Medication errors: an important component of nonadherence to medication in an outpatient population of lung transplant recipients.

Data about medication errors in outpatients are limited. Medication errors, defined as discordance between the most recent flow-sheet version, the patient's diary card or the contents of the pill container were assessed systematically after announcement in an outpatient setting of lung transplant recipients by a direct observation approach. A total of 101 patients took a median of 15 (13-17) different drugs and 31 (26-38) pills daily. A total of 2253 doses of drugs were further analyzed. A total of 152 errors were identified resulting in 303 incorrect doses. Lack of keeping a diary card was the only factor significantly associated with a higher rate of incorrect doses (regression coefficient 0.24, p = 0.02). Furthermore, a significant correlation of medication errors with clinical adverse events could be demonstrated. This study shows that medication errors are frequent in a population which has to comply with a complex drug regimen. The need for error control as a basic requirement for drug adherence must be accentuated. Mostly, medication errors seem to occur system-based. Therefore, redundant error control mechanisms and alertness of both the patient and the care-giver should be initiated systematically.

Random matrix analysis of human EEG data.

We use random matrix theory to demonstrate the existence of generic and subject-independent features of the ensemble of correlation matrices extracted from human EEG data. In particular, the spectral density as well as the level spacings was analyzed and shown to be generic and subject independent. We also investigate number variance distributions. In this case we show that when the measured subject is visually stimulated the number variance displays deviations from the random matrix prediction.

Antisymmetric spin filtering in one-dimensional electron systems with uniform spin-orbit coupling.

We theoretically analyze the possibility to use a ferromagnetic gate as a spin-polarization filter for one-dimensional electron systems formed in semiconductor heterostructures showing strong Rashba spin-orbit interaction. The proposed device is based on the effect of the breaking time-reversal symmetry due to the presence of weak magnetic fields. For a proper strength and magnetic field orientation there appears an energy interval in the electron energy spectrum at which the orientation of spin states is controlled by the direction of the electron velocity. It leads to the natural spin polarization of the electron current if the Fermi energy falls into this energy interval.

Understanding quantum scattering properties in terms of purely classical dynamics: two-dimensional open chaotic billiards.

We study classical and quantum scattering properties of particles in the ballistic regime in two-dimensional chaotic billiards that are models of electron- or micro-waveguides. To this end we construct the purely classical counterparts of the scattering probability (SP) matrix |S(n,m)|(2) and Husimi distributions specializing to the case of mixed chaotic motion (incomplete horseshoe). Comparison between classical and quantum quantities allows us to discover the purely classical dynamical origin of certain general as well as particular features that appear in the quantum description of the system. On the other hand, at certain values of energy the tunneling of the wave function into classically forbidden regions produces striking differences between the classical and quantum quantities. A potential application of this phenomenon in the field of microlasers is discussed briefly. We also see the manifestation of whispering gallery orbits as a self-similar structure in the transmission part of the classical SP matrix.

Classical versus quantum structure of the scattering probability matrix: chaotic waveguides.

The purely classical counterpart of the scattering probability matrix (SPM)/S(n,m)/(2) of the quantum scattering matrix S is defined for two-dimensional quantum waveguides for an arbitrary number of propagating modes M. We compare the quantum and classical structures of /S(n,m)/(2) for a waveguide with generic Hamiltonian chaos. It is shown that even for a moderate number of channels, knowledge of the classical structure of the SPM allows us to predict the global structure of the quantum one and, hence, understand important quantum transport properties of waveguides in terms of purely classical dynamics. It is also shown that the SPM, being an intensity measure, can give additional dynamical information to that obtained by the Poincaré maps.

Whispering gallery modes in open quantum billiards.

The poles of the S matrix and the wave functions of open two-dimensional quantum billiards with convex boundary of different shape are calculated by using the method of complex scaling. Two leads are attached to the cavities. The conductance of the cavities is calculated at energies with one, two, and three open channels in each lead. Bands of overlapping resonance states appear that are localized along the convex boundary of the cavities and contribute coherently to the conductance. These bands correspond to the whispering gallery modes known from classical calculations.

Effective coupling for open billiards.

