bluuebunny/crossref_metadata_2025_split huggingface dataset:
Studies on the synthesis and thermal properties of copoly(L‐lactic acid/glycolic acid) by direct melt polycondensation
Authors: Lan Ping , Zhang Yaopeng , Gao Qinwei , Shao Huili , Hu Xuechao 
Published: March 2004

AbstractA two‐step direct copolymerization process of L‐lactic acid (L‐LA)/glycolic acid (GA) was developed. The first step was to produce an oligomer of L‐LA/GA and then the oligomer was polymerized with binary catalyst tin chloride dihydrate/p‐toluenesulfonic acid. In this way, the copoly(L‐LA/GA) (PLGA), without any organic solvent, was synthesized directly. The thermal properties and solubility in chloroform of PLGA were studied by DSC and NMR. The results showed that the melting point of PLGA decreases with increasing mole fraction of GA units in copolymer. In addition, the melting point of polymer also decreased with increasing degree of racemization of polymer. The solubility of PLGA in chloroform decreased with the increase of the average lengths of the glycolic acid units. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 2163–2168, 2004
Effect of some service conditions on the electrical resistivity of conductive styrene–butadiene rubber–carbon black composites
Authors: Mohanraj G. T. , Chaki T. K. , Chakraborty A. , Khastgir D. 
Published: March 2004

AbstractConductive polymer composites were prepared using vulcanized styrene–butadiene rubber as a matrix and conductive carbon black as a filler. The filler loading was varied from 10 to 60 phr. The volume resistivity was measured against the loading of the carbon black to verify the percolation limit. The electrical conductivity of filled polymer composites is attributed to the formation of some continuous conductive networks in the polymer matrix. These conductive networks involve specific arrangements of conductive elements (carbon black aggregates) so that the electrical paths are formed for free movement of electrons. The effects of temperature and pressure on the volume resistivity of the composites were studied. The volume resistivity of all the composites increased with increase in temperature, and the rate of increase in the resistivity against temperature depended on the loading of carbon black. The change in volume resistivity during the heating and cooling cycle did not follow the same route, leading to the phenomena of electrical hysteresis and electrical set. It was found that the composites with 40 and 60 phr carbon black become more conductive after undergoing the heat treatment. Generally, all the composites showed a positive temperature coefficient of resistivity. The volume resistivity of all the composites decreased with increase in pressure. The relaxation characteristic of the volume resistivity of the composites was studied with respect to time under a constant load. It was found that the volume resistivity of the compressed specimen of the composites decreased exponentially with time. It was observed that initially a faster relaxation process and later a slower relaxation process occurred in these composites. Some mechanical properties of these composites were also measured to confirm the efficacy of these composites for practical applications. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 2179–2188, 2004
Atom‐transfer radical polymerization of methyl methacrylate with α,α′‐dichloroxylene/CuCl/N,N,N′,N″,N″‐pentamethyldiethylenetriamine initiation system under microwave irradiation
Authors: Li Xu , Zhu Xiulin , Cheng Zhenping , Xu Wenjian , Chen Gaojian 
Published: March 2004

AbstractThe atom‐transfer radical polymerization (ATRP) of methyl methacrylate (MMA), using α,α′‐dichloroxylene as initiator and CuCl/N,N,N′,N″,N″‐pentamethyldiethylenetriamine as catalyst was successfully carried out under microwave irradiation (MI). The polymerization of MMA under MI showed linear first‐order rate plots, a linear increase of the number‐average molecular weight with conversion, and low polydispersities, which indicated that the ATRP of MMA was controlled. Using the same experimental conditions, the apparent rate constant (k) under MI (k = 7.6 × 10−4 s−1) was higher than that under conventional heating (k = 5.3 × 10−5 s−1). © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 2189–2195, 2004
Spectroscopic study of the modification of cellulose with polyethylenimines
Authors: De La Orden M. U. , Matías M. C. , Martínez Urreaga J. 
Published: March 2004

