Energy Contour Research Articles

Numerical simulation of allocator annular flow field

The allocator is the key tool for the oilfield to realize the multi-layered polymer flooding. The most common allocator is the annular pressure-reducing groove structure. The selection of reasonable structural characteristics parameters has always been a difficult problem in the design of pressure reducing structure. The structural optimization design involves many parameters, and the numerical simulation method can effectively reduce the dependence on the experiment and the number of experiments. In this paper, the parametric modelling of the annular pressure-reducing groove structure is carried out, and the numerical simulation model of the power law fluid flowing in the annular channel is established. The turbulence calculation model is used to numerically calculate the flow field. The velocity, pressure, turbulent kinetic energy and strain rate contours are obtained and analysed. The numerical calculation results of the annulus flow field with four different structural characteristic parameters are compared and the optimal structural parameters are obtained, which can provide valuable reference for the design and improvement of the annular pressure-reducing groove allocator.

Group Sparse Representation With WaveNet Vocoder Adaptation for Spectrum and Prosody Conversion

The statistical approach to voice conversion typically consists of a feature conversion module followed by a vocoder. So far, the feature conversion studies are mainly focused on the conversion of spectrum. However, speaker identity is also characterized by prosodic features, such as fundamental frequency F0 and energy contour among others. In this paper, we study the transformation of speaker characteristics both in terms of spectrum and prosody. We propose two novel techniques that effectively use a limited amount of source-target training data and leverage a large general speech corpus to improve the voice conversion quality. First, we study the phonetic sparse representation under the group sparsity mathematical formulation. We use phonetic posteriorgrams PPGs together with spectral and prosody features to form tandem feature in the phonetic dictionary. The tandem feature allow us to estimate an activation matrix that is less dependent on source speakers, thus providing a better voice conversion quality. Second, we study the use of WaveNet vocoder that can be trained on general speech corpus from multiple speakers and adapted on target speaker data to improve the vocoding quality. We benefit from the large general speech databases that are used to train the PPG generator, and the WaveNet vocoder. The experiments show that the proposed conversion framework outperforms the traditional spectrum and prosody conversion techniques in both objective and subjective evaluations.

Effect of Differentiated Injection Ratio, Gas Flow Rate, and Slag Thickness on Mixing Time and Open Eye Area in Gas-Stirred Ladle Assisted by Physical Modeling

In this work, the effects of equal (50%/50%) or differentiated (75%/25%) gas flow ratio, gas flow rate, and slag thickness on mixing time and open eye area were studied in a physical model of a gas stirred ladle with dual plugs separated by an angle of 180°. The effect of the variables under study was determined using a two-level factorial design. Particle image velocimetry (PIV) was used to establish, through the analysis of the flow patterns and turbulence kinetic energy contours, the effect of the studied variables on the hydrodynamics of the system. Results revealed that differentiated injection ratio significantly changes the flow structure and greatly influences the behavior of the system regarding mixing time and open eye area. The Pareto front of the optimized results on both mixing time and open eye area was obtained through a multi-objective optimization using a genetic algorithm (NSGA-II). The results are conclusive in that the ladle must be operated using differentiated flow ratio for optimal performance.

Selective trapping of hexagonally warped topological surface states in a triangular quantum corral.

The surface of a three-dimensional topological insulator (TI) hosts two-dimensional massless Dirac fermions (DFs), the gapless and spin-helical nature of which leads to their high transmission through surface defects or potential barriers. Here, we report the behaviors of topological surface states (TSS) in a triangular quantum corral (TQC) which, unlike a circular corral, is supposed to be totally transparent for DFs. By real-space mapping of the electronic structure of TQCs, both the trapping and detrapping behaviors of the TSS are observed. The selection rules are found to be governed by the geometry and spin texture of the constant energy contour of TSS upon the strong hexagonal warping in Bi2Te3. Our work indicates the extended nature of TSS and elucidates the selection rules of the trapping of TSS in the presence of a complicated surface state structure, giving insights into the effective engineering of DFs in TIs.

The Role of Low-frequency Neural Oscillations in Speech Processing: Revisiting Delta Entrainment.

