Fractionation of metals and metalloids by chemical bonding from particles accumulated by electrostatic precipitation in an Argentine thermal power plant

A study was undertaken to evaluate the distribution of Al, As, Cr, Cu, Fe, Mn, Ni, Pb, Ti, V and Zn in fly ashes collected in the electrostatic precipitator of a thermal power plant in San Nicolás (Argentina). Five samples were collected during one week of operation. For the fractionation, the scheme applied consisted in extracting the elements in four fractions namely (i) soluble and exchangeable elements; (ii) carbonates, oxides and reducible elements; (iii) bound to sulfidic metals; and (iv) residual elements. Metals and metalloids at μg g^− 1 level were determined in each fraction by inductively coupled plasma optical emission spectrometry (ICP OES). For validation, a standard reference material (SRM 1633 coal fly ash) from NIST was subjected to the same chemical sequential extraction procedure that the samples. X-ray diffraction powder (XRD) analysis and scanning electron microscopy (SEM) were used to characterize the major minerals present in the matrix. Total analyte concentration (in μg g^− 1) varied from 10.6 for Pb to 17,622 for Al. Minimum and maximum concentrations (in μg g^− 1) found in individual samples in the four fractions were: Al, 92.7–9668; As, < 0.3–143; Cr, 2.0–10.4; Cu, < 0.2–35.6; Fe, < 0.3–4992; Mn, < 0.1–128; Ni, < 0.3–139; Pb, < 0.5–9.1; Ti, < 0.3–2243; V, 17.0–112.9; and Zn, < 0.1–68.2. The leachability of the 11 elements under study proved to be different. Low percentages of Al (1%), V (7%) and Cr (8%) were detected in the most bioavailable fraction. Arsenic was found to be most abundant in the non-silicate phase, represented by the second and third fractions, while Cr, Fe, Ni, Pb and Zn were mostly associated to the residual fraction.     

Trapping H- bound to the nitrogenase FeMo-cofactor active site during H2 evolution: characterization by ENDOR spectroscopy

We here show that the iron-molybdenum (FeMo)-cofactor of the nitrogenase alpha-70(Ile) molybdenum-iron (MoFe) protein variant accumulates a novel S = (1)/(2) state that can be trapped during the reduction of protons to H(2). (1,2)H-ENDOR measurements disclose the presence of two protons/hydrides (H(+/)(-)) whose hyperfine tensors have been determined from two-dimensional field-frequency (1)H ENDOR plots. The two H(+/)(-) have large isotropic hyperfine couplings, A(iso)( )() approximately 23 MHz, which shows they are bound to the cofactor. The favored analysis for these plots indicates that the two H(+/)(-) have the same principal values, which indicates that they are chemically equivalent. The tensors are further related to each other by a permutation of the tensor components, which indicates an underlying symmetry of binding relative to the cofactor. At present, no model for the structure of the iron-molybdenum (FeMo)-cofactor in the S = (1)/(2) state trapped during the reduction of H(+) can be shown unequivocally to satisfy all of the constraints generated by the ENDOR analysis. The data disfavors any model that involves protonation of sulfides, and thus suggests that the intermediate instead contains two chemically equivalent bound hydrides; it appears unlikely that these are terminal monohydrides.     

Synthesis,characterization and third-order nonlinear optical properties of ruthenium(II) complexes containing 2-(4-nitrophenyl)imidazo[4,5-f] [1,10]phenanthroline

Two novel Ru^II complexes [Ru(phen)₂(PNOPH)]²⁺ and [Ru(dmp)₂ (PNOPH)]²⁺ (phen = 1,10-phenanthroline, dmp = 2,9-dimethyl-1,10-phenanthroline, PNOPH = 2-(4-nitrophenyl)imidazo-[4,5-f][1,10]phenanthroline) and their deprotoned complexes were synthesized and characterized by ES–MS, ¹H - n.m.r, u.v.–vis. and electrochemistry. The crystal structure of the deprotonated complex [Ru(dmp)₂ (PNOP)][ClO₄] · CH₃CN was determined by means of X-ray single crystal diffraction. Nonlinear optical properties of the Ru^II complexes were investigated by Z-scan techniques in DMF solution, and all of them exhibited both NLO absorption and self-defocusing effect. The corresponding effective NLO susceptibilities |³ | of the complexes are 2.39 × 10^-12–5.80 × 10^-12 esu.     

