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A perspective for the Global spin alignment of vector mesons and strong force fields in heavy-ion collisions is provided in this short report., 4 pages, 2 figures

Using a quark combination model with the equal-velocity combination approximation, we study the production of hadrons with strangeness and charm flavor quantum numbers in Pb+Pb collisions at $\sqrt{s_{NN}}=$5.02 TeV. We present analytical expressions and numerical results for these hadrons' transverse momentum spectra and yield ratios. Our numerical results agree well with the experimental data available. The features of strange and charm hadron production in the quark--gluon plasma at the early stage of heavy ion collisions are also discussed., Comment: 12 pages, 9 figures

In non-central high energy heavy ion collisions, the colliding system possesses a huge orbital angular momentum along the normal direction of the reaction plane. Due to the spin orbit interaction in the system, such a huge orbital angular momentum leads to the spin polarization of quarks and anti-quarks in the quark matter system produced in the collision. Such an effect, known as the global polarization effect, was predicted many years ago and has been confirmed by the STAR collaboration at RHIC. The discovery of the global polarization effect opens a new avenue in heavy ion physics in general and in studying the properties of quark-gluon plasma in particular. This talk will briefly review the original ideas and calculations that lead to the prediction and summarize progresses and problems in related aspects., plenary talk at the 24th International Spin Symposium (SPIN2021)

We investigate the inclusive and semi-inclusive productions of spin-3/2 hadrons, such as $\Omega$, in unpolarized $e^+ e^-$ annihilation. The general differential cross sections are expressed in terms of structure functions in accordance to the polarization of the hadron and the azimuthal modulations. We derive a complete definition of quark transverse momentum dependent (TMD) fragmentation functions (FFs) to spin-3/2 hadrons for the first time from the decomposition of the quark-quark correlation matrix at leading twist, 14 of which are newly defined corresponding to rank-3 tensor polarized hadron. The collinear FFs are obtained from the $k_T$-integrated correlation matrix, and only two TMD FFs with rank-3 tensor polarization have nonvanishing collinear counterparts. Then we perform a leading order calculation of the unpolarized differential cross sections. In the single-hadron inclusive production, only two structure functions are found nonzero and none of the rank-3 tensor polarized FFs contributes. For the nearly back-to-back two-hadron production, half of the 48 structure functions are found nonzero even if the spin of the second hadron is not analyzed, and ten of the rank-3 tensor polarized TMD FFs contribute. Therefore, one can study the rank-3 tensor polarized FFs via the production of a spin-3/2 hadron and an unpolarized hadron in unpolarized $e^+ e^-$ collision experiments. These newly defined FFs can be further applied in semi-inclusive deep inelastic scattering processes for the study of nucleon structures., Comment: 42 pages, 4 figures, matching the published version in Physical Review D

We propose a relativistic theory for spin density matrices of vector mesons based on Kadanoff-Baym equations in the closed-time-path formalism. The theory puts the calculation of spin observables such as the spin density matrix element $\rho_{00}$ for vector mesons on a solid ground. Within the theory we formulate $\rho_{00}$ for $\phi$ mesons into a factorization form in separation of momentum and space-time variables. We argue that the main contribution to $\rho_{00}$ at lower energies should be from the $\phi$ fields that can polarize the strange quark and antiquark in the same way as electromagnetic fields. The key observation is that there is correlation inside the $\phi$ meson wave function between the $\phi$ field that polarizes the strange quark and that polarizes the strange antiquark. This is reflected by the fact that the contributions to $\rho_{00}$ are all in squares of fields which are nonvanishing even if the fields may strongly fluctuate in space-time. The fluctuation of strong force fields can be extracted from $\rho_{00}$ of quarkonium vector mesons as links to fundamental properties of quantum chromodynamics., Comment: ReVTex 4.1, 25 pages, 2 figures; The derivation of KB equations in Section III has been improved

We make a systematic study of Λ hyperon polarizations in unpolarized lepton induced semi-inclusive reactions such as e−N→e−ΛX and e+e−→ΛhX. We present the general form of cross sections in terms of structure functions obtained from a general kinematic analysis. This already shows that the produced hyperons can be polarized in three orthogonal directions, i.e., the longitudinal direction along the hyperon momentum, the normal direction of the production plane, and the transverse direction in the production plane. We present the parton model results at the leading twist and leading order in perturbative QCD using transverse momentum dependent factorization and provide the expressions for these structure functions and polarizations in terms of three-dimensional parton distribution functions and fragmentation functions. We emphasize in particular that by studying the longitudinal polarization and the transverse polarization in the production plane, we can extract the corresponding chiral-odd fragmentation functions H1Lq⊥Λ, H1TqΛ, and H1Tq⊥Λ. We also present numerical results of rough estimates utilizing available parametrizations of fragmentation functions and approximations. We discuss how to measure these polarizations and point out in particular that they can be carried out in future EIC and/or e+e− annihilation experiments such as Belle.

