1,721,210 research outputs found
Reconstruction of atomic resonances with attosecond streaking
Full text linkRecent development of spectroscopic techniques based on attosecond radiation has given the community the right tools to study the timing of the photoelectron process. In this work we investigate the effect of Fano resonances in attosecond streaking spectrograms and the application of standard phase-reconstruction algorithms. We show that while the existence of the infrared coupling (ac-Stark shift) hinders the applicability of FROG-like methods, under certain conditions it is still possible to use standard reconstruction algorithms to retrieve the photoemission delay of the bare resonance. Finally, we propose two strategies to study the strength of IR coupling using the attosecond streaking technique
Attosecond spectroscopy for the investigation of ultrafast dynamics in atomic, molecular and solid-state physics
Full text linkSince the first demonstration of the generation of attosecond pulses (1 as = 10(-18) s) in the extreme-ultraviolet spectral region, several measurement techniques have been introduced, at the beginning for the temporal characterization of the pulses, and immediately after for the investigation of electronic and nuclear ultrafast dynamics in atoms, molecules and solids with unprecedented temporal resolution. The attosecond spectroscopic tools established in the last two decades, together with the development of sophisticated theoretical methods for the interpretation of the experimental outcomes, allowed to unravel and investigate physical processes never observed before, such as the delay in photoemission from atoms and solids, the motion of electrons in molecules after prompt ionization which precede any notable nuclear motion, the temporal evolution of the tunneling process in dielectrics, and many others. This review focused on applications of attosecond techniques to the investigation of ultrafast processes in atoms, molecules and solids. Thanks to the introduction and ongoing developments of new spectroscopic techniques, the attosecond science is rapidly moving towards the investigation, understanding and control of coupled electron-nuclear dynamics in increasingly complex systems, with ever more accurate and complete investigation techniques. Here we will review the most common techniques presenting the latest results in atoms, molecules and solids
Refined ptychographic reconstruction of attosecond pulses
Full text linkAdvanced applications of attosecond pulses require the implementation of experimental techniques for a complete and accurate characterization of the pulse temporal characteristics. The method of choice is the frequency resolved optical gating for the complete reconstruction of attosecond bursts (FROG-CRAB), which requires the development of suitable reconstruction algorithms. In the last few years, various numerical techniques have been proposed and implemented, characterized by different levels of accuracy, robustness, and computational load. Many of them are based on the central momentum approximation (CMA), which may pose severe limits in the reconstruction accuracy. Alternative techniques have been successfully developed, based on the implementation of reconstruction algorithms which do not rely on this approximation, such as the Volkov-transform generalized projection algorithm (VTGPA). The main drawback is a notable increase of the computational load. We propose a new method, called refined iterative ptychographic engine (rePIE), which combines the advantages of a robust algorithm based on CMA, characterized by a fast convergence, with the accuracy of advanced algorithms not based on such approximation. The main idea is to perform a first fast iterative ptychographic engine (ePIE) reconstruction and then refine the result with just a few iterations of the VTGPA in order to correct for the error introduced by the CMA. We analyse the accuracy of the novel reconstruction method by comparing the residual error (i.e., the difference between the reconstructed and the simulated original spectrograms) when VTGPA, ePIE, and rePIE reconstructions are employed. We show that the rePIE approach is particularly useful in the case of short attosecond pulses characterized by a broad spectrum in the vacuum-ultraviolet (VUV)-extreme-ultraviolet (XUV) region
Semi-classical approach to compute RABBITT traces in multi-dimensional complex field distributions
Full text linkWe present a semi-classical model to calculate RABBITT (Reconstruction of Attosecond Beating By Interference of Two-photon Transitions) traces in the presence of a reference infrared field with a complex two-dimensional (2D) spatial distribution. The evolution of the electron spectra as a function of the pump-probe delay is evaluated starting from the solution of the classical equation of motion and incorporating the quantum phase acquired by the electron during the interaction with the infrared field. The total response to an attosecond pulse train is then evaluated by a coherent sum of the contributions generated by each individual attosecond pulse in the train. The flexibility of this model makes it possible to calculate spectrograms from non-trivial 2D field distributions. After confirming the validity of the model in a simple 1D case, we extend the discussion to describe the probe-induced phase in photo-emission experiments on an ideal metallic surface
Nonadiabatic quantum path analysis of the high-order harmonic generation in a highly ionized medium
No full textRevealing the time-dependent polarization of ultrashort pulses with sub-cycle resolution
