation cracks. The presence of δ-ferrite phase maintained a high mechanical strength providing improved elongation regarding the welded material mechanical properties.

Evolutions of microstructure and mechanical property of high nitrogen steel repaired by the underwater directed energy deposition technique

Damaged high nitrogen steel (HNS) plates were repaired by underwater laser direct metal deposition (UDMD) technique at the ambient pressure of 0.3 MPa. Both experiments and finite element method (FEM) simulations were employed to elucidate the influence mechanism of the underwater hyperbaric environment on the microstructure evolution. Carbides were the most typical precipitates in the HNS selected in this research, and their features were dominated by molten pool cooling rate and the intrinsic heat treatment (IHT) effect associated with the thermal cycles. Accelerated cooling rate induced by water chilling effect or the weakened laser energy input promoted the carbide precipitation. Against the build direction, carbides became coarse and the overall content decreased due to the cumulative IHT effect. Such carbide features evolution trend in UDMD repaired sample was more pronounced than that in DMD repaired sample. The shortened high-temperature duration owing to the intense thermal dissipation in the underwater environment highlighted the proportion of intrinsic heat treatment (IHT) effect on carbide features and dendrite size. Owing to the slow air cooling and enhanced thermal accumulation in the ground environment, the prolonged high-temperature duration facilitated the decomposition of unstable austenite into lamellar intragranular carbide and ferrite. Benchmarking mechanical properties against the DMD repaired sample counterpart demonstrated that UDMD repaired samples possessed higher strength and comparable impact toughness.

Effect of Ti addition and cast part size on solidification structure and mechanical properties of medium carbon, low alloy cast steel

In this work, the effect of Ti addition and the cast part size on the solidification structure and mechanical properties of a medium carbon, low alloy cast steel was analyzed. The experimental analysis involved the design of the melts by using Thermo-Calc® software, where different amounts of Ti added to a standard chemical composition of an AISI 13XX steel were simulated. Then, the solidification macrostructure (dendritic pattern and grain size) and microstructure were characterized by using conventional and specific metallographic techniques. Finally, the mechanical behavior in terms of hardness and tensile properties were evaluated. The results show that the addition of 0.12% of Ti promotes a fine dispersion of Ti nitrides and carbides, but when the Ti concentration raises to 0.2%, the size of the Ti nitrides and carbides increases while its amount decreases. Ti nitrides and carbides particles act as nucleation sites for the precipitation of ferrite from austenite, and it was found that the addition of Ti in the higher concentrations refines the solidification macrostructure (dendritic pattern) for both cast part sizes evaluated. Regarding mechanical properties, the addition of Ti does not significantly vary the ultimate tensile strength but reduces the total elongation for cast part sizes

Comparative Study on the Surface Remelting of Mo-Si-B Alloys with Laser and Electron Beam

The Mo-12Si-8.5B alloy was surface-remelted by laser and electron beam, and the microstructure of its melt pool and substrate regions were analyzed by scanning electron microscopy (SEM), X-ray diffraction (XRD), and energy spectrometry (EDS) techniques. It was found that the composition of the surface phases in the Mo-12Si-8.5B alloy did not change by the high-energy beam surface remelting process, but the microstructure of the molten pool region was significantly different from that of the substrate region, and its phase distribution was more uniform. Dendrites appeared on the surface of the material under the action of both processes, and the Si- and B-rich phases were mainly gathered in the interdendritic region. In the melt pool of the laser-remelted specimens, the α-Mo phase was continuously distributed with an average dendrite length of 70 µm, while the α-Mo phase distribution in the melt pool of the electron beam remelted specimens were relatively concentrated, with a larger dendrite size and an average dendrite length of 120 µm. The dendrite size in the melt pool of the laser remelted material was smaller, and the distribution of the elements was relatively uniform. Using a laser beam as the heat source was more favorable for the next step of the additive manufacturing of the core parts of hypersonic vehicles.

Microstructure and mechanical properties of Mn-Cu based damping alloy fabricated by laser melting deposition

The M2052 (Mn-20Cu-5Ni-2Fe, at%) damping alloy specimen was prepared by laser melting deposition (LMD). And we studied the mechanical properties and microstructure of M2052 alloy. Columnar dendrite penetrating multiple cladding layers appeared in the as-deposited sample, and the size of dendrite tends to coarsen with the increase of laser power. Microsegregation and martensitic transformation occurs in the as-deposited M2052 alloy. The tensile strength of samples in different directions under the same process, and in the same direction under different processes is all exceeds 500 MPa. The fracture surfaces exhibit intergranular fracture model. This work shows great potential for fabricating Mn-Cu based damping alloy by LMD technology.