AbstractThe reaction of cellulose with polyethylenimines (PEIs) was studied using diffuse reflectance ultraviolet–visible (UV–vis) spectroscopy, diffuse reflectance FTIR spectroscopy, and standard colorimetry. PEIs were applied from aqueous solutions at the natural pH (pH ∼ 11) and at pH = 6. The obtained materials were exposed to different thermal treatments in air. Celluloses treated at pH = 11 suffer the reversible formation of amine bicarbonate salts. This reaction was not observed in celluloses treated at pH = 6 because of the protonation of the amine groups. In all treated celluloses, the PEI amine groups reacted with cellulose carbonyl groups at moderate temperatures to form Schiff bases, which were responsible for the yellowing of the material. At higher temperatures other oxidation products were detected in the UV–vis and infrared spectra. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 2196–2202, 2004
Three‐dimensional architecture and distribution of collagen components in the goat hypophysis
Authors: Nishimura Shotaro , Tabata Shoji , Nakamura Yoshi‐Nori , Okano Kaoru , Iwamoto Hisao 
Published: March 2004

AbstractThe three‐dimensional architecture of collagen fibrils in the connective tissue framework and the distribution of collagen types in the goat hypophysis were studied by the cell maceration method in combination with scanning electron microscopy (SEM) and immunohistochemistry. The pars distalis of the adenohypophysis consisted of many cell clusters. SEM revealed that the wall of cell clusters appeared as various‐sized flat bundles of collagen fibrils woven in a basket‐like configuration. In the pars tuberalis, the aggregates of collagen fibrils were denser and bundles thicker compared to the pars distalis. The density of collagen fibrils changed from the pars tuberalis to pars distalis without a distinct border. The collagen framework in the pars intermedia was mainly divided into three parts, the dorsal region with large hollows, the middle region, and the ventral sheet facing the cavum hypophysis. In the lobus nervosus of the neurohypophysis, the collagen network exhibited a sponge‐like appearance at low magnification. Collagen fibrils of various sizes consisted of loose wavy bundles distributed around the cavities. Immunohistochemistry revealed types I, III, IV, V, and VI collagen throughout the hypophysis. It is concluded that to maintain structural and functional integration, the components of collagen are in different configurations throughout the regions of the goat hypophysis. Anat Rec Part A 277A:275–286, 2004. © 2004 Wiley‐Liss, Inc.
Identification of cDNA clones that encode hLAMP‐1, a component of the particulate matrix associated with cardiac mesenchyme formation
Authors: Sinning Allan R. , McKay Kimberly J. 
Published: March 2004

AbstractThe heart extracellular matrix protein hLAMP‐1 (lectin‐associated matrix protein in the heart) is a component of the particulate matrix that activates the AV endothelium prior to its transformation into mesenchyme within the atrioventricular canal and proximal outflow tract of the heart. The role of hLAMP‐1 in this process has yet to be determined, in part because of the limited amount of material available for analysis. To overcome this liability, a monoclonal antibody to hLAMP‐1 has been used to recognize proteins expressed by cDNA clones. The isolated cDNAs encode an mRNA consistent with previously published immunohistochemical results (Sinning and Hewitt, Acta Anat. 1996;155:219–230; Sinning, J. Cell Biochem. 1997;66:112–122). Expression profiles of these clones by in situ hybridization revealed staining in areas of the heart that expressed hLAMP‐1 by immunocytochemistry. Taken together, these results suggest that these clones, which represent an expressed sequence tag for hLAMP‐1, should provide the basis for isolating a full‐length cDNA of hLAMP‐1, a prerequisite for determining the functional role of this protein in heart development. Anat Rec Part A 277A:307–311, 2004. © 2004 Wiley‐Liss, Inc.
Accessibility and use of information sources among computer scientists and software engineers in Israel: Academy versus industry
Authors: Yitzhaki Moshe , Hammershlag Gloria 
Published: March 2004

AbstractHypothesizing that workplace significantly affects information‐seeking patterns, this study compared accessibility and use of information sources among 233 Israeli computer scientists and software engineers, employed in industry and academy, using a mail questionnaire, which yielded a usable reply rate of 33%. The two groups were found to differ significantly in age, education, seniority, and type of research they performed (basic vs. applied). Printed textbooks, professional journals, and oral discussions with colleagues or experts in the organization were common to both groups, topping almost all lists of accessibility and use. For most information sources, however, the two groups differed significantly and consistently. Printed professional journals as well as printed and electronic conference or meeting papers were consistently more accessible and more often used by the academy group, while the industry group reported greater access to and more frequent use of electronic textbooks and trade or promotional literature. In regard to handbooks and standards, in‐house technical reports (printed), government technical reports (Internet), librarians and technical specialists (Internet), and oral discussions with supervisors, no significant differences in accessibility were found, but their use by the industry group was much higher. In both groups, accessibility was only partly related to use, and more so among the academy than the industry group.
The relationships between half‐life (t1/2) and mean residence time (MRT) in the two‐compartment open body model
Authors: Sobol Eyal , Bialer Meir 
Published: March 2004

