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Water resources are in many countries transboundary and as such, especially in arid regions such as the Middle East, may provide a basis for conflict. War almost broke out between Syria and Iraq following the construction of a dam on the Euphrates River by Syria. This is even more critical in cases where conflict exists due to other reasons. Such is the case with the Israel and the Arab neighboring countries conflict with the water issues between Israel and the Palestinian Authority being particularly complicated since they are intertwined in all aspects. [ABSTRACT FROM AUTHOR]

In this paper we propose to use an instantaneous ICA method (BLUES) to separate the instruments in a real music stereo recording. We combine two strong separation techniques to segregate instruments from a mixture: ICA and binary time-frequency masking. By combining the methods, we are able to make use of the fact that the sources are differently distributed in both space, time and frequency. Our method is able to segregate an arbitrary number of instruments and the segregated sources are maintained as stereo signals. We have evaluated our method on real stereo recordings, and we can segregate instruments which are spatially different from other instruments. [ABSTRACT FROM AUTHOR]

In this paper a system that transforms speech waveforms to animated faces are proposed. The system relies on continuous state space models to perform the mapping, this makes it possible to ensure video with no sudden jumps and allows continuous control of the parameters in 'face space'. The performance of the system is critically dependent on the number of hidden variables, with too few variables the model cannot represent data, and with too many overfitting is noticed Simulations are performed on recordings of 3-5 sec. video sequences with sentences from the Timit database. From a subjective point of view the model is able to construct an image sequence from an unknown noisy speech sequence even though the number of training examples are limited. [ABSTRACT FROM AUTHOR]

Recently, various bacterial components have been suggested as initiating and modulating immune activation, thereby substantially affecting the complex and dynamic host/pathogen interactions. Herein, we present a valuable and simple methodology for determining the capacity of bacteria as well as defined bacterial structures to stimulate cellular effectors of the innate and cognate immune system. This assay format is based on the exposure of freshly prepared single-cell cultures of splenic cells derived from naive mice with the immunogen of interest. Herein, the determination of exclusive panels of cytokines by the ELISA, ELISpot, and FACS technology will serve as an indicator for the activation of defined arms of the immune system. An increased knowledge about microbial components with immunomodulatory properties will substantially contribute to a more detailed understanding of the dynamic interplay between the host and potential pathogens and, based on this knowledge, to the development of novel substances for the prevention and therapy of microbial infections. [ABSTRACT FROM AUTHOR]

Medium-sized ring lactams (7- to 15-membered) find widespread use in organic chemistry as key intermediates in the synthesis of more complex structures or as core structures in natural product or pharmaceutically important compounds. Until now, the generation of such rings is still a challenge in organic synthesis. During the past decade an increasing interest has focused on the generation of cyclic peptides as well as hairpin and β-turn mimics and the medium-sized rings were thought to represent suitable fragments. Furthermore, a range of complex natural products is characterized by such lactam structure and their total synthesis is a broad field for organic chemists to test new strategies and to develop new methods. The aim of the present chapter is to discus some modern strategies to synthesize seven- to fifteen-membered ring lactams, the scope is restricted to the generation to ring systems bearing a single lactam function. Although the range of reactions described concern only the generation of simple structures without complicated stereogenic properties, most of them seem to bear undiscovered potential with regard to stereoselective synthesis. However, the emphasis of the methods is focused on stereoselective processes. The review is subdivided in three major chapters of ring closure reactions and ring enlargements, additional information is given on cycloadditons and fragmentations. [ABSTRACT FROM AUTHOR]

Functionalized aziridines, especially aziridine-2-carboxylic esters, are highly valuable small-ring heterocycles for the synthesis of a large variety of anomalous amino acids, new types of ligands for catalytic purposes, new synthons, and four- and five-membered ring heterocycles through ring expansion reactions. This review highlights the aziridine chemistry with the focus on the utility of aziridine esters. The synthesis and chemistry of the highly strained azirine carboxylic esters is also briefly reviewed. [ABSTRACT FROM AUTHOR]

