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Based on an equivparticle model, we investigate the in-medium quark condensate in neutron stars. Carrying out a Taylor expansion of the nuclear binding energy to the order of ρ3, we obtain a series of EOSs for neutron star matter, which are confronted with the latest nuclear and astrophysical constraints. The in-medium quark condensate is then extracted from the constrained properties of neutron star matter, which decreases non-linearly with density. However, the chiral symmetry is only partially restored with non-vanishing quark condensates, which may vanish at a density that is out of reach for neutron stars.

The interface effects of quark matter play important roles in the properties of compact stars and small nuggets, such as strangelets and nonstrange quark matter (udQM) nuggets. By introducing a density derivative term to the Lagrangian density and adopting Thomas-Fermi approximation, we find it is possible to reproduce the results obtained by solving Dirac equations. Adopting certain parameter sets, the energy per baryon of udQM nuggets decreases with baryon number A and become more stable than nuclei at A≳300. The effects of quark matter symmetry energy are examined, where udQM nuggets at A≈1000 can be more stable than others if large symmetry energy is adopted. In such cases, larger udQM nuggets will decay via fission and the surface of a udQM star will fragment into a crust made of udQM nuggets and electrons, which resembles the cases of a strange star’s crust. The corresponding microscopic structures are then investigated adopting spherical and cylindrical approximations for the Wigner-Seitz cells, where the droplet phase is found to be the most stable configuration with udQM stars’ crusts and udQM dwarfs made of udQM nuggets (A≈1000) and electrons. For the cases considered here, the crust thickness of udQM stars is typically ∼200 m, which reaches a few kilometers if we neglect the interface effects and adopt Gibbs construction. The masses and radii of udQM dwarfs are smaller than typical white dwarfs, which would increase if the interface effects are neglected.

What if normal baryonic matter is compressed so tightly that atomic nuclei come into close contact? This question has been asked since 1930s. The fist answer was presented by Lev Landau whose speculation has been developed, and the concept of neutron star is then popularized. However, another answer is related to strange star, which becomes worthy of attention especially after the establishment of the standard model of particle physics in 1960s. The basic ideas of this study are introduced pedagogically. We must point out emphatically that flavour symmetry of and strong coupling between quarks would be essential in seeking true answer to the question. The final answer is expected to appear in the era of multimessenger astronomy. It is emphasized too that, besides the differences of global properties (e.g., mass-radius relation, maximum mass, tidal deformability), the strong-bound surface of strange star (rather than the gravity-bound one for conventional neutron star) could play an important role in identifying a strange star by astronomical observations., Comment: to appear in Astronomische Nachrichten

The properties of strangelets at finite temperature are studied within the framework of a baryon densitydependent quark mass model, where a new quark mass scaling and self-consistent thermodynamic treatment are adopted. The effects of finite volume and Coulomb energy are taken into account. Our results show that the temperature T, baryon number A, and perturbation interactions have strong influences on the properties of strangelets. It is found that the energy per baryon M/A and charge-to-mass ratio fz decrease with baryon number A, while the mechanically stable radius R and strangeness per baryon fS are increasing. For a strangelet with a fixed baryon number, we note that as temperature T increases the quantities M/A, R, and fS are increasing while fz is decreasing. The effects of confinement and perturbative interactions are investigated as well by readjusting the corresponding parameters.

Realistic estimations on the elastic properties of neutron star matter are carried out with a large strain (ε≲0.5) in the framework of relativistic-mean-field model with Thomas-Fermi approximation, where various crystalline configurations are considered in a fully three-dimensional geometry with reflection symmetry. Our calculation confirms the validity of assuming Coulomb crystals for the droplet phase above neutron drip density, which nonetheless does not work at large densities since the elastic constants are found to be decreasing after reaching their peaks. Similarly, the analytic formulae derived in the incompressible liquid-drop model give excellent description for the rod phase at small densities, which overestimates the elastic constants at larger densities. For slabs, due to the negligence on the variations of their thicknesses, the analytic formulae from liquid-drop model agree qualitatively but not quantitatively with our numerical estimations. By fitting to the numerical results, these analytic formulae are improved by introducing dampening factors. The impacts of nuclear symmetry energy are examined adopting two parameter sets, corresponding to the slope of symmetry energy L=41.34 and 89.39 MeV. Even with the uncertainties caused by the anisotropy in polycrystallines, the elastic properties of neutron star matter obtained with L=41.34 and 89.39 MeV are distinctively different, results in detectable differences in various neutron star activities.

