Orientation Switching Research Articles

Cortical tension overrides geometrical cues to orient microtubules in confined protoplasts

In plant cells, cortical microtubules (CMTs) generally control morphogenesis by guiding cellulose synthesis. CMT alignment has been proposed to depend on geometrical cues, with microtubules aligning with the cell long axis in silico and in vitro. Yet, CMTs are usually transverse in vivo, i.e., along predicted maximal tension, which is transverse for cylindrical pressurized vessels. Here, we adapted a microwell setup to test these predictions in a single-cell system. We confined protoplasts laterally to impose a curvature ratio and modulated pressurization through osmotic changes. We find that CMTs can be longitudinal or transverse in wallless protoplasts and that the switch in CMT orientation depends on pressurization. In particular, longitudinal CMTs become transverse when cortical tension increases. This explains the dual behavior of CMTs in planta: CMTs become longitudinal when stress levels become low, while stable transverse CMT alignments in tissues result from their autonomous response to tensile stress fluctuations.

The Prediction of Saliency Map for Head and Eye Movements in 360 Degree Images

By recording the whole scene around the capturer, virtual reality (VR) techniques can provide viewers the sense of presence. To provide a satisfactory quality of experience, there should be at least 60 pixels per degree, so the resolution of panoramas should reach 21600 × 10800. The huge amount of data will put great demands on data processing and transmission. However, when exploring in the virtual environment, viewers only perceive the content in the current field of view (FOV). Therefore if we can predict the head and eye movements which are important behaviors of viewer, more processing resources can be allocated to the active FOV. But conventional saliency prediction methods are not fully adequate for panoramic images. In this paper, a new panorama-oriented model, to predict head and eye movements, is proposed. Due to the superiority of computation in the spherical domain, the spherical harmonics are employed to extract features at different frequency bands and orientations. Related low- and high-level features including the rare components in the frequency domain and color domain, the difference between center vision and peripheral vision, visual equilibrium, person and car detection, and equator bias are extracted to estimate the saliency. To predict head movements, visual mechanisms including visual uncertainty and equilibrium are incorporated, and the graphical model and functional representation for the switch of head orientation are established. Extensive experimental results on the publicly available database demonstrate the effectiveness of our methods.

GO/PVA-integrated TFN RO membrane: Exploring the effect of orientation switching between PA and GO/PVA and evaluating the GO loading impact

In this work, a new membrane fabrication strategy is proposed to overcome the challenges of conventional nanofillers deposition and to develop novel thin film nanocomposite (TFN) membrane with enhanced performance for reverse osmosis (RO) application. Using polyvinyl alcohol (PVA) as adhesive for the hydrophilic graphene oxide (GO), TFN membranes with two different GO/PVA orientations (atop polyamide (PA) or between PA and substrate) at varying GO loading (0–0.02 wt/v%) were fabricated and characterized to evaluate their effects on membrane physicochemical properties and performances. Evidently, the membrane pure water flux (PWF) is significantly enhanced upon the incorporation of GO/PVA layer regardless of the orientations. Compared to the membrane without GO incorporation, the PWF of the membrane with GO/PVA atop PA layer and GO/PVA sandwiched between PA and substrate at optimum GO loading (0.015 wt/v%) was improved by 50.94% and 91.93%, respectively, mainly attributed to the improved surface hydrophilicity and altered structural properties. Besides exhibiting comparable separation efficiency (~98% NaCl rejection), the membrane with GO/PVA atop PA layer also showed better antifouling property (100% flux recovery, 5-h filtration using 1000 mg/L organic solutions) than the self-synthesized TFC and commercial RO membranes with negligible nanofillers leaching.

Social constructivist account of the world’s largest gay social app: Case study of Blued in China

Given China’s political conservativism and limited social acceptance of sexual minorities, it is paradoxical to find that Blued, a gay social app headquartered in Beijing, has become the largest app of this kind globally. Informed by the social construction of technology perspective and based on a yearlong ethnography, this article identifies three major factors that have shaped the developmental trajectory of Blued: (1) work with the Communist Party of China to employ Blued as a health education platform; (2) switch in orientation from a hookup app to a social app; and (3) push for the commercialization and internationalization of the app. This article spotlights that the voices of users were missing in the development process and argues that, for Blued to continue maintaining its success, it must stop relying on the “I-methodology” in its design and development. Lastly, it contributes to the SCOT scholarship and social app studies by deciphering the role of the state in app development in the Chinese context.

