bluuebunny/crossref_metadata_2025 huggingface dataset:
Minireview: Recent Progress in Gonadotropin-Releasing Hormone Neuronal Migration
Authors: Tobet Stuart A. , Schwarting Gerald A.
Published: December 2005

Neurons that synthesize GnRH are critical brain regulators of the reproductive axis, yet they originate outside the brain and must migrate over long distances and varied environments to get to their appropriate positions during development. Many studies, past and present, are providing clues for the types of molecules encountered and movements expected along the migratory route. Recent studies provide real-time views of the behavior of GnRH neurons in the context of in vitro preparations that model those in vivo. Live images provide direct evidence of the changing behavior of GnRH neurons in their different environments, showing that GnRH neurons move with greater frequency and with more alterations in direction after they enter the brain. The heterogeneity of molecular phenotypes for GnRH neurons likely ensures that multiple external factors will be found that regulate the migration of different portions of the GnRH neuronal population at different steps along the route. Molecules distributed in gradients both in the peripheral olfactory system and basal forebrain may be particularly influential in directing the appropriate movement of GnRH neurons along their arduous migration. Molecules that mediate the adhesion of GnRH neurons to changing surfaces may also play critical roles. It is likely that the multiple external factors converge on selective signal transduction pathways to engage the mechanical mechanisms needed to modulate GnRH neuronal movement and ultimately migration.
Minireview: Kisspeptin Neurons as Central Processors in the Regulation of Gonadotropin-Releasing Hormone Secretion
Authors: Dungan Heather M. , Clifton Donald K , Steiner Robert A.
Published: December 2005

The Kiss1 gene encodes a family of peptides called kisspeptins, which bind to the G protein-coupled receptor GPR54. Kisspeptin(s) and its receptor are expressed in the forebrain, and the discovery that mice and humans lacking a functional GPR54 fail to undergo puberty and exhibit hypogonadotropic hypogonadism implies that kisspeptin signaling plays an essential role in reproduction. Studies in several mammalian species have shown that kisspeptins stimulate the secretion of gonadotropins from the pituitary by stimulating the release of GnRH from the forebrain after the activation of GPR54, which is expressed by GnRH neurons. Kisspeptin is expressed abundantly in the arcuate nucleus (Arc) and the anteroventral periventricular nucleus (AVPV) of the forebrain. Both estradiol and testosterone regulate the expression of the Kiss1 gene in the Arc and AVPV; however, the response of the Kiss1 gene to these steroids is exactly opposite between these two nuclei. Estradiol and testosterone down-regulate Kiss1 mRNA in the Arc and up-regulate its expression in the AVPV. Thus, kisspeptin neurons in the Arc may participate in the negative feedback regulation of gonadotropin secretion, whereas kisspeptin neurons in the AVPV may contribute to generating the preovulatory gonadotropin surge in the female. Hypothalamic levels of Kiss1 and GPR54 mRNA increase dramatically at puberty, suggesting that kisspeptin signaling could mediate the neuroendocrine events that trigger the onset of puberty. Together, these observations demonstrate that kisspeptin-GPR54 signaling in the brain serves as an important conduit for controlling GnRH secretion in the developing and adult animal.
The Transcription Factor AP-2β Causes Cell Enlargement and Insulin Resistance in 3T3-L1 Adipocytes
Authors: Tao Yukari , Maegawa Hiroshi , Ugi Satoshi , Ikeda Kazuhiro , Nagai Yoshio , Egawa Katsuya , Nakamura Takaaki , Tsukada Shuichi , Nishio Yoshihiko , Maeda Shiro , Kashiwagi Atsunori
Published: December 2005

We have reported the association of variations in the activating protein-2β (AP-2β) transcription factor gene with type 2 diabetes. This gene was preferentially expressed in 3T3-L1 adipocytes in a differentiation stage-dependent manner, and preliminary experiments showed that subjects with the disease-susceptible allele showed stronger expression in adipose tissue than those without the susceptible allele. Thus, we overexpressed the AP-2β gene in 3T3-L1 adipocytes to clarify whether AP-2β might play a crucial role in the pathogenesis of type 2 diabetes through dysregulation of adipocyte function. In cells overexpressing AP-2β, cells increased in size by accumulation of triglycerides accompanied by enhanced glucose uptake. On the contrary, suppression of AP-2β expression by small interfering RNA inhibited glucose uptake. Enhancement of glucose uptake by AP-2β overexpression was attenuated by inhibitors of phospholipase C (PLC) and atypical protein kinase Cζ/λ (PKCζ/λ), but not by a phosphatidylinositol 3-kinase (PI3-K) inhibitor. Consistently, we found activation of PLC and atypical PKC, but not PI3-K, by AP-2β expression. Furthermore, overexpression of PLCγ enhanced glucose uptake, and this activation was inhibited by an atypical PKC inhibitor, suggesting that the enhanced glucose uptake may be mediated through PLC and atypical PKCζ/λ, but not PI3-K. Moreover, we observed the increased tyrosine phosphorylation of Grb2-associated binder-1 (Gab1) and its association with PLCγ, indicating that Gab1 may be involved in AP-2β-induced PLCγ activation. Finally, AP-2β overexpression was found to relate to the impaired insulin signaling. We propose that AP-2β is a candidate gene for producing adipocyte hypertrophy and may relate to the abnormal characteristics of adipocytes observed in obesity.
Fetal Programming: Prenatal Testosterone Treatment Leads to Follicular Persistence/Luteal Defects; Partial Restoration of Ovarian Function by Cyclic Progesterone Treatment
Authors: Manikkam Mohan , Steckler Teresa L. , Welch Kathleen B. , Inskeep E. Keith , Padmanabhan Vasantha
Published: December 2005

