bluuebunny/crossref_metadata_2025 huggingface dataset:
The effect of sucralfate tablets vs. suspension on oral doxycycline absorption in dogs
Authors: KuKanich K. , KuKanich B.
Published: September 2014

The purpose of this study was to determine the effect of concurrent sucralfate (tablet or suspension) on doxycycline pharmacokinetics and to determine the effects of delaying sucralfate by 2 h on doxycycline absorption. Five dogs were included in a crossover study receiving: doxycycline alone; doxycycline concurrently with sucralfate tablet; doxycycline followed 2 h by sucralfate tablet; doxycycline concurrently with sucralfate suspension; and doxycycline followed 2 h by sucralfate suspension. Doxycycline plasma concentrations were evaluated with liquid chromatography with mass spectrometry. No interaction was seen when sucralfate was administered as a tablet. Sucralfate tablet fragments were frequently observed in some dogs' feces. The area under the curve (AUC) and maximum plasma concentration (CMAX) were significantly lower (P < 0.001) in the concurrent sucralfate suspension group (AUC 7.2 h·μg/mL, CMAX 0.43 μg/mL) than with doxycycline alone (AUC 36.0 h·μg/mL, CMAX 2.53 μg/mL) resulting in a relative bioavailability of 20%. Delaying sucralfate suspension by 2 h after doxycycline administration resulted in no difference in doxycycline absorption as compared with doxycycline administration alone with a relative bioavailability of 74%. The lack of an interaction with sucralfate tablets suggests sucralfate should be administered as a suspension rather than tablet in dogs.
Ocean circulation model predicts high genetic structure observed in a long‐lived pelagic developer
Authors: Sunday J. M. , Popovic I. , Palen W. J. , Foreman M. G. G. , Hart M. W.
Published: September 2014

Understanding the movement of genes and individuals across marine seascapes is a long‐standing challenge in marine ecology and can inform our understanding of local adaptation, the persistence and movement of populations, and the spatial scale of effective management. Patterns of gene flow in the ocean are often inferred based on population genetic analyses coupled with knowledge of species' dispersive life histories. However, genetic structure is the result of time‐integrated processes and may not capture present‐day connectivity between populations. Here, we use a high‐resolution oceanographic circulation model to predict larval dispersal along the complex coastline of western Canada that includes the transition between two well‐studied zoogeographic provinces. We simulate dispersal in a benthic sea star with a 6–10 week pelagic larval phase and test predictions of this model against previously observed genetic structure including a strong phylogeographic break within the zoogeographical transition zone. We also test predictions with new genetic sampling in a site within the phylogeographic break. We find that the coupled genetic and circulation model predicts the high degree of genetic structure observed in this species, despite its long pelagic duration. High genetic structure on this complex coastline can thus be explained through ocean circulation patterns, which tend to retain passive larvae within 20–50 km of their parents, suggesting a necessity for close‐knit design of Marine Protected Area networks.
spxA2, encoding a regulator of stress resistance in Bacillus anthracis, is controlled by SaiR, a new member of the Rrf2 protein family
Authors: Nakano Michiko M. , Kominos‐Marvell Wren , Sane Bhagyashree , Nader Yaldah Mohammad , Barendt Skye M. , Jones Marcus B. , Zuber Peter
Published: September 2014

Spx, a member of the ArsC (arsenate reductase) protein family, is conserved in Gram‐positive bacteria, and interacts with RNA polymerase to activate transcription in response to toxic oxidants. In Bacillus anthracis str. Sterne, resistance to oxidative stress requires the activity of two paralogues, SpxA1 and SpxA2. Suppressor mutations were identified in spxA1 mutant cells that conferred resistance to hydrogen peroxide. The mutations generated null alleles of the saiR gene and resulted in elevated spxA2 transcription. The saiR gene resides in the spxA2 operon and encodes a member of the Rrf2 family of transcriptional repressors. Derepression of spxA2 in a saiR mutant required SpxA2, indicating an autoregulatory mechanism of spxA2 control. Reconstruction of SaiR‐dependent control of spxA2 was accomplished in Bacillus subtilis, where deletion analysis uncovered two cis‐elements within the spxA2 regulatory region that are required for repression. Mutations to one of the sequences of dyad symmetry substantially reduced SaiR binding and SaiR‐dependent repression of transcription from the spxA2 promoter in vitro. Previous studies have shown that spxA2 is one of the most highly induced genes in a macrophage infected with B. anthracis. The work reported herein uncovered a key regulator, SaiR, of the Spx system of stress response control.
Responsiveness of different citrus genotypes to the Xanthomonas citri ssp. citri‐derived pathogen‐associated molecular pattern (PAMP) flg22 correlates with resistance to citrus canker
Authors: Shi Qingchun , Febres Vicente J. , Jones Jeffrey B. , Moore Gloria A.
Published: September 2014

