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Search Results: 1 - 10 of 32564 matches for " Dejin Huang "
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Euler potentials’ discontinuity in the presence of field line-aligned currents
TianSen Huang,DeJin Wu
Chinese Science Bulletin , 2012, DOI: 10.1007/s11434-012-5043-0
Abstract: Since their use in the study of charged particle motion in the 1960s, Euler potentials (α,β) have been widely employed as magnetic field coordinates in both space plasma and fusion plasma studies. People related them to magnetic vector potential A via the relation A = α β, subject to gauge condition A·B = 0 (B is the magnetic induction). For a given magnetic field, the Euler potentials are often constructed with the relation B·ΔS = ΔαΔβ on a surface that crosses the field lines, where ΔS is the area-element surrounding by two line-elements corresponding to the changes in α and β, then mapping the values of α and β along field lines into space. In this short paper, we show that in the presence of field line-aligned currents, the mapping does not work and the orthogonality gauge condition is not satisfied.
Thickness-shear Frequencies of an Infinite Quartz Plate with Material Property Variation Along the Thickness
Ji Wang,Wenliang Zhang,Dejin Huang,Tingfeng Ma,Jianke Du
Physics , 2014,
Abstract: Properties of the quartz crystal blank of a resonator is assumed homogeneous, uniform, and perfect in design, manufacturing, and applications. As end products, quartz crystal resonators are frequently exposed to gases and liquids which can cause surface damage and internal degradation of blanks under increasingly hostile conditions. The combination of service conditions and manufacturing process including chemical etching and polishing can inevitably modify the surface of quartz crystal blanks with changes of material properties, raising the question of what will happen to vibrations of quartz crystal resonators of thickness-shear type if such modifications to blanks are to be evaluated for sensitive applications. Such questions have been encountered in other materials and structures with property variations either on purpose or as the effect of environmental or natural processes commonly referred to as functionally graded materials, or FGMs. Analyses have been done in applications as part of studies on FGMs in structural as well as in acoustic wave device applications. A procedure based on series solutions has been developed in the evaluation of frequency changes and features in an infinite quartz crystal plate of AT-cut with the symmetric material variation pattern given in a cosine function with the findings that the vibration modes are now closely coupled. These results can be used in the evaluation of surface damage and corrosion of quartz crystal blanks of resonators in sensor applications or development of new structures of resonators.
Thickness-shear Vibration Frequencies of an Infinite Plate with a Generalized Material Property Grading along the Thickness
Ji Wang,Wenliang Zhang,Dejin Huang,Tingfeng Ma,Jianke Du,Lijun Yi
Physics , 2015,
Abstract: For quartz crystal resonators of thickness-shear type, the vibration frequency and mode shapes, which are key features of resonators in circuit applications, reflect the basic material and structural properties of the quartz plate and its variation with time under various factors such as erosive gases and liquids that can cause surface and internal damages and degradation of crystal blanks. The accumulated effects eventually will change the surface conditions in terms of elastic constants and stiffness and more importantly, the gradient of such properties along the thickness. This is a typical functionally graded materials (FGM) structure and has been studied extensively for structural applications under multiple loadings such as thermal and electromagnetic fields in recent years. For acoustic wave resonators, such studies are equally important and the wave propagation in FGM structures can be used in the evaluation and assessment of performance, reliability, and life of sensors based on acoustic waves such as the quartz crystal microbalances (QCM). Now we studied the thickness-shear vibrations of FGM plates with properties of AT-cut quartz crystal varying along the thickness in a general pattern represented by a trigonometric function with both sine and cosine functions of the thickness coordinate. The solutions are obtained by using Fourier expansion of the plate deformation. We also obtained the frequency changes of the fundamental and overtone modes which are strongly coupled for the evaluation of resonator structures with property variation or design to take advantages of FGM in novel applications.
Basic plasma processes in solar-terrestrial activities
DeJin Wu,HengQiang Feng
Chinese Science Bulletin , 2012, DOI: 10.1007/s11434-012-5097-z
Abstract:
Exact solutions of dispersion equation for MHD waves with short-wavelength modification
Ling Chen,DeJin Wu
Chinese Science Bulletin , 2011, DOI: 10.1007/s11434-011-4409-z
Abstract: Dispersive magnetohydrodynamic (MHD) waves with short-wavelength modification have an important role in transforming energy from waves into particles. In this paper, based on the two-fluid mode, a dispersion equation, including the short-wavelength effect, and its exact solution are presented. The outcome is responsible for the short-wavelength modification versions of the three ideal MHD modes (i.e. the fast, slow and Alfvén). The results show that the fast and Alfvén modes are modified considerably by the shortwavelength effect mainly in the quasi-parallel and quasi-perpendicular propagation directions, respectively, while the slow mode can be affected by the short-wavelength effect in all propagation directions. On the other hand, the dispersive modification occurs primarily in the finite-β regime of 0:001 < β < 1 for the fast mode and in the high-β regime of 0:1 < β < 10 for the slow mode. For the Alfvén mode, the dispersive modification occurs from the low-β regime of β < 0:001 through the high-β regime of β > 1.
