The ultrafast photoinduced ring-opening of 1,3-cyclohexadiene constitutes a textbook example of electrocyclic reactions in organic chemistry and a model for photobiological reactions in vitamin D ...synthesis. Although the relaxation from the photoexcited electronic state during the ring-opening has been investigated in numerous studies, the accompanying changes in atomic distance have not been resolved. Here we present a direct and unambiguous observation of the ring-opening reaction path on the femtosecond timescale and subångström length scale using megaelectronvolt ultrafast electron diffraction. We followed the carbon-carbon bond dissociation and the structural opening of the 1,3-cyclohexadiene ring by the direct measurement of time-dependent changes in the distribution of interatomic distances. We observed a substantial acceleration of the ring-opening motion after internal conversion to the ground state due to a steepening of the electronic potential gradient towards the product minima. The ring-opening motion transforms into rotation of the terminal ethylene groups in the photoproduct 1,3,5-hexatriene on the subpicosecond timescale.
Recently, few-femtosecond pulses have become available at hard X-ray free-electron lasers. Coupled with the available sub-10 fs optical pulses, investigations into few-femtosecond dynamics are not ...far off. However, achieving sufficient synchronization between optical lasers and X-ray pulses continues to be challenging. We report a 'measure-and-sort' approach, which achieves sub-10 fs root-mean-squared (r.m.s.) error measurement at hard X-ray FELs, far beyond the 100-200 fs r.m.s. jitter limitations. This timing diagnostic, now routinely available at the Linac Coherent Light Source (LCLS), is based on ultrafast free-carrier generation in optically transparent materials. Correlation between two independent measurements enables unambiguous demonstration of ∼6 fs r.m.s. error in reporting the optical/X-ray delay, with single shot error suggesting the possibility of reaching few-femtosecond resolution.
The time–energy information of ultrashort X-ray free-electron laser pulses generated by the Linac Coherent Light Source is measured with attosecond resolution via angular streaking of neon 1s ...photoelectrons. The X-ray pulses promote electrons from the neon core level into an ionization continuum, where they are dressed with the electric field of a circularly polarized infrared laser. This induces characteristic modulations of the resulting photoelectron energy and angular distribution. From these modulations we recover the single-shot attosecond intensity structure and chirp of arbitrary X-ray pulses based on self-amplified spontaneous emission, which have eluded direct measurement so far. We characterize individual attosecond pulses, including their instantaneous frequency, and identify double pulses with well-defined delays and spectral properties, thus paving the way for X-ray pump/X-ray probe attosecond free-electron laser science.
Debriefing in the pediatric emergency department (PED) is an invaluable tool to improve team well-being, communication, and performance. Despite evidence, surveys have reported heavy workload as a ...barrier to debriefing leading to missed opportunities for improvement in an already busy ED. The study aims to determine the association between the incidence of debriefing after pediatric trauma resuscitations and PED crowding.
A total of 491 Trauma One activations in Riley Children's Hospital Pediatric Emergency Department that presented between April 2018 to December 2019 were included in the study. Debriefing documentations, patient demographics, time and date of presentation, mechanism of injury, injury severity score, disposition from PED, and length of stay (LOS) were collected and analyzed. The National Emergency Department Overcrowding Scale score at arrival, Average LOS, total PED census, total PED waiting room census, and rates of left without being seen were compared between groups.
Of 491 Trauma One activations presented to our PED, 50 (10%) trauma evaluations had documented debriefing. The National Emergency Department Overcrowding Scale score at presentation was significantly lower in those with debriefing versus without debriefing. In addition, the PED hourly census, waiting room census, average LOS, and left without being seen were also significantly lower in the group with debriefing. In addition, trauma cases with debriefing had a higher proportion of patients with profound injuries and discharges to the morgue.
Pediatric emergency department crowding is a significant barrier to debriefing after trauma resuscitations. However, profound injuries and traumatic pediatric deaths remain the strongest predictors in conducting debriefing regardless of PED crowding status.
The X-ray free-electron laser has opened a new era for photon science, improving the X-ray brightness by ten orders of magnitude over previously available sources. Similar to an optical laser, the ...spectral and temporal structure of the radiation pulses can be tailored to the specific needs of many experiments by accurately manipulating the lasing medium, that is, the electron beam. Here we report the generation of mJ-level two-colour hard X-ray pulses of few femtoseconds duration with an XFEL driven by twin electron bunches at the Linac Coherent Light Source. This performance represents an improvement of over an order of magnitude in peak power over state-of-the-art two-colour XFELs. The unprecedented intensity and temporal coherence of this new two-colour X-ray free-electron laser enable an entirely new set of scientific applications, ranging from X-ray pump/X-ray probe experiments to the imaging of complex biological samples with multiple wavelength anomalous dispersion.
X-ray and optical wave mixing GLOVER, T. E; FRITZ, D. M; FUCHS, M ...
Nature,
08/2012, Letnik:
488, Številka:
7413
Journal Article
Recenzirano
Odprti dostop
Light-matter interactions are ubiquitous, and underpin a wide range of basic research fields and applied technologies. Although optical interactions have been intensively studied, their microscopic ...details are often poorly understood and have so far not been directly measurable. X-ray and optical wave mixing was proposed nearly half a century ago as an atomic-scale probe of optical interactions but has not yet been observed owing to a lack of sufficiently intense X-ray sources. Here we use an X-ray laser to demonstrate X-ray and optical sum-frequency generation. The underlying nonlinearity is a reciprocal-space probe of the optically induced charges and associated microscopic fields that arise in an illuminated material. To within the experimental errors, the measured efficiency is consistent with first-principles calculations of microscopic optical polarization in diamond. The ability to probe optical interactions on the atomic scale offers new opportunities in both basic and applied areas of science.
Fragile X syndrome (FXS), caused by loss of the Fragile X Mental Retardation 1 (FMR1) gene product (FMRP), is the most common heritable cause of intellectual disability and autism spectrum disorders. ...It has been long hypothesized that the phosphorylation of serine 500 (S500) in human FMRP controls its function as an RNA-binding translational repressor. To test this hypothesis in vivo, we employed neuronally targeted expression of three human FMR1 transgenes, including wild-type (hFMR1), dephosphomimetic (S500A-hFMR1) and phosphomimetic (S500D-hFMR1), in the Drosophila FXS disease model to investigate phosphorylation requirements. At the molecular level, dfmr1 null mutants exhibit elevated brain protein levels due to loss of translational repressor activity. This defect is rescued for an individual target protein and across the population of brain proteins by the phosphomimetic, whereas the dephosphomimetic phenocopies the null condition. At the cellular level, dfmr1 null synapse architecture exhibits increased area, branching and bouton number. The phosphomimetic fully rescues these synaptogenesis defects, whereas the dephosphomimetic provides no rescue. The presence of Futsch-positive (microtubule-associated protein 1B) supernumerary microtubule loops is elevated in dfmr1 null synapses. The human phosphomimetic restores normal Futsch loops, whereas the dephosphomimetic provides no activity. At the behavioral level, dfmr1 null mutants exhibit strongly impaired olfactory associative learning. The human phosphomimetic targeted only to the brain-learning center restores normal learning ability, whereas the dephosphomimetic provides absolutely no rescue. We conclude that human FMRP S500 phosphorylation is necessary for its in vivo function as a neuronal translational repressor and regulator of synaptic architecture, and for the manifestation of FMRP-dependent learning behavior.
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