A geocomputational analysis of Twitter activity around different world cities

The penetration and use of social media services differs from city to city. This paper is aimed to provide a comparison of the use of Twitter between different cities of the world. We present a temporal analysis of activity on Twitter in 15 cities. Our study consists of two parts: First, we created temporal graphs of the activity in the 15 cities, through which hours of high and low activity could be identified. Second, we created heat map visualizations of the Twitter activities during the period of 19 September 2012–25 September 2013. The heat map visualizations make the periods of intense and sparse activity apparent and provide a snapshot of the activity during the whole year.     

Constraints on unconsolidated pyroclastic flow sediments related REE enrichments originated from potassic-alkaline Gölcük stratovolcano: Darıdere-Direkli-Yakaören (DDY) table 4deposits,southwestern Anatolia of Turkey

Acta Geochimica - In the last five decades, Rare Earth Elements (REE) are mostly produced from carbonatite complexes and alkaline magmatic environments. In this respect, pyroclastic flows produced...     

Spatial assessment of forest cover and land-use changes in the Hindu-Kush mountain ranges of northern Pakistan

Anthropogenic activities and natural processes are continuously altering the mountainous environment through deforestation, forest degradation and other land-use changes. It is highly important to assess, monitor and forecast forest cover and other land-use changes for the protection and conservation of mountainous environment. The present study deals with the assessment of forest cover and other land-use changes in the mountain ranges of Dir Kohistan in northern Pakistan, using high resolution multi-temporal SPOT-5 satellite images. The SPOT-5 satellite images of years 2004, 2007, 2010 and 2013 were acquired and classified into land-cover units. In addition, forest cover and land-use change detection map was developed using the classified maps of 2004 and 2013. The classified maps were verified through random field samples and Google Earth imagery (Quick birds and SPOT-5). The results showed that during the period 2004 to 2013 the area of forest land decreased by 6.4%, however, area of range land and agriculture land have increased by 22.1% and 2.9%, respectively. Similarly, barren land increased by 1.1%, whereas, area of snow cover/glacier is significantly decreased by 21.3%. The findings from the study will be useful for forestry and landscape planning and can be utilized by the local, provincial and national forest departments; and REDD+ policy makers in Pakistan.     

Geochemistry and Provenance of Maastrichtian Clastic Rocks in the Dikmendede Formation of Orhaniye in Kazan-Ankara-Turkey Region

An integrated petrographic and geochemical study of the sandstones of the Maastrichtian-aged in the Orhaniye (Kazan-Ankara-Turkey) was carried out to obtain more information on their provenance, sedimentological history and tectonic setting. Depending on their matrix and mineralogical content, the Maastrichtian sandstones are identified as lithic arenite/wacke. The Dikmendede sandstones derived from types of provenances, the recycled orogen and recycled transitional. The chemical characteristics of the Dikmendede sandstones, i.e., fairly uniform compositions, high Th/U ratios (>3.0), negative Eu anomalies (Eu/Eu* 0.72–0.99) and Th/Sc ratios (mostly less than 1.0), favor the OUC (old upper continental crust) provenance for the Dikmendede sandstones. The SiO2/Al2O3, Th/Sc (mostly <1.0) and La/Sc (<4.0) ratios are; however, slightly lower than typical OUC, and these ratios may suggest a minor contribution of young arc-derived material. The rare earth element (REE) pattern, and La/Sc versus Th/Co plot suggests that these sediments were mainly derived from felsic source rocks. The Dikmendede sandstones have high Cr (123–294 ppm) and Ni (52–212 ppm) concentrations, Cr/Ni ratio of 1.93, and a medium correlation coefficient between Cr and Ni and corresponding medium to high correlation of both (Cr and Ni, respectively) elements with Co. These relationships indicate a significant contribution of detritus from ophiolitic rocks. As rare earth element data are available for the Dikmendede sandstones, the Eu/Eu* is compared with LaN/YbN. Samples plot in the area of overlapping between continental collision, strike-slip and continental arc basins. The predominantly felsic composition of the Dikmendede sandstones is supported by the REE plots, which show enriched light REE, negative Eu anomaly and flat or uniform heavy REE. The Dikmendede sandstones have compositions similar to those of the average upper continental crust and post-Archean Australian shales. This feature indicates that the sediments were derived mainly from the upper continental crust. The Dikmendede sandstones have chemical index of alteration (CIA) values of 28–49, with an average of 40 indicating a low degree of chemical weathering in the source area. The compositional immaturity of the analyzed sandstone samples is typical of subduction-related environments, and their SiO2/Al2O3 and K2O/Na2O ratios and Co, Sc, Th and Zr contents reflect their oceanic and continental-arc settings. The Dikmendede sandstones were developed as flysch deposits derived from mixed provenance in a collision belt.     

