bluuebunny/crossref_metadata_2025 huggingface dataset:
Failure analysis of GaN-based Light-emitting diode with hole vertical structure
Authors: Fu Min  , Wen Shang-Sheng  , Xia Yun-Yun  , Xiang Chang-Ming  , Ma Bing-Xu  , Fang Fang  ,   State Key Laboratory of Luminescent Materials and Devices, South China University of Technology, Guangzhou 510640, China;,   Gold Medal Analytical and Testing Group, Guangzhou 511300, China
Published: December 2020

Light-emitting diode (LED) failure mechanism plays an important role in studying and manufacturing LEDs. In this paper, X-ray perspective instrument is used to carry out the non-invasive and real-time X-ray imaging detection of the representative LED packaging products purchased from 5 Chinese companies. A large number of the welded voids are founded in the thermal pad and the void ratio of thermal pad, which represents the ratio of void area to pad area, is more than 30% for all samples. 1 W warm white light LED of GaN-based vertical via structure is selected to study the mechanism of short-circuit invalidation. The method is carried out by the following steps. Firstly, the surface morphologies of failure samples are compared with those of normal samples by visual observation. Secondly, antistatic electric capacity testing instrument is used to detect the existences of the electrical parameter abnormalities of the failure of non-short-circuit samples. Thirdly, decapsulations are operated on samples by using Silica gel dissolving agent. And the microtopographies of the samples are characterized by optical microscope, energy dispersive spectrometer and scanning electron microscopy. Then the cross-sectional morphologies of failure samples are observed. The failure mechanism can be drawn from the characterizations mentioned above. The study shows that the failure mechanism of the vertical structure of GaN-based vias is that the existences of voids in the Ni-Sn alloy back gold layer and solid-crystal layer reduce the interface bonding strength and thermal conductivity of the LED chip. The heat building-up leads to thermal expansion of the air inside the voids, which increases the electrical stress and thermal stress distribution at the LED chip vias. Long-term heat accumulation and higher electrical stress in the through-hole region, where the chip current density is greatest, lead to the crack and break of GaN epitaxial layer, which is so brittle and fragile, around the through-hole region. It can eventually lead to short-circuit of PN junction and then failure of LED. Back gold layer is the heat-conductive and electric-conductive channel of LED. The concentrations of thermal stress and electrical stress caused by voids in the back gold layer further lead to the uneven current distribution on the chip. This is the main reason why GaN epitaxial layer cracks and breaks. Voids in the back gold layer and solid-crystal layer are the direct and indirect causes of LED short-circuit failure, respectively. Therefore, the packaging process should be standardized to avoid the void occurrence, based on the reasons why voids exist. It can finally improve reliability of LED.
Online real-time 7 Gbit/s physical random number generation utilizing chaotic laser pulses
Authors: Zhao Dong-Liang  , Li Pu  , Liu Xiang-Lian  , Guo Xiao-Min  , Guo Yan-Qiang  , Zhang Jian-Guo  , Wang Yun-Cai  ,   Key Laboratory of Advanced Transducers and Intelligent Control System, Ministry of Eduction and Shanxi Province, Taiyuan University of Technology, Taiyuan 030024, China;,   Institute of Optoelectronic Engineering, College of Physics and Optoelectronics, Taiyuan University of Technology, Taiyuan 030024, China
Published: December 2020

Random numbers are used to encrypt the information in the field of secure communications. According to one-time pad theory found by Shannon, the absolute security of the high-speed communication requires the ultrafast reliable random numbers to be generated in real-time.
Using complex algorithms can generate pseudorandom numbers, but they can be predicted due to their periodicity. Random numbers based on physical stochastic phenomena (such as electronic noise, frequency jitter of oscillator) can provide reliable random numbers. However, their generation rates are at a level of Mbit/s typically, limited by the bandwidth of traditional physical sources.
In recent years, high-speed physical random number generation based on chaotic laser has attracted much attention. Common methods of extracting random numbers are to sample and quantitate the chaotic signal in electronic domain with a 1-bit or multi-bit analog-to-digital converter (ADC) triggered by an RF clock and then post-process the original binary sequences into random numbers. However, the large jitter of the RF clock severely restricts the speed of ADC. Moreover, the existence of the subsequent post-processing process put a huge challenge to how the synchronization is kept among all the devices (e.g., XOR gates, memory buffers, parallel serial converters) by using an RF clock. Thus, to our knowledge, the fastest real-time speed of the reported physical random number generator is less than 5 Gbit/s.
In this paper, we propose a novel method of generating the real-time physical random numbers by utilizing chaotic laser pulses. Through sampling the chaotic laser in all-optical domain by using a mode-locked pulsed laser, chaotic laser pulse sequences can be obtained. Then, real-time physical random numbers are obtained directly by self-delay comparing the chaotic pulse sequences with no need of RF clock nor any post-processing.
Furthermore, a proof-of-principle experiment is carried out, in which an optical feedback chaotic semiconductor laser is employed as an entropy source. Experimental results show that the real-time random number sequences at rates of up to 7 Gbit/s can be achieved. The real-time speed is mainly limited by the bandwidth of the applied chaotic signal. If the chaotic laser with a higher bandwidth is adopted, the real-time generation rate can be further enhanced.
Quantitative analysis of chromium in vegetable oil by collinear double pulse laser-induced breakdown spectroscopy combined with dual-line internal standard method
Authors: Wu Yi-Qing  , Liu Jin  , Mo Xin-Xin  , Sun Tong  , Liu Mu-Hua  ,   Key Laboratory of Biological Optics-Electric Technique and Application, Jiangxi Agricultural University, Nanchang 330045, China
Published: December 2020

