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1. chinaXiv:201711.02426 [pdf]

基于初始运行状态的伽利略系统PPP国际时间比对

Mingjun,Ouyang; Baoqi,Sun; Yulong,Ge ; Qin,Weijin; Xuhai,Yang
分类: 物理学 >> 普通物理:统计和量子力学,量子信息等

GPS Precise Point Position (PPP) has become one of the main methods for time transfer in International Atomic Time (TAI) computation. The reliability and precision of TAI would be further increased with adding the new GNSS systems like Galileo and BeiDou. The Galileo initial service is officially launched on December 15, 2016, by the European Commission. This contribution investigates the possible performance of PPP time transfer with the Galileo constellation in the initial service phase toward UTC/TAI computation. We choose 7 stations with excellent external clocks to do Galileo PPP time transfer experiments. Daily RINEX files of 138 days, with a 30s sampling interval, were collected from December 15, 2016 until May 1, 2017. We designed seven solutions with different options on the parameter selection, products utilization and the frequency selection. For most links and solutions, the STD of time transfer differences between Galileo PPP and GPS PPP ranged from 0.2ns to 0.5ns. The time transfer performance was increased by fixing coordinates and/or troposphere delays to values obtained from GPS PPP. The results reveal that the stability of PPP time transfer with Galileo initial service could reach the level of sub-nanoseconds. The Galileo PPP technique will play a more important role in remote time transfer fields such as UTC/TAI computation.

提交时间: 2017-12-02 点击量290下载量79 评论 0

2. chinaXiv:201711.02787 [pdf]

光源混合频率调制的光热干涉工作点无源控制方法研究

李树旺
分类: 物理学 >> 普通物理:统计和量子力学,量子信息等

相位漂移现象是干涉测量中普遍存在的问题,对解调结果的准确度带来巨大影响。提出了一种光源混合频率调制的闭环工作点无源控制方法,通过直接高频调制光源的方式从单路干涉信号中提取出相位漂移信号,并利用低频控制信号对光源直接调制的方式予以补偿;通过高频、低频调制信号的配合,解决了单路干涉信号的工作点跟踪问题,以无源控制的方式保证干涉测量系统始终工作在最灵敏的线性区域。测试了光源在不同调制频率下的调制特性,比较了系统开、闭环状态下工作点的变化趋势,无源闭环工作点控制法与相位载波解调算法的对比解调结果表明两种方法解调结果相关度超过 ,证明该方法可行。

提交时间: 2017-11-29 点击量99下载量57 评论 0

3. chinaXiv:201711.02788 [pdf]

Analysis and mitigation of the carrier phase delay effect of the digital phase generated carrier algorithm

邵士勇
分类: 物理学 >> 普通物理:统计和量子力学,量子信息等

We present an improved digital phase generated carrier (PGC)algorithm based on the synchronous carrier restoration(SCR) method to mitigate the carrier phase delay effects. The most distinguishing feature of this method is that it picks up the carrier signal information (frequency and phase) from the interference signal directly and accomplishes the processing of carrier signal restoration synchronically. In comparison with the traditional one which adopts the initial carrier signal, the total-harmonic-distortions of the SCR method is only 0.091%, lower than the traditional one's 18.38%, and the signal-to-noise-ratio increases 29 dB. Further, we derive the analytic expression of distortion component and verify it by experiments. Thistechnique may be potentially applied in a long distance large-scale distributed fiber-optic interferometer sensors array.

