Strong Coupling Theory of Two Level Atoms in Periodic Fields

We present a new convergent strong coupling expansion for two-level atoms in external periodic fields, free of secular terms. As a first application, we show that the coherent destruction of tunnelling is a third-order effect. We also present an exact treatment of the high-frequency region, and compare it with the theory of averaging. The qualitative frequency spectrum of the transition probability amplitude contains an effective Rabi frequency.Comment: 4 pages with 3 figure

Statistical mechanics of temporal association in neural networks with transmission delays

We study the representation of static patterns and temporal sequences in neural networks with signal delays and a stochastic parallel dynamics. For a wide class of delay distributions, the asymptotic network behavior can be described by a generalized Gibbs distribution, generated by a novel Lyapunov functional for the determination dynamics. We extend techniques of equilibrium statistical mechanics so as to deal with time-dependent phenomena, derive analytic results for both retrieval quality and storage capacity, and compare them with numerical simulations

Sleutel van het verleden, sleutel tot de toekomst : de roemrijke cultuurhistorie van de Rijnstrangen als drijvende kracht voor economische vernieuwing. Een evaluatie van kwaliteiten en kansen

In het Rijnstrangengebied is het van groot belang om aan te sluiten bij ontwikkelingen, want er is sprake van een grote ruimtelijke dynamiek. Er zijn opgaven voor natuur, water en de landbouw. Daarnaast kent het gebied een grote toeristische en recreatieve potentie. Bij deze opgaven kan cultuurhistorie een rode lijn zijn, een verbindende factor

Aan de wieg van het waterschap : inventarisatie van dijken, kaden en watergangen in het Gelders rivierengebied : ontwerphandreikingen voor wateropgaven

De studie geeft een inventarisatie van ontginningspatronen van het rivierengebied. Deze patronen reflecteren de geschiedenis van de bewoners én de geschiedenis van het Waterschap. Dijken, kaden en weteringen vormden in tijden van weleer de begrenzing van de dorpspolders. De dorpspolders zijn de voorlopers van de waterschappen. Deze studie van een landschapsarchitect, landschapshistoricus en bodemkundige vertelt een verhaal. Een verhaal over de geschiedenis hoe dit gebied bewoonbaar en bewerkbaar wer

Calculation of Volterra kernels for solutions of nonlinear differential equations

We consider vector-valued autonomous differential equations of the form x' = f(x) + phi with analytic f and investigate the nonanticipative solution operator phi bar right arrow A(phi) in terms of its Volterra series. We show that Volterra kernels of order > 1 occurring in the series expansion of the solution operator A are continuous functions, and establish recurrence relations between the kernels allowing their explicit calculation. A practical tensor calculus is provided for the finite-dimensional case. In addition to analytically calculating the kernels, we present an algorithm to numerically obtain them from the output x(t) through sampling the input space by linear combinations of delta functions. We call this "differential sampling". It is a nonlinear analogue of the classical method of impulse response. We prove a continuity theorem stating that, in the finite-dimensional case, approximate delta functions give rise to approximate Volterra kernels and that continuity holds in the sense of weak convergence. Finally, we discuss a practical implementation of differential sampling and relate it to the Wiener method

On the Observability of Meso- and Macro-scopic Quantum Coherence of Domain Walls in Magnetic Insulators

Results are presented of a numerical calculation of the tunneling gap for a domain wall moving in the double well potential of a pair of voids in a magnetic insulator. Both symmetric and asymmetric double well potentials are considered. It is found that, even in the absence of dissipation, the prospects for observing quantum coherence on a meso- or macro-scopic scale appears unlikely.Comment: 15 pages, Plain LaTex, UBC TP-93-1

Quantum Tunneling of Magnetization in Single Molecular Magnets Coupled to Ferromagnetic Reservoirs

The role of spin polarized reservoirs in quantum tunneling of magnetization and relaxation processes in a single molecular magnet (SMM) is investigated theoretically. The SMM is exchange-coupled to the reservoirs and also subjected to a magnetic field varying in time, which enables the quantum tunneling of magnetization (QTM). The spin relaxation times are calculated from the Fermi golden rule. The exchange interaction with tunneling electrons is shown to affect the spin reversal due to QTM. Furthermore, it is shown that the switching is associated with transfer of a certain charge between the leads.Comment: 5 pages, 3 EPS figures, final version as publishe

Large Deviation Property of Free Energy in p-Body Sherrington-Kirkpatrick Model

Cumulant generating function phi(n) and rate function Sigma(f) of the free energy is evaluated in p-body Sherrington-Kirkpatrick model by using the replica method with the replica number n finite. From a perturbational argument, we show that the cumulant generating function is constant in the vicinity of n = 0. On the other hand, with the help of two analytic properties of phi(n), the behavior of phi(n) is derived again. However this is also shown to be broken at a finite value of n, which gives a characteristic value in the rate function near the thermodynamic value of the free energy. Through the continuation of phi(n) as a function of n, we find out a way to derive the 1RSB solution at least in this model, which is to fix the RS solution to be a monotone increasing function.Comment: 7 pages, 5 figures. accepted for publication in J.Phs.Soc.Jp

Statics and dynamics of an Ashkin-Teller neural network with low loading

An Ashkin-Teller neural network, allowing for two types of neurons is considered in the case of low loading as a function of the strength of the respective couplings between these neurons. The storage and retrieval of embedded patterns built from the two types of neurons, with different degrees of (in)dependence is studied. In particular, thermodynamic properties including the existence and stability of Mattis states are discussed. Furthermore, the dynamic behaviour is examined by deriving flow equations for the macroscopic overlap. It is found that for linked patterns the model shows better retrieval properties than a corresponding Hopfield model.Comment: 20 pages, 6 figures, Latex with postscript figures in one tar.gz fil