The general principles of cation binding to humic matter and the various aspects of modeling used in general-purpose speciation programs are discussed. The discussion will focus on (1) the ...discrimination between chemical and electrostatic interactions, (2) the binding site heterogeneity, (3) the models for the electrostatic interactions, such as the Donnan model and (4) the complications inherent to ion binding in multi-component systems, including a different stoichiometry for different ions. The basic NICA (non ideal competitive adsorption) model addresses issues (1), (2) and (4) and ensures thermodynamic consistency. The electrostatic interactions (3) can be included using the ion activity adjacent to the binding sites. To compute this activity it is necessary to use an electrostatic model that relates the particle charge and the characteristic particle potential. Several simplifications to arrive at such a relation are analyzed. The Donnan model is proposed as the most convenient model. A short derivation of the NICA–Donnan model is presented to illustrate that the derivation is quite straightforward once it is clear which assumptions should be made. The main parameters of the NICA model are the site density, the median affinity constants for the different ions, the ion stoichiometry and the width of the generic affinity distribution. All these parameters are intrinsic properties that are independent of pH, salt concentration or metal concentration. The key parameter of the Donnan model is the Donnan volume, for which an empirical relation with one adjustable parameter is advised. The NICA–Donnan model has been used in several studies. To illustrate the capabilities of the model some results obtained for purified humic acid are presented together with model predictions. Key features of the model are its ability to adjust to different heterogeneities and binding stoichiometries and its predictive abilities with respect to metal ion–proton and metal–metal ion competition. With the application the model should be regarded as semi-empirical because assumptions have been made for its derivation that are not met in practice. Both for this reason and since it is difficult, if not impossible, to find a unique set of parameters for a given system the interpretation of the parameter values may be difficult. A brief discussion is given on the generic NICA–Donnan description of fulvic and humic acids presented by Milne et al. C.J. Milne, D.G. Kinniburgh, E. Tipping, Environ. Sci. Technol. 35 (2001) 2049; C.J. Milne, D.G. Kinniburgh, W.H. van Riemsdijk, E. Tipping, Environ. Sci. Technol. 37 (2003) 958. Finally a brief literature review is presented on the use of the NICA–Donnan model for other heterogeneous natural sorbent systems.
We study the gauge-invariant ideal structure of the Nica-Toeplitz algebra
N
T
(
X
)
of a product system (
A
,
X
) over
N
n
. We obtain a clear description of
X
-invariant ideals in
A
, that is, ...restrictions of gauge-invariant ideals in
N
T
(
X
)
to
A
. The main result is a classification of gauge-invariant ideals in
N
T
(
X
)
for a proper product system in terms of families of ideals in
A
. We also apply our results to higher-rank graphs.
Knowledge of the speciation of heavy metals and the role of dissolved organic matter (DOM) in soil solution is a key to understand metal mobility and ecotoxicity. In this study, soil column-Donnan ...membrane technique (SC-DMT) was used to measure metal speciation of Cd, Cu, Ni, Pb, and Zn in eighteen soil solutions, covering a wide range of metal sources and concentrations. DOM in these soil solutions was also fractionated into humic acid (HA), fulvic acid (FA), hydrophilic acid (Hy), and hydrophobic neutral organic matter (HON) by a rapid batch technique using DAX-8 resin. Our results show that in soil solution Pb and Cu are dominant in complex form, whereas Cd, Ni and Zn mainly exist as free ions; for the whole range of soil solutions, only 26.2% of DOM is humic substances and consists mainly of fulvic acid (FA). The metal speciation measured by SC-DMT was compared to the predicted ones obtained via the NICA-Donnan model using the measured FA concentrations. The free ion concentrations predicted by speciation modeling were in good agreement with the SC-DMT measurement. Moreover, we show that to make accurate modeling of metal speciation in soil solutions, the knowledge of DOM composition, especially FA fraction, is the crucial information, especially for Cu and Cd; like in previous studies the modeling of Pb speciation is not optimal and an update of Pb generic binding parameters is required to reduce model prediction uncertainties.
•Only 26.2% of dissolved organic matter (DOM) in soil solutions is humic substances.•Fulvic acid is the most important fraction for metal binding in soil solutions.•Hydrophilic acid accounts for 68.2% of DOM, but has negligible effect on metal speciation.•Pb generic binding parameters in NICA-Donnan model need to be updated.
