Les macroinvertébrés benthiques littoraux : bioindicateurs de la qualité écologique des milieux humides en zone urbaine

Les milieux aquatiques en zone urbaine sont reconnus comme des îlots de biodiversité qui offrent de nombreux services écologiques. Dans cette étude, nous avons utilisé les macroinvertébrés comme bioindicateurs de la qualité écologique des étangs, petits lacs et marais de l’Île de Montréal. Les macroinvertébrés ont été récoltés durant l’été 2011 dans la zone littorale de 20 sites variant par leur urbanisation et leurs caractéristiques limnologiques. Nous avons évalué la variation dans la richesse en taxa, les indices de diversité et plusieurs métriques basées sur la composition taxonomique ou les traits fonctionnels. Nous avons déterminé la réponse des métriques aux changements dans l’urbanisation, l’aménagement et les conditions des plans d’eau. Notre étude montre que les étangs, marécages et petits lacs constituent des réserves importantes de biodiversité en zone urbaine. Les marécages naturels et les étangs et lacs permaments avaient une meilleure qualité écologique et supportaient des communautés de macroinvertébrés plus diverses et abondantes que les petits étangs temporaires aménagés. Le couvert de végétation aquatique, l’enrichissement en nutriments et en matière organique ainsi que la biomasse des algues expliquaient le plus de variation dans les macroinvertébrés. Les aménagements, la densité urbaine et la permanence de l’eau avaient aussi une bonne influence. Les métriques univariées avaient moins de potentiel que les métriques multivariées. Nous avons discuté les implications de notre étude pour le suivi environnemental de la biodiversité et la qualité écologique des milieux aquatiques en zone urbaine.

Une nouvelle méthode pour estimer la torsion géométrique en scoliose idiopathique de l’adolescent

La scoliose idiopathique de l’adolescent (SIA) est une déformation tridimensionnelle (3D) de la colonne vertébrale. Pour la plupart des patients atteints de SIA, aucun traitement chirurgical n’est nécessaire. Lorsque la déformation devient sévère, un traitement chirurgical visant à réduire la déformation est recommandé. Pour déterminer la sévérité de la SIA, l’imagerie la plus utilisée est une radiographie postéroantérieure (PA) ou antéro-postérieure (AP) du rachis. Plusieurs indices sont disponibles à partir de cette modalité d’imagerie afin de quantifier la déformation de la SIA, dont l’angle de Cobb. La conduite thérapeutique est généralement basée sur cet indice. Cependant, les indices disponibles à cette modalité d’imagerie sont de nature bidimensionnelle (2D). Celles-ci ne décrivent donc pas entièrement la déformation dans la SIA dû à sa nature tridimensionnelle (3D). Conséquemment, les classifications basées sur les indices 2D souffrent des mêmes limitations. Dans le but décrire la SIA en 3D, la torsion géométrique a été étudiée et proposée par Poncet et al. Celle-ci mesure la tendance d’une courbe tridimensionnelle à changer de direction. Cependant, la méthode proposée est susceptible aux erreurs de reconstructions 3D et elle est calculée localement au niveau vertébral. L’objectif de cette étude est d’évaluer une nouvelle méthode d’estimation de la torsion géométrique par l’approximation de longueurs d’arcs locaux et par paramétrisation de courbes dans la SIA. Une première étude visera à étudier la sensibilité de la nouvelle méthode présentée face aux erreurs de reconstructions 3D du rachis. Par la suite, deux études cliniques vont présenter la iv torsion géométrique comme indice global et viseront à démontrer l’existence de sous-groupes non-identifiés dans les classifications actuelles et que ceux-ci ont une pertinence clinique. La première étude a évalué la robustesse de la nouvelle méthode d’estimation de la torsion géométrique chez un groupe de patient atteint de la SIA. Elle a démontré que la nouvelle technique est robuste face aux erreurs de reconstructions 3D du rachis. La deuxième étude a évalué la torsion géométrique utilisant cette nouvelle méthode dans une cohorte de patient avec des déformations de type Lenke 1. Elle a démontré qu’il existe deux sous-groupes, une avec des valeurs de torsion élevées et l’autre avec des valeurs basses. Ces deux sous-groupes possèdent des différences statistiquement significatives, notamment au niveau du rachis lombaire avec le groupe de torsion élevée ayant des valeurs d’orientation des plans de déformation maximales (PMC) en thoraco-lombaire (TLL) plus élevées. La dernière étude a évalué les résultats chirurgicaux de patients ayant une déformation Lenke 1 sous-classifiées selon les valeurs de torsion préalablement. Cette étude a pu démontrer des différences au niveau du PMC au niveau thoraco-lombaire avec des valeurs plus élevées en postopératoire chez les patients ayant une haute torsion. Ces études présentent une nouvelle méthode d’estimation de la torsion géométrique et présentent cet indice quantitativement. Elles ont démontré l’existence de sous-groupes 3D basés sur cet indice ayant une pertinence clinique dans la SIA, qui n’étaient pas identifiés auparavant. Ce projet contribue dans la tendance actuelle vers le développement d’indices 3D et de classifications 3D pour la scoliose idiopathique de l’adolescent.