On the dynamics of sprays in complex gas turbine swirl injectors

Coupling of spray with the coherent structures of highly turbulent flow has been a long-standing problem, especially in the context of liquid fuel delivery systems in gas turbine combustors. In this work, we analyze the evolution of the hydrodynamic topology and consequent spray-flow interactions in a dual swirl injector assembly. We have shown (using time-resolved particle image velocimetry) that the geometry of the swirl cup (exit flare angle and mixing length), as well as the flow orientation (counter vs. co) in the primary and secondary swirlers, ascertain the hydrodynamic transitions in the resultant flow field. Width of the recirculation zone $$ \left( {{\raise0.7ex\hbox{$r$} \!\mathord{\left/ {\vphantom {r {R_{o} }}}\right.\kern-0pt} \!\lower0.7ex\hbox{${R_{o} }$}}} \right) $$ is identified as the key length-scale used to ascertain the global characteristics of the flow field. For a given flare angle, reduction in length scale $$ \left( {{\raise0.7ex\hbox{$r$} \!\mathord{\left/ {\vphantom {r {R_{o} }}}\right.\kern-0pt} \!\lower0.7ex\hbox{${R_{o} }$}}} \right) $$ is witnessed with orientation switch from counter-rotation to co-rotation configuration. Proper orthogonal decomposition (POD) is implemented over instantaneous flow field data to extract energetic spatial flow structures and temporal modes. POD revealed the existence of distinct frequency bands depending on the relative dominance of the primary or secondary swirler flow fields. Dynamic mode decomposition (DMD) also has been carried out to delineate the evolution of dominant frequency values with respect to the experimental variables.

Substrate-driven switchable molecular orientation in bulk heterojunction films identified using infrared reflection absorption spectroscopy

Substrate-driven molecular orientation switching could be possible to create electronic devices, such as transistors and solar cells.

Theoretical Investigation of All Optical Switching by Intersystem Crossing

The dynamics of spin flips induced by the femtosecond laser are theoretically investigated in this article. The spin flips in this scenario are attributed to the intersystem crossing (ISC) described within the frame of the Rabi model. This new explanation is a step attempting to explain the mechanism of the all-optical magnetic orientation switching in the perspective of the conservation of the angular momentum and breaks of the selection rule, which is ignored in the Raman scattering related explanations. The final spin states discussed herein are closely related to the intensity of the incident laser and the ISC decay rate. The quantitative analysis of the relation between decay rate, temperature and the intensity of the laser is discussed.

New hydrogen-bonded comblike polyimides with mesogenic side chains for stable orientation and fast switching of liquid crystals

ABSTRACTNew supramolecular comblike polyimides with mesogenic side chains for stable homeotropic orientation and fast electro-optical switching of liquid crystals (LCs) have been prepared through selective intermolecular hydrogen bonding between 4-(4-heptylphenyl)benzoic acid (4HPB) and host polyimide. A low concentration of 4HPB as the mesogenic guest molecule was hydrogen-bonded to polyimide backbone leading to the self-assembled comblike polyimide with enhanced homeotropic orientation properties. The electro-optical characteristics of the LC device containing hydrogen-bonded comblike polyimide exhibited better performance than those of LC cell with conventional polyimide. Because the conventional covalent approach for preparation of polyimides requires considerable synthetic efforts to achieve new functionality in polyimide materials, the proposed noncovalent method is a simple one and highly cost effective. Our controlled methodology should find wide application for the fabrication of functional alignment materials requiring high orientation ability.

A High‐Density Azobenzene Side Chain Polymer Brush for Azimuthal and Zenithal Orientational Photoswitching of a Nematic Liquid Crystal

AbstractThe azimuthal and zenithal orientational switching of nematic liquid crystals (NLCs) can be performed by photoresponsive azobenzene alignment layers called command surfaces. Such photoresponsive layers have been prepared by molecular assembly methods or by spincasting of polymer materials. This work reports on the photoswitching orientation behavior of an NLC on a high‐density brush of an azobenzene‐containing side chain liquid crystalline polymer. On the high‐density polymer brush surface, the zenithal homeotropic/planar photoalignment switching modes triggered by UV/visible light irradiation are reversed from those observed for traditional command surface systems, reflecting the azobenzene side chain orientation directing parallel to the substrate surface. Because the thermally stable trans‐azobenzene provides the in‐plane orientation of the NLC, irradiation with linearly polarized visible light readily switches the azimuthal direction to an arbitrary direction, and the resulting orientation is retained persistently. This paper discusses the features of the architecture of a high‐density polymer brush as the command surface for NLC orientation.

