bluuebunny/crossref_metadata_2025 huggingface dataset:
Influence of dialysis modality and membrane flux on insomnia severity in haemodialysis patients
Authors: Knezevic Marinela Z , Djordjevic Vladimir V , Jankovic Slobodan M , Djordjevic Vidojko M
Published: July 2013

Aim

Insomnia is an important problem in dialysis patients. A greater prevalence of insomnia in chronic kidney disease compared with non‐renal patients suggests a role for uraemic toxins in contributing to insomnia. The aim of this study was to examine if dialysis modality and membrane permeability is associated with the frequency and severity of insomnia in haemodialysis patients.

Methods

In our cross‐sectional study, we evaluated 122 patients who were divided into three groups: on‐line haemodiafiltration, high flux haemodialysis and low flux haemodialysis. The frequency and severity of insomnia was evaluated with the Insomnia Severity Index.

Results

Insomnia was present in 47.5% of all patients. The majority of patients who reported insomnia were receiving low flux haemodialysis (80%), followed by patients on high flux haemodialysis (43.6%) and haemodiafiltration (20.9%). Patients using low flux membranes, had a significantly higher Insomnia Severity Index (11.9 ± 6.6) compared with patients receiving high flux haemodialysis (6.8 ± 6.3) and haemodiafiltration (5.2 ± 7.0). The insomnia severity index did not differ between patients receiving high flux haemodialysis compared with on‐line haemodiafiltration.

Conclusion

This study indicates that different haemodialysis modalities are associated with insomnia and suggests a potential benefit of using high flux membranes.
Electroacupuncture improves burn‐induced impairment in gastric motility mediated via the vagal mechanism in rats
Authors: Song J. , Yin J. , Sallam H. S. , Bai T. , Chen Y. , Chen J. D. Z.
Published: July 2013

Background

Delayed gastric emptying (GE) is common in patients with severe burns. This study was designed to investigate effects and mechanisms of electroacupuncture (EA) on gastric motility in rats with burns.

Methods

Male rats (intact and vagotomized) were implanted with gastric electrodes, chest and abdominal wall electrodes for investigating the effects of EA at ST‐36 (stomach‐36 or Zusanli) on GE, gastric slow waves, autonomic functions, and plasma interleukin 6 (IL‐6) 6 and 24 h post severe burns.

Key Results

(i) Burn delayed GE (P < 0.001). Electroacupuncture improved GE 6 and 24 h post burn (P < 0.001). Vagotomy blocked the EA effect on GE. (ii) Electroacupuncture improved burn‐induced gastric dysrhythmia. The percentage of normal slow waves was increased with EA 6 and 24 h post burn (P = 0.02). (iii) Electroacupuncture increased vagal activity assessed by the spectral analysis of heart rate variability (HRV). The high‐frequency component reflecting vagal component was increased with EA 6 (P = 0.004) and 24 h post burn (P = 0.03, vs sham‐EA). (iv) Electroacupuncture attenuated burn‐induced increase in plasma IL‐6 at both 6 (P = 0.03) and 24 h post burn (P = 0.003).

Conclusions & Inferences

Electroacupuncture at ST‐36 improves gastric dysrhythmia and accelerates GE in rats with burns. The improvement seems to be mediated via the vagal pathway involving the inflammatory cytokine IL‐6.
Reduced transpiration response to precipitation pulses precedes mortality in a piñon–juniper woodland subject to prolonged drought
Authors: Plaut Jennifer A. , Wadsworth W. Duncan , Pangle Robert , Yepez Enrico A. , McDowell Nate G. , Pockman William T.
Published: July 2013

Global climate change is predicted to alter the intensity and duration of droughts, but the effects of changing precipitation patterns on vegetation mortality are difficult to predict. Our objective was to determine whether prolonged drought or above‐average precipitation altered the capacity to respond to the individual precipitation pulses that drive productivity and survival.

We analyzed 5 yr of data from a rainfall manipulation experiment in piñon–juniper (Pinus edulis–Juniperus monosperma) woodland using mixed effects models of transpiration response to event size, antecedent soil moisture, and post‐event vapor pressure deficit. Replicated treatments included irrigation, drought, ambient control and infrastructure control.

Mortality was highest under drought, and the reduced post‐pulse transpiration in the droughted trees that died was attributable to treatment effects beyond drier antecedent conditions and reduced event size. In particular, trees that died were nearly unresponsive to antecedent shallow soil moisture, suggesting reduced shallow absorbing root area. Irrigated trees showed an enhanced response to precipitation pulses.

Prolonged drought initiates a downward spiral whereby trees are increasingly unable to utilize pulsed soil moisture. Thus, the additive effects of future, more frequent droughts may increase drought‐related mortality.
Competition between plant and bacterial cells at the microscale regulates the dynamics of nitrogen acquisition in wheat (Triticum aestivum)
Authors: Jones David L. , Clode Peta L. , Kilburn Matt R. , Stockdale Elizabeth A. , Murphy Daniel V.
Published: July 2013

The ability of plants to compete effectively for nitrogen (N) resources is critical to plant survival. However, controversy surrounds the importance of organic and inorganic sources of N in plant nutrition because of our poor ability to visualize and understand processes happening at the root–microbial–soil interface.

