Outflow Pipe Research Articles

Heat extraction from abandoned petroleum wells utilizing coaxial borehole heat exchanger in Ordos basin, China

To extract geothermal energy from abandoned petroleum wells in Ordos basin, China, a coaxial deep borehole heat exchanger (DBHE) is studied through a 3D numerical model. Factors, such as thermophysical properties, geological characteristics and operational conditions, are considered. Given the geothermal gradients and rock/soil properties, numerical results suggest that a sustainable heat extraction rate can be achieved for building heating purpose in long term; after 20 years’ operation, with an injection rate of 30 m3/h at 20 °C and wellbore length being 2350 m, the outlet temperature is around 24 °C, the heat load per unit depth ranges from 89.2 W/m to 67.7 W/m. Through comparison between on-site tests and numerical modeling, it is suggested that factors like well integrity, operational conditions and insulation between the inflow and outflow pipe should be taken into account. Numerical modeling on variation of well depth is performed; results show that both the wellbore length of 1800 m and 2350 m could satisfy a heat extraction load of 80 W/m, and the greater the wellbore length, the larger the outlet temperature. According to results from a DBHE array model, the general 200 m–300 m wellbore interval would not cause thermal interaction.

Evaluation of risk associated with treatment of fat, oil, and grease: Grease interceptor from food processing industry effluent using bowtie analysis

AbstractFat, oil, and grease (FOG), a deposit in wastewater, develops from any processes in food and processing industries. FOG deposits in wastewater management systems can cause blockages in sewer systems. Grease Interceptor (GI) is one of the control measures to treat and prevent the blockage of FOG deposits in the sewer system. Nevertheless, few studies evaluate the extended hazard of GI application in FOG treatment. This study aims to assess the risk of GI in FOG treatment by using a bowtie technique. The hazard identified is FOG itself, whereas the top event was GI failure. The high contributions of the threats were an unsuitable variation of GI's type and design, no GI cleaning process schedule, and a clogged outflow pipe from GI. GI design according to standard and cleaning FOG deposits in GI by a licensed grease hauler were two suitable preventive barriers. The desludging process is essential to guarantee that the GI operates smoothly and is identified as an excellent recovery barrier. Inter‐rater reliability (IRR) analysis to measure the consistency of their ratings on the data provided. The experts had a 75% overall agreement value of IRR risk rating value on assets, while 50% agreement value on people.

The growth performance, antioxidative status and muscle quality of grass carp (Ctenopharyngodon idellus) cultured in the recirculating pond aquaculture system (RPAS)

The recirculating pond aquaculture system (RPAS) consisted of culture ponds, a purification pond, inflow ditch, outflow pipe, ecological ditch, and electrically driven pump. The performance of RPAS on grass carp (Ctenopharyngodon idellus) was explored in this study. In both the RPAS and the traditional pond aquaculture system (TPAS), water quality, fish growth performance, muscle quality, and tissue biochemical properties were assessed. Pond water was exchanged every seven days in RPAS and treated using a purification system that included an ecological ditch and a purification pond with a floating bed and aquatic plant. In RPAS, nitrate‑nitrogen, ammonia‑nitrogen, and nitrite‑nitrogen concentrations were lower than in TPAS. Fish cultured in RPAS exhibited significant higher growth rate and lower feed conversion rate. A significant increase in the expression of growth-related genes of myogenin (MyoG), myofactar-5 (Myf-5), insulin-like growth factor-I gene (igf-1), insulin-like growth factor-II gene (igf-2), and growth hormone receptor gene (ghr) were found in the fish cultured in the RPAS ponds. The content of malondialdehyde in either serum or liver and hepatic protein carbonyls content declined significantly in the RPAS ponds. The activities of T-SOD and GSH in liver and GSH in serum elevated significantly in RPAS fish. Muscular histological characteristics and texture profiles did not alter between two groups. The muscular contents of aromatic amino acids of aspartic acid and glutamic acid were significantly higher in RPAS than those in TPAS. It is inferred that RPAS is beneficial to promote fish growth, decrease oxidative stress, and increase muscle umami flavor.

