Traffic is an indispensable prerequisite for a tourism system. The ＂four vertical and four horizontal＂ HSR network represents an important milestone of the ＂traffic revolution＂ in China. It will affect the spatial...Traffic is an indispensable prerequisite for a tourism system. The ＂four vertical and four horizontal＂ HSR network represents an important milestone of the ＂traffic revolution＂ in China. It will affect the spatial pattern of tourism accessibility in Chinese cities, thus substan- tially increasing their power to attract tourists and their radiation force. This paper examines the evolution and spatial characteristics of the power to attract tourism of cities linked by China＇s HSR network by measuring the influence of accessibility of 338 HSR-linked cities using GIS analysis. The results show the following. （1） The accessibility of Chinese cities is optimized by the HSR network, whose spatial pattern of accessibility exhibits an obvious traf- fic direction and causes a high-speed rail-corridor effect. （2） The spatial pattern of tourism field strength in Chinese cities exhibits the dual characteristics of multi-center annular diver- gence and dendritic diffusion. Dendritic diffusion is particularly more obvious along the HSR line. The change rate of urban tourism field strength forms a high-value corridor along the HSR line and exhibits a spatial pattern of decreasing area from the center to the outer limit along the HSR line. （3） The influence of the higher and highest tourism field strength areas along the HSR line is most significant, and the number of cities that distribute into these two types of tourism field strengths significantly increases： their area expands by more than 100% HSR enhances the tourism field strength value of regional central cities, and the radiation range of tourism attraction extends along the HSR line.展开更多
Objective To investigate effect of MR field strength on texture features of cerebral T2 fluid attenuated inversion recovery(T2-FLAIR)images.Methods We acquired cerebral 3 D T2-FLAIR images of thirty patients who were ...Objective To investigate effect of MR field strength on texture features of cerebral T2 fluid attenuated inversion recovery(T2-FLAIR)images.Methods We acquired cerebral 3 D T2-FLAIR images of thirty patients who were diagnosed with ischemic white matter lesion(WML)with MR-1.5 T and MR-3.0 T scanners.Histogram texture features which included mean signal intensity(Mean),Skewness and Kurtosis,and gray level co-occurrence matrix(GLCM)texture features which included angular second moment(ASM),Contrast,Correlation,Inverse difference moment(IDM)and Entropy,of regions of interest located in the area of WML and normal white matter(NWM)were measured by ImageJ software.The texture parameters acquired with MR-1.5 T scanning were compared with MR-3.0 T scanning.Results The Mean of both WML and NWM obtained with MR-1.5 T scanning was significantly lower than that acquired with MR-3.0 T(P<0.001),while Skewness and Kurtosis between MR-1.5 T and MR-3.0 T scanning showed no significant difference(P>0.05).ASM,Correlation and IDM of both WML and NWM acquired with MR-1.5 T revealed significantly lower values than those with MR-3.0 T(P<0.001),while Contrast and Entropy acquired with MR-1.5 T showed significantly higher values than those with MR-3.0 T(P<0.001).Conclusion MR field strength showed no significant effect on histogram textures,while had significant effect on GLCM texture features of cerebral T2-FLAIR images,which indicated that it should be cautious to explain the texture results acquired based on the different MR field strength.展开更多
Objective: A comparison of the difference between the two types of field MR scan in diagnosis of shoulder joint injury. Method: Randomly selected 153 patients with arthroscopic or open arthroplasty who had shoulder pa...Objective: A comparison of the difference between the two types of field MR scan in diagnosis of shoulder joint injury. Method: Randomly selected 153 patients with arthroscopic or open arthroplasty who had shoulder pain or dysfunction treated in our hospital from 2014 to 2017 were divided into 1.5 T group and 3.0 according to the field strength of MRI examination. Postoperative pathology was a gold standard. The sensitivity, specificity, consistency, and predictive value of two field-strength MRI examinations in the diagnosis of rotator cuff tears were calculated and compared. Results: The sensitivity, specificity, crude consistency, positive predictive value, and negative predictive value of the 1.5 T group were 68.75%, 82.35%, 73.47%, 88.00%, and 58.33%, respectively. The 3.0 T group was 72.22%, 89.47%, 78.18%, 92.86% and 62.96%, the differences between the above indicators were not statistically significant (P > 0.05). Conclusion: There was no difference in the authenticity and benefit index of rotator cuff injury diagnosed by 1.5 T and 3.0 T MRI.展开更多