Corrélats neuronaux de la mémoire de travail en magnétoencéphalographie à l’état de repos.

Purpose: There are few studies demonstrating the link between neural oscillations in magnetoencephalography (MEG) at rest and cognitive performance. Working memory is one of the most studied cognitive processes and is the ability to manipulate information on items kept in short-term memory. Heister & al. (2013) showed correlation patterns between brain oscillations at rest in MEG and performance in a working memory task (n-back). These authors showed that delta/theta activity in fronto-parietal areas is related to working memory performance. In this study, we use resting state MEG oscillations to validate these correlations with both of verbal (VWM) and spatial (SWM) working memory, and test their specificity in comparison with other cognitive abilities. Methods: We recorded resting state MEG and used clinical neuropsychological tests to assess working memory performance in 18 volunteers (6 males and 12 females). The other neuropsychological tests of the WAIS-IV were used as control tests to assess the specificity of the correlation patterns with working memory. We calculated means of Power Spectrum Density for different frequency bands (delta, 1-4Hz; theta, 4-8Hz; alpha, 8-13Hz; beta, 13-30Hz; gamma1, 30-59Hz; gamma2, 61-90Hz; gamma3, 90-120Hz; large gamma, 30-120Hz) and correlated MEG power normalised for the maximum in each frequency band at the sensor level with working memory performance. We then grouped the sensors showing a significant correlation by using a cluster algorithm. Results: We found positive correlations between both types of working memory performance and clusters in the bilateral posterior and right fronto-temporal regions for the delta band (r2 =0.73), in the fronto-middle line and right temporal regions for the theta band (r2 =0.63) as well as in the parietal regions for the alpha band (r2 =0.78). Verbal working memory and spatial working memory share a common fronto-parietal cluster of sensors but also show specific clusters. These clusters are specific to working memory, as compared to those obtained for other cognitive abilities and right posterior parietal areas, specially in slow frequencies, appear to be specific to working memory process. Conclusions: Slow frequencies (1-13Hz) but more precisely in delta/theta bands (1-8Hz), recorded at rest with magnetoencephalography, predict working memory performance and support the role of a fronto-parietal network in working memory.

Interannual Variability of Upwelling Indices in the Southeastern Arabian Sea: A Satellite Based Study

Increase in sea surface temperature with global warming has an impact on coastal upwelling. Past two decades (1988 to 2007) of satellite observed sea surface temperatures and space borne scatterometer measured winds have provided an insight into the dynamics of coastal upwelling in the southeastern Arabian Sea, in the global warming scenario. These high resolution data products have shown inconsistent variability with a rapid rise in sea surface temperature between 1992 and 1998 and again from 2004 to 2007. The upwelling indices derived from both sea surface temperature and wind have shown that there is an increase in the intensity of upwelling during the period 1998 to 2004 than the previous decade. These indices have been modulated by the extreme climatic events like El–Nino and Indian Ocean Dipole that happened during 1991–92 and 1997–98. A considerable drop in the intensity of upwelling was observed concurrent with these events. Apart from the impact of global warming on the upwelling, the present study also provides an insight into spatial variability of upwelling along the coast. Noticeable fact is that the intensity of offshore Ekman transport off 8oN during the winter monsoon is as high as that during the usual upwelling season in summer monsoon. A drop in the meridional wind speed during the years 2005, 2006 and 2007 has resulted in extreme decrease in upwelling though the zonal wind and the total wind magnitude are a notch higher than the previous years. This decrease in upwelling strength has resulted in reduced productivity too.