Prenatal testosterone (T) excess during midgestation leads to estrous cycle defects and polycystic ovaries in sheep. We hypothesized that follicular persistence causes polycystic ovaries and that cyclic progesterone (P) treatment would overcome follicular persistence and restore cyclicity. Twice-weekly blood samples for P measurements were taken from control (C; n = 16) and prenatally T-treated (T60; n = 14; 100 mg T, im, twice weekly from d 30–90 of gestation) Suffolk sheep starting before the onset of puberty and continuing through the second breeding season. A subset of C and T60 sheep were treated cyclically with a modified controlled internal drug-releasing device for 13–14 d every 17 d during the first anestrus (CP, 7; TP, 6). Transrectal ovarian ultrasonography was performed for 8 d in the first and 21 d in the second breeding season. Prenatal T excess reduced the number, but increased the duration of progestogenic cycles, reduced the proportion of ewes with normal cycles, increased the proportion of ewes with subluteal cycles, decreased the proportion of ewes with ovulatory cycles, induced the occurrence of persistent follicles, and reduced the number of corpora lutea in those that cycled. Cyclic P treatment in anestrus, which produced one third the P concentration seen during luteal phase of cycle, did not reduce the number of persistent follicles, but increased the number of progestogenic cycles while reducing their duration. These findings suggested that follicular persistence might contribute to the polycystic ovarian morphology. Cyclic P treatment was able to only partially restore follicular dynamics, but this may be related to the low replacement concentrations of P achieved.
Dendritic Processing of Excitatory Synaptic Input in Hypothalamic Gonadotropin Releasing-Hormone Neurons
Authors: Roberts C. B. , Best J. A. , Suter K. J.
Published: December 2005

The activity of hypothalamic GnRH neurons results in the intermittent release of GnRH required for reproductive function. This intermittent neurosecretory activity has been proposed to reflect integration of intrinsic properties of and synaptic input to GnRH neurons. Determining the relative impact of synaptic inputs at different locations on the GnRH neuron is difficult, if not impossible, using only experimental approaches. Thus, we used electrophysiological recordings and neuronal reconstructions to generate computer models of GnRH neurons to examine the effects of synaptic inputs at varying distances from the soma along dendrites. The parameters of the models were adjusted to duplicate measured passive and active electrophysiology of cells from mouse brain slices. Our morphological findings reinforce the emerging picture of a complex dendritic structure of GnRH neurons. Furthermore, analysis of reduced morphology models indicated that this population of cells is unlikely to exhibit low-frequency tonic spiking in the absence of synaptic input. Finally, applying realistic patterns of synaptic input to modeled GnRH neurons indicates that synapses located more than about 30% of the average dendrite length from the soma cannot drive firing at frequencies consistent with neuropeptide release. Thus, processing of synaptic input to dendrites of GnRH neurons is probably more complex than simple summation.
Intronic Polymorphisms within TFAP2B Regulate Transcriptional Activity and Affect Adipocytokine Gene Expression in Differentiated Adipocytes
Authors: Tsukada Shuichi , Tanaka Yasushi , Maegawa Hiroshi , Kashiwagi Atsunori , Kawamori Ryuzo , Maeda Shiro
Published: December 2005

We have identified a gene encoding transcription factor activating enhancer binding protein-2β (TFAP2B) as a candidate for conferring susceptibility to type 2 diabetes. Although we have also found that TFAP2B was preferentially expressed in adipose cells in a differentiation-dependent manner, the mechanisms by which the gene and gene polymorphisms contribute to conferring susceptibility to the disease have not yet been elucidated. The aim of this study was to evaluate the impact of the polymorphisms within the TFAP2B gene on conferring susceptibility to type 2 diabetes. We identified that a 300-bp DNA fragment in intron 1 of TFAP2B had significant enhancer activity, and the variations of this region affected this enhancer activity in differentiated adipocytes. In an experiment using adenovirus vectors encoding TFAP2B, the expression of TNF-α gene was shown to be elevated in the TFAP2B overexpressing cells compared with those in control cells. Furthermore, we demonstrated that the expression of TFAP2B was increased in the adipose tissues of subjects with the disease-susceptibility allele, and the plasma levels of TNF-α and high sensitivity C-reactive peptide were significantly elevated in the patients with the disease-susceptibility allele. These results suggest that TFAP2B may contribute to the pathogenesis of type 2 diabetes through regulation of adipocytokine gene expression, and that TFAP2B may be a promising target for treatment or prevention of this disease.
pH-Dependent Dissociation of Carbohydrate Ligand Polycations from DNA Ternary Complexes
Authors: Asayama Shoichiro , Sekine Takashi , Kawakami Hiroyoshi , Nagaoka Shoji
Published: December 2005

