bluuebunny/crossref_metadata_2025 huggingface dataset:
Plasma protein adsorption to artificial ligament fibers
Authors: Stanislawski L. , De Nechaud B. , Christel P.
Published: December 2004

The adsorption of plasma proteins onto biomedical polymers is an important factor in the biocompatibility of biomaterials. We identified the plasma proteins adsorbed onto four polymeric fibers used for synthetic ligament replacement: polyarylamide, polylactic acid, polyester, and polypropylene. The adsorbed proteins were eluted and analyzed by one‐dimensional and two‐dimensional gel electrophoresis. Fibrinogen, albumin, IgG, high molecular weight kininogen (HMWK), and lipoproteins ApoA‐1 and ApoE were the major proteins adsorbed onto polyarylamide. The three others biomaterials bound albumin, fibrinogen, ApoA‐1, and ApoE; however, the proportions of proteins bound to each polymer differed. There was an inverse relationship between ApoA‐1 and fibrinogen binding for all four biomaterials; polyarylamide bound a high percentage of fibrinogen, but little ApoA‐1; polylactic acid, polyester, and polypropylene bound a high percentage of ApoA‐1, but little fibrinogen. These results support suggestions that low fibrinogen adsorption might be due to the preferential adsorption of Apo‐1. High fibrinogen binding to polyarylamide ligaments may favor fibroblast adherence, growth, and tissue repair. © 1995 John Wiley & Sons, Inc.
Adhesion of Staphylococcus epidermidis to biomedical polymers: Contributions of surface thermodynamics and hemodynamic shear conditions
Authors: Wang I‐Wen , Anderson James M. , Jacobs Michael R. , Marchant Roger E.
Published: December 2004

Adhesion studies of Staphylococcus epidermidis RP62A were conducted using a rotating disk system to determine the roles of surface physicochemistry and topographies under physiologic shear conditions. Six materials were investigated: biomedical reference polyethylene and polydimethylsiloxane; argon plasma‐treated reference polyethylene (Ar‐PE); Silastic®; expanded polytetrafluoroethylene; and woven Dacron. All of the polymers except Dacron demonstrated reduced bacterial adhesion with increasing shear stress. Argon plasma treatment of polyethylene reduced the level of staphylococcal adhesion. Adsorption of human plasma proteins effected significantly lower numbers of adherent bacteria. The lowest adhesion was observed for Ar‐PE in 1% human plasma protein solution, whereas Dacron had the highest number of adherent bacteria. The high adhesion on Dacron was attributed to increased bacterial flux caused by topography‐induced turbulent flow and physical entrapment of the bacteria in the fiber interstices. The results indicate that the driving force for S. epidermidis adhesion is strongly influenced by substrate physicochemistry, but this may be dominated by physical forces such as shear and turbulence. © 1995 John Wiley & Sons, Inc.
Release of hexavalent chromium from corrosion of stainless steel and cobalt—chromium alloys
Authors: Merritt Katharine , Brown Stanley A.
Published: December 2004

Experiments were undertaken to determine whether hexavalent chromium was released during corrosion of orthopedic implants. Uptake of chromium (Cr) by cells and separation using amberlite resin were the methods used to determine that hexavalent Cr was present. We used salts of chromium as trivalent chromium (chromic chloride) and hexavalent chromium (potassium dichromate) to verify that the amberlite separation technique separates hexavalent Cr into the upper phase and trivalent Cr into the lower phase. The use of the salts also verified that only the hexavalent Cr became red blood cell–associated and that most of this was intracellular rather than membrane bound. The use of the amberlite separation technique demonstrated that the hexavalent Cr in the red blood cells was rapidly reduced to trivalent Cr. Cellular uptake of chromium was documented in red blood cells following corrosion of stainless‐steel and cobalt–chromium implants in vivo, in the red blood cells of patients undergoing total joint revisions, and in fibroblasts subjected to products of fretting corrosion of stainless‐steel and cobalt–chromium implants. Thus, corrosion of implants can lead to the release of the biologically active hexavalent chromium into the body. This chromium is rapidly reduced to trivalent chromium in cells. © 1995 John Wiley & Sons, Inc.
Microhardness of bone at the interface with ceramic‐coated metal implants
Authors: Stea S. , Visentin M. , Savarino L. , Ciapetti G. , Donati M. E. , Moroni A. , Caja V. , Pizzoferrato A.
Published: December 2004

We evaluated bone microhardness at the interface with hydroxyapatite‐coated stainless‐steel pins used in an external fracture fixation system. Pins were transversally inserted into the diaphyses of sheep tibiae and were loaded in for 6 weeks. Uncoated pins were implanted as controls. Microhardness analysis, based on the measure of the resistance of the bone to the penetration of a small diamond pyramid, yielded an accurate and reproducible measure of the mineralization degree and of the orientation of collagen fibers. Bone tissue close to the pin is less hard than bone tissue far from it. Moreover, the presence of hydroxyapatite coating on the pins did not significantly affect bone hardness; actually, the mean hardness at the interface with the pins was 56.9 Vickers degrees, whereas at the interface with the uncoated pins it was 62.2. It can be concluded that, 6 weeks postsurgery, the bone growing into the threadings of a loaded screwed implant reached maturity at a degree lower than that of the host both uncoated and coated implants. © 1995 John Wiley & Sons, Inc.
Biological performance of a degradable poly(lactic acid‐ε‐caprolactone) nerve guide: Influence of tube dimensions
Authors: Den Dunnen W. F. A. , Van Der Lei B. , Robinson P. H. , Holwerda A. , Pennings A. J. , Schakenraad J. M.
Published: December 2004

