Analytical formulas for modulation responses of semiconductor DFBlasers

Analytical expressions for the modulation responses of semiconductor DFB lasers are derived from a rigorous standing-wave rate equation formulations. With proper approximations, these expressions are reduced to simple and insightful formulas, similar to those obtained from the conventional rate equations. Salient features of the DFB lasers, such as complex-couplings, phase-shifts, facet conditions, as well as variations of carrier and photon densities along the cavity caused by the longitudinal hole-burning, are considered in these approximate formulas. It is demonstrated that the modulation responses, predicted by the simple formulas are in excellent agreement with the exact solutions     

Side-mode suppression mechanism of gain-coupled DFB lasers with periodically etched quantum wells

The effect of the gain and index coupling on the side-mode suppression ratio (SMSR) is studied for gain-coupled DFB lasers with periodically etched quantum wells. An accurate expression for the SMSR based on the amplified spontaneous emission model is used with the local-normal-mode transfer-matrix method. The mechanism for the strong single-mode stability of the gain-coupled DFB lasers is explained by the difference between the effective gain and loss of the Bloch waves in the grating structures. This new view clearly shows the advantage of the gain-coupled DFB lasers in terms of single-mode stability.     

1.3-μm GaInAsP/InP transverse-mode stabilized buried-crescentlasers by a new fabrication technique using a reactive ion beam etching

Transverse-mode-stabilized, 1.3-μm, GaInAsP/InP, buried-crescent (BC) lasers fabricated using a reactive ion beam etching (RIBE) technique are presented. Yields of single-transverse-mode operation as high as 95% are achieved with low threshold currents of 11-25 mA. Transverse-mode stability under both high-power and long-term operation (50°C, 20 mW, 1000 h) is demonstrated. A coupling efficiency into a single-mode fiber of 63% and a coupled power of 40 mW at 160 mA are achieved. Stable continuous-wave operation is also confirmed under a constant power of 5 mW (50 and 70°C) and 20 mW (50°C) in an aging test     

Prevention of small black spots on sugar-coated tablets containing aluminum acetylsalicylic acid

Sugar-coated tablets containing aluminum acetylsalicylate gradually developed black spots on their surface. A factorial experiment was performed based on an L32 orthogonal array table in an attempt to halt this phenomenon. The factor responsible proved to be talc used to formulate the smooth coating layer over the subcoating layer containing aluminum acetylsalicylate. When HCl-treated talc was used as a filler for the smoothing layer, the black spots were markedly decreased. The spotting mechanism was considered to be due to hydrolysis of aluminum acetylsalicylate in the subcoating layer to salicylic acid and acetic acid, which sublimated into the pores of the smoothing layer. Then, ferrous ion substituted from magnesium ion in the talc molecule center was extracted by salicylic acid, acetic acid, and moisture. Finally, the ferrous ion was oxidized to ferric ion, and this produced an Fe³⁺ chelate compound together with salicylic acid.     

Highly conductive ZnO films with high near infrared transparency

We present an approach for deposition of highly conductive nominally undoped ZnO films that are suitable for the n‐type window of low band gap solar cells. We demonstrate that low‐voltage radio frequency (RF) biasing of growing ZnO films during their deposition by non‐reactive sputtering makes them as conductive as when doped by aluminium (ρ≤1·10⁻³Ω cm). The films prepared with additional RF biasing possess lower free‐carrier concentration and higher free‐carrier mobility than Al‐doped ZnO (AZO) films of the same resistivity, which results in a substantially higher transparency in the near infrared region (NIR). Furthermore, these films exhibit good ambient stability and lower high‐temperature stability than the AZO films of the same thickness. We also present the characteristics of Cu(InGa)Se₂, CuInSe₂ and Cu₂ZnSnSe₄‐based solar cells prepared with the transparent window bilayer formed of the isolating and conductive ZnO films and compare them to their counterparts with a standard ZnO/AZO bilayer. We show that the solar cells with nominally undoped ZnO as their transparent conductive oxide layer exhibit an improved quantum efficiency for λ > 900 nm, which leads to a higher short circuit current density J_SC. This aspect is specifically beneficial in preparation of the Cu₂ZnSnSe₄ solar cells with band gap down to 0.85 eV; our champion device reached a J_SC of nearly 39 mAcm⁻², an open circuit voltage of 378mV, and a power conversion efficiency of 8.4 %. Copyright © 2015 John Wiley & Sons, Ltd.     

Introduction to the Special Issue on Causal Discovery

Many empirical sciences, including the social sciences and life sciences, aim to study causal relationships. Researchers in these fields need computational methods for analyzing observed data and identifying causal structures among a set of variables. Such computational methods enable researchers to draw conclusions on the basis of both their assumptions and the observed data. Moreover, these methods are useful for developing hypotheses on causal relations, designing future observational studies, and planning future experimental studies that can potentially provide stronger evidence of estimated causal relations.

