Table-like magnetocaloric effect and enhanced refrigerant capacity in crystalline Gd55Co35Mn10 alloy melt spun ribbons

Gd₅₅Co₃₅Mn₁₀ ribbons were prepared by melt-spinning and subsequent crystallization treatment. Crystallization resulted in the precipitation of the Gd₃Co-type and Gd₁₂Co₇-type phases in the amorphous matrix. Under a magnetic field change of 0–5 T, a table-like magnetocaloric effect, with a maximum magnetic entropy change ${(?\mathrm{\Delta }{S}_{\mathrm{M}})}^{\max }$ of $5.46\text{J}{\text{kg}}^{?1}{\text{K}}^{?1}$ in the temperature range of 137–180 K and enhanced refrigerant capacity (RC) of $536.4\text{J}{\text{kg}}^{?1}$, was achieved in Gd₅₅Co₃₅Mn₁₀ ribbons crystallized at 600 K for 30 min. The table-like ${(?\mathrm{\Delta }{S}_{\mathrm{M}})}^{\max }$ feature and enhanced RC values make Gd₅₅Co₃₅Mn₁₀ crystallized ribbons promising for Ericsson-cycle magnetic refrigeration in the temperature range from 137 to 180 K.     

Detecting switching points using asymmetric detrended fluctuation analysis

This work uses the concept of Asymmetric Detrended Fluctuation Analysis (A-DFA) to investigate and characterize the occurrence of trend switching in financial series. A-DFA introduces two new roughness exponents, $H^{+}$ and $H^{?}$, which differ from the usual one $H$ by separately taking into account contributions to the fluctuations according to whether the local trend is, respectively, upward or downward. The developed methodology requires the evaluation of local values of $H\left(t\right),H^{+}\left(t\right)$, and $H^{?}\left(t\right)$, by restricting the size of the largest window around the value $t$. We show that $H^{+}\left(t\right)$ and $H^{?}\left(t\right)$ behave differently in the neighborhoods of switching points (SPs) where trends change sign. Properly taken differences between shifted local values of $H\left(t\right),H^{+}\left(t\right)$, and $H^{?}\left(t\right)$ allow to identify and characterize SP’s. Tests with Weiertrasse functions, isolated peaks, and actual financial series are presented, supporting the validity of the proposed method.     

On binding energy of trions in bulk materials

We study the negatively $T^{?}$ and positively $T^{+}$ charged trions in bulk materials in the effective mass approximation within the framework of a potential model. The binding energies of trions in various semiconductors are calculated by employing Faddeev equation in configuration space. Results of calculations of the binding energies for $T^{?}$ are consistent with previous computational studies and are in reasonable agreement with experimental measurements, while the $T^{+}$ is unbound for all considered cases. The mechanism of formation of the binding energy of trions is analyzed by comparing contributions of a mass-polarization term related to kinetic energy operators and a term related to the Coulomb repulsion of identical particles.     

Pressure dependence of negative thermal expansion in Zr2(WO4)(PO4)2

Negative thermal expansion materials can experience significant stresses when they are used in composites. Under ambient conditions Zr₂(WO₄)(PO₄)₂ displays anisotropic negative thermal expansion (NTE) (${\alpha }_v=?14.0\left(10\right)\times 10^{?6}{K}^{?1}$, ${\alpha }_a=?7.9\left(5\right)\times 10^{?6}{K}^{?1}$, ${\alpha }_b=2.5\left(5\right)\times 10^{?6}{K}^{?1}$, ${\alpha }_c=?8.7\left(2\right)\times 10^{?6}{K}^{?1}$ at 0 GPa). The effect of hydrostatic pressure on its thermal expansion characteristics was investigated by neutron diffraction between 300 and 60 K at pressures up to 0.3 GPa. No phase transitions were observed in the pressure and temperature range examined. The material was found to have a bulk modulus, B₀, of 61.3(8) GPa at ambient temperature, and unlike some other NTE materials, pressure had no detectable effect on thermal expansion (${\alpha }_v=?14.2\left(8\right)\times 10^{?6}{K}^{?1}$, ${\alpha }_a=?7.9\left(3\right)\times 10^{?6}{K}^{?1}$, ${\alpha }_b=2.9\left(5\right)\times 10^{?6}{K}^{?1}$, ${\alpha }_c=?9.2\left(2\right)\times 10^{?6}{K}^{?1}$ at 0.3 GPa).     

