The structure of phosphate glass biomaterials from neutron diffraction and 31P nuclear magnetic resonance data

Neutron diffraction and 31P nuclear magnetic resonance spectroscopy were used to probe the structure of phosphate glass biomaterials of general composition (CaO)0.5?x(Na2O)x(P2O5)0.5 (x = 0, 0.1 and 0.5). The results suggest that all three glasses have structures based on chains of Q2 phosphate groups. Clear structural differences are observed between the glasses containing Na2O and CaO. The P–O bonds to bridging and non-bridging oxygens are less well resolved in the neutron data from the samples containing CaO, suggesting a change in the nature of the bonding as the field strength of the cation increases Na+ ? Ca2+. In the (CaO)0.5(P2O5)0.5 glass most of the Ca2+ ions are present in isolated CaOx polyhedra whereas in the (Na2O)0.5(P2O5)0.5 glass the NaOx polyhedra share edges leading to a Na–Na correlation. The results of the structural study are related to the properties of the (CaO)0.4(Na2O)0.1(P2O5)0.5 biomaterial

Spectra and structural polynomials of graphs of relevance to the theory of molecular conduction

In chemistry and physics, distortivity of π-systems (stabilisation of bond-alternated structures) is an important factor in the calculation of geometric, energetic, and electronic properties of molecules via graph theoretical methods. We use the spectra of paths and cycles with alternating vertex and edge weights to obtain the eigenvalues and eigenvectors for a class of linear and cyclic ladders with alternating rung and backbone edge weights. We derive characteristic polynomials and other structural polynomials formed from the cofactors of the characteristic matrix for these graphs. We also obtain spectra and structural polynomials for ladders with flipped weights and/or Möbius topology. In all cases, the structural polynomials for the composite graphs are expressed in terms of products of polynomials for graphs of half order. This form of the expressions allows global deductions about the transmission spectra of molecular devices in the graph-theoretical theory of ballistic molecular conduction

The structure of calcium metaphosphate glass obtained from x-ray and neutron diffraction and reverse Monte Carlo modelling

The short range structure of (CaO)(0.5)(P2O5)(0.5) glass has been studied using x-ray and neutron diffraction and modelled using the reverse Monte Carlo method. Using this combination of techniques has allowed six interatomic correlations to be distinguished and fitted to obtain a set of bond lengths and coordination numbers that describe the structure of the glass. The glass consists of metaphosphate chains of phosphate tetrahedra and each phosphate unit has two non-bridging oxygen atoms available for coordination with Ca. The Ca-O correlation was fitted with two peaks at 2.35 and 2.86 angstrom, representing a broad distribution of bond lengths. The total Ca-O coordination is 6.9 and is consistent with distorted polyhedral units such as capped octahedra or capped trigonal prisms. It is found that most non-bridging oxygen atoms are bonded to two calcium atoms. All of these observations are consistent with Hoppe's model for phosphate glasses. Furthermore, the medium range order is revealed to consist of phosphate chains intertwined with apparently elongated clusters of Ca ions, and the Ca-O and Ca-P correlations contributed significantly to the first sharp diffraction peak in x-ray diffraction

A bulky glycocalyx fosters metastasis formation by promoting G1 cell cycle progression.

Metastasis depends upon cancer cell growth and survival within the metastatic niche. Tumors which remodel their glycocalyces, by overexpressing bulky glycoproteins like mucins, exhibit a higher predisposition to metastasize, but the role of mucins in oncogenesis remains poorly understood. Here we report that a bulky glycocalyx promotes the expansion of disseminated tumor cells in vivo by fostering integrin adhesion assembly to permit G1 cell cycle progression. We engineered tumor cells to display glycocalyces of various thicknesses by coating them with synthetic mucin-mimetic glycopolymers. Cells adorned with longer glycopolymers showed increased metastatic potential, enhanced cell cycle progression, and greater levels of integrin-FAK mechanosignaling and Akt signaling in a syngeneic mouse model of metastasis. These effects were mirrored by expression of the ectodomain of cancer-associated mucin MUC1. These findings functionally link mucinous proteins with tumor aggression, and offer a new view of the cancer glycocalyx as a major driver of disease progression