Using high‐resolution nano‐scale secondary ion mass spectrometry stable isotope imaging (NanoSIMS‐SII), we quantified the fate of 15N over both space and time within the rhizosphere. We pulse‐labelled the soil surrounding wheat (Triticum aestivum) roots with either or 15N‐glutamate and traced the movement of 15N over 24 h.

Imaging revealed that glutamate was rapidly depleted from the rhizosphere and that most 15N was captured by rhizobacteria, leading to very high 15N microbial enrichment. After microbial capture, approximately half of the 15N‐glutamate was rapidly mineralized, leading to the excretion of , which became available for plant capture. Roots proved to be poor competitors for 15N‐glutamate and took up N mainly as . Spatial mapping of 15N revealed differential patterns of 15N uptake within bacteria and the rapid uptake and redistribution of 15N within roots.

In conclusion, we demonstrate the rapid cycling and transformation of N at the soil–root interface and that wheat capture of organic N is low in comparison to inorganic N under the conditions tested.
The impact of initiatives to limit the advertising of food and beverage products to children: a systematic review
Authors: Galbraith‐Emami S. , Lobstein T.
Published: July 2013

In response to increasing evidence that advertising of foods and beverages affects children's food choices and food intake, several national governments and many of the world's larger food and beverage manufacturers have acted to restrict the marketing of their products to children or to advertise only ‘better for you’ products or ‘healthier dietary choices’ to children. Independent assessment of the impact of these pledges has been difficult due to the different criteria being used in regulatory and self‐regulatory regimes. In this paper, we undertook a systematic review to examine the data available on levels of exposure of children to the advertising of less healthy foods since the introduction of the statutory and voluntary codes. The results indicate a sharp division in the evidence, with scientific, peer‐reviewed papers showing that high levels of such advertising of less healthy foods continue to be found in several different countries worldwide. In contrast, the evidence provided in industry‐sponsored reports indicates a remarkably high adherence to voluntary codes. We conclude that adherence to voluntary codes may not sufficiently reduce the advertising of foods which undermine healthy diets, or reduce children's exposure to this advertising.
Bioelectrical impedance analysis to estimate body composition in children and adolescents: a systematic review and evidence appraisal of validity, responsiveness, reliability and measurement error
Authors: Talma H. , Chinapaw M. J. M. , Bakker B. , HiraSing R. A. , Terwee C. B. , Altenburg T. M.
Published: July 2013

Bioelectrical impedance analysis (BIA) is a practical method to estimate percentage body fat (%BF). In this systematic review, we aimed to assess validity, responsiveness, reliability and measurement error of BIA methods in estimating %BF in children and adolescents.We searched for relevant studies in Pubmed, Embase and Cochrane through November 2012. Two reviewers independently screened titles and abstracts for inclusion, extracted data and rated methodological quality of the included studies. We performed a best evidence synthesis to synthesize the results, thereby excluding studies of poor quality. We included 50 published studies. Mean differences between BIA and reference methods (gold standard [criterion validity] and convergent measures of body composition [convergent validity]) were considerable and ranged from negative to positive values, resulting in conflicting evidence for criterion validity. We found strong evidence for a good reliability, i.e. (intra‐class) correlations ≥0.82. However, test‐retest mean differences ranged from 7.5% to 13.4% of total %BF in the included study samples, indicating considerable measurement error. Our systematic review suggests that BIA is a practical method to estimate %BF in children and adolescents. However, validity and measurement error are not satisfactory.
Plaque‐Like Myofibroblastic Tumor: Report of Three Cases
Authors: Marqueling Ann L. , Dasher David , Friedlander Sheila F. , McCalmont Timothy H. , Frieden Ilona J.
Published: July 2013

Plaque‐like myofibroblastic tumor of infancy (PMTI) was first reported in 2007. The first two cases described large, plaque‐like tumors presenting in infancy with microscopic features consistent with dermatofibroma but with immunohistochemical features of myofibrocytic lineage. We present three additional cases of PMTI, the first cases reported since the initial two cases, and describe additional clinical features of this condition, including presentation in early childhood as opposed to infancy, development of ulceration, and aggressive growth. We propose shortening the name of this condition to plaque‐like myofibroblastic tumor because presentation can occur in infancy or in early childhood.
Differential clinical characteristics of acute liver failure caused by hemophagocytic lymphohistiocytosis in children
Authors: Ryu Jeong‐Min , Kim Kyung Mo , Oh Seak Hee , Koh Kyung Nam , Im Ho Joon , Park Chan‐Jeoung , Chi Hyun‐Sook , Seo Jong Jin
Published: July 2013

Background

Children with acute liver failure (ALF) caused by hemophagocytic lymphohistiocytosis (HLH) may be at risk of undergoing unnecessary liver transplantation (LT). The aim of this study was to compare the characteristics of ALF caused by HLH with those of ALF of unknown etiology in children.

Methods

The clinical features and laboratory findings for eight children with ALF caused by HLH (ALF‐HLH group) and 27 children with ALF of unknown etiology (ALF‐UK group) were retrospectively compared by reviewing medical records.

Results

The ALF‐HLH group had a higher incidence of pleural effusion, C‐reactive protein elevation (especially >5 mg/dL), thrombocytopenia, anemia, fever, splenomegaly, and hypoalbuminemia (<2.5 mg/dL), and a higher in‐hospital mortality rate. No significant differences were found in the white blood cell count, liver enzymes, coagulation profile, or incidence of hepatomegaly.

