Grasslands in northern China serve the country as both an ecological barrier and a livestock production base.There,installing enclosures has been becoming the major grassland restoration measure adopted by many local ...Grasslands in northern China serve the country as both an ecological barrier and a livestock production base.There,installing enclosures has been becoming the major grassland restoration measure adopted by many local governments.However,the effects of restoration on both ecological and production benefits of grassland remain unclear for implemented grassland restoration policies.Therefore,a representative rangeland in northern China,the Maodeng pasture in Inner Mongolia Autonomous Region was selected as the study area,and remote sensing monitoring analyses were carried out to quantify the ecological benefits and economic benefits from 2015 to 2021.The results showed that:1) in terms of ecological benefits,the grassland area with a grassland coverage rate of more than 60% accounts for 32.3% of the regional area,and 86.4% of its grassland grew significantly better than the same period in2015,showing a significant improvement in grassland growth.Using the average amount of carbon per unit area as the ecological benefit evaluation index,it increased by 27.1% to 32.48Tg C/yr from 2015 to 2021.2) In terms of economic benefits,both theoretical grass production and livestock carrying capacity increased from 2015 to 2021.Compared to 2015,the theoretical grass production in 2021 increased by 24.8% to 71 900 t.The livestock carrying capacity reached 52 100 sheep units in 2021,nearly 11 000 sheep units more than that in 2015.During the study period,multiple economic indicators(on a per capita basis of permanent residents) for the pastoral area of Xilinhot City to which the Maodeng pasture belongs,have grown steadily.Per capita total income rose from 29 630 yuan(RMB) in2015 to 62 859 yuan(RMB) in 2021.Relying on grassland resources to develop the pastoral ecology also broadens the potential economic development space.Overall,the establishment of the reserve and the experiment of implanting an enclosure policy have had a significant and positive impact on Maodeng pasture’s development from both an ecological and economic perspective.With the support of scientific evidence,enclosure policy can be extended to more than 110 000 km~2 of grasslands in northern China with similar precipitation and temperature conditions,enhancing the productive and ecological potential of grasslands.The above research results will contribute to the scientific formulation of grassland pasture quality improvement plans in northern China.展开更多
Natural convection flow in enclosure has different applications such as room ventilation, heat exchangers, the cooling system of a building etc. The Finite-Element method based on the Galerkin weighted residual approa...Natural convection flow in enclosure has different applications such as room ventilation, heat exchangers, the cooling system of a building etc. The Finite-Element method based on the Galerkin weighted residual approach is used to solve two-dimensional governing mass, momentum and energy-equations for natural convection flow in the presence of a magnetic field on a roof top with semi-circular heater. In the enclosure the horizontal lower wall was heated, the vertical two walls were adiabatic, inside the semi-circular heater, the wavy top wall cooled. The parameters Rayleigh number, Hartmann number and Prandtl number are considered. The effects of the Hartmann number and Rayleigh number on the streamlines, isotherms, velocity profiles and average Nusselt number are examined graphically. The local Nusselt number and the average Nusselt number of the heated portion of the enclosure with the semi-circular heater are presented in this paper. Finally, for the validation of the existing work, the current results are compared with published results and the auspicious agreement is achieved.展开更多
The hypertrophic subtropic Donghu Lake’s dense water bloom(of mainly Microcystis Anaabaena andOscillatoria)that occurred annually from the beginning of the 1970s, has disappeared since 1985. The infiuenceof planktivo...The hypertrophic subtropic Donghu Lake’s dense water bloom(of mainly Microcystis Anaabaena andOscillatoria)that occurred annually from the beginning of the 1970s, has disappeared since 1985. The infiuenceof planktivorous fishes (silver and bighead carps) on the water bloom was studied for three years usingthe enclosure method. The enclosures stocked densely with bighead and/or silver carp were free of waterbloom during the experimental period. The water bloom that appeared in the fish-free enclosures was completelyeliminated in 10-20 days by introduction of silver and/or bighead carp(grass carp was not effectivein controlling water bloom).This study showed clearly that grazing pressure by planktivorous fishes is a keyfactor in eliminating water bloom from the lake.展开更多
The aim of the proposed work is to study the solidification process within a rectangular enclosure provided with three internal rectangular fins attached to the left vertical wall of the cavity.This latest is filled w...The aim of the proposed work is to study the solidification process within a rectangular enclosure provided with three internal rectangular fins attached to the left vertical wall of the cavity.This latest is filled with a phase change material(PCM),initially liquid,at a temperature above its melting temperature.The solidification process was initiated by cooling the left wall and fins to a temperature lower than the melting temperature.In order to study and examine the thermal behavior and thermal performance of the proposed system,a mathematical model,based on the conservation equations of mass,momentum and energy was developed.The governing equations and their associated boundary and initial conditions were next adimensionalyzed.Therefore,several controlling parameters were appeared.The volume control method was used to discretize the equations.The resulting algebraic equations were solved iteratively.Numerical investigations were carried out to study and examine the effect of the dimensionless fin length on the hydrodynamic and thermal fields of the flow,the dimensionless heat flux,the solidified mass fraction and the dimensionless time of complete solidification.展开更多
