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At least 1,009 records · Page 56Linked to original sources
PubMed2004

Correlated electron transport in molecular electronics.

Theoretical and experimental values to date for the resistances of single molecules commonly disagree by orders of magnitude. By reformulating the transport problem using boundary conditions suitable for correlated many-electron systems, we approach electron transport across molecules from a new standpoint. Application of our correlated formalism to benzene-dithiol gives current-voltage characteristics close to experimental observations. The method can solve the open system quantum many-body problem accurately, treats spin exactly, and is valid beyond the linear response regime.

Journal Article↗
PubMed2004

Dynamics of electron holes in an electron-oxygen-ion plasma.

The dynamics of electron holes (EHs) in an electron-oxygen-ion plasma is studied by means of Vlasov simulations. It is found that EHs are attracted by ion density maxima but repelled by ion density minima. Standing EHs repel ions owing to the positive EH potential, creating an ion density cavity which ejects the EH, which propagates away from the cavity with a constant speed. On the other hand, propagating EHs can be trapped at ion density maxima. The results of our simulations will help in understanding the nonlinear dynamics of EHs in space and laboratory plasmas.

Journal Article↗
PubMed2004

Giant electron-electron scattering in the Fermi-liquid state of Na0.7CoO2.

The in-plane resistivity rho and thermal conductivity kappa of single crystal Na0.7CoO2 were measured down to 40 mK. Verification of the Wiedemann-Franz law, kappa/T=L(0)/rho as T-->0, and observation of a T2 dependence of rho at low temperature establish the existence of a well-defined Fermi-liquid state. The measured value of coefficient A reveals enormous electron-electron scattering, characterized by the largest Kadowaki-Woods ratio A/gamma(2) encountered in any material. The rapid suppression of A with magnetic field suggests a possible proximity to a magnetic quantum critical point. We also speculate on the possible role of magnetic frustration and proximity to a Mott insulator.

Journal Article↗
PubMed2004

Anomalous change in the field dependence of the electronic specific heat of an electron-doped cuprate superconductor.

We present specific heat measurements on Pr(2-x)CexCuO(4-delta) single crystals which show an unexpected change in the field dependence of the electronic specific heat (Cel) from linear at T = 2 K to nonlinear at T > or = 3 K. We consider several possible explanations for this change and propose, as a possible interpretation, a phase transition in the symmetry of the order parameter from nodal (e.g., d wave) at T > or = 3 K to gapped (e.g., s wave) at T = 2 K. Such a phase transition could be an explanation for the previous conflicting experimental results on the pairing symmetry in the electron-doped cuprates.

Journal Article↗
PubMed2004

Electron exchange in dissociative excitation of molecular hydrogen using polarized electrons.

The effects of electron exchange and spin orbit interaction in dissociative excitation processes in H2 molecules have been explored using excitation by polarized electrons. Observations of the circular and linear Stokes polarizations of the Balmer-alpha photons determined the alignment and orientation of the excited atomic hydrogen atoms, the excited molecular states, and the dissociative excitation processes via predissociation with short and long range transitions.

Journal Article↗
PubMed2005

Teleportation of electronic many-qubit states encoded in the electron spin of quantum dots via single photons.

We propose a teleportation scheme that relies only on single-photon measurements and Faraday rotation, for teleportation of many-qubit entangled states stored in the electron spins of a quantum dot system. The interaction between a photon and the two electron spins, via Faraday rotation in microcavities, establishes Greenberger-Horne-Zeilinger entanglement in the spin-photon-spin system. The appropriate single-qubit measurements, and the communication of two classical bits, produce teleportation. This scheme provides the essential link between spintronic and photonic quantum information devices by permitting quantum information to be exchanged between them.

Journal Article↗
PubMed2005

Emission of thermally activated electrons from rare gas clusters irradiated with intense VUV light pulses from a free electron laser.

