Results for "D. C. JOhnston"

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Stretched Exponential Relaxation Arising from a Continuous Sum of Exponential DecaysSep 13 2006Nov 01 2006Stretched exponential relaxation of a quantity n versus time t according to n = n_0 exp[-(lambda* t)^beta] is ubiquitous in many research fields, where lambda* is a characteristic relaxation rate and the stretching exponent beta is in the range 0 < beta ... More
Heavy Fermion Behaviors in LiV_{2}O_{4}Oct 25 1999Experiments of various types on the metallic transition metal oxide compound LiV_{2}O_{4} with the fcc normal-spinel structure are reviewed. The low-temperature T < 10 K data consistently indicate heavy fermion (HF) behaviors characteristic of those of ... More
Magnetic Susceptibility of Collinear and Noncollinear Heisenberg AntiferromagnetsJun 06 2012Predictions of the anisotropic magnetic susceptibility chi below the antiferromagnetic (AFM) ordering temperatures TN of local moment Heisenberg AFMs have been made previously using molecular field theory (MFT) but are very limited in their applicability. ... More
Elaboration of the alpha-Model Derived from the BCS Theory of SuperconductivityApr 08 2013The single-band alpha-model of superconductivity [H. Padamsee, et al., J. Low Temp. Phys. {\bf 12}, 387 (1973)] is a popular model that was adapted from the single-band Bardeen-Cooper-Schrieffer (BCS) theory of superconductivity mainly to allow fits to ... More
Singlet ground state in the spin-1/2 dimer compound Sr3Cr2O8Feb 13 2007Jul 30 2007Magnetic susceptibility and specific heat versus temperature measurements on polycrystalline samples of Sr3Cr2O8 and the isostructural, nonmagnetic compound Sr3V2O8 are reported. A Curie-Wiess fit to the high-temperature susceptibility data for Sr3Cr2O8 ... More
A renormalized expression for the turbulent energy dissipation rateDec 13 2000Conditional elimination of degrees of freedom is shown to lead to an exact expression for the rate of turbulent energy dissipation in terms of a renormalized viscosity and a correction. The correction is neglected on the basis of a previous hypothesis ... More
Thermodynamics of the Spin-1/2 Antiferromagnetic Uniform Heisenberg ChainFeb 09 2000We present a new application of the traditional thermodynamic Bethe ansatz to the spin-1/2 antiferromagnetic uniform Heisenberg chain and derive exact nonlinear integral equations for just {\em two} functions describing the elementary excitations. Using ... More
Low-dimensional magnetism in the mixed Cr valence spin-chain compound Sr_4Cr_3O_9Aug 22 2008Sr_4Cr_3O_9 is the n = 2 member of a family of quasi-one-dimensional compounds A_{n+2}T_{n+1}O_{3n+3} (A = Ca, Sr, or Ba, T = transition metal, and n = 1 to \infty) having a crystal structure which consists of chains of n TO_6 octahedra alternated by ... More
Ba{0.4}Rb{0.6}Mn2As2: A Prototype Half-Metallic FerromagnetJul 23 2015Half-metallic ferromagnetism (FM) in single-crystal Ba{0.39(1)}Rb{0.61(1)}Mn2As2 below its Curie temperature TC = 103(2) K is reported. The magnetization M versus applied magnetic field H isotherm data at 1.8 K show complete polarization of the itinerant ... More
Metallic behavior induced by potassium doping of the trigonal antiferromagnetic insulator EuMn2As2Jun 13 2016Aug 09 2016We report magnetic susceptibility \chi, isothermal magnetization M, heat capacity C_p and electrical resistivity \rho measurements on undoped EuMn2As2 and K-doped Eu0.96K0.04Mn2As2 and Eu0.93K0.07Mn2As2 single crystals with the trigonal CaAl2Si2-type ... More
Antiferromagnetism in EuCu2As2 and EuCu1.82Sb2 Single CrystalsMar 20 2015Jun 05 2015Single crystals of EuCu2As2 and EuCu2Sb2 were grown from CuAs and CuSb self-flux, respectively. The crystallographic, magnetic, thermal and electronic transport properties of the single crystals were investigated by room-temperature x-ray diffraction ... More
Physical properties of EuPd2As2 single crystalsFeb 14 2014May 24 2014The physical properties of self-flux grown EuPd2As2 single crystals have been investigated by magnetization M, magnetic susceptibility chi, specific heat Cp, and electrical resistivity rho measurements versus temperature T and magnetic field H. The crystal ... More
