1,133 research outputs found
Strong complexation of lead(II) by fulvic substances under environmental relevant conditions
No full textBecause of the high concern of lead(II) in the environment, its speciation had been largely investigated in the past years. Different ligands of lead(II) can be present in natural waters ranging from inorganic anions, often at high concentration (chloride, carbonate) with side reaction coefficient around 30
(1), to very strong complexing sites present in NOM (natural organic matter). Side reaction coefficients of lead(II) slightly higher than those for inorganic ligands have been reported for humic substances (2). These sites are at low concentration but display a high complexation strength. Consequently they will be the first to take up the metal, while the weaker sites contribute to complexation only at higher total metal concentrations.
Stronger lead(II) ligands have been detected in natural waters using a method with detection window much higher than the usual ones, based on the partition of the metal ion on complexing resins (3). Side reaction coefficients as high as about 106 were evaluated in natural waters. A similar method (4) was here used to determine the complexing properties for lead(II) of a fulvic acid extracted from a sediment (FA), at low concentration, 10-500 nM. It is based on the sorption of lead(II) on the ionexchange
complexing resins Chelex 100 and Amberlite CG 50.
In the FA at pH around neutrality strong complexation sites of lead(II) were detected, with concentration 2 10-3 mmol g-1-0.04 mmol g-1 similar to that determined by other methods (2), but conditional complexation constant as high as log K=13-15, much higher than that previously obtained, but similar to those found in natural waters (3). These sites heavily determine the lead(II) complexation since the metal in natural waters is present at nM
level. A large influence of the solution pH on the complexing properties of the strong ligands has been found. On the other hand, using an ion exchange resin (Dowex 50W-X8) with lower detection window, lead(II) ligands with lower side reaction coefficient, near to that determined in previous investigations (2), were detected.
(1) D. Turner, M. Whitfield, A.G. Dickson, Geochim. Cosmochim. Acta, 45 (1981) 855-874.
(2) M. Filella, R.M. Town, Sci. Tot. Environ. 300 (2002) 143–154.
(3) G. Alberti, R. Biesuz, M. Pesavento, Anal. Sci. 24 (2008) 1605-1611.
(4) M. Pesavento, A. Profumo, R. Biesuz, G. Alberti, Solv. Extr.Ion Exch. 26 (2008) 301-320.
(5) R. Biesuz, G. Alberti, M. Pesavento, J. Sol. Chem. 37 (2008) 527–541
CHIAPPINI, L.; MARTINS, M. H.; PESAVENTO, S. J. (Orgs.) Pampa e Cultura: de Fierro a Netto.
No full textCHIAPPINI, L.; MARTINS, M. H.; PESAVENTO, S. J. (Orgs.) Pampa e Cultura: de Fierro a Netto. PortoAlegre: Editora da UFRGS / Instituto Estadual do Livro, 2004. 285p.Resenhado por: Andrea Cristiane Kahman
Near-Optimal Unit Root Tests with Stationary Covariates with Better Finite Sample Size
No full textNumerous tests for integration and cointegration have been proposed in the literature. Since Elliott, Rothemberg and Stock (1996) the search for tests with better power has moved in the direction of finding tests with some optimality properties both in univariate and multivariate models. Although the optimal tests constructed so far have asymptotic power that is indistinguishable from the power envelope, it is well known that they can have severe size distortions in finite samples. This paper proposes a simple and powerful test that can be used to test for unit root or for no cointegration when the cointegration vector is known. Although this test is not optimal in the sense of Elliott and Jansson (2003), it has better finite sample size properties while having asymptotic power curves that are indistinguishable from the power curves of optimal tests. Similarly to Hansen (1995), Elliott and Jansson (2003), Zivot (2000), and Elliott, Jansson and Pesavento (2005) the proposed test achieves higher power by using additional information contained in covariates correlated with the variable being tested. The test is constructed by applying Hansen’s test to variables that are detrended under the alternative in a regression augmented with leads and lags of the stationary covariates. Using local to unity parametrization, the asymptotic distribution of the test under the null and the local alternative is analytically computed.Unit Root Test, GLS detrending.