Thermoelectric and topological properties of half-Heusler compounds ZrIrX(As,Sb, Bi)

The strain dependent electronic structures, thermoelectric and topological properties of the half-Heusler compounds ZrIrX(X=As, Sb, Bi) are investigated by the first-principle calculations. At the equilibrium lattice constants, all the three compounds are trivial insulators and good thermoelectric materials with the Seebeck coefficient S and the power factor over relaxation time $S^2\sigma /\tau$ as large as 1180 (μV/K) and 4.1 (${10}^{11}W{m}^{?1}{K}^{?2}{s}^{?1}$), respectively. The compressive strain enhances the band gap, while the tensile strain decreases the band gap. At some specific tensile strains, the compounds become Dirac-semimetals, with the s-type band ${\mathrm{\Gamma }}_6$ below p-type band ${\mathrm{\Gamma }}_8$, in the cubic phase. When we compress the a(b)-axis and elongate the c-axis of the compounds, they become the type-I Weyl semimetals. For ZrIrAs, the eight Weyl-Points (WPS) locate at (± K_x, 0, ± K_z), (0, ± K_y, ± K_z), ${\mathrm{K}}_x={\mathrm{K}}_y=0.008{\mathrm{\AA }}^{?1}$, ${\mathrm{K}}_z=0.043{\mathrm{\AA }}^{?1}$.     

Aeppli and Bott–Chern cohomology for bi-generalized Hermitian manifolds and d′d″-lemma

We define Aeppli and Bott–Chern cohomology for bi-generalized complex manifolds and show that they are finite dimensional for compact bi-generalized Hermitian manifolds. For totally bounded double complexes $(A,d^{\prime }{d}^{″})$, we show that the validity of $d^{\prime }{d}^{″}$-lemma is equivalent to having the same dimension of several cohomology groups. Some calculations of Bott–Chern cohomology groups of some bi-generalized Hermitian manifolds are given.     

Leibniz algebroids,generalized Bismut connections and Einstein–Hilbert actions

Connection, torsion and curvature are introduced for general (local) Leibniz algebroids. Generalized Bismut connection on $TM\oplus {\Lambda }^p{T}^{1}M$ is an example leading to a scalar curvature of the form $R+H^2$ for a closed $(p+2)$-form $H$.     

Lattice dynamics and phase transition of NiTi alloy

We have performed detailed first-principles calculations to investigate the structural and lattice dynamical properties of NiTi alloy. The calculated static structures consist well with the experimental data and other theoretical results. With quasi harmonic approximation, the phase boundary between B19′ and BCO phases can be described as a five order polynomial $T=100?89.28P+296.75P^2?717.94P^3+734.62P^4?274.25P^5$. The change of vibrational entropy is $0.07k_B$/atom at the transition temperature 100 K under zero pressure.     

Internal pair creation induced by nuclear coulomb excitation in heavy-ion collisions

Internal electron-positron pair creation caused by nuclear Coulomb excitation in heavy-ion collisions is compared with the spontaneous and induced positron production in overcritical quasimolecules with Z₁ + Z₂$?170. Using the rotation-vibration nuclear model in the calculation of the quadrupole Coulomb excitation and the conversion coefficient for electron-positron pair formation, the total cross section for the system ²³⁸₉₂U-²³⁸₉₂U was found to be ${\sigma }_C^{e^{+},e^{?}}=0.125mb$ at E_kin^c.m. = 797 MeV, which is four times smaller than the cross section ${\sigma }_{ind}^{e^{+},e^{?}}$ for the corresponding vacuum decay process if a K-shell vacancy production of L₀ = 10^? is assumed. Evaluation of the ratio $R=d{\sigma }_{ind}^{e^{+},e^{?}}({?}_{c.m.})/d{\sigma }_C^{e^{+},e^{?}}({?}_{c.m.})$ between the differential cross sections with respect to the ion angle ?_c.m leads to R = 60 at ?_c.m. = 160°. In contrast to the induced positron spectrum, the decay of excited nuclear levels in U is not followed by positrons with kinetic energy above 0.9 MeV. Therefore a unique determination of the decay of the vacuum in overcritical fields is experimentally possible provided that L₀ is not drastically reduced. In addition, similar calculations have been performed for pair creation resulting from nuclear Coulomb excitation for the systems U-Cf, Th-Th, Pb-Pb, Ni-Ni, Xe-Ba, Xe-Nd and Xe-Ce. The occupation of vacant bound states of superheavy electronic molecules by conversion electrons of γ-rays from nuclear transitions with E_γ < 1 MeV is also discussed.     

Dirac structures in Lagrangian mechanics Part I: Implicit Lagrangian systems

This paper develops the notion of implicit Lagrangian systems and presents some of their basic properties in the context of Dirac structures. This setting includes degenerate Lagrangian systems and systems with both holonomic and nonholonomic constraints, as well as networks of Lagrangian mechanical systems. The definition of implicit Lagrangian systems with a configuration space $Q$ makes use of Dirac structures on $T^{1}Q$ that are induced from a constraint distribution on $Q$ as well as natural symplectomorphisms between the spaces $T^{1}TQ$, $T{T}^{1}Q$, and $T^1{T}^{1}Q$. Two illustrative examples are presented; the first is a nonholonomic system, namely a vertical disk rolling on a plane, and the second is an L–C circuit, a degenerate Lagrangian system with holonomic constraints.