Core-excited states of SF6_{6} probed with soft X-ray femtosecond transient absorption of vibrational wavepackets

A vibrational wavepacket in SF$_6$, created by impulsive stimulated Raman scattering with a few-cycle infrared pulse, is mapped onto five sulfur core-excited states using table-top soft X-ray transient absorption spectroscopy between 170-200 eV. The amplitudes of the X-ray energy shifts of the femtosecond oscillations depend strongly on the nature of the state. The prepared wavepacket is controlled with the pump laser intensity to probe the core-excited levels for various extensions of the S-F stretching motion. This allows the determination of the relative core-level potential energy gradients, in good agreement with TDDFT calculations. This experiment demonstrates a new means of characterizing core-excited potential energy surfaces

High resolution x ray spectra of carbon monoxide reveal ultrafast dynamics induced by long UV pulse

In theoretical simulations of a UV x ray pump probe UVX PP setup, we show that frequency detuning of the pump UV pulse acts as a camera shutter by regulating the duration of the UVX PP process. This two photon absorption with long overlapping UV and x ray pulses, allowing for high spectral resolution, thereby provides information about ultrafast dynamics of the nuclear wave packet without the requirement of ultrashort pulses and controlled delay times. In a case study of carbon monoxide, the calculated UVX PP spectra of the O1s amp; 8722;12 amp; 960;1 and C1s amp; 8722;12 amp; 960;1 core excited states show different vibrational profiles. The interference of intermediate vibrational states reveals details of nuclear dynamics in the UVX PP process related to a variable duration time controlled by the UV detuning. Both O1s amp; 8722;12 amp; 960;1 and C1s amp; 8722;12 amp; 960;1 pump probe channels display a splitting of the spectral profile, which however is associated with different physical mechanisms. At the O1s amp; 8722;12 amp; 960;1 resonance, the observed dispersive and non dispersive spectral bands intersect and result in destructive interferenc

Acute effects of nicotine on visual search tasks in young adult smokers

Rationale Nicotine is known to improve performance on tests involving sustained attention and recent research suggests that nicotine may also improve performance on tests involving the strategic allocation of attention and working memory. Objectives We used measures of accuracy and response latency combined with eye-tracking techniques to examine the effects of nicotine on visual search tasks. Methods In experiment 1 smokers and non-smokers performed pop-out and serial search tasks. In experiment 2, we used a within-subject design and a more demanding search task for multiple targets. In both studies, 2-h abstinent smokers were asked to smoke one of their own cigarettes between baseline and tests. Results In experiment 1, pop-out search times were faster after nicotine, without a loss in accuracy. Similar effects were observed for serial searches, but these were significant only at a trend level. In experiment 2, nicotine facilitated a strategic change in eye movements resulting in a higher proportion of fixations on target letters. If the cigarette was smoked on the first trial (when the task was novel), nicotine additionally reduced the total number of fixations and refixations on all letters in the display. Conclusions Nicotine improves visual search performance by speeding up search time and enabling a better focus of attention on task relevant items. This appears to reflect more efficient inhibition of eye movements towards task irrelevant stimuli, and better active maintenance of task goals. When the task is novel, and therefore more difficult, nicotine lessens the need to refixate previously seen letters, suggesting an improvement in working memory

Time resolved study of recoil induced rotation by X ray pump X ray probe spectroscopy

Modern stationary X ray spectroscopy is unable to resolve rotational structure. In the present paper, we propose to use time resolved two color X ray pump probe spectroscopy with picosecond resolution for real time monitoring of the rotational dynamics induced by the recoil effect. The proposed technique consists of two steps. The first short pump X ray pulse ionizes the valence electron, which transfers angular momentum to the molecule. The second time delayed short probe X ray pulse resonantly excites a 1s electron to the created valence hole. Due to the recoil induced angular momentum the molecule rotates and changes the orientation of transition dipole moment of core excitation with respect to the transition dipole moment of the valence ionization, which results in a temporal modulation of the probe X ray absorption as a function of the delay time between the pulses. We developed an accurate theory of the X ray pump probe spectroscopy of the recoil induced rotation and study how the energy of the photoelectron and thermal dephasing affect the structure of the time dependent X ray absorption using the CO molecule as a case study. We also discuss the feasibility of experimental observation of our theoretical findings, opening new perspectives in studies of molecular rotational dynamic

