bluuebunny/crossref_metadata_2025 huggingface dataset:
The effect of alcohol intake on breastfeeding duration in Australian women
Authors: Giglia Roslyn C , Binns Colin W , Alfonso Helman S , Scott Jane A , Oddy Wendy H
Published: April 2008

Aim: This study investigated the relationships between alcohol consumption and breastfeeding initiation and duration.

Methods: Design and Setting: A 12‐month longitudinal study was conducted in two public hospitals in Perth, Australia between September 2002 and July 2003.

Intervention: Participating mothers completed a self‐administered baseline questionnaire. Follow‐up telephone interviews were conducted at 4, 10, 16, 22, 32, 40 and 52 weeks.

Main outcome measures: Association of the relationships between alcohol consumption and breastfeeding initiation and duration.

Results: After 6 months of follow‐up, women who consumed alcohol at levels of more than two standard drinks per day were almost twice as likely to discontinue breastfeeding than women who drank below these levels (HR 1.9, 95% CI 1.1, 3.0).

Conclusion: Consuming alcohol in excess of two standard drinks per day during lactation was found to be independently associated with shorter breastfeeding duration, even after consideration of previously identified predictors of breastfeeding duration. Guidelines that provide direction on safe alcohol consumption for lactating mothers may help support extended breastfeeding duration.
Tick‐borne encephalitis in Styrian children from 1981 to 2005: a retrospective study and a review of the literature
Authors: Fritsch Peter , Gruber‐Sedlmayr Ursula , Pansi Heike , Zöhrer Bettina , Mutz Ingomar , Spork Dietmar , Zenz Werner
Published: April 2008

Background: Tick‐borne encephalitis in children appears to be more benign than in adults and shows also a more favourable outcome. Only some authors report of sequelae like paralysis, paresis or seizures and behavioural abnormalities. The aim was to describe the clinical features of tick‐borne encephalitis in children with special attention to sequelae and to review the literature.

Methods: Retrospective review of all charts of children with serologically confirmed tick‐borne encephalitis hospitalised in Styria between 1981 and 2005.

Results: One hundred sixteen children were diagnosed with tick‐borne encephalitis. Ninety‐two children (79.3%) developed meningitis and 24 (20.7%) meningoencephalitis. Eleven patients with meningoencephalitis showed somnolence, 5 confusion, 5 tremors, 2 facial palsy, 1 ataxia, 1 epileptic seizure and 1 hemi paresis. Seven patients had to be admitted to the intensive care unit. Two children (1.7%) developed long time neurological sequelae: one epileptic seizure with requirement of antiepileptic therapy and one left‐sided hemi paresis. One hundred twelve children had been not and 3 incompletely vaccinated against tick‐borne encephalitis. Only one child had been fully vaccinated according to the Austrian vaccination schedule.

Conclusion: Our study provides further evidence that tick‐borne encephalitis in children has a substantial morbidity and in single cases severe long‐time neurological sequelae are observed.
Radiation, retardation and the developing brain: time is the crucial variable
Authors: Nowakowski Richard S , Hayes Nancy L
Published: April 2008

Background: Widespread radiation is a threat unique to the modern world. A recent report reveals that sub‐clinical damage to human foetuses between 8 and 25 weeks of gestation can result in cognitive deficits still manifest 16–18 years after birth. These previously unrecognised, long‐term effects are apparently produced by a relatively short pulse of exposure to radioactive fallout at levels that were previously thought not to be deleterious. This idea is plausible given the nature of the developmental events occurring in the brain during this period of gestation.

Conclusion: This exposed population should be examined for other neurological and psychiatric syndromes. If these findings are corroborated, in the event of future radiation exposures, steps should be taken to shield pregnant women who are within this window of vulnerability.
Romantic Literature and Colonialism
Authors: Bolton Carol
Published: April 2008

Current critical approaches to Romantic literature recognise the formative influence of historical and political developments on its creation. This article contributes to this understanding by focusing on British colonialism of the period from 1780 to 1830, in order to illustrate the relationship between these events and the writing which emerged from that context. The texts discussed include a wider variety of different forms of literary engagement with colonialism, and therefore a broader interpretation of Romantic literature than it is conventionally accorded. Travel narratives, missionary accounts, journalism and reports written to encourage settlement, as well as novels and poetry are all considered. Suggestions for further reading, particularly secondary works that discuss specific geographical regions in more detail, are provided in the Works Cited.
Estimating index of population trend by re‐sampling techniques (jackknife and bootstrap) and its application to the life table study of rice leaf roller,Cnaphalocrocis medinalis(Lepidoptera: Pyralidae)
Authors: Tao Fang‐Ling , Min Shi‐Fan , Wu Wei‐Jian , Liang Guang‐Wen , Zeng Ling
Published: April 2008