Conclusions

LT should be performed only after it is proven that ALF is not caused by HLH, if a child with ALF shows the differential clinical features of ALF caused by HLH. Further research with larger sample sizes, however, is needed.
Immobile and tough versus mobile and weak: effects of ultraviolet B radiation on eggs and larvae of Manduca sexta
Authors: POTTER KRISTEN A. , WOODS H. ARTHUR
Published: July 2013

Although indirect effects of solar ultraviolet (UV) radiation on insects are well known (e.g. UV radiation can modify plant chemistry), direct effects of solar radiation on insects have received little attention. Radiation in the UVB range (300–320 nm) is damaging because it is absorbed directly by proteins and DNA. UVB should be toughest on immobile or small life stages, such as eggs or early larval instars. In the present study, the effects of UVB radiation on eggs and larvae of the tobacco hornworm Manduca sexta L. (Lepidoptera: Sphingidae) are examined. The present study aimed to address: what natural levels of UV do they experience; how does UVB affect the performance of eggs; and how does it affect the performance of larvae? In addition, do M. sexta larvae use behaviour to avoid UVB exposure and, consequently, are they physiologically less robust to UVB? In these experiments, eggs and late larval instars of M. sexta are found to be robust to natural levels of UV radiation. By contrast, young larvae are not only more susceptible to damage from UVB, but also they use behavioural means to avoid it. The strategy of using behaviour may relax selection pressures on morphological and physiological mechanisms for preventing (or recovering from) damage by environmental UV radiation.
Fusarium solani f. sp. passiflorae: a new forma specialis causing collar rot in yellow passion fruit
Authors: Bueno C. J. , Fischer I. H. , Rosa D. D. , Firmino A. C. , Harakava R. , Oliveira C. M. G. , Furtado E. L.
Published: July 2013

The aim of this study was to characterize a Fusarium population obtained from yellow passion fruit (YPF) with collar rot using pathogenicity, morphocultural characteristics and molecular tests. Pathogenicity and disease severity were assessed in six plant species: YPF, zucchini, tomato, bean, soya bean and cucumber. Potato dextrose agar medium (PDA) was used to determine mycelial growth at five temperatures (15–35°C). The colour produced by isolates was also determined on PDA at 25°C. Synthetic nutrient agar medium was used to evaluate: (i) type of mycelium and phialides; (ii) size, shape and number of septa from conidia; and (iii) production of chlamydospores and perithecia. Molecular tests consisted of sequencing the ITS–5·8S rDNA region and elongation factor 1α (EF‐1α) gene. The isolates caused large lesions on YPF, zucchini and tomato, with YPF having the highest mean disease severity and being the only one that showed wilt symptoms and death of the plant. Thus the isolates showed host specificity. Maximum mycelial growth occurred at 25°C and the predominant colour was bluish‐white. The isolates produced long phialides, dense aerial mycelium, oval microconidia with a mean size of 9·5 × 2·6 μm, macroconidia of 32·7 × 3·4 μm with 3·3 septa, and chlamydospores; only one isolate lacked perithecia. Phylogenetic trees of the ITS region and EF‐1α gene showed that isolates from YPF formed a distinct group within the F. solani group and the formae speciales of F. solani. It is proposed to name all isolates from YPF as F. solani f. sp. passiflorae.
Quantifying resistance to Plasmodiophora brassicae in Brassica hosts
Authors: Cao T. , Rennie D. C. , Manolii V. P. , Hwang S. F. , Falak I. , Strelkov S. E.
Published: July 2013

Plasmodiophora brassicae causes clubroot of crucifers. A quantitative PCR (qPCR)‐based protocol was developed to measure P. brassicae DNA in the roots of susceptible, intermediately susceptible, intermediately resistant and resistant Brassica hosts, and the non‐host wheat, at 5, 10, 15, 20 and 42 days post‐inoculation (dpi). The final reaction of each plant genotype was recorded as an index of disease at 42 dpi. Plasmodiophora brassicae DNA showed an increase in susceptible and moderately resistant hosts from 5 to 42 dpi, in contrast to a decrease in a highly resistant host and the non‐host wheat over the same period. Index of disease was significantly positively correlated with the amount of P. brassicae DNA in the roots at 5, 15, 20 and 42 dpi in one experiment, and at 10, 15, 20 and 42 dpi in a repeated experiment. Significant positive correlations also existed between the amounts of P. brassicae DNA in the roots at 42 dpi and those at 5, 10, 15 and 20 dpi in one experiment, and those at 10, 15 and 20 dpi in a repeated experiment. The results generated by the qPCR assay were validated by microscopic examination of roots inoculated with P. brassicae. The qPCR‐based protocol developed in this study allows for the accurate quantification of P. brassicae DNA in host root tissues as early as 5 dpi, and may serve as a useful tool to evaluate pathogen proliferation and development in the roots.
What Do We Know about the Natural Outcomes of Preterm Labour? A Systematic Review and Meta‐Analysis of Women without Tocolysis in Preterm Labour
Authors: Hackney David N , Olson‐Chen Courtney , Thornburg Loralei L.
Published: July 2013

Background

Current knowledge of the natural outcomes of untreated women in preterm labour is both incomplete and outcomes vary significantly between the available studies. The aim of this study was to systematically review outcomes of preterm labour without tocolysis and determine if outcome variation could be accounted for by differences in study populations. Such data could potentially assist in the interpretation of intervention trials that do not include a no‐treatment arm.

