bluuebunny/crossref_metadata_2025 huggingface dataset:
Experimental investigation of the hypersonic boundary layer transition on a 7° straight cone
Authors: Liu Xiao-Lin  , Yi Shi-He  , Niu Hai-Bo  , Lu Xiao-Ge  , Zhao Xin-Hai  ,   College of Aerospace Science and Engineering, National University of Defense Technology, Changsha 410073, China
Published: December 2020

In this paper, the experiments about the boundary layer transition on a 7° half-angle straight cone are carried out in a Mach 6 low-noise wind tunnel. The wall fluctuation pressure is measured by the transducer with megahertz response frequency, and the development process of the disturbance in the hypersonic boundary layer is investigated. The peaks in power spectrum density of the fluctuation pressure are related to the second mode wave, which is indicated through verifying the existence of the longitudinal acoustic second mode waves reflected between the relative sonic line and the solid wall by the flow visualization result. The wavelength and the characteristic frequency of the second mode wave in the hypersonic boundary layer are found to be greatly influenced by Reynolds number. The characteristic frequency of the second mode wave changes from 55 kHz to about 226 kHz when the Reynolds number increases from 2×106 m-1 to 8×106 m-1. The second mode wave appears at the position closer to the upstream with a higher disturbance growth speed under higher unit Reynolds number. As the second mode wave propagates downstream, its characteristic frequency gradually decreases. The freestream noise level also has a great influence on the development of the disturbance wave. The characteristic frequency of the second mode wave decreases significantly in a relatively quiet environment. The cross-correlation analysis results show that the propagation velocity of the second mode wave in the boundary layer is about 0.8-0.9 times the local mainstream velocity. The wavelength of the second mode wave is about 5.01 mm at the location from X=380 mm to X=440 mm when the unit Reynolds number is 5×106 m-1. At 1° angle of attack, the development of the boundary layer on the windward side and the leeward side of the cone are significantly different. The characteristic frequency of the second mode wave in the leeward surface is almost the same as the result at zero angle of attack under the same unit Reynolds number. However, the position of the second mode wave is greatly advanced. Results show that the disturbance development in the boundary layer of the leeward surface is accelerated, and the second mode wave appears at the position closer to the upstream. The velocity of the second mode wave in the leeward surface rapidly increases when it propagates downstream. While on the windward side, the disturbance development is inhibited and the second mode wave has a higher characteristic frequency. The wavelength of second mode wave also decreases obviously.
Progress of joule balance and redifination of Kilogram
Authors: Li Zheng-Kun  , Zhang Zhong-Hua  , Lu Yun-Feng  , Bai Yang  , Xu Jin-Xin  , Hu Peng-Cheng  , Liu Yong-Meng  , You Qiang  , Wang Da-Wei  , He Qing  , Tan Jiu-Bin  ,   National Institute of Metrology, The Key Laboratory of AQSIQ of China, Beijing 100029, China;,   Harbin Institute of Technology, Harbin 150001, China;,   Tsinghua University, Beijing 100084, China
Published: December 2020

Kilogram, the unit of mass, is the last one of seven base units in International System of Units (SI) which is still defined and kept by a material artifact. 1 kg is defined as the mass of the International Prototype of the Kilogram (IPK) kept at the Bureau International des Poids et Mesures (BIPM) in Paris. One of the major disadvantages of this definition is the fact that the amount of material constituting the IPK changes with time. Because a more stable mass reference does not exist, the variation of IPK is completely unknown so far. The International Committee for Weights and Measures (CIPM) recommended redefining the kilogram by fixing the numerical value of the Planck constant h and called on every national metrology institute to study the measurement of the h. To avoid possible system errors from one method, more experiments especially based on different principles are expected and encouraged for the final determination of the Planck constant. The CCM required that at least three consistent results should be obtained before the redefinition. Since 1970 s, the Kibble balance (also known as the Kibble balance) experiment has been used by a number of national metrology institutes such as NPL, NIST, METAS, LNE and BIPM. The IAC including the PTB, NMIJ and NMIA used the XRCD method to measure the Avogadro constant. To make contribution to the redefinition of kilogram, the National Institute of Metrology of China (NIM) proposed a joule balance method in 2006, which is also an electrical way but different from the watt balance method in that the dynamic phase is replaced with a static phase to avoid the trouble in the dynamic measurement. The progress of these approaches and the current situation of the redefinition of the kilogram are presented in this paper. In 2013, a model apparatus was built to verify the principle of the joule balance. Then NIM started to build its new joule balance aiming to obtain an uncertainty of 10-8 level since 2013. In Dec. 2016, the new apparatus was built and could be used to measure the Planck constant h in vacuum. In May 2017, the measurement result was submitted to the Metrologia and accepted by the CODATA TGFC as the input data. However, the measurement result has an uncertainty bigger than 10-8 and was not used for the final determination of the h value. At present, the joule balance group of NIM, together with the Harbin Institute of Technology, Tsinghua University and China Jiliang University is still making great efforts to improve the joule balance apparatus. The uncertainty of 10-8 level is expected to be achieved in the next two years.
Adsorption of NO2 by hydrazine hydrate-reduced graphene oxide
Authors: Li Chuang , Cai Li , Li Wei-Wei , Xie Dan , Liu Bao-Jun , Xiang Lan , Yang Xiao-Kuo , Dong Dan-Na , Liu Jia-Hao , Li Cheng , Wei Bo ,   Department of Basic Science, Air Force Engineering University, Xi’an 710051, China,   Tsinghua National Laboratory for Information Science and Technology, Institute of Microelectronics, Tsinghua University, Beijing 100084, China,   The First Aeronautic Institute, Air Force Engineering University, Xinyang 464000, China,   Department of Chemical Engineering, Tsinghua University, Beijing 100084, China
Published: December 2020

