Coupling Junction Research Articles

Boosting thermoelectric performance of molecular junction by utilizing edge branches and weak coupling

In this study, we investigated the thermoelectric properties of molecular junctions, created by trapping naphthacene (C18H12) and rubrene (C42H28) molecules between two graphene electrodes. It is found that the charge transport of naphthacene-based and rubrene-based graphene junctions is not sensitive to the introduction of edge side branches or the increase in molecular length and still maintains resonance transport at the Fermi level. Notably, the presence of pendant branches on the molecular trunk in rubrene-based graphene junctions leads to a suppression of phonon transport, attributed to multiple scattering at the branch attachment points or Fano resonance scattering. The phonon thermal conductance of the rubrene junctions can be reduced by nearly half compared to that of naphthalene junctions. Furthermore, the room-temperature figure of merit (ZT) is significantly enhanced from 0.2 to 1.1 upon constructing weak coupling junctions, representing an almost tenfold increase over covalent junctions. These findings mean that it is highly desirable to find a mechanism that can suppress the phonon thermal conductance of self-assembled molecular films, while preserving their power factor at optimal levels to obtain high-efficiency thermoelectric performance.

Strong Electron-Vibration Signals in Weakly Coupled Molecular Junctions: Activation of Spin-Crossover.

Manipulating individual molecular spin states with electronic current has the potential to revolutionize quantum information devices. However, it is still unclear how a current can cause a spin transition in single-molecule devices. Here, we propose a spin-crossover (SCO) mechanism induced by electron-phonon coupling in an iron(II) phthalocyanine molecule situated on a graphene-decoupled Ir(111) substrate. We performed simulations of both elastic and inelastic electron tunneling spectroscopy (IETS), which reveal current-induced Fe-N vibrations and an underestimation of established electron-vibration signals. Going beyond standard perturbation theory, we examined molecules in various charge and spin states using the Franck-Condon framework. The increased probability of spin switching suggests that notable IETS signals indicate SCO triggered by the inelastic vibrational excitation associated with Fe-N stretching.

Simulation and implementation of photonic integrated circuits for the filtering and optical heterodyning of mode-locked comb-lines

We present the simulation and implementation of a photonic integrated circuit (PIC) designed for the filtering and optical heterodyning of comb-lines generated by a 20.97 GHz mode-locked fiber ring laser emitting at the optical C-band. We compare simulations obtained for the coupling junction of the microrings in the PIC with the use of an analytic approach and the finite difference time-domain (FDTD) method. A PIC designed for fabrication with the Triplex asymmetric double-stripe (ADS) waveguides was demonstrated. Using the PIC, we demonstrated the optical heterodyning of pairs of comb-lines filtered by tunable microrings. The phase noise of beat signals located at 20.97 and 41.94 GHz was characterized. We provide a discussion on enhancing the RF power of the beat signals with the use of optical injection locking.

BCM‐Inspired Synapses Constructed with Barrier‐Modulated Coupling Junctions for Enhancing Speech Recognition

AbstractBio‐inspired synaptic devices have garnered considerable interest in neuromorphic computing. The Bienenstock‐Cooper‐Munro (BCM) learning rule stands out as one of the most accurate synaptic models, featuring non‐monotonic behavior and threshold sliding effect, crucial for stable learning processes. The direct device strategy for completely mimicking the BCM rule is a tough issue since the current devices lack two competitive working modes within one device. In this work, a dual‐junction synaptic device with opposite built‐in electric fields using a W/WO2/WO3‐x/Au structure is demonstrated. The devices directly mimic two fundamental features of the BCM rule via a delicately‐designed bandgap engineering strategy. Furthermore, the working mechanisms are investigated and the promising potential of dual‐junction synaptic devices is demonstrated for enhancing speech recognition through Convolutional Neural Network (CNN)‐based digital speech recognition with a remarkable accuracy of 98% through a synaptic array. Even for speech recognition with 13% Gaussian noise, the accuracy remained at 83%. These findings provide a promising strategy for developing BCM‐based synaptic devices for neuromorphic computing applications.

Magnetic Eigenmodes in Chains of Coupled φ0-Josephson Junctions with Ferromagnetic Weak Links

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Air Pollution and Arrhythmias.

