The Lunar Environment heliospheric X-ray Imager(LEXI)and Solar wind Magnetosphere Ionosphere Link Explorer(SMILE)missions will image the Earth’s dayside magneto pause and cusps in soft X-rays after their respective l...The Lunar Environment heliospheric X-ray Imager(LEXI)and Solar wind Magnetosphere Ionosphere Link Explorer(SMILE)missions will image the Earth’s dayside magneto pause and cusps in soft X-rays after their respective launches in the near future,to specify glo bal magnetic reconnection modes for varying solar wind conditions.To suppo rt the success of these scientific missions,it is critical to develop techniques that extract the magnetopause locations from the observed soft X-ray images.In this research,we introduce a new geometric equation that calculates the subsolar magnetopause position(RS)from a satellite position,the look direction of the instrument,and the angle at which the X-ray emission is maximized.Two assumptions are used in this method:(1)The look direction where soft X-ray emissions are maximized lies tangent to the magnetopause,and(2)the magnetopause surface near the subsolar point is almost spherical and thus RSis nea rly equal to the radius of the magneto pause curvature.We create synthetic soft X-ray images by using the Open Geospace General Circulation Model(OpenGGCM)global magnetohydrodynamic model,the galactic background,the instrument point spread function,and Poisson noise.We then apply the fast Fourier transform and Gaussian low-pass filte rs to the synthetic images to re move noise and obtain accurate look angles for the soft X-ray pea ks.From the filte red images,we calculate RS and its accuracy for different LEXI locations,look directions,and solar wind densities by using the OpenGGCM subsolar magnetopause location as ground truth.Our method estimates RS with an accuracy of<0.3 RE when the solar wind density exceeds>10 cm-3.The accuracy improves for greater solar wind densities and during southward interplanetary magnetic fields.The method ca ptures the magnetopause motion during southwa rd interplaneta ry magnetic field turnings.Consequently,the technique will enable quantitative analysis of the magnetopause motion and help reveal the dayside reconnection modes for dynamic solar wind conditions.This technique will suppo rt the LEXI and SMILE missions in achieving their scientific o bjectives.展开更多
As highly integrated circuits continue to advance,accompanied by a growing demand for energy efficiency and weight reduction,materials are confronted with mounting challenges pertaining to thermal conductivity and lig...As highly integrated circuits continue to advance,accompanied by a growing demand for energy efficiency and weight reduction,materials are confronted with mounting challenges pertaining to thermal conductivity and lightweight properties.By virtue of numerous intrinsic mechanisms,as a result,the thermal conductivity and mechanical properties of the Mg alloys are often inversely related,which becomes a bottleneck limiting the application of Mg alloys.Based on several effective modification methods to improve the thermal conductivity of Mg alloys,this paper describes the law of how they affect the mechanical properties,and clearly indicates that peak aging treatment is one of the best ways to simultaneously enhance an alloy's thermal conductivity and mechanical properties.As the most frequently used Mg alloy,cast alloys exhibit substantial potential for achieving high thermal conductivity.Moreover,recent reports indicate that hot deformation can significantly improve the mechanical properties while maintaining,and potentially slightly enhancing,the alloy's thermal conductivity.This presents a meaningful way to develop Mg alloys for applications in the field of small-volume heat dissipation components that require high strength.This comprehensive review begins by outlining standard testing and prediction methods,followed by the theoretical models used to predict thermal conductivity,and then explores the primary influencing factors affecting thermal conductivity.The review summarizes the current development status of Mg alloys,focusing on the quest for alloys that offer both high thermal conductivity and high strength.It concludes by providing insights into forthcoming prospects and challenges within this field.展开更多
Magnetic holes are magnetic depression structures that exist widely in many plasma environments.The magnetic holes with durations of>1 s in the solar wind at Mercury’s orbit have drawn much attention,but the prope...Magnetic holes are magnetic depression structures that exist widely in many plasma environments.The magnetic holes with durations of>1 s in the solar wind at Mercury’s orbit have drawn much attention,but the properties of the magnetic holes with shorter durations are still unclear.Here,we investigate the magnetic holes with durations of 0.1-100 s in the upstream region of Mercury’s bow shock based on observations by the MESSENGER(MErcury Surface,Space ENvironment,GEochemistry,and Ranging)spacecraft.They can be divided into two groups according to the distribution of their duration:small-duration magnetic holes(SDMHs,<0.6 s)and large-duration magnetic holes(LDMHs,>0.6 s).The duration of each group approximately obeys a log-normal distribution with a median of~0.25 s and 3 s,respectively.Approximately 1.7%(32.6%)of the SDMHs(LDMHs)reduce the magnetic field strength by more than 50%.For both groups,some structures have a linear or quasi-linear polarization,whereas others have an elliptical polarization.The magnetic hole events in both groups tend to have a higher rate of occurrence when the interplanetary magnetic field strength is weaker.Their occurrence rates are also affected by Mercury’s foreshock,which can increase(decrease)the occurrence rate of the SDMHs(LDMHs).This finding suggests that Mercury’s foreshock might be one source of the SDMHs and that the foreshock can destroy some LDMHs.These observations suggest that a new group of magnetic holes with durations of<0.6 s exist in the upstream region of Mercury’s bow shock.展开更多
Geomagnetic storms can result in large magnetic field disturbances and intense currents in the magnetosphere and even on the ground.As an important medium of momentum and energy transport among the solar wind,magnetos...Geomagnetic storms can result in large magnetic field disturbances and intense currents in the magnetosphere and even on the ground.As an important medium of momentum and energy transport among the solar wind,magnetosphere,and ionosphere,field-aligned currents(FACs)can also be strengthened in storm times.This study shows the responses of FACs in the plasma sheet boundary layer(PSBL)observed by the Magnetospheric Multiscale(MMS)spacecraft in different phases of a large storm that lasted from May 27,2017,to May 29,2017.Most of the FACs were carried by electrons,and several FACs in the storm time also contained sufficient ion FACs.The FAC magnitudes were larger in the storm than in the quiet period,and those in the main phase were the strongest.In this case,the direction of the FACs in the main phase showed no preference for tailward or earthward,whereas the direction of the FACs in the recovery phase was mostly tailward.The results suggest that the FACs in the PSBL are closely related to the storm and could be driven by activities in the tail region,where the energy transported from the solar wind to the magnetosphere is stored and released as the storm is evolving.Thus,the FACs are an important medium of energy transport between the tail and the ionosphere,and the PSBL is a significant magnetosphere–ionosphere coupling region in the nightside.展开更多
