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Designing good multiple choice questions (MCQs) for education and assessment is time consuming and error-prone. An abundance of structured and semi-structured data has led to the development of automatic MCQ generation methods. Recently, ontologies have emerged as powerful tools to enable the automatic generation of MCQs. However, current question generation approaches focus on knowledge recall questions. In addition, questions that have so far been generated are, compared to manually created ones, simple and cover only a small subset of the required question complexity space in the education and assessment domain. In this paper, we focus on addressing the limitations of previous approaches by generating questions with complex stems that are suitable for scenarios beyond mere knowledge recall. We present a novel ontology-based approach that exploits classes and existential restrictions to generate case-based questions. Our contribution lies in: (1) the specification of procedure for generating case-based questions which involve (a) assembling complex stems, (b) selecting suitable options, and (c) providing explanations for option correctness/incorrectness, (2) an implementation of the procedure using a medical ontology and (3) and evaluation of our generation technique to test question quality and their suitability in practise. We implement our approach as an application for a medical education scenario on top of a large knowledge base in the medical domain. We generate more than 3 million questions for four physician specialities and evaluate our approach in a user study with 15 medical experts. We find that using a stratified random sample of 435 questions out of which 316 were rated by two experts, 129 (30%) are considered appropriate to be used in exams by both experts and a further 216 (50%) by at least one expert.

Stefania Biffi,1 Luca Petrizza,2 Chiara Garrovo,1 Enrico Rampazzo,2 Laura Andolfi,3 Pierangela Giustetto,4 Ivaylo Nikolov,5 Gabor Kurdi,5 Miltcho Boyanov Danailov,5 Giorgio Zauli,1 Paola Secchiero,6 Luca Prodi2 1Institute for Maternal and Child Health – IRCCS “Burlo Garofolo”, Trieste, 2Department of Chemistry ‘‘G Ciamician’’, University of Bologna, Bologna, 3IOM-CNR TASC Laboratory, Basovizza, Trieste, 4Ephoran – Multi-Imaging Solutions, Bioindustry Park Silvano Fumero, Torino, 5Elettra-Sincrotrone Trieste, Trieste, 6Department of Morphology, Surgery and Experimental Medicine and LTTA Centre, University of Ferrara, Ferrara, Italy Purpose: The aim of the present study was to develop nanoprobes with theranostic features, including – at the same time – photoacoustic, near-infrared (NIR) optical imaging, and photothermal properties, in a versatile and stable core–shell silica-polyethylene glycol (PEG) nanoparticle architecture. Materials and methods: We synthesized core–shell silica-PEG nanoparticles by a one-pot direct micelles approach. Fluorescence emission and photoacoustic and photothermal properties were obtained at the same time by appropriate doping with triethoxysilane-derivatized cyanine 5.5 (Cy5.5) and cyanine 7 (Cy7) dyes. The performances of these nanoprobes were measured in vitro, using nanoparticle suspensions in phosphate-buffered saline and blood, dedicated phantoms, and after incubation with MDA-MB-231 cells. Results: We obtained core–shell silica-PEG nanoparticles endowed with very high colloidal stability in water and in biological environment, with absorption and fluorescence emission in the NIR field. The presence of Cy5.5 and Cy7 dyes made it possible to reach a more reproducible and higher doping regime, producing fluorescence emission at a single excitation wavelength in two different channels, owing to the energy transfer processes within the nanoparticle. The nanoarchitecture and the presence of both Cy5.5 and Cy7 dyes provided a favorable agreement between fluorescence emission and quenching, to achieve optical imaging and photoacoustic and photothermal properties. Conclusion: We obtained rationally designed nanoparticles with outstanding stability in biological environment. At appropriate doping regimes, the presence of Cy5.5 and Cy7 dyes allowed us to tune fluorescence emission in the NIR for optical imaging and to exploit quenching processes for photoacoustic and photothermal capabilities. These nanostructures are promising in vivo theranostic tools for the near future. Keywords: dye-doped nanoparticles, optical imaging, NIR imaging, photoacoustic imaging, photothermal therapy, PEGylated nanoparticles

An important trend in extreme ultraviolet and soft X-ray free-electron laser (FEL) development in recent years has been the use of seeding by an external laser, aimed to improve the coherence and stability of the generated pulses. The high-gain harmonic generation seeding technique was first implemented at FERMI and provided FEL radiation with high coherence as well as intensity and wavelength stability comparable to table-top ultrafast lasers. At FERMI, the seed laser has another very important function: it is the source of external laser pulses used in pump–probe experiments allowing one to achieve a record-low timing jitter. This paper describes the design, performance and operational modes of the FERMI seed laser in both single- and double-cascade schemes. In addition, the planned upgrade of the system to meet the challenges of the upgrade to echo-enabled harmonic generation mode is presented. [ABSTRACT FROM AUTHOR]

