Two-channel Model Research Articles

Channel-selective non-Fermi liquid behavior in the two-channel Kondo lattice model under a magnetic field

Stimulated by anomalous behaviors found in non-Kramers $f$-electron systems in an applied magnetic field, we study a two-channel Kondo lattice model by using a cluster extension of the dynamical mean-field theory combined with the continuous-time quantum Monte Carlo method. We include the effect of the external magnetic field in two ways: the Zeeman coupling to conduction electron spins and an effective coupling to the quadrupole degree of freedom through the crystalline electric field splitting. We show that the magnetic field suppresses the antiferroic-spin order (physically, corresponding to the antiferroic-quadrupole order), and yields a channel-selective non-Fermi liquid state where one of the two channels (physically, spin-up or -down) exhibits non-Fermi liquid behavior while the other shows Fermi liquid behavior, before entering the Fermi liquid regime in higher fields. This anomalous state appears in a dome-shaped region which extends from inside the antiferroic-spin ordered phase to the paramagnetic phase. We find that the composite correlation, which is a measure of differentiation in the Kondo coupling between the two channels, is enhanced in this dome-shaped region. We also find that the specific heat coefficient is enhanced in this region in the paramagnetic side, indicating heavy fermion behavior not only in the vicinity of the critical field where the antiferroic-spin order vanishes but also in a certain region of the field and temperature. We discuss the results in comparison with the ordinary Kondo lattice model. We also discuss the implication of our findings to the peculiar behavior observed in the 1-2-20 compounds such as $\rm{PrIr_2Zn_{20}}$, $\rm{PrRh_2Zn_{20}}$, and $\rm{PrV_2Al_{20}}$ under a magnetic field.

Joint Motion Information Extraction and Human Behavior Recognition in Video Based on Deep Learning

Video surveillance has played a huge role in the safety and security tasks of various places for many years, and its application range is also expanding. The core problem that needs to be addressed in intelligent video surveillance is the identification and analysis of human behavior in video. In this paper, the structure and joint motion feature extraction of the two-channel deep convolutional neural network model are studied and designed. In the design of the network structure, the ventral and dorsal channels used in the processing of visual signals by the brain visual cortex were simulated. The spatial channel network and the time channel network are used to process static information and dynamic information respectively, and the two types of features are separately extracted. The superiority of the dual-channel structure is verified by comparing the recognition effects of the two-channel model with the single-channel model. Finally, experiments were performed on the KTH behavioral dataset. The results show that the human behavior recognition algorithm based on deep learning can achieve high recognition accuracy based on the good extraction of joint motion information.

Size Effects in the Thermal Conductivity of Amorphous Polymers

Manipulating thermal conductivity through nanoengineering is of critical importance to advance technologies, such as soft robotics, artificial skin, wearable electronics, batteries, thermal insulation, and thermoelectrics. Here, by examining amorphous polymers, including polystyrene, polypropylene, polyethylene, and ethylene vinyl alcohol, using molecular dynamics simulations, we find that the thermal conductivities of amorphous polymers can be reduced below their amorphous limit by size effects. Size-dependent thermal transport in amorphous materials is decomposed into crystalline, crystalline-to-amorphous, and amorphous regimes. In the amorphous regime, the mean free path of propagating heat carriers can range from tens of nanometers to more than 100 nm, contributing 16%--36% of the total thermal conductivity. A two-channel model that combines no size effect (i.e., difusons and locons) and size effect (i.e., propagons) is proposed to account for size-dependent thermal conductivity. We also find that the presence of charged molecules in polymers can significantly affect the thermal conductivity and its size effects due to electrostatic interactions. This work provides insights into the thermal conductivity of amorphous polymers that will have a broad impact on the nano- and chemical engineering of polymers for various energy-related applications.

