bluuebunny/crossref_metadata_2025_split huggingface dataset:
Preparation and properties of polyethylene/montmorillonite nanocomposites by in situ polymerization
Authors: Yang Feng , Zhang Xuequan , Zhao Haichao , Chen Bin , Huang Baotong , Feng Zhiliu 
Published: July 2003

AbstractPolyethylene (PE)/montmorillonite (MMT) nanocomposites were prepared by in situ coordination polymerization using a MMT/MgCl2/TiCl4 catalyst activated by Al(Et)3. The catalyst was prepared by first diffusing MgCl2 into the swollen MMT layers, followed by loading TiCl4 on the inner/outer layer surfaces of MMT where MgCl2 was already deposited. The intercalation of MMT layers by MgCl2 and TiCl4 was demonstrated by the enlarged interlayer spacing determined by WAXD. The nanoscale dispersion of MMT layers in the polyethylene matrix was characterized by WAXD and TEM. As a consequence, the crystallinity of the nanocomposite decreased sharply, whereas the tensile strength was significantly improved compared to that of virgin polyethylene of comparable molecular weight. The confinement of the nanodispersed MMT layers to molecular chain and the strong interaction between the nanoscale MMT layers and the resin matrix were thought to account for the decrease of crystallinity and the remarkable enhancement of strength. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 3680–3684, 2003
Investigations of heat transfer and pressure drop between parallel channels with pseudoplastic and dilatant fluids
Authors: Park Simsoo , Lee Dong‐Ryul 
Published: July 2003

AbstractCentral to the problem of heat exchangers design is the prediction of pressure drop and heat transfer in the noncircular exchanger duct passages such as parallel channels. Numerical solutions for laminar fully developed flow are presented for the pressure drop (friction factor times Reynolds number) and heat transfer (Nusselt numbers) with thermal boundary conditions [constant heat flux (CHF) and constant wall temperature (CWT) ] for a pseudoplastic and dilatant non‐Newtonian fluid flowing between infinite parallel channels. A shear rate parameter could be used for the prediction of the shear rate range for a specified set of operating conditions that has Newtonian behavior at low shear rates, power law behavior at high shear rates, and a transition region in between. Numerical results of the Nusselt number [constant heat flux (CHF) and constant wall temperature (CWT) ] and the product of the friction factor and Reynolds number for the Newtonian region were compared with the literature values showing agreement within 0.36% in the Newtonian region. For pseudoplastic and dilatant non‐Newtonian fluids, the modified power law model is recommended to use because the fluid properties have big discrepancies between the power law model and the actual values in low and medium range of shear rates. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 3601–3608, 2003
Study on rheological behavior of polypropylene/clay nanocomposites
Authors: Li Jian , Zhou Cixing , Wang Gang , Zhao Delu 
Published: July 2003

AbstractPolypropylene/montmorillonite nanocomposites (PPCN) were prepared by melt intercalation with maleic anhydride modified low isotactic polypropylene as the compatibilizer. The linear and nonlinear rheological properties of polypropylene/montmorillonite nanocomposites were studied. The deviation from linear behavior occurred at a strain of 100 that was quite less than that for the polymer matrix. The results of dynamic frequency scan showed that the percolation threshold of PPCN was near 3 wt %. Having been subjected to steady preshear, the tactoids could be oriented preferentially in the shear direction, and the percolation network was ruptured. The magnitudes of the stress overshoots observed in the reverse flow experiments were strongly dependent on the rest time, which indicated that the ruptured network could be reorganized even under quiescent conditions. Furthermore, PPCN displayed a strain‐scaling stress response to the startup of steady shear. The maxima of the stress overshoots appeared at the stain of 100, which was consistent with the strain where the deviation of linear viscoelastic behavior started. It might imply that subjected to the deformation less than 100, the network structure could be regard as elastic one. Additionally, the analogous strain‐scaling stress response to the startup steady shear elucidated the structural analogy between PPCN and liquid crystal polymer solution. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 3609–3617, 2003
Thermal stability and kinetics analysis of rubber‐modified epoxy resin by high‐resolution thermogravimetric analysis
Authors: Gu Aijuan , Liang Guozheng 
Published: July 2003

