Synchronization of the self-excited pendula suspended on the vertically displacing beam

We consider the synchronization of a number of self-excited identical pendula hanging on the same beam which can move vertically. We identify different synchronous configurations and investigate their stability. An approximate analytical analysis of the energy balance allows to derive the synchronization conditions, phase difference between pendula and explains the observed types of synchronizations.     

Simultaneous speciation analysis of inorganic nitrogen with the use of ion chromatography in highly salinated environmental samples

We present the development of a method for the simultaneous determination of inorganic nitrogen species in oxidized (NO₂^–, NO₃^–) and reduced (NH₄⁺) forms using ion chromatography with diode‐array detection (205, 208, and 425 nm, respectively). The oxidized forms were determined directly after the separation in the anion exchanger, while the reduced form was determined in the column hold‐up time after derivatization with the Nessler reagent. The use of an appropriate modifier (Seignette reagent) and mobile phase (NaCl) enabled the determination of inorganic nitrogen species in highly salinated environmental samples (water, sediments). Moreover, low detection limits were obtained of 0.04 mg/L for NH₄⁺ and 0.006 and 0.005 mg/L for NO₂^– and NO₃^–, respectively. The analysis of environmental samples indicated NH₄⁺ contents of up to 1161 ± 47 mg/kg and NO₃^– of up to 148 ± 6 mg/kg for sediment samples, as well as the NH₄⁺ concentrations of up to 0.98 ± 0.10 mg/L, NO₂^– of up to 24 ± 1 mg/L and NO₃^– of up to 20 ± 1 mg/L for water samples.     

Transition state differences in hydrolysis reactions of alkyl versus aryl phosphate monoester monoanions

Although aryl phosphates have been the subject of numerous experimental studies, far less data bearing on the mechanism and transition states for alkyl phosphate reactions have been presented. Except for esters with very good leaving groups such as 2,4-dinitrophenol, the monoanion of phosphate esters is more reactive than the dianion. Several mechanisms have been proposed for the hydrolysis of the monoanion species. (18)O kinetic isotope effects in the nonbridging oxygen atoms and in the P-O(R) ester bond, and solvent deuterium isotope effects, have been measured for the hydrolysis of m-nitrobenzyl phosphate. The results rule out a proposed mechanism in which the phosphoryl group deprotonates water and then undergoes attack by hydroxide. The results are most consistent with a preequilibrium proton transfer from the phosphoryl group to the ester oxygen atom, followed by rate-limiting P-O bond fission, as originally proposed by Kirby and co-workers in 1967. The transition state for m-nitrobenzyl phosphate (leaving group pK(a) 14.9) exhibits much less P-O bond fission than the reaction of the more labile p-nitrophenyl phosphate (leaving group pK(a) = 7.14). This seemingly anti-Hammond behavior results from weakening of the P-O(R) ester bond resulting from protonation, an effect which calculations have shown is much more pronounced for aryl phosphates than for alkyl ones.     

Photo-degradation of poly(neopentyl isophthalate). Part II: Mechanism of cross-linking

The mechanism of cross-linking of poly(neopentyl isophthalate) (PNI) by photo-degradation in nitrogen atmosphere was investigated. The exposure of PNI to UV light resulted in gel (insoluble material) formation. The gel material was collected and the morphology of the gel material was characterized with SEM. The gel has the highest density near the coating surface. To obtain information on the cross-linking at a molecular level the gel was decomposed by methanolysis and the decomposition products were analysed with LC-MS. Besides the expected “grafting” types of cross-links (phenyl-to-phenyl coupling) also “chain coupling” types of cross-links were detected (recombination of neopentyl glycol based moieties). Analysis of samples that had been exposed to UV light in air indicates that the phenyl-to-phenyl coupling also occurs in the presence of oxygen.     

Advances in Star‐Shaped π‐Conjugated Systems: Properties and Applications

Until recently π‐conjugated organic materials are based mainly on linear systems. Recent years, however, have brought about increasing interest in molecules boasting a dendritic, branched, or star‐shaped architecture. This tendency is a direct result of the ongoing search for materials with progressively better properties. Such compounds, featuring novel, 3D architectures, exhibit a multitude of interesting qualities, making them stand out from well‐known materials. The direction of star‐shaped compound application is determined by whether they are able to form aggregates, π‐stacks. This feature is a source of some astounding properties, coveted in numerous applications. Among this class of compounds high charge mobility, high fluorescence efficiency, and good charge separation are all found. Depending on the structure of the core, the molecule may adopt various types of symmetry. Similarly, the conjugation of orbitals may extend over the whole structure or be interrupted at chosen segments. The number of papers pertaining to star‐shaped oligomers and polymers is ascending with each year, evidencing a growing interest in them. Consequently, this Review focuses particularly on the most recent reports concerning modification of the structure and properties of the aforementioned type of compounds, as well as on the development of devices based on them.

     

Synthesis of Cyano‐Substituted Diaryltetracenes from Tetraaryl[3]cumulenes

A versatile, two‐step synthesis of highly substituted, cyano‐functionalized diaryltetracenes has been developed, starting from easily accessible tetraaryl[3]cumulenes. This unprecedented transformation is initiated by [2+2] cycloaddition of tetracyanoethylene (TCNE) to the proacetylenic central double bond of the cumulenes to give an intermediate zwitterion, which after an electrocyclization cascade and dehydrogenation yields 5,5,11,11‐tetracyano‐5,11‐dihydrotetracenes in a one‐pot procedure. A subsequent copper‐assisted decyanation/aromatization provided the target 5,11‐dicyano‐6,12‐diaryltetracene derivatives. All of the postulated structures were confirmed by X‐ray crystallography. The new chromophores are thermally highly stable and feature promising fluorescence properties for potential use in optoelectronic devices. They are selective chemosensors for Cu^I ions, which coordinate to one of the CN substituents and form a 1:1 complex with an association constant of K_a=1.5×10⁵ L mol^?1 at 298 K.     

On the relation between correlation dimension,approximate entropy and sample entropy parameters,and a fast algorithm for their calculation

We explore the relation between correlation dimension, approximate entropy and sample entropy parameters, which are commonly used in nonlinear systems analysis. Using theoretical considerations we identify the points which are shared by all these complexity algorithms and show explicitly that the above parameters are intimately connected and mutually interdependent. A new geometrical interpretation of sample entropy and correlation dimension is provided and the consequences for the interpretation of sample entropy, its relative consistency and some of the algorithms for parameter selection for this quantity are discussed. To get an exact algorithmic relation between the three parameters we construct a very fast algorithm for simultaneous calculations of the above, which uses the full time series as the source of templates, rather than the usual 10%. This algorithm can be used in medical applications of complexity theory, as it can calculate all three parameters for a realistic recording of 10⁴${10}^4$ points within minutes with the use of an average notebook computer.