Joint training of two-channel deep neural network for brain tumor classification

Brain tumor recognition is a challenging task, and accurate diagnosis increases the chance of patient survival. In this article, we propose a two-channel deep neural network architecture for tumor classification that is more generalizable. Initially, local feature representations are extracted from convolution blocks of InceptionResNetV2 and Xception networks and are vectorized using proposed pooling-based techniques. An attention mechanism is proposed that allows more focus on tumor regions and less focus on non-tumor regions which eventually helps to differentiate the type of tumor present in the images. The proposed two-channel model allows joint training of two sets of tumor image representations in an end-to-end manner to achieve good generalization. Empirical studies on Figshare and BraT’S2018, benchmark datasets, reveal that our approach is superior in terms of generalization and simple in terms of number of layers compared to the existing complex models that follow fine-tuning of deep CNN models. Avoiding too much preprocessing and augmentation techniques, the proposed model sets new state-of-the-art scores on both the brain tumor datasets.

Comparison of Frontal-Temporal Channels in Epilepsy Seizure Prediction Based on EEMD-ReliefF and DNN

Epilepsy patients who do not have their seizures controlled with medication or surgery live in constant fear. The psychological burden of uncertainty surrounding the occurrence of random seizures is one of the most stressful and debilitating aspects of the disease. Despite the research progress in this field, there is a need for a non-invasive prediction system that helps disrupt the seizure epileptiform. Electroencephalogram (EEG) signals are non-stationary, nonlinear and vary with each patient and every recording. Full use of the non-invasive electrode channels is impractical for real-time use. We propose two frontal-temporal electrode channels based on ensemble empirical mode decomposition (EEMD) and Relief methods to address these challenges. The EEMD decomposes the segmented data frame in the ictal state into its intrinsic mode functions, and then we apply Relief to select the most relevant oscillatory components. A deep neural network (DNN) model learns these features to perform seizure prediction and early detection of patient-specific EEG recordings. The model yields an average sensitivity and specificity of 86.7% and 89.5%, respectively. The two-channel model shows the ability to capture patterns from brain locations for non-fontal-temporal seizures.

Investigation of attractive interactions in a self-driven unidirectional two-channel model with periodic and open boundaries

The totally asymmetric exclusion process (TASEP) is an outstanding paradigm of self-driven particle models. A new two-channel TASEP model with short-range interactions in horizontal and vertical directions is given. The dynamic properties of the system with periodic boundary and open boundary are investigated by computer simulation and theoretical analysis. The analysis results based on the cluster mean-field method agree very well with the simulations. The flow rate of the system decreases for the strong attractive interaction, and the high-density phase region in the phase diagram extends accordingly.

Wiedemann-Franz law in a non-Fermi liquid and Majorana central charge: Thermoelectric transport in a two-channel Kondo system

Quantum dot devices allow one to access the critical point of the two-channel Kondo model. The effective critical theory involves a free Majorana fermion quasiparticle localized on the dot. As a consequence, this critical point shows both the phenomenon of non-Fermi liquid physics and fractionalization. Although a violation of the Wiedemann-Franz law is considered a defining feature of non-Fermi liquid systems, we show by exact calculations that it holds at the critical point, providing a counterexample to this lore. Furthermore, we show that the fractionalized Majorana character of the critical point can be unambiguously detected from the heat conductivity, opening the door to a direct experimental measurement of the elusive Majorana central charge $c=\tfrac{1}{2}$.

Localization properties of a two-channel 3D Anderson model

We study two coupled 3D lattices, one of them featuring uncorrelated on-site disorder and the other one being fully ordered, and analyze how the interlattice hopping affects the localization–delocalization transition of the former and how the latter responds to it. We find that moderate hopping pushes down the critical disorder strength for the disordered channel throughout the entire spectrum compared to the usual phase diagram for the 3D Anderson model. In that case, the ordered channel begins to feature an effective disorder also leading to the emergence of mobility edges but with higher associated critical disorder values. Both channels become pretty much alike as their hopping strength is further increased, as expected. We also consider the case of two disordered components and show that in the presence of certain correlations among the parameters of both lattices, one obtains a disorder-free channel decoupled from the rest of the system.