Taking a published natural population life table of rice leaf roller,Cnaphalocrocis medinalis(Lepidoptera: Pyralidae), as an example, we estimated the population trend index,I, via re‐sampling methods (jackknife and bootstrap), determined its statistical properties and illustrated the application of these methods in determining the control effectiveness of bio‐agents and chemical insecticides. Depending on the simulation outputs, the smoothed distribution pattern of the estimates ofIby delete‐1 jackknife is visually distinguishable from the normal density, but the smoothed pattern produced by delete‐djackknife, and logarithm‐transformed smoothed patterns produced by both empirical and parametric bootstraps, matched well the corresponding normal density. Thus, the estimates ofIproduced by delete‐1 jackknife were not used to determine the suppressive effect of wasps and insecticides. The 95% percent confidence intervals or the narrowest 95 percentiles andZ‐test criterion were employed to compare the effectiveness ofTrichogramma japonicumAshmead and insecticides (powder, 1.5% mevinphos + 3% alpha‐hexachloro cyclohexane) against the rice leaf roller based on the estimates ofIproduced by delete‐djackknife and bootstrap techniques. At α= 0.05 level, there were statistical differences between wasp treatment and control, and between wasp and insecticide treatments, if the normality is ensured, or by the narrowest 95 percentiles. However, there is still no difference between insecticide treatment and control. ByZ‐test criterion, wasp treatment is better than control and insecticide treatment withP‐value < 0.01. Insecticide treatment is similar to control withP‐value > 0.2 indicating that 95% confidence intervals procedure is more conservative. Although similar conclusions may be drawn by re‐sampling techniques, such as the delta method, about the suppressive effect of trichogramma and insecticides, the normality of the estimates can be checked and guaranteed, and the correlation among sequential life stages of rice leaf roller is also considered in the estimation. Judged by theP‐values fromZ‐test, the delta method is more conservative.
Development rate and lower temperature threshold in the eggs of Eurygaster integriceps (Heteroptera: Scutelleridae)
Authors: Kivan Mujgan
Published: April 2008

The sunn pest, Eurygaster integriceps Put. has a wide distribution in the Palearctic region. It is the most important pest problem of wheat in Turkey. The objective of this study was to attain better knowledge of the development of the sunn pest eggs. The lower temperature threshold and development rate of eggs were determined at 17, 20, 23, 26 and 32°C ± 1°C in the laboratory. A linear model was used to describe the developmental rate and temperature. The egg development required 90.9 degree‐days above the theoretical threshold of 11.7°C. The development time was 17.6 ± 0.1 days at 17°C, and 4.5 ± 0.01 days at 32°C. Incubation time was inversely related to temperature. The study showed that the eggs of E. integriceps needed shorter periods of time to complete their development than immature stages of their parasitoids Trissolcus spp.
Assessing the sensitivity of Melanoplus frigidus (Orthoptera: Acrididae) to different weather conditions: A modeling approach focussing on development times
Authors: Finch Oliver‐D. , Löffler Jörg , Pape Roland
Published: April 2008

The temperature and soil moisture conditions as well as vegetation patterns were studied to describe the habitat and to model the life cycle of Melanoplus frigidus, a true alpine grasshopper of the Scandes. In the low alpine belt of the Norwegian Scandes the species colonizes only the warmest microhabitats with maximum soil surface temperatures of 31°C. Vegetation of these habitats consists of shrub‐rich heath dominated by Vaccinium myrtillus and Calluna vulgaris. Using continuously measured temperature data, the development times for four different seasons were modeled and related to field observations. The maximum delay of adult molt was estimated to amount to 3 weeks, the delay being determined by the variation in spring temperature conditions between different years. The possibilities of using M. frigidus as an indicator organism of climate change effects on alpine zoo‐coenoses of the Scandes are discussed.
OUTSOURCING: TRANSACTION COST ECONOMICS AND SUPPLY CHAIN MANAGEMENT*
Authors: WILLIAMSON OLIVER E.
Published: April 2008

This article examines outsourcing from the transaction cost economics (TCE) perspective. The transaction is made the basic unit of analysis and the procurement decision, as between make and buy, is made (principally) with reference to a transaction cost economizing purpose. As sketched herein, the ease of contracting varies with the attributes of the transaction, with special emphasis on whether preserving continuity between a particular buyer–seller pair is the source of added value. The basic regularity is this: as bilateral dependency builds up, the efficient governance of contractual relations progressively moves from simple market exchange to hybrid contracting (with credibility supports) to hierarchy. This last corresponds to the “make” decision, which, as viewed from the TCE perspective, is viewed as the organization form of last resort. The article successively describes the lens of contract approach to economic organization, the operationalization of TCE, different styles of outsourcing, qualifications to the foregoing and the main lessons of TCE for the supply chain literature.
DEVELOPING PURCHASING'S FOUNDATION*
Authors: LEENDERS MICHIEL R. , FEARON HAROLD E.
Published: April 2008

This is the first of a two‐part paper, which reviews the evolution of the supply management function from the 18th century to 1940. A second paper will examine the continued evolution of supply management from 1940 until the present. The 1830–1940 period in North America was one of tremendous development for purchasing. It started with occasional reference in management texts and, particularly after 1900, saw the evolution of a host of ideas representing the foundation of today's perspective on supply management. At no time did purchasing practitioners and academics see the function as a narrow buying activity. Clearly, our predecessors were well aware of the benefits of integration and would have been comfortable with today's supply chain management precepts. They also recognized value, cost and price analysis, value analysis, purchasing research, talent management, outsourcing the supply function, supplier relationships, strategy and the need for performance measurement. They strived to contribute effectively to organizational goals and strategies, well aware of the potential impact of their actions on organizational success. An understanding of supply's evolution may not only assist today's supply management practitioners and academics in placing current practices and theories in context but also in charting our future.
Ground Water Budget Analysis and Cross‐Formational Leakage in an Arid Basin
Authors: Hutchison William R. , Hibbs Barry J.
Published: April 2008