Evolution of Water Conveyance Capacity through Hydraulic Transition Processes in Circular Drop Manholes

Circular drop manholes are widely implemented for steep catchments in urban drainage networks. Poor downstream hydraulic transition processes of a manhole system, i.e., the formation of hydraulic jump near the outlet entrance, and the sudden transition from free surface to pressurized flow with bursts of air in the outflow pipe can severely constraint the capacity of water conveyance. In this paper, we defined four basic hydraulic stages that indicate where hydraulic transition processes begin and end. The measurements of typical manhole models with different drop heights were conducted under different inflow and outflow conditions. Three types of transition processes covering all flow patterns have resulted into a graphical visualization by analyzing two pairs of dimensionless parameters. The flow inside a circular drop manhole was considered to reach its discharge capacity when the abrupt drop of manhole water level is visible in the fully aerated flow pattern. Four empirical equations revealing the water level filling ratio and discharge efficiency at different hydraulic stages were also presented for further predictions of choking risks.

Estimating the invasion extent of Asian swamp eel (Monopterus: Synbranchidae) in an altered river of the south-eastern United States

The first reported invasion of Asian swamp eels (Monopterus albus, ASE) in the continental United States was in the state of Georgia in 1994. This population was first discovered within several ponds on a private nature centre, but the ponds drained via an outflow pipe into marsh habitats along the Chattahoochee River. Our objective was to delineate the current invasion extent of ASE in the Chattahoochee River, Georgia, by sampling juvenile ASE within an occupancy modelling framework. We sampled 111 and 100 sites in 2015 and 2016 respectively, on 10 occasions, each within a 2-km radius of the purported invasion point to estimate the spatial extent of their invasion in this system. Leaf-litter traps (LLTs) were effective at documenting an increase in the invasion extent of ASE, from within 100m of the Chattahoochee Nature Center pond outflow to 1.6km away. Documenting the extent of invasion of this population has proven elusive in the past, but the use of LLTs to target juvenile eels has documented a larger invasion extent than previously known in the study system. The results of this research can be used to develop effective control and management strategies, such as locating potential breeding areas for targeted removal sampling.

Transient Atomization Modeling and Optimal Design of a Medical Air-Compressing Nebulizer

This paper studies three-dimensional transient flow characteristics of a medical air-compressing nebulizer which is widely used to treat respiratory diseases in the medical field. The transient atomization process of air and water was numerically simulated and reproduced by solving Navier-Stokes equations, turbulent transport equations, the volume of fluid (VOF) model, and discrete phase model (DPM). The water volume fraction inside the nebulizer was simulated and demonstrated under different time. Besides, to better the working performance of the nebulizer, the effects of different working parameters such as different orifice diameters, length of the outflow pipe, and air velocity on the secondary atomization were also studied and discussed. It was found that the most suitable diameter of the orifice for this air-compressing nebulizer is 1.0 mm. Most suitable length of the outflow pipe and the air velocity for producing small air-water bubbles are 10 mm and 4 m/s, respectively.

Response of freshwater mussel recruitment to hydrological changes in a eutrophic floodplain lake

Although eutrophication of freshwaters is a natural process, the human impact often leads to inland waters becoming overloaded with nutrients, impoverishing many valuable and vanishing habitats, such as floodplain lakes. These changes need to be reversed if the occurrence of endangered aquatic species is to be restored. In this paper we analyse the impact of a change in the water regime of a naturally eutrophic floodplain lake, which harbours a large diversity of Unionidae (large freshwater mussels), a globally threatened taxonomic group that provides important ecosystem functions and services. We found that a slight increase in the discharge from this waterbody, following the construction of an additional outflow pipe, positively influenced recruitment in three of the five mussel species inhabiting the lake. We also found that, after the construction of this additional outflow, the niches of juveniles of Anodonta cygnea and Unio spp. changed, revealing differences in their hydrological requirements. Our results suggest that, as in lotic habitats, complex hydraulic parameters are highly significant to unionid mussels in lentic conditions.

