bluuebunny/crossref_metadata_2025 huggingface dataset:
Estrogenic Compounds Downstream From Three Small Cities in Eastern Nebraska: Occurrence and Biological Effect1
Authors: Sellin Marlo K. , Snow Daniel D. , Akerly Debbie L. , Kolok Alan S.
Published: January 2009

Abstract:  Recent studies have detected estrogenic compounds in surface waters in North America and Europe. Furthermore, the presence of estrogenic compounds in surface waters has been attributed, in some cases, to the discharge of wastewater treatment plant (WWTP) effluent. The primary objective of the current study was to determine if WWTP effluent contributes estrogens to the surface waters of Nebraska. A second objective of this study was to determine if estrogens were found in concentrations sufficient enough to manifest feminizing effects on fish. These objectives were satisfied by deploying polar organic chemical integrative samplers (POCIS) and caged fathead minnows at eight field sites. Deployment sites included: three reference sites (Pawnee Creek, the Little Blue River, and the Middle Loup River), two sites upstream of the WWTPs at Grand Island and Columbus, and three sites downstream of the WWTPs at Grand Island, Columbus, and Hastings. Following the seven day deployments, POCIS extracts were analyzed for estrone, 17β‐estradiol, estriol and 17α‐ethinylestradiol using liquid chromatography tandem mass spectrometry (LC/MS/MS). 17β‐estradiol was detected in POCIS from six of the eight field sites with the greatest quantities recovered in POCIS deployed downstream from the Grand Island and Hastings WWTPs. Estrone was detected only in the POCIS deployed downstream from the Grand Island and Hastings WWTPs. Estrogenic effects were detected in caged minnows analyzed for the hepatic mRNA expression of two estrogen‐responsive genes, vitellogenin (vg1) and estrogen receptor α (ERα). Fish deployed at the site where the greatest quantities of estrogens were recovered (Hastings) had significantly higher expression of both vg1 and ERα than fish deployed at any of the other sites. These results confirm that WWTP effluent contributes biologically significant levels of estrogens to Nebraska surface waters.
Wastewater Effluent, Combined Sewer Overflows, and Other Sources of Organic Compounds to Lake Champlain1
Authors: Phillips P. , Chalmers A.
Published: January 2009

Abstract:  Some sources of organic wastewater compounds (OWCs) to streams, lakes, and estuaries, including wastewater‐treatment‐plant effluent, have been well documented, but other sources, particularly wet‐weather discharges from combined‐sewer‐overflow (CSO) and urban runoff, may also be major sources of OWCs. Samples of wastewater‐treatment‐plant (WWTP) effluent, CSO effluent, urban streams, large rivers, a reference (undeveloped) stream, and Lake Champlain were collected from March to August 2006. The highest concentrations of many OWCs associated with wastewater were in WWTP‐effluent samples, but high concentrations of some OWCs in samples of CSO effluent and storm runoff from urban streams subject to leaky sewer pipes or CSOs were also detected. Total concentrations and numbers of compounds detected differed substantially among sampling sites. The highest total OWC concentrations (10‐100 μg/l) were in samples of WWTP and CSO effluent. Total OWC concentrations in samples from urban streams ranged from 0.1 to 10 μg/l, and urban stream‐stormflow samples had higher concentrations than baseflow samples because of contributions of OWCs from CSOs and leaking sewer pipes. The relations between OWC concentrations in WWTP‐effluent and those in CSO effluent and urban streams varied with the degree to which the compound is removed through normal wastewater treatment. Concentrations of compounds that are highly removed during normal wastewater treatment [including caffeine, Tris(2‐butoxyethyl)phosphate, and cholesterol] were generally similar to or higher in CSO effluent than in WWTP effluent (and ranged from around 1 to over 10 μg/l) because CSO effluent is untreated, and were higher in urban‐stream stormflow samples than in baseflow samples as a result of CSO discharge and leakage from near‐surface sources during storms. Concentrations of compounds that are poorly removed during treatment, by contrast, are higher in WWTP effluent than in CSO, due to dilution. Results indicate that CSO effluent and urban stormwaters can be a significant major source of OWCs entering large water bodies such as Burlington Bay.
Lagrangian Sampling for Emerging Contaminants Through an Urban Stream Corridor in Colorado1
Authors: Brown Juliane B. , Battaglin William A. , Zuellig Robert E.
Published: January 2009

