1,721,007 research outputs found
Introductory Chapter
No full textThis book deals with the recent advancements in two topical subjects of condensed mater physics, superluidity, and superconductivity. In principle, the two phenomena are very similar because they occur as a function of temperature and in the presence of the vanishing of a physical quantity marking a phase transition below a critical temperature. A superluid is a luid having zero viscosity while a superconductor is a conductor with zero resistance. Superluidity occurs in liquid helium and in ultracold atomic gases while superconductivity is typical of elements
like niobium and lead, of some niobium alloys, or compounds like ytrium barium and copper oxide and compounds containing iron. Regarding the later, since the irst discoveries, the interplay between superconductivity and magnetism has also been investigated inding that the magnetic state of superconductors can be described as ideal diamagnetism. The behaviour toward the external magnetic ield allows to distinguish between irst- and second-type superconductors. Instead, the critical temperature in correspondence of which superconductivity
arises allows to distinguish between low- and high-critical temperature superconductors.
After their initial discovery, superluidity was explained as a quantum mechanical phenomenon, while superconductivity was described irst according to a phenomenological and classical theory and only in a second moment in terms of a microscopic quantum mechanical theory
Magnetic Skyrmions as Information Entropy Carriers
No full textA simple scheme to use Néel skyrmions hosted in a ferromagnetic material as information entropy carriers based on the analogy between the Boltzmann’s configurational entropy and the continuous limit of Shannon’s information entropy is outlined. It is proposed a simple application represented by a data communication system able to transmit information entropy. The binary source fixes the skyrmion thermodynamic state, and the ferromagnet in contact with a thermal bath and hosting the magnetic skyrmion is regarded as the communication channel. The magnetic skyrmion enables the transmission of the information entropy from the source to the receiver. Analytical and numerical calculations show that the information coded by the magnetic skyrmion increases as the information content diminishes in accordance with the rules of Shannon’s information systems. These results could pave the way to use magnetic skyrmions as carriers of information basing on their thermodynamics
Statistical Thermodynamics of Chiral Skyrmions in a Ferromagnetic Material
No full textSolitons are a challenging topic in condensed matter physics and materials science because of the interplay between their topological and physical properties and for the crucial role they play in topological phase transitions. Among them, chiral skyrmions hosted in ferromagnetic systems are axisymmetric solitonic states attracting a lot of attention for their dazzling physical properties and technological applications. In this paper, the equilibrium statistical thermodynamics of chiral magnetic skyrmions developing in a ferromagnetic material having the shape of an ultrathin cylindrical dot is investigated. This is accomplished by determining via analytical calculations for both Néel and Bloch skyrmions: (1) the internal energy of a single chiral skyrmion; (2) the partition function; (3) the free energy; (4) the pressure; and (5) the equation of state of a skyrmion diameters population. To calculate the thermodynamic functions for points (2)–(5), the derivation of the average internal energy and of the configurational entropy is crucial. Numerical calculations of the thermodynamic functions for points (1)–(5) are applied to Néel skyrmions. These results could advance the field of materials science with special regard to low-dimensional magnetic systems
Dynamical Properties of a Periodic Mass-Spring Nonlinear Seismic Metamaterial
No full textNonlinear seismic metamaterials are a challenging class of acoustic metamaterials
that are receiving growing attention. Here, it is shown that, in the presence of third-order forces,
in a periodic arrangement of an anharmonic mass-spring system, the rectangular bipolar pulse
distribution, ansatz solution of the equation of motion, can be projected onto the exact solution.
This latter is derived casting the equation of motion in the form of a cubic Duffing differential
equation and describes the wave propagating inside the system. Simple expressions for the
amplitude and the period of the rectangular distribution are derived from the matching of the
first-order contributions of the two solutions. These results could be employed to further
tailoring the properties of nonlinear seismic metamaterials for engineering applications
Trends in the Second Law of Thermodynamics
No full textThe Second Law of Thermodynamics represents a milestone in the history of not only physics but also chemistry, engineering, and, more generally, life and natural sciences. It has been known for over 150 years and is usually thought of as one of the most authoritative laws. It can be regarded as the completion of the First Law of Thermodynamics, which establishes the conservation of energy in thermodynamic systems as the counterpart to the conservation of mechanical energy in mechanical systems. It is a fundamental law of the universe and its universality can be proven by demonstrating its equivalence across all types of thermodynamic systems. To strengthen its generality and impact, it is sometimes elevated to the level of a principle and named the Second Principle of Thermodynamics, providing it with a philosophical nature
Special Issue on Selected Papers in the Section Materials 2022
No full textThe study of materials has entailed several efforts by materials scientists to gain a deep understanding of their structural, mechanical, chemical, optical, magnetic and electronic properties and engineering applications.
