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The Bobylev approach to the nonlinear Boltzmann equation is reviewed. The linearized problem is discussed and it is shown that eigenfunctions decaying like a negative power of the velocity are possible with Maxwell molecules only. The relaxation to equilibrium according to the nonlinear equation is discussed and the Krook-Wu conjecture on the status of the BKW mode is shown to be false in general. The buildup of the high-energy tails is considered and a phenomenon observed by Tjon is given a simple explanation. Finally, the method is illustrated with numerical calculations performed for two sets of initial conditions. 相似文献
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B. L. Smorodin 《Journal of Experimental and Theoretical Physics》2001,93(6):1231-1238
The stability of a poorly conducting fluid in a constant electric field of a horizontal capacitor is investigated under a variable temperature gradient. It is assumed that free charge in the fluid is generated only due to the nonhomogeneous conductivity of the fluid. The Floquet theory is used to determine the convection thresholds. The instability boundaries and the characteristics of critical perturbations are determined. In addition to the synchronous and subharmonic responses to an external action, the instability can be attributed to quasiperiodic perturbations. The low-frequency limit of modulation is considered by an asymptotic method. The critical electric Rayleigh number is represented as a function of inverse frequency and heating level. 相似文献
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High-Breakdown-Voltage Submicron InGaAs/InP Double Heterojunction Bipolar Transistor with ft=170GHz and fmax=253GHz 下载免费PDF全文
The layer structure of InGaAs/InP double heterojunction bipolar transistor (DHBT) is designed to enhance the frequency performance and breakdown voltage. The composition-graded base structure is used to decrease the base transit time. The InGaAs setback layer and two highly doped InGaAsP layers are used to eliminate the conduction band spike of the collector. The submicron-emitter InGaAs/InP DHBT is fabricated successfully. The base contact resistance is greatly decreased by optimization of contact metals. The breakdown voltage is more than 6V. The current gain cutoff frequency is as high as 170GHz and the maximum oscillation frequency reached 253GHz. The DHBT with such high performances can be used to make W-band power amplifier. 相似文献
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傅里叶变换红外光谱研究三种彝药材的指纹图谱,并初步分析了它们的有效药物成分和图谱的关系.在金丝杜仲的块根中,淀粉纤维素含量高,而在真金草和回心草中,纤维素和蛋白质的含量更高些.实验发现,金丝杜仲的止血功能和溶血功能可能与所含鞣质类物质和四环三萜类成分有关.真金草的抗梅毒作用可能源于其中的生物碱的生理活性,其活血作用也与四环三萜类物质成分有关,所含多糖和苷则对治疗肝炎有效.回心草的安神作用可能与所含的三萜皂元成分有关,三萜皂元具有安定作用.利用傅里叶变换红外光谱法可以方便、快速和准确地分析中药材的某些有效成分,文章对三种药材的部分药物疗效在分子水平上给出了一定的科学依据. 相似文献
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为了同时获取样品的表面和深度信息,研究光学相干层析的成像原理,建立了基于光学相干层析技术的内窥系统,实现了旋转扫描成像,系统的工作波长为1 310 nm,工作带宽为80 nm.理论推导及计算机仿真得到了系统信噪比与干涉仪的分光比、反射率之间的关系并分析了理论分辨率和探测深度.提出外径为5 mm的内窥镜扫描探头,聚焦距离为12 mm,数值孔径NA为0.47,折射率分布常量A=0.218 7.利用微型电机驱动直角棱镜实现扫描,旋转速度为25 rpm,旋转一周得到640个采样点.采用多层盖玻片和洋葱表皮作为样品进行实验分析,得到了盖玻片和洋葱的图像,横向分辨率和纵向分辨率分别为10 μm和15 μm.结果表明,设计的光学相干层析内窥系统能够用于旋转扫描成像,获取更多的组织信息. 相似文献
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由于单颗LED的功率很小,作为照明光源使用时需要采用LED阵列形式。首先推导LED阵列的照度叠加公式,根据叠加公式对阵列进行仿真,以圆形为例分析LED在平面上的均匀分布以及以球表面为例分析LED在曲面上的均匀分布。给出两种LED阵列分布的仿真结果,得出不同阵列的分布特点。指出圆面阵列的照射范围比较集中,此类阵列分布的灯具适用于照射面较小且比较集中的照射领域;球表面上的阵列的照射分布范围比较广,呈圆面,此类阵列分布的灯具适用于照射面较大但照度要求不是很高的照射区域。该结果为LED灯具设计提供了依据。 相似文献
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为了同时获取样品的表面和深度信息,研究光学相干层析的成像原理,建立了基于光学相干层析技术的内窥系统,实现了旋转扫描成像,系统的工作波长为1 310 nm,工作带宽为80 nm.理论推导及计算机仿真得到了系统信噪比与干涉仪的分光比、反射率之间的关系并分析了理论分辨率和探测深度.提出外径为5 mm的内窥镜扫描探头,聚焦距离为12 mm,数值孔径NA为0.47,折射率分布常量A=0.218 7.利用微型电机驱动直角棱镜实现扫描,旋转速度为25 rpm,旋转一周得到640个采样点.采用多层盖玻片和洋葱表皮作为样品进行实验分析,得到了盖玻片和洋葱的图像,横向分辨率和纵向分辨率分别为10 μm和15 μm.结果表明,设计的光学相干层析内窥系统能够用于旋转扫描成像,获取更多的组织信息. 相似文献
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为了提高微波光子下变频链路的性能,提出了基于集成双平行马赫-曾德尔调制器的微波光子下变频方法.通过理论推导和数值仿真分析了系统的增益和无杂散动态范围,实验搭建了基于双平行马赫-曾德尔调制器的下变频链路,控制直流偏置电压使双平行马赫-曾德尔调制器工作在高载波抑制的双边带调制模式,并对链路进行了性能测试.实验结果表明:该下变频链路的增益为7.43 d B,无杂散动态范围达到了110.85 d B/Hz2/3,工作频段可覆盖5—18 GHz的宽频范围.基于双平行马赫-曾德尔调制器的下变频方法可优化设计输出频谱,系统结构简单、易于实现,为微波光子下变频链路提供了有效的解决方案. 相似文献
