bluuebunny/crossref_metadata_2025 huggingface dataset:
Spatial and temporal patterns of bone formation in ectopically pre‐fabricated, autologous cell‐based engineered bone flaps in rabbits
Authors: Scheufler Oliver , Schaefer Dirk J. , Jaquiery Claude , Braccini Alessandra , Wendt David J. , Gasser Jürg A. , Galli Raffaele , Pierer Gerhard , Heberer Michael , Martin Ivan
Published: August 2008

Biological substitutes for autologous bone flaps could be generated by combining flap pre‐fabrication and bone tissue engineering concepts. Here, we investigated the pattern of neotissue formation within large pre‐fabricated engineered bone flaps in rabbits. Bone marrow stromal cells from 12 New Zealand White rabbits were expanded and uniformly seeded in porous hydroxyapatite scaffolds (tapered cylinders, 10–20 mm diameter, 30 mm height) using a perfusion bioreactor. Autologous cell‐scaffold constructs were wrapped in a panniculus carnosus flap, covered by a semipermeable membrane and ectopically implanted. Histological analysis, substantiated by magnetic resonance imaging (MRI) and micro‐computerized tomography scans, indicated three distinct zones: an outer one, including bone tissue; a middle zone, formed by fibrous connective tissue; and a central zone, essentially necrotic. The depths of connective tissue and of bone ingrowth were consistent at different construct diameters and significantly increased from respectively 3.1 ± 0.7 mm and 1.0 ± 0.4 mm at 8 weeks to 3.7± 0.6 mm and 1.4 ± 0.6 mm at 12 weeks. Bone formation was found at a maximum depth of 1.8 mm after 12 weeks. Our findings indicate the feasibility of ectopic pre‐fabrication of large cell‐based engineered bone flaps and prompt for the implementation of strategies to improve construct vascularization, in order to possibly accelerate bone formation towards the core of the grafts.
Endoluminal Norepinephrine Inhibits Smooth Muscle Activity of the Pig Pyeloureter by Stimulation of β‐Adrenoceptors without Side Effects
Authors: Mortensen Jens , Holst Uffe , Jakobsen Jørn Skibsted , Andreasen Frederik
Published: August 2008

Abstract:  It has been demonstrated in pigs that endoluminal administration of norepinephrine reduces the increase in renal pelvic pressure during perfusion. The purposes were to describe concentration–response relationship and receptor mechanism of the effect of norepinephrine on muscle function of pyeloureter and to reveal possible side effects on cardiovascular and renal functions. Renal pelvis was perfused, while pelvic pressure, cardiovascular and renal functional parameters were recorded. In group A, a pelvic pressure increase was examined during pressure flow studies with norepinephrine solutions (0, 1, 5, 50 and 100 µg/ml). In group B, pelvis was perfused with 6 ml/min. norepinephrine solutions (0, 0.001, 0.01, 0.1 and 1 µg/ml). In group C, pelvis was perfused with 6 ml/min. norepinephrine, norepinephrine + sotalol 10−6 mol/l and norepinephrine + phentolamine 10−6 mol/l. Norepinephrine solutions of 0, 10−8, 10−7, 10−6, 10−5 and 10−4 mol/l were used. In group A, all norepinephrine solutions lowered the pelvic pressure increase significantly. Large increases in plasma and urine norepinephrine occurred with 50 and 100 µg/ml, but cardiovascular and renal functions remained unchanged. In group B, a significant diminishing pelvic pressure increase with all solutions was seen with a significant difference between all solutions. In group C, norepinephrine demonstrated a concentration–response curve with EC50 between 10−8 and 10−7 mol/l (10−7.27±0.40). Sotalol had a smooth muscle inhibitory effect on the pyeloureter and inhibited the effect of norepinephrine increasing EC50 by about a factor 10 (10−6.40±1.17). No convincing effect of phentolamine was observed. Endoluminal norepinephrine probably stimulates β‐adrenoceptors and inhibits a renal pelvis pressure increase to perfusion in a dose‐related way without side effects. Endoluminal norepinephrine is safe in pigs and may be useful under endoscopy of the pyeloureter.
Physiologically Motivated Time‐Delay Model to Account for Mechanisms Underlying Enterohepatic Circulation of Piroxicam in Human Beings
Authors: Tvrdonova Martina , Dedik Ladislav , Mircioiu Constantin , Miklovicova Daniela , Durisova Maria
Published: August 2008

