Alignment Direction Research Articles

Interplay between nematic and cholesteric interactions in self-consistent field theory.

Chirality is a design feature of a number of biomolecules (e.g., collagen). In these molecules, cholesteric (chiral-nematic) behavior emerges from a combination of the tendency for the biopolymers to align (nematic interactions) and for the alignment direction to change with position, rotating around an axis normal to the alignment direction. This paper presents self-consistent field theory (SCFT) of chiral-nematic polymers, which takes into account polymer flexibility and the orientational degrees of freedom of polymer segments. Using the resulting SCFT, we construct a phase diagram showing regions of stability for isotropic, nematic, and cholesteric phases. Furthermore, we find that nematic interactions can stabilize the cholesteric phase, pushing the isotropic-cholesteric phase transition to lower cholesteric interaction strength, until the isotropic-nematic-cholesteric triple point is reached.

Language, identity, & social equity: educational responses to dialect hegemony

ABSTRACT For educators committed to promoting social equity, the question of how to address dialect hegemony is increasingly important. While linguists have long accepted the concept of dialect equality, educators have struggled with the issue, sparking a history of controversy and debate underscoring larger social issues of diversity and equity. For decades, educators have struggled with the most fundamental questions of when, how, and towards what purpose to address linguistic diversity. Drawing from the literature, debates, and practices in the U.S., this article examines the evolution of educational responses to the interrelated issues of disrespect for stigmatised dialects, expectations for Standard English in academic and professional settings, and students’ developing sense of self and authentic voice. Different pedagogies for addressing linguist diversity are reviewed and compared, including code-switching, literary analysis, and code-meshing. These pedagogies build on each other and are moving in the direction of greater alignment, with important considerations for educators who seek to broaden their understanding of linguistic diversity as part of an overarching commitment to equity and social justice.

Rapid fiber alignment quantification in direct write printing of short fiber reinforced composites

Short fiber reinforced polymer composites fabricated by direct ink writing (DW) have design flexibility, low cost, and tailored property advantages over traditional composite materials. Controlling fiber alignment in these composite systems can be used to design unique materials with direction-dependent properties, especially when coupled to topology optimization for light weighting and high strength. . This study focuses on controlling fiber alignment in short carbon fiber composites with two printing parameters common in DW systems: nozzle diameter and velocity ratio. To do so, a novel rapid fiber alignment analysis (RFAA) was developed to quickly collect large amounts of fiber alignment data. Compared to the conventional fiber alignment quantification technique, X-Ray CT, RFAA is a rapid, accurate, and low-cost alternative. It was determined that fiber alignment can be enhanced by printing with smaller nozzle diameters and higher velocity ratios. Longitudinal bending stiffness and bending strength improved as the fiber alignment increased. Composites printed with low fiber alignment exhibited isotropic mechanical properties. However, aligning the fibers in the composite resulted in direction-dependent properties with significantly enhanced modulus and strength in the alignment direction.

Physical contact with breast cancer weakens endothelial cell chirality

Cells have been recently discovered processing a phenotype‐specific chirality which can be seen as directional cell alignment, rotation, or migration. Endothelial cells (ECs) exhibit a strong right bias (or clockwise chirality) under normal conditions. Enervating this chirality impairs EC junction formation and leads to significant leakage of the blood vessels. Malfunction of endothelial barrier induced by malignant tumor cell (TC) facilitates metastasis; however, the role of EC chirality during its crosstalk with TCs is still poorly understood. Using a Transwell model, we evaluated the chirality of human umbilical vein endothelial cells (HUVECs) on a ring‐shaped micropattern with direct or indirect co‐culture of TCs. Our data show a significant loss, or partial reversal of EC chirality when MCF10A‐HRAS or MCF10A‐HER2 cells were directly introduced to EC populations, while indirect co‐culture with either type of TCs only caused a minor decrease in EC chirality. Furthermore, we characterized the bias of each EC on the micropattern using a cell organelle‐based labeling and image analysis. We found the ECs in direct contact with TCs trend to reverse their bias, while the “spaced ones” do not. Together, our results suggest direct physical contact with malignant TCs could cause the EC chirality weakening, which potentially compromises the overall endothelial integrity and contributes to cancer spread.