The NICA (Nuclotron-based Ion Collider fAcility) project is under realization at the Joint Institute for Nuclear Research (JINR, Dubna). The main goal of the project is a study of hot and dense ...strongly interacting matter in heavy ion collisions (up to Au) in the energy range up to sNN=11 GeV. Two modes of operation are foreseen, collider and extracted beam operations, with two detectors: MPD and BM@N. In the Au + Au collider mode the expected average luminosity is L=1027cm−2s−1. The proposed experimental program allows one to search for possible manifestations of the phase transitions and critical phenomena.
The project NICA (Nuclotron-based Ion Collider fAcility) is aimed to study hot and baryon rich QCD matter in heavy ion collisions in the energy range up to sNN=11GeV. The heavy ion program includes a ...study of collective phenomena, dilepton, hyperon and hypernuclei production under extreme conditions of highest baryonic density. This program will be performed at a fixed target experiment BM@N and with MPD detector at the NICA collider.
The anisotropic flow is one of the important observables sensitive to the equation of state (EOS) and transport properties of the strongly interacting matter created in relativistic heavy-ion ...collisions. In this work, we report a detailed multi-differential study of the directed ( v1 ), elliptic ( v2 ), triangular ( v3 ), and quadrangular ( v4 ) flow coefficients of protons in relativistic heavy-ion collisions at sNN = 2.2–4.5 GeV using several hadronic transport models. Recent published results for Au + Au collisions at sNN = 2.4 GeV from HADES experiment and at sNN = 3.0 GeV from the STAR experiment have been used for comparison. The study motivates further experimental investigations of the anisotropic collective flow of protons and neutrons in a high baryon density region.
A cosystem consists of a possibly nonselfadoint operator algebra equipped with a coaction by a discrete group. We introduce the concept of C*-envelope for a cosystem; roughly speaking, this is the ...smallest C*-algebraic cosystem that contains an equivariant completely isometric copy of the original one. We show that the C*-envelope for a cosystem always exists and we explain how it relates to the usual C*-envelope. We then show that for compactly aligned product systems over group-embeddable right LCM semigroups, the C*-envelope is co-universal, in the sense of Carlsen, Larsen, Sims and Vittadello, for the Fock tensor algebra equipped with its natural coaction. This yields the existence of a co-universal C*-algebra, generalizing previous results of Carlsen, Larsen, Sims and Vittadello, and of Dor-On and Katsoulis. We also realize the C*-envelope of the tensor algebra as the reduced cross sectional algebra of a Fell bundle introduced by Sehnem, which, under a mild assumption of normality, we then identify with the quotient of the Fock algebra by the image of Sehnem's strong covariance ideal. In another application, we obtain a reduced Hao-Ng isomorphism theorem for the co-universal algebras.
Let (G,P) be an abelian, lattice ordered group and let X be a compactly aligned product system over P with coefficients in A. We show that the C*-envelope of the Nica tensor algebra NTX+ coincides ...with both Sehnem's covariance algebra A×XP and the co-universal C⁎-algebra NOXr for injective, gauge-compatible, Nica-covariant representations of Carlsen, Larsen, Sims and Vittadello. We give several applications of this result on both the selfadjoint and non-selfadjoint operator algebra theory. First we guarantee the existence of NOXr, thus settling a problem of Carlsen, Larsen, Sims and Vittadello which was open even for abelian, lattice ordered groups. As a second application, we resolve a problem posed by Skalski and Zacharias on dilating isometric representations of product systems to unitary representations. As a third application we characterize the C⁎-envelope of the tensor algebra of a finitely aligned higher-rank graph which also holds for topological higher-rank graphs. As a final application we prove reduced Hao-Ng isomorphisms for generalized gauge actions of discrete groups on C⁎-algebras of product systems. This generalizes recent results that were obtained by various authors in the case where (G,P)=(Z,N).
Let P be a unital subsemigroup of a group G. We propose an approach to C⁎-algebras associated to product systems over P. We call the C⁎-algebra of a given product system E its covariance algebra and ...denote it by A×EP, where A is the coefficient C⁎-algebra. We prove that our construction does not depend on the embedding P↪G and that a representation of A×EP is faithful on the fixed-point algebra for the canonical coaction of G if and only if it is faithful on A. We compare this with other constructions in the setting of irreversible dynamical systems, such as Cuntz–Nica–Pimsner algebras, Fowler's Cuntz–Pimsner algebra, semigroup C⁎-algebras of Xin Li and Exel's crossed products by interaction groups.
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