Evolution of single and double Wolbachia symbioses during speciation in the Drosophila simulans complex.

Maternally inherited bacteria of the genus Wolbachia are responsible for the early death of embryos in crosses between uninfected females and infected males in several insect species. This phenomenon, known as cytoplasmic incompatibility, also occurs between strains infected by different symbionts in some species, including Drosophila simulans. Wolbachia was found in two species closely related to D. simulans, Drosophila mauritiana, and Drosophila sechellia, and shown to cause incompatibility in the latter species but not in D. mauritiana. Comparison of bacterial and mtDNA history clarifies the origins of bacterial and incompatibility polymorphisms in D. simulans. Infection in D. mauritiana is probably the result of introgression of an infected D. simulans cytoplasm. Some D. simulans and D. sechellia cytoplasmic lineages harbor two bacteria as a consequence of a double infection which probably occurred in a common ancestor. The descendant symbionts in each species are associated with similar incompatibility relationships, which suggests that little variation of incompatibility types has occurred within maternal lineages beyond that related to the density of symbionts in their hosts.

Crystal structure of an H-2Kb-ovalbumin peptide complex reveals the interplay of primary and secondary anchor positions in the major histocompatibility complex binding groove.

Sequence analysis of peptides naturally presented by major histocompatibility complex (MHC) class I molecules has revealed allele-specific motifs in which the peptide length and the residues observed at certain positions are restricted. Nevertheless, peptides containing the standard motif often fail to bind with high affinity or form physiologically stable complexes. Here we present the crystal structure of a well-characterized antigenic peptide from ovalbumin [OVA-8, ovalbumin-(257-264), SIINFEKL] in complex with the murine MHC class I H-2Kb molecule at 2.5-A resolution. Hydrophobic peptide residues Ile-P2 and Phe-P5 are packed closely together into binding pockets B and C, suggesting that the interplay of peptide anchor (P5) and secondary anchor (P2) residues can couple the preferred sequences at these positions. Comparison with the crystal structures of H-2Kb in complex with peptides VSV-8 (RGYVYQGL) and SEV-9 (FAPGNYPAL), where a Tyr residue is used as the C pocket anchor, reveals that the conserved water molecule that binds into the B pocket and mediates hydrogen bonding from the buried anchor hydroxyl group could not be likewise positioned if the P2 side chain were of significant size. Based on this structural evidence, H-2Kb has at least two submotifs: one with Tyr at P5 (or P6 for nonamer peptides) and a small residue at P2 (i.e., Ala or Gly) and another with Phe at P5 and a medium-sized hydrophobic residue at P2 (i.e., Ile). Deciphering of these secondary submotifs from both crystallographic and immunological studies of MHC peptide binding should increase the accuracy of T-cell epitope prediction.

Examining the Complex Relationships of Early Intervention on Language and Psychosocial Development in Families Facing Multiple Risks with a Focus on Children of Hispanic Immigrants

Abundant research has shown that poverty has negative influences on young child academic and psychosocial development, and unfortunately, disparities in school readiness between low and high income children can be seen as early the first year of life. The largest federal early care and education intervention for these vulnerable children is Early Head Start (EHS). To diminish these disparate child outcomes, EHS seeks to provide community based flexible programming for infants and toddlers and their families. Given how relatively recent these programs have been offered, little is known about the nuances of how EHS impacts infant and toddler language and psychosocial development. Using a framework of Community Based Participatory Research (CBPR) this paper had 5 goals: 1) to characterize the associations between domain specific and cumulative risk and child outcomes 2) to validate and explore these risk-outcome associations separately for Children of Hispanic immigrants (COHIs), 3) to explore relationships among family characteristics, multiple environmental factors, and dosage patterns in different EHS program types, 4) to examine the relationship between EHS dosage and child outcomes, and 5) to examine how EHS compliance impacts child internalizing and externalizing behaviors and emerging language abilities. Results of the current study showed that risks were differentially related to child outcomes. Poor maternal mental health was related to child internalizing and externalizing behaviors, but not related to emerging child language skills. Although child language skills were not related to maternal mental health, they were related to economic hardship. Additionally, parent level Spanish use and heritage orientation were associated with positive child outcomes. Results also showed that these relationships differed when COHIs and children with native-born parents were examined separately. Further, unique patterns emerged for EHS program use, for example families who participated in home-based care were less likely to comply with EHS attendance requirements. These findings provide tangible suggestions for EHS stakeholders: namely, the need to develop effective programming that targets engagement for diverse families enrolled in EHS programs.

I. The equilibrium in liquid mixtures of ammonia and xylene. II. The molecular weight of complex sodium tellurides in liquid ammonia,

Reprinted from articles by Charles A. Kraus and Edward H. Zeitfuchs in the Journal of the American Chemical Society, v. 44, no. 6, June, 1922 and v. 44, no. 12, December, 1922.