Air pollution is commonly defined as the contamination of the air we breathe by any chemical, physical, or biological agent that is potentially threatening to human and ecosystem health. The common pollutants known to be disease-causing are particulate matter, ground-level ozone, sulphur dioxide, nitrogen dioxide, and carbon monoxide. Although the association between increasing concentrations of these pollutants and cardiovascular disease is now accepted, the association of air pollution and arrhythmias is less well established. In this review we provide an in-depth discussion of the association of acute and chronic air pollution exposure and arrhythmia incidence, morbidity, and mortality, and the purported pathophysiological mechanisms. Increases in concentrations of air pollutants have multiple proarrhythmic mechanisms including systemic inflammation (via increases in reactive oxygen species, tumour necrosis factor, and direct effects from translocated particulate matter), structural remodelling (via an increased risk of atherosclerosis and myocardial infarction or by affecting the cell-to-cell coupling and gap junction function), and mitochondrial and autonomic dysfunction. Furthermore, we describe the associations of air pollution and arrhythmias. There is a strong correlation of acute and chronic air pollutant exposure and the incidence of atrial fibrillation. Acute increases in air pollution increase the risk of emergency room visits and hospital admissions for atrial fibrillation and the risk of stroke and mortality in patients with atrial fibrillation. Similarly, there is a strong correlation of increases of air pollutants and the risk of ventricular arrhythmias, out-of-hospital cardiac arrest, and sudden cardiac death.

Quantitative videomicroscopy reveals latent control of cell-pair rotations in vivo.

Collective cell rotations are widely used during animal organogenesis. Theoretical and in vitro studies have conceptualized rotating cells as identical rigid-point objects that stochastically break symmetry to move monotonously and perpetually within an inert environment. However, it is unclear if this notion can be extrapolated to a natural context, where rotations are ephemeral and heterogeneous cellular cohorts interact with an active epithelium. In zebrafish neuromasts nascent sibling hair cells invert positions by rotating≤180° around their geometric center after acquiring different identities via Notch1a-mediated asymmetric repression of Emx2. Here we show that this multicellular rotation is a three-phasic movement that progresses via coherent homotypic coupling and heterotypic junction remodeling. We found no correlation between rotations and epithelium-wide cellular flow or anisotropic resistive forces. Moreover, the Notch/Emx2 status of the cell dyad does not determine asymmetric interactions with the surrounding epithelium. Aided by computer modeling, we suggest that initial stochastic inhomogeneities generate a metastable state that poises cells to move, spontaneous intercellular coordination of the resulting instabilities enables persistently directional rotations, whereas Notch1a-determined symmetry breaking buffers rotational noise.

Electrothermal Coupling Model With Distributed Heat Sources for Junction Temperature Calculation During Surges

High junction temperature is usually the main factor leading to device failures in high-power working conditions, such as surges or avalanches. It is of great significance to obtain the junction temperature quickly and accurately. Direct measurement of junction temperature is inconvenient, and usually indirect electrical measurement combined with model calculation is used. An electrothermal coupling junction temperature calculation model with distributed heat sources is proposed in this article. This model can accurately and quickly predict the device behavior during the surge process, as well as the voltage drop and temperature changes of each part of the device, without actually performing surge tests. This article describes the theoretical basis and calculation principles of the model. By taking a commercial SiC merged PiN Schottky diode as an example, this article also explains the details of the establishment of the electrical and thermal characteristic models of the device, as well as the calculation steps of the junction temperature by the thermal coupling model. The calculated device voltage drop curve of the device is in good agreement with the measured ones, and the calculated junction temperature curve is more consistent with the device failure mechanism than the one by the traditional RC thermal circuit model.

Correlations between incident and emission polarization in nanowire-particle coupled junctions.

Plasmonic nanostructures with subwavelength confinement are of great importance for the development of integrated nanophotonic circuits and devices. Here, we experimentally investigate how the polarization of the emitted light from nanowire-particle junction relies on the incident polarization. We demonstrate that the correlations can be effectively modulated by the particle position relative to the wire. By varying the wire-particle gap with only several nanometers, the nanowire-particle junction can be changed from polarization maintainer to rotator. Then, by moving the particle along the wire within half of the surface plasmon polariton (SPP) beat, the polarization behaviors can be tuned from positive to negative correlation. The mechanism can be well understood by the hybridization of wire-particle coupled mode and propagating SPP modes, which is verified by finite-difference time-domain simulations. These findings would provide a new degree of freedom for manipulating light polarization at the nanometer scale and additional flexibility for constructing nanophotonic devices.

