95 research outputs found
Planung flexibler ProduktionskapazitÀten im Spannungsfeld logistischer und monetÀrer Ziele
[no abstract
Monitoring Bioeconomy Transitions with EconomicâEnvironmental and Innovation Indicators: Addressing Data Gaps in the Short Term
Monitoring bioeconomy transitions and their effects can be considered a Herculean task, as they cannot be easily captured using current economic statistics. Distinctions are rarely made between bio-based and non-bio-based products when official data is collected. However, production along bioeconomy supply chains and its implications for sustainability require measurement and assessment to enable considered policymaking. We propose a starting point for monitoring bioeconomy transitions by suggesting an adapted framework, relevant sectors, and indicators that can be observed with existing information and data from many alternative sources, assuming that official data collection methods will not be modified soon. Economicâenvironmental indicators and innovation indicators are derived for the German surfactant industry based on the premise that combined economicâenvironmental indicators can show actual developments and trade-offs, while innovation indicators can reveal whether a bioeconomy transition is likely in a sector. Methodological challenges are discussed and low-cost; high-benefit options for further data collection are recommended.Peer Reviewe
Towards analyzing the influence of measurement errors in magnetic resonance imaging of fluid flows : development of an interval-based iteration approach
Magnetic Resonance Imaging (MRI) provides an insight into opaque structures and does not only have a large number of applications in the field of medical examinations but also in the field of engineering. In technical applications, MRI enables a contactless measurement of the two- or threedimensional velocity field within minutes. However, various measurement methods would benefit from an acceleration of the measurement procedure. Compressed Sensing is a promising method to fit this need. A random undersampling of the sampled data points enables a significant reduction of acquisition time. As this method requires a nonlinear iterative reconstruction of unmeasured data to obtain the same data quality as for a conventional fully sampled measurement, it is essential to estimate the influence of uncertainty on the quantitative result. This paper investigates the implementation of interval arithmetic approaches with a focus on the applicability in the frame of compressed sensing techniques. These approaches are able to handle bounded uncertainty not only in the case of linear relationships between measured data and the computed outputs but also allow for solving the necessary optimality criteria for the fluid velocity reconstruction in an iterative manner under the assumption of set-valued measurement errors and bounded representations of noise
Chiral photoelectron angular distributions from ionization of achiral atomic and molecular species
We show that the combination of two achiral components - atomic or molecular
target plus a circularly polarized photon - can yield chirally structured
photoelectron angular distributions. For photoionization of CO, the angular
distribution of carbon K-shell photoelectrons is chiral when the molecular axis
is neither perpendicular nor (anti-)parallel to the light propagation axis. In
photo-double-ionization of He, the distribution of one electron is chiral, if
the other electron is oriented like the molecular axis in the former case and
if the electrons are distinguishable by their energy. In both scenarios, the
circularly polarized photon defines a plane with a sense of rotation and an
additional axis is defined by the CO molecule or one electron. This is
sufficient to establish an unambiguous coordinate frame of well-defined
handedness. To produce a chirally structured electron angular distribution,
such a coordinate frame is necessary, but not sufficient. We show that
additional electron-electron interaction or scattering processes are needed to
create the chiral angular distribution
Kinematically complete experimental study of Compton scattering at helium atoms near the ionization threshold
Compton scattering is one of the fundamental interaction processes of light
with matter. Already upon its discovery [1] it was described as a billiard-type
collision of a photon kicking a quasi-free electron. With decreasing photon
energy, the maximum possible momentum transfer becomes so small that the
corresponding energy falls below the binding energy of the electron. Then
ionization by Compton scattering becomes an intriguing quantum phenomenon. Here
we report a kinematically complete experiment on Compton scattering at helium
atoms below that threshold. We determine the momentum correlations of the
electron, the recoiling ion, and the scattered photon in a coincidence
experiment finding that electrons are not only emitted in the direction of the
momentum transfer, but that there is a second peak of ejection to the backward
direction. This finding links Compton scattering to processes as ionization by
ultrashort optical pulses [2], electron impact ionization [3,4], ion impact
ionization [5,6], and neutron scattering [7] where similar momentum patterns
occur.Comment: 7 pages, 4 figure
Angular dependence of the Wigner time delay upon tunnel ionization of
More than 100 years after its discovery and its explanation in the energy
domain, the duration of the photoelectric effect is still heavily studied. The
emission time of a photoelectron can be quantified by the Wigner time delay.
Experiments addressing this time delay for single-photon ionization became
feasible during the last 10 years. A missing piece, which has not been studied,
so far, is the Wigner time delay for strong-field ionization of molecules. Here
we show experimental data on the Wigner time delay for tunnel ionization of
molecules and demonstrate its dependence on the emission direction of
the electron with respect to the molecular axis. We find, that the observed
changes in the Wigner time delay can be quantitatively explained by
elongated/shortened travel paths of the electrons that are due to spatial
shifts of the electron's birth position after tunneling. This introduces an
intuitive perspective towards the Wigner time delay in strong-field ionization.Comment: 17 pages, 6 figure
Effect of quantum confinement on exciton-phonon interactions
We investigate the homogeneous linewidth of localized type-I excitons in
type-II GaAs/AlAs superlattices. These localizing centers represent the
intermediate case between quasi-two-dimensional (Q2D) and
quasi-zero-dimensional localizations. The temperature dependence of the
homogeneous linewidth is obtained with high precision from
micro-photoluminescence spectra. We confirm the reduced interaction of the
excitons with their environment with decreasing dimensionality except for the
coupling to LO-phonons. The low-temperature limit for the linewidth of these
localized excitons is five times smaller than that of Q2D excitons. The
coefficient of exciton-acoustic-phonon interaction is 5 ~ 6 times smaller than
that of Q2D excitons. An enhancement of the average exciton-LO-phonon
interaction by localization is found in our sample. But this interaction is
very sensitive to the detailed structure of the localizing centers.Comment: 6 pages, 4 figure
Observation of Photoion Backward Emission in Photoionization of He and N2
We experimentally investigate the effects of the linear photon momentum on
the momentum distributions of photoions and photoelectrons generated in
one-photon ionization in an energy range of 300 eV 40 keV.
Our results show that for each ionization event the photon momentum is imparted
onto the photoion, which is essentially the system's center of mass.
Nevertheless, the mean value of the ion momentum distribution along the light
propagation direction is backward-directed by times the photon momentum.
These results experimentally confirm a 90 year old prediction.Comment: 5 pages, 3 figure
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