Investigation and reduction of discretization Variance in decision tree induction

in Proceedings of ECML 2000, European Conference on Machine Learning (2000)

This paper focuses on the variance introduced by the discretization techniques used to handle continuous attributes in decision tree induction. Different discretization procedures are first studied ... [more ▼]

This paper focuses on the variance introduced by the discretization techniques used to handle continuous attributes in decision tree induction. Different discretization procedures are first studied empirically, then means to reduce the discretization variance are proposed. The experiments shows that discretization variance is large and that it is possible to reduce it significantly without notable computational costs. The resulting variance reduction mainly improves interpretability and stability of decision trees, and marginally their accuracy. [less ▲]

Investigation by testing of the structural response of semi-rigid joints

in proceedings of the RILEM Workshop on "Needs in testing metals" (1990)

Investigation et modélisation des tensions circonférentielles en simulation méridienne

Master of advanced studies dissertation (2008)

The computation time and the extraction of useful information remain severe drawbacks to systematic use of modern 3D Navier-Stokes codes in a design procedure of multistage turbomachines. That explains ... [more ▼]

The computation time and the extraction of useful information remain severe drawbacks to systematic use of modern 3D Navier-Stokes codes in a design procedure of multistage turbomachines. That explains why throughflow simulation is still widely used at industrial scale. The main limitation of throughflow is however the need for empirical models to reproduce blade-flow interactions and major 3D flow features. As an alternative, Adamczyk (1984) proposed three averaging operators (ensemble, time and passage) that lead to the average-passage model, linking the unsteady turbulent flow field to a steady flow field in a typical blade passage. This model involves additional terms that respectively bring back the mean effect of turbulence, deterministic unsteadiness and aperiodicity on the mean periodic flow. These terms need to be modelled; it is the closure problem. Harmonic closure, which consists in solving a linearized perturbation system in the frequency domain, revealed to be an efficient method to approximate deterministic stresses (He and Ning, 1998, Stridh, 2005, Vilmin, 2006). A fourth averaging can be performed, a circumferential averaging, giving rise to the throughflow model. Additional terms appear: the so-called circumferential stresses. It has been proven that these terms play an important role in the description of the flow (Jennions, 1986, Perrin, 1995), being at least as considerable as deterministic stresses. Introducing these terms in a throughflow simulation allows to reproduce the averaged 3D steady flow field (Simon, 2007). The purpose of this work is to investigate how far empiricism could be reduced by using the averaged-passage equations of Adamczyk, combined with a harmonic closure strategy. To that aim, in the first part of the work, results of a computation performed with a steady three-dimensional Navier-Stokes code are used to calculate the circumferential stresses. The importance of the latter to bring back the mean eff ect of circumferential non-uniformities, linked to 3D phenomena, is illustrated by injecting them into a throughfow simulation. Then the ability of truncated Fourier series to reproduce the flow and its level of non-uniformity in the core flow and near the hub and shroud walls is detailed. It is finally shown that the harmonic approximated stresses can lead to a good reproduction of local 3D flow features in throughflow simulation and to a better accuracy. In the second part of this work it is proposed to adapt the "Nonlinear Harmonic" method to the throughflow model, where the main non-linear system would be the common throughflow equations and the auxiliary systems would give access to a mean high order information; the circumferential stresses. On the way to the adaptation of this technique to the throughflow model, the work shows that a reformulation of the effect of the blades is needed. The latter cannot appear anymore as numerical local explicit impermeability conditions that could not be supported by Fourier series, needing a continuous circumferential evolution of the flow. To get rid of this issue, the blade effect is replaced by a smooth force field as in the "Immersed Boundary Method" of Peskin. A simple example of an inviscid flow around a cylinder illustrates the preceding developments, coupling the "Nonlinear Harmonic Method" to the "Immersed Boundary Method" in a throughflow model, to bring back the mean e ffect of the circumferential non uniformities into the meridional flow. [less ▲]

Investigation of advanced materials for fusion alpha particle diagnostics

in Fusion Engineering & Design (2013)