Here, we have demonstrated that carbohydrate ligand polycations are pH-dependently dissociated from DNA polyion complexes. In response to pH, DNA ternary complexes have dissociated the ligand polycations, resulting in DNA binary complexes. Namely, the ternary complexes of DNA, a poly(l-histidine) modified with aminoethyl groups, PLH-NH2, and a poly(l-lysine) conjugated with lactose molecules, PLL-Lac, at pH 7.5 have dissociated the PLL-Lac polycations by the protonation of imidazole groups of PLH-NH2 at pH 6.0. The pH-dependent dissociation of the ligand polycations from DNA polyion complexes at endosomal pH is expected to offer unique design for DNA delivery systems.
The Product-catalyzed [2,3]-Wittig Rearrangement of Silyl Enolates Generated from α-Allyloxy Ketones
Authors: Sato Yoshinori , Fujisawa Hidehiko , Mukaiyama Teruaki
Published: December 2005

The [2,3]-Wittig rearrangement of silyl enolates generated from α-allyloxy ketones proceeded smoothly in DMF by the promotion of a catalytic amount of metal alkoxides such as sodium benzylate to afford the corresponding rearrangement product in good yields at room temperature, which indicated that the oxygen anion initially formed in the above product effectively catalyzed the [2,3]-Wittig rearrangement as a Lewis base.
Recombinant viral RdRps can initiate RNA synthesis from circular templates
Authors: RANJITH-KUMAR C.T. , KAO C.C.
Published: December 2005

The crystal structure of the recombinant hepatitis C virus (HCV) RNA-dependent RNA polymerase (RdRp) revealed extensive interactions between the fingers and the thumb subdomains, resulting in a closed conformation with an established template channel that should specifically accept single-stranded templates. We made circularized RNA templates and found that they were efficiently used by the HCV RdRp to synthesize product RNAs that are significantly longer than the template, suggesting that RdRp could exist in an open conformation prior to template binding. RNA synthesis using circular RNA templates had properties similar to those previously documented for linear RNA, including a need for higher GTP concentration for initiation, usage of GTP analogs, sensitivity to salt, and involvement of active-site residues for product formation. Some products were resistant to challenge with the template competitor heparin, indicating that the elongation complexes remain bound to template and are competent for RNA synthesis. Other products were not elongated in the presence of heparin, indicating that the elongation complex was terminated. Lastly, recombinant RdRps from two other flaviviruses and from the Pseudomonas phage [phis]6 also could use circular RNA templates for RNA-dependent RNA synthesis, although the [phis]6 RdRp could only use circular RNAs made from the 3′-terminal sequence of the [phis]6 genome.
Protein tagging at rare codons is caused by tmRNA action at the 3′ end of nonstop mRNA generated in response to ribosome stalling
Authors: LI XIA , HIRANO RIEKO , TAGAMI HIDEAKI , AIBA HIROJI
Published: December 2005

It has been believed that protein tagging caused by consecutive rare codons involves tmRNA action at the internal mRNA site. We demonstrated previously that ribosome stalling either at sense or stop codons caused by certain arrest sequences could induce mRNA cleavage near the arrest site, resulting in nonstop mRNAs that are recognized by tmRNA. These findings prompted us to re-examine the mechanism of tmRNA tagging at a run of rare codons. We report here that either AGG or CGA but not AGA arginine rare-codon clusters inserted into a model crp mRNA encoding cAMP receptor protein (CRP) could cause an efficient protein tagging. We demonstrate that more than three consecutive AGG codons are needed to induce an efficient ribosome stalling therefore tmRNA tagging in our system. The tmRNA tagging was eliminated by overproduction of tRNAs corresponding to rare codons, indicating that a scarcity of the corresponding tRNA caused by the rare-codon cluster is an important factor for tmRNA tagging. Mass spectrometry analyses of proteins generated in cells lacking or possessing tmRNA encoding a protease-resistant tag sequence indicated that the truncation and tmRNA tagging occur within the cluster of rare codons. Northern and S1 analyses demonstrated that nonstop mRNAs truncated within the rare-codon clusters are detected in cells lacking tmRNA but not in cells expressing tmRNA. We conclude that a ribosome stalled by the rare codon induces mRNA cleavage, resulting in nonstop mRNAs that are recognized by tmRNA.
The antisense strand of small interfering RNAs directs histone methylation and transcriptional gene silencing in human cells
Authors: WEINBERG MARC S. , VILLENEUVE LOUISA M. , EHSANI ALI , AMARZGUIOUI MOHAMMED , AAGAARD LARS , CHEN ZHAO-XIA , RIGGS ARTHUR D. , ROSSI JOHN J. , MORRIS KEVIN V.
Published: December 2005

To determine mechanistically how siRNAs mediate transcriptional gene silencing (TGS) in human cells, we have measured histone methylation at targeted promoters, the dependency on active transcription, and whether or not both strands of the siRNA are required for siRNA-mediated TGS. We report here that siRNA treatment increases both H3K9 and H3K27 methylation of the targeted EF1A promoter and that this increase is dependent on nuclear specific delivery of the siRNA. We also find that TGS can be directed by the antisense strand alone, and requires active transcription by RNA polymerase II in human cells as evidenced by sensitivity to α-amanatin. The observation of antisense strand-specific siRNA-mediated TGS of EF1A was substantiated by targeting the U3 region of the HIV-1 LTR/promoter. Furthermore, we show that the antisense strand of siRNA EF52 associates with the transiently expressed Flag-tagged DNMT3A, the targeted EF1A promoter, and trimethylated H3K27. The observations reported here implicate a functional link between siRNA-mediated targeting of genomic regions (promoters), RNA Pol II function, histone methylation, and DNMT3A and support a paradigm in which the antisense strands of siRNAs alone can direct sequence-specific transcriptional gene silencing in human cells.
TarBase: A comprehensive database of experimentally supported animal microRNA targets
Authors: SETHUPATHY PRAVEEN , CORDA BENOIT , HATZIGEORGIOU ARTEMIS G.
Published: December 2005

