Aiming at the needs of mechanism analysis of rainstorms and development of numerical prediction models in south China, the Guangzhou Institute of Tropical and Marine Meteorology of China Meteorological Administration ...Aiming at the needs of mechanism analysis of rainstorms and development of numerical prediction models in south China, the Guangzhou Institute of Tropical and Marine Meteorology of China Meteorological Administration and the Chinese Academy of Meteorological Sciences jointly set up the Longmen Cloud Physics Field Experiment Base,China Meteorological Administration. This paper introduces the instruments and field experiments of this base, provides an overview of the recent advances in retrieval algorithms of microphysical parameters, improved understanding of microphysical characteristics, as well as the formation mechanisms and numerical prediction of heavy rainfalls in south China based on the field experiments dataset.展开更多
Based on the microdata of 705 wheat farmers in the Loess Plateau, this study empirically analyzes the impact of uncertainty on farmers' adoption of innovative seeds using a field experiment. The results indicate t...Based on the microdata of 705 wheat farmers in the Loess Plateau, this study empirically analyzes the impact of uncertainty on farmers' adoption of innovative seeds using a field experiment. The results indicate that farmers are generally ambiguity-averse and risk-averse. In addition, farmers with higher ambiguity aversion and risk aversion are less likely to adopt innovative wheat seeds, where their risk aversion plays a dominant role. Enhancing information access will alleviate the negative influence of ambiguity aversion on farmers' adoption of innovative seeds, and interlinked insurance and credit contracts will be beneficial to ease the adverse effect of risk aversion on the adoption of innovative wheat seeds. Meanwhile, heterogeneity analysis reveals that the inhibitory effects of ambiguity aversion and risk aversion on innovative seed adoption are more significant among farmers with lower education and household income.The government can establish both ex-ante and ex-post relevant guarantee mechanisms to help farmers preferably cope with various uncertainties in the production process, remitting farmers' ambiguity aversion and risk aversion to enhance new agricultural technology adoption rates.展开更多
Rainfall infiltration on a soil slope is usually an unsaturated seepage process that can be described by a water-air two-phase flow model.The effect of pore air pressure on rainfall infiltration has been widely recogn...Rainfall infiltration on a soil slope is usually an unsaturated seepage process that can be described by a water-air two-phase flow model.The effect of pore air pressure on rainfall infiltration has been widely recognized and validated by means of numerical simulations and laboratory experiments.However,whether a slope can actually seal pore air continues to be debated by researchers.In this study,a water-air two-phase flow model is used to simulate the rainfall infiltration process on a soil slope,and a field experiment is conducted to realistically test the sealing conditions of a slope.According to the numerical simulation,the areas of water and air flow in and out on the slope surface are relatively stable and can be classified as the“inhalation zone”and“overflow zone”,respectively.Intermittent rainfall on the soil slope has an amplifying effect on pore air pressure because rainfall intensity is usually at the millimeter level,and it causes pore air pressure to reach the cm level.A field experiment was performed to determine whether a slope can realistically seal pore air and subsequently verify the regularity of rainfall infiltration.Air pressure sensors were buried in the slope to monitor the pore air pressures during the rainfall process.The monitoring results show that the pore air pressure in the slope changed,which indicates that the slope can seal air.Moreover,the amplification effects of intermittent rainfall on pore air pressure were observed for natural rainfall,which agrees well with the numerical simulation results.展开更多
The 5G network has been intensively investigated to realize the ongoing early deployment stage as an effort to match the exponential growth of the number of connected users and their increasing demands for high throug...The 5G network has been intensively investigated to realize the ongoing early deployment stage as an effort to match the exponential growth of the number of connected users and their increasing demands for high throughput,bandwidth with Quality of Service(QoS),and low latency.Given that most of the spectrums below 6 GHz are nearly used up,it is not feasible to employ the traditional spectrum,which is currently in use.Therefore,a promising and highly feasible effort to satisfy this insufficient frequency spectrum is to acquire new frequency bands for next-generation mobile communications.Toward this end,the primary effort has been focused on utilizing the millimeter-wave(mmWave)as the most promising candidate for the frequency spectrum.However,though the mmWave frequency band can fulfill the desired bandwidth requirements,it has been demonstrated to endure several issues like scattering,atmospheric absorption,fading,and especially penetration losses compared to the existing sub-6 GHz frequency band.Then,it is fundamental to optimize the mmWave band propagation channel to facilitate the practical 5G implementation for the network operators.Therefore,this study intends to investigate the outdoor channel characteristics of 26,28,36,and 38 GHz frequency bands for the communication infrastructure at the building to the ground floor in both Line of Sight(LOS)and Non-Line of Sight(NLOS)environments.The experimental campaign has studied the propagation path loss models such as Floating-Intercept(FI)and Close-In(CI)for the building to ground floor environment in LOS and NLOS scenarios.The findings obtained from the field experiments clearly show that the CI propagation model delivers much better performance in comparison with the FI model,thanks to its simple setup,accuracy,and precise function.展开更多
