Coherent Component Research Articles

Quantum Coherence and Ergotropy.

Constraints on work extraction are fundamental to our operational understanding of the thermodynamics of both classical and quantum systems. In the quantum setting, finite-time control operations typically generate coherence in the instantaneous energy eigenbasis of the dynamical system. Thermodynamic cycles can, in principle, be designed to extract work from this nonequilibrium resource. Here, we isolate and study the quantum coherent component to the work yield in such protocols. Specifically, we identify a coherent contribution to the ergotropy (the maximum amount of unitarily extractable work via cyclical variation of Hamiltonian parameters). We show this by dividing the optimal transformation into an incoherent operation and a coherence extraction cycle. We obtain bounds for both the coherent and incoherent parts of the extractable work and discuss their saturation in specific settings. Our results are illustrated with several examples, including finite-dimensional systems and bosonic Gaussian states that describe recent experiments on quantum heat engines with a quantized load.

Coherent Stokes and anti-Stokes high-order components generation by biharmonic pumping via stimulated low-frequency Raman scattering.

In this Letter, we report on experimental effective coherent multiple Stokes and anti-Stokes high-order components generation by Stokes pulse injection at the process of stimulated low-frequency Raman scattering. This process can be used for effective generation the tunable spectral comb consisting of several equidistant spectral lines separated by a constant frequency spacing of several GHz.

Quench dynamics of a weakly interacting disordered Bose gas in momentum space

We theoretically study the out-of-equilibrium dynamics in momentum space of a weakly interacting disordered Bose gas launched with a finite velocity. In the absence of interactions, coherent multiple scattering gives rise to a background of diffusive particles, on top of which a coherent backscattering interference emerges. We revisit this scenario in the presence of interactions, using a diagrammatic quantum transport theory. We find that the dynamics is governed by coupled kinetic equations describing the thermalization of the diffusive and coherent components of the gas. This phenomenon leads to a destruction of coherent backscattering, well described by an exponential relaxation whose rate is controlled by the particle collision time. These predictions are confirmed by numerical simulations.

An algorithm and codes for fast computations of the opposition effects in a semi-infinite discrete random medium

We present an algorithm and FORTRAN codes to compute the opposition effects in the reflection of light from a semi-infinite discrete random medium at normal incidence to the boundary of the medium. It is assumed that the medium is sparse enough that the waves propagating between the scatterers are spherical. In this case, the reflection matrix is determined only by contributions of the incoherent (diffuse) and coherent components. When calculating the coherent component, the contribution of the doubly scattered radiation to the reflection matrix is rigorously taken into account, while the contributions of the higher orders are calculated approximately. To be more specific, the multiply scattered radiation coming to some point of the medium “from above” is calculated exactly, but the radiation coming “from below”, approximately. Under this supposition, the solution of the system of integral equations is reduced to that of the system of linear algebraic equations. The matrix of this system is calculated with the recurrent relation, which radically speeds up the computations as compared to the direct procedure. This allows the opposition effect characteristics to be computed rapidly enough so that the codes may be used in interpretation of the remotely measured intensity and polarization of light reflected by different media to estimate, at least at a qualitative level, their properties.

Efficient Clustering of Non-coherent and Coherent Components Regardless of Sources’ Powers for 2D DOA Estimation

Conventional decorrelation techniques that resolve all signals simultaneously are not efficient in mixture scenarios of non-coherent and coherent signals. In newer methods for one-dimensional arrays, non-coherent signals and coherent groups are resolved separately. However, employing an unreliable and non-adaptive threshold is the most significant disadvantage of these methods. On the other hand, they cannot be implemented for two-dimensional arrays. To deal with these issues, the signals separation using k-medoids clustering (SSKMC) algorithm was presented. Although the SSKMC algorithm does not have any of the shortcomings mentioned above, it relies on a basic limiting assumption that the sources should be equi-power. Therefore, the practical application of the SSKMC algorithm is facing a serious problem. In this paper, the SSKMC algorithm is extended so that it can be used even if the sources’ powers are not the same. First, the two-dimensional array is divided into several parallel linear sub-arrays. Then, by defining a components separation matrix, and employing its eigenvalues, the non-coherent and coherent components are identified. The effectiveness of the proposed solution is proven by mathematical facts. Simulation results verify the proofs and the benefit of the proposed solution.

