Break Excitation Research Articles

Cooper Pair Excitation Mediated by a Molecular Quantum Spin on a Superconducting Proximitized Gold Film.

Breaking a correlated pair in a superconductor requires an even number of fermions providing at least twice the pairing energy Δ. Here, we show that a single tunneling electron can also excite a pair breaking excitation in a proximitized gold film in the presence of magnetic impurities. Combining scanning tunneling spectroscopy with theoretical modeling, we map the excitation spectrum of an Fe-porphyrin molecule on the Au/V(100) proximitized surface into a manifold of entangled Yu-Shiba-Rusinov and spin excitations. Pair excitations emerge in the tunneling spectra as peaks outside the spectral gap only in the strong coupling regime, where the presence of a bound quasiparticle in the ground state ensures the even fermion parity of the excitation. Our results unravel the quantum nature of magnetic impurities on superconductors and demonstrate that pair excitations unequivocally reveal the parity of the ground state.

Ferroelectric FET-Based Implementation of FitzHugh-Nagumo Neuron Model

Ferroelectric field-effect transistor (FeFET)-based circuit implementation mimicking FitzHugh-Nagumo neuron is proposed in this work. The proposed circuit is shown to mimic biological neuron properties, such as excitation block and anodal break excitation which are not mimicked by an integrate and fire neuron model. We also show a winner-take-all circuit that can be used with this proposed neuron implementation. The neuron implementation requires just one FeFET, three baseline field-effect transistors, and one capacitor, making it area and energy-efficient. The neuron circuit, with minimum sized transistors, consumes approximately 10 pJ per spike. The neuron’s energy consumption per spike can be reduced to as low as 100 fJ by designing some of the transistors with aspect ratio less than one.

How Electrode Position Affects Selective His Bundle Capture: A Modelling Study.

We investigated the properties which affect the capture thresholds in order to improve selective pacing. We performed biophysically detailed, computer simulations of a His fibre running through a septal wedge preparation to compute capture thresholds under various configurations of electrode polarity and orientation. The myocardial capture threshold was close to that of the His bundle. The His fibre needed to intersect with the electrode tip to favor its activation. Inserting the electrode fully within the septum increased the myocardial capture threshold. Reversing polarity, to rely on anode break excitation, also increased the ease of selective pacing. Model results were consistent with clinical observations. For selective pacing, the tip needs to be in contact with the His fibre and anodal stimulation is preferable. This study provides insight into helping establish electrode and stimulation parameters for selective His bundle pacing in patients.

A Physical Perspective to the Inductive Function of Myelin-A Missing Piece of Neuroscience.

Starting from the inductance in neurons, two physical origins are discussed, which are the coil inductance of myelin and the piezoelectric effect of the cell membrane. The direct evidence of the coil inductance of myelin is the opposite spiraling phenomenon between adjacent myelin sheaths confirmed by previous studies. As for the piezoelectric effect of the cell membrane, which has been well-known in physics, the direct evidence is the mechanical wave accompany with action potential. Therefore, a more complete physical nature of neural signals is provided. In conventional neuroscience, the neural signal is a pure electrical signal. In our new theory, the neural signal is an energy pulse containing electrical, magnetic, and mechanical components. Such a physical understanding of the neural signal and neural systems significantly improve the knowledge of the neurons. On the one hand, we achieve a corrected neural circuit of an inductor-capacitor-capacitor (LCC) form, whose frequency response and electrical characteristics have been validated by previous studies and the modeling fitting of artifacts in our experiments. On the other hand, a number of phenomena observed in neural experiments are explained. In particular, they are the mechanism of magnetic nerve stimulations and ultrasound nerve stimulations, the MRI image contrast issue and Anode Break Excitation. At last, the biological function of myelin is summarized. It is to provide inductance in the process of neural signal, which can enhance the signal speed in peripheral nervous systems and provide frequency modulation function in central nervous systems.

Dynamical Transitions and Critical Behavior between Discrete Time Crystal Phases.

In equilibrium physics, spontaneous symmetry breaking and elementary excitation are two concepts closely related with each other: the symmetry and its spontaneous breaking not only control the dynamics and spectrum of elementary excitations, but also determine their underlying structures. In this Letter, based on an exactly solvable model, we propose a phase ramping protocol to study an excitationlike behavior of a nonequilibrium quantum matter: a discrete time crystal phase with spontaneous temporal translational symmetry breaking. It is shown that slow ramping could induce a dynamical transition between two Z_{2} symmetry breaking time crystal phases in time domain, which can be considered as a temporal analog of the soliton excitation spatially sandwiched by two degenerate charge density wave states in polyacetylene. By tuning the ramping rate, we observe a critical value at which point the transition duration diverges, resembling the critical slowing down phenomenon in nonequilibrium statistic physics. We also discuss the effect of stochastic sequences of such phase ramping processes and its implication to the stability of the discrete time crystal phase against noisy perturbations.

