Investigaciones sobre el aceite de Mauritia flexuosa L.

in Grasas Y Aceites (1987), 38(5), 303-307

Investigating a Bottom-up Approach for Extracting Ontologies from Urban Databases

in Teller, Jacques; Lee, John; Roussey, Catherine (Eds.) Ontologies for Urban Development (2007)

Investigating Circumferential Non-Uniformities in Throughflow Calculations using an Harmonic Reconstruction

in Proceedings of the ASME Turbo Expo 2008 (2008, June)

The flow field in a multistage turbomachine is very complex. It is 3D, unsteady and turbulent. Even if modern simulation tools can describe most of the flow features, the computation time needed and the ... [more ▼]

The flow field in a multistage turbomachine is very complex. It is 3D, unsteady and turbulent. Even if modern simulation tools can describe most of the flow features, the computation time needed and the extraction of useful information remain severe drawbacks to systematic use of URANS codes in a design procedure. In this context the throughflow simulation proved to be more convenient. Nevertheless the need for empiricism limits the potential of throughflow solvers. As an alternative, Admaczyck (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 aim of the present contribution is to prove that harmonic method can potentially be used to reconstruct circumferential stresses. The importance of circumferential stresses in a throughflow simulation is first highlighted on a single stage low speed compressor testcase, for viscous and non-viscous flow fields. The second step is the characterization of the frequency spectrum of the circumferential perturbation field. Next are compared the stresses associated to a Fourier reconstruction of the perturbation field with the real ones. Finally the approximated circumferential stresses are injected into a throughflow simulation tool to analyse and demonstrate their capability to reproduce a 3D averaged flow field. [less ▲]

Investigating Effect of Holidays on Daily Traffic Counts: Time Series Approach

in Proceedings of the 86th Annual Meeting of the Transportation Research Board (CD-ROM) (2007)

In this paper, different modeling philosophies are explored in order to explain and forecast daily traffic counts. The main objectives of this study are the analysis of the impact of holidays on daily ... [more ▼]

In this paper, different modeling philosophies are explored in order to explain and forecast daily traffic counts. The main objectives of this study are the analysis of the impact of holidays on daily traffic, and the forecasting of future traffic counts. Data coming from single inductive loop detectors, collected in 2003, 2004 and 2005, were used for the analysis. The different models that were investigated showed that the variation in daily traffic counts could be explained by weekly cycles. The Box-Tiao modeling approach was applied to quantify the effect of holidays on daily traffic. The results showed that traffic counts were significantly lower for holiday periods. When the different modeling techniques were compared with respect to forecasting with a large forecast horizon, Box-Tiao modeling clearly outperformed the other modeling strategies. Simultaneous modeling of both the underlying reasons of travel, and revealed traffic patterns, certainly is a challenge for further research. [less ▲]

Investigating Hardy-Weinberg equilibrium in case-control or cohort studies or meta-analysis.

in Breast Cancer Research and Treatment (2011), 128(1), 197-201

Yu et al. (Breast Cancer Res Treat 117:675-677, 2009) recently stated that testing for deviation from Hardy-Weinberg equilibrium (HWE) is necessary to identify systematic genotyping errors in case-control ... [more ▼]

Yu et al. (Breast Cancer Res Treat 117:675-677, 2009) recently stated that testing for deviation from Hardy-Weinberg equilibrium (HWE) is necessary to identify systematic genotyping errors in case-control studies. They criticized a meta-analytic study for the deviation from HWE in the case group of one study. The aim of this article is twofold. First, we derive recommendations on how to test for deviations from HWE in different study designs. Second, we develop a meta-analytic framework for assessing compatibility with HWE or measuring deviation from HWE. The authors sketch the possible reasons behind deviation from HWE and provide guidelines for proper investigation of HWE deviations in different study designs. The authors argue that the standard HWE chi(2) lack of fit test is logically flawed and provide a logically unflawed approach for measuring deviation from HWE using confidence intervals. The proposed method is applicable to meta-analyses of both case-control or cohort association studies. The proposed approach is illustrated using the meta-analysis criticized by Yu et al. Heterogeneity between studies can be assessed. The critique of Yu et al. to the article of Frank et al. (Breast Cancer Res Treat 111:139-144, 2008) can be refuted. Even more, validity of HWE can be proven for the pooled control sample. The authors advocate the use of a confidence interval-based approach to assess HWE. The latter should only be investigated in control populations. In multicenter studies or meta-analysis, deviation from HWE should be analyzed using a meta-analytic approach. [less ▲]

