Evaluation of Thiel cadaveric model for MRI-guided stereotactic procedures in neurosurgery

BACKGROUND: Magnetic resonance imaging (MRI)-guided deep brain stimulation (DBS) and high frequency focused ultrasound (FUS) is an emerging modality to treat several neurological disorders of the brain. Developing reliable models to train and assess future neurosurgeons is paramount to ensure safety and adequate training of neurosurgeons of the future. METHODS: We evaluated the use of Thiel cadaveric model to practice MRI-guided DBS implantation and high frequency MRI-guided FUS in the human brain. We performed three training sessions for DBS and five sonications using high frequency MRI-guided FUS in five consecutive cadavers to assess the suitability of this model to use in training for stereotactic functional procedures. RESULTS: We found the brains of these cadavers preserved in an excellent anatomical condition up to 15 months after embalmment and they were excellent model to use, MRI-guided DBS implantation and FUS produced the desired lesions accurately and precisely in these cadaveric brains. CONCLUSION: Thiel cadavers provided a very good model to perform these procedures and a potential model to train and assess neurosurgeons of the future

High-power Soliton-induced Supercontinuum Generation and Tunable Sub-10-fs VUV Pulses from Kagome-lattice HC-PCFs

We theoretically study a novel approach for soliton-induced high-power supercontinuum generation by using kagome lattice HC-PCFs filled with a noble gas. Anomalous dispersion and broad-band low loss of these fibers enable the generation of two-octave broad spectra by fs pulses, with high coherence and high spectral peak power densities up to five orders of magnitude larger than in standard PCFs. In addition, up to 20 percents of the output radiation energy forms a narrow UV/VUV band, which can be tuned by contolling the pressure in the range from 350 nm to 120 nm. In the temporal domain this corresponds to sub-10-fs UV/VUV pulses with pulse energy of few tens of microjoule, caused by the formation of a high-order soliton emitting non-solitonic radiation.Comment: 4 pages, 4 figure

Wishart Stochastic Volatility: Asymptotic Smile and Numerical Framework

In this paper, a study of a stochastic volatility model for asset pricing is described. Originally presented by J. Da Fonseca, M. Grasselli and C. Tebaldi, the Wishart volatility model identifies the volatility of the asset as the trace of a Wishart process. Contrary to a classic multifactor Heston model, this model allows to add degrees of freedom with regard to the stochastic correlation. Thanks to its flexibility, this model enables a better fit of market data than the Heston model. Besides, the Wishart volatility model keeps a clear interpretation of its parameters and conserves an efficient tractability. Firstly, we recall the Wishart volatility model and we present a Monte Carlo simulation method in sight of the evaluation of complex options. Regarding stochastic volatility models, implied volatility surfaces of vanilla options have to be obtained for a short time. The aim of this article is to provide an accurate approximation method to deal with asymptotic smiles and to apply this procedure to the Wishart volatility model in order to well understand it and to make its calibration easier. Inspired by the singular perturbations method introduced by J.P Fouque, G. Papanicolaou, R. Sircar and K. Solna, we suggest an efficient procedure of perturbation for affine models that provides an approximation of the asymptotic smile (for short maturities and for a two-scale volatility). Thanks to the affine properties of the Wishart volatility model, the perturbation of the Riccati equations furnishes the expected approximations. The convergence and the robustness of the procedure are analyzed in practice but not in theory. The resulting approximations allow a study of the parameters influence and can also be used as a calibration tool for a range of parameters.Wishart processes; stochastic volatility models; stochastic; correlation; singular perturbation, asymptotic smile; Monte Carlo simulation

A Study of the Effects of Cadmium on Beans (Phaseolus vulgaris, cv. Canadian Wonder), its Interactions With Zinc and Its Effect on Chlorophyll