The Mars Orbiter MAGnetometer(MOMAG)is a scientific instrument onboard the orbiter of China’s first mission for Mars—Tianwen-1.Since November 13,2021,it has been recording magnetic field data from the solar wind to ...The Mars Orbiter MAGnetometer(MOMAG)is a scientific instrument onboard the orbiter of China’s first mission for Mars—Tianwen-1.Since November 13,2021,it has been recording magnetic field data from the solar wind to the magnetic pile-up region surrounding Mars.Here we present its in-flight performance and first science results,based on its first one and one-half months’data.Comparing these early MOMAG observations to the magnetic field data in the solar wind from NASA’s Mars Atmosphere and Volatile EvolutioN(MAVEN)mission,we report that the MOMAG magnetic field data are at the same level in magnitude,and describe the same magnetic structures with similar variations in three components.We recognize 158 clear bow shock(BS)crossings in these MOMAG data;their locations match well statistically with the modeled average BS.We also identify and compare five pairs of datasets collected when Tianwen-1’s orbiter and the MAVEN probe made simultaneous BS crossings.These BS crossings confirm the global shape of modeled BS,as well as the south-north asymmetry of the Martian BS.Two cases presented in this paper suggest that the BS is probably more dynamic at flank than near the nose.So far,MOMAG performs well,and provides accurate magnetic field vectors.MOMAG is continuously scanning the magnetic field surrounding Mars.Data from MOMAG’s measurements complement data from MAVEN and will undoubt edly advance our understanding of the plasma environment of Mars.展开更多
Selective laser melting(SLM)is an emerging layer-wise additive manufacturing technique that can generate complex components with high performance.Particulate-reinforced aluminum matrix composites(PAMCs)are important m...Selective laser melting(SLM)is an emerging layer-wise additive manufacturing technique that can generate complex components with high performance.Particulate-reinforced aluminum matrix composites(PAMCs)are important materials for various applications due to the combined properties of Al matrix and reinforcements.Considering the advantages of SLM technology and PAMCs,the novel SLM PAMCs have been developed and researched in recent years.Therefore,the current research progress about the SLM PAMCs is reviewed.Firstly,special attention is paid to the solidification behavior of SLM PAMCs.Secondly,the important issues about the design and fabrication of high-performance SLM PAMCs,including the selection of reinforcement,the influence of parameters on the processing and microstructure,the defect evolution and phase control,are highlighted and discussed comprehensively.Thirdly,the performance and strengthening mechanism of SLM PAMCs are systematically figured out.Finally,future directions are pointed out on the advancement of high-performance SLM PAMCs.展开更多
As one of the seven scientific payloads on board the Tianwen-1 orbiter,the Mars Orbiter Magnetometer(MOMAG)will measure the magnetic fields of and surrounding Mars to study its space environment and the interaction wi...As one of the seven scientific payloads on board the Tianwen-1 orbiter,the Mars Orbiter Magnetometer(MOMAG)will measure the magnetic fields of and surrounding Mars to study its space environment and the interaction with the solar wind.The instrument consists of two identical triaxial fluxgate magnetometer sensors,mounted on a 3.19 meter-long boom with a seperation of about 90 cm.The dual-magnetometers configuration will help eliminate the magnetic field interference generated by the spacecraft platform and payloads.The sensors are controlled by an electric box mounted inside the orbiter.Each magnetometer measures the ambient vector magnetic field over a wide dynamic range(to 10,000 nT per axis)with a resolution of 1.19 pT.Both magnetometers sample the ambient magnetic field at an intrinsic frequency of 128 Hz,but will operate in a model with alternating frequency between 1 and 32 Hz to meet telemetry allocations.展开更多
The spatial structure characteristics of landform are the foundation of geomorphologic classification and recognition.This paper proposed a new method on quantifying spatial structure characteristics of terrain surfac...The spatial structure characteristics of landform are the foundation of geomorphologic classification and recognition.This paper proposed a new method on quantifying spatial structure characteristics of terrain surface based on improved 3D Lacunarity model.Lacunarity curve and its numerical integration are used in this model to improve traditional classification result that different morphological types may share the close value of indexes based on global statistical analysis.Experiments at four test areas with different landform types show that improved 3D Lacunarity model can effectively distinguish different morphological types per texture analysis.Higher sensitivity in distinguishing the tiny differences of texture characteristics of terrain surface shows that the quantification method by 3D Lacu-narity model and its numerical integration presented in this paper could contribute to improving the accuracy of land-form classifications and relative studies.展开更多
Field aligned current （FAC） distribution in the plasma sheet boundary layers （PSBLs） in the magnetotail is studied statistically by analysing magnetic field data from the Cluster 4-point measurements. The results ...Field aligned current （FAC） distribution in the plasma sheet boundary layers （PSBLs） in the magnetotail is studied statistically by analysing magnetic field data from the Cluster 4-point measurements. The results show that the FAC distribution on the dusk side is not the same as that on the dawn side in the magnetotail. On the each side earthward and tailward, FA C occurrences are different; occurrence and average current density of FA Cs in the northern hemisphere are different from those in the southern hemisphere. This implies that the FACs have dusk-dawn side asymmetry, polarity asymmetry and inter hemisphere difference in the magnetotail. The present results give a good observation evidence for study on the FAC mechanism.展开更多
