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The gear meshing noise generated by the helicopter main reducer is one of the important sources of noise in the helicopter cabin. By improving the isolation performance of the struts supporting reducer to the gear meshing vibration, the purpose of reducing the gear meshing noise in the helicopter cabin can be achieved. Piezoelectric stack periodic strut (PSPS) composed of piezoelectric stacks and passive materials periodically arranged is an original type of strut with active and passive hybrid isolation characteristics. Piezoelectric stacks and passive materials form a periodic structure, which makes PSPS have a unique stopband characteristic. The propagation of elastic waves in the stopband frequency range is attenuated, which can improve the broadband passive vibration isolation capability of the PSPS; The piezoelectric stacks can adjust the elastic wave propagation in the PSPS and improve the single-frequency or multifrequency active isolation performance of the PSPS. Since the driving voltage and current range of the piezoelectric stacks significantly affect the isolation performance of the PSPS, this article focuses on the relationship between the isolation performance of the PSPS and the voltage and current required by the piezoelectric stacks. Firstly, based on the passive material periodic structure transfer matrix model, the driving voltage and current of the piezoelectric stacks are introduced into the model, and a PSPS electromechanical coupling model based on the transfer matrix form is established. Secondly, the correctness of the model is verified by the finite element software. Based on the model, the design process of PSPS parameters is proposed. The optimal isolation performance of PSPS is predicted under the limitation of maximum driving voltage and current. The effects of damping loss factor, exciting force, period number and passive material on the requirements of electrical parameters for active control are studied. A three-period PSPS strut composed of piezoelectric stack actuator and PV strut is used for experimental research, and the matching of electrical parameters of this PSPS in the test is analyzed.

Genomic DNA was extracted from 1 038 peripheral blood samples from HIV-infected individuals in Henan Province. One-step single-tube nested PCR was performed to amplify the 529 bp repeating sequences of Toxoplasma gondii. Of the 1 038 samples （762 from males and 276 from females）, 66 showed positive PCR results, with a positive rate of 6.4%. The PCR positive rate in males and females was 6.3% （48/762） and 6.5% （18/276） respectively. The PCR positive rate in the married HIV individuals was 4.9%（25/508）, and that in unmarried, divorced and widowed HIV individuals was 7.7% （41/530）（χ2 = 3.451, P> 0.05）. The PCR positive rate in HIV individuals with a high-school educational level or above was 6.9%（34/489）, and that in those below the high-school level was 5.8% （32/549）（χ2 = 0.545, P> 0.05）. The highest infection rate was in the age group of 20-40 years（7.6%, 31/410）. In addition, the Toxoplasma infection rate in those with and without a history of venereal diseases, and those with an unknown history was 8.0%（9/113）, 6.5%（50/773） and 4.6%（7/152） respectively （χ2 = 0.355, P> 0.05）.