One of the ways to reconstruct a nerve defect is to use a biodegradable nerve guide. The aim of this study was to establish a nerve guide constructed of an amorphous copolymer of lactic acid‐caprolactone. A pilot study was set up to elucidate the effect of the tube dimensions on nerve regeneration. Four types of nerve guides, with internal diameters ranging from 1.12–1.23 mm and wall thicknesses ranging from 0.34–0.68, were tested for this purpose. We evaluated the biodegradation, foreign body reaction and nerve regeneration by light microscopy, after three different implantation times (1, 2, and 3 months). After 2 months, we observed that all types of nerve guides had changed from a transparent to an opaque and swollen state, and that they had lost their strength. The foreign body reaction was characterized by the presence of giant cells and fibroblasts surrounding the degrading nerve guide. From this pilot study, we conclude that nerve guide type 1, with an internal diameter of 1.23 mm and a wall thickness of 0.34 mm, can ensure nerve regeneration in the case of a 1‐cm gap in the sciatic nerve of the rat. Nerve guides types 3 and 4, with relatively small lumens, show nerve compression due to a more pronounced swelling of the degrading tube. © 1995 John Wiley & Sons, Inc.
In Vitro Reconstitution of Chromaffin Granule–Cytoskeleton Interactions: Ionic Factors Influencing the Association of F‐Actin With Purified Chromaffin Granule Membranes
Authors: Fowler Velia M. , Pollard Harvey B.
Published: December 2004

Chromaffin granules are the secretory vesicles directly involved in exocytosis of catecholamines, enkephalins, and other components from adrenal medullary cells. The granules occupy a large portion of the cytoplasmic volume and thus may interact extensively with cytoskeletal elements such as actin. Indeed, using both sedimentation techniques and falling ball viscometry [Fowler et al: J Cell Biol 88:388, 1981] to measure actin binding by membranes, we were able to show that chromaffin granules bind F‐actin via a protein site on the membrane, and that these interactions are reversibly inhibited by raising the free calcium ion concentration to micromolar levels ([Ca++]free for half‐maximal inhibition approximately 2.6 × 10−7M)[Fowler and Pollard: Nature 295:336, 1982]. Here, we show that F‐actin‐chromaffin granule interactions are unaffected by changes in pH between about pH 6.4 and 7.4 but are about 50% inhibited by raising the pH from 7.5 to 8.0. They are also 50% inhibited by increasing the KCl concentration to about 200 mM but are not significantly affected by increasing concentrations of K‐glutamate up to 500 mM or by varying the MgCl2 concentration between 0 and 6 mM. The interactions between chromaffin granule membranes and F‐actin are also reduced in the presence of AIP, AMP‐PNP, or free pyrophosphate; cAMP and AMP are without effect.

The ability of chromaffin granule membranes to interact with F‐actin under conditions that may approximate the resting intracellular environment (neutral pH, low KCl, 1–2 mM MgCl2, 1 mM ATP, [Ca++]free < 10−7M, 30°C) suggests that these interactions may partially reconstitute naturally occurring associations between chromaffin granules and the cytoskeleton. Further, regulation of chromaffin granule membrane‐actin interactions by ionic factors (pH, calcium, chloride ions, nucleotides) that could vary intracellularly leads us to propose that associations between actin and the chromaffin granule membrane could influence the location and dislocation of these organelles in the cytoplasm.
Effects of Divalent Cations, Trypsin, and Phospholipases on the Passive Permeability to Sodium of Inside‐Out Vesicles From Human Red Cells
Authors: Colvin Robert A. , Green James W.
Published: December 2004

Inside‐out vesicles (IOV) were prepared from human red blood cells. Steady‐state uptake of 22Na was observed to generally follow an exponential time course with a rate constant of 1.57 ± 0.09 h−1 (SE). One week of cold storage (0–4°C) increased the rate constant to 2.50 ± 0.12 h −1 (SE). Mg2+, Ca2+, or Sr2+ decreased the rate of 22Na uptake with no observable differences between the three divalent cations when tested at concentrations of 50 μM. Mg2+ was shown to decrease the rate of 22Na uptake at concentrations as low as 5 μM with maximal effect at 50 to 100 μM. The decrease in rate of 22Na uptake induced by Mg2+ could be enhanced by exposure of IOV to Mg2+ for longer periods of time. Trypsin treatment of IOV increased the rate of uptake of 22Na and was dependent on the concentration of trypsin added between 5 to 25 μg/ml (treated for 5 min at 25°C). The ability of Mg2+ (50 μM) to decrease the rate of 22Na uptake was still observed after maximal trypsin treatment. Phospholipase A2 or phospholipase C treatment of IOV increased the rate of 22Na uptake and was dependent on the amount of phospholipase A2 (0.1 to 1.0 units/ml) or phospholipase C (0.25 to 2.5 units/ml) added (treated for 5 min at 25°C). After phospholipase A2 treatment, the observed decrease in the rate of 22Na uptake induced by Mg2+ (50 μM) was generally greater than controls. After phospholipase C treatment, the observed decrease in rate of 22Na uptake induced by Mg2+ (50 μM) was less or absent when compared with controls. Phospholipase C treatment was less effective in preventing the Mg2+ effect the longer IOV were exposed to Mg2+. The results suggest that Mg2+ binds to phospholipid head‐groups to reduce Na permeability perhaps by inducing a change in bilayer structure or phospholipid association.
Immunological properties of gap junction protein from mouse liver
Authors: Traub Otto , Janssen‐Timmen Uwe , Drüge Petra Maria , Dermietzel Rolf , Willecke Klaus
Published: December 2004

Hepatic gap junctions were purified as plaques from BALB/c mice and separated by polyacrylamide gel electrophoresis in the presence of sodium dodecyl sulfate (SDS). Antisera were raised in rabbits and rats against gap junction plaques as well as against protein bands of the following apparent molecular weights: 44K to 49K (“dimer” proteins), 26K, and 21K. Using an enzyme immunoassay, we found that the reactivities of the different antisera towards gap junction plaques decreased in the following order: anti‐plaque antisera, anti‐26K antisera, anti‐“dimmer” protein antisera, and anti‐21K antisera.