Density and distribution of dendritiform cells in the peripheral cornea of healthy subjects using in vivo confocal microscopy

PurposeTo establish in a large healthy cohort, dendritiform cell (DC) density and morphological parameters in the central and peripheral cornea using in vivo confocal microscopy (IVCM). MethodsA prospective, cross-sectional, observational study was conducted in 85 healthy volunteers (n = 85 eyes). IVCM images of corneal center and four peripheral zones were analyzed for DC density and morphology to compare means and assess correlations (p < 0.05 being statistically significant). ResultsCentral corneas had lower DC density (40.83 ± 5.14 cells/mm2; mean ± SEM) as compared to peripheral corneas (75.42 ± 2.67 cells/mm2, p < 0.0001). Inferior and superior zones demonstrated higher DC density (105.01 ± 7.12 and 90.62 ± 4.62 cells/mm2) compared to the nasal and temporal zones (59.93 ± 3.42 and 51.77 ± 2.98 cells/mm2, p < 0.0001). Similarly, lower DC size, field and number of dendrites were observed in the central as compared to the average peripheral cornea (p < 0.0001), with highest values in the inferior zone (p < 0.001 for all, except p < 0.05 for number of dendrites in superior zone). DC parameters did not correlate with age or gender. Inter-observer reliability was 0.987 for DC density and 0.771–0.922 for morphology. ConclusionIn healthy individuals, the peripheral cornea demonstrates higher DC density and larger morphology compared to the center, with highest values in the inferior zone. We provide the largest normative cohort for sub-stratified DC density and morphology, which can be used in future clinical trials to compare differential changes in diseased states. Furthermore, as DC parameters in the peripheral zones are dissimilar, random sampling of peripheral cornea may be inaccurate.

Bisphenol-A impairs synaptic formation and function by RGS4-mediated regulation of BDNF signaling in the cerebral cortex.

ABSTRACTBisphenol-A (BPA) is a representative endocrine disruptor, widely used in a variety of products including plastics, medical equipment and receipts. Hence, most people are exposed to BPA via the skin, digestive system or inhalation in everyday life. Furthermore, BPA crosses the blood–brain barrier and is linked to multiple neurological dysfunctions found in neurodegenerative and neuropsychological disorders. However, the mechanisms underlying BPA-associated neurological dysfunctions remain poorly understood. Here, we report that BPA exposure alters synapse morphology and function in the cerebral cortex. Cortical pyramidal neurons treated with BPA showed reduced size and number of dendrites and spines. The density of excitatory synapses was also decreased by BPA treatment. More importantly, we found that BPA disrupted normal synaptic transmission and cognitive behavior. RGS4 and its downstream BDNF/NTRK2 pathway appeared to mediate the effect of BPA on synaptic and neurological function. Our findings provide molecular mechanistic insights into anatomical and physiological neurotoxic consequences related to a potent endocrine modifier.

Microstructure and mechanical properties of underwater laser deposition remanufactured 316LN stainless steel at a pressure of 0.3 MPa

The nuclear power steel 316LN stainless steel (SS) was first repaired by underwater laser directed metal deposition (UDMD) technique with various processing parameters in a simulated 30 m underwater environment. The microstructure and mechanical properties of the as-repaired samples were systematically characterized. The results were compared with those of the samples repaired by in-air directed metal deposition (in-air DMD). The results indicate that the sizes of the columnar dendrites and equiaxed grains in the UDMD samples increased with linear laser energy. The dendrite size in the UDMD samples was smaller than that in in-air DMD samples due to the water quenching effect involved in the UDMD process. During UDMD, many oxide inclusions were formed in the repaired zones due to the influence of the water film in the underwater local dry area. The number of inclusions decreased with the increase of linear laser energy. The microhardness of the UDMD samples decreased with the increase of linear laser energy. The microhardness of the UDMD samples was higher than that of the in-air DMD samples due to the fact that high densities of dislocations, inclusions and M7C3 carbides were distributed in the UDMD samples. For the UDMD samples, the increase of linear laser energy led to decreasing tensile strengths and increasing impact energies. The mechanical properties of the UDMD samples were superior to those of the in-air DMD samples. The results obtained from this study could provide useful guidance for repairing underwater nuclear power materials by UDMD.