This article describes GIS-based models successfully developed for predicting the coverage of Cityphone cellular network,visualizing the predicted signal strength,and analyzing the field strength coverage.In order to ...This article describes GIS-based models successfully developed for predicting the coverage of Cityphone cellular network,visualizing the predicted signal strength,and analyzing the field strength coverage.In order to predict the signal coverage strength of communication network more accurately,the spatial and nonspatial databases of a mobile cellular network are combined by GIS and produce the necessary parameters.A GIS model named COST-231-Walfisch–Ikegami model(WIM)is developed for signal coverage prediction in Ho Chi Minh City.Radio-line-of-sight and nonradio-lineof-sight conditions can be determined by this model.In addition,in case of nonradio-line-of-sight conditions,average building height,building separation,building width,incident radio path,and road orientation with respect to the direct radio path were obtained using GIS.Road orientation loss,multiscreen diffraction loss,and shadowing gain were predicted more accurate by this model.The scale of maps in the experiment was 1:2000 and the average of floor height was 3 m because there were no exact building height measurements.Statistical results show that the path loss predicted by the COST 231 WIM overcame the real path loss of each cell station.And this method can be used for signal coverage prediction of mobile cellular network in urban areas.Compared to the current situation with the Ho Chi Minh City Posts and Telecommunications system,this model can be effectively applied to improve the Cityphone mobile network quality as well as capability.Developed GIS models can help designers in predicting cell station coverage using real spatial maps that make the results more reliable.This research can help network operators improve the network quality and capability with the best investment efficiently.展开更多
It was ascertained that there is a great margin between the theoretical values and experimental medians of the field strength of RWM and RID signals during high solar activity period at Chinese Great Wall Station on A...It was ascertained that there is a great margin between the theoretical values and experimental medians of the field strength of RWM and RID signals during high solar activity period at Chinese Great Wall Station on Antarctica. The calculated values are, on average, less than the experimental, especially on the propagation path between RID and Antarctica. The field strength by the experiment may be used as the basic data for the research of HF propagation over the very long distance. Because of the large deviation it seems to be necessary to study HF propagation over the very long distance in details, especially the propagation model.展开更多
A significant number of fire-induced power disruptions are observed in several countries every year. The faults are normally phase-to-phase short circuiting or conductor-to-ground discharges at mid-span region of the ...A significant number of fire-induced power disruptions are observed in several countries every year. The faults are normally phase-to-phase short circuiting or conductor-to-ground discharges at mid-span region of the high-voltage transmission system. In any case, the wildfire plumes provide a conductive path. The electrical conductivity is due to intense heat in combustion zone of the fire which creates ion and electrons from flame inherent particulates. Increase in the ion concentration increases the electrical conductivity of the fire plume. The main purpose of this study was to measure dielectric breakdown electric field for vegetation and hydrocarbon flames. The experimental data is needed for validation of simulation schemes which are necessary for evaluation of power grid systems reliability under extreme wildfire weather conditions. In this study, hydrocarbon and vegetation fuels were ignited in a cylindrically shaped steel burner which was fitted with type-K thermocouples to measure flame temperature. The fuels consisted of dried weeping wattle (Peltophorum africanum) litter, butane gas and candle wax. Two pinned copper electrodes supported by retort stands were mounted to the burner and energized to a high voltage. This generated a strong electric field sufficient to initiate dielectric breakdown in the flames. Breakdown electric field strength (Ecrit) obtained from the experiment decreased from 10.5 to 6.9 kV/cm for the flames with temperature range of 1003 to 1410 K, respectively.展开更多
In this paper,it will be calculated the electromagnetic field strength and the Lorentz force in Geometric Algebra Cl_(3,0).And it will be compared with their equivalent in the tensor covariant formalism.Also,four extr...In this paper,it will be calculated the electromagnetic field strength and the Lorentz force in Geometric Algebra Cl_(3,0).And it will be compared with their equivalent in the tensor covariant formalism.Also,four extra equations not appearing in the classical formalism will be obtained and its meaning will be explained.In the same way,the electromagnetic Field strength elements and the velocity multivector of the particle will be expanded.New equations and new elements appearing will be explained,being the most important one,the Electromagnetic trivector B_(xyz).A field to be added to the magnetic(bivector-like)and electric(vector-like)fields.Lastly,an insight of the possible implications of these learnings in the Dirac Equation will be commented.展开更多