Based on high magnetic field helicon experiment(HMHX), HELIC code was used to study the effect of different magnetic fields on the power deposition under parabolic distribution. This paper is divided into three parts:...Based on high magnetic field helicon experiment(HMHX), HELIC code was used to study the effect of different magnetic fields on the power deposition under parabolic distribution. This paper is divided into three parts: preliminary calculation, actual discharge experiment and calculation. The results of preliminary calculation show that a magnetic field that is too small or too large cannot produce a good power deposition effect. When the magnetic field strength is 1200 Gs,a better power deposition can be obtained. The actual discharge experiment illustrates that the change of the magnetic field will have a certain influence on the discharge phenomenon. Finally, the results of verification calculation successfully verify the accuracy of the results of preliminary simulation. The results show that in the actual discharge experiment, it can achieve the best deposition effect when the magnetic field is 1185 Gs.展开更多
In order to meet the requirement of field direct seeding for super hybrid rice:1-3 seeds per hill,a pneumatic rice direct-seeder with six seeding metering devices was designed.Transmission system of pneumatic rice dir...In order to meet the requirement of field direct seeding for super hybrid rice:1-3 seeds per hill,a pneumatic rice direct-seeder with six seeding metering devices was designed.Transmission system of pneumatic rice direct-seeder and seed metering device were analyzed in this study.And the pipeline structure and vortex pump were designed and selected.The pressure distribution of the pipeline was tested.The pressure value of each sub-pipeline under the conditions of different main pipeline pressure value was obtained and the reasons for pressure loss were analyzed.The results showed that the variation coefficient between sub-pipelines was less than 5%.The pipeline pressure could be evenly distributed.Further,the field experiments were carried out on super hybrid rice Peizataifeng using two-factor testing,by which the effects of different negative pressure and different forward speed(namely,rotational speed of suction plate)for seeding precision were studied.It found that:(1)the optimal negative pressure was 2 kPa;(2)under the optimal negative pressure,the probabilities of 1-3 seeds per hill for the direct-seeder were 93.41%,95.47%and 97.50%,respectively,when the forward speed of the direct-seeded was high,medium and low speed;(3)the probability of empty hole was less than 2%,which satisfied the field direct seeding requirements of super hybrid rice.Additionally,hill spacing was measured,and the factors affecting the hill spacing were analyzed.The results showed that the fluctuation of hill spacing in the small range will not affect the seeding effect.In this study,a new type of pneumatic rice direct-seeder was designed.The main working components were tested and analyzed.The best parameters of field work were obtained.It provides the basis for the field application of the pneumatic rice precision seeder.展开更多
Soil compaction is a common problem facing conservation fields that restricts crop root growth and causes yield decrease.Subsoil techniques have been developed to break up the compaction layer.However,subsoil implemen...Soil compaction is a common problem facing conservation fields that restricts crop root growth and causes yield decrease.Subsoil techniques have been developed to break up the compaction layer.However,subsoil implement requires large draft power that hampered the development of subsoil techniques for most of developing countries due to lack of large scale tractors.Aiming to optimize the penetration resistance of the subsoiler and create a good working environment for the operators,a staggered vibrating subsoiler was developed.A new staggered vibrating mechanism was designed to generate the staggered vibration of the shanks meanwhile the V-shape shanks arrangement was adopted to keep relative balance for the subsoiler.In order to obtain optimum working parameters of the vibration frequency and forward speed,the trajectory of shanks was simulated by using the MATLAB software.The forward speed of 2-3 km/h with vibration frequency of 12 Hz was recommended to acquire an effective decrease in draft force.Field performance of this subsoiler was evaluated in terms of the draft force,power requirement and tractor wheel slippage.By comparing the two operation modes,staggered vibrating(SV)and rigid(NV)of shanks,the decrease ratios of draft force for SV were determined by 16.97%,12.12%and 9.02%at forward speeds of 2.2 km/h,2.6 km/h and 3.1 km/h,respectively.This is better than the research for the 1SZ-460 vibratory subsoiler that was decreased by 9.09%in draft force.The power requirement for SV was not significantly greater than that for NV.The obviously decreased wheel slippage was observed for SV by decrease of 12.47%,17.96%and 21.79%at forward speeds of 2.2 km/h,2.6 km/h and 3.1 km/h,respectively.In conclusion,the staggered vibrating subsoiler presents preferable working performance and is recommended to be applied in subsoil tillage process for developing countries.展开更多
Late blight caused by <i>Phytophthora</i> <i>infestans</i> (Mont.) De Bary is the most devastating disease of potato. This study was carried out to evaluate the efficacy of ten botanical extrac...Late blight caused by <i>Phytophthora</i> <i>infestans</i> (Mont.) De Bary is the most devastating disease of potato. This study was carried out to evaluate the efficacy of ten botanical extracts against the late blight disease incidence and severity in experimental potato field at University of Rajshahi, Bangladesh during 2019-2020. Crude aqueous extract of leaves of <i>Syzygium</i> <i>cumini</i>, <i>Psidium</i> <i>guajava</i>, <i>Eucalyptus</i> <i>globusus</i>, <i>Carica</i> <i>papaya</i> and <i>Lawsonia</i> <i>inermis</i>;fruits of <i>Terminalia</i> <i>bellirica</i>, <i>T.</i> <i>chebula</i> and <i>Piper</i> <i>nigrum</i>;flower buds of <i>Syzygium</i> <i>aromaticum</i> and cloves of <i>Allium</i> <i>sativum</i> were used at 5% (w/v) concentration for evaluation. Out of ten botanicals, <i>Syzygium</i> <i>cumini</i> leaves extract was found most effective in controlling the late blight disease incidence and severity up to 66 DAS (days after sowing) and increased the potato yield by 71.29% compare to untreated control. The efficacy of <i>Lawsonia</i> <i>inermis</i> extract against late blight disease was found promising and increased the potato yield by 48.51%. Other four botanical extracts (<i>Terminalia</i> <i>chebula</i>, <i>Piper</i> <i>nigrum</i>, <i>Syzygium</i> <i>aromaticum</i> and <i>Carica</i> <i>papaya</i>) showed moderate efficacy <span>against the incidence and severity of late blight disease, and increased 30% </span>more potato yield compare to control. These results suggest that botanical extract of <i>Syzygium</i> <i>cumini</i> ha<span style="font-family:;" "="">s</span><span style="font-family:;" "=""> a great potential as an alternative </span><span style="font-family:;" "="">of</span><span style="font-family:;" "=""> chemical fungicides to control the late blight disease of potato in</span><span style="font-family:;" "=""> </span><span style="font-family:;" "="">eco-friendly way.</span>展开更多
