Dipole Rotation Research Articles

Microwave-assisted method investigation for the selective and enhanced leaching of manganese from low-grade pyrolusite using pyrite as the reducing agent

The recovery mechanism of manganese from low-grade pyrolusite was studied through microwave and conventional leaching, respectively, and pyrite was used as the reducing agent. An improvement on the manganese leaching rate with microwave heating was noticed which may be caused by the suppressing of the formation of sulfur passivation layer by the unique dipole rotation heating mechanism of microwave energy. To confirm this hypothesis, the leaching time, the amount of reducing agent, and the concentration of sulfuric acid were studied, and the surface compositions of the leaching residues were analyzed. The results evidenced that the sulfur content on the surface of residue produced by microwave leaching was significantly reduced compared to the results produced by conventional heating, which proved the rationality of the hypothesis. The recovery of leaching assisted with microwave heating was improved compared to that assisted with conventional heating under the same experimental conditions (liquid-solid ratio: 10:1, leaching temperature: 90 ℃, M(pyrite)/M(pyrolusite): 0.2, sulfuric acid concentration: 1.2 mol/L, stirring speed: 400 rpm). The corresponding peak value of the leaching rate was 95.07 % and 75.08 %. Additionally, microwave leaching is very environmentally friendly since it significantly reduces the amount of reducing agent and sulfuric acid as well as reaction time.

Discovering the Elusive Global Minimum in a Ternary Chiral Cluster: Rotational Spectra of Propylene Oxide Trimer

AbstractThe chirality controlled conformational landscape of the trimer of propylene oxide (PO), a prototypical chiral molecule, was investigated using rotational spectroscopy and a range of theoretical tools for conformational searches and for evaluating vibrational contributions to effective structures. Two sets of homochiral (PO)3 rotational transitions were assigned and the associated conformers identified with theoretical support. One set of heterochiral (PO)3 transitions was assigned, but no structures generated by one of the latest, advanced conformational search codes could account for them. With the aid of a Python program, the carbon atom backbone and then the heterochiral (PO)3 structure were generated using 13C isotopic data. Excellent agreement between theoretical and experimental rotational constants and relative dipole moment components of all three conformers was achieved, especially after applying vibrational corrections to the rotational constants.

Discovering the Elusive Global Minimum in a Ternary Chiral Cluster: Rotational Spectra of Propylene Oxide Trimer.

The chirality controlled conformational landscape of the trimer of propylene oxide (PO), a prototypical chiral molecule, was investigated using rotational spectroscopy and a range of theoretical tools for conformational searches and for evaluating vibrational contributions to effective structures. Two sets of homochiral (PO)3 rotational transitions were assigned and the associated conformers identified with theoretical support. One set of heterochiral (PO)3 transitions was assigned, but no structures generated by one of the latest, advanced conformational search codes could account for them. With the aid of a Python program, the carbon atom backbone and then the heterochiral (PO)3 structure were generated using 13C isotopic data. Excellent agreement between theoretical and experimental rotational constants and relative dipole moment components of all three conformers was achieved, especially after applying vibrational corrections to the rotational constants.

Rutile TiO2 Nanoparticles Encapsulated in a Zeolitic Imidazolate Framework-Derived Hierarchical Carbon Framework with Engineered Dielectricity as an Excellent Microwave Absorber.