Computational Fluid Dynamics Analysis of Titanium Outflow Pipe Implant for Glaucoma Treatment in Biomechanical Engineering

Computational Fluid Dynamics Analysis of Titanium Outflow Pipe Implant for Glaucoma Treatment in Biomechanical Engineering

Solid residence time distribution in a cross-flow dense fluidized bed with baffles

The residence time distribution (RTD) of particles in a gas-solid dense fluidized bed with a continuous solid flow operation and baffles needs much more focus for the purpose of the wide industrial applications. The available models of solid RTD are not adequate in this case due to the additional convective diffusion induced by the cross-flow of the solid feeding and the complex geometry caused by the baffles. To address this problem, this work applied a two-phase Eulerian-Eulerian model combined with the species transport equation to predict solid RTD in a dense fluidized bed. The effects of the continuous solid feeding and baffles were considered. The solid dispersion coefficient Ds in the species transport equation was calculated by an analytical solution from kinetic theory of granular flow. Ds only needs the value at a molecular level due to the fact that the computational fluid dynamics (CFD) model is able to reproduce the RTD procedure exactly same as the practical experiments. To validate the established CFD model, a series of 3D lab-scale cold flow experiments were conducted in the free and baffled beds for the bed material with various severe non-spherical shapes. The measurement included the solid hydrodynamic characteristics at the outlet of the outflow pipe and solid RTD of the system. The reasonable agreement between the CFD prediction and experimental data demonstrated the good performance of the CFD model. 1D plug flow with dispersion model and the tanks-in-series model were further used to fit the calculated RTD curves. The estimated lateral dispersion coefficient of solids locates in a rational range compared with the data collected extensively from the literature. The results showed that the lateral dispersion coefficient of solids decreases when the baffles are installed.

Stormwater runoff driven phosphorus transport in an urban residential catchment: Implications for protecting water quality in urban watersheds

Increased stormwater runoff in urban watersheds is a leading cause of nonpoint phosphorus (P) pollution. We investigated the concentrations, forms, and temporal trends of P in stormwater runoff from a residential catchment (31 low-density residential homes; 0.11 km2 drainage area) in Florida. Unfiltered runoff samples were collected at 5 min intervals over 29 storm events with an autosampler installed at the stormwater outflow pipe. Mean concentrations of orthophosphate (PO4–P) were 0.18 ± 0.065 mg/L and total P (TP) were 0.28 ± 0.062 mg/L in all runoff samples. The PO4–P was the dominant form in >90% of storm events and other–P (combination of organic P and particulate P) was dominant after a longer antecedent dry period. We hypothesize that in the stormwater runoff, PO4–P likely originated from soluble and desorbed pool of eroded soil and other–P likely originated from decomposing plant materials i.e. leaves and grass clippings and eroded soil. We found that the runoff was co-limited with nitrogen (N) and P in 34% of storm events and only N limited in 66% of storm events, implicating that management strategies focusing on curtailing both P and N transport would be more effective than focussing on only N or P in protecting water quality in residential catchments.

Anthropogenic transport of macrofauna through a sand transfer plant

The South Lake Worth Inlet Sand Transfer Plant in Palm Beach County, Florida pumps subtidal sediment from the upcurrent to the downcurrent side of the jetty to correct jetty-induced sediment transport disruption. This pumping accounts for 35% of the overall net longshore transport. We investigated if living macrofauna could survive the sediment pumping process. We also examined the effects this activity had on the subtidal macrofaunal invertebrate communities. Subtidal sediment cores were taken near the intake pipe, at the outflow pipe, and just outside the direct effects of the sand transfer plant. Benthic macrofauna and sand grain size were examined and compared. Macrofauna, live and preserved, were confirmed exiting the outflow pipe. Low diversity, low abundance macrofaunal communities were found at all sample sites. Macrofaunal abundance was primarily isopods (79%) and polychaetes (14%). Three isopod and one polychaete species constituted 89% of the community diversity. Both inflow borrow pit and outflow deposition sampling sites exhibited different community structure compared to adjacent control sites. The inflow borrow pit presented a high population of the isopod Eurydice personata. The outflow deposition site had the highest species diversity. The outflow deposition site also showed much coarser mean sediment grain size compared to other sites. The differences found at the sites direct associated with the sand transfer plant demonstrated localized disturbance. We concluded that although the plant disturbs the adjacent community it also helps maintain the macrofaunal community structure and sand grain size on the downdrift side of the South Lake Worth Inlet. Further studies integrating abiotic and biotic components will assist in management practices and our understanding of nearshore systems.