Ti-6Al-4V specimens were fabricated by selective laser melting(SLM)to study the effect of thermal treatment on the phase transformation,elemental diffusion,microstructure,and mechanical properties.The results show tha...Ti-6Al-4V specimens were fabricated by selective laser melting(SLM)to study the effect of thermal treatment on the phase transformation,elemental diffusion,microstructure,and mechanical properties.The results show that vanadium enriches around the boundary ofαphases with increasing annealing temperature to 973 K,andα′phases transform intoα+βat 973 K.The typicalα′martensite microstructure transforms to fine-scale equiaxed microstructure at 973 K and the equiaxed microstructure significantly coarsens with increasing annealing temperature to 1273 K.The SLM Ti-6Al-4V alloy annealed at 973 K exhibits a well-balanced combination of strength and ductility((1305±25)MPa and(37±3)%,respectively).展开更多
To get a deep understanding of the evolution behavior of equiaxedαphase in Ti−8Al−1Mo−1V alloy during annealing,its static coarsening mechanism was studied based on the calculations of coarsening exponent n and the a...To get a deep understanding of the evolution behavior of equiaxedαphase in Ti−8Al−1Mo−1V alloy during annealing,its static coarsening mechanism was studied based on the calculations of coarsening exponent n and the activation energy forαboundary migration.The result of n=6 indicates a special coarsening mechanism of equiaxedαphase.The activation energy forαboundary migration is calculated to be 138 kJ/mol,which is close to the activation energy for grain growth of pureα-Ti.It is revealed that the coarsening of equiaxedαcan be mainly attributed to the self-diffusion of Ti atoms across theα/αboundaries.Based on the experimental findings,a static coarsening kinetics model of equiaxedαgrains in theα+βfield is established.At last,the effects of the coarsening behavior of equiaxedαon tensile properties were studied.展开更多
We have introduced a polymer precursor into molten magnesium and then in-situ pyrolyzed to produce castings of metal matrix composites(P-MMCs)containing silicon-carbonitride(SiCNO)ceramic particles.Stress-rupture meas...We have introduced a polymer precursor into molten magnesium and then in-situ pyrolyzed to produce castings of metal matrix composites(P-MMCs)containing silicon-carbonitride(SiCNO)ceramic particles.Stress-rupture measurements of as-cast P-MMCs was performed at 350 ℃(0.69TM)to 450 ℃(0.78TM)under dead load condition corresponding to tensile stress of 2.5 MPa to 20 MPa.The time-to-fracture data were analyzed using the classical Monkman–Grant equation.The time-to-fracture is thermally activated and follows a power-law stress exponent exhibiting dislocation creep.Fractography analysis revealed that while pure magnesium appears to fracture by dislocation slip,the P-MMCs fail from the nucleation and growth of voids at the grain boundaries.展开更多
The mobile satellite laser ranging system TROS1000, successfully developed in 2010, achieves a high repetition rate and enables daytime laser ranging. Its measurement range has reached up to 36000 km with an accuracy ...The mobile satellite laser ranging system TROS1000, successfully developed in 2010, achieves a high repetition rate and enables daytime laser ranging. Its measurement range has reached up to 36000 km with an accuracy as precise as 1 cm. Using recent observations in Wuhan, Jiufeng, Xianning, and Rongcheng, Shandong, we introduce the progress made using this mobile observation system.展开更多
A statistical study of interhemispheric comparison of dipole tilt angle effect on the latitude of the mid-altitude cusp is preformed by a data set of the Cluster cusp crossings over a 5-year period. The result shows t...A statistical study of interhemispheric comparison of dipole tilt angle effect on the latitude of the mid-altitude cusp is preformed by a data set of the Cluster cusp crossings over a 5-year period. The result shows that the dipole tilt angle has a clear control of the cusp latitudinal location. When the dipole tilts sunwards, the cusp is shifted poleward. The northern cusp moves 1° ILAT for every 15.4° increase in the dipole tilt angle, while the southern cusp moves 1° ILAT for every 20.8° increase in the dipole tilt angle. This suggests that an interhemispheric difference appears in the dependence of cusp latitudinal location on the dipole tilt angle.展开更多
Due to their ecological disadvantages, many mountain regions have experienced land-use abandonment and shrub encroachment on former grassland at higher altitudinal zones--especially during recent decades of urbanizati...Due to their ecological disadvantages, many mountain regions have experienced land-use abandonment and shrub encroachment on former grassland at higher altitudinal zones--especially during recent decades of urbanization. But does this trend also apply to the hinterland of urban settlements？ By using the Southern Colombian example of Popay^n, a medium-sized city located in the Northern Andes, we can show that the landscape changes observed between 1989 and 2010 can hardly be related to agricultural abandonment. Hypsometric variations of land-cover change indicate that, until 2001, woods or shrubland expanded faster at the lower altitudinal range adjacent to the city than at the more remote higher zones. In contrast, after 2001 grassland areas increased on former woods or shrnbland at all altitudinal belts. Both periods thus present developments that can be interpreted as the result of land-use expansion below 2000 m asl and land-use persistence in the tierrafrla of the mountain city＇s hinterland.展开更多
Using dynamics equation, acceleration of out-flowing ion during dipolarization in a substorm in the magneto-tail is simulated. The main results show that: (1) The ion distribution function that is initially exponentia...Using dynamics equation, acceleration of out-flowing ion during dipolarization in a substorm in the magneto-tail is simulated. The main results show that: (1) The ion distribution function that is initially exponentially decreasing with increasing speed is turned into a single peak distribution, and with time the peak moves towards higher speed. (2) The peak moves along V⊥ faster than that along V||, and the ion acceleration mainly occurs in the middle of the dipolarization. (3) The higher the initial energy, the faster the peak moves, and the more energy is obtained by the ions. The ion energy theoretically calculated is as high as about 102 keV, this is consistent with the observation.展开更多
Field-aligned current （FAC） density distribution at the plasma sheet boundary layers is statistically studied. The FAC is calculated by the so-called curlometer technique with the data from FGM onboard the four Clus...Field-aligned current （FAC） density distribution at the plasma sheet boundary layers is statistically studied. The FAC is calculated by the so-called curlometer technique with the data from FGM onboard the four Cluster spacecraft in 2001. By calculation we obtain a large number of FAC samples. In the samples, most of calculated FAC densities were very small and around zero caused by some errors or noise. In order to get the real FAC density distribution in the magnetotail, we use a three-Gaussian distribution to fit the errors, then subtract the estimated error contribution from the full distribution and obtain the FAC density distribution. The result shows that the FAC occurrence versus its density has a distribution consisting of a Gauss/an distribution with an additional decreasing exponential distribution. The most probable value of the FAC density is 3.45 pT/km.展开更多
