185 research outputs found
Quasifree Photoionization under the Reaction Microscope
We experimentally investigated the quasifree mechanism (QFM) in one-photon double ionization of He and H2 at 800 eV photon energy and circular polarization with a COLTRIMS reaction microscope. Our work provides new insight into this elusive photoionization mechanism that was predicted by Miron Amusia more than four decades ago. We found the distinct four-fold symmetry in the angular emission pattern of QFM electrons from H2 double ionization that has previously only been observed for He. Furthermore, we provide experimental evidence that the photon momentum is not imparted onto the center of mass in quasifree photoionization, which is in contrast to the situation in single ionization and in double ionization mediated by the shake-off and knock-out mechanisms. This finding is substantiated by numerical results obtained by solving the system’s full-dimensional time-dependent Schrödinger equation beyond the dipole approximation
Generating large labeled data sets for laparoscopic image processing tasks using unpaired image-to-image translation
In the medical domain, the lack of large training data sets and benchmarks is
often a limiting factor for training deep neural networks. In contrast to
expensive manual labeling, computer simulations can generate large and fully
labeled data sets with a minimum of manual effort. However, models that are
trained on simulated data usually do not translate well to real scenarios. To
bridge the domain gap between simulated and real laparoscopic images, we
exploit recent advances in unpaired image-to-image translation. We extent an
image-to-image translation method to generate a diverse multitude of
realistically looking synthetic images based on images from a simple
laparoscopy simulation. By incorporating means to ensure that the image content
is preserved during the translation process, we ensure that the labels given
for the simulated images remain valid for their realistically looking
translations. This way, we are able to generate a large, fully labeled
synthetic data set of laparoscopic images with realistic appearance. We show
that this data set can be used to train models for the task of liver
segmentation of laparoscopic images. We achieve average dice scores of up to
0.89 in some patients without manually labeling a single laparoscopic image and
show that using our synthetic data to pre-train models can greatly improve
their performance. The synthetic data set will be made publicly available,
fully labeled with segmentation maps, depth maps, normal maps, and positions of
tools and camera (http://opencas.dkfz.de/image2image).Comment: Accepted at MICCAI 201
Revealing the Two-Electron Cusp in the Ground States of He and H2 via Quasifree Double Photoionization
We report on kinematically complete measurements and ab initio
non-perturbative calculations of double ionization of He and H2 by a single 800
eV circularly polarized photon. We confirm the quasifree mechanism of
photoionization for H2 and show how it originates from the two-electron cusp in
the ground state of a two-electron target. Our approach establishes a new
method for mapping electrons relative to each other and provides valuable
insight into photoionization beyond the electric-dipole approximation.Comment: 7 pages, 4 figure
Coulomb explosion imaging of small polyatomic molecules with ultrashort x-ray pulses
Ultrashort x-ray pulses from free-electron lasers can efficiently charge up and trigger the full fragmentation of molecules. By coincident detection of up to five ions resulting from rapid Coulomb explosion of highly charged iodomethane, we show that the full three-dimensional equilibrium geometry of this prototypical polyatomic system can be determined from the measured ion momenta with the help of a charge buildup model. Supported by simulations of how the ion momenta would reflect specific changes in molecular bond lengths and angles, we demonstrate that Coulomb-explosion imaging with ultrashort x-ray pulses is a promising technique for recording movies of multidimensional nuclear wave packets, including hydrogen motions
X-ray multiphoton-induced Coulomb explosion images complex single molecules
Following structural dynamics in real time is a fundamental goal towards a better understanding of chemical reactions. Recording snapshots of individual molecules with ultrashort exposure times is a key ingredient towards this goal, as atoms move on femtosecond (10-15 s) timescales. For condensed-phase samples, ultrafast, atomically resolved structure determination has been demonstrated using X-ray and electron diffraction. Pioneering experiments have also started addressing gaseous samples. However, they face the problem of low target densities, low scattering cross sections and random spatial orientation of the molecules. Therefore, obtaining images of entire, isolated molecules capturing all constituents, including hydrogen atoms, remains challenging. Here we demonstrate that intense femtosecond pulses from an X-ray free-electron laser trigger rapid and complete Coulomb explosions of 2-iodopyridine and 2-iodopyrazine molecules. We obtain intriguingly clear momentum images depicting ten or eleven atoms, including all the hydrogens, and thus overcome a so-far impregnable barrier for complete Coulomb explosion imaging—its limitation on molecules consisting of three to five atoms. In combination with state-of-the-art multi-coincidence techniques and elaborate theoretical modelling, this allows tracing ultrafast hydrogen emission and obtaining information on the result of intramolecular electron rearrangement. Our work represents an important step towards imaging femtosecond chemistry via Coulomb explosion
Investigating charge-up and fragmentation dynamics of oxygen molecules after interaction with strong X-ray free-electron laser pulses
During the last decade, X-ray free-electron lasers (XFELs) have enabled the study of light–matter interaction under extreme conditions. Atoms which are subject to XFEL radiation are charged by a complex interplay of (several subsequent) photoionization events and electronic decay processes within a few femtoseconds. The interaction with molecules is even more intriguing, since intricate nuclear dynamics occur as the molecules start to dissociate during the charge-up process. Here, we demonstrate that by analyzing photoelectron angular emission distributions and kinetic energy release of charge states of ionic molecular fragments, we can obtain a detailed understanding of the charge-up and fragmentation dynamics. Our novel approach allows for gathering such information without the need of complex ab initio modeling. As an example, we provide a detailed view on the processes happening on a femtosecond time scale in oxygen molecules exposed to intense XFEL pulses
NDEL1-PDGFRB fusion gene in a myeloid malignancy with eosinophilia associated with resistance to tyrosine kinase inhibitors
NDEL1-PDGFRB fusion gene in a myeloid malignancy with eosinophilia associated with resistance to tyrosine kinase inhibitors
A next generation, pilot-scale continuous sterilization system for fermentation media
A new continuous sterilization system was designed, constructed, started up, and qualified for media sterilization for secondary metabolite cultivations, bioconversions, and enzyme production. An existing Honeywell Total Distributed Control 3000-based control system was extended using redundant High performance Process Manager controllers for 98 I/O (input/output) points. This new equipment was retrofitted into an industrial research fermentation pilot plant, designed and constructed in the early 1980s. Design strategies of this new continuous sterilizer system and the expanded control system are described and compared with the literature (including dairy and bio-waste inactivation applications) and the weaknesses of the prior installation for expected effectiveness. In addition, the reasoning behind selection of some of these improved features has been incorporated. Examples of enhancements adopted include sanitary heat exchanger (HEX) design, incorporation of a “flash” cooling HEX, on-line calculation of F(o) and R(o), and use of field I/O modules located near the vessel to permit low-cost addition of new instrumentation. Sterilizer performance also was characterized over the expected range of operating conditions. Differences between design and observed temperature, pressure, and other profiles were quantified and investigated
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