288 research outputs found
Photophysics of indole upon x-ray absorption
A photofragmentation study of gas-phase indole (CHN) upon
single-photon ionization at a photon energy of 420 eV is presented. Indole was
primarily inner-shell ionized at its nitrogen and carbon orbitals.
Electrons and ions were measured in coincidence by means of velocity map
imaging. The angular relationship between ionic fragments is discussed along
with the possibility to use the angle-resolved coincidence detection to perform
experiments on molecules that are strongly oriented in their recoil-frame. The
coincident measurement of electrons and ions revealed
fragmentation-pathway-dependent electron spectra, linking the structural
fragmentation dynamics to different electronic excitations. Evidence for
photoelectron-impact self-ionization was observed.Comment: 11 pages, 6 figure
Diffraction effects in the Recoil-Frame Photoelectron Angular Distributions of Halomethanes
Citation: Bomme, C., Anielski, D., Savelyev, E., Boll, R., Erk, B., Bari, S., . . . Rolles, D. (2015). Diffraction effects in the Recoil-Frame Photoelectron Angular Distributions of Halomethanes. 635(11). doi:10.1088/1742-6596/635/11/112020We have measured the Recoil Frame-Photoelectron Angular Distributions (RF-PADs) for inner-shell photoionization of CH3F, CH3I and CF3I halomethane molecules for photoelectron energies up to 300 eV detected within a 4? solid angle in the gas-phase. For high kinetic energies, the RF-PADs are dominated by diffraction effects that encode information on the molecular geometry. © Published under licence by IOP Publishing Ltd
High-repetition-rate and high-photon-flux 70 eV high-harmonic source for coincidence ion imaging of gas-phase molecules
Unraveling and controlling chemical dynamics requires techniques to image
structural changes of molecules with femtosecond temporal and picometer spatial
resolution. Ultrashort-pulse x-ray free-electron lasers have significantly
advanced the field by enabling advanced pump-probe schemes. There is an
increasing interest in using table-top photon sources enabled by high-harmonic
generation of ultrashort-pulse lasers for such studies. We present a novel
high-harmonic source driven by a 100 kHz fiber laser system, which delivers
10 photons/s in a single 1.3 eV bandwidth harmonic at 68.6 eV. The
combination of record-high photon flux and high repetition rate paves the way
for time-resolved studies of the dissociation dynamics of inner-shell ionized
molecules in a coincidence detection scheme. First coincidence measurements on
CHI are shown and it is outlined how the anticipated advancement of fiber
laser technology and improved sample delivery will, in the next step, allow
pump-probe studies of ultrafast molecular dynamics with table-top XUV-photon
sources. These table-top sources can provide significantly higher repetition
rates than the currently operating free-electron lasers and they offer very
high temporal resolution due to the intrinsically small timing jitter between
pump and probe pulses
TotalSegmentator: robust segmentation of 104 anatomical structures in CT images
We present a deep learning segmentation model that can automatically and
robustly segment all major anatomical structures in body CT images. In this
retrospective study, 1204 CT examinations (from the years 2012, 2016, and 2020)
were used to segment 104 anatomical structures (27 organs, 59 bones, 10
muscles, 8 vessels) relevant for use cases such as organ volumetry, disease
characterization, and surgical or radiotherapy planning. The CT images were
randomly sampled from routine clinical studies and thus represent a real-world
dataset (different ages, pathologies, scanners, body parts, sequences, and
sites). The authors trained an nnU-Net segmentation algorithm on this dataset
and calculated Dice similarity coefficients (Dice) to evaluate the model's
performance. The trained algorithm was applied to a second dataset of 4004
whole-body CT examinations to investigate age dependent volume and attenuation
changes. The proposed model showed a high Dice score (0.943) on the test set,
which included a wide range of clinical data with major pathologies. The model
significantly outperformed another publicly available segmentation model on a
separate dataset (Dice score, 0.932 versus 0.871, respectively). The aging
study demonstrated significant correlations between age and volume and mean
attenuation for a variety of organ groups (e.g., age and aortic volume; age and
mean attenuation of the autochthonous dorsal musculature). The developed model
enables robust and accurate segmentation of 104 anatomical structures. The
annotated dataset (https://doi.org/10.5281/zenodo.6802613) and toolkit
