Distortion Modes Research Articles

The efficiency of the active controlled rectifier operation in the mains voltage distortion mode

Goal. Checking the efficiency of the active rectifier with differences types of control systems in conditions of deep voltage distortions of a three-phase three-wire supply network. Methodology. The authors have used the Matlab/Simulink software environment to create a model of an active rectifier with various types of control systems as part of a frequency electric drive. We performed a series of simulations of the operating modes of an active rectifier with various control systems when the supply voltage is distorted. Results. When the active rectifier is operating in an unregulated mode, the distortions of the current and mains voltage exceed the maximum permissible values. The quality indicators of the mains current and mains voltage are significantly higher than the normally permissible values. In the absence of voltage distortions in the supply network, the operation of the active rectifier can effectively eliminate the distortions of the mains current, regardless of the type of control system of the active rectifier. In conditions of deep distortions of the supply network voltage, the operation of an active rectifier with a vector control system is more efficient than with a parametric control system. Originality. Criteria for determining the quality of consumed electricity at the connection point of the circuit are proposed. Practical significance. Recommendations have been developed for the use of active rectifier control systems when working with a distorted power supply voltage.

Enhanced hybrid improper ferroelectricity in Fe/Nb cosubstituted Ca3Mn2O7 ceramics

AbstractThe prototypical Ruddlesden‐Popper compound Ca3Mn2O7 has been predicted to possess hybrid improper ferroelectricity, where the polarization is induced by the condensation of two oxygen octahedral distortion modes. Nevertheless, it is a big challenge to switch the polarization at room temperature in Ca3Mn2O7 since the presence of intermediate nonpolar Acaa phase generally leads to the complex domain morphology. Here, the effects of Fe/Nb cosubstitution on hybrid improper ferroelectricity in Ca3Mn2O7 are reported, and easy polarization switching at room temperature is achieved in Ca3[Mn0.5(Fe0.5Nb0.5)0.5]2O7. The ferroelectric phase transition occurs directly from I4/mmm to A21am at a temperature far above room temperature without intermediate nonpolar Acaa phase. The distinct transition pathway forms the alternating 180°‐type ferroelectric domains rather than the irregular 90°‐type ferroelastic domains stacked along [001], resulting in easy polarization switching at room temperature. Moreover the enhanced ferroelectric polarization (Pr ~2.0 μC/cm2) is obtained due to the increased anti‐ferrodistortive displacements of Ca cations at A‐site, arising from the larger amplitudes of oxygen octahedral distortions. Chemical pressure is emphasized here for the tunability of phase transition, domain morphology, and ferroelectric characteristics, and it provides a useful approach for designing and creating high‐performance improper ferroelectrics.

Accurate Simulation of the Four Modes of Post-Die Extrudate Shape Distortion

Abstract A combined flow, thermal and structural analysis is employed to simulate post-die extrudate distortion in different profile dies. All four factors which can cause extrudate distortion, namely, nonuniform exit velocity distribution, extrudate shrinkage, extrudate draw down, and deformed shape of the calibrator or sizer profile, are simulated. To analyze the effect of exit velocity variation on extrudate distortion, the parameterized geometry of a simple profile die is optimized using an extrusion die optimization software. The simulation results presented for a bi-layer profile die successfully demonstrate how gradually changing profile shape in successive calibrators/sizers can be used to simplify the die design for extrusion of complex profiles. The predicted extrudate shape and layer structure for the bi-layer die are found to accurately match with those in the extruded product.

Hierarchical derivation of orthogonal cross-section modes for thin-walled beams with arbitrary sections

A new systematic approach is presented to derive the cross-section deformation modes of thin-walled beams with arbitrary sections within the framework of a higher-order beam theory (HoBT). New sets of higher-order modes, in this case warping and distortion, are derived hierarchically from the lowest mode set by considering the consistency between the strain field and the stress field generated by the modes in lower sets. Warping modes are derived by the shear stress of in-plane modes while distortion modes are induced by out-of-plane deformations via Poisson's effect. Higher-order modes are shown to be built as a linear combination of the integrated functions of lower-order modes, where the combination coefficients are determined by the orthogonality condition among the higher-order modes. Because the proposed method does not require any approximation when determining sectional mode shapes, no cross-section discretization, commonly used in existing studies, is needed. The effectiveness of the proposed mode derivation process is verified by comparing the static and modal analysis results of thin-walled beams with open, closed, and flanged cross-sections obtained by the proposed method, other HoBTs, and shell finite elements.