The bacterial agent of citrus canker disease (Xanthomonas citri ssp. citri, Xcc) has caused tremendous economic losses to the citrus industry around the world. Pathogen‐associated molecular pattern (PAMP)‐triggered immunity (PTI) is important to plant immunity. In this study, we compared the defence responses of citrus canker‐resistant and citrus canker‐susceptible genotypes to the Xcc‐derived PAMP flg22 (Xflg22) by analysing the expression of 20 citrus defence‐associated genes. We showed that, in the most resistant genotype, ‘Nagami’ kumquat, there was significant induction of several defence genes (EDS1, NDR1, PBS1, RAR1, SGT1, PAL1, NPR2 and NPR3) as early as 6 h and up to 72 h after Xflg22 treatment. At the other end of the spectrum, highly susceptible ‘Duncan’ grapefruit showed no induction of the same defence genes, even 120 h after treatment. Citrus genotypes with partial levels of resistance showed intermediate levels of transcriptional reprogramming that correlated with their resistance level. Xflg22 also triggered a rapid oxidative burst in all genotypes which was higher and accompanied by the induction of PTI marker genes (WRKY22 and GST1) only in the more resistant genotypes. Pretreatment with Xflg22 prior to Xcc inoculation inhibited bacterial growth in kumquat, but not in grapefruit. A flagellin‐deficient Xcc strain (XccΔfliC) showed greater growth increase relative to wild‐type Xcc in kumquat than in grapefruit. Taken together, our results indicate that Xflg22 initiates strong PTI in canker‐resistant genotypes, but not in susceptible ones, and that a robust induction of PTI is an important component of citrus resistance to canker.
Sudden cardiac death in haemodialysis patients: Preventative options
Authors: Chiu Diana Yuan Yng , Sinha Smeeta , Kalra Philip A , Green Darren
Published: September 2014

Sudden cardiac death (SCD) is the most common cause of death in haemodialysis patients, accounting for 25% of all‐cause mortality. There are many potential pathological precipitants as most patients with end‐stage renal disease have structurally or functionally abnormal hearts. For example, at initiation of dialysis, 74% of patients have left ventricular hypertrophy. The pathophysiological and metabolic milieu of patients with end‐stage renal disease, allied to the regular stresses of dialysis, may provide the trigger to a fatal cardiac event. Prevention of SCD can be seen as a legitimate target to improve survival in this patient group. In the general population, this is most effective by reducing the burden of ischaemic heart disease. However, the aetiology of SCD in haemodialysis patients appears to be different, with myocardial fibrosis, vascular calcification and autonomic dysfunction implicated as possible causes. Thus, the range of therapies is different to the general population. There are potential preventative measures emerging as our understanding of the underlying mechanisms progresses. This article aims to review the evidence for therapies to prevent SCD effective in the general population when applied to dialysis patients, as well as promising new treatments specific to this population group.
Prevalence and Characterization of Pruritus in Epidermolysis Bullosa
Authors: Danial Christina , Adeduntan Rasidat , Gorell Emily S. , Lucky Anne W. , Paller Amy S. , Bruckner Anna , Pope Elena , Morel Kimberly D. , Levy Moise L. , Li Shufeng , Gilmore Elaine S. , Lane Alfred T.
Published: September 2014

Qualitative data suggest that pruritus is a burdensome symptom in patients with epidermolysis bullosa (EB), but the prevalence of pruritus in children and adults with EB and factors that contribute to pruritus are unknown. The objective of the current study was to quantitatively identify and to characterize pruritus that EB patients experience using a comprehensive online questionnaire. A questionnaire was developed to evaluate pruritus in all ages and all types of EB. Questions that characterize pruritus were included and factors that aggravate symptoms were investigated. Patients from seven North American EB centers were invited to participate. One hundred forty‐six of 216 questionnaires were completed (response rate 68%; 73 male, 73 female; median age 20.0 years). Using a 5‐point Likert scale (1 = never, 2 = rarely, 3 = sometimes, 4 = often, 5 = always), itchiness was the most bothersome EB complication (mean 3.3). The average daily frequency of pruritus increased with self‐reported EB severity. Pruritus was most frequent at bedtime (mean 3.8) and interfered with sleep. Factors that aggravated pruritus included healing wounds, dry skin, infected wounds, stress, heat, dryness, and humidity. Pruritus is common in individuals with EB and can be bothersome. Future studies will need to investigate the most effective treatments given to individuals with EB for pruritus.
Dermatophytes and Transmission Risks to Family: A Retrospective Study of a Cohort of 256 Adopted Children from 1998 to 2012
Authors: Dupont Damien , Peyron François , Picot Stéphane , Wallon Martine , Bienvenu Anne‐Lise
Published: September 2014

In this 14‐year retrospective study we analyzed samples collected from 101 adopted children originating from developing countries in search of dermatophytosis; a dermatophyte was isolated in 44 children. We demonstrated that dermatophytoses often have a silent clinical presentation (16%) and in approximately 20% of cases cause family member contamination. This study highlights the importance of the clinical examination of children and families as well as systematic sampling of children to avoid dermatophyte transmission to other family members.
On the Spectral Stability of Kinks in Some ‐Symmetric Variants of the Classical Klein–Gordon Field Theories
Authors: Demirkaya A. , Kapitula T. , Kevrekidis P.G. , Stanislavova M. , Stefanov A.
Published: September 2014

