Effects Of Water Exchange Research Articles

Evaluating the effects of water exchange between surface rivers and karst aquifers on surface flood simulations at different watershed scales

The complex subsurface conditions and spatial anisotropy of water-bearing media in karst basins result in much more variable runoff generation and confluence processes and water circulation than those in nonkarst basins. Therefore, accurate flood forecasting is more difficult in karst areas, and it is challenging to accurately quantify the water exchange relationship between surface rivers and karst aquifers. To provide key technical support for accurate flood forecasts in karst basins, this study improved a distributed physical hydrologic model, the Karst-Liuxihe model, by improving the runoff generation and confluence algorithms and the parameter optimization algorithm to simulate surface floods in three different karst watersheds in southern China. Additionally, in the model calculations, this study focused on the influence of water exchange on surface flood simulations in changing watersheds. The results showed that for the largest basin, Xijiang Basin (353,100 km2), considering or not considering the water exchange between the surface river and karst aquifer had little effect on the surface flood simulation results. However, this water exchange had a great effect on the surface simulations for the smallest basin, the Beijiang Basin (1,700 km2). For instance, the simulated average peak flow showed a 29 % difference, and the total amount of flooding showed a 25 % difference between dry years and normal years. Therefore, when forecasting surface floods in small karst areas, the water exchange relationship between surface rivers and karst aquifers must be considered. The results showed that the impact of groundwater on surface rivers can be disregarded when forecasting surface floods in the large Xijiang karst basin and can be treated directly as surface flood forecasting in nonkarst areas. The application of this strategy will greatly simplify the cost of hydrologic modelling in the Xijiang basin. By improving the Karst-Liuxihe model, the accuracy of its flood simulation and general applicability in karst basins were greatly enhanced. The improvement in the karst hydrological model in this study provides a good tool for flood simulation and forecasting in the karst regions of Southwest China.

The atomic structure and dynamics at the CaCO3 vaterite-water interface: A classical molecular dynamics study.

Classical molecular and lattice dynamics were applied to explore the structure and dynamics of water on different surfaces of vaterite, the least abundant calcium carbonate polymorph. Surfaces were generated starting from the three possible structural models for vaterite (monoclinic, hexagonal/trigonal, and triclinic) and pre-screened using their surface energies in an implicit solvent. Surfaces with energies lower than 0.55 J/m2 were then run in explicit water. The majority of these surfaces dissolve in less than 100 ns, highlighting the low stability of this phase in abiotic environments. Three stable surfaces were identified; they exhibited only minor structural changes when in contact with explicit water and did not show any tendency to dissolve during 1 µs molecular dynamics simulations. The computed water density profiles show that all these surfaces have two distinct hydration layers. The water residence time at the various calcium sites was computed to be within 0.7 and 20.5 ns, which suggests that specific Ca ions will be more readily available to bind with organic molecules present in solution. This analysis is a step forward in understanding the structure of this complex mineral and its role in biomineralization, as it provides a solid theoretical background to explore its surface chemistry. In particular, this study provides realistic surface models and predicts the effect of water exchange at the surface active sites on the adsorption of other molecules.

The effect of water exchange on the leaching of alum shale

In recent years, there has been an increasing focus on the adverse environmental effects from naturally occurring radioactive materials (NORM). Acid rock drainage (ARD) produced by debris from mining and construction work is a major environmental issue, leading to release of highly acidic water as well as both NORM and stable trace elements. Batch leaching experiments with alum shale demonstrated that exchange of water will increase leaching of elements whose mobility is limited by concentration effects, such as Ba and the extremely radiotoxic, naturally occurring uranium daughter 226Ra. Periods of drying the alum shale in air increased leaching of Li, V, Mo and 226Ra, increasing their mobility in the environment. Acid production from sulphide oxidation did not cause pH values below 6.4 in the 28 weeks experiment. However, exchange of water did lead to reduction of inherent buffer capacity of the alum shale, which increases the risk of ARD as well as likely reducing the time before onset of ARD.

