Flow Tracing Research Articles

Abandonment of soil and water conservation structures in Mediterranean ecosystems

Traditional rainfed agriculture in semi-arid regions heavily relies on soil and water conservation (SWC) structures to supplement the sparse rainfall. As referring to the ecosystem functions of these constructions, when extensive such systems prevent any runoff into the fluvial system. The extent to which these dams and terraces resist major events is variable, and earthen dams can be major sediment sources. Extensification and increasing mechanization of rainfed agriculture in marginal areas have led to a change in cropping systems. Large-scale almond and olive plantations with widely spaced trees do not rely on runoff water, but draw the soil water from a large soil volume of bare soil maintained by regular shallow tillage. The high density of terraces has now become a nuisance to the farmers. The aim of this paper is to i) demonstrate the degradation of SWC structures and the relative importance of the driving forces, ii) assess the limits of the protection that earthen dams can provide by surveying their resistance during a heavy storm (return period 8.2 years) and iii) demonstrate the implications of the abandonment of SWC structures over the period 1956 2005 for the hydrological connectivity between croplands and the ephemeral rivers system. The headwaters of a marl catchment with a continuous area treated with SWC structures in Murcia region (Spain) already had a very high density of step terraces and check dams (182 m ha(-1)) in 1956. This density decreased by 27% in the period 1956-2005. Furthermore, many terraces have not been maintained and flow traces indicate that they no longer retain water. This is particularly true for the check dams in abandoned lands. The distance between the step terraces has increased over time, making them vulnerable to erosion. The mean drainage area of the dams that failed during the heavy storm was significantly (3.16 ha) higher than that of the ones that remained intact (1.11 ha). The probability of failure increases with drainage area from P=0.16 for an area of 1.8 ha to P=0.8 for an area of 20 ha. The percentage of cropland draining directly on the river system without interference of a check dam has increased from just 9% in 1956 to 31% in 2005 and 40% after the storm in November 2006. (C) 2008 Elsevier B. V. All rights reserved.

Transoesophageal Doppler Monitoring For Fluid And Hemodynamic Treatment During Lung Surgery

Patients undergoing lung resection are vulnerable to fluid overhydration. Recently, goal-directed fluid therapy using transoesophageal Doppler monitoring (TDM) has been shown to improve postoperative clinical outcome. The aim of this study was to assess the feasibility of TDM during open-chest procedures for guiding fluid and hemodynamic treatment. We performed an observational prospective study including 127 high-risk patients undergoing lung cancer resection. A restrictive fluid strategy was targeted to achieve a stroke volume index (SVI) > or = 30 ml/min/m(2). Besides standard hemodynamic measurements, stroke volume index (SVI), corrected flow time (FTc), maximal acceleration (MA) and velocity (PV) were recorded during two-lung ventilation (TLV) and one-lung ventilation (OLV). Doppler flow tracings could not be obtained in 4 patients during TLV (3.1%) and in 6 patients during OLV (4.9%). Preoperatively, 96 pts had SVI > or = 30 ml/min/m(2) (N-SVI group) whereas 21 patients had SVI < 30 ml/min/m(2) (L-SVI group) associated with lower FTc values. After OLV, SVI transiently decreased (-17 +/- 9%; P < 0.05) in the N-SVI group whereas in the L-SVI group, SVI increased steadily until the end of surgery (+40 +/- 12%). Other flow-related parameters as well as heart rate and mean arterial pressure remained unchanged. Surgical and medical characteristics did not differ between the two groups, except that larger volumes of colloids were administered intraoperatively in the L-SVI group (+2.2 +/- 0.6 ml/min/h compared with N-SVI group, P < 0.05). In thoracic surgical patients, TDM can be used to detect and correct low flow conditions and to guide hemodynamic support during the intraoperative period.

Computational Fluid Dynamics Simulation of Airflow in the Normal Nasal Cavity and Paranasal Sinuses

This study aimed to investigate airflow velocity, trace, distribution, and air pressure, as well as the airflow exchange between the nasal cavity and paranasal sinus in a normal subject using computational fluid dynamics. Fluent software is used to simulate nasal cavity and paranasal sinus structure after CT scanning of a normal adult subject. Airflow velocity, pressure, distribution, and trace lines were calculated by Navier-Stokes equation and numerically visualized. Airflow in the common and middle meatus accounted for >50 and 30% of total nasal cavity flow. Flow velocity was maximal in the common meatus, followed by the middle meatus. Flow velocity and flux in each paranasal sinus was extremely low. The flow trace in the inferior and lower part of the common meatus was predominately straight in form. Flow was parabolic in the middle and superior meatus and the middle and upper parts of the common meatus. Air pressure was high at the front end of the inferior and middle turbinate and the uncinate process. There was little pressure difference/flow exchange between inner and outer aspects of the paranasal sinus. The major airflow forms are straight (lower common and inferior meatus) and parabolic (middle and upper common meatus and middle superior). Flow force is strongest at the front end of the inferior and middle turbinate and uncinate process. There is very little exchange between the paranasal sinus and the nasal cavity during stable airflow.

