Search

A study of diffusion in liquids presents new experimental efforts designed to gain additional insights concerning the reorientation supercooled liquids. The study specifically investigated the rotational dynamics of stiff, molecular tracers with different symmetries in supercooled and glassy O-terphenyl both on the short-time and long-time scale. Among other results, it will be shown that the temperature dependence of the correlation times exhibits three clearly defined regimes on both the short- and long-time scales irrespective of the tracer.

Current standards introduce different test methods to be used for the determination of the dynamic properties of polymers. Some of these have been applied in the last years for the evaluation of the thermoviscoelastic properties of interlayer in laminated glass. Even the latest draft standards, which provide test methods for the determination of mechanical properties of laminated glass interlayers, hesitate in providing a definite test procedure and thus allow the use of three different test methods depending on the kind of interlayer. Here, a short review of the test methods collected from the literature is proposed and some considerations are made regarding their strengths and weaknesses. The scope of studies surveyed does not claim to be exhaustive, but simply to be representative of the variety of procedures employed in research. The necessity is stressed to converge to as limited a number of test methods as possible that are also adequately simple and can therefore be applied in most research laboratories. [ABSTRACT FROM AUTHOR]

Background: Initially known as the reproductive hormone, relaxin was shown to possess other therapeutically useful properties that include extracellular matrix remodeling, anti-inflammatory, anti-ischemic and angiogenic effects. All these findings make relaxin a potential drug for diverse medical applications. Its precursor, pro-relaxin, is an 18 kDa protein, that shows activity in in vitro assays. Since extraction of relaxin from animal tissues raises several issues, prokaryotes and eukaryotes were both used as expression systems for recombinant relaxin production. Most productive results were obtained when using Escherichia coli as a host for human relaxin expression. However, in such host, relaxin precipitated in the form of inclusion bodies and, therefore, required several expensive recovery steps as cell lysis, refolding and reduction. Results: To overcome the issues related to prokaryotic expression here we report the production and purification of secreted human pro-relaxin H2 by using the methylotrophic yeast Pichia pastoris as expression host. The methanol inducible promoter AOX1 was used to drive expression of the native and histidine tagged forms of pro-relaxin H2 in dual phase fed-batch experiments on the 22 L scale. Both protein forms presented the correct structure, as determined by mass spectrometry and western blotting analyses, and demonstrated to be biologically active in immune enzymatic assays. The presence of the tag allowed to simplify pro-relaxin purification obtaining higher purity. Conclusions: This work presents a strategy for microbial production of recombinant human pro-relaxin H2 in Pichia pastoris that allowed the obtainment of biologically active pro-hormone, with a final concentration in the fermentation broth ranging between 10 and 14 mg/L of product, as determined by densitometric analyses. [ABSTRACT FROM AUTHOR]

Thedynamic response at nanometers and nanoseconds was investigatedby electron spin resonance spectroscopy in random and block copolymersof an azobenzene methacrylate (MA4) and methyl methacrylate (MMA)with cholestane molecular tracer. The study evidenced the presenceof different molecular sites for the reorientation at nanoscale, thatwere modulated by the amount of MA4 counits in the random copolymersand by the self-assembly in supramolecular structures in the blockcopolymers. A number of dynamics features was revealed, such as thepresence of memory effects, the existence and the degree of couplingof the rotational dynamics to the structural relaxation of the matrixor to its viscosity, and the population of dynamic sites. This provideda detailed characterization of the mechanisms dictating the dynamicresponse of the structurally different copolymers. The influence ofmicrostructure on the relaxation properties of the random copolymerswas also discussed by considering the evaluated cooperativity coefficients,cooperativity indices, and packing lengths. [ABSTRACT FROM AUTHOR]

The research presented here investigates the interaction between acute exercise, biological sex and risk-taking behavior. The study involved 20 amateur athletes (19-33 years old), 10 males and 10 females, who were asked to undergo subsequent experimental sessions designed to compare their risky behaviors on the Balloon Analogue Risk Task (BART) [34] at rest and while exercising at moderate intensity (60% of their maximal aerobic power). Results showed that physical exercise affected male and female participants differently: Whereas males became more risk seeking, females became more risk averse during exercise. [ABSTRACT FROM AUTHOR]