Abstract:  The study was conducted to formulate a physiologically motivated time‐delay (PM TD) mathematical model for human beings, which incorporates disintegration of a drug formulation, dissolution, discontinuous gastric emptying and enterohepatic circulation (EHC) of a drug. Piroxicam, administered to 24 European, healthy individuals in 20 mg capsules Feldene® Pfizer, was used as a model drug. Plasma was analysed for piroxicam by a validated high‐performance liquid chromatography method. The PM TD mathematical model was developed using measured plasma piroxicam concentration‐time profiles of the individuals and tools of a computationally efficient mathematical analysis and modeling, based on the theory of linear dynamic systems. The constructed model was capable of (i) quantifying different fractions of the piroxicam dose sequentially disposable for absorption and (ii) estimating time delays between time when the piroxicam dose reaches stomach and time when individual of fractions of the piroxicam dose is disposable for absorption. The model verification was performed through a formal proof, based on comparisons of observed and model‐predicted plasma piroxicam concentration‐time profiles. The model verification showed an adequate model performance and agreement between the compared profiles. Accordingly, it confirmed that the developed model was an appropriate representative of the piroxicam fate in the individuals enrolled. The presented model provides valuable information on factors that control dynamic mechanisms of EHC, that is, information unobtainable with the models proposed for the EHC analysis previously.
Interphase Cytogenetics for 1p19q and t(1;19)(q10;p10) may Distinguish Prognostically Relevant Subgroups in Extraventricular Neurocytoma
Authors: Rodriguez Fausto J. , Mota Renan A. , Scheithauer Bernd W. , Giannini Caterina , Blair Hilary , New Kent C. , Wu Kevin J. , Dickson Dennis W. , Jenkins Robert B.
Published: August 2008

Co‐deletion of chromosome arms 1p and 19q, characteristic of oligodendroglial tumors, was recently found to be mediated by t(1;19)(q10;p10). To evaluate the prevalence of 1p19q co‐deletion and t(1;19) in extraventricular neurocytomas (EVN), we studied tumors from 23 patients, including 13 females and 10 males (median age at diagnosis 34 years, range 2–76 years). Fluorescence in situ hybridization (FISH) studies were performed with probes targeting 1p36/1q25 and 19q13/19p13 to assess for 1p19q co‐deletion, as well as chromosome 1 α‐satellite and 19p12 to detect t(1;19)(q10;p10). FISH was successful in 21 (91%) cases and demonstrated 1p19q co‐deletion in five cases (24%) or isolated 1p loss in two cases (10%). Evidence for t(1;19) was found in four (of five) cases with 1p19q co‐deletion. Three tumors with 1p19q loss and t(1;19) demonstrated atypical histologic features, compared with one (of 17) tumors without 1p19q co‐deletion (P = 0.01, Fisher exact test). In addition, tumors with t(1;19) showed increased mitotic activity compared with tumors without t(1;19) (P = 0.045; Wilcoxon rank sum test). The four patients with t(1;19) developed tumor recurrence (n = 3), or expired (n = 2) 3.5 to 5.5 years after first resection. These results suggest that 1p19q loss and t(1;19) occur in a subset of EVN, and may be associated with aggressive histology in these tumors.
Activation of ATP/UTP‐selective receptors increases blood flow and blunts sympathetic vasoconstriction in human skeletal muscle
Authors: Rosenmeier Jaya B. , Yegutkin Gennady G. , González‐Alonso José
Published: August 2008

Sympathetic vasoconstriction is blunted in the vascular beds of contracting skeletal muscle in humans, presumably due to the action of vasoactive metabolites (functional sympatholysis). Recently, we demonstrated that infusion of ATP into the arterial circulation of the resting human leg increases blood flow and concomitantly blunts α‐adrenergic vasoconstriction in a similar manner to that during moderate exercise. Here we tested the hypothesis that ATP, rather than its dephosphorylated metabolites, induces vasodilatation and sympatholysis in resting skeletal muscle via activation of ATP/UTP‐selective receptors. To this aim, we first measured leg blood flow (LBF), mean arterial pressure (MAP), cardiac output, leg arterial–venous (a–v) O2difference, plasma ATP and soluble nucleotidase activities during intrafemoral artery infusion of adenosine, AMP, ADP, ATP or UTP in nine healthy males. Comparison of the doses of nucleotides and adenosine required for a similar increase in LBF from ∼0.5 l min−1at baseline to ∼3.5 l min−1(without altering MAP but increasingsignificantly) revealed the following rank order of vasoactive potency: ATP (100) = UTP (100) >> adenosine (5.8) > ADP (2.7) > AMP (1.7). The infusions did not cause any shifts in plasma ATP level or soluble serum nucleotidase activities. Combined infusion of the vasodilatory compounds and the sympathetic vasoconstrictor drug tyramine increased plasma noradrenaline in all hyperaemic conditions, but only caused leg and systemic vasoconstriction and augmented O2extraction during adenosine, AMP and ADP infusion (LBF from 3.2 ± 0.3 to 1.8 ± 0.2 l min−1; 3.7 ± 0.4 to 1.7 ± 0.2 l min−1and 3.3 ± 0.4 to 2.4 ± 0.3 l min−1, respectively,P< 0.05). These findings in humans suggest that the vasodilatory and sympatholytic effects of exogenous ATP in the skeletal muscle vasculature are largely mediated via ATP itself rather than its dephosphorylated metabolites, most likely via binding to endothelial ATP/UTP‐selective P2Y2receptors. These data are consistent with a role of ATP in skeletal muscle hyperaemia in conditions of increased sympathetic nerve drive such as exercise or hypoxia.
Hyperthermia impairs short‐term memory and peripheral motor drive transmission
Authors: Racinais S. , Gaoua N. , Grantham J.
Published: August 2008

