The electrocatalytic N_(2)reduction reaction(NRR)is expected to supersede the traditional Haber-Bosch technology for NH3 production under ambient conditions.The activity and selectivity of electrochemical NRR are rest...The electrocatalytic N_(2)reduction reaction(NRR)is expected to supersede the traditional Haber-Bosch technology for NH3 production under ambient conditions.The activity and selectivity of electrochemical NRR are restricted to a strong polarized electric field induced by the catalyst,correct electron transfer direction,and electron tunneling distance between bare electrode and active sites.By coupling the chemical vapor deposition method with the poly(methyl methacylate)-transfer method,an ultrathin sandwich catalyst,i.e.,Fe atoms(polarized electric field layer)sandwiched between ultrathin(within electron tunneling distance)BN(catalyst layer)and graphene film(conducting layer),is fabricated for electrocatalytic NRR.The sandwich catalyst not only controls the transfer of electrons to the BN surface in the correct direction under applied voltage but also suppresses hydrogen evolution reaction by constructing a neutral polarization electric field without metal exposure.The sandwich electrocatalyst NRR system achieve NH3 yield of 8.9μg h^(−1)cm^(−2)and Faradaic Efficiency of 21.7%.The N_(2)adsorption,activation,and polarization electric field changes of three sandwich catalysts(BN-Fe-G,BN-Fe-BN,and G-Fe-G)during the electrocatalytic NRR are investigated by experiments and density functional theory simulations.Driven by applied voltage,the neutral polarized electric field induced by BN-Fe-G leads to the high activity of electrocatalytic NRR.展开更多
Image quality in positron emission tomography(PET)is affected by random and scattered coincidences and reconstruction protocols.In this study,we investigated the effects of scattered and random coincidences from outsi...Image quality in positron emission tomography(PET)is affected by random and scattered coincidences and reconstruction protocols.In this study,we investigated the effects of scattered and random coincidences from outside the field of view(FOV)on PET image quality for different reconstruction protocols.Imaging was performed on the Discovery 690 PET/CT scanner,using experimental configurations including the NEMA phantom(a body phantom,with six spheres of different sizes)with a signal background ratio of 4:1.The NEMA phantom(phantom I)was scanned separately in a one-bed position.To simulate the effect of random and scatter coincidences from outside the FOV,six cylindrical phantoms with various diameters were added to the NEMA phantom(phantom II).The 18 emission datasets with mean intervals of 15 min were acquired(3 min/scan).The emission data were reconstructed using different techniques.The image quality parameters were evaluated by both phantoms.Variations in the signal-to-noise ratio(SNR)in a 28-mm(10-mm)sphere of phantom II were 37.9%(86.5%)for ordered-subset expectation maximization(OSEM-only),36.8%(81.5%)for point spread function(PSF),32.7%(80.7%)for time of flight(TOF),and 31.5%(77.8%)for OSEM+PSF+TOF,respectively,indicating that OSEM+PSF+TOF reconstruction had the lowest noise levels and lowest coefficient of variation(COV)values.Random and scatter coincidences from outside the FOV induced lower SNR,lower contrast,and higher COV values,indicating image deterioration and significantly impacting smaller sphere sizes.Amongst reconstruction protocols,OSEM+PSF+TOF and OSEM+PSF showed higher contrast values for sphere sizes of 22,28,and 37 mm and higher contrast recovery coefficient values for smaller sphere sizes of 10 and 13 mm.展开更多
Hydrogenated amorphous carbon films were fabricated by using layer-by-layer deposition method and hydrogen dilution method in a small d.c.-assisted plasma enhanced chemical vapor deposition system. It was found that t...Hydrogenated amorphous carbon films were fabricated by using layer-by-layer deposition method and hydrogen dilution method in a small d.c.-assisted plasma enhanced chemical vapor deposition system. It was found that the hydrogen plasma treatment could change the sp2/sp3 ratio to some extent by chemical etching. The improvements of field emission characteristics were observed compared with that from conventionally deposited a-C films, which can be attributed to the large field enhancement effect due to the inhomogeneous distribution of nanometer scale sp2 clusters and the reduction of the surface emission barrier due to the hydrogen termination.展开更多
A field experiment was conducted on Chinese cabbage （Brassica campestris L. ssp. pekinensis （Lour.） Olsson） in a Nanjing suburb in 2003. The experiment included 4 treatments in a randomized complete block design w...A field experiment was conducted on Chinese cabbage （Brassica campestris L. ssp. pekinensis （Lour.） Olsson） in a Nanjing suburb in 2003. The experiment included 4 treatments in a randomized complete block design with 3 replicates： zero chemical fertilizer N （CK）; urea at rates of 300 kg N ha^-1 （U300） and 600 kg N ha^-1 （U600）, both as basal and two topdressings; and polymer-coated urea at a rate of 180 kg N ha^-1 （PCU180） as a basal application. The acetylene inhibition technique was used to measure denitrification （N2 ＋ N2O） from intact soil cores and N2O emissions in the absence of acetylene. Results showed that compared to （3K total