Auger decay and subsequent fragmentation pathways of ethylene following K-shell ionization

Citation: Gaire, B., Haxton, D. J., Sturm, F. P., Williams, J., Gatton, A., Bocharova, I., . . . Weber, T. (2015). Auger decay and subsequent fragmentation pathways of ethylene following K-shell ionization. Physical Review A, 92(1), 13. doi:10.1103/PhysRevA.92.013408The fragmentation pathways and dynamics of ethylene molecules after core ionization are explored using coincident measurements of the Auger electron and fragment ions by employing the cold target recoil-ion momentum spectroscopy method. The influence of several factors on the dynamics and kinematics of the dissociation is studied. These include propensity rules, ionization mechanisms, symmetry of the orbitals from which the Auger electrons originate, multiple scattering, conical intersections, interference, and possible core-hole localization for the double ionization of this polyatomic molecule. Energy correlation maps allow probing the multidimensional potential energy surfaces and, in combination with our multiconfiguration self-consistent field calculations, identifying the populated electronic states of the dissociating dication. The measured angular distributions of the Auger electrons in the molecular frame further support and augment these assignments. The deprotonation and molecular hydrogen ion elimination channels show a nearly isotropic Auger electron angular distribution with a small elongation along the direction perpendicular to the molecular axis. For the symmetric breakup the angular distributions show a clear influence of multiple scattering on the outgoing electrons. The lowest kinetic energy release feature of the symmetric breakup channel displays a fingerprint of entangled Auger and photoelectron motion in the angular emission pattern identifying this transition as an excellent candidate to probe core-hole localization at a conical intersection of a polyatomic molecule.Additional Authors: Landers, A. L.;Belkacem, A.;Dorner, R.;Weber, T

Neuro-cognitive effects of degraded visibility on illusory body ownership.

Based on visuo-tactile stimulation, the rubber hand illusion induces a sense of ownership for a dummy hand. Manipulating the visibility of the dummy hand during the stimulation influences cognitive aspects of the illusion, suggesting that the related brain activity may be influenced too. To test this, we analyzed brain activity (fMRI), subjective ratings, and skin conductance from 45 neurotypical participants undergoing a modified rubber hand illusion protocol where we manipulated the visibility (high, medium, and low) of a virtual hand, not the brush (virtual hand illusion; VHI). To further investigate the impact of visibility manipulations on VHI-related secondary effects (i.e. vicarious somatosensation), we recorded brain activity and skin conductance during a vicarious pain protocol (observation of painful stimulations of the virtual hand) that occurred after the VHI procedure. Results showed that, during both the VHI and vicarious pain periods, the activity of distinct visual, somatosensory, and motor brain regions was modulated by (i) visibility manipulations, (ii) coherence between visual and tactile stimulation, and (iii) time of visuo-tactile stimulation. Accordingly, embodiment-related subjective ratings of the perceived illusion were specifically influenced by visibility manipulations. These findings suggest that visibility modifications can impact the neural and cognitive effects of illusory body ownership, in that when visibility decreases the illusion is perceived as weaker and the brain activity in visual, motor, and somatosensory regions is overall lower. We interpret this evidence as a sign of the weight of vision on embodiment processes, in that the cortical and subjective aspects of illusory body ownership are weakened by a degradation of visual input during the induction of the illusion

Illusory Body Ownership Affects the Cortical Response to Vicarious Somatosensation

Fundamental human feelings such as body ownership (“this” body is “my” body) and vicariousness (first-person-like experience of events occurring to others) are based on multisensory integration. Behavioral links between body ownership and vicariousness have been shown, but the neural underpinnings remain largely unexplored. To fill this gap, we investigated the neural effects of altered body ownership on vicarious somatosensation. While recording functional brain imaging data, first, we altered participants’ body ownership by robotically delivering tactile stimulations (“tactile” stroking) in synchrony or not with videos of a virtual hand being brushed (“visual” stroking). Then, we manipulated vicarious somatosensation by showing videos of the virtual hand being touched by a syringe’s plunger (touch) or needle (pain). Only after the alteration of body ownership (synchronous visuo-tactile stroking) and specifically during late epochs of vicarious somatosensation, vicarious pain was associated with lower activation in premotor and anterior cingulate cortices with respect to vicarious touch. At the methodological level, the present study highlights the importance of the neural response’s temporal evolution. At the theoretical level, it shows that the higher-level (cognitive) impact of a lower-level (sensory) body-related processing (visuo-tactile) is not limited to body ownership but also extends to other psychological body-related domains, such as vicarious somatosensation