Fusion alpha particle diagnostics for ITER remain a challenging task. Standard escaping alpha particle detectors in present tokamaks are not applicable to ITER and techniques suitable for fusion reactor ... [more ▼]

Fusion alpha particle diagnostics for ITER remain a challenging task. Standard escaping alpha particle detectors in present tokamaks are not applicable to ITER and techniques suitable for fusion reactor conditions need further research and development [1,2]. The activation technique is widely used for the characterization of high fluence rates inside neutron reactors. Tokamak applications of the neutron activation technique are already well developed [3] whereas measuring escaping ions using this technique is a novel fusion plasma diagnostic development. Despite low alpha particle fluence levels in present tokamaks, promising results using activation technique combined with ultra-low level gamma-ray spectrometry [4] were achieved before in JET [5,6]. In this research work, we use new advanced detector materials. The material properties beneficial for alpha induced activation are (i) moderate neutron cross-sections (ii) ultra-high purity which reduces neutron-induced background activation and (iii) isotopic tailoring which increases the activation yield of the measured activation product. Two samples were obtained from GERDA[7], an experiment aimed at measuring the neutrinoless double beta decay in 76Ge. These samples, made of highly pure (9 N) germanium highly enriched to 87% in isotope Ge-76, were irradiated in real D-D fusion plasma conditions inside the TEXTOR tokamak. Comparison of the calculated and the experimentally measured activity shows good agreement. Compared to previously investigated high temperature ceramic material [8], this candidate detector offers better prospects for signal to background S/B ratio, energy resolution and particle selectivity due to a unique alpha particle signature. Applicability to ITER is discussed. Finally, research needs for further development of this diagnostic technique are outlined. © 2013. [less ▲]

Investigation of airway reactivity by barometric whole body plethysmography in cats with spontaneous bronchial disease

in 24th Symposium of the Veterinary Comarative Respiratory Society - Jena, Allemagne 8-10 octobre 2006 (2006, October)

Investigation of anaerobic digestion in a two-stage bioprocess producing hydrogen and methane

Conference (2010, November 17)

Hydrogen has received wide attention in the last decades as a clean energy vector. The major advantage of energy generation from hydrogen is the near-zero carbon emissions, since the utilization of ... [more ▼]

Hydrogen has received wide attention in the last decades as a clean energy vector. The major advantage of energy generation from hydrogen is the near-zero carbon emissions, since the utilization of hydrogen, either via combustion or via fuel cells, results in pure water. Recently, there has been increasing interest on the biological production of hydrogen gas from renewable biomass such as carbohydrates from agriculture or agro-food industries. This specific anaerobic digestion is called dark fermentation and is involved in the classic anaerobic digestion producing methane. Indeed, in a two-step process, i.e. when acido- and aceto-genesis are carried out in a different bioreactor than methanogenesis, it is feasible to generate separated biogas flows containing either H2 or CH4 depending on specific operating parameters. This paper deals with the comparison of the first stage performances whether operated in optimum conditions for H2 production with a mixed culture or a pure Clostridium butyricum strain. Hydrogen yields of about 1.75 and 2.3 mol H2/mol glucose were achieved respectively. The metabolites, mainly acetate and butyrate, contained in the spent medium were efficiently converted to methane in a second anaerobic digester with a methane yield of about 170 ml/g COD initially fed in the first stage. [less ▲]

Investigation of automatic memory during general anesthesia for elective surgery using the process dissociation procedure

in Anesthesiology (2005), 103

Background: This prospective study evaluated memory function during general anesthesia for elective surgery and its relation to depth of hypnotic state. The authors also compared memory function in ... [more ▼]

