Polyethylene-co-methacrylic acid healing agents for mendable epoxy resins

A new thermoplastic healing agent and associated healing agent delivery mechanism have been investigated. Polyethylene-co-methacrylic acid (EMAA) particles were mixed into an epoxy resin, resulting in an increase in the fracture strength of the resin. Damaged single edge notched bars and tapered double cantilever beams were healed at 150 °C for 30 min to achieve up to an 85% recovery in critical stress intensity and over 100% recovery in sustainable peak load. Optical and scanning electron microscopy revealed that strength recovery in the damaged resin was achieved via EMAA particle healing as well as the formation of an adhesive EMAA layer between adjacent epoxy fracture surfaces. Microscopy also showed that small bubbles in the EMAA particles act as a new healing agent delivery mechanism wherein expansion during heating forced larger volumes of healing agent into the damaged region of the resin.     

Thermal effects in packaging high power light emitting diode arrays

The package and system level temperature distributions of a high power (>1 W) light emitting diode (LED) array have been investigated using numerical heat flow models. For this analysis, a thermal resistor network model was combined with a 3D finite element submodel of an LED structure to predict system and die level temperatures. The impact of LED array density, LED power density, and active versus passive cooling methods on device operation were calculated. In order to help understand the role of various thermal resistances in cooling such compact arrays, the thermal resistance network was analyzed in order to estimate the contributions from materials as well as active and passive cooling schemes. Finally, an analysis of a ceramic packaging architecture is performed in order to give insight into methods to reduce the packaging resistance for high power LEDs.     

华尔街败局对大坝安全风险管理的启示

2008年全球金融危机的形成,就宏观的管理概念而言,是美国华尔街营运风险控管步入歧途的后果。这场造成世界经济严重衰退的风暴也为大坝安全管理人员在大坝安全风险管控方面起了警示作用。首先要冷静、客观地研究、了解、认识华尔街金融操作风险问题的核心所在,应用在大坝安全管理方面才能正确有效地理顺风险意识,建立风险控管机制。     

At-Site Flood Frequency Analysis Coupled with Multiparameter Probability Distributions

The proper design of hydraulic structures as well as river basin management are directly dependent on adequate estimates of maximum streamflow, preferably obtained from long historical series. However, the scarce hydrological monitoring, recurrent in developing countries and the need for estimates associated with high return periods (RPs) have led to the use of estimation methods based statistical procedures, such as at-site flood frequency analysis. This study presents a framework for at-site flood frequency analysis coupled with multiparameter probability distribution functions (PDFs) (GEV, LN3, PE3, GLO, GPA, KAP and WAK), in which all the statistical procedures are derived from L-moments, in order to investigate the applicability of these PDFs in comparison to those of 2-parameters (EV1, LN2 and Gamma). The modeling framework was evaluated considering 106 maximum annual streamflow (MAS) series for the Rio Grande do Sul State - Brazil. PDFs’ goodness-of-fit was studied in accordance with the Anderson-Darling test. It can be concluded that: i) the multiparameter distributions, especially KAP and WAK, had performance superior to the traditional 2-parameter distributions, providing a greater number of historical series better adjusted by such multiparameter PDFs; ii) shorter series were usually better represented by GEV when compared to the other PDFs, which is an important characteristic when long historical series are not frequently available; and iii) the quantile estimates derived from multiparameter PDFs presented lower Relative Absolute Error, thus emphasizing the importance of using such PDFs in water resources management and engineering projects.     

Modeling the impacts of climate change on the thermal and oxygen dynamics of Lake Volta

Climatic changes influence the thermal and oxygen dynamics of a lake and thus its ecological functioning. The impacts of climatic changes on tropical lakes are so far poorly studied and the extent of the effects is therefore uncertain, most investigations describing only potential effects. In this study, we applied the one-dimensional lake ecosystem model GOTM-ERGOM to quantify the effects of climate change on thermal stratification, oxygen dynamics, and primary production in meso-oligotrophic Lake Volta. GOTM-ERGOM was calibrated and validated using two years of observed data. The validated model was used to evaluate a series of future climate change scenarios. The model simulations showed good agreement with observed water temperature, dissolved oxygen and chlorophyll-a and indicated intensified stratification and reduced oxygen levels in the productive water layers of the lake. However, the longer-lasting stratification (prolonged stability) did not translate into permanent stratification. A relatively small (1?m) upward shift of thermocline depth resulted in an 8%–12% volume loss of the oxygen-rich upper mixed layer, which may be significant for the fisheries of the lake as it diminishes the size of suitable fish habitats. Light limitation of primary production renders the lake somewhat resilient to intensive algae blooms, as traceable in both the present and in the future climate scenarios. In the long term, the ongoing climate change may affect riparian communities that depend on the lake's fisheries for their livelihood. In consequence, future lake management strategies for implementation need to account for the impacts of future climate change.     

Thermal and mechanical characteristics of polylactide filaments drawn at different temperatures

Polylactide (PLA) filaments produced by melt spin-drawing in different conditions (draw ratio, temperature of the draw roll) have been studied to demonstrate the influence of the process conditions on the tensile properties of the PLA filaments. Draw ratio varies from 2 to 3.5 and temperature of the draw roll from 80°C to 120°C. The thermal characteristics have been investigated using modulated differential scanning calorimetry (MDSC) and crystallinity using X-Ray Diffraction (XRD). Shrinkage of PLA multifilaments depending on the processing conditions is also investigated. It is demonstrated that the temperature of the draw roll is essential to obtain PLA filaments with optimum properties. At 80°C, the size of the lamellar crystals, measured using DRX, is not the highest. It is necessary to set the temperature of the draw roll at 110°C to obtain thick lamellar crystals. So, in those conditions, the PLA filaments have their optimum mechanical properties.     

防患于未然:水坝潜在溃决模式探究与分析

本文简介三种常见水坝的一些具有代表性的潜在溃决模式和导致这些模式发生的根本原因（即所谓的风险因素和可能的理由）,俗云：“不经一事,不长一智”,冀望从过去的溃坝案例中吸取宝贵的教训,以正视每一个可能影响水坝安全的问题。本文略述近期发展的蓄水坝潜在溃决模式分析方法的步骤,借着制度面的革新,透过团队合作方式,以确认、判断可能存在的潜在溃决模式及其发生的相对可能性,采取必要的补救措施。