Non exponential relaxation in fully frustrated models

We study the dynamical properties of the fully frustrated Ising model. Due to the absence of disorder the model, contrary to spin glass, does not exhibit any Griffiths phase, which has been associated to non-exponential relaxation dynamics. Nevertheless we find numerically that the model exhibits a stretched exponential behavior below a temperature T_p corresponding to the percolation transition of the Kasteleyn-Fortuin clusters. We have also found that the critical behavior of this clusters for a fully frustrated q-state spin model at the percolation threshold is strongly affected by frustration. In fact while in absence of frustration the q=1 limit gives random percolation, in presence of frustration the critical behavior is in the same universality class of the ferromagnetic q=1/2-state Potts model.Comment: 7 pages, RevTeX, 11 figs, to appear on Physical Review

Asymptotic behavior of the density of states on a random lattice

We study the diffusion of a particle on a random lattice with fluctuating local connectivity of average value q. This model is a basic description of relaxation processes in random media with geometrical defects. We analyze here the asymptotic behavior of the eigenvalue distribution for the Laplacian operator. We found that the localized states outside the mobility band and observed by Biroli and Monasson (1999, J. Phys. A: Math. Gen. 32 L255), in a previous numerical analysis, are described by saddle point solutions that breaks the rotational symmetry of the main action in the real space. The density of states is characterized asymptotically by a series of peaks with periodicity 1/q.Comment: 11 pages, 2 figure

The effect of cross-linking on the molecular dynamics of the segmental and β Johari–Goldstein processes in polyvinylpyrrolidone-based copolymers