MicroRNAs (miRNAs) are ~22-nt RNA segments that are involved in the regulation of protein expression primarily by binding to one or more target sites on an mRNA transcript and inhibiting translation. MicroRNAs are likely to factor into multiple developmental pathways, multiple mechanisms of gene regulation, and underlie an array of inherited disease processes and phenotypic determinants. Several computational programs exist to predict miRNA targets in mammals, fruit flies, worms, and plants. However, to date, there is no systematic collection and description of miRNA targets with experimental support. We describe a database, TarBase, which houses a manually curated collection of experimentally tested miRNA targets, in human/mouse, fruit fly, worm, and zebrafish, distinguishing between those that tested positive and those that tested negative. Each positive target site is described by the miRNA that binds it, the gene in which it occurs, the nature of the experiments that were conducted to test it, the sufficiency of the site to induce translational repression and/or cleavage, and the paper from which all these data were extracted. Additionally, the database is functionally linked to several other useful databases such as Gene Ontology (GO) and UCSC Genome Browser. TarBase reveals significantly more experimentally supported targets than even recent reviews claim, thereby providing a comprehensive data set from which to assess features of miRNA targeting that will be useful for the next generation of target prediction programs. TarBase can be accessed at http://www.diana.pcbi.upenn.edu/tarbase.
RAKE and LNA-ISH reveal microRNA expression and localization in archival human brain
Authors: NELSON PETER T. , BALDWIN DON A. , KLOOSTERMAN WIGARD P. , KAUPPINEN SAKARI , PLASTERK RONALD H.A. , MOURELATOS ZISSIMOS
Published: December 2005

microRNAs (miRNAs) are small (~22 nucleotide) regulatory RNAs which play fundamental roles in many biological processes. Recent studies have shown that the expression of many miRNAs is altered in various human tumors and some miRNAs may function as oncogenes or tumor suppressor genes. However, with the exception of glioblastoma multiforme, the expression of miRNAs in brain tumors is unknown. Furthermore, methods to profile miRNAs from formalin-fixed, paraffin-embedded (FFPE) archival tissues or to study their cellular and subcellular localization in FFPE tissues have been lacking. Here we report the coordinated miRNA expression analysis from the tissue level to the subcellular level, using the RAKE (RNA-primed, array-based, Klenow Enzyme) miRNA microarray platform in conjunction with Locked Nucleic Acid (LNA)-based in situ hybridization (LNA-ISH) on archival FFPE human brains and oligodendroglial tumors. The ability to profile miRNAs from archival tissues at the tissue level, by RAKE microarrays, and at the cellular level by LNA-ISH, will accelerate studies of miRNAs in human diseases.
A general two-step strategy to synthesize lariat RNAs
Authors: WANG YANGMING , SILVERMAN SCOTT K.
Published: December 2005

We describe a general and efficient two-step strategy for lariat RNA synthesis. In the first step, a deoxyribozyme synthesizes 2′,5′-branched RNA. In the second step, T4 RNA ligase closes the loop that completes the lariat. The loop-closure reaction can form either a natural or unnatural lariat isomer, depending on which of the two 3′-termini of the branched RNA reacts with the lone 5′-end. We demonstrate two approaches to control formation of either lariat isomer. In conjunction with other routes for lariat RNA synthesis, the two-step strategy described here will facilitate biochemical studies that require lariat RNAs of varying nucleotide sequence.
40LoVe interacts with Vg1RBP/Vera and hnRNP I in binding the Vg1-Localization Element
Authors: CZAPLINSKI KEVIN , MATTAJ IAIN W.
Published: December 2005

Localizing mRNAs within the cytoplasm gives cells the ability to spatially restrict protein production, a powerful means to regulate gene expression. Localized mRNA is often visible in microscopically observable particles or granules, and the association of mRNA localization with these structures is an indication that particles or granules may be essential to the localization process. Understanding how such structures form will therefore be important for understanding the function of localization RNPs (L-RNPs). We previously identified a novel component of an L-RNP from the Vg1 mRNA from Xenopus oocytes called 40LoVe. 40LoVe interaction with the Vg1-localization element (Vg1LE) was previously shown to be dependent on the VM1 and E2 sequence motifs within the Vg1LE that cross-link to hnRNP I and Vg1RBP/Vera, respectively. We report interaction of these motif-binding proteins with 40LoVe and identify a 40LoVe-Xenopus hnRNP D/AUF1 interaction. We further demonstrate that titration of VM1 and E2 motif binding activity in vivo surprisingly suggests that the motif binding proteins have differing roles during Vg1LE-dependent mRNA localization.
Electrochemical Impedance Spectroscopy as a Tool for Studying Steel Corrosion Inhibition in Simulated Concrete Environments—Red Mud Used as Rebar Corrosion Inhibitor
Authors: Collazo A , Cristóbal MJ , Nóvoa XR , Pena G , Pérez MC
Published: December 2005

