Dipole Behavior Research Articles

Aerodynamic noise characteristics of tandem cylinders in a subcritical flow regime

The present experimental study investigates the noise generated from the subcritical flow past two tandem circular cylinders of different downstream-to-upstream diameter ratios ( d 2 /d 1). The configurations considered for the study are (A) d 2 /d 1 = 1, (B) d 2 /d 1 = 2.5 and (C) d 2 /d 1 = 0.4. The gap between cylinders has spacing to diameter ratios ( s/d) of 2 and 4, and the free stream Reynolds numbers vary from 8.4 × 103 to 3.6 × 104. At s/d = 2, acoustic tones from configurations A and B are associated with vortex shedding from the downstream cylinder, and configuration-C has broadband spectral variations. At s/d = 4, configuration-B has two acoustic tones corresponding to vortex shedding from both cylinders, with dominant higher-frequency tones from the smaller upstream cylinder, and Configuration-C has narrowband tones from the larger upstream cylinder. The mean wake velocities of configurations at s/d = 4 are lower, with relatively higher gradients than at s/d = 2. The corresponding turbulence levels are 8.3% and 6.5%, respectively. Peak tonal frequencies have a linear variation with free stream velocity, and the respective Strouhal numbers estimated are in the range from 0.17 to 0.20. Scaling of the spectra with sixth power of the free stream velocity shows the dipole behavior of noise sources. The tandem configurations have higher overall noise levels than the background noise by up to 26 dB at s/d = 2 and 21 dB at s/d = 4. Configuration-A at s/d = 2 has the highest noise level of 91 dB.

A comparative study of polymer viscosity modifiers: Flow field challenges & alternative trends

In recent years, substantial advancements have been achieved in augmenting the energy efficiency of hydraulic fluids through the integration of polymers. This study employs a multiscale approach, encompassing an analysis of polymer coil size evolution and flow field characteristics, with the aim of investigating the behavior of both dipole and non-dipole polymers within the host solvent. The ultimate goal is to establish a comprehensive understanding of the correlation between atomic properties of additives and the macroscopic properties of the polymer solution.To achieve this, the study employs an atomistic-continuum hybrid model that combines Brownian Dynamics and Lattice Boltzmann techniques within the bead-spring concept framework. Four chains, each comprising 64 particles, are subjected to varying shear rates. The primary focus centers on the examination of alterations in the radius of gyration and the velocity field within the polymer solution. Notably, the inclusion of dipole-dipole interactions exerts a profound influence on the configuration of the polymers. The results illuminate that non-dipole polymers display a more pronounced coupling with bulk flow hydrodynamics, leading to the confinement of particle motion in directions perpendicular to the primary stream. In contrast, dipole polymers experience a slower increase in coil size when compared to their non-dipole counterparts. These findings furnish valuable insights for the enhancement of energy-efficient hydraulic fluids and contribute to a fundamental comprehension of polymer behavior in lubricants, charting the course for the development of advanced hydraulic fluids in the future.

Dipole behavior in thin film heterostructure composed of Er-doped SnO2 and GaAs: Influence of polarization bias, temperature and stray light

The heterostructure system GaAs/SnO2 is built by resistive evaporation of Er-doped SnO2 powder on the top of GaAs semi-insulating substrate. The SnO2 powder comes from the drying of SnO2 sol-gel solution. The possible formation of dipoles in this heterostructure is investigated by the thermally stimulated depolarization current (TSDC) technique, and the possibilities for dipole formation are explored, such as the EL2 defect in the GaAs side, oxygen vacancies and Er ions in the SnO2 layer. The dipole relaxation activation energies are found in the range 0.2 eV to 0.3 eV, in good agreement with the ionization energies of these defects. The main TSDC bands: 213 meV with peak of −298 pA, for positive bias, and 218 meV with peak of 128 pA for negative bias, are modified by stray (room) light, which may correspond to the second ionization level of oxygen vacancies in SnO2, which are excited by the room lights and do not return to the original orientation.

Defect Dipole Behaviors on the Strain Performances of Bismuth Sodium Titanate-Based Lead-Free Piezoceramics.

