Columnar Arrays Research Articles

A flexible strategy to fabricate trumpet-shaped porous PDMS membranes for organ-on-chip application.

Porous polydimethylsiloxane (PDMS) membrane is a crucial element in organs-on-chips fabrication, supplying a unique substrate that can be used for the generation of tissue-tissue interfaces, separate co-culture, biomimetic stretch application, etc. However, the existing methods of through-hole PDMS membrane production are largely limited by labor-consuming processes and/or expensive equipment. Here, we propose an accessible and low-cost strategy to fabricate through-hole PDMS membranes with good controllability, which is performed via combining wet-etching and spin-coating processes. The porous membrane is obtained by spin-coating OS-20 diluted PDMS on an etched glass template with a columnar array structure. The pore size and thickness of the PDMS membrane can be adjusted flexibly via optimizing the template structure and spinning speed. In particular, compared to the traditional vertical through-hole structure of porous membranes, the membranes prepared by this method feature a trumpet-shaped structure, which allows for the generation of some unique bionic structures on organs-on-chips. When the trumpet-shape faces upward, the endothelium spreads at the bottom of the porous membrane, and intestinal cells form a villous structure, achieving the same effect as traditional methods. Conversely, when the trumpet-shape faces downward, intestinal cells spontaneously form a crypt-like structure, which is challenging to achieve with other methods. The proposed approach is simple, flexible with good reproducibility, and low-cost, which provides a new way to facilitate the building of multifunctional organ-on-chip systems and accelerate their translational applications.

Heteroatom-Promoted Polyhexagonal Saddle-Shaped Molecular Structures and their Supramolecular Coassembly with C60.

Molecules with curved architecture can exhibit unique optoelectronic properties due to the concave-convex π-surface. However, synthesizing negatively curved saddle-shaped aromatic systems has been challenging due to the internal structural strain. Herein, we report the facile synthesis of two polyhexagonal molecular systems, 1 and 2, with saddle shape geometry by judiciously varying the aromatic moiety, avoiding the harsh synthetic methods as that of heptagonal aromatic saddle systems. The unique geometry preferences of B, N, and S furnish suitable curvature to the molecules, featuring saddle shape. The saddle geometry also enables them to interact with fullerene C60 , and the supramolecular interactions of fullerene C60 with 1 and 2 modify their optoelectronic properties. Crystal structure analysis reveals that 1, with a small π-surface, forms a double columnar array of fullerenes in the solid state. In contrast, 2 with a large π-surface produces a supramolecular capsule entrapping two discrete fullerenes. The intermolecular interactions between B, N, S, and the aryl-π surface of the host and C60 guest are the stabilizing factors for creating these supramolecular structures. Comprehensive computational, optical, and Raman spectroscopic studies establish the charge transfer interactions between B-N doped heterocycle host and fullerene C60 guest.

Enhancing anti-chlorine corrosion of Ni3S2 by Mo-doping for mimic seawater electrolysis

Designing highly active electrocatalysts that can resist chloride ion (Cl-) corrosion during seawater electrolysis is still a challenge. Here, Mo-doping is introduced to synchronously improve the electrocatalytic activity and anti-chlorine corrosion of Ni3S2 toward the efficient overall seawater splitting. With commercial nickel-molybdenum foam (NMF) as the reactive substrates, Mo-doped Ni3S2 columnar arrays (Mo-Ni3S2/NMF) are fabricated via a one-step hydrothermal process, which expose abundant active sites with the ameliorated surface electronic configurations toward the enhanced binding with *OH (* denotes an active site) but the weakened one with *Cl. As expected, they afford the excellent bi-functionality for both oxygen and hydrogen evolution reactions (OER and HER), with the remarkably improved anti-corrosion to Cl- at anode as compared to pristine Ni3S2. In alkaline mimic seawater (1.0 M NaOH + 0.5 M NaCl), Mo-Ni3S2/NMF requires 330 mV (for OER) and 209 mV (for HER) overpotentials at the current density of ±100 mA cm−2, and a low cell voltage of 1.52 V at 10 mA cm−2 for overall seawater splitting. This work highlights a feasible strategy to explore highly active and stable electrocatalysts for sustainable H2 production.