Diphenyltin(IV) complexes of the 2-quinolinecarboxaldehyde Schiff bases of S-methyl- and S-benzyldithiocarbazate (Hqaldsme and Hqaldsbz): X-ray crystal structures of Hqaldsme and two conformers of its diphenyltin(IV) complex

New organometallic tin(IV) complexes of the empirical formula Sn(NNS)Ph2Cl (NNS = anionic forms of the 2-quinolinecarboxaldehyde Schiff bases of S-methyl- and S-benzyldithiocarbazate) have been prepared and characterized by IR, electronic, I H NMR and ES mass spectroscopic techniques. The molecular structures of the 2-quinolinecarboxaldehyde Schiff base of S-methyldithiocarbazate (Hqaldsme) and its diphenyltin(IV) complex, Sn(qaldsme)Ph2Cl, have been determined by X-ray diffraction. In the solid state, the ligand remains as the thione tautomer in which the dithiocarbazate chain adopts an E,E configuration and is almost coplanar with the quinoline ring. The Sn(qaldsme)Ph2Cl complex crystallizes in two distinctly different conformationally isomeric forms, each having the same space group but different lattice parameters. X-ray analysis shows that in each polymorph, the tin atom adopts a distorted octahedral geometry with the Schiff base coordinated to it as a uninegatively charged tridentate chelating agent via the quinoline nitrogen atom, the azomethine nitrogen atom and the thiolate sulfur atom. The two phenyl groups occupy axial positions and the chloride ligand occupies the sixth coordination position of the tin atom. The deprotonated ligand adopts an E,E,Z configuration in the complex. (C) 2004 Elsevier Ltd. All rights reserved.

What Counts Versus What Can Be Counted : The Complex Interplay of Market Orientation and Marketing Performance Measurement

Market orientation (MO) and marketing performance measurement (MPM) are two of the most widespread strategic marketing concepts among practitioners. However, some have questioned the benefits of extensive investments in MO and MPM. More importantly, little is known about which combinations of MO and MPM are optimal in ensuring high business performance. To address this research gap, the authors analyze a unique data set of 628 firms with a novel method of configurational analysis: fuzzy-set qualitative comparative analysis. In line with prior research, the authors find that MO is an important determinant of business performance. However, to reap its benefits, managers need to complement it with appropriate MPM, the level and focus of which vary across firms. For example, whereas large firms and market leaders generally benefit from comprehensive MPM, small firms may benefit from measuring marketing performance only selectively or by focusing on particular dimensions of marketing performance. The study also finds that many of the highest-performing firms do not follow any of the particular best practices identified.

Compatibilisation and stabilisation of immiscible polymer blends by reactive processing

The main objectives of this research were to develop optimised chemical compositions and reactive processing conditions for grafting a functional monomer maleic anhydride (MA) in polypropylene (PP), ethylene propylene diene monomer (EPDM) and mixtures of PP-EPDM, and to optimise synthetic routes for production of PP/EPDM copolymers for the purpose of compatibilisation of PP/EPDM blends. The MA-functionalisation was achieved using an internal mixer in the presence of low concentrations (less than 0.01 molar ratio) of a free radical initiator. Various methods were used to purify MA-functionalised PP and the grafting yield was determined using either FTIR or titrametry. The grafting yield of MA alone, which due to its low free-radical reactivity towards polymer macroradicals, was accompanied by severe degradation in the case of PP and crosslinking for EPDM. In the case of MA-functionalised PP/EPDM, both degradation and crosslinking occurred though not to a great extent. The use of tri-functional coagents e.g. trimethylopropane triacrylates (TRIS) with MA, led to high improvement of the grafting yield of MA on the polymers. This is almost certainly due to high free-radical activity of TRIS leading to copolymerisation of MA and TRIS which was followed by grafting of the copolymer onto the polymer backbone. In the case of PP, the use of coagent was also found to reduce the polymer degradation. PP/EPDM copolymers with optimum tensile properties were synthesised using a 'one-step' continues reactive processing procedure. This was achieved firstly by functionalisation of a mixture of PP (higher w/w ratio) and EPDM (low w/w ratio) with MA, in the presence of the coagent TRIS and a small concentration of a free radical initiator. This was then followed by an imidisation reaction with the interlinking agent hexamethylene diamine (HEMDA). Small amount of copolymers, up to 5 phr, which were interlinked with up to 15 phr of HEMDA, were sufficient to compatibilise PP/EPDM75/25 blends resulting in excellent tensile properties compared to binary PP/EPDM 75/25 blend. Improvement in blend's compatibility and phases-stabilisation (observed through tensile and SEM analysis) was shown in all cases with significant interphases adhesion improvement between PP and EPDM, and reduction in domain size across the fractured surface indicating efficient distribution of the compatibiliser.