Determination of Network Rental Components in a Competitive Electricity Market

The locational marginal pricing (LMP)-based settlement results in a surplus collected by the system operator from the consumers. The nonlinear transmission losses and the constrained operation of the power system due to operating limits, such as power flow limits on transmission lines, cause the accumulation of this surplus. This accumulated revenue, referred to as the network rental in this paper, has two main components: loss rental and constraint rental. This paper develops a method to calculate these different rental components paid by each consumer, by combining the power flow tracing and KKT optimality conditions. This yields quantitative determination of how each consumer has overpaid in the form of loss rental and constraint rental, which in turn can be used to get a better insight of how the rental is accumulated. Simple three- and four-bus systems are used to demonstrate the proposed method.

ADEQUACY-BASED POWER SYSTEM RELIABILITY STUDIES IN THE DEREGULATED ENVIRONMENT

The onset of deregulation in the electric power sector in the recent years has brought to the fore several pronounced issues related to reliability management, necessitating a revamping of the metrics. The element of markets and economic trading introduced in the operations of power systems has seen a paradigm shift even in the way customer-say is incorporated into the reliability apportioning. In order to better appreciate the sea-changes brought forward by deregulation, identification of areas of evolving reliability research in the regulated regime goes a long way in dealing with their deregulated counterparts. This paper caters to the view to provide a pointer to the significant issues that can profoundly impact the reliability studies in the liberalized environment. Emphasis in this paper is placed on a bilateral market structure, where all participants of competitive trading have mutually agreed upon pre-defined contracts to trade energy. With a view to improvise upon the existing nascent reliability network equivalent techniques, a realistic state space selection methodology, crucial to the contingency effects' evaluation is proposed, which makes a novel use of power flow tracing procedures. This research work is intended to pave the way for robust reliability models that take into account all the structural and consequent operational transmutations in power systems, yielding a concrete possibility of implementing non-uniform reliability as per the user requirements — a situation that was not feasible in the earlier regime.

Noninvasive Methods for Determining Pulmonary Vascular Function in Children with Pulmonary Arterial Hypertension: Application of a Mechanical Oscillator Model

Noninvasive diagnostics for pulmonary arterial hypertension (PAH) have traditionally sought to predict main pulmonary artery pressure from qualitative or direct quantitative measures of the flow velocity pattern obtained from spectral Doppler ultrasound examination of the main pulmonary artery. A more detailed quantification of flow velocity patterns in the systemic circuit has been obtained by parameterizing the flow trace with a simple dynamic system model. Here, we investigate such a model's utility as a noninvasive predictor of total right heart afterload and right heart function. Flow velocity and pressure was measured within the main pulmonary artery during right heart catheterization of patients with normal hemodynamics (19 subjects, 20 conditions) and those with PAH undergoing reactivity evaluation (34 patients, 69 conditions). Our model parameters were obtained by least-squares fitting the model velocity to the measured flow velocity. Five parameter means displayed significant (P < .05) differences between normotensive and hypertensive groups. The model stiffness parameter correlated to actual pulmonary vascular resistance (r = 0.4924), pulmonary vascular stiffness (r = 0.6811), pulmonary flow (r = 0.6963), and stroke work (r = 0.7017), while the model initial displacement parameter had good correlation to stiffness (r = 0.6943) and flow (r = 0.6958). As predictors of total right heart afterload (resistance and stiffness) and right ventricle work, the model parameters of stiffness and initial displacement offer more comprehensive measures of the disease state than previous noninvasive methods and may be useful in routine diagnostic monitoring of patients with PAH.

