On the classification of geometric codes by polynomial functions

It is shown how to represent algebraically all functions that have a zero sum on all -dimensional subspaces ofPG(n,q) or ofAG(n,q). In this way one can calculate the dimensions of related codes, or one can represent interesting sets of points by functions.     

Structure-based identification and clustering of protein families and superfamilies

Summary We describe an approach to protein structure comparison designed to detect distantly related proteins of similar fold, where the procedure must be sufficiently flexible to take into account the elasticity of protein folds without losing specificity. Protein structures are represented as a series of secondary structure elements, where for each element a local environment describes its relations with the elements that surround it. Secondary structures are then aligned by comparing their features and local environments. The procedure is illustrated with searches of a database of 468 protein structures in order to identify proteins of similar topology to porcine pepsin, porphobilinogen deaminase and serum amyloid P-component. In all cases the searches correctly identify protein structures of similar fold as the search proteins. Multiple cross-comparisons of protein structures allow the clustering of proteins of similar fold. This is exemplified with a clustering of /- and -class protein structures. We discuss applications of the comparison and clustering of three-dimensional protein structures to comparative modelling and structure-based protein design.     

The diagnonal multivariate natural exponential families and their classification

A natural exponential family (NEF)F in ? ⁿ ,n>1, is said to be diagonal if there existn functions,a ₁,...,a _n , on some intervals of ?, such that the covariance matrixV _F (m) ofF has diagonal (a ₁(m ₁),...,a _n (m _n )), for allm=(m ₁,...,m _n ) in the mean domain ofF. The familyF is also said to be irreducible if it is not the product of two independent NEFs in ? ^k and ? ^n-k , for somek=1,...,n?1. This paper shows that there are only six types of irreducible diagonal NEFs in ? ⁿ , that we call normal, Poisson, multinomial, negative multinomial, gamma, and hybrid. These types, with the exception of the latter two, correspond to distributions well established in the literature. This study is motivated by the following question: IfF is an NEF in ? ⁿ , under what conditions is its projectionp(F) in ? ^k , underp(x ₁,...,x _n )∶=(x ₁,...,x _k ),k=1,...,n?1, still an NEF in ? ^k ? The answer turns out to be rather predictable. It is the case if, and only if, the principalk×k submatrix ofV _F (m ₁,...,m _n ) does not depend on (m _k+1,...,m _n ).     

Total synthesis of 3,3′:4′,3″-ter-1,2,5-thiadiazole using a synthetic utility of S4N4·SbCl5 complex

3,3′:4′,3″-Ter-1,2,5-thiadiazole, an useful oligoheterocyclic compound, has been accomplished in seven steps from 1-(5-methyl-3-isoxazolyl)ethanone or diethyl acetylenedicarboxylate using a synthetic utility of tetrasulfur tetranitride antimony pentachloride (S₄N₄·SbCl₅) complex to make a 1,2,5-thiadiazole ring.     

Synthesis, characterization and Schlenk equilibrium studies of methylmagnesium compounds with O- and N-donor ligands - the unexpected behavior of [MgMeBr(pmdta)] (pmdta = N,N,N′,N″,N″-pentamethyldiethylenetriamine)

MgMe₂ (1) was found to react with 1,4-diazabicyclo[2.2.2]octane (dabco) in tetrahydrofuran (thf) yielding a binuclear complex [{MgMe₂(thf)}₂(μ-dabco)] (2). Furthermore, from reactions of MgMeBr with diglyme (diethylene glycol dimethyl ether), NEt₃, and tmeda (N,N,N′,N′-tetramethylethylenediamine) in etheral solvents compounds MgMeBr(L), (L = diglyme (5); NEt₃ (6); tmeda (7)) were obtained as highly air- and moisture-sensitive white powders. From a thf solution of 7 crystals of [MgMeBr(thf)(tmeda)] (8) were obtained. Reactions of MgMeBr with pmdta (N,N,N′,N″,N″-pentamethyldiethylenetriamine) in thf resulted in formation of [MgMeBr(pmdta)] (9) in nearly quantitative yield. On the other hand, the same reaction in diethyl ether gave MgMeBr(pmdta) · MgBr₂(pmdta) (10) and [{MgMe₂(pmdta)}₇{MgMeBr(pmdta)}] (11) in 24% and 2% yield, respectively, as well as [MgMe₂(pmdta)] (12) as colorless needle-like crystals in about 26% yield. The synthesized methylmagnesium compounds were characterized by microanalysis and ¹H and ¹³C NMR spectroscopy. The coordination-induced shifts of the ¹H and ¹³C nuclei of the ligands are small; the largest ones were found in the tmeda and pmdta complexes. Single-crystal X-ray diffraction analyses revealed in 2 a tetrahedral environment of the Mg atoms with a bridging dabco ligand and in 8 a trigonal-bipyramidal coordination of the Mg atom. The single-crystal X-ray diffraction analyses of [MgMe₂(pmdta)] (12) and [MgBr₂(pmdta)] (13) showed them to be monomeric with five-coordinate Mg atoms. The square-pyramidal coordination polyhedra are built up of three N and two C atoms in 12 and three N and two Br atoms in 13. The apical positions are occupied by methyl and bromo ligands, respectively. Temperature-dependent ¹H NMR spectroscopic measurements (from 27 to −80 °C) of methylmagnesium bromide complexes MgMeBr(L) (L = thf (4); diglyme (5); NEt₃ (6); tmeda (7)) in thf-d₈ solutions indicated that the deeper the temperature the more the Schlenk equilibria are shifted to the dimethylmagnesium/dibromomagnesium species. Furthermore, at −80 °C the dimethylmagnesium compounds are predominant in the solutions of Grignard compounds 4-6 whereas in the case of the tmeda complex7 the equilibrium constant was roughly estimated to be 0.25. In contrast, [MgMeBr(pmdta)] (9) in thf-d₈ revealed no dismutation into [MgMe₂(pmdta)] (12) and [MgBr₂(pmdta)] (13) even up to −100 °C. In accordance with this unexpected behavior, 1:1 mixtures of 12 and 13 were found to react in thf at room temperature yielding quantitatively the corresponding Grignard compound 9. Moreover, the structures of [MgMeBr(pmdta)] (9c), [MgMe₂(pmdta)] (12c), and [MgBr₂(pmdta)] (13c) were calculated on the DFT level of theory. The calculated structures 12c and 13c are in a good agreement with the experimentally observed structures 12 and 13. The equilibrium constant of the Schlenk equilibrium (2 9c ? 12c + 13c) was calculated to be K_gas = 2.0 × 10⁻³ (298 K) in the gas phase. Considering the solvent effects of both thf and diethyl ether using a polarized continuum model (PCM) the corresponding equilibrium constants were calculated to be K_thf = 1.2 × 10⁻³ and K_ether = 3.2 × 10⁻³ (298 K), respectively.     