The shear rheological behavior wasinvestigated in a series ofhigh molar mass liquid-crystalline polymers (PMA4 homopolymer andcopolymer samples) carrying an azobenzene mesogenic group in the sidechains (MA4). The focus was on studying the entanglement effects andtesting selected reptation models to ascertain their ability to reproducethe complex shear modulus of the copolymers. We found that ordinarydynamic models worked for the nematic PMA4 copolymers with methylmethacrylate (MMA), nicely reproducing the rheological response ofthe materials. We were able to obtain microscopic information on thematerials, such as Rouse time and entanglement molar mass, in a consistentway, as well as to get insight on the macroscopic effects of tubedilatation induced by the nematic order on the master curves of theentangled polymers. Model improvements, accounting for the differentnature of the counits, were also proposed in this work that singledout the friction coefficients of the counits MMA and MA4. The monomericfriction coefficient ζ0MA4was found tobe constant throughout the series, (5 ± 2) × 10–9kg s–1. Likewise, ζ0MMAhad the same value throughout the series, very similar to literaturedata for PMMA homopolymers, (2.0 ± 0.6) × 10–8kg s–1. Finally, in the framework of the packing-lengthmodel, constant packing lengths of 3.5 and 13 Å throughout theseries were found for MMA and MA4 counits, respectively. Also, itresulted that the viscoelastic behavior of any PMA4 random copolymercould be predicted, provided that the response of the extreme homopolymersof the series has been characterized. [ABSTRACT FROM AUTHOR]

Analysis of the dynamics of low-molar-mass linear homopolymers is important when trying to understand the mechanisms driving structural relaxation properties from molecular liquids to polymers. Theoretical models assume, in general, the same mobility of the different moieties of the macromolecule, but this hypothesis fails for low-molar-mass polymers. Therefore, isofrictional comparisons are necessary to interpret experimental data with theoretical models. In this work, the molar-mass dependence of the glass transition temperatures Tg, fragility indexes, and dynamic moduli of unentangled poly(ethyl acrylate) (PEA) melts are studied and discussed. All the results are interpreted in a coherent framework developed from the free-volume concept. The predictive power of this framework is also tested to fit theoretical and experimental master curves, introducing an 'inverse' isofrictional correction. [ABSTRACT FROM AUTHOR]

The rotational dynamics of the tracer cholestane dissolved in non-entangled nearly monodisperse poly(alkyl acrylate) melts has been investigated by means of electron spin resonance spectroscopy. Three samples with almost the same molecular weight were selected, poly(methyl acrylate), poly(ethyl acrylate) and poly(n-butyl acrylate) and their linear viscoelastic properties were also characterized. Large temperature intervals were found with power laws relating shear flow relaxation and probe rotational diffusion. The main aim of this paper was the study of the sharp crossover between two different fractional regimes that for all the samples was observed at a temperature TC = 1.15 - 1.25 Tg. The decoupling from structural relaxation at T < TC was ascribed to the onset of cooperative effects on the length scale probed by the tracer. These results fit in the general scenario regarding the dynamical information extractable from ESR on cholestane, a probe with its long-axis dimension greater than the typical length characterizing the rigid segment of polymers. [ABSTRACT FROM AUTHOR]

We studied by electron spin resonance (ESR) spectroscopy the reorientational dynamics of the cholestane spin probe dissolved in the matrix of the PMA4 40/60 copolymer containing methyl methacrylate (MMA, 40 mol%) and azobenzene methacrylate (MA4, 60 mol%) counits. Heterogeneities in the probe dynamics at the nanometer length scale were evidenced and attributed to the existence of molecular sites with slow and fast spinning correlation times. Different dynamic regimes were also observed with a crossover temperature T C that was correlated with the glass transition temperature T g of the copolymer, T C = 1.17 T g . Even though the nematic-to-isotropic transition temperature could not be detected, the probe dynamics experienced the onset of nematic order at the molecular level. The results are compared with those of the closely related nematic PMA4 30/70 copolymer. [ABSTRACT FROM AUTHOR]

Two copolymers containing nonmesogenic methyl methacrylate (MMA) and nematogenic azobenzene methacrylate (MA4) side groups (30/70 and 40/60 copolymers) azobenzene were studied in the linear viscoelastic regime. The time-temperature superposition principle was found to hold over the whole investigated temperature range, even across the nematic-isotropic transition in the 30/70 copolymer. Rheological steady state and oscillatory measurements were used to obtain the temperature dependence of the zero shear viscosity. The strength and dynamic fragility of these two copolymers were compared with those of the corresponding PMA4 and PMMA homopolymers, which pointed out the role of the structure of the main chain in dictating the relaxational dynamics. [ABSTRACT FROM AUTHOR]

