Properties and deformations of the rotating neutron stars in uniform strong magnetic field are calculated. The magnetic field will soften the equation of state of the neutron star matters and make an obvious effect on...Properties and deformations of the rotating neutron stars in uniform strong magnetic field are calculated. The magnetic field will soften the equation of state of the neutron star matters and make an obvious effect on the structure of the rotating neutron star. If the magnetic field is superstrong （B=10^17 T）, the mass, radius, and the deformation will become smaller effectively.展开更多
We discuss the dynamical behavior of strange quark matter components, in particular the effects of density dependent quark mass on the equation of state of strange quark matter. The dynamical masses of quarks are comp...We discuss the dynamical behavior of strange quark matter components, in particular the effects of density dependent quark mass on the equation of state of strange quark matter. The dynamical masses of quarks are computed within the Nambu-Jona-Lasinio model, then we perform strange quark matter calculations em- ploying the MIT bag model with these dynamical masses. For the sake of compar- ing dynamical mass interaction with QCD quark-quark interaction, we consider the one-gluon-exchange term as the effective interaction between quarks for the MIT bag model. Our dynamical approach illustrates an improvement in the obtained equation of state values. We also investigate the structure of the strange quark star using Tolman- Oppenheimer-Volkoff equations for all applied models. Our results show that dynamical mass interaction leads to lower values for gravitational mass.展开更多
In this paper, we calculate some structure functions of an idealized stellar model, which can be solved by the total mass and radius of a star. These functions have enlightening and pedagogical significance. We find t...In this paper, we calculate some structure functions of an idealized stellar model, which can be solved by the total mass and radius of a star. These functions have enlightening and pedagogical significance. We find that the equation of state of matter is decisive to the fate of a star. Only if the equation of state includes the driving effect of gravity on particles, then it satisfies some increasing and causal conditions and is compatible with Einstein’s field equation. In this case, we always have singularity-free balanced star, no matter how heavy the star is. Usually, we believe that the main factor determining the stellar structure is the pressure equilibrium of the thermonuclear reaction against gravity. But this opinion is inadequate. The calculation of this paper shows that, the pressure generated by the driving effect of gravity on particles is dominant.展开更多
A series of poly(ethylene oxide)(PEO) membranes with star-like structures for CO_2/H_2 separation were prepared by the photo-polymerization method. The structure of PEO membrane was characterized by Fourier transform ...A series of poly(ethylene oxide)(PEO) membranes with star-like structures for CO_2/H_2 separation were prepared by the photo-polymerization method. The structure of PEO membrane was characterized by Fourier transform infrared spectroscopy(FTIR). The thermal property and inter-segmental distance of polymer chain were investigated by differential scanning calorimetry and wide-angle X-ray diffraction, respectively. The density was determined by hydrostatic weighing method. The gas permeability, solubility and diffusivity of CO_2 and H_2 were investigated in the star-like PEO membranes. The relationship between gas permeation performances and physical properties was also discussed. The membrane exhibits outstanding CO_2 permeability(about 9.7×10^(-11) cm^3(STP) cm/cm^2/s/Pa) and CO_2/H_2 selectivity(about 11) compared with other membranes.展开更多
The morphology and kinematics of the spiral structure of the Milky Way are long-standing problems in astrophysics.In this review we firstly summarize various methods with different tracers used to solve this puzzle.Th...The morphology and kinematics of the spiral structure of the Milky Way are long-standing problems in astrophysics.In this review we firstly summarize various methods with different tracers used to solve this puzzle.The astrometry of Galactic sources is gradually alleviating this difficult situation caused mainly by large distance uncertainties, as we can currently obtain accurate parallaxes(a few μas) and proper motions(≈1 km s-1) by using Very Long Baseline Interferometry(VLBI).On the other hand, the Gaia mission is providing the largest, uniform sample of parallaxes for O-type stars in the entire Milky Way.Based upon the VLBI maser and Gaia O-star parallax measurements, nearby spiral structures of the Perseus, Local, Sagittarius and Scutum Arms are determined in unprecedented detail.Meanwhile, we estimate fundamental Galactic parameters of the distance to the Galactic center,R0, to be 8.35 ± 0.18 kpc, and circular rotation speed at the Sun, Θ0, to be 240±10 km s-1.We found kinematic differences between O stars and interstellar masers: the O stars, on average, rotate faster,>8 km s-1than maser-traced high-mass star forming regions.展开更多
