分类: 信息科学与系统科学 >> 信息科学与系统科学基础学科 分类: 物理学 >> 电磁学、光学、声学、传热、经典力学和流体动力学 分类: 天文学 >> 天文学 提交时间: 2024-05-22
摘要: The electromagnetic fields of point sources with time varying charges moving in the vacuum are derived using the Liénard-Wiechert potentials. The properties of the propagation velocities and the Doppler effect are discussed based on their far fields. The results show that the velocity of the electromagnetic waves and the velocity of the sources cannot be added like vectors; the velocity of electromagnetic waves of moving sources are anisotropic in the vacuum; the transverse Doppler shift is intrinsically included in the fields of the moving sources and is not a pure relativity effect caused by time dilation. Since the fields are rigorous solutions of the Maxwell’s equations, the findings can help us to abort the long-standing misinterpretations concerning about the classic mechanics and the classic electromagnetic theory. Although it may violate the theory of the special relativity, we show mathematically that, when the sources move faster than the light in the vacuum, the electromagnetic barriers and the electromagnetic shock waves can be clearly predicted using the exact solutions. Since they cannot be detected by observers in the region outside their shock wave zones, an intuitive and reasonable hypothesis can be made that the superluminal sources may be considered as a kind of electromagnetic blackholes.
分类: 物理学 >> 电磁学、光学、声学、传热、经典力学和流体动力学 提交时间: 2024-05-09
摘要: 工程中必须处理的以及人们在自然中碰到的流体,其流动在绝大多数情况下是湍动的,对这些流动的描述需要一种统计性的方法。容易描述的层流(Laminar flow)异常少见。我们相信,流体力学不能只局限于这些很少碰到的特殊情形,并且个别层流的经典描述虽然无疑重要而有价值,但是只能作为真正湍流理论的导引章节。在湍流理论中,研究的目标是宏观上相同外界条件下的流动系综的性质。
分类: 信息科学与系统科学 >> 信息科学与系统科学基础学科 分类: 物理学 >> 电磁学、光学、声学、传热、经典力学和流体动力学 分类: 电子与通信技术 >> 光电子学与激光技术 分类: 物理学 >> 地球物理学、天文学和天体物理学 分类: 物理学 >> 基本粒子与场物理学 提交时间: 2024-04-08
摘要: The Einstein’s theory of special relativity is based on his two postulates. The first is that the laws of physics are the same in all inertial reference frames. The second is that the velocity of light in the vacuum is the same in all inertial frames. The theory of special relativity is considered to be supported by a large number of experiments. This paper revisits the two postulates according to the new interpretations to the exact solutions of moving sources in the laboratory frame. The exact solutions are obtained using the classic Maxwell’s theory, which clearly show that the propagation velocity of the electromagnetic waves of moving sources in the vacuum is not isotropic; the propagation velocity of the electromagnetic waves and the moving velocity of the sources cannot be added like vectors; the transverse Doppler effect is intrinsically included in the fields of the moving sources. The electromagnetic sources are subject to the Newtonian mechanics, while the electromagnetic fields are subject to the Maxwell’s theory. We argue that since their behaviors are quite different, it is not a best choice to try to bind them together and force them to undergo the same coordinate transformations as a whole, like that in the Lorentz transformations. Furthermore, the Maxwell’s theory does not impose any limitations on the velocity of the electromagnetic waves. To assume that all objects cannot move faster than the light in the vacuum need more examinations. We have carefully checked the main experiment results that were considered as supporting the special relativity. Unfortunately, we found that the experimental results may have been misinterpreted. We here propose a Galilean-Newtonian-Maxwellian relativity, which can give the same or even better explanations to those experimental results.