AbstractA dynamic heating rate mode of high‐resolution thermogravimetric analysis was used to study the thermal and thermal‐oxidative stability, as well as kinetics analyses, of a model liquid rubber‐modified epoxy resin, Ep/CTBN, made up of bisphenol A diglycidyl ether‐based epoxy and carboxyl‐terminated butadiene acrylonitrile rubber (CTBN). Results show that the thermal degradation of Ep/CTBN resin in nitrogen and air consists of two and three independent steps, respectively. Moreover, Ep/CTBN has a higher initial degradation temperature and higher activation energy than those of pure epoxy resin in both gases, indicating that the addition of CTBN to epoxy can improve the thermal and thermal‐oxidative stability of pristine epoxy resin. Kinetic parameters such as activation energy, reaction order, and preexponential factor of each degradation step of both Ep/CTBN and pure epoxy resins in air and nitrogen were calculated. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 3594–3600, 2003
Mechanical, thermal, and microstructural properties of polypropylene/polyamide‐6/styrene‐ethylene‐butadiene‐styrene polymer alloys
Authors: Taşdemir Münir 
Published: July 2003

AbstractInterfacial agents as compatibilizers have recently been introduced into polymer blends to improve the microstructure and mechanical properties of thermoplastics. In this way, it is possible to prepare a mixture of polymeric materials that can have superior mechanical properties over a wide temperature range. In this study, an incompatible blend of polypropylene (PP) and polyamide‐6 (PA6) were made compatible by the addition of 10% styrene–ethylene–butadiene–styrene copolymer (SEBS). The mixing operation was conducted by using a twin‐screw extruder. The morphology and the compatibility of the mixtures were examined by SEM and DSC techniques. Furthermore, the elastic modulus, tensile and yield strengths, percentage elongation, hardness, melt flow index, Izod impact resistance, heat deflection temperature (HDT), and Vicat softening point values of polymer alloys of various ratios were determined. It was found that the addition of SEBS to the structures decreased the tensile strength, yield strength, elastic modulus, and hardness, whereas it increased the Izod impact strength and percentage elongation values. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 3485–3491, 2003
Stem cells from midguts of Lepidopteran larvae: Clues to the regulation of stem cell fate
Authors: Loeb Marcia J. , Clark Edward A. , Blackburn Michael , Hakim Raziel S. , Elsen Kim , Smagghe Guy 
Published: July 2003

AbstractPreviously, we showed that isolated stem cells from midguts of Heliothis virescens can be induced to multiply in response to a multiplication protein (MP) isolated from pupal fat body, or to differentiate to larval types of mature midgut cells in response to either of 4 differentiation factors (MDFs) isolated from larval midgut cell‐conditioned medium or pupal hemolymph. In this work, we show that the responses to MDF‐2 and MP in H. virescens stem cells decayed at different time intervals, implying that the receptors or response cascades for stem cell differentiation and multiplication may be different. However, the processes appeared to be linked, since conditioned medium and MDF‐2 prevented the action of MP on stem cells; MP by itself appeared to repress stem cell differentiation. Epidermal growth factor, retinoic acid, and platelet‐derived growth factor induced isolated midgut stem cells of H. virescens and Lymantria dispar to multiply and to differentiate to mature midgut cells characteristic of prepupal, pupal, and adult lepidopteran midgut epithelium, and to squamous‐like cells and scales not characteristic of midgut tissue instead of the larval types of mature midgut epithelium induced by the MDFs. Midgut stem cells appear to be multipotent and their various differentiated fates can be influenced by several growth factors. Arch. Insect Biochem. Physiol. 53:186–198, 2003. Published 2003 Wiley‐Liss, Inc.
Distinctions between c‐Rel and other NF‐κB proteins in immunity and disease
Authors: Liou Hsiou‐Chi , Hsia Constance Y. 
Published: July 2003