The effect of the cross-link density on the molecular dynamics of copolymers composed of vinylpyrrolidone (VP) and butyl acrylate (BA) was studied using differential scanning calorimetry (DSC) and dielectric relaxation spectroscopy (DRS). A single glass transition was detected by DSC measurements. The dielectric spectra exhibit conductive processes and three dipolar relaxations labeled as a, b and g in the decreasing order of temperatures. The cross-linker content affects both a and b processes, but the fastest g process is relatively unaffected. An increase of cross-linking produces a typical effect on the a process dynamics: (i) the glass transition temperature is increased, (ii) the dispersion is broadened, (iii) its strength is decreased and (iv) the relaxation times are increased. However, the b process, which possesses typical features of a pure Johari Goldstein relaxation, unexpectedly loses the intermolecular character for the highest cross-linker content.B.R.F., M.J.S., P.O.S. and M.C. gratefully acknowledge CICYT for grant MAT2012-33483. F.G. and J.M.G. acknowledge the Spanish Ministerio de Economia y Competitividad-FEDER (MAT2014-54137-R) and the Junta de Castilla y Leon (BU232U13).Redondo Foj, MB.; Sanchis Sánchez, MJ.; Ortiz Serna, MP.; Carsí Rosique, M.; García, JM.; García, FC. (2015). The effect of cross-linking on the molecular dynamics of the segmental and β Johari–Goldstein processes in polyvinylpyrrolidone-based copolymers. Soft Matter. 11:7171-7180. https://doi.org/10.1039/c5sm00714cS7171718011V. Bühler , Polyvinylpyrrolidone Excipients for Pharmaceuticals: Povidone, Crospovidone and Copovidone , Springer , Berlin , 2005Haaf, F., Sanner, A., & Straub, F. (1985). Polymers of N-Vinylpyrrolidone: Synthesis, Characterization and Uses. Polymer Journal, 17(1), 143-152. doi:10.1295/polymj.17.143Gallardo, A., Rocío Lemus, A., San Román, J., Cifuentes, A., & Díez-Masa, J.-C. (1999). Micellar Electrokinetic Chromatography Applied to Copolymer Systems with Heterogeneous Distribution. Macromolecules, 32(3), 610-617. doi:10.1021/ma981144pDevine, D. M., & Higginbotham, C. L. (2005). Synthesis and characterisation of chemically crosslinked N-vinyl pyrrolidinone (NVP) based hydrogels. European Polymer Journal, 41(6), 1272-1279. doi:10.1016/j.eurpolymj.2004.12.022Devine, D. M., Devery, S. M., Lyons, J. G., Geever, L. M., Kennedy, J. E., & Higginbotham, C. L. (2006). Multifunctional polyvinylpyrrolidinone-polyacrylic acid copolymer hydrogels for biomedical applications. International Journal of Pharmaceutics, 326(1-2), 50-59. doi:10.1016/j.ijpharm.2006.07.008Jin, S., Gu, J., Shi, Y., Shao, K., Yu, X., & Yue, G. (2013). Preparation and electrical sensitive behavior of poly (N-vinylpyrrolidone-co-acrylic acid) hydrogel with flexible chain nature. European Polymer Journal, 49(7), 1871-1880. doi:10.1016/j.eurpolymj.2013.04.022Borns, M. A., Kalakkunnath, S., Kalika, D. S., Kusuma, V. A., & Freeman, B. D. (2007). Dynamic relaxation characteristics of crosslinked poly(ethylene oxide) copolymer networks: Influence of short chain pendant groups. Polymer, 48(25), 7316-7328. doi:10.1016/j.polymer.2007.10.020Qazvini, N. T., & Mohammadi, N. (2005). Dynamic mechanical analysis of segmental relaxation in unsaturated polyester resin networks: Effect of styrene content. Polymer, 46(21), 9088-9096. doi:10.1016/j.polymer.2005.06.118Cook, W. D., Scott, T. F., Quay-Thevenon, S., & Forsythe, J. S. (2004). Dynamic mechanical thermal analysis of thermally stable and thermally reactive network polymers. Journal of Applied Polymer Science, 93(3), 1348-1359. doi:10.1002/app.20569Viciosa, M. T., Rouzé, N., Dionísio, M., & Gómez Ribelles, J. L. (2007). Dielectric and mechanical relaxation processes in methyl acrylate/tri-ethyleneglycol dimethacrylate copolymer networks. European Polymer Journal, 43(4), 1516-1529. doi:10.1016/j.eurpolymj.2007.01.043Jobish, J., Charoen, N., & Praveen, P. (2012). Dielectric properties and AC conductivity studies of novel NR/PVA full-interpenetrating polymer networks. Journal of Non-Crystalline Solids, 358(8), 1113-1119. doi:10.1016/j.jnoncrysol.2012.02.003Bekin, S., Sarmad, S., Gürkan, K., Keçeli, G., & Gürdağ, G. (2014). Synthesis, characterization and bending behavior of electroresponsive sodium alginate/poly(acrylic acid) interpenetrating network films under an electric field stimulus. Sensors and Actuators B: Chemical, 202, 878-892. doi:10.1016/j.snb.2014.06.051F. Kremer and A.Schönhals , Broadband Dielectric