Reduced graphene oxide, as a candidate for gas detection due to its unique atomic structure, is arousing the wide interest of researchers. In this paper, hydrazine hydrate is used to reduce graphene oxide prepared by the modified Hummers method. A chemical resistance gas sensor is fabricated. The prepared reduced graphene oxide is used as a gas sensitive layer of Au planar interdigital electrode. The gas sensing characteristics such as responsivity, recovery and repeatability of NO2 gas are studied. The results show that the graphene oxide reduced by hydrazine hydrate can detect the NO2 gas at a concentration of 1−40 ppm under room temperature. It has good responsivity and repeatability. The recovery rate can reach more than 71%. However, the sensitivity is only 0.00201 ppm–1, and there is much room for improvement. In addition, the response time and recovery time for NO2 at 5 ppm concentration are 319 s and 776 s, respectively. The sensing mechanism of the hydrazine hydrate-reduced graphene oxide gas sensor can be attributed to charge transfer between the NO2 molecule and the sensing material. The outstanding electrical properties of the reduced graphene oxide promote the electron transfer process. This allows the sensor to exhibit excellent gas sensing performance at room temperature. The reduced graphene oxide appears as a typical p-type semiconductor and the oxidizing gas NO2 acts as an electron acceptor. Therefore, the adsorption of NO2 gas leads to the enhancement of the hole density and conductivity of the reduced graphene oxide. Another reason is the presence of defects and oxygen-containing functional groups on graphene sheets. Some oxygen-containing groups remain on the graphene surface after an incomplete reduction reaction. Compared with pure graphene, the reduced graphene oxide has hydroxyl groups and epoxy groups remaining on the surface. These functional groups will functionalize the material and promote the adsorption of gases. At the same time, the reduction reaction will further produce vacancies and structural defects. This will provide more reaction sites and thus conduce to the material further adsorbing the gas. In summary, the experimental research in this paper is of significance for studying the mechanism and characteristics of the reduced graphene oxide by using hydrazine hydrate as a reducing agent, and it can provide reference and lay a foundation for the applications of future graphene sensors.
Rotation effect on spin current in curved space-time
Authors: Lü Teng-Bo , Zhang Pei , Wu Rui-Tao , Wang Xiao-Li ,   Shaanxi Key Laboratory for Quantum Information and Quantum Optoelectronic Devices, School of Science, Xi’an Jiaotong University, Xi’an 710049, China,   Department of Physics Science, School of Physics and Telecommunication Engineering, Shaanxi University of Technology, Hanzhong 723001, China
Published: December 2020

The spin-orbit interaction and spin Hall effect have drawn special attention. Not only theoretical predictions have been made, but also the generation of spin currents has been achieved in experiment. In this paper, we study the spin current and the spin Hall conductivity under the influence of rotation in the curved space-time. Our work shows that the nontrivial geometries could modify the spin-orbital interaction. By using the extended Drude model, we calculate the spin-dependent force and obtain a correction to this force by non-mediocre geometry. When considering the rotation effect, the general Dirac equation is given. The Hamiltonian under the non-relativistic approximation is obtained by the Foldy-Wouthuysen transform. According to this, we calculate the spin current and spin Hall conductance. The polarization vector is deformed due to the effect of the rotation in the curved space-time. The magnitude and direction of the spin current are changed because of the correction to rotation, and the spin Hall conductivity. The nontrivial space-time geometry leads to the anisotropic nature of the spin current. Our work uses a general method that does not depend on the model, so the result can be used to analyze the electromagnetic dynamics of charged spin particles in quantum Hall systems, and it also helps to theoretically study the defects in crystals. Our results can also be extended to the optical subsystem. Considering the spin effect of photons, based on the spin-orbit coupling of photon, a light splitting phenomenon emerges in an inhomogeneous medium, which is the spin hall effect of photon. Our discussion has a certain reference value for studying the behavior of the photonic spin Hall effect in the static gravitational field. At the same time, using the optical chips to simulate curved space-time, photon manipulation and precision measurement can give some theoretical support.
Ionospheric scintillation suppression based on chemical release
Authors: Zhao Hai-Sheng , Xu Zheng-Wen , Xu Zhao-Hui , Xue Kun , Zheng Yan-Shuai , Xie Shou-Zhi , Feng Jie , Wu Jian ,   National Key Laboratory of Electromagnetic Environment, China Research Institute of Radiowave Propagation, Qingdao 266107, China
Published: December 2020