The thesis concentrates on the environmental implications of Cd. The aspect being dealt with concerns the effect of cadmium on plants and particularly its effect on chlorophyll content. The thesis also deals with the relationship of Cd with pH and other trace metals particularly zinc. The first chapter is an introduction to the subject. It briefly reviews the history of studies on trace metals, their relationship and their effects on soils, animals and plants. It also includes information about factors such as pH, organic matter, interactions between elements etc. affecting the behaviour of trace metals. Chapter I contains a review on cadmium, its behaviour, its phytotoxicity and its presence in biological systems. It also reviews some previous works and suggestions and it ends by suggesting a frame work for this thesis with a brief description of each part. Chapter 2 is divided into two parts. Part (one deals with Cd as it is affected by pH which plays an important role in accounting for Cd behaviour and uptake by plants. Besides an introduction on Cd, this chapter contains a description of the experiments and the techniques used for the analysis. It also contains detailed data and the corresponding graphics. Investigations carried out in this chapter suggest that pH is undoubtedly an important factor interfering with the transport, translocation and uptake of Cd by plants. Part two of this chapter is aimed at studying the transport and distribution of Cd in a plant. It is also aimed at demonstrating the preferential localization of Cd by using radiolabelled Cd-109. The analysis was carried out using the solid scintillation technique. Information was obtained suggesting that Cd was preferably taken up by roots than by the other parts of the plant. It also indicates that leaves are less tolerant to high levels of Cd than roots and stems. Chapter 3 lays emphasis on the interaction of cadmium with other trace metals and most particularly with zinc because of their chemical similarities. The following levels of Cd and Zn are used for the investigation. Cd (mug) : 30 to 180 and Zn (mug): 2000 to 10,000. The interactions of Cd with other trace metals were also reviewed. In this chapter, some conclusions are drawn concerning the mutual effect between Cd and Zn. It also shows that the addition of Zn has a positive result in minimizing the toxic effect of Cd as is expressed in the delay of plant response to Cd compared to the findings in Chapter 2. A chemical approach is suggested to explain the nature of the interaction between Cd and Zn. Two possible types of interaction are more likely to occur: competition for sites at the root level and a direct substitution of Zn by Cd In zinc enzymes. The chemical approach seems to be valid because of the chemical similarities between the two elements. Symptoms of chlorosis or loss in chlorophyll were shown as a result of Cd effect on beans. Chapter 4 is devoted to the investigation of this matter aiming at explaining the causes of chlorophyll losses by studying the effect of Cd on chlorophyll formation and content. In Vitro and in Vivo experiments were carried out using atomic absorption and ultra violet spectroscopy. Some conclusions were drawn consequently such as: Cd suppresses chlorophyll content and also decreases Mg content. It is also suggested that Cd may disturb the formation of chlorophyll by interfering with Fe which is important for its synthesis. In this chapter some suggestions are put forward concerning the possible displacement of Mg by Cd. Chapter 5 carries out an assessment of all the points and suggestions encompassed in this thesis and considers the extent of the practicality of the results. It also assesses the prospects for future research which could be to be carried out in this area

Setting Up Of AWriting Process In Academic Context To Produce Meaning In French

Today pedagogy’s main preoccupation lies in focusing on postgraduate students’ writing in science classes. This is the case for two reasons. The first reason takes into account student’s difficulties in acquiring linguistic competences. Therefore, the overall curriculum has to allow more time for this activity. The second reason is related to the evolution in the pedagogical discourse, for it insists on the active role that students should benefit from during their language learning. It is in this way that they can learn to become efficient. To train science students in Morocco in understanding and producing a postgraduate scientific discourse in French requires a preparation, which will provide them with some clues regarding their writing ability. Indeed, by installing a writing process enhancing the building up of meaning, these students will become capable of deciphering and producing scientific discourse

Quantum-Fluctuation-Initiated Coherence in Multi-Octave Raman Optical Frequency Combs

We show experimentally and theoretically that the spectral components of a multi-octave frequency comb spontaneously created by stimulated Raman scattering in a hydrogen-filled hollow-core photonic crystal fiber exhibit strong self coherence and mutual coherence within each 12 ns driving laser pulse. This coherence arises in spite of the field's initiation being from quantum zero-point fluctuations, which causes each spectral component to show large phase and energy fluctuations. This points to the possibility of an optical frequency comb with nonclassical correlations between all comb lines.Comment: Accepted for publication, Physical Review Letters, 201

Vicarious Learning in a Digital Environment: A Case Study at a Big Four

In the United States, $162 billion was spent on corporate development in 2012. Yet, some studies unveil a “The Great Training Robbery”, showing that no more than 10% of training expenses are effective. This research examines the misalignment between the investment in formal training settings and the actual learning behaviors which rely mostly on informal learning and digital tools (i.e. symbolic environment), empowered by an increasingly interconnected world. This research aims at understanding the emerging behaviors of learning in context among auditors and consultants from a French affiliate of a Big Four company. Based on Bandura’s work on learning in an ultra-connected universe, we identify and develop four informal vicarious learning behaviors based on symbolic media. Our work has implications for Human Resources’ value proposition which shifts away from offering content-based training to developing learning capacity