Flux Coupling Research Articles

Complex dynamics of a neuron model with discontinuous magnetic induction and exposed to external radiation.

The last two decades have seen many literatures on the mathematical and computational analysis of neuronal activities resulting in many mathematical models to describe neuron. Many of those models have described the membrane potential of a neuron in terms of the leakage current and the synaptic inputs. Only recently researchers have proposed a new neuron model based on the electromagnetic induction theorem, which considers inner magnetic fluctuation and external electromagnetic radiation as a significant missing part that can participate in neural activity. While the flux coupling of the membrane is considered equivalent to a memductance function of a memristor, standard memductance model of has been used in the literatures, but in this paper we propose a new memductance function based on discontinuous flux coupling. Various dynamical properties of the neuron model with discontinuous flux coupling are studied and interestingly the proposed model shows hyperchaotic behavior which was not identified in the literatures. Furthermore, we consider a ring network of the proposed model and investigate whether the chimera state can emerge. The chimera state relates to the state with simultaneously coherence and incoherence in oscillatory networks and has received much attention in recent years.

Effect of Si on the partitioning of Mn between cementite and ferrite

ABSTRACTThe interlamellar spacings of pearlitic steels gradually increase as the isothermal transformation temperatures, correspondingly, the tensile strengths decrease, satisfying the Hall–Petch relationship. Si virtually completes its partitioning process during the eutectoid transformation. A depletion of Mn and an accumulation of Si are found in the concentration profiles of 0.95%-Si steel transformed at 793 K in the ferrite, but not in 0.22%-Si steel. It may attribute them to the Si–Mn diffusional flux couplings, which due to the strong interaction between Si and Mn atoms in the α-Fe. Transformation temperature increases to 873 K, a large amount of Mn atoms coming from ferrite cannot timely diffusion to cementite lamella core, forming a localised retention of Mn in the cementite phase side nearby the interface.This is part of a thematic issue on Pearlitic Steel Wires.

RESEARCH OF THE DIRECT TORQUE CONTROL SYSTEM BY INDUCTION MOTOR

The article presents a mathematical description of an induction motor with further modeling in the MATLAB program. In the model, the method of direct torque control (DTC) is implemented. The basic idea of control is that at each step of the calculation the optimum state of the inverter voltage is determined, which causes a change in both the moment and the stator flux coupling in the necessary direction. The obtained transient processes.

Performance of Inductive Coupled Power Transfer Versus the Coil Shape - Investigation using Finite Element Analysis

The objective of this paper is to investigate the impact of the spiral coil shape of inductive coupled power transfer on its performance. The coil shapes evaluated are: circular, square and pentagon spiral shapes. The coils are modelled in Ansoft Maxwell software. Simulations are carried out to determine the mutual inductance, coupling coefficient and magnetic flux density. The performance in term of magnetic flux density, mutual inductance and coupling coefficient of the three coils shapes are compared. Of the three shapes, the pentagon is shown to have the best performance in term of its mutual inductance, coupling coefficient and magnetic flux density.

Collective response, synapse coupling and field coupling in neuronal network

Based on an improved neuron model with electromagnetic induction, the collective responses of chain neuronal network are detected. Besides the gap junction coupling between adjacent neurons, magnetic flux coupling is used to describe the effect of field coupling among all neurons. A statistical factor of synchronization is calculated to find the pattern stability dependence on the coupling intensity of junction coupling and field coupling. Bifurcation analysis and wave propagation are presented. It is found that signal propagation can be suppressed by field coupling on the network driven by external stimulus with diversity. Otherwise, network synchronization can be enhanced when external current stimulus are imposed on neurons of the network uniformly.

Investigation on the dynamic behaviors of the coupled memcapacitor-based circuits**Project supported by the Fundamental Research Funds for China Central Universities (Grant No. 2015XKMS028).

