bluuebunny/crossref_metadata_2025 huggingface dataset:
Cultural antinomies of the contemporary Serbian society: Premodern mentality vs. Postmodern identity
Authors: Božilović Nikola
Published: December 2020

Globalization has permeated all aspects of social life (economic, political, cultural) and affected the daily life of people. Postindustrial society and postmodern culture have made a significant impact on the transformation of identities, which have truly become liquid - multidimensional, discontinuous, decentralized, fragmented, unstable and inconstant. Parallel with this, new tendencies in culture have almost completely narrowed the boundary between high and popular creativity, thus challenging the status of the established, until then recognized values. These changes have also become evident in the contemporary Serbian society, which is obsessed by preserving the tradition and long-developed identities. By chance, that society has had one foot in the postmodern information world, with the other stuck in the quagmire of old habits and misconceptions inherited from the period of premodern social awareness. By analysing crucial value aspects (traditionalism, conformism, authoritarianism and nationalism), the author of this paper attempts to provide an explanation (which is the basic precondition for the resolution) of the ambivalent and, seemingly, inescapable situation in which the culture of Serbian society finds itself.
State stability indicators in the globalized concept of security at the beginning of the 21st century
Authors: Mišev Gordana
Published: December 2020

The notion of security is a complex and ambiguous phenomenon, which goes beyond the traditional notions of security, where the only reference object is the state, and state security is a condition for survival. In the globalized concept of security, state borders are becoming porous, the free flow of capital, goods and people has been achieved, and also new security challenges, risks and threats, which exceeds the traditional understanding of security, wherefore it boils down not only to economic, legal, environmental and social segments of life, but also to social groups and individuals. The issue around which the paper focuses starts from what makes a country stable and secure, what those factors are and how they are measured. The sectoral approach of the Copenhagen School of Security will be used as a conceptual framework. The subject of the paper is the analysis of indicators used in the official reports of relevant international institutions, which show the stability of countries in the globalized concept of security. The aim of this paper is to analyze the various indicators of state stability in order to achieve the most important characteristics that build human, national and state security, and includes non-military factors of development and stability. This analysis shows that governance, economy and security are mutually reinforced, especially through a set of policies implemented by the government.
The use of military strategy in network-centric warfare
Authors: Beriša Hatidža
Published: December 2020

The period after the end of the Cold War and the reorganization of the world order brought new challenges to modern military organizations. Total technological progress and completely new threats and opponents in the form of nonlinearity have influenced modern warfare to change its shape and form to such an extent that most theorists believe that we are witnessing revolutionary changes in the character of war. The development of information technology particularly influences the development of new concepts of the use of the armed forces, with the most technologically advanced countries naturally leading the way. The development of information technology has a huge impact on the modernization and transformation of the armed forces, primarily in the West. In order to achieve a qualitatively new, higher level of precision and higher speed in conducting military operations, in the early 1990s, many segments of the US armed forces were specially equipped with modern technology, which is based on information networks. The revolution in military affairs and its implementation in the concept of network-centric warfare have become new military strategic models for the US armed forces, along with the process of redefining security policy, in line with the new situation. Network-centric warfare has set new standards in warfare, relying on information superiority. In this paper, the relation of military strategy and its principles to network-centric warfare is considered.
The EU multinational operations: The legal framework and importance of the engagement of the Serbian Armed Forces personnel
Authors: Jevtić Miloš
Published: December 2020

This paper focuses on the engagement of the Serbian Armed Forces and other defense forces outside the national territory, activities planned and carried out within multinational operations (MNOs) of the European Union (EU), in particular. The primary goal of this research has two aspects - firstly, to analyze and compare the positive legislation and contents of the most significant strategic documents, which regulate the engagement of these capacities in multinational operations, in compliance with the concept of MNO and critical judgment on the legal framework governing this area, and secondly, to systematically explain the significance of the participation of the Serbian Armed Forces capacities in such military activities of the European Union.
Modeling the organisational implementation of a drone and counter-drone operator into the Serbian Armed Forces rifle section
Authors: Žnidaršič Vinko , Radovanović Marko , Stevanović Dragan
Published: December 2020

Drones are one of the new threats to tactical units. The armed forces use them with various successes in operations. However, the smallest tactical unit such as rifle section is generally still unprepared to operate drones and perform counter measures. Drones have a wide range of capabilities and therefore can be used for both civilian and military purposes. Along with the development of drones, counter-drone systems have also been developed. Several small drones and counter-drone systems suitable for the use by one man are presented in the first part of the research results to show that there is more than one system that can be selected for operational use. This also shows that one soldier in rifle section is capable of operating a small drone and counter-drone systems. This research has aimed to survey the organizational structure and determine organizational capabilities to implement a drone and counter-drone operator duty in rifle section. For that purpose, the research team has conducted a series of interviews with officers and non-commissioned officers of the Serbian Armed Forces and the Ministry of Defense. This duty is defined as "a drone operator" and in this research the Serbian Armed Forces rifle section is modeled in such a way to include a duty for 1) a specialized rifleman, 2) a converted sniper, or 3) an embedded soldier.
Brave women sound the alarm – representations of men and women in the Swedish media coverage of #MeToo
Authors: Lindqvist Lisa , Ganetz Hillevi
Published: December 2020