Currently,the design of transformers insulation predominantly depends on the allowable alternating current(AC)field values for insulating oil established by Weidmann in the 1980s,lacking the research under direct curr...Currently,the design of transformers insulation predominantly depends on the allowable alternating current(AC)field values for insulating oil established by Weidmann in the 1980s,lacking the research under direct current(DC)voltage for converter transformers.This study selects naphthenic oils and paraffin-based oil transformer oil as research subjects,establishing a practical measurement platform to ascertain the oil breakdown characteristics under DC voltage.Furthermore,it statistically analyses the allowable DC field values of the oil.The findings elucidate that(1)the three-parameter Weibull dis-tribution is more suitable to conduct a statistical analysis for oil breakdown probability,yielding a fitting degree up to 99.95%.(2)For a constant electrode spacing,a 14.81%voltage increment escalates the breakdown probability of the oil gap from 3.33%to 73.33%.Concurrently,an increase in electrode spacing leads to a substantial decrement in the breakdown field strength of transformer oil,with KI25X experiencing a 54.51%reduction as electrode spacing extends from 5 to 25 mm.(3)The constant terms of the allowable DC field strength for S4,KI50X,and KI25X are found to be 19.728,17.221,and 19.281,respectively.(4)A thorough analysis for differences in physicochemical properties and electrical parameters elucidates the variations in insulation properties across different transformer oils.The findings presented in this study offer essential theoretical and technical foundations for the design,evaluation,and enhancement of insulation structures in converter transformers.展开更多
In recent years,the effect of pulsed magnetic fields on improving the solidification structure of alloys has attracted significant attention.A GH4738 nickel-based alloy smelted using a self-designed 20-kg electromagne...In recent years,the effect of pulsed magnetic fields on improving the solidification structure of alloys has attracted significant attention.A GH4738 nickel-based alloy smelted using a self-designed 20-kg electromagnetic casting system was taken as the research object.Finite element software was used to numerically simulate the magnetic field intensity,distribution,and temperature field of the casting device.The effect of the pulsed magnetic field on the solidification process of the GH4738 alloy was studied by means of low-magnification microstructural analysis.The measured magnetic field shows that when the duty cycle is 20%,the pulse frequency is 50 Hz,the output current is in the range of 150–250 A,and the peak magnetic field intensity of the crucible center is 68–116 mT.The crucible temperature is heated to 600℃and the melt center solidification time is 12.844 s.The microstructural analysis of the ingot shows that its shrinkage hole is reduced from 130 to 100 mm,and the equiaxed crystal area is increased from 2275 to 3150 mm^(2).The solidification angle of the dendrite is changed under the action of the pulsed magnetic field,and the tilt angle is 45°.The results show that the pulsed magnetic field promotes the primary crystal core of the GH4738 alloy,improves the nucleation rate of the melt,reduces the size difference of the solidification structure between the center and the edge of the ingot,and improves the uniformity of the solidification structure.展开更多
In this article, the fast multipole method （FMM） is applied to analgze the field strength of an ultra-wideband （UWB） signal. Small coverage of UWB communication systems and high efficiency of the algorithm make it...In this article, the fast multipole method （FMM） is applied to analgze the field strength of an ultra-wideband （UWB） signal. Small coverage of UWB communication systems and high efficiency of the algorithm make it possible to calculate the amplitude of electric field accurately. A homogeneous dielectric body and a multilayered dielectric object are studied. The computational results obtained by applying the FMM agree well with those obtained by applying the method of moments （MoM）.展开更多
Using very recently published X-ray and low frequency radio data we have calculated thelower limit of the magnetic field and several other related quantities for 25 clusters of galaxies（which are classified into '...Using very recently published X-ray and low frequency radio data we have calculated thelower limit of the magnetic field and several other related quantities for 25 clusters of galaxies（which are classified into 'normal', distant and steep spectrum clusters） and 12 radiogalaxies. Our main results are as follows: （1）The magnetic field in the extended lobes of radio galaxies is larger than 10-6 G.Thus radio galaxies, whether they belong to clusters or not, emit few X-rays through theinverse Compton effect. （2）The low frequency radio emission from clusters can be divided into two components:one or several radio galaxies, and an extended halo where the magnetic field is about 10-8G, and where inverse Compton X-rays are most probably emitted. （3）Our sample of distant clusters is biased towards high radio luminosity and givesresults comparable to those obtained for radio galaxies. This can naturally be explained bythe fact that the radio galaxy component daminates the radio emission. （4）In steep spectrum clusters, the equipartition magnetic field is the same as that in'normal' clusters, but the lower limit of the magnetic field has a rather high value andseems to increase with the spectral indcx. We explain this as follows: a high frequencyturnover can occur hi the weak intraculuster magnetic field; the extrapolation of the power lawelectron spectrum is then incorrect, and the magnetic field; the extrapolation of the power lawvalue.展开更多