Observation of [formula omitted] states in KCs by polarisation labelling spectroscopy technique. Modelling of the D(2)1Π ∼ (2)3Π1 system

A first attempt towards analysis of three strongly interacting electronic states in KCs molecule, D(2)1Π, (2)3Π, and (2)3Σ+, is presented. In this attempt a two-channel model is built for the D(2)1Π ∼ (2)3Π1 system. Our description results in two sets of Dunham-type coefficients and effective coupling terms, which allow to reproduce 2008 experimental values of energy levels for both states with an accuracy 0.029 cm−1 in the range of vibrational levels below v=13 where no influence from the (2)3Σ+ state is observed.

Hall-coefficient diagnostics of the surface state in pressurized SmB6

In this study, we report the first results of the high-pressure Hall coefficient (RH) measurements in the putative topological Kondo insulator SmB6 up to 37 GPa. Below 10 GPa, our data reveal that RH(T) exhibits a prominent peak upon cooling below 20 K. Remarkably, the temperature at which surface conduction dominates coincides with the temperature of the peak in RH(T). The temperature dependent resistance and Hall coefficient can be well fitted by a two-channel model with contributions from the metallic surface and the thermally activated bulk states. When the bulk of SmB6 becomes metallic and magnetic at ~ 10 GPa, both the RH(T) peak and the resistance plateau disappear simultaneously. Our results indicate that the RH(T) peak is a fingerprint to diagnose the presence of a metallic surface state in SmB6. The high-pressure magnetic state of SmB6 is robust to 180 GPa, and no evidence of superconductivity is observed in the metallic phase.

Simulation of IAEA Reactivity Initiated Transient Benchmarks Using Reactor Dynamics Code “REDAC”

Abstract This paper presents the analysis of reactivity initiated transients in an idealized, light water research reactor as a part of International Atomic Energy Agency (IAEA) safety related benchmark. The simulation model is based on point reactor kinetics coupled with one-dimensional (1D), two-channel model for thermal hydraulics. The point kinetics equations (PKEs) have been solved using an implicit Runge–Kutta (RK) method and the coolant transport equations have been solved using implicit finite difference formulation. Accuracy of the implemented models and methods has been demonstrated. Important safety parameters like peak power, peak fuel, and coolant temperatures have been predicted for a series of transients. Intercode comparison shows that the predictions of the present simulations are in good agreement with other codes. This approach provides a time efficient solution for safety analysis of reactors with tightly coupled core where point kinetics can be applied. To address the sensitivity of predictions with respect to important input parameters, simulations have been carried out with different sets of inputs reported in the literature. They indicate that predictions for fast transients are spread over a wider range compared to slow transients. For a given transient, predictions of peak power have a wider spread, while peak temperatures are relatively less sensitive to neutronic inputs. Also, for fast transients, prompt neutron generation time and delayed neutron fraction have dominant influence on the evolution of power. For slow transients, the reactivity feedback effects are equally important.

Role of the confinement-induced effective range in the thermodynamics of a strongly correlated Fermi gas in two dimensions

We theoretically investigate the thermodynamic properties of a strongly correlated two-dimensional Fermi gas with a confinement-induced negative effective range of interactions, which is described by a two-channel model Hamiltonian. By extending the many-body T-matrix approach by Nozi\`eres and Schmitt-Rink to the two-channel model, we calculate the equation of state in the normal phase and present several thermodynamic quantities as functions of temperature, interaction strength, and effective range. We find that there is a non-trivial dependence of thermodynamics on the effective range. In experiment, where the effective range is set by the tight axial confinement, the contribution of the effective range becomes non-negligible as the temperature decreases down to the degenerate temperature. We compare our finite-range results with recent measurements on the density equation of state, and show that the effective range has to be taken into account for the purpose of a quantitative understanding of the experimental data.