2D O(3) + 2D QGOct 04 1993It has been suggested that the peak in the specific heat observed numerically for random surface actions with extrinsic curvature on dynamical lattices might be the result of a low mass bound state in an asymptotically free theory, rather than the signal ... More
Damaging 2D Quantum GravityDec 16 1993We investigate numerically the behaviour of damage spreading in a Kauffman cellular automaton with quenched rules on a dynamical $\phi^3$ graph, which is equivalent to coupling the model to discretized 2D gravity. The model is interesting from the cellular ... More
Crossover Between Weakly and Strongly Self-avoiding Random SurfacesJul 21 1992We investigate the crossover between weak and strong self-avoidance in a simulation of random surfaces with extrinsic curvature. We consider both dynamically triangulated and rigid surfaces with the two possible discretizations of the extrinsic curvature ... More
Multiple Potts Models Coupled to Two-Dimensional Quantum GravityApr 13 1992We perform Monte Carlo simulations using the Wolff cluster algorithm of {\it multiple} $q=2,3,4$ state Potts models on dynamical phi-cubed graphs of spherical topology in order to investigate the $c>1$ region of two-dimensional quantum gravity. Contrary ... More
Observation of a Phase Transition at 55 K in Single-Crystal CaCu1.7As2Jul 20 2012Dec 05 2012We present the structural, magnetic, thermal and ab-plane electronic transport properties of single crystals of CaCu1.7As2 grown by the self-flux technique that were investigated by powder x-ray diffraction, magnetic susceptibility chi, isothermal magnetization ... More
Magnetic, Transport, and Thermal Properties of Single Crystals of the Layered Arsenide BaMn2As2Jan 21 2009Feb 12 2009Growth of BaMn2As2 crystals using both MnAs and Sn fluxes is reported. Room temperature crystallography, anisotropic isothermal magnetization M versus field H and magnetic susceptibility chi versus temperature T, electrical resistivity in the ab plane ... More
A Fast and Accurate Method to Capture the Solar Corona/Transition Region Enthalpy ExchangeMar 04 2019The brightness of the emission from coronal loops in the solar atmosphere is strongly dependent on the temperature and density of the confined plasma. After a release of energy, these loops undergo a heating and upflow phase, followed by a cooling and ... More
Freezing a Fluid Random SurfaceMay 10 1993We investigate a dynamically triangulated random surface action that consists of a gaussian term plus the modulus of the intrinsic scalar curvature. We find that the flips are frozen out and the internal geometry is regularized as the coefficient of the ... More
An Effective Model for Crumpling in Two Dimensions?Jun 08 1992We investigate the crumpling transition for a dynamically triangulated random surface embedded in two dimensions using an effective model in which the disordering effect of the $X$ variables on the correlations of the normals is replaced by a long-range ... More
Square GravityJun 14 1995We simulate the Ising model on dynamical quadrangulations using a generalization of the flip move for triangulations with two aims: firstly, as a confirmation of the universality of the KPZ/DDK exponents of the Ising phase transition, worthwhile in view ... More
Smooth Random Surfaces from Tight Immersions?Mar 11 1993We investigate actions for dynamically triangulated random surfaces that consist of a gaussian or area term plus the {\it modulus} of the gaussian curvature and compare their behavior with both gaussian plus extrinsic curvature and ``Steiner'' actions. ... More
A Numerical Test of KPZ Scaling: Potts Models Coupled to Two-Dimensional Quantum GravityApr 13 1992We perform Monte Carlo simulations using the Wolff cluster algorithm of the q=2 (Ising), 3, 4 and q=10 Potts models on dynamical phi-cubed graphs of spherical topology with up to 5000 nodes. We find that the measured critical exponents are in reasonable ... More
Magnetic, Thermal, and Transport Properties of Layered Arsenides BaRu2As2 and SrRu2As2Jan 28 2009Apr 08 2009The magnetic, thermal and transport properties of polycrystalline BaRu2As2 and SrRu2As2 samples with the ThCr2Si2 structure were investigated by means of magnetic susceptibility chi(T), electrical resistivity rho(T), and heat capacity Cp(T) measurements. ... More