AbstractRationale. In the one‐compartment model following i.v. administration the mean residence time (MRT) of a drug is always greater than its half‐life (t1/2). However, following i.v. administration, drug plasma concentration (C) versus time (t) is best described by a two‐compartment model or a two exponential equation:C=Ae−αt+Be–βt, where A and B are concentration unit‐coefficients and α and β are exponential coefficients. The relationships between t1/2 and MRT in the two‐compartment model have not been explored and it is not clear whether in this model too MRT is always greater than t1/2.Methods. In the current paper new equations have been developed that describe the relationships between the terminal t1/2 (or t1/2β) and MRT in the two‐compartment model following administration of i.v. bolus, i.v. infusion (zero order input) and oral administration (first order input).Results. A critical value (CV) equals to the quotient of (1−ln2) and (1−β/α) (CV=(1−ln2)/(1−β/α)=0.307/(1−β/α)) has been derived and was compared with the fraction (f1) of drug elimination or AUC (AUC‐area under C vs t curve) associated with the first exponential term of the two‐compartment equation (f1=A/α/AUC). Following i.v. bolus, CV ranges between a minimal value of 0.307 (1−ln2) and infinity. As long as f1<CV,MRT>t1/2 and vice versa, and when f1=CV, then MRT=t1/2. Following i.v. infusion and oral administration the denominator of the CV equation does not change but its numerator increases to (0.307+βT/2) (T‐infusion duration) and (0.307+β/ka) (ka‐absorption rate constant), respectively. Examples of various drugs are provided.Conclusions. For every drug that after i.v. bolus shows two‐compartment disposition kinetics the following conclusions can be drawn (a) When f1<0.307, then f1<CV and thus, MRT>t1/2. (b) When β/α>ln2, then CV>1>f1 and thus, MRT>t1/2. (c) When ln2>β/α>(ln4−1), then 1>CV>0.5 and thus, in order for t1/2>MRT, f1 has to be greater than its complementary fraction f2 (f1>f2). (d) When β/α<(ln4−1), it is possible that t1/2>MRT even when f2>f1, as long as f1>CV. (e) As β gets closer to α, CV approaches its maximal value (infinity) and therefore, the chances of MRT>t1/2 are growing. (f) As β becomes smaller compared with α, β/α approaches zero, the denominator approaches unity and consequently, CV gets its minimal value and thus, the chances of t1/2>MRT are growing. (g) Following zero and first order input MRT increases compared with i.v. bolus and so does CV and thus, the chances of MRT>t1/2 are growing. Copyright © 2004 John Wiley & Sons, Ltd.
Fine tuning of growth factor signals depends on fibrillin microfibril networks
Authors: Charbonneau Noe L. , Ono Robert N. , Corson Glen M. , Keene Douglas R. , Sakai Lynn Y. 
Published: March 2004

AbstractGrowth factors, potent regulators of cell differentiation, tissue morphogenesis, tissue homeostasis, and cellular response to injury, reside in the extracellular matrix. Genetic evidence in humans and mice as well as biochemical data implicate fibrillins and LTBPs in the extracellular control of TGFβ and BMP signaling. Fibrillins and LTBPs form tissue‐specific and temporally regulated microfibril networks. In the developing embryo, three fibrillins and four LTBPs contribute molecular heterogeneity to microfibril networks, and provide different templates upon which TGFβ‐related growth factors can be positioned. By accommodating this molecular heterogeneity, microfibril architecture can orchestrate a variety of different signals in very specific tissue locations. Human fibrillinopathies display a broad phenotypic spectrum from tall to short stature, from hypermobile joints to joint contractures and stiffness, and from severe to mild or no cardiovascular manifestations. A spectrum of growth factor dysregulation may be caused by differential effects of mutations in fibrillins on microfibril architecture, thus altering appropriate targeting or positioning of growth factors within microfibril networks. Growth factor dysregulation may help to explain the broad phenotypic spectrum of the fibrillinopathies. Birth Defects Research (Part C) 72:37–50, 2004. © 2004 Wiley‐Liss, Inc.
The role of ECM molecules in activity‐dependent synaptic development and plasticity
Authors: Pavlov Ivan , Lauri Sari , Taira Tomi , Rauvala Heikki 
Published: March 2004