There occur frequently the ionospheric scintillation events at low and middle latitudes, which seriously affect the radio transmission process of satellite link, resulting in the decline of satellite communication and navigation signal quality and even interrupt. During the gestation period before the ionospheric scintillation, the growth rate of plasma instability can be reduced and thus suppress the scintillation events by releasing the electron density-enhancing chemicals in the ionosphere plasma bubble, filling with plasma bubble, changing the plasma environmental characteristics, and regulating the ionospheric dynamics process. The theory and method of suppressing the ionospheric scintillation based on chemical release are tnvestigated. According to the change of the plasma environment caused by the chemical release, and the quantitatively calculating of the contribution of control factors to the growth rate of instability, an ionospheric scintillation suppression model is built, which is based on chemical release into ionosphere. The process of plasma bubble filling out is simulated and the results of the simulation show that the plasma cloud is completely filled with plasma bubbles after 1200 seconds, which reduces the plasma density gradient and suppresses the growth of plasma instability. The growth of plasma instability decreases from 0.2 before releasing to about 0.0004 after releasing, and no new instability is excited within 20 minutes after the plasma bubble has been filled up. Guangdong, South China Sea and other regions in China are at the peak of equatorial anomalies, and the occurrence rate and severity of scintillation are more significant than those in the equatorial and Polar Regions, thus these regions become the regions where there occur most frequently the scintillation and the most serious influence globally. The research work of this paper will lay a solid theoretical foundation for the technology of suppressing the satellite signal ionospheric scintillation in middle and low latitude area of China.
Reivew of silicon photonic switches
Authors: Tu Xin , Chen Zhen-Min , Fu Hong-Yan ,   Tsinghua-Berkeley Shenzhen Institute (TBSI), Tsinghua University, Shenzhen 518055, China
Published: December 2020

Silicon photonic switch is recognized as a cost-effective optical switching technology because it has many applications in long-haul telecommunication networks, short-reach data center and high-performance computing. In this paper, the research progress of various silicon photonic switch technologies is reviewed systematically. Firstly, the principles of three kinds of switch technologies including Mach-Zehnder interferometer (thermo-optic and carrier-injection types), micro-ring resonator (thermo-optic and carrier-injection types) and micro-electro-mechanical-system actuated waveguide coupler (electrostatic actuated type) are introduced. The switch technologies with the state-of-the-art insertion loss, crosstalk, switch time, footprint and power consumption are summarized and compared. Then the recent demonstrations of large-port silicon photonic matrix based on the above switch technologies are discussed. In this paper, we also investigate the key technologies such as topological architecture, passive components and optoelectronic packaging, which affect the performance of large-port optical switch matrix. Specifically, we study the scalability of various topologies, low-loss/broadband waveguide components, high-density optical/electrical packaging and control interface to improve the overall performance of the silicon photonic switch matrix. Finally, we discuss the critical technical challenges that might hamper the commercialization of silicon photonic switches and envision their future.
Recent progress of near-field studies of two-dimensional polaritonics
Authors: Duan Jia-Hua , Chen Jia-Ning ,   Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China,   School of Physical Sciences, University of Chinese Academy of Sciences, Beijing 100049, China,   Beijing National Laboratory for Condensed Matter Physics, Beijing 100190, China,   Songshan Lake Materials Laboratory, Dongguan 523808, China
Published: December 2020

Due to the capability of nanoscale manipulation of photons and tunability of light-matter interaction, polaritonics has attracted much attention in the modern physics. Compared with traditional noble metals, two-dimensional van der Waals materials provide an ideal platform for polaritons with high confinement and tunability. Recently, the development of scanning near-field optical microscopy has revealed various polaritons, thereby paving the way for further studying the quantum physics and nano-photonics. In this review paper, we summarize the new developments in two-dimensional polaritonics by near-field optical approach. According to the introduction of near-field optics and its basic principle, we show several important directions in near-field developments of two-dimensional polaritonics, including plasmon polaritons, phonon polaritons, exciton polaritons, hybridized polaritons, etc. In the final part, we give the perspectives in development of near-field optics.
Numerical study of metallic semiconductor nanolasers with double-concave cavity structures
Authors: Zhang Bai-Fu , Zhu Kang , Wu Heng , Hu Hai-Feng , Shen Zhe , Xu Ji ,   School of Electronic and Optical Engineering, Nanjing University of Science and Technology, Nanjing 210094, China,   College of Electronic and Optical Engineering & College of Microelectronics, Nanjing University of Posts and Telecommunications, Nanjing 210023, China
Published: December 2020

Metallic semiconductor nanolaser, as an ultra-small light source, has been increasingly attractive to researchers in last decade. It can have wide potential applications such as in photonic integrated circuits, on-chip interconnect, optical communications,etc. One obstacle to miniaturization of the laser size is that the loss increases rapidly with the cavity volume decreasing. In previous studies, a type of Fabry-Perot cavity with capsule-shaped structure was investigated and demonstrated both numerically and experimentally, showing that its cavity loss is reduced dramatically in contrast to the scenario of conventional rectangular cavities. However, when the cavity size is reduced down to nanoscale, capsule-shaped structure surfers high loss. To overcome this difficulty, in this paper, a novel type of double-concave cavity structure for metallic semiconductor nanolaser in a 1.55 μm wavelength range is proposed and numerically studied. The proposed structure consists of InGaAs/InP waveguide structure encapsulated by metallic clad, and has a cylindrical reflection end face and concave curved sidewalls.