The Ball Micromission Spacecraft (MSC) is a multi-purpose platform capable of supporting science missions at distances from the Sun ranging from 0.7 to 1.7 AU. In the baseline scenario, MSC is launched as a secondary payload on an Ariane 5 rocket from Kourou, French Guiana, to GTO using the Ariane 5 structure for auxiliary payloads (ASAP5). The maximum launch wet mass is 242 Kg and can include up to 45 Kg of payload depending on AV needs. The on-board propulsion system is used for maneuvering in the Earth-Moon system and injecting the spacecraft into its final orbit or trajectory. For Mars missions, MSC enables orbiting Mars for science payloads and/or communications and navigation assets, or for precision Mars fly-bys to drop up to six probes. The micromissions spacecraft bus can be used for science targets other than Mars, including the Moon, Earth, Venus, Earth-Sun Lagrange points, or other small bodies. This paper summarizes the current spacecraft concept and describes the multimission spacecraft bus implementation in more detail. [ABSTRACT FROM PUBLISHER]

The enthalpy relaxation mechanism of an azobenzene side chain liquid crystal polymethacrylate is investigated by means of DSC experiments after proper annealing procedures at temperatures below the glass transition. The data are analyzed according to a recently developed trap model. The model is found to be able to describe the experimental enthalpy relaxation data fairly well, providing a means to estimate the cooperativity length of the system. [ABSTRACT FROM AUTHOR]

The topic of dynamic changes undergone by glass-forming materials in the supercooled region is addressed in this study. Crossover regions and temperatures are generally considered as key features in order for the glass transition phenomenon to be understood. The attention is here focused on the crossover region of polymers and its dependence on the polymeric entangled dynamics. To avoid the superposition of possible dependence on the polymeric polydispersity, nearly monodisperse syntheses of poly(ethyl acrylates) have been used. Rotational dynamics have been investigated with electron spin resonance spectroscopy, dissolving the cholestane molecular tracer in a poly(ethyl acrylate) (Mn = 7500 amu). Comparison is carried out with the findings obtained in the case of an almost monodisperse poly(ethyl acrylate) with Mn = 58 200 amu. Different dynamic regimes and crossover regions were recognized in the temperature dependence of the molecular rotation. The crossover temperatures Tc were found to be dependent on the molecular weight. Moreover, the dynamics in non-Arrhenius regions were satisfactorily described as a fractionary law of structural relaxation. [ABSTRACT FROM AUTHOR]

ESR studies were carried out on the rotational dynamics of cholestane molecular tracer dissolved in liquid crystal homopolymer and copolymer from well above TNI down to below Tg. Rheological measurements also provided the flow relaxation properties of the polymer matrices. The distribution functions of molecular sites were determined, and their stability was monitored as a function of thermal history. The different molecular site distributions and cooperativity degrees were compared and discussed. [ABSTRACT FROM AUTHOR]

The mass contents in five samples of a nematic azobenzene polymethacrylate having different molar masses and molar mass distributions were evaluated starting from either Logarithmic Normal (LN) or Zimm-Schulz (ZS) distribution functions. Reliability of these two approaches was verified by comparing the experimental T g with those predicted (Fox-Flory) on the basis of the LN and ZS mass contents. A birefringent bit was induced in the various samples, and its stability on time was monitored at constant temperature. The optical bit was found to be quite stable at temperatures below that at which conformational disorder was frozen in the nematic phase. [ABSTRACT FROM AUTHOR]

The dynamics of the cholestane spin probe dissolved in a nematic azobenzene copolymer was studied by ESR following a suitable thermal procedure. Heterogeneities in the dynamics of the guest molecule resulted to occur only in the high temperature region, slightly above the nematic-isotropic transition temperature. A temperature region above the glass transition was signalled, in which stable optical writing could be obtained. Optical birefringence and topological writing experiments were carried out on polymer films at the macroscopic and nanometer length-scales, respectively. SNOM analysis showed a very homogenous substrate that could be suitable for optical nanowriting. [ABSTRACT FROM AUTHOR]

Dynamic processes effective on the nanometre length scale are of interest in supercooled fluids and polymers owing to their influence on structural and dynamic properties of these materials. In particular, nanometre and nanosecond scales mark the crossover from liquid to solid properties when approaching the glass transition. A possible explanation of the complex dynamic response of these systems for these length and time regions is provided in terms of heterogeneity. Heterogeneity in supercooled materials manifests itself by the presence of different domains, which relax towards equilibrium with different rates. Therefore, experimental techniques, which are sensitive to slow and fast molecules and able to follow their dynamics, are of paramount importance in this field of research. The present work is devoted to investigate heterogeneity in a polymer. We focused our attention on a side-chain liquid-crystal polymer (SCLCP). In this study a nanometre-scale molecular probe is dissolved in the SCLCP and its rotational dynamics are studied by linear and nonlinear electron spin resonance (ESR) spectroscopies, which are sensitive to the long and short time scales respectively of the rotational relaxation. In particular, linear ESR spectroscopy evidenced the presence of heterogeneity while on the short time scale detected by nonlinear ESR the correlation decay turns out to be homogeneous. [ABSTRACT FROM AUTHOR]

