Ccilia Castel  Xavier Fernandez  Louisette Lizzani‐Cuvelier  Andr‐Michel Loiseau  Christine Perichet  Claire Delbecque  Franois Jean‐ Arnaudo 《Flavour and Fragrance Journal》2006,21(1):59-67

Static‐headspace (S‐HS), headspace–solid phase microextraction (HS‐SPME) and headspace sorptive extraction (HSSE) have been applied to the analysis of different grades of benzoin gums Siam and Sumatra. This study led to the identification of 58 compounds by GC‐RI and GC‐MS: 42 of them were characterized in Siam benzoin gum (grades 3 and 5) and 40 of them in Sumatra (grades B and D). SPME using divinylbenzene[sol ]carboxen[sol ]polydimethylsiloxane fiber and HSSE are complementary in these conditions and seem to be the most suitable techniques to identify volatile compounds of benzoin gums. S‐HS is less sensitive but represents a good method for the quality control of these gums. For this reason it has been applied directly coupled to mass spectrometry for a rapid differentiation between several benzoin gum qualities. Copyright © 2005 John Wiley & Sons, Ltd.  相似文献   

    

Sonia Marín  Xavier Albareda  Antonio J Ramos  Vicente Sanchis 《Journal of the science of food and agriculture》2001,81(11):1060-1068

Fusarium verticillioides and F proliferatum isolates were inoculated in mixed cultures with Aspergillus parasiticus on irradiated maize grain at two different inoculum concentrations (2 × 10⁵ and 2 × 10² conidia g^?1 dry maize). The treatments were 0.93–0.98 water activity (a_w) and 15 and 25 °C for 28 days. A complex relationship was found between a_w, temperature, inoculum concentration and the interactions which took place between fumonisin and aflatoxin producers. In general, A parasiticus reduced F verticillioides and F proliferatum populations (by 6–36%) but did not affect fumonisin B₁ production by these species. In contrast, while the Fusarium species were not able to decrease A parasiticus populations, they significantly reduced aflatoxin B₁ accumulation (by 30–93%). © 2001 Society of Chemical Industry  相似文献   

    

Lorena Trigueros  Xavier Barber  Esther Sendra 《International Journal of Dairy Technology》2015,68(2):198-206

The effect of yoghurt starter cultures and probiotic Lactobacillus casei on the formation of conjugated linoleic acid (CLA) and microbial populations of fermented goat milk was investigated during 35 days of cold storage. The addition of hydrolysed sunflower oil as a source of free linoleic acid was investigated. The fermentation process enhanced the content of the cis9, trans11‐CLA isomer in milk, whereas the trans10, cis12‐CLA isomer was not detected in goat milk or control fermented milks. The use of both starters generated trans10, cis12‐CLA only when hydrolysed sunflower oil was supplemented. Populations of streptococci and lactobacilli were affected by the presence of hydrolysed sunflower oil.  相似文献   

    

Helder Manoel Venceslau  Daniela Cristina Lubke  Adilson Elias Xavier 《Optimization methods & software》2015,30(2):391-403

We consider the problem of optimally covering solid bodies by a given number of spheres. The mathematical modelling of this problem leads to a min–max–min formulation which, in addition to its intrinsic multi-level nature, has the significant characteristic of being non-differentiable. The use of the hyperbolic smoothing technique engenders a simple one-level nonlinear programming problem and allows overcoming the main difficulties presented by the original one. To illustrate the performance of the method we present computational results for two large test covering problems with up to 1,200,000 voxels. The first problem is the covering of a ring torus whose optimal solution is known whenever the number of covering spheres is small, and the second problem is a generic test problem.  相似文献   

    

Isabel Maria Xavier  Denise Mary Jepsen 《人机工程学与制造业中的人性因素》2015,25(5):534-547

This study investigated whether environmental stressors predict perceptions of psychological contract breach and associated feelings of violation in employees from a large manufacturing organization. It was proposed that increasing levels of job stress as a result of changes in the employment context may account for the rising incidence of perceived contract breach. The results suggest that breach and violation are more likely when employees are experiencing role conflict, perceive a lack of career progression, and perceive a lack of control over work. Further, control was found to moderate the relationship between stress and breach. This study has important practical implications, suggesting ways in which organizations may be able to reduce the likelihood of psychological contract breach and violation.  相似文献   

    

Jiazhou Chen  Gaël Guennebaud  Pascal Barla  Xavier Granier 《Computer Graphics Forum》2013,32(8):98-109