The safety quality of vegetable oil is very important for human life. The objective of this research is to determine the content of heavy metal chromium (Cr) in each of three kinds of vegetable oils (soybean oil, peanut oil, and corn oil) quantitatively by collinear double pulse laser-induced breakdown spectroscopy (DP-LIBS). In this study, a total of 24 vegetable oil samples are prepared, and each kind of vegetable oil has 8 samples. Fortune paulownia wood chips with a diameter of 20 mm and thickness of 3 mm are placed into the vegetable oil samples to collect the Cr element. After that, the 24 samples (fortune paulownia wood chips that have enriched Cr element) are dried in the oven, and the LIBS spectra of samples are acquired in a wavelength range of 206.28-481.77 nm by a dual-channel high-precision spectrometer. The spectral line of Cr (Cr I 425.39 nm) is chosen as the quantitative analysis spectral line, while CN (CN 421.39 nm) molecular spectral line, Ca (Ca I 422.64 nm) atomic spectral line and the sum of their spectral line intensities are selected as the internal standard lines. Then the calibration curves of Cr are obtained by the basic calibration method, single-line internal standard method (CN 421.39 nm or Ca I 422.64 nm as the internal standard line) and dual-line internal standard method (CN 421.39 nm and Ca I 422.64 nm as the internal standard lines). Finally, the validation samples are used to verify the performances of the calibration curves of Cr element. The results show that the values of fitting degree (R2) of the basic calibration curves for three kinds of vegetable oils are all above 0.97, and the relative errors of validation samples with low concentration are bigger than those with high concentration. The values of (R2) of calibration curves obtained by single-line internal standard method are above 0.98, and the relative errors of validation samples are lower than those obtained using basic calibration method. And the values of (R2) of calibration curves for soybean oils, corn oils and peanut oils are 0.995, 0.992 and 0.996, respectively, with using dual-line internal standard method. The relative errors between the two validation samples are 12.8%, 1.73%, 9.19%, 6.05% and 6.23%, 6.69%, respectively. And the results obtained by the dual-line internal standard method are better than those obtained by the basic calibration method and single-line internal standard method. Thus it can be seen that the dual-line internal standard method can reduce the error of quantitative analysis effectively and improve the predicting ability of LIBS technique for Cr element detection in vegetable oil.
Analysis of mode radiation characteristics in a non-magnetized cold plasma column
Authors: Li Wen-Qiu  , Wang Gang  , Su Xiao-Bao  ,   Institute of Electronics, Chinese Academy of Sciences, Beijing 100190, China;,   University of Chinese Academy of Sciences, Beijing 100049, China
Published: December 2020

The electromagnetic surface waves which propagate along a non-magnetized cold plasma column have a great value in the application of plasma antenna. In this paper, the dispersion properties, the transmission power distributions, and the radiation patterns for these electromagnetic surface waves which have lower frequencies than the electron plasma frequency are analyzed numerically. Based on Helmholtz equation, the specific expression of dispersion equation is derivedby the field matching method, then the exact values of complex axial wave vector kz under different wave frequencies are obtained by solving the transcendental dispersion relation. Using the specific value of kz obtained above, the exact expressions of transmission power profile in the plasma column and field profiles in the three regions, i.e., plasma, dielectric, and free space are derived, respectively. Finally, based on the complex form of electric conductivity that is derived from the Boltzmann-Vlasov equation with Krook term and the complex axial wave vector kz obtained above, the influence of the parameter pea/c on phase property, and the dependence of radiation pattern and transmission power profile on wave frequency of the non-magnetized cold plasma column in a cylindrical dielectric tube system are analyzed. The results show that the electron plasma frequency has a significant influence on the phase property, which is evidently confirmed by the fact that the propagation velocities of the three modes m=0, m=1 and m=2 are all near to the light speed when the value of parameter pea/c gradually increases. Meanwhile, through the investigation of the radiation patterns for the three modes, an important conclusion is that the radiation pattern has evident dependence on wave frequency. While the radiation direction of the main lobe is in the axial direction for the m=1 mode, the m1 modes each have an angle between the radiation direction of the main lobe and the axial direction, this crucial conclusion is in good agreement with the theoretical calculation results obtained from other researcher. Further, we find that with the increase of wave frequency, the angle between the main lobe radiation direction and the axial direction turns smaller for each of m=0 and m=2 modes, and the width of main lobe gradually narrows for each of all modes, and the amplitude of the first side lobe becomes notable for each of m=0 and m=2 modes and ignorable for the m=1 mode. Also, the transmission power increases as the wave frequency increases for each of all modes. These theoretical calculation results provide a detailed theoretical reference for the designing of plasma stealth and high-precision requirements of plasma antenna design, and giving a comprehensive optimization guidance for the modulation of plasma antenna.
First-principle study of initial irradiation damage in aluminum
Authors: Gao Yun-Liang  , Zhu Yuan-Jiang  , Li Jin-Ping  ,   Department of Nuclear Engineering, Rocket Force University of Engineering, Xi'an 710025, China;,   State Key Laboratory of High Temperature Gas Dynamics, Institute of Mechanics, Chinese Academy of Sciences, Beijing 100190, China
Published: December 2020