The cylindrical reflection end face can push the resonant mode into the cavity center and reduce the optical field overlap with metallic sidewalls, which can reduce the metallic loss. The curved-sidewalls topologically reduce the electric field component perpendicular to the sidewalls, and thus reducing the plasmonic loss. By optimizing the waist width of the double-concave cavity structure, the radiation loss can be effectively reduced, resulting in the improvement of cavity quality factor and the decrease of threshold current. Finite-difference time-domain simulations are conducted to investigate the properties of the proposed cavity structures such as resonant mode distribution, cavity quality factor, confinement factor, threshold gain and threshold current in this paper. The numerical results show that the double-concave cavity laser with cavity volume as small as 0.258 λ3 increases 24.8% of cavity quality factor and reduces 67.5% of threshold current, compared with the conventional capsule-shaped one, demonstrating an effective improvement of metallic nanolaser. With those advantages, the proposed structure can be used for realizing the ultra-small metallic semiconductor nanolasers and relevant applications.
Dephasing effect of quantum spin topological states in HgTe/CdTe quantum well
Authors: Yan Jie , Wei Miao-Miao , Xing Yan-Xia ,   Key Laboratory of Advanced Optoelectronic Quantum Architecture and Measurement, Micronano Centre, Beijing Key Laboratory of Nanophotonics and Ultrafine Optoelectronic Systems, School of Physics, Beijing Institute of Technology, Beijing 100081, China
Published: December 2020

HgTe/CdTe quantum well is a typical two dimensional topological material which supports the helical edge states and quantum spin Hall effect that is imposing in applying of spin electronic devices. The special plateau valued with \begin{document}$0.25\;h/e^{2}$\end{document} of nonlocal resistance in H-shaped four terminal devices can be used as the fingerprint of quantum spin Hall effect. Based on the HgTe/CdTe quantum well, with the aid of nonequilibrium Green's function theory and multi-terminal Landauer-Büttiker formula, we calculate the nonlocal resistance and study the dephasing effect of spin topological states in the presence of exchange field and external magnetic field. It is found the dephasing processes play a role completely different from exchange field and external magnetic field. The latter destroy time reversal symmetry and change the width and relative position of topological gap, but do not influent the topological stability of helical edge states. In the contrary, dephasing processes don't change the width and relative position, however, they broke the topological stability. We consider two kinds of dephasing: normal dephasing and spin dephasing. In the first kind, the carriers lose only the phase memory while maintaining the spin memory. In the second kind, the carriers lose both phase and spin memories. Because of the spin locking properties, normal dephasing almost have no influence on the helical edge states. While the spin dephasing will induce spin flip backscattering and finally destroy helical edge states seriously.
Huang-Rhys factor and its key role in the interpretation of some optical properties of solids
Authors: Xu Shi-Jie ,   Department of Physics and Shenzhen Institute of Research and Innovation, The University of Hong Kong, Hong Kong, China
Published: December 2020

Huang and Rhys published a quantum theoretical treatment to the light absorption in F-centre in solids, which has been widely recognized as the first detailed quantum-mechanical calculation. In the Huang-Rhys’s seminal theoretical treatment, they derived a dimensionless factor to characterize electron-phonon coupling strength which was named later as Huang-Rhys factor. Since then, Huang-Rhys factor has been generally accepted. In this short review, the physical nature of Huang-Rhys factor and several application examples in solids are introduced and presented in memory of the hundredth anniversary of Prof. Kun Huang. Due to limited publication space and my personal understanding on Huang-Rhys factor, only several cases including GaN, 2D WS2 monolayer semiconductor, inorganic CsPbBr3 perovskite nanosheets and NV centers in diamond, in which the extremely-weak and medium strong coupling between electron (exciton) and phonon occur, are discussed in this short review.
Optimization of optical control of nitrogen vacancy centers in solid diamond
Authors: Feng Yuan-Yao , Li Zhong-Hao , Zhang Yang , Cui Ling-Xiao , Guo Qi , Guo Hao , Wen Huan-Fei , Liu Wen-Yao , Tang Jun , Liu Jun ,   Key Laboratory of Instrumentation Science and Dynamic Measurement, Ministry of Education, North University of China, Taiyuan 030051, China,   School of Instrument and Electronics, North University of China, Taiyuan 030051, China
Published: December 2020