Effects of water flow rates on growth and welfare of Nile tilapia (Oreochromis niloticus) reared in a recirculating aquaculture system

The effects of water exchange on growth and welfare of Nile tilapia (Oreochromis niloticus) were investigated in a recirculating aquaculture system during an 8-week trial. Fish of initial body mass of ~ 27 g (n = 8 per tank) were reared in 60-L tanks with water exchange rates, corresponding to 1.5 (LE), 3 (ME) and 6 (HE) tank volumes/h. Treatments were triplicated and fish were fed at 3% of their biomass each day. The LE treatment resulted in significantly higher (p < 0.05) levels of ammonia nitrogen and phosphate in the culture water relative to the higher water exchange treatments. The specific growth rate (SGR) of fish cultured under the HE treatment (2.74% day−1) was significantly higher than the SGR (2.21% day−1) of the LE fish. Mean final body weights of the LE, ME and HE fish were 97.67 ± 8.13, 110.50 ± 22.45 and 123.92 ± 10.00 g, respectively. Higher prevalence of dermal ulcerations, oral lesions and poor fin conditions were associated with the LE and ME fish. After 4 weeks, 34 and 24% of the LE and ME fish, respectively, had advanced mouth lesions compared to 0% for the HE fish. Haematological indicators of long-term oxygen stress and disease conditions, as evidenced by erythrocyte and platelet indices, were generally higher in fish under the LE and ME treatments. This study has shown that although the Nile tilapia is a hardy species, long-term exposure to poor water conditions can result in reduced growth and compromised welfare.

Two-dimensional magnetization-transfer - CPMG MRI reveals tract-specific signatures in fixed rat spinal cord.

Multiexponential T2 (MET2) Relaxometry and Magnetization Transfer (MT) are among the most promising MRI-derived techniques for white matter (WM) characterization. Both techniques are shown to have histologically correlated sensitivity to myelin, but these correlations are not fully understood. Furthermore, MET2 and MT report on different WM features, thus they can be considered specific to different (patho)physiological states. Two-dimensional studies potentially resolving interactions, such as those commonly used in NMR, have been rarely performed in this context. Here, we investigated how off-resonance irradiation affects different MET2 components in fixed rat spinal cord white matter at 16.4 T. These 2D MT-MET2 experiments reveal that MT affects both short and long T2 components in a tract-specific fashion. The spatially distinct signal modulations enhanced contrast between microstructurally-distinct spinal cord tracts. Two hypotheses to explain these findings were proposed: either selective elimination of a short T2 component through pre-saturation combines with intercompartmental water exchange effects occurring on the irradiation timescale; or, other macromolecular species that exist within the tissue - other than myelin - such as neurofilaments, may be involved in the apparent microstructural segregation of the spinal cord (SC) from MET2. Though further investigation is required to elucidate the underlying mechanism, this phenomenon adds a new dimension for WM characterization.

Coastal water environment regulation and simulation based on tidal power control

As the carrier of water resources, water environment and water ecology, river course is very important to human and ecological environment in coastal areas. The rapid economic development of coastal areas needs to take into account the improvement of regional water environment in order to achieve a higher level of development. The characteristics of coastal water environment are closely related to tidal fluctuation. It is an important direction for coastal water control to improve the water environment and restore the self-purification capacity of the river by guiding and draining the tidal power. In this paper, the YACHONG River Basin, which borders Macau and Zhuhai, is selected as the study area. The semi-exchange period and water exchange rate are taken as the main evaluation indexes. The water quantity and quality model is used to simulate the scenario model and analyze the effect of water diversion and drainage regulation in different tidal periods. The results show that, compared with the drainage dispatch during spring tide, the drainage dispatch during neap tide prolongs the water exchange time, and the effect of water exchange is obviously better than that during spring tide. The research results of this paper provide reference for water environmental regulation in coastal area.

