Splitting between Bright and Dark excitons in Transition Metal Dichalcogenide Monolayers

The optical properties of transition metal dichalcogenide monolayers such as the two-dimensional semiconductors MoS$_2$ and WSe$_2$ are dominated by excitons, Coulomb bound electron-hole pairs. The light emission yield depends on whether the electron-hole transitions are optically allowed (bright) or forbidden (dark). By solving the Bethe Salpeter Equation on top of $GW$ wave functions in density functional theory calculations, we determine the sign and amplitude of the splitting between bright and dark exciton states. We evaluate the influence of the spin-orbit coupling on the optical spectra and clearly demonstrate the strong impact of the intra-valley Coulomb exchange term on the dark-bright exciton fine structure splitting.Comment: 6 pages, 2 figure

Exciton states in monolayer MoSe2: impact on interband transitions

We combine linear and non-linear optical spectroscopy at 4K with ab initio calculations to study the electronic bandstructure of MoSe2 monolayers. In 1-photon photoluminescence excitation (PLE) and reflectivity we measure a separation between the A- and B-exciton emission of 220 meV. In 2-photon PLE we detect for the A- and B-exciton the 2p state 180meV above the respective 1s state. In second harmonic generation (SHG) spectroscopy we record an enhancement by more than 2 orders of magnitude of the SHG signal at resonances of the charged exciton and the 1s and 2p neutral A- and B-exciton. Our post-Density Functional Theory calculations show in the conduction band along the $K-\Gamma$ direction a local minimum that is energetically and in k-space close to the global minimum at the K-point. This has a potentially strong impact on the polarization and energy of the excitonic states that govern the interband transitions and marks an important difference to MoS2 and WSe2 monolayers.Comment: 8 pages, 3 figure

Disfluences dans le vieillissement "normal" et la maladie d'Alzheimer : indices segmentaux, suprasegmentaux et gestuels

International audienceThe aim of the study is to analyze and compare multimodal language productions by 10 persons with Alzheimer's disease (AD) matched to 10 controls. First, different measures at the segmental and suprasegmental levels – errors, pauses and vocalic lengthenings – have been conducted in a repetition task with or without imposed gestures to characterize a disfluency, typical of AD, and then observed in link with the production of manual gestures. Results show a significant diminution of the AD participants' fluency: more lexical errors were obtained by the patient group and at the phonetic level among patients with moderate cognitive impairment, as well as numerous silent pauses often preceding or following the production of errors at the segmental level. Moreover, a significant augmentation of suprasegmental disfluencies and phonetic errors is observed in the task with imposed gestures impacting controls and patients' fluency.L'objectif de cette étude est d'analyser et comparer les productions langagières dans leur multimodalité de 10 personnes atteintes de la maladie d'Alzheimer (MA) appariées à 10 contrôles. Différentes mesures aux niveaux segmental et suprasegmental – erreurs, pauses et allongements vocaliques – ont été réalisées dans une tâche de répétition avec ou sans gestes imposés pour caractériser une disfluence, typique de la MA, puis observées en lien avec les gestes manuels produits. Les résultats montrent la diminution significative de la fluence chez les personnes atteintes de la MA, avec davantage d'erreurs produites au niveau lexical par le groupe Patient et au niveau phonétique par les patients au stade modéré de la maladie, ainsi que de nombreuses pauses silencieuses précédant ou suivant souvent les erreurs produites au niveau segmental. De plus, dans la tâche avec gestes imposés, la répétition de ceux-ci a impacté la fluence des groupes Contrôle et Patient avec une augmentation significative des disfluences au niveau suprasegmental et des erreurs phonétiques au niveau segmental

Disfluences dans le vieillissement "normal" et la maladie d'Alzheimer : indices segmentaux, suprasegmentaux et gestuels

International audienceThe aim of the study is to analyze and compare multimodal language productions by 10 persons with Alzheimer's disease (AD) matched to 10 controls. First, different measures at the segmental and suprasegmental levels – errors, pauses and vocalic lengthenings – have been conducted in a repetition task with or without imposed gestures to characterize a disfluency, typical of AD, and then observed in link with the production of manual gestures. Results show a significant diminution of the AD participants' fluency: more lexical errors were obtained by the patient group and at the phonetic level among patients with moderate cognitive impairment, as well as numerous silent pauses often preceding or following the production of errors at the segmental level. Moreover, a significant augmentation of suprasegmental disfluencies and phonetic errors is observed in the task with imposed gestures impacting controls and patients' fluency.L'objectif de cette étude est d'analyser et comparer les productions langagières dans leur multimodalité de 10 personnes atteintes de la maladie d'Alzheimer (MA) appariées à 10 contrôles. Différentes mesures aux niveaux segmental et suprasegmental – erreurs, pauses et allongements vocaliques – ont été réalisées dans une tâche de répétition avec ou sans gestes imposés pour caractériser une disfluence, typique de la MA, puis observées en lien avec les gestes manuels produits. Les résultats montrent la diminution significative de la fluence chez les personnes atteintes de la MA, avec davantage d'erreurs produites au niveau lexical par le groupe Patient et au niveau phonétique par les patients au stade modéré de la maladie, ainsi que de nombreuses pauses silencieuses précédant ou suivant souvent les erreurs produites au niveau segmental. De plus, dans la tâche avec gestes imposés, la répétition de ceux-ci a impacté la fluence des groupes Contrôle et Patient avec une augmentation significative des disfluences au niveau suprasegmental et des erreurs phonétiques au niveau segmental

Impact of perfluorooctylethane on the formation of a semi-crystalline liquid-condensed phase in a phospholipid monolayer and of perfluorooctyl bromide on the adsorption of albumin on such a monolayer

