College Physics

Quantum speed limit time

XU Kai, ZHANG Guo-feng

College Physics. 2021, 40(10): 1. doi:10.16854 / j.cnki.1000-0712.210015

Abstract ( 1035 )

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The minimum time required for the system to evolve from the initial state to the target

state is defined as the quantum speed limit time. This concept can be used to estimate the maximum

rate of evolution from a given quantum state to a desired target state. Here，the development of

quantum speed limit time from closed system to open system is reviewed，and the influence of

non-Markovian environment on the quantum speed limit time of open system is discussed. We hope

that our review is helpful for the future study of the quantum speed limit time.

Effect of parameter change on the polarization of square lattice nanoisland

CHEN Sheng, LU Jun-yi, TENG Bao-hua

College Physics. 2021, 40(10): 5. doi:10.16854 / j.cnki.1000-0712.210233

Abstract ( 718 )

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Based on the transverse field Ising model，the phase transition properties of

square lattice nanois- lands with a spin of 1 /2 are investigated using the usual decoupling

approximation and higher order decoupling ap- proximation of the Fermi green function. The

polarization diagram shows that when the initial spin orientation is ran- dom，multiple and pseudo

solutions may be produced，thus show unconventional results: reentry phenomenon. The

use of high-order decoupling approximation can not only explain the richer phase transition

phenomenon，but also in most cases，the higher-order decoupling approximate equations have only a unique solution，which

can avoid the generation of pseudo solutions. JS / J is the main reason for the stepped shape of

the polarization curve，but the high order decoupling approximately increases the relationship between the parameters.

Solving the problem on reflection and refraction by surface of moving medium applied with time-space diagram method

XU Guang-zhi, LI Yi-jie

College Physics. 2021, 40(10): 9. doi:10.16854 / j.cnki.1000-0712.210074

Abstract ( 800 )

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We investigate the law of reflection and refraction along the direction of propagation of

the light ray when the light incident on the surface of moving medium at any angle using the

space-time diagram method. The effects on the direction of reflected and refracted rays from

the velocity of moving medium，angle of the surface and incidence are discussed. The general

formulas of direction and frequency shift of reflected and refracted rays are giv- en in low-speed

approximation.

Study of molecular structure and spectrum of potassium fluoride under the external electric fields

ZHENG Jing-yan, Bumaliya Abulimiti, XIANG Mei, WANG Xing-chen, AN Huan

College Physics. 2021, 40(10): 14. doi:10.16854 / j.cnki.1000-0712.210177

Abstract ( 824 )

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In order to study the physical properties of potassium fluoride，the bond length，energy，charge dis- tribution，energy level distribution，energy gap and infrared spectra of KF molecules under different applied electric fields ( -0.02 ～ 0.02 a.u.) are investigated by density functional theory LSDA method at the level of 6-311G radical group. The results display that the applied electric field has a great influence on the structure of KF molecules. With the increase of the external electric field in the direction of Z ( F-K bond) ，the bond length and electric dipole mo- ment of KF molecules have been decreased，the total energy has been increasing，and the energy gap EG has been increased first and then decreased. At the same time，the strongest peak of the KF infrared spectrum undergoes a blue shift; The first 10 excited states are

redshifted. On the other hand，as the electric field strength increases，the dissociation energy of KF molecules increases，and vice versa，the dissociation energy decreases.

On the state space of angular momentum

YAN Er-bin

College Physics. 2021, 40(10): 18. doi:10.16854 / j.cnki.1000-0712.210071

Abstract ( 967 )

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For any pure state in the state space of spin angular momentum with spin quantum number

0.5，the component operator of spin angular momentum along a certain direction can be

found，and the pure state is the eigenstate of the component operator. However，for the pure

state in the state space of spin angular momentum with quantum number 1 or more，it is found that

only some states have corresponding conclusions. Therefore，pure states can be divided into two

categories. The existence and preparation methods of these two different pure states are dis-

cussed. It is found that there is no good experimental method to prepare the eigenstates which

cannot be the compo- nent operators of angular momentum in a certain direction，which poses a

thorny problem for experimental physi-cists.

Solving Schrödinger equations with multiple delta potentials by Fourier transformation

XIONG Lu-lin, TAN Xin, LUO Guang

College Physics. 2021, 40(10): 22. doi:10.16854 / j.cnki.1000-0712.210075

Abstract ( 1044 )

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The process of solving the Schrödinger equation with delta potentials is very

complicated. In this pa- per，the Fourier transform method is used to solve the Schrödinger equation

under the action of several delta poten- tials. Firstly，the Schrödinger equation with single delta

potential well is discussed，then the solution of the equation with double delta potentials is

studied. Furthermore，the solution of the equation of triple delta potentials is de-

duced. Finally，the problem of solving the Schrodinger equation under mutiple delta

potentials constraints is dis- cussed through odd and even delta potentials respectively.