Effect of myelin water exchange on DTI-derived parameters in diffusion MRI: Elucidation of TE dependence.

Water exchange exists between different neuronal compartments of brain tissue but is often ignored in most diffusion models. The goal of the current study was to demonstrate the dependence of diffusion measurements on echo time (TE) in the human brain and to investigate the underlying effects of myelin water exchange. Five healthy subjects were examined with single-shot pulsed-gradient spin-echo echo-planar imaging with fixed duration (δ) and separation (Δ) of diffusion gradient pulses and a set of varying TEs. The effects of water exchange and intrinsic T2 difference in cellular environments were investigated with Monte Carlo simulations. Both in vivo measurements and simulations showed that fractional anisotropy (FA) and axial diffusivity (AD) had positive correlations with TE, while radial diffusivity (RD) showed a negative correlation, which is consistent with a previous study. The simulation results further indicated the sensitivity of TE dependence to the change of g-ratio. The exchange between myelin and intra/extra-axonal water pools often plays a non-negligible role in the observed TE dependence of diffusion parameters, which may accompany or alter the effect of intrinsic T2 in causing such dependence. The TE dependence may potentially serve as a biomarker for demyelination processes (e.g., in multiple sclerosis and Alzheimer's disease). Magn Reson Med 79:1650-1660, 2018. © 2017 International Society for Magnetic Resonance in Medicine.

Multi-gradient-echo myelin water fraction imaging: Comparison to the multi-echo-spin-echo technique.

Myelin water fraction (MWF) mapping based on multi-gradient recalled-echo (MGRE) imaging has been proposed as an alternative to the conventional multi-echo-spin-echo (MESE) approach. In this work, we performed a comparative study of MESE and MGRE-derived MWFs in the same subject group. MESE and MGRE data were acquired in 12 healthy volunteers at 3T. T2* decay curves were corrected for the effects of field inhomogeneities and multicomponent analysis of T2 and T2* signals was performed using non-negative least-squares fitting. When comparing MGRE and MESE-MWFs across volunteers, no significant differences were observed between average values in WM, deep GM (dGM), and cortical GM (cGM) that were (14 ± 3%), (6 ± 2%), and (8 ± 2%) for MGRE, and (13 ± 2%), (6 ± 1%), and (7 ± 1%), respectively, for MESE. The MGRE and MESE-MWFs showed a strong correlation (r2 = 0.84) and Bland-Altman analysis revealed a small positive bias of (0.8 ± 1.6%) (absolute difference) for the MGRE-MWF. Overall, we observed excellent agreement between the two techniques. The small positive bias of the MGRE-MWF is thought to be a consequence of its potentially reduced sensitivity to water exchange effects, compared to the MESE-MWF. This work suggests that with careful correction for the effects of field inhomogeneities, MGRE-MWF imaging is a promising alternative to the MESE approach. Magn Reson Med 79:1439-1446, 2018. © 2017 International Society for Magnetic Resonance in Medicine.

Effects of water exchange and reducing dietary vitamin and mineral supplementation on survival and growth of Litopenaeus vannamei

A growth trial was conducted with Litopenaeus vannamei to evaluate effects of dietary vitamin and mineral supplementation (VMS) and water exchange on survival, growth and water quality. Four levels (0, 25, 50 and 100%) of VMS were evaluated using a 20% protein base diet. Postlarvae weighing 0.22 g were stocked for 26 days with either zero or high (5440% daily) water exchange. Growth was greater at zero than high exchange. However, growth was not affected by the level of VMS at both high and zero exchange. Survival for 0% VMS was lower than survivals for 25 to 100% VMS at high exchange. For 0% VMS, survival at high exchange was lower than survival at zero exchange. Results suggested that at zero water exchange, diets without VMS can replace diets with VMS without reducing survival.

