Phase Domain Walls in Weakly Nonlinear Deep Water Surface Gravity Waves.

We report a theoretical derivation, an experimental observation and a numerical validation of nonlinear phase domain walls in weakly nonlinear deep water surface gravity waves. The domain walls presented are connecting homogeneous zones of weakly nonlinear plane Stokes waves of identical amplitude and wave vector but differences in phase. By exploiting symmetry transformations within the framework of the nonlinear Schrödinger equation we demonstrate the existence of exact analytical solutions representing such domain walls in the weakly nonlinear limit. The walls are in general oblique to the direction of the wave vector and stationary in moving reference frames. Experimental and numerical studies confirm and visualize the findings. Our present results demonstrate that nonlinear domain walls do exist in the weakly nonlinear regime of general systems exhibiting dispersive waves.

Experimental Observation and Theoretical Description of Multisoliton Fission in Shallow Water.

We observe the dispersive breaking of cosine-type long waves [Phys. Rev. Lett. 15, 240 (1965)] in shallow water, characterizing the highly nonlinear "multisoliton" fission over variable conditions. We provide new insight into the interpretation of the results by analyzing the data in terms of the periodic inverse scattering transform for the Korteweg-de Vries equation. In a wide range of dispersion and nonlinearity, the data compare favorably with our analytical estimate, based on a rigorous WKB approach, of the number of emerging solitons. We are also able to observe experimentally the universal Fermi-Pasta-Ulam recurrence in the regime of moderately weak dispersion.

Experimental observation of dark solitons on the surface of water.

We present the first ever observation of dark solitons on the surface of water. It takes the form of an amplitude drop of the carrier wave which does not change shape in propagation. The shape and width of the soliton depend on the water depth, carrier frequency, and the amplitude of the background wave. The experimental data taken in a water tank show an excellent agreement with the theory. These results may improve our understanding of the nonlinear dynamics of water waves at finite depths.

Hydrodynamic supercontinuum.

We report the experimental observation of multi-bound-soliton solutions of the nonlinear Schrödinger equation (NLS) in the context of hydrodynamic surface gravity waves. Higher-order N-soliton solutions with N=2, 3 are studied in detail and shown to be associated with self-focusing in the wave group dynamics and the generation of a steep localized carrier wave underneath the group envelope. We also show that for larger input soliton numbers, the wave group experiences irreversible spectral broadening, which we refer to as a hydrodynamic supercontinuum by analogy with optics. This process is shown to be associated with the fission of the initial multisoliton into individual fundamental solitons due to higher-order nonlinear perturbations to the NLS. Numerical simulations using an extended NLS model described by the modified nonlinear Schrödinger equation, show excellent agreement with experiment and highlight the universal role that higher-order nonlinear perturbations to the NLS play in supercontinuum generation.

Extreme wave excitation from localized phase-shift perturbations.

The modulation instability is a focusing mechanism responsible for the formation of strong wave localizations not only on the water surface, but also in a variety of nonlinear dispersive media. Such dynamics is initiated from the injection of sidebands, which translate into an amplitude modulation of the wave field. The nonlinear stage of unstable wave evolution can be described by exact solutions of the nonlinear Schrödinger equation (NLSE). In that case, the amplitude modulation of such coherent extreme wave structures is connected to a particular phase-shift seed in the carrier wave. In this Letter, we show that phase-shift localization applied to the background, excluding any amplitude modulation excitation, can indeed trigger extreme events. Such rogue waves can be for instance generated by considering the parametrization of fundamental breathers, and thus by seeding only the local phase-shift information to the regular carrier wave. Our wave tank experiments show an excellent agreement with the expected NLSE hydrodynamics and confirm that even though delayed in their evolution, breather-type extreme waves can be generated from a purely regular wave train. Such a focusing mechanism awaits experimental confirmation in other nonlinear media, such optics, plasma, and Bose-Einstein condensates.

Nonlinear wave evolution with data-driven breaking.