In the present work we consider the introduction of ‐symmetric terms in the context of classical Klein–Gordon field theories. We explore the implication of such terms on the spectral stability of coherent structures, namely kinks. We find that the conclusion critically depends on the location of the kink center relative to the center of the ‐symmetric term. The main result is that if these two points coincide, the kink's spectrum remains on the imaginary axis and the wave is spectrally stable. If the kink is centered on the “lossy side” of the medium, then it becomes stabilized. On the other hand, if it becomes centered on the “gain side” of the medium, then it is destabilized. The consequences of these two possibilities on the linearization (point and essential) spectrum are discussed in some detail.
Preserving Residual Renal Function in Dialysis: What We Know
Authors: Patel Nikunjkumar , Hu Susie L.
Published: September 2014

Residual renal function confers a survival benefit among dialysis patients thought to be related to greater volume removal and solute clearance. Whether the presence of residual renal function is protective or merely a marker for better health is not clear. The basic mechanisms governing the decline or persistence of residual renal function are poorly understood and few studies have examined the role of medical therapy in its preservation. Dialysis modality, inflammatory processes often associated with comorbid diseases (including diabetes mellitus and obesity), volume dysregulation, and vitamin D deficiency are predictive of residual renal function decline. We review potential mechanisms for preservation of remaining glomerular filtration rate among chronic dialysis patients.
Tuning parameter selection in penalized generalized linear models for discrete data
Authors: Androulakis E. , Koukouvinos C. , Vonta F.
Published: September 2014

In recent years, we have seen an increased interest in the penalized likelihood methodology, which can be efficiently used for shrinkage and selection purposes. This strategy can also result in unbiased, sparse, and continuous estimators. However, the performance of the penalized likelihood approach depends on the proper choice of the regularization parameter. Therefore, it is important to select it appropriately. To this end, the generalized cross‐validation method is commonly used. In this article, we firstly propose new estimates of the norm of the error in the generalized linear models framework, through the use of Kantorovich inequalities. Then these estimates are used in order to derive a tuning parameter selector in penalized generalized linear models. The proposed method does not depend on resampling as the standard methods and therefore results in a considerable gain in computational time while producing improved results. A thorough simulation study is conducted to support theoretical findings; and a comparison of the penalized methods with theL1, the hard thresholding, and the smoothly clipped absolute deviation penalty functions is performed, for the cases of penalized Logistic regression and penalized Poisson regression. A real data example is being analyzed, and a discussion follows. © 2014 The Authors. Statistica Neerlandica © 2014 VVS.
Green Havens and Pollution Havens
Authors: Poelhekke Steven , van der Ploeg Frederick
Published: September 2014

We test for pollution haven effects in outward foreign direct investment (FDI) for different sectors using a comprehensive and exhaustive data set for outward FDI from the Netherlands, one of the most environmentally stringent countries and a major source of global FDI. Our evidence suggests that in the sectors, natural resources extraction and refining, construction, retail, food processing, beverages and tobacco, and utilities, a less stringent environmental policy in the host country, significantly attract FDI. What is important for these pollution haven effects is not only regulation but also enforcement of environmental policy. In contrast to earlier results, it is not only footloose industries that display pollution haven effects, but also the traditional pollution‐intensive industries. But for the machines, electronics and automotive and transportation and communication sectors, a more stringent and better enforced environmental policy attracts more FDI as this may help their reputation for sustainable management and CSR. These sectors display green haven effects. These findings have important implications for the sector distribution of FDI in destination countries.
Intravenous curcumin efficacy on healing and scar formation in rabbit ear wounds under nonischemic, ischemic, and ischemia–reperfusion conditions
Authors: Jia Shengxian , Xie Ping , Hong Seok Jong , Galiano Robert , Singer Adam , Clark Richard A. F. , Mustoe Thomas A.
Published: September 2014