Transient enclosure voltage(TEV),which is a phenomenon induced by the inner dielectric breakdown of SF_6 during disconnector operations in a gas-insulated switchgear(GIS),may cause issues relating to shock hazard and ...Transient enclosure voltage(TEV),which is a phenomenon induced by the inner dielectric breakdown of SF_6 during disconnector operations in a gas-insulated switchgear(GIS),may cause issues relating to shock hazard and electromagnetic interference to secondary equipment.This is a critical factor regarding the electromagnetic compatibility of ultra-high-voltage(UHV)substations.In this paper,the statistical characteristics of TEV at UHV level are collected from field experiments,and are analyzed and compared to those from a repeated strike process.The TEV waveforms during disconnector operations are recorded by a self-developed measurement system first.Then,statistical characteristics,such as the pulse number,duration of pulses,frequency components,magnitude and single pulse duration,are extracted.The transmission line theory is introduced to analyze the TEV and is validated by the experimental results.Finally,the relationship between the TEV and the repeated strike process is analyzed.This proves that the pulse voltage of the TEV is proportional to the corresponding breakdown voltage.The results contribute to the definition of the standard testing waveform of the TEV,and can aid the protection of electronic devices in substations by minimizing the threat of this phenomenon.展开更多
A numerical research on magnetohydrodynamic mixed convection flow in a lid-driven trapezoidal enclosure at non-uniform heating of bottom wall has been studied numerically. The enclosure consists of insulated top wall ...A numerical research on magnetohydrodynamic mixed convection flow in a lid-driven trapezoidal enclosure at non-uniform heating of bottom wall has been studied numerically. The enclosure consists of insulated top wall and cold side walls, too. It also contains a heated triangular block (<em>Rot</em> = 0<span style="font-family:Verdana, Helvetica, Arial;white-space:normal;background-color:#FFFFFF;">°</span> - 90<span style="font-family:Verdana, Helvetica, Arial;white-space:normal;background-color:#FFFFFF;">°</span>) located somewhere inside the enclosure. The boundary top wall of the enclosure is moving through uniform speed <em>U</em><sub>0</sub>. The geometry of the model has been represented mathematically by coupled governing equations in accordance with proper boundary conditions and then a two-dimensional Galerkin finite element based numerical approach has been adopted to solve this paper. The numerical computations have been carried out for the wide range of parameters Prandtl number (0.5 ≤ <em>Pr</em> ≤ 2), Reynolds number (60 ≤ <em>Re</em> ≤ 120), Rayleigh number (<em>Ra</em> = 10<sup>3</sup>) and Hartmann number (<em>Ha</em> = 20) taking with different rotations of heated triangular block. The results have been shown in the form of streamlines, temperature patterns or isotherms, average Nusselt number and average bulk temperature of the fluid in the enclosure at non-uniform heating of bottom wall. It is also indicated that both the streamlines, isotherm patterns strongly depend on the aforesaid governing parameters and location of the triangular block but the thermal conductivity of the triangular block has a noteworthy role on the isotherm pattern lines. Moreover, the variation of <em>Nu</em><sub>av</sub> of hot bottom wall and <em>θ</em><sub>av</sub> in the enclosure is demonstrated here to show the characteristics of heat transfer in the enclosure.展开更多
The organic carbon budget in shrimp polyculture ecosystems was studied with five experimental enclosures. The results showed that: (l ) the total Organic carbon income of the ecosystems varied from 4 847. 46 to 6 154....The organic carbon budget in shrimp polyculture ecosystems was studied with five experimental enclosures. The results showed that: (l ) the total Organic carbon income of the ecosystems varied from 4 847. 46 to 6 154. 67 g, averaged (5 646. 94 t 551.09) g, the average ratio among its components, i. e., (phytoplankton production ): (periphyte production ): (feed casted) was 0. 73: 0. 11: 0. 16; (2) the total output of organic carbon varied from 3 310. 28 to 3 974. 79 g, averaged (3 644. 21 281. 44) g, the average ratio among its components, i. e., (plankton community respiration): (periphyton respiration): (benthic community): (culture animal production): (culture animal respiration) was 0. 53: 0. 19: 0. 15: 0. 04:0. 09; (3) the organic carbon accumulation varied from 1 383. 45 to 2 707. 31 g, averaged (2 002. 73 546. 76) g, which was 26% --44 % of the total organic carbon income; the sequence of organic carbon accumulation in the ecosystems of different polyculture types was Y5 (Penaeus chinensis -- Argopecten irradians) > Y7 (P. chinensis -- Taiwan red tilapia) > Y4 (P. chinensis ) > T5 (P. chinensis -- Taiwan red tilapia -- Sinonovacula constricta ) > Y6 (P. chinensis S. constricta ); (4) the average conversion rate of organic carbon income to P. chinensis was (l. 77 0. 62) % (Y6>T5 > Y4 >YS > Y7), and that to total culture animals was (2. 18 0. 79) % (T5 >Y6 > Y5 > Y4 > Y7).展开更多
In this paper, we present a two-dimensional numerical analysis of the conjugate natural convection and radiation heat transfer in a double-space enclosure with two semitransparent walls. Two kinds of boundary conditio...In this paper, we present a two-dimensional numerical analysis of the conjugate natural convection and radiation heat transfer in a double-space enclosure with two semitransparent walls. Two kinds of boundary conditions are considered, the rst being the isothermal process of the opaque wall, and the other the incidence of a constant radiation ux in the left semitransparent wall. The renormalization group k ε model is adopted to simulate the turbulent ow in the enclosure. To compute the radia- tion heat transfer in a semitransparent medium, the discrete ordinates model is used. We compare the behaviors of enclosures with single and double semitransparent walls and determine the di erence in the results obtained for semitransparent and opaque partitions. The results indicate that a semitransparent partition facilitates a reduction in the heat loss or obtains a higher temperature distribution. The transmittance of a semitransparent wall has a great e ect on the thermal and ow char- acteristics in an enclosure. The change of wall temperature is found to be signi cant when the thermal conductivity values range from 0.05 to 0.5 W/(m K), and to be small when ranging from 0.5 to 10 W/(m K). These conclusions are helpful for green design and energy saving in solar buildings.展开更多