In this paper, by referring to the concept of coupled memristors (MRs) and considering the flux coupling connection, the constitutive relations for describing the coupled memcapacitors (MCs) are theoretically deduced. The dynamic behaviors of dual coupled MCs in serial and parallel connections are analyzed in terms of identical or opposite polarities for the first time. Based on the derived constitutive relations of the two coupled MCs, the modified relaxation oscillators (ROs) are obtained with the purpose of achieving controllable oscillation frequency and duty cycle. In consideration of different parameter configurations, the experimental investigation is carried out by using practical off-the-shelf circuit components to verify the correction of the theoretical calculation with numerical simulation of the coupled MCs and its application in ROs.

Low voltage ride-through capability improvement of photovoltaic systems using a novel hybrid control

This paper proposes an advanced hybrid control method to enhance low voltage ride-through (LVRT) capability of grid connected photovoltaic (PV) power plants. Using the proposed method, when a low voltage fault occurs at the point of common coupling, the grid connected inverter overcurrent and its DC-link overvoltage can be effectively suppressed by tuning the PV array output power and triggering the flux coupling fault current limiters (FCLs). The AC-side voltage sag of the inverter can be significantly mitigated by generating reactive power from the inverter and injecting this into the FCLs. Employing the proposed method can also reduce the regulating quantity of output power from the grid inverter and effectively improve PV system dynamic recovery. DC-link voltage fluctuations can also be significantly smoothed by the application of feed forward compensation and the FCLs. Related theoretical derivation and simulation analysis under various scenarios, including asymmetric faults, confirm that the proposed control method can not only enhance the LVRT capability but also strengthen the transient performance of PV systems.

A review of water and carbon flux partitioning and coupling in SPAC using stable isotope techniques

Soil-vegetation-atmosphere continuum (SPAC) is one of the important research objects in the field of terrestrial hydrology, ecology and global change. The process of water and carbon cycling, and their coupling mechanism are frontier issues. With characteristics of tracing, integration and indication, stable isotope techniques contribute to the estimation of the relationship between carbon sequestration and water consumption in ecosystems. In this review, based on a brief introduction of stable isotope principles and techniques, the applications of stable isotope techniques to water and carbon exchange in SPAC using optical stable isotope techniques were mainly explained, including: partitioning of net carbon exchange into photosynthesis and respiration; partitioning of evapotranspiration into transpiration and evaporation; coupling of water and carbon cycle at the ecosystem scale. Advanced techniques and methods provided long-term and high frequency measurements for isotope signals at the ecosystem scale, but the issues about the precision and accuracy for measurements, partitioning of ecosystem respiration, adaptability for models under non-steady state, scaling up, coupling mechanism of water and carbon cycles, were challenging. The main existing research findings, limitations and future research prospects were discussed, which might help new research and technology development in the field of stable isotope ecology.

Locations Where Space Weather Energy Impacts the Atmosphere

In this review we consider aspects of space weather that can have a severe impact on the terrestrial atmosphere. We begin by identifying the pre-conditioning role of the Sun on the temperature and density of the upper atmosphere. This effect we define as “space climatology”. Space weather effects are then defined as severe departures from this state of the atmospheric energy and density. Three specific forms of space weather are reviewed and we show that each generates severe space weather impacts. The three forms of space weather being considered are the solar photon flux (flares), particle precipitation (aurora), and electromagnetic Joule heating (magnetosphere–ionospheric (M-I) coupling). We provide an overview of the physical processes associated with each of these space weather forms. In each case a very specific altitude range exists over which the processes can most effectively impact the atmosphere. Our argument is that a severe change in the local atmosphere’s state leads to atmospheric heating and other dynamic changes at locations beyond the input heat source region. All three space weather forms have their greatest atmospheric impact between 100 and 130 km. This altitude region comprises the transition between the atmosphere’s mesosphere and thermosphere and is the ionosphere’s E-region. This region is commonly referred to as the Space Atmosphere Interaction Region (SAIR). The SAIR also acts to insulate the lower atmosphere from the space weather impact of energy deposition. A similar space weather zone would be present in atmospheres of other planets and exoplanets.