In the framework of Thomas-Fermi approximation, we study systematically the EOSs and microscopic structures of neutron star matter in a vast density range with $n_\mathrm{b}\approx 10^{-10}$-2 $\mathrm{fm}^{-3}$, where various covariant density functionals are adopted, i.e., those with nonlinear self couplings (NL3, PK1, TM1, GM1, MTVTC) and density-dependent couplings (DD-LZ1, DDME-X, PKDD, DD-ME2, DD2, TW99). It is found that the EOSs generally coincide with each other at $n_\mathrm{b}\lesssim 10^{-4}$ fm${}^{-3}$ and 0.1 fm${}^{-3}\lesssim n_\mathrm{b} \lesssim 0.3$ fm${}^{-3}$, while in other density regions they are sensitive to the effective interactions between nucleons. By adopting functionals with larger slope of symmetry energy $L$, the curvature parameter $K_\mathrm{sym}$ and neutron drip density generally increase, while the droplet size, proton number of nucleus, core-crust transition density, and onset density of non-spherical nuclei decrease. All functionals predict neutron stars with maximum masses exceeding the two-solar-mass limit, while those of DD2, DD-LZ1, DD-ME2, and DDME-X predict optimum neutron star radii according to the observational constraints. Nevertheless, the corresponding skewness coefficients $J$ are much lager than expected, while only the functionals MTVTC and TW99 meet the start-of-art constraints on $J$. More accurate measurements on the radius of PSR J0740+6620 and the maximum mass of neutron stars are thus essential to identify the functional that satisfies all constraints from nuclear physics and astrophysical observations. Approximate linear correlations between neutron stars' radii at $M=1.4 M_{\odot}$ and $2 M_{\odot}$, the slope $L$ and curvature parameter $K_\mathrm{sym}$ of symmetry energy are observed as well, which is mainly attributed to the curvature-slope correlations in the functionals adopted here., Comment: The EOS tables can be found at: teacher.yzu.edu.cn/CJXia/en/lwcg/492393/content/79242.htm

The properties of strange quark matter and the structures of (proto-)strange stars are studied within the framework of a baryon density-dependent quark mass model, where a novel quark mass scaling and self-consistent thermodynamic treatment are adopted. Our results indicate that the perturbative interaction has a significant impact on the properties of strange quark matter. It is determined that the energy per baryon increases with temperature, while the free energy decreases and eventually becomes negative. At fixed temperatures, the pressure at the minimum free energy per baryon is zero, suggesting that the thermodynamic self-consistency is preserved. Furthermore, the sound velocity v in quark matter approaches the extreme relativistic limit ( ) as the density increases. By increasing the strengths of the confinement parameter D and perturbation parameter C, the tendency for v to approach the extreme relativistic limit at high density is slightly weakened. For (proto-)strange stars, the novel quark mass scaling can accommodate massive proto-strange stars with their maximum mass surpassing twice the solar mass by considering the isentropic stages along the star evolution line, where the entropy per baryon of the star matter is set to be 0.5 and 1 with the lepton fraction = 0.4.

The pion production mechanism is explored based on the ultrarelativistic quantum molecular dynamics model (UrQMD) in which the $\mathrm{\ensuremath{\Delta}}$-mass dependence of the $\mathcal{M}$ matrix and $\mathrm{\ensuremath{\Delta}}$-mass dependence of the momentum ${p}_{N\mathrm{\ensuremath{\Delta}}}$ in $N\mathrm{\ensuremath{\Delta}}\ensuremath{\rightarrow}NN$ cross sections are taken into account. By analyzing the time evolution of the pion production rate and the density in the overlapped region for the reaction of Au+Au at the beam energy of $0.4A$ GeV, we find that characteristic density of pion observable is in the region of 1--2 times normal density. The process of pion production in the reaction is tracked, including the loops of $NN\ensuremath{\leftrightarrow}N\mathrm{\ensuremath{\Delta}}$ and $\mathrm{\ensuremath{\Delta}}\ensuremath{\leftrightarrow}N\ensuremath{\pi}$, and our calculations show that the sensitivity of ${\ensuremath{\pi}}^{\ensuremath{-}}/{\ensuremath{\pi}}^{+}$ to symmetry energy is weakened after 4--5 $N\text{\ensuremath{-}}\mathrm{\ensuremath{\Delta}}\text{\ensuremath{-}}\ensuremath{\pi}$ loops in the pion production path. The ${\ensuremath{\pi}}^{\ensuremath{-}}/{\ensuremath{\pi}}^{+}$ ratio in the reaction near the threshold energies retains its sensitivity to the symmetry energy, and it is insensitive to the nuclear incompressibility ${K}_{0}$ and effective mass when their values are selected in the commonly accepted range. By comparing the UrQMD calculations to the FOPI data at $0.4A$ GeV and considering the constraint of symmetry energy from neutron star properties, the slope of symmetry energy $L=54--91$ MeV and the symmetry energy at two times normal density $S(2{\ensuremath{\rho}}_{0})=48--59$ MeV are deduced, and they are also consistent with the constraint from the ASY-EOS flow data.

