Superparamagnetic colloids in a rotating field: Transition state from chains to disks.

When exposed to an external magnetic field, 2D layers of spherical superparamagnetic colloids form specific structures which depend on the features of the external field. If the magnetic field is constant along time, superparamagnetic colloids self-organize into chains oriented in the direction of the field. If the magnetic field is rotating in the plane of the suspension, below a critical frequency, the superparamagnetic beads still aggregate into chains, but these chains rotate with the magnetic field. When the rotation reaches a certain speed, the colloids aggregate in rotating disklike clusters. In this work, we focused on the early stages of the disklike clusters' aggregation and the dynamics of this process. In particular, we observed experimentally that before clustering into disklike structures, the colloids were aggregating into rotating chains, just as they did in suspensions submitted to a magnetic field rotating at a lower rate. Over time, the chains interact with one another and aggregate into disklike clusters, resulting in a mixture of chains and disks in the sample. Finally, we propose a model to characterize the suspension over time in terms of the proportion of chains and disklike clusters, and report its deduced temporal evolution for different frequencies and volume fractions.

[Feticide procedures in second and third trimesters terminations of pregnancy]. / Geste d'arrêt de vie fœtale : techniques pour les interruptions médicales de grossesse des deuxième et troisième trimestres.

Performing a feticide as part of termination of late pregnancy is recommended in many countries. Feticide avoids a live birth of a severely affected premature newborn and prevents fetal pain. There are limited data on feticide procedures since only a few countries in the world authorize late termination of pregnancy. The objective of this review was to assess the most appropriate feticide procedure based on published data during the last thirty years. Administration of an initial fetal analgesia followed by a lethal lidocaine injection through the umbilical cord, under ultrasound guidance, appears to be the most effective, safe and ethical way to perform feticide. According to the current knowledge regarding the risk of fetal pain and survival of extremely preterm infants, a feticide should be discussed as early as 20-22 weeks of gestation.

Effect of volume fraction on chains of superparamagnetic colloids at equilibrium.

For a few decades, the influence of a magnetic field on the aggregation process of superparamagnetic colloids has been well known on short time scale. However, the accurate study of the equilibrium state is still challenging on some aspects. On the numerical aspect, current simulations have only access to a restricted set of experimental conditions due to the computational cost of long-range interactions in many-body systems. In the present paper, we numerically explore a new range of parameters thanks to sped up numerical simulations validated by a recent experimental and numerical study. We first show that our simulations reproduce results from previous study in well-established conditions. Then we show that unexpectedly long chains are observed for higher volume fractions and intermediate fields. We also present theoretical developments taking into account the interaction between the chains which are able to reproduce the data that we obtained with our simulations. We finally confirm this model thanks to experimental data.

Wave Turbulence on the Surface of a Fluid in a High-Gravity Environment.

We report on the observation of gravity-capillary wave turbulence on the surface of a fluid in a high-gravity environment. By using a large-diameter centrifuge, the effective gravity acceleration is tuned up to 20 times Earth's gravity. The transition frequency between the gravity and capillary regimes is thus increased up to one decade as predicted theoretically. A frequency power-law wave spectrum is observed in each regime and is found to be independent of the gravity level and of the wave steepness. While the timescale separation required by weak turbulence is well verified experimentally regardless of the gravity level, the nonlinear and dissipation timescales are found to be independent of the scale, as a result of the finite size effects of the system (large-scale container modes) that are not taken currently into account theoretically.

Superparamagnetic colloids in viscous fluids.

The influence of a magnetic field on the aggregation process of superparamagnetic colloids has been well known on short time for a few decades. However, the influence of important parameters, such as viscosity of the liquid, has received only little attention. Moreover, the equilibrium state reached after a long time is still challenging on some aspects. Indeed, recent experimental measurements show deviations from pure analytical models in extreme conditions. Furthermore, current simulations would require several years of computing time to reach equilibrium state under those conditions. In the present paper, we show how viscosity influences the characteristic time of the aggregation process, with experimental measurements in agreement with previous theories on transient behaviour. Afterwards, we performed numerical simulations on equivalent systems with lower viscosities. Below a critical value of viscosity, a transition to a new aggregation regime is observed and analysed. We noticed this result can be used to reduce the numerical simulation time from several orders of magnitude, without modifying the intrinsic physical behaviour of the particles. However, it also implies that, for high magnetic fields, granular gases could have a very different behaviour from colloidal liquids.

