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Flow Variations (flow + variation)
Selected AbstractsHeat Flow Pattern in the Mainland of China and Its Geodynamic SignificanceACTA GEOLOGICA SINICA (ENGLISH EDITION), Issue 2 2000WANG Yang Abstract On the basis of 723 heat flow measurements in the mainland of China and over 2000 data from the global heat flow data set, the authors compiled the heat flow map of the mainland of China and its adjacent areas to exhibit the overall variation of the heat flow pattern in the mainland. The heat flow pattern of the mainland is complex, and can not be simply summarized as "low in the north and west and high in the south and east". Significant difference exists between eastern and western China in the spatial pattern of heat flow. Divided by the 105°E meridian, heat flow values in eastern China show a westward-decreasing trend; and a northward variation is observed in western China. The high-heat flow regions correspond to tectonically active belts such as Cenozoic orogens and extensional basins, where mantle heat flow is high; and the low-heat flow regions correspond to stable units such as the Tarim and Yangtze platforms. This heat flow pattern is controlled by India-Asia collision in the west and Pacific plate subduction in the east. The lateral variation in lithospheric strength corresponds to the heat flow variation, and there is a generally reversely proportional relation between heat flow and lithospheric strength in the mainland of China. The mosaic pattern of present deformation in the mainland results from lateral rheological heterogeneity. The good coincidence between weak strength domains and seismic zones demonstrates the intrinsic relation between the strength heterogeneity and regional seismicity pattern in the mainland of China. [source] Joule heating in electrokinetic flowELECTROPHORESIS, Issue 1 2008Xiangchun Xuan ProfessorArticle first published online: 30 NOV 200 Abstract Electrokinetic flow is an efficient means to manipulate liquids and samples in lab-on-a-chip devices. It has a number of significant advantages over conventional pressure-driven flow. However, there exists inevitable Joule heating in electrokinetic flow, which is known to cause temperature variations in liquids and draw disturbances to electric, flow and concentration fields via temperature-dependent material properties. Therefore, both the throughput and the resolution of analytic studies performed in microfluidic devices are affected. This article reviews the recent progress on the topic of Joule heating and its effect in electrokinetic flow, particularly the theoretical and experimental accomplishments from the aspects of fluid mechanics and heat/mass transfer. The primary focus is placed on the temperature-induced flow variations and the accompanying phenomena at the whole channel or chip level. [source] Process Considerations for Trolling Borehole Flow LogsGROUND WATER MONITORING & REMEDIATION, Issue 3 2006Phil L. Oberlander Horizontal hydraulic conductivity with depth is often understood only as a depth-integrated property based on pumping tests or estimated from geophysical logs and the lithology. A more explicit method exists for determining hydraulic conductivity over small vertical intervals by collecting borehole flow measurements while the well is being pumped. Borehole flow rates were collected from 15 deep monitoring wells on the Nevada Test Site and the Nevada Test and Training Range while continuously raising and lowering a high-precision impeller borehole flowmeter. Repeated logging passes at different logging speeds and pumping rates typically provided nine unique flow logs for each well. Over 60 km of borehole flow logs were collected at a 6.1-cm vertical resolution. Processing these data necessitated developing a methodology to delete anomalous values, smooth small-scale flow variations, combine multiple borehole flow logs, characterize measurement uncertainty, and determine the interval-specific lower limit to flow rate quantification. There are decision points in the data processing where judgment and ancillary analyses are needed to extract subtle hydrogeologic information. The analysis methodology indicates that processed measurements from a high-precision trolling impeller flowmeter in a screened well can confidently detect changes in borehole flow rate of ,0.7% of the combined trolling and borehole flow rate. An advantage of trolling the flowmeter is that the impeller is nearly always spinning as it is raised and lowered in the well and borehole flow rates can be measured at lower values than if measurements were taken while the flowmeter was held at a fixed depth. [source] Estimation of pulse wave velocity in main pulmonary artery with phase contrast MRI: Preliminary investigationJOURNAL OF MAGNETIC RESONANCE