Influence of solidification conditions on chemical heterogeneities and dislocations patterning in additively manufactured 316L stainless steel

The dendritic substructure of 316L stainless steel processed by Laser Powder Bed Fusion (L-PBF) is experimentally investigated on three specimens built with significantly different scanning speeds and solidification cooling rates. Microstructural features of interest are misorientations between dendrites, gradients of chemical composition and dislocations structures. Similar amplitudes of chemical heterogeneities are found for all three samples, possibly related to the conjunction of relatively low variations of solidification rates and large partition coefficients for the considered solute elements. No crystalline misorientations between neighboring dendrites are observed, implying that interdendritic dislocations are not geometrically necessary dislocations stemming from solidification but arise from thermomechanical straining during post-solidification cooling. Dislocations patterning appear to be closely correlated to the periodicity of microsegregations, hinting at an effect of the local chemistry. No simple Hall-Petch-like effect of the dendrite size is observed on compression tests, possibly due to different strengthening mechanisms depending on the dislocations structures.

Parallel GPU-accelerated adaptive mesh refinement on two-dimensional phase-field lattice Boltzmann simulation of dendrite growth

Simulations of dendritic solidification involving melt convection and solid motion usually require a considerably higher computational domain than the dendrite size, whose computational efficiency with a uniform mesh is extremely low. In this study, to accelerate those two-dimensional simulations using the phase-field and lattice Boltzmann (PF-LB) methods, we developed a parallel computing method with multiple graphics processing units (GPUs) for the adaptive mesh refinement (AMR) method with dynamic load balancing (parallel-GPU AMR). It was confirmed that parallel-GPU AMR simulations were faster than those with the uniform mesh when the number of grid points in the adaptive mesh was around 40% or less than those in the uniform mesh. We also demonstrate that the developed parallel-GPU AMR can greatly accelerate the PF-LB simulations of dendrite growth with melt convection and solid motion.

Solidification structure and high temperature oxidation resistance of nano titanium dioxide TiO2 added Inconel 718 deposits by arc melt

In order to refine the microstructure of Inconel 718 and achieve high performance, nanometer TiO2 particles (nano-TiO2) were adopted to modify the solidification structure. After pretreating nano-TiO2, oxide added 718 nickel alloy were prepared by using arc melting technology, and the microstructure and oxidation behavior were investigated in detail. The results show that the microstructures of Inconel 718 alloys with different content of nano-TiO2 are all dendritic-like, and the size of dendrite gradually decreases and the shape tends to become equiaxed grain with the increase of TiO2 content. The grain refinement effect is best for 0.6%TiO2 added alloy. The precipitated phases become finer and more uniform due to grain refinement. The high temperature oxidation experiments of Inconel 718 alloy with different volume fractions of TiO2 show that the main oxides are Cr2O3, accompanying with some Nb-Fe oxides. With the decrease of grain size, the size of oxides gradually decreases, and the oxidation layers are more and more compact, which effectively improves the oxidation resistance.

Effect of in situ observation of cooling rates on acicular ferrite nucleation

Abstract The effect of cooling rates on acicular ferrite (AF) nucleation was observed in situ by laser scanning confocal microscopy. The precipitation characteristics of TiN–MnS inclusions, the austenite grain size, and the content and morphologies of AF were analyzed and compared under different cooling rates. The results indicated that with the increase of the cooling rate, the size of TiN–MnS inclusions precipitated in the test steel gradually decreased while the inclusion number increased. When the cooling rate increased from 0.2 to 10°C·s−1, the average inclusion size decreased from 2.7 to 1.3 µm. The austenite grain size decreased gradually with the increase of the cooling rate, and the larger the cooling rate was, the more uniform the grain size distribution. The AF proportion increased first and then decreased, it reached the maximum when the cooling rate was 5°C·s−1, which accounted for 82.6%. Meanwhile, the dendrite size decreased gradually, the average length decreased from 30 to 5 µm, and the average width decreased from 2.8 to 0.7 µm when the cooling rate increased from 0.2 to 10°C·s−1.

