Direct Switching Research Articles

Actin-Membrane Release Initiates Cell Protrusions.

Despite the well-established role of actin polymerization as a driving mechanism for cell protrusion, upregulated actin polymerization alone does not initiate protrusions. Using a combination of theoretical modeling and quantitative live-cell imaging experiments, we show that local depletion of actin-membrane links is needed for protrusion initiation. Specifically, we show that the actin-membrane linker ezrin is depleted prior to protrusion onset and that perturbation of ezrin's affinity for actin modulates protrusion frequency and efficiency. We also show how actin-membrane release works in concert with actin polymerization, leading to a comprehensive model for actin-driven shape changes. Actin-membrane release plays a similar role in protrusions driven by intracellular pressure. Thus, our findings suggest that protrusion initiation might be governed by a universal regulatory mechanism, whereas the mechanism of force generation determines the shape and expansion properties of the protrusion.

Optical subpicosecond nonvolatile switching and electron-phonon coupling in ferroelectric materials

Direct optical ferroelectric switching (FE switch) has the advantage of being ultrafast over the traditional FE switch, which relies on domain nucleation and growth. However, how to realize nonvolatility in such an optical FE switch poses a serious challenge. Time-dependent density-functional theory molecular dynamics study reveals that subpicosecond nonvolatile FE switches can be realized in GeTe and ${\mathrm{PbTiO}}_{3}$. While optical tuning of the transition barrier and initiation of a directional atomic motion are crucial, the dephasing of the excited state holds the key for the realization of nonvolatility.

Regulation of Host Innate Immunity by Non-Coding RNAs During Dengue Virus Infection.

An estimated 3.9 billion individuals in 128 nations (about 40% of global population) are at risk of acquiring dengue virus infection. About 390 million cases of dengue are reported each year with higher prevalence in the developing world. A recent modeling-based report suggested that half of the population across the globe is at risk of dengue virus infection. In any given dengue outbreak, a percentage of infected population develops severe clinical manifestations, and this remains one of the “unsolved conundrums in dengue pathogenesis”. Although, host immunity and virus serotypes are known to modulate the infection, there are still certain underlying factors that play important roles in modulating dengue pathogenesis. Advanced genomics-based technologies have led to identification of regulatory roles of non-coding RNAs. Accumulating evidence strongly suggests that viruses and their hosts employ non-coding RNAs to modulate the outcome of infection in their own favor. The foremost ones seem to be the cellular microRNAs (miRNAs). Being the post-transcriptional regulators, miRNAs can be regarded as direct switches capable of turning “on” or “off” the viral replication process. Recently, role of long non-coding RNAs (lncRNAs) in modulating viral infections via interferon dependent or independent signaling has been recognized. Hence, we attempt to identify the “under-dog”, the non-coding RNA regulators of dengue virus infection. Such essential knowledge will enhance the understanding of dengue virus infection in holistic manner, by exposing the specific molecular targets for development of novel prophylactic, therapeutic or diagnostic strategies.

Singular dynamics for morphing aircraft switching on the velocity boundary

It has singularity problem for morphing aircraft to switch its structure in an infinitesimal short time. Many physical parameters such as aerodynamic coefficients and moment of inertia will be altered, and the thrust of aero engine may be different for different states of morphing aircraft. For a typical case, the sweep angle of wing changes to a relative large angle when the speed of morphing aircraft is higher than a critical speed, while it switches to a small angle for the speed of such an aircraft below the critical speed. It could have possibility that the speed of such a morphing aircraft chatters around the critical speed. If it is in unmanned operation, the aircraft will switch its structure in a high frequency for the aforementioned condition, which may be a high risk for the control and dynamic of the morphing aircraft. Therefore, it is necessary to study whether the morphing aircraft should switch its structure when the speed arrives the critical speed. To simplify the problem, the switchability of such a morphing aircraft will be studied based on the dynamical system in the longitudinal direction. The analytical passable and non-passable conditions for flow switching on the velocity boundary for such a morphing aircraft will be developed. For non-passable flows, the analytical conditions for onset and vanishing for flow sliding on the velocity boundary will also be given. Mapping structure will be used to describe the periodic motions of dynamical system for such an aircraft. Numerical simulations will be carried out to show the complexity for such a switchability problem. It will be found that with the development of switchability conditions, the morphing aircraft could obviously decrease the chatter phenomenon compared with the direct switch case.

