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The Earth Orientation Center of the International Earth Rotation and Reference Systems Service (IERS) has the task to provide the scientific community with the international reference time series of Earth orientation parameters (EOP), referred to as IERS EOP C04 or C04. These series result from a combination of operational EOP series derived from VLBI, GNSS, SLR, and DORIS. The C04 series were updated to provide EOP series consistent with the set of station coordinates of the ITRF 2014. The new C04, referred to as IERS EOP 14C04, is aligned onto the most recent versions of the conventional reference frames (ITRF 2014 and ICRF2). Additionally, the combination algorithm was revised to include an improved weighting of the intra-technique solutions. Over the period 2010–2015, differences to the IVS combination exhibit standard deviations of 40 μas for nutation and 10 μs for UT1. Differences to the IGS combination reveal a standard deviation of 30 μas for polar motion. The IERS EOP 14C04 was adopted by the IERS directing board as the IERS reference series by February 1, 2017.

Malfunctioning satellites are normally in tumbling state due to residual angular momentum, rendering direct capture impossible. Therefore, detumbling these objects is an indispensable phase for on-orbit safe capture. A novel detumbling method, using a flexible device (e.g., brush or rod) to approach and compliantly contact the target objects, has been proposed to successfully avoid the major drawback of potential risky collisions. Although efficient, the flexible-device-based method suffers from two limitations: (i) Due to complex three-axis rotary motion, it is extremely difficult to predetermine the contact position on the target satellite so as to ensure simultaneous suppression of rotation and nutation. (ii) The conventional finite-element-based dynamic model of the large-deformation device is high-dimensional, causing unacceptable computing time for the on-orbit task. To address these problems, this paper proposes an optimal nutation suppressing method to ensure the most efficient suppression of nutation during detumbling. In addition, a highly efficient data-driven model is proposed to accurately describe the large-deformation flexible device for real-time on-orbit computation. Finally, numerical simulations are carried out to verify the feasibility and efficiency of the present method.

The understanding of how spins move and can be manipulated at pico- and femtosecond timescales has implications for ultrafast and energy-efficient data-processing and storage applications. However, the possibility of realizing commercial technologies based on ultrafast spin dynamics has been hampered by our limited knowledge of the physics behind processes on this timescale. Recently, it has been suggested that inertial effects should be considered in the full description of the spin dynamics at these ultrafast timescales, but a clear observation of such effects in ferromagnets is still lacking. Here, we report direct experimental evidence of intrinsic inertial spin dynamics in ferromagnetic thin films in the form of a nutation of the magnetization at a frequency of ~0.5 THz. This allows us to reveal that the angular momentum relaxation time in ferromagnets is on the order of 10 ps.Inertial dynamics are observed in a ferromagnet. Specifically, a nutation is seen on top of the usual spin precession that has a lifetime on the order of 10 picoseconds.

In order to verify the time variability of free core nutation (FCN) period, global superconducting gravimeter (SG) observations were analyzed based on synthetic test data. The gravity data series were synthesized to check the detectability of resonance variation caused by FCN period change. The tests indicate that the discrepancy between the FCN periods determined by SG and VLBI observations is caused by the high correlation between the FCN parameter and the amplitude factor of the ψ1 wave. The K1 wave is more sensitive to the FCN period change than other diurnal waves. The limit of the standard deviation of the K1 wave is found for more precisely observing the FCN period change. Tidal parameters of diurnal waves estimated from long series of 20 global SG stations were analyzed. A common variation trend is found in the amplitude factor of both K1 and ψ1 waves in all 8 stations above the limit, which indicates the FCN period may be not so stable in time. Furthermore, the variation in the K1 and ψ1 waves constrains the FCN period change to between 2.5 and 4 sidereal days, which also agrees with the possible variation from the current VLBI and SG observations.

The single-stage double circular-arc spiral bevel gear nutation drive, primarily composed of a pair of nutation bevel gears and a ball-cage type constant velocity joint, exhibits advantages of compact structure and high transmission ratio. Based on the establishment of 3D models and virtual assembly of its key components, a dynamic simulation model for the single-stage nutation bevel gear drive was developed. Under the condition of transmitting power at 20 kW, dynamic simulation analysis was conducted for four models with input shaft speeds of 1000 r/min, 2000 r/min, 3000 r/min, and 4000 r/min in the first group. Subsequently, under the condition of input shaft speeds at 3000 r/min, dynamic simulation analysis was performed for four models with power levels of 10 kW, 20 kW, 30 kW, and 40 kW in the second group. The dynamic simulation results of the two groups of four models were analyzed and compared in terms of output shaft speed and gear meshing force. The analysis revealed that the relative error between the simulated output shaft speed and the theoretical value was minimal, indicating that the structural design of the single-stage nutation drive is reasonable and the simulation model is basically correct. Additionally, the influence of different input speeds and power levels on the meshing forces of the double circular-arc spiral bevel gear were analyzed. The dynamic simulation analysis results are of significant importance for further optimization and improvement of the single-stage double circular-arc spiral bevel gear nutation drive.

Ballistic gelatin is widely used as a kind of tissue simulants in wound ballistics. Evaluations of the wound tract of gelatin by projectiles are mainly based on fissures in the gelatin slices. For there are difficulties in building relationships between the areas and the fissures, a new method based on dye diffusion is proposed in this paper. Colored regions in the slices are obtained after penetration of a Chinese 7.62mm rifle bullet into the gelatin block. The colored regions can be divided into ‘X’, ‘I’ and branching ‘I’ shapes. In the second half of the penetration, there is a strong correlation between the areas of the regions and the energy dissipation of the bullet. However, the correlation is poor in the first half of the penetration. Branches of the colored regions mainly distributed at the heads and tails of the permanent cavities. The permanent cavities’ shapes have a great dependence on the nutation angles of the bullets. Orientation angles of the permanent cavities are determined by the precession angles of the bullets.

