Low temperature electron transfer in strongly condensed phase

Electron transfer coupled to a collective vibronic degree of freedom is studied in strongly condensed phase and at lower temperatures where quantum fluctuations are essential. Based on an exact representation of the reduced density matrix of the electronic+reaction coordinate compound in terms of path integrals, recent findings on the overdamped limit in quantum dissipative systems are employed. This allows to give for the first time a consistent generalization of the well-known Zusman equations to the quantum domain. Detailed conditions for the range of validity are specified. Using the Wigner transform these results are also extended to the quantum dynamics in full phase space. As an important application electronic transfer rates are derived that comprise adiabatic and nonadiabatic processes in the low temperature regime including nuclear tunneling. Accurate agreement with precise quantum Monte Carlo data is observed.Comment: 16 pages, 6 figures, revised version with minor change

Divergence alone cannot guarantee stable sparse activity patterns if connections are dense

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Detection of liquid xenon scintillation light with a Silicon Photomultiplier

We have studied the feasibility of a silicon photomultiplier (SiPM) to detect liquid xenon (LXe) scintillation light. The SiPM was operated inside a small volume of pure LXe, at -95 degree Celsius, irradiated with an internal Am-241 alpha source. The gain of the SiPM at this temperature was estimated to be 1.8 x 10^6 with bias voltage at 52 V. Based on the geometry of the setup, the quantum efficiency of the SiPM was estimated to be 22% at the Xe wavelength of 178 nm. The low excess noise factor, high single photoelectron detection efficiency, and low bias voltage of SiPMs make them attractive alternative UV photon detection devices to photomultiplier tubes (PMTs) for liquid xenon detectors, especially for experiments requiring a very low energy detection threshold, such as neutralino dark matter searches

Electron Transfer in Donor-Acceptor Systems: Many-Particle Effects and Influence of Electronic Correlations

We investigate electron transfer processes in donor-acceptor systems with a coupling of the electronic degrees of freedom to a common bosonic bath. The model allows to study many-particle effects and the influence of the local Coulomb interaction U between electrons on donor and acceptor sites. Using the non-perturbative numerical renormalization group approach we find distinct differences between the electron transfer characteristics in the single- and two-particle subspaces. We calculate the critical electron-boson coupling alpha_c as a function of $U$ and show results for density-density correlation functions in the whole parameter space. The possibility of many-particle (bipolaronic) and Coulomb-assisted transfer is discussed.Comment: 4 pages, 4 figure

Self-assembled guanine ribbons as wide-bandgap semiconductors

We present a first principle study about the stability and the electronic properties of a new biomolecular solid-state material, obtained by the self-assembling of guanine (G) molecules. We consider hydrogen-bonded planar ribbons in isolated and stacked configurations. These aggregates present electronic properties similar to inorganic wide-bandgap semiconductors. The formation of Bloch-type orbitals is observed along the stacking direction, while it is negligible in the ribbon plane. Global band-like conduction may be affected by a dipole-field which spontaneously arises along the ribbon axis. Our results indicate that G-ribbon assemblies are promising materials for biomolecular nanodevices, consistently with recent experimental results.Comment: 7 pages, 3 figures, to be published in Physica

Quantum Brownian Motion With Large Friction

Quantum Brownian motion in the strong friction limit is studied based on the exact path integral formulation of dissipative systems. In this limit the time-nonlocal reduced dynamics can be cast into an effective equation of motion, the quantum Smoluchowski equation. For strongly condensed phase environments it plays a similar role as master equations in the weak coupling range. Applications for chemical, mesoscopic, and soft matter systems are discussed and reveal the substantial role of quantum fluctuations.Comment: 11 pages, 6 figures, to appear in: Chaos: "100 years of Brownian motion

Inhibition of neurite outgrowth in differentiating mouse N2a neuroblastoma cells by phenyl saligenin phosphate: Effects on MAP kinase (ERK 1/2) activation, neurofilament heavy chain phosphorylation and neuropathy target esterase activity

Sub-lethal concentrations of the organophosphate phenyl saligenin phosphate (PSP) inhibited the outgrowth of axon-like processes in differentiating mouse N2a neuroblastoma cells (IC50 2.5 μM). A transient rise in the phosphorylation state of neurofilament heavy chain (NFH) was detected on Western blots of cell extracts treated with 2.5 μM PSP for 4 h compared to untreated controls, as determined by a relative increase in reactivity with monoclonal antibody Ta51 (anti-phosphorylated NFH) compared to N52 (anti-total NFH). However, cross-reactivity of PSP-treated cell extracts was lower than that of untreated controls after 24 h exposure, as indicated by decreased reactivity with both antibodies. Indirect immunofluorescence analysis with these antibodies revealed the appearance of neurofilament aggregates in the cell bodies of treated cells and reduced axonal staining compared to controls. By contrast, there was no significant change in reactivity with anti-a tubulin antibody B512 at either time point. The activation state of the MAP kinase ERK 1/2 increased significantly after PSP treatment compared to controls, particularly at 4 h, as indicated by increased reactivity with monoclonal antibody E-4 (anti-phosphorylated MAP kinase) but not with polyclonal antibody K-23 (anti-total MAP kinase). The observed early changes were concomitant with almost complete inhibition of the activity of neuropathy target esterase (NTE), one of the proposed early molecular targets in organophosphate-induced delayed neuropathy (OPIDN)

High-Resolution UV Spectroscopy of Molecular Complexes

Information on the structure, the rigidity and the intermolecular potential of molecular complexes is essential to our understanding of the physical and chemical properties of molecular complexes. In this work we would like to demonstrate that rotationally resolved UV spectroscopy provides precise new information on these topics. In particular, the structure and van der Waals bond length of benzene-X complexes (X = Ne, Ar, Kr, Xe, N2) have been experimentally determined. In the benzene-N2 complex with its parallel-stacked configuration, the two constituents, benzene and N2, can rotate against each other. Rotationally resolved vibronic van der Waals bands allow the clear assignment of the excited van der Waals vibrations. Their anharmonicity and the vibrationally averaged rotational constants provide basic information on the intermolecular potential. For the example of the benzene-Ar2 trimer it is shown that isomeric structures exist that are rigid on the nanosecond time scale