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Now showing items 1 - 16 of 17

  • New iron-based SiC spherical composite magnetic abrasive for magnetic abrasive finishing

    Guixiang Zhang   Yugang Zhao   Dongbiao Zhao…  

    SiC magnetic abrasive is used to polish surfaces of precise, complex parts which are hard, brittle and highly corrosion-resistant in magnetic abrasive finishing(MAF). Various techniques are employed to produce this magnetic abrasive, but few can meet production demands because they are usually time-consuming, complex with high cost, and the magnetic abrasives made by these techniques have irregular shape and low bonding strength that result in low processing efficiency and shorter service life. Therefore, an attempt is made by combining gas atomization and rapid solidification to fabricate a new iron-based SiC spherical composite magnetic abrasive. The experimental system to prepare this new magnetic abrasive is constructed according to the characteristics of gas atomization and rapid solidification process and the performance requirements of magnetic abrasive. The new iron-based SiC spherical composite magnetic abrasive is prepared successfully when the machining parameters and the composition proportion of the raw materials are controlled properly. Its morphology, microstructure, phase composition are characterized by scanning electron microscope(SEM) and X-ray diffraction(XRD) analysis. The MAF tests on plate of mold steel S136 are carried out without grinding lubricant to assess the finishing performance and service life of this new SiC magnetic abrasive. The surface roughness( Ra) of the plate worked is rapidly reduced to 0.051 mum from an initial value of 0.372 mum within 5 min. The MAF test is carried on to find that the service life of this new SiC magnetic abrasive reaches to 155 min. The results indicate that this process presented is feasible to prepare the new SiC magnetic abrasive; and compared with previous magnetic abrasives, the new SiC spherical composite magnetic abrasive has excellent finishing performance, high processing efficiency and longer service life. The presented method to fabricate magnetic abrasive through gas atomization and rapid solidification presented can significantly improve the finishing performance and service life of magnetic abrasive, and provide a more practical approach for large-scale industrial production of magnetic abrasive.
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  • Indicator-based evaluation of spatiotemporal characteristics of rice flood in Southwest China

    Jianying Yang   Zhiguo Huo   Li Wu   Tianying Wang   Guixiang Zhang  

    Highlights • Novel attempt to represent historical rice flood disasters. • Effect of extreme precipitation on rice flood hazard was investigated. • We established precipitation-based evaluation indicators of single-cropping rice flood. • Areas with high rice flood risk was highlighted. • Regional flood risk in the whole stage of rice showed a negative trend. Abstract Frequent occurrences of extreme rainfall events create severe rice floods. To prevent rainfall-induced rice floods and reduce potential losses, it is important to establish meteorological evaluation indicators and precisely understand the spatiotemporal characteristics of rice floods, to provide support for rice flood monitoring, prevention, and mitigation. In this study, precipitation, disaster and phenophase data of rice in Southwest China (Sichuan, Chongqing, Guizhou, and Yunnan provinces) were integrated to establish meteorological evaluation indicators of single-cropping rice floods, and the rice flood index (RFI) from 1961 to 2012 was thereby estimated to gain detailed information on rice flood disaster characteristics in that region. The threshold of rice flood in the transplanting-tillering stage was 120, 130, and 150 mm for 1, 2, and ≥3 d, respectively. This was 150, 160, and 180 mm for the jointing-booting stage, and 170, 200, and 230 mm for the tasselling-maturity stage, respectively. Identification results by rice flood level were found basically consistent with the historical occurrence of rice flood disasters, with 66.7% of historical records strongly consistent with the flood level assessment, and calculated errors of all validation data were within one level. High RFI was faced by the transplanting-tillering stage, followed by the jointing-booting and transplanting-tillering stages. High-RFI (>1) areas in the whole rice stage were southern and northeastern Yunnan, southern Guizhou, plus Chengdu, Meishan, and Deyang in Sichuan Province. Regional RFI in the whole stage showed a negative trend, with slope 0.0246 (R 2 = 0.1523). RFI at 120 stations, or 62.83% of all stations, decreased over the whole rice stage, while RFI increased at 70 stations, mainly in Guizhou, northeast of Sichuan.
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  • Sorption of simazine to corn straw biochars prepared at different pyrolytic temperatures

    Guixiang Zhang   Qing Zhang   Ke Sun   Xitao Liu   Wenjuan Zheng   Ye Zhao  

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  • Oleoylethanolamide alleviates macrophage formation <em>via</em> AMPK/PPARα/STAT3 pathway

