Eutrophication, phytoplankton dynamics and nutrient removal in two man-made urban lakes (Palácio de Cristal and Serralves), Porto, Portugal

Urban lakes are prone to eutrophication because of a number of factors, including a high water residence time (slow flushing rate), and high nutrient loads from artificial feeding of waterfowl and fish by visitors and from waterfowl faeces, falling leaves and nutrient run‐off from adjacent areas. This study focuses on the ecology of two similar‐sized urban lakes in Porto, Portugal, that exhibit some differing characteristics conducive to different trophic states and nutrient removal efficiencies. Although similar in many aspects, the two reservoirs developed quite diverse phytoplankton communities. The higher nitrogen load to Palácio de Cristal Lake could be the result of the higher concentration in its underground influent stream, while a less‐oxidized nitrogen form (ammonia) is higher in Serralves Lake. Nitrate concentrations are higher in Palácio de Cristal Lake than in Serralves as a result mainly of high nitrate loads (maximum values above 80 mg L⁻¹) in its influent stream. Interestingly, however, its nitrate removal efficiency is greater than for Serralves Lake. Cyanobacteria are the dominal phytoplankton In both lakes throughout the year. However, only one genus of this group (Pseudoanabaena mucicola) was the dominant phytoplankton in Palácio de Cristal Lake, while five Cyanobacteria species co‐dominated in Serralves lake. Regular monitoring of Cyanobacteria and their toxins in urban recreation lakes is advised.     

Dynamic Viscosity Modeling of Methane n-Decane and Methane Toluene Mixtures : Comparative Study of Some Representative Models

Viscosity measurements of well-defined mixtures are useful in order to evaluate existing viscosity models. Recently, an extensive experimental study of the viscosity at pressures up to 140 MPa has been carried out for the binary systems methane + n-decane and methane + toluene, between 293.15 and 373.15 K and for several methane compositions. Although very far from real petroleum fluids, these mixtures are interesting in order to study the potential of extending various models to the simulation of complex fluids with asymmetrical components (light/heavy hydrocarbon). These data (575 data points) have been discussed in the framework of recent representative models (hard sphere scheme, friction theory, and free volume model) and with mixing laws and two empirical models (particularly the LBC model which is commonly used in petroleum engineering, and the self-referencing model). This comparative study shows that the average absolute deviation of the models is between 3.8 and 49.8%, and the maximum deviation is between 11.6 and 78.4%, depending on the considered model.     

L2F anemometry measurements of the inter-row flow field within a transonic axial compressor provided with curved windows

INTRODUCTIONMultibladerowcalculationscanbeperformedusingsteady3DNScodesprovidedthatassumptionsaremadeforthecouplingofbladerows.Thesocalledmixing--planeapproachneedsthetangentialaveragesofflowquantitiesattheinterfaceplanebetweenadjacentbladerows.Butth...     

Manufacture of bioactive peptide-rich concentrates from Whey: Characterization of pilot process

This work was focused on the manufacture, at pilot scale, of cow whey protein and peptide concentrates, using selective filtration techniques—associated with hydrolysis brought about by proteolytic enzymes from Cynara cardunculus aqueous extracts, using as (optimal) conditions an enzyme/substrate ratio of 1.6% v/v, a pH of 5.2, a temperature of 55 °C and an incubation time of 7 h. The profiles of proteins and peptides were assessed by liquid chromatography and electrophoresis; ca. 87% of α-lactalbumin was hydrolyzed, but essentially no degradation of β-lactoglobulin (β-Lg) was observed. A bioactive peptide concentrate, its fraction below 3 kDa and a β-Lg-rich fraction were obtained as final products, containing ca. 73, 43 and 91% w/w protein (on a total solid mass basis). All these fractions were low in lactose and salt, and their microbial loads were reduced. Said fractions are high added-value products, so they can be used as nutritional and functional ingredients—thus yielding an economically viable alternative for upgrade of whey.     

A simplified approach for sheet forming processes design

A new approach is developed to improve sheet forming parts and sheet forming processes design. In order to apply classical optimization methods, an energetic characterization of the global transformation of an elasto-plastic structure is proposed. After a brief review of thermostatics in elastoplastic laws, an energetic criterion is defined. With a geometrical definition of sheet forming processes, it is shown how to use this criterion to find the optimal displacement path between a flat blank and the part shape. Then, the classical assumptions of rigid-plastic behaviour and of thin shell geometry are introduced. Eventually, the criterion is used to define a formability criterion, for use at the preliminary design stage of parts. This paper concludes with numerical applications of the approach and analysis of formability criterion applications.     