Interpretation of Uptake Coefficient Data Obtained with Flow Tubes

The uptake of trace gases such as OH and HO2 radicals, NH3, ClONO2, N2O5, ozone, and many other gases by water, aqueous solutions of acids, and salts has been reported by numerous investigators using a variety of techniques. Reported uptake coefficients vary greatly, ranging from 10(-8) to 1. This paper describes a new analysis of uptake data obtained in flow tubes that consolidates data obtained for various flow rates and trace gas concentrations. Previous analyses, which have been often used, are shown to be limiting cases or special cases of the analysis outlined here. Of particular emphasis are results for wetted-wall columns and trace gas uptake by aerosol entrained in flow tubes. In the absence of aerosol, the analysis is shown to predict the decrease in trace gas concentration due to bulk chemical reaction and/or reaction at the tube wall or gas-liquid interface. Uptake coefficients for OH and HO2 radicals on water in wetted-wall tubes are shown to range from 0.01 to 1, and on sulfuric acid, they vary from 0.008 to 0.03. For O3 on a water film doped with a scavenger, the uptake coefficient is found to be 0.0008. Uptake coefficients determined by different techniques are compared.

Maternal traces of deep common ancestry and asymmetric gene flow between Pygmy hunter–gatherers and Bantu-speaking farmers

Two groups of populations with completely different lifestyles-the Pygmy hunter-gatherers and the Bantu-speaking farmers-coexist in Central Africa. We investigated the origins of these two groups and the interactions between them, by analyzing mtDNA variation in 1,404 individuals from 20 farming populations and 9 Pygmy populations from Central Africa, with the aim of shedding light on one of the most fascinating cultural transitions in human evolution (the transition from hunting and gathering to agriculture). Our data indicate that this region was colonized gradually, with an initial L1c-rich ancestral population ultimately giving rise to current-day farmers, who display various L1c clades, and to Pygmies, in whom L1c1a is the only surviving clade. Detailed phylogenetic analysis of complete mtDNA sequences for L1c1a showed this clade to be autochthonous to Central Africa, with its most recent branches shared between farmers and Pygmies. Coalescence analyses revealed that these two groups arose through a complex evolutionary process characterized by (i) initial divergence of the ancestors of contemporary Pygmies from an ancestral Central African population no more than approximately 70,000 years ago, (ii) a period of isolation between the two groups, accounting for their phenotypic differences, (iii) long-standing asymmetric maternal gene flow from Pygmies to the ancestors of the farming populations, beginning no more than approximately 40,000 years ago and persisting until a few thousand years ago, and (iv) enrichment of the maternal gene pool of the ancestors of the farming populations by the arrival and/or subsequent demographic expansion of L0a, L2, and L3 carriers.

USCOM (Ultrasonic Cardiac Output Monitors) Lacks Agreement with Thermodilution Cardiac Output and Transoesophageal Echocardiography Valve Measurements

The USCOM (Ultrasonic Cardiac Output Monitors) device is a non-invasive cardiac output monitor, which utilises transaortic or transpulmonary Doppler flow tracing and valve area estimated using patient height to determine cardiac output. We evaluated USCOM against thermodilution cardiac outputs and transoesophageal echocardiography valve area measurements in 22 ASA PS4 cardiac surgical patients. Data collection commenced following pulmonary artery catheter insertion, with cardiac output measurements repeated after sternotomy closure. Failure to obtain transaortic Doppler readings using USCOM occurred in 5% of planned measurements. USCOM transaortic analysis was not planned for 11 patients with known aortic disease. Bias at the aortic window (n = 20) was -0.79 l/min with limits of agreement from -3.66 to 2.08 l/min. At the pulmonary window, failure to obtain Doppler readings occurred in 24% of planned measurements. Bias at the pulmonary window (n = 36) was -0.17 l/min with limits of agreement from -3.30 to 2.97 l/min. The USCOM estimates of valve area based on height showed poor correlation with the echocardiographic measurements of aortic and pulmonary valves (r = 0.57 and r = 0.17, respectively). It was concluded that USCOM showed poor agreement with thermodilution. The estimated valve area was identified as one source of error.

Transmission Loss Allocation Through Complex Power Flow Tracing

This paper presents a new method for transmission loss allocation. The method is based on tracing the complex power flow through the network and determining the share of each load on the flow and losses through each line. Transmission losses are taken into consideration during power flow tracing. Unbundling line losses is carried out using an equation, which has a physical basis, and considers the coupling between active and reactive power flows as well as the cross effects of active and reactive power on active and reactive losses. A tracing algorithm which can be considered direct to a good extent, as there is no need for exhaustive search to determine the flow paths as these are determined in a systematic way during the course of tracing. Results of application of the proposed method are also presented.

