bluuebunny/crossref_metadata_2025 huggingface dataset:
Frontal cortical afferents facilitate striatal nitric oxide transmission in vivo via a NMDA receptor and neuronal NOS‐dependent mechanism
Authors: Sammut Stephen , Park Diana J. , West Anthony R.
Published: July 2007

Striatal nitric oxide (NO) signaling plays a critical role in modulating neural processing and motor behavior. Nitrergic interneurons receive synaptic inputs from corticostriatal neurons and are activated via ionotropic glutamate receptor stimulation. However, the afferent regulation of NO signaling is poorly characterized. The role of frontal cortical afferents in regulating NO transmission was assessed in anesthetized rats using amperometric microsensor measurements of NO efflux and local field potential recordings. Low frequency (3 Hz) electrical stimulation of the ipsilateral cortex did not consistently evoke detectable changes in striatal NO efflux. In contrast, train stimulation (30 Hz) of frontal cortical afferents facilitated NO efflux in a stimulus intensity‐dependent manner. Nitric oxide efflux evoked by train stimulation was transient, reproducible over time, and attenuated by systemic administration of either the NMDA receptor antagonist MK‐801 or the neuronal NO synthase inhibitors 7‐nitroindazole and NG‐propyl‐l‐arginine. The interaction between NO efflux evoked via train stimulation and local striatal neuron activity was assessed using dual microsensor and local field potential recordings carried out concurrently in the contralateral and ipsilateral striatum, respectively. Systemic administration of the non‐specific NO synthase inhibitor methylene blue attenuated both evoked NO efflux and the peak oscillation frequency (within the delta band) of local field potentials recorded immediately after train stimulation. Taken together, these observations indicate that feed‐forward activation of neuronal NO signaling by phasic activation of frontal cortical afferents facilitates the synchronization of glutamate driven oscillations in striatal neurons. Thus, NO signaling may act to amplify coherent corticostriatal transmission and synchronize striatal output.
Reinstatement of Ethanol‐Seeking Behavior Following Intravenous Self‐Administration in Wistar Rats
Authors: Gass Justin T. , Olive M. Foster
Published: July 2007

Background:  In animal models of alcoholism, subjects are traditionally trained to self‐administer ethanol via the oral route. However, ethanol is also self‐administered intravenously (IV), a paradigm which offers several advantages over oral self‐administration methods, including immediate delivery to the bloodstream, more rapid onset of pharmacological effects, and elimination of the need to utilize tastants or sweeteners to mask the aversive orosensory properties of ethanol. However, no studies to date have examined reinstatement of ethanol‐seeking behavior in animals with a history of IV ethanol self‐administration.

Methods:  Male Wistar rats were implanted with indwelling jugular vein catheters and trained to self‐administer ethanol IV (1% v/v solution, equivalent to 1 mg/kg) in an operant lever‐pressing paradigm in twice daily 1 hour sessions. Each IV delivery of ethanol was paired with presentation of a light‐tone complex stimulus. After stabilization of response patterns, IV self‐administration behavior was subjected to extinction procedures. Next, animals were exposed to the three types of stimuli known to reinstate ethanol‐seeking behavior: presentation of ethanol‐associated cues, a priming dose of ethanol (0.5 g/kg i.p.), or exposure to stress via administration of the anxiogenic compound yohimbine (2.5 mg/kg i.p.) or its corresponding vehicle.

Results:  During the maintenance phase of self‐administration, animals exhibited significantly more presses on the lever that delivered the ethanol solution than the inactive lever, indicating that IV ethanol functioned as a positive reinforcer. Following extinction, it was found that ethanol‐seeking behavior could be reinstated by all three types of stimuli (cues, ethanol priming, and yohimbine). Vehicle injection did not affect responding on either lever.

Conclusions:  Ethanol serves as a reinforcer when self‐administered IV, and following extinction, ethanol‐seeking behavior can be reinstated by ethanol‐associated cues, ethanol priming, or a pharmacological stressor. Thus, reinstatement of ethanol‐seeking behavior in animals with a history of IV ethanol self‐administration may be a novel animal model of relapse.
Effect of Ionic Strength on the Stability of Binary Ceramic Suspensions
Authors: Wang Xiaoli , Zhang Hao , Guo Lucun
Published: July 2007

The colloidal stability of aqueous Al2O3/ZrO2 and Al2O3/SiC suspensions in the presence of electrolyte was investigated by rheological measurement. It was observed that the stability of binary systems improved with increasing ionic strength, where the solution pH value was maintained in the middle range of the two isoelectric points of the constituent powders. In this case, the electrostatic attractive interaction between dissimilar particles became more prominent when their number ratio approached unity. In addition, the salt‐dependent stability was studied over the entire range of pH and relative component fraction. The results showed that the role of ionic strength in promoting flocculation or stabilization of colloidal dispersions was mainly determined by the predominant electrostatic interaction between particles, and the experimental stability maps were used to distinguish the stable and unstable suspensions with the addition of an electrolyte.
Comparative analysis of skin sensitization potency of acrylates (methyl acrylate, ethyl acrylate, butyl acrylate, and ethylhexyl acrylate) using the local lymph node assay
Authors: Dearman Rebecca J , Betts Catherine J , Farr Craig , McLaughlin James , Berdasco Nancy , Wiench Karin , Kimber Ian
Published: July 2007

