Integrating cellular automata and Markov techniques to generate urban development potential surface: a study on Kolkata agglomeration

Uncontrolled, yet fragmented peripheral urban expansion has emerged as a menace to urban development. To cope with this rapid urban expansion process, identification of the forces responsible for this rapid urban expansion is a pre-requisite, especially when its threats to habitability are taken into consideration. This study tries to evaluate fragmented uncontrolled urban expansion faced by Kolkata using cellular automata-Markov chain. Urban growth patterns, land use/land cover transformations and spatial allocation correspondence with planning strategy is the main theme of this study. Depending upon the driving forces, the study result indicates a bi-directional urban development potential surface, which might be a result of the biased planning initiative along with middle-class residential demand. This simulation result provides evidence for the planning authority to evaluate the effectiveness of spatial allocation and urban expansion trends and provide flexibility to modify the current allocation scenario.     

Arsenic-enriched aquifers: Occurrences and mobilization of arsenic in groundwater of Ganges Delta Plain, Barasat, West Bengal, India

Hydrogeochemical characteristics and elemental features of groundwater and core sediments have been studied to better understand the sources and mobilization process responsible for As-enrichment in part of the Gangetic plain (Barasat, West Bengal, India). Analysis of water samples from shallow tubewells (depth 24.3–48.5 m) and piezometer wells (depth 12.2–79.2 m) demonstrate that the groundwater is mostly the Ca-HCO₃ type and anoxic in nature (mean Eh_SHE = 34 mV). Arsenic concentrations ranged from <10–538 μg/L, with high concentrations only present in the shallow to medium depth (30–50 m) of the aquifer along with high Fe (0.07–9.8 mg/L) and relatively low Mn (0.15–3.38 mg/L) as also evidenced in core sediments. Most groundwater samples contained both As(III) and As(V) species in which the concentration of As(III) was generally higher than that of As(V), exhibiting the reducing condition. Results show lower concentrations of NO₃, SO₄ and NO₂ along with higher values of DOC and HCO₃, indicating the reducing nature of the aquifer with abundant organic matter that can promote the release of As from sediments into groundwater. Positive correlations of As with Fe and DOC were also observed. The presence of DOC may actively drive the redox processes. This study revealed that reduction processes of FeOOH was the dominant mechanism for the release of As into the groundwater in this part of the Ganges Delta plain.     

Electrical resistivity investigation of the arsenic affected alluvial aquifers in West Bengal,India: usefulness in identifying the areas of low and high groundwater arsenic

This study aims at finding out possible relation between lithology and spatial pattern of dissolved arsenic (As) in groundwater around Chakdaha municipality, West Bengal, India. Satellite image, coupled with electrical resistivity survey and borehole drilling helps to delineate surface and sub-surface lithological framework of the As affected alluvial aquifers. The satellite imagery demonstrate that the high As area are presumably under active flood plain environment (low-lying areas), that constantly receive organics due to periodic flooding. Thick low resistive (fine-grained) layer was observed at the top around the high As areas, which, however, not found in low As areas. The result suggests that hydraulic properties of the surface/sub-surface soil/sediment have an important control on the fate and transport of As in the aquifer. This study demonstrates that electrical resistivity tools can be effectively used for the reconnaissance survey in characterizing the plausible lithological framework of an alluvial aquifer containing As.     

Contribution of galaxies to the background hydrogen-ionizing flux

We estimate the evolution of the contribution of galaxies to the cosmic background flux at 912 Å by means of a semi-analytic model of galaxy formation and evolution. Such modelling has been quite successful in reproducing the optical properties of galaxies. We assume that high-redshift damped Lyman α systems are the progenitors of present-day galaxies, and we design a series of models that are consistent with the evolution of cosmic comoving emissivities in the available near-infrared, optical, ultraviolet and far-infrared bands along with the evolution of the neutral hydrogen content and average metallicity of damped Lyman α systems. We use these models to compute the galactic contribution to the Lyman-limit emissivity and background flux for 0 ≃  z  ≤ 4. We take into account the absorption of Lyman-limit photons by H  I and dust in the interstellar medium of the galaxies. We find that the background Lyman-limit flux due to galaxies might dominate (or be comparable to) the contribution from quasars at almost all redshifts if the absorption by H  I in the interstellar medium is neglected. Such H  I absorption would result in a severe diminishing of this flux — by almost three orders of magnitude at high redshifts and by one to two orders at z  ≃ 0. Though the resulting galaxy flux is completely negligible at high redshifts, it is comparable to the quasar flux at z  ≃ 0.     