Abstract:  Recent national concerns regarding the environmental occurrence of emerging contaminants (ECs) have catalyzed a series of recent studies. Many ECs are released into the environment through discharges from wastewater treatment plants (WWTPs) and other sources. In 2005, the U.S. Geological Survey and the City of Longmont initiated an investigation of selected ECs in a 13.8‐km reach of St. Vrain Creek, Colorado. Seven sites were sampled for ECs following a Lagrangian design; sites were located upstream, downstream, and in the outfall of the Longmont WWTP, and at the mouths of two tributaries, Left Hand Creek and Boulder Creek (which is influenced by multiple WWTP outfalls). Samples for 61 ECs in 16 chemical use categories were analyzed and 36 were detected in one or more samples. Of these, 16 have known or suspected endocrine‐disrupting potential. At and downstream from the WWTP outfall, detergent metabolites, fire retardants, and steroids were detected at the highest concentrations, which commonly exceeded 1 μg/l in 2005 and 2 μg/l in 2006. Most individual ECs were measured at concentrations less than 2 μg/l. The results indicate that outfalls from WWTPs are the largest but may not be the sole source of ECs in St. Vrain Creek. In 2005, high discharge was associated with fewer EC detections, lower total EC concentrations, and smaller EC loads in St. Vrain Creek and its tributaries as compared with 2006. EC behavior differed by individual compound, and some differences between sites could be attributed to analytical variability or to other factors such as physical or chemical characteristics or distance from contributing sources. Loads of some ECs, such as diethoxynonylphenol, accumulated or attenuated depending on location, discharge, and distance downstream from the WWTP, whereas others, such as bisphenol A, were largely conservative. The extent to which ECs in St. Vrain Creek affect native fish species and macroinvertebrate communities is unknown, but recent studies have shown that fish respond to very low concentrations of ECs, and further study on the fate and transport of these contaminants in the aquatic environment is warranted.
PERSPECTIVE: Evolutionary genetics as a tool to target genes involved in phenotypes of medical relevance
Authors: Heyer Evelyne , Quintana‐Murci Lluis
Published: January 2009

There is an increasing interest in detecting genes, or genomic regions, that have been targeted by natural selection. Indeed, the evolutionary approach for inferring the action of natural selection in the human genome represents a powerful tool for predicting regions of the genome potentially associated with disease and of interest in epidemiological genetic studies. Here, we review several examples going from candidate gene studies associated with specific phenotypes, including nutrition, infectious disease and climate adaptation, to whole genome scans for natural selection. All these studies illustrate the power of the evolutionary approach in identifying regions of the genome having played a major role in human survival and adaptation.
ORIGINAL ARTICLE: Heart disease is common in humans and chimpanzees, but is caused by different pathological processes
Authors: Varki Nissi , Anderson Dan , Herndon James G. , Pham Tho , Gregg Christopher J. , Cheriyan Monica , Murphy James , Strobert Elizabeth , Fritz Jo , Else James G. , Varki Ajit
Published: January 2009

Heart disease is common in both humans and chimpanzees, manifesting typically as sudden cardiac arrest or progressive heart failure. Surprisingly, although chimpanzees are our closest evolutionary relatives, the major cause of heart disease is different in the two species. Histopathology data of affected chimpanzee hearts from two primate centers, and analysis of literature indicate that sudden death in chimpanzees (and in gorillas and orangutans) is commonly associated with diffuse interstitial myocardial fibrosis of unknown cause. In contrast, most human heart disease results from coronary artery atherosclerosis, which occludes myocardial blood supply, causing ischemic damage. The typical myocardial infarction of humans due to coronary artery thrombosis is rare in these apes, despite their human‐like coronary‐risk‐prone blood lipid profiles. Instead, chimpanzee ‘heart attacks’ are likely due to arrythmias triggered by myocardial fibrosis. Why do humans not often suffer from the fibrotic heart disease so common in our closest evolutionary cousins? Conversely, why do chimpanzees not have the kind of heart disease so common in humans? The answers could be of value to medical care, as well as to understanding human evolution. A preliminary attempt is made to explore possibilities at the histological level, with a focus on glycosylation changes.
PERSPECTIVE: Evolutionary biology and the avoidance of antimicrobial resistance
Authors: Read Andrew F. , Huijben Silvie
Published: January 2009

Evolutionary biologists have largely left the search for solutions to the drug resistance crisis to biomedical scientists, physicians, veterinarians and public health specialists. We believe this is because the vast majority of professional evolutionary biologists consider the evolutionary science of drug resistance to be conceptually uninteresting. Using malaria as case study, we argue that it is not. We review examples of evolutionary thinking that challenge various fallacies dominating antimalarial therapy, and discuss open problems that need evolutionary insight. These problems are unlikely to be resolved by biomedical scientists ungrounded in evolutionary biology. Involvement by evolutionary biologists in the science of drug resistance requires no intellectual compromises: the problems are as conceptually challenging as they are important.
Colour Doppler imaging evaluation of blood flow parameters in the ophthalmic artery in acute and chronic phases of optic neuritis in multiple sclerosis
Authors: Hradílek Pavel , Stourac Pavel , Bar Michal , Zapletalová Olga , Školoudík David
Published: January 2009

Purpose:  Optic neuritis (ON) is a common manifestation of multiple sclerosis (MS). It is caused by the immune‐mediated inflammation of the optic nerve. Some vascular factors that may influence blood flow in the ophthalmic artery (OA) have also been suggested as factors in the pathogenesis of ON. The purpose of our study was to evaluate blood flow velocities and resistance (RI) and pulsatile (PI) indices in the OA in both orbits in patients in the acute and chronic phases of unilateral ON and to compare these with equivalent findings in healthy control subjects.