The objective of this special issue is to present an up-to-date overview of causal discovery methods, which have witnessed rapid advancements in recent years. The chief editor and guest editors invited the following three survey papers on various hot topics related to causal discovery:

     

IR Practical Extinction Coefficients of Water in Alkali Lime Silicate Glasses Determined by Nuclear Reaction Analysis

Infrared spectroscopy (IR) is widely used to determine the water concentration in glasses, whereas determination of the IR practical extinction coefficient is necessary to deduce the absolute water concentration of glasses on the basis of Beer–Lambert law. From the nuclear reaction analysis data, the IR practical extinction coefficients of water were successfully determined for the alkali lime silicate glasses with different levels of sodium/potassium cation (Na/K) ratio. The two‐band method is well‐known to be useful for the determination of the water concentration in some alkali lime silicate glasses. It is proved here that the two‐band method is not applicable to the variety of composition for alkali lime silicate and soda lime aluminosilicate glasses, whereas it is valid for the similar composition of soda lime silicate glasses [SLS: Composition (in mol%) 16Na₂O·10CaO·74SiO₂]. The single‐band procedure with the IR practical extinction coefficient is crucial for the determination of the precise water concentration in the wide variety of glass composition although the determination of the IR practical extinction coefficient is troublesome. It also appears that the ion radius of alkali affects the IR practical extinction coefficient and the chemical state of OH group in glasses.     

防屈曲支撑的研究进展及其工程应用

简要介绍了防屈曲支撑的组成及工作机理,详细介绍了防屈曲支撑的发展和近年来中国学者在理论研究和类型创新方面取得的研究成果;着重讨论了三重钢管、端部铰式、中部接触环式等新型防屈曲支撑的性能;最后给出了防屈曲支撑在中国的应用情况.研究结果表明:防屈曲支撑以其良好的耗能性能会有很好的发展潜力;防屈曲支撑应该向着低屈服点设计、适用于大跨结构、便于安装等方向发展,并在实际工程中推广应用.     

Nondestructive Hygiene Monitoring on Pork Meat Surface Using Excitation–Emission Matrices with Two-Dimensional Savitzky–Golay Second-Order Differentiation

To develop a rapid and nondestructive hygiene-monitoring system in meat-processing plants, plate count and ATP content on pork meat surfaces were quantitatively determined with particular attention to NAD(P)H fluorescence produced by microorganisms. An excitation (Ex)–emission (Em) matrix (EEM) was obtained, and the five fluorescence peaks of tryptophan, NAD(P)H, zinc protoporphyrin IX, protoporphyrin IX, and riboflavin were observed. Plate count and ATP content were predicted with good accuracy [r _p?=?0.90–0.94 and root mean square error of prediction (RMSEP)?=?log₁₀ (0.68–0.79 CFU cm^?2) for plate count and r _p?=?0.84–0.89 and RMSEP?=?log₁₀ (0.61–0.71, mol cm^?2) for ATP content]. Two-dimensional Savitzky–Golay second-order differentiation was found to be a powerful preprocessing tool of EEMs to improve prediction accuracy. Better prediction accuracy was obtained when the sensitivity of the fluorescence spectrophotometer was set to focus on fluorescence from NAD(P)H than that from both tryptophan and NAD(P)H. However, little linear relationship was observed between plate count and fluorescence intensity from NAD(P)H (R ²?=?0.31). The absolute value of regression coefficient (RC) of partial least-squares regression (PLSR) at the wavelength assigned to NAD(P)H, zinc protoporphyrin IX, protoporphyrin IX, and riboflavin was high. It can be concluded that a good prediction model was developed in which four fluorescence compounds of NAD(P)H, zinc protoporphyrin IX, protoporphyrin IX, and riboflavin contribute to the prediction model, and these compounds are probably produced by microorganisms.     

Scattering of radiation by a fiber with a rough surface

We present a new theory on scattering of radiation by real fibers in engineering systems. The theory covers the scattering by fibers consistently over an entire range of fiber sizes from smaller to larger than the wavelength of radiation. A geometrical technique is presented for modeling a fiber with a rough surface of a three-dimensional homogeneous microstructure. Scattering characteristics of the fiber are described based on the electromagnetic wave theory of diffraction to investigate the relationship among three main factors of scattering: wavelength of radiation, fiber diameter, and fiber microstructure. With an increase in fiber diameter and a corresponding magnification of a rough fiber surface microstructure, the scattering changes from particle scattering to surface scattering. The transition occurs in a size parameter range of P = 100–300. © 1999 Scripta Technica, Heat Trans Asian Res, 28(4): 322–335, 1999