Electronic and optical properties of Y-doped $$\hbox {BaBiO}_{3}$$

We investigate the nature of bond disproportionation in $$\hbox {BaBi}_{0.9}\hbox {Y}_{0.1}\hbox {O}_{3}$$ (BYBO) and its manifestation in the valence band and the optical absorption spectra. Our room-temperature (RT) structural results show that both the parent and the doped (BYBO) compounds stabilise in monoclinic structure but with a change in space group from I2/m to P21/n on Y doping. The Raman scattering studies suggest decrement in the breathing mode distortion of $$\hbox {BiO}_{6}$$ octahedra. The valence band spectra show an increase in the gap and close to the Fermi edge, we observe significant modifications in the fine structures on Y doping. These were studied using band structure calculations under TB-mBJ. The results show that the electronic states of the Y ions play significant role in driving the electronic structure. We also observe the importance of O 2p holes and also transfer of electrons from O 2p to Bi1 6s, Bi2 6s, and Y states to bring about bond disproportionation in the doped compound. The intensity variations and the features in the optical absorption spectra were understood based on the E vs k point calculations performed in the irreducible part of the Brillouin zone. The behaviour of the gap on doping is also in line with the calculations and optical absorption studies. The behaviour of the optical absorption spectra suggests possible use in solar cell and optical sensor applications. A composite of the doped compound with $$\hbox {BaTiO}_{3}$$ may find applications in the field of high-energy density capacitor. We believe that our results will be helpful in understanding the role of the electronic states of the dopants in superconductivity, especially in comparison with the monoclinic phase exhibited in the superconducting phase of $$\hbox {BaPb}_{0.75}\hbox {Bi}_{0.25}\hbox {O}_{3}$$ .

Effective suppression of mode distortion induced by stimulated Raman scattering in high-power fiber amplifiers

Abstract Mode distortion induced by stimulated Raman scattering (SRS) has become a new obstacle for the further development of high-power fiber lasers with high beam quality. Here, an approach for effective suppression of the SRS-induced mode distortion in high-power fiber amplifiers has been demonstrated experimentally by adjusting the seed power (output power of seed source) and forward feedback coefficient of the rear port in the seed source. It is shown that the threshold power of the SRS-induced mode distortion can be increased significantly by reducing the seed power or the forward feedback coefficient. Moreover, it has also been found that the threshold power is extremely sensitive to the forward feedback power value from the rear port. The influence of the seed power on the threshold power can be attributed to the fact that the seed power plays an important role in the effective length of the gain fiber in the amplifier. The influence of the forward feedback coefficient on the threshold power can be attributed to the enhanced SRS configuration because the end surface of the rear port together with the fiber in the amplifier constitutes a half-opening cavity. This suppression approach will be very helpful to further develop the high-power fiber amplifiers with high beam quality.

Flutter analysis of mistuned bladed disks (Effect of bladed disk structure on flutter characteristics)

Although bladed disks are nominally designed to be cyclically symmetric (tuned system), the vibration characteristics of all the blades on a disk are slightly different due to the manufacturing tolerance, deviations in the material properties, and wear during operation. These small variations break the cyclic symmetry and split the eigenvalue pairs. Bladed disks with small variations are referred to as a mistuned system. In the forced response of a mistuned bladed disk, the responses of all the blades become different, and the response of a certain blade may become extremely large due to splitting of the duplicated eigenvalues and distortion of the vibration modes. On the other hand, many researchers suggest that mistuning suppresses blade flutter, because the complete traveling wave mode is not formed in a disk. In the previous paper, authors studied the forced response of the mistuned bladed disk, using the reduced order model SNM (Subset of Nominal system Modes), and clarified that the effect of the bladed disk structure on the amplification factor. This work is a follow-up study on the previous paper. The stability analyses of mistuned bladed disks with the free-standing blade structure and the continuous ring-blade structure are carried out extensively, using the reduced order model SNM. Comparing the results of the stability analyses of mistuned bladed disks, the effect of the bladed disk structure on the blade flutter is clarified.

