The water level of the Three Gorges Reservoir(TGR) rose to 172.5 m in two stages from September to November,2008.The hydrodynamic parameters and water quality parameters(e.g.flow velocity,temperature,turbidity and nut...The water level of the Three Gorges Reservoir(TGR) rose to 172.5 m in two stages from September to November,2008.The hydrodynamic parameters and water quality parameters(e.g.flow velocity,temperature,turbidity and nutrient content) had been continuously monitored to reveal the influence of the impounding process of the TGR on the water eutrophication in the Xiangxi Bay(XXB).The maximal daily rise of the water level of the TGR was about 2.38 m.The water exchange between the mainstream(the Changjiang River) and the XXB of the TGR was enhanced by density current,and its main characteristics were a density-stratified flow in different directions.The water exchange reduced the differences of the water quality parameters(for example,temperature,turbidity,nutrient level,pH,etc.) between the mainstream and the XXB during the impounding process.Meanwhile,the water stability index in the mainstream remained small but it was lowered in the XXB.The main causes included the dilution by water of lower concentration of the chlorophyll a(Chl.a) entering from the mainstream,the decline of the water stability,and the increase of suspended silt,which induced the Chl.a to decrease in the XXB during the impounding process.The grade of the water eutrophication changed from middle eutrophic level to mesotrophic state in the process.However,as available nutrients were imported into the XXB from the mainstream during the impounding process the risk of water eutrophication increases in the XXB in the future.展开更多
Background Atrial fibrillation (AF) is the most common supraventriculararrhythmia in clinical practice. Chronic atrial fibrillation (CAF) is associated with ionicremodeling. However, little is known about the activity...Background Atrial fibrillation (AF) is the most common supraventriculararrhythmia in clinical practice. Chronic atrial fibrillation (CAF) is associated with ionicremodeling. However, little is known about the activity of ATP-sensitive potassium current I_(K,ATP) during CAF. So we studied the changes of I_(K, ATP) density and allosteric modulation ofATP-sensitivity by intracellular pH during CAF. Methods Myocardium samples were obtained from theright auricular appendage of patients with rheumatic heart disease complicated with valvular diseasein sinus rhythm (SR) or CAF. There were 14 patients in SR group and 9 patients in CAF group. Singleatrial cells were isolated using an enzyme dispersion technique. IKiATP was recorded using thewhole-cell and inside-out configuration of voltage-clamp techniques. In whole-cell model, myocytesof SR and CAF groups were perfused with simulated ischemic solution to elicit I_(K, ATP). Ininside-out configuration, the internal patch membranes were exposed to different ATP concentrationsin pH 7. 4 and 6. 8. Results Under simulated ischemia, I_(K, ATP) current density of CAF group wassignificantly higher than in SR group [(83.5 ± 10.8) vs. (58.7 ±8.4) pA/pF, P < 0. 01 ] . I_(K,ATP) of the two groups showed ATP concentration-dependent inhibition. The ATP concentration for 50%current inhibition (IC_(50) ) for the SR group was significantly different in pH 7. 4 and pH 6. 8(24 vs. 74 μmol/L, P < 0. 01). The IC_(50) did not change significantly in CAF group when the pHdecreased from 7. 4 to 6. 8. Conclusions During CAF, I_(K, ATP) current density was increased andits allosteric modulation of ATP-sensitivity by intracellular pH was diminished.展开更多
Harmful algal blooms, which frequently occur in different tributaries, have become a serious water quality problem of the Three Gorges Reservoir (TGR) since its initial filling. A three-year monitoring campaign from 2...Harmful algal blooms, which frequently occur in different tributaries, have become a serious water quality problem of the Three Gorges Reservoir (TGR) since its initial filling. A three-year monitoring campaign from 2008 to 2010 was conducted to identify the controlling factors of algal blooms and effective preventive measures. The following results were obtained: 1) Layered and bidirectional currents, called intrusive density currents, dominate the tributary bays of the TGR year round; 2) continuously increasing water level can make the intruding density current shift from the middle to the surface, and surface intrusive water can reduce the surface water temperature and break the stable stratification of the tributary; 3) the appearing or fading away of algal blooms is closely associated with fluctuations in the TGR water level. Thus, the water level fluctuation patterns of different "tide-types" may prevent the occurrence of algal blooms in the spring and summer, and the "stair-type" tides may control autumn blooms during the impounding period. These methods were feasible and effective throughout the actual TGR's operation in 2009 2011. These patterns formed an eco-environmentally friendly operation (EEFO) to mitigate algal blooms. As an in situ treatment with easier operation and less negative impact and loss, compared with chemical and filter-feeding fish methods, the EEFO is currently considered as the most feasible remedial measure to remit the eco-environmental problems at the Three Gorges Dam (TGD).展开更多
