Simultaneously measuring the dichroism and the dielectric response of an azobenzene-doped organic glass former.

We have designed an experimental setup allowing to simultaneously measure both the dielectric response of a supercooled liquid and the dynamics of azobenzene chromophores dispersed in it. Both the azobenzene chromophores and the organic glass former have been synthesized with similar reaction paths: they are chemically similar, apart from the azobenzene group responsible for the strong optical absorption in the [350; 450 nm] range for the chromophores, while the embedding supercooled liquid is optically transparent. This material is deposited on transparent electrodes with an inter-electrode gap as small as 4 µm-obtained thanks to optical lithographic techniques. We show that our setup is sensitive enough to measure the coupling between the dielectric macroscopic response and the isomerization dynamics of 1% of chromophores excited by a 0.5-5 mW/cm2 light beam. We demonstrate that this coupling neither comes from the heating of the sample due to the light absorption nor from changes of the sample shape with light. Finally, we discuss the few physical effects, which may give rise to this coupling, and show that our experiment could test some recent predictions done in the framework of random first order transition theory of the glassy state.

Unifying different interpretations of the nonlinear response in glass-forming liquids.

This work aims at reconsidering several interpretations coexisting in the recent literature concerning nonlinear susceptibilities in supercooled liquids. We present experimental results on glycerol and propylene carbonate, showing that the three independent cubic susceptibilities have very similar frequency and temperature dependences, for both their amplitudes and phases. This strongly suggests a unique physical mechanism responsible for the growth of these nonlinear susceptibilities. We show that the framework proposed by two of us [J.-P. Bouchaud and G. Biroli, Phys. Rev. B 72, 064204 (2005)PRBMDO1098-012110.1103/PhysRevB.72.064204], where the growth of nonlinear susceptibilities is intimately related to the growth of glassy domains, accounts for all the salient experimental features. We then review several complementary and/or alternative models and show that the notion of cooperatively rearranging glassy domains is a key (implicit or explicit) ingredient to all of them. This paves the way for future experiments, which should deepen our understanding of glasses.

Experimental characterization of extreme events of inertial dissipation in a turbulent swirling flow.

The three-dimensional incompressible Navier-Stokes equations, which describe the motion of many fluids, are the cornerstones of many physical and engineering sciences. However, it is still unclear whether they are mathematically well posed, that is, whether their solutions remain regular over time or develop singularities. Even though it was shown that singularities, if exist, could only be rare events, they may induce additional energy dissipation by inertial means. Here, using measurements at the dissipative scale of an axisymmetric turbulent flow, we report estimates of such inertial energy dissipation and identify local events of extreme values. We characterize the topology of these extreme events and identify several main types. Most of them appear as fronts separating regions of distinct velocities, whereas events corresponding to focusing spirals, jets and cusps are also found. Our results highlight the non-triviality of turbulent flows at sub-Kolmogorov scales as possible footprints of singularities of the Navier-Stokes equation.

Fifth-order susceptibility unveils growth of thermodynamic amorphous order in glass-formers.

Glasses are ubiquitous in daily life and technology. However, the microscopic mechanisms generating this state of matter remain subject to debate: Glasses are considered either as merely hyperviscous liquids or as resulting from a genuine thermodynamic phase transition toward a rigid state. We show that third- and fifth-order susceptibilities provide a definite answer to this long-standing controversy. Performing the corresponding high-precision nonlinear dielectric experiments for supercooled glycerol and propylene carbonate, we find strong support for theories based on thermodynamic amorphous order. Moreover, when lowering temperature, we find that the growing transient domains are compact--that is, their fractal dimension d(f) = 3. The glass transition may thus represent a class of critical phenomena different from canonical second-order phase transitions for which d(f) < 3.

Thermoelectricity and thermodiffusion in charged colloids.

The Seebeck and Soret coefficients of ionically stabilized suspension of maghemite nanoparticles in dimethyl sulfoxide are experimentally studied as a function of nanoparticle volume fraction. In the presence of a temperature gradient, the charged colloidal nanoparticles experience both thermal drift due to their interactions with the solvent and electric forces proportional to the internal thermoelectric field. The resulting thermodiffusion of nanoparticles is observed through forced Rayleigh scattering measurements, while the thermoelectric field is accessed through voltage measurements in a thermocell. Both techniques provide independent estimates of nanoparticle's entropy of transfer as high as 82 meV K(-1). Such a property may be used to improve the thermoelectric coefficients in liquid thermocells.

Generation of a magnetic field by dynamo action in a turbulent flow of liquid sodium.

