bluuebunny/crossref_metadata_2025 huggingface dataset:
Can we reduce episodes of haemoglobin desaturation in full‐term babies restrained in car seats?
Authors: Tonkin Shirley L , McIntosh Christine G , Nixon Gillian M , Rowley Simon , Gunn Alistair J
Published: April 2008

Objectives: To determine whether episodes of haemoglobin oxygen (SpO2) desaturation in full‐term infants restrained in car seats can be reduced by a simple foam plastic infant car seat insert designed to push the body forward, with space for the protuberant occiput to lie behind the spine, and so reduce flexion of the infant's head on the trunk.

Methods: Eighteen healthy full‐term babies were evaluated while restrained in an infant car safety seat with, and without, the foam insert. Infants were monitored in each position for 30 min with continuous polygraphic recording of respiratory and heart rate, nasal airflow and SpO2.

Results: Placement of the insert in the car seat was associated with a significant reduction in the rate of apneas with a fall in SpO2 >5% (median, interquartile range: 4.4 (0, 10.6) vs. 9.2 (5.4, 15.2) events per hour, p = 0.03). The one clinically severe episode of apnea, with a fall in SpO2 of more than 30%, occurred in the car seat without the insert.

Conclusions: A car seat insert that allows the newborn's head to lie in a neutral position during sleep may reduce the frequency of mild episodes of reduced SpO2 in some full‐term newborn babies.
School stressors, psychological complaints and psychosomatic pain
Authors: Hjern Anders , Alfven Gösta , Östberg Viveca
Published: April 2008

Background: The proportion of Scandinavian school children reporting psychosomatic pain and psychological complaints have increased in recent decades. In this study we investigated these symptoms in relation to potential stressors in the school environment.

Methods: A cross‐sectional study was conducted based on child interviews linked to nationally representative household surveys in Sweden during 2002–2003 covering a sample of 2588 children aged 10–18 years. The main outcome variable of psychosomatic pain signified suffering from headache as well as recurrent abdominal pain on a weekly basis.

Results: School stressors, such as harassment by peers, schoolwork pressure and being treated poorly by teachers, were associated with psychosomatic pain as well as psychological complaints such as sadness, irritability, feeling unsafe and nervous. Harassment was identified as a particularly important determinant with adjusted odds ratios (ORs) ranging from 3.1 to 8.6 for psychosomatic pain. All psychological complaints were associated with psychosomatic pain with adjusted ORs ranging from 2.2 to 3.7, and mediated most of the association of harassment to psychosomatic pain.

Conclusions: School stressors are strongly associated with psychosomatic pain and psychological complaints in school children. Psychological complaints seem to function as mediators in the association of school stressors to psychosomatic pain symptoms to a great extent.
Recent anthropometric trends among Swedish school children: evidence for decreasing prevalence of overweight in girls
Authors: Sjöberg Agneta , Lissner Lauren , Albertsson‐Wikland Kerstin , Mårild Staffan
Published: April 2008

Aim: To assess the recent prevalence of overweight and obesity in 10 year old children in Göteborg, Sweden.

Methods: Cross‐sectional data on weight and height from school health examinations, including fourth grade children, born in 1974 (n = 4126), 1990 (n = 4683) and 1994 (n = 4193) and measured in academic years 1984/1985, 2000/2001 and 2004/2005, were used. Weight classification was based on age‐ and sex‐specific body mass index cutoff values. The two latest cohorts were classified according to socio‐economic areas.

Results: Between 2000/2001 and 2004/2005, the prevalence of overweight plus obesity in girls decreased from 19.6% to 15.9% (p < 0.01). Prevalence of obesity was 3.0% and 2.5% (nonsignificant), respectively. In boys, all differences between the corresponding cohorts were nonsignificant: 17.1% versus 17.6% were overweight (including obese) and 2.9% versus 2.8% were obese. In 1984/1985, prevalence of overweight plus obesity was only 8.6% among girls and 7.2% among boys, while 0.8% and 0.7% were classified as obese, respectively. The socio‐economic gradient in overweight prevalence remained, particularly in girls.

Conclusions: This study suggests that the obesity epidemic in 10–11 year olds may be easing off in urban Sweden, and possibly reversing among girls. Even if future monitoring confirms these findings, much health promoting work still remains since the power of the ‘obesogenic environment’ will probably continue to be strong.
Reproduction Diversity of Enteromorpha prolifera
Authors: Lin Apeng , Shen Songdong , Wang Jianwei , Yan Binlun
Published: April 2008

Enteromorpha prolifera (Muell.) J. Agardh (Chlorophyta, Ulvophyceae), which is distributed widely in the inter‐tidal zone of the ocean, is one of the most common fouling green algae. However, the present understandings of the life history of E. prolifera have been insufficient to explain their seasonal abundances. Thus it is essential to investigate how many reproductive strategies are likely to contribute to the successful colonization and flourishing of the green alga. In the present study the reproduction diversity of E. prolifera was observed and studied systematically by culturing chopped tissues. Our results showed that there are in total seven pathways of reproduction for E. prolifera including sexual, asexual and vegetative reproduction. It was indicated that the variety of the reproductive ways and the large quantity of reproductive cells produced and released during the reproductive season are the two key factors that facilitate colonization of E. prolifera. The reproduction of the alga E. prolifera mainly depends on asexual methods. The results presented here contribute to increasing our understanding about how the opportunistic macroalgae successfully maintain colonization and excessive growth.
Inhibition of Ageratina adenophora on Spore Germination and Gametophyte Development of Macrothelypteris torresiana
Authors: Zhang Kai‐Mei , Shi Lei , Jiang Chuang‐Dao , Li Zhen‐Yu
Published: April 2008

