Hydrofluorocarbons(HFCs)have been widely used in China as substitutes for ozone-depleting substances,the production and use of which are being phased out under the Montreal Protocol.China is a major consumer of HFCs a...Hydrofluorocarbons(HFCs)have been widely used in China as substitutes for ozone-depleting substances,the production and use of which are being phased out under the Montreal Protocol.China is a major consumer of HFCs around the world,with its HFC emissions in CO2-equivalent contributing to about 18%of the global emissions for the period2012-16.Three methods are widely used to estimate the emissions of HFCs-namely,the bottom-up method,top-down method and tracer ratio method.In this study,the tracer ratio method was adopted to estimate HFC emissions in the Yangtze River Delta(YRD),using CO as a tracer.The YRD region might make a significant contribution to Chinese totals owing to its rapid economic growth.Weekly flask measurements for ten HFCs(HFC-23,HFC-32,HFC-125,HFC-134 a,HFC-143 a,HFC-152 a,HFC-227 ea,HFC-236 fa,HFC-245 fa and HFC-365 mfc)were conducted at Lin’an Regional Background Station in the YRD over the period 2012-16,and the HFC emissions were 2.4±1.4 Gg yr-1 for HFC-23,2.8±1.2 Gg yr-1 for HFC-32,2.2±1.2 Gg yr-1 for HFC-125,4.8±4.8 Gg yr-1 for HFC-134 a,0.9±0.6 Gg yr-1 for HFC-152 a,0.3±0.3 Gg yr-1 for HFC-227 ea and 0.3±0.2 Gg yr-1 for HFC-245 fa.The YRD total HFC emissions reached 53 Gg CO2-e yr-1,contributing 34%of the national total.The per capita HFC CO2-equivalent emissions rate was 240 kg yr-1,while the values of per unit area emissions and per million GDP emissions reached 150 Mg km-2yr-1 and 3500 kg yr-1(million CNY GDP)-1,which were much higher than national or global levels.展开更多
In the original version of this article,the unit of the YRD total HFC emissions“Gg CO2-e yr^−1”in the abstract should be Tg CO2-e yr^−1.On Page 581,in the fifth line from the left bottom,the unit of the total CO2-eq...In the original version of this article,the unit of the YRD total HFC emissions“Gg CO2-e yr^−1”in the abstract should be Tg CO2-e yr^−1.On Page 581,in the fifth line from the left bottom,the unit of the total CO2-equivalent emissions of HFCs“Gg yr^−1”should be Tg yr^−1.展开更多
Objective The aim of the study was to compare tomotherapy-based bone marrow-sparing intensity-mod- ulated radiotherapy （BMS-IMRT） with intensity-modulated radiotherapy （IMRT） without entering the pelvic bone marro...Objective The aim of the study was to compare tomotherapy-based bone marrow-sparing intensity-mod- ulated radiotherapy （BMS-IMRT） with intensity-modulated radiotherapy （IMRT） without entering the pelvic bone marrow as a planning constraint in the treatment of cervical cancer after hysterectomy. Methods BMS-IMRT and IMRT plans were designed for a cohort of nine patients. The prescribed dose was 45 Gy in 1.8 Gy daily fractions, and 95% of the planned target volume received this dose. The doses were computed using a commercially available treatment planning system with the convolution/superposition algorithm. Plans were compared according to dose-volume histogram analysis in terms of planning target volume homogeneity and conformity indices （HI and CI） as well as organ at risk dose and volume parameters. Results BMS-IMRT had advantages over IMRT in terms of CI, but was equivalent to the latter in H1. V5, V10, V20, V30, and V40 of pelvic bone marrow in BMS-IMRT decreased by 0.06%, 17.33%, 22.19%, 13.85%, and 16.46%, respectively, compared with IMRT. Except for V30 of the small bowel and V30 and V40 of the bladder, no statistically significant differences were found between BMS-IMRT and IMRT in the small bowel, bladder, and rectum. Conclusion For cervical cancer patients receiving tomotherapy-based radiotherapy after hysterectomy, BMS-IMRT reduced pelvic bone marrow volume receiving low-dose radiation, and it may be conducive to preventing acute hematologic toxicity.展开更多
The integration of large-scale new energy and high-capacity DC transmission leads to a reduction in system inertia.Grid-forming renewable energy sources(GF-RES)has a significant improvement effect on system inertia.Co...The integration of large-scale new energy and high-capacity DC transmission leads to a reduction in system inertia.Grid-forming renewable energy sources(GF-RES)has a significant improvement effect on system inertia.Commutation failure faults may cause a short-term reactive power surplus at the sending end and trigger transient overvoltage,threatening the safe and stable operation of the power grid.However,there is a lack of research on the calculation method of transient overvoltage caused by commutation failure in high-voltage DC transmission systems with grid-forming renewable energy sources integration.Based on the existing equivalent model of highvoltage DC transmission systems at the sending end,this paper proposes to construct a model of the high-voltage DC transmission system at the sending end with grid-forming renewable energy sources.The paper first clarifies the mechanism of overvoltage generation,then considers the reactive power droop control characteristics of GF-RES,and derives the transient voltage calculation model of theDC transmission system with GF-RES integration.It also proposes a calculation method for transient overvoltage at the sending-end converter bus with GF-RES integration.Based on the PSCAD/EMTDC simulation platform,this paper builds an experimental simulation model.By constructing three different experimental scenarios,the accuracy and effectiveness of the proposed transient overvoltage calculation method are verified,with a calculation error within 5%.At the same time,this paper quantitatively analyzes the impact of grid strength,new energy proportion,and rated transmission power on transient overvoltage from three different perspectives.展开更多
