SOHAM DAS - Academia.edu (original) (raw)

Papers by SOHAM DAS

$Research paper thumbnail of On fractional version of oriented coloring$

Discrete Applied Mathematics

We introduce the fractional version of oriented coloring and initiate its study. We prove some ba... more We introduce the fractional version of oriented coloring and initiate its study. We prove some basic results and study the parameter for directed cycles and sparse planar graphs. In particular, we show that for every ǫ > 0, there exists an integer g ǫ ≥ 12 such that any oriented planar graph having girth at least g ǫ has fractional oriented chromatic number at most 4 + ǫ. Whereas, it is known that there exists an oriented planar graph having girth at least g ǫ with oriented chromatic number equal to 5. We also study the fractional oriented chromatic number of directed cycles and provide its exact value. Interestingly, the result depends on the prime divisors of the length of the directed cycle.

2021 Winter Simulation Conference (WSC), 2021

This study demonstrates the implementation of the stochastic ruler discrete simulation optimizati... more This study demonstrates the implementation of the stochastic ruler discrete simulation optimization method for calibrating an agent-based model (ABM) developed to simulate hepatitis C virus (HCV) transmission. The ABM simulates HCV transmission between agents interacting in multiple environments relevant for HCV transmission in the Indian context. Key outcomes of the ABM are HCV and injecting drug user (IDU) prevalences among the simulated cohort. Certain input parameters of the ABM need to be calibrated so that simulation outcomes attain values as close as possible to real-world HCV and IDU prevalences. We conceptualize the calibration process as a discrete simulation optimization problem by discretizing the calibration parameter ranges, defining an appropriate objective function, and then applying the stochastic ruler random search method to solve this problem. We also present a method that exploits the monotonic relationship between the simulation outcomes and calibration parameters to yield improved calibration solutions with lesser computational effort.

2019 Winter Simulation Conference (WSC), 2019

In this study, we develop a model of hepatitis C virus (HCV) transmission dynamics capable of ana... more In this study, we develop a model of hepatitis C virus (HCV) transmission dynamics capable of analyzing the health, economic and epidemiological impact of treatment and large-scale screening in the Indian context. The model simulates the interaction of infected and uninfected agents in environments wherein key risk factors of HCV transmission operate. The natural history of disease is simulated using a previously published and validated Markov model. The agent interaction/transmission environments simulated by the model include a home environment for transmission via unprotected sex, a medical environment for transmission via unsafe medical practices, educational and social interaction environments for conversion of non-injecting drug user (IDU) agents to IDUs and transmission via sharing of injecting equipment among IDUs. The model is calibrated to current HCV and IDU prevalence targets. We present model calibration results and preliminary results for the impact of treatment uptake rates on HCV and IDU prevalence.

Materials Science-Poland, 2020

Titanium aluminum nitride (TiAlN) thin films were deposited on Si(1 0 0 ) substrate using titaniu... more Titanium aluminum nitride (TiAlN) thin films were deposited on Si(1 0 0 ) substrate using titanium and aluminum targets in 1:1 ratio at various N2 flow rates using ion beam sputtering (IBS) technique. The morphology, particle and crystallite size of TiAlN thin films were estimated by field emission scanning electron microscope (FE-SEM), atomic force microscope (AFM), and grazing incidence X-ray diffraction (GIXRD) technique, respectively. The SEM images of the TiAlN thin films revealed smooth and uniform coating, whereas AFM images confirmed the particle size varying from 2.5 nm to 8.8 nm, respectively. The crystallite size and lattice strain were observed to vary from 4.79 nm to 5.5 nm and 0.0916 and 0.0844, respectively, with an increase in N2 flow rate in the TiAlN thin films. The X-ray absorption near edge structure (XANES) results showed Ti L, N K and O K-edges of TiAlN coating within a range of 450 eV to 470 eV, 395 eV to 410 eV and 480 eV to 580 eV photon energy, respectively...