denitrification losses were significantly greater （P ≤ 0.05） in the PCU180, U300, and U600 treatments,while N2O emissions in the U300 and U600 treatments were significantly higher （P ≤ 0.05） than （3K. In the U300 and U600 treatments peaks of denitrification and N2O emission were usually observed after N application. In the polymer-coated urea treatment （PCU180） during the period 20 to 40 days after transplanting, higher denitrification rates and N2O fluxes occurred. Compared with urea, polymer-coated urea did not show any effect on reducing denitrification losses and N2O emissions in terms of percentage of applied N. As temperature gradually decreased from transplanting to harvest, denitrification rates and N2O emissions tended to decrease. A significant （P ≤0.01） positive correlation occurred between denitrification （r = 0.872） or N2O emission （r = 0.781） flux densities and soil temperature in the CK treatment with a stable nitrate content during the whole growing season.展开更多
The controllable growth of three different morphologies of AlN nanostructures （nanorod, nanotip and nanocrater） arrays are successfully realized by using chemical vapour deposition （CVD） technology. All three nano...The controllable growth of three different morphologies of AlN nanostructures （nanorod, nanotip and nanocrater） arrays are successfully realized by using chemical vapour deposition （CVD） technology. All three nanostructures are of single crystal h-AlN with a growth orientation of [001]. Their growth is attributed to the vapour-liquid-solid （VLS） mechanism. To investigate the factors affecting field emission （FE） properties of AlN nanostructures, we compare their FE behaviours in several aspects. Experimental results show that AIN nanocrater arrays possess the best FE properties, such as a threshold field of 7.2 V/μm and an emission current fluctuation lower than 4%. Moreover, the three AlN nanostructures all have good field emission properties compared with a number of other excellent cathode nanomaterials, which suggests that they are future promising FE nanomaterials.展开更多
Measurements of N2O emissions from conventional rice cultivation （CRC）, CRC with straw mulching, system of rice intensification （SRI） and SRI with plastic film mulching were conducted through static chamber/gas-...Measurements of N2O emissions from conventional rice cultivation （CRC）, CRC with straw mulching, system of rice intensification （SRI） and SRI with plastic film mulching were conducted through static chamber/gas-chromatography techniques. The results show that daily fluctuation of N2O emissions in jointing stage are much higher than in others. A type peak of N2O seasonal emission presented between jointing and bearing stages companying with high daily average temperature and low precipitation. Biomass and leaf stomatal conductance were observed. Total quantities of N2O emission were budgeted. The results showed that after jointing stage the average N2O emission flux of SRI with plastic film mulching increased significantly than CRC with straw mulching and SRI, the leaf stomatal conductance of those showed the same trend （p〈 0.05）. Yield and total quantity of N20 emission in CRC with straw mulching enhanced 13. 7% and 10.7% compared with those of CRC, respectively. The total quantity of N20 emissions reduced 3. 6% in SRI with plastic film mulching compared with CRC, however, the yield increase of that was not significant.展开更多
Ammonia emission is one of the most important pathways of nitrogen loss from agricultural cultivated field. In this paper, we report the measurement of ammonia emission from paddy rice field obtained by surface applic...Ammonia emission is one of the most important pathways of nitrogen loss from agricultural cultivated field. In this paper, we report the measurement of ammonia emission from paddy rice field obtained by surface application of urea fertilizer with water management. The main objective of the present study were to assess the amount of NH3 emission and the loss of nitrogen from paddy field as affected by various N doses, i.e., 0 (control), 90 (N1), 180 (N2), 270 (N3) and 360 (N4) kg ha-1, following field surface application of urea fertilizer with water management. Ammonia emissions were measured by continuous airflow enclosure method from plots fertilized with the application of surface urea. Increase in urea-N dosage increased NH3 emission that was measured from paddy rice field. Ammonia emission started immediately and was almost complete within 12 days after top dressing of urea application to the soils. Ammonia emissions were nearly constant in all treatments from 12 days after fertilizer application. Highest ammonia emission rate was 28 g /day and total amount of ammonia emission was 56.21 kg ha-1 for 360 kg N ha-1 dose. No remarkable observation was found about temperature for ammonia emission. Due to proper water management practices less emission was observed throughout the experiment period. The results also show that N loss through NH3 emission accounted for 11 to 16% during the rice- growing season. These magnitudes of loss of N appear to be most important for environmental point of view.展开更多