The XY Model Coupled to Two-Dimensional Quantum GravityJun 11 1992We perform Monte Carlo simulations using the Wolff cluster algorithm of the XY model on both fixed and dynamical phi-cubed graphs (i.e. without and with coupling to two-dimensional quantum gravity). We compare the numerical results with the theoretical ... More
Spin Models on Thin GraphsAug 02 1995Aug 03 1995We discuss the utility of analytical and numerical investigation of spin models, in particular spin glasses, on ordinary ``thin'' random graphs (in effect Feynman diagrams) using methods borrowed from the ``fat'' graphs of two dimensional gravity. We ... More
A Remark on the Renormalization Group Equation for the Penner ModelJun 21 1994It is possible to extract values for critical couplings and gamma_string in matrix models by deriving a renormalization group equation for the variation of the of the free energy as the size N of the matrices in the theory is varied. In this paper we ... More
Frustrating and Diluting Dynamical Lattice Ising SpinsJun 21 1994We investigate what happens to the third order ferromagnetic phase transition displayed by the Ising model on various dynamical planar lattices (ie coupled to 2D quantum gravity) when we introduce annealed bond disorder in the form of either antiferromagnetic ... More
Thin AnimalsJul 06 1998Lattice animals provide a discretized model for the theta transition displayed by branched polymers in solvent. Exact graph enumeration studies have given some indications that the phase diagram of such lattice animals may contain two collapsed phases ... More
Ising (anti-)ferromagnet on dynamical triangulations and quadrangulationsJul 20 1993We write down matrix models for Ising spins with zero external field on the vertices of dynamical triangulated random surfaces (DTRS) and dynamically quadrangulated random surfaces (DQRS) and compare these with the standard matrix model approach which ... More
A Potts/Ising Correspondence on Thin GraphsJan 15 1999We note that it is possible to construct a bond vertex model that displays q-state Potts criticality on an ensemble of phi3 random graphs of arbitrary topology, which we denote as ``thin'' random graphs in contrast to the fat graphs of the planar diagram ... More
Symmetric Vertex Models on Planar Random GraphsDec 10 1998Sep 20 1999We solve a 4-(bond)-vertex model on an ensemble of 3-regular Phi3 planar random graphs, which has the effect of coupling the vertex model to 2D quantum gravity. The method of solution, by mapping onto an Ising model in field, is inspired by the solution ... More
Dynamic Behavior of Spin Glass Systems on Quenched Phi-3 GraphsJun 26 1996We study the dynamical out-of-equilibrium behavior of a $J = \pm 1$ Ising spin glass on quenched $\phi^{3}$ graphs. We show that magnetization and energy decay with a power law behavior, with exponents that are linear in $\frac{T}{T_{c}}$. Quenched $\phi^{3}$ ... More
EPR measurements of Eu{+2} spins in metallic EuCo{2-y}As2 single crystalsSep 07 2018Dec 17 2018The Eu{+2} spins S = 7/2 in the metallic compound EuCo{2-y}As2 order into an antiferromagnetic helical structure below a Neel temperature TN = 40 to 45 K. The effective magnetic moment mu_eff of the Eu spins in the paramagnetic state from 100 to 300 K ... More
Specific Heat (1.2-108 K) and Thermal Expansion (4.4-297 K) Measurements of the 3d Heavy Fermion Compound LiV_{2}O_{4}Nov 30 1998Specific heat C_{p}(T) measurements of the heavy fermion normal-spinel structure compound LiV_{2}O_{4} were carried out using a heat-pulse calorimeter over the temperature T range from 1.2 to 108 K. The electronic specific heat C_{e}(T) of LiV_{2}O_{4} ... More
Steiner Variations on Random SurfacesFeb 03 1993Ambartzumian suggested that the modified Steiner action functional had desirable properties for a random surface action. However, Durhuus and Jonsson pointed out that such an action led to an ill-defined grand-canonical partition function and suggested ... More
Linear-response reflection coefficient of the recorder air-jet amplifierFeb 07 2015Dec 09 2015In a duct-flute such as the recorder, steady-state oscillations are controlled by two parameters, the blowing pressure and the frequency of the acoustic resonator. As in most feedback oscillators, the oscillation amplitude is determined by gain-saturation ... More
