[Adult intramedullary gliomas]. / Tumeurs gliales intramédullaires de l'adulte : la série du rapport.

OBJECTIVES: Intramedullary gliomas are rare tumors accounting for less than 4% of all primary central nervous system tumors. The aims of this retrospective multicenter study were to assess their natural outcome as well as management. METHODS AND MATERIALS: We studied 332 patients from 1984 to 2011. Histopathological examination revealed 72% ependymomas (94% were low grade tumors), 24% astrocytomas (29% were high grade tumors), 2.4% mixed gliomas and 1.7% oligodendrogliomas. RESULTS: The mean age at diagnosis was 42.4 years for ependymomas, with male predominance, versus 39.6 years for astrocytomas. Pain was the most common initial presentation. In 20% of cases, astrocytomas were biopsied alone, but more than 80% of ependymomas had surgical resection. Radiotherapy and chemotherapy were reserved for malignant tumors, especially if they were ependymomas. The 5-year survival rate was 76.8% for astrocytomas and 94.5% for ependymomas. Histology, functional status prior to surgery, and tumor grade are among the prognostic factors. CONCLUSION: Our study showed that surgical treatment of gliomas is well codified, at least for ependymomas, but adjuvant treatment continues to play a marginal role in the management even in astrocytomas, which are infiltrative tumors.

Hypocretinergic dysfunction in neuromyelitis optica with coma-like episodes.

Devic's neuromyelitis optica (NMO) is a severe demyelinating disease of the central nervous system, often misdiagnosed as multiple sclerosis, and involving mainly optic nerves and the spinal cord. We report on a peculiar case of relapsing NMO with severe recurrent dysautonomia and hypersomnia, in which we had the opportunity to observe a dramatic decrease in hypocretin/orexin cerebrospinal fluid level.

Time-resolved torsional relaxation of spider draglines by an optical technique.

The sensitivity of the torsional pendulum demonstrates the self-shape-memory effect in different types of spider draglines. Here we report the time-resolved noncovalent bonds recovery in the protein structure. The torsional dynamics of such multilevel structure governed by reversible interactions are described in the frame of a nested model. Measurement of three different relaxation times confirms the existence of three energy storage levels in such two protein spidroin systems. Torsion opens the way to further investigations towards unraveling the tiny torque effects in biological molecules.

A dipole interaction model for magnetochiral birefringence.

We have developed a classical model to investigate the magnetochiral birefringence of an isotropic chiral medium submitted to a longitudinal magnetic field. This model, which is an extension of the atom dipole interaction model, yields direct calculations from the polarizabilities and positions of the atoms of the considered molecules. The numerical values obtained for the magnetochiral birefringence, as well as for the optical activity and Faraday rotation, are supported by the previously published experimental results on limonene, proline, and tartaric acid.

Lever-assisted two-noise stochastic resonance.

A critical interplay of two correlated noises in a nonlinear symmetrical two-well potential system is experimentally demonstrated. One state can become completely noise free, leading to an infinite Kramers time. If an independent lever breaks the potential symmetry, stochastic resonance is recovered. In this new regime, we obtain a plateau, i.e., a high signal-to-noise ratio even for vanishing forcing signals.

[Pneumomediastinum as a complication of recreational ecstasy use]. / Un pneumomédiastin, une complication exceptionnelle de la consommation d'ecstasy.

Ecstasy recreational use dramatically increased during the last decade in France. Multiples complications associated with ecstasy consumption have been reported. We describe an exceptional case of pneumomediastinum related to ecstasy recreational use. The patient was a 19-year old patient whose medical history was significant for asthma and was a moderate tobacco smoker. He reported regular ecstasy recreational use. He presented at the emergency unit for chest pain and cough, 48 hours after the ingestion of three tablets of ecstasy and the inhalation of three other tablets. Blood pressure was 90/60 mmHg, pulse rate was 120 per minute, respiratory rate was 32 per minute and pulse oximetry was 93%. Neck emphysema was noted. Chest radiograph and scanner diagnosed pneumomédiastinum. Outcome was favorable with symptomatic treatment and the patient was discharged home eight days later. Pneumomediastinum is an exceptional complication after ecstasy recreational use. Physician should be aware of the risk of such event.

Stochastic resonances in an optical two-order parameter vectorial system.

We show experimentally that optical two-dimensional systems such as vectorial lasers can exhibit novel stochastic resonances. All optical noise and modulation of this system allows the isolation of so-called inhibitional and rotational stochastic resonances. In particular, incoherent rotational tunneling is shown to be sensitive enough to be also induced by Faraday noise and by quantum noise, i.e., external spontaneous emission.

Rabi-Lorentzian profile of an atomic resonance obtained with Gaussian beams.