DNA Transformation, Cell Epigenetic Landscape and Open Complex Dynamics in Cancer Development

Statistical thermodynamics allowed the formulation of mesoscopic approach of DNA transformation in course of the excitation of collective distortion modes (denaturation bubbles) associated with hydrogen bond breaking between the base pairs. Intermediate (non-continual limit) of DNA modeling (the Peyrard-Bishop model) is combined with the field description (generalized Ginzburg-Landau approach) to analyze the dynamics of collective open complex modes associated with mesodefects in the DNA ensemble. Collective modes dynamics describes different scenario of gene expression according to statistically predicted form of out-of-equilibrium potential (epigenetic landscape) reflecting specific type criticality of “soft matter” with mesodefects (open complexes) – the structural-scaling transition. Principal difference of thermodynamics of non-continual and continual models is thermalization conditions related to thermal fluctuations responsible for the DNA breathing (localized excitation with breather dynamics) and structural-scaling parameter responsible for spinodal decomposition of out-of-equilibrium potential metastability due to generation of open complex collective modes. Open complex collective modes have the nature of self-similar solutions (breathers, auto-solitary and blow-up modes) of open complex evolution equation accounting qualitative different types of potential metastabilities. Sub-sets of collective modes represent the phase variables of attractors associated with different scenario of expression dynamics, which allows the interpretation of multistability of the epigenetic landscape and the Huang diagram of gene expression. It was shown different epigenetic pathway in attractors phase space corresponding to normal and cancer expression scenario. These scenarios were supported by laser interference microscopy of living normal and cancer cells illustrating multi- and monofractal dynamics.

Doubly resonant SFG and DFG spectroscopies: An analytic model for data analysis including distorted and rotated vibronic levels. I. Theory.

We present an analytic description of doubly resonant infrared-visible sum (SFG) and difference frequency generation (DFG) spectroscopies. Within the Born-Oppenheimer and Condon approximations for harmonic oscillators, we extend the usual theory, limited to linear electron-vibration coupling, and introduce the quadratic coupling phenomena (mode distortion and mode mixing) in the excited state. The excitation spectra of vibrations in SFG and DFG experiments are calculated in integral form for arbitrary mode distortions and small amplitude mode mixing between pairs of modes. Mode distortion modifies all orders of vibronic coupling including the fundamental process, whereas mode mixing appears as a perturbation added to the distorted mode case. For small quadratic coupling amplitudes, the results may be recast in simple analytic forms after the introduction of the overlap spectral function and developed in sums and products of Lorentzian functions.

Doubly resonant SFG and DFG spectroscopies: An analytic model for data analysis including distorted and rotated vibronic levels. II. Applications.

The influence of vibration mode distortion and mode mixing in the vibronic structure of molecules on the doubly resonant sum (SFG) and difference frequency generation spectroscopies is systematically studied in several examples. These phenomena modify the spectral overlap function at the heart of the modeling of the doubly resonant processes. When the visible beam is tuned, under the Franck-Condon approximation, each vibration mode generates two main peaks corresponding to the resonance of the molecular electronic transition with the visible and SFG energies, together with higher order ones driven by the amplitudes of the vibronic displacements. For a single mode system, mode distortion modifies the positions of the main peaks and the excitations of the higher order ones. For a two-mode system, mode mixing induces in addition a deep change in the balance between the intensities of the mixed modes. It also changes the phases of the vibrations, which makes curve fitting difficult. For multimode systems, mode mixing may greatly enhance intensity of a poorly active mode. For all these reasons, it seems mandatory to take mode distortion and mode mixing into account for an accurate analysis of second-order nonlinear spectroscopic experimental data.