Ground water budget analysis in arid basins is substantially aided by integrated use of numerical models and environmental isotopes. Spatial variability of recharge, storage of water of both modern and pluvial age, and complex three‐dimensional flow processes in these basins provide challenges to the development of a good conceptual model. Ground water age dating and mixing analysis with isotopic tracers complement standard hydrogeologic data that are collected and processed as an initial step in the development and calibration of a numerical model. Environmental isotopes can confirm or refute a priori assumptions of ground water flow, such as the general assumption that natural recharge occurs primarily along mountains and mountain fronts. Isotopes also serve as powerful tools during postaudits of numerical models. Ground water models provide a means of developing ground water budgets for entire model domains or for smaller regions within the model domain. These ground water budgets can be used to evaluate the impacts of pumping and estimate the magnitude of capture in the form of induced recharge from streams, as well as quantify storage changes within the system. The coupled analyses of ground water budget analysis and isotope sampling and analysis provide a means to confirm, refute, or modify conceptual models of ground water flow.
Heat shock factor activation in human muscles following a demanding intermittent exercise protocol is attenuated with hyperthermia
Authors: Palomero J. , Broome C. S. , Rasmussen P. , Mohr M. , Nielsen B. , Nybo L. , McArdle A. , Drust B.
Published: April 2008

Aim:  The present study investigated whether increased activation of heat shock factors (HSF) following exercise relates primarily to the increased muscle temperature or to exercise in general.

Methods:  Six subjects completed 40 min of intermittent cycling (15s : 15s exercise:recovery at 300 ± 22 W) at an ambient temperature of either 20.0 ± 1.3 or 40.3 ± 0.7 °C. Muscle biopsies were taken prior to and immediately following the exercise protocol with samples analysed for HSF DNA binding by electrophoretic mobility shift assay.

Results:  Exercise at 40 °C resulted in significantly increased oesophageal (39.3 ± 0.2 °C) and muscle temperature (40.0 ± 0.2 °C) at the end of the exercise protocol compared with 20 °C (oesophageal, 38.1 ± 0.1 °C; muscle, 38.9 ± 0.2 °C). However, an increased DNA binding of HSF was not evident following exercise at 40 °C (reduced by 21 ± 22%) whereas it increased by 29 ± 51% following exercise at 20 °C.

Conclusion:  It appears that increased temperature is not the major factor responsible for activation of HSF DNA binding.
Potassium channels sensitive to combination of charybdotoxin and apamin regulate the tone of diabetic isolated canine coronary arteries
Authors: Pataricza J. , Márton Z. , Lengyel Cs. , Tóth M. , Papp J. Gy. , Varró A. , Kun A.
Published: April 2008

Aims:  Functional roles of calcium‐activated potassium channels on the mechanical activity of epicardial coronary arteries obtained from a canine model of diabetes were investigated.

Methods:  Coronary arteries were isolated from healthy, alloxan‐diabetic and insulin‐treated diabetic dogs. Basal tensions, contractions induced by the prostaglandin (PG) analogue, U46619, and endothelium‐dependent relaxations to acetylcholine (ACh) were modified with charybdotoxin (CHTX) + apamin (APA), inhibitors of calcium‐activated potassium channels, as well as with Nω‐nitro‐l‐arginine (LNA) + indomethacin (INDO) to suppress the synthesis of nitric oxide (NO) and PGs. The relaxing effect of nitroprusside‐sodium (SNP), an NO donor, was also determined.

Results:  In diabetic coronary arteries, CHTX + APA did not change while LNA + INDO elevated the basal tension. PG‐induced contractions were enhanced by CHTX + APA and by LNA + INDO in all the three groups of animals. CHTX + APA decreased the maximal relaxations to ACh in a partly insulin‐dependent manner. LNA + INDO abolished the endothelium‐dependent relaxations to ACh. In diabetic coronary arteries, the sensitivity to SNP‐induced relaxation was enhanced, insulin independently, suggesting that NO could be partly responsible for maintaining intact ACh‐induced vasorelaxation.

Conclusion:  In diabetic canine coronary artery, the vasomotor responses reflect up‐regulation of calcium‐activated potassium channels. This endothelial mechanism of the canine epicardial coronary artery may oppose vasoconstrictions in diabetic vascular tissue.
Effect of medium‐ and long‐chain fatty acid diets on PPAR and SREBP‐1 expression and glucose homeostasis in ACBP‐overexpressing transgenic rats
Authors: Oikari S. , Ahtialansaari T. , Huotari A. , Kiehne K. , Fölsch U. R. , Wolffram S. , Jänne J. , Alhonen L. , Herzig K.‐H.
Published: April 2008

Aim:  Acyl‐CoAs are important intermediates and regulators of lipid metabolism. Binding proteins like acyl‐CoA binding protein (ACBP) can influence their regulatory functions. ACBP has also been shown to exert direct effects on gene regulation in vitro. As the physiological relevance of ACBP in the regulation of lipid metabolism under high fat diets is unclear, we investigated the influence of such diets on the metabolic responses in ACBP‐overexpressing rats.