There are currently available no systematic experimental data on the skin sensitizing properties of acrylates that are of relevance in occupational settings. Limited information from previous guinea‐pig tests or from the local lymph node assay (LLNA) is available; however, these data are incomplete and somewhat contradictory. For those reasons, we have examined in the LLNA 4 acrylates: butyl acrylate (BA), ethyl acrylate (EA), methyl acrylate (MA), and ethylhexyl acrylate (EHA). The LLNA data indicated that all 4 compounds have some potential to cause skin sensitization. In addition, the relative potencies of these acrylates were measured by derivation from LLNA dose–response analyses of EC3 values (the effective concentration of chemical required to induce a threefold increase in proliferation of draining lymph node cells compared with control values). On the basis of 1 scheme for the categorization of skin sensitization potency, BA, EA, and MA were each classified as weak sensitizers. Using the same scheme, EHA was considered a moderate sensitizer. However, it must be emphasized that the EC3 value for this chemical of 9.7% is on the borderline between moderate (<10%) and weak (>10%) categories. Thus, the judicious view is that all 4 chemicals possess relatively weak skin sensitizing potential.
Effects of compression force on fibroblast growth factor‐2 and receptor activator of nuclear factor kappa B ligand production by periodontal ligament cellsin vitro
Authors: Nakajima R. , Yamaguchi M. , Kojima T. , Takano M. , Kasai K.
Published: July 2007

Background and Objective: Mechanical stress by an orthodontic appliance induces biologically active substances. Fibroblast growth factor is a multifunctional cytokine that has various effects on fibroblast cells, and fibroblast growth factor‐2 plays an important role in remodeling of the periodontal ligament. The receptor activator of nuclear factor kappa B ligand (RANKL) is an important protein involved in osteoclastogenesis and we recently reported that RANKL levels were increased by compression forcein vitro. In the present study, we investigated the effects of compression force on fibroblast growth factor‐2 and RANKL production by human periodontal ligament cells.

Material and Methods: Compression force (0.5–4.0 g/cm2) was applied to human periodontal ligament cells for 0–24 h. The amounts of soluble RANKL (sRANKL) and fibroblast growth factor‐2 were measured using an enzyme‐linked immunosorbent assay, whereas mRNA levels were determined by the reverse transcription‐polymerase chain reaction. Furthermore, anti‐fibroblast growth factor‐2 was added to the cell culture media and we measured the release of sRANKL and fibroblast growth factor‐2 by enzyme‐linked immunosorbent assay.

Results: Compression force induced higher levels of sRANKL and fibroblast growth factor‐2 in both a time‐ and magnitude‐dependent manner. Treatment with anti‐fibroblast growth factor‐2 inhibited the release of sRANKL.

Conclusion: Fibroblast growth factor‐2 may be partly involved in osteoclastogenesis during orthodontic tooth movement.
A Role for Transportin in the Nuclear Import of Adenovirus Core Proteins and DNA
Authors: Hindley Clemence E. , Lawrence Fiona J. , Matthews David A.
Published: July 2007

Adenoviruses target their double‐stranded DNA genome and its associated core proteins to the interphase nucleus; this core structure then enters through the nuclear pore complex. We have used digitonin permeabilized cell import assays to study the cellular import factors involved in nuclear entry of virus DNA and the core proteins, protein V and protein VII. We show that inhibition of transportin results in aberrant localization of protein V and that transportin is necessary for protein V to accumulate in the nucleolus. Furthermore, inhibition of transportin results in inhibition of protein VII and DNA import, whereas disruption of the classical importin α–importin β import pathway has little effect. We show that mature protein VII has different import preferences from the precursor protein, preVII from which it is derived by proteolytic processing. While bacterially expressed glutathione S‐transferase (GST)‐preVII primarily utilizes the pathway mediated by importin α–importin β, bacterially expressed GST‐VII favours the transportin pathway. This is significant because while preVII is important during viral replication and assembly only mature VII is available during viral DNA import to a newly infected cell. Our results implicate transportin as a key import receptor for the nuclear localization of adenovirus core.
CLASS II COMPOSITES: PART II
Authors: Swift Edward J.
Published: July 2007

Improvements in adhesive materials and techniques have contributed to the clinical success of posterior composite restorations. However, even with those improvements, the gingival margin of a Class II composite restoration remains a difficult area to seal predictably and therefore represents a potential location for failure. Recent approaches to sealing the cervical margin have involved the use of materials such as resin‐modified glass ionomers, compomers, and flowable resins. This “Critical Appraisal” is the second part of a two‐part series on this subject.
RE‐WETTING AGENTS FOR DENTIN BONDING
Authors: Ritter Andre V. , Swift Edward J.
Published: July 2007