The Gonihedric Ising Model and GlassinessSep 10 2007The Gonihedric 3D Ising model is a lattice spin model in which planar Peierls boundaries between + and - spins can be created at zero energy cost. Instead of weighting the area of Peierls boundaries as the case for the usual 3D Ising model with nearest ... More
Ising Spins on Thin GraphsJul 28 1994The Ising model on ``thin'' graphs (standard Feynman diagrams) displays several interesting properties. For ferromagnetic couplings there is a mean field phase transition at the corresponding Bethe lattice transition point. For antiferromagnetic couplings ... More
Softening of First-Order Phase Transition on Quenched Random Gravity GraphsJul 16 1996We perform extensive Monte Carlo simulations of the 10-state Potts model on quenched two-dimensional $\Phi^3$ gravity graphs to study the effect of quenched coordination number randomness on the nature of the phase transition, which is strongly first ... More
Magnetic susceptibility of frustrated spin-s J1-J2 quantum Heisenberg magnets: High-temperature expansion and exact diagonalization dataJan 22 2014Motivated by recent experiments on low-dimensional frustrated quantum magnets with competing nearest-neighbor exchange coupling J1 and next nearest-neighbor exchange coupling J2 we investigate the magnetic susceptibility of two-dimensional J1-J2 Heisenberg ... More
Quenching 2D Quantum GravityJan 19 1994We simulate the Ising model on a set of fixed random $\phi^3$ graphs, which corresponds to a {\it quenched} coupling to 2D gravity rather than the annealed coupling that is usually considered. We investigate the critical exponents in such a quenched ensemble ... More
Oscillating magnetoresistance due to fragile spin structure in metallic GdPd$_3$Nov 05 2016Studies on the phenomenon of magnetoresistance (MR) have produced intriguing and application-oriented outcomes for decades--colossal MR, giant MR and recently discovered extremely large MR of millions of percents in semimetals can be taken as examples. ... More
Potts Models with (17) Invisible States on Thin GraphsMar 04 2013Apr 24 2013The order of a phase transition is usually determined by the nature of the symmetry breaking at the phase transition point and the dimension of the model under consideration. For instance, q-state Potts models in two dimensions display a second order, ... More
Antiferromagnetism in EuNiGe3Nov 15 2012The synthesis and crystallographic and physical properties of polycrystalline EuNiGe3 are reported. EuNiGe3 crystallizes in the noncentrosymmetric body-centered tetragonal BaNiSn3-type structure. The physical property data consistently demonstrate that ... More
The Dual Gonihedric 3D Ising ModelApr 16 2011We investigate the dual of the kappa=0 Gonihedric Ising model on a 3D cubic lattice, which may be written as an anisotropically coupled Ashkin-Teller model. The original kappa=0 Gonihedric model has a purely plaquette interaction, displays a first order ... More
Examining the metal-to-insulator transitions in Li1+xTi2-xO4 and LiAlyTi2-yO4 with a Quantum Site Percolation modelOct 26 2003We have studied the composition-induced metal-to-insulator transitions of cation substituted Lithium Titanate, in the forms Li1+xTi2-xO4 and LiAlyTi2-yO4, utilising a quantum site percolation model, and we argue that such a model provides a very reliable ... More
Thin Absolute VillainsOct 18 1995We perform simulations of an absolute value version of the Villain model on phi3 and phi4 Feynman diagrams, ``thin'' 3-regular and 4-regular random graphs. The phi4 results are in excellent quantitative agreement with the exact calculations by Dorey and ... More
Magnetic and thermal properties of the S = 1/2 zig-zag spin-chain compound In2VO5Aug 27 2007Aug 29 2007Static magnetic susceptibility \chi, ac susceptibility \chi_{ac} and specific heat C versus temperature T measurements on polycrystalline samples of In2VO5 and \chi and C versus T measurements on the isostructural, nonmagnetic compound In2TiO5 are reported. ... More