In the framework of the relativistic mean-field model with Thomas-Fermi approximation, we study the structures of low-density nuclear matter in a three-dimensional geometry with reflection symmetry. The numerical accuracy and efficiency are improved by expanding the mean fields according to fast cosine transformation and considering only one octant of the unit cell. The effect of finite cell size is treated carefully by searching for the optimum cell size. Typical pasta structures (droplet, rod, slab, tube, and bubble) arranged in various crystalline configurations are obtained for both fixed proton fractions and $\ensuremath{\beta}$ equilibration. It is found that the properties of droplets and bubbles are similar in body-centered cubic (bcc) and face-centered cubic (fcc) lattices, where the fcc lattice generally becomes more stable than bcc lattice as density increases. For the rod and tube phases, the honeycomb lattice is always more stable than the simple one. By introducing an $\ensuremath{\omega}\text{\ensuremath{-}}\ensuremath{\rho}$ cross coupling term, we further examine the pasta structures with a smaller slope of symmetry energy $L=41.34$ MeV, which predicts larger onset densities for core-crust transition and nonspherical nuclei. Such a variation due to the reduction of $L$ is expected to have impacts on various properties in neutron stars, supernova dynamics, and binary neutron star mergers.

We investigate systematically the quark-hadron mixed phase in dense stellar matter and its influence on compact star structures. The properties of quark matter and hadronic matter are fixed based on various model predictions. Beside adopting constant values, the surface tension Σ for the quark-hadron interface is estimated with the multiple reflection expansion method and equivparticle model. To fix the structures of quark-hadron pasta phases, a continuous dimensionality of the structure is adopted as proposed by Ravenhall et al. The corresponding properties of hybrid stars are then obtained and confronted with pulsar observations. It is found that the correlation between radius and tidal deformability in traditional neutron stars preserves in hybrid stars. For those permitted by pulsar observations, in almost all cases, the quark phase persists inside the most massive compact stars. The quark-hadron interface plays an important role in hybrid star structures once quark matter emerges. The surface tension Σ estimated with various methods increases with density, which predicts stiffer equation of states (EOSs) for the quark-hadron mixed phase and increases the maximum mass of hybrid stars. With or without the emergence of quark matter, the obtained EOSs of hybrid star matter are close to each other at densities n≲0.8 fm−3, while larger uncertainty is expected at higher densities.

We investigate the stability and ${e}^{+}{e}^{\ensuremath{-}}$ pair creation of supercritically charged superheavy nuclei, $ud\mathrm{QM}$ nuggets, strangelets, and strangeon nuggets based on the Thomas-Fermi approximation. The model parameters are fixed by reproducing masses and charge properties of these supercritically charged objects reported in earlier publications. It is found that $ud\mathrm{QM}$ nuggets, strangelets, and strangeon nuggets may be more stable than $^{56}\mathrm{Fe}$ at the baryon number $A\ensuremath{\gtrsim}315$, $5\ifmmode\times\else\texttimes\fi{}{10}^{4}$, and $1.2\ifmmode\times\else\texttimes\fi{}{10}^{8}$, respectively. For those stable against neutron emission, the most massive superheavy element has a baryon number $\ensuremath{\sim}965$, while $ud\mathrm{QM}$ nuggets, strangelets, and strangeon nuggets need to have baryon numbers larger than 39, 433, and $2.7\ifmmode\times\else\texttimes\fi{}{10}^{5}$. The ${e}^{+}{e}^{\ensuremath{-}}$ pair creation will inevitably start for superheavy nuclei with charge numbers $Z\ensuremath{\ge}177$, for $ud\mathrm{QM}$ nuggets with $Z\ensuremath{\ge}163$, for strangelets with $Z\ensuremath{\ge}192$, and for strangeon nuggets with $Z\ensuremath{\ge}212$. A universal relation $Q/{R}_{e}=({m}_{e}\ensuremath{-}{\overline{\ensuremath{\mu}}}_{e})/\ensuremath{\alpha}$ is obtained at a given electron chemical potential ${\overline{\ensuremath{\mu}}}_{e}$, where $Q$ is the total charge and ${R}_{e}$ the radius of electron cloud. The maximum number of $Q$ without causing ${e}^{+}{e}^{\ensuremath{-}}$ pair creation is then fixed by taking ${\overline{\ensuremath{\mu}}}_{e}=\ensuremath{-}{m}_{e}$. For supercritically charged objects with ${\overline{\ensuremath{\mu}}}_{e}l\ensuremath{-}{m}_{e}$, the decay rate for ${e}^{+}{e}^{\ensuremath{-}}$ pair production is estimated based on the Jeffreys-Wentzel-Kramers-Brillouin (JWKB) approximation. It is found that most positrons are emitted at $t\ensuremath{\lesssim}{10}^{\ensuremath{-}15}\text{ }\text{ }\mathrm{s}$, while a long lasting positron emission can be observed for large objects with $R\ensuremath{\gtrsim}1000\text{ }\text{ }\mathrm{fm}$. The emission of positrons and electron-positron annihilation from supercritically charged objects may be partially responsible for the short $\ensuremath{\gamma}$-ray burst during the merger of binary compact stars, the 511 keV continuum emission, as well as the narrow faint emission lines in x-ray spectra from galaxies and galaxy clusters.