Adhesive restorations have been increasingly used in restorative dentistry primarily because of their potential to generate sealed interfaces and to allow for conservative preparation designs. Adhesive restorative techniques demand a close interaction, either chemical or micro‐mechanical, between the tooth substrate (enamel and dentin) and the adhesive and restorative materials. For success in adhesive restorative dentistry, a number of substrate‐ or technique‐related variables are similarly influential. Acid‐etching is a commonly used technique in adhesive restorative dentistry. In treating the enamel and dentin substrates after acid‐etching, the clinician should recall that both overdrying and overwetting of the preparation might compromise the penetration of the adhesive into the etched substrate and, consequently, impair the performance of the restoration. This critical appraisal focuses on a technique that has been proposed to circumvent this problem, the use of re‐wetting agents with adhesive systems.
Modulation of the endocannabinoid system by focal brain ischemia in the rat is involved in neuroprotection afforded by 17β‐estradiol
Authors: Amantea Diana , Spagnuolo Paola , Bari Monica , Fezza Filomena , Mazzei Cinzia , Tassorelli Cristina , Morrone Luigi A. , Corasaniti Maria T. , Maccarrone Mauro , Bagetta Giacinto
Published: July 2007

Endogenous levels of the endocannabinoid anandamide, and the activities of the synthesizing and hydrolyzing enzymes, i.e. N‐acylphosphatidylethanolamine‐hydrolyzing phospholipase D and fatty acid amide hydrolase, respectively, were determined in the cortex and the striatum of rats subjected to transient middle cerebral artery occlusion. Anandamide content was markedly increased (∼ 3‐fold over controls; P < 0.01) in the ischemic striatum after 2 h of middle cerebral artery occlusion, but not in the cortex, and this elevation was paralleled by increased activity of N‐acylphosphatidylethanolamine‐hydrolyzing phospholipase D (∼ 1.7‐fold; P < 0.01), and reduced activity (∼ 0.6‐fold; P < 0.01) and expression (∼ 0.7‐fold; P < 0.05) of fatty acid amide hydrolase. These effects of middle cerebral artery occlusion were further potentiated by 1 h of reperfusion, whereas anandamide binding to type 1 cannabinoid and type 1 vanilloid receptors was not affected significantly by the ischemic insult. Additionally, the cannabinoid type 1 receptor antagonist SR141716, but not the receptor agonist R‐(+)‐WIN55,212‐2, significantly reduced (33%; P < 0.05) cerebral infarct volume detected 22 h after the beginning of reperfusion. A neuroprotective intraperitoneal dose of 17β‐estradiol (0.20 mg·kg−1) that reduced infarct size by 43% also minimized the effect of brain ischemia on the endocannabinoid system, in an estrogen receptor‐dependent manner. In conclusion, we show that the endocannabinoid system is implicated in the pathophysiology of transient middle cerebral artery occlusion‐induced brain damage, and that neuroprotection afforded by estrogen is coincident with a re‐establishment of anandamide levels in the ischemic striatum through a mechanism that needs to be investigated further.
Sexual Dysfunction Prior to First Drug Use Among Former Drug Addicts and Its Possible Causal Meaning on Drug Addiction: Preliminary Results
Authors: La Pera Giuseppe , Carderi Anna , Marianantoni Zelinda , Peris Filippo , Lentini Massimo , Taggi Franco
Published: July 2007

Introduction

Adolescence is one of the periods in which the risk of initial use of drugs is high. Among the reasons leading to first drug use (FDU), sexual disorders have so far been poorly investigated.

Aim

To evaluate the prevalence of premature ejaculation, erectile dysfunction, and low sexual desire in former drug addicts in the period prior to FDU; whether or not the former drug addicts claimed that sexual dysfunctions influenced their decision to start illicit drug taking, and whether or not the subjects had sought and used drugs aiming to improve sexual drive.

Methods

Eighty-six male former drug addicts (18–35 years old) were investigated using a questionnaire.

Main Outcome Measures

Fisher and Armitage tests.

Results

Before FDU, 61 (71%) subjects reported having one or more sexual dysfunctions. Only 25 (29%) had no sexual dysfunction prior to FDU. Among those with normal sexual function, only three (3.49%) stated that sexual dysfunctions had influenced their decision, whereas in the sexual dysfunction group, 27 (31.4%) confirmed this experience. This difference is statistically significant, Fisher test, P =0.0033.

The more severe the sexual dysfunction, the higher the percentage of those who stated that sexual dysfunction influenced their decision to start taking drugs. This trend is statistically significant, P <0.0025.

About 50% of the entire sample admitted they had used drugs to improve sexual performance.

Conclusions

Users of illicit drugs report a high prevalence of sexual disorders prior to FDU. A large percentage claimed that sexual dysfunction influenced their decision to start taking drugs. The higher the severity of the sexual disorders, the higher the percentage of those claiming that sexual dysfunction had influenced their decision. In our opinion, these data highlight a possible new strategy in the primary prevention of substance abuse in which sexual education and early treatment of sexual disorders, among adolescents, may prevent them from FDU.
A Case Series of Androgen Use in Breast Cancer Survivors with Sexual Dysfunction
Authors: Krychman Michael L. , Stelling Carla J. , Carter Jeanne , Hudis Clifford A.
Published: July 2007

Introduction

Sexual dysfunction, including problems with vaginal dryness, dyspareunia, decreased libido, and difficulty with orgasm, is a common complaint among female breast cancer survivors. Despite the prevalence of female sexual dysfunction, there is a lack of Food and Drug Administration (FDA)-approved treatment options for hypoactive sexual desire disorder (HSDD) in women. Testosterone therapy may be one option.