Studies that use measures of cerebro-acoustic coherence have shown that theta oscillations (3-10 Hz) entrain to syllable-size modulations in the energy envelope of speech. This entrainment creates sensory windows in processing acoustic cues. Recent reports submit that delta oscillations (<3 Hz) can be entrained by nonsensory content units like phrases and serve to process meaning-though such views face fundamental problems. Other studies suggest that delta underlies a sensory chunking linked to the processing of sequential attributes of speech sounds. This chunking associated with the "focus of attention" is commonly manifested by the temporal grouping of items in sequence recall. Similar grouping in speech may entrain delta. We investigate this view by examining how low-frequency oscillations entrain to three types of stimuli (tones, nonsense syllables, and utterances) having similar timing, pitch, and energy contours. Entrainment was indexed by "intertrial phase coherence" in the EEGs of 18 listeners. The results show that theta oscillations at central sites entrain to syllable-size elements in speech and tones. However, delta oscillations at frontotemporal sites specifically entrain to temporal groups in both meaningful utterances and meaningless syllables, which indicates that delta may support but does not directly bear on a processing of content. The findings overall suggest that, although theta entrainment relates to a processing of acoustic attributes, delta entrainment links to a sensory chunking that relates to a processing of properties of articulated sounds. The results also show that measures of intertrial phase coherence can be better suited than cerebro-acoustic coherence in revealing delta entrainment.

Experimental studies of flow characteristics in corrugated ducts

Structures of flow in a corrugated duct were experimentally examined employing the technique of Particle Image Velocimetry (PIV). The aspect ratio of the corrugated channel was selected as 0.3. Understanding the influences of phase shift, φ on the flow behavior and augmentation of heat transfer is one of the main objectives of this experimental work. Therefore, two different phase shifts such as φ = 0o and 90o and two different Reynolds Numbers, Re of 2 × 103 and 6 × 103 have been investigated for the available corrugated channel. In order to obtain the physics of the flow characteristics of the corrugated channel, the Turbulence Kinetic Energy, TKE, vorticity, and time-average velocity contours were calculated for both Reynold numbers, Re and phase shifts, φ. The experimental results revealed that transporting energy and increasing of momentum transfer by corrugated channel caused a better augmentation of the heat transfer rate for both phase shıft angles than the smooth channel. It appears that the turbulence generated by the sharp corner of the corrugated channels is the most influential factor in increasıng the entrainment between wake and core flows.

Dynamic analysis and criterion evaluation on rockburst considering the fractured dissipative energy

As one of the dynamic disasters of deep mining, rockburst significantly affects the safety of underground environment especially at great depth. First, the elastic energy and dissipative energy are deduced to characterize rockburst process separately employing the theoretical analysis and test technique. Then, a series of split-Hopkinson pressure bar system tests are conducted. After calculation, the percentage of fractured dissipative energy occupied in total input dynamic energy is obtained. Subsequently, the dynamic mechanical parameters of rock specimens and dynamic impact factors are fitted. Finally, a three-dimensional model is developed using the mechanical property of the host rock, constitutive model, and in situ geostress. The contours of energy and the damage conditions of host rock are predicted, and the tendentiousness of rockburst is estimated.

Autocorrelation of quasiparticle spectral intensities and its connection with quasiparticle scattering interference in cuprate superconductors

ABSTRACTThe quasiparticle excitation is one of the most fundamental and ubiquitous physical observables in cuprate superconductors, carrying information about the bosonic glue forming electron pairs. Here the autocorrelation of the quasiparticle excitation spectral intensities in cuprate superconductors and its connection with the quasiparticle scattering interference are investigated based on the framework of the kinetic-energy driven superconducting mechanism by taking into account the pseudogap effect. It is shown that the octet scattering model of the quasiparticle scattering processes with the scattering wave vectors connecting the hot spots on the constant energy contours is intrinsically related to the emergence of the highly anisotropic momentum-dependence of the pseudogap. Concomitantly, the sharp peaks in the autocorrelation of the quasiparticle excitation spectral intensities with the wave vectors are directly correlated to the regions of the highest joint density of states. Moreover, the momentum-space structure of the autocorrelation patterns of the quasiparticle excitation spectral intensities is well consistent with the momentum-space structure of the quasiparticle scattering interference patterns observed from Fourier-transform scanning tunnelling spectroscopy experiments. The theory therefore confirms an intimate connection between the angle-resolved photoemission spectroscopy autocorrelation and quasiparticle scattering interference in cuprate superconductors.