The Casulli's difference scheme was introduced into the three-dimensional ocean model in the present paper, and the wind-driven current and thermohaline current were simulated. The results show that, southwesterly...The Casulli's difference scheme was introduced into the three-dimensional ocean model in the present paper, and the wind-driven current and thermohaline current were simulated. The results show that, southwesterly monsoon in summer induces a clockwise circulation in the Beibu Gulf, and the density gradient induces a counter-clockwise one; but the density current is more intense than the wind- driven one in summer, espeially in surface layer. In addition, the northeasterly monsoon in winter in- duces a counter-clockwise circulation. The simulated results don't support the traditional condusion that there is a clockwise circulation in the Beibu Gulf in summer and a counter-clockwise one in winter, but support the statement that a counterclockwise circulation exists in the Beibu Gulf all year round.展开更多
Measuring the pre-breakdown current of long sparks in air is important for investigating the discharge mechanism.Since the breakdown of long air gaps is conducted by a series of streamer-leader processes,the correspon...Measuring the pre-breakdown current of long sparks in air is important for investigating the discharge mechanism.Since the breakdown of long air gaps is conducted by a series of streamer-leader processes,the corresponding current signals cover a bandwidth of 0 to more than 20 MHz.Measurement accuracy of the current from the high voltage side is affected by the displacement current and impulse electromagnetic interference.In this paper,a coaxial current sensor with a DC bandwidth of 74.45 MHz is developed.A displacement current-restrained electrode structure is proposed to reduce the equivalent capacitance between the current sensor and the ground over 30 times.Combined with the digital optical fiber synchronous acquisition unit,a current measurement system for long air gap discharge is established.For the purpose of the UHV system’s external insulation optimization design,the discharge current waveform of a 6 m rod-plane air gap under positive switching impulse voltage with 250µs and 1000µs time to crest is obtained.Discharge images and stressed voltage are combined to analyze the continuous feature of a current waveform under critical time to crest impulse and discontinuous feature under long front duration impulse.For the purposes of a lightning protection study,the current waveform of a 10 m rod-plane air gap is subjected to negative switching impulse.Finally,the pulse characteristics of the current corresponding to the single channel and branching stepped negative leader are discussed.展开更多
基金supported by the National Natural Science Foundation of China (Grant No 50679038)"115" Science and Technology Supporting of China (Grant No 2008BA B29B09)the Natural Science and Technology Major Special Program of China (Grant No 2008ZX07104-004)
文摘The water level of the Three Gorges Reservoir(TGR) rose to 172.5 m in two stages from September to November,2008.The hydrodynamic parameters and water quality parameters(e.g.flow velocity,temperature,turbidity and nutrient content) had been continuously monitored to reveal the influence of the impounding process of the TGR on the water eutrophication in the Xiangxi Bay(XXB).The maximal daily rise of the water level of the TGR was about 2.38 m.The water exchange between the mainstream(the Changjiang River) and the XXB of the TGR was enhanced by density current,and its main characteristics were a density-stratified flow in different directions.The water exchange reduced the differences of the water quality parameters(for example,temperature,turbidity,nutrient level,pH,etc.) between the mainstream and the XXB during the impounding process.Meanwhile,the water stability index in the mainstream remained small but it was lowered in the XXB.The main causes included the dilution by water of lower concentration of the chlorophyll a(Chl.a) entering from the mainstream,the decline of the water stability,and the increase of suspended silt,which induced the Chl.a to decrease in the XXB during the impounding process.The grade of the water eutrophication changed from middle eutrophic level to mesotrophic state in the process.However,as available nutrients were imported into the XXB from the mainstream during the impounding process the risk of water eutrophication increases in the XXB in the future.