Interaction between growing dendrite and rising bubble under convection

Prediction and control of gas porosity defect during solidification is challenging because of multiphase and multiphysics characteristics. In this work, a multiphase-field lattice Boltzmann method is employed to study the interaction between solidifying dendrite and rising bubble. The influencing factors are divided into two categories including external and internal factors, and the effects of the multiple factors are discussed and compared. The bubble changes the dendrite skeleton by hindering the solid growth, including entrapped in the dendrite root, tilting growth towards the neighboring bubble, forming the knot structure, and growing along the radial direction of the bubble. The bubble in the columnar dendrite array with random orientation distribution has larger effects on the average primary dendrite arm spacing. Based on the summary of different interaction results, a phase diagram is proposed to distinguish different interaction regimes. Further, the size of the closed liquid phase region is measured to evaluate the porosities tendency and guide how to reduce the porosities.

Self-supported iridium integrated leaf-shaped Fe3O4 columnar arrays toward highly efficient oxygen evolution at industrial-grade current density

The sluggish kinetics for oxygen evolution reaction (OER) significantly impede the practical applications of electrocatalytic water splitting technology for renewable energy source. The facile design of self-supporting electrocatalysts with high activity and stability for OER catalysis at industrial-grade current density is of paramount significance to mitigate the above bottlenecks. We report herein the construction of iron foam (IF) self-supported Ir-magnetite (Ir-Fe3O4/IF-T-x) electrode via galvanic replacement between IrCl62− ions and Fe2+ in Fe3O4 nanosheet arrays, which is simply synthesized by annealing IF in air and subsequent thermal treatment in reducing atmosphere. Such pre-treatment enables the growth of leaf-like Fe3O4 nanosheet arrays with rich Fe2+ species and oxygen defects, which facilitate the depositing of Ir on the surface of nanosheet arrays and thereby promote the electrochemical OER performance in basic electrolyte. Impressively, the optimized Ir-Fe3O4/IF-400-2 delivers the highest electrocatalytic activity with a low overpotential of 316 mV to obtain industrial-grade current density of 500 mA cm−2 for alkaline OER. Meanwhile, the catalyst still shows good long-term stability after 36 h V-t test at 100 mA cm−2. This study offers a simple and efficient pathway to prepare self-supporting electrode for alkaline OER at industrial-grade current density.

Photo-responsive droplet manipulation slippery lubricant-infused porous surface with ultra-high durability

Photo-responsive slippery lubricant-infused porous surface (SLIPS) for droplet manipulation is flexible, non-contact and non-destructive in droplet manipulation, which has promising applications in flexible robotics, microfluidics, biomedicine, and chemical analysis. However, the repeated manipulations for droplets of SLIPSs are quite limited in the works reported so far, the poor durability of droplet manipulation severely limits the practical application of the surfaces. In this paper, an Fe3O4-doped polydimethylsiloxane (PDMS)-based SLIPS is proposed and implemented to achieve ultra-high repeated droplet manipulation numbers under near-infrared ray (NIR) laser irradiation. Firstly, a micron columnar array structure with micro-pits on the top side, as well as, a wall structure out of the array is designed on SLIPS to reserve the lubricant. Secondly, the prototype of the SLIPS is fabricated by a 3-step ultraviolet (UV) lithography, and subsequently immersed in silicone oil for more than 96 h to obtain the ultra-high durability slippery lubricant-infused porous surface (UD-SLIPS). With a power of 25 mW–85 mW NIR laser, the repeated manipulation of microdroplets (≤ 5 μL) in the scale of 1 cm can exceed more than 3000 times which is far beyond that in previous reports. Finally, the droplet manipulation performance of this photo-responsive UD-SLIPS and the influence of infusion time on durability are investigated. The mechanism of the PDMS swelling effect is found to be the key factor in improving the droplet manipulation durability of SLIPS. The findings of this work would be of great significance for the development of highly durable photo-responsive functional surfaces for droplet manipulation.

