Superconductivity of elements

Fundamental understanding of domain dynamics in ferroic materials has been a longstanding issue because of its relevance to many systems and to the design of nanoscale domain-wall devices. Despite many theoretical and experimental studies, a full understanding of domain dynamics still remains incomplete, partly due to complex interactions between domain-walls and disorder. We report domain-shape-preserving deterministic domain-wall motion, which directly confirms microscopic return point memory, by observing domain-wall breathing motion in ferroelectric BiFeO3 thin film using stroboscopic piezoresponse force microscopy. Spatial energy landscape that provides new insights into domain dynamics is also mapped based on the breathing motion of domain walls. The evolution of complex domain structure can be understood by the process of occupying the lowest available energy states of polarization in the energy landscape which is determined by defect-induced internal fields. Our result highlights a pathway for the novel design of ferroelectric domain-wall devices through the engineering of energy landscape using defect-induced internal fields such as flexoelectric fields.

Experimental investigations were made on the transport properties of several superconducting systems in which the superconducting state was out of thermodynamic equilibrium. In such systems, the dynamics of the pairing processes governs the restoration of equilibrium. Systematic investigations into the nonequilibrium dynamics were made possible by creating a steady state depairing region at a supernormal interface with a transport current. Information Was obtained by direct probing of the potential profiles in the depairing region. Measurements were made with superconducting microcircuits with high spatial resolution extending to the scale of the wavelength of light which limits our fabrication system. It was found that at the depairing region, the experimental results can be described by the existence of two distinct potentials, one for the single electron excitations and one for the electron pairs. A theory for the dynamics of the nonequilibrium process was proposed and succeeded in accounting for most of the experimental observations. The relaxation time associated with this dynamics is found to be longer than the usual equilibrium relaxation time for the condensed electron pairs. Similar measurements were extended to nonequilibrium regions close to current carrying interfaces between two different superconductors. In this case it was found that the two-potential measurements performed within the nonequilibrium region can be described in terms of a time dependent boundary condition at the interface. To study the nonequilibrium superconductivity associated with this time dependent boundary condition in a controlled way, two such superconducting boundaries were brought very close to each other, creating a well defined boundary region less than one micron in length. It was found that the boundary region showed Josephson-like effects as well as a unique phenomenon in which electromagnetic radiation increases the apparent superconducting transition temperature. A model for this situation was proposed in which two complex wavefunctions with independent phase angles interfere quantum mechanically inside the boundary region. This model successfully explains most of the observed phenomena associated with the boundary region in the voltage sustaining nonequilibrium state.

Worldwide there is an increasing need for a more sustainable form of electrical power delivery with a growing share of renewable energy generation. In the distribution and transmission network, large-scale and small-scale wind and solar power plants will be introduced, in proportion to the annual economic growth. The transmission and distribution network will be expanded, focusing on the electricity transport, however, there will also be a need for exchanges with neighboring countries. Alternative solutions are needed in order to support the changes of the future grid. High temperature superconductors are an alternative to conventional conductors, due to their high current density and very low AC loss, and therefore deserve more attention. The purpose of this study is to explore ways to integrate high-temperature superconducting cables in a future network and to compare their favorable technical properties with, e.g., the conventional XLPE cable. The development of 2nd generation high temperature superconducting tapes results in a high tape quality, making it very attractive for use in superconducting power transmission cables. At the same time, the network requirements placed on the grid, based on society needs are changing, such as low magnetic field emissions, reducing space requirements, lower losses, minimizing visual intrusion, etc. Our study shows that superconducting cables compared to conventional cables score better on these societal requirements. From our comparison of three practical low and high temperature superconductors we can conclude that Yttrium Barium Copper Oxide is the most suitable superconductor for use in transmission cables. Our techno-economic analysis shows that superconducting cables become already competitive with conventional cable in the AC transmission, such as XLPE cables. Possible future problems concerning the transport capacity in the power grid where high temperature superconducting cables can offer a solution have been identified. For one promising location, we have formulated the requirements for the design of a high-temperature superconducting cable. Next, we propose two types of cable systems (with cold and warm dielectric). For both types we describe the core, the electrical insulation, the screen, the cryostat, the cooling system, etc. Also for the distribution grid a techno-economic investigation is conducted. To assess the feasibility of the application in distribution grids, we have experimentally demonstrated a reduction of AC conductor losses from 1 W/m to 0.1 W/m. We also carried out an experimental investigation to improve the developed cryostat design for a 6 km long cable connection. Despite these substantial technical improvements our economic study showed that the high-temperature superconducting distribution cable is not yet competitive with the present conventional distribution cable systems except for niche locations where additional advantages e.g. magnetic emission, reduced space usage, power density weighs more heavily. Besides the HVAC grid the Netherlands has HVDC interconnections with neighboring countries and there are initiatives for the use of DC high voltage connections to wind farms further out to sea. In our study, we make reference to a suitable location, where the above mentioned attractive features of the superconducting cable are applicable as well. We advised a modified design of a HTS HVDC cable which enables a possible upgrade of the transmission capacity of the HVDC link at such location. The main results from the investigation are that: • Based on our techno-economic analysis HTS cables offer the most competitive solution in transmission grids. Introduction of such cables will reduce HTS tape price, which in turn will stimulate further applications. • Conceptual designs of competitive HTS AC and DC transmission cables are formulated along with that for HTS AC distribution cable. Novel designs allow for much longer length between cooling stations. • Our experimental research has shown that HTS cable core losses may be reduced by a factor 10 (down to 0.11 W/m/phase at 3 kArms, 77 K, 50 Hz). • Dedicated low friction cable cryostat was developed and successfully tested for 47 meters length. Patented multi-layer thermal insulation improves the cable cryostat heat leak from 1 W/m to 0.1 W/m.