The aims of this study were to determine (i) the effect of passive hyperthermia on motor drive and cognitive function, and (ii) whether head cooling can limit the hyperthermia‐induced alterations. Sixteen subjects were randomly exposed for 2 h to three different conditions: control (Con, 20°C), hot (Hot, 50°C) and hot head cool (HHC – where cold packs were applied to the head under Hot conditions). Three cognitive tests measuring attention and two measuring memory were performed. Neuromuscular testing included electrically evoked muscle action potentials (M‐waves) and reflex waves (H‐reflex) at rest and during brief (4–5 s) and sustained (120 s) maximal voluntary contractions (MVC) of the plantar flexors. All the tests were performed in the environmental room. During brief MVC, torque was significantly lower in both Hot and HHC as compared to Con (P < 0.05). The decrease in muscle activation was significant in Hot (P < 0.05) but not in HBC (P= 0.07). This was accompanied by peripheral failures in the transmission of the neural drive at both spinal (significant decrements in H‐reflexes and V‐waves, P < 0.05) and neuromuscular junction (significant decrements in M‐waves, P < 0.05) levels. During sustained MVC, muscle activation was further depressed (P < 0.05) without any concomitant failures in M‐waves, suggesting neural activation adjustments occurring probably at the supraspinal level. Cerebral perturbations were confirmed by significant decrements in both memory tests in Hot as compared with Con (P < 0.05) but not in simple tests (attention tests) that were not affected by hyperthermia. The decrement in memory capacity suggested the existence of frontal lobe activity impairments. Thus, HHC preserved memory capacity but not the visual memory.
Dopamine D1 receptor inhibition of NMDA receptor currents mediated by tyrosine kinase‐dependent receptor trafficking in neonatal rat striatum
Authors: Tong Huaxia , Gibb Alasdair J.
Published: August 2008

NMDA receptors are of particular importance in the control of synaptic strength and integration of synaptic activity. Dopamine receptor modulation of NMDA receptors in neonatal striatum may influence the efficacy of synaptic transmission in the cortico‐striatal pathway and if so, this modulation will affect the behaviour of the basal ganglia network. Here, we show that in acute brain slices of neonatal (P7) rat striatum the dopamine D1 receptor agonist SKF‐82958 significantly decreases NMDA receptor currents in patch‐clamp whole‐cell recordings. This inhibition is not abolished by application of a G protein inhibitor (GDP‐β‐S) or irreversible G protein activator (GTP‐γ‐S) suggesting a G protein‐independent mechanism. In addition, intracellular application of protein tyrosine kinase inhibitors (lavendustin A or PP2) abolished D1 inhibition of NMDA currents. In contrast, in older animals (P28) D1 receptor activation produces a potentiation of the NMDA response which suggests there is a developmental switch in D1 modulation of striatal NMDA receptors. Single‐channel recordings show that direct D1 receptor inhibition of NMDA receptors cannot be observed in isolated membrane patches. We hypothesize that D1 inhibition in whole‐cell recordings from neonatal rats may be mediated by a change in NMDA receptor trafficking. Consistent with this hypothesis, intracellular application of a dynamin inhibitory peptide (QVPSRPNRAP) abolished D1 inhibition of NMDA receptor currents. We therefore conclude that a tyrosine kinase‐dependent alteration of NMDA receptor trafficking underlies D1 dopamine receptor‐mediated down‐regulation of NMDA receptor currents in medium spiny neurons of neonatal rat striatum.
Schwann cells modulate short‐term plasticity of cholinergic autaptic synapses
Authors: Perez‐Gonzalez Anna P. , Albrecht David , Blasi Juan , Llobet Artur
Published: August 2008

Nicotinic synapses in the autonomous nervous system display use‐dependent plasticity but the contribution of cellular environment, as well as the presynaptic mechanisms implicated in this process remain to be determined. To address these questions synaptic function was assayed in rat superior cervical ganglion (SCG) neurons microcultured in isolation from any other cell type and compared to those microcultured in the presence of Schwann cells of ganglionar origin. Schwann cells were not required for synapse formation in vitro because functional cholinergic autaptic synapses were established in both experimental conditions. The number of synapses was comparable between the two culture conditions but the frequency of spontaneous miniature excitatory postsynaptic currents was enhanced in those neurons grown in direct contact with glial cells. Autapses displayed facilitation and depression, both processes being determined by the fraction of vesicles from the readily releasable pool discharged by an action potential. At high release probabilities vesicles were more efficiently mobilized, thus promoting depression, whilst low release probabilities made facilitation likely to occur. Schwann cells did not modify significantly facilitation but increased synaptic depression. In single cell microcultures, paired pulse stimuli showed a monoexponential recovery from depression with a time constant of ∼60 ms, while in microcultures developed together with glial cells, recovery was bi‐exponential with a significantly slower time course. Altogether these results show that Schwann cells from sympathetic ganglia directly modulate use‐dependent plasticity of nicotinic synapses in vitro by enhancing short‐term depression.
Soret and Dufour Effects on Free Convection Heat and Mass Transfer From a Horizontal Flat Plate in a Darcy Porous Medium
Authors: Lakshmi Narayana P. A. , Murthy P. V. S. N.
Published: August 2008