Aiming to solve the poor response of titanium dioxide (TiO2) in the microwave frequency, versatile series of N-doped carbon (NC) components are employed to improve the conductivity and polarization strength of TiO2-based composites. The bimetallic zeolitic imidazolate framework-derived TiO2@NC complex (TNC-3) exhibits hierarchical microstructures and large-scale hetero-interfaces, whereas the pyrolysis composite of metal-polydopamine-coated TiO2 (TNC-4) possesses the vesicle-like NC shell and bulk TiO2 core. Thus, the optimal reflection loss and efficient absorption bandwidth of TNC-3 realize -44.0 dB at 3.0 mm and 5.4 GHz at only 2.0 mm of coating thickness, respectively. Nevertheless, the corresponding attenuation ability of TNC-4 is separately -24.3 dB and 4.8 GHz with a thickness of 5.0 and 2.0 mm, respectively. Importantly, the conduction and polarization loss can be enhanced by the large-scale interfacial contacts between nanoscale rutile nanoparticles and hierarchical graphitized carbon. Meanwhile, the superior performance of TNC-3 stems from the large proportion of pyridinic N and pyrrolic N, which provides asymmetric lone pairs to strengthen the dipole rotation. These results are of great value in constructing semiconductor-based complexes by carbon-coating engineering as functional materials.

A Study of Magnetic Properties of Manganite Substituted ZnFe2O4 Composites

Composites of ZnFe2O4/La0.67Sr0.33MnO3 with different weight percentages were synthesized using sol-gel method and their magnetic behavior was investigated. Powder X-ray diffraction studies show spinel structure for zinc ferrite and rhombohedral for La0.67Sr0.33MnO3. An additional minor phase of α −Fe2O3 and ZnO was also noticed in zinc ferrite suggesting non-stoichiometric nature. Fourier transform infrared spectroscopy studies display cohabitation of two phases belonging to ferrite and perovskite phase with varying peak intensities. Field-dependent magnetization measurement at room temperature shows partial variation in saturation magnetization and remanent magnetization values with increase in La0.67Sr0.33MnO3 weight percent in zinc ferrite. Except for zinc ferrite, $\left (\frac {dM}{dH}\right )$ shows single peak with smooth variation, pointing to easy rotation of magnetic dipoles under applied fields.

Reconstructing quantum molecular rotor ground states

Nanomolecular assemblies of C$_{60}$ can be synthesized to enclose dipolar molecules. The low-temperature states of such endofullerenes are described by quantum mechanical rotors, which are candidates for quantum information devices with higher-dimensional local Hilbert spaces. The experimental exploration of endofullerene arrays comes at a time when machine learning techniques are rapidly being adopted to characterize, verify, and reconstruct quantum states from measurement data. In this paper, we develop a strategy for reconstructing the ground state of chains of dipolar rotors using restricted Boltzmann machines (RBMs) adapted to train on data from higher-dimensional Hilbert spaces. We demonstrate accurate generation of energy expectation values from an RBM trained on data in the free-rotor eigenstate basis, and explore the learning resources required for various chain lengths and dipolar interaction strengths. Finally, we show evidence for fundamental limitations in the accuracy achievable by RBMs due to the difficulty in imposing symmetries in the sampling procedure. We discuss possible avenues to overcome this limitation in the future, including the further development of autoregressive models such as recurrent neural networks for the purposes of quantum state reconstruction.

Dipole Tilt Effect on Magnetopause Reconnection and the Steady‐State Magnetosphere‐Ionosphere System: Global MHD Simulations

AbstractThe Earth's dipole tilt angle changes both diurnally and seasonally and introduces numerous variabilities in the coupled magnetosphere‐ionosphere system. By altering the location and intensity of magnetic reconnection, the dipole tilt influences convection on a global scale. However, due to the nonlinear nature of the system, various other effects like dipole rotation, varying interplanetary magnetic field (IMF) orientation, and nonuniform ionospheric conductance can smear tilt effects arising purely from changes in coupling with the solar wind. To elucidate the underlying tilt angle dependence, we perform magnetohydrodynamic (MHD) simulations of the steady‐state magnetosphere‐ionosphere system under purely southward IMF conditions for tilt angles from 0–90°. We identify the location of the magnetic separator in each case and find that an increasing tilt angle shifts the 3‐D X line southward on the magnetopause due to changes in magnetic shear angle. The separator is highly unsteady above 50° tilt angle, characteristic of regular flux transfer event (FTE) generation on the magnetopause. The reconnection rate drops as the tilt angle becomes large, but remains continuous across the dayside such that the magnetosphere is open even for 90°. These trends map down to the ionosphere, with the polar cap contracting as the tilt angle increases, and region I field‐aligned current (FAC) migrating to higher latitudes with changing morphology. The tilt introduces a north‐south asymmetry in magnetospheric convection, thus driving more FAC in the Northern (sunward facing) hemisphere for large tilt angles than in the Southern independent of conductance. These results highlight the strong sensitivity to onset time in the potential impact of a severe space weather event.

