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Two ultrasonic modes, i.e., continuous and pulsed ultrasounds, were introduced into the directional solidification process of Cu68.3Al27.6Ni4.1 alloy. A columnar-to-equiaxed structure transition occurred to primary β(Cu3Al) phase within continuous ultrasonic field, which was accompanied with a grain size reduction by 7.5 times. Under pulsed ultrasound, β phase maintained the fine columnar structures with a similar grain size. In the former case, numerous β phase nucleation sites formed ahead of solid/liquid (S/L) interface because of the large local undercoolings induced by transient cavitation. Meanwhile, intensive acoustic streaming suppressed the liquid temperature gradient from 120 to 85 K/cm, which interrupted the solute transportation along heat flow direction and resulted in equiaxed microstructures. Under the intermittent ultrasonic action in the latter case, fewer nucleation sites were generated near S/L interface but small columnar β grains were split from the original ones under stable cavitation. Since no steady convection was driven, the liquid temperature gradient of 110 K/cm remained almost constant, making those grains grow into refined columnar structures. Under the action of pulsed ultrasound, the yield strength was enhanced by a factor of 1.5 because of grain refinement strengthening, together with 94 pct shape recovery rate due to columnar grain structures. [ABSTRACT FROM AUTHOR]

We demonstrate aluminum-on-silicon planar transmon qubits with time-averaged T1 energy relaxation times of up to 270 μs, corresponding to Q = 5 million, and a highest observed value of 501 μs. Through materials analysis techniques and numerical simulations we investigate the dominant source of energy loss, and devise and demonstrate a strategy toward its mitigation. Growing aluminum films thicker than 300 nm reduces the presence of oxide, a known host of defects, near the substrate-metal interface, as confirmed by time-of-flight secondary ion mass spectrometry. A loss analysis of coplanar waveguide resonators shows that this results in a reduction of dielectric loss due to two-level system defects. The correlation between the enhanced performance of our devices and the film thickness is due to the aluminum growth in columnar structures of parallel grain boundaries: transmission electron microscopy shows larger grains in the thicker film, and consequently fewer grain boundaries containing oxide near the substrate-metal interface. [ABSTRACT FROM AUTHOR]

Objective: To investigate cortical microstructural measures from diffusion MRI as "neurodegeneration" markers that could improve prognostic accuracy in mild cognitive impairment (MCI). Methods: The prognostic power of Amyloid/Tau/Neurodegeneration (ATN) biomarkers to predict progression from MCI to AD or non‐AD dementia was investigated. Ninety patients underwent clinical evaluation (follow‐up interval 32 ± 18 months), lumbar puncture, and MRI. Participants were grouped by clinical stage and cerebrospinal fluid Amyloid and Tau status. T1‐structural and diffusion MRI scans were analyzed to calculate diffusion metrics related to cortical columnar structure (AngleR, ParlPD, PerpPD+), cortical mean diffusivity, and fractional anisotropy. Statistical tests were corrected for multiple comparisons. Prognostic power was assessed using receiver operating characteristic (ROC) analysis and related indices. Results: A progressive increase of whole‐brain cortical diffusion values was observed along the AD continuum, with all A+ groups showing significantly higher AngleR than A−T−. Investigating clinical progression to dementia, the AT biomarkers together showed good positive predictive value (with 90.91% of MCI A+T+ converting to dementia) but poor negative predictive value (with 40% of MCI A−T− progressing to a mix of AD and non‐AD dementias). Adding whole‐brain AngleR as an N marker, produced good differentiation between stable and converting MCI A−T− patients (0.8 area under ROC curve) and substantially improved negative predictive value (+21.25%). Interpretation: Results support the clinical utility of cortical microstructure to aid prognosis, especially in A−T− patients. Further work will investigate other complexities of the real‐world clinical setting, including A−T+ groups. Diffusion MRI measures of neurodegeneration may complement fluid AT markers to support clinical decision‐making. [ABSTRACT FROM AUTHOR]

During the solidification process, microstructures are affected by the experimental conditions, the thermophysical characteristics of the alloy, and the type of grain-refining particles. Unidirectional solidification experiments were performed in a vertical Bridgman-type furnace to investigate the effect of the solidification front velocity on the solidified microstructure of a non-refined and refined Al-20%Cu alloy. The samples were solidified by rapidly increasing the sample velocity (v) range from 0.02 mm/s to 0.2 mm/s while maintaining an almost constant temperature gradient (~5 K/mm). As a result, despite changes in the solid/liquid front velocity along the sample, the microstructure of the non-refined alloys remained columnar. In the refined alloy, the columnar structure changed into an equiaxed structure at two different front velocities. [ABSTRACT FROM AUTHOR]

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The copper and copper alloys' ingots have been subjected to structural observation in order to estimate the Peclet Number at which these ingots were solidifying. It was stated that the formation of columnar structure within the ingots occurred at a high Peclet Number, higher than the threshold value of this parameter, Pe = 500. The formulated relationships of the Growth Law correspond to a high Peclet Number due to application of the adequate development in series of the Ivantsov's function. The Growth Law has been developed on the basis of the definition of the wavelength of perturbation which leads to the dispersion of the planar s/l interface. New definition of the index of stability connected with the behavior of solute concentration at the s/l interface has been delivered. The current definition is related to non-equilibrium solidification. The index can be easily calculated using some parameters delivered by a given Cu-X phase diagram. Physical meaning of the formulated Growth Law has also been presented. [ABSTRACT FROM AUTHOR]