The Microcystis bloom that once disappeared from Donghu Lake, a shallow eutrophic Chinese lake,was successfully resumed with the use of the enclosure method. Seston and dissolved organic carbon (DOC)dynamics during th...The Microcystis bloom that once disappeared from Donghu Lake, a shallow eutrophic Chinese lake,was successfully resumed with the use of the enclosure method. Seston and dissolved organic carbon (DOC)dynamics during the Microcystis bloom were investigated with particular emphasis on the effect of three Chinese domestic fishes (silver carp, bighead carp and grass carp). The results showed that the change of chlorophyll a obviously reated to the fish species and its stocking density. Du to the relare of exracelular ogranic carbon and increased bacterial activity, DOC increased apparently after silver and bighead carps were introduced. POC/DOC dropped considerably in the enclosures containing silver and bighead carps and in the surrounding lake water, which implied that the bacterial acivity was more pronounced in such ecosystems. Statistical analytis indicated that the linear relationship between POC and chiorophyll a could reflect the state of algal growth and nutrient metabolism. It was expected that this study would provide some information on biomanipulation in the shallow eutrophic lakes.展开更多
This study simulates natural convection flow resulting from heat partitions in an H-shaped enclosure filled with a nanofluid using an incompressible smoothed particle hydrodynamics(ISPH)method.The right area of the H-...This study simulates natural convection flow resulting from heat partitions in an H-shaped enclosure filled with a nanofluid using an incompressible smoothed particle hydrodynamics(ISPH)method.The right area of the H-shaped enclosure is saturated with non-Darcy porous media.The center variable partitions of the H-shaped enclosure walls are kept at a high-temperature Th.The left and right walls of the H-shaped enclosure are positioned at a low temperature Tc and the other walls are adiabatic.In ISPH method,the source term in pressure Poisson equation(PPE)is modified.The influences of the controlling parameters on the temperature distributions,the velocity field and average Nusselt number are discussed.The performed simulations proofed that the length of the heated partitions augments the velocity field and temperature distributions in an H-shaped enclosure.Rayleigh number rises the fluid velocity and heat transfer in an H-shaped enclosure.The porous layer on the right side of the H-shaped enclosure at a lower Darcy parameter causes a high resistance force for the fluid flow and heat transfer characteristic inside an H-shaped enclosure.Added nanoparticles reduces the velocity field and enhances the heat transfer inside an H-shaped enclosure.展开更多
Taking natural grassland on the northern slope of the Qilian Mountain for example, this paper investigated and compared aboveground and belowground biomass of grassland in multi-year enclosure(20 years), one-year encl...Taking natural grassland on the northern slope of the Qilian Mountain for example, this paper investigated and compared aboveground and belowground biomass of grassland in multi-year enclosure(20 years), one-year enclosure, control areas(natural grazing areas). The results showed that coverage and height of the enclosure sample plots were significantly higher than that of natural grazing area(P <0.05); mean aboveground biomass of grassland: multi-year enclosure(316.58 g/m^2) > one-year enclosure area(299.07 g/m^2) > multi-year enclosure control area(254.39 g/m^2) > one-year enclosure control area(187.37 g/m^2); belowground biomass: multi-year enclosure(2,906.90 g/m^2) > one-year enclosure area(2,587.26 g/m^2) > multi-year enclosure control area(2,378.93 g/m^2) > one-year enclosure control area(2,029.17 g/m^2); mean aboveground biomass of natural grassland was 263.60 g/m^2, mean belowground biomass 2,225.56 g/m^2; ratio of belowground biomass to aboveground biomass varied between 6.79 and 12.90, distribution of belowground biomass and aboveground biomass in each plot showed significant differences(P <0.05). Enclosure was favorable for improving the coverage and biomass of natural grassland plant communities in the Qilian Mountains.展开更多
In this article, we compute the enclosures eigenvalues (upper and lower bounds) using the quadratic method. The Schrodinger operator (A) (harmonic and anharmonic oscillator model) has used as an example. We study a ne...In this article, we compute the enclosures eigenvalues (upper and lower bounds) using the quadratic method. The Schrodinger operator (A) (harmonic and anharmonic oscillator model) has used as an example. We study a new technique to get more accurate bounds. We compare our results with Boulton and Strauss method.展开更多