Spectroscopy , Springer-Verlag , Berlin Heidelberg, New York , 2003Roland, C. M. (1994). Constraints on Local Segmental Motion in Poly(vinylethylene) Networks. Macromolecules, 27(15), 4242-4247. doi:10.1021/ma00093a027Patil, P. N., Rath, S. K., Sharma, S. K., Sudarshan, K., Maheshwari, P., Patri, M., … Pujari, P. K. (2013). Free volumes and structural relaxations in diglycidyl ether of bisphenol-A based epoxy–polyether amine networks. Soft Matter, 9(13), 3589. doi:10.1039/c3sm27525fCasalini, R., & Roland, C. M. (2010). Effect of crosslinking on the secondary relaxation in polyvinylethylene. Journal of Polymer Science Part B: Polymer Physics, 48(5), 582-587. doi:10.1002/polb.21925Carsi, M., Sanchis, M. J., Diaz-Calleja, R., Riande, E., & Nugent, M. J. D. (2012). Effect of Cross-Linking on the Molecular Motions and Nanodomains Segregation in Polymethacrylates Containing Aliphatic Alcohol Ether Residues. Macromolecules, 45(8), 3571-3580. doi:10.1021/ma202811pCarsí, M., Sanchis, M. J., Díaz-Calleja, R., Riande, E., & Nugent, M. J. D. (2013). Effect of slight crosslinking on the mechanical relaxation behavior of poly(2-ethoxyethyl methacrylate) chains. European Polymer Journal, 49(6), 1495-1502. doi:10.1016/j.eurpolymj.2012.12.012Kalakkunnath, S., Kalika, D. S., Lin, H., Raharjo, R. D., & Freeman, B. D. (2007). Molecular Dynamics of Poly(ethylene glycol) and Poly(propylene glycol) Copolymer Networks by Broadband Dielectric Spectroscopy. Macromolecules, 40(8), 2773-2781. doi:10.1021/ma070016aSabater i Serra, R., Escobar Ivirico, J. L., Meseguer Dueñas, J. M., Balado, A. A., Gómez Ribelles, J. L., & Salmerón Sánchez, M. (2009). Segmental dynamics in poly(ε-caprolactone)/poly(L-lactide) copolymer networks. Journal of Polymer Science Part B: Polymer Physics, 47(2), 183-193. doi:10.1002/polb.21629Nogales, A., Sanz, A., Ezquerra, T. A., Quintana, R., & Muñoz-Guerra, S. (2006). Molecular dynamics of poly(butylene tert-butyl isophthalate) and its copolymers with poly(butylene terephthalate) as revealed by broadband dielectric spectroscopy. Polymer, 47(20), 7078-7084. doi:10.1016/j.polymer.2006.07.044Sanz, A., Nogales, A., Ezquerra, T. A., Lotti, N., & Finelli, L. (2004). Cooperativity of theβ-relaxations in aromatic polymers. Physical Review E, 70(2). doi:10.1103/physreve.70.021502Johari, G. P., & Goldstein, M. (1970). Viscous Liquids and the Glass Transition. II. Secondary Relaxations in Glasses of Rigid Molecules. The Journal of Chemical Physics, 53(6), 2372-2388. doi:10.1063/1.1674335Johari, G. P., & Smyth, C. P. (1972). Dielectric Relaxation of Rigid Molecules in Supercooled Decalin. The Journal of Chemical Physics, 56(9), 4411-4418. doi:10.1063/1.1677882Paluch, M., Pawlus, S., Hensel-Bielowka, S., Kaminska, E., Prevosto, D., Capaccioli, S., … Ngai, K. L. (2005). Two secondary modes in decahydroisoquinoline: Which one is the true Johari Goldstein process? The Journal of Chemical Physics, 122(23), 234506. doi:10.1063/1.1931669Ngai, K. L. (1998). Relation between some secondary relaxations and the α relaxations in glass-forming materials according to the coupling model. The Journal of Chemical Physics, 109(16), 6982-6994. doi:10.1063/1.477334Ngai, K. L., & Paluch, M. (2004). Classification of secondary relaxation in glass-formers based on dynamic properties. The Journal of Chemical Physics, 120(2), 857-873. doi:10.1063/1.1630295Casalini, R., Ngai, K. L., & Roland, C. M. (2003). Connection between the high-frequency crossover of the temperature dependence of the relaxation time and the change of intermolecular coupling in glass-forming liquids. Physical Review B, 68(1). doi:10.1103/physrevb.68.014201Ngai, K. L., & Tsang, K. Y. (1999). Similarity of relaxation in supercooled liquids and interacting arrays of oscillators. Physical Review E, 60(4), 4511-4517. doi:10.1103/physreve.60.4511Donth, E. (1996). Characteristic length of the glass transition. Journal of Polymer Science Part B: Polymer Physics, 34(17), 2881-2892. doi:10.1002/(sici)1099-0488(199612)34:173.0.co;2-uWilliams, G. (s. f.). Molecular aspects of multiple dielectric relaxation processes in solid polymers. Electric Phenomena in Polymer Science, 59-92. doi:10.1007/3-540-09456-3_3Ngai, K., & Capaccioli, S. (2004). Relation between the activation energy of the Johari-Goldstein β relaxation and T_{g} of glass formers. Physical Review E, 69(3). doi:10.1103/physreve.69.031501Casalini, R., & Roland, C. M. (2003). Pressure Evolution of the Excess Wing in a Type-BGlass