In contemporary physics, there is an observed discrepancy in the mass calculations used to determine the strength of celestial gravitational fields. Therefore, physics is searching for dark matter candidate particles,...In contemporary physics, there is an observed discrepancy in the mass calculations used to determine the strength of celestial gravitational fields. Therefore, physics is searching for dark matter candidate particles, such as weakly interacting massive particles (WIMPs) and axions, while attempting to modify Newtonian dynamics and the law of universal gravitation. Inspired by the classical theories of electric and magnetic field mass-energy calculations, the present work proposes a new theoretical attempt to explore the dark matter in the universe and challenge theories that modify Newtonian dynamics and the law of universal gravitation. Like the formulas for calculating the mass-energy density of electric and magnetic fields, Newtonian static gravitational fields also have a mass-energy density. The matter in the gravitational field will also generate a new gravitational field and thus derive the formula for calculating the mass-energy of matter in the gravitational field. In this way, the gravitational mass-energy of celestial bodies should consider the ordinary visible matter and invisible matter of the gravitational field. The strength of a gravitational field is a vector, and the mass-energy density of a gravitational field is proportional to the square of its strength. The greater the strength of the gravitational field, the greater the mass-energy density of the gravitational field at that location. Assuming that ordinary matter is distributed uniformly within a sphere, it deduces that the mass-energy of the celestial body is not only related to that of ordinary matter but also to its structure. The higher the celestial structure factor of that body, the greater the mass-energy density of matter in the gravitational field inside and outside the body.展开更多
Water mist is one of the effective candidates for halon replacement used in electrical environment fire protec-tion. Water mist additives may greatly enhance fire suppres-sion effectiveness. In electrical environment,...Water mist is one of the effective candidates for halon replacement used in electrical environment fire protec-tion. Water mist additives may greatly enhance fire suppres-sion effectiveness. In electrical environment, electrical breakdown field strength (E) is one of the important factors that control the performance of electrical equipment. In this study the variation principles of electrical breakdown field strength and the electrical characteristics of MC additives were investigated by electrode discharging experiments. Ex-perimental results showed that electrical breakdown field strength was impacted obviously by the conductive metal ions and insulated fluorocarbon surfactants in MC additives. The attenuation percentages of E in different experimental cases were described, thus providing scientific guidance for the use of water mist and MC additives in electrical fire sup-pression.展开更多
Archean to Cenozoic mafic volcanic rocks from the North China craton are studied. They show Archean Proterozoic (Ar Pt) boundary and geochemical anomalies in Cenozoic basalts. Proterozoic mafic volcanics are enriche...Archean to Cenozoic mafic volcanic rocks from the North China craton are studied. They show Archean Proterozoic (Ar Pt) boundary and geochemical anomalies in Cenozoic basalts. Proterozoic mafic volcanics are enriched in most of the high field strength elements (HFSE) compared with Archean ones. Nb, Ta and Th show a distinct sequence of incompatibility in Archean and Proterozoic. The Cenozoic basalts are enriched in HFSE and Ni and their REEs are strongly differentiated with positive Eu anomalies ( δ (Eu)=1.14). The Ar Pt boundary could be related to change in oxygen fugacity and requires an increasing importance of enriched mantle source. The geochemistry of Cenozoic basalts implies a mantle source similar to OIB. Residuum from subducting partial melting of old basaltic oceanic crust and continental crust is likely to contribute to the formation of the enriched mantle.展开更多
Electromagnetic field is an available online method to increase bonding strength of clad sheet manufactured by horizontal twin-roll casting （HTRC）. In this paper, an electric current pulse （ECP） and a complex fie...Electromagnetic field is an available online method to increase bonding strength of clad sheet manufactured by horizontal twin-roll casting （HTRC）. In this paper, an electric current pulse （ECP） and a complex field （static magnetic field （SMF） together with ECP） are exerted during HTRC of steel/aluminum clad sheet. The produced clad sheet has good appearance, and no visible defects exist at the bonding interface. The inter-diffusion zone at Fe/A1 interface in ECP and SMF＋ECP sheets is 3 and 4 μm, respectively, and the latter increases slightly compared with that in non-field sheet. The average peel strengths （APS） of ECP and SMF＋ECP sheet are 14 and 21 N/mm, respectively, which increase by 2 and 9 N/mm compared with 12 N/mm of non-field sheet. The APS increment in SMF＋ECP sheet is resulted from the increment of interface bonding spots and the enhancement of inter-diffusion zone width.展开更多