Methods

Included studies reported outcomes of women in clinically diagnosed preterm labour without tocolytic treatment between 1950 and 2011. Studies that were limited to preterm prelabour rupture of membranes, recurrent preterm labour or in which the women without tocolysis represented a potentially biased subgroup, or were not tocolysed because of contraindications were excluded. Study quality, design, and population characteristics were abstracted. Outcomes included pregnancy prolongation and the proportion of women undelivered at 48–72 h, 7 days, and term. Study characteristics associated with differing odds of preterm birth were explored through logistic regression.

Results

Three hundred and eighty‐five citations were initially identified, of which 26 were included encompassing 1383 women. The percentage of patients who were undelivered at 48–72 hours was 62.8%, at 7 days 53.4% and 40.4% delivered at term, though the range was very wide. Characteristics associated with decreased odds of delivery were not consistent among reported outcome measures.

Conclusions

Most women without tocolysis do not deliver within 7 days, although the range is very wide. The majority of this variation is unrelated to reported differences in study design or reported population characteristics.
Microbial dolomite in fresh water carbonate deposits
Authors: García‐Del‐Cura María Ángeles , Sanz‐Montero María Esther , De‐los‐Ríos María Asunción , Ascaso Carmen
Published: July 2013

This article reports evidence for biologically mediated precipitation of dolomite in a fresh water spring in the south‐east of Spain. Build‐ups in the spring consisted of calcite, minor dolomite, barite and gypsum crystals formed by the mineralisation of microbial biofilms and bryophytes. A detailed microscopic study, coupled with geochemical analysis of the dolomite‐precipitating biofilms, showed that dolomite crystals occurred in association with living coccoid micro‐organisms, providing strong evidence that micro‐organisms play a fundamental role in the precipitation of this mineral. Many of the calcite crystals observed were associated with extracellular polymeric substances. Moreover, microbial involvement in the precipitation of calcite was further supported by the presence of living cyanobacteria within the calcite crystals. Two different types of build‐up were found in the spring: soft spongy moss tufa and laminated crusts. Two types of crusts were identified as follows: simple pink crusts and laminated crusts, the latter forming in both sub‐aquatic and sub‐aerial environments. Sub‐aquatic accumulation of simple detached pink crust fragments occurred sporadically. Both tufa and the carbonate crusts hosted cyanobacterial‐dominated biofilms with different bacteria and diatoms and their extracellular polymeric substances. The δ13C values of calcite showed some biogenic involvement in the origin of this mineral. The δ18O values were similar in the tufa and carbonate crusts and corresponded to current climatological characteristics. The occurrence of different groups of minerals (carbonates and sulphates) in close spatial association with micro‐organisms suggests the presence of different macro‐environmental and micro‐environmental conditions that facilitate mineral precipitation within biofilms. These findings extend the known range of aerobic microbial dolomites to include springs, and show that the precipitation of both dolomite and calcite carbonates occurs while organisms are alive.
Genotype List String: a grammar for describing HLA and KIR genotyping results in a text string
Authors: Milius R. P. , Mack S. J. , Hollenbach J. A. , Pollack J. , Heuer M. L. , Gragert L. , Spellman S. , Guethlein L. A. , Trachtenberg E. A. , Cooley S. , Bochtler W. , Mueller C. R. , Robinson J. , Marsh S. G. E. , Maiers M.
Published: July 2013

Knowledge of an individual's human leukocyte antigen (HLA) genotype is essential for modern medical genetics, and is crucial for hematopoietic stem cell and solid‐organ transplantation. However, the high levels of polymorphism known for the HLA genes make it difficult to generate an HLA genotype that unambiguously identifies the alleles that are present at a given HLA locus in an individual. For the last 20 years, the histocompatibility and immunogenetics community has recorded this HLA genotyping ambiguity using allele codes developed by the National Marrow Donor Program (NMDP). While these allele codes may have been effective for recording an HLA genotyping result when initially developed, their use today results in increased ambiguity in an HLA genotype, and they are no longer suitable in the era of rapid allele discovery and ultra‐high allele polymorphism. Here, we present a text string format capable of fully representing HLA genotyping results. This Genotype List (GL) String format is an extension of a proposed standard for reporting killer‐cell immunoglobulin‐like receptor (KIR) genotype data that can be applied to any genetic data that use a standard nomenclature for identifying variants. The GL String format uses a hierarchical set of operators to describe the relationships between alleles, lists of possible alleles, phased alleles, genotypes, lists of possible genotypes, and multilocus unphased genotypes, without losing typing information or increasing typing ambiguity. When used in concert with appropriate tools to create, exchange, and parse these strings, we anticipate that GL Strings will replace NMDP allele codes for reporting HLA genotypes.
Characterization of a novel allele, HLA‐B*15:139
Authors: Zhang W. D. , Wang L. J. , Zhang K. Y. , Shan X. Y. , Jia Y. J.
Published: July 2013