The spontaneous emission property ofΛ-type three-level atom driven by the bichromatic field in the anisotropic double-band photonic crystal is calculated by n-times iteration method.The influence of different paramet...The spontaneous emission property ofΛ-type three-level atom driven by the bichromatic field in the anisotropic double-band photonic crystal is calculated by n-times iteration method.The influence of different parameters on atomic spontaneous emission is studied,and the phenomena of atomic spontaneous emission are explained in the dressed state representation.It is found that the spontaneous emission spectra of the atom driven by the bichromatic field presents a multi-peak comb structure.The position of the emission peak is determined by the initial state of the atom,and the interval between the neighboring emission peaks is the detuningδof the bichromatic field.When the ratio between Rabi frequency intensity and the detuningδof the bichromatic field remains unchanged,the intensity of each emitted peak remains invariant.The spontaneously emitted peak can be annihilated in the band gap and enhanced near the band edge in the anisotropic photonic crystals.Meanwhile,we also observe the fluorescence quenching phenomenon in the spontaneous emission spectra.The research in this paper provides the theoretical guidance for the control of atomic spontaneous emission.展开更多
Graphene films are deposited on copper （Cu） and aluminum （Al） substrates, respectively, by using a microwave plasma chemical vapour deposition technique. Furthermore, these graphene films are characterized by a fi...Graphene films are deposited on copper （Cu） and aluminum （Al） substrates, respectively, by using a microwave plasma chemical vapour deposition technique. Furthermore, these graphene films are characterized by a field emission type scanning electron microscope （FE-SEM）, Raman spectra, and field emission （FE） I-V measurements. It is found that the surface morphologies of the films deposited on Cu and Al substrates are different： the field emission property of graphene film deposited on the Cu substrate is better than that on the Al substrate, and the lowest turn-on field of 2.4 V/p-m is obtained for graphene film deposited on the Cu substrate. The macroscopic areas of the graphene samples are all above 400 mm2.展开更多
The field emission （FE） properties of vertically aligned graphene sheets （VAGSs） grown on different SiC substrates are reported. The VAGSs grown on nonpolar SiC （10-10） substrate show an ordered alignment with t...The field emission （FE） properties of vertically aligned graphene sheets （VAGSs） grown on different SiC substrates are reported. The VAGSs grown on nonpolar SiC （10-10） substrate show an ordered alignment with the graphene basal plane-parallel to each other, and show better FE features, with a lower turn-on field and a larger field enhancement factor. The VAGSs grown on polar SiC （000-1 ） substrate reveal a random petaloid-shaped arrangement and stable current emission over 8 hours with a maximum emission current fluctuation of only 4%. The reasons behind the differing FE characteristics of the VAGSs on different SiC substrates are analyzed and discussed.展开更多
In this paper,we report the effect of nitrogen on the deposition and properties of boron doped diamond films synthesized by hot filament chemical vapor deposition.The diamond films consisting of micro-grains(nano-grai...In this paper,we report the effect of nitrogen on the deposition and properties of boron doped diamond films synthesized by hot filament chemical vapor deposition.The diamond films consisting of micro-grains(nano-grains) were realized with low(high) boron source flow rate during the growth processes.The transition of micro-grains to nano-grains is speculated to be strongly(weekly) related with the boron(nitrogen) flow rate.The grain size and Raman spectral feature vary insignificantly as a function of the nitrogen introduction at a certain boron flow rate.The variation of electron field emission characteristics dependent on nitrogen is different between microcrystalline and nanocrystalline boron doped diamond samples,which are related to the combined phase composition,boron doping level and texture structure.There is an optimum nitrogen proportion to improve the field emission properties of the boron-doped films.展开更多
This study was carried out in paddy fields to explore how organic manure applications would affect greenhouse emissions in South China. The results showed that the seasonal emission of CH4 under the chemical fertiliz...This study was carried out in paddy fields to explore how organic manure applications would affect greenhouse emissions in South China. The results showed that the seasonal emission of CH4 under the chemical fertilizer （CF） treatment was 271.47 kg/hm^2. In comparison, the seasonal emissions of CH4 under the treatment of pig manure （PM）, chicken manure （CM） and rice straw （RS） increased by 50.61,260.22 and 602.82 kg/hm^2, respectively. N2O emission under the CF treatment was 1.22 kg/hm^2, while the N20 seasonal emissions under tile PM, CM and RS treatment decreased by 23.6% （P〈0.05）, 31.7% （P〈0.05） and 30.9% （P〈0.05）, respectively. Meanwhile, the readily oxidized organic carbon （which was oxidized by 167 mmol/L potassium permanganate, ROC167） of manure, paddy soil Eh value and temperature could also affect the CH4 emissions. The average yield of the organic fertilizer treatments increased by 6.8% compared with that of the CF treatment. Among all the organic fertilizer treatments, the PM treatment offered the lowest global warming potential and greenhouse gas intensity, in which the PM was of no significant difference from NF （no fertilizing） and CF. Therefore, the pig manure is capable of coordinating the relationship between environment and yield, and it also has a low ROC167 content, so the PM is considered worthy of recommendation.展开更多
