Experimental Performance Evaluation and Frame Aggregation Enhancement in IEEE 802.11n WLANs

The IEEE 802.11n standard promises to extend today’s most popular WLAN standard by significantly increasing reach, reliability, and throughput. Ratified on September 2009, this standard defines many new physical and medium access control (MAC) layer enhancements. These enhancements aim to provide a data transmission rate of up to 600 Mbps. Since June 2007, 802.11n products are available on the enterprise market based on the draft 2.0. In this paper we investigate the effect of most of the proposed 802.11n MAC and physical layer features on the adhoc networks performance. We have performed several experiments in real conditions. The experimental results demonstrated the effectiveness of 802.11n enhancement. We have also examined the interoperability and fairness of 802.11n. The frame aggregation mechanism of 802.11n MAC layer can improve the efficiency of channel utilization by reducing the protocol overheads. We focused on the effect of frame aggregation on the support of voice and video applications in wireless networks. We also propose a new frame aggregation scheduler that considers specific QoS requirements for multimedia applications. We dynamically adjust the aggregated frame size based on frame's access category defined in 802.11e standard

On the Construction of Load-Balanced (k,r-hop)-Connected Dominating Set for WSNs

International audienceConnected Dominating Sets (CDS) are selected to construct a virtual backbone in Wireless Sensor Networks (WSNs). Indeed, CDS are used for fault tolerant broadcasting, routing and even efficient gathering of data. On the other hand, r-hop connected k-dominating sets ((k,r-hop)-CDS) are introduced to reduce the size of CDS and the total amount of information to be transmitted. Unfortunately, no work considers the load-balance factor of (k,r-hop)-CDS. Recently, there is a proposition of constructing load-balanced CDS for WSNs. In this paper we re-use the same concept of selecting load-balanced CDS to construct a Load-Balanced (k,r-hop)-CDS (LB(k,r-hop)-CDS). Then, the allocation of dominatees to the appropriate dominators is done. Through simulations, the proposed method of constructing LB(k,r-hop)-CDS extends network lifetime by an important rate compared with the most recent (k,r-hop)-CDS construction method

Effet de l’interaction lumiere-salinite sur l’activite du photosysteme ii des feuilles excisees de maïs

La diminution de la croissance vegetative observée chez nombreuses plantes, soumises au stress salin et exposées à des conditions naturelles d’ensoleillement, est souvent associée à une baisse de leur activité photosynthétique. Cependant les mécanismes de l’inhibition photosynthétique sont encore peu étudiés. Le photosystème II (PS II) est considéré un des facteurs clé dans la réponse de la photosynthèse des feuilles aux stress environnementaux. L’association de la lumière et du stress salin parait avoir des effets synergétiques sur l’activité photochimique du PSII conduisant, ainsi à la photoinhibition. L’objectif de cette etude est de diagnostiquer l’effet de l’interaction lumière- salinité sur l’activité photochimique du photosystème II au cours de la photosynthèse. Le materiel vegetal est constitué de deux variétés de maïs (Zea mays L.) fourrager: Aristo et Arper. Des feuilles détachées de plantes cultivées sur milieu témoin (eau distilée), sont incubées pendant 6 heures dans des solutions salines à différentes concentrations (0, 100, 200 et 300 mM NaCl), soit en absence ou en présence de lumière (1000 μmol m-2 s-1). Puis, leurs teneurs en sodium ont été déterminées. Pour vérifiers’il y’aura récupération de leur activité photochimique, d’autres feuilles qui ont été mises à absorber du NaCl dans une solution de 300 mM à la lumière pendant 4 heures, sont transferees dans de l’eau distillée en obscurité ou en lumière. Les resultants montrent une stabilité du rendement quantique maximal (Fv/Fm) pour les feuilles mises à absorber du NaCl à l’obscurité.Par contre l’éclairement associé avec la salinité engender une photoinhibition qui se manifeste par une diminution du rendement quantique maximal du PSII. Cette photoinhibition, due à une accumulation excessive des ions Na+dans les tissus foliaires, est réversible. En effet, en absence d’un seul des facteurs de l’association lumière-salinité le PSII récupère son activité photochimique.Mots Clés: fluorescence chlorophyllienne, feuillesexcisées, stress lumineux, chlorure de sodium, Zea maysEnglish AbstractThe decline in growth observed in many plants, subjected to salt stress and exposed to sunlight conditions, is often associated with a decrease in their photosynthetic activity. No clear mechanisms of the inhibited photosynthesis have emerged since photosystem II (PS II) is considered to play a key role in the response of leaf photosynthesis to environmental  perturbations. The combination of light and salt stress appears to have synergistic effects on the photochemical activity of PSII driving, and to photoinhibition. The objective of this study was to evaluate the reversible effect of salinity and light interaction on maximal quantum efficiency of photosystem II (Fv/Fm.). In this experiment, detached leaves of two forage maize (Zea mays L.) varieties, Aristo and Arper were placed during 6 hours in solutions of different concentrations of NaCl (0, 100, 200 and 300 mM) and subjected to light (1000 μmol m-2 s-1) or obscurity. Then, their contents of sodium were determined. In order to verify the photo-inhibition reversibility, other leaves which were incubated in a solution of 300 Mm NaCl, during 4 hours were transferred in distilled water and also subjected to light or to obscurity. Results indicate that leaves which had been put to absorb NaCl in obscurity showed no change in maximal efficiency of PSII (Fv/Fm). Nevertheless, light treatment associated with salinity generates a photo-inhibition of PSII manifested by a significant decrease in maximal efficiency of PSII. This photo-inhibition, due to an excessive accumulation of sodium in leaves, is reversible. It is quite sufficient to eliminate only one factor of the association light-salinity for the PSII activity resume.Keywords: Light stress, sodium chloride, Zea may

