[en] The effects of magnetic correlation on the electric properties in the multiferroic materials are studied, where the phase transition temperature of the magnetic subsystem T_m is lower than that of the electric subsystem T_e. A Heisenberg-type Hamiltonian and a transverse Ising model are employed to describe the ferromagnetic and ferroelectric subsystems, respectively. We find that the magnetic correlation can influence the electric properties above the T_m, and magnetic transverse and longitudinal correlations have opposite functions. In the curves of temperature dependence of polarization, kinks appear at T_m which is dominated by the sharp change of decreasing rate of the magnetic correlation. The kinks can be eliminated by an external magnetic field. The magnetic transverse and longitudinal correlations play contrary roles on the manipulation of polarization by the external magnetic field. - Highlights: • Both magnetic longitudinal and transverse correlations can influence the electric subsystem through magnetoelectric (ME) coupling at any temperature. • The magnetic longitudinal and transverse correlations have contrary effects in influencing the phase transition temperature of electric subsystem. • The electric phase transition temperature decrease with the ME coupling strength, while it was not so by mean-field theory. • An external field can make the influence smoother around the transition point, and can enhance the electric polarization. • Magnetic longitudinal and transverse correlations have contrary effects on the manipulation of polarization by magnetic field at temperature above the magnetic phase transition point

[en] The corrected version of the figure including P53 expression appears below. This correction does not change any conclusions of the paper.

[en] In previous work, we presented experimental and theoretical evidence that podophyllum derivatives substituted by chlorine atom in the 3-posititon of 2-aminopyridine exhibited significantly elevated potency. In this study, a series of podophyllum derivatives substituted in the 3-position of 2-aminopyridine, including methyl and fluorine groups, were synthesized. Their chemical structures were confirmed by the spectral (¹H-nuclear magnetic resonance, ¹³C-nuclear magnetic resonance, electrospray ionization mass spectrometry) and elemental analyses. These derivatives were tested for their respective cytotoxicities in HeLa, BGC-823, A549, Huh7, and MCF-7 cells by MTT assay and the pharmacological results showed that most of them displayed potent cytotoxicities against at least one of the tested cancer cell lines. Structure–activity relationship study suggested that the introduction of the fluorine atom into the 3-posititon of 2-aminopyridine had enhanced the cytotoxicity against numerous tumor cells compared to the chlorine atom, while the methyl group did not. Furthermore, other biological experiments were consistent with the beneficial effect of fluorine atom substituent in the 3-position of 2-aminopyridine, which then inhibited the microtubule polymerization and activity of topoisomerase II when 2-amino-3-fluoropyridine substituted in podophyllotoxin and 4′-O-demethylepipodophyllotoxin, and that they work by effecting the target proteins which induce P53-dependent apoptosis.

[en] This work presents a systematic density functional theory study of the structural, electronic, and magnetic properties of the golden cage doped with a transition-metal atom, M@Au₁₆^q (M=Cr, Mn; q=0, −1). We found that the endohedral structures are always favored. The Cr@Au₁₆⁻ clusters show smaller X-A energy gaps, suggesting that its geometric and electronic structures alter remarkably due to the addition of Cr atom. However, the characteristics of the Mn@Au₁₆⁻ species include their remarkably high X-A energy gaps, indicating doping by Mn atom could stabilize the hollow Au₁₆⁻ cage. Furthermore, the magnetic moment of the impurity Mn/Cr atom is slightly quenched. - Highlights: • The endohedral structures are always favored for Cr@Au₁₆^q and Mn@Au₁₆^q clusters. • All the doped cluster anions show larger ADE and VDE. • Atom like magnetism is maintained by doping into the golden hollow cage. • A new endohedral golden cage with varying magnetic properties may exist

[en] The solutions of a particle’s Dirac equation contains a negative kinetic energy (NKE) branch. Such an energy spectrum has an upper limit but no lower limit, so that the system with this spectrum, called NKE system, is of negative temperature. Fundamental formulas of statistical mechanics and thermodynamics of NKE systems are presented. All the formulas have the same forms of those of positive kinetic energy (PKE) systems. Almost all thermodynamic quantities, except entropy and specific heat, have a contrary sign compared to those of PKE systems. Specially, pressure is negative and its microscopic mechanism is given. Entropy is always positive and Boltzmann entropy formula remains valid. The three laws of thermodynamics remain valid, as long as the thermodynamic quantities have a negative sign. Negative temperature Carnot engine can work between two negative temperatures. Since the NKE levels need not be fully filled, it is argued that the concept of Dirac’s Fermion Sea can be totally abandoned. (paper)

