bluuebunny/crossref_metadata_2025_split huggingface dataset:
Chiralitätsverstärkung in dynamischen supramolekularen Aggregaten
Authors: Palmans Anja R. A. , Meijer E. W. 
Published: October 2007

AbstractDie Frage nach dem Ursprung der Chiralität in biologischen Systemen löste die Suche nach nichtlinearen Effekten in der Katalyse aus, und man suchte nach Wegen, um ausgehend von minimalen Enantiomerenüberschüssen optisch reine Verbindungen zu erhalten. Intensiv erforscht wurde bereits die Chiralitätsverstärkung in Polymeren als Folge kooperativer Prozesse. Vor zehn Jahren wurde dieser Effekt erstmals auch für nichtkovalente, dynamische supramolekulare Systeme nachgewiesen. Seitdem hat sich gezeigt, dass auch für niedermolekulare Verbindungen eine Chiralitätsverstärkung möglich ist, wenn nichtkovalente Wechselwirkungen wie Wasserstoffbrücken, hydrophobe und π‐π‐Stapelwechselwirkungen aufeinander abgestimmt werden. Wir fassen die Resultate der letzten zehn Jahre zusammen und leiten daraus einige allgemeine Regeln ab. Eine Chiralitätsverstärkung kann zwar immer noch nicht sicher vorhergesagt werden, essenziell sind aber wohl ein ausgewogenes Verhältnis der beteiligten Wechselwirkungen und oftmals die Bildung eines intrinsisch chiralen Objekts sowie kooperative Aggregationsprozesse.
Amplification of Chirality in Dynamic Supramolecular Aggregates
Authors: Palmans Anja R. A. , Meijer E. W. 
Published: October 2007

AbstractThe quest to understand the origin of chirality in biological systems has evoked an intense search for nonlinear effects in catalysis and pathways to amplify slight enantiomeric excesses in racemates to give optically pure molecules. The amplification of chirality in polymeric systems as a result of cooperative processes has been intensely investigated. Ten years ago, this effect was shown for the first time in noncovalent dynamic supramolecular systems. Since then, it has become clear that a subtle interplay of noncovalent interactions such as hydrogen‐bonding, π–π stacking, and hydrophobic interactions is also sufficient to observe amplification of chirality in small molecules. Here we summarize the results obtained over the past decade and the general guidelines we can deduce from them. Predicting amplification of chirality is still impossible, but it appears to be a balance between different types of interactions, the formation of an intrinsically chiral object, and cooperative aggregation processes.
Optimization of combined heat and mass exchanger networks using pinch technology
Authors: Isafiade Adeniyi , Fraser Duncan 
Published: October 2007

AbstractThis article examines the benefits that may be obtained by combining the optimisation of heat and mass exchanger networks. This study uses a Pinch Technology approach to the targeting of Combined Heat and Mass Exchanger Networks (CHAMENs), and illustrates it with application to three examples. The first example has just one external mass separating agent (MSA), the second has both process and external MSAs, and the third is an extension of the second with a heat exchanger network integrated. The major benefits arise when it is possible to cool the process MSA with an excess capacity to remove mass. This reduces the flowrate of the external MSA (since this exists below the pinch) and can even do away entirely with the need for it. This also leads to a reduction in the capital cost requirements of both the process and the external MSAs, as well as a reduction in regeneration costs. The implication of this is that a limitation to the use of the available capacity of process MSAs is their mass exchange temperature. It was also found (in the example in which hot/cold utilities are used to enhance mass exchange) that the mass exchanger network synthesis (MENS) costs generally dominate over the heat exchanger network synthesis (HENS) costs. Other examples presented in this article support these conclusions. Copyright © 2007 Curtin University of Technology and John Wiley & Sons, Ltd.
Fault detection and isolation for dynamic processes using recursive principal component analysis (PCA) based on filtering of signals
Authors: Jeng Jyh‐Cheng , Li Cheng‐Chih , Huang Hsiao‐Ping 
Published: October 2007