Allelopathy of Ageratina adenophora plays an important role in its invasion. However, we have little knowledge of its allelpathic effects on ferns. In Petri dish bioassays, the inhibitory potential of aqueous leachates from roots, stems and leaves of A. adenophora was studied on the spore germination and gametophyte development of Macrothelypteris torresiana. All leachates inhibited the spore germination and growth of the first rhizoid of M. torresiana and inhibitory effects increased with increasing leachate concentrations. Root leachates proved most inhibitory. Gametophyte rhizoids of M. torresiana treated with stem and leaf leachates of A. adenophora were erect, which was similar to those of the control. However, gametophyte rhizoids of M. torresiana treated with root leachates of A. adenophora were erect, but also curving or swollen. Moreover, curving and swollen rhizoids increased with increasing concentrations. As time went by, rhizoids treated with root leachates were not so curved and the swelling almost disappeared. Possible causes are discussed in the present study. The increasing concentrations of leaf leachates also delayed the stages of gametophyte development. With the treatment of root leachates, the delay was more obvious. Thus A. adenophora inhibited the spore germination and gametophyte development of M. torresiana and the root leachates were most inhibitory.
Modeling Size‐number Distributions of Seeds for Use in Soil Bank Studies
Authors: Casco Hugo , Dias Alexandra Soveral , Dias Luís Silva
Published: April 2008

Knowledge of soil seed banks is essential to understand the dynamics of plant populations and communities and would greatly benefit from the integration of existing knowledge on ecological correlations of seed size and shape. The present study aims to establish a feasible and meaningful method to describe size‐number distributions of seeds in multi‐species situations. For that purpose, size‐number distributions of seeds with known length, width and thickness were determined by sequential sieving. The most appropriate combination of sieves and seeds dimensions was established, and the adequacy of the power function and the Weibull model to describe size‐number distributions of spherical, non‐spherical, and all seeds was investigated. We found that the geometric mean of seed length, width and thickness was the most adequate size estimator, providing shape‐independent measures of seeds volume directly related to sieves mesh side, and that both the power function and the Weibull model provide high quality descriptions of size‐number distributions of spherical, non‐spherical, and all seeds. We also found that, in spite of its slightly lower accuracy, the power function is, at this stage, a more trustworthy model to characterize size‐number distributions of seeds in soil banks because in some Weibull equations the estimates of the scale parameter were not acceptable.
Invasion Possibility and Potential Effects of Rhus typhina on Beijing Municipality
Authors: Wang Guangmei , Jiang Gaoming , Yu Shunli , Li Yinghao , Liu Hui
Published: April 2008

Rhus typhina, an alien species introduced from North America, was identified as a main afforestation species in Beijing municipality. However, its invasiveness is still at odds. To clarify this problem, we applied the North American Screening System and the Australian Screening System to preliminarily predict its invasion possibility. Both screening systems gave the same recommendation to “reject”. The geographical distribution was surveyed, with the population features of R. typhina against the native plant communities being assessed. With anthropogenic assistance, R. typhina has been scattered on almost all habitats from downtown to mountains, including roadsides, farmlands and protected areas. As a clonal shrub, R. typhina possessed a high spreading rate, varying from 6.3 m/3 years at sterile habitats to 6.7 m/3 years at fertile ones. Significantly lower species richness, individual density and diversity were observed in the R. typhina community than those of the native Vitex negundo Linn.var. heterophylla (Franch.) Rehd. community at both sterile and fertile habitats. Continual wide plantation of R. typhina may further foster its population expansion, which helps the species to overcome spatial isolation. The fact that each root fragment can develop into a new individual makes R. typhina very difficult to be eradicated once established. From a biological point of view, we believe that R. typhina is a plant invader in Beijing. We therefore suggest the government should remove the name of R. typhina from the main tree species list in afforesting Beijing.
Two New Triterpenoid Saponins from Gymnema sylvestre
Authors: Zhu Xu‐Min , Xie Ping , Di Ying‐Tong , Peng Shu‐Lin , Ding Li‐Sheng , Wang Ming‐Kui
Published: April 2008

Two new oleanane‐type triterpenoid saponins, gymnemoside‐W1 and W2, together with seven known compounds were isolated from the leaves of Gymnema sylvestre R. Br. By means of spectral and chemical analysis, the structures of the new compounds were elucidated as 16 β‐hydroxyl olean‐12‐en‐3‐O‐[β‐D‐glucopyranosyl (1→6)‐β‐D‐glucopyranosyl]‐28‐O‐β‐D‐glucopyranoside(1) and 16 β,21 β,28‐trihydroxyl‐olean‐12‐ene‐3‐O‐glucoronopyranoside (2). The EtOH/H2O extracts of this plant were shown to be able to inhibit glucose absorption in rats.
Microbial‐based motor fuels: science and technology
Authors: Wackett Lawrence P.
Published: April 2008