Near omni-conductors and insulators: Alternant hydrocarbons in the SSP model of ballistic conduction

Within the source-and-sink-potential model, a complete characterisation is obtained for the conduction behaviour of alternant π-conjugated hydrocarbons (conjugated hydrocarbons without odd cycles). In this model, an omni-conductor has a molecular graph that conducts at the Fermi level irrespective of the choice of connection vertices. Likewise, an omni-insulator is a molecular graph that fails to conduct for any choice of connections. We give a comprehensive classification of possible combinations of omni-conducting and omni-insulating behaviour for molecular graphs, ranked by nullity (number of non-bonding orbitals). Alternant hydrocarbons are those that have bipartite molecular graphs; they cannot be full omni-conductors or full omni-insulators but may conduct or insulate within well-defined subsets of vertices (unsaturated carbon centres). This leads to the definition of "near omni-conductors" and "near omni-insulators." Of 81 conceivable classes of conduction behaviour for alternants, only 14 are realisable. Of these, nine are realised by more than one chemical graph. For example, conduction of all Kekulean benzenoids (nanographenes) is described by just two classes. In particular, the catafused benzenoids (benzenoids in which no carbon atom belongs to three hexagons) conduct when connected to leads via one starred and one unstarred atom, and otherwise insulate, corresponding to conduction type CII in the near-omni classification scheme

Predicting local adaptation in fragmented plant populations: Implications for restoration genetics

Understanding patterns and correlates of local adaptation in heterogeneous landscapes can provide important information in the selection of appropriate seed sources for restoration. We assessed the extent of local adaptation of fitness components in 12 population pairs of the perennial herb Rutidosis leptorrhynchoides (Asteraceae) and examined whether spatial scale (0.7-600 km), environmental distance, quantitative (QST) and neutral (FST) genetic differentiation, and size of the local and foreign populations could predict patterns of adaptive differentiation. Local adaptation varied among populations and fitness components. Including all population pairs, local adaptation was observed for seedling survival, but not for biomass, while foreign genotype advantage was observed for reproduction (number of inflorescences). Among population pairs, local adaptation increased with QST and local population size for biomass. QST was associated with environmental distance, suggesting ecological selection for phenotypic divergence. However, low FST and variation in population structure in small populations demonstrates the interaction of gene flow and drift in constraining local adaptation in R. leptorrhynchoides. Our study indicates that for species in heterogeneous landscapes, collecting seed from large populations from similar environments to candidate sites is likely to provide the most appropriate seed sources for restoration

Tablets for Teaching and Learning : A Systematic Review and Meta-Analysis

Tablets and smart mobile devices are the most recent addition to the long list of technological innovations believed to support and enhance the teaching process and learning process. This review aimed at going beyond the general hype around tablets and smart mobile devices to investigate the evidence supporting their use in educational contexts. To achieve this purpose, a systematic review of quantitative and qualitative research studies published since 2010 was completed. A rigorous review process resulted in the inclusion of 27 quantitative studies that were subjected to a full-scale meta-analytic procedure, and 41 qualitative research studies that were reviewed for substantive study characteristics. A significant average effect size was found for studies comparing tablet use contexts with no tablet use contexts (g+ = 0.23, k = 28). For studies comparing two different uses of tablets by students, the average effect size (g+ = 0.68, k = 12) showed a significant favouring of more student-centred pedagogical use of technology. Although not statistically tested, the findings also indicate that higher effect sizes are achieved when the devices are used with a student-centred approach rather than within teacher-led environments. Similarly, the qualitative literature review revealed that tablets and smart mobile devices are garnering positive perceptions within educational contexts, with the strongest support showing for the technologies’ effectiveness in particular tasks and when used within more student-active contexts. Finally, the review provides an overview of the Turkish Fatih Project as a case study and highlights the lessons learned