Quantized charge pumping through a quantum dot by surface acoustic waves

We present a realization of quantized charge pumping. A lateral quantum dot is defined by metallic split gates in a GaAs/AlGaAs heterostructure. A surface acoustic wave whose wavelength is twice the dot length is used to pump single electrons through the dot at a frequency f=3GHz. The pumped current shows a regular pattern of quantization at values I=nef over a range of gate voltage and wave amplitude settings. The observed values of n, the number of electrons transported per wave cycle, are determined by the number of electronic states in the quantum dot brought into resonance with the fermi level of the electron reservoirs during the pumping cycle.Comment: 8 page

Geotechnical Prediction and Performance of Eastern Scheldt Storm Surge Barrier

The construction of the Eastern Scheldt storm surge barrier was completed in 1986. The monitoring system meant to verify the functioning of the barrier during storm conditions became operational in 1988. Data concerning the geotechnical response was collected during the 4 days storm period between February 26 and March 2, 1990. In the paper some results are described. Conclusions with respect to the expected behaviour of the barrier during more extreme storms in future will be drawn in near future

von Neumann Lattices in Finite Dimensions Hilbert Spaces

The prime number decomposition of a finite dimensional Hilbert space reflects itself in the representations that the space accommodates. The representations appear in conjugate pairs for factorization to two relative prime factors which can be viewed as two distinct degrees freedom. These, Schwinger's quantum degrees of freedom, are uniquely related to a von Neumann lattices in the phase space that characterizes the Hilbert space and specifies the simultaneous definitions of both (modular) positions and (modular) momenta. The area in phase space for each quantum state in each of these quantum degrees of freedom, is shown to be exactly $h$, Planck's constant.Comment: 16 page

Reminiscence bump in memory for public events

People tend to recall more personal events from adolescence and early adulthood than from other lifetime periods. Most evidence suggests that differential encoding causes this reminiscence bump. However, the question why personal events are encoded better in those periods is still unanswered. To shed more light on this discussion, we examined memory for public events. Since it is often impossible to ascertain that queried events are equally difficult, we circumvented the issue of equivalence by calculating deviation scores for each trial. We found that participants more frequently answered questions correctly about events that occurred in the period in which they were between 10 and 25 years old. Furthermore, we found that the reminiscence bump was more pronounced for cued recall than for recognition. We argue that these results support the biological account that events are stored better, because the memory system is working more efficiently during adolescence and early adulthood. These results do not falsify the other accounts for differential encoding, because they are not mutually exclusive. People speak of autobiographical memory when they are referring to the memories they have of their own life experiences (Robinson, 1986). Autobiographical memory does not only consist of personal memories that are remembered vividly, but also of autobiographical facts (Brewer, 1986). Some researchers have examined the contents of autobiographical memories (e.g., Fitzgerald, 1988; Niedźwieńska, 2003; Robinson, 1976), whereas other researchers have focused on the temporal distribution of memories of personal events across the lifespan (e.g., Janssen, Chessa, &amp

Multi-Resolution Analysis and Fractional Quantum Hall Effect: an Equivalence Result

In this paper we prove that any multi-resolution analysis of \Lc^2(\R) produces, for some values of the filling factor, a single-electron wave function of the lowest Landau level (LLL) which, together with its (magnetic) translated, gives rise to an orthonormal set in the LLL. We also give the inverse construction. Moreover, we extend this procedure to the higher Landau levels and we discuss the analogies and the differences between this procedure and the one previously proposed by J.-P. Antoine and the author.Comment: Submitted to Journal Mathematical Physisc

Many-body correlations in a multistep variational approach

We discuss a multistep variational approach for the study of many-body correlations. The approach is developed in a boson formalism (bosons representing particle-hole excitations) and based on an iterative sequence of diagonalizations in subspaces of the full boson space. Purpose of these diagonalizations is that of searching for the best approximation of the ground state of the system. The procedure also leads us to define a set of excited states and, at the same time, of operators which generate these states as a result of their action on the ground state. We examine the cases in which these operators carry one-particle one-hole and up to two-particle two-hole excitations. We also explore the possibility of associating bosons to Tamm-Dancoff excitations and of describing the spectrum in terms of only a selected group of these. Tests within an exactly solvable three-level model are provided.Comment: 24 pages, 6 figures, to appear in Phys. Rev.

Conductance and localization in disordered wires: role of evanescent states

This paper extends an earlier analytical scattering matrix treatment of conductance and localization in coupled two- and three Anderson chain systems for weak disorder when evanescent states are present at the Fermi level. Such states exist typically when the interchain coupling exceeds the width of propagating energy bands associated with the various transverse eigenvalues of the coupled tight-binding systems. We calculate reflection- and transmission coefficients in cases where, besides propagating states, one or two evanescent states are available at the Fermi level for elastic scattering of electrons by the disordered systems. We observe important qualitative changes in these coefficients and in the related localization lengths due to ineffectiveness of the evanescent modes for transmission and reflection in the various scattering channels. In particular, the localization lengths are generally significantly larger than the values obtained when evanescent modes are absent. Effects associated with disorder mediated coupling between propagating and evanescent modes are shown to be suppressed by quantum interference effects, in lowest order for weak disorder

Correlated Initial Conditions in Directed Percolation

We investigate the influence of correlated initial conditions on the temporal evolution of a (d+1)-dimensional critical directed percolation process. Generating initial states with correlations ~r^(sigma-d) we observe that the density of active sites in Monte-Carlo simulations evolves as rho(t)~t^kappa. The exponent kappa depends continuously on sigma and varies in the range -beta/nu_{||}<=kappa<=eta. Our numerical results are confirmed by an exact field-theoretical renormalization group calculation.Comment: 10 pages, RevTeX, including 5 encapsulated postscript figure