Understanding molecular femtosecond dynamics under intense X-ray exposure is critical to progress in biomolecular imaging and matter under extreme conditions. Imaging viruses and proteins at an ...atomic spatial scale and on the time scale of atomic motion requires rigorous, quantitative understanding of dynamical effects of intense X-ray exposure. Here we present an experimental and theoretical study of C60 molecules interacting with intense X-ray pulses from a free-electron laser, revealing the influence of processes not previously reported. Our work illustrates the successful use of classical mechanics to describe all moving particles in C60, an approach that scales well to larger systems, for example, biomolecules. Comparisons of the model with experimental data on C60 ion fragmentation show excellent agreement under a variety of laser conditions. The results indicate that this modelling is applicable for X-ray interactions with any extended system, even at higher X-ray dose rates expected with future light sources.
The ability to create thick tissues is a major tissue engineering challenge, requiring the development of a suitable vascular supply. Current trends are seeing the utilization of cells seeded into ...hybrid matrix/scaffold systems to create in vitro vascular analogues. Approaches that aim to create vasculature in vitro include the use of biological extracellular matrices such as collagen hydrogels, porous biodegradable polymeric scaffolds with macro- and micro-lumens and micro-channels, co-culture of cells, incorporation of growth factors, culture in dynamic bioreactor environments, and combinations of these. Of particular interest are those approaches that aim to create bioengineered tissues in vitro that can be readily connected to the host's vasculature following implantation in order to maintain cell viability.
Molecules can efficiently and selectively convert light energy into other degrees of freedom. Disentangling the underlying ultrafast motion of electrons and nuclei of the photoexcited molecule ...presents a challenge to current spectroscopic approaches. Here we explore the photoexcited dynamics of molecules by an interaction with an ultrafast X-ray pulse creating a highly localized core hole that decays via Auger emission. We discover that the Auger spectrum as a function of photoexcitation--X-ray-probe delay contains valuable information about the nuclear and electronic degrees of freedom from an element-specific point of view. For the nucleobase thymine, the oxygen Auger spectrum shifts towards high kinetic energies, resulting from a particular C-O bond stretch in the ππ* photoexcited state. A subsequent shift of the Auger spectrum towards lower kinetic energies displays the electronic relaxation of the initial photoexcited state within 200 fs. Ab-initio simulations reinforce our interpretation and indicate an electronic decay to the nπ* state.
The Linac Coherent Light Source free electron laser is a source of high brightness x rays, 2×10(11) photons in a ∼5 fs pulse, that can be focused to produce double core vacancies through rapid ...sequential ionization. This enables double core vacancy Auger electron spectroscopy, an entirely new way to study femtosecond chemical dynamics with Auger electrons that probe the local valence structure of molecules near a specific atomic core. Using 1.1 keV photons for sequential x-ray ionization of impulsively aligned molecular nitrogen, we observed a rich single-site double core vacancy Auger electron spectrum near 413 eV, in good agreement with ab initio calculations, and we measured the corresponding Auger electron angle dependence in the molecular frame.
The first time-resolved x-ray/optical pump-probe experiments at the SLAC Linac Coherent Light Source (LCLS) used a combination of feedback methods and post-analysis binning techniques to synchronize ...an ultrafast optical laser to the linac-based x-ray laser. Transient molecular nitrogen alignment revival features were resolved in time-dependent x-ray-induced fragmentation spectra. These alignment features were used to find the temporal overlap of the pump and probe pulses. The strong-field dissociation of x-ray generated quasi-bound molecular dications was used to establish the residual timing jitter. This analysis shows that the relative arrival time of the Ti:Sapphire laser and the x-ray pulses had a distribution with a standard deviation of approximately 120 fs. The largest contribution to the jitter noise spectrum was the locking of the laser oscillator to the reference RF of the accelerator, which suggests that simple technical improvements could reduce the jitter to better than 50 fs.
Management of dyspepsia remains a controversial area. Although the European Helicobacter pylori study group has advised empirical eradication therapy without oesophagogastroduodenoscopy (OGD) in ...young H pylori positive dyspeptic patients who do not exhibit alarm symptoms, this strategy has not been subjected to clinical trial.
To compare a "test and treat" eradication policy against management by OGD.
Consecutive subjects were prospectively recruited from open access OGD and outpatient referrals.
H pylori status was assessed using the carbon-13 urea breath test. H pylori positive patients were randomised to either empirical eradication or OGD. Symptoms and quality of life scores were assessed at baseline and subsequent reviews over a 12 month period.
A total of 104 H pylori positive patients aged under 45 years were recruited. Fifty two were randomised to receive empirical eradication therapy and 52 to OGD. Results were analysed using an intention to treat policy. Dyspepsia scores significantly improved in both groups over 12 months compared with baseline; however, dyspepsia scores were significantly better in the empirical eradication group. Quality of life showed significant improvements in both groups at 12 months; however, physical role functioning was significantly improved in the empirical eradication group. Fourteen (27%) in the empirical eradication group subsequently proceeded to OGD because of no improvement in dyspepsia.
This randomised study strongly supports the use of empirical H pylori eradication in patients referred to secondary practice; it is estimated that 73% of OGDs in this group would have been avoided with no detriment to clinical outcome.
•250kA toroidal field coil joints.•Electrical joint testing using a variety of interfaces and contact pressures.•Comparison with NSTX contact resistances.
Spherical Tokamaks used in magnetic fusion ...have a small centre-stack by design which causes a higher field on the conductor. ST40 1 is a 3 Tesla spherical tokamak with a major radius of R=40cm and minor radius of a=26cm being built by Tokamak Energy Ltd. The high toroidal field (TF) requirement requires a wire current of 250kA flowing in each of the 24 limbs totalling 6MA in the centre-stack. Joint testing was used to investigate the interface resistance between the centre-stack and return limbs under a variety of contact pressures, using different shims, different coatings on the conductor and soldering. Initially a DC 400A current source was used and later an air-core pulsed transformer delivering up to 16kA of current was specifically designed and built for these measurements. Results from this paper can be used to predict the behaviour of critical joints in the region at the ends of the centre-stack where current is passed to the TF return limbs. A comparison with TF joint data from the National Spherical Torus Experiment (NSTX) is also given. This will aid in deciding which jointing method to use for ST40 and the required pressure to pre-load the interface.
This study assessed the hypothesis that popularity in adolescence takes on a twofold role, marking high levels of concurrent adaptation but predicting increases over time in both positive and ...negative behaviors sanctioned by peer norms. Multimethod, longitudinal data, on a diverse community sample of 185 adolescents (13 to 14 years), addressed these hypotheses. As hypothesized, popular adolescents displayed higher concurrent levels of ego development, secure attachment, and more adaptive interactions with mothers and best friends. Longitudinal analyses supported a popularity-socialization hypothesis, however, in which popular adolescents were more likely to increase behaviors that receive approval in the peer group (e.g., minor levels of drug use and delinquency) and decrease behaviors unlikely to be well received by peers (e.g., hostile behavior with peers).
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