과부하 4방향 사각형 합류맨홀에서의 에너지 손실 저감을 위한 실험 연구

과부하 맨홀에서의 에너지 손실은 도심지의 침수피해를 가중시키는 요인이 된다. 그러므로 과부하 4방향 합류맨홀에서 에너지 손실의 저감을 위한 흐름특성 분석이 필요하다. 본 연구에서는 현황조사 결과를 고려하여 수리실험 장치를 제작하였으며, 사각형 맨홀 및 연결관은 하수도시설 기준을 준용하여 1/5로 축소 제작하였다. 또한 과부하 4방향 사각형 합류맨홀에서 에너지 손실을 저감 시킬 수 있는 인버트 형상 조건을 도출하기 위하여 Fluent 6.3모형으로 수치모의를 실시하였다. 선정된 수리실험 조건인 유출유량(<TEX>$Q_{out}$</TEX>)에 대한 측면 유입유량(<TEX>$Q_{lar}$</TEX>)의 비(<TEX>$Q_{lat}/Q_{out}$</TEX>)와 유출유량(2.0, 3.0, 4.0, 4.8 l/sec) 및 인버트 형상 변화 조건(십자형, 개선형)을 변화시키며 수리실험을 실시하였다. 십자형 인버트는 과부하 4방향 합류 맨홀의 배수능력 향상에 영향이 미미한 것으로 분석되었다. 그러나 개선된 직사각 개거형 인버트와 정사각 개거형 인버트는 각각 평균적으로 약 7%, 28%의 손실계수가 감소하여 배수능력을 개선하는 것으로 분석되었다. 따라서 도시 관거 시설의 배수능력을 증대시키기 위하여 본 연구에서 제시된 개선형 인버트의 설치 및 활용이 가능할 것으로 판단된다. Energy loss at manholes under surcharged flow is considered as one of the major causes of inundation in urban area. Therefore, it is necessary to analyze the flow characteristics to reduce the energy loss in the surcharged four-way combining manhole. In this study, hydraulic experimental apparatus was constructed considering the results of the present survey. Square manholes and pipe diameters were reduced to 1/5 by applying sewer facility standards. Numerical simulations were carried out with the Fluent 6.3 model to derive the invert condition which can reduce the energy loss in the surcharged four-way combining square manhole. The hydraulic experiments were carried out according to the various conditions of the lateral flow rate(<TEX>$Q_{lat}/Q_{out}$</TEX>), discharge of outflow pipe (2.0, 3.0, 4.0, 4.8 l/sec), and invert shape (rectangle and square open conduit type). The crossed invert was not found to improve the drainage capacity of the surcharged four-way rectangular combining manhole. However, the improved rectangle open conduit type invert and square open conduit type invert were analyzed to improve the drainage capacity by reducing the head loss coefficients by about 8% and 28%, respectively. Therefore, in order to increase the drainage capacity of urban facilities, it is possible to install and use the improved invert proposed in this study.