The effect of Soret and Dufour parameters on free convection from a horizontal flat plate in a Darcian fluid saturated porous medium is analyzed using the similarity solution technique. With constant wall temperature and concentration, the similarity solution is possible even when Soret and Dufour effects are considered in the medium. The transformed coupled systems of ordinary differential equations involve parameters such as the buoyancy ratio parameter N and diffusivity ratio Le in addition to the Soret Sr and Dufour Df parameters. The effect of all these parameters on the convective transport has been analyzed, and the variation of heat and mass transfer coefficients with Dufour and Soret parameters is presented through computer generated graphs.
Effect of Velocity and Temperature Boundary Conditions on Convective Instability in a Ferrofluid Layer
Authors: Nanjundappa C. E. , Shivakumara I. S.
Published: August 2008

A variety of velocity and temperature boundary conditions on the onset of ferroconvection in an initially quiescent ferrofluid layer in the presence of a uniform magnetic field is investigated. The lower boundary of the ferrofluid layer is assumed to be rigid-ferromagnetic, while the upper boundary is considered to be either rigid-ferromagnetic or stress-free. The thermal conditions include a fixed heat flux at the lower boundary and a general convective, radiative exchange at the upper boundary, which encompasses fixed temperature and fixed heat flux as particular cases. The resulting eigenvalue problem is solved using the Galerkin technique and also by the regular perturbation technique when both boundaries are insulated to temperature perturbations. It is observed that an increase in the magnetic number and the nonlinearity of fluid magnetization as well as a decrease in Biot number are to destabilize the system. Further, the nonlinearity of fluid magnetization is found to have no effect on the onset of ferroconvection in the absence of the Biot number.
Noise Prediction of a Centrifugal Fan: Numerical Results and Experimental Validation
Authors: Ballesteros-Tajadura Rafael , Velarde-Suárez Sandra , Hurtado-Cruz Juan Pablo
Published: August 2008

Centrifugal fans are widely used in several applications, and in some cases, the noise generated by these machines has become a serious problem. The centrifugal fan noise is frequently dominated by tones at the blade passing frequency as a consequence of the strong interaction between the flow discharged from the impeller and the volute tongue. In this study, a previously published aeroacoustic prediction methodology (Cho, Y., and Moon, Y.J., 2003, “Discrete Noise Prediction of Variable Pitch Cross-Flow Fans by Unsteady Navier-Stokes Computations,” ASME J. Fluids Eng., 125, pp. 543–550) has been extended to three-dimensional turbulent flow in order to predict the noise generated by a centrifugal fan. A three-dimensional numerical simulation of the complete unsteady flow on the whole impeller-volute configuration has been carried out using the computational fluid dynamics code FLUENT®. The unsteady forces applied by the fan blades to the fluid are obtained from the data provided by the simulation. The Ffowcs Williams and Hawkings model extension of Lighthill’s analogy has been used to predict the aerodynamic noise generated by the centrifugal fan from these unsteady forces. Also, the noise generated by the fan has been measured experimentally, and the experimental results have been compared to the numerical results in order to validate the aerodynamic noise prediction methodology. Reasonable agreement has been found between the numerical and the experimental results.
Fractal Model for Thermal Contact Conductance
Authors: Zou Mingqing , Yu Boming , Cai Jianchao , Xu Peng
Published: August 2008

A random number model based on fractal geometry theory is developed to calculate the thermal contact conductance (TCC) of two rough surfaces in contact. This study is carried out by geometrical and mechanical investigations. The present study reveals that the fractal parameters D and G have important effects on TCC. The predictions by the proposed model are compared with existing experimental data, and good agreement is observed by fitting parameters D and G. The results show that the effect of the bulk resistance on TCC, which is often neglected in existing models, should not be neglected for the relatively larger G and D. The main advantage of this model is the randomization of roughness distributions on rough surfaces. The present results also show a better agreement with the practical situation than the results of other models. The proposed technique may have the potential in prediction of other phenomena such as friction, radiation, wear and lubrication on rough surfaces.
Determination of Gasket Stress Levels During Thermal Transients
Authors: Brown Warren , Derenne Michel , Bouzid Abdel-Hakim
Published: August 2008

The leakage of bolted flange joints at high temperature or during transient thermal shock is a well recognised problem. However, the present pressure vessel design codes do not address the effects of temperature on the integrity of the bolted joint, other than material properties. A research project currently being conducted at Ecole Polytechnique is intended to provide designers with an analytic approach for establishing the effects of thermal loading on the joint sealing ability. This paper is the fourth to be published as part of this research project. The presented analysis method enables the determination of the temperature response of the joint components to a transition in internal fluid temperature. Using this data, the worst case operating scenario may be selected and calculations performed to determine the impact of the temperature transition on the gasket stress levels. The presented analytical method is verified by comparison to finite element analysis and experimental measurement.
Simplified Sealing Test Procedure of Gaskets Based on Compressive Strain
Authors: Kobayashi Takashi , Nishida Takahito , Yamanaka Yuki
Published: August 2008