Curcumin, a spice found in turmeric, is widely used in alternative medicine for its purported anti‐inflammatory and antioxidant activities. The goal of this study was to test the curcumin efficacy on rabbit ear wounds under nonischemic, ischemic, and ischemia–reperfusion conditions. Previously described models were utilized in 58 New Zealand White rabbits. Immediately before wounding, rabbits were given intravenous crude or pure curcumin (6 μg/kg, 30 μg/kg, or 60 μg/kg) dissolved in 1% ethanol. Specimens were collected at 7–8 days to evaluate the effects on wound healing and at 28 days to evaluate the effects on hypertrophic scarring. Student's t test was applied to screen difference between any treatment and control group, whereas analysis of variance was applied to further analyze for all treatment groups in aggregate in some specific experiments. Treatment with crude curcumin suggested accelerated wound healing that reached significance for reepithelialization in lower and medium doses and granulation tissue formation in lower dose. Purified curcumin became available and was used for all later experiments. Treatment with pure curcumin suggested accelerated wound healing that reached significance for reepithelialization in lower and medium doses and granulation tissue formation in lower dose. Treatment with pure curcumin significantly promoted nonischemic wound healing in a dose–response fashion compared with controls as judged by increased reepithelialization and granulation tissue formation. Improved wound healing was associated with significant decreases in pro‐inflammatory cytokines interleukin (IL)‐1 and IL‐6 as well as the chemokine IL‐8. Curcumin also significantly reduced hypertrophic scarring. The effects of curcumin were examined under conditions of impaired healing including ischemic and ischemia–reperfusion wound healing, and beneficial effects were also seen, although the dose response was less clear. Systemically administrated pure curcumin significantly promotes nonischemic wound healing and reduces hypertrophic scarring. Improvements in wound healing were associated with decreased inflammatory markers in wounds. Further study is needed to optimize dosing in ischemic and ischemia–reperfusion wound healing. In aggregate, the studies strongly support the systemic administration of curcumin to improve wound healing.
Impact of a novel, antimicrobial dressing on in vivo, Pseudomonas aeruginosa wound biofilm: Quantitative comparative analysis using a rabbit ear model
Authors: Seth Akhil K. , Zhong Aimei , Nguyen Khang T. , Hong Seok J. , Leung Kai P. , Galiano Robert D. , Mustoe Thomas A.
Published: September 2014

The importance of bacterial biofilms to chronic wound pathogenesis is well established. Different treatment modalities, including topical dressings, have yet to show consistent efficacy against wound biofilm. This study evaluates the impact of a novel, antimicrobial Test Dressing on Pseudomonas aeruginosa biofilm‐infected wounds. Six‐mm dermal punch wounds in rabbit ears were inoculated with 106 colony‐forming units of P. aeruginosa. Biofilm was established in vivo using our published model. Dressing changes were performed every other day with either Active Control or Test Dressings. Treated and untreated wounds were harvested for several quantitative endpoints. Confirmatory studies were performed to measure treatment impact on in vitro P. aeruginosa and in vivo polybacterial wounds containing P. aeruginosa and Staphylococcus aureus. The Test Dressing consistently decreased P. aeruginosa bacterial counts, and improved wound healing relative to Inactive Vehicle and Active Control wounds (p < 0.05). In vitro bacterial counts were also significantly reduced following Test Dressing therapy (p < 0.05). Similarly, improvements in bacterial burden and wound healing were also achieved in polybacterial wounds (p < 0.05). This study represents the first quantifiable and consistent in vivo evidence of a topical antimicrobial dressing's impact against established wound biofilm. The development of clinically applicable therapies against biofilm such as this is critical to improving chronic wound care.
Toward Automatic Tolerancing of Mechanical Assemblies: Assembly Analyses
Authors: Mohan Prashant , Haghighi Payam , Vemulapalli Prabath , Kalish Nathan , Shah Jami J. , Davidson Joseph K.
Published: September 2014

Generating geometric dimensioning and tolerancing (GD&T) specifications for mechanical assemblies is a complex and tedious task, an expertise that few mechanical engineers possess. The task is often done by trial and error. While there are commercial systems to facilitate tolerance analysis, there is little support for tolerance synthesis. This paper presents a systematic approach toward collecting part and assembly characteristics in support of automating GD&T schema development and tolerance allocation for mechanical assemblies represented as neutral B-Rep. First, assembly characteristics are determined, then a tentative schema is determined and tolerances allocated. This is followed by adaptive iterations of analyses and refinement to achieve desired goals. This paper will present the preprocessing steps for assembly analysis needed for tolerance schema generation and allocation. Assembly analysis consists of four main tasks: assembly feature recognition (AFR), pattern detection, directions of control, and loop detection. This paper starts with identifying mating features in an assembly using the computer-aided design (CAD) file. Once the features are identified, patterns are determined among those features. Next, different directions of control for each part are identified and lastly, using all this information, all the possible loops existing in an assembly are searched.
A Two-Dimensional Multibody Integral Approach for Forces in Inviscid Flow With Free Vortices and Vortex Production
Authors: Li Juan , Bai Chen-Yuan , Wu Zi-Niu
Published: September 2014

In this paper, we propose an integral force approach for potential flow around two-dimensional bodies with external free vortices and with vortex production. The method can be considered as an extension of the generalized Lagally theorem to the case with continuous distributed vortices inside and outside of the body and is capable of giving the individual force of each body in the case of multiple bodies. The lift force formulas are validated against two examples. One is the Wagner problem with vortex production and with moving vortices in the form of a vortex sheet. The other is the lift of a flat plate when there is a standing vortex over its middle point. As a first application, the integral approach is applied to study the lift force of a flat plate induced by a bounded vortex above the plate. This bounded vortex may represent a second small airfoil at incidence. For this illustrative example, the lift force is found to display an interesting distance-dependent behavior: for a clockwise circulation, the lift force acting on the main airfoil is attractive for small distance and repulsive for large distance.
Parametric Analysis and Optimization of Inlet Deflection Angle in Torque Converters1
Authors: Liu Cheng , Untaroiu Alexandrina , Wood Houston G. , Yan Qingdong , Wei Wei
Published: September 2014

