Finite Element Modelling of Micro-cantilevers Used as Chemical Sensors

Nowadays, silicon micro-cantilevers with different geometrical shapes are widely used as micro-electro-mechanical systems and, more recently, as force sensor probes in atomic force microscopy (AFM). During the last ten years, several applications, which include these AFM micrometer-sized cantilevers as mass probes in microbalances or as chemical sensors in chemical micro-system devices, were developed. In the case of complex shapes of cantilevers, where the cross-section is not constant along the cantilever length (case of “V-shaped” micro-cantilevers), their resonant frequencies can not be analytically calculated. Firstly, in order to validate the accuracy of our FEM approach, we carried out a comparison between analytical, experimental and FEM-computed values of the resonant frequencies for homogenous rectangular shaped micro-cantilevers. Then, we performed a modeling of silicon beams coated with a thin sensitive layer (50 nm of Gold). To precisely calculate the resonant frequencies of these multilayer-cantilevers, the influence of the mesh parameters on the calculated frequencies was strongly investigated. Secondly, the sensitivity of different “V-shaped” silicon cantilevers was estimated, as a function of their geometrical dimensions and of their mechanical parameters (Young modulus, density). The resonant frequencies of uncoated cantilevers were calculated and compared with the values experimentally determined. Then, a similar approach was employed to predict the sensitivities of such cantilevers recovered with a sensitive layer

