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981.
Mining companies typically seek ways to hedge risks affecting their production. One useful instrument to mitigate the financial risk is the futures contracts on commodity prices. Information from the transactions in futures markets is publicly available and can be analysed with the Schwartz–Smith two-factor model (SSTF). However, finding the parameters governing this model can be very challenging. This step is done using a deterministic optimisation approach called the Expectation–Maximisation algorithm (EM). The starting values of the model will have a significant effect on the convergence of the EM. To ensure the solution does not get stuck in a local maximum, the EM algorithm is performed multiple times with different starting values. This paper assesses the value of genetic algorithms (GA) to optimise the parameters of the SWTF model. Although they are slower than EM algorithms because they use random number generators to search for the optimal solution, GA optimise a population of solutions instead of working on only one solution at the time. Moreover, a constraint on the range parameter can be applied to ensure the parameter has a sound economic meaning. Once the SWTF parameters have been calibrated on the observation of futures contracts, the model can be used for the simulation of spot and futures prices. To demonstrate the performance of the proposed approach, a case study was conducted on a copper deposit. The simulations based on the SWTF model whose parameters are determined by GA are used. An active management strategy of the stockpile, dependent on discrepancies in commodity futures prices is tested. Results show that the active management strategy produces positive returns over the passive investment approach. 相似文献
982.
Sónia Simões Filomena Viana Volker Ventzke Mustafa Koçak A. Sofia Ramos M. Teresa Vieira Manuel F. Vieira 《Journal of Materials Science》2010,45(16):4351-4357
With the stimulus of temperature and pressure Ni and Al can quickly react and produce the intermetallic compound NiAl. This
reaction is highly exothermic and high temperatures can be attained in the surroundings. These characteristics make Ni/Al
multilayers very attractive to technological applications as localised heat sources. In this study, Ni/Al multilayer thin
films are used to promote bonding between TiAl intermetallic alloys. Ni and Al alternated nanolayers were deposited by d.c.
magnetron sputtering onto TiAl samples, with periods of 5, 14 and 30 nm. Joining experiments were performed at 900 °C for
60 or 30 min, in a vertical furnace with a vacuum level better than 10−2 Pa. Applied pressures of 5 MPa were tested. The microstructure of the cross-sections of the bond interface was analysed by
energy dispersive X-ray spectroscopy and characterised by scanning electron microscopy. The observation of the microstructure
for 14 and 30 nm period multilayers revealed sound bonding, while for 5 nm period porosity and cracks within the interlayer
thin film were observed. The interface is divided into three distinct zones: one with columnar grains, another with very small
equiaxed grains and the third with larger equiaxed grains. The joining process appears to depend on the diffusion of Ni and
Ti across the interface and is assisted by the nucleation of nanometric grains at the interface. The mechanical strength of
the joints was evaluated by shear tests. The bonds produced at 900 °C/5 MPa/60 min/14 nm exhibited the highest shear strength
of 314 MPa. 相似文献
983.
The article describes a convenient synthesis and Cr(VI) extraction efficiency of a novel p-tert-butylcalix[8]areneoctamide impregnated Amberlite (XAD-4) resin. Using p-tert-butylcalix[8]arene macrocyclic building block, two strategies have been developed; i.e., derivatization of p-tert-butylcalix[8]arene framework with sophisticated ionophoric groups having efficiency to extract oxoanions from aqueous media and, impregnation of p-tert-butylcalix[8]arene derivative onto the polymeric support. Liquid-liquid and solid-liquid extraction experiments have been performed to evaluate the Cr(VI) extraction efficiency of both p-tert-butylcalix[8]arene derivative and the impregnated resin. From the results, it has been deduced that solid-phase extraction method is more convenient and efficient than liquid-liquid extraction process. The impregnated XAD-4 resin has been found regenerable with better extracting efficiency as compared to the simple p-tert-butylcalix[8]areneoctamide ionophore. 相似文献
984.
Halogenated volatile organic compounds from the use of chlorine-bleach-containing household products
Odabasi M 《Environmental science & technology》2008,42(5):1445-1451
Sodium hypochlorite (NaOCl) and many organic chemicals contained in household cleaning products may react to generate halogenated volatile organic compounds (VOCs). Halogenated VOC emissions from eight different chlorine bleach containing household products (pure and diluted) were investigated by headspace experiments. Chloroform and carbon tetrachloride were the leading compounds along with several halogenated compounds in the headspace of chlorine bleach products. One of the most surprising results was the presence of carbon tetrachloride (a probable human carcinogen and a powerful greenhouse gas that was banned for household use by the U.S. Food and Drug Administration) in very high concentrations (up to 101 mg m(-3)). By mixing surfactants or soap with NaOCl, it was shown that the formation of carbon tetrachloride and several other halogenated VOCs is possible. In addition to quantitatively determined halogenated VOCs (n = 15), several nitrogen-containing (n = 4), chlorinated (n = 10), oxygenated compounds (n = 22), and hydrocarbons (n = 14) were identified in the headspace of bleach products. Among these, 1,1-dichlorobutane and 2-chloro-2-nitropropane were the most abundant chlorinated VOCs, whereas trichloronitromethane and hexachloroethane were the most frequently detected ones. Indoor air halogenated VOC concentrations resulting from the use of four selected household products were also measured before, during, and 30 min after bathroom, kitchen, and floor cleaning applications. Chloroform (2.9-24.6 microg m(-3)) and carbon tetrachloride (0.25-459 microg m(-3)) concentrations significantly increased during the use of bleach containing products. During/ before concentration ratios ranged between 8 and 52 (25 +/- 14, average +/- SD) for chloroform and 1-1170 (146 +/- 367, average +/- SD) for carbon tetrachloride, respectively. These results indicated that the bleach use can be important in terms of inhalation exposure to carbon tetrachloride, chloroform and several other halogenated VOCs. 相似文献
985.
