1,108 research outputs found
Simultaneous localization and mapping using Rao-Blackwellized particle filters in multi robot systems
Microaerophilicâaerobic sequential decolourization/biodegradation of textile azo dyes by a facultative Klebsiella sp. strain VN-31
Four different azo dyes were decolourized and biodegraded in a sequential microaerophilicâaerobic treatment by a facultative Klebsiella sp. strain VN-31, a bacterium isolated from activated sludge process of the textile industry. Dye decolourization was performed under microaerophilic conditions until no colour was observed (decolourization percentage >94%). The medium was then aerated to promote the biodegradation of the amines produced. The presence of aromatic amine in the microaerophilic stage and its absence in the aerobic stage demonstrate azo bond reduction and an oxidative biodegradation process, respectively. Total Organic Carbon (TOC) reduction for the growth medium plus dyes was âŒ50% in the microaerophilic stage and âŒ80% in the aerobic stage. The degradation products were also characterized by FT-IR and UVâvis techniques and their toxicity measured using Daphnia magna. The results provide evidence that the successive microaerophilic/aerobic stages, using a single Klebsiella sp. strain VN-31 in the same bioreactor, were able to form aromatic amines by the reductive break down of the azo bond and to oxidize them into non-toxic metabolites.The authors would like to thank the Portuguese Foundation of Science and Technology (FCT) for providing the grant to Andrea Zille (SFRH/BPD/24238/2005) and the Brazilian Foundations for the Coordination of Training Graduated Pessoal of the Ministry of Education (CAPES) and the National Counsel for Technological and Scientific Development (CNPq) for providing the grant to Elisangela Franciscon
Inverse problem of photoelastic fringe mapping using neural networks
This paper presents an enhanced technique for inverse analysis of photoelastic fringes using neural networks to determine the applied load. The technique may be useful in whole-field analysis of photoelastic images obtained due to external loading, which may find application in a variety of specialized areas including robotics and biomedical engineering. The presented technique is easy to implement, does not require much computation and can cope well within slight experimental variations. The technique requires image acquisition, filtering and data extraction, which is then fed to the neural network to provide load as output. This technique can be efficiently implemented for determining the applied load in applications where repeated loading is one of the main considerations. The results presented in this paper demonstrate the novelty of this technique to solve the inverse problem from direct image data. It has been shown that the presented technique offers better result for the inverse photoelastic problems than previously published works
Polymerization study of the aromatic amines generated by the biodegradation of azo dyes using the laccase enzyme
Four different azo dyes were decolorized (color reduction >90%) by bacteria isolated from a textile wastewater effluent. Dye decolorizing was carried out under microaerobic conditions until completion, after which the aromatic amine concentration was determined. A laccase from Myceliophthora thermophila was used to catalyze coupling reactions of the aromatic amines produced from decolorizing the dyes. The reaction was carried out with stirring (100 rpm) in a weak acidic buffer solution (pH 5.0) at 45 °C for 3 days. The presence of aromatic amines in the samples after bacterial decolorizing confirmed the azo bond was reduced in the process. In addition, the UVâvis spectrum was shifted significantly after the sequential bacterial-laccase treatment also indicating a chemical transformation of the dyes. After laccase treatment the solutions formed colored soluble and precipitated products. The particles sizes making up the precipitates formed after laccase treatment varied between 105 and 483 nm as determined by Photon Correlation Spectroscopy (PCS). The laccase treatment also reduced the COD of the dye solutions by âŒ20%. We show that successive bacterial-laccase treatment is effective in decolorized azo dyes by reduction of the azo bonds, and promoting coupling reactions between the aromatic amines formed. Promoting coupling reactions between the aromatic amines using enzymes may prove useful for the physical removal and reuse of these amines.The authors would like to thank the Brazilian Foundation Coordenacao de Aperfeicoamento de Pessoal de Nivel Superior of the Ministry of Education (CAPES) and the National Counsel for Technological and Scientific Development (CNPq) for providing grants to Elisangela Franciscon
Genetic and demographic vulnerability of adder populations: Results of a genetic study in mainland Britain
Genetic factors are often overlooked in conservation planning, despite their importance in small isolated populations. We used mitochondrial and microsatellite markers to investigate population genetics of the adder (Vipera berus) in southern Britain, where numbers are declining. We found no evidence for loss of heterozygosity in any of the populations studied. Genetic diversity was comparable across sites, in line with published levels for mainland Europe. However, further analysis revealed a striking level of relatedness. Genetic networks constructed from inferred first degree relationships suggested a high proportion of individuals to be related at a level equivalent to that of half-siblings, with rare inferred full-sib dyads. These patterns of relatedness can be attributed to the high philopatry and low vagility of adders, which creates high local relatedness, in combination with the polyandrous breeding system in the adder, which may offset the risk of inbreeding in closed populations. We suggest that reliance on standard genetic indicators of inbreeding and diversity may underestimate demographic and genetic factors that make adder populations vulnerable to extirpation. We stress the importance of an integrated genetic and demographic approach in the conservation of adders, and other taxa of similar ecology