Thermal lens technique to study the effect of pH on electronic energy transfer in organic dye mixtures.

The effect of pH on the fluorescence efficiency of fluorescein is evaluated using thermal lens technique. Fluorescence efficiency increases as the sample becomes more and more alkaline. But when fluorescein is mixed with rhodamine B fluorescence quenching of fluorescein takes place with the excitation of rhodamine B. The electronic energy transfer in this mixture is investigated using Optical Parametric Oscillator as the excitation source. The effect of pH on the efficiency of energy transfer in fluorescein–rhodamine B mixture is presented.

Farm Programmes of Electronic Media: A Comparative Study of Audience Perception in Kerala

Farm communication and extension programs are vital part of the farm development attempts. Electronic media plays a major role in farm extension activities. Kerala, the consumer state, which was a complete agricultural state in pre-independence period, is the sprouting land of agricultural extension and publication activities in print media. Later AIR (All India Radio) farm programs and farm broadcasting of Doordarshan enriched the role of electronic media in farm extension activities. The media saturated southern state of India received this new electronic media farm communication revolution whole heartedly. However, after 1990, Kerala witnessed a flood of private T V channels and currently there are 24 channels in this regional language, named Malayalam. All major news and entertainment channels are broadcasting farm programs. Farm programs of AIR and Doordarshan, broadcasted in Malayalam language, have been well accepted to the farmers‘ in Kerala. However, post-independence period, witnessed the formation of Kerala state in Indian Union and the first ballot-elected communist Government started its administration. After the land reform bills, the state witnessed a gradual decrease in agricultural production. Even if it is not reflected much in the attitude and practices of farm community and farm broadcast of traditional electronic broadcasting, a change is observable after the post-liberalization era of India. Private Television channels, which were focused on entertainment value of programs, started broadcasting farm programs and the parameters of program production went through certain changes. In this situation, there is ample relevance for a study about the farm programs of electronic media in terms of a comparative study of audience perception. The study is limited in the state of Kerala as it is the most media saturated state in India. The study analyzes the rate, nature and scope of adoption of farming methods transmitted through electronic media (T.V. and Radio) in Malayalam language.All kinds of Farm programs including comprehensive program serials, success stories, seasonal cropping methods, experts opinion, been analyzed on the basis of the following objectives.  To find whether propagating new farm methods through farm programs in electronic media or the availability of adequate infrastructure and economic factors make a farmer to adopt a new farming method.  To find which electronic media has more influence on farmers to adopt agricultural programs.  To find which form of electronic media gets better feedback from farmers  To find out whether the programs of T.V. or Radio is more acceptable to farmers than the print media.  To find whether farmers gets the message through their preferred medium for the message. The researcher recorded opinions from a panel of agricultural officers, farm Information officers, agro extension researchers and experts. According to their opinions and guidelines, a pilot study is designed and conducted in Kanjikuzhy Panchayath, in Alappuzha district, Kerala. The Panchayath is selected by considering its ideal nature of being the sample for a social Science research. Besides, the nature of farming in the Panchayath, which devoid of the cultivation of cash crops also supported its sample value. As per the observations from the pilot study, researcher confirmed the Triangulation method as the methodology of research. The questionnaire survey, being the primary part contained 42 Questions with 6 independent and 32 dependent variables. The survey is conducted among 400 respondents in Idukki, Alappuzha and Pathanamthitta districts considering geographical differences and distribution of different types of crops. The response from a total of 360 respondents, 120 from each district, finally selected for tabulation and data analysis.The data analysis, based on percentage analysis, along with the results from focus group discussion among a selected group of 20 farmers, together produced the results as follows. Farmers, who are the audience of farm programs, have a very serious approach towards the medium. They are maintaining a critical point of view towards the content of the programs. Farmers are reasonably aware about the financial side of the programs and the monitory aspirations of both private and Government owned Television channels. Even though, the farmers are not aware on the technical terminology and jargons, they have ideas about success stories, program serials and they are even informed about channels are not maintaining an audience research section like AIR. Though the farmers accept Doordarshan as the credential source of farm information and methods, they are inclined to the entertainment value of programs too. They prefer to have more entertainment value for the programs of Doordarshan. Surprisingly, they have very solid suggestions on even about the shots which add entertainment value to the farm broadcasting methods of Doordarshan. Farmers are very much aware about the fact that media is just an instrument for inspiration and persuasion. They strongly believe that the source of information and new methods is agricultural research and an effective change happens only when there are adequate infrastructure and marketing facilities, along with the proper support from Government agricultural guideline and support systems like Krishi Bhavans. They strongly believe that media alone cannot create any magic in increasing agricultural production. Farmers are pointing out the lack of response to the feedback and queries of farmers on farming methods, as an evidence for the difference in levels of commitment of Government and private owned Television channels.Farmers are still perceiving AIR farm programs are far more committed to farmers and farming than any other electronic medium. However, they are seriously lacking Radio receivers with medium wave reception facility. Farmers perceive that the farming methods on new crops are more adoptable than the farming methods of traditional crops in both private and Government owned Television channels. There are multiple factors behind this observation from farmers. Farmers changed in terms of viewing habits and they prefer success stories, which are totally irrelevant and they even think that such stories encourage people to go for farming and they opined that such stories are good sources of inspiration. However, they are all very much sure about the importance and particular about the presence of entertainment factor even in farm programs. Farmers expect direct interaction of any expert of the new farming method to implement the method in their agriculture practices. Though introduction of a new idea in the T.V. is acceptable, farmers need the direct instruction of expert on field to start implementing the new farming practices Farmers still have an affinity towards print media reports and agricultural pages and they have complaints to print media on the removal of agricultural information pages from news papers. They prefer the reports in print media as it facilitates them to collect and refer articles when they need it. Farmers are having an eye of doubt about the credibility of farm programs by private T.V. channels. Even if they prefer private Television channels for listening and adopting new farming methods and other farm information, they scrutinize programs to know whether they are sponsored programs by agrochemical or agro-fertilizer manufacturer.

