Detection of potentially pathogenic bacteria in the drinking water distribution system of a hospital in Hungary

The drinking water distribution system of a hospital was investigated using standard cultivation techniques, taxon-specific PCRs targeting pathogenic bacteria, denaturing gradient gel electrophoresis, cloning and sequencing. The results obtained verify the higher sensitivity of PCR compared to cultivation for detecting Legionella and Pseudomonas aeruginosa. Moreover, several other opportunistic pathogenic bacteria, such as Escherichia albertii, Acinetobacter lwoffi and Corynebacterium tuberculostrearicum, were detected, emphasizing that drinking water systems, especially those with stagnant water sections, could be the source of nosocomial infections

Concentration-dependent mobility in organic field-effect transistors probed by infrared spectromicroscopy of the charge density profile

We show that infrared imaging of the charge density profile in organic field-effect transistors (FETs) can probe transport characteristics which are difficult to access by conventional contact-based measurements. Specifically, we carry out experiments and modeling of infrared spectromicroscopy of poly(3-hexylthiophene) (P3HT) FETs in which charge injection is affected by a relatively low resistance of the gate insulators. We conclude that the mobility of P3HT has a power-law density dependence, which is consistent with the activated transport in disorder-induced tails of the density of states.Comment: 3+ pages, 2 figure

Accounting for both electron--lattice and electron--electron coupling in conjugated polymers: minimum total energy calculations on the Hubbard--Peierls hamiltonian

Minimum total energy calculations, which account for both electron--lattice and electron--electron interactions in conjugated polymers are performed for chains with up to eight carbon atoms. These calculations are motivated in part by recent experimental results on the spectroscopy of polyenes and conjugated polymers and shed light on the longstanding question of the relative importance of electron--lattice vs. electron--electron interactions in determining the properties of these systems.Comment: 6 pages, Plain TeX, FRL-PSD-93GR

Dynamical study on polaron formation in a metal/polymer/metal structure

By considering a metal/polymer/metal structure within a tight-binding one-dimensional model, we have investigated the polaron formation in the presence of an electric field. When a sufficient voltage bias is applied to one of the metal electrodes, an electron is injected into the polymer chain, then a self-trapped polaron is formed at a few hundreds of femtoseconds while it moves slowly under a weak electric field (not larger than $$ V/cm). At an electric field between $1.0\times 10^4$ V/cm and $$ V/cm, the polaron is still formed, since the injected electron is bounded between the interface barriers for quite a long time. It is shown that the electric field applied at the polymer chain reduces effectively the potential barrier in the metal/polymer interface

Impurity relaxation mechanism for dynamic magnetization reversal in a single domain grain

The interaction of coherent magnetization rotation with a system of two-level impurities is studied. Two different, but not contradictory mechanisms, the `slow-relaxing ion' and the `fast-relaxing ion' are utilized to derive a system of integro-differential equations for the magnetization. In the case that the impurity relaxation rate is much greater than the magnetization precession frequency, these equations can be written in the form of the Landau-Lifshitz equation with damping. Thus the damping parameter can be directly calculated from these microscopic impurity relaxation processes

Infrared Imaging of the Nanometer-Thick Accumulation Layer in Organic Field-Effect Transistors

We report on infrared (IR) spectro-microscopy of the electronic excitations in nanometer-thick accumulation layers in FET devices based on poly(3-hexylthiophene). IR data allows us to explore the charge injection landscape and uncovers the critical role of the gate insulator in defining relevant length scales. This work demonstrates the unique potential of IR spectroscopy for the investigation of physical phenomena at the nanoscale occurring at the semiconductor-insulator interface in FET devices.Comment: 15 pages, 4 figure

Zero frequency divergence and gauge phase factor in the optical response theory

The static current-current correlation leads to the definitional zero frequency divergence (ZFD) in the optical susceptibilities. Previous computations have shown nonequivalent results between two gauges (${\bf p\cdot A}$ and ${\bf E \cdot r}$) under the exact same unperturbed wave functions. We reveal that those problems are caused by the improper treatment of the time-dependent gauge phase factor in the optical response theory. The gauge phase factor, which is conventionally ignored by the theory, is important in solving ZFD and obtaining the equivalent results between these two gauges. The Hamiltonians with these two gauges are not necessary equivalent unless the gauge phase factor is properly considered in the wavefunctions. Both Su-Shrieffer-Heeger (SSH) and Takayama-Lin-Liu-Maki (TLM) models of trans-polyacetylene serve as our illustrative examples to study the linear susceptibility $\chi^{(1)}$ through both current-current and dipole-dipole correlations. Previous improper results of the $\chi^{(1)}$ calculations and distribution functions with both gauges are discussed. The importance of gauge phase factor to solve the ZFD problem is emphasized based on SSH and TLM models. As a conclusion, the reason why dipole-dipole correlation favors over current-current correlation in the practical computations is explained.Comment: 17 pages, 7 figures, submitted to Phys. Rev.

Giant infrared intensity of the Peierls mode at the neutral-ionic phase transition

We present exact diagonalization results on a modified Peierls-Hubbard model for the neutral-ionic phase transition. The ground state potential energy surface and the infrared intensity of the Peierls mode point to a strong, non-linear electron-phonon coupling, with effects that are dominated by the proximity to the electronic instability rather than by electronic correlations. The huge infrared intensity of the Peierls mode at the ferroelectric transition is related to the temperature dependence of the dielectric constant of mixed-stack organic crystals.Comment: 4 pages, 4 figure

Excitons in quasi-one dimensional organics: Strong correlation approximation

An exciton theory for quasi-one dimensional organic materials is developed in the framework of the Su-Schrieffer-Heeger Hamiltonian augmented by short range extended Hubbard interactions. Within a strong electron-electron correlation approximation, the exciton properties are extensively studied. Using scattering theory, we analytically obtain the exciton energy and wavefunction and derive a criterion for the existence of a $B_u$ exciton. We also systematically investigate the effect of impurities on the coherent motion of an exciton. The coherence is measured by a suitably defined electron-hole correlation function. It is shown that, for impurities with an on-site potential, a crossover behavior will occur if the impurity strength is comparable to the bandwidth of the exciton, corresponding to exciton localization. For a charged impurity with a spatially extended potential, in addition to localization the exciton will dissociate into an uncorrelated electron-hole pair when the impurity is sufficiently strong to overcome the Coulomb interaction which binds the electron-hole pair. Interchain coupling effects are also discussed by considering two polymer chains coupled through nearest-neighbor interchain hopping $t_{\perp}$ and interchain Coulomb interaction $V_{\perp}$. Within the $t$ matrix scattering formalism, for every center-of-mass momentum, we find two poles determined only by $V_{\perp}$, which correspond to the interchain excitons. Finally, the exciton state is used to study the charge transfer from a polymer chain to an adjacent dopant molecule.Comment: 24 pages, 23 eps figures, pdf file of the paper availabl