Flexible fiber motion in the flow field of a cylinder

In the forming section of a papermachine, a water suspension of pulp fibers is drained through a forming fabric. One canonical test case that incorporates some key features of this process is that which studies the interaction of a single fiber with a cylinder. This article concerns numerical simulations of this interaction.     

侧伏规律在岩质边坡结构面编录中的应用

理论上,据边坡设计坡面来编录展示结构面的迹线分布应与其在坡面内的侧伏交线一致。把握一定的侧伏规律,处以适当的素描技法,既可吻合实际情况,又可提高绘图效率和资料质量,对边坡结构模型的准确分析不无裨益。有鉴于此,经过现场观测总结,分析了结构面与坡面的各种交切关系及其迹线的侧伏特征。在侧伏规律公式推导的基础上,根据两者产状提出其特征三角形判别法,并编制相应的算图,可校核以及在适当条件下推测某一产状要素。讨论了实践中几类难以作图的特殊情况下侧伏规律的应用。     

On Quillen?s Theorem A for posets

A theorem of McCord of 1966 and Quillen?s Theorem A of 1973 provide sufficient conditions for a map between two posets to be a homotopy equivalence at the level of complexes. We give an alternative elementary proof of this result and we deduce also a stronger statement: under the hypotheses of the theorem, the map is not only a homotopy equivalence but a simple homotopy equivalence. This leads then to stronger formulations of the simplicial version of Quillen?s Theorem A, the Nerve Lemma and other known results. In particular we establish a conjecture of Kozlov on the simple homotopy type of the crosscut complex and we improve a well-known result of Cohen on contractible mappings.     

Harmonic and intermodulation performance of optical-fiber Mach–Zehnder microphone

In this paper, closed-form mathematical expressions are obtained for the amplitudes of the harmonic and intermodulation products of the fiber optic Mach–Zehnder microphone excited by a multitone acoustical perturbation. The results show the strong dependence of the harmonic and intermodulation performance on the amplitude of the acoustical perturbation tones and the phase shift produced by the DC bias voltage applied to the reference fiber of the Mach–Zehnder interferometer. The results also show that depending on the phase shift produced by the DC bias voltage, either the third-order or the second-order intermodulation will be dominant. Compared to previously published results for other types of microphones, it appears that the phase shift produced by the DC bias voltage plays an important role in deciding the order of the dominant intermodulation product.     

Energy bands: Chern numbers and symmetry

Energy bands formed by rotation–vibrational states of molecules in the presence of symmetry and their qualitative modifications under variation of some control parameters are studied within the semi-quantum model. Rotational variables are treated as classical whereas a finite set of vibrational states is considered as quantum. In the two-state approximation the system is described in terms of a fiber bundle with the base space being a two-dimensional sphere, the classical phase space for rotational variables. Generically this rank 2 complex vector bundle can be decomposed into two complex line bundles characterized by a topological invariant, the first Chern class. A general method of explicit calculation of Chern classes and of their possible modifications under variation of control parameters in the presence of symmetry is suggested. The construction of iso-Chern diagrams which split the space of control parameters into connected domains with fixed Chern numbers is suggested. A detailed analysis of the rovibrational model Hamiltonian for a D₃ invariant molecule possessing two vibrational states transforming according to the two-dimensional irreducible representation is done to illustrate non-trivial restrictions imposed by symmetry on possible values of Chern classes.     

A full-duplex radio-over-fiber link with 12-tupling mm-wave generation and wavelength reuse for upstream signal

A full-duplex radio-over-fiber (RoF) link with a novel scheme to generate 60 GHz mm-waves from a 5 GHz RF signal source is investigated. In the RoF downlink, the required frequency of the RF oscillator is reduced greatly. Since the optical carrier is not modulated by downstream data, part of it is reused to carry upstream data and the upstream data is transmitted to the central station using optical single-sideband modulation. In this way, a single wavelength is used for both downstream and upstream transmissions. Based on this scheme, a full-duplex RoF link is built and its transmission performance is analyzed. Theoretical analysis and numerical simulation show that the downstream signal cannot only eliminate code form distortion caused by time shift of the code edges, but also reduce the influence of the fading effect as the 60 GHz DSB optical mm-wave signal is transmitted along the fiber, and the upstream signal is immune to both fading effect and time shift of the code edges.     

Photonic generation of microwave signals using dual-wavelength single-longitudinal-mode fiber lasers

Photonic generation of microwave signals is demonstrated with a dual-wavelength single-longitudinal-mode erbium-doped fiber ring laser. Microwave signal with a frequency of 21.07 GHz is obtained by aligning the reflection band of a uniform fiber Bragg grating to the two transmission peaks within a fiber Bragg grating-based Fabry-Perot filter. Stable dual-wavelength single-longitudinal-mode operation is guaranteed by means of the combined filtering effect of a saturable absorber and the Fabry-Perot filter. This approach provides an effective solution to the photonic generation of high-frequency microwave signals.     

Effects of angle of probe laser and pinhole diameter on the time-resolved optical inspection system

A real-time in-situ time-resolved optical inspection system comprising two He-Ne probe lasers, a digital oscilloscope, and three fast photodetectors is developed. The effects of angle of probe laser and pinhole diameter on the time-resolved optical inspection system are investigated during excimer laser crystallization. The longest melt duration and ablation excimer laser fluence are independent of pinhole size. The pinhole with a diameter of 0.3 mm is recommended to use in the time-resolved optical inspection system. Determination of melt duration and observation of explosive crystallization oscillation are independent of angle of probe laser, but four criteria for the relationship between probe lasers and photodetectors should be followed.     

Modeling and characterization of fiber Bragg grating for maximum reflectivity

This paper presents the modeling and characterization of an optical fiber grating for maximum reflectivity. Grating length and change in refractive index are the critical parameters in contributing to the performance of fiber Bragg grating. The wavelength chosen for analysis is from the third window to minimize the attenuation. The reflection spectra, bandwidth and side lobes strength were analyzed with different lengths and change in refractive index. The simulations are based on solving coupled mode equations by transfer matrix method that describes the interaction of guided modes.     

Improvement of the dynamic range of a fiber specklegram sensor based on volume speckle recording in photorefractive materials

In this work, the improvement of the dynamic range of a micro displacement sensor based on fiber specklegrams holographically stored in a photorefractive BSO (Bi₁₂SiO₂₀) crystal is reported. In our experimental setup, a plastic optical fiber (POF) was used to generate a subjective speckle pattern that was recorded in the crystal using a two-wave mixing arrangement. The speckle size was controlled by modifying the diameter of a pupil aperture adjacent to a lens producing the image of the speckle. Fringe patterns were obtained at the output of the system by producing micro displacements of the fiber output end. An increase in the visibility of the fringe patterns was appreciated when the pupil aperture diameter decreased even without controlling the average modulation of the intensity of the light pattern, i.e. when the speckle length increased and the average light modulation simultaneously decreased. This behavior allowed recovering the autocorrelation functions of fringe patterns associated with displacements that initially led to decorrelation, and therefore, significantly to improve the dynamic range of the metrological system. To the best of our knowledge this is the first report about the influence of speckle size on the dynamic range of fiber specklegrams sensors recorded on photorefractive materials.