Aim

This is a case series describing the experience of breast cancer patients who used testosterone to treat sexual dysfunction.

Methods

We report on three patients with a history of breast cancer who chose to continue testosterone therapy for improved sexual function despite conflicting reports of efficacy and lack of safety data on testosterone use in breast cancer patients. The patients described here expressed understanding of the risks and adamantly wished to continue testosterone therapy.

Main Outcome Measures

All patients received a comprehensive sexual medicine evaluation including complete gynecological and psychosexual evaluations.

Results

The improved sexual functioning is a quality-of-life parameter for these patients, and the unknown testosterone safety profile is an individually accepted level of risk. As studies emerge reporting beneficial effects of testosterone on libido and sexual function, the use of testosterone-containing therapies can be expected to increase among postmenopausal women.

Conclusions

Further studies are needed to investigate the long-term effects of testosterone use in patients with breast cancer or at increased risk for developing breast cancer to definitively address the safety issues.
On the Effects of Permuted Input on Conformational Sampling of Drug‐like Molecules: an Evaluation of Stochastic Proximity Embedding
Authors: Agrafiotis Dimitris K. , Bandyopadhyay Deepak , Carta Giorgio , Knox Andrew J. S. , Lloyd David G.
Published: July 2007

Conformational sampling is a problem of central importance in computer‐aided drug design. A good conformational search method must not exhibit any intrinsic bias, and must provide confidence that important regions of conformational space are not missed during the search. A recent study by Carta et al. showed that this is not always the case, and that several popular conformational search methods, such as Omega, are very sensitive to the relative ordering of atoms and bonds in the connection table. Here, we examine the performance of a newer method known as stochastic proximity embedding, or SPE, using five diverse bioactive ligands extracted from the PDB. Our results confirm that the conformational ensembles produced by SPE using different permuted inputs are statistically indistinguishable, and well within the range of variability that would be expected from the stochastic nature of the method itself. This, along with the results of a more comprehensive comparative study (Agrafiotis et al., J. Chem. Info. Model, 2007, in press), provides further evidence that SPE is one of the most robust and competitive conformational search methods described to date.
The Antimicrobial Peptide PR‐39 has a Protective Effect Against HeLa Cell Apoptosis
Authors: Ross Christopher R. , Ricevuti Giovanni , Scovassi Anna Ivana
Published: July 2007

PR‐39 is a cathelicidin with antimicrobial properties, which acts as a suppressor of inflammation and exerts a number of additional activities. We investigated for the first time the effect of PR‐39 on human cells, by addressing the possible interference with HeLa cell metabolism. We observed that the continuous administration of PR‐39 to HeLa cell cultures was not cytotoxic and did not interfere with DNA synthesis. When used in combination with a panel of drugs inducing apoptosis through different mechanisms of action, i.e. etoposide, bleomycin, tert‐butylhydroperoxide and 2‐deoxy‐d‐ribose, PR‐39 attenuated the apoptotic response of HeLa cells.
4‐Cyclohexyl‐1‐substituted‐4H‐[1,2,4]triazolo [4,3‐a] quinazolin‐5‐ones: Novel Class of H1‐antihistaminic Agents
Authors: Alagarsamy V. , Meena S. , Ramaseshu K. V. , Solomon V. Raja , Kumar T. Durai Ananda
Published: July 2007

A series of novel 1‐substituted‐4‐cyclohexyl‐4H‐[1,2,4]triazolo [4,3‐a] quinazolin‐5‐ones were synthesized by the cyclization of 3‐cyclohexyl‐2‐hydrazino‐3H‐quinazolin‐4‐one with various one carbon donors. When tested for their in vivo H1‐antihistaminic activity on guinea‐pigs, all the test compounds protected the animals from histamine induced bronchospasm significantly. The compound 4‐cyclohexyl‐1‐methyl‐4H‐[1,2,4]triazolo[4,3‐a] quinazolin‐5‐one (II) emerged as the most active compound of the series and it is more potent (72.96% protection) when compared to the reference standard chlorpheniramine maleate (71.00% protection). The compound II shows negligible sedation (9%) when compared to chlorpheniramine maleate (30%). Hence, it could serve as prototype molecule for further development as a new class of H1‐antihistamines.
Analysis and Design of Buried Pipelines for Ice Gouging Hazard: A Probabilistic Approach
Authors: Nobahar Arash , Kenny Shawn , King Tony , McKenna Richard , Phillips Ryan
Published: July 2007

In cold environments, marine pipelines may be at risk from ice keels that gouge the seabed. Large quantities of material are displaced and soil deformations beneath a gouge may be substantial. To meet safety criteria, excessive strains are avoided by burying pipelines to a sufficient depth. In this paper, a probabilistic approach for the analysis and design of buried pipelines is outlined. Environmental actions are applied through distributions of gouge width, gouge depth, subgouge soil deformations, and bearing pressure. Three-dimensional pipe/soil interaction problem is modeled using nonlinear soil springs and special beam elements using the finite element method to estimate pipe response for statistically possible ranges of gouge depths, gouge widths, and burial depths. Relevant failure mechanisms have been considered, including local buckling and a variety of strain and stress based criteria. The methodology presented in the paper was developed and successfully used for several pipeline and electrical cable projects in ice gouge environments. Significantly reduced burial depth requirements have been demonstrated through the application of the probabilistic approach and through the use of strain-based design criteria. Because ice actions are applied through displacements of the soil, more ductile pipes are often necessary to meet reliability targets.
Nonlinear Identification and Input-Output Representation of the Modal Dynamics of Marine Slender Structures
Authors: Xiros Nikolaos I. , Chatjigeorgiou Ioannis K.
Published: July 2007