While the global demand for energy continues to grow, the world’s depots of fossil fuels decrease. Logically, scientists have researched in different ways of creating sustainable energy. Dams, solar power and wind energy are all different ways of extracting power from nature. Having neither mountains nor many hours of annual sunshine, Denmark is, however, a flat country with many kilometers of coast line and calm weather, and therefore is perfectly suited for wind energy. Because of these facts, Denmark has always been a pioneer within the wind industry, building the world’s first off-shore wind energy park in 1991. In recent years, wind turbines have grown dramatically in size and capacity. Scientists predict that in order to make wind energy a more suitable alternative to fossil fuels, the wind turbines have to become even larger. The major problem with these super wind turbines, however, is the weight of the nacelle, of which a heavy part is the gear box. In order to avoid having a gear box in the wind turbine, a direct driven generator has been proposed, where superconductors play an important role. Energy losses due to Joule heating will be eliminated and high temperature superconductors are capable of working in high magnetic fields (several Teslas). The alternative to superconductors are permanent magnets, but the required amount would become expensive and inaccessible, while superconductors can be made from easily accessible elements. However, using superconductors also pose considerable challenges; low temperature cooling systems are required and the superconductors need to be of high quality. High temperature superconductors is a relatively new field of study, with the first discoveries made in the 1980s. Having found materials with superconducting properties at relatively high temperatures, the issue of optimizing other properties arose. A pinning center is an irregularity in the crystal, which destroys the superconducting properties. Here the magnetic field lines can penetrate without causing further damage to the superconductor. In 2005 Misko et al. found that a gradient in density of pinning centers could increase the critical current density (Jc) in a magnetic field. Pinning centers had been known to optimize superconductors, but with this new information, scientists have been equipped with a new tool to make superconductors more suitable for wind turbines. Since Misko et al. first predicted that different pinning densities throughout the superconductor could improve superconductors; many attempts have been made in order to show this property experimentally. Different methods to create the desired pinning patterns experimentally include Molecular Beam Epitaxy and E-beam Lithography. These methods are, however, both very expensive, making them less attractive for industrial production. This project investigates different options of creating simple gradients in the pinning center density.

Recent developments in the field of solid state synthesis have given us access to synthesis conditions that range from effective negative pressures of about ‐1 GPa to high positive values exceeding 10 or even 100 GPa. Thus, it becomes necessary to explore not only the landscape of potential energy, but also the enthalpy landscapes for a wide range of pressures when attempting to predict possible crystalline modifications in a chemical system. In this work, we present the enthalpy landscapes for the earth alkaline oxides. The results are compared with experimental and theoretical studies, and we predict that it should be possible to synthesize at least some of these compounds in the so‐called 5‐5 modification.