Bismuth sodium titanate (BNT)-based, lead-free piezoelectric materials have been extensively studied due to their excellent strain characteristics and environmental friendliness. In BNTs, the large strain (S) usually requires a relatively large electric field (E) excitation, resulting in a low inverse piezoelectric coefficient d33* (S/E). Moreover, the hysteresis and fatigue of strain in these materials have also been bottlenecks impeding the applications. The current common regulation method is chemical modification, which mainly focuses on forming a solid solution near the morphotropic phase boundary (MPB) by adjusting the phase transition temperature of the materials, such as BNT-BaTiO3, BNT-Bi0.5K0.5TiO3, etc., to obtain a large strain. Additionally, the strain regulation based on the defects introduced by the acceptor, donor, or equivalent dopant or the nonstoichiometry has proven effective, but its underlying mechanism is still ambiguous. In this paper, we review the generation of strain and then discuss it from the domain, volume, and boundary effect perspectives to understand the defect dipole behavior. The asymmetric effect caused by the coupling between defect dipole polarization and ferroelectric spontaneous polarization is expounded. Moreover, the defect effect on the conductive and fatigue properties of BNT-based solid solutions is described, which will affect the strain characteristics. The optimization approach is appropriately evaluated while there are still challenges in the full understanding of the defect dipoles and their strain output, in which further efforts are needed to achieve new breakthroughs in atomic-level insight.

Evolution behavior of the coherent vortex dipole in oceanic turbulence.

The propagation of a Gaussian Schell-model (GSM) beam with a coherent vortex dipole (CVD) through oceanic turbulence is studied in detail. The creation and annihilation of the CVDs occur with propagation, which is similar to the case of atmospheric turbulence. However, the appearance and vanishment of a coherent vortex may occur by varying the propagation distance, oceanic turbulence parameters, or beam parameters, which is different from the case of atmospheric turbulence. The stronger the oceanic turbulence, the faster the evolution process of the CVD carried by GSM beams.

Aerodynamic noise characteristics of non-circular cylinders in subcritical flow regime

The present study experimentally investigates the aerodynamic noise from the flow around cylinders of square and equilateral triangle cross-sections at different angles of incidence ( α). The cylinder models have a side dimension of 10 mm and a span of 300 mm. The free stream velocity ( U 0) is in the range of 12–36 m/s, and the corresponding Reynolds numbers are 7.8 × 103 to 2.3 × 104, which is in the subcritical flow regime. The characteristic acoustic tones are generated at α = 30° and 45° for square and triangular cylinders. The frequency of acoustic tones linearly increases with the free stream velocity, and the corresponding Strouhal numbers are found to be in the range of 0.13–0.16. Depending on the angle of incidence, the overall sound pressure level is higher than the background noise by 4–24 dB for the square cylinder and 3–15 dB for the triangular cylinder at U 0 = 36 m/s. The highest noise level of the square cylinder is 90 dB at α = 45° and 79 dB at α = 30° for the triangular cylinder. The spectral scaling with the sixth power of the free stream velocity indicates the dipole behaviour of the acoustic tones. The mean and root-mean-square velocity profiles in the wake region characterise the noise emissions at different angles of incidence. The comparative acoustic study of the non-circular cylinders with a circular counterpart showed that the highest noise level is from the square cylinder at α = 45°. The directivity study shows that the noise level of the square cylinder at α = 45° at 90° angular location ( θ) is higher by 6.5 dB than that at θ = 30°.

Micro-pressure wave radiation from tunnel portals in deep cuttings

The reflection and radiation of steep-fronted wavefronts at a tunnel exit to a deep cutting is studied and contrasted with the more usual case of radiation from over-ground portals. A well-known difference between radiation in odd and even dimensions is shown to have a significant influence on reflected wavefronts, notably causing increased distortion that complicates analyses, but that can have practical advantages when rapid changes are undesirable. Likewise, micro-pressure waves radiating from the portal into a cutting are shown to exhibit strong dispersion that does not occur in the corresponding radiation into an open terrain. In the latter case, formulae that represent the behaviour of monopoles and dipoles are commonly used to estimate conditions beyond tunnel portals, but no such simple formula exists (or is even possible) for cylindrical radiation that is characteristic of MPWs in cuttings. An important outcome of the paper is the development of an approximate relationship that predicts the maximum amplitudes of these MPWs with an accuracy that should be acceptable in engineering design, at least for initial purposes. The formula shows that peak pressure amplitudes decay much more slowly than those from an overground portal, namely varying approximately as r −0.5 compared with r −1, where r denotes the distance from the portal.

