Rotational symmetry of a methane molecule and the bond angle

The rotational symmetry of a methane molecule can be used to great advantage to calculate the bond angle. The problem is worked out in this article.

Wide-angle X-ray scattering study of structural parameters in non-crystalline polymers

The paper presents an analysis of WAXS (wide-angle X-ray scattering) data which aids an understanding of the structure of non-crystalline polymers. Experimental results are compared with calculations of scattering from possible models. Evidence is presented which supports the view that the chains in molten PE do not lie parallel but have a conformation in accord with the predictions of energy calculations. However, the evidence indicates that in “molten” PTFE the chains lie parallel over distances well in excess of their diameters. WAXS-based proposals are made for the conformations of a-PMMA and a-PS.

Eliminating the small-angle component of the scattering calculated for models

A straightforward procedure (assuming spherical symmetry) is described, which enables the unwanted small-angle component of the scattering for a finite model to be calculated. The method may be applied to models of any shape or size. It is illustrated by means of a single polymer chain.

A wide-angle X-ray study of the development of molecular orientation in crosslinked natural rubber

Molecular orientation parameters have been measured for the non-crystalline component of crosslinked natural rubber samples deformed in uniaxial tension as a function of the extension ratio and of temperature. The orientation parapeters 〈P2(cosα)〉 and 〈P4(cosα)〉 were obtained by an analysis of the anisotropy of the wide-angle X-ray scattering functions. For the measurements made at high temperatures the level of crystallinity detected was negligible and the orientation-strain behaviour could be compared directly with the predictions of molecular models of rubber elasticity. The molecular orientation behaviour with strain was found to be at variance with the estimates of the affine model particularly at low and moderate strains. Extension of the crosslinked rubber at room temperature led to strain-crystallization and measurements of both the molecular orientation of the non-crystalline chains and the degree of crystallinity during extension and relaxation enabled the role of the crystallites in the deformation process to be considered in detail. The intrinsic birefringence of the non-crystalline component was estimated, through the use of the 〈P2(cosα)〉 values obtained from X-ray scattering measurements, to be 0.20±0.02.

Wide-angle X-ray scattering for swollen and glassy poly(2-hydroxyethyl methacrylate)

The wide angle X-ray scattering from glassy poly(2-hydroxyethyl methacrylate) (1) is presented together with that obtained from oriented and swollen samples. The scattering is compared with that previously reported for poly(methyl methacrylate) (PMMA) and the structure discussed in relation to this polymer. The chain conformation is similar to that of PMMA, although some measure of molecular interlocking appears to reduce the main interchain peak while correlated regions of inaccessible free volume between the substantial side groups are held responsible for the main peak at s = 1,25 Å−1.

Application of cylindrical distribution functions to wide-angle X-ray scattering from oriented polymers

A systematic approach is presented for obtaining cylindrical distribution functions (CDF's) of noncrystalline polymers which have been oriented by extension. The scattering patterns and CDF's are also sharpened by the method proposed by Deas and by Ruland. Data from atactic poly(methyl methacrylate) and polystyrene are analysed by these techniques. The methods could also be usefully applied to liquid crystals.

Conformational analysis of oriented non-crystalline polymers using wide angle X-ray scattering

A procedure is presented for obtaining conformational parameters from oriented but non-crystalline polymers. This is achieved by comparison of the experimental wide angle X-ray scattering with that calculated from models but in such a way that foreknowledge of the orientation distribution function is not required. X-ray scattering intensity values for glassy isotactic poly(methylmethacrylate) are analysed by these techniques. The method could be usefully applied to other oriented molecular systems such as liquid crystalline materials.

The evolution of innovation capability in multinational enterprise subsidiaries: dual network embeddedness and the divergence of subsidiary specialisation in Taiwan

This paper examines how innovation-related capabilities for production, design and marketing develop at the subsidiary level within multinational enterprises (MNEs). We focus on how subsidiary autonomy and changing opportunities to access internal (MNE) and external (host country) sources of capability contribute in a combined way to the accumulation of specialist capabilities in five Taiwan-based MNE subsidiaries in the semiconductor industry. Longitudinal analysis shows how the accumulation process is subject to discontinuities, as functional divisions are (re)opened and closed during the lifetime of the subsidiary. A composite set of innovation output measures also shows significant variations in within-function levels of capability across our sample. We conclude that subsidiary specialisation and unique subsidiary-specific advantages have evolved in a way that is strongly influenced by the above factors.

