A numerical study of the unsteady MHD free convection with hall current

Effect of Hall current on the hydromagnetic free-convection flow of an electrically-conducting viscous incompressible fluid past an impulsively accelerated vertical porous plate in the presence of a uniform transverse magnetic field subjected to a constant transpiration velocity is analyzed for the case of small magnetic Reynolds number. Numberical solutions are obtained for the axial and transverse components of the velocity as well as the skin-friction by employing the Crank-Nicolson implicit finite-difference method for all probable values of the Prandtl number. The results are discussed with the effects of the Grashof number Gr, the transpiration velocity parameter , the Hall current parameterm, and the magnetic field parameterM for the Prandtl number Pr=0.71 which represents air at 20° C.     

Drought adaptation measures and their effectiveness at Barind Tract in northwest Bangladesh: a perception study

Natural Hazards - Drought is a natural calamity frequently occurs at Barind Tract in northwest Bangladesh and affects both the human and natural life. An initiative has been taken...     

Geochemistry of subsurface Late Quaternary ironstones in Rajshahi and Bogra Districts,Bangladesh: implications for genetic and depositional conditions

The present study deals with the geochemistry of Late Quaternary ironstones in the subsurface in Rajshahi and Bogra districts, Bangladesh with the lithological study of the boreholes sediments. Major lithofacies of the studied boreholes are clay, silty clay, sandy clay, fine to coarse grained sand, gravels and sands with (fragmentary) ironstones. The ironstones contain major oxides, Fe₂O₃* (* total Fe) (avg. 66.6 wt%), SiO₂ (avg. 15.3 wt%), Al₂O₃ (avg. 4.0 wt%), MnO (avg. 7.7 wt%), and CaO (avg. 3.4 wt%). These geochemical data imply that the higher percentage of Fe₂O₃* along with Al₂O₃ and MnO indicate the ironstone as goethite and siderite, which is also validated by XRD data. A comparatively higher percentage of SiO₂ indicates the presence of relative amounts of clastic quartz and manganese-rich silicate or clay in these rocks. These ironstones also have significant amounts of MnO (avg. 7.7 wt%) suggesting their depositional environments under oxygenated condition. Chemical data of these ironstones suggest that the source rock suffered deep chemical weathering and iron was mostly carried in association with the clay fraction and organic matter. Iron concretion was mostly formed by bacterial build up in swamps and marshes, and was subsequently embedded in clayey mud. Within the coastal environments, the water table fluctuates and goethite and siderite with mud and quartz became dry and compacted to form ironstone.

     

R?le du brassage et du stockage magmatique dans l’homogénéisation des granito?des calco-alcalins: Cas du pluton composite de Za?r (Maroc central)

Resume.  Le pluton calco-alcalin de Za?r est composé de trois principaux faciès pétrographiques répartis en deux unités granitiques imbriquées. Ces faciès, de différents degrés d’hybridation et de différenciation, résultent de mélanges magmatiques entre des magmas basiques mantelliques de type ?HAB? (basalte hyperalumineux) et un magma anatectique issu de la fusion partielle de matériaux crustaux (métapélites ou métagrauwackes). La répartition des faciès granitiques de Za?r peut s’expliquer selon un modèle pétrogénétique de type ?MASH? (melting-assimilation-storage-homogenization) où des magmas hybrides seraient formés suivant différentes proportions de mélanges magmatiques acide-basique. Ces magmas auraient subides conditions d’ascension spécifiques et seraient mis en place sous forme de 3 grandes injections successives:

Landslide susceptibility mapping using AHP and fuzzy methods in the Gilan province,Iran

GeoJournal - Landslides are natural destructive phenomena that can cause great damage to property and life loss. One of the fundamental proceedings to reduce the possible damage is identifying...     

Investigating the removal of ethylbenzene from aqueous solutions using modified graphene oxide: application of response surface methodology

This research focused on the application of response surface methodology (RSM) for the removal of ethylbenzene by the graphene oxide grafted with polymethyl vinyl ketone and aniline (GO-MVK-ANI) from wastewater. The adsorbent was prepared through polymerization of graphene oxide with methyl vinyl ketone using ammonium persulfate initiator and further modification by aniline. The synthesized material was characterized via Fourier transform infrared resonance spectroscopy, scanning electron microscopy, energy-dispersive X-ray spectroscopy and Brunauer–Emmett–Teller analysis. RSM was used to minimize the number of experiments and investigate the effect of three selected parameters (contact time, initial pH and adsorbent dose) on the removal efficiency of ethylbenzene. Additionally, the affecting parameters were optimized based on the selected target (ethylbenzene removal efficiency). The results show that 73% ethylbenzene could be adsorbed with initial ethylbenzene concentration of 20 mg/l under the optimum conditions (the contact time of 11 min, pH of 5.64 and adsorbent dose of 3.75 g/l). In this paper, high R ²-value (97.18%) for ethylbenzene removal and a good agreement with adjusted R ²-value (94.65%) indicated that the model was successful and the results demonstrated a reasonable proportion of the experimental and the predicted results.     