Statistics of the antenna arrays field with heterogeneous errors (Average antenna characteristics)

A methodology for studying the directional properties of antenna arrays with heterogeneous (in dispersion) errors in the excitation and placement of radiators is described. Mechanisms of origin and the mathematical model of heterogeneous errors are determined. Features and differences in statistical effects inherent in the average antenna characteristics of heterogeneous and uniform errors are revealed. General properties of the average power radiation pattern (RP), represented as an expansion into coherent and scattered components, for arbitrary antenna arrays, error values, and their distribution law are investigated. The coherent component does not depend on the correlation properties of errors and is formed by a statistical amplitude-phase distribution (APD), the differences of which from a regular APD depend on the degree of error heterogeneity. The degree of error correlation affects the directional properties of the dissipated power. For completely correlated errors, the average RP does not coincide with the RP in the absence of errors. Numerical results are given for linear antenna arrays and three types of heterogeneous phase errors with increasing/decreasing dispersion towards the edges of the antenna and its two-level value. A criterion for the equivalence of heterogeneous phase errors by the intensity of their impact on the radiated fields is selected. The analysis of the average RP, the limiting average level of lateral radiation was carried out using a generalized angular variable, which allowed us to extend the results to antenna arrays with transverse, inclined, and axial radiation with different electric sizes and steps, as well as compare them with continuous radiated systems and determine the areas where the results coincide. The question of the average directive gain (DG) is studied. For antenna arrays with axial radiation, the optimal relations are determined to achieve its maximum value, taking into account the type of heterogeneous phase errors, their correlation properties, and the antenna arrays spacing. It is shown that it is advisable to take into account the properties of error heterogeneity in the statistical analysis of the antenna field, since the nature of their influence on the directional and energy parameters of the array and its sensitivity depends significantly on their type and amplitude distribution. The types of phase errors causing increased distortion of the average characteristics are determined. The obtained theoretical data generalize the results of the theory of antenna arrays with uniform errors and supplement them with new ideas about the characteristics of random fields and ways of practical use of research results.

The Influence of Defects of Second Type by Krivoglaz to Coherent Component of X-Rays Scattering in Monocrystalline Materials of Nanoindustry

The Influence of Defects of Second Type by Krivoglaz to Coherent Component of X-Rays Scattering in Monocrystalline Materials of Nanoindustry

Long memory effects in excitonic systems dynamics: Spectral relations and excitation transport.

The main quantity that controls excitation relaxation and transport in molecular systems is the environment-induced fluctuation correlation function. Commonly used models assume the exponentially decaying correlation function, characterized by a given characteristic time, which allows us to define the Markovian conditions and, hence, allows us to use rate equations for excitation dynamics. A long memory fractional correlation function is studied in this paper as an alternative model. Such a function has an infinite characteristic decay time, and thus, system decay to equilibrium becomes poorly defined. Consequently, it becomes impossible to define the Markovian regime. By assuming the weak system-bath coupling regime, we apply the non-Markovian equations of motion to describe the equilibration process in an excitonic molecular aggregate. The long memory model causes a weaker decay of coherent components in excitonic system relaxation dynamics. Nevertheless, the short time dynamics, which is important in optical spectroscopy, depends on the short time interval of the fluctuation correlation function. Excitation relaxation in this window appears to be well described by non-Markovian approaches.

ON COHERENT AND INCOHERENT SCATTERING OF FAST CHARGED PARTICLES IN ULTRATHIN CRYSTALS

We consider the fast charged particles scattering in ultrathin crystals on the base of the Born approximation of quantum electrodynamics. The main attention is paid to the question of the scattering cross section splitting into coherent and incoherent components when one of the crystallographic axes and planes is oriented along the direction of particle motion. It is shown that both the coherent and the incoherent components of the scattering cross section considerably depend on the orientation of the crystallographic axes relatively to the incident beam. In particular, it was shown that when particles are scattered by the crystal planes of atoms, the incoherent scattering cross section does not contain the Debye-Waller factor.

