A low‐cost photovoltaic emulator for static and dynamic evaluation of photovoltaic power converters and facilities

In testing maximum power point tracking (MPPT) algorithms running on electronic power converters for photovoltaic (PV) applications, either a PV energy source (PV module or PV array) or a PV emulator is required. With a PV emulator, it is possible to control the testing conditions with accuracy so that it is the preferred option. The PV source is modeled as a current source; thus, the emulator has to work as a current source dependent on its output voltage. The proposed emulator is a buck converter with an average current mode control loop, which allows testing the static and dynamic performance of PV facilities up to 3 kW. To validate the concept, the emulator is used to evaluate the MPPT algorithm of a 230‐W experimental microinverter working from a single PV module. Copyright © 2012 John Wiley & Sons, Ltd.     

Reductive Amination Without the Aldehyde: Use of a Ketolactol as an Aldehyde Surrogate

To overcome stability issues associated with the use of an aldehyde in a catalytic reductive amination reaction, a cyclic ketolactol (ω-hydroxylactone) was employed as an aldehyde surrogate to form a γ-aminoacid. The reaction proceeded most favorably over a Pt/C catalyst. The thermodynamics of each step were evaluated using density functional theory calculations, which correctly predicted the dominance of the ring-closed lactol reactant, yet suggested a preference for a ring-opened iminium intermediate upon the initial, slightly endoergic addition of amine substrate. Exoergic hydrogenation of this intermediate provided the thermodynamic driving force for the overall transformation. During development, the reaction was observed to depend significantly on the volumetric gas to liquid mass transfer coefficient (k_La) and this parameter was optimized to ensure successful scale up in a 400 L stirred tank reactor.

     

Influence of Maternal Diet During Early Pregnancy on the Fatty Acid Profile in the Fetus at Late Pregnancy in Rats

The aim of the study was to determine the effects of different dietary fatty acids during the first half of pregnancy on the fatty acid composition of maternal adipose tissue and of maternal and fetal plasma at mid- and late-pregnancy. Pregnant rats received soybean-, olive-, fish-, linseed- or palm-oil diets from conception to day 12 of gestation. Virgin rats receiving the same treatments were studied in parallel. At day 12, some rats were sacrificed and others were returned to the standard diet and studied at day 20. At day 12, the concentrations of most fatty acids in plasma reflected the dietary composition and individual fatty acids in lumbar adipose tissue of pregnant rats correlated with those in the diet. At day 20, the plasma concentration of each fatty acid was higher in pregnant than in both virgin rats and day-12 pregnant rats. The composition in 20-day pregnant (but not in virgin) rats resembled the diet consumed during the first 12 days. Fatty acid concentration in fetal plasma was also influenced by the maternal diet during the first 12 days of pregnancy, and long-chain polyunsaturated fatty acid (LC-PUFA) concentrations correlated with those in the mothers. In conclusion, during the first half of pregnancy maternal adipose tissue stores dietary-derived fatty acids, which are released into blood during late pregnancy enabling LC-PUFA to become available to the fetus.     

A formalization of the demographic transition theory

Conclusion According to the transition theory, the transformation of an agricultural society into an industrial urbanized society is associated with a decline of the death rate and with a lagged decline of the birth rate. A variety of mathematical formulations of these trends are conceivable. In this paper, the following assumptions were adopted: (1) that the rate of change of the death rate is a maximum when the death rate is midway between an upper and a lower equilibrium level, and that it is the closer to zero, the closer the death rate is to the equilibrium levels, and (2) that the birth rate follows the death rate after a time lag. This formulation of the transition theory yields a doubly asymptotic population trend corresponding to a modified logistic curve.     