In autumn 2017 in Sweden, the #MeToo movement and sexual assault became a focus of broad debate. Swedish media coverage of the movement was centred around the many petitions made by anonymous groups of women to illuminate the extent of the problem of sexual assault, as well as a few cases of accusations against well-known and powerful men in both the culture and media industries. In order to elicit common representations of men and their female accusers, this study applies critical discourse analysis (CDA) to news media coverage and Facebook comments of three of those accused men: TV personality Martin Timell, journalist Fredrik Virtanen and culture personality Jean-Claude Arnault. The results indicate that representations of women as both witnesses and heroines work to reinforce notions of female responsibility as a means to halt sexual assault, while representations of men as sexual predators build on demarcations of illegal and mere misogynistic or “bad” behaviour, which in turn reinforce notions of male victimhood. These representations point to legal discourse as hegemonic, as it seems to limit the discussion and only present individual solutions, such as women bearing witness, to the structural problem of sexual assault. Simultaneously, the results indicate that the #MeToo movement and other feminist discourse have also had an effect on news media representations of sexual assault by broadening the concept beyond the consent/rape dichotomy.
Sports Journalism, Interns and #MeToo – did anything change?
Authors: Røsok-Dahl Heidi , Orgeret Kristin Skare
Published: December 2020

Norwegian news media were central actors in the dissemination of information about the #MeToo movement. Simultaneously, the media are made up of institutions and workplaces that are at times characterized by asymmetrical power relations. The aim of this article is to understand how those considered at the bottom of such power relations: young (female) interns in the sports journalism departments, experienced the effects of the #MeToo movement. Addressing the question if #MeToo changed anything, this article emphasizes the importance of combining the position that sexual harassment is not necessarily associated with a specific gender, at the same time recognizing that such harassment has first and foremost been part of a structural suppression of women. The article illustrates how facets of the journalistic culture and the myth of the “male genius” have marginalized those with unequal access to power in sports journalism, but also that the #MeToo movement has the potential to change this.
Prediction on mechanical parameters of inconsistently random composites by statistical second-order two-scale method
Authors: Han Fei  , Cui Jun-Zhi  , Yu Yan  ,   (1)西北工业大学应用数学系，西安  710129; (2)西北工业大学应用数学系，西安  710129；中国科学院数学与系统科学研究院，北京  100080
Published: December 2020

The statistical second-order two-scale method is developed to predicte the mechanical parameters of the composite structure with inconsistently random distribution, including stiffness parameters and elastic limit strength parameters. This kind of structure, in which random inclusion dispersions are not the same everywhere but gradually changing in space, is called the structure with inconsistently random distribution. So, it possesses continuously varying macro-mechanical properties in space. In this paper, the microstructure of the composites with consistently/inconsistently random distributions is represented. The statistical second-order two-scale analysis formulation is established. And the strength criterion of the inconsistent random composite structure is discussed. Finally, the numerical results for different inconsistent composite structures are obtained and compared with the experiment data. Their agreement shows that the statistical second-order two-scale method is feasible to predict mechanical parameters of inconsistently random composites.
Modelling of macrosegregation in large steel ingot with considering solid movement
Authors: Liu Dong-Rong  , Sang Bao-Guang  , Kang Xiu-Hong  , Li Dian-Zhong  ,   (1)中国科学院金属研究所,沈阳材料科学国家（联合）实验室，沈阳  110016; (2)中国科学院金属研究所,沈阳材料科学国家（联合）实验室，沈阳  110016；哈尔滨理工大学材料科学与工程学院，哈尔滨  150040
Published: December 2020

Based on the Eulerian and the volume averaging methods, a mathematical model of macrosegregation formation with considering solid movement during solidification of large steel ingot is developed. The cases with and without solid movement are studied and compared. The result shows that the A segregation band results from a narrow channel that forms around the position where the solidified shell in the horizontal direction meets the one in the vertical direction, which serves as a barrier to the fluid flow, leading to the accumulation of solute. Effects of critical solid fraction and density of solid on evolution of macrosegregation are investigated. The results indicate that both the positive segregation in the A segregation band and the bottom negative segregation become more pronounced with the critical solid fraction increasing. As the density of solid increases, stronger macrosegregations occur at the upper and bottom parts of the ingot. However, the length of A segregation band is not increased with density of solid. Calculated results show good agreement with experimental ones, except a larger bottom negative segregation zone.
Study on MacPherson-Srolovitz's grain growth rate equation with Monte Carlo simulation
Authors: Wang Hao  , Liu Guo-Quan  , Yue Jing-Chao  , Luan Jun-Hua  , Qin Xiang-Ge  ,   (1)北京科技大学材料科学与工程学院，北京  100083; (2)北京科技大学材料科学与工程学院，北京  100083；北京科技大学新金属材料国家重点实验室，北京  100083; (3)佳木斯大学材料科学与工程学院，佳木斯  154007
Published: December 2020

MacPherson-Srolovitz's three-dimensional grain growth rate equation proposed recently by MacPherson and Srolovitz indicates that the change rate of grain volume depends on the mean width of grains and the total length of the triple lines. This rate equation is studied by large-scale Potts model-Monte Carlo simulation in this paper. The result shows that the data of averaged grain growth rate fit the MacPherson-Srolovitz’s three-dimensional grain growth rate equation very well, thereby this rate equation is preliminary verified.
Modelling the strain induced precipitation in Nb-containing micro-alloyed steels
Authors: Liu Hong  , Wang Xi-Tao  , Chen Leng  ,   (1)北京科技大学材料科学与工程学院，北京  100083; (2)北京科技大学新金属材料国家重点实验室，北京  100083
Published: December 2020

