Search results for "Focu"
showing 10 items of 1182 documents
Higher-order Kerr terms allow ionization-free filamentation in gases.
2010
We show that higher-order nonlinear indices ($n_4$, $n_6$, $n_8$, $n_{10}$) provide the main defocusing contribution to self-channeling of ultrashort laser pulses in air and Argon at 800 nm, in contrast with the previously accepted mechanism of filamentation where plasma was considered as the dominant defocusing process. Their consideration allows to reproduce experimentally observed intensities and plasma densities in self-guided filaments.
Measurement of high order Kerr refractive index of major air components
2009
International audience; We measure the instantaneous electronic nonlinear refractive index of N2 , O2 , and Ar at room temperature for a 90 fs and 800 nm laser pulse. Measurements are calibrated by post-pulse molecular alignment through a polarization technique. At low intensity, quadratic coefficients n2 are determined. At higher intensities, a strong negative contribution with a higher nonlinearity appears, which leads to an overall negative nonlinear Kerr refractive index in air above 26 TW/cm2 .
Measurement of high order Kerr refractive index of major air components: erratum
2010
A clarification is missing concerning the high order Kerr non-linearities deduced from our experimental data published in [Opt. Express 17, 13429-13434 (2009)]. Here, we rectify this omission by making explicit the distinction between cross-Kerr and Kerr effects, and by extrapolating the value of the nonlinear refractive index for the last effect. Since the occurrence of sign inversion in the Kerr effect is not affected, the overall report in [Opt. Express 17, 13429-13434] remains valid.
General approach to spatiotemporal modulational instability processes
2011
International audience; In this article, we derive the general exact solution of the modulation instability gain. The solution described here is valid for 1-D, 2-D, and 3-D cases considering any temporal response function of the medium and with possible higher order Kerr nonlinearities. In particular, we show that the gain induced by modulation instability is initial condition dependent, while the usual calculations do not lead to such a dependence. Applications for current and high-interest nonlinear propagation problems, such as 1-D optical fiber propagation with delayed Raman response and 2-D filamentation in gases, are investigated in detail. More specifically, we demonstrate that the 2-D …
Spectral dependence of purely-Kerr driven filamentation in air and argon
2010
5 pags, 4 figs.-- PACS number(s): 42.65.Jx, 42.65.Tg, 78.20.Ci. -- Publisher error corrected 27 September 2010, Erratum Phys. Rev. A 82, 039905 (2010): https://doi.org/10.1103/PhysRevA.82.033826
Ensikielen tunnistamisen merkityksestä suullisen kielitaidon arvioinnissa Yleisissä kielitutkinnoissa
2020
In this paper, we present a multidisciplinary study addressing fairness in the speaking test in a high-stakes language proficiency test in Finnish, National Certificates of Language Proficiency. The background of the research lies in studies on language assessment and (reversal) linguistic stereotyping and language attitudes. The focus L1 groups were Thai, Estonian, Finland Swedish, Arabic and Russian. Altogether 49 speech samples of test takers of these L1s were rated on a digital platform by 44 raters of the test system. The current paper reports on the sub-study that investigated whether the raters’ recognition of the test takers’ L1 affected their ratings and whether the effect differed…
Framework Towards a Virtual Tool for the Front-End of Employee-Driven Innovation in Healthcare
2017
This paper combines entrepreneurial behaviour and service innovation in order to investigate the use of the Idea Window; a virtual tool planned for employee-driven service development in a healthcare organisation. The empirical study investigates the tool used as a method for supporting employees' collaborative knowledge sharing in front-end of innovation in two study cases. Particularly, the research findings focus on how the virtual tool can be used for tackling the unknown - tacit knowledge, hidden possibilities, and initiatives in the context. The results are based on Idea Window entries and survey data collected in a Finnish hospital ward.
Mobile e-Services
2015
E-services are services delivered over the Internet. Such services have different proper- ties and dimensions, e.g. targeting different sectors, being accessible through different channels, or intended for frequent or infrequent use. Throughout this article we address e-services from a mobility perspective. We do this by 1) positioning mobile e-services within the research field; 2) reviewing related work on mobile e-services; and 3) present- ing and examining existing difficulties and opportunities when combining mobility and e-services. We see mobile e-services as the next generation of internet-based services and discuss important focus areas and future directions, giving extra notion to…
The compendium of self-enactable techniques to change and self-manage motivation and behaviour v.1.0.
2019
Behaviour change techniques describe the content of behaviour change interventions, but do not adequately account for the actions that people must themselves undertake to successfully change or self-manage motivation or behaviour. This paper describes the development of a compendium of self-enactable techniques, combining behaviour- and motivation-regulation techniques across six existing classifications of behaviour change techniques and three scoping reviews. The compendium includes 123 techniques, each of which is labelled, defined and presented with instructive examples to facilitate self-enactment. Qualitative feedback was gathered from intervention developers and the general public to…
A Framework for Small Group Support in Online Collaborative Learning - Combining Collaboration Scripts and Online Tutoring
2017
Many learners experience difficulties engaging in collaborative learning activities online. Computer-supported collaborative learning (CSCL) scripts have been implemented to support online learners. Collaboration scripts have shown much potential in facilitating students’ general collaboration skills. However, reported effects of collaboration scripts on domain-specific knowledge acquisition have been less positive. In this paper, I suggest an alternative framework for supporting CSCL learners by combining collaboration scripting and online tutoring. While collaboration scripts can facilitate the acquisition of general collaboration skills, the online tutor is capable of monitoring and asse…