Understanding the thermal properties and enhancing the performance of zirconium diboride (ZrB 2) under extreme conditions is crucial, especially given its role as a burnable absorber in nuclear fuel pellets and its potential applications in accident-tolerant fuels. This study explores the structural alterations of ZrB 2 crystals induced by gamma irradiation and subsequent thermal annealing. ZrB 2 crystals were exposed to absorption doses of 300 kGy, 1000 kGy, 1500 kGy, and 3000 kGy using a 60Co gamma source, followed by thermal treatment at 1173 K under vacuum conditions. Also, Monte Carlo simulations were utilized to analyze the energy deposition and distribution of gamma quanta within the material during irradiation, highlighting Compton effects up to 0.23 MeV. X-ray diffraction analysis elucidated the impact of gamma radiation on ZrB 2 crystal lattice parameters, space group, and volume expansion coefficient. Post-irradiation analysis revealed a maximum degree of amorphization and investigated mechanisms governing lattice parameter expansion. Thermal annealing at 1173 K significantly enhanced crystallinity, reducing amorphization to 0.2 % at an absorption dose of 3000 kGy and facilitating the restoration of the crystal's columnar structure. This comprehensive investigation provides insights into the intricate interplay between gamma irradiation, thermal processing, and resulting structural changes in ZrB 2 nanocrystals, essential for applications in radiation-exposed environments. • ZrB 2 exhibited a maximum amorphization of 1.2% at an absorption dose of 3000 kGy. • Thermal treatment at 1173 K reducing amorphization to 0.2% at 3000 kGy without inducing phase transitions or oxide formation. • At (101) diffraction peak revealed a threefold increase in crystalline regularity at 1173 K. [ABSTRACT FROM AUTHOR]

Yttria-stabilized zirconia (YSZ) is the most common material used as a thermal barrier in several engineering applications. In order to improve the insulator potential of these thin films, an oblique-angle deposition approach was used to grow YSZ with tilted columnar structures. Initially, the period (n) was defined as the repetition unit composed of two layers each with different columnar growth directions, and then, n was increased (n = 1, 2, 10, 30, and 50), keeping constant the total thickness (~3.50 µm). The influence of (n) on the structure, roughness, grain size, microstructure, and thermal conductivity (κ) of thin films deposited was determined by X-ray diffraction (XRD), atomic force microscopy (AFM), scanning electron microscopy (SEM), transmission electron microscopy, and hot-plate technique, respectively. For all the samples, XRD patterns indicate the presence of the characteristic 8YSZ tetragonal phase peaks. Through AFM analysis, it was established that the roughness of the films deposited decreases from (4.0 ± 0.6) to (2.0 ± 0.6) nm when n is increased. Cross-sectional images recorded by SEM corroborate the formation of marked interfaces when growth direction changes occur, allowing to identify a multilayer system with a "zigzag" microstructure and an evolution towards more refined and isolated columns. Moreover, the SEM images reveal that for n = 10, 30, 50, and 70, the growth direction of the column is perpendicular to the substrate plane, losing its tilted form and the "zigzag" behavior becomes intracolumnar, reaching nanometer scale. Finally, analyses by hot-plate technique for different n repetition units showed that the thermal conductivity of YSZ films decreases from 0.151 W/m K to 0.064 W/m K, establishing the direct influence of the "zigzag" microstructure on the j value. This study shows the potential of growing YSZ thin films by oblique-angle deposition as an effective method to improving the thermal insulator potential of this material. [ABSTRACT FROM AUTHOR]

CaO-MgO-Al 2 O 3 -SiO 2 (CMAS) is a primary contributor to the failure of thermal barrier coatings, particularly those with columnar structures fabricated via electron beam physical vapor deposition (EB-PVD). This paper presents the laser micro glazing (LMGing) of EB-PVD using an ultraviolet pulsed ultrashort pulsed laser. With the disappearance of inter-columnar gaps, a smooth LMGed layer with extremely narrow cracks (<0.9 μm in width) were formed on the surface. Employing the sessile-drop method, heat treatment demonstrated that the LMGed layer effectively suppressed the wettability, penetration, and degradation behaviors of CMAS. Compared to the original, the spreading area of CMAS on the LMGed layer was decreased by 48 % (37.8 mm2 → 19.5 mm2), while the contact angle was increased by 116 % (6.2° → 13.4°). Meanwhile, a small amount of CMAS was found in the inter-columnar gaps, while no CMAS aggregated at the bottom. The depth of the corrosion layer at the CMAS-coating interface decreased by 68 % (9.9 μm → 3.2 μm), ensuring the blocking effect of the LMGed layer. • EB-PVD 8YSZ coatings were laser micro glazed (LMGed) by an ultraviolet picosecond ultrashort pulsed laser. • The inter columnar gaps were disappeared and extremely narrow cracks (<0.9 μm) were formed in smooth LMGed layers. • The wettability, penetration, and degradation behaviors of CMAS on LMGed layer were inhibited. • The corrosion resistance mechanism of LMGed layer to CMAS swas systemically investigated. [ABSTRACT FROM AUTHOR]

We report on the spontaneous formation of lateral composition modulations (LCMs) in Ga(As,Bi) epilayers grown by low-temperature (<300 °C) molecular beam epitaxy (MBE) on GaAs(001). Both cross-section and plan-view transmission electron microscopy techniques are used to investigate the nature of the LCMs, consisting of Bi-rich cylinder-like nanostructures lying along the [001] growth direction. The observed LCMs are the consequence of a two-dimensional phase separation process occurring at the surface of the growing epilayers, and their columnar nature is consistent with a surface-directed spinodal decomposition process. Although LCMs are thermodynamically driven, we show how they can be kinetically controlled, in particular, through the As/Ga flux ratio and the substrate temperature. This is a result of LCMs developing from surface atomic diffusion processes, since the atomic dimer configurations on the surface alter adatom diffusivity. The significant role of the surface reconstructions is also discussed. [ABSTRACT FROM AUTHOR]