The gap junction protein bands separated by SDS‐polyacrylamide gel electrophoresis were transferred by blotting onto nitrocellulose paper and the immunological cross‐reactivities were compared: the anti‐26K antisera reacted with the dimer protein bands and the 26K band but did not cross‐react with the 21K protein band. The rabbit anti‐21K antiserum reacted weakly with the 21K protein. The missing immunological cross‐reaction of the 26K and the 21K protein band can be most easily explained if both proteins were independent of each other.

No inhibition of metabolic cooperation between fibroblastoid mouse 3T6 cells was observed in the presence of Fab fragments prepared from rabbit anti‐plaque antiserum or from rabbit anti 26K antiserum. When the total proteins of plasma membranes from mouse liver were separated by SDS‐polyacrylamide electrophoresis, only the 26K protein reacted with rabbit anti 26K antiserum. This result opens the possibility for direct quantitation of gap junction protein in tissues and cell fractions.
Elevated intracellular concentrations of cyclic AMP inhibited serum‐stimulated, density‐arrested BALB/c‐3T3 cells in mid G1
Authors: Leof Edward B. , Wharton Walker , O'Keefe Edward , Pledger W. J.
Published: December 2004

The stimulation of DNA synthesis in quiescent, density‐arrested BALB/c‐3T3 cells by platelet‐derived growth factor in plasma‐supplemented medium was inhibited by the presence of isobutylmethylxanthine (IBMX) and cholera toxin, although neither IBMX or cholera toxin when used alone inhibited the stimulation of DNA synthesis. The cells were reversibly inhibited in mid G1 at a point 6 hr prior to the initiation of DNA synthesis. The inhibition of cell cycle traverse was associated with a 10–15 fold increase in cellular cyclic AMP concentration over basal levels. The reversal of this inhibition by removal of IBMX was correlated with a dramatic decrease in cyclic AMP levels. The traverse of late G1 and the initiation of DNA synthesis after release from the cholera toxin and IBMX inhibition was dependent on the presence of plasma in the medium. Either somatomedin C (10–20 ng/ml) or insulin (10−6–10−5 M) completely replaced the plasma requirement for late G1 progression and entry into S phase. Once the inhibited cells were released from the IBMX and cholera toxin block a subsequent increase in cyclic AMP did not prevent entry into S phase. The presence of cholera toxin alone inhibited the stimulation of human dermal fibroblasts. The elevation of intracellular cyclic AMP levels in the human dermal fibroblasts by cholera toxin was two to three fold greater than that found in the BALB/c‐3T3 cells in the presence of cholera toxin and IBMX.
Sexual agglutination factors from the yeast pichia amethionina
Authors: Mendonça‐Previato Lucia , Burke David , Ballou Clinton E.
Published: December 2004

Pichia amethionina is a heterothallic yeast isolated from necrotic cactus tissue. Haploid cells of opposite mating type, designated a and α, agglutinate strongly when mixed. The agglutination factors of the two cell types have been solubilized from the cell walls by β‐glucanase digestion and then partially purified by affinity adsorption to the opposite cell type and by gel filtration. From α‐cells was obtained a large, heat‐stable glycoprotein with the ability to agglutinate a‐cells. This α‐agglutinin was inactivated by mercaptoethanol, probably because the recognition sites are linked to the glycoprotein core by disulfide bonds. Digestion of a‐cells with β‐glucanase released a large heat‐labile glycoprotein that did not agglutinate α‐cells but did inhibit agglutination of a‐cells by α‐agglutinin. Subtilisin digestion of this a‐factor released a carbohydrate‐free protein of 27,000 daltons that retained the biological activity of the factor. These agglutination factors are sex‐ and species‐specific and are not found on the surface of heterozygous diploid cells.
Role of epidermal growth factor‐stimulated protein kinase in control of proliferation of A431 cells
Authors: Gill Gordon N. , Buss Janice E. , Lazar Cheri S. , Lifshitz Aliza , Cooper Jonathan A.
Published: December 2004

Epidermal growth factor (EGF), which stimulates tyrosine‐specific protein kinase activity both in vivo and in vitro, inhibits proliferation of A431 human epidermoid carcinoma cells. After mutagenesis clonal cell lines that were resistant to the growth inhibitory effects of EGF were selected. All six variants examined contained decreased EGF‐stimulated protein kinase. The number of EGF receptors in variant cells decreased in parallel with EGF‐stimulated protein kinase activity so that the specific activity of EGF‐stimulated protein kinase per EGF receptor remained constant in variant cell lines with up to tenfold reductions in both activities. This result suggests that both EGF‐ binding and kinase activities reside in the same or closely coupled molecules. The effect of EGF on growth of two resistant variants was examined in detail. Clone 29 contains ∼50% and clone 4 contains ∼20% of the EGF‐stimulated protein kinase activity of the parental A431 cell line. In serum‐supplemented medium, EGF stimulated proliferation of clone 29 but did not affect growth of clone 4. In a l:1 mixture of DME and F‐12 medium without scrum, EGF caused both clone 29 and clone 4 to grow as well as in 10% serum. These variants, which were selected for resistance to the growth inhibitory effects of EGF, thus exhibit a strong mitogenic response to EGF. This result suggests that resistance to the growth inhibitory effect of EGF may involve both a decrease in EGF‐stimulated protein kinase and an alteration in the response pathway.
Transforming genes in human tumors
Authors: Pulciani Simonetta , Santos Eugenio , Lauver Anne V. , Long Linda K. , Barbacid Mariano
Published: December 2004