With the expansion of the scale of coal mining, the safety problems caused by the reburning of coal are becoming more and more serious. In this paper, the pyrolysis characteristics of gas coal and the exothermic characteristics of reoxidation of residues were studied by using a synchronous thermal analyzer. The functional groups of pyrolysis residues were tested, and the group content and characteristic structural parameters were calculated based on quantum chemistry method. The results show that with the increase of pyrolysis temperature, Volatile maximum separation rate (Vmax) and the change in the residual weight of the coal sample (ΔWvp) increase. The increase of temperature will lead to the decrease of hydroxyl and aliphatic hydrocarbon content in coal, and the increase of aromatic hydrocarbon. With the deepening of pyrolysis, the ignition point temperature of coal samples decreases first and then rises, the combustion intensity and combustion concentration are strengthened. The pyrolysis results show that 462.8°C is the critical temperature for the transition during pyrolysis. The ignition point of the residue is less affected by the pyrolysis conditions, and the ignition temperature of the raw coal and the pyrolysis residue varies within 330.57°C–334.98°C.

The fluid in global equilibrium must fulfill some constraints. These constraints can be derived from quantum statistical theory or kinetic theory. In this paper we will show that how these constraints can be applied to determine the non-dissipative transport coefficients for chiral systems along with the energy-momentum conservation, chiral anomaly for charge current and trace anomaly in energy-momentum tensor., Comment: 9 pages, no figures, submitted to Symmetry for the special issue "Symmetry with Chiral Magnetic Effects and Chiral Transports"

Polarized quarks and antiquarks in high-energy heavy-ion collisions can lead to the spin alignment of vector mesons formed by quark coalescence. Using the relativistic spin Boltzmann equation for vector mesons derived from Kadanoff-Baym equations with an effective quark-meson model for strong interaction and quark coalescence model for hadronizaton, we calculate the spin density matrix element $\rho_{00}$ for $\phi$ mesons and show that anisotropies of local field correlations or fluctuations with respect to the spin quantization direction lead to $\phi$ meson's spin alignment. We propose that the local correlation or fluctuation of $\phi$ fields is the dominant mechanism for the observed the $\phi$ meson's spin alignment and its strength can be extracted from experimental data as functions of collision energies. The calculated transverse momentum dependence of $\rho_{00}$ agrees with STAR's data. We further predict the azimuthal angle dependence of $\rho_{00}$ which can be tested in future experiments., Comment: ReVTex 4.1, 14 pages, 4 figures. A large part of the paper has been rewritten with the focus on extracting local correlations or fluctuations of phi fields from STAR's data and predictions for dependences of $\rho_{00}$ on the transverse momentum and azimuthal angle

We make a systematic study of $\Lambda$ hyperon polarizations in unpolarized lepton induced semi-inclusive reactions such as $e^-N\to e^-\Lambda X$ and $e^+e^-\to\Lambda h X$. We present the general form of cross sections in terms of structure functions obtained from a general kinematic analysis. This already shows that the produced hyperons can be polarized in three orthogonal directions, i.e., the longitudinal direction along the hyperon momentum, the normal direction of the production plane, and the transverse direction in the production plane. We present the parton model results at the leading twist and leading order in perturbative QCD and provide the expressions for these structure functions and polarizations in terms of parton distribution functions and fragmentation functions. We emphasize in particular that by studying the longitudinal polarization and the transverse polarization in the production plane, we can extract the corresponding chiral-odd fragmentation functions $H_{1Lq}^{\perp\Lambda}$, $H_{1Tq}^{\Lambda}$ and $H_{1Tq}^{\perp\Lambda}$. We also present numerical results of rough estimates utilizing available parameterizations of fragmentation functions and approximations. We discuss how to measure these polarizations and point out in particular that they can be carried out in future EIC and/or $e^+e^-$ annihilation experiments such as Belle., Comment: 13 pages, 7 figures; to be published on PRD

We make a systematic study of the isospin symmetry of fragmentation functions by taking decay contributions into account. We assume the isospin symmetry in strong interactions and show that in the unpolarized case the isospin symmetry is held for fragmentation functions of $\Lambda$ and only tiny violations are allowed for other hadrons such as nucleon and pions due to the contributions from weak decays. We present a rough estimate of the magnitudes of such violations. In the polarized case, we show that the isospin symmetry violation for $\Lambda$ production should be tiny and the recent Belle data on the transverse polarization of $\Lambda$ can be reproduced if the isospin symmetry is kept in the corresponding polarized fragmentation functions., Comment: 6 pages, 3 figures