986.
Silver compounds have extensive use among the antimicrobial agents in textiles. Silver particles are released into the water during washing processes in particular and they are released from the textile in time due to use. In this work, silver ion release from cotton and polyester antimicrobial fabrics which are the most widely used textiles have been studied. Two well-known silver-based commercial agents and silver-doped calcium phosphate powder-based antibacterial finishing agent which was developed in our previous work were applied to the fabric samples. The release of silver from the fabric samples during washing and incubation was determined by ICP-OES. The effects of fabric composition, time and laundering process on the silver release were studied. It was found that significant amount of silver was released from textile fabrics during washing due to the mechanical forces exerted on the fabrics. The total released silver varied from 73.43 to 92.27% for cotton fabrics and 76.49 to 89.70% for PES fabrics after 20 washing cycles. Results also showed that calcium phosphate can reduce the amount of silver release significantly. It was also found that even a smaller quantity of nanosilver particles was sufficient for strong antibacterial activity. 相似文献
987.
Characterization of Grape Molasses/Sesame Paste/Honey Blends: Multiple Response Optimization of Some Physicochemical,Bioactive, Viscoelastic and Sensory Properties 下载免费PDF全文
988.
Sakip Onder Ayse Ceren Calikoglu-Koyuncu Gamze Torun Kose Kursat Kazmanli Fatma Nese Kok Mustafa Urgen 《JOM Journal of the Minerals, Metals and Materials Society》2017,69(7):1195-1205
TiN and (Ti,Mg)N thin film coatings were deposited on Ti substrates by an arc-physical vapor deposition technique. The effect of cell presence on hydroxyapatite (HA) formation was investigated using surfaces with four different Mg contents (0, 8.1, 11.31, and 28.49 at.%). Accelerated corrosion above 10 at.% Mg had a negative effect on the performance in terms of both cell proliferation and mineralization. In the absence of cells, Mg-free TiN coatings and low-Mg (8.1 at.%)-doped (Ti,Mg)N surfaces led to an early HA deposition (after 7 days and 14 days, respectively) in cell culture medium (DMEM), but the crystallinity was low. More crystalline HA structures were obtained in the presence of the cells. HA deposits with an ideal Ca/P ratio were obtained at least a week earlier, at day 14, in TiN and low-Mg (8.1 at.%)-doped (Ti,Mg)N compared with that of high-Mg-containing surfaces (>10 at.%). A thicker mineralized matrix was formed on low-Mg (8.1 at.%)-doped (Ti,Mg)N relative to that of the TiN sample. Low-Mg doping (<10 at.%) into TiN coatings resulted in better cell proliferation and thicker mineralized matrix formation, so it could be a promising alternative for hard tissue applications. 相似文献
989.
Md. Mahfujur Rahman Wan Jefrey Basirun Subha Bhassu Nur Raifana Abdul Rashid Shuhaimi Mustafa 《Food additives & contaminants. Part A, Chemistry, analysis, control, exposure & risk assessment》2016,33(1):10-18
This paper describes a short-amplicon-based TaqMan probe quantitative real-time PCR (qPCR) assay for the quantitative detection of canine meat in chicken nuggets, which are very popular across the world, including Malaysia. The assay targeted a 100-bp fragment of canine cytb gene using a canine-specific primer and TaqMan probe. Specificity against 10 different animals and plants species demonstrated threshold cycles (Ct) of 16.13 ± 0.12 to 16.25 ± 0.23 for canine DNA and negative results for the others in a 40-cycle reaction. The assay was tested for the quantification of up to 0.01% canine meat in deliberately spiked chicken nuggets with 99.7% PCR efficiency and 0.995 correlation coefficient. The analysis of the actual and qPCR predicted values showed a high recovery rate (from 87% ± 28% to 112% ± 19%) with a linear regression close to unity (R2 = 0.999). Finally, samples of three halal-branded commercial chicken nuggets collected from different Malaysian outlets were screened for canine meat, but no contamination was demonstrated. 相似文献
990.
A Bioactive Constituent of Ginger, 6‐Shogaol,Prevents Adipogenesis and Stimulates Lipolysis in 3T3‐L1 Adipocytes 下载免费PDF全文