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Characterization of a fiber reinforced semirigid liquid crystalline polymer
1997
In this work, samples of a semirigid Liquid crystalline polymer reinforced with carbon and glass fibers has been characterized. Semirigid liquid crystalline polymers (LCPs) show some advantages with respect to rigid LCPs: in particular lower processing temperatures, and better compatibility with flexible thermoplastics, but also some disadvantages: lower mechanical properties and poor thermomechanical resistance. Both properties can be improved by adding inorganic fillers. Although elastic modulus and tensile strength of the glass fiber filled LCP improve remarkably with increasing the filler content, the same properties for the carbon fiber-filled samples do not increase with increasing ti…
Effects of filler type and mixing method on the physical properties of a reinforced semirigid liquid crystal polymer
1996
Semirigid liquid crystalline polymers (LCPs) show some advantages with respect to rigid LCP: in particular lower processing temperatures, better compatibility with flexible thermoplastics, but also some disadvantages. Thermal resistance of rigid LCPs is much better and the maximum working temperature is, in general, very high. The thermomechanical properties can be improved by adding inorganic fillers. In this work processing, mechanical and thermomechanical properties of a filled semirigid liquid crystal copolyester are reported. Several inorganic fillers have been used in order to put in evidence the influence of shape and dimensions of the particles on the properties of the filled materi…
Tenascin in denervated human muscle
1996
Tenascin is a large oligomeric glycoprotein of the extracellular matrix. Its location is limited in innervated muscle tissues. We investigated immunohistologically, using two monoclonal antibodies (mab) against Tenascin, biopsied denervated human muscle of children and adults. Tenascin was present in the interstitial space among denervated muscle fibres. Accumulation of Tenascin in denervated adult muscle tissue was frequent, accumulation in denervated muscle tissue of children was sparse and weak. The two antibodies reacted correspondingly. Tenascin was not only found in the vicinity of atrophic muscle fibres, but also close to normally sized fibres, suggesting an early stage of denervatio…
Citrate Sensing by the C 4 -Dicarboxylate/Citrate Sensor Kinase DcuS of Escherichia coli : Binding Site and Conversion of DcuS to a C 4 -Dicarboxylat…
2007
ABSTRACT The histidine protein kinase DcuS of Escherichia coli senses C 4 -dicarboxylates and citrate by a periplasmic domain. The closely related sensor kinase CitA binds citrate, but no C 4 -dicarboxylates, by a homologous periplasmic domain. CitA is known to bind the three carboxylate and the hydroxyl groups of citrate by sites C1, C2, C3, and H. DcuS requires the same sites for C 4 -dicarboxylate sensing, but only C2 and C3 are highly conserved. It is shown here that sensing of citrate by DcuS required the same sites. Binding of citrate to DcuS, therefore, was similar to binding of C 4 -dicarboxylates but different from that of citrate binding in CitA. DcuS could be converted to a C 4 -…
Polymer chains confined into tubes with attractive walls: A Monte Carlo simulation
1994
A bead-spring off-lattice model of a polymer chain with repulsive interactions among repeating units confined into straight tubes of various cross sections, DT2, is studied by Monte Carlo simulation. We are also varying the chain length from N = 16 to 128 and the strength of a short-range attractive interaction between the repeating units and the walls of the tube. Longitudinal and perpendicular static linear dimensions of the chains are analyzed, as well as the density profile of repeating units across the tube. These data are interpreted in terms of scaling concepts describing the crossover between three-dimensional and quasi-one-dimensional chain conformations and the adsorption transiti…
Anomalous scaling of the critical temperature of unmixing with chain length for two-dimensional polymer blends
2003
The thermodynamics, structure and the chain configurations of symmetrical polymer mixtures confined into ultrathin films are studied by Monte Carlo simulations of the bond fluctuation model. It is shown that the Flory-Huggins–type scaling of the critical temperature (Tc ~ N) with chain length N in the bulk is replaced by a weaker increase, Tc ~ N1/2, in an ultrathin film, and this is interpreted in terms of geometric arguments. The pair-correlation function g(r) of monomers from different chains exhibits a pronounced correlation hole, and the density of intermolecular contacts zc decreases with N as zc ~ N−1/2.
Monte Carlo simulation studies of the interfaces between polymeric and other solids as models for fiber-matrix interactions in advanced composite mat…
1996
As a coarse-grained model for dense amorphous polymer systems interacting with solid walls (i.e., the fiber surface in a composite), the bond fluctuation model of flexible polymer chains confined between two repulsive surfaces is studied by extensive Monte Carlo simulations. Choosing a potential for the length of an effective bond that favors rather long bonds, the full temperature region from ordinary polymer melts down to the glass transition is accessible. It is shown that in the supercooled state near the glass transition an “interphase” forms near the walls, where the structure of the melt is influenced by the surface. This “interphase” already shows up in static properties, but also h…
Biomolecular-solvent stereodynamic coupling probed by deuteration.
1983
Thermodynamic interpretation of experiments with isotopically perturbed solvent supports the view that solvent stereodynamics is directly relevant to thermodynamic stability of biomolecules. According with the current understanding of the structure of the aqueous solvent, in any stereodynamic configuration of the latter, connectivity pathways are identifiable for their topologic and order properties. Perturbing the solvent by isotopic substitution or, e.g., by addition of co-solvents, can therefore be viewed as reinforcing or otherwise perturbing these topologic structures. This microscopic model readily visualizes thermodynamic interpretation. In conclusion, the topologic stereodynamic str…
Single-pump heart-cutting two-dimensional liquid chromatography applied to the determination of fatty alcohol ethoxylates.
2014
Abstract A setup for heart-cutting bi-dimensional liquid chromatography (LC–LC), constructed with a chromatograph provided with a single pump, an auxiliary 6-port 2-position valve (V 6/2 ) and a column selector valve (V CS ), is described. The possible ways of connecting the two valves for LC–LC, namely with V 6/2 first followed by V CS and vice versa, are compared. The possibility of using the setups for preconcentration followed by the backwards transfer of the preconcentrated solutes to the detector or to a second column is also shown. The V 6/2 -first configuration for LC–LC was applied to the characterization of industrial fatty alcohol ethoxylates (FAEs) using UV–vis detection. For th…
Theoretical Study of the Elimination Kinetics of Carboxylic Acid Derivatives in the Gas Phase. Decomposition of 2-Chloropropionic Acid
1997
The reaction mechanism for the decomposition of 2-chloropropionic acid in the gas phase to form hydrogen chloride, carbon monoxide, and acetaldehyde has been theoretically characterized. Analytical gradients have been used by means of AM1 and PM3 semiempirical procedures and ab initio methods at HF and DFT (BLYP) levels with the 6-31G** basis set. The correlation effects were also included by using the perturbational approach at the MP2 level with the 6-31G** and 6-31++G** basis sets and the variational approach at the CISD/6-31G** level and by means of MCSCF wave functions with a (6,6) complete active space and the 6-31G** basis set. The global potential energy surface has been studied, an…