Investigating the impacts of DNA binding mode and sequence on thermodynamic quantities and water exchange values for two small molecule drugs

Doxorubicin and nogalamycin are antitumor antibiotics that interact with DNA via intercalation and threading mechanisms, respectively. Because the importance of water, particularly its impact on entropy changes, has been established in other biological processes, we investigated the role of water in these two drug-DNA binding events. We used the osmotic stress method to calculate the number of water molecules exchanged (Δnwater), and isothermal titration calorimetry to measure Kbinding, ΔH, and ΔS for two synthetic DNAs, poly(dA·dT) and poly(dG·dC), and calf thymus DNA (CT DNA). For nogalamycin, Δnwater<0 for CT DNA and poly(dG·dC). For doxorubicin, Δnwater>0 for CT DNA and Δnwater<0 for poly(dG·dC). For poly(dA·dT), Δnwater~0 with both drugs. Net enthalpy changes were always negative, but net entropy changes depended on the drug. The effect of water exchange on the overall sign of entropy change appears to be smaller than other contributions.

Effects of transcytolemmal water exchange on the assessment of myocardial extracellular volume with cardiovascular MRI.

Quantitative analysis of the myocardial interstitial space is gaining increased interest as a biomarker in the MRI and clinical cardiovascular communities. To investigate the effect of water exchange on the calculation of myocardial extracellular volume (ECV), we employed two tissue models: the standard ECV two-point model (SM) and the shutter speed model (SSM). Twenty individuals (18 men and two women; age 61.9 ± 10.3 years) underwent MRI at 1.5 T with pre-contrast and post-contrast dynamic T1 quantification. Means, standard deviations and ranges for SM and SSM model parameters were calculated. Infarct and viable myocardial model parameters as well as apparent ECV values calculated with the SM and SSM were statistically compared. Viable ECV(SM) remained temporally constant (27.3-28.0%: P = 0.5) and infarcted myocardial ECV(SM) changed significantly (49.3-58.8%; P < 0.001), reaching a steady-state value after 15 min. The intracellular lifetime of water was three times greater in infarcted myocardium when compared with viable myocardium (τi: 66.6 ± 115 versus 208.7 ± 72.7 ms) and accompanied a twofold increase in ECV (ECV(SSM) : 30.3 ± 11.1 versus 71.0 ± 13.1%; P < 0.001). There was a consistent significant difference in ECV values of infarcted myocardium at different timepoints between the SM and SSM, but not viable myocardium, presumably due to slower water exchange. In summary, we found a significant change in apparent ECV and water exchange in infarcted myocardium when compared with viable myocardium. This was visualized by changes in dynamic contrast enhanced curve shapes and quantified using the SSM as not only an increase in apparent ECV but also a decrease in water exchange.

Effects of water exchange on water quality parameters, nutrient utilization and growth of African catfish (Clarias gariepinus)

This experiment investigated the effects of water exchange on water quality parameters and growth of Clarias gariepinus. 225 C. gariepinus of mean weight 2.60 ± 0.01 g were stocked at 15 fish per treatment in three replicates. Water quality and growth parameters such as mean weight gain (MWG), specific growth rate (SGR), food conversion ratio (FCR) and protein efficiency ratio (PER) were calculated using standard procedures. pH of T3 (9.15) was significantly higher p<0.05 than other treatments. Dissolved oxygen indicated that T5 (3.45 mg/l) was significantly lower than other treatments. The ammonia values revealed that T5 (0.08 mg/l) was significantly higher p < 0.05 than other treatments. MWG of T1 (29.43 g) and T2 (27.77 g) were significantly higher p < 0.05 than T3, T4 and T5. SGR and PER of T1 (2.26%), (5.74) and T2 (2.22%) (5.31) increased significantly p < 0.05 than other treatments. The FCR of T1 (0.40) and T2 (0.42) were significantly lower than other treatments. It was evident in this study that exchange of water has an increase or decrease in the state of water quality parameters and growth of a fish. Key words: Water exchange, water quality parameters, proximate compositionfish carcass, growth parameters, Clarias gariepinus.

