Hybrid Matrices Research Articles

Sol-gel hosts doped with porphyrin derivatives. Part I. Spectroscopy, hole-burning and spectral diffusion

Pure inorganic sol-gel matrices as well as hybrid organic/inorganic xerogels have been doped with porphyrins derivatives and studied using line narrowing techniques. The role of residual hydroxyl groups is investigated. Free-base porphyrins are protonated in pure inorganic hosts, but the matrix acidity is reduced in hybrid matrices or when fluorinated porphyrins derivatives are used. The linear electron-phonon coupling can be controlled with the choice of the organic group in organic/inorganic matrices. Persistent spectral hole widths increase with temperature according a glass-like T n dependence and evidence of spectral diffusion is shown in one of these systems.

Sol-gel hosts doped with porphyrin derivatives. Part II. Site selection spectra and vibronic analysis

The detailed vibrational analysis of the fine structured fluorescence and excitation spectra of tetraphenylporphyrin and of tetra(pentafluorophenyl)porphyrin embedded in polystyrene film or in inorganic or hybrid organic/inorganic sol-gel matrices under selective laser excitation at low temperature is presented. The fine structure fluorescence spectra of tetra(pentafluorophenyl)chlorin present as a contaminant in the samples have been fully analyzed. The change in the activity of some low frequency vibration modes observed in inorganic hosts is associated with a change in the orientation of the phenyl groups which intend to be parallel to the macrocycle. This is in contrast with what is observed in polystyrene or in hybrid matrices.

Enhancement of the photochromic performance of spirooxazine in sol-gel derived organic-inorganic hybrid matrices by additives

Organic-inorganic hybrid materials synthesized via sol-gel processing are excellent solid matrices for photochromic dyes like spirooxazine, and the photochromic performance can be further enhanced by introducing suitable additives. This work describes the effects of additives on the photochromic intensity (ΔA 0), decolouration rate (k) and photostability of spirooxazine in sol-gel derived organic-inorganic hybrid matrices. They include fluoroalkylsilane (FAS), bisphenolA (BPA) and methyl-imidazole (MI). FAS enhances both ΔA 0 and photostability, but has little effect onk. The higher the content of BPA, the higher the ΔA 0 and the higher the photostability, but the lower thek. The effect of MI on ΔA 0 andk is not so considerable as that of BPA and is a little complicated, while significant improvement in photostability is achieved by the addition of MI at an optimum concentration with the presence of BPA at a higher content.

Enhancement of the photochromic performance of spirooxazine in sol-gel derived organic-inorganic hybrid matrices by additives

Enhancement of the photochromic performance of spirooxazine in sol-gel derived organic-inorganic hybrid matrices by additives

Spirooxazine- and spiropyran-doped hybrid organic–inorganic matrices with very fast photochromic responses

Both spirooxazine and spiropyran dyes have been embedded into two different hybrid matrices, which were formed from hydrolysis and cocondensation between diethoxydimethylsilane and zirconium propoxide and between methyldiethoxysilane (DH) and triethoxysilane (TH) respectively. The nature and the kinetics of the photochromic response depend strongly on the hydrophobic/hydrophilic balance (HHB) of the hybrid material. The HHB controls the competition between direct and reverse photochromism. The photochromic behaviour of the strongly hydrophobic spirooxazine-doped DH/TH coatings is direct, highly efficient (ΔA>1), reversible and extremely fast (thermal bleaching time constant, k=0.2 s -1 ). The photochromic kinetics of this hybrid material are, to the best of our knowledge, much faster than those reported for spirooxazine in any other solid matrix.

Photochromism of Spirooxazine-Doped Gels

Spirooxazine photochromic dyes were trapped in gel thin films. Organically modified doped gels showed normal photochromism. The kinetics of the photochromism in these gels was quantified using both Gaussian and simple biexponential models in order to take into account the inhomogeneous distribution of free volume in the gel matrix and to compare the photodynamics with that in organic polymers. In organic−inorganic hybrid matrices, a competition was observed between normal and reverse photochromisms because of the presence of two chemical environments for the dye molecules. The kinetics of photodegradation for dye-doped gels was deduced from the recording of the excitation/emission spectra during UV light irradiation.

A COMPUTER METHOD FOR THE FORMULATION OF AVERAGED MODELS FOR DC/DC POWER CONVERTER CIRCUITS

A computer method for deriving averaged circuit models for a class of power converter circuits is proposed. The proposed method is applicable to any dc/dc converter circuit whose switching frequency is much greater than the natural frequency of each constituent circuit topology. The method starts with decomposing the original circuit into two multiport sub-circuits. One contains the "fast" part, called the Minimum Separable Switching Configuration (MISSCO), and the other contains the remaining "slow" part of the circuit. A hybrid matrix that relates the port voltages and currents of the MISSCO to these constant sources is determined for each switching cycle. By applying one-cycle averaging operation to the hybrid matrices, the low frequency averaged model of the MISSCO is derived. This averaged model can then be combined with the rest of the circuit to form a complete equivalent circuit. For brevity we demonstrate the method in this paper for DC/DC converter circuits in the absence of parasitics. To illustrate the proposed method, the Ćuk converter is considered and its averaged model is derived for the discontinuous inductor-current mode of operation.