提交时间: 2017-11-29 点击量94下载量48 评论 0

4. chinaXiv:201711.02791 [pdf]

Magnetic entropy change associated with critical behavior in the precursor region of single crystalline FeGe

张蕾
分类: 物理学 >> 凝聚态:电子结构、电、磁和光学性质

Cubic helimagnet FeGe has emerged as a class of skyrmion materials near room temperature that may impact future information technology. Experimentally identifying the detailed properties of skyrmion materials enables their practical application acceleratedly. Here we study the magnetic entropy change (MEC) of single crystalline FeGe in its precursor region and clarify its close relation to the critical exponents of a second-order phase transition in this area. The maximum MEC is found to be 2.86 J/kg.K for 7.0 T magnetic field change smaller than that of common magnetocaloric materials indicating the multiplicity and complexity of the magnetic structure phases in the precursor region. This result also implies that the competition among the multimagnetic phases can partly counteract the magnetic field driven force and establishes a stable balance. Based on the obtained MEC and the critical exponents, the exact Curie temperature of single crystalline FeGe under zero magnetic field is confirmed to be 279.1 K, higher than previously reported 278.2 K. This finding pave the way for reconstruction of FeGe phase diagram in the precursor region.

提交时间: 2017-11-27 点击量76下载量37 评论 0

5. chinaXiv:201711.02792 [pdf]

2017-Fe05Co05Si.pdf

张蕾
分类: 物理学 >> 凝聚态:电子结构、电、磁和光学性质

The magnetic entropy change [ΔSM(T;H)] around the phase transition temperature TC is investigated by the scaling method for Fe0:5Co0:5Si, which exhibits a skyrmion phase below TC. The parameters of ΔSM(T;H) exhibit field dependent behaviors. The ΔSM(T;H) curves under high field can be well scaled into a single universal curve independent of external field and temperature. However, ΔSM(T;H) curves under low field become divergent just below TC, which indicates a characteristic of first-order transition. The scaling investigation of ΔSM(T;H) curves indicates that the phase transition in Fe0:5Co0:5Si is of a weak first-order type in low field region, while it is driven into a second-order one under high field. This weak first-order phase transition in low field region resembles that in typical skyrmion system MnSi which is caused by the critical fluctuation. The result suggests that critical fluctuation plays an important role in the phase transition and formation of skyrmion state.

提交时间: 2017-11-27 点击量41下载量27 评论 0

6. chinaXiv:201711.02790 [pdf]

2017-CrNbS.pdf

张蕾
分类: 物理学 >> 凝聚态:电子结构、电、磁和光学性质

The magnetism of the single crystal Cr1=3NbS2, which exhibits chiral soliton lattice (CSL) state, is investigated. The magnetization displays strong magnetic anisotropy when the field is applied perpendicularly and parallel to the c-axis in low field region (H < HS, HS is the saturation field). The critical exponents of Cr1=3NbS2 are obtained as β = 0.370(4), γ = 1.380(2), and δ = 4.853(6), which are close to the theoretical prediction of three-dimensional Heisenberg model. Based on the scaling equation and the critical exponents, the H 􀀀 T phase diagram in the vicinity of the phase transition is constructed, where two critical points are determined. One is a tricrtical point which locates at the intersection between the CSL, forced ferromagnetic (FFM), and paramagnetic (PM) states. The other one is a critical point situated at the boundaries between CSL, helimagnetic (HM), and PM states.

提交时间: 2017-11-27 点击量30下载量16 评论 0

7. chinaXiv:201711.02797 [pdf]

Critical phenomenon in the itinerant ferromagnet Cr11Ge19 studied by scaling of the magnetic entropy change

张蕾
分类: 物理学 >> 凝聚态:电子结构、电、磁和光学性质

Critical phenomenon of the noncentrosymmetric Cr11Ge19, which exhibits an itinerant ferromagnetic ground state, is investigated by scaling of the magnetic entropy change [ΔSM(T;H)]. It is found that parameters #14;FWHM (the full width at half maximum), 􀀀ΔSmax M (the maximum of the magnetic entropy change), and RCP (the relative cooling power) of ΔSM(T) are governed by the power law of critical exponents. With the critical exponents, ΔSM(T;H) curves are scaled into a universal curve independent of temperature and field, which suggests that the magnetic transition is of a second order type. The universal collapse of ΔSM(T;H) indicates that the critical behavior of Cr11Ge19 can be well described by the scaling laws for the critical phenomenon. Moreover, the ΔSM follows the power law of Hn with n(T;H) = dlnjΔSMj=dln(H). The temperature dependence of n values reach minimum at #24; 71.5 K. Based on the magnetic specific change ΔCp(T;H), the actual magnetic transition temperature is strictly determined as TC = 71:3 #6; 0:2 K for the single crystal Cr11Ge19.