Wave breaking is the main mechanism that dissipates energy input into ocean waves by wind and transferred across the spectrum by nonlinearity. It determines the properties of a sea state and plays a crucial role in ocean-atmosphere interaction, ocean pollution, and rogue waves. Owing to its turbulent nature, wave breaking remains too computationally demanding to solve using direct numerical simulations except in simple, short-duration circumstances. To overcome this challenge, we present a blended machine learning framework in which a physics-based nonlinear evolution model for deep-water, non-breaking waves and a recurrent neural network are combined to predict the evolution of breaking waves. We use wave tank measurements rather than simulations to provide training data and use a long short-term memory neural network to apply a finite-domain correction to the evolution model. Our blended machine learning framework gives excellent predictions of breaking and its effects on wave evolution, including for external data.

Rogue wave observation in a water wave tank.

The conventional definition of rogue waves in the ocean is that their heights, from crest to trough, are more than about twice the significant wave height, which is the average wave height of the largest one-third of nearby waves. When modeling deep water waves using the nonlinear Schrödinger equation, the most likely candidate satisfying this criterion is the so-called Peregrine solution. It is localized in both space and time, thus describing a unique wave event. Until now, experiments specifically designed for observation of breather states in the evolution of deep water waves have never been made in this double limit. In the present work, we present the first experimental results with observations of the Peregrine soliton in a water wave tank.

Nonconservative higher-order hydrodynamic modulation instability.

The modulation instability (MI) is a universal mechanism that is responsible for the disintegration of weakly nonlinear narrow-banded wave fields and the emergence of localized extreme events in dispersive media. The instability dynamics is naturally triggered, when unstable energy sidebands located around the main energy peak are excited and then follow an exponential growth law. As a consequence of four wave mixing effect, these primary sidebands generate an infinite number of additional sidebands, forming a triangular sideband cascade. After saturation, it is expected that the system experiences a return to initial conditions followed by a spectral recurrence dynamics. Much complex nonlinear wave field motion is expected, when the secondary or successive sideband pair that is created is also located in the finite instability gain range around the main carrier frequency peak. This latter process is referred to as higher-order MI. We report a numerical and experimental study that confirms observation of higher-order MI dynamics in water waves. Furthermore, we show that the presence of weak dissipation may counterintuitively enhance wave focusing in the second recurrent cycle of wave amplification. The interdisciplinary weakly nonlinear approach in addressing the evolution of unstable nonlinear waves dynamics may find significant resonance in other nonlinear dispersive media in physics, such as optics, solids, superfluids, and plasma.

Modulation Instability and Phase-Shifted Fermi-Pasta-Ulam Recurrence.

Instabilities are common phenomena frequently observed in nature, sometimes leading to unexpected catastrophes and disasters in seemingly normal conditions. One prominent form of instability in a distributed system is its response to a harmonic modulation. Such instability has special names in various branches of physics and is generally known as modulation instability (MI). The MI leads to a growth-decay cycle of unstable waves and is therefore related to Fermi-Pasta-Ulam (FPU) recurrence since breather solutions of the nonlinear Schrödinger equation (NLSE) are known to accurately describe growth and decay of modulationally unstable waves in conservative systems. Here, we report theoretical, numerical and experimental evidence of the effect of dissipation on FPU cycles in a super wave tank, namely their shift in a determined order. In showing that ideal NLSE breather solutions can describe such dissipative nonlinear dynamics, our results may impact the interpretation of a wide range of new physics scenarios.

Further characterization and thrombolytic activity in a rat model of a fibrinogenase from Vipera lebetina venom.

Vipera lebetina fibrinogenase (VlF) was shown to render fibrinogen incoagulable and to solubilize fibrin. The fibrinogenolytic activity of this enzyme was found to be 33 mg fibrinogen/min/mg protein. The study of the specificity of this enzyme revealed that it has no effect on purified factor X, prothrombin and protein C and on the specific chromogenic substrates of their active form. Plasminogen was not activated by VlF but slightly degraded. We have also compared the effect of VlF and plasmin on fibrinogen and shown that these two enzymes have a different sites of cleavage. This enzyme inhibited human platelet aggregation on PRP initiated by ADP and collagen but was without effect on the aggregation of washed rabbit platelets using thrombin as agonist. Administration of VlF in rat did not show any necrosis or hemorrhage in treated rats organ's. We therefore, examined the thrombolytic activity of VlF in a rat model of venous thrombosis. Thrombus was produced in the posterior vena cava by injection of human fibrinogen and thrombin. Injection of 5 mg/Kg body weight showed an evident flow restoration after one hour and measurement of the fibrinogen level a decrease of about 30% after 3 hrs. VlF's action is not dependent on plasminogen activators and may act synergistically with them, thereby providing an intriguing potential clinical application for dissolution of blood clots.

