Influence of the implanted pulse generator as reference electrode in finite element model of monopolar deep brain stimulation.

Electrical deep brain stimulation (DBS) is an efficient method to treat movement disorders. Many models of DBS, based mostly on finite elements, have recently been proposed to better understand the interaction between the electrical stimulation and the brain tissues. In monopolar DBS, clinically widely used, the implanted pulse generator (IPG) is used as reference electrode (RE). In this paper, the influence of the RE model of monopolar DBS is investigated. For that purpose, a finite element model of the full electric loop including the head, the neck and the superior chest is used. Head, neck and superior chest are made of simple structures such as parallelepipeds and cylinders. The tissues surrounding the electrode are accurately modelled from data provided by the diffusion tensor magnetic resonance imaging (DT-MRI). Three different configurations of RE are compared with a commonly used model of reduced size. The electrical impedance seen by the DBS system and the potential distribution are computed for each model. Moreover, axons are modelled to compute the area of tissue activated by stimulation. Results show that these indicators are influenced by the surface and position of the RE. The use of a RE model corresponding to the implanted device rather than the usually simplified model leads to an increase of the system impedance (+48%) and a reduction of the area of activated tissue (-15%).

Ultra-rapid opiate detoxification using deep sedation and prior oral buprenorphine preparation: long-term results.

BACKGROUND: New methods of ultra-rapid opiate detoxification (URD) under intravenous sedation have been criticized because of limited data on safety and long-term follow-up. Premedication with buprenorphine has been advocated to improve safety by decreasing vomiting. Prior research has not explored URD in socially impaired patients. METHOD: Sixteen patients were detoxified with URD and prospectively evaluated over at least 30 months. Data of this procedure were compared with those of our previous study without buprenorphine preparation (Drug Alcohol Depend. 52(3) (1998) 243). The 16 patients were followed up by a general practitioner (GP) before and after URD. The GPs also supervised the 7-day course of buprenorphine treatment prescribed for the 16 patients prior to URD. RESULTS: During the procedure, only one episode of vomiting occurred instead of 13 out of 20 in our previous study. Post-procedure, only two patients experienced moderate withdrawal symptoms, such as persistent nausea, abdominal cramps and vomiting lasting from 24 to 48 h, in comparison with most patients in the previous study without buprenorphine. After a period of at least 30 months (36.0+/-6.38), the 16 patients were still alive and were regularly monitored by their GP. Only two of the 16 never relapsed after URD and reported total opiate abstinence. Fourteen patients relapsed; 12 of these were prescribed a licensed methadone substitution program and two were still using heroin. CONCLUSION: In this small sample, the data indicated that URD with buprenorphine preparation was safe and that it markedly decreased post-procedure morbidity. No patient died over a minimum 30-month follow-up period. Furthermore, the procedure was employed with socially impaired patients. In the long term, a few patients were still free of opiates, while the majority opted for a methadone maintenance program, showing that URD can serve as one possible step in a long-term treatment program.

Growth mechanisms and timing of emplacement of a vertically layered mafic intrusion in the feeder zone of an ocean island volcano (Fuerteventura, Canary islands)