Objective The aim of the study was to compare flattening filter-free(FFF) beams and conventional flattening filter(FF) beams in volumetric modulated arc therapy(VMAT) for cervical cancer after surgery, through a retro...Objective The aim of the study was to compare flattening filter-free(FFF) beams and conventional flattening filter(FF) beams in volumetric modulated arc therapy(VMAT) for cervical cancer after surgery, through a retrospective planning study.Methods VMAT plans of FFF beams and normal FF beams were designed for a cohort of 15 patients. The prescribed dose was 45 Gy to 1.8 Gy per fraction, and at least 95% of the planning target volume received this dose. Doses were computed with a commercially available treatment planning system using a Monte Carlo(MC) algorithm. Plans were compared according to dose-volume histogram analysis in terms of planning target volume homogeneity and conformity indices(HI and CI), as well as organs at risk(OAR) dose and volume parameters. Results FFF-VMAT was similar to FF-VMAT in terms of CI, but inferior to FF-VMAT considering HI. No statistically differences were observed between FFF-VMAT and FF-VMAT in following organ at risks including pelvic bone marrow, small bowel, bladder, rectum, and normal tissue(NT)..Conclusion For patients with cervical cancer after hysterectomy, the FFF beam achieved target and OAR dose distribution similar to that of the FF beam. Reduction of beam-on time in cervical cancer is beneficial.展开更多
Phosphorus is an important limiting nutrient in many ecosystems. Consequently, there is increasing interest on phosphate uptake and algal growth due to the increasing frequency and magnitude of algal blooms induced by...Phosphorus is an important limiting nutrient in many ecosystems. Consequently, there is increasing interest on phosphate uptake and algal growth due to the increasing frequency and magnitude of algal blooms induced by eutrophication. The co-existence of surface adsorbed and intracellular phosphorus pools indicate that phosphate uptake by phytoplankton is, to some extent, a two-stage kinetic process. However, almost all previous uptake models considered the internal uptake stage only and ignored the possible impact of surface adsorption. In this article, a two-stage kinetic uptake model considering both surface adsorption and P-stress on phosphate uptake by algae was constructed and compared to conventional one-stage models, based on experimental data on short-term uptake kinetics of a green algae S. quadricauda. Results indicated that with suitable parameters, the two-stage uptake model not only fit the experimental data better, but also gave more reasonable and realistic explanations to the phosphate uptake process. The results are meaningful as surface-adsorption of phosphate may affect the uptake process of phosphate and assist in understanding realistic phosphate uptake kinetics in phytoplankton.展开更多
Laser micro cladding deposition manufacturing(Ll CDM) is a newly developed rapid manufacturing method for metals.The Ll CDM technology adopts a novel powder feeding method based on alternating friction and inertia for...Laser micro cladding deposition manufacturing(Ll CDM) is a newly developed rapid manufacturing method for metals.The Ll CDM technology adopts a novel powder feeding method based on alternating friction and inertia force, and this powder feeding method can effectively improve the accuracy and orientation of the powder injection, resulting in a smaller molten pool size and a higher cooling rate of liquid metal.Therefore, the components fabricated by Ll CDM could obtain the finer microstructures and the improved mechanical properties.It is found that the components fabricated by Ll CDM are fully dense free of cracks or pores and exhibit columnar prior b grains with a finer acicular a0 phase microstructure.The microhardness(HV0.2) of the thin-wall component is HV 400–HV 500 in the majority part of the cross section and can reach about HV 850 in the top region.The ultimate tensile strength(UTS) and elongation show insignificant dependence on the testing directions of the tensilespecimens.The UTS is between 1,002 and 1,100 MPa, and the elongation is between 10.0 % and 14.7 %.展开更多
Near-equiaxed β grain was achieved in the near-α Ti60(Ti-5.7Al-4.0Sn-3.5Zr-0.4Mo-0.4Si-0.4Nb-1.0Ta-0.05C) titanium alloy via laser directed energy deposition(LDED). The microstructural evolution along the building d...Near-equiaxed β grain was achieved in the near-α Ti60(Ti-5.7Al-4.0Sn-3.5Zr-0.4Mo-0.4Si-0.4Nb-1.0Ta-0.05C) titanium alloy via laser directed energy deposition(LDED). The microstructural evolution along the building direction and the room-temperature tensile properties along the horizontal and vertical directions(building direction) were systematically studied through SEM and OM. EBSD and XRD were utilized to accurately demonstrate the texture of the α and β phases. The results showed that the α phase presented a low texture intensity, which was ascribed to the weak textured β grain with near-equiaxed morphology, since there are Burgers orientation relationships during the β →α transition. In addition, numerical simulation, combined with the CET curve of Ti60 alloy considering the effect of multi-composition,was utilized to elucidate the formation mechanism of the near-equiaxed β grains. Furthermore, according to the solidification theory, we proposed that the solidification temperature range ΔTfwas more accurate than the growth restriction factor Q in predicting the formation tendency of equiaxed β grain in different titanium alloys. Tensile results showed that the horizontal and vertical samples had similar strength,while the former exhibited larger elongation than the latter. The effect of the near-equiaxed β grain and the internal α phase on mechanical properties were revealed at last.展开更多
We developed a predictive model for the pipeline friction in the 520-730 m^3/h transmission range using the multi-layerperceptron-back-propagation(MLP-BP)method and analyzing the unit friction data after the pigging o...We developed a predictive model for the pipeline friction in the 520-730 m^3/h transmission range using the multi-layerperceptron-back-propagation(MLP-BP)method and analyzing the unit friction data after the pigging of a hot oil pipeline.In view of the shortcomings of the MLP-BP model,two optimization methods,the genetic algorithm(GA)and mind evolutionary algorithm(MEA),were used to optimize the MLP-BP model.The research results were applied to the standard friction prediction of three sections of a hot oil pipeline.After the GA and MEA optimizations,the average errors of the three sections were 0.0041 MPa for the GA and 0.0012 MPa for the MEA,and the mean-square errors were 0.083 and 0.067,respectively.The MEA-BP model prediction results were characterized by high precision and small dispersion.The MEABP prediction model was applied to the analysis of the wax formation 60 and 90 days after pigging.The analysis results showed that the model can effectively guide pipe pigging and optimization.There was little sample data for the individual transmission and oil temperature steps because the model was based on actual production data modeling and analysis,which may have affected the accuracy and adaptability of the model.展开更多