Coalfield fire area reburning is one of the serious disasters in fire prevention and safety production. In this study, a synchronous thermal analyzer was used to conduct isothermal pyrolysis of jet coal at different temperatures, and the reaction characteristic parameters of different pyrolysis residual structures were analyzed. FTIR was used to measure group contents in raw coal and different pyrolysis residues. Programmed oxidation thermogravimetric experiments were carried out on the residues to obtain their oxidation characteristic parameters. The results demonstrated that the reaction characteristic parameters of the residual structures changed at 450 °C. The pyrolysis reaction mainly affected the variation of hydroxyl, aliphatic hydrocarbon, and aromatic hydrocarbon groups. The increase in pyrolysis temperature resulted in the decline in hydroxyl and aliphatic hydrocarbon groups as well as the increase in the aromatic hydrocarbon group. After pyrolysis, the ignition point temperature of the coal sample decreased, which causes the coal more likely to spontaneously ignite. It indicated that the pyrolysis residue at 450 °C is most likely to reburn. Compared with raw coal, the maximum combustion intensity of the pyrolysis residue was greatly increased, which reached the peak at 500 °C.

We make a systematic study of $��$ hyperon polarizations in unpolarized lepton induced semi-inclusive reactions such as $e^-N\to e^-��X$ and $e^+e^-\to��h X$. We present the general form of cross sections in terms of structure functions obtained from a general kinematic analysis. This already shows that the produced hyperons can be polarized in three orthogonal directions, i.e., the longitudinal direction along the hyperon momentum, the normal direction of the production plane, and the transverse direction in the production plane. We present the parton model results at the leading twist and leading order in perturbative QCD and provide the expressions for these structure functions and polarizations in terms of parton distribution functions and fragmentation functions. We emphasize in particular that by studying the longitudinal polarization and the transverse polarization in the production plane, we can extract the corresponding chiral-odd fragmentation functions $H_{1Lq}^{\perp��}$, $H_{1Tq}^��$ and $H_{1Tq}^{\perp��}$. We also present numerical results of rough estimates utilizing available parameterizations of fragmentation functions and approximations. We discuss how to measure these polarizations and point out in particular that they can be carried out in future EIC and/or $e^+e^-$ annihilation experiments such as Belle., 13 pages, 7 figures; to be published on PRD

In non-central high energy heavy ion collisions, the colliding system posses a huge orbital angular momentum in the direction opposite to the normal of the reaction plane. Due to the spin-orbit coupling in strong interaction, such huge orbital angular momentum leads to the polarization of quarks and antiquarks in the same direction. This effect, known as the global polarization effect, has been recently observed by STAR Collaboration at RHIC that confirms the theoretical prediction made more than ten years ago. The discovery has attracted much attention to the study of spin effects in heavy ion collision. It opens a new window to study properties of QGP and a new direction in high energy heavy ion physics—Spin Physics in Heavy Ion Collisions. In this chapter, we review the original ideas and calculations that lead to the predictions. We emphasize the role played by spin-orbit coupling in high energy spin physics and discuss the new opportunities and challenges in this connection.

We give a brief overview of the kinetic theory for spin-1/2 fermions in Wigner function formulism. The chiral and spin kinetic equations can be derived from equations for Wigner functions. A general Wigner function has 16 components which satisfy 32 coupled equations. For massless fermions, the number of independent equations can be significantly reduced due to the decoupling of left-handed and right-handed particles. It can be proved that out of many components of Wigner functions and their coupled equations, only one kinetic equation for the distribution function is independent. This is called the disentanglement theorem for Wigner functions of chiral fermions. For massive fermions, it turns out that one particle distribution function and three spin distribution functions are independent and satisfy four kinetic equations. Various chiral and spin effects such as chiral magnetic and votical effects, the chiral seperation effect, spin polarization effects can be consistently described in the formalism., Comment: 32pages, no figures, published version in IJMPA, more references are added

The spin alignment of vector meson produced in high energy reactions is determined by the spin-dependent fragmentation function $D_{1LL} (z,\mu_f)$ that is shown to be independent of the polarization of the fragmenting quark. In this paper, we extract the spin-dependent fragmentation function $D_{1LL} (z,\mu_f)$ from data on the spin alignment of $K^{*0}$ in $e^+e^-$ annihilation at LEP in two different scenarios and apply them to make predictions in $pp$ collisions. We make detailed analysis of contributions from different sub-processes and show that the spin alignment should be quite significant also in high energy $pp$ collisions., Comment: 12 pages, 16 fgiures,version printed in PRD

We show that the experimental data of transverse momentum ($p_{T}$) spectra of $\Omega$ baryon and $\phi$ meson at mid-rapidity in heavy-ion collisions exhibit the constituent quark number scaling in a wide energy range from RHIC to LHC. Such a scaling behavior is a direct consequence of quark combination mechanism via equal velocity combination and provides a very convenient way to extract the $p_{T}$ spectrum of strange quarks at hadronization. We present the results of strange quarks obtained from the available data and study the properties in particular the energy dependence of the averaged transverse momentum $\langle p_{T}\rangle$ and the transverse radial flow velocity $\langle\beta\rangle$ with a hydrodynamics-motivated blast-wave model.