AbstractGrowth and guidance of neurites (axons and dendrites) during development is the prerequisite for the establishment of functional neural networks in the adult organism. In the adult, mechanisms similar to those used during development may regulate plastic changes that underlie important nervous system functions, such as memory and learning. There is now ever‐increasing evidence that extracellular matrix (ECM)‐associated factors are critically involved in the formation of neuronal connections during development, and their plastic changes in the adult. Here, we review the current literature on the role of ECM components in activity‐dependent synaptic development and plasticity, with the major focus on the thrombospondin type I repeat (TSR) domain‐containing proteins. We propose that ECM components may modulate neuronal development and plasticity by: 1) regulating cellular motility and morphology, thus contributing to structural alterations that are associated with the expression of synaptic plasticity, 2) coordinating transsynaptic signaling during plasticity via their cell surface receptors, and 3) defining the physical parameters of the extracellular space, thereby regulating diffusion of soluble signaling molecules in the extracellular space (ECS). Birth Defects Research (Part C) 72:12–24, 2004. © 2004 Wiley‐Liss, Inc.
Matrix loading: Assembly of extracellular matrix collagen fibrils during embryogenesis
Authors: Kadler Karl 
Published: March 2004

AbstractNothing in biology stimulates the imagination like the development of a single fertilized egg into a newborn child. Consequently, a major focus of biomedical research is aimed at understanding cell differentiation, proliferation, and specialization during child health and human development. However, the fact that the increase in size and shape of the growing embryo has as much to do with the extracellular matrix (ECM) as with the cells themselves, is largely overlooked. Cells in developing tissues are surrounded by a fiber‐composite ECM that transmits mechanical stimuli, maintains the shape of developing tissues, and functions as a scaffold for cell migration and attachment. The major structural element of the ECM is the collagen fibril. The fibrils, which are indeterminate in length, are arranged in different tissues in exquisite supramolecular architectures, including parallel bundles, orthogonal lamellae, and concentric weaves. This article reviews our current understanding of the synthesis and assembly of collagen fibrils, and discusses challenging questions about how cells assemble an organized ECM during embryogenesis. Birth Defects Research (Part C) 72:1–11, 2004. © 2004 Wiley‐Liss, Inc.
Fibulins in development and heritable disease
Authors: Chu Mon‐Li , Tsuda Takeshi 
Published: March 2004

AbstractFibulins are a family of five extracellular glycoproteins found in a variety of tissues in association with diverse supramolecular structures, including elastic fibers, basement membrane networks, fibronectin microfibrils, and proteoglycan aggregates. Studies of the developmental expression patterns have indicated that several fibulins are prominently expressed at sites of epithelial‐mesenchymal transformations during embryogenesis; among these sites, the cardiovascular system has been analyzed in more detail. Gene targeting of fibulins in mice has provided important insights into their biological roles, and has led to the identification of gene mutations in a congenital disorder of humans, cutis laxa. Genetic linkage and molecular studies have also associated several fibulin genes with various human heritable disorders that affect a wide range of organs, including limb, eye, blood, and arteries. In this review, we discuss the role of fibulins in development, with an emphasis on the cardiovascular system, and their involvement in human genetic disease. Birth Defects Research (Part C) 72:25–36, 2004. © 2004 Wiley‐Liss, Inc.
Peptide design using α,β‐dehydro amino acids: From β‐turns to helical hairpins
Authors: Mathur Puniti , Ramakumar S. , Chauhan V. S. 
Published: March 2004

AbstractIncorporation of α,β‐dehydrophenylalanine (ΔPhe) residue in peptides induces folded conformations: β‐turns in short peptides and 310‐helices in larger ones. A few exceptions—namely, α‐helix or flat β‐bend ribbon structures—have also been reported in a few cases. The most favorable conformation of ΔPhe residues are (ϕ,ψ) ∼ (−60°, −30°), (−60°, 150°), (80°, 0°) or their enantiomers. ΔPhe is an achiral and planar residue. These features have been exploited in designing ΔPhe zippers and helix–turn–helix motifs. ΔPhe can be incorporated in both right and left‐handed helices. In fact, consecutive occurrence of three or more ΔPhe amino acids induce left‐handed screw sense in peptides containing L‐amino acids. Weak interactions involving the ΔPhe residue play an important role in molecular association. The CH···OC hydrogen bond between the ΔPhe side‐chain and backbone carboxyl moiety, π–π stacking interactions between ΔPhe side chains belonging to enantiomeric helices have shown to stabilize folding. The unusual capability of a ΔPhe ring to form the hub of multicentered interactions namely, a donor in aromatic CH···π and CH···OC and an acceptor in a CH3···π interaction suggests its exploitation in introducing long‐range interactions in the folding of supersecondary structures. © 2004 Wiley Periodicals, Inc. Biopolymers (Pept Sci), 2004
Insights into stabilizing weak interactions in designed peptide β‐hairpins
Authors: Searle Mark S. 
Published: March 2004