Micromagnetic simulation of electrochemically deposited Co nanowire arrays for wideband microwave applications

We study the magnetic properties of arrays of Co nanowires which exhibit zero bias-field ferromagnetic resonance absorptions in a 0–30 GHz range. Columnar arrays of Co nanowires with lengths of 8–15 µm were electrochemically grown using ∼20 µm thick anodic alumina membranes with 50 nm pore diameters. Microstructural, static magnetic, and microwave properties of five different nanowire arrays were characterized. The studied Co nanowires present different crystal structure textures and magnetic properties. The static magnetic loop shapes and the ferromagnetic resonance frequencies of the nanowire arrays were correctly reproduced using the Mumax3 micromagnetic software. For each sample input parameters dependent on the x-ray diffraction and microstructural data, were fine-tuned to allow the best fit of the experimental hysteresis loops and the related microwave spectra. Using this method, it was possible to analyze the rather complex interplay between geometry and magneto-structural features of the different arrays, defining which parameters play a key role in the development of nano-systems with specific microwave properties.

Green non-fluorinated gradient anisotropic microcolumn array: Enables droplet transition to a low viscosity state on highly viscous substrates

Superhydrophobic surfaces with low adhesion and self-cleaning properties have broad application prospected in various fields. However, the current methods for preparing low-adhesion superhydrophobic surfaces typically require toxic chemicals or fluorination modifications, which are prone to environmental pollution and health hazards, and still face challenges for applications in industries such as food and medical care. This paper aims to prepare anisotropic gradient array surfaces (AGAS) with low adhesion on stainless steel substrates by WEDM, without the need for modification with low-surface-energy materials. AGAS can achieve a stable Cassie state with a low adhesion performance by controlling the dimensional parameters and structural inclination of columnar arrays. Experiments and numerical simulations show that owing to the anisotropic gradient structure, pinning and de-pinning occur asymmetrically in time at the contact lines of the leading and trailing edges of droplets impacting the AGAS. On AGAS, droplets can jump and roll in the direction of gradient descent during the impact process to complete self-cleaning. Due to the discontinuity of the solid–liquid–gas three-phase contact line and the stepped arrangement of the column array, the prepared surface can achieve low adhesion and self-cleaning properties for many common liquid foods in daily life, including milk and juice.

Study of heat transfer performance of miniature heat sink for integrated circuit packaging field

The miniature heat sink is an essential component in integrated circuit packaging, playing a vital role in ensuring the stable and reliable performance of integrated circuits. In this paper, we establish a simulation model of the heat transfer performance of a miniature heat sink with a square columnar array microstructure and study the effect of the dimensional parameters of the miniature heat sink on the heat transfer performance. Then, the mathematical equations between the heat source temperature and the dimensional parameters of the miniature heat sink are obtained based on the response surface method, and the dimensional parameters are optimized. Finally, wire electrical discharge machining (WEDM) was used to prepare miniature heat sinks and to test the heat transfer performance. The experimental results show that both the simulation model and the mathematical equations have high accuracy, and the heat source temperature of the miniature heat sink with column width, column distance, and column height of 364 μm, 331 μm, and 1500 μm, respectively, can be reduced to 101.8 °C, which is 93.5 °C lower than the heat source temperature of 195.3 °C without heat sink, and the temperature reduction reaches 47.9%. The miniature heat sink has a simple manufacturing process, low manufacturing cost, small overall size, and good heat transfer performance, which has a broad application prospect in the field of integrated circuit packaging.

Investigations of Spoilers to Mitigate Columnar Vortices in Propeller Turbines at Speed-No-Load Based On Steady and Unsteady Flow Simulations

Abstract With the introduction of an ever-larger share of renewable but intermittent energy sources on electrical grids, hydraulic turbines are more often used as network stabilizers. In such a role, they are generally operated in off-design operations like speed-no-load (SNL). No energy is extracted from the flow at SNL operation, but the runner rotates at the synchronous speed linked to the electrical grid. The flow inside the runner of low-head turbines operating at SNL is often dominated by a columnar vortex array that may induce damaging pressure fluctuations. This paper presents the study of a control device to mitigate those vortices. At SNL, the small guide vane opening leads to a high swirl in the runner generating secondary flows such as columnar vortices and backflows. The proposed concept is to move SNL operation toward a higher guide vane opening and hence lower swirl, preventing the formation of a columnar vortex array. Lowering the input swirl of SNL is accomplished by opening up the guide vanes while using a control device to limit the discharge. The control device, like a spoiler on an aircraft wing, is introduced on the guide vanes to generate added head losses, significantly decreasing the discharge. This paper compares the hydrodynamics of the flow in a propeller turbine with different spoiler geometries. The study is based on both RANS and URANS flow simulations. It highlights how such devices can successfully mitigate columnar vortices and their associated pressure fluctuations on runner blades.