Detection of seismic reflections from seismic attributes through fractal analysis

The concept of fractals is used here for the identification of seismic reflectors with special emphasis on thin‐bed delineation, which is generally overlooked during standard data processing. A new fractal analysis scheme is applied to both synthetic and real field seismic data. The fractal dimensions of the three seismic attributes – amplitude, phase, and instantaneous frequency – have been analysed and evaluated. A change in fractal dimension is found to occur whenever there is a reflection. However, the resolution in the delineation of reflectors varies, depending on the attribute under consideration and the method of fractal dimension estimation used. Fractal analysis is performed on both noise‐free and noisy synthetic data to establish the noise tolerance limit for both the ‘divider method’ and the ‘Hurst method’. It is then tested with different peak frequencies of the source wavelet to establish the criteria for using the divider method and the Hurst method. The divider method is found to be suitable for high peak frequency source wavelets (> 25 Hz), while the Hurst method is best suited for low peak frequency source wavelets (< 25 Hz). Finally, when applied to the digitally processed and migrated field seismic data, it could even delineate reflectors which otherwise went undetected on the migrated time section.     

A study of self-similar cylindrical MHD shock waves in monochromatic radiation

It is never too strange to expect that an eventual fifth repulsive interaction may also be mediated by a spin-2 field. On the other hand, it is highly unlikely that a spin-1 field may mediate an attractive force.     

First Order Seismic Microzonation of Delhi,India Using Geographic Information System (GIS)

A first order seismic microzonation map of Delhi is prepared using five thematic layers viz., Peak Ground Acceleration (PGA) contour, different soil types at 6 m depth, geology, groundwater fluctuation and bedrock depth, integrated on GIS platform. The integration is performed following a pair-wise comparison of Analytical Hierarchy Process (AHP), wherein each thematic map is assigned weight in the 5-1 scale: depending on its contribution towards the seismic hazard. Following the AHP, the weightage assigned to each theme are: PGA (0.333), soil (0.266), geology (0.20), groundwater (0.133) and bedrock depth (0.066). The thematic vector layers are overlaid and integrated using GIS. On the microzonation theme, the Delhi region has been classified into four broad zones of vulnerability to the seismic hazard. They are very high (> 52%), high (38–52%), moderate (23–38%) and less ( < 23%) zones of seismic hazard. The “very high” seismic hazard zone is observed where the maximum PGA varies from 140 to 210 gal for a finite source model of M_w 8.5 in the central seismic gap. A site amplification study from local and regional earthquakes for Delhi region using Delhi Telemetry Network data shows a steeper site response gradient in the eastern side of the Yamuna fluvial deposits at 1.5 Hz. The ‘high’ seismic hazard zone occupies most of the study area where the PGA value ranges from 90 to 140 gal. The ‘moderate’ seismic hazard zone occurs on either side of the Delhi ridge with PGA value varying from 60 to 90 gal. The ‘less’ seismic hazard zone occurs in small patches distributed along the study area with the PGA value less than 60 gal. Site response studies, PGA distribution and destruction pattern of the Chamoli earthquake greatly corroborate the seismic hazard zones estimated through microzonation on GIS platform and also establishes the methodology incorporated in this study.     

Sunyaev–Zel'dovich distortion from early galactic winds

We consider the distortion in the cosmic microwave background (CMB) resulting from galactic winds at high redshift. Winds outflowing from galaxies have been hypothesized to be possible sources of metals in the intergalactic medium, which is known to have been enriched to 10^−2.5 Z_⊙ at z ∼3. We model these winds as functions of mass of the parent galaxy and redshift, assuming that they activate at a common initial redshift, z _in, and calculate the mean y -distortion and the angular power spectrum of the distortion in the CMB. We find that the thermal Sunyaev–Zel'dovich (SZ) effect resulting from the winds is consistent with previous estimates. The distortion arising from the kinetic SZ (kSZ) effect is, however, found to be more important than the thermal SZ (tSZ) effect. We find that the distortion resulting from galactic winds is an important contribution to the power spectrum of distortion at very small angular scales ( l ∼10⁴). We also find that the power spectrum resulting from clustering dominates the Poisson power spectrum for l ≤(4–5)×10⁵. We show explicitly how the combined power spectrum from wind dominates over that of clusters at 217 GHz, relevant for PLANCK . We also show how these constraints change when the efficiency of the winds is varied.