Résumé pour le grand public L'île de Fuerteventura (Canaries) offre l'occasion rare d'observer les racines d'un volcan océanique édifié il y a 25 à 30 millions d'années et complètement érodé. On y voit de nombreux petits plutons de forme et composition variées, témoignant d'autant d'épisodes de l'activité magmatique. L'un de ces plutons, appelé PX1, présente une structure inhabituelle formée d'une alternance de bandes verticales d'épaisseur métrique à hectométrique de roches sombres de composition pyroxénilique ou gabbroïque. Les pyroxénites résultent clairement de l'accumulation de cristaux de pyroxènes et non de la simple solidification d'un magma? Se pose dès lors la question de la nature du processus qui a conduit à l'accumulation verticale de niveaux concentrés en pyroxènes. En effet, les litages pyroxénitiques classiques sont subhorizontaux, car ils résultent de l'accumulation gravitaire des cristaux séparés du magma dont ils cristalli¬sent par sédimentation. Cette étude vise à identifier et comprendre les mécanismes qui ont engendré ce Iitage minéralogique vertical et l'im¬portant volume de ces faciès cumulatifs. Nous nous sommes également intéressés aux conditions de pression et de température régnant au moment de la mise en place du pluton, ainsi qu'à sa durée de vie et à sa vitesse de refroidis¬sement. Enfin une approche géochimique nous a permis de préciser la nature de la source mantellique des magmas liés à cette activité magmatique. PX1 est en réalité un complexe filonien formé à des conditions de pression et de température de 1-2 kbar et 1050- 1100°C; sa construction a nécessité au moins 150 km3 de magma. L'alternance d'horizons gabbroïques et pyroxéniti¬ques représente des injections successives de magma sous la forme de filons verticaux, mis en place dans un contexte régional en extension. L'étude des orientations des minéraux dans ces faciès révèle que les horizons gabbroïques enregistrent l'extension régionale, alors que les pyroxénites sont générées par une compaction au sein du pluton. Ceci suggère que le régime des contraintes, qui était extensif lors de l'initiation de la mise en place de PX1, est pério¬diquement devenu compressif au sein même du pluton. Cette compression serait liée à des cycles de mise en place où la vitesse de croissance du pluton dépassait celle de l'extension régionale. La différenciation observée au sein de chaque horizon, depuis des pyroxénites riches en olivine jusqu'à des pyroxé¬nites à plagioclase interstitiel et des gabbros, ainsi que la composition géochimique des minéraux qui les constituent suggèrent que chaque filon vertical s'est mis en place à partir d'un magma de composition identique, puis a évolué indépendamment des autres en fonction du régime thermique et du régime des contraintes local. Lorsque le magma en train de cristalliser s'est trouvé en compression, le liquide résiduel a été séparé des cristaux déjà formés et extrait du système, laissant derrière lui une accumulation de cristaux dont la nature et les proportions dépendaient du stade de cristallisation atteint par le magma au moment de l'extraction. Ainsi, les niveaux de pyroxénites à olivine (premier minéral à cristalliser) ont été formés lorsque le magma correspondant était encore peu cristallisé; à l'inverse, les py¬roxénites riches en plagioclase (minéral plus tardif dans la séquence de cristallisation) et certains gabbros à caractère cumulatif résultent d'une compression tardive dans le processus de cristallisation du filon concerné. Les liquides résiduels extraits des niveaux pyroxénitiques sont rarement observés dans PX1, certaines poches et filonets de com¬position anorthositique pourraient en être les témoins. L'essentiel de ces liquides a probablement gagné des niveaux supérieurs du pluton, voire la surface du volcan. L'origine du régime compressif périodique affectant les filons en voie de cristallisation est attribuée aux injections suivantes de magma au sein du pluton, qui se sont succédées à un rythme plus rapide que la vitesse de consolidation des filons. Des datations U/Pb de haute précision sur des cristaux de zircon et de baddeleyite ainsi que40Ar/39Ar sur des cris¬taux d'amphibole révèlent une initiation de la mise en place de PX1 il y a 22.1 ± 0,7 Ma; celle-ci a duré quelque 0,48 ± 0,22 à 0,52 ± 0,29 Ma. Ce laps de temps est compatible avec celui nécessaire à la cristallisation des filons individuels, qui va de moins d'une année lors de l'initiation du magmatisme à 5 ans lors du maximum d'activité de PX1. La présence de cristaux résorbés enregistrant une cristallisation complexe suggère l'existence d'une chambre mag¬matique convective sous-jacente à PX1 et périodiquement rechargée. Les compositions isotopiques des roches étu¬diées révèlent une source mantellique profonde de type point chaud avec une contribution du manteau lithosphéri- que métasomatisé présent sous les îles Canaries. Résumé L'intrusion mafique Miocène PX1 fait partie du soubassement superficiel (0.15-0.2 GPa, 1100 °Q d'un volcan d'île océanique. La particularité de ce pluton est l'existence d'alternances d'unités de gabbros et de pyroxénites qui met¬tent en