Optofluidic conical microresonator for precise displacement sensing

In the present work we report fabrication of a compact optical displacement sensor based on whispering gallery mode with common materials on Polydimethylsiloxane (PDMS) medium with mold master technique. Conical and hollow geometry of microcavity filled with Rhodamine B-doped Glycerol as active medium. The fabricated device can be utilized for sensing applications. Coupling junction can be tuned so that moving the conical microcavity of about 100 μm in the axial direction is equivalent to ∼1.5 nm shift in resonant wavelength. Also, a small change in concentration of active medium results in a shift in the resonant wavelength which provides the feasibility of sensing the refractive index. The proposed structure demonstrates the ability of considerably high-resolution sensing for fine displacement steps which is limited by the resolution of the spectrometer (0.6 nm).

Evolution of the Topological Energy Band in Graphene Nanoribbons.

Topological theory has been recently applied in graphene nanoribbons (GNRs) and predicts the existence of topological quantum states in junctions connecting GNRs of different topological classes. Through the periodic alignment of the topological states along a GNR backbone, frontier GNR electronic bands with tunable band gaps and band widths could be generated. In this work, we demonstrate the evolution of the topological band by fabricating GNR structures hosting a single topological junction, dimerized junctions, and multiple coupled junctions with on-surface synthesis, which guarantees the atomic precision of these nanostructures. Their structural and electronic properties are investigated by scanning tunneling microscopy and spectroscopy supported by tight-binding theory. The 1D superlattice of the topological junction states can be described by an effective two-band tight-binding Su-Schrieffer-Heeger (SSH) type model considering two alternating coupling motifs.

An ultralow voltage circuit for energy harvesting with 3.3 mW capacity

This brief describes an astable multivibrator aimed to low voltage energy harvesting using inductive coupling and bipolar junction transistors. The topology needs a bias voltage at the bases, and we propose a circuit called starting block to generate this voltage from the supply. A proof-of-concept circuit with discrete devices was able to work with a voltage as low as 50 mV and deliver 3.3 mW from a 100 mV supply. To the authors’ knowledge, it is the energy harvesting circuit with highest power capacity. It has the additional advantage of using conventional devices, in contrast with other approaches that use special devices like junction field effect transistors and native metal–oxide-semiconductor field effect transistors (MOSFETs). The circuit also needs a smaller transformer when compared to its version using conventional MOSFETs.

Severe T-System Remodeling in Pediatric Viral Myocarditis.

Chronic heart failure (HF) in adults causes remodeling of the cardiomyocyte transverse tubular system (t-system), which contributes to disease progression by impairing excitation-contraction (EC) coupling. However, it is unknown if t-system remodeling occurs in pediatric heart failure. This study investigated the t-system in pediatric viral myocarditis. The t-system and integrity of EC coupling junctions (co-localization of L-type Ca2+ channels with ryanodine receptors and junctophilin-2) were analyzed by 3D confocal microscopy in left-ventricular (LV) samples from 5 children with myocarditis (age 14 ± 3 months), undergoing ventricular assist device (VAD) implantation, and 5 children with atrioventricular septum defect (AVSD, age 17 ± 3 months), undergoing corrective surgery. LV ejection fraction (EF) was 58.4 ± 2.3% in AVSD and 12.2 ± 2.4% in acute myocarditis. Cardiomyocytes from myocarditis samples showed increased t-tubule distance (1.27 ± 0.05 μm, n = 34 cells) and dilation of t-tubules (volume-length ratio: 0.64 ± 0.02 μm2) when compared with AVSD (0.90 ± 0.02 μm, p < 0.001; 0.52 ± 0.02 μm2, n = 61, p < 0.01). Intriguingly, 4 out of 5 myocarditis samples exhibited sheet-like t-tubules (t-sheets), a characteristic feature of adult chronic heart failure. The fraction of extracellular matrix was slightly higher in myocarditis (26.6 ± 1.4%) than in AVSD samples (24.4 ± 0.8%, p < 0.05). In one case of myocarditis, a second biopsy was taken and analyzed at VAD explantation after extensive cardiac recovery (EF from 7 to 56%) and clinical remission. When compared with pre-VAD, t-tubule distance and density were unchanged, as well as volume-length ratio (0.67 ± 0.04 μm2 vs. 0.72 ± 0.05 μm2, p = 0.5), reflecting extant t-sheets. However, junctophilin-2 cluster density was considerably higher (0.12 ± 0.02 μm−3 vs. 0.05 ± 0.01 μm−3, n = 9/10, p < 0.001), approaching values of AVSD (0.13 ± 0.05 μm−3, n = 56), and the measure of intact EC coupling junctions showed a distinct increase (20.2 ± 5.0% vs. 6.8 ± 2.2%, p < 0.001). Severe t-system loss and remodeling to t-sheets can occur in acute HF in young children, resembling the structural changes of chronically failing adult hearts. T-system remodeling might contribute to cardiac dysfunction in viral myocarditis. Although t-system recovery remains elusive, recovery of EC coupling junctions may be possible and deserves further investigation.