Weakly compressible SPH simulation of cnoidal waves with strong plunging breakers

Ocean Dynamics - Hydrodynamics of highly nonlinear cnoidal waves and their subsequent strong plunging breakers are among the least understood and most significant issues in coastal engineering. In...     

Neoproterozoic nascent island arc volcanism from the Nubian Shield of Egypt: Magma genesis and generation of continental crust in intra-oceanic arcs

The Neoproterozoic Wadi Ranga metavolcanic rocks, South Eastern Desert of Egypt, constitute a slightly metamorphosed bimodal sequence of low-K submarine tholeiitic mafic and felsic volcanic rocks. The mafic volcanic rocks are represented by massive and pillow flows and agglomerates, composed of porphyritic and aphyric basalts and basaltic andesites that are mostly amygdaloidal. The felsic volcanic rocks embrace porphyritic dacites and rhyolites and tuffs, which overlie the mafic volcanic rocks. The geochemical characteristics of Wadi Ranga volcanic rocks, especially a strong Nb depletion, indicate that they were formed from subduction-related melts. The clinopyroxene phenocrysts of basalts are more akin to those crystallizing from island-arc tholeiitic magmas. The tholeiitic nature of the Wadi Ranga volcanics as well as their LREE-depleted or nearly flat REE patterns and their low K₂O contents suggest that they were developed in an immature island arc setting. The subchondritic Nb/Ta ratios (with the lowest ratio reported for any arc rocks) and low Nb/Yb ratios indicate that the mantle source of the Wadi Ranga mafic volcanic rocks was more depleted than N-MORB-source mantle. Subduction signature was dominated by aqueous fluids derived from slab dehydration, whereas the role of subducted sediments in mantle-wedge metasomatization was subordinate, implying that the subduction system was sediment-starved and far from continental clastic input. The amount of slab-derived fluids was enough to produce hydrous magmas that follow the tholeiitic but not the calc-alkaline differentiation trend. With Mg# > 64, few samples of Wadi Ranga mafic volcanic rocks are similar to primitive arc magmas, whereas the other samples have clearly experienced considerable fractional crystallization.The low abundances of trace elements, together with low K₂O contents of the felsic metavolcanic rocks indicate that they were erupted in a primitive island arc setting. The felsic volcanic rocks are characterized by lower K/Rb ratios compared to the mafic volcanic rocks, higher trace element abundances (~ 2 to ~ 9 times basalt) on primitive arc basalt-normalized pattern and nearly flat chondrite-normalized REE patterns, which display a negative Eu anomaly. These features are largely consistent with fractional crystallization model for the origin of the felsic volcanic rocks. Moreover, SiO₂-REE variations for the Wadi Ranga volcanic rocks display steadily increasing LREE over the entire mafic to felsic range and enriched La abundances in the felsic lavas relative to the most mafic lavas, features which are consistent with production of the felsic volcanic rocks through fractional crystallization of basaltic melts. The relatively large volume of Wadi Ranga silicic volcanic rocks implies that significant volume of silicic magmas can be generated in immature island arcs by fractional crystallization and indicates the significant role of intra-oceanic arcs in the production of Neoproterozoic continental crust. We emphasize that the geochemical characteristics of these rocks such as their low LILE and nearly flat REE patterns can successfully discriminate them from other Egyptian Neoproterozoic felsic volcanic rocks, which have higher LILE, Zr and Nb and fractionated REE patterns.     