Self-assembly processes of superparamagnetic colloids in a quasi-two-dimensional system.

Superparamagnetic colloids gather depending on the magnitude of the magnetic field applied, forming chains and ribbons in a quasi-two-dimensional chamber. The results presented in this work are in good agreement with recent experimental multistable data for the mean length of the aggregates in thermodynamic equilibrium.

Ribbons of superparamagnetic colloids in magnetic field.

While the aggregation process of superparamagnetic colloids in strong magnetic field is well known on short time since a few decades, recent theoretical works predicted an equilibrium state reached after a long time. In the present paper, we present experimental observations of this equilibrium state with a two-dimensional system and we compare our data with the predictions of a pre-existing model. Above a critical aggregation size, a deviation between the model and the experimental data is observed. This deviation is explained by the formation of ribbon-shaped aggregates. The ribbons are formed due to lateral aggregation of chains. An estimation of the magnetic energy for chains and ribbons shows that ribbons are stable structures when the number of magnetic grains is higher than N = 30 .

Remote control of self-assembled microswimmers.

Physics governing the locomotion of microorganisms and other microsystems is dominated by viscous damping. An effective swimming strategy involves the non-reciprocal and periodic deformations of the considered body. Here, we show that a magnetocapillary-driven self-assembly, composed of three soft ferromagnetic beads, is able to swim along a liquid-air interface when powered by an external magnetic field. More importantly, we demonstrate that trajectories can be fully controlled, opening ways to explore low Reynolds number swimming. This magnetocapillary system spontaneously forms by self-assembly, allowing miniaturization and other possible applications such as cargo transport or solvent flows.

[Chylous ascites complicating domiciliary ventilation by tracheostomy]. / Ascite chyleuse compliquant une ventilation à domicile par trachéotomie.

INTRODUCTION: Despite the development of non-invasive ventilation there remain indications for domiciliary ventilation by tracheostomy (TDV). The principal complications are mechanical and infective. We report a case of chylous ascites secondary to compression of the thoracic duct by the tracheostomy cuff. CASE REPORT: A man of 65 had had TDV for over one year. During hospitalisation for possible weening chylous ascites was discovered. The classical causes of this condition were excluded. CT scan of the neck and thorax showed evidence of significant dilatation (over 45 mm) of the upper part of the trachea in association with an over-inflated cuff, leading to compression of the thoracic duct. On reducing the inflation pressure of the cuff the chylous ascites has not recurred. CONCLUSION: The management of the tracheostomy tube cuff is an important matter for the personel involved in the management of TDV. Regular radiological surveillance is useful to ensure that there is no tracheal dilatation in association with the cuff.

[Pleural effusion following hepatic radiofrequency]. / Pleurésies post radiofréquence hépatique.

INTRODUCTION: Surgery is the treatment of choice for primary or secondary hepatic tumours. If surgery is contra-indicated radiofrequency offers an alternative treatment capable of destroying tumours small in size and/or number. It is undertaken percutaneously, during laparotomy or endoscopically. Respiratory physicians should be familiar with certain complications. CASE REPORTS: We report two cases of pleurisy following hepatic radiofrequency. The effusions were diagnosed 15 days and one month after radiofrequency treatment for liver metastases from colonic carcinoma. The effusions were exudative and predominantly lymphocytic. The first effusion required thoracoscopy to establish the diagnosis; the second dried up following 5 pleural aspirations. CONCLUSION: Post radiofrequency pleurisy may develop late and present problems in diagnosis and treatment.

[Spontaneous pneumothorax revealing malignant pleural mesothelioma. Three case reports]. / Trois cas de pneumothorax spontané révélant un mésothéliome pleural malin.