A physical metallurgy principle based model to predict flow stress, recovery, recrystallization and precipitation of Nb-containing micro-alloyed steels during hot rolling is developed. Precipitation kinetics is simulated by the model during hot rolling. The driving force and the equilibrium concentrations are calculated by Thermo-Calc software. The volume fraction of precipitation particles and the particle size of Nb-containing micro-alloyed steels during hot rolling are calculated with considering the effect of recovery and recrystallization on precipitation. The model is verified by the experimental results, and the volume fraction of precipitation particles and the particle sizes are predicted in different hot rolling processes.
Diffusion of oxygen atom near Zr(0001) surface
Authors: Yao Rui  , Wang Fu-He  , Zhou Yun-Song  ,   首都师范大学物理系，北京  100048
Published: December 2020

Based on the density functional theory calculations， the diffusion of oxygen atoms near the Zr（0001）surface is studied by using the nudged elastic band method. Firstly， the active energy of diffusion of oxygen atoms from the surface face-centred cubic （SFCC） sites into surface hexagonal close-packed sites in Zr（0001） surface is calculated. The active energy for the diffusion is 0.77 eV. Secondly， the active energy of diffusion of oxygen atoms from the SFCC into octahedral interstitial sites between the second and third layers Octa（2，3） via octahedral interstitial sites between the first and second layers Octa（1，2） is calculated too. There are two energy barriers for oxygen atom to overcome. The active energies are 2.14 and 2.57 eV， respectively. As a result， the diffusion of oxygen atom above the Zr（0001） surface is easier than the diffusion into the subsurface.
Non-equilibrium grain boundary segregation of phosphorous during high temperature plastic deformation
Authors: Chen Xian-Miao  , Song Shen-Hua  ,   哈尔滨工业大学深圳研究生院材料科学与工程系，深圳  518055
Published: December 2020

The quasi-thermodynamics and the kinetics of deformation-induced non-equilibrium grain boundary segregation are described. This model is used to predict non-equilibrium segregation of P during high temperature plastic deformation in an austenite microstructure. There is a segregation concentration peak of P near 800 ℃ for a strain rate of 1×10-3 s-1 and the deformation magnitude is 20%. When the deformation reaches 20% in magnitude at 1000 ℃ the segregation of P at grain boundaries increases with increasing strain rate. The predictions are generally consistent with some available experimental observations.
A density functional theory study on water adsorption on TiO2-terminated SrTiO3（001） surface
Authors: Lin Feng  , Zheng Fa-Wei  , Ouyang Fang-Ping  ,   (1)清华大学物理系，北京  100084; (2)清华大学物理系，北京  100084；中南大学物理科学与技术学院，长沙  410083
Published: December 2020

Water adsorptions on TiO2-terminated SrTiO3（001） surfaces at four kinds of coverages （0.25 monolayer（ML），0.5ML，0.75ML and 1ML） are investigatedby by using density functional theory calculations. Molecular and dissociative adsorptions of water are comparatively investigated. The nudged elastic band method is employed to calculate the dissociative energy barrier. The obtained results showed that dissociative adsorptions were energetically more favourable at low coverages （0.25ML and 0.5ML）， whereas molecular adsorption was more favourable at high coverage （1ML）， and particularly a special mixed adsorption was more favourable at 0.75ML. Based on these results， the influence of adsorption coverage on water dissociation is analyzed.
Structural，elastic and electronic properties of L12 aluminum phases from first principles calculation
Authors: Wang Na  , Tang Bi-Yu  ,   湘潭大学材料与光电物理学院，湘潭  411105
Published: December 2020

First principles calculations are performed to study structural， elastic and electronic properties of typical L12 precipitates of Al-based alloys （Al3Sc and Al3Zr）. The calculated formation energy and the cohesive energy show that both typical L12 precipitates of aluminum alloys have a strong alloying ability and Al3Zr phase has a higher structural stability than Al3Sc phase. According to the calculated density of states of these phases， it is found that the higher structural stability of Al3Zr is attributed to an increase in the number of bonding electrons below Fermi level. Three independent single-crystal elastic constants （C11，C12 and C44） at zero-pressure as well as polycrystalline mechanical parameters such as bulk modulus B， shear modulus G， Youngs modulus Y， Poissons ratio ν and anisotropy value A for both phases are calculated. The mechanical properties of both phases are further analyzed and discussed in comparison with experimental observations and other theory results.
Molecular dynamics study of the shear deformation in TiAl/Ti3Al system
Authors: Liu Yong-Li  , Zhao Xing  , Zhang Zong-Ning  , Zhang Lin  , Wang Shao-Qing  , Ye Heng-Qiang  ,   (1)东北大学理学院，沈阳  110004; (2)东北大学理学院，沈阳  110004；辽宁工业大学数理科学系，锦州  121001; (3)中国科学院金属研究所，沈阳材料科学国家（联合）实验室，沈阳  110016
Published: December 2020

