Simultaneous synthesis of carbon nanobelts and carbon/Fe-Cu hybrids for microwave absorption

By acetylene decomposition at 450 °C over the Fe-Cu nanoparticles (Fe:Cu molar ratio = 29:1, 5:1) derived from a combined sol-gel/reduction method, carbon nanobelts (CNBs) and carbon/Fe-Cu hybrid nanoparticles (CNPs) were synthesized simultaneously with high yield. The two carbon species could be easily separated according to color and were collected at different locations of the ceramic plates where the catalysts were placed. Over Fe-Cu nanoparticles of high Cu content (Fe:Cu = 2:1), the product was carbon nanofibers. A series of comparison experiments was designed to study the optimal conditions for the formation of CNBs, and the results indicate that CNBs and CNPs can be selectively synthesized at 450 °C by adjusting the Cu content of the catalyst. Moreover, the complex permittivity and permeability of the mixture that contains CNPs or CNBs (30 wt.%) (paraffin wax as binder matrix) were measured in the 2-18 GHz frequency range. Despite the low mass percentage of CNBs, microwave absorption is good. Below −10 dB, there are two, three, and four distinct reflection loss peaks when the thicknesses of CNB composites are within the 5.5-7.5 mm, 9.5-11.5 mm, and 11.5-13.5 mm ranges, respectively.     

Nonlinear dynamic analysis of frames with plastic hinges at arbitrary locations

This paper presents a method for nonlinear dynamic analysis of frames subjected to distributed loads, which is based on the semi‐rigid technique and moving node strategy. The plastic hinge is modelled as a pseudo‐semi‐rigid connection with nonlinear hysteretic moment–curvature characteristics at element ends. The stiffness matrix with material and geometric nonlinearities is expressed as a sum of products of the standard and geometric stiffness matrices with their corresponding correction matrices based on the plasticity‐factors developed from the section flexural stiffness at the plastic hinge locations. Each beam member is modelled by two elements. The moving node strategy is applied to the intermediate node to track the exact location of any intermediate plastic hinge that may be formed. Equilibrium iterations and geometry updating are carried out in every time step. Stiffness degradation is adopted to describe the deterioration of plastic hinges, and the effects of various parameters in the degradation model are evaluated. Examples are used to illustrate the applicability and excellent performance of the proposed method. Copyright © 2009 John Wiley & Sons, Ltd.     

彩南油田彩X井区低阻油气层的识别

常规气测解释图版在低阻油气层的识别中存在一定的困难。该文以彩X井区已完钻井的气测、试油资料为主要依据，分析总结了该井区低阻油气层在常规气测解释图版中的表现特征，为现场识别低阻油气层提出一种新的思路。推而广之，在现场识别低阻油气层中具有一定的实用价值。     

Vibration of railway bridges under a moving train by using bridge-track-vehicle element

During the last two decades, much attention has been paid to various vibration problems associated with railways. They include the dynamic response of railway bridges and railway tracks at grade under the action of moving trains. However, studies on the role of track structures on the vibration of railway bridges are rather limited. In this paper, a new element called bridge-track-vehicle element is proposed for investigating the interactions among a moving train, and its supporting railway track structure and bridge structure. The moving train is modelled as a series of two-degree-of-freedom mass-spring-damper systems at the axle locations. A bridge-track-vehicle element consists of vehicles modelled as mass-spring-damper systems, an upper beam element to model the rails and a lower beam element to model the bridge deck. The two beam elements are interconnected by a series of springs and dampers to model the rail bed. The investigation shows that the effect of track structure on the dynamic response of bridge structure is insignificant. However, the effect of the bridge structure on the dynamic response of the track structure is considerable.     

The effects of different UV‐B radiation intensities on morphological and biochemical characteristics in Ocimum basilicum L.

BACKGROUND: The effects of short‐term ultraviolet B (UV‐B) irradiation on sweet basil (Ocimum basilicum L. cv. Cinnamon) plants at the 3–4 leaf pair and flowering stages were examined in controlled environment growth chambers. Plants were exposed to 0 (reference), 2 and 4 kJ UV‐B m^?2 day^?1 over 7 days. RESULTS: Exposure of basil plants to supplementary UV‐B light resulted in increased assimilating leaf area, fresh biomass and dry biomass. Stimulation of physiological functions in young basil plants under either applied UV‐B dose resulted in increased total chlorophyll content but no marked variation in carotenoid content. At the flowering stage the chlorophyll and carotenoid contents of basil were affected by supplementary UV‐B radiation, decreasing with enhanced UV‐B exposure. Both total antioxidant activity (2,2‐diphenyl‐1‐picrylhydrazyl free radical assay) and total phenolic compound content were increased by UV‐B light supplementation. Young and mature basil plants differed in their ascorbic acid content, which was dependent on UV‐B dose and plant age. UV‐B radiation resulted in decreased nitrate content in young basil plants (3–4 leaf pair stage). CONCLUSION: These results indicate that the application of short‐exposure UV‐B radiation beneficially influenced both growth parameters and biochemical constituents in young and mature basil plants. © 2012 Society of Chemical Industry     

Semiconductor saturable absorber mirrors (SESAM's) for femtosecondto nanosecond pulse generation in solid-state lasers

Intracavity semiconductor saturable absorber mirrors (SESAM's) offer unique and exciting possibilities for passively pulsed solid-state laser systems, extending from Q-switched pulses in the nanosecond and picosecond regime to mode-locked pulses from 10's of picoseconds to sub-10 fs. This paper reviews the design requirements of SESAM's for stable pulse generation in both the mode-locked and Q-switched regime. The combination of device structure and material parameters for SESAM's provide sufficient design freedom to choose key parameters such as recovery time, saturation intensity, and saturation fluence, in a compact structure with low insertion loss. We have been able to demonstrate, for example, passive modelocking (with no Q-switching) using an intracavity saturable absorber in solid-state lasers with long upper state lifetimes (e.g., 1-μm neodymium transitions), Kerr lens modelocking assisted with pulsewidths as short as 6.5 fs from a Ti:sapphire laser-the shortest pulses ever produced directly out of a laser without any external pulse compression, and passive Q-switching with pulses as short as 56 ps-the shortest pulses ever produced directly from a Q-switched solid-state laser. Diode-pumping of such lasers is leading to practical, real-world ultrafast sources, and we will review results on diode-pumped Cr:LiSAF, Nd:glass, Yb:YAG, Nd:YAG, Nd:YLF, Nd:LSB, and Nd:YVO₄     

A fuzzy approach to partitioning continuous attributes for classification

Classification is an important topic in data mining research. To better handle continuous data, fuzzy sets are used to represent interval events in the domains of continuous attributes, allowing continuous data lying on the interval boundaries to partially belong to multiple intervals. Since the membership functions of fuzzy sets can profoundly affect the performance of the models or rules discovered, the determination of membership functions or fuzzy partitioning is crucial. In this paper, we present a new method to determine the membership functions of fuzzy sets directly from data to maximize the class-attribute interdependence and, hence, improve the classification results. In other words, it forms a fuzzy partition of the input space automatically, using an information-theoretic measure to evaluate the interdependence between the class membership and an attribute as the objective function for fuzzy partitioning. To find the optimum of the measure, it employs fractional programming. To evaluate the effectiveness of the proposed method, several real-world data sets are used in our experiments. The experimental results show that this method outperforms other well-known discretization and fuzzy partitioning approaches.