Methods:  Orbital colour Doppler imaging (CDI) was performed in 40 consecutive MS patients during acute unilateral ON prior to corticosteroid treatment. Optic neuritis was diagnosed on the basis of clinical presentation and facultative assessment of visual evoked potentials (VEPs). The peak systolic (PSV) and end‐diastolic (EDV) velocities and RI and PI were measured in the OA in both eyes. We compared results from affected and unaffected orbits using the paired t‐test. The same measurements were performed in 114 MS patients with a history of acute unilateral ON that occurred > 1 year prior to ultrasound examination. We also measured the same parameters in the middle cerebral arteries (MCAs) on both sides in all subjects in both groups. The same measurements were obtained in healthy controls.

Results:  The PSV (p < 0.0001), RI (p < 0.0001) and PI (p < 0.0001) in the OA in the eye affected with acute ON were significantly higher than in the unaffected eye. There was no difference in EDV in the OA between affected and unaffected eyes (p > 0.05) in the group with acute ON. We did not observe any significant differences between eyes in either blood flow velocities or the RI or PI (p > 0.05) in the group in the chronic phase of ON or in the control group. All the parameters in the MCAs on both sides were normal in both the acute and chronic groups, as well as in the control group.

Conclusions:  Pathophysiological changes during acute unilateral ON influence orbital haemodynamics, as is indicated by increased PSV, RI and PI in the OA in eyes affected with ON. However, these changes do not persist over longer periods.
Intraocular lens as a drug delivery system for dexamethasone
Authors: Kugelberg Maria , Shafiei Kayvan , Van Der Ploeg Ingeborg , Zetterström Charlotta
Published: January 2009

Purpose:  To evaluate the effect of an intraocular lens (IOL) coated with dexamethasone on postoperative inflammation after cataract surgery.

Methods:  Clear lens extraction was performed bilaterally in eight 8‐week‐old rabbits. An uncoated silicone IOL (CeeOn; AMO, Santa Ana, CA, USA) was implanted in one randomly selected eye. In the other eye, the same silicone IOL model was implanted but was coated with dexamethasone. Aqueous humour was obtained preoperatively and on days 1, 3, 7, 14 and 28 postoperatively. Three inflammatory parameters were measured and compared between the eyes: prostaglandin E2 (PGE2), white blood cell (WBC) count and protein content. The animals were killed on day 28 postoperatively.

Results:  PGE2 levels measured on days 1, 3 and 7 were significantly lower in eyes with a coated IOL compared to eyes with an uncoated IOL (p < 0.01). The WBC count was significantly lower in eyes with a coated IOL on days 1 (p < 0.01) and 3 (p < 0.05). There was significantly less protein in eyes with a coated IOL on days 1 and 3 (p < 0.01).

Conclusion:  Coating a silicone IOL with dexamethasone significantly reduced postoperative inflammation after clear lens extraction in rabbits.
Are Animals Stuck in Time or Are They Chronesthetic Creatures?
Authors: Clayton N. S. , Russell J. , Dickinson A.
Published: January 2009

Although psychologists study both the objective (behavior) and the subjective (phenomenology) components of cognition, we argue that an overemphasis on the subjective drives a wedge between psychology and other closely related scientific disciplines, such as comparative studies of cognition and artificial intelligence. This wedge is particularly apparent in contemporary studies of episodic recollection and future planning, two related abilities that many have assumed to be unique to humans. We shall challenge this doctrine. To do so, we shall adopt an ethological approach to comparative cognition and this necessitates two requirements. The first is that memory and planning need to be characterized in terms of objectively defined properties as opposed to purely phenomenological ones; the ability to remember what happened, where, and how long ago is a critical behavioral criterion for episodic memory. The second requirement is the identification of an ethological context in which these memories would confer a selective advantage. As a consequence, we turn this debate into an empirical evaluation in nonlinguistic animals and one embodied in synthetic creatures. Indeed, our behavioral conception of flexibly deployable information about “what, where, and when” has so far supported a comparative cognition in animals as diverse as corvids and primates. We argue that this approach may clarify and challenge ideas that have been based solely on research with human subjects, without the need to be constrained by phenomenological assumptions based on human‐centric ways of thinking.
A Bayesian Account of Reconstructive Memory
Authors: Hemmer Pernille , Steyvers Mark
Published: January 2009

It is well established that prior knowledge influences reconstruction from memory, but the specific interactions of memory and knowledge are unclear. Extending work by Huttenlocher et al. (Psychological Review, 98 [1991] 352; Journal of Experimental Psychology: General, 129 [2000] 220), we propose a Bayesian model of reconstructive memory in which prior knowledge interacts with episodic memory at multiple levels of abstraction. The combination of prior knowledge and noisy memory representations is dependent on familiarity. We present empirical evidence of the influences of prior knowledge at multiple levels of abstraction, showing that the reconstruction of familiar objects is influenced toward the specific prior for that object, while unfamiliar objects are influenced toward the overall category.
“Shallow Draughts Intoxicate the Brain”: Lessons from Cognitive Science for Cognitive Neuropsychology
Authors: Patterson Karalyn , Plaut David C.
Published: January 2009