We have conducted a large-field simultaneous survey of 12 CO,13 CO and C18O J=1-0 emission toward the Orion A giant molecular cloud(GMC)with a sky coverage of4.4 deg2 using the Purple Mountain Observatory(PMO)-13.7 m ...We have conducted a large-field simultaneous survey of 12 CO,13 CO and C18O J=1-0 emission toward the Orion A giant molecular cloud(GMC)with a sky coverage of4.4 deg2 using the Purple Mountain Observatory(PMO)-13.7 m millimeter-wavelength telescope.We use the probability distribution function of the column density(N-PDF)to investigate the distribution of molecular hydrogen in the Orion A GMC.The H2 column density,derived from the 13CO emission,of the GMC is dominated by a log-normal distribution in the range from4×1021 to1.5×1023 cm-2 with excesses both at the low-density and high-density ends.The excess of the low-density end is possibly caused by an extended and low-temperature(10 K)component with velocities in the range of 5-8 km s-1.Compared with the northern sub-regions,the southern sub-regions of the Orion A GMC contain less gas with column density in NH2>1.25×1022 cm-2.The dispersions of the N-PDFs of the sub-regions are found to correlate with the evolutionary stages of the clouds across the Orion A GMC.The structure hierarchy of Orion A GMC is explored with the DENDROGRAM algorithm,and it is found that the GMC is composed of two branches.All structures except one in the tree have virial parameters less than 2,indicating self-gravity is important on the spatial scales from0.3 to4 pc.Although power-laws and departures from lognormal distributions are found at the high-density end of N-PDFs for active star-forming regions,the N-PDFs of structures in the Orion A GMC are predominantly lognormal on scales from R0.4 to 4 pc.展开更多
We have calculated the structural properties of a strange quark star with a static model in the presence of a strong magnetic field. To this end, we use the MIT bag model with a density dependent bag constant. To para...We have calculated the structural properties of a strange quark star with a static model in the presence of a strong magnetic field. To this end, we use the MIT bag model with a density dependent bag constant. To parameterize the density dependence of the bag constant, we have used our results for the lowest order constrained variational calculation of the asymmetric nuclear matter. By calculating the equation of state of strange quark matter, we have shown that the pressure of this system increases by increasing both density and magnetic field. Finally, we have investigated the effect of density dependence of the bag constant on the structural properties of a strange quark star.展开更多
By means of the first-principles calculations, we have investigated the structural stability and electronic properties of carbon star lattice monolayer and nanoribbons. The phase stability of the carbon star lattice i...By means of the first-principles calculations, we have investigated the structural stability and electronic properties of carbon star lattice monolayer and nanoribbons. The phase stability of the carbon star lattice is verified through phononmode analysis and room temperature molecular dynamics simulations. The carbon star lattice is found to be metallic due to the large states across the Fermi-level contributed by Pz orbital. Furthermore, the nanoribbons are also found to be metallic and no spin polarization occurs, except for the narrowest nanoribbon with one C12 ring, which has a ferromagnetic ground state. Our results show that carbon star lattice monolayer and nanoribbons have rich electronic properties with great potential in future electronic nanodevices.展开更多
The analytical and numerical solutions of structure and curvature of two kinds of static spherically symmetric neutron stars are calculated. The results show that Ricci tensor and curvature scalar cannot denote the cu...The analytical and numerical solutions of structure and curvature of two kinds of static spherically symmetric neutron stars are calculated. The results show that Ricci tensor and curvature scalar cannot denote the curly character of the space directly, however, to static spherically symmetric stars, these two quantities can present the relative curly degree of the space and the matter distribution to a certain extent.展开更多