The dynamical shear deformation induced hexagonal close-packed （HCP）face-centred cubic （FCC） processes in TiAl/Ti3Al system are investigated by the molecular dynamics method. The details of the dislocation initiation， the microstructure evolution and the force field effect are presented and discussed. The analyses of the potential variation and the structural snapshots show that the shear deformation is related to the “stick-slip” behaviour. The interface can transit the energy and counterpoise the deformation between the hetero-phases. The HCP-Ti3Al （FCC-TiAl） shows obvious （little） covariant deformation stage before the initiation of the fault transition. For HCP-Ti3Al， the final structure is the continued FCC stacking in a region with the large force field， and the FCC and HCP plates alternatively occur near the interface. For FCC-TiAl， twin and SISF are the main remnants， and the meta-stable HCP phase may occur with the increment of the force field.
Effects of helium plasma treatment on tensile behaviour of nano-SiO2 sol-gel coating T300 carbon fiber
Authors: Zhang Ying-Chen  , Zhu Hai-Yan  , Wu Hong-Yan  , Qiu Yi-Ping  ,   (1)东华大学纺织学院，上海  201620; (2)东华大学纤维材料改性国家重点实验室，上海  201620；东华大学纺织学院，上海  201620; (3)东华大学纤维材料改性国家重点实验室，上海  201620；东华大学纺织学院，上海  201620；中原工学院河南省功能性纺织材料重点实验室，郑州  450007；中原工学院纺织学院，郑州  450007; (4)中原工学院纺织学院，郑州  450007
Published: December 2020

The purpose of the present work is to investigate the effects of helium plasma treatment on tensile deformation of nano-SiO2 sol-gel coating T300 carbon fiber and provide a new concept for the nano-structural interphase between fiber surface and nano-coating. The tensile test results show that the activation volumes of T300 carbon fibers untreated and treated with helium plasma ranging from 681.9628 to 32342 nm3 by following Eyrings equation are important descriptors for the properties of the nano-structural interface between fiber surface and nano-coating, and the ductility of the nano-SiO2 sol-gel coating T300 carbon fibers treated by helium plasma is enhanced. From the results of the scanning electron microscope, X-ray photoelectron spectroscopy and Fourier transform infrared spectroscopy, it is found that the uniform dispersion of the nano-SiO2 coating of the T300 carbon fibers treated by helium plasma can not only fill the micro-flaws, but also cause the occurrence of effective activation surface interaction between carbon fibers and nano-SiO2 coating, along with the introduced activated functional groups on the fiber surfaces.
Modelling of solidification microstructure evolution of twin-roll casting magnesium strip using cellular automaton
Authors: Huang Feng  , Di Hong-Shuang  , Wang Guang-Shan  ,   东北大学轧制技术及连轧自动化国家重点实验室，沈阳  110004
Published: December 2020

Cellular automaton （CA） is applied to simulating the microstructure evolution during the solidification， and finite element method （FEM） was used for solving the conservation equations which govern the macro-transport phenomena during the twin-roll casting process of the magnesium strip in the molten pool. Coupling CA with FEM can predict the microstructure evolution during solidification involving nucleation and growth of the grains. On the basis of this CA-FEM method，the effects of the main parameters involving pouring temperature， casting speed and pool height on the characteristic of solidification microstructure such as grain size and orientation can be quantitatively clarified by numerical simulation， which can provide the theoretical basis for the optimization of the processing parameters and the control of the solidification structure.
Phase field simulation on sideplates formation in Ti-6Al-4V alloy
Authors: Wang Gang  , Xu Dong-Sheng  , Yang Rui  ,   中国科学院金属研究所，沈阳  110016
Published: December 2020

Ti-6Al-4V is a typical α+β titanium alloys. It presents the diversiform microstructures and thus various properties under different heat-treatment regimes and thermomechanical conditions. The thorough understanding of the formation mechanisms and the evolution rules of different microstructures is crucial to the optimization of the alloys. In this paper, the formation and the evolution of sideplates in Ti-6Al-4V alloy are simulated by using phase field method, with the thermodynamics and the mobility databases used as the input of the phase field model and the primary α phase assumed to exist at the grain boundary. The simulation results show that under a certain condition the grain boundary α phase can grow into β matrix and form sideplates, and that the morphology of α colony is related to the interfacial energy anisotropy. The grain boundary orientation has a strong effect on the sideplate structure. In addition, the heat-treatment temperature can also change the morphological features of sideplates. Higher temperature can slow down the growth of sideplates and result in wider sideplate spacing as well.
First principles study of neutral and charged small tungsten clusters
Authors: Xu Yong  , Wang Xian-Long  , Zeng Zhi  ,   中国科学院固体物理研究所材料物理重点实验室，合肥  230031
Published: December 2020

Geometries of anionic, neutral and cationic small tungsten clusters Wn （n=3—6） are studied by the first principles method based on the density functional theory. For each of clusters studied, a number of low-lying states with specific geometries are found and some possible candidates for the global minimum are determined. It is found that all global minimum candidates have relatively low spins: singlet or triplet for the neutral clusters, and doublet or quartet for the ionic clusters. When n>3, the clusters undergo a transition from two-dimensional structure to three-dimensional structure, which is not the same as sliver clusters. In order to determine the most promising global minimum candidates for anionic clusters, the photoelectron spectra are simulated and the vertical detachment energy is calculated. All results obtained are in good agreement with available experimental data.
Effects of gauge transformations on symmetries of Birkhoffian system
Authors: Ding Guang-Tao  ,   安徽师范大学物理与电子信息学院，芜湖  241000
Published: December 2020