Dissolved organic matter fluorescence as a water-flow tracer in the tropical wetland of Pantanal of Nhecolândia, Brazil

The Nhecolândia is a sub-region of the Brazilian Pantanal wetland, where saline and freshwater lakes coexist in close proximity. Measurements of dissolved organic carbon (DOC) content and analysis of fluorescence excitation–emission matrices (EEM) were conducted in an effort to characterize spatial variability in concentration and source of dissolved organic matter (DOM) and to further understand the hydrochemical functioning of this complex environment. Increasing pH under the influence of evaporation resulted in an increasing DOC solubility ranging from 50 to over 300 mgC L − 1 in surface water. Spectrofluorescence characterisation indicates the presence of several families of dissolved organic matter (fulvic and humic-type and proteinaceous materials), which are related to the type of lake and its hydro–bio–geochemical functioning. Moreover, the fluorescence signatures from lake water DOM and from surrounding soil–water-extracted organic matter (WEOM) show strong similarities although some labile proteinaceous compounds disappeared during humification. Results from the characterisation of DOM and WEOM not only suggest that spectrofluorescence is a reliable technique for the tracing of water flows, but also for the marking of the origin of organic horizons in this environment.

Unified control flow and data dependence traces

We describe the design, generation, and compression of the extended whole program path (eWPP), representation that not only captures the control flow history of a program execution but also its data dependence history. This representation is motivated by the observation that, typically, a significant fraction of data dependence history can be recovered from the control flow trace. To capture the remainder of the data dependence history, we introduce disambiguation checks in the program whose control flow signatures capture the results of the checks. The resulting extended control flow trace enables the recovery of otherwise irrecoverable data dependences. The code for the checks is designed to minimize the increase in program execution time and the extended control flow trace size when compared to directly collecting control flow and address traces. Our experiments show that compressed eWPPs are only one-quarter of the size of combined compressed control flow and address traces. However, their collection incurs a 5× increase in runtime overhead relative to the overhead required for directly collecting the control flow and address traces, respectively.

An OPF based approach for assessing the minimal reactive power support for generators in deregulated power systems

Reactive power support is an important ancillary service for secure and reliable operation in power markets. It has recently been recognized that the reactive power support for a generator has two components: one for supporting its own real power transmission and the other for supplying reactive demand, improving system security, and controlling system voltage; and that only the second part should receive financial compensation in competitive power markets. This makes the problem of separating these two components a new focus of current research. An OPF based reactive power optimization model along with a power flow tracing based method is proposed in this paper to tackle this problem. The methodology is tested on four test systems. Detailed analysis of the results of the 39-bus test system is reported.

Modeling of the through EHD-flow structure in a wire-wire system

In this article, we show the results of computer modeling of a nonsymmetric EHD flow in a symmetric wire-wire electrode system. This problem was solved using the ANSYS program, which is based on the finite-elements method. We develop the computer modeling of a nonsymmetric EHD-flow algorithm in a stationary variant, which helps us to solve a wide range of electrohydrodynamic problems. In this way, we show the results of solving the problem of a symmetric and nonsymmetric liquid flow in a wire-wire electrode system. A new type of charge diffusion was found, and the disruption of the symmetry when the flow traces are at an acute angel to the center along the axis of symmetry. In this case, the nonsymmetric EHD flow is generated.

Superplastic Extrusion of Nano-Structured Si&lt;sub&gt;2&lt;/sub&gt;N&lt;sub&gt;2&lt;/sub&gt;O-Sialon

Nano-structured Si2N2O-Sialon composites were prepared by liquid phase sintering method with the amorphous nano-sized Si3N4 and nano-sized AlN powders. Nano-sized Al2O3 and Y2O3 powders synthesized by polyacrylamide gel method were introduced as additives. SEM examination shows the grain size of sintered body to be less than 80nm. Superplastic extrusion can be undertaken at 1550°C with a high velocity of 0.5mm/min and a big extrusion ratio of 3.57. There are a lot ring-shaped structure just like “annual ring” of trees in radial fracture and clear flow trace in axial fracture, all which is very similar to deformed metal materials and approve good superplastic deformation capability of Si2N2O-Sialon composites.

Analysis of Reactive Power Support of Generators Using Power Flow Tracing Methods

With the emergence of competitive electricity power markets, reactive power ancillary services and reactive power markets have attracted attention from researchers and system operators all over the world. Reactive power is an important system support service for secure and reliable operation of power systems. Improper management of reactive power can also hinder the operational efficiency of other power markets. It has been recognized that the reactive power of a generator has several roles, namely, supplying reactive demand, maintaining system security and supporting its real power transmission. It is rational that the minimal reactive power used to support its real power transmission should not receive financial compensation in power markets. Hence, this component of reactive power can be regarded as the minimal reactive power support of a generator. A reactive power optimization model along with a power flow tracing based method is proposed in this article to tackle this problem. The validity and rationality of the approach are verified using a simple meshed 5-bus system.