Abstractc‐Rel is a proto‐oncogene first identified as the cellular counterpart of the v‐Rel oncogene derived from the avian reticuloendotheliosis retrovirus (REV‐T). It was subsequently discovered that c‐Rel belongs to the NF‐κB/Rel transcription factor family whose members share a common DNA recognition motif and similar signaling pathways. Despite the similarities, however, each NF‐κB/Rel member possesses unique properties with regard to tissue expression pattern, response to receptor signals and target gene specificity. These differences are fairly evident from the non‐redundant phenotypes exhibited by individual NF‐κB/Rel knockout mice. Hence the work described in this review will compare and contrast the various physiological functions of c‐Rel to those of other NF‐κB members, particularly with respect to the regulation of proliferation, survival and effector functions in multiple hematopoietic and immunological cell types. The study of c‐Rel knockout mice in several disease models will also be discussed as they reveal an important role for c‐Rel in response to allergens, auto‐antigens, allo‐antigens and pathogenic infection. BioEssays 25:767–780, 2003. © 2003 Wiley Periodicals, Inc.
Left/right, up/down: The role of endogenous electrical fields as directional signals in development, repair and invasion
Authors: Robinson Kenneth R. , Messerli Mark A. 
Published: July 2003

AbstractA fundamental aspect of biological systems is their spatial organization. In development, regeneration and repair, directional signals are necessary for the proper placement of the components of the organism. Likewise, pathogens that invade other organisms rely on directional signals to target vulnerable areas. It is widely understood that chemical gradients are important directional signals in living systems. Less well recognized are electrical fields, which can also provide directional information. Small, steady electrical fields can directly guide cell movement and growth and can generate chemical gradients of charged macromolecules against the leveling action of diffusion. At the site of a lesion in an ion‐transporting epithelium, for example, a substantial electrical field is instantly generated and may extend over many cell diameters. There are numerous other situations in which relatively long‐range electrical fields have been shown to exist naturally. Recently, there has been substantial progress in identifying specific processes that are controlled, to some extent, by these endogenous electrical fields. This review highlights these recent data and discusses possible mechanisms by which the fields might affect biological processes. BioEssays 25:759–766, 2003. © 2003 Wiley Periodicals, Inc.
The polarisation of the anteroposterior axis in Drosophila
Authors: López‐Schier Hernán 
Published: July 2003

AbstractThe polarisation of the embryonic anteroposterior (AP) axis requires the establishment of positional cues with spatial information, and often involves complex intercellular communications, cell adhesion and cell movement. Recent work on several fronts has begun to shed light on how the initial asymmetries are established and maintained. In this review, I discuss the polarisation of the AP axis during Drosophila oogenesis, focusing on the function of the Notch signalling pathway and its relationship to the activation of the epidermal growth factor receptor. I make special reference to some aspects of Notch activity regulation during oogenesis that appear to depart from the canonical pathway. Finally, I hypothesise on possible similarities between these activities of Notch signalling during Drosophila oogenesis and vertebrate somitogenesis. BioEssays 25:781–791, 2003. © 2003 Wiley Periodicals, Inc.
The formation of sense organs in Drosophila: A logical approach
Authors: Ghysen Alain , Thomas René 
Published: July 2003

AbstractThe genetic analysis of development has revealed the importance of small sets of interacting genes in most morphogenetic processes. The results of gene interactions have so far been examined intuitively. This approach is largely sufficient when one deals with simple interactions, a feedback circuit for example. As more components become involved, however, it is difficult to make sure that the intuitive approach gives a comprehensive view of the behaviour of the system. In this paper, we illustrate the use of a logical approach to describe the genetic circuit that underlies the singling out of sense organ precursor cells in Drosophila. We show how to apply logical modelling to a realistic problem, and how this approach allows an easy assessment of the dynamic properties of the system, i.e., of its possible evolutions and of its reactions to fluctuations and perturbations. BioEssays 25:802–807, 2003. © 2003 Wiley Periodicals, Inc.
From Eden to a hell of uniformity? directed evolution in humans
Authors: Brosius Jürgen 
Published: July 2003

