Ghaleh-khargushi rhyodacite and Gorid andesite from Iran: characterization,uses, and durability

Durability of building stones is an important issue in sustainable development. Crystallization of soluble salts is recognized as one of the most destructive weathering agents of building stones. For this reason, durability of Ghaleh-khargushi rhyodacite and Gorid andesite from Iran was investigated against sodium sulfate crystallization aging test. Petrographic and physico-mechanical properties and pore size distribution of these stones were examined before and after the aging test. The characteristics of the microcracks were quantified with fluorescence-impregnated thin sections. Durability and physico-mechanical characteristics of Ghaleh-khargushi rhyodacite are mainly influenced by preferentially oriented preexisting microcracks. Stress induced by salt crystallization led to the widening of preexisting microcracks in Ghaleh-khargushi rhyodacite, as confirmed by the pore size distributions before and after the aging test. The preexisting microcracks of Gorid andesite were attributed to the mechanical stress induced by contraction of lava during cooling. The number of transcrystalline microcracks was significantly increased after the aging test. The degree of plagioclase microcracking was proportional to its size. Durability of the studied stones depends on initial physico-mechanical properties, pore size distribution, and orientation of microcracks. Initial effective porosity is found to be a good indicator of the stones’ durability. Salt crystallization resulted in an increase in the effective porosity with a parallel decrease in the wave velocities. Surface microroughness parameters increased with the development of salt crystallization-induced microcracking. Gorid andesite showed higher quality and durability than Ghaleh-khargushi rhyodacite.     

Sensitive Ion‐Flotation Separation of Ag(I) Traces Using 2‐(2‐Methoxyphenyl)benzimidazole before Flame Atomic Absorption Spectrometric Determination in Water

A sensitive, reliable, and environmentally friendly method for simple separation and preconcentration of Ag(I) traces in aqueous samples is presented prior to their flame atomic absorption spectrometric determinations. At pH 7.0, Ag(I) was separated with 2‐(2‐methoxyphenyl)benzimidazole (MPBI) as a new complexing agent and floated after adding sodium dodecyl sulfate (SDS) as a foaming reagent. The floated layer was then dissolved in proper amount of concentrated nitric acid in methanol and introduced to the flame atomic absorption spectrometer (FAAS). The effects of pH, concentration of MPBI, type and amount of surfactant as the floating agent, type and amount of eluting agent, and influence of foreign ions on the recovery of the analyte ion were investigated. Also, using a nonlinear curve fitting method, the formation constant of 1.62 × 10⁶ was obtained for Ag(I)–MPBI complex. The analytical curve was linear in the range of 1.8 × 10^?7–1.7 × 10^?6 mol/L for determination of Ag(I). The relative standard deviation (RSD; N = 10) corresponding to 0.7 × 10^?6 mol/L of Ag(I), the limit of detection (10 blanks), and the enrichment factor were obtained as 1.7%, 2.9 × 10^?8 mol/L, and 43.0, respectively. The proposed procedure was then applied successfully for determination of silver ions in different water samples.     

Spatially-Weighted Factor Analysis for Extraction of Source-Oriented Mineralization Feature in 3D Coordinates of Surface Geochemical Signal

Natural Resources Research - This contribution proposes a spatially weighted factor analysis (SWFA) to recognize effectively the underlying mineralization-related feature(s) in geochemical signals....     

Multiple linear regression,multi-layer perceptron network and adaptive neuro-fuzzy inference system for forecasting precipitation based on large-scale climate signals

ABSTRACT

Nowadays, mathematical models are widely used to predict climate processes, but little has been done to compare the models. In this study, multiple linear regression (MLR), multi-layer perceptron (MLP) network and adaptive neuro-fuzzy inference system (ANFIS) models were compared for precipitation forecasting. The large-scale climate signals were considered as inputs to the applied models. After selecting the most effective climate indices, the effects of large-scale climate signals on the seasonal standardized precipitation index (SPI) of the Maharlu-Bakhtaran catchment, Iran, simultaneously and with a delay, was analysed using a cross-correlation function. Hence, the SPI time series was forecasted up to four time intervals using MLR, MLP and ANFIS. The results showed that most of the indices were significant with SPI of different lag times. Comparison of the SPI forecast results by MLR, MLP and ANFIS models showed better performance for the MLP network than the other two models (RMSE = 0.86, MAE = 0.74 for the first step ahead of SPI forecasting).

Editor D. Koutsoyiannis; Associate editor F. Pappenberger     

Neural network prediction of solar cycle 24

The ability to predict the future behavior of solar activity has become extremely import due to its effect on the environment near the Earth.Predictions of both the amplitude and timing of the next solar cycle will assist in estimating the various consequences of space weather.The level of solar activity is usually expressed by international sunspot number (Rz).Several prediction techniques have been applied and have achieved varying degrees of success in the domain of solar activity prediction.We predict a...     

Petrology of ultramafic rocks and Mg-rich carbonate minerals in southeast of Dehshir,Central Iran

The study area is located southeast of Dehshir between the Urumieh-Dokhtar Magmatic Arc and Nain-Baft Ophiolite Belt comprising the Nain, Dehshir, Shahr Babak, and Baft ophiolite complexes. The Dehshir Ophiolitic Complex which obducted in the Late Cretaceous, consists mainly of ultramafic rocks. These remnants of oceanic crust are extensively faulted and fractured. The severe faulting and brecciating of the ophiolite sequence have undergone high-grade alteration and changed it to the tectonic mélange. The Dehshir colored mélange is bounded to the west by Dehshir fault which is a right-lateral offset of the Nain-Baft suture. In this research, the petrographic studies of the area showed that the ultramafic rocks consist mainly of dunite and harzburgite intruded by diabasic dikes. Syntectonic hydrothermal fluids circulated throughout these rocks. Migration of Mg-rich fluids and hydrothermal brecciating occurred within highly altered and brecciated zones. Magnesite precipitated from hydrothermal solutions and formed the massive, lenticular, and vein-type ore deposits in serpentinized-hosted rocks. Later on, magnesite turned into hydromagnesite due to hydration at the lower depths near the surface. According to the X-ray diffraction and X-ray fluorescence analysis, hydromagnesite is the most dominant and widely occurring Mg-rich carbonate mineral in this area. The main alteration is serpentinization but birbiritization also occurs as a result of interaction between fluids and ultramafic rocks.