The effects of gauge transformation on Noether symmetry, Lie symmetry and Mei symmetry of a Birkhoff system are studied. Under certain conditions, the system can keep its Noether symmetry and conserved quantity. The Lie symmetry and Hojman conserved quantity of the system will still remain unchanged. The Mei symmetry and a new-type conserved quantity of the system may very, and the conditions under which the Mei symmetry and the new-type conserved quantity will remain are obtained. An example is given to illustrate the application of the results.
Birkhoff symmetries and conserved quantities of generalized Birkhoffian systems
Authors: Zhang Yi  ,   苏州科技学院土木工程学院，苏州  215011
Published: December 2020

The problem of Birkhoff symmetry for generalized Birkhoffian systems is studied, and the corresponding conserved quantities are given. A theorem known for nonsingular equivalent Lagrangians is generalized to the generalized Birkhoffian systems. We prove that under certain conditions the matrix Λ, which is related with the generalized Birkhoffian equations obtained from two groups of dynamical functions B,Rμ,Λμ and B,Rμ,Λμ, has the property that the traces of all its integer powers are the conserved quantities of the system. An example is given to illustrate the application of the results.
Lagrange symmetries and conserved quantities for nonholonomic systems of non-Chetaev’s type
Authors: Zhang Yi  , Ge Wei-Kuan  ,   (1)湖州师范学院物理系,湖州  313000; (2)苏州科技学院土木工程学院，苏州  215011
Published: December 2020

This paper focuses on Lagrange symmetries and conserved quantities for nonconservative mechanical systems with nonholonomic constraints of non-Chetaev's type. The definition and criterion of Lagrange symmetry of the systems are given. The conditions under which a Lagrange symmetry can lead to a new conserved quantity（first integral)are obtained and the form of the new conserved quantity（first integral)is presented. Two examples are given to illustrate the application of the results.
Thermal particles model and radiation power of static spherically symmetric black holes
Authors: Meng Qing-Miao  , Jiang Ji-Jian  , Wang Shuai  ,   菏泽学院物理系,菏泽  274015
Published: December 2020

Using the thermal particles model of the static spherically symmetric black holes, the thermal radiation laws of the black hole are studied. When η takes the value of inherent thickness, the following results can be obtained. For all Schwarzschild black holes, the radiation power are the same, and the radiation energy flux on the event horizon is inversely proportional to the square of the black hole mass. While the radiation energy flux received by the observer far away from the black hole is inversely proportional to the square of the distance between the observer and the black hole. For Reissner-Nordstrm black holes, the radiation energy flux and the radiation power on the event horizon are not only related to the black hole mass, but also the charge of black holes. For fixed values of η, m and Q, the radiation energy flux received by the observer is also inversely proportional to the square of the distance between the observer and the black hole. For extreme Reissner-Nordstrm black holes, the radiation energy flux and the radiation power are all equal to zero.
The high temperature weak degeneration effect of charged particle system in two external field
Authors: Sun Yan-Qing  , Huang Chao-Jun  , Long Shu-Ming  , Liu Ya-Feng  , Yin Ji-Wu  ,   陕西理工学院物理系,汉中  723001
Published: December 2020

In light of the semiclassical statistical theory and method proposed by Thomas-Fermi, this paper conducts a research of the thermodynamic properties of charged particle system restricted by the homogeneous electric and the resonance field. Based on the derivation of the quantum state density of the charged particle system under the condition of high temperature and weak degeneration, the analytic formula of its chemical potential, internal energy and heat capacity is calculated, follow by a detailed analysis of the influence of the two fields on the chemical potential, internal energy and heat capacity. It is finally concluded that the two external fields exert a high temperature and weak degeneration effect on the charged particle system.
Sliding mode variable-structure control of chaos in direct-driven permanent magnet synchronous generators for wind turbines
Authors: Yang Guo-Liang  , Li Hui-Guang  ,   燕山大学电力电子节能与传动控制河北省重点实验室，秦皇岛  066004
Published: December 2020

The directly driven wind turbine with permanent magnet synchronous generator （D-PMSG） is investigated. Its mathematical model is deduced and chaotic behaviors is demonstrated while its parameters have a certain range of values or under certain working conditions. A sliding mode variable structure method for controlling chaos in D-PMSG is presented, and realized through controlling pitch angle β. In view of the non-linear property and parameter changing characteristic, etc. for wind turbine, and based on the mechanism of the wind turbine, this paper obtained the wind turbines linear model at a certain condition point under some assumptions, and then proposed the sliding model control strategy by taking full use of the SMCs non-sensitivity merit towards the model error and the parameter change as well as exterior disturbance. the simulation result indicates that the proposed control plan is effective, the control property of response is obtained quickly and the system also has good robustness, and is suitable for uncertain parameter in the system. Research results may have value for D-PMSG chaos control.
Fractal characterization for subharmonic motion of completely inelastic bouncing ball
Authors: Jiang Ze-Hui  , Zhao Hai-Fa  , Zheng Rui-Hua  ,   哈尔滨工业大学物理系，哈尔滨  150001
Published: December 2020

The motion of a completely inelastic ball dropped vertically on the vibrating table will undergo a series of subharmonic bifurcations, controlled solely by the normalized vibration acceleration. It has been shown that the bifurcation diagram for the ball’s motion consists of almost equally spaced dense regions, in which the bifurcation behavior is sensitively dependent on the control parameter. The dense regions have complex interior geometrical structures. Here they are treated as fractal entities, and the fractal dimension for each of them is calculated. It is shown that the magnitude of the fractal dimension gradually increases, approaching a constant around 1.785.
Calculation of positron lifetime of single crystals of elements of the periodic table with the theory of local density approximation
Authors: Chen Xiang-Lei  , Kong Wei  , Du Huai-Jiang  , Ye Bang-Jiao  ,   中国科学技术大学近代物理系,合肥  230026
Published: December 2020