    Yun Zhao   Lu Yan   Lu Peng   XueFeng Huang   GuiXiang Zhang   BingQian Chen   Jie Ren   Yu Zhou   LiChao Yang   Li Peng   Xin Jin   YiQing Wang  

    Highlights • OEA possessed dual-directional regulative capacity in respect of monocyte chemotaxis modulation. • OEA modulated MCP-1 production in macrophages through AMPK/PPARα/STAT3 pathway. • The suppressive effect of OEA on macrophage formation was verified in vivo . Abstract Background Atherosclerosis is the main underlying cause of most cardiovascular diseases, and monocyte migrating to the vascular wall and subsequently differentiating into macrophage are critical steps in the process of atherosclerosis. The goal of this study was to clarify the effect of oleoylethanolamide (OEA) on monocyte migration and subsequent macrophage formation in the vascular wall. Methods We studied OEA in two monocyte-migrating systems in vitro : one was a single cell system whereby monocytes were exposed to OEA directly; the other was a co-culture system whereby monocytes were exposed to OEA-treated macrophages. The effect of OEA on macrophage content in the vascular wall in vivo was measured in apolipoprotein E (apoE)−/− mice by CD68 immunohistochemistry. The protein and mRNA expressions with OEA treatment were examined using western blot and real-time PCR. Results Interestingly, OEA possessed dual-directional regulation of monocyte chemotaxis in vitro , with a stimulatory effect in the single cell system and a suppressive effect in the co-culture system. And OEA restrained macrophage deposition in the vascular wall of apoE−/− mice. The underlying mechanism of OEA suppressing monocyte migration in the co-culture system was that OEA increased phosphorylation of AMP-activated protein kinase (AMPK) and peroxisome proliferator-activated receptor α (PPARα) level, and decreased phosphorylation of signal transducer and activator of transcription 3 (STAT3) and monocyte chemoattractant protein-1 (MCP-1) level in macrophages, which was reinforced by the in vivo experiment. Conclusions OEA restrains excessive macrophage formation in the progressive lesion by inhibiting MCP-1 production of the existent macrophages through the AMPK/PPARα/STAT3 pathway.
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  • Differentiation between adrenal adenomas and nonadenomas using dynamic contrast-enhanced computed tomography

    Xifu Wang   Kangan Li   Haoran Sun   Jinglong Zhao   Linfeng Zheng   Zhuoli Zhang   Renju Bai   Guixiang Zhang  

    This study was performed to evaluate the findings including the time density curve (TD curve), the relative percentage of enhancement washout (Washr) and the absolute percentage of enhancement washout (Washa) at dynamic contrast-enhanced computed tomography (DCE-CT) in 70 patients with 79 adrenal masses (including 44 adenomas and 35 nonadenomas) confirmed histopathologically and/or clinically. The results demonstrated that the TD curves of adrenal masses were classified into 5 types, and the type distribution of the TD curves was significantly different between adenomas and nonadenomas. Types A and C were characteristic of adenomas, whereas types B, D and E were features of nonadenomas. The sensitivity, specificity and accuracy for the diagnosis of adenoma based on the TD curves were 93%, 80% and 87%, respectively. Furthermore, when myelolipomas were excluded, the specificity and accuracy for adenoma were 90% and 92%, respectively. The Washr and the Washa values for the adenomas were higher than those for the nonadenomas. The diagnostic efficiency for adenoma was highest at 7-min delay time at DCE-CT; Washr was more efficient than Washa. Washr ≥34% and Washa ≥43% were both suggestive of adenomas and, on the contrary, suspicious of nonadenomas. The sensitivity, specificity and accuracy for the diagnosis of adenoma were 84%, 77% and 81%, respectively. When myelolipomas were precluded, the diagnostic specificity and accuracy were 87% and 85%, respectively. Therefore, DCE-CT aids in characterization of adrenal tumors, especially for lipid-poor adenomas which can be correctly categorized on the basis of TD curve combined with the percentage of enhancement washout.
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  • Effect of superfine grinding on the physicochemical properties and antioxidant activity of red grape pomace powders