Alkylations of 4-cyano-1,3-dioxanes (cyanohydrin acetonides) represent a highly practical approach to syn-1,3-diol synthesis. Herein we present a comprehensive summary of cyanohydrin acetonide chemistry, with particular emphasis on practical aspects of couplings, as well as their utility in natural product synthesis. Both 4-acetoxy-1,3-dioxanes and 4-lithio-1,3-dioxanes have emerged as interesting anti-1,3-diol synthons. The preparation and utility of these two synthons are described. [ABSTRACT FROM AUTHOR]

An in depth account of intramolecular 1,3-dipolar cycloadditions involving dipoles such as nitrile oxides, silyl nitronates, H-nitrones, azides, and nitrilimines is presented with particular emphasis on the stereochemistry during the cycloaddition. Various methods employed for the generation of the dipoles and their applications to stereoselective synthesis are also discussed. [ABSTRACT FROM AUTHOR]

Self-assembling systems composed of organic molecules and metal ions represent one of the topics in modern supramolecular chemistry. Up to now, their physical characterization was essentially limited to crystals or to surface layers. Studies on solubilized systems, e.g., on their molecular mass distribution or association behavior, are rare. We have explored whether sedimentation equilibrium analysis in the Beckman Optima XL-A analytical ultra-centrifuge can be successfully applied. A grid-like cobalt coordination array ("[2×2]-Co(II)-grid") was used as a model compound. The technical problem involved, concerning the chemical resistance of the cell components against organic solvents, was solved by using titanium centerpieces and polyethylene gaskets. Another potential problem, the high UV absorbance of the solvents, could be circumvented by measuring the absorbance versus radius profiles in the visible wavelength range, where "grids" and most other related compounds show absorption bands. Special efforts were made to solve the remaining problems: (1) the suppression of nonidealities in sedimentation behavior, which could prevent or greatly complicate a successful analysis of self-associating systems, and (2) the determination of the partial specific volume $$\bar v$$ of the complexes, in particular considering compounds either not available in sufficient quantities for density measurements or exhibiting low solubility. With respect to problem (1), solvent/salt systems were found in which the model compound apparently shows ideal sedimentation behavior. Procedures are suggested to overcome problem (2). [ABSTRACT FROM AUTHOR]

The unimolecular reactions of ions in a mass spectrometer are remarkably well correlated with both photochemical and thermochemical reactions of the corresponding neutrals. The reactivity correlations are seldom quantitative and exceptions to the correlation should be expected when heteroatoms or delocalization effects convey unusual stability to the ions in the mass spectrometer as compared to their neutral analogs. In spite of the special effects on ionic stability and the relatively large amount of energy that is available in 70 eV electron impact, it appears that mass spectra will be an increasingly useful guide to new photochemical and thermochemical reactions. [ABSTRACT FROM AUTHOR]

Benzenoid (chemical) isomers are, in a strict sense, the benzenoid systems compatible with a formula CnHs≡(n; s). The cardinality of CnHs, viz. CnHs≡n, s is the number of isomers pertaining to the particular formula. The generation of benzenoid isomers (aufbau) is treated and some fundamental principles are formulated in this connection. Several propositions are proved for special classes of benzenoids defined in relation to the place of their formulas in the Dias periodic table (for benzenoid hydrocarbons). Constant-isomer series for benzenoids are treated in particular. They are represented by certain CnHs formulas for which n; s=n1; s1=n2; s2=…, where (nk; sk) pertains to the k times circumscribed CnHs isomers. General formulations for the constant-isomer series are reported in two schemes referred to as the Harary-Harborth picture and the Balaban picture. It is demonstrated how the cardinality n; s for a constant-isomer series can be split into two parts, and explicit mathematical formulas are given for one of these parts. Computational results are reported for many benzenoid isomers, especially for the constant-isomer series, both collected from literature and original supplements. Most of the new results account for the classifications according to the symmetry groups of the benzenoids and their Δ values (color excess). [ABSTRACT FROM AUTHOR]

A synthon model of organic chemistry is described. A synthon is determined as a molecular graph in which a certain part of vertices is distinguished and those vertices are called the virtual vertices. The virtual vertices correspond to functional groups or molecular fragments that do not directly participate in chemical transformations (though these transformations may be substantially influenced by them). The synthon precursors or successors are formed from a given synthon by special sort of reaction graph in such a way that all valence states of atoms (vertices) in a precursor or successor are classified as stable valence states. The program PEGAS represents an implementation of the synthon model. Its basic features, scopes, and algorithms are briefly outlined. The effectiveness of the program PEGAS is illustrated by many examples of interest for organic chemists. [ABSTRACT FROM AUTHOR]