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无衍射光的中心光斑直径相对于高斯光束较小且发散角为零,在自由空间光通信领域具有良好的应用前景。介绍了一种自由空间无衍射光通信模拟实验系统,它通过串口连接上位机,应用微处理器进行信号的调制与解调,采用双头脉冲间隔调制,无衍射光的发生使用圆锥透镜法,在接收端使用PIN光电二极管将光信号转换为电信号,再经过放大电路、整形电路和微处理器的解调,最后通过串口将数据传输给上位机。上位机通过对发送数据与接收数据的对比计算出误码率,进而给出整个系统的传输性能评价。在无衍射光的最大传输距离内,当比特率为9 600 bps时,该系统的误码率优于610-5。 相似文献
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Laser is applied to guide and tweeze the vascular endothelial cells for assembly. The system is composed of three modules: laser guidance, micro channels and laser tweezers. The micro channel includes the assembly area, main channel and branch channels. The optical module is equipped with laser source, beam splitter, reflectors and lenses. The endothelial cells are delivered to main channel and guided through branch channel to the assembly area by laser. The optical tweezers then move the cells to the proper position. The design of optical modules is conducted for the maximum capability of manipulating cells. The micro channel is designed based on fluid mechanics to minimize the fluidic disturbance to the cells in the assembly area, and is fabricated by photo lithography. Polystyrene micro beads and endothelial cells are successfully guided and tweezed by this approach. The associated escape velocity and dragging force are investigated. 相似文献
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Ariel Caticha 《Annalen der Physik》2019,531(3)
Entropic Dynamics (ED) is a framework in which Quantum Mechanics (QM) is derived as an application of entropic methods of inference. The magnitude of the wave function is manifestly epistemic: its square is a probability distribution. The epistemic nature of the phase of the wave function is also clear: it controls the flow of probability. The dynamics is driven by entropy subject to constraints that capture the relevant physical information. The central concern is to identify those constraints and how they are updated. After reviewing previous work I describe how considerations from information geometry allow us to derive a phase space geometry that combines Riemannian, symplectic, and complex structures. The ED that preserves these structures is QM. The full equivalence between ED and QM is achieved by taking account of how gauge symmetry and charge quantization are intimately related to quantum phases and the single‐valuedness of wave functions. 相似文献
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Donald H. Kobe 《International Journal of Theoretical Physics》1982,21(8-9):685-702
The gauge invariance of the Dirac equation is reviewed and gauge-invariant operators are defined. The Hamiltonian is shown
to be gauge dependent, and an energy operator is defined which is gauge invariant. Gauge-invariant operators corresponding
to observables are shown to satisfy generalized Ehrenfest theorems. The time rate of change of the expectation value of the
energy operator is equal to the expectation value of the power operator. The virial theorem is proved for a relativistic electron
in a time-varying electromagnetic field. The conventional approach to probability amplitudes, using the eigenstates of the
unperturbed Hamiltonian, is shown in general to be gauge dependent. A gaugeinvariant procedure for probability amplitudes
is given, in which eigenstates of the energy operator are used. The two methods are compared by applying them to an electron
in a zero electromagnetic field in an arbitrary gauge.
Presented at the Dirac Symposium, Loyola University, New Orleans, May 1981. 相似文献
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The geometric representation of the crack front propagation is examined in a Finsler space in the context of the discontinuity theory. The structure of the medium is taken into account via the connectivity coefficients of the Finsler space and its metric. It is demonstrated that this approach leads to the construction of fiber spaces and allows the gauge invariance to be introduced correctly and noncontradictorily into the fracture theory. The Lie derivative is used to proceed from discontinuities to differentials. The equation of the front crack surface is retrieved. 相似文献
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建立了位错塞集引发的裂纹原子集团模型,采用递归法计算了钛的电子结构参量,并研究了氧、氯、钯等元素对钛电子结构的影响.发现氧能降低费米能级附近的态密度,使钛的物理化学活性降低.氧降低钛的原子结合能,与钛原子之间有较大的亲和力,易与钛反应形成氧化膜.Cl在钛中的稳定性及与钛的亲和力均不及氧,很难取代钛表层中的氧,使得钛的氧化膜非常稳定,不会出现过钝化现象.Pd在钛中裂纹处的环境敏感镶嵌能较低,易扩散到裂纹处,且Pd元素使H在裂纹处的环境敏感镶嵌能明显升高,有效减小H向裂纹处的扩散,提高钛的应力腐蚀抵抗力.
关键词:
钛
腐蚀
钝化
电子结构 相似文献