Estimating Phylogenies from Lacunose Distance Matrices, with Special Reference to DNA Hybridization Data

Distance methods for producing phylogenies require n* comparisons among y1 taxa to generate a complete matrix. Moreover, techniques for generating distances-such as DNA hybridization-are subject to both systematic and random experimental errors, so that the measurements do not satisfy the mathematical properties of distances. We have explored the possibility of reconstructing trees from incomplete data. In our simulations, we discard one or both of reciprocal pairs from a complete matrix, estimate these values, reconstruct a tree, and compare the topology and branch lengths of the estimated tree with the phylogeny based on complete data. We investigated separately and jointly the effects of rate variation and random and systematic errors, added to a fabricated ultrametric matrix, and then passed on to simulation experiments with several complete DNA hybridization matrices. Our empirical results show that topological and metric recovery is always very good provided no terminal sister taxa lack both reciprocal measurements or extremely short internodes are involved. We then present two applications of the method for estimating phylogenies from incomplete DNA hybridization matrices-the first illustrating reconstruction of a matrix with about 27% of missing cells, and the second suturing two matrices where some data are held in common but 29% are missing from the combined table. Thus, considerable information may be implicit in very sparse matrices, and this circumstance has practical consequences for distance studies when money, material, or time are limited.

Structure of a Duplex Oligodeoxynucleotide Containing Propanodeoxyguanosine Opposite a Two-Base Deletion in the (CpG)3 Frame-Shift Hotspot of Salmonella typhimurium hisD3052 Determined by 1H NMR and Restrained Molecular Dynamics

Structural refinement from solution 1H NMR data was performed on the 5'-d[ATCGC(PdG)-CGGCATG]-3'.5'-d[CATGCCGCGAT]-3' duplex, in which the adducted oligodeoxynucleotide containing the exocyclic lesion 1,N2-propano-2'-deoxyguanosine (PdG) was annealed with the complementary strand which contained a CpG deletion. The resulting duplex required PdG and one adjacent cytosine to be unpaired. A total of 352 distances were utilized to restrain molecular dynamics calculations, of which 264 were NOE-derived. These distances were calculated using complete relaxation matrix methods from hybrid matrices, which were comprised of the experimentally determined distances and additional distances derived from either A-form or B-form DNA. A simulated annealing protocol combined with the distance restraints was able to refine a single structure with an average rms deviation of < 1.35 A. The accuracy of the refined structure was assessed using full relaxation matrix calculations, which gave good agreement with measured NOE intensities. PdG was found to be stacked into the helix below base pair C3.G18, whereas C5 was found to be unpaired and extruded toward the major groove and parallel to base pair G6.C17. This created a localized bend in the DNA helix of approximately 20-35 degrees at the junction between PdG and C5. The bending corroborated previous assays performed on this modified sequence [Moe, J. G., Reddy, G. R., Marnett, L. J., & Stone, M. P. (1994) Chem. Res. Toxicol. 7, 319-328].

Full-wave analysis of radiating planar resonators with the method of lines

The method of lines (MoL) is extended to analyze radiating planar resonators by the use of absorbing boundary conditions. For stratified layers, an equivalent network is derived to set up a system equation by simple multiplication of hybrid matrices. As an example, the complex resonant frequency of a microstrip patch is computed and compared to results achieved with the integral equation method in spectral domain. The radiation in the near-field region is depicted by a vector plot of the energy flow, given by the real part of the Poynting vector. >

Bootstrap approaches to estimating confidence intervals for molecular dissimilarities and resultant trees

Varied approaches to estimating confidence intervals for immunological and hybridization distances can be uniformly applied to any matrix of distances. One procedure bootstraps the pairwise dissimilarities between the distances of every pair of taxa to all others, creating a derived matrix of distances for which dispersions can be estimated. Another approach bootstraps the sample of differences between pairwise homologous branch lengths concerning each pair of taxa and between asymmetric halves of the matrix, to find a standard error of the dispersions. This allows comparison of the robustness of trees among different sources of data. DNA hybridization, transferrin immunology and protein immunodiffusion matrices all yield much the same result once standard deviations of dissimilarities are acknowledged: namely, unresolvable trichotomies among the human-chimp-gorilla clade and among this clade with orang and gibbon; conventional relationships among hominoids, cercopithecoids, ceboids and strepsirhines; and a polychotomy among anthropoids, strepsirhines, tarsiers, tupaiids and dermopterans.