Influence des élevages extensifs en étang sur les rivièrese

Si de nombreux travaux ont porté sur l'influence des piscicultures intensives sur les rivières, on s'est peu intéressé aux conséquences des nombreuses créations de plan d'eau sur le milieu. Le but de cet article est de présenter en s'appuyant sur des exemples précis les différentes modifications apportées sur le milieu par une surface en eau d'élevage extensif.Les aspects hydrologiques sont peu importants. Les changements physico-chimiques ont par contre de nombreuses conséquences, directes et indirectes :- la température : le réchauffement estival agit sur les réactions chimiques, l'équilibre des biocénoses, la pathologie des poissons,- le potentiel hydrogène, très variable en cas de faible dureté,- l'oxygénation, liée à la température dont le déficit agit directement sur la faune pisciaire,- la fertilisation par l'azote et les phosphates,- les matières en suspension : action surtout manifeste lors des vidanges, directe sur le colmatage des frayères, indirecte sur la structure des communautés floristique et faunistique.Le repeuplement des rivières par les poissons d'étang est fréquent. Les conséquences vont du déséquilibre faunistique à l'introduction d'espèces indésirables ou nuisibles. Dans l'ensemble, on note un impact négatif sur les eaux courantes, particulièrement sur les rivières à salmonidés (1ère catégorie). Sur les cours d'eau de 2e catégorie, l'impact est toujours plus faible et on peut noter une action bénéfique due au lagunage.Une hiérarchisation des influences est donnée en tenant compte du type de plan d'eau et de son mode de gestion.Although many studies relate to the influence of fish farming on rivers, little interest has been given to the environmental impact of artificial ponds. The aim of this article is to show through precise examples the various alterations in the environmental system caused by extensive fish breeding farms.Hydrological aspectsEven in the absence of any breeding, the presence of a water surface brings about variations in the local water balance.- losses due to infiltration may increase through the drilling of an impermeable substratum when digging the pond, but new springs are often observed, resulting in an inscreased stream flow.- fosses due to evaporation vary according to local climate and environment.Pond dams sometimes act as buffers against floods.Influences can only be significant under particular conditions : regional temperature and humidity and the nature of the substratum.Physico-chemical aspectsDuring the filling period, one of the greatest risks is the rise in temperature. Even though the latter only occasionally reaches 10 % of its initial value, the effects are numerous :- reduction of dissolved oxygen content and acceleration of microbial processes of aerobic decomposition.- effect on biocenosis : a 3 to 4 °C rise in average maximal temperature may result in a typological change in the streams normally hosting Salmonidae. The disappearance of benthic Invertebrata may be observec as well as their replacement by groups whose development is stimulated by temperature : e.g. Mollusca and Worms.- effect on pollution : a 1 °C rise in temperature, from pH to basic values results in a growing concentration in ammoniacal nitrogen which turns out to be toxic. On the other band, a possible favourable affect upon second class fish breeding streams must be noted. Eutrophization and enhancement of the environment also occur in addition to an accelerated gametogenesis in some species. In the late summer, this results gametogenesis in some species. In the late summer, this results in larger fish an, consequently, increased chances of survival lacer. An EEC rule has set the tolerance limits of temperature rise according to the type of river (table 4).If It remains sustined, the discharge of suspended matter may also have various influences. Except for accidents, the risk is slight, measured values are generally inferior to EEC standards. However, it is essential to consider that discharges minerals and organic compounds such as some phytosanitary products (Lindane, Atrazine) likely to cause immediate or delayed toxic effects.The creation of a pond is clearly a cause of instability in the composition of water immediately downstream, especially regarding the pH and, indirectly, NH3 content. This risk is all the greater since restituted water is the result of overflow. As for oxygen, the problem may be assessed differently, according to the mode of restitution; overflow may improve oxygenation whereas overflow caused by an emptying device may cause deoxygenation. Whatever the mode of restitution, downstream water is enriched with soluble and particulate organic matter which can promote bacterial development and oxygen intake.Finally, it is worth noting that pend phytoplankton is likely to culture the downstream river, all the more intensely since the sluggishness of water flow will be stopped up.The impact will depend upon the kind of pond involved : a « ballast tank » unconnected with the stream will have a lesser influence than a derivated pond. Since maximal impact will occur in the discharging channel before reaching the stream's downstream zone. The influence will be much more harmful to Salmonidae streams which are more sensitive to a reduction in dissolved oxygen. The imbalance will be heightened by fish losses which are likely to happen, since all species must compete with the surrounding fauna and will be favored by environ mental imbalance.During the emptying operation, besides the circulation of elements trapped by sediment, the addition of suspended matter will involve e high risk for fishbreeding downstream from the discharge. If, during the draining operation, discharge volume is lower than EEC standards (25 mg/l), the emptying operation causes content to reach more than 100 mg/l, with immediate or delayed side affects.The most direct harm done is asphyxiation of most fish under certain circumstances. This is heightened is a real risk of bringing about a rise in temperature : passing from a Salmonidae to a Cyprinidae environment both through disruption of the inverterbrata fauna, and sealing of the spawining places dug in the streambed gravel at emptying periods. The risk of a reduction in fauna varies and invertebrata biomass should also be brought up.Whenever fish are discharged, repopulation of the river usually results. In this case again, the affects will be negative for Salmonidae streams or intermediate-type water in which the replacement and introduction of new species can occur. Everything will depend upon the breeding carried out in the pond.In 2nd-category fish-breeding rivers, only a reinforcement of population and possibly a diversification of species will be observed.As a conclusion, all artificial ponds have a negative impact upon freshwater especially in 1st-category fish farming rivers : e.g. changes in physico-chemical characteristics, introduction of species. This impact occurs during the filling period of the pond (variation in temperature) and the emptying operation (various discharges). In some cases, favourable consequences can be observed (table 1) : natural creation of a lagoon with trapping of elements in solution (phosphates, nitrogen). Moreover, the presence of alcalinity is stronger because of water sediment transfers, as is pH, showing a better fish farming potential.The impact on freswater depends upon the type of pond and the method used for emptying

Facile enhancement of bulk heterojunction solar cells performance by utilizing PbSe nanorods decorated with graphene

