Flexural modulus prediction of symmetric structural polymer foams with complex density profiles

In this work, a new phenomenological model is proposed to predict the flexural modulus of symmetric structural foams with complex density distribution across their thickness. The model is based on a generalized Fourier series to represent the density profile and the simple square power-law relation to relate density with modulus. The model predictions are compared with data on polyethylene (LDPE and HDPE) structural foams produced by compression and injection molding. The results show that a very high degree of agreement (less than 3% deviation) can be obtained for these complex structures.     

Development of a multi-purpose solar tunnel dryer for use in humid tropics

Particularly in tropical countries, a high percentage of crops are spoiled during the drying period due to permanently high relative humidity and sudden rainfalls. Open air sun drying and smoke drying, which are traditional drying methods in these regions, lead to insufficient product quality. In order to be marketable, the produce meant for sale on the world market has to meet high quality standards. Otherwise the price will decline resulting in low profits for the exporting country and the producing farmer. To produce high quality products for the world market as well as to reduce losses, the development of suitable dryers for tropical regions is urgently needed. A multi-purpose solar tunnel dryer, orginally developed for the use in arid zones, was modified to enable operation under tropical weather conditions. This type of dryer consists of a small centrifugal blower, a collector and a tunnel drying chamber. To prevent penetration of water into the construction and subsequent flooding, the solar dryer was installed on a wooden substructure. To heat the drying air during cloudy and rainy days, particularly in the rainy season, a biomass furnace with heat exchanger was integrated into the solar drying system. The construction consists exclusively of materials available in Java. Only low energy requirements are necessary to run the blower. Results showed that compared to natural sun drying, the drying time of cocoa, coffee and coconut could be reduced up to 40%. Solar drying improves the quality of the products in terms of colour, flavour and appearance, reduces the risk of microorganism growth, prevents insect infestation and contamination by foreign matters and mycotoxins. The products dried with the solar drying system meet the national and ingternational market standards. Investigations further showed that even during the rainy season it was possible to dry the products to the final moisture content which is needed for storage and marketing. The modular system allows adaptation to different farm sizes as well as cooperative use.     

PtRu/C electrocatalysts prepared using γ-irradiation

PtRu/C electrocatalysts (carbon-supported PtRu nanoparticles) were prepared submitting water/ethylene glycol solutions containing Pt(IV) and Ru(III) ions and the carbon support to γ-irradiation. The water/ethylene glycol ratio (v/v) and the total dose (kGy) were evaluated as synthesis parameters. The electrocatalysts were characterized by energy dispersive X-ray analysis (EDX), X-ray diffraction (XRD), transmission electron microscopy (TEM) and cyclic voltammetry and tested for methanol electro-oxidation aiming fuel cell application. The obtained PtRu/C electrocatalysts were more active for methanol electro-oxidation than the commercial PtRu/C electrocatalyst at ambient temperature and the electrocatalytic activity depends on the water/ethylene glycol ratio used in the preparation.     

甲醇/汽油混合燃料发动机非常规排放成分测量方法研究

对使用气相色谱仪检测甲醇／汽油混合燃料发动机排气中醇醛类排放方法进行了研究，优化选择了采样方法、载气流速、柱温等参数，证明安装PEG色谱柱的GC2010完全可以对甲醇／汽油混合燃料发动机排气中的醇、醛进行精确的检测分析。发动机尾气测试结果表明，汽油机燃用M10混合燃料时，排气中的甲醛中低负荷高达0．2mg／L。此外，发动机燃用市售汽油和M10两种燃料时，排气中的甲醇、乙醇和乙醛量相差在10％左右，经三效催化转化器后，可以被控制到接近零排放的水平。     

Single versus Multiple Prime Contracting

Policies regarding public building construction affect the interests of taxpayers, construction authorities, general contractors, specialty contractors, and other stakeholders. At the state level, the debate as to the optimal form such policies should take has become an ongoing struggle among competing interests. This study presents a systematic analysis of the main issues regarding single versus multiple prime contracting with the purpose of providing objective data to illuminate the debate. A statistical analysis of project bids and final costs from a national sample of state construction projects reveals that public construction projects organized with multiple prime contracts tend to have 5% less direct costs than projects using a single prime contractor. Moreover, approximately 80% of these savings are attributable to lower bid costs for multiple prime projects. The results of this study are in agreement with theoretical bidding models and efficient risk allocation models. Theoretical bidding models suggest that, in the absence of disruptions, multiple prime projects should have lower direct costs than single prime jobs. Efficient cost allocation models suggest that when specialty contractors do not bear the risks associated with the single prime contracting method (e.g., bid shopping and payment delays) they are willing to lower their bids, and forego the premium they would normally charge in response to such risks, as seems to be the case in multiple prime jobs.     