• FePt(BN-VN, Ag, C) film shows high perpendicular magnetic anisotropy. • FePt(BN-VN, Ag, C) film illustrates high out-of-plane coercivity. • The FePt grains present a more uniform columnar structure with VN doping. • The microstructure was improved by grain boundary segregation of VN. Segregants are essential materials for forming the complexation or granular microstructure in thin films for magnetic recording media. One such film, FePt-BN, has a metallic L1 0 FePt main phase as its matrix, in addition to having BN and C segregants at the grain boundaries. Amorphous BN has sufficient mechanical strength to support the columnar growth of FePt grains, however, it has a lower deposition rate resulting in columnar grains with a nonuniform aspect ratio. Moreover, some B diffuses in the interstitial site of FePt lattices. To overcome these limitations, this study added the transition nitride VN and ZrN with equal volume percentages to replace some BN segregants in FePt(BN, Ag, C) films: substantially different segregation behaviors were observed. Microstructural imaging mapping revealed that although VN segregated the FePt grains boundary, ZrN was diffused in the lattice. The FePt-BN-ZrN film thus had more disordered grains contributing to a higher in-plane magnetization and wider hard axis magnetic hysteresis loops than did FePt-BN-VN. The FePt-BN-VN film has the highest perpendicular magnetic anisotropy constant (K u = 2.17 × 106 J/m3) and coercivity (H c = 4 T); moreover, parallel remanence magnetization was minimal with a linear in-plane magnetization loop. The FePt-BN-VN film was sputtered directly on MgO(100) but depositing the FePt-BN-ZrN film required a 2-nm-thick FePt nucleation layer. The high atomic number of Zr and high sputter yield ratio (Y N /Y metal) of ZrN may increase the sites occupied by N, potentially affecting ZrN segregation. [ABSTRACT FROM AUTHOR]

Self-assembled oxide thin films have tremendous potential applications in next generation of multifunctional systems. However, the manipulation of nanostructures and understanding on the relationship between nanostructures and functionalities remain as substantial challenges. Recently, an interesting architecture transformation between two basic nanocomposite structures has been demonstrated, i.e., from a horizontal layered structure to a vertical columnar structure, simply by tuning the film compositions in the (YBa2Cu3O7-δ)1-x:(BaZrO3)x system. In this work, the architecture dependence of functionalities has been investigated. The nanostructure manipulation has been revealed to largely affect the lattice structures and superconductive properties, especially at the critical composition of nanostructure transformation. The present work represents a novel approach to tune the self-assembled nanostructures and to further understand that how the nanostructures contribute to the functionalities in oxide thin films. [ABSTRACT FROM AUTHOR]

We present a double-charge model for the interaction between parallel polarizable hard spherocylin-ders subject to an external electric field. Using Monte Carlo simulations and free-energy calculations, we predict the phase behaviour for this model as a function of the density and electric field strength, at a fixed length-to-diameter ratio L/D = 5. The resulting phase diagram contains, in addition to the well-known nematic, smectic A, ABC crystal, and columnar phases, a smectic C phase, and a low temperature crystal Xphase. We also find a string fluid at low densities and field strengths, resembling results found for dipolar spheres. [ABSTRACT FROM AUTHOR]

The surface microstructure and growth behavior of an Fe0.4 mass%C alloy formed by lithium-added salt-bath nitrocarburizing were investigated. The Fe0.4 mass%C alloy was prepared by arc melting and nitrocarburized by a salt-bath containing Li+, Na+, K+, CNO-, and CN- at 823K from 0.1 h up to 10 h. A compound layer forms on the surface at the beginning of nitrocarburizing, and then an oxide layer forms on the compound layer after nitrocarburizing for 1.0 h. Afterwards, the thickness of both layers increase. A grain boundary oxide forms at the interfaces of columnar crystals in the compound layer. The oxide consists of LixFe1-xO with an NaCl-type structure, and the growth of the oxide layer is controlled by the outward diffusion of iron in the oxide layer. Meanwhile, the compound layer consists mainly of an ε-Fe2(N,C)1-y phase and a slight £A-Fe4(N,C)1+z phase near the substrate. [ABSTRACT FROM AUTHOR]

The growth of InAs columnar quantum dots (CQDs) on GaAs substrates by molecular beam epitaxy was investigated. The CQDs were formed by depositing a 1.8 monolayer (ML) InAs seed dot layer and a short period GaAs/InAs superlattice (SL). It was found that the growth of the CQDs is very sensitive to growth interruption (GI) and growth temperature. Both longer GI and higher growth temperature impact the size dispersion of the CQDs, which causes the broadening of photoluminescence (PL) spectrum and the presence of the additional PL peak tails. By properly choosing the GI and the growth temperature, CQDs including GaAs (3 ML)/InAs (0.62 ML) SL with period number up to 35 without plastic relaxation were grown. The corresponding equivalent thickness of the SL is 41 nm which is two times higher than the theoretical critical thickness of the strained InGaAs layer with the same average In composition of 16%. The increase of the critical thickness is partially associated with the formation of the CQDs. Based on a five-stack CQD active region, laser diodes emitting around 1120 nm at room temperature were demonstrated, indicating a high material quality. CQDs with nearly isotropic cross section (20 nm×20 nm dimensions) were formed by depositing a 16-period GaAs (3 ML)/InAs (0.62 ML) SL on an InAs seed dot layer, indicating the feasibility of artificial shape engineering of QDs. Such a structure is expected to be very promising for polarization insensitive device applications, such as semiconductor optical amplifiers. [ABSTRACT FROM AUTHOR]

Taking advantage of recent estimates, by one of us, of the critical temperature of the isotropic-ferroelectric transition of high density dipolar hard spheres, we performed new Monte Carlo simulations in the close vicinity of these estimates and applied histogram reweighting methods to obtain refined values of the critical temperatures from the crossing of the fourth-order cumulant for different system sizes. The ferroelectric line is determined in the density range ρ*=0.80–0.95, and the onset of columnar ordering is located. [ABSTRACT FROM AUTHOR]