The present work treats the problem of the dynamic behavior of a vertical slender structure subject to combined axial and transverse motions. The solution method is based on a Galerkin-type semi-analytical formulation. The responses to sinusoidal monochromatic excitation are assessed with respect to the significance of each mode and their spectral content. As a result, a reduced, yet nonlinear, lumped model for each one of the significant modes of the structure is generated. The parameters of these fixed-structure models can be determined systematically by two methods relying on the spectral analysis of the numerically calculated modal responses of the structure. The resulting models constitute an explicit input-output relationship between the imposed motions and the modes of the structure, useful for stability analysis, design and control.
A Theoretical Analysis of Dynamic Elastic Response of a Circular Ring to Water Waves
Authors: Dong G. H. , Hao S. H. , Zong Z. , Zheng Y. N.
Published: July 2007

Fish farming in the open ocean is becoming a dominant form of fishery aquaculture due to the dramatic drop of fishery resources in near shore. Deep water anti-stormy fish cages are the most important tool for fish farming in the open ocean. The floatation ring, as a pivotal component of the fish cage, undergoes large deformations and it has been found that the floatation ring oscillates when moving in water waves. In the most serious cases, its deformation is so large it can be damaged. The floatation ring is simplified as a free circular ring, and the governing equations of motion and deformation of the ring can be built up according to the force equilibrium and curved beam theory. The numerical calculation is carried out in terms of the modal superposition method. The motion and the deformation of the ring are analyzed, and two corresponding equations in which the elastic deformations are neglected and considered are given, respectively. By comparing the results of the above two equations, we get the resonant frequencies and the frequency scope influenced by the elastic deformation. It is concluded that the influence of the deformation of the ring is very important for the oscillation of the ring, particularly the former three modes of the elastic deformation which cannot be neglected.
Analysis of Recent Fatigue Data Using the Structural Stress Procedure in ASME Div 2 Rewrite
Authors: Dong Pingsha , Hong Jeong K. , De Jesus Abílio M. P.
Published: July 2007

In support of the ASME Div 2 Rewrite, a master S-N curve approach has been developed using a mesh-insensitive structural stress procedure for fatigue evaluation of welded components. The effectiveness of the master S-N curve approach has been demonstrated in a number of earlier publications for many joint types and loading conditions for pipe and vessel components as well as plate joints. To further validate the structural stress method, a series of recent test data (small weld details and a full-scale vessel) published by De Jesus et al. (2004, Fatigue and Fracture of Engineering Materials and Structures, 27, pp. 799–810) were analyzed in this paper. A comparative assessment of various existing procedures and their effectiveness in correlating the fatigue test data by De Jesus is also presented. These assessment procedures include current ASME Sec. VIII Div 2, weld classification approach in PD 5500, and the surface extrapolation-based hot spot stress approach in recently approved European EN 13445 Standards.
Simulation of Structural Deformations of Flexible Piping Systems by Acoustic Excitation
Authors: Maess Matthias K. , Gaul Lothar
Published: July 2007

Valve actuation and pump fluctuation in piping systems generate propagating sound waves in the fluid path which in turn can lead to undesired excitation of structural components. This vibro-acoustic problem is addressed by studying the propagation dynamics as well as the excitation mechanism. Fluid-structure interaction has a significant influence on both hydroacoustics and on structural deformation. Therefore, pipe models are generated in three dimensions by using finite elements in order to include higher-order deflection modes and fluid modes. The acoustic wave equation in the fluid is hereby fully coupled to the structural domain at the fluid-structure interface. These models are used for simulating transient response and for performing numerical modal analysis. Unfortunately, such 3D models are large and simulation runs turn out to be very time consuming. To overcome this limitation, reduced pipe models are needed for efficient simulations. The proposed model reduction is based on a series of modal transformations and modal truncations, where focus is placed on the treatment of the nonsymmetric system matrices due to the coupling. Afterwards, dominant modes are selected based on controllability and observability considerations. Furthermore, modal controllabilities are used to quantify the excitation of vibration modes by a white noise acoustic source at the pipe inlet. The excitation of structural elements connected to the piping system can therefore be predicted without performing transient simulations. Numerical results are presented for a piping system consisting of straight pipe segments, an elbow pipe, joints, and a target structure. This example illustrates the usefulness of the presented method for vibro-acoustic investigations of more complex piping systems.
Some Advances on Understanding of High Cycle Thermal Fatigue Crazing
Authors: Taheri Said
Published: July 2007