This Special Issue collects selected papers in the Section Materials 2022 that had
an important impact on the materials community, including modeling and simulations, measurements and data analysis to reproduce materials’ properties
Absence of Spontaneous Spin Symmetry Breaking in 1D and 2D Quantum Ferromagnetic Systems with Bilinear and Biquadratic Exchange Interactions
No full textSome measurements have shown that the second-order exchange interaction is non-negligible in ferromagnetic compounds whose microscopic interactions are described by means of half-odd integer quantum spins. In these spin systems the ground state is either ferromagnetic or antiferromagnetic when the bilinear exchange interaction is dominant. Instead, in ferromagnetic systems characterized by bilinear and biquadratic exchange interactions of comparable magnitude, the energy minimum occurs when spins are in a canting ground-state. To this aim, a one-dimensional (1D) quantum spin chain and a two-dimensional (2D) lattice of quantum spins subjected to periodic boundary conditions are modeled via the generalized quantum Heisenberg Hamiltonian containing, in addition to the isotropic and short-range bilinear exchange interaction of the Heisenberg type, a second-order interaction, the isotropic and short-range biquadratic exchange interaction between nearest-neighbors quantum spins. For these 1D and 2D quantum systems a generalization of the Mermin–Wagner–Hohenberg theorem (also known as Mermin–Wagner–Berezinksii or Coleman theorem) is given. It is demonstrated, by means of quantum statistical arguments, based on Bogoliubov’s inequality, that, at any finite temperature, (1) there is absence of long-range order and that (2) the law governing the vanishing of the order parameter is the same as in the bilinear case for both 1D and 2D quantum ferromagnetic systems. The physical implications of the absence of a spontaneous spin symmetry breaking in 1D spin chains and 2D spin lattices modeled via a generalized quantum Heisenberg Hamiltonian are discussed
Trasformata di Hilbert-Huang per lo studio di linee elettriche di sistribuzione in smart grids
No full textHigh-Mobility Topological Semimetals as Novel Materials for Huge Magnetoresistance Effect and New Type of Quantum Hall Effect
No full textThe quantitative description of electrical and magnetotransport properties of solid-state
materials has been a remarkable challenge in materials science over recent decades. Recently, the
discovery of a novel class of materials—the topological semimetals—has led to a growing interest
in the full understanding of their magnetotransport properties. In this review, the strong interplay
among topology, band structure, and carrier mobility in recently discovered high carrier mobility topological semimetals is discussed and their effect on their magnetotransport properties is outlined. Their large magnetoresistance effect, especially in the Hall transverse configuration, and a new version of a three-dimensional quantum Hall effect observed in high-mobility Weyl and Dirac semimetals are reviewed. The possibility of designing novel quantum sensors and devices based on solid-state semimetals is also examined
Entropy Density Acceleration and Minimum Dissipation Principle: Correlation with Heat and Matter Transfer in Glucose Catabolism
No full textThe heat and matter transfer during glucose catabolism in living systems and their relation with entropy production are a challenging subject of the classical thermodynamics applied to biology. In this respect, an analogy between mechanics and thermodynamics has been performed via the definition of the entropy density acceleration expressed by the time derivative of the rate of entropy density and related to heat and matter transfer in minimum living systems. Cells are regarded as open thermodynamic systems that exchange heat and matter resulting from irreversible processes with the intercellular environment. Prigogine’s minimum energy dissipation principle is reformulated using the notion of entropy density acceleration applied to glucose catabolism. It is shown that, for out-of-equilibrium states, the calculated entropy density acceleration for a single cell is finite and negative and approaches as a function of time a zero value at global thermodynamic equilibrium for heat and matter transfer independently of the cell type and the metabolic pathway. These results could be important for a deeper understanding of entropy generation and its correlation with heat transfer in cell biology with special regard to glucose catabolism representing the prototype of irreversible reactions and a crucial metabolic pathway in stem cells and cancer stem cells
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