Formation rates of Dark Matter Haloes

We derive an estimate of the rate of formation of dark matter halos per unit volume as a function of the halo mass and redshift of formation. Analytical estimates of the number density of dark matter halos are useful in modeling several cosmological phenomena. We use the excursion set formalism for computing the formation rate of dark matter halos. We use an approach that allows us to differentiate between major and minor mergers, as this is a pertinent issue for semi-analytic models of galaxy formation. We compute the formation rate for the Press-Schechter and the Sheth-Tormen mass function. We show that the formation rate computed in this manner is positive at all scales. We comment on the Sasaki formalism where negative halo formation rates are obtained. Our estimates compare very well with N-Body simulations for a variety of models. We also discuss the halo survival probability and the formation redshift distributions using our method.Comment: 30 pages, 9 figure

Microplastics pollution in inland aquatic ecosystems of india with a global perspective on sources, composition, and spatial distribution

Study region Indian inland aquatic ecosystems. Study focus Microplastics (MPs) have been identified as emerging contaminants, potentially impacting public and ecosystem health. This comprehensive review discusses the current state of knowledge on MP contamination and mechanistic process understanding in Indian inland aquatic ecosystems. It highlights knowledge gaps regarding current MP data and discusses methodological differences in MP sampling and sample processing that can lead to contrasting results. New hydrological insight for the region Most studies reviewed here have provided evidence of MP contamination in water, sediment and certain indicator species of inland aquatic ecosystems at specific locations and times. Significant seasonal variations in MP concentrations have been identified for pre-, during and post-monsoon periods. We found that only a few of the reviewed studies have considered the inherent spatio-temporal variability of MP concentrations, and the intricate interplay with hydrological key parameters has largely been overlooked. However, in order to improve our understanding of how MPs are transported within these aquatic ecosystems (e.g., river networks) and decide on potential pollution mitigation, it is imperative to link data on MP concentration and physico-chemical characteristics with key hydrological information such as flow velocity or discharge. This will provide information on MP loads and help to establish loading functions for these aquatic ecosystems that are needed to better understand the impacts of MP pollution on public and ecosystem health

Increase in wheat production through management of abiotic stresses : A review

About 9% of area on earth is under crops out of which 91% is under various stresses. On an average, about 50% yield losses are due to abiotic stresses mostly due to high temperature (20%), low temperature (7%), salinity (10%), drought (9%) and other abiotic stresses (4%). As there is no scope for increasing area under agriculture, the increased productivity from these stressed land is a must to meet the ever increasing demand. Further, the severity of abiotic stresses is likely to increase due to changing climate leading to adverse effect on crops. Therefore, abiotic stresses like drought, salinity, sodicity, acidity, water logging, heat, nutrient toxicities/ deficiencies etc need to be effectively addressed through adoption of management practices like tillage and planting options, residue management, sowing time, stress tolerant cultivars, irrigation scheduling and integrated nutrient management to conserve natural resources, mitigating their adverse effect and sustainable wheat production

Fractal Dimension as a measure of the scale of Homogeneity

In the multi-fractal analysis of large scale matter distribution, the scale of transition to homogeneity is defined as the scale above which the fractal dimension of underlying point distribution is equal to the ambient dimension of the space in which points are distributed. With finite sized weakly clustered distribution of tracers obtained from galaxy redshift surveys it is difficult to achieve this equality. Recently we have defined the scale of homogeneity to be the scale above which the deviation of fractal dimension from the ambient dimension becomes smaller than the statistical dispersion. In this paper we use the relation between the fractal dimensions and the correlation function to compute the dispersion for any given model in the limit of weak clustering amplitude. We compare the deviation and dispersion for the LCDM model and discuss the implication of this comparison for the expected scale of homogeneity in the concordant model of cosmology. We estimate the upper limit to the scale of homogeneity to be close to 260 Mpc/h for the LCDM model. Actual estimates of the scale of homogeneity should be smaller than this as we have considered only statistical contribution to the dispersion in fractal dimension and we have ignored cosmic variance and contributions due to survey geometry and the selection function. We find that as long as non linear correction are insignificant, scale of homogeneity as defined above does not change with epoch. The scale of homogeneity depends very weakly on the choice of tracer of the density field. Thus the suggested definition of the scale of homogeneity is fairly robust.Comment: 7 pages, two figures. Accepted for publication in the MNRA

Assessment of traditional rainwater harvesting system in barren lands of a semi-arid region: a case study of Rajasthan (India)

Study region Dudu station, Rajasthan, India Study focus Rainwater harvesting can be used as a method to recharge aquifers. This can happen with a variety of scales and technologies. One such example is shallow infiltration ponds (Chaukas) which recharge groundwater and increase soil moisture facilitating pastureland development. A HYDRUS-1D model was used to estimate potential groundwater recharge. The model was calibrated using field data from 2019 and validated using data from 2020. The time series of Normalized Difference Vegetation Index (NDVI) was derived at annual scale to assess changes in the vegetation cover. New hydrological insights for the region The modeling revealed that an additional 5% of the rainfall depth was being recharged into the groundwater. In addition, the additional soil moisture was allowing natural grass cover to develop, which could be used by the local community as pastureland. These twin benefits that the local communities are realizing could be scaled up beyond Dudu, to India, and worldwide, as many regions have barren land that is slightly sloping, together with permeable soils, which are the only conditions for the construction of Chaukas. These Chauka systems have helped in sustainable water resources management in these water-stressed regions and the additional livelihood support through developed pastures for animal husbandry