1,062 research outputs found
Interference stabilization of autoionizing states in molecular studied by time- and angular-resolved photoelectron spectroscopy
An autoionizing resonance in molecular N is excited by an ultrashort XUV
pulse and probed by a subsequent weak IR pulse, which ionizes the contributing
Rydberg states. Time- and angular-resolved photoelectron spectra recorded with
a velocity map imaging spectrometer reveal two electronic contributions with
different angular distributions. One of them has an exponential decay rate of
fs, while the other one is shorter than 10 fs. This observation is
interpreted as a manifestation of interference stabilization involving the two
overlapping discrete Rydberg states. A formalism of interference stabilization
for molecular ionization is developed and applied to describe the autoionizing
resonance. The results of calculations reveal, that the effect of the
interference stabilization is facilitated by rotationally-induced couplings of
electronic states with different symmetry.Comment: 8 pages, 6 figure
Timelines Are Expressive Enough to Capture Action-Based Temporal Planning
Planning problems are usually expressed by specifying which actions can be
performed to obtain a given goal. In temporal planning problems, actions come
with a time duration and can overlap in time, which noticeably increase the
complexity of the reasoning process. Action-based temporal planning has been
thoroughly studied from the complexity-theoretic point of view, and has been
proved to be EXPSPACE-complete in its general formulation. Conversely,
timeline-based planning problems are represented as a collection of variables
whose time-varying behavior is governed by a set of temporal constraints, called
synchronization rules. Timelines provide a unified framework to reason about
planning and execution under uncertainty. Timeline-based systems are being
successfully employed in real-world complex tasks, but, in contrast to
action-based planning, little is known on their computational complexity and
expressiveness. In particular, a comparison of the expressiveness of the action-
and timeline-based formalisms is still missing. This paper contributes a first
step in this direction by proving the EXPSPACE-completeness of timeline-based
planning with no temporal horizon and bounded temporal relations only. The
result is shown via a reduction from action-based temporal planning, thus
proving that timelines are expressive enough to capture it
Equivalence of using a desktop virtual reality science simulation at home and in class
The use of virtual laboratories is growing as companies and educational institutions try to expand their reach, cut costs, increase student understanding, and provide more accessible hands on training for future scientists. Many new higher education initiatives outsource lab activities so students now perform them online in a virtual environment rather than in a classroom setting, thereby saving time and money while increasing accessibility. In this paper we explored whether the learning and motivational outcomes of interacting with a desktop virtual reality (VR) science lab simulation on the internet at home are equivalent to interacting with the same simulation in class with teacher supervision. A sample of 112 (76 female) university biology students participated in a between-subjects experimental design, in which participants learned at home or in class from the same virtual laboratory simulation on the topic of microbiology. The home and classroom groups did not differ significantly on post-test learning outcome scores, or on self-report measures of intrinsic motivation or self-efficacy. Furthermore, these conclusions remained after accounting for prior knowledge or goal orientation. In conclusion, the results indicate that virtual simulations are learning activities that students can engage in just as effectively outside of the classroom environment
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Population transfer to high angular momentum states in infrared-assisted XUV photoionization of helium
An extreme-ultraviolet (XUV) laser pulse consisting of harmonics of a fundamental near-infrared (NIR) laser frequency is combined with the NIR pulse to systematically study two-color photoionization of helium atoms. A time-resolved photoelectron spectroscopy experiment is carried out where energy- A nd angle-resolved photoelectron distributions are obtained as a function of the NIR intensity and wavelength. Time-dependent Schrödinger equation calculations are performed for the conditions corresponding to the experiment and used to extract residual populations of Rydberg states resulting from excitation by the XUV + NIR pulse pair. The residual populations are studied as a function of the NIR intensity (3.5 à 1010-8 à 1012 W cm-2) and wavelength (760-820 nm). The evolution of the photoelectron distribution and the residual populations are interpreted using an effective restricted basis model, which includes the minimum set of states relevant to the features observed in the experiments. As a result, a comprehensive and intuitive picture of the laser-induced dynamics in helium atoms exposed to a two-color XUV-NIR light field is obtained. © 2020 The Author(s). Published by IOP Publishing Ltd