Although magnetotelluric sounding method applied to the land is advanced, there are many difficulties when it is applied to marine environment, one of which is how to lay magnetic field sensors down to the seafloor to...Although magnetotelluric sounding method applied to the land is advanced, there are many difficulties when it is applied to marine environment, one of which is how to lay magnetic field sensors down to the seafloor to complete measurements. To protect the magnetic field sensors from intense erosion and high pressure, suitable high-pressure sealed cabins must be designed to load them. For the consideration of magnetic measurement and marine operation, the sealed pressure cabin should be nonmagnetic and transportable. Among all optional materials, LC4 super-hard aluminum alloy has the highest performance of price/quality ratio to make the sealed pressure cabin. However, it does not mean that the high-pressure sealed cabin made using LC4 will be perfect in performance. In fact, because of its weak magnetism, the pressure cabin made using LC4 has distorting effect on frequency responses of the magnetic field sensors sealed in it. This distorting effect does not affect the use of the magnetic field sensor, but if we want to eliminate its effect, we should study it by experimental measurements. In our experiment tests, frequency sweep magnetic field as excitation signal was used, and then responses of the magnetic field sensor before and after being loaded into the high-pressure sealed cabin were measured. Finally, normalized abnormal curves for the frequency responses were obtained, through which we could show how the high-pressure sealed cabin produces effects on the responses of the magnetic field sensor. Experimental results suggest that the response distortion induced by the sealed pressure cabin appears on mid- andhigh-frequency areas. Using experimental results as standardization data, the frequency responses collected from seafloor magnetotelluric measurements can be corrected to restore real information about the seafloor field source.展开更多
In order to solve the problems which are widespread in potato seeding planter, such as lower operating efficiency, unideal performance index, higher replay rate and leakage rate and uneven spacing sowing in seeding op...In order to solve the problems which are widespread in potato seeding planter, such as lower operating efficiency, unideal performance index, higher replay rate and leakage rate and uneven spacing sowing in seeding operating, a trailed potato fertilization seeder was designed. The key components of the special structure had been got through the description of the structure and working principle of the whole machine. A crossing seed-taken technology along with the vibration component was adopted to achieve precision seeding. The results showed in the field test of the machine: all the performance indexes of the machine met the agronomic requirement of potato planting; the multiple and missing index were low; it completed the ditching, fertilizing, seeding as well as ridging in one planting process; its operation efficiency was high and the stability was good. This design of the trailed potato fertilization seeder provided a reference for the development of large traction-type potato seeding machine.展开更多
The waveform of the explosion shock wave under free-field air explosion is an extremely complex problem.It is generally considered that the waveform consists of overpressure peak,positive pressure zone and negative pr...The waveform of the explosion shock wave under free-field air explosion is an extremely complex problem.It is generally considered that the waveform consists of overpressure peak,positive pressure zone and negative pressure zone.Most of current practice usually considers only the positive pressure.Many empirical relations are available to predict overpressure peak,the positive pressure action time and pressure decay law.However,there are few models that can predict the whole waveform.The whole process of explosion shock wave overpressure,which was expressed as the product of the three factor functions of peak,attenuation and oscillation,was proposed in the present work.According to the principle of explosion similarity,the scaled parameters were introduced and the empirical formula was absorbed to form a mathematical model of shock wave overpressure.Parametric numerical simulations of free-field air explosions were conducted.By experimental verification of the AUTODYN numerical method and comparing the analytical and simulated curves,the model is proved to be accurate to calculate the shock wave overpressure under free-field air explosion.In addition,through the model the shock wave overpressure at different time and distance can be displayed in three dimensions.The model makes the time needed for theoretical calculation much less than that for numerical simulation.展开更多
In order to solve the deformation of the hydrostatic thrust bearing with multi-pad annular recess in the heavy computer numerical control(CNC)equipment,the simulation concerning pressure field of hydrostatic thrust be...In order to solve the deformation of the hydrostatic thrust bearing with multi-pad annular recess in the heavy computer numerical control(CNC)equipment,the simulation concerning pressure field of hydrostatic thrust bearing with multi-pad annular recesses was carried out.The finite volume method of computational fluid dynamics(CFD)was used to compute the three-dimensional pressure field of gap fluid between the rotary worktable and the base.The influence of the rotational speed on the bearing pressure performance was studied based on CFD and lubrication theory,and the method revealed the pressure distribution law.The results qualitatively agree well with the experimental data.The results indicate that the oil cavity pressure decreases gradually with rotational speed enhancing.The reliability of a hydrostatic thrust bearing with multi-pad annular recess can be predicted through this method,and the optimal design of such products can be achieved,and the numerical simulation method can provide reasonable data for design,lubrication,experiment,and deformation computation of hydrostatic thrust bearing in the heavy CNC equipment.展开更多