Titanium aluminium nitride (TiAlN) thin films are now commonly used as protective layer in variou... more Titanium aluminium nitride (TiAlN) thin films are now commonly used as protective layer in various fields as these films have high thermal stability and sound corrosion resistance. Due to high hardness and wear resistance at elevated temperature, it is one of the most important thin film coating material for cutting tools. Various deposition methods such as physical vapour deposition (PVD), chemical vapour deposition (CVD), sputtering technique, etc., are used by many researchers to synthesize TiAlN coatings. To analyse morphological, structural, and mechanical characteristics, various tests such as SEM, AFM, xrd, Raman, and nanoindentation have been carried out by many researchers. This paper basically summarizes the properties of TiAlN monolayer, nanolayer, and multilayer thin films.

2017 IEEE Symposium on Computers and Communications (ISCC), 2017

Data aggregation is a critical operation in many big-data applications; for example, data residin... more Data aggregation is a critical operation in many big-data applications; for example, data residing in several source racks (mappers) are to be aggregated into one or more specified racks called aggregators (reducers) in the data center network during the shuffle phase of a map-reduce task. In this paper, we explore algorithms for data aggregation to two aggregators in a data center network under the constraint that data from a source rack must be routed to each aggregator using a single path. We derive bounds on the approximation ratios of two classes of aggregation algorithms- Restricted 1-Round (R1R) and Restricted 2-Round (R2R). For the case when racks have exactly 2 optical links (uplinks in Top-of-Rack switches), we propose another strategy using the 2Chain topology for aggregation and show that the optimal 2Chain cannot have an aggregation time greater than that of the optimal R1R and R2R topologies. For the case when racks have at least 4 optical links, we propose a 1-round a...

Ceramics International, 2021

Abstract In this experimental investigation, the influence of different N2 gas flow rates on diff... more Abstract In this experimental investigation, the influence of different N2 gas flow rates on different properties (e.g. morphological, mechanical, etc.) of chemical vapor deposited (CVD) Titanium nitride (TiN) coatings has been discussed. The TiN coatings had been grown on Si (100) substrate at elevated temperature (1000 °C) using Titanium dioxide (TiO2) powder. SEM images reveal a dense uniform microstructure with an irregular surface pattern. The surface roughness of the coatings was found to be increased from 12.42 to 28.56 nm with an increase in flow rate. XRD results indicate a B1 NaCl crystal structure of the film with reduced crystallite size with the increasing N2 flow rate. Through the corrosion test, it has been observed that due to the variation of N2 flow rate the corrosion resistance of the films decreases with increasing N2 flow rate. The mismatch of thermal expansion co-efficient in between Si substrate and TiN thin film reduces with higher N2 flow rate. The acoustic and optic phonon mode of TiN coatings have been shifted to higher intensities with higher N2 flow rate. The mechanical properties of the film reveal that the maximum value of hardness (H) and Young's modulus (E) are 30.14 and 471.85 GPa respectively.

PROCEEDINGS OF ADVANCED MATERIAL, ENGINEERING & TECHNOLOGY, 2020

Materials Chemistry and Physics, 2021

This is a PDF file of an article that has undergone enhancements after acceptance, such as the ad... more This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

Ceramics International, 2020

In the present study, Titanium carbon nitride (TiCN) thin films have been synthesized over Si (10... more In the present study, Titanium carbon nitride (TiCN) thin films have been synthesized over Si (100) substrate using chemical vapour deposition (CVD) process under N 2 gas flow rate to study the suitability of CVD for the growth of TiCN coating over machine tools. The morphological, structural, corrosion behavior and mechanical properties of the coatings have been characterized using a scanning electron microscope (SEM), atomic force microscopy (AFM), x-ray diffraction (XRD), corrosion test and Nano-indentation. SEM images revealed a smoother morphology of the TiCN coating surface without any pores. The AFM results revealed an increase in surface roughness from 40.88 nm to 48.25 nm. The particle size of TiCN thin film also found to be increasing with a higher N 2 flow rate. The XRD peaks of TiCN were observed in the range of 37°-38°. 44°-44.5°and 61°-62°a ttributed to (111), (200) and (220) crystal plane. The XRD results also confirmed the presence of stress in the coatings. The polarization test indicates a reduction of corrosion resistance with a higher N 2 gas flow rate. The mechanical properties investigated by the nano-indentation method indicated an increase in Hardness (H) and Young's modulus (E) of the coating with a higher N 2 flow rate. The maximum H and E of the coatings were observed as 27.85 GPa and 486.22 GPa respectively.