The symmetry energy obtained with the effective Skyrme energy density functional is related to the values of isoscalar effective mass and isovector effective mass, which is also indirectly related to the incompressibility of symmetric nuclear matter. In this work, we analyze the values of symmetry energy and its related nuclear matter parameters in five-dimensional parameter space by describing the heavy ion collision data, such as isospin diffusion data at 35 MeV/u and 50 MeV/u, neutron skin of $^{208}$Pb, and tidal deformability and maximum mass of neutron star. We obtain the parameter sets which can describe the isospin diffusion, neutron skin, tidal deformability and maximum mass of neutron star, and give the incompressibility $K_0$=250.23$\pm$20.16 MeV, symmetry energy coefficient $S_0$=31.35$\pm$2.08 MeV, the slope of symmetry energy $L$=59.57$\pm$10.06 MeV, isoscalar effective mass $m_s^*/m$=0.75$\pm$0.05 and quantity related to effective mass splitting $f_I$=0.005$\pm$0.170. At two times normal density, the symmetry energy we obtained is in 35-55 MeV. To reduce the large uncertainties of $f_I$, more critical works in heavy ion collisions at different beam energies are needed., 10 pages, 11 figures, 2 tables, accepted by Phys.Rev.C. This article draws heavily from arXiv:1911.05380. In the v1 version, we modified two typos in Table II

Inspired by various astrophysical phenomenons, it is suggested that pulsar-like compact stars are comprised entirely of strangeons (quark-clusters with three-light-flavor symmetry) and a small amount of electrons. In order to better constrain the properties of strangeon stars, we propose a linked bag model to describe the condensed matter by the strong interaction (i.e., strong condensed matter) in both 2-flavored (nucleons) and 3-flavored (hyperons, strangeons, etc.) scenarios. The model parameters are calibrated to reproduce the saturation properties of nuclear matter, which are later applied to hyperon matter and strangeon matter. Compared with baryon matter, the derived energy per baryon of strangeon matter is reduced if the strangeon carries a large number of valence quarks, which stiffens the equation of state and consequently increases the maximum mass of strangeon stars. In a large parameter space, the maximum mass and tidal deformability of strangeon stars predicted by the linked bag model are consistent with the current astrophysical constraints. It is found that the maximum mass of strangeon stars can be as large as [Formula: see text], while the tidal deformability of a [Formula: see text] strangeon star lies in the range of [Formula: see text].

The state of supranuclear matter in compact stars remains puzzling, and it is argued that pulsars could be strangeon stars. The consequences of merging double strangeon stars are worth exploring, especially in the new era of multi-messenger astronomy. To develop the “strangeon kilonova” scenario proposed in Paper I, we make a qualitative description about the evolution of ejecta and light curves for merging double strangeon stars. In the hot environment of the merger, the strangeon nuggets ejected by tidal disruption and hydrodynamical squeezing would suffer from evaporation, in which process particles, such as strangeons, neutrons and protons, are emitted. Taking into account both the evaporation of strangeon nuggets and the decay of strangeons, most of the strangeon nuggets would turn into neutrons and protons, within dozens of milliseconds after being ejected. The evaporation rates of different particles depend on temperature, and we find that the ejecta could end up with two components, with high and low opacity respectively. The high opacity component would be in the directions around the equatorial plane, and the low opacity component would be in a broad range of angular directions. The bolometric light curves show that the spin-down power of the long-lived remnant would account for the whole emission of kilonova AT2017gfo associated with GW170817, if the total ejected mass ∼ 10−3 M ⊙. The detailed picture of merging double strangeon stars is expected to be tested by future numerical simulations.

