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Thermal Instability (thermal + instability)
Selected AbstractsThermostability of Lyocell Dopes Modified with Surface-Active AdditivesMACROMOLECULAR MATERIALS & ENGINEERING, Issue 8 2005Frank Wendler Abstract Summary: Cellulose/N -methylmorpholine- N -oxide monohydrate (NMMO) spinning solutions were modified with surface-active additives to yield Lyocell fibers with functional properties. Based on cellulose fibers, a new class of materials with tailored adsorption characteristics are produced. Activated charcoal and carbon black used as additives significantly affect the thermostability of the spinning solutions. Considering the degree of filling three general tendencies become evident. It is most obvious that the onset temperature of dope decomposition is shifted towards lower values accompanied by viscosity reduction after annealing at elevated temperatures and an enhanced formation of degradations products. Morpholine, N -methylmorpholine and formaldehyde as the main degradation products were detected in aqueous distillates by means of HPLC. To study the rate of by-product formation during preparation of the solution kinetic measurements were carried out. Thermal instabilities are not only initiated by heavy metal ions, especially Fe(II), but also by the particle size and porosity of the charcoal. The nano-scaled carbon black used causes autocatalytic reactions as revealed by calorimetric measurements. Relationships between amount of Acc versus onset temperature (Ton) and concentration of N -methylmorpholine. [source] Influence of the Wall Characteristics on the Development of MARFE in TokamaksCONTRIBUTIONS TO PLASMA PHYSICS, Issue 7-9 2006O. Marchuk Abstract Multifaceted asymmetric radiation from the edge (MARFE) normally develops in fusion devices close to the density limit. MARFE is considered a result of thermal instabilities excited under critical conditions through different mechanisms: impurity radiation, recycling of neutral particles, anomalous transport of charged particles and energy. Recent experiments on tokamaks TEXTOR and JET show that plasma-wall interaction, leading to release of recycling neutrals and impurities, plays a very important role for the formation of MARFE. In the present contribution we develop further the MARFE models based on the instability of particle recycling on the tokamak wall by including a simple description for the release of recycling neutrals from the wall surface into the plasma. This development takes into account the time delay between the out flow of charged particles from the plasma and in flux of neutrals. The linear stability analysis shows that this does not change the critical plasma density for the MARFE formation but modifies significantly the growth rate of unstable perturbations developing when the density exceeds the threshold. These findings are confirmed in a non-linear consideration by solving the equations for the particle, momentum and energy transfer in the plasma coupled with the wall particle balance equations. This is done in a one-dimensional approximation by taking into account the variation of the main plasma parameters in the poloidal direction and making averaging in the radial direction over the plasma edge width of the penetration depth of neutrals. The intrinsic poloidal asymmetry of the system, defining the MARFE localization, is introduced by the Shafranov shift of magnetic flux surfaces. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Multi-Fluid Modeling of Low-Recycling Divertor RegimesCONTRIBUTIONS TO PLASMA PHYSICS, Issue 3-5 2010R. D. Smirnov Abstract The low-recycling regimes of divertor operation in a single-null NSTX magnetic configuration are studied using computer simulations with the edge plasma transport code UEDGE. The edge plasma transport properties pertinent to the low-recycling regimes are demonstrated. These include the flux-limited character of the parallel heat transport and the high plasma temperatures with the flattened profiles in the scrape-off-layer. It is shown that to maintain the balance of particle fluxes at the core interface the deuterium gas puffing rate should increase as the divertor recycling coefficient decreases. The radial profiles of the heat load to the outer divertor plate, the upstream radial plasma profiles, and the effects of the cross-field plasma transport in the low-recycling regimes are discussed. It is also shown that recycling of lithium impurities evaporating from the divertor plate at high surface temperatures can reverse the low-recycling divertor operational regime to the high-recycling one and may cause thermal instability of the divertor plate (© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] A flammability performance comparison between synthetic and natural clays in polystyrene nanocompositesFIRE AND MATERIALS, Issue 4 2005Alexander B. Morgan Abstract Polymer-clay nanocomposites are a newer class of flame retardant materials of interest due to their balance of mechanical, thermal and flammability properties. Much more work has been done with natural clays than with synthetic clays for nanocomposite flammability applications. There are advantages