半导电屏蔽层对绝缘层空间电荷的分布起着重要作用,绝缘层中空间电荷积累是制约高压直流(high voltage direct current,HVDC)电缆发展的关键因素之一。采用熔融接枝将氯乙酸丙烯酯(CAAE)接枝到乙烯-丙烯酸丁酯共聚物(ethylene-butyl acr...半导电屏蔽层对绝缘层空间电荷的分布起着重要作用,绝缘层中空间电荷积累是制约高压直流(high voltage direct current,HVDC)电缆发展的关键因素之一。采用熔融接枝将氯乙酸丙烯酯(CAAE)接枝到乙烯-丙烯酸丁酯共聚物(ethylene-butyl acrylate copolymer,EBA)大分子链上,制备了CAAE接枝EBA/炭黑(carbon black,CB)半导电屏蔽料,对其进行了形貌及结构表征,测试了其体积电阻率和其作电极时交联聚乙烯(crosslinked polyethylene,XLPE)绝缘层的空间电荷分布特性及击穿场强,系统研究了CAAE的含量对半导电屏蔽料电性能及XLPE绝缘层空间电荷分布特性和击穿场强的影响。结果表明,CAAE接枝EBA基半导电屏蔽料的体积电阻率随着CAAE含量的增加呈先增加后降低的趋势,CAAE接枝改性半导电屏蔽可以降低XLPE绝缘层中的电场畸变,其中CAAE含量为1.0phr时,接枝改性半导电屏蔽料的体积电阻率最低,相较于EBA/CB作电极时,XLPE中的最大电场畸变率在30、40和80℃时分别降低了43.2%、69.0%和72.4%,不同温度下XLPE的击穿场强得到了明显提高。展开更多
基金Foundation： National Natural Science Foundation of China, No. 41271134
文摘Traffic is an indispensable prerequisite for a tourism system. The ＂four vertical and four horizontal＂ HSR network represents an important milestone of the ＂traffic revolution＂ in China. It will affect the spatial pattern of tourism accessibility in Chinese cities, thus substan- tially increasing their power to attract tourists and their radiation force. This paper examines the evolution and spatial characteristics of the power to attract tourism of cities linked by China＇s HSR network by measuring the influence of accessibility of 338 HSR-linked cities using GIS analysis. The results show the following. （1） The accessibility of Chinese cities is optimized by the HSR network, whose spatial pattern of accessibility exhibits an obvious traf- fic direction and causes a high-speed rail-corridor effect. （2） The spatial pattern of tourism field strength in Chinese cities exhibits the dual characteristics of multi-center annular diver- gence and dendritic diffusion. Dendritic diffusion is particularly more obvious along the HSR line. The change rate of urban tourism field strength forms a high-value corridor along the HSR line and exhibits a spatial pattern of decreasing area from the center to the outer limit along the HSR line. （3） The influence of the higher and highest tourism field strength areas along the HSR line is most significant, and the number of cities that distribute into these two types of tourism field strengths significantly increases： their area expands by more than 100% HSR enhances the tourism field strength value of regional central cities, and the radiation range of tourism attraction extends along the HSR line.
文摘Objective To investigate effect of MR field strength on texture features of cerebral T2 fluid attenuated inversion recovery(T2-FLAIR)images.Methods We acquired cerebral 3 D T2-FLAIR images of thirty patients who were diagnosed with ischemic white matter lesion(WML)with MR-1.5 T and MR-3.0 T scanners.Histogram texture features which included mean signal intensity(Mean),Skewness and Kurtosis,and gray level co-occurrence matrix(GLCM)texture features which included angular second moment(ASM),Contrast,Correlation,Inverse difference moment(IDM)and Entropy,of regions of interest located in the area of WML and normal white matter(NWM)were measured by ImageJ software.The texture parameters acquired with MR-1.5 T scanning were compared with MR-3.0 T scanning.Results The Mean of both WML and NWM obtained with MR-1.5 T scanning was significantly lower than that acquired with MR-3.0 T(P<0.001),while Skewness and Kurtosis between MR-1.5 T and MR-3.0 T scanning showed no significant difference(P>0.05).ASM,Correlation and IDM of both WML and NWM acquired with MR-1.5 T revealed significantly lower values than those with MR-3.0 T(P<0.001),while Contrast and Entropy acquired with MR-1.5 T showed significantly higher values than those with MR-3.0 T(P<0.001).Conclusion MR field strength showed no significant effect on histogram textures,while had significant effect on GLCM texture features of cerebral T2-FLAIR images,which indicated that it should be cautious to explain the texture results acquired based on the different MR field strength.
文摘Objective: A comparison of the difference between the two types of field MR scan in diagnosis of shoulder joint injury. Method: Randomly selected 153 patients with arthroscopic or open arthroplasty who had shoulder pain or dysfunction treated in our hospital from 2014 to 2017 were divided into 1.5 T group and 3.0 according to the field strength of MRI examination. Postoperative pathology was a gold standard. The sensitivity, specificity, consistency, and predictive value of two field-strength MRI examinations in the diagnosis of rotator cuff tears were calculated and compared. Results: The sensitivity, specificity, crude consistency, positive predictive value, and negative predictive value of the 1.5 T group were 68.75%, 82.35%, 73.47%, 88.00%, and 58.33%, respectively. The 3.0 T group was 72.22%, 89.47%, 78.18%, 92.86% and 62.96%, the differences between the above indicators were not statistically significant (P > 0.05). Conclusion: There was no difference in the authenticity and benefit index of rotator cuff injury diagnosed by 1.5 T and 3.0 T MRI.