This article presents a sobering view of the discipline of cognitive neuropsychology as practiced over the last three or four decades. Our judgment is that, although the study of abnormal cognition resulting from brain injury or disease in previously normal adults has produced a catalogue of fascinating and highly selective deficits, it has yielded relatively little advance in understanding how the brain accomplishes its cognitive business. We question the wisdom of the following three “choices” in mainstream cognitive neuropsychology: (a) single‐case methodology, (b) dissociation between functions as the most important source of evidence, and (c) a central goal of diagramming the functional architecture of cognition rather than specifying how its components work. These choices may all stem from an excessive commitment to strict and fine‐grained modularity. Although different brain regions are undoubtedly specialized for different functions, we argue that parallel and interactive processing is a better assumption about cognitive processing. The essential goal of specifying representations and processes can, we claim, be significantly assisted by computational modeling which, by its very nature, requires such specification.
In vitro characterization of HCN channel kinetics and frequency dependence in myocytes predicts biological pacemaker functionality
Authors: Zhao Xin , Bucchi Annalisa , Oren Ronit V. , Kryukova Yelena , Dun Wen , Clancy Colleen E. , Robinson Richard B.
Published: January 2009

The pacemaker current, mediated by hyperpolarization‐activated cyclic nucleotide‐gated (HCN) channels, contributes to the initiation and regulation of cardiac rhythm. Previous experiments creating HCN‐based biological pacemakers in vivo found that an engineered HCN2/HCN1 chimeric channel (HCN212) resulted in significantly faster rates than HCN2, interrupted by 1–5 s pauses. To elucidate the mechanisms underlying the differences in HCN212 and HCN2 in vivo functionality as biological pacemakers, we studied newborn rat ventricular myocytes over‐expressing either HCN2 or HCN212 channels. The HCN2‐ and HCN212‐over‐expressing myocytes manifest similar voltage dependence, current density and sensitivity to saturating cAMP concentrations, but HCN212 has faster activation/deactivation kinetics. Compared with HCN2, myocytes expressing HCN212 exhibit a faster spontaneous rate and greater incidence of irregular rhythms (i.e. periods of rapid spontaneous rate followed by pauses). To explore these rhythm differences further, we imposed consecutive pacing and found that activation kinetics of the two channels are slower at faster pacing frequencies. As a result, time‐dependent HCN current flowing during diastole decreases for both constructs during a train of stimuli at a rapid frequency, with the effect more pronounced for HCN2. In addition, the slower deactivation kinetics of HCN2 contributes to more pronounced instantaneous current at a slower frequency. As a result of the frequency dependence of both instantaneous and time‐dependent current, HCN2 exhibits more robust negative feedback than HCN212, contributing to the maintenance of a stable pacing rhythm. These results illustrate the benefit of screening HCN constructs in spontaneously active myocyte cultures and may provide the basis for future optimization of HCN‐based biological pacemakers.
Mechanistic basis of differential conduction in skeletal muscle arteries
Authors: Tran Cam Ha T. , Vigmond Edward J. , Plane Frances , Welsh Donald G.
Published: January 2009

The goal of this investigation was to probe intercellular conduction in skeletal muscle feed arteries and to address why smooth muscle‐initiated responses fail to robustly spread like their endothelial counterpart. Using computational and experimental approaches, two interrelated rationales were developed to explain this apparent discrepancy in cell‐to‐cell communication. The first rationale stressed that smooth muscle electrical responses, if initiated, will be actively dissipated as they spread from cell‐to‐cell along the arterial wall. Charge dissipation is promoted within arteries by the structural and connectivity properties of vascular cells. The second rationale centred on the idea that when agents other than KCl stimulate a limited number of smooth muscle cells, they fail to generate the currents required to elicit a localized membrane potential (VM) response. This insufficiency results in part from charge loss, via gap junctions, to neighbouring unstimulated cells. Experiments confirmed the latter rationale by showing that focal phenylephrine application: (1) elicited a localized constriction insensitive to L‐type Ca2+ channel blockade; and (2) failed to substantially depolarize vascular smooth muscle cells. Further investigation revealed that while focal phenylephrine‐induced constriction was VM independent, it was reliant on internal Ca2+ mobilization and the activation of inositol 1,4,5‐trisphosphate (IP3) receptors. The preceding findings illustrate that by using computational modelling and experimentation in a complementary manner, one can isolate key cellular properties and rationally examine their role in limiting the conduction of smooth muscle‐initiated responses. Functionally, these observations enable investigators to assign the concept of ‘local and global’ blood flow control to the electrical and/or non‐electrical behaviour of specific cell types.
True Cross Sectional Area of Screw Threads With Helix and Root Radius Geometries Taken Into Consideration
Authors: Fukuoka Toshimichi , Nomura Masataka
Published: January 2009

When evaluating the strength of threaded fasteners under external loads, stress area is commonly used. However, in order to elucidate the mechanical behavior of bolted joints more rigorously and extensively, it is desired to derive an analytical expression of the true cross sectional area of screw threads, with the effects of the helix and root radius taken into account. In this paper, a series of closed-form algebraic equations, which can calculate true cross sectional areas of internal and external screw threads, is derived. The equations obtained can be applied to both metric and inch screw threads with a coarse or a fine pitch. Then, the equivalent diameter of the true sectional area is defined and compared with the pitch diameter and stress area diameter.
Risk-Based Inspection Analysis for High-Pressure Hydrogenation Cracking Unit
Authors: Zhao Jian-Ping
Published: January 2009