The novel allele HLA‐B*15:139 was closest to HLA‐B*15:02,*15:18, with a single‐nucleotide mismatch in exon 2.
The novel HLA‐A*24:215 allele, identified by sequencing‐based typing of a stem cell transplant patient and the sibling donor
Authors: Plaisier L. , Geerts N. , van Ginkel W. , van der Weerd R. , Spierings E.
Published: July 2013

We identified a new human leukocyte antigen‐A allele, designated HLA‐A*24:215, by sequencing‐based typing of a stem cell transplant patient.
Polycystic ovary syndrome and the differential diagnosis of hyperandrogenism
Authors: Meek Claire L , Bravis Vassiliki , Don Abigail , Kaplan Felicity
Published: July 2013

Key content

The presence of clinical or biochemical evidence of hyperandrogenism is a defining feature of polycystic ovary syndrome (PCOS).

As the criteria for diagnosing PCOS becomes more inclusive, there is an increased risk of misdiagnosing women with other causes of hyperandrogenism.

Biochemical testing for serum testosterone concentrations in women has important limitations.

Patients with concerning features should be investigated for other causes of hyperandrogenism.

Learning objectives

To review the different criteria for diagnosing PCOS and the repercussions for disease prevalence.

To learn about the differential diagnosis of hyperandrogenism.

To learn about the limitations of biochemical testing for testosterone in women.

Ethical issues

Hyperandrogenism causing hirsutism and virilisation can have significant effects on physical and psychological wellbeing.

Misdiagnosis can delay appropriate treatment and may affect future fertility.
Pelvic congestion syndrome
Authors: Osman Mohamed Waseem , Nikolopoulos Ilias , Jayaprakasan Kannamannadiar , Raine‐Fenning Nicholas
Published: July 2013

Key content

Pelvic congestion syndrome is a poorly understood condition that forms part of chronic pelvic pain syndrome – this makes up 10–40% of gynaecological outpatient department referrals.

Pelvic congestion syndrome is thought to affect 3.8% of women of childbearing age yet the clinicians evaluating these patients are usually unaware of the condition and a significant number of trainees are not up to date with the current diagnostic and management options.

Learning objectives

To learn about the pathophysiology and the risk factors.

To learn to recognise the condition.

To be able to discuss various management options and choose a definitive mode of treatment tailored to individual need.

Ethical issues

Are we doing justice to patients if we as clinicians are not actually aware of this common and significant condition?

Due to current gynaecological investigations not being able to diagnose this condition and general unawareness of the current available diagnostic tests, should we not be more aware of all the investigative modalities and the most appropriate ones for our patients so that a more definitive diagnosis can be made?
Postpartum psychosis
Authors: Di Florio Arianna , Smith Sue , Jones Ian
Published: July 2013

Key content

Postpartum psychosis is a severe mental illness with a dramatic onset shortly after childbirth.

All women should be screened antenatally for the known risk factors.

Women with bipolar disorder have at least a 1 in 4 risk and need close contact and review during the perinatal period even if they are well.

Prompt recognition of the illness and rapid institution of treatment are of vital importance.

Learning objectives

To recognise women at high risk for severe postpartum mental illness.

To recognise and appreciate the severity of postpartum psychosis and the need for prompt assessment and treatment.

Ethical issues

Who should ultimately make decisions about taking medications in pregnancy – the clinician or the woman and her family?

What advice should a woman at high risk of postpartum psychosis be given if she is considering pregnancy?
In-Situ Continuous Coke Deposit Removal by Catalytic Steam Gasification for Fuel-Cooled Thermal Management
Authors: Huang He , Tang Xia , Haas Martin
Published: July 2013

Fuel-cooled thermal management, including endothermic cracking and reforming of hydrocarbon fuels, is an enabling technology for advanced aero engines and offers potential for cycle improvements and pollutant emissions control. The principal engine operability issue that will affect this enabling hydrocarbon fuel cooling technology is coke formation. Furthermore, the extent to which the benefits of high heat sink cooling technology can be realized is directly related to our ability to suppress coke formation. The successful implementation of this enabling technology is, therefore, predicated on coke suppression. In-situ continuous coke deposit removal by catalytic steam gasification is being developed and successfully demonstrated as a means for suppressing pyrolytic coke deposit in fuel-cooled thermal management systems for advanced aero engines. The objective of this research is to investigate the in-situ continuous coke deposit removal by catalytic steam gasification for suppressing pyrolytic coke deposition using a single-tube reactor simulator under representative hypersonic operating conditions. A coke removal system removes coke deposit from the walls of a high temperature passage in which hydrocarbon fuel is present. The system includes a carbon-steam gasification catalyst and a water source. The carbon-steam gasification catalyst is applied to the walls of the high temperature passage. The water reacts with the coke deposit on the walls of the fuel passage side to remove the coke deposit from the walls by carbon-steam gasification in the presence of the carbon-steam gasification catalyst. Experimental data shows the in-situ continuous coke deposit removal by catalytic steam gasification is able to reduce coke deposit rate by more than 10 times.
Characterizing the Mechanism of Lean Blowout for a Recirculation-Stabilized Premixed Hydrogen Flame
Authors: Karalus Megan F. , Fackler K. Boyd , Novosselov Igor V. , Kramlich John C. , Malte Philip C.
Published: July 2013