Exposure of Artemia salina to glyphosate and bioremediation by isotherapy

Introduction: Artemia salina, an ecotoxicity bioindicator, is a microcrustacean belonging to the order Anostraca. Glyphosate is an herbicide widely used to control weeds. However, its intoxication can cause serious damage to human health and the balance of the environment, given its effects as an endocrine disruptor. Objective: verify the possible protection of the artemia exposed to glyphosate by the addition of its isotherapic into water, by means of the evaluation of the behavioral and morphological features of nauplii and of the physical properties of remedies and treated water, to elucidate the involved mechanisms. Methods: Artemia salina cysts were kept in culture bottles containing artificial seawater containing glyphosate at LC 10 (lethal concentration 10%), to promote hatching within 48 hours. The isotherapic preparations were inserted in each bottle in a 10% of the total water volume. Part of the nauplii was distributed in transparent tubes, being 10 nauplii per tube and 6 tubes per group, for behavioral analysis, and part were collected for a detailed morphological analysis, under an optical microscope. About 80 to 270 nauplii were analyzed per group. The reserved water was divided into aliquots for physicochemical analysis, that is, evaluation of the water dipole behavior by Cartwright´s method. Results: Gly 6cH presented selective effects on nauplii hatching (p=0.02) and on defected/healthy ratio (p=0.001), representing some protective action. This result was dependent of the salinity of water and presented correspondence with the effects on solvatochromic dyes, indicating that charges and ions can be critical factors involved in the mechanism of action. We concluded that the use of isotherapics could be a plausible tool to reduce the environmental impact of the indiscriminate use of glyphosate, since these results can be reproduced in further studies.

Deferred Polarization Saturation Boosting Superior Energy-Storage Efficiency and Density Simultaneously under Moderate Electric Field in Relaxor Ferroelectrics

High-temperature dielectric Bi0.5Na0.5TiO3 (BNT)-based relaxors near a morphotropic phase boundary are developed with excellent energy storage performance. Random distribution of polar nanoregions induced by composition modulation would disrupt the ferroelectric long-range dipolar alignment and weaken the coupling between the ferroelectric domains, yielding slender and deferred polarization–electric field hysteresis loops with relatively high saturation polarization. The reversible nano-domain orientation and growth in relaxors under a delayed electric field result in negligible remnant polarization and advantageous energy storage properties. Simultaneously, superior recoverable energy storage density and efficiency are gained, significantly surpassing the state-of-the-art dielectric energy storage materials under similar moderate electric fields. Vacancies, defect dipole behavior, and structural evolution that relied on an electric field and temperature are discussed to disclose the underlying mechanism associated with phase transition. Even thermal stability and large electrostrictive strain with low hysteresis are achieved in elevated temperatures. These features demonstrate the promising candidates for dielectric energy-storage application and provide a strategy in designing relaxors.

Highly Oriented Organic Ferroelectric Films with Single-Crystal-Level Properties from Restrained Crystallization

Crystallization is a key for ferroelectricity which is a collective behavior of microscopic electric dipoles. On the other hand, uncontrolled crystallization leads to uneven morphology and random crystal orientations, which undermines the application potential of ferroelectric thin films. In this work, we introduce a film fabrication method of low-temperature physical vapor deposition followed by restrained crystallization, with electrical properties monitored in real-time by in situ measurements. This method was adopted to fabricate films of 2-methylbenzimidazole (MBI), whose molecule crystals are proton-transfer type biaxial ferroelectrics and tend to grow into a hedgehog-shaped spherulites morphology. The in situ measurements confirm that the crystallization, corresponding to a clear transition of physical properties, occurs dominantly during post-deposition warming. This enables the fabrication of micron-thick films in disk-shaped morphology with one polarization axis aligned along the out-of-plane direction, while the measured spontaneous polarization and coercive field are comparable to the single-crystal values. These results mark an important advancement of film growth that is expected to benefit widely the fabrication of molecular materials films whose functional properties hinge on crystallization to achieve desirable morphology and crystallinity.