DNAs isolated from a variety of human tumor cell lines as well as from naturally occurring human carcinomas and sarcomas were shown to induce morphologic transformation upon transfection into NIH/3T3 cells. All tested transformants contained human DNA sequences, some of which specifically cosegregated with the malignant phenotype in additional cycles of transfection. Southern blot analysis of second cycle transformants derived from T24 human bladder carcinoma cells showed the presence of a single 15 kbp EcoRI fragment of human DNA. These sequences were molecularly cloned utilizing λ Charon 9A as the cloning vector. The resulting recombinant DNA molecule, designated λ T24‐15A, was shown to contain an internal 6.6 kbp Bam HI fragment of human DNA that transformed NIH/3T3 fibroblasts with a specific activity of 5 × 104 focus forming units per picomol. These results indicate that we have moleculary cloned an oncogene present in T24 bladder carcinoma cells. Comparison of molecular clones containing the T24 oncogene and its normal homologue did not reveal biochemical differences that helped to explain the malignant properties of this oncogene. Finally, we report preliminary results indicating that the T24 bladder carcimoma oncogene is highly related to the transforming gene of BALB‐MSV, an acute transforming retrovirus.
Intracellular accumulation of a fluorescent derivative of paromomycin in human fibroblasts
Authors: Buchanan J.H. , Rattan S.I.S. , Stevens A. , Holliday R.
Published: December 2004

Human fetal lung fibroblasts grown in the presence of dansyl‐paromomycin (DNS‐Pm), a fluorescent derivative of the aminoglycoside antibiotic, paromomycin, probably accumulate DNS‐Pm in the lysosomes. The intracellular concentration of DNS‐Pm is proportional to the extracellular concentration and to the length of time cells are exposed to the compound. The accumulation of DNS‐Pm by human fibroblasts continued to increase for several days, reaching a saturation after 7 days. The kinetic data are consistent with the establishment of a steady state in the cell between fluid‐phase pinocytosis and exocytosis of DNS‐Pm. About 80% of the intracellular DNS‐Pm was released in 24 hr when fresh medium without the analogue was added. The residual 20% remained within the cells, suggesting that it may be irreversibly bound to the lysosomes, endoplasmic reticulum, or ribosonius. The uptake of paromomycin by cells in culture may be a useful means to study error propagation during growth and lifespan of cells in vitro.
Toxic ligand conjugates as tools in the study of receptor‐ligand interactions
Authors: Herschman Harvey R. , Simpson David L. , Cawley Daniel B.
Published: December 2004

We have constructed hybrid proteins in which the toxic A chains of ricin or diptheria toxin have been linked to either asialofetuin, fetuin, or epidermal growth factor (EGF). Both ASF‐RTA and ASF‐DTA are potent toxins on cultured rat hepatocytes, cells that display the asialoglycoprotein receptor. Toxicity of these two compounds is restricted to hepatocytes and can be blocked by asialoglycoproteins but not the native glycoproteins or asialoagalactoglycoprotein derivatives, indicating that the toxicity of the conjugates is mediated by the hepatic asialoglycoprotein receptor. The EGF‐RTA conjugate is an extremely potent toxin on cells that can bind the hormone, but is only poorly effective on cells that are unable to bind EGF. The EGF‐DTA conjugate, in contrast, is unable to kill 3T3 cells and is at least two orders of magnitude less effective than EGF‐RTA on A431 cells, a cell line with 1‐2 × 106 EGF receptors per cell. However, when EGF‐RTA and EGF‐DTA were tested on primary liver hepatocyte cultures, which were susceptible to both ASF‐RTA and ASF‐DTA, both EGF conjugates were potent toxins. Sensitivity of the hepatocyte cultures to ricin toxicity increases slightly during a 52‐hr culture period. In contrast, sensitivity to EGF‐RTA and ASF‐RTA decline dramatically during this period. Receptors for both ligands remain plentiful on the cell surface during this time.
Effect of interferon on phospholipid methylation by peripheral blood mononuclear cells
Authors: Bougnoux P. , Bonvini E. , Chang Z.L. , Hoffman T.
Published: December 2004

The effect of human interferon (IFN) preparations on the metabolic pathway leading to the synthesis of phosphatidylcholine (PC) by a stepwise addition of methyl groups to phosphatidylethanolamine (PE) was investigated in human peripheral blood mononuclear (PBMN) cells. An inhibition of the synthesis of PC via this pathway was regularly observed with both α‐ (recombinant or natural) and β‐IFN. This inhibition was apparent within the first 5 min of treatment, reached its maximum between 15 min and 1 hr, and persisted at the same level until 6 hr, the last time point examined. Each of the transmethylated products of PF underwent a similar inhibition, as measured by the turnover rate of individual products. The intracellular pool of the methyl donors, methionine and S‐adenosyl‐methionine (SAM), was shown to be unaffected. The methyltransferase activity of IFN‐pretreated cell extracts was unchanged. These findings support the hypothesis that IFN induces a functional change in phospholipid methylation at the level of organized membrane‐bound phospholipid methyltransferase enzymes in intact cells.
Comparative studies on human placental insulin and basic somatomedin receptors
Authors: Armstrong G. D. , Hollenberg M. D. , Bhaumick B. , Bala R. M.
Published: December 2004

The disuccinimidy! suberate, affinity‐labeling procedure, and proteolytic mapping techniques have been employed to characterize further the human placental receptors for insulin and basic somatomedin. Electrophoretic analysis of the basic somatomedin receptor, selectively crosslinked to 125I basic somatomedin in the presence of excess native insulin revealed, under reducing conditions, major labeled constituents of 270‐280 and 125‐140 kd, substantiating our previous work employing a photoaffinity labeling reagent. Affinity labeling also demonstrated the presence of less intensely labeled components with apparent molecular weights of 40 and 45 kd but failed to reveal a distinct 90‐ to 100‐kd species observed in parallel experiments with insulin. In the absence of β‐mercaptoethanol, all components specifically labeled with 125I basic somatomedin migrated in the 300‐ to 400‐kd range. In comparison, selective affinity labeling of the insulin receptor in the presence of excess native basic somatomedin revealed components, upon electrophoresis under reducing conditions, with apparent molecular weights of 270‐280, 125‐140, 90‐100, and 40 kd. The major insulin‐labeled component (125‐140 kd) comigrated with the major constituent (125‐140 kd) selectively labeled with basic somatomedin. When digestion was performed prior to solubilization, chymotryptic and tryptic proteolysis of the membrane‐localized selectively labeled insulin, and basic somatomedin receptors yielded quite similar gel electrophoretic maps. However, when digestion was done subsequent to solubilization, chymotryptic and tryptic proteolysis of selectively labeled insulin and basic somatomedin receptors solubilized in SDS yielded similar but not identical gel electrophoretic maps. We conclude that the receptors for basic somatomedin and insulin are highly homologous structures with respect to their disulfide crosslinked composition, and with respect to the size of the major components detected by selective affinity‐labeling procedures. Nevertheless, the detection of electrophoretically distinct labeled receptor components upon analysis of specifically labeled intact or proteolytically digested receptors points to subtle differences between the polypeptide compositions of the two receptors.
Integration of HBV‐DNA into liver and hepatocellular carcinoma cells during persistent HBV infection
Authors: Shafritz David A.
Published: December 2004

