bluuebunny/crossref_metadata_2025_split huggingface dataset:
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

AbstractBackgroundCurrent 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.MethodsIncluded 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.ResultsThree 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.ConclusionsMost 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

AbstractThis 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

AbstractKnowledge 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.
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?
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.
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.
Low NOx Combustion Concepts in Support of the NASA Environmentally Responsible Aircraft Program
Authors: Prociw Alex , Ryon Jason , Goeke Jerry 
Published: July 2013

NASA’s “Environmentally Responsible Aircraft” (ERA) N+2 advanced, low NOx combustor technologies program is looking at combustion technologies suitable for the 2020 time frame. The objective of this program is to develop fuel-air mixing concepts and associated fuel control valves. The low emissions combustor concept must be capable of meeting or exceeding the N+2 LTO NOx goal of 75% reduction from the ICAO standard adopted by CAEP 6 at engine pressure ratios of at least 55. Goodrich Engine Components is working with NASA to demonstrate concepts with these capabilities.
In the early 2000’s, Goodrich partnered with NASA in demonstrating the ability of a multipoint lean direct injection (LDI) concept to achieve very low NOx emissions index (EI) levels as tested at NASA test facilities. The program was successful in demonstrating the ability of the multipoint concept to deal with NOx at high power conditions but was not optimized to perform equally as well at low power conditions such as start, ground idle, and flight idle conditions.
After review of previous work, Goodrich is investigating a new multipoint combustor design for the N+2 program. The basic multipoint premise of injecting fuel through a large number of injection sites to promote rapid mixing has been retained, but at a much reduced number of nozzles compared to the original work. In the new version, nozzles are arranged in a staggered array pattern and are manifolded in radial stages. The radial stages can be utilized to control radial temperature distribution to the turbine. Radial staging is also being used to maintain sufficient temperature levels around specific nozzles at low power conditions to provide adequate emissions and stability at these conditions.
In addition to the modifications of the general arrangement, injector design features are optimized by stage such that much higher air/fuel mixing rates with lower central recirculation zones dominate high power conditions while more conventional swirl stabilization dominates at low power conditions when inlet temperatures are low. The design work is being guided by CFD analysis as well as qualitative and quantitative rig testing before the final configurations are fabricated and tested at the NASA flame tube rigs.
This paper will discuss elements of prior designs compared to current designs and discuss the status of Computational Fluid Dynamic (CFD) simulations completed in the first phase of this program.
Low-Order Modelling of the Response of Ducted Flames in Annular Geometries
Authors: Graham Owen S. , Dowling Ann P. 
Published: July 2013

The adoption of lean premixed prevaporised combustion systems can reduce NOx emissions from gas turbines, but unfortunately also increases their susceptibility to thermoacoustic instabilities. Initially, acoustic waves can produce heat release fluctuations by a variety of mechanisms, often by perturbing the equivalence ratio. If correctly phased, heat release fluctuations can subsequently generate more acoustic waves, which at high amplitude can result in significant structural damage to the combustor. The prediction of this phenomenon is of great industrial interest.
In previous work, we have coupled a physics based, kinematic model of the flame with a network model to provide the planar acoustic response necessary to close the feedback loop and predict the onset and amplitude of thermoacoustic instabilities in a lab-scale, axisymmetric single burner combustor. The advantage of a time domain approach is that the modal interaction, the influence of harmonics, and flame saturation can be investigated. This paper extends this approach to more realistic, annular geometries, where both planar and circumferential modes must be considered.
In lean premixed prevaporised combustors, fluctuations in equivalence ratio have been shown to be a dominant cause of unsteady combustion. These can occur, for example, due to velocity perturbations in the premix ducts, which can lead to equivalence ratio fluctuations at the fuel injectors, which are subsequently convected downstream to the flame surfaces. Here, they can perturb the heat release by locally altering the flame speed, enthalpy of combustion, and, indirectly, the flame surface area.
In many gas turbine designs, particularly aeroengines, the geometries are composed of a ring of premix ducts linking a plenum and an annular combustor. The most unstable modes are often circumferential modes. The network model is used to characterise the flow response of the geometry to heat fluctuations at an appropriate location, such as the fuel injectors. The heat release at each flame holder is determined in the time domain using the kinematic flame model derived, as a function of the flow perturbations in the premix duct. This approach is demonstrated for an annular ring of burners on a in a simple geometry. The approach is then extended to an industrial type gas turbine combustor, and used to predict the limit cycle amplitudes.
Nonlinear Phenomena in Thermoacoustic Systems With Premixed Flames
Authors: Kashinath Karthik , Hemchandra Santosh , Juniper Matthew P. 
Published: July 2013

Nonlinear analysis of thermoacoustic instability is essential for prediction of frequencies, amplitudes and stability of limit cycles. Limit cycles in thermoacoustic systems are reached when the energy input from driving processes and energy losses from damping processes balance each other over a cycle of the oscillation.
In this paper an integral relation for the rate of change of energy of a thermoacoustic system is derived. This relation is analogous to the well-known Rayleigh criterion in thermoacoustics, but can be used to calculate the amplitudes of limit cycles, as well as their stability. The relation is applied to a thermoacoustic system of a ducted slot-stabilized 2-D premixed flame. The flame is modelled using a nonlinear kinematic model based on the G-equation, while the acoustics of planar waves in the tube are governed by linearised momentum and energy equations. Using open-loop forced simulations, the flame describing function (FDF) is calculated. The gain and phase information from the FDF is used with the integral relation to construct a cyclic integral rate of change of energy (CIRCE) diagram that indicates the amplitude and stability of limit cycles. This diagram is also used to identify the types of bifurcation the system exhibits and to find the minimum amplitude of excitation needed to reach a stable limit cycle from another linearly stable state, for single-mode thermoacoustic systems. Furthermore, this diagram shows precisely how the choice of velocity model and the amplitude-dependence of the gain and the phase of the FDF influence the nonlinear dynamics of the system.
Time domain simulations of the coupled thermoacoustic system are performed with a Galerkin discretization for acoustic pressure and velocity. Limit cycle calculations using a single mode, as well as twenty modes, are compared against predictions from the CIRCE diagram. For the single mode system, the time domain calculations agree well with the frequency domain predictions. The heat release rate is highly nonlinear but, because there is only a single acoustic mode, this does not affect the limit cycle amplitude. For the twenty-mode system, however, the higher harmonics of the heat release rate and acoustic velocity interact resulting in a larger limit cycle amplitude. Multi-mode simulations show that in some situations the contribution from higher harmonics to the nonlinear dynamics can be significant and must be considered for an accurate and comprehensive analysis of thermoacoustic systems.