The nitrogen-vacancy (NV) centers in diamond have the advantages of stable triaxial structure, ultra-long electron spin coherence time and simple optical readout at room temperature. A nitrogen atom in the diamond crystal replaces a carbon atom and a vacancy is generated at the adjacent position, forming a point defect in the C3v space group structure. Its ground state and excited state are both spin triplet states. It is the key to achieving efficient preparation of optical initial state and extracting NV color center’s information in the researches of highly sensitive sensing magnetic detection, temperature detection, biological imaging, quantum computing, etc. However, there was no systematic study on relevant parameters of laser for high-concentration NV color center’s samples in previous experimental studies. Based on a high concentration diamond NV ensemble, we use pulsed optical detection magnetic resonance (ODMR) technology to systematically study the relationship among laser initial polarization time, information reading time and laser power, and the influence of laser incident polarization angle on the accuracy of sensing information. The effects of various laser parameters on the NV1 peak of ODMR on the [111] axis of the NVs of diamond are also investigated. The contrast of ODMR increases firstly with a sigmoid function and then decreases with an e-exponential function as the information reading time increases. The incident polarization angle of the laser is sinusoidal, with a period of 90°. According to the above experimental results, we finally choose the appropriate experimental parameters at 45.8 W/cm2 (300 μs of polarization, 700 ns, reading time, laser incident angle is 220°) for ODMR test. Compared with previous experimental parameters (polarization time was 50 us, read the time of 3000 ns, laser incident angle was 250°), the experimental results show that the contrast of ODMR increases from 2.1% to 4.6%, and the typical magnetic sensitivity is improved from 21.6 nT/Hz1/2 to 5.6 nT/Hz1/2. The optimization of the optical control of NVs in solid diamond is realized. The above results provide an effective support for the detection of high-sensitivity manipulation sensing based on high-concentration NV ensemble.
Preparation and properties for X-ray scintillation screen based on ZnO:In nanorod arrays
Authors: Li Qian-Li , Hu Ya-Hua , Ma Yi-Fan , Sun Zhi-Xiang , Wang Min , Liu Xiao-Lin , Zhao Jing-Tai , Zhang Zhi-Jun ,   School of Materials Science and Engineering, Shanghai University, Shanghai 200444, China,   College of Nanhu, Jiaxing University, Jiaxing 314001, China,   School of Physics Science and Engineering, Tongji University, Shanghai 200092, China
Published: December 2020

X-ray scintillation screens as the core component of X-ray imaging detectors have widespread applications in the medical imaging, security inspection, high energy physics, radiochemistry, and so on. For a long time, the development of X-ray scintillation screen mainly focuses on improving the light yield in order to enhance its detection efficiency. However, a novel tendency has recently emerged for ultrafast time performance of the X-ray imaging detector. The indium doping zinc oxide (ZnO:In) with high radiation hardness, higher light yield(>10000 photons/MeV) and subnanosecond decay time is a promising scintillation material for ultrafast detections. In order to satisfy the requirements of X-ray scintillation screens with ultrafast and high-spatial-resolution in the existing and upcoming high energy physics experiments, the ZnO:In nanorod arrays have been prepared on a 100-nm-thick ZnO-seeded substrate by hydrothermal reaction method and then treated by hydrogen plasma in present work. The results of SEM demonstrate the average diameter and length of the ZnO:In nanorods are about 0.5 and 12 μm, respectively. The XRD shows the ZnO:In nanorods are highly aligned perpendicular to the substrate along c-axis direction. The X-ray excited luminescence spectra show that two luminescence bands are observed, i.e. an ultraviolet emission peak located at about 395 nm and a visible emission band at 450–750 nm. It is particularly important to point out that hydrogen plasma treatment can enhance the ultraviolet emission of ZnO:In nanorod arrays and suppress its visible emission. The reason is attributed to the formation of shallow donors through hydrogen entering the ZnO and the combination of VO and Oi. In addition, the fluorescence decay times of the ultraviolet and visible emissions for the ZnO:In nanorod arrays are subnanosecond and nanosecond, respectively, satisfying the demand of the fast X-ray imaging. The spatial resolution of ZnO:In nanorod arrays has been characterized in X-ray imaging beamline at the Shanghai Synchrotron Radiation Facility. Under excitation of the X-ray beam with the energy of 20 keV, a system spatial resolution of 1.5 μm could be achieved by using an 12 μm thickness ZnO:In nanorod arrays as the scintillation screen, which is exceeded the highest level had ever been reported on ZnO:In nanorod arrays scintillation screen. In conclusion, this present work shows that it is a feasible solution for X-ray detection and imaging with high temporal and spatial resolution by using ZnO:In nanorod arrays as the X-ray scintillation screen.
Influence of screen gird aperture diameter in outer region on performance of dual-mode ion thruster
Authors: Zhao Yi-De , Li Juan , Wu Zong-Hai , Huang Yong-Jie , Li Jian-Peng , Zhang Tian-Ping ,   Key Laboratory of Science and Technology on Vacuum Technology and Physics, Lanzhou Institute of Physics, Lanzhou 730000, China
Published: December 2020