分类: 物理学 >> 电磁学、光学、声学、传热、经典力学和流体动力学 提交时间: 2023-12-18 合作期刊: 《应用力学学报》
摘要: 有限深度土体运动对弹性地基上梁的动力学特性和非线性响应均有显著影响。为丰富和深化相关研究内容,本研究基于引入土体运动影响的Winkler地基梁的非线性动力学模型,关注了有限深度土体运动如何影响弹性地基上梁在1/3次亚谐共振条件下的行为。通过应用Galerkin方法和多尺度法推导出了梁在1/3次亚谐共振情况下的频率响应方程以及位移的二阶近似解。进而根据响应方程进行数值计算,得到了Winkler地基上梁的1/3次亚谐共振的幅频响应曲线,分析了与土体运动密切相关的参数(地基深度、质量、弹性模量、地基刚度和阻尼等)和激励幅值等对梁亚谐共振的影响。结果表明:考虑有限深度土体运动的影响后,梁的1/3次亚谐共振响应的区域和幅值均减小; 随弹性地基深度、质量、弹性模量和刚度变化,幅频响应曲线的偏转程度、共振区域和响应幅值均发生定量改变; 外激励幅值对梁1/3次亚谐共振响应的特性无影响,而对响应幅值和共振区域则有显著影响; 地基阻尼对梁的1/3次亚谐共振有明显的抑制作用。
分类: 物理学 >> 电磁学、光学、声学、传热、经典力学和流体动力学 提交时间: 2023-12-18 合作期刊: 《应用力学学报》
摘要: 针对使用传统卡尔曼滤波(Kalman filter,KF)算法进行结构响应重构时测量噪声方差估计及多类型响应重构难的问题,提出了一种融合噪声方差估计和多类型响应重构的方法。首先在移动窗口卡尔曼滤波算法中引入近似计算的方法,提出递推移动窗口卡尔曼滤波算法(recursive moving-window Kalman filter,RMWKF)实时递推估计测量噪声方差,然后基于有限位置的应变片和加速度传感器的测量数据,并结合模态法对结构各个位置的应变、位移、速度以及加速度响应进行重构。最后对二维桁架和悬臂梁分别进行数值模拟和试验分析,验证了所提方法的有效性。试验结果表明,所提方法能对测量噪声方差进行有效地估计,能实现有效的多类型结构响应重构,同时减小了数据储存空间和计算量。
分类: 物理学 >> 电磁学、光学、声学、传热、经典力学和流体动力学 提交时间: 2023-12-18 合作期刊: 《应用力学学报》
摘要: 确定性横向迁移(deterministic lateral displacement,DLD)是一种常用的微粒分离技术,依据粒子尺寸和微流道层流特征分离颗粒。传统的DLD理论一般只考虑刚性粒子,难以描述细胞等柔性颗粒的分离过程。结合分子动力学粗粒度模型和雷诺相似性原理,对DLD装置中柔性细胞的分离、变形和受力情况进行了研究。仿真结果发现,纳观尺度下的DLD细胞分离路线与宏观尺度的一般分离原理相符。而在微观尺度下,细胞分离过程中细胞的变形破坏主要出现在细胞与微柱接触处,而且该处所受应力最大。研究结果揭示了柔性颗粒通过DLD装置的运动细节。
分类: 物理学 >> 电磁学、光学、声学、传热、经典力学和流体动力学 提交时间: 2023-12-18 合作期刊: 《应用力学学报》
摘要: 针对某两栖式清淤机器人,基于计算流体力学(computationalfluid dynamics,CFD)分析其静浮态和航行阻力。采用重叠网格方法计算静浮态下的吃水深度和纵倾角; 分别采用静态网格方法和重叠网格方法预测两栖式清淤机器人静水直航工况的航行阻力,并对这两种方法进行对比。研究结果表明:采用重叠网格的方法可以有效计算两栖式清淤机器人静浮态下的吃水深度和纵倾角; 静态网格方法和重叠网格方法均能有效预测两栖式清淤机器人水上航行阻力,静态网格方法计算效率高,但仅适用于航速较低的工况,而重叠网格方法适用于不同航速下的航行阻力预测,但计算效率较低。研究结果对两栖式清淤机器人的设计及改进有较大参考价值。
分类: 物理学 >> 电磁学、光学、声学、传热、经典力学和流体动力学 提交时间: 2023-12-18 合作期刊: 《应用力学学报》
摘要: 根据形状记忆合金(shape memory alloy,SMA)的高阻尼特性,应用能量分析方法,将其应用到单自由度惯容器系统中,通过自由能函数与耗散函数关系推导出SMA的恢复力,并对系统的时域和频域响应进行计算分析。由于惯容器的惯容系数与质量无关,因此可以在不改变质量的情况下,对其相关参数进行选样分析,并通过共振峰值投影的等高图实现参数优化,结果表明选用合理的参数能够使惯容器起到更佳的减振效果,以达到优化目标。
分类: 物理学 >> 电磁学、光学、声学、传热、经典力学和流体动力学 提交时间: 2023-11-16
摘要: A new X-ray imaging and biomedical application beamline (BL13HB) has been implemented at the Shanghai Radiation Synchrotron Facility (SSRF) as an upgrade to the old X-ray imaging and biomedical application beamline (BL13W1). This is part of the Phase II construction project of the SSRF. The BL13HB is dedicated to 2D and 3D static and dynamic X-ray imaging, with a field of view of up to 48.5 5.2 mm2 and spatial resolution as high as 0.8 m. A super-bending magnet is used as the X-ray source in BL13HB, which has a maximum magnetic field of 2.293 T. The energy range of monochromatic X-ray photons from a double-multiplayer monochromator was 8-40 keV, and the white beam mode was provided on the beamline for dynamic X-ray imaging and dynamic X-ray micro-CT. While maintaining the previous experimental setup of BL13W1, new equipment was added to the beamline experimental station. The beamline is equipped with different sets of X-ray imaging detectors for several experimental methods such as micro-CT, dynamic micro-CT, and pair distribution function (PDF). The experimental station of BL13HB is designed specifically for various in situ dynamic experiments, and BL13HB has been open to users since June 2021.
