The modified cosmology like quintessence model with kination phase predicted the Hubble expansion rate of the universe before Big Bang Nucleosynthesis is different from the standard cosmological scenario. The modified...The modified cosmology like quintessence model with kination phase predicted the Hubble expansion rate of the universe before Big Bang Nucleosynthesis is different from the standard cosmological scenario. The modified expansion rate leaves its imprint on the relic density of asymmetric dark matter. In this work, we review the calculation of relic density of asymmetric WIMP dark matter in the standard cosmological scenario and quintessence model with kination phase. Then we use the Planck data to find constraints on the annihilation cross section and the mass of the asymmetric dark matter in those models.展开更多
This study aims to discuss anisotropic solutions that are spherically symmetric in the quintessence field,which describe compact stellar objects in the modified Rastall teleparallel theory of gravity.To achieve this g...This study aims to discuss anisotropic solutions that are spherically symmetric in the quintessence field,which describe compact stellar objects in the modified Rastall teleparallel theory of gravity.To achieve this goal,the Krori and Barua arrangement for spherically symmetric components of the line element is incorporated.We explore the field equations by selecting appropriate off-diagonal tetrad fields.Born-Infeld function of torsion f(T)=β√λT+1-1 and power law form h(T)=δTn are used.The Born-Infeld gravity was the first modified teleparallel gravity to discuss inflation.We use the linear equation of state pr=ξρto separate the quintessence density.After obtaining the field equations,we investigate different physical parameters that demonstrate the stability and physical acceptability of the stellar models.We use observational data,such as the mass and radius of the compact star candidates PSRJ 1416-2230,Cen X-3,&4U 1820-30,to ensure the physical plausibility of our findings.展开更多
基于弯曲波在声黑洞(acoustic black hole,ABH)结构中振幅不断增大的特性,提出了一种新型径向夹心式径-弯复合换能器,该换能器由径向夹心式圆环换能器与外围的环形ABH结构组成.ABH结构的存在实现了换能器径向振动与弯曲振动之间的转换,...基于弯曲波在声黑洞(acoustic black hole,ABH)结构中振幅不断增大的特性,提出了一种新型径向夹心式径-弯复合换能器,该换能器由径向夹心式圆环换能器与外围的环形ABH结构组成.ABH结构的存在实现了换能器径向振动与弯曲振动之间的转换,提高了换能器的声辐射性能.利用几何声学的方法建立了ABH结构弯曲振动的解析模型,给出了其弯曲振动的本征频率,并结合有限元方法讨论了换能器机电转换性能随尺寸变化的关系.通过有限元方法给出了该换能器在空气中的辐射声压场、辐射声强以及辐射指向性,仿真结果表明,ABH结构的存在能够改善换能器弯曲振动的机电转换性能,提高换能器的声辐射性能,使换能器呈现出一定的辐射指向性.最后通过实验对换能器样机的电阻抗特性以及振动模态进行测量,实验结果与仿真相符合.展开更多
声学黑洞(acoustic black hole,ABH)效应可以产生强烈的能量集中,能够将高频率低振幅的低品质振动能量转化为高振幅的高品质振动能量,从而便于利用。提出并研究了一种环形二维声学黑洞压电能量收集装置。有限元分析结果表明,环形二维AB...声学黑洞(acoustic black hole,ABH)效应可以产生强烈的能量集中,能够将高频率低振幅的低品质振动能量转化为高振幅的高品质振动能量,从而便于利用。提出并研究了一种环形二维声学黑洞压电能量收集装置。有限元分析结果表明,环形二维ABH结构能在宽频域内显著提高能量收集效率。搭建了环形二维声学黑洞压电能量收集器试验测试平台,通过试验验证了仿真结果的正确性。与经典二维ABH结构相比,环形二维ABH结构具有更好的能量收集效率和结构强度。分析了压电片几何尺寸等因素对装置能量收集效率的影响,得到了能获得较高输出功率的几何尺寸范围,并进行了正交试验设计,研究了截断厚度、压电片尺寸、中央平台直径、幂指数等多因素的综合影响。展开更多
为减少联合收获机振动对谷物流量传感器监测结果的干扰,设计了一种基于声学黑洞(ABH,acoustic black hole)原理的谷物流量传感器龙门支架减振结构,通过有限元方法分析减振结构的振动特性,分析了二维声学黑洞比例系数ε、幂函数指数m和半...为减少联合收获机振动对谷物流量传感器监测结果的干扰,设计了一种基于声学黑洞(ABH,acoustic black hole)原理的谷物流量传感器龙门支架减振结构,通过有限元方法分析减振结构的振动特性,分析了二维声学黑洞比例系数ε、幂函数指数m和半径R对其减振性能的影响规律。结果表明,声学黑洞能够显著降低龙门支架的振动,ε、m和R对声学黑洞减振性能的影响均未表现出明显线性关系,当ε=0.001 2、m=2.5、R=15 mm时声学黑洞的减振效果最好。以振动速度平方和作为优化目标,建立了多项式回归代理模型,通过遗传算法对声学黑洞比例系数ε、幂函数指数m和半径R的取值进行了优化。相比于未添加声学黑洞的原始龙门支架和初始声学黑洞方案,优化后龙门支架的振动速度平方和分别降低68.92%和2%,表明优化方案具有更佳的减振性能。提出的基于声学黑洞的减振结构和优化设计方法为农业机械被动宽频减振研究提供了理论参考。展开更多
In the study of weak cosmic censorship conjectures(WCCC),some research finds that the Reissner-Nordström black hole might be destroyed by a test particle with particular mass and charge under some conditions,whic...In the study of weak cosmic censorship conjectures(WCCC),some research finds that the Reissner-Nordström black hole might be destroyed by a test particle with particular mass and charge under some conditions,which means that the naked singularity of the black hole could be observed.This is not allowed in WCCC.We have never observed such naked singularities which should not exist in theory,so we need to find a proper way to protect the black hole from being destroyed by such particles.In this paper,we study a Reissner-Nordström black hole that is surrounded by quintessence(RN-Q)and find that the black hole would be stable and safe because of the effective potential barrier induced by the quintessence term.This result may also show in a sense that the quintessence might have more potential value.展开更多
文摘The modified cosmology like quintessence model with kination phase predicted the Hubble expansion rate of the universe before Big Bang Nucleosynthesis is different from the standard cosmological scenario. The modified expansion rate leaves its imprint on the relic density of asymmetric dark matter. In this work, we review the calculation of relic density of asymmetric WIMP dark matter in the standard cosmological scenario and quintessence model with kination phase. Then we use the Planck data to find constraints on the annihilation cross section and the mass of the asymmetric dark matter in those models.