We revisit the chiral anomaly in the quantum kinetic theory in the Wigner function formalism under the background field approximation. Our results show that the chiral anomaly is actually from the Dirac sea or the vacuum contribution in the un-normal-ordered Wigner function. We also demonstrate that this contribution modifies the chiral kinetic equation for antiparticles., 7 pages, Version submitted to PRD

Recent data on the production of $D$ mesons and $\Lambda_c^+$ baryons in heavy ion collisions at the Relativistic Heavy Ion Collider and the Large Hadron Collider exhibit a number of striking characteristics such as enhanced yield ratios $D_s^+/D^0$, $\Lambda_c^+/D^0$ and their transverse momentum dependences. In this paper, we derive the momentum dependence of open charm mesons and singly charmed baryons produced in ultra-relativistic heavy ion collisions via the equal-velocity quark combination. We present analytic expressions and numerical results of yield ratios and compare them with the experimental data available. We make predictions for other charmed hadrons., Comment: 2 tables, 8 figures

We solve the Wigner equation for massless spin-1/2 charged fermions near global equilibrium. The Wigner function can be obtained order by order in the power expansion of the vorticity and electromagnetic field. The Wigner function has been derived up to the second order from which the non-dissipative charge currents and the stress tensor can be obtained. The charge and energy densities and the pressure have contributions from the vorticity and electromagnetic field at the second order. The vector and axial Hall currents can be induced along the direction orthogonal to the vorticity and electromagnetic field at the second order. We also find that the trace anomaly emerges natually in renormalizing the stress tensor by including the quantum correction from the electromagnetic field., 31 pages, no figures, accepted version, general solution derived, more detail and more references added

In non-central high energy heavy ion collisions the colliding system posses a huge orbital angular momentum in the direction opposite to the normal of the reaction plane. Due to the spin-orbit coupling in strong interaction, such huge orbital angular momentum leads to the polarization of quarks and anti-quarks in the same direction. This effect, known as the global polarization effect, has been recently observed by STAR Collaboration at RHIC that confirms the theoretical prediction made more than ten years ago. The discovery has attracted much attention on the study of spin effects in heavy ion collision. It opens a new window to study properties of QGP and a new direction in high energy heavy ion physics -- Spin Physics in Heavy Ion Collisions. In this chapter, we review the original ideas and calculations that lead to the predictions. We emphasize the role played by spin-orbit coupling in high energy spin physics and discuss the new opportunities and challenges in this connection., Comment: prepared for "Lecture Notes in Physics", to appear

We use a geometric model for the hadron polarization with an emphasis on the rapidity dependence. It is based on the model of Brodsky, Gunion, and Kuhn and that of the Bjorken scaling. We make predictions for the rapidity dependence of the hadron polarization in the collision energy range 7.7-200 GeV by taking a few assumed forms of the parameters. The predictions can be tested by future experiments., RevTex 4, 16 pages, 11 figures

This is prepared for a featured article in Nuclear Physics News. Recently, the global polarization of \Lambda and \bar{\Lambda} hyperons in heavy-ion collisions (HIC) has been observed by the STAR Collaboration at the Relativistic Heavy Ion Collider in Brookhaven National Laboratory. The discovery confirms the theoretical prediction made more than ten years ago and indicates that the quark gluon plasma (QGP) produced in HIC possesses a vorticity as high as 10^21s^-1, much higher than any other fluid observed in nature. This opens a new window to study properties of QGP and a new direction in high energy heavy ion physics. This featured article is aimed to report the basic idea, current status and outlook., Comment: 4 pages, 11 figures, to appear in Nuclear Physics News