This paper investigated the effects of pre-heating treatment temperatures(T_(pre))on the flowability and wax deposition characteristics of a typical waxy crude oil after adding wax inhibitors.It is found that there is...This paper investigated the effects of pre-heating treatment temperatures(T_(pre))on the flowability and wax deposition characteristics of a typical waxy crude oil after adding wax inhibitors.It is found that there is little difference in wax precipitation exothermic characteristics of crude oils at different T_(pre),as well as the wax crystal solubility coefficient in the temperature range of 25-30℃.For the undoped crude oil,the flowability after wax precipitation gets much improved and the wax deposition is alleviated as T_(pre)increasing.At T_(pre)=50℃,the viscosity and wax deposition rate of crude oil adding wax inhibitors are higher than those of the undoped crude oil.When the T_(pre)increases to 60,70,and 80℃,the flowability of the doped crude oil are largely improved and the wax deposition is suppressed with the T_(pre)increase,but the wax content of wax deposit increases gradually.It is speculated that,on the one hand,the T_(pre)increase helps the dispersion of asphaltenes into smaller sizes,which facilitates the co-crystallization with paraffin waxes and generates more aggregated wax crystal flocs.This weakens the low-temperature gel structure and increases the solid concentration required for the crosslink to form the wax deposit.On the other hand,the decrease in viscosity increases the diffusion rate of wax molecules and accelerates the aging of wax deposits.The experimental results have important guiding significance for the pipeline transportation of doped crude oils.展开更多
Methane(CH4)is one of the most important greenhouse gases in the atmosphere,making it worthwhile to study its temporal and vertical distributions in source areas,e.g.,North China.For this purpose,a ground-based high-r...Methane(CH4)is one of the most important greenhouse gases in the atmosphere,making it worthwhile to study its temporal and vertical distributions in source areas,e.g.,North China.For this purpose,a ground-based high-resolution Fourier transform infrared spectrometer(FTIR),the Bruker IFS 125 HR,along with an in-situ instrument,the Picarro G2301,were deployed in Xianghe County(39.8°N,117.0°E),Hebei Province,China.Data have been recorded since June2018.For the FTIR measurements,we used two observation modes to retrieve the mole fraction of CH4:the Total Carbon Column Observing Network(TCCON)method(retrieval algorithm:GGG2014),and the Network for the Detection of Atmospheric Composition Change(NDACC)method(retrieval algorithm:SFIT4).Combining FTIR with in-situ measurements,we found the temporal and vertical distributions of atmospheric CH4 within three vertical layers(near the ground,in the troposphere,and in the stratosphere),and throughout the whole atmosphere.Regarding the diurnal variation of CH4 near the ground,the concentration at night was higher than during the daytime.Regarding the seasonal variation,CH4 was low in spring and high in summer,for all three vertical layers.In addition,there was a peak of CH4 in winter near the ground,both in the troposphere and the whole atmosphere.We found that variation of CH4 in the tropospheric column was close to that of the in-situ measurements near the ground.Furthermore,the variations of CH4 in the stratospheric column could be influenced by vertical motions,since it was higher in summer and lower in winter.展开更多
Objective To compute and compare the tumor control probability(TCP) of volumetric modulated arc therapy(VMAT) for breast cancer after conservative surgery based on two types of multileaf collimator(MLC) through a retr...Objective To compute and compare the tumor control probability(TCP) of volumetric modulated arc therapy(VMAT) for breast cancer after conservative surgery based on two types of multileaf collimator(MLC) through a retrospective planning study.Methods For a group of 9 patients diagnosed with left breast cancer,VMAT plan based on Agility MLC and beam modulator(BM) MLC were designed.The prescription dose was 50 Gy covering at least 95% of the planning target volume,2 Gy per fraction.TCPs were calculated according to dose-volume histogram(DVH) analysis.Results The TCP of the BM VMAT plan was slightly higher than that of the Agility VMAT plan(94.61% vs 94.23%) but was inferior with respect to delivery efficiency;the delivery time was reduced for Agility VMAT plan by 35% compared to BM VMAT plan.Conclusion For breast cancer radiation therapy after conservative surgery,BM VMAT plans provide slightly higher TCP while the delivery of Agility VMAT plans is significantly faster than the BM VMAT plans.展开更多
This paper presents an investigation into modelling the rheological properties of epoxy asphalt concrete( EAC) by using the Huet-Sayegh model. Complex modulus tests were conducted on EAC specimens at various temperatu...This paper presents an investigation into modelling the rheological properties of epoxy asphalt concrete( EAC) by using the Huet-Sayegh model. Complex modulus tests were conducted on EAC specimens at various temperature and loading frequency conditions. Dynamic modulus and phase angles obtained from the complex modulus tests were used in the construction of the Huet-Sayegh model. The dynamic modulus master curve was developed by the Huet-Sayegh model as well as the Burgers model for comparison purpose. The results showed that EAC exhibits typical rheological behavior whose dynamic modulus decreases with the increase of temperature while increases with the increase of frequency,and phase angles increase with the decrease of frequencies and the increase of temperatures. The Huet-Sayegh model predicts the dynamic modulus master curve of EAC very well and much better than the Burgers model over a wide range of frequencies.展开更多