X-ray diffraction patterns showed that crystallinity of the annealed ZnO films was improved by thermal annealing. Transmission electron microscopy images showed that columnar structures were preferentially formed in ZnO thin films due to thermal annealing, and electron energy loss spectroscopy images showed that annealing caused O2 atoms to diffuse out from the upper region in the ZnO thin film. The effects of thermal treatment on the formation of the columnar structures in ZnO thin films grown on Si (100) substrates are described on the basis of the experimental results. [ABSTRACT FROM AUTHOR]

By Plasma Spray-Physical Vapor Deposition (PS-PVD), major fractions of the powder feedstock can be evaporated so that the coating builds up mainly from vapor phase. In this work, the deposition mechanisms at different PS-PVD conditions were investigated. Depending on the plasma flow conditions and the substrate temperature, the columns in the coatings possess successively pyramidal, cauliflower, and lamellar shaped tops. In addition, the different microstructures show characteristic crystallographic textures, in which different in-plane and out-of-plane orientations were observed by pole figures. Based on investigations by electron back-scatter diffraction (EBSD), the overall coating growth process can be roughly divided into three subsequent stages: equiaxed growth, competitive growth, and preferential growth. Influences of diffusion and shadowing on final coating microstructure and orientation were discussed. The formation of equiaxed grains was proposed to be caused by high nucleation rates, which are probably induced by large undercooling and super-saturation at the beginning of deposition. The preferential growth orientation was preliminarily explained based on an evolutionary selection mechanism. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • Transparent model alloy allows for in-situ observation of the solidification. • Solidification experiments performed in g-levels ranging from zero-g up to 10g 0. • Growth of columnar dendrites nearly independent of the g-level. • High g-levels result in a cascade-like settling of growing equiaxed dendrites. • The columnar to equiaxed transition is accelerated in hyper-g environment. Abstract Centrifugal casting is an important method to produce superior-quality cast parts. The microstructure and therefore materials properties strongly depend on the hyper-gravity level. To investigate the effect of gravity level on the solidification behavior, the transparent model alloy Neopentylglycol-(D)Camphor is used, which solidifies like metals. Its optical transparency allows for in-situ observation of columnar and equiaxed crystal growth. The experiments were carried out in a constant temperature gradient with two different cooling rates, and for g-levels ranging from zero-g in microgravity environment up to 10g 0 on a centrifuge. It is found that the overall temperature and solutal fields close to the solidification front are not significantly altered by the laminar 3D melt flow in hyper-g environment. As a consequence, the growth velocity and primary spacing of columnar dendrites is nearly independent of the g-level. Increasing the cooling rate allows for nucleation and growth of equiaxed dendrites in the undercooled region ahead of the columnar solid-liquid interface. Here, at high g-levels the nucleation rate increases significantly and an accelerated, cascade-like settling of the growing equiaxed dendrites is observed. As a result, an earlier transition from columnar to equiaxed dendritic growth is detected in hyper-g environment. [ABSTRACT FROM AUTHOR]

Abstract Computer simulation is the most promising approach for the systematical permeability prediction of liquid flow in the mushy zone for various solidification conditions. In this study, we propose a permeability prediction method by using large–scale simulation of phase–field and lattice Boltzmann methods. Using the proposed method, permeability predictions are performed for the flow normal to the columnar solidification structures with multiple dendrites/cells. In addition, the prediction is also performed for columnar solidification structures with periodically arranged dendrites/cells to evaluate the permeability in the full range of solidification fraction and investigate the effect of primary arm array on the permeability. As a result, it is concluded that the dimensionless permeability using a specific interface area of columnar solidification structures can be well approximated by that of a regular hexagonal array of cylinders. Moreover, it is confirmed that the columnar dendrite/cell structure with a periodic regular hexagonal array provides realistic permeability predictions for columnar solidification structures. Graphical abstract Image 1 [ABSTRACT FROM AUTHOR]

Highlights • Electrolyte with a thickness less than grain size was fabricated by cost-effective method. • Bamboo-structured thin electrolyte effectively reduces ohmic resistance of protonic ceramic fuel cell. • Electrode reactions were analyzed by distribution of relaxation time method. • Surface diffusion of an adsorbed oxygen to the triple phase boundaries at cathode is the most probable rate determining step. Abstract High-performance and cost-effective fabrications should be simultaneously achieved for practical applications of fuel cells. Unfortunately, protonic ceramic fuel cells, which are considered next-generation solid oxide fuel cells operating at lower temperatures (≤600 °C), do not satisfy the requirements. While thin electrolyte and rapid reactions at electrode/electrolyte interfaces are crucial for cell performance, the thickness of the electrolyte via cost-effective ceramic processes is still not satisfactory (currently capable of >10 μm) and the electrode reaction(s) are yet to be clarified. Here we demonstrate the fabrication of a columnar-structured thin electrolyte (∼2.5 μm) of BaCe 0.55 Zr 0.3 Y 0.15 O 3-δ , in which no perpendicular grain boundaries exist against the current direction, through a low-cost screen printing method. A high open-cell voltage of 1.10 V ensures that the thin electrolyte is sufficiently dense for gas-tightness, thereby achieving an extraordinary maximum power density of 350 mW/cm2 at 500 °C. The electrode reactions are investigated by distribution of relaxation time method based on electrochemical impedance spectroscopy as a function of oxygen partial pressure and hydrogen partial pressure at 500 °C, suggesting that the reaction step corresponding to the surface diffusion of an adsorbed oxygen to the triple phase boundaries at the cathode is most probably the main contributor to the overall polarization resistances. [ABSTRACT FROM AUTHOR]

Focuses on a study which attempted to clarify the anisotropy in the optical absorption and nanostructure of thin films prepared by oblique codeposition of silver and SiO[sub2]. Condition of the columnar structure at a low concentration of silver; Situation where an inhomogeneous distribution of silver particles is obtained; Role of the anisotropic optical absorption of silver and SiO[sub2] hybrid films.