Thermo-hydraulic performance augmentation of solar air duct using modified forms of conical vortex generators

The present work investigates the thermo-hydraulic performance improvement of a solar air duct by deploying modified conical vortex generators (VGs) on the absorber plate heated with uniform heat flux of 1000 W/m2. Half and truncated half conical VGs at six different angle of attacks are considered for numerical simulation at a wide relevant range of Reynolds number varying from 3000 to 15,000. Commercial CFD tool, ANSYS FLUENT is used for simulating eighty four simulations on three dimensional model of VG integrated solar air heater with turbulent flow. RNG k-e turbulent model is employed to solve the complex governing equations of CFD. Results are analysed in detail based on different performance parameters namely Nusselt number (Nu), friction factor (f), thermal enhancement factor (Numod/Nus), friction factor enhancement factor (fmod/fs) and thermohydraulic performance parameter (THPP). The modified geometries are found to enhance Nu by about 7% and 4% compared to that of a smooth and conical VG integrated duct respectively. However there is an enhancement of 21% and 16% in local Nu due to the modifications in conical VG. Optimization based on performance at different angle of attack is carried out for both the modified conical VGs. At a higher Reynolds number value, truncated conical VG gives higher value of THPP. A maximum THPP of 1.06 is obtained for half conical VG at an angle of attack of 60° as compared to 1.02 for conical VG. The results are further supported and explained by exploring the temperature field, x-velocity, static pressure, turbulent kinetic energy and helicity contours. Modified conical VG shows a remarkable enhancement in overall performance as compared to conical VG.

Phase field modeling of fracture and crack growth

Predicting crack growth in structural components is a computationally intensive process. Phase field models of crack growth reduce the computational complications associated with singularities, and allow finite element predictions of crack propagation without remeshing. A novel approach to derive governing equations based on a Lagrangian density is proposed and the phase evolution is shown to be governed by a diffusion type equation with a source term. We correlate the phase to the micromechanical response. The model was incorporated in a finite element code and used to predict crack growth phenomena including (1) values of critical stress, (2) crack path, and (3) crack bifurcation. It was shown that the values of the critical stresses can be accurately estimated by the change in the phase field crack tip velocity or by the use of energy contour integral. The phase field crack analysis is compared against LEFM results.

Numerical investigation of heat transfer and friction characteristics for turbulent flow in various corrugated tubes

Thermal and hydraulic characteristics of turbulent water flow in a transverse corrugated tube with various corrugation direction (inward/outward) and corrugation shape (triangle, curve, rectangle, and trapezoid) are numerically investigated. The axisymmetric model of corrugated tubes with 10 mm inner diameter was investigated by changing the geometrical parameters for Reynolds number ranging from 5000 to 61,000 and constant heat flux boundary condition. Structured, nonuniform grid system is applied. Momentum, continuity, and energy equations were treated by means of a finite volume method using the SIMPLE scheme with the k–ε turbulence model and enhanced wall treatment. The results reveal that corrugation direction and corrugation shape have perceptible effects upon the heat transfer in the form of Nusselt number ( Nu) and pressure drop in the form of friction factor (ƒ). The average Nu for (inward) trapezoidal, rectangular, curved, and triangular corrugation shapes are 52.61%, 50.12%, 47.82%, and 44.96%, respectively, higher than the smooth tube. The average Nu for (outward) trapezoidal, curved, triangular, and rectangular corrugation shapes are 48.31%, 45.72%, 41.23%, and 40.94%, respectively, which are higher than a smooth tube. The results reveal that both inward/outward curved and triangular roughness shape have the superior performance evaluation criterion than rectangular and trapezoidal. Turbulence kinetic energy contour shows the increase in heat transfer performance for all corrugated tubes compared with a smooth tube. Inward corrugated tube provides the highest turbulence kinetic energy along the tube length and, consequently, the highest heat transfer. In addition, inward corrugated tubes provide the highest values and homogeneity of the velocity distribution along the core of tubes.

Topological phases in the TaSe3 compound

Based on first-principles calculations, we show that stoichiometric TaSe3, synthesized in space group P21/m, belongs to a three-dimensional (3D) strong topological insulator (TI) phase with Z2 invariants (1;100). The calculated surface spectrum shows clearly a single Dirac cone on surfaces, with helical spin texture at a constant energy contour. To check the stability of the topological phase, strain effects have been systematically investigated, showing that many topological phases survive in a wide range of the strains along both the a- and c-axes, such as strong TI (STI), weak TI (WTI) and Dirac semimetal phases. TaSe3 provides us an ideal platform for experimental study of topological phase transitions. More interestingly, since superconductivity in TaSe3 has been reported for a long time, the co-existence of topological phases and superconducting phase suggests that TaSe3 is a realistic system to study the interplay between topological and superconducting phases in the future.

