412 research outputs found
Conductance of a single molecule anchored by an isocyanide substituent to gold electrodes
The effect of anchoring group on the electrical conductance of a single
molecule bridging two Au electrodes was studied using di-substituted
(isocyanide (CN-), thiol (S-) or cyanide (NC-)) benzene. The conductance of a
single Au/1,4-diisocyanobenzene/Au junction anchored by isocyanide via a C atom
(junction with the Au-CN bond) was (). The
value was comparable to of a single
Au/1,4-benzenedithiol/Au junction with the Au-S bond. The
Au/1,4-dicyanobenzene/Au molecular junction with the Au-NC bond did not show
well-defined conductance values. The metal-molecule bond strength was estimated
by the distance over which the molecular junction was stretched before
breakdown. The stretched length of the molecular junction with the Au-CN bond
was comparable to that of the Au junction, indicating that the Au-CN bond was
stronger than the Au-Au bond.Comment: 3 figures, to be appear in Appl. Phys. Let
4p states and X-Ray Spectroscopy
The 4p states in transition metals and their compounds usually play minor
roles on their physical quantities. Recent development of resonant x-ray
scattering (RXS) at the K-edge of transition metals, however, casts light on
the 4p states, because the signals on orbital and magnetic superlattice spots
are brought about by the modulation in the 4p states. The 4p states are
extending in solids and thereby sensitive to electronic states at neighboring
sites. This characteristic determines the mechanism of RXS that the intensity
on the orbital superlattice spots are mainly generated by the lattice
distortion and those on magnetic superlattice spots by the coupling of the 4p
states with the orbital polarization in the 3d states at neighboring sites.
Taking up typical examples for orbital and magnetic RXS, we demonstrate these
mechanisms on the basis of the band structure calculation. Finally, we study
the MCD spectra at the K-edge, demonstrating that the same mechanism as the
magnetic RXS is working.Comment: 9 pages, 9 figures, submitted to Physica Scripta (comment
Theoretical Analysis of Resonant Inelastic X-Ray Scattering Spectra in LaMnO3
We analyze the resonant inelastic x-ray scattering (RIXS) spectra at the K
edge of Mn in the antiferromagnetic insulating manganite LaMnO3. We make use of
the Keldysh-type Green-function formalism, in which the RIXS intensity is
described by a product of an incident-photon-dependent factor and a
density-density correlation function in the 3d states. We calculate the former
factor using the 4p density of states given by an ab initio band structure
calculation and the latter using a multi-orbital tight-binding model. The
ground state of the model Hamiltonian is evaluated within the Hartree-Fock
approximation. Correlation effects are treated within the random phase
approximation (RPA). We obtain the RIXS intensity in a wide range of
energy-loss 2-15 eV. The spectral shape is strongly modified by the RPA
correlation, showing good agreement with the experiments. The
incident-photon-energy dependence also agrees well with the experiments. The
present mechanism that the RIXS spectra arise from band-to-band transitions to
screen the core-hole potential is quite different from the orbiton picture
previously proposed, enabling a comprehensive understanding of the RIXS
spectra.Comment: 20 pages, 10 figures, To be published in PR
Initial wave packets and the various power-law decreases of scattered wave packets at long times
The long time behavior of scattered wave packets from a
finite-range potential is investigated, by assuming to be
initially located outside the potential. It is then shown that can
asymptotically decrease in the various power laws at long time, according to
its initial characteristics at small momentum. As an application, we consider
the square-barrier potential system and demonstrate that exhibits
the asymptotic behavior , while another behavior like can
also appear for another .Comment: 5 pages, 1 figur
The various power decays of the survival probability at long times for free quantum particle
The long time behaviour of the survival probability of initial state and its
dependence on the initial states are considered, for the one dimensional free
quantum particle. We derive the asymptotic expansion of the time evolution
operator at long times, in terms of the integral operators. This enables us to
obtain the asymptotic formula for the survival probability of the initial state
, which is assumed to decrease sufficiently rapidly at large .
We then show that the behaviour of the survival probability at long times is
determined by that of the initial state at zero momentum . Indeed,
it is proved that the survival probability can exhibit the various power-decays
like for an arbitrary non-negative integers as ,
corresponding to the initial states with the condition as .Comment: 15 pages, to appear in J. Phys.