RF inductors with sputtered nanomagnetic films on glass substrates

Inductors utilize spiral or helical designs to enhance magnetic flux and inductance. Spiral inductors require large footprint while solenoid inductors require thick substrates to achieve adequate flux coupling. As such, both these designs impose trade offs in inductance density, Q, and frequency stability. Nanomagnetic films with stable and high permeability can enhance inductance density and correspondingly the Q factor. However, nanomagnetic films suffer from two disadvantages. They have high losses beyond 1.0 GHz. They are also sputter-deposited as thin films that are less than five microns. Therefore, the benefits of nanomagnetic films in RF inductors are not clear. Performance improvements and trade-offs in RF inductors with nanomagnetic films are analyzed through material and component-level modeling. In the first part of the paper, nanomagnetic films and properties are modeled. The inductance density and Q trade-offs with nanomagnetic films are simulated after imposing their constraints: frequency dependence and thickness of five microns. Both helical and spiral inductors are considered with and without the nanomagnetic films. The simulations show enhancement in inductance by 5× with mild degradation in Q for spiral inductors. However, the Q degraded more with solenoid inductors. Higher resistivity and ferromagnetic resonance frequency are critical to improve the performance of nanomagnetic film inductors.

Electron transport through a linear tri-quantum-dot molecule Aharonov-Bohm interference

Using the non-equilibrium Keldysh Green's function technique, electron transport properties through a two-terminal linear tri-quantum-dot molecule Aharonov-Bohm (A-B) interference are investigated. The conductance as a function of electron energy is numerically calculated. The influence of magnetic flux and interdot coupling strength on the conductance is researched. Fano resonances emerge in the conductance spectrum, and two bound states in the continuum form simultaneously when the interdot couplings take appropriate values. A conductance dip is observed and evolves into an antiresonance band with increasing magnetic flux. The system can be designed as a quantum switch by adjusting the intramolecular couplings.

Clostridium butyricum maximizes growth while minimizing enzyme usage and ATP production: metabolic flux distribution of a strain cultured in glycerol

BackgroundThe increase in glycerol obtained as a byproduct of biodiesel has encouraged the production of new industrial products, such as 1,3-propanediol (PDO), using biotechnological transformation via bacteria like Clostridium butyricum. However, despite the increasing role of Clostridium butyricum as a bio-production platform, its metabolism remains poorly modeled.ResultsWe reconstructed iCbu641, the first genome-scale metabolic (GSM) model of a PDO producer Clostridium strain, which included 641 genes, 365 enzymes, 891 reactions, and 701 metabolites. We found an enzyme expression prediction of nearly 84% after comparison of proteomic data with flux distribution estimation using flux balance analysis (FBA). The remaining 16% corresponded to enzymes directionally coupled to growth, according to flux coupling findings (FCF). The fermentation data validation also revealed different phenotype states that depended on culture media conditions; for example, Clostridium maximizes its biomass yield per enzyme usage under glycerol limitation. By contrast, under glycerol excess conditions, Clostridium grows sub-optimally, maximizing biomass yield while minimizing both enzyme usage and ATP production. We further evaluated perturbations in the GSM model through enzyme deletions and variations in biomass composition. The GSM predictions showed no significant increase in PDO production, suggesting a robustness to perturbations in the GSM model. We used the experimental results to predict that co-fermentation was a better alternative than iCbu641 perturbations for improving PDO yields.ConclusionsThe agreement between the predicted and experimental values allows the use of the GSM model constructed for the PDO-producing Clostridium strain to propose new scenarios for PDO production, such as dynamic simulations, thereby reducing the time and costs associated with experimentation.