Uniaxial pressure induced stripe order rotation in La1.88Sr0.12CuO4

Static stripe order is detrimental to superconductivity. Yet, it has been proposed that transverse stripe fluctuations may enhance the inter-stripe Josephson coupling and thus promote superconductivity. Direct experimental studies of stripe dynamics, however, remain difficult. From a strong-coupling perspective, transverse stripe fluctuations are realized in the form of dynamic “kinks”—sideways shifting stripe sections. Here, we show how modest uniaxial pressure tuning reorganizes directional kink alignment. Our starting point is La1.88Sr0.12CuO4 where transverse kink ordering results in a rotation of stripe order away from the crystal axis. Application of mild uniaxial pressure changes the ordering pattern and pins the stripe order to the crystal axis. This reordering occurs at a much weaker pressure than that to detwin the stripe domains and suggests a rather weak transverse stripe stiffness. Weak spatial stiffness and transverse quantum fluctuations are likely key prerequisites for stripes to coexist with superconductivity.

Photoaligned Liquid Crystal Devices with Switchable Hexagonal Diffraction Patterns.

Highly efficient optical diffraction can be realized with the help of micrometer-thin liquid crystal (LC) layers with a periodic modulation of the director orientation. Electrical tunability is easily accessible due to the strong stimuli-responsiveness in the LC phase. By using well-designed photoalignment patterns at the surfaces, we experimentally stabilize two dimensional periodic LC configurations with switchable hexagonal diffraction patterns. The alignment direction follows a one-dimensional periodic rotation at both substrates, but with a 60° or 120° rotation between both grating vectors. The resulting LC configuration is studied with the help of polarizing optical microscopy images and the diffraction properties are measured as a function of the voltage. The intricate bulk director configuration is revealed with the help of finite element Q-tensor simulations. Twist conflicts induced by the surface anchoring are resolved by introducing regions with an out-of-plane tilt in the bulk. This avoids the need for singular disclinations in the structures and gives rise to voltage induced tuning without hysteretic behavior.

Individual cells generate their own self-reinforcing contact guidance cues through local matrix fiber remodeling.

Directed cell migration arises from cells following a microenvironmental gradient (e.g. of a chemokine) or polarizing feature (e.g. a linear structure). However cells not only follow, but in many cases, also generate directionality cues by modifying their microenvironment. This bi-directional relationship is seen in the alignment of extracellular matrix (ECM) fibers ahead of invading cell masses. The forces generated by many migrating cells cause fiber alignment, which in turn promotes further migration in the direction of fiber alignment via contact guidance and durotaxis. While this positive-feedback relationship has been widely described for cells invading en masse, single cells are also able to align ECM fibers, as well as respond to contact guidance and durotaxis cues, and should therefore exhibit the same relationship. In this study, we directly tested this hypothesis by studying the migration persistence of individual HT-1080 fibrosarcoma cells migrating in photocrosslinked collagen matrices with limited remodeling potential. Our results demonstrate that this positive-feedback relationship is indeed a fundamental aspect of cell migration in fibrillar environments. We observed that the cells’ inability to align and condense fibers resulted in a decrease in persistence relative to cells in native collagen matrices and even relative to isotropic (glass) substrates. Further experiments involving 2D collagen and electrospun polymer scaffolds suggest that substrates composed of rigid, randomly oriented fibers reduce cells’ ability to follow another directionality cue by forcing them to meander to follow the available adhesive area (i.e. fibers). Finally, our results demonstrate that the bi-directional relationship between cell remodeling and migration is not a “dimensionality” effect, but a fundamental effect of fibrous substrate structure.

Combining 3D-Printing and Electrospinning to Manufacture Biomimetic Heart Valve Leaflets.

