Sagnik Dey - Academia.edu (original) (raw)

Papers by Sagnik Dey

Atmospheric Research

A discrimination of aerosol types over the Indo-Gangetic Basin (IGB) region during pre-monsoon pe... more A discrimination of aerosol types over the Indo-Gangetic Basin (IGB) region during pre-monsoon period was made using multi-year ground based sun/sky radiometer measured aerosol products associated with the size of aerosols and radiation absorptivity. High dust enriched aerosols (i.e. polluted dust, PD) were found to contribute more over the central IGB station at Kanpur (KNP, 62%) as compared to the eastern IGB station at Gandhi College (GC, 31%) whereas vice-versa was observed for polluted continental (PC) aerosols, which contain high anthropogenic and less dust aerosols. Contributions of carbonaceous particles having high absorbing (mostly black carbon, MBC) and low absorbing (mostly organic carbon, MOC) aerosols were found to be 11% and 10%, respectively at GC, which was~46% and 62% higher than the observed contributions at KNP; however, very less contribution of non-absorbing (NA) aerosols was observed only at GC (2%). Variability in aerosol types together with single scattering albedo (SSA) at both the stations were also studied during the forenoon (FN) and afternoon (AN) hour, which suggests their strong association with emission sources. Results were well substantiated with the air mass backtrajectories and the fire products. Spectral information of SSA for each aerosol type discriminates the dominance of natural dust (SSA increases with increasing wavelength) with anthropogenic aerosols (SSA decreases with increasing wavelength) at both the locations. The estimated absorption Ångström exponent (AAE) values suggest relative dominance of absorbing type aerosols over the central part of IGB (due to dominant dust absorption) as compared to the eastern part during pre-monsoon period.

Pure and Applied Geophysics, 2015

ABSTRACT In the present study, simulations have been carried out to study the relationship betwee... more ABSTRACT In the present study, simulations have been carried out to study the relationship between winter-time precipitations and the large-scale global forcing (ENSO) using the tropical band version of Regional Climate Model (RegT-Band) for 5 El Niño and 4 La Niña years. The RegT-Band model is integrated with the observed sea-surface temperature and lateral boundary conditions from National Center for Environmental Prediction (NCEP)-Department of Energy (DOE) reanalysis 2 (NCEP-DOE2). The model domain extends from 50°S to 50°N and covers the entire tropics at a grid spacing of 45 km, i.e., it includes lateral boundary forcing only at the southern and northern boundaries. The performance evaluation of the model in capturing the large-scale fields followed by ENSO response with winter-time precipitation has been carried out by using model simulations against NCEP-DOE2 and Global Precipitation Climatology Project (GPCP) precipitation data. The analysis suggests that the model is able to reproduce the upper airfields and large-scale precipitation during winter time, although the model has some systematic biases compared to the observations. A comparison of model-simulated precipitation with observed precipitation at 17 station locations has been carried out. It is noticed that the RegT-Band model simulations are able to bring out the observed features reasonably well. Therefore, this preliminary study indicates that the tropical band version of the regional climate model can be effectively used for the better understanding of the large-scale global forcing.