Full text linkWe report on the first experiments characterizing the complete time-dependent 2D vector potential of a few-cycle laser pulse. The instantaneous amplitude and orientation of the electric field is determined with sub-cycle resolution, directly giving access to the polarization state of the pulse at any instant in time. This is achieved by performing an attosecond streaking experiment using a reaction microscope, where the full pulse characterization is performed directly in the target region
Current Status of Oral Disease-Modifying Treatment Effects on Cognitive Outcomes in Multiple Sclerosis: A Scoping Review
Full text linkIntroduction: Cognitive impairment represents one of the most hidden and disabling clinical aspects of multiple sclerosis (MS). In this regard, the major challenges are represented by the need for a comprehensive and standardised cognitive evaluation of each patient, both at disease onset and during follow-up, and by the lack of clear-cut data on the effects of treatments. In the present review, we summarize the current evidence on the effects of the available oral disease-modifying treatments (DMTs) on cognitive outcome measures. Materials and methods: In this systematised review, we extract all the studies that reported longitudinally acquired cognitive outcome data on oral DMTs in MS patients. Results: We found 29 studies that evaluated at least one oral DMT, including observational studies, randomised controlled trials, and their extension studies. Most of the studies (n = 20) evaluated sphingosine-1-phosphate (S1P) modulators, while we found seven studies on dimethyl fumarate, six on teriflunomide, and one on cladribine. The most frequently used cognitive outcome measures were SDMT and PASAT. Most of the studies reported substantial stability or mild improvement in cognitive outcomes in a short-time follow-up (duration of most studies ≤2 years). A few studies also reported MRI measures of brain atrophy. Conclusion: Cognitive outcomes were evaluated only in a minority of prospective studies on oral DMTs in MS patients with variable findings. More solid and numerous data are present for the S1P modulators. A standardised cognitive evaluation remains a yet unmet need to better clarify the possible positive effect of oral DMTs on cognition
Transient hair loss during treatment with dimethyl-fumarate for multiple sclerosis
No full textIntroduction Dimethyl-fumarate is a recently approved drug for relapsing-remitting Multiple Sclerosis in Italy. Clinical case A 55-year-old woman started therapy with dimethyl-fumarate on June 2014; it was well-tolerated aside from moderate flushing. Starting September 2014 she noticed a progressive hair loss, that neither the dermatological examination nor clinical and medical history nor blood investigations could explain. The hair loss slowed down after two months and was followed by a hair growth back. Discussion Transient hair loss is not a reported side effect of dimethyl-fumarate therapy but by excluding any known cause we attributed it to the beginning of the new therapy
Muscle involvement in myasthenia gravis: Expanding the clinical spectrum of myasthenia-myositis association from a large cohort of patients
No full textMyastenia-Inflammatory Myopathy (MG-IM) association has been described in less than 50 cases, as isolated reports or in few case series. In most cases, MG and IM onset occur simultaneously even if the overlapping clinical manifestations could lead to delay the diagnosis in the early stage of disease. In these cases, thymic pathology is present in more than 50% of cases. Pathological findings can be consistent of polymyositis (63%), dermatomyositis (25%) or granulomatosis (12%). Accurate clinical manifestations and severity of IM in MG, including muscle specific antibodies (MSA) and muscle MRI, have not been systematically investigated and focal or mild subclinical myositis have not been reported. We observed that focal myositis or asymptomatic CK elevation can also occur in MG. In this review we have also retrospectively re-analyzed the clinical, serological, pathological and muscle imaging data from 13 patients with MG- IM from our cohort of 441 MG patients (2,9%). Clinical onset occurred simultaneously in 10/13 patients, whereas in 2 patients the IM appeared later in MG disease course (range 10-14 years) and conversely in 1 patient MG symptoms occurred later in IM disease course (4 years). Median age at disease onset was 51 year (range 24-73 years) regardless of clinical onset (MG or IM). Median clinical follow-up was 88 months (range 31-237 months). IM was suspected by CK elevation in all patients (ranging 800-3000 UI/L at first detection) and non-fatigable muscle weakness unresponsive to acetylcholinesterase inhibitors. All the patients presented mild to moderate MG symptoms. Three main categories of muscle involvement, sometimes overlapping, were recognizable: distal, proximal and subclinical myositits, leading to three main clinical groups (A,B,C) and two overlapping subgroups (A/B and B/C). Thymus pathology was present in 10/13 patients. Anti-AChR was detected in al all patients associated with anti-Titin and -RyR1 in those patients with thymoma. No MSA, nor MAA antibodies were detected. Muscle biopsy confirmed IM in all patients. In conclusion we redefined the clinical spectrum of muscle involvement in MG-IM association, which represent a continuum among 3 main clinical groups: distal, proximal and subclinical muscle involvement. Minimal muscle involvement and focal myositis could be underestimated among myasthenic patients and early aggressive immunotherapy could be required in focal group
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