EuCo2P2: A Model Molecular-Field Helical Heisenberg AntiferromagnetDec 09 2015The Eu spins-7/2 in EuCo2P2 with the tetragonal ThCr2Si2-type structure have the prototypical noncollinear helical antiferromagnetic structure below the Neel temperature TN = 66.5 K as previously determined from single-crystal neutron diffraction measurements. ... More
Unusual Magnetic, Thermal, and Transport Behaviors of Single Crystal EuRh2As2Feb 02 2009An antiferromagnetic transition is observed in single crystal EuRh2As2 at a high temperature T_N = 47 K compared to the ferromagnetic Weiss temperature theta = 12 K. We show that this is, surprisingly, consistent with mean field theory. A first-order ... More
Statistical Analysis of Extra-galactic Rotation MeasuresOct 27 2004We have performed a statistical analysis of a sample of 1100 extra-galactic rotation measures (RMs) obtained from the literature. Using a subsample of approximately 800 reliable RMs we compute a rotation measure sky and determine reliable large scale ... More
A Gauge Invariant Dual Gonihedric 3D Ising ModelJun 23 2011We note that two formulations of dual gonihedric Ising models in 3d, one based on using Wegner's general framework for duality to construct a dual Hamiltonian for codimension one surfaces, the other on constructing a dual Hamiltonian for two-dimensional ... More
Scaling in Steiner Random SurfacesNov 26 1993It has been suggested that the modified Steiner action functional has desirable properties for a random surface action. In this paper we investigate the scaling of the string tension and massgap in a variant of this action on dynamically triangulated ... More
Synthesis, Characterization and Magnetic Susceptibility of the Heavy Fermion Transition Metal Oxide LiV_{2}O_{4}Dec 01 1998The preparative method, characterization and magnetic susceptibility \chi measurements versus temperature T of the heavy fermion transition metal oxide LiV_{2}O_{4} are reported in detail. The intrinsic \chi(T) shows a nearly T-independent behavior below ... More
Helical Antiferromagnetic Ordering in Lu{1-x}Sc{x}MnSi (x = 0, 0.25, 0.50)May 01 2014Polycrystalline samples of Lu{1-x}Sc{x}MnSi (x= 0, 0.25, 0.50) are studied using powder x-ray diffraction (XRD), heat capacity Cp, magnetization M, magnetic susceptibility chi, and electrical resistivity rho measurements versus temperature T and magnetic ... More
Softening Transitions with Quenched 2D GravitySep 27 1996We perform extensive Monte Carlo simulations of the 10-state Potts model on quenched two-dimensional $\Phi^3$ gravity graphs to study the effect of quenched connectivity disorder on the phase transition, which is strongly first order on regular lattices. ... More
Gonihedric 3D Ising ActionsAug 24 1995Feb 28 1996We investigate a generalized Ising action containing nearest neighbour, next to nearest neighbour and plaquette terms that has been suggested as a potential string worldsheet discretization on cubic lattices by Savvidy and Wegner. We use both mean field ... More
Spin Glasses on Thin GraphsMay 08 1995Jun 27 1995In a recent paper we found strong evidence from simulations that the Isingantiferromagnet on ``thin'' random graphs - Feynman diagrams - displayed amean-field spin glass transition. The intrinsic interest of considering such random graphs is that they ... More
Large Miscibility Gap in the Ba(Mn_xFe_{1-x})2As2 SystemApr 01 2011Jul 20 2011The compounds BaMn2As2 and BaFe2As2 both crystallize in the body-centered-tetragonal ThCr2Si2-type (122-type) structure at room temperature but exhibit quite different unit cell volumes and very different magnetic and electronic transport properties. ... More
Another Dual Gonihedric 3D Ising ModelJun 01 2011The gonihedric Ising Hamiltonians defined in three and higher dimensions by Savvidy and Wegner provide an extensive, and little explored, catalogue of spin models on (hyper)cubic lattices with many interesting features. In three dimensions the kappa=0 ... More
The Information Geometry of the Ising Model on Planar Random GraphsJul 24 2002Sep 30 2002It has been suggested that an information geometric view of statistical mechanics in which a metric is introduced onto the space of parameters provides an interesting alternative characterisation of the phase structure, particularly in the case where ... More