The study of buoyancy driven flow within bottom-heated vertical concentric cylindrical enclosure was important with respect to the processes in chemical and nuclear industries. In this research paper, experimental and...The study of buoyancy driven flow within bottom-heated vertical concentric cylindrical enclosure was important with respect to the processes in chemical and nuclear industries. In this research paper, experimental and numerical study of the axial temperature gradient and the heat transfer mechanism within the enclosure were performed. The numerical simulations were validated by comparing the numerical results with experimentally measured axial temperature. The numerical results of the streamlines within the enclosure depicted the real picture of the buoyancy effects. Eighteen different experiments were performed by using inner cylinder of different materials and outer cylinder of different diameters within the bottom disc temperature range of 353 - 433 K. The CFD simulations were performed to study the buoyancy effects within the enclosure. At the bottom disc with temperature up to 393 K, the streamlines within the inner cylinder were almost the same for both con- figurations being independent of outer cylinder diameter, while at 433 K streamlines within the inner cylinders varied. With larger diameter outer cylinder configuration, the buoyancy effects in the outer annulus were stronger as compared to smaller one.展开更多
The transmission line matrix time domain (TLM-TD) method is used to simulate the electromagnetic pulse (EMP) cou-pled inside a shielding box with an aperture. Simulations for different electromagnetic pulses regarding...The transmission line matrix time domain (TLM-TD) method is used to simulate the electromagnetic pulse (EMP) cou-pled inside a shielding box with an aperture. Simulations for different electromagnetic pulses regarding to different rise time and fall time have been performed. The results for shielding effectiveness of these different excitations have been presented. A simple method that uses an extra metal for reducing the interference has also been proposed and tested.展开更多
Experimental study was conducted to determine the effect of velocity of axial fan,outlet vent height,position,area,and aspect ratio(h/w)of ventilated enclosure on convection heat transfer.Rectangular wooden ventilated...Experimental study was conducted to determine the effect of velocity of axial fan,outlet vent height,position,area,and aspect ratio(h/w)of ventilated enclosure on convection heat transfer.Rectangular wooden ventilated enclosure having top and front transparent wall was made up of Perspex for visualization,and internal physical dimensions of box were 200 mm×200 mm×400 mm.Inlet vent was at bottom while outlet vents were at the side and top wall.Electrically heated cylindrical heat source having 6.1 slenderness ratio was fabricated and hanged at the centre of the enclosure.To calculate heat transfer rates,thermocouples were attached to the inner surface of heat source with silica gel.Heat source was operated at constant heat flux in order to quantify the effect of velocity of air on heat transfer.It was observed that average Nusselt number was increased from 68 to 216 by changing velocity from 0 to 3.34 m/s at constant modified Grashof number i.e.5.67E+09.While variation in outlet height at the front wall did not affect heat transfer in forced convection region.However,Nusselt number decreased to 5%by changing the outlet position from top to the front wall or by 50%reduction in outlet area during forced convection.Mean rise in temperature of enclosure increased from 8.19 K to 9.40 K by increasing aspect ratio of enclosure from 1.5 to 2 by operating heat source at constant heat flux i.e.541.20 w/m^(2).展开更多
In this paper we introduce the sign matrix of a nonlinear system of equations x = Gx to characterize its hybrid and asynchronous monotonicity as well as convexity. Based on the configuration of the matrix, we define a...In this paper we introduce the sign matrix of a nonlinear system of equations x = Gx to characterize its hybrid and asynchronous monotonicity as well as convexity. Based on the configuration of the matrix, we define a new type of regular splittings of the system with which the solvability and construction of solutions for the system are transformed to those of the couple systems of the splitting formIt is shown that this couple systems is a general model for developing monotonic enclosure methods of solutions for various types of nonlinear system of equations.展开更多
A two-dimensional numerical study of laminar natural convection in a square enclosure filled with air with a wall partially heated on the bottom is presented.The heat source is located on the lower wall with different...A two-dimensional numerical study of laminar natural convection in a square enclosure filled with air with a wall partially heated on the bottom is presented.The heat source is located on the lower wall with different heated widths varied from 20 to 80%(ε=0.2–0.8)of the total width of the lower wall and different heights h=H/4 and H/2 of the partition.The effect of the partition height on the main system dynamics is investigated through solution of the two-dimensional Navier-Stokes equations and the energy equation by means of a finite volume method based on the SIMPLE algorithm.The influence of the Rayleigh number(Ra=10^(3) to 10^(6))and the hot wall length is also examined.It is shown that the average Nusselt number grows whenεincreases and when h decreases.For a given value ofεand h,the average Nusselt number increases as Ra increases.It is concluded that the partition height causes a decrease in the average Nusselt number.展开更多
In this study, the enclosure system exhibited perfect nitrogen removal performance with in situ oxygen-enhanced indigenous aerobic denitrifying bacteria in an enclosure experiment. We explored changes in the microbial...In this study, the enclosure system exhibited perfect nitrogen removal performance with in situ oxygen-enhanced indigenous aerobic denitrifying bacteria in an enclosure experiment. We explored changes in the microbial community during the nitrogen removal process using the MiSeq high-throughput sequencing technology. The results revealed a total of 7974 and 33653 operational taxonomic units(OTUs) for water and sediment systems, respectively, with 97% similarity. The OTUs were found to be affiliated with eight main phyla(Proteobacteria, Actinobacteria, Cyanobacteria, Bacteroidetes, Planctomycetes, Chloroflexi, Firmicutes, and Actinobacteria). The diversity of the enhanced system was found to be higher than that of the control system. Principal component analysis(PCA) revealed that significant spatial and temporal differences were exhibited in the microbial community during nitrogen removal in the enclosure experiment. Redundancy analysis(RDA)indicated that physical parameters(temperature, dissolved oxygen, and pH), nitrogen(total nitrogen and nitrate), functional genes(nirK and nirS), and dissolved organic carbon(DOC) were the most important factors affecting bacterial community function and composition. Lastly, the results suggested that the variation in the microbial community could be analyzed through the MiSeq high-throughput sequencing technology,which may provide technical support for future field tests.展开更多