Splitting of the surface modes for bubble oscillations near a boundary

The aim of this study is to describe the effect of the interface between media with different mechanical properties on the behavior of a gas bubble. The presence of a boundary leads to the breaking of the degeneracy of the surface modes, which are the perturbations of the spherically symmetric shape of the equilibrium bubble. The splitting of the surface modes was determined by using perturbation and numerical techniques. The results obtained can be applied to elucidate the physical mechanisms underlying a new ultrasonic cleaning technique, the ultrasonically activated stream. An experimental observation of the described effect is possible when analyzing a scattered signal under conditions of two-frequency excitation: a pump wave with a frequency close to the resonant frequency of the bubble parametrically generates distortion modes and a high-frequency signal wave that effectively scatters from distortion modes.

Thermal Distortion of Signal Propagation Modes Due to Dynamic Loading in Medium-Voltage Cables

Temperature variation from dynamic cable loading affects the propagation characteristics of transient signals. The distortion of modal signal components as a function of temperature in a three-phase medium-voltage cable is investigated. The temperature influence arises mainly through the complex insulation permittivity, which has a non-linear relationship with temperature. Near the maximum operating temperature of the cross-linked polyethylene insulation, the propagation velocity increases by 0.56% per degree centigrade but is an order of magnitude less sensitive at ambient temperature. The paper presents modeling results based on cable impedance and admittance matrices obtained from electromagnetic field simulation, taking into account the time-varying temperature distribution in the cable cross-section. The results are verified by applying Rayleigh–Schrödinger perturbation analysis. In the time domain, signal patterns shift when the modal propagation velocities change upon cable loading. Moreover, separation of degenerate modes is observed when the cable phase conductors carry an unbalanced current. The perspectives for exploiting the temperature dependency of signal propagation for pinpointing cable defects and for dynamic rating of underground power cables are discussed.

Analysis of forming-induced distortion of dissimilar Ti6Al4V/AA1050 laminate made by non-equal channel lateral co-extrusion

The aim of this study is to identify ways for controlling forming-induced distortion of a dissimilar Ti6Al4V/AA1050 laminate prepared by a novel non-equal channel lateral co-extrusion process, which is a modified equal-channel angular pressing process (ECAP) and is characterized by stimulant diffusion bonding via a decrease in the activation energy. First, a thermo-mechanical model of non-equal channel lateral co-extrusion based on the DEFORM-3D software was established along with the introduction of modeling technology. Second, the forming-induced distortions of the dissimilar Ti6Al4V/AA1050 laminate were evaluated in terms of all designed extrusion parameters such as the stripping angle, average velocity relative deviation, average temperature relative deviation, and extrusion force. Third, the process optimization for the mitigation of co-extrusion distortions was performed by employing the orthogonal experimental design and signal-to-noise ratio method. Finally, the experimental validation of numerical model was carried out by using the optimal process configuration. The variable analysis of the results indicates that the pre-heating temperature and the ram speed have a considerable effect on forming-induced distortion modes. The influences of process parameters on the average temperature relative deviation are obviously greater than that on the stripping angle and average velocity relative deviation. In addition, the impact of process parameters on the extrusion force is similar to that of the average temperature relative deviation. The experimental forming-induced distortion of the co-extruded laminate is in good agreement with the simulation result. Thus, this work provides an alternative guideline for the manufacture and distortion control of dissimilar bimetal laminates prepared by co-extrusion.

Electrical Characteristics of a Modal Filter With a Passive Conductor in the Reference Plane Cutout

A wider range of operating frequencies, lower supply voltage levels, and increased circuit density of radio-electronic equipment (REE) increase its susceptibility to electromagnetic interferences. Elements of REE are becoming more sensitive to electromagnetic environment especially to ultra-short pulses (USPs) penetrating through front door or back door channels. There is a large variety of noise suppressing devices, but their construction characteristics lead to limited efficiency. Modal filters (MFs), which are based on modal distortion, protect REE from USPs. In this article, the authors present the results of the study of a new method for implementing a MF with a passive conductor in a reference plane cutout and propose two prototypes of the MF with strong and weak couplings. The article presents the results of full-scale and computational experiments in time and frequency domains. For the first time, the decomposition of a USP in the proposed MF configurations is experimentally shown. Besides, we experimentally demonstrated the arrival of additional pulses, the time of which is determined by a linear combination of per-unit-length delays multiplied by the line length. Thus, the proposed approach allows implementing a simple and inexpensive technique for protection against USPs in multilayer printed circuit boards.