    Xiaoyan Zhao   Haitao Zhu   Guixiang Zhang   Weidong Tang  

    Abstract The objectives of this study were to determine the physicochemical properties and antioxidant activity of red grape pomace powders (GPPs) from winemaking residue with particle sizes of > 300, 250–125, 125–70, 70–38, and < 18.83 μm. Superfine grinding treatment could decrease bulk density (from 0.40 to 0.21 kg/m 3 ), tapped density (from 0.51 to 0.31 kg/m 3 ), and fluidity (repose angle from 33.87 to 56.34° and slid angle from 36.76 to 71.97°, respectively) of GPPs, but improve the solubility (from 9.38 to 48.86%). The extract of GPP with a particle size of < 18.83 μm showed that highest total polyphenolic content (757.36 mg GAE/100 g) and flavanol content (19.46 mg CE/100 g) accompanied with the best antioxidant activity through all antioxidant assays (p < 0.05). SEM images revealed the shape and surface morphology of GPPs with different sizes. FTIR analysis showed that the superfine grinding did not damage the main structure of phenols as the powder particle size decreased. The results indicated that after superfine grinding treatment, GPPs could serve as a potential resource of natural ingredients for food and nutraceutical application. Graphical abstract Highlights • Different particle size grape pomace powders (GPPs) were prepared by superfine grinding method. • The impact of superfine grinding on physicochemical properties of five GPPs was evaluated. • High total polyphenolic and flavanol content in fine powders was found. • Superfine grinding can improve the antioxidant activity of GPPs.
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  • Targeted cancer theranostics using alpha-tocopheryl succinate-conjugated multifunctional dendrimer-entrapped gold nanoparticles

    Jingyi Zhu   Linfeng Zheng   Shihui Wen   Yueqin Tang   Mingwu Shen   Guixiang Zhang   Xiangyang Shi  

    Abstract Development of multifunctional theranostic nanoplatforms for targeted cancer imaging and therapy still remains a great challenge. Herein, we report the use of multifunctional dendrimer-entrapped gold nanoparticles (Au DENPs) covalently linked with α-tocopheryl succinate (α-TOS) as a platform for targeted cancer computed tomography (CT) imaging and therapy. In this study, amine-terminated poly(amidoamine) dendrimers of generation 5 (G5.NH 2 ) conjugated with fluorescein isothiocyanate (FI), polyethylene glycol (PEG)-modified α-TOS, and PEGylated folic acid (FA) were used as templates to synthesize Au DENPs, followed by acetylation of the remaining dendrimer terminal amines. The formed multifunctional Au DENPs were characterized via different techniques. We show that the Au DENPs conjugated with approximately 9.8 α-TOS molecules per dendrimer and with an Au core size of 3.3 nm are water-dispersible, and stable under different pH and temperature conditions and in different aqueous media. The FA modification onto the Au DENPs enables efficient targeting of the particles to cancer cells overexpressing FA receptors (FAR), and effective targeted CT imaging of the cancer cells in vitro and the xenografted tumor model in vivo . Likewise, the covalent conjugation of α-TOS does not compromise its therapeutic activity, instead significantly improves its water solubility. Importantly, thanks to the role of FA-directed targeting, the formed multifunctional Au DENPs are able to exert the specific therapeutic efficacy of α-TOS to the FAR-overexpressing cancer cells in vitro and the xenografted tumor model in vivo . The developed multifunctional Au DENPs may hold a great promise to be used as a unique theranostic nanoplatform for targeted CT imaging and therapy of different types of cancer.
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  • Analysis of genetic diversity and population structure of Chinese yak breeds (Bos grunniens) using microsatellite markers

    Guixiang Zhang   Weisheng Chen   Ming Xue   Zhigang Wang   Hong Chang   Xu Han   Xinjun Liao   Donglei Wang  

    Nine Chinese yak breeds (Maiwa,Tianzhu White,Qinghai Plateau,Sibu,Zhongdian,Pall,Tibetan High Mountain,Jiulong,and Xin-jiang) and Gayal were analyzed by means of 16 microsatellite markers to determine the level of genetic variation within populations,genetic relationship between populations,and population structure for each breed.A total of 206 microsatellite alleles were observed.Mean F-statistics (0.056) for 9 yak breeds indicated that 94.4% of the genetic variation was observed within yak breeds and 5.6% of the genetic variation existed amongst breeds.The Neighbor-Joining phylogenetic free was constructed based on Nei's standard genetic dis-tances and two clusters were obtained.The Gayal separated from the yaks far away and formed one cluster and 9 yak breeds were grouped together.The analysis of population structure for 9 yak breeds and the Gayal showed that they resulted in four clusters; one clus-ter includes yaks from Tibet Autonomous Region and Qinghai Province,one cluster combines Zhongdian,Maiwa,and Tianzhu White,and Jiulong and Xinjiang come into the third cluster.Pali was mainly in the first cluster (90%),Jiulong was mainly in the second cluster (87.1%),Zhongdian was primarily in the third cluster (83%),and the other yak breeds were distributed in two to three clusters.The Gayal was positively left in the fourth cluster (99.3%).
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  • Interactions of simazine, metsulfuron-methyl, and tetracycline with biochars and soil as a function of molecular structure