(https://www.github.com/wasserth/TotalSegmentator) are publicly available.Comment: Accepted at Radiology: Artificial Intelligenc
Origin of non-uniform plasticity in a high-strength Al-Mn-Sc based alloy produced by laser powder bed fusion
ENUNCIAÇÕES ESTÉTICAS EM VÍDEOS ESCOLARES NA CULTURA DIGITAL: por uma outra forma de olhar os estudos midiáticos na escola
Uma típica comunicação contemporânea é cada dia mais carregada pelo componente estético enunciado em muitos trabalhos escolares juvenis em vídeos definidos como paródias no YouTube. Nesse sentido, esse ensaio propõe a reflexão de uma típica produção contemporânea juvenil baseada na narrativa videográfica. Trata-se de uma comunicação dialógica onde quem vê algo, vê e (re)age atribuindo sentidos que não só técnica e/ou criticamente, pois que o faz com todos seus poros, dilatando seu olhar com todas as pupilas materiais e imateriais de seu corpo, pele e alma. Uma produção que se mantém ativada na relação dinâmica também com fruidores/leitores dessas comunicações e que, em sintonia com a cultura digital, convida-nos a investigar a relação discursiva enunciada esteticamente nessas narrativas dispostas nas paródias videográficas escolares
Strongly aligned gas-phase molecules at Free-Electron Lasers
We demonstrate a novel experimental implementation to strongly align
molecules at full repetition rates of free-electron lasers. We utilized the
available in-house laser system at the coherent x-ray imaging beamline at the
Linac Coherent Light Source. Chirped laser pulses, i. e., the direct output
from the regenerative amplifier of the Ti:Sa chirped pulse amplification laser
system, were used to strongly align 2,5-diiodothiophene molecules in a
molecular beam. The alignment laser pulses had pulse energies of a few mJ and a
pulse duration of 94 ps. A degree of alignment of
\left = 0.85 was measured, limited by the
intrinsic temperature of the molecular beam rather than by the available laser
system. With the general availability of synchronized chirped-pulse-amplified
near-infrared laser systems at short-wavelength laser facilities, our approach
allows for the universal preparation of molecules tightly fixed in space for
experiments with x-ray pulses.Comment: 10 pages, 5 figure
Multiple-core-hole resonance spectroscopy with ultraintense X-ray pulses
Understanding the interaction of intense, femtosecond X-ray pulses with heavy
atoms is crucial for gaining insights into the structure and dynamics of
matter. One key aspect of nonlinear light-matter interaction was, so far, not
studied systematically at free-electron lasers -- its dependence on the photon
energy. Using resonant ion spectroscopy, we map out the transient electronic
structures occurring during the complex charge-up pathways. Massively hollow
atoms featuring up to six simultaneous core holes determine the spectra at
specific photon energies and charge states. We also illustrate how the
influence of different X-ray pulse parameters that are usually intertwined can
be partially disentangled. The extraction of resonance spectra is facilitated
by the fact that the ion yields become independent of the peak fluence beyond a
saturation point. Our study lays the groundwork for novel spectroscopies of
transient atomic species in exotic, multiple-core-hole states that have not
been explored previously.Comment: Supplementary information is include
Charge transfer in dissociating iodomethane and fluoromethane molecules ionized by intense femtosecond X-ray pulses
Citation: Boll, R., Erk, B., Coffee, R., Trippel, S., Kierspel, T., Bomme, C., . . . Rudenko, A. (2016). Charge transfer in dissociating iodomethane and fluoromethane molecules ionized by intense femtosecond X-ray pulses. Structural Dynamics, 3(4). doi:10.1063/1.4944344Additional Authors: Marchenko, T.;Miron, C.;Patanen, M.;Osipov, T.;Schorb, S.;Simon, M.;Swiggers, M.;Techert, S.;Ueda, K.;Bostedt, C.;Rolles, D.;Rudenko, A.Ultrafast electron transfer in dissociating iodomethane and fluoromethane molecules was studied at the Linac Coherent Light Source free-electron laser using an ultraviolet-pump, X-ray-probe scheme. The results for both molecules are discussed with respect to the nature of their UV excitation and different chemical properties. Signatures of long-distance intramolecular charge transfer are observed for both species, and a quantitative analysis of its distance dependence in iodomethane is carried out for charge states up to I21+. The reconstructed critical distances for electron transfer are in good agreement with a classical over-the-barrier model and with an earlier experiment employing a near-infrared pump pulse. © 2016 Author(s)
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