Decorating Random QuadrangulationsAug 01 2001On various regular lattices (simple cubic, body centred cubic..) decorating an edge with an Ising spin coupled by bonds of strength L to the original vertex spins and competing with a direct anti-ferromagnetic bond of strength alpha L can give rise to ... More
Gonihedric Ising ActionsJul 01 1996We discuss a generalized Ising action containing nearest neighbour, next to nearest neighbour and plaquette terms that has been suggested as a potential string worldsheet discretization on cubic lattices by Savvidy and Wegner. This displays both first ... More
Dgsos on DTRSAug 27 1993We perform simulations of a discrete gaussian solid on solid (DGSOS) model on dynamical $\phi^3$ graphs, which is equivalent to coupling the model to 2d quantum gravity, using the cluster algorithms recently developed by Evertz use on fixed ... More
Oscillating magnetoresistance due to fragile spin structure in metallic GdPd$_3$Nov 05 2016Feb 25 2017Studies on the phenomenon of magnetoresistance (MR) have produced intriguing and application-oriented outcomes for decades--colossal MR, giant MR and recently discovered extremely large MR of millions of percents in semimetals can be taken as examples. ... More
Thermodynamics of the Noninteracting Bose Gas in a Two-Dimensional BoxAug 31 2015Bose-Einstein condensation (BEC) of a noninteracting Bose gas of N particles in a two-dimensional box with Dirichlet boundary conditions is studied. Confirming previous work, we find that BEC occurs at finite N at low temperatures T without the occurrence ... More
Dysonian Electron-Spin-Resonance Spectra of Local Magnetic Moments in MetalsAug 16 2018Dec 18 2018The absorptive and dispersive components of the frequency-dependent magnetic susceptibility both contribute to the electron-spin resonance (ESR) radio-frequency (rf) power absorption of local magnetic moments in metals according to Dyson's theory. The ... More
Magnetic Structure and Magnetization of Helical Antiferromagnets in High Magnetic Fields Perpendicular to the Helix Axis at Zero TemperatureJul 11 2017Sep 06 2017The zero-temperature angles of magnetic moments in a helix or sinusoidal fan confined to the xy plane, with respect to an in-plane magnetic field Hx applied perpendicular to the z axis of a helix or fan, are calculated for commensurate helices and fans ... More
Gonihedric (and Fuki-Nuke) OrderJul 13 2012A 3D Ising model with a purely plaquette, 4-spin interaction displays a planar flip symmetry intermediate between a global and a gauge symmetry and as a consequence has a highly degenerate low temperature phase and no standard magnetic order parameter. ... More
Ising and Potts Models on Quenched Random Gravity GraphsJul 29 1999We report on single-cluster Monte Carlo simulations of the Ising, 4-state Potts and 10-state Potts models on quenched ensembles of planar, tri-valent random graphs. We confirm that the first-order phase transition of the 10-state Potts model on regular ... More
Translated Chemical Reaction NetworksMay 24 2013Jun 11 2013Many biochemical and industrial applications involve complicated networks of simultaneously occurring chemical reactions. Under the assumption of mass action kinetics, the dynamics of these chemical reaction networks are governed by systems of polynomial ... More
A Computational Approach to Extinction Events in Chemical Reaction Networks with Discrete State SpacesJan 08 2017Jan 10 2017Recent work of M.D. Johnston et al. has produced sufficient conditions on the structure of a chemical reaction network which guarantee that the corresponding discrete state space system exhibits an extinction event. The conditions consist of a series ... More
Magnetic Dipole Interactions in CrystalsMay 04 2015Jan 15 2016The influence of magnetic dipole interactions (MDIs) on the magnetic properties of local-moment spin systems is investigated. The eigenvalues and eigenvectors of the MDI tensor are determined for a wide variety of spin lattices and magnetic wavevectors ... More
Unified Molecular Field Theory for Collinear and Noncollinear Heisenberg AntiferromagnetsJul 23 2014Feb 27 2015A unified molecular field theory (MFT) is presented that applies to both collinear and planar noncollinear Heisenberg antiferromagnets (AFs) on the same footing. The spins in the system are assumed to be identical and crystallographically equivalent. ... More