Short Circuit and Broken Rotor Faults Severity Discrimination in Induction Machines Using Non-invasive Optical Fiber Technology

Multiple techniques continue to be simultaneously utilized in the condition monitoring and fault detection of electric machines, as there is still no single technique that provides an all-round solution to fault finding in these machines. Having various machine fault-detection techniques is useful in allowing the ability to combine two or more in a manner that will provide a more comprehensive application-dependent condition-monitoring solution; especially, given the increasing role these machines are expected to play in man’s transition to a more sustainable environment, where many more electric machines will be required. This paper presents a novel non-invasive optical fiber using a stray flux technique for the condition monitoring and fault detection of induction machines. A giant magnetostrictive transducer, made of terfenol-D, was bonded onto a fiber Bragg grating, to form a composite FBG-T sensor, which utilizes the machines’ stray flux to determine the internal condition of the machine. Three machine conditions were investigated: healthy, broken rotor, and short circuit inter-turn fault. A tri-axial auto-data-logging flux meter was used to obtain stray magnetic flux measurements, and the numerical results obtained with LabView were analyzed in MATLAB. The optimal positioning and sensitivity of the FBG-T sensor were found to be transverse and 19.3810 pm/μT, respectively. The experimental results showed that the FBG-T sensor accurately distinguished each of the three machine conditions using a different order of magnitude of Bragg wavelength shifts, with the most severe fault reaching wavelength shifts of hundreds of picometres (pm) compared to the healthy and broken rotor conditions, which were in the low-to-mid-hundred and high-hundred picometre (pm) range, respectively. A fast Fourier transform (FFT) analysis, performed on the measured stray flux, revealed that the spectral content of the stray flux affected the magnetostrictive behavior of the magnetic dipoles of the terfenol-D transducer, which translated into strain on the fiber gratings.

Magnetic dipole aspect of binary chemical reactive Cross nanofluid and heat transport over composite cylindrical panels

Heat transport in magnetohydrodynamic (MHD) flow has given huge contribution in the field of engineering and biological systems like material selection, machinery efficiency, reaction kinetics, bio preservation, cryosurgery, heat, or cold treatments to destroy tumors, and treatment of several diseases by controlling the physical parameters. This research inquires the heat transport inMHDCross nanofluid via thermal conductivity with presence of Brownian motion, thermophoresis, and binary chemical reaction in cylindrical coordinates. Velocity of nanofluid is observed through imposed perpendicular magnetic dipole field and behavior concentration is depicted by activation energy (AE). Judgment of physical quantities is made through statistical graphs for nearly all involved parameters. Cross fluid model fetches the partial differential equations (PDEs) from Navier Stokes equation and the well-known shooting technique converted PDEs into ordinary differential equations. Further, for numerical solutions of obtained ODEs are passed through Matlab scheme bvp4c.

Manipulating temperature stability in KNN-based ceramics via defect design

The designed defect-engineering has been proved to be an effective way to promote properties in potassium sodium niobate (KNN)-based ceramics. Here, we focus on the introduction of Fe element into different sites of KNN-based ceramics to form defects and optimize properties. Two types of defect dipoles can be formed, FeA..−VA′ for A-site and FeNb″−VO.. for B-site. Compared with the defect dipoles of A-site, the defect dipoles of B-site are sensitive to both electric field and temperature. So that, the B-site defect dipoles switch easily under the thermo-electric treatment, and share the same behavior with spontaneous polarization after removing the electric field, which compensates the remnant polarization. In addition, the domain miniaturizes as the Fe ions doping. Both of the defect dipole behavior and nanodomain lead to the preferable temperature stability: remnant polarization (Pr) and unipolar strain (S) of the B-site engineered ceramics vary less than 10% and 15% in the temperature range of 20-140 °C. We hope that the strategy of designed defect dipoles is helpful for improving electrical properties and further promoting the development of KNN-based ceramics.