Former. Physical Review Letters, 91(1). doi:10.1103/physrevlett.91.015702Redondo-Foj, B., Carsí, M., Ortiz-Serna, P., Sanchis, M. J., García, F., & García, J. M. (2013). Relaxational study of poly(vinylpyrrolidone-co-butyl acrylate) membrane by dielectric and dynamic mechanical spectroscopy. Journal of Physics D: Applied Physics, 46(29), 295304. doi:10.1088/0022-3727/46/29/295304Redondo-Foj, B., Carsí, M., Ortiz-Serna, P., Sanchis, M. J., Vallejos, S., García, F., & García, J. M. (2014). Effect of the Dipole–Dipole Interactions in the Molecular Dynamics of Poly(vinylpyrrolidone)-Based Copolymers. Macromolecules, 47(15), 5334-5346. doi:10.1021/ma500800aBershtein, V. A., Egorova, L. M., Yakushev, P. N., Pissis, P., Sysel, P., & Brozova, L. (2002). Molecular dynamics in nanostructured polyimide-silica hybrid materials and their thermal stability. Journal of Polymer Science Part B: Polymer Physics, 40(10), 1056-1069. doi:10.1002/polb.10162Alves, N. M., Gómez Ribelles, J. L., & Mano, J. F. (2005). Enthalpy relaxation studies in polymethyl methacrylate networks with different crosslinking degrees. Polymer, 46(2), 491-504. doi:10.1016/j.polymer.2004.11.016Scott, T. F., Cook, W. D., & Forsythe, J. S. (2002). Kinetics and network structure of thermally cured vinyl ester resins. European Polymer Journal, 38(4), 705-716. doi:10.1016/s0014-3057(01)00244-0Wagner, K. W. (1914). Erklärung der dielektrischen Nachwirkungsvorgänge auf Grund Maxwellscher Vorstellungen. Archiv für Elektrotechnik, 2(9), 371-387. doi:10.1007/bf01657322Hodge, I. M., Ngai, K. L., & Moynihan, C. T. (2005). Comments on the electric modulus function. Journal of Non-Crystalline Solids, 351(2), 104-115. doi:10.1016/j.jnoncrysol.2004.07.089Williams, G., & Watts, D. C. (1970). Non-symmetrical dielectric relaxation behaviour arising from a simple empirical decay function. Transactions of the Faraday Society, 66, 80. doi:10.1039/tf9706600080Williams, G., Watts, D. C., Dev, S. B., & North, A. M. (1971). Further considerations of non symmetrical dielectric relaxation behaviour arising from a simple empirical decay function. Transactions of the Faraday Society, 67, 1323. doi:10.1039/tf9716701323Havriliak, S., & Negami, S. (1967). A complex plane representation of dielectric and mechanical relaxation processes in some polymers. Polymer, 8, 161-210. doi:10.1016/0032-3861(67)90021-3Havriliak, S., & Negami, S. (2007). A complex plane analysis of α-dispersions in some polymer systems. Journal of Polymer Science Part C: Polymer Symposia, 14(1), 99-117. doi:10.1002/polc.5070140111S. Havriliak and S.Negami , Dielectric and Mechanical Relaxation in Materials , Hanser , Munich , 1997 , p. 57Glatz-Reichenbach, J. K. W., Sorriero, L., & Fitzgerald, J. J. (1994). Influence of Crosslinking on the Molecular Relaxation of an Amorphous Copolymer Near Its Glass-Transition Temperature. Macromolecules, 27(6), 1338-1343. doi:10.1021/ma00084a010Cole, K. S., & Cole, R. H. (1941). Dispersion and Absorption in Dielectrics I. Alternating Current Characteristics. The Journal of Chemical Physics, 9(4), 341-351. doi:10.1063/1.1750906Boyd, R. H. (1985). Relaxation processes in crystalline polymers: experimental behaviour — a review. Polymer, 26(3), 323-347. doi:10.1016/0032-3861(85)90192-2Laredo, E., Grimau, M., Sánchez, F., & Bello, A. (2003). Water Absorption Effect on the Dynamic Properties of Nylon-6 by Dielectric Spectroscopy. Macromolecules, 36(26), 9840-9850. doi:10.1021/ma034954wHuo, P., & Cebe, P. (1992). Dielectric relaxation of poly(phenylene sulfide) containing a fraction of rigid amorphous phase. Journal of Polymer Science Part B: Polymer Physics, 30(3), 239-250. doi:10.1002/polb.1992.090300303Noda, N., Lee, Y.-H., Bur, A. J., Prabhu, V. M., Snyder, C. R., Roth, S. C., & McBrearty, M. (2005). Dielectric properties of nylon 6/clay nanocomposites from on-line process monitoring and off-line measurements. Polymer, 46(18), 7201-7217. doi:10.1016/j.polymer.2005.06.046Ryabov, Y. E., Nuriel, H., Marom, G., & Feldman, Y. (2002). Relaxation peak broadening and polymer chain dynamics in aramid-fiber-reinforced nylon-66 microcomposites. Journal of Polymer Science Part B: Polymer Physics, 41(3), 217-223. doi:10.1002/polb.10384Janik, P., Paluch, M., Ziolo, J., Sulkowski, W., & Nikiel, L. (2001). Low-frequency dielectric relaxation in rubber. Physical Review E, 64(4). doi:10.1103/physreve.64.042502Feldman, Y., Puzenko, A., & Ryabov, Y. (2002). Non-Debye dielectric relaxation in complex materials. Chemical