We present a semiempirical model based on the shadowing effect to describe quantitatively the aggregation of columnar structure during physical vapor condensation onto a surface with an array of line seeds and a flat surface. Specifically, we predict the relationship between the column angle and the incident flux angle and how this relationship changes with processing conditions and materials. The model uses one input parameter, the fan angle generated at normal incident flux. The model describes well our experimental data on the Ge column angle evolution as a function of a wide range of incident flux angles. [ABSTRACT FROM AUTHOR]

Abstract In the present investigation, we wish to report a new class of blue light emitting liquid crystalline bowl-shaped molecules based on oxadiazole calix[4]arene has been designed and synthesized. These supramolecular compounds were investigated by polarizing optical microscope (POM), differential scanning calorimetry (DSC), thermo gravimetric analysis (TGA), high temperature X-ray diffraction and photophysical studies. We have prepared total six newly supramolecular derivatives having butyl alkyl bridge with oxadiazole ring and variable trisubstituted side alkoxy chain on the lower rim of calix[4]arene. The present synthesized bowl-shaped molecules are promising to stabilize the hexagonal columnar phase over a broad thermal range. Thermal behavior as well as photophysical behaviors of these new bowl-shaped molecules are extremely dependent on the number and types of peripheral tail group present in the lower rim of calix[4]arene inbuilt with schiff-base linking unit. Additionally, these synthesized oxadiazole calix[4]arene based supramolecular compounds showed blue luminescence in solution as well as thin films under long wavelength UV light. These properties of present material suggest that these may have promising applications in organic electronics. Graphical abstract Unlabelled Image Highlights • The supramolecular bowl-shaped oxadiazole calix[4]arene derivatives were synthesized. • They are promising to stabilize the hexagonal columnar phase with broad temperature range. • The derivatives showed blue luminescence in solution as well as thin film under long wavelength UV light. • The derivatives showed good quantum yields in solution and solid film. [ABSTRACT FROM AUTHOR]

Entasis, upward curvature, columnar inclination and several other manipulations or deviations from the strict geometrical rules were known in Ancient Greece and Rome and some of them - entasis could be taken as example - were used up to the beginning of the 20th century in eclectic and historicizing architecture. The article mentions historical texts about entasis from Vitruvius up to Renaissance works. Mainly Vignola's description of proper and elegant way of how to construct columnar entasis curve of the Tuscan and Doric order columns is discussed in detail and expressed mathematically. [ABSTRACT FROM AUTHOR]

Highlights • Improvement mechanism of sputtered AlN films by high-temperature was investigated. • A two-layer structure with different sizes and strain was in sputtered AlN films. • Columnar structure split into small domains and coalesced during annealing. • The polarity switched from N- to Al-polar in the growth direction owing to O 2. Abstract The improvement mechanism of sputtered AlN films by high temperature annealing in nitrogen ambient has been investigated. Sputtered AlN films were annealed at 1100–1700 °C and their microstructures were observed by scanning transmission electron microscopy. A two-layer structure consisting of columnar domains with different sizes was observed in the as-grown sputtered AlN films. The first layer with 10 nm thickness located at the AlN/sapphire interface, comprised columnar domains with diameters of nm order and was compressively strained owing to the lattice mismatch between AlN and sapphire. The diameter of columnar domains in the other layer was approximately 25 nm. The columnar domains split into irregularly shaped and coalesced at an elevated annealing temperature, resulting in improved crystal quality. When the annealing temperature was 1700 °C, the domain boundaries in AlN films were almost annihilated and the full width at half maximum of the (0 0 0 2)- and (1 0 −1 2)-plane X-ray rocking curves were improved to as low as 49 and 310 arcsec, respectively. The polarity switched from N-polar to Al-polar after about 4–10 AlN layers in the growth direction. The oxygen element content slightly increased at the polarity inversion boundary, which may have caused the polarity to switch. [ABSTRACT FROM AUTHOR]

Metallographic studies performed on a cross-section of static steel ingot allow the observation of the following morphological zones: a) columnar grains (treated as austenite single crystals), b) zone of the columnar into equiaxed grains transformation (CET), and c) equiaxed grains at the ingot axis. These zones are reproduced theoretically by the numerical simulation. The simulation is based on the calculation of both the temperature field in a solidifying large steel ingot and the thermal gradient field obtained for the same boundary conditions. In particular, a new, innovative method based on the mathematical treatment applied to different functions resulting from both the aforementioned fields, are used in the structural predictions. The method developed, firstly for the massive steel ingot, has subsequently been applied to theoretically predict the structural zones in continuously cast brass ingots. In the case of continuously cast brass ingots three different morphologies were revealed experimentally: a) columnar structures, b) equiaxed structures preceded by the CET (sharp transition), and c) single crystals situated axially. The above model for the structural zones prediction is useful in plastic deformation design for: a) steel forging ingots assigned for the crankshafts applied to the ship engines, and b) continuously cast brass ingots assigned for special applications in the shipbuilding industry. [ABSTRACT FROM AUTHOR]