Abstractβ‐Hairpin peptides (two anti‐parallel strands linked by a reverse β‐turn) have emerged as the simplest systems for probing weak interactions in β‐sheet folding. We describe a model 16‐residue hairpin system (peptide β1: KKYTVSINGKKITVSI) designed around the anti‐parallel β‐sheet DNA binding motif of the Met repressor dimer in which two β‐strand sequences are linked through an Asn‐Gly type I′ β‐turn. The peptide is significantly folded in aqueous solution and has a well‐defined conformation as evident from an abundance of NOE data. We review a number of analogues of β1 designed to estimate the energetic contribution of electrostatic (ion pairing) interactions to hairpin stability, to examine effects of cooperativity and preorganization in determining the energetics of weak interactions, and examine the effects on stability and conformation of incorporation of a three‐histidine motif on one face of the hairpin capable of zinc complexation. © 2004 Wiley Periodicals, Inc. Biopolymers (Pept Sci), 2004
Amphipathic peptides and drug delivery
Authors: Fernández‐Carneado Jimena , Kogan Marcelo J. , Pujals Silvia , Giralt Ernest 
Published: March 2004

AbstractThe discovery of cell‐penetrating peptides as gene delivery systems and the interest in the mechanism by which these vectors cross the cell membrane have generated a large number of studies. Among the parameters involved in the translocation process, controversy has arisen about the role of the amphipathicity of the carriers in the interaction and reorganization of the cell membrane. In this review we have summarized the vectors with primary or secondary amphipathicity related to secondary structure. Some of the insights into the relationship between the aggregation state of the peptide at the concentrations used for internalization studies and its interaction with the cell membrane result from our contribution to the field with a new family of amphipathic proline‐rich peptides. © 2004 Wiley Periodicals, Inc. Biopolymers (Pept Sci), 2004
Preparation of mammalian cell‐enclosing subsieve‐sized capsules (<100 μm) in a coflowing stream
Authors: Sakai Shinji , Kawabata Kenji , Ono Tsutomu , Ijima Hiroyuki , Kawakami Koei 
Published: March 2004

AbstractThe droplet breakup technique with an immiscible liquid coflowing stream was investigated for the preparation of mammalian cell‐enclosing subsieve‐sized capsules of less than 100 μm in diameter. The major parts of the droplet generation device were a needle of several hundred micrometers in diameter for extruding the cell‐suspending sodium alginate zzueous solution and a tubule of 2.5 mm in diameter through which the extruded alginate solution flowed into ambient immiscible liquid paraffin. The needle was positioned upstream in the vicinity of the coaxial tubule. The droplet diameter of the viscous sodium alginate aqueous solution could be controlled from several dozen to several hundred micrometers by changing the velocities of the inner and ambient fluids and the diameter of the needle. By utilizing a 300‐μm diameter needle, CHO‐K1 cell‐enclosing droplets of 48 ± 8 μm in diameter were obtained by extruding a cell‐suspending sodium alginate solution at a velocity of 1.2 cm/sec into the ambient liquid paraffin flowing at a velocity of 23.5 cm/sec. The breakup process did not influence the viability of the enclosed cells, since more than 95% of the CHO‐K1 cells remained alive after the enclosing process. © 2004 Wiley Periodicals, Inc.
Luftpiraten an der Küste: Papageitaucher und Nahrungsschmarotzer
Authors: Rüppell Georg 
Published: March 2004

AbstractPapageitaucher sind erfolgreiche Fischjäger des Nordatlantiks. Ihre Eigenart, viele Fische im Schnabel zur Bruthöhle zu tragen, lädt zum Nahrungsschmarotzen ein. Die verschiedenen Möwenarten sind dabei mit ihren speziellen Verhaltensweisen unterschiedlich erfolgreich. Besonders auf den Farne‐Inseln in Nordost‐England nehmen die Papageitaucher und damit auch das Nahrungsschmarotzen zu. Ein Bericht über verhaltensbiologische und ökologische Zusammenhänge.