The inlet deflection angle is an important blade design parameter with respect to both performance and manufacturability of torque converters. This study investigated the influence of the inlet deflection angle on the performance of torque converters and a method of optimizing the inlet deflection angle for torque converters based on 3D flow simulation is presented. Parameter analysis and multi-objective optimization were performed on an automated 3D flow simulation platform. The results indicate that the mass flow rate increases with a decreasing difference between the pump outlet deflection angle and the turbine inlet deflection angle, consequently increasing pump capacity factor. The advantages of the method proposed are an improved design quality and a significantly shorter design cycle.
Investigation of Patterned Textures in Ball-on-Disk Lubricated Point Contacts
Authors: Wenzhong Wang , Dian Shen , Shengguang Zhang , Ziqiang Zhao
Published: September 2014

The numerical simulations of surface textures in point-contact lubrication are conducted based on the unified Reynolds equation model. The textures are numerically produced on one of the interacting surfaces. The lubricant rheological parameters used in the simulations are calibrated by experiments. The numerical results show good agreements with those from experiments. The friction reduction mechanism is investigated by systemically analyzing the periodic change of friction coefficient of textures. It is illustrated that the transient friction coefficient is minimal when the dent moves to the front boundary edge of the Hertzian contact zone. A local film enhancement region will be formed on the trail of the dent within the Hertzian contact region. The results suggest that a bigger local film enhancement area will offer stronger film thickness enhancement as well as a lower friction coefficient. Different pattern distributions are also studied to find the optimal distribution of patterned textures, which not only achieves a lower friction coefficient, but also offers stronger film thickness enhancement; moreover, the optimal distribution is numerically proved to be applicable for a wide range of working conditions.
Modified Particle Swarm Optimization Algorithm for Multi-Objective Optimization Design of Hybrid Journal Bearings
Authors: Chan Chia-Wen
Published: September 2014

The objective of design optimization is to determine the design that minimizes the objective function by changing design variables and satisfying design constraints. During multi-objective optimization, which has been widely applied to improve bearing designs, designers must consider several design criteria or objective functions simultaneously. The particle swarm optimization (PSO) method is known for its simple implementation and high efficiency in solving multifactor but single-objective optimization problems. This paper introduces a new multi-objective algorithm (MOA) based on the PSO and Pareto methods that can greatly reduce the number of objective function calls when a suitable swarm size is set.
LCF Assessment of Electron-Beam-Welded Notched Parts of Nickel-Based Superalloy Inconel 718
Authors: Yuan Huang , Fang Jie
Published: September 2014

In the present work the local mechanical behavior and fatigue resistance of the welding material were investigated with help of the instrumented indentation technique in combining with FEM computations. By assuming a power-law strain hardening, the elastic-plastic properties of the welding material were identified from inverse indentation analysis with help of finite element simulation. A critical plane based Cruse-Meyer model was introduced to predict the LCF fatigue life of the weld joints. Combined with the critical distance concept, the fatigue life in center-holed specimens was investigated and verified with experiments.
Wide Gap Brazing of IN 738 With Boron Free Ni-Co-Zr-Hf-Cr-Ti-Al Braze Alloy
Authors: Huang Xiao
Published: September 2014

In this study, a new boron and silicon free braze alloy, based on Ni-Co-Zr-Hf-Cr-Ti-Al, was used to repair IN 738 superalloy employing a wide gap brazing (WGB) process under two process conditions. It was found that using a combination of Hf and Zr primarily as melting point depressants the amount of each melting point depressant (MPD) could effectively be reduced while still achieving a relatively low liquidus. During WGB process, the new braze alloy was able to bond IN 738 filler powder particles to each other and to the substrate cast IN 738 and achieve defect free joint. The microstructure analysis showed the presence of Zr-containing phase(s) remained in WGB joint, however, the hardness of the Zr-containing phase(s) was similar to that of superalloy substrate. Extended brazing cycle had limited effect on reducing the Zr-containing phase(s); rather it encouraged the formation of larger eutectic γ/γ′ phases.
Robust Optimal Operation of a Gas Turbine Cogeneration Plant Under Uncertain Energy Demands
Authors: Yokoyama Ryohei , Ohkura Masashi , Wakui Tetsuya
Published: September 2014

Some optimal operation methods based on the mixed-integer linear programming have been proposed to operate energy supply plants properly from the viewpoints of economics, energy saving, and CO2 emission reduction. However, most of the methods are effective only under certain energy demands. In operating an energy supply plant actually, it is necessary to determine the operational strategy properly based on predicted energy demands. In this case, realized energy demands may differ from the predicted ones. Therefore, it is necessary to determine the operational strategy so that it is robust against the uncertainty in energy demands. In this paper, an optimization method based on the mixed-integer linear programming is proposed to conduct the robust optimal operation of energy supply plants under uncertain energy demands. The uncertainty in energy demands is expressed by their intervals. The operational strategy is determined to minimize the maximum regret in the operational cost under the uncertainty. In addition, a hierarchical relationships among operation modes and on/off states of equipment, energy demands, and energy flow rates of equipment are taken into account. First, a general formulation of a robust optimal operation problem is presented, which is followed by a general solution procedure. Then, in a numerical study, the proposed method is applied to a gas turbine cogeneration plant for district energy supply. Through the study, some features of the robust optimal operation are clarified, and the validity and effectiveness of the proposed method are ascertained.
Comparative Study of Using R-410A, R-407C, R-22 and R-134a as Cooling Medium in the Condenser of a Steam Power Plant
Authors: Yousef Khaled , Assefa Abebayehu , Hegazy Ahmed , Engeda Abraham
Published: September 2014