Low-speed approximation of Lorentz transformation

WEI Yi-huan, QI Xiao-hua

College Physics. 2021, 40(10): 28. doi:10.16854 / j.cnki.1000-0712.200540

Abstract ( 1023 )

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Lorentz transformation is an important content in the theory of special

relativity. It is generally be- lieved that Lorentz transform will be converted into Galileo

transformation for the low-speed case. The results show that in addition to the low-speed

condition，there should also be restriction on spatial coordinate to go back to Gali- leo

transformation.

Direct deriving the formula of aberration by 　　the principle of constancy of light velocity

LIU Jia-ming

College Physics. 2021, 40(10): 30. doi:10.16854 / j.cnki.1000-0712.200513

Abstract ( 1009 )

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In this paper，the formula of aberration is direct derived by the principle of constancy

of light veloci- ty without the Lorentz transformation. This method has much in common with the

methods of deriving the time dila- tion effect and the length contraction effect. It can be used

as the extended discussion or the practice after class in the lesson of the principle of constancy

of light velocity.

Misunderstandings in the experiment of measuring acceleration of gravity with Kate 　　pendulum 　　——— Taking virtual simulation experiment as an example

SHENG Yan

College Physics. 2021, 40(10): 32. doi:10.16854 / j.cnki.1000-0712.210066

Abstract ( 2050 )

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Kate pendulum is an accurate and ingenious experimental method to measure the

acceleration of gravity. In this paper，based on the principle，the model of Kate pendulum is

introduced，the experimental method is summed up，some common experimental errors are pointed out，and

the analysis is given so as to guide the ex- perimenters to pay attention to understand the

experimental principles and avoids going into the experimental errors.

Design experiment of university physics: research on demonstration device of Lissajous graphic

WU Han¹, YU Yao¹, YOU Yin-tao¹, TANG Yong-jun¹, ZHANG Jin-long²

College Physics. 2021, 40(10): 36. doi:10.16854 / j.cnki.1000-0712.210147

Abstract ( 2905 )

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In this paper，a comprehensive design experiment of university physics，the self-making

Lissajous graphic demonstration device is introduced. The reason why Lissajous figures is formed

through theoretically analy- zing the thin film ' s forced vibration. The experimental

results show that the shape and size of Lissajous figures change periodically when the

frequency of the sound source increases. Finally，the effective surface tension value is estimated

to be about 46.00 N / m through the measured resonance frequency when the surface area of latex

ballon is twice the normal area，indicating that the device has certain practical applicability.

Virtual simulation of panoramic aiming system based on TracePro software

XU Hai-bin, GU Ju-guan

College Physics. 2021, 40(10): 40. doi:10.16854 / j.cnki.1000-0712.200547

Abstract ( 857 )

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In order to improve the teaching quality of image conversion function of prism and lens

in engineer- ing optics，the model of panoramic aiming system is built by using TracePro software.

The changes of the image at various locations are clearly observed under combined rotation of

isosceles right angle prism and Daowei prism. The

virtual simulation results are consistent with the theory in textbooks. It can deepen students'

understanding of image conversion function of prism and lens，and enable them to master the optical

structure and the principle of panoram- ic aiming system so as to improve the teaching quality and

classroom efficiency，and to stimulate students' interest in optical system design and research.

The extensive development of optical virtual simulation should provide a use-

ful supplement for enriching the online and offline teaching of optical courses.

Freeman Dyson: more than a physicist

HU Yu-chen¹, LU Jian-long²

College Physics. 2021, 40(10): 45. doi:10.16854 / j.cnki.1000-0712.210178

Abstract ( 1131 )

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We overview the life experience and achievements of American physicist Freeman

Dyson and his contribution and achievements as physicist，science writers，and physical educators.

Dyson has got the Wolf Award as a physicist，the Thomas Award as a writer and the Oster Award as a

physics teacher. He is one of the founders of quantum electrodynamics. His scientific

autobiography “Disturbing the universe”is popular in the world，and he regards family and

child education as the most important thing in his life. This article introduces Dyson's life

experi- ence，summaries his life's glory and achievements，commemorates the legendary master who has

just passed away.

Analysis of the refraction phenomenon of the swimmer's “body and head separation”in the swimming pool

SHAO Yun

College Physics. 2021, 40(10): 52. doi:10.16854 / j.cnki.1000-0712.210102

Abstract ( 1117 )

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This paper first proposes a refraction phenomenon of the swimmer's “body head

separation”in the swimming pool; and then，as the bedding，it introduces the strict image position

of the underwater object refracting through the water surface. Using the knowledge of plane

geometry and trigonometric function，the visual separation distance function of the underwater

object's image and object ( that is，the swimmer's “body head”) in the eyes of the observer are

derived，and the actual observation is verified by the data. By using the functions

deduced and graphs drawed，the paper finds that the visual separation distance between the

underwater image and the object will increase with the increase of the visual angle and the

distance of the observer，but it will first increase and then de- crease until it tends to zero with

the increase of the depth of the object point. Several special cases are discussed， and it is

pointed out that the analytical results and the numerical method of the visual separation distance

have their own advantages and disadvantages.