Bimode Foster’s Equivalent Circuit of Arbitrary Planar Periodic Structures and Its Application to Design Polarization Controller Devices

Foster's equivalent circuit for 2-D planar periodic structures (PPSs) that exhibit an arbitrary geometry is presented for first time in this article. The proposed four-port network shows an invariant circuit topology to the PPS geometry and is completely comprised of invariant-frequency lumped elements. The circuit is the simplest in terms of number of elements within the bimode bandwidth for a certain geometry, and its topology makes it possible both a standardized process to obtain the equivalent circuit of an arbitrary geometry and the use of the circuit theory to design a multitude of devices. To perform a validation, the equivalent circuit of two different PPSs (a rotated dipole and a defected slotted ring) has been obtained and analyzed in single-layer and multilayer configurations. The circuit is also used as a tool to develop elliptical to linear (or circular) polarization converters. One of the designs presented at 20 GHz (in transmission) converts an incident elliptical polarization of axial ratio 5 and tilted φ = 20° into a purely linear vertical polarization of XP <; - 30$ dB, with near-zero reflections and insertion loss better than 0.1 dB. The designed device is also manufactured and tested, and the measurements are in good agreement with simulations.

Deforming charged black holes with dipolar differential rotation boundary

Motivated by the recent studies of the novel asymptotically global hbox {AdS}_4 black hole with deformed horizon, we consider the action of Einstein–Maxwell gravity in AdS spacetime and construct the charged deforming AdS black holes with differential boundary. In contrast to deforming black hole without charge, there exists at least one value of horizon for an arbitrary temperature. The extremum of temperature is determined by charge q and divides the range of temperature into several parts. Moreover, we use an isometric embedding in the three-dimensional space to investigate the horizon geometry. The entropy and quasinormal modes of deforming charged AdS black hole are also studied in this paper. Due to the existence of charge q, the phase diagram of entropy is more complicated. We consider two cases of solutions: (1) fixing the chemical potential mu ; (2) changing the value of mu according to the values of horizon radius and charge. In the first case, it is interesting to find there exist two families of black hole solutions with different horizon radii for a fixed temperature, but these two black holes have same horizon geometry and entropy. The second case ensures that deforming charged AdS black hole solutions can reduce to standard RN–AdS black holes.

Enhanced Rotation by Ground State Destabilization in Amphidynamic Crystals of a Dipolar 2,3-Difluorophenylene Rotator as Established by Solid State 2H NMR and Dielectric Spectroscopy

We report the synthesis and rotational dynamics of the pillared metal–organic framework Zn2(F2BDC)2(DABCO) where F2BDC = 2,3-difluorobenzene-1,4-dicarboxylate acts as a rotating dipolar linker and DABCO = 1,4-diazabicyclo[2.2.2]octane acts as a spacer (F2MOF 1). The pillared structure of F2MOF 1 was confirmed by X-ray diffraction and CP-MAS 13C NMR analyses. Using variable temperature solid state 2H NMR and broadband dielectric spectroscopy, we characterized the rotational dynamics of the dipolar F2BDC linker in the solid state. Variable temperature (VT) quadrupolar echo 2H NMR measurements revealed a rotational activation energy of Ea = 6.8 ± 0.1 kcal/mol, which agreed well with temperature- and frequency-dependent dielectric measurements, indicating a barrier of Ea = 7.1 ± 0.5 kcal/mol. Structural data from single crystal X-ray diffraction and quantum mechanical calculations (DFT) suggest that the rotational potential is determined by steric interactions between the dipolar rotator and the stator linkers such that fluorine atoms in the F2BDC linker reduce the activation energy by destabilization of the coplanar BDC ground state.