évidence un litage magmatique vertical (NNE-SSW). Les horizons gabbroiques et pyroxénitiques sont constitués d'unités de différenciation métriques qui suggèrent tine mise en place par injections périodiques de filons verticaux de magma formant un complexe filonien. Chaque filon vertical a subi une différenciation parallèle à un front de solidification sub-vertical parallèle aux bords du filon. Les pyroxénites résultent du fractionnement et de l'accumulation d'olivine ± clinopyroxene ± plagioclase à partir d'un magma basaltique faiblement alcalin et sont interprétées comme étant des imités de différenciation tronquées dont le liquide interstitiel a été extrait par compaction. L'orientation préférentielle des clinopyroxènes dans ces pyroxe- nites (obtenues par analyse EBSD et micro-tomographique) révèle une composante de cisaillement simple dans la genèse de ces roches, ce qui confirme cette interprétation. La compaction des pyroxénites est probablement causée par a mise en place de filons de magma suivants. Le liquide interstitiel expulsé est probablement par ces derniers. Les clinopyroxènes des gabbros, montrent une composante de cisaillement pure suggérant qu'ils sont affectés par une déformation syn-magmatique parallèle aux zones de cisaillement NNE-SSW observées autour de PX1 et liées au contexte tectonique Miocène d'extension régionale. Ceci suggère que les gabbros sont liés à des taux de mise en place faibles à la fin de cycles d'activité magmatique et sont peu ou pas affectés par la compaction. L'initiation et la géométrie de PX1 sont donc contrôlées par le contexte tectonique régional d'extension alors que les taux et les volumes de magma dépendent de facteurs liés à la source. Des taux d'injection élevés résultent probable¬ment en une croissance du pluton supérieure à la place crée par cette extension. Dans ce cas de figure, la propagation des nouveaux dykes et l'inaptitude du magma à circuler à travers les anciens dykes cristallisés pourrait causer une augmentation de la pression non-lithostatique sur ces derniers, exprimée par un cisaillement simple et l'expulsion du liquide interstitiel qu'ils contiennent (documenté par les zones de collecte anorthositiques). Les compositions en éléments majeurs et traces des gabbros et pyroxenites de PX1 sont globalement homogènes et dépendent de la nature cumulative des échantillons. Cependant, de petites variations des concentrations en éléments traces ainsi que les teneurs en éléments traces des bordures de clinopyroxenes suggèrent que ces derniers ont subi un processus de rééquilibrage et de cristallisation in situ. L'homogénéité des compositions chimiques des échantillons, ainsi que la présence de grains de clinopyroxene résorbés suggère que le complexe filonien PX1 s'est mis en place au dessus d'une chambre magmatique périodiquement rechargée dans laquelle la convection est efficace. Chaque filon est donc issu d'un même magma, mais a subi une différenciation par cristallisation in situ (jusqu'à 70% de fraction¬nement) indépendamment des autres. Dans ces filons cristallisés, les minéraux cumulatifs subissent un rééquilibrage partiel avec les liquide interstitiel avant que ce dernier ne soit expulsé lors de la compaction (mettant ainsi un terme à la différenciation). Ce modèle de mise en place signifie qu'un minimum de 150Km3 de magma est nécessaire à la genèse de PX1, une partie de ce volume ayant été émis par le 'Central Volcanic Complex' de Fuerteventura. Les rapports isotopiques radiogéniques mesurés révèlent la contribution de trois pôles mantelliques dans la genèse du magma formant PX1. Le mélange de ces pôles HIMU, DMM et EM1 refléterai l'interaction du point chaud Cana¬rien avec un manteau lithosphérique hétérogène métasomatisé. Les petites variations de ces rapports et des teneurs en éléments traces au sein des faciès pourrait refléter des taux de fusion partielle variable de la source, résultant en un échantillonnage variable du manteau lithosphérique métasomatisé lors de son interaction avec le point chaud. Des datations U/Pb de haute précision (TIMS) sur des cristaux de zircon et de baddeleyite extraits de gabbros de PX1 révèlent que l'initiation de la cristallisation du magma a eu lieu il y a 22.10±0.07 Ma et que l'activité magmatique a duré un minimum de 0.48 à 0.52 Ma. Des âges 40Ar/39Ar obtenus sur amphibole sont de 21.9 ± 0.6 à 21.8 ± 0.3 Ma, identiques aux âges U/Pb. La combinaison de ces méthodes de datations, suggère que le temps maximum nécessaire à PX1 pour se refroidir en dessous de la température de fermeture de l'amphibole est de 0.8Ma. Ceci signifie que la durée de vie de PX1 est de 520 000 à 800 000 ans. La coexistence de cristaux de baddeleyite et de zircon dans un gabbro est attribuée à son interaction avec un fluide riche en C02 relâché par les carbonatites encaissantes lors du métamorphisme de contact généré par la mise en place de PX1 environ 160 000 ans après le début de sa mise en place. Les durées de vie obtenue sont en accord avec le modèle de mise en place suggérant une durée de cristallisation poux chaque filon allant de 1 an à 5 ans. Abstract The Miocene PX1 gabbro-pyroxenite