分类: 物理学 >> 电磁学、光学、声学、传热、经典力学和流体动力学 提交时间: 2023-09-06
摘要: Theaim of this researchis to reconstruct the 3D X-ray refractive index gradient mapsbythe proposed vector Radon transform and its inverse, assuming that the small-angle deviation condition is met. Theoretical analysesshowthat the X-ray beam can be modeled as a streamline with continuous change of direction in a rowwhen measured in one grating period, which allowsthe extraction of the refraction angle signals.Experimental results show thatall the 2D refraction signals of different directions can be acquired by a standard circular scanning procedure, which is typically used in the X-ray differential phase-contrast computed tomography. Furthermore, the 3D refractive index gradient maps that contain the directional density changes, can also be accurately reconstructed.
分类: 物理学 >> 电磁学、光学、声学、传热、经典力学和流体动力学 提交时间: 2023-08-25
摘要: Waveguide design has always been an important part of photonic integrated devices, and its research is also developing. In this paper, the coupling between waveguides is studied from two aspects of coupled mode theory and finite element simulation. In addition, this paper gives an example of dispersion engineering caused by dual-core waveguides structure, which has a wide range of applications in supercontinuum. To sum up, coupled mode theory has important reference significance for the design of modern photonic devices.
分类: 物理学 >> 电磁学、光学、声学、传热、经典力学和流体动力学 提交时间: 2023-08-25
摘要: Expanding the bandwidth of frequency combs in microcavities is currently a prominent research area, and one effective approach is to introduce dispersive waves using higher-order dispersion.However, The exploration of high-order dispersion control on quartz microsphere platforms has been limited by the challenge of preserving high Q factors across a broad range of sizes.Here, we fabricated quartz microspheres through arc discharge with diameters ranging from 100-260 m, achieving Q factors in the range of 108.We achieved a broadband Kerr frequency comb with dispersive wave radiation by manipulating the dispersion of the microsphere through size adjustment. Our experimental results demonstrate that the spectral span of the dispersive wave frequency combs can be extended up to 360 nm.At the same time, we have also demonstrated Raman lasers and Raman-Kerr frequency combs in small microspheres with normal dispersion.This work provides a reference for developing broadband, high-coherence frequency combs on microsphere platforms and offers an efficient implementation scheme for low-noise integrated broadband frequency combs.
