146 research outputs found

    Impact of a cooled cooling air system on the external aerodynamics of a gas turbine combustion system

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    To manage the increasing turbine temperatures of future gas turbines a cooled-cooling air system has been proposed. In such a system some of the compressor efflux is diverted for additional cooling in a heat exchanger located in the by-pass duct. The cooled air must then be returned, across the main gas path, to the engine core for use in component cooling. One option is do this within the combustor module and two methods are examined in the current paper; via simple transfer pipes within the dump region or via radial struts in the pre-diffuser. This paper presents an experimental investigation to examine the aerodynamic impact these have on the combustion system external aerodynamics. This included the use of a fully annular, isothermal test facility incorporating a bespoke 1.5 stage axial compressor, engine representative outlet guide vanes, pre-diffuser and combustor geometry. Area traverses of a miniature five-hole probe were conducted at various locations within the combustion system providing information on both flow uniformity and total pressure loss. The results show that, compared to a datum configuration, the addition of transfer pipes had minimal aerodynamic impact in terms of flow structure, distribution and total pressure loss. However, the inclusion of pre-diffuser struts had a notable impact increasing the pre-diffuser loss by a third and consequently the overall system loss by an unacceptable 40

    Impact of a cooled cooling air installation on the external aerodynamics of a gas turbine combustion system

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    The trend for higher overall pressure ratios means that turbine entry temperatures are continually increasing. Furthermore, the development of lean, low-emission combustion systems reduces the availability of cooling air and is accompanied by new problems at the combustor/turbine interface. For example, the exit temperature traverse differs from that found in traditional rich-burn combustors with increased swirl and a much flatter profile. Effectively cooling the turbine components is becoming increasingly difficult. One solution is to employ cooled cooling air (CCA) where some of the compressor efflux is diverted for additional cooling in a heat exchanger located in the by-pass duct. An example CCA system is presented which includes an off-take within the dump cavity and the addition of radial struts within the pre-diffuser through which the cooled air is returned to the engine core. This paper addresses the impact this CCA system has on the combustion system external aerodynamics. This included the development of a fully annular, isothermal test facility which incorporated a bespoke 1.5 stage axial compressor, engine relevant outlet guide vanes, pre-diffuser and combustor geometry. A datum aerodynamic performance was established for a non-CCA configuration with a clean, un-strutted prediffuser. Results for this baseline CCA system demonstrated that inclusion of a bleed in the dump cavity had limited effect on the overall flow field. However, the inclusion of struts within the pre-diffuser caused a reduction in area ratio and a notable increase in system loss. Consequently an alternative pre-diffuser was designed (using CFD) with the aim of increasing the area ratio back to that of the un-strutted datum. A so-called hybrid diffuser was designed in which the CCA bleed was moved to the pre-diffuser outer wall. The bleed was then used to re-energize the boundary layer, preventing flow separation, enabling the area ratio to be increased close to the datum value. The mechanisms of the hybrid diffuser are complex; the geometry of the off-take and its location with respect to the OGV and strut leading edge were seen to be critical. Experimental evaluation of the final design demonstrated the effective operation the hybrid diffuser with the result that the system loss returned to a level close to that of the datum. Only small differences were seen in the overall flow field

    Automated Dispersive Liquid–Liquid Microextraction–Gas Chromatography–Mass Spectrometry