We demonstrate that the interaction between atoms and a Gaussian beam changes the Lorentzian resonance into a so-called Rabi-Lorentzian resonance profile. The existence of such profiles is experimentally evidenced in a dark resonance situation for metastable (4) He, in the absence of any external perturbation. A topological mechanism is shown theoretically to account for the measured profiles. We observe a 3% systematic residual with respect to a pure Lorentzian profile, which could play a role in the search of high precision in the measurement of fundamental constants.

Measurement of positive and negative Goos--Hänchen effects for metallic gratings near Wood anomalies.

Large Goos-Hänchen effects are isolated for reflection on a metallic grating. These shifts occur in the vicinity of Wood anomalies. Depending on the nature of the anomaly, these displacements are found to be either positive or, contrary to the usual GH effect, clearly negative. Those shifts, associated with forward and backward leaky surface waves, are as large as plus or minus tens of wavelengths for a classic metallic grating.

Direct measurement of the wigner delay associated with the goos-Hanchen effect

It is shown experimentally that the nonspecular reflection of light on an interface induces a time delay, as predicted by Wigner's scattering theory. A differential femtosecond technique is used to directly isolate this delay, associated with the Goos-Hanchen spatial shift produced by a grating near a resonant Wood anomaly. A delay of 4.4 fs is observed between TE and TM pulses, in agreement with the expected Wigner delay obtained from phase shift dispersion measurements.

Existence of two coupling constants in microchip lasers.

We implemented two different experimental setups to probe directly the nonlinear coupling between modes in microchip lasers. We show that, remarkably, the results can be interpreted by use of Lamb's coupling constant. In an Er, Yb:glass microchip laser, we measured C(12) = 0.80 between longitudinal modes and C(xy) = 0.95 between orthogonally linearly polarized eigenstates. The high values obtained give some physical insight into the single-frequency operation of such lasers.

Temporal behavior of an unstable optical cavity.

The relaxation of a geometrically unstable Fabry-Perot cavity is theoretically and experimentally investigated. It is observed that the usual sum of the exponential decays of the intensities in the different transverse modes of the cavity is replaced by a more complex behavior. In particular, light couplings into the fundamental mode of the cavity with initial wave excitation factors larger than unity, i.e., larger than in the case of mode-matched injection, are directly observed. The influence of the cavity Fresnel number and of transverse mode crossings and anticrossings on these cavity decays is isolated.

Self-mode-locked pulsed monomode laser.

We predict the existence of a new pulsed-laser operation regime, when the phases and polarizations of the two coupled cold-cavity eigenstates of a monomode solid-state laser are taken into account in the derivation of the Maxwell-Bloch equations. This monomode pulsed regime is experimentally observed, without any normal mode locking or Q switching occurring inside the cavity. We obtain close agreement between experiments and theory, even in the simple case of a Nd:YAG microchip laser, for which sech(2) pulses at nearly megahertz repetition rates are readily observed.

Coherent addition of adjacent lasers by forked eigenstate operation.

Forked laser eigenstates are shown to provide a powerful tool both to phase lock spatially separated laser oscillators and to add their powers coherently into a TEM(00) output beam. Coherent addition of the powers extracted from two fiber-coupled diode-pumped Nd:YAG channels is theoretically and experimentally demonstrated. Pure TEM(00) oscillation is obtained with a 20% optical-to-optical conversion efficiency. The coherence of the two-propagation-axis laser is proved, and single-frequency operation is demonstrated. The scalability of the scheme is discussed.

Resonant cavity gas-phase polarimeter.

A high-sensitivity polarimeter is demonstrated for application to gas-phase chirality measurement. This device is based on the physics of the eigenstates of a Fabry-Perot cavity, permitting improvement in the sensitivity with respect to the usual polarimeters. Typical measurements of rotations of 50 (±1) × 10(-)(5)° induced by the optical activity of (R)-(+)-limonene and (S)-(-)-limonene in the vapor phase are shown. A noise level corresponding to a rotation of 10(-)(6)° is experimentally demonstrated. Application to the polarimetric monitoring of an enantiomer mixing racemization of limonene in the gas phase is also presented.

Internal reflections of the Gaussian beams in Faraday isolators.

The reflection coefficient of the Faraday isolator-mirror system in the presence of internal reflections of the incident Gaussian beam is theoretically and experimentally explored for three different architectures of a Faraday isolator. In every case, these internal reflections are shown to alter widely the behavior of the system. In particular, we propose and test a design using a quarter-wave plate that can, in some experiments, give better isolation ratios than conventional isolators.

Tunable optical microwave source using spatially resolved laser eigenstates.

A two-propagation-axis solid-state laser is shown to provide a widely tunable optical microwave source. The spatial separation of the laser eigenstates is shown to enable an étalon to act as a coarse tuner, forcing oscillation in any nonadjacent cavity modes. The frequency difference between opposite helicoidal eigenstates operating in nonadjacent cavity modes can then be tuned continuously. The beat note from such a solid-state laser is shown to vary from dc to 26 GHz, i.e., 30 times the laser free-spectral range, and is limited only by the free-spectral range of the étalon.