[en] A wave function can be written in the form of Re^iS/ℏ. We put this form of wave function into quantum mechanics equations and take hydrodynamic limit, i. e., let Planck constant be zero. Then equations of motion (EOM) describing the movement of macroscopic bodies are retrieved. From Schrödinger equation, we obtain Newtonian mechanics, including Newton’s three laws of motion; from decouple Klein–Gordon equation with positive kinetic energy (PKE), we obtain EOM of special relativity in classical mechanics. These are for PKE systems. From negative kinetic energy (NKE) Schrödinger equation and decoupled Klein–Gordon equation, the EOM describing low momentum and relativistic motions of macroscopic dark bodies are derived. These are for NKE systems, i. e., dark systems. In all cases scalar and vector potentials are also taken into account. The formalism obtained is collectively called macromechanics. For an isolated system containing PKE and NKE bodies, both total momentum and total kinetic energy are conserved. A dark ideal gas produces a negative pressure, and its microscopic mechanism is disclosed. Two-body problems, where at least one is of NKE, are investigated for both macroscopic bodies and microscopic particles. A NKE proton and a PKE electron can compose a stable PKE atom, and its spectral lines have blue shifts compared to a hydrogen atom. The author suggests to seek for these spectral lines in celestial spectra. This provides a way to seek for dark particles in space. Elastic collisions between a body and a dark body are researched. (paper)

[en] A fundamental belief is that the formulism of relativistic quantum mechanics equations (RQMEs) should remain in low momentum motion. However, it is found that some formulas from RQMEs were lost in Schrödinger equation. For example, a free relativistic particle has positive and negative energy branches. The former includes positive kinetic energy (PKE) and the latter negative kinetic energy (NKE). The latter should be treated on an equal footing as the former. Nevertheless, from Schrödinger equation, a free particle can have only PKE. Starting from RQMEs and taking low momentum approximation, we derive NKE Schrödinger equation which is for the cases that free particles have NKE. Thus negative energy branch of RQMEs can be retained in low momentum motion. We point out a fact that whether Schrödinger equation is applicable in a region where a particle’s energy E is less than potential V, E < V, has never been quantitatively verified. In such a region NKE Schrödinger equation should be employed. With the help of NKE Schrödinger equation, the lost formulas are recovered. The so-called difficulty of negative probability of Klein–Gordon equation for free particles is solved. A PKE (NKE) particle can have stationary motion only when it is subject to an attractive (repulsive) potential, which is determined by Virial theorem. Two NKE electrons in a potential can constitute a stable system, a new kind of possible mechanism for electron paring. The whole discussion stems from RQMEs with no any new postulation. Experiments are suggested, which may confirm that there are indeed NKE electrons. (paper)

[en] Highlights: • The antiferromagnetism on FCC lattices is investigated in detail by the J₁-J₂ model. • At the parameter boundaries J₂/J₁ = 0 and 0.5, there are nonzero Neel temperature. • At both parameter boundaries, there may occur phase transition with temperature rising. • The coexistence of two states of NiS₂ detected experimentally is explained. The antiferromagnetic systems on the face-centered-cubic lattices are studied in detail by the Heisenberg J₁-J₂ model by the Green’s function method. The studied configurations contain the well-known three ones, called type-I, II and III, respectively, and an intermediate one suggested from experiment of MnSe₂. Our results show that the intermediate configuration cannot be described by the present model. For the well-known three configurations, at the parameter boundaries J₂/J₁ = 0 and 0.5, nonzero Néel temperatures can be calculated. At the boundary J₂/J₁ = 0, both the type-I and type-III can exist, and the former is more stable than the latter at T = 0⁺ K. At the boundary J₂/J₁ = 0.5, only the type-II is stable at T = 0⁺K, but above some very low temperature, the type-III will be more stable. When the J₂ value is less and very close to 0.5, there may be other magnetically disordered configurations at T = 0⁺K. We find that under appropriate J₂/J₁ ratios, the sublattice magnetizations versus temperature of the type-I and II can be almost identical, which explains the neutron scattering experiment in NiS₂ that showed the coexistence of the two states.

[en] The ferromagnetism of VS₂ monolayers are studied by the extended Heisenberg J₁-J₂ model with exchange anisotropy, inter-monolayer coupling J₃ and external magnetic field. With appropriate anisotropy strength and inter-monolayer coupling strength, the Curie point of monolayers can reach room temperature, which is consistent with experiments. The coercivity in our results are compared with the values in experiments at different temperatures. The coercivity for L = 3–5 monolayers are close to the experimental result at T = 50 K, but at T = 300 K the coercivity for L = 4–5 monolayers need larger anisotropy strength. Both the Curie point and coercivity are sensitive to the anisotropy strength and inter-monolayer coupling strength. The reasonable interaction strength between magnetic V-atoms, the exchange anisotropy and the inter-monolayer coupling strength are discussed by comparing our results with experiments. The small exchange anisotropy and large inter-monolayer exchange coupling for L > 1 monolayers may implies that the 1T-VS₂ is more stable for monolayers while the 2H-VS₂ is more stable for one monolayer near room temperature.

[en] In this paper, we present a comprehensive investigation of the effects of the transverse correlation function (TCF) on the thermodynamic properties of Heisenberg antiferromagnetic (AFM) and ferromagnetic (FM) systems with cubic lattices. The TCF of an FM system is positive and increases with temperature, while that of an AFM system is negative and decreases with temperature. The TCF lowers internal energy, entropy and specific heat. It always raises the free energy of an FM system but raises that of an AFM system only above a specific temperature when the spin quantum number is S ≥ 1. Comparisons between the effects of the TCFs on the FM and AFM systems are made where possible