An efficient and scalable block parallel algorithm of Neville elimination as a tool for the CMB maps problem

This paper analyses the performance of several versions of a block parallel algorithm in order to apply Neville elimination in a distributed memory parallel computer. Neville elimination is a procedure to transform a square matrix A into an upper triangular one. This analysis must take into account the algorithm behaviour as far as execution time, efficiency and scalability are concerned. Special attention has been paid to the study of the scalability of the algorithms trying to establish the relationship existing between the size of the block and the performance obtained in this metric. It is important to emphasize the high efficiency achieved in the studied cases and that the experimental results confirm the theoretical approximation. Therefore, we have obtained a high predicting ability tool of analysis. Finally, we will present the elimination of Neville as an efficient tool in detecting point sources in cosmic microwave background maps.     

Analyzing Scalability of Neville Elimination

The scalability of a parallel system is a measure of its capacity to effectively use an increasing number of processors. Several performance evaluation metrics have been developed to study the scalability of parallel algorithms and architectures. The isoefficiency function is one of those metrics. It relates the size of the problem being solved to the number of processors required to maintain efficiency at a fixed value. This work studies the scalability of Neville elimination, which is a method to solve a linear equation system. This process appears naturally when the Neville strategy of interpolation is used to solve linear systems. The scalability behavior of some algorithms of this method is studied on an IBM SP2 and also over a network of personal computers using the isoefficiency function and the scaled efficiency.     

Erratum to: Preserving the activity of enzymes under harsh oxidizing conditions: sol–gel entrapped alkaline phosphatase exposed to bromine

Chemically reactive sol–gel matrices hold the ability of protecting entrapped enzymes from destruction by external harsh chemicals. We show this concept by exposing alkaline phosphatase (AlP) to a strong oxidizing agent—bromine. In solution, AlP is immediately destroyed by this oxidant. When AlP was entrapped in hybrid silica sol–gel materials carrying double bonds, the reactivity of AlP was preserved after exposure to bromine under conditions which totally destroy it in solution. The matrices studied were vinylated and allylated silicas, and their protectability was compared to n-alkylated silicas and to silica itself. For instance, the reactivity of AlP entrapped in allylated silica after exposure to 25.6 mM bromine solution is 40 times higher than its reactivity when entrapped in pure silica; and in solution the enzyme is totally destroyed at this concentration. Molecular level mechanisms for these observations are proposed.     

Preserving the activity of enzymes under harsh oxidizing conditions: sol–gel entrapped alkaline phosphatase exposed to bromine

Chemically reactive sol–gel matrices hold the ability of protecting entrapped enzymes from destruction by external harsh chemicals. We show this concept by exposing alkaline phosphatase (AlP) to a strong oxidizing agent—bromine. In solution, AlP is immediately destroyed by this oxidant. When AlP was entrapped in hybrid silica sol–gel materials carrying double bonds, the reactivity of AlP was preserved after exposure to bromine under conditions which totally destroy it in solution. The matrices studied were vinylated and allylated silicas, and their protectability was compared to n-alkylated silicas and to silica itself. For instance, the reactivity of AlP entrapped in allylated silica after exposure to 25.6 mM bromine solution is 40 times higher than its reactivity when entrapped in pure silica; and in solution the enzyme is totally destroyed at this concentration. Molecular level mechanisms for these observations are proposed.     

Chemical communication between solids placed at distance: Sol-gel entrapped acids and bases

Chemical reactions between “far-away” components are quite common in the living world and in geological processes, and are affected by communicating shuttling molecules and ions. Surprisingly, there has been little attention in the chemical literature to model these natural processes by bench-laboratory heterogeneous reactions. Towards that goal we report the study of chemical communication between solid acids and bases placed at distance. The porous solids were prepared by entrapping various acids and bases in silica sol-gel matrices. We recall that while, of course, dissolved acids and bases titrate each other, when solid acids and bases are placed in the same pot, titration can be affected only through an ion-exchange process. This property is used here to cause the two distantly placed solids to communicate with each other. In particular, we use here the entrapped acids as senders of messenger-hydronium ions and as receivers of hydroxyl ions, and entrapped bases as senders of messenger-hydroxyls. We demonstrate the possibility to control the parameters of the communication between these solids.     

Linear Variational Diophantine Techniques in Mass Balance of Chemical Reactions

Linear algebraic techniques based on minimization of thermodynamic functional and/or other constraints are illustrated for mass balance of chemical reactions that do not exhibit stoichiometrically unique solutions in the linear algebraic vector space. The techniques demonstrate elegant casting of chemical equations in terms of generalized linear Diophantine matrices and generalized elimination and variational schemes.     