A diplexer with direct coupled resonant junction

AbstractConventionally, diplexers are designed by connecting two filters of different frequencies using a transmission T‐line junction which acts as a distribution network serving the individual filters. Here, a novel diplexer has been proposed and designed to utilize a directly coupled resonator as the distribution network. The directly coupled resonator is designed using two square open‐loop resonators of the same resonant frequency of 1.95 GHz. Coupling of the two resonators is achieved using a λ/4 transmission line to directly couple them. This process made the resonator pair to possess a dual‐mode resonator function, resonating at 1.85 and 2.05 GHz. Two bandpass filters are then designed in the corresponding modes of the resonator pair with 5% fractional bandwidth and coupled accordingly. This technique allowed the resonator pair to contribute to the resonant poles of the diplexer while functioning as the distribution network.

Cascade domino lithography for extreme photon squeezing

Squeezing photons into deep sub-wavelength volumes and few-nanometer gaps has led to the investigation of interesting phenomena, including strong coupling, quantum plasmonics, nonlinearity enhancement, nonlocality, and molecular junctions. The common configuration of bowtie nanoantennas has been extensively studied owing to the great enhancement of the localized electromagnetic field. The enhancement rapidly increases as the tips become sharper and the gap becomes narrower. However, reliable fabrication of nanoantennas that are extremely sharp with sub-10 nm gaps is statistically prohibited due to the fundamental limitation of the proximity effect of electron beam lithography. Here, an intuitive “fall-to-rise” scheme is proposed and experimentally validated using a new concept of cascade domino lithography. In this report, we successfully establish a controllable lithography method of making extremely sharp bowtie nanoantennas with sub-1 nm radius of curvature reaching the size of a gold nanocluster as well as single-digit-nanometer gaps between such sharp tips. In addition, a proof-of-concept application of surface enhanced Raman spectroscopy is demonstrated along with rigorous full-wave electromagnetic simulations and numerical analysis. This control of falling nanostructures opens up an unexplored gateway towards conquering the limitations of experimentally exploring the realm of plasmonics down to the sub-nanometer regime.

The Quantitative Relationship among the Number of the Pacing Cells Required, the Dimension, and the Diffusion Coefficient.

The purpose of the paper is to derive a formula to describe the quantitative relationship among the number of the pacing cells required (NPR), the dimension i, and the diffusion coefficient D (electrical coupling or gap junction G). The relationship between NPR and G has been investigated in different dimensions, respectively. That is, for each fixed i, there is a formula to describe the relationship between NPR and G; and three formulas are required for the three dimensions. However, there is not a universal expression to describe the relationship among NPR, G, and i together. In the manuscript, surveying and investigating the basic law among the existed data, we speculate the preliminary formula of the relationship among the NPR, i, and G; and then, employing the cftool in MATLAB, the explicit formulas are derived for different cases. In addition, the goodness of fit (R2) is computed to evaluate the fitting of the formulas. Moreover, the 1D and 2D ventricular tissue models containing biological pacemakers are developed to derive more data to validate the formula. The results suggest that the relationship among the NPR, i, and the G (D) could be described by a universal formula, where the NPR scales with the i (the dimension) power of the product of the square root of G (D) and a constant b which is dependent on the strength of the pacing cells and so on.