The production of biofuels via microbial biotechnology is a very active field of research. A range of fuel molecule types are currently under consideration: alcohols, ethers, esters, isoprenes, alkenes and alkanes. At the present, the major alcohol biofuel is ethanol. The ethanol fermentation is an old technology. Ongoing efforts aim to increase yield and energy efficiency of ethanol production from biomass. n‐Butanol, another microbial fermentation product, is potentially superior to ethanol as a fuel but suffers from low yield and unwanted side‐products currently. In general, biodiesel fuels consist of fatty acid methyl esters in which the carbon derives from plants, not microbes. A new biodiesel product, called microdiesel, can be generated in engineered bacterial cells that condense ethanol with fatty acids. Perhaps the best fuel type to generate from biomass would be biohydrocarbons. Microbes are known to produce hydrocarbons such as isoprenes, long‐chain alkenes and alkanes. The biochemical mechanisms of microbial hydrocarbon biosynthesis are currently under study. Hydrocarbons and minimally oxygenated molecules may also be produced by hybrid chemical and biological processes. A broad interest in novel fuel molecules is also driving the development of new bioinformatics tools to facilitate biofuels research.
T‐DNA insertion, plasmid rescue and integration analysis in the model mycorrhizal fungusLaccaria bicolor
Authors: Kemppainen Minna , Duplessis Sebastien , Martin Francis , Pardo Alejandro G.
Published: April 2008

Ectomycorrhiza is a mutualistic symbiosis formed between fine roots of trees and the mycelium of soil fungi. This symbiosis plays a key role in forest ecosystems for the mineral nutrition of trees and the biology of the fungal communities associated. The characterization of genes involved in developmental and metabolic processes is important to understand the complex interactions that control the ectomycorrhizal symbiosis.Agrobacterium‐mediated gene transfer (AMT) in fungi is currently opening a new era for fungal research. As whole genome sequences of several fungi are being released studies about T‐DNA integration patterns are needed in order to understand the integration mechanisms involved and to evaluate the AMT as an insertional mutagenesis tool for different fungal species. The first genome sequence of a mycorrhizal fungus, the basidiomyceteLaccaria bicolor, became public in July 2006. Release ofLaccariagenome sequence and the availability of AMT makes this fungus an excellent model for functional genomic studies in ectomycorrhizal research. No data on the integration pattern inLaccariagenome were available, thus we optimized a plasmid rescue approach for this fungus. To this end the transformation vector (pHg/pBSk) was constructed allowing the rescue of the T‐DNA right border (RB)–genomic DNA junctions inEscherichia coli. Fifty‐oneAgrobacterium‐transformed fungal strains, picked up at random from a larger collection of T‐DNA tagged strains (about 500), were analysed. Sixty‐nine per cent were successfully rescued for the RB of which 87% were resolved for genomic integration sequences. Our results demonstrate that the plasmid rescue approach can be used for resolving T‐DNA integration sites inLaccaria. The RB was well conserved during transformation of this fungus and the integration analysis showed no clear sequence homology between different genomic sites. Neither obvious sequence similarities were found between these sites and the T‐DNA borders indicating non‐homologous integration of the transgenes. Majority (75%) of the integrations were located in predicted genes.Agrobacterium‐mediated gene transfer is a powerful tool that can be used for functional gene studies inLaccariaand will be helpful along with plasmid rescue in searching for relevant fungal genes involved in the symbiotic process.
The Intersecting Roles of Consumer and Producer: A Critical Perspective on Co‐production, Co‐creation and Prosumption
Authors: Humphreys Ashlee , Grayson Kent
Published: April 2008

The terms ‘co‐creation’, ‘co‐production’, and ‘prosumption’ refer to situations in which consumers collaborate with companies or with other consumers to produce things of value. These situations sometimes appear to blur the traditional roles of ‘producer’ and ‘consumer’. Building on Marx's distinction between ‘use value’ and ‘exchange value’, we argue that, when consumers perform tasks normally handled by the company, this does not necessarily represent a fundamental change in exchange roles or economic organization. We then argue that, when individuals who are traditionally defined as ‘consumers’ produce exchange value for companies, this does represent a fundamental change.
The efficacy of ursodeoxycholic acid and bezafibrate combination therapy for primary biliary cirrhosis: A prospective, multicenter study
Authors: Iwasaki Shinji , Ohira Hiromasa , Nishiguchi Shuhei , Zeniya Mikio , Kaneko Shuichi , Onji Morikazu , Ishibashi Hiromi , Sakaida Isao , Kuriyama Shigeki , Ichida Takafumi , Onishi Saburo , Toda Gotaro ,   Study Group of Intractable Liver Diseases for Research on a Specific Disease, Health Science Research Grant, Ministry of Health, Labour and Welfare of Japan
Published: April 2008

Aim:  Treatment with ursodeoxycholic acid (UDCA) improves the survival of stage I and II primary biliary cirrhosis (PBC) patients. However, new therapeutic options are needed for patients who are refractory to UDCA and for those whose disease is at an advanced stage. Bezafibrate could be useful in PBC treatment, since it increases phospholipid output into the bile and reduces the cytotoxicity of hydrophobic bile acids, which are increased with cholestasis.