Methods:  A transgenic rat line overexpressing the ACBP gene was used to study the effects of 4 weeks of feeding with medium‐ (MC) or long‐chain (LC) fatty acid‐containing diets. Glucose tolerance tests were performed. Expression of transcription factors was measured by quantitative RT‐PCR and protein levels of AMP‐activated protein kinase were determined by western blotting.

Results:  Transgenic animals fed the MC diet had an improved glucose tolerance and lower serum insulin levels compared with controls. Their liver PPARγ (by 43%) and SREBP‐1 (by 35%) mRNA levels were found to be decreased, while adipose tissue PPARγ expression was increased by 31%. Tg animals fed the LC diet did not exhibit changes in glucose or insulin levels but exhibited increased mRNA levels of liver PPARs and SREBP‐1 (1.5–3.5 times) and decreased protein levels of AMPKα (by 48%).

Conclusions:  Our results demonstrate that ACBP overexpression affects metabolic responses to diets with distinct difference in their fatty acid chain lengths. The molecular regulatory mechanism behind these effects seems to be an ACBP‐induced tissue‐specific regulation of expression of PPARs and SREBP.
Sociospatial Applications of Remote Sensing in Urban Environments
Authors: Gatrell Jay D. , Jensen Ryan R.
Published: April 2008

Although the development and application of remote sensing data and techniques has been uneven, new sensors, techniques, and research questions have enabled human geographers and workers in other fields to use geospatial technologies to study sociospatial phenomena in built areas. This article describes how remote sensing data have been used in urban areas and highlights some research areas where remote sensing may continue to aid urban geographical inquiry, and some potential pitfalls. It is concluded that remote sensing has a critical role to play in the analysis of the interactions that occur between people and urban environments that may help shape our understanding of humans and the principle environment in which they live. The article also demonstrates how remote sensing can be used to improve the quality of life in the sustainability of cities.
The Geographic Cluster: A Historical Review
Authors: Vorley Tim
Published: April 2008

The notion of the cluster has become a highly interdisciplinary project, although it remains intrinsic to human and more specifically economic geography as a discipline. This article reviews the concept of the cluster from its origin in the work of Alfred Marshall and the industrial district, and how it has come to inform much subsequent thinking. Despite the strong foundation of Marshall's work, the contemporary cluster has become repopularised through the work of Michael Porter whose brand of cluster has rejuvenated interest in the cluster by policymakers and academics alike. However, Porter's work has also created a more critical revival of the cluster that has seen the concept examined in terms of innovation systems and other non‐Porterian alternatives. The article reviews these alternatives in terms of whatBenneworth and Henry (2004) term a ‘multiperspectival approach’, and argues the strength of the cluster concept to be as a dynamics and metaphorical construct rather than as a scientifically analysable conceptper se.
Why Do People Join Groups? Three Motivational Accounts from Social Psychology
Authors: Hogg Michael A. , Hohman Zachary P. , Rivera Jason E.
Published: April 2008

This paper describes and contrasts three contemporary social psychological theories that focus on why people join and identify with groups: the sociometer model, terror management theory, and uncertainty–identity theory. The sociometer model argues that people have a need to be socially included, and that self‐esteem is a meter of successful inclusion and group belonging. Terror management theory argues that people are motivated to reduce fear of the inevitability of their own death, and that the consensual belief–confirmation provided by groups drives people to belong. Uncertainty–identity theory argues that people have a basic need to reduce uncertainty about themselves, their attributes, and their place in the world, and that cognitive processes associated with group identification reduce such uncertainty. We critically contrast these three accounts to conclude that all three motivational processes may play a role, but that self‐uncertainty may have the benefit of wide generality to all groups and group contexts and of detailed specification of cognitive processes.
Social Identities in Childhood: When Does the Group Become a Part of the Self‐Concept?
Authors: Bennett Mark , Sani Fabio
Published: April 2008

Research in developmental psychology has almost invariably neglected to distinguish betweencategorization of the self in group termsandsubjective identification with a group.Methodologically, this has been exemplified in investigators’ widespread assumption that children's ascription of group labels (e.g., ‘I'm a Chinese American’) reflects proper identification with the named category. We argue that more subtle measures are required in order to determine whether social groups have become assimilated to the self‐concept, as would be required in order to infer that identification (rather than mere categorization) has taken place. Following a review of extant literature, we introduce our own program of research, conducted over the last decade, which draws upon methods from cognitive social psychology. Based on this research, we conclude that genuine identification with social groups is likely to be in place at least by the age of five years. However, our findings suggest that cognitive aspects of identification are likely to antecede affective aspects.
Personal Projects and Free Traits: Personality and Motivation Reconsidered
Authors: Little Brian R.
Published: April 2008