and disadvantages to both natural and synthetic clay use in a nanocomposite, and some of these, both fundamental and practical, will be discussed in this paper. To compare natural and synthetic clays in regards to polymer flammability, two clays were used. The natural clay was a US mined and refined montmorillonite, while the synthetic clay was a fluorinated synthetic mica. These two clays were used as inorganic clays for control experiments in polystyrene, and then converted into an organoclay by ion exchange with an alkyl ammonium salt. The organoclays were used to synthesize polystyrene nanocomposites by melt compounding. Each of the formulations was analysed by X-ray diffraction (XRD), thermogravimetric analysis (TGA) and transmission electron microscopy (TEM). Flammability performance was measured by cone calorimeter. The data from the experiments show that the synthetic clay does slightly better at reducing the heat release rate (HRR) than the natural clay. However, all the samples, including the inorganic clay polystyrene microcomposites, showed a decreased time to ignition, with the actual nanocomposites showing the most marked decrease. The reason for this is postulated to be related to the thermal instability of the organoclay (via the quaternary alkyl ammonium). An additional experiment using a more thermally stable organoclay showed a time to ignition identical to that of the base polymer. Finally, it was shown that while polymer-clay nanocomposites (either synthetic or natural clay based) greatly reduce the HRR of a material, making it more fire safe, they do not provide ignition resistance by themselves, at least, at practical loadings. Specifically, the cone calorimeter HRR curve data appear to support that these nanocomposites continue to burn once ignited, rather than self-extinguish. Copyright © 2004 John Wiley & Sons, Ltd. [source] Determination of particle heterogeneity and stability of recombinant adenovirus by analytical ultracentrifugation in CsCl gradientsJOURNAL OF PHARMACEUTICAL SCIENCES, Issue 2 2008Xiaoyu Yang Abstract Recombinant adenoviruses (rAd), widely used as vectors for gene therapy, are generally purified by column chromatography and frequently contain empty capsids and other aberrant forms of virus particles. To determine particle heterogeneity we utilized analytical ultracentrifugation (AUC) in CsCl density gradients. Preparations of three different rAd vectors were assessed. AUC was able to resolve multiple density forms including two empty capsid types in various virus preparations. One unusual density form (form V), was noninfectious and lacked protein VI. AUC was able to quantify empty capsids and monitor their removal during process development. Their relative concentrations were reduced by either addition of an immobilized zinc affinity chromatography (IZAC) step or by extension of the infection time. The Adenovirus Reference Material (ARM), a wild-type Ad5, had 2.2% empty capsids and no other detectable minor particle forms. Finally, AUC was utilized to monitor the thermal instability of the three rAd vectors via the transformations of different density forms. The vector and empty capsids containing protein IX were more stable than those without IX. Together, these results exemplify AUC in CsCl density gradients as a valuable technique for evaluating product particle heterogeneity and stability. © 2007 Wiley-Liss, Inc. and the American Pharmacists Association J Pharm Sci 97:746,763, 2008 [source] Thermal stability of vaccinesJOURNAL OF PHARMACEUTICAL SCIENCES, Issue 2 2003Duane T. Brandau Abstract Worldwide vaccination programs against infectious diseases and toxins are estimated to save approximately 3 million lives yearly. Tragically, however, another 3 million individuals (primarily children) die of vaccine-preven diseases. A significant portion of this problem results from the thermal instability of many of the currently used vaccines. This review argues that modern methods of physical and chemical analysis permit for the first time characterization of the degradative pathways of thermally labile vaccines. A rigorous description of these pathways permit a more rational and systematic approach to the stabilization of vaccines. A direct result of the replacement of currently employed, primarily empirical, approaches to vaccine stabilization with a more molecular-based methodology should be the development of more universally available vaccinations against life-threatening diseases. This has the potential to have a dramatic impact on world health. © 2003 Wiley-Liss, Inc. and the American Pharmaceutical Association J Pharm Sci 92:218,231, 2003 [source] Synthesis and characterization of novel liquid-crystalline copolymers containing thermally stable photochromic groupsJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 10 2007Jui-Hsiang Liu Abstract To overcome the defects of the thermal instability of azobenzene, a series of novel photochromic, chiral, liquid-crystalline monomers and polymers were synthesized from (+)-camphor. The copolymerization of the photochromic monomers with comonomers was carried out. The synthesized monomers and polymers were identified with nuclear magnetic resonance, Fourier