First principles calculations of the electric field gradient tensors of Ba2NaOsO6, a Mott insulator with strong spin orbit coupling

We present first principles calculations of the electrostatic properties of Ba2NaOsO6 (BNOO), a 5d1 Mott insulator with strong spin orbit coupling (SOC) in its low temperature quantum phases. In light of recent NMR experiments showing that BNOO develops a local octahedral distortion that is accompanied by the emergence of an electric field gradient (EFG) and precedes the formation of long range magnetic order (Lu et al 2017 Nat. Commun. 8 14407, Liu et al 2018 Phys. Rev. B 97 224103; Liu et al 2018 Physica B 536 863), we calculated BNOO’s EFG tensor for several different model distortions. The local orthorhombic distortion that we identified as most strongly agreeing with experiment corresponds to a Q2 distortion mode of the Na–O octahedra, in agreement with conclusions given in (Liu et al 2018 Phys. Rev. B 97 224103). Furthermore, we found that the EFG is insensitive to the type of underlying magnetic order. By combining NMR results with first principles modeling, we have thus forged a more complete understanding of BNOO’s structural and magnetic properties, which could not be achieved based upon experiment or theory alone.

First-principles description of intra-chain exciton migration in an oligo(para-phenylene vinylene) chain. I. Generalized Frenkel-Holstein Hamiltonian.

A generalized Frenkel-Holstein Hamiltonian is constructed to describe exciton migration in oligo(para-phenylene vinylene) chains, based on excited state electronic structure data for an oligomer comprising 20 monomer units (OPV-20). Time-dependent density functional theory calculations using the ωB97XD hybrid functional are employed in conjunction with a transition density analysis to study the low-lying singlet excitations and demonstrate that these can be characterized to a good approximation as a Frenkel exciton manifold. Based on these findings, we employ the analytic mapping procedure of Binder et al. [J. Chem. Phys. 141, 014101 (2014)] to translate one-dimensional (1D) and two-dimensional (2D) potential energy surface (PES) scans to a fully anharmonic, generalized Frenkel-Holstein (FH) Hamiltonian. A 1D PES scan is carried out for intra-ring quinoid distortion modes, while 2D PES scans are performed for the anharmonically coupled inter-monomer torsional and vinylene bridge bond length alternation modes. The kinetic energy is constructed in curvilinear coordinates by an exact numerical procedure, using the TNUM Fortran code. As a result, a fully molecular-based, generalized FH Hamiltonian is obtained, which is subsequently employed for quantum exciton dynamics simulations, as shown in Paper II [R. Binder and I. Burghardt, J. Chem. Phys. 152, 204120 (2020)].

Parametric upconversion of Ince-Gaussian modes.

The Ince-Gaussian (IG) mode, a recently discovered type of structured Gaussian beam, corresponds to eigenfunctions of the paraxial wave equation in elliptical coordinates. This propagation-invariant mode is of significance in various domains, in particular, its nonlinear transformation; however, there have been few relevant studies to date. In this Letter, we report the parametric upconversion of IG modes and associated full-field selection rule for the first time, to the best of our knowledge. We demonstrate that IG signals can be perfectly upconverted by a flattop-beam pump; in contrast, significant mode distortion occurred when using the most common Gaussian pump. Particular attention was given to the origin of the distortion, i.e., radial-mode degeneration induced by the sum-frequency generation excited by a Gaussian pump. This proof-of-principle demonstration has great significance in relevant areas, such as high-dimensional quantum frequency interfacing and upconversion imaging.

On the Discrepancy between Experimental and Calculated Raman Intensities for Conjugated Phenyl and Thiophene Derivatives.