The hepatitis B virus carrier state (persistent HBV infection) is characterized by the presence of viral surface antigen (HBsAg) and virion particles (Dane particles) in the blood. From 1% to 10% of carriers develop chronic liver disease and/or hepatocellular carcinoma. Recent studies have demonstrated integrated HBV‐DNA in hepatocellular carcinomas and in several human hepatoma cell lines. In hepatoma patients, integrated HBV‐DNA has been found in all HBsAg carriers. Nontumorous liver also revealed integrated HBV‐DNA with the same or a different hybridization pattern from that observed in the tumor. To explore when integration occurs, carriers of short‐term (<2 years) or long‐term (> 8‐10 years) were evaluated. DNA extracts from percutaneous (needle) liver biopsies showed free viral DNA with no specific integration bands in short‐term carriers. In long‐term carriers, HBV‐DNA was integrated into the host genome with either a diffuse or a unique hybridization pattern. HBV‐DNA integration correlated with the duration of the carrier state and absence of virions in the serum but did not correlate with histologic evidence of chronic hepatitis. These studies suggest that integration of HBV‐DNA occurs during persistent HBV infection irrespective of liver disease and precedes development of hepatocellular carcinoma.
Delimitation of a DNA sequence which confers inducibility by glucocorticoid hormones
Authors: Groner Bernd , Herrlich Peter , Kennedy Nick , Ponta Helmut , Rahmsdorf Ursula , Hynes Nancy E.
Published: December 2004

A chimeric long terminal repeat‐thymidinc kinasc (LTR‐tk) gene has been used to define the sequence requirements for glucocorticoid induction of gene expression. The original LTR‐tk gene contains an entire mouse mammary tumor virus (MMTV) LTR preceding the tk gene. This gene can be expressed in a hormone‐responsive fashion upon transfection into L tk – cells to produce a chimeric LTR‐tk mRNA. Stepwise deletion of nuclcotide sequences 5′ of the viral RNA initiation site revealed that 202 nucleotides upstream of the viral cap site are sufficient for the hormonal regulation. Deletion of 5′ sequences up to 59 nucleotides upstream of the viral cap site abolished RNA initiation in the LTR and hormonal induction.
Loss of EGF binding and cation transport response during differentiation of mouse neuroblastoma cells
Authors: Mummery C. L. , van der Saag P. T. , de Laat S. W.
Published: December 2004

Mouse neuroblastoma cells (clone N1E‐115) differentiate in culture upon withdrawal of serum growth factors and acquire the characteristics of neurons. We have shown that exponentially growing N1E‐115 cells possess functional epidermal growth factor (EGF) receptors but that the capacity for binding EGF and for stimulation of DNA synthesis is lost as the cells differentiate. Furthermore, in exponentially growing cells, EGF induces a rapid increase in amiloride‐sensitive Na+ influx, followed by stimulation of the (Na+ ‐K+)ATPase, indicating that activation of the Na+/H+ exchange mechanism in N1E‐115 cells [1] may be induced by EGF. The ionic response is also lost during differentiation, but we have shown that the stimulation of both Na+ and K+ influx is directly proportional to the number of occupied receptors in all cells whether exponentially growing or differentiating, thus only indirectly dependent on the external EGF concentration. The linearity of the relationships indicates that there is no rate‐limiting step between EGF binding and the ionic response. Our data would suggest that as neuroblastoma cells differentiate and acquire neuronal properties, their ability to respond to mitogens, both biologically and in the activation of cation transport processes, progressively decreases owing to the loss of the appropriate receptors.
Function cones and interpolation
Authors: Cerdà Joan , Coll Heribert
Published: January 2005

We consider interpolation of operators acting on functions that belong to a given cone Q with the so‐called decomposition property. The set of all positive functions whose level sets are the level sets of a given function is the main example, and the cone of all decreasing functions is a particular case. As applications, we obtain conditions for the identity (E0 ∩ Q,E1 ∩ Q)θ,p = (E0,E1)θ,p ∩ Q and interpolation results for operators which are bounded when restricted to a given family of characteristic funcions. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
The factorization method for a class of inverse elliptic problems
Authors: Kirsch Andreas
Published: January 2005

In this paper the factorization method from inverse scattering theory and impedance tomography is extended to a class of general elliptic differential equations in divergence form. The inverse problem is to determine the interface ∂Ω of an interior change of the material parameters from the Neumann‐Dirichlet map. Since absorption is allowed a suitable combination of the real and imaginary part of the Neumann‐Dirichlet map is needed to explicitely characterize Ω by the data. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Non‐compactness of the solution operator to $ \bar \partial $ on the Fock‐space in several dimensions
Authors: Schneider Georg
Published: January 2005

We consider the canonical solution operator to $ \bar \partial $ restricted to (0, 1)‐forms with coefficients in the generalized Fock‐spaces

equation image

We will show that the canonical solution operator restricted to (0, 1)‐forms with $ {\cal F}{m} $‐coefficients can be interpreted as a Hankel‐operator. Furthermore we will show that the canonical solution operator is not compact for m ≥ 2. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Detecting Mechanochemical Degradation of Nitrocellulose by Combining Dynamic Mechanical Analysis with Mass Spectrometry
Authors: Vyazovkin Sergey , Dranca Ion , Lang Anthony J.
Published: December 2004

Summary: Dynamic mechanical analysis is combined with mass spectrometry to study nitrocellulose under oscillating strain. At a constant temperature (150–160 °C) and frequency (400–600 Hz) nitrocellulose fractures demonstrating a modulus drop and release of products with m/z: 30 and 44. At linear heating (2 °C · min−1) and a frequency of 10–50 Hz similar products are released in two steps, the second of which demonstrates a modulus drop and a temperature increase indicating ignition.