Sa1430 Outcomes of the Water Exchange Technique During Screening Colonoscopy At an Academic Medical Center

Prior studies of water-assisted colonoscopy, mostly in men, have demonstrated less insertion pain, better tolerance of minimal sedation, and a reduced need for pain medication compared with standard air insufflation (AI) colonoscopy. Effects on adenoma detection rates (ADRs) have been mixed. Aims: To evaluate and compare the effect of Water Exchange (WE) colonoscopy on procedure -and patient-related outcomes with conventional air insufflation (AI) colonoscopy in a cohort of men and women undergoing screening colonoscopy at an academic medical center.

Measurement of myocardial blood volume and water exchange using ferumoxytol

Background Accurate, quantitative mapping of myocardial blood volume (MBV) could potentially serve as a novel biomarker for cardiovascular disease. However, quantitative measurement of MBV can be technically difficult. Typical gadolinium based contrast agents leak out of the vasculature and are more suited towards measuring extracellular volume than MBV. Even with a completely intravascular contrast agent, water exchange between the intraand extravascular comparments has been shown to introduce error into MBV measurements. The Hazlewood two comparment model has been used to describe water exchange effects, and Donahue et al adapted this model to quantify the error water exchange introduces into blood volume measurements. Here we use ferumoxytol, a wholly intravascular iron based contrast agent, to characterize water exchange and quantify blood volume in a group of healthy volunteers.

Measurement of regional cerebral glucose uptake by magnetic resonance spin-lock imaging

PurposeThe regional uptake of glucose in rat brain in vivo was measured at high resolution using spin-lock magnetic resonance imaging after infusion of the glucose analogue 2-deoxy-d-glucose (2DG). Previous studies of glucose metabolism have used 13C-labeled 2DG and NMR spectroscopy, 18F-labeled fluorodeoxyglucose (FDG) and PET, or chemical exchange saturation transfer (CEST) MRI, all of which have practical limitations. Our goal was to explore the ability of spin-lock sequences to detect specific chemically-exchanging species in vivo and to compare the effects of 2DG in brain tissue on CEST images. MethodsNumerical simulations of R1p and CEST contrasts for a variety of sample parameters were performed to evaluate the potential specificity of each method for detecting the exchange contributions of 2DG. Experimental measurements were made in tissue phantoms and in rat brain in vivo which demonstrated the ability of spin-lock sequences for detecting 2DG. ResultsR1p contrast acquired with appropriate spin-lock sequences can isolate the contribution of exchanging protons in 2DG in vivo and appears to have better sensitivity and more specificity to 2DG–water exchange effects than CEST. ConclusionSpin-lock imaging provides a novel approach to the detection and measurement of glucose uptake in brain in vivo.

Cardiac T 1 Imaging

T(1) mapping of the heart has evolved into a valuable tool to evaluate myocardial tissue properties, with or without contrast injection, including assessment of myocardial edema and free water content, extracellular volume (expansion), and most recently cardiomyocyte hypertrophy. The magnetic resonance imaging pulse sequence techniques developed for these applications have had to address at least 2 important considerations for cardiac applications: measure magnetization-inversion recoveries during cardiac motion with sufficient temporal resolution for the shortest expected T(1) values, and, second, obtain these measurements within a time during which a patient can comfortably suspend breathing. So-called Look-Locker techniques, and variants thereof, which all sample multiple points of a magnetization recovery after each magnetization preparation, have therefore become a mainstay in this field. The rapid pace of advances and new findings based on cardiac T(1) mapping for assessment of diffuse fibrosis or myocardial edema show that these techniques enrich the capabilities of magnetic resonance imaging for myocardial tissue profiling, which is arguably unmatched by other cardiac imaging modalities.