The Antley-Bixler syndrome. A new case without radiohumeral synostosis.

The author report a new case of the syndrome described by Antley and Bixler. It concerns a female new-born who presents a craniosynostosis with brachycephaly, midface hypoplasia, unilateral choanal atresia, multiple joint contractures and arachnodactyly. There was no bowing of the femora and only the radius and the ulna were bowed. The absence of radiohumeral synostosis reported in all observations of the literature represents the main particularity of this observation.

[Wolman disease]. / La maladie de Wolman.

BACKGROUND: Wolman disease is a severe disease associated with hepatosplenomegaly and adrenal calcifications; it is nearly always fatal in the first year of life. CASE REPORT: A boy was born to consanguineous parents. His weight was 3,500 g, height 53 cm. Hepatomegaly was observed at the age of 26 days; he also had vomiting and watery stools with failure to thrive. Diagnosis of Wolman disease was suspected due to family history. Two sisters had died at the age of 3 months without precise diagnosis; both had abdominal distension, hepatosplenomegaly, anemia and inanition; CT scan showed calcifications of adrenal glands in one of them that had been attributed to adrenal hemorrhage. Investigations in our patient showed no adrenal calcification, hepatomegaly without splenomegaly, anemia (Hb: 8 g/100 ml). Liver biopsy showed enlarged and vacuolated parenchymal and Kupffer cells but the marrow did not contain foam cells. Acid lipase deficiency was demonstrated in cultured skin fibroblasts, permitting prenatal diagnosis in a further sib. CONCLUSION: This case of Wolman disease was the first seen in Tunisia; it was inherited as an autosomal recessive disorder; this patient, as two of his sisters, died during the first 6 months of life.

[Biological effects of pleural talc in neoplastic pleurisy]. / Effets biologiques du talcage pleural au cours des pleurésies néoplasiques.

A study was carried out on ten patients who had received talc by thoracoscopy for secondary neoplastic pleural involvement. The study was in two parts. First, a laboratory study on blood specimens was made including the full blood count, sedimentation rate and alpha-2 globulins. Secondly, the pleural liquid was examined over a 24 hour period, measuring the leucocyte count/ml and also the pleural sugar. The studies revealed the occurrence of an early rise (J0) in the level of polynuclear neutrophil (PNN) in the pleural liquid, with a 24 hour peak preceded by a leucocytosis and a moderate polymorphonuclear response without any change in the sedimentation rate. These changes provide evidence for the role of PNN in the genesis of pleural symphysis during talc therapy. There was also an early fall in pleural sugar, and this was in parallel with the diminution of the quantity of pleural fluid drained and would be linked to a rise in the local cellular metabolism and to a disturbance in the exchange across the thickened pleural membrane, as a result of fibrosis.

[An experimental anatomopathological study of pleural talcosis]. / Etude anatomopathologique expérimentale du talcage pleural.

The aim of this work was to study the anatomical and pathological reaction and the mechanism of the formation of the pleural symphysis during pleural talcosis. The experiment was performed on fifteen dogs of similar breed, divided into three groups of five subjects each. After thoracoscopy under general anaesthesia, 2 ml of intrapleural physiological saline were injected in group I (controls) and 2 or 4 ml of talc granules in group II and III. A drainage tube was positioned at the end of the examination. One dog in each group was sacrificed on the 1st, 2nd, 7th, 15th, and 30th days post-thoracoscopy. At autopsy a detailed macroscopic study was carried out and some biopsies were taken for histology. In the control group, the inflammatory reaction was very moderate and rapidly disappeared whereas in the groups treated with talc, the talc led to an exudate of several millimeters, the exudate of inflammatory reaction was acute and early (J1) and involved the pleural in particular on the costal surface and was more moderate on the visceral surface and only involved the lung to a thickness of 2 or 3 mm and a few peripheral alveolar spaces. The granulomatous reaction occurred later (from the 3rd day) and was accompanied by the formation of a symphysis by the deposition and coagulation of fibrin which continued from the 7th to the 15th day, and became solid on the 30th day post-thoracoscopy. There was no significant difference between the two groups treated with talc, implying that the reaction was linked to the talc and was independent of the dose used.

[Tracheal atresia. A case report]. / Atresie tracheale. A propos d'un cas.