Linear optical properties of one-dimensional Frenkel exciton systems with intersite energy correlations
We analyze the effects of intersite energy correlations on the linear optical
properties of one-dimensional disordered Frenkel exciton systems. The
absorption line width and the factor of radiative rate enhancement are studied
as a function of the correlation length of the disorder. The absorption line
width monotonously approaches the seeding degree of disorder on increasing the
correlation length. On the contrary, the factor of radiative rate enhancement
shows a non-monotonous trend, indicating a complicated scenario of the exciton
localization in correlated systems. The concept of coherently bound molecules
is exploited to explain the numerical results, showing good agreement with
theory. Some recent experiments are discussed in the light of the present
theory.Comment: 18 pages, 3 figues, REVTeX, to appear in Physical Review
Stability of Polymer:PCBM Thin Films under Competitive Illumination and Thermal Stress
The combined effects of illumination and thermal annealing on the morphological stability and photodimerization in polymer/fullerene thin films are examined. While illumination is known to cause fullerene dimerization and thermal stress their dedimerization, the operation of solar cells involves exposure to both. The competitive outcome of these factors with blends of phenylâC61âbutyric acid methyl ester (PCBM) and polystyrene (PS), supported on PEDOT:PSS is quantified. UVâvis spectroscopy is employed to quantify dimerization, timeâresolved neutron reflectivity to resolve the vertical composition stratification, and atomic force microscopy for demixing and coarsening in thin films. At the conventional thermal stress test temperature of 85 °C (and even up to the PS glass transition), photodimerization dominates, resulting in relative morphological stability. Prior illumination is found to result in improved stability upon high temperature annealing, compatible with the need for dedimerization to occur prior to structural relaxation. Modeling of the PCBM surface segregation data suggests that only PCBM monomers are able to diffuse and that illumination provides an effective means to control dimer population, and thus immobile fullerene fraction, in the timescales probed. The results provide a framework for understanding of the stability of organic solar cells under operating conditions
Kinetics of photoelectrochemical oxidation of methanol on hematite photoanodes
The kinetics of photoelectrochemical (PEC) oxidation of methanol, as a model organic substrate, on α-Fe2O3 photoanodes are studied using photoinduced absorption spectroscopy and transient photocurrent measurements. Methanol is oxidized on α-Fe2O3 to formaldehyde with near unity Faradaic efficiency. A rate law analysis under quasi-steady-state conditions of PEC methanol oxidation indicates that rate of reaction is second order in the density of surface holes on hematite and independent of the applied potential. Analogous data on anatase TiO2 photoanodes indicate similar second-order kinetics for methanol oxidation with a second-order rate constant 2 orders of magnitude higher than that on α-Fe2O3. Kinetic isotope effect studies determine that the rate constant for methanol oxidation on α-Fe2O3 is retarded âŒ20-fold by H/D substitution. Employing these data, we propose a mechanism for methanol oxidation under 1 sun irradiation on these metal oxide surfaces and discuss the implications for the efficient PEC methanol oxidation to formaldehyde and concomitant hydrogen evolution
Diamond Mirrors for High-Power Lasers
High-power lasers have numerous scientific and industrial applications. Some
key areas include laser cutting and welding in manufacturing, directed energy
in fusion reactors or defense applications, laser surgery in medicine, and
advanced photolithography in the semiconductor industry. These applications
require optical components, in particular mirrors, that withstand high optical
powers for directing light from the laser to the target. Ordinarily, mirrors
are comprised of multilayer coatings of different refractive index and
thickness. At high powers, imperfections in these layers lead to absorption of
light, resulting in thermal stress and permanent damage to the mirror. Here we
design, simulate, fabricate, and demonstrate monolithic and highly reflective
dielectric mirrors which operate under high laser powers without damage. The
mirrors are realized by etching nanostructures into the surface of
single-crystal diamond, a material with exceptional optical and thermal
properties. We measure reflectivities of greater than 98% and demonstrate
damage-free operation using 10 kW of continuous-wave laser light at 1070 nm,
with intensities up to 4.6 MW/cm2. In contrast, at these laser powers, we
observe damage to a standard dielectric mirror based on optical coatings. Our
results initiate a new category of broadband optics that operate in extreme
conditions
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