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"Chatterjee, S"
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Handbook of regression analysis
\"Written by two established experts in the field, the purpose of this handbook is to provide a practical, one-stop reference on regression analysis. The focus is on the tools that both practitioners and researchers use in real life. It is intended to be a comprehensive collection of the theory, methods, and applications of the subject matter, but it is deliberately written at an accessible level. The handbook will provide a quick and convenient reference or \"refresher\" on ideas and methods that are useful for the accurate analysis of data and its resulting interpretations. Students can use the book as an introduction to and/or summary of key concepts in regression and related course work (such as linear, nonlinear, and nonparametric regressions). Plentiful references are supplied for the more motivated readers. Theory is presented when necessary, and always supplemented by hands-on examples. Software routines are available via an author-maintained web site\"-- Provided by publisher.
Book
Disparities in exposure and accessibility to health: A Spatial Assessment of Covid 19 Pandemic Situation of South Bengal
Inequality and disparities of health is prevalent in a developing nation like India. The emergence of the Novel Corona virus has further aggravated this existing problem. The major issue that has been observed in dealing with the pandemic situation is the lack of facilities for testing and inadequate health infrastructure to support the huge population of this nation. This infrastructural deficiency has evidently become severe as we move away from the city areas. In this study, we have tried to assess this rural-urban disparity of health infrastructure in the settings of the COVID 19 pandemic situation. The study has been conducted to measure rural-urban disparities of eight districts i.e. Howrah, Hooghly, Kolkata, North 24 Parganas and South 24 Parganas concerning risk factors and access to health care infrastructure. To achieve the desired objectives, we have used a multidisciplinary technique incorporating statistical, GIS techniques, composite index with several aspects e.g., geographical coverage and sufficiency of COVID care and testing facilities (CCF, CTF), economic status of people, medical costs, and susceptibility to covid risk factors i.e., number of infected populations, and population density. A significant correlation between access to CCF and CTF and the proportion of urban inhabitants has been found, i.e., urban populations mostly enjoy better access to treatment and testing with dense CTFs and CCFs over space. The density and serviceability of care facilities over rural regions decrease with less urbanized areas. Urban areas are found to be at higher risk in terms of the number of active cases, population density. The study helps us to geo visualize the current COVID scenario of South Bengal in terms of regional disparities. This will help us identify the nearest testing and care facilities to any location within the study area and will be useful in mitigating infrastructural lacuna.
Journal Article
Imaging stress and magnetism at high pressures using a nanoscale quantum sensor
Pressure alters the physical, chemical, and electronic properties of matter. The diamond anvil cell enables tabletop experiments to investigate a diverse landscape of high-pressure phenomena. Here, we introduce and use a nanoscale sensing platform that integrates nitrogen-vacancy (NV) color centers directly into the culet of diamond anvils. We demonstrate the versatility of this platform by performing diffraction-limited imaging of both stress fields and magnetism as a function of pressure and temperature. We quantify all normal and shear stress components and demonstrate vector magnetic field imaging, enabling measurement of the pressure-driven α ↔ ϵ phase transition in iron and the complex pressure-temperature phase diagram of gadolinium. A complementary NV-sensing modality using noise spectroscopy enables the characterization of phase transitions even in the absence of static magnetic signatures.
Journal Article
Near room temperature sensing of nitric oxide using SnO2/Ni-decorated natural cellulosic graphene nanohybrid film
In recent years, metal oxide nanoparticles and their composites with graphene have received significant research attention in toxic gas sensor applications. Herein, we demonstrate a novel approach to develop a sensor by combining SnO
2
nanoparticles and Ni-decorated natural cellulosic graphene (Ni-NCG) derived from lotus petals to form SnO
2
/Ni-NCG nanohybrid. The morphology, microstructure and elemental composition of the nanohybrids were investigated by a number of techniques which confirmed presence of nanometer sized SnO
2
particles having large surface area on sheets of few layered Ni-decorated NCG. Upto 15% response was observed when exposed to 40 ppm of NO with high reproducibility at temperature as low as 60 °C which is remarkable when compared to previously reported SnO
2
based NO sensors operating at high temperatures (~ 200 °C or more). Further, the nanohybrid showed excellent selectivity to NO when tested against other gases. A mechanism have been proposed for the improved sensitivity at low temperature based on the improved surface area of SnO
2
nanoparticles leading to larger adsorption of gas molecules combined with an improved conduction of charges provided by the Ni-decorated NCG network. The results show enormous potential for the SnO
2
/Ni-NCG nanohybrid film as near room temperature NO sensor.
Journal Article
Effect of Keyhole Gas Tungsten Arc Welding and Post-welding Heat Treatment on Microstructure and Hardness of Inconel 740H
Keyhole mode gas tungsten arc welding (GTAW) is used to obtain crack-free full-penetration welds in Ni-base superalloy Inconel 740H. Associated spatial variation in microstructure and microhardness are correlated. Local softening in the heat-affected zone (HAZ) is observed after welding. This cannot be explained by changes in grain size, twin fraction or heterogeneous strain distribution, but instead can be attributed to the dissolution of ultra-fine grain boundary carbides. Fusion zone microstructure consists of large, columnar
γ
dendrites and Ti- and Nb-rich carbides at the interdendritic region. The relatively large grain size in the FZ results in a reduction in hardness compared to the base metal. Elemental partitioning during solidification is estimated from composition measurements in the FZ and compared against existing reports for conventional GTAW. The effect of different post-weld heat treatments (PWHTs) on the precipitation of
γ
′
, disappearance of the dendritic microstructure, composition homogenization and spatial variation of microhardness is also investigated. Specifically, grain growth in the HAZ is observed after two-step PWHTs, and not for the single-step direct aging, which could have important implications for the creep response of the material.