    Guixiang Zhang   Xitao Liu   Ke Sun   Qiusheng He   Tianwei Qian   Yulong Yan  

    Biochars are increasingly recognized as effective, inexpensive, and environmentally friendly sorbents for abating organic contaminants. In this study, the sorption and competitive sorption characteristics of simazine (SZ), metsulfuron-methyl (ME), and tetracycline (TC) to corn straw biochars and soil were examined to understand the interactions of herbicides and antibiotics with biochars and the potential role of biochars as engineered sorbents.Biochars were obtained by pyrolyzing corn straw at 400, 500, and 600 A degrees C for 6 h under oxygen-limited conditions and were characterized via elemental analysis, N-2-BET surface area determination, C-13 nuclear magnetic resonance spectroscopy, and Fourier transform infrared spectroscopy. Soil was collected from North Tanggu Farm in Tianjin, and its organic carbon, cation exchange capacity, and particle size distribution were analyzed. The batch sorption experiments were performed to obtain the sorption isotherms of SZ, ME, and TC to biochars and soil.The biochars that were pyrolyzed at higher temperatures had higher sorption affinities for SZ, ME, and TC, which may be due to the enhancement of hydrophobic interactions, charge transfer (pi-pi*) interactions, and pore-filling mechanism. The sorption affinities for these compounds to all biochars decreased in the order SZ > TC > ME, indicating that the neutral molecule with a stronger hydrophobicity is more easily adsorbed by biochars. For soil, the decrease of the sorption affinities followed the order TC > SZ > ME due to the high sorption affinity of TC with clays in the soil. Moreover, the sorption affinities of TC by biochars were lower than by soil, indicating that corn straw biochars may be not an ideal sorbent for the immobilization of TC. Biochars were much more effective in sorbing SZ and ME than soil, indicating that corn straw biochars can potentially prevent transport of the herbicides to surface and ground water. Nevertheless, the presence of TC significantly hinders biochar adsorption of SZ and ME, implying that the coexisting contaminants should be considered when developing biochars as engineered sorbents.The observations in this study demonstrated that the sorption of organic contaminants by biochars is dependent on the properties of the biochars and the molecular structures of the contaminants. Corn straw biochars effectively retain SZ and ME and hinder their transportation to surface and ground water; however, the coexisting contaminants should be considered. Our results will be helpful for designing biochars as engineered sorbents for environmental applications.
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  • Comparison of dynamic contrast-enhanced magnetic resonance imaging with T2-weighted imaging for preoperative staging of early endometrial carcinoma

    Linfeng Zheng   Sujuan Zheng   Xiaochun Yuan   Xifu Wang   Zhuoli Zhang   Guixiang Zhang  

    PurposeThis study aimed to compare dynamic contrast-enhanced magnetic resonance imaging (DCE-MRI) with T2-weighted imaging (T2WI) for the preoperative staging of early endometrial carcinoma.MethodsThis retrospective study included 22 subjects with early endometrial carcinoma who underwent 3.0 T MRI examination prior to hysterectomy. DCE-MRI and T2WI were evaluated for the preoperative staging of endometrial carcinoma. The sensitivity, specificity, positive predictive value (PPV), negative predictive value (NPV), and accuracy of DCE-MRI and T2WI were assessed and compared using the revised International Federation of Gynecology and Obstetrics surgical staging guidelines (2009) as the reference standard.ResultsOut of the 22 cases of endometrial carcinoma, the use of the reference standard method led to the staging of 14 as IA and eight as IB. The sensitivity, specificity, PPV, NPV, and accuracy of DCE-MRI for preoperative staging were 100% (95% confidence interval: 0.73–1.0), 62.5% (95% CI: 0.26–0.90), 82.4% (95% CI: 0.56–0.95), 100% (95% CI: 0.46–1.0), and 86.4%, respectively, and these values were 85.7% (95% CI: 0.56–0.97), 75% (95% CI: 0.36–0.96), 85.7% (95% CI: 0.56–0.97), 75% (95% CI: 0.36–0.96), and 81.8%, respectively, for T2WI. Thus, the sensitivity and accuracy of DCE-MRI were greater than those of T2WI for preoperative endometrial carcinoma staging.ConclusionDCE-MRI was more sensitive but less specific than T2WI for the preoperative staging of early endometrial carcinoma. DCE-MRI may serve as a useful and reliable tool for the preoperative assessment of endometrial carcinoma.
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  • Sorption of tetracycline to sediments and soils: assessing the roles of pH, the presence of cadmium and properties of sediments and soils