Abnormal Wave Propagation in Tilted Linear‐Crossing Metamaterials

The propagation properties of electromagnetic waves depend on media dispersion in momentum space, which can be characterized using isofrequency contours (IFCs). Normal linear‐crossing metamaterials (NLCMMs), which undergo a new type of topological transition between two kinds of hyperbolic media, are attracting attention because of their potential as a new avenue for controlling light propagation and verifying unusual phenomena involving zero‐index and hyperbolic media. Herein, the rotation of the optical axis is treated as a new degree of freedom and a tilted linear‐crossing metamaterial (TLCMM) is theoretically proposed. Upon rotating the optical axis angle such that it is equal to the cone angle, it is found that this special TLCMM has the shape of a type‐III Dirac cone, in condensed matter physics. Boundary conditions and the causality law are used to reveal that electromagnetic waves in this critical TLCMM can achieve abnormal refraction without reflection and filtering. Moreover, these phenomena are observed experimentally in a planar circuit‐based system. The results regarding the manipulation of electromagnetic waves may enable their use in planar‐integrated photonics, including for directional propagation, cloaking, and switching.

Fluctuations in Intracellular CheY-P Concentration Coordinate Reversals of Flagellar Motors in E. coli.

Signal transduction utilizing membrane-spanning receptors and cytoplasmic regulator proteins is a fundamental process for all living organisms, but quantitative studies of the behavior of signaling proteins, such as their diffusion within a cell, are limited. In this study, we show that fluctuations in the concentration of the signaling molecule, phosphorylated CheY, constitute the basis of chemotaxis signaling. To analyze the propagation of the CheY-P signal quantitatively, we measured the coordination of directional switching between flagellar motors on the same cell. We analyzed the time lags of the switching of two motors in both CCW-to-CW and CW-to-CCW switching (∆τCCW-CW and ∆τCW-CCW). In wild-type cells, both time lags increased as a function of the relative distance of two motors from the polar receptor array. The apparent diffusion coefficient estimated for ∆τ values was ~9 µm2/s. The distance-dependency of ∆τCW-CCW disappeared upon loss of polar localization of the CheY-P phosphatase, CheZ. The distance-dependency of the response time for an instantaneously applied serine attractant signal also disappeared with the loss of polar localization of CheZ. These results were modeled by calculating the diffusion of CheY and CheY-P in cells in which phosphorylation and dephosphorylation occur in different subcellular regions. We conclude that diffusion of signaling molecules and their production and destruction through spontaneous activity of the receptor array generates fluctuations in CheY-P concentration over timescales of several hundred milliseconds. Signal fluctuation coordinates rotation among flagella and regulates steady-state run-and-tumble swimming of cells to facilitate efficient responses to environmental chemical signals.

Compact and efficient PC-based directional coupler all-optical switch

Abstract Recently, the photonic crystal–based optical components and devices have attracted many researchers’ attention because of its nanoscale size which makes it suitable for the photonic integrated applications. Hence, the design of all-optical switch based on photonic crystal structure have been investigated in the past few decades to meet the requirement of ultracompact size with optimized performances such as fast response time, high extinction ratio with low insertion loss. Here, the design of directional coupler–based all-optical switch operating at the wavelength of 1550 nm is proposed with new design values. The resonant operating wavelength of the switch is identified with the help of finite element method. Then, the cross-state switching operation is analysed with the help of finite-difference time-domain method by applying a nonlinear optical Kerr effect switching mechanism. The important performance metrics of the proposed design such as insertion loss, extinction ratio, directivity and the response time are obtained as −0.008 , 26.98, 20.44 dB and 0.13ps, respectively. The total footprint of the proposed optical switch is approximately 128 µm2.