We present a study of the pre-protostellar core (PPC) L1498. A series of self-consistent, three-dimensional continuum radiative transfer models are constructed. The outputs of these models are convolved with appropria...We present a study of the pre-protostellar core (PPC) L1498. A series of self-consistent, three-dimensional continuum radiative transfer models are constructed. The outputs of these models are convolved with appropriate telescope beam responses, including the effect of beam chopping to simulate SCUBA observations. The simulated observations are compared with existing observational data. An automated search is conducted in the multi-dimensional parameter space to identify the best-fit model. Grids of models are constructed in the vicinity of the best fit in order to understand the sensitivity/uncertainty of the results. We find that the source is well fit by a prolate spheroid of cutoff (and thus approximately outer) radius rcut = 0.073 ± 0.005 pc, axis ratio q = 2.0 ± 0.2, a central luminosity L* -3 Lsun, and an optical depth in the visible of τv = 20 ± 5. We find that the PPC is illuminated by two external radiation fields: a uniform ISRF of strength sISRF= 0.5 ± 0.25 and a local plane-parallel radiation field sPPRF = 1.0 ± 0.5. Both of these radiation fields are locally attenuated, with τISRF = 1.0 ± 0.25, and τPPRF = 1.25 ± 0.75, consistent with the fact that L1498 is embedded in a larger cloud. Most interestingly, the density fall-off at the outer edge is extremely steep, having a power law of m > 10. This is effectively a “sharp edge” to the PPC, and together with the constant density interior, is interpreted as potential signs of a pressure-confined core.展开更多
We identify 225 filaments from an H2 column density map constructed using simultaneous 12CO,13CO and C18O(J=1-0) observations carried out as a part of the Milky Way Imaging Scroll Painting(MWISP) project.We select 46 ...We identify 225 filaments from an H2 column density map constructed using simultaneous 12CO,13CO and C18O(J=1-0) observations carried out as a part of the Milky Way Imaging Scroll Painting(MWISP) project.We select 46 long filaments with lengths above 1.2 pc to analyze the filament column density profiles.We divide the selected filaments into 397 segments and calculate the column density profiles for each segment.The symmetries of the profiles are investigated.The proportion of intrinsically asymmetrical segments is 65.3%,and that of intrinsically symmetrical ones is 21.4%.The typical full width at half maximum(FWHM) of the intrinsically symmetrical filament segments is - 0.67 pc with the Plummer-like fitting,and - 0.50 pc with the Gaussian fitting,respectively.The median FWHMs derived from the second-moment method for intrinsically symmetrical and asymmetrical profiles are - 0.44 and 0.46 pc,respectively.Close association exists between the filamentary structures and the YSOs in the region.展开更多
We report a multi-wavelength study of two evolved planetary nebulae(PNs)M 2–55 and Abell 2.Deep optical narrow-band images([O III],Hα,and[N II])of M 2–55 reveal two pairs of bipolar lobes and a new faint arc-like s...We report a multi-wavelength study of two evolved planetary nebulae(PNs)M 2–55 and Abell 2.Deep optical narrow-band images([O III],Hα,and[N II])of M 2–55 reveal two pairs of bipolar lobes and a new faint arc-like structure.This arc-shaped filament around M 2–55 appears as a well-defined boundary from southwest to southeast,strongly suggesting that this nebula is in interaction with its surrounding interstellar medium.From the imaging data of Wide-field Infrared Survey Explorer(WISE)all-sky survey,we discovered extensive mid-infrared halos around these PNs,which are approximately twice the size of their main nebulae seen in the visible.We also present a mid-resolution optical spectrum of M 2–55,which shows that it is a high-excitation evolved PN with a low electron density of 250 cm^-3.Furthermore,we investigate the properties of these nebulae from their spectral energy distributions(SEDs)by means of archival data.展开更多
The suitability of computational fluid dynamics (CFD) for marine renewable energy research and development and in particular for simulating extreme wave interaction with a wave energy converter (WEC) is considered. Fu...The suitability of computational fluid dynamics (CFD) for marine renewable energy research and development and in particular for simulating extreme wave interaction with a wave energy converter (WEC) is considered. Fully nonlinear time domain CFD is often considered to be an expensive and computationally intensive option for marine hydrodynamics and frequency-based methods are traditionally preferred by the industry. However, CFD models capture more of the physics of wave-structure interaction, and whereas traditional frequency domain approaches are restricted to linear motions, fully nonlinear CFD can