We report the observation of dynamo action in the von Kármán sodium experiment, i.e., the generation of a magnetic field by a strongly turbulent swirling flow of liquid sodium. Both mean and fluctuating parts of the field are studied. The dynamo threshold corresponds to a magnetic Reynolds number R(m) approximately 30. A mean magnetic field of the order of 40 G is observed 30% above threshold at the flow lateral boundary. The rms fluctuations are larger than the corresponding mean value for two of the components. The scaling of the mean square magnetic field is compared to a prediction previously made for high Reynolds number flows.

[MRI in infectious and spontaneous tumoral epidural hemorrhagic pathology]. / IRM et pathologie épidurale tumorale infectieuse et hémorragique spontanée.

Several studies have served to underline the interest of MRI in the diagnosis and assessment of epidural abscess and malignant extradural spinal tumors. In our work, one of the quantitatively greatest published to this day, 64 patients presenting epidural pathology were evaluated by means of MRI. All the explorations were brought about through weighted multiplaned sequences T1, T2 and gadolinium injection. The pathological spectrum encountered is comprised of: metastatic extradural spinal tumors (58%), primary extradural spinal tumors (7%), epidural localizations of hematological diseases (9%), epidural abscess (25%), and one case of epidural hematoma. Assessment was brought to bear upon behavior in relation to type of sequence, spread of disease, medullary effects, type of enhancement following gadolinium injection. Degree of correlation with clinical data and surgical findings was also appraised. As concerns tumourous epidural pathology, positive diagnosis due to a lesion hinges upon the T1 and T2 sequences. Gadolinium's contribution is restricted to analysis of perivertebral and vertebral spreading; it also facilitates recognition of the spinal cord in circumferential epiduritis. So much said, gadolinium appears to be essential in frequently less compressive forms of infectious epiduritis; it plays a pronounced role in both follow-up of their evolution and recognition of acute epidural hematoma.

[Adamantinoma of the tibia. X-ray computed tomographic and MRI study. Apropos of a case]. / Adamantinome du tibia. Etude tomodensitométrique et par IRM. A propos d'un cas.

Adamantinoma of the long bones in a very rare tumor that mainly affects the tibia. Its diagnosis is difficult both radiologically, as the lesion appears as a poorly specific metaphyseal lacuna with or without periosteal reaction, and histologically. Its prognosis used to be guarded because of recurrence and of possible metastatic diffusion, but it has been considerably improved by wide resection with reconstruction. On the occasion of a new case, the authors describe the appearance observed with MRI and the merits of this examination for the preoperative assessment.

[Leiomyosarcoma of the inferior vena cava. Diagnostic difficulties]. / Léiomyosarcomes de la veine cave inférieure. Difficultés diagnostiques.

As leiomyosarcomas of the inferior vena cava are extremely infrequent, the preoperative diagnosis of such tumors is rarely established. We report two cases in which the diagnosis was suggested by modern imaging prior to surgery. Three examination techniques allo contemplating this diagnosis. Ultrasound and cavography show either an intraluminal, multilobulated, roughly hyperechogenic lacuna on one of the segments of the vena cava, without any remote thrombosis image, or a complete obstruction of the vena cava with collateral circulation and a hyperechogenic right paraaortic mass. Computed tomography demonstrates the extraluminal extension. It reveals the presence of a right lateroaortic tumor with heterogeneous tissue density, in which the vena cava is concealed. The association of an intraluminal lacuna and of a tumoral syndrome on CT is highly suggestive. These three techniques are equally essential for the assessment of this tumor, which is primarily based on vascular findings. Exeresis is always difficult and the prognosis very poor.

[X-ray computed tomography in the surveillance of the course of acute pancreatitis. Values of a new classification of inflammatory lesions]. / La tomodensitométrie dans la surveillance évolutive des pancréatites aiguës. Intérêts d'une nouvelle classification des coulées inflammatoires.

378 tomodensitometric investigations were performed in cases of acute pancreatitis. The evolution of inflammatory lesions were analyzed with special attention to tissue aggressive inflammation in order to recognize early signs of gravity on CAT scans. Pancreatic lesions less than 15 mm in diameter called "hypodense islets-1" are compatible with oedematous lesions while lesions greater than 15 mm in diameter ("hypodense islets-2") are characteristic of developing necrosis. Tissue aggressive inflammatory lesions were classified in five grades retrospectively and showed that the incidence of abcesses was greater in grade II (76.5%) than in grade I lesions (11.75%).