Red mud is the main by-product of the Bayer process for alumina extraction from bauxite. Rich in iron, aluminum and silicon oxides, it is believed to have corrosion protection properties. Some are studied in the present paper. The corrosion behavior of steel rebars in chlorine containing solutions and mortars is studied and compared with the same systems containing red mud in suspension (case of solutions) or added as powder to the mix (case of mortars). The results in solution show that red mud is able to maintain steel passivity for more than 90 days in highly chlorinated alkaline solutions while in NaOH and Ca(OH)2 solutions having the same pH pit formation is observable at 25 and 55 days, respectively. Additions of red mud to mortar as powder representing 2 % by weight of cement are able to block chloride depassivation. EIS data allow understanding the protecting mechanism and comparing the behavior in mortar and in solution.
Low Strain-Rate Microstructural Deformation Behavior in 316 Stainless Steel Irradiated in EBR-II
Authors: Cole JI , Allen TR , Tsai H , Yoshitake T , Yamagata I , Akasaka N , Nakamura Y
Published: December 2005

In order to better understand the influence of the radiation-induced defect microstructures on changes in stainless steel deformation behavior, the microstructures of irradiated 12 % cold-worked 316 stainless steel were examined following slow-strain-rate tensile testing. Tensile samples were fabricated from two hexagonal ducts that were irradiated in the outer rows of the Experimental Breeder Reactor. The samples were irradiated at temperatures ranging from approximately 383 to 443°C and doses up to approximately 41 displacements per atom. The tensile tests were conducted at a strain rate of 1 × 10−7 s−1 and test temperature of ∼430°C. Transmission electron microscopy was employed to quantify the defect microstructures of three pairs of samples, each pair having been exposed to similar irradiation conditions. One sample of each pair was taken from the gauge section of a tested tensile sample, and the other was untested. The influence of the defect microstructure on the deformation and fracture behavior is evaluated and results are discussed in light of current theories of deformation behavior in irradiated metals.
Using Dynamic Rheology to Measure Cement-Admixture Interactions
Authors: Chen C-T , Struble LJ , Zhang H
Published: December 2005

The objective of this study was to explore the effects of water-reducing admixtures on the flow behavior of cement pastes using small-amplitude oscillatory rheology. In this technique, a small shear force is applied to the specimen, the strain response is measured, and rheological parameters are calculated. Gelled suspensions exhibit high elastic modulus and yield stress values and dispersed suspensions exhibit low values. The high-range water-reducing admixture based on carboxylic acrylate ester (CAE) fully dispersed the four portland cements used in this study, while the admixture based on sulfonated naphthalene formaldehyde (SNF) dispersed only one of the cements and caused the other three to gel. Such gelation indicates cement-admixture incompatibility. At the same dosage, the CAE gave greater dispersion and more retardation of stiffening than the SNF when mixed with the same cement, but stiffening behaviors were more similar when the admixture dosages were adjusted to provide a similar initial elastic modulus. The incompatible cement-admixture combinations were dispersed when the admixture addition was delayed by a few minutes. Dispersion was also enhanced by increasing the shearing when mixing the paste.
Different Approaches for the Verification of Force Values Measured with Instrumented Charpy Strikers
Authors: Lucon E , Chaouadi R , van Walle E
Published: December 2005

The Charpy test plays a fundamental role in the nuclear field for evaluating the neutron embrittlement of the reactor pressure vessel, specifically in the framework of the so-called Enhanced Surveillance Approach, developed at SCK·CEN and aimed at extracting as much information as possible from Charpy impact tests performed with an instrumented striker. Careful analysis of the instrumented force/deflection traces allows defining important parameters which can help investigate material characteristics such as flow properties, microcleavage fracture stress, crack arrest behavior and alternative characteristic (index) temperatures. For this advanced approach to be successfully applied, confidence in the quality of instrumented force values must be high; as a consequence, extensive research has been performed in order to establish an optimal procedure for the verification of instrumented Charpy strikers. Various approaches will be described in this paper and their applicability and effectiveness discussed. A procedure based on the comparison between yield stresses measured from tensile tests and calculated from instrumented Charpy curves has recently been adopted at SCK·CEN as the recommended in-house procedure for verifying instrumented strikers. This method has shown that for all strikers investigated, the so-called “dynamic” calibration (based on the equalization of dial and calculated energies) yields the most accurate results.
Damping Behavior of AI6061/Albite MMCs
Authors: Seah KHW , Sharma SC , Krishna M
Published: December 2005

AI6061 based metal matrix composites (MMCs) were prepared with 2, 4, and 6 % by weight of albite particulates, respectively, using the liquid metallurgical technique. Sample specimens of dimensions 70 mm by 10 mm by 2 mm were machined from the prepared ingots. The damping properties of the unreinforced matrix alloy and the MMCs were studied over a temperature range of 50° C to 500°C using a dynamic mechanical analyzer. The damping capacity of the composites was observed to increase with the increase in temperature whereas the dynamic modulus was found to decrease with increase in temperature. The damping capacity at a lower temperature may be attributed to the coefficient of thermal expansion mismatch induced dislocations and intrinsic damping of the matrix alloy whereas damping capacity at a higher temperature may be attributed to the matrix/reinforcement interface. Theoretical calculations accurately predicted the damping capacities of the specimen materials only up to the eutectic temperature of the matrix material (200°C). Above this temperature, the discrepancy between theoretical and experimental values increased sharply with increase in temperature. An explanation for this phenomenon is proposed in this paper.
Relationship Between Indentation Hardness and Water to Cement Ratio of Hardened Mortar and Concrete
Authors: Cong DX , Reed MH , Powers LJ , Shotwell BL , Brown BD
Published: December 2005