The stability of hydrogen combustion under lean premixed conditions in a back-mixed jet-stirred reactor (JSR), is experimentally and numerically investigated. The goal is to understand the mechanism of flame extinction in this recirculation-stabilized flame environment. Extinction is achieved by holding the air flow rate constant and gradually decreasing the flow rate of the hydrogen fuel until a blowout event occurs. In order to gain insight on the mechanism controlling blowout, two dimensional computational fluid dynamic (CFD) simulations are carried out for the lean premixed combustion (LPM) of hydrogen as the fuel flow rate is reduced. The CFD model illustrates the evolution of the flow-field, temperature profiles, and flame structure within the JSR as blowout is approached. A single element chemical reactor network (CRN) consisting of a plug flow reactor (PFR) with recirculation is constructed based on the results of the CFD simulations, and its prediction of blowout is in good agreement with the experimental results. The chemical mechanism of Li et al. is used in both the CFD and CRN models, and GRI is used in the CRN for comparison. The modeling suggests that lean blowout does not occur with the flame in a spatially homogeneous condition, but rather under a zonal structure. Specifically, the flame is stabilized by the entrainment of combustion products from the re-circulation zone into the base of the reactant jet. The mixture of hot products and incoming premixed reactants proceeds through an ignition induction period followed by an ignition event. As the fuel flow decreases, the induction period increases and the ignition event is pushed further around the recirculation zone. Eventually, the induction period becomes so long that the ignition is incomplete at the point where the recirculating gas is entrained into the jet. This threshold leads to overall flame extinction.
A Hybrid-LES-RANS Transported PDF Combustion Model for Non-Premixed Flames
Authors: Brandl Alexander , Pfitzner Michael
Published: July 2013

The intention of this work is to combine Large-Eddy-Simulation (LES) for the prediction of flow and mixture fraction fields with a Reynolds-Averaged-Navier-Stokes (RANS) transported probability density function (TPDF) method for the prediction of turbulent non-premixed flames. The motivation for this work is based upon the property of LES to provide a better description of complex flow fields than most current RANS methods can offer, while TPDF-methods excel in predicting the reacting species fields. However, using the straight forward extension of PDF methods for LES, the filtered density function (FDF) approach requires a large number of PDF particles in each LES cell and is thus computationally expensive. Therefore, a method is proposed to use the time-averaged LES flow field, mixture fraction field and mixture fraction PDF as a turbulence model for a RANS TPDF method operating on a much coarser grid. A projection of the mixture fraction conditioned PDF to evaluate the instantaneous LES density field is proposed as coupling device. The reconstruction of mixture fraction PDF from a LES simulation and the coupling to the TPDF method in postprocessing mode is validated using the TNF Sandia D flame, showing good agreement with experiment.
A Method for Determining the Laminar Flame Speed of Jet Fuels Using Combustion Bomb Pressure
Authors: Yates Andy , Burger Victor , Viljoen Carl
Published: July 2013

This paper describes the use of a spherical combustion bomb to determine the laminar flame speed and Markstein length of a selection of hydrocarbon fuels. The fuels nominally represented Jet A-1 but some were doped with various component compounds which were chosen so as to vary particular jet fuel specification in relative isolation.

Analyses of this kind are typically based on optical measurements and, to simplify the analysis, an approximation of constant pressure is usually achieved by limiting the useable data to the early stages of flame propagation only. The analysis methodology presented in this paper differs inasmuch that calculations were based solely on the recorded pressure data. Moreover, by deducing the response of the flame speed to pressure and temperature, it was possible to utilize the whole combustion pressure record which significantly increased the volume of useful data that could be obtained from each experiment. Other practical difficulties that are often encountered such as flame winkling at large diameters, especially with rich mixtures, were minimized by using a small bomb of only 100mm diameter. The method of analysis via the pressure trace rendered any flame winkling easily discernable wherefrom it could be easily eliminated.

For each fuel, at least six repeat combustion pressure records (about 90 data points each) were obtained for each of six different air-fuel ratios spanning the range from lean to rich and the whole sequence was repeated at a higher initial temperature. This provided a database of over 6000 individual calculations of laminar flame speed from which the relevant parameter coefficients were obtained by means of a regression technique. It was found that the effects of changing the blend composition could be discerned in the various laminar flame speed results and that significant variation in laminar flame speed could possibly be “tailored” into a synthetic jet fuel formulation.
Low Single Digit NOx Emissions Catalytic Combustor for Advanced Hydrogen Turbines for Clean Coal Power Systems
Authors: Alavandi Sandeep K. , Etemad Shahrokh , Baird Benjamin D.
Published: July 2013

Precision Combustion, Inc., (PCI) in close collaboration with Solar Turbines, Incorporated, has developed and demonstrated a catalytic combustion system for hydrogen fueled turbines that can reduce oxides of nitrogen (NOx) emissions to low single digit levels while maintaining or improving current levels of efficiency and eliminating emissions of carbon dioxide.

A full scale Rich Catalytic Hydrogen (RCH) injector was developed and successfully tested at Solar Turbines, Incorporated high pressure test facility, demonstrating low single digit NOx emissions for hydrogen fuel in the primary zone temperature range of 1200°C–1500°C (2200°F–2750°F). The testing also demonstrated low combustion noise with stable and robust operation.