The structure of the proton is the forefront of studies on the deep structure of matter. With developments of high energy experiments in particular deeply inelastic lepton nucleon scattering (DIS), a dynamical picture of the structure of the proton has been developed, i.e., the quantum chromodynamics (QCD) based parton model. According to this picture, a proton moving close to the speed of light can be viewed as a bunch of free partons, and the collision between two high energy protons can be viewed as the collision between partons. Partons in the proton are described by parton distribution functions (PDFs). This picture is very successful in describing data from different experiments. It has been widely accepted in high energy physics community and is now taken as the standard picture for the dynamical structure of hadrons. The picture has changed the concepts of structures of matter in the sense that the number of partons in a proton depends on the space and time resolution of the probe. The studies of the proton structure provide not only the necessary initial condition of high energy collision but also the most active and fruitful frontier for studying properties of QCD where new QCD application techniques have been developed such as the collinear expansion and factorization theorem. With developments of experimental techniques, the studies have been extended to include spin degree of freedom and to use different probes such as electrons and muons. These studies have lead to many new discoveries, initiated the well known "proton spin crisis" and the "proton radius puzzle", and attracted much more attention in the field of particle and nuclear physics. The experimental data from polarized DIS has revealed that quark spin contributes to only a small fraction of the proton spin and initiated the question where the proton spin comes from. The electromagnetic radius of the proton measured from the electron-proton interaction does not coincide with that measured from the muon-proton interaction and initiated the proton radius puzzle. The experimental data on single-spin asymmetries in inclusive hadron production in proton-proton collisions have lead the studies of the QCD parton model from the simplest one dimensional longitudinal distribution case to the three dimensional case including spin and transverse momentum dependences. The physics in the three-dimensional case is definitely much more abundant and interesting. The transverse momentum dependent (TMD) PDFs include the simple number densities, the helicity distributions, the transversity, and many spin-momentum correlation functions as well, such as the Sivers function, the Boer-Mulders function, the Collins function, worm-gear, pretzelosity and also many so-called higher twist distributions describing quantum interference effects. Both experimental and theoretical efforts have been made in last years and many progresses have been made. The planned new instrumentations such as the Electron-Ion Collider (EIC) in the United States will definitely bring the field to a new era of rapid developments. Several new equipment discussed in China, including Super-Z Factory, Circular Electron Positron Collider (CEPC) and EIC of China (EicC) at High Intensity heavy ion Accelerator Facility (HIAF) and so on can also bring very significant contributions even play dominant role in some of the aspects in this exciting field.

In this study, underground coal gasification (UCG) technology with the strip mining method was recommended to avoid the instability of surrounding rock in the UCG cavity and possible groundwater pollution, in which mechanical performance and reasonable size of the strip pillar play the crucial role. The respective innovative calculation method considering the thermo-mechanical coupling effect was proposed and applied to size designs of pillars in the UCG projects of the Shanjiaoshu Mine and Mazino coal deposit . The proposed method feasibility was experimentally validated and yielded the following predictions of the coal pillar mechanical performance evolution during the UCG process . Heat-affected zones in the coal pillar and immediate roof gradually increased with the following decline. High temperatures above 250 °C affected the coal and rock masses only at a distance not exceeding 2 m from the surface, but their effect continued even after the UCG termination. High temperatures reduced the load-bearing capacity in the area near the coal pillar surface and induced long-term thermal stresses in coal pillars, which alternatively played a dominant role in affecting the ultimate strength of the coal pillar at different stages. The plastic zone width xp in the pillar is varied and will remain unchanged once it reaches its peak value. The width of strip pillars Wp is greatly influenced by high temperatures; it exhibits a W-shaped variation pattern during the UCG process and slowly drops after gasification. The strip pillar width of UCG can be determined using the maximum value of function Wp(t) considering a certain safety factor. While the wide pillar's total strength and size are slightly affected by the temperature, its width can be obtained from Wp(0) with a safety factor. This study can be used for predicting the mechanical performance evolution and size determination of pillars in the UCG process.

We show that the experimental data of transverse momentum ( p T ) spectra of identified hadrons released recently by ALICE collaboration for p–Pb collisions at s N N = 5.02 TeV exhibit a distinct universal behavior — the quark number scaling. We further show that the scaling is a direct consequence of quark (re-)combination mechanism of hadronization and can be regarded as a strong indication of the existence of the underlying source with constituent quark degree of freedom for the production of hadrons in p–Pb collisions at such high energies. We make also predictions for production of other hadrons.

We show that the experimental data of transverse momentum (pT) spectra of identified hadrons released recently by ALICE collaboration for p–Pb collisions at sNN=5.02 TeV exhibit a distinct universal behavior — the quark number scaling. We further show that the scaling is a direct consequence of quark (re-)combination mechanism of hadronization and can be regarded as a strong indication of the existence of the underlying source with constituent quark degree of freedom for the production of hadrons in p–Pb collisions at such high energies. We make also predictions for production of other hadrons.

In order to recover the abandoned coal resource of steeply inclined thin coal seams (SITCS), a field trial of underground coal gasification (UCG) with shaft method has been successfully carried out at Zhongliangshan coal mine in China. Many technological measures have been taken according to the geological conditions of coal seams. These technologies include the hollow-bottom and wall-style gasifiers, pinnate-pattern boreholes, the controlled moving multipoint gas injection, multi-component oxygen-rich gasification agent, and micro-seismic detection of flame working face. Some of the technologies were used for monitoring and controlling the UCG process, including gas-producing conditions and gasifier running states. The trial results show that it’s feasible to recover the abandoned coal resource and produce clean gas energy. The gaseous product of gasification consists of 5–10% H2, 14–16% CO and 5–8% CH4 and generated at a flow rate of 1400–1600 Nm3/h with a heat value of 1200–1400 kcal/Nm3.