The high-pressure hydrogenation cracking unit is the core equipment system in the aromatic hydrocarbon factory, which is subjected simultaneously to the action of hydrogen, high pressure, and high temperature. In this paper, quantitative analysis method of risk-based inspection (RBI) was carried out with a commercially available RBI software. In API 581, the risk situation for each type of equipment in the system was classified into four grades: low-risk grade, medium-risk grade, medium-high-risk grade, and high grade. This is expressed as a risk matrix. The entire risk distribution of 553 equipment and/or piping items of the systems that compose the unit was obtained. The hydrocracking reactors and the reactor effluent air coolers are in the “medium-high-risk” category. Based on the RBI results, an optimum inspection plan was developed by the author to reduce the risk level for the hydrogenation cracking unit. Upon validation of the inspection activity in 2004, it is concluded that the optimum inspection plan was in compliance with the engineering specification of the aromatic hydrocarbon factory.
The Effect of the Distance From the Center of a Weld to the Fixed End on the Residual Stress and Stress Intensity Factor of a Piping Weld
Authors: Miyazaki Katsumasa , Numata Masanori , Saito Koichi , Mochizuki Masahito
Published: January 2009

The fixed conditions of butt welds between straight pipe and the valves or pump in an actual piping system are different from those of straight pipes. However, the effect of the fixed condition on the residual stress and the stress intensity factor for the evaluation of the structural integrity of cracked piping is not clear. In this study, finite element analyses were conducted by considering the differences in the distance from the center of weld to the fixed end L, to clarify the effect of the fixed condition on the residual stress and the stress intensity factor. For 600A piping, the residual stress distribution was not affected by L. Furthermore, the stress intensity factors of circumferential cracks under the residual stress field can be estimated by using an existing simplified solution for piping.
An Experimental Study of the Crack Growth Behavior of 16MnR Pressure Vessel Steel
Authors: Wang Xiaogui , Gao Zengliang , Zhao Tianwen , Jiang Yanyao
Published: January 2009

An experimental investigation was conducted on the crack growth behavior of a pressure vessel steel, 16MnR, in ambient air. Standard compact tension specimens were subjected to Mode I loading with several R-ratios and loading amplitudes. Three circular notch sizes ranging from very sharp notch to blunt notch were used. In addition to constant amplitude loading, experiments were conducted to study the influences of overload and loading sequence on crack growth. The results show that the R-ratio has an insignificant influence on the crack growth of the material. The size of the notch together with the R-ratio and loading amplitude has a great influence on the early crack growth from the notch. A single tensile overload during a constant amplitude loading experiment retards the crack growth significantly. Right after the application of an overload, the crack growth rate is higher than that of the stable crack growth observed in the constant amplitude loading. The crack growth rate decreases and reaches a minimum value before it gradually increases and reaches the stable crack growth curve. In high-low sequence loading with the maximum load in the second step lower than that of the first loading step, the preceding higher constant amplitude loading results in a significant crack growth retardation in the second loading step. This phenomenon is similar to the effect of a single tensile overload on the constant amplitude loading. An existing model making use of the stress intensity factor is discussed with respect to its capability to describe the observed crack growth behavior with the influence of overload and sequence loading.
Modeling Micro Mass and Heat Transfer for Gases Using Extended Continuum Equations
Authors: Torrilhon Manuel , Struchtrup Henning
Published: January 2009

This paper presents recent contributions to the development of macroscopic continuum transport equations for micro gas flows and heat transfers. Within the kinetic theory of gases, a combination of the Chapman–Enskog expansion and the Grad moment method yields the regularized 13-moment equations (R13 equations), which are of high approximation order. In addition, a complete set of boundary conditions can be derived from the boundary conditions of the Boltzmann equation. The R13 equations are linearly stable, and their results for moderate Knudsen numbers stand in excellent agreement with direct simulation Monte Carlo (DSMC) method simulations. We give analytical expressions for heat and mass transfer in microchannels. These expressions help to understand the complex interaction of fluid variables in microscale systems. Additionally, we compare interesting analogies such as a mass flux and energy Knudsen paradox. In particular, the R13 model is capable of predicting and explaining the detailed features of Poiseuille microflows.
Numerical Simulation Assisted Curve Compensation in Compression Molding of High Precision Aspherical Glass Lenses
Authors: Wang Fei , Chen Yang , Klocke Fritz , Pongs Guido , Yi Allen Y.
Published: January 2009