Continuously tunable fiber laser based on Fano resonance filter of thin-fiber-taper-coupled conical microresonator

Through Fano resonance, the resonant modes exhibiting peak-like shapes on the bandpass spectrum of the thin-fiber-taper-coupled conical microresonator are generated. For the first time, this thin-fiber-taper-coupled conical microresonator functions as a Fano filter, and is applied as a tunable internal-cavity bandpass filter for an Erbium-doped fiber ring laser. If the size of the conical microresonator in the coupling junction is adjusted by displacing the fiber taper along the resonator axis, the wavelength of the output laser is able to be tuned linearly and continuously with a coefficient of 0.225 nm/mm.

Effect of general coupling conditions on the vibration and power flow characteristics of a two-plate built-up plate structure

This paper presents the modeling approach, dynamic response analysis and the effect of coupling junction properties on the vibration characteristics of two plates elastically coupled in the form a T shaped structure with elastic boundary conditions. These built-up plate structures are the most commonly used configurations in the design of engineering platforms both floating and stationary. The coupling junction has been represented as a combination of translational and rotational spring stiffness’s, thus making the junction state general in nature. The analysis has been carried out using a Fourier cosine series representation for the bending and in-plane plate displacements modified with inclusion of derived auxiliary function. The derived auxiliary functions are also presented in form of the product of a single Fourier cosine series expansion and one polynomial function. The Rayleigh-Ritz method is employed to the Lagrangian function to derive the natural frequency and dynamic response matrix. Both the free vibration and power transmission characteristics of the plate structure has been numerically presented. Validation of the modified Fourier function has been presented for an L shaped plate structure in comparison with existing literature results for free vibration analysis. Finally, the effect of variation of the coupling junction condition on the vibration and power flow characteristics of the T-plate structure has been presented. The modified Fourier function has proved to generate simple theoretical formulations and accurate results in numerical analysis of a T plate coupled configuration. The modified Fourier series function can be universally and efficiently extended to undertake vibration analysis of any type of coupled plate system with any configuration of boundary or coupling configurations. Communicated by J. Logo

Bioelectrical model of head-tail patterning based on cell ion channels and intercellular gap junctions

Robust control of anterior-posterior axial patterning during regeneration is mediated by bioelectric signaling. However, a number of systems-level properties of bioelectrochemical circuits, including stochastic outcomes such as seen in permanently de-stabilized “cryptic” flatworms, are not completely understood. We present a bioelectrical model for head-tail patterning that combines single-cell characteristics such as membrane ion channels with multicellular community effects via voltage-gated gap junctions. It complements the biochemically-focused models by describing the effects of intercellular electrochemical coupling, cutting plane, and gap junction blocking of the multicellular ensemble. We provide qualitative insights into recent experiments concerning planarian anterior/posterior polarity by showing that: (i) bioelectrical signals can help separated cell domains to know their relative position after injury and contribute to the transitions between the abnormal double-head state and the normal head–tail state; (ii) the bioelectrical phase-space of the system shows a bi-stability region that can be interpreted as the cryptic system state; and (iii) context-dependent responses are obtained depending on the cutting plane position, the initial bioelectrical state of the multicellular system, and the intercellular connectivity. The model reveals how simple bioelectric circuits can exhibit complex tissue-level patterning and suggests strategies for regenerative control in vivo and in synthetic biology contexts.

Synthetic Weyl Points and Chiral Anomaly in Majorana Devices with Nonstandard Andreev-Bound-State Spectra.

We demonstrate how to design various nonstandard types of Andreev-bound-state (ABS) dispersions, via a composite construction relying on Majorana bound states (MBSs). Here, the MBSs appear at the interface of a Josephson junction consisting of two topological superconductors (TSCs). Each TSC harbors multiple MBSs per edge by virtue of a chiral or unitary symmetry. We find that, while the ABS dispersions are 2π periodic, they still contain multiple crossings which are protected by the conservation of fermion parity. A single junction with four interface MBSs and all MBS couplings fully controllable, or networks of such coupled junctions with partial coupling tunability, open the door for topological band structures with Weyl points or nodes in synthetic dimensions, which in turn allow for fermion-parity (FP) pumping with a cycle set by the ABS-dispersion details. In fact, in the case of nodes, the FP pumping is a manifestation of chiral anomaly in 2D synthetic spacetime. The possible experimental demonstration of ABS engineering in these devices further promises to unveil new paths for the detection of MBSs and higher-dimensional chiral anomaly.