Superconductivity and phonon self-energy effects in Fe1+yTe0.6Se0.4

The measurement of superconducting gaps on different Fermi surface pockets is necessary for elucidating the pairing mechanism in multi-band superconductors. Inelastic light scattering, or Raman spectroscopy, have been shown to provide the best bulk probe to study the Cooper pair breaking excitations. This paper presents polarization-resolved Raman spectroscopic study of the pair breaking excitations in FeTe0.6Se0.4 iron-based superconductor.

Neural Gutzwiller-projected variational wave functions

Variational wave functions have enabled exceptional scientific breakthroughs related to the understanding of novel phases of matter. Examples include the Bardeen-Cooper-Schrieffer theory of superconductivity, the description of the fractional quantum Hall effect through the Laughlin state, and Feynman's variational understanding of large-scale quantum effects in liquid Helium. More recently, Gutzwiller-projected wave functions, typically constructed from fermionic degrees of freedom, have been employed to examine quantum spin models in the presence of competing interactions, where exotic phases with no spontaneous symmetry breaking and fractional excitations may exist. In this work, we investigate the aforementioned fermionic wave functions supplemented with neural networks, specifically with the so-called restricted Boltzmann machine (RBM), to boost their accuracy and obtain reliable approximations to the ground state of generic spin models. In particular, we apply our neural augmented fermionic construction to the description of both magnetically ordered and disordered phases of increasing complexity, including cases where the ground state displays a non-trivial sign structure. Even though the RBM state is by far more effective for N\'eel states endowed with a particularly simple sign structure, it provides a significant improvement over the original fermionic state in highly frustrated regimes where a complex sign structure is anticipated, thus marking the path to an understanding of strongly-correlated spin models on the lattice via neural Gutzwiller-projected variational wave functions.

Modeling bipolar stimulation of cardiac tissue.

Unipolar stimulation of cardiac tissue is often used in the design of cardiac pacemakers because of the low current required to depolarize the surrounding tissue at rest. However, the advantages of unipolar over bipolar stimulation are not obvious at shorter coupling intervals when the tissue near the pacing electrode is relatively refractory. Therefore, this paper analyzes bipolar stimulation of cardiac tissue. The strength-interval relationship for bipolar stimulation is calculated using the bidomain model and a recently developed parsimonious ionic current model. The strength-interval curves obtained using different electrode separations and arrangements (electrodes placed parallel to the fibers versus perpendicular to the fibers) indicate that bipolar stimulation results in more complex activation patterns compared to unipolar stimulation. An unusually low threshold stimulus current is observed when the electrodes are close to each other (a separation of 1 mm) because of break excitation. Unlike for unipolar stimulation, anode make excitation is not present during bipolar stimulation, and an abrupt switch from anode break to cathode make excitation can cause dramatic changes in threshold with very small changes in the interval. These results could impact the design of implantable pacemakers and defibrillators.

Bidomain Predictions of Virtual Electrode-Induced Make and Break Excitations around Blood Vessels

Virtual electrodes formed by field stimulation during defibrillation of cardiac tissue play an important role in eliciting activations. It has been suggested that the coronary vasculature is an important source of virtual electrodes, especially during low-energy defibrillation. This work aims to further the understanding of how virtual electrodes from the coronary vasculature influence defibrillation outcomes. Using the bidomain model, we investigated how field stimulation elicited activations from virtual electrodes around idealized intramural blood vessels. Strength-interval curves, which quantify the stimulus strength required to elicit wavefront propagation from the vessels at different states of tissue refractoriness, were computed for each idealized geometry. Make excitations occurred at late diastolic intervals, originating from regions of depolarization around the vessel. Break excitations occurred at early diastolic intervals, whereby the vessels were able to excite surrounding refractory tissue due to the local restoration of excitability by virtual electrode-induced hyperpolarizations. Overall, strength-interval curves had similar morphologies and underlying excitation mechanisms compared with previous experimental and numerical unipolar stimulation studies of cardiac tissue. Including the presence of the vessel wall increased the field strength required for make excitations but decreased the field strength required for break excitations, and the field strength at which break excitations occurred was generally greater than 5 V/cm. Finally, in a more realistic ventricular slice geometry, the proximity of virtual electrodes around subepicardial vessels was seen to cause break excitations in the form of propagating unstable wavelets to the subepicardial layer. Representing the blood vessel wall microstructure in computational bidomain models of defibrillation is recommended as it significantly alters the electrophysiological response of the vessel to field stimulation. Although vessels may facilitate excitation of relatively refractory tissue via break excitations, the field strength required for this is generally greater than those used in the literature on low-energy defibrillation. However, the high-intensity shocks used in standard defibrillation may elicit break excitation propagation from the coronary vasculature.