Understanding and controlling the thermal transport at nanoscale is a key ingredient for the development of future nanoelectronical devices. In this study of thin silicon carbide (SiC) membrane we demonstrate the potential of free electron laser extreme ultraviolet (EUV) transient grating (TG) technique as contactless probe for thermoelastic response at length scales of 84 nm, where the Fourier heat diffusion law is no longer valid. The results have revealed that the mechanical behavior of the system can be fully described in the framework of Lamb waves. Moreover, by use of a bidimensional spatial detector to measure the TG signal, a new feature is the observed, time dependence in the emission angle of the transient diffraction, correlated to the transient grating signal intensity. [ABSTRACT FROM AUTHOR]

The rapid development of extreme ultraviolet (EUV) and x-ray ultrafast coherent light sources such as free electron lasers (FELs) has triggered the extension of wave-mixing techniques to short wavelengths. This class of experiments, based on the interaction of matter with multiple light pulses through the Nth order susceptibility, holds the promise of combining intrinsic ultrafast time resolution and background-free signal detection with nanometer spatial resolution and chemical specificity. A successful approach in this direction has been the combination of the unique characteristics of the seeded FEL FERMI with dedicated four-wave-mixing (FWM) setups, which leads to the demonstration of EUV-based transient grating (TG) spectroscopy. In this perspective paper, we discuss how the TG approach can be extended toward more general FWM spectroscopies by exploring the intrinsic multiparameter nature of nonlinear processes, which derives from the ability of controlling the properties of each field independently. [ABSTRACT FROM AUTHOR]

Abstract: Sub-micrometer periodic structures were prepared on the surface of poly-carbonate films by UV laser treatment methods: a) grating-like structures having a period of 156 nm were induced by ArF excimer laser, b) 416 nm and 833 nm periodic gratings were prepared by two-beam interference realized by the fourth harmonic of a Nd:Yag laser. The sub-micrometer adhesion pattern accompanying the topographical structure was determined by pulsed force mode atomic force microscopy. The difference between the measured adhesion modulation and the adhesion profile calculated based on the topography was explained by the UV laser illumination caused phase and chemical changes. XPS investigations proved that chemical modification of the polymer occurs and the degree of the photo-degradation depends on the treating laser wavelength as well as on the number and fluence of the laser pulses. It was demonstrated by tapping mode atomic force microscopy that bovine serum albumin attaches to surface parts having higher adhesion. The dependence of the protein adherence on the surface treatment conditions was demonstrated based on the C 1s and O 1s spectra and on the proteinaceous nitrogen level. [Copyright &y& Elsevier]

Broad-band amplification of femtosecond laser pulses using the scheme of noncollinear optical chirped pulse parametric amplification is modeled. The effect of two-photon absorption at the pump wavelength was also taken into account. The signal pulses range from 220 to 410 nm with pump pulses at 267, 248, and 213 nm. The best four crystals chosen among 12 possible ones are BBO, KDP, CLBO, and LB4. In an experiment, 30-fs laser pulses at 400 nm were amplified in a BBO crystal pumped by 267 nm pulses, exhibiting a single pass gain of 3550. The gain was found spectrally flat within the available 17-nm bandwidth of the signal pulse. [ABSTRACT FROM PUBLISHER]

A misaligned stretcher or compressor in a chirped pulse amplification laser introduces residual angular dispersion into the beam, resulting in temporal distortion of the pulse. We demonstrate that an imaging spectrograph is capable for measuring the angular dispersion of a laser beam by an accuracy of 0.2 μrad/nm. Using this technique, the analytical expressions of residual angular dispersion of misaligned prism and grating compressors are experimentally proved. Temporal degradations of short pulses due to angular dispersion are studied by measuring the temporal stretch of 16-fs pulses, while the issues of contrast deterioration are also discussed. It is proved that the simultaneous measurement of angular dispersion and pulse duration offers the most precise alignment procedure of prismatic and grating compressors. [ABSTRACT FROM PUBLISHER]