The Puzzle of High Temperature Superconductivity in Layered Iron Pnictides and ChalcogenidesMay 24 2010Aug 10 2010The response of the worldwide scientific community to the discovery in 2008 of superconductivity at Tc = 26 K in the Fe-based compound LaFeAsO_{1-x}F_x has been very enthusiastic. In short order, other Fe-based superconductors with the same or related ... More
Thermodynamic Properties of the van der Waals FluidFeb 05 2014The van der Waals (vdW) theory of fluids is the first and simplest theory that takes into account interactions between the particles of a system that result in a phase transition versus temperature. Combined with Maxwell's construction, this mean-field ... More
Electronic Band Structure, Wavefunctions, and Electron Probability Densities of the One-Dimensional Kronig-Penney Dirac delta-Function ModelMay 28 2019The Dirac delta-function version of the one-dimensional Kronig-Penney model of the electronic band structure for an electron in a ring containing a large number N of positive ions with period a is considered, following the outlines of the formalism previously ... More
The Wrong Kind of GravityMay 11 1999The KPZ formula shows that coupling central charge less than one spin models to 2D quantum gravity dresses the conformal weights to get new critical exponents, where the relation between the original and dressed weights depends only on the central charge. ... More
Glassy transition and metastability in four-spin Ising modelDec 07 1998Sep 29 1999Using Monte Carlo simulations we show that the three-dimensional Ising model with four-spin (plaquette) interactions has some characteristic glassy features. The model dynamically generates diverging energy barriers, which give rise to slow dynamics at ... More
Crystallization of a supercooled liquid and of a glass - Ising model approachMay 31 2001Using Monte Carlo simulations we study crystallization in the three-dimensional Ising model with four-spin interaction. We monitor the morphology of crystals which grow after placing crystallization seeds in a supercooled liquid. Defects in such crystals ... More
The Yang Lee Edge Singularity on Feynman DiagramsJan 21 1998We investigate the Yang-Lee edge singularity on non-planar random graphs, which we consider as the Feynman Diagrams of various d=0 field theories, in order to determine the value of the edge exponent. We consider the hard dimer model on phi3 and phi4 ... More
A Linear Programming Approach to Dynamical Equivalence, Linear Conjugacy, and the Deficiency One TheoremJan 22 2016Mar 01 2016The well-known Deficiency One Theorem gives structural conditions on a chemical reaction network under which, for any set of parameter values, the steady states of the corresponding mass action system may be easily characterized. It is also known, however, ... More
A Computational Approach to Steady State Correspondence of Regular and Generalized Mass Action SystemsJul 17 2014Jul 21 2014It has been recently observed that the dynamical properties of mass action systems arising from many models of biochemical reaction networks can be derived by considering the corresponding properties of a related generalized mass action system. The correspondence ... More
Tensionless structure of glassy phaseJun 12 2001We study a class of homogeneous finite-dimensional Ising models which were recently shown to exhibit glassy properties. Monte Carlo simulations of a particular three-dimensional model in this class show that the glassy phase obtained under slow cooling ... More
Cooling-rate effects in a model of (ideal?) glassOct 22 1999Using Monte Carlo simulations we study cooling-rate effects in a three-dimensional Ising model with four-spin interaction. During coarsening, this model develops growing energy barriers which at low temperature lead to very slow dynamics. We show that ... More
Influence of classical anisotropy fields on the properties of Heisenberg antiferromagnets within unified molecular field theoryOct 09 2017A comprehensive study of the influence of classical anisotropy fields on the magnetic properties of Heisenberg antiferromagnets within unified molecular field theory versus temperature T, magnetic field H, and anisotropy field parameter hA1 is presented ... More