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    An innovative automated procedure, low-density solvent based/solvent demulsification dispersive liquid–liquid microextraction (automated DLLME) coupled to gas chromatography–mass spectrometry (GC/MS) analysis, has been developed. The most significant innovation of the method is the automation. The entire procedure, including the extraction of the model analytes (phthalate esters) by DLLME from the aqueous sample solution, breaking up of the emulsion after extraction, collection of the extract, and analysis of the extract by GC/MS, was completely automated. The applications of low-density solvent as extraction solvent and the solvent demulsification technique to break up the emulsion simplified the procedure and facilitated its automation. Orthogonal array design (OAD) as an efficient optimization strategy was employed to optimize the extraction parameters, with all the experiments conducted auotmatically. An OA<sub>16</sub> (4<sup>1</sup> × 2<sup>12</sup>) matrix was initially employed for the identification of optimized extraction parameters (type and volume of extraction solvent, type and volume of dispersive solvent and demulsification solvent, demulsification time, and injection speed). Then, on the basis of the results, more levels (values) of five extraction parameters were investigated by an OA<sub>16</sub> (4<sup>5</sup>) matrix and quantitatively assessed by the analysis of variance (ANOVA). Enrichment factors of between 178- and 272-fold were obtained for the phthalate esters. The linearities were in the range of 0.1 and 50 μg/L and 0.2 and 50 μg/L, depending on the analytes. Good limits of detection (in the range of 0.01 to 0.02 μg/L) and satisfactory repeatability (relative standard deviations of below 5.9%) were obtained. The proposed method demonstrates for the first time integrated sample preparation by DLLME and analysis by GC/MS that can be operated automatically across multiple experiments

    Subsampling bias and the best-discrepancy systematic cross validation

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    Statistical machine learning models should be evaluated and validated before putting to work. Conventional k-fold Monte Carlo Cross-Validation (MCCV) procedure uses a pseudo-random sequence to partition instances into k subsets, which usually causes subsampling bias, inflates generalization errors and jeopardizes the reliability and effectiveness of cross-validation. Based on ordered systematic sampling theory in statistics and low-discrepancy sequence theory in number theory, we propose a new k-fold cross-validation procedure by replacing a pseudo-random sequence with a best-discrepancy sequence, which ensures low subsampling bias and leads to more precise Expected-Prediction-Error (EPE) estimates. Experiments with 156 benchmark datasets and three classifiers (logistic regression, decision tree and na¨ıve bayes) show that in general, our cross-validation procedure can extrude subsampling bias in the MCCV by lowering the EPE around 7.18% and the variances around 26.73%. In comparison, the stratified MCCV can reduce the EPE and variances of the MCCV around 1.58% and 11.85% respectively. The Leave-One-Out (LOO) can lower the EPE around 2.50% but its variances are much higher than the any other CV procedure. The computational time of our cross-validation procedure is just 8.64% of the MCCV, 8.67% of the stratified MCCV and 16.72% of the LOO. Experiments also show that our approach is more beneficial for datasets characterized by relatively small size and large aspect ratio. This makes our approach particularly pertinent when solving bioscience classification problems. Our proposed systematic subsampling technique could be generalized to other machine learning algorithms that involve random subsampling mechanism

    Automated Agitation-Assisted Demulsification Dispersive Liquid–Liquid Microextraction

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    Dispersive liquid–liquid microextraction (DLLME) is an extremely fast and efficient sample preparation procedure. For its capability and applicability to be fully exploited, full automation of its operations seamlessly integrated with analysis is necessary. In this work, for the first time, fully automated agitation-assisted demulsification (AAD)-DLLME integrated with gas chromatography/mass spectrometry was developed for the convenient and efficient determination of polycyclic aromatic hydrocarbons in environmental water samples. The use of a commercially available multipurpose autosampler equipped with two microsyringes of different capacities allowed elimination or significant reduction of manpower, labor, and time with the large-volume microsyringe used for liquid transfers and the small-volume microsyringe for extract collection and injection for analysis. Apart from enhancing accessibility of DLLME, the procedure was characterized by the application of agitation after extraction to break up the emulsion (that otherwise would need centrifugation or a demulsification solvent), further improving overall operational efficiency and flexibility. Additionally, the application of low-density solvent as extractant facilitated the easy collection of extract as the upper layer over water. Some parameters affecting the automated AAD-DDLME procedure were investigated. Under the optimized conditions, the procedure provided good linearity (ranging from a minimum of 0.1–0.5 μg/L to a maximum of 50 μg/L), low limits of detection (0.010–0.058 μg/L), and good repeatability of the extractions (relative standard deviations, below 5.3%, <i>n</i> = 6). The proposed method was applied to analyze PAHs in real river water samples

    Low-Dose Strontium-90 Irradiation Is Effective in Preventing the Recurrence of Pterygia: A Ten-Year Study