intrusion (Fuerteventura, Canary Islands), is interpreted as the shallow-level feeder-zone (0.15-0.2 GPa and 1100-1120°C), to an ocean island volcano. The particularity of PX1 is that it displays a NNE-SSW trending vertical magmatic banding expressed by alternating gabbro and pyroxeriite sequences. The gabbro and pyroxenite sequences consist of metre-thick differentiation units, which suggest emplacement by pe¬riodic injection of magma pulses as vertical dykes that amalgamated, similarly to a sub-volcanic sheeted dyke com¬plex. Individual dykes underwent internal differentiation following a solidification front (favoured by a significant lateral/horizontal thermal gradient) parallel to the dyke edges. Pyroxenitic layers result from the fractionation and accumulation of clinopyroxene ± olivine ± plagioclase crystals from a mildly alkaline basaltic liquid and are interpre¬ted as truncated differentiation sequences, from which residual melts were extracted by compaction. Clinopyroxene mineral orientation in pyroxenites (evidenced by EBSD and micro X-ray tomography analysis) display a marked pure shear component, supporting this interpretation. Compaction and squeezing of the crystal mush is ascribed to the incoming and inflating magma pulses. The resulting expelled interstitial liquid was likely collected and erupted along with the magma flowing through the newly injected dykes. Gabbro sequences represent crystallised coalesced magma batches, emplaced at lower rates at the end of eruptive cycles, and underwent minor melt extraction as evi¬denced by clinopyroxene orientations that record a simple shear component suggesting syn-magmatic deformation parallel to observed NNF.-SSW trending shear-zones induced by the regional tensional Miocene stress-field. The initiation and geometry of PX1 is controlled by the regional extensional tectonic regime whereas rates and vo¬lumes of magma depend on source-related factors. High injection rates are likely to induce intrusion growth rates larger than could be accommodated by the regional extension. In this case, dyke tip geometry and the inability of magma to circulate through previously emplaced and crystallised dykes could result in an increase of non-lithostatic pressure on previously emplaced mushy dyke walls; generating strong pure-shear compaction and interstitial melt expulsion within the feeder-zone as recorded by the cumulitic pyroxenite bands and anorthositic collection zones. The whole-rock major and trace-element chemistry of PX1 gabbros and pyroxenites is globally homogeneous and controlled by the cumulate nature of the samples (i.e. on the modal proportions of olivine, pyroxene, plagioclase and oxides). However, small variations of whole-rock trace-element contents as well as trace-element contents of clinopyroxene rims suggest that in-situ re-equilibration and crystallisation has occurred. Additionally, the global homogeneity and presence of complex zoning of rare resorbed clinopyroxene crystals suggest that the PX1 feeder- zone overlies a periodically replenished and efficiently mixed magma chamber. Each individual dyke of magma thus originated from a compositionally constant mildly alkaline magma and differentiated independently from the others reaching up to 70% fractionation. Following dyke arrest these are affected by interaction with the trapped interstitial liquid prior to its compaction-linked expulsion (thus stopping the differentiation process). This emplacement model implies that minimum amount of approximately 150 km3 of magma is needed to generate PX1, part of it having been erupted through the overlying Central Volcanic Complex of Fuerteventura. The radiogenic isotope ratios of PX1 samples reveal the contribution on three end-members during magma genesis. This mixing of the H1MU, EMI and DMM end-members could reflect the interaction of the deep-seated Canarian mantle plume with a heterogeneous metasomatic and sepentininsed lithospheric mantle. Additionally, the observed trace-element and isotopic variations within the same fades groups could reflect varying degrees of partial melting of the source region, thus tapping more or less large areas of the metasomatised lithospheric mantle during interac¬tion with the plume. High precision ID-TIMS U/Pb zircon and baddeleyite ages from the PX1 gabbro samples, indicate initiation of magma crystallisation at 22.10 ± 0.07 Ma. The magmatic activity lasted a minimum of 0.48 to 0.52 Ma. 40Ar/39Ar amphibole ages are of 21.9 ± 0.6 to 21.8 ± 0.3, identical within errors to the U/Pb ages. The combination of the 40Ar/39Ar and U/Pb datasets imply that the maximum amount of time PX1 took to cool below amphibole Tc is 0.8 Ma, suggesting PX1 lifetime of 520 000 to 800 000 years. On top of this, the coexistence of baddeleyite and zircon in a single sample is ascribed to the interaction of PX1 with C02-rich carbonatite-derived fluids released from the host-rock carbonatites during contact metamorphism 160 000 years after PX1 initiation. These ages are in agreement with the emplacement model, implying a crystallisation time of less than 1 to 5 years for individual dykes.