分类: 物理学 >> 电磁学、光学、声学、传热、经典力学和流体动力学 提交时间: 2023-08-25
摘要: We demonstrate dispersion engineered dissipative soliton mode locked lasers, by means of intracavity spatial light modulation (SLM). The inline cavity GVD control of wide range (-0.28 ps2 ~ 0.06 ps2) in the laser cavity is realized, by which we achieve continuous and stable switching of traditional solitons, dispersion-managed solitons and dissipative solitons. A transient process of pulse-adaptive reconstruction is observed during the switching of different solitons. Transitions of soliton dispersive waves from Kelly sidebands, and transforms to quartic solitons have been observed via tuning the high-order dispersion coefficients. w-shaped solitons are demonstrated under negitive second-order dispersion and positive fourth order dispersion.
分类: 物理学 >> 电磁学、光学、声学、传热、经典力学和流体动力学 分类: 物理学 >> 交叉学科物理及相关领域的科学与技术 提交时间: 2023-07-12
摘要: I review the discovery as well as the band structure of the Zhang lattice.
分类: 物理学 >> 电磁学、光学、声学、传热、经典力学和流体动力学 提交时间: 2023-07-05
摘要: Whether the speed of light at the surface of rotating Earth is isotropic or not is both an important theoretical problem and one that has significant implications for scientific practices. Especially the unit of length, a meter, is defined as the length of the path travelled by light in vacuum in 1/299792458 of a second, on the basis that the speed of light is constant, c = 299792458 m/s. By applying the GPS range equation whose correctness has been fully verified by GPS practices, we found that the speed of light on rotating Earth's surface is neither constant nor isotropic, but rE c' c v d , where rE v is the local linear velocity of Earth's rotation, and d is the unit vector of the light propagation's direction. It follows that the anisotropy of the speed of light at the Earth's surface has a significant impact on the definition of the meter. For example, at the equator, in 1/299792458 of a second the length of the eastward light path is 3.1 m shorter than the westward one's. Based on this, and the difference between Earth rotation's Sagnac effects on the equator and the meridian, we propose a crucial experiment to examine the anisotropy of the speed of light: let a stable pulsed laser emitting pulses in two opposite directions, use the ultrafast imaging techniques for visualizing, measuring and comparing the spacing of the pulses in opposite directions. Then we can decisively conclude whether the speed of light is anisotropic or not.