Wolbachia infection and dramatic intraspecific mitochondrial dna divergence in a fig wasp

Mitochondria and Wolbachia are maternally inherited genomes that exhibit strong linkage disequilibrium in many organisms. We surveyed Wolbachia infections in 187 specimens of the fig wasp species, Ceratosolen solmsi, and found an infection prevalence of 89.3%. DNA sequencing of 20 individuals each from Wolbachia-infected and -uninfected subpopulations revealed extreme mtDNA divergence (up to 9.2% and 15.3% in CO1 and cytochrome b, respectively) between infected and uninfected wasps. Further, mtDNA diversity was significantly reduced within the infected group. Our sequencing of a large part of the mitochondrial genome from both Wolbachia-infected and -uninfected individuals revealed that high sequence divergence is common throughout the mitochondrial genome. These patterns suggest a partial selective sweep of mitochondria subsequent to the introduction of Wolbachia into C. solsmi, by hybrid introgression from a related species.

Contact angle of a hemispherical bubble: an analytical approach

We have calculated the equilibrium shape of the axially symmetric Plateau border along which a spherical bubble contacts a flat wall, by analytically integrating Laplace’s equation in the presence of gravity, in the limit of small Plateau border sizes. This method has the advantage that it provides closed-form expressions for the positions and orientations of the Plateau border surfaces. Results are in very good overall agreement with those obtained from a numerical solution procedure, and are consistent with experimental data. In particular we find that the effect of gravity on Plateau border shape is relatively small for typical bubble sizes, leading to a widening of the Plateau border for sessile bubbles and to a narrowing for pendant bubbles. The contact angle of the bubble is found to depend even more weakly on gravity.

Synthesis and crystal structures of μ-oxido- and μ-hydroxido-bridged dinuclear iron(III) complexes with an N2O donor ligand - a theoretical study on the influence of weak forces on the Fe-O-Fe bridging angle

The synthesis and crystal structures of three nonheme di-iron(III) complexes with a tridentate N,N,O Schiff-base ligand, 2-({[2-(dimethylamino) ethyl] imino} methyl) phenol (HL), are reported. Complexes [Fe2OL2(NCO)(2)] (1a) and [Fe2OL2(SAL)(2)]center dot H2O [SAL = o-(CHO)C6H4O-] (1b) are unsupported mu-oxido-bridged dimers, and [Fe-2(OH)L-2(HCOO)(2)-(Cl)] (2) is a mu-hydroxido-bridged dimer supported by a formato bridging ligand. All complexes have been characterized by X-ray crystallography and spectroscopic analysis. Complex 1b has been reported previously; however, it has been reinvestigated to confirm the presence of a crucial water molecule in the solid state. Structural analyses show that in 1a the iron atoms are pentacoordinate with a bent Fe-O-Fe angle [142.7(2)degrees], whereas in 2 the metal centers are hexacoordinate with a normal Fe-OH-Fe bridging angle [137.9(2)degrees]. The Fe-O-Fe angles in complexes 1a and 1b differ significantly to those usually shown by (mu-oxido) Fe-III complexes. A theoretical study has been performed in order to rationalize this deviation. Moreover, the influence of the water molecule observed in the solid-state structure of 1b on the Fe-O-Fe angle is also analyzed theoretically.

Quantitative genetic divergence and standing genetic (co)variance in thermal reaction norms along latitude

Although the potential to adapt to warmer climate is constrained by genetic trade-offs, our understanding of how selection and mutation shape genetic (co)variances in thermal reaction norms is poor. Using 71 isofemale lines of the fly Sepsis punctum, originating from northern, central, and southern European climates, we tested for divergence in juvenile development rate across latitude at five experimental temperatures. To investigate effects of evolutionary history in different climates on standing genetic variation in reaction norms, we further compared genetic (co)variances between regions. Flies were reared on either high or low food resources to explore the role of energy acquisition in determining genetic trade-offs between different temperatures. Although the latter had only weak effects on the strength and sign of genetic correlations, genetic architecture differed significantly between climatic regions, implying that evolution of reaction norms proceeds via different trajectories at high latitude versus low latitude in this system. Accordingly, regional genetic architecture was correlated to region-specific differentiation. Moreover, hot development temperatures were associated with low genetic variance and stronger genetic correlations compared to cooler temperatures. We discuss the evolutionary potential of thermal reaction norms in light of their underlying genetic architectures, evolutionary histories, and the materialization of trade-offs in natural environments.

Disentangling sources of incomplete acquisition: an explanation for competence divergence across heritage grammars.

This article brings to light an important variable involved in explaining a type of competence divergence in an instance of bilingual acquisition: heritage speaker (HS) bilingualism. We present results of experiments with European Portuguese (EP) heritage speakers (HSs), showing that they have full morpho-syntactic and semantic competence of inflected infinitives, similar to EP monolinguals. We show this constitutes clear evidence of competence mismatches between heritage speakers of European and Brazilian Portuguese, comparing our results to Rothman’s (2007) experimental evidence that Brazilian Portuguese (BP) heritage speakers lack knowledge of inflected infinitives. These comparative results are especially relevant because inflected infinitives were argued (Pires, 2002, 2006) to have been lost in colloquial BP dialects, although educated monolinguals demonstrate target competence.