Atmósfera, 2015

ABSTRACT Climate prediction over the Western Himalaya is a challenging task due to the highly var... more ABSTRACT Climate prediction over the Western Himalaya is a challenging task due to the highly variable altitude and orientation of orographic barriers. Surface characteristics also play a vital role in climate simulations and need appropriate representation in the models. In this study, two land surface parameterization schemes (LSPS), the Biosphere-Atmosphere Transfer Scheme (BATS) and the Common Land Model (CLM, version 3.5) in the regional climate model (RegCM, version 4) have been tested over the Himalayan region for nine distinct winter seasons in respect of seasonal precipitation (three years each for excess, normal and deficit). Reanalysis II data of the National Centers for Environmental Prediction (NCEP)/Department of Energy (DOE) have been used as initial and lateral boundary conditions for the RegCM model. In order to provide land surface boundary conditions in the RegCM model, geophysical parameters (10 min resolution) obtained from the United States Geophysical Survey were used. The performance of two LSPS (CLM and BATS) coupled with the RegCM is evaluated against gridded precipitation and surface temperature data sets from the India Meteorological Department (IMD). It is found that the simulated surface temperature and precipitation are better represented in the CLM scheme than in the BATS when compared with observations. Further, several statistical analysis such as bias, root mean square error (RMSE), spatial correlation coefficient (CC) and skill scores like the equitable threat score (ETS) and the probability of detection (POD) are estimated for evaluating RegCM simulations using both LSPS. Results indicate that the RMSE decreases and the CC increases with the use of the CLM compared to BATS. ETS and POD also indicate that the performance of the model is better with the CLM than with the BATS in simulating seasonal scale precipitation. Overall, results suggest that the performance of the RegCM coupled with the CLM scheme improves the model skill in predicting winter precipitation (by 15-25%) and temperature (by 10-20%) over the Western Himalaya.

2006 IEEE International Reliability Physics Symposium Proceedings, 2006

ABSTRACT The focus of this work is to demonstrate the effect of mechanical stress in the channel ... more ABSTRACT The focus of this work is to demonstrate the effect of mechanical stress in the channel on the impact ionization rate (IIR) and on hot carrier reliability for both NMOS and PMOS devices. In addition, this study will explain the reason for the wide disagreement between published reports on this behavior. It is shown for the first time that the IIR reaches a maximum value with strain for NMOS and then reduces as higher levels of strain are applied. Compressive strained PMOS devices do not show this peak in IIR

2010 Symposium on VLSI Technology, 2010

We present novel and cost effective integration schemes with high performance analog and high vol... more We present novel and cost effective integration schemes with high performance analog and high voltage components to enable system-on-chip (SOC) designs in advanced CMOS technologies. The new transistors have superior analog performance compared to the standard logic devices resulting in significant area savings and greater analog functionality. The new high voltage (HV) transistors enable reliable 6V capability with high performance

IEEE Journal of the Electron Devices Society, 2015

An improved analytical model for flicker noise (1/f noise) in MOSFETs is presented. Current model... more An improved analytical model for flicker noise (1/f noise) in MOSFETs is presented. Current models do not capture the effect of high trap density in the halo regions of the devices, which leads to significantly different bias dependence of flicker noise across device geometry. The proposed model is the first compact model implementation capturing such effect and show distinct improvements over other existing noise models. The model is compatible with BSIM6, the latest industry standard model for bulk MOSFET, and is validated with measurements from 45nm low power CMOS technology node.

IEEE Transactions on Computer-Aided Design of Integrated Circuits and Systems, 2015

Theoretical and Applied Climatology, 2015

ABSTRACT The climatology, amplitude error, phase error, and mean square skill score (MSSS) of tem... more ABSTRACT The climatology, amplitude error, phase error, and mean square skill score (MSSS) of temperature predictions from five different state-of-the-art general circulation models (GCMs) have been examined for the winter (December-January-February) seasons over North India. In this region, temperature variability affects the phenological development processes of wheat crops and the grain yield. The GCM forecasts of temperature for a whole season issued in November from various organizations are compared with observed gridded temperature data obtained from the India Meteorological Department (IMD) for the period 1982-2009. The MSSS indicates that the models have skills of varying degrees. Predictions of maximum and minimum temperature obtained from the National Centers for Environmental Prediction (NCEP) climate forecast system model (NCEP_CFSv2) are compared with station level observations from the Snow and Avalanche Study Establishment (SASE). It has been found that when the model temperatures are corrected to account the bias in the model and actual orography, the predictions are able to delineate the observed trend compared to the trend without orography correction.