PaintNet: A shape-constrained generative framework for generating clothing from fashion model

Recent years have witnessed the proliferation of online fashion blogs and communities, where a large amount of fashion model images with chic clothes in various scenarios are publicly available. To facilitate users to find the corresponding clothes, we focus on studying how to generate pure wellshaped clothing items with the best view from the complex model images. Towards this end, inspired by painting, where the initial sketches and following coloring are both essential, we propose a two-stage shape-constrained clothing generative framework, dubbed as PaintNet. PaintNet comprises two coherent components: shape predictor and texture renderer. The shape predictor is devised to predict the intermediate shape map for the to-be-generated clothing item based on the latent representation learning, while the texture renderer is introduced to generate the final clothing image with the guidance of the predicted shape map. Extensive qualitative and quantitative experiments conducted on the public Lookbook dataset verify the effectiveness of PaintNet in clothing generation from fashion model images. Moreover, we also explore the potential of PaintNet in the task of cross-domain clothing retrieval, and the experiment results show that PaintNet can achieve, on average, 5.34% performance improvement over the traditional non-generative retrieval methods.

Untangling the Incoherent and Coherent Scattering Components in GNSS-R and Novel Applications

As opposed to monostatic radars where incoherent backscattering dominates, in bistatic radars, such as Global Navigation Satellite Systems Reflectometry (GNSS-R), the forward scattered signals exhibit both an incoherent and a coherent component. Current models assume that either one or the other are dominant, and the calibration and geophysical parameter retrieval (e.g., wind speed, soil moisture, etc.) are developed accordingly. Even the presence of the coherent component of a GNSS reflected signal itself has been a matter of discussion in the last years. In this work, a method developed to separate the leakage of the direct signal in the reflected one is applied to a data set of GNSS-R signals collected over the ocean by the Microwave Interferometer Reflectometer (MIR) instrument, an airborne dual-band (L1/E1 and L5/E5a), multi-constellation (GPS and Galileo) GNSS-R instrument with two 19-elements antenna arrays with 4 beam-steered each. The presented results demonstrate the feasibility of the proposed technique to untangle the coherent and incoherent components from the total power waveform in GNSS reflected signals. This technique allows the processing of these components separately, which increases the calibration accuracy (as today both are mixed and processed together), allowing higher resolution applications since the spatial resolution of the coherent component is determined by the size of the first Fresnel zone (300–500 meters from a LEO satellite), and not by the size of the glistening zone (25 km from a LEO satellite). The identification of the coherent component enhances also the location of the specular reflection point by determining the peak maximum from this coherent component rather than the point of maximum derivative of the incoherent one, which is normally noisy and it is blurred by all the glistening zone contributions.

Latitudinal Structure of the Meridional Overturning Circulation Variability on Interannual to Decadal Time Scales in the North Atlantic Ocean

AbstractThe latitudinal structure of the Atlantic meridional overturning circulation (AMOC) variability in the North Atlantic is investigated using numerical results from three ocean circulation simulations over the past four to five decades. We show that AMOC variability south of the Labrador Sea (53°N) to 25°N can be decomposed into a latitudinally coherent component and a gyre-opposing component. The latitudinally coherent component contains both decadal and interannual variabilities. The coherent decadal AMOC variability originates in the subpolar region and is reflected by the zonal density gradient in that basin. It is further shown to be linked to persistent North Atlantic Oscillation (NAO) conditions in all three models. The interannual AMOC variability contained in the latitudinally coherent component is shown to be driven by westerlies in the transition region between the subpolar and the subtropical gyre (40°–50°N), through significant responses in Ekman transport. Finally, the gyre-opposing component principally varies on interannual time scales and responds to local wind variability related to the annual NAO. The contribution of these components to the total AMOC variability is latitude-dependent: 1) in the subpolar region, all models show that the latitudinally coherent component dominates AMOC variability on interannual to decadal time scales, with little contribution from the gyre-opposing component, and 2) in the subtropical region, the gyre-opposing component explains a majority of the interannual AMOC variability in two models, while in the other model, the contributions from the coherent and the gyre-opposing components are comparable. These results provide a quantitative decomposition of AMOC variability across latitudes and shed light on the linkage between different AMOC variability components and atmospheric forcing mechanisms.