Metal distribution and metallothionein in loggerhead (Caretta caretta) and green (Chelonia mydas) sea turtles

The first aim of our study was to determine the concentrations of selected trace elements (Zn, Cu, Fe, Mn, Cd and Pb) in tissues of green turtles from Tortuguero National Park on the North Caribbean coast of Costa Rica and of loggerheads from the Mediterranean Sea. Zn, Cu, Fe, Mn and Cd were present at detectable concentrations in all samples and showed clear organotropism, whereas Pb was not always over the detection limit and did not show any particular tissue distribution. The two species presented significant differences: Cu and Cd in liver and kidney of Chelonia mydas were significantly higher with respect to the concentrations found in Caretta caretta. The second and major goal of our study was to evaluate hepatic and renal metallothionein (MT) as a biomarker of environmental metal exposure. The present paper is the first to describe and quantify MT in kidney and liver of loggerhead turtles and in kidney of green turtles. MT concentrations were higher in green than in loggerhead turtles. In addition, positive correlations were found between Cu and Cd concentrations and Cu-MT and Cd-MT in liver and kidney in both species, suggesting a pivotal role of MT in metal storage and detoxification. The quantification of metals and MT in liver and kidney may be a valid biomarker of metal exposure in the aquatic environment to assess the health of marine sea turtles as long as accurate analytical methods are adopted.     

Thermo and pH Sensitive Copolymer Based on Acrylic Acid and N-Isopropylacrylamide Grafted onto Polypropylene

Summary Binary graft copolymerization of pH sensitive of acrylic acid (AAc) and thermosensitive N-isopropylacrylamide (NIPAAm) monomers onto polypropylene films (PP), was carried out by two step method, and their pH and thermal sensitivity were studied. Graft polymerization of AAc onto PP was carried out by a pre-irradiation oxidative method using a ⁶⁰Co gamma radiation source (Gammabeam 651-PT, Nordion International Inc.) NIPAAm was grafted onto PP-g-AAc a second step. The influence of synthesis conditions, such as pre-irradiation dose, reaction time, monomer concentration, and reaction temperature was studied. The PP samples grafted with the binary monomers were characterized with thermogravimetric analysis and differential scanning calorimetry. The lower critical solution temperature (LCST) and pH critical were obtained by swelling and water contact angle determinaions.     

DNA-damaging disinfection byproducts: alkylation mechanism of mutagenic mucohalic acids

Hydroxyhalofuranones form a group of genotoxic disinfection byproduct (DBP) of increasing interest. Among them, mucohalic acids (3,4-dihalo-5-hydroxyfuran-2(5H)-one, MXA) are known mutagens that react with nucleotides, affording etheno, oxaloetheno, and halopropenal derivatives. Mucohalic acids have also found use in organic synthesis due to their high functionalization. In this work, the alkylation kinetics of mucochloric and mucobromic acids with model nucleophiles aniline and NBP has been studied experimentally. Also, the alkylation mechanism of nucleosides by MXA has been studied in silico. The results described allow us to reach the following conclusions: (i) based on the kinetic and computational evidence obtained, a reaction mechanism was proposed, in which MXA react directly with amino groups in nucleotides, preferentially attacking the exocyclic amino groups over the endocyclic aromatic nitrogen atoms; (ii) the suggested mechanism is in agreement with both the product distribution observed experimentally and the mutational pattern of MXA; (iii) the limiting step in the alkylation reaction is addition to the carbonyl group, subsequent steps occurring rapidly; and (iv) mucoxyhalic acids, the hydrolysis products of MXA, play no role in the alkylation reaction by MXA.     

Relationships between volatile composition and sensory evaluation in eight varieties of netted muskmelon (Cucumis melo L var reticulatus Naud)

The quality parameter of muskmelon (Cucumis melo L var reticulatus Naud) is often identified with the sugar content, particularly sucrose. However, high soluble solids concentration at harvest does not always correspond with high overall fruit quality and should be used in conjunction with the evaluation of aroma. In order to find quality indices, correlations were checked between aroma compounds detected on the melon pulp by headspace gas chromatography and sensory evaluation. Eight cultivars of muskmelon were analysed for their aroma content and other quality parameters. Aroma compounds were mainly esters, while (Z)‐6‐nonenal and (E)‐6‐nonenol, characteristic of melon, were not detected with the technique used. The data were subjected to statistical analyses in order to find significant correlations. High values of correlation were not found between chromatographic and sensory data, but a high correlation was found between total aromas and ethyl esters, both data of analytical source. This fact means that ethyl esters could be very important compounds for melon flavour and could be considered as markers of a good‐quality aroma. © 2002 Society of Chemical Industry