AbstractA systematic procedure for the fault detection and isolation of dynamic systems is presented. The inputs of the process first pass through the dynamic filters which represent the process dynamics. Then, principal component analysis (PCA) is applied to the data matrix consisting of these filtered signals and the process outputs for fault detection. In case of a fault being detected, owing to an artificial linear relationship existing in the data matrix, the last principal component (LPC) is adopted for fault isolation. A recursive algorithm for PCA based on rank‐one matrix update of the covariance is derived to compute the LPC on line. Patterns of the LPC are devised to isolate these faults, which include constant‐bias and high‐frequency noises originating from sensor measurement, errors resulting from input disturbance and change in the process gain. Furthermore, the magnitude of the fault can also be identified from the computed LPC. An illustrative example is used to verify the effectiveness of the proposed method. Copyright © 2007 Curtin University of Technology and John Wiley & Sons, Ltd.
Delay‐compensated controllers for two‐input/two‐output (TITO) multivariable processes
Authors: Seshagiri Rao A. , Rao V. S. R. , Chidambaram M. 
Published: October 2007

AbstractA decentralized controller design based on the direct synthesis method for two‐input/two‐output (TITO) processes in the Smith predictor configuration is proposed. The decentralized controllers are designed individually on the basis of the diagonal individual transfer functions of the process. Using the direct synthesis principle, the two decentralized controllers are designed using the individual diagonal transfer functions of the process matrix and the individual desired diagonal closed‐loop transfer functions. Further, these direct synthesis controllers are implemented in the Smith predictor configuration for each output. While converting from the synthesis controller to the Smith predictor configuration, the decentralized controller parameters are directly obtained in terms of the individual closed‐loop desired tuning parameters. The method is compared with the recently reported methods. Copyright © 2007 Curtin University of Technology and John Wiley & Sons, Ltd.
Disturbance observer design for continuous systems with delay
Authors: Jones R. W. , Tham M. T. 
Published: October 2007

AbstractDisturbance observers (DOs), which are popularly used for improving the disturbance rejection capability of mechatronic servo control systems, offer several attractive features that could prove beneficial for process control systems. The tuning is simple and intuitive and they allow independent tuning of disturbance rejection characteristics, which is particularly helpful in situations in which gains need to be tuned on‐line. This paper is concerned with examining DO design for continuous‐time systems with delay. Two methods for incorporating time delay into traditional DO design are considered, to assess their relative performance, stability, and noise rejection characteristics. The performance of one of these time‐delay‐based DO approaches is then compared with proportional, integral and derivative (PID) control, designed using a maximum sensitivity approach, on a representative process model. The paper concludes by briefly examining the incorporation of a DO into a two‐degrees‐of‐freedom (2DOF) control structure. Copyright © 2007 Curtin University of Technology and John Wiley & Sons, Ltd.
Transitions and relaxations of copolypropylene molecules in copolypropylene–clay composites
Authors: Zhong Weixia , Qiao Xiuying , Cao Ming , Sun Kang , Zhang Guoding 
Published: October 2007

AbstractThree commercial organoclays pretreated with C18H37N+H3, C18H37N+(CH3)3 and (C18H37)2N+(CH3)2, were used to prepare a series of copolypropylene (cPP)‐clay nancomposites by melt blending. Then, the effects of the clay content and pretreatment history on the transition and relaxation of cPP molecules in different composites were investigated in detail by dynamic mechanical analysis. The results show that the α‐relaxation, ascribed to the movement of polymer main chains within the crystalline regions of different cPP composites, is activated by the increase of clay content. The main β‐relaxation, assigned to the glass‐rubber transition of cPP segments in amorphous portions, is greatly limited by about 3–5 wt % clay loading, whereas drastically motivated with 7 wt % clay loading, which correlates closely with the dispersion order of clay layers in different composites. Lastly, the γ‐relaxation, associated with the motion of ethylene sequence of cPP chains, is restricted because of the increasing clay content. Additionally, it is found that the miscibility between cPP molecules and organoclay layers was strengthened as the clay premodifier varied from C18H37N+H3 to C18H37N+(CH3)3, but somewhat weakened when the premodifier changed as (C18H37)2N+(CH3)2. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008
Macromolecular assemblies of segmented poly(ester urethane)s and poly(ether urethane)s
Authors: Ioan Silvia , Lupu Mihaela , Epure Virginia , Ioanid Aurelia , Macocinschi Doina 
Published: October 2007