The tracheal agenesis is a rare malformation of the respiratory tract. It must be suspected in any new born with respiratory distress, absence of crying, and difficulty or impossibility of intubation. Since the initial case report by Payne in 1900, 87 cases have been reported in the literature. The authors report one case of tracheal agenesis out of 2500 autopsy realised in the laboratory.

[Fetal pathology study of 88 cases of letal spina bifida]. / Etude foeto-pathologique de 88 cas de spina bifida létaux.

Lethal spina bifida continue to be frequent in Tunisia; we report 88 cases of letal spina bifida: 1.05 per thousand births. This pathology was more frequent with women. The up letal spina bifida situated is predominant with female and the dow spina bifida situated is frequent with male. We have noted an association with anencephalia (46 cases) and hydrocephaly (21 cases). Prevention is based on obstetric health care and hygiene dietetic advices to avoid alimentary deficit.

[Diagnosis of holoprosencephalia. Report of 17 cases]. / Diagnostic de l'holoprosencephalie. A propos de 17 cas.

OBJECTIVE: To establish the epidemiologic profile of holoprosencephalia and determine benefits of ultrasound and foetopathologic examination to the diagnostic. METHODS AN MATERIAL: [corrected] Retrospective study about 17 cases of holoprosencephalia observed in CMNT between Janaury 1992 and September 2000. RESULTS: Ultrasound diagnosis was made in 13 cases (75%). Ultrasound criteria were; absence of median structure of the brain and unique ventricule. The prognosis was always bad. Foetopathologic examination revealed 7 cases of lobar holoproencephalia and 10 of semi lobar. Fascial dysmorphia were noted in 82% of cases. CONCLUSION: The foetopathology and genetic counselling looking for fascial, dysmorphia in family's members gives a good evaluation of recurrences.

[Lyme borreliosis situation in North Africa]. / Situation de la borreliose de Lyme au Maghreb.

Many epidemiological studies were conducted for studying Lyme borreliosis (LB) which represents a new global public health problem. It is now the most common vector-borne disease in Europe and North America. The causative agent Borrelia burgdorferi sl is a bacterial species complex comprising 12 delineated and named species. In North Africa, few studies based on clinical and serological features, have suggested that LB could occur. Indeed, recent studies conducted in Tunisia, Algeria and Morocco have showm that Ixodes ricinus is present in cooler and humid area of these regions. These studies also revealed that this species is a vector of B. burgdorferi sl with high prevalence of infection. Using IFI and PCR tests, the mean rate of Borrelia-infection ranged from 50 to 60% in I. ricinus adult collected in Tunisia and Morocco and from 30 to 40% in nymphs; in contrast, the prevalence in larvae is less than 2.5%. Several strains of B. burgdorfer were isolated from adult and nymph I ricinus collected in Tunisia and Morocco. The identification of these strains and DNAs directly extracted from Ixodes was done by PCR-RFLP and sequence analysis. The results showed that B. lusitaniae (genotypes Poti B2 and Poti B3) is the predominant species circulating in I. ricinus in Tunisia and Morocco, B. garinii and B. burgdorferi ss and B lusitaniae were also present but very rare. These results provide the evidence for the existence of B. burgdorferi sl in North Africa; however, the impact of LB in the human population seem to be negligible and the seroprevalence of Borrelia in forest workers (considered as population at high risk) in Tunisia is less than 4%.

[Rhinopneumonia and equine viral arteritis: seroepidemiological study in the northeast of Tunisia]. / La rhinopneumonie et l'artérite à virus du cheval: etude séro-épidémiologique dans le Nord-Est de la Tunisie.

A seroepidemiological survey was realized in the Nord-Est Tunisia to study the prevalence of complement fixing and neutralizing antibodies to equine rhinopneumonitis and viral arteritis of horse, respectively. Four hundred sera were tested, using complement fixation reaction and seroneutralization test. The results show that 8.75% of sera have antibodies to viral arteritis and only 1.25% are positive for equine rhinopneumonitis.

[Epizootic equine influenza in Tunisia]. / A propos d'une épizootie de grippe équine survenue en Tunisie.

The authors describe an equine influenza epizootic that occurred in Tunisia during February and March 1998 in the regions of Tozeur, Sousse and Tunis. They relate the symptoms, the different stages of diagnosis and the serological results.