An efficient approach for improving the photoelectrical conversion efficiency (PCE) of the bulk heterojunction (BHJ) solar cells, based on poly(3-hexylthiophene) (P3HT) and [6,6]-phenyl-C61 butyric acidmethyl ester (PC61BM), by incorporating PbSe nanorods decorated with graphene (G) into their active layer has been reported for the first time. Pristine PbSe and PbSe:G composites (with different amount of graphene) are synthesized via hydrothermal process and the formation mechanism is explained. The systematic investigation indicates that the crystallite size of PbSe:G increases with increasing grapheme content. The PCE of the classical BHJ solar cells based on P3HT:PC61BM is improved from 2.32 up to 2.57% by the incorporation of pristine PbSe. It is also enhanced by the incorporation of PbSe:G up to certain composition of graphene in which a maximum PCE value of 5.16% is achieved. The external quantum efficiency of the BHJ solar cells is also investigated. The photovoltaic parameters are discussed based on the morphology variation detected by scanning electron microscope and atomic force microscope of the active layers together with their UV–VIS absorption measurements

Mechanical properties of nanotubes of polyelectrolyte multilayers

The elastic properties of nanotubes fabricated by layer-by-layer (LbL) assembly of polyelectrolytes in the nanopores of polycarbonate track-etched membranes have been investigated by resonant contact Atomic Force Microscopy (AFM), for nanotube diameters in the range of 100 to 200 nm. The elastic modulus of the nanotubes was computed from the resonance frequencies of a cantilever resting on freely suspended LbL nanotubes. An average value of 115MPa was found in air for Young's modulus of these nanostructures, well below the values reported for dry, flat multilayers, but in the range of values reported for water-swollen flat multilayers. These low values are most probably due to the lower degree of ionic cross-linking of LbL nanotubes and their consequently higher water content in air, resulting from the peculiar mode of growth of nanoconfined polyelectrolyte multilayers

Improvement of pentathiophene/fullerene planar heterojunction organic photovoltaic cells through MoO3/CuI anode buffer bilayer

Organic photovoltaic cells (OPVCs) are based on a heterojunction electron donor (ED)/electron acceptor (EA). In the present work, the electron donor which is also the absorber of light is pentathiophene. The typical cells were ITO/ABL/Pentathiophene/fullerene /Alq3/Al with ABL = MoO3, CuI, MoO3/CuI. After optimisation of the pentathiophene thickness, 70 nm, the highest efficiency, 0.81%, is obtained with the bilayer MoO3/CuI as ABL. In order to understand these results the pentathiophene films deposited onto the different ABLs were characterized by scanning electron microscopy, atomic force microscopy, X-rays diffraction, optical absorption and electrical characterization. It is shown that CuI improves the conductivity of the pentathiophene layer through the modification of the film structure, while MoO3 decreases the leakage current. Using the bilayer MoO3/CuI allows cumulating the advantages of each layer

Relationship between photo-physical and electrochemical properties of D-π-A compounds regarding solar cell applications. 1. Substituent type effect in photovoltaic performance

Studying the electrochemical characteristics is an important step for determining interactions between molecules and the chemical environment. Moreover, the electrochemical evaluation of dyes is highly needed to establish the behavior of electro-active chemical species inside dye-sensitized solar cells (DSSCs). Four compounds, M8-1, M8-2, M8-O1, and M8-O2 (with a common organic structure (E)-2-cyano-3-(5-((E)-2-(9,9-diethyl-7-(phenylamino)-9H-fluoren-2-yl)vinyl)thiophen-2-yl)acrylic acid), are studied in two solvents, tetrahydrofuran (THF) and dimethylsulfoxide (DMSO). Among the studied compounds, M8-1 has highlighted characteristics compared with the others: its ground and excited states oxidation potential are the highest (1.14 and −1.22 V, respectively). Also, it shows the lowest energy gap between the excited state oxidation potential and the TiO2 conduction band. Relating to the substituent effect, the shorter the length, the higher the energetic difference in the electronic transition (M8-1 and 2). Comparing characteristics through quantum chemistry, the values obtained in DMSO are the most predictable. The injection energies signal that M8-1 is the best injector. The performances in solar cells are measured in three TiO2 materials: Degussa (D-TiO2), active opaque (A-TiO2), and transparent (T-TiO2). The IPCE results show the A > T > D average tendency, and the family of substituted alkyl has higher values than the alcoxyl one. Furthermore, in the first family the methyl substituent has a higher value than the ethyl one. M8-1 has the highest IPCE value, on average. In terms of efficiency, the alkyl substituted family again has higher values than the alcoxyl family. On average, the methyl substituent has a higher value than the ethyl one in both families. M8-1 has the highest efficiency value

