R. A. Serota

Phenomenological theory of amorphous magnets with small random anisotropy

The phenomenological model is proposed for amorphous magnets with ferromagnetic exchange and small random anisotropy. A new type of spin-glass state is described. Its behaviour in an external magnetic field is shown to deviate strongly from mean-field theory predictions. The effect of coherent anisotropy is discussed.

A model for stock returns and volatility

We prove that Student’s t-distribution provides one of the better fits to returns of S&P component stocks and the generalized inverse gamma distribution best fits VIX and VXO volatility data. We further prove that stock returns are best fit by the product distribution of the generalized inverse gamma and normal distributions. We find Brown noise in VIX and VXO time series and explain the mean and the variance of the relaxation times on approach to the steady-state distribution.

Distribution of wealth in a network model of the economy

We show, analytically and numerically, that wealth distribution in the Bouchaud–Mezard network model of the economy is described by a three-parameter generalized inverse gamma distribution. In the mean-field limit of a network with any two agents linked, it reduces to the inverse gamma distribution.

Magnetic properties of solids with small random anisotropy

Abstract Equilibrium state and magnetic excitations are studied within a phenomenological model for disordered magnetic systems with ferromagnetic exchange and weak random anisotropies. These systems exhibit the new type of magnetic behaviour characterized by finite ferromagnetic correlation length at zero temperature. Effects of coherent anisotropy and external magnetic field are considered.

Polarizability and absorption of small conducting particles in a time-varying electromagnetic field

Abstract We study small conducting particles and thin films in an oscillating longitudinal electric field. We find the charge, current, and field distribution in the particle, the polarizability and the electric dipole absorption. We account for Thomas–Fermi screening by adding a Ficks diffusion term to Ohms law. Alternatively, we describe a particle as a dielectric body with a non-local dielectric constant which is derived in a microscopic linear-response theory. We show that both approaches are equivalent.

Distribution of Human Response Times

We confirm that distributions of human response times have power-law tails and argue that, among closed-form distributions, the generalized inverse gamma distribution is the most plausible choice for their description. We speculate that the task difficulty tracks the half-width of the distribution and show that it is related to the exponent of the power-law tail. V C 2015 Wiley Periodicals, Inc. Complexity 000: 00–00, 2015

CLASSICAL ABSORPTION IN SMALL METAL PARTICLES AND THIN FILMS

We study the electric dipole absorption in small metal particles and thin films in a longitudnal electric field. In diffusive approximation, we give both the phenomenological and microscopic derivations with the account for Thomas-Fermi screening and Drude relaxation.

Change is time: a comment on "Physiologic time: a hypothesis".

Before Einstein imagined bending a beam of light, he understood that ultimately time is relative and the interval is the proper measure of the space–time continuum. The physiological time hypothesis offers a similar proposal for biological systems. It views state transitions as dependent on rate-limiting relational transactions, rather than a systemindependent timekeeper. The target article proposes a scaling distribution to characterize body mass fluctuations. Moreover, the section of West and West [1] on Stochastic Ontogenetic Mass Growth (SMOG) represents a very general entry point into many biological, social, and other so-called “open” systems. The SOMG model falls squarely into a class of stochastic “birth–death” models described by the following equation:

LEVEL CORRELATIONS AND PERSISTENT CURRENTS IN MESOSCOPIC METALS

We use the exact correlation function of the density of energy levels in a magnetic field to evaluate persistent currents in mesoscopic metals. We also analyze the perturbation theory limit of the correlation function vis-a-vis the perturbation theory limit of the orbital response.

Van Vleck response of a two-level system and mesoscopic orbital magnetism of small metals

We evaluate the mean value of the van Vleck response of a two-level system with level spacing distribution and argue that it describes the orbital magnetism of small conducting particles.