On the basis of local density approximation, superposed-neutral-atom model and the finite-difference method （SNA-FD） are used to calculate the positron bulk lifetime and positron monovacancy lifetime in crystals of elements of the periodic table. The distribution of positron wavefunction and positron annihilation rate are analyzed. The calculated results of positron bulk lifetime in elementary substance agree well with the experiment results in literatures, which shows that the method of SNA-FD is an effective method in the study of positron annihilation in elementary substance.
Research on tunable erbium-doped ring fiber laser based on a high-birefringence Sagnac loop: theory and experiment
Authors: Wang Jing  , Zheng Kai  , Li Jian  , Liu Li-Song  , Chen Gen-Xiang  , Jian Shui-Sheng  ,   北京交通大学光波技术研究所，北京  100044
Published: December 2020

A simple erbium-doped ring fiber laser based on a high-birefringence Sagnac loop filter is proposed. The Sagnac is composed of a polarization controller （PC） and a polarization-maintaining fiber （PMF）. The effect of PC and PMF on tunable laser is analyzed in theory. In experiment， the single， double and multiple wavelength lasers are obtained by adjusting the PC. The interval of wavelength varies with the length of PMF. The experimental results are in good agreement with the theorefical analysis. In experiment the stable laser output with 20% slope efficiency， 0.016 nm 3 dB line-width， 0.097 nm 30 dB line-width and 40 dB SMSR was obtained.
Focusing property of two-dimensional photonic crystals with ring-shaped air holes
Authors: Kong Ling-Kai  , Zheng Zhi-Qiang  , Feng Zhuo-Hong  , Li Xiao-Yan  , Jiang Cui-Hua  , Ming Hai  ,   (1)福建师范大学物理与光电信息科技学院，福州  350007; (2)武警福州指挥学院，福州  350002; (3)中国科学技术大学物理系，合肥  230026
Published: December 2020

Imaging properties of two-dimensional photonic crystal slab lens consisting of a triangular lattice of ring-shaped air holes in a high-refraction-index dielectric medium have been studied. The results calculated by the plane wave expansion method （PWE） and the finite-difference time-domain method （FDTD） show that the effective index n=-1 can be realized in this structure. A perfect image can be obtained by increasing the inner radius of ring-shaped holes from 0 to 0.13a with the outer radius 0.4a at the normalized frequency 0.3（a/λ）. Based on the result of normalized frequency with effective refraction index -1 versus inner radius of ring-shaped holes we theoretically analyzed the effects of structure parameters to equifrequency contours of respective normalized frequency and imaging properties.
Coupling characteristics of dual-core high birefringence photonic crystal fibers
Authors: Fu Bo  , Li Shu-Guang  , Yao Yan-Yan  , Zhang Lei  , Zhang Mei-Yan  , Liu Si-Ying  ,   燕山大学理学院，亚稳材料制备技术与科学国家重点实验室，秦皇岛  066004
Published: December 2020

A kind of dual-core high birefringence photonic crystal fibers （DHB-PCFs） has been proposed in this paper. The birefringence， coupling length and dispersion characteristics of DHB-PCFs have been studied by multipole method using mode coupling theory. It is found that the birefringence of DHB-PCF with pitch 1.2 μm and air-hole diameter 1.0 μm is 1.24×10-2 in optical communication band of 1.55 μm wavelength. Correspondingly， dual-core coupling lengths are 21.6 μm and 24.3 μm for x-polarized mode and y-polarized mode， respectively. The DHB-PCF with high degree of polarization and very short coupling length is useful for manufacturing minitype photonic apparatus.
Discrete element method simulation on the force chains in the two-dimensional granular system under gravity
Authors: Yi Chen-Hong  , Mu Qing-Song  , Miao Tian-De  ,   (1)兰州大学土木工程与力学学院力学系，兰州  730000; (2)中国工程物理研究院流体物理研究所冲击波物理与爆轰物理实验室，绵阳  621900
Published: December 2020

The discrete element method is used to research the distribution of forces within the two-dimensional granular system under gravity. The force chains among the particles are generated according to the magnitudes of the forces. Then the simulation results are compared with the well-known q-model，α-model and experimental results obtained through the photoelastic test under the same conditions. According to the computational solution， we conclude that the simulation results are similar to the experimental results are some what different from the two probability models. In addition， we also obtained that the probability distribution of the force is very uneven. The probability of the large force decays exponentially and the distribution of the force chains takes on a fractal character.
Effect of exit Reynolds number on self-preservation of a plane jet
Authors: Mi Jian-Chun  , Feng Bao-Ping  , Deo Ravinesh C  , Nathan Graham J  ,   (1)School of Mechanical Engineering,The University of Adelaide,South Australia 5005,Australia; (2)北京大学工学院及湍流与复杂系统研究国家重点实验室,北京  100871; (3)北京大学工学院及湍流与复杂系统研究国家重点实验室,北京  100871；School of Mechanical Engineering,The University of Adelaide,South Australia 5005,Australia
Published: December 2020