Aluminum and its alloy play an important role in nuclear industry, where irradiation damage continually occurs and significantly affects the structures and physical properties of materials: especially long-term irradiation can lead to the formation of helium bubbles and holes in the substrate. During the initial irradiation damage, point defects are the major defects.Studying the point defects is of great significance for understanding the irradiation damages and the mechanism of defect development. In this paper, three possible intrinsic point defects (Al vacancies, Al tetrahedral interstitials and Al octahedral interstitials) and three possible helium defects (substituted He, He tetrahedral interstitials and He octahedral interstitials) produced by initial irradiation damage in aluminum are studied by the first-principle plane wave pseudo-potential method within the framework of density functional theory. The formation of the defects and their effects on the stability of the system are compared through crystal structure, formation energy and binding energy. Besides, the electronic mechanism is analyzed from the point of view of density of states (DOS), partial density of states (PDOS), electron density difference and charge populations. It is shown that for the same type of defects, the greater the lattice distortions, the lower the stability of system is and the more difficult the formation of defects. For the formation of the same type of defects, the extent of difficulty in forming defects is in the following order: vacancies (substituted atoms), octahedral interstitials, and tetrahedral interstitials. However, for the same sites, although the intrinsic defects cause greater lattice distortions than the helium defects, they are in fact relatively easier to form, which indicates that the difference between the bonding performances of Al and He plays a leading role in determining the interaction between defects and the aluminum substrate. Besides, the results of binding energy and optimization show that interstitials readily combine with vacancies, and Al has stronger combining ability than He. On the whole, interstitials mainly exist in octahedral interstices, and both octahedral Al and He can cause some electrons to transfer to higher energy levels, lead to some weakening of the covalent interaction between atoms nearest to the interstitials, and eventually reduce the stability of the system. And further study shows that the bond between interstitial Al and its nearest atom features a strongly covalent state, while the interaction between He and its nearest atom is dominated by van der Walls force with weak ionic bond, which accounts for the lower stability of system doped with helium defects.
Preperetions of bi-layer and multi-layer graphene on copper substrates by atmospheric pressure chemical vapor deposition and their mechanisms
Authors: Li Hao  , Fu Zhi-Bing  , Wang Hong-Bin  , Yi Yong  , Huang Wei  , Zhang Ji-Cheng  ,   State Key Laboratory Cultivation Base for Nonmetal Composite and Functional Materials, Southwest University of Science and Technology, Mianyang 621900, China;,   Research Center of Laser Fusion, China Academy of Engineering Physics, Mianyang 621900, China
Published: December 2020

Chemical vapor deposition is widely utilized to synthesize graphene with controlled properties for many applications. And it is one of the most important methods for the preparation of graphene with high quality in large area. Cu substrate is most commonly used for the preparation of graphene in chemical vapor deposition. As is well known, the properties of graphene are greatly affected by the number of layers. However, the syntheses and mechanisms of bi-layer and multi-layer graphene on Cu substrates are still under debate. And how to make a breakthrough in realizing the controllable syntheses of bi-layer and multi-layer graphene on Cu substrates has become a direction for many researchers.
In this work, we report bi-layer and multi-layer graphene on Cu substrates prepared by atmospheric pressure chemical vapor deposition. Firstly, the Cu foil is placed on the quartz slides of the tube furnace and heated to 1000℃ with a rate of 15℃/min. After reaching 1000℃, the Cu foilis annealed for 2 h in a gas mixture of hydrogen (20 sccm) and argon (380 sccm). After that, the graphene growth is carried out at 1000℃ under an 80 sccm gas mixture of argon and ethanol. Then, the samples are cooled down to the room temperature with a rate of 100℃/min in a protection gas of hydrogen and argon, and then taken out of the furnace. The graphene is prepared on the Cu foils and finally transferred onto the SiO2/Si substrates.
The quality and number of layers of the as-produced graphene are assessed by field emission scanning electron microscopy (SEM), transmission electron microscopy (TEM), Raman spectroscopy, and optical microscopy. By tuning the graphene growth, the monolayer, bi-layer and multi-layer graphene with higer quality and better continuity are obtained. And the growth times of monolayer, bi-layer, and four-layers graphene are respectively 25, 40, and 60 s. And wefind that the graphene layer will be increased in the process of insulation. The growth mechanisms of bi-layer and multi-layer graphene on copper substrates by atmospheric pressure chemical vapor deposition are also discussed. There will be some indiffusible carbon atoms or radicals near the copper foil surface due to the small molecular diffusion mean free path under normal pressure. We suggeste that the bi-layer and multi-layer graphene grown on copper substrates by atmospheric pressure chemical vapor deposition is dominated by van der Waals epitaxial mechanism. This work provides a reference for improving the quality of chemical vapor deposition monolayer, bi-layer and multi-layer graphene.
Improved algorithm of spectral coarse graining method of complex network
Authors: Zhou Jian  , Jia Zhen  , Li Ke-Zan  ,   College of Science, Guilin University of Technology, Guilin 541004, China;,   School of Mathematics and Computing Science, Guilin University of Electronic Technology, Guilin 541004, China
Published: December 2020

