Almost Sure Practical Exponential Stability of Nonlinear Disturbed Stochastic Systems with Guaranteed Decay Rate

In this paper, we consider nonlinear stochastic differential equations driven by multiplicative noises and affected by exogenous disturbances. Sufficient conditions are investigated for almost sure practical exponential stability of the non trivial solutions of these equations. A lower bound of the decay rate of these solutions is guaranteed.     

Numerical study of the THM effects on the near-field safety of a hypothetical nuclear waste repository—BMT1 of the DECOVALEX III project. Part 2: Effects of THM coupling in continuous and homogeneous rocks

An evaluation of the importance of the thermo-hydro-mechanical couplings (THM) on the performance assessment of a deep underground radioactive waste repository has been made as a part of the international DECOVALEX III project. It is a numerical study that simulates a generic repository configuration in the near field in a continuous and homogeneous hard rock. A periodic repository configuration comprises a single vertical borehole, containing a canister surrounded by an over-pack and a bentonite layer, and the backfilled upper portion of the gallery. The thermo-hydro-mechanical evolution of the whole configuration is simulated over a period of 100 years. The importance of the rock mass's intrinsic permeability has been investigated through scoping calculations with three values: 10⁻¹⁷, 10⁻¹⁸ and 10⁻¹⁹ m². Comparison of the results predicted by fully coupled THM analysis as well as partially coupled TH, TM and HM analyses, in terms of several predefined indicators of importance for performance assessment, enables us to identify the effects of the different combinations of couplings, which play a crucial role with respect to safety issues. The results demonstrate that temperature is hardly affected by the couplings. In contrast, the influence of the couplings on the mechanical stresses is considerable.     

ECHO: A speech recognition package for the design of robust interactive speech-based applications

This paper describes speech recognition software called ECHO (Environnement de Communication Homme-Ordinateur) which is devoted to the design of usable interactive speech-based applications. Usability refers to the stability of the Speech Recognition system performance under ordinary usage conditions (i.e., different acoustic environments) rather than high performance in a limited set of well-known conditions. In order to reach this objective, the system must be able to anticipate any change in the environment and adapt itself to the different usage conditions. One solution for this problem has been achieved by connecting some specialized modules of speech signal pre-processing and post-processing to the automatic speech recognition engine. These different modules interact as a mirror with the speech engine in order to force it to adapt its runtime parameters, thus improving its performance and its robustness.     

POTENTIAL PETROLEUM SOURCE ROCKS IN THE TERMIT BASIN,NIGER

Potential source rocks from wells in the Termit Basin, eastern Republic of Niger, have been analysed using standard organic geochemical techniques. Samples included organic‐rich shales of Oligocene, Eocene, Paleocene, Maastrichtian, Campanian and Santonian ages. TOC contents of up to 20.26%, Rock Eval S₂ values of up to 55.35 mg HC/g rock and HI values of up to 562 mg HC/g TOC suggest that most of the samples analysed have significant oil‐generating potential. Kerogen is predominantly Types II, III and II–III. Biomarker distributions were determined for selected samples. Gas chromatograms are characterized by a predominance of C₁₇– C₂₁ and C₂₇– C₂₉ n‐alkanes. Hopane distributions are characterized by 22S/(22S+22R) ratios for C₃₂ homohopanes ranging from 0.31 to 0.59. Gammacerane was present in Maastrichtian‐Campanian and Santonian samples. Sterane distributions are dominated by C₂₉ steranes which are higher than C₂₇ and C₂₈ homologues. Biomarker characteristics were combined with other geochemical parameters to interpret the oil‐generating potential of the samples, their probable depositional environments and their thermal maturity. Results indicate that the samples were in general deposited in marine to lacustrine environments and contain varying amounts of higher plant or bacterial organic matter. Thermal maturity varies from immature to the main oil generation phase. The results of this study will contribute to an improved understanding of the origin of the hydrocarbons which have been discovered in Niger, Chad and other rift basins in the Central African Rift System.     

Formation and properties of C-S-H–PEG nano-structures

Results of an investigation of the intercalation potential of polyethylene glycol (PEG) with synthetic and pre-treated C-S-H are reported. The partial intercalation of PEG molecules in the interlayer of C-S-H is discussed. The effective and strong interaction of PEG molecules with the C-S-H surface was shown using XRD, ¹³C CP and ²⁹Si MAS NMR, and DTGA. The position and character of the 002 low angle XRD peak of C-S-H are affected by drying procedures and concomitant chemical treatment preceding intercalation and the reaction temperature. Recovery of the initial 002 position after severe drying and intercalation with distilled water or PEG is incomplete but is accompanied by an increase in intensity. It is inferred that the stability of C-S-H binders in concrete can be impacted by a variation in nanostructure dependent on curing temperature and use of chemical admixtures.     

Modelling of induced anisotropic damage in granites

This paper deals with numerical modelling of induced damage in three granites. A continuous anisotropic damage model is proposed in the framework of thermodynamics and fracture mechanics. A second rank tensor is used to describe damage state which is directly related to orientation and density of microcracks. Both time independent and time dependent (or sub-critical) growth of microcracks are taken into account. A simple procedure for the determination of model parameters from standard laboratory tests is proposed. Comparisons between model simulation and experimental data are presented for some basic loading paths. Finally the application of the model to stability analysis of the Mine-by test tunnel of the URL in Manitoba (Canada) is presented. A comparison between numerical predictions and in situ observations makes it possible to evaluate the performance of the proposed model.     

Damage-induced permeability changes in granite: a case example at the URL in Canada

This paper concerns both in situ measurements of permeability and numerical modelling of changes in permeability induced by microcrack growth. Hydraulic experiments including pulse tests with the SEPPI probe are in progress. These tests are a part of the tunnel sealing experiment (TSX) at the 420 m level of Canada's Underground Research Laboratory, whose aim is to estimate the in situ hydraulic properties of Lac du Bonnet granite. Based on laboratory investigations, the anisotropic damage model developed by Homand et al. (Comput. Geotech. 22 (1998) 135) and recently reviewed by Shao et al. (Int. J. Rock Mech. Min. Sci. 36 (1999) 1001) has been extended in order to account for changes in permeability induced by microcrack growth. We have implemented this extension in the three-dimensional code (FLAC^3D). Triaxial compression tests, with permeability measurements carried out on two different granites, provide a verification of the numerical implementation with a good agreement between experiments and predictions. Comparison between in situ measurements of permeability and predictions indicates that both the results of numerical modelling and observations are globally in agreement. Finally, numerical modelling as well as the in situ measurements indicate that a depth of 50–70 cm is a good estimation of the extent of excavation disturbed zone in the TSX tunnel.     

Full order H ∞ filtering for linear systems in the frequency domain

This paper proposes an easier frequency domain solution to the standard H _∞ filtering problem using a polynomial approach. The design of the H _∞ filter in the frequency domain is first obtained from the time domain solution which is related to a Riccati equation, and then by the use of the connecting relationship between the time and frequency domain approach given by Hippe [8], its representation in the frequency domain is derived. The filter is easy to calculate as it requires the computation of a single gain and it is easily implementable also. A numerical example is given to illustrate the presented approach.