Discovery of a broad iron line in the black hole candidate Swift J1753.5−0127, and the disc emission in the low/hard state revisited

We analysed simultaneous archival XMM–Newton and Rossi X-ray Timing Explorer observations of the X-ray binary and black hole candidate Swift J  1753.5−0127  . In a previous analysis of the same data, a soft thermal component was found in the X-ray spectrum, and the presence of an accretion disc extending close to the innermost stable circular orbit was proposed. This is in contrast with the standard picture in which the accretion disc is truncated at large radii in the low/hard state. We tested a number of spectral models and found that several of them fit the observed spectra without the need of a soft disc-like component. This result implies that the classical paradigm of a truncated accretion disc in the low/hard state cannot be ruled out by these data. We further discovered a broad iron emission line between 6 and 7 keV in these data. From fits to the line profile we found an inner disc radius that ranges between ∼6 and 16 gravitational radii, which can be in fact much larger, up to ∼250 gravitational radii, depending on the model used to fit the continuum and the line. We discuss the implications of these results in the context of a fully or partially truncated accretion disc.     

Infinitesimal Orbits Around the Libration Points in the Elliptic Restricted Three Body Problem

The objective of the present work is to develope explicit analytical expressions for the small amplitude orbits of the infinitesimal mass about the equilibrium points in the elliptic restricted three body problem. To handle this dynamical problem, the Hamiltonian for the elliptic problem is formed with the true anomaly and then with the eccentric anomaly as independent variables. The origin is then transformed to a fixed point and the Hamiltonian is developed up to O(4) in the eccentricity, e, (which plays the role of the small parameter of the problem) of the primaries. The integration of the model problem under consideration is undertaken by means of a perturbation technique based on Lie series developments, which leads to the solution of the canonical equations of motion.     

Using Na/K Ratios to Identify the Potential Impacts of Sewage Effluent on Groundwater Quality in Sohag,Egypt

Improper disposal of wastewater is an important source of groundwater contamination, as it poses serious threats to the environment and human health. In this case study, 18 groundwater and 3 sewage effluent samples were collected from the area adjacent to a wastewater treatment plant in Sohag, Egypt. These samples were subjected to detailed chemical and bacteriological analyses to quantify the potential impact of sewage effluent on the groundwater quality using geochemical indicators. The groundwater aquifer in the study area is represented by the highly permeable Qena Sands that are composed of sands and gravels. The bacteriological analyses indicated the presence of fecal coliform in groundwater at wells nearby the wastewater ponds and farm lands. NH₄ concentration of the contaminated groundwater samples ranged from 0.36 to 5.70 mg/L (78% of the samples > 1.20 mg/L) and the NH₄ in the non‐impacted samples ranged from 0.40 to 2.23 mg/L (22% > 1.20 mg/L). Variations in NH₄ concentrations are due to the transformation processes occurring in the aquifer. The groundwater samples were categorized based on the Na/K ratio into two classes. The first class shows the Na/K ratios vary from 2.52 to 12.19 for sewage effluent and contaminated samples, while in the second class they range from 12.85 to 31.60 for non‐impacted samples. As a result, the Na/K ratio in combination with other chemical and microbiological indicators is a useful screening tool for assessing possible sewage influence on shallow groundwater from shallow wells.     

Rise and Fall of an Egyptian Oasis: Artesian Flow,Irrigation Soils,and Historical Agricultural Development in El‐Deir,Kharga Depression,Western Desert of Egypt

The present study examines the geoarchaeological history of an oasis in Kharga Depression in central Egypt. El‐Deir is renowned for its Ptolemaic temple and Roman fortress on the road from former Hibis (Kharga) to the Nile Valley. During the survey, spring mounds and irrigation soils belonging to an ancient agricultural zone were discovered, and further documented by ceramics found on the site. Our methodology combines the geomorphological interpretation of landforms (especially yardangs) with ceramics and ¹⁴C‐dated charcoal to distinguish and date former agricultural areas in El‐Deir. The results show that the oasis experienced several phases of soil accretion and destruction through time. Playa sediments were deposited in the humid early Holocene and severely eroded by deflation before the onset of irrigated agriculture between Pharaonic and Persian times. Very fast vertical soil accretion occurred in the Ptolemaic period, but irrigation soils were later destroyed during the Roman period by a combination of wind deflation and flash floods (second to fourth century A.D.), suggesting a period of climate instability. The case of El‐Deir invites reevaluation of constructive agencies for the development of irrigated land and destructive agencies as limiting factors for the sustainability of agricultural practices in late antiquity.     