Conductions through head-to-head and tail-to-tail domain walls in LiNbO3 nanodevices

Conducting domain walls in an insulating ferroelectric matrix are interesting for the development of next generation multifunctional nanodevices with large output powers. However, electrical conductions are diversified among head-to-head (H-H), neutral (N), and tail-to-tail (T-T) domain walls (DWs) with disputable conduction mechanisms. It is generally accepted that the charged DWs are more electrically conductive than the neutral DWs. However, the charged walls are unstable due to high depolarization energies. Here, we stabilized the H-H DWs, NDWs and T-T DWs within a LiNbO3 transistor by controlling charge injection in compensation of the domain boundary charge under applied drain–gate, drain–source and gate–source voltages. The walls were created through the local 180° domain reversals in different inclined angles, and the transistors in different sizes were fabricated at the surfaces of 5 mol.% MgO-doped LiNbO3 single crystals in monodomain patterns. The NDWs are positively charged due to small inclination angles (~1°) and local sideways meandering behavior of the charged dipoles with electrical conduction that is three orders of magnitude higher than that across the T-T DWs but is one order of magnitude lower than that across the H-H DWs. Voltage dependences of wall currents can be fitted according to the space-charge-limited current equation with an exponential coefficient varying between 2.1 and 3.7 in some specific voltage ranges, implying discontinuous domain retraction in different inclined wall angles against the reduced applied voltage to affect the wall current. This finding provides the fundamental physics to improve domain wall conduction via domain reconstruction and broadens the domain wall application in future nano-devices.

Clouds and Vegetation Modulate Shallow Groundwater Table Depth

AbstractA 10-yr simulation of shallow groundwater table (GWT) depth over a temperate region in northwestern Europe, using a physics-based integrated hydrological model at kilometer scale, exhibits a strong seasonal cycle. This is also well captured in terms of near-surface soil moisture anomalies, terrestrial water storage anomalies, and shallow GWT depth anomalies from observations over the region. The modeled monthly anomaly of GWT depth exhibits a statistically significant (p < 0.05) moderate positive/negative correlation with non-rain- and rain-affected monthly anomalies of incoming solar radiation. The vegetation cover also produces a strong local control on the variability of shallow GWT depth. Thus, much of the variability in the simulated seasonal cycle of shallow GWT depth could be linked to the distribution of clouds and vegetation. The spatiotemporal distribution of clouds, partly influenced by the Rhine Massif, modulates the seasonal variability of incoming solar radiation and precipitation over the region. Particularly, the southwestern and northern part of the Rhine Massif divided by the Rhine Valley exhibits a dipole behavior with relatively high (low) shallow GWT depth fluctuations, associated with positive (negative) anomaly of incoming solar radiation and negative (positive) anomaly of precipitation.

Unique determination for an inverse problem from the vortex dynamics

We consider the problem of reconstructing a background potential from the dynamical behavior of vortex dipole. We prove that under suitable conditions, one can uniquely reconstruct a real-analytic potential by measuring the entrance and exit positions as well as travel times between boundary points. In particular, the work removes the flatness assumption on the potential from the earlier result. A key step of our method is a constructional procedure of recovering the boundary jet of the potential.

Analyzing the geomagnetic axial dipole field moment over the historical period from new archeointensity results at Bukhara (Uzbekistan, Central Asia)