I review a social ecological model of human development that stimulates reconsideration of some traditional views in personality and motivational psychology. I propose that the quality of lives is contingent upon the sustainable pursuit of core personal projects. Project pursuit may occasionally require the suspension of biogenic fixed traits and the adoption of ‘free traits’, and I review some preliminary research on this recent topic. Free traits are culturally scripted patterns of conduct that are strategically crafted to advance projects about which a person cares deeply. Biogenic introverts, for example, may act as extraverts in order to advance projects requiring expressions of enthusiastic assertiveness. This may not only enhance well‐being by promoting successful project pursuit but may also compromise well‐being because of challenges to the autonomic nervous system. The costs of free‐traited behavior can be mitigated by the provision and use of restorative resources. When viewed through this perspective seeming inconsistencies and paradoxes of daily life become less puzzling as well as more intriguing. By tracing these themes through the lives of a hypothetical couple, George and Elizabeth, I hope to provide a stimulant to theory, research, and applications that can both explain and enhance the quality of lives.
Dental treatment in a patient with epidermolysis bullosa
Authors: Siqueira Maria Alice , De Souza Silva Juliana , Silva Francisco Wanderley Garcia de Paula e , Díaz‐Serrano Kranya Victória , Freitas Aldevina Campos de , Queiroz Alexandra Mussolino de
Published: April 2008

Epidermolysis bullosa (EB) is a rare inherited group of genodermatoses characterized by mucocutaneous fragility and blister formation, either spontaneously or as a result of minimal mechanical trauma. The repetition of these episodes in the oral cavity leads to atrophy of the mucosa, causing microstomia, ankyloglossia, tongue denudation, and vestibule obliteration, characteristics that make dental treatment difficult. Patients with EB are at high risk for caries due to the presence of dental anomalies; they also tend to have a soft diet and difficulties with mechanical removal of the dental biofilm. This case report presents a patient diagnosed with EB and describes the difficulties faced by the clinician during dental treatment as well as the measures adopted to safely manage the patient's dental care.
Carbon-Free Hydrogen and Electricity From Coal: Options for Syngas Cooling in Systems Using a Hydrogen Separation Membrane Reactor
Authors: De Lorenzo Luca , Kreutz Thomas G. , Chiesa Paolo , Williams Robert H.
Published: April 2008

Conversion of coal to carbon-free energy carriers, H2 and electricity, with CO2 capture and storage may have the potential to satisfy at a comparatively low cost much of the energy requirements in a carbon-constrained world. In a set of recent studies, we have assessed the thermodynamic and economic performance of numerous coal-to-H2 plants that employ O2-blown, entrained-flow gasification and sour water-gas shift (WGS) reactors, examining the effects of system pressure, syngas cooling via quench versus heat exchangers, “conventional” H2 separation via pressure swing adsorption versus novel membrane-based approaches, and various gas turbine technologies for generating coproduct electricity. This study focuses on the synergy between H2 separation membrane reactors (HSMRs) and syngas cooling with radiant and convective heat exchangers; such “syngas coolers” invariably boost system efficiency over that obtained with quench-cooled gasification. Conventional H2 separation requires a relatively high steam-to-carbon ratio (S/C) to achieve a high level of H2 production, and thus is well matched to relatively inefficient quench cooling. In contrast, HSMRs shift the WGS equilibrium by continuously extracting reaction product H2, thereby allowing a much lower S/C ratio and consequently a higher degree of heat recovery and (potentially) system efficiency. We first present a parametric analysis illuminating the interaction between the syngas coolers, high temperature WGS reactor, and HSMR. We then compare the performance and cost of six different plant configurations, highlighting (1) the relative merits of the two syngas cooling methods in membrane-based systems, and (2) the comparative performance of conventional versus HSMR-based H2 separation in plants with syngas coolers.
Particle Image Velocimetry Measurements of In-Cylinder Flow in a Four-Stroke Utility Engine and Correlation With Combustion Measurements
Authors: Bevan Karen E. , Ghandhi Jaal B.
Published: April 2008

Large-scale flows in internal combustion engines directly affect combustion duration and emission production. The effect of intake port geometry on combustion performance was studied in a four-stroke spark-ignition utility engine. Three intake port geometries were investigated at three port orientations. In-cylinder flows in orthogonal planes were measured using particle image velocimetry (PIV). The PIV data were processed to calculate the large-scale mean vorticity and mean high-pass filtered velocity. Combustion performance data were separately acquired at two load conditions at a fixed equivalence ratio, and compared with the PIV data. The cumulative distribution functions of the flow parameters did not show significant port-to-port differences in either measurement plane. The mean vorticity and high-pass filtered velocity did exhibit differences due to port orientation in the horizontal plane, but not in the vertical plane. The 0 deg ports (tangential orientation) consistently produced the highest values of large-scale mean vorticity and mean high-pass filtered velocity in the horizontal plane. The kinetic energy present at ignition was also calculated to characterize the flow. The ensemble-averaged values of the mean large-scale vorticity, high-pass filtered velocity, and kinetic energy were compared to the combustion duration. The vertical-plane vorticity and high-pass filtered velocity did not correlate with combustion performance. The horizontal-plane vorticity and high-pass filtered velocity were found to exhibit modest correlation at the fixed torque condition, and somewhat lower correlation at the wide open throttle condition. The correlation between kinetic energy and combustion duration was poor. The best correlation of flow field structure with engine performance was achieved for ports at the 0 deg port orientation. Ports at this orientation generated coherent, large-scale swirl.
Cycle-Controlled Water Injection for Steady-State and Transient Emissions Reduction From a Heavy-Duty Diesel Engine
Authors: Stanglmaier Rudolf H. , Dingle Philip J. , Stewart Daniel W.
Published: April 2008