Influence of Mo on the Microstructure and Corrosion Behavior of Laser Cladding FeCoCrNi High-Entropy Alloy Coatings.

FeCoCrNi and FeCoNiCrMo0.2 high-entropy alloy powders were prepared by gas atomization. Two kinds of coatings were prepared on the surface of 304 stainless steel by laser cladding technology. The effect of Mo element on the microstructure of laser cladding FeCoCrNi coating and its corrosion behavior in 3.5 wt.% NaCl solution was investigated. Both FeCoCrNi and FeCoCrNiMo0.2 powders exhibit a single-phase FCC structure. Due to the remelting and multiple heat treatments during the preparation of the laser cladding coating, a small amount of σ and μ phases appeared in the FeCoCrNiMo0.2 coating. The microstructures of the two coatings from the bonding area to the top layer are planar, columnar and equiaxed grains, respectively. The addition of the Mo element causes the dendrite size in the middle region of the FeCoCrNiMo0.2 coating increases significantly and exhibits obvious orientation characteristics. FeCoCrNiMo0.2 coating has high corrosion potential (−0.01 VSHE) and low current density (0.94 × 10−7 A/cm2) in 3.5 wt.% NaCl solution, showing excellent corrosion resistance. The passivation film formed on corroded the FeCoCrNiMo0.2 coating contains high content of oxides of Cr and Mo. The addition of the Mo element enhances the compactness and pitting resistance of the passivation film.

Effect of melt overheating treatment on the microstructure and mechanical properties of Zn–Al alloy

This study focused on the effect of overheating treatment on the microstructure and tensile mechanical property of zinc-aluminum alloy. Ingots with designed composition were manufactured by melting pure metals and cast at different temperatures from 500 °C to 650 °C. Microstructure, strength and fracture mechanism were studied and their relationships with overheating temperature were analyzed. Dendrite size decreased with increasing overheating temperature and turned to equiaxed crystal at 650 °C. The yield stress, ultimate tensile stress and elongation increased by 16%, 31% and 163%, respectively after overheating treatment. It was also found that with the increase of overheating temperature, the brittle fracture mechanism gradually turns to a mixed fracture mechanism.

Effect of surface morphology and microstructure on the hot corrosion behavior of TiC/IN625 coatings prepared by extreme high-speed laser cladding

Extreme high-speed laser cladding (EHLA) was used to develop a pore- and crack-free TiC/IN625 coating. The surface roughness of EHLA could be as low as 6.004 µm. A more uniform dendrite size and composition distribution was obtained by EHLA. The mass gain of EHLA was 57.5% lower than that of the conventional laser cladding sample after hot corrosion in a mixed salt of 75%Na2SO4 + 25% NaCl at 900 ℃ for 60 h. High hot corrosion resistance of EHLA was mainly attributed to the lower surface roughness, smaller dendrite size, smaller grain size, and higher amount of low-angle grain boundaries.

A strategy to design Ti-based in-situ bulk metallic glass composites containing controllable volume fraction and composition of the dendrite phase using conventional titanium alloy Ti–6Al–4V

Up to now, the composition design in the field of Ti-based in-situ dendrite reinforced bulk metallic glass composites (BMGCs) has been a great challenge. In this work, a simple but effective strategy is proposed to tailor the dendrite composition and volume fraction by using conventional Titanium alloy Ti–6Al–4V, and a series of in-situ dendrite reinforced BMGCs (Z1-Z4) are prepared based on it. The dendrite volume fraction can be adjusted by changing the proportion of the Titanium alloy Ti–6Al–4V, while the compositions of the dendrites are highly correlated with Ti–6Al–4V. In these alloys, with the increase of the mass percent of the added Titanium alloy Ti–6Al–4V, the volume fraction of the dendrite phase increases monotonically from Z1 to Z4 alloy. Z1 alloy behaves like a BMG with a high yield strength and limited plasticity due to its small dendrite size. Z2-Z4 alloys show excellent plasticity and significant work-hardening ability, because the dendrite size is appropriate and the dendrites undergo stress-induced martensite transformation during compression. From Z2 to Z4 alloy, with the increase of dendrite volume fraction from 56% to 78%, the yield strength does not decrease, which is due to the gradually enhanced stability of the dendrites. This composition design strategy is effective and universal, which can provide a new perspective for the composition design and development of TiZr-based in-situ dendrite reinforced BMGCs.