Methane emissions from Chinese paddy soil (Zhejiang Province) were measured over the rice growing seasons. Different fertilizers (organic and chemical) were applied, emissions of methane were high during two periods(5...Methane emissions from Chinese paddy soil (Zhejiang Province) were measured over the rice growing seasons. Different fertilizers (organic and chemical) were applied, emissions of methane were high during two periods(5 days after peak tillering and 7 days after heading flowering stage) and significant effect of fertilizers was observed. Methanogenic activities in soils treated with organic manures were obviously higher than those with chemical fertilizers. Among the organic manured fields the maximum methane emission from green manure, biogas residue and beef manure treatment were 52, 20 and 19 times respectively of that given by control, and among chemical fertilizers it was NH\-4HCO\-3>CO(NH 2) 2>(NH 4) 2SO 4>NH 4Cl>NaNO 3 with 2\^4, 2, 1\^5,1\^3 and 0\^2 times respectively of that from control.展开更多
Large-area patterned films of boron nanowires（BNWs） are fabricated at various densities by chemical vapor deposition（CVD）. Different widths of unit-cell of Mo masks are used as templates. The widths of unit-cell o...Large-area patterned films of boron nanowires（BNWs） are fabricated at various densities by chemical vapor deposition（CVD）. Different widths of unit-cell of Mo masks are used as templates. The widths of unit-cell of Mo masks are100 μm, 150 μm, and 200 μm, respectively. The distance between unit cells is 50 μm. The BNWs have an average diameter of about 20 nm and lengths of 10 μm–20 μm. High-resolution transmission electron microscopy analysis shows that each nanowire has a β-tetragonal structure with good crystallization. Field emission measurements of the BNW films show that their turn-on electric fields decrease with width of unit-cell increasing.展开更多
Nano-diamond particles are co-deposited on Ti substrates with metal(Ti/Ni) nanoparticles(NPs) by the electrophoretic deposition(EPD) method combined with a furnace annealing at 800℃ under N_(2) atmosphere. Modificati...Nano-diamond particles are co-deposited on Ti substrates with metal(Ti/Ni) nanoparticles(NPs) by the electrophoretic deposition(EPD) method combined with a furnace annealing at 800℃ under N_(2) atmosphere. Modifications of structural and electron field emission(EFE) properties of the metal-doped films are investigated with different metal NPs concentrations. Our results show that the surface characteristics and EFE performances of the samples are first enhanced and then reduced with metal NPs concentration increasing. Both the Ti-doped and Ni-doped nano-diamond composite films exhibit optimal EFE and microstructural performances when the doping quantity is 5 mg. Remarkably enhanced EFE properties with a low turn-on field of 1.38 V/μm and a high current density of 1.32 mA/cm^(2) at an applied field of 2.94 V/μm are achieved for Ni-doped nano-diamond films, and are superior to those for Ti-doped ones. The enhancement of the EFE properties for the Ti-doped films results from the formation of the TiC-network after annealing. However, the doping of electron-rich Ni NPs and formation of high conductive graphitic phase are considered to be the factor, which results in marvelous EFE properties for these Ni-doped nano-diamond films.展开更多
Large-area boron nanowire（BNW） films were fabricated on the Si（111） substrate by chemical vapor deposition（CVD）. The average diameter of the BNWs is about 20 nm, with lengths of 5–10 μm. Then, graphene-capped ...Large-area boron nanowire（BNW） films were fabricated on the Si（111） substrate by chemical vapor deposition（CVD）. The average diameter of the BNWs is about 20 nm, with lengths of 5–10 μm. Then, graphene-capped boron nanowires（GC-BNWs） were obtained by microwave plasma chemical vapor deposition（MPCVD）. Characterization by scanning electron microscopy indicates that few-layer graphene covers the surface of the boron nanowires. Field emission measurements of the BNWs and GC-BNW films show that the GC-BNW films have a lower turn-on electric field than the BNW films.展开更多
By simply adjusting the temperature and the number of materials, rod-like ZnO with different morphology, such as ZnO nanoneedles, were synthesized by a flexible thermal evaporation method. The ZnO nanorod array has th...By simply adjusting the temperature and the number of materials, rod-like ZnO with different morphology, such as ZnO nanoneedles, were synthesized by a flexible thermal evaporation method. The ZnO nanorod array has the lowest turn-on field, the highest current density, and the highest emission efficiency due to its good contact with the substrate and relatively weak field shielding effect. Experiments show that the morphology and orientation of one-dimensional ZnO nanomaterials have a great influence on its conduction field and emission current density, and the nanoarrays also contribute to electron emission. The research results have a certain reference value for the application of ZnO nanorod arrays as cathode materials for field emission devices.展开更多