Abstract A molecular dynamics simulation has been carried out to investigate the effect of the incident angle in the oblique-angle deposition method on the atomic structure of the resulted hydrogenated amorphous silicon (a-Si:H) thin film. The atomic interaction in Si H system was calculated by Murty-Tersoff potential. The simulation results show that the a-Si:H thin film grew in a two-dimension mode at low or normal incidence (0°, 15° and 30°), however, it changed to follow a columnar or island-like mode at high incidence. As incident angles increased from 0° to 75°, the surface roughness increased, the adsorption rate decreased, and the a-Si:H thin film had more porous, lower density and higher content of the dangling bond. The analysis of atomic diffusion indicated that the incident angle played a crucial role in affecting the diffusion of atoms: the diffusion ability of high incidence was greater than that of low incidence. The growth mode, microstructure of a-Si:H thin film, and atomic diffusion ability were mainly influenced by shadowing effect. Highlights • The a-Si:H thin film grew in a two-dimension mode at low or normal incidence (0°, 15° and 30°). • The a-Si:H thin film grew in a columnar or island-like mode at high incidence. • The incident angle played a crucial role in affecting the diffusion of atoms. • The growth mode, microstructure of a-Si:H thin film, and atomic diffusion ability were mainly influenced by shadowing effect. [ABSTRACT FROM AUTHOR]

To investigate the effect of three-dimension (3D) thermal convection on columnar-to-equiaxed transition (CET), the CET transition during the solidification of an Al-Cu alloy was simulated by 3D cellular automaton model coupled with the fi nite element method (CAFE). The thermal convection in the liquid phase was considered. The results show that the thermal convection in the liquid phase promotes the CET. When the convection is present, the temperature gradient at the start position of CET increases and the growth velocity of columnar dendrite decreases. The convection influences the formation of elongated equiaxed grain through changing the local temperature gradient and dendritic growth velocity. [ABSTRACT FROM AUTHOR]

In this contribution we discuss the structural, morphological and optical properties of ZnO thin films deposited on glass substrates by radio frequency magnetron sputtering technique. Our results indicate that an increase in deposition time leads to a change in the film growth mechanism. Three different growth regimes can be observed when the deposition time changes. Islands initially start to nucleate and grow into rough and highly stressed films. Increasing the surface population leads to island coalescence compatible with a planar architecture, where the stress is relieved, and the roughness is minimized. Longer still deposition times induce the growth of columnar structures. The increase in deposition time brings about a stress relaxation and grain growth together with a reduction of the texture coefficient, c-lattice contraction and an increase of band gap values. [ABSTRACT FROM AUTHOR]

The Baihetan super-high arch dam is constructed under complicated geological conditions, including large-scale columnar jointed basalt with closely spaced joints and multiple interlayer and intralayer shear belts at the lower part of dam base. Due to large excavation depth and scale at the dam base, unloading deformation and relaxation of columnar jointed basalt and shear belts were revealed by field investigation, in situ testing, monitoring, and numerical simulations. It was found that the relaxation depth of columnar jointed basalt was related to geostress, rock mass quality, and gently dipping shear belts. The time effect of unloading relaxation is also obvious in the columnar jointed basalt. In terms of unloading deformation control, comprehensive reinforcement measures and proper construction sequence at the dam base were proposed, including reservation of a 5-m-thick rock mass layer as the protective layer, consolidation grouting on the protective layer, preinstallation of mortar anchors through consolidation grouting hole, excavation of protective layers with controlled blasting in small benches, timely anchorage by prestressed cables upon exposure of foundation surface, and additional consolidation grouting for shallow foundation rock mass under concrete cover weight. With the comprehensive reinforcement measures at the dam base, the relaxation depth of columnar jointed basalt was small and shear deformation of shear belts was effectively controlled. Thus, the proposed reinforcement measures were proven to be proper and effective, which could meet the requirements of dam base and provide some reference for similar hydropower projects. [ABSTRACT FROM AUTHOR]

The heat transfer and columnar grains growth in the laser welding pool of 2A14 aluminum alloy under different welding parameters are investigated through macro-micro modeling and simulation. A macroscopic heat transfer model is proposed to calculate the temperature field in the laser welding pool under different welding parameters. Computed fusion profiles agree well with experimental measurements. The equations of transient pulling velocity, temperature gradient and columnar grains growth orientation during solidification of the laser welding pool are developed. A phase field model coupled with transient pulling velocity, temperature gradient, columnar grains growth orientation and the flow field is developed to simulate columnar grains growth in the laser welding pool under different welding parameters. Laser welding experiments are also carried out to observe columnar grains growth in the laser welding pool under different welding parameters. Simulated columnar grains morphology, spacing and growth orientation give a good agreement with experimental measurements. Competitive growth of columnar grains with different growth orientations is also predicted by the phase field model. Predicted competitive growth process is in accordance with experimental findings. [ABSTRACT FROM AUTHOR]

A series of high and low symmetry hexa- peri -hexabenzocoronene derivatives, compounds 1 – 3 , was successfully synthesized and applied for corrosion resistance on iron surfaces. In particular, compound 1 exhibited excellent anti-corrosion behavior, as demonstrated by electrochemical impedance spectroscopy (EIS) and contact angle (CA) measurements. A high resistance of 186.7 kΩ/cm 2 and excellent hydrophobicity (CA ∼143.9°) with brine solution were obtained. The discotic columnar liquid crystals (DCLCs) coating on the iron surface provide protection under various environments, including exposure to air and solutions with different pH values. This characteristic is attributed to the excellent hydrophobicity and self-healing properties of discotic columnar liquid crystals. [ABSTRACT FROM AUTHOR]

In the EU-APR1400, an ex-vessel core catcher system, a key design component of considerable interest is the engineered corium cooling system. It consists of a cooling channel in which many short columnar structures called studs are placed to support the static and dynamic loads on the core catcher body and to provide the coolant flow path underneath the core catcher body. This study investigated the effect of aligned obstacles on the inclined downward facing critical heat flux (CHF) under a low flow condition using a high-speed camera and an optical fiber microprobe measuring the local void fraction. A laboratory-scale experimental apparatus for a prototypical core catcher system was built, and experiments were conducted with various mass fluxes and obstacle shapes under atmospheric pressure. Results showed a linear proportional relation between the inlet mass flux and corresponding CHF with the existence of a transition flow rate, beyond which the proportionality becomes double. It was also confirmed that the aligned flow obstacles had a positive effect on the CHF under a relatively high mass flux, but a negative effect appeared in the pool boiling condition. Computational fluid dynamics helped in the understanding of key physical mechanisms through which the obstacles affect the CHF, on the basis of the experimental results. [ABSTRACT FROM AUTHOR]