    Guixiang Zhang   Xitao Liu   Ke Sun   Ye Zhao   Chunye Lin  

    Batch sorption experiments were conducted to evaluate the sorption behavior of tetracycline (TC, H 3L) on sediments and soils in the presence and absence of cadmium (Cd), as affected by pH and properties of sediments and soils. The results indicated stronger nonlinearity and higher capacity of TC sorption on sediments than on soils. Sorption of TC also strongly depended on environmental factors and sediment/soil properties. Lower pH facilitated TC sorption through a cation exchange mechanism, which also took place at pH values above 5.5, where TC existed as a zwitterion (H 2L 0) or anions (HL - and L 2-). When pH was above 7, however, ligand-promoted dissolution of TC might occur due to TC weakening the Al-O bond of aluminum oxide and the Fe-O bond of iron oxide. Natural organic matter (NOM) plays a more important role in TC sorption than cation exchange capacity (CEC) and clay contents. The presence of Cd (II) increased TC sorption on both sediments and soils, which resulted from the decrease of equilibrium solution pH caused by Cd 2+ exchange with H + ions of sediment/soil surfaces. The increase of TC sorption was also related to the formation of TC-Cd complexes, where Cd 2+ acted as a bridge between the sediment/soil and TC.
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  • The effects of different biochars on microbial quantity, microbial community shift, enzyme activity, and biodegradation of polycyclic aromatic hydrocarbons in soil

    Guixiang Zhang   Xiaofang Guo   Yuen Zhu   Xitao Liu   Zhiwang Han   Ke Sun   Li Ji   Qiusheng He   Lanfang Han  

    Abstract Plant-residue derived biochars from walnut shell, corn cob, corn straw, and rice straw obtained at three heat treatment temperatures (HTTs) (250 °C, 400 °C, and 600 °C) were applied in an incubation experiment to investigate how feedstocks, HTTs, and biochar properties affect the quantity of microorganisms, microbial community shift, enzyme activity, and biodegradation of polycyclic aromatic hydrocarbons (PAHs) in an aged contaminated soil. The microbial quantities (bacteria and fungi) and enzyme activities (catechol 2,3-dioxygenase and ligninolytic enzymes) generally decreased with the increase in HTTs. Microbial quantities had significantly positive correlations with the aliphatic carbon (C) ( p  < 0.01) but negative correlations with the aromatic C of biochars ( p  < 0.01). Similar findings were observed with enzyme activities, which had significantly positive correlations with microbial quantities ( p  < 0.05). Meanwhile, there were significantly positive correlations between C23O activity and bacterial quantity ( p  < 0.01) and between ligninolytic enzyme activities and the quantity of fungi ( p  < 0.05). These results indicate that the increase in recalcitrant aromatic C in biochars that occurs with the increase in HTT is unfavorable for the microbial growth and enzyme activity in the soil studied. Generally, application of biochars had little influence on the biodegradation rates of total PAHs. However, the effects of biochars on the biodegradation rates of major individual PAH (e.g., Nap, Phe, Pyr, and Chr) depended on both the types of biochars and the PAH properties such as benzene ring number and angular pattern of the ring linkage. Highlights • Microbial quantity and enzyme activity generally decreased with the increase in HTTs. • Recalcitrant aromatic C is unfavorable for the microbial growth and enzyme activity. • Application of biochars had little impact on the biodegradation rates of total PAHs. • PAH molecular structure affect the biodegradation rates of PAHs in biochar-treated soil.
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  • Reduction in Hami melon (<em>Cucumis melo</em> var. <em>saccharinus</em>) softening caused by transport vibration by using hot water and shellac coating

    Ran Zhou   Xichang Wang   Yunsheng Hu   Guixiang Zhang   Peiqiang Yang   Bailin Huang  

