Terahertz electromagnetic radiation from quantum wells

The observation of terahertz electromagnetic dipole radiation from quantum well structures has finally proven the existence of charge oscillations in semiconductors associated with wave packet dynamics. This article closely examines the physics behind the emission of terahertz electromagnetic radiation from excitonic charge oscillations in such quantum well structures, points out similarities and differences between the various generation schemes, and discusses the various relaxation mechanisms involved. Finally, we show how both amplitude and phase of charge oscillations and the corresponding terahertz emission can be manipulated using phase-locked optical pulses.     

Analysis of the product gas from biomass gasification by means of laser spectroscopy

The use of biomass and waste for decentralised combined heat and power production (CHP) requires highly efficient gasification processes. In the Technische Universität München (TUM), an innovative gasification technology has been developed. This allothermal gasifier is producing a hydrogen- rich, high-calorific gas, that can be further used in a microturbine or a fuel cell producing energy. For the operation of such a system, the online analysis of the composition of the product gas is of high importance, since the efficient working of the machines is linked with the gas quality. For this purpose an optical measurement system based on laser spectroscopy has been applied. This system can measure not only the basic components of the product gas (H₂, CH₄, CO, CO₂, H₂O), but it also gives information concerning the content of high hydrocarbons, the so-called tars, in the product gas.     

电阻分压器-3 dB频率与上升时间的关系

 研究了无电感补偿和有电感补偿的一级和两级电阻分压器的幅频特性-3 dB频率与阶跃响应10%~90%上升时间的关系。无电感补偿一级分压器的-3 dB频率与阶跃响应上升时间之积为常数0.350;对无电感补偿两级分压器,该乘积在0.349附近很小范围内变动;对电感补偿一级分压器,该乘积由过冲决定,当过冲在0~10%范围内变化时,该乘积在0.35~0.29之间线性变化;对电感补偿两级分压器,该乘积随过冲和分压器参数变化,在不大于10%的确定过冲下,变化范围约为±10%;当两级分压器第一级的时间常数远大于第二级的时间常数时,可能难以在第二级进行有效的电感补偿。     

Summarizing complexity in high dimensions

High-dimensional, multispectral data on complex physical systems are increasingly common. As the amount of information in data sets increases, the difficulty of effectively utilizing it also increases. For such data, summary information is required for understanding and modeling the underlying dynamics. It is here proposed to use an extension of computational mechanics [C. R. Shalizi and J. P. Crutchfield, J. Stat. Phys. 104, 817 (2001)] to arbitrary spatiotemporal and spectral dimension, for providing such summary information. An example of the use of these tools to identify state evolution in the brain, an archetypal, complex biophysical system, serves as an illustration.     

Image watermarking by using phase retrieval algorithm in gyrator transform domain

We propose an image watermarking scheme based on the phase retrieval algorithm in gyrator domain. The watermark is converted into a noise-like image by Arnold transform. The scrambled image is regarded as the amplitude of gyrator spectrum. The Gerchberg-Saxton algorithm is employed to obtain the unknown phase function in gyrator pair, in which the host image is the amplitude of input function. The phase information and the parameters of the two transforms serve as the key of watermarking algorithm. The numerical simulation has demonstrated the performance of the proposed algorithm.     

Beyond Flory-Huggins theory: new classes of blend miscibility associated with monomer structural asymmetry

Flory-Huggins (FH) theory is restricted to polymer mixtures whose monomers are structurally identical, a situation limited to isotopic blends and computer simulations. We investigate the influence of monomer structure on blend miscibility and scattering properties using the lattice cluster theory generalization of the FH model. Monomer structural asymmetry is shown to profoundly affect blend miscibility (T(c),phi(c)), chain swelling (T(theta)), and the scale (xi) and intensity [S(0)] of composition fluctuations. Four distinct blend miscibility classes are identified and experimental evidence for these classes is discussed.     

Simulations of Co‐GISAXS during kinetic roughening of growth surfaces

The recent development of surface growth studies using X‐ray photon correlation spectroscopy in a grazing‐incidence small‐angle X‐ray scattering (Co‐GISAXS) geometry enables the investigation of dynamical processes during kinetic roughening in greater detail than was previously possible. In order to investigate the Co‐GISAXS behavior expected from existing growth models, calculations and (2+1)‐dimension simulations of linear Kuramoto–Sivashinsky and non‐linear Kardar–Parisi–Zhang surface growth equations are presented which analyze the temporal correlation functions of the height–height structure factor. Calculations of the GISAXS intensity auto‐correlation functions are also performed within the Born/distorted‐wave Born approximation for comparison with the scaling behavior of the height–height structure factor and its correlation functions.     

ZnS Nanospheres for Optical Modulator in an Erbium-Doped Fiber Laser

Zinc sulfide (ZnS), which belongs to transition metal monochalcogenides, is a semiconductor material with wide direct band gap. It can potentially show some special applications (such as luminescence, phosphor, sensors, infrared window materials, photocatalysis) by changing the morphology, size, and crystal structure of semiconductor materials. However, ZnS nanospheres have not been studied as optical modulators until now. Herein, ZnS nanospheres are synthesized by the hydrothermal method and are used to realize optical modulators in an Er-doped fiber laser. The evanescent field effect is utilized to incorporate the ZnS nanospheres on a tapered fiber. Furthermore, with the increase in pump power, the modulation interval gradually decreases to a minimum of 34.36 ns corresponding to the modulation frequency of 29.1 MHz, which is the highest modulation frequency to our knowledge in a ring cavity all-fiber laser. These results demonstrate ZnS nanospheres together with the interaction of dispersion and nonlinearity in optical fibers can modulate the proposed lasers. This not only provides a new method for controlling the power and frequency of all optical modulators, but also marks an important step for ZnS materials in optics research and device applications.