A series of Al 7Si based alloys with trace addition of Sr, Ce or P were prepared using melt-spinning at two different high cooling rates, and the microstructure as well as the hardness of the ribbons was comprehensively studied. The results show that Sr or Ce induces the formation of columnar transition zone and modifies the morphology of eutectic Si phase from dispersed particle chains to fine fibers only at extremely high cooling rate. However, P has little effect on the microstructure of either α-Al or eutectic Si. Compared with conventional casting, the Al 7Si ribbons exhibit extremely high hardness due to the fine dispersion of eutectic Si, the grain refinement and the supersaturation of Si. The hardness is further enhanced by Sr or Ce addition at extremely high cooling rate, especially for columnar and equiaxed zones, attributing to the modification effect on Si phase. [ABSTRACT FROM AUTHOR]

Si 3 N 4 has attracted much attention as the thermally conductive fillers owing to its high thermal conductivity, high electrical resistivity and low dielectric loss. This paper presented the preparation of well-dispersed columnar Si 3 N 4 particles by carbothermal reduction–nitridation (CRN) strategy with assistance of unique CaF 2 additive under an elevated N 2 pressure. The average diameter of columnar particles was 4 μm and aspect ratio was 3. The speculation for the inherent growth mechanism of the Si 3 N 4 particles was tentatively proposed. It was speculated that CaF 2 could promote the formation of β-Si 3 N 4 with columnar structure through a V-L-S (vapor-liquid-solid) route by forming Ca-containing liquid phase with SiO 2 . Moreover, appropriate content of CaF 2 are beneficial for fabricating Si 3 N 4 particles with good dispersity because of the proper the evaporation rate of Ca and F. [ABSTRACT FROM AUTHOR]

For new Ni-base ODS superalloy manufactured by mechanical alloying, zone annealing experiment was implemented with parameters of temperature and hot zone velocity in order to develop the directionally recrystallized columnar grains. The progressive growth front of the columnar grains is synchronized with the hot zone movement, and columnar grains in millimeter scale were accomplished by appropriate hot zone velocity. This is secondary recrystallization through preferentially abnormal grain growth of the primarily recrystallized grains with the texture of cube orientation (001)[0 1 ¯ 0] as well as Goss orientation (110)[001]. The growth rate of the columnar grains estimated by using the grain boundary energy (ΔG gb ) of the primarily recrystallized grains, pinning force by oxide particles (ΔG pin ) and mobility of the grain boundary is relatively comparable to the hot zone velocity. The steep temperature gradient ahead of hot zone is substantially critical to keep the small size of the primarily recrystallized grains that lead to higher driving force for columnar grain growth due to the large grain boundary stored energy. [ABSTRACT FROM AUTHOR]

Abstract: CdTe solar cells have reached efficiencies comparable to multicrystalline silicon and produce electricity at costs competitive with traditional energy sources. Recent efficiency gains have come partly from shifting from the traditional CdS window layer to new materials such as CdSe and MgZnO, yet substantial headroom still exists to improve performance. Thin film technologies including Cu(In,Ga)Se2, perovskites, Cu2ZnSn(S,Se)4, and CdTe inherently have many grain boundaries that can form recombination centers and impede carrier transport; however, grain boundary engineering has been difficult and not practical. In this work, it is demonstrated that wide columnar grains reaching through the entire CdTe layer can be achieved by aggressive postdeposition CdTe recrystallization. This reduces the grain structure constraints imposed by nucleation on nanocrystalline window layers and enables diverse window layers to be selected for other properties critical for electro‐optical applications. Computational simulations indicate that increasing grain size from 1 to 7 µm can be equivalent to decreasing grain‐boundary recombination velocity by three orders of magnitude. Here, large high‐quality grains enable CdTe lifetimes exceeding 50 ns. [ABSTRACT FROM AUTHOR]

In this paper, we investigate the properties of rapidly rotating decaying turbulence using numerical simulations and phenomenological modeling. We find that as the turbulent flow evolves in time, the Rossby number decreases to ∼10−3, and the flow becomes quasi-two-dimensional with strong coherent columnar structures arising due to the inverse cascade of energy. We establish that a major fraction of energy is confined in Fourier modes (±1, 0, 0) and (0, ±1, 0) that correspond to the largest columnar structure in the flow. For wavenumbers (k) greater than the enstrophy dissipation wavenumber (kd), our phenomenological arguments and numerical study show that the enstrophy flux and spectrum of a horizontal cross section perpendicular to the axis of rotation are given by ϵ ω ⁡ exp ( − C ( k / k d ) 2 ) and C ϵ ω 2 / 3 k − 1 ⁡ exp ( − C ( k / k d ) 2 ) , respectively; for this 2D flow, ϵω is the enstrophy dissipation rate, and C is a constant. Using these results, we propose a new form for the energy spectrum of rapidly rotating decaying turbulence: E ( k ) = C ϵ ω 2 / 3 k − 3 ⁡ exp ( − C ( k / k d ) 2 ). This model of the energy spectrum is based on wavenumber-dependent enstrophy flux, and it deviates significantly from power law energy spectrum reported earlier. [ABSTRACT FROM AUTHOR]