A homogeneous payload specific performance index for robot manipulators based on the kinetic energy

Performance indices are extensively used in the optimization of robot structures. However, in the case of manipulators with mixed translational and rotational DOFs, traditional indices are not readily applicable due to the non-homogeneity of the Jacobian matrix. In this paper, special cases of generalized inertia ellipsoid, GIE, [1] and rms velocity norm [2] are used to define a payload specific performance index based on the transferred kinetic energy to the payload. The proposed kinetic energy index, KEI, is dimensionally homogeneous and is independent from the units. Moreover, this index is scale invariant and simultaneously considers both of the translational and rotational motions. A unit KEI indicates that a uniform kinetic energy is transferred to the payload for all the feasible joint velocities. For better representations, kinetic energy ellipsoids are drawn using a new vector form definition of the kinetic energy. A two-link manipulator and a 3-RRR robot are considered as case studies for evaluation of the proposed index. The kinetic energy ellipsoids and contours of KEI value are plotted over the entire workspace of the two robots. For a given payload with specified dynamic characteristics, KEI can be used to design an optimal structure of the manipulator such that a uniform kinetic energy is transferred to the payload.

Emotional speech analysis using harmonic plus noise model and Gaussian mixture model

Extracting the valuable information from the emotional speech is one of the major challenges in the areas of emotion recognition and human-machine interfaces. Most of the research in emotion recognition is based on the analysis of fundamental frequency, energy contour, duration of silence, formant, Mel-band energies, linear prediction cepstral coefficients, and Mel frequency cepstral coefficients. It was observed that emotion classification using sinusoidal features perform better as compared to the linear prediction and cepstral features. Harmonic models are considered as a variant of the sinusoidal model. In order to improve emotional speech classification rate and conversion of neutral speech to emotional speech, analysis using different harmonic features of emotional speech is a critical step. In this paper, investigations have been carried out using Berlin emotional speech database to analyze gender-based emotional speech using harmonic plus noise model (HNM) features and Gaussian mixture model (GMM). Analysis has been performed with the HNM features like pitch, harmonic amplitude, maximum voiced frequency and noise components. From the results, it can be observed that different emotional speech of male and female speakers can be represented with K components of GMM distribution. The optimal number of GMM components have been decided on the basis of Akaike information criterion (AIC) score.

Small business electricity disaggregation: Where can we improve? Towards increased transparency of appliance modal parameters

Small commercial buildings (<50,000 ft2 in floor area) consume 44% of all U.S. commercial primary electricity, with plug loads accounting for 31% of that portion and growing. In response, a bottom-up building energy assessment resource (BEAR) was previously developed as a practical approach to disaggregating building energy use, including plug loads. This article examines the performance of BEAR in estimating plug load consumption, specifically appliance energy consumption, through use of smart meters in two building types, food service and office.Results of the analysis reveal that BEAR is capable of providing building stakeholders with meaningful energy information. Accuracy of BEAR's energy consumption estimates could be improved by 25% to 59% through better data on modal (i.e. appliance operating mode such as standby mode) usage and power demand, respectively. These results stress the importance of detailed modal information, because when modal power information was available the median difference between BEAR and the smart meter measured data was 36% compared with 223% in appliances where modal data was not available. In response to these findings, this study develops and presents energy contour plots, a visual tool for plotting modal usage and modal power in a two-dimensional form of energy consumption contours. Moreover, it is the recommendation of this study that increased transparency of modal power be implemented at the manufacturer label or specification to achieve increased accuracy of targeted energy improvements.

Optically tunable spin texture of the surface state for Bi2Se3 and SmB6 topological insulators.

The spin texture of the surface state for topological insulators can be manipulated by the polarization of light, which might play a potential role in the applications in spintronics. However, the study so far in this direction mainly focuses on the classical light-topological-insulators interactions; TIs coupled to quantized light remains barely explored. In this paper, we develop a formalism to deal with this issue of spin texture of the surface state for topological insulators (for example Bi2Se3 and SmB6) irradiated by a quantum field, and we find that the coupling between an electron and a single-mode quantum field modulates only the arrow length that represents the spin polarization of a topological surface state. Specifically, when the photon number of a single-mode quantum field is fixed, the azimuth angle between the quantum light and the material surface manipulates the spin textures along the constant energy contour rotating (clockwise or counterclockwise) around the high symmetry point, and the polar angle controls the magnitude of the spin polarization. These results are quite different from the situation where an external field is not applied to an electron in a crystal or where a classical external field is utilized to control the spin polarization of a photoemitted electron in a vacuum. Our results have potential applications in quantum optics and condensed-matter physics.