The relation between mining pressure field-fracture field and gas emission of working face is analyzed, and the concept that there is a stress point （or strain point） among permeability of coal is presented. It is b...The relation between mining pressure field-fracture field and gas emission of working face is analyzed, and the concept that there is a stress point （or strain point） among permeability of coal is presented. It is believed that the mutation of coal permeability caused by the sudden loading or unloading of working face roof as periodic weighting occurs is the main reason that a lot of gas pour into the working face. Based on the above concept, the relation is established among abutment pressure during periodie weighting, permeability of coal seam and gas emission, and relation graph is drawn. Then the loading and unloading features of coal at the moment of fracture and non-fracture of main roof are revealed. And finally it is presented that the process of sudden loading or unloading as periodic weighting occurs plays an important role in rupture propagation of coal, analytical movement of gas and gas emission.展开更多
文摘The electrocatalytic N_(2)reduction reaction(NRR)is expected to supersede the traditional Haber-Bosch technology for NH3 production under ambient conditions.The activity and selectivity of electrochemical NRR are restricted to a strong polarized electric field induced by the catalyst,correct electron transfer direction,and electron tunneling distance between bare electrode and active sites.By coupling the chemical vapor deposition method with the poly(methyl methacylate)-transfer method,an ultrathin sandwich catalyst,i.e.,Fe atoms(polarized electric field layer)sandwiched between ultrathin(within electron tunneling distance)BN(catalyst layer)and graphene film(conducting layer),is fabricated for electrocatalytic NRR.The sandwich catalyst not only controls the transfer of electrons to the BN surface in the correct direction under applied voltage but also suppresses hydrogen evolution reaction by constructing a neutral polarization electric field without metal exposure.The sandwich electrocatalyst NRR system achieve NH3 yield of 8.9μg h^(−1)cm^(−2)and Faradaic Efficiency of 21.7%.The N_(2)adsorption,activation,and polarization electric field changes of three sandwich catalysts(BN-Fe-G,BN-Fe-BN,and G-Fe-G)during the electrocatalytic NRR are investigated by experiments and density functional theory simulations.Driven by applied voltage,the neutral polarized electric field induced by BN-Fe-G leads to the high activity of electrocatalytic NRR.
基金supported by the Tehran University of Medical Sciences under Grant No.36291PET/CT and Cyclotron Center of Masih Daneshvari Hospital at Shahid Beheshti University of Medical Sciences。
文摘Image quality in positron emission tomography(PET)is affected by random and scattered coincidences and reconstruction protocols.In this study,we investigated the effects of scattered and random coincidences from outside the field of view(FOV)on PET image quality for different reconstruction protocols.Imaging was performed on the Discovery 690 PET/CT scanner,using experimental configurations including the NEMA phantom(a body phantom,with six spheres of different sizes)with a signal background ratio of 4:1.The NEMA phantom(phantom I)was scanned separately in a one-bed position.To simulate the effect of random and scatter coincidences from outside the FOV,six cylindrical phantoms with various diameters were added to the NEMA phantom(phantom II).The 18 emission datasets with mean intervals of 15 min were acquired(3 min/scan).The emission data were reconstructed using different techniques.The image quality parameters were evaluated by both phantoms.Variations in the signal-to-noise ratio(SNR)in a 28-mm(10-mm)sphere of phantom II were 37.9%(86.5%)for ordered-subset expectation maximization(OSEM-only),36.8%(81.5%)for point spread function(PSF),32.7%(80.7%)for time of flight(TOF),and 31.5%(77.8%)for OSEM+PSF+TOF,respectively,indicating that OSEM+PSF+TOF reconstruction had the lowest noise levels and lowest coefficient of variation(COV)values.Random and scatter coincidences from outside the FOV induced lower SNR,lower contrast,and higher COV values,indicating image deterioration and significantly impacting smaller sphere sizes.Amongst reconstruction protocols,OSEM+PSF+TOF and OSEM+PSF showed higher contrast values for sphere sizes of 22,28,and 37 mm and higher contrast recovery coefficient values for smaller sphere sizes of 10 and 13 mm.
基金supported by the NSFof China(59802004)Jiangsu Province,China(BK99047)+1 种基金RGC of Hongkong(No.CUHK 4173/98E)support of Groucher Foundation of Hong Kong
文摘Hydrogenated amorphous carbon films were fabricated by using layer-by-layer deposition method and hydrogen dilution method in a small d.c.-assisted plasma enhanced chemical vapor deposition system. It was found that the hydrogen plasma treatment could change the sp2/sp3 ratio to some extent by chemical etching. The improvements of field emission characteristics were observed compared with that from conventionally deposited a-C films, which can be attributed to the large field enhancement effect due to the inhomogeneous distribution of nanometer scale sp2 clusters and the reduction of the surface emission barrier due to the hydrogen termination.
