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A theoretical method to determine the initial fracture toughness K I ini of concrete for central-notched split-tension specimens was developed based on the extreme theory. In this method, the K I ini , critical crack tip opening displacement CTOD c , and half critical effective crack extension Δ ɑ c could be obtained by the experimental peak load of a single specimen. The measurement of critical crack mouth opening displacement CMOD c was unnecessary in this method. The fracture parameters were calculated using the cube and cylinder split-tension specimens. Results showed that the values of K I ini obtained by the proposed method were slightly smaller than those obtained by the double- K method, and the difference between them generally decreases with the loading rates. And the values of CTOD c and Δ ɑ c obtained by the proposed method were more stable compared with those obtained by the double- K method. [ABSTRACT FROM AUTHOR]

• Size effect on the unstable fracture toughness of quartz-diorite rock is investigated based on the analytical method. • Unstable fracture toughness of rock specimen increases with the increase of specimen depth. • Unstable fracture toughness will converge to the size-independent fracture toughness of Bažant's size effect model. • Unstable fracture toughness changes with the alteration of initial normalized crack length. • Specimen depth and boundary affect the rock unstable fracture toughness. In this paper, an analytical method was introduced to investigate the size effect on the unstable fracture toughness of fine-grained quartz-diorite. The analytical method can predict the axial load, crack mouth opening displacement, and crack resistance curve of the three-point bend specimen when the elastic modulus, tensile strength, fracture energy, and initial fracture toughness are given. Mode I fracture tests were conducted on the three-point bend specimen with five different depths to acquire these parameters. And, the effectiveness of the analytical method was validated by the experimental results. The analytical method is then utilized to compute the unstable fracture toughness of three-point bend specimens with different sizes and normalized initial crack lengths. The results reveal that unstable fracture toughness is a size-dependent parameter that first increases and then remains unchanged with the increase of the specimen size. The nominal stress follows Bažant's size effect law and the unstable fracture toughness will converge to the size-independent mode I fracture toughness obtained by Bažant's size effect model with the increase of specimen depth. Furthermore, for the specimen with a small depth, unstable fracture toughness decreases with the increase in normalized initial crack length, which further illustrates the boundary effect on the unstable fracture toughness of rock specimens. [ABSTRACT FROM AUTHOR]

Abstract: The concentrations of air pollutants depend on meteorological conditions and pollutant emission level. From the statistical properties of air pollutants the number of times the daily average concentrations exceed the assigned air quality standard (AQS) can be estimated, as well as the level of reduction of particle matter emission sources required to meet the AQS. In this paper three statistical distributions (lognormal, Weibull and type V Pearson distribution) were used to fit the complete set of PM10 data for the Belgrade urban area during a three-year period (2003–2005). The method of moments and the method of least squares were both used to estimate the parameters of the three theoretical distributions. The type V Pearson distribution represented the PM10 daily average concentration most closely. However, the parent distributions sometimes diverged in predicting a high PM10 concentration and therefore asymptotic distributions of extreme values were used to fit the high PM10 concentration distribution more correctly. This method can successfully predict the return period and exceedances over a critical concentration in succeeding years. The estimated emission source reduction of PM10 to meet the assigned standard varied from 53% to 63% in the Belgrade urban area. The results provide useful information for air quality management and could be used to examine the similarities and differences among air pollution types in diverse areas. [Copyright &y& Elsevier]

Abstract: We prove almost sure limit theorems for the maximum of a stationary normal sequence under some conditions. [Copyright &y& Elsevier]