With the recent increase of safety and environmental concern, the estimation of leak rate of a gasketed flanged connection in piping systems is an important subject to be studied. In order to estimate the leak rate, the sealing behavior of a gasket must be known. Currently, evaluation methods of the sealing behavior are proposed in the North America and Europe independently. One of the problems is that the representations of the sealing behavior are rather complex in both the methods. Thus, gasket tests take a long time to perform and cost much. The authors have carried out investigations on the sealing behavior of compressed fiber sheet gaskets and have shown that the leak rate is uniquely determined by the compressive strain of gasket. This fact makes the test procedure much easier eliminating complex loading-unloading sequences. A simplified leak testing procedure, in which a simple one-way loading is employed, has proposed. Furthermore, an equation for the sealing behavior of gasket, in which the effect of dimensions of gaskets is taken into consideration, has proposed. In this study, investigations on the sealing behaviors are overviewed first. Then, it is shown that the conventional sealing behavior based on the gasket stress is easily obtained from the sealing behavior based on the gasket strain and the stress-strain diagram of gasket. Both the sealing behavior and the stress-strain diagram of gasket are expressed by equations in this method. Finally, it has also shown that the sealing behavior obtained by the simplified test can be fully converted to the ROTT (ROom Temperature Tightness Test) forms.
A Simplified Modeling of Gasket Stress-Strain Curve for FEM Analysis in Bolted Flange Joint Design
Authors: Nagata Satoshi , Shoji Yasumasa , Sawa Toshiyuki
Published: August 2008

Semi-metal and non-metal gaskets (spiral wound, joint sheet, etc.) are well known that their stress-strain curve shows strong nonlinearity and hysteresis. These characteristics should be considered, when we analyze the behavior of a bolted flange joint. Regarding the analysis of bolted flange joints, authors had proposed a simplified modeling method of gasket stress-strain curve for FEM analysis in the previous PVP conferences. The method approximates the nonlinearity of gasket stress-strain relation using two different linear elastic moduli in loading and unloading, respectively. This paper provides that the comparison of computed results due to the simplified analysis and the ones due to accurate nonlinear analysis that uses a nonlinear-hysteresis gasket model. This paper also proposes the guidance to determine the two linear elastic moduli for the simplified modeling. Since the simplified analysis gives a good approximation, we conclude that the method is very useful for the analysis of bolted flange joints, especially in design stage of pressure vessel flanges or piping flanges.
An Experimental Investigation on Frictional Properties of Bolted Joints
Authors: Jiang Yanyao , Zhang Ming , Park Tae-Won , Lee Chu-Hwa
Published: August 2008

By using an approach developed to determining the torque-tension relationship for bolted joints, frictional properties of several typical bolted joints were studied experimentally. The approach allows for the direct determination of the thread friction and the bearing friction between the nut and its bearing surface independently. Detailed studies were made on the influences of the size and shape of the hole, the use of a slot in a bolted joint, contact area and position, and other factors such as turning speed, coating, and the use of wax on the bearing surface. The contact area and position of the washer have a marginal effect on the bearing friction. The organic coating on the nuts reduces the bearing friction significantly. Nuts with organic coating over a washer with zinc finish provide the smallest and the most consistent bearing friction. Experiments on thread friction shows that prevailing torque nuts with distorted threads and nylon inserts provided trivial benefits for preventing “self-loosening” of the nut. Repeated tightening-loosening generally increases frictions in a bolted joint. It was noted that the data scatter of the experimental results of frictions in a bolted joint may overshadow the influence of size, speed, and contact positions. The results from the experimental investigation will help to better design bolted joints.
Systematical FE Analysis of Bolt Assembly Process of Pipe Flange Connections
Authors: Takaki Tomohiro , Fukuoka Toshimichi
Published: August 2008

In bolt assembly process of pipe flange connections, repeated bolt-up operations are conducted to achieve uniform preloads. Nobody, however, knows how many times of bolt-up operation is required to achieve uniform preloads. It is important for practicing workers to know the number of bolt-up operations. The number of bolt-up operation required to get uniform bolt preloads depends on the nominal diameter of pipe flange, the number of bolts, the types of gasket, etc. In this study, systematical finite element analyses of bolt-up operation are conducted for JPI class 150in and 300in flanges with a compressed asbestos sheet gasket. The number of bolt-up operations required to achieve uniform preloads is estimated for each pipe flange connection.
Comparison of Leak Rates Predicted by ROTT Constants With Experimental Data From a 16″ and 24″ Pressure Vessel
Authors: Bibel George D.
Published: August 2008

Leak rates on two pressure vessels were experimentally determined. The first vessel was tested with a pair of 24″ flanges class 150 raised face weld neck flanges, the second vessel had a pair of 16″ class 300 RFWN. Comparisons between the experimental data and the predictions made by the ROTT gasket constants were made.
Fracture Behaviour of Mis-Matched Dissimilar Welds: Experimental Results
Authors: Martin Gre´goire , Hornet Patrick , Koc¸ak Mustafa , Motarjemi Afshin K.
Published: August 2008

In nuclear plants, ferritic-austenitic welded joints are commonly used. To better understand their fracture performances, EDF and GKSS have carried out a joint R&D project. In order to study the only influence of the strength mismatch and not of the Heat Affected Zone (HAZ), diffusion bonding process has been used. The characterization plan included numbers of tensile and fracture mechanics tests, on homogenous and bi-material specimens. Some Single Edge Notched Bending specimens (SENB) with the crack at different positions (that is to say in the ferrific side, austenitic side and finally at the interface) were used for the fracture toughness evaluation of the bi-material configuration. They showed the effect of strength mismatch relaxing the crack tip stress state at the interface. The paper will discuss in detail further features of the ductile and brittle fracture observed on this bi-material system.
Fracture Behaviour of Mis-Matched Dissimilar Welds: Numerical Simulation Using Local Approach
Authors: Madi Yazid , Besson Jacques , Martin Gre´goire , Hornet Patrick , Koc¸ak Mustafa
Published: August 2008