Approximate theoretical calculation of the trajectories of rotating cards

ZHU Shi-dong¹, ², LI Qiu-hang¹, HOU Ji-xuan¹, CHEN Qian¹

College Physics. 2021, 40(10): 56. doi:10.16854 / j.cnki.1000-0712.210097

Abstract ( 789 )

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From the perspective of rigid body mechanics and aerodynamics，this paper

has carried out theoretical analysis and certain experimental verification on the 17th

question " Playing Card" of the international Young Physicists Championship 2020 ( IYPT2020)

，and worked out a trajectory equation of a rotating card. Some rules of card’s movement

are discussed through parameter analysis. It is found that the main force affecting the

movement of card is the air resistance on the lower surface，which on the one hand

causes the precession of the card，on the other hand，produces the component force in three

directions through the precession，thus affecting the trajectory of the card.Finally，this paper

verifies the rationality of the theory by a self-designed card launcher.

The stable structure of 60 charged particles in a spherical surface: A Monte Carlo 　　simulation

ZHOU Zheng¹, YAN Zheng², LI Wei¹

College Physics. 2021, 40(10): 62.

Abstract ( 621 )

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In this paper，a theoretical simulation is carried out for the studies on the nature of

60-charged par- ticles on a spherical surface based on the Monte Carlo method，and is revealed a new

structure with composited of 116 triangles，which has the lowest energy in compared to the

previous found spherical structures，including the truncated icosahedron or Fullerence

structure，the rhombic dodecahedron，and the snub dodecahedron structure.

The importance of this paper not only provides a rich knowledge for the undergraduate students in

the fundamental educations，but also sheds a new light into the search for exotic molecule

structures based on the Monte Carlo simu- lations.

Twisted magnetic field of magnetar in force-free condition

ZHANG Ming-hao, YU Cong

College Physics. 2021, 40(10): 66. doi:10.16854 / j.cnki.1000-0712.200542

Abstract ( 854 )

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Magnetars are a type of neutron stars with extremely powerful magnetic fields，which also

have the strongest magnetic fields in the universe ever discovered by human. The magnetic field of

a magnetar has not only a poloidal component. Because of its high intensity，it can apply enough

stress on the shell of the star to cause shear， which leads to the twist of the magnetic field

around the stellar surface. Magnetars fit the force-free condition be- cause their

magnetic energy is dominated by magnetic pressure. Plasma pressure in the magnetosphere

is far less than magnetic pressure so it can be ignored. In this paper，we tried to find

the variable separated stream function solution around the surface of magnetar under

force-free condition and carry out numerical simulation of field lines， as well as numerical

calculation of twist angle and magnetic energy.

Home experiment: fractal geometry of crumpled paper ball

LUO Jie, QIAN Jun

College Physics. 2021, 40(10): 73. doi:10.16854 / j.cnki.1000-0712.200522

Abstract ( 2578 )

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During the pandemic period，experiments in home are set up in basic physics

experiment course. Because of the simple preparation and easy measurement，the hand-crumpled

paper ball experiment is chosen by many students. In this paper the fractal in the

experiment of crumpled paper balls is discussed. The definition of fractal dimension is

introduced to describe the internal irregularity of the crumpled paper balls. The fractal

dimen- sion of normal A4 printing paper is measured experimentally and the influence of different

paper hardness and paper layers on the fractal dimension of paper ball is studied.

Single-pixel imaging system based on Raspberry Pi

HE Zi-hao, HAN Jia-cheng, WANG Lin-miao, ZHAO Tian-ci, ZHANG Su-heng

College Physics. 2021, 40(10): 77. doi:10.16854 / j.cnki.1000-0712.210024

Abstract ( 1036 )

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In this paper，a single-pixel imaging system based on Raspberry Pi is proposed. The

proposed sys- tem takes the Raspberry Pi as the core and the base-scan single-pixel imaging

technology as the basis，which has a simple structure，low cost，and strong operability.

Therefore，it is very suitable for application in experimental teaching. First，the principle

of the base-scan single-pixel imaging is given，and then the system structure is intro- duced in

detail from the aspects of hardware and software. Finally，the experimental results of Hadamard and

Fou- rier single-pixel imaging are shown. This work provids a new idea for carrying out optical

information processing ex- periments.

Statistical approach to the parton distribution functions of mesons

XIE Xiu-peng, LV Zhun

College Physics. 2021, 40(10): 83. doi:10.16854 / j.cnki.1000-0712.200537

Abstract ( 613 )

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The statistical model is applied to study the parton distribution function of the K and

the π mesons. By using the parameterized form for the parton distribution function of the meson

obtained from the statistical model and combining the meson induced Drell-Yan data，the u quark

distribution function of the K meson is extracted， the values of the parameters are

determined. The extraction shows that the statistical approach can describe the ratio of the

K-nucleon Drell-Yan and π-nucleon fairly well. It is also found that the chemical potential of

the u quark with positive helicity inside the K meson is larger than that inside the π meson.

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