In this article we have described the different types of reactions that have been investigated by means of optically active compounds. It remains to determine the scope of the different mechanisms suggested, and to formulate stereochemical rules for use in further synthetic work. [ABSTRACT FROM AUTHOR]

It is evident from the results presented above that the cis-(−N=N−) bond has powerful coordinating properties towards low valent transition metals. Due to the unique electronic structure of the diazeno group, many different modes of interaction have been observed and it seems promising that this ability of the N=N function may be utilized in catalytic processes. Since diazene itself is a proposed intermediate in biological nitrogen-fixation, the observed modes of coordination are of some relevance to this problem. The results obtained from the cycloaddition reactions are of general importance for the investigation of the factors determining photochemical or thermal reactions of coordinated ligands. The ability of iron carbonyls to activate the diazeno group towards attack by unsaturated molecules like alkynes, offers a convenient synthesis of novel organic heterocycles. Together with the recently reported conversion of coordinated dinitrogen into diazeno and diazenato complexes4), these reactions may be key steps in the incorporation of N2 into organic compounds. [ABSTRACT FROM AUTHOR]

A computer program has been developed which automatically generates sequences of chemical reactions. As reactions are treated quite formally, all conceivable reactions are obtained irrespective of whether they axe already known or are without precedence. This program is especially useful for planning organic syntheses and fox generating the products of starting materials. The system is in very active development but the present version can already serve as a tool for the chemist in studying problems of immediate interest. Examples for applications are given to demonstrate the flexibility and performance of the program. [ABSTRACT FROM AUTHOR]

The above examples of the unique possibilities of stereo chemically fixed aromatic rings in multibridged, multilayered and multistepped hydrocarbon compounds show that these classes of compounds are most appropriate for the study of intramolecular, steric and electronic interactions, from which too little quantitative relations are known. Again, it follows that further synthetic approaches are not only possible, but also necessary for a more accurate differentiation and analysis of the frequently overlapping electronic and steric effects. More progress in this field is sure to be expected, above all when synthetic and spectroscopic chemists, and physicists adhere to interdisciplinary, collaborative work. [ABSTRACT FROM AUTHOR]

While in the early days of organic mass spectrometry the ortho effect was preferentially used as a diagnostic tool for structure elucidation, the recent research activities have concentrated on mechanisms and related aspects. Among these the following were the most important topics: hydrogen transfer and especially the question of concerted or multistep reaction; the influence of the structure on the selectivity of hydrogen migration via higher-membered transition states; the apparent cleavage of carbon/heteroatom bonds induced by hydrogen transfer; the redox processes which formally correspond to photochemical transformations, but which are completely different according to the reaction mechanisms; the different types of cyclization reactions; and the field of exchange processes preceding or accompanying unimolecular decompositions of ions in the gas phase. If a prognosis concerning the future activities in the field of electron impact induced ortho effects may be risked, the following aspects will probably become more important in addition to the topics discussed in this review:(i)Kinetic studies in the time range of nanoseconds to elucidate the time dependence of the different ortho effect reactions;(ii)ion/molecule reactions with the scope to obtain more information concerning the reactivities of open and closed shell systems;(iii)comparative studies in the fields of mass spectrometry, photochemistry and electrochemistry. In principle all these studies may extend our knowledge concerning the inherent properties of isolated ionic species. [ABSTRACT FROM AUTHOR]

The strengths and weaknesses of EXAFS in determining the radial distribution of the first nearest neighbours in coordination compounds are well known. We point out here how local information given by EXAFS upon the first coordination sphere can be used to characterize short or long range order or disorder in low dimensional materials. Low temperature measurements, use of several absorbing species in the same compound, comparison between seemingly contradictory X-Ray diffraction and EXAFS data allow to solve three dimensional structural problems related to physical properties. The materials studied are insulating uni- or bimetallic magnetic chains and pure or intercalated MPS3 layers. [ABSTRACT FROM AUTHOR]