A system for coinjecting mixtures of diesel fuel and water into a heavy-duty diesel engine has been developed and evaluated at the Southwest Research Institute. This system features prototype Lucas electronically controlled injectors, full electronic control, and can vary the percentage of water in the mixture on a cycle-resolved basis. Tests of this system were conducted on a production Volvo D-12 engine, and have produced reduced NOx and smoke emissions over steady-state and transient conditions. Water-diesel coinjection yielded a considerable improvement in NOx-smoke and NOx-BSFC trade-offs under steady-state engine operation. In addition, control of the water percentage on a cycle-resolved basis was shown to be an effective method for mitigating NOx and smoke emissions over step-load transients. Results from this work show that a combination of aggressive EGR and diesel+water coinjection is very promising for producing very low levels of engine-out exhaust emissions, reducing the water storage requirements, and improving fuel efficiency. Further refinement of this injection technology is in progress.
Optical Diagnostics of Late-Injection Low-Temperature Combustion in a Heavy-Duty Diesel Engine
Authors: Lachaux Thierry , Musculus Mark P. B. , Singh Satbir , Reitz Rolf D.
Published: April 2008

A late-injection, high exhaust-gas recirculation rate, low-temperature combustion strategy is investigated in a heavy-duty diesel engine using a suite of optical diagnostics: chemiluminescence for visualization of ignition and combustion, laser Mie scattering for liquid-fuel imaging, planar laser-induced fluorescence (PLIF) for both OH and vapor-fuel imagings, and laser-induced incandescence for soot imaging. Fuel is injected at top dead center when the in-cylinder gases are hot and dense. Consequently, the maximum liquid-fuel penetration is 27 mm, which is short enough to avoid wall impingement. The cool flame starts 4.5 crank angle degrees (CAD) after the start of injection (ASI), midway between the injector and bowl rim, and likely helps fuel to vaporize. Within a few CAD, the cool-flame combustion reaches the bowl rim. A large premixed combustion occurs near 9 CAD ASI, close to the bowl rim. Soot is visible shortly afterward, along the walls, typically between two adjacent jets. OH PLIF indicates that premixed combustion first occurs within the jet and then spreads along the bowl rim in a thin layer, surrounding soot pockets at the start of the mixing-controlled combustion phase near 17 CAD ASI. During the mixing-controlled phase, soot is not fully oxidized and is still present near the bowl rim late in the cycle. At the end of combustion near 27 CAD ASI, averaged PLIF images indicate two separate zones. OH PLIF appears near the bowl rim, while broadband PLIF persists late in the cycle near the injector. The most likely source of broadband PLIF is unburned fuel, which indicates that the near-injector region is a potential source of unburned hydrocarbons.
Reduction of Numerical Parameter Dependencies in Diesel Spray Models
Authors: Abani Neerav , Munnannur Achuth , Reitz Rolf D.
Published: April 2008

Numerical grid and time-step dependencies of discrete droplet Lagrangian spray models are identified. The two main sources of grid dependency are due to errors in predicting the droplet-gas relative velocity and errors in describing droplet-droplet collision and coalescence processes. For reducing grid dependency due to the relative velocity effects, a gas-jet theory is proposed and applied to model diesel sprays. For the time-step dependency, it is identified that the collision submodel results in drop size variation in the standard spray model. A proposed spray model based on the gas-jet theory is found to improve the time-step independency also along with the mesh independency. The use of both Eulerian (collision mesh) and Lagrangian (radius of influence) collision models along with the gas-jet theory is found to provide mesh-independent results.
Modeling the Effect of Injector Nozzle-Hole Layout on Diesel Engine Fuel Consumption and Emissions
Authors: Park Sung Wook , Reitz Rolf D.
Published: April 2008

Numerical simulations were used to study the effect of reduced nozzle-hole size and nozzle tip hole configuration on the combustion characteristics of a high speed direct injection diesel engine. The KIVA code coupled with the CHEMKIN chemistry solver was used for the calculations. The calculations were performed over wide ranges of equivalence ratio and injection timing. Three nozzle-hole layouts were considered: the base line conventional nozzle, and multi- and group-hole configurations. In the multihole case, the number of holes was doubled and the hole size was reduced, while keeping the same hole area as for the base line nozzle. The group-hole configuration used the same hole number and hole size as the multihole case, but pairs of holes were grouped with a close (0.2mm) spacing between the holes. The results of the mixture distributions showed that the group-hole configuration provides similar penetration and lower inhomogeneity to those of the base line large hole nozzle with the same nozzle flow area. Consequently, the fuel consumption and pollutant emissions, such as CO and soot, are improved by using the group-hole nozzle instead of the conventional hole nozzle over wide operating ranges. On the other hand, the multihole nozzle has advantages in its fuel consumption and CO emissions over the conventional hole layout at intermediate equivalence ratios (equivalence ratios from 0.56 to 0.84) and conventional injection timings (start of injection: 15deg before top dead center).
Multi-Objective Optimization of a Microturbine Compact Recuperator
Authors: Micheli Diego , Pediroda Valentino , Pieri Stefano
Published: April 2008