In the summer of 2010/2011 Chile suffered the third most severe energy and water supply crisis in only one decade. This may be surprising as the Andes which accompany the country along 4,200 km are a water tower and c...In the summer of 2010/2011 Chile suffered the third most severe energy and water supply crisis in only one decade. This may be surprising as the Andes which accompany the country along 4,200 km are a water tower and could provide more electricity and water than needed. On top of that, it has to be mentioned that Chile also counts with sunny and windy climates and with excellent geothermal energy resources and thus has a huge potential as far as renewable energies are concerned. After analyzing the existing natural conditions, the infrastructure and the present challenges of climate change, it has to be asked in which way Chile can make use of this potential in the near future, considering the legal and political situation and the technological opportunities. It seems that the resources are still hidden in the Andes, and only the key is missing to realize the country＇s natural potential. This research has been based on the analysis of existing literature, media, quantitative data from government institutions and other antecedents obtained by the authors in field work done in the South of Chile in 2OLO. The added value of this compilation lies in the comprehensive perspective, linking the knowledge of climatologists, hydrologists, mountain researchers and energy experts in order to support a sustainable energy and water supply for the future in Chile. From this present research, it can be concluded that Chile necessarilyhas to adopt new energy-related strategies, particularly those aimed at diminishing the strong dependence on traditional sources of energy and establishing new techniques and technologies for generating electrieity and utilizing the vast potential that the country is ready to offer, such as that provided by the Andes along 4,200 kilometers.展开更多
The bipolar electric field solitary(EFS)structures observed frequently in space plasmas by satellites have two different polarities,first positive electric field peak then negative(i.e.,positive/negative)and first neg...The bipolar electric field solitary(EFS)structures observed frequently in space plasmas by satellites have two different polarities,first positive electric field peak then negative(i.e.,positive/negative)and first negative then positive peak(i.e.,negative/positive).We provide the physical explanation on the polarity of observed bipolar EFS structures with an electrostatic ion fluid model.The results show that if initial electric field𝐸E_(0)>0,the polarity of the bipolar EFS structure will be positive/negative;and if𝐸E_(0)<0,the polarity of the bipolar EFS structure will be negative/positive.However,for a fixed polarity of the EFS,either positive/negative or negative/positive,if the satellite is located at the positive side of the EFS,the observed polarity should be positive/negative,if the satellite is located at the negative side of the EFS,the observed polarity should be negative/positive.Therefore,we provide a method to clarify the natural polarity of the EFS with observed polarity by satellites.Our results are significant to understand the physical process in space plasma with the satellite observation.展开更多
Selective laser melting(SLM)or Laser-based powder bed fusion(LBPF)is gaining much attention for the fabrication of novel materials with complex shapes,improved functionalities,and properties.An attempt has been made t...Selective laser melting(SLM)or Laser-based powder bed fusion(LBPF)is gaining much attention for the fabrication of novel materials with complex shapes,improved functionalities,and properties.An attempt has been made to fabricate hard and brittle silicon via SLM in the absence of any cracks.Two different powder batches were used,where one of the powder batches has 0.3wt%Fe and the other batch with 0.02wt%Fe.The parameter optimization process shows that the SLM Si samples were successfully fabricated from the powders with the minor addition of Fe.The deliberate addition of Fe facilitates heterogeneous nucleation of Si and aids in absorbing the laser energy beam more efficiently.SLM Si samples with 98.5%theoretical density were fabricated with a hardness of around 10.65±40 GPa.The experimental results show that SLM can successfully fabricate Si without cracks and with near theoretical density(of 99%)and complex shapes,which opens their use in wider industrial applications.展开更多
基金supported by NASA(Grant Nos.80NSSC19K0844,80NSSC20K1670,80MSFC20C0019,and 80GSFC21M0002)support from NASA Goddard Space Flight Center internal funding programs(HIF,Internal Scientist Funding Model,and Internal Research and Development)。
文摘The Lunar Environment heliospheric X-ray Imager(LEXI)and Solar wind Magnetosphere Ionosphere Link Explorer(SMILE)missions will image the Earth’s dayside magneto pause and cusps in soft X-rays after their respective launches in the near future,to specify glo bal magnetic reconnection modes for varying solar wind conditions.To suppo rt the success of these scientific missions,it is critical to develop techniques that extract the magnetopause locations from the observed soft X-ray images.In this research,we introduce a new geometric equation that calculates the subsolar magnetopause position(RS)from a satellite position,the look direction of the instrument,and the angle at which the X-ray emission is maximized.Two assumptions are used in this method:(1)The look direction where soft X-ray emissions are maximized lies tangent to the magnetopause,and(2)the magnetopause surface near the subsolar point is almost spherical and thus RSis nea rly equal to the radius of the magneto pause curvature.We create synthetic soft X-ray images by using the Open Geospace General Circulation Model(OpenGGCM)global magnetohydrodynamic model,the galactic background,the instrument point spread function,and Poisson noise.We then apply the fast Fourier transform and Gaussian low-pass filte rs to the synthetic images to re move noise and obtain accurate look angles for the soft X-ray pea ks.From the filte red images,we calculate RS and its accuracy for different LEXI locations,look directions,and solar wind densities by using the OpenGGCM subsolar magnetopause location as ground truth.Our method estimates RS with an accuracy of<0.3 RE when the solar wind density exceeds>10 cm-3.The accuracy improves for greater solar wind densities and during southward interplanetary magnetic fields.The method ca ptures the magnetopause motion during southwa rd interplaneta ry magnetic field turnings.Consequently,the technique will enable quantitative analysis of the magnetopause motion and help reveal the dayside reconnection modes for dynamic solar wind conditions.This technique will suppo rt the LEXI and SMILE missions in achieving their scientific o bjectives.