An analysis of BCS-BEC crossover under three different approaches and evaluation of critical temperature Tlt;subgt;clt;/subgt;

BCS-BEC crossover regimes can be studied using three approaches (i) from 1D and 2D Hubbard model (ii) from two-channel model for system of ultra-cold alkali atoms (iii) via Feshbach resonance method. It has been observed that in 40K, the appearance of the condensate in BCS regime is accompanied by a significant decrease in the width of the non-condensate fraction. The origin of this phenomenon is yet unknown and requires further study. Another important aspect of the BCS-BEC transition is that one studies the nature of the condensate formed when the system is taken across the resonance. It is not known if the condensate is in the intermediate region of resonance then what will happen whether one will take the linear combination of Cooper pairs and tightly bound molecules or some complex state.

Phase Change and Heat Transfer Characteristics of a Corrugated Plate Heat Exchanger

In order to reveal the evolution law of heat transfer during phase change in a corrugated plate flow passage of a plate heat exchanger, a two-dimensional two-channel model was established to simulate the process of heat transfer during phase change in an unsteady flow passage. The results show that when the time was <3/5T, the average Nusselt number and average heat flux of the heat exchange wall surface decreased with time, the average temperature of the cold fluid outlet increased, the average temperature of the hot fluid outlet decreased, and the volume fraction of the gas phase was no higher than 0.2. When the time was >3/5T, the average Nusselt number and the average heat flux of the heat exchange wall, as well as the outlet average temperature of the cold and hot fluid, reached stability, while the volume fraction of the gas phase increased rapidly. During the whole heat transfer process, the change in Nusselt number and heat flux along the heat transfer wall surface was basically the same, and its value fluctuated along the wall surface, displaying extrema at the exit, entrance, and corrugated corner. The temperature of the heat exchange wall fluctuated and increased along the Y-axis, and began stabilizing after a time >3/5T. As time went on, the temperature gradient of the hot and cold fluid outlet and the temperature difference between the two sides of the heat exchange wall decreased, whereas the relative parameters of the heat flow inlet section of the corrugated passage reached stability before those of the cold flow inlet section. The whole simulation process fully reflects the heat transfer mechanism during phase change in a corrugated plate flow passage of a plate heat exchanger.

Kondo temperature equation for the Fermi liquid and the non-Fermi liquid regime for a two-channel anderson model

Multichannel Kondo resonance causes non-Fermi liquid behavior in many systems, as nanostructured metallic quantum dots and metallic alloys. The Kondo effect occurs at low temperatures and its indicating parameter is the Kondo temperature TK. This parameter can be used to renormalize thermodynamic and transport properties. The Kondo temperature is an important quantity to analyze the antiferromagnetic interaction between a localized spin and itinerant ones in a fermionic bath. There are many different definitions of the Kondo temperature. One of them is that it universalizes magnetic impurity susceptibility. This version was created for the one-channel Anderson model, but it is also valid in two-channel Anderson models, where a single magnetic impurity interacts with the conduction band electrons by two different channels. If the two coupling parameters are different, the model exhibits the well known Fermi liquid regime. When the coupling parameters are equal, the model displays the non-Fermi liquid regime. Each one shows different universal magnetic susceptibility behavior with appropriate TK value. In this article, Numerical Renormalization Group method is applied to study the Kondo temperature systematically. Different values of the coupling parameters in a two-channel Anderson model are examined. Finally, a single analytic expression for the Kondo temperature, valid in the Fermi and non-Fermi liquid regime, is presented.

Width and shift of Fano-Feshbach resonances for van der Waals interactions

We revisit the basic properties of Fano-Feshbach resonances in two-body systems with van der Waals tail interactions, such as ultracold neutral atoms. Using a two-channel model and two different methods, we investigate the relationship between the width and shift of the resonances and their dependence on the low-energy parameters of the system. Unlike what was previously believed [Rev. Mod. Phys. 82, 1225 (2010)] for magnetic resonances, we find that the ratio between the width and the shift of a resonance does not depend only on the background scattering length, but also on a closed-channel scattering length. We obtain different limits corresponding to different cases of optical and magnetic resonances. Although the generalisation of the theory to the multi-channel case remains to be done, we found that our two-channel predictions are verified for a specific resonance of lithium-6.