AbstractFor the first time during evolution of life on this planet, a species has acquired the ability to direct its own genetic destiny. Following 200,000 years of evolution, modern man now has the technologies not only to eradicate genetic disease but also to prolong life and enhance desired physical and mental traits. These technologies include preimplantation diagnosis, cloning, and gene therapy in the germline on native chromosomes or by adding artificial ones. At first glance, we should all be in favor of eliminating genetic diseases and enhancing genetic traits. Evolutionary considerations, however, uncover hidden dangers and suggest caution against the total embracement of such actions. The first major concern is that the genome will never be a completely reliable crystal ball for predicting human phenotypes. This is especially true for predictions concerning the performance of alleles in future generations whose populations might be subjected to different environmental and social challenges. The second, and perhaps more important, concern is that the end result of germline intervention and genetic enhancement will likely lead to the impoverishment of gene variants in the human population and deprive us of one of our most valued assets for survival in the future, our genetic diversity. BioEssays 25:815–821, 2003. © 2003 Wiley Periodicals, Inc.
Cooperative interactions between epigenetic modifications and their function in the regulation of chromosome architecture
Authors: Weissmann Frank , Lyko Frank 
Published: July 2003

AbstractEpigenetic information is encoded by DNA methylation and by covalent modifications of histone tails. While defined epigenetic modification patterns have been frequently correlated with particular states of gene activity, very little is known about the integration level of epigenetic signals. Recent experiments have resulted in the characterization of several epigenetic adaptors that mediate interactions between distinct modifications. These adaptors include methyl‐DNA binding proteins, chromatin remodelling enzymes and siRNAs. Complex interactions between epigenetic modifiers and adaptors provide the foundation for the stability of epigenetic inheritance. In addition, they also provide an explanation for the long‐range effects of epigenetic mechanisms. We propose that a major aspect of epigenetic regulation lies in the modification of chromosome architecture and that local changes in gene expression would be secondary consequences. This view is consistent with many results from recent genomic analyses. BioEssays 25:792–797, 2003. © 2003 Wiley Periodicals, Inc.
Human genetic diversity: Lewontin's fallacy
Authors: Edwards A.W.F. 
Published: July 2003

AbstractIn popular articles that play down the genetical differences among human populations, it is often stated that about 85% of the total genetical variation is due to individual differences within populations and only 15% to differences between populations or ethnic groups. It has therefore been proposed that the division of Homo sapiens into these groups is not justified by the genetic data. This conclusion, due to R.C. Lewontin in 1972, is unwarranted because the argument ignores the fact that most of the information that distinguishes populations is hidden in the correlation structure of the data and not simply in the variation of the individual factors. The underlying logic, which was discussed in the early years of the last century, is here discussed using a simple genetical example. BioEssays 25:798–801, 2003. © 2003 Wiley Periodicals, Inc.
The quest for the function of simple epithelial keratins
Authors: Owens Dewi W. , Lane E. Birgitte 
Published: July 2003

AbstractSimple epithelial keratins K8 and K18 are components of the intracellular cytoskeleton in the cells of the single‐layered sheet tissues inside the body. As members of the intermediate filament family of proteins, their function has been a matter for debate since they were first discovered. Whilst there is an indisputable case for a structural cell‐reinforcing function for keratins in the mutilayered squamous epithelia of external barrier tissues, some very different stress‐protective features now seem to be emerging for the simple epithelial keratins. Even the emerging evidence of pathological mutations in K8/K18 looks very different from mutations in stratified epithelial keratins. K8/K18‐like keratins were probably the first to evolve and, whilst stratified epithelial (keratinocyte) keratins have diversified into a large group of keratins highly specialised for providing mechanical stability, the simple epithelial keratins have retained early features that may protect the internal epithelia from a broader range of stresses, including osmotic stress and chemical toxicity. BioEssays 25:748–758, 2003. © 2003 Wiley Periodicals, Inc.
Are poly(ADP‐ribosyl)ation by PARP‐1 and deacetylation by Sir2 linked?
Authors: Zhang Jie 
Published: July 2003