Feedback solutions for low crosstalk in dense arrays of high-Tc SQUIDs for on-scalp MEG

Magnetoencephalography (MEG) systems based on a dense array of high critical temperature (high-Tc) superconducting quantum interference devices (SQUIDs) can theoretically outperform a state-of-the-art MEG system. On the way towards building such a multichannel system, we evaluate feedback methods suitable for use in dense high-Tc SQUID arrays where the sensors are in very close proximity to the head (on-scalp MEG). We test on-chip superconducting coils and direct injection of the feedback current into the SQUID loop as alternatives to the wire-wound copper coils commonly used in single-channel high-Tc SQUID-based MEG systems. For the evaluation, we have performed coupling, noise, and crosstalk measurements. We conclude that direct injection is the optimal solution for dense on-scalp MEG as it gives crosstalk below 0.5% even between SQUIDs whose pickup loops are within 0.8 mm of one another. Further, this solution provides sufficient flux coupling without adding additional noise. Finally, it does not compromise the standoff distance, which is important for on-scalp MEG.

Phase synchronization between two neurons induced by coupling of electromagnetic field

Based on an improved neuron model with electromagnetic induction being considered, the phase synchronization approaching is investigated on a four-variable Hindmarsh–Rose neuron model by describing the electromagnetic induction with magnetic flux. The effect of time-varying electromagnetic field is described by magnetic flux and the coupling of electromagnetic field is also described by exchange of magnetic flux. It is found that magnetic flux coupling between neurons can induce perfect phase synchronization, the Lyapunov exponent spectrum and local Lyapunov dimension are calculated by using wolf scheme to detect phase synchronization of chaotic time series for membrane potentials. These results confirmed that neurons exposed to external electromagnetic field can induce phase synchronization and appropriate behaviors can be selected. It could give new mechanism explanation for phase synchronization by applying field coupling between neurons.

Transport properties of C and O in UN fuels

Uranium nitride fuel is considered for fast reactors (GEN-IV generation and space reactors) and for light water reactors as a high-density fuel option. Despite this large interest, there is a lack of information about its behavior for in-pile and out-of-pile conditions. From the present literature, it is known that C and O impurities have significant influence on the fuel performance. Here we perform a systematic study of these impurities in the UN matrix using electronic-structure calculations of solute-defect interactions and microscopic jump frequencies. These quantities were calculated in the $\mathrm{DFT}+U$ approximation combined with the occupation matrix control scheme, to avoid convergence to metastable states for the $5f$ levels. The transport coefficients of the system were evaluated with the self-consistent mean-field theory. It is demonstrated that carbon and oxygen impurities have different diffusion properties in the UN matrix, with O atoms having a higher mobility, and C atoms showing a strong flux coupling anisotropy. The kinetic interplay between solutes and vacancies is expected to be the main cause for surface segregation, as incorporation energies show no strong thermodynamic segregation preference for (001) surfaces compared with the bulk.

Magnetic flux and strain effects on electron transport in a linear array of nanoscopic rings

Electron transport through a linear array of nanoscopic rings with six quantum dot sites per ring is investigated in the presence of an external magnetic flux producing an Aharonov-Bohm phase shift effect. A tight-binding model is employed to analytically calculate the transmission as a function of electron energy, external flux, and inter-site coupling parameters. Current vs. voltage relationships of the ring system are computed using a standard scattering theory of transport and shown to modulate between semiconductor and ohmic characteristics. System parameters are adjusted in order to study the effects of a longitudinal strain on the transmission properties of the linear multiple-ring array. Longitudinal strain is modeled with a Slater-Koster type theory and is demonstrated to affect the transmission properties primarily by narrowing the transmission bands and opening up additional bandgaps in the band structure. In addition, a universal resonant transmission condition as a function of flux is extended to show that the application of strain causes the resonant transmission peaks to converge towards one-half of a flux quantum.