A path integral ground state replica trick approach for the computation of entanglement entropy of dipolar linear rotors.

We calculate the second Rényi entanglement entropy for systems of interacting linear rotors in their ground state as a measure of entanglement for continuous rotational degrees of freedom. The entropy is defined in relation to the purity of a subsystem in a bipartite quantum system, and to compute it, we compare two sampling ensembles based on the path integral ground state (PIGS) formalism. This scheme centers on the replica trick and is aided by the ratio trick, both developed in this context by Hastings et al. [Phys. Rev. Lett. 104, 157201 (2010)]. We study a system composed of linear quantum rotors on a lattice in one dimension, interacting via an anisotropic dipole-dipole potential. The ground state second Rényi entropies estimated by PIGS are benchmarked against those from the density matrix renormalization group for various interaction strengths and system sizes. We find that the entropy grows with an increase in interaction strength, and for large enough systems, it appears to plateau near log(2). We posit that the limiting case of many strongly interacting rotors behaves akin to a lattice of two-level particles in a cat state, in which one naturally finds an entanglement entropy of log(2).

Effect of Dipolar Interaction on Information Entropy in Precession Bose-Einstein Condensates

In this paper, we study the formation of Shannon information entropy in a two axes rotating precessing Bose-Einstein condensates subject to dipole-dipole interactions. Our results show that how the Shannon information entropy depends on the second rotational frequency Ωx and dipole strength gd. With the increasing of gd, the position component Sr increases and momentum component Sk decreases at the same Ωx. Furthermore, we find that Landsberg’s order parameter η monotonically decreases with increasing Ωx and η increases with increasing gd at the same Ωx. Finally, we find that the increasing of dipole strength has no effect on the dynamic formation process of information entropy.

Strain-Induced Modification of the Optical Characteristics of Quantum Emitters in Hexagonal Boron Nitride.

Quantum emitters in hexagonal boron nitride (hBN) are promising building blocks for the realization of integrated quantum photonic systems. However, their spectral inhomogeneity currently limits their potential applications. Here, tensile strain is applied to quantum emitters embedded in few-layer hBN films and both red and blue spectral shifts are realized with tuning magnitudes up to 65 meV, a record for any 2D quantum source. Reversible tuning of the emission and related photophysical properties is demonstrated. Rotation of the optical dipole in response to strain is also observed, suggesting the presence of a second excited state. A theoretical model is derived to describe strain-based tuning in hBN, and the rotation of the optical dipole. The study demonstrates the immense potential for strain tuning of quantum emitters in layered materials to enable their employment in scalable quantum photonic networks.

Control of Ice Nucleation for Subzero Food Preservation

Freezing processes have long been employed for the preservation of foods, providing minimum nutrition loss with a long shelf life period. Freezing plays an essential role in ensuring the safety of food products in all regions of the world. Nonetheless, slow freezing rates and frequently freezing/thawing lead to permanent physicochemical changes, damage of structure, degradation of nutrition values, and color changes through the formation of large ice crystals in food matrix during the cold storage. The size of ice crystals is highly related to the duration of phase transition and degree of supercooling. This paper reviews that the degree of supercooling and nucleation temperature can be controlled by positive or negative pressure and vibration of the dipole and dipole rotation water molecule techniques. Controlling nucleation temperature and suppression of ice crystals in the food matrix could not be achieved by current freezing methods such as air blast, contact, and immersion freezing in the food industry. These present freezing methods are especially focused on increasing the heat transfer rate in foods. Rapid freezing technology may depend on the size and shape of food. However, the size of ice crystals and the suppression of nucleation could be achieved by alternative freezing technologies to overcome the drawbacks of current freezing technologies in the food industry. Conventional freezing technologies can be replaced by emerging freezing techniques, ultrasound irradiation, high pressure, electric field, magnetic field, and microwave-assisted freezing to control the properties of the nucleation and degree of supercooling in the food industry.