AbstractPoly(ADP‐ribose) polymerase‐1 (PARP‐1) safeguards genomic integrity by limiting sister chromatid exchanges. Overstimulation of PARP‐1 by extensive DNA damage, however, can result in cell death, as prolonged PARP‐1 activation depletes NAD+, a substrate, and elevates nicotinamide, a product. The decline of NAD+ and the rise of nicotinamide may downregulate the activity of Sir2, the NAD+‐dependent deacetylases, because deacetylation by Sir2 is dependent on high concentration of NAD+ and inhibited by physiologic level of nicotinamide. The Sir2 deacetylase family has been implicated in mediating gene silencing, longevity and genome stability. It is conceivable that poly(ADP‐ribosyl)ation by PARP‐1, which is induced by DNA damage, could modulate protein deacetylation by Sir2 via the NAD+/nicotinamide connection. The possible linkage of the two ancient pathways that mediate broad biological activities may spell profound evolutionary roles for the conserved PARP‐1 and Sir2 gene families in multicellular eukaryotes. BioEssays 25:808–814, 2003. © 2003 Wiley Periodicals, Inc.
NTE: One target protein for different toxic syndromes with distinct mechanisms?
Authors: Glynn Paul 
Published: July 2003

AbstractEpidemics of organophosphate‐induced delayed neuropathy (OPIDN) have paralysed thousands of people. This syndrome of nerve axon degeneration is initiated by organophosphates which react with neuropathy target esterase (NTE). Dosing experiments with adult chickens raise the possibility that OPIDN is initiated by a gain‐of‐function mechanism. By contrast, loss of NTE function by mutation causes massive apoptosis in Drosophila brain. Now, Winrow et al. show that nte−/− mice die by mid‐gestation, but nte+/− mice appear hyperactive and are more sensitive than wild‐type mice to a fatal form of OP toxicity.1 Thus, different toxic syndromes may be initiated via a single target protein. BioEssays 25:742–745, 2003. © 2003 Wiley Periodicals, Inc.
Male genes: X‐pelled or X‐cluded?
Authors: Rogers David W. , Carr Martin , Pomiankowski Andrew 
Published: July 2003

AbstractTwo recent studies by Parisi et al.1 and Ranz et al.,2 catalogue sex differences in gene expression across the whole genome of the fruit fly Drosophila melanogaster. Both report striking associations of sex‐biased gene expression with the X chromosome. Genes with male‐biased expression are depauperate on the X chromosome, whereas genes with female‐biased expression show weaker evidence of being in excess. A number of evolutionary hypotheses for the expulsion or exclusion of male‐biased genes from the X chromosome have been suggested. None is entirely consistent with the available evidence. BioEssays 25:739–741, 2003. © 2003 Wiley Periodicals, Inc.
Animal allure and health linked by plant pigments
Authors: Hõrak Peeter , Saks Lauri 
Published: July 2003

AbstractDarwin1 introduced the idea that ornamental secondary sexual traits have evolved in response to female preferences for showy males. Among such traits, yellow and red carotenoid‐based ornaments have been considered as particularly good candidates for explaining why and how females would benefit from mating with showy partners. Because carotenoids can be used for promotion of both health and appearance, colourful male ornaments should honestly reveal the vigour of the bearers. Two recent experiments with birds2,3 now show how allocation of bodily carotenoids to sexual signalling is traded off against the use of carotenoids for boosting immune function. BioEssays 25:746–747, 2003. © 2003 Wiley Periodicals, Inc.