Methods:  We conducted two prospective, multicenter randomized open studies in non‐cirrhotic patients with PBC to evaluate the efficacy of bezafibrate. One study compared UDCA and bezafibrate monotherapy (study 1: 45 patients [37 females], mean age 55.9 years), and the other evaluated the addition of bezafibrate to patients who were refractory to UDCA (study 2: 21 patients [18 females], mean age 54.1 years).

Results:  Study 1 demonstrated that bezafibrate monotherapy was as effective as UDCA and study 2 revealed that bezafibrate combined with UDCA was effective in improving and maintaining biliary enzymes where the ineffectiveness of long‐term treatment with UDCA was confirmed.

Conclusion:  This multicenter, randomized, open study revealed that combination therapy of bezafibrate and UDCA improved biliary enzymes in non‐cirrhotic Japanese patients with PBC refractory to UDCA. Further studies are needed to evaluate whether combination therapy improves histological staging and prognosis.
Flexure Pivot Tilting Pad Hybrid Gas Bearings: Operation With Worn
Clearances and Two Load-Pad Configurations
Authors: San Andrés Luis , Ryu Keun
Published: April 2008

Gas film bearings enable the successful deployment of high-speed microturbomachinery. Foil bearings are in use; however, cost and lack of calibrated predictive tools prevent their widespread application. Other types of bearing configurations, simpler to manufacture and fully engineered, are favored by commercial turbomachinery manufacturers. Externally pressurized tilting pad bearings offer a sound solution for stable rotor support. This paper reports measurements of the rotordynamic response of a rigid rotor, 0.825kg and 28.6mm in diameter, supported on flexure pivot tilting pad hybrid gas bearings. The tests are performed for various imbalances, increasing supply pressures, and under load-on-pad (LOP) and load-between-pad (LBP) configurations. Presently, the initial condition of the test bearings shows sustained wear and dissimilar pad clearances after extensive testing reported earlier, (Zhu, X., and San Andrés, L., 2007, “Rotordynamic Performance of Flexure Pivot Hydrostatic Gas Bearings for Oil-Free Turbomachinery,” ASME J. Eng. Gas Turbines Power, 129, pp. 1020–1027). In the current measurements, there are no noticeable differences in rotor responses for both LOP and LBP configurations due to the light-weight rotor, i.e., small static load acting on each bearing. External pressurization into the bearings increases their direct stiffnesses and reduces their damping, while raising the system critical speeds with a notable reduction in modal damping ratios. The rotor supported on the worn bearings shows an ∼10% drop in first critical speeds and roughly similar modal damping than when tested with pristine bearings. Pressurization into the bearings leads to large times for rotor deceleration, thus demonstrating the little viscous drag typical of gas bearings. Rotor deceleration tests with manually controlled supply pressures eliminate the passage through critical speeds, thus paving a path for rotordynamic performance without large amplitude motions over extended regions of shaft speed. The rotordynamic analysis shows critical speeds and peak amplitudes of motion agreeing very well with the measurements. The synchronous rotor responses for increasing imbalances demonstrate the test system linearity. Superior stability and predictable performance of pressurized flexure pivot gas bearings can further their implementation in high performance oil-free microturbomachinery. More importantly, the measurements show the reliable performance of the worn bearings even when operating with enlarged and uneven clearances.
Data Visualization, Data Reduction and Classifier Fusion for Intelligent Fault Diagnosis in Gas Turbine Engines
Authors: Donat William , Choi Kihoon , An Woosun , Singh Satnam , Pattipati Krishna
Published: April 2008

In this paper, we investigate four key issues associated with data-driven approaches for fault classification using the Pratt and Whitney commercial dual-spool turbofan engine data as a test case. The four issues considered here include the following. (1) Can we characterize, a priori, the difficulty of fault classification via self-organizing maps? (2) Do data reduction techniques improve fault classification performance and enable the implementation of data-driven classification techniques in memory-constrained digital electronic control units (DECUs)? (3) When does adaptive boosting, an incremental fusion method that successively combines moderately inaccurate classifiers into accurate ones, help improve classification performance? (4) How to synthesize classifier fusion architectures to improve the overall diagnostic accuracy? The classifiers studied in this paper are the support vector machine, probabilistic neural network, k-nearest neighbor, principal component analysis, Gaussian mixture models, and a physics-based single fault isolator. As these algorithms operate on large volumes of data and are generally computationally expensive, we reduce the data set using the multiway partial least squares method. This has the added benefits of improved diagnostic accuracy and smaller memory requirements. The performance of the moderately inaccurate classifiers is improved using adaptive boosting. These results are compared to the results of the classifiers alone, as well as different fusion architectures. We show that fusion reduces the variability in diagnostic accuracy, and is most useful when combining moderately inaccurate classifiers.
Combustion Chamber Steam Injection for Gas Turbine Performance Improvement During High Ambient Temperature Operations
Authors: Bouam Abdallah , Aissani Slimane , Kadi Rabah
Published: April 2008