Accurately estimating the water-to-cementitious materials ratio (w/cm) of hardened concrete is one of the most difficult tasks frequently requested of concrete petrographers. Different methods have been developed and implemented with varying degrees of success. To increase the reliability of estimated w/cm, the indentation hardness of laboratory prepared specimens of neat paste, mortar, and concrete was evaluated using a Buehler semi-automatic testing machine. Preliminary results indicate good correlations between the average indentation hardness measured on the Rockwell HRL scale and the w/cm of the specimens. The data demonstrate a potential for using these correlations to estimate the w/cm of hardened concrete. Testing protocols, sample preparation requirements, and the effects of aggregate and of the composition of concrete mixtures (portland cement and fly ash content) are illustrated. Directions for future work are also discussed.
Effect of Tightening Speed on Thread and Under-Head Coefficient of Friction
Authors: Oliver MP , Jain VK
Published: December 2005

Applying torque to a fastener creates friction as well as clamp-load. Friction and clamp-load are inversely proportional: as friction increases, the amount of clamp-load generated decreases. The speed at which a fastener is tightened has a pronounced affect on the magnitude of friction, and thereby clamp-load generated in a metal joint. This paper examines the relationship between the tightening speed with friction and clamp-load. The applied torque, clamp-load, and under-head torque were measured as the fastener was tightened within a torque/tension load cell. The corresponding thread torque, under-head and thread coefficients of friction values were calculated from equations given in both the DIN946 and ISO16047 standards. One bolt, one washer, and one nut (all of similar hardness) were used for all trials of this study. Two different anti-seize lubricants were used (one composed of molybdenum-disulfide and graphite and the other of mineral oil, nickel, and graphite). Lubricant was applied to both the thread and under-head regions of the bolt prior to torquing. Further trials were executed with the bolt, washer, and nut in the dry, or plain, condition (all of similar hardness). The results of this investigation indicated that the thread and under-head coefficients of friction decreased as speed increased. The programmed speeds ranged from 25 to 700 r/min, with a torque target of 28 N·m. Since the friction coefficients decreased, the amount of clamp-load generated at target torque increased with increasing speed. The average difference in clamp-load from minimum to maximum speed was determined to be 6.3 kN for both lubricants and 1.2 kN for the unlubricated condition.
Influence of Cold Rolling Threads Before or After Heat Treatment on the Fatigue Resistance of High Strength Coarse Thread Bolts for Multiple Preload Conditions
Authors: Stephens RI , Bradley NJ , Horn NJ , Arkema JM , Gradman JJ
Published: December 2005

SI class 12.9 high strength steel bolts were used to investigate the fatigue behavior of bolt threads rolled before/after heat treatment using five different preload values. Bolts were 3/8 UNRC-16 (coarse) and preloads were taken as 1, 50, 75, 90, and 100 % of roll before heat treatment proof stress. Since proof stress was lowered 10 % for roll after heat treatment, these preloads for roll after heat treatment bolts were then actually 1.1, 55, 83, 100, and 110 %. The tests produced a range of R-ratios between 0.03 and 0.92. Maximum near surface residual compressive stresses, obtained via X-ray diffraction, ranged from −600 to −1000 MPa. Axial loads were applied through the nut and all fatigue failures occurred at the first thread of the nut/bolt interface with crescent-shaped cracks dominating in most tests. SEM evaluation indicated all fatigue crack growth regions contained multiple fatigue facets, while final fracture regions contained ductile dimples. Cyclic creep/ratcheting was monitored and little, or none, was observed for preload tests equal to or less than 75 %. The fatigue resistance of the threads rolled after heat treatment with preload stresses of 1 % caused a 147 % increase in 107 cycles fatigue strength compared to roll before heat treatment. This is in agreement with other roll before/after low R-ratio results. However, with higher preload stresses, the roll after heat treatment fatigue strength did not increase. Constant life Haigh diagrams at 105 and 107 cycles were not always in agreement with VDI 2230 bolt preload guidelines.
3D FEA Simulations to Assess Residual Stresses in Riveting Processes
Authors: Atre A , Johnson WS
Published: December 2005

Multiple site damage (MSD) in aircraft structures can be defined by the presence of numerous minute cracks arising at different locations such as rivet holes in lap joints. One source of initiation can be due to residual stresses induced in the lap joints during the riveting process. This paper describes a finite element methodology of a quasistatic, displacement controlled riveting process to capture the local geometry features representative of service hole quality for accurate simulation of residual stresses in riveted lap joints. A three-dimensional finite element (FE) model that takes into account material, geometric, and contact non-linearities is developed using ABAQUS/Standard 6.4-1 to simulate the joining process. The interest of FE simulations is to conduct parametric studies to observe effects of varying hole clearance, misaligned holes, friction, and presence of debris on the residual stress state in the skin. Based on studies conducted, comments are made regarding any observed variation in tensile hoop stress, which is the primary source of fatigue cracks in riveted lap joints. A relation between the rivet-head deformation ratio and rivet-head height with applied displacement is developed using the finite element model, as a means of controlling the rivet-head deformation.
Analysis of Charpy Impact Verification Data: 1993–2003
Authors: Splett JD , McCowan CN
Published: December 2005