The 2014-2015 Ebola Virus Disease (EVD) outbreaks which began in Guinea and later spread to Liberia, Sierra Leona and other countries have been responsible for a number of infections and deaths among the communities i...The 2014-2015 Ebola Virus Disease (EVD) outbreaks which began in Guinea and later spread to Liberia, Sierra Leona and other countries have been responsible for a number of infections and deaths among the communities including health workers. The natural host of the EVD virus has not been identified even when scientific evidence points to bats as the natural reservoirs to similar strains of EVD virus. EVD male survivors have also been identified as a potential source of infection among the populations. Some of the reasons attributed to this rapid spread of EVD to other countries have been weak early warning systems to identify and notify health authorities of such diseases of high epidemic potential. Liberia has been one of the countries to be declared EVD free on two different occasions in 2015 each with a different epicenter. Despite a number of international organizations coming together to support control efforts in Liberia, the coordination of response activities by the Ministry of Health and Social Welfare and replicated at all levels of the surveillance systems was the key in suppressing the outbreak. Adoption of the Integrated Disease Surveillance and Response (IDSR) guidelines as recommended by World Health Organization (WHO/AFRO) was a positive step towards the structuring of response activities. Capacity building of health workers in infection control and prevention and surveillance was important to improve skills of health workers to triage EVD cases as recommended by WHO. Training community health volunteers in contact tracing and active case search was important in strengthening the Early Warning Disease surveillance system. Decentralization of response activities in addition to establishing Ebola Treatment units and Community Care Centers in all counties was vital in containing the spread of infection. Even when EVD was associated to high levels of stigma, community and individual counseling sessions led by community leaders enabled building community trust to refer cases for treatment. The EVD survivors distributed in different parts of the country are potential sources of new EVD infections. This will require strengthening early warning systems and response capacity at all levels.展开更多
This research is to share qualitative data of one preservice teacher,and one early childhood entrepreneur,who educated young children in an exclusive outdoor preschool.The study was conducted in a rural community wher...This research is to share qualitative data of one preservice teacher,and one early childhood entrepreneur,who educated young children in an exclusive outdoor preschool.The study was conducted in a rural community where most preschools were held in the traditional venue-inside.The Coronavirus-19 pandemic presented many obstacles to the placement of preservice teachers in an appropriate early childhood setting.The university discouraged all direct contact with children.Instead,preservice teachers were expected to view videos of veteran teachers,who in former years,submitted teaching videos to obtain a“National Boards Certification.”The objective was that the preservice teachers would“reflect”and learn from the electronic source.This electronic substitution was unacceptable to the researcher.Practicum experiences allow for rich collaboration between preservice teacher and child.Electronic sources can never replicate the rich learning that happens during an authentic face-to face encounter with a child.Thus,the vision for the study was born.As an alternative to exclusive electronic learning,the preservice university supervisor initiated the opportunity for preservice teachers to participate with a local entrepreneur who was in the process of designing and implementing an exclusive outdoor school.Nature and environmental field experience opportunities for preservice teachers are promising alternatives to the traditional preschool setting.Venues that encourage nature and environmental studies enhance early childhood programs and create opportunities for preservice teachers,and the children they serve,to appreciate the nature around them enhancing their natural curiosity and investigative skills to seek,study,and share.This research article shares the reflections of both the preschool entrepreneur as well as the preservice teacher.It is a pragmatic description of how the exclusive outdoor environment is feasible and presents the challenges and assets that the environmental venue provides.展开更多
基金National Natural Science Foundation of China(U22422203,42030610,41975138,41975046,42075086,42275008)the High-level Science and Technology Journals Projects of Guangdong Province(214040990009)+1 种基金National Key Research and Development Program of China under Grant(2017YFC1501701,2017YFC1501703)Science and Technology Foundation of CAMS(2020KJ021)。
文摘Aiming at the needs of mechanism analysis of rainstorms and development of numerical prediction models in south China, the Guangzhou Institute of Tropical and Marine Meteorology of China Meteorological Administration and the Chinese Academy of Meteorological Sciences jointly set up the Longmen Cloud Physics Field Experiment Base,China Meteorological Administration. This paper introduces the instruments and field experiments of this base, provides an overview of the recent advances in retrieval algorithms of microphysical parameters, improved understanding of microphysical characteristics, as well as the formation mechanisms and numerical prediction of heavy rainfalls in south China based on the field experiments dataset.
