Effectiveness factor for immobilized biocatalysts: two substratestwo products reactions

Immobilized enzymes are being increasingly used as biocatalysts in numerous processes to obtain high-value products for the pharmaceutical, flavour and fragrance industries (Gandhi et al., 2000). The major advantages of immobilization include the increase in enzyme stability, the possibility of enzyme reutilization and the easy separation of the biocatalysts from the reaction mixture. However, it is necessary to account for mass transfer limitations that, under some conditions, may arise in these systems (Gómez et al., 2003; Jeison et al., 2003). These resistances comprise the effects of intraparticle diffusion and external mass-transfer. Given the complexity of the kinetics of multisubstrate enzyme reactions, reactor modelling studies that account for mass-transfer phenomena are so far limited to single-substrate ones (Gómez et al., 2003). To compare the observed reaction rate with the reaction rate in the absence of mass-transfer limitations, an overall effectiveness factor is usually calculated (Gómez et al., 2003; Jeison et al., 2003). In this work, a model is developed to calculate the overall effectiveness factor for immobilized enzymes that carry out irreversible two substrates-two products reactions following kinetic mechanisms such as the Ternary Complex or the Ping-Pong Bi-Bi with inhibition by the second substrate. The model has two dimensionless parameters for each substrate – Thiele modulus (reaction/intraparticle diffusion), Biot number (film diffusion/intraparticle diffusion) – and one related to the reaction kinetics. Their influence on the effectiveness factor is analysed. The results obtained can be applied in the design and simulation of enzymatic reactors

Direct current control of an active power filter for harmonic elimination, power factor correction and load unbalancing compensation

An active power filter is designed, simulated, implemented, and tested. It can work in different modes: active power filtering, power factor correction, and load unbalance compensation. It is based on a current controlled voltage-source inverter with fixed carrier PWM. The control algorithm generates the source reference currents based on the controlled DC link voltage. The dimensioning criteria of the inductive and capacitive power components is discussed. The implementation is validated with simulated and experimental results obtained in a 5 kVA prototype

Pressure and chemical substitution effects in the local atomic structure of BaFe2As2

The effects of K and Co substitutions and quasi-hydrostatic applied pressure (P<9 GPa) in the local atomic structure of BaFe2As2, Ba(Fe{0.937}Co{0.063})2As2 and Ba{0.85}K{0.15}Fe2As2 superconductors were investigated by extended x-ray absorption fine structure (EXAFS) measurements in the As K absorption edge. The As-Fe bond length is found to be slightly reduced (<~ 0.01 Angstroms) by both Co and K substitutions, without any observable increment in the corresponding Debye Waller factor. Also, this bond is shown to be compressible (k = 3.3(3)x10^{-3} GPa^{-1}). The observed contractions of As-Fe bond under pressure and chemical substitutions are likely related with a reduction of the local Fe magnetic moments, and should be an important tuning parameter in the phase diagrams of the Fe-based superconductors.Comment: 7 pages, 6 figure

Investigação no âmbito da utilização de materiais compósitos no reforço de estruturas de betão

Nos últimos anos tem sido crescente a utilização de materiais compósitos no reforço de estruturas de betão armado. Para tal contribui as melhores propriedades mecânicas destes materiais, a sua maior resistência à acção de agentes agressivos e a sua maior leveza e facilidade de aplicação, quando se tem por base de comparação materiais convencionais tais como o aço e o betão. No Subgrupo de Estruturas do Departamento de Engª Civil da Escola de Engª da Universidade do Minho tem-se efectuado investigação experimental e numérica no âmbito da utilização de laminados em fibra de carbono (CFRP) no reforço de estruturas de betão. Estes materiais compósitos têm sido utilizados no reforço à flexão e ao corte de pilares e vigas. A ligação CFRP-adesivo-betão tem sido caracterizada por forma a ser estabelecida a lei que define a transferência de tensões entre os materiais constituintes desta ligação, lei esta a ser implementada num modelo de interface, no quadro do método dos elementos finitos. Os resultados mais significativos obtidos na investigação efectuada são apresentados no presente trabalho

Near surface mounted CFRP-based technique for the strengthening of concrete structures

To assess the effectiveness of the Near Surface Mounted (NSM) strengthening technique, an experimental program was carried out involving reinforced concrete (RC) columns and beams. In columns failing in bending the present work shows that the failure strain of the Carbon Fiber Reinforced Polymer (CFRP) laminates can be attained using the NSM technique. Beams failing in bending were also strengthened with CFRP laminates in order to double their load carrying capacity. This goal was attained and maximum strain levels of about 90% of the CFRP failure strain were recorded. Performance of externally bonded reinforcing (EBR) and NMS techniques was compared for strengthening RC beams failing in shear. NMS was much more effective, not only in terms of the increase of the load carrying capacity and deformability at beam failure, but also with respect to the time consuming nature of the corresponding strengthening procedures. To assess the bond behavior of CFRP to concrete, pulloutbending tests were carried out. The influences of bond length and concrete strength on the bond behavior were analyzed.S&P®. Bettor MBT® Portugal. Secil. Nordesfer. Ferseque. Casais. Solusel. VSL. Unibetão (Braga). Cemacom