Improvement of pentathiophene/fullerene planar heterojunction photovoltaic cells by improving the organic films morphology through the anode buffer bilayer

Organic photovoltaic cells (OPVCs) are based on a heterojunction electron donor (ED)/electron acceptor (EA). In the present work, the electron donor which is also the absorber of light is pentathiophene. The typical cells were ITO/HTL/pentathiophene/fullerene/Alq3/Al with HTL (hole transport layer) = MoO3, CuI, MoO3 /CuI. After optimisation of the pentathiophene thickness, 70 nm, the highest efficiency, 0.81%, is obtained with the bilayer MoO3/CuI as HTL. In order to understand these results the pentathiophene films deposited onto the different HTLs were characterized by scanning electron microscopy, atomic force microscopy, X-rays diffraction, optical absorption and electrical characterization. It is shown that CuI improves the conductivity of the pentathiophene layer through the modification of the film structure, while MoO3 decreases the leakage current. Using the bilayer MoO3/CuI allows cumulating the advantages of each layer

Electron beam induced radio emission from ultracool dwarfs

We present the numerical simulations for an electron-beam-driven and loss-cone-driven electron-cyclotron maser (ECM) with different plasma parameters and different magnetic field strengths for a relatively small region and short time-scale in an attempt to interpret the recent discovered intense radio emission from ultracool dwarfs. We find that a large amount of electromagnetic field energy can be effectively released from the beam-driven ECM, which rapidly heats the surrounding plasma. A rapidly developed high-energy tail of electrons in velocity space (resulting from the heating process of the ECM) may produce the radio continuum depending on the initial strength of the external magnetic field and the electron beam current. Both significant linear polarization and circular polarization of electromagnetic waves can be obtained from the simulations. The spectral energy distributions of the simulated radio waves show that harmonics may appear from 10 to 70$\nu_{\rm pe}$ ($\nu_{\rm pe}$ is the electron plasma frequency) in the non-relativistic case and from 10 to 600$\nu_{\rm pe}$ in the relativistic case, which makes it difficult to find the fundamental cyclotron frequency in the observed radio frequencies. A wide frequency band should therefore be covered by future radio observations.Comment: 10 pages, 19 figures, accepted for publication in the Astrophysical Journa

Synthesis, Characterization, Morphology and Photovoltaic Properties of Aniline-Tiophene Based Polymers

Monomers composed of thiophene and aniline rings, 4-(2-thiophen)aniline and 4-(3-thiophen)aniline, were successfully synthetized through the Suzuki-Miyaura cross coupling reaction and then polymerized. The polymers poly 4-(2-tiophen)aniline and poly 4-(3-tiophen)aniline (P4,2TA and P4,3TA) were characterized via spectroscopycal NMR, optical and electrochemical methodologies. Subsequently the morphology of deposits were characterized using atomic force microscopy (AFM) and X-ray diffraction (XRD). The photovoltaic devices were constructed under the same conditions, observing differences in the photovoltaic yield of each polymer. P4,2TA exhibited higher photovoltaic yield in comparison with P4,3TA, indicating that the molecular geometry affects the crystallinity and surface morphology of the polymeric deposits, and the photovoltaic propertie