A class of Baker-Akhiezer arrangementsDec 14 2012We study a class of arrangements of lines with multiplicities on the plane which admit the Chalykh-Veselov Baker-Akhiezer function. These arrangements are obtained by adding multiplicity one lines in an invariant way to any dihedral arrangement with invariant ... More
Superconductivity above 10 K in Non-Cuprate OxidesSep 26 2010Nov 04 2010Beginning in 1973, several non-cuprate transition metal and non-transition metal oxides were discovered with superconducting transition temperatures between 10 and 30 K. Retrospectives about these discoveries in spinel structure LiTi2O4 and perovskite ... More
Gravity and Random Surfaces on the Lattice - A ReviewJul 08 1996Jul 09 1996We review recent work in the lattice approach to random surfaces and quantum gravity. Our task is made somewhat easier by some very interesting results, particularly in four dimensions, that have appeared recently and which are reported elsewhere in these ... More
A note on "MAPK networks and their capacity for multistationarity due to toric steady states"Jul 21 2014We provide a short supplement to the paper "MAPK networks and their capacity for multistationarity due to toric steady states" by P\'erez Mill\'an and Turjanski. We show that the capacity for toric steady states in the three networks analyzed in that ... More
Evidence for a first order transition in a plaquette 3d Ising-like actionJul 01 1996We investigate a 3d Ising action which corresponds to a a class of models defined by Savvidy and Wegner, originally intended as discrete versions of string theories on cubic lattices. These models have vanishing bare surface tension and the couplings ... More
Experimental evidence of a collinear antiferromagnetic ordering in the frustrated CoAl2O4 spinelAug 23 2013Nuclear magnetic resonance (NMR), neutron diffaction (ND), x-ray diffraction, magnetic susceptibility and specific heat measurements on the frustrated A-site spinel CoAl2O4 compound reveal a collinear antiferromagnetic ordering below Tn = 9.8(2) K. A ... More
Single Crystal 31P NMR Studies of the Frustrated Square Lattice Compound Pb2(VO)(PO4)2Sep 18 2009Dec 04 2009The static and dynamic properties of V^{4+} spins (S = 1/2) in the frustrated square lattice compound Pb2(VO)(PO4)2 were investigated by means of magnetic susceptibility chi and 31P nuclear magnetic resonance (NMR) shift (K) and 31P nuclear spin-lattice ... More
Multi-gap superconductivity and Shubnikov-de Haas oscillations in single crystals of the layered boride OsB_2Jun 29 2010Single crystals of superconducting OsB_2 [T_c = 2.10(5) K] have been grown using a Cu-B eutectic flux. We confirm that OsB_2 crystallizes in the reported orthorhombic structure (space group Pmmn) at room temperature. Both the normal and superconducting ... More
String tension in gonihedric 3D Ising modelsMar 12 1997Mar 13 1997For the 3D gonihedric Ising models defined by Savvidy and Wegner the bare string tension is zero and the energy of a spin interface depends only on the number of bends and self-intersections, in antithesis to the standard nearest-neighbour 3D Ising action. ... More
Superconducting and normal state properties of the layered boride OsB2Dec 22 2006Nov 28 2007OsB_2 crystallizes in an orthorhombic structure (Pmmn) which contains alternate boron and osmium layers stacked along the c-axis. The boron layers consist of puckered hexagons as opposed to the flat graphite-like boron layers in MgB_2. OsB_2 is reported ... More
Competing Magnetic Fluctuations in Iron Pnictide Superconductors: Role of Ferromagnetic Spin Correlations Revealed by NMRAug 29 2015In the iron pnictide superconductors, theoretical calculations have consistently shown enhancements of the static magnetic susceptibility at both the stripe-type antiferromagnetic (AFM) and in-plane ferromagnetic (FM) wavevectors. However, the possible ... More
^{7}Li NMR Study of Heavy Fermion LiV2O4 Containing Magnetic DefectsFeb 09 2008We present a systematic study of the variations of the ^{7}Li NMR properties versus magnetic defect concentration up to 0.83 mol% within the spinel structure of polycrystalline powder samples and a collection of small single crystals of LiV2O4 in the ... More