Distinct chemotactic behavior in the original Escherichia coli K-12 depending on forward-and-backward swimming, not on run-tumble movements

Most motile bacteria are propelled by rigid, helical, flagellar filaments and display distinct swimming patterns to explore their favorable environments. Escherichia coli cells have a reversible rotary motor at the base of each filament. They exhibit a run-tumble swimming pattern, driven by switching of the rotational direction, which causes polymorphic flagellar transformation. Here we report a novel swimming mode in E. coli ATCC10798, which is one of the original K-12 clones. High-speed tracking of single ATCC10798 cells showed forward and backward swimming with an average turning angle of 150°. The flagellar helicity remained right-handed with a 1.3 μm pitch and 0.14 μm helix radius, which is consistent with the feature of a curly type, regardless of motor switching; the flagella of ATCC10798 did not show polymorphic transformation. The torque and rotational switching of the motor was almost identical to the E. coli W3110 strain, which is a derivative of K-12 and a wild-type for chemotaxis. The single point mutation of N87K in FliC, one of the filament subunits, is critical to the change in flagellar morphology and swimming pattern, and lack of flagellar polymorphism. E. coli cells expressing FliC(N87K) sensed ascending a chemotactic gradient in liquid but did not spread on a semi-solid surface. Based on these results, we concluded that a flagellar polymorphism is essential for spreading in structured environments.

Tuning band alignment and optical properties of 2D van der Waals heterostructure via ferroelectric polarization switching

Favourable band alignment and excellent visible light response are vital for photochemical water splitting. In this work, we have theoretically investigated how ferroelectric polarization and its reversibility in direction can be utilized to modulate the band alignment and optical absorption properties. For this objective, 2D van der Waals heterostructures (HTSs) are constructed by interfacing monolayer MoS2 with ferroelectric In2Se3. We find the switch of polarization direction has dramatically changed the band alignment, thus facilitating different type of reactions. In In2Se3/MoS2/In2Se3 heterostructures, one polarization direction supports hydrogen evolution reaction and another polarization direction can favour oxygen evolution reaction. These can be used to create tuneable photocatalyst materials where water reduction reactions can be selectively controlled by polarization switching. The modulation of band alignment is attributed to the shift of reaction potential caused by spontaneous polarization. Additionally, the formed type-II van der Waals HTSs also significantly improve charge separation and enhance the optical absorption in the visible and infrared regions. Our results pave a way in the design of van der Waals HTSs for water splitting using ferroelectric materials.

Structure and Function of Stator Units of the Bacterial Flagellar Motor

Many bacteria use the flagellum for locomotion and chemotaxis. Its bidirectional rotation is driven by a membrane-embedded motor, which uses energy from the transmembrane ion gradient to generate torque at the interface between stator units and rotor. The structural organization of the stator unit (MotAB), its conformational changes upon ion transport, and how these changes power rotation of the flagellum remain unknown. Here, we present ~3Å-resolution cryoelectron microscopy reconstructions of the stator unit in different functional states. We show that the stator unit consists of a dimer of MotB surrounded by a pentamer of MotA. Combining structural data with mutagenesis and functional studies, we identify key residues involved in torque generation and present a detailed mechanistic model for motor function and switching of rotational direction.

Sex differences in glucoprivic regulation of glycogen metabolism in hypothalamic primary astrocyte cultures: Role of estrogen receptor signaling

Hypoglycemia causes sex-reliant changes in hypothalamic astrocyte glycogen metabolism in vivo. The role of nuclear versus membrane astrocyte estrogen receptors (ER) in glucoprivic regulation of glycogen is unclear. Here, primary hypothalamic astrocyte cultures were treated with selective ER antagonists during glucoprivation to investigate the hypothesis that ER mediate sex-specific glycogen responses to glucoprivation. Results show that glucoprivic down-regulation of glycogen synthase expression is mediated by transmembrane G protein-coupled ER-1 (GPER) signaling in each sex and estrogen receptor (ER)-beta (ERβ) activity in females. Glucoprivic inhibition of glycogen phosphorylase involves GPER and ERβ in females, but ER-independent mechanisms in males. GPER, ERβ, and ER-alpha (ERα) inhibit or stimulate AMPK protein expression in male versus female astrocytes, respectively. Glucoprivic augmentation of phospho-AMPK profiles in male glia was opposed by GPER activation, whereas GPER and ERβ suppress this protein in females. Astrocyte ERα and GPER content was down-regulated in each sex during glucose deficiency, whereas ERβ levels was unaltered (males) or increased (females). Glucoprivation correspondingly elevated or diminished male versus female astrocyte glycogen content; ER antagonism reversed this response in males, but not females. Results identify distinctive ER variants involved in sex-similar versus sex-specific astrocyte protein responses to withdrawal of this substrate fuel. Notably, glucoprivation elicits a directional switch or gain-of-effect of GPER and ERβ on specific glial protein profiles. Outcomes infer that ERs are crucial for glucoprivic regulation of astrocyte glycogen accumulation in males. Alternatively, estradiol may act independently of ER signaling to disassemble this reserve in females.