Two Gaps in Semiconducting EuSbTe3 Studied by Angle-Resolved Photoemission Spectroscopy**Supported by the National Key R&D Program of China under Grant No 2016YFA0300204, the National Basic Research Program of China under Grant No 2015CB654901, the National Natural Science Foundation of China under Grant Nos 11574337, 11227902, 11474147 and 11704394, the Shanghai Sailing Program under Grant No 17YF1422900, and the Award for

Using angle-resolved photoemission spectroscopy, we study the low-energy electronic structure of a layered ternary telluride EuSbTe3 semiconductor. It is found that the photoemission constant energy contours can be well described by the simple two-parameter (tperp and tpara) tight-binding model based on the Te orbitals in square-net planes of EuSbTe3, suggesting its Te 5p orbitals dominated low-lying electronic structure, which is reminiscent of other rare-earth tritellurides. However, a possible charge-density-wave gap of 80 meV is found to persist in 300 K, which renders the unexpected semiconducting properties in EuSbTe3. Moreover, we reveal an extra band gap occurring around 200 meV below the Fermi level at low temperatures, which can be attributed to the interaction between the main and folded bands due to lattice scatterings. Our findings provide the first comprehensive understanding of the electronic structure of layered ternary tellurides, which lays the basis for future research on these compounds.

Automatic syllabification of speech signal using short time energy and vowel onset points

This paper describes a language independent method for automatic syllabification of speech signal. This method utilizes the valleys in short time energy (STE) contour and location of vowel onset points (VOP) for marking the syllable boundaries. In the proposed method, automatic syllabification is performed in three steps. First, long silence/pause regions are marked with the help of speech/non-speech detection. Then VOPs are located from the Hilbert Envelope of LP residual. The existence of more than one VOP in a continuous speech region (identified using speech/non-speech detection in the first step) is an indication of syllable boundaries within the region. Location with minimum energy in the STE contour between two consecutive VOP is identified as the syllable boundary. Since automatic VOP detection algorithm fails to detect some of the VOPs, certain syllable boundaries will be missed. Therefore, at the third step, additional syllable boundaries are detected from STE contour by fixing a valley threshold which is equal to the mean value of STE corresponding to each speech region between two consecutive syllable boundaries. This method is evaluated for 50 sentences each in read, extempore and conversational mode speech of Malayalam and Bengali languages. Overall accuracy of 80% is obtained with ± 50 ms tolerance with reference to manually marked syllable boundaries for this database. Method also shows good accuracy in case of TIMIT and NTIMIT data without tuning of thresholds and other parameters. This method is useful for applications that do not require exact syllable boundaries, rather a meaningful separation of syllables. Application of this technique for prosody based emotion recognition is illustrated using Emo-DB German emotional database.

Contact angle hysteresis and motion behaviors of a water nano-droplet on suspended graphene under temperature gradient

In the present work, the effect of temperature gradient on the behavior of a water nano-droplet resting on a suspended graphene was studied based on a non-equilibrium molecular dynamics simulation. The acquired results indicate that the applied temperature gradient to the suspended graphene drives the water nano-droplet to the colder region. The droplet accelerates its motion toward the cold reservoir as the temperature gradient is increased. In addition to the translational motion of the nano-droplet, the vortical motion of the water molecules was also observed. Contact angle analysis was also utilized to describe the directional motion of the nano-droplet. The translational motion of the droplet leads to the estimation of contact angle hysteresis through advancing and receding contact angles while the rotational motion resulted in the advancing and receding fronts being switched with one another through the simulation. The average displacement vector of the water molecules shows that parts of the droplet seem to stagnate while other parts rotate around them. The reason behind this particular behavior was studied based on interaction energy contours between a water molecule and the suspended graphene. The obtained data indicate that the rotational motion is in agreement with the migration of the water molecules to low interaction energy regions in order to avoid high interaction energy areas.

Symmetry analysis of strain, electric and magnetic fields in the Bi2Se3-class of topological insulators

Based on group theoretical arguments we derive the most general Hamiltonian for the Bi2Se3-class of materials including terms to third order in the wave vector, first order in electric and magnetic fields, first order in strain and first order in both strain and wave vector. We determine analytically the effects of strain on the electronic structure of Bi2Se3. For the most experimentally relevant surface termination we analytically derive the surface state (SS) spectrum, revealing an anisotropic Dirac cone with elliptical constant energy contours giving rise to a direction-dependent group velocity. The spin-momentum locking of strained Bi2Se3 is shown to be modified. Hence, strain control can be used to manipulate the spin degree of freedom via the spin–orbit coupling. We show that for a thin film of Bi2Se3 the SS band gap induced by coupling between the opposite surfaces changes opposite to the bulk band gap under strain. Tuning the SS band gap by strain, gives new possibilities for the experimental investigation of the thickness dependent gap and optimization of optical properties relevant for, e.g., photodetector and energy harvesting applications. We finally derive analytical expressions for the effective mass tensor of the Bi2Se3 class of materials as a function of strain and electric field.