Stabilisation of isocyanate cross linked polybutadiene binder

Isocyanate cross-linked hydroxy terminated polybutadiene is used as a binder for solid rocket propellant. Rocket motors containing this propellant require a storage life of at least 20 years. During storage it has been found that the important rubbery properties of the binder can be lost due to oxidative cross-linking of the polybutadiene chains. This could cause catastrophic failure when the rocket motor is required. At present the bis-hindered phenol Calco 2246 is used as a thermal oxidative stabiliser, but it's performance is only adequate. This has led to the search for a more efficient stabiliser system. To hasten the evaluation of new antioxidant systems the use of dynamic thermal analysis was investigated. Results showed that a tentative relationship existed between predictions by thermal analysis and the long term oven ageing for simple single antioxidant systems. But for more complex systems containing either autosynergistic or mixed antioxidants no relationship was observed suggesting that results for such an "accelerated" technique cannot be used for the purpose of extrapolation for long term performance. This was attributed to the short time and more aggressive condition used (hjgher temperature and oxygen rich atmosphere in thermal analysis) altering the mechanism of action of the antioxidants and not allowing time for co-operative effect of the combined antioxidant system to form. One potential problem for the binder system is the use of an diisocyanate as a cross-linking agent. This reacts with the hydroxyl hydrogen on the polymer as well as other active hydrogens such as those contained in a number of antioxidants, affecting both cross-linking and antioxidant effectiveness. Studies in this work showed that only antioxidants containing amine moieties have a significant affect on binder preparation, with the phenolic antioxidants not reacting. This is due to the greater nucleophilicity of the amines. Investigation of a range of antioxidant systems, including potentially homo, hetero and autosynergistic systems, has highlighted a number of systems which show considerably greater effectiveness than the currently used antioxidant Calco 2246. The only single antioxidant which showed improvement was the partially unhindered phenol y-Tocopherol. Of the mixed systems combinations of the sulphur containing antioxidants e.g. DLTP with higher levels of chain-breaking antioxidants, especially Calco 2246, were the most promising. Also the homosynergistic mix of an aromatic amine and a phenol was seen to be very effective but the results were inconsistent. This inconsistency could be explained by the method of sample preparation used. It was shown that the efficiency of a number of antioxidant.s could be dramatically improved by the use of ultrasound during the mixing stage of preparation. The reason for this increase in performance is unclear but in the case of the homosynergistic amine/phenol mix both more efficient mixing and/or the production of a novel mechanism of action are suggested

Investigation of the oxidative degradation mechanisms and melt stabilisation of a new generation metallocene polytehylene