Physics, 284(1-2), 139-168. doi:10.1016/s0301-0104(02)00545-1Ortiz-Serna, P., Díaz-Calleja, R., Sanchis, M. J., Floudas, G., Nunes, R. C., Martins, A. F., & Visconte, L. L. (2010). Dynamics of Natural Rubber as a Function of Frequency, Temperature, and Pressure. A Dielectric Spectroscopy Investigation. Macromolecules, 43(11), 5094-5102. doi:10.1021/ma1004869Ortiz-Serna, P., Díaz-Calleja, R., Sanchis, M. J., Riande, E., Nunes, R., Martins, A., & Visconte, L. (2011). Dielectric spectroscopy of natural rubber-cellulose II nanocomposites. Journal of Non-Crystalline Solids, 357(2), 598-604. doi:10.1016/j.jnoncrysol.2010.06.044E. Riande and R.Díaz-Calleja , Electrical Properties of Polymers , Marcel Dekker , New York , 2004Fulcher, G. S. (1925). ANALYSIS OF RECENT MEASUREMENTS OF THE VISCOSITY OF GLASSES. Journal of the American Ceramic Society, 8(6), 339-355. doi:10.1111/j.1151-2916.1925.tb16731.xTammann, G., & Hesse, W. (1926). Die Abhängigkeit der Viscosität von der Temperatur bie unterkühlten Flüssigkeiten. Zeitschrift für anorganische und allgemeine Chemie, 156(1), 245-257. doi:10.1002/zaac.19261560121Lunkenheimer, P., Schneider, U., Brand, R., & Loid, A. (2000). Glassy dynamics. Contemporary Physics, 41(1), 15-36. doi:10.1080/001075100181259Angell, C. A. (1995). Formation of Glasses from Liquids and Biopolymers. Science, 267(5206), 1924-1935. doi:10.1126/science.267.5206.1924C. A. Angell , Complex Behavior of Glassy Systems; Proceedings of the XIV Sitges Conference , Sitges, Barcelona, Spain, 1996F. J. Bermejo , H. E.Fischer , M. A.Ramos , A.de Andrés , J.Dawidowski and V.Fayos , in Complex Behaviour of Glassy Systems , Springer Lecture Notes in Physics , ed. M. Rubí and C. Pérez-Vicente , Springer , Berlin-Heidelberg , 1997Böhmer, R., Ngai, K. L., Angell, C. A., & Plazek, D. J. (1993). Nonexponential relaxations in strong and fragile glass formers. The Journal of Chemical Physics, 99(5), 4201-4209. doi:10.1063/1.466117Böhmer, R., & Angell, C. A. (1992). Correlations of the nonexponentiality and state dependence of mechanical relaxations with bond connectivity in Ge-As-Se supercooled liquids. Physical Review B, 45(17), 10091-10094. doi:10.1103/physrevb.45.10091Böhmer, R., & Angell, C. A. (1993). Elastic and viscoelastic properties of amorphous selenium and identification of the phase transition between ring and chain structures. Physical Review B, 48(9), 5857-5864. doi:10.1103/physrevb.48.5857Merino, E. G., Atlas, S., Raihane, M., Belfkira, A., Lahcini, M., Hult, A., … Correia, N. T. (2011). Molecular dynamics of poly(ATRIF) homopolymer and poly(AN-co-ATRIF) copolymer investigated by dielectric relaxation spectroscopy. European Polymer Journal, 47(7), 1429-1446. doi:10.1016/j.eurpolymj.2011.04.006Angell, C. . (1991). Relaxation in liquids, polymers and plastic crystals — strong/fragile patterns and problems. Journal of Non-Crystalline Solids, 131-133, 13-31. doi:10.1016/0022-3093(91)90266-9Qin, Q., & McKenna, G. B. (2006). Correlation between dynamic fragility and glass transition temperature for different classes of glass forming liquids. Journal of Non-Crystalline Solids, 352(28-29), 2977-2985. doi:10.1016/j.jnoncrysol.2006.04.014Kohlrausch, R. (1854). Theorie des elektrischen Rückstandes in der Leidener Flasche. Annalen der Physik und Chemie, 167(2), 179-214. doi:10.1002/andp.18541670203Zorn, R. (1999). Applicability of distribution functions for the Havriliak-Negami spectral function. Journal of Polymer Science Part B: Polymer Physics, 37(10), 1043-1044. doi:10.1002/(sici)1099-0488(19990515)37:103.0.co;2-hNgai, K. L., & Roland, C. M. (1993). Intermolecular cooperativity and the temperature dependence of segmental relaxation in semicrystalline polymers. Macromolecules, 26(11), 2688-2690. doi:10.1021/ma00063a008K. L. Ngai , Relaxation and diffusion in complex systems , Springer , Berlin , 2011Ikeda, M., & Aniya, M. (2010). Correlation between fragility and cooperativity in bulk metallic glass-forming liquids. Intermetallics, 18(10), 1796-1799. doi:10.1016/j.intermet.2010.01.009Patkowski, A., Paluch, M., & Gapiński, J. (2003). Relationship between T0, Tg and their pressure dependence for supercooled liquids. Journal of Non-Crystalline Solids, 330(1-3), 259-263. doi:10.1016/j.jnoncrysol.2003.09.002Delpouve, N., Delbreilh, L., Stoclet, G., Saiter, A., & Dargent, E. (2014). Structural Dependence of the Molecular Mobility in the Amorphous Fractions of Polylactide. Macromolecules, 47(15), 5186-5197. doi:10.1021/ma500839