基金Project supported by the National Natural Science Foundation of China (No. 40171048)the Science and Technique Key Project of the Tenth Five-Year Plan of China (No. 2002BA516A03)
文摘A field experiment was conducted on Chinese cabbage （Brassica campestris L. ssp. pekinensis （Lour.） Olsson） in a Nanjing suburb in 2003. The experiment included 4 treatments in a randomized complete block design with 3 replicates： zero chemical fertilizer N （CK）; urea at rates of 300 kg N ha^-1 （U300） and 600 kg N ha^-1 （U600）, both as basal and two topdressings; and polymer-coated urea at a rate of 180 kg N ha^-1 （PCU180） as a basal application. The acetylene inhibition technique was used to measure denitrification （N2 ＋ N2O） from intact soil cores and N2O emissions in the absence of acetylene. Results showed that compared to （3K total denitrification losses were significantly greater （P ≤ 0.05） in the PCU180, U300, and U600 treatments,while N2O emissions in the U300 and U600 treatments were significantly higher （P ≤ 0.05） than （3K. In the U300 and U600 treatments peaks of denitrification and N2O emission were usually observed after N application. In the polymer-coated urea treatment （PCU180） during the period 20 to 40 days after transplanting, higher denitrification rates and N2O fluxes occurred. Compared with urea, polymer-coated urea did not show any effect on reducing denitrification losses and N2O emissions in terms of percentage of applied N. As temperature gradually decreased from transplanting to harvest, denitrification rates and N2O emissions tended to decrease. A significant （P ≤0.01） positive correlation occurred between denitrification （r = 0.872） or N2O emission （r = 0.781） flux densities and soil temperature in the CK treatment with a stable nitrate content during the whole growing season.
基金supported by the National Basic Research Program of China(Grant No 2007CB935500)the National High Technology Research and Development Program of China(Grant No 2007AA03Z305)+5 种基金the National Science Foundation for Young Scientists of China(Grant No 50802117)the National Joint Science Fund with Guangdong Province(Grant Nos U0634002 and U0734003)the Specialized Research fund for the Doctoral Program of High Education of China(Grant No 20070558063)the Science and Technology Department of Guangdong Provincethe Education Department of Guangdong Provincethe Science and Technology Department of Guangzhou City,China
文摘The controllable growth of three different morphologies of AlN nanostructures （nanorod, nanotip and nanocrater） arrays are successfully realized by using chemical vapour deposition （CVD） technology. All three nanostructures are of single crystal h-AlN with a growth orientation of [001]. Their growth is attributed to the vapour-liquid-solid （VLS） mechanism. To investigate the factors affecting field emission （FE） properties of AlN nanostructures, we compare their FE behaviours in several aspects. Experimental results show that AIN nanocrater arrays possess the best FE properties, such as a threshold field of 7.2 V/μm and an emission current fluctuation lower than 4%. Moreover, the three AlN nanostructures all have good field emission properties compared with a number of other excellent cathode nanomaterials, which suggests that they are future promising FE nanomaterials.
文摘Measurements of N2O emissions from conventional rice cultivation （CRC）, CRC with straw mulching, system of rice intensification （SRI） and SRI with plastic film mulching were conducted through static chamber/gas-chromatography techniques. The results show that daily fluctuation of N2O emissions in jointing stage are much higher than in others. A type peak of N2O seasonal emission presented between jointing and bearing stages companying with high daily average temperature and low precipitation. Biomass and leaf stomatal conductance were observed. Total quantities of N2O emission were budgeted. The results showed that after jointing stage the average N2O emission flux of SRI with plastic film mulching increased significantly than CRC with straw mulching and SRI, the leaf stomatal conductance of those showed the same trend （p〈 0.05）. Yield and total quantity of N20 emission in CRC with straw mulching enhanced 13. 7% and 10.7% compared with those of CRC, respectively. The total quantity of N20 emissions reduced 3. 6% in SRI with plastic film mulching compared with CRC, however, the yield increase of that was not significant.
基金the author is wishing to express his gratitude to the National Natural Science Foundation of China(2002CB410807)for subsiding this research.
文摘Ammonia emission is one of the most important pathways of nitrogen loss from agricultural cultivated field. In this paper, we report the measurement of ammonia emission from paddy rice field obtained by surface application of urea fertilizer with water management. The main objective of the present study were to assess the amount of NH3 emission and the loss of nitrogen from paddy field as affected by various N doses, i.e., 0 (control), 90 (N1), 180 (N2), 270 (N3) and 360 (N4) kg ha-1, following field surface application of urea fertilizer with water management. Ammonia emissions were measured by continuous airflow enclosure method from plots fertilized with the application of surface urea. Increase in urea-N dosage increased NH3 emission that was measured from paddy rice field. Ammonia emission started immediately and was almost complete within 12 days after top dressing of urea application to the soils. Ammonia emissions were nearly constant in all treatments from 12 days after fertilizer application. Highest ammonia emission rate was 28 g /day and total amount of ammonia emission was 56.21 kg ha-1 for 360 kg N ha-1 dose. No remarkable observation was found about temperature for ammonia emission. Due to proper water management practices less emission was observed throughout the experiment period. The results also show that N loss through NH3 emission accounted for 11 to 16% during the rice- growing season. These magnitudes of loss of N appear to be most important for environmental point of view.