Electronic structure of few-electron concentric double quantum rings

The ground state structure of few-electron concentric double quantum rings is investigated within the local spin density approximation. Signatures of inter-ring coupling in the addition energy spectrum are identified and discussed. We show that the electronic configurations in these structures can be greatly modulated by the inter-ring distance: At short and long distances the low-lying electron states localize in the inner and outer rings, respectively, and the energy structure is essentially that of an isolated single quantum ring. However, at intermediate distances the electron states localized in the inner and the outer ring become quasidegenerate and a rather entangled, strongly-correlated system is formed.

Electronic structure and properties of Cu2O

The structural and electronic properties of Cu2O have been investigated using the periodic Hartree-Fock method and a posteriori density-functional corrections. The lattice parameter, bulk modulus, and elastic constants have been calculated. The electronic structure of and bonding in Cu2O are analyzed and compared with x-ray photoelectron spectroscopy spectra, showing a good agreement for the valence-band states. To check the quality of the calculated electron density, static structure factors and Compton profiles have been calculated, showing a good agreement with the available experimental data. The effective electron and hole masses have been evaluated for Cu2O at the center of the Brillouin zone. The calculated interaction energy between the two interpenetrated frameworks in the cuprite structure is estimated to be around -6.0 kcal/mol per Cu2O formula. The bonding between the two independent frameworks has been analyzed using a bimolecular model and the results indicate an important role of d10-d10 type interactions between copper atoms.