Electrochemical electron transfer and its relation to charge transport in single molecule junctions

Abstract Ability to control charge transport at nanometer scale lies in the heart of design of fast reliable electronic devices. Molecular electronics thrive to use functional molecules for such transport. If the molecule contains redox center(s), a diode-like or transistor-like behavior can be easily explored by controlling not only the voltage difference between two metallic contacts of the molecular junction but also the potential of one of the contacting electrodes with respect to some reference. Thus, one needs to understand the relationship between electrochemical electron transfer and charge transport in metal–molecule–metal junctions. This review presents latest theoretical approaches toward understanding of such relationship and discusses pivotal experimental works to validate them. Tunneling and hopping pathways may operate in parallel (two-channel model), but experimental conditions dictate the channel preference.

Three-body interaction near a narrow two-body zero crossing

We calculate the effective three-body force for bosons interacting with each other by a two-body potential tuned to a narrow zero crossing in any dimension. We use the standard two-channel model parametrized by the background atom-atom interaction strength, the amplitude of the open-channel to closed-channel coupling, and the atom-dimer interaction strength. The three-body force originates from the atom-dimer interaction, but it can be dramatically enhanced for narrow crossings, i.e., for small atom-dimer conversion amplitudes. This effect can be used to stabilize quasi-two-dimensional dipolar atoms and molecules.

Statistical characteristics of Thomson scattering data

Thomson scattering is used to measure the electron temperature of plasmas. It is essentially a counting experiment. The distribution of detected photons (photoelectrons) in a number of channels yields an estimate of the scattered light spectrum and, thereby, of the plasma electron temperature and density. Repeated measurements at fixed plasma parameters yield a range of values of the measured electron temperature. The spread in these values is typically broader toward high temperatures and the peak (mode) of the temperature density function is lower than the nominal plasma temperature, while the mean is higher. This spread is intrinsic to these measurements, as actual data samples and simulations show. Here a two-channel analytic model of the distribution of temperature readings from non-relativistic, thermal plasmas is used to obtain an intuitive picture of the significance of data from this means of measurement. The model is applied to data from three experiments with electron densities ranging from 5⋅ 1017 m−3 to 7⋅ 1022 m−3, with similar temperatures in widely different profiles of the probability density function. The model is consistent with observed scattered and background light and can, for example, help identify artifacts of diagnostic response, such as apparent high temperatures, and, supplemented by data from additional detector channels, deviations from a thermal electron population, electron drift, and relativistic effects. This is a chance to look in a modern way at some metrological features of this well-established measurement technique.

Unusual lattice thermal conductivity in the simple crystalline compounds TlXTe2(X=Ga,In)

It is generally believed that the lattice thermal conductivity in crystalline solids is mainly carried by phonons, whereas diffusons are regarded as the most important vibrational entity in amorphous solids. Contrary to this belief, here we show that the behavior of lattice thermal conductivity (LTC) of simple crystalline $\mathrm{Tl}X\mathrm{T}{\mathrm{e}}_{2}(X=\mathrm{Ga},\mathrm{In})$ compounds cannot be characterized either by phonons or diffusons alone. The calculated LTC based on first-principles density functional theory and the semiclassical Boltzmann transport equation (BTE) is only half of the experimental value. We show that the relatively weak bonding between Tl atoms and rigid $X\mathrm{T}{\mathrm{e}}_{2}$ chains gives rise to strong vibrational anharmonicity, which suppresses the mean free path of a large portion of phonon modes to even below the Ioffe-Regel limit and thus invalidates the precondition of the semiclassical BTE. We further show that the ultralow LTC of $\mathrm{Tl}X\mathrm{T}{\mathrm{e}}_{2}(X=\mathrm{Ga},\mathrm{In})$ can be rationalized by using the two-channel transport model. This finding would enhance the understanding of the underlying heat transport behavior in such materials.