Modification of peripheral mountain ranges by former ice sheets: The Brecon Beacons, Southern UK

The Brecon Beacons in southern Wales is a large upland area (900 km 2) close to the periphery of the former British–Irish Ice Sheet. The geomorphology of the Brecon Beacons highlands and surrounding areas was mapped using satellite imagery and a digital elevation model (DEM). A fragmentary pattern of glacial lineations is inferred to represent ice build-up in the mountains. A more coherent set of glacial lineations formed by southward ice flow across the area from the Welsh Ice Cap represents recession from the Last Glacial Maximum (LGM). During this phase the Brecon Beacons acted as an obstacle, deflecting the ice around higher terrain. Most of the higher terrain in the Brecon Beacons therefore appears to have escaped significant glacial erosion during both phases of ice-flow due to cold-based ice or low basal ice velocities beneath a local ice cap. Landforms previously interpreted as cirques in fact have v-shaped profiles and lack evidence of major over-deepening. They are interpreted to have been formed primarily by processes other than glacial erosion. The overall impact of glaciation in the Brecon Beacons appears to be limited primarily to the time when the area was over-run by the Welsh Ice Cap and the influence of local glaciation has been minimal. This study has two main implications for landscape evolution in mountain ranges that lie at the periphery of former ice sheets. First, due to the presence of cold-based ice or low basal ice velocities beneath a local ice cap it may be possible to find fragmentary traces of pre-LGM ice flow. Second, the pattern of glacial lineations in and around the Brecon Beacons indicates that peripheral mountain ranges may have deflected ice flow at the LGM, resulting in low basal ice flow velocities and possible frozen-bed conditions over higher terrain which consequently resulted in ineffective glacial erosion within the mountains themselves.

Modeling of nonstationary EHD flows in a wire-plane electrode system

The object of this work is nonstationary EHD flow modeling in a wire-plane electrode system for researching processes of space-charge formation and evolution, and the features of its movement in the interelectrode gap are investigated. The set of equations describing the modeling process is appreciably nonlinear. The final-element modeling package ANSYS was used for solving this problem. A special algorithm was developed. It was realized as a package of programs based on the approximation that the charge is “frozen” in the liquid. Results of calculations are represented as velocity vector plot evolution, pressure distributions, and EHD flow traces. A typical feature of EHD flow is the formation of a charged thin stream that crosses the interelectrode gap.

The combination of optical tweezers and microwell array for cells physical manipulation and localization in microfluidic device

A microfluidic device combined with the microwell array and optical tweezers was set up for cell manipulation, localization and cultivation. Yeast cells were manipulated by a 1,064 nm laser and transferred to microwell array as a demonstration. The flow velocities at which the yeast cell can be confined in microwells of different sizes are characterized. The simulation of the cell's flow trace in the microwell at different flow velocities is consisting with our experiment result. And we also proved a trapping laser power of 0.30 W is harmless for yeast cell cultivation. As a simple approach, this method can push forward the cell cultivation, cell interaction and other cell biology or biomedical studies in microfluidic system.

An enhanced technique in construction of the discrete drainage network from low-resolution spatial database

A digital elevation model (DEM) of a watershed can be used to acquire various parameters such as basin-wide information about overland flow direction, flow accumulation and area contributing flow to any point. The resolution and quality of a DEM are important to achieve a significant level of accuracy in derived parameters. Inadequate elevation information exacerbated by applied interpolation methods, reduce DEM accuracy, resulting in pits and flat areas and makes flow tracing a difficult task. These types of problems are more prominent in cases of residual undulating terrains. In the present paper, an attempt has been made to review and suggest an improved method for the generation of a DEM from raster contour data. Further, a criteria-based region growing method (CBRGM) is presented for the extraction of discrete drainage network (cell size: 20×20 m) of the watershed. Here, the flat area removal algorithm, with a variable increment, is used to generate the DEM. This induces a gradual slope even in the case of a large contour interval (20 m) extended over larger area, as is commonly available from a topographic map at a scale of 1:50,000. Further, in order to capture topographic information in flow tracing, the CBRGM is followed. The rasterised stream network from the same topographic sheet is used as ancillary data to make the concentrated flow lines to follow the channel. The methodology has been tested over Gandheshwari subwatershed under the lower part of Chhotanagpur Plateau in Eastern India. The DEM generated using this method gives a better representation of the terrain, which shows good agreement with the terrain information delineated by using the contour and channel information available in the topographic sheet. The drainage network derived shows additional extra-concentrated flow lines, many of which match the drainage network obtained from satellite imagery (cell size: 23.5×23.5 m). The algorithm thus shows superiority over other available methods for the extraction of drainage networks.