Data for an isothermal dynamic mechanical analysis–mass spectrometry experiment performed at 160 °C.

image

Data for an isothermal dynamic mechanical analysis–mass spectrometry experiment performed at 160 °C.
A practice‐orientated study of the complex „processing and handling–application–resultant properties”︁ of autopolymerizing PMMA bone cements
Authors: Müller K.
Published: December 2004

Bone cements which are used for the fixation of alloplasties as well as for filling and/or bridging of bone defects had been intensively investigated during the past 15 years. Scientists payed close attention to the subjects of “biocompatibility in view of chemical and thermal effects; polymerization process; structure and properties of bone cements”. As a rule, especially tests for the evaluation of strength properties were carried out with more or less standardized and relatively small specimen. The fund of experience, obtained by the methods mentioned above, don't let us hope to have any further significant progress concerning the transferability of these results to practise. A possible step further in the approximation of model experiments with respect to practical problems in the author's opinion should be the methodically combination of the known single aspects to a larger total complex. As a start in this direction a testing method was developed which enables processing and insertion of bone cements as well as the implantation of endoprostheses‐shafts into tubular spaces under similar geometrical and thermal conditions as they are present in big tubular bones.

Shape and dimensions of the originated bone cement‐ “quivers” or “jackets” are chosen in a way that experiments are practicable for the comparison of different types of bone cements and implantating methods as well as the testing of intended or unintended admixtures (for example X‐ray contrast agent, antibiotics, blood) with respect to the mechanical loading capacity.

Furthermore comparisons with the results of conventional mechanical material testings are possible.

The contruction of the testing apparatus and the testing procedure will be presented. Its applicability for tests to compare different types of bone cements with respect to the parameters “processing and insertion method”, “implantating endoprostheses‐shafts” and “admixtures” will be discussed by means of obtained results. Finally the question is asced wether a method like this can be an aid for training and objectively valuation of the methodical abilities of budding operating surgeons in this field.
Ermüdung von Stahl × 20 Cr 13. Rißwachstum bei Lastwechselfrequenzen von 10−3 Hz bis zu 21 KHz, Bestimmung des Grenzwertes ΔK0 mit Ultraschall
Authors: Speidel Markus O. , Stanzl Stefanie E. , Tschegg Elmar
Published: December 2004

Bruchmechanische Ermüdungsversuche wurden sowohl niederfrequent (bis 10−3 Hertz) als auch hochfrequent (mit Hilfe von Ultraschall und Hochgeschwindigkeitschromatographie bis 2,1 × 104 Hertz) durchgeführt. Dabei zeigt sich, daß der Einfluß korrosiver Umgebungen auf die Ermüdungsrißwachstumsgeschwindigkeit zu höheren Frequenzene hin abnimmt. Ultraschallermüdung des Stahls in Wasser führt zu gleichen Rißgeschwindigkeiten wie niederfrequente Ermüdung im Vakuum. Insbesondere für den Bereich kleiner Spannungsintensitätswerte bietet der Ultraschall‐Ermüdungsversuch den Vorteil, den Schwellwert ΔK0 der Spannungsintensität, unter dem kein Rißfortschritt festzustellen ist, in kurzer Zeit zu ermitteln.
Laser Heat Treatment of piston rings
Authors: Chauxuan Ding
Published: December 2004

The laser heat treatment of piston rings is discussed. The hardened layer formed on the surface can increase the wear‐resistance and hence the service life on the piston ring.

Compared with rings treated by chromium‐plating or molybdenum‐spraying, the new technique of laser hardening of the piston ring offers many advantages, such as low cost, noble metal saving, no pollution, energy saving, simple working procedure, easy automation production, etc.
Auswertung und metallkundliche Aussagen rechnergesteuerter Warmflachstauchversuche
Authors: Streißelberger A. , Peichl L. , Kaspar R. , Pawelski O.
Published: December 2004

Während des Versuchsablaufs werden kontinuierlich die Probentemperatur, die Stauchkraft und der Werkzeugweg digital erfaßt und weiter ausgewertet. Die Ermittlung von Fließkurven ermöglicht Aussagen über die Umformkräfte und das Entfestigungsverhalten des Werkstoffs. Die differenzierten Abkühlkurven der gestauchten Probe liefern Informationen über den Umwandlungsablauf im Gefüge. Die Größe der Flachstauchprobe erlaubt eine umfassende Werkstoffprüfung nach der Simulation und damit eine Optimierung thermomechanischer Behandlungsverfahren.
Ein Beitrag zum Abbrandverhalten von hochlegierten Drahtelektroden
Authors: Vida Jochen , Weisweiler Werner , Schwarzbach Eberhard
Published: December 2004

Durch Analyse des Schweißrauches läßt sich Aufschluß über das Abbrandverhalten von Drahtelektroden gewinnen. Beim MAG‐Schweißen unter sauerstoffarmen Schutzgasen wird der Schwermetall‐Abbrand durch die Partialdrucke der Legierungskomponenten kontrolliert.
Untersuchungen zur lokalen Zusammensetzung von Glasfasern mit Hilfe der Röntgenmikroanalyse
Authors: Ehrenstein G. W. , Bledzki A. , Spaude R. , Neikes Th.
Published: December 2004