Complex network as a key approach to understanding many complex systems, such as biological, chemical, physical, technological and social systems, is ubiquitous in nature and society. Synchronization of large-scale complex networks is one of the most important issues in network science. In the last two decades, much attention has been paid to the synchronization of complex dynamic networks, especially the meso-scale networks. However, many real networks consist of even hundreds of millions of nodes. Analyzing the synchronization of such large-scale coupled complex dynamic networks often generate a large number of coupled differential equations, which may make many synchronization algorithms inapplicable for meso-scale networks due to the complexities of simulation experiments. Coarse graining method can map the large-scale networks into meso-scale networks while preserving some of topological properties or dynamic charac-teristics of the original network. Especially, the spectral coarse-graining scheme, as a typical coarse graining method, is proposed to reduce the network size while preserving the synchronization capacity of the initial network. Nevertheless, plenty of studies demonstrate that the components of eigenvectors for the eigenvalue of the coupling matrix, which can depict the ability to synchronizing networks, distribute unevenly. Most of the components distribute concentrically and the intervals are small, while some other components distribute dispersedly and the intervals are large, which renders the applications of original spectral coarse graining method unsatisfactory. Inspired by the adaptive clustering, we propose an improved spectral coarse graining algorithm, which clusters the same or the similar nodes in the network according to the distance between the components of eigenvectors for the eigenvalue of network coupling matrices, so that the nodes with the same or the similar dynamic properties can be effectively clustered together. Compared with the original spectral coarse graining algorithm, this method can improve the accuracy of the result of clustering. Meanwhile, our method can greatly reduce algorithm complexity, and obtain better spectral coarse graining result. Finally, numerical simulation experiments are implemented in four typical complex networks: NW network, ER network, BA scale-free network and clustering network. The comparison of results demonstrate that our method outperforms the original spectral coarse graining approach under various criteria, and improves the effect of coarse graining and the ability to synchronize networks.
Traceable trans-scale heterodyne interferometer with subnanometer resolution
Authors: He Yin-Zhu  , Zhao Shi-Jie  , Wei Hao-Yun  , Li Yan  ,   State Key Laboratory of Precision Measurement Technology and Instruments, Department of Precision Instruments, Tsinghua University, Beijing 100084, China;,   Graduate School at Shenzhen, Tsinghua University, Shenzhen 518055, China;,   Beijing Aerospace Control Device Institute, Beijing 100854, China
Published: December 2020

In order to realize the traceable trans-scale displacement measurements with high resolutions in the fields of fundamental scientific research and ultra-precision machining, we demonstrate a trans-scale heterodyne interferometer with a sub-nanometer resolution, through assembling a compact iodine-stabilized laser at 532 nm. Using modulation transfer spectroscopy, the green laser is traced back to the transition line R(56)32-O(a10), which is one of the recommended spectral lines for meter redefinition. The Allan standard deviation of the laser frequency is 1.310-12 within an average time of 1 s. Compared with most He-Ne lasers, the green laser has a short wavelength and good stability, which leads to a higher resolution. We use two acoustic-optic modulators driven by a two-channel acoustic-optic driver sharing the same crystal oscillator to separate input beams spatially. The frequency of one beam is shifted by 80 MHz and the other is shifted by 82 MHz, which results in a beat frequency of 2 MHz. As a result, the nonlinearity caused by source mixing substantially is reduced. The phase noises of the fibers and two acoustic-optic modulators are well compensated. In order to minimize the difficulty in adjusting the optical path and the error of the measurement, we integrate the interferometry components and design a monolithic prism. The optical resolution of the interferometer reaches to /4. The experiment is carried out in a vacuum environment to reduce the influence of the refractive index of air. High-precision phase measurement technology is used to improve the accuracy of the interferometer. The errors of the interferometer can be classified as random and systematic errors. Random errors include the error from the frequency instability of the laser and the error due to environmental effects. Systematic errors include the phase measurement error and the nonlinearity error. To verify the performance of the interferometer, these errors must be evaluated. In a span of 100 mm, the measurement uncertainties caused by laser wavelength uncertainty, the air refractive index uncertainty, the phase measurement uncertainty and the nonlinearity error are 3 pm, 300 pm, 6.3 pm and 118 pm, respectively. Finally, the performance evaluation shows that the combined uncertainty of the interferometer reaches 322 pm in a span of 100 mm, which is mainly due to the refractive index of air. The heterodyne interferometer meets the requirements for traceable trans-scale measurement with a sub-nanometer resolution, which can be widely used in instrument calibration, length standard making, and geometric measurement.
Ductile and electronic properties of La-doped gamma-TiAl systems based on density functional theory
Authors: Song Qing-Gong  , Zhao Jun-Pu  , Gu Wei-Feng  , Zhen Dan-Dan  , Guo Yan-Rui  , Li Ze-Peng  ,   Institute of Low Dimensional Materials and Technology, College of Science, Civil Aviation University of China, Tianjin 300300, China;,   Sino-European Institute of Aviation Engineering, Civil Aviation University of China, Tianjin 300300, China
Published: December 2020