基金supported by the National Natural Science Foundation of China (71973087 and 72003215)the 72nd General Program of China Postdoctoral Science Foundation (2022M720170)+1 种基金the Soft Science Project of the Department of Science and Technology of Shaanxi Province, China (2022KRM131)the Special Fund Project of Basic Scientific Research Operation Funds of Central Universities, China (20SZYB21)。
文摘Based on the microdata of 705 wheat farmers in the Loess Plateau, this study empirically analyzes the impact of uncertainty on farmers' adoption of innovative seeds using a field experiment. The results indicate that farmers are generally ambiguity-averse and risk-averse. In addition, farmers with higher ambiguity aversion and risk aversion are less likely to adopt innovative wheat seeds, where their risk aversion plays a dominant role. Enhancing information access will alleviate the negative influence of ambiguity aversion on farmers' adoption of innovative seeds, and interlinked insurance and credit contracts will be beneficial to ease the adverse effect of risk aversion on the adoption of innovative wheat seeds. Meanwhile, heterogeneity analysis reveals that the inhibitory effects of ambiguity aversion and risk aversion on innovative seed adoption are more significant among farmers with lower education and household income.The government can establish both ex-ante and ex-post relevant guarantee mechanisms to help farmers preferably cope with various uncertainties in the production process, remitting farmers' ambiguity aversion and risk aversion to enhance new agricultural technology adoption rates.
基金sponsored by The National Natural Science Foundation of China(Grant Nos.51939004 and 51279090)The National Key Research and Development Program of China(2017YFC1501100)the Hubei Key Laboratory of Construction and Management in Hydropower Engineering(2020KSD11).
文摘Rainfall infiltration on a soil slope is usually an unsaturated seepage process that can be described by a water-air two-phase flow model.The effect of pore air pressure on rainfall infiltration has been widely recognized and validated by means of numerical simulations and laboratory experiments.However,whether a slope can actually seal pore air continues to be debated by researchers.In this study,a water-air two-phase flow model is used to simulate the rainfall infiltration process on a soil slope,and a field experiment is conducted to realistically test the sealing conditions of a slope.According to the numerical simulation,the areas of water and air flow in and out on the slope surface are relatively stable and can be classified as the“inhalation zone”and“overflow zone”,respectively.Intermittent rainfall on the soil slope has an amplifying effect on pore air pressure because rainfall intensity is usually at the millimeter level,and it causes pore air pressure to reach the cm level.A field experiment was performed to determine whether a slope can realistically seal pore air and subsequently verify the regularity of rainfall infiltration.Air pressure sensors were buried in the slope to monitor the pore air pressures during the rainfall process.The monitoring results show that the pore air pressure in the slope changed,which indicates that the slope can seal air.Moreover,the amplification effects of intermittent rainfall on pore air pressure were observed for natural rainfall,which agrees well with the numerical simulation results.
基金supported by the School of Fundamental Science and Engineering,Faculty of Science and Engineering,Waseda University,Japansupported under the Dana Impak Perdana(DIP)Grant Scheme DIP-2018-040 and FRGS/1/2018/TK04/UKM/02/17.
文摘The 5G network has been intensively investigated to realize the ongoing early deployment stage as an effort to match the exponential growth of the number of connected users and their increasing demands for high throughput,bandwidth with Quality of Service(QoS),and low latency.Given that most of the spectrums below 6 GHz are nearly used up,it is not feasible to employ the traditional spectrum,which is currently in use.Therefore,a promising and highly feasible effort to satisfy this insufficient frequency spectrum is to acquire new frequency bands for next-generation mobile communications.Toward this end,the primary effort has been focused on utilizing the millimeter-wave(mmWave)as the most promising candidate for the frequency spectrum.However,though the mmWave frequency band can fulfill the desired bandwidth requirements,it has been demonstrated to endure several issues like scattering,atmospheric absorption,fading,and especially penetration losses compared to the existing sub-6 GHz frequency band.Then,it is fundamental to optimize the mmWave band propagation channel to facilitate the practical 5G implementation for the network operators.Therefore,this study intends to investigate the outdoor channel characteristics of 26,28,36,and 38 GHz frequency bands for the communication infrastructure at the building to the ground floor in both Line of Sight(LOS)and Non-Line of Sight(NLOS)environments.The experimental campaign has studied the propagation path loss models such as Floating-Intercept(FI)and Close-In(CI)for the building to ground floor environment in LOS and NLOS scenarios.The findings obtained from the field experiments clearly show that the CI propagation model delivers much better performance in comparison with the FI model,thanks to its simple setup,accuracy,and precise function.