Implications of back-and-forth motion and powerful propulsion for spirochetal invasion

The spirochete Leptospira spp. can move in liquid and on a solid surface using two periplasmic flagella (PFs), and its motility is an essential virulence factor for the pathogenic species. Mammals are infected with the spirochete through the wounded dermis, which implies the importance of behaviors on the boundary with such viscoelastic milieu; however, the leptospiral pathogenicity involving motility remains unclear. We used a glass chamber containing a gel area adjoining the leptospiral suspension to resemble host dermis exposed to contaminated water and analyzed the motility of individual cells at the liquid-gel border. Insertion of one end of the cell body to the gel increased switching of the swimming direction. Moreover, the swimming force of Leptospira was also measured by trapping single cells using an optical tweezer. It was found that they can generate sim 17 pN of force, which is sim 30 times of the swimming force of Escherichia coli. The force-speed relationship suggested the load-dependent force enhancement and showed that the power (the work per unit time) for the propulsion is sim 3.1 × 10–16 W, which is two-order of magnitudes larger than the propulsive power of E. coli. The powerful and efficient propulsion of Leptospira using back-and-forth movements could facilitate their invasion.

Switching between positive and negative movement near an air/water interface through lateral laser illumination

The directional movement of an aqueous solution containing gold nanoparticles under laser irradiation (532 nm) through the vicinity of an air/water interface is reported. It is shown that unidirectional flow is generated along the path of light-travel when a laser is irradiated parallel to the interface. On the contrary, liquid flow toward the light source is caused when the incident angle of the laser is tuned so as to make the total reflection at an air/water interface. Such switching of the flow direction, positive or negative to the light propagation, was applied to the movement of mm-sized floating object, revealing that repetitive back and forth motion of the solid object is generated. This directional switching of photo-induced movement is interpreted by taking into account the flow caused by the spatial gradient of the surface tension due to the thermal effect of the incident laser. A numerical model with a Navier–Stokes-type equation reproduces the essential aspects of the switching of the direction observed in the present study.

The macroevolutionary dynamics of symbiotic and phenotypic diversification in lichens

Symbioses are evolutionarily pervasive and play fundamental roles in structuring ecosystems, yet our understanding of their macroevolutionary origins, persistence, and consequences is incomplete. We traced the macroevolutionary history of symbiotic and phenotypic diversification in an iconic symbiosis, lichens. By inferring the most comprehensive time-scaled phylogeny of lichen-forming fungi (LFF) to date (over 3,300 species), we identified shifts among symbiont classes that broadly coincided with the convergent evolution of phylogenetically or functionally similar associations in diverse lineages (plants, fungi, bacteria). While a relatively recent loss of lichenization in Lecanoromycetes was previously identified, our work instead suggests lichenization was abandoned far earlier, interrupting what had previously been considered a direct switch between trebouxiophycean and trentepohlialean algal symbionts. Consequently, some of the most diverse clades of LFF are instead derived from nonlichenized ancestors and re-evolved lichenization with Trentepohliales algae, a clade that also facilitated lichenization in unrelated lineages of LFF. Furthermore, while symbiont identity and symbiotic phenotype influence the ecology and physiology of lichens, they are not correlated with rates of lineage birth and death, suggesting more complex dynamics underly lichen diversification. Finally, diversification patterns of LFF differed from those of wood-rotting and ectomycorrhizal taxa, likely reflecting contrasts in their fundamental biological properties. Together, our work provides a timeline for the ecological contributions of lichens, and reshapes our understanding of symbiotic persistence in a classic model of symbiosis.