New data on the Late Cenozoic basaltic volcanism in Syria,applied to its origin

New data on geology and 21 K–Ar dates of the Late Oligocene–Quaternary basalts in Syria, combined with analysis of the new and previous data are used to reconstruct the volcanic history and relations between it and tectonic events. Volcanism began at the end of Oligocene (26–24 Ma) and was concentrated in the Late Oligocene–Early Miocene along a N-trending band, which stretches from the Jebel Arab (Harrat Ash Shaam) up to Kurd Dagh and southern Turkey. Activity waned in the Middle Miocene (17–12 Ma), but was resumed in the same band in the Tortonian and increased in the Messinian and Early Pliocene (6.3–4 Ma), when volcanism spread to the Shin Plateau and its coastal extension. After a brief hiatus ～ 4–3.5 Ma, volcanism became still more intensive and spread from the N-trending band to the east into the northern margin of the Mesopotamian Foredeep and to the west into the Dead Sea Transform zone. Additional eruptions continued into the Holocene.Volcanism lasted > 25 million years in the Jebel Arab Highland and > 15 million years in the Aleppo Plateau. The long duration of volcanism in the same parts of the moving Arabian plate and absence of records of one-way migration of the activity mean that the magmatic sources moved together with the plate, i.e., they were situated within the lithosphere mantle. Coincidence of the tectonic and volcanic stages of the Arabian plate development proves that volcanic activity depended on the geodynamic situation, caused by the plate motion. Situated within the lithosphere, magmatic sources within this transverse band were possibly caused by thermal and deforming influences of the asthenospheric lateral flow, moved laterally from the Ethiopia–Afar deep superplume.     

An enhanced constitutive model for crushable granular materials

Studies in the past have tried to reproduce the mechanical behaviour of granular materials by proposing constitutive relations based on a common assumption that model parameters and parameters describing the properties, including gradation of individual grains are inevitably linked. However successful these models have proved to be, they cannot account for the changes in granular assembly behaviour if the grains start to break during mechanical loading. This paper proposes to analyse the relation between grading change and the mechanical behaviour of granular assembly. A way to model the influence of grain breakage is to use a critical state‐based model. The influence of the amount of grain breakage during loading, depending on the individual grain strength and size distribution, can be introduced into constitutive relations by means of a new parameter that controls the evolution of critical state with changes in grain size distribution. Experimental data from a calcareous sand, a quartz sand, and a rockfill material were compared with numerical results and good‐quality simulations were obtained. The main consequences of grain breakage are increased compressibility and a gradual dilatancy disappearance in the granular material. The critical state concept is also enriched by considering its overall relation to the evolution of the granular material. Copyright © 2009 John Wiley & Sons, Ltd.     

Pore scale study of permeability and tortuosity for flow through particulate media using Lattice Boltzmann method

In this paper, Lattice Boltzmann method (LBM) has been used to study the effects of permeability and tortuosity on flow through saturated particulate media and identify the relationships between permeability and tortuosity with other parameters such as particles diameter, grain specific surface, and porosity. LBM is a simple kinematic model that can incorporate the essential physics of microscopic and mesoscopic processes involved in flow through granular soils. The obtained results indicate that the 2D LB model, due to its inherent theoretical advantages, is capable of demonstrating that the porosity and specific surface are the most influential parameters in determining the intrinsic permeability of granular media. The obtained results show that particles' size diameter has a two‐fold effect on the coefficient of permeability: one is through specific surface and the other is by tortuosity factor. Numerical study also reveals that tortuosity of granular soils decreases almost linearly with increasing the porosity. Copyright © 2010 John Wiley & Sons, Ltd.