On the numerical stability of surface–atmosphere coupling in weather and climate models

Abstract. Coupling the atmosphere with the underlying surface presents numerical stability challenges in cost-effective model integrations used for operational weather prediction or climate simulations. These are due to the choice of large integration time steps compared to the physical timescale of the problem, aiming at reducing computational burden, and to an explicit flux coupling formulation, often preferred for its simplicity and modularity. Atmospheric models therefore use the surface-layer temperatures (representative of the uppermost soil, snow, ice, water, etc.) at the previous integration time step in all surface–atmosphere heat-flux calculations and prescribe fluxes to be used in the surface model integrations. Although both models may use implicit formulations for the time steps, the explicit flux coupling can still lead to instabilities.In this study, idealized simulations with a fully coupled implicit system are performed to derive an empirical relation between surface heat flux and surface temperature at the new time level. Such a relation mimics the fully implicit formulation by allowing one to estimate the surface temperature at the new time level without solving the surface heat diffusion problem. It is based on similarity reasoning and applies to any medium with constant heat diffusion and heat capacity parameters. The advantage is that modularity of the code is maintained and that the heat flux can be computed in the atmospheric model in such a way that instabilities in the snow or ice code are avoided. Applicability to snow–ice–soil models with variable density is discussed, and the loss of accuracy turns out to be small. A formal stability analysis confirms that the parametrized implicit-flux coupling is unconditionally stable.

Realization of minute-long steady-state H-mode discharges on EAST

In the 2016 EAST experimental campaign, a steady-state long-pulse H-mode discharge with an ITER-like tungsten divertor lasting longer than one minute has been obtained using only RF heating and current drive, through an integrated control of the wall conditioning, plasma configuration, divertor heat flux, particle exhaust, impurity management, and effective coupling of multiple RF heating and current drive sources at high injected power. The plasma current (Ip ∼ 0.45 MA) was fully-noninductively driven (Vloop < 0.0 V) by a combination of ∼2.5 MW LHW, ∼0.4 MW ECH and ∼0.8 MW ICRF. This result demonstrates the progress of physics and technology studies on EAST, and will benefit the physics basis for steady state operation of ITER and CFETR.

Discovering missing reactions of metabolic networks by using gene co-expression data

Flux coupling analysis is a computational method which is able to explain co-expression of metabolic genes by analyzing the topological structure of a metabolic network. It has been suggested that if genes in two seemingly fully-coupled reactions are not highly co-expressed, then these two reactions are not fully coupled in reality, and hence, there is a gap or missing reaction in the network. Here, we present GAUGE as a novel approach for gap filling of metabolic networks, which is a two-step algorithm based on a mixed integer linear programming formulation. In GAUGE, the discrepancies between experimental co-expression data and predicted flux coupling relations is minimized by adding a minimum number of reactions to the network. We show that GAUGE is able to predict missing reactions of E. coli metabolism that are not detectable by other popular gap filling approaches. We propose that our algorithm may be used as a complementary strategy for the gap filling problem of metabolic networks. Since GAUGE relies only on gene expression data, it can be potentially useful for exploring missing reactions in the metabolism of non-model organisms, which are often poorly characterized, cannot grow in the laboratory, and lack genetic tools for generating knockouts.

Cotransport of water and solutes in plant membranes: The molecular basis, and physiological functions

Current concepts of plant membrane transport are based on the assumption that water and solutes move across membranes via separate pathways. According to this view, coupling between the fluxes is more or less exclusively constituted via the osmotic force that solutes exert on water transport. This view is questioned here, and experimental evidence for a cotransport of water and solutes is reviewed. The overview starts with ion channels that provide pathways for both ion and water transport, as exemplified for maxi K + channels from cytoplasmic droplets of Chara corallina . Aquaporins are usually considered to be selective for water (just allowing for slippage of some other small, neutral molecules). Recently, however, a “dual function” aquaporin has been characterized from Arabidopsis thaliana (AtPIP2.1) that translocates water and at the same time conducts cations, preferentially Na + . By analogy with mammalian physiology, other candidates for solute-water flux coupling are cation-chloride cotransporters of the CCC type, and transporters of sugars and amino acids. The last part is dedicated to possible physiological functions that could rely on solute-water cotransport. Among these are the generation of root pressure, refilling of embolized xylem vessels, fast turgor-driven movements of leaves, cell elongation (growth), osmoregulation and adjustment of buoyancy in marine algae. This review will hopefully initiate further research in the field.