The aim of this paper is to improve the understanding of high cycle thermal fatigue crazing observed in some areas of residual heat removal (RHR) systems made of 304L stainless steel in PWR nuclear plants. High cycle thermal crazing and the absence of crazing under purely mechanical loading are explained through the arrest of cracks initiated at the surface in the thickness of the component for thermal fatigue. This arrest is due to high stress gradients in the case of thermal loading due to the high frequency of the thermal load. It is shown that close to the weld, the crack network configuration is related to the tensile weld residual stress field in accordance with the detrimental effect of tensile mean stress on fatigue life. However, these results are in apparent contradiction with the material uniaxial fatigue tests, where a beneficial effect of tensile mean stress is observed in load-controlled fatigue tests. Moreover, it is shown that near the weld, the absence of a crack network is related to the compressive weld residual stress field in accordance with the beneficial effect of compressive mean stress on fatigue life. This result is however, in apparent contradiction with the observation of crazing far from the weld under a highly compressive stress. These contradictions may be explained by the detrimental effect of prehardening in strain control and the beneficial effect of prehardening in stress control for stainless steels. From these results it is concluded that shot peening which is usually considered to be beneficial for ferritic steel may be detrimental in high cycle thermal fatigue for stainless steels. It may also be concluded that in high cycle thermal fatigue of stainless steel, improvement of fatigue life would be possible with heat treatment by reduction of strain-hardening rather than with shot peening.
Estimation of Master Curve Based RTTO Reference Temperature From CVN Data
Authors: Wallin Kim R. W. , Nagel Gerhard , Keim Elisabeth , Siegele Dieter
Published: July 2007

The ASME code cases N-629 and N-631 permit the use of a master curve-based index temperature (RTTo≡T0+19.4°C) as an alternative to traditional RTNDT-based methods of positioning the ASME KIC and KIR curves. This approach was adopted to enable the use of master curve technology without requiring the wholesale changes to the structure of the ASME code that would be needed to use all aspects of master curve technology. For the brittle failure analysis considering irradiation embrittlement an additional procedure to predict the adjustment of fracture toughness for end of life (EOL) from irradiation surveillance results must be available as by NRC R.G. 1.99 Rev. 2, e.g., the adjusted reference temperature is defined as ART=initialRTNDT+ΔRTNDT+margin. The conservatism of this procedure when RTNDT is replaced by RTTo is investigated for western nuclear grade pressure vessel steels and their welds. Based on a systematic evaluation of nearly 100 different irradiated material data sets, a simple relation between RTToirr, RTToref, and ΔT41JRG is proposed. The relation makes use of the R.G. 1.99 Rev. 2 and enables the minimizing of margins, necessary for conventional correlations based on temperature shifts. As an example, the method is used to assess the RTTo as a function of fluence for several German pressure vessel steels and corresponding welds. It is shown that the method is robust and well suited for codification.
Limit Load Solutions for Pipes With Through-Wall Crack Under Single and Combined Loading Based on Finite Element Analyses
Authors: Huh Nam-Su , Kim Yun-Jae , Kim Young-Jin
Published: July 2007

The present paper provides plastic limit load solutions for axial and circumferential through-wall cracked pipes based on detailed three-dimensional (3D) finite element (FE) limit analysis using elastic-perfectly plastic behavior. As a loading condition, axial tension, global bending moment, internal pressure, combined tension and bending, and combined internal pressure and bending are considered for circumferential through-wall cracked pipes, while only internal pressure is considered for axial through-wall cracked pipes. In particular, more emphasis is given for through-wall cracked pipes subject to combined loading. Comparisons with existing solutions show a large discrepancy in short through-wall crack (both axial and circumferential) for internal pressure. In the case of combined loading, the FE limit analyses results show the thickness effect on limit load solutions. Furthermore, the plastic limit load solution for circumferential through-wall cracked pipes under bending is applied to derive plastic η and γ factor of testing circumferential through-wall cracked pipes to estimate fracture toughness. Being based on detailed 3D FE limit analysis, the present solutions are believed to be meaningful for structural integrity assessment of through-wall cracked pipes.
Analysis of Loads for Nozzles in API 650 Tanks
Authors: Lengsfeld Manfred , Bardia Ken , Taagepera Jaan , Hathaitham Kanajett , La Bounty Donald , Lengsfeld Mark
Published: July 2007

The analysis of tank nozzles for API 650, (American Petroleum Institute, 1998, API Standard 650, 10th ed.) tanks is a complex problem. Appendix P of API 650 provides a method for determining the allowable external loads on tank shell openings. The method in Appendix P is based on two papers, one by Billimoria and Hagstrom, 1997, ASME Paper No. 77-PVP-19 and the other by Billimoria and Tam 1980, ASME Paper No. 80-C2/PVP-5. Although Appendix P is optional, the industry has used it for a number of years for large diameter tanks. For tanks less than 120feet(33.6m) in diameter this Appendix is not applicable. In previously published papers, the authors used finite element analysis (FEA) to verify the experimental results reported by Billimoria and Tam for low-type nozzles. The analysis showed the variance between stiffness coefficients and stresses obtained by FEA and API 650 methods for tanks. In this paper, the authors have expanded the scope to include almost any size of nozzle as well as tank size. Stress factors for nozzles at different elevations on the shell are provided. Nozzles located away from a discontinuity are analyzed based on the method provided by the Welding Research Council (WRC), New York, Bulletin No. 297, 1987. Stress reduction factors have been developed using FEA for nozzles located closer to a discontinuity. Mathematical equations are provided together with the curves for the stress factors. The results of this paper have been incorporated into Appendix P of API 650 with the Addendum 3 of the 10th edition which was issued in 2003.
Effect of Temperature on Acoustic Emission Evaluation of FRP Vessels (Tensile Specimens)
Authors: Chen Yizhuo , Ziehl Paul , Ramirez Guillermo , Fowler Timothy J.
Published: July 2007