Investigating rock-slope failures in the Tien Shan: State-of-the-art and perspectives of international cooperation (M111).

Scientific conference (2005)

Investigating the factors for fermentative biohydrogen improvement: original bioreactors design and hydrogen partial pressure effect

in WHEC 2012, Toronto June 3rd - 7th (2012, June 05)

The anaerobic production of hydrogen from biomass offers the potential production of usable biogas from a variety of renewable resources. However, in order to produce hydrogen at high yields and ... [more ▼]

The anaerobic production of hydrogen from biomass offers the potential production of usable biogas from a variety of renewable resources. However, in order to produce hydrogen at high yields and production rates the biotechnological process needs to be further optimized and efficient bioreactors must be designed [1]. At the CWBI, a continuous horizontal rotating cylinder bioreactor has been designed and investigated to produce biohydrogen from glucose by the strain Clostridium butyricum [2] at good yields (1,9molH2•molglucose-1) and production rates (48,6mmolH2•Lmilieu-1.molhexose-1•h-1). This reactor has an internal volume of 2.3L and a small working volume (300ml) (fig.1). It enhances the hydrogen production rates (by about three times more than a completely stirred bioreactor) by partially immobilizing the bacteria on the porous support. Moreover, the rotating cylinder design enables efficient H2 gas transfer from the liquid phase increasing hydrogen yields by about 25% compared to a completely stirred bioreactor [3-4]. Other original bioreactors, such as a trickle bed, have been built with the same aim of lowering the hydrogen partial pressure and led to similar results. Our work shows the importance of a good liquid to gas transfers in the biohydrogen-producing reactors to reach higher performances. [less ▲]

Investigating the liquid distribution in a reactive distillation packing using high energy X-ray tomography

Conference (1996)

Investigating the performance of model order reduction techniques for nonlinear radiative heat transfer problems

in Proceedings of the International Conference on Advanced Computational Methods in Engineering (2011)

The problem of nonlinear radiative heat transfer is one of great importance to the aerospace industry. However, analysing large-scale, nonlinear, multiphysical, dynamical structures, by using mathematical ... [more ▼]

The problem of nonlinear radiative heat transfer is one of great importance to the aerospace industry. However, analysing large-scale, nonlinear, multiphysical, dynamical structures, by using mathematical modelling and simulation, e.g. Finite Element Modelling (FEM), can be computationally expensive. This provides motivation for the development of Model-Order Reduction (MOR) techniques capable of reducing simulation times without the loss of important information. The objective is to demonstrate the method of Proper Orthogonal Decompostition (POD) as a technique for nonlinear MOR. The nonlinear radiative exchanges between a linear benchmark beam within an external box (Figure 1) are analysed and a reduction procedure for this fully coupled, nonlinear, multiphysical, thermomechanical system is established. The solution to the strongly coupled, thermomechanical equations of motion is found by making use of an extended version of the implicit generalized-alpha scheme. In the reduced model, the residual of the unreduced system of equations need to be evaluated at each Newton iteration of each time step. In order to optimise the efficiency of the reduction method it is shown that the internal forces can be split into their linear and nonlinear counterparts. Only the nonlinear terms change at each time step, thus only these terms need to remain in the iterative loop significantly reducing the number of parameters that are to be computed at each step. These efficiency improvements to the method are discussed and the results are given. [less ▲]

Investigating the role of myostatin in the determinism of double muscling characterizing Belgian Texel sheep

(1998)