Compression molding is an effective high volume and net-shape fabrication method for aspherical lenses and precision glass optical components in general. Geometrical deviation (or curve change as often referred to in industry) incurred during heating, molding, and cooling processes is a critically important manufacturing quality parameter. In the compression glass molding process, there are many factors that could lead to curve change in final products, such as thermal expansion, stress and structural relaxation, and inhomogeneous temperature distribution inside the molding machine. In this research, an integrated numerical simulation scheme was developed to predict curve change in molded glass aspherical lenses. The geometrical deviation in the final lens shape was analyzed using both an experimental approach and a numerical simulation with a finite element method program. Specifically, numerical simulation was compared with experimental results to validate the proposed manufacturing approach. The measurements showed that the difference between numerical simulation and experimental results was less than 2 μm. Based on the comparison, the mold curve was revised using numerical simulation in order to produce more accurate lens shapes. The glass lenses molded using the compensated molds showed a much better agreement with the design value than the lenses molded without compensation. It has been demonstrated in this research that numerical simulation can be used to predict the final geometrical shape of compression molded precision glass components. This research provided an opportunity for optical manufacturers to achieve a lower production cost and a shorter cycle time.
Surface Model Based Modeling and Simulation of Filling Process in Gas-Assisted Injection Molding
Authors: Li Jianhui , Chen Lei , Zhou Huamin , Li Dequn
Published: January 2009

Present gas-assisted injection molding simulations are all based on either a midplane model or a 3D model, in which second modeling is unavoidable for a midplane model, and a 3D simulation needs a full-scale three-dimensional discretization of parts leading to unsustainable computing time and unstable numerical analysis. In this paper, surface model based modeling and numerical simulation of gas-assisted injection molding are proposed. By taking the influence of gas penetration on melt flow as boundary conditions of the melt-filling region, a hybrid control-volume finite element/finite-difference method (CV/FEM/FDM) similar to conventional injection molding simulation is employed. The gas penetration interface within the gas channel is solved by applying the matching asymptotic expansion method, which educes an analytical model of the gas penetration thickness ratio. A technology of generating gas-channel mesh semiautomatically is put forward, which combines selecting the path of gas channel manually and calculating the parameters of gas nodes automatically. The second modeling is thus avoided. The proposed model and simulation are verified by comparing with the experiment.
An Evaluation of Abrasive Waterjet Peening With Elastic Prestress
Authors: Sadasivam B. , Hizal A. , Park S. , Arola D.
Published: January 2009

Abrasive waterjet peening (AWJP) has been conceived as a new surface treatment process capable of achieving desired changes in surface texture, chemistry, and residual stress simultaneously. In the present investigation, the influence of elastic prestress on the residual stress resulting from AWJP was studied. Treatments were conducted on steel, as well as nickel and titanium alloy targets subjected to an elastic prestress ranging from 0% to 75% of the material’s yield strength. The results showed that a tensile elastic prestress increases the surface residual stress and the depth of the compressive stress zone. The surface residual stress in each metal increased nonuniformly with magnitude of prestress; the maximum surface residual stress was obtained at an applied prestress between 45% and 60% of the substrate yield strength. Overall, the increases in surface stress and depth that were obtained reached 100% and 50%, respectively. There were no changes to the surface texture caused by the prestress. According to results of this study, application of an elastic prestress can serve as an effective method for improving characteristics of the residual stress field in components treated using AWJP.
Parametric Modeling and Optimization of Chemical Vapor Deposition Process
Authors: Lin Po Ting , Jaluria Yogesh , Gea Hae Chang
Published: January 2009

This paper focuses on the parametric modeling and optimization of the chemical vapor deposition (CVD) process for the deposition of thin films of silicon from silane in a vertical impinging CVD reactor. The parametric modeling using radial basis function for various functions, which is related to the deposition rate and uniformity of the thin films, is studied. These models are compared and validated with additional sampling data. Based on the parametric models, different optimization formulations for maximizing the deposition rate and the working areas of thin film are performed.
Common Rail Injection for Marine Four-Stroke Engines
Authors: Paro Daniel , Jay Dave
Published: January 2009

Common rail injection is not a new idea. For example Sulzer was running tests with a mechanical common rail system as early as 1915. Also the idea of an electronically controlled injection system is more than three decades old. At the moment common rail injection is state of the art for trucks and diesel passenger cars.
A Novel Internal Combustion Engine With Simultaneous Injection of Fuel and Pre-Compressed Pre-Heated Air
Authors: Coney Mike W. , Linnemann Claus , Morgan Rob E. , Bancroft Tom G. , Sammut Richard M.
Published: January 2009

A new type of high efficiency reciprocating internal combustion engine is being developed, which has separate cylinders for compression and combustion on a common crankshaft. The combustion air is compressed quasi-isothermally using dense water sprays, preheated using engine waste heat and injected into the combustion chamber simultaneously with the fuel. This novel process is predicted to allow net electrical efficiencies of up to 60%. The present paper focuses on the combustion process and the cooling system of a 3 MW four-cylinder prototype engine, which is currently under construction. This includes development of the design for high thermal loading and for combustion, in which pre-compressed and pre-heated air is introduced into the cylinder simultaneously with the fuel. The overall development is aimed at a 7 MW commercial engine with eight cylinders.
Looking at New Concepts for Ultra-Low Emission Diesel Combustion System
Authors: Beatrice Carlo , Bertoli Claudio , Del Giacomo Nicola , Migliaccio Marianna
Published: January 2009