Experiments were conducted from June to September, 1995 in a controlled integrated culture pond-enclosure ecosystem.The principal objective of this study was to quantify the rate of heterotrophic bacterioplankton prod...Experiments were conducted from June to September, 1995 in a controlled integrated culture pond-enclosure ecosystem.The principal objective of this study was to quantify the rate of heterotrophic bacterioplankton production in situ in a fertilization pond ecosystem.This paper presents a method by which bacterial production was estimated through incubation in situ and measurement of increased bacterial abundance with time. Bacterial growth rates. production and tumover per day during the periods of culture were estimated. The influence of zooplankton grazing, substrate limiting and water temperature on the bacterial growth rates and production were studied also.展开更多
基金Under the auspices of the Inner Mongolia Autonomous Region Science and Technology Achievement Transformation Special Project(No.2020CG0123)the Strategic Priority Research Program of Chinese Academy of Sciences(No.XDA26050301-01)。
文摘Grasslands in northern China serve the country as both an ecological barrier and a livestock production base.There,installing enclosures has been becoming the major grassland restoration measure adopted by many local governments.However,the effects of restoration on both ecological and production benefits of grassland remain unclear for implemented grassland restoration policies.Therefore,a representative rangeland in northern China,the Maodeng pasture in Inner Mongolia Autonomous Region was selected as the study area,and remote sensing monitoring analyses were carried out to quantify the ecological benefits and economic benefits from 2015 to 2021.The results showed that:1) in terms of ecological benefits,the grassland area with a grassland coverage rate of more than 60% accounts for 32.3% of the regional area,and 86.4% of its grassland grew significantly better than the same period in2015,showing a significant improvement in grassland growth.Using the average amount of carbon per unit area as the ecological benefit evaluation index,it increased by 27.1% to 32.48Tg C/yr from 2015 to 2021.2) In terms of economic benefits,both theoretical grass production and livestock carrying capacity increased from 2015 to 2021.Compared to 2015,the theoretical grass production in 2021 increased by 24.8% to 71 900 t.The livestock carrying capacity reached 52 100 sheep units in 2021,nearly 11 000 sheep units more than that in 2015.During the study period,multiple economic indicators(on a per capita basis of permanent residents) for the pastoral area of Xilinhot City to which the Maodeng pasture belongs,have grown steadily.Per capita total income rose from 29 630 yuan(RMB) in2015 to 62 859 yuan(RMB) in 2021.Relying on grassland resources to develop the pastoral ecology also broadens the potential economic development space.Overall,the establishment of the reserve and the experiment of implanting an enclosure policy have had a significant and positive impact on Maodeng pasture’s development from both an ecological and economic perspective.With the support of scientific evidence,enclosure policy can be extended to more than 110 000 km~2 of grasslands in northern China with similar precipitation and temperature conditions,enhancing the productive and ecological potential of grasslands.The above research results will contribute to the scientific formulation of grassland pasture quality improvement plans in northern China.
文摘Natural convection flow in enclosure has different applications such as room ventilation, heat exchangers, the cooling system of a building etc. The Finite-Element method based on the Galerkin weighted residual approach is used to solve two-dimensional governing mass, momentum and energy-equations for natural convection flow in the presence of a magnetic field on a roof top with semi-circular heater. In the enclosure the horizontal lower wall was heated, the vertical two walls were adiabatic, inside the semi-circular heater, the wavy top wall cooled. The parameters Rayleigh number, Hartmann number and Prandtl number are considered. The effects of the Hartmann number and Rayleigh number on the streamlines, isotherms, velocity profiles and average Nusselt number are examined graphically. The local Nusselt number and the average Nusselt number of the heated portion of the enclosure with the semi-circular heater are presented in this paper. Finally, for the validation of the existing work, the current results are compared with published results and the auspicious agreement is achieved.
基金This work was supported by FEBL(State Key Laboratory for Freshwater Ecology and Biotechnology of China)fundsNational Natural Science Foundation of China (Grant NO.3937014)
文摘The hypertrophic subtropic Donghu Lake’s dense water bloom(of mainly Microcystis Anaabaena andOscillatoria)that occurred annually from the beginning of the 1970s, has disappeared since 1985. The infiuenceof planktivorous fishes (silver and bighead carps) on the water bloom was studied for three years usingthe enclosure method. The enclosures stocked densely with bighead and/or silver carp were free of waterbloom during the experimental period. The water bloom that appeared in the fish-free enclosures was completelyeliminated in 10-20 days by introduction of silver and/or bighead carp(grass carp was not effectivein controlling water bloom).This study showed clearly that grazing pressure by planktivorous fishes is a keyfactor in eliminating water bloom from the lake.