The ionization dynamics of Ar and Xe clusters irradiated with intense vacuum ultraviolet light from a free-electron laser is investigated using photoelectron spectroscopy. Clusters comprising between 70 and 900 atoms were irradiated with femtosecond pulses at 95 nm wavelength (approximately 13 eV photon energy) and a peak intensity of approximately 4 x 10(12) W/cm2. A broad thermal distribution of emitted electrons from clusters with a maximum kinetic energy up to 30-40 eV is observed. The observation of relatively low-energy photoelectrons is in good agreement with calculations using a time-dependent Thomas-Fermi model and gives experimental evidence of an outer ionization process of the clusters, due to delayed thermoelectronic emission.

Journal Article↗
PubMed2005

Doping evolution of the electronic properties of hole- and electron-doped high-T(c) cuprates: role of density wave correlations.

We show that the presence of two topological quantum critical points (QCP's) in 2D electronic system on a square lattice imposes strong constraints on density-wave (DW) correlations in the high-T(c) cuprates. Electronic properties of the corresponding strongly correlated system are highly reminiscent of the experimental trends in the high-T(c) cuprates. The most interesting results are the existence at low doping of two single-particle gaps different by order of magnitude both increasing towards low doping and of the specific insulating state characterized by a small chemical potential jump.

Journal Article↗
PubMed2006

Detecting electronic coherence in excited-state electron transfer in fluorinated benzenes.

Photoinduced electron transfer (ET) in heavily fluorinated benzenes in solution has been studied with broadband transient absorption spectroscopy. Spectrally resolved kinetics exhibit oscillations with amplitude up to 70% of the signal. The oscillation frequency is specific for each probe; in addition, for pentafluorobenzene it markedly depends on solvent, being 86 cm(-1) in hexane and 94 cm(-1) in acetonitrile. We argue that the observed behavior is not related to vibrational coherences, but originate from coherent electronic motion between an optically excited and an ET state.

Journal Article↗
PubMed2006

Detection of the electron spin resonance of two-dimensional electrons at large wave vectors.

We have investigated the electron spin resonance at nonzero wave vector in GaAs single quantum wells by combining the virtues of high frequency surface acoustic wave generation to produce excitations with large wave numbers with a sensitive optical scheme to detect resonant absorption. The observed large deviations from the single particle Zeeman energy are attributed to the exchange interaction. The enhancement of the electronic g* factor is, however, substantially smaller compared with theoretical predictions for spin waves when adopting a bare Coulomb interaction potential.

Journal Article↗
PubMed2006

Anti-hermitian contracted schrödinger equation: direct determination of the two-electron reduced density matrices of many-electron molecules.

Two-electron reduced density matrices (2-RDMs) of many-electron molecules are directly determined without calculation of their wave functions by solving the anti-Hermitian contracted Schrödinger equation. Approximation of the 3-RDM in the anti-Hermitian contracted Schrödinger equation by a corrected cumulant expansion [Mazziotti, Phys. Rev. A 60, 3618 (1999)] permits the direct calculation of the energy and 2-RDM with many high-order correlation effects included. The method is illustrated for the molecules BeH2, H2O, NH3, CH4, and CO as well as the dissociation of BH. Correlation energies are obtained within 95%-100% of full-configuration interaction, and 2-RDMs very nearly satisfy known N-representability conditions.

Journal Article↗
PubMed1994

The Role of Ascorbate Free Radical as an Electron Acceptor to Cytochrome b-Mediated Trans-Plasma Membrane Electron Transport in Higher Plants.

The action of ascorbate free radical as an electron acceptor to cytochrome b-mediated trans-plasma membrane electron transport is demonstrated. Addition of ascorbate free radical to ascorbate-loaded plasma membrane vesicles caused a rapid oxidation of the cytochrome, followed by a slower re-reduction. The fully reduced dehydroascorbate was ineffective.

Journal Article↗
PubMed2004

Transmission electron microscopy and electron diffraction study of the short-range ordering structure of alpha-LiFeO2.