We introduce a new approach for defining continuous non‐oriented gradient fields from discrete inputs, a fundamental stage for a variety of computer graphics applications such as surface or curve reconstruction, and image stylization. Our approach builds on a moving least square formalism that computes higher‐order local approximations of non‐oriented input gradients. In particular, we show that our novel isotropic linear approximation outperforms its lower‐order alternative: surface or image structures are much better preserved, and instabilities are significantly reduced. Thanks to its ease of implementation (on both CPU and GPU) and small performance overhead, we believe our approach will find a widespread use in graphics applications, as demonstrated by the variety of our results.  相似文献   

    

Geraldo Miguez  Adilson Elias Xavier  Nelson Maculan 《International Transactions in Operational Research》2014,21(5):835-854

The backpropagation algorithm is one of the most used tools for training artificial neural networks. However, this tool may be very slow in some practical applications. Many techniques have been discussed to speed up the performance of this algorithm and allow its use in an even broader range of applications. Although the backpropagation algorithm has been used for decades, we present here a set of computational results that suggest that by replacing bihyperbolic functions the backpropagation algorithm performs better than the traditional sigmoid functions. To the best of our knowledge, this finding was never previously published in the open literature. The efficiency and discrimination capacity of the proposed methodology are shown through a set of computational experiments, and compared with the traditional problems of the literature.  相似文献   

    

Nicolas Jeannin  Xavier Boulanger  Laurent Féral  Laurent Castanet  Frédéric Lacoste 《International Journal of Satellite Communications and Networking》2014,32(5):407-421

This set of two companion papers aims at providing a statistical framework to quantify the inter‐annual variability observed on the statistics of rain attenuation or rainfall rate derived from Earth‐space propagation measurements. This part I is more specifically devoted to the theoretical study of the variance of estimation of empirical complementary cumulative distribution functions (ECCDFs) derived from Earth‐space rain attenuation or rainfall rate time series. To focus the analysis on the statistical variability but without loss of generality, synthetic rain attenuation time series are considered. A large variability on the ECCDFs, which depends on the duration of the synthetic data, is first put into evidence. The variance of estimation is then derived from the properties of the statistical estimator. The formulation is validated numerically, by comparison with the ECCDF variances derived from the synthetic data. The variance of the fluctuations around the CCDF is then shown to be dependent on the average of the correlation function of the time series, on the probability level and on the measurement duration. This variance of estimation is needed as a prerequisite in conjunction with the knowledge of the climatic variability to characterize the yearly fluctuations of propagation statistics computed from experimental time series. The extensions from simulations to experiments as well as the application to system planning are detailed in part II. Copyright © 2013 John Wiley & Sons, Ltd.  相似文献   

    

Stella Vallejos  Polona Umek  Toni Stoycheva  Fatima Annanouch  Eduard Llobet  Xavier Correig  Patrizia De Marco  Carla Bittencourt  Chris Blackman 《Advanced functional materials》2013,23(10):1226-1226

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Pedro Xavier Ramos  Laurent Schindfessel  João Pedro Pêgo  Tom De Mulder 《水科学与水工程》2019,12(3):235-243

Confluences play a major role in the dynamics of networks of natural and man-made open channels,and field measurements on river confluences reveal that discordance in bed elevation is common.Studies of schematized confluences with a step at the interface between the tributary and the main channel bed reveal that bed elevation discordance is an important additional control for the confluence hydrodynamics.This study aimed to improve understanding of the influence of bed elevation discordance on the flow patterns and head losses in a right-angled confluence of an open channel with rectangular cross-sections.A large eddy simulation(LES)-based numerical model was set up and validated with experiments by others.Four configurations with different bed discordance ratios were investigated.The results confirm that,with increasing bed elevation discordance,the tributary streamlines at the confluence interface deviate less from the geometrical confluence angle,the extent of the recirculation zone(RZ) gets smaller,the ratio of the water depth upstream to that downstream of the confluence decreases,and the water level depression reduces.The bed elevation discordance also leads to the development of a large-scale structure in the lee of the step.Despite the appearance of the large-scale structure,the reduced extent of the RZ and associated changes in flow deflection/contraction reduce total head losses experienced by the main channel with an increase of the bed discordance ratio.It turns out that bed elevation discordance converts the lateral momentum from the tributary to streamwise momentum in the main channel more efficiently.  相似文献