Heavy metal biosorption by bacterial cells

Microbial biomass provides available ligand groups on which metal ions bind by different mechanisms. Biosorption of these elements from aqueous solutions represents a remediation technology suitable for the treatment of metal-contaminated effluents. The purpose of the present investigation was the assessment of the capability of Brevibacterium sp. cells to remove bivalent ions, when present alone or in pairs, from aqueous solutions, using immobilized polyacrylamide cells of the microorganism in a flow-through system. The biosorption capacity of Brevibacterium cells was studied for lead, cadmium and copper. The metal cell binding capacity followed the order Cu > Pb > Cd, based on estimated q_max. These values, expressed as mmol metal/g dry weight cells, were 0.54 for Cu, 0.36 for Pb and 0.14 for Cd. Polyacrylamide-gel immobilized cells were effective in Pb, Cu and Cd removal. Lead removal was not affected by the presence of Cd and Cu; lead instead inhibited Cd and Cu removal. The desorption of the metal, by fluxing a chelating solution, restored the metal binding capacity of the cells, thus affording the multiple use of the same biomass in the remediation treatment. Received: 31 July 1997 / Revised: 22 December 1997 / Accepted: 30 December 1997     

Ditocopheryl Sulfides and Disulfides: Synthesis and Antioxidant Profile

Symmetrical ditocopheryl disulfides ( Toc ) ₂ S₂ and symmetrical and unsymmetrical ditocopheryl sulfides ( Toc )₂ S were simply prepared under remarkably mild conditions with complete control of the regiochemistry by using δ-, γ-, and β-tocopheryl-N-thiophthalimides ( Toc-NSPht ) as common starting materials. The roles of sulfur atom(s), H-bond and aryl ring substitution pattern on the antioxidant profile of these new compounds, which were assembled by linking together two tocopheryl units, are also discussed.     

MaxVaR with non-Gaussian distributed returns

The common fallacy in risk measurement throughout a long investment horizon is to handle only the terminal risk. This pathology affects Value-at-Risk, hence a recent contribution in the literature has proposed the concept of within-horizon risk as a solution to the problem. The quantification of this type of risk leads to the so called MaxVaR measure, but the assumption of Gaussian distributed returns biases this model. This study analyzes the consequences of non-Gaussian returns to the MaxVaR inference. An example of application to long-term risk management is provided.     

Monomial characters of finite solvable groups

Archiv der Mathematik - We give new evidence to the fact that the structure of a solvable group can be controlled by irreducible monomial characters. In particular, we inspect the role of monomial...     

A rod-airfoil experiment as a benchmark for broadband noise modeling

A low Mach number rod-airfoil experiment is shown to be a good benchmark for numerical and theoretical broadband noise modeling. The benchmarking approach is applied to a sound computation from a 2D unsteady-Reynolds-averaged Navier–Stokes (U-RANS) flow field, where 3D effects are partially compensated for by a spanwise statistical model and by a 3D large eddy simulation. The experiment was conducted in the large anechoic wind tunnel of the Ecole Centrale de Lyon. Measurements taken included particle image velocity (PIV) around the airfoil, single hot wire, wall pressure coherence, and far field pressure. These measurements highlight the strong 3D effects responsible for spectral broadening around the rod vortex shedding frequency in the subcritical regime, and the dominance of the noise generated around the airfoil leading edge. The benchmarking approach is illustrated by two examples:

Invariant Operators Between Spaces of h-Monogenic Polynomials

In this paper we study properties of invariant differential operators acting between spaces of h-monogenic functions. In this way one obtains differential operators acting between invariant (m)-modules which can be seen as the Hermitean analogues of the classical Rarita-Schwinger operators. Received: October, 2007. Accepted: February, 2008.     

Polynomials whose coefficients coincide with their zeros

In this paper we consider monic polynomials such that their coefficients coincide with their zeros. These polynomials were first introduced by S. Ulam. We combine methods of algebraic geometry and dynamical systems to prove several results. We obtain estimates on the number of Ulam polynomials of degree N. We provide additional methods to obtain algebraic identities satisfied by the zeros of Ulam polynomials, beyond the straightforward comparison of their zeros and coefficients. To address the question about the existence of orthogonal Ulam polynomial sequences, we show that the only Ulam polynomial eigenfunctions of hypergeometric type differential operators are the trivial Ulam polynomials \(\{x^N\}_{N=0}^\infty \). We propose a family of solvable N-body problems such that their stable equilibria are the zeros of certain Ulam polynomials.     

An a posteriori error estimator based on shifts for positive Hermitian eigenvalue problems

This work deals with an a posteriori error estimator for Hermitian positive eigenvalue problems. The proposed estimator is based on the residual and the definition of suitable shifts in the matrix spectrum. The mathematical properties (certification and sharpness) are investigated and some numerical experiments are proposed.     

On the effect of catalyst status in the quantitative determination of platinum in Pt-Sn/MgO materials

The development of an analytical method for the determination of platinum in MgO based Pt/Sn catalysts is described. Electrothermal atomic absorption spectroscopy (ETAAS) was chosen because of its high sensitivity and robustness against spectral interferences. All the sources of chemical interferences were statistically analyzed and corrections were adopted for the presence of magnesium oxide support. The effectiveness of different mineralization procedures was critically evaluated as a function of the chemical of the solid catalyst. Microwave digestion allowed recovery of metal of 100% for all the catalysts analyzed and exhibited significant better precision values than other digestion methods, which could nevertheless be utilized under proper conditions in selected cases. Received: 31 July 2000 / Revised: 17 October 2000 / Accepted: 24 October 2000