simulate wave breaking and overtopping. Furthermore, with continuing advances in computing power and speed and the development of new algorithms for CFD, it is becoming a more popular option for design applications in the marine environment. In this work, different CFD approaches of increasing novelty are assessed: two commercial CFD packages incorporating recent advances in high resolution free surface flow simulation;a finite volume based Euler equation model with a shock capturing technique for the free surface;and meshless Smoothed Particle Hydrodynamics (SPH) method. These different approaches to fully nonlinear time domain simulation of free surface flow and wave structure interaction are applied to test cases of increasing complexity and the results compared with experimental data. Results are presented for regular wave interaction with a fixed horizontal cylinder, wave generation by a cone in driven vertical motion at the free surface and extreme wave interaction with a bobbing float (The Manchester Bobber WEC). The numerical results generally show good agreement with the physical experiments and simulate the wave-structure interaction and wave loading satisfactorily. The grid-based methods are shown to be generally less able than the meshless SPH to capture jet formation at the face of the cone, the resolution of the jet being grid dependent.展开更多
The disparity in the transfer of carriers(electrons/mass)during the reaction in zinc-air batteries(ZABs)results in sluggish kinetics of the oxygen reduction reaction(ORR)and oxygen evolution reaction(OER),along with e...The disparity in the transfer of carriers(electrons/mass)during the reaction in zinc-air batteries(ZABs)results in sluggish kinetics of the oxygen reduction reaction(ORR)and oxygen evolution reaction(OER),along with elevated overpotentials,thereby imposing additional constraints on its utilization.Therefore,the pre-design and target-development of inexpensive,high-performance,and long-term stable bifunctional catalysts are urgently needed.In this work,an apically guiding dual-functional electrocatalyst(Ag-FeN_(x)-N-C)was prepared,in which a hierarchical porous nitrogen-doped carbon with three-dimensional(3D)hollow star-shaped structure is used as a substrate and high-conductivity Ag nanoparticles are coupled with iron nitride(FeN_(x))nanoparticles.Theoretical calculations indicate that the Mott-Schottky heterojunction as an inherent electric field comes from the two-phase bound of Ag and FeN_(x),of which electron accumulation in the FeN_(x)phase region and electron depletion in the Ag phase region promote orientated-guiding charge migration.The effective modulation of local electronic structures felicitously reforms the d-band electron-group distribution,and intellectually tunes the masstransfer reaction energy barriers for both ORR/OER.Additionally,the hollow star-s haped hierarchical porous structure provides an apical region for fast mass transfer.Experimental results show that the halfwave potential for ORR is 0.914 V,and the overpotential for OER is only 327 mV at 10 mA cm^(-2).A rechargeable ZAB with Ag-FeN_(x)-N-C as the air cathode demonstrates long-term cycling performance exceeding 1500 cycles(500 h),with a power density of 180 mW cm^(-2).Moreover,when employing AgFeN_(x)-N-C as the air cathode,flexible ZABs demonstrate a notable open-circuit voltage of 1.42 V and achieve a maximum power density of 65.6 mW cm^(-2).Ag-FeN_(x)-N-C shows guiding electron/mass transfer route and apical reaction microenvironment for the electrocatalyst architecture in the exploration prospects of ZABs.展开更多
基于本地化差分隐私多关系表示上的Star-JOIN查询已得到研究者广泛关注.现有基于OLH机制与层次树结构的Star-JOIN查询算法存在根节点泄露隐私风险、τ-截断机制没有给出如何选择合适τ值等问题.针对现有算法存在的不足,提出一种有效且...基于本地化差分隐私多关系表示上的Star-JOIN查询已得到研究者广泛关注.现有基于OLH机制与层次树结构的Star-JOIN查询算法存在根节点泄露隐私风险、τ-截断机制没有给出如何选择合适τ值等问题.针对现有算法存在的不足,提出一种有效且满足本地化差分隐私的Star-JOIN查询算法LPRR-JOIN(longitudinal path random response for join).该算法充分利用层次树的纵向路径结构与GRR机制,设计一种纵向本地扰动算法LPRR,该算法以所有属性纵向路径上的节点组合作为扰动值域.每个用户把自身元组映射到相应节点组合中,再利用GRR机制对映射后的元组进行本地扰动.为了避免事实表上存在的频率攻击,LPRR-JOIN算法允许每个用户利用阈值τ本地截断自身元组个数,大于τ条元组删减、小于τ条元组补充.为了寻找合适的τ值,LPRR-JOIN算法利用τ-截断带来的偏差与扰动方差构造总体误差函数,通过优化误差目标函数获得τ值;其次结合用户分组策略获得τ值的总体分布,再利用中位数获得合适的τ值.LPRR-JOIN算法与现有算法在3种多关系数据集上进行比较,实验结果表明其响应查询算法优于同类算法.展开更多
基金The project supported by National Natural Science Foundation of China under Grant Nos. 10647116 and 10575140 and the China Postdoctoral Science Foundation under Grant No. 2005037175
文摘Properties and deformations of the rotating neutron stars in uniform strong magnetic field are calculated. The magnetic field will soften the equation of state of the neutron star matters and make an obvious effect on the structure of the rotating neutron star. If the magnetic field is superstrong （B=10^17 T）, the mass, radius, and the deformation will become smaller effectively.
