Two-color polarization control on angularly resolved attosecond time delays

Measured photoionization time delays may exhibit large variations as a function of the emission angles, even for spherically symmetric targets, as shown in recent RABBITT (reconstruction of attosecond beating by interference of two-photon transitions) experiments. The contributions from different pathways to the two-photon quantum channels can already explain the observed phase jumps that shape those angular distributions. Here, we propose a simple analytical model to describe angularly-resolved RABBITT spectra as a function of the relative polarization angle between the ionizing attosecond pulse train and the assisting IR field. We demonstrate that the angular dependencies of the measured delays can be analytically predicted and the position of the phase jumps reduced to the analysis of a few relevant parameters.Comment: 10 pages, 4 figure

Multimedia Vocabularies on the Semantic Web

This document gives an overview on the state-of-the-art of multimedia metadata formats. Initially, practical relevant vocabularies for developers of Semantic Web applications are listed according to their modality scope. In the second part of this document, the focus is set on the integration of the multimedia vocabularies into the Semantic Web, that is to say, formal representations of the vocabularies are discussed

Neural response development during distributional learning.

We investigated online electrophysiological components of distributional learning, specifically of tones by listeners of a non-tonal language. German listeners were presented with a bimodal distribution of syllables with lexical tones from a synthesized continuum based on Cantonese level tones. Tones were presented in sets of four standards (within-category tokens) followed by a deviant (across-category token). Mismatch negativity (MMN) was measured. Earlier behavioral data showed that exposure to this bimodal distribution improved both categorical perception and perceptual acuity for level tones [1]. In the present study we present analyses of the electrophysiological response recorded during this exposure, i.e., the development of the MMN response during distributional learning. This development over time is analyzed using Generalized Additive Mixed Models and results showed that the MMN amplitude increased for both within- and across-category tokens, reflecting higher perceptual acuity accompanying category formation. This is evidence that learners zooming in on phonological categories undergo neural changes associated with more accurate phonetic perception.This research was also supported by a Research Networking grant (ESF) NetwordS No. 6609 to NB and a Leiden University AMT Individual Researcher Grant to JSN

Short-term exposure enhances perception of both between- and within-category acoustic information.

A critical question in speech research is how listeners use non-discrete acoustic cues for discrimination between discrete alternative messages (e.g. words). Previous studies have shown that distributional learning can improve listeners’ discrimination of non-native speech sounds. Less is known about effects of training on perception of within-category acoustic detail. The present research investigates adult listeners’ perception of and discrimination between lexical tones without training or after a brief training exposure. Native speakers of German (a language without lexical tone) heard a 13-step pitch continuum of the syllable /li:/. Two different tasks were used to assess sensitivity to acoustic differences on this continuum: a) pitch height estimation and b) AX discrimination. Participants performed these tasks either without exposure or after exposure to a bimodal distribution of the pitch continuum. The AX discrimination results show that exposure to a bimodal distribution enhanced discrimination at the category boundary (i.e. categorical perception) of high vs. low tones. Interestingly, the pitch estimation task results followed a categorisation (sigmoid) function without exposure, but a linear function after exposure, suggesting estimates became less categorical in this task. The results suggest that training exposure may enhance not only discrimination between contrastive speech sounds (consistent with previous studies), but also perception of withincategory acoustic differences. Different tasks may reveal different skills

Reflecting on Hybrid Events: Learning from a Year of Hybrid Experiences

The COVID-19 pandemic led to a sudden shift to virtual work and events, with the last two years enabling an appropriated and rather simulated togetherness - the hybrid mode. As we return to in-person events, it is important to reflect on not only what we learned about technologies and social justice, but about the types of events we desire, and how to re-design them accordingly. This SIG aims to reflect on hybrid events and their execution: scaling them across sectors, communities, and industries; considering trade-offs when choosing technologies; studying best practices and defining measures of "success"for hybrid events; and finally, identifying and charting the wider social, ethical, and legal implications of hybrid formats. This SIG will consolidate these topics by inviting participants to collaboratively reflect on previous hybrid experiences and what can be learned from them

Tracking the ultraviolet-induced photochemistry of thiophenone during and after ultrafast ring opening

Photoinduced isomerization reactions lie at the heart of many chemical processes in nature. The mechanisms of such reactions are determined by a delicate interplay of coupled electronic and nuclear dynamics occurring on the femtosecond scale, followed by the slower redistribution of energy into different vibrational degrees of freedom. Here we apply time-resolved photoelectron spectroscopy with a seeded extreme ultraviolet free-electron laser to trace the ultrafast ring opening of gas-phase thiophenone molecules following ultraviolet photoexcitation. When combined with ab initio electronic structure and molecular dynamics calculations of the excited- and ground-state molecules, the results provide insights into both the electronic and nuclear dynamics of this fundamental class of reactions. The initial ring opening and non-adiabatic coupling to the electronic ground state are shown to be driven by ballistic S–C bond extension and to be complete within 350 fs. Theory and experiment also enable visualization of the rich ground-state dynamics that involve the formation of, and interconversion between, ring-opened isomers and the cyclic structure, as well as fragmentation over much longer timescales

δ-Aminolevulinic acid transport in murine mammary adenocarcinoma cells is mediated by beta transporters

δ-aminolevulinic acid, the precursor of porphyrin biosynthesis has been used to induce the endogenous synthesis of the photosensitiser protoporphyrin IX for photodynamic therapy in the treatment of various tumours. The aim of this work was to characterise the δ-aminolevulinic acid transport system in the murine mammary adenocarcinoma cell line LM3 using 14C-δ-aminolevulinic acid, to finally improve δ-aminolevulinic acid incorporation in mammalian cells. Our results showed that δ-aminolevulinic acid is incorporated into these cells by two different mechanisms, passive diffusion which is important at the beginning of the incubation, and active transport. Specificity assays suggested that the transporter involved in δ-aminolevulinic acid incorporation is a BETA transporter, probably GAT-2