The Energetic Cost of Work Extraction.

We analyze work extraction from a qubit into a waveguide (WG) acting as a battery, where work is the coherent component of the energy radiated by the qubit. The process is stimulated by a wave packet whose mean photon number (the battery's charge) can be adjusted. We show that the extracted work is bounded by the qubit's ergotropy, and that the bound is saturated for a large enough battery's charge. If this charge is small, work can still be extracted. Its amount is controlled by the quantum coherence initially injected in the qubit's state, that appears as a key parameter when energetic resources are limited. This new and autonomous scenario for the study of quantum batteries can be implemented with state-of-the-art artificial qubits coupled to WGs.

Inverse methods in aeroacoustic three-dimensional volumetric noise source localization and quantification

Acoustic source mapping usually involves planar microphone arrays and calculation points located on a surface at a certain distance with respect to the array. An implicit assumption that sources are located on this surface is therefore performed. However, in some application, such as aeroacoustic source identification, this assumption may be wrong and produce misleading results. For this reason, it is interesting to extend the common acoustic mapping techniques to three-dimensional volumetric mapping. Direct beamforming techniques are not suited for volumetric imaging due to poor spatial resolution in radial direction from the array centre. Therefore, more refined algorithms, like deconvolution techniques or inverse methods, are required to obtain intelligible and accurate results.This paper describes the use of inverse methods in the context of aeroacoustic three-dimensional volumetric noise imaging. An Equivalent Source Method is formulated, based on Iteratively Reweighted Least Squares and on Bayesian Regularization. Moreover, a novel approach based on CLEAN-SC as decomposition tool of Cross-Spectral-Matrix in coherent source components is presented.The method proposed is applied on an aircraft model in wind tunnel. Performance are preliminary assessed with simulated test cases. A comparative investigation in exploiting a single planar array or multiple planar arrays observing noise sources from different directions is performed.

Characteristics of temperature dissipation rate in a turbulent near wake

This work aims to provide in-depth understanding of the effects the quasi-periodical Kármán vortices produce on the temperature dissipation rate in a turbulent cylinder near wake. Measurements are made at x/d = 10, 20 and 40, where x is the streamwise distance from the cylinder axis and d is the cylinder diameter, with a Reynolds number of 2.5 × 103 based on d and the free-stream velocity. A multi-wire probe is deployed to measure simultaneously the fluctuating temperature and its gradient vector, at nominally the same spatial point in the plane of the mean shear. It is found that the coherent streamwise and spanwise temperature derivatives are similarly distributed with respect to the spanwise vortex, exhibiting twin peaks at the temperature fronts, while the coherent lateral component is linked to the rib-like structures. The temperature variance dissipation rate is found to be statistically independent of the temperature fluctuation when the Kármán vortex is so weak (say at x/d = 40) that the large-scale temperature front resulting from the vortex entrainment ceases to be present and the coherent strain rate at the saddle region is relatively small. In addition, the most effective turbulent mixing is found to take place around the temperature front near the wake centerline, which is in contrast to the conjecture by Hussain and Hayakawa (1987).

Dissimilarity between turbulent heat and momentum transfer induced by a streamwise travelling wave of wall blowing and suction

A series of direct numerical simulations of a fully developed turbulent channel flow is conducted in order to clarify the effects of travelling wave-like wall blowing and suction on dissimilar heat transfer enhancement. While the wave form is kept sinusoidal and its amplitude is set to be 5 % of the bulk mean velocity, the wavelength and phase speed of the travelling wave are systematically changed in a wide parameter space. As a result, the global optimum of the parameter set for maximizing the analogy factor, which is defined as the ratio between the Stanton number and the skin-friction coefficient, is identified. Interestingly, the obtained globally optimal mode agrees well with that predicted from the optimal control theory taking into account the future dynamics within a limited time horizon by Yamamoto et al. (J. Fluid Mech., vol. 733, 2013, pp. 189–220). The instantaneous velocity and thermal fields are decomposed into coherent and random components in order to evaluate the contribution from each component to dissimilar heat transfer enhancement. The detailed mechanisms of dissimilarity are explained by the budget analyses of the coherent and random contributions. Also, their relationships with the near-wall turbulent structures modified by the applied control are discussed through flow visualization. It is found that the random component makes a dominant contribution to dissimilarity, and this can be explained by an indirect effect through the modification of the coherent field by the applied control. Based on the above mechanisms, we propose a simple unsteady Reynolds-averaged Navier–Stokes (URANS) approach, where the phase-averaged velocity and thermal fields are solved directly whereas the effects of the random component are modelled by the Boussinesq eddy viscosity and diffusivity hypothesis. It is shown that the present URANS can capture the overall trend of dissimilar heat transfer enhancement in a wide parameter range. The present results also explain why the optimal control theory with a limited time horizon succeeds in predicting the globally optimal control mode.