Lauramine is widely considered to be an asphaltene flocculant,but its effect on the modification of crude oil by PPDs has been little studied.In this paper,the effect of LA dosage on the rheology improvement of EVA PP...Lauramine is widely considered to be an asphaltene flocculant,but its effect on the modification of crude oil by PPDs has been little studied.In this paper,the effect of LA dosage on the rheology improvement of EVA PPDs(100 ppm)on Qinghai waxy crude oil was investigated through rheological measurement,wax precipitating analysis,granularity test and resins/asphaltenes FTIR analysis.Compared with pure EVA,the compounding of LA and EVA obviously enhances the agglomeration degree and reduces the number of fine wax crystals,thus further enhancing the rheology of the oil samples,and the best performance is at the LA dosage of 200 ppm.At relatively small LA dosages,the LA facilitates the adsorption of EVA molecules on the asphaltene surfaces,which favors the becoming of EVA/asphaltenes composite particles;but at relatively high LA dosages,the LA makes the asphaltenes more aggregated and disturbs the EVA adsorption on the asphaltenes,which is adverse for the formation of EVA/asphaltenes compound particles.The compound particles can serve as wax precipitating templates and significantly influence its morphology,thus further improving the crude oil rheology.In consequence,the rheology improvement of EVA PPDs on Qinghai waxy crude oil first increases and then decreases with increasing the LA dosage.展开更多
In petroleum industry, crude oil emulsions are commonly formed in oilfields. The asphaltenes and fine particles in crude oil may affect the stability of the emulsions by adsorbing at the water/oil interface. In this r...In petroleum industry, crude oil emulsions are commonly formed in oilfields. The asphaltenes and fine particles in crude oil may affect the stability of the emulsions by adsorbing at the water/oil interface. In this research, the effect of silica nanoparticles and asphaltenes on emulsion stability is explored first. The asphaltenes are proved to benefit emulsion stability. Unlike the asphaltenes, however, the modified silica nanoparticles may have positive or negative effect on emulsion stability, depending on the asphaltene concentration and aggregation degree in the emulsions. Further, it is confirmed by conducting interfacial experiment that the asphaltenes and particles can adsorb at the interface simultaneously and determine the properties of the interfacial layer. More in-depth experiments concerning contact angle and asphaltene adsorption amount on the particles indicate that the asphaltenes can modify the wettability of the particles. Higher concentration and lower aggregation degree of the asphaltenes can increase their adsorption amount on the surface of particles and then improve the modification effectiveness of the particles. Resultantly, the particles with good modification effectiveness can enhance the emulsion stability while the particles with poor modification effectiveness will weaken the emulsion stability.展开更多
Nd-Fe-B permanent magnets play a crucial role in energy conversion and electronic devices.The essential magnetic properties of Nd-Fe-B magnets,particularly coercivity and remanent magnetization,are significantly infue...Nd-Fe-B permanent magnets play a crucial role in energy conversion and electronic devices.The essential magnetic properties of Nd-Fe-B magnets,particularly coercivity and remanent magnetization,are significantly infuenced by the phase characteristics and microstructure.In this work,Nd-Fe-B magnets were manufactured using vacuum induction melting(VIM),laser directed energy deposition(LDED)and laser powder bed fusion(LPBF)technologies.Themicrostructure evolution and phase selection of Nd-Fe-B magnets were then clarified in detail.The results indicated that the solidification velocity(V)and cooling rate(R)are key factors in the phase selection.In terms of the VIM-casting Nd-Fe-B magnet,a large volume fraction of theα-Fe soft magnetic phase(39.7 vol.%)and Nd2Fe17Bxmetastable phase(34.7 vol.%)areformed due to the low R(2.3×10-1?C s-1),whereas only a minor fraction of the Nd2Fe14B hard magnetic phase(5.15 vol.%)is presented.For the LDED-processed Nd-Fe-B deposit,although the Nd2Fe14B hard magnetic phase also had a low value(3.4 vol.%)as the values of V(<10-2m s-1)and R(5.06×103?C s-1)increased,part of theα-Fe soft magnetic phase(31.7vol.%)is suppressed,and a higher volume of Nd2Fe17Bxmetastable phases(47.5 vol.%)areformed.As a result,both the VIM-casting and LDED-processed Nd-Fe-B deposits exhibited poor magnetic properties.In contrast,employing the high values of V(>10-2m s-1)and R(1.45×106?C s-1)in the LPBF process resulted in the substantial formation of the Nd2Fe14B hard magnetic phase(55.8 vol.%)directly from the liquid,while theα-Fe soft magnetic phase and Nd2Fe17Bxmetastable phase precipitation are suppressed in the LPBF-processed Nd-Fe-B magnet.Additionally,crystallographic texture analysis reveals that the LPBF-processedNd-Fe-B magnets exhibit isotropic magnetic characteristics.Consequently,the LPBF-processed Nd-Fe-B deposit,exhibiting a coercivity of 656 k A m-1,remanence of 0.79 T and maximum energy product of 71.5 k J m-3,achieved an acceptable magnetic performance,comparable to other additive manufacturing processed Nd-Fe-B magnets from MQP(Nd-lean)Nd-Fe-Bpowder.展开更多
In response to the challenges of aerospace defense caused by the rapid development of hypersonic targets in recent years,the research on the unsupervised classification of flight states for hypersonic targets is carri...In response to the challenges of aerospace defense caused by the rapid development of hypersonic targets in recent years,the research on the unsupervised classification of flight states for hypersonic targets is carried out in this paper,which is based on the Hyperspectral Features(HFs)of hypersonic targets covered with plasma sheath during high-speed flight.First,a new concept of the super node is defined to improve classification accuracy by alleviating the intraclass variability of HFs.Then,the frequency domain information of the curve of HFs is utilized to reduce the feature redundancy according to the prior theoretical knowledge that the fluctuation characteristics of HFs of the same flight states are similar.Finally,an unsupervised classification method based on the Density Peak Clustering(DPC)for HFs is designed to class flight states after eliminating the impact of intraclass variability and feature dimension redundancy.The proposal is compared with the traditional classification algorithms on simulated hyperspectral data sets of typical flight states of the hypersonic vehicle and an actual-observation hyperspectral data set.The results indicate that the performance of our proposal has competitive advantages in terms of Overall Accuracy(OA),Average Accuracy(AA)and Kappa coefficient.展开更多
