We present a high precision frequency determination method for digitized NMR FID signals.The method employs high precision numerical integration rather than simple summation as in many other techniques.With no indepen...We present a high precision frequency determination method for digitized NMR FID signals.The method employs high precision numerical integration rather than simple summation as in many other techniques.With no independent knowledge of the other parameters of a NMR FID signal(phaseφ,amplitude A,and transverse relaxation time T_(2))this method can determine the signal frequency f_(0)with a precision of 1/(8π^(2)f_(0)^(2)T_(2)^(2))if the observation time T≫T_(2).The method is especially convenient when the detailed shape of the observed FT NMR spectrum is not well defined.When T2 is+∞and the signal becomes pure sinusoidal,the precision of the method is 3/(2π^(2)f_(0)^(2)T_(2))which is one order more precise than the±1 count error induced precision of a typical frequency counter.Analysis of this method shows that the integration reduces the noise by bandwidth narrowing as in a lock-in amplifier,and no extra signal filters are needed.For a pure sinusoidal signal we find from numerical simulations that the noise-induced error in this method reaches the Cramer-Rao Lower Band(CRLB)on frequency determination.For the damped sinusoidal case of most interest,the noise-induced error is found to be within a factor of 2 of CRLB when the measurement time T is 2 or 3 times larger than T2.We discuss possible improvements for the precision of this method.展开更多
The measurement of parity-violating （PV） observables in few-nucleon system can shed light on our current understanding of the weak interaction between nucleons.Theoretical models describe the nucleonnucleon weak int...The measurement of parity-violating （PV） observables in few-nucleon system can shed light on our current understanding of the weak interaction between nucleons.Theoretical models describe the nucleonnucleon weak interaction at low energies use a series of undetermined parameters.Two parity violating measurements have been considered： the capture of polarized slow neutrons on hydrogen （n ＋ p → d ＋ γ） at Los Alamos National Laboratory for first phase and Oka Ridge National Laboratory for second phase and the helicity dependence of the deuteron photodisintegration cross section using circularly polarized photons （γ ＋ d → n ＋ p） at Shanghai Institute of Applied Physics.The goal of both experiments is to constraint the weak meson-nucleon couplings to a precision of 1 ×10^-8 .The introduction of both experiments is presented.展开更多
基金supported by the Department of Energy and by NSF grant PHY-1068712.support from the Indiana University Center for Spacetime Symmetries and the Indiana University Collaborative Research Grant program+1 种基金supported by NSF grant PHY-1207656.support.C.Fu acknowledges the support from the Specialized Research Fund for the Doctoral Program of Higher Education under grant 20120073110065.
文摘We present a high precision frequency determination method for digitized NMR FID signals.The method employs high precision numerical integration rather than simple summation as in many other techniques.With no independent knowledge of the other parameters of a NMR FID signal(phaseφ,amplitude A,and transverse relaxation time T_(2))this method can determine the signal frequency f_(0)with a precision of 1/(8π^(2)f_(0)^(2)T_(2)^(2))if the observation time T≫T_(2).The method is especially convenient when the detailed shape of the observed FT NMR spectrum is not well defined.When T2 is+∞and the signal becomes pure sinusoidal,the precision of the method is 3/(2π^(2)f_(0)^(2)T_(2))which is one order more precise than the±1 count error induced precision of a typical frequency counter.Analysis of this method shows that the integration reduces the noise by bandwidth narrowing as in a lock-in amplifier,and no extra signal filters are needed.For a pure sinusoidal signal we find from numerical simulations that the noise-induced error in this method reaches the Cramer-Rao Lower Band(CRLB)on frequency determination.For the damped sinusoidal case of most interest,the noise-induced error is found to be within a factor of 2 of CRLB when the measurement time T is 2 or 3 times larger than T2.We discuss possible improvements for the precision of this method.
基金Supported by One Hundred Person Project of Chinese Academy of Sciences (26010701)Knowledge Innovation Project of the Chinese Academy of Sciences (KJCX2-SW-N13)+1 种基金Pujiang Talent Project of the Shanghai Science and Technology Committee (06PJ14114)National Natural Science Foundation of China (10675156)
文摘The measurement of parity-violating （PV） observables in few-nucleon system can shed light on our current understanding of the weak interaction between nucleons.Theoretical models describe the nucleonnucleon weak interaction at low energies use a series of undetermined parameters.Two parity violating measurements have been considered： the capture of polarized slow neutrons on hydrogen （n ＋ p → d ＋ γ） at Los Alamos National Laboratory for first phase and Oka Ridge National Laboratory for second phase and the helicity dependence of the deuteron photodisintegration cross section using circularly polarized photons （γ ＋ d → n ＋ p） at Shanghai Institute of Applied Physics.The goal of both experiments is to constraint the weak meson-nucleon couplings to a precision of 1 ×10^-8 .The introduction of both experiments is presented.