Coal pyrolysis under high-temperature and high-stress conditions was studied experimentally in this work. Which experimental table should be chosen was studied, and parameter settings such as the final pyrolysis temperature, heating rate, and stresses were investigated. Pyrolysis experiments of Xinglongzhuang gas coal and Huating long-flame coal were conducted using an improved Paterson gas-medium high-pressure and high-temperature testing (Paterson HPT) system at temperatures of up to 1000 °C and under different stresses conditions. The results were compared to those of coal pyrolysis experiments without any stress and using a GR.TF80/11 tube furnace. The average heating rates used in these experiments were as low as 0.44 K/min. The produced gas and semicoke (coke) yields both increased with increasing stress, while the tar yield decreased. However, the variations in the yields of the pyrolysis products induced by the same increase in stress gradually decreased as the stress increased and nearly reached ...

In order to study the distribution characteristics and related parameters of the temperature field in underground coal gasification stope, Laplace transform and inverse Laplace transform were used to determine the analytical solution to temperature propagation in the stope under type one boundary conditions. Additionally, Mathematic software was used to conduct numerical simulation. Results indicate that in an unsteady stage, the temperature field gradually propagated in the coal seam, and that the propagation rate became steady after a gradual increase. The time required for the temperature field in the coal seam undergoing gasification to transform from the unsteady to the steady state was inversely proportional to the advance rate of the flame working face. During the stages of temperature increase and decrease, the temperature field in the roof, floor, and surrounding coal seam gradually moved towards the interior. During the temperature increase stage, the peak of the temperature field occurred on the surface of the surrounding rock and gradually increased; it also moved inward from the surface and gradually decreased during the temperature decrease stage. The temperature decrease stage had greater influence on the temperature field in the roof, floor, and surrounding seam than the temperature increase stage. The influence of the temperature increase stage was related to the advance rate of the flame working face; this influence is negligible when the advance rate of the flame working face exceeded a threshold value. Finally, based on the features of the envelope curves of temperature curve families, the ranges of the surrounding coal seam with no load-bearing capacity and coking cycle were obtained, as were after determination of their respective criteria and temperature threshold values.

We show that the experimental data of transverse momentum ($p_{T}$) spectra of $\Omega$ baryon and $\phi$ meson at mid-rapidity in heavy-ion collisions exhibit the constituent quark number scaling in a wide energy range from RHIC to LHC. Such a scaling behavior is a direct consequence of quark combination mechanism via equal velocity combination and provides a very convenient way to extract the $p_{T}$ spectrum of strange quarks at hadronization. We present the results of strange quarks obtained from the available data and study the properties in particular the energy dependence of the averaged transverse momentum $\langle p_{T}\rangle$ and the transverse radial flow velocity $\langle\beta\rangle$ with a hydrodynamics-motivated blast-wave model., Comment: 7 pages, 5 figures

We present the complete first order relativistic quantum kinetic theory with spin for massive fermions derived from the Wigner function formalism in a concise form that shows explicitly how the 32 Wigner equations reduce to 4 independent transport equations. We solve modified on-shell conditions to obtain the general solution and present the corresponding transport equations in three different forms that are suitable for different purposes. We demonstrate how different spin effects arise from the kinetic theory by calculating the chiral separation effect with mass correction, the chiral anomaly from the axial current and the quantum magnetic moment density induced by vorticity and magnetic field. We also show how to generate the global polarization effect due to spin vorticity coupling. The formalism presented may serve as a practical theoretical framework to study different spin effects in relativistic fermion systems encountered in different areas such as heavy ion, astro-particle and condensed matter physics as well., 5 pages, Typos fixed and references updated

We show that the experimental data of transverse momentum ($p_{T}$) spectra of $��$ baryon and $��$ meson at mid-rapidity in heavy-ion collisions exhibit the constituent quark number scaling in a wide energy range from RHIC to LHC. Such a scaling behavior is a direct consequence of quark combination mechanism via equal velocity combination and provides a very convenient way to extract the $p_{T}$ spectrum of strange quarks at hadronization. We present the results of strange quarks obtained from the available data and study the properties in particular the energy dependence of the averaged transverse momentum $\langle p_{T}\rangle$ and the transverse radial flow velocity $\langle��\rangle$ with a hydrodynamics-motivated blast-wave model., 7 pages, 5 figures