To eliminate the erosion in the apertures at the edge of the decelerate grid of a dual-mode ion thruster three-grid optical system, a new method of reducing the diameter of the apertures in the outer region of the screen grid is proposed. In order to investigate the method of influencing the discharge loss and the uniformity of the beam current density and also reducing the aperture erosion region and erosion rate of the decelerate grid, two kinds of three-grid optical systems are designed and fabricated with the same material and physical parameters except the diameter of the apertures in the outer region of the screen grid. The first kind is that the diameter of the aperture in the outer region of the screen grid is equal to that in middle region of the screen grid, it is designated as the same aperture diameter grid optical system. The second kind of three-grid optical system is that the diameter of screen apertures whose center distance from the center of grid is larger than 0.95 times the beam radius, is reduced by 26% and therefore the physical transparency of optical system is reduced by 8.8%, it is designated as the small aperture diameter grid optical system. The comparison between the same aperture diameter grid optical system and small aperture diameter grid optical system is performed by assembling them into a 30-cm-diameter dual-mode ion thruster, and the ion thruster performance test, beam flatness test and 600-h-endurance test are conducted in the two typical operation modes, namely the low thrust-high specific impulse mode and large thrust-high power mode. A comparison of small aperture diameter grid optical system with the same aperture diameter grid optical system shows that the discharge loss of the 30-cm dual-mode ion thruster in the low thrust-high specific impulse mode and large thrust-high power mode are reduced by 10% and 21% respectively, the beam flatness is decreased by 3% and 10% respectively, the number of rows of the apertures which are sputtered by beam ions at the edge of the decelerate grid is reduced from 5 to 1. In addition, the erosion rate is significantly reduced and the erosion phenomenon disappears after 900-h-long-duration operation. These results signify that reducing the screen grid aperture diameter in the outer region is an effective method to eliminate aperture erosion at the edge of the decelerate grid of a dual-mode ion thruster three-grid optical system and that this method will not reduce the efficiency of the thruster, but cause the beam current uniformity to worsen.
Diffusion and separation of binary mixtures of chiral active particles driven by time-delayed feedback
Authors: Liao Jing-Jing , Lin Fu-Jun ,   School of Science, Jiangxi University of Science and Technology, Ganzhou 341000, China,   College of Applied Science, Jiangxi University of Science and Technology, Ganzhou 341000, China,   School of Physics and Telecommunication Engineering, South China Normal University, Guangzhou 510006, China
Published: December 2020

Considering the periodic boundary conditions, a new prescription for separating binary mixtures of chiral active particles by time-delayed feedback in a two-dimensional square box is proposed. We investigate the angular velocity, the feedback intensity, the delayed time, the rotational diffusion coefficient, the self-propelled speed and the packing fraction as functions of the effective diffusion coefficient and the separation coefficient numerically by the extensive Brownian dynamics simulations. It is found that mixed chiral active particles be separated without time-delayed feedback, but the dynamics of chiral active particles are different obviously and mixed chiral particles can be separated when the time-delayed feedback is introduced. The particle configuration (mixing or demixing) is determined by the dominant factor of particles’ diffusion. We can control the extent to which the diffusion of counterclockwise (CCW) active particles is affected by the diffusion of clockwise (CW) active particles adjusting the strength and the delayed time of the feedback. The response to the feedback for different chiral particles show different behaviors under different system parameters. When the feedback intensity is strong and the delayed time is long enough, the angular velocity of counterclockwise particles is accelerated and the diffusion of which is dominated by the interactions between particles completely. However, the angular speed of clockwise particles change little and the diffusion of which is determined by its parameters and particle interactions jointly. In this case, the counterclockwise particles aggregate to form clusters easily, and the clockwise particles diffuse quickly, therefore, the mixed chirality active particles are separated. When the feedback intensity is weak and the delayed time is short, the chirality difference between different chiral particles modulated by the feedback is smaller than the former case. The diffusions of counterclockwise particles and clockwise particles are both determined by their parameters and particle interactions, and the particles are mixed. Our findings provide novel strategies for the experimental pursuit of separating mixed chiral active particles and could be applied practically in many biological circle swimmers, such as autochemotactic particles, the bacteria in an external light field and sperm cells with vortex motion.
Recent research progress of two-dimensional intrinsic ferroelectrics and their multiferroic coupling
Authors: Ye Qian , Shen Yang , Yuan Ye , Zhao Yi-Feng , Duan Chun-Gang ,   Key Laboratory of Polarized Materials and Devices of Ministry of Education, School of Physics and Electronic Science, East China Normal University, Shanghai 200241, China,   Collaborative Innovation Center of Extreme Optics, Shanxi University, Taiyuan 030006, China
Published: December 2020

Ferroelectric materials have become a research focus of condensed matter physics because of their electric polarization state which can be regulated by external field and has potential applications in sensors, optoelectronic devices and information memory devices. With the rapid development of microelectronic integration technology, electronic devices are becoming more and more miniaturized, integrated and multifunctional. Due to the size effect and interface effect, the traditional bulk ferroelectric materials are difficult to meet the requirements for this development. Therefore, low-dimensional ferroelectric materials have received extensive attention of the academic circle. In recent years, stable room temperature intrinsic two-dimensional ferroelectric materials have been successfully prepared. The prediction and design of new materials in theoretical method such as first principles calculation also promote the development of two-dimensional ferroelectric materials. At the same time, the multiferroic coupling effect of two-dimensional ferroelectricity, ferrovalley and magnetism can be used to realize the electronic valley polarization, electronic magnetic control and other regulatory mechanisms. The coupling of multiple degrees of freedom will produce strange physical properties such as optical selectivity of circular (linear) polarization between energy valleys and quantum spin Hall effect, which is of great significance for developing spintronics, valley electronics and optics. In this paper, the recent progress of theoretical and experimental research of new two-dimensional ferroelectric materials is introduced, and the applications of two-dimensional ferroelectric materials in two-dimensional ferroelectric devices such as ferroelectric tunnel junctions and ferroelectric diodes are presented. Secondly, the multiferroic coupling effect of two-dimensional electrically controlled ferroelectric valley and electronically controlled magnetism and their derived new physical phenomena and mechanisms are described. Finally, the rich physical connotation and broad application prospects of coupling two-dimensional ferroelectric materials with other physical properties are analyzed and discussed.
Evaluation of the Vertical Marginal Fit of CAD-CAM Zirconia, Pressable Lithium Disilicate, CAD-CAM Cobalt Chromium and Direct Metal Laser Sintered Cobalt Chromium Copings- An Invitro Comparative Analysis
Authors: Kandi Nikita , Sabane Ajay , Patil Abhijit
Published: December 2020