基金supported by the National Natural Science Foundation of China (Grant Nos. 11975163 and 12175160)the Priority Academic Program Development of Jiangsu Higher Education Institutions (PAPD)。
文摘Based on high magnetic field helicon experiment(HMHX), HELIC code was used to study the effect of different magnetic fields on the power deposition under parabolic distribution. This paper is divided into three parts: preliminary calculation, actual discharge experiment and calculation. The results of preliminary calculation show that a magnetic field that is too small or too large cannot produce a good power deposition effect. When the magnetic field strength is 1200 Gs,a better power deposition can be obtained. The actual discharge experiment illustrates that the change of the magnetic field will have a certain influence on the discharge phenomenon. Finally, the results of verification calculation successfully verify the accuracy of the results of preliminary simulation. The results show that in the actual discharge experiment, it can achieve the best deposition effect when the magnetic field is 1185 Gs.
基金Authors wish to thank the funding from 13th five-year plan National key research program(No.2016YFD0200606)National Natural Science Foundation of China(No.51105147)+1 种基金Foundation of Guangdong Province of China(No.S2011010001948)Commonweal Project(Project No.201203059).
文摘In order to meet the requirement of field direct seeding for super hybrid rice:1-3 seeds per hill,a pneumatic rice direct-seeder with six seeding metering devices was designed.Transmission system of pneumatic rice direct-seeder and seed metering device were analyzed in this study.And the pipeline structure and vortex pump were designed and selected.The pressure distribution of the pipeline was tested.The pressure value of each sub-pipeline under the conditions of different main pipeline pressure value was obtained and the reasons for pressure loss were analyzed.The results showed that the variation coefficient between sub-pipelines was less than 5%.The pipeline pressure could be evenly distributed.Further,the field experiments were carried out on super hybrid rice Peizataifeng using two-factor testing,by which the effects of different negative pressure and different forward speed(namely,rotational speed of suction plate)for seeding precision were studied.It found that:(1)the optimal negative pressure was 2 kPa;(2)under the optimal negative pressure,the probabilities of 1-3 seeds per hill for the direct-seeder were 93.41%,95.47%and 97.50%,respectively,when the forward speed of the direct-seeded was high,medium and low speed;(3)the probability of empty hole was less than 2%,which satisfied the field direct seeding requirements of super hybrid rice.Additionally,hill spacing was measured,and the factors affecting the hill spacing were analyzed.The results showed that the fluctuation of hill spacing in the small range will not affect the seeding effect.In this study,a new type of pneumatic rice direct-seeder was designed.The main working components were tested and analyzed.The best parameters of field work were obtained.It provides the basis for the field application of the pneumatic rice precision seeder.
基金This work was supported by China’s Ministry of Agriculture,Agricultural Public Welfare Industry Research(201503117)China’s Ministry of Agriculture,Agricultural Public Welfare Industry Research(201503116-16)the Soil-Machine-Plant Key Laboratory of the Ministry of Agriculture of China.
文摘Soil compaction is a common problem facing conservation fields that restricts crop root growth and causes yield decrease.Subsoil techniques have been developed to break up the compaction layer.However,subsoil implement requires large draft power that hampered the development of subsoil techniques for most of developing countries due to lack of large scale tractors.Aiming to optimize the penetration resistance of the subsoiler and create a good working environment for the operators,a staggered vibrating subsoiler was developed.A new staggered vibrating mechanism was designed to generate the staggered vibration of the shanks meanwhile the V-shape shanks arrangement was adopted to keep relative balance for the subsoiler.In order to obtain optimum working parameters of the vibration frequency and forward speed,the trajectory of shanks was simulated by using the MATLAB software.The forward speed of 2-3 km/h with vibration frequency of 12 Hz was recommended to acquire an effective decrease in draft force.Field performance of this subsoiler was evaluated in terms of the draft force,power requirement and tractor wheel slippage.By comparing the two operation modes,staggered vibrating(SV)and rigid(NV)of shanks,the decrease ratios of draft force for SV were determined by 16.97%,12.12%and 9.02%at forward speeds of 2.2 km/h,2.6 km/h and 3.1 km/h,respectively.This is better than the research for the 1SZ-460 vibratory subsoiler that was decreased by 9.09%in draft force.The power requirement for SV was not significantly greater than that for NV.The obviously decreased wheel slippage was observed for SV by decrease of 12.47%,17.96%and 21.79%at forward speeds of 2.2 km/h,2.6 km/h and 3.1 km/h,respectively.In conclusion,the staggered vibrating subsoiler presents preferable working performance and is recommended to be applied in subsoil tillage process for developing countries.