For reentry communication,owing to the influence of the highly dynamic plasma sheath(PS),the parasitic modulation effect can occur and the received phase shift keying(PSK)signal constellation can be severely rotated,l...For reentry communication,owing to the influence of the highly dynamic plasma sheath(PS),the parasitic modulation effect can occur and the received phase shift keying(PSK)signal constellation can be severely rotated,leading to unacceptable demodulation performance degradation.In this work,an adaptive non-coherent bit-interleaved coded modulation with iterative decoding(BICM-ID)system with binary PSK(BPSK)modulation and protograph lowdensity parity-check under the PS channel is proposed.The proposed protograph-based BICMID(P-BICM-ID)system can achieve joint processing of demodulation and decoding,where the soft information is adaptively estimated by reversible-jump Markov chain Monte Carlo(RJMCMC)algorithms.Simulation results indicate that compared to existing algorithms,the proposed system can adapt well to the dynamic characteristics of the PS channel and can obtain a 5dB performance improvement at a bit error rate of 10^(-6).展开更多
基金supported by the National Natural Science Foundation of China(Grant Nos.41575114 and 41730103)the Zhejiang Provincial Natural Science Foundation(Grant No.LY19D050002)the Meteorological Science and Technology Program of Zhejiang Province(Grant No.2019ZD12)。
文摘Hydrofluorocarbons(HFCs)have been widely used in China as substitutes for ozone-depleting substances,the production and use of which are being phased out under the Montreal Protocol.China is a major consumer of HFCs around the world,with its HFC emissions in CO2-equivalent contributing to about 18%of the global emissions for the period2012-16.Three methods are widely used to estimate the emissions of HFCs-namely,the bottom-up method,top-down method and tracer ratio method.In this study,the tracer ratio method was adopted to estimate HFC emissions in the Yangtze River Delta(YRD),using CO as a tracer.The YRD region might make a significant contribution to Chinese totals owing to its rapid economic growth.Weekly flask measurements for ten HFCs(HFC-23,HFC-32,HFC-125,HFC-134 a,HFC-143 a,HFC-152 a,HFC-227 ea,HFC-236 fa,HFC-245 fa and HFC-365 mfc)were conducted at Lin’an Regional Background Station in the YRD over the period 2012-16,and the HFC emissions were 2.4±1.4 Gg yr-1 for HFC-23,2.8±1.2 Gg yr-1 for HFC-32,2.2±1.2 Gg yr-1 for HFC-125,4.8±4.8 Gg yr-1 for HFC-134 a,0.9±0.6 Gg yr-1 for HFC-152 a,0.3±0.3 Gg yr-1 for HFC-227 ea and 0.3±0.2 Gg yr-1 for HFC-245 fa.The YRD total HFC emissions reached 53 Gg CO2-e yr-1,contributing 34%of the national total.The per capita HFC CO2-equivalent emissions rate was 240 kg yr-1,while the values of per unit area emissions and per million GDP emissions reached 150 Mg km-2yr-1 and 3500 kg yr-1(million CNY GDP)-1,which were much higher than national or global levels.
文摘In the original version of this article,the unit of the YRD total HFC emissions“Gg CO2-e yr^−1”in the abstract should be Tg CO2-e yr^−1.On Page 581,in the fifth line from the left bottom,the unit of the total CO2-equivalent emissions of HFCs“Gg yr^−1”should be Tg yr^−1.
基金Supported by a grant of the Military Medical Metrology Project(No.2011-JL2-005)
文摘Objective The aim of the study was to compare tomotherapy-based bone marrow-sparing intensity-mod- ulated radiotherapy （BMS-IMRT） with intensity-modulated radiotherapy （IMRT） without entering the pelvic bone marrow as a planning constraint in the treatment of cervical cancer after hysterectomy. Methods BMS-IMRT and IMRT plans were designed for a cohort of nine patients. The prescribed dose was 45 Gy in 1.8 Gy daily fractions, and 95% of the planned target volume received this dose. The doses were computed using a commercially available treatment planning system with the convolution/superposition algorithm. Plans were compared according to dose-volume histogram analysis in terms of planning target volume homogeneity and conformity indices （HI and CI） as well as organ at risk dose and volume parameters. Results BMS-IMRT had advantages over IMRT in terms of CI, but was equivalent to the latter in H1. V5, V10, V20, V30, and V40 of pelvic bone marrow in BMS-IMRT decreased by 0.06%, 17.33%, 22.19%, 13.85%, and 16.46%, respectively, compared with IMRT. Except for V30 of the small bowel and V30 and V40 of the bladder, no statistically significant differences were found between BMS-IMRT and IMRT in the small bowel, bladder, and rectum. Conclusion For cervical cancer patients receiving tomotherapy-based radiotherapy after hysterectomy, BMS-IMRT reduced pelvic bone marrow volume receiving low-dose radiation, and it may be conducive to preventing acute hematologic toxicity.
基金supported by Key Natural Science Research Projects of Colleges and Universities in Anhui Province(2022AH051831).
文摘The integration of large-scale new energy and high-capacity DC transmission leads to a reduction in system inertia.Grid-forming renewable energy sources(GF-RES)has a significant improvement effect on system inertia.Commutation failure faults may cause a short-term reactive power surplus at the sending end and trigger transient overvoltage,threatening the safe and stable operation of the power grid.However,there is a lack of research on the calculation method of transient overvoltage caused by commutation failure in high-voltage DC transmission systems with grid-forming renewable energy sources integration.Based on the existing equivalent model of highvoltage DC transmission systems at the sending end,this paper proposes to construct a model of the high-voltage DC transmission system at the sending end with grid-forming renewable energy sources.The paper first clarifies the mechanism of overvoltage generation,then considers the reactive power droop control characteristics of GF-RES,and derives the transient voltage calculation model of theDC transmission system with GF-RES integration.It also proposes a calculation method for transient overvoltage at the sending-end converter bus with GF-RES integration.Based on the PSCAD/EMTDC simulation platform,this paper builds an experimental simulation model.By constructing three different experimental scenarios,the accuracy and effectiveness of the proposed transient overvoltage calculation method are verified,with a calculation error within 5%.At the same time,this paper quantitatively analyzes the impact of grid strength,new energy proportion,and rated transmission power on transient overvoltage from three different perspectives.