Spatial Resolution in GNSS-R Under Coherent Scattering

Global Navigation Satellite Systems Reflectometry can be understood as a multistatic radar using satellite navigation signals as signals of opportunity. The scattered signals over sea ice, flooded areas, even under dense vegetation, and in some cases, over land show a significant coherent component. Under coherent scattering conditions, it is usually stated that the coherent signal component comes from an area equal to the first Fresnel zone. This letter analyzes in more detail the spatial resolution in this forward scattering configuration, showing that, when coherent scattering is nonnegligible, the spatial resolution is mostly determined by the geometry and not by typical surface roughness values. As the scattering area around the specular reflection point increases and encompasses the first Fresnel zone, the received power increases and then it fluctuates as higher order Fresnel zones are included (rapid phase changes due to the spherical waves). These contributions may explain in part the large scattering encountered over inhomogeneous land regions, as these different contributions add or subtract, depending on the phase of the electric field, and are weighted by different scattering coefficients (i.e., changes in the dielectric constant and/or surface roughness, such in water ponds or some agricultural fields). Finally, over homogeneous targets, when all Fresnel zones are included, the received power tends asymptotically to the value obtained using the free-space propagation with a total path length equal to the sum of the path lengths, weighted by the reflection coefficient. This value can also be interpreted as coming from an effective region that is actually ~0.6 times the first Fresnel zone.

Dynamical effects in the integrated X-ray scattering intensity from imperfect crystals in Bragg diffraction geometry. I. Semi-dynamical model.

The analytical expressions for the coherent and diffuse components of the integrated reflection coefficient are considered in the case of asymmetric Bragg diffraction geometry for a single crystal of arbitrary thickness, which contains randomly distributed Coulomb-type defects. The possibility to choose the combinations of diffraction conditions optimal for characterizing defects of several types by accounting for dynamical effects in the integrated coherent and diffuse scattering intensities, i.e. primary extinction and anomalous absorption, has been analysed based on the statistical dynamical theory of X-ray diffraction by imperfect crystals. The measured integrated reflectivity dependencies of the imperfect silicon crystal on azimuthal angle were fitted to determine the diffraction parameters characterizing defects in the sample using the proposed formulas in semi-dynamical and semi-kinematical approaches.

Diagonal Denoising for Conventional Beamforming via Sparsity Optimization

Conventional beamforming (CBF) is widely used in underwater acoustic applications due to its simplicity and robustness. Under certain circumstances, incoherent noise is the main disturbance for hydrophone arrays and can lead to a serious decline in the signal power estimation accuracy and signal detection ability of CBF. Since incoherent noise contamination is concentrated along the diagonal of the covariance matrix, we propose to improve the performance of CBF by reducing the diagonal as much as possible to suppress the incoherent noise until the output spatial spectrum becomes sparsest. Mathematically, the denoising problem is convex; hence, it can be solved with guaranteed efficiency and convergence properties. The proposed denoising algorithm is named the sparsity-optimization-based diagonal denoising (SO-DD) algorithm, and its capability is investigated and compared with the recently developed positive-semidefinite-constrained diagonal denoising (PSC-DD) algorithmvia simulation and experiments. The results suggest that both SO-DD and PSC-DD work well under ideal conditions where noise is perfectly incoherent, while SO-DD performs more reliably when noise is partially coherent due to limited sampling and the existence of coherent noise component in practice.

Estimation of direct sound by temporal and spatial extraction of interchannel coherent component

Estimation of direct sound by temporal and spatial extraction of interchannel coherent component