Because of the low density, high specific strength and excellent performance at high temperature, -TiAl based alloy has become a new generation of materials in the aeronautic field. However, its poor ductility at room temperature set a limitation to its wide applications. In this paper, the crystal structures, stabilities and ductilities of La-doped -TiAl systems are investigated by using first principles method based on density functional theory, in which Ti or Al is substituted by La and the impurity content values are 1.85 at.%, 2.78 at.%, 4.17 at.%, 6.25 at.%, 8.33 at.% and 12.5 at.%, respectively. The results show that all of the La-doped alloys have good energy stabilities, namely they can be prepared experimentally, when the impurity concentration x of system is less than or equal to 12.5 at.%. And the density of the La-doped system is less than 4.6 gcm-3. La doping induces the lattice parameters and the axial ratio of the alloy system to change. The axial ratio of La-doped system with low impurity concentration (x6.25 at.%) is closer to 1, which is very beneficial to improving the ductility of the materials. It is predicted that the system Ti11LaAl12 would have the best ductility among those of the investigated systems, for its axial ratio is the closest to 1. The electronic effect about the ductility of La-doped system is discussed through the comparisons of the populations, charge densities and densities between the states of systems Ti11LaAl12 and Ti12Al12. It is found that the system Ti11LaAl12 presents a state of electron redistribution in valence electron orbitals of Al and Ti due to an atom of titanium substituted with that of lanthanum. The charge numbers of Ti-d and Al-p orbitals and the numbers of electrons can be delocalized by reducing the p-d orbital hybridization. Thus, the intensity of p-d orbital hybridization is weakened, the resistance of dislocation movement is reduced, and the ductility of TiAl systems can be improved. Actually, the new electron redistribution shows different properties of some chemical bonds, in which some of covalent AlTi bonds are replaced by ionic AlLa bonds and some of covalent TiTi bonds are replaced by metallic TiLa bonds. Therefore, the covalent and directional properties of chemical bonds are reduced distinctly while the metallic properties of materials are strengthened. The average intensity of AlAl bonds decreases and those of AlTi and TiTi bonds are increased in the La-doped -TiAl system (Ti11LaAl12). As a result, the differences between the three kinds of chemical bonds diminish and the degree of isotropy of the crystal structure increases, which can greatly improve the ductility of -TiAl alloy.
Investigation on the large tensile deformation and mechanical behaviors of graphene kirigami
Authors: Han Tong-Wei  , Li Pan-Pan  ,   Faculty of Civil Engineering and Mechanics, Jiangsu University, Zhenjiang 212013, China
Published: December 2020

One of the main challenges in developing future stretchable nanoelectronics is the mismatch between the hard inorganic semiconductor materials and the ductility requirements in the applications. This paper shows how the kirigami architectural approach, inspired by the ancient Japanese art of cutting and folding paper applied on macroscale, might be an effective strategy to overcome this mismatch on nanoscale. In this work, the tensile large deformation and mechanical behaviors of armchair and zigzag graphene kirigami with rectangles and half circles cutting patterns are investigated based on classical molecular dynamics simulations. The effects of three non-dimensional geometric parameters that control the cutting patterns on the mechanics and ductility of graphene kirigami are also studied systematically. The results indicate that the enhancement in fracture strain can reach more than five times the fracture strain of pristine graphene. The defined three parameters can be adjusted to tailor or manipulate the ductility and mechanical behaviors of graphene. These results suggest that the kirigami architectural approach may be a suitable technique to design super-ductile two-dimensional nanomaterials and potentially expand their applications to other strain-engineered nanodevices and nanoelectronics.
Modification of the photocatalytic properties of anatase TiO2 (101) surface by doping transition metals
Authors: Su Qiao-Zhi  , Han Qing-Zhen  , Gao Jin-Hua  , Wen Hao  , Jiang Zhao-Tan  ,   School of Physics, Beijing Institute of Technology, Beijing 100081, China;,   State Key Laboratory of Multiphase Complex System, Institute of Process Engineering, Chinese Academy of Sciences, Beijing 100190, China
Published: December 2020