Strains of Paramecium quadecaurelia from Namibia, Africa; Genetic and Molecular Studies
Summary. New strains of Paramecium quadecaurelia were found in Namibia, Africa. Previously, this species from the P. aurelia complex was known only from Australia, Emily Gap. Namibian strains were identified by mating reaction; their relationship with the Australian strain was studied by classical strain crosses (survival in F1 and F2 generations) and by comparison of cytosol-type hsp70 gene sequences. Phylogenetic trees of the Namibian and Australian strains of P. quadecaurelia and the other species of the P. aurelia complex were generated based on the maximum-likelihood method
ASCA Observations of the Supernova Remnant IC 443: Thermal Structure and Detection of Overionized Plasma
We present the results of X-ray spatial and spectral studies of the
``mixed-morphology'' supernova remnant IC 443 using ASCA. IC 443 has a
center-filled image in X-ray band, contrasting with the shell-like appearance
in radio and optical bands. The overall X-ray emission is thermal, not from a
synchrotron nebula. ASCA observed IC 443 three times, covering the whole
remnant. From the image analysis, we found that the softness-ratio map reveals
a shell-like structure. At the same time, its spectra require two (1.0 keV and
0.2 keV) plasma components; the emission of the 0.2 keV plasma is stronger in
the region near the shell than the center. These results can be explained by a
simple model that IC 443 has a hot (1.0 keV) interior surrounded by a cool (0.2
keV) outer shell. From the emission measures, we infer that the 0.2 keV plasma
is denser than the 1.0 keV plasma, suggesting pressure equilibrium between the
two. In addition, we found that the ionization temperature of sulfur, obtained
from H-like K to He-like K intensity ratio, is 1.5 keV,
significantly higher than the gas temperature of 1.0 keV suggested from the
continuum spectrum. The same can be concluded for silicon. Neither an
additional, hotter plasma component nor a multi-temperature plasma successfully
accounts for this ratio, and we conclude that the 1.0 keV plasma is
overionized. This is the first time that overionized gas has been detected in a
SNR. For the gas to become overionized in the absence of a photoionizing flux,
it must cool faster than the ions recombine. Thermal conduction from the 1.0
keV plasma to the 0.2 keV one could cause the 1.0 keV plasma to become
overionized, which is plausible within an old (3 yr) SNR.Comment: 11 pages, 15 figures, 2 tables, accepted for publication in The
Astrophysical Journa
Detection of a Fully-resolved Compton Shoulder of the Iron K-alpha Line in the Chandra X-ray Spectrum of GX 301-2
We report the detection of a fully-resolved, Compton-scattered emission line
in the X-ray spectrum of the massive binary GX 301-2 obtained with the High
Energy Transmission Grating Spectrometer onboard the Chandra X-ray Observatory.
The iron K-alpha fluorescence line complex observed in this system consists of
an intense narrow component centered at an energy of E = 6.40 keV and a redward
shoulder that extends down to ~6.24 keV, which corresponds to an energy shift
of a Compton back-scattered iron K-alpha photon. From detailed Monte Carlo
simulations and comparisons with the observed spectra, we are able to directly
constrain the physical properties of the scattering medium, including the
electron temperature and column density, as well as an estimate for the metal
abundance.Comment: 13 pages, 4 figures, 1 table, accepted for publication in ApJ Lette
X-Ray Magnetic Circular Dichroism at the K edge of Mn3GaC
We theoretically investigate the origin of the x-ray magnetic circular
dichroism (XMCD) spectra at the K edges of Mn and Ga in the ferromagnetic phase
of Mn3GaC on the basis of an ab initio calculation. Taking account of the
spin-orbit interaction in the LDA scheme, we obtain the XMCD spectra in
excellent agreement with the recent experiment. We have analyzed the origin of
each structure, and thus elucidated the mechanism of inducing the orbital
polarization in the p symmetric states. We also discuss a simple sum rule
connecting the XMCD spectra with the orbital moment in the p symmetric states.Comment: 5 pages, 5 figures, accepted for publication in Physical Review
Three-generation Models from E_8 Magnetized Extra Dimensional Theory
We study 10D super Yang-Mills E8 theory on the 6D torus compactification with
magnetic fluxes. We study systematically the possibilities for realizing 4D
supersymmetric standard models with three generations of quarks and leptons. We
also study quark mass matrices.Comment: 30 page
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