The superconducting proximity effect, in which superconductivity diffuses from a superconductor into an adjacent nonsuperconductor, was investigated using the SNS sandwich method in order to test the predictions of the de Gennes-Werthamer theory of temperature dependence of the Ginzburg-Landau equation. Sandwiches were made in which Pb injected superconductivity into a central layer of In, so that the maximum lossless current through the In could be found as a function of temperature down to the In transition temperature (3.4K). Techniques were used to insure uniform current flow, and to avoid annealing. The log of the critical current density of the sandwiches decreased linearly with temperature above the In transition; the current became much larger below the transition. The de Gennes-Werthamer theory was extended by the addition of the nonlinear term in the Ginzburg-Landau equation; exact solutions of the one-dimensional Ginzburg-Landau equation in the presence of current (but with A_ = 0) were used to find the theoretical temperature variation of the critical current density. The experimental and theoretical curves showed the same linear behavior (although there were slope and value variations), thus verifying the de Gennes-Werthamer theory near the transition temperature of a material.

We elucidate the magnetic phases and superconducting (SC) transition temperatures (Tc) in Sr2VFeAsO3−δ (21113V), an iron-based superconductor with a thick-blocking layer fabricated from a perovskite-related transition metal oxide. At low temperatures (T < 37.1 K), 21113V exhibited a SC phase in the range 0.031 ⩽ δ ⩽ 0.145 and an antiferromagnetic (AFM) iron sublattice in the range 0.267 ⩽ δ ⩽ 0.664. Mixed-valent vanadium exhibited a dominant AFM phase in 0.031 ⩽ δ ⩽ 0.088, and a partial ferrimagnetic (Ferri.) phase in the range 0.124 ⩽ δ ⩽ 0.664. The Ferri. phase was the most dominant at a δ value of 0.267, showing an AFM phase of Fe at T < 20 K. Increasing the spontaneous magnetic moments reduced the magnetic shielding volume fraction due to the SC phase. This result was attributed to the magnetic phase of vanadium, which dominates the superconductivity of Fe in 21113V. The Tc–δ curve showed two maxima. The smaller and larger of Tc maxima occurred at δ = 0.073 and δ = 0.145, respectively; the latter resides on the phase boundary between AFM and the partial Ferri. phases of vanadium. 21113V is a useful platform for verifing new mechanisms of Tc enhancement in iron-based superconductors.

As one of the most fundamental processes, excited-state proton transfer (ESPT) plays a major role in both chemical and biological systems. In the past several decades, experimental and theoretical studies on ESPT systems have attracted considerable attention because of their tremendous potential in fluorescent probes, biological imaging, white-light-emitting materials, and organic optoelectronic materials. ESPT is related to fluorescence properties and usually occurs on an ultrafast time scale at or below 100 fs. Consequently, steady-state and femtosecond time-resolved absorption, fluorescence, and vibrational spectra have been used to explore the mechanism of ESPT. However, based on previous experimental studies, direct information, such as transition state geometries, energy barrier, and potential energy surface (PES) of the ESPT reaction, is difficult to obtain. These data are important for unravelling the detailed mechanism of ESPT reaction and can be obtained from state-of-the-art ab initio excited-state calculations. In recent years, an increasing number of experimental and theoretical studies on the detailed mechanism of ESPT systems have led to tremendous progress. This Account presents the recent advances in theoretical studies, mainly those from our group. We focus on the cases where the theoretical studies are of great importance and indispensable, such as resolving the debate on the stepwise and concerted mechanism of excited-state double proton transfer (ESDPT), revealing the sensing mechanism of ESPT chemosensors, illustrating the effect of intermolecular hydrogen bonding on the excited-state intramolecular proton transfer (ESIPT) reaction, investigating the fluorescence quenching mechanism of ESPT systems by twisting process, and determining the size of the solute·(solvent) n cluster for the solvent-assisted ESPT reaction. Through calculation of vertical excitation energies, optimization of excited-state geometries, and construction of PES of the ESPT reactions, we provide modifications to experimentally proposed mechanisms or completely new mechanism. Our proposed new and inspirational mechanisms based on theoretical studies can successfully explain the previous experimental results; some of the mechanisms have been further confirmed by experimental studies and provided guidance for researchers to design new ESPT chemosensors. Determination of the energy barrier from an accurate PES is the key to explore the ESPT mechanism with theoretical methods. This approach becomes complicated when the charge transfer state is involved for time-dependent density functional theory (TDDFT) method and optimally tuned range-separated TDDFT provides an alternative way. To unveil the driving force of ESPT reaction, the excited-state molecular dynamics combined with the intrinsic reaction coordinate calculations can be employed. These advanced approaches should be used for further studies on ESPT systems.

