Recovery time of a plasma-wakefield accelerator.

The interaction of intense particle bunches with plasma can give rise to plasma wakes1,2 capable of sustaining gigavolt-per-metre electric fields3,4, which are orders of magnitude higher than provided by state-of-the-art radio-frequency technology5. Plasma wakefields can, therefore, strongly accelerate charged particles and offer the opportunity to reach higher particle energies with smaller and hence more widely available accelerator facilities. However, the luminosity and brilliance demands of high-energy physics and photon science require particle bunches to be accelerated at repetition rates of thousands or even millions per second, which are orders of magnitude higher than demonstrated with plasma-wakefield technology6,7. Here we investigate the upper limit on repetition rates of beam-driven plasma accelerators by measuring the time it takes for the plasma to recover to its initial state after perturbation by a wakefield. The many-nanosecond-level recovery time measured establishes the in-principle attainability of megahertz rates of acceleration in plasmas. The experimental signatures of the perturbation are well described by simulations of a temporally evolving parabolic ion channel, transferring energy from the collapsing wake to the surrounding media. This result establishes that plasma-wakefield modules could be developed as feasible high-repetition-rate energy boosters at current and future particle-physics and photon-science facilities.

Energy Compression and Stabilization of Laser-Plasma Accelerators.

Laser-plasma accelerators outperform current radio frequency technology in acceleration strength by orders of magnitude. Yet, enabling them to deliver competitive beam quality for demanding applications, particularly in terms of energy spread and stability, remains a major challenge. In this Letter, we propose to combine bunch decompression and active plasma dechirping for drastically improving the energy profile and stability of beams from laser-plasma accelerators. Realistic start-to-end simulations demonstrate the potential of these postacceleration phase-space manipulations for simultaneously reducing an initial energy spread and energy jitter of ∼1-2% to ≲0.1%, closing the beam-quality gap to conventional acceleration schemes.

Probing Strong-Field QED with Doppler-Boosted Petawatt-Class Lasers.

We propose a scheme to explore regimes of strong-field quantum electrodynamics (SF QED) otherwise unattainable with the currently available laser technology. The scheme relies on relativistic plasma mirrors curved by radiation pressure to boost the intensity of petawatt-class laser pulses by Doppler effect and focus them to extreme field intensities. We show that very clear SF QED signatures could be observed by placing a secondary target where the boosted beam is focused.

[A mentalization-based perspective on childhood autism treatment]. / Perspective de prise en charge d'enfants atteints de troubles du spectre autistique par psychothérapie inspirée des thérapies basées sur la mentalisation.

Mentalization is a process by which a subject makes sense of both his own mental representations and of those around him. Disturbances in the mentalization process are found in several psychiatric disorders, notably borderline personality disorders for which mentalization-based treatments (MBT) have been developed and evaluated. Children with Autism Spectrum Disorder (ASD) display a theory of mind impairments, which corresponds to disturbances in the mentalization process. Although no MBT protocol for patients with ASD has been described in the literature, such treatment appears promising to improve theory of mind and functional outcome of these children. In this paper, we propose to discuss the theoretical ground of MBT therapeutic effect in children with ASD without intellectual disabilities and to describe a clinical protocol to test this perspective.

Relativistic Acceleration of Electrons Injected by a Plasma Mirror into a Radially Polarized Laser Beam.

We propose a method to generate femtosecond, relativistic, and high-charge electron bunches using few-cycle and tightly focused radially polarized laser pulses. In this scheme, the incident laser pulse reflects off an overdense plasma that injects electrons into the reflected pulse. Particle-in-cell simulations show that the plasma injects electrons ideally, resulting in a dramatic increase of charge and energy of the accelerated electron bunch in comparison to previous methods. This method can be used to generate femtosecond pC bunches with energies in the 1-10 MeV range using realistic laser parameters corresponding to current kHz laser systems.

Emittance preservation in a plasma-wakefield accelerator.

Radio-frequency particle accelerators are engines of discovery, powering high-energy physics and photon science, but are also large and expensive due to their limited accelerating fields. Plasma-wakefield accelerators (PWFAs) provide orders-of-magnitude stronger fields in the charge-density wave behind a particle bunch travelling in a plasma, promising particle accelerators of greatly reduced size and cost. However, PWFAs can easily degrade the beam quality of the bunches they accelerate. Emittance, which determines how tightly beams can be focused, is a critical beam quality in for instance colliders and free-electron lasers, but is particularly prone to degradation. We demonstrate, for the first time, emittance preservation in a high-gradient and high-efficiency PWFA while simultaneously preserving charge and energy spread. This establishes that PWFAs can accelerate without degradation-an essential step toward energy boosters in photon science and multistage facilities for compact high-energy particle colliders.

Reduced model of plasma evolution in hydrogen discharge capillary plasmas.