Effects of phenol on physicochemical properties and treatment performances of partial nitrifying granules in sequencing batch reactors

This study attempts to investigate the effect of phenol on physicochemical properties and treatment performances of partial nitrifying granules (PNGs). Two sequencing batch reactors (SBRs) fed with synthetic ammonium wastewaters were operated in absence (R1) or presence (R2) of phenol. The PNGs in R1 maintained excellent partial nitrification performance and relatively stable physicochemical properties, and exhibited compact and regular shaped structure with a cocci-dominant surface. However, as phenol concentration was stepwise increased from 0 to 300mg/L in R2, filamentous bacteria appeared and gradually dominated within granules, which in turn resulted in settleability deterioration. Most notably, granules in R2 got easier to agglomerate in the reactor walls and then been washed out with effluent, leading to significant biomass loss, frequent outflow pipe blockage, and eventual system failure. The extracellular polymeric substances (EPS) contents including proteins and polysaccharides in R2 reached 1.8 and 1.7 times of that in R1, respectively, indicating that the presence of phenol played an important role on EPS production. Removal efficiency of ammonium and phenol remained high, but dropped sharply when phenol concentration reached 300mg/L. Moreover, the failed maintenance of partial nitrification was observed due to the revival of nitrite oxidizing bacteria (NOB) within granules after phenol exposure, which was confirmed by quantitative fluorescence in situ hybridization (FISH) analysis. Overall this study demonstrates that phenol had negative effects on PNGs, and pretreatment to eliminate phenolic substances is recommended when using PNGs for wastewater treatment.

Simple deterministic model of the hydraulic buffer effect in septic tanks

AbstractSeptic tanks are widely used in on‐site wastewater treatment systems. In addition to anaerobic pretreatment, hydraulic buffering is one of the roles attributed to septic tanks. However, there is still no tool for assessing it, especially in dynamic conditions. For gravity fed‐system, it could help both researchers and system designers. This technical note reports a simple mechanistic model based on the assumption of flow transition between the septic tank and the outflow pipe. The only parameter of this model was calibrated using computational fluid dynamics (CFD) modeling for a wide range of discharge rates. The resulting model highlights that a septic tank plays a hydraulic buffer role when faced with sudden and large discharge flow, but this role tends to disappear when input hydrographs are smoother. In those cases, there is an observable lag between the input hydrograph and outflow hydrograph.

Choking conditions inside plunging flow dropshafts

Severe rain events can subject our existing drainage systems to capacity. While the conveyance capacity of sewers can be increased by temporarily tolerating a full pipe flow condition, the complex dynamics of water–air mixture occurring in vertical dropshafts can largely restrict the overall conveyance capacity of drainage systems. In this study, the hydraulic performance of plunging flow dropshafts is investigated experimentally with respect to their conveyance capacity. The model dropshaft consisted of an upstream horizontal inflow pipe, a vertical circular shaft, and an outflow pipe discharging to the atmosphere. Five setups were built with Ds/Difrom 1.0 to 3.0 for the range of drop heights H/Ds= 3.0 to 21.0, where Diis the inlet pipe diameter, Dsthe shaft diameter, and H the drop height. A wide range of discharges up to Q* = 25 was tested, where Q* = Q/(gDi5)(1/2). Flow patterns recognized within the shaft (free flow, surface roller, plug flow, slug flow, and full pipe flow) help to assess the two stages of choking: the incipient and fully choked state. Criteria to predict choking occurrences were developed experimentally. The flow is considered to reach its conveyance capacity when an incipient choking state is visible. For a typical dropshaft with Ds/Di= 2, Q* was found to be approximately 5.

Energy losses at three-way circular drop manholes under surcharged conditions

Energy loss at manholes is of importance in the design of storm sewer networks and in flood-analysis. Some researchers have already investigated the energy loss at three-way manholes under surcharged conditions. However, formulation to calculate the energy loss at manholes, including all variables of structural elements of the pipes and of the manhole has not yet been accomplished. Therefore, more study to formulate the energy loss at three-way drop manholes is needed. In this study, the ratio of the diameter between inflow pipes and an outflow pipe, the ratio of flow rates between those pipes, water depth in a manhole and the drop gaps between those pipes are considered and the energy loss at three-way circular drop manholes is examined. Finally, a modified formula, more accurate than that in the U.S. Federal Highway Administration's 2001 Urban Drainage Design Manual is proposed. The proposed formula takes the influence of the ratio of the diameter between inflow pipes and outflow pipe and drop gaps between those pipes into consideration. The calculated energy loss coefficients in both straight-through and lateral pipes successfully reproduce the measured values.