IOP Conference Series: Materials Science and Engineering, 2018

Titanium aluminium nitride (TiAlN) thin film coatings were synthesized via Atmospheric pressure c... more Titanium aluminium nitride (TiAlN) thin film coatings were synthesized via Atmospheric pressure chemical vapour deposition (APCVD) at various deposition temperature using titanium di-oxide (TiO2) powder, Al powder (99% pure) and N2 gas. The thin films were characterized by scanning electron microscopy (SEM), Raman spectroscopy and X-ray photoelectron spectroscopy (XPS) for analysing the morphological, vibrational and compositional characteristics of the deposited film. SEM images showed successful deposition of TiAlN thin film over Si wafers. Raman peaks revealed the optical phonon bands of the coated thin film within a range of 214.6-335.1 cm-1and 552.63-815.23 cm-1 for acoustic and optic range respectively at different processing temperatures. XPS spectra clearly showed the presence of different phases like Ti-N, Ti-O-N, Al2O3, N-Al, TiO2 Al-O in Ti (2p), Al (2p) and N (1s) orbitals, which is in a good agreement with past work.

Journal of Alloys and Compounds, 2018

Titanium silicon nitride (TiSiN) thin films were deposited on p-type c-Si (100) with different N ... more Titanium silicon nitride (TiSiN) thin films were deposited on p-type c-Si (100) with different N 2 flow rate by using chemical vapor deposition (CVD) technique. The microstructure, phonon modes, mechanical properties and compositional studyof TiSiN thin films were characterised by scanning electron microscope (SEM), X-ray diffraction (XRD), Raman spectroscopy, nanoindentation and X-ray photoelectron spectroscopy (XPS),respectively. The SEM images show increases insurface roughness with increasing of N 2 flow rate, however, improvesthe hardness and Young's modulus of TiSiN thin film. The XRD analysis reveals the presence of strain in TiSiN films. The estimated crystallites of TiSiN thin films was 7.51 and 7.39 nm for 40 and 100 sccm N 2 flow rate. The XPS reveals the presence of 20 at. % Si content at 40 sccm N 2 flow rate in the TiSiNfilm. To analyse the broad Raman spectra of TiSiN thin films, the peaks were convoluted into six individual Gaussian peaks. The quantitative and qualitative analysis XPS and Raman spectra of TiSiN thin films were carried out by using Origin 9.0 software.

IEEE/ACM Transactions on Networking, 2016

The missing author biography follows. Soham Das received the B.Tech. degree in computer science f... more The missing author biography follows. Soham Das received the B.Tech. degree in computer science from the Institute of Engineering and Management, Kolkata, India, the M.Tech. degree in computer science from IIT Delhi, and the Ph.D. degree in computer science from the University of Florida in 2016. His research interests are approximation algorithms, data center networks, and modeling and analysis of complex networks.

2015 IEEE Symposium on Computers and Communication (ISCC), 2015

We consider the problem of data aggregation using two aggregators. We assume that the source rack... more We consider the problem of data aggregation using two aggregators. We assume that the source racks can split the data they need to send to the aggregators across multiple paths. We show that obtaining a topology that minimizes aggregation time is NP-hard for k = 2, 3, 4, where k the degree of ToR (topof-rack) switches. We also show that an optimal topology can be computed in polynomial time for k = 5 and 6 and conjecture this to be the case when k > 6 as well. Experimental results show that, when k = 6, our topology optimization algorithm reduces the aggregation time by as much as 83.3% and reduces total network traffic by as much as 99.5% relative to the torus heuristic, proposed by [1].

International Journal of Metaheuristics, 2015

In this paper, we develop algorithms for the data aggregation problem which arises in the context... more In this paper, we develop algorithms for the data aggregation problem which arises in the context of big data applications that employ the MapReduce operation. For the case when source racks can se...