Verschiedene Glasfasertypen weisen gegenüber aggressiven Umgebungsmedien eine unterschiedliche Chemikalienresistenz auf. Durch die Einwirkung saurer oder alkalischer Medien können einige Elementarglasfasern ausgelaugt werden, was sich optisch verfolgen lassen kann, andere Glasfasern wiederum zeigen kaum optische Veränderungen. Mit Hilfe der Röntgenmikroanalyse besteht nun die Möglichkeit die durch den Auslaugprozeß hervorgerufene chemische Veränderung der Glasfaserzusammensetzung verschiedener Typen quantitativ bzw. semiquantitativ zu erfassen. Dadurch lassen sich Korrosionsvorgänge an einzelnen Elementarglasfasern besser beschreiben als bisher.
Kurzzeitschwingfestigkeit von duktilen Stählen unter mehrachsiger Beanspruchung
Authors: Sonsino C. M. , Grubisic V.
Published: December 2004

Um das Kurzzeitschwingfestigkeitsverhalten von zyklisch entfestigenden und verfestigenden Stählen unter mehrachsigen elasto‐plastischen Beanspruchungen zu untersuchen, wurden dehnungs‐ und scherungsgesteuerte Schwingfestigkeitsversuche unter Einstufenbeanspruchung durchgeführt. Für den zyklisch entfestigenden Vergütungsstahl 30 CrNiMo 8 und zyklisch verfestigenden austenitischen Stahl X 10 CrNiTi 189 wurden Anrißwöhlerlinien unter reiner Dehnung, reiner Scherung sowie unter kombinierter phasengleicher und phasenverschobener Beanspruchung ermittelt.

Bei beiden Stählen, die im Behälter und Rohrleitungsbau häufig verwendet werden, tritt durch die phasenverschobene Beanspruchung (δ = 90°) gegenüber der phasengleichen eine deutliche Minderung der Anrißlebensdauer auf. Diese Minderung erfolgt durch eine Veränderung der Hauptdehnungsrichtungen und durch eine gegenseitige Beeinflussung von Verformungen in verschiedenen Richtungen der Oberfläche. Dieses Verhalten wird durch ein Berechnungsverfahren erfaßt, mit dem eine Vergleichsdehnung abgeleitet wird. Auf der Basis von unter einachsiger Belastung ermittelten Dehnungswöhlerlinien wird anschließend die Anrißlebensdauer für kombinierte Beanspruchung abgeschätzt.
Spannungsintensitätsfaktoren für lange axiale Oberflächenrisse in Rohren bei Thermoschockbelastung
Authors: Grebner H. , Strathmeier U.
Published: December 2004

Mit einem Thermoschockproblem lassen sich die Vorgänge in den Primärkreisrohren bei einer Notkühlung konservativ beschreiben. Die entstehenden Wärmespannungen werden hier als Belastung für einen langen axialen Oberflächenriß eingesetzt. Mit Hilfe der Gewichtsfunktionsmethode werden Spannungsintensitätsfaktoren für diesen Lastfall berechnet.
E‐Modul‐Messungen an amorphen Legierungen
Authors: Cao Z. Y. , Bergmann H. W.
Published: December 2004

Der E‐Modul von amorphen Legierungen wurde durch Bestimmung der Schallgeschwindigkeit und der Dichte ermittelt. Untersucht wurden Metall‐Metalloid‐Gläser und Metall‐Metall‐Gläser der Typen (Fe100−xMx)83B17 bzw. Zr100−xMx. Die erreichbaren Genauigkeiten bei der E‐Modul‐Bestimmung werden mit denen anderer Autoren verglichen. Speziell wurde der Einfluß der Zusammensetzung auf den sich einstellenden E‐Modul untersucht und die erhaltenen Ergebnisse im Hinblick auf Nahordnungsverhalten, Atomradienverhältnis und Valenzelektronendichte diskutiert.
Spannungsintensitätsfaktoren für vollständig umlaufende Oberflächenumfangsrisse in Rohren bei Thermoschockbelastung
Authors: Grebner H. , Strathmeier U.
Published: December 2004

Bei einer Notkühlung werden in den Primärkreisrohren Wärmespannungen erzeugt, die sich konservativ durch ein Thermoschockproblem beschreiben lassen. Die Wärmespannungen werden hier als Belastung für vollständig umlaufende Oberflächenumfangsrisse eingesetzt. Mit Hilfe der Gewichtsfunktionsmethode werden Spannungsintensitätsfaktoren für diesen Lastfall berechnet.
Thermochemische Behandlung von Titan und Titanlegierungen durch Laserumschmelzen und Gaslegieren
Authors: Bergmann H. W.
Published: December 2004

Es wird gezeigt, daß es beim Umschmelzen von Titanlegierungen mit einem Laser unter Verwendung geeigneter Prozeßgase möglich ist, harte Oberflächenschichten zu erzielen. Die erhaltenen Proben sind goldglänzend, riß‐ und porenfrei und weisen nach dem Umschmelzen nur einen geringen Verzug sowie eine minimale Rauhigkeit auf. Die bisher erhaltenen Ergebnisse werden mit denen äquivalenter Verfahren verglichen.
Bemerkungen zu Versagenskriterien und Bauteilfestigkeit bei Keramik
Authors: Willmann G.
Published: December 2004

Trotz eines hohen Kenntnisstandes über die mechanischen Eigenschaften keramischer Werkstoffe fehlen heute noch ausreichend belastbare Erfahrungen, um Versagenskriterien für den konstruktiven Entwurf zu formulieren. Die Einflüsse von Bauteilvolumen, Oberflächenbeschaffenheit und Streuung der Werte für mechanische Festigkeit auf die Gestaltsfestigkeit werden diskutiert.
Hydrogen‐Induced Crack Formation in the low‐alloy steel 26 NiCrMoV 145 with a yield strength of approx. 850 N/mm
Authors: David W. , Schleithoff K. , Schmitz F.
Published: December 2004

In recent years intergranular stress corrosion cracking has occurred worldwide in the shrink‐fitted discs of low‐pressure turbine rotors made of low‐alloy steels.