A model describing the evolution of the average plasma temperature inside a discharge capillary device including Ohmic heating, heat loss to the capillary wall, and ionization and recombination effects is developed. Key to this approach is an analytic quasistatic description of the radial temperature variation which, under local thermal equilibrium conditions, allows the radial behavior of both the plasma temperature and the electron density to be specified directly from the average temperature evolution. In this way, the standard set of coupled partial differential equations for magnetohydrodynamic (MHD) simulations is replaced by a single ordinary differential equation, with a corresponding gain in simplicity and computational efficiency. The on-axis plasma temperature and electron density calculations are benchmarked against existing one-dimensional MHD simulations for hydrogen plasmas under a range of discharge conditions and initial gas pressures, and good agreement is demonstrated. The success of this simple model indicates that it can serve as a quick and easy tool for evaluating the plasma conditions in discharge capillary devices, particularly for computationally expensive applications such as simulating long-term plasma evolution, performing detailed input parameter scans, or for optimization using machine-learning techniques.

Neuronal expression of a thyroid hormone receptor α mutation alters mouse behaviour.

In humans, alterations in thyroid hormone signalling are associated with mood and anxiety disorders, but the neural mechanisms underlying such association are poorly understood. The present study investigates the involvement of neuronal thyroid hormone receptor α (TRα) in anxiety, using mouse genetics and Cre/loxP technology to specifically alter TRα signalling in neurons. We evaluated the behaviour of mice expressing a dominant negative, neuron-specific mutation of TRα (TRαAMI/Cre3 mice), using the elevated-plus maze, light-dark box and open-field tests. In a first experiment, mice were housed individually, and the behaviour of TRαAMI/Cre3 mice differed significantly from that of control littermates in these 3 tests, suggesting heightened anxiety. In a second experiment, designed to evaluate the robustness of the results with the same 3 tests, mice were housed in groups. In these conditions, the behaviour of TRαAMI/Cre3 mice differed from that of control littermates only in the light-dark box. Thus, TRαAMI/Cre3 mice appear to be more likely to develop anxiety under stressful housing conditions than control mice. These results suggest that in adult mice, thyroid hormone signalling in neurons, via TRα, is involved in the control of anxiety behaviour.

Dissociated neural representations induced by complex and simple odorant molecules.

An important challenge in olfaction research is to understand how percepts relate to the molecular structure of stimuli. Previous psychophysical studies showed that, whereas structurally simple odorant molecules evoked a more uniform qualitative perception as revealed by the use of a small number of labels to describe their olfactory quality, more complex odorants evoked a larger variety of olfactory qualities, reflecting a more heterogeneous qualitative perception. The present study examined how this influence of odorant molecular complexity on perception is reflected in the human brain. To this end, participants were stimulated with structurally simple and complex odorant molecules and their brain responses were assessed by functional magnetic resonance imaging (fMRI). Low- and high-complexity odorants were judged to have the same intensity, pleasantness and familiarity (p>0.05 in all cases), whereas complex odorants induced more quality labels than simple odorants (p<0.02) as expected. Imaging analysis of complex vs. simple odorants revealed significant activation in dorsal anterior cingulate gyrus, but not in primary olfactory areas. Taken together, these findings suggest dissociated neural representations of uniform and heterogeneous olfactory perception, highlighting for the first time the impact of odorant complexity on activity of the cingulate gyrus.

An electrophysiological study of the mental rotation of polygons.

Reaction times and event-related potentials (ERPs) were recorded during a task requiring subjects to decide whether two sequentially presented polygons had the same shape regardless of differences in orientation. Reaction times increased approximately linearly with angular departure from upright orientation, which suggests that mental rotation was involved in the comparison process. The ERPs showed, between 665 and 1055 ms, a late posterior negativity also increasing with angular disparity from upright, which we assumed to reflect mental rotation. Two other activities were exhibited, from 265 to 665 ms, which may be related either to an evaluation of the stimulus or a predetermination of its orientation, and from 1055 to 1600 ms attributed to the decision process.

Two auditory components in the 130-230 ms range disclosed by their stimulus frequency dependence.

The auditory P2 wave has been studied by means of scalp potential and scalp current density (SCD) mapping. Two components were described. One, peaking around 150 ms, probably reflects a major activity in both supra temporal planes as revealed by SCD maps (P150). The other is a bilateral temporo-parietal component peaking around 220 ms (P220). These two components were functionally disclosed by their stimulus frequency dependence. The P150 potential and SCD amplitudes significantly decrease with increasing frequencies. Whereas this could be interpreted as a modulation of the neural activity, it may also be related to a tonotopical organization of the underlying generators distinct from that previously found for the N100. No frequency effect was found on P220.

Lipoprotein lipase and metabolic activities in incubated bovine adipose tissue explants: effects of insulin, dexamethasone, and fetal bovine serum.