基金supported by the Research Institute for Astronomy and Astrophysics of Maragha
文摘We discuss the dynamical behavior of strange quark matter components, in particular the effects of density dependent quark mass on the equation of state of strange quark matter. The dynamical masses of quarks are computed within the Nambu-Jona-Lasinio model, then we perform strange quark matter calculations em- ploying the MIT bag model with these dynamical masses. For the sake of compar- ing dynamical mass interaction with QCD quark-quark interaction, we consider the one-gluon-exchange term as the effective interaction between quarks for the MIT bag model. Our dynamical approach illustrates an improvement in the obtained equation of state values. We also investigate the structure of the strange quark star using Tolman- Oppenheimer-Volkoff equations for all applied models. Our results show that dynamical mass interaction leads to lower values for gravitational mass.
文摘In this paper, we calculate some structure functions of an idealized stellar model, which can be solved by the total mass and radius of a star. These functions have enlightening and pedagogical significance. We find that the equation of state of matter is decisive to the fate of a star. Only if the equation of state includes the driving effect of gravity on particles, then it satisfies some increasing and causal conditions and is compatible with Einstein’s field equation. In this case, we always have singularity-free balanced star, no matter how heavy the star is. Usually, we believe that the main factor determining the stellar structure is the pressure equilibrium of the thermonuclear reaction against gravity. But this opinion is inadequate. The calculation of this paper shows that, the pressure generated by the driving effect of gravity on particles is dominant.
基金Funded by the National Natural Science Foundation of China(Nos.21776217,21506160)the Science and Technology Plans of Tianjin(Nos.17PTSYJC00050,18PTSYJC 00190)
文摘A series of poly(ethylene oxide)(PEO) membranes with star-like structures for CO_2/H_2 separation were prepared by the photo-polymerization method. The structure of PEO membrane was characterized by Fourier transform infrared spectroscopy(FTIR). The thermal property and inter-segmental distance of polymer chain were investigated by differential scanning calorimetry and wide-angle X-ray diffraction, respectively. The density was determined by hydrostatic weighing method. The gas permeability, solubility and diffusivity of CO_2 and H_2 were investigated in the star-like PEO membranes. The relationship between gas permeation performances and physical properties was also discussed. The membrane exhibits outstanding CO_2 permeability(about 9.7×10^(-11) cm^3(STP) cm/cm^2/s/Pa) and CO_2/H_2 selectivity(about 11) compared with other membranes.
基金sponsored by the MOST (Grant No.2017YFA0402701)the NSFC (Grant Nos.11873019, 11673066 and 11503033)+4 种基金the CAS (Grant No.QYZDJ-SSW-SLH047)the Youth Innovation Promotion Association of CASsupported by the Key Laboratory for Radio Astronomy, CASthe Open Project Program of the Key Laboratory of FAST, NAOC, CASFunding for the DPAC has been provided by national institutions, in particular the institutions participating in the Gaia Multilateral Agreement
文摘The morphology and kinematics of the spiral structure of the Milky Way are long-standing problems in astrophysics.In this review we firstly summarize various methods with different tracers used to solve this puzzle.The astrometry of Galactic sources is gradually alleviating this difficult situation caused mainly by large distance uncertainties, as we can currently obtain accurate parallaxes(a few μas) and proper motions(≈1 km s-1) by using Very Long Baseline Interferometry(VLBI).On the other hand, the Gaia mission is providing the largest, uniform sample of parallaxes for O-type stars in the entire Milky Way.Based upon the VLBI maser and Gaia O-star parallax measurements, nearby spiral structures of the Perseus, Local, Sagittarius and Scutum Arms are determined in unprecedented detail.Meanwhile, we estimate fundamental Galactic parameters of the distance to the Galactic center,R0, to be 8.35 ± 0.18 kpc, and circular rotation speed at the Sun, Θ0, to be 240±10 km s-1.We found kinematic differences between O stars and interstellar masers: the O stars, on average, rotate faster,>8 km s-1than maser-traced high-mass star forming regions.