文摘Background Atrial fibrillation (AF) is the most common supraventriculararrhythmia in clinical practice. Chronic atrial fibrillation (CAF) is associated with ionicremodeling. However, little is known about the activity of ATP-sensitive potassium current I_(K,ATP) during CAF. So we studied the changes of I_(K, ATP) density and allosteric modulation ofATP-sensitivity by intracellular pH during CAF. Methods Myocardium samples were obtained from theright auricular appendage of patients with rheumatic heart disease complicated with valvular diseasein sinus rhythm (SR) or CAF. There were 14 patients in SR group and 9 patients in CAF group. Singleatrial cells were isolated using an enzyme dispersion technique. IKiATP was recorded using thewhole-cell and inside-out configuration of voltage-clamp techniques. In whole-cell model, myocytesof SR and CAF groups were perfused with simulated ischemic solution to elicit I_(K, ATP). Ininside-out configuration, the internal patch membranes were exposed to different ATP concentrationsin pH 7. 4 and 6. 8. Results Under simulated ischemia, I_(K, ATP) current density of CAF group wassignificantly higher than in SR group [(83.5 ± 10.8) vs. (58.7 ±8.4) pA/pF, P < 0. 01 ] . I_(K,ATP) of the two groups showed ATP concentration-dependent inhibition. The ATP concentration for 50%current inhibition (IC_(50) ) for the SR group was significantly different in pH 7. 4 and pH 6. 8(24 vs. 74 μmol/L, P < 0. 01). The IC_(50) did not change significantly in CAF group when the pHdecreased from 7. 4 to 6. 8. Conclusions During CAF, I_(K, ATP) current density was increased andits allosteric modulation of ATP-sensitivity by intracellular pH was diminished.
基金supported by the National Natural Science Foundation of China (Grant Nos. 51179095, 51179205, 51009081 and 51209123)
文摘Harmful algal blooms, which frequently occur in different tributaries, have become a serious water quality problem of the Three Gorges Reservoir (TGR) since its initial filling. A three-year monitoring campaign from 2008 to 2010 was conducted to identify the controlling factors of algal blooms and effective preventive measures. The following results were obtained: 1) Layered and bidirectional currents, called intrusive density currents, dominate the tributary bays of the TGR year round; 2) continuously increasing water level can make the intruding density current shift from the middle to the surface, and surface intrusive water can reduce the surface water temperature and break the stable stratification of the tributary; 3) the appearing or fading away of algal blooms is closely associated with fluctuations in the TGR water level. Thus, the water level fluctuation patterns of different "tide-types" may prevent the occurrence of algal blooms in the spring and summer, and the "stair-type" tides may control autumn blooms during the impounding period. These methods were feasible and effective throughout the actual TGR's operation in 2009 2011. These patterns formed an eco-environmentally friendly operation (EEFO) to mitigate algal blooms. As an in situ treatment with easier operation and less negative impact and loss, compared with chemical and filter-feeding fish methods, the EEFO is currently considered as the most feasible remedial measure to remit the eco-environmental problems at the Three Gorges Dam (TGD).
基金This study was supported by the Youth Ocean Sience Funds of State Oceanic Administration under contract No. 97301.
文摘The Casulli's difference scheme was introduced into the three-dimensional ocean model in the present paper, and the wind-driven current and thermohaline current were simulated. The results show that, southwesterly monsoon in summer induces a clockwise circulation in the Beibu Gulf, and the density gradient induces a counter-clockwise one; but the density current is more intense than the wind- driven one in summer, espeially in surface layer. In addition, the northeasterly monsoon in winter in- duces a counter-clockwise circulation. The simulated results don't support the traditional condusion that there is a clockwise circulation in the Beibu Gulf in summer and a counter-clockwise one in winter, but support the statement that a counterclockwise circulation exists in the Beibu Gulf all year round.
基金supported by the Fund of the National Basic Research of China(2011CB 209403).
文摘Measuring the pre-breakdown current of long sparks in air is important for investigating the discharge mechanism.Since the breakdown of long air gaps is conducted by a series of streamer-leader processes,the corresponding current signals cover a bandwidth of 0 to more than 20 MHz.Measurement accuracy of the current from the high voltage side is affected by the displacement current and impulse electromagnetic interference.In this paper,a coaxial current sensor with a DC bandwidth of 74.45 MHz is developed.A displacement current-restrained electrode structure is proposed to reduce the equivalent capacitance between the current sensor and the ground over 30 times.Combined with the digital optical fiber synchronous acquisition unit,a current measurement system for long air gap discharge is established.For the purpose of the UHV system’s external insulation optimization design,the discharge current waveform of a 6 m rod-plane air gap under positive switching impulse voltage with 250µs and 1000µs time to crest is obtained.Discharge images and stressed voltage are combined to analyze the continuous feature of a current waveform under critical time to crest impulse and discontinuous feature under long front duration impulse.For the purposes of a lightning protection study,the current waveform of a 10 m rod-plane air gap is subjected to negative switching impulse.Finally,the pulse characteristics of the current corresponding to the single channel and branching stepped negative leader are discussed.