The possible existence of stable up-down quark matter (udQM) was recently proposed, and it was shown that the properties of udQM stars are consistent with various pulsar observations. In this work we investigate the stability of udQM nuggets and found at certain size those objects are more stable than others if a large symmetry energy and a small surface tension were adopted. In such cases, a crust made of udQM nuggets exists in quark stars. A new family of white dwarfs comprised entirely of udQM nuggets and electrons were also obtained, where the maximum mass approaches to the Chandrasekhar limit.

We study the thermodynamics and the susceptibilities of quark matter in the framework of two-flavor Nambu-Jona-Lasinio model at finite isospin chemical potential and temperature. Isospin number density, normalized energy density and trace anomaly are shown to be in good agreement with the available lattice data as well as with the results from chiral perturbation theory at zero temperature. We also study how susceptibilities depend on the isospin chemical potential and on temperature. We find a peak for the chiral, pion, and isospin susceptibilities at the critical isospin chemical potential, $\mu_I^c(T)$, at the boundary of the phase transition between the normal and pion superfluid phase. Moreover, temperature makes the transition from normal to pion condended phase smoother. We also note that the pion susceptibility always remains zero in the normal phase while it is finite in the superfluid phase., Comment: 8 pages, 6 figures. updated to match EPJC version

We study the interface effects of a quark-hadron mixed phase in compact stars. The properties of nuclear matter are obtained based on the relativistic-mean-field model. For the quark phase, we adopt a perturbation model with running quark masses and coupling constant. At certain choices of parameter sets, it is found that varying the quark-hadron interface tension will have sizable effects on the radii (ΔR≈600 m) and tidal deformabilities (ΔΛ/Λ≈50%) of 1.36 solar mass hybrid stars. These provide possibilities for us to constrain the quark-hadron interface tension with future gravitational wave observations as well as the ongoing NICER mission.

The interface effects play important roles for the properties of strange quark matter (SQM) and the related physical processes. We show several examples on the implications of interface effects for both stable and unstable SQM. Based on an equivparticle model and adopting mean-field approximation (MFA), the surface tension and curvature term of SQM can be obtained, which are increasing monotonically with the density of SQM at zero external pressure. For a parameter set constrained according to the 2$M_\odot$ strange star, we find the surface tension is $\sim$2.4 MeV/fm${}^2$, while it is larger for other cases., Comment: To appear in the AIP Proceedings of the Xiamen-CUSTIPEN Workshop on the EOS of Dense Neutron-Rich Matter in the Era of Gravitational Wave Astronomy, Jan. 3-7, Xiamen, China

We investigate the bulk viscosity of strange quark matter in the framework of the equivparticle model, where analytical formulae are obtained for certain temperature ranges, which can be readily applied to those with various quark mass scalings. In the case of adopting a quark mass scaling with both linear confinement and perturbative interactions, the obtained bulk viscosity increases by orders of magnitude compared with those in bag model scenarios. Such an enhancement is mainly due to the large quark equivalent masses adopted in the equivparticle model, which are essentially attributed to the strong interquark interactions and are related to the dynamical chiral symmetry breaking. Due to the high bulk viscosity, the predicted damping time of oscillations for a canonical 1.4 strange star is less than one millisecond, which is shorter than previous findings. Consequently, the obtained -mode instability window for the canonical strange stars well accommodates the observational frequencies and temperatures for pulsars in low-mass X-ray binaries (LMXBs).

Computed tomography (CT) is an effective tool for three-dimensional (3D) imaging by using optical detectors to capture the two-dimensional (2D) projections of tested parameters from multiple views and realizing 3D reconstruction through various algorithms. However, for practical applications, typically only a few detectors can be applied due to their high expense and the limited optical access of the test environment. The realization of high precision reconstruction with a few projections is of great significance for promoting the development and application of CT technology. The spatial arrangement of the detectors determines the amount of useful information collected by the system, which greatly affects the quality of CT reconstruction. Therefore, in this work we study the optimization method of projection arrangement based on the 3D Mojette transform theory.Mojette transform is a special discrete form of Radon transform, which can realize projection sampling with minimum redundancy and accurate tomographic reconstruction from less projection angles. It provides a new way to realize the CT technology with fewer projections. However, the existing researches mainly focus on the reconstruction theories of 2D Mojette transform, which is used for realizing the 2D slice tomography. In order to realize the real 3D tomographic reconstruction, in this work we establish a mathematical model of 3D Mojette transform, and study its accurate reconstruction condition. The results show that the 3D Mojette transform is a combination of twice 2D Mojette transform in two directions. The accurate reconstruction condition of 3D Mojette transform is that the sum of the absolute values of projection vectors’ components in x, y, and z directions is greater than the number of discrete grids in each direction. The correctness of the mathematical model and the accurate reconstruction condition are verified by numerical simulations.Considering the limitation of the pixels in the practical detectors, the method to determine the optimal arrangement of projection angles is proposed. The results indicate that the optimal arrangement is that all detectors are located in the same horizontal plane around the tested object, where the projection model is reduced to 2D Mojette transform. In this case, the minimum projection angles and pixels are required and the projection angles can be positioned in a smaller spatial range. If the condition cannot be satisfied in practice, projection vectors with smaller |pi| and |qi| should be chosen. This research provides the theoretical basis for establishing the actual CT system.