Filling constraints for spin-orbit coupled insulators in symmorphic and nonsymmorphic crystals

We determine conditions on the filling of electrons in a crystalline lattice to obtain the equivalent of a band insulator--a gapped insulator with neither symmetry breaking nor fractionalized excitations. We allow for strong interactions, which precludes a free particle description. Previous approaches that extend the Lieb-Schultz-Mattis argument invoked spin conservation in an essential way and cannot be applied to the physically interesting case of spin-orbit coupled systems. Here we introduce two approaches: The first one is an entanglement-based scheme, and the second one studies the system on an appropriate flat "Bieberbach" manifold to obtain the filling conditions for all 230 space groups. These approaches assume only time reversal rather than spin rotation invariance. The results depend crucially on whether the crystal symmetry is symmorphic. Our results clarify when one may infer the existence of an exotic ground state based on the absence of order, and we point out applications to experimentally realized materials. Extensions to new situations involving purely spin models are also mentioned.

The one-electron description of excited states: Natural excitation orbitals of density matrix theory and Kohn–Sham orbitals of density functional theory as ideal orbitals

Linear response density matrix functional theory has been shown to solve the main problems of time-dependent density functional theory (deficient in case of double, charge transfer and bond breaking excitations). However, the natural orbitals preclude the description of excitations as (approximately) simple orbital-to-orbital transitions: many weakly occupied ‘virtual’ natural orbitals are required to describe the excitations. Kohn–Sham orbitals on the other hand afford for many excitations such a simple orbital description. In this communication we show that a transformation of the set of weakly occupied NOs can be defined such that the resulting natural excitation orbitals (NEOs) restore the single orbital transition structure for excitations generated by the linear response DMFT formalism.

Skin receptors and intradermal nerves do not generate the sensory double peak.

The cause of the double peak observed at submaximal stimulation of sensory nerves is unknown. The first peak is generated under the cathode and the second under the anode. The double peak is thought to arise from intradermal nerves or skin receptors, and in this study we tested this assumption. We studied the effect of different stimulus durations on anodal peak latency in volunteers. Biphasic anodal stimulation was used to investigate the latent additive effect of the trailing negative phase on the partial depolarization induced by the initial positive phase. We further tested the maximal amplitude of anode-generated potentials to estimate the number of neural structures involved in their generation. Increased stimulus duration caused anode-generated potential delay. Biphasic stimulation increased anode-generated amplitude 4-fold compared with monophasic stimulation. The anode-generated potential produced up to 85% of the supramaximal cathode-generated amplitude. The results suggest that the double peak arises from anodal break excitation and not from intradermal nerves or receptors.

Electrical properties of Lupinus angustifolius L. stem. II. Accommodation and anode break excitation

Under electrical stimulation of Lupinus stem phenomena of accommodation and anode break excitation appear. Their characteristic is the same as in the axon or nerve. Only their duration is about 10<sup>3</sup>-10<sup>4</sup> longer in plants. The constant characterizing the rate of accommodation was calculated. A limiting threshold value was found beyond which excitation occurs, irrespective of the rate of stimulus rise (voltage gradient). The accommodation rate is approximately constant, whereas the range of accommodation varies and is dependent on the difference between the rheobase value and the limiting threshold value. Hence plants with a low rheobase are characterized by a wider range of accommodation. It is suggested that the changes in potential (including AP) recorded on the stem surface are connected with changes of the potential on cell membranes (Sibaoka, 1962).

Wave dispersion and attenuation on human femur tissue.

Cortical bone is a highly heterogeneous material at the microscale and has one of the most complex structures among materials. Application of elastic wave techniques to this material is thus very challenging. In such media the initial excitation energy goes into the formation of elastic waves of different modes. Due to “dispersion”, these modes tend to separate according to the velocities of the frequency components. This work demonstrates elastic wave measurements on human femur specimens. The aim of the study is to measure parameters like wave velocity, dispersion and attenuation by using broadband acoustic emission sensors. First, four sensors were placed at small intervals on the surface of the bone to record the response after pencil lead break excitations. Next, the results were compared to measurements on a bulk steel block which does not exhibit heterogeneity at the same wave lengths. It can be concluded that the microstructure of the tissue imposes a dispersive behavior for frequencies below 1 MHz and care should be taken for interpretation of the signals. Of particular interest are waveform parameters like the duration, rise time and average frequency, since in the next stage of research the bone specimens will be fractured with concurrent monitoring of acoustic emission.

Effects of premature anodal stimulations on cardiac transmembrane potential and intracellular calcium distributions computed by anisotropic Bidomain models.