AbstractPolyurethanes containing different soft and hard segments were investigated by fluorescence and scanning electron microscopy. The polarity dependence of the vibrational structure of the pyrene emission spectrum indicated the formation of aggregates at concentrations, which are significantly below the critical concentrations, which define the separation of dilute‐semidilute domains. Unlike the samples with 4,4′‐methylene diphenylene diisocyanate, the samples with 2,4‐tolylene diisocyanate in hard segments give the fluorescence spectra in which the pyrene excimer appears. The supermolecular structures associated with the form of spherulites or of spherical micelles were detected by scanning electron microscopy. The results were compared with previous reports concerning viscometric data. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008
Mechanical properties of crosslinked polyurethane elastomers based on well‐defined prepolymers
Authors: Król Piotr , Pilch‐Pitera Barbara 
Published: October 2007

AbstractThis article presents research findings for selected mechanical properties of polyurethane elastomers. The studied elastomers were synthesized with the prepolymer‐based method with the use of controlled molecular weight distribution (MWD) urethane oligomers and with the classical single‐stage method. Prepolymers with defined MWDs were obtained with the use of a multistage method, that is, step‐by‐step polyaddition. To produce elastomers, isocyanate oligomers were then crosslinked with triethanolamine, whereas hydroxyl oligomers were crosslinked with 4,4′,4′′‐triphenylmethane triisocyanate (Desmodur RE). The tensile strength of the obtained elastomers ranged from 1.0 to 7.0 MPa, the ultimate elongation approached 1700%, the Shore A hardness varied from 40 to 93°, and the abrasion resistance index fell within 15–140. The effects of the types of raw materials used, the chemical structures, the production methods, and the supermolecular structures on the mechanical properties of the obtained polyurethane elastomers were examined. When the obtained findings were generalized, it was concluded that the structural changes in the polyurethanes, which were favorable for intermolecular interactions, improved the tensile strength, hardness, and abrasion resistance of the materials and impaired their ultimate elongation at the same time. More orderly supermolecular structures and, therefore, superior mechanical properties were found for polyurethane elastomers produced with the prepolymer method. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008
Effect of olive residue benzylation on the thermal and mechanical properties of poly(vinyl chloride)/olive residue composites
Authors: Djidjelli H. , Boukerrou A. , Rabouhi A. , Founas R. , Kaci M. , Zefouni O. , Djillali N. , Belmouhoub L. 
Published: October 2007

AbstractThe changes in mechanical properties, the thermal stability, and the water absorption capacity of poly (vinyl chloride)/olive residue flour composites were studied as a function of various residue olive flour ratios, i.e., 0, 5, 15, and 25% by weight taking into account the effect of benzylation chemical treatment of the filler. The study showed that composite samples prepared with the untreated filler exhibited higher tensile modulus and hardness compared with the neat resin, whereas elongation and tensile strength were observed to decline. On the other hand, the PVC hardness was found to increase with addition of the untreated olive residue flour (ORF), however the composite samples prepared with the benzylated flour exhibited lower hardness than those prepared with untreated olive residue. Moreover, the amount of absorbed water depends on the amount of filler in the composite. The comparison of the results obtained from the samples of F5, F20, and F30 formulations between the untreated and treated ORF indicated a reduction in absorbed water for the composite samples containing treated ORF with benzyl chloride. As a result, the mechanical properties of the treated composites were improved. Furthermore, the thermal characterization of the different samples carried out by color change test and thermogravimetric analysis revealed an increase in the onset temperatures of decomposition for the treated composites. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008
Curing kinetics study of an epoxy resin system for T800 carbon fiber filament wound composites by dynamic and isothermal DSC
Authors: Chen Weiming , Li Peng , Yu Yunhua , Yang Xiaoping 
Published: October 2007