Adenine-Driven Structural Switch from a Two- to Three-Quartet DNA G-Quadruplex.

A G‐rich sequence found in the regulatory region of the RANKL gene, which is associated with homeostasis of bone metabolism, folds into a two‐quartet basket‐type G‐quadruplex stabilized by A⋅G⋅A and G⋅G⋅G base‐triads. Perusal of local structural features together with G/A‐to‐T modifications uncovered the critical role of A5 for the formation of a distinct antiparallel two‐quartet topology and not the three‐quartet topology that would be expected based on the sequence with four GGG‐tracts alone. The structural changes induced by the A5‐to‐T5 modification include a switch in orientation and relative positions of G‐strands that together with anti to syn reorientation of G12 provide insights into the complexity of the interactions that influence the folding of G‐rich DNA. Understanding the impact of loop residues on the stability and formation of G‐quadruplexes advances our knowledge and ability to predict structures adopted by G‐rich sequences, which are involved in regulatory mechanisms in the cell, and may also facilitate drug design.

Adenine‐Driven Structural Switch from a Two‐ to Three‐Quartet DNA G‐Quadruplex

AbstractA G‐rich sequence found in the regulatory region of the RANKL gene, which is associated with homeostasis of bone metabolism, folds into a two‐quartet basket‐type G‐quadruplex stabilized by A⋅G⋅A and G⋅G⋅G base‐triads. Perusal of local structural features together with G/A‐to‐T modifications uncovered the critical role of A5 for the formation of a distinct antiparallel two‐quartet topology and not the three‐quartet topology that would be expected based on the sequence with four GGG‐tracts alone. The structural changes induced by the A5‐to‐T5 modification include a switch in orientation and relative positions of G‐strands that together with anti to syn reorientation of G12 provide insights into the complexity of the interactions that influence the folding of G‐rich DNA. Understanding the impact of loop residues on the stability and formation of G‐quadruplexes advances our knowledge and ability to predict structures adopted by G‐rich sequences, which are involved in regulatory mechanisms in the cell, and may also facilitate drug design.

Anatomy of magnetic anisotropy induced by Rashba spin-orbit interactions

Magnetic anisotropy controls the orientational stability and switching properties of magnetic states, and therefore plays a central role in spintronics. First-principles density-functional-theory calculations are able, in most cases, to provide a satisfactory description of bulk and interface contributions to the magnetic anisotropy of particular film/substrate combinations. In this paper we focus on achieving a simplified understanding of some trends in interfacial magnetic anisotropy based on a simple tight-binding model for quasiparticle states in a heavy-metal/ferromagnetic-metal bilayer film. We explain how to calculate the magnetic anisotropy energy of this model from the quasiparticle spin-susceptibility, compare with more conventional approaches using either a perturbative treatment of spin-orbit interactions or a direct calculation of the dependence of the energy on the orientation of the magnetization, and show that the magnetic anisotropy can be interpreted as a competition between a Fermi-sea term favoring perpendicular anisotropy and a Fermi-surface term favoring in-plane anisotropy. Based on this finding, we conclude that perpendicular magnetic anisotropy should be expected in an itinerant electron thin film when the spin magnetization density is larger than the product of the band exchange splitting and the Fermi level density-of-states of the magnetic state.

