A Method for Predicting the Number of Near Mid-Air Collisions in a Defined Airspace<Superscript>†</Superscript>

A method is proposed for calculating the number of Near Mid-Air Collisions to be expected in a volume of airspace about which the traffic patterns are known. Whilst not providing absolute predictions, because of the difficulty of modelling the human elements in such a system, the technique does enable those areas of particular air traffic control complexity to be highlighted.     

Highway noise barriers: new shapes

This paper describes the relative acoustical performances established by scale model testing of a number of relatively novel noise barriers in typical highway situations. The various barriers were thin, wide, T-profiled, cylindrically topped, corrugated, inclined, Y-profiled, arrow-profiled and of the thnadner principle, and some were treated with sound absorptive material. The highway situations involved a single barrier with a protected receiver (i.e., a receiver behind the barrier), a single barrier with a receiver on the opposite side of the highway, and parallel barriers, one on each side of the highway. In the single barrier, protected receiver case, higher noise reduction was found for wide top barriers, especially those of T-profile, and especially T-profile absorptive top barriers with cap widths of 0·6 m (2 ft) or more and of small cap thickness. Absorptive side treatment was effective in reducing a small, but measurable sound increase found when a reflective sided barrier is installed on the opposite side of the highway to receivers, and in reducing the degradation in performance that occurs when there is a barrier on each side of the highway rather than on just one.     

Durability of sound absorbing materials for highway noise barriers

This paper presents the results of a research study into two properties of sound absorbing materials intended for highway noise barrier applications: their durability and their sound absorption coefficients before and after exposure to adverse weather. After surveying the products of 34 manufacturers, eight materials and one “absorption system” were tested in the field and the laboratory. Even though there is no single, accepted test for weather endurance for these kinds of material, the results of the study provide in ormation on their likely future behaviour when installed on a barrier. The results apply at least partially to other outdoor situations too, and augment the limited information presently available on sound absorptive materials for outdoor use.     

Boson description of many-exciton systems in polar semiconductors

Using a unitary transformation the Hamiltonian of interacting polar excitons is established. Two representative states of the many-exciton systems, the biexciton and the dielectric excitonic liquid are discussed for the materials CdS, CuCl and CuBr.     

Surface microcracks decoration and disclination defects of wholly aromatic liquid crystalline copolyesters

An intensive study has been conducted to map the director fields of disclination of nematic liquid crystalline copolyesters. In this study, films of two wholly aromatic main-chain polyesters containing para- (ABA/MH/TFTA) and meta-linkages (ABA/MH/TFIA) (ABA, p-acetoxybenzoic acid; MH, maleic hydrazine; TFTA, tetrafluoroterephthalic acid; TFIA, tetrafluoroisophthalic acid) were synthesized to investigate the effects of kinks on liquid crystallinity, disclination strength (S), and surface microcracks decoration. These two copolyesters were prepared by in-situ thin film polymerization and characterized by polarizing light microscope, wide-angle X-ray diffraction, as well as "rotational isomeric states" (RIS) Metropolis Monte Carlo (RMMC) simulation. An optical microscope shows that the surface microcracks forms in the nematic-mosaic texture during a rapid quenching. The ABA/MH/TFTA film exhibits disclination strength with S = +1 and S = -(1)/(2); however, disclination strengths with S = +/-1 have been observed in the ABA/MH/TFIA system. To our best knowledge, this is the first paper reporting the effects and evidence of kink (meta and para moieties) on topological defect of disclination. In addition, the RMMC analysis supports the liquid crystal formation in both polyester films with a persistence ratio greater than 6.42.     

Oxoneptunium(v) as part of the framework of a polyoxometalate

(NH4)14Na4[(Np3W4O15)(H2O)3(BiW9O33)3].62H2O (1) and (NH4)14.5Na3.5[(Np3W4O15)(H2O)3(SbW9O33)3].40.5H2O (2) each contain three neptunyl(v) moieties encapsulated within heteropolyoxotungstate frameworks in which axial {NpO2}+ oxygens form one face of a WO6 octahedron.     

Application of Chitosan-Based Biomaterials for Blood Vessel Regeneration

Summary: Vascular diseases are the leading cause of morbidity and mortality in the western world. Autologous vessels remain the standard for coronary grafting and peripheral bypass surgery; however, their availability in patients can be limited. Therapeutic angiogenesis using growth factors, genes, or progenitor cells has been given considerable scientific attention over the last decade, but has not yet provided a definitive clinical benefit. Biomaterials could be developed to protect protein, DNA and cells against hostile conditions. Chitosan, a natural polymer of glucosamine and N-acetyl glucosamine, has been widely studied in tissue engineering due to its biocompatibility, biodegradability, and muco-adhesive and antimicrobial properties. Notably, the application of chitosan has been gaining attention in the vascular field due to its structural similarity to glycosaminoglycans, which are components of a tissue's extracellular matrix. In this review, chitosan-based materials, and their use in tissue engineered blood vessels, and as protein, gene and cell vectors for angiogenic therapy are discussed.     

Isomorphism of Modular Group Algebras of p-Mixed Abelian Groups

Let A be a torsion-free abelian group and F a free subgroup of A. We prove that if A/F is a reduced p-group and A/(F + C) is reduced for every p-pure subgroup C of A, then A is free.

Let KG be the group algebra of an abelian group G over a field K of prime characteristic p. Denote by S(KG) the p-component of the group V(KG) of normalized units of KG (of augmentation 1). Let H be an arbitrary group and KH ? KG as K-algebras. We prove the following. First, assume that G is a splitting group, the p-component G _p of G is simply presented, and the field K is perfect. Then H _p  ? G _p . If, in addition, G is p-mixed, then G _p is a direct factor of S(KG), and G is a direct factor of V(KG), each with the same simply presented complement. Secondly, we introduce a class of special p-mixed abelian groups and prove that, if G belong to this class, then any group basis of the group algebra KG splits. Besides, H is p-mixed and splits. Thirdly, if G is a special p-mixed abelian group and G _p is a reduced totally projective p-group, then H ? G. These results correct some essential inaccuracies and incompleteness in the proofs of results in this direction of Danchev [3-8 Danchev , P. V. ( 1998 ). Isomorphism of commutative group algebras of mixed splitting groups . Compt. Rend. Acad. Bulg. Sci. 51 : 13 – 16 . Danchev , P. V. ( 2000 ). Isomorphism of modular group algebras of totally projective abelian groups . Communications in Algebra 28 : 2521 – 2531 . Danchev , P. V. ( 2001 ). On a question of W. L. May concerning the isomorphism of modular group algebras . Communications in Algebra 29 : 1953 – 1958 . Danchev , P. V. ( 2001 ). Normed units in Abelian group rings . Glasg. Math. J. 43 : 365 – 373 . Danchev , P. V. ( 2002 ). Invariants for group algebras of splitting abelian groups with simply presented components . Compt. Rend. Acad. Bulg. Sci. 55 : 5 – 8 . Danchev , P. V. ( 2004 ). A note on the isomorphic modular group algebras of abelian groups with simply presented p-components . Compt. Rend. Acad. Bulg. Sci. 57 : 13 – 14 . ].