Exploring new types of photocatalysts and modifying the photocatalytic activity have attracted more and more extensive attention in many research fields. Anatase TiO2, a promising photocatalyst widely studied, can only absorb the ultraviolet light and thus only make little use of the power in visible light. Therefore, it is an urgent task to make theoretical and experimental investigations on the photocatalytic mechanism in anatase TiO2 and then improve its visible light response so as to utilize more visible light. Now, in the present paper, we carry out a systematic theoretical investigation on modifying the photocatalytic properties of the anatase TiO2 (101) surface via doping transition metal neutral atoms such as Fe, Ni, Pd, Pt, Cu, Ag, and Au by using the plane wave ultrasoft pseudopotential method of the density functional theory. The dependence of the macroscopic catalytic activity on electronic structure and optoelectronic property is uncovered by making a comparative analysis of the geometric structures, the electronic structures, and the optical properties of the undoped and doped anatase TiO2 (101) surfaces. Our numerical results show that doping certain transition metals can suppress the band gap or induce extra impurity energy levels, which is beneficial to improving the visible light response of the TiO2 (101) surface in different ways. In most cases, the new impurity energy levels will appear in the original band gap, which comes from the contribution of the d electronic states in the transition metal atoms. Moreover, the photocatalytic activity of the TiO2 (101) surface can be changed differently by doping different transition metal atoms, which is closely dependent on the bandgap width, Fermi energy, the impurity energy level, and the electron configuration of the outermost shell of the dopants. This research should be an instructive reference for designing TiO2 (101) photocatalyst and improving its capability, and also helpful for understanding doping transition metal atoms in other materials.
Trap distribution and direct current breakdown characteristics in polypropylene/Al2O3 nanodielectrics
Authors: Ma Chao  , Min Dao-Min  , Li Sheng-Tao  , Zheng Xu  , Li Xi-Yu  , Min Chao  , Zhan Hai-Xia  ,   State Key Laboratory of Electrical Insulation and Power Equipment, Xi'an Jiaotong University, Xi'an 710049, China;,   Technical Research Center, Xi'an Electric Research Institute Co. LTD., Xi'an 710077, China;,   Research and development Department, Xi'an XD Power Capacitor Co. LTD., Xi'an 710082, China
Published: December 2020

Polypropylene (PP) is widely used as capacitor films due to its better dielectric, mechanical, and thermal performance. In order to reduce the cost and size of capacitor, high energy density for PP dielectric is pursued. Since energy density is in quadratic proportion to direct current (dc) breakdown strength for linear dielectric, the enhancement of dc breakdown strength for PP dielectric is a primary choice to improve the energy density. Considering that the incorporation of nano-Al2O3 is an effective method to improve the dc breakdown strength for polymer, it is required to study the dc breakdown strength of PP/Al2O3 nanodielectric.
In order to explore the breakdown mechanism, PP/Al2O3 nanodielectrics with different nano-particle contents are prepared by melt blending, and the samples are prepared by hot pressing. Their microstructures are observed by scanning electron microscopic. Isothermal surface potential decay, bulk resistivity, and dc breakdown strength of the samples are also measured. The experimental results show that the energy and density of deep traps, bulk resistivity, and dc breakdown strength first increase and then decrease with the increase in nano-Al2O3 content. The maximum values are obtained at a filer content value of 0.5 wt%, where dc breakdown strength can be increased by about 27%. Based on interface model, the relation between microstructure and trap is investigated. In view of space charge breakdown theory, the mechanism of dc breakdown for PP/Al2O3 nanodielectric is explored by trap parameters. It is indicated that the interface can provide more deep traps in PP/Al2O3 nanodielectric, while the decrease in the energy and density of deep traps can be attributed to the overlap of interfaces in electrical double layer. The increase in the energy and density of deep traps makes more carriers trapped near the injecting contact, thus reducing the effective field for carrier injection due to the internal field generated by the trapped carriers. The reduction of carrier injection can moderate the distortion of field in PP dielectric, consequently, resulting in enhancing the dc breakdown strength.
Afterdepolarlizations induced by wave pattern in human ventricular tissue
Authors: Wang Xiao-Yan  , Wang Peng  , Tang Guo-Ning  ,   College of Physical Science and Technology, Guangxi Normal University, Guilin 541004, China
Published: December 2020

Recently, arrhythmogenic condition has attracted special attention of scientists in the field of different disciplines because sudden cardiac death is often caused by cardiac arrhythmia. Arrhythmias can have different underlying causes. But the underlying mechanism of arrhythmia is not fully understood due to cardiac complexity. As is well known, one particular group of arrhythmias is often associated with the afterdepolarizations. So far, afterdepolarizations have been studied mainly in isolated cardiac cells. The question how the afterdepolarization is produced at a tissue level has not been widely studied yet. In this paper, we use the model of human heart to study how spiral wave or other wave patterns induces the afterdepolarizations in two-dimensional myocardial tissue. We try to obtain the instantaneous spatial distribution of afterdepolarizations by changing the L-type calcium and fast potassium conductance. In order to avoid bringing in afterdepolarizations, the applied parameters avoid evoking the afterdepolarizations at a single-cell and one-dimensional tissues level. The numerical simulation results show that spiral wave and other wave patterns can cause the phase II and III early afterdepolarizations, the delayed afterdepolarization, the enhanced automaticity, the delayed excitation and the delayed enhanced automaticity to occur. Moreover, we observe the weak oscillation of the membrane potential during the phase I of action potential. The afterdepolarizations generally occur in the spiral-wave core. They are generated by the phase singularity of spiral wave. The afterpolarizations can also appear in other region of spiral wave pattern. The afterpolarization is characterized by scattered distribution. When parameters are appropriately chosen, we observe the outbreaks of different afterpolarizations under the state of spiral wave. The corresponding spatial and temporal distributions of the early afterdepolarizations, the delayed afterdepolarizations, and the enhanced automaticity become spiral line distributions, which exhibits memory effect. It is shown that the outbreaks of afterdepolarizations in the system do not necessarily lead to the breakup of spiral wave. By observing the changes of different ion currents we find that when sodium current exciting cell is very small, the weak excitation with small sodium current can cause the L-type calcium current and the sodium calcium exchange current to increase, and the slow potassium current and rapid potassium current to decrease, leading to the occurrences of various afterdepolarizations. Therefore, increasing sodium current can effectively suppress the occurrences of afterdepolarizations.
Barrier growth temperature of InGaAs/AlGaAs-quantum well infrared photodetector
Authors: Huo Da-Yun  , Shi Zhen-Wu  , Zhang Wei  , Tang Shen-Li  , Peng Chang-Si  ,   School of Optoelectronics Information Science and Engineering, Collaborative Innovation Center of Suzhou Nano Science and Technology, Soochow University, Suzhou 215006, China
Published: December 2020