Neuro-cognitive effects of degraded visibility on illusory body ownership

Based on visuo-tactile stimulation, the rubber hand illusion induces a sense of ownership for a dummy hand. Manipulating the visibility of the dummy hand during the stimulation influences cognitive aspects of the illusion, suggesting that the related brain activity may be influenced too. To test this, we analyzed brain activity (fMRI), subjective ratings, and skin conductance from 45 neurotypical participants undergoing a modified rubber hand illusion protocol where we manipulated the visibility (high, medium, and low) of a virtual hand, not the brush (virtual hand illusion; VHI). To further investigate the impact of visibility manipulations on VHI-related secondary effects (i.e. vicarious somatosensation), we recorded brain activity and skin conductance during a vicarious pain protocol (observation of painful stimulations of the virtual hand) that occurred after the VHI procedure. Results showed that, during both the VHI and vicarious pain periods, the activity of distinct visual, somatosensory, and motor brain regions was modulated by (i) visibility manipulations, (ii) coherence between visual and tactile stimulation, and (iii) time of visuo-tactile stimulation. Accordingly, embodiment-related subjective ratings of the perceived illusion were specifically influenced by visibility manipulations. These findings suggest that visibility modifications can impact the neural and cognitive effects of illusory body ownership, in that when visibility decreases the illusion is perceived as weaker and the brain activity in visual, motor, and somatosensory regions is overall lower. We interpret this evidence as a sign of the weight of vision on embodiment processes, in that the cortical and subjective aspects of illusory body ownership are weakened by a degradation of visual input during the induction of the illusion

A low-dimensional representation of arm movements and hand grip forces in post-stroke individuals

Characterizing post-stroke impairments in the sensorimotor control of arm and hand is essential to better understand altered mechanisms of movement generation. Herein, we used a decomposition algorithm to characterize impairments in end-effector velocity and hand grip force data collected from an instrumented functional task in 83 healthy control and 27 chronic post-stroke individuals with mild-to-moderate impairments. According to kinematic and kinetic raw data, post-stroke individuals showed reduced functional performance during all task phases. After applying the decomposition algorithm, we observed that the behavioural data from healthy controls relies on a low-dimensional representation and demonstrated that this representation is mostly preserved post-stroke. Further, it emerged that reduced functional performance post-stroke correlates to an abnormal variance distribution of the behavioural representation, except when reducing hand grip forces. This suggests that the behavioural repertoire in these post-stroke individuals is mostly preserved, thereby pointing towards therapeutic strategies that optimize movement quality and the reduction of grip forces to improve performance of daily life activities post-stroke

Tetanus toxin Hc fragment induces the formation of ceramide platforms and protects neuronal cells against oxidative stress

Tetanus toxin (TeTx) is the protein, synthesized by the anaerobic bacteria Clostridium tetani, which causes tetanus disease. TeTx gains entry into target cells by means of its interaction with lipid rafts, which are membrane domains enriched in sphingomyelin and cholesterol. However, the exact mechanism of host membrane binding remains to be fully established. In the present study we used the recombinant carboxyl terminal fragment from TeTx (Hc-TeTx), the domain responsible for target neuron binding, showing that Hc-TeTx induces a moderate but rapid and sustained increase in the ceramide/sphingomyelin ratio in primary cultures of cerebellar granule neurons and in NGF-differentiated PC12 cells, as well as induces the formation of ceramide platforms in the plasma membrane. The mentioned increase is due to the promotion of neutral sphingomyelinase activity and not to the de novo synthesis, since GW4869, a specific neutral sphingomyelinase inhibitor, prevents neutral sphingomyelinase activity increase and formation of ceramide platforms. Moreover, neutral sphingomyelinase inhibition with GW4869 prevents Hc-TeTx-triggered signaling (Akt phosphorylation), as well as the protective effect of Hc-TeTx on PC12 cells subjected to oxidative stress, while siRNA directed against nSM2 prevents protection by Hc-TeTx of NSC-34 cells against oxidative insult. Finally, neutral sphingomyelinase activity seems not to be related with the internalization of Hc-TeTx into PC12 cells. Thus, the presented data shed light on the mechanisms triggered by TeTx after membrane binding, which could be related with the events leading to the neuroprotective action exerted by the Hc-TeTx fragment

Location matters:Valuing firm-specific nonmarket risk in the global mining industry

Research summary Using collective action and social movement theory, we investigate the potential incentives and ability of stakeholders to engage in collective action that can increase firm-specific nonmarket risk of mining companies. We argue that proximity to the nearest environmentally sensitive water source increases the probability that local stakeholders will take collective actions that impose material costs on the focal mine. We hypothesize that stock markets recognize this nonmarket risk and apply a discount on announcements related to mines located near such areas, and that these risks are moderated by the type of mineral, the nature of the water source, and the strength of host country institutions. Using a unique data set and an event study method, we find support for most of our arguments. Managerial summary We argue that mines located near environmentally sensitive water sources are subject to nonmarket risks arising from the potential collective actions of local stakeholders and their allies. Stakeholder mobilization can impose material costs on a mine in the form of delays, regulatory hurdles, and closure. We find that stock markets recognize these nonmarket risks and apply a discount on announcements by mining companies whose mines are located near environmentally sensitive water sources, particularly rivers. However, we also find that investor reaction is stronger in countries with strong institutions that support collective action. Thus, nonmarket risk management is important even in countries that are typically characterized by low political and institutional risks. We discuss the degree to which these results can be generalized beyond mining