Investigation on the thermal degradation of acrylic polymers with fluorinated side-chains

The thermal degradation of poly-2,2′,3,3′,4,4′,5,5′,6,6′,7,7′,7″-tridecafluoroheptylacrylate and poly-2,2′,3,3′,4,4′,5,5′,6,6′,7,7′-dodecafluoroheptylmethacrylate has been studied in isothermal conditions at 450-750 °C using pyrolysis-gas chromatography. The type and composition of the pyrolysis products give useful information about mechanism of thermal degradation. It was shown that the main thermal degradation process for both polymers is random main-chain scission. The major degradation products for fluorinated polyacrylate are monomer, dimer, saturated diester, trimer, and corresponding methacrylate. The fluorinated polymethacrylate gives monomer as the main product of thermal destruction. As a result of side-chain reaction, the thermal degradation of the fluorinated polyacrylate also produces remarkable amounts of alcohol. On the other hand, the respective alcohol is only a minor component among the pyrolysis products of the fluorinated polymethacrylate. For both polymers, the main nontrivial degradation product coming from the alkyl ester decomposition is the corresponding fluorinated cyclohexane. The formation of the fluorinated cyclohexanes may be accounted for a nucleophilic bimolecular substitution pathway.     

QSPR Modeling of Gibbs Free Energy of Organic Compounds by Weighting of Nearest Neighboring Codes

We examine the encoding of chemical structure of organic compounds by Labeled Hydrogen-Filled Graphs (LHFGs). Quantitative Structure-Property Relationships (QSPR) for a representative set of 150 organic molecules have been derived by means of the optimization of correlation weights of local invariants of the LHFGs. We have tested as local invariants Morgan extended connectivity of zero- and first order, numbers of path of length 2 (P2) and valence shells of distance of 2 (S2) associated with each atom in the molecular structure, and the Nearest Neighboring Codes (NNC). The best statistical characteristics for the Gibbs free energy has been obtained for the NNC weighting. Statistical parameters corresponding to this model are the following n = 100, r² = 0.9974, s = 5.136 kJ/mol, F = 38319 (training set); n = 50, r² = 0.9990, s = 3.405 kJ/mol, F = 48717 (test set). Some possible further developments are pointed out.     

N,N′,N″-Tri-Boc-guanidine (TBG): a common starting material for both N-alkyl guanidines and amidinoureas

In this Letter, we describe the unexpected reaction pattern of N,N′N″-tri-Boc-guanidine (TBG) with amines at room temperature and under reflux conditions affording N-substituted guanidines and amidinoureas, potentially important compounds with extensive applications in medicinal chemistry. This investigation shows that TBG is an excellent, readily available common starting material for the synthesis of various N-alkyl guanidines as well as N-alkyl-N′-substituted amidinoureas by simply manipulating the reaction conditions.     

Order-disorder at Fe sites in SrFe2/3B″1/3O3 (B″=Mo, W, Te, U) tetragonal double perovskites

We have prepared SrFe_2/3B″_1/3O₃ (B″=Mo, U, Te, and W) double perovskites in polycrystalline form by ceramic methods. Phases with B″=U, Te and W have been studied by X-ray powder diffraction and the results have been compared with neutron diffraction data available for B″=Mo. At room temperature, the stoichiometric samples crystallize in the tetragonal crystal system (space group I4/m, Z=4). Cell parameters when B″=U, Te and W are a=5.6936(1) Å, c=8.0637(1)Å; a=5.5776(1) Å, c=7.9144(3) Å and a=5.5707(3) Å, c=7.9081(5) Å, respectively.The Mössbauer spectra at room temperature for all compounds show hyperfine parameters belonging to two Fe³⁺ sites located at lattice positions with different degrees of distortion. This is in agreement with diffraction data that indicate that the series of compounds display different degrees of Fe-site disorder, which increases in the following sequence: Mo<U<Te<W.     

基于RS编码及网格编码调制的光PPM通信纠错技术

分析了RS(Reed-Solomon)纠错码和网格编码调制（Trellis Coded Modulation,TCM）技术在光脉冲位置调制通信中的应用.在此基础上,提出了以RS码作为外码,以网格编码调制技术作为内码,用于光脉冲位置调制通信的新编码方案,能以几乎不减少通信速率的优势,提高传统RS码系统在时变带限光信道中的通信性能.模拟研究了在不同空间光信道条件下,传统RS码的符号正确传输率和误码率,并对网格编码调制的编码增益、RS码与网格编码调制级联时的编码增益进行了仿真研究,证实了本方案的有效性.