Effect of different levels of CO2 on the antioxidant content and the polyphenol oxidase activity of ‘Rocha’ pears during cold storage

Pears (Pyrus communis L. cv. ‘Rocha’) were exposed to air or controlled atmosphere (CA) containing various concentrations of CO₂: 0, 0.5 and 5 kPa, all with 2 kPa O₂. After 4 months of storage at 2 °C, the fruits were transferred to air at room temperature, and assessed in terms of soluble solids, titratable acidity, pH, incidence of brown heart and flesh browning, phenolic content, vitamin C content and polyphenol oxidase activity. By 4 months of storage, soluble solids and pH increased, and acidity decreased relative to harvest, but no differences were detected between pears stored under air or any of the CA tested. Higher contents of hydroxycinnamic derivatives and flavan‐3‐ols in the peel than in the flesh were recorded. However, the content of arbutin was higher in the flesh than in the peel, whereas flavonols were only detected in the peel. In general, hydroxycinnamic derivatives and flavonols were stable throughout storage, but flavan‐3‐ols decreased in concentration under air or CA. Arbutin was the only phenolic compound that increased in concentration as time elapsed. No clear relation was found between the storage conditions tested and the phenolic concentration in pears. Regarding ascorbic acid (AA) and dehydroascorbic acid (DHA), their concentrations were higher in the peel than in the flesh. Furthermore, AA and DHA were strongly affected by storage: the former decreased, whereas the latter increased in content. A decrease in PPO activity was apparent after harvest and during storage, particularly under higher levels of CO₂. The combination 2 kPa O₂ + 5 kPa CO₂ increased the incidence of internal disorders (viz. brown heart and flesh browning) after storage. Copyright © 2005 Society of Chemical Industry     

XRD study of the grain growth in CdTe films annealed at different temperatures

The CdTe thin films electrodeposited on stainless steel substrates were annealed in air at various temperatures and time durations in order to investigate the influence of post-deposition heat treatments on the grain growth of the films. The recrystallization process at lower annealing temperature is different from that of the high-temperature annealing. The annealing at lower temperature promotes better grain growth by maintaining the preference for the (1 1 1) plane. In general the grain size increases due to annealing and the recrystallization happens in three phases. The grain growth exponent is a function of temperature and time. In the beginning of the annealing, irrespective of the annealing temperatures the grain growth obeys the ideal parabolic law and for longer annealing times it deviates from the ideal case.     

HIx system thermodynamic model for hydrogen production by the Sulfur–Iodine cycle

The HI_x ternary system (H₂O–HI–I₂) is the latent source of hydrogen for the Sulfur–Iodine thermo-chemical cycle. After analysis of the literature data and models, a homogeneous approach with the Peng–Robinson equation of state used for both the vapor and liquid phase fugacity calculations is proposed for the first time to describe the phase equilibrium of this system. The MHV2 mixing rule is used, with UNIQUAC activity coefficient model combined with of hydrogen iodide solvation by water. This approach is theoretically consistent for HI_x separation processes operating above HI critical temperature. Model estimation is done on selected literature vapor–liquid, liquid–liquid, vapor–liquid–liquid and solid–liquid equilibrium data for the ternary system and the three binaries subsystems. Validation is done on the remaining literature data. Results agree well with the published data, but more experimental effort is needed to improve modeling of the HI_x system.     

Bunsen section thermodynamic model for hydrogen production by the sulfur–iodine cycle

A model for the Bunsen section of the Sulfur–Iodine thermo-chemical cycle is proposed, where sulfur dioxide reacts with excess water and iodine to produce two demixing liquid aqueous phases (H₂SO₄ rich and HI rich) in equilibrium. Considering the mild temperature and pressure conditions, the UNIQUAC activity coefficient model combined with Engels' solvation model is used. The complete model is discussed, with HI solvation by water and by iodine as well as H₂SO₄ solvation by water, leading to a very high complexity with almost hundred parameters to be estimated from experimental data. Taking into account the water excess, a successful reduced model with only 15 parameters is proposed after defining new apparent species. Acids total dissociation and total H⁺ solvation by water are the main assumptions. Results show a good agreement with published experimental data between 25 °C and 120 °C.