ABSTRACTFor type II superconductors (SC), magnetic field can be trapped, or pinned due to persistent internal current. Upon magnetization, SC samples behave in some ways similar to a metallic permanent magnet. The trapped field is high and quasi-persistent, and we refer to it as a “magnet replica”. So far, nearly 1T @ 65 K, and over 0.4 T @ 77 K have been measured within small (about 1 × 1 × 0.6 cm3) melt-textured Yba2Cu3Ox (MT-Y123) samples. Based on our theoretical studies, extrapolation to larger scale magnets indicates that 2–4 Tesla in liquid Nitrogen (and even larger field at lower temperatures) is achievable with our high temperature superconductor (HTS) material. Using this effect, magnets with dipole, quadrupole, or more complicated configurations can be made of existing MT-Y123 material, thus bypassing the need for HTS wires. Two types of motors have been successfully constructed, using the trapped field in MT-Y123 samples.The spatial distribution of the trapped magnetic field on MT-Y123 materials has been studied. A phenomenological model has been developed to account for the trapped field intensity and profile in HTS samples. General features of magnet replicas by HTS will also be discussed.

Recent studies of Cu-Zr glasses have reported a rapid variation in the amorphous phase density near the optimal glass forming compositions, supporting the belief that the densest liquids are also the best glass formers. Here, we show that the measured densities of the Cu-Zr liquids at higher temperatures are not peaked sharply near these compositions, but the volume expansivities are. Theoretical studies have shown that the expansivity correlates with fragility near T(g); the experimental results presented here show that at high temperature they become anticorrelated. From energy landscape arguments, this indicates the existence of a crossover temperature for the expansivity-fragility correlation that scales inversely with the liquid fragility. These results lead to an improved understanding of the high temperature properties of liquids that form glasses and suggest a new method for identifying the best glass forming compositions within an alloy system from the properties of the equilibrium liquids.

ABSTRACTThis paper concentrates on theoretical and experimental nonlinear stiffness study of milling machine tool spindle angle contact ball bearing. The theoretical study allows us to build an analytical model to define nonlinear stiffness of angle contact ball bearings based on geometrical and physical parameters. Modifications were done on literature's models (e.g. Balls deformations) having positives impacts on conformity of models to experimental results.FEM model using ANSYS is constructed to analyze the different parameters affecting the nonlinear stiffness of ball bearing. Among those parameters are physical including the geometry, friction coefficient and the boundary conditions of the model and Numerical parameters such as mesh density and penetration.Experimental tests were done on the spindle ball bearing 7014, to measure the rigidity. Universal tensile testing machine is used to achieve load displacement curves. The developed theoretical model, constructed finite element model and experimental results showed good conformity.

A theoretical and experimental study of the formation mechanism of 4-X-chalcones by the Claisen–Schmidt reaction

Bubbles play crucial roles in various fields, including naval and ocean engineering, chemical engineering, and biochemical engineering. Numerous theoretical analyses, numerical simulations, and experimental studies have been conducted to reveal the mysteries of bubble motion and its mechanisms. These efforts have significantly advanced research in bubble dynamics, where theoretical study is an efficient method for bubble motion prediction. Since Lord Rayleigh introduced the theoretical model of single-bubble motion in incompressible fluid in 1917, theoretical studies have been pivotal in understanding bubble dynamics. This study provides a comprehensive review of the development and applicability of theoretical studies in bubble dynamics using typical theoretical bubble models across different periods as a focal point and an overview of bubble theory applications in underwater explosion, marine cavitation, and seismic exploration. This study aims to serve as a reference and catalyst for further advancements in theoretical analysis and practical applications of bubble theory across marine fields.

Synthesis, spectroscopic, X-ray diffraction and tautomeric properties of 5-(diethylamino)-2-((2-(5-(3-methyl-3-phenylcyclobutyl)-6H-1,3,4-thiadiazin-2yl)hydrazono)methyl)phenol: A combined experimental and theoretical study

Experimental and theoretical studies on the structure and vibrational properties of nitropyrazoles