The C-type lectin receptor CLECSF8 (CLEC4D) is expressed by myeloid cells and triggers cellular activation through syk kinase

11 pags, 7 figsCLECSF8 is a poorly characterized member of the "Dectin-2 cluster" of C-type lectin receptors and was originally thought to be expressed exclusively by macrophages. We show here that CLECSF8 is primarily expressed by peripheral blood neutrophils and monocytes and weakly by several subsets of peripheral blood dendritic cells. However, expression of this receptor is lost upon in vitro differentiation of monocytes into dendritic cells or macrophages. Like the other members of the Dectin-2 family, which require association of their transmembrane domains with signaling adaptors for surface expression, CLECSF8 is retained intracellularly when expressed in non-myeloid cells. However, we demonstrate that CLECSF8 does not associate with any known signaling adaptor molecule, including DAP10, DAP12, or the FcRγ chain, and we found that the C-type lectin domain of CLECSF8 was responsible for its intracellular retention. Although CLECSF8 does not contain a signaling motif in its cytoplasmic domain, we show that this receptor is capable of inducing signaling via Syk kinase in myeloid cells and that it can induce phagocytosis, proinflammatory cytokine production, and the respiratory burst. These data therefore indicate that CLECSF8 functions as an activation receptor on myeloid cells and associates with a novel adaptor molecule. Characterization of the CLECSF8-deficient mice and screening for ligands using oligosaccharide microarrays did not provide further insights into the physiological function of this receptor. © 2012 by The American Society for Biochemistry and Molecular Biology, Inc.This work was funded by the Wellcome Trust, the National Research Foundation, the Deutscher Akademischer Austauschdienst, the University of Cape Town, the UK Research Council Basic Technology Initiative “Glycoar-rays” (GRS/79268), and the UK Medical Research Council. A. S. P is a fellowof the Fundação para a Ciência e Tecnologia (SFRH/BPD/26515/2006, Portugal) and M. A. C. of the Consejo Superior de Investigaciones Cientificas, Programe “Junta para la Ampliación de Estudios” (JaeDoc/098/2011) cofinanced by the Fondo Social Europeo

Young's double-slit experiment using two-center core-level photoemission: Photoelectron recoil effects

Core-level photoemission from N-2 can be considered an analogue of Young's double-slit experiment (YDSE) in which the double-slit is replaced by a pair of N 1s orbitals. The measured ratio between the 1 sigma(g) and 1 sigma(u) photoionization cross-sections oscillates as a function of photoelectron momentum, due to two-center YDSE interference, exhibiting a remarkable dependence on the vibrational sub-levels of the core ionized state. We theoretically demonstrate that the recoil of the photoelectron given to the ionized N atom strongly influences this interference pattern. The reason for this is that the momentum transfer affects the phases of the photoionization amplitudes. (c) 2007 Published by Elsevier B.

Probing hydrogen bond strength in liquid water by resonant inelastic X-ray scattering

Local probes of the electronic ground state are essential for understanding hydrogen bonding in aqueous environments. When tuned to the dissociative core-excited state at the O1s pre-edge of water, resonant inelastic X-ray scattering back to the electronic ground state exhibits a long vibrational progression due to ultrafast nuclear dynamics. We show how the coherent evolution of the OH bonds around the core-excited oxygen provides access to high vibrational levels in liquid water. The OH bonds stretch into the long-range part of the potential energy curve, which makes the X-ray probe more sensitive than infra-red spectroscopy to the local environment. We exploit this property to effectively probe hydrogen bond strength via the distribution of intramolecular OH potentials derived from measurements. In contrast, the dynamical splitting in the spectral feature of the lowest valence-excited state arises from the short-range part of the OH potential curve and is rather insensitive to hydrogen bonding

Selective gating to vibrational modes through resonant X ray scattering

The dynamics of fragmentation and vibration of molecular systems with a large number of coupled degrees of freedom are key aspects for understanding chemical reactivity and properties. Here we present a resonant inelastic X ray scattering RIXS study to show how it is possible to break down such a complex multidimensional problem into elementary components. Local multimode nuclear wave packets created by X ray excitation to different core excited potential energy surfaces PESs will act as spatial gates to selectively probe the particular ground state vibrational modes and, hence, the PES along these modes. We demonstrate this principle by combining ultra high resolution RIXS measurements for gas phase water with state of the art simulation