An automatic approach for the multi-objective shape optimization of microgas turbine heat exchangers is presented. According to the concept of multidisciplinary optimization, the methodology integrates a CAD parametric model of the heat transfer surfaces, a three-dimensional meshing tool, and a CFD solver, all managed by a design optimization platform. The repetitive pattern of the surface geometry has been exploited to reduce the computational domain size, and the constant flux boundary conditions have been imposed to better suit the real operative conditions. A new approach that couples cold and warm fluids in a periodic unitary cell is introduced. The effectiveness of the numerical procedure was verified comparing the numerical results with available literature data. The optimization objectives are maximizing the heat transfer rate and minimizing both friction factor and heat transfer surface. The paper presents the results of the optimization of a 50kWMGT recuperator. The design procedure can be effectively extended and applied to any industrial heat exchanger application.
Influence of Hot Streak Temperature Ratio on Low Pressure Stage of a Vaneless Counter-Rotating Turbine
Authors: Qingjun Zhao , Fei Tang , Huishe Wang , Jianyi Du , Xiaolu Zhao , Jianzhong Xu
Published: April 2008

In order to explore the influence of hot streak temperature ratio on the low pressure stage of a vaneless counter-rotating turbine, three-dimensional multiblade row unsteady Navier–Stokes simulations have been performed. The predicted results show that hot streaks are not mixed out by the time they reach the exit of the high pressure turbine rotor. The separation of colder and hotter fluids is observed at the inlet of the low pressure turbine rotor. After making interactions with the inner-extending and outer-extending shock waves in the high pressure turbine rotor, the hotter fluid migrates toward the pressure surface of the low pressure turbine rotor, and most of the colder fluid migrates to the suction surface of the low pressure turbine rotor. The migrating characteristics of the hot streaks are dominated by the secondary flow in the low pressure turbine rotor. The results also indicate that the secondary flow intensifies in the low pressure turbine rotor when the hot streak temperature ratio is increased. The effects of the hot streak temperature ratio on the relative flow angle at the inlet of the low pressure turbine rotor are very remarkable. The isentropic efficiency of the vaneless counter-rotating turbine decreases as the hot streak temperature ratio is increased.
Damping Performance of Axial Turbine Stages With Loosely Assembled Friction Bolts: The Nonlinear Dynamic Assessment
Authors: Szwedowicz J. , Secall-Wimmel Th. , Dünck-Kerst P.
Published: April 2008

An entire family of twisted and tapered low pressure steam turbine fast rotating condensation blading (SK) blades with pinned radial root and loosely assembled conical bolts is designed by scaling the aerodynamic and mechanical properties of the smallest airfoil. For SK blades operating with variable speed, the friction bolts, mounted in the upper airfoil part, provide either damping or coupling capabilities for the blades with respect to resonance conditions. The damping and coupling performance have been proven experimentally in the test rig of the real turbine. The measurements of the smallest SK-disk assembly under different operating conditions have allowed us to understand the dynamic and damping behavior of the bolts that are either friction dampers or coupling devices for the vibrating blades depending on the excitation level. In this paper, nonlinear dynamic analyses of the smallest and large SK-turbine stage are performed and compared with the experimental data. The modal blade dynamics is defined by 30 complex finite element (FE) mode shapes of the freestanding blades coupled by the disk whereby the bolt’s motion is described by six rigid body modes. The sticking contact condition between the blades and bolts is represented by the normal and tangential contact stiffnesses. These values are firstly estimated analytically with Hertz’s formulas for the FE reaction forces and contact areas. More realistic contact stiffness values are obtained from the iterative process, in which the resonance frequencies are calculated with the steady-state simulations and compared to the FE nodal diameter curves for sticking contact conditions that meet the experimental frequencies very well (Szwedowicz, J. et al., 2007, “Scaling Concept for Axial Turbine Stages With Loosely Assembled Friction Bolts: The Linear Dynamic Assessment Part 1,” Proceedings of ASME Turbo Expo 2007, Montreal, Canada, May 14–17, ASME Paper No. GT2007-27502). In nonlinear simulations, in case of exceeding the sticking contact condition, the induced friction forces are linearized by the harmonic balance method. In this manner, the microslipping and sticking contact behavior at all contact points are calculated iteratively for the specified excitation amplitudes, friction coefficient, contact roughness, and aerodamping values that are known from the experiment. The computed results of the tuned smallest SK blades agree with the experimental resonance stresses of 12 measured blades. Differences between the computed and measured stresses are caused by mistuning, which was not quantified in the experiment. The nonlinear dynamic analyses provide evidence of good damping performance for the smallest and large SK blades with respect to a wide range of excitation forces, different friction coefficients, and various aerodynamic damping values. For the analyzed resonances of the eighth engine order, the scalability of damping performance is found for the SK blades of different sizes.
Stress Singularity at the Free Surface of a Dynamically Growing Crack
Authors: Gudmundson Peter , O¨stlund So¨ren
Published: April 2008