基金funded by the National Natural Science Foundation of China (Grant No. 11975145)
文摘This study aims to discuss anisotropic solutions that are spherically symmetric in the quintessence field,which describe compact stellar objects in the modified Rastall teleparallel theory of gravity.To achieve this goal,the Krori and Barua arrangement for spherically symmetric components of the line element is incorporated.We explore the field equations by selecting appropriate off-diagonal tetrad fields.Born-Infeld function of torsion f(T)=β√λT+1-1 and power law form h(T)=δTn are used.The Born-Infeld gravity was the first modified teleparallel gravity to discuss inflation.We use the linear equation of state pr=ξρto separate the quintessence density.After obtaining the field equations,we investigate different physical parameters that demonstrate the stability and physical acceptability of the stellar models.We use observational data,such as the mass and radius of the compact star candidates PSRJ 1416-2230,Cen X-3,&4U 1820-30,to ensure the physical plausibility of our findings.
文摘基于弯曲波在声黑洞(acoustic black hole,ABH)结构中振幅不断增大的特性,提出了一种新型径向夹心式径-弯复合换能器,该换能器由径向夹心式圆环换能器与外围的环形ABH结构组成.ABH结构的存在实现了换能器径向振动与弯曲振动之间的转换,提高了换能器的声辐射性能.利用几何声学的方法建立了ABH结构弯曲振动的解析模型,给出了其弯曲振动的本征频率,并结合有限元方法讨论了换能器机电转换性能随尺寸变化的关系.通过有限元方法给出了该换能器在空气中的辐射声压场、辐射声强以及辐射指向性,仿真结果表明,ABH结构的存在能够改善换能器弯曲振动的机电转换性能,提高换能器的声辐射性能,使换能器呈现出一定的辐射指向性.最后通过实验对换能器样机的电阻抗特性以及振动模态进行测量,实验结果与仿真相符合.
文摘声学黑洞(acoustic black hole,ABH)效应可以产生强烈的能量集中,能够将高频率低振幅的低品质振动能量转化为高振幅的高品质振动能量,从而便于利用。提出并研究了一种环形二维声学黑洞压电能量收集装置。有限元分析结果表明,环形二维ABH结构能在宽频域内显著提高能量收集效率。搭建了环形二维声学黑洞压电能量收集器试验测试平台,通过试验验证了仿真结果的正确性。与经典二维ABH结构相比,环形二维ABH结构具有更好的能量收集效率和结构强度。分析了压电片几何尺寸等因素对装置能量收集效率的影响,得到了能获得较高输出功率的几何尺寸范围,并进行了正交试验设计,研究了截断厚度、压电片尺寸、中央平台直径、幂指数等多因素的综合影响。
文摘为减少联合收获机振动对谷物流量传感器监测结果的干扰,设计了一种基于声学黑洞(ABH,acoustic black hole)原理的谷物流量传感器龙门支架减振结构,通过有限元方法分析减振结构的振动特性,分析了二维声学黑洞比例系数ε、幂函数指数m和半径R对其减振性能的影响规律。结果表明,声学黑洞能够显著降低龙门支架的振动,ε、m和R对声学黑洞减振性能的影响均未表现出明显线性关系,当ε=0.001 2、m=2.5、R=15 mm时声学黑洞的减振效果最好。以振动速度平方和作为优化目标,建立了多项式回归代理模型,通过遗传算法对声学黑洞比例系数ε、幂函数指数m和半径R的取值进行了优化。相比于未添加声学黑洞的原始龙门支架和初始声学黑洞方案,优化后龙门支架的振动速度平方和分别降低68.92%和2%,表明优化方案具有更佳的减振性能。提出的基于声学黑洞的减振结构和优化设计方法为农业机械被动宽频减振研究提供了理论参考。
基金supported by Foundation Research Project of Shaanxi Province in Natural Science (Grant No.2019JQ-919)Special Project of Education Department of Shaanxi Province in Natural Science (Grant No.20JK0635)Talent Foundation of Weinan Normal University (Grant No.201120039)。
文摘In the study of weak cosmic censorship conjectures(WCCC),some research finds that the Reissner-Nordström black hole might be destroyed by a test particle with particular mass and charge under some conditions,which means that the naked singularity of the black hole could be observed.This is not allowed in WCCC.We have never observed such naked singularities which should not exist in theory,so we need to find a proper way to protect the black hole from being destroyed by such particles.In this paper,we study a Reissner-Nordström black hole that is surrounded by quintessence(RN-Q)and find that the black hole would be stable and safe because of the effective potential barrier induced by the quintessence term.This result may also show in a sense that the quintessence might have more potential value.
