27 research outputs found
Strong-field physics with mid-IR fields
Strong-field physics is currently experiencing a shift towards the use of
mid-IR driving wavelengths. This is because they permit conducting experiments
unambiguously in the quasi-static regime and enable exploiting the effects
related to ponderomotive scaling of electron recollisions. Initial measurements
taken in the mid-IR immediately led to a deeper understanding of
photo-ionization and allowed a discrimination amongst different theoretical
models. Ponderomotive scaling of rescattering has enabled new avenues towards
time resolved probing of molecular structure. Essential for this paradigm shift
was the convergence of two experimental tools: 1) intense mid-IR sources that
can create high energy photons and electrons while operating within the
quasi-static regime, and 2) detection systems that can detect the generated
high energy particles and image the entire momentum space of the interaction in
full coincidence. Here we present a unique combination of these two essential
ingredients, namely a 160\~kHz mid-IR source and a reaction microscope
detection system, to present an experimental methodology that provides an
unprecedented three-dimensional view of strong-field interactions. The system
is capable of generating and detecting electron energies that span a six order
of magnitude dynamic range. We demonstrate the versatility of the system by
investigating electron recollisions, the core process that drives strong-field
phenomena, at both low (meV) and high (hundreds of eV) energies. The low energy
region is used to investigate recently discovered low-energy structures, while
the high energy electrons are used to probe atomic structure via laser-induced
electron diffraction. Moreover we present, for the first time, the correlated
momentum distribution of electrons from non-sequential double-ionization driven
by mid-IR pulses.Comment: 17 pages, 11 figure
Imaging an aligned polyatomic molecule with laser-induced electron diffraction
Laser-induced electron diffraction is an evolving tabletop method, which aims
to image ultrafast structural changes in gas-phase polyatomic molecules with
sub-{\AA}ngstr\"om spatial and femtosecond temporal resolution. Here, we
provide the general foundation for the retrieval of multiple bond lengths from
a polyatomic molecule by simultaneously measuring the C-C and C-H bond lengths
in aligned acetylene. Our approach takes the method beyond the hitherto
achieved imaging of simple diatomic molecules and is based upon the combination
of a 160 kHz mid-IR few-cycle laser source with full three-dimensional
electron-ion coincidence detection. Our technique provides an accessible and
robust route towards imaging ultrafast processes in complex gas phase molecules
with atto- to femto-second temporal resolution.Comment: 16 pages, 4 figure
Ultrastable, high-repetition-rate attosecond beamline for time-resolved XUV-IR coincidence spectroscopy
The implementation of attosecond photoelectron-photoion coincidence
spectroscopy for the investigation of atomic and molecular dynamics calls for a
high-repetition-rate driving source combined with experimental setups
characterized by excellent stability for data acquisition over time intervals
ranging from a few hours up to a few days. This requirement is crucial for the
investigation of processes characterized by low cross sections and for the
characterization of fully differential photoelectron(s) and photoion(s) angular
and energy distributions. We demonstrate that the implementation of
industrial-grade lasers, combined with a careful design of the delay line
implemented in the pump-probe setup, allows one to reach ultrastable
experimental conditions leading to an error in the estimation of the time
delays of only 12 as. This result opens new possibilities for the investigation
of attosecond dynamics in simple quantum systems
Erratum to: Bioaccumulation in aquatic systems: methodological approaches, monitoring and assessment
Bioaccumulation in aquatic systems: methodological approaches, monitoring and assessment
Bioaccumulation, the accumulation of a chemical in an organism relative to its level in the ambient medium, is of major environmental concern. Thus, monitoring chemical concentrations in biota are widely and increasingly used for assessing the chemical status of aquatic ecosystems. In this paper, various scientific and regulatory aspects of bioaccumulation in aquatic systems and the relevant critical issues are discussed. Monitoring chemical concentrations in biota can be used for compliance checking with regulatory directives, for identification of chemical sources or event related environmental risk assessment. Assessing bioaccumulation in the field is challenging since many factors have to be considered that can effect the accumulation of a chemical in an organism. Passive sampling can complement biota monitoring since samplers with standardised partition properties can be used over a wide temporal and geographical range. Bioaccumulation is also assessed for regulation of chemicals of environmental concern whereby mainly data from laboratory studies on fish bioaccumulation are used. Field data can, however, provide additional important information for regulators. Strategies for bioaccumulation assessment still need to be harmonised for different regulations and groups of chemicals. To create awareness for critical issues and to mutually benefit from technical expertise and scientific findings, communication between risk assessment and monitoring communities needs to be improved. Scientists can support the establishment of new monitoring programs for bioaccumulation, e.g. in the frame of the amended European Environmental Quality Standard Directive
Diagnosis and treatment of neurogenic dysphagia - S1 guideline of the German Society of Neurology.
INTRODUCTION
Neurogenic dysphagia defines swallowing disorders caused by diseases of the central and peripheral nervous system, neuromuscular transmission, or muscles. Neurogenic dysphagia is one of the most common and at the same time most dangerous symptoms of many neurological diseases. Its most important sequelae include aspiration pneumonia, malnutrition and dehydration, and affected patients more often require long-term care and are exposed to an increased mortality. Based on a systematic pubmed research of related original papers, review articles, international guidelines and surveys about the diagnostics and treatment of neurogenic dysphagia, a consensus process was initiated, which included dysphagia experts from 27 medical societies.
RECOMMENDATIONS
This guideline consists of 53 recommendations covering in its first part the whole diagnostic spectrum from the dysphagia specific medical history, initial dysphagia screening and clinical assessment, to more refined instrumental procedures, such as flexible endoscopic evaluation of swallowing, the videofluoroscopic swallowing study and high-resolution manometry. In addition, specific clinical scenarios are captured, among others the management of patients with nasogastric and tracheotomy tubes. The second part of this guideline is dedicated to the treatment of neurogenic dysphagia. Apart from dietary interventions and behavioral swallowing treatment, interventions to improve oral hygiene, pharmacological treatment options, different modalities of neurostimulation as well as minimally invasive and surgical therapies are dealt with.
CONCLUSIONS
The diagnosis and treatment of neurogenic dysphagia is challenging and requires a joined effort of different medical professions. While the evidence supporting the implementation of dysphagia screening is rather convincing, further trials are needed to improve the quality of evidence for more refined methods of dysphagia diagnostics and, in particular, the different treatment options of neurogenic dysphagia. The present article is an abridged and translated version of the guideline recently published online ( https://www.awmf.org/uploads/tx_szleitlinien/030-111l_Neurogene-Dysphagie_2020-05.pdf )
Steering the electron in H2+ by nuclear wave packet dynamics
By combining carrier-envelope phase (CEP) stable light fields and the traditional method of optical pump-probe spectroscopy we study electron localization in dissociating H[subscript 2][superscript +] molecular ions. Localization and localizability of electrons is observed to strongly depend on the time delay between the two CEP-stable laser pulses with a characteristic periodicity corresponding to the oscillating molecular wave packet. Variation of the pump-probe delay time allows us to uncover the underlying physical mechanism for electron localization, which are two distinct sets of interfering dissociation channels that exhibit specific temporal signatures in their asymmetry response