Influence of POSS structure on the fire retardant properties of epoxy hybrid networks

Monofunctional Polyhedral Oligomeric Silsesquioxanes (POSS), differing in chemical structure, were introduced into an epoxy-amine formulation in order to obtain hybrid organic/inorganic epoxy networks. The process developed allows the POSS to be either covalently bonded to the network and organized in small amorphous domains, or completely dispersed in larger crystalline domains. Morphology, thermal and fire retardant properties were studied through electron microscopy, DSC, TGA, cone calorimeter experiments and UL94 tests. It was demonstrated that POSS nanoclusters induced an effective fire retardant effect, which was controlled by several factors. It was shown that POSS bearing phenyl ligands were far more effective than POSS with isobutyl ligands, and that the presence of a chemical linkage between the phenyl-based POSS clusters and the matrix favoured the dispersion of the nanoclusters, resulting in enhanced fire retardancy. The fire retardant effect was only slightly enhanced by increasing the amount of POSS nanoclusters.     

Generation of hierarchically correlated multivariate symbolic sequences

We introduce a method to generate multivariate series of symbols from a finite alphabet with a given hierarchical structure of similarities based on the Hamming distance. The target hierarchical structure of similarities is arbitrary, for instance the one obtained by some hierarchical clustering method applied to an empirical matrix of similarities. The method that we present here is based on a generating mechanism that does not make use of mutation rate, which is widely used in phylogenetic analysis. Here we use the proposed simulation method to investigate the relationship between the bootstrap value associated with a node of a phylogeny and the probability of finding that node in the true phylogeny. The results of this analysis are compared with those obtained in the literature according to an evolutionary model with a per-symbol constant mutation rate. We observe that the relationship between the bootstrap value of a node and the probability of the corresponding clade being correct is sensitive to both the length of data series and the length of the branch connecting the node to its closest ancestor in the phylogenetic tree, whereas such a relationship is only slightly affected by the topology of the true phylogeny and by the absolute value of similarity.     

多面齐聚倍半硅氧烷——高分子材料的多功能性新组分

综述了多面齐聚倍半硅氧烷(POSS)的结构、性能及其类型,分析和讨论了以反应型POSS制得的均聚物和共聚物及以非反应型POSS制得的聚合物/POSS纳米复合材料的特点及其应用,简要介绍了目前国外POSS及其相关物的生产及市场。     

The Möbius function of permutations with an indecomposable lower bound

We show that the Möbius function of an interval in a permutation poset where the lower bound is sum (resp. skew) indecomposable depends solely on the sum (resp. skew) indecomposable permutations contained in the upper bound, and that this can simplify the calculation of the Möbius sum. For increasing oscillations, we give a recursion for the Möbius sum which only involves evaluating simple inequalities.     

Solution of and bounding in a linearly constrained optimization problem with convex,polyhedral objective function

A dual method is presented to solve a linearly constrained optimization problem with convex, polyhedral objective function, along with a fast bounding technique, for the optimum value. The method can be used to solve problems, obtained from LPs, where some of the constraints are not required to be exactly satisfied but are penalized by piecewise linear functions, which are added to the objective function of the original problem. The method generalizes an earlier solution technique developed by Prékopa (1990). Applications to stochastic programming are also presented.This research was supported by the National Science Foundation, Grant No. DMS-9005159.Corresponding author.     

A branch-and-cut algorithm for the equicut problem

We describe an algorithm for solving the equicut problem on complete graphs. The core of the algorithm is a cutting-plane procedure that exploits a subset of the linear inequalities defining the convex hull of the incidence vectors of the edge sets that define an equicut. The cuts are generated by several separation procedures that will be described in the paper. Whenever the cutting-plane procedure does not terminate with an optimal solution, the algorithm uses a branch-and-cut strategy. We also describe the implementation of the algorithm and the interface with the LP solver. Finally, we report on computational results on dense instances with sizes up to 100 nodes.     

A simple method to synthesize polyhedral hexagonal boron nitride nanofibers

Hexagonal boron nitride (h-BN) fibers with polyhedral morphology were synthesized with a simple-operational, large-scale and low-cost method. The sample obtained was studied by X-ray photoelectron spectrometer (XPS), electron energy lose spectroscopy (EELS), X-ray powder diffraction (XRD), Fourier transformation infrared spectroscopy (FT-IR), etc., which matched with h-BN. Environment scanning electron microscopy (ESEM) and transmission electron microscope (TEM) indicated that the BN fibers possess polyhedral morphology. The diameter of the BN fibers is mainly in the range of 100–500 nm.     

Enhancing electroluminescence performance of MEH-PPV based polymer light emitting device via blending with organosoluble polyhedral oligomeric silsesquioxanes

Organosoluble polyhedral oligomeric silsesquioxanes (POSS) blending effect on electroluminescence properties of MEH-PPV based polymer light emitting device was investigated. Excellent compatibility and surface morphology of organosoluble POSS and MEH-PPV based composite films were observed using AFM spectroscopy. The surface roughness of POSS:MEH-PPV composite film increased with increasing POSS content. Interfacial area between the light-emitting layer and cathode was favorably enhanced for cathode electron-injection. MEH-PPV blended with POSS would create a better balance between the electron and hole fluxes for POSS:MEH-PPV composite film based devices. This led to greater current efficiency of the POSS:MEH-PPV composite film based device as compared to one with a light emitting layer of MEH-PPV. Organosoluble POSS concentration effects on the PL spectra and EL performances were also studied for the POSS:MEH-PPV composite film based polymer light emitting devices.     

The enumeration of electron-rich and electron-poor polyhedral clusters

We present as dual processes the capping of closed triangulated polyhedra with apical atoms and the making of holes in such polyhedra either by puncture of the surface or by excision of atoms and their edges. These processes are shown to generate stable chemical species containing respectively less or more than 2n + 2 skeletal electrons. The former species are designated as electron-poor whereas the latter are called electron-rich. Pólya's enumeration method is used to enumerate the distinct ways of capping and excising the closed, triangulated polyhedra to yield systems containing from four to twelve vertices. For the enumeration of cappings the appropriate cycle index is that of the dual of the polyhedron being capped, whilst for the enumeration of the excisions the cycle index is that of the polyhedron being excised.     

Thermo-oxygen degradation mechanisms of POSS/epoxy nanocomposites

A series of polyhedral oligomeric silsesquioxane/epoxy nanocomposites (POSS/EP) containing 0 wt%, 5 wt%, 10 wt% and 15 wt% content of POSS were prepared. Mechanical properties were used as the index to show the effect of POSS on the thermo-oxygen degradation resistance of epoxy resin. And the thermo-oxygen degradation mechanism was investigated by scanning electron microscopy (SEM) and thermogravimetric analysis (TGA). Results showed that the incorporation of POSS into epoxy networks enhanced the thermo-oxygen resistance of epoxy. POSS led to the formation of inert layer on the surface of materials which could protect the internal structure from decomposition. As a result, the retention of mechanical properties of EP/POSS hybrids increased with the POSS content increasing.