The physical ageing of a side-chain liquid-crystal polymer is investigated by means of differential scanning calorimetry, which allows one to follow the enthalpy relaxation of the glass. Measurements are performed for different thermal treatments and compared with the predictions of two phenomenological models where the nonlinearity of the ageing process is accounted for by multiparameter expressions. The experimental results can be described with the model based on the Narayanaswamy expression for nonlinearity, although it seems that the model based on the Hodge expression fits experimental data more satisfactorily. In particular, a single set of parameters is determined which describes different experiments. However, the value of the enthalpy loss as a function of the ageing time is greatly overestimated by both models. [ABSTRACT FROM AUTHOR]

The rotational dynamics of the spin probe 2,2,6,6-tetramethyl-piperidin-1-oxyl (TEMPO) dissolved in the molecular glass former phenyl salicylate (Salol) have been investigated via electron spin resonance spectroscopy, in a temperature interval ranging from the supercooled to the glassy state of Salol. The comparison of experimental data with predictions of both diffusive and jump reorientational models has been made. It has been proved that in both the supercooled and the glassy state, the TEMPO spin probe rotates according to a jump process. In the investigated temperature range, the angular jump size Φ has been found to be constant and holds 75°. Moreover, the temperature dependence of the reorientational correlation times, which is well described by a double Arrhenius law, has been studied. The crossing temperature from the first to the second Arrhenius regime is found to be near to the glass transition temperature. Comparison with the results of a previous study on the reorientational dynamics of a TEMPO probe in o -terphenyl, has shown that rotational motion happens in structural cages with comparable free volumes. [ABSTRACT FROM AUTHOR]

The short-time rotational dynamics of nearly spherical and cylindrical spin probes in supercooled and glassy o-terphenyl is investigated by nonlinear electron spin resonance spectroscopy. At higher temperatures, the relaxation is exponential and the Debye-Stokes-Einstein law holds, tau (eta/T). tau is the rotational correlation time, eta the shear viscosity and T the temperature. On cooling, the coupling of the short-time rotational dynamics and the shear viscosity weakens, and a fractional Debye-Stokes-Einstein law tau (eta/T)xi, with xi constant, is observed. At the lower temperatures, the rotation is activated. A scaling of the short-time rotational dynamics of the different molecular probes is obtained for the overall range of temperature. [ABSTRACT FROM AUTHOR]

We investigated the rotational dynamics of molecular tracers dissolved in a polymeric mesophase using two magnetic resonance spectroscopies. It is found that the coupling between the reorientation and the viscous flow is partial and well described by the fractional Debye-Stokes-Einstein law tau etaxi with 0 < xi 1, tau and eta being the rotational correlation times of the tracers and the viscosity respectively. [ABSTRACT FROM AUTHOR]

Anisotropic jump reorientation occurs in glasses, polymers, and plastic crystals. A general theoretical frame to describe such processes is presented. It generalizes previous work by Ivanov [Sov. Phys. JETP 18, 1041 (1964)]. A tractable model is given by a simple phenomenological assumption on the jump distribution. Analytical results and fast numerical methods to evaluate the relevant quantities are derived. The model is validated by comparing the predictions with ESR experiments on stiff, cylindrical tracers dissolved in the glassformer o-terphenyl. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Abstract The phenomenon of substance abuse during pregnancy has fostered much controversy, specifically regarding treatment vs. punishment. Should the pregnant mother who engages in substance abuse be viewed as a criminal or as someone suffering from an illness requiring appropriate treatment? As it happens, there is a noticeably wide range of responses to this matter in the various states of the United States, ranging from a strictly criminal perspective to one that does emphasize the importance of the mother's treatment. This diversity of dramatically different responses illustrates the failure to establish a uniform policy for the management of this phenomenon. Just as there is lack of consensus among those who favor punishment, the same lack of consensus characterizes those states espousing treatment. Several general policy recommendations are offered here addressing the critical issues. It is hoped that by focusing on these fundamental issues and ultimately detailing statistics, policymakers throughout the United States will consider the course of action that views both pregnant mother and fetus/child as humanely as possible.