文摘Late blight caused by <i>Phytophthora</i> <i>infestans</i> (Mont.) De Bary is the most devastating disease of potato. This study was carried out to evaluate the efficacy of ten botanical extracts against the late blight disease incidence and severity in experimental potato field at University of Rajshahi, Bangladesh during 2019-2020. Crude aqueous extract of leaves of <i>Syzygium</i> <i>cumini</i>, <i>Psidium</i> <i>guajava</i>, <i>Eucalyptus</i> <i>globusus</i>, <i>Carica</i> <i>papaya</i> and <i>Lawsonia</i> <i>inermis</i>;fruits of <i>Terminalia</i> <i>bellirica</i>, <i>T.</i> <i>chebula</i> and <i>Piper</i> <i>nigrum</i>;flower buds of <i>Syzygium</i> <i>aromaticum</i> and cloves of <i>Allium</i> <i>sativum</i> were used at 5% (w/v) concentration for evaluation. Out of ten botanicals, <i>Syzygium</i> <i>cumini</i> leaves extract was found most effective in controlling the late blight disease incidence and severity up to 66 DAS (days after sowing) and increased the potato yield by 71.29% compare to untreated control. The efficacy of <i>Lawsonia</i> <i>inermis</i> extract against late blight disease was found promising and increased the potato yield by 48.51%. Other four botanical extracts (<i>Terminalia</i> <i>chebula</i>, <i>Piper</i> <i>nigrum</i>, <i>Syzygium</i> <i>aromaticum</i> and <i>Carica</i> <i>papaya</i>) showed moderate efficacy <span>against the incidence and severity of late blight disease, and increased 30% </span>more potato yield compare to control. These results suggest that botanical extract of <i>Syzygium</i> <i>cumini</i> ha<span style="font-family:;" "="">s</span><span style="font-family:;" "=""> a great potential as an alternative </span><span style="font-family:;" "="">of</span><span style="font-family:;" "=""> chemical fungicides to control the late blight disease of potato in</span><span style="font-family:;" "=""> </span><span style="font-family:;" "="">eco-friendly way.</span>
基金This paper is supported by the National "863" Program in the Tenth Five-Year-Plan (No. 2002AA615020)Eleventh Five-Year-Plan (No. 2006AA09A201)the Focused Subject Program of Beijing (No. XK104910598).
文摘Although magnetotelluric sounding method applied to the land is advanced, there are many difficulties when it is applied to marine environment, one of which is how to lay magnetic field sensors down to the seafloor to complete measurements. To protect the magnetic field sensors from intense erosion and high pressure, suitable high-pressure sealed cabins must be designed to load them. For the consideration of magnetic measurement and marine operation, the sealed pressure cabin should be nonmagnetic and transportable. Among all optional materials, LC4 super-hard aluminum alloy has the highest performance of price/quality ratio to make the sealed pressure cabin. However, it does not mean that the high-pressure sealed cabin made using LC4 will be perfect in performance. In fact, because of its weak magnetism, the pressure cabin made using LC4 has distorting effect on frequency responses of the magnetic field sensors sealed in it. This distorting effect does not affect the use of the magnetic field sensor, but if we want to eliminate its effect, we should study it by experimental measurements. In our experiment tests, frequency sweep magnetic field as excitation signal was used, and then responses of the magnetic field sensor before and after being loaded into the high-pressure sealed cabin were measured. Finally, normalized abnormal curves for the frequency responses were obtained, through which we could show how the high-pressure sealed cabin produces effects on the responses of the magnetic field sensor. Experimental results suggest that the response distortion induced by the sealed pressure cabin appears on mid- andhigh-frequency areas. Using experimental results as standardization data, the frequency responses collected from seafloor magnetotelluric measurements can be corrected to restore real information about the seafloor field source.
基金Supported by Funding(2016YFD0701600)from Research and Development of Potato Harvesting Technology and EquipmentSpecial Funds for Construction of Modern Agricultural Technology System(CARS-10-P22)Study on Key Technical Equipment for Scale of Potato Planting(GA15B401)
文摘In order to solve the problems which are widespread in potato seeding planter, such as lower operating efficiency, unideal performance index, higher replay rate and leakage rate and uneven spacing sowing in seeding operating, a trailed potato fertilization seeder was designed. The key components of the special structure had been got through the description of the structure and working principle of the whole machine. A crossing seed-taken technology along with the vibration component was adopted to achieve precision seeding. The results showed in the field test of the machine: all the performance indexes of the machine met the agronomic requirement of potato planting; the multiple and missing index were low; it completed the ditching, fertilizing, seeding as well as ridging in one planting process; its operation efficiency was high and the stability was good. This design of the trailed potato fertilization seeder provided a reference for the development of large traction-type potato seeding machine.