2013 IEEE 13th International Conference on Data Mining, 2013

The least cost influence (LCI) problem, which asks to identify a minimum number of seed users who... more The least cost influence (LCI) problem, which asks to identify a minimum number of seed users who can eventually influence a large number of users, has become one of the central research topics recently in online social networks (OSNs). However, existing works mostly focused on a single network while users nowadays often join several OSNs. Thus, it is crucial to investigate the influence in multiplex networks, i.e. the influence is diffused across a set of networks via shared users, in order to obtain the best set of seed users. In this paper, we propose a unified framework to represent and analyze the influence diffusion in multiplex networks. More specifically, we tackle the LCI problem in multiplex OSNs by reducing multiplex networks to a single network via various coupling schemes while preserving the most influence propagation properties. Besides the coupling schemes to represent the diffusion process, the framework also includes the influence relay, a new metric to measure the flow of influence inside and between networks. The experiments on both real and synthesized datasets validate the effectiveness of the coupling schemes as well as provide some interesting insights into the process of influence propagation in multiplex networks.

2014 14th IEEE/ACM International Symposium on Cluster, Cloud and Grid Computing, 2014

In this paper, we show that the problem of configuring the topology of a data center network to o... more In this paper, we show that the problem of configuring the topology of a data center network to optimize data aggregation is NP-hard even when the number of aggregators is 1. Further, the approximation ratio of the algorithm proposed by Wang, Ng, and Shaikh [3] for the case of a single aggregator is (k+1)/2, where k is the degree of ToR (top-of-rack) switches and this algorithm also exhibits an anomalous behavior-increase in the switch degree may result in an increase in the aggregation time. By comparison, if topology configuration is done using the longest processing time (LPT) scheduling rule, the approximation ratio is (4/3-1/(3k)). We show that for every instance of the single aggregator topology configuration problem, the time required to aggregate using the LPT configuration is no more than that using the Wang et al. rule. By coupling the LPT rule with the rule of Wang et al., we achieve a better throughput as promised by LPT and at the same time reduce the total network traffic. Experimental results show that the LPT rule reduces aggregation time by up to 90% compared to the Wang et al. rule. The reduction in aggregation time afforded by a known improvement, COMBINE, of LPT relative to Wang et al. is up to 90.5%. More interestingly, when either of the LPT rule or COMBINE is augmented with the Wang et al. rule, total network traffic is reduced by up to 90% relative to using LPT and COMBINE with chains.

IEEE Transactions on Knowledge and Data Engineering, 2012

The increasing popularity of social networks has initiated a fertile research area in information... more The increasing popularity of social networks has initiated a fertile research area in information extraction and data mining. Anonymization of these social graphs is important to facilitate publishing these data sets for analysis by external entities. Prior work has concentrated mostly on node identity anonymization and structural anonymization. But with the growing interest in analyzing social networks as a weighted network, edge weight anonymization is also gaining importance. We present Anónimos, a Linear Programming based technique for anonymization of edge weights that preserves linear properties of graphs. Such properties form the foundation of many important graph-theoretic algorithms such as shortest paths problem, k-nearest neighbors, minimum cost spanning tree, and maximizing information spread. As a proof of concept, we apply Anónimos to the shortest paths problem and its extensions, prove the correctness, analyze complexity, and experimentally evaluate it using real social network data sets. Our experiments demonstrate that Anónimos anonymizes the weights, improves k-anonymity of the weights, and also scrambles the relative ordering of the edges sorted by weights, thereby providing robust and effective anonymization of the sensitive edge-weights. Additionally, we demonstrate the composability of different models generated using Anónimos, a property that allows a single anonymized graph to preserve multiple linear properties.

SSRN Electronic Journal, 2021

For resource-constrained health systems, it becomes important to evaluate the cost-effectiveness ... more For resource-constrained health systems, it becomes important to evaluate the cost-effectiveness of a breast cancer (BC) screening program prior to its real-world implementation. In this paper, we provide an overview of a new simulation model of BC incidence, progression, and diagnosis developed to maximize the cost-effectiveness of a BC screening program. We describe the development of the modules for BC incidence, tumor growth and diagnosis, and survival estimation of diagnosed patients. Incidence of BC is based on published risk factors and publicly available national cancer registry reports. Survival curves for diagnosed patients based on specific characteristics such as age group and stage of diagnosis are generated using a single published survival curve for the entire population and hazard ratios for each characteristic. Our simulation development approach can provide a model development template for researchers working to develop BC simulation models in other settings with data availability similar to our case.