基金supported by National Key R&D Program of China(2017YFA0402701)Key Research Program of Frontier Sciences of CAS(QYZDJSSW-SLH047)supports by the National Natural Science Foundation of China(Grant Nos.11503086 and 11503087)。
文摘We have conducted a large-field simultaneous survey of 12 CO,13 CO and C18O J=1-0 emission toward the Orion A giant molecular cloud(GMC)with a sky coverage of4.4 deg2 using the Purple Mountain Observatory(PMO)-13.7 m millimeter-wavelength telescope.We use the probability distribution function of the column density(N-PDF)to investigate the distribution of molecular hydrogen in the Orion A GMC.The H2 column density,derived from the 13CO emission,of the GMC is dominated by a log-normal distribution in the range from4×1021 to1.5×1023 cm-2 with excesses both at the low-density and high-density ends.The excess of the low-density end is possibly caused by an extended and low-temperature(10 K)component with velocities in the range of 5-8 km s-1.Compared with the northern sub-regions,the southern sub-regions of the Orion A GMC contain less gas with column density in NH2>1.25×1022 cm-2.The dispersions of the N-PDFs of the sub-regions are found to correlate with the evolutionary stages of the clouds across the Orion A GMC.The structure hierarchy of Orion A GMC is explored with the DENDROGRAM algorithm,and it is found that the GMC is composed of two branches.All structures except one in the tree have virial parameters less than 2,indicating self-gravity is important on the spatial scales from0.3 to4 pc.Although power-laws and departures from lognormal distributions are found at the high-density end of N-PDFs for active star-forming regions,the N-PDFs of structures in the Orion A GMC are predominantly lognormal on scales from R0.4 to 4 pc.
基金the Research Institute for Astronomy and Astrophysics of Maragha
文摘We have calculated the structural properties of a strange quark star with a static model in the presence of a strong magnetic field. To this end, we use the MIT bag model with a density dependent bag constant. To parameterize the density dependence of the bag constant, we have used our results for the lowest order constrained variational calculation of the asymmetric nuclear matter. By calculating the equation of state of strange quark matter, we have shown that the pressure of this system increases by increasing both density and magnetic field. Finally, we have investigated the effect of density dependence of the bag constant on the structural properties of a strange quark star.
基金supported by the National Natural Science Foundation of China(Grant No.11274356)the Ministry of Environmental Protection of China(Grant Nos.200909086 and 201109037)
文摘By means of the first-principles calculations, we have investigated the structural stability and electronic properties of carbon star lattice monolayer and nanoribbons. The phase stability of the carbon star lattice is verified through phononmode analysis and room temperature molecular dynamics simulations. The carbon star lattice is found to be metallic due to the large states across the Fermi-level contributed by Pz orbital. Furthermore, the nanoribbons are also found to be metallic and no spin polarization occurs, except for the narrowest nanoribbon with one C12 ring, which has a ferromagnetic ground state. Our results show that carbon star lattice monolayer and nanoribbons have rich electronic properties with great potential in future electronic nanodevices.
基金The project supported by National Natural Science Foundation of China under Grant No. 10275099 and the China Postdoctoral Science Foundation under Grant No. 2005037175
文摘The analytical and numerical solutions of structure and curvature of two kinds of static spherically symmetric neutron stars are calculated. The results show that Ricci tensor and curvature scalar cannot denote the curly character of the space directly, however, to static spherically symmetric stars, these two quantities can present the relative curly degree of the space and the matter distribution to a certain extent.