Electrospinning has become a widely used technique in cardiovascular tissue engineering as it offers the possibility to create (micro-)fibrous scaffolds with adjustable properties. The aim of this study was to create multilayered scaffolds mimicking the architectural fiber characteristics of human heart valve leaflets using conductive 3D-printed collectors. Models of aortic valve cusps were created using commercial computer-aided design (CAD) software. Conductive polylactic acid was used to fabricate 3D-printed leaflet templates. These cusp negatives were integrated into a specifically designed, rotating electrospinning mandrel. Three layers of polyurethane were spun onto the collector, mimicking the fiber orientation of human heart valves. Surface and fiber structure was assessed with a scanning electron microscope (SEM). The application of fluorescent dye additionally permitted the microscopic visualization of the multilayered fiber structure. Tensile testing was performed to assess the biomechanical properties of the scaffolds. 3D-printing of essential parts for the electrospinning rig was possible in a short time for a low budget. The aortic valve cusps created following this protocol were three-layered, with a fiber diameter of 4.1 ± 1.6 µm. SEM imaging revealed an even distribution of fibers. Fluorescence microscopy revealed individual layers with differently aligned fibers, with each layer precisely reaching the desired fiber configuration. The produced scaffolds showed high tensile strength, especially along the direction of alignment. The printing files for the different collectors are available as Supplemental File 1, Supplemental File 2, Supplemental File 3, Supplemental File 4, and Supplemental File 5. With a highly specialized setup and workflow protocol, it is possible to mimic tissues with complex fiber structures over multiple layers. Spinning directly on 3D-printed collectors creates considerable flexibility in manufacturing 3D shapes at low production costs.

Combining 3D-Printing and Electrospinning to Manufacture Biomimetic Heart Valve Leaflets

Electrospinning has become a widely used technique in cardiovascular tissue engineering as it offers the possibility to create (micro-)fibrous scaffolds with adjustable properties. The aim of this study was to create multilayered scaffolds mimicking the architectural fiber characteristics of human heart valve leaflets using conductive 3D-printed collectors. Models of aortic valve cusps were created using commercial computer-aided design (CAD) software. Conductive polylactic acid was used to fabricate 3D-printed leaflet templates. These cusp negatives were integrated into a specifically designed, rotating electrospinning mandrel. Three layers of polyurethane were spun onto the collector, mimicking the fiber orientation of human heart valves. Surface and fiber structure was assessed with a scanning electron microscope (SEM). The application of fluorescent dye additionally permitted the microscopic visualization of the multilayered fiber structure. Tensile testing was performed to assess the biomechanical properties of the scaffolds. 3D-printing of essential parts for the electrospinning rig was possible in a short time for a low budget. The aortic valve cusps created following this protocol were three-layered, with a fiber diameter of 4.1 ± 1.6 µm. SEM imaging revealed an even distribution of fibers. Fluorescence microscopy revealed individual layers with differently aligned fibers, with each layer precisely reaching the desired fiber configuration. The produced scaffolds showed high tensile strength, especially along the direction of alignment. The printing files for the different collectors are available as Supplemental File 1, Supplemental File 2, Supplemental File 3, Supplemental File 4, and Supplemental File 5. With a highly specialized setup and workflow protocol, it is possible to mimic tissues with complex fiber structures over multiple layers. Spinning directly on 3D-printed collectors creates considerable flexibility in manufacturing 3D shapes at low production costs.

Saccade-related neural communication in the human medial temporal lobe is modulated by the social relevance of stimuli.

Humans predominantly explore their environment by moving their eyes. To optimally communicate and process visual information, neural activity needs to be coordinated with the execution of eye movements. We investigated the coordination between visual exploration and interareal neural communication by analyzing local field potentials and single neuron activity in patients with epilepsy. We demonstrated that during the free viewing of images, neural communication between the human amygdala and hippocampus is coordinated with the execution of eye movements. The strength and direction of neural communication and hippocampal saccade-related phase alignment were strongest for fixations that landed on human faces. Our results argue that the state of the human medial temporal lobe network is selectively coordinated with motor behavior. Interareal neural communication was facilitated for social stimuli as indexed by the category of the attended information.