Long duration response to levodopa in advanced Parkinson's disease patients treated with subthalamic deep brain stimulation

Résumé La levodopa (LD) est le traitement antiparkinsonien le plus efficace et le plus répandu. Son effet est composé d'une réponse de courte (quelques heures) et de longue durée (jours à semaines). La persistance de cette dernière dans les phases avancées de la maladie de Parkinson est controversée, et sa mesure directe n'a jamais été faite en raison des risques liés à un sevrage complet de LD. La stimulation du noyau sous-thalamique est un nouveau traitement neurochirurgical de la maladie de Parkinson, indiqué dans les formes avancées, qui permet l'arrêt complet du traitement médicamenteux chez certains patients. Nous avons étudié 30 patients qui ont bénéficié d'une telle stimulation, et les avons évalués avant l'intervention sans médicaments, et à 6 mois postopératoires, sans médicaments et sans stimulation. Chez 19 patients, la médication a pu être complètement arrêtée, alors qu'elle a dû être réintroduite chez les 11 patients restants. Au cours des 6 mois qui ont suivi l'intervention, le parkinsonisme s'est aggravé de façon significative dans le groupe sans LD, et non dans le groupe avec LD. Cette différence d'évolution s'explique par la perte de l'effet à long terme de la LD dans le groupe chez qui ce médicament a pu être arrêté. En comparant cette aggravation à la magnitude de l'effet à court terme, la réponse de longue durée correspond environ à 80 pourcent de la réponse de courte durée, et elle lui est inversement corrélée. Parmi les signes cardinaux de la maladie, la réponse de longue durée affecte surtout la bradycinésie et la rigidité, mais pas le tremblement ni la composante axiale. La comparaison du parkinsonisme avec traitement (stimulation et LD si applicable) ne montre aucune différence d'évolution entre les 2 groupes, suggérant que la stimulation compense tant la réponse de courte que de longue durée. Notre travail montre que la réponse de longue durée à la LD demeure significative chez les patients parkinsoniens après plus de 15 ans d'évolution, et suggère que la stimulation du noyau sous-thalamique compense les réponses de courte et de longue durée. Abstract Background: Long duration response to levodopa is supposed to decrease with Parkinson's disease (PD) progression, but direct observation of this response in advanced PD has never been performed. Objective: To study the long duration response to levodopa in advanced PD patients treated with subthalamic deep-brain stimulation. Design and settings: We studied 30 consecutive PD patients who underwent subthalamic deep-brain stimulation. One group had no antiparkinsonian treatment since surgery (no levodopa), while medical treatment had to be reinitiated in the other group (levodopa). Main outcome measures: motor Unified Parkinson's Disease Rating Scale (UPDRS). Results: In comparison with preoperative assessment, evaluation six months postoperatively with stimulation turned off for three hours found a worsening of the motor part of UPDRS in the no-levodopa group. This worsening being absent in the levodopa group, it most probably reflected the loss of the long duration response to levodopa in the no-levodopa group. Stimulation turned on, postoperative motor UPDRS in both groups were similar to preoperative on medication scores, suggesting that subthalamic deep-brain stimulation compensated for both the short and long duration responses to levodopa. Conclusions: Our results suggest that the long duration response to levodopa remains significant even in advanced PD, and that subthalamic deep-brain stimulation compensates for both the short and the long duration resposes to levodopa.