Femtosecond pulses at 400 nm were amplified using a noncollinear optical parametric amplifier pumped by picosecond pulses at 267 nm. A flat spectral gain exceeding 3500 was achieved in single pass within the available 17 nm bandwidth of the signal pulse. The effect of pump depletion, group delay difference, and the geometry of the interacting pulses on the spectral gain are also investigated. © 2002 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Abstract: Closed analytical formulae are given for the residual angular dispersion resulted from the non-parallel surfaces of both a grating pair and a prism pair pulse compressor. Accurate measurements of the angular dispersion of pulses leaving the misaligned pulse compressors agree well with the first principle simulation curves. The corresponding lengthening of the transform limited 18 fs pulses was also determined. Finally, it is experimentally proved that by simultaneous monitoring of angular dispersion and pulse duration, the stretcher–compressor system of a chirped pulse amplification laser can be aligned very precisely. [Copyright &y& Elsevier]

Abstract: Grating-like structures having a period of 416 nm were produced on the surface of poly-carbonate films by two-beam interference realized by the fourth harmonic of Nd:Yag laser. The period of the structures was half of that the applied master grating, the ratio of the width of the valleys to the period was tuned by the intensity, the depth of the modulation was increased by the number of laser pulses. Pulsed force mode atomic force microscopy was applied to study the topography and the adhesion on structured surfaces with sub-micrometer resolution. The adhesion modulation caused by the topography was calculated along line cross-sections of the AFM pictures taking into account the tip and surface geometry. The separation of the effects of the topography and the laser-induced material changes proved that the adhesion is increased at the areas illuminated by laser beam having a fluence above the melting threshold. The laser-induced material changes cause an additional adhesion increase at the valleys of the structure. It was shown that the adherence of albumin results in dense packing on poly-carbonate surface parts having sub-micrometer periodic adhesion modulation. [Copyright &y& Elsevier]

A liquid carbon (l-C) sample is generated through constant volume heating exposing an amorphous carbon foil to an intense ultrashort laser pulse. Time-resolved x-ray absorption spectroscopy at the C K edge is used to monitor the dynamics of the melting process revealing a subpicosecond rearrangement of the electronic structure associated with a sudden change of the C bonding hybridization. The obtained l-C sample, resulting from a nonthermal melting mechanism, reaches a transient equilibrium condition with a temperature of about 14 200 K and pressure in the order of 0.5 Mbar in about 0.3 ps, prior to hydrodynamic expansion. A detailed analysis of the atomic and electronic structure in solid-density l-C based on time-resolved x-ray absorption spectroscopy and theoretical simulations is presented. The method can be fruitfully used for extending the experimental investigation of the C phase diagram in a vast unexplored region covering the 10³-104K temperature range with pressures up to 1 Mbar. [ABSTRACT FROM AUTHOR]

The extension of nonlinear optical techniques to the extreme-ultraviolet (EUV), soft and hard x-ray regime represents one of the open challenges of modern science since it would combine chemical specificity with background-free detection and ultrafast time resolution. We report on the first observation of a four-wave-mixing (FWM) response from solid-state samples stimulated exclusively by EUV pulses. The all-EUV FWM signal was generated by the diffraction of high-order harmonics of the FERMI free-electron laser (FEL) from the standing wave resulting from the interference of two crossed FEL pulses at the fundamental wavelength. From the intensity of the FWM signal, we are able to extract the first-ever estimate of an effective value of ~6×10-24m²V-2 for the third-order nonlinear susceptibility in the EUV regime. This proof of principle experiment represents a significant advance in the field of nonlinear optics and sets the starting point for a manifold of techniques, including frequency and phase-resolved FWM methods, that are unprecedented in this photon-energy regime. [ABSTRACT FROM AUTHOR]

Ultrashort deep ultraviolet (DUV) pulses serve as indispensable tools for investigating molecular dynamics on the femtosecond scale. Nonlinear frequency upconversion of near-infrared (NIR) light sources in a sequence of nonlinear crystals is a common method for their generation. However, preserving the temporal duration of the starting source encounters challenges owing to phase-matching bandwidth limitations within the harmonic generation process. Here we propose an approach for circumventing this limitation and demonstrate it for the case of generation of the third harmonic of 800 nm pulses in a two-stage scheme (second harmonic generation succeeded by sum-frequency mixing of the fundamental and second harmonic pulses). Expanding the bandwidth of the DUV pulse involves the utilization for the last mixing process of two nonlinear crystals, detuned to convert opposite sides of the spectrum. The implementation of this approach yields 20 µJ, 263 nm DUV pulses as short as 19 fs after compression. The setup is very compact and extremely stable due to the common-path scheme, which makes it very interesting for a variety of advanced ultrafast spectroscopy applications.