Nova abordagem no reforço de estruturas com materiais compósitos

Neste trabalho apresentam-se os resultados mais significativos da investigação experimental realizada para avaliar o desempenho de uma técnica de reforço baseada na fixação de laminados de CFRP em ranhuras efectuadas no betão de recobrimento de elementos estruturais. Com esta técnica foram reforçados e ensaiados elementos de pilar e de viga de betão armado com rotura por flexão, e vigas de betão armado com rotura por corte. De modo a caracterizar a ligação betão-adesivo-CFRP procedeu-se à realização de ensaios de aderência

Production of esters by biocatalysed transesterification in supercritical CO2 and Hexane

The development of sustainable processes that use renewable raw materials and minimize chemical and energetic waste has attracted considerable attention and represents a great challenge to both academic researchers and industrial experts. The use of enzymes to catalyse chemical transformations can constitute a more sustainable alternative to some traditional chemical processes and more than 100 biotransformations are already operated at an industrial scale [1]. Lipases usually operate in mild conditions and can catalyse both hydrolytic and synthetic reactions, depending on the surrounding medium. The hydrolysis of esters can be performed in water, but the reverse production reactions are not favoured in this medium, and are usually performed in organic solvents. Supercritical CO2 can constitute a more sustainable alternative to organic solvents as a reaction medium, provided that it does not have a direct adverse effect on the enzyme's active site or significantly reduce its activity. Decyl acetate was chosen as a model compound and its production by a transesterification reaction catalysed by Novozym 435 (immobilized Candida Antarctica Lipase B) was studied in both hexane and supercritical CO2. A comparative analysis between these two alternatives was performed, focusing on the differences on the enzyme's catalytic activity, solubilities of the substrates and mass transfer rates; which significantly affect the outcome of the reaction process and its productivity and provide information on when such solvents can be used. [1] Straathof, A.J.J., Panke, S., Schmid, A. The production of fine chemicals by biotransformations. Current Opinion in Biotechnology, 2002, 13(6), 548-556

The effects of auditory stimulation with music on heart rate variability in healthy women

OBJECTIVES: There are no data in the literature with regard to the acute effects of different styles of music on the geometric indices of heart rate variability. In this study, we evaluated the acute effects of relaxant baroque and excitatory heavy metal music on the geometric indices of heart rate variability in women. METHODS: We conducted this study in 21 healthy women ranging in age from 18 to 35 years. We excluded persons with previous experience with musical instruments and persons who had an affinity for the song styles. We evaluated two groups: Group 1 (n = 21), who were exposed to relaxant classical baroque musical and excitatory heavy metal auditory stimulation; and Group 2 (n = 19), who were exposed to both styles of music and white noise auditory stimulation. Using earphones, the volunteers were exposed to baroque or heavy metal music for five minutes. After the first music exposure to baroque or heavy metal music, they remained at rest for five minutes; subsequently, they were re-exposed to the opposite music (70-80 dB). A different group of women were exposed to the same music styles plus white noise auditory stimulation (90 dB). The sequence of the songs was randomized for each individual. We analyzed the following indices: triangular index, triangular interpolation of RR intervals and Poincaré plot (standard deviation of instantaneous beat-by-beat variability, standard deviation of the long-term RR interval, standard deviation of instantaneous beat-by-beat variability and standard deviation of the long-term RR interval ratio), low frequency, high frequency, low frequency/high frequency ratio, standard deviation of all the normal RR intervals, root-mean square of differences between the adjacent normal RR intervals and the percentage of adjacent RR intervals with a difference of duration greater than 50 ms. Heart rate variability was recorded at rest for 10 minutes. RESULTS: The triangular index and the standard deviation of the long-term RR interval indices were reduced during exposure to both music styles in the first group and tended to decrease in the second group whereas the white noise exposure decreased the high frequency index. We observed no changes regarding the triangular interpolation of RR intervals, standard deviation of instantaneous beat-by-beat variability and standard deviation of instantaneous beat-by-beat variability/standard deviation in the long-term RR interval ratio. CONCLUSION: We suggest that relaxant baroque and excitatory heavy metal music slightly decrease global heart rate variability because of the equivalent sound level

Co-substitution effects on the Fe-valence in the BaFe2As2 superconducting compound: A study of hard x-ray absorption spectroscopy

The Fe K X-ray absorption near edge structure (XANES) of BaFe2-xCoxAs2 superconductors was investigated. No appreciable alteration in shape or energy position of this edge was observed with Co substitution. This result provides experimental support to previous ab initio calculations in which the extra Co electron is concentrated at the substitute site and do not change the electronic occupation of the Fe ions. Superconductivity may emerge due to bonding modifications induced by the substitute atom that weakens the spin-density-wave ground state by reducing the Fe local moments and/or increasing the elastic energy penalty of the accompanying orthorhombic distortion.Comment: 4+ pages, 4 figures. Published in Phys. Rev. Let