Porous Silicon (PS) based sensors are compatible to Si IC processing and can be integrated on the... more Porous Silicon (PS) based sensors are compatible to Si IC processing and can be integrated on the same chip with its signal processing unit. PS can be modeled as a distributive RC network and the dielectric constant of the porous layer changes under external stimuli like ambient humidity, pressure etc. Thus a phase sensitive signal conditioning unit that can be integrated with the transducer on the same chip can form an integrated sensor that can detect humidity, pressure, etc. In order to develop the ASIC design for such a phase detecting signal conditioning unit and to perform CAD simulations and verify our design, we have developed a model for the PS transducer. In this paper we discuss the model for the PS transducer that can be incorporated as a SPICE model file for simulation. The SPICE model file incorporates as model parameters the different process and design parameters.

Scaling the conventional CMOS transistor beyond the 45 nm generation ushers in several fundamenta... more Scaling the conventional CMOS transistor beyond the 45 nm generation ushers in several fundamental limitations. Control of leakage currents and sustaining electrostatic integrity while maintaining historic enhancements in performance requires such ultra-thin gate-dielectrics and heavily doped bodies that a process window sufficiently large for manufacturing might not be found. While conventional SiO2 might need to be replaced by high-kappa dielectric and metal gate, it might be necessary that the conventional planar MOSFET architecture be also substituted to address the electrostatics challenges. In addition high mobility materials need to be explored to garner the additional enhancement in performance. In this paper we demonstrate a PMOSFET device architecture that integrates such a high mobility material with high-kappa/metal gate in a 3D non-planar gate-all-around architecture (GAA).

Solid-State Electronics

Multiple cantilever channel MOSFET formed by multiple fully or partially-depleted silicon gate-al... more Multiple cantilever channel MOSFET formed by multiple fully or partially-depleted silicon gate-all-around (GAA) cantilever channels suspended between source drain (S/D) “anchors” might be a very attractive architecture as gate lengths are scaled below 100 nm. In this paper we shall demonstrate that although such an architecture may be ideal for sub-100 nm nodes it suffers from current-crowding effects towards the top cantilever channels leading to a higher current density in the cantilevers towards the top than those near the substrate. Hence, the drive current cannot be scaled linearly in such a device by stacking higher number of cantilever channels vertically without consuming additional Si real estate. It is shown that although the drive current does not saturate after a particular number of cantilevers, the drive current enhancement is lower than expected based on the effective electrical width and is dependent on the S/D series resistance.

Pure and Applied Geophysics, 2014

ABSTRACT The present study examines the performance of convective parameterization schemes at two... more ABSTRACT The present study examines the performance of convective parameterization schemes at two different horizontal resolutions (90 and 30 km) in simulating winter (December–February; DJF) circulation and associated precipitation over the Western Himalayas using the regional climate model RegCM4. The model integrations are carried out in a one-way nested mode for three distinct precipitation years (excess, normal and deficit) using four combinations of cumulus schemes. The National Center for Environment Prediction—Department of Energy Reanalysis-2 project utilized gridded data, observed precipitation data from the India Meteorological Department and station data from the Snow and Avalanche Study Establishment were used to evaluate model performance. The seasonal mean circulation patterns and precipitation distribution are well demonstrated by all of the cumulus convection schemes. However, model performance varies using different schemes. Statistical analysis confirms that the root mean square error is reduced by about 2–3 times and the correlation coefficient (CC) increases in the fine resolution (30 km) simulations compared to coarse resolution (90 km) simulations. A statistically significant CC (at a 10 % significance level) is found only in the fine resolution simulations. The Grell cumulus model with a Fritsch–Chappell closure (Grell-FC) is better at simulating seasonal mean patterns and inter-annual variability of two contrasting winter seasons than the other scheme combinations.

2005 International Semiconductor Device Research Symposium, 2005

ABSTRACT Not Available

2006 64th Device Research Conference, 2006

2007 65th Annual Device Research Conference, 2007

Demonstration of a 3X enhancement in hole mobility, in comparison to the universal Si / SiO2 curv... more Demonstration of a 3X enhancement in hole mobility, in comparison to the universal Si / SiO2 curve, is reported for epitaxially grown SiGe layers on (110) silicon substrates. This channel material is targeted for applications in high performance MOSFETs in a hybrid orientation ...