Quantitative domain engineering for realizing d36 piezoelectric coefficient in tetragonal ceramics

Piezoelectric devices based on d36 mode are remarkably stable that depolarization rarely occurs in d36 face shear mode, because d36 mode is completely different from d15 thickness shear mode, where the applied electric field is perpendicular to poling direction and depolarization is ineluctable due to 90° dipole rotation. However, piezoelectric ceramics conventionally possess three piezoelectric coefficients (i.e., d33, d31, and d15), while d36 only exists in single crystals of specific point groups and cut directions. In this work, we propose a method to realize d36 piezoelectric coefficient in tetragonal piezoelectric ceramics by mechanical and electric domain engineering. This method is successfully applied in bismuth scandium-lead titanate (abbreviated as BS-PT) high-temperature piezoelectric ceramics with a resultant d36 up to 160 pC/N, which broadens the application of BS-PT ceramics, such as face shear actuator, energy harvester, transducer, etc. We find that domain engineering by transversal electric poling is preferred compared with the transversal mechanical poling, due to the simpler process, higher reliability, and higher resultant d36 piezoelectric coefficient. By combining the Diffraction-Plane-Transformation (DPT) model with the domain engineering via transversal electric poling, we demonstrate a quantitative domain engineering method for the first time, which could be used for optimizing the piezoelectric properties by precise design of the domain structures in piezoelectric materials.

Cyclic variations in the main components of the solar large-scale magnetic field

ABSTRACT We consider variations of the dipole and quadrupole components of the solar large-scale magnetic field. Both axial and equatorial dipoles exhibit a systematic decrease during the past four cycles, in accordance with the general decrease of solar activity. The transition of the pole of a dipole from the polar region to the midlatitudes occurs rather quickly, so that the longitude of the pole changes little. With time, however, this inclined dipole region shifts to larger longitudes, which suggests an acceleration of dipole rotation. The mean rotation rate exceeds the Carrington velocity by 0.6 per cent. The behaviour of a quadrupole differs dramatically. Its decrease over the last four cycles was much smaller than that of the dipole moment. The ratio of the quadrupole and dipole moments has increased for four cycles more than twice, in contrast to sunspot numbers, which displayed a twofold decrease for the same time interval. Regarding quadrupole rotation, the mean longitude of the poles of one sign decreased by 600° over four cycles, which suggests that the mean rotation rate was lower than the Carrington velocity by 0.28 per cent. We do not, however, see any conclusive evidence that, in the period under discussion, a mode of quadrupole symmetry was excited in the Sun along with the dipole mode.

Bayesian Analysis of Theoretical Rotational Constants from Low-Cost Electronic Structure Methods.

With an ever-increasing usage of electronic structure programs by the microwave spectroscopy community, there is a growing need to assess the performance of commonly used, low-cost quantum chemical methods, particularly with respect to rotational constants because these quantities are central in guiding experiments. Here, we systematically benchmark the predictive power afforded by several low-level ab initio and density functionals combined with a variety of basis sets that are commonly employed in the rotational spectroscopy literature. The data set in our analysis consists of 6916 optimized geometries of 76 representative species where high-resolution experimental gas-phase rotational constants are available. We adopted a Bayesian approach for analyzing the performance of each method and basis set combination, employing Hamiltonian Monte Carlo sampling to determine the uncertainty in theoretical predictions of rotational constants and dipole moments. Our analysis establishes a hierarchy of accuracy and uncertainty, with commonly used methods in the rotational spectroscopy literature such as B3LYP and MP2 yielding lower accuracy and higher uncertainty than newer-generation functionals such as those from the Minnesota family, and ωB97X-D, which, when paired with a modestly sized 6-31+G(d) basis, provides optimal performance with respect to computational cost. Additionally, we provide statistical scaling factors that can be used to empirically correct for vibration-rotation effects, as a means to further improve the accuracy of rotational constants predicted from these relatively low-cost theoretical methods. As part of this, we demonstrate that the uncertainties can be used in simulations of rotational spectra to cross-correlate with broadband spectra, a methodology that could be used to quickly and efficiently survey experimental spectra for new molecules.

