Sub-cycle time resolution of multi-photon momentum transfer in strong-field ionization

During multi-photon ionization of an atom it is well understood how the involved photons transfer their energy to the ion and the photoelectron. However, the transfer of the photon linear momentum is still not fully understood. Here, we present a time-resolved measurement of linear momentum transfer along the laser pulse propagation direction. Beyond the limit of the electric dipole approximation we observe a time-dependent momentum transfer. We can show that the time-averaged photon radiation pressure picture is not generally applicable and the linear momentum transfer to the photoelectron depends on the ionization time within the electromagnetic wave cycle using the attoclock technique. We can mostly explain the measured linear momentum transfer within a classical model for a free electron in a laser field. However, corrections are required due to the interaction of the outgoing photoelectron with the parent ion and due to the initial momentum when the electron appears in the continuum. The parent ion interaction induces a measurable negative attosecond time delay between the appearance in the continuum of the electron with minimal linear momentum transfer and the point in time with maximum ionization rate

Rashba and Dresselhaus effects in 2D Pb-I-based perovskites

Bulk hybride halide perovskites are governed by significant Rashba and Dresselhaus splitting. This indicates that such effects will not only affect their optoelectronic properties but also those of their two dimensional layered relatives. This work aims at understanding how different ways of symmetry breaking influence these effects in those materials. For this purpose, model structures are adopted where the organic compounds are replaced by Cs atoms. Disregarding possible distortions in the inorganic layers, results in structures with composition Cs$_{n+1}$Pb$_n$I$_{3n+1}$. Using the all-electron full-potential density-functional-theory code \texttt{exciting}, the impact of atomic displacement on the band structure is systematically studied for $n=1$, 2, 3 and $\infty$. The displacement patterns that yield Rashba or Dresselhaus splitting are identified, and the amount of the splitting is determined as a function of displacement. Furthermore, the spin textures in the electronic states around the band gap are analyzed to differentiate between Rashba and Dresselhaus effects. This study reveals in-plane Pb displacements as the origin of the strongest effects.Comment: 10 pages, 8 figures, 1 tabl

Distribution of infection with gastro-intestinal nematodes in different groups of dairy goats in Switzerland and its influence on milk production

The aim of this field study was to investigate interactions between gastro-intestinal nematode (GIN) infection, milk performance and age in goats in order to identify animal groups with higher susceptibility to GIN. On 3 farms (farm A: n = 29, farm B: n = 33, farm C: n = 117 milking goats) fecal egg count reduction tests (FECRT) were performed in summer. All 179 milking goats were enrolled in FECRT and individual milk performance was recorded before and after FEC for FECRT. Furthermore, in early summer and autumn bulk fecal samples were cultured for every farm and GIN genera were determined

Hybrid Materials: Still Challenging for Ab Initio Theory?

Hybrid inorganic/organic systems (HIOS) open new avenues for tailoring them with respect to desired features and functions by exploiting the respective advantages of their components. Therefore, these materials are actively explored in many experimental studies and devices. On the theory side, similar investigations are rather scarce as such interfaces, in addition to exhibiting large unit cells, require highest-level theories to be described reliably. Consequently, hybrid materials pose a challenge for electronic structure theory, starting from density-functional theory to methods beyond, particularly many-body perturbation theory. This concerns both conceptual aspects and computational bottlenecks. In this perspective, the performance of state-of-the-art theoretical approaches applied to HIOS is summarized, mainly focusing on optoelectronic properties. Recent achievements, open challenges, and urgent needs are addressed.Peer Reviewe

Characterizing molecule–metal surface chemistry with ab initio simulation of X‑ray absorption and photoemission spectra

X-ray photoemission and X-ray absorption spectroscopy are important techniques to characterize chemical bonding at surfaces and are often used to identify the strength and nature of adsorbate–substrate interactions. In this study, we judge the ability of X-ray spectroscopic techniques to identify different regimes of chemical bonding at metal–organic interfaces. To achieve this, we sample different interaction strength regimes in a comprehensive and systematic way by comparing two topological isomers, azulene and naphthalene, adsorbed on three metal substrates with varying reactivity, namely the (111) facets of Ag, Cu, and Pt. Using density functional theory, we simulate core-level binding energies and X-ray absorption spectra of the molecular carbon species. The simulated spectra reveal three distinct characteristics based on the molecule-specific spectral features which we attribute to types of surface chemical bonding with varying strength. We find that weak physisorption only leads to minor changes compared to the gas-phase spectra, weak chemisorption leads to charge transfer and significant spectral changes, and strong chemisorption leads to a loss of the molecule-specific features in the spectra. The classification we provide is aimed at assisting interpretation of experimental X-ray spectra for complex metal–organic interfaces