Extended characterization of a vacuum gas oil by offline LC‐high‐temperature comprehensive two‐dimensional gas chromatography

In a context of environmental preservation, purification and conversion of heavy petroleum cuts into high‐quality fuel becomes essential. The interest for the characterization of those very complex matrices becomes a trendy analytical challenge, when it comes to get molecular information for the optimization of industrial processes. Among new analytical techniques, high‐temperature 2‐D GC has recently proved its applicability to heavy petroleum matrices, but lacks in selectivity to separate all chemical groups. To gain resolution, heart cutting is demonstrated for LC separation of saturated, aromatic and polar compounds prior to high‐temperature 2‐D GC. Therefore, an extended global resolution was obtained, especially by a better distinction of saturated compounds. This includes iso‐paraffins and biomarker polynaphthenic structures, which are impossible to quantify with MS methods. This new way to analyze heavy petroleum fractions gives innovative opportunities for the construction of global weight distributions by carbon atoms number and by chemical families. This can right now be employed for quantitative analysis of heavy petroleum fractions and for studying conversion processes.     

Competitive photodecomposition reactions of chloroiodomethane

Two different dissociation processes occur when chloroiodomethane is photolysed with laser radiation at 266.2 nm. Linear absorption leads to the cleavage of the carbon—iodine bond, while methylene radicals are formed by the absorption of two UV photons. The chemical reactions of the different photofragments are discussed. Recombination of two chloromethyl radicals leads to chemically activated 1,2-dichloroethane molecules, which either are stabilized or decompose by elimination of hydrogen chloride.     

Unexpected high energy ions from a chemical ionization source

Doubly charged rare gas cations are produced in a chemical ionization source under conditions in which the energy of the primary ionizing electrons is more than 20 eV below the energetic threshold. The formation mechanism consists of creating secondary electrons outside the ion source followed by the acceleration of some of these electrons into the source where they initiate high energy ionization processes. Evidence suggesting that the secondary electrons arise from ionizing collisions between accelerated ions and background gas is presented. This process is expected to occur generally when positive ion chemical ionization is performed in magnetic deflection instruments.     

Chemical Modifiers Based on Platinum-Group Metal Compounds in Electrothermal Atomic Absorption Spectrometry

Mechanisms of the action of chemical modifiers based on platinum-group metals have been considered. It has been shown that the efficiency of a chemical modifier is determined mainly by chemical processes occurring at the pyrolysis step. By combining the results obtained using different methods, these processes have been described step-by-step. The systematic study of Pd, Pt, Rh, Ru, and Ir in chloride and sulfate media as chemical modifiers has revealed a correlation between the relative efficiencies and some chemical properties of the modifiers. It has been shown that, in the presence of matrices weakly interacting with platinum-group metals (for example, sodium chloride), the best modifiers are metals that most intensely interact with the analytes (ruthenium and iridium in determining metalloids). However, if the chemical modifier strongly interacts with the sample matrix, the efficiency of the modifier is determined by the interaction processes. For example, in the presence of a sulfate matrix capable of reacting with platinum-group metals, the best modifier is palladium. The correlations found may be useful for the practical application of platinum-group metals as chemical modifiers in the analysis of complex samples by electrothermal atomic absorption spectrometry.     

The characterization and structure-property relations of epoxies

The structure-deformation/failure process-mechanical property relations of epoxies used as matrices in high performance fibrous composites are presented. Such composites are fabricated either from fiber-epoxy prepregs or by filament winding. The parameters that affect the processing, cure reactions and the resultant chemical and physical structure of the epoxies are discussed. The deformation and failure processes of these glasses are described. The structural parameters that control the deformation and failure processes, the mechanical response and aging of epoxies are addressed and means of improving their processing and performance are described.     

Interstellar matrices: the chemical composition and evolution of interstellar ices as observed by ISO

Matrix isolation techniques have been developed in the early sixties as a tool for studying the spectroscopic properties of out of equilibrium species (atoms, radicals, ions, reactive molecules), embedded in rare gas inert matrices at low temperatures. Cold interstellar grains surfaces are able to condense out gas phase molecules, routinely observed by radioastronomy. These grain 'mantles' can be considered as 'interstellar matrices'. However, these matrices are not clean and unreactive. They are made principally of dirty ices whose composition must be determined carefully to assess the importance of the solid state chemistry that takes place in the Interstellar Medium. Infrared spectroscopy, both in astronomy and in the laboratory, is the unique tool to determine the chemical composition of these ices. Astronomical spectra can directly be compared with laboratory ones obtained using classical matrix isolation techniques. Furthermore, dedicated experiments may be undertaken to further improve the understanding of the basic physico-chemical processes that take place in cosmic ices.     