«Giornale Iuav» n. 57, Architettura della costruzione
No full textLa strategia formativa del biennio di Architettura della Costruzione poggia su un assunto di fondo: l’architettura (cultura e prassi) deve perseguire una sintesi tra l’approfondirsi in se stessa e la realizzazione di un compito e uno scopo pubblici: un’antinomia imprescindibile, intellettualmente e tecnicamente, che rende l’architettura essenzialmente difficile (secondo un’efficace locuzione di Nicola Emery). Praticare la didattica dell’architettura entro questo antitetico binomio non significa assolutamente adeguare-ridurre la formazione a standard professionali correnti, ecc.: è perseguire l’autonomia di una cultura progettuale (ideazione e costruzione) fortemente connessa alla materialità del problema-progetto (bisogni-vincoli-risorse), è orientare la trasmissione di saperi e competenze secondo un modo di intendere la forma in architettura
La mostra conclusiva dei Workshop
No full textil testo precede la sezione dedicata alla grande esposizione collettiva, sommatoria di singoli allestimenti, sforzo corale di studenti, collaboratori, docenti di dare risposte a temi attuali, condivisi da un progetto culturale, che si fa sempre più evidente all'interno della far: l'apertura della Scuola verso il mondo esterno, qualunque esso sia, con offerte di gran lunga superiori alle domande e proposte di scenari caratterizzati da un alto profilo culturale e di qualità.
La mostra collettiva, vera biennale ma annuale, occupa tutti gli spazi didattici dell'Iuav: exCotonificio e Terese, calli e ponti compresi. Con questo numero inauguriamo una sezione dedicata alle singole mostre, così come con questa edizione abbiamo inaugurato il Giornale dei workshop
Resine poli(ammido-amminiche): sintesi e studio degli equilibri di protonazione e complesso-formazione verso il Cu(II)
No full textHigh selectivity and sensitivity sensor based on MIP and SPR in tapered plastic optical fibers for the detection of l-nicotine
No full textA biomimetic sensor based on molecularly imprinted polymer (MIP) and surface plasmon resonance(SPR) transduction, in connection with tapered plastic optical fiber (POF), has been developed for themarker-free, direct and selective detection of low molecular weight substances. The device has beenexperimentally tested for l-nicotine ((−)-1-methyl-2-(3-pyridyl)pyrrolidine, MW = 162.24). The sensorsystem developed made the selective and fast detection of l-nicotine possible, with a low cost, easy torealize and small sample volume procedure. The sensor can discriminate between l- and d-nicotine. Thelinearity range was from 0 to 10−3M, and the sensitivity strongly depended on the characteristics of thetapered fiber, ranging from 1.3 × 104nm/M, for a taper ratio 1.8, to 1.7 × 103nm/M for a taper ratio 1, i.e.a not-tapered fiber
General procedure for the determination of trace amounts of iodine in natural water samples of unknown composition by spectrophotometric titration
No full textIodine in -1 oxidation state is oxidized by iodate, and the titration is monitored spectrophotometrically. Total iodine concentration is obtained by previous reduction. Interferences from oxidizing and reducing substances are eliminated. The reaction is favoured in solution at high chloride concentration. Iodine at very low concentration level (2 10^(-7) M) can be titrated in complex matrices
Modelling of hydro-thermo-chemo-mechanical phenomena in building materials
No full textA general approach to modelling chemical degradation processes in building materials, due to combined action of variable hydrothermal, chemical and mechanical
loads, is presented. Mechanics of multiphase porous media and damage mechanics are applied for this purpose, and kinetics of degradation processes is described with evolution equations based on thermodynamics of chemical reactions. The mass-, energy - and momentum balances, as well as the evolution equations, constitutive and physical relations are briefly summarized. Then, the model governing equations are numerically solved with the finite element method. Three examples of the model application for analyzing degradation processes of building materials are presented and discussed. The first one deals with capillary suction of the salt solution by two different building materials, the second one with the salt crystallization during drying of a brick wall, and the third one concerns calcium leaching from a concrete wall due to the chemical attack of pure water under pressure gradient at two different temperatures
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