Multiplication et bulbaison in vitro du glaïeul (Gladiolus grandiflorus Hort.)

In vitro Multiplication and Bulb Formation of (Gladiolus grandiflorus Hort.). In order to set up a new bulb formation and micropropagation of gladiolus in vitro, trials were undertaken using two ornemental gladiolus cultivars 'Peter pears' and 'White friend ship'. The explants used are apical buds with 2 to 3 mm length taken from the cormes. In vitro initiation and multiplication were done for the two cultivars on Murashige and Skoog medium to which 2 mg. l-1 of BA and 0.5 mgl-1 of AIB were added. In vitro root development and bulb formation have been occurred in MS Agar Agar medium with 0.5 mg.l-1 of AIB 30 days later than the same MS medium containing 6% of saccharose and without Agar

DCEP - Digital Corpus of the European Parliament

The paper presents a new highly multilingual sentence-aligned parallel corpus consisting of various document types and covering a wide range of subject domains. With a total of 1.37 billion words in 23 languages (253 language pairs), gathered in the course of ten years, this is the largest single release of documents by a European Union institution. Corpus statistics, required preprocessing, sentence alignment, and possible gains in statistical machine translation when adding this corpus to the previously existing ones are also considered.JRC.G.2-Global security and crisis managemen

Non-linear electro-elastic coupling in non-centrosymmetric materials

International audienceWe propose an extended symmetry-based thermodynamical model of third-order electro-elastic coupling. The entanglement of electrostriction non-linear piezoelectricity and other non-linear phenomena, is studied in details at the same level of theory. Symmetry properties of materials and nanostructures are taken into account. Density Functional Theory (DFT) is used to calculate the complete set of linear and non-linear coefficients. Electrostriction dominates for nitride compounds in the Würtzite structure, but non-linear elasticity and piezoelectricity must be taken into account for strain and electric field evaluation

Surface effects on the Mott-Hubbard transition in archetypal V2_2O3_3

We present an experimental and theoretical study exploring surface effects on the evolution of the metal-insulator transition in the model Mott-Hubbard compound Cr-doped V$_2$O$_3$. We find a microscopic domain formation that is clearly affected by the surface crystallographic orientation. Using scanning photoelectron microscopy and X-ray diffraction, we find that surface defects act as nucleation centers for the formation of domains at the temperature-induced isostructural transition and favor the formation of microscopic metallic regions. A density functional theory plus dynamical mean field theory study of different surface terminations shows that the surface reconstruction with excess vanadyl cations leads to doped, and hence more metallic surface states, explaining our experimental observations.Comment: 5 pages, 4 figure