The DI (Direct Injection) Diesel engine, which is inherently capable of achieving very low CO2 emissions, is affected by PM (Particulate Matter) that is the typical emission of turbulent diffusion flames and has the drawback of high NOx (nitrogen oxides) emissions. In Europe, the recent progress of diesel technology allows complying, with difficulty, with the EURO IV stage of European light duty vehicles regulation and limits planned for 2008 seem at the moment unachievable without a strong and innovative improvement of the combustion system configuration. In the present paper a new concept of highly diluted and low temperature combustion is presented and analyzed. In particular the mechanism of soot suppression at low flame temperature is achieved by the use of high-rate cooled exhaust gas recirculation. Tests were carried out on a medium duty engine equipped with a mechanical in-line injection pump and two modem common rail prototypes engines.
Experimental and Numerical Study on the Combustion Characteristics of a Premixed Charge Compression Ignition Engine
Authors: Kim Dae Sik , Lee Ki Hyung , Lee Chang Sik
Published: January 2009

The objective of this work is to investigate the effect of premixed fuel ratio on the combustion and emission characteristics in diesel engine by the experimental and numerical method. In order to investigate the effect of various factors such as the mixing ratio, EGR rate, and engine load on the exhaust emissions from the premixed charge compression ignition diesel engine, the injection amount of premixed fuel is controlled by electronic port injection system. The range of mixing ratio between dual fuels used in this study is between 0 and 0.85, and the exhaust gas is recirclulated until 30 percent of EGR rate.
Theoretical Investigation of Autoignition of Combustible Gas Mixtures in Rapid Compression Machines
Authors: Shi Shaoping , Lee Daniel , McSurdy Sandra , McMillian Michael , Richardson Steven , Rogers William
Published: January 2009

In any theoretical investigation of ignition processes in natural gas reciprocating engines, physical and chemical mechanisms must be adequately modeled and validated in an independent manner. The Rapid Compression Machine (RCM) has been used in the past as a tool to validate both autoignition models as well as turbulent mixing effects. In this study, two experimental cases were examined. In the first experimental case, the experimental measurements of Lee and Hochgreb (1998a) were chosen to validate the simulation results. In their experiments, hydrogen/oxygen/argon mixtures were used as reactants. In the simulations, a reduced chemical kinetic mechanism consisting of 10 species and 19 elementary reactions coupled to a CFD software, Fluent 6, was used to simulate the autoignition. The ignition delay from the simulation agreed very well with that from the experimental data of Lee and Hochgreb, (1998b). In the second case, experimental data derived from an RCM with two opposed, pneumatically driven pistons (Brett et al., 2001) were used to study the autoignition of methane/oxygen/argon mixtures. The reduced chemical kinetic mechanism DRM22, derived from the GRI-Mech reaction scheme coupled to Fluent 6, was applied in the simulations. The DRM22 scheme included 22 species and 104 reactions. When methane/oxygen/argon mixture were simulated for the RCM, the ignition delay deviated about 15% from the experimental results. The simulation approaches as well as the validation results are discussed in detail in this paper. The paper also discusses an evaluation of reduced reaction models available in the literature for subsequent Fluent modeling.
Flamelet Modeling of Pollutant Formation in a Gas Turbine Combustion Chamber Using Detailed Chemistry for a Kerosene Model Fuel
Authors: Riesmeier Elmar , Honnet Sylvie , Peters Norbert
Published: January 2009

Combustion and pollutant formation in a gas turbine combustion chamber is investigated numerically using the Eulerian Particle Flamelet Model (EPFM). The code solving the unsteady flamelet equations is coupled to an unstructured CFD code providing solutions for the flow and mixture field from which the flamelet parameters can be extracted. Flamelets are initialized in the fuel rich region close to the fuel injectors of the combustor. They are represented by marker particles which are convected through the flow field. Each flamelet takes a different pathway through the combustor leading to different histories for the flamelet parameters. Equations for the probability of finding a flamelet at a certain position and time are additionally solved in the CFD code. To model the chemical properties of kerosene, a detailed reaction mechanism for a mixture of n-decane and 1,2,4-trimethylbenzene is used. It includes a detailed NOx submechanism and the build-up of polycyclic aromatic hydrocarbons (PAHs) up to four aromatic rings. The kinetically based soot model describes the formation of soot particles by inception, further growth by coagulation and condensation as well as surface growth and oxidation. Simulation results are compared to experimental data obtained on a high pressure rig. The influence of the model on pollutant formation is shown, and the effect of the number of flamelets on the model is investigated.
Improving the NOx-BSFC Trade Off of a Turbocharged Large Diesel Engine Using Performance Simulation
Authors: Kim Ki-Doo , Kim Dong-Hun
Published: January 2009