基金financially supported by the National Key Research and Development Program of China(2022YFB3709300)the National Natural Science Foundation of China(Grant No.U2167213)+1 种基金the Sichuan Science and Technology Program,China(2023YFSY0016)the Chongqing Special Project of Science and Technology Innovation,China(cstc2021yszx-jcyjX0007)。
文摘As highly integrated circuits continue to advance,accompanied by a growing demand for energy efficiency and weight reduction,materials are confronted with mounting challenges pertaining to thermal conductivity and lightweight properties.By virtue of numerous intrinsic mechanisms,as a result,the thermal conductivity and mechanical properties of the Mg alloys are often inversely related,which becomes a bottleneck limiting the application of Mg alloys.Based on several effective modification methods to improve the thermal conductivity of Mg alloys,this paper describes the law of how they affect the mechanical properties,and clearly indicates that peak aging treatment is one of the best ways to simultaneously enhance an alloy's thermal conductivity and mechanical properties.As the most frequently used Mg alloy,cast alloys exhibit substantial potential for achieving high thermal conductivity.Moreover,recent reports indicate that hot deformation can significantly improve the mechanical properties while maintaining,and potentially slightly enhancing,the alloy's thermal conductivity.This presents a meaningful way to develop Mg alloys for applications in the field of small-volume heat dissipation components that require high strength.This comprehensive review begins by outlining standard testing and prediction methods,followed by the theoretical models used to predict thermal conductivity,and then explores the primary influencing factors affecting thermal conductivity.The review summarizes the current development status of Mg alloys,focusing on the quest for alloys that offer both high thermal conductivity and high strength.It concludes by providing insights into forthcoming prospects and challenges within this field.
基金the Fundamental Research Funds for the Central Universities(Grant No.HIT.OCEF.2022041)the National Natural Science Foundation of China(Grant Nos.42241155,41974205,42130204,and 42241133)+4 种基金the Guangdong Basic and Applied Basic Research Foundation(Grant Nos.2022A1515011698,2023A1515030132,and 2022A1515010257)the Shenzhen Science and Technology Research Program(Grant Nos.JCYJ20210324121412034 and JCYJ20210324121403009)the Shenzhen Key Laboratory Launching Project(Grant No.ZDSYS20210702140800001)the Joint Open Fund of Mengcheng National Geophysical Observatory(Grant No.MENGO-202315)the Macao Foundation,the pre-research Project on Civil Aerospace Technologies(Grant No.D020103)funded by the China National Space Administration,and the Chinese Academy of Sciences Center for Excellence in Comparative Planetology。
文摘Magnetic holes are magnetic depression structures that exist widely in many plasma environments.The magnetic holes with durations of>1 s in the solar wind at Mercury’s orbit have drawn much attention,but the properties of the magnetic holes with shorter durations are still unclear.Here,we investigate the magnetic holes with durations of 0.1-100 s in the upstream region of Mercury’s bow shock based on observations by the MESSENGER(MErcury Surface,Space ENvironment,GEochemistry,and Ranging)spacecraft.They can be divided into two groups according to the distribution of their duration:small-duration magnetic holes(SDMHs,<0.6 s)and large-duration magnetic holes(LDMHs,>0.6 s).The duration of each group approximately obeys a log-normal distribution with a median of~0.25 s and 3 s,respectively.Approximately 1.7%(32.6%)of the SDMHs(LDMHs)reduce the magnetic field strength by more than 50%.For both groups,some structures have a linear or quasi-linear polarization,whereas others have an elliptical polarization.The magnetic hole events in both groups tend to have a higher rate of occurrence when the interplanetary magnetic field strength is weaker.Their occurrence rates are also affected by Mercury’s foreshock,which can increase(decrease)the occurrence rate of the SDMHs(LDMHs).This finding suggests that Mercury’s foreshock might be one source of the SDMHs and that the foreshock can destroy some LDMHs.These observations suggest that a new group of magnetic holes with durations of<0.6 s exist in the upstream region of Mercury’s bow shock.
基金funded by the National Natural Science Foundation of China(NSFCGrant Nos.42204177,42274219,41974205,42130204,42241155,and 42241133)+5 种基金the Guangdong Basic and Applied Basic Research Foundation-Natural Science Foundation of Guangdong(Grant Nos.2022A1515010257,2022A1515011698,and 2023A1515030132)the Shenzhen Science and Technology Research Program(Grant Nos.JCYJ20210324121403009 and JCYJ20210324121412034)the Macao foundation,the Fundamental Research Funds for the Central Universities(Grant No.HIT.OCEF.2022041)the Shenzhen Key Laboratory Launching Project(Grant No.ZDSYS20210702140800001)the pre-research project on Civil Aerospace Technologies(Grant No.D020103)funded by the China National Space Administration.YuanQiang Chen was also funded by China Postdoctoral Science Foundation(Grant No.2022M720944)supported by the Chinese Academy of Sciences Center for Excellence in Comparative Planetology.
