A method for evaluating the frequency of deficiency-states ofelectric-power systems

A novel method for evaluating the frequency of deficiency-states of power systems is suggested. The method uses exact generation-capacity states and system load-duration and load-frequency characteristics. The approach accurately models load daily diagrams, including multimodal diagrams. The generating units are modeled as multistate elements. Analytic expressions for the frequency of deficiency-states are derived in closed form to avoid the accumulation of rounding errors that might appear in recursive approaches. Illustrative application examples are included     

Cross-hole techniques in a deep seated rock mass

Bulletin of Engineering Geology and the Environment - A cooperative project between seven countries—the Stripa Project—is currently underway in an abandoned iron ore mine located in...     

Free radical copolymerization of N,N‐dimethylaminoethyl methacrylate with styrene and methyl methacrylate: monomer reactivity ratios and glass transition temperatures

BACKGROUND: The properties of copolymers depend strongly on their composition; therefore in order to tailor some for specific applications, it is necessary to control their synthesis, and, in particular, to know the reactivity ratios of their constituent monomers. Free radical copolymerizations of N,N‐dimethylaminoethyl methacrylate (DMAEM) with styrene (ST) and methyl methacrylate (MMA) in toluene solution using 1‐di(tert‐butylperoxy)‐3,3,5‐trimethylcyclohexane as initiator at 70 °C were investigated. Monomer reactivity ratios were determined for low conversions using both linear and nonlinear methods. RESULTS: For the DMAEM/ST system the average values are r₁ = 0.43 and r₂ = 1.74; for the DMAEM/MMA system the average values are r₁ = 0.85 and r₂ = 0.86. The initial copolymerization rate, R_p, for DMAEM/ST sharply decreases as the content of ST in the monomer mixture increases up to 30 mol% and then attains a steady value. For the DMAEM/MMA copolymerization system the composition of the feed does not have a significant influence on R_p. The glass transition temperatures (T_g) of the copolymers were determined calorimetrically and calculated using Johnston's sequence length method. A linear dependence of T_g on copolymer composition for both systems is observed: T_g increases with increasing ST or MMA content. CONCLUSION: Copolymerization reactivity ratios enable the design of high‐conversion processes for the production of copolymers of well‐defined properties for particular applications, such as the improvement of rheological properties of lubricating mineral oils. Copyright © 2009 Society of Chemical Industry     

Thermal Stability of Lubricating Oil Additives Based on Styrene and n-Alkyl Methacrylate Terpolymers

In this work the thermal stability of polymeric additives for the improvement of rheological behavior of mineral lubricating oils was investigated. The systems studied comprised methyl methacrylate (MMA)/dodecyl methacrylate (DDMA)/octadecyl methacrylate (ODMA) and styrene (Sty)/DDMA/ODMA terpolymers. The composition of the terpolymers was determined by the ¹H nuclear magnetic resonance spectroscopy and molar mass distribution by the size exclusion chromatography. The thermal degradation of terpolymers was studied by the thermogravimetric analysis. Sty/DDMA/ODMA terpolymers exhibited an improved thermal stability in comparison with MMA/DDMA/ODMA terpolymers of the corresponding compositions. Thus, the temperatures of 50% weight loss were found to be 313°C and 363°C for MMA terpolymer and Sty terpolymer, respectively, where x (MMA) = x (Sty) = 30 mol%.     

Numerical investigation of particle saltation in the bed-load regime

This paper numerically investigates particle saltation in a turbulent channel flow having a rough bed consisting of 2–3 layers of densely packed spheres.In this study,we combined three the state-of-the-art technologies,i.e.,the direct numerical simulation of turbulent flow,the combined finite-discrete element modelling of the deformation,movement and collision of the particles,and the immersed boundary method for the fluid-solid interaction.Here we verify our code by comparing the flow and particle statistical features with the published data and then present the hydrodynamic forces acting on a particle together with the particle coordinates and velocities,during a typical saltation.We found strong correlation between the abruptly decreasing particle stream-wise velocity and the increasing vertical velocity at collision,which indicates that the continuous saltation of large grain-size particles is controlled by collision parameters such as particle incident angle,local rough bed packing arrangement,and particle density,etc.This physical process is different from that of particle entrainment in which turbulence coherence structures play an important role.Probability distribution functions of several important saltation parameters and the relationships between them are presented.The results show that the saltating particles hitting the windward side of the bed particles are more likely to bounce off the rough bed than those hitting the leeside.Based on the above findings,saltation mechanisms of large grain-size particles in turbulent channel flow are presented.     

Influence of chemical functionalization of carbon nanotubes on their dispersibility in alkyl methacrylate polymer matrix

Nanocomposites based on poly(methyl methacrylate) (PMMA) and poly(methyl methacrylate‐co‐octadecyl methacrylate) (M/O) matrices and four different types of multiwall carbon nanotubes: pristine, oxidized (MWCNT–COOH), methyl ester (MWCNT–COOCH₃), and dodecyl ester (MWCNT–COOC₁₂H₂₅) functionalized, were prepared in situ by radical (co)polymerization. The effectiveness of preparation of nanocomposites regarding dispersion and distribution of various MWCNT in polymer matrices was sized by Scanning electron microscopy. In case of PMMA matrix, the best dispersion and distribution were accomplished for MWCNT–COOCH₃ due to their chemical resemblance with polymer matrix. After the introduction of 10 mol % of octadecyl methacrylate in polymer matrix a fairly good dispersion and distribution of MWCNT–COOCH₃ were retained. The addition of 1 wt % of MWCNTs caused a significant reduction in the degree of polymerization of the PMMA matrix. But at the same time, the present MWCNTs increased storage modulus of PMMA nanocomposites except for dodecyl ester functionalized MWCNT. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46113.     

Biomonitoring of mercury in polluted coastal area using transplanted mussels

The Kastela Bay is heavily polluted with inorganic mercury originated from direct discharges from the chlor-alkali plant, which operated in the period from 1950 to 1990. Even though the plant was closed 15 years ago, elevated levels of total mercury are still evident in surface sediments of the bay. In order to assess the availability of remobilized mercury to marine organisms, cultured mussels (M. galloprovincialis) were transplanted from pristine area to Kastela Bay, in the period from September 2000 to March 2001. Mussel samples were collected for the analysis of THg and MeHg in whole soft tissue, gills and digestive gland. Surface sediments and suspended matter were collected for the analysis of THg. Digestive gland was the target organ for the accumulation of THg, while concentrations of MeHg were similar in all analyzed tissues. The percentage of MeHg in mussel tissues (4-27%) was characteristic for the areas contaminated with inorganic mercury. A significant negative correlation was observed between the THg concentration in the tissues and the percentage of MeHg. Concentrations of THg in mussel tissues, which were decreasing from the source of contamination in an anticlockwise direction towards the exit of the bay, were significantly positively correlated to THg content in sediment and suspended particles. Spatial distribution of mercury species (THg and MeHg) in different environmental compartments was in accordance with the prevailing circulation in the bay. Data obtained through 6 months of biomonitoring experiment indicated that digestive gland was more sensitive indicator of THg concentrations in the environment than the whole organism or gills. As for MeHg, all tissues were equally suitable as biomonitors of MeHg concentrations in the environment.