文摘The aim of the proposed work is to study the solidification process within a rectangular enclosure provided with three internal rectangular fins attached to the left vertical wall of the cavity.This latest is filled with a phase change material(PCM),initially liquid,at a temperature above its melting temperature.The solidification process was initiated by cooling the left wall and fins to a temperature lower than the melting temperature.In order to study and examine the thermal behavior and thermal performance of the proposed system,a mathematical model,based on the conservation equations of mass,momentum and energy was developed.The governing equations and their associated boundary and initial conditions were next adimensionalyzed.Therefore,several controlling parameters were appeared.The volume control method was used to discretize the equations.The resulting algebraic equations were solved iteratively.Numerical investigations were carried out to study and examine the effect of the dimensionless fin length on the hydrodynamic and thermal fields of the flow,the dimensionless heat flux,the solidified mass fraction and the dimensionless time of complete solidification.
基金supported by the National Basic Research Program of China(973 Program) under grant 2011CB209405
文摘Transient enclosure voltage(TEV),which is a phenomenon induced by the inner dielectric breakdown of SF_6 during disconnector operations in a gas-insulated switchgear(GIS),may cause issues relating to shock hazard and electromagnetic interference to secondary equipment.This is a critical factor regarding the electromagnetic compatibility of ultra-high-voltage(UHV)substations.In this paper,the statistical characteristics of TEV at UHV level are collected from field experiments,and are analyzed and compared to those from a repeated strike process.The TEV waveforms during disconnector operations are recorded by a self-developed measurement system first.Then,statistical characteristics,such as the pulse number,duration of pulses,frequency components,magnitude and single pulse duration,are extracted.The transmission line theory is introduced to analyze the TEV and is validated by the experimental results.Finally,the relationship between the TEV and the repeated strike process is analyzed.This proves that the pulse voltage of the TEV is proportional to the corresponding breakdown voltage.The results contribute to the definition of the standard testing waveform of the TEV,and can aid the protection of electronic devices in substations by minimizing the threat of this phenomenon.
文摘A numerical research on magnetohydrodynamic mixed convection flow in a lid-driven trapezoidal enclosure at non-uniform heating of bottom wall has been studied numerically. The enclosure consists of insulated top wall and cold side walls, too. It also contains a heated triangular block (<em>Rot</em> = 0<span style="font-family:Verdana, Helvetica, Arial;white-space:normal;background-color:#FFFFFF;">°</span> - 90<span style="font-family:Verdana, Helvetica, Arial;white-space:normal;background-color:#FFFFFF;">°</span>) located somewhere inside the enclosure. The boundary top wall of the enclosure is moving through uniform speed <em>U</em><sub>0</sub>. The geometry of the model has been represented mathematically by coupled governing equations in accordance with proper boundary conditions and then a two-dimensional Galerkin finite element based numerical approach has been adopted to solve this paper. The numerical computations have been carried out for the wide range of parameters Prandtl number (0.5 ≤ <em>Pr</em> ≤ 2), Reynolds number (60 ≤ <em>Re</em> ≤ 120), Rayleigh number (<em>Ra</em> = 10<sup>3</sup>) and Hartmann number (<em>Ha</em> = 20) taking with different rotations of heated triangular block. The results have been shown in the form of streamlines, temperature patterns or isotherms, average Nusselt number and average bulk temperature of the fluid in the enclosure at non-uniform heating of bottom wall. It is also indicated that both the streamlines, isotherm patterns strongly depend on the aforesaid governing parameters and location of the triangular block but the thermal conductivity of the triangular block has a noteworthy role on the isotherm pattern lines. Moreover, the variation of <em>Nu</em><sub>av</sub> of hot bottom wall and <em>θ</em><sub>av</sub> in the enclosure is demonstrated here to show the characteristics of heat transfer in the enclosure.
基金the National Natural Science Foundation of China under contract! No. 39430150 National Scaling He
文摘The organic carbon budget in shrimp polyculture ecosystems was studied with five experimental enclosures. The results showed that: (l ) the total Organic carbon income of the ecosystems varied from 4 847. 46 to 6 154. 67 g, averaged (5 646. 94 t 551.09) g, the average ratio among its components, i. e., (phytoplankton production ): (periphyte production ): (feed casted) was 0. 73: 0. 11: 0. 16; (2) the total output of organic carbon varied from 3 310. 28 to 3 974. 79 g, averaged (3 644. 21 281. 44) g, the average ratio among its components, i. e., (plankton community respiration): (periphyton respiration): (benthic community): (culture animal production): (culture animal respiration) was 0. 53: 0. 19: 0. 15: 0. 04:0. 09; (3) the organic carbon accumulation varied from 1 383. 45 to 2 707. 31 g, averaged (2 002. 73 546. 76) g, which was 26% --44 % of the total organic carbon income; the sequence of organic carbon accumulation in the ecosystems of different polyculture types was Y5 (Penaeus chinensis -- Argopecten irradians) > Y7 (P. chinensis -- Taiwan red tilapia) > Y4 (P. chinensis ) > T5 (P. chinensis -- Taiwan red tilapia -- Sinonovacula constricta ) > Y6 (P. chinensis S. constricta ); (4) the average conversion rate of organic carbon income to P. chinensis was (l. 77 0. 62) % (Y6>T5 > Y4 >YS > Y7), and that to total culture animals was (2. 18 0. 79) % (T5 >Y6 > Y5 > Y4 > Y7).