The gas turbines are generally used for large scale power generation. The basic gas turbine cycle has low thermal efficiency, which decreases in the hard climatic conditions of operation, so the cycles with thermodynamic improvement is found to be necessary. Among several methods shown their success in increasing the performances, the steam injected gas turbine cycle (STIG) consists of introducing a high amount of steam at various points in the cycle. The main purpose of the present work is to improve the principal characteristics of gas turbine used under hard condition of temperature in Algerian Sahara by injecting steam in the combustion chamber. The suggested method has been studied and compared to a simple cycle. Efficiency, however, is held constant when the ambient temperature increases from ISO conditions to 50°C. Computer program has been developed for various gas turbine processes including the effects of ambient temperature, pressure ratio, injection parameters, standard temperature, and combustion chamber temperature with and without steam injection. Data from the performance testing of an industrial gas turbine, computer model, and theoretical study are used to check the validity of the proposed model. The comparison of the predicted results to the test data is in good agreement. Starting from the advantages, we recommend the use of this method in the industry of hydrocarbons. This study can be contributed for experimental tests.
An Experimental Study of Spark Anemometry for In-Cylinder Velocity Measurements
Authors: Gardiner D. P. , Wang G. , Bardon M. F. , LaViolette M. , Allan W. D.
Published: April 2008

It has been demonstrated by previous researchers that an approximate value of the bulk flow velocity through the spark plug gap of a running spark ignition engine may be deduced from the voltage and current wave forms of the spark. The technique has become known as spark anemometry and offers a robust means of velocity sensing for engine combustion chambers and other high temperature environments. This paper describes an experimental study aimed at improving performance of spark anemometry as an engine research tool. Bench tests were conducted using flow provided by a calibrated nozzle apparatus discharging to atmospheric pressure. While earlier studies had relied upon assumptions about the shape of the stretching spark channel to relate the spark voltage to the flow velocity, the actual spark channel shape was documented using high-speed video in the present study. A programmable ignition system was used to generate well-controlled constant current discharges. The spark anemometry apparatus was then tested in a light duty automotive engine. Results from the image analysis of the spark channel shape undertaken in the present study have shown that the spark kernel moves at a velocity of less than that of the freestream gas velocity. A lower velocity threshold exists below, which there is no response from the spark. It is possible to obtain a consistent, nearly linear relationship between the first derivative of the sustaining voltage of a constant current spark and the freestream velocity if the velocity falls within certain limits. The engine tests revealed a great deal of cycle-to-cycle variation in the in-cylinder velocity measurements. Instances where the spark restrikes occur during the cycle must also be recognized in order to avoid false velocity indications.
The Fuel Mix Limits and Efficiency of a Stoichiometric, Ammonia, and Gasoline Dual Fueled Spark Ignition Engine
Authors: Grannell Shawn M. , Assanis Dennis N. , Bohac Stanislav V. , Gillespie Donald E.
Published: April 2008

An overall stoichiometric mixture of air, gaseous ammonia, and gasoline was metered into a single cylinder, variable compression ratio, supercharged cooperative fuel research (CFR) engine at varying ratios of gasoline to ammonia. The engine was operated such that the combustion was knock-free with minimal roughness for all loads ranging from idle up to a maximum load in the supercharge regime. For a given load, speed, and compression ratio, there was a range of ratios of gasoline to ammonia for which knock-free, smooth firing was obtained. This range was investigated at its rough limit and also at its maximum brake torque (MBT) knock limit. If too much ammonia was used, then the engine fired with an excessive roughness. If too much gasoline was used, then knock-free combustion could not be obtained while the maximum brake torque spark timing was maintained. Stoichiometric operation on gasoline alone is also presented, for comparison. It was found that a significant fraction of the gasoline used in spark ignition engines could be replaced with ammonia. Operation on about 100% gasoline was required at idle. However, a fuel mix comprising 70% ammonia∕30% gasoline on an energy basis could be used at normally aspirated, wide open throttle. Even greater ammonia to gasoline ratios were permitted for supercharged operation. The use of ammonia with gasoline allowed knock-free operation with MBT spark timing at higher compression ratios and higher loads than could be obtained with the use of gasoline alone.
A Comparison of Two Trending Strategies for Gas Turbine Performance Prediction
Authors: Sekhon Rajat , Bassily Hany , Wagner John
Published: April 2008

Complex multidomain dynamic systems demand reliable health monitoring to minimize breakdowns and downtime, thereby enabling cost savings and increased operator safety. Diagnostic and prognostic strategies monitor a system’s transient and steady-state operations, detecting deviations from normal operating scenarios and warning operators of potential system anomalies. System diagnostics detect, identify, and isolate a system fault while prognostics offer strategies to predict system behavior at a future operating time to define the useful period before failure criterion is reached. This paper presents the development and the experimental application of two methods to predict the system behavior based on trends in performance. Statistical regression concepts have been used to analyze dynamic plant signals, and based on these results, future plant operation was estimated. Wavelet transforms were used to condition the signal, and the denoised signals were subsequently forecast. The case study presented here applies the two methodologies to the operational data from a simple cycle 85MW General Electric gas turbine. Those operating data were used to train and validate the algorithms. A comparison of the two methodologies reveals that the wavelet forecast is better than the statistical strategy with lower forecasting error. The developed approaches may be used in parallel with a diagnostic algorithm to monitor gas turbine system behavior.
Creep-Fatigue Tests on Full Scale Directionally Solidified Turbine Blades
Authors: Yan Xiaojun , Nie Jingxu
Published: April 2008