A Switch in Microtubule Orientation during C. elegans Meiosis

In oocytes of many organisms, meiotic spindles form in the absence of centrosomes [1-5]. Such female meiotic spindles have a pointed appearance in metaphase with microtubules focused at acentrosomal spindle poles. At anaphase, the microtubules of acentrosomal spindles then transition to an inter-chromosomal array, while the spindle poles disappear. This transition is currently not understood. Previous studies have focused on this inter-chromosomal microtubule array and proposed a pushing model to drive chromosome segregation [6, 7]. This model includes an end-on orientation of microtubules with chromosomes. Alternatively, chromosomes were thought to associate along bundles of microtubules [8, 9]. Starting with metaphase, this second model proposed a pure lateral chromosome-to-microtubule association up to the final meiotic stages of anaphase. Here, we applied large-scale electron tomography [10] of staged C.elegans oocytes in meiosis to analyze the orientation of microtubules in respect to chromosomes. We show that microtubules at metaphase I are primarily oriented laterally to the chromosomes and that microtubules switch to an end-on orientation during progression through anaphase. We further show that this switch in microtubule orientation involves a kinesin-13 microtubule depolymerase, KLP-7, which removes laterally associated microtubules around chromosomes. From this, we conclude that both lateral and end-on modes of microtubule-to-chromosome orientations are successively used in C.elegans oocytes to segregate meiotic chromosomes.

Neotectonic implications and regional stress field constraints on mud volcanoes in offshore southwestern Taiwan

Recently discovered numerous mud volcanoes (MVs) and mud diapirs (MDs) in SW Taiwan, both onshore and offshore, show eruption lineaments suspected to be related to neotectonic processes. Spatial and temporal distribution of the MVs eruption events shows an obvious switch of the lineament orientation from NNE-, NE-, N-S-, NW- and E-W-trending in N-S direction. The mud volcanoes have experienced multi-stage eruptions, and should have occurred <50 km from the earthquake rupture zones. Along with the weakness zones, the intrusion appears to have occurred on the possible vertical feeder dikes along N25°E and N30°W directions. In this paper, the Coulomb stress changes have been employed to calculate these earthquakes to model the relationship between the fractures and volcanoes, and the source fault geometry of a total of 15 earthquakes constructed from the Globe CMT center and USGS Earthquake and Hazard Program. According to the regional fault geometry, we built the receiver feeder dikes parameters as 330/25/0 and 25/25/0 in strike/dip/rake directions, respectively. Coulomb normal stress changes were computed for the short-time eruption analysis and strain stress changes for the long-scale eruption assessment. Our results indicate that the stress changes are sensitive to the distribution of the eruption events and the Coulomb stress change should be able to facilitate prediction of the future eruptions triggered by the seismicity activities. Finally, the schematic model we proposed well demonstrated the neotectonic effects and regional stress field constraints on the MVs eruption mechanism.

Effects of stimulus pair orientation and hand switching on reaction time estimates of interhemispheric transfer.

Two behavioral estimates of interhemispheric transfer time, the crossed-uncrossed difference (CUD) and the unilateral field advantage (UFA), are thought to, respectively, index transfer of premotor and visual information across the corpus callosum in neurotypical participants. However, no attempt to manipulate visual and motor contingencies in a set of tasks while measuring the CUD and the UFA has yet been reported. In two go/no-go comparison experiments, stimulus pair orientations were manipulated. The hand of response changed after each correct response in the second, but not the first experiment. No correlation was found between the CUD and the UFA, supporting the hypothesis that these two measures index different types of information transfer across hemispheres. An effect of manipulation of stimulus pair orientation on UFAs was attributed to the homotopy of callosal fibers transferring visual information, while an effect of hand switching on CUDs was attributed mostly to spatial compatibility.

Effect of ac electric field on the dynamics of a vesicle under shear flow in the small deformation regime.

Vesicles or biological cells under simultaneous shear and electric field can be encountered in dielectrophoretic devices or designs used for continuous flow electrofusion or electroporation. In this work, the dynamics of a vesicle subjected to simultaneous shear and uniform alternating current (ac) electric field is investigated in the small deformation limit. The coupled equations for vesicle orientation and shape evolution are derived theoretically, and the resulting nonlinear equations are handled numerically to generate relevant phase diagrams that demonstrate the effect of electrical parameters on the different dynamical regimes such as tank treading (TT), vacillating breathing (VB) [called trembling (TR) in this work], and tumbling (TU). It is found that while the electric Mason number (Mn), which represents the relative strength of the electrical forces to the shear forces, promotes the TT regime, the response itself is found to be sensitive to the applied frequency as well as the conductivity ratio. While higher outer conductivity promotes orientation along the flow axis, orientation along the electric field is favored when the inner conductivity is higher. Similarly a switch of orientation from the direction of the electric field to the direction of flow is possible by a mere change of frequency when the outer conductivity is higher. Interestingly, in some cases, a coupling between electric field-induced deformation and shear can result in the system admitting an intermediate TU regime while attaining the TT regime at high Mn. The results could enable designing better dielectrophoretic devices wherein the residence time as well as the dynamical states of the vesicular suspension can be controlled as per the application.