The safety assessment of welded structures still remains an important industrial problem. In this study, a simple diffusion bonded bi-material jonction has been made in order to analyse the mismatch effect. It consists of an assembly of ferritic and austenitic steels which are representative of nuclear pressure vessel. Each material has been tested using smooth and notched tensile bars. These tests were used to adjust the parameters of local approach based on the Rousselier model. Bi-material structures including notch tensile bars, Charpy specimens and single-edge notch bend specimens were tested and simulated using the Finite Element method. The correct test/computation agreement shows that the adjusted parameters on the homogeneous specimens can be transferred to heterogeneous structures.
Lump-Pass Welding Simulation Technology Development for Shipbuilding Applications
Authors: Yang Y. P. , Brust F. W. , Kennedy J. C.
Published: August 2008

A lump-pass welding simulation technology was developed for shipbuilding and ship repair applications based on Battelle and Caterpillar developed VFT™ weld modeling software. To develop this technology, we reanalyzed a 3D multi-pass model that was originally used in the NIST project where VFT™ was developed. In this model, good agreement was achieved between the moving arc simulation and the experimental data. By reanalyzing this model using lump-pass technology, the heat input calculation method was developed. To further establish the efficiency of the lump-pass technology, we performed analyses on a structural configuration common to the maritime industry. The structure consisted of many longitudinal and transverse stiffeners that were welded vertically at stiffener interface locations and welded horizontally to a one-inch thick base plate. These welds included numerous multi-pass tee and butt joints. For verifying the accuracy of the lump-pass weld simulation technology, an actual structural mock-up was built with FCAW and SMAW processes. Additionally, we performed a detailed moving arc solution to compare with the lump-pass solution of the same weld sequence to further evaluate the efficacy of the lump-pass approach. The simulation results show that the lump-pass approach is suitable for predicting weld-induced distortion in ship fabrication.
Generation Behavior of Thermal and Residual Stresses Due to Phase Transformation During Welding Heat Cycles
Authors: Mochizuki Masahito , Matsushima Shogo , Toyoda Masao , Zhang Zhiliang , Gundersen O̸yvind , Thaulow Christian
Published: August 2008

Weld residual stress is possible to be controlled by considering and changing mechanical properties of the materials. History of thermal stress due to phase transformation and residual stress during welding heat cycles is studied in order to investigate the generating mechanism of residual stress and the effects of material properties on stress generation. Two materials of high-tensile strength steels are used in the numerical simulation and experiment. Material property of each microstructural phase is used and the time- and temperature-dependant proportion of microstructure are considered by using CCT-diagram in the analysis. Thermal stress history obtained by the simulation agrees well with the experimental result during welding heat cycles.
Determination of Constraint-Modified J-R Curves for Carbon Steel Storage Tanks
Authors: Lam P.-S. , Chao Y. J. , Zhu X.-K. , Kim Y. , Sindelar R. L.
Published: August 2008

Mechanical testing of A285 carbon steel, a storage tank material, was performed to develop fracture properties based on the constraint theory of fracture mechanics. A series of single edge-notched bend (SENB) specimen designs with various levels of crack tip constraint were used. The variation of crack tip constraint was achieved by changing the ratio of the initial crack length to the specimen depth. The test data show that the J-R curves are specimen-design-dependent, which is known as the constraint effect. A two-parameter fracture methodology is adopted to construct a constraint-modified J-R curve, which is a function of the constraint parameter, A2, while J remains the loading parameter. This additional fracture parameter is derived from a closed form solution and can be extracted from the finite element analysis for a specific crack configuration. Using this set of SENB test data, a mathematical expression representing a family of the J-R curves for A285 carbon steel can be developed. It is shown that the predicted J-R curves match well with the SENB data over an extensive amount of crack growth. In addition, this expression is used to predict the J-R curve of a compact tension specimen (CT), and reasonable agreement to the actual test data is achieved. To demonstrate its application in a flaw stability evaluation, a generic A285 storage tank with a postulated axial flaw is used. For a flaw length of 10% of the tank height, the predicted J-R curve is found to be similar to that for a SENB specimen with a short notch, which is in a state of low constraint. This implies that the use of a J-R curve from the ASTM (American Society for Testing and Materials) standard designs, which typically are high constraint specimens, may be overly conservative for analysis of fracture resistance of large structures.
Investigating the Constraint Effect in a Particulate Composite Material
Authors: Liu C. T.
Published: August 2008

In this study, the effect of constraint on the critical Mode I stress intensity factor for the onset of crack growth was investigated in a particulate composite material, containing hard particles in a rubbery matrix. Uniaxial specimens with different specimen thicknesses and initial crack lengths were tested under a constant strain rate of 8 cm/cm/min at room temperature. The tested data was analyzed and the results are discussed.
Fracture Toughness Properties of Savannah River Site Storage Tank ASTM A285 Low Carbon Steel
Authors: Subramanian K. H. , Duncan A. J. , Sindelar R. L.
Published: August 2008