A primary benefit of the catalytic hydrogen combustor technology is the capability for significantly-reduced NOx without costly post-combustion controls. This translates into reduced dilution requirements for a target NOx level, substantially improving efficiency and reducing operating costs. In addition, quiet combustor operation increases gas turbine component life. These advantages advance Department of Energy (DOE’s) objectives for achievement of low NOx emissions, improvement in efficiency vs. post-combustion controls, fuel flexibility, a significant net reduction in Integrated Gasification Combined Cycle (IGCC) system net capital and operating costs, and a route to commercialization across the power generation field from micro turbines to industrial and utility turbines.
Influence of Fuel Physical Properties and Reaction Rate on Threshold Heterogeneous Gas Turbine Combustion
Authors: Burger Victor , Yates Andy , Viljoen Carl
Published: July 2013

The paper presents the findings from a study of the lean blowout (LBO) behaviour of sixteen fuel blends in a heterogeneous laboratory combustor. The LBO results were correlated with fuel blend properties that included the D86 distillation profile, density, viscosity, flash point and ignition delay as represented by derived cetane number (DCN). A spherical bomb was employed to measure laminar flame speed and Markstein length based on pressure measurements. The experiments were conducted with two different starting temperatures and over a range of air fuel ratios from rich to lean. The atomisation behaviour of the fuels was evaluated using a pressure atomised nozzle and a laser diffraction particle sizer. The data allowed the Sauter mean diameter (SMD) values at extinction to be estimated based on the fuel pressure.

Each individual LBO test was conducted at constant air flow rate with the extinction point being attained by reducing the fuel flow rate. The test series for each fuel spanned a range of air flow rates based on combustor liner relative pressure drops from 1% to 6%. These results exhibited three distinct regions (A1, A2 and B) that were evident to varying degrees in the results obtained with all sixteen test fuels. The transition between A1 and A2 was ascribed to combustor flow and was shown to be independent of the fuel being tested. The transition between B and A2 was ascribed to the change from the LBO behaviour being dominated by atomization to it being a mixing / turbulence dominated regime. The individual transitions were found to be dependent on the test fuel blend. In order to accommodate the LBO results in a multivariate analysis the observed trends were represented by three parameters that were determined through curve fitting to the different regions. The three parameters were the SMD and air mass flow rate at the transition between region B and A2 and a projected LBO equivalence ratio at zero air mass flow.

The data was cross correlated between all determined properties and it was shown that the extinction behaviour correlated with chemical reactivity, flame stretch, density and volatility to different degrees in the two regions of operation. It was concluded that there is potential for influencing threshold extinction limits through both chemical and physical jet fuel properties, and the need to take cognisance thereof in fuel formulation, was highlighted.
Experimental Study on the Influence of Pressure on the Flame Stabilization in Porous Inert Media (PIM)
Authors: Bedoya Cesar , Habisreuther Peter , Zarzalis Nikolaos , Prathap Chockalingam , Ebrahimi Hadi
Published: July 2013

Porous burners offer a possible solution to attain higher combustion stability under premixed conditions with ultra low pollutant emissions. To analyze the feasibility of PIM (porous inert media) in energy conversion processes, studies at elevated pressure have been carried out. In the present work, burning velocity of natural gas-air mixtures for lean mixture conditions at elevated pressure is obtained in a conical PIM by determining the flame location using thermocouples. Pressure, thermal power, equivalence ratio and initial temperature were varied in order to study their effect on the flame stability. The pressure was varied from 1.1 to 14.0 bar, and initial temperatures from 300 to 400K. The burning velocity data obtained from present measurements show good agreement with literature data at atmospheric pressure. The results show that the burning velocities measured in PIM decreased non-linearly with increase in pressure. Also, the decrease in the burning velocity in the PIM with pressure is more pronounced for lean mixture conditions. Present results indicate that the PIM produces stable flames for a wide range of operating conditions and generate low pollutant emissions, which show that it is a potential alternative for conventional burners.
Design and Validation of a Burner With Variable Geometry for Extended Combustion Range
Authors: Giuliani Fabrice , Woisetschläger Jakob , Leitgeb Thomas
Published: July 2013

A study on innovative gas turbine core concepts supported by the NEWAC project (NEW Aero-engine Core concepts, Integrated Project co-funded by the European Commission within the Sixth Framework Programme under contract No. AIP5-CT-2006-030876) focused on the ability of the combustor to maintain combustion during a drastic reduction of the main air, e.g. due to an active control on the core flow to improve the off-design efficiency. A feasibility study was performed at Graz University of Technology including dimensioning, design and validation of a test burner with variable geometry. A low power premixed methane / air burner with swirl-stabilised flame was chosen, on which the outlet surface and the ratio axial to tangential momentum on the mass flow rate could be controlled. During testing at atmospheric conditions, special attention was paid to the extension of the flammability domain and to the flame dynamics (transition attached-detached, flame stability, blowout limits). It was established for instance that based on this technology, a detached flame can be maintained when reducing the design mass flow rate by 40 per cent within a safe stability range. The paper discusses the background of the study, the burner’s design and technology, the measurement techniques and the results of the validation campaign. A discussion on possible advantages of using variable geometry in a combustion chamber versus conventional technologies closes the paper, taking into account the technical challenges to be met.
Thermoacoustic Analysis of Combustion Instability Through a Distributed Flame Response Function
Authors: Campa Giovanni , Camporeale Sergio Mario , Cosatto Ezio , Mori Giulio
Published: July 2013