文摘This article describes GIS-based models successfully developed for predicting the coverage of Cityphone cellular network,visualizing the predicted signal strength,and analyzing the field strength coverage.In order to predict the signal coverage strength of communication network more accurately,the spatial and nonspatial databases of a mobile cellular network are combined by GIS and produce the necessary parameters.A GIS model named COST-231-Walfisch–Ikegami model(WIM)is developed for signal coverage prediction in Ho Chi Minh City.Radio-line-of-sight and nonradio-lineof-sight conditions can be determined by this model.In addition,in case of nonradio-line-of-sight conditions,average building height,building separation,building width,incident radio path,and road orientation with respect to the direct radio path were obtained using GIS.Road orientation loss,multiscreen diffraction loss,and shadowing gain were predicted more accurate by this model.The scale of maps in the experiment was 1:2000 and the average of floor height was 3 m because there were no exact building height measurements.Statistical results show that the path loss predicted by the COST 231 WIM overcame the real path loss of each cell station.And this method can be used for signal coverage prediction of mobile cellular network in urban areas.Compared to the current situation with the Ho Chi Minh City Posts and Telecommunications system,this model can be effectively applied to improve the Cityphone mobile network quality as well as capability.Developed GIS models can help designers in predicting cell station coverage using real spatial maps that make the results more reliable.This research can help network operators improve the network quality and capability with the best investment efficiently.
基金The research is supported by the National Natural Science Foundation of China State Antarctic Committee
文摘It was ascertained that there is a great margin between the theoretical values and experimental medians of the field strength of RWM and RID signals during high solar activity period at Chinese Great Wall Station on Antarctica. The calculated values are, on average, less than the experimental, especially on the propagation path between RID and Antarctica. The field strength by the experiment may be used as the basic data for the research of HF propagation over the very long distance. Because of the large deviation it seems to be necessary to study HF propagation over the very long distance in details, especially the propagation model.
文摘A significant number of fire-induced power disruptions are observed in several countries every year. The faults are normally phase-to-phase short circuiting or conductor-to-ground discharges at mid-span region of the high-voltage transmission system. In any case, the wildfire plumes provide a conductive path. The electrical conductivity is due to intense heat in combustion zone of the fire which creates ion and electrons from flame inherent particulates. Increase in the ion concentration increases the electrical conductivity of the fire plume. The main purpose of this study was to measure dielectric breakdown electric field for vegetation and hydrocarbon flames. The experimental data is needed for validation of simulation schemes which are necessary for evaluation of power grid systems reliability under extreme wildfire weather conditions. In this study, hydrocarbon and vegetation fuels were ignited in a cylindrically shaped steel burner which was fitted with type-K thermocouples to measure flame temperature. The fuels consisted of dried weeping wattle (Peltophorum africanum) litter, butane gas and candle wax. Two pinned copper electrodes supported by retort stands were mounted to the burner and energized to a high voltage. This generated a strong electric field sufficient to initiate dielectric breakdown in the flames. Breakdown electric field strength (Ecrit) obtained from the experiment decreased from 10.5 to 6.9 kV/cm for the flames with temperature range of 1003 to 1410 K, respectively.
文摘In this paper,it will be calculated the electromagnetic field strength and the Lorentz force in Geometric Algebra Cl_(3,0).And it will be compared with their equivalent in the tensor covariant formalism.Also,four extra equations not appearing in the classical formalism will be obtained and its meaning will be explained.In the same way,the electromagnetic Field strength elements and the velocity multivector of the particle will be expanded.New equations and new elements appearing will be explained,being the most important one,the Electromagnetic trivector B_(xyz).A field to be added to the magnetic(bivector-like)and electric(vector-like)fields.Lastly,an insight of the possible implications of these learnings in the Dirac Equation will be commented.
基金National Natural Science Foundation of China,Grant/Award Number:52107148China Postdoctoral Science Foundation,Grant/Award Number:2020M680485Fundamental Research Funds for the Central-Universities,Grant/Award Number:2021MS004。
文摘Currently,the design of transformers insulation predominantly depends on the allowable alternating current(AC)field values for insulating oil established by Weidmann in the 1980s,lacking the research under direct current(DC)voltage for converter transformers.This study selects naphthenic oils and paraffin-based oil transformer oil as research subjects,establishing a practical measurement platform to ascertain the oil breakdown characteristics under DC voltage.Furthermore,it statistically analyses the allowable DC field values of the oil.The findings elucidate that(1)the three-parameter Weibull dis-tribution is more suitable to conduct a statistical analysis for oil breakdown probability,yielding a fitting degree up to 99.95%.(2)For a constant electrode spacing,a 14.81%voltage increment escalates the breakdown probability of the oil gap from 3.33%to 73.33%.Concurrently,an increase in electrode spacing leads to a substantial decrement in the breakdown field strength of transformer oil,with KI25X experiencing a 54.51%reduction as electrode spacing extends from 5 to 25 mm.(3)The constant terms of the allowable DC field strength for S4,KI50X,and KI25X are found to be 19.728,17.221,and 19.281,respectively.(4)A thorough analysis for differences in physicochemical properties and electrical parameters elucidates the variations in insulation properties across different transformer oils.The findings presented in this study offer essential theoretical and technical foundations for the design,evaluation,and enhancement of insulation structures in converter transformers.