The purpose of this study is to determine the optimum intake valve closing time of a large diesel engine having lower fuel consumption and lower NOx emission. The performance simulation has been conducted for this purpose, and a phenomenological combustion model is verified by experimental data of heat release rate and NOx emission in order to enhance the prediction quality of the performance simulation. The results of performance simulation are compared with measured data to confirm the modeling method and results. The fuel injection system simulation has been also performed to get fuel injection rate, and the results is also verified by experimental data of fuel injection pump pressure and injected fuel mass. The performance simulation investigate the application of Miller cycle to a large diesel engine, and so, the intake valve closing time is determined at the condition of reducing NOx emission and fuel consumption at the same time. As that result, Miller cycle has a feature that the maximum reduction of NOx emission is 15.7% while the improvement of specific fuel oil consumption is 1.7g/kWh.
Flow Dynamics of Charge Stratification in Small GDI Two-Stroke Engines
Authors: Zanforlin Stefania , Gentili Roberto , Dell’Orto Pierluigi
Published: January 2009

Direct high-pressure liquid fuel injection is able to control the mixing process inside the cylinder for getting either stratified charge at partial loads or quasi-homogeneous conditions, as it is required at full load. This paper shows the development of this solution for small two-stoke engines, using multidimensional modelling. The aim is investigating how the design of scavenging ducts and combustion chamber influences charge stratification behaviour, taking into account fuel distribution and stratification stability varying engine load and speed.
The Impact of Cylinder Pressure on Fuel Jet Penetration and Mixing
Authors: Olsen Daniel B. , Willson Bryan D.
Published: January 2009

Investigations of fuel jet penetration and fuel and air mixing are performed in a static piston, pressurized optical engine. The pressure in the cylinder that the gas is injected into is varied to study the effect of the compression process. The engine has the same piston and cylinder geometry as a Cooper-Bessemer GMV-4TF two-stroke cycle natural gas engine. A 14” quartz cylinder section allows the cylinder gases to be radiated with an Nd:YAG UV laser, and imaged with an ICCD camera. Nitrogen gas that is seeded with acetone, which fluoresces in the visible range when irradiated with UV light, is injected through the fuel valves. Two types of fuel injectors are studied, a low pressure (45 psi) and a high pressure (500 psi) gas injection valve. Both fuel injection valves are manufactured by Woodward Governor. Planar laser induced fluorescence is implemented to image fuel concentration within the cylinder at various times during the injection and mixing processes. Spatial standard deviations of the variations of fuel concentration (“unmixedness”) and the volume fraction of gas in the flammable range (“mixedness”) across the image plane are computed.
Study of Transient Heat Transfer of Components in Internal Combustion Chamber
Authors: Yang Wanli , Chen Guohua , Chen Yan
Published: January 2009

The high cycle fatigue (thermal fatigue) is common in engines with high specific power output. In order to get the accurate temperature and heat flux distribution of the components with steep temperature gradients in the combustion chamber, an analytical solution in the case of a semi-infinite solid of constant properties is investigated by employing measured instantaneous heat flux as the boundary conditions. The new method is applied to an engine.
New Heat Transfer Equation Applicable to Hydrogen-Fuelled Engines
Authors: Shudo T. , Suzuki H.
Published: January 2009

Equations to describe heat transfer from burning gas to a combustion chamber have been empirically derived from hydrocarbon combustion engines. Previous research has analyzed the applicability of the equations to hydrogen combustion and showed that they calculate a lower cooling loss than experimental values. By focusing on the gas velocity term in the heat transfer equation and investigating replacement terms to better fit to hydrogen combustion, a new equation including rate of heat release in the gas velocity term is proposed. It is shown that the new equation is more applicable to hydrogen combustion than the widely used Woschni’s equation.
Feasibility Study of an On-Board Natural Gas to DME Reactor for DME Pre-Injection and Enhanced Ignition
Authors: Horstman David , Abata Duane , Keith Jason , Oberto Leroy
Published: January 2009

Dual fuel (CI) engines provide an excellent means of maintaining high thermal efficiency and power while reducing emissions. This is particularly true in situations where the main CI fuel does not exhibit good auto-ignition characteristics, such as diesel engines operating on natural gas usually in stationary applications such as a pipeline installation. This paper explores the feasibility of chemically synthesizing DME from natural gas ‘on-board’ and using it as an ignition source for a dual fuel engine. Assuming a 5% pilot amount, a ‘once through’ process has been modeled and a first law analysis (using practical isentropic efficiencies) demonstrates that this combined system can be operated with a reduction of between 5–10% of the equivalent diesel efficiency. Significant quantities (∼30 vol.%) of hydrogen are introduced to the natural gas as a byproduct of the DME synthesis process. The corresponding increase in combustion efficiency must be validated by experiments to determine DME and H2 requirements for successful pilot ignition of the natural gas/H2 mixture.
Uncertainty in the Determination of Thermal Efficiency in Natural Gas Engines
Authors: Kubesh John T.
Published: January 2009

This paper discusses the measurement of thermal efficiency for natural gas-fueled engines and the resulting uncertainty. Two methods for determining thermal efficiency are described in detail. For each method, the sources of uncertainty are identified and quantified, and an estimate of the overall uncertainty is calculated. The analysis indicates that a thermal efficiency calculation that uses a mass fuel flow rate measurement directly as a basis for the energy input rate provides less uncertainty than the other method that uses a volumetric flow measurement.