[X-ray computed tomographic study of the ethmoid and middle meatus. II. Radio-anatomy (axial incidence) and morphological variations]. / Exploration tomodensitométrique de l'ethmoïde et du méat moyen. II. Radio-anatomie (incidence axiale) et variations morphologiques.

Chronic rhinosinusitis endoscopic surgery needs an accurate evaluation of diseases and paranasal sinus anatomic variations. High resolution CT by thin section (2 mm) allow this pre-operative assessment. An anatomical study of the ethmoid air cell system is always possible in axial plane. The bidimensional CT exploration (axial and coronal plane) displays the anatomic variations of ostiomeatal unit, that have been reported to predispose sinusitis. They are nasal septal deviation, pneumatization and paradoxical curvature of the middle turbinate, pneumatization of unciform process, Haller's cells, prominent agger nasi cell and ethmoid bulla. The endoscopic endonasal surgery landmarks, the individual morphologic variations, the topographic relations to the orbit and to the brain are also well shown by CT.

[Calcifications after intra-disk injection of triamcinolone hexacetonide in lumbar disk hernia. Evaluation of therapeutical results in 3 years]. / Etude des calcifications apparues après injection intradiscale d'hexacétonide de triamcinolone dans les hernies discales lombaires. Evaluation des résultats thérapeutiques à 3 ans.

The development of disk or epidural calcifications is a frequent possibility following intra-disk injection of triamcinolone hexacetonide. It was found 10 times in 26 follow-up CT scans obtained 2 to 3 years after the injection. These calcifications are often clinically silent, but they sometimes accompany a recurrence of the initial painful symptomatology. Furthermore, evaluation at 3 years of therapeutic results in a previously published series of patients who had received an intra-disk injection of triamcinolone hexacetonide showed a marked decrease in favourable results (30% vs 67% at 6 months). These two arguments: disappointing long term results and possibility of disk calcifications, are felt by the authors to justify abandoning the technique of triamcinolone hexacetonide by intra-disk injection in the treatment of lumbar disk prolapse.

[X-ray computed tomographic study of the ethmoid and middle meatus. I. radioanatomy (coronal plane)]. / Exploration tomodensitométrique de l'ethmoïde et du méat moyen. I. Radio-anatomie (incidence coronale).

The advance of endoscopic endonasal surgery allows limited surgical resection in chronic rhinosinusitis. An accurate topographic evaluation of diseases and individual morphologic variation are necessary for this functional surgery. The preoperative radiological investigations require a precise knowledge of ethmoid and osteo-meatal unit anatomy. Thin sections by high resolution CT were performed in coronal plane. The anatomical land marks and the ethmoidal bony roots, which allow a study of the osteo-meatal unit and ethmoid air cells system, are showed. Like endoscopic view, coronal slices better display the different grooves for paranasal sinus draining and their relations with the ethmoid.

[Intrathoracic chondrosarcoma arising at a rib in a patient with multiple exostoses]. / Chondrosarcome intrathoracique à point de départ costal chez un patient porteur d'une maladie des exostoses multiples.

A case of chondrosarcoma arising from the 7th left rib in a patient with multiple exostosis disease is reported. The initial CT scan feature is a purely intrathoracic mass with a parietal and pericardial junction and calcifications within the tumor. A review of the literature about the costal chondrosarcoma and their CT scan features is done and shows the uncommon initial aspect of this case.

[Radiological and magnetic resonance aspects in cerebral venous angioma]. / Aspects radiologiques et en résonance magnétique des angiomes veineux cérébraux.

This report based on a series of 8 cases deals with the appearance of cerebral venous angiomas with computed tomography (CT), arteriography and magnetic resonance imaging (MRI). The CT data are not conclusive, and venous involvement is demonstrated by arteriography, as well as the site of involvement. Magnetic resonance imaging seems to be useful owing to the morphological information and data on flow phenomena it provides.

[Reversible cerebral lesions in eclampsia. Clinical and x-ray computed tomographic study]. / Lésions cérébrales réversibles dans l'éclampsie. Etude clinique et tomodensitométrique.

The appearance observed with CT during and following eclampsia seem to be related to edema, hemorrhagic lesions and ischemic lesions. The authors report on a reversible appearance of hypodense central grey nuclei and of the calcarine cortex fitting into this new context.

[Pelvic cystic lymphangioma. Apropos of a case in an adult]. / Lymphangiome kystique pelvien. A propos d'un cas chez un adulte.

The authors report about the observation of a subperitoneal pelvic cystic lymphangioma in an adult patient: ultrasound and CT dat had yet never been described for the rare pelvic form, and are the same as with the other locations of cystic lymphangioma in adults.