Current views on the structure and function of biological membranes imply a great variety of dynamical aspects. These range from the dynamic phase behaviour of phospholipids and conformational variations of membrane proteins during membrane-associated processes, to the interactions between membranes in fusion and pore formation. The structural description of these processes, many of which imply the possibility of intermediate structures, calls for fast time-resolved diffraction methods, i.e. the cinematographic approach. The present article gives first an overview on the specific problems and the theories for their solution in X-ray diffraction on membranes, and then reviews the present possibilities of time-resolved structural studies using synchrotron radiation on phospholipid model systems and functional membranes (sarcoplasmic reticulum membrane). It is shown that such studies bear great promise in entering the millisecond time domain and bridging the existing gap between static structural information and the wealth of dynamic data derived from spectroscopic methods. [ABSTRACT FROM AUTHOR]

Small angle X-ray scattering and diffraction methods can provide information about chromatin structure at the levels of nucleosomes, chromatin fibre and whole nuclei. Making use of the high flux and point focusing achieved on synchrotron radiation cameras it has been possible to carry out systematic static and kinetic investigations of chromatin structure with minimum damage or perturbation on fresh samples. The results provide a strong evidence for a preformed 3-D zigzag structure at low ionic strength which folds instantaneously into the "30 nm filament" upon increasing the ionic strength. The extent of folding at a given ionic strength depends on the nature of the cations and can be influenced by other substances which bind to DNA. Models of chromatin fibre structure are discussed in the context of various experimental results. [ABSTRACT FROM AUTHOR]

The use of anomalous X-ray scattering of light elements like sulfur and phosphorus is of particular interest in biological structure research. These elements serve as native labels in proteins, nucleic acids and membranes. Their medium scattering power is drastically changed at their K absorption edges at wavelengths between 5 and 6 Å where X-ray absorption excludes the use of open air diffractometers. The construction of a new diffractometer tunable to wavelengths between 1.2 and 7 Å is presented. First results of anomalous scattering from sulfur in bacteriorhodopsin near the K absorption edge have been obtained recently. Their possible impact on crystallography will be considered. A comparison with nuclear spin dependent neutron scattering is given. [ABSTRACT FROM AUTHOR]

Applications of X-ray absorption spectroscopy in two areas of liquid state studies using synchrotron radiation are reviewed. One area concerns with the determination of the local structure, bonding and dynamics at the metal site of transition metal complexes using Extended X-Ray Absorption Fine Structures (EXAFS) and X-Ray Absorption Near Edge Structures (XANES). Emphasis are placed on the implications of the derived parameters to the reactivity of the complexes in exchange reactions (ligand and electron) in solution and to the subtle electronic and structural change of the complexe upon dissolution. The other area deals with the principles and practices of X-ray induced photo-conductivity of hydrocarbon solutions. The conductivity measurements of EXAFS of organometallics in hydrocarbon solution is described. The special feature of the technique. EXAFS measurement under the condition of total X-ray absorption, is discussed in some details. Current developments is related areas are also noted. [ABSTRACT FROM AUTHOR]

The first observations of an increase of the reactivity between gases in the presence of a metal were made, almost one hundred years ago, by chemists like Davy or Thenard. This pioneer work led Berzelius and Mitscherlich to define the concept of "decomposition of species by contact under a catalytic force". Since then much work has been done in order to understand the behavior of these small transition metal clusters which are able to promote some chemical reactions. In fact, catalysis has become a field of enormous economical interest. It spans a wide variety of areas from oil reforming to the preparation of synthetic fibers or fertilizers. Theoretical research as well as chemical engineering are therefore deeply involved and many current studies deal with the knowledge of such materials. It is not always easy to characterize the electronic and crystallographic structures of very small aggregates. Their size (a few nanometers) is due to the fact that as many atoms as possible must be active and therefore must be at the surface. Moreover, the analysis has to be done in situ, under the true reaction conditions, in order to build a physical model for the role of the catalyst. Then, many experimental techniques have been used, including most recently electron microscopy and X-ray absorption. We focus our attention here on the EXAFS (Extended X-ray Absorption Fine Structure) technique and its possibilities for the study of supported metal catalysts. Most of the examples come from a collaboration between LURE and some public CNRS laboratories (Strasbourg, Meudon) and a private one (IFP — Rueil Malmaison). We begin with some generalities about the technique and the type of catalysts studied, then move to several examples of application. [ABSTRACT FROM AUTHOR]