A materials test program was developed to measure mechanical properties of ASTM A285 Grade B low carbon steel for application to structural and flaw stability analysis of storage tanks at the Department of Energy (DOE) Savannah River Site (SRS). Under this plan, fracture toughness and tensile testing are being performed at conditions that are representative of storage tank conditions on steels that span compositions within ASTM A285 specifications. The testing is being done within the framework of a statistical test matrix and the data collected will be used to develop a predictive model for materials properties. The results presented herein are limited to a subset of data comparing for comparison of a recent vintage steel versus an older steel for fracture resistance behavior. These preliminary results indicate that dynamic loading rates result in a greater increase in the fracture toughness response in the case of the recent vintage steels of lower carbon content when compared to the archival heat of high carbon content. In addition, ductile tearing in the archival, high carbon steel was more likely to be interrupted by cleavage fracture at lower fracture energies than the modern, low carbon steel.
The Effects of Intercritical Heat Treatment of the SA508 Grade 3 Class 1 Steel Before Welding on the Mechanical Properties in Its Welded Joint
Authors: Kim Jeong-Tae , Yang Byung-Il , Kwon Hee-Kyung
Published: August 2008

In order to improve the toughness in the welded heat affected zone (HAZ) of the SA508 Grade 3 Class 1 steel, the intercritical heat treatment (IHT) has been applied before the welding. The application of the IHT before welding resulted in the decrease of fracture appearance transition temperature (FATT50) and 68Joule transition temperature (vTr68). The improved effects of the IHT on the mechanical properties of this steel have been consistently preserved in the HAZ and the effect of the IHT before welding on the transition temperatures in the HAZ of this steel was much better than those of base metal. These positive results were closely related with the newly formed sub-grains, the spheoridized carbides precipitated at sub-grain boundaries and lath boundaries which would have been acted as obstacles to the cleavage propagation.
Air Clearing Oscillation Produced by APR1400 Prototype Sparger
Authors: Cho Seok , Park Choon-Kyung , Kim Hwan-Yeol , Chun Se-Young , Song Chul-Hwa , Baek Won-Pil
Published: August 2008

KAERI has performed a series of experiments to investigate the performance of APR1400 prototype sparger in view of the dynamic load oscillation with the variation of test conditions such as discharged air mass, submergence of the sparger, valve opening time, and pool temperature during the air-clearing phase. The air mass and pool temperature are in the range of 0.8 ∼ 1.5 kg and 20 ∼ 90°C, respectively. The valve opening time can be adjusted in the range of 0.6 ∼ 1.7 sec according to the POSRV operating conditions. The maximum positive pressure amplitude, which is observed at the bottom of the quench tank, is increased with the submergence depth and maximum header pressure of sparger. The valve opening time has a considerable effect on the maximum amplitude. As the opening time decreases, the maximum amplitudes at the tank wall are increased. Air mass and pool temperature, however, have a weak effect on the maximum amplitude. Oscillation frequency is decreased with air mass in the range of 2.5 ∼ 4.5Hz.
Unit Cell Sparger Test Program and Preliminary Test Results for APR1400
Authors: Park Choon-Kyung , Cho Seok , Song Chul-Hwa , Chun Se-Young
Published: August 2008

KAERI has performed a series of blowdown tests to assess the performance of prototypic steam sparger which will be used in a APR1400 reactor. The test program consists of 22 blowdown tests and each test simulates air clearing phase during an opening of depressurization valves. The major test parameters include air mass in the discharge line, air temperature, flow area, valve opening time, IRWST water temperature, and submergence of a sparger. The CPT-3 test was conducted for typical PWR condition. Following valve actuation, the pressure within the discharge line underwent pressure transient and the discharged high pressure air formed air bubbles, which expanded and compressed periodically in the simulated IRWST. Loop behavior as well as hydraulic load caused by air bubble oscillation during the air clearing phase were described. In addition, water level variation in the sparger during operation of a vacuum breaker was also discussed.
Numerical Simulation of the HDR Blowdown Experiment V31.1 at Karlsruhe
Authors: Andersson Lars , Andersson Per , Lundwall Jan , Sundqvist Jan , Veber Pascal
Published: August 2008

This paper presents a comparison between experimental results and numerical simulations of a reactor pressure vessel internals response due to a rapid depressurization associated to a pipe break. The experiment is designed to fulfil conditions relative to a Pressurised Water Reactor (PWR). The numerical simulation is performed with the computer program package ADINA. The calculations are performed both with and without Fluid Structure Interaction (FSI) effects. It is shown that FSI effects are very important for this problem. The comparison between experimental and numerical results is performed for local pressure in the water and displacements and strains in the reactor vessel and internals. Our experience is that good numerical results can be achieved for this type of loading for all compared quantities. Note that the experiment was set up to show the importance of FSI-phenomena, the effect of this could then be stronger in the experiment compared to a “real” case.
Waterhammer Analysis of Fire Protection System Due to Draining of High Elevation Headers
Authors: Husaini S. Mahmood , Qashu Riyad K. , Arai David Y. , Summy Jeffrey S.
Published: August 2008

