9,073 research outputs found
Image-charge induced localization of molecular orbitals at metal-molecule interfaces: Self-consistent GW calculations
Quasiparticle (QP) wave functions, also known as Dyson orbitals, extend the
concept of single-particle states to interacting electron systems. Here we
employ many-body perturbation theory in the GW approximation to calculate the
QP wave functions for a semi-empirical model describing a -conjugated
molecular wire in contact with a metal surface. We find that image charge
effects pull the frontier molecular orbitals toward the metal surface while
orbitals with higher or lower energy are pushed away. This affects both the
size of the energetic image charge shifts and the coupling of the individual
orbitals to the metal substrate. Full diagonalization of the QP equation and,
to some extent, self-consistency in the GW self-energy, is important to
describe the effect which is not captured by standard density functional theory
or Hartree-Fock. These results should be important for the understanding and
theoretical modeling of electron transport across metal-molecule interfaces.Comment: 7 pages, 6 figure
Efficient quantum transport simulation for bulk graphene heterojunctions
The quantum transport formalism based on tight-binding models is known to be
powerful in dealing with a wide range of open physical systems subject to
external driving forces but is, at the same time, limited by the memory
requirement's increasing with the number of atomic sites in the scattering
region. Here we demonstrate how to achieve an accurate simulation of quantum
transport feasible for experimentally sized bulk graphene heterojunctions at a
strongly reduced computational cost. Without free tuning parameters, we show
excellent agreement with a recent experiment on Klein backscattering [A. F.
Young and P. Kim, Nature Phys. 5, 222 (2009)].Comment: 5 pages, 3 figure
A sensitive survey for 13CO, CN, H2CO and SO in the disks of T Tauri and Herbig Ae stars
We use the IRAM 30-m telescope to perform a sensitive search for CN N=2-1 in
42 T Tauri or Herbig Ae systems located mostly in the Taurus-Auriga region.
CO J=2-1 is observed simultaneously to indicate the level of confusion
with the surrounding molecular cloud. The bandpass also contains two
transitions of ortho-HCO, one of SO and the CO J=2-1 line which
provide complementary information on the nature of the emission.
While CO is in general dominated by residual emission from the cloud,
CN exhibits a high disk detection rate % in our sample. We even report CN
detection in stars for which interferometric searches failed to detect
CO, presumably because of obscuration by a foreground, optically thick,
cloud. Comparison between CN and o-HCO or SO line profiles and intensities
divide the sample in two main categories. Sources with SO emission are bright
and have strong HCO emission, leading in general to [HCO/CN].
Furthermore, their line profiles, combined with a priori information on the
objects, suggest that the emission is coming from outflows or envelopes rather
than from a circumstellar disk. On the other hand, most sources have
[HCO/CN], no SO emission, and some of them exhibit clear
double-peaked profiles characteristics of rotating disks. In this second
category, CN is likely tracing the proto-planetary disks. From the line flux
and opacity derived from the hyperfine ratios, we constrain the outer radii of
the disks, which range from 300 to 600 AU. The overall gas disk detection rate
(including all molecular tracers) is , and decreases for fainter
continuum sources.
This study shows that gas disks, like dust disks, are ubiquitous around young
PMS stars in regions of isolated star formation, and that a large fraction of
them have AU.Comment: 31 pages (including 59 figures
Different control strategies for a yeast fermentation bioreactor
Biological systems are usually highly sensitive to process conditions variations, such as temperature, pH, substrate concentration. For this reason, it is important to adequately control and monitor the process in order to guaranteeing product quality while maintaining adequate performance and productivity. The production of ethanol by fermentation is certainly one of the most important industrial bioprocesses, being ethanol an alternative source of energy. For this reason, valuable models of this process based on different kinetic considerations are available in literature, and they can be considered a valid benchmark to investigate control system and estimation techniques for biological reactors. Three different control strategies have been analysed: direct reactor temperature control, cascade control where the primary loop uses delayed ethanol measurements, and 2x2 control system with inferential control for the product concentration. The proposed configurations have been compared at different operating conditions and results show that the use of the inferential control is the most effective in case of severe disturbances
A geometric observer-assisted approach to tailor state estimation in a bioreactor for ethanol production
In this work, a systematic approach based on the geometric observer is proposed to design a model-based soft sensor, which allows the estimation of quality indexes in a bioreactor. The study is focused on the structure design problem where the set of innovated states has to be chosen. On the basis of robust exponential estimability arguments, it is found that it is possible to distinguish all the unmeasured states if temperature and dissolved oxygen concentration measurements are combined with substrate concentrations. The proposed estimator structure is then validated through numerical simulation considering two different measurement processor algorithms: the geometric observer and the extended Kalman filter
Model 1738 tape recorder/reproducer. general test requirements
Test requirements of tape recorder for Mariner progra
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