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    <div><h3>Background</h3><p>To study the long-term effects of low-dosage strontium-90 (Sr90) irradiation on the recurrence of pterygium.</p> <h3>Methodology/Principal Findings</h3><p>One hundred twenty eyes from 104 patients with primary or recurrent pterygia were treated with surgery followed by Sr90 irradiation. In brief, starting on the sixth day after surgery, patients were treated with irradiation three times every other day at a total combined dosage of 2000 cGy to 3000 cGy. Corneal topography was used to evaluate ocular surface regularity before and after treatment. Patient follow-up was performed 2 days, 5 days, 2 weeks, 1 month, 3 months, 1 year, 5 years, and 10 years after surgery. Recurrence of pterygium was not observed in any of the patients in this study. Obvious cataract progression was observed in 6 eyes, which may be due to aging. During follow-up studies, only one eye was reported with dryness and foreign-body sensation. Significant pterygium-induced astigmatism was observed in corneal topography, which decreased after surgery.</p> <h3>Conclusions/Significance</h3><p>Sr90 irradiation is effective in preventing the recurrence of primary and recurrent pterygia. We recommend delivering a total combined dosage of 2000 cGy to 3000 cGy of Sr90 irradiation administered in three batches every other day starting from the sixth day after surgery. Surgery is important in the rapid recovery of the cornea from pterygium-induced astigmatism.</p> </div

    Number of eyes (%) with different ocular manifestations in the follow-ups.

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    <p>Number of eyes (%) with different ocular manifestations in the follow-ups.</p

    Characteristics of the included studies.

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    BackgroundRopivacaine is a long-acting local anesthetic that is used to treat postoperative pain. Adjuvant use of dexmedetomidine in regional anesthesia may prolong the duration of analgesia. The objective of this systematic review and meta-analysis was to investigate the duration and effect of ropivacaine alone vs. ropivacaine in combination with dexmedetomidine for postoperative analgesia.MethodsThe PubMed, EMBASE, Web of Science, and Google Scholar databases were searched for randomized controlled trials (RCTs) of ropivacaine alone or ropivacaine in combination with dexmedetomidine for regional anesthesia. The primary outcome was duration of analgesia, defined as the time from onset of the block to the time of the first analgesic request or initial pain report. Secondary outcomes were duration of sensory block, duration of motor block, consumption of sufentanil for analgesia, length of hospital stay, and incidence of postoperative nausea and vomiting.ResultsEighteen studies with 1148 patients were included. Overall quality of the RCTs, as assessed by the Jadad scale, was high. The meta-analysis demonstrated that ropivacaine combined with dexmedetomidine significantly prolonged the duration of postoperative analgesia from local anesthetics compared to ropivacaine alone (WMD: 4.14h; 95%CI: 3.29~5.0h; P2 = 99%). There was evidence of high heterogeneity between studies. The duration of sensory and motor block was significantly increased, and consumption of sufentanil for analgesia and the incidence of postoperative nausea and vomiting were significantly reduced in patients who received ropivacaine combined with dexmedetomidine compared to ropivacaine alone. There was no significant difference in length of hospital stay.ConclusionsCompared to ropivacaine alone, ropivacaine combined with dexmedetomidine significantly prolonged the duration of postoperative analgesia and sensory and motor block, and reduced consumption of sufentanil for analgesia and the incidence of postoperative nausea and vomiting, across an array of surgeries.</div

    Improved Fitting of Solution X-ray Scattering Data to Macromolecular Structures and Structural Ensembles by Explicit Water Modeling

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    A new procedure, AXES, is introduced for fitting small-angle X-ray scattering (SAXS) data to macromolecular structures and ensembles of structures. By using explicit water models to account for the effect of solvent, and by restricting the adjustable fitting parameters to those that dominate experimental uncertainties, including sample/buffer rescaling, detector dark current, and, within a narrow range, hydration layer density, superior fits between experimental high resolution structures and SAXS data are obtained. AXES results are found to be more discriminating than standard Crysol fitting of SAXS data when evaluating poorly or incorrectly modeled protein structures. AXES results for ensembles of structures previously generated for ubiquitin show improved fits over fitting of the individual members of these ensembles, indicating these ensembles capture the dynamic behavior of proteins in solution
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