Borate Distribution in Stabilized Stainless-Steel Slag

Disintegration of stainless-steel slag during cooling is caused by the β→γ transformation of dicalcium silicate (2CaO·SiO₂ or C₂S). It is well established that disintegration can be avoided by borate additions, which are commonly believed to stabilize the high-temperature polymorphs by forming a solid solution with C₂S. In this study, the borate distributions in slowly cooled synthetic and industrial slag samples are determined. The slag microstructures are characterized using electron probe microanalysis (EPMA), quantitative X-ray diffraction (QXRD), and wavelength dispersive spectroscopy (WDS). The results show that only a limited fraction of the added borates forms a solid solution with the C₂S phase, while the main fraction is found in a calcium borosilicate phase. In combination with literature data, this suggests that slag stabilization involves more than the chemical stabilization of the high-temperature C₂S polymorphs.     

Time trends of polybrominated diphenyl ethers in sediment cores from the Pearl River Estuary, South China

The present study provides information on the time trend of PBDEs in three sediment cores from the Pearl River Estuary (PRE), South China, using 210Pb dating technique. The sigmaPBDEs (except for BDE 209) concentrations in all sediment cores increased gradually from the bottom (mid-1970s) to the middle layer (later 1980s and early 1990s) followed by different temporal trends in different locations to the surface sediments, reflecting the variations in the consumption of commercial penta-BDEs mixture in different regions of the Pearl River Delta. The BDE 209 concentrations remained constant until 1990 and thereafter increased exponentially to the present, with doubling times of 2.6 +/- 0.5-6.4 +/- 1.6 years, suggesting the increasing market demands for deca-BDE mixture after 1990 in China. The inventories of sigmaPBDEs and BDE 209 in sediments of the PRE were 56.0 and 368.2 ng cm(-2), respectively, and the total burden of PBDEs in the PRE were estimated at 8.6 metric tons. The current sigmaPBDEs and BDE 209 fluxes to the PRE were 2.1 and 29.7 ng cm(-2) yr(-1), respectively. The concurrent increase of BDE 209 fluxes and the annual gross industrial output values of electronics manufacturing revealed that the rapid growth of electronics manufacturing in this region since the early 1990s was responsible for the sharp rise of BDE 209 fluxes in the past decade. The PBDE congener compositions of the cores indicated the various input pathways for PBDEs transport to different locations of the estuary.     

Parallel Algorithm for SWFFT Using 3D Data Structure

Sliding-Window Fast Fourier Transform (SWFFT) is a very important and widely used time-frequency representation of a signal. In the paper, we mainly focus on the problem of how to implement non-recursive SWFFT in parallel programming. To avoid repeated calculations, non-recursive SWFFT algorithms always save the calculated results and use for later calculations. So the current calculations need the results from the earlier calculations, and this leads to the main obstacle of implementing SWFFT in parallel programming.     

Polybrominated diphenyl ethers in airborne particulates collected during a research expedition from the Bohai Sea to the Arctic

In July to September 2003, particulates in the oceanic atmosphere from the Bohai Sea to the high Arctic (37 degrees N to 80 degrees N) were collected aboard a research expedition icebreaker, Xuelong (Snow Dragon), under the 2003 Chinese Arctic Research Expedition Program (CHINARE 2003). These samples were analyzed to elucidate the atmospheric distributions of polybrominated diphenyl ethers (PBDEs) in the North Pacific Ocean and adjacent Arctic region. The levels of 11 PBDE congeners (BDE-28, -47, -66, -100, -99, -85, -154, -153, -138, -183, and -209; the sum was defined as sigma11PBDE) in the oceanic atmosphere of Far East Asia (34-48 degrees N/122-148 degrees E) ranged from 2.25 to 198.9 pg/m3 with a mean of 58.3 pg/m3. BDE-47, -99, -100, and -209 were the dominant congeners in all the samples, suggesting that the widely used commercial penta- and deca-BDE products were the original sources. The PBDE levels exhibited a decreasing trend from the mid- to high-latitudinal regions of the North Pacific Ocean, probably resulting from dilution, deposition, and decomposition of PBDEs during long-range transport of air masses. On the other hand, no apparent geographical pattern of PBDE distribution was observed within the Arctic, attributable to unstable air circulation and strong air mixing. Correlations among the PBDE congeners suggested that air masses collected from the North Pacific Ocean were relatively fresh, whereas those from the Arctic were aged as a result of photodecompoisiton. The higher average level (17.3 pg/m3) of PBDE congeners in the Arctic than those in the adjacent North Pacific Ocean (12.8 pg/m3) or other remote areas reported in the literature was attributed to the impact of the North American continent and temperature effects, which was consistent with the hypotheses of global fractionation.     

Mesoporous Silica Preparation Using Sodium Bicarbonate as Template and Application of the Silica for Hydrocracking of Used Cooking Oil into Biofuel

Silicon - The hydrocracking of used cooking oil into biofuel over mesoporous silica was systematically studied. This research aims to induce the silica pores using NaHCO3 and employ the heteropore...