Since the mid-19th century, direct measurements of both intensity and direction of the Earth's magnetic field have been available, allowing an accurate determination of its spatio-temporal variations. Prior to this time, between ~1600 and 1840, only direct directional measurements are available. Therefore, the construction of global field models over this period requires either a specific treatment of the axial dipole field component or the use of archeomagnetic intensity data. In this study, we use a regional approach based on the construction of an archeointensity variation curve in Central Asia. We analyze baked clay brick fragments sampled in Bukhara (Uzbekistan), dated between the end of the 16th century and the beginning of the 19th century. This city is of particular interest for archeomagnetism due to the well-preserved old buildings accurately dated by documentary archives. A series of archeointensity results is obtained using the Triaxe experimental protocol, which shows a decreasing trend in intensity from ~1600 to ~1750, with intensities during the 18th century lower than expected from global geomagnetic field models. These new data appear consistent with other Triaxe data previously obtained in western Europe and western Russia, when transferred to Bukhara using the field geometry of the gufm1 model. Together, these data are used to recalibrate the axial dipole moment evolution provided by this model. The resulting evolution appears non-linear, with a clear relative minimum in the magnitude of the axial dipole during the late 18th century. We illustrate the fact that at present this evolution can neither be satisfactorily confirmed nor refuted by other datasets available in western Eurasia (as well as at a wider spatial scale), mainly due to the significant dispersion of the data. Our interpretation relies on the accuracy of the field geometry of the gufm1 model, which appears less reliable prior to ~1750. Nevertheless, the minimum proposed in the 18th century seems to be a true feature of axial dipole behavior.

Understanding the Dipole Moment of Liquid Water from a Self-Attractive Hartree Decomposition.

The dipole moment of a single water molecule in liquid water has been a critical concept for understanding water's dielectric properties. In this work, we investigate the dipole moment of liquid water through a self-attractive Hartree (SAH) decomposition of total electron density computed by density functional theory, on water clusters sampled from ab initio molecular dynamics simulation of bulk water. By adjusting one parameter that controls the degree of density localization, we reveal two distinct pictures of water dipoles that are consistent with bulk dielectric properties: a localized picture with smaller and less polarizable monomer dipoles and a delocalized picture with larger and more polarizable monomer dipoles. We further uncover that the collective dipole-dipole correlation is stronger in the localized picture and is key to connecting individual dipoles with bulk dielectric properties. On the basis of these findings, we suggest considering both individual and collective dipole behaviors when studying the dipole moment of liquid water and propose new design strategies for developing water models.

Growth, spectral, mechanical, electrical and optical characterization of guanidinium hydrogen succinate single crystal

Slow evaporation method was employed to grow an organic crystal: guanidinium hydrogen succinate (GHS). Monoclinic structure of GHS was confirmed by single-crystal X-ray diffraction study and its space group was determined to be $${P2}_{1}/{c}$$ . Different functional groups present in GHS were estimated qualitatively by Fourier transform infrared analysis. The crystalline quality of the grown GHS was ascertained by high-resolution X-ray diffraction study. The UV–Vis absorption spectrum reveals a lower cut-off wavelength of 235 nm. The minimum absorption shows the wide optical transparency in the entire visible region. Work hardening co-efficient value ( $$n = 1.7$$ ) shows that the GHS crystal belongs to soft material category. Behaviour of dipoles in the crystal was examined through dielectric study. The third-order nonlinear optical analysis was carried out on GHS crystal through Z-scan technique. The nonlinear refractive index $$(n_2)$$ , nonlinear absorption coefficient ( $$\beta $$ ) and third-order nonlinear optical susceptibility ( $$\chi ^{(3)}$$ ) were estimated to be $$ - 5.78 \times 10^{-8}\hbox { cm}^{2}\hbox { W}^{-1}$$ , $$0.72 \times 10^{-4}\hbox { cm W}^{-1}$$ and $$8.09 \times 10^{-6}\hbox { esu}$$ , respectively.

Counter-Wound Normal-Mode Helical Antenna as an Electrically Small Electro-Quasi-Static Exciter

An electrically small electro-quasi-static exciter is demonstrated using a counter-wound normal-mode helical antenna. The arms are counter-rotated to cancel the generation of magnetic fields in the quasi-static regime. The field equations are derived and verified to show the degradation of magnetic fields with minimal effects to the electric field. The long wire lengths give sinusoidal current distribution and fields that are not strongly dependent on the feed structure. As a result, the measured electro-quasi-static field agrees well with the dipole behavior over long ranges. In addition, the circuit model for the antenna is presented and verified with measurements.