International audienc

Observation of the sliding phason mode of the incommensurate magnetic texture in Fe/Ir(111)

The nanoscopic magnetic texture forming in a monolayer of iron on the (111) surface of iridium, Fe/Ir(111), is spatially modulated and uniaxially incommensurate with respect to the crystallographic periodicities. As a consequence, a low-energy magnetic excitation is expected that corresponds to the sliding of the texture along the incommensurate direction, i.e., a phason mode, which we explicitly confirm with atomistic spin simulations. Using scanning tunneling microscopy (STM), we succeed to observe this phason mode experimentally. It can be excited by the STM tip, which leads to a random telegraph noise in the tunneling current that we attribute to the presence of two minima in the phason potential due to the presence of disorder in our sample. This provides the prospect of a floating phase in cleaner samples and, potentially, a commensurate-incommensurate transition as a function of external control parameters.Comment: 6 Figure

Effects of immersive virtual reality on sensory overload in a random sample of critically ill patients.

BACKGROUND Sensory overload and sensory deprivation have both been associated with negative health outcomes in critically ill patients. While there is a lack of any clear treatment or prevention strategies, immersive virtual reality is a promising tool for addressing such problems, but which has not been repetitively tested in random samples. Therefore, this study aimed to determine how critically ill patients react to repeated sessions of immersive virtual reality. METHODS This exploratory study was conducted in the mixed medical-surgical intermediate care unit of the University Hospital of Bern (Inselspital). Participants (N = 45; 20 women, 25 men; age = 57.73 ± 15.92 years) received two immersive virtual reality sessions via a head-mounted display and noise-canceling headphones within 24 h during their stay in the unit. Each session lasted 30-min and showed a 360-degree nature landscape. Physiological data were collected as part of the participants' standard care, while environmental awareness, cybersickness, and general acceptance were assessed using a questionnaire designed by our team (1 = not at all, 10 = extremely). RESULTS During both virtual reality sessions, there was a significant negative linear relationship found between the heart rate and stimulation duration [first session: r(43) = -0.78, p < 0.001; second session: r(38) = -0.81, p < 0.001] and between the blood pressure and stimulation duration [first session: r(39) = -0.78, p < 0.001; second session: r(30) = -0.78, p < 0.001]. The participants had a high comfort score [median (interquartile range {IQR}) = 8 (7, 10); mean = 8.06 ± 2.31], did not report being unwell [median (IQR) = 1 (1, 1); mean = 1.11 ± 0.62], and were not aware of their real-world surroundings [median (IQR) = 1 (1, 5); mean = 2.99 ± 3.22]. CONCLUSION The subjectively reported decrease in environmental awareness as well as the decrease in the heart rate and blood pressure over time highlights the ability of immersive virtual reality to help critically ill patients overcome sensory overload and sensory deprivation. Immersive virtual reality can successfully and repetitively be provided to a randomly selected sample of critically ill patients over a prolonged duration

Virtual reality stimulation to reduce the incidence of delirium in critically ill patients: study protocol for a randomized clinical trial.

BACKGROUND Delirium has been long considered as a major contributor to cognitive impairments and increased mortality following a critical illness. Pharmacologic and non-pharmacologic strategies are used against delirium in the intensive care unit (ICU), despite these strategies remaining controversial. Previous studies have shown the feasibility of using virtual reality within the ICU setting, and we propose to use this technology to investigate the effect of immersive virtual reality stimulation on the incidence of delirium in the ICU. Moreover, we propose to use motion sensors to determine if patient movement patterns can lead to early prediction of delirium onset. METHODS This study is conducted as a randomized clinical trial. A total of 920 critically ill patients in the ICU will participate. The control group will receive standard ICU care, whereas the intervention group will, in addition to the standard ICU care, receive relaxing 360-degree immersive virtual reality content played inside a head-mounted display with noise-cancelling headphones, three times a day. The first 100 patients, regardless of their group, will additionally have their movement patterns recorded using wearable and ambient sensors. Follow-up measurements will take place 6 months after discharge from the ICU. DISCUSSION Delirium is widely present within the ICU setting but lacks validated prevention and treatment strategies. By providing patients with virtual reality stimulation presented inside a head-mounted display and noise-cancelling headphones, participants may be isolated from disturbances on an ICU. It is believed that by doing so, the incidence of delirium will be decrease among these patients. Moreover, identifying movement patterns associated with delirium would allow for early detection and intervention, which may further improve long-term negative outcomes associated with delirium during critical care. TRIAL REGISTRATION ClinicalTrials.gov NCT04498585 . Registered on August 3, 2020

Investigating the role of auditory and visual sensory inputs for inducing relaxation during virtual reality stimulation

Stress is a part of everyday life which can be counteracted by evoking the relaxation response via nature scenes presented using immersive virtual reality (VR). The aim of this study was to determine which sensory aspect of immersive VR intervention is responsible for the greatest relaxation response. We compared four conditions: auditory and visual combined (audiovisual), auditory only, visual only, and no artificial sensory input. Physiological changes in heart rate, respiration rate, and blood pressure were recorded, while participants reported their preferred condition and awareness of people, noise, and light in the real-world. Over the duration of the stimulation, participants had the lowest heart rate during the audiovisual and visual only conditions. They had the steadiest decrease in respiration rate and the lowest blood pressure during the audiovisual condition, compared to the other conditions, indicating the greatest relaxation. Moreover, ratings of awareness indicated that participants reported being less aware of their surroundings (i.e., people, noise, light, real environment) during the audiovisual condition versus the other conditions (p < 0.001), with a preference for audiovisual inputs. Overall, the use of audiovisual VR stimulation is more effective at inducing a relaxation response compared to no artificial sensory inputs, or the independent inputs