Picosecond pulse-shaping for strong three-dimensional field-free alignment of generic asymmetric-top molecules

Fixing molecules in space is a crucial step for the imaging of molecular structure and dynamics. Here, we demonstrate three-dimensional (3D) field-free alignment of the prototypical asymmetric top molecule indole using elliptically polarized, shaped, off-resonant laser pulses. A truncated laser pulse is produced using a combination of extreme linear chirping and controlled phase and amplitude shaping using a spatial-light-modulator (SLM) based pulse shaper of a broadband laser pulse. The angular confinement is detected through velocity-map imaging of H+ and C2+ fragments resulting from strong-field ionization and Coulomb explosion of the aligned molecules by intense femtosecond laser pulses. The achieved three-dimensional alignment is characterized by comparing the result of ion-velocity-map measurements for different alignment directions and for different times during and after the alignment laser pulse to accurate computational results. The achieved strong three-dimensional field-free alignment of < {cos }^{2}delta > =0.89 demonstrates the feasibility of both, strong three-dimensional alignment of generic complex molecules and its quantitative characterization.

Pursuit-evasion games of multiple cooperative pursuers and an evader: A biological-inspired perspective

Multi-player pursuit-evasion games are fascinating in both nature and the artificial world. In these games, the purpose of pursuers is to capture the evader who attempt to avoid being captured. This article solves the pursuit-evasion games with communication constraints, and obtains the pursuit and escape strategies of all players and the corresponding capture zones. The successful capture conditions of multiple pursuers are defined according to the laws of nature, including distance conditions and quantity conditions. From the biological-inspired perspective, we formulate a concise dynamic and design the pursuit and escape strategies. The collision avoidance, gathering, and direction alignment between pursuers are realized by introducing repulsion, attraction, and alignment functions in the pursuit strategy. Furthermore, the influence of parameter variation on the system’s dynamic performance is investigated by introducing the distance-cost, energetic-cost, and time-cost. The phase-transition lines that separate the whole space into the capture zone and escape zone are obtained by analysing various pursuit-evasion scenarios. The results are consistent with natural observations and disclose some natural laws in the predation scene of terrestrial creatures.

Polarization-dependent conversion efficiency of carbon nanotube-Si heterojunction solar cells based on aligned carbon nanotube films

We have fabricated solar cells that implement heterojunctions of Si and aligned carbon nanotube (CNT) films. Polarization-dependent optical absorption of highly aligned CNTs led to polarization-dependent conversion efficiencies, which in turn provided insight into the role of the CNT layer in the power generation mechanism in these heterojunction solar cells. When the incident light polarization was parallel to the CNT alignment direction so that the light absorption in the CNT layer was maximized, the short circuit photocurrent decreased by ∼25%. This indicates that electron–hole pair generation in the CNT layer does not directly lead to power generation and that the CNT-Si heterojunctions in our devices are Schottky junctions rather than p–n junctions.

Shear direction switching phenomena in twisted nematic liquid crystal cells for novel differential interference contrast imaging systems

AbstractA lateral shear occurs between ordinary and extraordinary rays in general optical uniaxial crystals, and we can observe a double image through the crystal, indicating a typical birefringence phenomenon. Small lateral shears occur in typical liquid crystal (LC) cells under small voltage applications, where the molecular alignment direction is generally inclined. The small lateral shear is useful for differential interference contrast (DIC) imaging systems, although it must be negligible in a typical LC display panel. In particular, unique lateral shearing properties are exhibited by twisted nematic (TN) LC cells, which are popular and important LC display modes. The 45°‐oblique lateral shear occurs according to the direction of the surface molecular alignment, and the inclination direction (+45° or −45°) depends on the molecular twist direction. If it is possible to switch the twist direction in the TN cell, the lateral shear direction can be switched by 90°, and a full DIC imaging system can be attained because the normal DIC system can obtain one‐directional derivative information along the shear direction. In this work, twist direction switching phenomena in TN cells are investigated by applying a magnetic field in the direction parallel to the cell surface.