Design of a molecular memory element with an alternating circular array of dipolar rotors and rotation suppressors.

As a new element for electric-field driven molecular memory, we developed a hexaarylbenzene derivative in which three difluorophenyl groups and three aryl groups as a dipolar rotor and a rotation suppressor, respectively, are alternately positioned on the central benzene core. This molecule has two rotational isomeric forms, both of which preserve their conformational states at room temperature but exhibit interconversion at high temperatures. Amorphous thin films fabricated from the hexaarylbenzene show a reversible change in surface potential by application of electric fields.

Dielectric Properties of Foods

Dielectric properties of materials are used for evaluating their interactions with electromagnetic energy. Dielectric properties of food materials are required for various applications in food industry such as microwave (at 915 or 2450 MHz), radio wave (at 13.56, 27.12 or 40.68 MHz) and magnetic field processing. In order to understand the response of food materials to electromagnetic energy, dielectric parameters must be determined as a function of frequency, temperature, composition and moisture content. In this review, the dielectric properties of different food groups were listed depending on temperature and frequency ranges. In addition to the literature data of dielectric properties, the penetration depths of microwave or radio wave through food groups were calculated. The effects of temperature and composition (mostly moisture content) on dielectric properties depend on the type of the food and sometimes on frequency. However, the effect of frequency is constant; increased frequency decreased dielectric constant, loss factor and penetration depth. The lowest calculated penetration depth belonged to the fish surimi gel as 3.39 mm at microwave frequency whereas they were high generally for fats, oily seeds and flours (max was 372602 mm for corn flour). It appears that dielectric properties of foods should be investigated further depending on the interactions between frequency, temperature and composition. And then, dielectric heating based on the aim of the process can be applied accordingly. Besides, it appears that the moisture content and especially the dipole rotation and the conductivity movements of the molecules in free water content of the food are some of the most critical factors influencing the dielectric properties of food materials.

Deforming black holes with odd multipolar differential rotation boundary

Motivated by the novel asymptotically global AdS$_4$ solutions with deforming horizon in [JHEP {\bf 1802}, 060 (2018)], we analyze the boundary metric with odd multipolar differential rotation and numerically construct a family of deforming solutions with tripolar differential rotation boundary, including two classes of solutions: solitons and black holes. We find that the maximal values of the rotation parameter $\varepsilon$, below which the stable large black hole solutions could exist, are not a constant for $T> T_{schw}=\sqrt{3}/2\pi\simeq0.2757$. When temperature is much higher than $ T_{schw}$, even though the norm of Killing vector $\partial_{t}$ keeps timelike for some regions of $\varepsilon<2$, solitons and black holes with tripolar differential rotation could be unstable and develop hair due to superradiance. As the temperature $T$ drops toward $T_{schw}$, we find that though there exists the spacelike Killing vector $\partial_{t}$ for some regions of $\varepsilon>2$, solitons and black holes still exist and do not develop hair due to superradiance. Moreover, for $T\leqslant T_{schw}$, the curves of entropy firstly combine into one curve and then separate into two curves again, in the case of each curve there are two solutions at a fixed value of $\varepsilon$. In addition, we study the deformations of horizon for black holes by using an isometric embedding in the hyperbolic three-dimensional space. Furthermore, we also study the quasinormal modes of the solitons and black holes, which have analogous behaviours to that of dipolar rotation and quadrupolar rotation.