Electrical Actuation of a DNA Origami Nanolever on an Electrode.

Development of electrically powered DNA origami nanomachines requires effective means to actuate moving origami parts by externally applied electric fields. We demonstrate how origami nanolevers on an electrode can be manipulated (switched) at high frequency by alternating voltages. Orientation switching is long-time stable and can be induced by applying low voltages of 200 mV. The mechanical response time of a 100 nm long origami lever to an applied voltage step is less than 100 μs, allowing dynamic control of the induced motion. Moreover, through voltage assisted capture, origamis can be immobilized from folding solution without purification, even in the presence of excess staple strands. The results establish a way for interfacing and controlling DNA origamis with standard electronics, and enable their use as moving parts in electro-mechanical nanodevices.

Shuttlecock-Shaped Molecular Rectifier: Asymmetric Electron Transport Coupled with Controlled Molecular Motion

A fullerene derivative with five hydroxyphenyl groups attached around a pentagon, (4-HOC6H4)5HC60 (1), has shown an asymmetric current-voltage (I-V) curve in a conducting atomic force microscopy experiment on gold. Such molecular rectification has been ascribed to the asymmetric distribution of frontier molecular orbitals over its shuttlecock-shaped structure. Our nonequilibrium Green's function (NEGF) calculations based on density functional theory (DFT) indeed exhibit an asymmetric I-V curve for 1 standing up between two Au(111) electrodes, but the resulting rectification ratio (RR ∼ 3) is insufficient to explain the wide range of RR observed in experiments performed under a high bias voltage. Therefore, we formulate a hypothesis that high RR (>10) may come from molecular orientation switching induced by a strong electric field applied between two electrodes. Indeed, molecular dynamics simulations of a self-assembled monolayer of 1 on Au(111) show that the orientation of 1 can be switched between standing-up and lying-on-the-side configurations in a manner to align its molecular dipole moment with the direction of the applied electric field. The DFT-NEGF calculations taking into account such field-induced reorientation between up and side configurations indeed yield RR of ∼13, which agrees well with the experimental value obtained under a high bias voltage.

Critical switching fluence of L10-FePt nanoparticles with practical size to ultrafast all-optical polarization switching

The magnetic storage industry will be pushed into a new era by emerging magnetic materials and ingenious read/write techniques. Recently, L10-FePt nanoparticles with exceptionally high uniaxial anisotropy, combined with the technique of all-optical magnetic switching, have increasingly drawn the attention of researchers. Focusing on L10-FePt nanoparticles, we report the superparamagnetic size limits and three elaborate stages of magnetic orientation switching, which demonstrate that in terms of the opto-magnetic responses of L10-FePt nanoparticles with the size of 6 nm, the fluence of an ultrashort laser pulse should not be larger than the level of 40 mJ/cm2 in order to achieve the helicity-dependent all-optical switching.

Spin texture motion in antiferromagnetic and ferromagnetic nanowires

We propose a Hamiltonian dynamics formalism for the current and magnetic field driven dynamics of ferromagnetic and antiferromagnetic domain walls in one dimensional systems. To demonstrate the power of this formalism, we derive Hamilton equations of motion via Poisson brackets based on the Landau-Lifshitz-Gilbert phenomenology, and add dissipative dynamics via the evolution of the energy. We use this approach to study current induced domain wall motion and compute the drift velocity. For the antiferromagnetic case, we show that a nonzero magnetic moment is induced in the domain wall, which indicates that an additional application of a magnetic field would influence the antiferromagnetic domain-wall dynamics. We consider both cases of the magnetic field being parallel and transverse to the N{\'e}el field. Based on this formalism, we predict an orientation switch mechanism for antiferromagnetic domain walls which can be tested with the recently discovered N{\'e}el spin orbit torques.