文摘We present a study of the pre-protostellar core (PPC) L1498. A series of self-consistent, three-dimensional continuum radiative transfer models are constructed. The outputs of these models are convolved with appropriate telescope beam responses, including the effect of beam chopping to simulate SCUBA observations. The simulated observations are compared with existing observational data. An automated search is conducted in the multi-dimensional parameter space to identify the best-fit model. Grids of models are constructed in the vicinity of the best fit in order to understand the sensitivity/uncertainty of the results. We find that the source is well fit by a prolate spheroid of cutoff (and thus approximately outer) radius rcut = 0.073 ± 0.005 pc, axis ratio q = 2.0 ± 0.2, a central luminosity L* -3 Lsun, and an optical depth in the visible of τv = 20 ± 5. We find that the PPC is illuminated by two external radiation fields: a uniform ISRF of strength sISRF= 0.5 ± 0.25 and a local plane-parallel radiation field sPPRF = 1.0 ± 0.5. Both of these radiation fields are locally attenuated, with τISRF = 1.0 ± 0.25, and τPPRF = 1.25 ± 0.75, consistent with the fact that L1498 is embedded in a larger cloud. Most interestingly, the density fall-off at the outer edge is extremely steep, having a power law of m > 10. This is effectively a “sharp edge” to the PPC, and together with the constant density interior, is interpreted as potential signs of a pressure-confined core.
基金supported by National Key R&D Program of China (Grant 2017YFA0402701)Key Research Program of Frontier Sciences of CAS (Grant QYZDJ-SSW-SLH047)+1 种基金support by the National Natural Science Foundation of China (NSFC,Grant No.1973091)supports by the NSFC (Nos.11503086 and 11503087)。
文摘We identify 225 filaments from an H2 column density map constructed using simultaneous 12CO,13CO and C18O(J=1-0) observations carried out as a part of the Milky Way Imaging Scroll Painting(MWISP) project.We select 46 long filaments with lengths above 1.2 pc to analyze the filament column density profiles.We divide the selected filaments into 397 segments and calculate the column density profiles for each segment.The symmetries of the profiles are investigated.The proportion of intrinsically asymmetrical segments is 65.3%,and that of intrinsically symmetrical ones is 21.4%.The typical full width at half maximum(FWHM) of the intrinsically symmetrical filament segments is - 0.67 pc with the Plummer-like fitting,and - 0.50 pc with the Gaussian fitting,respectively.The median FWHMs derived from the second-moment method for intrinsically symmetrical and asymmetrical profiles are - 0.44 and 0.46 pc,respectively.Close association exists between the filamentary structures and the YSOs in the region.
基金supported by MoST grant(108-2112-M-008-001)support of the staff of the Lijiang 2.4m telescope+4 种基金Funding for the telescope has been provided by Chinese Academy of Sciences and the People’s Government of Yunnan ProvinceFinancial support for this work is supported by the grants from The Science and Technology Development Fund,Macao SAR(file no061/2017/A2and 0007/2019/A)the Faculty Research Grants of Macao University of Science and Technology(project codeFRG-19-004-SSI)supported by the National Natural Science Foundation of China(NSFC,Grant No.U1731122)NSFC(Grant No.11973099)for financial support
文摘We report a multi-wavelength study of two evolved planetary nebulae(PNs)M 2–55 and Abell 2.Deep optical narrow-band images([O III],Hα,and[N II])of M 2–55 reveal two pairs of bipolar lobes and a new faint arc-like structure.This arc-shaped filament around M 2–55 appears as a well-defined boundary from southwest to southeast,strongly suggesting that this nebula is in interaction with its surrounding interstellar medium.From the imaging data of Wide-field Infrared Survey Explorer(WISE)all-sky survey,we discovered extensive mid-infrared halos around these PNs,which are approximately twice the size of their main nebulae seen in the visible.We also present a mid-resolution optical spectrum of M 2–55,which shows that it is a high-excitation evolved PN with a low electron density of 250 cm^-3.Furthermore,we investigate the properties of these nebulae from their spectral energy distributions(SEDs)by means of archival data.
文摘The suitability of computational fluid dynamics (CFD) for marine renewable energy research and development and in particular for simulating extreme wave interaction with a wave energy converter (WEC) is considered. Fully nonlinear time domain CFD is often considered to be an expensive and computationally intensive option for marine hydrodynamics and frequency-based methods are traditionally preferred by the industry. However, CFD models capture more of the physics of wave-structure interaction, and whereas traditional frequency domain approaches are restricted to linear motions, fully nonlinear CFD can simulate wave breaking and overtopping. Furthermore, with continuing advances in computing power and speed and the development of new algorithms for CFD, it is becoming a more popular option for design applications in the marine environment. In this work, different CFD approaches of increasing novelty are assessed: two commercial CFD packages incorporating recent advances in high resolution free surface flow simulation;a finite volume based Euler equation model with a shock capturing technique for the free surface;and meshless Smoothed Particle Hydrodynamics (SPH) method. These different approaches to fully nonlinear time domain simulation of free surface flow and wave structure interaction are applied to test cases of increasing complexity and the results compared with experimental data. Results are presented for regular wave interaction with a fixed horizontal cylinder, wave generation by a cone in driven vertical motion at the free surface and extreme wave interaction with a bobbing float (The Manchester Bobber WEC). The numerical results generally show good agreement with the physical experiments and simulate the wave-structure interaction and wave loading satisfactorily. The grid-based methods are shown to be generally less able than the meshless SPH to capture jet formation at the face of the cone, the resolution of the jet being grid dependent.