Dimensionality plays a key role in the emergence of ordered phases, such as charge density-waves (CDW), which can couple to, and modulate, the topological properties of matter. In this work, we study the out-of-equilibrium dynamics of the paradigmatic quasi-one-dimensional material (TaSe 4 ) 2 I, which exhibits a transition into an incommensurate CDW phase when cooled to just below room temperature, namely at T CDW = 263 K. We make use of both optical laser and free-electron laser (FEL) based time-resolved spectroscopies in order to study the effect of a selective excitation on the normal-state and on the CDW phases by probing the near-infrared/visible optical properties both along and perpendicularly to the direction of the CDW, where the system is metallic and insulating, respectively. Excitation of the core-levels by ultrashort X-ray FEL pulses at 47 eV and 119 eV induces reflectivity transients resembling those recorded when only exciting the valence band of the compound - by near-infrared pulses at 1.55 eV - in the case of the insulating sub-system. Conversely, the metallic sub-system displays relaxation dynamics which depend on the energy of photo-excitation. Moreover, excitation of the CDW amplitude mode is recorded only for excitation at a low-photon-energy. This fact suggests that the coupling of light to ordered states of matter can predominantly be achieved when directly injecting delocalized carriers in the valence band, rather than localized excitations in the core levels. Complementing this, table-top experiments allow us to prove the quasi-unidirectional nature of the CDW phase in (TaSe 4 ) 2 I, whose fingerprints are detected along its c -axis only. Our results provide new insights into the symmetry of the ordered phase of (TaSe 4 ) 2 I perturbed by a selective excitation, and suggest a novel approach based on complementary table-top and FEL spectroscopies for the study of complex materials.

Expanding the activity of wide bandgap semiconductors from the UV into the visible range has become a central goal for their application in green solar photocatalysis. The hybrid plasmonic/semiconductor system, based on silver nanoparticles (Ag NPs) embedded in a film of CeO 2 , is an example of a functional material developed with this aim. In this work, we take advantage of the chemical sensitivity of free electron laser (FEL) time-resolved soft X-ray absorption spectroscopy (TRXAS) to investigate the electron transfer process from the Ag NPs to the CeO 2 film generated by the NPs plasmonic resonance photoexcitation. Ultrafast changes (<200 fs) of the Ce N 4,5 absorption edge allowed us to conclude that the excited Ag NPs transfer electrons to the Ce atoms of the CeO 2 film through a highly efficient electron-based mechanism. These results demonstrate the potential of FEL-based TRXAS measurements for the characterization of energy transfer in novel hybrid plasmonic/semiconductor materials.

Advances in developing ultrafast coherent sources operating at extreme ultraviolet (EUV) and x-ray wavelengths allow the extension of nonlinear optical techniques to shorter wavelengths. Here, we describe EUV transient grating spectroscopy, in which two crossed femtosecond EUV pulses produce spatially periodic nanoscale excitations in the sample and their dynamics is probed via diffraction of a third time-delayed EUV pulse. The use of radiation with wavelengths down to 13.3 nm allowed us to produce transient gratings with periods as short as 28 nm and observe thermal and coherent phonon dynamics in crystalline silicon and amorphous silicon nitride. This approach allows measurements of thermal transport on the ~10-nm scale, where the two samples show different heat transport regimes, and can be applied to study other phenomena showing nontrivial behaviors at the nanoscale, such as structural relaxations in complex liquids and ultrafast magnetic dynamics.

Time-resolved investigations have begun a new era of chemistry and physics, enabling the monitoring in real time of the dynamics of chemical reactions and matter. Induced transient optical absorption is a basic ultrafast electronic effect, originated by a partial depletion of the valence band, that can be triggered by exposing insulators and semiconductors to sub-picosecond extreme-ultraviolet pulses. Besides its scientific and fundamental implications, this process is very important as it is routinely applied in free-electron laser (FEL) facilities to achieve the temporal superposition between FEL and optical laser pulses with tens of femtoseconds accuracy. Here, a set of methodologies developed at the FERMI facility based on ultrafast effects in condensed materials and employed to effectively determine the FEL/laser cross correlation are presented.

Free-electron lasers (FELs) currently represent a step forward on time-resolved investigations on any phase of matter through pump-probe methods involving FELs and laser beams. That class of experiments requires an accurate spatial and temporal superposition of pump and probe beams on the sample, which at present is still a critical procedure. More efficient approaches are demanded to quickly achieve the superposition and synchronization of the beams. Here, we present what we believe is a novel technique based on an integrated device allowing the simultaneous characterization and the fast spatial and temporal overlapping of the beams, reducing the alignment procedure from hours to minutes.