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Study of Current Sheath Velocity and Its Distribution Using Tridimensional Magnetic Probe in Sahand Plasma Focus

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Plasma Science and Technology 2015年第5期17卷 353-357页

作者： M.A.MOHAMMADI S.HEDYEH department of Atomic and Molecular physics Faculty of PhysicsUniversity of Tabriz Research center of astrophysics and Applied physics University of Tabriz

The current sheath velocity in 0.25 Torr gas pressure of Filippov type plasma focus is studied experimentally. By using two tridimensional magnetic probes on top of the anode surface, the current sheath velocity is measured for argon, oxygen and nitrogen. Additionally, the effect of charging voltage on the current sheath velocity is studied in both axial and radial phases. We found that, the maximum current sheath velocities at both radial and axial phases are respectively 4.33 ± 0.28 （cm/μs） and 3.92 ± 0.75 （cm/μs） with argon as the working gas at 17 kV. Also, the minimum values of current sheath velocity are 1.48 ± 0.15 （cm/μs） at the radial phase and 1.14 ± 0.09 （cm/μs） at the axial phase with oxygen at 12 kV. The current sheath velocity at the radial phase is higher than that at the axial phase for all gases and voltages. In this study, variation of the full width half maximum （FWHM） of magnetic probe signals with voltage is investigated for different gases at radial and axial phases.

关键词： plasma focus tridimensional magnetic probe current sheath dynamics

A cosmological model with negative energy photons

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Chinese physics B 2010年第1期19卷 606-610页

作者：覃一平 center for astrophysics Guangzhou University physics department Guangxi University

According to recent investigations of states of quantum fields, we postulate that there exist negative energy photons in the universe. With this assumption, we find a solution of Einstein＇s equation without introducing the cosmological constant. A new and sizable type Ia supernovae sample is employed to perform a fit with our model and the conventional model. Both models can well account for the current type Ia supernovae observation and they are not distinguishable. With the new model, the cause of the accelerated expansion of the universe and the mechanism of the negative pressure existing in outer space can be explained in ordinary physical terms.

关键词： relativistic cosmology observational cosmology

Understanding PDF uncertainty in W boson mass measurements

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Chinese physics C 2022年第12期46卷 179-193页

作者：高俊刘殿宇谢可平 NPAC Shanghai Key Laboratory for Particle Physics and CosmologySchool of Physics and AstronomyShanghai Jiao Tong UniversityShanghai 200240China Key Laboratory for Particle astrophysics and Cosmology(MOE) Shanghai 200240China Pittsburgh Particle physics Astrophysicsand Cosmology CenterDepartment of Physics and AstronomyUniversity of PittsburghPittsburghPA 15260USA

We study the dependence of the transverse mass distribution of charged leptons and the missing energy on parton distributions(PDFs)adapted to W boson mass measurements at the CDF and ATLAS experiments.We compare the shape variations of the distribution induced by different PDFs and find that the spread of predictions from different PDF sets can be significantly larger than the PDF uncertainty predicted by a specific PDF set.We suggest analyzing the experimental data using up-to-date PDFs to gain a better understanding of the PDF uncertainties in W boson mass measurements.We also perform a series of Lagrange multiplier scans to identify the constraints on the transverse mass distribution imposed by individual data sets in the CT18 global analysis.In the case of the CDF measurement,the distribution is mostly sensitive to d-quark PDFs in the intermediate x region,which are largely constrained by DIS and Drell-Yan data on deuteron targets and Tevatron lepton charge asymmetry data.

关键词： W-boson mass PDF uncertainty CT18

Development of the spectrum of gamma-ray burst pulses influenced by the intrinsic spectral evolution and the curvature effect

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Chinese physics B 2009年第2期18卷 825-844页

作者：覃一平 center for astrophysics Guangzhou University physics department Guangxi University

The spectral evolution of gamma-ray burst pulses assumed to arise from the emission of fireballs is explored. It is found that due to the curvature effect, the integrated flux is well related to peak energy by a power law in the decaying phase of pulses, where the index is about 3, which does not depend on intrinsic emission and the Lorentz factor. The spectra of pulses in the decaying phase are slightly different from each other when different intrinsic spectral evolution patterns are considered, indicating that it is dominated by the curvature effect. In the rising phase, the integrated flux keeps increasing whilst the peak energy remains unchanged when the intrinsic emission bears an unchanged spectrum. Within this phase, the flux decreases with the increase of the peak energy for a hard-to-soft intrinsic spectrum, and for a soft-to-hard-to-soft intrinsic spectrum, the flux generally increases with the increase of the peak energy. An intrinsic soft-to-hard-to-soft spectral evolution within a co-moving pulse would give rise to a pulse-like evolutionary curve for the peak energy.

关键词： gamma-ray bursts gamma-rays relativity

Morphology and structural stability of Pt–Pd bimetallic nanoparticles

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Chinese physics B 2015年第3期24卷 149-156页

作者：刘暾东郑骥文邵桂芳范天娥文玉华 center for Cloud Computing and Big Data Department of AutomationXiamen University Institute of Theoretical physics and astrophysics Department of PhysicsXiamen University

The morphologies and structures of Pt–Pd bimetallic nanoparticles determine their chemical and physical properties.Therefore, a fundamental understanding of their morphologies and structural stabilities is of crucial importance to their applications. In this article, we have performed Monte Carlo simulations to systematically explore the structural stability and structural features of Pt–Pd alloy nanoparticles. Different Pt/Pd ratios, and particle sizes and shapes were considered.The simulated results reveal that the truncated octahedron, which has the remarkably lowest energy among all the considered shapes, exhibits the best structural stability while the tetrahedron has the worst invariably. Furthermore, all the structures of Pt–Pd alloy nanoparticles present Pd-rich in the outmost layer but Pt-rich in the sub-outmost layer. Especially, atomic distribution and chemical short-range order parameter were applied to further characterize the structural features of Pt–Pd alloy nanoparticles. This study provides a significant insight not only into the structural stability of Pt–Pd alloy nanoparticles with different compositions, and particle sizes and shapes but also to the design of bimetallic nanoparticles.