Current American Society of Mechanical Engineers (ASME) provisions require that acoustic emission testing for class II vessels be carried out at operating temperature in the event that the operating temperature exceeds 120°F(49°C). This causes increased cost due to the need for a boiler. Safety is also a concern due to the possibility of a leak or failure of the vessel during testing. More important than these two items is the lack of data that is available from fiber reinforced polymer (FRP) vessels and/or components that have been subjected to acoustic emission evaluation at elevated temperature. This has lead to speculation regarding the appropriateness of conducting acoustic emission evaluations at elevated temperature. To address these issues an experimental investigation was conducted on representative coupon specimens at differing temperatures. The results of the investigation are described.
Fatigue Response and Characterization of 350WT Steel Under Semi-Random Loading
Authors: Rushton Philip A. , Taheri Farid , Stredulinsky David C.
Published: July 2007

Novel data obtained through experimental investigation into the fatigue response of 350WT steel, subjected to semi-random loading, comprised of various combinations of intermittent tensile overloads and compressive underloads are presented. An effective model for predicting the fatigue response is also introduced. For that, the capabilities of some of the currently available models are investigated and then an exponential delay model, being capable of accounting for the effects of not only overload ratio, but also stress ratio and overload/underload ratio is introduced. Since most variable amplitude models are based on a constant amplitude model, efforts were also expended to identify a constant amplitude fatigue crack growth model that would be easy to use, requiring the calibration of few (if any) empirical curve-fitting parameters. The integrity of a selected model is examined and results are presented.
Emergency Assessment and Repairs of a Process Tower Subjected to Corrosion Under Insulation
Authors: Rodery Clay D.
Published: July 2007

A large process tower in a petroleum refinery was discovered to have severe corrosion under insulation (CUI) in two areas. The areas were confined to the vicinity of external rings, but spanned 360deg of the tower. The remaining thickness of the shell in these areas ranged from 3mm to 9mm (0.13in. to 0.35in.) (original thickness was 23mm(15∕16in.)). The tower was assessed for immediate risk of collapse and emergency stabilizing bracing was installed while options for a permanent repair could be defined and selected. An external automated weld overlay technique was selected as a permanent repair method that restored the corroded areas to original thickness. This paper describes the engineering process taken to assess the immediate risk of collapse of the tower, including the emergency repairs taken to stabilize the tower. The review and selection of longer term repair options and the analysis involved in coordinating the removal of the emergency repairs with the installation of the permanent repairs in such a manner that the tower was returned to service well ahead of schedule are also covered.
Analytical Approach in Autofrettaged Spherical Pressure Vessels Considering the Bauschinger Effect
Authors: Adibi-Asl R. , Livieri P.
Published: July 2007

This paper presents an analytical study of spherical autofrettage-treated pressure vessels, considering the Bauschinger effect. A general analytical solution for stress and strain distributions is proposed for both loading and unloading phases. Different material models incorporating the Bauschinger effect depending on the loading phase are considered in the present study. Some practical analytical expressions in explicit form are proposed for a bilinear material model and the modified Ramberg–Osgood model.
Effect of Tightening Speed on the Torque-Tension and Wear Pattern in Bolted Connections
Authors: Nassar Sayed A. , Ganeshmurthy Saravanan , Ranganathan Ramanathan M. , Barber Gary C.
Published: July 2007

In an effort to enhance the reliability of clamp load estimation in bolted joints, this experimental study investigates the effect of tightening speed and coating on both the torque-tension relationship and wear pattern in threaded fastener applications. The fastener torque-tension relationship is highly sensitive to normal variations in the coefficients of friction between threads and between the turning head and the surface of the joint. Hence, the initial level of the joint clamp load and the overall integrity and reliability of a bolted assembly are significantly influenced by the friction coefficients. The effect of repeated tightening and loosening is also investigated using M12, class 8.8 fasteners with and without zinc coating. The torque-tension relationship is examined in terms of the nondimensional nut factor K. The wear pattern is examined by monitoring the changes in surface roughness using a WYKO optical profiler and by using a LECO optical microscope. A Hitachi S-3200N scanning electron microscope is used to examine the contact surfaces under the fastener head after each tightening/loosening cycle. Experimental data on the effect of tightening speed, fastener coating, and repeated tightening are presented and analyzed.
Interaural fluctuations and the detection of interaural incoherence. III. Narrowband experiments and binaural models
Authors: Goupell Matthew J. , Hartmann William M.
Published: July 2007