The Radius of Metric Subregularity

There is a basic paradigm, called here the radius of well-posedness, which quantifies the "distance" from a given well-posed problem to the set of ill-posed problems of the same kind. In variational analysis, well-posedness is often understood as a regularity property, which is usually employed to measure the effect of perturbations and approximations of a problem on its solutions. In this paper we focus on evaluating the radius of the property of metric subregularity which, in contrast to its siblings, metric regularity, strong regularity and strong subregularity, exhibits a more complicated behavior under various perturbations. We consider three kinds of perturbations: by Lipschitz continuous functions, by semismooth functions, and by smooth functions, obtaining different expressions/bounds for the radius of subregularity, which involve generalized derivatives of set-valued mappings. We also obtain different expressions when using either Frobenius or Euclidean norm to measure the radius. As an application, we evaluate the radius of subregularity of a general constraint system. Examples illustrate the theoretical findings.Comment: 20 page

Concentration Dependence of Superconductivity and Order-Disorder Transition in the Hexagonal Rubidium Tungsten Bronze RbxWO3. Interfacial and bulk properties

We revisited the problem of the stability of the superconducting state in RbxWO3 and identified the main causes of the contradictory data previously published. We have shown that the ordering of the Rb vacancies in the nonstoichiometric compounds have a major detrimental effect on the superconducting temperature Tc.The order-disorder transition is first order only near x = 0.25, where it cannot be quenched effectively and Tc is reduced below 1K. We found that the high Tc's which were sometimes deduced from resistivity measurements, and attributed to compounds with .25 < x < .30, are to be ascribed to interfacial superconductivity which generates spectacular non-linear effects. We also clarified the effect of acid etching and set more precisely the low-rubidium-content boundary of the hexagonal phase.This work makes clear that Tc would increase continuously (from 2 K to 5.5 K) as we approach this boundary (x = 0.20), if no ordering would take place - as its is approximately the case in CsxWO3. This behaviour is reminiscent of the tetragonal tungsten bronze NaxWO3 and asks the same question : what mechanism is responsible for this large increase of Tc despite the considerable associated reduction of the electron density of state ? By reviewing the other available data on these bronzes we conclude that the theoretical models which are able to answer this question are probably those where the instability of the lattice plays a major role and, particularly, the model which call upon local structural excitations (LSE), associated with the missing alkali atoms.Comment: To be published in Physical Review

Broadband Dielectric Spectroscopy on Glass-Forming Propylene Carbonate

Dielectric spectroscopy covering more than 18 decades of frequency has been performed on propylene carbonate in its liquid and supercooled-liquid state. Using quasi-optic submillimeter and far-infrared spectroscopy the dielectric response was investigated up to frequencies well into the microscopic regime. We discuss the alpha-process whose characteristic timescale is observed over 14 decades of frequency and the excess wing showing up at frequencies some three decades above the peak frequency. Special attention is given to the high-frequency response of the dielectric loss in the crossover regime between alpha-peak and boson-peak. Similar to our previous results in other glass forming materials we find evidence for additional processes in the crossover regime. However, significant differences concerning the spectral form at high frequencies are found. We compare our results to the susceptibilities obtained from light scattering and to the predictions of various models of the glass transition.Comment: 13 pages, 9 figures, submitted to Phys. Rev.