We investigated in experiment the effect of exit Reynolds number on self-preservation of a turbulent plane jet. Centerline velocity statistics were measured in plane jets issuing from the same nozzle but， respectively， with seven Reynolds numbers varying between Re = 4，582 and Re = 57，735， where Re ≡ Uj h/ν（Uj being the momentum-averaged exit mean velocity， h the slot height and ν　the kinematic viscosity）. All measurements were conducted using single hot-wire anemometry and over an axial distance （x） of 40　h. These measurements revealed a significant Re-dependence of either the mean or turbulent flow field.　As Re increases， the pace of the jet development decreases and， as a result， both the mean and turbulent properties reach their self-preserving states over a longer downstream distance （x）.　The centerline integral scale L　for all jets grows linearly with x and the growth rate decreases as Re is increased. It is also found that the local Reynolds number ReL scales with x as ReL∝x1/2. The study suggests that differences of the self-preserving states observed may be related to the differences in the underlying turbulence structures in the near field of the seven jets.
Phonon spectra and specific heat calculation of single wall carbon nanotube
Authors: Wu Yan-Zhao  , Xie Ning  , Liu Jian-Jing  , Jiao Yong-Fang  ,   天津科技大学理学院,天津  300222
Published: December 2020

In this paper, the phonon spectra of infinite length single-wall carbon nanotubes are calculated based on the force constant model. The dependence of specific heat on the tube diameter and temperature is discussed. It is found that the specific heat will increase with increasing temperature and In this paper, the phonon spectra of infinite length single-wall carbon nanotubes are calculated based on the force constant model. The dependence of specific heat on the tube diameter and temperature is discussed. It is found that the specific heat will increase with increasing temperature and diameter and approaches to a constant value. Also, the vibrational spectra of the finite length （5,5） carbon nanotube are calculated. The relationships between the vibrational frequency and length are presented for some particularly modes.diameter and approaches to a constant value. Also, the vibrational spectra of the finite length （5,5） carbon
Study on the thermal stability of carbon nanotubes by simulation
Authors: Zhu Ya-Bo  , Bao Zhen  , Cai Cun-Jin  , Yang Yu-Jie  ,   (1)中国矿业大学材料科学与工程学院,徐州  221008; (2)中国人民解放军徐州空军学院,徐州  221000
Published: December 2020

Tight-binding molecular dynamics was used to simulate the thermal behavior of carbon nanotubes （CNTs） in this paper. A few kinds of single wall CNTs （SWCNTs） and double wall CNTs （DWCNTs） were studied during the simulation experiment at temperatures of 300—4000 K and the pressure of 1 atm. The results showed that the chiral SWCNTs have higher thermally stability than the armchair and zigzag type, and that the bigger the nanotube diameter is, the more stable the nanotube stucture is for those with the same chiral angles. The DWCNTs with at least one chiral structured wall are more stable than the others, but that with two zigzag walls were damaged badly, which also gives support to the study about SWCNT thermo-stability. One factor to describe CNTs in connection with their thermo-stability was proposed, and some data were theoretically analyzed based on carbon bond structures.
Martensitic transformation and magnetocaloric effect in Ni-Co-Mn-Sn Heusler alloy
Authors: Zhang Hao-Lei  , Li Zhe  , Qiao Yan-Fei  , Cao Shi-Xun  , Zhang Jin-Cang  , Jing Chao  ,   上海大学物理系，上海  200444
Published: December 2020

The crystal structure and phase transition in Ni50-xCoxMn38Sn12（x=1, 2, 4, 6, 8） Heusle alloys were investigated by means of structure analysis and magnetism measurements. The results show that the doping of the Co atom affects neither the original structure of Ni-Mn-Sn Heusler alloys, nor the ferromagnetic interaction strengthens in the austenitic state. Furthermore, based on Maxwell equation, the magnetic entropy change （ΔSM） of three samples （x=2, 4, 6） has been calculated. A large magnetic entropy change of 37.09 J/kg K at about 320 K for a magnetic field change of 50 kOe is obtained in Ni48Co2Mn38Sn12 alloy.
Effect of hydrogenation on the luminescence evolution of GaN under low energy electron beam irradiation
Authors: Wang Yan  , Shen Bo  , Dierre Benjamin  , Sekiguchi Takashi  , Xu Fu-Jun  ,   (1)Advanced Electronic Materials Center,National Institute for Materials Science,Namiki 1-1,Tsukuba 305-0044,Japan; (2)北京大学物理学院人工微结构和介观物理国家重点实验室，北京  100871
Published: December 2020

Luminescence evolution of GaN irradiated by low energy electron beam before and after hydrogenation has been investigated by means of cathodoluminescence （CL）, in connection with the diffusion properties of hydrogen in GaN. It is found that under low energy electron beam irradiation, the band to band emission of GaN shows a decrease before hydrogenation, while it shows an initial increase and a subsequent decrease after hydrogenation, and the decrease after hydrogenation is relatively weak. Moreover, there is no luminescence recovery in 20 hours after the first irradiation after hydrogenation. The experimental results indicate a luminescence enhancement effect of hydrogen by passivating certain defects in GaN. However, such effect must be realized by overcoming high migration barrier in GaN. In the experiments, low energy electron beam supports enough energy to hydrogen to diffuse and passivate defects in GaN. These results show strongly the importance of diffusion of hydrogen in the passivation process in semiconductors.
Tunneling coefficient and persistent current in triple-arm quantum ring with double δ　barrier
Authors: Du Jian  , Wang Su-Xin  , Yang Shu-Min  ,   承德民族师范高等专科学校物理系,承德  067000
Published: December 2020