Analysis of Electrical Characteristics of N-Doped TiO2 and Si Heterojunction Diodes

Heterojunction photodiodes play a crucial role in various industries and daily life. They find application in fields such as photoelectric detection, aerospace, and intelligent manufacturing. In this study, we employed a series of growth processes, including physical vapor deposition techniques such as magnetron sputtering, high-temperature annealing, and hydrothermal growth, to fabricate N-doped TiO2 heterojunction diode devices with Si as a substrate material. The surface of the device exhibited a columnar array structure with rutile phase TiO2. Additionally, the doping of N element led to the bending of the energy band of TiO2 by approximately 0.2 eV, and the Fermi level also shifted to the valence band, without any effect on the band gap. The I–V characteristics varied in vacuum and air, with ideal factors (η) of 4.1 and 8.72, respectively. The study is expected to broaden the application scope of doped photodiodes.

Control Flow Duplication for Columnar Arrays in a Dynamic Compiler

Columnar databases are an established way to speed up online analytical processing (OLAP) queries. Nowadays, data processing (e.g., storage, visualization, and analytics) is often performed at the programming language level, hence it is desirable to also adopt columnar data structures for common language runtimes. While there are frameworks, libraries, and APIs to enable columnar data stores in programming languages, their integration into applications typically requires developer interference. In prior work, researchers implemented an approach for *automated* transformation of arrays into columnar arrays in the GraalVM JavaScript runtime. However, this approach suffers from performance issues on smaller workloads as well as on more complex nested data structures. We find that the key to optimizing accesses to columnar arrays is to identify queries and apply specific optimizations to them. In this paper, we describe novel compiler optimizations in the GraalVM Compiler that optimize queries on columnar arrays. At JIT compile time, we identify loops that access potentially columnar arrays and duplicate them in order to specifically optimize accesses to columnar arrays. Additionally, we describe a new approach for creating columnar arrays from arrays consisting of complex objects by performing **multi-level storage transformation**. We demonstrate our approach via an implementation for JavaScript `Date` objects. [ full abstract at https://doi.org/10.22152/programming-journal.org/2023/7/9 ]

Highly sensitive and wide linearity flexible pressure sensor with randomly distributed columnar arrays

Highly sensitive and wide linearity flexible pressure sensor with randomly distributed columnar arrays

Discotic liquid crystals 45 years later. Dendronized discs and crowns increase liquid crystal complexity to columnar from spheres, cubic Frank-Kasper, liquid quasicrystals and memory-effect induced columnar-bundles

In 1977 Chandrasekhar laboratory reported the first examples of a new class of thermotropic liquid crystals self-organized from planar disc-like molecules substituted with alkyl groups. X-ray analysis demonstrated that these disc-like molecules stack on top of each other at irregular spacing in columns located in the paraffin melt of their alkyl groups. These supramolecular columns self-organize in a hexagonal array defined as the new thermotropic discotic or columnar hexagonal liquid crystal phase. This new thermotropic liquid crystal phase has translational periodicity in two dimensions and liquid-like disorder in the third one, along the column axis. In 2002 Bushby and Lozman dedicated a brief review article to the 25 anniversary of discotic liquid crystals. This review also included a brief discussion of supramolecular discs and columns self-organized from self-assembling dendrons and dendrimers. The current publication is not another review but a brief perspective on new liquid crystal phases self-organized from dendronized rigid planar and conformationally flexible discs as well as from crown-like molecules. Crown-like molecules are the most stable conformation of a transient unstable disc. All dendronized disc-like and crown molecules adopt a crown conformation that self-assemble helical columns and spherical helices. A large diversity of new liquid crystalline phases self-organize from these helical columns and spherical helices. They include helical columnar hexagonal phases from crowns and from supramolecular spheres, Frank-Kasper A15 (known as cubic phase of space group Pm3¯n), σ phase (also known as tetragonal of space group P42/mnm), 12-fold quasi liquid crystals (QLC) and supramolecular orientational memory (SOM) derived complex bundles of supramolecular columnar hexagonal arrays that are not yet completely elucidated. The impact of Chandrasekhar on the discovery of self-assembling dendrons and dendrimers via his biaxial nematic liquid crystal concept will also be discussed. This perspective is dedicated to the 45 anniversary of the discovery of discotic liquid crystals and to the memory of Professor Sivaramakrishna Chandrasekhar, a modest, respectful and great scientist.