Both anodic stress corrosion cracking and hydrogen‐induced crack formation have been mentioned in the literature as possible failure mechanisms. Clarification of the role of hydrogen induced cracking was sought by carrying out a variety of tests with the low‐alloy steel 26 NiCrMoV 145. The results indicate that hydrogen plays a decisive role in the failure mechanism, provided it is available in sufficiently high quantities.
Über den Einfluß von Probendicke und ‐geometrie auf die Ermüdungsrißausbreitung und die Bruchzähigkeit von Polycarbonat
Authors: Krey J. , Walter R. , Friedrich K.
Published: December 2004

Diese Studie befaßt sich mit dem Einfluß von Probendicke und ‐geometrie auf das Bruchverhalten von Polcarbonat bei Raumtemperatur. Mit abnehmender Probendicke war sowohl eine Erhöhung des Widerstandes gegen Ermüdungsrißfortschritt als auch eine Zunahme in der Bruchzähigkeit unter statischer Belastung zu verzeichnen. Zusätzlich durchgeführte J‐Integral‐Vergleich ließen einen Vergleich mit den Bruchzähigkeitskennwerten zu. Rasterelektronemikroskopische Untersuchungen der Bruchflächen ergaben Hinweise über den Ablauf der Schädigung und die einzelnen Bruchmechanismen. Letztere lieferten gezielte Informationen zur Interpretation der mechanischen Kennwerte in Abhängigkeit von der Probengeometrie.
Die spezifische Wärmekapazität von metallischen Werkstoffen. III. Teil: NiCr 15 Fe (INCONEL 600) und vier weitere Werkstoffe aus der Gruppe der NE‐Metalle
Authors: Richter F. , Born L.
Published: December 2004

Im Rahmen der Ermittlung der Temperaturabhängigkeit der wahren und der mittleren spezifischen Wärmekapazität von metallischen Werkstoffen wird in der vorliegenden dritten und abschließenden Untersuchung über NiCr 15 Fe (INCONEL 600), stellvertretend für die Gruppe der Nickel‐Basis‐Legierungen, und über vier weitere Werkstoffe, die den NE‐Metallen zuzuordnen sind, berichtet.

Der Temperaturverlauf der spezifischen Wärmekapazität von NiCr 15 Fe ist ähnlich demjenigen des reinen Nickels ohne magnetische Ordnung, das heißt nach Abzug des ferromagnetischen Anteils zur spezifischen Wärmekapazität. Oberhalb 600°C wird ein Zusatzbeitrag beobachtet, der auf die Bildung von Ni3Cr‐Clustern zurückzuführen ist.

Des weiteren wurden die beiden Ti‐Werkstoffe Ti 99,5 (CONTIMET 55) und TiAl 5 Sn 2 (CONTIMET AlSn 52) ausgewählt. Während sich Ti 99,5 wie reines Titan verhält – mit leichter Abweichung im Bereich der Phasenumwandlung – liegen die Zahlenwerte für TiAl 5 Sn 2 etwas oberhalb der Werte des unlegierten Titans. Den Abschluß bilden die beiden gegenüber Meerwasser korrosionsbeständigen Legierungen CuNi 10 Fe und CuNi 30 Fe. Beide verhalten sich ähnlich wie reines Kupfer, wobei sich bei CuNi 10 Fe im Bereich der nachweisbaren Entmischung ein zusätzlicher Beitrag zur wahren spezifischen Wärmekapazität beobachten läßt. Die Entmischung in CuNi 30 Fe zeigt keinen meßbaren Einfluß auf den Temperaturverlauf der spezifischen Wärmekapazität.
Die Werkstoffdämpfung von Stählen bei hohen Dehnungsamplituden
Authors: Gudmundson P. , Wüthrich C.
Published: December 2004

Am Beispiel von zwei martensitischen Chromstählen (X 22 CrMoV 12 1, X 20 Cr 13) und eines kaltverformten Austeniten (X 12 CrNiWTi 16 13) wird die amplitudenabhängige Werkstoffdämpfung bei Raumtemperatur untersucht. Die martensitischen Werkstoffe weisen infolge der magneto‐elastischen Effekte eine hohe amplitudenabhängige Dämpfung auf. Es kann gezeigt werden, daß eine Erhöhung der Festigkeit durch Absenken der Anlaßtemperatur zu einer Abnahme der Werkstoffdämpfung führt. Der untersuchte austenitische Werkstoff besitzt nach Kaltverformung eine beträchtliche Dämpfung, die jedoch beim Tempern bereits bei Temperaturen oberhalb von 100 °C auf die bei Austeniten üblichen tiefen Werte absinkt. Dieser Effekt wird der Verankerung der Versetzungen beim Tempern zugeschrieben.
Möglichkeiten und Konsequenzen des Leichtbaus. Beispiele zur Betriebsfestigkeit von Vorderachs‐, Lenksystem‐ und Antriebsbauteilen
Authors: Krüger L. , Naundorf H.
Published: December 2004

Das Streben nach weitgehendem Leichtbau führt im Automobilbau neben dem immer gezielteren Einsatz der klassischen Materialien zunehmend zur Verwendung von leichteren Werkstoffen. Nicht nur bei Karosserie‐ und Ausstattungsbauteilen, sondern auch bei Fahrwerks‐, Lenksystem‐ und Antriebsbauteilen ist dieser Trend festzustellen. Bei der Auswahl alternativer Werkstoffe ist zu berücksichtigen, daß die Wirtschaftlichkeit neben den oft vielfältigen Funktionsgesichtspunkten und der Zuverlässigkeit einen entscheidenden Einfluß hat.

In diesem Beitrag werden die dynamischen und statischen Prüfstandsergebnisse, die mit Bauteilen aus verschiedenen Materialien erzielt wurden, dargestellt und miteinander verglichen.