마산만 재해방지시설을 이용한 해수교환 방안에 관한 연구

마산만은 반폐쇄성 해역으로, 느린 유속과 육상오염물질의 하천부하 등으로 인해 심각한 수질문제를 가지고 있으며, 동시에 폭풍해일에 취약한 입지적 특성을 나타내고 있다. 이 중 폭풍해일 저감대책으로 제시된 재해방지시설을 운용함과 동시에 이를 마산만 내측 수질개선에 활용하는 방안을 모색하였다. 즉, 재해방지시설을 가동하여 마산만 내측과 외측의 수위조건이 다를 때 발생하는 수두차를 이용하여 만 내 외의 해수를 교환하였다. 재해방지시설의 위치를 기존 만 입구부, 마창대교 인근, 그리고 돝섬 인근으로 가정하였으며, 선박운항 횟수와 연간조위를 분석하여 통항빈도가 가장 낮은 새벽시간(01~05) 및 수두차가 가장 큰 대조기에 운용된다고 가정하였다. 또한, 재해방지시설과 함께 약 10km 길이의 유출 입 관로를 통한 내 외해수의 해수교환 촉진을 위한 추가 실험안을 구성하였다. 수치모의 결과, 현재상태의 경우 마산만 전체 해수교환율은 38.62%을 나타냈으며, 모든 실험안에서 마산만 내 모든 구역에서 꾸준한 증가 추세를 보이고 있다. 이에 반해, 마산만 입구부와 비교한 마산만 내측의 해수교환율은 매우 낮게 나타나 반폐쇄성 내만해역의 특성을 잘 재현하는 것으로 판단된다. 재해방지시설과 관로를 이용한 실험안을 분석한 결과, 현재상태와 비교하여 재해방지시설을 운용한 경우 해수교환율이 높고, 그 운용빈도가 많아질수록 더 많은 순환이 이루어지는 것으로 나타났다. 또한, 재해방지시설에 의해 발생된 수두차를 이용하여 관로를 통해 해수를 유입 혹은 유출한 경우 마산만 가장 내측의 수질이 개선되는 것으로 나타났다. 재해방지시설의 위치는 마창대교 남측과 비교하여 마산만 입구와 돝섬에 위치한 경우 해수교환 효과가 더 좋게 나타났다. 한편 마산만 전체영역에 대한 해수교환율은 만 입구에 재해방지시설이 위치한 경우가 돝섬에 위치한 경우보다 높지만, 마산만 내측을 포함한 해수교환율은 반대로 돝섬에 위치한 경우가 더 높게 나타났다. Masan bay with a semi-enclosed waters has serious water quality problems due to the low flow and river pollution load from land, and shows the vulnerable locational characteristics to storm surge. We are seeking the way of both operating disaster prevention facilities and water quality improvement measures in the bay. That is, the water was exchanged using the head difference occurred by operating disaster prevention facilities. The location of disaster prevention facilities was assumed to be in the inlet of the bay, in the vicinity of Machang bridge, and in the vicinity of Dot island and the operation time was assumed to be early morning hours(01~05) considering the number of shipping passage and annual tide, and spring tide of the largest head difference. In addition, the experiment case of water exchange including the in-outflow feeder pipe was tested. According to the simulation results, water exchange rate in all experiments has shown a steady increase. Water exchange rate of the whole of Masan bay in the case of present is 38.62%. The water exchange rate of the inside of Masan bay compared with the inlet of bay, appeared to be very low. Thus, we judged that the characteristics of semi-enclosed waters were well reproduced. On the results of the experiment of disaster prevention facilities and in-outflow feeder pipe, the case of the operation of disaster prevention facilities, water exchage rate is high compared with the case of present. And, the higer the operating frequency, the more water exchange is appeared. The cases of water exchange prevention facilities through the in-outflow feeder pipe caused by the head difference, also showed the higest improvement of the water quality. Compared with the south of Machang bridge, the effect of water exchange was better in the inlet of Masan bay and Dot island. On the other hand, the inlet of Masan bay is higer than Dot island as for water exchange of the whole of Masan bay, but opposite, water change rate including Masan inside was higher in the case of Dot island.