Deep-hole drilling process, monitoring system and sensors modifications

 In the drilling processes and especially deep-hole drilling process, the monitoring system and having control on mechanical parameters (e.g. Force, Torque,Vibration and Acoustic emission) are essential. The main focus of this thesis work is to study the characteristics of deep-hole drilling process, and optimize the monitoring system for controlling the process. The vibration is considered as a major defect area of the deep-hole drilling process which often leads to breakage of the drill, therefore by vibration analysis and optimizing the workpiecefixture, this area is studied by finite element method and the suggestions are explained. By study on a present monitoring system, and searching on the new sensor products, the modifications and recommendations are suggested for optimize the present monitoring system for excellent performance in deep-hole drilling process research and measurements.

T-Flux implant versus Healon GV in deep sclerectomy.

PURPOSE: To compare the efficacy and safety of T-Flux implant versus Healon GV in deep sclerectomy. METHODS: Randomized prospective trial of 23 eyes of 20 patients with medically uncontrolled open angle glaucoma over a period of 24 months, who underwent deep sclerectomy with either Healon GV or T-Flux implant. RESULTS: Mean postoperative intraocular pressure was 13.2 +/- 3.0 mm Hg with T-Flux implant (group 1) and 12.2 +/- 3.5 mm Hg with Healon GV (group 2), with a pressure reduction of 53.0% in group 1 (13.2 mm Hg vs. 28.1 mm Hg) and of 48.1% in group 2 (12.2 mm Hg vs. 23.5 mm Hg). Qualified and complete successes were 100% and 95.4% respectively. Pressures equal to or less than 15 mm Hg were 81.8% in group 1 and 90.9% in group 2 with or without treatment, and 63.6% in group 1 and 81.8% in group 2 without treatment. The number of glaucoma treatments dropped from 2.5 +/- 0.9 to 0.4 +/- 0.7 in group 1 and from 2.2 +/- 1.0 to 0.2 +/- 0.4 in group 2. The goniopuncture rate was 63.6% in group 1 and 36.4% in group 2, with a mean pressure drop of 6.1 +/- 3.9 mm Hg and 3.25 +/- 1.2 mm Hg respectively. Overall, slit-lamp diagnosed surgery-related complications included positive Seidel (13.6%), hyphaema (22.7%), choroidal detachment, and iris incarceration (4.5% each). At 2 years, ultrasound biomicroscopy showed mainly low reflective (40.1%) and flattened (36.4%) blebs. Principally latter ones were associated with the need for adjunctive treatment. A hypoechoic area in the suprachoroidal space was seen in at least 59.1% of eyes at 2 years and was not associated with lower intraocular pressure. CONCLUSION: Deep sclerectomy is an effective and safe surgery. However, longer follow up and larger study groups are required to assess the additional benefit of nonabsorbable implants.

Neurotrophic activity of human adipose stem cells isolated from deep and superficial layers of abdominal fat.

New approaches to the clinical treatment of traumatic nerve injuries may one day utilize stem cells to enhance nerve regeneration. Adipose-derived stem cells (ASC) are found in abundant quantities and can be harvested by minimally invasive procedures that should facilitate their use in such regenerative applications. We have analyzed the properties of human ASC isolated from the deep and superficial layers of abdominal fat tissue obtained during abdominoplasty procedures. Cells from the superficial layer proliferate significantly faster than those from the deep layer. In both the deep and superficial layers, ASC express the pluripotent stem cell markers oct4 and nanog and also the stro-1 cell surface antigen. Superficial layer ASC induce the significantly enhanced outgrowth of neurite-like processes from neuronal cell lines when compared with that of deep layer cells. However, analysis by reverse transcription with the polymerase chain reaction and by enzyme-linked immunosorbent assay has revealed that ASC isolated from both layers express similar levels of the following neurotrophic factors: nerve growth factor, brain-derived neurotrophic factor and glial-derived neurotrophic factor. Thus, human ASC show promising potential for the treatment of traumatic nerve injuries. In particular, superficial layer ASC warrant further analysis of their neurotrophic molecules.

Long-Term Follow-Up of Multilayer Amniotic Membrane Transplantation (MLAMT) for Non-Traumatic Corneal Perforations or Deep Ulcers with Descemetocele.

Background: To evaluate the long-term efficacy of multilayer amniotic membrane transplantation for reconstruction of epithelium and stroma in non-traumatic corneal perforations (less than 2 mm) or deep ulcers with descemetocele.Design: Retrospective, non-comparative, interventional case series.Patients and Methods: Eleven consecutive patients with non-traumatic corneal perforations or deep corneal ulcers with descemetocele refractory to conventional treatments: herpetic or zoster keratitis (n = 4), Sjögren's syndrome (n = 2), rosacea (n = 1), hydrops (n = 1), mucous membrane pemphigoid (n = 1), bacterial keratitis (n = 1) and perforation after protontherapy for melanoma (n = 1). Intervention was: multilayer amniotic membrane transplantation with cryopreserved amniotic membrane. Complication rate and clinical outcome were evaluated in this long-term follow-up.Results: Mean follow-up was 32 months (12 to 60). Integration of the multilayer amniotic membrane was obtained in 10 cases after one year. Corneal epithelium healed above the membrane in 10 cases within 3 weeks and remained stable after 32 months in 9 cases. Thickness of the stroma was increased and remained stable during the follow-up in 9 cases. In one case herpetic keratitis recurred with a corneal perforation. The clearing of the amniotic membrane was gradually obtained over a period of 11 months. Complications occurred in 15 % of the eyes during the long-term follow-up.Conclusion: Multilayer amniotic membrane transplantation is a safe and efficient technique for a long restoration of the corneal integrity after non-traumatic corneal perforations or deep corneal ulcers with descemetocele. Long-term prognosis of these eyes depends of the gravity of the initial disease.