FEG-EPMA mapping and Fe-Ti oxide mineral chemistry of Brahmaputra River sediments in Bangladesh: provenance and petrogenetic implications

The present research deals with the FEG-EPMA mapping and Fe-Ti oxide mineral chemistry of Brahmaputra River sediments in Bangladesh. Major heavy minerals in the sediments consist of garnet (8.5–21.3%), kyanite (5.35–11.9%), monazite (2.3–5.3%), sillimanite (1.8–4.7%), zircon (3.6–9.1%), and a considerable amount of opaques mainly Fe-Ti oxide minerals (23.1–35.4%). The detrital Fe-Ti oxide minerals carry significant clues to the parent rocks or sources. In these contexts, detrital opaques (Fe-Ti oxides) have been analyzed with an electron probe microanalyzer (EPMA). These opaques (Fe-Ti oxide) display six types of textural patterns, dominantly seriate with granular, emulsion, and acicular sandwich structures and trellis type of textural patterns. These textural patterns belong to five intergrowths of Fe-Ti oxide minerals such as (1) ilmenite-hematite, (2) magnetite-ilmenite, (3) hematite-rutile, (4) ilmenite-hematite-rutile, and (5) ilmenite-rutile, where ilmenite-hematite intergrowth is common. Alteration is seen in both exsolved and unexsolved ilmenites. Textural patterns and mineral chemistry of the studied ilmenite minerals provide lines of evidence of low-temperature magmatic inheritance, later modified by diffusional processes. The estimated temperature and oxygen fugacity from the magnetite-ilmenite exsolution range from 547.6 to 558.2 °C and from 10^?21.4 to 10^?21.7, respectively. The data are also consistent with hematite-ilmenite temperature (between 537 and 540 °C) and oxygen fugacity (10^?21.7 to 10^?21.9) measurements in Cox’s Bazar beach placers. These temperatures and oxygen fugacities specify Fe-Ti oxide assemblages equilibrated in a T-fO₂ field very near to the FMQ buffer curve suggesting a crustal source (magmatic and/or metamorphic), which is modified significantly by metamorphic processes.     

Biodiversity and biomass of a natural and degraded mangrove forest of Peninsular Malaysia

Anthropogenic activities have always been the cause of most environmental degradation, and mangrove disappearance is no exception. A comparative assessment on the biodiversity of natural and degraded mangrove forests has been undertaken, looking at the biomass, both above-ground and below-ground. The natural and the degraded mangrove forests were situated at Kuala Selangor and Sungai Haji Dorani, respectively, both on the West coast of Peninsular Malaysia. A random sample scheme with quadrate sample plots (10 m × 10 m) was adopted for the measurement of the diameter at breast height and total height of individual tree species at both forests. Diversity indices and above- and below-ground biomass were estimated from this inventory. Eight mangrove tree species were identified at both study areas, namely: Bruguiera parviflora, Avicennia officinalis, Rhizophora mucronata, Sonneratia alba, Avicennia marina, Bruguiera cylindrica, Xylocarpus mekongensis and Excoecaria agallocha. The mangrove species in Sungai Haji Dorani showed high diversity with a Shannon–Weiner Index (H′) value of 0.91, compared to the natural mangrove of Kuala Selangor which has a lower value, H′ = 0.55. The dominant species in the natural mangrove area was B. parviflora, with the highest Important Value Index (IVI) of 70.96 %, as opposed to A. marina which was the most common species in the degraded mangrove area, with IVI of 49.16 %. An estimate of 305.46 t/ha of above-ground biomass was calculated for the natural mangrove, while 122.78 t/ha was obtained for the degraded mangrove forest. This contrasts with the below-ground biomass estimates, which were 14.09 t/ha for the natural mangrove and 36.35 t/ha for the degraded mangrove.     

Effects of two temperature electrons on Gardner solitons and double layers in a nonthermal dusty electronegative plasma

Gardner solitons (GSs) and double layers (DLs) of dust ion acoustic (DIA) waves in an electronegative plasma (composed of inertial positive and negative ions, Maxwellian cold electrons, non-thermal hot electrons, and negatively charged static dust) are studied. The reductive perturbation method is employed to derive the Korteweg-de Vries (K-dV), modified K-dV, and standard Gardner equations, which admits solitary wave and DLs solutions for σ around its critical value σ _c (where σ _c is the value of σ corresponding to the vanishing of the nonlinear coefficient of the K-dV equation). The parametric regimes for the existence of the GSs and DLs, are obtained. The basic features of DIA GSs and DLs (associated with negative structure only) are analyzed. It has been found that the characteristics of DIA GSs and DLs, are different from that of the K-dV solitons and mK-dV (mixed K-dV) solitons. The implications of our results to different space and laboratory plasma situations are discussed.