The stress singularity at the intersection between the crack front and the free surface of a dynamically growing crack in a linear elastic isotropic material has been numerically evaluated by an especially developed finite element program. The singularity parameter (λ), defined by σ ~ Rλ−1, is presented as a function of the crack-tip velocity and the angle (β) between the crack front and the free surface. The angle (β) at which the singularity (λ) equals 0.5 was found to be 101 deg almost independently of the crack-tip velocity.
Effective Elastic Moduli of Ribbon-Reinforced Composites
Authors: Zhao Y. H. , Weng G. J.
Published: April 2008

Based on the Eshelby-Mori-Tanaka theory the nine effective elastic constants of an orthotropic composite reinforced with monotonically aligned elliptic cylinders, and the five elastic moduli of a transversely isotropic composite reinforced with two-dimensional randomly-oriented elliptic cylinders, are derived. These moduli are given in terms of the cross-sectional aspect ratio and the volume fraction of the elliptic cylinders. When the aspect ratio approaches zero, the elliptic cylinders exist as thin ribbons, and these moduli are given in very simple, explicit forms as a function of volume fraction. It turns out that, in the transversely isotropic case, the effective elastic moduli of the composite coincide with Hill’s and Hashin’s upper bounds if ribbons are harder than the matrix, and coincide with their lower bounds if ribbons are softer. These results are in direct contrast to those of circular fibers. Since the width of the Hill-Hashin bounds can be very wide when the constituents have high modular ratios, this analysis suggests that the ribbon reinforcement is far more effective than the traditional fiber reinforcement.
Spectral Moments and Pre-Envelope Covariances of Nonseparable Processes
Authors: Di Paola Mario , Petrucci Giovanni
Published: April 2008

A critical review of the definition of the spectral moments of a stochastic process in the nonstationary case is presented. An adequate time-domain representation of the spectral moments in the stationary case is first established, showing that the spectral moments are related to the variances of the stationary analytical pre-envelope processes. The extension to the nonstationary case is made in the time domain evaluating the covariances of the nonstationary pre-envelope showing the differences between the proposed definition and the classical one made introducing the evolutionary power.
Plane-Strain Crack-Tip Fields for Pressure-Sensitive Dilatant Materials
Authors: Li F. Z. , Pan J.
Published: April 2008

Plane-strain crack-tip stress and strain fields are presented for materials exhibiting pressure-sensitive yielding and plastic volumetric deformation. The yield criterion is described by a linear combination of the effective stress and the hydrostatic stress, and the plastic dilatancy is introduced by the normality flow rule. The material hardening is assumed to follow a power-law relation. For small pressure sensitivity, the plane-strain mode I singular fields are found in a separable form similar to the HRR fields (Hutchinson, 1968a, b; Rice and Rosengren, 1968). The angular distributions of the fields depend on the material-hardening exponent and the pressure-sensitivity parameter. The low-hardening solutions for different degrees of pressure sensitivity are found to agree remarkably with the corresponding perfectly-plastic solutions. An important aspect of the effects of pressure-sensitive yielding and plastic dilatancy on the crack-tip fields is the lowering of the hydrostatic stress and the effective stress directly ahead of the crack tip, which may contribute to the experimentally-observed enhancement of fracture toughness in some ceramic and polymeric composite materials.
Axisymmetric Inclusion in a Half Space
Authors: Yu H. Y. , Sanday S. C.
Published: April 2008

An alternate method of approach for solving the axisymmetric elastic fields in the half space with an isotropic spheriodal inclusion is proposed. This new approach involves the application of the Hankel transformation method for the solution of prismatic dislocation loops and Eshelby’s solution for ellipsoidal inclusions. Existing solutions by other methods for the inclusion with pure dilatational misfit in a half space are shown to be special cases of the present, more general solution.
Crack-Path Effect on Material Toughness
Authors: Rubinstein Asher A.
Published: April 2008

The material-toughening mechanism based on the crack-path deflection is studied. This investigation is based on a model which consists of a macrocrack (semi-infinite crack), with a curvilinear segment at the crack tip, situated in a brittle solid. The effect of material toughening is evaluated by comparison of the remote stress field parameters, such as the stress intensity factors (controlled by a loading on a macroscale), to effective values of these parameters acting in the vicinity of a crack tip (microscale). The effects of the curvilinear crack path are separated into three groups: crack-tip direction, crack-tip geometry pattern-shielding, and crack-path length change. These effects are analyzed by investigation of selected curvilinear crack patterns such as a macrocrack with simple crack-tip kink in the form of a circular arc and a macrocrack with a segment at the crack tip in the form of a sinusoidal wave. In conjunction with this investigation, a numerical procedure has been developed for the analysis of curvilinear cracks (or a system of cracks) in a two-dimensional linear elastic solid. The formulation is based on the solution of a system of singular integral equations. This numerical scheme was applied to the cases of finite and semi-infinite cracks.