AbstractCuring kinetics of DGEAC/DDM/DETDA/DGEB epoxy resin system was studied using dynamic and isothermal differential scanning calorimetry (DSC) for the preparation of T800 carbon fiber filament wound composites. In dynamic experiment, four kinds of epoxy resin systems were studied. Curing characteristics, such as curing range and curing temperatures of the epoxy resin system with mixed hardeners (DGEAC/DDM/DETDA), were found lying within those of the two epoxy resin systems with a single hardener (DGEAC/DDM, DGEAC/DETDA). The addition of reactive diluter (DGEB) caused increase in curing range and exothermic heat. In addition, the activation energies calculated by the isoconversional method of all four resin systems decreased to the minimum value in the early stage due to the autocatalytic role of hydroxyl groups in the curing reaction and then increased due to the increased viscosity and crosslink of epoxy systems. The addition of reactive diluter led to the decrease in activation energies on the initial stage (conversion = 0.1–0.3). In isothermal experiment, a series of isothermal DSC runs provided information about the curing kinetics of the DGEAC/DDM/DETDA/DGEB system over a wide temperature range. The results showed that the isothermal kinetic reaction of the epoxy resin followed an autocatalytic kinetic mechanism. The autocatalytic kinetic expression chosen in this work was suitable to analyze the curing kinetics of this system. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008
Laser scanning confocal microscope characterization of dye diffusion in nylon 6 fibers treated with atmospheric pressure plasmas
Authors: Wang Chunxia , Zhu Lu , Qiu Yiping 
Published: October 2007

AbstractThe effect of atmospheric pressure plasma treatment on wettability and dyeability of nylon 6 fibers is investigated. The plasma treatments resulted in an average of 10°–20° decrease in the advancing contact angle and 20°–30° decrease in the receding contact angle. An increased dye diffusion rate of nylon 6 fibers was observed using laser scanning confocal microscope (LSCM). Scanning electron microscope confirmed that the fiber surfaces were roughened, and X‐ray photoelectron spectroscopy showed that the polar groups on the fiber surfaces increased after the plasma treatments. As the plasma treatment time increased, a greater degree of etching was achieved and more polar groups such as hydroxyl and carboxyl groups produced on the surfaces of the nylon 6 fibers, leading to a better wettability and thus a better dyeability of the fiber. This study proved that LSCM may be effectively used in detecting the change of dye diffusion rate in nylon fibers treated with plasmas and the mounting medium should have a close refractive index as the fiber to avoid distortion of the fiber cross section image. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008
Effect of the different rigidity of the chiral crosslinker on phase behaviors of side‐chain chiral liquid crystalline elastomers
Authors: Zhang Bao‐Yan , He Xiao‐Zhi , Liao Qing‐Feng , Zhou Qun‐Hua 
Published: October 2007

AbstractIn the present work, the phase behaviors of two series of side‐chain liquid crystalline elastomers (PI and PII series) derived from the same nematic liquid crystalline monomer and the different rigidity of chiral bisolefinic crosslinking units have been compared and studied extensively, and the effect of the different rigidity of crosslinker on the phase behavior of elastomers has been discussed. The chemical structure of the monomers and polymers obtained were confirmed by FTIR and 1H NMR spectroscopy. The phase behaviors were investigated by differential scanning calorimetry, polarizing optical microscopy measurement, thermogravimetric analyses, and X‐ray diffraction measurement. The two series of elastomers showed smectic or cholesteric phases. When the amount of different crosslinking units was less than 15 mol %, both of the elastomers displayed elasticity, reversible phase transition with wide mesophase temperature ranges, and high thermal stability. It is shown that the isotropization temperature values of PII series are higher than those of PI series, and the glass transition temperature values of PII series varied smoothly and that of PI series changed smoothly first and then abruptly with increasing the contents of crosslinkers with different rigidity. In addition, PI series showed an interesting change in LC texture near clearing point, but PII series did not. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008
Superabsorbent hydrogel composed of covalently crosslinked gum arabic with fast swelling dynamics
Authors: Favaro Silvia L. , de Oliveira Fernando , Reis Adriano V. , Guilherme Marcos R. , Muniz Edvani C. , Tambourgi Elias B. 
Published: October 2007