A step-by-step technique has been implemented in the analytical study of heat transfer and pressure gradient characteristics of refrigerants R-410A, R-407C, R-22 and R-134a used as cooling media in the condenser of a steam power plant. Refrigerants are optimized to replace water/air as coolant in the condenser of a steam power plant. Refrigerants have much lower temperatures and much higher heat transfer rates than water or air. The thermal resistances that affect heat transfer characteristics and surface condenser performance are included. The effect of inlet refrigerant temperature and mass flow rate are reported for the four refrigerants. Calculations are performed at two inlet refrigerant temperatures −21 °C and −30 °C and mass flow rate ranging from 92.905 to 132.905 kg/s. The results revealed that the overall heat transfer coefficient, heat transfer rate and condensation rate increased with refrigerant mass flow rate, with higher values at lower inlet refrigerant temperatures. For a given refrigerant mass flow rate and inlet temperature, the analytical study indicated that R-410A has higher values of overall heat transfer coefficient, heat transfer rate and condensation rate than R-407C, R-22 and R-314a, respectively. Moreover, it is found that R-410A, at −30 °C and 132.905 kg/s, is superior in condensing all steam entering the condenser than the other refrigerants; this corresponds to higher exergy efficiency. The condenser pressure was observed to be slightly higher for R-410A than the other refrigerants.
Location Effect of Boundary Layer Suction on Compressor Hub-Corner Separation
Authors: Chen Ping-Ping , Qiao Wei-Yang , Liesner Karsten , Meyer Robert
Published: September 2014

The large secondary flow area in the compressor hub-corner region usually leads to three-dimensional separation in the passage with large amounts of total pressure loss. In this paper numerical simulations of a linear high-speed compressor cascade, consisting of five NACA 65-K48 stator profiles, were performed to analyze the flow mechanism of hub-corner separation for the base flow. Experimental validation is used to verify the numerical results. Active control of the hub-corner separation was investigated by using boundary layer suction. The influence of the selected locations of the endwall suction slot was investigated in an effort to quantify the gains of the compressor cascade performance. The results show that the optimal chordwise location should contain the development section of the three-dimensional corner separation downstream of the 3D corner separation onset. The best pitchwise location should be close enough to the vanes’ suction surface. Therefore the optimal endwall suction location is the MTE slot, the one from 50% to 75% chord at the hub, close to the blade suction surface. By use of the MTE slot with 1% suction flow ratio, the total-pressure loss is substantially decreased by about 15.2% in the CFD calculations and 9.7% in the measurement at the design operating condition.
DNS of the Flow Near the Endwall in a Linear Low Pressure Turbine Cascade With Periodically Passing Wakes
Authors: Koschichow Denis , Fröhlich Jochen , Kirik Ilker , Niehuis Reinhard
Published: September 2014

Direct numerical simulations (DNS) were used to study the effects of periodic incoming wakes on the flow near the endwall in a linear turbine cascade T106. The moving cylindrical bars generating the wakes in the experiment were represented by means of appropriate unsteady turbulent inflow conditions. In the simulations, two cases, with and without incoming wakes, were conducted at a Reynolds number of 90,000 based on chord length and outlet velocity. The results were validated with experimental data. Due to constructive limitations of the experimental setup, the incoming boundary layer is very thin, so that some features of the secondary flow are absent or small. Employing phase-averaging, however, the periodic formation of vortical structures caused by the wakes can be identified in the vicinity of the endwall.
Fuel Influence on Targeted Gas Turbine Combustion Properties: Part I — Detailed Diagnostics
Authors: Mosbach Thomas , Burger Victor , Gunasekaran Barani
Published: September 2014

The threshold combustion performance of different fuel formulations under simulated altitude relight conditions were investigated in the altitude relight test facility located at the Rolls-Royce plc. Strategic Research Centre in Derby, UK. The combustor employed was a twin-sector representation of an RQL gas turbine combustor. Eight fuels including conventional crude-derived Jet A-1 kerosene, synthetic paraffinic kerosenes (SPKs), linear paraffinic solvents, aromatic solvents and pure compounds were tested. The combustor was operated at sub-atmospheric air pressure of 41 kPa and air temperature of 265 K. The temperature of all fuels was regulated to 288 K. The combustor operating conditions corresponded to a low stratospheric flight altitude near 9 kilometres.