A new experimental method, in which a full scale directionally solidified (DS) alloy turbine blade is loaded by a special design rig employing friction force and heated by eddy current induction, is proposed to conduct creep-fatigue life tests in this investigation. The method can take factors such as geometry, volume, especially cast procedures, etc., into creep-fatigue life assessment. Principle and design of the test rig are fully explained. Creep-fatigue tests of turbine blades made of DZ4 alloy (one type of DS alloys) were conducted and test data were analyzed. Life prediction based on test data of this investigation shows good agreement with actual flight experience of these blades. The method of this article provides a new way to estimate the potential creep-fatigue or low cycle fatigue life for turbine blades.
A Micromechanics Based Representation of Combined Mode I and II Toughness of Brittle Materials and Interfaces
Authors: Ahmad J.
Published: April 2008

The work of Evans and Hutchinson (1989) on micromechanics modeling of combined mode fracture is used as the basis for proposing an expression for combined Mode I and Mode II fracture toughness of brittle monolithic materials as well as bimaterial interfaces. The results of the proposed expression are compared with experimental data.
High Temperature Low-Cycle Fatigue of Friction Welded Joints-Type 304-304 Stainless Steel and Alloy 718-718 Nickel Base Superalloy
Authors: Wakai T. , Sakane M. , Ohnami M. , Okita K. , Fukuchi Y.
Published: April 2008

This paper assesses the high-temperature low-cycle fatigue of the Type 304 stainless steel and Alloy 718 superalloy friction-welded joints. Strain controlled low-cycle fatigue tests for 304-304 and 718-718 friction-welded specimens were carried out at 923K in air to obtain the fatigue strength of the joints. These materials were selected as the cyclic hardening and softening materials, respectively. The 304-304 welded specimens showed inferior fatigue strength in comparison with the base metal while the 718-718 specimens exhibited fatigue strength equivalent to that of the base metal. The difference in the fatigue strength between the two materials is discussed from the viewpoint of the cyclic deformation behavior and strain reduction at weld interface.
In-Situ Compressive Strength of Carbon/Epoxy AS4/3501-6 Laminates
Authors: Colvin G. E. , Swanson S. R.
Published: April 2008

An experimental program has been conducted to evaluate how changes in laminate lay-up can influence the compression behavior of fiber-dominated, resin-based composites. The testing utilized a cylindrical, 3.81 cm (1.5 in.) diameter test specimen because it provides inherent resistance to global buckling failure modes and lack of free edge effects. Seven different laminates representing 0° dominated lay-ups, axial bias lay-ups, and quasi-isotropic lay-ups were tested. The measured macroscopic stress strain failure data showed a strong in-situ dependence of the 0° failure strain on the lay-up. The quasi-isotropic laminate failure strains were nearly twice the 0° dominated laminate failure strains. Photomicrographs of the failure zone from sections of failed specimens showed the presence of fiber kinking in all the laminate failures.
Machinability of Fiber-Reinforced Thermoplastics in Drilling
Authors: Hocheng H. , Puw H. Y.
Published: April 2008

Polymer-based composite materials are used in a variety of industry. Recently, thermoplastic polymer suitable for the resinous matrix in carbon fiber-reinforced composites has been introduced for lower material and processing costs, improved damage tolerance and higher moisture resistance. The successful use of this material requires sophisticated production technology, however little reference of machining of thermoplastics composites can be found. The existing published results are almost exclusively for epoxy-based composite materials showing difficulty in avoiding poor finish, serious tool wear and delamination at hole entrance and exit due to the brittle material response to machining. Thermoplastics-based composite materials possesses better machinability. The current work reveals the machinability of an example of carbon fiber-reinforced ABS (Acrylonitrile Butadiene Styrene) in drilling compared to representative metals and thermoset-based composites. The observation of chips reveals that considerable plastic deformation is involved. Compared to the chip formation of thermoset plastics, it contributes to the improved edge quality in drilling. The edge quality is generally fine except in the case of concentrated heat accumulation at tool lips, which is generated by high cutting speed and low feed rate. Plastics tend to be extruded out of the edge rather than neatly cut. The average surface roughness along hole walls in commonly below one micron for all sets of cutting conditions in the experiment, values between 0.3 and 0.6 microns are typical. The high speed steel drill presents only minor tool wear during the tests. Based on these results, one concludes that the carbon fiber-reinforced ABS demonstrates good machinability in drilling.
Integrated Simulation of Fluid Flow and Heat Transfer in Injection Molding for the Prediction of Shrinkage and Warpage
Authors: Chiang H. H. , Himasekhar K. , Santhanam N. , Wang K. K.
Published: April 2008