Journal Article
Asymmetric mass ratios for bright double neutron-star mergers
The discovery of a radioactively powered kilonova associated with the binary neutron-star merger GW170817 remains the only confirmed electromagnetic counterpart to a gravitational-wave event
1
,
2
. Observations of the late-time electromagnetic emission, however, do not agree with the expectations from standard neutron-star merger models. Although the large measured ejecta mass
3
,
4
could be explained by a progenitor system that is asymmetric in terms of the stellar component masses (that is, with a mass ratio
q
of 0.7 to 0.8)
5
, the known Galactic population of merging double neutron-star systems (that is, those that will coalesce within billions of years or less) has until now consisted only of nearly equal-mass (
q
> 0.9) binaries
6
. The pulsar PSR J1913+1102 is a double system in a five-hour, low-eccentricity (0.09) orbit, with an orbital separation of 1.8 solar radii
7
, and the two neutron stars are predicted to coalesce in
470
−
11
+
12
million years owing to gravitational-wave emission. Here we report that the masses of the pulsar and the companion neutron star, as measured by a dedicated pulsar timing campaign, are 1.62 ± 0.03 and 1.27 ± 0.03 solar masses, respectively. With a measured mass ratio of
q
= 0.78 ± 0.03, this is the most asymmetric merging system reported so far. On the basis of this detection, our population synthesis analysis implies that such asymmetric binaries represent between 2 and 30 per cent (90 per cent confidence) of the total population of merging binaries. The coalescence of a member of this population offers a possible explanation for the anomalous properties of GW170817, including the observed kilonova emission from that event.
Pulsar timing measurements show a mass ratio of about 0.8 for the double neutron-star system PSR J1913+1102, and population synthesis models indicate that such asymmetric systems represent 2–30% of merging binaries.
Journal Article
A repeating fast radio burst associated with a persistent radio source
The dispersive sweep of fast radio bursts (FRBs) has been used to probe the ionized baryon content of the intergalactic medium
1
, which is assumed to dominate the total extragalactic dispersion. Although the host-galaxy contributions to the dispersion measure appear to be small for most FRBs
2
, in at least one case there is evidence for an extreme magneto-ionic local environment
3
,
4
and a compact persistent radio source
5
. Here we report the detection and localization of the repeating FRB 20190520B, which is co-located with a compact, persistent radio source and associated with a dwarf host galaxy of high specific-star-formation rate at a redshift of 0.241 ± 0.001. The estimated host-galaxy dispersion measure of approximately
903
−
111
+
72
parsecs per cubic centimetre, which is nearly an order of magnitude higher than the average of FRB host galaxies
2
,
6
, far exceeds the dispersion-measure contribution of the intergalactic medium. Caution is thus warranted in inferring redshifts for FRBs without accurate host-galaxy identifications.
A repeating fast radio burst co-located with a persistent radio source and associated with a dwarf host galaxy of a high star-formation rate has been detected.
Journal Article
A GIS-based liquefaction susceptibility mapping utilising the morphotectonic analysis to highlight potential hazard zones in the East Ganga plain
Earthquakes in the Himalayas pose a significant hazard to the densely populated Indo-Gangetic Plains (IGP). Due to liquefaction of soils, ground settlements and structural tilting are prevalent during earthquakes. This study aims to identify liquefaction potential zones in the North-Bihar region of the East Ganga Plains by performing morphotectonic analysis over six drainage basins and liquefaction susceptibility mapping using Analytical Hierarchy Process (AHP) while taking site-specific parameters into account. The Index of Relative Active Tectonic (IRAT) value for Gandak and Mahananda was determined to be 1, indicating that the basins are extremely active, whereas Burhi Gandak, Bagmati, and Kosi were moderately active with a 2 IRAT value. The Kamla basin is the least active with an IRAT value of 4. The Liquefaction Susceptibility Map (LSM) was divided into three categories: liquefaction not likely (24%), liquefaction possible (45%), and liquefaction likely (31%); the estimated RMSE values were 0.0084, 0.00048, and 0.00031, respectively. The integrated analysis, which employs both techniques, demonstrates how the individual basins will be affected by liquefaction during an earthquake. The proposed methodology would be beneficial to decision-makers when designing strategies for urban planning projects, as well as structural engineers when selecting sites for field-based surveys.
Journal Article
A bimodal burst energy distribution of a repeating fast radio burst source
The event rate, energy distribution and time-domain behaviour of repeating fast radio bursts (FRBs) contain essential information regarding their physical nature and central engine, which are as yet unknown
1
,
2
. As the first precisely localized source, FRB 121102 (refs.
3
–
5
) has been extensively observed and shows non-Poisson clustering of bursts over time and a power-law energy distribution
6
–
8
. However, the extent of the energy distribution towards the fainter end was not known. Here we report the detection of 1,652 independent bursts with a peak burst rate of 122 h
−1
, in 59.5 hours spanning 47 days. A peak in the isotropic equivalent energy distribution is found to be approximately 4.8 × 10
37
erg at 1.25 GHz, below which the detection of bursts is suppressed. The burst energy distribution is bimodal, and well characterized by a combination of a log-normal function and a generalized Cauchy function. The large number of bursts in hour-long spans allows sensitive periodicity searches between 1 ms and 1,000 s. The non-detection of any periodicity or quasi-periodicity poses challenges for models involving a single rotating compact object. The high burst rate also implies that FRBs must be generated with a high radiative efficiency, disfavouring emission mechanisms with large energy requirements or contrived triggering conditions.
For FRB 121102, 1,652 burst events are detected over 47 days, with a peak burst rate of 122 per hour, a bimodal burst rate energy distribution, and no periodicity or quasi-periodicity.
Journal Article