Spontaneous pneumothorax is an uncommon inaugural presentation of malignant pleural mesothelioma. We report three cases in men aged 65, 30 and 76 years. The diagnosis was suggested at medical imaging and was confirmed at histological analysis of biopsies obtained by thoracoscopy in two patients and thoracotomy in one. The first patient (age 65 years) died two months after the initial diagnosis. The second patient (age 30 years) was alive 40 months after 15 chemotherapy cycles using a platinim-gemcitabine combination. Complete tumor response was achieved in the third patient (age 76 years) after 9 chemotherapy cycles with the same combination. Since mid-term prognosis is fatal for this type of tumor, we propose thoracoscopy in all patients over 30 years who develop spontaneous pneumothorax with no morphological features increasing the risk of pneumothorax, and particularly in patients with asbestos exposure.

[Rapid identification of pneumococcal antigenes in urines by the Now Streptococcus pneumoniae Binax test]. / Détection rapide des antigènes pneumococciques urinaires par le test Now Streptococcus pneumoniae Binax.

Streptococcus pneumoniae is responsible for many infectious conditions but probably with an underestimated incidence especially because of the fragility of the bacteria. The present study has evaluated a new test which detects a pneumococcal antigen in urine (Now S.p Binax). Urine samples from 181 children and 40 adults have been tested. All the patients presented with typical clinical signs of pneumococcal infection. Sensitivity = 91.7 %; specificity = 54.2 %; positive predictive value = 50 %; and negative predictive value = 92.9 % have been observed. Although the sensitivity and specificity were lower than those announced by the manufacturer, the test is easy to handle and provides a rapid argument for the diagnosis of pneumococcal infection, especially in the case of invasive infections like meningitis and bacteraemia.

[Pulmonary aspergillosis complicating chronic septic granulomatosis. Treatment with itraconazole and gamma interferon]. / Aspergillose pulmonaire compliquant une granulomatose septique chronique. Traitement par itraconazole et interféron gamma.

A 20-year-old patient suffering from chronic granulomatous disease developed pulmonary aspergillosis with thoracic wall invasion. Treatment with itraconazole combined with 3-weekly injections of interferon gamma (INF gamma) improved the patient's general state of health within two months. Functional signs resolved totally and x-ray images continued to improve for 6 months. INF gamma was withdrawn after 11 months and was replaced with cotrimoxasole. Itraconazole was continued in a long-term regimen. Four years after onset of treatment, the clinical status of the patient remained satisfactory, and the radiological aspect was unchanged. Pulmonary aspergillosis affects up to 40% of patients suffering from chronic granulomatous disease. Mortality is high, to the order of 25%. The classical treatment is based on amphotericin B, but this case points out the significant contribution of itraconazole as first-line therapy. This antimycotic has been suggested for prophylaxis. The combined use of INF gamma can be discussed due to the uncertainties about its long-term effects and because of the requirement for 3-weekly injections. High cost is another important consideration.

[Semi-invasive pulmonary aspergillosis. Apropos of a case]. / L'aspergillose pulmonaire semi-invasive. A propos d'une observation.

A 43-year-old man was admitted to hospital for excavated pneumopathy of the upper part of the right lung, revealed by signs of respiratory infection evolving for a few weeks and involving a 10-kg weight loss. The radiological and clinical evolution and the demonstration of Aspergillus fumigatus allowed establishing a diagnosis of semi-invasive aspergillosis. The treatment, associating amphotericin B and 5-fluorocytosine, replaced by itraconazole 15 days later, soon produced clinical healing and radiological improvement. Since serology remained positive, surgery was performed to remove the residual lesions after a 7-month course of itraconazole. Within the scope of this case, the diagnostic criteria of this form of pulmonary aspergillosis are discussed, as well as the merits and limitations of itraconazole.

[Bilateral Torulopsis glabrata pneumonia]. / Pneumopathie bilatérale à Torulopsis glabrata.

In a 48-year old male patient hospitalized for evaluation of fatigue with non-productive cough and dyspnoea, standard radiography and computerized tomography of the chest showed nodular opacities in both lung apices. Examination of intrabronchial specimens revealed mycelial filaments, and Torulopsis glabrata grew in culture. Under antifungal treatment the clinical signs rapidly improved and the radiological abnormalities disappeared more slowly, which confirmed the diagnosis of T. glabrata pneumonia. The authors recall the pathogenic role of this yeast-like fungus, closely related to Candida albicans, which mainly causes severe opportunistic infections. The diagnostic criteria, the part played by immunodepression in the disease and the therapeutic problems encountered are also discussed.