Modeling of a superconducting sensor with microring-embedded gold-island space–time control

A superconducting sensing circuit using silicon microring-embedded gold-island space–time control is proposed for a low-current source sensor. Feeding an optical field centered at a wavelength of 1.50 µm into the circuit with suitable parameters results in the formation of a whispering-gallery mode. The electric field is the space source, being multiplexed in time to construct the space–time function. Space–time control is achieved using two side phase modulators to obtain a path difference between the polaritons (trapped electrons) at resonance. The space and time uncertainty saturate simultaneously due to the nonlinear Kerr effect. The polariton oscillation obeys a two-level system in which the oscillation time collapses at resonance. The oscillation signal is recognized as the Rabi oscillation, which enables the operation of the circuit under forward- or reverse-biased directional switching. The results of this work show that the current of the proposed circuit increases exponentially in both the forward- and reverse-bias directions. The switching time of the Rabi oscillation is 1.50 µs, while the current–voltage characteristic of the circuit exhibits sensitivity values ranging from 0.82 to 1.90 µA nV−1. This performance confirms that the microring circuit can be used as a superconducting sensing circuit for low-current sensor applications.

Phytoplankton response to long-term wind dynamics at large shallow Lake Taihu (shallow lake phytoplankton response to long-term wind dynamics)

Shallow lakes are highly sensitive to respond wind dynamics. The phytoplankton biomass production and distribution scenarios vary annually and seasonally in shallow lakes. The present study investigated the impact of long-term wind dynamics to phytoplankton biomass at Lake Taihu. The response of phytoplankton taxonomic groups to annual and seasonal wind dynamics using generalized additive model showed significant correlation. The critical annual and seasonal wind speed was 2.2 m/s showing the highest correlation with phytoplankton biomass whereas, wind speed declined by 0.02 m/s annually from Jan 2000 to Dec 2016 at Lake Taihu. The lower to medium wind speeds with frequent directional switching toward shore areas developed higher mixing scenarios which helped in reduction of water temperatures, distribution and colony formation of phytoplankton near the Meiliang Bay. The onshore winds were most frequent winds with low wind speeds whereas, offshore winds have been observed with medium to higher wind speeds. The results of generalized additive model well described the wind impacts on phytoplankton biomass and successfully modeled the response of phytoplankton to wind speed. Therefore, it has been concluded that long-term wind dynamic control the movement, mixing and colony formation processes of phytoplankton at Lake Taihu. The fundamental mechanism found in the present study was the long-term higher variations (annual and seasonal) of the wind-induced phytoplankton biomass changes which has been considered as the major physical factor regulating the phytoplankton blooms formation in the large shallow lake Taihu.

Experiments and low-order modelling of intermittent transitions between clockwise and anticlockwise spinning thermoacoustic modes in annular combustors

Annular combustion chambers of gas turbines and aircraft engines are subject to unstable azimuthal thermoacoustic modes leading to high amplitude acoustic waves propagating in the azimuthal direction. For certain operating conditions, the propagating direction of the wave switches randomly. The strong turbulent noise prevailing in gas turbine combustors is a source of random excitation for the thermoacoustic modes and can be the cause of these switching events. A low-order model is proposed to describe qualitatively this property of the dynamics of thermoacoustic azimuthal modes. This model is based on the acoustic wave equation with a destabilizing thermoacoustic source term to account for the flame’s response and a stochastic term to account for the turbulent combustion noise. Slow-flow averaging is applied to describe the modal dynamics on times scales that are slower than the acoustic pulsation. Under certain conditions, the model reduces formally to a Fokker-Planck equation describing a stochastic diffusion process in a potential landscape with two symmetric wells: One well corresponds to a mode propagating in the clockwise direction, the other well corresponds to a mode propagating in the anticlockwise direction. When the level of turbulent noise is sufficient, the stochastic force makes the mode jump from one well to the other at random times, reproducing the phenomenon of direction switching. Experiments were conducted on a laboratory scale annular combustor featuring 12 hydrogen-methan flames. System identification techniques were used to fit the model on the experimental data, allowing to extract the potential shape and the intensity of the stochastic excitation. The statistical predictions obtained from the Fokker–Planck equation on the mode’s behaviour and the direction switching time are in good agreement with the experiments.