Dendrite Refinement and Improved Mechanical Properties of SiC/TiC/Al Hybrid Nanocomposites

Hybrid nano-(SiCp + TiCp)/Al composites were fabricated by liquid ultrasonic assisted semisolid stirring processing. The eutectic silicon of Al matrix changes from acicular to fine granular with addition of nanoparticles and the dendrite size of primary α-Al decreases with increased nanoparticles. After adding the hybrid nanoparticles with 3 vol%, the minimum average dendrite size can be refined to 30 μm. EDS analysis shows that nano-SiCp and -TiCp particles are uniformly dispersed in Al matrix. The YS and UTS of the composites have reached 200 MPa and 228 MPa, respectively, which are increased by 34.1% and 33.3%, respectively. The elongation of the composites has reached 9.8%, which is increased by 40%. The strengthening mechanism of hybrid nano-(SiCp + TiCp)/Al composites is mainly Orowan strengthening and minorly Hall–Petch strengthening, and the effect of load transfer strengthening is the least.

An experimental investigation on the effect of gas tungsten arc welding current modes upon the microstructure, mechanical, and fractography properties of welded joints of two grades of AISI 316L and AISI310S alloy metal sheets

In this investigation, dissimilar welded joints of AISI 316 L and AISI 310S stainless steels were produced using continuous and pulsed modes current of the gas tungsten arc welding process. A filler metal type ER309L was used to strengthen the welded joints. The fracture mode of the tensile and Charpy impact test samples was studied using a field emission scanning electron microscope (FE-SEM). Results showed that the welded joints were broken in the 316 L steel side during the tensile test due to the presence of lower alloying elements in this steel compared with the AISI 310S stainless steel. As well, microhardness and Charpy impact tests results showed that changing the welding current from continuous to the pulsed one increased the values of these two mentioned attributes. Fractography analysis, performed on the fracture surfaces of both joints, showed a completely ductile fracture under both tensile and Charpy impact tests. Moreover, microstructural observations showed that the weld metal (WM) structure was austenitic-ferritic (AF) and contained columnar and equiaxed dendrites. Changing the welding current from the continuous to the pulsed one led to the transformation of the columnar dendrites to the very fine equiaxed dendrites. This welding current variation reduced the dendrite size of the WM and decreased the area of the unmixed zone (UMZ). Finally, XRD results indicated that austenite was the predominant phase in the welded joints.

Numerical Analysis of Nucleation and Growth of Stray Grain Formation during Laser Welding Nickel-Based Single-Crystal Superalloy Part I: Morphology and Size of Dendrite Growth

The dependency of morphology development and dendrite growth on welding conditions (laser power, welding speed and welding configuration) is numerically analyzed to decrease nucleation and growth of stray grain formation during laser processing aerospace component surface of ternary Ni-Cr-Al single-crystal superalloy. Proper (001)/[100] welding configuration crystallographically initiates three axisymmetrical distributions of microstructure development, i.e. stray grain formation, morphology development and dendrite trunk spacing, alongside the advancing solid/liquid interface of molten pool, whereby metallurgical properties are increased. Unpromising (001)/[110] welding configuration tends to crystallographically possesses unaxisymmetrical microstructure development to favor substantial crack-vulnerable dendrite size and morphology. Epitaxial [001] columnar dendrite growth region is favored for single-crystal dendrite growth, while vulnerable [100] equiaxed dendrite growth region is more susceptible to solidification cracking. The lower heat input is used, the smaller stray grain formation, negligible columnar/equiaxed transition (CET) and finer dendrite trunk spacing are consistently promoted by narrower constitutional undercooling ahead of solid/liquid interface to improve crack-resistant microstructure development and weld integrity. When comparing between [100] dendrite growth region on the right side and [010] dendrite growth region on the left side, (001)/[110] welding configuration spontaneously engenders severer stray grain formation, insidious columnar/equiaxed transition and coarser dendrite trunk spacing on the right side to deteriorate microstructure development with restriction of the same heat input on both sides of weld pool. The mechanism of asymmetrical solidification cracking as result of crystallography-induced microstructure degradation is therefore proposed. The theoretical predictions of asymmetrical solidification cracking susceptibility are comparable with experiments.