Introduction: The longevity, durability and success of conventional fixed partial dentures and single crowns have been known to be attributed to the marginal fit of these restorations. Therefore, many studies lay emphasis on accurate marginal fit of the crowns. It has been the focus of various investigations in literature. However, there is limited literature comparing marginal accuracy CAD/CAM zirconia, Pressable Lithium Disilicate, CAD/CAM Cobalt-Chromium and Direct Metal Laser Sintered (DMLS) copings. Aim: Verification and comparative evaluation of the vertical marginal adaptation of CAD/CAM Zirconia, Pressable lithium Disilicate, CAD/CAM Cobalt-Chromium and DMLS copings. Materials and Methods: This invitro study was planned with an aim to evaluate the vertical marginal adaptation of CAD/CAM Zirconia, Pressable Lithium Disilicate, CAD/CAM Cobalt-Chromium and DMLS copings. A custom- made metal master model was prepared simulating the shape and dimension of tooth preparation resembling a first premolar using a Computer Numerically Controlled (CNC) milling machine. An elastomeric impression of the custom-made stainless steel model was made with addition silicone using dual mix/double step technique. All impressions were poured in Type IV dental stone and 60 stone dies were obtained. The samples were divided into four groups and each group had 15 samples (stone dies)- CAD/CAM zirconia (Group A), Pressable Lithium Disilicate (Group B), CAD/CAM Cobalt Chromium (Group C), and Direct Metal Laser Sintered Cobalt Chromium copings (Group D). The marginal fit was analysed at four reference marks on the working die stone model i.e., 0° (Buccal surface), 90° (Mesial Surface), 180° (Lingual surface), and 270° (Distal surface) on the stone die using a stereomicroscope. Comparison between groups was done by using one-way ANOVA test followed by a Post-Hoc Tukey-Kramer multiple comparisons test. Results: The mean marginal gap (in μm) for Group A was 53.185±25.83, respectively. The mean marginal gap (in μm) of Group B was 66.08±22.27, respectively. The mean marginal gap (in μm) of Group C was 108.62±23.93, respectively. The mean marginal gap (in μm) of Group D was 28.54±13.53, respectively. Tukey’s post-hoc analysis showed that the mean difference in the vertical marginal gap in Group C and the other three groups was statistically significant (p<0.05) i.e., marginal discrepancy of group C was more than Group A, Group B and Group D. Conclusion: The marginal fit of DMLS copings is more accurate as compared to CAD/CAM Zirconia, Pressable Lithium Disilicate and CAD/CAM Cobalt-Chromium copings.
Smile Aesthetics among Late Adolescents: Perspective of Adolescents, General Dentists and Orthodontists
Authors: Marusamy Kavitha Odathurai , Nayak Ullal Anand , Nayak Prathibha Anand , Ramasamy Saravanan
Published: December 2020

Introduction: An adolescent’s personal experiences, peer influences and social environment can affect their preference towards smile aesthetics and have influence apart from the opinion of their orthodontists. Aim: To evaluate and compare the preferences regarding smile arc, gingival display, midline symmetry, shape and size of incisor teeth, buccal corridor space and smile index of adolescent subjects between late adolescents, general dentists and orthodontists. Materials and Methods: A total of 52 orthodontists, 111 general dentists and 275 adolescents (156 females, 119 males) had participated in this cross-sectional study from 1st September 2019 to 31st January 2020. Each participant was shown a photo album consisting of 5 sets of photographs of male and female adolescent subjects and was asked to rate them on 7 selected variables. The data obtained was subjected to comparison between the groups using Chi-square test. Results: While assessing smile of the female subject, other than the incisal edge position, the intergroup comparisons of gingival display (p=0.0001), midline symmetry (p=0.0001), shape of incisor teeth (p-value=0.0001), buccal corridor space (p=0.001), ratio of central: lateral incisor (p=0.016) and smile index (p=0.0001) were statistically significant. While assessing smile of the male subject, the intergroup comparisons of incisal edge position (p=0.0001), gingival display (p=0.001), midline symmetry (p=0.007), shape of incisor teeth (p-value=0.0001), buccal corridor space (p=0.0001), ratio of central: lateral incisor (p=0.0001) and smile index (p=0.0001) were statistically significant. Orthodontists’ accepted gingival display of 0-2 mm, midline deviation up to 2 mm and buccal corridor space of upto 5 mm and upto 25% increase in smile index in both genders. Conclusion: The Orthodontists and dentists have more similarities than differences in comparison to adolescents with respect to the smile preferences of adolescent subjects.
Variations in the Axillary Artery Branching Pattern
Authors: Singh Deepshikha , Malhotra Minakshi , Agarwal Sneh
Published: December 2020

