845 research outputs found
Incoherent Transport through Molecules on Silicon in the vicinity of a Dangling Bond
We theoretically study the effect of a localized unpaired dangling bond (DB)
on occupied molecular orbital conduction through a styrene molecule bonded to a
n++ H:Si(001)-(2x1) surface. For molecules relatively far from the DB, we find
good agreement with the reported experiment using a model that accounts for the
electrostatic contribution of the DB, provided we include some dephasing due to
low lying phonon modes. However, for molecules within 10 angstrom to the DB, we
have to include electronic contribution as well along with higher dephasing to
explain the transport features.Comment: 9 pages, 5 figure
First Energy and Angle differential Measurements of e^+e^- -pairs emitted by Internal Pair Conversion of excited Heavy Nuclei
We present the first energy and angle resolved measurements of e+e- pairs
emitted from heavy nuclei (Z>=40) at rest by internal pair conversion (IPC) of
transitions with energies of less than 2MeV as well as recent theoretical
results using the DWBA method, which takes full account of relativistic
effects, magnetic substates and finite size of the nucleus. The 1.76MeV E0
transition in Zr90 (Sr source) and the 1.77MeV M1 transition in Pb207 (Bi
source) have been investigated experimentally using the essentially improved
set-up at the double-ORANGE beta-spectrometer of GSI. The measurements prove
the capability of the setup to cleanly identify the IPC pairs in the presence
of five orders of magnitude higher beta- and gamma background from the same
source and to yield essentially background-free sum spectra despite the large
background. Using the ability of the ORANGE setup to directly determine the
opening angle of the e+e- pairs, the angular correlation of the emitted pairs
was measured. In the Zr90 case the correlation could be deduced for a wide
range of energy differences of the pairs. The Zr90 results are in good
agreement with recent theory. The angular correlation deduced for the M1
transition in Pb207 is in strong disagreement with theoretical predictions
derived within the Born approximation and shows almost isotropic character.
This is again in agreement with the new theoretical results.Comment: LaTeX, 28 pages incl. 10 PS figures; Accepted by Z.Phys.
First-principles modelling of molecular single-electron transistors
We present a first-principles method for calculating the charging energy of a
molecular single-electron transistor operating in the Coulomb blockade regime.
The properties of the molecule are modeled using density-functional theory, the
environment is described by a continuum model, and the interaction between the
molecule and the environment are included through the Poisson equation. The
model is used to calculate the charge stability diagrams of a benzene and
C molecular single-electron transistor
Positron spectra from internal pair conversion observed in {238}U + {181}Ta collisions
We present new results from measurements and simulations of positron spectra,
originating from 238U + 181Ta collisions at beam energies close to the Coulomb
barrier. The measurements were performed using an improved experimental setup
at the double-Orange spectrometer of GSI. Particular emphasis is put on the
signature of positrons from Internal-Pair-Conversion (IPC) processes in the
measured e+ energy spectra, following the de-excitation of electromagnetic
transitions in the moving Ta-like nucleus. It is shown by Monte Carlo
simulations that, for the chosen current sweeping procedure used in the present
experiments, positron emission from discrete IPC transitions can lead to rather
narrow line structures in the measured energy spectra. The measured positron
spectra do not show evidence for line structures within the statistical
accuracy achieved, although expected from the intensities of the observed
transitions (E keV) and theoretical conversion
coefficients. This is due to the reduced detection efficiency for IPC
positrons, caused by the limited spatial and momentum acceptance of the
spectrometer. A comparison with previous results, in which lines have been
observed, is presented and the implications are discussed.Comment: LaTeX, 20 pages including 5 EPS figures; Accepted by Eur. Phys.Jour.
Critical Discussion of Ex situ and In situ TEM Measurements on Memristive Devices
Memristors are promising candidates for new memory technologies and are capable to mimic synapses in artificial neural networks. The switching in memristive devices occurs typically in few nanometer thin dielectric layers. The direct observation of the switching mechanism is crucial for better comprehension and improvements of memristors. Therefore, in situ experiments are conducted in a transmission electron microscope (TEM). However, sample preparation processes and electron beam irradiation can lead to a chemical and structural modification of the active layers. Moreover, devices may show significant device-to-device variability due to the details of processing parameters. Thus, it is essential to characterize the identical device electrically before microstructural analysis
New Results on e+e- Line Emission in U+Ta Collisions
We present new results obtained from a series of follow-up e+e- coincidence
measurements in heavy-ion collisions, utilizing an improved experimental set-up
at the double-Orange beta-spectrometer of GSI. The collision system U+Ta was
reinvestigated in three independent runs at beam energies in the range
(6.0-6.4)xA MeV and different target thicknesses, with the objective to
reproduce a narrow sum-energy e+e- line at ~635 keV observed previously in this
collision system. At improved statistical accuracy, the line could not be found
in these new data. For the ''fission'' scenario, an upper limit (1 sigma) on
its production probability per collision of 1.3x10^{-8} can be set which has to
be compared to the previously reported value of [4.9 +- 0.8 (stat.) +- 1.0
(syst)]x10^{-7}. In the light of the new results, a reanalysis of the old data
shows that the continuous part of the spectrum at the line position is
significantly higher than previously assumed, thus reducing the production
probability of the line by a factor of two and its statistical significance to
< 3.4sigma.Comment: 15 pages, standard LaTeX with 3 included PS figures; Submitted to
Physics Letters
Jurisprudencia Civil Cubana, 02
Case law digest, v. 2. Civil law cases – Actos Propios (cont.)https://ecollections.law.fiu.edu/diaz-cruz-index/1064/thumbnail.jp
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