文摘Geomagnetic storms can result in large magnetic field disturbances and intense currents in the magnetosphere and even on the ground.As an important medium of momentum and energy transport among the solar wind,magnetosphere,and ionosphere,field-aligned currents(FACs)can also be strengthened in storm times.This study shows the responses of FACs in the plasma sheet boundary layer(PSBL)observed by the Magnetospheric Multiscale(MMS)spacecraft in different phases of a large storm that lasted from May 27,2017,to May 29,2017.Most of the FACs were carried by electrons,and several FACs in the storm time also contained sufficient ion FACs.The FAC magnitudes were larger in the storm than in the quiet period,and those in the main phase were the strongest.In this case,the direction of the FACs in the main phase showed no preference for tailward or earthward,whereas the direction of the FACs in the recovery phase was mostly tailward.The results suggest that the FACs in the PSBL are closely related to the storm and could be driven by activities in the tail region,where the energy transported from the solar wind to the magnetosphere is stored and released as the storm is evolving.Thus,the FACs are an important medium of energy transport between the tail and the ionosphere,and the PSBL is a significant magnetosphere–ionosphere coupling region in the nightside.
基金supported by the NSFC(Grant Nos 42130204 and 42188101)the Strategic Priority Program of the Chinese Academy of Sciences(Grant No.XDB41000000)the support of the Tencent Foundation.
文摘The Mars Orbiter MAGnetometer(MOMAG)is a scientific instrument onboard the orbiter of China’s first mission for Mars—Tianwen-1.Since November 13,2021,it has been recording magnetic field data from the solar wind to the magnetic pile-up region surrounding Mars.Here we present its in-flight performance and first science results,based on its first one and one-half months’data.Comparing these early MOMAG observations to the magnetic field data in the solar wind from NASA’s Mars Atmosphere and Volatile EvolutioN(MAVEN)mission,we report that the MOMAG magnetic field data are at the same level in magnitude,and describe the same magnetic structures with similar variations in three components.We recognize 158 clear bow shock(BS)crossings in these MOMAG data;their locations match well statistically with the modeled average BS.We also identify and compare five pairs of datasets collected when Tianwen-1’s orbiter and the MAVEN probe made simultaneous BS crossings.These BS crossings confirm the global shape of modeled BS,as well as the south-north asymmetry of the Martian BS.Two cases presented in this paper suggest that the BS is probably more dynamic at flank than near the nose.So far,MOMAG performs well,and provides accurate magnetic field vectors.MOMAG is continuously scanning the magnetic field surrounding Mars.Data from MOMAG’s measurements complement data from MAVEN and will undoubt edly advance our understanding of the plasma environment of Mars.
基金Project(GJHZ20190822095418365)supported by Shenzhen International Cooperation Research,ChinaProject(2019011)supported by NTUT-SZU Joint Research Program,China+2 种基金Project(2019040)supported by Natural Science Foundation of Shenzhen University,ChinaProject(JCYJ20190808144009478)supported by Shenzhen Fundamental Research Fund,ChinaProject(ZDYBH201900000008)supported by Shenzhen Bureau of Industry and Information Technology,China。
文摘Selective laser melting(SLM)is an emerging layer-wise additive manufacturing technique that can generate complex components with high performance.Particulate-reinforced aluminum matrix composites(PAMCs)are important materials for various applications due to the combined properties of Al matrix and reinforcements.Considering the advantages of SLM technology and PAMCs,the novel SLM PAMCs have been developed and researched in recent years.Therefore,the current research progress about the SLM PAMCs is reviewed.Firstly,special attention is paid to the solidification behavior of SLM PAMCs.Secondly,the important issues about the design and fabrication of high-performance SLM PAMCs,including the selection of reinforcement,the influence of parameters on the processing and microstructure,the defect evolution and phase control,are highlighted and discussed comprehensively.Thirdly,the performance and strengthening mechanism of SLM PAMCs are systematically figured out.Finally,future directions are pointed out on the advancement of high-performance SLM PAMCs.
基金supported by the Chinese National Space Administration,and the science team of MOMAG is supported by the Strategic Priority Program(Grant No.XDB41000000)the key Research Program of Frontier Sciences(No.QYZDB-SSW-DQC015)of the Chinese Academy of Sciences.
文摘As one of the seven scientific payloads on board the Tianwen-1 orbiter,the Mars Orbiter Magnetometer(MOMAG)will measure the magnetic fields of and surrounding Mars to study its space environment and the interaction with the solar wind.The instrument consists of two identical triaxial fluxgate magnetometer sensors,mounted on a 3.19 meter-long boom with a seperation of about 90 cm.The dual-magnetometers configuration will help eliminate the magnetic field interference generated by the spacecraft platform and payloads.The sensors are controlled by an electric box mounted inside the orbiter.Each magnetometer measures the ambient vector magnetic field over a wide dynamic range(to 10,000 nT per axis)with a resolution of 1.19 pT.Both magnetometers sample the ambient magnetic field at an intrinsic frequency of 128 Hz,but will operate in a model with alternating frequency between 1 and 32 Hz to meet telemetry allocations.