Indirect verification tests used to verify the performance of Charpy impact machines according to ASTM Standard E23 were evaluated by the National Institute of Standards and Technology (NIST), and the data from these tests are collected in a database. The data include the capacity and the pendulum design of the impact machine, the energy obtained for each specimen tested, the reference energy for the specimen lot tested, and the test date. The principal use of this data is to track the performance of individual impact machines. However, the data also provide an opportunity to evaluate existing and proposed requirements for the indirect verification of Charpy impact machines. The results of more than 16 000 verification tests are used to compare the current verification requirements of ASTM Standard E23 with those of ISO Standard 148–2. Discussions focus on the identification of reasonable, practical, and meaningful verification requirements that might be proposed for use in both documents.
Anomalous Fatigue Crack Growth Data Generated Using the ASTM Standards
Authors: Forth SC , Newman JC , Forman RG
Published: December 2005

The ASTM standard for fatigue crack growth, E 647, was co-developed by industry and government in the late 1970s to define a standard procedure for generating material crack growth behavior under a variety of loading conditions. The standard specifies tolerances on laboratory procedures, specimen configurations to generate material characterization information of a high integrity. Recent research developing fatigue crack growth rate data has uncovered significant issues with the standard test method and specimen configurations. The data generated has been largely dependent on specimen configuration, i.e., M(T) and C(T) specimens produce very different crack growth rate curves; C(T) specimens of different sizes do not generate the same material response; and finally, the development of steady-state, as defined using constant ΔK testing, does not agree with the data generated with the standard ASTM test method. Therefore, in this paper the authors present data that does not lend confidence in the integrity of the standard C(T) specimen tested using the ASTM standard method and investigate causes for the observed anomalous crack growth rate behavior.
Plasma Cleaning of a Commercially Available Hydroxyapatite-Coated External Fixation Pin by the Radio Frequency Glow Discharge Technique
Authors: Kumar S , Skinner WM
Published: December 2005

The surface chemistry of a commercially available hydroxyapatite (HA)-coated external fixation pin in its as-received state has been studied using X-ray photoelectron spectroscopy (XPS). The XPS investigations revealed that the HA coating on the pin was contaminated with silicon (organosilicone) and it exhibited sub-stoichiometric chemical composition (i.e., Ca/P∼0.9). A comparison of the high resolution XPS spectra of both the HA-coated pin and the inside of its protective elastomer cap revealed that silicon to be in the form of an organosilane transferred from the protective cap to the HA surface, thus contaminating the latter. A parallel plate radio frequency glow discharge plasma cleaning system was successfully employed for removing the surface contaminant (organosilicone) from the HA-coated pin. As confirmed by XPS, plasma cleaning for 15 min was sufficient for achieving complete removal of the silicon contaminant and exposing a clean HA layer with a stoichiometric Ca/P ratio of 1.7.
Analytical Methods and Acceptance Criteria for Cleaning Validation Protocols for Medical Devices
Authors: LeBlanc DA
Published: December 2005

This paper presents alternative methods to utilize in measuring the effectiveness of cleaning processes and to measure effects of changes in a cleaning process for the manufacture of medical device implants. Recommended methods for setting cleaning validation acceptance criteria for various residues are presented, along with analytical methodologies to measure those residues. The advantages of the proposed analytical methods include their applicability to devices other than metallic implants and the fact that they are established analytical technologies.
Survey of Orthopedic Implant Cleanliness Test Methods
Authors: Treece BL
Published: December 2005

In the past, orthopedic implant cleanliness assessment has largely relied on visual and microbiological evaluations; this may not be the case in the future. Test methods to quantity and identify manufacturing residues may need to be added to the cleanliness toolbox to verify that contact materials have been removed to acceptable levels. ASTM has begun exploring this new territory with the F04.15.17. Cleanliness Testing Committee. This paper addresses the need for test methods by reporting a few techniques that may be successful in assessing the cleanliness of metallic implants. The survey describes an extraction technique and several methods that quantify categories of typical contact materials, such as machining oils, coolants and detergents. The methods range from simple gravimetric measurements to employing analytical instrumentation, including Total Organic Analyzers, Inductively Coupled Plasma Spectrometers and Fourier Transform Infrared Spectrometers. The approach of classifying residues as particular categories of contact materials facilitates the application of the techniques across many products and manufacturing processes and allows for a greater degree of standardization, as opposed to identifying specific components of an individual material. The methods described may prompt discussions and provide guidance for future ASTM efforts to develop new standards for orthopedic implants.
An International Evaluation of the Neutron Cross Section Standards
Authors: Carlson AD , Badikov SA , Chen Z , Gai EV , Hale GM , Hambsch F-J , Hofmann HM , Kawano T , Larson NM , Oh S-Y , Pronyaev VG , Smith DL , Tagesen S , Vonach H
Published: December 2005

Work is reported here on the process and present results of an international evaluation of the neutron cross section standards. The evaluations include the H(n,n), 3He(n,p), 6Li(n,t), 10B(n,α), 10B(n,α1γ), 197Au(n,γ), 235U(n,f), and 238U(n,f) standard reactions as well as the 238U(n,γ) and 239Pu(n,f) reactions. This evaluation was performed to include new experiments on the standards that have been made since the ENDF/B-VI evaluation was completed and to improve the evaluation process. Evaluations have been completed for the 6Li(n,t), 197Au(n,γ) and 238U(n,γ) cross sections. Also below 20 MeV the H(n,n), 235U(n,f), 238U(n,f) and 239Pu(n,f) cross sections are completed. Many of the cross sections being evaluated are used in neutron dosimetry for fluence determination. The general trend observed for the evaluations is an increase in the cross sections for most of the reactions from fractions of a percent to several percent compared with the ENDF/B-VI results.
Extensive Revision of the Kernel-based PREVIEW Program and Its Input Data
Authors: Serén T , Wasastjerna F
Published: December 2005