Compared with experimental spectra, calculations for conjugated phenyl and thiophene oligomers tend to overestimate the ground state Raman intensities of higher-frequency vibrations (1200-1800 cm-1) relative to the intensities at lower frequencies (<1200 cm-1). The discrepancy was observed in previous benchmarking work that examined the method dependence of the calculated Raman spectra for a series of aromatic molecules. This paper further investigates the nature of the discrepancy by examining the role of anharmonic corrections and the dependence of the calculated Raman spectra on the inter-ring torsion angle for the representative molecules biphenyl (BP), 2-phenylthiophene (PT), and 2,2'-bithiophene (BT). Perturbative anharmonic corrections to the spectra calculated using density functional theory (DFT) provide only slightly better agreement with experiment. On the other hand, calculations at larger torsion angles give up to 30% improvement in the relative Raman intensities compared with the spectra calculated at the optimized geometries. The torsion-angle dependence of the Raman intensities is most pronounced for delocalized C-C and C-S stretching modes, and less pronounced for bending and ring distortion modes that do not involve inter-ring stretching. Higher-level calculations using the coupled cluster with single, double, and perturbative triple excitations [CCSD(T)] method indicate that DFT underestimates the energy barrier for torsion isomerization at small angles, and it overestimates the barriers at large angles, thus predicting minimum geometries at torsion angles that are too small. Therefore, the results suggest that the discrepancy in relative Raman intensities may be related to an overestimation of inter-ring conjugation by DFT, which also tends to favor geometries that are too planar.

Origin of the persistence of soft modes in metallic ferroelectrics

Metallicity and ferroelectriclike polar distortion are mutually noncompatible, and their coexistence in the same system is an intriguing subject of fundamental interest in the field of structure phase transition. However, it is unclear what mechanism may extend the limit of metallicity that allows polar distortion. We investigate the polar instability and soft modes in electron-doped ${\mathrm{PbTiO}}_{3}$ using linear-response density functional calculations. We find that ferroelectric instability can remarkably sustain up to an electron concentration of ${n}_{e}=0.7$ per unit cell, which is beyond the limit that causes the polar catastrophe in ${\mathrm{LaAlO}}_{3}/{\mathrm{SrTiO}}_{3}$. Our study further reveals two discoveries: (i) electron doping can turn nonsoft mode into soft mode, which leads to different microscopic mechanism for ferroelectricity when the system is strongly metallic; (ii) the frequency change $\mathrm{\ensuremath{\Delta}}\ensuremath{\omega}/\mathrm{\ensuremath{\Delta}}{n}_{e}$ is surprisingly flat at large ${n}_{e}$, which is pivotal for the persistence of soft mode and polar distortion at high metallicity. We also provide an interesting physical origin---which is caused by the strong mode-mode interaction---to explain these phenomena, and the finding of this origin may further extend the limit where metallicity and polar distortion coexist.

A nonlinear cross-section deformable thin-walled beam finite element model with high-order interpolation of warping displacement

In this paper, a new finite element model is developed for nonlinear analysis of thin-walled beams by introducing a high-order interpolation for the warping displacement field to better simulate actual cross-section deformation. It is discovered that, due to the significant coupling between bending and membrane deformations in each wall, it is crucial for a nonlinear thin-walled beam finite element to be capable to describe complex warping displacement distribution over the cross-section. In the geometrically exact beam element model developed, the warping displacement is expressed by using a higher-order interpolation scheme, while the distortion displacements are independently described by using a number of cross-section in-plane deformation modes. Numerical results are presented to demonstrate the effectiveness of the proposed model and investigate possible impacts of interpolation schemes for the warping displacement distribution on the solution accuracy under different problem settings. The results show that with an appropriate high-order warping displacement interpolation scheme, the proposed beam model can produce very accurate results even in the case of small wall thickness, outperforming many of the existing models. It is therefore concluded that special attention is needed on the warping displacement field for a finite element model to accurately simulate the cross-section distortional deformation of thin-walled beams. • A geometrically exact cross-section deformable thin-walled beam finite element model is developed. • The distortion and warping displacements are described by distortion modes and high-order interpolation, respectively. • Numerical examples are presented for a comprehensive investigation of the present finite element model. • The importance of warping displacement field for ensuring solution accuracy is pointed out.