基金Under the auspices of National Natural Science Foundation of China (No.40930531,41171320,41001301)
文摘The spatial structure characteristics of landform are the foundation of geomorphologic classification and recognition.This paper proposed a new method on quantifying spatial structure characteristics of terrain surface based on improved 3D Lacunarity model.Lacunarity curve and its numerical integration are used in this model to improve traditional classification result that different morphological types may share the close value of indexes based on global statistical analysis.Experiments at four test areas with different landform types show that improved 3D Lacunarity model can effectively distinguish different morphological types per texture analysis.Higher sensitivity in distinguishing the tiny differences of texture characteristics of terrain surface shows that the quantification method by 3D Lacu-narity model and its numerical integration presented in this paper could contribute to improving the accuracy of land-form classifications and relative studies.
基金Supported by the National Natural Science Foundation of China under Grant Nos 40674091, 40621003 and 40874084, and the Specialized Research Fund for State Key Laboratories.
文摘Field aligned current （FAC） distribution in the plasma sheet boundary layers （PSBLs） in the magnetotail is studied statistically by analysing magnetic field data from the Cluster 4-point measurements. The results show that the FAC distribution on the dusk side is not the same as that on the dawn side in the magnetotail. On the each side earthward and tailward, FA C occurrences are different; occurrence and average current density of FA Cs in the northern hemisphere are different from those in the southern hemisphere. This implies that the FACs have dusk-dawn side asymmetry, polarity asymmetry and inter hemisphere difference in the magnetotail. The present results give a good observation evidence for study on the FAC mechanism.
基金Project(2020A1515110869)supported by Guangdong Basic and Applied Basic Research Foundation,ChinaProject(GJHZ20190822095418365)supported by Shenzhen International Cooperation Research,China+3 种基金Project(51775351)supported by the National Natural Science Foundation of ChinaProject(2019011)supported by the NTUT-SZU Joint Research Program,ChinaProject(2019040)supported by the Natural Science Foundation of SZU,ChinaProject(ASTRA6-6)supported by the European Regional Development Fund,European Union。
文摘Ti-6Al-4V specimens were fabricated by selective laser melting(SLM)to study the effect of thermal treatment on the phase transformation,elemental diffusion,microstructure,and mechanical properties.The results show that vanadium enriches around the boundary ofαphases with increasing annealing temperature to 973 K,andα′phases transform intoα+βat 973 K.The typicalα′martensite microstructure transforms to fine-scale equiaxed microstructure at 973 K and the equiaxed microstructure significantly coarsens with increasing annealing temperature to 1273 K.The SLM Ti-6Al-4V alloy annealed at 973 K exhibits a well-balanced combination of strength and ductility((1305±25)MPa and(37±3)%,respectively).
基金financial supports from the China Scholarship Council(No.201906935013)the National Natural Science Foundation of China(No.51801132).
文摘To get a deep understanding of the evolution behavior of equiaxedαphase in Ti−8Al−1Mo−1V alloy during annealing,its static coarsening mechanism was studied based on the calculations of coarsening exponent n and the activation energy forαboundary migration.The result of n=6 indicates a special coarsening mechanism of equiaxedαphase.The activation energy forαboundary migration is calculated to be 138 kJ/mol,which is close to the activation energy for grain growth of pureα-Ti.It is revealed that the coarsening of equiaxedαcan be mainly attributed to the self-diffusion of Ti atoms across theα/αboundaries.Based on the experimental findings,a static coarsening kinetics model of equiaxedαgrains in theα+βfield is established.At last,the effects of the coarsening behavior of equiaxedαon tensile properties were studied.
基金the Metals and Nanomaterials program in the Division of Materials Research at the National Science Foundation under Grant No.DMR1105347.
文摘We have introduced a polymer precursor into molten magnesium and then in-situ pyrolyzed to produce castings of metal matrix composites(P-MMCs)containing silicon-carbonitride(SiCNO)ceramic particles.Stress-rupture measurements of as-cast P-MMCs was performed at 350 ℃(0.69TM)to 450 ℃(0.78TM)under dead load condition corresponding to tensile stress of 2.5 MPa to 20 MPa.The time-to-fracture data were analyzed using the classical Monkman–Grant equation.The time-to-fracture is thermally activated and follows a power-law stress exponent exhibiting dislocation creep.Fractography analysis revealed that while pure magnesium appears to fracture by dislocation slip,the P-MMCs fail from the nucleation and growth of voids at the grain boundaries.
基金supported by the National Natural Science Foundation of China (40774013, 41274189)
文摘The mobile satellite laser ranging system TROS1000, successfully developed in 2010, achieves a high repetition rate and enables daytime laser ranging. Its measurement range has reached up to 36000 km with an accuracy as precise as 1 cm. Using recent observations in Wuhan, Jiufeng, Xianning, and Rongcheng, Shandong, we introduce the progress made using this mobile observation system.
基金Supported by the National Natural Science Foundation of China under Grant Nos 40674091 and 40621003, and the CAS International Partnership Programme for Creative Research Teams.
文摘A statistical study of interhemispheric comparison of dipole tilt angle effect on the latitude of the mid-altitude cusp is preformed by a data set of the Cluster cusp crossings over a 5-year period. The result shows that the dipole tilt angle has a clear control of the cusp latitudinal location. When the dipole tilts sunwards, the cusp is shifted poleward. The northern cusp moves 1° ILAT for every 15.4° increase in the dipole tilt angle, while the southern cusp moves 1° ILAT for every 20.8° increase in the dipole tilt angle. This suggests that an interhemispheric difference appears in the dependence of cusp latitudinal location on the dipole tilt angle.