AbstractA superabsorbent hydrogel (SH) with fast swelling dynamics and good mechanical stability in the swollen state was prepared. The SH was obtained from chemically modified gum arabic (MGA) with glycidyl methacrylate (GMA), acrylic acid (AAc), and acrylamide (AAm). The water‐transport mechanisms and equilibrium swelling ratio (SR) were the parameters used to describe the water‐absorption profile of SH. A 23 factorial design with a central point was built to evaluate the influence of the chemical modification of gum arabic (GA) on the SH sensitivity to water. The main effects of the temperature and amount of GMA and the interaction effect of the temperature and amount of GMA on the SR responses were statistically significant. It was demonstrated that the amount of GMA had a more prominent effect on gel swelling. Lower elastic modulus values for the SH were found when a decreased amount of GMA was used (0.05 g), which produced an SH with a high SR capacity. The SH matrix consisting of 3.0 g of AAc, 0.5 g of AAm, and 0.5 g of MGA was more suitable to absorb a large amount of water (SR = 503.17 ± 22.65 within 60 min of water immersion) without its mechanical stability being affected. Better GA modifying conditions to produce such an SH were as follows: 60°C for the temperature, 24 h for the time of MGA, and 0.05 g for the amount of GMA. It exhibited a diffusional exponent higher than 0.89, which corresponded to the supercase II type of penetrating transport mechanism, indicating that its water‐absorption mechanism exclusively depended on the macromolecular relaxation of the polymer chains. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008
Effect of maleic anhydride grafted polypropylene on the mechanical and morphological properties of chemically modified short‐pineapple‐leaf‐fiber‐reinforced polypropylene composites
Authors: Hujuri Ujwala , Chattopadhay Sanjay K. , Uppaluri Ramagopal , Ghoshal Aloke K. 
Published: October 2007

AbstractWith the rising cost of petroleum‐based fibers, the utilization of plant fibers in the manufacture of polymer–matrix composites is gaining importance worldwide. The scope of this study was to examine the perspective of the use of pineapple leaf fibers (PALFs) as reinforcements for polypropylene (PP). These fibers are environmentally friendly, low‐cost byproducts of pineapple cultivation and are readily available in the northeastern region of India. Here, both untreated and treated pineapple fibers were used. Maleic anhydride grafted polypropylene (MA‐g‐PP) was used as a compatibilizing agent. The polymer matrix of PP was used to prepare composite specimens with different volume fractions (5–20%) of fibers by the addition of 5% of MA‐g‐PP. These specimens were tested for their mechanical properties, and additional assessments were made via observations by scanning electron microscopy, thermogravimetric analysis, and IR spectroscopy. Increase in the impact behavior, flexural properties, and tensile moduli of the composites were noticed, and these were more appreciable in the treated fibers mixed with MA‐g‐PP. PALF in 10 vol % in PP mixed with MA‐g‐PP was the optimum and recommended composition, where the flexural properties were the maximum. The impact strength and the tensile modulus were also considerably high. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008
Dynamic photorheological analysis of photopolymerizable urethane dimethacrylate resins with varying diluent content and light fluence
Authors: Piguet‐Ruinet F. , Love B. J. 
Published: October 2007

AbstractThe in situ measurement of dynamic changes in viscosity induced by illumination has been performed on a range of photosensitive urethane dimethacrylates (UDMA) evaluating the response at three different illuminations intensities (1, 2, and 5 W cm−2) and at three different diluent concentrations (15, 30, and 50%), using 1,6‐hexanediol dimethacrylate (HDDMA). The initial viscosity value ranged between 1 and 10 Pa s for the mixtures with final viscosities approaching 1 × 107 Pa s after illumination. The initial rise in viscosity was analyzed using an exponential model with an exponent ranging from 1.0 to 2.5 with time under exposure. Higher conversion rates were observed with both higher intensity and lower HDDMA content. The analytical approach taken here could aid in developing more sophisticated models that consider simultaneous flow and cure advancement in other thermosets. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008