An in vitro system was used to study the regulation of lipoprotein lipase (LPL) activity in bovine adipose tissue. The utilization of two energetic and lipogenic substrates, acetate and glucose, and the activity of glucose-6-phosphate dehydrogenase (G6PDH), an enzyme involved in de novo lipogenesis, were also studied. Nine nonlactating, nonpregnant Holstein cows were given limited amounts of feed for 10 d, then they were overfed for 3 to 5 wk. Samples of perirenal adipose tissue were incubated for 24 or 48 h. Insulin (2 mU/mL) increased (P < .001) daily glucose and acetate utilization and attenuated (P < .001) the loss of G6PDH activity detected after 1 or 2 d of incubation. Dexamethasone (DEX, 10 nM) added to the insulin-supplemented medium decreased (P < .02) glucose utilization, but it did not change acetate utilization or G6PDH activity. A higher concentration of DEX (100 nM) potentiated (P < .004) the ability of insulin to attenuate the decrease in G6PDH activity without changing substrate utilization. Under basal conditions, LPL activity was decreased by approximately 66% after 2 d of incubation. The decline in LPL activity was attenuated by insulin addition (P < .02) and was further attenuated (P < .004) by 100 nM of DEX. The addition of 10% fetal bovine serum alone to the medium had no effect on LPL activity, and fetal bovine serum decreased this activity when it was added to the insulin-supplemented medium.

[Acébutolol: conditions of its interference in the estimation of urinary 17-oxosteroids. Method of estimation by Zimmerman's reaction (author's transl)]. / L'acébutolol conditions de son interférence dans le dosage des 17-oxostéroïdes urinaires. Méthode de dosage par la réaction de Zimmermann.

Acebutolol at therapeutic dosage may considerably disturb the determination of urinary 17-oxosteroids by Zimmerman's reaction. This interference, very variable according to the various technics which may be used, depends mainly on the pH of the urine at the time of extraction. In very acid medium (pH less than 1,5) no acebutolol metabolite passes into the solvents of low polarity; in very alkaline medium, (pH greater than 13) the passage la quantitative. The estimation of 17-oxostéroids in the presence of acebutolol, is possible provided the extraction is carried out in sufficiently acid medium, such as that used for hydrolysis in presence of hydrochloric acid. This is moreover the procedure used for classical methods were no interference is observed. The selective estimation of acebutolol and of its metabolites may be carried out simply by Zimmerman's reaction, after extraction at pH 13 of non-hydrolysed urine, thanks to the absence of conjugated derivatives.

[Bamifylline. Conditions of its interference in the estimation of urinary 17-oxosteroids. Method of estimation using Zimmermann's reaction (author's transl)]. / La bamifylline. Conditions de son interférence dans le dosage des 17-oxostéroïdes urinaires. Méthode de dosage par la réaction de Zimmermann.

Bamifylline in therapeutic dosage may markedly disturb the determination of urinary 17-oxosteroids by Zimmermann's reaction, although the conditions of extraction and formation of this chromogenic substance are not always optimal for the metabolites of bamifylline. It is easy to suspect this interference as the chromogenic substance is produced as soon as the reagents are introduced, contrary to 17-oxosteroids, and it presents a more bluish colour. It is possible to separate completely both types of metabolite by washing the chloroform extracts with acid solutions which form salts with bamifylline and thus extract it. From these acid solutions, bamifylline may be recovered and estimated Zimmermann's reaction which is, for this purpose, modified.

[Ovarian stimulation test using H.M.G]. / Test de stimulation ovarienne par les H.M.G.

PIP: A new ovarian stimulation test, using HMG only, is described, and clinical experiences with 37 patients, aged 17-32 years, are reported. The test requires 15 ampoules of HMG, given in 3 injections, 1 daily or 1 every 3 days. 17 patients with primary amenorrhea and 20 with hypoestrogenic secondary amenorrhea of at least 2 years duration were studied. A positive response, demonstrating the presence of follicles in the ovary, was obtained in 31 patients. Test reactions were more frequently and more clearly positive in patients in whom urinary gonadotropin levels were normal, than in those with low or variable levels. Response in secondary amenorrhea is stronger than in primary am enorrhea. In 4 patients hyperstimulation (purely biological in 3 cases) was observed, emphasizing the necessity for the strictest precautions in using HMG even alone.^ieng

A portable experimental apparatus for human olfactory fMRI experiments.

Human olfactory perception can be measured using psychophysical tools or more complex odor generating devices systems, namely olfactometers. The present paper is aimed at presenting a new inexpensive, non-voluminous portable olfactometer adapted for human fMRI experiments. The system adjusts odorant stimulus presentation to human nasal respiration and records behavioral responses in the same experimental device. Validation by psychophysical measures and photo-ionization detection showed a linear increase in both odor intensity perception and vapor concentration as a function of odorant concentration. Further validation by brain imaging revealed neural activation in typical olfactory areas. In summary, the system represents a new low-cost, easy-use, easy-maintenance portable olfactometry tool for brain imaging, opening up new possibilities for investigating neural response to odors using event-related fMRI designs.