基金supported by National Natural Science Foundation of China(No.52074092)the Fundamental Research Funds for Inner Mongolia University of Science&Technology(No.2023QNJS007)+1 种基金Program for Young Talents of Science and Technology in Universities of Inner Mongolia Autonomous Region(No.NJYT23115)the Inner Mongolia Natural Science Foundation(No.2022MS05039).
文摘In recent years,the effect of pulsed magnetic fields on improving the solidification structure of alloys has attracted significant attention.A GH4738 nickel-based alloy smelted using a self-designed 20-kg electromagnetic casting system was taken as the research object.Finite element software was used to numerically simulate the magnetic field intensity,distribution,and temperature field of the casting device.The effect of the pulsed magnetic field on the solidification process of the GH4738 alloy was studied by means of low-magnification microstructural analysis.The measured magnetic field shows that when the duty cycle is 20%,the pulse frequency is 50 Hz,the output current is in the range of 150–250 A,and the peak magnetic field intensity of the crucible center is 68–116 mT.The crucible temperature is heated to 600℃and the melt center solidification time is 12.844 s.The microstructural analysis of the ingot shows that its shrinkage hole is reduced from 130 to 100 mm,and the equiaxed crystal area is increased from 2275 to 3150 mm^(2).The solidification angle of the dendrite is changed under the action of the pulsed magnetic field,and the tilt angle is 45°.The results show that the pulsed magnetic field promotes the primary crystal core of the GH4738 alloy,improves the nucleation rate of the melt,reduces the size difference of the solidification structure between the center and the edge of the ingot,and improves the uniformity of the solidification structure.
文摘In this article, the fast multipole method （FMM） is applied to analgze the field strength of an ultra-wideband （UWB） signal. Small coverage of UWB communication systems and high efficiency of the algorithm make it possible to calculate the amplitude of electric field accurately. A homogeneous dielectric body and a multilayered dielectric object are studied. The computational results obtained by applying the FMM agree well with those obtained by applying the method of moments （MoM）.
文摘Using very recently published X-ray and low frequency radio data we have calculated thelower limit of the magnetic field and several other related quantities for 25 clusters of galaxies（which are classified into 'normal', distant and steep spectrum clusters） and 12 radiogalaxies. Our main results are as follows: （1）The magnetic field in the extended lobes of radio galaxies is larger than 10-6 G.Thus radio galaxies, whether they belong to clusters or not, emit few X-rays through theinverse Compton effect. （2）The low frequency radio emission from clusters can be divided into two components:one or several radio galaxies, and an extended halo where the magnetic field is about 10-8G, and where inverse Compton X-rays are most probably emitted. （3）Our sample of distant clusters is biased towards high radio luminosity and givesresults comparable to those obtained for radio galaxies. This can naturally be explained bythe fact that the radio galaxy component daminates the radio emission. （4）In steep spectrum clusters, the equipartition magnetic field is the same as that in'normal' clusters, but the lower limit of the magnetic field has a rather high value andseems to increase with the spectral indcx. We explain this as follows: a high frequencyturnover can occur hi the weak intraculuster magnetic field; the extrapolation of the power lawelectron spectrum is then incorrect, and the magnetic field; the extrapolation of the power lawvalue.
文摘In contemporary physics, there is an observed discrepancy in the mass calculations used to determine the strength of celestial gravitational fields. Therefore, physics is searching for dark matter candidate particles, such as weakly interacting massive particles (WIMPs) and axions, while attempting to modify Newtonian dynamics and the law of universal gravitation. Inspired by the classical theories of electric and magnetic field mass-energy calculations, the present work proposes a new theoretical attempt to explore the dark matter in the universe and challenge theories that modify Newtonian dynamics and the law of universal gravitation. Like the formulas for calculating the mass-energy density of electric and magnetic fields, Newtonian static gravitational fields also have a mass-energy density. The matter in the gravitational field will also generate a new gravitational field and thus derive the formula for calculating the mass-energy of matter in the gravitational field. In this way, the gravitational mass-energy of celestial bodies should consider the ordinary visible matter and invisible matter of the gravitational field. The strength of a gravitational field is a vector, and the mass-energy density of a gravitational field is proportional to the square of its strength. The greater the strength of the gravitational field, the greater the mass-energy density of the gravitational field at that location. Assuming that ordinary matter is distributed uniformly within a sphere, it deduces that the mass-energy of the celestial body is not only related to that of ordinary matter but also to its structure. The higher the celestial structure factor of that body, the greater the mass-energy density of matter in the gravitational field inside and outside the body.