关键词： nanoparticles,structural stability,Monte Carlo simulation

The redshift number density evolution of Mg Ⅱ absorption systems

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Research in Astronomy and astrophysics 2013年第6期13卷 641-650页

作者： Zhi-Fu Chen department of physics and Telecommunication Engineering Baise University center for astrophysics Guangzhou University

We make use of the recent large sample of 17 042 Mg Ⅱ absorption systems from Quider et al. to analyze the evolution of the redshift number density. Regardless of the strength of the absorption line, we find that the evolution of the redshift number density can be clearly distinguished into three different phases. In the intermediate redshift epoch （0.6 ≤ z ≤ 1.6）, the evolution of the redshift number density is consis- tent with the non-evolution curve, however, the non-evolution curve over-predicts the values of the redshift number density in the early （z ≤ 0.6） and late （z ≥ 1.6） epochs. Based on the invariant cross-section of the absorber, the lack of evolution in the red- shift number density compared to the non-evolution curve implies the galaxy number density does not evolve during the middle epoch. The fiat evolution of the redshift number density tends to correspond to a shallow evolution in the galaxy merger rate during the late epoch, and the steep decrease of the redshift number density might be ascribed to the small mass of halos during the early epoch.

关键词： methods： statistical -- galaxies： evolution -- quasars： absorption lines

Evolution of dark energy–dark matter-coupled expanding universe

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Chinese Science Bulletin 2014年第33期59卷 4473-4477页

作者： Ti-Pei Li Mei Wu department of physics Center for Astrophysics Tsinghua University Key Laboratory of Particle astrophysics Institute of High Energy Physics Chinese Academy of Sciences

The present universe is dominated by repulsive dark energy. It is natural that the coupling between the dark energy and the attractive gravity has to be taken into account in studying the evolution of our universe. Here, we induce an evolution equation for dark energy–dark mattercoupled universe. The solutions of the dynamic equation provide a specific picture of cosmic evolution, which is well compatible with current observed evolution histories of both Hubble parameter and equation of state parameter of dark energy. In this picture, the already observed universe has undergone through three epochs—the epoch of equilibrium between gravity and dark energy at cosmological redshifts z [ 1, the phase transition epoch at z between about 0.5 and 1, and the present acceleration epoch starting from z ' 0:5. The expected matter-dominated deceleration epoch has not been seen yet, which requires future deep observations to look back upon more early universe.

关键词：膨胀宇宙暗能量耦合暗物质演变演化方程动力学方程吸引力

Missing completely of the CMB quadrupole in WMAP data

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Chinese Science Bulletin 2013年第11期58卷 1243-1249页

作者： LIU Hao LI TiPei Key Laboratory of Particle astrophysics Institute of High Energy Physics Chinese Academy of Sciences Department of Physics and Center for Astrophysics Tsinghua University

In cosmic microwave background (CMB) experiments, foreground-cleaned temperature maps are still contaminated by the residual dipole due to uncertainties of the Doppler dipole direction and microwave radiometer sidelobe. To obtain reliable CMB maps, such contamination has to be carefully removed from observed data. We have previously built a software package for map-making, residual dipole-contamination removal, and power spectrum estimation from the Wilkinson Microwave Anisotropy Probe (WMAP) raw data. This software has now been significantly improved. With the improved software, we obtain a negative result of CMB quadrupole detection with the WMAP raw data, which is 3.2±3.5 K2 from the seven-year WMAP (WMAP7) data. This result is evidently incompatible with ～1000 K2 expected from the standard cosmological model ΛCDM. The completely missing of CMB quadrupole poses a serious challenge to the standard model and sets a strong constraint on possible models of cosmology. Due to the importance of this result for understanding the origin and early evolution of our universe, the software codes we used are opened for public checking.

关键词： WMAP 威尔金森微波各向异性探测器四级宇宙微波背景辐射标准宇宙模型地图制作原始数据微波辐射计

Extending the correlation of L_R-L_X to gamma-ray bursts

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Research in Astronomy and astrophysics 2015年第5期15卷 617-622页

作者： Jing L Jing-Wen Xing Yuan-Chuan Zou Wei-Hua Lei Qing-Wen Wu Ding-Xiong Wang GXU-NAOC center for astrophysics and Space Sciences Department of PhysicsGuangxi University Guangxi Key Laboratory for Relativistic astrophysics School of physics Huazhong University of Science and Technology

The well-known correlation between radio luminosity （LR） and X-ray luminosity （Lx）, LR/LX 10^-5, holds for a variety of objects, such as active galactic nuclei, Galactic black holes, solar flares and cool stars. Here we extend the relation to gamma-ray bursts （GRBs） and find that the GRBs also obey a similar LR - LX relation, with a slightly different slope of LR ∝ LX^1.1. This relation implies that the explosions that occur on different scales may have a common underlying origin.

关键词： gamma-ray bursts general -- quasars general -- stars black holes