The basic structure of alpha-LiFeO2, lithium iron oxide, is a cubic NaCl-type structure with a lattice constant of 0.42 nm; some short-range ordering characterized by octahedral clusters exists. The local structure of the short-range ordering was investigated by transmission electron microscopy and electron diffraction. A new short-range ordering structure was found in local areas. The local structure has a cubic lattice with a doubled lattice constant. The occupation factors of cations on Wyckoff sites 4(a) and 4(b) are different from those on 24(d) sites, but the stoichiometric composition in cubic clusters is the same as the macroscopic composition. The number of pairs in which iron cations exist in nearest-neighbor sites and next nearest-neighbor sites is reduced in the structure. This means that a magnetic interaction between the iron cations is reduced by cation ordering even without spin ordering at room temperature.

Journal Article↗
PubMed2006

Analytical transmission electron microscopy and electron diffraction for characterization of multiphase Ni-P-Ti surface layer on Ti-6Al-4V alloy.

The microstructure, chemical and phase composition of the hard Ni-P-Ti layer formed on the Ti-6Al-4V alloy after duplex surface treatment were investigated by light microscopy, X-ray diffraction, scanning electron microscopy and analytical/high-resolution transmission electron microscopy. These investigations showed that the improved mechanical and tribological properties of the surface-treated alloy were related to the presence of a multilayered microstructure containing several phases from the Ni-Ti-P-Al system.

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PubMed2006

Metal particles in a ceramic matrix--scanning electron microscopy and transmission electron microscopy characterization.

This paper is concerned with ceramic matrix (Al(2)O(3)) composites with introduced metal particles (Ni, Fe). The composites were obtained via sintering of powders under very high pressure (2.5 GPa). Scanning electron microscopy and transmission electron microscopy were chosen as the tools for the identification and description of the shape, size and distribution of the metal particles. The Al(2)O(3)-Ni composite contained agglomerates of the Ni particles surrounded by ceramic grains and nanometre-size Ni particles located inside the ceramic grains and at the ceramic grain boundaries. In the Al(2)O(3)-Fe composite, the Fe particles were mostly surrounded by ceramic grains. Moreover, holes left by the Fe particles were found. The high pressure used in the fabrication of the composites changed the shape of the metal and ceramic powder grains via plastic deformation.

Journal Article↗
PubMed2006

New system for secondary electron detection in variable-pressure scanning electron microscopy.

A novel secondary electron detection system combining a two-stage detector head and a differential pumping system is presented. The detector head consisted of a scintillation Everhart-Thornley detector and a microsphere plate, separating it from the lower vacuum in the intermediate chamber (below 0.1 mbar). The system was arranged asymmetrically, which should contribute to a lower gas leakage through the plate and a longer life span of the plate. The system offered all the advantages of the scintillator detector in a wide range of gas pressures, from high vacuum to those of the order of 10 mbar, typical of high-pressure scanning electron microscopy.

Journal Article↗
PubMed2001

Measuring the success of electronic medical record implementation using electronic and survey data.

Computerization of physician practices is increasing. Stakeholders are demanding demonstrated value for their Electronic Medical Record (EMR) implementations. We developed survey tools to measure medical office processes, including administrative and physician tasks pre- and post-EMR implementation. We included variables that were expected to improve with EMR implementation and those that were not expected to improve, as controls. We measured the same processes pre-EMR, at six months and 18 months post-EMR. Time required for most administrative tasks decreased within six months of EMR implementation. Staff time spent on charting increased with time, in keeping with our anecdotal observations that nurses were given more responsibility for charting in many offices. Physician time to chart increased initially by 50%, but went down to original levels by 18 months. However, this may be due to the drop-out of those physicians who had a difficult time charting electronically.

Attitude of Health Personnel↗
PubMed2004

[Application of electronic signature for electronic medical documents].

This work deals with analysis of technical and legal aspects of qualified electronic signature implementation in the area of electronic medical information systems with respect to real usability of such a signature as an equivalent to a manual signature on paper medical documents.

Computer Security↗