基金This work was supported by the China National Key Basic Research Special Funds(Grant No.2001CB409600)the National Natural Science Foundation of China(Grant No.50323005)the Anhui Development Fund of Person with Ability(Grant No.2003Z019).
文摘Water mist is one of the effective candidates for halon replacement used in electrical environment fire protec-tion. Water mist additives may greatly enhance fire suppres-sion effectiveness. In electrical environment, electrical breakdown field strength (E) is one of the important factors that control the performance of electrical equipment. In this study the variation principles of electrical breakdown field strength and the electrical characteristics of MC additives were investigated by electrode discharging experiments. Ex-perimental results showed that electrical breakdown field strength was impacted obviously by the conductive metal ions and insulated fluorocarbon surfactants in MC additives. The attenuation percentages of E in different experimental cases were described, thus providing scientific guidance for the use of water mist and MC additives in electrical fire sup-pression.
文摘Archean to Cenozoic mafic volcanic rocks from the North China craton are studied. They show Archean Proterozoic (Ar Pt) boundary and geochemical anomalies in Cenozoic basalts. Proterozoic mafic volcanics are enriched in most of the high field strength elements (HFSE) compared with Archean ones. Nb, Ta and Th show a distinct sequence of incompatibility in Archean and Proterozoic. The Cenozoic basalts are enriched in HFSE and Ni and their REEs are strongly differentiated with positive Eu anomalies ( δ (Eu)=1.14). The Ar Pt boundary could be related to change in oxygen fugacity and requires an increasing importance of enriched mantle source. The geochemistry of Cenozoic basalts implies a mantle source similar to OIB. Residuum from subducting partial melting of old basaltic oceanic crust and continental crust is likely to contribute to the formation of the enriched mantle.
基金supported by the Industry-Academia-Research projects of Guangdong province, P. R. China (Grant Nos. 2014B090903012, 2013B090200008 and 2013B090600015)
文摘Electromagnetic field is an available online method to increase bonding strength of clad sheet manufactured by horizontal twin-roll casting （HTRC）. In this paper, an electric current pulse （ECP） and a complex field （static magnetic field （SMF） together with ECP） are exerted during HTRC of steel/aluminum clad sheet. The produced clad sheet has good appearance, and no visible defects exist at the bonding interface. The inter-diffusion zone at Fe/A1 interface in ECP and SMF＋ECP sheets is 3 and 4 μm, respectively, and the latter increases slightly compared with that in non-field sheet. The average peel strengths （APS） of ECP and SMF＋ECP sheet are 14 and 21 N/mm, respectively, which increase by 2 and 9 N/mm compared with 12 N/mm of non-field sheet. The APS increment in SMF＋ECP sheet is resulted from the increment of interface bonding spots and the enhancement of inter-diffusion zone width.
文摘半导电屏蔽层对绝缘层空间电荷的分布起着重要作用,绝缘层中空间电荷积累是制约高压直流(high voltage direct current,HVDC)电缆发展的关键因素之一。采用熔融接枝将氯乙酸丙烯酯(CAAE)接枝到乙烯-丙烯酸丁酯共聚物(ethylene-butyl acrylate copolymer,EBA)大分子链上,制备了CAAE接枝EBA/炭黑(carbon black,CB)半导电屏蔽料,对其进行了形貌及结构表征,测试了其体积电阻率和其作电极时交联聚乙烯(crosslinked polyethylene,XLPE)绝缘层的空间电荷分布特性及击穿场强,系统研究了CAAE的含量对半导电屏蔽料电性能及XLPE绝缘层空间电荷分布特性和击穿场强的影响。结果表明,CAAE接枝EBA基半导电屏蔽料的体积电阻率随着CAAE含量的增加呈先增加后降低的趋势,CAAE接枝改性半导电屏蔽可以降低XLPE绝缘层中的电场畸变,其中CAAE含量为1.0phr时,接枝改性半导电屏蔽料的体积电阻率最低,相较于EBA/CB作电极时,XLPE中的最大电场畸变率在30、40和80℃时分别降低了43.2%、69.0%和72.4%,不同温度下XLPE的击穿场强得到了明显提高。