Population transfer to high angular momentum states in infrared-assisted XUV photoionization of helium
An extreme-ultraviolet (XUV) laser pulse consisting of harmonics of a fundamental near-infrared (NIR) laser frequency is combined with the NIR pulse to systematically study two-color photoionization of helium atoms. A time-resolved photoelectron spectroscopy experiment is carried out where energy- and angle-resolved photoelectron distributions are obtained as a function of the NIR intensity and wavelength. Time-dependent Schrödinger equation calculations are performed for the conditions corresponding to the experiment and used to extract residual populations of Rydberg states resulting from excitation by the XUV + NIR pulse pair. The residual populations are studied as a function of the NIR intensity (3.5 Ă 1010 â 8 Ă 1012 W cmâ2) and wavelength (760â820 nm). The evolution of the photoelectron distribution and the residual populations are interpreted using an effective restricted basis model, which includes the minimum set of states relevant to the features observed in the experiments. As a result, a comprehensive and intuitive picture of the laser-induced dynamics in helium atoms exposed to a two-color XUVâNIR light field is obtained
Role of Spin-Orbit Coupling in High-order Harmonic Generation Revealed by Super-Cycle Rydberg Trajectories
High-harmonic generation is typically thought of as a sub-laser-cycle
process, with the electron's excursion in the continuum lasting a fraction of
the optical cycle. However, it was recently suggested that long-lived Rydberg
states can play a particularly important role in atoms driven by the
combination of the counter-rotating circularly polarized fundamental light
field and its second harmonic. Here we report direct experimental evidence of
long and stable Rydberg trajectories contributing to high-harmonic generation.
We confirm their effect on the harmonic emission via Time-Dependent
Schr{\"o}dinger Equation simulations and track their dynamics inside the laser
pulse using the spin-orbit evolution in the ionic core, utilizing the
spin-orbit Larmor clock. Our observations contrast sharply with the general
view that long-lived Rydberg orbits should generate negligible contribution to
the macroscopic far-field high harmonic response of the medium. Indeed, we show
how and why radiation from such states can lead to well collimated macroscopic
signal in the far field
Evaluation of the prognostic value of electrocardiography parameters and heart rhythm in patients with pulmonary hypertension
Background: Several studies have analyzed arrhythmias in patients with pulmonary hypertension (PH) and increased P-wave duration was identified as a risk factor for development of atrial fibrillation (AF).
Methods: We retrospectively analyzed the incidence of arrhythmias in patients with an initial diagnosis of PH during long-term follow-up and assessed the prognostic value of electrocardiography (ECG) data. Data from 167 patients were analyzed (Dana Point Classification: Group 1: 59 patients, Group 2: 28 patients, Group 3: 39 patients, Group 4: 41 patients). Clinical, 6-minÂute walk distance test, echocardiography and right heart catheterization data were collected, and baseline/follow-up ECGs were analyzed.
Results: Baseline ECGs revealed sinus rhythm in 137 patients. Thirteen patients had newly onset AF during follow-up. In 30 patients, baseline ECG showed AF. Patients with baseline AF showed higher atrial diameters and higher right atrial pressure. Patients with P-wave duÂration > 0.11 s had shorter survival. Other ECG parameters (PQ-interval, QRS-width, QT-/ /QTc-interval) were not associated with survival. Mean survival times were 79.4 ± 5.4 months (sinus rhythm), 64.4 ± 12.9 months (baseline AF) and 58.8 ± 8.9 months (newly onset AF during follow-up) (p = 0.565).
Conclusions: Atrial fibrillation predict adverse prognosis in patients with PH and a longer P-wave (> 0.11 s) is associated with shorter survival time
Free and cued selective reminding test predicts progression to Alzheimer's disease in people with mild cognitive impairment
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