Influences of the substrate strain on microstructures of L10 FePt-X thin films by using phase field simulation

The microstructure evolution of the FePt-X (segregant) thin films is studied by employing a two-dimensional phase field model based on the elastic effect. Simulated results show that the lattice mismatch between the FePt-X thin film and substrate leads to slight rafting (preferential coarsening) of columnar FePt grains along the direction of the misfit strain, and produces more rounded grains, while an amorphous segregant is doped. The elastic energy primarily affects the areas between the FePt grains, where more than 90% of the elastic energy is concentrated. Moreover, the elastic energy is relaxed gradually with the formation of columnar periodic arrays of FePt grains. To generate columnar FePt grains microstructure in the FePt-X thin films, the lattice mismatch between the thin film and substrate should be controlled within 3% when the thermal expansion difference between the thin film and substrate is ignored.

Fabrication of 3D array ferromagnetic photocatalyst with enhanced visible-light photocatalytic activity

A photocatalyst consisting of ZnFe2O4/Ag nanocomposite particles deposited on a 3D columnar array Si substrate was prepared. The photocatalytic performance under visible light of the 3D columnar array Si/ZnFe2O4/Ag photocatalyst was compared with that of planar Si/ZnFe2O4/Ag and planar Si/ZnFe2O4. The effect of an applied magnetic field was also investigated. The interfacial contact in Si/ZnFe2O4/Ag increases carrier transfer, whereas the 3D columnar array substrate provides more photocatalytic reaction sites, increasing the utilization of photogenerated electrons and holes. The photocurrent density of 3D columnar array Si/ZnFe2O4/Ag (0.621 mA/cm2) was higher than that of planar Si/ZnFe2O4/Ag (0.09 mA/cm2). Additionally, applying a 1000 Oe magnetic field to 3D columnar array Si/ZnFe2O4/Ag resulted in a high photocurrent of 1.315 mA/cm2. In addition, the 3D columnar array Si/ZnFe2O4/Ag photocatalyst can also be effectively used for photodegradation of Methyl orange, and exhibits high stability. At the same time, the external magnetic field can further improve its photodegradation efficiency. The I–V experiments demonstrated that the Si/ZnFe2O4/Ag has a more negative magnetoresistance than Si/ZnFe2O4. Thus, the spin moments of the photocatalyst align parallel to each other under a magnetic field, allowing more photogenerated carriers to transfer through the interface and thus improving the photocatalytic performance. These results provide a relatively simple method for the development of efficient photocatalysts and improvement of existing photocatalysts.

Laser interference induced dielectrophoresis for cell manipulation

In this paper, laser interference induced dielectrophoresis (LIIDEP) was presented for cell manipulation and three-dimensional array assembly. Two-beam and three-beam interference systems were built to manipulate yeast cells in deionized water. When the laser power was 60 μW and the sinusoidal AC signal was 6 V at 10 kHz, the two-beam interference pattern manipulated the cells into a single-row array distribution. For three-beam interference, when the laser power was 70 μW and the frequency was 4.5 kHz, the voltage of 2.5 V enabled each spot to control one cell, and 7.5 V enabled many spots to control multiple cells. When the cell concentration was 2 × 107 cells/mL and the electrical signal was 8 V and 4.5 kHz, the cells were assembled into a three-dimensional columnar array. The feature size of laser interference pattern was adjusted to microscale and maintained sharp boundaries, which effectively improved the manipulation accuracy. Compared to the projector or laser as the ODEP light source, LIIDEP has the advantages of high manipulation resolution, good contrast and large dielectrophoretic force. This work provides an effective way for high resolution three-dimensional array manipulation and assembly of a large number of living cells on the microscale in liquid environments.