Kinematics of a simple reciprocal model swimmer at intermediate Reynolds numbers

We computationally study the kinematics of a simple model reciprocal swimmer (asymmetric dumbbell) as a function of the Reynolds number (Re) and investigate how the onset and gradual increase of inertia impacts the swimming behavior: a reversal in the swim direction, flow directions, and the swim stroke. We divide the swim stroke into the expansion and compression of the two spheres and relate them to power and recovery strokes. We find that the switch in swim direction also corresponds to a switch in power and recovery strokes. We obtain expressions for the mean swimming velocity by collapsing the net displacement during expansion and compression under power law relationships with respect to Re, the swimmer's amplitude, and the distance between the two spheres. Analyzing the fluid flows, we see the averaged flow field during expansion always resembles a pusher and compression always a puller, but when averaged over the whole cycle, the flow that dominates is the one that occurs during the power stroke. We also relate the power and recovery strokes to the swimming efficiency during times of expansion and compression, and we find that the power stroke is, surprisingly, not always more efficient than the recovery stroke. Our results may have important implications for biology and ultimately the design of artificial swimmers.

Throttled explicit guidance for pinpoint landing under bounded thrust acceleration

Onboard computation of a fuel-optimal trajectory is an indispensable technology for future lunar and planetary missions with pinpoint landings. This paper proposes a throttled explicit guidance (TEG) scheme under bounded constant thrust acceleration. TEG is capable of achieving fuel-optimal large diversions with good accuracy and can find optimal solutions. Thus far, the TEG algorithm is unique as it offers an explicit and simultaneous search method for the fuel-optimal thrust direction and thrust magnitude switching in predictor-corrector iterations. Fast numerical search is realized with a straightforward computation of seven final states (position, velocity, and the Hamiltonian) from seven unknowns (six adjoint variables for position and velocity and one final time). In addition, global convergence capability is enhanced by implementing the damped Newton's method. A number of simulations of large diversions show the excellent convergence of the TEG algorithm within at most 15 iterations from a cold start. The experimental results of the runtime measurement of the TEG algorithm support its real-time feasibility on a flight processor. These features of the TEG are suitable for onboard guidance of pinpoint landings.

Sensitive and selective photoelectrochemical immunosensing platform based on potential-induced photocurrent-direction switching strategy and a direct Z-scheme CdS//hemin photocurrent-direction switching system

Herein, we develop a novel ultrasensitive and selective photoelectrochemical (PEC) immunosensor based on a potential-induced photocurrent-direction switching of the CdS-chitosan nanoparticles (CdS-CS NPs) and a direct Z-scheme CdS/hemin photocurrent-direction switching system. Taking the detection of Prion (PrPC) as example, the CdS-CS NPs served as photoactive materials showed a cathodic photocurrent by the potential-stimulated switching of the photocurrent direction strategy, after immobilization of the captured antibody of PrPC (Ab1) onto the surface of CdS-CS NPs, nitrogen-doped porous carbon (NPC)-hemin polyhedra labelled with secondary antibody of PrPC (Ab2) were subsequently introduced onto the immunosensing interface due to the antigen−antibody specific recognition, and could act as a photocurrent-direction converter of CdS-CS NPs to produce a big anodic photocurrent which was opposite to that of CdS-CS NPs, owe to the well-matched energy levels between CdS and hemin to form a direct Z-scheme CdS/hemin system. By coupling the potential-stimulated switching of the photocurrent direction strategy and direct Z-scheme photocurrent-direction switching system, PrPC was detected sensitively with a wide linear response range from 4 to 1000 aM and a low detection limit of 0.53 aM. Also, the developed PEC immunosensing platform showed excellent selectivity. Going beyond the conventional “signal-off” or “signal-on” driven immunosensor, this strategy may has promising applications in bioanalysis, disease diagnostics, and clinical biomedicine.