Koi carps frequently swim in burst-and-coast style, which consists of a burst phase and a coast phase. We quantify the swimming kinematics and the flow patterns generated by the carps in burst-and-coast swimming. In the burst phase, the carps burst in two modes: in the first, the tail beats for at least one cycle (multiple tail-beat mode); in the second, the tail beats for only a half-cycle (half tail-beat mode). The carp generates a vortex ring in each half-cycle beat. The vortex rings generated during bursting in multiple tail-beat mode form a linked chain, but only one vortex ring is generated in half tail-beat mode. The wake morphologies, such as momentum angle and jet angle, also show much difference between the two modes. In the burst phase, the kinematic data and the impulse obtained from the wake are linked to obtain the drag coefficient (C d,burst Ϸ0.242). In the coast phase, drag coefficient (C d,coast Ϸ0.060) is estimated from swimming speed deceleration. Our estimation suggests that nearly 45% of energy is saved when burst-and-coast swimming is used by the koi carps compared with steady swimming at the same mean speed.

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Optical frequency combs have become an essential tool for distance metrology, showing great advantages compared with traditional laser interferometry. However, there is not yet an appropriate method for air refractive index correction to ensure the high performance of such techniques when they are applied in air. In this study, we developed a novel heterodyne interferometry technique based on two-colour frequency combs for air refractive index correction. In continuous 500-second tests, a stability of 1.0 × 10−11 was achieved in the measurement of the difference in the optical distance between two wavelengths. Furthermore, the measurement results and the calculations are in nearly perfect agreement, with a standard deviation of 3.8 × 10−11 throughout the 10-hour period. The final two-colour correction of the refractive index of air over a path length of 61 m was demonstrated to exhibit an uncertainty better than 1.4 × 10−8, which is the best result ever reported without precise knowledge of environmental parameters.

We present (1) the dynamical equations of deforming body and (2) an integrated method for deforming body dynamics and unsteady fluid dynamics, to investigate a modelled freely self-propelled fish. The theoretical model and practical method is applicable for studies on the general mechanics of animal locomotion such as flying in air and swimming in water, particularly of free self-propulsion. The present results behave more credibly than the previous numerical studies and are close to the experimental results, and the aligned vortices pattern is discovered in cruising swimming.

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High-accuracy two-color heterodyne interferometry based on fundamental and second harmonic of frequency combs for air refractive index correction is developed. A monitor interferometer as well as a probe interferometer is constructed to compensate the phase noises and drifts, which are caused by introducing the acousto-optic modulators for heterodyne interferometer, to realize high-accuracy measurement of optical distance. A relative stability of 10−10 to the total length for 500 s is achieved in the measurement of an optical path length difference between two wavelengths. In long-term measurements, the interferometric measurement results and the calculations from empirical equation of air refractive indices are in good agreement with a standard deviation of 4.1 × 10−10 throughout the 10 h period. By applying the two-color method, high-accuracy correction of air refractive index with an uncertainty of 8.9 × 10−8 is achieved during 10 h continuous measurements while the total refractive index changes with a range of 2.0 × 10−6.

The synthesis and magnetic properties of Pr x Ce 1−x Fe 2 have been investigated. The formation of Pr x Ce 1−x Fe 2 is found to depend strongly on annealing temperature. Pure singlephase compound can be synthesized at ambient pressure when x 0.5. The main phase of the Laves structure can still be observed up to x = 0.8. The study of crystalline parameters, magnetic moments and Mössbauer spectra for single-phase Pr x Ce 1−x Fe 2 is performed. Curie temperature and local Fe magnetic moment increase with the increasing Pr concentration. Extrapolating the trends the spontaneous magnetization and anisotropy constant of PrFe 2 are 4.98 µ B fu −1 and 7.3 × 10 5 J m −3 at 1.5 K, respectively. Magnetostriction increases with increasing x and the largest saturation magnetostriction, 200 ppm, is observed for x = 0.5. With the increase of Pr concentration, lattice parameter and spontaneous magnetization anomalies exist in a specific range 0.2 < x < 0.5 that can be attributed to the change of Ce ion valence toward tetravalent.

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