基金partially sponsored by Foundation of PLA Rocket Force
文摘The waveform of the explosion shock wave under free-field air explosion is an extremely complex problem.It is generally considered that the waveform consists of overpressure peak,positive pressure zone and negative pressure zone.Most of current practice usually considers only the positive pressure.Many empirical relations are available to predict overpressure peak,the positive pressure action time and pressure decay law.However,there are few models that can predict the whole waveform.The whole process of explosion shock wave overpressure,which was expressed as the product of the three factor functions of peak,attenuation and oscillation,was proposed in the present work.According to the principle of explosion similarity,the scaled parameters were introduced and the empirical formula was absorbed to form a mathematical model of shock wave overpressure.Parametric numerical simulations of free-field air explosions were conducted.By experimental verification of the AUTODYN numerical method and comparing the analytical and simulated curves,the model is proved to be accurate to calculate the shock wave overpressure under free-field air explosion.In addition,through the model the shock wave overpressure at different time and distance can be displayed in three dimensions.The model makes the time needed for theoretical calculation much less than that for numerical simulation.
基金National Natural Science Foundations of China(No.51075106,No.51005063,No.50975066)Technology Items of Heilongjiang Provincial Education Department,China(No.12511087,No.12521096,No.12511086,No.12511088,No.11551080,No.12521119)+1 种基金Projects of the Special Fund on the Science and Technology Innovation People of Harbin,China(No.2012RFQXG077)the 2012 National College of Innovative Pilot Project,China(No.201210214027)
文摘In order to solve the deformation of the hydrostatic thrust bearing with multi-pad annular recess in the heavy computer numerical control(CNC)equipment,the simulation concerning pressure field of hydrostatic thrust bearing with multi-pad annular recesses was carried out.The finite volume method of computational fluid dynamics(CFD)was used to compute the three-dimensional pressure field of gap fluid between the rotary worktable and the base.The influence of the rotational speed on the bearing pressure performance was studied based on CFD and lubrication theory,and the method revealed the pressure distribution law.The results qualitatively agree well with the experimental data.The results indicate that the oil cavity pressure decreases gradually with rotational speed enhancing.The reliability of a hydrostatic thrust bearing with multi-pad annular recess can be predicted through this method,and the optimal design of such products can be achieved,and the numerical simulation method can provide reasonable data for design,lubrication,experiment,and deformation computation of hydrostatic thrust bearing in the heavy CNC equipment.
文摘The 2014-2015 Ebola Virus Disease (EVD) outbreaks which began in Guinea and later spread to Liberia, Sierra Leona and other countries have been responsible for a number of infections and deaths among the communities including health workers. The natural host of the EVD virus has not been identified even when scientific evidence points to bats as the natural reservoirs to similar strains of EVD virus. EVD male survivors have also been identified as a potential source of infection among the populations. Some of the reasons attributed to this rapid spread of EVD to other countries have been weak early warning systems to identify and notify health authorities of such diseases of high epidemic potential. Liberia has been one of the countries to be declared EVD free on two different occasions in 2015 each with a different epicenter. Despite a number of international organizations coming together to support control efforts in Liberia, the coordination of response activities by the Ministry of Health and Social Welfare and replicated at all levels of the surveillance systems was the key in suppressing the outbreak. Adoption of the Integrated Disease Surveillance and Response (IDSR) guidelines as recommended by World Health Organization (WHO/AFRO) was a positive step towards the structuring of response activities. Capacity building of health workers in infection control and prevention and surveillance was important to improve skills of health workers to triage EVD cases as recommended by WHO. Training community health volunteers in contact tracing and active case search was important in strengthening the Early Warning Disease surveillance system. Decentralization of response activities in addition to establishing Ebola Treatment units and Community Care Centers in all counties was vital in containing the spread of infection. Even when EVD was associated to high levels of stigma, community and individual counseling sessions led by community leaders enabled building community trust to refer cases for treatment. The EVD survivors distributed in different parts of the country are potential sources of new EVD infections. This will require strengthening early warning systems and response capacity at all levels.
文摘This research is to share qualitative data of one preservice teacher,and one early childhood entrepreneur,who educated young children in an exclusive outdoor preschool.The study was conducted in a rural community where most preschools were held in the traditional venue-inside.The Coronavirus-19 pandemic presented many obstacles to the placement of preservice teachers in an appropriate early childhood setting.The university discouraged all direct contact with children.Instead,preservice teachers were expected to view videos of veteran teachers,who in former years,submitted teaching videos to obtain a“National Boards Certification.”The objective was that the preservice teachers would“reflect”and learn from the electronic source.This electronic substitution was unacceptable to the researcher.Practicum experiences allow for rich collaboration between preservice teacher and child.Electronic sources can never replicate the rich learning that happens during an authentic face-to face encounter with a child.Thus,the vision for the study was born.As an alternative to exclusive electronic learning,the preservice university supervisor initiated the opportunity for preservice teachers to participate with a local entrepreneur who was in the process of designing and implementing an exclusive outdoor school.Nature and environmental field experience opportunities for preservice teachers are promising alternatives to the traditional preschool setting.Venues that encourage nature and environmental studies enhance early childhood programs and create opportunities for preservice teachers,and the children they serve,to appreciate the nature around them enhancing their natural curiosity and investigative skills to seek,study,and share.This research article shares the reflections of both the preschool entrepreneur as well as the preservice teacher.It is a pragmatic description of how the exclusive outdoor environment is feasible and presents the challenges and assets that the environmental venue provides.