Matrix representation in reconstructing phylogenetic relationships among the eukaryotes

The application of the method of matrix representation (MRP) addresses several problems associated with reconstructing phylogenetic relationships among composite organisms such as the eukaryotes. By allowing multiple molecular-sequence and non-molecular data sets to be combined into a single, relatively compact matrix for joint analysis, MRP addresses problems associated with the depth, diversification and specialization of eukaryotic lineages. Characters whose distributions may have been affected by endosymbiotic lateral transfer can be identified by compatibility analysis of MRP-generated hybrid matrices. In conjunction with variant-filtering techniques, MRP can be used to map patterns of lateral transfer in a given phylogenetic tree. These applications are illustrated with molecular-sequence and non-molecular data sets for eukaryotes.

Transformerless synthesis of transistor and thyristor switching RLC 1‐ports

AbstractAs an extension of the synthesis method developed in a previous paper, the transformerless synthesis of reciprocal switched 1‐ports is presented in this paper. the transformerless structures of resistance switching n‐ports described by impedance, admittance or hybrid matrices have been proposed. These structures enable the synthesis of dynamical switching RC, RL and RLC 1‐ports. Using the state variables method, the realizability conditions and identification formulae for constant and sinusoidal input functions have been derived. Three numerical examples illustrate the developed methods. the present theory can be applied to create new thyristor and transistor arrangements, particularly compensators and auxiliary switching LC circuits facilitating the commutation of thyristors and transistors.

PECULIARITIES OF SELF-ORGANIZATION IN THE PRODUCTION OF INTERPENETRATING POLYMER NETWORKS

Abstract Interpenetrating polymer networks (IPN's) are the basis of a new generation of binders for polymer composites: hybrid matrices [1]. A wide range of composites, which may be characterized either as mixtures of network polymers (IPN) or of network and linear polymers (semi-IPN's or pseudo-IPN's), are attributed to this class of polymer networks. This classification of IPN's was suggested by Sperling [2]. Based on the method of synthesis, the original definition given by Millar in 1966 [3] supposed a molecular level of mixing of chains between crosslinks of constituent networks and the formation of molecular entanglements between them.

Non-isothermal crystallization kinetics of filled blends of polypropylene and low density polyethylene

Non-isothermal crystallization kinetics of filled polymer blends was investigated by DTA. Crystallization in hybrid matrices containing small amounts of low density polyethylene was shown to proceed more rapidly than that in pure polypropylene. This effect was more pronounced in the presence of a mineral filler. The Kolmogorov-Avrami kinetic model can be used to describe the crystallization process under non-isothermal conditions.

Circuits, k-ports, hidden modes, and stability of interconnected k-ports

This paper exclusively considers lumped <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">k</tex> -ports and circuits which contain linear time-invariant elements, independent sources, and controlled sources. The <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">k</tex> -ports are represented by their hybrid matrices. Tableau equations of circuits are used as a special case of polynomial matrix description. The hidden modes of a circuit are determined by inspection from its tableau equations in the Hermite row form. The same form is used also to determine the exponential stability of the circuit and that of the <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">k</tex> -port. Finally, necessary and sufficient conditions for exponential stability of interconnected <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">k</tex> -ports are given; the hidden modes of the interconnection are studied. The paper is self-contained.

Automatic generation of hybrid and displacement-type finite elements

Computational experiences have shown that, for most of the finite element models, the bulk of the computing time is taken up by the numerical integration of the finite element matrices. The algorithmic representation of the element properties and the automated analytical integration facility presented in this paper drastically reduce the computational efforts for the generation of the hybrid and displacement-type finite element matrices in general-purpose finite element programs.

Structural characteristics of polymeric hybrid matrices caused by microphase separation

The data presented lead to the conclusion that the structural characteristics of hybrid binders cause microphase separation leading to thermodynamically unstable systems; due to kinetic factors they remain mechanically stable for any time required. Hybrid binders appearing during hardening can be described adequately on the basis of the principles of irreversible thermodynamics [22] and the concept of dissipative structures [15]. The discussions based on the thermodynamics of equilibrium phase separation refer particularly to structure formation and to the conditions of microphase separation which follow either a nucleation or spinodal separation mechanism.

Nonconventional two‐port matrix decompositions and their realization

AbstractGeneral conditions for sum and product matrix decomposition are applied to the sum of the chain matrices and the product of the immittance and the hybrid matrices. The corresponding connection of the partial two‐ports is realized by special three‐ports containing operational amplifiers and current and voltage controlled sources.

Existence of hybrid matrices for active n‐ports encountered in the analysis of transistor networks

AbstractIt is shown that hybrid matrices exist for certain types of active n‐ports constructed using resistors and controlled sources. Furthermore, it is shown that the existence of these hybrid matrices implies that a certain well‐known set of necessary and sufficient conditions, which guarantees the uniqueness of solutions to the nonlinear DC equations of transistor networks, can be simplified. Additional results are presented which show how the amount of computation required to verify these conditions can be reduced.