Fluorimetric determination of salsalate in urine, serum and pharmaceutical preparations

A method for the determination of salsalate at concentrations between 0.10 and 1.00 mug ml(-1) by means of fluorescence spectrometry technique is proposed. Salsalate, lightly soluble in water, is totally extracted into chloroform. In this organic phase, the drug shows low fluorescence but when an alkaline medium is provided, salsalate undergoes a substantial increase of the fluorescent intensity. Thus, the determination is performed in a chloroformic medium, where pyrrolidine chloroformic solution is added to give the basic character. The fluorescence measurements to quantify salsalate are carried out in its fluorescent band centered at lambda(ex)=299 nm and lambda(em)=410 nm. The method was successfully applied to the determination of salsalate in authentic pharmaceutical preparations, urine and serum. Samples of these latter two matrices, urine and serum, are extracted into chloroform, using in the aqueous phase a pH 4.8, provided by adding acetic acid/sodium acetate buffer solution. Owing to matrix interference, the method of standard additions was used to determine salsalate in the serum. The sensitivity and repeatability achieved with the proposed method are adequate for the determination of salsalate in these matrices.     

Light‐Induced Click Reactions

Spatial and temporal control over chemical and biological processes, both in terms of “tuning” products and providing site‐specific control, is one of the most exciting and rapidly developing areas of modern science. For synthetic chemists, the challenge is to discover and develop selective and efficient reactions capable of generating useful molecules in a variety of matrices. In recent studies, light has been recognized as a valuable method for determining where, when, and to what extent a process is started or stopped. Accordingly, this Minireview will present the fundamental aspects of light‐induced click reactions, highlight the applications of these reactions to diverse fields of study, and discuss the potential for this methodology to be applied to the study of biomolecular systems.     

The analysis of salen complexes by fast atom bombardment mass spectrometry and atmospheric pressure chemical ionization mass spectrometry

Fast atom bombardment (FAB) mass spectrometry provides useful structural information about salen complexes and salen-based oxo transfer catalysts that are not appreciably soluble in organic solvents. It was discovered that initial dissolution of these complexes in trifluoroacetic acid was crucial for producing good FAB mass spectra. Trifluoroacetic acid helps dissolve the salen-based catalysts, concentrates the analyte molecules at the matrix surface, and most importantly, suppresses the reduction process, which is a well-known phenomenon when protic matrices are used. The best FAB matrices for these catalysts were found to be thioglycerol and “magic bullet.” However, dechlorination occurred under the acid conditions for complexes containing iron chloride and manganese chloride. Demetalation also occurred for nickel-containing oxo transfer salen-based complexes. When the salen-based complexes are soluble in LC solvents, they can be analyzed easily by atmospheric pressure chemical ionization (APCI) mass spectrometry without the employment of relatively nonvolatile matrices. In addition, APCI/MS provides much more sensitive detection for manganese-salen complexes when compared with FAB results. No dechlorination or demetalation were observed when a negative ion mode APCI was employed. To our knowledge, this is the first time that an intact molecule of this type of complex has been observed by mass spectrometry.     

Pharmaceutical residues in environmental waters and wastewater: current state of knowledge and future research

Pollution from pharmaceuticals in the aquatic environment is now recognized as an environmental concern in many countries. This has led to the creation of an extensive area of research, including among others: their chemical identification and quantification; elucidation of transformation pathways when present in wastewater-treatment plants or in environmental matrices; assessment of their potential biological effects; and development and application of advanced treatment processes for their removal and/or mineralization. Pharmaceuticals are a unique category of pollutants, because of their special characteristics, and their behavior and fate cannot be simulated with other chemical organic contaminants. Over the last decade the scientific community has embraced research in this specific field and the outcome has been immense. This was facilitated by advances in chromatographic techniques and relevant biological assays. Despite this, a number of unanswered questions exist and still there is much room for development and work towards a more solid understanding of the actual consequences of the release of pharmaceuticals in the environment. This review tries to present part of the knowledge that is currently available with regard to the occurrence of pharmaceutical residues in aquatic matrices, the progress made during the last several years on identification of such compounds down to trace levels, and of new, previously unidentified, pharmaceuticals such as illicit drugs, metabolites, and photo-products. It also tries to discuss the main recent findings in respect of the capacity of various treatment technologies to remove these contaminants and to highlight some of the adverse effects that may be related to their ubiquitous existence. Finally, socioeconomic measures that may be able to hinder the introduction of such compounds into the environment are briefly discussed.     

