Hydrochemical characterization of groundwater using multivariate statistical analysis: the Maritime Djeffara shallow aquifer (Southeastern Tunisia)

Worldwide, groundwater resources have been considered as the main sources of drinking, domestic uses, industrial and agriculture water demands, especially in arid and semiarid regions. Accordingly, the monitoring of the groundwater quality based on different tools and methods becomes a necessity. The aim of this study was to apply several approaches to assess the water quality and to define the main hydrochemical process which affect groundwater of the Maritime Djeffara shallow aquifer. In addition to the hydrochemical approach, two multivariate statistical analyses, hierarchical clusters analysis (HCA) and principal component analysis (PCA), were carried out to identify the natural and the anthropogenic processes affecting groundwater chemistry. Hydrochemical approach, based on 47 analyzed groundwater samples, shows that most of samples present a sulfate to mixed chloride, with sodi-potassic tendency facies. According to their chemically composition, the HCA revealed three different groups (C1, C2 and C3) according to their electrical conductivity (EC) values: C1 (average EC = 4500 µS/cm), C2 (average EC = 7040 µS/cm) and C3 (average EC = 9767 µS/cm). Furthermore, PCA results show two principal factors account 84.05% of the total variance: (1) F1 represents the natural component, and (2) F2 symbolizes the anthropic component. Moreover, the groundwater quality map of the Maritime Djeffara shows three categories: suitable, doubtful and unsuitable water for irrigation. These different results should be taken to protect water resources in arid and semiarid regions, especially at the alluvial coastal regions. Also, they help to make a suitable planning to manage and protect the groundwater resources.     

Investigation of heat pipe heat exchanger effectiveness and energy saving in air conditioning systems using silver nanofluid

The present study attempts to use the methanol?Csilver nanofluid filled heat pipe heat exchanger and compares the effectiveness as well as the energy saving with pure methanol. A heat pipe heat exchanger has been tested in a test rig under steady-state conditions. The lengths of both the evaporator and the condenser sections of the heat exchanger were 700?mm, and its central adiabatic section had a length of 160?mm. The heat exchanger had 36 plate finned copper thermosyphons arranged in three rows. The inlet air temperature across the evaporator section was varied in the range of 33?C43?°C while the inlet air temperature to the condenser section was nearly constant to be 13?°C. First, pure methanol was used as the working fluid with a fill ratio of 50?% of the evaporator section length, and then dilute dispersion of silver nanoparticles in methanol was employed as the working fluid. The nanofluid used in the present study is 20?nm diameter silver nanoparticles. The experiments were performed to compare the heat pipe heat exchanger effectiveness and energy saving, using nanofluid and pure methanol. The inlet air relative humidity across the evaporator section was varied between 35 and 80?%. The sensible effectiveness of the heat pipe heat exchanger obtained from experiments varied about 5?C22?% for pure methanol and 9?C32?% for methanol?Csilver nanofluid. Based on these experimental results, using methanol?Csilver nanofluid leads to energy saving around 8.8?C31.5?% for cooling and 18?C100?% for reheating the supply air stream in an air conditioning system.     

Land transformation assessment using the integration of remote sensing and GIS techniques: a case study of Al-Anbar Province,Iraq

Human activities and climate changes significantly affect our environment, altering hydrologic cycles. Several environmental, social, political, and economical factors contribute to land transformation as well as environmental changes. This study first identified the most critical factors that affect the environment in Al-Anbar city including population growth, urbanization expansion, bare land expansion, and reduction in vegetation cover. The combination of remote sensing data and fuzzy analytic hierarch process (Fuzzy AHP) enabled exploration of land transformations and environmental changes in the study area during 2001 to 2013 in terms of long and short-term changes. Results of land transformation showed that the major changes in water bodies increased radically (94 %) from the long-term change in 2001 to 2013 because of water policies. In addition, the urban class expanded in two short-term periods (2001–2007 and 2007–2013), representing net changes of 46 and 60 %, respectively. Finally, barren land showed 25 % reduction in the first period because of the huge expansion of water in the lake; a small percentage of growth gain was observed in the second period. Based on the land transformation results, the environmental degradation assessment showed that the study area generally had high level of environmental degradation. The degradation was mostly in the center and the north part of the study area. This study suggested for further studies to include other factors that also responsible for environmental degradation such as water quality and desertification threatening.     

Velocity and abundance precisions for future high‐resolution spectroscopic surveys: A study for 4MOST

In preparation for future, large‐scale, multi‐object, high‐resolution spectroscopic surveys of the Galaxy, we present a series of tests of the precision in radial velocity and chemical abundances that any such project can achieve at a 4 m class telescope. We briefly discuss a number of science cases that aim at studying the chemo‐dynamical history of the major Galactic components (bulge, thin and thick disks, and halo) – either as a follow‐up to the Gaia mission or on their own merits. Based on a large grid of synthetic spectra that cover the full range in stellar parameters of typical survey targets, we devise an optimal wavelength range and argue for a moderately high‐resolution spectrograph. As a result, the kinematic precision is not limited by any of these factors, but will practically only suffer from systematic effects, easily reaching uncertainties <1km s^–1. Under realistic survey conditions (namely, considering stars brighter than r = 16 mag with reasonable exposure times) we prefer an ideal resolving power of R ∼20 000 on average, for an overall wavelength range (with a common two‐arm spectrograph design) of [395;456.5] nm and [587;673] nm. We show for the first time on a general basis that it is possible to measure chemical abundance ratios to better than 0.1 dex for many species (Fe, Mg, Si, Ca, Ti, Na, Al, V, Cr, Mn, Co, Ni, Y, Ba, Nd, Eu) and to an accuracy of about 0.2 dex for other species such as Zr, La, and Sr. While our feasibility study was explicitly carried out for the 4MOST facility, the results can be readily applied to and used for any other conceptual design study for high‐resolution spectrographs. (© 2013 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)