Intelligent Financial Fraud Detection Practices: An Investigation

Financial fraud is an issue with far reaching consequences in the finance industry, government, corporate sectors, and for ordinary consumers. Increasing dependence on new technologies such as cloud and mobile computing in recent years has compounded the problem. Traditional methods of detection involve extensive use of auditing, where a trained individual manually observes reports or transactions in an attempt to discover fraudulent behaviour. This method is not only time consuming, expensive and inaccurate, but in the age of big data it is also impractical. Not surprisingly, financial institutions have turned to automated processes using statistical and computational methods. This paper presents a comprehensive investigation on financial fraud detection practices using such data mining methods, with a particular focus on computational intelligence-based techniques. Classification of the practices based on key aspects such as detection algorithm used, fraud type investigated, and success rate have been covered. Issues and challenges associated with the current practices and potential future direction of research have also been identified.Comment: Proceedings of the 10th International Conference on Security and Privacy in Communication Networks (SecureComm 2014

Theory of Coexistence of Superconductivity and Ferroelectricity : A Dynamical Symmetry Model

We propose and investigate a model for the coexistence of Superconductivity (SC) and Ferroelectricity (FE) based on the dynamical symmetries $su(2)$ for the pseudo-spin SC sector, $h(4)$ for the displaced oscillator FE sector, and $su(2) \otimes h(4)$ for the composite system. We assume a minimal symmetry-allowed coupling, and simplify the hamiltonian using a double mean field approximation (DMFA). A variational coherent state (VCS) trial wave-function is used for the ground state: the energy, and the relevant order parameters for SC and FE are obtained. For positive sign of the SC-FE coupling coefficient, a non-zero value of either order parameter can suppress the other (FE polarization suppresses SC and vice versa). This gives some support to "Matthias' Conjecture" [1964], that SC and FE tend to be mutually exclusive. For such a Ferroelectric Superconductor we predict: a) the SC gap $\Delta$ (and $T_c$) will increase with increasing applied pressure when pressure quenches FE as in many ferroelectrics, and b) the FE polarization will increase with increaesing magnetic field up to $H_c$. The last result is equivalent to the prediction of a new type of Magneto-Electric Effect in a coexistent SC-FE material. Some discussion will be given of the relation of these results to the cuprate superconductors.Comment: 46 page

Local influence of boundary conditions on a confined supercooled colloidal liquid

We study confined colloidal suspensions as a model system which approximates the behavior of confined small molecule glass-formers. Dense colloidal suspensions become glassier when confined between parallel glass plates. We use confocal microscopy to study the motion of confined colloidal particles. In particular, we examine the influence particles stuck to the glass plates have on nearby free particles. Confinement appears to be the primary influence slowing free particle motion, and proximity to stuck particles causes a secondary reduction in the mobility of free particles. Overall, particle mobility is fairly constant across the width of the sample chamber, but a strong asymmetry in boundary conditions results in a slight gradient of particle mobility.Comment: For conference proceedings, "Dynamics in Confinement", Grenoble, March 201

Dielectric and thermal relaxation in the energy landscape

We derive an energy landscape interpretation of dielectric relaxation times in undercooled liquids, comparing it to the traditional Debye and Gemant-DiMarzio-Bishop pictures. The interaction between different local structural rearrangements in the energy landscape explains qualitatively the recently observed splitting of the flow process into an initial and a final stage. The initial mechanical relaxation stage is attributed to hopping processes, the final thermal or structural relaxation stage to the decay of the local double-well potentials. The energy landscape concept provides an explanation for the equality of thermal and dielectric relaxation times. The equality itself is once more demonstrated on the basis of literature data for salol.Comment: 7 pages, 3 figures, 41 references, Workshop Disordered Systems, Molveno 2006, submitted to Philosophical Magazin