In this paper tunneling coefficient and persistent current in triple-arm quantum ring with double δ　barrier is investigated. The results show that the tunneling coefficient and persistent current show oscillating behavior with the length of the semiconductor quantum ring increasing. The tunneling coefficient and persistent current depend not only on spin orientation of tunneling electrons but also on the ferromagnetic magnetization direction. When the size of the quantum ring is fixed, the tunneling coefficient and persistent current will generate isochronal oscillation with the increasing of the AB magnetic flux. Furthermore, δ　barrier and Rashba spin-orbit interaction have different effect on the properties of the tunneling coefficient and persistent current.
High performance white organic light-emitting devices based on a novel red fluorescent dye 3-(dicyanomethylene)-5, 5-dimethyl-1-(4-dimethylamino-styryl) cyclohexene
Authors: Wen Wen  , Wang Bo  , Li Lu  , Yu Jun-Sheng  , Jiang Ya-Dong  ,   (1)电子科技大学光电信息学院,电子薄膜与集成器件国家重点实验室，成都  610054; (2)中国人民解放军63916部队，北京  100142
Published: December 2020

White organic light-emitting devices based on a red fluorescent dye 3-（dicyanomethylene）-5, 5-dimethyl-1-（4-dimethylamino-styryl） cyclohexene（DCDDC） were fabricated and investigated. Two kinds of devices were processed using ultrathin technology and doping technology. The structures of the devices were as followed: 1） indium-tin oxide （ITO）/N, N′-diphenyl-N, N′-bis（1-naphthyl-pheny1）-1, 1′-biphenyl-4, 4′-diamine （NPB）/4, 4′-bis（2, 2′-diphenylvinyl）-1, 1′-diphenyl （DPVBi）/tris（8-quinolinolato） aluminum （Alq3）/DCDDC/Alq3/Mg:Ag; 2） ITO/NPB /Alq3:DCDDC/NPB/2, 9-dimethyl-4, 7-diphenyl-1, 10-phenanthroline （BCP）/Mg:Ag. The luminescence and efficiency characteristics of these two devices were measured and compared. The results showed that both devices A and B exhibited white light consisting of RGB three primary colors. Moreover, device A had a turn on voltage of 4 V, a maximum power efficiency of 2.4 lm/W at 5.5 V and a maximum luminance of 16690 cd/m2 at 185 V. Also, pure white emission with Commissions Internationale De L’Eclairage （CIE） coordinates near （0.330. 0.300） having a slight variation of （-0.020, +0.002） in a wide range of voltages was observed. In contrast, devices B showed a turn on voltage of 5 V, a maximum power efficiency of 1.4 lm/W at 5.5 V and a maximum luminance of 12580 cd/m2 at 17 V. The CIE coordinates had a red shift as the voltage increased and then kept near the optimum white point of （0.33, 0.33） over 9 V. It was found that the difference in characteristics of these two devices was dependent on the variation of charge recombination zone. To be specific, it was due to the direct charge trapping effect of DCDDC ultrathin layer and the properties of incomplete energy transfer in Alq3:DCDDC doping system.
Optical constants of sol-gel derived TiO2 films characterized by spectroscopic ellipsometry
Authors: Wang Xiao-Dong  , Shen Jun  , Wang Sheng-Zhao  , Zhang Zhi-Hua  ,   同济大学，波耳固体物理研究所，上海市特殊人工微结构材料与技术重点实验室，上海  200092
Published: December 2020

Nanostructured titanium oxide films were deposited on silicon substrate via sol-gel dip coating method with tetrabutyl titanate as precursor. With reflective spectroscopic ellipsometry, the ellipsometric parameters Ψ and Δ of TiO2 films were measured. Then, with the Cauchy model, the ellipsometric data were fitted, and both the thickness and the optical constants at 380—800 nm wavelength of the films were obtained. A comparison was made between the reflectance of the films derived with the spectrophotometer and the simulated results. Meanwhile, the thickness of the films was calculated by interference method. Moreover, with the atomic force microscopy the surface microstructures of the films annealed at different temperatures were observed, and the relationship between the surface microstructures and optical constants of films was further discussed. The results showed that Cauchy model works well in describing the dispersion relationship of the TiO2 films, and the variation rules of optical constants （the refractive index, the extinction coefficient） with wavelength were obtained. The optical constants of the films were related with the microstructure. Those simulated reflectance spectrum accorded well with the measured result. And with a deviation of only 25%, the calculated value of the thickness was in accordance with which was obtained by spectroscopic ellipsometry.
Diagnosis of vertical helicity, divergence flux and their extensions in heavy-rainfall events
Authors: Ran Ling-Kun  , Chu Yan-Li  ,   (1)中国科学院大气物理研究所，北京  100029; (2)中国气象局北京市城市气象研究所，北京  100089
Published: December 2020

On the basis of vertical helicity, we define three parameters, namely, the divergence flux, moisture vertical helicity and moisture divergence flux. The parameters are calculated with NCEP/NCAR real analysis data in the two heavy-rainfall events occurring in China. The result shows that the parameters are closely related to the precipitation systems since they are capable of describing the typical vertical structure of dynamical and moisture fields. The anomalies of the parameters vertically integrated well correspond with the observed 6h-accumulated surface rainfall. This suggests that the parameters are capable of predicting and indicating the development and propagation of precipitation systems. The calculation with the 6-hour forecasting data of NCEP-GFS shows that the parameters have the ability of predicting precipitation and the moisture divergence flux is significantly beller than the other parameters in predicting precipitation.