基金Project supported by the Natural Science Foundation of Jilin Province of China(Grant No.20220101031JC)。
文摘The spontaneous emission property ofΛ-type three-level atom driven by the bichromatic field in the anisotropic double-band photonic crystal is calculated by n-times iteration method.The influence of different parameters on atomic spontaneous emission is studied,and the phenomena of atomic spontaneous emission are explained in the dressed state representation.It is found that the spontaneous emission spectra of the atom driven by the bichromatic field presents a multi-peak comb structure.The position of the emission peak is determined by the initial state of the atom,and the interval between the neighboring emission peaks is the detuningδof the bichromatic field.When the ratio between Rabi frequency intensity and the detuningδof the bichromatic field remains unchanged,the intensity of each emitted peak remains invariant.The spontaneously emitted peak can be annihilated in the band gap and enhanced near the band edge in the anisotropic photonic crystals.Meanwhile,we also observe the fluorescence quenching phenomenon in the spontaneous emission spectra.The research in this paper provides the theoretical guidance for the control of atomic spontaneous emission.
基金Project supported by the Shanghai Human Resources and Social Security Bureau,China(Grant No.2009023)
文摘Graphene films are deposited on copper （Cu） and aluminum （Al） substrates, respectively, by using a microwave plasma chemical vapour deposition technique. Furthermore, these graphene films are characterized by a field emission type scanning electron microscope （FE-SEM）, Raman spectra, and field emission （FE） I-V measurements. It is found that the surface morphologies of the films deposited on Cu and Al substrates are different： the field emission property of graphene film deposited on the Cu substrate is better than that on the Al substrate, and the lowest turn-on field of 2.4 V/p-m is obtained for graphene film deposited on the Cu substrate. The macroscopic areas of the graphene samples are all above 400 mm2.
基金Project supported by the National Key Basic Research Program of China (Grant No.2011CB932700)the National Natural Science Foundation of China (Grant Nos.51272279,51072223,and 50972162)
文摘The field emission （FE） properties of vertically aligned graphene sheets （VAGSs） grown on different SiC substrates are reported. The VAGSs grown on nonpolar SiC （10-10） substrate show an ordered alignment with the graphene basal plane-parallel to each other, and show better FE features, with a lower turn-on field and a larger field enhancement factor. The VAGSs grown on polar SiC （000-1 ） substrate reveal a random petaloid-shaped arrangement and stable current emission over 8 hours with a maximum emission current fluctuation of only 4%. The reasons behind the differing FE characteristics of the VAGSs on different SiC substrates are analyzed and discussed.
基金financially supported by The Program for New Century Excellent Talents in University (NCET)the National Natural Science Foundation of China (NSFC) under Grant No.50772041
文摘In this paper,we report the effect of nitrogen on the deposition and properties of boron doped diamond films synthesized by hot filament chemical vapor deposition.The diamond films consisting of micro-grains(nano-grains) were realized with low(high) boron source flow rate during the growth processes.The transition of micro-grains to nano-grains is speculated to be strongly(weekly) related with the boron(nitrogen) flow rate.The grain size and Raman spectral feature vary insignificantly as a function of the nitrogen introduction at a certain boron flow rate.The variation of electron field emission characteristics dependent on nitrogen is different between microcrystalline and nanocrystalline boron doped diamond samples,which are related to the combined phase composition,boron doping level and texture structure.There is an optimum nitrogen proportion to improve the field emission properties of the boron-doped films.
文摘This study was carried out in paddy fields to explore how organic manure applications would affect greenhouse emissions in South China. The results showed that the seasonal emission of CH4 under the chemical fertilizer （CF） treatment was 271.47 kg/hm^2. In comparison, the seasonal emissions of CH4 under the treatment of pig manure （PM）, chicken manure （CM） and rice straw （RS） increased by 50.61,260.22 and 602.82 kg/hm^2, respectively. N2O emission under the CF treatment was 1.22 kg/hm^2, while the N20 seasonal emissions under tile PM, CM and RS treatment decreased by 23.6% （P〈0.05）, 31.7% （P〈0.05） and 30.9% （P〈0.05）, respectively. Meanwhile, the readily oxidized organic carbon （which was oxidized by 167 mmol/L potassium permanganate, ROC167） of manure, paddy soil Eh value and temperature could also affect the CH4 emissions. The average yield of the organic fertilizer treatments increased by 6.8% compared with that of the CF treatment. Among all the organic fertilizer treatments, the PM treatment offered the lowest global warming potential and greenhouse gas intensity, in which the PM was of no significant difference from NF （no fertilizing） and CF. Therefore, the pig manure is capable of coordinating the relationship between environment and yield, and it also has a low ROC167 content, so the PM is considered worthy of recommendation.