We study the interface effects in strangelets adopting mean-field approximation (MFA). Based on an equivparticle model, the linear confinement and leading-order perturbative interactions are included with density-dependent quark masses. By increasing the confinement strength, the surface tension and curvature term of strange quark matter (SQM) become larger, while the perturbative interaction does the opposite. For those parameters constrained according to the 2 M⊙ strange star, the surface tension is ∼2.4 MeV/fm2, while unstable SQM indicates a slightly larger surface tension. The obtained results are then compared with those predicted by the multiple reflection expansion (MRE) method. In contrast to the bag model case, it is found that MRE method overestimates the surface tension and underestimates the curvature term. To reproduce our results, the density of states in the MRE approach should be modified by proper damping factors.

We systematically study the properties of single-$\mathrm{\ensuremath{\Lambda}},\mathrm{\ensuremath{\Xi}}$, and $\mathrm{\ensuremath{\Sigma}}$ hypernuclei within the framework of relativistic mean-field model. The $YN$ coupling constants are constrained according to the experimental data and previous theoretical efforts. By adding a hyperon to $^{40}\mathrm{Ca}$, we investigate its mean-field potentials, single-hyperon levels, density distributions, and binding energies, where the consequences of introducing different types of hyperons ($\mathrm{\ensuremath{\Lambda}},{\mathrm{\ensuremath{\Xi}}}^{0,\ensuremath{-}}$, and ${\mathrm{\ensuremath{\Sigma}}}^{+,0,\ensuremath{-}}$) are examined. In general, the $\mathrm{\ensuremath{\Lambda}}$ and ${\mathrm{\ensuremath{\Sigma}}}^{0}$ hyperons show similar behaviors in bulk properties since both of them are electroneutral and have similar coupling constants; ${\mathrm{\ensuremath{\Xi}}}^{0}$ hyperon owns the shallowest mean-field potential well with the most extended density distribution; and Coulomb interactions play vital roles in the charged ${\mathrm{\ensuremath{\Xi}}}^{\ensuremath{-}},\phantom{\rule{0.16em}{0ex}}{\mathrm{\ensuremath{\Sigma}}}^{\ensuremath{-}}$, and ${\mathrm{\ensuremath{\Sigma}}}^{+}$ hyperons. As a result, those hyperons have different impurity effects on the nuclear core $^{40}\mathrm{Ca}$. The $\ensuremath{\omega}YY$ tensor couplings are included and show remarkable effects on the spin-orbit splitting which even change the level ordering of $\mathrm{\ensuremath{\Xi}}$ hyperon. Finally, the single-hyperon binding energy of hypernuclei generally increases with the mass number. However, there is a turning point for ${\mathrm{\ensuremath{\Sigma}}}^{+}$ hypernuclei at $_{{\mathrm{\ensuremath{\Sigma}}}^{+}}^{91}\mathrm{Nb}$ where the binding energy begins to decrease. This is mainly due to the increasing Coulomb repulsive potential at large proton numbers.

We explore the effects of strangeness and $\mathrm{\ensuremath{\Delta}}$ resonance in baryonic matter and compact stars within the relativistic-mean-field models. The parameter set PKDD is adopted for $N\text{\ensuremath{-}}N$ interaction, parameters fixed based on finite hypernuclei and neutron stars are taken for the hyperon-meson couplings, and the universal baryon-meson coupling scheme is adopted for the $\mathrm{\ensuremath{\Delta}}$-meson couplings. In light of the recent observations of GW170817 with the dimensionless combined tidal deformability $197\ensuremath{\le}\overline{\mathrm{\ensuremath{\Lambda}}}\ensuremath{\le}720$, we find it is essential to include the $\mathrm{\ensuremath{\Delta}}$ resonances in compact stars, and small $\mathrm{\ensuremath{\Delta}}\text{\ensuremath{-}}\ensuremath{\rho}$ coupling ${g}_{\ensuremath{\rho}\mathrm{\ensuremath{\Delta}}}$ is favored if the mass ${2.27}_{\ensuremath{-}0.15}^{+0.17}\text{ }\text{ }{M}_{\ensuremath{\bigodot}}$ of PSR $\mathrm{J}2215+5135$ is confirmed.