The experimental work at the Rolls-Royce (RR) test-rig consisted of classical relight envelope ignition and extinction tests, and ancillary optical measurements: Simultaneous high-speed imaging of the OH* chemiluminescence and of the soot luminosity was used to visualize both the transient combustion phenomena and the combustion behaviour of the steady burning flames. Flame luminosity spectra were also simultaneously recorded with a spectrometer to obtain information about the different combustion intermediates and about the thermal soot radiation curve. This paper presents first results from the analysis of the weak extinction measurements. Further detailed test fuel results are the subject of a separate complementary paper [1].

It was found in general that the determined weak extinction parameters were not strongly dependent on the fuels investigated, however at the leading edge of the OH* chemiluminescence intensity development in the pre-flame region fuel-related differences were observed.
Development of a Course on Gas and Steam Turbines Supported by Cost-Efficient Turbomachinery Experiments
Authors: aus der Wiesche Stefan
Published: September 2014

Based on a voice-of-the-industry survey covering major turbine manufactures as well as power plant owners and operators an undergraduate course on gas and steam turbines was developed at Muenster University of Applied Sciences. This course is also supported by cost-efficient experiments. The experimental investigations on laboratory test rigs are making the students more familiar with turbomachinery phenomena like gas turbine cycle performance, fundamental rotordynamics, blade vibrations, and flow through turbine cascades and loss correlations. The experiments and test rigs were developed in great part by students as part of their Bachelor or Master theses. Furthermore, the experiments did not require tremendous efforts or an expensive infrastructure; they were operated in typical University laboratory environments.
Online Performance Monitoring of Industrial Compressors Using Meanline Modelling
Authors: Cicciotti Matteo , Xenos Dionysios P. , Bouaswaig Ala E. F. , Thornhill Nina F. , Martinez-Botas Ricardo F.
Published: September 2014

This paper proposes a framework for detecting mechanical degradation online and assessing its effect on the performance of industrial compressors. It consists of a model of the machine in undegraded condition and of a degradation adaptive model. The proposed methodology for online degradation detection differentiates itself from those found in the literature as the undegraded model is not linearized and ambient/inlet conditions are explicitly taken into account. The degradation is modelled through adaptive parameters which are estimated and updated online through the solution of a constrained minimization problem within a moving window. It uses available process measurements of flow, pressures, temperatures and composition. The update of the parameters guarantees the model accuracy and it permits the estimation of the effects of mechanical degradation away from the compressor running line.

The performance monitoring framework has been successfully applied on an industrial air centrifugal compressor. It was found that after 3250 hours of operation from the previous maintenance the efficiency and the pressure ratio had dropped approximately 5.5% and 2.5% of their respective undegraded values. Furthermore, it was found that the performance deviations from the baseline depend from the position of the operative point in the performance map. In fact, the pressure ratio drop was lower (2%) and efficiency drop was higher (6%) for lower inlet guide vanes opening whereas pressure ratio drop was higher (3%) and efficiency drop was lower (1.6%) for higher inlet guide vane opening.
Aerodynamics Study of a Linearly-Arranged 5-Swirler Array
Authors: Kao Yi-Huan , Tambe Samir B. , Jeng San-Mou
Published: September 2014

In this experimental work, a series of tests have been conducted to further study the aerodynamics of linearly-arranged 5-swirler arrays, using Laser Doppler Velocimetry (LDV). Two major parameters have been investigated for the 5-swirler arrays in this work, including the inter-swirler spacing, and the end wall distance. An additional effect of dome recession was studied for a single swirler in order to provide some insight into the results for the 5-swirler arrays.

The 5-swirler arrays with an inter-swirler spacing of 1.75D, 2D, 2.5D, and 2.75D were studied, where D is the diameter of swirler exit. For the inter-swirler spacing of 1.75D or 2D, the center swirler is shown to have a weak, large center toroidal recirculation zone (CTRZ). The swirlers next to the center swirlers have strong, compact CTRZs whereas the outer swirlers have weak, large CTRZs. Thus, starting from the center swirler, the CTRZs exhibit a large – small – large pattern in either direction. For the swirler spacing of 2.5D or 2.75D, the trend is reversed, with a strong CTRZ for the center swirler and a small – large – small CTRZ pattern.

The end wall distances of 0.75D, 1D, 1.25D, and 2D cases were studied. The end wall distances are seen to affect the strength of each CTRZ and the corner swirling flow pattern, though the bulk flow structure did not change significantly.

The dome recession shows a clear impact on the expansion of swirling flow generated by a single swirler. As the dome recession distance increases, the expansion angle of the swirling jet reduces significantly for the unconfined cases.