文摘Methane emissions from Chinese paddy soil (Zhejiang Province) were measured over the rice growing seasons. Different fertilizers (organic and chemical) were applied, emissions of methane were high during two periods(5 days after peak tillering and 7 days after heading flowering stage) and significant effect of fertilizers was observed. Methanogenic activities in soils treated with organic manures were obviously higher than those with chemical fertilizers. Among the organic manured fields the maximum methane emission from green manure, biogas residue and beef manure treatment were 52, 20 and 19 times respectively of that given by control, and among chemical fertilizers it was NH\-4HCO\-3>CO(NH 2) 2>(NH 4) 2SO 4>NH 4Cl>NaNO 3 with 2\^4, 2, 1\^5,1\^3 and 0\^2 times respectively of that from control.
基金supported by the National Basic Research Program of China(Grant Nos.2013CB933604)the National Natural Science Foundation of China(Grant No.51572290)the Fund from the Chinese Academy of Sciences(Grant Nos.1731300500015 and XDB07030100)
文摘Large-area patterned films of boron nanowires（BNWs） are fabricated at various densities by chemical vapor deposition（CVD）. Different widths of unit-cell of Mo masks are used as templates. The widths of unit-cell of Mo masks are100 μm, 150 μm, and 200 μm, respectively. The distance between unit cells is 50 μm. The BNWs have an average diameter of about 20 nm and lengths of 10 μm–20 μm. High-resolution transmission electron microscopy analysis shows that each nanowire has a β-tetragonal structure with good crystallization. Field emission measurements of the BNW films show that their turn-on electric fields decrease with width of unit-cell increasing.
基金supported by the Science and Technology Major Project of Shanxi Province,China (Grant No. 20181102013)the Fund from the “1331 Project”Engineering Research Center of Shanxi Province,China (Grant No. PT201801)。
文摘Nano-diamond particles are co-deposited on Ti substrates with metal(Ti/Ni) nanoparticles(NPs) by the electrophoretic deposition(EPD) method combined with a furnace annealing at 800℃ under N_(2) atmosphere. Modifications of structural and electron field emission(EFE) properties of the metal-doped films are investigated with different metal NPs concentrations. Our results show that the surface characteristics and EFE performances of the samples are first enhanced and then reduced with metal NPs concentration increasing. Both the Ti-doped and Ni-doped nano-diamond composite films exhibit optimal EFE and microstructural performances when the doping quantity is 5 mg. Remarkably enhanced EFE properties with a low turn-on field of 1.38 V/μm and a high current density of 1.32 mA/cm^(2) at an applied field of 2.94 V/μm are achieved for Ni-doped nano-diamond films, and are superior to those for Ti-doped ones. The enhancement of the EFE properties for the Ti-doped films results from the formation of the TiC-network after annealing. However, the doping of electron-rich Ni NPs and formation of high conductive graphitic phase are considered to be the factor, which results in marvelous EFE properties for these Ni-doped nano-diamond films.
基金Project supported by the National Basic Research Program of China(Grant No.2013CB933604)the National Natural Science Foundation of China(Grant No.51572290)the Chinese Academy of Sciences(Grant Nos.1731300500015 and XDB07030100)
文摘Large-area boron nanowire（BNW） films were fabricated on the Si（111） substrate by chemical vapor deposition（CVD）. The average diameter of the BNWs is about 20 nm, with lengths of 5–10 μm. Then, graphene-capped boron nanowires（GC-BNWs） were obtained by microwave plasma chemical vapor deposition（MPCVD）. Characterization by scanning electron microscopy indicates that few-layer graphene covers the surface of the boron nanowires. Field emission measurements of the BNWs and GC-BNW films show that the GC-BNW films have a lower turn-on electric field than the BNW films.
文摘By simply adjusting the temperature and the number of materials, rod-like ZnO with different morphology, such as ZnO nanoneedles, were synthesized by a flexible thermal evaporation method. The ZnO nanorod array has the lowest turn-on field, the highest current density, and the highest emission efficiency due to its good contact with the substrate and relatively weak field shielding effect. Experiments show that the morphology and orientation of one-dimensional ZnO nanomaterials have a great influence on its conduction field and emission current density, and the nanoarrays also contribute to electron emission. The research results have a certain reference value for the application of ZnO nanorod arrays as cathode materials for field emission devices.
基金Natural Science Foundation of China (No.50974054)Doctoral Program Foundation of the Ministry of Education (No.20070460001)National Key Basic Research and Development Program (No.2012CB723103)
文摘The relation between mining pressure field-fracture field and gas emission of working face is analyzed, and the concept that there is a stress point （or strain point） among permeability of coal is presented. It is believed that the mutation of coal permeability caused by the sudden loading or unloading of working face roof as periodic weighting occurs is the main reason that a lot of gas pour into the working face. Based on the above concept, the relation is established among abutment pressure during periodie weighting, permeability of coal seam and gas emission, and relation graph is drawn. Then the loading and unloading features of coal at the moment of fracture and non-fracture of main roof are revealed. And finally it is presented that the process of sudden loading or unloading as periodic weighting occurs plays an important role in rupture propagation of coal, analytical movement of gas and gas emission.