基金supported by the Shanghai Economic and Information Technology Committee Special Fund (CXY-2016-012)
文摘In this paper, we present a two-dimensional numerical analysis of the conjugate natural convection and radiation heat transfer in a double-space enclosure with two semitransparent walls. Two kinds of boundary conditions are considered, the rst being the isothermal process of the opaque wall, and the other the incidence of a constant radiation ux in the left semitransparent wall. The renormalization group k ε model is adopted to simulate the turbulent ow in the enclosure. To compute the radia- tion heat transfer in a semitransparent medium, the discrete ordinates model is used. We compare the behaviors of enclosures with single and double semitransparent walls and determine the di erence in the results obtained for semitransparent and opaque partitions. The results indicate that a semitransparent partition facilitates a reduction in the heat loss or obtains a higher temperature distribution. The transmittance of a semitransparent wall has a great e ect on the thermal and ow char- acteristics in an enclosure. The change of wall temperature is found to be signi cant when the thermal conductivity values range from 0.05 to 0.5 W/(m K), and to be small when ranging from 0.5 to 10 W/(m K). These conclusions are helpful for green design and energy saving in solar buildings.
文摘The Microcystis bloom that once disappeared from Donghu Lake, a shallow eutrophic Chinese lake,was successfully resumed with the use of the enclosure method. Seston and dissolved organic carbon (DOC)dynamics during the Microcystis bloom were investigated with particular emphasis on the effect of three Chinese domestic fishes (silver carp, bighead carp and grass carp). The results showed that the change of chlorophyll a obviously reated to the fish species and its stocking density. Du to the relare of exracelular ogranic carbon and increased bacterial activity, DOC increased apparently after silver and bighead carps were introduced. POC/DOC dropped considerably in the enclosures containing silver and bighead carps and in the surrounding lake water, which implied that the bacterial acivity was more pronounced in such ecosystems. Statistical analytis indicated that the linear relationship between POC and chiorophyll a could reflect the state of algal growth and nutrient metabolism. It was expected that this study would provide some information on biomanipulation in the shallow eutrophic lakes.
基金The authors would like to extend their appreciations to the Deanship of Scientific Research at King Khalid University,Abha,Saudi Arabia,for funding this work through the Research Group Project under Grant Number(R.G.P 2/70/41).
文摘This study simulates natural convection flow resulting from heat partitions in an H-shaped enclosure filled with a nanofluid using an incompressible smoothed particle hydrodynamics(ISPH)method.The right area of the H-shaped enclosure is saturated with non-Darcy porous media.The center variable partitions of the H-shaped enclosure walls are kept at a high-temperature Th.The left and right walls of the H-shaped enclosure are positioned at a low temperature Tc and the other walls are adiabatic.In ISPH method,the source term in pressure Poisson equation(PPE)is modified.The influences of the controlling parameters on the temperature distributions,the velocity field and average Nusselt number are discussed.The performed simulations proofed that the length of the heated partitions augments the velocity field and temperature distributions in an H-shaped enclosure.Rayleigh number rises the fluid velocity and heat transfer in an H-shaped enclosure.The porous layer on the right side of the H-shaped enclosure at a lower Darcy parameter causes a high resistance force for the fluid flow and heat transfer characteristic inside an H-shaped enclosure.Added nanoparticles reduces the velocity field and enhances the heat transfer inside an H-shaped enclosure.
基金Sponsored by National Natural Science Foundation of China(31360201,91225301,91425301)
文摘Taking natural grassland on the northern slope of the Qilian Mountain for example, this paper investigated and compared aboveground and belowground biomass of grassland in multi-year enclosure(20 years), one-year enclosure, control areas(natural grazing areas). The results showed that coverage and height of the enclosure sample plots were significantly higher than that of natural grazing area(P <0.05); mean aboveground biomass of grassland: multi-year enclosure(316.58 g/m^2) > one-year enclosure area(299.07 g/m^2) > multi-year enclosure control area(254.39 g/m^2) > one-year enclosure control area(187.37 g/m^2); belowground biomass: multi-year enclosure(2,906.90 g/m^2) > one-year enclosure area(2,587.26 g/m^2) > multi-year enclosure control area(2,378.93 g/m^2) > one-year enclosure control area(2,029.17 g/m^2); mean aboveground biomass of natural grassland was 263.60 g/m^2, mean belowground biomass 2,225.56 g/m^2; ratio of belowground biomass to aboveground biomass varied between 6.79 and 12.90, distribution of belowground biomass and aboveground biomass in each plot showed significant differences(P <0.05). Enclosure was favorable for improving the coverage and biomass of natural grassland plant communities in the Qilian Mountains.
文摘In this article, we compute the enclosures eigenvalues (upper and lower bounds) using the quadratic method. The Schrodinger operator (A) (harmonic and anharmonic oscillator model) has used as an example. We study a new technique to get more accurate bounds. We compare our results with Boulton and Strauss method.