Laser-based directed energy deposition (LDED) additive manufacturing of Ni-rich NiTi shape memory alloys was shown to produce inhomogeneous precipitate morphologies and characteristic grain structures consisting of columnar grains coexisting with equiaxed and subgrain structures. Post-processing solutionizing and aging heat treatments impacted microstructure and martensitic phase transformation (MT) responses underpinning superelastic shape memory responses. A solution treatment of 950 °C for 24 h was found to produce a uniform composition of the B2 austenite parent phase without affecting the coexistence of columnar and equiaxed substructures. Aging the solution treated material brought about a spatially uniform Ni 4 Ti 3 precipitate morphology. Due to the uniform morphology, an underlying austenite-martensite interface motion accompanies the compressive stress-induced MT (SIMT). Reversible interface motion underpinned the compressive superelastic response for the solutionized and aged condition. On the other hand, strain concentrations existed at different spatial locations in the as built condition as well as when the as built material was aged. The stark contrasts in the SIMT exposed precipitate morphology as a controlling factor in tailoring the superelastic response of Ni-rich NiTi SMAs fabricated by LDED. [ABSTRACT FROM AUTHOR]

Selective Laser Melting (SLM) technology is a complex process controlled by mass and heat transfer. It is very important to understand the microstructure of single track. This work predicted the single track's microstructure of SLMed AlSi10Mg by calculating the thermal variables and using columnar to equiaxed transition (CET) criterion. Firstly, a high accurate transient three-dimensional finite element model was established with anisotropic thermal conductivities verified by both molten pool dimensions and track surface feature. Secondly, the finite element model was used to accurately predict the thermal variables, such as temperature gradient, cooling rate and solidification rate of the molten pool. Thirdly, a columnar to equiaxed transition criterion was established by connecting the predicted thermal variables and experimental microstructure, the experimental results verified that it can predict the microstructure of SLMed AlSi10Mg very well. [ABSTRACT FROM AUTHOR]

The structural properties of polycrystalline Si (poly-Si) thin films formed by using ICPCVD and LIA-ICPCVD methods under different H dilution ratios were investigated. Columnar-structured poly-Si films with 82% crystalline volume fraction were obtained by ICPCVD at a lower H dilution ratio of 50%. In the case of LIA-ICPCVD, to obtain nearly the same crystalline volume fraction (80%), a higher H dilution ratio (98%) was required and the poly-Si films obtained were mostly of cone-shaped columnar structure. The reverse effect is due to the difference in the antenna design in these systems, which changes the plasma characteristics. Multilayer deposition process, and subsequent H treatment and annealing were used in ICPCVD for producing highly crystallized poly-Si thin films from microcrystalline Si films. In the case of LIA-ICPCVD, annealing the ITO coated glass substrate in the deposition chamber prior to Si:H film deposition together with the optimization of process pressure yielded highly crystalline poly-Si film. [ABSTRACT FROM AUTHOR]

Achieving a uniform structure with few defects in heavy steel ingot is of high commercial importance. In this present work, in order to verify the potential of pulsed magneto-oscillation (PMO) applied in the production of heavy ingot, an induction coil was located at the hot top of the steel ingot to develop a novel technique, named hot top pulsed magneto oscillation (HPMO). The influences of HPMO on the solidification structure, macro segregation and compactness of a cylindrical medium carbon steel ingot with the weight of 160 kg were systematically investigated by optical microscope (OM) and laser induced breakdown spectroscopy original position metal analyzer (LIBSOPA-100). The results show that HPMO not only causes significant grain refinement and promotes the occurrence of columnar to equiaxed transition (CET) but also can homogenize the carbon distribution and enhance the compactness of the steel ingot. Therefore, HPMO technique has the potential to be applied in the production of heavy steel ingots on an industrial scale. [ABSTRACT FROM AUTHOR]

WN and W-C (14.8 at.%)-N coatings were prepared by reactive magnetron sputtering to investigate the oxidation behavior during heat treatment. The results show that the deposited WN and WCN coatings are compact and grow with a columnar structure. The incorporation of carbon does not affect the columnar structure and some amorphous phases formed among the columnar grain boundaries. The addition of carbon to columnar WN coating could improve the oxidation resistance by increasing the bonding energy, decreasing the pores among the columnar grain boundaries, squeezing the amorphous phase to withstand the expansion of oxidation and consuming some oxygen by oxidizing amorphous phase. [ABSTRACT FROM AUTHOR]

Variations in the crystallographic texture in Ni-25 at.%Mo alloys fabricated by selective laser melting with different scanning strategies were designed for the first time. Single-crystalline-like texture with a short-range order of Mo atoms can be produced via bidirectional scanning along one axis (X-scan) and bidirectional scanning with a 90° rotation in each layer (XY-scan), while only fiber texture was formed in bidirectional scanning with a 67° rotation (Rot-scan). The aligned crystal orientation along the build direction can be varied by the scanning strategy; 〈001〉 is preferred in the XY- and Rot-scan samples, while 〈101〉 is preferred in the X-scan sample. The controlling mechanisms of the texture, focusing on the preferential growth directions of the columnar cells and the following epitaxial growth, are discussed. [ABSTRACT FROM AUTHOR]

This paper is the first to report a large-scale directcurrent electrodeposition of columnar nanotwinned copper within through silicon via (TSV) with a high aspect ratio (~4). With this newly developed technique, void-free nanotwinned copper array could be fabricated in low current density (30 mA/cm2) and convection conditions (300 rpm), which are the preconditions for copper deposition with a uniform deep-hole microstructure. The microstructure of a whole cross-section of deposited copper array was made up of (111) orientated columnar grains with parallel nanoscale twins that had thicknesses of about 22 nm. The hardness was also uniform along the growth direction, with 2.34 and 2.68 GPa for the top and bottom of the TSV, respectively. The gelatin additive is also first reported hereas a key factor in forming nanoscale twins by adsorbing on the cathode surface, in order to enhance the overpotential for cathodic reaction during the copper deposition process. [ABSTRACT FROM AUTHOR]