The InGaAs/AlGaAs quantum wells have been extensively applied to quantum well infrared photodetector of mid-wavelength. In this letter, four samples of 2.4 nm In0.35Ga0.65As/40 nm Al0.34Ga0.66As multi-quantum wells are grown by molecular beam epitaxy with the InGaAs wells growing all at a temperature of 465℃ but the AlGaAs wells growing at temperatures of 465℃, 500℃, 545℃, and 580℃ respectively. The dependence of InGaAs quantum well strain relaxation on the AlGaAs growth temperature is systematically studied by photoluminescence spectroscopy and X-ray diffraction and then the thermal-induced relaxations of three key-stages are clearly observed in the following temperature ranges. 1) 465-500℃ for the stage of elastic relaxation: the phase separation begins to take place with a low defect density; 2) 500-545℃ for the transition stage from elastic relaxation to plastic relaxation: the phase separation will be further intensified with defect density increasing; 3) 545-580℃ for the fast stage dominated by elastic relaxation and the defect density will sharply increase. Especially when AlGaAs temperature increases to 580℃, a very serious plastic relaxation will take place and the InGaAs quantum well will be dramatically destroyed.
Research progress of in-fiber Fabry-Perot interferometric temperature and pressure sensors
Authors: Li Zi-Liang  , Liao Chang-Rui  , Liu Shen  , Wang Yi-Ping  ,   Key Laboratory of Optoelectronic Devices and Systems of Ministry of Education and Guangdong Province, College of Optoelectronic Engineering, Shenzhen University, Shenzhen 518060, China
Published: December 2020

Optical fiber sensors based on Fabry-Perot interferometer (FPI) have attracted intensive attention for sensing applications in temperature and pressure measurement, owing to their compact, small size, fast responses, high resolution, high sensitivity, good stability, and resistance to electromagnetic interference. It's known that the in-fiber optic interferometers based on single-mode fibers can exhibit compact structures, easy fabrication and low cost. In this paper, firstly, the basic principle of in-fiber FPIs is introduced. Secondly, we review several kinds of typical in-fiber FPIs formed in single-mode fibers fabricated with different post-processing techniques, such as chemical etching, arc discharge, femtosecond laser micromachining, and polymer coating, etc. Finally, the optical sensors based on in-fiber FPIs, with a capability of simultaneous multi-parameter sensing of temperature and pressure, are summarized and prospected.
Recent progress in ultra-long distributed fiber-optic sensing
Authors: Rao Yun-Jiang  ,   Key Laboratory of Optical Fiber Sensing and Communications(Education Ministry of China), University of Electronic Science and Technology of China, Chengdu 611731, China
Published: December 2020

Distributed fiber-optic sensing (DFOS) is one of the most important parts in the fiber-optic sensing field, due to the following advantages:1) there is no need to manufacture sensors on the fiber; 2) fibers are able to realize transmission and detection simultaneously; 3) long-distance/large-scale sensing and networking can be accomplished prospectively; 4) the spatial distribution and measurement information of physical parameters such as temperature, strain and vibration, can be obtained continuously along the fiber link, and the number of sensing points on a single fiber can be up to several tens of thousands. Due to the above tremendous superiority, DFOS has found wide application prospects, including perimeter security, oil/gas exploration, electrical facilities and structure monitoring, etc. This paper overviews recent progress in ultra-long distributed fiber-optic static (Brillouin optical time-domain analyzer) and dynamic (phase-sensitive optical time-domain reflectometer) sensing at Key Laboratory of Optical Fiber Sensing and Communications, UESTC. This paper summarizes our work on both basic and application studies.
Advances in optical fiber photothermal interferometry for gas detection
Authors: Miao Yin-Ping  , Jin Wei  , Yang Fan  , Lin Yue-Chuan  , Tan Yan-Zhen  , Hoi Lut  ,   Department of Electrical Engineering, The Hong Kong Polytechnic University, Hong Kong, China;,   The Hong Kong Polytechnic University Shenzhen Research Institute, Shenzhen 518057, China
Published: December 2020

We report our recent work on the development of a highly sensitive gas detection technique-photothermal interferometry spectroscopy with hollow-core optical fibers. The basic principle of operation, generation and detection of dynamic photothermal phase modulation, and method to improve the response time of the hollow-core fiber sensors are described. The technique has ultra-high sensitivity and dynamic range, and the measurement is not affected by reflection/scattering and other non-absorbing losses. Sensors based on such a technique could be made compact in size with remote detection, multiplexing and networking capability, which would enable a range of high performance applications in environmental, medical and safety monitoring.
Regulation of shoot meristem shape by photoperiodic signaling and phytohormones during floral induction of Arabidopsis
Authors: Kinoshita Atsuko , Vayssières Alice , Richter René , Sang Qing , Roggen Adrian , van Driel Annabel D , Smith Richard S , Coupland George
Published: December 2020