To optimize the gasification process and improve the underground coal gasification (UCG) technology for power generation, a pilot project of UCG integrated with the power generation was built in the abandoned mine “Ankou”. The UCG industrial tests with different oxygen concentrations of oxidant along with the pulsed injection method, and power generation experiments using UCG syngas were conducted. The results indicate that a decrease in the rate of air blowing for a short time exhibited a limited influence on syngas production, but a change in the amount of oxygen injection presented an obvious effect. With the increase in the oxygen concentration in the agent, the H2 content, combustible components and calorific value of syngas, flow ratio, and the consumption of coal, steam and oxygen increased, along with a rise in the gasification efficiency after an initial drop. The oxygen-enriched gasification trials showed higher air consumption, lower consumption of coal, steam and oxygen, and a low combustible components and calorific value of syngas compared to the gasification tests of the oxygen-enriched steam. The evaporation of ground water and coal moisture in the UCG panel provided steam for the oxygen-enriched gasification process, and its utilization rate was about 6–32 wt%. From the characteristics of UCG syngas, the technical transformations such as exhaust gas booster combustion control, high energy ignition, low pressure intake, expansion of the air, and gas inlet pipe diameter were carried out on the existing gas generator sets. The effectiveness of the measures was verified by the power generation experiments.

To investigate temperature field expansion behavior during the ignition stage, the variation of temperature fields of 12 sites versus time were studied using thermocouples during the ignition process. The results showed that the temperatures measured, and combustion processes, were not uniform. At the position where the igniter had started successfully, igniter 10 showed the smoothest flow in its exhaust holes, followed by igniters 4 and 1, successively. At the position of igniter 10, the ignition materials burned well and the temperature curve was smooth, but the highest combustion temperature of oil-containing split wood layer and coke layer was only 393 °C, the highest combustion temperature of block coal layer and solid coal wall was only 591 °C and 936 °C respectively. At the position of igniter 1, the ignition materials burned inadequately and the temperature curve was rough, but the highest combustion temperatures of oil-containing split wood layer, coke layer, block coal layer and solid coal wall were as high as 960 °C, 983 °C, 899 °C and 1280 °C respectively. The presence of the ignition source ensured, but did not determine, the occurrence of ignition. The temperature field in the gasified area could expand transversely by spreading combustion of the burning front and transverse movement of high-temperature gases to ignite the ignition materials away from fire sources. In locations with high exhaust resistance, the temperature field expanded primarily through the spreading of the burning front, while in the area with low exhaust resistance, the temperature field mainly through expanded the transverse movement of high-temperature gases.

We present a new method of solving the probability distribution for baryons, antibaryons and mesons at the hadronization of constituent quark and antiquark system. The hadronization is governed by the quark combination rule in the quark combination model developed by the Shandong Group. We use the method of the generating function to derive the outcome of the quark combination rule, which is much simpler and easier to be generalized than the original method. Furthermore, we use the formula of the quark combination rule and its generalization to study the property of multiplicity distribution of net-protons. Taking a naive case of quark number fluctuations and correlations at hadronization, we calculate ratios of multiplicity cumulants of final-state net-protons and discuss the potential applicability of quark combination model in studying hadronic multiplicity fluctuations and the underlying phase transition property in relativistic heavy-ion collisions., 17 pages, 3 figures. To be published in Chinese Physics C

We develop a general formalism for the quantum kinetics of chiral fermions in a background electromagnetic field based on a semiclassical expansion of covariant Wigner functions in the Planck constant $\hbar$. We demonstrate to any order of $\hbar$ that only the time-component of the Wigner function is independent while other components are explicit derivative. We further demonstrate to any order of $\hbar$ that a system of quantum kinetic equations for multiple-components of Wigner functions can be reduced to one chiral kinetic equation involving only the single-component distribution function. These are remarkable properties of the quantum kinetics of chiral fermions and will significantly simplify the description and simulation of chiral effects in heavy ion collisions and Dirac/Weyl semimetals. We present the unintegrated chiral kinetic equations in four-momenta up to $O(\hbar ^2)$ and the integrated ones in three-momenta up to $O(\hbar)$. We find that some singular terms emerge in the integration over the time component of the four-momentum, which result in a new source term contributing to the chiral anomaly, in contrast to the well-known scenario of the Berry phase term. Finally we rewrite our results in any Lorentz frame with a reference four-velocity and show how the non-trivial transformation of the distribution function in different frames emerges in a natural way., RevTex 4, 14 pages, no figure. Section II and III have been re-organized and expended to three sections (II-IV) to include more details of calculations. Section V has been expanded to include more discussions. A new section (VI) is added about Wigner functions in a general Lorentz frame. Some references are added

We show that the experimental data of transverse momentum ( pT ) spectra of identified hadrons released recently by ALICE collaboration for p –Pb collisions at sNN=5.02 TeV exhibit a distinct universal behavior — the quark number scaling. We further show that the scaling is a direct consequence of quark (re-)combination mechanism of hadronization and can be regarded as a strong indication of the existence of the underlying source with constituent quark degree of freedom for the production of hadrons in p –Pb collisions at such high energies. We make also predictions for production of other hadrons.