Modeling of the Nonuniform Microstructure and Microsegregation Formation of the Shell in Round Billet Continuous Casting

To explore the influence of nonuniform heat transfer on the grain structure and microsegregation of carbon in shells inside the mold, a multiscale model considering heat conduction and dendritic growth is constructed for the round billet continuous casting. Adopting measured heat flux as the boundary conditions, heat conduction in the mold is solved by the finite difference scheme, and dendritic growth is modeled by the cellular automaton model. The temperature distribution of the round billet under measured heat flux is calculated, and the grain structure and the microsegregation of carbon in four selected regions are simulated. Herein, it is shown in the results that the different local heat fluxes lead to dissimilar variations in the surface temperature and grain structure of the shell. A close relationship exists between the carbon microsegregation and local heat flux; the carbon microsegregation decreases with heat flux. The high heat flux accelerates columnar dendritic growth and fines the columnar dendritic array so that the secondary arms are less developed and the microsegregation is improved.

Modeling of microstructure formation with gas porosity growth during columnar dendritic solidification of aluminum alloys

In this paper, microstructure formation with gas bubble growth during columnar dendritic solidification has been numerically investigated by using the coupled lattice Boltzmann-cellular automaton-finite difference (LB-CA-FD) model, which combines the physical mechanisms of the redistribution of hydrogen components at the solid–liquid interface and the transportation of hydrogen atoms in liquid. Hydrogen transportation, bubble nucleation and growth are computed by the LB method while the growth of columnar dendrite and the transport of solutes are described by the CA-FD model. Predicted results show that the bubbles begin to nucleate at the roots of primary dendritic trunk and secondary arms, and elongated irregular bubbles are sandwiched between neighboring dendrites after merging and moving during the growth stage. Columnar dendritic change from coarse and ordered to fine and disordered as the cooling rate is increased. Meanwhile, the cooling rate has a significant effect on the incubation time for gas bubbles and the maximum growth rate of porosity. It was found that the misorientation angle has limited effects on the solid fraction and porosity percentage but strongly influences on the morphologies of the columnar dendritic arrays, resulting in the different distributions of bubbles.

Self-organization of rectangular bipyramidal helical columns by supramolecular orientational memory epitaxially nucleated from a Frank-Kasper σ phase

Programming living and soft complex matter via primary structure and self-organization represents the key methodology employed to design functions in biological and synthetic nanoscience. Memory effects have been used to create commercial technologies including liquid crystal displays and biomedical applications based on shape memory polymers. Supramolecular orientational memory (SOM), induced by an epitaxial nucleation mediated by the close contact spheres of cubic phases, emerged as a pathway to engineer complex nanoscale soft matter of helical columnar hexagonal arrays. SOM preserves the crystallographic directions of close contact supramolecular spheres from the 3D phase upon cooling to the columnar hexagonal periodic array. Despite the diversity of 3D periodic and quasiperiodic nanoarrays of supramolecular dendrimers, including Frank-Kasper and quasicrystal, all examples of SOM to date were mediated by Im3¯m (body-centered cubic, BCC) and Pm3¯n (Frank-Kasper A15) cubic phases. Expanding the scope of SOM to non-cubic arrays is expected to generate additional morphologies that were not yet available by any other methods. Here we demonstrate the SOM of a dendronized triphenylene that self-organizes into helical columnar hexagonal and tetragonal P42/mnm (Frank-Kasper σ) phases. Structural analysis of oriented fibers by X-ray diffraction reveals that helical columnar hexagonal domains self-organize an unusual rectangular bipyramidal morphology upon cooling from the σ phase. The discovery of SOM in a non-cubic Frank-Kasper phase indicates that this methodology may be expanded to other periodic and quasiperiodic nanoarrays organized from self-assembling dendrimers and, most probably, to other soft and living complex matter.