This paper presents a methodology for analyzing the potential for water hammer in fire protection systems of nuclear power plants due to draining of high elevation headers. A transient thermal hydraulic analysis was performed that modeled the combined San Onofre Nuclear Generating Station (SONGS) Units 2 and 3 Fire Protection System in general and the high elevation piping in minute detail. The purpose of this analysis was to simulate a postulated scenario that actuates a sprinkler system resulting in the draining of high elevation headers, followed by the start up of the main pumps. The analysis was based on a generalized computer program that utilizes the Method of Characteristics (MOC) numerical scheme. The forcing functions generated by the hydraulic analyses indicated that some hangers would be over loaded. In order to mitigate the water hammer and reduce the loads, the system was analyzed by modeling vacuum breakers at selected locations. The cushioning effect of the air introduced into the system by using vacuum breakers was found to significantly reduce the intensity of the water hammer. Subsequent stress and pipe support analysis predicted there will be no damage to the hangers. The details of the hydraulic analysis, such as the model, pressure and velocity time histories at selected locations, and forcing functions for the cases with and without vacuum breakers are included. Only the conclusions of the stress and pipe support analysis are presented.
Effects of Tube Rupture Modeling Methods on MSSV Lift Time Following a MSGTR Event in PWR
Authors: Jeong Ji Hwan , Choi Ki Yong , Chang Keun Sun
Published: August 2008

A multiple steam generator tube rupture (MSGTR) event in APR1400, an advanced pressurized water reactor, is investigated using the best estimate thermal hydraulic system code, MARS1.4. The effects of parameters such as the number of ruptured tubes, rupture location, affected steam generator on analysis of the MSGTR event in APR1400 are taken into account. In particular, the effects of tube rupture modeling are compared. In the present study, single tube (STM) and double tube modeling (DTM) are examined for assessment on the main steam safety valve (MSSV) lift time. Nuclear steam supply system (NSSS) and several safety systems that are relevant to the APR1400 are modeled. Automatic safety systems are assumed to mitigate the MSGTR events including the reactor protection trip, reactor coolant pump trip, the pressurizer heaters, high-pressure safety injection (HPSI) pumps, and the valves for atmospheric dump, main steam safety, main steam isolation, and turbine stop and bypass. When five tubes are ruptured, the STM permits the operator response time of 2085 seconds before lifting of MSSVs. The effects of rupture location on the MSSV lift time is not significant in case of STM, while the MSSV lift time for tube-top rupture is found to be 25.3% larger than that for rupture at hog-leg side tube sheet in case of DTM. The MSSV lift time for the cases that both steam generators are affected (4C5x, 4C23x) are found to be larger than that for the single steam generator cases (4A5x, 4B5x) due to a bifurcation of the primary leak flow. The discharge coefficient of Cd is found to affect the MSSV lift time only for smaller value of Cd below 0.5. For larger values of Cd than 0.5, its effect on the leak flow rates as well as the MSSV lift time become negligible. It is found that the most dominant parameter governing the MSSV lift time is the leak flow rate. Whichever modeling method is used, it gives the similar MSSV lift time if the leak flow rate is similar, except the case of both steam generators are affected. Therefore, the system performance and the MSSV lift time of the APR1400 are strongly dependent on the break flow model used in the best estimate system code.
Acoustic and Structural Modeling of Farley Main Steam Flow-Induced Vibration
Authors: Zysk Gregory
Published: August 2008

Piping vibration has been observed in the Farley Unit 2 main steam system since plant start-up. Dynamic pressure and accelerometer data obtained during operation indicated that this was flow induced vibration. Acoustic modeling was utilized to evaluate potential origination locations of the pressure oscillation in the main steam system. Forcing pressure oscillations or “exciters” over a broad range of frequencies were imposed at various locations to simulate turbulent sources within the system. The relative magnitude of the acoustic response at the measured locations was compared to the data and used as a basis for determining the location of the source oscillation. The acoustic model was also used to generate forcing functions for a piping structural model that was used to evaluate measured accelerometer data.
Numerical Analysis of Unsteady Conjugate Heat Transfer and Thermal Stress for a PWR Pressurizer Surge Line Pipe Subjected to Thermal Stratification
Authors: Jo Jong Chull , Choi Young Hwan , Choi Seok Ki
Published: August 2008

This paper addresses three-dimensional numerical analyses of the unsteady conjugate heat transfer and thermal stress for a PWR pressurizer surge line pipe with a finite wall thickness, subjected to internally thermal stratification. A primary emphasis of the present study is placed on the investigation of the effects of surge flow direction on the determinations of the transient temperature and thermal stress distributions in the pipe wall. In the present numerical analysis, the thermally stratified flows (in-surge flow and out-surge flow) in the pipe line are simulated using the standard κ-ε turbulent model and a simple and convenient numerical method of treating the unsteady conjugate heat transfer on a non-orthogonal coordinate system is developed. The unsteady conjugate heat transfer analysis method is implemented in a finite volume thermal-hydraulic computer code based on a non-staggered grid arrangement, SIMPLEC algorithm and higher-order bounded convection scheme. The finite element method is employed for the thermal stress analysis to calculate non-dimensional stress distributions at the piping wall as a function of time. Some numerical calculations are performed for a PWR pressurizer surge line pipe model with shortened length, subjected to internally thermal stratification caused either by insurge or outsurge flow with a specified velocity, and the results are discussed in detail.