This work employs a coupled analysis of the fluid flow and heat transfer in the polymer melt during the filling and post-filling stages of the injection-molding process and of mold cooling/heating which occurs during the entire process. Polymer melt analysis (PMA) has been carried out through a unified theoretical model implemented using a hybrid finite-element/finite-difference/control-volume numerical solution of the generalized Hele-Shaw flow of a compressible viscous fluid under non-isothermal conditions. Further, mold-cooling analysis (MCA) has been carried out utilizing a periodic heat conduction model implemented using a modified three-dimensional boundary-element method. To faithfully accommodate the effects of mold cooling on the fluid flow and heat transfer in the polymer melt, PMA and MCA have been coupled for appropriate data exchange and iterations carried out until a convergent solution for mold temperatures and for flow, pressure and temperatures within the polymer melt is obtained. The results obtained from this integrated simulation for different test cases have been compared with experimental data and a favorable agreement has been noticed. Using an illustrative example, the results are discussed in detail.
Thermal-Induced Transformation of Retained Austenite in the Simulated Case of a Carburized Steel
Authors: Neu R. W. , Sehitoglu Huseyin
Published: April 2008

Systematic experiments were conducted on carburized 4320 steel to study thermalinduced transformation of austenite to bainite by measuring the volumetric transformation strains. Up to about 210°C, thermal-induced transformation involved a diffusion-controlled reaction and therefore was time dependent. The mechanism is similar to that described by the second stage of tempering. An Arhennius-type relation was used to model the kinetics of the reaction leading to a volume increase. A positive hydrostatic stress tended to increase the rate of transformation. The anisotropy of the transformation strains were proportional to the deviatoric stress.
Influence of Superimposed Hydrostatic Pressure on Bending Fracture and Formability of a Low Carbon Steel Containing Globular Sulfides
Authors: Kao A. S. , Kuhn H. A. , Spitzig W. A. , Richmond O.
Published: April 2008

Bend tests under superimposed hydrostatic pressure were carried out on a low carbon steel containing globular sulfide inclusions to investigate the variation of ductile fracture and forming limits due to supression of void growth. Results show that increasing pressure enhances formability, as expressed by increasing intercept and decreasing slope of the forming limit line, due to a pressure-induced transition in fracture mechanism. A continuum mechanical model based on the growth and coalescence of voids under applied pressure is proposed that explains the experimental results and predicts the fracture limit under actual metalforming conditions.
Characterization of Sheet Metal Forming Using Acoustic Emission
Authors: Liang S. Y. , Dornfeld D. A.
Published: April 2008

The application of acoustic emission signal analysis for characterization of sheet metal forming operations is discussed in this paper. Two particular sheet metal forming operations are examined: punch stretching and deep drawing. The acoustic emission signal characteristics, including the energy content, the spectral properties, and time series behaviors, as functions of the process state, are experimentally studied. Using plastic work analysis, an analytical relationship between acoustic emission energy rate and punch stretching parameters (punch feed rate, workpiece thickness, punch size, holder diameter, amount of plastic deformation, and workpiece material properties) is developed and supporting experimental results presented. During the forming processes, acoustic emission signal features show strong correlations with punch/workpiece contact, yielding, deformation, flange wrinkling, necking and fracture. Therefore, acoustic emission can be effectively used for in-process monitoring of sheet metal forming operations.
Thermo-Mechanical Fatigue of Mar-M247: Part 2—Life Prediction
Authors: Sehitoglu Huseyin , Boismier D. A.
Published: April 2008

A life prediction model is proposed based on microstructural observations of damage in thermo-mechanical fatigue and isothermal fatigue experiments on Mar-M247 Nickel based Superalloy. The model incorporates damage accumulation due to fatigue, environment (oxidation and γ′ depletion), and creep processes. The model is capable of predicting lives at different temperatures, strain rates and temperature-strain phasing conditions. The model successfully predicted the shorter lives at high strain amplitudes in in-phase thermo-mechanical fatigue cases and the shorter lives at lower strain amplitudes in out-of-phase thermo-mechanical fatigue cases and the associated crossover in life. The prediction of a nonproportional strain-temperature history (diamond shaped) was very satisfactory. A unified constitutive equation was utilized to predict the stresses, which influenced the creep damage term. The oxidation term is a function of mechanical strain range, temperature-strain phasing and incorporated oxidation and γ′ depletion kinetics.
Micromechanical Analysis of the Creep Response of Unidirectional Composites
Authors: Yancey R. N. , Pindera Marek-Jerzy
Published: April 2008

The paper outlines the use of the micromechanics model proposed by Aboudi in predicting the creep response of unidirectional composites consisting of linearly viscoelastic matrices and elastic fibers. The closed-form expressions for the effective elastic moduli given in terms of the phase moduli and volume fractions provided by the micromechanics model facilitate a straightforward application of the viscoelastic Correspondence Principle. The inversion of the effective moduli in the Laplace transform domain to the time domain is subsequently accomplished using the Bellman method. The predictions of the model are compared with the creep response of T300/934 graphite/epoxy unidirectional coupons at two different temperatures. Very good correlation between theory and experiment is illustrated for the linearly viscoelastic response characterized by relatively small creep strains.
The Constitutive Equation for Silicon and Its Use in Crystal Growth Modeling
Authors: Tsai C. T. , Dillon O. W. , De Angelis R. J.
Published: April 2008