Floral transition, the onset of plant reproduction, involves changes in shape and identity of the shoot apical meristem (SAM). The change in shape, termed doming, occurs early during floral transition when it is induced by environmental cues such as changes in day-length, but how it is regulated at the cellular level is unknown. We defined the morphological and cellular features of the SAM during floral transition ofArabidopsis thaliana. Both cell number and size increased during doming, and these changes were partially controlled by the gene regulatory network (GRN) that triggers flowering. Furthermore, dynamic modulation of expression of gibberellin (GA) biosynthesis and catabolism enzymes at the SAM contributed to doming. Expression of these enzymes was regulated by two MADS-domain transcription factors implicated in flowering. We provide a temporal and spatial framework for integrating the flowering GRN with cellular changes at the SAM and highlight the role of local regulation of GA.
Community-led Work and Its Impact on Deprofessionalization: The Case of Public Library Professionals
Authors: Nilsson Jenny
Published: December 2020

The objective of this empirical study was to explore the impact of community-led work on the (de-)professionalization process among public library professionals in Canada through the analyzation of transcripts from 11 semi-structured interviews and a guideline document. The results were analyzed and sensitized through Abbott’s professionalization theory (1988) and Bourdieu’s praxeology theory (1986; 1992). With the methodology of grounded theorization, the study found that the profession has changed, and is changing, into the direction of possible deprofessionalization, due to not only external but also internal factors in the form of a collegial conflict.
Jämförelse av CKD-EPI och MDRD ekvationsformler för estimerad glomerulär filtrationshastighet.
Authors: Lundén Amanda , Hafstad Ulrika , Larsson Sara
Published: December 2020

Introduction: In the profession as radiology nurse contrast media is used daily in radiologic examinations. In order to determine the volume of contrast media that patients should be administered and to prevent contrast-induced nephropathy equation formulas are applied to calculate the kidney function glomerular filtration rate. Two formulas were compared the CKD-EPI and MDRD. The aim was to compare which of the two most commonly used equation formulas is the most optimal for calculating estimated GFR.
Methods: This study was conducted as a literature study, where 11 articles were quality assessed and compiled.
Results: The CKD-EPI formula generally showed better performance for estimating GFR in accuracy, precision and bias than the MDRD formula. However, both equation formulas present inadequacies and are not universal as they are not applicable to all individuals.
Conclusions: At the moment the CKD-EPI formula appears to be the most applicable, although more research is required in order to develop equation formulas which cater to all types of patients.
Traditional and Non-Traditional Values in Russia, Bulgaria and Slovakia: Ethnolinguistic, Comparative and Historical Dimensions
Authors:   Institute of Slavic Studies, Russian Academy of Sciences, Sedakova Irina , Kitanova Marija ,   Institute for Bulgarian Language “Professor Liubomir Andreichin”, Bulgarian Academy of Sciences, Žeňuch Peter ,   Jan Stanislav Institute of Slavistics of the Slovak Academy of Sciences, Bratislava, Gusev Nikita ,   Institute of Slavic Studies, Russian Academy of Sciences
Published: December 2020

The article embodies some results of a joint international research project on linguistic and ethnocultural dynamics of traditional and non-traditional values in the three countries of the Slavic world. First, the terminology in Russian, Bulgarian and Slovakian languages is analyzed, with the outcome that the term ‘value(s)’ as denoting an abstract notion is a recent development in Slavic languages. Second, the notions of the traditional and non-traditional values are characterized in a comparative way and the possible border (lexical, pragmatical, etc.) between them is marked. Thirdly, the dynamics of changes in the axiological hierarchy is investigated and the reasons for the changes of evaluation are defined with the examples by the development of several values (‘old age’, ‘friend’, etc.). Finally, axiological historical methodology is illustrated by the review of Russian-Bulgarian sources that give an opportunity to reflect on values. The study demonstrates its actuality as COVID-19 has spread all over the world, drastically changing the routines and preferences of people, correspondingly the hierarchy of values and its vocabulary. Language is at the center of this axiological study, being the main source of and engine for evaluation.
Milestones in Baltic Studies in Moscow
Authors:   Institute of Slavic Studies, Russian Academy of Sciences, Moscow, Russia, Zavyalova Maria
Published: December 2020

The article describes the history of research on Baltic languages in Moscow from the second half of the 19th century, when the Lithuanian language began to be taught at Moscow University. At different times, the Moscow State University, the Institute of Slavic Studies of the Russian Academy of Sciences, the “Baltrušaitis House” at the Embassy of the Republic of Lithuania in the Russian Federation, and the Institute of Linguistics of the Russian Academy of Sciences were the centers of research on Baltic studies in Moscow. The article describes the main directions in development of Balto-Slavic studies in Moscow, gives the names of prominent scholars in this field and provides a bibliography of the major publications.