We derive an explicit expression for the coupling constants of individual eigenstates of a closed billiard that is opened by attaching a waveguide. The Wigner time delay and the resonance positions resulting from the coupling constants are compared to an exact numerical calculation. Deviations can be attributed to evanescent modes in the waveguide and to the finite number of eigenstates taken into account. The influence of the shape of the billiard and of the boundary conditions at the mouth of the waveguide are also discussed. Finally we show that the mean value of the dimensionless coupling constants tends to the critical value when the eigenstates of the billiard follow random-matrix theory.

Headways in traffic flow: remarks from a physical perspective.

Traffic flow can be understood as a realization of a broad class of one dimensional physical systems, where a hard core repulsive interaction competes with a longer ranged attraction between the particles. It can be shown rigorously that the statistical properties of such systems in thermal equilibrium are well described by a family of distributions that stems from the random matrix theory. Analyzing the traffic data from different sources, we show that traffic on real roads belongs to that class of random matrix distributions. Also, various traffic simulation models show a similar behavior. It is demonstrated in such a way that the headway distribution of a highway traffic, that serves usually as a paradigm of systems driven far from equilibrium, is reasonably well described by a distribution originating from equilibrium statistical physics.

Comment on "Models of intermediate spectral statistics".

In this Comment we point out that the semi-Poisson is well suited only as a reference point for the so-called "intermediate statistics," which cannot be interpreted as a universal ensemble, like the Gaussian orthogonal ensemble or the Poissonian statistics. In Ref. 2 it was proposed that the nearest-neighbor distribution P(s) of the spectrum of a Poissonian distributed matrix perturbed by a rank one matrix is similar to the semi-Poisson distribution. We show, however, that the P(s) of this model differs considerably in many aspects from the semi-Poisson. In addition, we give an asymptotic formula for P(s) as s-->0, which gives P'(0)=pisqrt[3]/2 for the slope at s=0. This is different not only from the GOE case, but also from the semi-Poisson prediction.

Two-component interference effect: model of a spin-polarized transport.

The effect of spin-involved interaction on the transport properties of disordered two-dimensional electron systems with ferromagnetic contacts is described using a two-component model. Components representing spin-up and spin-down states are supposed to be coupled at a discrete set of points. We have found that due to the additional interference arising in two-component systems the difference between conductances for the parallel and antiparallel orientations of the contact magnetization changes its sign as a function of the length of the conducting channel.

Spectroscopic studies in open quantum systems

The Hamiltonian H of an open quantum system is non-Hermitian. Its complex eigenvalues E(R) are the poles of the S matrix and provide both the energies and widths of the states. We illustrate the interplay between Re(H) and Im(H) by means of the different interference phenomena between two neighboring resonance states. Level repulsion may occur along the real or imaginary axis (the latter is called resonance trapping). In any case, the eigenvalues of the two states avoid crossing in the complex plane. We then calculate the poles of the S matrix and the corresponding wave functions for a rectangular microwave resonator with a scatter as a function of the area of the resonator as well as of the degree of opening to a waveguide. The calculations are performed by using the method of exterior complex scaling. Re(H) and Im(H) cause changes in the structure of the wave functions which are permanent, as a rule. The resonance picture obtained from the microwave resonator shows all the characteristic features known from the study of many-body systems in spite of the absence of two-body forces. The effects arising from the interplay between resonance trapping and level repulsion along the real axis are not involved in the statistical theory (random matrix theory).

Collective modes in an open microwave billiard

Numerical calculations for a microwave Sinai billiard coupled strongly to a lead are performed as a function of the coupling strength between billiard and lead. They prove the formation of different time scales in an open quantum system at large coupling strength. The short-lived collective states are formed together with many long-lived trapped states.

Frobenius-perron resonances for maps with a mixed phase space

Resonances of the time evolution (Frobenius-Perron) operator P for phase space densities have recently been shown to play a key role for the interrelations of classical, semiclassical, and quantum dynamics. Efficient methods to determine resonances are thus in demand, in particular, for Hamiltonian systems displaying a mix of chaotic and regular behavior. We present a powerful method based on truncating P to a finite matrix which not only allows us to identify resonances but also the associated phase space structures. It is demonstrated to work well for a prototypical dynamical system.