With introduction of the first-order strain-gradient of surface micro-beams into the energy density function,we developed a two-dimensional dynamic model for a compound quartz crystal resonator（QCR） system,consistin...With introduction of the first-order strain-gradient of surface micro-beams into the energy density function,we developed a two-dimensional dynamic model for a compound quartz crystal resonator（QCR） system,consisting of a QCR and surface micro-beam arrays.The frequency shift that was induced by micro-beams with consideration of strain-gradients is discussed in detail and some useful results are obtained,which have important significance in resonator design and applications.展开更多
Aeromagnetic gradients are often used to enhance details or add new insights for interpretation. The gradients may be measured or derived from the total field or from transformation between horizontal and vertical gra...Aeromagnetic gradients are often used to enhance details or add new insights for interpretation. The gradients may be measured or derived from the total field or from transformation between horizontal and vertical gradients. At present, vertical, horizontal, and triaxial aeromagnetic gradiometers are in operation throughout the world, while the first two are used more widely. Transformations between horizontal and vertical gradients are needed for acquiring three gradient components or for checking the validity of measured gradients. Transformation of potential field by fast Fourier transform technique in frequency domain is popularly used; however, when applied to transforming between gradients, there is a problem that needs resolving. Because those expressions of transform operators are undefined when u or v is equal to zero or u and v are simultaneously equal to zero （u is the frequency in x-direction, and v is the frequency in y-direction）, the operators cannot be sampled at these frequencies. Consequently, the transformation cannot be implemented by fast Fourier transform technique directly. In this article, shift sampling theory is employed for resolving this problem. Model test results show that the technique has good accuracy, and the real case of transformation indicates that the computed results agree better with the measured gradients; it demonstrates not only the effective- ness of method but also the reliability of the measured gradients.展开更多
This paper proposes an adaptive parameter identification method for breaking chaotic shift key communication from the transmitted signal in public channel. The sensitive dependence property of chaos on parameter misma...This paper proposes an adaptive parameter identification method for breaking chaotic shift key communication from the transmitted signal in public channel. The sensitive dependence property of chaos on parameter mismatch is used for chaos adaptive synchronization and parameter identification. An index function about the synchronization error is defined and conjugate gradient method is used to minimize the index function and to search the transmitter＇s parameter （key）. By using proposed method, secure key is recovered from transmitted signal generated by low dimensional chaos and hyper chaos switching communication. Multi-parameters can also be identified from the transmitted signal with noise.展开更多
A method of measuring in-situ magnetic field gradient is proposed in this paper. The magnetic shield is widely used in the atomic magnetometer. However, there is magnetic field gradient in the magnetic shield, which w...A method of measuring in-situ magnetic field gradient is proposed in this paper. The magnetic shield is widely used in the atomic magnetometer. However, there is magnetic field gradient in the magnetic shield, which would lead to additional gradient broadening. It is impossible to use an ex-situ magnetometer to measure magnetic field gradient in the region of a cell, whose length of side is several centimeters. The method demonstrated in this paper can realize the in-situ measurement of the magnetic field gradient inside the cell, which is significant for the spin relaxation study. The magnetic field gradients along the longitudinal axis of the magnetic shield are measured by a spin-exchange relaxation-free （SERF） magnetometer by adding a magnetic field modulation in the probe beam＇s direction. The transmissivity of the cell for the probe beam is always inhomogeneous along the pump beam direction, and the method proposed in this paper is independent of the intensity of the probe beam, which means that the method is independent of the cell＇s transmissivity. This feature makes the method more practical experimentally. Moreover, the AC-Stark shift can seriously degrade and affect the precision of the magnetic field gradient measurement. The AC-Stark shift is suppressed by locking the pump beam to the resonance of potassium＇s D1 line. Furthermore, the residual magnetic fields are measured with σ＋- and σ--polarized pump beams, which can further suppress the effect of the AC-Stark shift. The method of measuring in-situ magnetic field gradient has achieved a magnetic field gradient precision of better than 30 pT/mm.展开更多
基金supported by the National Science Foundation of China(Grants 11272127 and 51435006)Research Fund for the Doctoral Program of Higher Education of China(Grant 20130142110022)the Grant from the Impact and Safety of Coastal Engineering Initiative Program of Zhejiang Provincial Government at Ningbo University(Grant zj1213)
文摘With introduction of the first-order strain-gradient of surface micro-beams into the energy density function,we developed a two-dimensional dynamic model for a compound quartz crystal resonator（QCR） system,consisting of a QCR and surface micro-beam arrays.The frequency shift that was induced by micro-beams with consideration of strain-gradients is discussed in detail and some useful results are obtained,which have important significance in resonator design and applications.