A phenomenological description is discussed to understand the reason for the periodically alternating CTRZ pattern observed in the experimental results of the 5-swirler arrays.
Investigations on Fluid Flow and Heat Transfer Performances Within a Real Turbine Blade Channel
Authors: Ke Zhaoqing , Pu Jian , Wang Jianhua , Wang Lei , Zhang Zhiqiang , Wu Xiangyu
Published: September 2014

The characteristics of fluid flow and heat transfer within a smooth three-pass channel of a real low pressure (LP) turbine blade have been investigated through experimental and numerical approaches. The serpentine channel consists of two inlet passes, two dividing walls, two 180 degree bends, twenty-five exits at the trailing edge, and two exits at the blade tip. In the experiments, purified water was used as working medium, the secondary flow patterns at five cross-sections were captured by a particle image velocimetry (PIV) system, the inlet Reynolds number was controlled by a turbine flow meter, and the mass flow rate ejected from each exit was measured by rotameters. Using the commercial software ANSYS CFX 13.0, numerical investigations were carried out. The practicability of four turbulence models, the SSG RSM, SST k-ω, RNG k-ε and standard k-ε models, were estimated. Through qualitative and quantitative comparisons of the secondary flow patterns, local velocity variation trends and mass flow rates between the experimental data and numerical results, the SSG RSM was selected as the most appropriate model in the following numerical investigations. Using ideal gas as working medium, the impacts of Reynolds numbers and rotation numbers on the heat transfer performances were numerically investigated. The numerical results predicted three interesting phenomena: 1) The locally averaged Nusselt number increases generally with the inlet Reynolds numbers. However, the increasing amplitude is significantly different from the correlation suggested by Dittus-Boelter, Nuo = 0.023Re0.8Pr0.4. The effect of the Reynolds number on the Nusselt number is substantially enhanced due to the serpentine channel design with two 180 degree-bends. The enhancement amplitude is described by two fitted coefficients based on Dittus-Boelter correlation. 2) Under a rotation condition, in the 1st and 3rd passes, the enhancement amplitude of the average Nusselt number on the pressure side (PS) is more significant than that on the suction side (SS), whereas in the 2nd pass, the enhancement amplitude on the PS is lower than that on the SS. 3) In the 3rd pass, a higher rotation number leads to a more uniform distribution of the local Nusselt number along the streamwise direction on both the PS and SS.
Development of an Engine Representative Combustor Simulator Dedicated to Hot Streak Generation
Authors: Koupper Charlie , Bonneau Guillaume , Caciolli Gianluca , Facchini Bruno , Tarchi Lorenzo , Gicquel Laurent , Duchaine Florent
Published: September 2014

Nowadays, the lack of confidence in the prediction of combustor-turbine interactions and more specifically our ability to predict the migration of hot spots through this interface leads to the application of extra safety margins, which are detrimental to an optimized turbine design and efficiency. To understand the physics and flow at this interface, a full 360° non-reactive combustor simulator representative of a recent lean burn chamber together with a 1.5 turbine stage is instrumented at DLR in Gottingen (Germany) within the European project FACTOR. The chamber operates with axial swirlers especially designed to reproduce engine-realistic velocity and temperature distortion profiles allowing the investigation of the hot streaks transport through the high pressure stage. First, a true scale three injector annular sector of the combustor simulator without turbine is assembled and tested at the University of Florence. To generate the hot steaks the swirlers are fed by an air flow at 531 K, while the liners are cooled by an effusion system fed with air at ambient temperature. In addition to static pressure taps and thermocouples, the test rig will be equipped with an automatic traverse system which allows detailed measurements at the combustor exit by means of a 5-hole probe, a thermocouple and hot wire anemometers. This paper presents the design process and instrumentation of the trisector combustor simulator, with a special focus on Large Eddy Simulations (LES) which were widely used to validate the design choices. It was indeed decided to take advantage of the ability and maturity of LES to properly capture turbulence and mixing within combustion chambers, despite an increased computational cost as compared to usual RANS approaches. For preliminary design, simulations of a single periodic sector (representative of the DLR full annular rig) are compared to simulations of the trisector test rig, showing no difference on the central swirler predictions, comforting the choice for the trisector. In parallel, to allow hot wire anemometry measurements, the selection of an isothermal operating point, representative of the nominal point, is assessed and validated by use of LES.
Evaluation and Enhancement of a One-Dimensional Performance Analysis Method for Centrifugal Compressors
Authors: Klausner Enrico , Gampe Uwe
Published: September 2014

The one-dimensional flow analysis along a mean streamline is an appropriate and established procedure for initial design and performance analysis of turbomachinery. One such method for performance analysis of centrifugal compressors was published by Aungier in the 1990s. The latest description of Aungier’s performance prediction model was applied to a set of centrifugal compressor stages published in literature. For each test case the whole performance map was calculated and compared with measurement data. The calculation results correspond well with measured data over a wide operating range. However, near choke or stall the mean streamline performance prediction deviates from measurements. After evaluation of this “standard” mean streamline model specific loss correlations, e.g. for choking, incidence and shock losses were replaced by theoretical models. The aim was to implement a more physical based loss model which is able to predict the performance of compressor stages outside the limits of the standard procedure. The modified procedure was again validated against measurements of the above mentioned compressor stages. The modified procedure gives a better prediction of operating performance and behavior. Shortcomings of the procedure are still the overestimation of vaneless diffuser losses at low mass flow rates and the uncertainty in prediction of choke limit. In conclusion recommendations for advancement of the one-dimensional performance analysis method are given.