提交时间: 2017-11-27 点击量38下载量21 评论 0

8. chinaXiv:201711.02793 [pdf]

Scaling investigation of the magnetic entropy change in helimagnet MnSi

张蕾
分类: 物理学 >> 凝聚态:电子结构、电、磁和光学性质

The B20 compound MnSi exhibits a skyrmion phase in a certain range of temperature (T) and external magnetic ¯eld (H) in addition to the helimagnetic ordering. In this work, the magnetic entropy change (¢SM) in the single crystal helimagnet MnSi has been investigated by the scaling analysis. The ¢SM(T;H) curves in higher ¯eld range (2 kOe < H < 5.6 kOe) collapse onto an universal curve after scaling, which is independent of T and H. Based on this universal curve, the ¢SM(T;H) (excluding the skyrmion entropy change) at any T and H can be calculated. On the other hand, a small valley is found on the ¢SM(T) curve at » 28.5 K in the ¯eld range from » 1 kOe to » 2 kOe, which is resulted from the skyrmion phase. Subsequently, the magnetic entropy change of the skyrmion phase [¢SskX M (T;H)] can be derived by subtraction of the calculated ¢Scal M (T;H) from the experimental ¢Sexp M (T;H). The obtained results show that ¢SskX M reaches the maximum at » 1.6 kOe, which indicates the highest number of skyrmion vortices at that ¯eld.

提交时间: 2017-11-27 点击量37下载量18 评论 0

9. chinaXiv:201711.02794 [pdf]

Critical phenomenon of the single crystal helimagnet MnSi

张蕾
分类: 物理学 >> 凝聚态:电子结构、电、磁和光学性质

The critical behavior of the single crystal helimagnet MnSi is investigated by means of bulk dc-magnetization at the boundary between the conical state and paramagnetic phase. We obtain the critical exponents (¯ = 0:242 § 0:006, ° = 0:915 § 0:003, and ± = 4:734 § 0:006), where the self-consistency and reliability are veri¯ed by the Widom scaling law and the scaling equation. The critical exponents of MnSi belong to the universality class of tricritical mean-¯eld theory, which unambiguously indicates a tricritical phenomenon at the boundary between the ¯rst-order phase transition and the second-order one induced by the external magnetic ¯eld. The tricritical point (TCP) is determined as HTCP ¼ 3200 Oe at the critical temperature, consistent with the previous report [Phys. Rev. Lett. 110, 177207 (2013)]. The critical behavior suggests a long-range magnetic coupling with the exchange distance decaying as J(r) ¼ r¡4:3 in MnSi.

提交时间: 2017-11-27 点击量42下载量23 评论 0

10. chinaXiv:201711.02795 [pdf]

Electron Paramagnetic Resonance Study of the Pyrochlore Iridate Gd2Ir2O7

张蕾
分类: 物理学 >> 凝聚态:电子结构、电、磁和光学性质

The pyrochlore iridate Gd2Ir2O7 has been investigated by means of the electron paramagnetic resonance (EPR) spectroscopy. A magnetic transition at T¤ » 20 K is found in addition to the transition at TC » 130 K, which has not been reported previously. The phase transition at TC, which corresponds to a resistivity transition, is resulted from the long-range spin ordering of Ir4+ ions in all-in/all out state. However, the magnetic transition at T¤, which is regardless of resistivity transition, is not caused by Ir4+ but Gd3+ ions. Both of the magnetic transitions are irrelevant to the lattice distortion. We suggest that the competition between the enhanced paramagnetism of Gd3+ ions and the f ¡ d interaction should be responsible for the magnetic transition at T¤.

提交时间: 2017-11-27 点击量39下载量23 评论 0

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