Based on relativistic mean field (RMF) models, we study finite $\Lambda$-hypernuclei and massive neutron stars. The effective $N$-$N$ interactions PK1 and TM1 are adopted, while the $N$-$\Lambda$ interactions are constrained by reproducing the binding energy of $\Lambda$-hyperon at $1s$ orbit of $^{40}_{\Lambda}$Ca. It is found that the $\Lambda$-meson couplings follow a simple relation, indicating a fixed $\Lambda$ potential well for symmetric nuclear matter at saturation densities, i.e., around $V_{\Lambda} = -29.786$ MeV. With those interactions, a large mass range of $\Lambda$-hypernuclei can be well described. Furthermore, the masses of PSR J1614-2230 and PSR J0348+0432 can be attained adopting the $\Lambda$-meson couplings $g_{\sigma\Lambda}/g_{\sigma N}\gtrsim 0.73$, $g_{\omega\Lambda}/g_{\omega N}\gtrsim 0.80$ for PK1 and $g_{\sigma\Lambda}/g_{\sigma N}\gtrsim 0.81$, $g_{\omega\Lambda}/g_{\omega N}\gtrsim 0.90$ for TM1, respectively. This resolves the Hyperon Puzzle without introducing any additional degrees of freedom., Comment: 5 figures, 1 table, to be published in Chinese Physics C

It becomes common practice to reduce a large-scale power grid into a simplified one using transient stability simulator and have it modeled on electromagnetic transients programs. However, the procedure of network reduction may produce negative resistance, which may result in some problems in electromagnetic transient simulation. This paper firstly demonstrates that the negative resistance will probably lead to numerical instability in electromagnetic transient simulation. And then the forming mechanism of the negative resistance during network reduction using Gaussian Elimination is revealed. Several schemes for negative resistance elimination are presented at last.

The chaos particle swarm optimization algorithm was presented to solving optimal power flow. The proposed OPF considers the total cost of generators as the objective functions. To enhance the performance of algorithm, a premature convergence strategy was proposed. The strategy can be divided into two parts. In the first part, a method is introduced to judge premature convergence, while another part provides an advance method to improve the performance of algorithm with searching the solution in total feasible region. The control strategy used to prevent premature convergence will obtain starting values for initial particle before program iterating, so it can provide bitter probability of detecting global optimum solution. The simulation results on standard IEEE 30-bus system minimizing fuel cost of generator show the effectiveness of the chaos particle swarm optimization algorithm, and can obtain a good solution.

With the rapid development of DG, especially the access of large-scale renewable energy, traditional simple distribution network with unique source turns into ADN with multiple sources, making the distribution network more complicated. In this paper, The power source and grid planning of traditional and intelligent distribution network are discussed, based on which the problems ADN faces and the research difficulty are focused on. The key technology of ADN planning is analyzed, including the uncertainty of load forecasting, the ADN absorption capacity for DG and the cost-effectiveness of ADN planning. Some suggestions for the research direction of ADN in the future are made at the end, providing reference for the ADN planning with large-scale renewable energy access.

When DC transmission system adopts monopole earth or bipolar imbalance operation mode, the DC grounding electrode will inject large amount of current into the earth, and then disturb the running of the power grid. In view of the influence which is created by DC transmission system in Guangdong power grid, this paper derived the mathematical expressions of the transformer neutral point current after creating a calculation model, and concluded the main influence factors; The subject applied the linear regressing analysis theory to calculate the regression equations of transformers so that the slope of the regressing equation can be used to estimate the influence scope of grounding DC. Finally it concludes that: transformer neutral point current and the power transmitted by DC system has positive correlation; For ±800kV DC Chu Sui, the transformers ,which is more than 80 km away from DC grounding electrode, will no longer be affected; The application of DC suppression devices will affect the neutral point current of the transformers nearby.

In this paper, a new system splitting scheme based on the identification of weak connection is proposed. This paper firstly claims that if two nodes in a transmission line are related to two different generator groups or irrelated to any generator group, the transmission line is regarded as weak connection. And matrix R is presented to reflect the relevance between load nodes and generator groups after faults are cleared. The candidate strategy space is composed of these transmission lines of weak connection. Secondly, the procedure of searching the splitting surfaces is listed to illustrate how the splitting scheme works. Finally IEEE 39-bus system is used to verify the feasibility of this splitting scheme.