Components and coupling in enzyme-catalyzed reactions

Many enzyme-catalyzed reactions involve coupling of two or more reactions that could otherwise be catalyzed separately. When biochemical reactions are coupled, the equilibrium composition is very different from that when the reactions are not coupled. The number of components in a chemical reaction is equal to the number of independent conservation equations for atoms of elements, but the number of components in an enzyme-catalyzed reaction that is coupled is larger than the number of independent conservation equations for atoms of elements. The investigation of these additional conservation equations by use of linear algebra is complicated by the fact that in dilute aqueous solutions, the activity of water is taken to be unity. This causes an incompatibility of conservation matrices and stoichiometric number matrices that can be avoided by use of the further transformed Gibbs energy G' ' that provides the criterion for spontaneous change and equilibrium when the standard transformed Gibbs energy of water is constant. In the most striking example discussed, the enzyme mechanism of a ligase reaction introduces three constraints in addition to conservation of atoms of elements. This is completely unheard of in chemical reaction thermodynamics.     

Multivariate curve resolution applied to Fourier transform infrared spectra of macromolecules: structural characterisation of the acid form and the salt form of humic acids in interaction with lead

The significance of evolving mixtures structural spectroscopic studies might appear limited when the experimental spectra do not present a sufficient quality for a precise interpretation. It is the case when the chemical behaviour of macromolecules is studied on the basis of infrared spectra. If the effective resolution is low, the spectral profiles appear similar despite the applied chemical conditions change. This makes impossible the interpretation of the raw spectra and mathematical treatments are required to separate the different contributions that overlap.To determine the behaviour of the reactive sites of humic acids in the binding with heavy metals, infrared spectra are recorded under various chemical conditions. The cation to be considered is Pb²⁺ and the two chemical variables to be studied are pH and initial lead concentration. Four series of FTIR spectra are recorded, but no visible difference can be directly assigned to the different chemical states of the macromolecules. Multivariate self-modelling curve resolution is thus proposed as a tool for resolving these complex and strong overlapping datasets. First, initial estimates are obtained from pure variable detection methods: it comes out that two spectra are enough to reconstruct the experimental matrices. In a further step, the application of the multivariate curve resolution-alternating least squares (MCR-ALS) algorithm with additional constraints on each individual dataset, as well as on column-wise augmented matrices, allows to optimise the profiles and spectra that appear to be highly characterising the acid and the salt form of the molecule. Moreover, the concentrations profiles associated to these two limit spectral forms allow interpreting the analytical measurements made during the reactions between humic acids and H⁺ or Pb²⁺. Consequently, depending on the initial state of the humic acid, two distinct reactional mechanisms are proposed.     

Matrix isolation FTIR spectroscopic and theoretical study of dimethyl sulfite

The preferred conformations of dimethyl sulfite and their vibrational spectra were studied by matrix-isolation Fourier transform infrared spectroscopy and theoretical methods (density functional theory (DFT) and Moller-Plesset (MP2), with basis sets of different sizes, including the quadruple-zeta, aug-cc-pVQZ basis). Five minima were found at these levels of theory. At the MP2/6-31++G(d,p) and DFT/B3LYP/aug-cc-pVQPZ levels, the GG conformer (where the O-S-O-C dihedral angles are 73.2 and 70.8 degrees ) resulted in the conformational ground state. At the highest level of theory used, the GT conformer (O-S-O-C = +68.5 and -173.2 degrees ) is 0.83 kJ mol(-1) higher in energy than the GG form, while conformer GG' (O-S-O-C = +85.7 and -85.7 degrees ) has a relative energy of 1.18 kJ mol(-1). The remaining two conformers (G'T and TT) are high-energy forms and not experimentally relevant. In consonance with the theoretical predictions, conformer GG was found to be the most stable conformer in the gaseous phase as well as in the low-temperature matrices. Annealing of the argon matrices first promotes the GG'-->GT isomerization, which is followed by conversion of GT into the most stable conformer. There is no evidence of occurrence of GG'-->GG direct conversion in the low-temperature matrices. On the other hand, during deposition of the xenon matrices conformer GG' totally converts to conformer GT. Two observations demonstrated this fact: no evidence of bands corresponding to GG' were observed in xenon matrices and the GG/GT intensity ratio became similar to the GG/(GT + GG') intensity ratio observed in argon matrices. All these results could be explained by taking into account the relative values of the theoretically predicted energy barriers for the different isomerization processes: GG'-->GT, 1.90 kJ mol(-1); GT-->GG, 9.64 kJ mol(-1); and GG'-->GG, 19.46 kJ mol(-1).