Electronic structure and magnetic interactions of the spin-chain compounds Ca2CuO3 and Sr2CuO3

The results are presented of a combined periodic and cluster model approach to the electronic structure and magnetic interactions in the spin-chain compounds Ca2CuO3 and Sr2CuO3. An extended t-J model is presented that includes in-chain and interchain hopping and magnetic interaction processes with parameters extracted from ab initio calculations. For both compounds, the in-chain magnetic interaction is found to be around -240 meV, larger than in any of the other cuprates reported in the literature. The interchain magnetic coupling is found to be weakly antiferromagnetic, -1 meV. The effective in-chain hopping parameters are estimated to be ~650 meV for both compounds, whereas the value of the interchain hopping parameter is 30 meV for Sr2CuO3 and 40 meV for Ca2CuO3, in line with the larger interchain distance in the former compound. These effective parameters are shown to be consistent with expressions recently suggested for the Néel temperature and the magnetic moments, and with relations that emerge from the t-J model Hamiltonian. Next, we investigate the physical nature of the band gap. Periodic calculations indicate that an interpretation in terms of a charge-transfer insulator is the most appropriate one, in contrast to the suggestion of a covalent correlated insulator recently reported in the literature.

Effective t-J model Hamiltonian parameters of monolayered cuprate superconductors from ab initio electronic structure calculations

The magnetic coupling constant of selected cuprate superconductor parent compounds has been determined by means of embedded cluster model and periodic calculations carried out at the same level of theory. The agreement between both approaches validates the cluster model. This model is subsequently employed in state-of-the-art configuration interaction calculations aimed to obtain accurate values of the magnetic coupling constant and hopping integral for a series of superconducting cuprates. Likewise, a systematic study of the performance of different ab initio explicitly correlated wave function methods and of several density functional approaches is presented. The accurate determination of the parameters of the t-J Hamiltonian has several consequences. First, it suggests that the appearance of high-Tc superconductivity in existing monolayered cuprates occurs with J/t in the 0.20¿0.35 regime. Second, J/t=0.20 is predicted to be the threshold for the existence of superconductivity and, third, a simple and accurate relationship between the critical temperatures at optimum doping and these parameters is found. However, this quantitative electronic structure versus Tc relationship is only found when both J and t are obtained at the most accurate level of theory.

Electronic structure of a neutral oxygen vacancy in SrTiO3

The electronic structure of an isolated oxygen vacancy in SrTiO3 has been investigated with a variety of ab initio quantum mechanical approaches. In particular we compared pure density functional theory (DFT) approaches with the Hartree-Fock method, and with hybrid methods where the exchange term is treated in a mixed way. Both local cluster models and periodic calculations with large supercells containing up to 80 atoms have been performed. Both diamagnetic (singlet state) and paramagnetic (triplet state) solutions have been considered. We found that the formation of an O vacancy is accompanied by the transfer of two electrons to the 3d(z2) orbitals of the two Ti atoms along the Ti-Vac-Ti axis. The two electrons are spin coupled and the ground state is diamagnetic. New states associated with the defect center appear in the gap just below the conduction band edge. The formation energy computed with respect to an isolated oxygen atom in the triplet state is 9.4 eV.

Electronic and magnetic structure of LaMnO3 from hybrid periodic density-functional theory

The electronic and magnetic structures of the LaMnO3 compound have been studied by means of periodic calculations within the framework of spin polarized hybrid density-functional theory. In order to quantify the role of approximations to electronic exchange and correlation three different hybrid functionals have been used which mix nonlocal Fock and local Dirac-Slater exchange. Periodic Hartree-Fock results are also reported for comparative purposes. The A-antiferromagnetic ground state is properly predicted by all methods including Hartree-Fock exchange. In general, the different hybrid methods provide a rather accurate description of the band gap and of the two magnetic coupling constants, strongly suggesting that the corresponding description of the electronic structure is also accurate. An important conclusion emerging from this study is that the nature of the occupied states near the Fermi level is intermediate between the Hartree-Fock and local density approximation descriptions with a comparable participation of both Mn and O states.