Quantum effective potential, electron transport and conformons in biopolymers

In the Kirchhoff model of a biopolymer, conformation dynamics can be described in terms of solitary waves, for certain special cross-section asymmetries. Applying this to the problem of electron transport, we show that the quantum effective potential arising due to the bends and twists of the polymer enables us to formalize and quantify the concept of a {\it conformon} that has been hypothesized in biology. Its connection to the soliton solution of the cubic nonlinear Schr\"{o}dinger equation emerges in a natural fashion.Comment: to appear in J. Phys.

Atomistic model of diopside–K-jadeite (CaMgSi2O6–KAlSi2O6) solid solution

Atomistic model was proposed to describe the thermodynamics of mixing in the diopside–K-jadeite solid solution (CaMgSi2O6–KAlSi2O6). The simulations were based on minimization of the latticeenergies of 800 structures within a 2 × 2 × 4 supercell of C2/c diopside with the compositions betweenCaMgSi2O6 and KAlSi2O6 and with variable degrees of order/disorder in the arrangement of Ca/K cations in M2 site and Mg/Al in Ml site. The energy minimization was performed with the help of a force-field model. The results of the calculations were used to define a generalized Ising model, which included 37 pair interaction parameters. Isotherms of the enthalpy of mixing within the range of 273–2023 K were calculated with a Monte Carlo algorithm, while the Gibbs free energies of mixing were obtained by thermodynamic integration of the enthalpies of mixing. The calculated T–X diagram for the system CaMgSi2O6–KAlSi2O6 at temperatures below 1000 K shows several miscibility gaps, which are separated by intervals of stability of intermediate ordered compounds. At temperatures above 1000 K a homogeneous solid solution is formed. The standard thermodynamic properties of K-adeite (KAlSi2O6) evaluated from quantum mechanical calculations were used to determine location of several mineral reactions with the participation of the diopside–K-jadeite solid solution. The results of the simulations suggest that the low content of KalSi2O6 in natural clinopyroxenes is not related to crystal chemical factors preventing isomorphism, but is determined by relatively high standard enthalpy of this end member

Order/disorder phase transition in cordierite and its possible relationship to the development of symplectite reaction textures in granulites

Based on a consistent set of empirical interatomic potentials, static structure energy calculations of various Al/Si configurations in the supercell of Mg-cordierite and Monte Carlo simulations the phase transition between the orthorhombic and hexagonal modifications of cordierite (Crd) is predicted at 1623 K. The temperature dependences of the enthalpy, entropy, and free energy of the Al/Si disorder were calculated using the method of thermodynamic integration. The simulations suggest that the commonly observed crystallization of cordierite in the disordered hexagonal form could be related to a tendency of Al to occupy T1 site, which is driven by local charge balance. The increase in the Al fraction in the T1 site over the ratio of 2/3(T1): 1/3(T2), that characterizes the ordered state, precludes formation of the domains of the orthorhombic phase. This intrinsic tendency to the crystallization of the metastable hexagonal phase could have significantly postponed the formation of the association of orthorhombic cordierite and orthopyroxene over the association of quartz and garnet in metapelites subjected to granulite facies metamorphism. The textures of local metasomatic replacement (the formation of Crd + Opx or Spr + Crd symplectites between the grains of garnet and quartz) indicate the thermodynamic instability of the association of Qtz + Grt at the moment of the metasomatic reaction. This instability could have been caused by the difficulty of equilibrium nucleation of orthorhombic cordierite

Using strain to uncover the interplay between two- and three-dimensional charge density waves in high-temperature superconducting YBa₂Cu₃O_y

Uniaxial pressure provides an efficient approach to control charge density waves in YBa2Cu3Oy. It can enhance the correlation volume of ubiquitous short-range two-dimensional charge-density-wave correlations, and induces a long-range three-dimensional charge density wave, otherwise only accessible at large magnetic fields. Here, we use x-ray diffraction to study the strain dependence of these charge density waves and uncover direct evidence for a form of competition between them. We show that this interplay is qualitatively described by including strain effects in a nonlinear sigma model of competing superconducting and charge-density-wave orders. Our analysis suggests that strain stabilizes the 3D charge density wave in the regions between disorder-pinned domains of 2D charge density waves, and that the two orders compete at the boundaries of these domains. No signatures of discommensurations nor of pair density waves are observed. From a broader perspective, our results underscore the potential of strain tuning as a powerful tool for probing competing orders in quantum materials

The Physics of the B Factories

This work is on the Physics of the B Factories. Part A of this book contains a brief description of the SLAC and KEK B Factories as well as their detectors, BaBar and Belle, and data taking related issues. Part B discusses tools and methods used by the experiments in order to obtain results. The results themselves can be found in Part C

Solid–aqueous equilibrium in the BaSO4–RaSO4–H2O system: First-principles calculations and a thermodynamic assessment

Phase relations in the BaSO4–RaSO4–H2O system are important for understanding the role of barite-type minerals in controlling the concentration of Ra2+ in natural water reservoirs. These relations are extremely sensitive to the difference in the solubility products of the end-members and to the degree of non-ideality of the solid solution phase. Experimental constraints to the standard entropy of RaSO4 and the regular interaction parameter of the barite–RaSO4 solid solution are ambiguous. This study is focused on determination of these parameters from first principles. The phonon density of states of RaSO4 is computed with the aid of the density functional perturbation theory. The regular interaction parameter in the BaSO4–RaSO4 solid solution, WBaRa, is interpreted as the slope of the enthalpy of mixing in the limit of infinite dilution (xRa = 0) and is calculated from the change in the total energy of a 2 2 2 supercell of BaSO4 due to the insertion of a single substitutional defect of Ra. The method is validated by computing W values for a wider range of binary solid solutions with barite and aragonite structures. The computed value of WBaRa = 2.50 ± 1.00 kJ/mol implies that the solid–aqueous equilibrium in the BaSO4–RaSO4–H2O system may have an alyotropic point in close proximity to the BaSO4 end-member. The assessment of available data on re-crystallization of barite in Ra-bearing aqueous solutions suggests that the barite crystals may fully equilibrate on the time scale of hundred days