    Highlights • Effects of transport vibration on Hami melon softening during storage were studied. • The physiological and biochemical characteristics related to softening were monitored. • MR images, T 2 relaxation times and water traits of the fruits were measured. • HW in combination with shellac can reduce melon softening caused by vibration. Abstract The effects of transport vibration on Hami melon ( Cucumis melo var. saccharinus ) softening during storage (room temperature) were studied. Hot water (HW) and HW in combination with shellac coating (HW+shellac) were used to reduce melon softening caused by vibration. Changes in flesh firmness, hydrolase activities, cell wall constituents, cell membrane permeability and weight loss were monitored periodically in stored fruits for 28 days following vibration treatment. Magnetic resonance imaging (MRI) and nuclear magnetic resonance (NMR) were used to assess the internal morphological characteristics, transverse relaxation times, and water distribution of Hami melons. The results revealed that vibration contributes to Hami melon softening during storage. Compared to HW treatment, HW+shellac was more effective in reducing melon softening by reducing cell wall hydrolase activity, cell membrane leakage, fruit weight loss, and loss of cell wall constituents. The results were confirmed by MRI and NMR.
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  • Corrigendum to “Effect of biochar on the presence of nutrients and ryegrass growth in the soil from an abandoned indigenous coking site: The potential role of biochar in the revegetation of contaminated site” [Sci. Total Environ. 601–602 (2017) 469–477]

    Guixiang Zhang   Yuen Zhu   Xiaofang Guo   Zhiwang Han   Qiusheng He   Fengsong Zhang  

    Graphical abstract Image 1
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  • Morphological measurements in computed tomography correlate with airflow obstruction in chronic obstructive pulmonary disease: systematic review and meta-analysis

    Xueqian Xie   Pim A. de Jong   Matthijs Oudkerk   Ying Wang   Nick N H T ten Hacken   Jingtao Miao   Guixiang Zhang   Geertruida Hendrika de Bock   Rozemarijn Vliegenthart  

    To determine the correlation between CT measurements of emphysema or peripheral airways and airflow obstruction in chronic obstructive pulmonary disease (COPD). PubMed; Embase and Web of Knowledge were searched from 1976 to 2011. Two reviewers independently screened 1;763 citations to identify articles that correlated CT measurements to airflow obstruction parameters of the pulmonary function test in COPD patients; rated study quality and extracted information. Three CT measurements were accessed: lung attenuation area percentage < -950 Hounsfield units; mean lung density and airway wall area percentage. Two airflow obstruction parameters were accessed: forced expiratory volume in the first second as percentage from predicted (FEV1 %pred) and FEV1 divided by the forced volume vital capacity. Seventy-nine articles (9;559 participants) were included in the systematic review; demonstrating different methodologies; measurements and CT airflow obstruction correlations. There were 15 high-quality articles (2;095 participants) in the meta-analysis. The absolute pooled correlation coefficients ranged from 0.48 (95 % CI; 0.40 to 0.54) to 0.65 (0.58 to 0.71) for inspiratory CT and 0.64 (0.53 to 0.72) to 0.73 (0.63 to 0.80) for expiratory CT. CT measurements of emphysema or peripheral airways are significantly related to airflow obstruction in COPD patients. CT provides a morphological method to investigate airway obstruction in COPD. • Computed tomography is widely performed in patients with chronic obstructive pulmonary disease (COPD) • CT provides quantitative morphological methods to investigate airflow obstruction in COPD • CT measurements correlate significantly with the degree of airflow obstruction in COPD • Expiratory CT measurements correlate more strongly with airflow obstruction than inspiratory CT • Low-dose CT decreases the radiation dose for diagnosis and quantitative emphysema evaluation
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  • Efficiency optimisation at DC drives for small electrical vehicles

    Guixiang Zhang   Schmidhofer, A.   Schmid, A.  

    Electrical vehicles are well recognised for zero emission operation but have severe limitations in practical application due to the restricted energy capacity of batteries. For long operating distances highest overall efficiency is required. DC machines are still considered for cost saving applications when standard machines can be used for small electrical vehicles, especially when modernising existing DC machine cars without changing the mechanics. An efficiency optimised power conversion system with main emphasis on choppers and the power-optimised operation is described. The sources of losses are DC connection lines, fuses, magnetically operated circuit breakers, the drive converter, the auxiliary supply converter (e.g. for lights), the connection lines from converter to motor, the motor and the mechanical power train. All these losses are defined and calculated. The efforts, expenditures and final results for loss minimisation are presented. The MOSFET chopper is designed for highest efficiency with low on-state and switching losses. Despite the fundamental disadvantages of DC motors (rotor windings cooling, commutator, problematic operation at standstill) the overall system can be competitive with AC drives. The described loss minimisation measures increase efficiency remarkable especially for low battery voltages.
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