Effect of Water Exchange and Mechanical Aeration on Grow-out of the Amazon River Prawn in Ponds

Exchange and aeration of pond water are common practices in semi-intensive freshwater prawn culture, but there is lack of scientifically based information on the results. We evaluated the effects of water flow through the ponds and mechanical aeration in semi-intensive cultures of Macrobrachium amazonicum. A total of 40 juveniles/m 2 were stocked for 4 mo in 12 earthen ponds. Four randomly assigned treatments were applied: no aeration +no water exchange (NN), diurnal aeration +no water exchange (DA), nocturnal aeration +no water exchange (NA), and continuous water flow (CF). Temperature, pH, total suspended solids, and soluble orthophosphate in the water column did not differ among treatments. Dissolved oxygen (DO) concentrations in ponds with nocturnal aeration were significantly higher than in other treatments. The concentration of inorganic nitrogen was significantly higher in the CF treatment, whereas organic nitrogen was higher in treatments NN, DA, and NA. This suggests that primary production is higher in static ponds. Thermal stratification started at 0900 h, and the maximum difference between surface and bottom temperature varied from 1.5 (CF) to 2.8 C (NN). The difference between DO levels in the surface and bottom water of the ponds began to appear at 0800 h and varied from 0.50 (CF) to 5.23 mg/L (NN). Diurnal aeration and high continuous water flow were efficient in disrupting the stratification. No significant difference was found for survival, mean weight, apparent feed conversion rate, and productivity among treatments. Thus, disrupting water stratification, aerating ponds at night, or exchanging the pond water are ineffective in Amazon River prawn farming in semi-intensive systems, at least for stocking densities lower than 40 individuals/m 2 . About 1000 kg of Amazon River prawn can be produced in static ponds with no aeration in approximately 4 mo. This management strategy saves water and energy and reduces production costs.

Water exchange-minimizing DCE-MRI protocol to detect changes in tumor vascular parameters: effect of bevacizumab/paclitaxel combination therapy

The purpose of this study was to assess changes in the tumor microvasculature induced by combination antiangiogenic therapy in MCF-7 breast tumor mouse models, using a noninvasive DCE-MRI method that minimizes the effect of water exchange. 3D quantitative DCE-MRI images were acquired with a heavily T1-weighted saturation recovery gradient echo sequence with a recovery delay of 20 ms. Tumor vascular volume (VV) and vascular permeability-surface area product (PS) were obtained through a linear regression of the albumin-Gd-DTPA-enhanced dynamic image intensity on MCF-7 breast tumor mouse models treated with combination bevacizumab/paclitaxel therapy. Measured tumor VV values were significantly higher than the values that have been reported previously using quantitative T1 mapping, and are in good agreement with micro-CT (computed tomography) results reported earlier from other tumor models. A trend of decreasing tumor PS was detected in the group of MCF-7 tumor bearing mice treated with the bevacizumab/paclitaxel combination regimen. VV and PS maps obtained by a heavily T1-weighted acquisition protocol revealed the large peripheral blood vessels as well as the permeable areas within the tumor. A 12-day/three-dose combination treatment of bevacizumab and paclitaxel resulted in delayed tumor growth and a trend of decreasing tumor vascular permeability surface area product.

Water exchange effect on eutrophication in landscape water body supplemented by treated wastewater

Artificial landscape water bodies filled by treated wastewater pose a risk of developing algal blooms due to high nutrient levels of treated wastewater. In this study, water exchange experiments were conducted using treated wastewater in an artificial landscape pond, and a eutrophication model was calibrated and applied to evaluate the effects of water exchange on algae growth in the pond. The results indicate that the joint dilution process and nutrient supply process of water exchange initially cause the algae level to rise and then rapidly decline as the hydraulic resident time (HRT) decreases, and HRT has a critical point at which the pond faces the highest risk of algal bloom. The study also indicates that phosphorus (instead of nitrogen) is the primary limiting factor of algae growth. Therefore, the critical HRT should be avoided and phosphorus is the target pollutant to be controlled in landscape pond water management.