基金Supported by a grant of the Military Medical Metrology Project(No.2011-JL2-005)
文摘Objective The aim of the study was to compare flattening filter-free(FFF) beams and conventional flattening filter(FF) beams in volumetric modulated arc therapy(VMAT) for cervical cancer after surgery, through a retrospective planning study.Methods VMAT plans of FFF beams and normal FF beams were designed for a cohort of 15 patients. The prescribed dose was 45 Gy to 1.8 Gy per fraction, and at least 95% of the planning target volume received this dose. Doses were computed with a commercially available treatment planning system using a Monte Carlo(MC) algorithm. Plans were compared according to dose-volume histogram analysis in terms of planning target volume homogeneity and conformity indices(HI and CI), as well as organs at risk(OAR) dose and volume parameters. Results FFF-VMAT was similar to FF-VMAT in terms of CI, but inferior to FF-VMAT considering HI. No statistically differences were observed between FFF-VMAT and FF-VMAT in following organ at risks including pelvic bone marrow, small bowel, bladder, rectum, and normal tissue(NT)..Conclusion For patients with cervical cancer after hysterectomy, the FFF beam achieved target and OAR dose distribution similar to that of the FF beam. Reduction of beam-on time in cervical cancer is beneficial.
基金supported by the National Major Projects on Control and Rectification of Water Body Pollution(No. 2009ZX07106-001)the National High Technology Research and Development Program (863) of China(No.2006AA10Z411)the National Basic Research Program (973) of China(No. 2008CB418000)
文摘Phosphorus is an important limiting nutrient in many ecosystems. Consequently, there is increasing interest on phosphate uptake and algal growth due to the increasing frequency and magnitude of algal blooms induced by eutrophication. The co-existence of surface adsorbed and intracellular phosphorus pools indicate that phosphate uptake by phytoplankton is, to some extent, a two-stage kinetic process. However, almost all previous uptake models considered the internal uptake stage only and ignored the possible impact of surface adsorption. In this article, a two-stage kinetic uptake model considering both surface adsorption and P-stress on phosphate uptake by algae was constructed and compared to conventional one-stage models, based on experimental data on short-term uptake kinetics of a green algae S. quadricauda. Results indicated that with suitable parameters, the two-stage uptake model not only fit the experimental data better, but also gave more reasonable and realistic explanations to the phosphate uptake process. The results are meaningful as surface-adsorption of phosphate may affect the uptake process of phosphate and assist in understanding realistic phosphate uptake kinetics in phytoplankton.
基金financially supported by the National Natural Science Foundation of China (No. 50975152)
文摘Laser micro cladding deposition manufacturing(Ll CDM) is a newly developed rapid manufacturing method for metals.The Ll CDM technology adopts a novel powder feeding method based on alternating friction and inertia force, and this powder feeding method can effectively improve the accuracy and orientation of the powder injection, resulting in a smaller molten pool size and a higher cooling rate of liquid metal.Therefore, the components fabricated by Ll CDM could obtain the finer microstructures and the improved mechanical properties.It is found that the components fabricated by Ll CDM are fully dense free of cracks or pores and exhibit columnar prior b grains with a finer acicular a0 phase microstructure.The microhardness(HV0.2) of the thin-wall component is HV 400–HV 500 in the majority part of the cross section and can reach about HV 850 in the top region.The ultimate tensile strength(UTS) and elongation show insignificant dependence on the testing directions of the tensilespecimens.The UTS is between 1,002 and 1,100 MPa, and the elongation is between 10.0 % and 14.7 %.
基金supported by the National Key Technologies R&D Program (Nos. 2016YFB1100102, 2018YFB1106003).
文摘Near-equiaxed β grain was achieved in the near-α Ti60(Ti-5.7Al-4.0Sn-3.5Zr-0.4Mo-0.4Si-0.4Nb-1.0Ta-0.05C) titanium alloy via laser directed energy deposition(LDED). The microstructural evolution along the building direction and the room-temperature tensile properties along the horizontal and vertical directions(building direction) were systematically studied through SEM and OM. EBSD and XRD were utilized to accurately demonstrate the texture of the α and β phases. The results showed that the α phase presented a low texture intensity, which was ascribed to the weak textured β grain with near-equiaxed morphology, since there are Burgers orientation relationships during the β →α transition. In addition, numerical simulation, combined with the CET curve of Ti60 alloy considering the effect of multi-composition,was utilized to elucidate the formation mechanism of the near-equiaxed β grains. Furthermore, according to the solidification theory, we proposed that the solidification temperature range ΔTfwas more accurate than the growth restriction factor Q in predicting the formation tendency of equiaxed β grain in different titanium alloys. Tensile results showed that the horizontal and vertical samples had similar strength,while the former exhibited larger elongation than the latter. The effect of the near-equiaxed β grain and the internal α phase on mechanical properties were revealed at last.
基金supported by National Natural Science Foundation of China(51904327,51774311)Natural Science Foundation of Shandong Province of China(ZR2017MEE022)+1 种基金China Postdoctoral Science Foundation(2019TQ0354,2019M662468)Qingdao postdoctoral researchers applied research project.
文摘We developed a predictive model for the pipeline friction in the 520-730 m^3/h transmission range using the multi-layerperceptron-back-propagation(MLP-BP)method and analyzing the unit friction data after the pigging of a hot oil pipeline.In view of the shortcomings of the MLP-BP model,two optimization methods,the genetic algorithm(GA)and mind evolutionary algorithm(MEA),were used to optimize the MLP-BP model.The research results were applied to the standard friction prediction of three sections of a hot oil pipeline.After the GA and MEA optimizations,the average errors of the three sections were 0.0041 MPa for the GA and 0.0012 MPa for the MEA,and the mean-square errors were 0.083 and 0.067,respectively.The MEA-BP model prediction results were characterized by high precision and small dispersion.The MEABP prediction model was applied to the analysis of the wax formation 60 and 90 days after pigging.The analysis results showed that the model can effectively guide pipe pigging and optimization.There was little sample data for the individual transmission and oil temperature steps because the model was based on actual production data modeling and analysis,which may have affected the accuracy and adaptability of the model.
基金The authors thank the financial support from the National Natural Science Foundation of China(51904327,U19B2012)China University of Petroleum Innovation Project(22CX06050A).