Background: This prospective study evaluated memory function during general anesthesia for elective surgery and its relation to depth of hypnotic state. The authors also compared memory function in anesthetized and nonanesthetized subjects. Methods: Words were played for 70 min via headphones to 48 patients (aged 18–70 yr) after induction of general anesthesia for elective surgery. Patients were unpremedicated, and the anesthetic regimen was free. The Bispectral Index (BIS) was recorded throughout the study. Within 36 h after the word presentation, memory was assessed using an auditory word stem completion test with inclusion and exclusion instructions. Memory performance and the contribution of explicit and implicit memory were calculated using the process dissociation procedure. The authors applied the same memory task to a control group of nonanesthetized subjects. Results: Forty-seven patients received isoflurane, and one patient received propofol for anesthesia. The mean ( SD) BIS was 49 9. There was evidence of memory for words presented during light (BIS 61–80) and adequate anesthesia (BIS 41–60) but not during deep anesthesia (BIS 21–40). The process dissociation procedure showed a significant implicit memory contribution but not reliable explicit memory contribution (mean explicit memory scores 0.05 0.14, 0.04 0.09, and 0.05 0.14; mean automatic influence scores 0.14 0.12, 0.17 0.17, and 0.18 0.21 at BIS 21–40, 41–60, and 61–80, respectively). Compared with anesthetized patients, the memory performance of nonanesthetized subjects was better, with a higher contribution by explicit memory and a comparable contribution by implicit memory. Conclusion: During general anesthesia for elective surgery, implicit memory persists even in adequate hypnotic states, to a comparable degree as in nonanesthetized subjects. [less ▲]

Investigation of biohydrogen production in a 20l – Sequenced batch bioreactor using a pure Clostridum strain.

Poster (2007, October 11)

Investigation of blood oxidant/antioxidant markers in healthy competition horses of different breeds

in Equine Veterinary Journal. Supplement (2006), 36

REASONS FOR PERFORMING STUDY: There is increasing evidence that the equine athlete is exposed to exercise-induced changes of its oxidant/antioxidant balance and antioxidant supplementation is frequently ... [more ▼]

REASONS FOR PERFORMING STUDY: There is increasing evidence that the equine athlete is exposed to exercise-induced changes of its oxidant/antioxidant balance and antioxidant supplementation is frequently recommended. However, it is unknown whether there is a specific need for antioxidants according to performance, breed, gender or age. OBJECTIVES: To assess whether breed-, gender- and age-related differences of blood oxidant/antioxidant markers occur in competition horses. METHODS: Healthy horses (n = 493) underwent oxidant/ antioxidant blood marker determination. Vitamin E, lipophilic antioxidant capacity (ACL), ascorbic acid (AA), glutathione (GSH, GSSG), gluthione peroxidase (GPx), superoxide dismutase (SOD), selenium (Se), copper (Cu), zinc (Zn), lipid peroxides (Pool), oxidised proteins (Protox) were determined, as well as magnesium (Mg), creatine phosphokinase (CPK), lactate dehydrogenase (LDH), packed cell volume (PCV) and haemoglobin (Hb). A mixed linear model assessed the effect of breed, gender and age category. P<0.05 was considered significant. RESULTS: Thoroughbreds showed the highest values of vitamin E, ACL, GPx, PCV and Hb, whilst standardbreds had the highest values of AA and LDH. Jumping horses had the highest Protox values. Females had significantly higher SOD values, whereas most of the other markers were higher in stallions and geldings. Horses age 2-6 years had higher AA, SOD and LDH values than horses age >6 years. Correlation analyses were positive and significant between vitamin E and GPx, VitE and ACL, Se and GPx, Cu and Pool and negative between Pool and vitamin E, Pool and ACL, Protox and GPx, Protox and vitamin E. CONCLUSIONS: Blood oxidant/ antioxidant status of horses is influenced by breed, gender and age. The correlation analyses suggest synergistic relations between GPx, vitamin E and Se and an antagonistic relation between Protox-GPx, Protox-vitamin E, and Pool-vitamin E. POTENTIAL RELEVANCE: The results of this investigation provide definition of the specific need for antioxidants and vitamins in competition horses. [less ▲]

Investigation of candidate genes with potential influence on litter size in two commercial pig cross populations

Doctoral thesis (2006)