The evidence for the evolution of interplanetary small flux ropes: Boundary layers
HengQiang Feng,JieMin Wang,DeJin Wu
Chinese Science Bulletin , 2012, DOI: 10.1007/s11434-011-4960-7
Abstract: We have examined theWind data in 1996 and identified 21 small interplanetary magnetic flux ropes (SIMFRs), and all the 21 SIMFRs have boundary layer structures. The durations of the boundary layers varied from several minutes to 30 minutes. These boundary layers also have properties of high proton temperature, density, and plasma beta. These boundary layers are formed by magnetic reconnections. In addition, in three events magnetic reconnections were occurring inside the boundary layers. It indicates that the flux rope structures have propagated for some period of time, and their boundaries were still evolving through interaction with the background solar wind. Namely it is very possible that the SIMFRs came from the solar corona.
A new type of oceanic crust and its dynamical significance
Qi Zhang,Dejin Zhou,Yu Chen
Chinese Science Bulletin , 1997, DOI: 10.1007/BF02882522
Abstract: There are two types of oceanic crust: the “Troodos type” with stratiform and thick oceanic crust, characterized by the development of sheeted dike swarms and thick cumulative rocks; and the “Shuanggou type” with thin oceanic crust composed of mafic plutonic and volcanic rocks, without sheeted dike swarms and ultramafic cumulates. The different types of oceanic crust represent the different dynamic processes under the mid-oceanic ridges, which relate with not only the spreading velocity of oceanic plate, but also the formation and volume of magmas under spread ridges. It is suggested that the spreading velocity of oceanic plate is most probably related with the rock assemblage, not the composition of oceanic crust.
Electromagnetic ion-cyclotron instability driven by combined loss-cone and temperature anisotropy distribution of suprathermal ions
YuePing Hua,DeJin Wu,DeYu Wang
Chinese Science Bulletin , 2011, DOI: 10.1007/s11434-010-4267-0
Abstract: Electromagnetic ion cyclotron (EMIC) waves, particularly their generation and excitation mechanisms, have been a subject of wide interest because of their potential importance in ion acceleration and heating. In this work, the parameter-dependence of EMIC instabilities is investigated with a combined loss-cone and temperature anisotropy distribution for suprathermal ions. The calculation of the linear growth rate of EMIC waves with an arbitrary propagation angle is presented. The results show that the growth rates of EMIC waves propagating quasi-perpendicular to the ambient magnetic field increase as the loss-cone parameter α increases, whereas the growth rates of EMIC waves propagating quasi-parallel to the ambient magnetic field increase as the temperature anisotropy parameter A T increases. This indicates that the free energies associated with the loss-cone and temperature anisotropic distributions are primarily responsible for the excitation of the quasi-perpendicular and parallel propagating EMIC waves, respectively, and provides us with a more comprehensive understanding of excitation and generation mechanisms for EMIC waves in space plasmas.
A new type of oceanic crust and its dynamical significance

Qi Zhang,Dejin Zhou,Yu Chen,

科学通报(英文版) , 1997,
Abstract: Conclusions There are two types of oceanic crust: the “Troodos type” with stratiform and thick oceanic crust, characterized by the development of sheeted dike swarms and thick cumulative rocks; and the “Shuanggou type” with thin oceanic crust composed of mafic plutonic and volcanic rocks, without sheeted dike swarms and ultramafic cumulates. The different types of oceanic crust represent the different dynamic processes under the mid-oceanic ridges, which relate with not only the spreading velocity of oceanic plate, but also the formation and volume of magmas under spread ridges. It is suggested that the spreading velocity of oceanic plate is most probably related with the rock assemblage, not the composition of oceanic crust.
A nonlocal wave-wave interaction among Alfven waves in an intermediate-beta plasma
Zhao Jinsong,Wu Dejin,Lu Jianyong
Physics , 2011, DOI: 10.1063/1.3568840
Abstract: A nonlocal coupling mechanism to directly transfer the energy from large-scale Magnetohydrodynamic(MHD) Alfven waves to small-scale kinetic Alfven waves is presented. It is shown that the interaction between a MHD Alfven wave and a reversely propagating kinetic Alfven wave can generate another kinetic Alfven wave, and this interaction exists in the plasmas where the thermal to magnetic pressure ratio is larger than the electron to ion mass ratio. The proposed nonlocal interaction may have a potential application to account for the observed electron scale kinetic Alfven waves in the solar wind and solar corona plasmas.
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