基金the financial support of the National Natural Science Foundation of China(52002079,22378074,22179025 and U20A20340)the Guangdong Basic and Applied Basic Research Foundation(2022A1515140085)+2 种基金the Research Fund Program of Guangdong Provincial Key Laboratory of Fuel Cell Technology(FC202209)the Guangzhou Hongmian Project(HMJH-20200012)the Foshan Introducing Innovative and Entrepreneurial Teams(1920001000108)。
文摘The disparity in the transfer of carriers(electrons/mass)during the reaction in zinc-air batteries(ZABs)results in sluggish kinetics of the oxygen reduction reaction(ORR)and oxygen evolution reaction(OER),along with elevated overpotentials,thereby imposing additional constraints on its utilization.Therefore,the pre-design and target-development of inexpensive,high-performance,and long-term stable bifunctional catalysts are urgently needed.In this work,an apically guiding dual-functional electrocatalyst(Ag-FeN_(x)-N-C)was prepared,in which a hierarchical porous nitrogen-doped carbon with three-dimensional(3D)hollow star-shaped structure is used as a substrate and high-conductivity Ag nanoparticles are coupled with iron nitride(FeN_(x))nanoparticles.Theoretical calculations indicate that the Mott-Schottky heterojunction as an inherent electric field comes from the two-phase bound of Ag and FeN_(x),of which electron accumulation in the FeN_(x)phase region and electron depletion in the Ag phase region promote orientated-guiding charge migration.The effective modulation of local electronic structures felicitously reforms the d-band electron-group distribution,and intellectually tunes the masstransfer reaction energy barriers for both ORR/OER.Additionally,the hollow star-s haped hierarchical porous structure provides an apical region for fast mass transfer.Experimental results show that the halfwave potential for ORR is 0.914 V,and the overpotential for OER is only 327 mV at 10 mA cm^(-2).A rechargeable ZAB with Ag-FeN_(x)-N-C as the air cathode demonstrates long-term cycling performance exceeding 1500 cycles(500 h),with a power density of 180 mW cm^(-2).Moreover,when employing AgFeN_(x)-N-C as the air cathode,flexible ZABs demonstrate a notable open-circuit voltage of 1.42 V and achieve a maximum power density of 65.6 mW cm^(-2).Ag-FeN_(x)-N-C shows guiding electron/mass transfer route and apical reaction microenvironment for the electrocatalyst architecture in the exploration prospects of ZABs.
文摘基于本地化差分隐私多关系表示上的Star-JOIN查询已得到研究者广泛关注.现有基于OLH机制与层次树结构的Star-JOIN查询算法存在根节点泄露隐私风险、τ-截断机制没有给出如何选择合适τ值等问题.针对现有算法存在的不足,提出一种有效且满足本地化差分隐私的Star-JOIN查询算法LPRR-JOIN(longitudinal path random response for join).该算法充分利用层次树的纵向路径结构与GRR机制,设计一种纵向本地扰动算法LPRR,该算法以所有属性纵向路径上的节点组合作为扰动值域.每个用户把自身元组映射到相应节点组合中,再利用GRR机制对映射后的元组进行本地扰动.为了避免事实表上存在的频率攻击,LPRR-JOIN算法允许每个用户利用阈值τ本地截断自身元组个数,大于τ条元组删减、小于τ条元组补充.为了寻找合适的τ值,LPRR-JOIN算法利用τ-截断带来的偏差与扰动方差构造总体误差函数,通过优化误差目标函数获得τ值;其次结合用户分组策略获得τ值的总体分布,再利用中位数获得合适的τ值.LPRR-JOIN算法与现有算法在3种多关系数据集上进行比较,实验结果表明其响应查询算法优于同类算法.