The two main objectives of the research work conducted were firstly, to investigate the processing and rheological characteristics of a new generation metallocene catalysed linear low density polyethylene (m-LLDPE), in order to establish the thermal oxidative degradation mechanism, and secondly, to examine the role of selected commercial stabilisers on the melt stability of the polymers. The unstabilised m-LLDPE polymer was extruded (pass I) using a twin screw extruder, at different temperatures (210-285°C) and screw speeds (50-20rpm) and was subjected to multiple extrusions (passes, 2-5) carried out under the same processing conditions used in the first pass. A traditional Ziegler/Natta catalysed linear low density polyethylene (z-LLDPE) produced by the same manufacturer was also subjected to a similar processing regime in order to compare the processability and the oxidative degradation mechanism (s) of the new m-LLDPE with that of the more traditional z-LLDPE. The effect of some of the main extrusion characteristics of the polymers (m-LLDPE and z-LLDPE) on their melt rheological behaviour was investigated by examining their melt flow performance monitored at two fixed low shear rate values, and their rheological behaviour investigated over the entire shear rates experienced during extrusion using a twin-bore capillary rheometer. Capillary rheometric measurements, which determine the viscous and elastic properties of polymers, have shown that both polymers are shear thinning but the m-LLDPE has a higher viscosity than z-LLDPE and the extent of reduction in viscosity of the former when the extrusion temperature was increased from 210°C to 285°C was much higher than in the case of the z-LLDPE polymer. This was supplied by the findings that the m-LLDPE polymer required higher power consumption under all extrusion conditions examined. It was fUliher revealed that the m-LLDPE undergoes a higher extent of melt fracture, the onset of which occurs under much lower shear rates than the Ziegler-based polymer and this was attributed to its higher shear viscosity and narrower molecular weight distribution (MWD). Melt flow measurements and GPC have shown that after the first extrusion pass, the initial narrower MWD of m-LLDPE is retained (compared to z-LLDPE), but upon further multiple extrusion passes it undergoes much faster broadening of its MWD which shifts to higher Mw polymer fractions, paliicularly at the high screw speeds. The MWD of z-LLDPE polymer on the other hand shifts towards the lower Mw end. All the evidence suggest therefore the m-LLDPE undergoes predominantly cross-linking reactions under all processing conditions whereas z-LLDPE undergoes both cross-linking and chain scission reactions with the latter occurring predominantly under more severe processing conditions (higher temperatures and screw speeds, 285°CI200rpm). The stabilisation of both polymers with synergistic combinations of a hindered phenol (Irganox 1076) and a phosphite (Weston 399) at low concentrations has shown a high extent of melt stabilisation in both polymers (extrusion temperatures 210-285°C and screw speeds 50-200rpm). The best Irganox 1076/Weston 399 system was found to be at an optimum 1:4 w/w ratio, respectively and was found to be most effective in the z-LLDPE polymer. The melt stabilising effectiveness of a Vitamin E/Ultranox 626 system used at a fraction of the total concentration of Irganox 1076/Weston 399 system was found to be higher in both polymers (under all extrusion conditions). It was found that AOs which operate primarily as alkyl (Re) radical scavengers are the most effective in inhibiting the thermal oxidative degradation of m-LLDPE in the melt; this polymer was shown to degrade in the melt primarily via alky radicals resulting in crosslinking. Metallocene polymers stabilised with single antioxidants of Irganox HP 136 (a lactone) and Irganox E201 (vitamin E) produced the highest extent of melt stability and the least discolouration during processing (260°C/1 OOrpm). Furthermore, synergistic combinations of Irganox HP I 36/Ultranox 626 (XP-60) system produced very high levels of melt and colour stability (comparable to the Vitamin E based systems) in the mLLDPE polymer. The addition of Irganox 1076 to an Irganox HP 136/Ultranox 626 system was found not to result in increasing melt stability but gave rise to increasing discolouration of the m-LLDPE polymer. The blending of a hydroxylamine (lrgastab FS042) with a lactone and Vitamin E (in combination with a phosphite) did not increase melt stability but induced severe discolouration of resultant polymer samples.

The adsorption of phenolic and organotin compounds by clays and cation exchanged clays

Quaternary ammonium exchanged laponites (Quat-laponites) show selectivity in the adsorption of phenols and chlorinated phenols. Strong adsorbate-adsorbent interactions are indicated by adsorption isotherms. Adsorption of phenols and chlorinated phenols by Quat-smectites is greater than that by the Bi Quat-Smectites prepared in this study. It is thought that the quaternary ammonium exchanged smectite components of the Bi Quat-smectites interact with each other (adsorbent-adsorbent interactions) reducing the number of sites available for adsorbate-adsorbent interactions. Solidification/stabilisation studies of 2-chlorophenol show that a blend of ground granulated blast furnace slag and ordinary Portland cement attenuates 2-chlorophenol more effectively than ordinary Portland cement alone. Tetramethyl ammonium- (TMA-) and tetramethyl phosphonium- (TMP-) montmorillonites were exposed to solutions of phenol or chlorinated phenols. TMP- montmorillonite was the better adsorbent and preferentially adsorbed 4-chlorophenol over phenol. Hydration of the interlayer cations occurs to a greater extent in the TMA-montmorillonite than the TMP-montmorillonite restricting interlayer adsorption. Contrary to that observed for phenols and chlorinated phenols, the Quat-smectites were ineffective as adsorbents for triphenyltin hydroxide and bis(tributyltin) oxide at room temperature. Under microwave conditions, only bis(tributyltin) oxide was adsorbed by the quaternary ammonium exchanged smectites. Bis(tributyltin) oxide was adsorbed from ethanol on the surface of the smectite clays at room temperature and under microwave conditions. The adsorbate-adsorbent interactions were weak. Adsorption is accompanied by conversion of bis(tributyltin) oxide to a different tin(IV) species and the release of sodium cations from the montmorillonite interlayer region. Attempts to introduce conditions suitable for charge transfer interactions between synthesised quaternary ammonium compounds and 2,4,6-trichlorophenol are documented. Transition metal complex exchanged clays adsorb 2,4,6-trichlorophenol and phenol. Strong adsorbate-adsorbent interactions (Type I isotherms) occur when the adsorbate is 2,4,6-trichlorophenol and when the adsorbent is [Fe(bipy)3]2+ exchanged montmorillonite or [Co(bipy)3]3+ exchanged montmorillonite. The 2,2'-bipyridyl ligands of the adsorbents are electron rich and the 2,4,6-trichlorophenol is electron deficient. This may have enhanced adsorbate-adsorbent interactions.