文摘This paper investigated the effects of pre-heating treatment temperatures(T_(pre))on the flowability and wax deposition characteristics of a typical waxy crude oil after adding wax inhibitors.It is found that there is little difference in wax precipitation exothermic characteristics of crude oils at different T_(pre),as well as the wax crystal solubility coefficient in the temperature range of 25-30℃.For the undoped crude oil,the flowability after wax precipitation gets much improved and the wax deposition is alleviated as T_(pre)increasing.At T_(pre)=50℃,the viscosity and wax deposition rate of crude oil adding wax inhibitors are higher than those of the undoped crude oil.When the T_(pre)increases to 60,70,and 80℃,the flowability of the doped crude oil are largely improved and the wax deposition is suppressed with the T_(pre)increase,but the wax content of wax deposit increases gradually.It is speculated that,on the one hand,the T_(pre)increase helps the dispersion of asphaltenes into smaller sizes,which facilitates the co-crystallization with paraffin waxes and generates more aggregated wax crystal flocs.This weakens the low-temperature gel structure and increases the solid concentration required for the crosslink to form the wax deposit.On the other hand,the decrease in viscosity increases the diffusion rate of wax molecules and accelerates the aging of wax deposits.The experimental results have important guiding significance for the pipeline transportation of doped crude oils.
基金funded by the National Key R&D Program of China(Grant Nos.2017YFB0504000 and 2017YFC1501701)the National Natural Science Foundation of China(Grant No.41975035)。
文摘Methane(CH4)is one of the most important greenhouse gases in the atmosphere,making it worthwhile to study its temporal and vertical distributions in source areas,e.g.,North China.For this purpose,a ground-based high-resolution Fourier transform infrared spectrometer(FTIR),the Bruker IFS 125 HR,along with an in-situ instrument,the Picarro G2301,were deployed in Xianghe County(39.8°N,117.0°E),Hebei Province,China.Data have been recorded since June2018.For the FTIR measurements,we used two observation modes to retrieve the mole fraction of CH4:the Total Carbon Column Observing Network(TCCON)method(retrieval algorithm:GGG2014),and the Network for the Detection of Atmospheric Composition Change(NDACC)method(retrieval algorithm:SFIT4).Combining FTIR with in-situ measurements,we found the temporal and vertical distributions of atmospheric CH4 within three vertical layers(near the ground,in the troposphere,and in the stratosphere),and throughout the whole atmosphere.Regarding the diurnal variation of CH4 near the ground,the concentration at night was higher than during the daytime.Regarding the seasonal variation,CH4 was low in spring and high in summer,for all three vertical layers.In addition,there was a peak of CH4 in winter near the ground,both in the troposphere and the whole atmosphere.We found that variation of CH4 in the tropospheric column was close to that of the in-situ measurements near the ground.Furthermore,the variations of CH4 in the stratospheric column could be influenced by vertical motions,since it was higher in summer and lower in winter.
基金Supported by a grant from the Innovation Project of the PLA Army General Hospital of China(No.2015-LC-18)
文摘Objective To compute and compare the tumor control probability(TCP) of volumetric modulated arc therapy(VMAT) for breast cancer after conservative surgery based on two types of multileaf collimator(MLC) through a retrospective planning study.Methods For a group of 9 patients diagnosed with left breast cancer,VMAT plan based on Agility MLC and beam modulator(BM) MLC were designed.The prescription dose was 50 Gy covering at least 95% of the planning target volume,2 Gy per fraction.TCPs were calculated according to dose-volume histogram(DVH) analysis.Results The TCP of the BM VMAT plan was slightly higher than that of the Agility VMAT plan(94.61% vs 94.23%) but was inferior with respect to delivery efficiency;the delivery time was reduced for Agility VMAT plan by 35% compared to BM VMAT plan.Conclusion For breast cancer radiation therapy after conservative surgery,BM VMAT plans provide slightly higher TCP while the delivery of Agility VMAT plans is significantly faster than the BM VMAT plans.
基金Sponsored by the Natgional Natural Science Foundation of China(Grant No.51208103)the China Postdoctoral Science Foundation(Grant No.2012M520976)the Basic Research Foundation of Southeast University
文摘This paper presents an investigation into modelling the rheological properties of epoxy asphalt concrete( EAC) by using the Huet-Sayegh model. Complex modulus tests were conducted on EAC specimens at various temperature and loading frequency conditions. Dynamic modulus and phase angles obtained from the complex modulus tests were used in the construction of the Huet-Sayegh model. The dynamic modulus master curve was developed by the Huet-Sayegh model as well as the Burgers model for comparison purpose. The results showed that EAC exhibits typical rheological behavior whose dynamic modulus decreases with the increase of temperature while increases with the increase of frequency,and phase angles increase with the decrease of frequencies and the increase of temperatures. The Huet-Sayegh model predicts the dynamic modulus master curve of EAC very well and much better than the Burgers model over a wide range of frequencies.
基金financially supported by the National Natural Science Foundation of China(grant number 51774311,51904327)China Postdoctoral Science Foundation(grant number 2019TQ0354,2019M662468)。
文摘Lauramine is widely considered to be an asphaltene flocculant,but its effect on the modification of crude oil by PPDs has been little studied.In this paper,the effect of LA dosage on the rheology improvement of EVA PPDs(100 ppm)on Qinghai waxy crude oil was investigated through rheological measurement,wax precipitating analysis,granularity test and resins/asphaltenes FTIR analysis.Compared with pure EVA,the compounding of LA and EVA obviously enhances the agglomeration degree and reduces the number of fine wax crystals,thus further enhancing the rheology of the oil samples,and the best performance is at the LA dosage of 200 ppm.At relatively small LA dosages,the LA facilitates the adsorption of EVA molecules on the asphaltene surfaces,which favors the becoming of EVA/asphaltenes composite particles;but at relatively high LA dosages,the LA makes the asphaltenes more aggregated and disturbs the EVA adsorption on the asphaltenes,which is adverse for the formation of EVA/asphaltenes compound particles.The compound particles can serve as wax precipitating templates and significantly influence its morphology,thus further improving the crude oil rheology.In consequence,the rheology improvement of EVA PPDs on Qinghai waxy crude oil first increases and then decreases with increasing the LA dosage.