ENERGY LOSS AT THREE-WAY CIRCULAR MANHOLE UNDER SURCHARGE FLOW

The energy loss at manholes is of importance in the design of storm sewer networks and in the flood-analysis. Some researchers have already investigated the energy loss at three-way manholes. However, formulation on the energy loss at three-way drop manholes has not been enough studied yet. In this study, firstly the ratio between the diameter of an inflow pipe and that of an outflow pipe, the ratio of flow rates between those pipes, water depth in a manhole and a drop between those pipes were considered, and secondly the energy loss at three-way circular drop manholes was examined. Thirdly a modified formula which is more accurate than that in Urban Drainage Design Manual (USA, 2001) is proposed. In the proposed formula, influence of the ratio of the diameter among inflow pipes and an outflow pipe and drop gaps between inflow pipes and an outflow pipe are considered. Calculated energy loss coefficients in both straight through and lateral pipes reproduce measured values.

INVESTIGATION INTO HEAVY METALS IN STORM WASTEWATER FROM VILNIUS ŽIRMŪNAI DISTRICT AND POLLUTANTITS SPREAD MODEL IN NERIS RIVER

The paper discusses investigation into uncleaned storm wastewater pollution with heavy metals in Vilnius Žirmūnai district. The goal is to determine the dependency of storm wastewater pollution with heavy metals on transport intensity. After determining this dependency, sweeps from street points is experimentally studied with the most intensive transport flows. As the street sweeps together with storm wastewater are both outflow from streets and through outflow pipes directly to the Neris, heavy metals in the outflow pipe sludge are also studied for each pool. The following heavy metals have been experimentally studied: Pb, Mn, Cr, Zn, Cu, Ni. The flame atomic absorption spectrometry method was used. The process of analysis is explained in short and its results are provided. A mathematical model by Phoenics 3.5 version program showing the distribution of heavy metals in the Neris river stream is made on the basis of the results received. Santrauka Nagrinejama nevalomu lietaus nuoteku tarša sunkiaisiais metalais Vilniaus Žirmūnu rajone. Siekiant nustatyti ryši tarp lietaus nuoteku užterštumo sunkiaisiais metalais nuo transporto eksperimentiškai tiriamos sašlavos nuo gatviu, kuriuos su lietumi išplaunamos i upe. Taip pat tiriami sunkieji metalai iš lietaus ištekamuju vamzdžiu i Neri. Eksperimentiškai nagrinejami šie sunkieji metalai: Pb, Mn, Cr, Zn, Cu, Ni. Tam panaudotas liepsnos absorbcijos spektrometrinis metodas. Trumpai aptariamas analizes procesas ir pateikiami tyrimu rezultatai. Remiantis gautais rezultatais sudaromas matematinis teršalu sklaidos modelis Neries upes tekmeje taikant Phoenics 3.5 programa. Резюме Исследуется загрязнение неочищаемых дождевых стоков тяжелыми металлами в районе Жирмунай г. Вильнюса. Для определения степени загрязнения дождевых стоков тяжелыми металлами от транспорта экспериментально исследовался мусор с улиц, вымываемый с дождем в реку. Также исследовались тяжелые металлы в дождевых стоках, попадающих в реку Нерис. Экспериментально с применением абсорбционно-спектрометрического метода исследовались тяжелые металлы Pb, Mn, Cr, Zn, Cu, Ni. Рассмотрен процесс анализа и результаты исследований. На основе полученных результатов составлена математическая модель распределения загрязняющих веществ в течении реки.