The kernel-based PREVIEW program, which calculates fluences, fluence rates, reaction and damage rates, etc. at a few important out-of-core locations in the Loviisa VVER-440 reactors has been extensively revised. New location-specific dosimetry cross sections based on the newly released IRDF-2002 library have been developed. A few cross-section condensation codes are tried and compared. Generally the results are in good agreement. Small differences may be attributable to the use of single precision and to different representations of the weighting spectrum. Also, some codes use the basic ENDF-format data directly while others use processed data with reduced precision.
Spent Fuel Monitoring with Silicon Carbide Semiconductor Neutron/Gamma Detectors
Authors: Natsume T , Doi H , Ruddy FH , Seidel JG , Dulloo AR
Published: December 2005

Silicon carbide semiconductor radiation detectors have been demonstrated for neutron and gamma-ray monitoring of spent nuclear fuel. Neutrons and gamma rays were monitored simultaneously over a 2050-h period, resulting in a gamma dose of over 6000 Gy to the SiC detector. No changes in the neutron and gamma-ray sensitivity were observed as a result of the gamma-ray exposure. After the spent-fuel measurements, the absolute neutron sensitivity was determined in a standard neutron field, and the degree of gamma-ray and neutron spectrum overlap were determined through exposures in intense gamma ray fields. No overlap was observed for gamma-ray dose rates up to 100 G/h.
Verification of MultiTrans Calculations by the VENUS-3 Benchmark Experiment
Authors: Kotiluoto P
Published: December 2005

The MultiTrans software has been developed at VTT Technical Research Centre of Finland for 3D radiation transport problems. Adaptive tree multigrid technique is used as a deterministic solution method. This enables local refinement of the calculation grid combined with the use of effective multigrid acceleration on tree-structured nested grids: starting from a fast solution on coarse grid, successive solutions are obtained on finer and finer grids. In the MultiTrans code, simplified spherical harmonics (SP3) radiation transport approximation is used. In order to test the applicability of the new MultiTrans code to reactor dosimetry problems, light water reactor pressure vessel steel (LWR-PVS) benchmark experiment VENUS-3 (with partial length shielded assemblies) was chosen. The results show good agreement to the experimental reaction rates of the VENUS-3 benchmark, demonstrating the applicability of the new MultiTrans code in reactor dosimetry.
Neutron and Photon Dosimetry at the LR-0 Reactor Using Paired Detectors
Authors: Fernandes AC , Novák E , Cardoso J , Santos L , Marques JG , Rýpar V
Published: December 2005

Paired thermoluminescence dosimeters and ionization chambers were used for characterizing mixed (neutron and photon) radiation fields at the LR-0, a zero power model of VVER reactors. Detector responses were investigated in standard photon and thermal neutron fields. A good agreement was obtained among the doses measured with the two methods. Furthermore, the measured photon and neutron attenuation values are consistent with those from evaluated, independent data.
Determination of Adjusted Neutron Spectra in Different MUSE Configurations by Unfolding Techniques
Authors: Plaschy M , Destouches C , Chawla R , Beretz D , Mellier F , Servière H , Fougeras P , Chaussonnet P , Domergue C , Laurens J-M , Philibert H
Published: December 2005

Investigations of spectrum adjustment by unfolding techniques for different locations of critical and driven subscritical MUSE4 configurations are presented. The current analysis is based on the recent accomplishment of specific foil activation measurements and on the use of the unfolding code STAY'SL in conjunction with IRDF-90 and IRDF-2002 dosimetry libraries. Specific developments have been conducted to consider the uncertainties associated with the determination of the experimental absolute reaction rates and the initial calculated spectrum in the most realistic manner. In this context, the iterative adjustment process for the neutron spectrum is established on the basis of variance/covariance matrices defined for the three types of input parameters, i.e., the experimental reaction rates, the initial spectrum, and the dosimetry nuclear data files. The results highlight the spectral variations between different locations of the MUSE4 cores, in particular the characteristic behavior of a subcritical configuration driven by an external T(d,n)He4 (14 MeV neutrons) source.
Experimental and Calculation Investigations of the Space-Energy Neutron and Photon Distribution in the Vicinity of Reactor Pressure Vessel and Surveillance Specimen Box of New Type in the WWER-1000 Mock-Up
Authors: Ošmera B , Mařík M , Cvachovec F , Tsofin V , Lomakin S , Zaritsky S , Egorov A , Brodkin E
Published: December 2005

The radiation field parameters in the vicinity of new type of WWER-1000 surveillance specimens boxes and in RPV simulator have been investigated in the WWER-1000 Mock-up in the reactor LR-0. The neutron and photon spectra have been measured with stilbene cylindrical crystals in the energy range approximately from 0.5 MeV to 10 MeV. The experimental values of integral neutron field parameters (attenuations of integral neutron flux densities between different points of mock-up as well as the spectral indices, i.e., ratios of integral neutron flux densities with different thresholds) were obtained also. The mock-up (LR-0 reactor) power monitoring during measurements was carried out with two fission chambers, one fixed, one moveable axially, so that four orders in power were covered. The experimental data (spectra, attenuation factors, and spectral indices) have been compared with the calculation results. The sensitivity to parameters of calculation model and method was evaluated also.