In 2013, China Southern Power Grid (CSG) installed three ±200Mvar STATCOMs on the 500kV substations which are adjacent to the receiving ends of multiple HVDC lines. Based on the project of STATCOM test in CSG, the ±200Mvar cascaded STATCOM simulation model is established in the real-time digital simulator (RTDS) ,the aim is to study the modeling technology of H Bridge valve group by using small time-step and main control strategy .Amounts of tests has been done to verify the validity of the cascaded STATCOM model in different control modes. The RTDS STATCOM model also tested in the closed-loop CSG power network and the transient state response characteristics has been compared with real STATCOM control and protection devices for engineering prototype to verify the feasibility of the model. The constructed model has been successfully applied on the analysis of impacts on AC/DC paralleled CSG with STATCOM using RTDS.

We investigated the properties of strange quark matter in an external strong magnetic field with both confinement and leading-order perturbative interactions considered. It was found that the leading-order perturbative interaction can stiffen the equation of state of magnetized quark matter, while the magnetic field lowers the minimum energy per baryon. By solving the Tolman–Oppenheimer–Volkoff equations, we obtain the internal structure of strange stars. The maximum mass of strange stars can be as large as 2 times the solar mass.

We study strange quark matter (SQM) objects ranging from strangelets to strange stars based on our recently proposed unified description. The important interface effects are investigated by adopting a constant surface tension as well as the multiple reflection expansion (MRE) method. It is shown that the properties of SQM objects are strongly affected by the different surface treatments. In the former case, strangelets are more compact, an electric dipole is predicted on the surface of the quark part, and a local minimum of the energy per baryon appears for unusually small values of the surface tension. In the latter case, on the other hand, an electric potential well is formed, and the energy per baryon decreases monotonically with the SQM object's size. It is found that the MRE scenario coincides with the constant-surface-tension one if realistic values are considered. However, the effects of quark depletion on the quark-vacuum interface cannot be solely described by a constant surface tension. Thus we conclude that the MRE scenario is more reasonable.

The conventionally separated treatments for strangelets and strange stars are now unified with a more comprehensive theoretical description for objects ranging from strangelets to strange stars. After constraining the model parameter according to the Witten-Bodmer hypothesis and observational mass-radius probability distribution of pulsars, we investigate the properties of this kind of objects. It is found that the energy per baryon decreases monotonously for increasing baryon number and reaches its minimum at the maximum baryon number, corresponding to the most massive strange star. Due to the quark depletion, an electric potential well for negatively charged particles is formed on the surface of the quark part, which may provide some unique observables. For a rotational bare strange star, a magnetic field with the typical strength of pulsars is generated.

The previous thermodynamic treatment for models with density and/or temperature dependent quark masses is shown to be inconsistent with the requirement of fundamental thermodynamics. We therefore study a fully self-consistent one according to the fundamental differential equation of thermodynamics. After obtaining a new quark mass scaling with the inclusion of both confinement and leading-order perturbative interactions, we investigate properties of strange quark matter in the fully consistent thermodynamic treatment. It is found that the equation of state become stiffer, and accordingly, the maximum mass of strange stars is as large as about 2 times the solar mass, if strange quark matter is absolutely or metastable.

We investigate the properties of strange quark matter in a strong magnetic field with quark confinement by the density dependence of quark mass considering the total baryon number conservation, charge neutrality and chemical equilibrium. The strength of the magnetic field considered in this article is $10^{16} \sim 10^{20}$ G. It is found that an additional term should appear in the pressure expression to maintain thermodynamic consistency. At fixed density, the energy density of magnetized strange quark matter varies with the magnetic field strength. The exists a minimum with increasing the field strength, depending on the density. It is about $6\times10^{19}$ Gauss at two times the normal nuclear saturation density.

The stability of excited superheavy nuclei (SHN) with $100 \leq Z \leq 134$ against neutron emission and fission is investigated by using a statistical model. In particular, a systematic study of the survival probability against fission in the 1n-channel of these SHN is made. In present calculations the neutron separation energies and shell correction energies are consistently taken from the calculated results of the finite range droplet model which predicts an island of stability of SHN around Z=115 and N=179. It turns out that this island of stability persists for excited SHN in the sense that the calculated survival probabilities in the 1n-channel of excited SHN at the optimal excitation energy are maximized around Z=115 and N=179. This indicates that the survival probability in the 1n-channel is mainly determined by the nuclear shell effects., Comment: 5 pages, 3 EPS figures, to be published in "Science China Physics, Mechanics and Astronomy"