Robust reconstruction of aliased data using autoregressive spectral estimates

Autoregressive modeling is used to estimate the spectrum of aliased data. A region of spectral support is determined by identifying the location of peaks in the estimated spatial spectrum of the data. This information is used to pose a Fourier reconstruction problem that inverts for a few dominant wavenumbers that are required to model the data. Synthetic and real data examples are used to illustrate the method. In particular, we show that the proposed method can accurately reconstruct aliased data and data with gaps.     

A stochastic model of soil erosion

The erosion model computes the rill and inter-rill flow over a surface with random roughness, and the erosion caused by this flow. The measured roughness of a surface is analysed and used to generate random surfaces for the simulation process. Computations are carried out over a number of time intervals; the steady state condition is assumed for each interval. Changes in the surface geometry due to erosion during an interval are used to revise the surface for the subsequent interval. The model includes simplified mechanisms to simulate ponding, deposition and failure of side slopes of rills.     

Monitoring and analysing the Emirate of Dubai’s land use/land cover changes: an integrated,low-cost remote sensing approach

This study presents a modified low-cost approach, which integrates the spectral angle mapper and image difference algorithms in order to enhance classification maps for the purpose of monitoring and analysing land use/land cover change between 2000 and 2015 for the Emirate of Dubai. The approach was modified by collecting 320 training samples from QuickBird images with a spatial resolution of 0.6 m, as well as carrying out field observations, followed by the application of a 3?×?3 Soble filter, sieving classes, majority/minority analysis, and clump classes of the obtained classification maps. The accuracy assessment showed that the targeted 2000, 2005, 2010 and 2015 classification maps have 88.1252%, 89.0699%, 90.1225% and 96.0965% accuracy, respectively. The results showed that the built-up area increased by 233.721?km² (5.81%) between 2000 and 2005 and continues to increase even up and till the present time. The assessment of changes in the periods 2000–2005 and 2010–2015 confirmed that net vegetation area losses were more pronounced from 2000 to 2005 than from 2010 to 2015, dropping from 47,618 to 40,820?km², respectively. This study is aimed to assist urban planners and decision-makers, as well as research institutes.     

Numerical modelling-based comparison of longitudinal dispersion coefficient formulas for solute transport in rivers

River water quality models usually apply the Fischer equation to determine the longitudinal dispersion coefficient (D_x) in solving the advection–dispersion equation (ADE). Recently, more accurate formulas have been introduced to determine D_x in rivers, which could strongly affect the accuracy of the ADE results. A numerical modelling-based approach is presented to evaluate the performance of various D_x formulas using the ADE. This approach consists of a finite difference approximation of the ADE, a MATLAB code and a MS Excel interface; it was tested against the analytical ADE solution and demonstrated using eight well-known D_x formulas and tracer study data for the Chattahoochee River (USA), the Severn (UK) and the Athabasca (Canada). The results show that D_x has an important effect on tracer concentrations simulated with the ADE. Comparison between the simulated and measured concentrations confirms the appropriate performance of Zeng and Huai’s formula for D_x estimation. Use of the newly proposed equations for D_x estimation could enhance the accuracy of solving the ADE.     

Chemometric Differentiation of Oil Families and Their Potential Source Rocks in the Gulf of Suez

Natural Resources Research - An oil–oil and oil–source rock correlation study was carried out using chemometric methods applied to geochemical data for 123 Upper Cretaceous—Lower...