Diurnal tidal oscillations in the coupled atmosphere–ocean system generate important contributions to the Earth’s free core nutation (FCN) and annual and sub-annual components of forced nutation in the celestial pole offsets. The determination of FCN parameters cannot avoid the influence of geophysical fluid excitation neither with the direct analysis of FCN signal (direct approaches) nor with the resonance analysis of forced nutation (resonance approaches). There is a significant difference in the FCN parameters obtained with resonance and direct approaches from celestial pole offsets observed through very long baseline interferometry (VLBI). The source of the difference between the two lacks quantitative analysis, which causes difficulties in interpreting the validity of the derived FCN parameters. Using both approaches, we conducted a simulation of celestial pole offsets to quantitatively demonstrate how geophysical fluid excitation affects the determination of FCN parameters from VLBI observations. Using the same excitation source, the FCN period obtained by the direct approach deviated from the set value (430.21 d) by more than 10 d, while the FCN period obtained by the resonance approach showed no deviation from the set value by more than 1 d. The results indicate that the resonance approach more accurately reflects the intrinsic period of the FCN. The impact of atmospheric and oceanic contributions on the determination of the FCN period with the resonance approach was within 2 d. Numerical simulation shows that discrepancies in FCN parameters caused by geophysical excitation were nonnegligible in constructing accurate FCN models.

We compare nutation time series determined by several International VLBI Service for geodesy and astrometry (IVS) analysis centers. These series were made available through the International Earth Rotation and Reference Systems Service (IERS). We adjust the amplitudes of the main nutations, including the free motion associated with the free core nutation (FCN). Then, we discuss the results in terms of physics of the Earth’s interior. We find consistent FCN signals in all of the time series, and we provide corrections to IAU 2000A series for a number of nutation terms with realistic errors. It appears that the analysis configuration or the software packages used by each analysis center introduce an error comparable to the amplitude of the prominent corrections. We show that the inconsistencies between series have significant consequences on our understanding of the Earth’s deep interior, especially for the free inner core resonance: they induce an uncertainty on the FCN period of about 0.5 day, and on the free inner core nutation (FICN) period of more than 1000 days, comparable to the estimated period itself. Though the FCN parameters are not so much affected, a 100 % error shows up for the FICN parameters and prevents from geophysical conclusions.

The attempt to quantify the corrections of lunisolar nutation components was made after analysis of six sets of Earth’s orientation parameters (EOP). The deviations of the long-term nutation components about IAU2006/IAU2000A precession–nutation model are consistent with the uncertainties suggested by Mathews et al. (J Geophys Res Solid Earth, 2002. https://doi.org/10.1029/2001JB000390 ), but they exceed the errors determined in this work. The corrections are validated using the IERS 14C04 and IVS 19q4e combined solutions. After applying the corrections found in this work to the 14C04 nutation residuals, we analyzed the remaining signals, which contain the signature of the free core nutation (FCN). The eigenperiod of the FCN is fixed to the value derived from the resonance of the non-hydrostatic earth model in a priori. The amplitude of FCN is computed by fitting observations to the empirical model using a sliding window, the length of window is determined by taking into account the interference between those close nutation components and the FCN. In addition, we also fitted the nutation residuals by a viscous damping function; both methods produce the same results in the amplitudes of FCN. The magnitude of the free core nutation bears a “V-shape” distribution, and furthermore, the oscillation of the FCN shows a decay and a steady reinforcement before and after 1999. In order to examine the origin of the modulation in FCN’s magnitude, we briefly analyzed the possible damping or beating mechanism behind it. We diagnosed the magnitude and running phase changes of FCN by comparing it with the occurrence of the transient geomagnetic jerks. The weighted root mean square errors of nutation residuals are minimally reduced about 36 % when the corrections to the 21 nutation components and the FCN signature are considered together.

Quantum emitters respond to resonant illumination by radiating part of the absorbed energy. A component of this radiation field is phase coherent with the driving tone, whereas another component is incoherent and consists of spontaneously emitted photons, forming the fluorescence signal 1 . Atoms, molecules and colour centres are routinely detected by their fluorescence at optical frequencies, with important applications in quantum technology 2 , 3 and microscopy 4 – 7 . By contrast, electron spins are usually detected by the phase-coherent echoes that they emit in response to microwave driving pulses 8 . The incoherent part of their radiation—a stream of microwave photons spontaneously emitted upon individual spin relaxation events—has not been observed so far because of the low spin radiative decay rate and of the lack of single microwave photon detectors (SMPDs). Here using superconducting quantum devices, we demonstrate the detection of a small ensemble of donor spins in silicon by their fluorescence at microwave frequencies and millikelvin temperatures. We enhance their radiative decay rate by coupling them to a high-quality-factor and small-mode-volume superconducting resonator 9 , and we connect the device output to a newly developed SMPD 10 based on a superconducting qubit. In addition, we show that the SMPD can be used to detect spin echoes and that standard spin characterization measurements (Rabi nutation and spectroscopy) can be achieved with both echo and fluorescence detection. We discuss the potential of SMPD detection as a method for magnetic resonance spectroscopy of small numbers of spins. An ensemble of electron spins is detected by their microwave fluorescence using a superconducting single microwave photon counter, making single-spin electron spin resonance spectroscopy a possible future prospect.