The nuts and bolts of core-hole constrained ab initio simulation for K-shell x-ray photoemission and absorption spectra

Abstract: X-ray photoemission (XPS) and near edge x-ray absorption fine structure (NEXAFS) spectroscopy play an important role in investigating the structure and electronic structure of materials and surfaces. Ab initio simulations provide crucial support for the interpretation of complex spectra containing overlapping signatures. Approximate core-hole simulation methods based on density functional theory (DFT) such as the delta-self-consistent-field (ΔSCF) method or the transition potential (TP) method are widely used to predict K-shell XPS and NEXAFS signatures of organic molecules, inorganic materials and metal–organic interfaces at reliable accuracy and affordable computational cost. We present the numerical and technical details of our variants of the ΔSCF and TP method (coined ΔIP-TP) to simulate XPS and NEXAFS transitions. Using exemplary molecules in gas-phase, in bulk crystals, and at metal–organic interfaces, we systematically assess how practical simulation choices affect the stability and accuracy of simulations. These include the choice of exchange–correlation functional, basis set, the method of core-hole localization, and the use of periodic boundary conditions (PBC). We particularly focus on the choice of aperiodic or periodic description of systems and how spurious charge effects in periodic calculations affect the simulation outcomes. For the benefit of practitioners in the field, we discuss sensible default choices, limitations of the methods, and future prospects

Lightshow: a Python package for generating computational x-ray absorption spectroscopy input files

First-principles computational spectroscopy is a critical tool for interpreting experiment, performing structure refinement, and developing new physical understanding. Systematically setting up input files for different simulation codes and a diverse class of materials is a challenging task with a very high barrier-to-entry, given the complexities and nuances of each individual simulation package. This task is non-trivial even for experts in the electronic structure field and nearly formidable for non-expert researchers. Lightshow solves this problem by providing a uniform abstraction for writing computational x-ray spectroscopy input files for multiple popular codes, including FEFF, VASP, OCEAN, EXCITING and XSPECTRA. Its extendable framework will also allow the community to easily add new functions and to incorporate new simulation codes.Comment: 3 pages, 1 figure, software can be found open source under the BSD-3-clause license at https://github.com/AI-multimodal/Lightsho

Commission des Communautes Europeennes: Groupe du Porte-Parole. Reunion de la Commission du mercredi 29 octobre 1980 = Commission of European Communities: Spokesman Group. Meeting of the Commission on Wednesday, 29 October 1980. Spokesman Service Note to National Offices Bio No. (80) 432, 30 October 1980

We study strong-field ionization and rescattering beyond the long-wavelength limit of the dipole approximation with elliptically polarized mid-IR laser pulses. Full three-dimensional photoelectron momentum distributions (PMDs) measured with velocity map imaging and tomographic reconstruction revealed an unexpected sharp ridge structure in the polarization plane (2018 Phys. Rev. A 97 013404). This thin line-shaped ridge structure for low-energy photoelectrons is correlated with the ellipticity-dependent asymmetry of the PMD along the beam propagation direction. The peak of the projection of the PMD onto the beam propagation axis is shifted from negative to positive values when the sharp ridge fades away with increasing ellipticity. With classical trajectory Monte Carlo simulations and analytical analysis, we study the underlying physics of this feature. The underlying physics is based on the interplay between the lateral drift of the ionized electron, the laser magnetic field induced drift in the laser propagation direction, and Coulomb focusing. To apply our observations to emerging techniques relying on strong-field ionization processes, including time-resolved holography and molecular imaging, we present a detailed classical trajectory-based analysis of our observations. The analysis leads to the explanation of the fine structure of the ridge and its non-dipole behavior upon rescattering while introducing restrictions on the ellipticity. These restrictions as well as the ionization and recollision phases provide additional observables to gain information on the timing of the ionization and recollision process and non-dipole properties of the ionization process.ISSN:1361-6455ISSN:0368-3508ISSN:0953-4075ISSN:0022-370