A stress analysis that describes the crystal growing process requires a material model that is valid over a wide temperature range and includes dislocation motion and multiplication. The stresses developed in the growing process could induce residual stresses, changes in dislocation density and buckling into the growing crystals. The dislocation density is introduced as an internal variable in the constitutive model. The stress-strain and dislocation density-strain characteristics of silicon crystals are discussed as a function of temperature, strain rate, and initial dislocation density.
Elasto-Viscoplastic Constitutive Equations for Clay and Its Application to Consolidation Analysis
Authors: Adachi T. , Oka F. , Mimura M.
Published: April 2008

The mathematical structure of Adachi and Oka’s model, a typical overstress type elasto-viscoplastic constitutive model, for normally consolidated clays is discussed. Since it has been recognized that the overstress type models cannot describe the acceleration creep and creep rupture, the Adachi and Oka’s model was modified so that it can explain the creep rupture including acceleration creep of normally consolidated clays. In addition, based on the Adachi and Oka’s constitutive model and Biot’s consolidation theory, one-dimensional consolidation problems were analyzed numerically by the finite element method. Results show that the proposed method can describe the effect of sample thickness and aging on consolidation phenomena.
Quantitative NDE of Advanced Composites Using Ultrasonic Velocity Measurements
Authors: Kline R. A.
Published: April 2008

In this work, the use of ultrasonic velocity analysis for the quantitative nondestructive evaluation of the mechanical properties of composite laminates is discussed. The composite laminate is modeled as a layer or set of layers of transversely isotropic material of known orientation. The method described utilizes velocity measurements for ultrasonic wave propagation at multiple angles of incidence. Since the equations are algebraically cumbersome, a numerical procedure employing a commercially available nonlinear equation solving subroutine is utilized. Applications to composite laminates are presented.
Determination of Continuum Fracture Parameters for a Particulate Composite
Authors: Smith C. W. , Czarnek R. , Rezvani M.
Published: April 2008

Rocket motor grain consists of rigid particles embedded in a soft, rubbery matrix. The ingredients are chosen to maximize the burning properties, but when cracks develop during curing or storage, burn properties are altered. The present study was directed towards a study of the loss of the inverse square root singularity in the neighborhood where a crack intersects the free surface in simulated motor grain. Experiments were conducted on both cracked simulated pure binder and cracked simulated motor grain and algorithms were developed for computing fracture parameters from the data. Severe crack tip blunting prior to crack growth initiation was observed in the simulated motor grain which required a modification of the algorithm used for single phase materials. Efforts to determine the dominant eigenvalue after crack growth have met with limited success to date due to increasing data scatter.
Leaky Lamb Waves for the Ultrasonic Nondestructive Evaluation of Adhesive Bonds
Authors: Mal Ajit K. , Xu Pei-cheng , Bar-Cohen Yoseph
Published: April 2008

The critical role played by interface zones in the fracture and failure of composites and other bonded materials is well known. However, the existing nondestructive evaluation methods are not capable of yielding useful quantitative information on either elastic or strength related properties of the interface. The authors are investigating the feasibility of applying an ultrasonic method to determine some of the interface properties nondestructively. The method uses guided waves and is based on the fact that the dispersive properties of these waves are strongly affected by the elastic properties of the interface. A coordinated theoretical and experimental program of research has revealed that the correlation between the interfacial properties and the phase velocity of the guided waves is quite strong and is identifiable at least in laboratory specimens. Some recent results of this research are reported in this paper.
Dynamic Distribution of Displacement and Stress Considerations in the Ultrasonic Immersion Nondestructive Evaluation of Multilayered Plates
Authors: Nayfeh A. H. , Taylor T. W.
Published: April 2008

A unified theoretical treatment is presented for the calculation of displacements and stresses within multilayered media subjected to incident ultrasonic waves. The wave is supposed to be incident from water, at an arbitrary angle, upon a plate consisting of an arbitrary number of different isotropic material layers. In the first part of the analysis displacements and stresses are determined as functions of position within the plate while all layer interfaces are assumed to be rigidly bonded. A smooth interface is subsequently introduced to simulate debonding of two material layers. The composite plate is assumed to be bounded at the bottom by either a free surface, a fluid half-space or an elastic solid half-space. A byproduct of the analysis is the derivation of the reflection and transmission coefficients for the systems. Extensive numerical results are given in order to delineate the influence of the plate material orderings, layer thicknesses and interfacial conditions on the displacements and stresses within the plate. The model developed here will be of value in material characterization and in the nondestructive evaluation of advanced material applications.
An Axial-Torsional Extensometer for Finite Deformation
Authors: Wu Han-Chin , Xu Zhiyou
Published: April 2008

An axial-torsional extensometer has been designed, constructed and tested. This extensometer is suitable for use in the experimental determination of multiaxial plastic deformation and determination of fatigue fracture under moderately large strain range. The extensometer is applicable to tubular or solid cylindrical specimens, with enlarged ends, and measures the axial and shear deformations within a gage section of the specimen. It has been calibrated, and error bounds are given in terms of linearity, crosstalk, and hysteresis. The diametral strain can also be measured, which is especially useful in the testing of materials with voids. An application has been made to combined axial-torsional loading of a metal tubular specimen. Test results are presented.