文摘The study of buoyancy driven flow within bottom-heated vertical concentric cylindrical enclosure was important with respect to the processes in chemical and nuclear industries. In this research paper, experimental and numerical study of the axial temperature gradient and the heat transfer mechanism within the enclosure were performed. The numerical simulations were validated by comparing the numerical results with experimentally measured axial temperature. The numerical results of the streamlines within the enclosure depicted the real picture of the buoyancy effects. Eighteen different experiments were performed by using inner cylinder of different materials and outer cylinder of different diameters within the bottom disc temperature range of 353 - 433 K. The CFD simulations were performed to study the buoyancy effects within the enclosure. At the bottom disc with temperature up to 393 K, the streamlines within the inner cylinder were almost the same for both con- figurations being independent of outer cylinder diameter, while at 433 K streamlines within the inner cylinders varied. With larger diameter outer cylinder configuration, the buoyancy effects in the outer annulus were stronger as compared to smaller one.
文摘The transmission line matrix time domain (TLM-TD) method is used to simulate the electromagnetic pulse (EMP) cou-pled inside a shielding box with an aperture. Simulations for different electromagnetic pulses regarding to different rise time and fall time have been performed. The results for shielding effectiveness of these different excitations have been presented. A simple method that uses an extra metal for reducing the interference has also been proposed and tested.
文摘Experimental study was conducted to determine the effect of velocity of axial fan,outlet vent height,position,area,and aspect ratio(h/w)of ventilated enclosure on convection heat transfer.Rectangular wooden ventilated enclosure having top and front transparent wall was made up of Perspex for visualization,and internal physical dimensions of box were 200 mm×200 mm×400 mm.Inlet vent was at bottom while outlet vents were at the side and top wall.Electrically heated cylindrical heat source having 6.1 slenderness ratio was fabricated and hanged at the centre of the enclosure.To calculate heat transfer rates,thermocouples were attached to the inner surface of heat source with silica gel.Heat source was operated at constant heat flux in order to quantify the effect of velocity of air on heat transfer.It was observed that average Nusselt number was increased from 68 to 216 by changing velocity from 0 to 3.34 m/s at constant modified Grashof number i.e.5.67E+09.While variation in outlet height at the front wall did not affect heat transfer in forced convection region.However,Nusselt number decreased to 5%by changing the outlet position from top to the front wall or by 50%reduction in outlet area during forced convection.Mean rise in temperature of enclosure increased from 8.19 K to 9.40 K by increasing aspect ratio of enclosure from 1.5 to 2 by operating heat source at constant heat flux i.e.541.20 w/m^(2).
文摘In this paper we introduce the sign matrix of a nonlinear system of equations x = Gx to characterize its hybrid and asynchronous monotonicity as well as convexity. Based on the configuration of the matrix, we define a new type of regular splittings of the system with which the solvability and construction of solutions for the system are transformed to those of the couple systems of the splitting formIt is shown that this couple systems is a general model for developing monotonic enclosure methods of solutions for various types of nonlinear system of equations.
文摘A two-dimensional numerical study of laminar natural convection in a square enclosure filled with air with a wall partially heated on the bottom is presented.The heat source is located on the lower wall with different heated widths varied from 20 to 80%(ε=0.2–0.8)of the total width of the lower wall and different heights h=H/4 and H/2 of the partition.The effect of the partition height on the main system dynamics is investigated through solution of the two-dimensional Navier-Stokes equations and the energy equation by means of a finite volume method based on the SIMPLE algorithm.The influence of the Rayleigh number(Ra=10^(3) to 10^(6))and the hot wall length is also examined.It is shown that the average Nusselt number grows whenεincreases and when h decreases.For a given value ofεand h,the average Nusselt number increases as Ra increases.It is concluded that the partition height causes a decrease in the average Nusselt number.
基金supported by the National Science and Technology Pillar Program(Grant No.2012BAC04B02)the National Natural Science Foundation of China(Grant No.51478378)
文摘In this study, the enclosure system exhibited perfect nitrogen removal performance with in situ oxygen-enhanced indigenous aerobic denitrifying bacteria in an enclosure experiment. We explored changes in the microbial community during the nitrogen removal process using the MiSeq high-throughput sequencing technology. The results revealed a total of 7974 and 33653 operational taxonomic units(OTUs) for water and sediment systems, respectively, with 97% similarity. The OTUs were found to be affiliated with eight main phyla(Proteobacteria, Actinobacteria, Cyanobacteria, Bacteroidetes, Planctomycetes, Chloroflexi, Firmicutes, and Actinobacteria). The diversity of the enhanced system was found to be higher than that of the control system. Principal component analysis(PCA) revealed that significant spatial and temporal differences were exhibited in the microbial community during nitrogen removal in the enclosure experiment. Redundancy analysis(RDA)indicated that physical parameters(temperature, dissolved oxygen, and pH), nitrogen(total nitrogen and nitrate), functional genes(nirK and nirS), and dissolved organic carbon(DOC) were the most important factors affecting bacterial community function and composition. Lastly, the results suggested that the variation in the microbial community could be analyzed through the MiSeq high-throughput sequencing technology,which may provide technical support for future field tests.
文摘Experiments were conducted from June to September, 1995 in a controlled integrated culture pond-enclosure ecosystem.The principal objective of this study was to quantify the rate of heterotrophic bacterioplankton production in situ in a fertilization pond ecosystem.This paper presents a method by which bacterial production was estimated through incubation in situ and measurement of increased bacterial abundance with time. Bacterial growth rates. production and tumover per day during the periods of culture were estimated. The influence of zooplankton grazing, substrate limiting and water temperature on the bacterial growth rates and production were studied also.