基金Support from the National Natural Science Foundation of China(Grant No. 51704315)。
文摘In petroleum industry, crude oil emulsions are commonly formed in oilfields. The asphaltenes and fine particles in crude oil may affect the stability of the emulsions by adsorbing at the water/oil interface. In this research, the effect of silica nanoparticles and asphaltenes on emulsion stability is explored first. The asphaltenes are proved to benefit emulsion stability. Unlike the asphaltenes, however, the modified silica nanoparticles may have positive or negative effect on emulsion stability, depending on the asphaltene concentration and aggregation degree in the emulsions. Further, it is confirmed by conducting interfacial experiment that the asphaltenes and particles can adsorb at the interface simultaneously and determine the properties of the interfacial layer. More in-depth experiments concerning contact angle and asphaltene adsorption amount on the particles indicate that the asphaltenes can modify the wettability of the particles. Higher concentration and lower aggregation degree of the asphaltenes can increase their adsorption amount on the surface of particles and then improve the modification effectiveness of the particles. Resultantly, the particles with good modification effectiveness can enhance the emulsion stability while the particles with poor modification effectiveness will weaken the emulsion stability.
基金supported by the National Key R&D Program of China(Grant No.2022YFB4600300)the National Natural Science Foundation of China(No.U22A20189,52175364)the China Scholarship Council(Grant No.202206290134)。
文摘Nd-Fe-B permanent magnets play a crucial role in energy conversion and electronic devices.The essential magnetic properties of Nd-Fe-B magnets,particularly coercivity and remanent magnetization,are significantly infuenced by the phase characteristics and microstructure.In this work,Nd-Fe-B magnets were manufactured using vacuum induction melting(VIM),laser directed energy deposition(LDED)and laser powder bed fusion(LPBF)technologies.Themicrostructure evolution and phase selection of Nd-Fe-B magnets were then clarified in detail.The results indicated that the solidification velocity(V)and cooling rate(R)are key factors in the phase selection.In terms of the VIM-casting Nd-Fe-B magnet,a large volume fraction of theα-Fe soft magnetic phase(39.7 vol.%)and Nd2Fe17Bxmetastable phase(34.7 vol.%)areformed due to the low R(2.3×10-1?C s-1),whereas only a minor fraction of the Nd2Fe14B hard magnetic phase(5.15 vol.%)is presented.For the LDED-processed Nd-Fe-B deposit,although the Nd2Fe14B hard magnetic phase also had a low value(3.4 vol.%)as the values of V(<10-2m s-1)and R(5.06×103?C s-1)increased,part of theα-Fe soft magnetic phase(31.7vol.%)is suppressed,and a higher volume of Nd2Fe17Bxmetastable phases(47.5 vol.%)areformed.As a result,both the VIM-casting and LDED-processed Nd-Fe-B deposits exhibited poor magnetic properties.In contrast,employing the high values of V(>10-2m s-1)and R(1.45×106?C s-1)in the LPBF process resulted in the substantial formation of the Nd2Fe14B hard magnetic phase(55.8 vol.%)directly from the liquid,while theα-Fe soft magnetic phase and Nd2Fe17Bxmetastable phase precipitation are suppressed in the LPBF-processed Nd-Fe-B magnet.Additionally,crystallographic texture analysis reveals that the LPBF-processedNd-Fe-B magnets exhibit isotropic magnetic characteristics.Consequently,the LPBF-processed Nd-Fe-B deposit,exhibiting a coercivity of 656 k A m-1,remanence of 0.79 T and maximum energy product of 71.5 k J m-3,achieved an acceptable magnetic performance,comparable to other additive manufacturing processed Nd-Fe-B magnets from MQP(Nd-lean)Nd-Fe-Bpowder.
基金funded by the National Natural Science Foundation of China(Nos.61871302,62101406,and 62001340)the Innovation Capability Support Program of Shaanxi,China(No.2022TD-37)+1 种基金the Fundamental Research Funds for the Central Universities,China(No.JB211311)the Innovation Fund of Xidian University,China(No.YJS2217).
文摘In response to the challenges of aerospace defense caused by the rapid development of hypersonic targets in recent years,the research on the unsupervised classification of flight states for hypersonic targets is carried out in this paper,which is based on the Hyperspectral Features(HFs)of hypersonic targets covered with plasma sheath during high-speed flight.First,a new concept of the super node is defined to improve classification accuracy by alleviating the intraclass variability of HFs.Then,the frequency domain information of the curve of HFs is utilized to reduce the feature redundancy according to the prior theoretical knowledge that the fluctuation characteristics of HFs of the same flight states are similar.Finally,an unsupervised classification method based on the Density Peak Clustering(DPC)for HFs is designed to class flight states after eliminating the impact of intraclass variability and feature dimension redundancy.The proposal is compared with the traditional classification algorithms on simulated hyperspectral data sets of typical flight states of the hypersonic vehicle and an actual-observation hyperspectral data set.The results indicate that the performance of our proposal has competitive advantages in terms of Overall Accuracy(OA),Average Accuracy(AA)and Kappa coefficient.
基金financial support from National Natural Science Foundation of China(Nos.61871302,62101406 and 62001340)the Fundamental Research Funds for the Central Universities(No.JB211311)。
文摘For reentry communication,owing to the influence of the highly dynamic plasma sheath(PS),the parasitic modulation effect can occur and the received phase shift keying(PSK)signal constellation can be severely rotated,leading to unacceptable demodulation performance degradation.In this work,an adaptive non-coherent bit-interleaved coded modulation with iterative decoding(BICM-ID)system with binary PSK(BPSK)modulation and protograph lowdensity parity-check under the PS channel is proposed.The proposed protograph-based BICMID(P-BICM-ID)system can achieve joint processing of demodulation and decoding,where the soft information is adaptively estimated by reversible-jump Markov chain Monte Carlo(RJMCMC)algorithms.Simulation results indicate that compared to existing algorithms,the proposed system can adapt well to the dynamic characteristics of the PS channel and can obtain a 5dB performance improvement at a bit error rate of 10^(-6).