Particle transport method for convection-diffusion-reaction problems

Convective transport, both pure and combined with diffusion and reaction, can be observed in a wide range of physical and industrial applications, such as heat and mass transfer, crystal growth or biomechanics. The numerical approximation of this class of problemscan present substantial difficulties clue to regions of high gradients (steep fronts) of the solution, where generation of spurious oscillations or smearing should be precluded. This work is devoted to the development of an efficient numerical technique to deal with pure linear convection and convection-dominated problems in the frame-work of convection-diffusion-reaction systems. The particle transport method, developed in this study, is based on using rneshless numerical particles which carry out the solution along the characteristics defining the convective transport. The resolution of steep fronts of the solution is controlled by a special spacial adaptivity procedure. The serni-Lagrangian particle transport method uses an Eulerian fixed grid to represent the solution. In the case of convection-diffusion-reaction problems, the method is combined with diffusion and reaction solvers within an operator splitting approach. To transfer the solution from the particle set onto the grid, a fast monotone projection technique is designed. Our numerical results confirm that the method has a spacial accuracy of the second order and can be faster than typical grid-based methods of the same order; for pure linear convection problems the method demonstrates optimal linear complexity. The method works on structured and unstructured meshes, demonstrating a high-resolution property in the regions of steep fronts of the solution. Moreover, the particle transport method can be successfully used for the numerical simulation of the real-life problems in, for example, chemical engineering.

Theoretical and numerical study of thermomagnetic convection in magnetic fluids

In this thesis, the magnetic field control of convection instabilities and heat and mass transfer processesin magnetic fluids have been investigated by numerical simulations and theoretical considerations. Simulation models based on finite element and finite volume methods have been developed. In addition to standard conservation equations, themagnetic field inside the simulation domain is calculated from Maxwell equations and the necessary terms to take into account for the magnetic body force and magnetic dissipation have been added to the equations governing the fluid motion.Numerical simulations of magnetic fluid convection near the threshold supportedexperimental observations qualitatively. Near the onset of convection the competitive action of thermal and concentration density gradients leads to mostly spatiotemporally chaotic convection with oscillatory and travelling wave regimes, previously observed in binary mixtures and nematic liquid crystals. In many applications of magnetic fluids, the heat and mass transfer processes including the effects of external magnetic fields are of great importance. In addition to magnetic fluids, the concepts and the simulation models used in this study may be applied also to the studies of convective instabilities in ordinary fluids as well as in other binary mixtures and complex fluids.

Aspects opératoires et péri-opératoires de la stimulation cérébrale profonde [Operative and perioperative aspects of deep brain stimulation].

La stimulation cérébrale profonde (SCP) nécessite l'implantation chirurgicale d'un système comprenant électrodes cérébrales et boîtier(s) de stimulation. Les noyaux cérébraux visés par la méthodologie stéréotaxique d'implantation doivent être visualisés au mieux par une imagerie à haute résolution. La procédure chirurgicale d'implantation des électrodes se fait si possible en anesthésie locale pour faire des mesures électro-physiologiques et tester en peropératoire l'effet de la stimulation, afin d'optimiser la position de l'électrode définitive. Dans un deuxième temps, le ou les générateur(s) d'impulsions sont implantés en anesthésie générale. La SCP pour les mouvements anormaux a une très bonne efficacité et un risque de complications graves faible quoique non nul. Les complications liées au matériel sont les plus fréquentes. Deep brain stimulation (DBS) requires the surgical implantation of a system including brain electrodes and impulsion generator(s). The nuclei targeted by the stereotaxic implantation methodology have to be visualized at best by high resolution imaging. The surgical procedure for implanting the electrodes is performed if possible under local anaesthesia to make electro-physiological measurements and to test intra-operatively the effect of the stimulation, in order to optimize the position of the definitive electrode. In a second step, the impulsion generator(s) are implanted under general anaesthesia. DBS for movement disorders has a very good efficacy and a low albeit non-zero risk of serious complications. Complications related to the material are the most common.