We propose alternative methods to measure the global polarization of $\Lambda$ hyperons. These methods involve event averages of proton's and $\Lambda$'s momenta in the lab frame. We carry out simulations using these methods and show that all of them work equivalently well in obtaining the global polarization of $\Lambda$ hyperons., Comment: Revtex 4, 7 pages, 2 figures; To be published in Chinese Physics C

We present the complete twist-4 results for the semi-inclusive annihilation process ${e}^{+}+{e}^{\ensuremath{-}}\ensuremath{\rightarrow}h+\overline{q}+X$ at the tree level of perturbative quantum chromodynamics. The calculations are carried out by using the formalism obtained by applying the collinear expansion to this process, where the multiple gluon scattering is taken into account and gauge links are obtained systematically and automatically. We present the results for structure functions in terms of gauge invariant fragmentation functions up to twist-4 and the corresponding results for the azimuthal asymmetries and polarizations of hadrons produced. The results obtained show in particular that, similar to that for semi-inclusive deeply inelastic scattering, for structure functions associated with the sine or cosine of an odd number of azimuthal angle(s), there are only twist-3 contributions, while for those of an even number of azimuthal angle(s), there are leading twist and twist-4 contributions. For all of those structure functions that have leading twist contributions, there are twist-4 addenda to them. Hence, twist-4 contributions may even have large influences on extracting leading twist fragmentation functions from the data. We also suggest a method for a rough estimation of twist-4 contributions based on the leading twist fragmentation functions.

We show that the experimental data of $p_T$ spectra of identified hadrons released recently by ALICE collaboration for $p$-Pb collisions at $\sqrt{s_{NN}}=5.02$ TeV exhibit a distinct universal behavior --- the quark number scaling. We further show that the scaling is a direct consequence of quark (re-)combination mechanism of hadronization and can be regarded as a strong indication of the existence of the underlying source with constituent quark degree of freedom for the production of hadrons in $p$-Pb collisions at such high energies. We make also predictions for production of other hadrons., 5 pages, 3 figures

The longitudinal polarization of a hyperon in e+e- annihilation at high energies depends on the longitudinal polarization of the quark produced at the e+e- annihilation vertex, whereas the spin alignment of vector mesons is independent of it. They exhibit very different energy dependences. We use the longitudinal polarization of the Lambda hyperon and the spin alignment of K* as representative examples to present numerical results of energy dependences and demonstrate such distinct differences. We present the results at the leading twist with perturbative QCD evolutions of fragmentation functions at the leading order.

The presentation is a summary of a series of papers~[1-4] on fragmentation function studies in $e^+e^-$-annihilation at high energies published recently by the SDU group on QCD and hadron physics. After a brief description of the three-dimensional fragmentation functions defined via quark-quark correlator for hadrons with different spins (0, 1/2 and 1) at leading and higher twists, we discuss how to study them in hadron production processes in $e^+e^-$-annihilation at high energies. We first present the general framework to express the cross section in terms of the corresponding structure functions based on the general kinematic analysis then give the parton model results for the differential cross sections and/or different spin asymmetries up to twist-3 in terms of gauge invariant fragmentations. The results can serve as a basis for experimental and phenomenological studies in this reaction.

We propose alternative methods to measure the global polarization of $��$ hyperons. These methods involve event averages of proton's and $��$'s momenta in the lab frame. We carry out simulations using these methods and show that all of them work equivalently well in obtaining the global polarization of $��$ hyperons., Revtex 4, 7 pages, 2 figures; To be published in Chinese Physics C

In order to study temperature field distribution in burnt surrounding rock and to determine ranges of burnt surrounding rock, coal-wall coking cycle and heat influence in the underground coal gasification (UCG) stope, based on the Laplace transform and inversion formula, we studied the temperature analytical solution of one-dimensional unsteady heat conduction for multi-layer overlying strata under the first and the forth kinds of boundary conditions, and we also carried out a numerical simulation of two-dimensional unsteady heat conduction by the COMSOL multiphysics. The results show that when the boundary temperature of surrounding rock has a linear decrease because of a directional movement of heat source in the UCG flame working face, the temperature in surrounding rock increases first and then decreases with time, the peak of temperature curve decreases gradually and its position moves inside surrounding rock from the boundary. In the surrounding rock of UCG stope, there is an envelope curve of temperature curve clusters. We analyzed the influence of thermophysical parameters on envelope curves and put forward to take envelope curve as the calculation basis for ranges of burnt surrounding rock, coal-wall coking cycle and heat influence. Finally, the concrete numerical values are given by determining those judgement standards and temperature thresholds, which basically tally with the field geophysical prospecting results. Keywords: Underground coal gasification (UCG), Temperature distribution, Laplace transform, Envelope curve, Burnt surrounding rock, Coking cycle

We propose alternative methods for measurement of the global polarization of Λ hyperons. These methods involve event averages of proton and Λ momenta in the laboratory frame. We carry out simulations using these methods and show that all of them work equally well in obtaining the global polarization of Λ hyperons.