In the first two articles of this series, reproducible noises with a fixed value of interaural coherence (0.992) were used to study the human ability to detect interaural incoherence. It was found that incoherence detection is strongly correlated with fluctuations in interaural differences, especially for narrow noise bandwidths, but it remained unclear what function of the fluctuations best agrees with detection data. In the present article, ten different binaural models were tested against detection data for 14- and 108-Hz bandwidths. These models included different types of binaural processing: independent-interaural-phase-difference/interaural-level-difference, lateral-position, and short-term cross-correlation. Several preprocessing transformations of the interaural differences were incorporated: compression of binaural cues, temporal averaging, and envelope weighting. For the 14-Hz bandwidth data, the most successful model postulated that incoherence is detected via fluctuations of interaural phase and interaural level processed by independent centers. That model correlated with detectability at r=0.87. That model proved to be more successful than short-term cross-correlation models incorporating standard physiologically-based model features (r=0.78). For the 108-Hz bandwidth data, detection performance varied much less among different waveforms, and the data were less able to distinguish between models.
Intracochlear pressure and derived quantities from a three-dimensional model
Authors: Yoon Yong-Jin , Puria Sunil , Steele Charles R.
Published: July 2007

Intracochlear pressure is calculated from a physiologically based, three-dimensional gerbil cochlea model. Olson [J. Acoust. Soc. Am. 103, 3445–3463 (1998); 110, 349–367 (2001)] measured gerbil intracochlear pressure and provided approximations for the following derived quantities: (1) basilar membrane velocity, (2) pressure across the organ of Corti, and (3) partition impedance. The objective of this work is to compare the calculations and measurements for the pressure at points and the derived quantities. The model includes the three-dimensional viscous fluid and the pectinate zone of the elastic orthotropic basilar membrane with dimensional and material property variation along its length. The arrangement of outer hair cell forces within the organ of Corti cytoarchitecture is incorporated by adding the feed-forward approximation to the passive model as done previously. The intracochlear pressure consists of both the compressive fast wave and the slow traveling wave. A Wentzel–Kramers–Brillowin asymptotic and numerical method combined with Fourier series expansions is used to provide an efficient procedure that requires about 1s to compute the response for a given frequency. Results show reasonably good agreement for the direct pressure and the derived quantities. This confirms the importance of the three-dimensional motion of the fluid for an accurate cochlear model.
Experimental investigation of an inversion technique for the determination of broadband duct mode amplitudes by the use of near-field sensor arrays
Authors: Castres Fabrice O. , Joseph Phillip F.
Published: July 2007

This paper is an experimental investigation of an inverse technique for deducing the amplitudes of the modes radiated from a turbofan engine, including schemes for stablizing the solution. The detection of broadband modes generated by a laboratory-scaled fan inlet is performed using a near-field array of microphones arranged in a geodesic geometry. This array geometry is shown to allow a robust and accurate modal inversion. The sound power radiated from the fan inlet and the coherence function between different modal amplitudes are also presented. The knowledge of such modal content is useful in helping to characterize the source mechanisms of fan broadband noise generation, for determining the most appropriate mode distribution model for duct liner predictions, and for making sound power measurements of the radiated sound field.
Acoustic detection of North Atlantic right whale contact calls using spectrogram-based statistics
Authors: Urazghildiiev Ildar R. , Clark Christopher W.
Published: July 2007

This paper considers the problem of detection of contact calls produced by the critically endangered North Atlantic right whale, Eubalaena glacialis. To reduce computational time, the class of acceptable detectors is constrained by the detectors implemented as a bank of two-dimensional linear FIR filters and using the data spectrogram as the input. The closed form representations for the detectors are derived and the detection performance is compared with that of the generalized likelihood ratio test (GLRT) detector. The test results demonstrate that in the presence of impulsive noise, the spectrogram-based detector using the French hat wavelet as the filter kernel outperforms the GLRT detector and decreases computational time by a factor of 6.
Effect of filter spacing on melody recognition: Acoustic and electric hearing
Authors: Kasturi Kalyan , Loizou Philipos C.
Published: July 2007

This paper assesses the effect of filter spacing on melody recognition by normal-hearing (NH) and cochlear implant (CI) subjects. A new semitone filter spacing is proposed for music. The quality of melodies processed by the various filter spacings is also evaluated. Results from NH listeners showed nearly perfect melody recognition with only four channels of stimulation, and results from CI users indicated significantly higher scores with a 12-channel semitone spacing compared to the spacing used in their daily processor. The quality of melodies processed by the semitone filter spacing was preferred over melodies processed by the conventional logarithmic filter spacing.
Loudness growth observed under partially tripolar stimulation: Model and data from cochlear implant listeners
Authors: Litvak Leonid M. , Spahr Anthony J. , Emadi Gulam
Published: July 2007

Most cochlear implant strategies utilize monopolar stimulation, likely inducing relatively broad activation of the auditory neurons. The spread of activity may be narrowed with a tripolar stimulation scheme, wherein compensating current of opposite polarity is simultaneously delivered to two adjacent electrodes. In this study, a model and cochlear implant subjects were used to examine loudness growth for varying amounts of tripolar compensation, parameterized by a coefficient σ, ranging from 0 (monopolar) to 1 (full tripolar). In both the model and the subjects, current required for threshold activation could be approximated by I(σ)=Ithr(0)∕(1−σK), with fitted constants Ithr(0) and K. Three of the subjects had a “positioner,” intended to place their electrode arrays closer to their neural tissue. The values of K were smaller for the positioner users and for a “close” electrode-to-tissue distance in the model. Above threshold, equal-loudness contours for some subjects deviated significantly from a linear scale-up of the threshold approximations. The patterns of deviation were similar to those observed in the model for conditions in which most of the neurons near the center electrode were excited.