基金funded by the Austrian Science Fund (FWF) [Project No. P24692]
文摘Due to their ecological disadvantages, many mountain regions have experienced land-use abandonment and shrub encroachment on former grassland at higher altitudinal zones--especially during recent decades of urbanization. But does this trend also apply to the hinterland of urban settlements？ By using the Southern Colombian example of Popay^n, a medium-sized city located in the Northern Andes, we can show that the landscape changes observed between 1989 and 2010 can hardly be related to agricultural abandonment. Hypsometric variations of land-cover change indicate that, until 2001, woods or shrubland expanded faster at the lower altitudinal range adjacent to the city than at the more remote higher zones. In contrast, after 2001 grassland areas increased on former woods or shrnbland at all altitudinal belts. Both periods thus present developments that can be interpreted as the result of land-use expansion below 2000 m asl and land-use persistence in the tierrafrla of the mountain city＇s hinterland.
基金the National Natural Science Foundation of China under Grant Nos.49674242 and 49834040。
文摘Using dynamics equation, acceleration of out-flowing ion during dipolarization in a substorm in the magneto-tail is simulated. The main results show that: (1) The ion distribution function that is initially exponentially decreasing with increasing speed is turned into a single peak distribution, and with time the peak moves towards higher speed. (2) The peak moves along V⊥ faster than that along V||, and the ion acceleration mainly occurs in the middle of the dipolarization. (3) The higher the initial energy, the faster the peak moves, and the more energy is obtained by the ions. The ion energy theoretically calculated is as high as about 102 keV, this is consistent with the observation.
基金Supported by the National Natural Science Foundation of China under Grant Nos 40621003, 40674091 and 40374057, and the International Collaboration Research Team Programme of the Chinese Academy of Sciences.
文摘Field-aligned current （FAC） density distribution at the plasma sheet boundary layers is statistically studied. The FAC is calculated by the so-called curlometer technique with the data from FGM onboard the four Cluster spacecraft in 2001. By calculation we obtain a large number of FAC samples. In the samples, most of calculated FAC densities were very small and around zero caused by some errors or noise. In order to get the real FAC density distribution in the magnetotail, we use a three-Gaussian distribution to fit the errors, then subtract the estimated error contribution from the full distribution and obtain the FAC density distribution. The result shows that the FAC occurrence versus its density has a distribution consisting of a Gauss/an distribution with an additional decreasing exponential distribution. The most probable value of the FAC density is 3.45 pT/km.
文摘In the summer of 2010/2011 Chile suffered the third most severe energy and water supply crisis in only one decade. This may be surprising as the Andes which accompany the country along 4,200 km are a water tower and could provide more electricity and water than needed. On top of that, it has to be mentioned that Chile also counts with sunny and windy climates and with excellent geothermal energy resources and thus has a huge potential as far as renewable energies are concerned. After analyzing the existing natural conditions, the infrastructure and the present challenges of climate change, it has to be asked in which way Chile can make use of this potential in the near future, considering the legal and political situation and the technological opportunities. It seems that the resources are still hidden in the Andes, and only the key is missing to realize the country＇s natural potential. This research has been based on the analysis of existing literature, media, quantitative data from government institutions and other antecedents obtained by the authors in field work done in the South of Chile in 2OLO. The added value of this compilation lies in the comprehensive perspective, linking the knowledge of climatologists, hydrologists, mountain researchers and energy experts in order to support a sustainable energy and water supply for the future in Chile. From this present research, it can be concluded that Chile necessarilyhas to adopt new energy-related strategies, particularly those aimed at diminishing the strong dependence on traditional sources of energy and establishing new techniques and technologies for generating electrieity and utilizing the vast potential that the country is ready to offer, such as that provided by the Andes along 4,200 kilometers.
基金Supported by the National Natural Science Foundation of China under Grant Nos 40874084,41074114 and 40921063the Knowledge Innovation Project of Chinese Academy of Sciences under Grant No KJCX2-YW-T13-3by the Project Supported by the Specialized Research Fund for State Key Laboratories.
文摘The bipolar electric field solitary(EFS)structures observed frequently in space plasmas by satellites have two different polarities,first positive electric field peak then negative(i.e.,positive/negative)and first negative then positive peak(i.e.,negative/positive).We provide the physical explanation on the polarity of observed bipolar EFS structures with an electrostatic ion fluid model.The results show that if initial electric field𝐸E_(0)>0,the polarity of the bipolar EFS structure will be positive/negative;and if𝐸E_(0)<0,the polarity of the bipolar EFS structure will be negative/positive.However,for a fixed polarity of the EFS,either positive/negative or negative/positive,if the satellite is located at the positive side of the EFS,the observed polarity should be positive/negative,if the satellite is located at the negative side of the EFS,the observed polarity should be negative/positive.Therefore,we provide a method to clarify the natural polarity of the EFS with observed polarity by satellites.Our results are significant to understand the physical process in space plasma with the satellite observation.
基金by the Shenzhen Institute of Information Technology School-Enterprise Collaborative Innovation(No.SZIIT2021KJ057)the High-end Foreign Experts Recruitment Program(No.G2021163004L)+2 种基金the Natural Science Foundation of Guangdong Province(2020A1515011242)the Guangdong International Science and Technology Cooperation Program((No.2021A0505050002)the European Regional Development Grant(No.ASTRA6-6)。
文摘Selective laser melting(SLM)or Laser-based powder bed fusion(LBPF)is gaining much attention for the fabrication of novel materials with complex shapes,improved functionalities,and properties.An attempt has been made to fabricate hard and brittle silicon via SLM in the absence of any cracks.Two different powder batches were used,where one of the powder batches has 0.3wt%Fe and the other batch with 0.02wt%Fe.The parameter optimization process shows that the SLM Si samples were successfully fabricated from the powders with the minor addition of Fe.The deliberate addition of Fe facilitates heterogeneous nucleation of Si and aids in absorbing the laser energy beam more efficiently.SLM Si samples with 98.5%theoretical density were fabricated with a hardness of around 10.65±40 GPa.The experimental results show that SLM can successfully fabricate Si without cracks and with near theoretical density(of 99%)and complex shapes,which opens their use in wider industrial applications.