Microstructure Evolution of Graphene and the Corresponding Effect on the Mechanical/Electrical Properties of Graphene/Cu Composite during Rolling Treatment.

Rolling enables the directional alignment of the reinforcements in graphene/Cu composites while achieving uniform graphene dispersion and matrix grain refinement. This is expected to achieve a breakthrough in composite performance. In this paper, the process parameters of rolling are investigated, and the defects, thickness variations of graphene and property changes of the composite under different parameters are analyzed. High-temperature rolling is beneficial to avoid the damage of graphene during rolling, and the prepared composites have higher electrical conductivity. The properties of graphene were investigated. Low-temperature rolling is more favorable to the thinning and dispersion of graphene; meanwhile, the relative density of the composites is higher in the low-temperature rolling process. With the increase of rolling deformation, the graphene defects slightly increased and the number of layers decreased. In this paper, the defect states of graphene and the electrical conductivity with different rolling parameters is comprehensively investigated to provide a reference for the rolling process of graphene/copper composites with different demands.

Enhanced current path by circularly and periodically-aligned semiconducting single-walled carbon nanotubes for logic circuit device

Improving the performance of solution-processed single-walled carbon nanotube thin film transistors (SWCNT TFTs) is essential to their wide usage in next generation large-area electronic devices. However, uncontrollable tube-tube junction and random network formation from conventional solution processes of SWCNTs has limited mobility and on-current level of SWCNT TFTs. Herein, we demonstrate a facile method by switching idea of reducing coffee-ring of the conventionally solution-processed or inkjet-printed thin films. Spontaneous coffee-ring formation of the inkjet-printed droplets is found to enhance directional alignment of SWCNTs in the outer rim of the coffee-rings. The evaporation-driven capillary flow toward the rim inside induces migration of SWCNT and thus forms densely aligned SWCNT rings. Periodic connection of such rings can provide high-current path at a given voltage. Therefore, by additionally forming the periodically connected rings on a pre-established random network of SWCNT in channel area of TFTs, we significantly improved the mobility and I on/I off ratio of SWCNT TFTs without degradations in other electrical parameters such as threshold voltage and subthreshold swing. We also demonstrated all-solution-processed inverters with higher voltage-gain in comparison with conventional ones.

Ionic liquid crystal elastomers-based flexible organic electrochemical transistors: Effect of director alignment of the solid electrolyte

Organic electrochemical transistors (OECTs) have attracted great attention since their discovery in 1984 due to their flexibility and biocompatibility. Although an intense focus has been put on the design of new organic semiconductors, fewer efforts are directed toward the development of optimized electrolytes. However, the electrolyte is an integral part of OECTs and strongly influences the transient responses of these devices. Also, best performing OECTs currently use liquid electrolytes, but there is a growing need for solid electrolytes, as they can be easily integrated into wearable devices. In this paper, we demonstrate that ionic liquid crystal elastomers (iLCEs) can be used as solid electrolytes of flexible, substrate-free organic electrochemical transistors. We introduce the alignment of the director of the liquid crystal elastomers as a new parameter to tune and improve both steady state and transient responses. The normalized maximum transconductance gm/w of the most sensitive iLCE was found to be the highest (7 Sm−1) among all solid state-based OECTs.