Cardiac unipolar electrode stimulations induce a particular structure of the transmembrane potential distribution (Vm), called virtual electrode polarization (VEP), which plays an important role in the mechanisms of cardiac excitation, reentry induction, and ventricular defibrillation. Recent experimental studies, based on the optical mapping techniques, have shown that premature stimulations also induce significant changes in the intracellular calcium (Cai) spatial distribution. The aim of this work is to investigate and compare by means of numerical simulations the morphology of the Vm and Cai patterns, generated by applying an S1-S2 stimulation protocol with a premature S2 anodal pulse. We perform parallel finite element simulations of a three-dimensional orthotropic Bidomain model on a block of ventricular tissue by using four membrane models of two species (guinea pig and rabbit), that incorporate the phenomenological or more detailed mechanistic descriptions of the calcium dynamics. During the S2 anodal stimulus, the Cai spatial distribution, computed with all the considered models, presents a configuration similar to the typical VEP pattern of Vm, with a minimum inside the virtual anode and two maxima in the virtual cathodes. After the S2 stimulus turns off, the anode break excitation mechanism yields a Vm pattern exhibiting a clearly propagating wavefront. Differently, the Cai patterns do not show a clear separation between the resting and the activated regions, with the exception of one of the phenomenological models considered, but they show warped dog-bone shaped equi-level lines around an elevation in the virtual anode region. The VEP pattern of the Cai spatial distribution during the S2 stimulus is in agreement with the previous experimental studies. Moreover, the Cai minimum in the virtual anode can be mainly attributable to the outflow of calcium ions produced by the sodium-calcium (NCX) exchanger, without a significant contribution of the ICaL current.

Mechanism of reentry induction by a 9-V battery in rabbit ventricles

Although the application of a 9-V battery to the epicardial surface is a simple method of ventricular fibrillation induction, the fundamental mechanisms underlying this process remain unstudied. We used a combined experimental and modelling approach to understand how the interaction of direct current (DC) from a battery may induce reentrant activity within rabbit ventricles and its dependence on battery application timing and duration. A rabbit ventricular computational model was used to simulate 9-V battery stimulation for different durations at varying onset times during sinus rhythm. Corresponding high-resolution optical mapping measurements were conducted on rabbit hearts with DC stimuli applied via a relay system. DC application to diastolic tissue induced anodal and cathodal make excitations in both simulations and experiments. Subsequently, similar static epicardial virtual electrode patterns were formed that interacted with sinus beats but did not induce reentry. Upon battery release during diastole, break excitations caused single ectopics, similar to application, before sinus rhythm resumed. Reentry induction was possible for short battery applications when break excitations were slowed and forced to take convoluted pathways upon interaction with refractory tissue from prior make excitations or sinus beats. Short-lived reentrant activity could be induced for battery release shortly after a sinus beat for longer battery applications. In conclusion, the application of a 9-V battery to the epicardial surface induces reentry through a complex interaction of break excitations after battery release with prior induced make excitations or sinus beats.

752 鋼棒切断加振法によるテンタゲートの動的安定判別法とその実用(計測・制御II,学術講演)

752 鋼棒切断加振法によるテンタゲートの動的安定判別法とその実用(計測・制御II,学術講演)

Dynamic stability of practical Tainter gate "E" using steel-rod breaking excitation test

Dynamic stability of practical Tainter gate "E" using steel-rod breaking excitation test

Classification of a Supersolid: Trial Wavefunctions, Symmetry Breakings and Excitation Spectra

A state of matter is characterized by its symmetry breaking and elementary excitations. A supersolid is a state which breaks both translational symmetry and internal U(1) symmetry. Here, we review some past and recent works in phenomenological Ginsburg-Landau theories, ground state trial wavefunctions and microscopic numerical calculations. We also write down a new effective supersolid Hamiltonian on a lattice. The eigenstates of the Hamiltonian contains both the ground state wavefunction and all the excited states (supersolidon) wavefunctions. We contrast various kinds of supersolids in both continuous systems and on lattices, both condensed matter and cold atom systems. We provide additional new insights in studying their order parameters, symmetry breaking patterns, the excitation spectra and detection methods.

Simulation of axonal excitability using LABVIEW

Objective In this paper a new application of LABVIEW in neural electrophysiological simulation was applied to simulate axonal excitability.Methods A variety of axonal excitability of the squid giant axon was modeled with LABVIEW,including action potential threshold,refractoriness,temporal summation,anode break excitation,repetitive firing and conduction velocity.Results The LABVIEW program accurately described the permeability changes of Na+ and K+ and their effects on the action potential,and the membrane excitability had been well predicted.Conclusion The graphical programming language of LABVIEW allows the user to complete the programming by dragging and dropping icons and connecting wires,the users can quickly and easily construct their own biological research systems. Key words: Axon; Action potential; Ion channel; LABVIEW; Graphical programming