transform infrared, and elemental analysis. The composition of the copolymers was estimated with elemental analysis. The specific rotation of the chiral compounds and polymers was evaluated. The thermal stability and phases of the polymers during heating and cooling cycles were studied with differential scanning calorimetry and thermogravimetric analysis. The phases of the polymers were identified with polarized optical microscopy textures and X-ray diffraction analysis. The distance between the layers of smectic liquid crystals was estimated from the diffraction angles. Photoisomerization of the configurational E/Z structures was investigated with an ultraviolet,visible spectrophotometer with 300-nm ultraviolet irradiation. The thermal stability of the Z-structural segment in the polymers was confirmed through the heating of the polymer at 70 °C for over 10 h. The photoisomerization and thermal stability of the CC bond in the polymeric materials were demonstrated through a series of novel chiral polymers synthesized in this investigation. Both the polarity of the center part and the molecular length at the ends of the molecules were found to be necessary factors for the formation of liquid-crystalline molecules. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 2026,2037, 2007 [source] Interpretation of the 1998 outburst of the unique X-ray transient CI Camelopardalis (XTE J0421+560)MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 1 2006imon ABSTRACT We present an analysis of the 1998 outburst of the peculiar X-ray binary and X-ray transient CI Cam (XTE J0421+560). We discuss the observations in the framework of several possible models and argue that this outburst can be explained by the thermal instability of the accretion disc, analogous to the outbursts of soft X-ray transients. Applying the model by King & Ritter and Shahbaz, Charles & King on the X-ray light curve, we obtain a realistic mass of the disc at the peak of outburst to be Mh(0) , 1.5 × 1023 g (the distance d= 5 kpc) or 3.8 × 1022 g (d= 2.5 kpc). The disc radius at this moment is then Rh(0) , 2.5 × 1010 cm (d= 5 kpc) or 1.6 × 1010 cm (d= 2.5 kpc), provided that the factor f (the ratio of the mass of the hot disc at that moment with respect to its maximum possible mass) is close to unity. Even if we take a quite low f= 0.05, we still obtain Rh(0) by only 2.7 times larger. The reddening in the outburst maximum and brighter peak absolute magnitude of CI Cam with respect to those of soft X-ray transients in outbursts can be explained if the disc in CI Cam heats up an extended envelope and/or a strong jet is formed. We thus bring firm arguments for Robinson, Ivans & Welsh's hypothesis. On the other hand, we bring the arguments against the mass transfer burst from the donor and the periastron passage of the compact object. [source] Role of polymers in CVD growth of nanocrystalline diamond films on foreign substratesPHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 11-12 2009A. Kromka Abstract Spin coating of PVA polymer with fine grained diamond powder is used as the nucleation treatment for achieving growth of nanocrystalline diamond (NCD) thin films. The growth is realized by standard microwave plasma chemical vapor deposition (CVD). The morphology and character of deposited NCD film is strongly related to the growth temperature. The low temperature process (430°C) results in a growth of well-faceted continuous films. The high temperature process (830,°C) results in voids and openings in the layer. Addition of PVA as the interlayer between the substrate and the seeding polymer composite leads to more openings. The effect is the most pronounced at 830,°C. This is assigned to thermal instability of PVA and oxygen chemistry present in the early beginning of the CVD growth. An optimized seeding process based on the polymer composite procedure at low substrate temperature and low PVA amount allows the diamond growth on extremely soft substrates. [source] Formation of "air-gap" structure at a GaN epilayer/substrate interface by using an InN interlayerPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 7 2003A. Yamamoto Abstract We propose a new technique for "air-gap" formation at a GaN/sapphire interface by using an InN interlayer. This is aimed to grow epitaxial GaN films with reduced stress and cracks. First, an InN interlayer of about 0.2 ,m thick is grown at 600 °C in atmospheric pressure. Then a 30 nm-thick GaN buffer layer is grown on the InN layer at 550 °C. The substrate temperature is ramped up to 1000 °C in the NH3 flow, and finally a 1.5 ,m-thick GaN epilayer is grown on the annealed GaN buffer layer using nitrogen carrier gas. Consequently, an "air-gap" structure is naturally formed close to the substrate surface. During the ramping period of substrate temperature, the InN layer decomposes due to its thermal instability and metallic In is formed. It is found that metallic In drops as a result of InN decomposition contribute to the air-gap formation. No cracks are found on the GaN surface and a reduced stress in the layer is confirmed by PL and Raman shift measurements. (© 2003 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] | |||||||||||||