基金supported by China Aero Geophysical Survey & Remote Sensing Center for Land & Resources (863 Program, No. 2006AA06A201)
文摘Aeromagnetic gradients are often used to enhance details or add new insights for interpretation. The gradients may be measured or derived from the total field or from transformation between horizontal and vertical gradients. At present, vertical, horizontal, and triaxial aeromagnetic gradiometers are in operation throughout the world, while the first two are used more widely. Transformations between horizontal and vertical gradients are needed for acquiring three gradient components or for checking the validity of measured gradients. Transformation of potential field by fast Fourier transform technique in frequency domain is popularly used; however, when applied to transforming between gradients, there is a problem that needs resolving. Because those expressions of transform operators are undefined when u or v is equal to zero or u and v are simultaneously equal to zero （u is the frequency in x-direction, and v is the frequency in y-direction）, the operators cannot be sampled at these frequencies. Consequently, the transformation cannot be implemented by fast Fourier transform technique directly. In this article, shift sampling theory is employed for resolving this problem. Model test results show that the technique has good accuracy, and the real case of transformation indicates that the computed results agree better with the measured gradients; it demonstrates not only the effective- ness of method but also the reliability of the measured gradients.
基金Project supported by the China Postdoctoral Science Foundation (Grant No 20060390318)Natural Science Foundation of Shaanxi Province (Grant No 2007F017)Fok Ying Tong Education Foundation
文摘This paper proposes an adaptive parameter identification method for breaking chaotic shift key communication from the transmitted signal in public channel. The sensitive dependence property of chaos on parameter mismatch is used for chaos adaptive synchronization and parameter identification. An index function about the synchronization error is defined and conjugate gradient method is used to minimize the index function and to search the transmitter＇s parameter （key）. By using proposed method, secure key is recovered from transmitted signal generated by low dimensional chaos and hyper chaos switching communication. Multi-parameters can also be identified from the transmitted signal with noise.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.61227902,61374210,and 61121003)
文摘A method of measuring in-situ magnetic field gradient is proposed in this paper. The magnetic shield is widely used in the atomic magnetometer. However, there is magnetic field gradient in the magnetic shield, which would lead to additional gradient broadening. It is impossible to use an ex-situ magnetometer to measure magnetic field gradient in the region of a cell, whose length of side is several centimeters. The method demonstrated in this paper can realize the in-situ measurement of the magnetic field gradient inside the cell, which is significant for the spin relaxation study. The magnetic field gradients along the longitudinal axis of the magnetic shield are measured by a spin-exchange relaxation-free （SERF） magnetometer by adding a magnetic field modulation in the probe beam＇s direction. The transmissivity of the cell for the probe beam is always inhomogeneous along the pump beam direction, and the method proposed in this paper is independent of the intensity of the probe beam, which means that the method is independent of the cell＇s transmissivity. This feature makes the method more practical experimentally. Moreover, the AC-Stark shift can seriously degrade and affect the precision of the magnetic field gradient measurement. The AC-Stark shift is suppressed by locking the pump beam to the resonance of potassium＇s D1 line. Furthermore, the residual magnetic fields are measured with σ＋- and σ--polarized pump beams, which can further suppress the effect of the AC-Stark shift. The method of measuring in-situ magnetic field gradient has achieved a magnetic field gradient precision of better than 30 pT/mm.