Variations in axillary artery branching pattern can lead to iatrogenic injuries during invasive procedures. Knowledge of the same is critical to prevent such events. Multiple bilateral variations were observed in the branching pattern of axillary artery. These variations were noted in a female cadaver, during routine undergraduate dissection in September 2019 in Lady Hardinge Medical College, New Delhi. On the left side, an anomalous branch running with the medial pectoral nerve was found. A common stem arising from the 2nd part of left axillary artery divided to give the lateral thoracic artery, the subscapular artery and an alar artery. Another alar branch arose from the left subscapular artery before it bifurcated into thoraco-dorsal and circumflex scapular arteries. The right axillary artery gave an aberrant branch proximal to the lateral thoracic artery. A common trunk arising from the 2nd part of right axillary branched out to give the posterior circumflex humeral artery, the subscapular artery and an alar artery. The brachial artery divided 13.5 cm proximal to the intercondylar line of humerus on the left and 14.4 cm on the right side. On both sides, the ulnar artery arose proximally and the radial and common inter-osseous arteries continued as a common trunk and divided distally. This case study reports multiple bilateral axillary artery anomalies and complements to the existing knowledge of vascular anomalies. Comprehensive knowledge of these variations is essential from anatomical, radiological and surgical point of view. During surgeries involving axillary and pectoral group of lymph nodes, such variations should be kept in mind.
High-sensitivity C-reactive Protein as a Marker of Future Cardiovascular Events in Chronic Kidney Disease Stage-5 Patients
Authors: Abraham Nisha , Beena C , Varghese Sangeetha Merrin
Published: December 2020

Introduction: Chronic Kidney Disease (CKD) has been recognised as a worldwide health threat and understanding its complex patho-physiological mechanisms could go a long way in taking care of patients with CKD. One of the most important causes for mortality in End Stage Renal Disease (ESRD) patients is Cardiovascular Disease (CVD). ESRD is a low grade chronic inflammatory state, suspected to promote atherosclerosis. Aim: To determine, if there is any association between elevated High-sensitivity C-Reactive Protein (hs-CRP) and development of future cardiovascular events in stage-5 CKD patients. Materials and Methods: Forty-five CKD stage-5 patients were included in the study, after ruling out patients with established CVD. According to categorisation proposed by the American Heart Association for the cut-off value of hs-CRP-value (3 mg/L), patients were divided into two groups. Those who had hs-CRP more than 3 mg/L were considered to have ‘elevated hs-CRP’ and those who had a value 3 mg/L and below were considered to have ‘normal hs-CRP’ levels. These patients were followed-up monthly, for a period of one year to record any occurrence of cardiovascular events (coronary events/cerebrovascular accidents/peripheral occlusive vascular disease). Statistical Package for the Social Sciences (SPSS) 16.0 was used for analysis. Chi-square test and Mann-Whitney U-test were used for statistical comparison between the groups and a p-value of 0.05 or less was considered to be statistically significant. Receiver Operating Characteristic (ROC) curve was also plotted to determine the cut-off value for hs-CRP based on the occurrence of any cardiovascular event. Results: Baseline hs-CRP level was more than 3 mg/L in 42% of patients. Among those who had elevated hs-CRP, 78.9% of patients developed cardiovascular events during the follow-up period. This signifies a strong association between elevated hs-CRP and CVD in ESRD patients. The hs-CRP cut-off point of 3 mg/L was obtained from ROC curve. Conclusion: There was a significant association between elevated hs-CRP and development of cardiovascular events in ESRD patients. Hence, hs-CRP can be used as a marker of future cardiovascular events in CKD stage-5 patients.
Evaluation of Bacteriological Profile and their Antimicrobial Susceptibility Pattern in Blood Stream Infections in a Multispeciality Hospital
Authors: Yousuf Mariyah , Sarwat Tarana , Kakru Dalip K
Published: December 2020

Introduction: Bloodstream Infections (BSIs) are one of the major cause of morbidity and mortality worldwide. To decrease the mortality from septicaemia early diagnosis and appropriate treatment of BSIs is most important. Early diagnosis of a BSI will markedly improve patient management. Aim: To identify various pathogenic organisms causing BSIs and determine their susceptibility to various antibiotics. Materials and Methods: A total of 1367 blood samples were received in the bacteriology laboratory for culture out of which 274 samples showed culture positivity. Among the positive cases 32 cases of Multidrug Resistance (MDR) were found. MDR cases show resistance to ≥3 classes of antibiotics. Enterobacteriaceaefamily showed highest MDR cases. Blood cultures were repeated for confirmation of results. Simple descriptive analysis of data was done and results presented in frequencies and percentages. Results: Out of 274 positive samples obtained, Coagulase Negative Staphylococci (CoNS) constituted maximum proportion of isolates (66%) followed by Pseudomonas species(12%),Escherachia coli(6.2%),Klebsiella species(3.2%),Citrobacter spp.(2.9%),Staphylococcus aureus(2.9%) andEnterococcus(2.9%). Conclusion: The present study highlighted the bacteriological aetiology of BSIs along with their antibiogram that may provide necessary information for the formulation of antibiotic policy in effective management of such cases.