Parametric Integer Programming Analysis: A Contraction Approach

An algorithm is presented for solving families of integer linear programming problems in which the problems are "related" by having identical objective coefficients and constraint matrix coefficients. The righthand-side constants have the form b + θd where b and d are conformable vectors and θ varies from zero to one.The approach consists primarily of solving the most relaxed problem (θ = 1) using cutting planes and then contracting the region of feasible integer solutions in such a manner that the current optimal integer solution is eliminated.The algorithm was applied to 1800 integer linear programming problems with reasonable success. Integer programming problems which have proved to be unsolvable using cutting planes have been solved by expanding the region of feasible integer solutions (θ = 1) and then contracting to the original region.     

The Use of Versatile Distribution Families in Some Stochastic Inventory Calculations

Previous works on stochastic inventory problems have often assumed that an item's lead time demand follows a "convenient" distribution such as the normal, the γ or the Weibull. First, this paper argues that these convenient distributions may be overly restrictive and unrealistic, and points out the versatility and realism of using four-parameter distributions of the Pearson's and the Schmeiser-Deutsch's systems. Second, using these four-parameter distributions, this paper presents practical `manual" methods for computing the stock-out probability, reorder level and expected lost sales of an inventory item and for solving the lot-size reorder-point model. Some of these methods are actually simpler than the ones developed previously for the more restrictive distributions.     

Doing Something about the Future

This paper is concerned with the need for more interdisciplinary, systems oriented, research directed towards major problems encountered by decision makers in industry and government; a need which is more difficult to meet in the face of traditional methods of organising knowledge and research. It emphasises the need to acknowledge the true complexity of the problems and the interactive nature of any effective research procedure. As an illustration, both of the need and the problems involved in meeting it, the development of a new program of research into problems of Management and Technology at the International Institute of Applied Systems Analysis, which is supported by seventeen nations of all political complexions, is analysed. The implication is that we can do something about the future, but we must be prepared to do.     

A Cutting Planes Algorithm for the <Emphasis Type="Italic">m</Emphasis>-Salesmen Problem

The existence of reliable and flexible FORTRAN programs for integer linear programming has recently enabled the development of very efficient algorithms for the travelling salesman problem. The main characteristic of these algorithms is the relaxation of most of the constraints of the problem during its solution. The same approach can be used for the solution of the m-salesmen problem in which m salesmen starting from the same city must visit only once n cities at minimum cost. The number of salesmen can be fixed in advance or allowed to vary, upper and lower bounds set on the number of salesmen and even fixed costs associated with the salesmen. The results obtained so far are very encouraging. Problems of up to 100 cities have been solved optimally for the m-travelling salesmen case and other more complex problems are currently under study.     

Teaching Operational Research Technique

Good technique, i.e. competence in carrying out operational research, is as vital for the practitioner to acquire as competence in the traditional ‘techniques’. It is suggested that universities should teach students how to conduct simple projects prior to alerting them to more sophisticated methodological issues.As an aid to this task, the traditional five or six parts of an operational research project are broken down and extended into 39 steps, and regrouped into three phases. Also, five skills are identified as being conceptually essential to "good" operational research, which students can develop through tackling suitable case studies.     

Biosensors designed for environmental and food quality control based on screen-printed graphite electrodes with different configurations

Graphite electrodes fabricated by screen-printing have been used as amperometric detectors in biosensors based on NAD(+)-dependent dehydrogenases, tyrosinase, or genetically modified acetylcholinesterases. The mono-enzyme sensors have been optimized as disposable or reusable devices for detection of a variety of substrates important in the food industry ( D-lactic acid, L-lactic acid, acetaldehyde) or in environmental pollution control (phenols and dithiocarbamate, carbamate and organophosphorus pesticides). The sensors were prepared in four configurations differing in enzyme confinement, enzyme immobilization and location of the immobilization agent in the biosensor assembly. Tests on real samples have been performed with the biosensors; D-lactic acid and acetaldehyde have been detected in wine and phenols in air.     

Complexing processes in M(II)-dithiomalonamide-diacetyl triple systems (M= Ni,Cu) in ethanol solution and in a metal(II)hexacyanoferrate(II) gelatin-immobilized matrix materials

The complexing processes in the M ^II -dithiomalonamide-diacetyl triple system (M=Ni, Cu) occuring in the nickel(II)- and copper(II)hexacyanoferrate(II) gelatin-immobilized matrix in contact with aqueous alkaline solutions (pH~12) containing dithiomalonamide and diacetyl at room temperature, and between MCl₂, dithiomalonamide and diacetyl in EtOH solutions upon heating to$80°C, have been studied. In the Ni ^II -dithiomalonamide-diacetyl system, template synthesis occurs in EtOH solution but does not occur in the gelatin-immobilized matrix, whereas in the Cu ^II -dithiomalonamide-diacetyl system, template synthesis occurs in the gelatin-immobilized matrix but not in EtOH solution. Dithiomalonamide and diacetyl are the ligand synthons in the processes indicated.