Development of a PC Tool for Estimating Pressure Drops in Forced-convection Boiler Tubes

Kaksifaasivirtauksen kuvaamiseen käytettävät mallit, ja menetelmät kaksifaasivirtauksen painehäviön määrittämiseksi kehittyvät yhä monimutkaisimmiksi. Höyrystinputkissa tapahtuvien painehäviöiden arvioinnin vaatiman laskennan suorittamiseksi tietokoneohjelman kehittäminen on välttämätöntä. Tässä työssä on kehitetty itsenäinen PC-ohjelma painehäviöiden arvioimiseksi pakotetulle konvektiovirtaukselle pystysuorissa höyrykattilan höyrystinputkissa. Veden ja vesihöyryn aineominaisuuksien laskentaan käytetään IAPWS-IF97 –yhtälökokoelmaa sekä muita tarvittavia IAPWS:n suosittelemia yhtälöitä. Höyrystinputkessa kulloinkin vallitsevan virtausmuodon määrittämiseen käytetään sovelluskelpoisia virtausmuotojen välisiä rajoja kuvaavia yhtälöitä. Ohjelmassa käytetään painehäviön määritykseen kirjallisuudessa julkaistuja yhtälöitä, virtausmuodosta riippuen, alijäähtyneelle virtaukselle, kupla-, tulppa- ja rengasvirtaukselle sekä tulistetun höyryn virtaukselle. Ohjelman laskemia painehäviöarvioita verrattiin kirjallisuudesta valittuihin mittaustuloksiin. Laskettujen painehäviöiden virhe vaihteli välillä –19.5 ja +23.9 %. Virheiden itseisarvojen keskiarvo oli 12.8 %.

Delayed presentation of deep penetrating trauma to the subaxial cervical spine.

PURPOSE: To present a rare case of deep penetrating neck trauma in which a retained foreign body in the cervical spine (a broken knife blade) resulted in delayed radicular injury. We describe the surgical management using a retrojugular approach. CASE REPORT: Our patient sustained a stab wound to the supraclavicular triangle from a small pocketknife. He was initially managed in a local hospital by simple primary wound closure without any radiological examinations, and was discharged home. The patient re-consulted in a delayed fashion with mild local persistent neck pain. Subsequent radiological investigations revealed a foreign body (the broken blade of a pocket knife) embedded in the left neural foramen between the C6 and C7 vertebrae penetrating the disc space. The blade was lying between the left C7 nerve root and the ipsilateral vertebral artery (VA) at the transition of V1 and V2 segments. Initial neurological evaluation was normal. Some days later, the patient developed a delayed left C7 radicular deficit. We undertook urgent exploration along the wound corridor through a retrojugular, transforaminal approach with successful removal of the blade. DISCUSSION: To our knowledge, this is a unique case where a retained foreign body penetrated the soft tissues of the neck, embedding deep in the vertebral column without vascular, aerodigestive or significant primary neurological injury, while causing delayed neck pain and delayed onset radicular injury. We describe our surgical management for removal of the retained blade. The retrojugular approach gives excellent access to all of the important anatomical structures of the neck from an anterolateral approach.

Bilateral deep brain stimulation: the placement of the second electrode is not necessarily less accurate than that of the first one.

BACKGROUND: Deep brain stimulation (DBS) is recognized as an effective treatment for movement disorders. We recently changed our technique, limiting the number of brain penetrations to three per side. OBJECTIVES: The first aim was to evaluate the electrode precision on both sides of surgery since we implemented this surgical technique. The second aim was to analyse whether or not the electrode placement was improved with microrecording and macrostimulation. METHODS: We retrospectively reviewed operation protocols and MRIs of 30 patients who underwent bilateral DBS. For microrecording and macrostimulation, we used three parallel channels of the 'Ben Gun' centred on the MRI-planned target. Pre- and post-operative MRIs were merged. The distance between the planned target and the centre of the implanted electrode artefact was measured. RESULTS: There was no significant difference in targeting precision on both sides of surgery. There was more intra-operative adjustment of the second electrode positioning based on microrecording and macrostimulation, which allowed to significantly approach the MRI-planned target on the medial-lateral axis. CONCLUSION: There was more electrode adjustment needed on the second side, possibly in relation with brain shift. We thus suggest performing a single central track with electrophysiological and clinical assessment, with multidirectional exploration on demand for suboptimal clinical responses.