IMAGING, Issue 6 2006Hsu-Hsia Peng MS Abstract Purpose To assess the feasibility and reproducibility of a noninvasive MRI method to measure pulse wave velocity (PWV) in the main pulmonary artery (MPA). Materials and Methods A total of 17 subjects without history of pulmonary diseases (38.2 ± 18.4 years) participated in this study. Series of MR velocity maps of the MPA were acquired at 2 cm above the pulmonary valves using a two-dimensional phase-contrast sequence. Effective temporal resolution was 11 msec after interleaving two dynamic series with different values of electrocardiograph (ECG) trigger delay. PWV was derived as the rate of MPA flow variations per unit change in MPA cross-sectional area, during early systole. Seven healthy subjects underwent three repetitive examinations to investigate intrascan and interscan reproducibility. Results Flow vs. area was highly linear in the MPA during early systole, with Pearson's coefficients ranging from 0.982 to 0.999, rendering derivation of PWV with little difficulty. Average value of PWV in MPA was 1.96 ± 0.27 m/second, in good agreement with literature values measured using invasive means. The percentage intra- and interscan differences were 5.46% and ,10.86%, respectively. Conclusion Phase-contrast MRI to noninvasively measure PWV in the MPA is feasible with good reproducibility. J. Magn. Reson. Imaging 2006. © 2006 Wiley-Liss, Inc. [source] Measurement of bone blood flow using the hydrogen washout technique,part II: Validation by comparison to microsphere entrapmentJOURNAL OF ORTHOPAEDIC RESEARCH, Issue 6 2008Mikko Larsen Abstract Accurate and reproducible measurement of bone blood flow has important clinical and experimental applications. Hydrogen washout is simple, safe, and widely used, but its use in bone tissue has not been validated. To this end, we have compared cortical bone blood flow measurements obtained by radioactive-labeled microsphere entrapment with those from hydrogen washout. Blood flow was measured in tibial cortical bone of 12 New Zealand White rabbits by radioactive microsphere entrapment and by hydrogen washout. Besides a control group (n,=,6), four animals were treated with systemic epinephrine (0.8 µg/kg/min) (group 2) and two with nitroprusside (100 µg/kg/min) (group 3). Furthermore, nine femora from seven rats were isolated on their vascular pedicles and repeated bone blood flow measurements were made at each location with the hydrogen washout method to confirm reproducibility of blood flow determinations by hydrogen washout. An average flow of 2.3,±,2.0 mL/min/100 g was obtained with the microsphere method and 2.0,±,0.5 mL/min/100 g with the hydrogen washout method. There was a significant correlation and agreement: R2,=,0.97 (p,<,0.01). No consistent flow variations were found with systemic vasoactive drug administration. Hydrogen washout provided reproducible results and showed high sensitivity to flow changes. Hydrogen washout is both sensitive and reproducible in measuring bone blood flow. Results agree well with flow values obtained by labeled microsphere entrapment. © 2008 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 26:746,752, 2008 [source] COMPROMISE PROGRAMMING METHODOLOGY FOR DETERMINING INSTREAM FLOW UNDER MULTIOBJECTIVE WATER ALLOCATION CRITERIA,JOURNAL OF THE AMERICAN WATER RESOURCES ASSOCIATION, Issue 5 2006Jenq-Tzong Shiau ABSTRACT: This paper presents a quantitative assessment framework for determining the instream flow under multiobjective water allocation criteria. The Range of Variability Approach (RVA) is employed to evaluate the hydrologic alterations caused by flow diversions, and the resulting degrees of alteration for the 32 Indicators of Hydrologic Alteration (IHAs) are integrated as an overall degree of hydrologic alteration. By including this index in the objective function, it is possible to optimize the water allocation scheme using compromise programming to minimize the hydrologic alteration and water supply shortages. The proposed methodology is applied to a case study of the Kaoping diversion weir in Taiwan. The results indicate that the current release of 9.5 m3/s as a minimum instream flow does not effectively mitigate the highly altered hydrologic regime. Increasing the instream flow would reduce the overall degree of hydrologic alteration; however, this is achieved at the cost of increasing the water supply shortages. The effects on the optimal instream flow of the weighting factors assigned to water supplies and natural flow variations are also investigated. With equal weighting assigned to the multiple objectives, the optimal instream flow of 26 m3/s leads to a less severely altered hydrologic regime, especially for those low-flow characteristics, thereby providing a better protection of the riverine environment. [source] | |||||||||||||