Intrinsic alignments of the extended radio continuum emission of galaxies in the EAGLE simulations

ABSTRACT We present measurements of the intrinsic alignments (IAs) of the star-forming gas of galaxies in the EAGLE simulations. Radio continuum imaging of this gas enables cosmic shear measurements complementary to optical surveys. We measure the orientation of star-forming gas with respect to the direction to, and orientation of, neighbouring galaxies. Star-forming gas exhibits a preferentially radial orientation–direction alignment that is a decreasing function of galaxy pair separation, but remains significant to $\gtrsim 1\, {\rm Mpc}$ at z = 0. The alignment is qualitatively similar to that exhibited by the stars, but is weaker at fixed separation. Pairs of galaxies hosted by more massive subhaloes exhibit stronger alignment at fixed separation, but the strong alignment of close pairs is dominated by ∼L⋆ galaxies and their satellites. At fixed comoving separation, the radial alignment is stronger at higher redshift. The orientation–orientation alignment is consistent with random at all separations, despite subhaloes exhibiting preferential parallel minor axis alignment. The weaker IA of star-forming gas than for stars stems from the former’s tendency to be less well aligned with the dark matter (DM) structure of galaxies than the latter, and implies that the systematic uncertainty due to IA may be less severe in radio continuum weak lensing surveys than in optical counterparts. Alignment models equating the orientation of star-forming gas discs to that of stellar discs or the DM structure of host subhaloes will therefore overestimate the impact of IAs on radio continuum cosmic shear measurements.

On Far-infrared and Submillimeter Circular Polarization

Abstract Interstellar dust grains are often aligned. If the grain alignment direction varies along the line of sight, the thermal emission becomes circularly polarized. In the diffuse interstellar medium, the circular polarization at far-infrared and submillimeter wavelengths is predicted to be very small, and probably unmeasurable. However, circular polarization may reach detectable levels in photodissociation regions viewed through molecular clouds, in infrared dark clouds, and in protoplanetary disks. Measurement of circular polarization could help constrain the structure of the magnetic field in infrared dark clouds, and may shed light on the mechanisms responsible for grain alignment in protoplanetary disks.

Achieving parallelly-arranged Ti3C2Tx in epoxy coating for anti-corrosive/wear high-efficiency protection

Two-dimensional Ti 3 C 2 T x has demonstrated great potential for enhancing the protection performance of epoxy coating , but randomly-arranged Ti 3 C 2 T x fails to meet higher expectations on the anti-corrosion/wear under extreme conditions. Here, the positively-charged Ti 3 C 2 T x (f + -Ti 3 C 2 T x ) flakes obtained by functionalization and protonation were directionally distributed in the epoxy coating using an electrophoretic deposition method. The migration/rotation of f + -Ti 3 C 2 T x flakes under electric field force and their mutual repulsion are responsible for the parallel alignment with the horizontal direction of coating. In particular, the epoxy coating incorporated with 1 wt % f + -Ti 3 C 2 T x exhibits a near-perfect internal arrangement structure. When exposed to saline solution for the long period, its water absorption is decreased by 85.33% and the lowest-frequency impedance is increased by four orders of magnitude compared with randomly-arranged Ti 3 C 2 T x hybrid epoxy coating, because parallelly-arranged f + -Ti 3 C 2 T x with orientation factor can maximize the internal tortuosity and optimize the barrier properties of epoxy coating against aggressive ions. Furthermore, a significant friction reduction and an order of magnitude reduction in wear rate are obtained, mainly based on the increase of the deflection and branching of cracks in the friction process thus decreasing the probability of coating exfoliation . Therefore, the directional alignment of Ti 3 C 2 T x in the epoxy coating can immediately upraise the protection properties’ ceiling, specifically suitable for long-term anti-corrosion/wear applications. • The positively charged f + -Ti 3 C 2 T x is successfully arranged in parallel by electric field action. • The physical barrier network with the largest tortuosity formed by the parallelly-arranged f + -Ti 3 C 2 T x array significantly inhibits the penetration rate of corrosive ions. • The horizontal regular arrangement of f + -Ti 3 C 2 T x increases deflection and branching of cracks during defect growth, and thus reducing coating exfoliation. • This work raises the anti-corrosion/wear ceiling of Ti 3 C 2 T x -based epoxy coatings, and the facile preparation process is conducive to large-scale practical applications.