Intravascular Functional Maps of Common Neurovascular Lesions Derived From Volumetric 4D CT Data

Current computed tomography angiography (CTA) postprocessing tools do not support quantitative assessment of intravascular physiology. Dynamic volumetric CT, acquired at a sufficiently high temporal resolution, is ideal for such analysis. Following preliminary experiments in flow phantoms, we examine the segmentation of blood vessels from 4D CT angiography by curve fit and encoding of functional blood flow information into the resulting functional intravascular maps. Flow phantoms were constructed consisting of a single pipe input and 4 simultaneous outputs of varying flow rates. Two outflow pipe diameters were tested. Bolus transit time (TT), time to peak (TTP), and time of arrival (TOA) were analyzed using contrast bolus profiles generated from 4D volumetric CT examinations on a 320 detector scanner in regions of interest placed 10 cm apart in all outflow pipes. Six subjects with various neurovascular lesions were next examined using a volumetric contrast-enhanced 4D CT angiography protocol. Segmentation was performed by quadratic curve fit after comparative analysis and optimization of the segmentation technique using quadratic curves, the gamma variate function, and a simplified formulation of the gamma variate function. After segmentation, quantitative analysis of spatially congruent intravascular voxels including TTP, rise, TT, and slope of the contrast upstroke was employed to encode physiologic information into the segmentations and produce intravascular functional maps. Comparison was made in each case to the patient's routine imaging. Increasing volumetric flow rates correspond to reduction of bolus TT in flow phantoms. TT elongation was observed as the contrast bolus moved distally in all pipes, with greater elongation seen at slower flow rates and larger pipe diameters. A greater difference was observed between TTP proximally and distally in pipes compared with TOA, an effect most prominent at slower flow rates and larger pipe lumens, and thus TTP was chosen for functional encoding into segmentations of the clinical series. In vivo, the quadratic function demonstrated the lowest coefficient of variation when fit to intravascular time density series and outperformed 2 formulations of the gamma variate function. After segmentation with quadratic curves, Gaussian distributions were chosen over gamma variate functions to characterize contrast bolus profiles while neglecting recirculation and to calculate functional parameters for spatial encoding. Intravascular functional maps free of bone artifacts were created in every case that demonstrated all appropriate vessels and showed agreement with conventional imaging modalities in terms of vessel delineation and the diagnosis of vascular pathology. The most useful and interesting functional maps are discussed in each case. The above approach to quantitative CT angiography provides a method of evaluating dynamic CTA data by means of intravascular functional maps. The techniques are broadly applicable in the clinical assessment of a variety of vascular diseases.

NITROGEN LEACHING IN FIELD-GROWN LETTUCE

Previous studies in southern Sweden have shown that during a season of intensive production of field-grown lettuce there may be a progressive accumulation in the soil profile of large amounts of residual nitrogen, which subsequently leach into the surrounding environment. In spring 2003 an observation field was established on the southern aspect of the Bjarehalvon peninsula. The measuring station was connected to the outflow pipe of a well-delineated and documented drainage system comprising approx. 0.8 ha. The water flow from the drainage system was measured using a triangular weir (90°). Water was sampled automatically by extracting flow-proportional (biweekly) bulk samples (one sub-sample per 0.1 mm runoff) with a peristaltic pump connected to the datalogger. The water samples were analysed for nitrate-N and total-N. Annual leaching was calculated for the period 1 June of one growing year to 31 May in the following year. The first culture was planted in March and covered with horticultural fleece. Culture 2 was sown at the end of June or in the first half of July. On average for the three years, the total amount of N supplied was approx. 350 kg/ha bed area and year, or around 260 kg/ha field area and year. The reported annual yields of commercial produce were between 30 and 35 tonnes fresh weight per ha field area. On the same basis, the N-harvest was around 90 kg/ha field area and year, giving an N use efficiency of approx. 34%. Average for annual precipitation and irrigation was 676 mm respectively 62 mm, and annual mean runoff from the drainage system was 228 mm per season. The weighted mean concentrations of nitrate-N and total-N in drainage water were 38 and 42 mg N/L resp., giving an annual N-leaching of 87 and 92 kg N/ha resp.