分类: 物理学 >> 基本粒子与场物理学 分类: 物理学 >> 电磁学、光学、声学、传热、经典力学和流体动力学 提交时间: 2023-04-10
摘要: 本文回顾了推导达朗贝尔波动方程的全过程,其中最重要的一步是用高斯定律和安培定律,分别导出了标势和矢势的达朗贝尔波动方程。本文强调:高斯定律是库伦定律的微分形式,其中的源电荷与观测者即场点是相对静止的;在安培定律中,源电流载体与观测者即场点也是相对静止的。本文的结论是:麦克斯韦方程组和达朗贝尔波动方程都是在源-观相对静止条件下的方程,达朗贝尔波动方程中的常数C是在真空环境中,源-观相对静止条件下的传播速度。 在这样的特殊条件下,电磁波的传播空间是均匀和各向同性的,因此,无论传播的距离和方位几何,无论源-观所在的实验室位于哪个星球上,绝对运动如何,电磁波传播速度都相同,这是合乎逻辑的。 真空中的电磁波从源电荷、源电流发出,向各处的观测者传播,源-观相对静止,传播空间均匀而各向同性的,这是一个准确的物理图像,是准确理解光速不变原理的物理基础。
分类: 物理学 >> 电磁学、光学、声学、传热、经典力学和流体动力学 提交时间: 2023-02-06
摘要: 对密度不变的孤立系统中物质的内在惯性和相互作用的研究结果表明,自旋是可证明的物质惯性之一,可以孤立系统的角速度wn=ddtn=u表征。考虑并补充了物质点所占空间为无限趋近于零但不为零的体积后,本研究的结论行证据可补充牛顿第一定律,并可以值解释物质波粒二象性。对含两个耦合物质的基本的孤立系统进行了进一步的研究。所揭示的耦合特性可以解释DNA结构、时光锥及运动轨迹的拓扑球面。两物质间的相互作用被证明为孤立系统的匀速直线运动与匀教室自旋的耦合结果,这也许对统一万有引力和电磁力有所帮助。
分类: 物理学 >> 地球物理学、天文学和天体物理学 分类: 物理学 >> 电磁学、光学、声学、传热、经典力学和流体动力学 分类: 天文学 >> 星系和宇宙学 提交时间: 2022-11-03
摘要: 本文以物理学中标准钟和标准尺的定义实质和爱因斯坦的相对论物理为基础,从自然哲学层次出发讨论了物理的时空观。提出在已有的时空标度的概念基础上,应该进一步明确区分时空标度和时空背景。根据爱因斯坦相对论的实际逻辑可以作如下理解,满足相对论性变化的是时空标度,而时空标度是人为地根据物质实体中发生或存在的固有物理事件定义的,时空背景作为反映时空标度的长短或大小变化的必备基础和参考背景,应该是绝对的。空间标度的长短尺度在本质上应该理解为固有物理事件在空间的绝对背景上截取的线段的长度。最后以此时空观为基础,探讨了经典力学框架下的质点动力学方程,自然地得出了新形式的质点动力学方程。新动力学方程可以直接应用到任何实际的,(相对宇宙绝对背景)无转动的参考系中。而惯性力的本质正是作用到参考物体上的真实受力。这一经典质点动力学改造的本质是修正了牛顿第二定律传统体系中存在的一个理论缺陷。然而,可能更为重要的是,在形式上具备明显优越性的新质点动力学方程反过来强烈地暗示了时空背景的绝对性。文章最后结合广义相对论的引力几何化思想,探讨了引力对时空标度的物理效应。
分类: 物理学 >> 电磁学、光学、声学、传热、经典力学和流体动力学 提交时间: 2022-10-17
摘要: 声学失配模型和漫散射失配模型被广泛应用于界面热导的计算,两种模型分别建立在极端光滑和粗糙界面的假设基础上。由于实际界面结构与两种假设的区别较大,造成两种模型预测结果与实际界面热导偏差较大。近期提出的混合失配模型考虑了界面结构对声子镜面透射和漫散射透射比例的影响,预测的准确度有所提高。但该模型需要通过分子动力学模拟获取界面声子信息较为复杂。为此,本文通过引入测量的粗糙度数值简化混合失配模型,并增加考虑界面结构对接触面积的影响,实现对界面热导简单快捷、准确地预测。基于该模型,本文计算预测了金属(铝、铜、金)和半导体(硅、碳化硅、砷化镓、氮化镓)的界面热导。并将铝/硅界面的结果与实验测量结果对比,数据吻合较好。该模型不仅有助于界面导热机理的理解,而且利于与测量结果对比。
分类: 物理学 >> 电磁学、光学、声学、传热、经典力学和流体动力学 提交时间: 2022-09-26 合作期刊: 《桂林电子科技大学学报》
摘要: 脉动热管被认为是超高热流密度功耗的工况中最具前景的散热元器件之一,与逐渐发展成熟的纳米技术一同被广泛应用于电子散热设备当中,因此探究纳米流体脉动热管的运行与热特性变化机理十分重要。通过采用外加磁场的方法来强化纳米磁流体脉动热管传热的实验研究,搭建了纳米磁流体脉动热管的传热测试可视化实验台。分别测量了在磁场大小为25、5、1、0 mT以及在2种不同磁场方向(脉动热管蒸发段的正后方与正下方)作用下,板式脉动热管的温度分布和传热速率,研究了纳米磁流体、热负载功耗、磁感应强度大小与磁铁摆放位置等因素对其换热性能的影响。实验结果表明,采用四氧化三铁/乙醇纳米流体作为工作流体,在磁场作用下可以显著强化脉动热管的传热性能,其中置于脉动热管蒸发段正下方的永磁体能够更多的优化脉动热管的传热性能,这可为超高热流密度功耗的工况提供借鉴指导。