Dynamics in Liver Stiffness Measurements Predict Outcomes in Advanced Chronic Liver Disease

Background &amp; Aims:Liver stiffness measurements (LSMs) provide an opportunity to monitor liver disease progression and regression noninvasively. We aimed to determine the prognostic relevance of LSM dynamics over time for liver-related events and death in patients with chronic liver disease. Methods:Patients with chronic liver disease undergoing 2 or more reliable LSMs at least 180 days apart were included in this retrospective cohort study and stratified at baseline (BL) as nonadvanced chronic liver disease (non-ACLD, BL-LSM &lt; 10 kPa), compensated ACLD (cACLD; BL-LSM ≥ 10 kPa), and decompensated ACLD. Data on all consecutive LSMs and clinical outcomes were collected. Results: There were 2508 patients with 8561 reliable LSMs (3 per patient; interquartile range, 2–4) included: 1647 (65.7%) with non-ACLD, 757 (30.2%) with cACLD, and 104 (4.1%) with decompensated ACLD. Seven non-ACLD patients (0.4%) and 83 patients with cACLD (10.9%) developed hepatic decompensation (median follow-up, 71 months). A 20% increase in LSM at any time was associated with an approximately 50% increased risk of hepatic decompensation (hazard ratio, 1.58; 95% CI, 1.41–1.79; P &lt;.001) and liver-related death (hazard ratio, 1.45; 95% CI, 1.28–1.68; P &lt;.001) in patients with cACLD. LSM dynamics yielded a high accuracy to predict hepatic decompensation in the following 12 months (area under the receiver operating characteristics curve = 0.933). The performance of LSM dynamics was numerically better than dynamics in Fibrosis-4 score (0.873), Model for End-Stage Liver Disease (0.835), and single time-point LSM (BL-LSM: 0.846; second LSM: 0.880). Any LSM decrease to &lt;20 kPa identified patients with cACLD with a substantially lower risk of hepatic decompensation (hazard ratio, 0.13; 95% CI, 0.07–0.24). If reliable, LSM also confers prognostic information in decompensated ACLD. Conclusions: Repeating LSM enables an individual and updated risk assessment for decompensation and liver-related mortality in ACLD.</p

New quantitative radiographic parameters for vertical and horizontal instability in acromioclavicular joint dislocations.

PURPOSE The aim of this study was to identify the most accurate and reliable quantitative radiographic parameters for assessing vertical and horizontal instability in different Rockwood grades of acromioclavicular joint (ACJ) separations. Furthermore, the effect of projectional variation on these parameters was investigated in obtaining lateral Alexander view radiographs. METHODS A Sawbone model of a scapula with clavicle was mounted on a holding device, and acromioclavicular dislocations as per the Rockwood classification system were simulated with the addition of horizontal posterior displacement. Projectional variations for each injury type were performed by tilting/rotating the Sawbone construct in the coronal, sagittal or axial plane. Radiographic imaging in the form of an anterior-posterior Zanca view and a lateral Alexander view were taken for each injury type and each projectional variation. Five newly defined radiographic parameters for assessing horizontal and vertical displacement as well as commonly used coracoclavicular distance view were measured. Reliability, validity and the effect of projectional variation were investigated for these radiographic measurements. RESULTS All radiographic parameters showed excellent intra- and interobserver reliability. The validity was excellent for the acromial centre line to dorsal clavicle (AC-DC) in vertical displacement and for the glenoid centre line to posterior clavicle (GC-PC) in horizontal displacement, whilst the remaining measurements showed moderate validity. For AC-DC and GC-PC, convergent validity expressed strong correlation to the effective distance and discriminant validity demonstrated its ability to differentiate between various grades of ACJ dislocations. The effect of projectional variation increased with the degree of deviation and was maximal (3 mm) for AC-DC in 20° anteverted malpositioning and for GC-PC in 20° retroverted malpositioning. CONCLUSIONS AC-DC and the GC-PC are two novel quantitative radiographic parameters of vertical and horizontal instability in ACJ dislocations that demonstrate excellent reliability and validity with reasonable inertness to malpositioning. The use of AC-DC for assessing vertical displacement and GC-PC for assessing horizontal displacement in a single Alexander view is recommended to guide the appropriate management of ACJ dislocations. A better appreciation of the degree of horizontal instability, especially in lower Rockwood grades (II, III) of ACJ dislocations, may improve management of these controversial injuries