Modern gas turbines equipped with lean premixed dry low emission combustion systems suffer the problem of thermoacoustic combustion instability. The acoustic characteristics of the combustion chamber and of the burners, as well as the response of the flame to the fluctuations of pressure and equivalence ratio, exert a fundamental influence on the conditions in which the instability may occur. A three dimensional finite element code has been developed in order to solve the Helmholtz equation with a source term that models the heat release fluctuations. The code is able to identify the frequencies at which thermoacoustic instabilities are expected and the growth rate of the pressure oscillations at the onset of instability. The code is able to treat complex geometries such as annular combustion chambers equipped with several burners. The adopted acoustic model is based upon the definition of the Flame Response Function (FRF) to acoustic pressure and velocity fluctuations in the burners.

In this paper, data from CFD simulations are used to obtain a distribution of FRF of the κ-τ type as a function of the position within the chamber. The intensity coefficient, κ, is assumed to be proportional to the reaction rate of methane in a two-step mechanism. The time delay τ is estimated on the basis of the trajectories of the fuel particles from the injection point in the burner to the flame front.

The paper shows the results obtained from the application of FRF with spatial distributions of both κ and τ. The present paper also shows the comparison between the application of the proposed model for the FRF and the traditional application of the FRF over a concentrated flame in a narrow area at the entrance to the combustion chamber. The distribution of the intensity coefficient and the time delay proves to have an influence, both on the eigenfrequency values and on the growth rates, in several of the examined modes.

The proposed method is therefore able to establish a theoretical relation of the characteristics of the flame (depending on the burner geometry and operating conditions) to the onset of the thermoacoustic instability.
Pressure Effects on the Turbulent Consumption Speeds of High H2 Mixtures
Authors: Marshall Andrew D. , Venkateswaran Prabhakar , Seitzman Jerry M. , Lieuwen Tim C.
Published: July 2013

This paper describes measurements and correlations of turbulent consumption speeds, ST,GC, of hydrogen/carbon monoxide (H2/CO) fuel mixtures, with a focus on recently acquired elevated pressure data. Turbulent consumption speed data were obtained at mean flow velocities and turbulence intensities of 30 < U0 < 50 m/s and 5 < u′rms/SL,0 < 30, respectively, for H2/CO mixtures ranging from 30–90% H2 by volume at 5 and 10 atm. Experiments were conducted where the mixture equivalence ratio, ϕ was adjusted at each fuel composition to have nominally the same un-stretched laminar flame speed, SL,0. In comparing two blends with the same composition, SL,0 value, and flow conditions, the 5 and 10 atm data have ST,GC values that are consistently about 1.8 and 2.2 times larger than the 1 atm data, respectively. These data are also correlated with a scaling law derived from quasi-steady leading points concepts using detailed kinetics calculations of highly stretched flames. For a given pressure, these scalings do an excellent job in scaling data obtained across the H2/CO fuel composition and fuel/air range. However, the pressure sensitivities are not captured by this scaling. This pressure sensitivity may be more fundamentally a reflection of the non-quasi-steady nature of the flame leading points. In support of this argument, we show that the spread in the data can largely be correlated with the ratio of a chemical time scale to a flow time scale.
Autoignition of Hydrogen / Natural Gas / Nitrogen Fuel Mixtures at Reheat Combustor Operating Conditions
Authors: Fleck Julia , Griebel Peter , Aigner Manfred , Steinberg Adam M.
Published: July 2013

Previous autoignition studies at conditions relevant to reheat combustor operation have indicated that the presence of relatively small amounts of natural gas (NG) in H2/N2 fuel significantly changes the autoignition behavior. The present study further elucidates the influence of NG on autoignition, kernel propagation, and subsequent flame stabilization at conditions that are relevant for the practical operation of gas turbine reheat combustors (p = 15 bar, Tinlet > 1000 K, hot flue gas, appropriate residence times). The experimental investigation was carried out in a generic, optically accessible reheat combustor. Autoignition events in the mixing zone were recorded by a high-speed camera at frame rates of up to 30,000 fps. This paper describes the autoignition behavior as the H2 volume fraction is increased (decreasing NG) in a H2/NG/N2 fuel mixture for two different jet penetration depths. Additionally, the subsequent flame stabilization phenomena and the structure of the stabilized flame are discussed. The results reveal that autoignition kernels occurred even for the lowest H2 fuel fraction, but they did not initiate a stable flame in the mixing zone. Increasing the H2 volume fraction decreased the distance between the initial position of the autoignition kernels and the fuel injector, finally leading to flame stabilization. The occurrence of autoignition kernels at lower H2 volume fractions (H2/(H2+NG) < 85%) was not found to be significantly influenced by the fluid dynamic and mixing field differences related to the different jet penetration depths. In contrast, autoignition leading to flame stabilization was found to depend on jet penetration; flame stabilization occurred at lower H2 fractions for the higher jet penetration depth (H2/(H2+NG) ≈ 89 compared to H2/(H2+NG) ≈ 95 vol. %).