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The determination of nuclear symmetry energy and, in particular, its density dependence is a long-standing problem for the nuclear physics community. Previous studies have found that the product of electric dipole polarizability ${\ensuremath{\alpha}}_{D}$ and symmetry energy at saturation density $J$ has a strong linear correlation with $L$, the slope parameter of symmetry energy. However, the current uncertainty of $J$ hinders the precise constraint on $L$. We investigate the correlations between electric dipole polarizability ${\ensuremath{\alpha}}_{D}$ (or times symmetry energy at saturation density $J$) in Sn isotopes and the slope parameter of symmetry energy $L$ using the quasiparticle random-phase approximation based on the Skyrme Hartree-Fock-Bogoliubov model. A strong linear correlation between ${\ensuremath{\alpha}}_{D}$ and $L$ is found in neutron-rich Sn isotopes where pygmy dipole resonance (PDR) gives a considerable contribution to ${\ensuremath{\alpha}}_{D}$, attributed to the pairing correlations playing important roles through PDR. This newly discovered linear correlation would help one to constrain $L$ and neutron-skin thickness $\mathrm{\ensuremath{\Delta}}{R}_{n}p$ stiffly if ${\ensuremath{\alpha}}_{D}$ is measured with high resolution in neutron-rich nuclei. Additionally, a linear correlation between ${\ensuremath{\alpha}}_{D}J$ in a nucleus around the $\ensuremath{\beta}$-stability line and ${\ensuremath{\alpha}}_{D}$ in a neutron-rich nucleus can be used to assess ${\ensuremath{\alpha}}_{D}$ in neutron-rich nuclei.

A Piezo-hydraulic Energy Harvester(PHEH) was presented based on solid-fluid coupling vibration to harvest low-frequency and high-level vibration energy,and its structure as well as working principle were introduced.With an established energy-conversion model,the influence factors on the piezo-hydraulic harvester were analyzed.The theoretic results show that the output performance of the PHEH depends on the vibration frequency/level,the structure and size of piezodisc/cylinder,liquid volume/performance,and system backpressure.The desired performance can not be achieved unless the above parameters are matched well.By a piezodisc with a diameter of 60 mm and a thickness of 0.9 mm and a cylinder with a diameter of 16 cm and a length of 100 cm,a PHVI was fabricated and tested by taking water as liquid medium at different frequencies/backpressures/exciter-amplitudes.The test results suggest that there is an optimal vibration frequency(8 Hz) for the PHEH to achieve the maximal output voltage,which rises with the increasing of backpressure and vibration level.In the case of unvaried other parameters,the achieved voltage from the PHEH under 0.4 MPa is 1.65 times that under 0.2 MPa.